JPH09187884A - Organic composite coated steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an organic composite coated steel plate with an excellent anti-blackened modification, paint adhesiveness, and also lubricating ability while maintaining good corrosion resistivity. SOLUTION: There is each provided a steel plate given a zinc or zinc alloy plated layer, a chromate finished layer having an adhesion quantity in the range of 1-200mg/m<2> at metallic chrome conversion, and a resin film formed in the range of a thickness of 0.1-5μm on the chromate finished layer, wherein the resin layer has as a primary component a composite resin comprising (A) a reaction product of ethylene ionomer resin with an epoxy group containing compound of 60-99wt.%, and (B) silica fine particles of 1-40wt.%.

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 used for home electric appliances or building materials.

[0002]

2. Description of the Related Art An organic composite coated steel sheet in which a chromate treatment layer and a resin film are formed on a zinc or zinc-based alloy-coated steel sheet (hereinafter abbreviated as zinc-based steel sheet) has excellent corrosion resistance and fingerprint resistance. Therefore, it is widely used in various industrial fields.

[0003] Such an organic composite coated steel sheet is often used without painting, and is required to have not only corrosion resistance without painting but also good appearance without painting. With regard to corrosion resistance, the requirements have been met to some extent by using an organic composite coated steel sheet having a chromate layer as a lower layer and a resin coating layer as an upper layer.

[0004] However, when these organic composite coated steel sheets are stored in an unpainted state, particularly when stored in a high-temperature and humid environment, the surface is partially or entirely blackened over time, a so-called discoloration. A blackening phenomenon may occur, which causes a problem that the commercial value is significantly impaired in appearance. Further, since the organic composite coated steel sheet may be used after being coated, it is also necessary to have paint adhesion at the same time.

That is, it is required to satisfy all of corrosion resistance, blackening resistance and paint adhesion.

[0006] Against this background, the following techniques have been proposed.

(1) JP-A-5-220445 (hereinafter referred to as Prior Art 1) (2) JP-A-7-52310 (hereinafter referred to as Prior Art 2)
These technologies disclose a technique for improving the blackening resistance of an organic composite coated steel sheet by providing a resin layer based on an ethylene ionomer resin as an upper layer.

(3) JP-A-4-61966 (hereinafter referred to as prior art 3) (4) JP-A-4-290582 (hereinafter referred to as prior art 4) These include ethylene and unsaturated carboxylic acid. There is disclosed a technique for improving the paint adhesion of an organic composite coated steel sheet by providing a resin layer based on an acid copolymer as an upper layer.

[0009]

However, the above-mentioned prior art has the following problems.

That is, in the prior arts 1 and 2, although it is possible to improve the blackening resistance of the organic composite-coated steel sheet by having the resin layer based on the ethylene-based ionomer resin as the upper layer, it is possible with these techniques. The produced steel sheet has insufficient paint adhesion.

Further, in the prior arts 3 and 4, a copolymer layer of ethylene and an unsaturated carboxylic acid is used as a base, and a resin layer containing a lubricant is provided as an upper layer, so that the paint adhesion of the organic composite coated steel sheet and the Although the lubricity can be improved, the blackening resistance of the steel sheets produced by these techniques is insufficient.

As described above, the prior art has not yet provided an organic composite coated steel sheet satisfying all of corrosion resistance, blackening resistance and paint adhesion.

The present invention has been made in view of the above circumstances, and is one in which black corrosion resistance, while maintaining good corrosion resistance,
It is an object of the present invention to provide an organic composite coated steel sheet having excellent paint adhesion.

[0014]

In order to solve the above-mentioned problems, the present invention provides a steel sheet coated with a zinc or zinc-based alloy plating layer and a steel sheet formed on the plating layer of the steel sheet. A chromate-treated layer having a coverage in the range of ˜200 mg / m ² and a thickness of 0.1 on the chromate-treated layer.
To a resin film formed in the range of 5 μm, the resin film being a reaction product of (A) an ethylene-based ionomer resin and an epoxy group-containing compound: 60 to 99% by weight,
(B) Silica fine particles: An organic composite-coated steel sheet comprising a composite resin composed of 1 to 40% by weight as a main component.

