JPH01192544A - Laminated steel plate for can excellent in content holdability - Google Patents

Abstract

PURPOSE:To obtain a steel plate for a can capable of keeping the freshness of its contents over a long period of time, by allowing a proper amount of an Ni film to be present on the surface of the steel plate becoming the inner surface side of the can and further allowing a thermoplastic film excellent in oxygen permeability to be present on the upper surface thereof. CONSTITUTION:The oxygen carried in a can transmits through a thermoplastic film to be consumed by the reaction with the inner surface of a steel plate but, when the plating of Ni or an Ni alloy is applied to the single surface of the thin steel plate becoming the inner surface side of the can in a bonding amount of 5-100mg/m<2>, a deoxygenating speed is enhanced. As the Ni film, any film containing Ni such as pure Ni, Ni-Fe, Ni-Sn or Ni-Cr may be used and the Ni film can be simply formed to the surface of the steel plate by electroplating. As the plastic film adapted to the Ni-containing layer, a film having good oxygen permeability composed of polyethylene or polybutadinene is selected and the thickness thereof is set to 15-100mum. In a laminating method, for example, a solvent type adhesive such as a urethane or epoxy adhesive is thinly applied before the film is laminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a steel plate for metal containers (cans) for filling and storing beer, carbonated drinks, juices, general foods, etc. as contents.

[Conventional technology]

As a steel sheet for metal containers, "Tin-free steel" (electrolytic chromic acid treated steel sheet) is well known, and it can be used for welded cans, adhesive cans or 01 cans (cans formed by drawing and ironing) ).These materials are often coated with a 5-10 μm thick organic coating before or after can manufacturing, and their corrosion resistance mainly relies on the organic coating. The current situation is that

In this case, thermosetting paints such as epoxy, epoxy-phenol, vinyl, and polyester are used as the organic coating.

[Problem that the invention seeks to solve]

When a metal container (can) is filled with contents, oxygen is contained in the contents themselves or in the internal space of the can, and this oxygen is inevitably carried into the can.

As is well known, oxygen is a component that causes various drinks and foods to spoil, so it is important to prevent its presence in cans as much as possible. In conventional can bodies, there is no effective method for removing the oxygen that is inevitably brought in, and the taste and odor of the contents inevitably deteriorate over time.

The present invention provides a steel plate for cans that quickly removes oxygen inevitably brought into the can and maintains the freshness of the contents over a long period of time without causing any deterioration in the taste or odor of the contents. It is.

[Means for solving problems]

The main constituent elements of the present invention are the film structure on the surface of the steel plate, which is the can-contacting side, and the first is that an appropriate amount of Ni is present on the surface of the steel plate. The second method is to provide a thermoplastic film with excellent oxygen permeability above the appropriate amount of Ni-containing layer.

The presence of the Ni film, which is the first film constituent factor, is a very important item in determining the oxygen removal speed. The oxygen brought into the can passes through the thermoplastic film, reacts with the surface of the steel plate, and is consumed.In this case, it is important to determine the deoxidation speed by controlling the amount of Ni present. This is the aim of the invention. The basis for determining Nii is that below the lower limit (5■/rrf), the deoxidation speed is slow and no effect is observed;
Even with the above, the deoxidation speed was slow and no effect was observed, so this range was set. Although it is not clear why the deoxidation speed improves in a specific Ni deposit area, it is believed that the local presence of Ni on the steel sheet surface contributes to the activation of the corrosion reaction. Conceivable.

The Ni film to be applied is pure Ni or Ni-F.
Any material containing Ni such as e, Ni-5n, NiCr, etc. may be used. Although the effect of pure Ni is greater, the reactivity may be too strong, and in that case, it is desirable to apply alloy plating.

These Ni films can be easily formed on the steel plate surface mainly by electroplating, but are not limited to electroplating, and can be formed by other methods such as vacuum evaporation, chemical plating, alloying by thermal diffusion, etc. It can also be obtained by methods.

Next, regarding the plastic film layer applied on the Ni-containing layer, a film with good oxygen permeability such as polyethylene, polybutadiene, or polymethylpentene must be selected. The oxygen sealed in the can will pass through these films and reach the surface of the steel plate, so it is desirable that the film be as thin as possible, but if it is too thin, it may cause pinholes in the film itself or Due to problems such as migration of corrosion products to the contents, the thickness is set at an appropriate level. If it is too thick, the oxygen permeation rate becomes slow, which is not preferable and is also disadvantageous in terms of cost. From this point of view, the film thickness in the present invention is 15~
It was set to 100 μm.

The lamination method for these films includes a suitable adhesive layer,
For example, you can apply a very thin layer of solvent-based adhesive such as urethane-based (two-component type) or epoxy-based adhesive and then laminate the film, or you can make the resin that makes up the film itself have self-adhesive properties, and then apply it on a heated steel plate. Laminated by thermocompression bonding. At this time, whether or not the laminated films are melted or not is not a big problem with respect to the desired oxygen scavenging ability.

The surface structure constituting the inner surface of the can and its manufacturing method have been explained using the above method. Next, the constituent elements of the outer surface of the can will be explained.

In the present invention, the outer surface of the can is not particularly limited, but coatings such as Sn plating, Cr plating, or Ni plating that are currently in practical use as steel sheets for containers can be used. It should be noted that in the case of any type of plating, chromate treatment is often applied to improve paintability (.

These plating films are different from the plating film or film on the inside of the can, so they must be done in a separate plating solution, but in terms of the order of plating, the chromate treatment on the outside of the can is done last. things are desirable. The reason for this is that if a trace amount of Cr exists under the film, it will reduce the oxygen consumption reaction, so that desired results may not be obtained.

