JPH01192545A - Laminated steel plate for can excellent in processability and corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a steel plate for a can excellent in corrosion resistance, by providing an Sn plating film to the single surface of a thin steel plate while providing a tin plating film and/or a chromium film to the other surface thereof and further providing a polyester resin film having an amorphous structure on the upper surface of each of both films. CONSTITUTION:An Sn plating film is applied to the single surface of a thin steel plate, and an Sn plating film and/or a chromium film is applied to the other surface thereof and a polyester resin film having an amorphous structure and having a m.p. of 200-240 deg.C and a thickness of 10-100mum is applied to the upper surface of each of both films. In this case, Sn plating is applied to the single surface and/or both surfaces of the steel plate at first after degreasing and pickling next, single surface electrolytic treatment consisting of electrolytic treatment (the inner surface of the can on the side of a laminated surface), and immersion treatment (the outer surface of the can on the side of the non-laminated surface) is simultaneously performed in chromic acid and a polyester resin is laminated at the final stage. The polyester resin is once heated to the m.p. or more thereof and subsequently cooled to be formed into an amorphous structure.

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. It is used for two-piece cans and lids, where the bottom and can body are integrally molded.

[Prior art] As a steel plate for metal containers, tinplate or tin-free steel (electrolytic chromic acid treated steel plate) is well known, and welded cans, adhesive cans or DI cans (drawn and ironed) are well known. These materials are often coated with a 5-10 μm thick organic coating before or after the can manufacturing process, and their corrosion resistance is mainly Currently, we are relying on organic paints.

For example, JP-A-54-94585 and JP-A-54-1
Publication No. 3268 proposes performing DI processing after painting a steel plate.

At that time, thermosetting paints such as epoxy, epoxy-phenol, vinyl, and polyester are generally used as organic paints.

[Problem that the invention seeks to solve]

In the case of a 2-piece can where the bottom and body are integrally formed, 2
It is formed by drawing up to 3 times (DRD can) or by drawing 2 times and then ironing in 2 to 3 stages (DI can). The material used is tin-plated steel plate (tin plate) or aluminum plate, but in the case of tin plate, the inner surface is coated twice after molding because its corrosion resistance is insufficient. With one coating, the coating film cannot completely cover the surface of the steel plate, which causes iron to be leached into the contents, resulting in a decrease in taste and flavor and even the formation of perforated cans.

The present invention provides a steel plate for cans with extremely excellent corrosion resistance in order to solve these problems in two-piece cans.

[Means for Solving the Problems] The present invention has Sn plating on one side of a thin steel plate, Sn plating and/or chrome film on the other side, and an upper layer having a melting point of 200 to 240''C. It is characterized by having a polyester resin film of 10 to 100 μm and having an amorphous structure.

For the outer surface of the can, a Sn plating film is required because lubricity during ironing is important, and the coating is 1.0 to 10.0 g/r.
A coating amount on the order of RF is required. At that time, 5n-Fe
Since the alloy layer is hard and brittle, it must be kept as low as possible from the viewpoint of a lubricating surface. Even when a glossy appearance is required by the molten metal treatment after Sn plating, the amount of the alloy layer must be kept as low as possible, for example, about 0.6 g/rrf (in terms of tin) or less.

For the inner surface of the can, ensuring corrosion resistance is most important. To this end, the present invention aims to laminate a specific polyester resin film of 10 to 100 μm on the surface of the steel plate before DI processing, and to obtain a film with good coverage even on the inner surface of the can after processing.

The following describes the polyester resin film necessary for the present invention.
゛The characteristics will be explained in detail. First, regarding the thickness of the polyester resin film, it was limited to a range of 10 to 100 μm. If it is less than 10μm, the film thickness after DI molding will be 3~3μm.
4μm, and the occurrence of film defects is unavoidable.
No improvement in corrosion resistance can be expected.

The thicker the film thickness, the better the corrosion resistance.
Considering the cost, too thick a film is not practical, so the upper limit was set at 100 μm.

Considering both corrosion resistance and cost, the more desirable range is 30.
~60 μm.

