JP2600218B2 - Multi-layer plated steel sheet for cans - Google Patents

Description

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

[Prior art] Tin-free steel in which tin is electroplated on a steel plate, tin-free steel in which chromium or nickel is electroplated on a steel plate, or an aluminum sheet is often used as a material for food and beverage cans. Among these materials, the surface-treated steel sheet obtained by electroplating the steel sheet has strength even if 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 opener. Has features.

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

However, if the material of the can body and the material of the lid are made of different metals, one of them is preferentially melted and corroded on the inner surface of the can, so-called bimetallic corrosion, resulting in this convenient can. Is preventing the spread of

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, if the can body is a tin and the can lid is made of aluminum sheet, the standard electrode potential of Al is -1.66V.
Whereas that of tin is -0.14V, which is much more precious than tin. 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) In general, aluminum lids and tin cylinders are coated with paint on the inside of the can, so the above reaction occurs over the entire surface. not,
On the aluminum side, this 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 up 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 investigated (for example, iron and steel No. 73,3 (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 If the contents of the can contain chloride ions such as salt because the problem has not been solved, the use is still limited.

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] The present invention is a steel plate used for a can body of a can body having a can lid made of an aluminum sheet and a can body made of a steel plate, wherein at least one surface of the steel plate has Zn, Ni, Cr, Sn, Ti, Cu, or a thickness of at least one layer including at least one plating layer made of any one of Fe or an alloy plating layer made of two or more of the metals.
This is a multi-layer plated steel sheet for cans having a plating layer having a thickness of 1 μm to 5 μm as a lower layer, and a plating layer of Ti or a Ti alloy having a thickness of 0.001 μm to 2 μm as an upper layer on the lower layer.

In the present invention, the upper layer is made of a plated layer of Ti or Ti alloy because the difference between the natural electrode potential of Ti and that of Al is only 0.034 V, which is extremely small. This is also because bimetallic corrosion is extremely unlikely to occur. Ti is hard to corrode in the air,
The stability of the draft section of the beverage can is excellent, and anticorrosion performance can be expected over a long period of time. In this case, the plating thickness of Ti or a Ti alloy needs to be 0.001 μm to 2 μm. Thickness
When the thickness is less than 0.001 μm, the potential of the film is unstable, and the upper limit is set to 2 μm from a practical viewpoint in consideration of economy.

In the present invention, it is necessary to provide a lower layer for imparting corrosion resistance under the coating film. Here, the lower layer is a general term for a plating layer that imparts corrosion resistance under a coating film, and includes Zn, Ni, Cr, Sn, Ti, and C.
u or a plating layer made of any one of Fe or a plating layer containing at least one alloy plating layer made of two or more of the metals. Therefore, it may be a single layer or a multilayer. This lower layer complements the corrosion resistance under the coating which is insufficient with the upper layer of the Ti or Ti alloy plating layer. Therefore, the above-mentioned corrosion-resistant plating layer other than the upper Ti or Ti alloy plating layer is required. Here, the thickness of the lower layer needs to be in the range of 0.001 μm to 5 μm. If it is less than 0.001 μm, sufficient under-coat corrosion resistance cannot be exhibited. When the thickness exceeds 5 µm, the upper limit of the thickness is 5 µm because there is no improvement in the corrosion resistance under the coating film in the rate of increase in the plating thickness.

The aluminum sheet of the present invention is directed to an aluminum sheet made of an Al metal, an Al alloy, or the like.

[Function] When the multilayer plated steel sheet of the present invention is used as a can material,
Ti or Ti alloy (for example, Ti-Al alloy) for aluminum lid
Using a multi-layer plated steel sheet with a plating layer as the upper layer for the can body,
Since the difference between the natural electrode potential of Ti and that of Al is extremely small, the difference is used to minimize the difference in electrode potential between the lid and the can body. This makes bimetallic corrosion extremely unlikely to occur. In this case, Ti or Ti alloy is generally a metal having corrosion resistance even to the contents of the can, but these plating layers are for adjusting the potential, and the corrosion resistance under the coating film is insufficient. The action of the lower plating layer according to the present invention complements them 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) A cold-rolled steel sheet having a thickness of 0.22 mm was electroplated with Ni using the following bath, and electroplated with Sn using a ferrostan bath. The Sn plating film was reflow-melted to finish the lower plating layer, and an upper plating film of Ti was formed thereon using a vacuum evaporation method.

