JPS63130796A - Composite chemical conversion coating steel sheet having excellent corrosion resistance and paint adhesion and production thereof - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and paint adhesion of the title steel sheet by electrolytically chromating the surface of a Zn plated steel sheet in a bath contg. Cr<6+>, colloidal silica, alumina sol, and fluorides, and then treating the sheet with a silane coupling agent. CONSTITUTION:The surface of a Zn plated steel sheet is electrolytically chromated with the steel sheet as a cathode at 1-50A/dm<2> current density and 1-100C/dm<2> quantity of electricity in the bath contg. 2.6-78g/l Cr<6+>, 0.5-75g/l colloidal silica and alumina sol respectively as SiO2 and Al2O3, and 0.05-5g/l fluoride as F. By this treatment, a film contg. 10-300mg/m<2> hydrated chromium oxide consisting essentially of Cr<3+> (Cr<6+>/Cr<3+>=1/100-1/5) as the total Cr content is formed. The sheet is treated with the silane coupling agent, and a silane coupling treated film is formed at 1-100mg/m<2>. By this method, a composite chemical conversion coating steel sheet having excellent paint adhesion and corrosion resistance can be obtained only with the formation of the thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a composite chemical conversion treated steel sheet with excellent corrosion resistance and paint adhesion for use in automobile bodies, home appliances, etc., and a method for manufacturing the same.

<Prior art and its problems> Chemical conversion treatments for Zn-based plated steel sheets generally include chromate treatment and phosphate treatment, but chromate treatment is effective as a treatment that provides both corrosion resistance and paint adhesion.

Conventional chromate treatment is classified into three types, electrolytic chromate treatment, reactive chromate treatment, and coating-type chromate treatment, depending on the treatment method, and each type has the following characteristics in terms of the quality of the chromate film.

The electrolytic chromate treatment method uses an aqueous solution of chromic acid or its salt as a basic component, and cathodic electrolysis is performed in a bath to which an appropriate amount of anion such as sulfuric acid is added as necessary. This is a method of producing a chromate film made of Cr"+.The chromate film obtained by this method has a small amount of water-soluble Cr6+, so the ratio of Cr6 molecules/Cr3+ is small, is poorly soluble in water, and is relatively porous. Therefore, Cr6
Since the self-repairing effect of + cannot be expected, sufficient corrosion resistance cannot be obtained.

Similar to the electrolytic chromate treatment bath, the reactive chromate treatment method involves adding mineral acids such as sulfuric acid and nitric acid and appropriate amounts of butic acid and phosphoric acid to a bath based on chromic acid. In this method, a Zn-plated steel sheet is immersed in a treatment bath, and a chromate film is generated on the surface of the Zn-based plating through the dissolution of base metal Zn by free acid and the chemical reaction with Cr6+ ions. In the chromate film obtained by this method, the ratio of Cr''/Cr3+ is not necessarily constant, and there is considerable variation;
For materials that are difficult to dissolve, it is necessary to significantly increase the free acid concentration, and different processing solutions must be prepared depending on the plating type.

Regarding the coating type chromate treatment method, a predetermined amount of a treatment solution made by adding an inorganic polymer such as silica sol to an aqueous solution using chromic acid is applied to the surface of a Zn-plated steel sheet and dried. Since the chromate film obtained by
It has the best corrosion resistance among the different types of chromate films mentioned above, and high corrosion resistance can be expected depending on the amount of Cr deposited. However, since Cr6+ is soluble in water, it is easily washed away and is subject to deterioration over time, so there is a limit to the effective deposition amount, including in terms of cost.

In order to improve these above-mentioned drawbacks, Japanese Patent Laid-Open No. 61-23
No. 766 discloses a steel plate in which a chromate film is applied to the surface of a plated steel plate by either reactive chromate treatment or coating-type chromate treatment, and then a coupling treatment is performed. However, even with the two-layer composite coated plated steel sheet, it is impossible to prevent the elution of Cr6+ and the gradual reaction between the upper coupling film components and Cr6+, resulting in changes over time and a decrease in corrosion resistance and paint adhesion.

