JPS6234838B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a metal chromium lower layer on the surface of a steel plate,
The present invention relates to a stain-free steel having an upper layer of hydrated chromium oxide, and in particular to an electrolytically chromate-treated steel sheet having excellent retort treatment resistance as a material for adhesive cans. Electrolytic chromate treated steel sheet is called tainfree still chromium type (hereinafter abbreviated as TFS), and its use has been increasing in recent years as it has been recognized as a material for cans that can replace tinplate. Because TFS has metallic chromium and a hydrated chromium oxide coating on its surface, it does not have sufficient welding performance, so when making cans, the can body is coated with epoxy/phenolic resin and then bonded with nylon adhesive. There is. Recently, the use of TFS cans has expanded, not only for low-temperature packs in which contents such as carbonated drinks and beer are filled at low temperatures, but also for so-called hot packs, in which contents such as fruit juice and coffee are sterilized at high temperatures. In addition, cans that require retort treatment, which involves sterilization treatment at high temperatures after packaging, have come to be used, causing problems such as the can bodies breaking. This hotpack uses TFS during retort processing.
Tears in the can body that occur in adhesive cans are caused by hot water penetrating through the nylon adhesive layer at the joint, causing poor adhesion at the interface between the paint film and TFS.
This occurs due to separation from the interface. Many studies have been conducted to obtain TFS with excellent adhesion, and sulfuric acid added to chromium plating baths and electrolytic chromic acid baths eutectoids into the hydrated chromium oxide film and is eluted during retort processing. Coating film - TFS
Based on the view that interfacial peeling may occur, the sulfate radicals contained in the chromium hydrated oxide film are reduced as much as possible, and products using fluorine ions instead (for example,
53440, JP-A No. 56-142897) have been proposed. However, in order to achieve this, it is necessary not only to add sulfuric acid to the chromium plating bath, but also to the electrolytic chromic acid treatment bath that forms the hydrated chromium oxide film on the top surface of TFS, and instead add a fluorine compound. However, in this case, the precipitation efficiency of metallic chromium is poor, resulting in a significant decrease in manufacturing efficiency or
Many industrial problems remained, such as frequent surface stains on TFS, poor product quality stability, and poor yield. In order to solve this problem, the inventors of the present application proposed that after chromium plating in a chromium plating bath containing sulfuric acid, reverse electrolysis is performed using the steel plate as an anode in the solution, and then chromium oxide without adding sulfuric acid is used. proposed electrolytic chromic acid treatment in an aqueous solution
(See No. 177998). However, subsequent research revealed that this method, which involves inserting a reverse electrolysis process using a steel plate as an anode between the chromium plating process and the electrolytic chromic acid treatment process, is extremely effective in improving paint adhesion. In the steel sheet after reverse electrolysis, the growth of chromium hydrated oxide film in the subsequent electrolytic chromic acid treatment process is suppressed, and TFS exhibits excellent paint adhesion.
It was found that in order to stably obtain chromic acid, a large amount of electricity is required in the electrolytic chromic acid treatment process, which is not economical. The present invention was made in view of the above-mentioned situation, and an object of the present invention is to provide a TFS that can be manufactured economically and efficiently and has extremely excellent retort processing resistance. In the present invention, a thin steel plate is plated with 50 to 200 mg/ ^m2 of metallic chromium on one side, and the surface of the metallic chromium layer is coated with 50 to 30 mg/m2 of metallic chromium.
It concerns TFS with a chromium hydrated oxide coating of mg/m ² . If the metallic chromium layer is less than 50mg/ ^m2 , the corrosion resistance will be poor and it is not good. Furthermore, even if the amount exceeds 200mg/ ^m2 , further improvement in corrosion resistance cannot be expected.
Typical TFS has a metallic chromium layer of 50-200 mg/ ^m2 . On the other hand, the chromium hydrated oxide coating was 5mg/
If it is less than ³⁰ m2, the desired paint adhesion cannot be obtained;
If it exceeds mg/m ² , the appearance will deteriorate and cracks will appear in the chromium hydrated oxide film during processing, making it impractical. Furthermore, the most desirable amount of chromium hydrated oxide coating is 8 to 25 mg/m ² . The inventors of the present application have previously developed a coating with excellent paint adhesion.
The TFS production method involves chromium plating in a chromium plating bath containing sulfuric acid, followed by reverse electrolysis using the steel plate as an anode in the solution, and then electrolytic chromic acid treatment in a chromic acid aqueous solution that does not contain sulfuric acid. (Refer to Japanese Patent Application Laid-Open No. 177998-1988). As a result of subsequent investigation, this method of inserting a reverse electrolytic process using a steel plate as an anode between the chromium plating process and the electrolytic chromic acid treatment process was found to be suitable for TFS, which has good paint adhesion.
