JP3367454B2 - Method for producing chromate-treated galvanized steel sheet with excellent organic resin film adhesion and edge creep resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a chromate-treated zinc-based plated steel sheet having excellent adhesion to an organic resin film and excellent edge creep resistance.

[0002]

2. Description of the Related Art As a household electric appliance and a building material, a product called a laminated steel plate in which a surface-treated steel plate is coated with an organic resin film through an adhesive is widely used. As the laminated steel sheet, a zinc-based plated steel sheet is used when high corrosion resistance is required. Further, for the purpose of improving the corrosion resistance and the film adhesion, the zinc-based plated steel sheet is subjected to a phosphate treatment or a chromate treatment as a pre-lamination treatment.

Generally, chromate treatment is carried out by spraying or dipping, followed by washing with water, reactive chromate treatment, coating and drying a chromate treatment liquid, and electrolysis in a chromate treatment liquid to form a chromate film. There is an electrolytic chromate treatment to form.

However, the steel sheet subjected to these treatments does not always have sufficient performance as a laminated base steel sheet, as described below.

That is, the phosphate treatment produces phosphate crystals on the surface of the steel sheet, and the adhesion of the film can be improved by the anchor effect due to the micro unevenness formed by the phosphate crystals.

However, since phosphate crystals are poor in toughness and weak in deformation due to processing, etc., when the laminated steel sheet is subjected to a high degree of forming processing, the film may peel off from the steel sheet.

On the other hand, the chromate film is an amorphous film, and since the amount of the film deposited is smaller than that of the phosphate film, it is considered to be advantageous in terms of adhesion after the molding process. Various chromate films have been developed for use as resin film bases.

For example, JP-A-61-1508 and JP-A-9-296276 disclose that a coating type chromate imparts excellent adhesiveness and edge creep resistance.

However, the coating type chrome requires equipment such as a roll coater for applying the coating, and thus requires equipment investment. Moreover, it is difficult to control the coating amount, and the coating amount tends to be non-uniform in the width direction of the steel sheet for high-speed processing. Therefore, it has been difficult to secure the performance as an organic resin film base and the appearance quality of the steel sheet.

Further, the coating type chromate does not wash with water after the application of the chromate treatment liquid, so that excess Cr ⁶⁺ remains in the chromate film, and the chromate film easily absorbs moisture, resulting in adhesion of the film in a wet environment. It is difficult to secure sex. At the same time, the edge creep resistance tended to be reduced.

The reason for this is not always clear, but it is considered that the chromate film is likely to absorb moisture, so that a water film is easily formed between the film and the steel sheet, and corrosion of the steel sheet is likely to occur.

Further, as a method for reducing the excessive amount of Cr ⁶⁺ remaining in the film, there is baking at a high temperature of 100 to 200 ° C. However, a baking furnace is required for the baking at a high temperature, Capital investment is required.

The reactive chromate contains Cr ⁶⁺ ,
Chromium ions such as Cr ³⁺ and SO ₄ ²⁻ , NO ^{3 −} , F ⁻ , PO
₄ one containing anions ³ are common. Since reactive chromate is washed with water after chromate treatment, excess Cr ⁶⁺ is unlikely to remain in the chromate film,
It is advantageous in resistance to edge creep. However, in general, the chromate film cannot have an uneven structure that contributes to the anchor effect, and the adhesiveness of the organic resin film was insufficient.

On the other hand, in the electrolytic chromate treatment for cathodic electrolytically treating a steel sheet, Cr ⁶⁺ is electrically reduced to Cr ³⁺ on the surface of the steel sheet, and further, the pH of the treatment liquid near the surface of the steel sheet rises to increase Cr. The hydrated oxide film of is formed on the surface of the steel sheet. Therefore, the amount of the film deposited on the steel sheet can be controlled by the amount of electricity, and it is easy to increase the speed.

The electrolytic chromate treatment film is a film mainly containing Cr ³⁺ in principle.

