JPS58177489A - 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 assistants except unavoidable impurities and controlling the bath thereof to specific pH or below. CONSTITUTION:Cr plating is applied on a steel plate in a Cr plating bath, whereafter the steel plate is reversely electrolyzed in the Cr plating bath to elute part of the hydroxidized film of Cr formed in the stage of the Cr plating and the anions of the assistant codeposited on the hydroxidized film of Cr. The steel plate is then thoroughly rinsed in a rinsing bath. Further the steel plate is subjected to cathodic treatment at <=1pH in a Cr acid treatment bath contg. chromic anhydride and a compd. of >=1 kind among chromate and dichromate as a base component, contg. anion of the unavoidable impurity occuring in the base component and being not added with any assistant.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a tin-free steel sheet for retort treatment, which has excellent adhesion between a metal chromium coating and a chromium water conservation oxide coating, and excellent adhesion between a chromium water conservation oxide coating and a paint. be.

The conventional two-component method deposits metallic chromium and hydrated chromium oxide film separately, so it has the advantage of being able to easily control the amount of each deposited.
In formula 5, the enemy compositions of both numbers are different, so if the steel plate after chromium plating is directly transferred to the electrolytic chromic acid treatment bath, the plating aid anions will eutectoid in the chromium hydrated oxide produced during chromium plating. remaining in the coating of the final product,
The chromium plating solution deposited on the steel surface 1 is brought into the electrolytic chromic acid treatment bath, which may cause fluctuations in the amount of chromium water-retaining oxide film deposited or re-precipitation of partially eluted auxiliary anions. This will cause inconvenience. Therefore, it is necessary to thoroughly wash with water after chromium plating and before entering the electrolytic chromic acid treatment bath to prevent blistering, but washing with water after chromium plating alone will not remove the chromium water-containing oxides produced during chromium plating. It is difficult to remove chromium plating aid anions. In particular, in chromium plating using sulfuric acid or its compounds as an auxiliary agent, even if electrolytic chromic acid treatment is performed using a chromic acid bath solution, the sulfuric acid radicals in the final chromium hydrated oxide remain. This causes problems in the Wi layer properties with the coating film due to eutectoid deposition.

As a method to eliminate this drawback, by performing reverse electrolysis in the solution after chromium plating, it is possible to reduce the chromium water-containing oxides generated during chromium plating and the auxiliary anions in this, and then electrolytic chromic acid treatment. It has been found that thoroughly washing with water before bathing, followed by applying electrolytic chromic acid to JmT in an aqueous chromic acid solution, is extremely effective in improving retort resistance.
It is proposed as No. 2766 (hereinafter referred to as Nuclear Power 6).

However, after reviewing his research, it was found that although nuclear power plants are extremely effective in improving retort resistance, the chromium water oxide film may become non-uniform. As a result of repeated research, it was possible to obtain a uniform ROM hydrated oxide film, and the retort treatment resistance was further improved, leading to the present invention.

In the present invention, a cold-rolled steel sheet is plated with 20 to 200 q/g of metal chromium on one side, and the surface of this metal chromium layer is coated with 5 to 50 q/g of metal chromium.
C metal chromium layer is 20w5i, which is related to tee/free steel sheet with chromium water conservation oxide coating of 19/j.
If it is less than 200-v/Ig/d, there will be many micro cranks, pinholes, etc., resulting in poor corrosion resistance.If it is more than 200-v/Ig/, the same corrosion resistance cannot be expected. A hydrated chromium oxide film (hereinafter referred to as Cr) having a metallic chromium layer of /a/
If the coating is less than 5q/d, the desired paint adhesion cannot be achieved, and if it is more than 50wv/d, the appearance may deteriorate or cracks may appear in the C, OX coating during processing, making it difficult to put into practical use. Not on point. Furthermore, Cr. The practical range of x-peritoneal amount is 10 to 30 wq/wl, which is most desirable.

