JPS58177490A - Production of tin-free steel plate - Google Patents

Abstract

PURPOSE:To obtain a Cr<ox> film which has a uniform film construction and good resistance to a retort treatment in the stage of applying an electrolytic chromic acid treatment on a steel plate by using an aq. chromic acid soln. which contains no assistant except unavoidable impurities and applying the electrolytic chromic acid treatment dividedly in two stages on the steel plate. CONSTITUTION:Cr plating is applied on a steel plate in a Cr plating bath, whereafter the steel plate is reverse electrolyzed in the Cr plating bath to elute a part of the hydrated oxide film of Cr formed in the stage of the Cr plating and the anion of the assistant codeposited on the hydrated oxide film of Cr. The steel plate is then thoroughly washed in an aqueous washing bath. Further the steel plate is subjected to the 1st electrolytic chromic acid treatment in a Cr acid treatment bath contg. chromic anhydride and a compd. of >=1 kind of chromate and dichromate as a base component, contg anions of the unavoidable impurity anions occuring in the base component and being not added with any assistant, at the low current density of 0.1-10A/dm<2> and 0.1-10coulomb/dm<2> quantity of electricity. The treated steel plate is subjected to the 2nd electrolytic chromic acid treatment by using another electrode at current density of >=10A/ dm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the adhesion between a metallic chromium coating and a chromium hydrated oxide coating, and the adhesion between a chromium hydrated oxide coating and a chromium hydrated oxide coating (a method for manufacturing a din-free steel sheet for retort treatment). It is something.

In the conventional two-part system, the metal chromium and the chromium water-conserving oxide film are precipitated separately, so it has the advantage of being able to easily control the amount of each precipitation. Because the liquid composition is different, if the steel plate after chromium plating is directly transferred to the electrolytic chromic acid treatment bath, the plating aid anions eutectoided in the chromium hydrated oxide generated during chromium plating will remain in the final product composite film. or
#III! Chromium plating particles adhering to IN+ are brought into the electrolytic chromic acid treatment bath, causing problems such as fluctuations in the amount of chromium water-retaining oxide film deposited and re-precipitation of partially eluted auxiliary anions. . Therefore, it is necessary to thoroughly wash with water before chromium plating and electrolytic chromic acid treatment bath to prevent this, but washing with water after chromium plating alone will not remove the chromium hydrated oxide produced during chromium plating. It is difficult to remove the chromium plating auxiliary anions in the chromium plating solution.In chromium plating using sulfuric acid or its compounds as an auxiliary agent, it is difficult to remove the chromium plating auxiliary anions. , At, sulfate radicals are eutectoid in the finally formed chromium hydrated oxide, resulting in m! This is causing some inconvenience due to the lack of space between the membrane and the column.

A method to overcome this drawback is to perform reverse electrolysis in the solution after chromium plating.Thus, it is possible to reduce the amount of chromium hydrated oxide produced during chromium plating and the auxiliary anions contained therein. We have found that washing with water for 7 minutes before entering the chromium brewing bath, followed by applying electrolytic chromic acid in an aqueous solution of chromic acid, is extremely effective in improving retort resistance, and we have already developed a special method. Gansho 56-6
No. 2766 (hereinafter referred to as "nuclear"), but after repeated research, it was found that "nuclear" was extremely effective in improving retort resistance, but that the chromium hydrated oxide film was uneven. As a result of repeated research to solve this drawback, it was found that uniform ROM water 1ee
A chemical compound film can be obtained, and the retort processability has been greatly improved, leading to the present invention. The present invention involves applying metallic chromium plating of 20 to 200q/- on one side to a cold-sharpened steel plate, and removing the surface of this metallic chromium layer. 5-50q/
Tin-free steel I with chromium hydrated oxide film formed
This is related to N. If the metal chromium layer is less than 20q/wl, there will be many microcracks and pinholes, resulting in poor corrosion resistance, and if it is more than 200q/wl, no improvement in corrosion resistance can be expected.
It has a metal chromium layer of 0 to 200 wv/-.

-If the amount of hydrated chromium natural oxide film (hereinafter referred to as crOX film) is less than 5 drops/d, the desired paint adhesion cannot be expected, and if it is more than 50q/-, the appearance may deteriorate,
It is not practical because the CrOx film may crack during processing. Furthermore, the amount of CrOx coating is within the practical range of 10 to 30 drops/d, and is most desirable.