By such electrolytic chromate treatment,
A method for improving corrosion resistance and paint adhesion by forming a chromate film on the surface of a zinc-based plated steel sheet is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-44088.
Hereinafter, this method is referred to as Prior Art 1.

Prior art 1 is Cr ⁶⁺ , Cr ³⁺ , Zn ²⁺ ,
Ni ²⁺ , SO ₄ ²⁻ , a treatment liquid containing oxide sol such as SiO ₂ or Al ₂ O ₃ as a main component defines the treatment liquid pH and the treatment temperature, and an excellent appearance by cathodic electrolysis treatment, It is a method for producing a chromate-treated zinc-based plated steel sheet that obtains corrosion resistance and paint adhesion.

Further, Japanese Patent Publication No. 4-30475 discloses that
Metallic Cr layer, with Cr mainly on it ³⁺Chromic acid consisting of
Oxide layer, SiO on it₂, Al₂0₃And Cr³⁺Subject
In Cr⁶⁺From the outermost layer of oxides and hydrated oxides containing
The chromate-treated layer is treated with electrolytic chromate to produce zinc.
No coating corrosion resistance by forming on the system plating layer
Adhesiveness, adhesiveness of coating film and vinyl chloride, etc.
Chromate-treated zinc-based plating with excellent adhesiveness
A steel plate is disclosed. Hereinafter, this method is referred to as Prior Art 2
Say.

[0019]

However, the prior art 1 is excellent in corrosion resistance without coating, paint adhesion, and adhesion between the organic resin film and the steel sheet when the organic resin film is formed through an adhesive. However, there is a problem that sufficient performance cannot be obtained in the entire range disclosed in Prior Art 1 with respect to the corrosion resistance after adhering the organic resin film via the adhesive, particularly the edge creep resistance. Was.

Further, although the prior art 2 is excellent in non-coating corrosion resistance, coating adhesion and adhesiveness of vinyl chloride film etc., it is similar to the prior art 1 in corrosion resistance after sticking an organic resin film, particularly However, there is a problem that the edge creep resistance is poor.

[0021]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to solve the above problems, and have obtained the following findings.

The unpainted corrosion resistance and the corrosion resistance such as edge creep resistance after coating with an organic resin do not always match.

Although the reason for this is not always clear, in the non-coating corrosion resistance and the corrosion resistance under the organic resin film, the route of the corrosion factor reaching the chromate film, the pH and the corrosion generation on the surface of the chromate film achieved during the corrosion progress It is conceivable that the materials and the like differ greatly, and the film constituent factors that contribute to corrosion prevention differ accordingly.

If the chromate film contains an excessive amount of Cr ⁶⁺ , the edge creep resistance is not necessarily excellent, and in many cases, the edge creep resistance tends to be lowered. In particular, this phenomenon becomes remarkable when the baking process is not performed.

The reason for this is that the chromate film has a soluble C content.
It is presumed that the excessive inclusion of r ⁶⁺ facilitates the moisture absorption of the chromate film and promotes the penetration of corrosion factors.

When silica is contained in the chromate film, the adhesion of the organic resin film is improved. It is presumed that this is due to the anchor effect resulting from the unevenness of the silica contained in the film.

When Ni is contained in the chromate treatment liquid, the precipitation of colloidal silica in the film is promoted.
This is because when Ni is present in the treatment liquid, Ni is deposited on the zinc surface, and the overvoltage of hydrogen generation on the Zn plating surface is reduced, so that the pH increase of the chromate treatment liquid near the zinc-based plating surface is promoted. It is presumed to be due to this.

When a zinc-based plated steel sheet is subjected to cathodic electrolysis in a chromate treatment solution with a relatively large amount of electricity, the edge creep resistance of the steel sheet coated with an organic resin film is significantly lower than that when the amount of electricity is relatively small. .

