JPH04254588A - Organic composite coated steel sheet excellent in corrosion resistance, weldability, coating adhesion, electrodeposition coating suitability and discriminability and its production - Google Patents

Abstract

PURPOSE:To produce an org. composite coated steel sheet having excellent corrosion resistance, weldability, coating adhesion and electrodeposition coating suitability and with the kind of the steel sheet corresponding to the plating amt. and the front and rear capable of being discriminated. CONSTITUTION:A chromate film at a specified deposition amt. as the first layer and a film of the resin composition consisting of the specified formulation of the epoxy resin, curing agent, silica, hardly soluble chromate and org. pigment, preferably a condensed-polycyclic or phthalocyanine-based pigment, as the second layer are formed on the surface of a zinc plated steel sheet respectively in specified thickness to obtain the composite coated steel sheet. In this case, a chromating soln. having a specified composition is applied on the steel sheet, the sheet is dried without being washed, and then the resin composition is applied and heat-treated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet that is used for automobile bodies, home appliances, etc. and has excellent corrosion resistance, weldability, paint adhesion, electrodeposition coating properties, and distinguishability.

0002

[Prior Art] In recent years, steel sheets used for automobile bodies are required to have excellent corrosion resistance, and the ratio of use of surface-treated steel sheets with excellent corrosion resistance is increasing in place of the conventionally used cold-rolled steel sheets. This is the current situation. As such surface-treated steel sheets, Japanese Patent Application Laid-open No. 64-8033 and Japanese Patent Application Laid-open No. 2-1
An organic composite coated steel sheet as shown in No. 5177 is known. These steel sheets are based on zinc-plated steel sheets, have a chromate film as the first layer, and an organic resin film on top of that as the second layer, and have excellent corrosion resistance, weldability, paint adhesion, and electrodeposition. It has excellent paintability.

0003

[Problem to be Solved by the Invention] Recently, automobile manufacturers have been changing the anti-rust specifications of automobiles depending on the type and grade of the automobile and the destinations such as Japan, Europe and America, which have different corrosive environments. For this reason, various types of steel sheets, such as steel sheets with different coating weights and ordinary cold-rolled steel sheets, coexist even within the same factory. It is necessary to accurately identify the type of steel plate for reasons such as the need to change welding conditions depending on the type of steel plate. Further, some steel plates have an organic composite coating on only one side, and others have different types of coatings on the front and back sides, and it is necessary to accurately identify the front and back sides of such steel plates. However, the front and back sides of these different types of steel plates and steel plates,
It is not easy to distinguish from the steel plate itself, and therefore, in order to prevent misuse of the steel plate, it is currently necessary to strictly control the coils.

The present invention was made to solve the above-mentioned problems, and has excellent corrosion resistance, weldability, paint adhesion and electrodeposition coating properties as a surface-treated steel sheet for automobiles, etc. It is an object of the present invention to provide a steel plate with a different coating weight, an organic composite coated steel plate that can distinguish between the front and back sides of the steel plate, and a method for manufacturing the same.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the organic composite coated steel sheet of the present invention has the following configuration.

(1) A chromate layer with an adhesion amount of 10 to 200 mg/m2 in terms of metallic chromium is provided as a first layer on the surface of a zinc-based plated steel sheet, and a second layer on top of the chromate layer is (
A) At least one type selected from the group consisting of a base resin in which one or more basic nitrogen atoms and two or more primary hydroxyl groups are added to the terminal of an epoxy resin, and a polyisocyanate compound and a blocked isocyanate compound. Corrosion resistance comprising an organic resin film with a thickness of 0.2 to 2 μm containing an organic resin (B) silica (C) poorly soluble chromate (D) organic coloring pigment in the following proportions and a curing agent; Organic composite coated steel sheet with excellent weldability, paint adhesion, electrocoatability, and identification. ■Weight ratio of organic resin to silica and poorly soluble chromate:
Organic resin/(silica + poorly soluble chromate) = 80/20
~50/50 ■Weight ratio of silica and sparingly soluble chromate: silica/poorly soluble chromate = 37/3 to 20/20 ■Weight ratio of base resin and curing agent in organic resin: Base resin/curing agent =95/5~
60/40■ Weight ratio of organic resin, silica, and poorly soluble chromate to organic coloring pigment: (organic resin + silica + poorly soluble chromate)/organic coloring pigment = 100/10 to 100/3

