JP2600217B2 - Multi-layer plated steel sheet for cans - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface-treated steel sheet used in combination with aluminum, particularly as a material for cans filled with beverages and foods.

[Prior Art] As a material for food cans and beverage cans, tinplate electroplated tin or steel plate, tin-free steel electroplated chromium or nickel steel plate, or aluminum sheet has been often used. Of these materials, the surface-treated steel sheet that has been subjected to electroplating of the steel sheet has strength even though it is thin, and the aluminum sheet is easy to be worked like easy open which can be opened with bare hands without using a can It has the characteristic.

In recent years, using these features, the use of safe and convenient easy-open cans in which the can body is made of surface-treated steel sheet and the can lid is made of aluminum sheet has been seen.

However, when the material of the can body and the material of the lid are made of different metals, so-called bimetallic corrosion occurs, in which one of them is preferentially melted and corroded on the inner surface of the can. It is preventing its spread.

Bimetallic corrosion constitutes a battery when metals having different electrode potentials come into electrical contact in the presence of an electrolyte, in which a current flows from a metal having a higher potential to a metal having a lower potential, and a base having a lower potential. This is a phenomenon in which the metal becomes ionized and melts out. For example, when the can body is a tin and the can lid is made of an aluminum sheet, the standard electrode potential of aluminum is -1.
The value of tin is -0.14v, whereas tin is much more noble than 66v. For this reason, an anodic reaction (1) occurs on the surface of the aluminum, and the aluminum dissolves. At the same time, a cathodic reaction (2) occurs on the surface of the tin, generating hydrogen.

Al → Al ³⁺ 3e… (1) 3H ⁺ + 3e → 3 / 2H ₂ …… (2) Generally, aluminum lids and tin cylinders are coated with paint on the inner surface of the can, so the above reaction occurs over the entire surface. not,
On the aluminum side, it occurs concentrated on the coating defect, and as the reaction progresses, holes are opened in the aluminum lid. On the tin side, the generated hydrogen lifts the coating film, causing blisters. As this progresses, the coating film peels off.

This phenomenon occurs very remarkably when the contents of the can contain chloride ions such as salt.

As described above, the case of aluminum and tin has been described.
The potential of Ni is much higher than that of Al, and the situation is the same as in the case of tin plating (tin).

In food cans, to withstand corrosion by the contents for a long time,
The surface-treated steel sheet for cans is used after being coated with a can inner surface paint. Therefore, the material for cans is required not to cause the bimetallic corrosion described above and to have the original corrosion resistance under the coating film.

In order to deal with such problems, attempts have been made to hamper the formation of the battery by devising a paint and a coating method for the inner surface of the can, particularly by strengthening the coating of the aluminum lid. In relation to the internal environment, the anodic polarization characteristics of the aluminum lid and the cathodic polarization characteristics of the can body have been examined (for example, iron and steel 73, No. 3 (1987) p431), but a satisfactory solution has not yet been obtained. Not been.

[Problems to be Solved by the Invention] As described above, the easy open-end can using a surface-treated steel plate such as tinplate or tin-free steel for the can body and using aluminum for the can lid is a bimetallic corrosion-based Since the problem is still unresolved, its use is still limited in cases where the contents of the can contain chloride ions such as salt.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a surface-treated steel sheet for a can body which does not cause bimetallic corrosion and has good corrosion resistance under a coating film.

[Means for Solving the Problems] A steel plate used for a can body of a can body in which the can lid is an Al plate or an Al alloy plate and the can body is a steel plate, and Zn, Ni, Cr, Sn, Ti, Cu, or a plating layer of a different component selected from a plating layer of any one of Fe or an alloy plating layer of two or more of the metals And a composite plating layer having a total thickness of 0.001 μm to 5 μm as a lower layer, and A having a thickness of 0.001 μm to 2 μm is formed on the composite plating layer.
A multilayer plated steel sheet for cans, characterized by having a plated layer of l or Al alloy as an upper layer.