This method is effective in manufacturing, but in the steel plate after reverse electrolysis, the growth of chromium hydrated oxide film in the subsequent electrolytic chromic acid treatment process is suppressed, and it is necessary to stably obtain TFS that shows excellent paint adhesion. It was found that the electrolytic chromic acid treatment process required a large amount of electricity and was not economical. The cause of this is not certain, but it is thought to be because the properties of the surface layer of the steel sheet changed due to the reverse electrolytic treatment that was applied after chromium plating, using the steel sheet as an anode. The inventors of this application are interested in the characteristics of the surface of chromium-plated steel sheets altered by this reverse electrolysis, and
Regarding the adhesion of TFS to paint, we have doubts about the conventional theory that the sulfuric acid radicals eutectoid in the chromium hydrated oxide film are harmful. The relationship between retort treatment resistance, S and O content, and alkali soluble content (thermal alkali soluble content) was quantitatively investigated for TFS having various sulfuric acid contents produced through the process. As a result, in TFS manufactured by the process of chromium plating → reverse electrolysis → electrolytic chromic acid treatment using sulfuric acid as an aid, S and O in the hydrated chromium oxide film were found to be S/O ≥ 0.18, alkali soluble content ≧30%
It was discovered that extremely excellent adhesion properties can be obtained with this method, and this led to the completion of the present invention. The test method for retorting resistance and the method for measuring the S/O ratio and alkali soluble content in the hydrated chromium oxide film used to understand the quality characteristics of TFS are as follows. (1) Retort resistance treatment method 60 mg/dm ² of phenol-epoxy paint was applied to the surface 1 of the TFS sample and baked at 210°C for 12 minutes. 25mg/d of the same paint on another sample surface 2
^m2 was applied and baked under the same conditions. These two samples were each cut to 70 mm in width and 60 mm in length, and two specimens with different coating thicknesses were cut at both ends in the length direction (1A and 2).
A) was overlapped by 8mm, a 100μm nylon film 3 (adhesive) was sandwiched between them, and after preheating at 200℃ for 120 seconds using a hot press, 3Kg/
Crimping was carried out at 200° C. for 30 seconds under a pressure of cm ² (see FIG. 1a). Ten sets of these test pieces 4 were made, and after rounding them in advance to a radius of about 100 mm like a can body,
mm angle 5 as shown in Figure 1b,
In a retort pot at 125-130℃, 1.6-1.7Kg/ ^cm2
The presence or absence of peeling was examined after 300 minutes. The number of peeled pieces in 10 sets was used as an index of retort processing resistance. The evaluation method is as follows. 〇…Number of peeled pieces during retort processing 0/10 pieces△…Number of pieces peeled off during retort treatment 1 to 2/10 pieces ×…Number of pieces peeled off during retort treatment 3 or more/10 pieces (2) S/0 ratio measurement TFS water The content of sulfate radicals in the chromium oxide film was investigated by Aussier electron spectroscopy (abbreviated as AES), and as shown in Figure 2, it was determined as the value of the intensity ratio S/0 of the oxygen peak and sulfur peak on the AES chart. Indicated. Please note that AES measurements are performed at a vacuum level of 1.0×
The experiment was carried out at 10 ^-9 torr and a beam voltage of 10.0 KV. Accelerating the Ar sputter with voltage to perform depth analysis
4.0KV, current density 0.6μA/m ² , degree of vacuum 2.2×
I went at 0 ^-7 torr. The distribution of S/0 in the depth direction in the film takes its maximum value slightly inside the outermost surface (at a depth of about 10 Å). In the present invention, this maximum value was defined as the S/0 value of each sample. (3) Alkali-soluble content After baking TFS at 210℃ for 12 minutes, 7.5N―
It was immersed in NaOH at 110°C for 10 minutes in a hot alkaline solution, and the amount of chromate film dissolved at that time was divided by the original amount of chromate film. A large value indicates that it is difficult for the chromate film to become insolubilized by dry baking. When manufacturing the TFS of the present invention, a thin steel plate is electrolytically degreased in a conventional manner, washed with water, and then pickled with sulfuric acid.
CrO ₃ 100-200g/, H ₂ SO ₄ 0.5-1g/,
Cathode treatment is carried out in a chromium plating bath having a composition of 5 to 8 g of Na ₂ SiF ₆ , followed by reverse electrolytic treatment in the solution with a quantity of electricity of 0.3 to 9 coulombs/dm ² using a steel plate as an anode. , Chromic anhydride after washing with water
The steel plate was treated as a cathode in an electrolytic chromic acid bath prepared by adding 30 to 90 g of sulfuric acid and 0.05 to 0.9 g of sulfuric acid. The amount of hydrated chromium oxide film formed on the surface of the obtained TFS was determined by the addition of a hot alkaline aqueous solution (7.5N
The amount of surface chromium before and after dissolution with NaOH) was detected by fluorescent X-ray analysis, and the dissolved amount was defined as the amount of hydrated chromium oxide. The sample used had a metallic chromium content of 100 to 120 by adjusting the amount of electricity during chromium plating and electrolytic chromic acid treatment.
