JPS6234839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a stain-free steel having a lower layer of metallic chromium and an upper layer of hydrated chromium oxide on the surface of the steel plate, particularly as a material for adhesive cans, which is retort resistant and hot bender. This invention relates to electrolytic chromate-treated steel sheets with excellent paint adhesion that can withstand long-term storage. Electrolytic chromate-treated steel sheet is called chromate-free steel (hereinafter abbreviated as TFS) and has been recognized for its properties as a material for cans that can replace tinplate, and its usage has been increasing in recent years. TFS
Because it 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 joined with nylon adhesive. ing. Recently, the uses of TFS cans have 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. Or, after packaging, cans that require retort treatment at high temperatures are being used, causing problems such as the can body breaking. Additionally, there have been cases of coffee cans and other items that have recently become popular, breaking when stored for long periods in hot vending machines. Such can body tears that occur in TFS-adhesive cans are caused by hot water penetrating through the nylon adhesive layer at the joint, which deteriorates the adhesion at the interface between the paint film and TFS, and causes the paint to peel off from the paint film-TFS interface. This occurs because of this. In particular, much research has been carried out with the aim of obtaining TFS with excellent retort treatment resistance. Based on the idea that the sulfuric acid radicals contained in the chromium hydrated oxide film will be eluted and cause peeling at the paint film-TFS interface,
Instead, products using fluoride ions (for example,
57-53440, JP-A No. 56-142897) have been proposed. However, in order to achieve this, a method was adopted in which sulfuric acid was not added to the chromium plating bath as well as to the electrolytic chromic acid treatment bath that forms the hydrated chromium oxide film on the top surface of TFS, but instead a fluorine compound was added. However, in that case, the precipitation efficiency of metallic chromium is poor,
Significantly reduce manufacturing efficiency or reduce the resulting TFS
The quality of the product is unstable due to frequent surface stains.
The yield was poor, and many problems remained industrially. 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 in the solution using a steel plate as an anode, and then chromium plating without adding sulfuric acid is performed. proposed electrolytic chromic acid treatment in an acid aqueous solution (Japanese Patent Application Laid-Open No. 1983-
(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 the electrolytic chromic acid treatment process requires a large amount of electricity in order to stably obtain the chromic acid, 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 that has excellent retort processing resistance and durability during hot bender storage. In the present invention, a thin steel plate is plated with 50 to 200 mg/m ² of metallic chromium on one side, and the surface of the metallic chromium layer is coated with 5 to 200 mg/m 2 of metallic chromium.
TFS with 30mg/ ^m2 chromium hydrated oxide coating
It is related to. If the metallic chromium layer is less than 50mg/ ^m2 , the corrosion resistance will be poor and it is not good. Also, 200mg/
Since further improvement in corrosion resistance cannot be expected with more than m ² , a typical TFS has a metallic chromium layer of 50 to 200 mg/m ² . On the other hand, the chromium hydrated oxide coating
If it is less than mg/m ^{2 ,} desired paint adhesion cannot be obtained, and if it is more than 30 mg/m ² , the appearance deteriorates or cracks 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 inventor of the present application has 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. (See Patent No. 177998-1986). 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 in which the steel sheet was used as an anode after chromium plating. The inventors of the present application were interested in the characteristics of the surface of a chromium-plated steel sheet altered by this reverse electrolysis, and also investigated the adhesion of TFS to paint by eutectoiding sulfate groups in the chromium hydrated oxide film. In order to question the conventional theory that fluorine ions are harmful and harmless, we conducted retort-resistant treatment for TFS with various sulfuric acid contents manufactured through the process of chromium plating → reverse electrolysis → electrolytic chromic acid treatment. properties, high-temperature durability after retort treatment, S, F, and O contents of the hydrated chromium oxide film, alkali-soluble content (thermal alkali-soluble content)