(2) After applying a chromate treatment liquid whose liquid composition is adjusted under the conditions of (2) below to the surface of a zinc-based plated steel sheet, the chromate treatment is performed by drying without washing with water. ~200mg/m
A chromate layer with a coating weight of 2 is formed, and then (A)
A base resin in which one or more basic nitrogen atoms and two or more primary hydroxyl groups are added to the terminals of an epoxy resin, and at least one curing member selected from the group consisting of a polyisocyanate compound and a blocked isocyanate compound. Applying an organic resin composition in which organic resin (B) silica (C) poorly soluble chromate (D) organic coloring pigment is blended in the following proportions,
By heat treatment, an organic resin film with a film thickness of 0.2 to 2 μm is formed on the upper layer of the chromate layer, which improves corrosion resistance, weldability, paint adhesion, electrodeposition coating property, and identifiability. A method for producing an excellent organic composite coated steel sheet. ■ Chromate treatment solution composition (a) Chromic anhydride: 5 to 100 g/l (b) Phosphate ion: 0.5 to 20 g/l (c) Zirconium fluoride ion: 0.2 to 4 g/l (d) Zinc Ion: 0.2~
7g/l (e) Hexavalent chromate ion/trivalent chromate ion: 3/
4 to 3/2 (weight ratio) (f) Chromic acid/zirconium fluoride ion: 10/
1 to 100/1 (weight ratio) ■Organic resin composition (weight ratio of non-volatile components) (a) Weight ratio of organic resin to silica and poorly soluble chromate: Organic resin/(silica + poorly soluble chromate) =80/20
~50/50 (b) Weight ratio of silica and poorly soluble chromate: silica/slightly soluble chromate = 37/3 to 20/20 (c
) Weight ratio of base resin and curing agent in organic resin: Base resin/
Curing agent = 95/5 to 60/40 (d) Weight ratio of organic resin, silica and poorly soluble chromate to organic coloring pigment: (organic resin + silica + poorly soluble chromate) / organic coloring pigment =
100/10~100/3

[0008] In each of the above configurations, the organic coloring pigment blended into the organic resin film or organic resin composition is preferably one selected from the group consisting of condensed polycyclic organic pigments and phthalocyanine organic pigments. More than one type of pigment is used.

[0009]

[Function] Examples of the zinc-based plated steel sheet which is the base of the steel plate of the present invention include galvanized steel plate, Zn-Ni alloy plated steel plate, Zn-Fe alloy plated steel plate, Zn-Mn alloy plated steel plate, Zn-Al alloy plated steel plate. , Zn-Co-C
Examples include r-alloy plated steel sheets and zinc-based composite plated steel sheets in which metal oxides are dispersed in the plating of these steel sheets. Alternatively, it may be a multilayer plated steel sheet plated with two or more layers of the same or different types of plating as described above. As a plating method, any practicable method among electrolytic method, melting method, and vapor phase method can be adopted, but from the viewpoint of selectivity of the underlying cold-rolled steel sheet,
Electrolytic methods are advantageous.

[0010] The chromate layer formed on the surface of the zinc-based plated steel sheet suppresses corrosion of the zinc-based plated steel sheet through the self-healing action of hexavalent chromate ions. The amount of adhesion of this chromate layer is 10 to 20 in terms of metallic chromium.
0 mg/m2, preferably 30 to 150 mg/m2. If the amount of adhesion is less than 10 mg/m2 in terms of metallic chromium, sufficient corrosion resistance cannot be expected;
If it exceeds mg/m2, chromium elution and weldability will deteriorate.

[0011] Chromate treatment is carried out by applying a treatment solution with the composition shown below to a plated steel plate, drying it without washing with water,
Obtain a film. (a) Chromic anhydride: 5-100 g/l (b) Phosphate ion: 0.5-20 g/l (c) Zirconium fluoride ion: 0.2-4 g/l (d) Zinc ion: 0.2 ~
7g/l (e) Hexavalent chromate ion/trivalent chromate ion: 3/
4 to 3/2 (weight ratio) (f) Chromic acid/zirconium fluoride ion: 10/
1 to 100/1 (weight ratio)

[0012] Here, the concentration of chromic anhydride is 5 g/l.
If it is less than that, a chromate layer cannot be sufficiently formed on the surface of the plated steel sheet, resulting in poor corrosion resistance. On the other hand, if the concentration of chromic anhydride exceeds 100 g/l, the amount of chromate film deposited will be too large and weldability will deteriorate. Phosphate ions have the effect of preventing gelation of trivalent chromate ions and the effect of reacting with zinc ions to form poorly soluble salts and improve corrosion resistance, but if it is less than 0.5 g/l, the present invention At the [hexavalent chromate ion]/[trivalent chromate ion] ratio in the coating-type chromate treatment solution specified by , the effect of preventing gelation becomes insufficient and there is a tendency for precipitation to occur in the treatment solution. On the other hand, if it exceeds 20 g/l, the p
Excessively lowering the H content promotes the dissolution of the zinc-plated steel sheet that is the object to be treated, and deteriorates the corrosion resistance.

Among fluorides, zirconium fluoride ions in particular form a complex with hexavalent chromate ions and suppress excessive elution of hexavalent chromate ions, which contribute most to corrosion resistance, from the chromate film. Although it is effective, if the concentration is less than 0.2 g/l, the effect of suppressing the elution of hexavalent chromate ions is insufficient, and the hexavalent chromate ions are quickly consumed, resulting in a slight deterioration of corrosion resistance. On the other hand, the concentration is 4g
If it exceeds /l, the surface of the zinc-based plated steel sheet will be excessively etched, and the corrosion resistance will deteriorate. Among metal ions, especially zinc ions, by converting the hexavalent chromate ions in the chromate film into zinc chromate, the hexavalent chromate ions are eluted during the degreasing process, which is a pretreatment process for automobile painting. However, when the concentration is 0.
If it is less than 2 g/l, the effect of suppressing the elution of hexavalent chromate ions is insufficient, and when the waste liquid of the degreasing liquid is released into the environment, it is necessary to treat the waste liquid to remove chromium ions. On the other hand, if the concentration exceeds 7 g/l, the chromate treatment solution tends to gel, which is not preferable.

