JP2000129460A - Organic coated galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic coated galvanized steel sheet having excellent corrosion resistance (white rust resistance) and adhesion equal to those by chromate treatment without using chromium. SOLUTION: The surface of a steel sheet is provided with a galvanizing layer as a 1st layer, an amorphous film layer obtd. by applying a mixed aq. soln. of the primary phosphate of polyvalent metal and metallic oxide sols and executing drying by 0.05 to 1 g/m2 as a 2nd layer and an organic film layer by 0.5 to 2 g/m2 as a 3rd layer. As to the amorphous film as the 2nd layer, an acid aq. soln. in which metallic oxide sols are contained by 10 to 50 pts.wt. based on 100 pts.wt. polyvalent metal primary phosphate is applied, and, drying is executed at 120 to 200 deg.C. As to the organic film layer as the 3rd layer, an alkaline aq. resin soln. is applied, and, drying is executed. Into the organic film as the 3rd layer, at least one kind among the metallic oxide sols contained in the 2nd layer is incorporated by 5 to 40 pts.wt. based on 100 pts.wt. organic resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet mainly used for home appliances, which does not contain any harmful hexavalent chromium on the steel sheet and which is used in a manufacturing process.
The present invention relates to a galvanized steel sheet which has no emission of chromium (V) and has the same corrosion resistance and paint adhesion as a conventional chromate-treated steel sheet containing hexavalent chromium.

[0002]

2. Description of the Related Art Zinc-based plated steel sheets are widely used as steel sheets for home appliances, building materials and automobiles from the viewpoint of corrosion resistance.
However, zinc-based plating alone is inferior in white rust resistance,
When used as a coating base, chromate treatment or zinc phosphate treatment is usually performed because adhesion to the paint cannot be ensured. In the case of the chromate treatment, the function of suppressing white rust is great, but the adhesion to the paint is not always sufficient. In addition, there is a problem that a large amount of harmful hexavalent chromium is contained. On the other hand, in the case of the zinc phosphate treatment, the adhesion to the paint is relatively good, but when used naked, the function of suppressing white rust is extremely weak, and therefore contains the same harmful hexavalent chromium as in the normal chromate treatment. Sealing treatment is performed with the treatment liquid. A steel sheet in which a chromate layer is formed as a first layer on a zinc-based plating, and an organic coating is further provided on the chromate layer is also known. In this case, although there is no elution of hexavalent chromium, the content is not zero due to the chromate treatment, and in the manufacturing process, hexavalent chromium is inevitably discharged, which is environmentally unfavorable. No change. To solve these problems, it has been proposed to dispose the chromate layer and provide an organic coating layer directly on the galvanized layer. For example, JP-A-53-92846 proposes formation of an organic-inorganic composite film of an organic resin, a silane coupling agent and silica. Japanese Patent Application Laid-Open No. 6-316686 proposes forming a film directly on zinc plating with fine particles of a copolymer of methyl methacrylate, styrene and a crosslinkable monomer. Further, Japanese Unexamined Patent Publication No.
Japanese Patent No. 221595 proposes a treatment on zinc plating using a carbodiimide bond-containing resin. Further, Japanese Patent Application Laid-Open Nos. 8-67834 and 8-239776,
No. 267004 discloses an aqueous resin and a rust preventive, S
Alternatively, a rust-preventing composition on galvanization containing a P compound is disclosed. In each of the above examples, a relatively good corrosion resistance can be ensured by increasing the film thickness.However, when trying to obtain the same corrosion resistance as that of the chromate treatment, the film thickness becomes extremely thick, which is uneconomical. At the same time, problems such as welding and processing also occur. Furthermore, when used as a coating base, the adhesion between the top coat is good, but since there is no chromate layer or zinc phosphate layer that mediates the adhesion between the zinc and the film, the There is a problem that the adhesion is extremely poor, and in particular, the water-resistant adhesion cannot be secured at all. Japanese Patent Application Laid-Open No. Hei 5-200357 discloses that an epoxy-based silane coupling agent is added on zinc plating.
Although a method of forming a resin coating film made of a liquid reaction type epoxy resin is disclosed, also in this case, adhesion in a water-resistant environment between zinc plating and the resin coating film is not sufficient, and about 80 μm is required to ensure corrosion resistance. Need a thick film. Such a thick film has problems in weldability and workability, and is unsuitable as a general-purpose steel sheet for home appliances. In the case of zinc, the affinity of the metal surface with water or oxygen is greater than that of a metal such as iron, so even if the resin is directly adhered to the zinc surface, for example, in a water-resistant environment, water It is considered that the dissociative adsorption bond easily replaces the bond between zinc and the resin, so that it is difficult to secure adhesion. In order to improve this problem, for example, in Japanese Patent Application Laid-Open No. 58-98248,
A method is disclosed in which a lithium silicate layer is formed on a galvanized layer, and an organic-inorganic composite film is further formed thereon. However, even in this case, the performance is not always sufficient as compared with the chromate treatment.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and provides an organic-coated zinc-coated steel sheet which is excellent in corrosion resistance (white rust resistance) and adhesion as compared with chromate treatment without using chromium. The purpose is to do.