Further, the present invention provides an organic composite coated steel sheet wherein the unsaturated carboxylic acid in the ethylene ionomer resin in the resin film is methacrylic acid.

Further, there is provided the organic composite-coated steel sheet described above, wherein the epoxy group-containing compound in the resin film is a diglycidyl ether or polyglycidyl ether of a polyhydric alcohol.

Furthermore, in the reaction product of the ethylene ionomer resin and the epoxy group-containing compound in the resin coating, the ratio of the epoxy group containing compound is 0.1 to 30 parts by weight based on 100 parts by weight of the ethylene ionomer resin. An organic composite coated steel sheet is provided.

As a result of intensive studies to solve the above problems in the organic composite coated steel sheet, the present inventors formed a chromate treatment layer on the plating layer of the zinc-based plated steel sheet,
It has been found that by forming a special resin layer on it, it is possible to obtain an organic composite-coated steel sheet that is excellent in blackening resistance and is also excellent in paint adhesion while maintaining good corrosion resistance. That is, by forming a film having a specific range of thickness on the chromate-treated layer having a predetermined thickness, the main component of which is a reaction product of an ethylene ionomer resin and an epoxy group-containing compound, its molecular structure It has been found that due to the high adhesion due to the above, not only the blackening resistance but also the paint adhesion is improved. The present invention was made based on such findings of the present inventors.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a chromate-treated layer is formed on the surface of a zinc-based plated steel sheet, and a reaction product of (A) an ethylene-based ionomer resin and an epoxy group-containing compound thereon: 60 to 99 weight. %, (B) fine silica particles: 1 to 40% by weight, and a resin film containing a composite resin as a main component is formed.

In the present invention, the main component of the resin formed as the upper layer is a reaction product of an ethylene-based ionomer resin and an epoxy group-containing compound.

The ethylene ionomer resin is a polymer having a polymer main chain composed mainly of hydrocarbons, having a carboxyl group in the side chain, and at least a part of the carboxyl group being neutralized with a metal cation. is there. Specific examples of the ionomer resin include a partially neutralized product of a copolymer of ethylene and an unsaturated carboxylic acid, wherein at least a part of the carboxyl group contained in the copolymer is neutralized with a metal cation.

Examples of the unsaturated carboxylic acid which is a component of the ethylene-unsaturated carboxylic acid copolymer include those having 3 to 8 carbon atoms. Specific examples of the unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, isocrotonic acid, allylsuccinic acid, mesaconic acid, glutaconic acid, and nadic acid ( Endocis-bicyclo [2,2,1]
Hept-2-ene-5,6-dicarboxylic acid), methylnadic acid, tetrahydrophthalic acid, methylhexanehydrophthalic acid, and the like. Of these, methacrylic acid is particularly preferred.

The ethylene-unsaturated carboxylic acid copolymer constituting the main skeleton of the ethylene-based ionomer resin may contain a third component in addition to ethylene and the unsaturated carboxylic acid. As the third component, unsaturated carboxylic esters such as methyl (meth) acrylate, ethyl (meth) acrylate, and isopropyl (meth) acrylate;
And vinyl esters such as vinyl acetate.

The ethylene content of the ethylene-unsaturated carboxylic acid copolymer is usually 95 to 60% by weight.
And preferably 92 to 75% by weight. The content of the unsaturated carboxylic acid is usually from 5 to 40% by weight, and particularly preferably from 8 to 25% by weight. When the ethylene-unsaturated carboxylic acid copolymer contains a third component, the third component is preferably present in an amount of 40% by weight or less.

In the ethylene ionomer resin of the present invention, examples of the metal cation neutralizing at least a part of the carboxyl group in the side chain of the ethylene-unsaturated carboxylic acid copolymer include, for example, 1 to 3 valences. And a monovalent metal cation is preferable from the viewpoint that an ionomer resin having good emulsifying property can be obtained. Of these monovalent metal cations, sodium and potassium are particularly preferred.

