JPH0752310A - Organic composite coated steel sheet - Google Patents

Abstract

PURPOSE:To provide an organic composite coated steel sheet which is excellent in blackening resistance and difficult to generate flaws or the like while good corrosion resistance is being maintained. CONSTITUTION:In an organic composite coated steel sheet, a chromate-treated layer is provided by a coating weight of 1-200mg/m<2> in conversion to metallic chromium onto a zinc and zinc alloy coating layer, and a resin film of 0.1-5mum thickness is formed on the chromate-treated layer The resin film is made of composite resin wherein copolymer of ethylene and alpha, beta-ethylene unsaturated carboxylic acid is taken as a principal chain component and a silica fine grain is contained within a range of 1-50wt.% in an ethylene ionomer resin in which 60-80% of carboxylic group is neutralized with a metallic ion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite coated steel sheet in which a chromate treatment layer and a resin coating are formed on a zinc-plated steel sheet. Such an organic composite coated steel sheet is mainly used for home electric appliances, building materials and the like.

[0002]

2. Description of the Related Art Zinc or zinc-based alloy plated steel sheet (hereinafter referred to as
Zinc-based plated steel sheet) is widely used in various industrial fields because of its excellent corrosion resistance. In particular, for household electrical appliances, the number of parts that have been previously painted and used without being applied is increasing. Therefore, not only the corrosion resistance without painting but also the good appearance without painting Is required.

Regarding the corrosion resistance, the requirement is satisfied to some extent by performing a corrosion-resistant chromate treatment in which a white rust generation time is about 100 hours in a salt spray test, instead of a general chromate treatment as a primary rust preventive. However,
When these chromate-treated steel sheets are stored in an unpainted state, especially when stored in a high temperature / humid environment, a so-called black discoloration phenomenon occurs, in which the surface partially or wholly changes its color to black over time. In some cases, there is a problem in that the product value is significantly impaired in appearance.

Blackening is considered to be an initial corrosion phenomenon, and moisture and oxygen pass through the chromate-treated film during storage,
It is believed that the formation of oxides, hydroxides, hydrated oxides, etc. on the surface layer of the plating to cause visible light to be easily absorbed and scattered is the cause of the black appearance. This reaction occurs because lead, aluminum, etc. remaining in a trace amount in the galvanized layer promotes anodization of zinc,
Foreign substances or impurities (for example, SO
₄ ^2- and Cl ^- plating bath components, such as, is further promoted by the uneven adhesion of the impurity ions or oil) in the chromate bath.

In consideration of such a phenomenon, in order to improve the blackening resistance of the zinc-based plated steel sheet, the concentration control of impurities in the plating layer, the cleaning of the surface after plating, etc. are carried out. Not enough effect has been obtained.

[0006] Against this background, in order to meet the demand for preventing blackening from the viewpoint of plating or chromate treatment, JP-A-60-63385 and JP-A-60-
Several techniques have been proposed, such as 77988 and Japanese Patent Laid-Open No. 2-8374.

[0007]

SUMMARY OF THE INVENTION In these prior arts, by stabilizing the plating layer, it is possible to suppress the non-uniform formation of the reactive chromate-treated layer which promotes the blackening reaction, and the chromate-treated or plated layer. This is intended to suppress black discoloration by improving the chromate treatment, and the effect is recognized in a relatively mild storage condition. However, in a severe environment of high temperature and humidity, the effect of suppressing black discoloration is insufficient, and it is not possible to satisfy both the blackening resistance and the fading resistance and corrosion resistance associated with the elution of chromium. Further, the steel sheets in these techniques are likely to have handling flaws in processes such as slitting and carrying, and it is not possible to avoid deterioration of corrosion resistance at those portions.

On the other hand, as a zinc-based plated steel sheet, a resin layer is provided on a chromate-treated layer, for example, Japanese Patent Laid-Open No.
Techniques such as JP-A-136840 and JP-A-2-48941 have been proposed, but none of them are aimed at improving the blackening resistance, and the actual blackening resistance is poor when actually tested. .