Therefore, it is better to apply electrolytic chromate treatment to Zn-based plated steel sheets, which is the most stable treatment and does not deteriorate over time, but it is necessary to eliminate defects in the chromate film and to contain an appropriate amount of Cr6+. For example, as mentioned above, there are problems such as insufficient corrosion resistance.

Furthermore, the adhesion of electrolytic chromate films to paints is not necessarily sufficient, and there are also problems such as the need to suppress deterioration over time, especially in corrosive environments.

<Object of the Invention> The object of the present invention is to solve the problems of the prior art described above, and to provide a surface-treated steel sheet that is used as an automobile body material, a home appliance material, or a building material in a harsh corrosive environment, and in particular, to improve its corrosion resistance and paint properties. An object of the present invention is to provide a composite chemical conversion treated steel sheet with excellent adhesion and a method for manufacturing the same.

<Structure of the Invention> As a result of intensive research, the present inventors obtained the following knowledge and arrived at the present invention.

1. Since the electrolytic chromate film is mainly composed of Cr3+, it is stable with little deterioration over time, and it also contains an appropriate amount of SiO2 and/or Al2O3 and Cr6+.
By containing it, corrosion resistance can be improved.

2. A treated film with a silane coupling agent is formed on the electrolytic chromate film to improve paint adhesion.

That is, according to the present invention, a Cr3+-based chromium hydrated oxide (C
r"/Cr"=l/100 to 115) as a total Cr content of 10 to 300 mg/m", and a silane coupling treated film of 1 to 100 mg/m2 as a second layer thereon. Provided is a composite chemical conversion treated steel sheet having excellent corrosion resistance and paint adhesion.

Further, according to the present invention, 2.6 to 78 g/l of Cr6+ and 5j02 of colloidal silica and/or alumina sol are applied to the surface of a Zn-based plated steel plate, using the steel plate as a cathode.
and/or 120. As 0.5-75g/JZ
, in a bath containing 0.05 to 5 g/u of fluoride as F, with a current density of 1 to 50/dm2. Electricity 1~100 C/
A method for manufacturing a composite chemical conversion treated steel sheet with excellent corrosion resistance and paint adhesion, which comprises performing electrolytic chromate treatment under dm2 electrolytic chromate treatment conditions, and then performing coupling treatment with a silane coupling agent. is provided.

The present invention will be explained in more detail below.

The Zn-based plating of the present invention includes the following (1) Galvanization such as electrogalvanization and hot-dip galvanization. Also, these have been subjected to reflow processing.

(2) Zn and Ni, Go, Fe, Cr,
Mn, Mo, W, V.

Zn-based alloy plating containing one or more of Ti, Zr, Sn, P, etc.

(3) Hot-dip Zn alloy plating containing Zn and one or more of AR, Cr, Sn, Si, etc.

(4) In addition to (1), (2) or (3) above, SiO
2. Zn-based alloy composite plating containing dispersed one or more of oxides such as Al, 203, TlO2, ZrO2, etc.

(5) Laminated plating in which the platings of (1) to (4) above are formed in multiple layers, and laminated plating in which Fe plating or Fe-rich plating is applied to the upper layer.

The type and size of the steel plate used in the present invention are not limited, and the Zn-based plating is applied to the surface of the steel plate after pretreatment such as degreasing, pickling, and water washing according to a conventional method. Any steel plate that has been used will suffice.

In the present invention, the electrolytic chromate film, which is the first layer on the surface of the Zn-based plated steel sheet, is made of SiO2 and/or Al.
10 to 300 mg7m2 of cr3+-based chromium hydrated oxide film containing 1,03 and Cr6+ as total Cri
It is preferable to have The reason for this is that the total Cr amount is 10 mg/
If the corrosion resistance is less than 300Il1g/m2, the corrosion resistance is insufficient.
This is because if it exceeds 112, the chromate film will be easily destroyed during severe molding processing, and paint adhesion will decrease.

