JP5481875B2 - Surface-treated steel sheet for welding can and manufacturing method thereof - Google Patents

Description

  The present invention is a steel material for welding cans widely used in applications such as beverage cans, food cans, and general cans, and particularly economical, high-speed weldability, rust resistance, filamentous rust resistance, corrosion resistance, and organic resin. The present invention relates to a surface-treated steel sheet for welding cans excellent in properties such as adhesion and a method for producing the same.

  In recent years, as can manufacturing methods have been remarkably diversified and developed, the practical application of welded cans in the three-piece can field has been rapidly progressing. Three-piece cans are categorized as solder cans, adhesive cans, and weld cans depending on the joining method. Among these, weld cans have high joint strength and a high content leakage rate due to poor joints. It has advantages such as being very low, a small wrap margin at the joint, a beautiful appearance, and a small investment in canning equipment.

As steel materials for welding cans, surface-treated steel sheets such as Sn-plated steel sheets (covers) and electrolytic Cr-plated steel sheets (TFS: tin-free steel) have been conventionally used. In tinplate, the amount of Sn plating so far has been as high as 2.8 g / m ² or 5.6 g / m ² , but the cost reduction by thin Sn plating (LTS) has been directed at the rising price of Sn. However, when LTS is achieved, thread-like rust is likely to occur on the outer surface of the can, and a brittle Sn oxide layer is formed and grows on the surface due to the presence of non-alloyed metal Sn, and adhesion to paint and laminate resin Cause a decline. Although an alloyed Sn-plated steel sheet (ATP: alloy plate) with a reduced amount of non-alloyed metal Sn has also been proposed to the limit, there is no rust prevention effect due to non-alloyed metal Sn, so in the air during storage Rust is likely to occur due to moisture.

  On the other hand, TFS that does not use Sn is less expensive than tinplate, and there is no problem of lowering adhesion, but it has a chromate treatment layer consisting of Cr hydrated oxide and metal Cr layer on the surface layer. The resistance value at the time of welding becomes high, and the weldability is lowered as compared with the case of tin using Sn, and the generation of dust becomes a problem.

  In addition, in order to compensate for the above-described drawbacks of LTS, a technique has been proposed in which Ni plating is applied to improve adhesion, corrosion resistance, rust resistance, weldability, and the like. For example, in Patent Document 1, Ni plating and Sn plating are sequentially performed on a steel plate, Sn plating is made into a Sn-Ni alloy using heat during paint baking, and non-alloyed metal Sn is reduced to achieve adhesion. Techniques for improving the above are disclosed. Patent Document 2 discloses a technique in which Fe-Sn alloy plating and Ni plating are sequentially performed on a steel sheet, and the surface is completely covered with Ni to improve rust resistance and corrosion resistance. In Patent Document 3, Ni plating and Sn plating are sequentially performed on a steel plate, followed by heat-melting treatment, Sn of the plating layer on the outer surface of the can is completely alloyed, and Sn of the plating layer on the inner surface of the can is A technique is disclosed in which chromate treatment is performed without alloying to improve adhesion and weldability. In addition, a surface-treated steel sheet for welding cans has been proposed in which Ni plating and chromate treatment are sequentially performed on the steel sheet. However, such a technique for applying Ni plating cannot only avoid an increase in cost, but since Ni plating is hard, cracks occur in the plating film due to processing, and deterioration of corrosion resistance and the like is likely to occur.

Recently, Patent Document 4 discloses that the Fe—Sn alloy layer is provided on both surfaces of the steel plate in order to solve the above-described problem of the steel material for welding can without using Ni, and the Fe—Sn alloy layer. The amount of the non-alloyed metal Sn is less than 0.1 g / m ² , and a 2.0 to 20 mg / m ² metallic Cr layer is further formed thereon, and 2.0 to 20 mg / m ² Cr water in terms of metallic Cr is further formed thereon. There has been proposed a surface-treated steel sheet for welded cans, which is excellent in weldability, corrosion resistance, adhesion to organic resins, yellowing resistance, and can suppress the generation of powdered Sn during canning.