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems in zinc-based plated steel sheets, and as a result, formed a chromate treatment layer on the plated layer of the zinc-based plated steel sheet, and formed a resin film thereon. When forming the layer, ethylene having a thickness in a specific range and α, β-ethylenically unsaturated carboxylic acid as main chain components are used as the resin film layer, and 60 to 80% of the carboxyl groups are neutralized with metal ions. By mainly using a composite resin containing silica fine particles in the above-mentioned ethylene-based ionomer resin, while maintaining good corrosion resistance even at a low film drying temperature of 80 ° C. level, the barrier effect due to its molecular structure Improves the blackening resistance,
It was also found that the scratch resistance and the like are also improved.

The present invention was made based on the above findings, and an object thereof is to provide an organic composite-coated steel sheet which is excellent in blackening resistance and is less likely to cause defects while maintaining good corrosion resistance. To do.

[0011]

An organic composite-coated steel sheet according to the present invention is a steel sheet, a zinc or zinc-based alloy plating layer formed on the steel sheet, and is formed on this plating layer. A chromate-treated layer having a deposition amount of 200 mg / m ² and a thickness of 0.
It has a resin film of 1 to 5 μm, and this resin film is
The main chain component is a copolymer of ethylene and α, β-ethylenically unsaturated carboxylic acid, and the carboxyl group is 60-80.
The silica-based fine particles are contained in the ethylene-based ionomer resin whose% is neutralized with metal ions, and the content ratio of the silica fine particles is in the range of 1 to 50% by weight based on the total amount of the resin and the silica fine particles. That is, in the present invention, the chromate-treated layer is formed on the surface of the zinc-based plated steel sheet, and the film containing the composite resin as the main component is formed thereon.

[0012]

As the zinc-based plated steel sheet, an electro-pure galvanized steel sheet in which blackening is particularly likely to occur, and another zinc- or zinc-based alloy-plated steel sheet having a plating layer formed by the electroplating method or the hot dip coating method Can be mentioned.

The chromate treatment for forming the chromate treatment layer may be a known chromate treatment such as a reaction type, a coating type, an electrolytic type, etc., but the chromium deposition amount is 1 to 200 mg / m on one side of the steel sheet in terms of metal chromium. ² , it is necessary to form a chromate layer of 10 to 100 mg / m ² . If the adhesion amount is less than 1 mg / m ² , the corrosion resistance is insufficient, and if it exceeds 200 mg / m ² , not only the effect of improving the corrosion resistance corresponding to the amount cannot be obtained, but also bending work accompanied by deformation of the steel plate, etc. When applied,
Cohesive failure of the chromate layer is likely to occur.

As a specific example of the chromate treatment liquid, the composition of the reactive chromate treatment liquid is 1 to 100 g / l in terms of metallic chromium and a water-soluble chromium compound, and 0.2 to
One containing 20 g / l sulfuric acid as a main component, and the content of trivalent chromium in the total chromium is 50% by weight or less,
It is preferably 20 to 35% by weight or less, and if necessary, appropriate amounts of metal ions such as Zn ²⁺ , Co ²⁺ ,
It may be one in which Fe ³⁺ or the like and another mineral acid such as phosphoric acid or hydrofluoric acid are added.

Specific examples of the coating type chromate treatment liquid include silica sol having a particle size of several nm to several tens nm, fumed silica, and / or molecules in a liquid having the same composition as the above reactive chromate treatment liquid. A water-soluble organic polymer resin containing a large amount of carboxyl groups and compatible with a liquid having the same composition as the above reactive chromate treatment liquid was added, and p
The thing which adjusted H to 2.0-3.5 is mentioned. This organic polymer resin has an average molecular weight of 1,000 to 500.
It is preferably 000. The amount added is generally in the range of 0.02 to 30 g / l in terms of resin content.

In any case, the adhesion amount of the chromate layer as the first layer is, as described above, 1 in terms of metallic chromium.
It may be in the range of up to 200 mg / m ² . In the present invention, the main component of the resin film formed as the upper layer is mainly a copolymer of ethylene and α, β-ethylenically unsaturated carboxylic acid, and, if necessary, other copolymerizable components. It is an ethylene-based ionomer resin having a basic structure of a chain and 60 to 80% of carboxyl groups neutralized with metal ions. The ethylene-based ionomer resin preferably has an α, β-ethylenically unsaturated carboxylic acid content of 3 to 40 mol%.
A polymer obtained by neutralizing the carboxyl group of a copolymer of ethylene with α, β-ethylenically unsaturated carboxylic acid and other copolymer components used as necessary with a specific ion or ionic compound. is there.