Here, Cr6+ is 1/100 to 115 of the total Cr amount.
It is preferable that The lower limit was set to l/100 because
This is because if the Cr6+ content is lower than this, the self-repairing effect will be weakened and no improvement in corrosion resistance will be observed. Also, 115
This is because if the amount exceeds this amount, the film will be significantly colored and the adhesion of the paint will be impaired.

In the present invention, SiO2 and/or Al2O3 each or in total amount is 1/40% of the total Cr in the film.
It is best to set it to ~1/2. The reason for this is that if it is less than 1740, the film-forming effect which is the original purpose of SiO2 and/or L203 is weak, the defective parts of the electrolytic chromate film cannot be completely covered, and the improvement in corrosion resistance by the barrier layer is poor. Moreover, if the upper limit of 172 is exceeded, not only will there be limitations due to adhesion to rolls etc. during production, but also the film will become too thick, inhibiting paint adhesion.

Furthermore, the present inventors have found that Ar1.203 along with SiO2
It has been found that when present, a relatively small amount has an excellent effect. In addition, when coexisting, the amount of 120 is Si
The appropriate ratio was /10 to 1/2 of O2.

In this way, AIt along with SiO2 is present in the chromate film.
The reason for the effect of improving corrosion resistance and paint adhesion when 203 is contained can be considered as follows.

Generally, Al2O3 sol is positively charged in acid salt,
When the strip is used as a cathode for electrolysis, a uniform and strong film is deposited on the cathode along with SiO2, which has a good barrier effect, and this is caused by strong hydrogen bonds between the hydroxyl groups on the active Al2O3 colloid surface and the functional groups of the paint. This can be mentioned.

Next, in order to significantly improve corrosion resistance and paint adhesion, 1 to 100 mg of the silane coupling film is formed as a second layer on the first layer of electrolytic chromate film.
/m2 is preferable. The reason for this is that if the silane coupling film is less than 1111871112, no improvement effect will be observed, and if it exceeds 100 mg/rn2, the effect will not only be saturated but also increase the cost due to the increased amount of adhesion. In addition, as the amount of adhesion increases, high temperature and long drying times are required, and high-speed EGL (electrical Zn
This is because it becomes difficult to apply to high-speed lines such as plating lines).

The drying conditions of the present invention are 70 to 140°C, 2 to 20°C.
It can be done in a short time at a temperature of about seconds.

The silane coupling treatment for forming the silane coupling film of the present invention will be described later, and the silane coupling agent has the following structure.

Yn 5i(OH)3-n where Y: organic reactive group, n+1.2 The reason why a trace amount of the silane coupling film shows remarkable effects is considered as follows. That is, in the electrolytic chromate film of the first layer, there are Sin and/or 81203 having active hydroxyl groups (OH) on the surface, which react with the silanol group (SiOH) of silane coupling formula 1, Creates strong bonds through dehydration condensation. In addition, the organic reactive group of the coupling agent is bonded to the paint side and exhibits strong adhesion.

Furthermore, hydrogen bonding between the silane coupling agent and the surface of the electrolytic chromate film is also considered to contribute to improved adhesion.

The composite chemical conversion treated steel sheet with excellent corrosion resistance and paint adhesion according to the present invention is basically constructed as described above.
The manufacturing method will be explained in more detail below.

The first layer electrolytic chromate film treatment is performed on a Zn-based plated steel sheet under the following conditions.

Cr6+ is required as the main component to form a chromate film, and CrO3, chromate, dichromate, etc. can be used, but the most common one is CrO.
It is better to use 3. Even if electrolytic treatment is performed in a single CrO3 bath, the chromate film will hardly grow and only a very thin film will be obtained.

