JPH08302489A - Highly corrosion-resistant surface-treated steel sheet and its production - Google Patents

Abstract

PURPOSE: To develop a plated steel sheet excellent in resistance to corrosion and powdering by forming an etched pit on the surface of a plate steel sheet, adsorbing a specified org. inhibitor compd, or forming a chromate film and an org. film on the surface, thereof. CONSTITUTION: A steel sheet plated with Zn, Al, etc., is treated with an aq. soln. of inorg. acid such as sulfuric acid and hydrochloric acid to form many etched pits of 0.01-10μm diameter on the plating layer surface. The sheet is then treated with an aq. soln. contg. an org. inhibitor such as alkine and alkinol to adsorb the inhibitor in the center of the pit and then dried to improve the corrosion resistance. A chromate film is formed on the plating layer at 1-200mg/m<2> , expressed in terms of metallic chromium, and further a film of thermosetting org. resin is formed in 0.1-2μm thickness and baked to further improve the corrosion resistance of the surface-treated steel sheet. Consequently, an org. composite coated steel sheet with the coated corrosion resistance and powdering resistance remarkably improved is produced.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a surface-treated steel sheet, particularly a plated steel sheet, which is suitable as a material for automobiles, home electric appliances, building materials and the like and which is excellent in corrosion resistance, especially after painting and powdering resistance. The present invention relates to an organic composite coated steel sheet and a method for manufacturing the same.

[0002]

2. Description of the Related Art Recently, in many industrial fields including automobiles, the amount of various surface-treated steel sheets, especially plated steel sheets, is increasing. Along with this, demands for performance of surface-treated steel sheets are also increasing, and particularly for automobiles, long-term high corrosion resistance such as "10-year warranty with perforation resistance" is required.

A typical surface-treated steel sheet that has already been put into practical use as an anticorrosion steel sheet for automobile bodies is a plated steel sheet, particularly a steel sheet obtained by hot dipping or electroplating zinc or a zinc alloy. However, in such a zinc-based plated steel sheet,
Corrosion resistance was still insufficient in a severe corrosive environment such as a cold region in winter where salt is sprayed to prevent road freezing.

In response to this demand, an organic composite coated steel sheet has been developed in which a plated steel sheet (particularly zinc or zinc alloy plated steel sheet) is used as a base material and a chromate film layer and a thin resin film layer are provided in this order on the base material. . This organic composite coated steel sheet has an anticorrosive effect of the chromate film and a corrosive environment blocking effect of the organic coating in addition to the anticorrosive effect of the plating film, and has overwhelmingly superior corrosion resistance among various anticorrosive steel plates ( (See, for example, Japanese Patent Laid-Open No. 64-80522).

Generally, an organic composite coated steel sheet has excellent bare corrosion resistance (that is, corrosion resistance in an unpainted state), but the organic composite coated steel sheet was further subjected to electrodeposition coating, intermediate coating and top coating. At present, the post-corrosion resistance (that is, the post-painting corrosion resistance, particularly the scratch corrosion resistance, the end face corrosion resistance, etc.) is still insufficient.

As a means for improving the corrosion resistance of the plated layer of a zinc-based electroplated steel sheet, a highly corrosion-resistant plated steel sheet in which fine particles having a corrosion-preventing ability are dispersed and co-deposited in the plated layer has been developed.

For example, Japanese Patent Laid-Open No. 2-159398 discloses poorly soluble chromate fine particles or oxide fine particles (Si).
_{O 2, Al 2 O 3,} TiO 2, ZrO 3, Cr 2 O 3, SnO 3, and a mixture of Sb ₂ O _5, etc. particulates), a monomer or polymer having a quaternary ammonium salt type cationic polar group Electrolytic plated steel sheets with high corrosion resistance obtained by electrolytic treatment with a zinc or zinc alloy plating solution containing a compound have been proposed.

Japanese Unexamined Patent Publication (Kokai) No. 2-270998 discloses Zn-Cr alloy plating with the above oxide fine particles and cationic polymer.
It has been proposed to form a plating film containing (a polymer having a quaternary ammonium salt group) by an electroplating method.

Japanese Unexamined Patent Publication (Kokai) No. 3-87399 discloses an organic composite coating excellent in corrosion resistance of a processed part, in which a chromate film and an organic film are sequentially formed on a Zn-Cr alloy electroplating film on which a cationic polymer is co-deposited. Steel plates have been proposed.

