JPS5927400B2 - Manufacturing method of electrolytically chromate treated steel sheet with excellent wet sliding adhesion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytically chromated steel sheet having a lower layer of metallic chromium and an upper layer of hydrated chromium oxide on the surface of the steel sheet, particularly an electrolytically chromated steel sheet having excellent wet adhesion properties as a material for cans. This invention relates to a method for producing chromate-treated steel sheets.

More specifically, the present invention relates to a method for forming a uniform and highly water-resistant hydrated chromium oxide layer on the surface of an electrolytically chromated steel sheet. Electrolytic chromate-treated steel sheet is called chromium type tin-free steel (hereinafter abbreviated as TFS), and its usage has been increasing in recent years as it has been recognized for its properties as a material for cans that can replace tinplate.

Until now, TFS has been mainly used as a material for cans such as carbonated beverage and beer cans, and can manufacturing is carried out by bonding the can body with a polyamide adhesive. Since the filling of contents into such cans is carried out using so-called low-temperature packs, which are carried out in a low-temperature state,
There was no problem of the polyamide adhesive used in joining the can bodies described above peeling off from the joints. However, recently, the use of TFS cans has expanded, and they are now being used for so-called hot packs, in which the contents are sterilized at high temperature before being filled, such as fruit juice and coffee, or for cans that require retort processing, in which sterilization is performed at high temperatures after packaging. It's starting to be done. Therefore, when conventional TFS cans are subjected to hot pack or retort processing, defects such as tearing of the can body, which were unthinkable with low temperature packs, have become a problem.

Generally, the can bodies of TFS cans cannot be joined with solder like tin cans, so after painting the inside and outside of the can,
This is done by adhering using a polyamide resin adhesive as described above.

TFS cans joined by such a method are generally referred to as TFS adhesive cans, and at the joint, the inner and outer coatings are adhered to each other via a polyamide resin layer. The tear in the can body that occurs in the TFS bonded can during hot pack and retort processing is caused by hot water penetrating through the resin layer at the joint, which deteriorates the adhesion at the interface between the paint film and TFS. This occurs because the coating film peels off from the TFS interface. Conventionally, electrolytic chromate steel sheets have been manufactured by the following two methods.

(1) A method in which a lower metallic chromium layer and an upper hydrated chromium oxide layer are simultaneously formed on the surface of a steel sheet by electrolytic chromate treatment (hereinafter referred to as the one-liquid method).

, and (2) by depositing a metallic chromium layer on the surface of the steel plate in a chromium plating process and then cathodic electrolysis treatment in another chromate treatment solution: forming a hydrated chromium oxide layer on the metallic chromium layer. (hereinafter referred to as the two-liquid method).

Even if the electrolytic chromate steel sheet (TFS) manufactured by either method (1) or (2) above is used as a material for cans, tearing of the can body during the high-temperature treatment during the hot pack or retort processing described above cannot be avoided. I couldn't do it.

Therefore, the present inventors conducted an investigation to find out the cause of the can body breakage that occurs during high-temperature treatment as described above, and found that the breakage of the can body is due to adhesion at the interface between the TFS and the paint film caused by hot water. (hereinafter referred to as wet bond strength), and the decrease in wet bond strength is due to the following two facts: (a) the amount of hydrated chromium oxide deposited on the metal chromium layer; It was found that this is due to the fact that the metal chromium layer is exposed due to non-uniformity, and (b) the water resistance of the hydrated chromium oxide is poor.

Based on the above-mentioned knowledge, the present inventors have determined the above (a).
As a result of further research into countermeasures to eliminate the causes of (b) and (b), the method described below was discovered.

First of all, the cause of (a) above is that the wet adhesive strength decreases when the amount of hydrated chromium oxide attached decreases, and the wet adhesive strength of the metallic chromium layer is extremely poor, and the bond between the paint film and the metallic chromium layer is It has been found that this occurs due to peeling between the metal chromium layers, etc., and that a necessary countermeasure is to uniformly adhere hydrated chromium oxide onto the metal chromium layer to reduce the exposure of the metal chromium layer. I understand.

