JPH07256816A - Organic composite coated steel panel excellent in corrosion resistance against rust slobbing from other place under alkaline condition - Google Patents

Abstract

PURPOSE:To obtain an org. composite coated steel panel excellent in corrosion resistance against rust slobbing from other places under an alkaline condition by providing a chromate treatment layer, a cation selective org. film and an arbitrary org. film on the surface of a galvenized steel panel and specifying the sum thickness of the org. films. CONSTITUTION:A chromate treatment layer is provided to the surface of a galvanized steel panel in an amt. of 10-200mg/m<2> in terms of metal chromium and a cation selective org. film with a thickness of 0.2mum or more is provided thereon as a second layer and an arbitrary org. film with a thickness of 0.2mum or more is further provided thereon as a third layer to obtain an org. composite coated steel panel wherein the sum thickness of the org. films is 2.2mum or less. As a treatment method for forming the chromate layer, any one of electrolytic type, coating type and reaction type treatment methods can be adapted but the coating type treatment method is advantageous because treatment is easiest and addition capacity can be imparted by various additives.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an automobile body, a home electric appliance,
It has excellent corrosion resistance when used unpainted or after painting, especially for construction materials, especially when it is exposed to iron rust under alkaline conditions in unpainted areas or areas where the coating does not spread well. The present invention relates to an organic composite coated steel sheet.

[0002]

2. Description of the Related Art In recent years, in cold regions such as Northern Europe and North America, corrosion of automobile bodies has become severe due to salt used for freezing in winter, and various surface-treated steel sheets have been used in place of conventional cold-rolled steel sheets. Has become. Among them, a so-called organic composite coated steel sheet, in which an organic film having a film thickness of several microns is provided on a zinc-based plated steel sheet through a chromate treatment layer, has excellent bare corrosion resistance in a salt water environment and is excellent in electrodeposition coating. It has attracted attention as a surface-treated steel sheet having both adhesion, powdering resistance during processing, and weldability. For example, JP-A-2-185436 and JP-A-4-745.
Examples thereof can be found in Japanese Patent Laid-Open No. 71, Japanese Patent Laid-Open No. 5-23638, and the like. When the organic composite-coated steel sheet is used as a material for an automobile body, even in a portion such as a door hem where electrodeposition coating is difficult to cover, the presence of the organic coating in advance can significantly delay the time until the occurrence of corrosion.

[0003]

However, recently, the corrosion resistance of an organic composite-coated steel sheet in a salt water environment is
It has been found that the organic surface is significantly inferior under conditions where it may come in contact with iron flow rust. For example, compared with the case where the organic composite steel plates are used in combination in the door as the outer plate, when the cold-rolled steel plate is used for the outer plate and the organic composite coated steel plate is used for the inner plate, the internal corrosion test by salt water The time required for perforation corrosion on the plate side, that is, on the organic composite steel plate side is about half. This is because the flow rust from the cold-rolled steel plate used for the outer plate contacts the organic surface of the inner plate. Further, even when the organic composite coated steel plate is used for both the inner and outer plates, if other parts of the vehicle body, for example, a hot rolled steel plate or the like is used as a reinforcing material for the door hinge, the flow rust from there is rust in the hem. As it accumulates and contacts the organic surfaces of the inner and outer skins, its corrosion rate is still much higher than would be expected from a laboratory salt corrosion test in the absence of iron rust.

As described above, the conventional organic composite-coated steel sheet has a problem in corrosive corrosion resistance, and none of the above-mentioned conventional techniques has solved this problem. It is an object of the present invention to provide an organic composite coated steel sheet having excellent corrosion resistance when iron rust adheres under alkaline conditions.