However, in all of these, an organic inhibitor having a corrosion inhibiting effect is added to the electroplating solution, and the inhibitor is co-deposited in the plated layer which has been electrodeposited to improve the corrosion resistance. In this method, the inhibitor may be decomposed by electroplating, and the rust preventive effect of the inhibitor may not be sufficiently exhibited. Further, if the amount of inhibitor co-deposition is increased in order to further improve the corrosion resistance, the composition of the plated layer tends to become non-uniform, and the plated crystal will not be dense. Therefore, the plating layer becomes brittle,
When subjected to processing, the phenomenon called powdering tends to occur, in which the plating film or organic composite coating of the processed part peels off in a powder form, which greatly reduces the corrosion resistance of the processed part, both bare corrosion resistance and post-painting corrosion resistance. .

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems associated with plated steel sheets and organic composite coated steel sheets. Specifically, the object of the present invention is a highly corrosion-resistant plated steel sheet coexisting with an organic inhibitor and an organic composite coated steel sheet using this plated steel sheet as a base material, in which peeling of the plating film of the worked portion during working occurs. It is an object of the present invention to provide a highly corrosion-resistant plated steel sheet and an organic composite-coated steel sheet which are difficult to be improved in powdering resistance. Another object of the present invention is to provide a plated steel sheet and an organic composite-coated steel sheet having improved corrosion resistance after painting.

[0012]

[Means for Solving the Problems] The present inventors diligently studied means for improving the corrosion resistance after coating of a plated steel sheet or an organic composite coated steel sheet without lowering the powdering resistance.
As a result, they have found that it is effective to lightly pickle the plated steel sheet and then treat the plated steel sheet with an aqueous solution containing an organic inhibitor having a corrosion inhibiting effect. By pickling, an etch pit is formed on the plating surface, and the organic inhibitor is adsorbed and held in the etch pit in the treatment in the next step, so that the corrosion resistance is remarkably improved.
Even if a large amount of the organic inhibitor is adsorbed on the plating layer by this method, the composition of the plating layer and the denseness of the crystal are not affected, so that the powdering resistance does not deteriorate. Further, since the electroplating has already been completed, decomposition of the organic inhibitor does not occur.

The present invention is summarized by the following (1) to (3).

(1) A total of at least one organic inhibitor compound is formed on the plated steel plate on which the etch pits are formed.
Highly corrosion-resistant plated steel sheet characterized by being adsorbed at 0.1 mg / m ² or more.

(2) The plated steel sheet is treated with an acidic aqueous solution to form an etch pit on the plated surface, and then at least 1
Treating with an aqueous solution containing a species of organic inhibitor compound to adsorb the compound at 0.1 mg / m ² or more,
Manufacturing method of high corrosion resistance plated steel sheet.

(3) On the plated surface of the high corrosion resistant plated steel sheet described in (1) above, a chromate film with a Cr deposit of 1 to 200 mg / m ² and an organic film with a film thickness of 0.1 to 2 μm are formed on the chromate film. A high corrosion-resistant organic composite coated steel sheet, which has.

[0017]

The structure and operation of the present invention will be described in detail below.
The feature of the present invention is that the plated steel sheet is subjected to a specific treatment to adsorb the organic inhibitor on the plated surface. Regarding the plated steel sheet as the base material for treatment, and the chromate film and the organic film formed on the plating layer in the organic composite coated steel sheet, the same as the conventional plated steel sheet and the organic composite coated steel sheet may be used. explain.

[0018] There is no particular limitation on the plating composition of the base metal plated steel sheet base material plated steel sheet excellent zinc or aluminum-based plated steel sheet corrosion resistance is preferable. For example, pure Zn, Zn-X alloy (X = F
Examples of the steel sheet include a plating layer of e, Co, Ni, Mn, Cr, Mg, Al), pure Al, or an Al-Mn alloy. The plating method may be any of electroplating, hot dipping, molten salt electrolytic plating, vapor plating, and either single-sided plating or double-sided plating. The amount of plating applied is not particularly limited, but 10-60 g / m ² per side for balance between workability and corrosion resistance.
Is preferably within the range.

Further, on at least one surface of the above-mentioned zinc-based or aluminum-based plated steel sheet, an electroplating layer of a thin film generally called flash plating as an upper plating layer (usually an adhesion amount of 15 g / m ² or less). May be further provided. When the plating layer immediately below is formed by the electroplating method, flash electroplating is performed only by washing with water without a drying step. When the plating layer immediately below is formed by hot dip plating or vapor phase plating, in order to activate the surface, dip it in an aqueous solution of 60 to 80 ° C containing 40 to 120 g / L NaOH, Flash electroplating is performed after washing with water to remove alkali.

Treatment with acidic aqueous solution (shape of etch pit
The plated steel sheet is treated with an acidic aqueous solution to generate etch pits on the surface of the plated layer. As a result, when the organic inhibitor is adsorbed in the next step, it becomes possible to adsorb a large amount of the inhibitor required for significantly improving the corrosion resistance on the plating film. If this step is omitted, only a very small amount of inhibitor is adsorbed on the plating film, and a sufficient effect of improving corrosion resistance cannot be obtained.