mg/m ² , and the amount of hydrated chromium oxide was maintained within the range of 10 to 20 mg/m ² . Figure 3 shows the retort treatment resistance of the tested TFS in terms of the S/0 value of the hydrated chromium oxide film and the relationship between the alkali soluble content. It can be seen that TFS having a surface coating with an S/0 value of 0.18 or more and an alkali soluble content of 30% or more has extremely excellent retort resistance. From the above results, the S/0 value in the chromium hydrated oxide film is 0.18 in TFS manufactured by the method of performing reverse electrolytic treatment using the chromium-plated steel plate as an anode, followed by electrolytic chromic acid treatment. As described above, it has been found that if the alkali soluble content is 30% or more, the adhesion of the paint can be maintained at an extremely good level. According to many previously published research results, sulfate radicals eutectoid on hydrated chromium oxide generally impair retortability, and the hydrated chromium oxide film becomes easily insolubilized during air firing. It was generally accepted that a high value of the alkali soluble content, which is an indicator of , impairs retortability. In the present invention, in TFS, which employs a reverse electrolytic process in which the steel plate is treated as an anode between the chromium plating process and the electrolytic chromic acid treatment process, the presence of a certain amount or more of eutectoid sulfate radicals can adversely affect retort resistance. They discovered that they could create a product with improved properties and better high-temperature durability than ever before after retort treatment. Although the details of the characteristic improvement mechanism are not clear, the thin hydrated chromium oxide film on the surface of the steel sheet is altered by the reverse electrolytic treatment after chromium plating, and in the subsequent electrolytic chromic acid treatment process, the treatment bath containing sulfuric acid is added. This is thought to have affected the properties of the film formed inside, which has a large number of eutectoid sulfate groups and is difficult to be insolubilized by alkali during the dry firing process, and has significantly improved the adhesiveness of the obtained TFS. The present invention will be specifically described below with reference to Examples and Comparative Examples. A cold-rolled steel plate (T4CA) with a thickness of 0.22 mm was electrolytically degreased with a homezaline solution at 80°C and a current density of 15 A/dm ² for 10 seconds, and after washing with water, it was immersed in 10% H ₂ SO ₄ for 5 seconds and washed with water. After that, the main treatment was carried out under the following conditions.
This treatment is performed in the order of (1) chromium plating process → (2) reverse electrolytic treatment process → (3) electrolytic chromic acid treatment process, and (1) and (2)
were carried out continuously in the same electrolytic solution, and washing with water was performed between (2) and (3) and after (3). (1) Chrome plating Plating solution composition CrO ₃ 150g/ H ₂ SO ₄ 0.3-1.0g/ Na ₂ SiF ₆ 7g/ Plating conditions Cathode treatment at solution temperature 50℃ and current density 50A/ ^dm2 (2) Reverse Electrolytic treatment Reverse electrolytic treatment was performed at 0.5 to 3 coulombs/dm ² using a steel plate as an anode. For comparison, Table 1 also shows examples in which reverse electrolysis was not performed. (3) Electrolytic chromic acid treatment Composition CrO ₃ 60g/H ₂ SO ₄ 0.05-0.6g/Liquid temperature 40-45°C Cathode treatment was performed in chromic acid baths with different sulfuric acid degrees. When preparing the sample, adjust the amount of electricity during chromium plating and electrolytic chromic acid treatment to obtain a metallic chromium amount of 100 to 200 mg/m ² and a hydrated chromium oxide amount of 10 to 20 mg/m 2 .
mg/ ^m2 . Table 1 shows the retort treatment resistance, alkali soluble content of the hydrated chromium oxide film, and S/0 value measured for the obtained sample. From the results in Table 1, (1) chrome plating → (2) reverse electrolysis →
(3) In TFS manufactured through the process of electrolytic chromic acid treatment using sulfuric acid as an aid, the hydrated chromium oxide film on the surface contains S with an AES peak intensity ratio of S/0≧0.18, and the alkali-soluble content If it is 30% or more, it can be seen that the retort processing resistance is extremely good. Even if TFS has been treated in a similar process using reverse electrolytic treatment, if the S/0 value and alkali soluble content do not satisfy the above range, the characteristics are insufficient. In addition, when reverse electrolytic treatment is not performed, the obtained
Even if the hydrated chromium oxide film of TFS satisfies the above range in terms of S/0 value and alkali soluble content, it exhibits extremely poor paint adhesion. 【table】

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the retort treatment resistance test method for TFS paint adhesion, Figure 2 is an AES measurement chart, and Figure 3 is the retort treatment resistance of TFS and S/0 value of hydrated chromium oxide film. FIG.

Claims (1)

[Claims] 1. A stain-free product made by forming a chromium plating layer on a thin steel plate, which is subjected to reverse electrolytic treatment after electroplating, and a hydrated chromium oxide film formed by electrolytic chromic acid treatment using sulfuric acid as an auxiliary agent. In steel, the hydrated chromium oxide film on the surface contains S with an AES peak intensity ratio of S/O≧0.18, and dissolves at least 30wt% in a 7.5N hot alkaline solution after baking at 210℃ for 12 minutes. A stain-free steel with excellent adhesive properties.