[0005]

In order to solve such a problem, the inventors of the present invention firstly conducted a diligent study on the corrosion mechanism of an organic composite coated steel sheet when iron rust adhered, and found that the same salt water corrosion environment. It was also found below that the mechanism of corrosion greatly differs depending on the presence or absence of iron rust. That is, under the condition that there is no iron rust, chlorine ions that have reached the zinc-based plating through the organic film gradually change zinc to chloride, but corrosion products are retained under the organic film. Due to lack of oxygen supply, pseudo equilibrium is established between zinc, chlorine, and corrosion products, and it takes a long time for corrosion to proceed. On the other hand, when iron rust is present, zinc dissolved by chlorine ions becomes ions and permeates the organic film, and is deposited as a thin film of basic zinc chloride on the coating film. The basic zinc chloride thus deposited has the function of gradually eroding the organic film. In particular, when a resin having insufficient alkali resistance is used for the coating film, this process proceeds rapidly and the organic film is destroyed in a short time,
The underlying zinc-based plating is directly exposed to corrosion factors. Furthermore, the elution of zinc ions through the organic film disrupts the pseudo-equilibrium of zinc, chlorine, and corrosion products under the coating film, so the corrosion progresses under the coating film even before the organic film is destroyed. early.

A closer examination of the zinc elution reveals that the zinc elution amount in a closed system where the corrosive liquid that comes into contact with the organic coating surface is not exchanged, for example, in the door hem away from the drain hole. The corrosive liquid tends to become alkaline (pH 11 or more) as the value increases. In such a system, when the corrosive liquid turns alkaline, zinc is rapidly eluted as zincate ions (anions), and as a result, rust corrosion of the organic composite-coated steel sheet rapidly progresses.

[0007] The inventors of the present invention have made extensive studies as to a method for improving the rust-corrosion resistance of the organic composite-coated steel sheet under such alkaline conditions. As a result, the cation selectivity between the zinc-based plating layer and the organic film is improved. It has been found that, by providing a layer containing an organic substance and / or a metal compound having the above, the elution of zinc in the presence of iron rust is suppressed and the rust corrosion resistance is significantly improved.

The present invention was made based on the above findings and has the following constitution. (1) 10 on the surface of zinc-based plated steel sheet in terms of metallic chromium
˜200 mg / m ² of chromate-treated layer, a second layer having a cation-selective organic coating having a thickness of 0.2 μm or more, and a third layer having a thickness of 0.2 μm. An organic composite-coated steel sheet having an arbitrary organic film of micron or more, and the total film thickness of the organic film is 2.2 microns or less.

(2) In the organic composite-coated steel sheet as described in (1) above, an anion-selective organic film having a thickness of 0.2 μm or more is provided between the cation-selective organic film of the second layer and the organic film of the third layer. An organic composite-coated steel sheet having a film and having a total organic film thickness of 2.2 microns or less. (3) 10 on the surface of zinc-based plated steel sheet in terms of metallic chromium
~ 200 mg / m ² of chromium oxide and hydroxide are essential, and cation-selective organic material is 10 to 300 mg / m ^2.
It has a chromate-treated layer containing 10 to 500 mg / m ^{2 of} m ² or / and a cation-selective metal acid salt in terms of metal atom, and a second layer having a thickness of 0.2 μm or more and 2.2 μm as a second layer thereon. An organic composite-coated steel sheet having any of the following organic coatings.

(4) In the organic composite-coated steel sheet according to (3) above, an anion-selective organic coating having a thickness of 0.2 μm or more is provided between the chromate-treated layer and the second organic coating. An organic composite coated steel sheet having a total film thickness of 2.2 microns or less.

[0011]

The details and reasons for limitation of the present invention will be described below. As the underlying zinc-based plated steel sheet, a zinc-plated steel sheet, a Zn-Ni alloy-plated steel sheet, a Zn-Fe alloy-plated steel sheet, a Zn-Cr alloy-plated steel sheet, a Zn-Al alloy-plated steel sheet, a Zn-Mn alloy-plated steel sheet, a Zn- Examples thereof include a Ti alloy plated steel sheet, and a zinc-based composite plated steel sheet in which a metal hydroxide, an inorganic oxide such as silica, a sparingly soluble chromate such as barium chromate, an organic polymer and the like are dispersed. Further, it may be a multi-layer plated steel sheet obtained by plating two or more layers of the same kind or different kinds among the above-mentioned plating. As the plating method, any of an electrolytic method, a melting method and a vapor phase method may be adopted.

