JPH11335862A - Production of surface treated steel plate having excellent corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a surface treated steel plate having safety and excellent corrosion resistance by treating a zinc plated steel plate with a chromium free aqueous treating solution. SOLUTION: A chemical conversion coating film is formed in 0.005-2 μm thickness on a galvanized surface by treating a zinc plated steel plate with an acidic aq. solution of pH 1.0-4.0 followed by heat-treating. The acidic aq. solution contains silicate and/or silica fine particles and Al ion, and moreover contains nitric acid ion as an anion, more preferably contains one or more than two kinds selected from metal ions of Ca, Sr, Ba, Hf, Zr, V, Ti, Ce, La, Ni, Co, Fe, Mn and a water soluble cation contg. one of these metals.

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 surface-treated steel sheet suitable for use in automobiles, home appliances, building materials, and the like. An environment that does not contain any heavy metals such as chromium, lead, cadmium, and mercury that are harmful to the environment and the human body in manufacturing processes and products in order to adapt to environmental issues such as volatilization and elution of harmful substances from products in the use environment. The present invention relates to a method for manufacturing an adaptive surface-treated steel sheet.

[0002]

2. Description of the Related Art Steel sheets for home appliances, steel sheets for building materials,
For automotive steel sheets, a treatment solution containing chromic acid, dichromic acid or salts thereof as the main component for the purpose of improving the corrosion resistance (white rust resistance, red rust resistance) on the surface of galvanized steel sheets and aluminum-coated steel sheets Are widely used. This chromate treatment is an economical treatment method that can impart excellent corrosion resistance to a steel sheet and can be performed relatively easily.

[0003] However, since chromate treatment uses hexavalent chromium, which is a pollution control substance, it is difficult for chromate salts to have an adverse effect on the human body in the treatment process, and it is difficult to dispose of chromium sludge after wastewater treatment. In addition, there are various problems, for example, that hexavalent chromium may be eluted from the product after the chromate treatment. For this reason, as the use control standards for chromic acids have become stricter, the management of chromate treatment plants, wastewater treatment, and secondary contamination by chromate treatment have become a problem. In addition, measures are taken to minimize the emission of chromium ions to the outside.
In addition, in the process of degreasing the rust-preventive oil and press oil attached to the chromate-treated steel sheet by the user, when using an alkaline degreasing solution, the elution of chromium into the degreasing solution is considerably increased. Dechrome treatment is required.

[0004] In view of such circumstances, in order to prevent the generation of white rust on a zinc-based plated steel sheet, many pollution-free treatment techniques not based on chromate treatment have been proposed. For example,
There is a method of using an inorganic compound, an organic compound, an organic polymer material, or a combination thereof to form a thin film by a method such as immersion, coating, or electrolytic treatment. Above all, a technique of forming a film made of silicon oxide on a galvanized surface using a solution containing a silicate such as water glass, a silicate sol, an alkyl silicate, or a silane coupling agent is relatively inexpensive. The point of using silicon,
It is a relatively promising technique because silicon oxide is effective in inhibiting zinc corrosion.

[0005] Among these techniques, a method using a processing solution containing an alkyl silicate or a silane coupling agent is not suitable because these added components are unstable in an aqueous solution.
It is necessary to use a solvent for the treatment liquid. However, when a solvent is used as a treatment liquid, there are many problems in terms of deterioration of the working environment, management of volatile substances, stability of chemicals, etc. It is desirable to use a base.