This is because a hydrated oxide film covers the surface in the very early stages of electrolytic treatment, lowering the current efficiency, so a small amount of etching agent is required to destroy the thin part of the film and allow the film to grow further. is necessary. Generally, sulfate ions and carbide ions are often used, but sulfate ions have a high CrO3 concentration, and when the current density is high, metallic chromium tends to precipitate, and the plated surface tends to blacken.

Therefore, in the present invention, a carbide is used as an etching agent. As a compound, +l F63-.

Representative examples include Na salts such as SiF62-, BF4-, and F-, but they may be used alone or in combination as long as they can be added in the same amount as the F concentration.

The Cr6+ concentration was limited to 2.6-78 g/l because
This is because if it is less than 2.6371, the supply of Cr" at the plating interface is insufficient and a good film cannot be formed.
If it exceeds ft, metallic chromium tends to precipitate and the chromium hydrated oxide becomes thinner, and the Zn dissolution reaction occurs simultaneously, so it tends to turn yellowish brown and the appearance becomes poor.

The above-mentioned F concentration of the abbreviated substance is 0.05 to 0.05.
It is preferable to use it by adding 5 g/l.

The reason for this is that if it is less than 0.05 g/fi, the etching power will be weak and the film will not grow. On the contrary, 5g/I! This is because, if added in excess of , the etching power is too strong, which may dissolve the hydrated oxide film or etch the plating surface, causing Zn dissolution and uneven reaction.

However, the film formed only with Cr6+ and fluoride is still thin, and the film cannot grow simply by increasing the amount of electricity. Therefore, the corrosion resistance is also insufficient.

Therefore, in the present invention, when colloidal silica and/or alumina sol are added as a third component as a film-forming agent at 0.5 to 75 g/fi as SiO2 and/or Al2O3, respectively or in total, the adsorption power of colloidal silica and/or alumina sol Alternatively, a thick chromate film can be obtained due to the three-dimensional structure.

As for colloidal silica, Snowtex 0. c. Representative examples of the cationic type include Snowtex AK and BK (both manufactured by Ichisan Kagaku). In particular, when cationic colloidal silica is used, since the plating side is the cathode, the transport of colloidal silica to the plating surface is promoted. In addition, Cr1) on the colloidal silica surface, Cr2O,'- and Cr in the aqueous solution
Since it adsorbs the anion of y4'- and is adsorbed to the cathode, it acts as a self-healing ability in the electrolytic chromate film (Cr6
It is possible to form a film containing the + component and having good corrosion resistance.

Note that alumina sol is a cationic type and exhibits the same behavior as above. Addition amount of SiO2 and/or 8u20
3 is limited to 0.5 to 75g/fi.
This is because there is almost no effect if it is less than 75 g/1.
If it exceeds g/l, it is not preferable because the electrical conductivity in the chromate bath decreases, or the film becomes too thick and becomes noticeably colored, or the thickness of the film becomes uneven.

Furthermore, in order to contain AIL203 together with SiO2 in the chromate film as described above, it is preferable to add colloidal silica and alumina sol to the electrolytic chromate treatment solution. The amount of alumina sol added is preferably 1/10 to 1/2 of 5i (h) as 11203.A
This is because if the amount of 12O3 is less than 1/10 of SiO2, the effect is small, and if it exceeds 1/2, adsorption of SiO2 to the plated surface becomes uneven.

Here, SiO2 and 12 into the electrolytic chromate treatment solution
The following two methods are available for adding o3.

■Add appropriate amounts of colloidal silica and alumina sol separately.

■ Add an appropriate amount of alumina sol adsorbed around SiO2.

Good treatment can be achieved in both cases (1) and (2) above, but (2) is particularly excellent in controlling the content of colloidal sol in the chromate film.

In the above-mentioned Rakuchu, the anode is an insoluble anode, for example, Pb-
A suitable electrode such as 5N (5% Sn) is used, and the bath temperature is preferably between 30 and 70°C. In addition, although there is a relationship with processing time, generally the current density is 1 to 50A.
It is preferable to process between /d1112. In this range, as the amount of electricity increases, the amount of chromate film also increases. Therefore, by controlling the current density and the amount of electricity depending on the purpose or line speed, it is possible to obtain a chromate film with a target coating amount.