[0004]

SUMMARY OF THE INVENTION The gist of the present invention is as follows: (1) a steel sheet having a zinc-based plating layer as a first layer on the surface thereof;
As the second layer, an amorphous coating layer formed by applying and drying a mixed aqueous solution of a polyvalent metal primary phosphate and a metal oxide sol is used as a second layer.
0.5 to 1 g / m ^2, and an organic film layer as a third layer having a thickness of 0.1 g / m ² .
A galvanized steel sheet having excellent corrosion resistance, characterized by having a content of 5 to ² g / m ² . (2) The second amorphous film is a polyvalent metal monophosphate 1
The galvanized steel sheet according to the above (1), wherein an acidic aqueous solution containing 10 to 50 parts by weight of a metal oxide sol is applied to 00 parts by weight and dried at 120 to 200 ° C. (3) The zinc-plated steel sheet according to the preceding paragraph, wherein the third organic coating layer is obtained by applying and drying an alkaline aqueous resin solution. (4) The organic coating of the third layer contains at least one kind of the metal oxide sol contained in the second layer in an amount of 5 to 40 parts by weight based on 100 parts by weight of the organic resin. Galvanized steel sheet. (5) The first phosphate of the polyvalent metal in the second layer is Mg salt, A
The galvanized steel sheet according to the preceding clause, which is one or a mixture of two or more of a 1 salt, a Ca salt, a Zn salt, and a Mn salt. (6) The metal oxide sol of the second layer is one or two of silica sol, alumina sol, titania sol, and zirconia sol.
The galvanized steel sheet according to the preceding paragraph, which is a mixture of more than one kind. It is.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The zinc-coated steel sheet of the present invention has a chromate treatment with a multi-layer coating having an inorganic coating on a zinc-based plating layer and an organic coating on the inorganic coating. It achieves the same corrosion resistance and paint adhesion as in the case. Here, the zinc-based plating is not limited to any means such as electricity, melting, vapor deposition, and the like, and even if pure zinc plating is used, metals other than zinc, for example, Ni, Co, Al, M
Alloy plating with g, Mn, etc. may be used.

[0006] The coating formed on the zinc-based plating layer is essentially composed of a polyvalent metal primary phosphate and a metal oxide sol.
Of the primary phosphates (also called biphosphoric acid), Na salt, K
Salts, ammonium salts and the like need to be polyvalent metal salts because the formed film has no water resistance. In particular, Mg salts, Al salts, Ca salts, Zn salts, and Mn salts are preferred, and one of these may be used, or a mixture of two or more thereof may be used.
The metal oxide sol imparts water resistance to the film to be formed, and is essential for ensuring the adhesion to the upper organic film. Silica sol, alumina sol, titania sol, and zirconia sol are preferable. Also, a mixture of two or more kinds may be used. The preferred range of the ratio of the polyvalent metal primary phosphate and the metal oxide sol is such that the metal oxide sol is in the range of 10 to 50 parts by weight based on 100 parts by weight of the polyvalent metal primary phosphate. is there. If the amount is less than 10 parts by weight, the water resistance may decrease depending on the combination with the organic resin of the third layer. If the amount exceeds 50 parts by weight, the adhesion to the plating layer may decrease depending on the adhesion amount. That's why. In the process of applying and drying an aqueous solution of a polyvalent metal primary phosphate and metal oxide sol on a zinc-based plating, and evaporating water, Zn, primary phosphate and metal oxide It is considered that a reaction occurs with the sol, and a dense, amorphous film excellent in corrosion resistance and adhesion is formed. The weight of such a film is required to be 0.05 to 1 g / m ^2, is less than 0.05 g / m ^2, corrosion resistance is insufficient, while, in a layer as a 1 g / m ² greater Because the adhesiveness with the organic coating layer to be formed is deteriorated and the water resistance is also deteriorated,
Insufficient corrosion resistance. The drying temperature is 120 to 20 at the plate temperature.
0 ° C. is desirable, and if it is lower than 120 ° C., the water resistance may be deteriorated. On the other hand, if it is higher than 200 ° C., the coating is liable to be cracked and the corrosion resistance is easily degraded, and the load on the drying equipment is large. Further, it is also preferable to perform water cooling by water spray or the like after baking, since easily soluble components which may remain in the film are removed. The aqueous solution of primary phosphate is acidic, but in order to react more efficiently with Zn during plating, a solution in which a small amount of acid (phosphoric acid, condensed phosphoric acid, etc.) is added to lower the pH is applied. This is especially effective for plating of a molten system in which the oxide film on the plating surface is thick. In addition, various rust preventive additives and thickeners can be added.