The reason for this is that the electrolytic chromate treatment involves hydrogen generation, and when the amount of electricity applied is more than the amount required for film formation, hydrogen is generated to form pores in the chromate film, and the organic resin film In a corrosive environment such as the one below, it is presumed that the corrosion proceeds mainly in the pores.

The present invention was made based on the above findings.

According to the first aspect of the present invention, a zinc-based plated steel sheet is dipped in a chromate treatment solution having the following composition, and the amount of deposited Cr (corresponding to a metal Cr value) is 5 m on the surface of the zinc-based plated steel sheet.
forming a chromate film of g / m ² or more, and
Having the characteristics of soluble components in the chromate coating <br/> it to be eluted by washing with water.

Chromate treatment liquid composition Cr ⁶⁺ + Cr ³⁺ (total Cr amount): 5-50 g / l Ni ²⁺ : 2-20 g / l SO ₄ ^2- : 10-100 g / l SiO ₂ : 1-50 g / l Treatment liquid pH: 2 to 4 Treatment liquid temperature: 30 to 70 ° C The invention according to claim 2 electrolyzes a zinc-based plated steel sheet in a chromate treatment liquid having the following composition at an electric quantity of 8 C / dm ² or less, On the surface of the zinc-based plated steel sheet, a chromate film having a Cr deposition amount (metal Cr conversion value) of 5 mg / m ² or more is formed, and a soluble film in the chromate film is formed.
It is characterized in that the components are eluted by washing with water .

Chromate treatment liquid composition Cr ⁶⁺ + Cr ³⁺ (total Cr amount): 5 to 50 g / 1 Ni ²⁺ : ^{2 to} 20 g / 1 SO ₄ ^2- : 10 to 100 g / 1 SiO ₂ : 1 to 50 g / 1 Treatment liquid pH: 2 to 4 Treatment liquid temperature: 30 to 70 ° C

[0034]

The present invention will be described more specifically.

Organic resin film: In the present invention, the organic resin film means a resin film such as a vinyl chloride resin film, a polyethylene resin film, a fluororesin film or the like. However, no limitation is imposed on the use of resin films other than the above.

[0036] Cr ⁶⁺ and Cr ^3+: Cr ⁶⁺ containing in the processing liquid and Cr ³⁺ can be added with anhydrous chromic acid, alkali metal salts or ammonium salts of chromic acid and bichromate. At this time, it is also possible to use a mixture of the chromic acid compounds. May by reducing Cr ⁶⁺ to Cr ³⁺ advance by alcohols such as for Cr ^3+, may be added directly to Cr ³⁺ compound in the treatment liquid.

At this time, the total sum of Cr ⁶⁺ and Cr ^{3+ in} the treatment liquid should be limited to the range of 5 to 50 g / 1 in terms of the total Cr amount in the treatment liquid. This is because when the total Cr amount is less than 5 g / 1, the formation of the chromate film is not sufficiently performed, while on the other hand, 50 g / 1
Even if it exceeds the above, the performance improvement of the steel sheet cannot be expected, and the amount of the treatment liquid attached to the galvanized steel sheet and taken out from the chromate treatment layer excessively increases, resulting in an increase in the treatment liquid cost.

The Cr ³⁺ / total Cr weight ratio in the treatment liquid is preferably 0.3 or less.

This is because, if the ratio exceeds 0.3, in the cathodic electrolysis treatment, the precipitation efficiency of Cr becomes very high even with the same amount of applied electricity, and a significantly colored film is formed, which is not preferable in appearance. Is.

Zn ²⁺ : Zn ²⁺ is preferably 6 g / 1 or less. If it exceeds 6 g / 1, the chromate film formed becomes a zinc-rich film, and the film itself becomes brittle when subjected to cathodic electrolytic treatment, and the adhesion of the organic resin film when subjected to processing is increased. Because it will decrease. As a method for controlling the amount of Zn ²⁺ in the treatment liquid, equipment such as all drain may be used.

