JPS6283499A - Production of tin-free steel - Google Patents

Abstract

PURPOSE:To produce a tin-free steel which obviates the deterioration in adhesive powder at a high temp. by depositing a hydrated oxide of chromium at an adequate cathode current density on a metallic chromium layer in liquid essentially consisting of chromic anhydride and contg. a halogen compd. CONSTITUTION:A steel sheet subjected to a treatment such as degreasing and pickling is subjected to chromium electroplating to form the metallic chromium layer to about 30-300mg/m<2> thereon. Mainly the hydrated oxide layer of chromium is then deposited on the upper layer of the above-mentioned metallic chromium layer. The steel sheet is subjected to the cathodic electrolysis treatment at about >=30A/dm<2>, more preferably about >=50A/dm<2> cathode current density in the treating liquid which contains about 30-200g/l chromic anhydride as the essential component and is added with about <=2g/l halogen compd. such as hydrofluoric acid or hydrochloric acid for the above-mentioned purpose. The tin-free steel which obviates the deterioration of the adhesive power when worked to an adhered can and subjected to a sterilization treatment is thus obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is made of tin-free steel that does not cause a decrease in adhesive strength when it is processed into an adhesive can and subjected to sterilization treatment by z4tsu or retort treatment. The present invention provides a method for manufacturing.

[Conventional technology]

Tin-free steel (hereinafter referred to as TFS), which is composed of metal chromium-chromium hydrated oxide, is used for various purposes as a material for cans that does not use expensive tin. A method of simultaneously depositing the chromium oxide layer and the chromium hydrated oxide layer by cathodic electrolytic treatment (see 1 below)
- step method), and a method in which a step of mainly depositing a metallic chromium layer and a step of depositing a hydrated chromium oxide thereon by cathodic electrolytic treatment are separately performed (hereinafter referred to as 2-step method). ) is well known. After painting, TFS manufactured by any of these methods is molded into cans using nylon resin as an adhesive, and is then filled with food or soft drinks using high-temperature filling (
TFS
Adhesion may decrease at the interface between the surface and the coating due to the penetration of contents and/or moisture from the retort pot, resulting in peeling of the can body joint.

In order to prevent such peeling, the thickness of the chromium hydrated oxide layer is limited to a specific range, the components and concentration of the treatment solution are limited to reduce impurities in the film, or even higher temperatures are used. Various methods have been proposed for removing impurities deposited in a film by using water or aqueous solution ultrasonic waves or electrolytic treatment. The aim of these proposals is that, as introduced in JP-A-59-76895, for example, if a large amount of sulfate ions and fluoride ions are present in the chromium hydrated oxide layer, it may cause problems during hot hacking or retort processing. It is clear that this is an attempt to reduce these impurities since peeling of the bonded portion is likely to occur. Among these methods, in the method of limiting the components and concentration of the processing liquid in the second step of the two-step method, the concentration of halogen compounds such as sulfate ions and fluorides is preferably unavoidably mixed in at a certain amount or less. It is desirable to precipitate a chromium hydrated oxide layer in a treatment solution with a limited amount of impurities.
As disclosed in Publication No. 98, non-uniform precipitation occurs in the chromium hydrated oxide layer in the conventional method. However, it has the disadvantage that the precipitation efficiency of chromium hydrated oxide in the subsequent cathodic electrolytic treatment is poor.

For this reason, it is industrially advantageous to limit the concentration of sulfate ions to the amount required as an unavoidable impurity and to use a bath containing a trace amount of halogen compounds; It is not possible to effectively prevent the halogen element from being precipitated into the hydrated chromium oxide from the halogen compound in the treatment liquid.

[Purpose of the invention]

It is an object of the present invention to solve these problems and provide a method for depositing a chromium hydrated oxide layer with less precipitation of halogen elements from a treatment bath containing a halogen compound by cathodic electrolysis treatment. .

[Structure and operation of the invention]

The features and effects of the TFS manufacturing method according to the present invention are as follows.

Manufacturing of the steel plate used as the raw material for TFS, and degreasing and pickling treatment in the plating line are carried out using conventional methods.

Further, following the degreasing and pickling treatment in the plating line, a metallic chromium layer and a chromium hydrated oxide layer are formed by a so-called two-step method.