In the present invention, the reason why the uppermost layer is made of the Al or Al alloy plating layer is to prevent bimetallic corrosion by making the potential of the Al lid coincide with the potential of the can body. In this case, the plating thickness of Al or Al alloy needs to be 0.001 μm to 2 μm. When the thickness is less than 0.001 μm, the coupling current as the coating is unstable, and the upper limit is set to 2 μm from a practical viewpoint in consideration of economy. Further, in the present invention, it is necessary to provide a composite plating layer comprising a multilayer plating layer as a lower layer.
The reason why the multi-layered plating layer is used is that a predetermined thickness provides superior under-film corrosion resistance and complements insufficient under-film corrosion resistance of the uppermost Al or Al alloy plating layer. Therefore, it is necessary to use a corrosion-resistant composite plating layer other than the uppermost Al or Al alloy plating layer. A composite plating layer is formed by laminating at least two plating layers of different components composed of alloy plating layers of two or more metals. Here, the thickness of the composite plating layer is set to 0.001 μm to 5 μm.
It must be in the range of μm. If it is less than 0.001 μm, sufficient under-coat corrosion resistance cannot be exhibited. Also 5μm
If the thickness exceeds the upper limit, the upper limit is set to 5 μm because there is no improvement in the corrosion resistance under the coating film even if the plating thickness is increased. In the present invention, it suffices that at least one side of the steel sheet has a multilayer plating film combining the upper layer and the lower layer. When it is provided on one side, it may be used as the inner surface of the can.

[Function] When the multilayer plated steel sheet of the present invention is used as a can material,
Al metal, Al-Mg, Al-Cu alloy, etc. are used for the Al lid, but in the present invention, as the uppermost layer, for example, Al is used for the Al metal lid.
A multi-layer plated steel sheet having a plating layer, an Al-Ti alloy plating layer, and an Al-Mg alloy plating layer for an Al-Mg alloy lid is used for the can body. As described above, the plating film composition of Al or an Al alloy is finely selected according to the material of the can lid, and the potentials of the can lid and the can body are made to precisely match. Thereby, bimetallic corrosion can be prevented as much as possible. In this case, the plating layer of Al or Al alloy is a metal having corrosion resistance even to the contents of the can, but these plating films are for matching the potential with the Al lid, and the corrosion resistance under the coating film is insufficient. Therefore, the composite plating layer according to the present invention complements them as an effect and improves the corrosion resistance under the coating film.

[Examples of the Invention] Examples of the multilayer plated steel sheet according to the present invention will be specifically described below. Here, the conditions of vacuum deposition were as follows.

Vacuum degree: 6 × 10 ^-6 Torr, substrate temperature: 200 ° C., evaporation method: electron beam heating, substrate-crucible distance: 50 cm (Example 1) Ni is applied to a cold-rolled steel sheet having a thickness of 0.22 mm using a Watt bath. Was electroplated, and Sn was electroplated thereon using a ferrostan bath. The Sn plating film is reflow-melted to finish the lower plating layer.
Was produced.

Here, the watt bath and electrolysis conditions are as follows.

Nickel sulfate: 330 g / l, nickel chloride: 45 g / l, boric acid: 40 g / l, pH: 4.0, bath temperature: 50 ° C, current density: 5 A / cm ² .

(Example 2) A cold rolled steel sheet having a thickness of 0.21 mm was coated with Cr using a Sargent bath.
Was applied, Ni was plated thereon, and an upper plating film of Al was formed thereon by a vacuum evaporation method.

Here, the surge bath and electrolysis conditions are as follows.

Chromic anhydride: 250 g / l, boric acid: 25 g / l, bath temperature: 50 ° C, current density: 15 A / cm ² .

(Example 3) Ni, Cr, Cu were formed on a cold rolled steel sheet having a thickness of 0.21 mm by a vacuum evaporation method.
The above three types of plating were applied, and on top of that, three types of plating of Zn, Sn, Fe-Zn, were applied and combined, and as an upper layer, Al, Al-Mg was subjected to a vacuum deposition process. . Note that Fe in the Fe-Zn plating layer was 50% by weight.