[Hexavalent chromate ion]/[3
If the weight ratio of valent chromate ions is less than 3/4, the chromate treatment solution tends to gel, and the chromate film lacks hexavalent chromate ions, resulting in poor corrosion resistance. On the other hand, if the weight ratio of [hexavalent chromate ion]/[trivalent chromate ion] exceeds 3/2, the water resistance of the chromate film will deteriorate and the paint adhesion will be poor. [
If the weight ratio of [chromic acid]/[zirconium fluoride ion] is less than 10/1, the complex formation reaction with hexavalent chromate ion by zirconium fluoride ion proceeds excessively, and the hexavalent chromate ion inhibits the self-repairing effect of oxidation and deteriorates corrosion resistance. On the other hand, when the ratio exceeds 100/1, the complex formation reaction becomes insufficient and corrosion resistance also deteriorates.

Comparing the chromate films obtained by coating type chromate treatment and electrolytic chromate treatment, the coating type has superior corrosion resistance because it contains more hexavalent chromate ions in the coating. On the other hand, the electrolytic type has the advantage that the amount of chromium eluted during a pre-painting treatment process such as an automobile degreasing process is small, and the amount of film deposited can be easily adjusted. When considering corrosion resistance, coating type chromate treatment is most preferable.

Chromic acid in the chromate solution can be obtained by adding chromic anhydride, and [hexavalent chromate ion]
/ [Trivalent chromate ion] can be adjusted using oxalic acid, tannic acid,
This is carried out by reducing hexavalent chromate ions in the bath to trivalent chromate ions using a reducing agent such as starch, alcohol, or hydrazine. Further, phosphate ions can be obtained by adding orthophosphoric acid, ammonium phosphate, etc. Furthermore, zirconium fluoride ions are preferably added in the form of divalent ZrF6 ions, and (NH4)2ZrF6, H
It can be obtained by adding 2ZrF6 or the like.

The chromate solution in the present invention can be applied by any method such as a roll coater method, a dipping method, or a spray method.

[0018] The organic resin film formed as a second layer on the chromate film formed on the surface of the zinc-based plated steel sheet prevents excessive elution of hexavalent chromate ions in the chromate layer into the corrosive environment. In addition to suppressing corrosion and sustaining the anticorrosion effect, the silica and chromate added to the organic resin film further improve corrosion resistance.

The organic resin is selected from the group consisting of a base resin in which one or more basic nitrogen atoms and two or more primary hydroxyl groups are added to the end of an epoxy resin, a polyisocyanate compound, and a blocked isocyanate compound. and at least one selected curing agent. From the viewpoint of corrosion resistance and paint adhesion, the base resin is preferably a solvent-type epoxy resin that does not easily draw water into the film in a corrosive environment. As the above-mentioned epoxy resin, an epoxy resin which is a condensation product obtained by condensing bisphenol A and epichlorohydrin is excellent in terms of corrosion resistance, paint adhesion, etc. Examples of this epoxy resin include Epicoat 828, 1001, 1004, and 1 manufactured by Yuka Shell Epoxy Co., Ltd.
007, 1009, 1010, etc. can be used alone or in combination.

[0020] Furthermore, basic epoxy resins with one or more basic nitrogen atoms added to their terminals have a resin structure that is particularly resistant to alkali generated at the interface during cationic electrodeposition coating, which is applied to automobiles. Good adhesion is obtained without deterioration. Furthermore, by introducing 2 moles or more of primary hydroxyl groups into one molecule of the epoxy resin, the resin structure can be made more dense. In order to introduce a basic nitrogen atom and a primary hydroxyl group into an epoxy resin, for example, there is a method of adding an alkanolamine and/or an alkylalkanolamine to the epoxy group of the epoxy resin. These amines include, for example, monoethanolamine,
Examples include diethanolamine, dimethylaminoethanol, monopropanolamine, dipropanolamine, dibutanolamine, and these amines can be used alone or in combination.

Furthermore, if an average of 2 moles or more of primary hydroxyl groups can be introduced into one molecule of the epoxy resin, the epoxy resin can be partially modified with other compounds. Methods for partial modification include (1) esterification with monocarboxylic acids, (2) modification with aliphatic or aromatic amines, and (3) modification with oxyacids. There is also a modification method using dicarboxylic acid, but this method is not suitable for the resin composition of the present invention because it makes it difficult to control the molecular weight.