Here, if the amount of α, β-ethylenically unsaturated carboxylic acid in ethylene exceeds 40 mol%, the hydrophilicity becomes high, and blackening resistance and corrosion resistance as a film are apt to decrease, which is not preferable. . On the other hand, if the amount is less than 3 mol%, the adhesive force to the steel sheet side as the base is lowered, and it is difficult to obtain a desired film.

The α, β-ethylenically unsaturated carboxylic acid in the ethylenic ionomer resin in the present invention includes acrylic acid, methacrylic acid, fumaric acid, itaconic acid, maleic acid, etc. Degeneration,
Methacrylic acid is particularly excellent in terms of quality such as corrosion resistance.

As the molecular weight of the copolymer, a weight average molecular weight of 10,000 to 200,000 is preferable, and a weight average molecular weight of 50,000 to 150,000 is particularly preferable. The ions used for neutralizing the carboxylic acid include alkali metal such as lithium, sodium and potassium, metal ion of alkaline earth metal such as magnesium and calcium, and metal compound ion such as hydroxide of transition metal. Other examples include complex ions of an organic amine and a transition metal, and sodium ions are particularly preferable from the viewpoints of blackening resistance, corrosion resistance and chemical solution stability.

The degree of neutralization is 80, assuming a low film drying temperature, for example, in-line treatment in a plating production line.
From the viewpoint of obtaining good blackening resistance and corrosion resistance even at low temperatures of the ° C level, the range is 60 to 80%. If it is less than 60%, the blackening resistance is insufficient, and if it exceeds 80%, the viscosity becomes high and the chemical solution stability is lowered, and further, the hygroscopicity becomes high, so the blackening resistance and the corrosion resistance are lowered.

In the present invention, since the resin constituting the resin layer has an ionic cross-linking structure, it is possible to prepare a water-dispersion type coating liquid without using an emulsifier which may cause deterioration of film characteristics. Therefore, the surface of the steel sheet can be easily coated with a thin film. Since the dried film strongly adheres to the base and is chemically stable, the steel sheet on which such a film is formed exhibits excellent blackening resistance and corrosion resistance. Further, since the resin film is firmly formed on this steel sheet, flaws are less likely to occur.

The above composite resin can dramatically improve the corrosion resistance by combining silica fine particles or a silane compound and silica fine particles. The silica fine particles used in the present invention have a primary particle diameter of 50 nm or less,
It is preferable to use ultrafine amorphous silica particles having a secondary particle diameter of 500 nm or less. If the primary particle diameter exceeds 50 nm, cracks will form in the coating after drying, so it will be difficult to form a dense coating, and corrosion resistance will easily deteriorate. The silica fine particles have a silanol group on the particle surface, and are classified into, for example, the following three types depending on the supply form to the market, and any of them can be applied to the present invention.

(1) Silica fine powder Generally referred to as dry silica, which has a primary particle diameter of 50 nm or less and is produced by combustion of silicon tetrachloride. This fine silica powder is used in the form of either an aqueous dispersion or an organic solvent dispersion.

(2) Organic Solvent Dispersible Silica So-called organosilica sol, which is, for example, dispersed in an organic solvent by the production method described in US Pat. No. 2,285,449 can be mentioned. That is, a silica sol obtained by substituting water in an aqueous colloidal silica dispersion with an organic solvent, in which alcohols such as methanol, isopropanol, and butyl cellosolve are used as a dispersion medium is particularly useful.

(3) Water-dispersible silica So-called colloidal silica, which is sodium dewatering of water glass (by ion exchange method, acid decomposition method, peptization method, etc.)
And has a primary particle size of 50 nm or less.
This water-dispersible silica is usually supplied as an aqueous dispersion.