An organic film is further formed on the above film. Thereby, not only water resistance and corrosion resistance are improved, but also fingerprint resistance and lubricity can be imparted. The organic coating layer needs to be 0.5 to ² g / m ² ,
If it is less than 5 g / m ² , the corrosion resistance is not sufficient. 2g /
exceeds m ² is not preferable electric resistance of the surface becomes too large. The organic coating is particularly preferably formed by applying and drying an alkaline aqueous resin liquid. The alkalinity is preferable in order to neutralize unreacted primary phosphate which may possibly remain in the lower amorphous film and fix it as an insoluble salt. Sex is further improved. The organic coating preferably contains the same metal oxide sol as that contained in the lower coating. Thereby, the adhesion between the lower amorphous film layer and the organic film layer is further improved. If the metal oxide sol in the amorphous film is a mixture of a plurality of sols, at least one of them may be added to the organic film layer.
The ratio of the organic resin to the metal oxide sol in the organic coating layer is preferably 5 to 40 parts by weight of the metal oxide sol based on 100 parts by weight of the solid content of the organic resin. If the amount is less than 5 parts by weight, the adhesion between the amorphous film and the organic film is not always sufficient, and the corrosion resistance is not necessarily sufficient.
If the amount exceeds 40 parts by weight, the elongation of the film is reduced, and there is a concern that the corrosion resistance of the processed portion is deteriorated, which is not preferable. The organic resin is not particularly limited, and an aqueous solution, an aqueous emulsion, or a dispersion of an acrylic resin, an olefin resin, a urethane resin, an epoxy resin, or the like can be used. Although the drying temperature is not particularly limited, it is necessary to evaporate the water at a minimum, so that a plate temperature of about 80 ° C. is required. If the resin is a thermosetting resin, the temperature may be raised to a temperature required for the reaction. However, in consideration of manufacturing facilities, it is practically preferable to be about 100 ° C. to 200 ° C. A rust preventive additive or a wax can be added to the organic coating as needed. Further, at the time of coating, it is also possible to add additives (leveling agent, thickener, defoaming agent, etc.) so as to obtain a uniform coating appearance.

[0008]

Examples of the present invention will be described below. Example 1 An electrogalvanized steel sheet (sheet thickness 0.7 mm, basis weight 20 g / m ² / one side) was used as a sample preparation base material, and after alkali spray degreasing, various primary phosphates (heavy phosphorus) were used. Aqueous solutions obtained by mixing (acid salts) and metal oxide sols at various mixing ratios were applied and dried to form films. Further, an aqueous solution adjusted to pH 9.2 by combining 100 parts by weight of an ethylene-acrylic acid copolymer-based resin and 30 parts by weight of a silica sol was further applied thereon.
After drying at a temperature of 1 ° C., a film of 1 g / m ² was formed. As a comparative chromate treatment, the same original plate was subjected to coating chromate consisting of 50% reduced chromic acid and silica sol,
One having a chromate layer of 40 mg / m ² was used.