We quantitatively investigated the relationship between As a result, in TFS manufactured through the process of chromium plating → reverse electrolysis → electrolytic chromic acid treatment using sulfuric acid and fluoride as aids, S, F, and O in the hydrated chromium oxide film were
Peak intensity ratio of S/O≧0.20 and F/O≦0.30
×(S/0) relationship, alkali soluble content ≧40
%, it was discovered that extremely excellent adhesiveness could be obtained, and this led to the completion of the present invention. Retort treatment resistance used to understand the quality characteristics of TFS, test method for high temperature durability after retort treatment, S/O ratio in hydrated chromium oxide film, F/O
The method for measuring the ratio and alkali soluble content is as follows. (1) Retort treatment resistance A phenol-epoxy paint was applied at 60 mg/dm ² to the TFS sample surface 1 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, 3
Crimping was carried out at 200° C. for 30 seconds under a pressure of Kg/cm ² (see FIG. 1a). Ten sets of these test pieces 4 were made, and after being pre-rounded to a radius of about 100 mm like a can body, they were fixed to an angle 5 with a base of 70 mm as shown in Figure 1b, and heated at 125 to 130°C and 1.6 to 1.7 kg/cm. The presence or absence of peeling was examined after 300 minutes in the retort pot of ^{No. 2} . The number of peeled pieces in 10 sets was used as an index of retort processing resistance. (2) High-temperature durability after retort treatment Similar to the test piece preparation method for retort treatment resistance tests, epoxy/phenol paint is applied to the TFS surface one side at a time and baked, and then heated and bonded with nylon adhesive. 0.6%
After performing retort treatment in NaCl aqueous solution at 135℃ for 90 minutes, and then immersing in the same solution at 90℃ for 14 days,
A T-peel test was conducted using an Instron tensile tester at a constant tensile speed of 200 mm/min to measure the peel strength. The test was conducted using five test pieces each, and the average value is shown as the test result. (3) Measurement of S/O and F/O ratio The content of sulfate radicals in the hydrated chromium oxide film of TFS was investigated using Auger electron spectroscopy (abbreviated as AES). It is shown as the intensity ratio S/O and F/O of the oxygen peak and sulfur peak. In addition, AES measurement is 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×
It was conducted at 10 ^-7 torr. Examining the distribution in the depth direction in the film, S/O takes its maximum value slightly inside the outermost surface (at a depth of about 10 Å), and F/O takes its maximum value at the outermost surface.
In the present invention, the maximum value of this is the S/O of each sample,
It was taken as F/O value. (4) 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 the usual 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. After washing with water, the steel plate is treated as a cathode in an electrolytic chromic acid bath prepared by adding sulfuric acid and an auxiliary agent containing silicic acid, borofluoric acid, hydrofluoric acid, and their salts to an aqueous chromic acid anhydride solution. did. 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 metal chromium content of 100 by adjusting the amount of electricity during chromium plating and electrolytic chromic acid treatment.
~120 mg/m ² , and the amount of hydrated chromium oxide was maintained in the range of 10 to 20 mg/m ² . A retort treatment resistance test was conducted on each sample using the method described above, and the results were organized in terms of the S/O value of the chromium hydrated oxide film and the alkali-soluble chromium (%). As a result, the S/O value was 0.18. Consists of a surface coating with an alkali soluble content of 30% or more.
It was found that with TFS, bond failure did not occur during retort processing. Next, high temperature durability after retort treatment was investigated.
FIG. 3 shows the obtained results arranged in relation to the S/O value of the hydrated chromium oxide film and the alkali-soluble chromium (%). To ensure durability when retorted beverage cans are stored for long periods in a hot bender, a T-peel strength of 3 kg/5
It is considered that it should have a strength of mm, but the third
According to the results shown in the figure, there are those with an S/O value of 0.2 or more and soluble chromium of 40% or more that satisfy the conditions, but in the area where S/O ≧0.2 and alkali-soluble chromium ≧40%. Among them, there were some that showed insufficient values of about 2 to 3 kg/5 mm. For samples in this region, the S/O value and F/O value were plotted in order to further clarify the relationship between the characteristics of the hydrated chromium oxide film and the high temperature durability after retort treatment. The results are shown in FIG.