In the conventional one-component method described in (1) above, the metal chromium layer and the hydrated chromium oxide layer are formed simultaneously, so the hydrated chromium oxide layer is relatively uniform.

However, in industrial production lines, steel plates are subjected to electrolytic treatment while passing through numerous treatment tanks. Due to constraints on electrode placement, hydrated chromium oxide is precipitated and dissolved during electrolysis of steel plates, and water is generated. As a result of repeated non-current dissolution of Japanese chromium oxide in chromate solution,
It is unavoidable that the dissolution of hydrated chromium oxide when electricity is applied and the dissolution when electricity is not applied are non-uniform. Therefore, if the amount of hydrated chromium oxide deposited is small, exposure of metallic chromium from a portion of the bore is unavoidable, resulting in poor wet adhesion.

On the other hand, if the amount of hydrated chromium oxide deposited is increased, defects such as exposure of metallic chromium can be removed, but other problems such as deterioration of surface appearance and reduction in commercial value are brought about.
In addition, as a method of sealing a part of the bore of the hydrated chromium oxide layer to eliminate the above-mentioned defects, the present inventors previously filed a patent application in 1973.
As proposed in No. 3-53792 or Japanese Patent Application No. 54-12798, there is a method of performing immersion chemical conversion treatment using a chromate treatment solution containing resin after electrolytic chromate treatment. For example, surface defects such as roll flaws and uneven drawing may occur due to roll drawing, and there is also the problem of controlling the amount of film deposited, so this is not a satisfactory method.

On the other hand, in the case of the two-liquid method described in (2) above, a hydrated chromium oxide layer is deposited on the metal chromium layer plated on the steel plate in the first step, and then in the second step. Influenced by the surface condition of the substrate, hydrated chromium oxide precipitates intensively in the active part of the metal chromium layer, while hydrated chromium oxide hardly precipitates in the inactive part of the metal chromium layer. As a result, the hydrated chromium oxide layer becomes non-uniform, and exposure of the metallic chromium layer cannot be avoided, which in turn reduces the wet adhesion.

Therefore, the first step to improving wet adhesion is to make the unevenness of the hydrated chromium oxide layer as uniform as possible, which is unavoidable in any of the above methods, and to minimize the exposure of the metallic chromium layer. I came to the conclusion that this is the method. Next, as a result of examining the cause of (b) above, we found that when the interface between TFS and the paint film comes into contact with hot water, the adhesive force at the interface decreases due to differences in the structure of hydrated chromium oxide. It turned out to be different.

Although the relationship between the structure of hydrated chromium oxide and water resistance has not yet been clarified, the wet adhesive strength of hydrated chromium oxide produced under various electrolytic conditions is We found that the structure of hydrated chromium oxide is important because it changes even if the amount is constant. Therefore, it was concluded that producing water-resistant hydrated chromium oxides is a second way to improve wet adhesion.

As mentioned above, the present inventors have conducted extensive research into the cause of the decrease in wet adhesive strength of electrolytic chromate steel sheets and the countermeasures thereof, and as a result, they have arrived at the present invention.

