JPS61250198A - Production of chrome plated steel sheet having excellent adhesiveness to paint - Google Patents

Abstract

PURPOSE:To produce a chrome plated steel sheet having excellent adhesiveness to a paint by executing an anodic treatment in succession of a cathodic treatment under specific conditions in a dip washing stage which is an intermediate stage between a plater part and a chemical part. CONSTITUTION:The steel sheet is subjected to the cathodic electrolytic treatment in an aq. soln. (plater part) consisting essentially of a chromic anhydride to deposit mainly metallic chromium. The steel sheet is then subjected to the cathodic treatment at 5-20A/dm<2> current density and >=1C/dm<2> current conduction rate to make uniform the ununiform chromium oxide film on the surface of the steel sheet in the dip washing stage (drag out) in which 20-100g/l chromic anhydride is made to exist. The steel sheet is further subjected to the anodic treatment at 2-10A/dm<2> current density and 0.2-5C/dm<2> current conduction rate in the same bath to uniformly dissolve away the chromium oxide film. The chromium oxide film is thereafter deposited thereon by the cathodic electrolytic treatment in an electrolyte (chemical part) in which 20-200g/l chromic anhydride and 0.05-3g/l material such as ammonium fluoride and sodium fluoride for forming F<-> ions in terms of fluorine are made to exist.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a chromium-plated steel sheet, particularly a chromium-plated steel sheet with excellent retort resistance as a material for adhesive cans.

[Conventional technology and problems]

Developed as a new material for cans to replace tinplate, chromium-plated steel sheets had problems with weldability and solderability because the surface was made of metallic chromium and a chromium oxide film, and when they were first developed, they were used for top and bottom plates and miscellaneous cans. It was just a matter of time. Later, with the advancement of adhesive methods, resin body making technology was established, and beer, carbonated drinks, etc. /R-tsuku, then it has come to be used for so-called retort cans, which require high-temperature sterilization of coffee and other products. However, when the cans were used for hot packs and retorts, problems began to occur in which the bodies of adhesive cans broke.

As mentioned above, the chromium-plated steel plate has a two-layer structure with the lower layer being metal (Rom) and the upper layer being a chromium oxide film, and in the case of a steel body, the bonding interface is between the chromium oxide film and the resin.

The network breakage occurs at the interface between this chromium oxide film and the resin, and the characteristics of the chromium oxide film have a significant effect on the network breakability C retort resistance a) of the Tsukken retort. As is already known, the retort resistance of this chromium oxide film is due to: (1) Fewer sulfate groups eutectoid in the chromium oxide film.

(2) Degree of oxidation of chromium oxide film (0 in chromium oxide film)
The ratio of Or -0-Or bonds to r-0-Or bonds) is high.

(3) The amount of chromium oxide film must be maintained to a certain extent and be uniform.

The goal is to ensure that the above three points are satisfied.

To reduce the amount of sulfuric acid radicals eutectoid in the chromium oxide film, for example, as described in Japanese Patent Application Laid-Open No. 57-35699, 11% sulfuric acid is added to 0.0% in the chemical part (step of depositing the chromium oxide film). It has been proposed to regulate it to 3P/# or less. This invention has the following features: 1. Although it is effective in improving the situation, it has the following problems. Usually, the plater bath in the plater section (a step in which metallic chromium is mainly deposited) is a sulfuric acid-added bath due to the efficiency of metallic chromium precipitation.

The chromium oxide film precipitated on a portion of the silator contains sulfate ions, and the chromium oxide film precipitated on a portion of the silator cannot be sufficiently removed by washing with water in the second lug-out (immersion water washing process). Therefore, even if the sulfuric acid concentration is controlled in the chemical part, a chromium oxide film containing sulfate radicals already exists, and it is insufficient to reduce the sulfuric acid radicals.

The ninth solution to this problem, for example,
No. 8, JP-A-58-177491, JP-A-Sho 5
As described in Japanese Patent Application Laid-open No. 9-74297, a method of applying reverse electrolysis at the final portion of the plater,
As described in Japanese Patent Laid-open No. 796 and Japanese Patent Application Laid-open No. 57-194295, a method has been proposed in which anodic treatment alone or cathode treatment alone is performed in a specific solution between a part of the collector and a chemical part. There is.

