JPH0523638A - Organic composite coated steel plate having excellent outer surface corrosion resistance and image clarity and its production - Google Patents

Abstract

PURPOSE:To secure mainly excellent outer surface corrosion resistance and image clarity by laminating a specified chromate layer as a primary layer and a specified organic film consisting essentially of block urethane modified epoxy resin as secondary layer on a zinc electroplated steel plate. CONSTITUTION:An organic composite coated steel plate is constituted of chromate layer provided as a primary layer on a zinc electroplated steel plate and, upper the primary layer, an organic coating layer as secondary layer. The chromate layer is specified to 10-200mg/m<3> attached quantity expressed in terms of metallic chromium. On the other hand, an organic coating is composed by adding a rust preventive additive (D) to block urethane-modified epoxy resin (C) at a wt. ratio of C/D=90/10-40/60 which is formed by mixing block urethane (B) consisting of polyol, polyisocianate and a blocking with modified epoxy resin (A) consisting of an epoxy resin and a multifunctional amine at a wt. ratio of A/B=95/5-50/50, and the thickness of the coating is specified to 0.2-2mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an organic composite which is used for automobile bodies, home electric appliances, etc., and has excellent external surface rust resistance and image clarity as well as powdering resistance, weldability and paint adhesion. The present invention relates to a coated steel sheet and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, in cold regions such as North America and Northern Europe, corrosion of automobile bodies due to salt used for road freezing prevention in winter has become a major social problem. As one of the measures for rust prevention of automobile bodies, the present situation is that the use ratio of the surface-treated steel sheet excellent in corrosion resistance is increasing in place of the conventional cold-rolled steel sheet.

As such a surface-treated steel sheet, Japanese Patent Laid-Open No.
The organic composite-coated steel sheet as disclosed in JP-A No. 4-8033 and JP-A No. 2-15177 can be mentioned.
These steel sheets are based on a zinc-based plated steel sheet and have a chromate film on the first layer, and a second layer on the first layer, and one or more basic nitrogen atoms and two nitrogen atoms at the end of the epoxy resin as the second layer. A base resin to which the above primary hydroxyl groups are added, and an organic resin film obtained by adding silica and a sparingly soluble chromate in a specific ratio to an organic resin composed of a polyisocyanate compound and a block isocyanate compound. An organic composite coated steel sheet having excellent corrosion resistance, weldability, powdering resistance, and paint adhesion.

[0004]

On the other hand, with the recent trend toward higher quality and individuality of automobiles, the finish quality after painting, especially the sharpness has come to be emphasized. However, although the organic composite coated steel sheet as described above has excellent properties with respect to the perforation resistance required for the outer surface and inner surface of the automobile body, the outer and outer surfaces of the automobile body are When applied to the outer surface side of the outer plate for the purpose of improving the outer surface rust resistance of the outer side, there is a problem that the sharpness is slightly inferior to the conventionally used zinc-based plated steel sheet. Further, it is hard to say that these organic composite coated steel sheets have sufficient characteristics in terms of outer surface rust resistance.

The present invention has been made to solve the above-mentioned problems, and when applied to the outer panel of an automobile body, it has excellent outer surface rust resistance and image clarity. It is an object of the present invention to provide an organic composite coated steel sheet having the above and a manufacturing method thereof.

[0006]

In order to achieve such an object, the organic composite coated steel sheet of the present invention has the following constitution.

(1) On the surface of a zinc-based plated steel sheet, a chromium layer having an adhesion amount of 10 to 200 mg / m ^{2 in} terms of metallic chromium is provided as a first layer, and an epoxy resin and a multi-layer resin are provided as a second layer on the chromium layer. For the modified epoxy resin (A) composed of a functional amine, a block urethane (B) composed of a polyol, polyisocyanate and a blocking agent is added A / B =
The block urethane-modified epoxy resin mixed in the ratio of 95/5 to 50/50 (weight ratio) has a rust-preventive additive of block urethane-modified epoxy resin / rust-preventive additive = 90/10.
Film thickness of 0.2 added at a ratio of 40 to 60 (weight ratio)
An organic composite-coated steel sheet having an outer coating of ˜2 μm and excellent in external surface rust resistance and image clarity.