The ratio of the carboxyl groups neutralized with a metal cation to all the carboxyl groups in the side chain of the ethylene-unsaturated carboxylic acid copolymer, that is, the degree of neutralization is such that the adhesion of the coating film is excellent and From the viewpoint of obtaining an aqueous dispersion having good stability, it is usually 20 to 100%, preferably 30 to 80%.

This ethylene-based ionomer resin is obtained, for example, by copolymerizing ethylene, an unsaturated carboxylic acid, and optionally the above-mentioned third component by a high pressure radical polymerization method to obtain an ethylene-unsaturated carboxylic acid copolymer. Method for neutralizing carboxyl group of compound with compound having metal cation, graft copolymerization of unsaturated carboxylic acid with polyethylene, and neutralizing carboxyl group of copolymer obtained with compound having metal cation It can be manufactured by a treatment method or the like. In this production, the required components may be supplied to an extruder and melt-kneaded to cause a reaction, or the reaction may be performed in an appropriate solution.

The epoxy group-containing compound to be reacted with the ethylene ionomer resin includes carboxylic acid and 2,3-
Examples thereof include glycidyl esters obtained by the reaction of epoxy propanol and the like, and glycidyl ethers obtained by the reaction of epichlorohydrin with a monovalent or polyvalent metal alkoxide.

Examples of the carboxylic acid for obtaining glycidyl esters include saturated monocarboxylic acids such as acetic acid, propionic acid, butyric acid and valeric acid; saturated dicarboxylic acids such as malonic acid, succinic acid, glutaric acid and adipic acid; Aromatic carboxylic acids such as benzoic acid and phthalic acid; unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid; maleic acid, fumaric acid, itaconic acid, crotonic acid, isocrotonic acid, citraconic acid, allylsuccinic acid, mesaconic acid, glutacon Acid, nadic acid (endocis-bicyclo [2,2,1]
Unsaturated dicarboxylic acids such as hept-2-ene-5,6-dicarboxylic acid), methyl nadic acid, tetrahydrophthalic acid, and methylhexanehydrophthalic acid.
One kind or two or more kinds of these carboxylic acids may be contained in the glycidyl esters.

Specific examples of glycidyl esters used as the epoxy group-containing compound include adipic acid diglycidyl ester, phthalic acid diglycidyl ester, and terephthalic acid diglycidyl ester.

The monovalent or polyvalent metal alkoxide for obtaining the glycidyl ethers used as the epoxy group-containing compound is a compound obtained by reacting a monovalent or polyvalent alcohol with a metal. Examples of monohydric alcohols used here include methanol, ethanol, propanol, butanol, hexanol, and the like, and examples of polyhydric alcohols include ethylene glycol, resorcin, glycerin, and the like. Examples of the metal used here include alkali metals such as lithium, sodium, potassium, magnesium and calcium, alkaline earth metals and the like.

Specific examples of the monovalent or polyvalent metal alkoxide include sodium alkoxide and the like. One of these metal alkoxides may be contained alone or two or more of them may be contained in the glycidyl ethers.

Specific examples of the glycidyl ethers used as the epoxy group-containing compound include sorbitol polyglycidyl ether, sorbitan polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether. Ether, trimethylolpropane polyglycidyl ether, neopentyl glycol polyglycidyl ether, ethylene glycol polyglycidyl ether, polyethylene glycol polyglycidyl ether, tetraethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 2,2 -Bis (4'-glycidyl oxyf Yl) propane glycidyl ether.

The epoxy group-containing compound to be reacted with the ethylene ionomer resin in the present invention may contain one kind of the above glycidyl esters and glycidyl ethers, or may contain two or more kinds thereof. .

This epoxy group-containing compound reacts with the carboxyl group of the ethylene-based ionomer resin by heating to form a coating film excellent in paint adhesion, and in particular, diglycidyl ether or polyglycidyl ether of polyhydric alcohol. Is preferred.

Further, the viscosity of this epoxy group-containing compound is 5 to 30,000 cps at 25 ° C., especially 10 to 200 cps.
It is preferably in the range of 00 cps.