Tin-free steel sheets are used as food can materials only after being painted, and when used as food cans, the adhesion with the coating film is particularly important. In order to obtain a tin-free steel sheet with excellent adhesion to 1711M and excellent retort resistance after filling, this steel plate was plated with chromium in a general-purpose chromium plating bath using an auxiliary agent containing an anion such as am or its compound. Reverse electrolysis of 0.1 to 15 coulombs/dd is performed in the bath, and then chromic acid water #! is passed through the washing tank. We are proposing a method of electrolytic chromic acid treatment in the water between nuclear power plants.The tin-free copper plates obtained by this method are extremely effective in improving retort treatment resistance, but this treatment alone will cause the CrOx film to become uneven. As mentioned above, this may occur.

Therefore, in the present invention, after degreasing and pickling steel sheets as in the past, chromium plating is performed 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 complete the chromium plating. 8 co-deposited into the CF”** produced at the time.
After reducing the auxiliary anions such as 04"-, electrolytic chromic acid treatment is performed, and the feature is that this treatment is performed under the conditions described below. In other words, electrolytic chromic acid @ coral When applying c
In order to obtain the r''i film, chromic acid water S without intentionally adding any auxiliary agent other than unavoidably containing impurity anions.
Electrolytic chromic acid III sensitizer and C are applied to uniformly modify the CrOx film roughened by reverse electrolysis using a liquid treatment bath.
Electrolytic chromic acid applied to ensure the amount of rOx film [24
Electrolytic chromic acid treatment is applied in two stages of 6 corals in an Oka treatment bath or a separate treatment bath.The main ingredients of the chromic acid treatment aqueous solution used in this treatment are chromic anhydride, chromate, and heavy It is composed of at least one compound selected from chromates, and contains inevitable impurity anions derived from the main ingredient, but no auxiliary agents are intentionally added. 0 Dichromates include alkali metal salts of dichromic acid. , alkaline earth metal salts, ammonium salts, etc., and as chromates, alkali metal salts of chromic acid, alkaline earth gold 1II4 salts, ammonium salts, etc. are suitable, but in particular, compounds such as ¥! Class ii is not 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.

The degree of # of the chromic acid aqueous solution that inevitably contains impurities does not need to be particularly limited, but it is 10 to 200 in terms of Cr.
A range of /l is appropriate. If the setting is less than 10 f/, the electrical resistance of the bath will increase, causing problems such as overvoltage of the setting device and heating of the steel plate, which is not preferable.

Furthermore, even if it exceeds 200 f/l, it is not desirable to expect much improvement in the effect of the coagulation period, and the economic loss due to taking out the bath will be large. Therefore, the appropriate bath temperature for the romic acid treatment bath is 35 to 60°C. If it is lower than 0.35°C, temperature control will become difficult due to the increase in cooling water temperature in summer, and if it is higher than 60°C, the material of the electrolytic cell can withstand chromium water rupture. is limited. When reverse electrolysis is performed in the same solution after chromium plating, the Cr0K film formed during chromium plating is dissolved, and at the same time or after completion of the process, an anode Cr film different from the previous cathode Cr film is formed on the metallic chromium layer. be done. It has been revealed that due to the formation of this film, the exposure of metallic chromium is less than that of the conventional blind electrode film, but depending on the at type of auxiliary agent used for chromium plating, the bath Ra degree, and the reverse electrolytic conditions, the metal chromium may be formed anodically. Abnormal precipitation may be observed in a part of the CrOx film. When electrolytic chromic acid treatment using the conventional two-component method is applied to this film, the retort treatment resistance is good, but abnormal precipitation of the CrOx film is sometimes observed. How to avoid this. Without intentionally adding auxiliary agents,
After conducting various studies on chromic acid solution #1 containing unavoidable impurity anions, we first found that electrolytic chromium 1l11 was produced at low current density and low electrical quantity in chromic acid aqueous solution.
1 treatment was found to be effective and 1-0. During electrolytic chromic acid treatment, salt gas is generated by electrolysis of water at the cathode, and - near the cathode rises. An all compound with a high degree of integration is formed in which a hydroxyl group or a water molecule is coordinated with a valent chromium ion. In the present invention, the first treatment of chromium t11 is performed with a low electric RvB degree and a low electric lid, thereby minimizing the generation of Cr0X skin, and in addition, electric j! After the first treatment with electrolytic chromic acid, the Cr film is formed thin and uniformly because it accelerates its dissolution in the chromic acid water bath after the completion of Iji. This is applied to modify the Cr film to make it uniform when the polar CrOx film becomes rough, and is not intended to increase the CrOx film thickness.The area near the cathode during zero electrolysis is treated with dichromic acid. The higher the composition of salts and chromates, the opposite is the case in a bath containing only chromic anhydride. Therefore, the ratio of all bonds in the CrOx film formed during electrolysis is also different between the two, and the CrOx film during electrolysis is The repetition of dissolution and formation and the dissolution behavior after the end of electrolysis are also different, but in both cases, Cr0xFILjI! formed after the first treatment with electrolytic chromic acid!
The electrolytic conditions for the first electrolytic chromium l12 treatment in this study are at a low electric fifM degree of α1-1OA/&, and from 0-1 to 10
It is better to use a low electrical quantity of coulomb/6d. If the current density is less than 0.1 μm/-, the intended purpose cannot be achieved, and if it exceeds 10 μm/M, abnormal precipitation of Cr0X amount will occur, causing inconvenience. Sometimes. Further, if the amount of electricity is less than α1 coulombs/6d, the intended purpose cannot be achieved, and if it exceeds 10 coulombs/υ, the amount of CrOx becomes excessive, which may cause abnormal precipitation and cause problems.