The constitutions of the chromate layer and the organic coating layer will be described in order separately for the coating constitutions (1) to (4). In the organic composite steel sheet described as the film configuration (1), the chromate-treated layer formed on the surface of the zinc-based plated steel sheet suppresses corrosion of the zinc-based plated steel sheet due to the self-repairing action of hexavalent chromium, and is trivalent. It functions to secure the adhesion of chromium oxide and hydroxide to the organic film.

If the amount of chromate deposited is less than 10 g / m ² , the corrosion resistance is insufficient, and if it exceeds 200 mg / m ² , the weldability is impaired. The range of ^{20 to} 90 mg / m ² is preferable in order to achieve both high corrosion resistance and weldability. As a treatment method for forming a chromate layer, any of an electrolytic type, a coating type, and a reaction type can be applied, but the treatment is the easiest, and various additives can provide additional performance. The coating type is advantageous. The coating type chromate treatment has a partially reduced chromic acid aqueous solution as a main component, silica,
Treatment liquid containing one or more kinds of oxide colloids or powders such as alumina, phosphoric acids such as phosphoric acid and polyphosphoric acid, water-soluble or water-dispersible organic resins, and fluorides such as silicofluoride as necessary. Is applied to a galvanized steel sheet and dried without washing with water. The treatment may be carried out by coating with a roll coater, dipping or spraying, and then adjusting the coating amount with an air knife or a roll squeeze.

The cation-selective organic film formed as the second layer on the chromate layer formed as described above is zinc dissolved by chlorine infiltration in an alkaline salt water corrosive environment in which iron rust is present. Has the effect of preventing elution as an anion through the coating film, and is a component forming the center of the present invention. If the thickness of the cation-selective organic film of the second layer is less than 0.2 μm, the barrier effect is not sufficiently exerted, while if the total film thickness with other organic film layers exceeds 2.2 μm, welding is performed. Sex is impaired.

The resin applicable as a cation-selective organic film has a sulfone group, a carboxyl group, a phenolic hydroxyl group, a phosphone group, etc. in its molecular structure. For example, a sulfonated polystyrene-divinylbenzene copolymer, Examples thereof include phenol sulfonic acid resin, methacrylic acid-divinylbenzene copolymer, phenol carboxylic acid resin, phosphonic acid resin, and phosphonous acid resin. Further, if necessary, two or more of them may be mixed to form a multilayer structure. Further, a mixture of these resins with another resin, or a modification of another resin with these resins is also included. Examples of the modified resin include phenol modified epoxy resin.

A third layer is formed on the above cation-selective organic film.
The organic film formed as a layer is necessary for imparting adhesiveness to electrodeposition coating and for ensuring image clarity after topcoat coating. If the film thickness is less than 0.2 μm, it is difficult to secure adhesiveness. If the total film thickness with other organic coating layers exceeds 2.2 microns, the weldability will be impaired. In order to impart high weldability, adhesiveness, and corrosion-corrosion-corrosion resistance, the total thickness of the organic coating is preferably in the range of 0.5 to 1.5 μm. Also, to achieve a high degree of adhesion with the electrodeposition coating,
Advantageously, the third layer organic coating is composed of the same epoxy resin as the cationic electrodeposition coating. In this case, considering the interlayer adhesion to the cation-selective organic film of the second layer, it is preferable to use either a phenol-modified epoxy resin or a phenol sulfonic acid resin as the second layer.

Next, the organic composite coated steel sheet having the coating composition (2) will be described. The underlying zinc-based plated steel sheet, the chromate-treated layer of the first layer, and the cation-selective organic coating of the second layer are the same as those of the organic composite-coated steel sheet of coating structure (1). The anion-selective organic film provided as the third layer on the cation-selective organic film of the second layer is a zinc ion (cation) eluted under neutral to acidic conditions at the initial stage of corrosion.
It is for suppressing. By providing this layer, it is possible to secure the rust corrosion resistance of the organic composite-coated steel sheet for a longer period of time.