(2) The organic composite coated steel sheet according to (1) above, wherein the rust preventive additive constituting the organic coating is silica and which is excellent in outer surface rust resistance and image clarity.

(3) The organic composite-coated steel sheet according to (1) above, wherein the rust-preventive additive constituting the organic film is a poorly soluble chromate, which is excellent in external surface rust resistance and image clarity. steel sheet.

(4) In the organic composite-coated steel sheet according to (1) above, the rust-preventive additive constituting the organic coating is silica and sparingly soluble chromate in the following proportions (weight ratios) and rust-resistant outer surface. Organic coated steel sheet with excellent transparency and sharpness. Silica / Slightly soluble chromate = 90/10 to 10/9
0 Moreover, the manufacturing method of this invention for obtaining such an organic composite coating steel plate has the following structures.

(5) Chrome on the surface of the zinc-based plated steel sheet
Solution is applied and a chromate treatment of drying without washing with water is performed, and then a modified epoxy resin (A) composed of an epoxy resin and a polyfunctional amine is treated with a polyol,
A block urethane-modified epoxy resin obtained by mixing a block urethane (B) composed of polyisocyanate and a blocking agent at a ratio of A / B = 95/5 to 50/50 (weight ratio of non-volatile content) is blocked with a rust preventive additive. Urethane-modified epoxy resin / antirust additive = 90/10 to 40/60 (weight ratio of non-volatile content) The coating composition is applied and baked, which is characterized in the above (1). A method for producing an organic composite coated steel sheet excellent in the described outer surface rust resistance and image clarity.

(6) A method for producing an organic composite-coated steel sheet excellent in outer surface rust resistance and image clarity, wherein the rust preventive additive constituting the coating composition is silica in the production method described in (5) above.

(7) In the production method described in (5) above, an organic composite coated steel sheet excellent in outer surface rust resistance and image clarity, in which a rust preventive additive constituting a coating composition is a poorly soluble chromate. Manufacturing method.

(8) In the production method described in (5) above, the rust-preventive additive constituting the coating composition is silica having the following proportions (weight ratio) and a sparingly soluble chromate. And a method for producing an organic composite coated steel sheet having excellent image clarity. Silica / Slightly soluble chromate = 90/10 to 10/90

[0015]

The details of the present invention and the reasons for limitation thereof will be described below. Examples of the zinc-based plated steel sheet serving as a base are a zinc-plated steel sheet, a Zn-Ni alloy-plated steel sheet, a Zn-Fe alloy-plated steel sheet, a Zn-Mn alloy-plated steel sheet, a Zn-Al alloy-plated steel sheet, a Zn-Cr alloy-plated steel sheet. , Zn-Co-
Examples thereof include Cr alloy-plated steel sheets, and further zinc-based composite plated steel sheets obtained by dispersing and plating metal oxides, sparingly soluble chromates, polymers and the like on these. Further, it may be a multi-layer plated steel sheet obtained by plating two or more layers of the same kind or different kinds of plating as described above. As the plating method, any of the electrolytic method, the melting method, and the vapor phase method that can be implemented can be adopted, but the electrolytic method is advantageous from the selectivity of the cold-rolled steel sheet as the base.

The chromate layer formed on the surface of the zinc-based plated steel sheet suppresses corrosion of the zinc-based plated steel sheet by the self-repairing action of hexavalent chromium by chromate ions. The amount of adhesion of this chromate layer is 1 in terms of metallic chromium.
If it is less than 0 mg / m ² , sufficient corrosion resistance cannot be expected, while if it exceeds 200 mg / m ² , weldability deteriorates. Therefore, the amount of adhesion of the chromate layer is 10 to ²⁰⁰ mg / m ^{2 in} terms of metallic chromium. Further, in order to satisfy higher corrosion resistance and weldability, it is preferably in the range of ²⁰ to 100 mg / m ^{2 in} terms of metallic chromium.

As the chromate treatment for forming the chromate layer, any of reactive type, electrolytic type and coating type methods can be applied. From the viewpoint of corrosion resistance,
A coating type containing a large amount of hexavalent chromium chromate ions in the coating layer is preferable.