The above-mentioned epoxy resin can also be used as a water-dispersed or water-soluble resin by neutralizing its base portion with a low-molecular acid. However, when used in this way, it is not possible to obtain a strong film when heat-treated at low temperatures, and the acidic compound used for water solubilization forms a salt in the film, causing water to evaporate in a humid environment. Because it is easy to draw into the film, corrosion resistance and paint adhesion deteriorate. Furthermore, when used as a water-dispersed or water-soluble resin, there is a problem in that hexavalent chromate ions in the underlying chromate film are eluted into the resin solution, causing the resin solution to gel. Also from the above points, the resin composition is preferably a solvent type.

[0023] The type of solvent used in the resin composition is one of hydrocarbon type, ketone type, ester type, ether type, low molecular weight (C4 or less) alcohols, or alcohols having secondary or tertiary hydroxyl groups. A mixture of two or more types can be used, but alcoholic solvents with high boiling points are not preferred because they inhibit the curing reaction of the resin film.

[0024] In curing the resin composition, it is preferable that the main reaction is a urethanization reaction between the isocyanate of the curing agent and the hydroxyl group in the base resin, but in order to stably store the resin composition before coating, In order to control the reactivity of the isocyanate groups of the curing agent, it is necessary to block the isocyanate compound. As this blocking method, there is a blocking method in which the blocking group is removed during heating and the isocyanate group is regenerated.

Isocyanate compounds include aliphatic compounds having at least two isocyanate groups in one molecule;
There are alicyclic (including heterocycle) or aromatic isocyanate compounds, or compounds obtained by partially reacting these compounds with polyhydric alcohols. Examples of this include: (1) m- or p-phenylene diisocyanate, 2
, 4- or 2,6-tolylene diisocyanate, or p-xylene diisocyanate, hexamethylene diisocyanate, dimer acid diisocyanate, isophorone diisocyanate (2) The compound of (1) above alone or in a mixture, and a polyhydric alcohol (ethylene glycol, It is a reaction product of dihydric alcohols such as propylene glycol, trihydric alcohols such as glycerin and trimethylolpropane, tetrahydric alcohols such as pentaerythritol, hexahydric alcohols such as sorbitol and dipentaerythritol, etc. Compounds with at least two remaining isocyanate groups

[0026] Further, as the blocking agent, for example,
(1) Aliphatic monoalcohols such as methanol, ethanol, propanol, butanol, and octyl alcohol (
2) Monoethers such as ethylene glycol and/or diethylene glycol (3) Aromatic alcohols such as phenol and cresol (
4) There are oximes such as acetoxime and methyl ethyl ketone oxime, and by reacting one or more of these with the isocyanate compound, it is possible to obtain an isocyanate compound that is stably blocked at least at room temperature.

[0027] Such an isocyanate compound is blended into the base resin as a curing agent, and the blending ratio is base resin/curing agent = 95/5 to 60/40 (weight ratio of non-volatile content).
, preferably 90/10 to 70/30. Isocyanate compounds have water absorption properties, and if the base resin/curing agent ratio exceeds 90/10, the curing of the resin film will be insufficient, and corrosion resistance and paint adhesion will deteriorate, especially if the ratio exceeds 90/5. The trend becomes even more pronounced. On the other hand, 70/3
When the ratio is less than 0, paint adhesion deteriorates, and this tendency becomes more pronounced when the ratio is less than 60/40. Furthermore, an alkyl etherified amino resin obtained by reacting formaldehyde with one or more selected from melamine, urea, and benzoguanamine as a curing agent may be combined with an isocyanate compound.

Although the organic resin is sufficiently cured with the above-mentioned curing agent, it is desirable to use a curing accelerating catalyst in order to further increase the reactivity at low temperatures. Examples of the curing accelerating catalyst include N-ethylmorpholine, dibutyltin dilaurylate, cobalt naphthenate, stannous chloride, zinc naphthenate, and bismuth nitrate. Also,
Aiming at improving paint adhesion, processability, etc., acrylic, alkyd, or polyester resins may be used in combination with a resin composition having an epoxy resin as a base resin.

[0029] The present invention further improves corrosion resistance by blending silica and sparingly soluble chromate into the above-mentioned organic resin. It is presumed that when divalent Zn ions and the like are eluted from the base plating, silica reacts with the Zn ions, forms stable corrosion products over the entire surface of the steel plate, and exerts a corrosion-preventing effect. On the other hand, poorly soluble chromate elutes a small amount of hexavalent chromate ion, and the passivation effect of this hexavalent chromate ion exerts an anticorrosive effect, and the dissolution of SST, etc., progresses continuously. It is highly effective in such corrosive environments. The silica used in the present invention includes hydrophilic silica and hydrophobic silica, which are called colloidal silica and fumed silica. Among these silicas, hydrophilic silica can also be expected to improve corrosion resistance, but as will be described later, hydrophobic silica significantly improves corrosion resistance. The particle size of silica is 1 mμ to 50
A value of 0 mμ is suitable, and a range of 5 mμ to 100 mμ is particularly preferred.

Hydrophilic silica, known as colloidal silica (silica sol) or fumed silica, has its surface covered with hydroxyl groups (silanol groups) and exhibits hydrophilicity. Since this silanol group is highly reactive, it easily reacts with various organic compounds and can organicize the silica surface. Hydrophobic silica is obtained by subjecting some or most of the silanol groups on the surface of such hydrophilic silica to a substitution reaction with methyl groups, alkyl groups, etc. to make the silica surface hydrophobic. There are many different manufacturing methods for hydrophobic silica.
Typical examples include reactions with organic solvents such as alcohols, ketones, and esters, silanes, silazane, and polysiloxanes. There are heating methods, etc.