That is, in this invention, a thin steel plate is electrolyzed cathodically in a bath containing chromium, and a lower layer of metallic chromium is formed on the surface of the thin steel plate with a chromium content of 0.03 to 0.20 Tf! 9/
After simultaneously forming an upper layer of hydrated chromium oxide of Dm, then a lower layer of metallic chromium and the hydrated chromium oxide of 0.03 to 0.20 η/d in terms of chromium amount. Chromic anhydride C
rO35O~250 miq and fluorine concentration 1~4
% (based on CrO3) of at least one inorganic fluorine compound selected from fluoric acid, hydrosilicic acid, hydroborofluoric acid and their water-soluble salts, and cryolite. The present invention provides a method for producing an electrolytic chromate-treated steel sheet with excellent wet adhesion, which is characterized by cathodic electrolytic treatment in an electrolytic chromate treatment solution. As used herein, the term "chromium-containing bath" refers to a conventional electrolytic bath used for electrolytic chromate treatment or chromium plating. Furthermore, the features of this invention will be described in detail below. In the first treatment step, two layers, a lower layer of metallic chromium and an upper layer of hydrated chromium oxide, are deposited simultaneously on the surface of the thin steel sheet. Form a uniform layer. On this occasion,
The amount of the hydrated chromium oxide layer is converted to the amount of chromium and is 0.
03 to 0.20 Tf19/d is necessary, and this amount is a necessary condition for forming a uniform hydrated chromium oxide layer in the second treatment step. Then, in a second treatment step, a uniform hydrated chromium oxide layer is formed by further performing cathodic electrolysis treatment. Therefore,
The two-step processing method as described above is the first feature of the present invention.

Furthermore, it is necessary to include a fluorine compound in the electrolytic chromate treatment solution in the second treatment step so as to give a fluorine concentration of 1 to 4% by weight relative to CrO3 in the treatment solution. .

Containing fluorine ions in the electrolytic chromate treatment solution means that in the second treatment step, the fluorine ions in the treatment solution are absorbed into the upper hydrated chromium oxide layer generated in the second treatment step. Even if hot water penetrates into the layer, the fluorine ions are not water-solubilized and the bond with chromium in the hydrated chromium oxide layer is maintained, and the fluorine ions are This is the result of the discovery that the product forms a strong film and has high water resistance even with a small amount of the hydrated chromium oxide. Therefore, the second feature of the present invention is to use an electrolytic chromate treatment solution containing a fluorine compound at a predetermined concentration. In this invention, in the first treatment step, two layers, a metal chromium layer and a hydrated chromium oxide layer, are simultaneously formed on the surface of the steel sheet, and the amount of the hydrated chromium oxide is controlled at the same time. 0.03 to 0.20 in terms of chromium content
Only by limiting η/Dm2 can the treatment with the electrolytic chromate treatment solution containing a fluorine compound be effective in the next second treatment step.

Thus, in the first treatment step of the present invention, by specifying the amount of hydrated chromium oxide within the above range,
In the second electrolytic chromate treatment step of the next step, the hydrated chromium oxide layer produced in the first treatment step is converted into a hydrated chromium oxide layer with excellent water resistance due to the effect of fluorine ions in the electrolytic chromate treatment solution. The second hydrated chromium oxide layer is not simply laminated on top of the hydrated chromium oxide layer generated in the first treatment step. do not have. In other words, in the second electrolytic chromate treatment step of the present invention, a hydrated chromium oxide layer with excellent water resistance is finally produced. Therefore, this invention uses the method of Japanese Patent Publication No. 47-35172, in which a hydrated chromium oxide layer is simply laminated on a metallic chromium layer by a conventional second chromate electrolytic treatment, or the surface produced by chromium plating. This method is clearly distinguished from the method of Japanese Patent Publication No. 35618/1983, in which a portion of the hydrated chromium oxide layer is dissolved and a second hydrated chromium oxide layer is deposited thereon. Next, the configuration of the present invention will be explained below.

In this invention, the electrolytic chromate treatment liquid (hereinafter simply referred to as the first liquid) used in the first treatment step is:
Any conventional electrolytic solution for electrolytic chromating or electrolytic solution for chrome plating can be used as appropriate.