Ni plating conditions: Bath composition: nickel sulfate 50 g / l, boric acid 10 g / l, pH: 4.0, bath temperature 30 ° C, current density 1 A / dm ² .

(Example 2) Cr is rolled on a cold rolled steel sheet having a thickness of 0.21 mm using a surge bath.
Electroplating of Ni, and two types of lower plating layers, Ni-plated or Ni-Zn alloy-plated, are made on it, and Ti or Ti-Al is deposited on each plating layer by vacuum evaporation. An upper plating film was prepared. Here, the surge bath and electrolysis conditions are as follows.

Chromic anhydride: 250 g / l, boric acid: 25 g / l, bath temperature: 30 ° C, current density: 1 A / dm ² .

(Example 3) Ni, Cr, Cu was deposited on a cold rolled steel sheet having a thickness of 0.21 mm by a vacuum evaporation method.
The three types of plating are applied, and on top of this, three types of plating of Zn, Fe-Zn, and Sn are applied by the same vacuum deposition and combined.
Vacuum deposition of Ti was performed as the upper layer. 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 liquid containing 5% and 1.5% citric acid at 38 ° C. for 72 hours, and it was observed whether or not under-coating corrosion occurred.

The resistant bimetallic corrosion tests, an epoxy phenolic paint was coated to a thickness of 50 mg / dm ² on the test surface, 21
Baking was performed at 0 ° C. for 10 minutes, and the aluminum plate subjected to the same paint baking was connected with a conductive wire via an ammeter and coupled. In this state, so that both expose the same area,
The non-exposed surface was sealed with a tape 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. Bimetallic corrosion is more likely to occur as the coupling current increases.

In the evaluation, tin (tin-plated steel sheet) and tin-free steel (chrome-plated steel sheet), 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. In the bimetallic corrosion resistance, the coupling current of the example was smaller by one digit than that of the conventional treated steel sheet, indicating that the bimetallic corrosion resistance was extremely excellent.

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. If it is provided on one side, that side may be used as the inner surface of the can. Of course, it may be provided on both sides. This multilayer plating film has very good corrosion resistance in the air, and especially the uppermost Ti or Ti alloy plating layer has excellent corrosion resistance. In addition, the Ti or Ti alloy plating layer is beautiful and excellent in appearance, and particularly the coating applied by the dry process has a fine texture and is excellent in printability in combination with its lightness.

In the present invention, the above-mentioned coating film can sufficiently exert its effect. However, the surface thereof is further subjected to aluminum chemical conversion treatment (phosphate treatment, chromate treatment, chromic phosphate treatment, etc., by immersion, spraying, electrolytic treatment, etc.). The effect is improved by providing the formed film (layer thickness of about 0.01 to 0.1 μm).

[Effects of the Invention] As described above, the present invention has one or more plating layers in the lower layer and a Ti-based plating layer in the upper layer. 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. As a result, a safe and convenient can body exhibiting the characteristics of the aluminum sheet and the steel plate can be put to practical use, and the effect of the invention is great.

 ──────────────────────────────────────────────────続 き Continued 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 of Kokan Co., Ltd. (72) Inventor Tadahiko Mishima 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Examiner of Nippon Kokan Co., Ltd. Satoshi Sera (56) References JP-A-63-45045 (JP, A) JP-A-63-282291 (JP, A) JP-A-63-50493 (JP, A) JP-A-1-111185 (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 a can lid is an aluminum sheet and a can body is a steel plate, wherein Zn, Ni, Cr, Sn, Ti, Cu, or A thickness of at least one layer including at least one of a plating layer composed of any one of Fe and an alloy plating layer composed of two or more of the metals.
A multi-layer plated steel sheet for cans, characterized by having a plating layer having a thickness of 1 μm to 5 μm as a lower layer, and a plating layer of Ti or a Ti alloy having a thickness of 0.001 μm to 2 μm as an upper layer on the lower layer.