JP3216537B2 - Organic composite coated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an organic composite coated steel sheet in which a chromate treatment layer and a resin film 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, this type of organic composite coated steel sheet 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 the blackening resistance of the organic composite coated steel sheet can be improved by providing a resin layer based on an ethylene ionomer resin as an upper layer, the production is performed by these techniques. The coated steel sheet has insufficient paint adhesion.

In the prior arts 3 and 4, the paint adhesion of the organic composite coated steel sheet can be improved by providing the upper layer with a resin layer based on a copolymer of ethylene and an unsaturated carboxylic acid. However, steel sheets manufactured by these techniques have insufficient blackening resistance.

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 such circumstances, and it is an object of the present invention to provide an organic composite coated steel sheet which is excellent in blackening resistance and excellent in paint adhesion while maintaining good corrosion resistance. Make it an issue.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a steel sheet provided with a zinc or zinc-based alloy plating layer, a steel sheet formed on the plating layer of the steel sheet, and having a metal chromium equivalent of 1%. A chromate-treated layer having an adhesion amount in the range of 200 to 200 mg / m ² , 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) Mixture of a reaction product of an ethylene ionomer resin and an epoxy group-containing compound with an epoxy emulsion: 60 to 99% by weight, (B) silica fine particles: 1
Provided is an organic composite-coated steel sheet mainly containing a composite resin of about 40% by weight.

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, the present invention provides an organic composite coated steel sheet, wherein the epoxy group-containing compound in the resin film is a polyhydric alcohol di- or polyglycidyl ether.

Further, in the reaction product of the ethylene ionomer resin and the epoxy group compound in the resin film, 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. An organic composite coated steel sheet is provided.

Further, the epoxy emulsion in the resin film has a basic skeleton of a high molecular weight epoxy resin having a molecular weight of 2,000 to 5,000 and is emulsified by utilizing the hydrophilicity of an acrylic resin. Provide steel sheet.

Further, the weight ratio of the reaction product of the ethylene ionomer resin and the epoxy group-containing compound to the epoxy emulsion in the resin film is 1/9 by weight.
To 9/1, to provide an organic composite coated steel sheet.

The present inventors have conducted intensive studies to solve the above-mentioned problems in the organic composite coated steel sheet, and as a result, formed a chromate treatment layer on a plating layer of a zinc-based coated steel sheet,
It has been found that by forming a special resin layer thereon, it is possible to obtain an organic composite coated steel sheet having excellent blackening resistance and excellent paint adhesion while maintaining good corrosion resistance. That is, on a chromate treatment layer having a specific range of thickness, a film having a specific range of thickness and a main component being a reaction product of an ethylene-based ionomer resin and an epoxy group-containing compound and a mixture of an epoxy emulsion and By forming, by the high adhesion force due to its molecular structure,
It has been found that the paint adhesion is improved together with the blackening resistance.
The present invention has been made based on such findings of the present inventors.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a chromate-treated layer is formed on the surface of a galvanized steel sheet, and (A) a reaction product of an ethylene ionomer resin and an epoxy group-containing compound, and an epoxy emulsion. Mixture: 6
0 to 99% by weight, (B) silica fine particles: 1 to 40% by weight
A resin film composed mainly of a composite resin composed of

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

The ethylene ionomer resin is a polymer having a polymer main chain mainly composed of hydrocarbon, having a carboxyl group in a 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.

The unsaturated carboxylic acid which is a component of the ethylene-unsaturated carboxylic acid copolymer includes one 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 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 content of ethylene in the ethylene-unsaturated carboxylic acid copolymer is usually from 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, the metal cations in the side chain of the ethylene-unsaturated carboxylic acid copolymer which neutralize at least a part of the carboxyl groups include, for example, 1 to 3 valences. And a monovalent metal cation is preferred in that an ionomer resin having good emulsifying properties can be obtained. Of these monovalent metal cations, sodium and potassium are particularly preferred.

The ratio of the carboxyl group neutralized with the 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, It is usually 20 to 100%, preferably 30 to 80%, in that an aqueous dispersion having good stability can be obtained.

The ethylene-based ionomer resin is obtained, for example, by copolymerizing ethylene with an unsaturated carboxylic acid and, if necessary, the third component used by a high-pressure radical polymerization method to obtain an ethylene-unsaturated carboxylic acid copolymer. A method of neutralizing the carboxyl group of the union with the compound having the metal cation, graft-copolymerizing an unsaturated carboxylic acid to polyethylene, and neutralizing the carboxyl group of the obtained copolymer with the compound having the metal cation. It can be manufactured by a processing 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.