Tin-free steel sheets are used as food can materials only after being painted, and when used as food cans, adhesion with the coating film is particularly important. In order to obtain a tin-free steel sheet with excellent layer properties with the coating film and excellent resistance to retort treatment after filling, chromium plating is performed using a general-purpose chromium plating bath using an auxiliary agent containing anions such as sulfuric acid or its compounds. ,
We proposed a method for nuclear power plants to perform reverse electrolysis at 01 to 15 coulombs/dxl in this bath, and then perform electrolytic chromic acid treatment in an aqueous chromic acid solution via a water washing tank.
6c The line-free steel sheet obtained by this process is extremely effective in improving retort treatment resistance, but as mentioned above, this treatment alone may cause the C, OX film to become non-uniform.6+- Therefore, In the present invention, a conventionally degreased and pickled steel plate is chromium plated in a chromium plating bath containing sulfuric acid or its compounds as an auxiliary agent, and then subjected to reverse electrolysis in this bath.
8 eutectoid in the crOxi film generated during chromium plating
After reducing the auxiliary anions such as 04'-, electrolytic chromic acid treatment is carried out, and the feature is that this treatment is carried out under the conditions described below. During application, in order to obtain a CrOx film with a uniform electrolytically deposited film structure and good retort resistance, chromic acid water #! without intentionally adding any auxiliary agents other than unavoidable impurities! Chromic acid treatment bath is used, and the pH of this bath is kept below 1.0. The main component of the chromic acid aqueous solution is at least 1 m of chromic acid anhydride, electrochromate, and chromate. Monochromates include alkali metal salts of dichromic acid, alkaline earth metal salts, ammonium salts, etc., and chromates include alkali metal salts of chromic acid, alkaline earth metal salts, alkaline earth metal salts, etc. Although ammonium salts and the like are suitable, the type of compound is not particularly limited.

Chromic acid water S* contains unavoidable impurities due to the base agent, and the concentration of this water bath solution does not need to be particularly limited, but a range of 10-200 f/t in terms of CrO3 is appropriate. If the concentration is less than 10 t/, the electrical resistance of the bath increases and the regulation f
This is not preferable because it causes inconveniences such as overvoltage of L6 and heating of the steel plate.

Moreover, even if it exceeds 2009/l, it is not desirable to expect much improvement in the desired effect and there will be a large economic loss due to the leakage of the bath. As shown above, the bath temperature of the romic acid treatment bath is 3
A temperature of 5°C to 60°C is suitable.

If the temperature is lower than 35°C, temperature control becomes difficult due to the rise in the temperature of the cooling water in the IL field, and if the temperature is lower than 60°C, the materials for the amelioration tank that can withstand the chromic acid water bath are limited.

When reverse electrolysis is performed in the chromium plating layer after chromium plating, the C and OX films formed during plating are decomposed, and at the same time or after completion of the plating, the chromium plating layer before the cathode is removed. Anode Cr which is different from X film. An X coating is formed on the metallic chromium layer. It is clear that due to the formation of this film, the exposure of the metal chromium is less than that of the conventional cathode film, but depending on the composition of the K% chromic acid treatment chamber, the metal chromium may be precipitated and formed on the metal chromium during electrolysis. Abnormal precipitation was observed in some parts of the Cr0X film.To avoid this, various studies were conducted on chromic acid aqueous solutions containing unavoidable impurities without intentionally cooling the auxiliary agent. As a result, regardless of the blending ratio of chromic acid and its salts, it was possible to secure the desired thickness of CrOx film in a bath of -10 or less, and to obtain a film with good croXvys uniformity. Chromic acid solution has also been found to have excellent retort resistance. Chromic acid water is generally a combination of chromic acid and its salts. The pH of this aqueous solution is determined by the concentration of chromic acid and its salts. 0 determined by the type of cation and its concentration
Furthermore, it is known that P)l near the cathode increases during electrolytic chromic acid treatment. This is due to the electrolysis of water near the anode during electrolysis. Gas is generated and a lot of OH- is produced and the voice rises. Therefore, chromic acid water I
When the level of the W solution is low, the level near the cathode during electrolysis increases.0 Cr generated at this time. x has many all bonds (:r
(OH) It is considered to be an all compound close to CrOx, which easily dissolves in an aqueous chromic acid solution, making it impossible to secure a large amount of CrOx.

In addition, as the pH of the chromic acid aqueous solution is lowered, the number of oxo bonds increases rather than all bonds, and the quality of insolubility of Cr0X increases. The sound becomes non-uniform, and there are many all-bonds in the high-pitched parts of the voice, and after the end of the electric 'ps, the sound is exposed to the romic acid water bath.

In addition, in areas with low pH, there are many oxo bonds, and most of them are insoluble, so even after the bath is dissolved, they cannot be extracted into the chromic acid water bath and seem to remain.

This is thought to be because the buffering effect of the chromic acid aqueous solution disappears when the temperature exceeds 0, causing a rapid change in pH in the vicinity of the cathode.

Therefore, if the pH of the chromic acid water bath solution is too low, the amount of Cr0X cannot be secured, and if the pH is higher than 1.0, the amount of Cr0X cannot be ensured.
It is thought that the distribution becomes non-uniform. When the number of chromium watering solutions is set to 10 or less as in the present invention, homogeneous CrO, which is difficult to dissolve in the chromic acid water bath solution with many oxo bonds, is produced.
It is thought that x is generated uniformly.