Further, as a technique using a silicate or a silicic acid sol, containing no hexavalent chromium such as chromate in the treatment liquid, and using an aqueous treatment liquid, the following techniques are known. Are known. (1) A method using a treatment solution obtained by further adding phosphate ions, molybdate ions, etc. to an aqueous solution containing silicic acid (Japanese Patent Application Laid-Open No. 52-90435). (2) Silica made alkaline by adding a volatile base. Treatment using an aqueous acid solution (JP-A-54-5835)

(3) An acidic aqueous solution containing an oxidizing agent,
A treatment method using an aqueous solution containing trivalent chromium ions, various metal salts, and silicates or silicate compounds (Japanese Patent Laid-Open No.
No. 7-181379) (4) Ti, Zr, Mg, Ba,
Sr, W, Ni, Co, V, Ca, Mo, Cu, Al,
A treatment method using an aqueous solution to which one or more metal ions selected from Sn, Be, and Mn are added (Japanese Patent Application Laid-Open No. 63-50484)

(5) It contains nitrate ions and silica fine particles or silicate, and contains Ni, Co, Mn, Cr, Cu, Fe,
A method of immersing in an aqueous solution containing one or more selected from metal ions of Sn and Zn (Japanese Patent Laid-Open No. 4-1
(76875) (6) A method of using a treatment solution obtained by further adding nitric acid to permanganic acid and ultrafine silica particles (JP-A-4-202)
No. 674)

[0009]

However, it is difficult to obtain sufficient corrosion resistance by any of the above methods. That is, in order to obtain a corrosion resistance equivalent to that of a chromate film by using a silica-based coating (silica layer), a very dense silica layer must be formed on the zinc-based plating layer. In the chromate film, since the extreme surface layer of the zinc-based plating layer becomes a part of the film due to the etching of zinc during the treatment, a film having a high bonding force between the film and the plating layer and having no defect is formed. In order to give the same effect to the silica layer, it is necessary to cause a reaction in which zinc is bonded to silica via oxygen in the film formation process.

However, in the method (1), the reaction between silicic acid and zinc is hindered by the reaction between phosphate ions and zinc, so that the bonding force at the interface between the plating surface and the silica layer is not sufficient. For this reason, a dense silica layer having a level at which corrosion resistance equivalent to that of a chromate film is obtained is not formed. In addition, since the alkaline processing liquid system such as the method (2) has a lower ability to etch zinc by the liquid than the acidic aqueous solution, it is not possible to form the interface reaction layer as described above in a short time. It is difficult and also has the disadvantage that the bonding force at the interface is weak.

Similarly, in the above method (4), essential components such as a zinc etching agent for controlling a reaction interface between silica and zinc are not specified. For this reason, it is difficult to form the silica layer on the zinc-based plating layer in a dense and high-bonding state, and therefore, the corrosion resistance level is only 10% or more in a salt spray test for 72 hours or more. Not obtained.

In the above methods (5) and (6), addition of nitrate ions is essential for etching zinc, and it is necessary to form a silica layer on a zinc-based plating layer effectively. It can be said that this is an effective method. In these methods, when zinc dissolves in the acidic treatment liquid, a large amount of H ions are consumed due to the presence of nitrate ions, so that the pH of the reaction interface between the treatment liquid and the plating layer surface increases, and The stable silicate or silica sol gels. Furthermore, the hydroxide of zinc generated by the reaction and a part of the silica fine particles are bonded via oxygen. As a result, it is considered that a relatively large number of silica layers are formed on the surface of the zinc-based plating layer due to the presence of nitrate ions.

However, in the methods (5) and (6), both the fine silica particles and the silicate form fine silica particles having an amorphous structure. Rather than being present on the surface, it is merely present on the surface of the plating layer as a massive micro-dispersion. Therefore, even with these methods, it is difficult to obtain the same corrosion resistance as a chromate film.

The method (3) does not use hexavalent chromium, but cannot be said to be an original chromium-free film because the film is essentially composed of a chromium component. If trivalent chromium is also oxidized in the processing solution,
It may become valent chromium, and therefore, the problem of no pollution in terms of waste liquid treatment and the like has not been solved.

Accordingly, an object of the present invention is to solve the problems of the prior art described above, and to treat a zinc-based plated steel sheet with a chromium-free and aqueous solution-based treatment solution, thereby providing a safe, harmless, and excellent treatment. It is an object of the present invention to provide a method for producing a surface-treated steel sheet capable of producing a surface-treated steel sheet having corrosion resistance.