In the present invention, the epoxy group-containing compound to be reacted with the ethylene ionomer resin includes glycidyl esters obtained by reacting carboxylic acid with 2,3-epoxypropanol and the like, and epichlorohydrin and monovalent or polyvalent metal. Glycidyl ethers obtained by reaction with an alkoxide and the like can be mentioned.

Examples of carboxylic acids 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, allyl succinic acid, mesaconic acid, glutacon Acid, nadic acid (endosis-bicyclo [2,2,1]
Unsaturated dicarboxylic acids such as hept-2-ene-5,6-dicarboxylic acid), methylnadic acid, tetrahydrophthalic acid and methylhexahydrophthalic acid. These carboxylic acids may be contained alone or in combination of two or more in the glycidyl esters.

Specific examples of the glycidyl esters used as the epoxy group-containing compound include diglycidyl adipate, diglycidyl phthalate, and diglycidyl terephthalate.

The monovalent or polyvalent metal alkoxide for obtaining 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 the monohydric alcohol include methanol, ethanol, propanol, butanol, and hexanol. Examples of the polyhydric alcohol include ethylene glycol, resorcin, and glycerin. As metal,
For example, alkali metals or alkaline earth metals such as lithium, sodium, potassium, magnesium, calcium and the like can be mentioned.

Specific examples of the monovalent or polyvalent metal alkoxide include sodium alkoxide. These metal alkoxides may be included alone or in combination of two or more in the glycidyl ethers.

Specific examples of 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, and glycerol polyglycidyl. Ether, trimethylolpropane polyglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, tetraethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 2,2 -Bis (4'-glycidyloxyphenyl) Propane diglycidyl ether, and the like.

In the present invention, when obtaining the main component of the resin formed as the upper layer, the epoxy group-containing compound to be reacted with the ethylene ionomer resin may be one of the glycidyl esters and glycidyl ethers described above. Any of those containing a combination of two or more types may be used.

The epoxy group-containing compound reacts with the carboxyl group of the ethylene ionomer resin by heating to form a coating film having excellent paint adhesion. In particular, di- or polyglycidyl ether of a polyhydric alcohol is used. preferable.

The viscosity of the epoxy group-containing compound is 25
5-30,000 cps at C, especially 10-20,000 cps
It is preferably in the range of ps.

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

The reaction product of the ethylene ionomer resin and the epoxy group-containing compound may be prepared, for example, by dissolving the epoxy group-containing compound in the aqueous dispersion of the ethylene ionomer resin, or by dissolving the aqueous dispersion of the ethylene ionomer resin. A method of mixing an aqueous solution of an epoxy group-containing compound with,
An ethylene-based ionomer resin and an epoxy group-containing compound,
And a mixture of water and water is heated and melted, and emulsification is carried out at once.

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

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

Further, in the reaction product of the ethylene ionomer resin and the epoxy group-containing compound, the content ratio of the ethylene ionomer resin and the epoxy group-containing compound is as follows:
Depends on the molecular weight, epoxy equivalent, etc. of the epoxy group-containing compound used.When applied to the chromate-treated layer of a zinc-plated steel sheet that has been subjected to chromate treatment, the composite resin has excellent water resistance and adhesion to the topcoat paint. From the viewpoint that a resin coating layer having excellent properties is obtained, the proportion of the epoxy group-containing compound is preferably 0.05 to 50 parts by weight, more preferably 100 parts by weight, based on 100 parts by weight of the ethylene ionomer resin.
The amount is preferably 1 to 30 parts by weight, more preferably 0.5 to 20 parts by weight.

In the present invention, as the epoxy emulsion to be mixed with the reaction product of the ethylene ionomer resin and the epoxy group-containing compound, the liquid epoxy resin or solid epoxy resin is heated and melted or dissolved in an organic solvent and then forcedly emulsified in water. What was manufactured by using it is used. Emulsions include epoxy-based emulsions, urethane-based emulsions, acrylic-based emulsions, alkyd-based emulsions, olefin-based emulsions, and the like, but paint adhesion is significantly improved only when an epoxy emulsion is used. For this reason, the present invention employs an epoxy emulsion.

The epoxy emulsion mixed with the reaction product of the ethylene ionomer resin and the epoxy group-containing compound in order to obtain the main component of the resin formed as the upper layer as described above has an adhesive property to the top coat paint. In terms of obtaining an excellent resin coating layer, the molecular weight is 2,000 to 5,000.
It is particularly desirable to use a polymer epoxy resin basic skeleton of the above and emulsified using the hydrophilicity of an acrylic resin.

