JPH0230796A - Chromium plating steel sheet excellent in corrosion resistance and weldability - Google Patents

Abstract

PURPOSE:To obtain a chromium plating steel sheet for a vessel which is excellent in corrosion resistance and weldability by providing an iron plating layer on the surface of the steel sheet and providing both a metallic chromium layer and a chromium oxidative film layer on the upper layer thereof at the specified build-up amount respectively. CONSTITUTION:After a steel sheet wherein refining and rolling have been performed is degreased and pickled to activate it, an iron plating layer of 10-2,000mg/m<2> is formed on the surface by electroplating. Thereafter both a metallic chromium layer of 30-150mg/m<2> and a chromium oxidative film layer of 5-20mg/m<2> expressed in terms of metallic chromium are provided on the upper layer thereof. This metallic chromium layer and the chromium oxidative film layer are formed by electroplating of one or two steps. In this case, reverse electrolysis of anodic-treatment is partially added and thereby granular metallic chromium is preferaby formed in the metallic chromium layer. Thereby the chromium plating steel sheet for a vessel which is excellent in both weldability at a time of can making and post-working corrosion resistance is obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention has excellent weldability, corrosion resistance,
This invention relates to a chromium-plated steel sheet for containers, which has an iron plating layer as its base that has excellent resistance to contents.

<Conventional technology> Conventionally, chrome-plated steel sheets (hereinafter referred to as TFS) have been used in the field of food and beverage cans for DRD cans and bonded cans, and in the field of gallon cans for welded cans in which the coating is welded after grinding. Ta.

Until now, tinplate and light-weight tinplate (LTS) have been used as can materials for welded cans in the food and beverage can fields, but from a cost perspective, LTS is more expensive than TFS, making it less commercially viable. TFS is more suitable. However, TFS cannot be welded without grinding due to its high surface resistance, high melting point of chromium metal, and high hardness, so when manufacturing TFS food cans as 3-piece cans, the main steps are to bond each 2-piece can. When manufactured as a DRD can, it is used as a DRD can.

In the case where three pieces are glued together, when the contents of the can are subjected to high-temperature sterilization, the bonded portion may be torn and the can may break. Although the modification of the chromium oxide film of TFS has significantly improved the problem, adhesive cans always carry such risks. In addition, when used for welded cans, 1st of grinding
Not only does it require more steps and the work is more complicated, but it also has drawbacks such as scattering of chromium powder. Therefore, in order to use TFS as a welding can, it is necessary to use TFS that can be welded without grinding.
The need for S has become increasingly important. If TFS that can be welded without grinding is developed, not only will this problem be eliminated, but the overlap of the joints will be reduced to 5vara (
Since the thickness is 0.2 to 0.4 mm from the adhesive can, the material can be saved, and there are also benefits such as preventing the risk of vacuum leakage from the seaming part.

Although weldability is improved by lowering the amount of metallic chromium and chromium oxide in TFS (Japanese Patent Publication No. 57-19752, Japanese Patent Publication No. 57-36986), corrosion resistance deteriorates.

A method of applying nickel plating to the base and applying thin chrome plating for the purpose of improving corrosion resistance (Special Publication No. 63-3)
No. 959), the corrosion resistance is slightly improved by covering the pinholes in the chrome plating with nickel plating, but this is not sufficient for practical use, and nickel itself cannot withstand the corrosive environment on the inside of the can. In addition, the knowledge that weldability is improved when chromium plating is granulated (
JP-A-61-213399, JP-A-61-28189
There is also No. 9), but since it makes metal chromium non-uniform, corrosion resistance may deteriorate. As described above, all attempts to weld TFS without grinding have problems and are difficult to put into practical use.

In the case of DRD cans that use TFS in two pieces, the development has been remarkable due to the advantage that there is no joint in the can body, but single coating is being implemented because the entire material is subjected to strong processing and the painting process is streamlined. In terms of corrosion resistance,
Unfavorable can-making methods are being developed, and therefore there is a significant demand for improved corrosion resistance of TFS materials or improved corrosion resistance after coating.

<Problems to be Solved by the Invention> Therefore, the present inventors aim to improve the problems in the prior art described above, and to obtain a TFS that has good weldability and excellent corrosion resistance before and after painting.

(Means for Solving the Problems) The present inventors have repeatedly researched TFS that has good weldability and at the same time excellent post-painting corrosion resistance, and as a result, has arrived at the present invention.

That is, the present invention has an iron plating layer of 10 to 2000 tag/+2 on the surface of the steel plate, and an iron plating layer of 3 on the upper layer.
Provided is a chromium-plated steel sheet for containers, characterized by having a chromium metal layer of 0 to 150 mg/m' and a chromium oxide film layer of 5 to 20 mg/m' in terms of chromium metal.

Moreover, the metal layer chromium of the steel plate may have granular metal chromium.

The present invention will be explained in detail below.