Ni ²⁺ : The addition of Ni ²⁺ has the effect of promoting the precipitation of SiO ₂ as described above. Also, Ni alone is effective for the adhesion of paints and the like. Ni ²⁺ is 2 to 2
It is necessary to limit the range to 0 g / 1. This is Ni ²⁺
Is less than 2 g / 1, the above-mentioned effect cannot be obtained, and when it exceeds 20 g / 1, especially when cathodic electrolysis is performed, the coating is excessively colored and unevenness is likely to occur.

Here, the method of adding Ni ²⁺ is, but it may be added to the treatment liquid in the form of Ni sulfate, Ni carbonate, Ni chloride, Ni nitrate or the like.

SO ₄ ^2- : Conventionally, S in the chromate treatment liquid
It has been said that when a small amount of O ₄ ²⁻ is contained, a non-uniform film is formed in the cathodic electrolytic treatment, the corrosion resistance and other performances are deteriorated, and the appearance is deteriorated.

However, according to the study of the present inventors, when SO ₄ ²⁻ is contained in the range of 10 to 100 g / 1, the quality performance such as the adhesion of the organic resin film and the edge creep resistance is impaired. It was found that the stability of the chromate treatment liquid can be improved and a chromate film having a uniform appearance can be obtained without any problem.

When SO ₄ ²⁻ is less than 10 g / 1, the appearance after chromate treatment is deteriorated as described above, and 1
Performance cannot be improved even if it exceeds 00g / 1.
This is not preferable because it causes an increase in processing liquid cost.

Therefore, in the present invention, SO ₄ ^2- contained in the treatment liquid is limited to the range of 10 to 100 g / 1.

SiO ₂ : S in the processing liquid as described above
The addition of iO ₂ is effective in improving the adhesiveness of the organic resin film, but when the addition amount is less than 10 g / 1, the above-mentioned effects cannot be obtained, while when the addition amount exceeds 100 g / 1, Silica is excessively deposited in the cathodic electrolysis treatment to make the coating brittle and reduce the adhesion of the organic resin film during processing. Therefore, the amount of SiO ₂ added to the treatment liquid is 10
To 100 g / 1.

As a method for adding SiO ₂ , commercially available colloidal silica such as Snowtex manufactured by Nissan Chemical Co., Ltd. may be used. Although there are various particle sizes of colloidal silica, if the particle size is too large, precipitation tends to occur in the treatment liquid, which is not preferable and at the same time, the adhesiveness of the organic resin film is lowered. Therefore, the colloidal silica preferably has an average particle diameter of 50 mm or less. On the other hand, if the colloidal silica has a particle size smaller than this, it is also possible to mix and use particles having various particle sizes. Further, in the present invention, since the chromate treatment liquid is acidic, it is necessary to use colloidal silica which is stable in the acid treatment liquid.

In the present invention, the addition of SiO _{2 to} the treatment liquid has been described, but addition of oxide sol such as Al ₂ O ₃ , SnO ₂ and TiO _{2 which} can be expected to have an anchoring effect like colloidal silica is also added. It is possible.

Components inevitably mixed in the treatment liquid: Fe, Al, Mn, C as components inevitably mixed in the chromate treatment liquid from the galvanized steel sheet and the electrodes.
O, Mo, Pb, etc. are conceivable, but there is no problem if the amount is small. In addition, as other cations, alkali metal ions such as Na and K, and alkaline earth metal ions such as Mg and Ca, which are contained in SO ₄ ² -supplied salt or additives such as an electric conduction aid and a pH buffering agent. It may be possible to contain ammonium ion, but this invention does not cause any problem.

PH of chromate treatment liquid: The pH of the chromate treatment liquid must be limited to pH 2 to 4. pH 2
When it is less than 1, the appearance after the chromate treatment is blackened, which is not preferable. Further, when the pH exceeds 4, the stability of the treatment liquid is deteriorated and the treatment liquid is precipitated. The pH of the treatment liquid may be adjusted by adding sulfuric acid or alkali metal hydroxide to the chromate treatment liquid.