If the thickness of the anion-selective organic film of the third layer is less than 0.2 μm, a sufficient barrier effect is not exhibited, while the total film thickness with other organic film layers is 2.2 μm. If it exceeds, weldability is impaired. The resin applicable as the organic film of the anion-selective resin is an organic compound containing at least one of a quaternary ammonium salt, a tertiary amino group and a secondary amino group in the molecular structure, such as an amino resin and an acrylamide resin. , Polyethyleneimine resin,
Examples thereof include a polyamide resin and an anion exchange resin such as a styrene-divinylbenzene copolymer having a quaternary ammonium group bonded to a benzene ring. Also, if necessary, two or more of these may be used for mixing,
Alternatively, a multi-layer structure is also included. Further, a mixture of these resins with another resin, or a modification of another resin with these resins is also included. Examples of the modified resin include amine modified epoxy resin, polyamide modified epoxy resin, amino alkyd resin, polyamide modified alkyd resin, imide modified alkyd resin, and trisamino modified alkyd resin.

A fourth layer is formed on the anion-selective organic film.
The organic film formed as a layer is necessary for imparting adhesiveness to electrodeposition coating and for ensuring image clarity after topcoat coating. If the film thickness is less than 0.2 μm, it is difficult to secure adhesiveness. If the total film thickness with other organic coating layers exceeds 2.2 microns, the weldability will be impaired. Weldability, adhesion,
In order to highly impart corrosion resistance and rust corrosion resistance, it is desirable that the total film thickness of the organic film is in the range of 0.5 to 1.5 μm.

Further, in order to realize a high degree of adhesion with the electrodeposition coating film, it is advantageous that the organic film of the third layer is composed of the same epoxy resin as the cationic electrodeposition coating film. In this case, interlayer adhesion between the fourth layer organic film and the third layer anion-selective organic film, interlayer adhesion between the third layer anion-selective organic film and the second layer cation-selective organic film, and Considering the ion separation efficiency between the 3rd layer and the 2nd layer,
As the combination of the organic resins used for the third layer / second layer, amine modified epoxy resin / phenol modified epoxy resin, amine modified epoxy resin / phenol sulfonic acid resin, polyamide modified epoxy resin / phenol modified epoxy resin, polyamide modified epoxy resin It is preferable to use either / phenol sulfonic acid resin.

Next, the organic composite coated steel sheet having the coating composition (3) will be described. The chromate-treated layer formed on the surface of the underlying zinc-based plated steel sheet requires partially reduced chromic acid, and one of the additives in the bath shown in the description of the coating chromate of the organic composite-coated steel sheet having the film constitution (1) is used. It is formed by treating a zinc-based plated steel sheet with a treatment bath containing cation-selective organic substances and / or metal acid salts as an essential component, as well as adding more than one kind as necessary. It functions to suppress the corrosion of zinc-based plated steel sheet due to the repairing action and to secure the adhesion to the organic film due to the oxide and hydroxide of trivalent chromium, and in the alkaline salt water corrosive environment where iron rust exists, It has an effect of preventing the dissolved zinc due to the invasion of chlorine from being eluted through the coating film, and is a constituent element forming the center of the present invention. That is, in the organic composite-coated steel sheet having the coating composition (3), the cation-selective organic coating of the second layer in the organic composite-coated steel sheet having the coating composition (1) was omitted, and the function was imparted to the first chromate layer. It is a thing.

If the amount of chromate deposited is less than 10 mg / m ² , the corrosion resistance is insufficient, and if it exceeds 200 mg / m ² , the weldability is impaired. The range of ^{20 to} 90 mg / m ² is preferable for achieving both high corrosion resistance and weldability. Further, the coating method is preferable as the treatment method for forming the chromate layer. As the cation-selective organic resin to be added to the chromate treatment bath, in consideration of the stability in the bath, among those listed in the organic composite coated steel sheet having the film constitution (1),
Phenol sulfonic acid resin, sulfonated polystyrene-divinylbenzene copolymer, methacrylic acid-divinylbenzene copolymer and the like are suitable. It is also effective to add an organic phosphorus compound such as monoalkyl phosphate, dialkyl phosphate, alkylphosphonic acid or dialkylphosphonic acid as a cation-selective organic liquid to the bath.
Furthermore, as the cation-selective metal acid salt, zirconium phosphate, zirconium tungstate or the like can be applied.