The coating type chrome treatment is mainly carried out on a partially reduced chromic acid aqueous solution, and is made of a water-soluble or water-dispersible acrylic resin, polyester resin or other organic resin silica, alumina, titania, zirconia or the like. Oxide colloids and / or powders Acids such as molybdic acid, tungstic acid, vanadic acid and / or salts thereof Phosphoric acid such as phosphoric acid, polyphosphoric acid Zirconium fluoride, silicofluoride, titanium fluoride, etc. Zinc ion, etc. Conductive fine powder such as metal ion iron phosphide, antimony-deposited tin oxide, etc. Of the above-mentioned components (1) to (3), if necessary, one or more kinds of treatment liquids are applied to a zinc-based plated steel sheet, Dry without washing with water. The coating type chrome treatment is usually
The treatment liquid is applied by a roll coater method, but it is also possible to adjust the application amount by an air knife method or a roll drawing method after applying by a dipping method or a spray method.

As described above, the organic film formed as the second layer on the upper layer of the chromate layer formed on the surface of the zinc-based plated steel sheet is the hexavalent chromate ion in the chromate layer. It suppresses excessive elution into the corrosive environment, maintains the anticorrosion effect, and further improves the corrosion resistance by silica and chromate added in the organic film. If the film thickness of this organic film is less than 0.2 μm, sufficient corrosion resistance cannot be expected, while if it exceeds 2 μm, the weldability and sharpness deteriorate. Therefore, the film thickness of the organic film is 0.2 to 2 μm.
And Further, in order to satisfy higher corrosion resistance, weldability and sharpness, a range of 0.3 to 1.5 μm is preferable.

This organic film comprises a modified epoxy resin (A) consisting of an epoxy resin and a polyfunctional amine, and a polyolefin.
Block urethane (B) consisting of a polyisocyanate and a blocking agent, A / B = 95/5 to 50/50
Of the block urethane-modified epoxy resin and a rust preventive additive added in a predetermined ratio.

As the epoxy resin, bisphenol A, bisphenol F, novolac, etc. are glycidyl ether.
It is possible to use a tellurized epoxy resin, an epoxy resin obtained by adding propylene oxide or ethylene oxide to bisphenol A to give a glycidyl ether, and the like. Furthermore, an aliphatic epoxy resin, an alicyclic epoxy resin, and a polyether type epoxy resin can also be used,
It is also possible to use two or more of these epoxy resins in combination. Here, the epoxy equivalent of the epoxy resin is preferably 400 or more from the viewpoint of corrosion resistance.

A modified epoxy resin (A) is obtained by reacting a glycidyl group of these epoxy resins with a polyfunctional amine.
Can be obtained. Examples of polyfunctional amines include ethanol
Primary alkanolamines such as ruamine, propanolamine, isopropanolamine, butanolamine,
Primary alkylamines such as propylamine, butylamine, octylamine, decylamine, ethylenediamine,
Examples thereof include diethylenetriamine, tetraethylenepentamine, xylenediamine, aminoethylpiperazine, norbornanediaminomethyl and the like having two or more active hydrogens in one molecule, and it is also possible to use two or more kinds of these amines in combination. As the polyfunctional amine, alkanolamine is particularly preferable from the viewpoint of corrosion resistance and coating adhesion.

As a synthetic example of the modified epoxy resin (A), the active hydrogen of the polyfunctional amine is mixed in an amount of 1.1 to 1.8 times the equivalent of the glycidyl group of the epoxy resin, and both are mixed to obtain 70 to 150. It can be obtained by reacting at 4 ° C. for 4 to 10 hours.

The blocked urethane of the present invention is a compound in which the isocyanate group having a strong activity of the isocyanate compound is protected by a suitable compound to make it inactive, and the blocking agent is dissociated by heating to easily release the isocyanate. It regenerates the activity of the group. That is, it has a role as a curing agent for the modified epoxy resin.