Next, the reason why the melting point of the polyester resin was specified as 200 to 240°C will be explained. DI bottom forming is characterized by greatly reducing the side wall of the can after drawing by ironing. For example, in the case of commercially available beer cans, 0.30
It is processed until it becomes approximately 1/3 mm → 0.10 m + a. Extremely large amount of heat is generated during this processing (material heat generation + frictional heat)
It was discovered that this occurs and the material temperature rises to about 200°C.

If the melting point of the laminated resin is low, the resin will melt during the DI bottom molding process, and the resin will stick to the punch surface, causing problems in continuous molding, and the coverage of the resin on the inner surface of the molded can will be extremely deteriorated. Therefore, it will not contribute to improving corrosion resistance. Therefore, the lower limit of the melting point of the resin was set at 200°C.

On the other hand, the upper limit of the resin melting point is related to a problem in manufacturing technology of the steel sheet of the present invention.

When manufacturing the steel sheet of the present invention, metal plating is performed first,
It is more rational to laminate the resin after that.

This is because at least a chromium film must exist under the polyester resin to stabilize adhesion.
Furthermore, in order to improve corrosion resistance, it is desirable to have Sn plating in the lower layer. Furthermore, it is necessary to perform a light chromate treatment on the Sn plating on the outer surface of the can.

Therefore, Sn plating is first performed on one or both sides of the steel plate after degreasing and pickling, followed by electrolytic treatment in chromic acid (laminated side: can inner surface) and immersion treatment (non-laminated side: can outer surface). At the same time, single-sided electrolytic treatment consisting of
At the final stage, polyester resin is laminated. This process is the most process-saving, and there is no need to worry about "scratching" the resin surface after lamination.

Therefore, regarding the upper limit regulation of the resin melting point, one problem is the alloying of tin, and the other problem is the problem of controlling the crystallization of the resin. How to control the crystal structure of laminated polyester resin is a difficult problem, but polyester resin with an amorphous structure can withstand severe DI bottom molding and has extremely good coverage after molding. This discovery led to the present invention. In the case of polyester resins that have a stretched structure or a randomly oriented structure (crystalline structure), DI molding is not possible, or even if molding is possible, many cracks occur during molding, and the resin coverage is poor, making it impractical for practical use. It has no characteristics.

Therefore, in the present invention, the polyester resin to be laminated is -
heated above the melting point, water cooled below the melting point,
Make it an amorphous structure. Therefore, it is necessary to heat the steel plate itself to a temperature higher than the melting point of the resin, but if the temperature is too high, an excessive alloying reaction will occur in the already existing Sn plating layer, causing the lubrication on the outer surface of the can to deteriorate. Therefore, the heating temperature of the steel plate is limited to 250° C., resulting in a decrease in the corrosion resistance of the inner surface of the can. In order to make the resin amorphous at this temperature, the melting point must be about 10°C lower, and the upper limit of the resin melting point was set at 240°C.

The polyester resin used in the present invention is composed of a dibasic acid component containing terephthalic acid, isophthalic acid, adipic acid, or sebacic acid as a raw material, and a diol component such as ethylene glycol, butylene glycol, butanediol, etc. Thermoplastic copolyesters or copolyester blends are used, and esterified versions of these are used.

[For production]

In this way, by specifying the melting point and crystal structure of the resin, it is possible to obtain a surface-treated steel sheet that has excellent lubricity on the outer surface and corrosion resistance on the inner surface during DI molding.

When considering the corrosion resistance of the resin itself, an amorphous structure is not necessarily preferable, but the polyester resin of the can side wall undergoes a process similar to so-called stretching during ironing, so a considerable amount of orientation occurs. Therefore, D
There is no growth of thermal crystals even during heating during external printing after I-processing or repair painting of the internal surface, the resin does not become brittle, and it can withstand subsequent processing.

If the steel plate according to the present invention is used, the resin coating after DI processing is very good, so the can can be used without painting by simply cleaning the inner surface of the can, and the inner surface painting process after DI processing can be done. This can be significantly reduced.

The steel sheet of the present invention is applicable to all can bodies that are subjected to severe processing conditions other than two-piece cans such as DI cans and DRD cans.

Examples will be described below.

