JPS6123280B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a stain-free steel sheet for retort treatment, which has excellent adhesion between a metallic chromium coating and a chromium hydrated oxide coating, and excellent adhesion between a chromium hydrated oxide coating and a paint. The conventional two-part method deposits metallic chromium and the hydrated chromium oxide film separately, so it has the advantage of being able to easily control the amount of each deposited. Because the compositions are different, if a steel plate after chromium plating is directly transferred to an electrolytic chromic acid treatment bath, the tanning aid anions eutectoid in the chromium hydrated oxide generated during chromium plating will be deposited in the coating of the final product. The chromium plating solution that remains or adheres to the steel surface may be brought into the electrolytic chromic acid treatment bath, causing fluctuations in the amount of chromium hydrated oxide film deposited, or re-precipitation of partially eluted auxiliary anions. This may cause inconveniences such as Therefore, it is necessary to thoroughly wash with water after chromium plating and before entering the electrolytic chromic acid treatment bath to prevent this, but washing with water after chrome plating alone will not remove the chromium water generated during chrome plating. It is difficult to remove the chromium plating aid anion in the oxide. In particular, in chromium plating using sulfuric acid or its compounds as an aid, even if electrolytic chromic acid treatment is performed using a chromic acid solution, sulfuric acid groups are eutectoid in the final chromium hydrated oxide. This causes problems in adhesion with the paint film. As a method to overcome this drawback, by performing reverse electrolysis in the solution after chromium plating, it is possible to reduce the chromium hydrated oxide produced during chromium plating and the auxiliary anions therein. We have found that thoroughly washing with water before entering the electrolytic chromic acid treatment bath and then applying electrolytic chromic acid in an aqueous chromic acid solution is extremely effective in improving retort resistance. Gansho 56-62766
(hereinafter referred to as the original invention). However, after repeated research, it was discovered that although the original invention is extremely effective in improving retort-resistant treatment methods, the chromium hydrated oxide film may become non-uniform. As a result of repeated research, it was possible to obtain a uniform chromium hydrated oxide film, and the retort processability was further improved, leading to the present invention. In the present invention, a cold-rolled steel sheet is plated with metallic chromium of 20 to 200 mg/ ^m2 on one side, and the surface of this metallic chromium layer is
This relates to a stain-free steel sheet with a chromium hydrated oxide coating of ~50 mg/m ² . If the metallic chromium layer is less than 20mg/ ^m2 , there will be many microcracks and pinholes, resulting in poor corrosion resistance.
If the ^amount is more than 200 mg/m2, no improvement in corrosion resistance can be expected, so normal chrome-plated steel sheets are used at 20 to 200 mg/ ^m2.
It has a metallic chromium layer. On the other hand, if the amount of hydrated chromium oxide film (hereinafter referred to as Cr ^OX film) is less than 5 mg/m ² , the desired paint adhesion cannot be expected, and if it is more than 50 mg/m ² , the appearance may deteriorate or Cracks may appear in the Cr ^OX film, making it impractical. Furthermore, Cr ^OX
The coating amount is within the practical range of 10 to 30 mg/m ² and is most desirable. A stain-free steel plate can only be used as a food can material after being painted, and when used as a food can, adhesion with the coating film is particularly important. In order to obtain a stain-free steel sheet with excellent adhesion to the coating film and resistance to retort treatment after filling, chrome plating is performed using a general-purpose chromium plating bath using an auxiliary agent containing anions such as sulfuric acid or its compounds. The original invention proposes a method in which reverse electrolysis is then carried out at 0.1 to 15 coulombs/dm ² in this bath, and then electrolytic chromic acid treatment is carried out in an aqueous chromic acid solution via a water washing tank. The stain-free steel sheets obtained by this method are extremely effective in improving retort treatment methods, but
As mentioned above, this treatment alone may cause the Cr ^OX film to become non-uniform. Therefore, in the present invention, a conventionally degreased and pickled steel sheet is chromium plated in a chromium plating bath containing sulfuric acid or its compounds as an auxiliary agent, and then reverse electrolysis is performed in this bath to form a chrome plating layer. generated at the time