[0031] Although silica has an excellent anticorrosion effect,
Hydrophobic silica is particularly effective in improving corrosion resistance. For example, in the above-mentioned Japanese Patent Application Laid-Open No. 58-224174, etc., it is disclosed that hydrophilic colloidal silica is added to an organic resin. However, due to its strong hydrophilicity, hydrophilic silica has poor compatibility with solvents, and due to its strong hydrophilicity, it easily invites water penetration, which causes a decrease in corrosion resistance, especially in the initial stage in a humid environment. It is estimated that it is susceptible to rust. Therefore, in the present invention, it is preferable to blend silica whose surface has been made hydrophobic (hydrophobic silica) into the basic epoxy resin to improve compatibility with the basic epoxy resin and obtain high corrosion resistance. Examples of such hydrophobic silica include silica whose surface has been made hydrophobic with an organic solvent or a reactive silane compound, that is, hydrophobic ultrafine particle silica (for example, R974, R81 manufactured by Nippon Aerosil Co., Ltd.).
1, R812, R805, T805, R202, RY2
00, RX200, etc.). The hydrophobic silica described above is stably dispersed in the basic epoxy resin.

[0032] It is also believed that the hardly soluble chromate added to the resin suppresses corrosion of zinc-based plated steel sheets through a corrosion protection mechanism similar to that of the chromate layer. The sparingly soluble chromates used in the present invention include barium chromate (BaCrO4), strontium chromate (SrC
rO4), calcium chromate (CaCrO4), zinc chromate (ZnCrO4・4Zn(OH)2), potassium zinc chromate (K2O・4ZnO・4CrO3・3H
There are fine powders such as lead chromate (PbCrO4) and lead chromate (PbCrO4).

It is also possible to use a mixture of two or more of the above-mentioned poorly soluble chromates. However, from the viewpoint of corrosion resistance, barium chromate and strontium chromate are preferred because they can be expected to maintain the self-repairing effect of chromate ions over a long period of time. Moreover, barium chromate is preferable from the viewpoint of minimizing the elution of water-soluble chromium from the organic resin film in the pre-painting treatment process for automobiles.

[0034] In the present invention, by adding silica and slightly soluble chromate in a specific ratio to the organic resin composition, the most excellent corrosion resistance can be achieved due to the synergistic effect of the anticorrosion effects of both. That is, the weight ratio of silica and poorly soluble chromate is (a) organic resin/(silica + poorly soluble chromate) = 80
/20-50/50 (b) Silica/slightly soluble chromate = 37/3-20/2
When blended at a ratio of 0.0%, it is possible to obtain the most excellent corrosion resistance. Here, if the ratio of organic resin/(silica + sparingly soluble chromate) exceeds 80/20, the anticorrosion effect of silica and sparingly soluble chromate will not be sufficiently exerted, resulting in poor corrosion resistance. On the other hand, if it is less than 50/50, the effect of the organic resin as a binder will be insufficient and paint adhesion will deteriorate. In addition, the ratio of silica/poorly soluble chromate is 37.
Even if it exceeds /3 or less than 20/20, the synergistic effect will be insufficient and the corrosion resistance will be slightly inferior. In this way, by adding silica and poorly soluble chromate together in a limited amount, excellent corrosion resistance can be obtained even under a severe corrosive environment. In addition, even when silica and poorly soluble chromate are added together in this way, it is possible to use two or more different types of silica and poorly soluble chromate in combination, and it will work well under the conditions of the above mixing ratio. It is possible to obtain excellent corrosion resistance.

[0035] In the present invention, an organic coloring pigment is added in a specific ratio to the organic resin composition consisting of the above-mentioned organic resin, silica, and slightly soluble chromate, thereby coloring the organic resin film. , good identifiability can be achieved. That is, the weight ratio (nonvolatile content) of the organic resin, silica, and poorly soluble chromate to the organic coloring pigment in the organic resin composition.
However, when blended in the ratio of (organic resin + silica + poorly soluble chromate)/organic coloring pigment = 100/10 to 100/3, the best corrosion resistance, weldability, paint adhesion, and electrodeposition coating are achieved. It becomes possible to obtain uniqueness and distinctiveness. Here, if the ratio of (organic resin + silica + poorly soluble chromate)/organic coloring pigment is less than 100/10, the film becomes porous and corrosion resistance deteriorates. On the other hand, when it exceeds 100/3, the degree of coloring of the organic film is low and the distinguishability is poor.