[0016]

The features of the present invention for solving such a problem are as follows. [1] A zinc-based plated steel sheet is treated with an acidic aqueous solution containing silicate and / or silica fine particles and Al ions and containing nitrate ions as anions and having a pH of 1.0 to 4.0, and then heated. A method for producing a surface-treated steel sheet having excellent corrosion resistance, comprising forming a chemical conversion film having a thickness of 0.005 to 2.0 μm on a plating film surface by drying.

[2] In the production method of the above [1], the acidic aqueous solution is Ca, Sr, Ba, Hf, Zr, V, Ti, C
e, La, Ni, Co, Fe, Mn, and one or more selected from water-soluble cations containing any of these metals, and are excellent in corrosion resistance. Manufacturing method of surface treated steel sheet.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limiting the same will be described below. In the method for producing a surface-treated steel sheet of the present invention, a zinc-based plated steel sheet is treated with an acidic aqueous solution containing silicate and / or silica fine particles and Al ions and containing nitrate ions as anions, and then heated and dried. Thus, a chemical conversion film having a predetermined thickness is formed on the surface of the plating film.

First, the reason why the treatment solution is an acidic aqueous solution and silicate and / or silica fine particles and nitrate ions are added to the treatment solution will be described. The silicon contained in the film formed on the surface of the zinc-based plating exists on the zinc plating as chemically stable amorphous silicon oxide, and the dense network of siloxane bonds blocks corrosion factors. It is considered to improve the white rust resistance of the zinc-based plating film. However, the zinc-based plated steel sheet is simply treated (immersion or coating) with an aqueous solution in which silica fine particles are stably present, or 100% or more.
A technique of merely performing the drying and heating treatment at a temperature of not less than ℃ does not provide a sufficient level of corrosion resistance.

For example, when a zinc-based plated steel sheet is treated with an aqueous solution based on an alkali silicate such as lithium silicate, a treatment liquid based on fine silica particles composed of five or more SiO ₂ units such as silica sol is used. In comparison, it is known that a mixture of a monomer or a dimer of SiO ₂ , which is very small particles, can be converted into a film, so that a dense film can be formed. However, even if such a dense silica layer is formed, its corrosion resistance level is not sufficient. The present inventors conducted a detailed study on the cause, and as a result, obtained the following conclusions.

That is, when the processing solution is alkaline such as an aqueous solution of an alkali silicate, the reaction with zinc saturates at a very early stage as compared with the acidic aqueous solution, and the reaction between zinc and the processing solution during the processing process. Is not enough. As a result, the bond between the zinc-based plating layer and the silica layer is not sufficiently obtained, corrosion easily proceeds from the interface between the zinc-based plating layer and the silica layer, and the zinc layer is not whitened without the silica layer's original blocking effect. Rust occurs.

Further, an alkali silicate is treated and stabilized in an acidic aqueous solution, a silicic acid sol called colloidal silica is stabilized in an acidic aqueous solution, or a hydrofluoric acid such as hydrosilicic acid is used. It has been found that a similar phenomenon occurs also in a processing solution composed of an acidic aqueous solution using fluoride. An acidic aqueous solution has higher reactivity with zinc than an alkaline aqueous solution, and dissolves or oxidizes with the generation of hydrogen. However, since zinc has a relatively large hydrogen overvoltage, a pH of about 2 to 4 at which a silicic acid sol can stably exist. In the region (1), the reaction amount of zinc is still small, so that zinc does not change to a hydroxide or oxide to improve the bonding with silica.

Based on the above findings,
As a result of examining the processing solution components effective for the reaction between the zinc-based plating and the processing solution, the presence of nitrate ions causes appropriate oxidation of zinc, and furthermore, ZnO or Zn of the zinc plating surface layer is formed on a part of the formed silica layer. It has been found that by incorporating (OH) _{2 and the} like, a sufficient bond between zinc and silica occurs. It is considered that this is because a bond via oxygen is formed between silica and zinc during the heating step performed during or after the treatment process.