In the present invention, the epoxy group-containing compound usually has an epoxy equivalent of 80 to 2500 g, especially 1
Those in the range of 20 to 2000 g are used. Here, the epoxy equivalent means the number of grams of the epoxy group-containing compound per gram equivalent of the epoxy group. For example, when the epoxy group-containing compound having a molecular weight of 100 has one epoxy group in one molecule, the epoxy equivalent of the epoxy group-containing compound is 100 g. Also, the molecular weight is 100
When the epoxy group-containing compound (1) has two epoxy groups in one molecule, the epoxy equivalent of the epoxy group-containing compound is 50 g.

The reaction product of the ethylene ionomer resin and the epoxy group-containing compound is prepared, for example, by a method of dissolving the epoxy group containing compound in an aqueous dispersion of the ethylene ionomer resin, an ethylene ionomer resin, an epoxy group containing compound, And a mixture of water and a method of mixing a mixture of an ethylene-based ionomer resin, an epoxy group-containing compound, and water with heating and collectively emulsifying the mixture.

An aqueous dispersion of an ethylene-based ionomer resin can be easily prepared and is usually 1 to 60 relative to water.
It can be prepared by a method in which an ethylene ionomer resin having a solid content of weight% is mixed, heated and melted at a temperature of 100 to 270 ° C., and dispersed.

The concentrations of the ethylene-based ionomer resin and the epoxy group-containing compound in the coating solution of the composite resin are not particularly limited, and are appropriately adjusted according to the coating method, the apparatus used for coating and the like. Usually, the total amount of the ethylene ionomer resin and the epoxy group-containing compound is appropriately 5 to 50% by weight, preferably 10 to 40% by weight.
It is.

Further, in the reaction product of the ethylene-based ionomer resin and the epoxy group-containing compound, the content ratio of the ethylene-based ionomer resin and the epoxy group-containing compound is
The molecular weight of the epoxy group-containing compound used, it depends on the epoxy equivalent, etc., when the composite resin is applied on the chromate-treated layer, from the viewpoint of obtaining a resin coating layer having excellent water resistance and adhesion to the topcoat paint. The amount of the epoxy group-containing compound is preferably 0.05 to 50 parts by weight, more preferably 0.1 to 30 parts by weight, and 0.5 to 20 parts by weight per 100 parts by weight of the ethylene-based ionomer resin. preferable.

As the silica fine particles used in the present invention, ultrafine amorphous silica particles having a primary particle diameter of 5 to 50 nm and a secondary particle diameter of 500 nm or less are suitable. If the primary particles exceed 50 nm, cracks will form in the film after drying, so that it is difficult to form a dense film, and the corrosion resistance is likely to deteriorate. Silica fine particles have a silanol group on the particle surface, and are classified into, for example, the following three types according to the supply form to the market, and any of them can be applied to the present invention.

(1) Silica fine powder Generally called dry silica, which has a primary particle diameter of 50 nm or less and is produced by burning silicon tetrachloride. This silica fine 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 and using an alcohol such as methanol, isopropanol or butyl cellosolve 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 5 to 50 nm.
The water-dispersible silica is usually supplied as an aqueous dispersion.

In the present invention, the proportion of silica fine particles in the composite resin which is the main component of the resin film is in the range of 1 to 40% by weight from the viewpoint of corrosion resistance and brittleness of the film. If the amount is less than 1% by weight, the corrosion resistance is reduced. On the other hand, if it exceeds 40% by weight, the film becomes brittle and no effect of improving corrosion resistance is recognized, and the resin solution becomes too thick and difficult to coat, resulting in incomplete film formation, corrosion resistance and blackening resistance. , And the paint adhesion also decreases.

As a result of limiting the ratio of the silica fine particles in this way, the ratio of the reaction product of the ethylene ionomer resin and the epoxy group-containing compound to the composite resin is:
Inevitably, it becomes 60 to 99% by weight.

In the present invention, the above silica and a chromium compound such as a chromate compound may be used in combination and added in a total amount of 50% by weight or less. As the chromium compound in this case, chromic anhydride (CrO ₃ ), strontium chromate (SrCrO ₄ ), barium chromate (B
Acro _4), lead chromate (PbCrO _4), basic zinc chromate _{(ZnCrO 4 · 4Zn (OH)} 2) , such as 6
A chromic acid compound, a chromium chromate compound, or the like can be used.