For example, an electrolytic solution containing chromic acid and a tan sorter,
An electrolytic solution containing chromic acid, a tan sorter, and a fluorine compound, an electrolytic solution containing chromic acid and a compound having a sulfate radical SO42-, and an electrolyte containing chromic acid, a compound having a sulfate radical, and a fluorine compound Any electrolytic solution may be used as long as it is used as an electrolytic solution for TFS. In this invention, a thin steel plate is cathodic electrolyzed using the first liquid as described above, and a lower metallic chromium layer and an upper hydrated chromium oxide layer are simultaneously deposited on the surface of the thin steel plate. let

At this time, the amount of the hydrated chromium oxide to be precipitated is 0.
It is important to set the value to 03 to 0.20 η/DTrI.
The reason is that the amount of hydrated chromium oxide is 0.03 mg.
This is because if the amount of the hydrated chromium oxide is less than 0.20η/Dm, the formed film will not exhibit sufficient wet adhesive strength even if the next second treatment step is performed. If it exceeds this, it is hardly possible to expect an improvement in the wet adhesive strength, and on the contrary, it becomes difficult to sufficiently form a new hydrated chromium oxide having excellent water resistance in the second treatment step. Next, the thin steel sheet subjected to the cathodic electrolytic treatment as described above was subsequently treated with 50 to 2509/l of chromic acid.
An electrolytic chromate treatment solution containing an inorganic fluorine compound with a fluorine concentration of 1 to 4% by weight (based on CrO3)
(hereinafter simply referred to as the second solution), by cathodic electrolytic treatment, the amount of the final hydrated chromium oxide layer is within the range of 0.03 to 0.20 chromium/Dm'' in terms of chromium amount. Adjust to.

The reason for limiting the fluorine concentration in the second liquid to 1 to 4% by weight is that if it is less than 1% by weight, the desired film cannot be formed, and therefore satisfactory wet adhesion cannot be obtained. On the other hand, if it exceeds 4% by weight, the produced hydrated chromium oxide will be easily dissolved, which will actually reduce the performance of the film.

In addition, the chromic acid concentration in the second liquid was set to 50 to 2509/
The reason why it is limited to 1 is because if it is less than 509/l, the bath resistance will increase and there will be operational problems, whereas if it exceeds 2509/l, surface cleaning such as water washing after treatment will become difficult. The inorganic fluorine compound used in the second liquid includes HF
, fluorides such as NaF, LiF, ZnF2, acidic fluorides such as NH4゛2, KHF2, NaHF2, H2Si
F6, (NH4)2SiF6, NiSiF6, ZnSi
Silicates such as F6, Na2SiF6, HBF4, N
Borifides such as aBF4, KBF4 or A/1F
Any one type or two or more types of inorganic fluorine compounds such as 3.3NaF (cryolite) can be used.

Furthermore, the amount of the final hydrated chromium oxide layer by the above second cathode electrolytic treatment is 0.03~
Adjusting within the range of 0.20η/D7TI is 0.0
If it is less than 3η/D7rI, the wet adhesion of the obtained electrolytic chloromate-treated steel sheet will be poor; on the other hand, if it is less than 0.20Tf!
This is because if it exceeds 9/di, not only the wet adhesion will deteriorate, but also the appearance will deteriorate.

Therefore, the cathode current density needs to be adjusted so that a predetermined hydrated chromium oxide within the above range is produced. In addition, the temperature of the treatment liquid in the second treatment step is 30 to 80°C.
It is necessary to

This is because temperature control is difficult below 30°C;
This is because if the temperature exceeds 80°C, no improvement in performance can be obtained.
As mentioned above, the present invention does not involve simply laminating a second hydrated chromium oxide layer on top of the hydrated chromium oxide layer, as in conventional electrolytic chromate treatment. That is, the second cathodic electrolytic chromate treatment not only generates hydrated chromium oxide, but also simultaneously generates a metallic chromium layer and a hydrated chromium oxide layer. By replacing the hydrated chromium oxide layer produced by the second treatment with the metallic chromium layer and hydrated chromium oxide layer produced by the second treatment, a film with excellent wet adhesion is produced. It has the most important characteristics. Next, the effects of the second cathodic electrolytic chromate treatment in the present invention will be demonstrated through test examples.
Test Example 1 509/l or 2509/l CrO was used as the electrolytic chromate treatment solution (i.e., first solution) in the first treatment step
3, 1% and 2% by weight relative to the CrO3, respectively.
%, 4%, 6%, and 8% concentrations of H2SO4, and an electrolytic solution containing CrO3 alone, a cold rolled steel plate was used as a cathode, current density was 20A/Dm'', electrolysis time was 3 seconds, and liquid temperature was 45%. Processed at ℃, 0.5-1.5η/D
The lower layer of metallic chromium of 7TI and the amount of chromium are 0.
A coating consisting of a top layer of hydrated chromium oxide of 20 η/d was produced.