The reason why the presence of nitrate ions in the treatment solution causes zinc to be oxidized appropriately is presumed as follows. That is, since nitrate ions are themselves reduced in the reaction with zinc, they act as an oxidizing agent, and more zinc can be oxidized as compared with an acidic aqueous solution to which ordinary anions are added. Further, since nitrite ions generated by reduction consume H ions, the pH of the reaction interface between the processing solution and the plating surface is easily increased, and zinc forms hydroxide and was stable in an acidic aqueous solution. Silicate and silica sol gel. As a result, gel-like silica containing water composed of a siloxane bond or a hydroxide is preferentially formed at the reaction interface between the treatment solution and the zinc-based plating film together with the hydroxide of zinc, and the dehydration treatment by heat drying treatment is performed. Later, it is conceivable that a strong bond appears at the interface. On the other hand, other oxidizing agents such as permanganate were also examined as the oxidizing agent, but it was found that nitrate ions were most suitable from the viewpoints of the stability of the processing solution and the size of the oxidizing ability.

Next, the reason why Al ions are added to the processing solution will be described. When the zinc-based plating film is treated with an acidic aqueous solution to which silicate and / or silica fine particles and nitrate ions are added, the silica layer is not treated even if the interface between the silica layer and the zinc-based plating film is sufficiently bonded. It has been found that it is difficult to form a dense film that is easily aggregated and free from defects. This is because, when the pH of the treatment liquid at the reaction interface with the zinc-based plating surface rises during the treatment, the charge balance that has repelled the silica to stabilize it in the acidic treatment liquid has a lack of H ions. This was presumed to be caused by collapse and aggregation of the silica particles.

Then, as a result of examining the added cation in the acidic treatment solution, it was found that the film forming property was improved only when Al ions were present. This is considered to be because Al ions displace a part of Si in the very surface layer portion of the silica layer during the treatment and change the charge state of the silica layer surface, and as a result, silica hardly causes aggregation. . On the other hand, among silica fine particles that are stable in an acidic aqueous solution, there is known one in which Al is added in advance to impart stability in a sol state. However, even if only the Al-modified silica fine particles are used in a treatment liquid free of Al ions, the above-described effects cannot be obtained. It is considered to be effective for improving the film properties. The form of Al ions in the treatment liquid is preferably not a complex or the like, but is preferably in the form of an aquo ion as much as possible. .

The acidic treating solution used in the present invention further comprises Ca, Sr, Ba, Hf, Zr, V, Ti, Ce, L
a, Ni, Co, Fe, and Mn, and one or more selected from water-soluble cations containing any of these metals, thereby providing more excellent white rust resistance. A zinc-based plated steel sheet can be obtained.

Here, Ca, Sr, Ba, Hf, Zr,
The metal ions of V, Ti, Ce, La, Ni, Co, Fe, and Mn, and the water-soluble cation containing any of these metals are, for example, Ca ions (divalent), Sr ions (divalent), Ba ion (divalent), Hf ion (tetravalent),
HfO ion (divalent), Zr ion (tetravalent), ZrO ion (divalent), V ion (divalent), VO ion (2
Valence), VO ₂ (monovalent), Ti ion (divalent, trivalent and tetravalent)
Valence), TiO ion (divalent), TiO ₂ ion (2
Valence), Ce ion (trivalent), La ion (trivalent), Ni
Hydrated ions that can be stably present in an acidic aqueous solution such as ions (divalent ions), Co ions (divalent), Fe ions (divalent and trivalent), and Mn ions (divalent ions) are exemplified. In addition to these, a complex ion of each of the above metals with a halogen such as Cl, phosphoric acid, carboxylic acid, boric acid or the like can be added.