O plate thickness 0, which will be specifically explained below regarding the treatment according to the present invention.
．． A 22g1+ cold-rolled steel plate was subjected to pretreatment of degreasing and pickling using a conventional method.

)1ssO41f / 11lN1m5tF 10
T / T w-containing v-ru chromium plating bath, bath temperature 55℃
Electrolysis was performed for 1.0 seconds at a temperature of 60 m/y.

Cr at this time. Figure 2 shows the EPMA line analysis of the X film.

After chromium plating, reverse electrolysis was performed in the solution for 02 seconds at a t concentration of 5 μm/ν. EPMA of X film
The line analysis is shown in Figure 3. After thoroughly washing this chromium-plated steel sheet with water, the bath composition shown in Table 1, which contains impurity anions but without the intentional addition of auxiliary agents, and the pH determined by the composition. Using a chromic acid treatment bath of As the pl of the bath increases, Cr0
The amount of ,C at this time
, shows a 400x optical microscope photograph of the OK film. For comparison, the results of EPMA line analysis and 400x optical micrographs are shown in FIGS. 5 and 7, respectively, when electrolytic chromic acid treatment was performed in a bath with a pH of 1 and 10, which is outside the scope of the present invention. Looking at the results of the line analysis, we can see that the broom in Figure 4, which has been treated according to the present invention, the broom in Figures 2 and 3, which has not been treated according to the present invention, and the one in Figure 5, which is outside the scope of the present invention. Cr. It can be seen that the x film is homogeneous. In addition, looking at the micrographs, it is clear that the C, OX film is homogeneous and even, which is according to the present invention (in Figure 6, it is clear that the C, OX film is homogeneous and even, but the film is outside the scope of the present invention).
In Figure 7), we can see that many uneven spots (looking like black spots) are generated in the C, OX film. Table 1 (Measurement of Cr0X amount 3) Detected from the difference in the amount of C9 measured after M was immersed in a strength soda solution of /l for 10 minutes.
#J foot with 0CrOX amount placed using # is Fluorescence XII
d method (Xray40KV60IIIA1 monitor 60 seconds HC.

(#1 foot of EPMA) CrOxsFkU was fixed with a carbon group, and then metallic chromium was dissolved with nital from the base steel side, and then placed on a clean platinum foil, and line analysis was performed with EPMA under the following conditions.

Acceleration voltage 20KV Electron beam intensity 0.02μA Beam diameter 2P Next, the present invention will be explained in detail with reference to examples.

[Example 1] A cold-rolled steel plate with a thickness of 0.22 m was electrolytically degreased for 10 seconds at 15 Vdll10) in a 5% Homezason solution at 15 Vdll10), then washed with water and heated to 10XWL at room temperature. After immersing in acid for 5 seconds and washing with water, this treatment was performed under the following conditions.

Chrome plating treatment bath composition Cry, 250 t/1HsSDa
1t/1 Na2SIFs 10 f/' Bath 1! 55°C Electrolysis conditions: 50 Vdj x 1.5 seconds After the above chromium plating, reverse electrolysis treatment was performed in the same solution under the following conditions.Reverse electrolysis conditions: 5. OVdyrt x 0.5 seconds After this, it was washed with water and immediately subjected to electrolytic chromic acid treatment under the following conditions. 〇 Electrolytic chromic acid treatment bath composition: 60 f/ into the mouth Bath temperature: 40C pHO, 411 (room temperature) Electrolytic conditions: I S , After the electrolytic chromic acid treatment at 1 JdII/x for 1.0 seconds, the sample was immediately washed with water, roughly washed with hot water, and then tumbled to prepare a sample.

[Example 2] Example 1 except that the electrolytic chromium treatment was performed under the following conditions.
〇Electrolytic chromic acid treatment bath composition C150f/l N & zCrlOy 10f/ was subjected to the same treatment as -40℃ pHO,! ! 5 (Normal temperature electrolysis conditions 15 Vdd
The same process was performed.

Electrolytic chromic acid treatment bath composition Crys 40 t/1NazCr=
Oy 20 t/ bath temperature 40°C pH 0.62 (normally 11K) Electrolysis conditions 15) v/dd X 1.9 seconds [Comparative Example 1
] Example 1 except that the electrolytic chrome carpet treatment was performed under the following conditions.
Electrolytic chromic acid treatment bath composition crys 10 t/1Na2Cr3
0y 50'/'' Bath @ 40°C pH 1,10 (room temperature) Electrolytic conditions 15 VdII/X 1.0 seconds [Comparative Example 2] Example 1 except that electrolytic chromic acid treatment was performed under the following conditions.
0 electrolytic chromic acid treatment bath composition
40°C pH 31 (room temperature) Electrolysis conditions 15 Vdd x 1.0 seconds [Comparative Example 3] Same as Example 1 except that it was immersed in chromic acid*1iljlt for 5 seconds and electrolytic chromic acid treatment was performed under the following conditions. ◎ Electrolytic chromium sapon treatment bath composition: Cros60 f/1 Bath temperature: 40c pHO-48 (room temperature) Electrolytic conditions: I S A/dll/X 1.0 seconds or more on the tin-free steel sheet obtained as above. A TIN peel test was conducted on the sample.