The mixture of the reaction product of the ethylene-based ionomer resin and the epoxy group-containing compound and the epoxy emulsion is prepared by, for example, dissolving the epoxy-group-containing compound in an aqueous dispersion of the ethylene-based ionomer resin and further dissolving the epoxy emulsion. It can be prepared by a method.

The aqueous dispersion of the ethylene ionomer resin can be easily prepared, and is usually 1 to 60 based on 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 concentration of the mixture of the epoxy emulsion and the reaction product of the ethylene ionomer resin and the epoxy group-containing compound in the composite resin is not particularly limited, and may vary depending on the coating method, the equipment used for coating, and the like. It is prepared appropriately. Usually, the total amount of the reaction product of the ethylene-based ionomer resin and the epoxy group-containing compound and the epoxy emulsion is appropriately 5 to 50%, preferably 10 to 40% by weight.

Further, in the mixture of the reaction product of the ethylene-based ionomer resin and the epoxy group-containing compound and the epoxy emulsion, the ratio of the epoxy emulsion to the reaction product of the ethylene-based ionomer resin and the epoxy-group-containing compound depends on the epoxy used. Depending on the molecular weight of the emulsion, epoxy equivalent, etc., when coated on a chromate-treated layer of a zinc-plated steel sheet with a chromate treatment, the resin coating has excellent water resistance and excellent adhesion to the topcoat paint. In that you get a layer,
The weight ratio of the reaction product of the ethylene ionomer resin and the epoxy group-containing compound to the epoxy emulsion is preferably 1/9 to 9/1, and 2/8 to 8/2.
Is more 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 preferable. 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 referred to as dry silica, having a primary particle diameter of 50 nm or less, and manufactured 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 A so-called organosilica sol, for example, one dispersed in an organic solvent by a production method described in US Pat. No. 2,285,449. 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 A so-called colloidal silica, which is a sodium-free water glass (by an ion exchange method, an acid decomposition method, a 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 the silica fine particles in the composite resin as 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.

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.

Since the amount of the silica particles is 1 to 40% by weight, the ratio of the mixture of the reaction product of the ethylene ionomer resin and the epoxy group-containing compound and the epoxy emulsion to the composite resin is inevitable. 60 to 9
9% by weight.

In the present invention, the thickness of the resin film is 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.

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

The formation of the composite resin film can be performed, for example, by the following method. That is, first, a coating liquid of the composition containing the above-mentioned 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. After dipping the galvanized steel sheet, the film is formed by controlling the amount of adhesion by a roll or air blowing, and then the film is dried. Drying may be performed at normal temperature, but is usually performed by heating the steel sheet to about 60 ° C. or more, preferably 80 to 200 ° C., using a hot air oven or an induction heating device.

The galvanized steel sheet used in the present invention includes electropure galvanized steel sheet in which black discoloration is particularly concerned, other galvanized steel sheet having a plating layer formed by electroplating or hot dip coating, And zinc-based alloy-plated steel sheets.

The chromate-treated layer has effects of imparting excellent corrosion resistance to the steel sheet and facilitating the formation of a 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.

As a specific example, the composition of the reaction type chromate treatment solution is 1 to 100 in terms of chromium metal.
g / l of a water-soluble chromium compound and 0.2 to 20 g / l of sulfuric acid as main components, and the content of trivalent chromium in all chromium is 50% by weight or less, preferably 2% by weight.
0 to 35% by weight or less, if necessary, to which an appropriate amount of metal ions such as Zn ²⁺ , Co ²⁺ , Fe ^{3+ and the} like and other mineral acids such as phosphoric acid, hydrofluoric acid, etc. are added It may be.

As a specific example of the coating type chromate treatment liquid, a solution having the same composition as in the above-mentioned reaction type chromate treatment may be used.
A water-soluble organic polymer resin containing a large amount of carboxyl groups in the molecule and compatible with a liquid having the same composition as the above-mentioned reaction type chromate treatment liquid is added, and the pH is adjusted to 2.0 to 3.5.
Adjusted to. The organic polymer preferably has an average molecular weight of 1,000 to 500,000. The amount of addition is generally 0.02 in terms of resin content.
３０30 g / l.

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

[0065]

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. 100 g of a partially neutralized ethylene-methacrylic acid copolymer (methacrylic acid content: 15%, degree of neutralization: 50%, neutralizing agent: sodium hydroxide)
It melted at 0 degreeC, and prepared the ethylene ionomer resin melt.

This ethylene-based ionomer resin melt was charged with 300 g of water and heated to 170 ° C. to obtain an inner volume 1
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% by weight aqueous solution of tetraethylene glycol diglycidyl ether was prepared, and this aqueous solution was used as the aqueous dispersion 1 of the ethylene ionomer resin obtained above.
An aqueous dispersion of a reaction product of the ethylene-based ionomer resin and the epoxy group-containing compound was obtained by adding 5.0 g of the mixture to 00 g and stirring the mixture.