The above proposal is effective in removing the chromium oxide film deposited on the plater portion, reducing the sulfuric acid radicals in the chromium oxide film, and is extremely effective in improving retort resistance, but under the above three conditions. It was found that this was insufficient to reliably satisfy the requirements.

For example, JP-A-57-177998 #JP-A-58
As described in Japanese Patent No. 177491, the reverse electrolysis (anodic treatment) method at the end of the plater section has the following problems. In other words, since the pre-cooling bath contains high concentrations of chromic acid and anions, it has high chemical solubility for the chromium oxide film. For this reason, the remaining amount of the chromium oxide film deposited on the plater part is not necessarily uniform.If reverse electrolysis treatment is performed on a part of the same silator in this state, if the electrolytic conditions are too strong, the chromium oxide film will definitely be removed. Although the chromium oxide film can be removed quickly, the thin parts of the chromium oxide film reach the point where metallic chromium is leached out, causing the surface of the metallic chromium to become non-uniform. If the electrolytic conditions are weakened to prevent unevenness of metal chromium, the thick chromium oxide film cannot be reliably dissolved and removed, resulting in residual chromium oxide film precipitated at plater parts and non-uniformity of the chromium oxide film. cause In the former case, the chromium oxide film may become unrestrained in the treatment of the keratinized part in the next process, causing unevenness of oxide P. In the latter case, the chromium oxide film precipitated on a part of the silator is sufficiently removed. However, it is difficult to reduce the sulfate radicals in the chromium oxide film.

As a countermeasure against this, 2 proposals have been made to regulate the current density and quantity of electricity of the reverse electrolysis at the end of the plater part, as described in JP-A No. 59-74296, but in any case, precipitation occurs in the plater part. The resulting chromium oxide film remains in a non-uniform state, and the surface becomes non-uniform after anodizing.

For example, JP-A-56-169796;
7-194295 (proposal of carrying out only anodic treatment or only cathodic treatment in a specific bath in the intermediate process between one part of one pre-unit and the chemical part) is also insufficient for the same reason as above. It is.

[Purpose of the invention]

The present invention was made with the aim of solving the above problems, and an object of the present invention is to provide a method for producing a chromium-plated steel sheet that exhibits excellent paint can 7iF properties even under hollow and retort treatments.

[Means for solving problems]

The gist of the present invention to achieve the above object is to precipitate mainly metallic chromium by cathodic electrolyzing a steel plate in an aqueous solution (plater part) with chromic anhydride, and then precipitate mainly metallic chromium with chromic anhydride. 100? Is the current density 5 to 20 k/dW at t/c of the immersion washing process (P lug out) with /Z present? , energizing t1 coulomb/dt
r? After performing the above cathodic treatment, the current density is 2 to 10 k/dtr in the same bath. , conduct anodization with a current flow of 0.2 to 5 coulombs/dm", and then chromic anhydride 20 to 200 F//l and a substance that generates F- ions, such as ammonium fluoride and sodium fluoride, to fluorine. 0.05-3't/I as an amount.

This is a method for producing a chromium-plated steel sheet with excellent N properties for paints, which is characterized by depositing a 19-chromium oxide film in a cathodic electrolytic treatment in an electrolytic solution (chemical part).

[Interval I [Next stage to be solved in 1] As a result of various studies in view of the above problems, the present inventors have solved the above three conditions without impairing productivity and have excellent retort resistance. These nine methods led to the discovery of a method for manufacturing chromium-plated steel sheets.

The present invention will be explained in further detail below.

First, the main point of the present invention is to perform cathodic treatment followed by anodic treatment in the immersion water washing step (P rag act) which is an intermediate step between the silator part and the chemical part. The reason why cathodic treatment is performed first in this immersion water washing is that in order to uniformly dissolve and remove the chromium oxide film in the subsequent anodic treatment, the surface unevenness or chromium oxide film deposited in the plague bath can be repaired and the chromium oxide film can be uniformly removed. Nari ROM oxidation! l!
lt- to obtain. As mentioned earlier, the Plater bath has a high chromic acid concentration and contains many anions, so the chromium oxide film is soluble. For this reason, the chromium oxide film after the plater part is non-uniform, and if anodization is performed when the chromium oxide film is non-uniform, the non-uniformity of the chromium oxide film may be promoted. Uniformity may be affected, and non-uniformity of the chromium oxide film may be precipitated by chemicals in the next process, resulting in deterioration of retort resistance.