Next, using the electrolytic chromate-treated steel sheet treated as described above as a cathode, in a second treatment step, CrO37O9/l was converted to CrO37O9/l.
Fluorine concentration is 2% by weight AlF3 based on CrO3.
By performing electrolytic chromate treatment in the second chromate treatment solution (i.e., second solution) containing 3NaF at a current density of 20A/Dm2, an electrolysis time of 1 second, and a solution temperature of 45%, the hydrated chromium oxide in the film can be removed. The amount is 0.12η/D
A hydrated chromium oxide film of rrl was formed.

The amount of SO42 remaining in the hydrated chromium oxide layer in the electrolytic chromate film produced by the above treatment was measured by X-ray fluorescence analysis. The results are shown in FIG. In FIG. 1, the ● mark indicates the case where the CrO3 concentration in the first liquid used in the first step is 509/l, and the ○ mark indicates the case where the CrO3 concentration in the first liquid is 2509/l, Further, the solid line indicates the case where the second liquid treatment was performed in the second treatment step, and the dotted line indicates the case where the second liquid treatment was not performed.

As shown in FIG. 1, the amount of SO42 remaining in the hydrated chromium oxide layer in the electrolytic chromate film treated using only the first solution is as shown by the dotted line in the figure. The amount of SO42 remaining in the hydrated chromium oxide layer increases as the H2SO4 concentration in the liquid increases, but when the second liquid treatment is performed, as shown by the solid line in the figure, the amount of SO42 remaining in the hydrated chromium oxide layer increases. The SO caused by the first liquid is significantly reduced.
42- It can be seen that the amount has decreased to such an extent that it is hardly affected by the residual amount. Test Example 2 As the first liquid in the first treatment step, CrO325O
9/l, H2SO4 at a concentration of 2% by weight relative to CrO3
Using an electrolytic solution to which was added, the treatment was carried out in the same manner as in Test Example 1, using a cold-rolled steel plate as a cathode, at a current density of 20 A/Dm2, an electrolysis time of 3 seconds, and a liquid temperature of 45°C, resulting in an electrolyte of 0.8W/Dm2.
The lower layer of metallic chromium and the amount of chromium is 0.20η
/Dm2 of hydrated chromium oxide.

Next, the steel plate treated as described above was used as a cathode, and in the second treatment step, 209/20% of each was used as a second liquid.
l, 509/l, 1009/l, 1509/2 and 2
009/l of CrO3 and AlF3.3NaF with a fluorine concentration of 2% by weight relative to CrO3 were added, the treatment time was 1 second, the liquid temperature was 45°C, and the current density was adjusted to electrolytically chromate. treatment to reduce the amount of hydrated chromium oxide in the film to 0.10 to 0.20W1, respectively.
I made it to 9/d.

Then, the amount of SO42 remaining in the electrolytic chromate film produced by the above-described treatment was measured by fluorescent X-ray analysis. The results are shown in FIG. As shown in FIG. 2, the CrO3 concentration in the second liquid is 509/
1 or more, the amount of SO42 in the electrolytic chromate film produced by the treatment with the second liquid does not decrease and the amount does not become almost constant.