JP 63-266094 JP 59-205494 A Japanese Patent Publication No. 8-26477 JP 2008-150641 A

  However, the surface-treated steel sheet for welding cans described in Patent Document 4 is required to have further improved weldability, particularly stable high-speed weldability, from the viewpoint of improving the productivity of welded cans and reducing the cost of canning.

  An object of the present invention is to provide a surface-treated steel sheet for a welding can that does not use Ni and has stable high-speed weldability and excellent rust resistance, yarn rust resistance, corrosion resistance, and adhesion to an organic resin. To do.

  As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.

  i) When the amount of non-alloyed metal Sn on the Fe-Sn alloy layer becomes extremely small, the high-speed weldability becomes unstable.

  ii) Change the amount of non-alloyed metal Sn on the Fe-Sn alloy layer on both sides of the steel sheet to reduce the amount of non-alloyed metal Sn to the limit and to secure a certain amount of non-alloyed metal Sn. Stable high-speed welding is possible if the surface with reduced amount of alloyed metal Sn comes to the outer surface of the can when making cans, and the surface with a certain amount of non-alloyed metal Sn secured to the inner surface of cans when making cans. Compatibility with excellent yarn rust resistance.

  iii) After reducing the amount of Sn oxide present on both sides of the steel sheet, by providing a chromate treatment layer consisting of a metal Cr layer and Cr hydrated oxide, excellent rust resistance, corrosion resistance, adhesion to organic resin Sex is obtained.

The present invention has been made on the basis of such knowledge, and on both surfaces of the steel sheet, in order from the steel sheet surface, has a Fe-Sn alloy layer, a chromium layer and a chromate treatment layer composed of a Cr hydrated oxide. The Sn adhesion amount on both sides of the steel plate is 0.4 g / m ² or more per side, and the non-alloyed metal Sn amount on the Fe-Sn alloy layer on one steel plate surface is less than 0.1 g / m ² , The amount of non-alloyed metal Sn on the Fe-Sn alloy layer on the steel plate surface is 0.2 to 2.0 g / m ² and the amount of Sn oxide on both sides of the steel plate is less than 2.0 mC / cm ² as the amount of reducing electricity per side In addition, the adhesion amount of the metal Cr layer of the chromate treatment layer on both sides of the steel sheet is 10-30 mg / m ² per side, and Cr hydrated oxide is 10-30 mg / m ² per side in terms of Cr equivalent. A surface-treated steel sheet for welding cans is provided.

  According to the present invention, it is possible to obtain a surface-treated steel sheet for a welding can that does not use Ni and has stable high-speed weldability and excellent rust resistance, yarn rust resistance, corrosion resistance, and adhesion to an organic resin.

  The surface-treated steel sheet for welding cans of the present invention has a Fe—Sn alloy layer and a chromate-treated layer in order from the steel sheet surface on both surfaces of a cold-rolled steel sheet, which is a known plating original sheet. Below, the detail of each layer is demonstrated.

1) Fe-Sn alloy layer Fe-Sn alloy layers are provided on both sides of the steel sheet. Fe-Sn alloy layer ensures yarn rust resistance and corrosion resistance. Further, the Sn adhesion amount on both surfaces of the steel plate is 0.4 g / m ² or more per one surface. This is because when the Sn adhesion amount is less than 0.4 g / m ² , the coverage with the Fe—Sn alloy layer becomes insufficient, and the yarn rust resistance and corrosion resistance deteriorate.