The amount of metallic chromium is generally 30 to 3001R9//rn2, and the present invention does not specify this amount.

In addition, a chromium hydrated oxide layer is inevitably deposited at the same time in the first step, which is mainly for depositing metallic chromium. This chromium hydrated oxide layer contains sulfate ions and 7-rhodan elements due to the addition of 7-rhodan compounds such as 7-rhodan compounds.

In the so-called 2-step method, in order to form a new spherical chromium hydrated oxide layer on top of this chromium hydrated oxide layer, sulfate ions and nitrogen ions in the chromium hydrated oxide co-precipitated during the precipitation of metallic chromium are removed. -Although the influence of the Rodan element is relatively small, it goes without saying that it is desirable to remove all impurities as much as possible by known methods. That is, the present invention provides the first method using conventionally proposed methods such as high-temperature water or aqueous solution, ultrasonic waves, or electrolytic treatment.
This does not negate the combined use of removing all impurities in the chromium hydrated oxide layer generated in the process.

Subsequently, in the second step, a chromium hydrated oxide layer is newly deposited, but the chromic anhydride concentration of the treatment solution is 30 to 20011/2.
A range of 13 is desirable. That is, below 30 g/l, the precipitation efficiency of the chromium hydrated oxide layer is low and the electrical conductivity of the solution is low, so the power consumed in cathodic electrolytic treatment increases, which is economically disadvantageous. ．． At OOE/13 or higher, there is a large loss of chromic anhydride due to the liquid being carried out, which is not economical.

Furthermore, this applies to the case where a halogen compound is added to the processing liquid. If neither sulfate ions nor rhodan compounds are added to the treatment solution, the entire anodic electrolytic treatment is required after the first step, and even if anodic electrolytic treatment is performed, chromium hydrated oxide will be removed in the second step. However, when only sulfate ions are added, a large amount of sulfate ions precipitate into the hydrated chromium oxide, making it unsuitable for industrial production. This is so that you will not be affected.

By adding a halogen compound to the processing solution, there is no need to add sulfate ions, so the present invention does not restrict the concentration of sulfate ions in the processing solution, but as is well known, it is desirable that the concentration be lower. , 0. Good results are obtained when the concentration is below 1 g/l.

As the halogen compound, one or more of hydrofluoric acid or hydrochloric acid, alkali metal salts of fluorine or chlorine, ammonium salts, silicofluoric acid, fluoroboric acid, or their salts may be selected, and the concentration thereof is generally 2 g or less. However, since the present invention is effective regardless of the concentration, the concentration is not particularly defined.

The feature of the present invention is that the cathode current density of the cathode electrolytic treatment in the second step is 30 A//dm2 or more, preferably 50 A7
dm or more.

Conventionally, the cathode current density employed in the second step of the two-step method was generally 10 to 30 A/dm2, but the present inventors investigated It has been found that the amount of the cathode current density is controlled by the cathode current density, and the effective range of the cathode current density has also been found.

As an example, Figure 1 shows fluorine contained in a chromium hydrated oxide film deposited directly on a steel plate from a 100 g force aqueous chromic acid aqueous solution containing 0.111/II and 1.0 potassium fluoride. amount (F of the outermost layer by Auger spectroscopy)
10 peak ratio) and the cathode current density of cathode electrolytic treatment. In this case, the amount of electricity in the cathode electrolytic treatment was kept constant at 20 corons/dm2, and the amount of chromium hydrated oxide film was 13 to 16 mEl/m2 as chromium.
It remained almost constant within the range of .

It has already been shown in JP-A-51-7 that when forming into a TFS 'i adhesive can and subjecting it to hot pack or retort treatment, the lower the impurities in the chromium hydrated oxide layer, the less the decrease in adhesive strength.
Publication number 6895? As cited, it can be easily inferred that the known hydrated chromium oxide produced when treated at a high cathode current density has a lower fluorine content and therefore has superior adhesive strength. Also, from Figure 1, it can be seen that the smaller the amount of fluorine compounds in the treatment solution, the less fluorine is deposited in the hydrated chromium oxide, but the effect of cathode current density is However, the present invention can provide the same effects regardless of the concentration range of the herodane compound in the treatment bath.