Next, a 40% by weight aqueous solution of an epoxy emulsion having an epoxy skeleton having a molecular weight of 3500 was prepared, and this aqueous solution was added to 100 g of a water dispersion of a reaction product of an ethylene ionomer resin and an epoxy group-containing compound. 62.5 g was added and stirred to obtain a water-dispersed resin liquid A.

The same applies to resin liquids having different types of copolymers, types of epoxy group-containing compounds, types of epoxy emulsions, and ratios of the epoxy emulsion to the reaction product of the ethylene ionomer resin and the epoxy group-containing compound. Were synthesized under the following conditions.

The resins having different base resins used in the comparative examples were synthesized in the same manner. Further, the resins are specified in Tables 1 to 3 described below.

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

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

(Examples 1 to 35) A reaction type chromate treatment or a coating type chromate treatment is applied to a plating layer of an electrogalvanized steel sheet having a thickness of 0.8 mm and a plating amount of 20 g / m ² and then dried. 10 to 200
A chromate treated layer of mg / m ² was formed.

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

(Comparative Examples 1 to 75) In these comparative examples, the same electrogalvanized steel sheet as in the example was used, and a chromate treated layer having an adhesion amount of 25 mg / m ² was formed on the plated layer by a reactive chromate treatment. Various resin films outside the scope of the present invention were formed on the chromate-treated layer under the conditions shown in Tables 2 and 3.

The amounts of chromate adhering in Tables 1 to 3 are as follows:
The amount of metal chromium is displayed, the content of the epoxy group-containing compound is expressed in parts by weight based on 100 parts by weight of the ethylene ionomer resin, and the ratio of the epoxy emulsion is the ratio of the ethylene ionomer resin to the epoxy group-containing compound. The weight ratio of the reactant to the epoxy emulsion is indicated, and the silica content in the resin film is indicated by% when the total of the resin and silica is 100%.

In Tables 1 to 3, the symbols in the column of the type of resin are as follows.

A: Ethylene-methacrylic acid copolymer, Na-neutralized ionomer (Resin A in Synthesis Example) B: Ethylene-acrylic acid copolymer, Na-neutralized ionomer C: Ethylene-fumaric acid copolymer, in Na Japanese 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 epoxy group-containing compound are as follows.

A: tetraethylene glycol diglycidyl ether b: 2,2-bis (4′-glycidyloxyphenyl)
Propandilicidyl ether c: diglycidyl adipate d: diglycidyl phthalate Further, the symbols in the column of the type of epoxy emulsion are as shown below.

Aa: an epoxy emulsion having an epoxy skeleton having a molecular weight of 3500 bb: an epoxy emulsion having an epoxy skeleton having a molecular weight of 4500 cc: an epoxy emulsion having an epoxy skeleton having a molecular weight of 300 dd: an epoxy emulsion having an epoxy skeleton having a molecular weight of 2,000 The organic composite-coated steel sheets of Examples and Comparative Examples obtained as described above were evaluated for blackening resistance, corrosion resistance, paint adhesion, and lubricity by the following test methods. The results are shown in Tables 4 to 6.

(1) Resistance to blackening 50 days at 50 ° C. and 95% RH for 60 days
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 ×: L value change exceeds 5

(2) Corrosion resistance A salt spray test based on JIS Z2371 was performed.
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% ×: 50% or more

(3) Paint adhesion (melamine alkyd paint) Melamine alkyd paint (Dai Nippon Paint: Delicon #)
700) was spray-coated to a thickness of 30 μm, baked at 130 ° C. for 30 minutes to prepare a test piece, immersed in boiling water for 30 minutes, and then 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.

◎: No abnormality at all ○: Peeling area less than 5% Δ: Peeling area of 5% or more and less than 30% ×: Peeling area of 30% or more, less than 50% XX: Peeling area of 50% or more.

(4) Paint Adhesion (Polyester Powder Coating) Evaluation was performed in the same manner as in (3) using a polyester powder coating.

(5) Paint Adhesion (Epoxy Powder Coating) Evaluation was performed in the same manner as (3) using an epoxy powder coating.

(6) Paint Adhesion (Acrylic Paint) An acrylic paint was used and evaluated in the same manner as in (3).

(7) Paint Adhesion (Urethane-Based Paint) The same evaluation as in (3) was performed using a urethane-based paint.