Evaluation method “Nude corrosion resistance” After processing a flat plate and Erichsen 7 mm (in each case, the edges and the back surface are tape-sealed),
The area ratio of white rust and total discoloration after 10 days was measured by a salt water spray test according to JIS-Z-2371. (×
×; 100%, ×; 80 to 99%, Δ; 50 to 79%,
；: 20 to 49%, ◎; 1 to 20%, ◎; 0%) “Adhesion”: 20 parts of Amirac # 1000 manufactured by Kansai Paint
After μ coating, (primary adhesion) 1mm cross cut tape,
(Secondary adhesion) After immersion in boiling water for 30 minutes, further immersion in hot water at 50 ° C. for 3 days, peeling off 1 mm square tape, extruding 7 mm Erichsen after 1 mm square, and peeling off the tape. Evaluated by peeling area ratio. (Xx; 100%, x; 80-99%, △;
50-79%, ；; 20-49%, ；; 1-20%, ◎
◎; 0%) Tables 1 and 2 show the results. In the examples of the present invention, the corrosion resistance,
Although the paint adhesion was superior to or equal to that of the conventional chromate-treated steel sheet, the performance degraded when the conditions were out of the conditions specified in the present invention.

[0010]

[Table 1]

[0011]

[Table 2] (Example 2) galvanized steel sheet sample preparation preform (thickness 0.8mm, Zn60
g / m ² / one side), and after alkali degreasing, a mixed aqueous solution of 100 parts by weight of Mg biphosphate and 30 parts by weight of silica sol was applied and baked at 180 ° C. to form a 0.7 g / m ² film. Furthermore, various organic resins shown in Tables 3 and 4 were applied thereon, and dried at 100 ° C. to form films.

Evaluation method The evaluation method is the same as in the first embodiment.

Tables 3 and 4 show the results. In the examples of the present invention, both the corrosion resistance and the paint adhesion were excellent, but those deviating from the conditions specified in the present invention deteriorated some performance.

[0014]

[Table 3]

[0015]

[Table 4]

[0016]

According to the present invention, there is provided an organic-coated zinc-coated steel sheet which is excellent in both corrosion resistance (white rust resistance) and adhesion without using any chromium. This indicates that the performance of the conventional chromate-treated galvanized steel sheet could be replaced without containing harmful components, and its significance is significant.
In addition, since it is an organic coating treatment, it is excellent in fingerprints and workability compared to chromate treatment, and it can easily respond to various functional requirements by combining various additives in the organic coating. It is.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 20/06 C23C 20/06 F term (Reference) 4D075 BB24X BB24Z BB75X BB75Z BB87X CA33 DB02 DB05 DC10 DC18 EA06 EC02 4K022 AA02 AA32 BA02 BA15 BA20 BA22 BA26 BA33 CA28 DA06 EA02 4K044 AA02 AB02 BA10 BA12 BA13 BA14 BB04 BC02 BC04 CA11 CA13 CA15 CA18 CA62

Claims (6)

[Claims] 1. A non-crystalline material comprising a zinc-based plating layer as a first layer on a surface of a steel sheet, and a second layer coated and dried with a mixed aqueous solution of a polyvalent metal primary phosphate and a metal oxide sol. quality coating layer has 0.05 to 1 g / m ^2, galvanized steel sheet excellent in corrosion resistance, characterized in that the organic coating layer having 0.5 to 2 g / m ² as a third layer. 2. A second layer of an amorphous film comprising 10 to 5 parts by weight of a metal oxide sol per 100 parts by weight of a polyvalent metal monophosphate.
0 parts by weight of an acidic aqueous solution is applied,
The galvanized steel sheet according to claim 1, which is dried at 0 ° C. 3. The galvanized steel sheet according to claim 1, wherein the third organic coating layer is formed by applying and drying an alkaline aqueous resin liquid. 4. The method according to claim 1, wherein at least one of the metal oxide sols contained in the second layer is contained in the organic resin of the third layer.
The galvanized steel sheet according to any one of claims 1 to 3, wherein the content is 5 to 40 parts by weight based on 00 parts by weight. 5. The polyvalent metal primary phosphate in the second layer is M
one or two of g salt, Al salt, Ca salt, Zn salt, Mn salt
The galvanized steel sheet according to any one of claims 1 to 4, wherein the zinc-based steel sheet is a mixture of two or more kinds. 6. The metal oxide sol of the second layer is one of silica sol, alumina sol, titania sol and zirconia sol.
The galvanized steel sheet according to any one of claims 1 to 5, wherein the zinc-based steel sheet is a kind or a mixture of two or more kinds.