[Example 1] After degreasing and pickling a steel plate with a thickness of 0.50H, one side of the steel plate was coated with Sn (coating amount: 6 g/rd) in a normal ferrostane bath.
), and then coated the other side with metallic chromium (deposition amount: 68 μ/d) in a plating bath containing chromic acid as the main component.
and hydrated chromium oxide film (18+n as coating amount Cr)
g/%) by electrolysis, and the Sn-plated surface was subjected to electroless chromate treatment.

Thereafter, the steel plate is heated, and a biaxially stretched polyester film (50 μm
) at 170°C, the temperature was further increased to melt the polyester film to eliminate the stretching orientation,
When the plate temperature reached 240°C, the plate was cooled with water to become amorphous.

At this time, the amount of Sn-Fe alloy layer produced was 0.35g
/rrr, which was a very small amount. With the resin surface of the finished steel plate facing the inner surface of the can, it was drawn twice and ironed three times from a 110mm blank to a diameter of 40mm.
created a can. At this time, the thickness of the side wall is 0.20 m
m, which means that the plate thickness was reduced by 0.30 mm due to ironing.

After degreasing the molded can with a weakly alkaline cleaner, in order to evaluate the integrity of the can inner coating, 1% saline solution was poured into the can, an electrode was inserted, and the can was used as an anode for 6 seconds. A voltage was applied. The current value that flowed was extremely small at 0.3 mA.
It was demonstrated that the polyester film had good coverage after molding.

[Example 2] After degreasing and pickling a steel plate with a thickness of 0.30 mm, it was coated with Sn plating (coating amount 5.6/2.7 g/bo) in a normal ferrostane bath. Then, in a bath containing chromic acid as the main component, metallic chromium (adhesion amount 28 / n ()) and hydrated chromium oxide film (
The adhesion amount Cr is 16 / E) and the thickness S is formed by electrolysis.
A chromium film of 3 mg/rrf was formed on the n-plated side by dipping treatment.

Thereafter, a biaxially stretched polyester film (40 μm) with a melting point of 215°C obtained by blending polyethylene terephthalate, polyethylene isophthalate, and polybutylene terephthalate was prepared in the same manner as in Example 1.
It was laminated in an amorphous state on the n-plated side. The highest plate temperature reached at this time was 230°C, and no melting of Sn occurred, giving the plate a milky white appearance as plated.

For DI forming, from a blank diameter of 138fi, the side wall thickness is 0.10 by drawing forming twice and ironing in three stages.
I tried to make it so that it was mm. There are no problems with DI molding,
We were able to perform extremely smooth machining. Example 1
When the continuity of the inner surface film was examined in the same manner as above, the current value was 0.5a+A, which was extremely excellent.

[Comparative Example 1] After plating was performed in the same manner as in Example 1, when laminating polyethylene terephthalate/isophthalate films, slow cooling was performed in the air instead of water cooling to form a film with a crystalline structure. Created.

Processing and evaluation were carried out in the same manner as in Example 1, and when the continuity of the inner surface film was examined, the current value was as large as 80 mA, indicating that many film defects occurred due to processing.

[Comparative Example 2] After plating was performed in the same manner as in Example 1, a sample was prepared by laminating and rapidly cooling at a maximum temperature of 285° C. in order to layer polyethylene terephthalate (melting point 265° C.), which has a high melting point.

DI molding was attempted under the same conditions as in Example 1, but due to poor external lubrication, continuous molding was only possible several times as long, and practical moldability could not be obtained.

[Example 3] After plating in the same manner as in Example 2, 7μIIl of thermosetting epoxy paint was applied on both sides (205
℃, 10 ml, baking), DI molding was performed using that surface as the inner surface of the can.

Although DI could be carried out without any problem, the continuity of the coating film on the inside of the can was extremely large with a current value of 230 mA, which was an impractical performance.

Claims (1)

[Claims] A thin steel plate has a Sn plating film on one side, a chromium film or a tin plating film on the other side, a chromium film on the surface layer, and a chromium film on the top layer with a melting point of 200 to 240°C.
A laminated steel sheet for cans having excellent workability and corrosion resistance, characterized by having an amorphous structure and a polyester resin film of 10 to 100 μm.