In P rackout, the concentration of bechromic acid is lower than that in the plater part, and the amount of anions contained is also small, so the chemical solubility in the chromium oxide film is low. Then, in the ρ rack-out, cathodic treatment is first performed to repair the chromium oxide film. The reason for performing the anodization next is to dissolve and remove the chromium oxide film containing sulfate radicals. By performing cathodic treatment followed by anodic treatment in the immersion washing step, it becomes possible to uniformly remove the chromium oxide film deposited on the plater portion.

The concentration of the anhydrous chromic acid solution used for water washing and dipping is 20 to 10
0 g/l is suitable. That is, if it is less than 20P/7, the electrical resistance of the solution is large, and the bath voltage becomes large during electrolytic treatment, resulting in wasted power. Moreover, when i o o t7t>exceeds, the solubility of the chromium oxide film increases, which may cause non-uniformity of the chromium oxide film during cathodic treatment.

Furthermore, the treatment conditions for cathode electrolysis are a current density of 5 to 20 kld.
& , a current flow amount of 10/d- or more is appropriate. Current density 5
If it is less than A/d-, the chromium oxide film deposited on the plater part cannot be repaired, and 20A/d m"
If the current density is higher than that, the effect will be saturated. If the amount of current applied is less than 10/dm", the effect of repairing the chromium oxide film will not be recognized.The upper limit of the amount of current applied should be determined in relation to economic efficiency and is not particularly specified, but it Taking this into consideration, 10 coulombs/dn?atrium is appropriate.

Furthermore, the treatment conditions for anodic electrolysis are a current density of 2 to 10 A/
di- energization to, 2 to 5 coulombs/d- is appropriate.

Current density 2A/drI? If the current density is less than 10 A/d-, the effect on dissolving the chromium oxide film will be saturated; This is because there is a possibility of dissolving the metal chromium on the surface layer.Also, for the same reason as the queen, the appropriate amount of current is 0.2 to 5 coulombs/d?

Furthermore, chromic anhydride solution used for chemical treatment! 20 g/l to 200 g/l is suitable for one degree.

If it is less than 20971, the electrical resistance of the treatment liquid is high (the bath voltage becomes high during electrolytic treatment, resulting in wasted power).

7c200? This is because when the temperature exceeds /Z, no improvement can be achieved even if chromic anhydride is added any further.

A suitable amount of fluorine is 0,059/# to 3 f/l. The reason for adding fluorine ions in a chemical bath is that by adding F- ions, it is possible to uniformly deposit a chromium oxide film with high current density and high current flow, and it is possible to uniformly deposit a chromium oxide film with a high degree of oxidation. Because you can get it.

This effect does not occur below 0.05P/J, and
3? This is because if the amount exceeds /j, no significant effect can be achieved even if more is added.

Examples of the method according to the present invention are shown below.

(Example 1) A cold-rolled steel plate with a thickness of 0.22 m was electrolytically degreased according to a conventional method, and then immersed in acid pickling, and the main treatment was performed on fc and vk under the following conditions.

Plating bath (chromium plating treatment) bath set for part of the silator Tic 0rbs 1809/#+H*SOa
O, 59/Ik+Nm1SiF6 5.4? /Z bath @ 45c Electrolytic density 100 A/dm"Xo, 5 seconds (cathode treatment) After that, it was immersed in water and washed, and immediately subjected to cathode treatment in the same washing bath under the following conditions, followed by anode treatment.

Bath temperature 40℃ Cathode treatment 5 A/dm'X 1 second Anodization 5A/dm"X1 second Next, a ROM oxide film was deposited under the following conditions.