One side of each of the above-mentioned ink-free steel plates was painted with 5ci5wIP/- for sizing, baked at 190C for 1o, then the remaining opposite side was painted with the same amount of gold, and heated to 210℃ for 10 minutes.
After that, a nylon adhesive synthetic resin tape (thickness 100 μm 1 width 5 cm) was sandwiched between the sizing painted surface and the gold painted surface, and heated to 190℃ using a hot press. /- for 30 seconds to bond and create a plurality of test pieces. These test pieces immediately after adhesion were subjected to a T-peel test using an Instron tensile tester at a constant tensile rate of 200 W/strip to measure peel*@K.

Furthermore, using another test piece, a sample containing 159/l of sucrose, pH 3,3-com@t with citric acid, and 70% sucrose dispersion with citric acid.
The peel strength was measured under the same conditions as above after soaking for 7 days in C0. Both tests were carried out using 5 pieces of each test build. The test results are shown in Table 2 below, and the results are shown as the average value.
[This is something that takes advantage of the adhesion of O.Also, when performing retort processing such as high temperature sterilization,! If there is a large amount of Cr dissolved in the water that penetrates the film, the paint film and Cr
TI after being immersed for 7 days at 070°C, where the adhesive strength with Ox decreases and the retort treatment resistance deteriorates! The peel test value performs this evaluation.

From the test results in Table 2, the tin-free steel plate according to the present invention (
During the period of implementation from January to March, there was no unevenness in the CrOx film, whereas in the conventional Deinf IJ + Steel 41 (comparisons 1 to 3), unevenness occurred in the CrOx film and the retort treatment resistance I know it's bad.

As is clear from the above explanation, according to the present invention, f
CrO with good Wj adhesion with Ii material and retort processing resistance
A tin-free steel sheet with a uniform coating was obtained, and this is suitable for retort processing.- It is suitable for manufacturing can bodies such as heat cans and food cans, but is not limited to food cans, but can also be used for food cans. If so, it can be used for both gallon cans and miscellaneous cans.The paint used for painting is not limited to paints called sizing or gold, but can be any paint made with organic solvents, and the sealant can only be nylon-based. It is not limited to.

Table 2

[Brief explanation of the drawing]

Figure 1 is a graph showing the composition of the chromic acid water bath solution and the relationship between the door determined by this and the generated Or t, Figure 2 is an EPMA line analysis diagram of crOX skin after chromium plating, and Figure 3 is the reverse graph. E P of C, OX film after electrolysis
The M A line analysis diagram, Figure 4, is according to the present invention.
(Cr0X after electrolytic chromic acid treatment using a bath of 0.55
Film E P I! IA line analysis diagram and Straw 5 diagram are EP after electrolytic chromic acid treatment using a pH 1.10 bath.
MA Line Analysis Garden, llI! - Figures and 1117
! @I is a 40-degree optical microscope photograph of the surface structure of the metal, Figure 6 is a microscope photograph of the same sample as in Figure 4, and Figure 7 is a microscope photograph of the same sample as in Figure IF5. Patent applicant: Kawasaki Steel Corporation Kawasaki 1 Figure pH0480,550620700,871,1036
0 ￥ 2 Figure challenge 3 Figure 4 Figure 48.41 S Makoto 5 Figure 8A Figure 6 Figure 7

Claims (1)

[Claims] A steel plate that uses a chromium plating bath and an electrolytic chromic acid treatment bath that is separated from the other by a water washing bath, and has a metallic chromium coating on a steel plate and a coating mainly composed of chromium water-conserving oxide formed over this. /In manufacturing free steel sheets, the steel sheet is chromium plated in a chromium plating bath and then subjected to reverse electrolysis in the chromium plating bath to remove part of the chromium water-retention oxide film and chromium water-retention oxide produced during chromium plating. The auxiliary agent R ions eutectoided in the film are eluted, and then thoroughly washed with water in a water washing bath. Tin-free, characterized in that it contains a chromic acid treatment bath containing an unavoidable impurity anion originating from the main agent, and no auxiliary agent is intentionally added, and the pH of this bath is reduced to 10 l or less to perform cathodic treatment. Steel plate manufacturing method 0