The amount of the cation-selective substance applied is 10 mg.
If it is less than / m ² , a sufficient barrier effect is not exhibited, and if it is 300 mg / m ^{2 in} the case of an organic substance and 500 mg / m ^{2 in} terms of metal atom in the case of a metal acid salt, the weldability deteriorates. In order to achieve both high corrosion resistance and weldability, when adding each independently, the organic matter is 50 to 50%.
100 mg / m ² , metal acidic salt 30-200 mg / m
It is preferably in the range of ² . In addition, when both are used as a mixture, a high barrier effect is exhibited with a smaller addition amount due to a synergistic effect. When the addition amount of both is in the above range, the preferable mixing ratio of organic substance / acid salt of metal is 1 to
2, and no synergistic effect can be seen outside this range.

The organic film of the second layer formed on the above chromate-treated layer is necessary for imparting adhesion with electrodeposition coating and ensuring the image clarity after top coating, and has a film thickness of 0. If it is less than 2 microns, it is difficult to secure the adhesiveness.
If it exceeds 2 microns, the weldability is impaired. The thickness of the organic coating of the second layer is preferably in the range of 0.5 to 1.5 μm in order to impart high adhesion, sharpness and weldability.

Next, the organic composite coated steel sheet having the coating composition (4) will be described. The underlying zinc-plated steel sheet and the first chromate-treated layer are the same as those of the organic composite-coated steel sheet having the film structure (3). The anion-selective organic film provided as the second layer on the chromate-treated layer of the first layer is for suppressing zinc ions (cations) eluted under neutral to acidic conditions at the initial stage of corrosion. By providing this layer, it is possible to secure the rust corrosion resistance of the organic composite-coated steel sheet for a longer period of time.

If the thickness of the anion-selective organic film of the second layer is less than 0.2 μm, a sufficient barrier effect is not exhibited, while the total film thickness with other organic film layers is 2.2 μm. If it exceeds, weldability is impaired. The resin applicable as the anion-selective coating is the same as the organic composite-coated steel sheet having the coating structure (2). The organic film formed as the third layer on the anion-selective organic film is necessary for imparting adhesiveness with electrodeposition coating and ensuring the image clarity after the top coating, and has a film thickness of 0. If it is less than 2 microns, it is difficult to secure adhesion, and if the total film thickness with other organic coating layers exceeds 2.2 microns, weldability is impaired. Weldability, adhesion,
In order to impart high corrosion resistance to rust and corrosion, the total thickness of the organic coating is preferably in the range of 0.5 to 1.5 microns.

[0027]

EXAMPLE As a surface-treated steel sheet for automobile bodies, a zinc-based plated steel sheet was alkali degreased, washed with water, dried, subjected to chromate treatment, and then coated with an organic resin by a roll coater and baked. When the organic coating has a multi-layer structure, coating and baking were performed for each layer. The obtained organic composite-coated steel sheet was tested for rust corrosion resistance, paint adhesion, and weldability. The processing conditions of the example are as follows.

(1) Zinc-based plated steel sheet A cold-rolled steel sheet having a thickness of 0.7 mm was subjected to various zinc-based plating shown in Table 1 to obtain a processed original plate. (2) Chromate treatment method The plated steel sheet was subjected to the chromate treatment shown in Table 2.

(3) Organic resin As a cation-selective resin, phenolsulfonic acid resin, phenol-modified epoxy resin, phosphonic acid resin, methacrylic acid-divinylbenzene copolymer, dialkyl phosphate (di (2-ethylhexyl) phosphoric acid, D2E
HPA) was used as the anion-selective resin, an amine-modified epoxy resin and an acrylamide resin, and an uppermost layer epoxy resin and an olefin acrylic resin were used under the conditions shown in Tables 3 to 8, respectively.

(4) Anti-corrosion rust corrosion test After immersing the cold-rolled steel sheet in 5% saline solution at 40 ° C. and saturating it with iron rust, the test material was left unpainted and immersed in this solution 2 Time-Pulled out from the liquid and allowed to stand for 2 hours. After repeating 100 cycles, the appearance was evaluated. ◎: White rust less than 10% ○: White rust 10% or more and less than 100% △: White rust on the entire surface ×: Red rust occurred (5) Paint adhesion test Zinc phosphate treatment, electrodeposition coating (20 μm), medium After applying a coating (35 μm) and a top coating (35 μm), it was immersed in ion-exchanged water at 40 ° C. for 10 days. Engrave 100 squares on the removed test piece at 1 mm intervals,
The peeling rate was evaluated when the adhesive tape was attached and peeled.