The blending ratio of the silica fine particles and the ethylene ionomer resin in the present invention is in the range of 1 to 50% by weight based on the total amount of the resin and the silica fine particles, in view of corrosion resistance and flexibility of the film. To be included in. If it is less than 1% by weight, the corrosion resistance is lowered. If it exceeds 50% by weight, the effect of improving the corrosion resistance is not recognized, and since the resin liquid becomes too thick and coating becomes difficult, the film formation becomes incomplete, and the corrosion resistance and blackening resistance are deteriorated. descend.

In the present invention, the silane compound having one silicon atom and 2 to 4 silyl ether bonds in the molecule, which is compounded in the resin and reacted with the ethylene-based ionomer resin, is a silicon atom in the molecule. It is a compound in which 2 to 4 alkoxy groups, allyloxy groups, or aryloxy groups are bonded to one. Condensates of these compounds can also be used in the reaction with the ionomer resin, and the silane compound and the condensates of these compounds (hereinafter, abbreviated as reactive silane) are specifically as follows. Examples thereof include those having the structures represented by the general formulas (1) and (2). (1) General formula

[0028]

[Chemical 1] (R ₁ is an alkyl group having 1 to 8 carbon atoms which may contain an alkoxy group, an allyl group, or an aryl group, and m is 0 to 11
Is a tetraalkyl (or tetraaryl, or tetraallyl) orthosilicate or a polysilicate that is a condensate of these orthosilicates. Specifically, for example, methyl orthosilicate, ethyl orthosilicate, n-propyl orthosilicate, n-butyl orthosilicate, n-octyl orthosilicate, phenyl orthosilicate, benzyl orthosilicate, phenethyl orthosilicate, allyl orthosilicate, methallyl orthosilicate. There are silicates and the like, and polysilicates produced by dehydration condensation of these orthosilicates are also used.

[0029] (2) In formula _{(R 2) 3-n -Si-} (OR 1) n + 1 (R 1 are defined as for R ₁ in the above reduction 1, R ₂ is C1-8 Represents an optionally substituted alkyl group, an allyl group, an aryl group, or a vinyl group, and n represents 1 or 2.).

Examples of the alkyl group represented by R ₂ include a methyl group, an ethyl group, a γ-chloropropyl group, a γ-aminopropyl group, a γ- (2-aminoethyl) aminopropyl group, and a γ-glycidoxypropyl group. , Β- (3,4-epoxycyclohexyl) ethyl group, γ-methacryloyloxypropyl group and the like.

Specifically, for example, divinylethoxysilane, divinyl-β-methoxyethoxysilane, di (γ
-Glycidoxypropyl) dimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, vinyltris-β-methoxyethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, β- (3 , 4-epoxycyclohexyl) ethyltrimethoxysilane, γ-
Examples thereof include mercaptopropyltrimethoxysilane. In short, the reactive silane of the present invention may be any one as long as a hydrolyzable group ether-bonded to a silicon atom such as an alkoxy group in the reactive silane produces a silanol group and an alcohol by a hydrolysis reaction under specific conditions. Can be used as

The proportion of the reactive silane used is preferably 0.5 to 15 parts by weight, based on 100 parts by weight of the total solid content of both components of silica and the ethylene ionomer resin.
It is particularly preferable that the amount is 1 to 10 parts by weight from the viewpoint of the reaction promoting effect and the stability of the system, and if the amount is out of the preferable range, the corrosion resistance becomes poor.

The method for synthesizing the composite resin in the present invention is not particularly limited, but the following method is usually adopted. First, an ethylene-based ionomer resin is dissolved or dispersed in a hydrophilic solvent such as an alcohol-based solvent or a solvent composed mainly of water to a solid content of 40% by weight or less, and silica particles and a reactive silane are added while stirring this. . Then, a basic hydrolysis catalyst (metal hydroxide, ammonia, amines) or water is added as necessary to cause a reaction.

In producing the composite resin of the present invention, first of all, it is an essential condition that the reactive silane is hydrolyzed to form a silanol group.
By reacting at a temperature of not less than 0 ° C and not more than the boiling point, a composite resin can be obtained by hydrolysis and condensation reaction. From the viewpoint of obtaining a tough film, it is desirable to continuously heat the mixed solution at a temperature of 50 ° C. or higher and a boiling point of the solvent or water, and specifically, to heat both at 50 to 90 ° C. The components can be combined well.