[0036] Coloring pigments are broadly classified into organic and inorganic types, but since adding too much color pigment will deteriorate corrosion resistance, it is preferable to add as little color pigment as possible. From this point of view, in the present invention, an organic pigment with strong coloring power is used in the same amount. In addition, organic pigments are broadly classified into azo pigments, phthalocyanine pigments, and condensed polycyclic pigments, but there are few azo pigments that satisfy both acid/alkali resistance and solvent resistance, and are used in the pre-painting process of automobiles. Pigments may be eluted into degreasing liquids or phosphate treatment liquids, or into cationic electrodeposition coatings or top coats, causing problems such as color bleeding. On the other hand, phthanocyanine-based and condensed polycyclic pigments satisfy acid resistance, alkali resistance, and solvent resistance in a well-balanced manner. Preferably, one or more pigments are used. However, phthanocyanine pigments have only blue and green hues, so they have the disadvantage of poor versatility. In addition, among condensed polycyclic organic pigments, it has particularly excellent coloring power, acid/alkali resistance, and solvent resistance.
These include quinophthalone, quinacridone, and isoindolinone.

In addition, in the present invention, in addition to the above-mentioned additive components such as silica, poorly soluble chromate, and organic coloring pigment, other known additives (such as surfactants) and antirust pigments (such as chromium-based , non-chromium rust-preventive pigments, etc.), extender pigments, etc. can be blended. In the organic resin coating treatment in the present invention, the resin composition is usually applied by a roll coater method and then heat treated. , it is also possible to perform heat treatment.

The thickness of the organic resin film is 0.2 to 2 μm. If the film thickness is less than 0.2 μm, sufficient corrosion resistance cannot be expected, while if it exceeds 2 μm, weldability and electrodeposition coating properties will deteriorate. In addition, even higher corrosion resistance, weldability,
In order to satisfy electrodeposition coating properties, the thickness is 0.3 to 1.5 μm.
A range of is preferred. The baking treatment after applying the organic resin composition is carried out at a plate temperature of 50 to 200°C, preferably 60 to 150°C, and a dry film is obtained by maintaining this temperature for several seconds to several minutes. This baking is usually done by supplying hot air, but is not limited to this. In the present invention, a desired film can be obtained by baking at a relatively low temperature. Here, the above baking temperature is 50℃
If it is less than that, there is a problem that the amount of chromium eluted increases, so a temperature of 60° C. or higher is preferable from the viewpoint of chromium elution. On the other hand, if the baking temperature exceeds 200°C, not only will economic efficiency be impaired, but the corrosion resistance will also deteriorate. This is because when baking at a high temperature exceeding 200°C, the moisture contained in the chromate film components volatilizes and the dehydration condensation reaction between the hydroxyl groups added to chromium progresses rapidly, causing cracks in the chromate film and damage to the chromate film. This is presumed to be due to progress of destruction and reduction of hexavalent chromate ions, which reduces the passivation effect of hexavalent chromate ions. The baking temperature is preferably 150° C. or lower, which is advantageous in terms of corrosion resistance and economical efficiency. Further, when the present invention is applied to a high-strength steel plate having bake hardenability (so-called BH steel plate), a baking temperature of 150° C. or lower is particularly preferable.

According to the present invention, the above-described composite coating can be applied to both or one side of a plated steel sheet to produce, for example, a surface-treated steel sheet in the following embodiment. (1) One side... Plating film - Chromate film - Organic resin composition film One side... Fe side (2) One side... Plating film - Chromate film - Organic resin composition film One side... Plating film (3) Both sides... Plating film - chromate film - organic resin composition film The composite coated steel sheet of the present invention can be used not only for automobiles but also for home appliances, building materials, etc.

[0040]

[Example] As a surface-treated steel sheet for an automobile body, a galvanized steel sheet was degreased with alkali, washed with water, dried, and subjected to chromate treatment. Then, an organic resin composition was applied with a roll coater and baked.

The obtained organic composite coated steel sheet was subjected to various evaluation tests for corrosion resistance, paint adhesion, weldability, cationic electrodeposition paintability, distinguishability, alkali resistance, and bleed resistance. The processing conditions of this example are as follows. (1) Zinc-based plated steel plate A zinc-based plated steel plate with a thickness of 0.8 mm shown in Table 1 was used as an original plate. (2) Chromate treatment chromic acid concentration, phosphate ion concentration, zirconium fluoride ion concentration, zinc ion concentration,
A treatment solution with various weight ratios of hexavalent chromate ions/trivalent chromate ions and chromic acid/zirconium fluoride ions was applied to the steel plate using a roll coater,
Dry without rinsing. The composition of the treatment liquid is shown in Tables 2 and 3.