The steel plate used in the present invention is not particularly limited, and a cold-rolled steel plate obtained by using an ordinary tin plate, a tin-free steel plate, etc. as a surface-treated base plate, and further annealing and skin-pass rolling is used.

This steel plate is subjected to degreasing treatment and activation treatment by pickling, and then iron plating is applied.

The iron plating method is not particularly specified, but a normal electroplating method may be used.

As for the composition of the plating bath, it is preferable to use an electrolytic bath that can reduce the hardness of the plating layer, such as iron (If) chloride-calcium chloride, iron (II) chloride-potassium chloride, or the like.

For example, in the case of iron chloride (It)-calcium chloride solution, the concentration of iron chloride (!■) aqueous solution is 50 to 500 g/
Il is preferred. If it is less than 50 g/n, the plating voltage will be high and the electricity cost will increase, making it uneconomical. If it exceeds 500 g/n, salt will crystallize when the temperature drops, causing pipe clogging, making it difficult to operate. Because it will be.
In addition, the temperature of the bath is 60 to 95°C, and the pH is 1.0 to 3.0.
It is preferable to do so.

Furthermore, although the magnitude of the current density at this time is not particularly specified, plating can be carried out sufficiently at about 5 to 20 A/di2.

Also, the amount of adhesion per side is 10 to 2000ffIg/
ff12 is required. Adhesion amount of iron plating layer is 10
If it is less than mg/m2, no improvement in the surface properties of the iron plate is observed, and uniform electrodeposition of chromium plating on the produced iron plating layer is not improved. Therefore, bare corrosion resistance, post-processing corrosion resistance,
and no improvement in weldability can be obtained. In addition, if the amount of iron plating layer adhered exceeds 2000 rng/m,
The performance improvement effect described above becomes saturated and becomes uneconomical.

After iron plating, chrome plating is applied next.
When iron plating is applied to a cold rolled steel sheet after annealing, it is better to apply chromium plating immediately because the iron plating layer oxidizes quickly. There are no particular regulations regarding chrome plating, but the method used in the normal TFS chrome plating process will be adopted.

For example, Cry, -5o4” bath, Cr03-Na2
S i F6-So4'-based bath, or SO4'-
C containing only a trace amount of free fluorine
r O3N H4F-HBF4-3o42-based bath, etc.
SO4'-F-SO4'-+ as an anion in Cry3
A plating bath containing F- is used.

The amount of oxidized Cro3 in this bath is preferably 30 to 300 g/β. Further, a suitable bath temperature is 30 to 80°C.

In these plating baths, plating of steel plates provided with iron plating is preferably carried out at a current density of 30 to 150 A/dm2. This is because if it is less than 30 A/dm2, metal chromium will not precipitate, and if it exceeds 150 A/dm2, the temperature of the steel plate will rise too much due to electrical resistance heat.

In the case of chromium plating, a so-called one-step method is used, in which a metal chromium layer and a chromium hydroxide layer are generated simultaneously, and a portion of the chromium hydroxide layer is removed during plating to adjust the amount of the chromium hydroxide layer. After providing a metallic chromium layer and a chromium hydroxide layer by Cr plating, most of the chromium hydroxide is dissolved, and a new electrolytic chromic acid treatment is performed in a separate electrolytic bath.
Both chromium plating methods can be used, including a two-step method in which the amount of the chromium hydroxide layer is adjusted.

The electrolytic chromic acid treatment bath in the two-step method consists of CrO3H
2SO4 series, Cry3-H25o4Na2SiF6 series, etc. are suitable in the present invention. The electrolytic chromic acid treatment conditions may be the same as those of the known two-step method.

In the present invention, the coating amount of the chromium plating layer is preferably 30 to 150 m/m2 per side of the metal chromium layer. If the amount of the metal chromium layer is less than 30 mg/m'', the uniform coverage of the metal chromium layer will not be sufficient and sufficient corrosion resistance will not be obtained.
In addition, if the metal chromium layer exceeds 150 mg/m'', the metal chromium layer is susceptible to damage such as cracking during processing, and corrosion resistance tends to deteriorate, and
Weldability also deteriorates.

Further, the chromium oxide film layer on the metal chromium layer is limited to a range of 5 to 20 rag/m2 per side. If the amount is less than 5 mg/m2 in terms of metallic chromium, the uniform coverage of the chromium oxide film layer over the metallic chromium layer will be insufficient, and sufficient coating performance will not be obtained.

If it exceeds 20 mg/m2, the coating performance improvement effect will be saturated, the appearance will be yellowed, the product value will be impaired, and the chromium oxide layer will be more likely to crack, causing cracks in the coating. This can easily lead to deterioration of coating performance.

Further, in the present invention, better weldability can be obtained by applying a method in which a part of the metal chromium layer is transformed into grains by adding anodization (reverse electrolysis) during the chromium plating.

This is applicable to both the one-step method and the two-step method.

