JPS62139897A - Production of tin-free steel sheet having retort treatment resistance - Google Patents

Abstract

PURPOSE:To produce a tin-free steel sheet having excellent retort treatment resistance by anodizing a chrome plated steel sheet in a chromium-contg. aq. soln. having an adequate concn. of Cr<3+> then subjecting the steel sheet to an electrolytic chromate treatment. CONSTITUTION:The thin steel sheet is subjected to chrome plating essentially consisting of metallic chromium by cathodic electrolysis to about 50-200mg/m<2> on one side in an aq. soln. contg. chromium. The chrome plated steel sheet obtd. in such a manner is subjected to the reverse electrolysis of an anodic treatment in the above-mentioned chrome plating liquid or another chromium- contg. aq. soln. in succession thereto. The concn. of Cr<3+> in the electrolyte in the above-mentioned reverse electrolysis is limited to about <=10g/l, more preferably about 3-6g/l. The steel sheet subjected to the reverse electrolysis treatment is subjected to the electrolytic chromate treatment in the aq. soln. essentially consisting of >=1 kinds among chromic anhydride, chromate, and dichromate to form a hydrated chromium oxide film to about 5-30mg/m<2> in terms of Cr on the surface of the metallic chromium layer.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing a tin-free steel plate with excellent retort resistance, and in particular to a method for manufacturing a tin-free steel plate with excellent retort resistance as a material for adhesive cans. Regarding manufacturing technology.

<Prior art and its problems> Electrolytic chromate-treated steel sheets are called tin-free steel chromium type (hereinafter abbreviated as TFS), and have been recognized for their properties as a material for cans that can replace tinplate, and their usage has increased in recent years. ing.

Because TFS has a gold-14 chromium and chromium hydrated oxide coating on its surface, it does not have sufficient welding performance, and when making cans, the can body is coated with epoxy-phenolic resin and then joined with polyamide adhesive. There is.

Recently, the uses of TFS cans have been expanding, and they are not only used for cold punctures, where filling of contents such as carbonated drinks and beer is done at low temperatures, but also for so-called cold punctures, where filling of contents such as carbonated drinks and beer is done at low temperatures, and also for so-called so-called so-called cans, which are filled after high temperature sterilization, such as fruit juice and coffee. As the can ICs are used for hot packs or for retort punctures which are sterilized at high temperatures after being packaged, troubles have arisen in which can ICs break.

The reason for this hot puncture and retort pack breakage in the can body is that the adhesion between the paint film and TFS deteriorates due to the hot water penetrating through the paint film at the joint of the can body, causing the paint film-TFS interface to deteriorate. This is caused by peeling.

As a result of the investigation, it was found that sulfuric acid, which was conventionally added to chromium plating solution and electrolytic chromic acid treatment solution, was eutectoid in the chromium hydrated ugliness film, and during retort treatment, this sulfuric acid was eluted and peeled off at the coating film-TFS interface. In order to deal with this, various proposals have been made, including a method in which sulfuric acid is not added to the plating bath and a method in which sulfuric acid is not used in pickling performed as a pre-plating treatment.

However, these methods significantly reduce TFS production efficiency and result in poor product quality stability.

Low yield and many problems in industry? F remained.

<Object of the Invention> An object of the present invention is to solve the problems of the above-mentioned prior art and to provide a method for manufacturing a tin-free steel sheet that does not cause interfacial peeling between the TFS and the coating film due to retort treatment.

<Structure of the Invention> The present inventors first performed a reverse electrolytic treatment using a steel plate as an anode after chromium plating as a method to eliminate the drawbacks of this sulfuric acid eutectoid, and then performed an electrolytic chromic acid treatment in an aqueous chromic acid solution. This was disclosed in Japanese Patent Application No. 56-62766. This reverse electrolytic bath may be carried out in the same bath as the chromium plating treatment in the previous step, or may be carried out in a separate aqueous solution containing chromium, but it is convenient to use the same bath.

The main ingredient in the chromium plating bath is chromic anhydride, sulfuric acid,
A fluorine compound or the like is usually added as an auxiliary agent.

This is to efficiently deposit metallic chromium. It is well known that when electrolysis is continued in an aqueous chromic acid anhydride solution containing such an auxiliary agent, Cra+ is generated in the electrolyte. When a large amount of Cra+ is generated, the bath voltage increases and power consumption increases, so it is usually
3"6 degrees can be kept below 10g/l. This means that if the plating tank is sufficiently lined, Cr3 on the cathode side can be kept below 10g/l.
The production of `` and the consumption of Cra+ by oxidation of Cr3+ to era+ on the anode side are balanced and maintained within the above range.