(8) Ink Adhesion (Epoxy Ink) Epoxy Screen Ink (Seiko Advance)
# 1000) was silk-printed to a film thickness of 10 μm and baked at 120 ° C. for 40 minutes to obtain a test piece, which was evaluated in the same manner as (3).

[0093]

[Table 1]

[0094]

[Table 2]

[0095]

[Table 3]

[0096]

[Table 4]

[0097]

[Table 5]

[0098]

[Table 6]

As apparent from Table 4, Examples 1 to 35
Showed good blackening resistance, corrosion resistance and paint adhesion. Above all, the blackening resistance of Examples 1 to 23 using an ethylene-methacrylic acid copolymer and a Na-neutralized ionomer as the base resin was particularly excellent. Further, the resin film layer is a mixture of a reaction product of an ethylene ionomer resin and an epoxy group-containing compound with an epoxy emulsion, and the epoxy group-containing compound is a dihydric or polydiglycidyl ether of a polyhydric alcohol. The ratio is 0.5 to 20 parts by weight with respect to 100 parts by weight of the ethylene ionomer resin, and the ratio of the reaction product of the ethylene ionomer resin and the epoxy group-containing compound to the epoxy emulsion is 1/1 by weight. Examples 1 to 10, 13, 14, 1 satisfying all of 9 to 9/1
Nos. 7, 20, 21, and 24 to 35 were confirmed to be particularly excellent in blackening resistance, corrosion resistance, and paint adhesion of the above six coating systems.

On the other hand, as is apparent from Tables 5 and 6, in Comparative Examples 1 to 75, all of blackening resistance, corrosion resistance and paint adhesion could not be satisfied at the same time. That is, in Comparative Examples 5 and 6, the content of the epoxy group-containing compound was 1 to 3 with respect to 100 parts by weight of the ethylene ionomer resin.
Since the amount was out of the range of 0 parts by weight, paint adhesion was poor. Comparative Example 21 was inferior in paint adhesion because it did not contain an epoxy emulsion, and Comparative Example 22 was inferior in blackening resistance and corrosion resistance because it used only an epoxy emulsion.
Comparative Examples 1, 2, 7, 8, 23, and 24 were inferior in corrosion resistance because the silica content was out of the range of the present invention. Comparative Examples 3, 9, and 25 were inferior in corrosion resistance because the resin film thickness was smaller than the lower limit. Comparative Examples 4, 10, and 26 were inferior in blackening resistance because the resin film thickness was larger than the upper limit. Comparative Examples 11 to
In Nos. 20, 27-31, the type of resin was different, so that blackening resistance, corrosion resistance, and paint adhesion were insufficient. Comparative Example 3
2 to 53 do not contain an epoxy emulsion,
Among the six paint systems, there were paint systems with poor paint adhesion. Moreover, in Comparative Examples 54 to 75, there was no reaction with the epoxy-containing compound, so that there were still six paint systems having poor paint adhesion among the six paint systems.

[0101]

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

Continuation of the front page (56) References JP-A-8-39725 (JP, A) JP-A-6-246229 (JP, A) JP-A-5-287607 (JP, A) JP-A-4-26881 (JP) JP-A-4-290582 (JP, A) JP-A-4-61966 (JP, A) JP-A-5-220445 (JP, A) JP-A-7-52310 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B32B 15/00-15/20 B05D ⁷ /14-7/18 C23C 28/00

Claims (6)

(57) [Claims] 1. A steel sheet provided with a zinc or zinc-based alloy plating layer, and a chromate treatment layer formed on the plating layer of the steel sheet and having an adhesion amount of 1 to 200 mg / m ^{2 in} terms of chromium metal. A resin film formed on the chromate-treated layer to a thickness of 0.1 to 5 μm, wherein the resin film comprises: (A) a reaction product of an ethylene ionomer resin and an epoxy group-containing compound; And (B) silica fine particles: 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 organic composite coated steel sheet according to claim 1, wherein the epoxy group-containing compound in the resin film is a dihydric or polyglycidyl ether of a polyhydric alcohol. 4. The reaction product of an ethylene ionomer resin and an epoxy group compound in the resin film, wherein the proportion 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. The organic composite coated steel sheet according to any one of claims 1 to 3, characterized in that: 5. An epoxy emulsion according to claim 1, wherein the epoxy emulsion in the resin film is a polymer epoxy resin having a molecular weight of 2,000 to 5,000 as a basic skeleton and emulsified by utilizing the hydrophilicity of an acrylic resin. The organic composite coated steel sheet according to claim 4. 6. The weight ratio of a reaction product of an ethylene ionomer resin and an epoxy group-containing compound to an epoxy emulsion in the resin film is 1/9 to 9/1. An organic composite coated steel sheet according to any one of claims 1 to 5.