As for the cathode current density, as seen in Figure 1, 30
Below A/dm2, there is almost no difference in the amount of chromium elements precipitated into hydrated chromium oxide, and from 30 A/dm2 to 5
The effect gradually increases in the range of 0 A/dm2, and the
Since the amount becomes almost constant at A/dm2 or more, 30 A/dm2 or more is required, and more preferably 50 A/dm2 or more.

〔Example〕

Next, the present invention will be explained in detail based on examples.

N
Anodic electrolysis treatment at 15 A/dm2X for 2 seconds in an aqueous solution of 40 g of aOH followed by washing with water, followed by 30 g of H2So4.
After cathodic electrolytic treatment at 20 A/dm2 x 2 seconds in an aqueous solution of ill, it was washed with water and subjected to electrochromium plating.

Electrochrome plating is Cr03150-2001//l.

H2so40.75~1 gill, Na2SiF6
4.5~6 y/l! The bath temperature was 48-52°C, the cathode current density was 60-90 IV/dm265-70 coulombs/dm2, and the amount of metallic chromium was approximately 90-120 IV/dm2.
It was in the range of mFl/m2. Following electrochromium plating, Examples 1 to 4 and Comparative Examples 1 to 2 were washed with tap water at room temperature, and Examples 5 to 8 and Comparative Examples 3 to 4 were washed with 95°C high temperature tap water. Nos. 9 to 12 and Comparative Examples 5 to 6 were subjected to anodic electrolysis treatment at 5 A/dm2×0.2 seconds in a plating solution, and then washed with tap water at room temperature. After completing these treatments, Examples 1 to 4 and Comparative Examples 1 to 2 contained chromic anhydride of 50 g/l and sulfate ion of 0.051! /l.

Sodium fluoride 1. Examples 5 to 8 and Comparative Examples 3 to 4 were aqueous solutions at 42°C containing Oi/l k. 05 g,/l
In Examples 9 to 12 and Comparative Examples 5 to 6, chromic anhydride was 100 g/l and sulfate ion was 0.
, 039/l, sodium silicofluoride 2.0 gil
A cathodic electrolytic treatment was performed using an aqueous solution containing 1* at 45°C. The cathode current density and electrolysis time in each example were shown in Table 1.

TFS manufactured by these methods is washed with water, dried, and oiled, then coated with epoxy phenol and baked, and molded into a can body using nylon resin as an adhesive.
% citric acid aqueous solution and 20 cans in each example.
temperature of 130℃)! The adhesive performance was evaluated based on the peeling of the adhesive portion.

Table 2 shows all the amounts of hydrated chromium oxide, amounts of impurity components, and retort test results for each example.

The amount of chromium hydrated oxide in Table 2 is determined by the fluorescent X-ray method for chromium, and the atomic percent for other elements is determined from the peak intensity ratio of the outermost layer of the film by Auger spectroscopy, and the atomic weight ratio with chromium. It was converted by

When the cathode current density in the step of depositing a chromium hydrated oxide film by cathodic electrolytic treatment is in the range of 30 A//dm2, the content of 7-rodan element in the film decreases, and accordingly, the content of 7-rodan element in the film decreases. It can be seen that the transmission that causes adhesive peeling is also reduced, and the effect is particularly significant at 50 A/dm2 or higher.

〔Effect of the invention〕

According to the present invention, peeling is significantly reduced during retort treatment of the bonded portion, and the function of the bonded portion can be fully exhibited.

Moreover, the structure can be reliably achieved by controlling the current density, and excellent effects such as industrially stable operation can be obtained.

It is an explanatory chart showing the relationship between the amount of fluorine in the film and the amount of fluorine in the film.

11・： Kishi 1) Positive line Shij-jl Figure 1 Sui Go Den Yo wo Tomoe A/dyyt'

Claims (1)

[Claims] It consists of two steps: a step of mainly depositing a metallic chromium layer, and a step of depositing a chromium hydrated oxide layer on top of the metal chromium layer. The cathode current density of cathode electrolysis treatment in a treatment solution containing an acid as the main component and a halogen compound added is 30A/dm^2.
A method for producing tin-free steel, characterized by the above processing.