In the present invention, instead of the above silica, chromic anhydride (CrO ₃ ), strontium chromate (SrCrO ₄ ), barium chromate (BaCrO ₃ ).
₄ ), lead chromate (PbCrO ₄ ), basic zinc chromate (ZnCrO ₄ .4Zn (OH) ₂ ) or other hexavalent chromium compound or chromium chromate compound is added to the coating in an amount of 50% by weight or less. May be. It is also possible to add silica and a chromium compound in a total amount of 50% by weight or less.

Further, the composite resin may be mixed with a lubricating substance such as wax to impart lubricity. Further, it is also possible to impart conductivity by mixing a conductive substance in the above composite resin, whereby electric weldability,
It is possible to improve the electrophoretic coating property and further the grounding property of the film. Examples of such conductive substances include zinc, aluminum, iron, cobalt, nickel, manganese, chromium, molybdenum, tungsten, copper, lead,
Examples thereof include metal powders such as tin and alloy powders thereof, aluminum-doped zinc oxide powders, semiconductor oxides such as tin oxide-titanium oxide, tin oxide-barium sulfate, and nickel oxide-alumina.

In addition, Japanese Patent Publication No.
-Chelates such as titanium, zirconium and aluminum as described in JP-B-41711, or JP-B-57-30867 and JP-B-55-6297.
The curability can be improved by using the oxyacid salts, metal salts, and the like as described in JP-A-1 in combination.

Further, it is also possible to disperse pigments or dyes usually used in the field of paints to obtain a composition for forming a colored film. The thickness of the composite resin film in the present invention is in the range of 0.1 μm to 5 μm, preferably 0.
It is in the range of 3 μm to 3 μm. If it is less than 0.1 μm, not only a barrier effect against corrosion resistance and blackening resistance cannot be expected, but also scratches due to handling cannot be prevented. On the other hand, if it exceeds 5 μm, peeling of the coating tends to occur when subjected to severe processing.

The composite resin film can be formed, for example, by the following method. That is, first, a coating liquid of the composition containing the composite resin as a main component is applied by a known coating method such as a roll coater, a curtain flow coater, or a spray, or a galvanized steel sheet is dipped in these coating liquids. Then, the adhered amount is controlled by a roll or air blowing, and then this is dried. Drying may be performed at room temperature, but normally, the temperature of the steel sheet is 60 to 250 by a hot air stove or an induction heating device.
C., preferably by heating to 80.degree. C. to 200.degree. When the drying temperature is lower than 60 ° C., the film is not sufficiently dried, and it is difficult to obtain sufficient corrosion resistance and blackening resistance. Further, if the temperature exceeds 250 ° C., the resin film is deteriorated due to heat and the voids are generated, which is not preferable.

[0040]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. In the following description, “parts” and “%” are based on weight, unless otherwise specified (mol%, degree of neutralization). (Synthesis Example of Composite Resin) First, the synthesis method of the base resin will be described. Ethylene with a methacrylic acid content of 20 mol%
Methacrylic acid copolymer neutralized with sodium hydroxide to 70
% Neutralized resin, effective volume 1 maintained at 170 ° C
Dissolve 4k of the above resin in an 8-liter homomixer.
Water is supplied at a flow rate of g / hr and water is supplied at a flow rate of 18 liters / hr, and strong stirring is performed to produce a water-dispersed resin liquid, while the water-dispersed resin liquid is kept so as to keep the liquid surface constant. It was taken out continuously. As a result, a water-dispersed resin liquid A containing no emulsifier and having a solid content of 20.4% was obtained. Further, resin liquids having different kinds of copolymers, neutralized metal ions, and different degrees of neutralization were also synthesized under basically the same conditions. Other resins containing an emulsifier were also synthesized as the resins used in Comparative Examples.
The resins are specified in Tables 1 and 2 described later.