As the polyol, ethylene glycol
, Propylene glycol, 1,6-hexanedio-
, Diethylene glycol, triethylene glycol and other divalent alcohols, glycerin, trimethylolpropane and other trivalent alcohols, pentaerythritol and other low molecular weight polyols, and caprolactone or low molecular weight Examples include polyester polyols obtained from polyols and dicarboxylic acids, and high molecular weight polyols having a molecular weight of 400 or more, such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol. It is also possible to use two or more kinds of polyol together. Here, as the polyol, when a polymer polyol is used, an appropriate hydrophilicity is imparted to the organic film, the compatibility with the cationic electrodeposition coating is improved, and a smooth electrodeposition coated surface is obtained. It is preferable because it has excellent image clarity after top-coating.

As the polyisocyanate, aliphatic isocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate. ,
Use of aromatic isocyanate such as 2,6-tolylene diisocyanate, alicyclic isocyanate such as isophorone diisocyanate, norbornane diisocyanate methyl, and mixtures and polynuclear compounds thereof You can

As the blocking agent, a phenol type compound such as phenol, a lactam type compound such as ε-caprolactam, an oxime type compound such as methyl ethyl ketoxime,
An imine compound such as ethyleneimine can be used, and a mixture of two or more kinds of these can also be used.

As the block isocyanate (B), a prepolymer is synthesized by mixing and reacting both of them so that the isocyanate group of the polyisocyanate becomes excessive with respect to the hydroxyl group of the polyol. It can be obtained by protecting the residual isocyanate group of the prepolymer with a blocking agent. The reaction temperature of these is 30 to 100 ° C.

The block urethane-modified epoxy resin of the present invention can be obtained by mixing the above-mentioned modified epoxy resin (A) and block urethane (B). The mixing ratio (weight ratio of non-volatile components) is in the range of A / B = 95/5 to 50/50. If the ratio of the modified epoxy resin (A) to the block urethane (B) exceeds 95/5, there is a problem that the image clarity after the middle / top coating is deteriorated. Further, if the ratio of the modified epoxy resin (A) is less than 50/50, the corrosion resistance deteriorates. Further, in order to obtain higher image clarity and corrosion resistance, it is preferable that the range of A / B is 90/10 to 60/40.

In the present invention, corrosion resistance can be improved by incorporating silica and / or a sparingly soluble chromate into the block urethane-modified epoxy resin.

Silica has the effect of promoting the formation of basic zinc chloride, which is effective in suppressing corrosion, among the corrosion products of galvanized steel sheets, and it dissolves in trace amounts in the corrosive environment to form silicate ions. It is presumed that, by functioning as a film-forming corrosion inhibitor, the anticorrosion effect is exerted. Here, as the amount of silica added to the block urethane-modified epoxy resin, if the weight ratio of the block urethane-modified epoxy resin / nonvolatile content of silica exceeds 90/10, the anticorrosion effect due to silica is not sufficiently exerted and the corrosion resistance Is inferior. On the other hand, if it is less than 40/60, the effect of the block urethane-modified epoxy resin as a binder becomes insufficient, and the coating adhesion deteriorates. Therefore, the weight ratio of the non-volatile component of the block urethane modified epoxy resin / silica is preferably 90/10 to 40/60.

The silica used in the present invention is dry silica (for example, AEROSIL 130 manufactured by Nippon Aerosil Co., Ltd.,
AEROSIL 200, AEROSIL 300, AEROSIL 380, AEROSIL R97
2, AEROSIL R811, AEROSIL R805, etc., organosilica sol (for example, MA-ST, IPA-ST, manufactured by Nissan Chemical Industries, Ltd.)
NBA-ST, IBA-ST, EG-ST, XBA-ST, ETC-ST, DMAC-ST
Etc.), precipitated wet silica (eg T manufactured by Tokuyama Soda Co., Ltd.)
-32 (S), K-41, F-80, etc.), gel wet silica (eg,
Syloid 244, Syloid 150, Syloid 72, Syloid 65, SHIELDEX, etc. manufactured by Fuji Davisson Chemical Co., Ltd.) can be used. It is also possible to use a mixture of two or more of the above silicas.