As described above, the reverse electrolytic bath is used in combination with a chromium plating bath. As we continued to produce tin-free steel sheets using the reverse electrolysis method, we discovered that some types had good retort resistance and others had poor retort resistance. As a result of investigating the cause of this, it was discovered that retort resistance changes depending on the Cr3+ concentration in the reverse electrolytic bath, and the present invention was completed based on this knowledge.

According to the present invention, there is a step of plating a thin steel sheet with chromium mainly consisting of metallic chromium by cathodic electrolysis in an aqueous solution containing chromium, and subsequently plating the chromium-plated steel sheet in the chromium plating solution or a separate chromium-containing aqueous solution. A process of performing anodization (reverse electrolysis), and treating the reverse electrolysis treated steel sheet with chromic anhydride, chromate and dichromium I
A method for manufacturing a tin-free steel sheet comprising a step of performing electrolytic chromic acid treatment in an aqueous solution containing one or more selected from %i salts as a main component, wherein the Cra+ concentration in the electrolyte in the reverse electrolysis step is set at 10 g. Provided is a method for manufacturing a tin-free steel sheet with excellent retort treatment resistance, characterized in that the tin-free steel plate has a tin-free steel plate with excellent retort treatment resistance.

The present invention will be explained in detail below.

In the present invention, a thin steel plate is plated with metallic chromium at a concentration of 50 to 200 mg/m2 on one side, and the surface of the metallic chromium layer is coated with 5 to 30 mg/m2 of chromium hydrated oxide in terms of Cr. The present invention relates to a TFS that has the following characteristics.

If the amount of metallic chromium is less than 50 ffIg/112, the corrosion resistance will be poor, and even if it exceeds 200 ffIg/m2, no further improvement in corrosion resistance can be expected.
It has a metal chromium layer of 0 to 200 B/i2.

On the other hand, if the chromium water-conserving oxide film contains less than 5 mg/m2 in terms of Cr, the required paint adhesion cannot be obtained;
If it exceeds 2, the appearance will deteriorate and the chromium hydrated oxide film will crack during processing, making it impractical.

Generally, the chromium plating solution and electrolytic chromic acid treatment solution used to produce TFS are an aqueous solution containing one or more of anhydrous chromic acid, chromate, or dichromate, and various auxiliaries added thereto. As this auxiliary agent, sulfate radicals, fluorine ions, etc. are used alone or in combination, and these anions are eutectoid in large quantities in the chromium hydrated oxide film formed on the TFS surface. In particular, the sulfate groups eutectoided in the coating are eluted during the TFS adhesive adhesion-tort treatment and the coating film-TFS
As mentioned above, peeling occurs at the interface, which is harmful.

Next, in order to investigate the influence of the Cr3+ concentration in the bath on retortability in reverse electrolytic treatment, we conducted the following basic experiment.

That is, after a thin steel plate was electrolytically degreased in the usual manner, washed with water, and then pickled with sulfuric acid, Gr03100~200g1n, N
a2 SiF 65-8g/l,)12SO40,5
Cr3+ was added to the electrolyte solution containing ~1 g/i of 0, 1, and 1 g/i, respectively.
2゜6.10, 14.20g/vertical addition was carried out in each bath for chromium plating, followed by reverse electrolytic treatment in the same baths using a steel plate as an anode, and after washing with water, the product was adjusted to special grade C "03". Electrolytic chromic acid treatment was performed in a CrO3 aqueous solution using a steel plate as a cathode.

In order to examine the paint adhesion and retort resistance of the TFS thus obtained, a retort resistance test for paint adhesion was conducted.

The test method is to first apply 60 mg/d+s2 of phenol-epoxy paint to one side of sample 1, and then apply 1 coat at 210°C.
After baking for 2 minutes to form a coating film 2, the same paint was applied to the opposite side of the same sample at a dose of 25 mg/da2 and baked under the same conditions to form a coating film 2°. Cut out two pieces of paper with a width of 70 m and a length of 60 mm from the sample 1 coated in this way, and cut out two pieces of paper with a width of 70 m and a length of 60 mm.
1004rn nylon film 3 between them.
After preheating at 200°C for 120 seconds using a hot press, press 200°C under a pressure of 3 Kg/Cm2.
``Crimping was carried out for 0130 seconds (see Figure 1a),
Ten sets of these test pieces 4 were made, set in the jig 5 as shown in Fig. 1b, and heated at 125 to 130°C, t, and e to 1.7K.
Test piece 4 when held in a retort pot of g/Cff12
The presence or absence of peeling was examined, and the retort processing resistance was compared based on the retort durability time in which 9 out of 10 pairs remained without peeling.