In the plating film treated with the acid treatment solution to which these ions were added, the formation of a composite hydroxide containing the above elements and zinc, aluminum and some silicon was recognized together with the above amorphous silicon. ,
This is considered to contribute to the improvement of the white rust resistance of the plating film. Although the reason is not always clear, Ca, S
r, Ba, Hf, Zr, V, Ti, Ce, La, Ni,
Each of the metal ions of Co, Fe, and Mn, or a simple hydroxide formed from a water-soluble cation containing any of these metals, has a relatively wide stable region on the alkali side, and Ni, Co , Fe and Mn are also stable at the oxygen reduction potential. For this reason, first, the pH of the treatment liquid at the reaction interface is reduced by the effect of nitrate ions during the treatment.
As a result, a sparingly soluble hydroxide due to these ions is formed together with zinc, aluminum or silicate. Furthermore, even when zinc is corroded in a humid environment and in the coexistence of oxygen, a sparingly soluble compound can be maintained at the cathode site, and as a result, it is presumed to contribute to the suppression of zinc corrosion.

When Zr ion (tetravalent) and ZrO ion (divalent) are added among the above various ions,
In particular, it is effective in preventing the generation of spot rust that occurs in a relatively mild humid environment containing no salt water. This is probably because the presence of zirconium forms a film with few defects.

In the present invention, one or more selected from silicate and silica fine particles are added to the acidic aqueous solution. As the silicate to be added to the acidic treatment liquid in the present invention, a fluoride such as hexafluorosilicic acid is particularly preferable. Similarly, silica fine particles which are stable in an acidic aqueous solution (for example, Nissan Chemical "Snowtex O", "Snowtex OS",
"Snowtex OXS" etc. are suitable. In particular, when silica sol is used, it is advantageous that the particle size is as small as possible to obtain excellent corrosion resistance.
Those having a particle size of about nm are optimal.

The concentration of the silicate and / or silica fine particles in the acidic treatment liquid is not particularly limited, but is preferably about 0.010 to 3.0 mol / L in terms of SiO ₂ . If the concentration is less than 0.010 mol / L, the effect of improving the corrosion resistance by the silica cannot be sufficiently obtained, while the effect of the silica is 3.0.
If it exceeds mol / L, it becomes difficult to form a thin chemical conversion treatment film, and the film adhesion tends to deteriorate. In addition, the total concentration of the silicate and / or silica fine particles particularly preferable from such a viewpoint is 0.1 to 0.5 mol / L.

Al ions, Ca, Sr,
Ba, Hf, Zr, V, Ti, Ce, La, Ni, C
Metal ions of o, Fe, and Mn and water-soluble cations containing any of these metals are preferably added in the form of nitrates, but other than these, chlorides, acetates, sulfates, carbonates, boric acid They may be added in the form of salts, phosphates, fluorides and the like. The concentration of Al ions in the acid treatment solution is 0.001 to
Preferably it is 2.0 mol / L. If the Al ion concentration is less than 0.001 mol / L, the effect of the addition of Al ions is not sufficient. On the other hand, if the Al ion concentration exceeds 2.0 mol / L, the thickness of the obtained film becomes large and the adhesion of the film is reduced. Further, A is particularly preferable from such a viewpoint.
The l-ion concentration is 0.1 to 1.0 mol / L.

Ca, Sr, Ba, Hf, Zr, V, T
i, Ce, La, Ni, Co, Fe, Mn, each metal ion, and the total concentration in one or more kinds of acidic treatment solutions selected from water-soluble cations containing any of these metals is as follows: It is preferably 0.001 to 2.0 mol / L. When the total concentration thereof is less than 0.001 mol / L, the effect of adding the water-soluble cation is not sufficient,
On the other hand, if it exceeds 2.0 mol / L, the thickness of the obtained film becomes large, so that the adhesion of the film is reduced. From such a viewpoint, a particularly preferable total concentration is 0.01 to 1.0.
0 mol / L. The pH of the acidic treatment liquid is 1.0 to 4.
Set to 0. If the pH is less than 1.0, a poorly soluble composite oxide is less likely to be formed on the plating film, and sufficient corrosion resistance cannot be obtained. On the other hand, if the pH exceeds 4.0, silica is easily gelled, which is not preferable. In addition, a particularly preferable range of pH from such a viewpoint is 1.0 to 2.5.