As is clear from the results shown in Figures 1 and 2, the amount of SO42 in the film produced by the treatment with the first liquid was compared with the amount of SO42 in the film produced by the treatment with the second liquid. Therefore, the hydrated chromium oxide produced by the treatment with the second liquid in this invention does not contain the hydrated chromium oxide produced by the treatment with the first liquid, and new hydrated chromium oxide is generated. is found.

In other words, the hydrated chromium oxide produced by the treatment with the first liquid contains approximately 50% SO42-, whereas the hydrated chromium oxide produced by the treatment with the second liquid contains almost 50% SO42-. , compared to the hydrated chromium oxide produced by the treatment with the first liquid, only 1/10 or less of SO42- is present, and as a result, most of the hydrated chromium oxide produced by the treatment with the first liquid is , it can be seen that the new hydrated chromium oxide produced by the treatment with the second liquid was substituted.

This invention will be further explained by way of Examples in comparison with other inventions.

Comparative example of electrolytic chromate treatment (first chromate treatment) using A first solution 1 A cold rolled steel plate was used as a cathode, CrO3lOOfl/l, NaS
CNO. In an electrolytic chromate treatment solution containing 5 g/l and AlF3.3NaF49/l, the current density was 20 A/l.
Electrolytic chromate treatment was performed at Dml, electrolysis time of 3 seconds, and liquid temperature of 45°C, and 0.8 m9/d of metallic chromium and 0.8 m9/d of metallic chromium were removed.
15W1f! /Dm'' of hydrated chromium oxide was formed.

Comparative example 2 A cold rolled steel plate was used as a cathode, CrO3l5O9/l, NaSC
No. In an electrolytic chromate treatment solution containing 5 g/l and AlF3.3NaF49/l, the current density was 30 A/d.
A. Electrolytic chromate treatment was performed at an electrolysis time of 3 seconds and a solution temperature of 55°C, and metal chromium of 0.81~/d and 0.05
η/Dm'' of hydrated chromium oxide.

Comparative Example 3 A cold-rolled steel sheet was subjected to electrolytic chromate treatment under the same conditions as those described in Comparative Example 1 above, and then immersed in the same treatment solution without electricity, leaving only the metallic chromium layer.

Comparative example 4 of electrolytic chromate treatment (second chromate treatment) using a steel plate treated with BA as a cathode and an electrolytic solution containing only chromic acid and no fluorine ions as a second solution 4 Electrolytic chromate treatment treated in Comparative Example 1 above A steel plate is used as a cathode, and a current density of 5A is applied in an electrolyte of CrO37Og/l.
/di, electrolytic chromate treatment was performed at an electrolysis time of 1 second and a liquid temperature of 45°C.

Comparative Example 5 Using the electrolytically chromate-treated steel sheet treated in Comparative Example 2 above as a cathode, electrolytic chromate treatment was performed under the same conditions as described in Comparative Example 4 above.

Comparative Example 6 Using the electrolytically chromate-treated steel sheet treated in Comparative Example 3 above as a cathode, electrolytic chromate treatment was carried out under the same conditions as described in Comparative Example 4 above.

Example 1 Electrolytic chromate treatment (second chromate treatment) using a steel plate treated with CA as a cathode and an electrolytic solution containing fluorine ions as a second solution.The electrolytic chromate treatment steel plate treated in Comparative Example 1 above was used as a cathode, and CrO37O9/ In an electrolytic solution containing 29/l of silicic acid and a current density of 20 A/DTI. Electrolysis time 1
Electrolytic chromate treatment was performed at a temperature of 45° C. and a liquid temperature of 45° C.

Example 2 Electrolytic chromate treatment was carried out under the same conditions as described in Example 1 using the electrolytically chromate treated steel sheet treated in Comparative Example 2 above as a cathode.

Comparative Example 7 Using the electrolytically chromate-treated steel sheet treated in Comparative Example 3 above as a cathode, electrolytic chromate treatment was carried out under the same conditions as described in Example 1 above.