Then, various additives such as a silane compound and silica were added to this resin to obtain a composite resin composition. As an example, 4.1 parts of fumed silica (Nippon Aerosil Co., Ltd., trade name Aerosil 300, primary particle size 7 nm) is charged with 100 parts of Resin A charged in a flask and sufficiently stirred at room temperature. Was gradually added in about 10 minutes. After addition, γ-methacryloxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM50
3) 1.0 part of the mixture was dropped and mixed under stirring, then heated to 85 ° C. and kept at that temperature for 2 hours for reaction to obtain a composite resin composition.

(Examples 1 to 23) A reaction chromate treatment or a coating-type chromate treatment was performed on a plated layer of an electrogalvanized steel sheet having a plate thickness of 0.8 mm and a plating amount of 20 g / m ² , and then dried and adhered. A chromate-treated layer having an amount of 10 to 200 mg / m ² was formed. Then, on the chromate-treated layer, the composite resin composition synthesized in the above-described Synthesis Example or an aqueous dispersion obtained by adding a silane compound and silica to the composite resin composition was applied by a roll coater. Then, the coating liquid was dried by heating in a hot-air drying oven until the temperature of the steel plate reached 80 ° C. to form a resin film layer. Table 1 shows conditions in each example.

Comparative Examples 1 to 13 Using electrogalvanized steel sheets under the same conditions as in Examples, a chromate-treated layer having an adhesion amount of 40 mg / m ² was formed on the plated layer by reactive chromate treatment. Various resin coating layers were formed on the chromate-treated layer under the conditions shown in Table 2.

The chromate deposits in Tables 1 and 2 are
The amount of metal chromium is displayed, and the silica content in the resin coating layer is% by weight when the total amount of the resin and silica is 100% by weight, and the content of the silane compound is the total amount of the resin and silica. It is expressed in parts by weight when the amount is 100 parts by weight. The symbols in the resin type column are as follows: A: Resin of Synthesis Example B: Ethylene-acrylic acid copolymer, Na-neutralized ionomer C: Ethylene-acrylic acid copolymer, Zn-neutralized ionomer D: Ethylene- Fumaric acid copolymer, Na-neutralized ionomer E: Ethylene-maleic acid copolymer, Na-neutralized ionomer F: Ethylene-itaconic acid copolymer, Na-neutralized ionomer G: Ethylene-acrylic acid copolymer (with emulsifier) ) H: Acrylic resin emulsion (with emulsifier) I: Epoxy resin emulsion (with emulsifier) J: Water-soluble urethane resin (with emulsifier) K: Vinyl acetate-acrylic acid copolymer (with emulsifier) L: Ethylene-vinyl acetate copolymer Polymer (with emulsifier) All of G to L are aqueous coating solutions using an emulsifier.

The blackening resistance and corrosion resistance of the thus obtained organic composite zinc-based plated steel sheets of Examples and Comparative Examples were evaluated by the following test methods. The results are shown in Tables 1 and 2.

(1) Blackening resistance It is left for 60 days in a high temperature humid environment of 50 ° C. and 95% RH,
The blackening resistance was evaluated from the difference in L value (JIS Z8730 6.3.2 (1980), lightness index in Hunter's color difference formula) of the steel sheet before and after the test.

(2) Corrosion resistance A salt spray test based on JIS Z2371 was carried out, and the white rust generation area ratio after 240 hours was measured to evaluate the corrosion resistance.

As is clear from Table 1, Examples 1 to 23
In all, good blackening resistance and corrosion resistance were exhibited. In particular, Examples 1 to 13 using an ethylene-methacrylic acid copolymer as the ethylene-based ionomer resin showed particularly good blackening resistance, and Examples 1 to 6, 8 among Examples containing a silica or silane compound. , 9, 12 to 18 have been confirmed to exhibit particularly good corrosion resistance.

On the other hand, as is clear from Table 2, Comparative Examples 1 to 13 did not satisfy both the blackening resistance and the corrosion resistance. That is, Comparative Examples 1 and 2 have a neutralization degree of
Comparative Example 3 has a resin film thickness, Comparative Examples 4 and 12 have a silica content, and Comparative Examples 5 to 11 have a resin type of the resin film.
In Comparative Example 13, the film thickness of the resin film deviates from the present invention. Comparative Examples 1, 6 and 13 have good corrosion resistance but poor blackening resistance, and Comparative Example 4 has good blackening resistance but poor corrosion resistance.
The other comparative examples were not satisfactory in corrosion resistance and blackening resistance.