After reducing the auxiliary anions such as SO ₄ ^2- that have eutectoided in the Cr ^OX film, electrolytic chromic acid treatment is performed, and the feature is that this treatment is performed under the conditions described below. . In other words, when performing electrolytic chromic acid treatment,
In order to obtain a Cr ^OX film with a uniform electrolytically deposited film structure and good retort treatment resistance, a treatment bath of a chromic acid aqueous solution was used in which no auxiliary agents were intentionally added, except for the unavoidable presence of impurity anions. The same treatment is divided into two stages: the first electrolytic chromic acid treatment is applied to uniformly modify the Cr ^OX film roughened by reverse electrolysis, and the second electrolytic chromic acid treatment is applied to ensure the amount of Cr ^OX film. Electrolytic chromic acid treatment is carried out in a bath or a separate treatment bath. The main ingredient of the chromic acid treatment aqueous solution used in the present invention is:
It is composed of at least one compound selected from chromic anhydride, chromate, and dichromate, and contains inevitable impurity anions derived from the base agent, but no auxiliary agent is intentionally added. Suitable dichromates include alkali metal salts, alkaline earth metal salts, and ammonium salts of dichromic acid, and suitable chromates include alkali metal salts, alkaline earth metal salts, and ammonium salts of chromic acid. However, the type of compound is not particularly limited. The composition of chromic acid and other salts in the electrolytic chromic acid aqueous solution bath may be the same in the first treatment and the second treatment, or may be different depending on the electrolytic conditions and the like. The concentration of the chromic acid aqueous solution that inevitably contains impurities does not need to be particularly limited, but it should be 10 to 10% in terms of _CrO3 .
A range of 200g/ is appropriate. Concentration is 10g/
If it is less than this, the electrical resistance of the bath increases, causing problems such as overvoltage of the rectifier and heating of the steel plate, which is not preferable. Moreover, if the amount exceeds 200 g/l, it is not desirable to improve the desired effect much, and the economic loss due to taking out the bath will be large. The bath temperature of such a chromic acid treatment bath is 35 to 60℃.
is appropriate. If it is lower than 35°C, temperature control becomes difficult due to the rise in cooling water temperature in the summer, and if it is higher than 60°C, the materials for the electrolytic cell that can withstand the chromic acid aqueous solution are limited. When reverse electrolysis is performed in the same solution after chrome plating, the Cr ^OX film formed during chrome plating is dissolved.
At this time or after the previous cathode Cr ^OX
An anodic Cr ^OX film, which is foreign to the film, is formed on the metallic chromium layer. It has been revealed that the exposure of metallic chromium is less due to the formation of this film than in the conventional cathodic film, but depending on the type of auxiliary agent used for chromium plating, the bath concentration, and the reverse electrolytic conditions, the metal chromium may be formed anodically. Abnormal precipitation may be observed in some parts of the Cr ^OX film. When the conventional two-component electrolytic chromic acid treatment was performed on this film, the retort treatment resistance was good, but abnormal precipitation of the Cr ^OX film was sometimes observed. As for ways to avoid this, we conducted various studies on chromic acid aqueous solutions containing unavoidable impurity anions without intentionally adding auxiliary agents, and first of all, in chromic acid aqueous solutions with low current density and low electricity quantity. It was found that performing the first electrolytic chromic acid treatment was effective. During electrolytic chromic acid treatment, H ₂ gas is generated by electrolysis of water at the cathode, and the pH near the cathode increases. Along with this, an ol compound with a high degree of polymerization is formed in which a hydroxyl group or a water molecule is coordinated with a low-valent chromium ion. In the present invention, the formation of a Cr ^OX film is minimized by performing the first chromic acid treatment with a low current density and a low amount of electricity.
In addition, since dissolution in the chromic acid aqueous solution is promoted immediately after electrolysis is completed, a thin and uniform Cr ^OX film is formed. The first electrolytic chromic acid treatment according to the present invention is carried out in order to modify and make the Cr ^OX film uniform when the anode Cr ^OX film formed on metal chromium ^becomes rough due to reverse electrolysis. It is not intended to increase the amount of film. The pH near the cathode during electrolysis increases as the composition of dichromate and chromate increases, and the opposite is true in a bath containing only chromic anhydride.