When anodizing is performed, electrochemical non-uniform dissolution occurs and granular precipitation occurs in Cr plating after anodizing.

The amount of electricity for anodizing is 0.03 to II per unit coating amount.
C/mg is preferable.

This is because if it is less than 0.03 C/mg, sufficient precipitation of granular Cr will not occur, and if it exceeds 11 C/B, the dissolution of the plated metal Cr will be large, making it difficult to obtain a predetermined amount of plating.

Granular metal Cr has a grain diameter of 10 to 200 nm and 1
It is preferable that they be formed at a density of x1011 to 1 x 10'7 pieces/m'<1'). If the grain size is less than 10 nm, there is no effect of improving weldability, and if it exceeds 2001 m, the color tone of the steel sheet will deteriorate. Further, if the grain density is less than I×10 grains/m2, there is no effect of improving weldability, and if it exceeds 1×10" grains/m2, the grains become too dense and have no effect as grains.

When the metallic chromium layer is changed to a granular form, the adhesive strength is also improved, especially in adhesive cans that are subjected to retort processing.
It has the advantage of being durable enough to be used as an adhesive can.

In addition, after painting TFS, it is drawn and DR
Even in the case of D cans and DTR cans, the paint adhesion is excellent, so there is no peeling of the film during processing, and the corrosion resistance after painting is excellent.

<Example> Hereinafter, the present invention will be specifically explained based on Examples.

(Example 1) After degreasing and pickling using an annealed and temper-rolled steel plate, iron plating was performed under the conditions shown in (a). The amount of the coating was adjusted by the amount of electricity, and the predetermined amount of iron shown in Table 1 was provided, and various chromium platings were applied under the conditions shown in (b), (C), and (d). The amount of coating of the metal chromium layer and chromium oxide layer of this chromium plating layer can be determined by adjusting the amount of electricity during plating and the immersion time after electrolysis in the plating process, so that the amount of coating shown in Table 1 is determined. Layers were provided.

(a) Iron plating conditions/plating bath FeCn 2 ・nH2O 300g/
jZCaCu2180g/11 pH 1,5 ・Bath temperature
85℃・Current density 5-10A
/dm2 (b) Chrome plating conditions/plating V valley CrO3200g/βH2SO40,
9g/j2 Na2SiF65, Og/l ・Bath temperature
50'C'・Current density 30~1
00A/d+n2(c) Anodizing conditions・Chromium plating mentioned above・Bath temperature
50℃・Current density 1-20A/d
+n2(d) Electrolytic chromic acid/muffing bath Cr 0, 50 g/I
tH2S040, 4 g/jZ・Bath temperature 40℃・Current density
5-208/dm2 (Comparative Example 1) (b), (
Various chromium platings were applied under the conditions shown in c) and (d). The amount of coating of the metal chromium layer and chromium oxide layer of this chromium plating layer can be determined by adjusting the amount of electricity during plating and the immersion time after electrolysis in the plating process, so that the amount of coating layer is the specified amount shown in Table 2. has been established.

・Evaluation method (1) Bare corrosion resistance 5% sodium chloride solution (pH 7.0) in a tank at 35%
Spray at °C. Observations were made every 30 minutes to measure the area where rust had developed.

◎: 0% ○: Less than 5% △: 5-20% ×: 20% or more (2) After coating with corrosion-resistant epoxy phenol paint, perform DRD processing to a can diameter of 74 mm and can height of 24 IQIIl. 1.
Backed with 5% sodium chloride and 1.5% citric acid solution with a head space of 10 mm, immersed at 55°C for 72 hours,
The corrosion situation under the paint film was observed and the number of blisters was counted.

◎: 0 pieces 021-3 pieces △: 3-20 pieces ×: 20 pieces or more (3) Weldability After coating blanking, weldability was evaluated using a Sudronitsa type welding machine. Weldability is determined by the appropriate welding current range (A
The size of CR) was compared with the ACR of light tinplate (LTS).

◎:＞LTS ○:=LTS △:<LTS Performance was obtained, and superior effects were obtained compared to the comparative example.

<Effects of the Invention> According to the present invention described above, the amount of chrome plating can be reduced from the conventional T.
Due to improved uniform electrodeposition even when reduced compared to FS,
The present invention provides a steel sheet for containers that provides good weldability during can manufacturing and corrosion resistance after processing, and has the effect of providing a steel sheet for containers of excellent quality at a low cost.

Claims (2)

[Claims] (1) Iron plating layer of 10 to 2000 mg/m^2 on the surface of the steel plate, and on top of that a metallic chromium layer of 30 to 150 m/m^2 and a chromium oxide film layer of 5 to 20 mg/m^2 in terms of metallic chromium. A chromium-plated steel sheet for containers, characterized by having the following. (2) The chromium-plated steel sheet for containers according to claim 1, wherein the metal chromium layer of the steel sheet has granular metal chromium.