FIG. 1 shows the neutralization degree of the base resin and the blackening resistance of Examples 1 to 3 and Comparative Examples 1 and 2, with the horizontal axis representing the degree of neutralization and the vertical axis representing the degree of blackening resistance. Shows the relationship with.
From this figure, it was confirmed that particularly excellent blackening resistance is exhibited at a neutralization degree of 60 to 80%.

Regarding the effect of the film thickness of the resin film on the blackening resistance, from Examples 1, 7 and 8 and Comparative Examples 3 and 13, the film thickness of 0.3 μm to 3.0 μm was particularly excellent. Although it showed resistance to blackening, it was confirmed that when the film thickness was out of the range of the present invention of 0.05 μm, corrosion resistance and blackening resistance were inferior, and when it was out of the range of 7.0 μm, the black resistance was inferior.

Further, as for the base resin, when the base resin other than the ethylene-based ionomer resin is used as described above, the blackening resistance is inferior as in Comparative Examples 5 to 11, but the ethylene-based ionomer resin is used as the base resin. By so doing, good blackening resistance can be obtained as in Examples 1 to 23. Moreover, even though the same ethylene-based ionomer resin was used, an example using methacrylic acid was compared with Examples 14 to 18 in which α, β-ethylenically unsaturated carboxylic acid other than methacrylic acid was used as the copolymer component. It can be seen that 2 shows a particularly excellent resistance to blackening.

[0053]

As described in detail above, according to the organic composite coated steel sheet of the present invention, by using a specific resin film, excellent corrosion resistance is maintained and blackening resistance is excellent.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

[Brief description of drawings]

FIG. 1 is a graph showing the effect of the degree of neutralization on blackening resistance.

Claims (7)

[Claims] 1. A steel sheet, a zinc or zinc-based alloy plating layer applied on the steel sheet, and a chromate treatment layer formed on the plating layer and having an adhesion amount of 1 to 200 mg / m ^{2 in} terms of metallic chromium. And a resin film having a thickness of 0.1 to 5 μm formed on the chromate-treated layer, the resin film comprising a copolymer of ethylene and an α, β-ethylenically unsaturated carboxylic acid as a main chain component. And 60 of the carboxyl group
Characterized in that silica particles are included in an ethylene-based ionomer resin having 80% to 80% neutralized with metal ions, and the content ratio of the silica particles is in the range of 1 to 50% by weight based on the total amount of the resin and the silica particles. Organic composite coated steel sheet. 2. The organic composite coating according to claim 1, wherein the content of the α, β-ethylenically unsaturated carboxylic acid in the ethylenic ionomer resin in the resin film is 3 to 40 mol%. steel sheet. 3. The organic composite-coated steel sheet according to claim 1 or 2, wherein the α, β-ethylenically unsaturated carboxylic acid in the ethylene-based ionomer resin in the resin film is methacrylic acid. 4. The organic composite-coated steel sheet according to claim 1, wherein the metal ions in the ethylene ionomer resin in the resin film are sodium ions. 5. The ethylene-based ionomer resin in the resin film comprises a silane compound having one silicon atom and 2 to 4 silyl ether bonds in the molecule and / or a condensate thereof, both silica and resin. Total solid content of ingredients 100
The organic composite-coated steel sheet according to any one of claims 1 to 4, which is a composition containing 0.5 to 15 parts by weight with respect to parts by weight. 6. The silica fine particles in the resin film,
Fumed silica or colloidal silica having a primary particle size of 50 nm or less is used, and the organic composite-coated steel sheet according to any one of claims 1 to 5, wherein: 7. The resin film is formed by applying a water-dispersible resin containing the composite resin as a main component and containing no emulsifier, and drying at a plate temperature of 60 to 250 ° C. Item 7. The organic composite-coated steel sheet according to any one of Items 1 to 6.