Etch pits are minute depressions having a diameter of about 0.01 to 10 μm formed when a solid surface is corroded. As long as the etch pits can be formed, the type, concentration, treatment temperature, treatment time, etc. of the acid in the acidic aqueous solution are not particularly specified. The treatment temperature may be room temperature, but if necessary, the treatment may be performed under heating. As the acidic aqueous solution, an acidic plating solution may be used in addition to the acidic aqueous solution used for pickling. The pH of the acidic aqueous solution is preferably 4 or less. As the acid, inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid which are inexpensive and easily available are preferable. Further, instead of the acid, an acid salt that exhibits acidity when dissolved in water can be used.

The treatment of the plated steel sheet with the acidic aqueous solution can be carried out by dipping or spraying. The acidic aqueous solution is not an acidic plating solution, but a simple acid aqueous solution such as a pickling solution.
In other words, in the case of an aqueous solution that does not cause electrodeposition due to energization, the galvanized steel sheet may be energized and electrolyzed in an acidic aqueous solution as in the case of electrolytic pickling or acidic electrolytic cleaning. In this case, a treatment using a plated steel sheet as an anode (anodic treatment) is preferable. After finishing the treatment with the acidic aqueous solution, it is preferable to dry the treated plated steel sheet without washing with water.

When an acidic plating solution is used as the acidic aqueous solution, the treatment is performed without electricity. In this case, it is not necessary to separately provide a treatment tank for the main treatment, and the plating tank can be used as it is for treating the acidic aqueous solution, which is efficient.
That is, after energizing the steel plate immersed in the acidic plating solution in the plating tank to form a predetermined plating film, stop energizing,
By immersing in an acidic plating solution in a non-energized state, an etch pit can be formed in the formed plating film. In the case of a continuous plating line, it can be dealt with by providing a non-energized region in the latter half of the plating tank.

The adsorbed amount of the organic inhibitor in the next step may vary depending on the depth and density of the etch pits formed by the treatment with the acidic aqueous solution. The target for the formation of etch pits is that the desired amount of inhibitor of 0.1 mg / m ² or more is adsorbed in the next step. The density of generated etch pits required for this is generally 1 × 10 ² holes / mm ² or more, and if the density is less than this, the amount of inhibitor adsorbed is too small and the corrosion resistance is insufficiently improved. Further, since the effect is saturated even if the etch pit generation density is too high, the etch pit generation density is preferably 1 × 10 ² to 1 × 10 ^8.
/ mm ² range. For example, when treated with dilute sulfuric acid, which is a typical pickling solution, a necessary number of etch pits can be formed on the surface of the plating layer in a short time of several seconds to 1 minute at room temperature.

Adsorption of Inhibitor The plated steel sheet treated with an acidic aqueous solution to form etch pits on the surface of the plating layer is treated with an aqueous solution containing an organic inhibitor having a corrosion inhibiting effect to adsorb the organic inhibitor in the etch pits. . This treatment can also be carried out by dipping or spraying. The temperature of the aqueous inhibitor solution used for the treatment is not particularly limited, but ordinary temperature is usually sufficient. Adjust the inhibitor concentration of the aqueous solution and the treatment time (line speed for continuous plating line) so that the desired amount of inhibitor of 0.1 mg / m ² or more is adsorbed to the plating film.
For example, in the case of a continuous plating line with a line speed of 40 to 200 m / sec, the inhibitor concentration of the aqueous solution used for processing is 0.
The range of 01 to 10% by weight is preferred.

If the inhibitor adsorption amount is less than 0.1 mg / m ² , the inhibitor cannot sufficiently obtain the effect of improving the corrosion resistance. The upper limit of the inhibitor adsorption amount is not particularly limited, but if it exceeds 200 mg / m ² , the inhibitor effect is saturated and it is economically disadvantageous. Therefore, the adsorption amount is
The range of 0.1 to 200 mg / m ² is preferred. From the viewpoint of performance, the more preferable inhibitor adsorption amount is 0.5 to 50 mg / m ² , especially 0.5.
The range is up to 25 mg / m ² .

The adsorption amount of the inhibitor on the plated steel sheet is determined by the amount of carbon contained in the inhibitor by a fluorescent X-ray apparatus.
(FX) or X-ray photoelectron analyzer (ESCA) can be used for measurement.