The nitrate ions in the acidic treatment solution are desirably added in the form of the above-mentioned metal nitrate or as nitric acid. The concentration of the nitrate ion in the acidic treatment liquid is not particularly limited, and the p of the treatment liquid is adjusted according to the amount of the metal salt to be added.
The amount of H may be in the range of 1.0 to 4.0, but the concentration is preferably in the range of 0.001 to 6.0 mol / L. If the nitrate ion concentration is less than 0.001 mol / L, the effect of the addition of nitrate ions is not sufficient.
If the amount exceeds 0 mol / L, the etching property becomes high, so that the film becomes non-uniform and the corrosion resistance may be reduced. From such a viewpoint, a particularly preferable nitrate ion concentration is 0.01 to 1.2 mol / L. The temperature of the acidic treatment liquid is not particularly limited, either, but is preferably room temperature to 60 ° C. If the temperature is lower than room temperature, equipment such as cooling is required, which is uneconomical. If the temperature is higher than 60 ° C., water tends to evaporate, so that it becomes difficult to manage the processing liquid.

The acidic treatment liquid used in the present invention may further contain a water-dispersible resin such as an acrylic resin, an ethylene resin (polyolefin resin), an alkyd resin, an epoxy resin, a urethane resin, or the like. Soluble fumed silica, titania sol, inorganic pigments such as zirconia sol, coloring dyes such as water-soluble azo metal dyes, chelating agents such as tannic acid, thiol, etc., adversely affect the reaction between zinc and silica. It may be added to an unlimited extent.

In the present invention, the surface of the galvanized steel sheet is treated with the above-mentioned acidic aqueous solution, and then heated and dried to form a chemical conversion treatment film on the surface of the plating film. As a method of treating the galvanized steel sheet with the acid treatment solution, any method such as a coating method, a dipping method, and a spray method can be adopted.
As a coating method, any method such as a roll coater (three-roll system, two-roll system, etc.), a squeeze coater, a die coater, and the like may be used. In addition, after the coating, dipping or spraying with a squeeze coater,
It is also possible to adjust the coating amount, make the appearance uniform, and make the film thickness uniform by an air knife method or a roll drawing method.

Usually, the treatment solution with an acidic aqueous solution is dried by heating without washing with water. However, the acidic treatment solution used in the present invention forms a hardly soluble salt by reaction with the zinc-coated zinc-coated steel sheet. After the treatment, washing may be performed. The purpose of the heat-drying treatment performed after the treatment with the acidic treatment solution is to evaporate the moisture in the treatment solution attached to the plating surface. It aims to strengthen the network of chemical conversion coatings formed by dehydration condensation between zinc oxide and silica existing as.

In the heating and drying treatment, a dryer, a hot air oven,
A high-frequency induction heating furnace, an infrared furnace, or the like can be used.
The heat treatment is performed at an ultimate plate temperature of 50 to 300 ° C, preferably 1 to 300 ° C.
It is desirable to carry out in the range of 00 ° C to 200 ° C. If the heating temperature is lower than 50 ° C., a large amount of water in the film remains, and the corrosion resistance becomes insufficient. On the other hand, if the heating temperature exceeds 300 ° C., it is not only uneconomical, but also there is a possibility that a defect occurs in the film and the corrosion resistance is reduced. In the present invention, the film thickness of the chemical conversion treatment film formed after heating and drying is 0.005 to 2.
0 μm. When the film thickness is less than 0.005 μm, the coatability on the surface of the plating film is not sufficient, and local film defects occur, resulting in poor corrosion resistance. On the other hand, when the film thickness exceeds 2.0 μm, the weldability, the film adhesion, and the like deteriorate. Further, from such a viewpoint, a particularly preferable film thickness is 0.01 to 1.0 μm.