Chromate treatment liquid temperature: The temperature of the chromate treatment liquid is limited to the range of 30 to 70 ° C. This is because if the temperature of the chromate treatment liquid is lower than 30 ° C., undissolved components are likely to be generated in the treatment liquid, and the electric conductivity of the treatment liquid is lowered to hinder the deposition of the chromate film. If it exceeds the limit, the treatment liquid adhering to the steel sheet will be easily dried, and the appearance of the chromate film will be deteriorated due to contact with a roll or the like.

Electricity in cathodic electrolysis: The quantity of electricity applied to the steel sheet in cathodic electrolysis must be limited to 8 C / dm ² or less. When it exceeds 8 C / dm ² , the edge creep resistance is significantly deteriorated as described above. The current density at this time is preferably 20 A / dm ² or less. Even if it exceeds 20 A / dm ² , the edge creep resistance is deteriorated.

Cr deposition amount: When dipping or spraying is carried out without performing cathodic electrolysis, the amount of chromate coating cannot be controlled by the amount of electricity. However,
In this case, if the treatment time is controlled so that the Cr adhesion amount is 5 mg / m ² or more, excellent organic resin film adhesion and edge creep resistance can be obtained. C
If the r deposition amount is less than 5 mg / m ² , sufficient performance cannot be obtained.

The zinc-based plated steel sheet to be subjected to the chromate treatment of the present invention is a galvanized steel sheet such as electrogalvanized or hot-dip galvanized sheet, Zn--Ni, Zn--Fe, Zn--.
Examples include zinc alloy plated steel sheets such as Mn and Zn-Al.

The organic resin film adhesion and edge creep resistance provided by the present invention are not due to the steel sheet itself, but are due to the effect of the chromate film formed on the upper layer thereof.

Prior to the present chromate treatment, it is also possible to apply alkaline cleaning, surface polishing, or flash treatment with Fe, Ni, Co, Cr, etc. to the surface of the zinc-based plated steel sheet as a pretreatment. What is flash processing?
The zinc-plated steel sheet may be brought into contact with the treatment liquid by immersion or spraying in the treatment liquid containing the metal. However, such processing is not an essential requirement for the present invention.

[0058]

Embodiments of the present invention will be described below. (1) Treated original plate The following plated steel plate was used as the treated original plate. EG: Electrogalvanized steel sheet (zinc coating amount 20 g / m ² per side), GI: Hot dip galvanized steel sheet (zinc coating amount 60 g / m ² per side), EZN: Zn-Ni alloy plated steel sheet (Ni-12 wt) ．
% Content, plating basis weight per side 30 g / m ² ), Al—Zn: Al—Zn alloy plated steel sheet (5% Al—Z
n, coating weight per side 60 g / m ² ) (2) Chromate treatment method A chromate film was formed on the galvanized steel sheet under the chromate treatment liquid and treatment conditions shown in Table 1. In the table, the current density of 0 indicates the immersion treatment in the treatment tank. In this example, the chromate treatment by electrolysis or immersion was followed by removal of soluble components by washing with water and drying. (3) Organic resin film coating The chromate-treated zinc-plated copper plate subjected to the chromate treatment was coated with an organic resin film by the following procedure. (I) Applying a polyester adhesive to 2 μm (ii) Heating a steel plate to a plate temperature of 200 ° C. in a heating furnace (iii) Pressing a vinyl chloride film (200 μm) with a roll (iv) Water cooling (v) Hot air drying The organic resin film adhesion and the corrosion resistance (edge creep resistance) of the prepared sample were evaluated by the following methods. (Appearance) The appearance of the processed sample was evaluated according to the following criteria. ◯: Uniform and uniform, without excessive coloring. X: Occurrence of unevenness or excessive coloring, or excessive coloring and unevenness occur simultaneously. (Adhesiveness) The adhesiveness test was carried out according to the method described in JIS-K6744 for the Erichsen and peeling test. Regarding Erichsen, in addition to the primary adhesion described in JIS-K6744, the Erichsen test described in JIS-K6744 was performed after immersing the test piece in boiling water for 3 hours to evaluate the secondary adhesion. The evaluation criteria for the primary and secondary Erichsen tests were as follows. ⊚: No peeling of film ○: Slight peeling of film ×: Clear peeling of film Also, the peeling test was evaluated according to the following criteria. ◎: 4.5 kgf / 20 mm or more ○: 3.5 kgf / 20 mm or more, 4.5 kgf / 20
Less than mm x: less than 3.5 kgf / 20 mm (corrosion resistance (edge creep resistance)) A test piece of 50 mm x 100 mm was cut out from the prepared sample, and JIS was used.
It was subjected to a salt spray test according to the method described in A1415 for 4 weeks. Then, the steel plate was immersed in dimethylformamide to peel off the vinyl chloride film.