As described above, the CrOx film roughened by reverse electrolysis is modified by the electrolytic chromic acid #11 treatment.Furthermore, in the present invention, after the first chromic acid treatment, the same It is effective to carry out the electrolytic chromium s2 treatment using a bath with a different composition or a different composition under the electrolytic conditions described below.

The conditions for the electrolytic layer are those that provide the necessary amount of electricity to ensure the CR sL weight, and are not particularly limited, but the current density for the second electrolytic chromic acid treatment is preferably in the range of 10 to 80 A/-. When the current density is less than IOA/dm', the desired Cr
This is because the electrolysis time is too long to ensure the amount of Ox film, making it impractical, and if the electrolysis time exceeds 80 μm/dd, abnormal precipitation of C, OX FjLB may occur. The bath composition may be the same as the electrolytic chromic acid first treatment solution, but if the first treatment bath is composed mostly of chromate or electrochromate, the amount of electrolysis may be large.
In this case, it is economically desirable to use a sword with a high composition of chromic anhydride.

Next, the processing according to the present invention will be explained in detail.

A cold-rolled steel plate with a thickness of 0.22 m was subjected to pretreatment of degreasing and pickling using conventional methods, and then subjected to Cros250 f/l.

A chromium plating bath containing H, 80, 2, 5 f/l,
Electrolysis was performed for 1.0 seconds at a bath temperature of 55° C., a current density of 60 μm, and 7th+/. Line analysis of the CrOx film at this time by EPMA is shown in Figure 1tl1. Immediately after chromium plating, a current of 15 A/ds/ was applied in the same solution! 02 in it density
Reverse electrolysis for seconds was applied. EPM of the CrOx film at this time
Line analysis by A [shown in Figure 2] After thoroughly washing this chromium-plated steel plate with water, cry, 50 t/
Bath 1 with a composition of 1% Na, Cr, Q, 10 f/l and containing unavoidable impurity anions! 1ml of chromic acid water at 40°C! Electricity RWj degree Te 0.2 of 5 m/dd in liquid
The Cr0X at this time was subjected to the first electrolytic chromic acid treatment for seconds.
Figure 3 shows a line analysis of the film using EPMA. After this first treatment, it was heated for 10 seconds at a current density of 15 A/M in a chromic acid water bath containing 60 t/l of chromic anhydride and at a bath temperature of 40°C. The Cr at this time was subjected to the second electrolytic chromic acid treatment.
Figure 4 shows line analysis of the film by EPMA. In addition, an optical micrograph at 400x is shown in Figure 6.
As a f0 comparison, after chromium plating, it was immersed in the same vinegar for 5 seconds and then immersed in a chromic acid bath containing 601/l of chromic anhydride at 40°C.
Figure 5 shows line analysis using Cr"BLllN) EPMA when electrolytic chromic acid treatment was applied for 5A/4d x 1.9 seconds, and Figure 7 shows a 400x optical micrograph. See the results of O line analysis. The products shown in Figures 3 and 4 that have undergone the treatment of the present invention are those after chromium plating (Figure 1) and those after reverse electrolysis (Figure 2) without conventional electrolytic chromic acid treatment. CrOx (Fig. 5)
It can be seen that there is little abnormal precipitation and the film is uniform.