The zinc-coated steel sheet serving as the base of the surface-treated steel sheet of the present invention includes a zinc-coated steel sheet, a Zn-Ni alloy-coated steel sheet, a Zn-Fe alloy-coated steel sheet (electroplated steel sheet and galvannealed steel sheet), Zn-Cr alloy plated steel sheet, Zn-Mn alloy plated steel sheet, Zn-Co
Alloy plated steel sheet, Zn-Co-Cr alloy plated steel sheet, Z
n-Cr-Ni alloy plated steel sheet, Zn-Cr-Fe alloy plated steel sheet, Zn-Al alloy plated steel sheet (for example, Zn
-5% Al alloy-plated steel sheet, Zn-55% Al alloy-plated steel sheet), and a zinc-based composite plated steel sheet (for example, Zn-SiO ₂ ) in which a metal oxide, a polymer, and the like are dispersed in a plating film of these plated steel sheets. Dispersion-plated steel sheet) can be used.

Further, among the above-described platings, a multi-layer plated steel sheet obtained by plating two or more layers of the same type or different types may be used. Alternatively, the steel plate surface may be preliminarily plated with a thin coating of Ni or the like, and the various platings as described above may be performed thereon. As a plating method, any practicable method can be adopted among an electrolysis method (electrolysis in an aqueous solution or electrolysis in a non-aqueous solvent), a melting method, and a gas phase method.

The surface-treated steel sheet manufactured by the method of the present invention includes a steel sheet having a chemical conversion coating film formed on both sides or one side formed by the above-described treatment. Therefore, examples of the form of the surface-treated steel sheet include the following. (1) One side: Plating film-Chemical conversion treatment film, One side: Plating film (2) One surface: Plating film-Chemical conversion treatment film, One surface: Known phosphate treatment film, etc. (3) Both surfaces: Plating film-Chemical conversion treatment film

The surface of the surface-treated steel sheet produced by the method of the present invention is further coated with an organic resin film or an organic composite silicate film having a thickness of about 0.1 to 3 μm for the purpose of improving the corrosion resistance and the paintability after alkali degreasing. It may be formed with a film thickness. If the thickness of these films is less than 0.1 μm, the effect of improving the corrosion resistance after alkali degreasing and the effect of improving the coating properties are insufficient. On the other hand, if the film thickness exceeds 3 μm, the film cannot be applied to sites where spot welding or the like is performed.

[0044]

[Embodiment] Electro-galvanized steel sheet, hot-dip galvanized steel sheet and hot-dip zinc-5wt% Al-0.1wt% misch metal alloy-coated steel sheet are used as surface-treated steel sheets for home appliances, building materials and automobile parts. Was washed with water and dried after alkali degreasing. Subsequently, a treatment liquid having a composition shown in Tables 2 to 5 to which the SiO ₂ source shown in Table 1 was added was applied by a roll coater, and then dried by heating in a hot air oven.
A chemical conversion coating was formed on the surface of the plated steel sheet. The thickness of the chemical conversion coating was adjusted by the concentration of the processing solution and the temperature of the processing solution.
In addition, nitrate ions are used so that the pH of the processing solution becomes a predetermined value.
It was added to the treatment solution with nitric acid. In Tables 2 to 5, the nitrate ion concentration in the processing solution satisfying the conditions of the present invention was in the range of 0.001 to 6.0 mol / L. Tables 6 to 10 show the results of evaluating the corrosion resistance, paint adhesion, and film adhesion of the obtained surface-treated steel sheet. The drying temperature was measured by directly measuring the plate temperature with a thermocouple.