For all the electrolytic chromate-treated steel sheets treated in Comparative Examples 1 to 7 and Examples 1 to 2, the amount of metallic chromium and the amount of hydrated chromium oxide in the formed film was measured. The results are shown in Table 1. As shown in Table 1, after a cold-rolled steel sheet is treated with the first chromate treatment, that is, the A treatment, the second liquid is treated with an electrolyte that does not contain fluorine ions as a second liquid.
When chromate treatment, that is, treatment B, is performed, the amount of hydrated chromium oxide in the final film is such that a part of the hydrated chromium oxide in the film generated in treatment A remains in the final film. As a result, the amount of hydrated chromium oxide in the film produced in the above treatment B increased slightly, and the amount of increase increased as the amount of hydrated chromium oxide in the film produced in the above treatment A increased. I understand that.

On the other hand, when a cold-rolled steel sheet is treated with the above A treatment and then subjected to a second chromate treatment, that is, a C treatment, using an electrolytic solution containing fluorine ions as a second solution, the The amount of hydrated chromium oxide is the same as the amount of hydrated chromium oxide produced in the above treatment C, as no hydrated chromium oxide remains in the film produced in the above treatment A.

That is, according to the C treatment of the present invention, only the hydrated chromium oxide produced by the C treatment becomes the final product, without being affected by the amount of hydrated chromium oxide produced by the A treatment. It is thought that it exists in the film. This is also clear from FIG. 3, which shows the relationship between the amount of hydrated chromium oxide in the film after the first chromate treatment and the amount of SO42 remaining in the film after each of the above treatments. In FIG. 3, the X mark indicates the case where the above-mentioned process A is performed, the ● mark indicates the case where the above-mentioned process B is performed, and the ○ mark indicates the case where the above-mentioned process C is performed. As shown in FIG. 3, in the case of the C process,
It can be seen that the amount of residual SO42 is significantly decreased compared to the treatment A, and also decreased compared to the treatment B. That is, according to the C treatment of the present invention, the amount of SO42 remaining in the film after the first chromate treatment, that is, the A treatment, is significantly reduced, so that the amount of SO42 generated in the A treatment is significantly reduced in the final film. Hydrated chromium oxide is not included, and the C
It is thought that only new hydrated chromium oxides produced during processing are present. Next, the wet adhesive strength of the formed film was measured for all the electrolytic chromate treated steel plates treated in Comparative Examples 1 to 7 and Examples 1 to 2.

Wet adhesive strength was measured using a sample obtained by coating the electrolytic chromate-treated steel plate with epoxyphenol can paint and baking it, then applying polyamide adhesive to the paint surface in a width of 5 mm and heat bonding the paint surfaces together. The sample was dissolved in a 0.5% citric acid aqueous solution (temperature 70°C) for 6 hours.
After being immersed for a day, it was measured by a T-peel test and expressed by its tensile strength. The results are shown in FIG. Fourth
In the figure, the x mark indicates the case where the above-mentioned process A is performed, the ● mark indicates the case where the above-mentioned process B is performed, and the ○ mark indicates the case where the above-mentioned process C is performed. As shown in FIG. 4, it can be seen that the wet adhesive strength is significantly improved only by treating the treated steel sheet after the first chromate treatment, that is, the A treatment, with the second chromate treatment, that is, the C treatment of the present invention. . Furthermore, the relationship between the fluorine ion concentration in the second liquid used in the second chromate treatment of the present invention and the wet adhesive strength of the electrolytically chromate treated steel sheet was investigated.

That is, the electrolytic chromate-treated steel sheet treated in Comparative Example 2 was used as a cathode, and CrO37O9/l and AlF3.3
The fluorine ion concentration of NaF is 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 for CrΩ3, respectively.
0, 6.0, 7.0 and 8.0% (over weight 01))
in each second liquid containing a current density of 2.

A second chromate treatment was performed at 0 A/Drrl, an electrolysis time of 1 second, and a liquid temperature of 45°C. Each of the electrolytic chromate treated steel sheets treated in this way was subjected to a T-peel test using the method described above, and the tensile strength of each was determined. was taken as the wet adhesive strength.