In the present invention, the resin film has a thickness of 0.1.
-5 μm, preferably 0.3-3 μm. If the thickness is less than 0.1 μm, not only a barrier effect for suppressing the blackening resistance of the resin film can not be expected at all, but also it is not possible to prevent scratches due to handling or the like, which is not preferable. On the other hand, when the thickness exceeds 5 μm, the film is apt to peel off when subjected to severe processing, which is not preferable.

If necessary, metal oxides, pigments and dyes, and other additives for imparting various functions may be added to the resin film of the present invention.

The composite resin film can be formed by the following method, for example. 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 roll coater, or a spray, or a chromate treatment is applied to these coating liquids. The zinc-plated steel sheet is dipped, then a film is formed by controlling the amount of adhesion by a roll or air blowing, and then the film is dried. Although the drying may be performed at room temperature, it is usually performed by heating the steel sheet to a temperature of about 60 ° C. or higher, preferably 80 to 200 ° C., using a hot-air stove, an induction heating device, or the like.

As the zinc-based plated steel sheet of the present invention, an electro-pure galvanized steel sheet in which blackening is particularly concerned, and another zinc-based plated steel sheet or zinc having a plating layer formed by electroplating or hot dip coating Examples include alloy-plated steel sheets.

The chromate-treated layer has the effect of imparting excellent corrosion resistance to the steel sheet and facilitating the formation of the resin film. The chromate treatment for forming this layer may be a known chromate treatment such as a reaction type, a coating type, and an electrolytic type.
It is necessary to form a chromate layer of 00 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 corrosion resistance improvement effect corresponding to the amount cannot be obtained, but also bending work involving deformation of the steel sheet. Is applied, cohesive failure of the chromate treatment layer is likely to occur. The more preferable amount of the chromate-treated layer is in the range of 10 to 100 mg / m ² per one side of the steel sheet in terms of chromium metal.

To give a concrete example, the composition of the reactive chromate treatment liquid is 1 to 100 in terms of metallic chromium.
The main components are g / l of a water-soluble chromium compound and 0.2 to 20 g / l of sulfuric acid, and the content of trivalent chromium in the total chromium is 50% by weight or less. Is 20 to 35% by weight or less, and if necessary, appropriate amounts of metal ions such as Zn ²⁺ , Co ²⁺ , Fe ³⁺ and other mineral acids such as phosphoric acid and hydrofluoric acid are added. It may be one.

As a specific example of the coating type chromate treatment liquid, a liquid having the same composition as that of the above reaction type chromate treatment,
A water-soluble liquid containing a large amount of carboxyl groups in the molecule and having a composition similar to that of the reaction type chromate treatment liquid, and a water-soluble and reactive type chromate treatment liquid containing a large amount of carboxyl groups in the molecule, An example is one in which an organic polymer resin compatible with a liquid having the same composition is added to adjust the pH to 2.0 to 3.5. As this organic polymer,
The average molecular weight is preferably 1,000 to 500,000. The addition amount is generally 0.02 to 3 in terms of resin content.
It is in the range of 0 g / l.

In any case, the adhesion amount of the chromate layer as the first layer is 1 in terms of metallic chromium as described above.
It may be in the range of to 200 mg / m ^2.

[0057]

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.

(Synthesis Example 1 of Composite Resin) First, the synthetic method of the base resin will be described. Partially neutralized ethylene
Methacrylic acid copolymer (methacrylic acid content 15%, neutralization degree 50%, neutralizing agent: sodium hydroxide) 100 g 2
An ethylene-based ionomer resin melt was prepared by melting at 50 ° C.

This ethylene-based ionomer resin melt was charged with 300 g of water and heated to 170 ° C.
The mixture was charged into a 1 liter pressure-resistant homomixer over about 2 hours while stirring at 1000 rpm. Further, the mixture was cooled to room temperature with stirring for 30 minutes to obtain an aqueous dispersion of an ethylene ionomer resin. The resulting aqueous dispersion of the ethylene ionomer resin has a resin concentration of 25% and a viscosity of 600 c.
ps (25 ° C.), and the average particle size was 1 μm or less.