(3) Organic resin composition Table 4 shows the organic resins (base resin and curing agent) used. In addition, resin A, resin B, curing agent a, and curing agent b in the same table were created by the method shown below. ■Resin A: Epicoat 1009 manufactured by Yuka Shell Epoxy Co., Ltd. (1880 g = 0.5 mol) and methyl isobutyl ketone/xylene = 1/1 were placed in a reaction apparatus equipped with a stirring device, a reflux condenser, a thermometer, and a liquid dropping device. After adding 1000 g of the mixed solvent (weight ratio), the mixture was stirred and heated to uniformly dissolve the mixture at the boiling point of the solvent. Next, 70g of di(n-propanol)amine was cooled to 70°C and collected into a liquid dropping device.
was added dropwise over a period of 30 minutes. During this time, the reaction temperature was kept at 70°C.
was held at After the dropwise addition was completed, the temperature was maintained at 120°C for 2 hours to complete the reaction. The obtained reaction product is referred to as resin A. The active ingredient of Resin A is 66%. ■Resin B: In a reaction apparatus equipped with a reflux condenser, a stirring device, a thermometer, and a nitrogen gas blowing device, pelargonic acid (reagent) was added to Epicoat 1004 (1600 g) manufactured by Yuka Shell Epoxy Co., Ltd.
57 g and 80 g of xylene were added, and the reaction was carried out at 170° C. until the acid value of the reactant became approximately 0. Next, xylene was removed under reduced pressure to obtain a reaction intermediate. This reaction intermediate (1650 g) and 1000 g of xylene were added to a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a liquid dropping apparatus, and then heated to 100°C, and 65 g of diethanolamine and 65 g of diethanolamine separated into a liquid dropping apparatus were heated to 100°C. 30 g of monoethanolamine was added dropwise over 30 minutes. After the dropwise addition was completed, the temperature was maintained at 120°C for 2 hours to complete the reaction. The obtained reaction product is referred to as resin B. The active ingredient of Resin B was 63%. ■
Curing agent a: 250 g of 4,4-diphenylmethane diisocyanate and 50 g of diisobutyl ketone were placed in a reaction apparatus equipped with a thermometer, a stirrer, and a reflux condenser, and after stirring and mixing them uniformly, 184 g of ethylene glycol monoethyl ether was added, and the mixture was heated at 90°C. The mixture was reacted for 2 hours at 110° C. and then for 3 hours at 110° C. to obtain a completely urethanized curing agent a. The active ingredient of curing agent a was 89%. ■ Curing agent b: Isophorone diisocyanate 222
After adding 100 g of methyl isobutyl ketone to it and dissolving it uniformly, 88 g of a 50% solution of trimethylolpropane in methyl isobutyl ketone was added to the isocyanate solution under stirring kept at 70°C from the dropping funnel. It took some time to drip. Next, the temperature was further maintained at 70°C for 1 hour, and then at 90°C for 1 hour. Thereafter, 230 g of n-butyl alcohol was added and reacted at 90° C. for 3 hours to obtain blocked isocyanate. This reaction product is referred to as curing agent b. The active ingredient of hardening agent b is 76%
Met.

Furthermore, Tables 5, 6 and 7 show the silica, poorly soluble chromate and color pigments to be added to the organic resin, respectively. Tables 8 to 21 show the structure of the organic resin-coated steel sheet produced as described above and the evaluation results of corrosion resistance, paint adhesion, weldability, electrodeposition coating property, identifiability, alkali resistance, and bleed resistance. The evaluation method for each characteristic is as follows.

(1) Corrosion Resistance After the test material was degreased with alkali, the back surface and edges were sealed with tape, and a salt spray test was conducted for 3,000 hours, and the area of rust formation was evaluated. ◎: Less than 50% white rust ○: 50% or more white rust and no red rust △: Less than 5% red rust ×: 5% or more red rust

(2) Paint adhesion The test material was subjected to phosphate treatment, cationic electrodeposition coating (U-600, 20 μm, manufactured by Nippon Paint Co., Ltd.), and top coating (Lugabake B-531, manufactured by Kansai Paint Co., Ltd.). 35μm)
After that, the sample was immersed in ion-exchanged water at 40° C. for 240 hours, and then a 1 mm grid tape peeling test was conducted, and the peeled area of the coating film was evaluated. ◎: No peeling ○: Peeling area less than 3% △: Peeling area 3% or more, less than 10% ×: Peeling area 10% or more

(3) Weldability Electrode: CF type, pressure: 200 kgf, energization time: 10 cycles/50 Hz, welding current: 9 kA. Continuous dot performance was tested and evaluated by the number of continuous dots. ◎: 5000 points or more ○: More than 4000 points, less than 5000 points △: More than 3000 points, less than 4000 points ×: Less than 3000 points

(4) Electrodeposition coating properties After the test materials were treated with phosphate, cationic electrodeposition coating (U-600, 20 μm, manufactured by Nippon Paint Co., Ltd.) was performed, and evaluation was made based on the density of craters. ◎: No craters ○: 1 piece/dm2 or more, less than 5 pieces/dm2 △: 6 pieces/dm
m2 or more, less than 10 pieces/dm2 ×: 11 pieces/dm2 or more

(5) Distinguishability The degree of coloring was evaluated visually. ◎: Easily distinguishable colors ○: Somehow able to identify colors △: Difficult to distinguish colors ×: Impossible to identify color

(6) Alkali Resistance The test materials were degreased with alkali (FC-L4460 manufactured by Nippon Parkerizing Co., Ltd.), and the change in color before and after degreasing was visually evaluated. ◎: No color change ○: Slight color change observed △: Color change easily observed ×: Completely bleached

(7) Bleed resistance test material was coated under the same conditions as (2) and coated on a cold rolled steel plate (2).
), and the degree of color bleeding from the base was visually evaluated. ◎: No change in color ○: Slight color bleeding △: Slight color bleeding ×: Color bleeding is clearly observed