The investigation results are shown in FIG. 2, and it was found that when the Cr3+ concentration in the reverse electrolyte exceeds log/i, the retort resistance sharply decreases.

The reason for this is thought to be as follows. Namely.

The reason why reverse electrolytic treatment is effective in improving retort resistance is that it removes auxiliary anions, especially sulfate radicals, eutectoid in the chromium hydrated oxide film produced during chromium plating.

Since sulfate radicals are anions, they are electrically attracted to the steel plate, which is an anode, during reverse electrolysis.The reason why sulfate radicals are reduced by reverse electrolysis is that the chromium hydrated oxide film containing a large amount of sulfate radicals is dissolved by reverse electrolysis. It is considered to occur incidentally when

The dissolution of the chromium hydrated oxide film is expressed by the following equation.

c.Q! (m) □ Cr6” (aq)...
-・----・(1) By the way, the anodic reaction that occurs during reverse electrolysis includes the dissolution of metallic chromium Cr' (0) -m-Or" (aq)...
・= (2) and the oxidation reaction of Cr3+ in the electrolyte Cr3” (aq) Cr” (aq) −=
- There is (3).

Therefore, when Cra+ increases in the reverse electrolyte, the reaction (
The influence of 3) becomes large, and reaction (1), which is advantageous for improving retort resistance, becomes difficult to occur, and as a result, a graph as shown in FIG. 2 is obtained. That is, sufficient retort resistance can be obtained if the Cr3+ concentration in the reverse electrolyte is 10 g/U or less. More preferably 6g/! When continuous operation is carried out, the Cra+ concentration in the bath gradually increases and becomes stable at around 3 g/l, so it is more preferable for the Cr3+ concentration to exceed 3 g/l.

〔Example〕

A cold-rolled steel plate with a thickness of 0.22+em was electrolytically degreased in a 5z homezaline solution, washed with water, and then washed in a 10X 82SOd solution (40°C).
After pickling by immersing in water for 5 seconds, the main treatment was carried out in the following order. That is, Cr03170g/l, Na2BF45g/fL
, H2SO40.8g/b, Cr3" in 4g/l solution (50°C) after cathodic treatment (chromium plating) of 5OA/da2.1.2 seconds.

After anodic treatment (reverse electrolysis) at 3 A/da for 2.0.3 seconds in the same bath, cathodic treatment (electrolytic chromic acid treatment) was performed in an aqueous solution of Cr0360 gin (40°C) to obtain a tin-free steel plate.

This sample was examined for retort resistance as shown in Figures 1a and tb as described above.
Even after 40 minutes had passed, no peeling occurred in any of the 10 sets.

[Comparative example]

C "3" in the chrome plating bath (also a reverse 711j decomposition bath)
+Processed in the same manner as in Example except that the concentration was 20 g/l. The tin-free steel sheet treated in this way has extremely poor retort resistance, with 10
All of them were peeled off.

<Effects of the Invention> As detailed above, according to the present invention, the r
By limiting 3+5 degrees to 4 to 10 g/l, a tin-free steel plate with excellent retort treatment resistance can be produced.

[Brief explanation of drawings]

FIGS. 1a and 1b are explanatory diagrams of a method for evaluating retort resistance of paint adhesion. Figure 52 is a graph showing the relationship between the Cr3+ concentration in the reverse 7 arsenic solution and the i-ruto durability time. Explanation of symbols 1... Sample, 2, 2°... Paint film, 3... Nylon film, 4... Test piece FIG, 1a

Claims (1)

[Claims] (1) A step of plating a thin steel sheet with mainly metallic chromium by cathodic electrolysis in an aqueous solution containing chromium, and then anodizing the chromium-plated steel sheet in the chromium plating solution or a separate chromium-containing aqueous solution. a step of performing electrolytic chromic acid treatment on the reverse electrolytically treated steel sheet in an aqueous solution containing one or more selected from anhydrous chromic acid, chromates and dichromates as a main component; In the method for manufacturing a tin-free steel sheet, C in the electrolyte in the reverse electrolysis step
A method for manufacturing a tin-free steel sheet with excellent retort treatment resistance, characterized by limiting the r^3^+ concentration to 10 g/l or less.