After the treatment, it is preferable to dry without washing with water. When producing an organic composite coated steel sheet, the undried plated steel sheet can be subjected to chromate treatment immediately after completion of the treatment without performing this drying, but it is possible that an inhibitor is brought into the chromate treatment liquid. Therefore, it is preferable to reduce the carried-in amount of the inhibitor by squeezing the liquid with a rubber roll or the like after the treatment with the aqueous solution of the inhibitor.

As the organic inhibitor, various conventionally known compounds can be used. Suitable organic inhibitors for use in the present invention are alkynes, alkynols, amines or salts thereof, thio compounds, heterocyclic compounds and aliphatic compounds. It is at least one compound selected from the group consisting of polycarboxylic acids or salts thereof, aromatic carboxylic acids or salts thereof, α-hydroxycarboxylic acids or salts thereof, and ligninsulfonic acid or salts thereof. These compounds will be described below.

(1) Alkyne: An organic compound containing a carbon-carbon triple bond. Specific examples include pentin, hexyne, heptin, octyne and the like.

(2) Alkynol: An organic compound in which one or more hydrogen atoms of alkyne are substituted with hydroxyl groups. Specific examples include propargyl alcohol, 1-hexyne-3-ol, 1-heptin-3-ol and the like.

(3) Amine: Any of aliphatic, alicyclic and aromatic, and any of primary amine, secondary amine and tertiary amine. Specific examples include alkyl amines such as octyl amine, nonyl amine, decyl amine, lauryl amine, tridecyl amine and cetyl amine;
Examples thereof include alkenylamines such as propenylamine and butenylamine; alicyclic amines such as cyclohexylamine; aromatic amines such as aniline and substituted aniline.

(4) Thio compound: An organic compound containing at least one sulfur atom in the molecule. Specific examples include alkyl mercaptans such as decyl mercaptan and cetyl mercaptan; dialkyl sulfides such as dimethyl sulfide; thiourea and its derivatives; thioglycolic acid.

(5) Heterocyclic compound: A cyclic organic compound containing an atom other than carbon as a constituent atom of the ring. Specific examples include pyridine, benzothiazole, benzotriazole, quinoline, indole, thiophene, pyrrole, furan, purine, and substituted derivatives thereof.

(6) Aliphatic polycarboxylic acid: An aliphatic compound containing two or more carboxyl groups in the molecule. Specific examples include citric acid, succinic acid, malonic acid, adipic acid, azelaic acid, sebacic acid and the like.

(7) Aromatic carboxylic acid: A compound having a carboxyl group bonded to an aromatic ring (benzene ring, naphthalene ring, etc.). Specific examples include benzoic acid, cinnamic acid, salicylic acid, toluic acid, and naphthalenecarboxylic acid.

(8) α-Hydroxycarboxylic acid: an aliphatic or aromatic compound in which a carboxyl group and an alcoholic hydroxyl group are bonded to the carbon at the α position. Specific examples include lactic acid, glyceric acid, tartaric acid, tropic acid, benzylic acid and the like.

(9) Lignin sulfonic acid: a sulfonated derivative of lignin produced by treating a raw material containing lignin such as wood with a solution of sulfite, bisulfite or sulfite. As a by-product of sulfite process pulp production, it is an inexpensive organic substance that is recovered in large quantities from the sulfite process waste liquid.

Of the above, amines, carboxylic acids (aliphatic polycarboxylic acids, aromatic carboxylic acids, α-hydroxycarboxylic acids) and ligninsulfonic acid are as follows:
It is also possible to use the salt. That is, in the case of amines, the acid addition salts (eg, sulfates, hydrochlorides, etc.), in the case of carboxylic acids and ligninsulfonic acid, metal salts (eg, alkali metal salts, alkaline earth metal salts, zinc salts, etc.) and It is also possible to use ammonium salts.

The plated steel sheet of the present invention obtained by the above treatment has a sufficient amount of an inhibitor having a corrosion suppressing effect adsorbed in the fine recesses (etch pits) formed by the treatment with an acidic aqueous solution, which results in a corrosion resistance ( Both the bare corrosion resistance and the post-painting corrosion resistance) are significantly improved compared to the untreated plated steel sheet. In addition, unlike the conventional eutectoid plating method in which an inhibitor is added to a plating solution to eutectoid the inhibitor on the plating layer, the inhibitor forms another inhibitor layer on the plating layer, which makes the plating layer brittle. It is possible to avoid the adverse effect that the powdering resistance is deteriorated.

In order to further enhance the corrosion resistance of the plated steel sheet treated as described above, a chromate film and an organic film may be sequentially formed on this plated layer, similarly to the conventional organic composite coated steel sheet. Also in this case, an organic composite-coated steel sheet having significantly improved corrosion resistance, particularly corrosion resistance after coating, can be obtained as compared with a case where an untreated plated steel sheet is an organic composite-coated steel sheet. The chromate film and the organic film will be described below.