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

[0055]

[Table 5]

[0056]

[Table 6]

[0057]

[Table 7]

[0058]

[Table 8]

[0059]

[Table 9]

[0060]

[Table 10]

[0061]

[Table 11]

[0062]

[Table 12]

[0063]

[Table 13]

[0064]

[Table 14]

[0065]

[Table 15]

[0066]

[Table 16]

[0067]

[Table 17]

[0068]

[Table 18]

[0069]

[Table 19]

[0070]

[Table 20]

[0071]

[Table 21]

[0072]

As described above, according to the present invention, by coloring the resin film layer of an organic composite coated steel sheet with a specific pigment, excellent corrosion resistance, weldability, paint adhesion, and electrodeposition coating properties can be achieved. Furthermore, it is possible to obtain an organic composite-coated steel sheet that can easily identify the type of steel sheet and the front and back sides of the steel sheet according to the coating amount, etc., and can also be easily distinguished from a cold-rolled steel sheet.

Claims (4)

[Claims] Claim 1: A chromate layer with an adhesion amount of 10 to 200 mg/m2 in terms of metallic chromium is provided as a first layer on the surface of a zinc-plated steel sheet, and a second layer on top of the chromate layer is formed of (1) an epoxy resin terminal layer; consisting of a base resin to which one or more basic nitrogen atoms and two or more primary hydroxyl groups are added, and at least one curing agent selected from the group consisting of polyisocyanate compounds and blocked isocyanate compounds. Organic resin (2) Silica (3) Slightly soluble chromate (4) Organic resin film with a thickness of 0.2 to 2 μm containing organic coloring pigments in the following proportions for corrosion resistance, weldability, and paint adhesion. , an organic composite coated steel sheet with excellent electrodeposition coating properties and distinguishability. ■Weight ratio of organic resin to silica and poorly soluble chromate:
Organic resin/(silica + poorly soluble chromate) = 80/20
~50/50 ■Weight ratio of silica and sparingly soluble chromate: silica/poorly soluble chromate = 37/3 to 20/20 ■Weight ratio of base resin and curing agent in organic resin: Base resin/curing agent =95/5～
60/40■ Weight ratio of organic resin, silica, and poorly soluble chromate to organic coloring pigment: (organic resin + silica + poorly soluble chromate)/organic coloring pigment = 100/10 to 100/3 2. The organic coloring pigment blended into the organic resin film is one or more pigments selected from the group consisting of condensed polycyclic organic pigments and phthalocyanine organic pigments. Organic composite coated steel sheet with excellent corrosion resistance, weldability, paint adhesion, electrocoatability, and identification. [Claim 3] After applying a chromate treatment liquid whose liquid composition is adjusted to the following conditions (■) to the surface of a zinc-based plated steel sheet,
By performing chromate treatment by drying without washing with water, a chromate layer with an adhesion amount of 10 to 200 mg/m2 in terms of metal chromium is formed, and then (1) one or more basic nitrogen atoms are attached to the end of the epoxy resin. an organic resin (2) comprising a base resin to which is added two or more primary hydroxyl groups, and at least one curing agent selected from the group consisting of a polyisocyanate compound and a blocked isocyanate compound; and silica (3). Applying an organic resin composition containing a sparingly soluble chromate (4) organic coloring pigment in the following proportions,
By heat treatment, an organic resin film with a film thickness of 0.2 to 2 μm is formed on the upper layer of the chromate layer, which improves corrosion resistance, weldability, paint adhesion, electrodeposition coating property, and identifiability. A method for producing an excellent organic composite coated steel sheet. ■ Chromate treatment solution composition (a) Chromic anhydride: 5 to 100 g/l (b) Phosphate ion: 0.5 to 20 g/l (c) Zirconium fluoride ion: 0.2 to 4 g/l (d) Zinc Ion: 0.2~
7g/l (e) Hexavalent chromate ion/trivalent chromate ion: 3/
4 to 3/2 (weight ratio) (f) Chromic acid/zirconium fluoride ion: 10/
1 to 100/1 (weight ratio) ■Organic resin composition (weight ratio of non-volatile components) (a) Weight ratio of organic resin to silica and poorly soluble chromate: Organic resin/(silica + poorly soluble chromate) =80/20
~50/50 (b) Weight ratio of silica to poorly soluble chromate: silica/slightly soluble chromate = 37/3 to 20/20 (c) Weight ratio of base resin to curing agent in organic resin: Base Resin/curing agent=9
5/5 to 60/40 (d) Weight ratio of organic resin, silica, and poorly soluble chromate to organic coloring pigment: (organic resin + silica + poorly soluble chromate)/organic coloring pigment = 100/10 to 100 /3 4. The organic coloring pigment blended into the organic resin composition is one or more pigments selected from the group consisting of fused polycyclic organic pigments and phthalocyanine organic pigments. A method for producing an organic composite coated steel sheet that has excellent corrosion resistance, weldability, paint adhesion, electrodeposition coating properties, and identification.