When hydrophobic silica whose surface is made hydrophobic by substituting a silanol group on the silica surface with a methyl group or the like is added to the block urethane-modified epoxy resin,
The organic film and the cationic electrodeposition coating become poorly compatible and a smooth electrodeposition coating surface cannot be obtained, resulting in poor image clarity after the middle / top coating. Therefore, in order to obtain excellent image clarity, silica whose surface is not made hydrophobic is preferable.

Further, the sparingly soluble chromate added to the organic film is dissolved in a corrosive environment in a trace amount, so that 6
It is considered that valent chromate ions are released and the corrosion of the zinc-based plated steel sheet is suppressed by a mechanism similar to that of the chromate layer. As for the amount of the poorly soluble chromate added to the block urethane-modified epoxy resin, if the weight ratio of the nonvolatile content of the block urethane-modified epoxy resin / the poorly soluble chromate exceeds 90/10, the poorly soluble chromium salt is added. Corrosion resistance is poor because the anticorrosive effect of acid salts is not fully exerted. On the other hand, 40 /
If it is less than 60, the effect of the block urethane-modified epoxy resin as a binder becomes insufficient and the coating adhesion deteriorates. Therefore, the weight ratio of non-volatile component of block urethane modified epoxy resin / hardly soluble chromate is 90 /
It is preferably 10 to 40/60.

The sparingly soluble chromate used in the present invention includes barium chromate (BaCrO ₄ ), strontium chromate (SrCrO ₄ ), calcium chromate (CaCrO ₄ ), zinc chromate (ZnCrO ₄ .4Zn (OH) ) ₂ ), zinc potassium chromate (K ₂ O ・ 4ZnO
_{· 4CrO 3 · 3H 2 O)} , it can be used fine powder such as lead chromate (PbCrO _4). It is also possible to use a mixture of two or more of the above-mentioned hardly soluble chromates. However, from the viewpoint of corrosion resistance, it is preferable to use barium chromate or strontium chromate, which can be expected to have a self-repairing effect by chromate ions for a long period of time. In addition, barium chromate, which has a low solubility in water, is preferable from the viewpoint of minimizing the elution of water-soluble chromium from the organic film in the pretreatment process for coating on automobiles.

In the present invention, the block urethane-modified epoxy resin is compounded with silica and a sparingly soluble chromate in a specific ratio, whereby the most excellent corrosion resistance can be realized due to the synergistic effect of both anticorrosion effects. That is, in the weight ratio of non-volatile components of silica and sparingly soluble chromate, block urethane modified epoxy resin / (silica + sparingly soluble chromate) = 90/10 to 40/60 silica / sparingly soluble chromate = 90 / When it is mixed in a ratio of 10 to 10/90, the best corrosion resistance can be obtained. Here, when the block urethane-modified epoxy resin / (silica + slightly soluble chromate) exceeds 90/10, the anticorrosion effect due to silica and the sparingly soluble chromate is not sufficiently exerted, resulting in poor corrosion resistance. On the other hand, 40/60
If the amount is less than the above, the effect of the block urethane-modified epoxy resin as a binder becomes insufficient, and the adhesiveness of the paint deteriorates. Also, silica / slightly soluble chromate is 90/10
Even if it exceeds, even if it is less than 10/90, the synergistic effect becomes insufficient and the corrosion resistance is slightly inferior.

In the present invention, the above silica and / or
Alternatively, the sparingly soluble chromate is the main additive component in the block urethane-modified epoxy resin, but other than that, a silane coupling agent, a coloring pigment (for example, a condensed polycyclic organic pigment, a phthalocyanine organic pigment, etc.) , Coloring dyes (eg, azo dyes, azo metal complex salt dyes, etc.), lubricants (eg, polyethylene wax, Teflon, graphite, molybdenum disulfide, etc.), rust preventive pigments (eg, aluminum dihydrogen tripolyphosphate, It is also possible to further blend one or more of aluminum phosphomolybdate, zinc phosphate, etc.), conductive pigments (eg, iron phosphide, antimony tin oxide, etc.), surfactants and the like.