Therefore, the ratio of all bonds in the Cr ^OX film formed during electrolysis is different between the two, and the repetition of dissolution and formation of the Cr ^OX film during electrolysis and the dissolution behavior immediately after the end of electrolysis are also different, but in both cases, electrolytic chromic acid The Cr ^OX film formed after the first treatment is uniform. The electrolytic conditions for the first electrolytic chromic acid treatment in the present invention are a low current density of 0.1 to 10 A/ ^dm2 , and a
It is preferable to use a low amount of electricity of coulomb/dm ² . If the current density is less than 0.1 A/dm ² , the intended purpose cannot be achieved, and if it exceeds 10 A/dm ² , abnormal precipitation of Cr ^OX may occur, resulting in inconvenience. Also, the amount of electricity
If it is less than 0.1 coulombs/dm ^{2 ,} the desired purpose cannot be achieved, and if it exceeds 10 coulombs/dm ² , the amount of Cr ^OX becomes excessive, which may cause abnormal precipitation and cause problems. As described above, the first electrolytic chromic acid treatment modifies the Cr ^OX film that has become rough due to reverse electrolysis. Furthermore, in the present invention, after the first chromic acid treatment,
It is effective to perform the second electrolytic chromic acid treatment using a bath of the same or different composition as used in the first treatment and under the electrolytic conditions described below. The electrolytic conditions are those that provide the amount of electricity necessary to ensure the amount of Cr ^OX film and are not particularly limited, but the current density of the second electrolytic chromic acid treatment is 10~
A range of 80A/ ^dm2 is good. Current density is 10A/dm ²
If it is less than 80 A/dm 2 , the electrolysis time is too long to ensure the desired amount of Cr ^OX film, which is not practical, and if it exceeds 80 A/dm ² , abnormal precipitation of the Cr ^OX film may occur. In addition, the bath composition of the electrolytic chromic acid second treatment may be the same as the electrolytic chromic acid first treatment solution, but if the first treatment bath is mostly composed of chromate or dichromate, Since a large amount is required, in this case it is economically desirable to use a bath with a high composition of chromic anhydride. Next, the processing according to the present invention will be specifically explained. After pre-treating a cold-rolled steel plate with a thickness of 0.22 mm by conventional methods such as degreasing and pickling, 250 g of CrO ₂ /,
In a chromium plating bath containing 2.5g/H ₂ SO ₄ ,
Electrolysis was carried out for 1.0 seconds at a bath temperature of 55° C. and a current density of 60 A/dm ² . Figure 1 shows the EPMA line analysis of the Cr ^OX film at this time. Immediately after chromium plating, reverse electrolysis was performed in the same solution at a current density of 15 A/dm ² for 0.2 seconds. Figure 2 shows the EPMA line analysis of the Cr ^OX film at this time. After washing this chrome-plated steel plate thoroughly with water,
With a composition of CrO ₂ 50g/, Na ₂ Cr ₂ O ₇ 10g/,
A first electrolytic chromic acid treatment was performed at a current density of 5 A/dm ² for 0.2 seconds in a chromic acid aqueous solution containing unavoidable impurity anions at a bath temperature of 40°C. Figure 3 shows the EPMA line analysis of the Cr ^OX film at this time. After this first treatment, a second electrolytic chromic acid treatment was performed at a current density of 15 A/dm ² for 1.0 seconds in an aqueous chromic acid solution containing 60 g of chromic anhydride and a bath temperature of 40°C. Figure 4 shows the EPMA line analysis of the Cr ^OX film at this time. Furthermore, an optical micrograph at 400x magnification is shown in Fig. 6. For comparison, after chromium plating, 60 g of chromic anhydride was immersed in the same solution for 5 seconds.
Cr ^OX film when subjected to electrolytic chromic acid treatment at 15 A/dm ² × 1.0 seconds in a chromic acid bath at 40°C.