Next, a 50% aqueous solution of tetraethylene glycol diglycidyl ether was prepared, and 5.0 g of this aqueous solution was added to 100 g of the aqueous dispersion of the ethylene-based ionomer resin, and the mixture was stirred to form a water dispersion type. Resin solution A was obtained.

Further, resin liquids having different kinds of copolymers, kinds of epoxy group-containing compounds and different contents were basically synthesized under the same conditions.

Resins having different base resins used in Comparative Examples were similarly synthesized. The resins are specified in Tables 1 and 2 described later.

Silica fine particles were added to these resins to obtain a composite resin composition. An example is shown below.

100 parts of Resin A was charged into a flask, and fumed silica (manufactured by Nippon Aerosil Co., Ltd .: trade name Aerosil 300, primary particle size: 7 nm) was charged with sufficient stirring at room temperature.
3.2 g was gradually added in about 10 minutes to obtain a composite resin composition.

(Examples 1 to 22) By subjecting a galvanized steel sheet having a plate thickness of 0.8 mm and a plating amount of 20 g / m ^{2 to} a plating layer, a reactive chromate treatment or a coating chromate treatment was performed and drying was performed. Deposition amount 10-200m
A chromate treated layer of g / m ² was formed.

Next, the various composite resin compositions synthesized in the above Synthesis Example were applied onto the chromate-treated layer by a roll coater, and then heated by an induction heating device until the temperature of the steel sheet reached 140 ° C. Was dried to form a resin film. Table 1 shows the conditions in each example.

Comparative Examples 1 to 16 In these comparative examples, the same electrogalvanized steel sheets as in the examples were used, and a chromate-treated layer having an adhesion amount of 25 mg / m ² was formed on the plated layer by the reactive chromate treatment. Various resin coatings outside the scope of the present invention were formed on the chromate-treated layer under the conditions shown in Table 2.

The amounts of chromate adhered in Tables 1 and 2 are
The amount of metal chromium is displayed, the content of the epoxy group-containing compound is expressed in parts by weight relative to 100 parts by weight of the ethylene-based ionomer resin, and the silica content in the resin film is 100 in total of the resin and silica. It is displayed in% when it is set to%.

In Tables 1 and 2, the symbols in the resin type column are as shown below.

A: ethylene-methacrylic acid copolymer, N
a neutralized ionomer (resin A of the synthesis example) B: ethylene-acrylic acid copolymer, Na neutralized ionomer C: ethylene-fumaric acid copolymer, Na neutralized ionomer D: ethylene-itaconic acid copolymer, Na Neutralized ionomer E: ethylene-maleic acid copolymer, Na neutralized ionomer F: ethylene-acrylic acid copolymer G: acrylic resin emulsion H: water-soluble urethane resin I: vinyl acetate-acrylic acid copolymer J: ethylene -Vinyl acetate copolymer The symbols in the column of the type of epoxy group-containing compound are as shown below.

A: tetraethylene glycol diglycidyl ether b: 2,2-bis (4′-glycidyloxyphenyl)
Propane glycidyl ether c: adipic acid diglycidyl ester d: phthalic acid diglycidyl ester The blackening resistance, corrosion resistance, paint adhesion and lubricity of the thus obtained organic composite coated steel sheets of Examples and Comparative Examples are as follows. It evaluated by the test method shown in. The results are also shown in Tables 1 and 2.

(1) Black Decoloration Resistance It was left for 60 days in a high temperature humid environment of 50 ° C. and 95% RH,
L value of steel sheet before and after the test (JIS Z8730 6.6.
2 (1980), lightness index in Hunter's color difference equation)
Was evaluated for blackening resistance. The evaluation criteria are as follows.

⊚: L value change is less than 1 ◯: L value change is 1 to 3 Δ: L value change is 3 to 5 x: L value change is more than 5.