Chromate Film The chromate film can be formed by any of a coating type, a reaction type and an electrolytic type, but a coating type chromate film having particularly good corrosion resistance is preferable. The coating type chromate film can be formed by applying a chromate treatment liquid by a conventional means such as a roll coater and baking it at a temperature of 80 to 250 ° C.

The chromate treatment liquid used to form the chromate film may contain Cr ⁶⁺ , and conventionally known chromate treatment liquids of various compositions can be used. In addition to Cr ⁶⁺ , this treatment liquid may contain one or more kinds of various additives such as colloidal silica, a silane coupling agent, an acid (phosphoric acid, hydrofluoric acid, etc.). The amount of chromate film deposited is 10 to 200 mg / m as the amount of metallic Cr.
² , preferably 30 to 120 mg / m ² .

Partial reduction as a coating type chromate treatment liquid
When a (two-step reduction) type chromate treatment liquid is used, film formation proceeds efficiently, and a chromate film can be formed by baking at a low temperature and / or a short time. The reduction rate of this partially reduced chromate treatment liquid is Cr ³⁺ / total Cr [= Cr ³⁺ /
The ratio of (Cr ³⁺ + Cr ⁶⁺ )] is preferably in the range of 0.4 to 0.6.

Organic film An organic resin film having a thickness of 0.1 to 2 μm is provided on the chromate film. When the thickness of the organic film is less than 0.1 μm, the corrosion resistance is insufficient, and when it exceeds 2 μm, the weldability and the electrodeposition coating property are significantly deteriorated.

This organic film can be formed by using various resin-based coating compositions that have been conventionally used for producing coated steel sheets. The organic film is industrially preferably a thermosetting resin film which is simple in apparatus and fast in film formation, but may be an ultraviolet ray or electron beam curing resin film or a room temperature curing resin film. Further, it may be a room temperature dry type or a heat dry type thermoplastic resin film.

The thermosetting organic resin film is formed by applying a thermosetting resin liquid, heating it to an appropriate temperature and baking the coating film. A preferred resin type is an epoxy resin having a dense film and excellent in corrosion resistance. In addition, acrylic resin, urethane resin, polyester resin and the like can be used.

In the resin liquid used for coating, in addition to the resin,
Contains one or more of a cross-linking agent, a solvent, an inorganic filler, pigments (rust preventive pigment, extender pigment, especially coloring pigment), plasticizer, lubricity imparting component, catalyst, reaction accelerator and the like. May be.

As the epoxy type resin which is a preferable resin type, any glycidyl ether type epoxy resin such as bisphenol A type, bisphenol F type, novolac type and brominated epoxy can be used. Further, a modified epoxy resin such as an epoxy ester resin obtained by reacting an epoxy group and a hydroxyl group in an epoxy resin with a carboxyl group in a drying oil fatty acid and a urethane modified epoxy resin obtained by reacting with an isocyanate can also be used.

In the epoxy resin liquid, the workability of the film,
A resin other than an epoxy resin may be added for the purpose of improving flexibility, lubricity, and electrodeposition coating property. For example, addition of a butyral resin for imparting flexibility to the coating, addition of a water-soluble resin for improving electrodeposition coating property, and the like. If the addition amount of non-epoxy resin is too large, the corrosion resistance will decrease, so 50% by weight of the total resin solids in the resin liquid
Below.

As the cross-linking agent for the epoxy resin, one or more known cross-linking agents such as phenol resin, amino resin, polyamide, amino polyamide, amine, blocked isocyanate and acid anhydride may be used. You can The use of the crosslinking agent further improves the corrosion resistance of the film. The addition amount of the cross-linking agent is preferably in a range such that the molar ratio of the functional group in the cross-linking agent to the total amount of the epoxy group and the hydroxy group in the epoxy resin is 0.1 to 2.

Another preferred class of thermosetting resins are polyhydroxypolyether resins. This resin is a polymer obtained by polycondensing a dihydric phenol with an approximately equimolar amount of epihalohydrin in the presence of an alkali catalyst,
Since the epoxy group completely reacts and disappears, it is not an epoxy resin, but the raw material is the same as the bisphenol A type epoxy resin and forms a resin film having high corrosion resistance comparable to that of the epoxy resin.

Examples of the inorganic filler which may be added to the resin liquid for the purpose of improving the corrosion resistance include colloidal silica and
Examples include various silicate minerals, alumina, calcium carbonate, zinc phosphate, calcium phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, and the like. The addition amount of the inorganic filler is preferably in the range of 1 to 30% by weight with respect to the resin solid content.