As described above, high-speed weldability becomes unstable when the amount of non-alloyed metal Sn on the Fe—Sn alloy layer is extremely reduced. Therefore, in the present invention, the amount of non-alloyed metal Sn on the Fe-Sn alloy layer provided on both sides is changed, and the amount of non-alloyed metal Sn on one side is less than 0.1 g / m ² , On the surface, the amount of non-alloyed metal Sn is controlled to 0.2 to 2.0 g / m ² . In this way, the amount of non-alloyed metal Sn on the Fe-Sn alloy layer was changed on each side, and the surface where the amount of non-alloyed metal Sn was less than 0.1 g / m ^{2 at} the time of can-making, If the amount of 0.2 to 2.0 g / m ² is placed on the inner surface of the can, excellent thread-like rust resistance can be obtained on the outer surface of the can, and non-alloyed metal Sn on the inner surface of the can ensures stable high-speed weldability. Is done. If the amount of non-alloyed metal Sn on the outer surface of the can is 0.1 g / m ² or more, the thread-like rust resistance deteriorates. This is thought to be due to generation and growth. Further, in the non-alloyed metals Sn amount is 0.2 to 2.0 g / m ² is the inner surface of the can, a high speed weldability becomes unstable in less than 0.2 g / m ^2, when it exceeds 2.0 g / m ² high speed welding This is because the effect of stabilizing the property is saturated and the cost is increased.

  Here, the amount of non-alloyed metal Sn is the same as that of non-alloyed metal Sn in the potential-time curve in accordance with the tin adhesion amount test method for tin plating by the electrolytic stripping method specified in the appendix of JIS G 3303-1969. It is calculated from the holding time at the stagnation potential due to dissolution. Further, the amount of Sn in the Fe—Sn alloy is calculated from the time during which the alloy Sn melting potential is maintained in the test method. The Sn adhesion amount in the present invention is the sum of the amount of non-alloyed metal Sn that can be calculated as the adhesion amount and the amount of Sn alloyed with Fe-Sn.

When a Sn-plated steel sheet having a Sn-plated layer is heated to a temperature equal to or higher than the melting point of Sn, an Fe—Sn alloy layer and non-alloyed metal Sn are formed thereon, and Sn oxide is formed on the surface. When the amount of Sn oxide is 2.0 mC / cm ² or more as the amount of reducing electricity per side, Sn oxide cohesively breaks down from the inside during coating and organic resin lamination, regardless of the inner and outer surfaces of the can. In addition, the organic resin layer is easily peeled off and the adhesion is lowered. At the same time, corrosion factors such as water and oxygen are likely to enter the interface between the organic resin and the steel sheet, and corrosion progresses in the lower layer of the organic resin, leading to deterioration of corrosion resistance. Therefore, the amount of Sn oxide on both sides of the steel plate needs to be less than 2.0 mC / cm ² as the amount of reduced electricity per one side, but if it is less than 0.5 mC / cm ² , stronger adhesion can be obtained. At the same time, it is preferable because the corrosion resistance can be maintained in the portion subjected to the can making process such as the expanding process or the neck-in process.

Here, the reducing electricity quantity of Sn oxide is obtained by cathodic electrolysis at a constant current of 0.05 mA / cm ² in 0.001 mol / L hydrobromic acid aqueous solution degassed dissolved oxygen by bubbling nitrogen gas. It is calculated from the obtained potential-time curve.

2) Chromate treatment layer A chromate treatment layer is provided on the outermost layer of the steel sheet on the Fe-Sn alloy layer as described above.
This is because the chromate treatment layer is indispensable for exhibiting adhesion to the organic resin, and at the same time functions as a barrier layer against oxygen reduction reaction, and maintains good thread-like rust resistance, rust resistance, and corrosion resistance. Because. The chromate treatment layer is composed of a metal Cr layer and a Cr hydrated oxide formed on the metal Cr layer. At this time, when the adhesion amount of the metal Cr layer of the chromate treatment layer is less than 10 mg / m ² or when the Cr hydrated oxide is less than 10 mg / m ^{2 in} terms of Cr conversion, the rust resistance deteriorates. If the adhesion amount of the metal Cr layer exceeds 30 mg / m ² or the Cr hydrated oxide exceeds 10 mg / m ² in terms of Cr, dust will be generated during welding, or the color will turn yellowish brown and the appearance will deteriorate. To do. Therefore, the adhesion amount of the metal Cr layer of the chromate treatment layer needs to be 10 to 30 mg / m ² , and the Cr hydrated oxide needs to be 10 to 30 mg / m ² in terms of Cr conversion.