Furthermore, looking at the X-ray micrograph, it is clear that the CrOx film formed by the present invention (Fig. 6) is homogeneous and even, but the CrOx film formed by the conventional electrolytic chromic acid treatment (Fig. 7) is clear. It can be seen that a large number of uneven CrO3 skin changes (black spots visible) are generated.

Table 1 below shows the determination of unevenness of the Cr film and the results of the T-peel test as described below for the above-mentioned inventive examples and comparative examples.

Table 1 (Measurement of amount of Cr) Prepared caustic soda #100℃, 5oot7t
! The amount of 0crOX was measured using the calibration curve based on the difference in the measured Cr amount after 10 minutes of wIJ immersion in the water.
0 seconds].

(KPMA foot measurement) The Cr0X film was fixed with a carbon film, and then the gold ingot chromium was dissolved with nital from the base chain side, and then placed on a clean platinum foil, and line analysis was performed using EPMA.

Accelerating voltage: 20KV Electron beam intensity: 0.02μ Human beam diameter: 2P Next, the present invention will be explained in detail with reference to examples.〇 [Example 1] A cold-rolled steel plate with a thickness of 022 was soaked in a 5% homethazone solution at 80KV.
After electrolytic degreasing for 10 seconds at a current density of 15 μm/d, /, the sample was washed with water, immersed in 10X' sulfuric acid at room temperature for 5 seconds, washed with water, and then subjected to the main treatment under the following conditions.

Chromium plating treatment bath composition Cro, 250 f/l H, So, 2.5 t/ bath Temperature 55°C Electrolytic conditions s o VdylIx i, s seconds After the above chromium plating, reverse electrolytic treatment was carried out in the same solution under the following conditions. Reverse electrolysis conditions: 15 A/dd x 0.2 seconds After that, it was washed with water and immediately subjected to electrolytic chromium cleaning treatment under the following conditions. ,
10 f/ bath temperature 40°C Electrolysis conditions 5 V × 0.2 seconds Electrolytic chromic acid 11r2 treatment bath composition Cry, 50 y/g, crzOt
i Of / I-bath Temperature 40℃ Electrolytic conditions I S A / dj x 1.0 seconds Electrolytic chromium 1 lil I [2 samples were prepared by washing with water and then washing with hot water and drying [Example 2] Example 1 except that electrolytic chromic acid treatment was performed under the following conditions.
7L performs the same process as .

Electrolytic chromic acid 1st treatment bath composition C Tsuru 50 tit "f" Oa 10 f/ bath Temperature 40℃ Electrolytic conditions 10 Vds/ x O, 2 seconds Electrolytic chromic acid 2nd treatment bath composition crOJ601/! 40℃ Electrolytic conditions 10 iv'd, d x 1.0 [Example 3] Example 1 except that electrolytic chromic acid treatment was performed under the following conditions.
The same process was performed.

Electrolytic chrome! I2 First treatment bath composition Na, Cr, 0. 60 y / bath
Temperature: 40℃ Electrolysis conditions: 5 A/dpd x O, 2 seconds electrolysis ROM! Second treatment bath composition Cryj60 t / bath Temperature 40°C Electrolysis conditions 10 A/ds/ x 1.0 seconds [Comparative Example 1
] After the chromium plating, the same treatment as in Example 1 was performed, except that the sample was immersed in the same solution for 5 seconds and subjected to electrolytic chromic acid treatment under the following conditions.

Electrolytic chromic acid treatment bath composition: Cry, 601/L Latent temperature: 40C Electrolytic conditions: 15 Vd+st' Actual 1a Example 1 and IW except for the treatment
I did the processing for Mr. J.