As the pigment, metal chromate-based rust preventive pigments such as strontium chromate and zinc chromate, which are known to show a high anticorrosion improving effect, are effective for the purpose of improving the corrosion resistance. Further, when the organic composite coating of the present invention is formed on only one side, if the uppermost resin film contains a coloring pigment and the film is colored, it becomes easy to distinguish the front and back, and it is easy for the user to work. It is convenient. As the coloring pigment, in addition to inorganic pigments such as iron oxide, titanium oxide pigment and carbon, organic pigments can be used.

A resin solution is applied onto the chromate film by an appropriate application means such as a roll coater, and if necessary, heated to cure the film to form an organic resin film. The heating temperature is 80 to 250 ° C in the case of epoxy resin, preferably 1
20-200 ℃.

[0056]

【Example】

(Example 1) Preparation of base material-plated steel sheet Various one-layer or two-layer plated steel sheets whose plating compositions are shown in Table 1 were used as a base material. In each of these plated steel sheets, the base steel sheet was a cold rolled steel sheet having a plate thickness of 0.8 mm. In the case of one-layer plating, only the plating layer shown in Table 1 as the lower-layer plating was formed, and in the case of two-layer plating, the upper-layer electroplating layer was formed by flash plating on the lower-layer plating shown in Table 1. . All plating was single-sided plating.

The plating method of the lower layer plating is as shown in the margin of Table 1. Of these, electroplating of zinc and zinc alloys was performed under the following conditions using a sulfate bath in which a plating solution was unidirectionally flowed in a plating tank.

Among the hot-dip galvanizing, the Zn-Al alloy plating was carried out by dipping in an ordinary hot-dip galvanizing bath. The Zn-Fe alloy plating was carried out by the galvannealing method, and the Al-Mn alloy plating was carried out by molten salt electrolysis. The plating method was used. Vapor plating was performed by the vacuum vapor deposition method.

All the flash plating layers of the upper layer are electroplating layers, and when the lower layer is the electroplating layer, after the electroplating of the lower layer is finished, the electroplating of the upper layer was performed without washing and only by washing with water. When the lower layer is Zn-Fe alloy plating formed by the alloying hot dip galvanizing method, the above-mentioned activation treatment is performed after the lower layer plating is finished, and then the upper layer is electroplated.

Treatment of Base Material-Plated Steel Sheet A base material-plated steel sheet having one or two plating layers shown in Table 1 was immersed in a dilute sulfuric acid aqueous solution having a concentration of 1 g / l for 1 second at room temperature.
After soaking for 1 minute, it was dried at 50 ° C. without washing with water. Then, it was immersed in an aqueous solution of the organic inhibitor shown in Table 1 at room temperature, and the plated steel sheet taken out from this aqueous solution was dried at room temperature without being washed with water. Inhibitor aqueous solution concentration 0.01 ~ 10
The adsorption amount of the inhibitor was changed by changing the soaking time within the range of g / L and the soaking time within the range of 1 to 50 seconds.

Table 1 shows the results of determination of the inhibitor adsorption amount of the plated steel sheet treated by the method of the present invention using a fluorescent X-ray apparatus. Further, when the surface of each plated steel sheet after being dipped in a dilute sulfuric acid aqueous solution and dried was observed by SEM, fine pits were observed on the surface of the plated layer, and etch pits were formed. As shown in Table 1,
By preliminarily immersing in a dilute sulfuric acid aqueous solution to form etch pits, the inhibitor could be adsorbed in a wide range of 0.1 to 300 mg / m ² .

With respect to the plated steel sheet treated in this way, the corrosion resistance after coating, that is, the corrosion resistance at the scratches and the end surface after coating,
And the powdering resistance was tested by the following method.
The results of these tests are also shown in Table 1.

[Scratch part corrosion resistance after coating] A 70 mm x 150 mm test piece was cut out, and this unprocessed flat plate was used as a degreasing agent FC4336.
After degreasing and treating with the surface conditioning solution PZT, chemical conversion treatment is performed using the phosphate treatment solution PB-L3030 (all of which are manufactured by Nippon Parkerizing Co., Ltd.), and then U-80 (manufactured by Nippon Paint Co., Ltd.). Applying cationic electrodeposition coating with a thickness of 20 ± 1μm,
It was baked at 175 ° C for 25 minutes. After that, an intermediate coating (40 μm) for an automobile alkyd coating, baking, and a top coating (40 μm) for melamine / polyester coating and baking were performed to prepare a coating test piece.

A cross-cut reaching the steel plate substrate was put on the evaluation surface (painted surface) side of this coating test piece with a cutter knife, and then salt spray (5% -NaCl, 35 ° C., 7 hours) → dry (50
A complex corrosion cycle test was conducted, in which 1 cycle of (° C, 2 hours) → wetting (RH85%, 50 ° C, 15 hours) was performed. The width of the blister in the cross-cut portion was obtained for the test piece after 30 cycles of the above corrosion cycle, and the flaw corrosion resistance after coating was evaluated in the following categories. ⊚ and ○ are passing levels.