3) Forming method of Fe-Sn alloy layer To manufacture the surface-treated steel sheet for welding cans of the present invention, after annealing, on both sides of the cold-rolled steel sheet subjected to temper rolling, first, a philostane bath, halogen bath, MSA Using a plating bath such as a bath, an Sn plating layer having an Sn deposition amount of 0.4 g / m ² or more per side is formed on both sides under normal conditions. At this time, in order to leave the target non-alloyed metal Sn amount after performing the heat-melting process described later, the current density and the electrolysis time are independently adjusted on the front and back sides, and the adhesion amount is changed on the front and back sides to perform plating. Next, the Sn plating layer is heated to a temperature equal to or higher than the melting point of Sn by a resistance heating method or a high frequency heating method to form an Fe—Sn alloy layer. At this time, the amount of Sn adhesion on each surface is individually controlled so as to be the amount of non-alloyed metal Sn on each surface, and the amount of Sn adhesion on the front and back surfaces is different, and the ultimate temperature is equal to or higher than the melting point of Sn. By adjusting the holding time, the amount of non-alloyed metal Sn is changed on each surface. In this way, the amount of non-alloyed metal Sn on one side is less than 0.1 g / m ^{2 and the} amount of non-alloyed metal Sn on the other side is 0.2 to 2.0 g / m ² .

And the Sn oxide formed on the surface by the above heating is an electric charge of about 1 to 50 C / dm ² in an electrolyte aqueous solution such as an aqueous solution of sodium carbonate, an aqueous solution of sodium bicarbonate, an aqueous solution of sodium hydroxide or hydrobromic acid. Cathodic electrolysis treatment is performed, and the amount of reducing electricity is reduced to less than 2.0 mC / cm ² and removed. It is preferable to wash with water after the cathodic electrolysis treatment. In addition, since Sn oxide increases somewhat with time, the measurement of the reduction electric quantity for evaluating the amount of Sn oxide is performed within 24 hours after the production of the Sn-plated steel sheet.

4) Formation method of chromate treatment layer After forming Fe-Sn alloy layers on both sides of the steel plate and adjusting the amount of non-alloyed metal Sn in the upper layer, chromic anhydride, various chromic acid Na, K or Cathodic electrolytic treatment in an aqueous solution of ammonia salt, particularly in an aqueous solution generally used for electrolytic chromate treatment, in which SO ₄ ion, F ion or a mixture thereof is added to 20-100 g / L of CrO ₃ , chromating adhesion amount per one side is made of a metallic Cr layer of 10 to 30 mg / m ^2, and Cr hydrous oxide is per side 10 to 30 mg / m ² of Cr equivalent coating weight on the metal Cr layer Form a layer.