The amount of electricity is preferably 1 to 100 C/dm2.

Chromate film 10 mg/m for IC less than 76 m2
2 or more cannot be obtained, and if the temperature exceeds 100 C/dm2, the amount of chromate film deposited exceeds 300 mg/m2.

After the electrolytic chromate treatment as described above, washing is performed with running water, and the next coupling treatment is performed. In addition, if necessary,
You can dry it after washing with running water.

Next, the second layer coupling treatment is performed on the electrolytic chromate film under the following conditions.

The coupling process may be performed in a conventional manner without any special measures. As a stable and efficient treatment method, a dipping method and a spray method are preferred. In the immersion method, a Zn-based plated steel sheet after electrolytic chromate treatment is added to a solution prepared by mixing a coupling agent and water in an alcoholic solvent and stirring well, or a solution prepared by adding a coupling agent to water and stirring well. Soak. After immersion, excess processing liquid is removed by roll squeezing or gas squeezing, and the coupling agent is dehydrated and condensed to be fixed on the electrolytic chromate film.

In the case of the spray method, a treatment liquid having a composition similar to that of Habo is applied by spraying.

Any coupling treatment agent may be used as long as it has the structure described above, but typical examples include vinyltrichlorosilane, vinyltrimethoxysilane, γ-(methacryloxypropyl)trimethoxysilane, and β-(3,4 epoxycyclohexyl). Ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyljethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane , N-phenyl-γ-
Aminobutyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, and the like can be used.

<Example> Next, the present invention will be specifically described with reference to Examples.

Examples of Zn-based plated steel sheets include electrolytic Zn-plated steel sheets (coating amount 20 g/m2), Zn-1:o alloy plated steel sheets (coating amount 20 gerII2, Go content 2 wt%), Zn-
A Ni alloy plated steel plate (coating amount 20 g/m2, Ni content 12 wt%) and a Zn-8 alloy plated steel plate (coating amount 50 g/m2.1 content 5 wt%) were used.

The composite chemical conversion treatment process was as follows.

(1a) Electrolytic chromate treatment was performed under the following conditions.

Crys: 20-50 g/l Na25IF6 (as F): 0.5-1.5
g/lSin2 and/or AR, 203:3-3
The target electrolytic chromate film was obtained by adjusting the current application time (amount of electricity) within the range of 0 g/42 current density = 5 to 30 A/dm2.

(1b) Chromate treatment as a comparative material was performed under the following conditions.

CrO2: 40 g/I1. , ethylene glycol: 10 g/l aqueous solution and coated to a predetermined amount of Cr.

(2) After washing the electrolytic chromate treated material with water, γ
Silane coupling treatment was performed using -aminopropyltriethoxysilane as a representative example. Note that the same good results were obtained with other silane coupling agents.

Silane coupling agent: γ-aminopropyltriethoxysilane 0.1 to 1.0 parts Water: 2.0 parts Methyl alcohol: Prepared by mixing a liquid consisting of 99.9 to 99.0 parts with thorough stirring. .

The immersion time in the coupling treatment is 1 to 10 seconds,
The desired coupling film was obtained.

(3) After roll squeezing, a quality investigation was conducted on the sample that was dried at 120° C. for 7 seconds. The results are summarized in Table 1.

Corrosion resistance and coating test conditions were as follows.

(1) Corrosion resistance of unpainted materials It was conducted under the following cycle of corrosion conditions based on the salt spray test (SST: JIS-Z-2371), and evaluated in the state of white rust occurrence.