As a result, many products with a high F/O value exhibit relatively insufficient high temperature durability, but the limit value cannot be determined unconditionally, and when the S/O value is high, the F/O
Values are also allowed up to high values, F/O≦0.30×(S/
The range of O) is the high temperature durability after retort treatment T
It was found that the peel strength was 3 kg/5 mm or more, indicating excellent paint adhesion. The reason for this is not clear, but it is thought that as the S/O value increases, the chromium hydrated oxide film is more likely to undergo oxo conversion, and its adhesion with paint deteriorates. This means an increase in the F/O value, which is thought to lead to improved adhesion with the paint, so it is presumed that when the S/O value is large, the allowable amount of the F/O value will also be large. Combining the above results, the S/O value in the chromium hydrated oxide film of TFS manufactured by chromium plating, reverse electrolytic treatment using the steel plate as an anode, and electrolytic chromic acid treatment is is 0.2 or more, alkali soluble content is 40% or more, F/O≦0.30
When ×(S/O) is satisfied, the adhesion of the paint can be maintained at an extremely good level. In particular, the high-temperature durability test after retort processing is a more severe test than the shell breakage test of the bonded parts during retort processing, but it is an essential characteristic now that vending machines (hot vendors) that hold cans at high temperatures have become widespread. be. As long as it satisfies the S/O value, F/O value, and alkali soluble content range of the present invention, it also satisfies the above-mentioned severe high temperature durability. According to many previously published research results, sulfuric acid radicals eutectoid on hydrated chromium oxide generally impair retortability, and the hydrated chromium oxide film becomes easily insolubilized during air firing. It was a common belief that a high value of the alkali soluble content, which is an indicator of , impairs retortability. The present invention employs a reverse electrolytic process in which a steel plate is used as an anode between the chromium plating process and the electrolytic chromic acid treatment process.
In TFS, the presence of a certain amount or more of eutectoid sulfate radicals improves retort resistance, and also creates a product with unprecedented high-temperature durability after retort treatment.
At that time, it was discovered that the F/O value should be within an allowable range depending on the S/O value. 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. After washing with water, 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 (2) are carried out consecutively in the same electrolyte, and (2) and
Washing with water was performed during and after (3). (1) Chrome plating Plating liquid composition CrO ₃ 150 g / H ₂ SO ₄ 0.3-1.5 g / Na ₂ SiF ₆ 7 g / Plating conditions Cathode treatment ( ² ) Reverse electrolytic treatment Reverse electrolytic treatment was performed at 0.5 to 10 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 80 g/ H ₂ SO ₄ 0.08-0.8 g/ NaF and or Na ₂ SiF ₆
0 to 10 g/liquid temperature: 40 to 45°C Cathode treatment was carried out in chromic acid baths with different concentrations of auxiliary agents such as sulfuric acid, sodium fluoride, and sodium silicofluoride. When preparing the sample, adjust the amount of electricity during chromium plating and electrolytic chromic acid treatment to determine the amount of metallic chromium.
100-200mg/ ^m2 , amount of hydrated chromium oxide 10-20mg/ ^m2
It was processed so that Retort treatment resistance, high temperature durability after retort treatment, alkali soluble content of the hydrated chromium oxide film, measured on the obtained sample,
Table 1 shows the S/O and F/O values. From the results in Table 1, it is clear that in TFS manufactured through the process of (1) chromium plating process → (2) reverse electrolytic treatment process → (3) electrolytic chromic acid treatment process using sulfuric acid and fluoride as auxiliaries, water on the surface The chromium oxide film contains S with an AES peak intensity ratio of S/O≧0.20, and F/O≦0.3.
It can be seen that when x(S/O) is 40% or more of alkali soluble content, retort treatment resistance and high temperature durability after retort treatment are extremely good. Even if TFS has been treated using a similar process of reverse electrolytic treatment, if the S/O value, F/O value, and alkali soluble content do not satisfy the above ranges, the properties are insufficient. . In addition, when reverse electrolytic treatment is not performed, the hydrated chromium oxide film of the obtained TFS is
Even if it satisfies the above range in terms of value, F/O 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 high temperature durability of TFS after retort treatment and the S of hydrated chromium oxide film. A graph showing the relationship between /O value and alkali soluble content, Figure 4 is S/O
≧0.2, alkali soluble content≧40% is a graph showing the relationship between the S/O value and F/O value of the hydrated chromium oxide film of the sample and the high temperature durability after retort treatment. Explanation of symbols 1, 2...TFS sample, 3...Nylon film, 4...Test piece, 5...Angle.

Claims (1)

[Claims] 1. On a thin steel plate, a chromium plating layer is electroplated and then subjected to reverse electrolytic treatment, and a hydrated chromium oxide film is formed on top of the chromium plating layer by electrolytic chromic acid treatment using sulfuric acid and fluoride as aids. In the stainless steel, S, F and O contained in the hydrated chromium oxide film on the surface have an AES peak intensity ratio of S/
An adhesive having a relationship of O≧0.20 and F/O≦0.30×(S/O), and is characterized by dissolving 40wt% or more in a 7.5N hot alkaline solution after baking at 210°C for 12 minutes. A stain-free steel with excellent properties.