◎: No peeling ○: Less than 5% △: 5% or more and less than 20% ×: 20% or more (6) Weldability test Using CF electrode, applied pressure 200 kgf, welding current 10 k
A continuous spotting property test was performed with A, and the number of spots was evaluated.

◎: 2000 points or more ○: 1000 points or more and less than 2000 points Δ: 500 points or more and less than 1000 points ×: Less than 500 points The performance evaluation of the various coated steel sheets described above is shown in Tables 3 to 8 The steel sheet of No. 3 shows excellent performance in corrosion resistance, rust corrosion resistance, paint adhesion, and weldability.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

[Table 6]

[0039]

[Table 7]

[0040]

[Table 8]

[0041]

As described above, according to the present invention, in addition to excellent paint adhesion and weldability, an organic composite-coated steel sheet excellent in bare corrosion resistance when iron rust adheres, which has not been solved by the prior art. Is obtained.

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Claims (8)

[Claims] 1. A zinc-plated steel sheet having a chromate-treated layer of 10 to 200 mg / m ^{2 in} terms of metallic chromium, and a cation-selective organic film having a thickness of 0.2 μm or more as a second layer thereon. And further has an organic film having a thickness of 0.2 μm or more as a third layer thereon,
An organic composite-coated steel sheet excellent in rust corrosion resistance under alkaline conditions, characterized in that the total thickness of the organic coating is 2.2 microns or less. 2. A second layer of a cation-selective organic film and a third layer.
Anion-selective organic film having a thickness of 0.2 μm or more is provided between the organic films of the layers, and the total film thickness of the organic films is 2.2.
An organic composite-coated steel sheet having a micron or less and excellent corrosion-corrosion corrosion resistance under alkaline conditions according to claim 1. 3. A cation-selective organic film of the second layer / third
The organic composite-coated steel sheet excellent in rust corrosion resistance under alkaline conditions according to claim 1, wherein the combination of the organic coatings of the layers is either phenol-modified epoxy resin / epoxy resin or phenol sulfonic acid resin / epoxy resin. 4. A combination of a cation-selective organic film / anion-selective organic film of the second layer is a phenol sulfonic acid resin / amine modified epoxy resin, phenol modified epoxy resin / amine modified epoxy resin, phenol sulfonic acid resin / polyamide. An organic composite-coated steel sheet excellent in rust corrosion resistance under alkaline conditions according to claim 2, which is either a modified epoxy resin or a phenol modified epoxy resin / polyamide modified epoxy resin. 5. The surface of the zinc-based plated steel sheet contains 10 to ²⁰⁰ mg / m ² of chromium oxide and hydroxide in terms of metallic chromium, and contains 10 to 30 cation-selective organic substances.
Has a 0 mg / m ² and / or chromate treatment layer containing 10 to 500 mg / m ² cation selective metal acid salt in terms of metal atom, the film thickness as a second layer thereon 0.
An organic composite-coated steel sheet excellent in rust corrosion resistance under alkaline conditions, which is characterized by having an arbitrary organic film of 2 microns or more and 2.2 microns or less. 6. An anion selective organic coating having a thickness of 0.2 μm or more is provided between the chromate-treated layer and the second organic coating, and the total thickness of the organic coating is 2.2 μm or less. Item 5. An organic composite-coated steel sheet excellent in rust corrosion resistance under alkaline conditions according to Item 5. 7. The ratio (cation-selective organic substance / cation-selective metal acid salt) of cation-selective organic substance and cation-selective metal acid salt (in terms of metal atom) contained in the chromate-treated layer is 1 to 2. And the total content is 300
The organic composite-coated steel sheet having excellent resistance to rust corrosion under alkaline conditions according to claim 5 or 6, which is not more than mg / m ² . 8. The alkaline composite according to claim 1, wherein in the organic composite-coated steel sheet, the uppermost organic film is a water-dispersed or solvent-type epoxy resin. Organic composite coated steel sheet with excellent rust and corrosion resistance under conditions.