(2) Corrosion resistance A salt spray test based on JIS Z2371 was carried out, and 2
The white rust generation area ratio after 40 hours was measured, and the corrosion resistance was evaluated. The evaluation criteria are as follows.

⊚: Less than 10% ◯: 10% or more and less than 30% Δ: 30% or more and less than 50% x: 50% or more.

(3) Paint adhesion Melamine alkyd paint (Dainippon Paint Co., Ltd .: Dericon #
700) by spraying so as to have a film thickness of 30 μm, and baking the sample at 130 ° C. for 30 minutes as a test piece, immersing it in boiling water for 30 minutes, and then using the cross-cut tape method (J
1 mm × based on IS K5400 8.5.2.
A 100 grid was inserted, and the adhesion of the paint was evaluated based on the state of the paint after the tape was peeled off. The evaluation criteria are as follows.

⊚: None at all ◯: Peeling area is less than 10% Δ: Peeling area is 10% or more and less than 50% ×: Peeling area is 50% or more.

[0078]

[Table 1]

[0079]

[Table 2]

As is clear from Table 1, Examples 1-22
Showed good blackening resistance, corrosion resistance and paint adhesion. Among them, the blackening resistance of Examples 1 to 14 using the ethylene-methacrylic acid copolymer and Na-neutralized ionomer as the base resin is particularly excellent, and the epoxy group-containing compound is a diglycidyl ether of a polyhydric alcohol. Alternatively, it is polyglycidyl ether, and its content is 0.5 to 2 with respect to 100 parts of the ethylene-based ionomer resin.
The paint adhesion of Examples 1 to 8, 11, and 12, which are 0 parts, is particularly excellent.

On the other hand, as is clear from Table 2,
In Comparative Examples 1 to 16, all of blackening resistance, corrosion resistance and paint adhesion could not be satisfied at the same time. That is, Comparative Examples 1 and 2 are inferior in corrosion resistance because the content of the epoxy group-containing compound is outside the range of the present invention in which the content of the epoxy group-containing compound is 1 to 30 parts relative to 100 parts of the ethylene-based ionomer resin. Comparative Examples 3 and 4 are inferior in corrosion resistance because the silica content is out of the range of the present invention. Comparative Example 5 is inferior in corrosion resistance because the resin film thickness is smaller than the lower limit. In Comparative Example 6, the blackening resistance is poor because the resin film thickness is larger than the upper limit. In Comparative Examples 7 to 16, since the types of resins are different, blackening resistance, corrosion resistance, and paint adhesion are insufficient.

[0082]

According to the present invention, there is provided an organic composite-coated steel sheet which is excellent in blackening resistance and coating adhesion while maintaining good corrosion resistance.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location C08L 63/02 NJP C08L 63/02 NJP C09D 163/02 PKE C09D 163/02 PKE C23C 22/24 C23C 22/24 28/00 28/00 C

Claims (4)

[Claims] 1. A steel sheet provided with a zinc or zinc-based alloy plating layer, and a chromate treatment formed on the plating layer of the steel sheet and having a deposition amount in the range of 1 to 200 mg / m ^{2 in} terms of metallic chromium. Layer and a resin film formed on the chromate-treated layer in a thickness of 0.1 to 5 μm, wherein the resin film is a reaction product of (A) an ethylene-based ionomer resin and an epoxy group-containing compound: 60-99% by weight,
(B) Silica fine particles: An organic composite-coated steel sheet containing a composite resin composed of 1 to 40% by weight as a main component. 2. The organic composite coated steel sheet according to claim 1, wherein the unsaturated carboxylic acid in the ethylene ionomer resin in the resin film is methacrylic acid. 3. The epoxy group-containing compound in the resin film is a diglycidyl ether or a polyglycidyl ether of a polyhydric alcohol.
Alternatively, the organic composite-coated steel sheet according to claim 2. 4. In the reaction product of the ethylene ionomer resin and the epoxy group-containing compound in the resin coating, the ratio of the epoxy group containing compound is 0.1 to 30 parts by weight with respect to 100 parts by weight of the ethylene ionomer resin. The organic composite-coated steel sheet according to any one of claims 1 to 3, characterized in that.