In this sample, the area where the plating disappeared due to corrosion was measured by image processing, and the corrosion area ratio in the sample area was calculated and evaluated. The evaluation criteria were as follows. ⊚: Corrosion area ratio less than 15% ◯: Corrosion area ratio 15% or more and less than 30% ×: Corrosion area ratio 30% or more These evaluation results are shown in Tables 1 and 2.

[0060]

[Table 1]

[0061]

[Table 2] As is clear from Table 1, the examples of the present invention were excellent in all of the appearance of the sample, the adhesion of the organic resin film, and the edge creep resistance.

On the other hand, as is apparent from Table 2, in Comparative Examples outside the scope of the present invention, at least one of the sample appearance, organic resin film adhesion and edge creep resistance was inferior.

[0063]

As described above, according to the present invention, as an organic resin film-coated base steel sheet, an organic resin-coated chromate-treated zinc-based plating excellent in appearance, organic resin film adhesion, and edge creep resistance is provided. A useful effect that a steel plate can be obtained is brought about.

Continuation of the front page (72) Inventor Satoshi Ando 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) Reference JP-A-9-296275 (JP, A) JP-A-5-44088 ( JP, A) JP-A-3-223493 (JP, A) JP-B-4-30475 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 22 / 00-22 / 86

Claims (2)

(57) [Claims] 1. A zinc-based plated steel sheet is dipped in a chromate treatment solution having the following composition, and C is applied to the surface of the zinc-based plated steel sheet.
r A chromate film with an adhesion amount (metal Cr converted value) of 5 mg / m ² or more is formed, and
A method for producing a chromate-treated zinc-based plated steel sheet excellent in organic resin film adhesion and edge creep resistance, which comprises dissolving soluble components by washing with water . Chromate treatment liquid composition Cr ⁶⁺ + Cr ³⁺ (total Cr amount): 5 to 50 g / l Ni ²⁺ : ^{2 to} 20 g / l SO ₄ ^2- : 10 to 100 g / l SiO ₂ : 1 to 50 g / l treatment liquid pH: 2 to 4 Treatment liquid temperature: 30 to 70 ° C 2. A zinc-based plated steel sheet is electrolyzed in a chromate treatment solution having the following composition with an electric quantity of 8 C / dm ² or less, and a Cr adhesion amount (metal Cr converted value) of 5 mg is applied to the surface of the zinc-based plated steel sheet. / M ² or more chromate film is formed, and soluble components in the chromate film are washed with water.
A method for producing a chromate-treated zinc-based plated steel sheet excellent in organic resin film adhesion and edge creep resistance, which is characterized in that it is eluted by . Chromate treatment liquid composition Cr ⁶⁺ + Cr ³⁺ (total Cr amount): 5 to 50 g / l Ni ²⁺ : ^{2 to} 20 g / l SO ₄ ^2- : 10 to 100 g / l SiO ₂ : 1 to 50 g / l treatment liquid pH: 2 to 4 Treatment liquid temperature: 30 to 70 ° C