◎: Blister width <0.5 mm ○: Blister width <1.0 mm △: Blister width <2.0 mm ×: Blister width <3.0 mm × ×: Blister width ≧ 3.0 mm.

[Corrosion resistance of end surface after coating] The punch of the test piece was punched by adjusting the clearance of the mold so that the burrs on the end surface of the test piece would be 10% of the plate thickness. Coating, intermediate coating and top coating were performed to prepare coating test pieces. This coating test piece was subjected to the above-mentioned complex corrosion cycle test.

For the evaluation, the red rust occurrence area ratio of the end face was obtained for the test piece after 60 cycles of corrosion cycle, and the end face corrosion resistance after coating was evaluated in the following categories. ⊚ and ○ are passing levels. ◎: No red rust occurred ○: 5% or less △: 10% or less ×: 30% or less XX: more than 30% [Powdering resistance] Powdering property by the amount of peeling by the tape test of the processed part after cylindrical molding drawing Was determined, and whether or not the value was close to the value when an electrogalvanized steel sheet having good powdering resistance was evaluated by the same method (good = reduction rate within 20%) was judged.

◯: Good ×: Poor

[0069]

[Table 1]

(Comparative Example 1) For comparison, the untreated one-layer or two-layer plated steel sheet of the base material was tested for corrosion resistance after coating and powdering resistance in the same manner as in Example 1.
(Test No. 1, 4 to 12). Regarding the Zn-Ni alloy-plated steel sheet, the base metal-plated steel sheet was directly treated with the inhibitor aqueous solution in the same manner as in Example 1 without treatment with the dilute sulfuric acid aqueous solution to adsorb the inhibitor on the plated film ( Test No. 2, 3).

The above test results are shown in Table 2 together with the plating species and the adhesion amount of the base material plated steel sheet and the adsorption amount of the inhibitor (Test Nos. 2 and 3).

[0072]

[Table 2]

From the comparison between Table 1 and Table 2, the following points become clear. As shown in Test Nos. 1 and 4 to 12 in Table 2, the untreated base metal-plated steel sheet has good powdering resistance,
The corrosion resistance after coating was poor, and the rust-proofing ability of parts such as flaws and end faces which were not protected by the coating film by coating was significantly reduced. In addition, in Test Nos. 2 and 3 in Table 2 in which the base metal-plated steel sheet was suddenly treated with an aqueous inhibitor solution, the inhibitor adsorption amount was less than 0.1 mg / m ² , and the inhibitor adsorption amount was too small, resulting in corrosion resistance after coating. The improvement effect was not obtained.

On the other hand, as shown in Table 1, when the base material-plated steel sheet is treated with the acidic aqueous solution and then with the inhibitor aqueous solution according to the present invention, a large amount of the inhibitor is adsorbed on the plating film. The corrosion resistance after coating was remarkably improved while maintaining good powdering resistance.

Comparative Example 2 One-layer or two-layer plated steel sheets shown in Table 3 were produced by the conventional inhibitor eutectoid plating method as follows.

On the same base steel sheet as used in Example 1,
By electroplating in a sulfuric acid / hydrochloric acid plating solution containing an inhibitor shown in Table 3, an underlayer plating film made of a zinc-based or zinc alloy in which the inhibitor was co-deposited was formed in the plating layer. In the case of two-layer plating, after completion of the lower layer plating, the upper layer flash plating was carried out by electroplating using a plating solution which did not add an inhibitor but was simply washed with water and not dried. The electroplating conditions for the lower layer and the upper layer were the same as in Example 1 except that an inhibitor was added to the lower layer plating solution.

The amount of inhibitor co-deposition in the plating layer was determined by fluorescence X
The results obtained by the wire apparatus are shown in Table 3 together with the test results of the corrosion resistance after coating and the powdering resistance, which were carried out in the same manner as in Example 1.

[0078]

[Table 3]

As can be seen from Table 3, the corrosion resistance after coating can be remarkably improved by means of eutectoid inhibitor in the plating layer. But in this case,
Poor powdering resistance. That is, when the processing is performed, the plating film in the processed portion is likely to be powdered and peeled off, and the rust preventive ability of the processed portion cannot be secured. On the other hand, in the present invention, as shown in Table 1, the corrosion resistance after coating is remarkably improved without deteriorating the powdering resistance.