[SST: 18h] → [Humidity: 40°C, relative humidity 9
5%, 4 hours] → [Drying: 60°C, 2 hours] ◎ No white rust occurred O White rust occurred 10% △ White rust occurred 30% × White rust occurred 50% After 5 days, the electrolytic Zn-plated steel sheet became Zn-[:o Alloy plated steel plate and Zn-AR, alloy plated steel plate after 10 days, Zn-AR
-Ni alloy plated steel sheets were evaluated after 20 days.

(2) Electrodeposition coating material After applying a rotating brush to the surface of the plated steel plate to create a disc-shaped scratch with a diameter of 10 mm that reaches the base steel plate, a normal dip-type phosphate treatment is applied, and then Electrodeposition coating was performed under the following conditions.

Paint: Cationic electrodeposition coating (Power Top U-30 manufactured by Nippon Paint) Coating film thickness: 20 houses baking = 180°C x 25 minutes Composite corrosion test (CCT) was conducted under the cycle conditions of (1) above.

The maximum coating film blistering width at the scratched outer periphery of the plating layer was observed.

◎ No blister O bulge width 2 mm or less △ bulge width 2 to 5 mm × bulge width 5 mm or more After 15 days, Zn-Go gold alloy coated steel plate and Zn-AI! , alloy-plated steel sheet Z after 30 days
The n-Ni alloy plated steel sheet was evaluated after 45 days.

(3) 3-coat material The sample plated steel sheet was subjected to a normal dip-type phosphate treatment, and then, after the electrodeposition coating described in (2) above, an intermediate coat and a top coat were applied.

Intermediate coating: Surfacer (manufactured by Kansai Paint) 40 units Baked at 140℃ for 30 minutes Top coat Near Miracle Paint (manufactured by Kansai Paint), 40 units
Door Baking 140℃ x 30 minutes Secondary adhesion to warm water Immersed in pure water at 40℃ for 30 days, 2m immediately after lifting
100 m-squares were marked with a cutter knife and immediately peeled off with cellophane tape. The evaluation was expressed by the presence rate of the coating film.

◎ Residual rate: 100% O residual rate: 70% or more △ Residual rate: 70-40% × Residual rate: 40% or less As can be seen from Table 1, in the examples of the present invention, a composite chemical conversion coating is applied to a Zn-based plated steel sheet. Therefore, it shows excellent effects on corrosion resistance and paint adhesion, etc.

<Effects of the Invention> According to the present invention, 7. The composite chemical conversion coating formed on the surface of the n-based plated steel sheet is extremely thin, so it does not reduce spot weldability, electrodeposition coating properties, workability, etc.
A composite chemical conversion treated steel sheet with excellent corrosion resistance and paint adhesion that is used in extremely harsh corrosive environments such as automobile body materials, home appliance materials, or building materials can be obtained.

Further, according to the present invention, the composite chemical conversion treated steel sheet can be efficiently manufactured.

Claims (2)

[Claims] (1) Si is added as the first layer on the surface of the Zn-based plated steel sheet.
O_2 and/or Al_2O_3 and Cr^6^
Cr^3^+-based chromium hydrated oxide (Cr^
6^+/Cr^3^+=1/100 to 1/5) to all Cr
Corrosion resistance and paint adhesion characterized by having a film containing an amount of 10 to 300 mg/m^2 and a silane coupling treated film having a second layer of 1 to 100 mg/m^2 thereon. Excellent composite chemical conversion treated steel sheet. (2) On the surface of a Zn-based plated steel plate, using the steel plate as a cathode, 2.6 to 78 g/l of Cr^6^+ and 0.5 to 75 g/l of colloidal silica and/or alumina sol as SiO_2 and/or Al_2O_3. l, a bath containing 0.05 to 5 g/l of fluoride as F, and a current density of 1
After the electrolytic chromate treatment is performed under electrolytic chromate treatment conditions of ~50 A/dm^2 and an electrical quantity of 1 to 100 C/dm^2, a coupling treatment is performed using a silane coupling agent. A method for producing composite chemically treated steel sheets with excellent corrosion resistance and paint adhesion.