The quality performance of the surface-treated steel sheet was evaluated as follows. (1) Corrosion resistance (white rust resistance) For each sample, salt spray test (JIS-Z-23)
71) was carried out, and evaluated by the area ratio of white rust occurrence after 72 hours. The evaluation criteria are as follows. ◎: White rust occurrence area rate less than 1% ○: White rust occurrence area rate 1% or more and less than 10% △: White rust occurrence area rate 10% or more and less than 50% ×: White rust occurrence area rate 50% or more

(2) Corrosion resistance after alkali degreasing (white rust resistance) Each sample was spray-degreased with an alkali degreasing solution (“CLN364S” manufactured by Nippon Parkerizing Co., Ltd.), and then immediately washed with water and dried. This sample was subjected to a salt spray test (JIS-Z-2371), and evaluated by the area ratio of white rust occurrence after 72 hours. The evaluation criteria are as follows. ◎: White rust occurrence area rate less than 5% ○: White rust occurrence area rate 5% or more, less than 25% △: White rust occurrence area rate 25% or more, less than 50% ×: White rust occurrence area rate 50% or more

(3) Adhesiveness of paint For each sample, a melamine baking paint (film thickness 30
μm), immersed in boiling water for 2 hours, immediately cut in a grid (10 × 10 grids at 1 mm intervals), adhered and peeled with an adhesive tape, and peeled area of the coating film Rate was evaluated. The evaluation criteria are as follows. ：: No peeling ○: Peeling area rate less than 5% △: Peeling area rate 5% or more, less than 20% ×: Peeling area rate 20% or more

(4) Coating Adhesion Each sample was subjected to 0T bending, and the bent portion was SE.
M, and the film adhesion of the chemical conversion treatment film was evaluated as follows. ：: slight peeling of chemical conversion coating ×: large missing part of chemical conversion coating due to peeling

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

[Table 6]

[0055]

[Table 7]

[0056]

[Table 8]

[0057]

[Table 9]

[0058]

[Table 10]

According to Tables 6 to 10, the surface-treated steel sheets of the examples of the present invention all show excellent performance, whereas the surface-treated steel sheets of comparative examples are inferior in performance. That is, A
l solution containing no ions (treatment solutions No. 43 to No. 43).
48. However, the treatment liquid No. 46-No. No. 48 does not contain nitrate ions). 55-No.
The surface-treated steel sheet No. 60 was inferior in corrosion resistance because the effect of the addition of Al was not obtained, and the pH of the steel sheet No. 60 obtained by treating with a treatment liquid having alkaline pH (treatment liquids Nos. 52 to 56). 64-No. No. 68 obtained by treating with a surface-treated steel sheet or a treatment solution (treatment solution No. 50, No. 51) whose pH is out of the range of 1.0 to 4.0 even in the case of an acidic aqueous solution. 62, No. The surface-treated steel sheet No. 63 also has poor corrosion resistance. In addition, No. 3 in which the film thickness of the chemical conversion treatment film exceeded the range of the present invention. The surface-treated steel sheet No. 70 has poor adhesion of the chemical conversion coating. Further, No. 1 obtained by processing with a processing solution containing no nitrate ion (processing solutions No. 59 and No. 60). 71, No. The 72 surface-treated steel sheets also have poor corrosion resistance.

[0060]

As described above, the surface-treated steel sheet manufactured by the method of the present invention does not contain any chromium in the processing solution or the film component of the product at the time of manufacture, and is used for building materials, home appliances, automobiles and the like. It has high corrosion resistance as a surface-treated steel sheet, and also has excellent properties such as film adhesion and paint adhesion.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masaru Sagiyama 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (2)

[Claims] The present invention relates to a method for producing a zinc-based coated steel sheet by using a silicate and / or
Alternatively, after treatment with an acidic aqueous solution containing silica fine particles and Al ions and containing nitrate ions as anions and having a pH of 1.0 to 4.0, and then drying by heating, the thickness of the plating film on the surface of the plating film becomes 0. A method for producing a surface-treated steel sheet having excellent corrosion resistance, characterized by forming a chemical conversion coating of 005 to 2.0 μm. 2. The method according to claim 1, wherein the acidic aqueous solution is Ca, Sr, Ba, H
f, Zr, V, Ti, Ce, La, Ni, Co, Fe,
The surface-treated steel sheet having excellent corrosion resistance according to claim 1, characterized in that it contains one or two or more kinds selected from metal ions of Mn and water-soluble cations containing any of these metals. Production method.