After cold rolling annealing and temper rolling plating plate (thickness 0.2mm), alkaline electrolytic degreasing and sulfuric acid washing, then Sn plating treatment using the following bath (a), higher than the melting point of Sn The Fe—Sn alloy layer was formed. At this time, the amount of Sn deposition is adjusted by changing the electrolysis time and current density, the surface to be the outer surface and the surface to be the inner surface after canning are designated, and the temperature reached and the retention time above the Sn melting point are adjusted accordingly. The amount of non-alloyed metal Sn was adjusted. Then, A: 10 g / L Na carbonate aqueous solution (50 ° C), B: 5.5 g / L Na hydroxide aqueous solution (50 ° C), C: 3.5 g / L hydrobromic acid (25 ° C) In (aqueous electrolyte solution), as shown in Table 1, the amount of Sn oxide (reduction electricity) on both surfaces of the steel sheet was adjusted by changing the amount of cathodic electrolysis and washed with water. At this time, in the same steel plate, the amount of Sn oxide was made the same on both sides. Next, cathodic electrolytic treatment was performed using the following (b) bath, and chromate treatment layers were formed on both surfaces of the steel plates to prepare surface-treated steel plates No. 1 to 24. At this time, as shown in Table 2, changing the sulfate ion concentration, electrolysis time and current density in the treatment liquid, the amount of metal Cr layer in the chromate treatment layer and the amount of Cr hydrated oxide (Cr equivalent adhesion amount) It was adjusted.
(a) Bath
Sn ion concentration: 20g / L
Free methanesulfonic acid: 25 g / L
Brightener: Appropriate amount Antioxidant: Appropriate amount Bath temperature: 45 ° C
Current density: 5-10A / dm ²
(b) Bath chromic anhydride: 20 g / L
Sulfate ion: 0.05 to 1.0 g / L
Bath temperature: 30-50 ° C
Current density: 20-30A / dm ²
Then, high-speed weldability, rust resistance, yarn rust resistance, corrosion resistance, and adhesion to organic resins were investigated by the following test methods.
High-speed weldability: Lap allowance of 0.4mm, pressurization 441N (45kgf), heat input time required to form 1 nugget is 0.9ms, welding speed is 600 cans / min. Perform seam welding and obtain the tap value of the current setting device corresponding to the minimum current value at which sufficient welding strength is obtained and the tap value of the current setting device corresponding to the maximum current value at which the welding appearance deteriorates due to strong heat input, The difference was made into the welding possible electric current range. At this time, the welding strength was determined by a commonly used tear test, and the deterioration of the weld appearance was determined by the presence or absence of generation of dust indicating scattering of molten metal. And, the weldable current range is 6 points or more, the weldable current range is more than 3 points and less than 6 points and there is no void reaching the steel sheet surface, the weldable current range is 3 points or less, or The case where the generation of voids reaching the steel sheet surface was marked with x.
Rust resistance: Retort treatment was performed at 120 ° C. for 20 minutes, and the degree of rust generation was visually observed. For surface should be can manufacturing after the outer surface, the case where all rust on the entire surface did not occur ◎, a case where 1 cm ² per rust 1-5 points were observed ○, 6 to 10 pieces of point per 1 cm ² △ if rust is observed, x if 11 to 30 spot rust per cm ² is observed, or if slight rust is observed on the entire surface, × if remarkable rust is observed on the entire surface. XX was evaluated. In practice, it can be used without any problem as long as ○ or ◎.
Anti-thread-like rust resistance: After the can is made, the epoxy / phenolic paint is applied to the outer surface to be 50 mg / dm ² and baked at a steel plate temperature of 210 ° C. for 10 minutes. Using an Erichsen extrusion machine, 5mm height extrusion was performed. Next, after being immersed in a 6 mass% NaCl aqueous solution for 1 minute and taken out, it was stored indoors for 4 weeks, and the occurrence of thread rust from the crosscut portion was visually observed. ◎ when no thread-like rust has occurred, ○ when thread-like rust is formed with an average of less than 0.5 mm at the Erichsen extrusion part, thread-like rust with an average of 0.5 mm or more and less than 1 mm is formed at the Erichsen extrusion part △, when the Eriksen extrusion part has an average thread formation of 1 mm or more and less than 3 mm ×, and when the Eriksen extrusion part has an average formation of thread rust of 3 mm or more as XX did. In practice, it can be used without any problem as long as ○ or ◎.
Corrosion resistance 1 (Iron dissolution test): After coating the can, the surface that should be the inner surface is coated with an epoxy / phenolic paint to 50 mg / dm ² and baked at a steel plate temperature of 210 ° C. for 10 minutes, then 4 cm x 8 cm in size And the back and end surfaces were sealed. Put two cuts (4 cm length) until reaching the iron core with a cutter knife on the painted surface (cross cut), and add 80 mass of test solution mixed with the same amount of 1.5 mass% NaCl aqueous solution and 1.5 mass% citric acid aqueous solution. It was immersed, and after 4 days at 55 ° C., it was taken out and the amount of iron elution was measured. The iron elution amount was evaluated as ◎ when 0.03 g / L or less, ○ when 0.03 g / L or less and 0.06 g / L or less, △ when less than 0.06 g / L and less than 0.2 g / L, and × when 0.2 g / L or more. In practice, it can be used without any problem as long as ○ or ◎.
Corrosion resistance 2 (tomato juice immersion test): After making a can, the surface that should be the inner surface is coated with an epoxy-phenolic paint to 50 mg / dm ² and baked at a steel plate temperature of 210 ° C for 10 minutes, then 4 cm x 8 cm Cut to size and sealed back and end faces. Subsequently, it was immersed in commercially available tomato juice at 55 ° C. for 20 days, and the presence or absence of peeling of the coating film and generation of rust was visually observed. ◎ when there is no film peeling or corrosion, ◯ when there is no film peeling, very little point-like corrosion occurs, △ when there is no film peeling or many point-like corrosion occurs, partially The case where the coating film was peeled off and the occurrence of corrosion was evaluated as x, and the case where the coating film was peeled off on the entire surface and significant corrosion occurred was evaluated as xx. In practice, it can be used without any problem as long as ○ or ◎.
Adhesion with organic resin (T peel test): Epoxy / phenolic paint is 50 mg / dm ^{2 on the} surface that should be the outer surface or the inner surface after canning of two surface-treated steel sheets of the same type After coating and baking for 10 minutes at a steel plate temperature of 210 ° C, after making the two steel plates, the surface to be the outer surface or the surface to be the inner surface is sandwiched with a nylon film facing each other and hot-pressed, This was divided into 5 mm wide test pieces to prepare tensile test pieces. The adhesion strength of the surface-treated steel sheets bonded face to face was measured with a tensile tester. For each of the surfaces that should be the outer surface and the inner surface after making the can, the adhesive strength is 3.5 kg / 5 mm or more, ◎, 1.5 kg / 5 mm or more and less than 3.5 kg / mm, ○, 1.0 kg / 5 mm or more, 1.5 kg / 5 mm Less than Δ was evaluated as less than Δ, and less than 1.0 kg / 5 mm was evaluated as ×. In practice, it can be used without any problem as long as ○ or ◎.