(Example 2) A single-layer plated steel sheet on which a Zn plating layer was formed by the same electroplating method as in Example 1 was used as a base material and treated with a dilute sulfuric acid aqueous solution and an inhibitor aqueous solution in the same manner as in Example 1. After that, a chromate film and an organic film were formed on the plating layer as described below to obtain an organic composite-coated steel sheet (Test Nos. 1 to 4).

The chromate film was formed by a coating type chromate treatment using a commercially available partially reducing type chromate treating solution as a stock solution. A chromate treatment liquid was applied on the plated surface by a bar coater and then baked at 110 ° C. for 60 seconds.

The organic film was prepared by dissolving 65 parts by weight of a bisphenol A type epoxy resin, 15 parts by weight of a phenolic resin curing agent, 15 parts by weight of dry silica, and 5 parts by weight of a lubricating component in cyclohexanone to obtain NV (nonvolatile component) = 20. % Of the resin solution was applied onto the chromate film with a bar coater and baked at 110 ° C. for 60 seconds to cure the resin.

For comparison, using the same electric Zn-plated steel sheet as a base material, a chromate film and an organic film were formed on the plated surface of an untreated base material-plated steel sheet in the same manner as above to obtain an organic composite-coated steel sheet. (Test No. 5).

The obtained organic composite-coated steel sheet was tested for corrosion resistance after coating and powdering resistance in the same manner as in Example 1, and the results were used to show the amount of plating deposition, the amount of inhibitor species and adsorption, the amount of chromate film deposition, and the organic coating. The film thickness is shown in Table 4.

[0085]

[Table 4]

As can be seen from Table 4, when the plated steel sheet is directly coated with the chromate film and the organic film (Test No. 5 in Table 5), the powdering resistance is good, but the corrosion resistance after coating is still insufficient. Is. On the other hand, according to the present invention, when the chromate film and the organic coating were formed after the inhibitor was adsorbed on the surface of the plated steel sheet, the corrosion resistance after coating was remarkably improved while the powdering resistance was kept good.

(Comparative Example 3) By carrying out eutectoid electroplating using a plating solution containing an inhibitor as in Comparative Example 2, a Zn plating layer having an eutectoid inhibitor was prepared.
A layer-plated steel sheet was produced. Using this eutectoid plated steel sheet as a base material, a chromate film and an organic film were formed on the plated surface in the same manner as in Example 2 to obtain an organic composite coated steel sheet.

The obtained organic composite-coated steel sheet was tested for corrosion resistance after coating and powdering resistance in the same manner as in Example 1, and the results were used to show the amount of plating deposit, the amount of inhibitor species and eutectoid, the amount of chromate film deposit and the organic content. It is shown in Table 5 together with the film thickness of the film.

[0089]

[Table 5]

When a chromate film and an organic film were formed using a eutectoid plated steel sheet in which an inhibitor was co-deposited in the plating layer as a base material, the plating film became brittle and the powdering resistance became poor. Not only that, but also the corrosion resistance after painting,
Compared with the organic composite-coated steel sheet (test No. 5 in Table 5) using an untreated plated steel sheet as a base material, the corrosion resistance at the scratched portion was at the same level, and the end surface corrosion resistance was slightly deteriorated. The reason is that the plating film becomes brittle due to the eutectoid of the inhibitor, and the powdering resistance is deteriorated. In addition, since the inhibitor is difficult to be uniformly distributed, the corrosion resistance deteriorates due to the local battery action at the exposed bare surface such as the end face. Is thought to have occurred.

[0091]

According to the present invention, the corrosion resistance after coating can be significantly improved without lowering the powdering resistance of the plated steel sheet and the organic composite-coated steel sheet. This makes it possible to obtain a plated steel sheet and an organic composite-coated steel sheet that are resistant to peeling of the plating film even when subjected to processing and have excellent bare corrosion resistance as well as excellent corrosion resistance of the flaws and end faces after coating. These surface-treated steel sheets are most suitable for automobile bodies, but can of course be used for other applications such as building materials and home appliances.

Claims (3)

[Claims] 1. 0.1 mg of at least one organic inhibitor compound is formed on a plated steel plate having an etch pit formed thereon.
Highly corrosion resistant plated steel sheet characterized by being adsorbed at a rate of / m ² or more. 2. A plated steel sheet is treated with an acidic aqueous solution to form etch pits on the plated surface, and then treated with an aqueous solution containing at least one organic inhibitor compound to adsorb 0.1 mg / m ² or more of the compound. A method for producing a highly corrosion-resistant plated steel sheet, which comprises: 3. A chromate film having a Cr deposit of 1 to 200 mg / m ² and an organic film having a film thickness of 0.1 to 2 μm on the plated surface of the high corrosion resistant plated steel sheet according to claim 1. A highly corrosion-resistant organic composite coated steel sheet characterized by the above.