[For production]

As detailed above, the main feature of the present invention is to provide a steel plate surface that can quickly remove oxygen brought into the can in order to improve the preservation of the contents inside the can. It can be applied to any content that is disliked, and is mainly used for can lids.

Examples will be described below.

[Example 1] After degreasing and pickling, one side of a thin steel plate with a thickness of 0.24 rrmh was plated with 2.5 g/n of Sn in a normal ferrostane bath, and then the other side was plated with Sn at a rate of 2.5 g/n (Sn plating). Ni plating with a Nt deposition amount of 15 μ/bo was performed in a Watt bath. After washing with water and drying, 30 μ/N was deposited on the Ni-plated surface.
Polymethylpentene with a film thickness of m was laminated by thermal bonding. At that time, the polymethylpentene film had a two-layer structure, and an acid-modified film with self-adhesive ability was used on the steel plate side, and was pressure-bonded to the steel plate preheated to 220"C. Cathodic electrolysis treatment was carried out in a bath containing the main components, and the Sn-plated surface was treated with metallic Cr and hydrated chromium oxide (total chromium amount: 23 mg/%).

The lid was manufactured so that the surface with the polymethylpentene film became the inner surface of the can, and a conventional product (a welded tin can with thermosetting epoxy coating on the inner surface) was used as the can body.

After being filled with beer and stored at 20°C for one month, the oxygen removal rate was measured and showed very excellent performance with an average of 65%. There was no problem with iron elution, and in sensory tests such as taste and flavor, the level was significantly superior to that of conventional products.

[Example 2] Sn plating (2.5g/
After r+(), Ni-Fe alloy plating containing 20% Ni (deposition amount 80 mg/n() was performed. After that,
Polymethylpentene with a thickness of 30 μm was laminated on the Ni-Fe alloy plating via a 1.5 μm urethane adhesive. After that, the characteristics were evaluated using the same method as in Example 1, and the oxygen removal rate after storage at 20°C for one month was 50% on average, showing excellent performance, and the taste and flavor were also better than conventional products. It was at an extremely high level.

[Example 3] Sn plating was performed using the same method as in Example 1 (coating amount: 2.
After performing Ni plating (coating amount: 25 g/bo), a polyethylene film with a film thickness of 50 μm was coated with 1.5
They were laminated via a μm urethane adhesive.

Thereafter, characteristics were evaluated in exactly the same manner as in Example 1, and the oxygen removal rate after storage at 20°C for one month was 40% on average, showing excellent performance. Sensory tests regarding flavor and taste showed that it was almost the same as conventional products.

[Example 4] Metallic Cr (coating amount: 70 g/rrr) was coated on one side of a thin steel plate with a thickness of 0.25 mm, and a hydrated chromium oxide film (
After plating with a coating amount of Cr of 15 g/r+(), Ni-F containing 35% Ni is applied to the other side.
E-alloy plating (deposition amount: 100 mg/rrf) was performed. After that, 1 piece of polybutadiene film with a film thickness of 40 μm was
．． They were laminated via a 5 μm urethane adhesive.

As a result of an actual can test with the polybutadiene film surface as the inner surface, the oxygen removal rate after storage for one month at 20°C was excellent with an average of 55%.

[Comparative Example 1] Both sides of a thin steel plate with a thickness of 0.25 mm were plated with metal Cr (deposition amount 90 g/rd), and the upper layer was plated with a hydrated chromium oxide film (deposition amount Cr: 16 g/rrf). Afterwards, an epoxyphenol paint (film thickness: 5 μm) was applied and baked, and the can lid was processed.

When an actual can test was conducted using the same can body as in Example 1, the oxygen removal rate after storage at 20°C for one month was 2% or less, and the product had almost no oxygen removal ability.

[Comparative Example 2] After performing Sn plating (coating amount 2.5 g/rrf) on both sides of a thin steel plate with a thickness of 0.25 mm, it was placed in a sodium dichromate bath (25-g/CpH = 4.0). Chemical treatment mainly using chromium oxide (coating amount 5)
．． 6■/n() was performed. After applying and baking a thermosetting vinyl paint (film thickness: 5 μm), the can lid was processed.

When an actual can test was conducted using the same can body as in Example 1, the oxygen removal rate after storage at 20° C. for one month was 2% or less, and there was almost no oxygen removal ability.

In addition, the oxygen removal rate is the amount of oxygen after a certain period of time,
It is calculated by the following formula using the numerical values a and b shown in FIG.

Oxygen removal rate (%) = (a/b) We provide a steel plate for cans that can maintain the freshness of the contents over a long period of time without causing any deterioration of the content.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the storage period of a beer can and the oxygen concentration inside the can. Stitch period (days)

Claims (3)

[Claims] (1) Ni or Ni alloy plating is applied to one side of the thin steel plate, which will become the inner side of the can after can manufacturing, with a Ni adhesion amount of 5 to 100 mg/m^2, and the upper layer is coated with a thickness of 100 mg/m^2, which has excellent oxygen permeability.
A laminated steel sheet for cans having excellent content retention properties, characterized by laminating resin films of 5 to 100 μm. (2) The laminated steel sheet for cans according to claim 1, in which polyethylene, polybutadiene, or polymethylpentene is laminated as a resin film. (3) The laminated steel sheet for cans according to claim 1 or 2, which has a film of Sn plating, Cr plating, or Ni plating on the surface of the thin steel sheet that becomes the outer surface of the can after can manufacturing.