Processing bath composition in chemical section 0rbs 100 r/ #+NH4F Z5
? / Z+NaOHO, 07 mol/1 Bath temperature 40°C Electrolytic conditions 4-OA/dy/XQ, 7 seconds (Example 2) After depositing chromium plating under the same conditions as Example 1, cathode treatment was performed in a water washing bath under the following conditions. t6 Bath temperature 4θ°C Cathode treatment 10 A/dm'X 1 second Anodization 10 A/dm'X 1 second Subsequently, the same treatment in the chemical section as in Example 1 was performed.

(Example 3) After depositing chromium plating under the same conditions as in Example 1, cathode treatment was performed under the same conditions as in Example 1 in a water washing bath.

Perform anodization and deposit a chromium oxide film under the following conditions.

Processing bath composition in chemical department Orb Tofu 75? / #+NH4F 1.2
f/Z+NaOHO,l Orno l/1 Bath temperature 40℃ Electrolysis conditions 35mu/dn? X0.7 seconds (Comparative Example 11 Under the same conditions as in Example 1, cathodic treatment alone was performed in an interbath after immersion and washing with water, and the same chemical treatment as in Example 1 was performed.

(Comparative Example 2) Under the same conditions as in Example 1, anodization alone was performed in an interbath after immersion and washing, and the same treatment in the chemical part as in Example 1 was performed.

(Comparative Example 3) Immediately after immersion and washing under the same conditions as in Example 1, the same chemical treatment as in Example 1 was performed.

(Comparative Example 4) Immediately after electrolysis in a plater bath under the same conditions as in Example 1, anodization was performed in the same bath under the following conditions.

Anodic treatment 5 A/dm"X 1 second bath temperature 40 c A friend who performs the same chemical treatment as in Example 1.

Examples 1 to 3 above. Regarding the chromium-plated steel sheets manufactured in Comparative Examples 1 to 5, the unevenness of the L chromium oxide film was observed using an optical microscope, the amount of chromium oxide film was analyzed using a fluorescent X-ray method, and the amount of S in the chromium oxide film layer was analyzed.

Furthermore, a retort hard copper resistance evaluation test was conducted.

Here, in the retort fracture Ni4a evaluation test, paint baking was performed on a chrome-plated steel plate at an outer surface of 185°C x 10'#inner surface of 210°C.
x 10 minutes, nylon Teso was temporarily attached, then cylindrical molded, and bonded using high frequency A-conduction heating to form the can body.
Tighten the en-P. Next, fill the citric acid aqueous solution (Step 3) at room temperature and tighten the entire top plate. In this test, 10 of the above samples were prepared for each condition, and cooling was repeated from 125° C. for 30 minutes to 20° C., and the number of cycles until half of the cans broke was measured.

The results are shown in Table 1.

The unevenness and retort resistance in the chromium oxide film in Table 1 are as follows. [Effects of the Invention] As explained above, according to the present invention, in the immersion washing process after chromium plating, the cathode-anode By carrying out the treatment and further cathodic electrolytic treatment in an F-ion added bath, it is possible to uniformly deposit a chromium oxide film with excellent retortability, and the retort resistance etc. can be dramatically improved. Effects such as this can be obtained. The present invention is paint dense NV! This makes it possible to manufacture sub-chromium-plated steel sheets with excellent E, and has great industrial effects.

Agent Patent Attorney Masaaki Aki Sawa 2 others

Claims (1)

[Scope of Claims] A steel plate is subjected to cathodic electrolysis treatment in an aqueous solution containing mainly chromic anhydride (plater part) to deposit mainly metallic chromium, and then immersion washing in the presence of 20 to 100 g/l of chromic anhydride. In the step (drag out), cathode treatment is performed at a current density of 5 to 20 A/dm^2 and a current flow of 1 coulomb/dm^2 or more, and then the current density is 2 to 10 A/dm^2 in the same bath.
A/dm^2, anodization is performed at a current flow rate of 0.2 to 5 coulombs/dm^2, and then chromic anhydride of 20 to 200 g/l and F^- ions such as ammonium fluoride and sodium fluoride are generated. A method for producing a chromium-plated steel sheet with excellent paint adhesion, characterized by depositing a chromium oxide film by cathodic electrolysis treatment in an electrolytic solution (chemical part) in which a substance is present in an amount of 0.05 to 3 g/l as fluorine. .