Line analysis by EPMA is shown in Figure 5, 400
A double optical microscope photograph is shown in FIG. Looking at the results of line analysis, the products shown in Figures 3 and 4 that were treated according to the present invention are those after chrome plating (Figure 1), those after reverse electrolysis (Figure 2), It can be seen that there is less abnormal precipitation of Cr ^OX and the film is more uniform than that after conventional electrolytic chromic acid treatment (Figure 5). Moreover, looking at the micrograph, the one according to the present invention (Fig. 6) has
It is clear that the Cr ^OX film is homogeneous and even.
In the figure), it can be seen that many non-uniform irregularities (looking like black spots) are formed in the Cr ^OX film. Table 1 below shows the evaluation of the unevenness of the Cr ^OX film and the results of the T-peel test as described below for the above-mentioned inventive examples and comparative examples.

[Example 1]

A cold-rolled steel plate with a thickness of 0.22 mm was electrolytically degreased in a 5% fomethazone solution at 80°C and at a current density of 15 A/dm ² for 10 seconds, then washed with water, and immersed in 10% sulfuric acid at room temperature for 5 seconds. After washing with water, the main treatment was performed under the following conditions. Chromium plating treatment bath composition: 250 g of CrO ₃ / 2.5 g of H ₂ SO ₄ / Bath temperature: 55° C. Electrolytic conditions: 50 A/dm ² × 1.5 seconds After the above chromium plating, reverse electrolytic treatment was performed in the same solution under the following conditions. Reverse electrolysis conditions: 15A/dm ² ×0.2 seconds Thereafter, the sample was washed with water and immediately subjected to electrolytic chromic acid treatment under the following conditions. Electrolytic chromic acid first treatment bath composition CrO ₃ 50g / Na ₂ Cr ₂ O ₇ 10g / Bath temperature 40℃ Electrolytic conditions 5A / dm ² × 0.2 seconds Electrolytic chromic acid second treatment bath composition CrO ₃ 50g / Na ₂ Cr ₂ O ₇ 10g/Bath temperature: 40°C Electrolysis conditions: 15A/dm ² ×1.0 seconds Immediately after the second electrolytic chromic acid treatment, the sample was washed with water, further washed with hot water, and then dried to prepare a sample. [Example 2] The same treatment as in Example 1 was performed except that the electrolytic chromic acid treatment was performed under the following conditions. Electrolytic chromic acid first treatment bath composition CrO ₃ 50g / Na ₂ CrO ₄ 10g / Bath temperature 40℃ Electrolytic conditions 10A/dm ² × 0.2 seconds Electrolytic chromic acid second treatment bath composition CrO ₃ 60g / Bath temperature 40℃ Electrolytic conditions 10A /dm ² ×1.0 seconds [Example 3] The same treatment as in Example 1 was performed except that the electrolytic chromic acid treatment was performed under the following conditions. Electrolytic chromic acid first treatment bath composition Na ₂ Cr ₂ O ₇ 60g/bath temperature 40℃ Electrolysis conditions 5A/dm ² ×0.2 seconds Electrolytic chromic acid second treatment bath composition CrO ₃ 60g/bath temperature 40℃ Electrolysis conditions 10A/dm ² × 1.0 seconds [Comparative Example 1] After the above chromium plating, immersion in the same solution for 5 seconds,
The same treatment as in Example 1 was performed except that the electrolytic chromic acid treatment was performed under the following conditions. Electrolytic chromic acid treatment bath composition: 60 g of CrO ₃ / bath temperature: 40°C Electrolytic conditions: 15 A/dm ² × 1.0 seconds [Comparative Example 2] After the above-mentioned chromium plating, immerse in the same solution for 5 seconds,
The same treatment as in Example 1 was performed except that the electrolytic chromic acid treatment was performed under the following conditions. Electrolytic chromic acid first treatment bath composition CrO ₃ 50g / Na ₂ Cr ₂ O ₇ 10g / Bath temperature 40℃ Electrolytic conditions 5A / dm ² × 0.2 seconds Electrolytic chromic acid second treatment bath composition CrO ₃ 50g / Na ₂ Cr ₂ O ₇ 10g/Bath temperature: 40°C Electrolysis conditions: 15A/dm ² ×1.0 seconds A T-peel test was conducted on the stain-free steel plate obtained as described above. 50±5mg/d on one side of each of the above stain-free steel plates
After applying sizing paint with ^m2 and baking at 190℃ for 10 minutes, apply the same amount of gold paint to the remaining opposite side.