Electrolytic chromium #1 treatment bath composition Cry, 50 f/jNa, CrA1
0 t/l- Bath temperature 40°C Electrolysis conditions 5mm/dd x O, 2 seconds electrolytic Rom Shun 2nd tank composition Cr0,50f/l Na, Cr, CI, 10 t/l
Temperature: 40°C Electrolytic conditions: 15 A/4111' After applying sizing coating and baking at 190°C for 10 minutes, the same amount of gold coating was applied to the remaining opposite side and baking was performed at 21°C for 10 minutes. After this, a nylon-based adhesive synthetic resin 7-
A plurality of test pieces were prepared by sandwiching a strip (thickness: 100 pwa, width: 5 M) and bonding by hot pressing at 190 DEG C. and 1-/- for 30 seconds.

For these test pieces immediately after adhesion, a T-peel test was conducted using an Instron tensile tester at a constant tensile speed of 200 w/m to measure the peel strength i.Furthermore, using another test piece, The peel strength was measured under the same conditions as above after being immersed in a sugar acid solution containing 15 f/l of sucrose and adjusted to pH 3.3 with citric acid at 70°C for 7 days.

All tests were conducted using five test pieces of each test piece. The test results are shown in Table 2 below, and the results are shown as the average value.
(The T-peel test value immediately after adhesion is used to judge the adhesion of the paint film after painting1. Also, when performing retort treatment such as high temperature sterilization, water that has penetrated through the paint film If there is a large amount of dissolved CrOx, the adhesive force between the coating film and Cr will decrease, and retort treatment resistance will deteriorate.70
The T layer peeling test value after 7 days of immersion at ℃ is used for this evaluation.

In addition, from the test results in Table 2, the tin-free steel sheets according to the present invention (Examples 1 to 3) have no unevenness in the CrOx film and have excellent retort treatment resistance, but the conventional examples 1 and 2 In this case, unevenness occurs in the CrOX film,
It is clear that the retort resistance is also poor.

As is clear from the above explanation, according to the present invention, a homogeneous tin-free steel sheet with a CrOx film having good adhesion with paint and retort treatment resistance can be obtained, and this can be used for coffee cans and food cans for retort treatment. In addition, adhesive cans can also be used for long cans and miscellaneous cans.In addition, the paint used for painting is not limited to paints called sizing or gold, but any paint made with an organic solvent may be used. Also, only nylon type #c [will not be added.

Table 2

[Brief explanation of drawings]

Figure wi1 is an EPM mu line analysis diagram of CrOx film after chromium plating, Figure 2 is an EPMA line analysis diagram of CrO3 film after reverse electrolysis, and Figure 3 is an electrolytic chromic acid a
Fig. 4 is an EPM mullline analysis diagram of the CrOx film after treatment with electrolytic chromic acid, and Figure 5 is the EPMA line of the CrOx film after conventional electrolytic chromic acid treatment. Analysis diagrams, Figures 6 and 7 are 400x magnification microscope photographs of the surface structure of metals, Figure 96 is a microscope photograph of the same sample as Figure 4, and Figure 117 is a microscope photograph of the same sample as Figure 5. This is a photo taken by Kenko. Patent Applicant: Kawasaki Steel Co., Ltd. Mouse 1 Figure 6 ¥2 Figure Castle 3 Figure Castle 4 Figure 8A Internal organs 50 48 voices

Claims (1)

[Claims] Using a chromium plating bath and an electrolytic chromic acid treatment bath separated from the bath by a water washing bath, the steel plate has a metallic chromium coating and a coating mainly composed of chromium water-conserving oxide formed on the steel plate. In manufacturing free steel sheets, reverse electrolysis is performed in a chromium plating bath in which the steel sheet is plated with chromium, and a part of the chromium water-retention oxide film generated during chromium plating and the chromium water-retention oxide film are removed. The auxiliary anion eutectoided in the mixture is eluted, and then thoroughly washed with water in a washing bath, and then at least one compound selected from chromic anhydride, chromate, and dichromium Al salt is added as the main ingredient. A low current density of 0.1 to 10 mph in a chromic acid treatment bath containing unavoidable impurity anions originating from the base agent and without intentional addition of auxiliary agents;
Electrolytic chromic acid 1 treatment is carried out with a low electricity amount of 1 to 10 coulombs/υ, and electrolytic chromic acid II 2 treatment is carried out using a separate electrode from the first treatment at a current density of 10 μm/- or more. Manufacturing method C of tin-free steel plate characterized by performing luck