The results are shown in FIG. As shown in FIG. 5, if the fluorine ion concentration in the second liquid is less than 1%, sufficient wet adhesive strength cannot be obtained, while if it exceeds 5%, the wet adhesive strength may actually decrease. Recognize.

Furthermore, as shown in FIG. 6, the fluorine ion concentration in the second liquid influences the properties of the film formed by the second liquid treatment, and the metallic chromium formed in the second liquid This affects the replacement of hydrated chromium oxide produced by the one-component process.

In other words, when the fluorine ion concentration in the second liquid is 1 to 4%, there is a large amount of metallic chromium in the film formed by the second liquid treatment, and this metallic chromium is oxidized by hydrated chromium at the final stage. It is believed that this has an effect on the formation of the product and, in turn, is useful for improving the wet adhesive strength. Figure 6 correlates with Figure 5, which shows the relationship between fluorine ion concentration and wet bond strength, since the production of metallic chromium actually decreases when the fluorine ion concentration exceeds 5%. That is clear. As is clear from FIGS. 5 and 6 above, the electrolytic chromate treatment requires that the fluorine ion concentration in the second liquid used in the second chromate treatment of the present invention be 1 to 4% with respect to CrO3. It is most suitable for improving the wet adhesive strength of steel plates.

As described above, according to the present invention, a metallic chromium layer as a lower layer and a hydrated chromium oxide layer as an upper layer are simultaneously formed on the surface of a steel sheet in an electrolytic chromate or electrochromic plating bath, and the hydrated chromium oxide layer is By replacing the hydrated chromium oxide produced in the first liquid with the metallic chromium produced in the second liquid and the hydrated chromium oxide while leaving the chromium oxide layer present, electrolysis with excellent wet adhesion is achieved. It is possible to obtain a chromate-treated steel sheet, that is, TFS.

TFS produced in accordance with the present invention is useful as a can material that can withstand hot pack and retort processing well.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the H2SO4 concentration in the first liquid and the amount of SO42 remaining in the film after electrolytic chromate treatment, and Figure 2 is a diagram showing the relationship between the CrO3 concentration in the second liquid and the amount of SO42 remaining in the film after electrolytic chromate treatment. FIG. 3 is a diagram showing the relationship between the amount of SO42 remaining in the film after liquid treatment, and FIG. 3 shows the relationship between the amount of hydrated chromium oxide in the film generated by the first liquid treatment and the film after each electrolytic chromate treatment. Figure 4 shows the relationship between the amount of SO42 remaining in the film and the amount of hydrated chromium oxide in the film produced by the first liquid treatment and the wet adhesive strength of the film after each electrolytic chromate treatment. FIG. 5 is a diagram showing the relationship between the fluorine ion concentration in the second liquid and the wet adhesive strength of the film after the second liquid treatment, and FIG. , is a diagram showing the relationship between the fluorine ion concentration in the second liquid and the amount of metallic chromium in the film produced by the second liquid treatment.

Claims (1)

[Claims] 1 A thin steel plate is electrolyzed cathodically in a bath containing chromium, and a lower layer of metallic chromium and hydrated chromium of 0.03 to 0.20 mg/dm^2 in terms of chromium amount are formed on the surface of the thin steel plate. After forming the upper layer of oxide at the same time, the lower layer of metallic chromium and the lower layer of chromium are then formed on the surface.
The thin steel sheet on which the upper layer of the hydrated chromium oxide of 03 to 0.20 mg/dm^2 is formed is coated with chromic anhydride Cr.
O_350~250g/l and fluorine concentration 1~
A method for producing an electrolytically chromate-treated steel sheet with excellent wet adhesion, characterized by carrying out cathodic electrolytic treatment in an electrolytically chromate treatment solution containing 4% by weight (based on CrO_3) of an inorganic fluorine compound.