Baking was performed at 210°C for 10 minutes. After this, a nylon adhesive synthetic resin tape (thickness 100 μm,
Narrow the width (5 mm) and heat at 190℃ using a hot press.
A plurality of test pieces were prepared by crimping at Kg/cm ² for 30 seconds to bond. These test pieces immediately after adhesion were subjected to a T-peel test using an Instron tensile tester at a constant tensile speed of 200 mm/mm to measure the peel strength. Furthermore, using another test piece, 15 g of sucrose/
Contains sugar acid solution adjusted to PH3.3 with citric acid.
The peel strength after immersion at 70°C for 7 days was measured under the same conditions as above. All tests were conducted using five test pieces of each type. The test results are shown in Table 2 below, and the results are expressed as average values. The T-peel test value immediately after adhesion is used to judge the adhesion of the coating after painting. Furthermore, when performing retort processing such as high-temperature sterilization, if there is a large amount of Cr ^OX dissolved in the water that has penetrated through the paint film, the adhesive strength between the paint film and Cr ^OX will decrease, resulting in poor retort resistance. Processability deteriorates. The T-peel test value after 7 days of immersion at 70°C is used for this evaluation. In addition, from the test results in Table 2, it is clear that Cr ^OX
There is no unevenness in the film and the retort treatment resistance is excellent, but in Conventional Examples 1 and 2, Cr ^OX
It is clear that unevenness occurs in the film and that the retort treatment resistance is also poor. As is clear from the above explanation, according to the present invention, a homogeneous, stain-free steel sheet with a Cr ^OX film having good adhesion to paint and retort processing resistance can be obtained, and this can be used for coffee cans for retort processing and food products. In addition to cans, adhesive cans can also be used for gallon cans and miscellaneous cans. Further, the paint used for painting is not limited to a paint called sizing or gold, but any paint made of an organic solvent may be used, and the adhesive is not limited to nylon.

【table】 [Brief explanation of the drawing]

Figure 1 shows EPMA of Cr ^OX film after chrome plating.
Line analysis diagram, Figure 2 shows Cr ^OX after reverse electrolysis
Figure 3 is an EPMA line analysis diagram of the Cr ^OX film after the first electrolytic chromic acid treatment. Figure 4 is an EPMA line analysis diagram of the Cr ^OX film after the second electrolytic chromic acid treatment. 5
The figure shows the Cr ^OX film after conventional electrolytic chromic acid treatment.
The EPMA line analysis diagram, Figures 6 and 7 are 400x optical micrographs of the surface structure of the metal, Figure 6 is a micrograph of the same sample as Figure 4, and Figure 7 is the same sample as Figure 5. This is a microscopic photograph.

Claims (1)

[Claims] 1 Using a chromium plating bath and an electrolytic chromic acid treatment bath separated from it by a water washing bath, a metallic chromium coating is formed on a steel plate, and a coating consisting mainly of chromium hydrated oxide formed over this is coated on a steel plate. In order to produce a stain-free steel sheet with chromium plating, the steel sheet is chromium plated in a chromium plating bath and then reverse electrolyzed in the chromium plating bath to remove the chromium hydrated oxide film formed during chromium plating. The auxiliary anion co-deposited in the chromium hydrated oxide film is eluted, and then thoroughly washed with water in a water washing bath.Then, the main ingredient is selected from chromic anhydride, chromate, and dichromate. A chromic acid treatment bath containing at least one compound of
A first electrolytic chromic acid treatment is performed at a low current density of 0.1 to 10 A/dm ² and a low amount of electricity of 0.1 to 10 coulombs/dm ² , followed by a separate treatment from the first treatment at a current density of 10 A/dm ² or more. Electrolytic chromic acid secondary using an electrode
A method for manufacturing a stain-free steel sheet, which comprises performing a treatment.