  The results are shown in Table 3.

  The surface-treated steel sheets No. 1 to 13, which are examples of the present invention, have a stable weldable current range of 6 points or more, stable high-speed weldability, and excellent adhesion to organic resins. , Excellent rust resistance and thread-like rust resistance as the outer surface after can-making, excellent corrosion resistance as the inner surface after can-making, satisfying performance required for surface-treated steel sheets for welding cans doing. On the other hand, the surface-treated steel sheets No. 14 to 24, which are comparative examples, are inferior in performance of any one or more of high-speed weldability, rust resistance, thread-like rust resistance, adhesion to organic resins, and corrosion resistance.

Claims (1)

The steel sheet has a Fe-Sn alloy layer formed by heating to the temperature equal to or higher than the melting point of Sn in order from the steel sheet surface on both surfaces of the steel sheet, and a chromate-treated layer composed of a metal Cr layer and Cr hydrated oxide. The amount of Sn adhesion on both sides is 0.4 g / m ² or more per side, and the amount of non-alloyed metal Sn on the Fe-Sn alloy layer on one steel plate surface to be the outer surface after canning is 0.01 g / m ² Less than, the amount of non-alloyed metal Sn on the Fe-Sn alloy layer on the other steel plate surface that should be the inner surface after canning is 0.2 to 2.0 g / m ² , and heating when forming the Fe-Sn alloy layer Cathode electrolytic treatment was performed so that the amount of Sn oxide on both sides of the steel plate formed by the method was less than 2.0 mC / cm ² as the amount of reducing electricity per side, and one steel plate surface to be the outer surface after canning The amount of metal Cr layer in the chromate-treated layer is 20-30 mg / m ² per side , Cr hydrated oxide is 15-30 mg / m ² per side in terms of Cr , and is the inner surface after making the can. The other steel Welded can adhesion amount of the metal Cr layer of chromate treatment layer of the surface is 10 to 30 mg / m ^2, Cr hydrous oxide per side is characterized in that it is a single-sided per 10 to 30 mg / m ² of Cr equivalent coating weight Surface treated steel sheet.