With respect to the surface-treated steel sheet subjected to the above treatment, the corrosion resistance under the coating film and the bimetallic corrosion resistance were evaluated in consideration of the inner surface condition of the can.

The undercoat corrosion resistance was evaluated by a UCC test (undercutting corrosion test). The epoxy phenol paint was applied to a thickness of 50 mg / dm ² on the test surface in this study, 21
After baking at 0 ° C. for 10 minutes, a test piece was prepared by cross-cutting the coating film with a cutter. This test piece was NaCl 1.
It was immersed in a corrosive solution containing 5% and 1.5% citric acid at 38 ° C. for 72 hours, and it was observed whether or not undercoat corrosion occurred.

The resistant bimetallic corrosion tests, an epoxy phenolic paint was coated to a thickness of 50 mg / m ² on the test surface, 210
It was baked at 10 ° C. for 10 minutes, and was connected with an aluminum plate similarly painted and baked with a conductive wire via an ammeter.
In this state, the non-exposed surface was sealed with a tape so that the same area was exposed on both sides to obtain a test piece. This test piece was immersed in a 0.3% NaCl aqueous solution at 125 ° C. for 60 minutes (retort treatment), and then another 0.3% NaCl kept at 80 ° C.
It was immersed in an aqueous solution, and the coupling current flowing between the plated steel sheet and the aluminum plate was measured.

In the evaluation, tinplate (tin-plated steel plate) and tin-free steel (chrome-plated steel plate), which are widely used as materials for cans, were used as comparative examples.

 The test results are shown in Tables 1 and 2.

According to the results shown in Tables 1 and 2, in the UCC test, all the examples of the present invention are superior to the conventional tin and tin-free steel. Further, in the bimetallic corrosion characteristics, the coupling current of the example was one digit smaller than that of the conventional treated steel sheet, indicating that it was extremely excellent.

In the present invention, although the above-mentioned coating alone exerts its effect sufficiently, the surface thereof is further subjected to an aluminum chemical conversion treatment (a phosphate treatment, a chromate treatment, a chromic phosphate treatment or the like is performed by dipping, spraying, electrolytic treatment or the like). By providing a coating (layer thickness of about 0.01 to 0.1 μm) formed by
Further, the effect is improved.

[Effects of the Invention] As described above, in the present invention, since the lower layer has two or more plating layers and the upper layer has an Al-based plating layer, this is used for the can body and combined with the Al lid. Even when an open-end can is made, bimetallic corrosion does not occur, and the corrosion resistance under the coating film is also remarkably improved. Thus, a safe and convenient can body exhibiting the features of Al and steel can be put into practical use without being restricted by the contents of the can, and the effect of the invention is great.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Ishikawa 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Hiroshi Kagechi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Inside the Kokan Co., Ltd. (72) Inventor Tadahiko Mishima 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Examiner, Nippon Kokan Co., Ltd. Satoshi Sera (56) References JP-A-64-75665 (JP, A) JP-A-64-17877 (JP, A) JP-A-63-50483 (JP, A) JP-A-63-282291 (JP, A) JP-A-63-50493 (JP, A) JP-A-1-118553 (JP, A) JP, A) "Iron and steel" Vol. 73 (1987) No. 3, p. 427-436

Claims (1)

(57) [Claims] 1. A steel plate used for a can body of a can body in which the can lid is an Al plate or an Al alloy plate and the can body is a steel plate, wherein Zn, Ni, Cr, Sn, Ti , Cu, or at least two layers of plating layers of different components selected from plating layers of any one of Fe or alloy plating layers of two or more of the metals And a composite plating layer having a total thickness of 0.001 μm to 5 μm as a lower layer, and a thickness of 0.001 μm on the composite plating layer.
A multi-layer plated steel sheet for cans, which has a plated layer of Al or an Al alloy of up to 2 μm as an upper layer.