As a method for applying the above coating composition to a zinc-based plated steel sheet, the coating composition is usually applied by a roll coater method, but after applying by a dipping method or a spray method, an air knife is used. It is also possible to adjust the coating amount by a roll method or a roll drawing method. Further, as the heat treatment method after applying the coating composition, a hot air oven, a high frequency induction heating oven, an infrared oven, or the like can be used. The heat treatment is performed at an ultimate plate temperature of 50 to 300 ° C, preferably 60 to 250 ° C. Furthermore, when the present invention is applied to a BH steel sheet, heat treatment at 150 ° C. or lower is preferable.

The organic composite-coated steel sheet of the present invention usually has a zinc-based plating film + chromate layer + organic film on both sides, but if necessary, it is applied to only one side and the other side is the steel sheet surface, zinc. It is also possible to use a system-plated surface or a zinc-based plating film + chromate film surface.

[0040]

[Example] As a surface-treated steel sheet for automobile bodies, a zinc-based plated steel sheet was degreased with alkali, washed with water and dried, and then chrome-coated.
The coating composition was applied by a roll coater and baked. Each of the obtained organic composite coated steel sheets was tested for outer surface rust resistance, image clarity, paint adhesion, and weldability. The processing conditions of this example are as follows.

(1) Zinc-based plated steel sheet A cold-rolled steel sheet having a thickness of 0.8 mm and a surface roughness (Ra) of 1.0 μm was subjected to various zinc-based plating and used as a treated original plate.
(See Table 1)

(2) Chromate treatment Coating type chromate treatment A chromate treatment liquid having the following liquid composition was used as a roll coater.
And dried without washing with water. Krome
The amount of adhesion of the coating layer was adjusted by changing the peripheral speed ratio of the pickup roll of the roll coater and the applicator roll. Chromic anhydride: 20 g / l Phosphate ion: 4 g / l Zirconium fluoride ion: 1 g / l Zinc ion: 1 g / l Hexavalent chromium / Trivalent chromium: 3/3 (weight ratio) Chromic anhydride / zirconium fluoride Ion: 20/1
(Weight ratio)

Chromic anhydride 30 g / l, sulfuric acid 0.2 g / l, bath temperature 40
The zinc-plated steel sheet was subjected to cathodic electrolysis at a current density of 10 A / dm ² using a treatment liquid at ℃, washed with water and dried. The amount of the chromate layer deposited was adjusted by controlling the amount of electricity applied in the cathodic electrolysis treatment.

Chromic anhydride 30 g / l, phosphoric acid 10 g / l, NaF
A zinc-based plated steel sheet was spray-treated with a treatment solution of 0.5 g / l, K ₂ TiF ₆ 4 g / l and a bath temperature of 60 ° C., washed with water and dried. The adhesion amount of the chromate layer was adjusted by changing the treatment time.

(3) Organic Resin Table 2 shows the organic resin used. The modified epoxy resin (A) and the block urethane (B) shown in the table were prepared by the method shown below.

Modified epoxy resin (A) 1200 parts of a bisphenol A type epoxy resin having an epoxy equivalent of 2000, 800 parts of xylene, and 1050 parts of cyclohexanone are put in a reactor equipped with a condenser, a stirrer and a thermometer. It was heated and dissolved under stirring. further,
36 parts of isopropanolamine was added and reacted at 100 ° C. for 5 hours to obtain a modified epoxy resin A having a resin content of 40%.

Block urethane (B) 440 parts of polyethylene glycol having a molecular weight of 1000 and 125 parts of xylene are put into a reactor equipped with a condenser, a stirrer and a thermometer, and heated at 60 ° C. under stirring to 6-
153 parts of tolylene diisocyanate was added. The NCO% of this intermediate was 4.8%. Further, 106 parts of ε-caprolactam was added to continue the reaction, and NCO% was 0.
After confirming that, 175 parts of butanol was added to obtain a block urethane B1 having a resin content of 70%. Under the same equipment and reaction conditions, 500 parts of polypropylene glycol having a molecular weight of 4000, 300 parts of xylene and 42 parts of hexamethylene diisocyanate gave an intermediate having an NCO% of 1.2. Further, 23 parts of methyl ethyl ketoxime was added and the reaction was continued. After confirming that NCO% was 0, 77 parts of butanol was added to obtain a block urethane B2 having a resin content of 60%.

Further, the silica added in the organic film is shown in Table 3.
Table 4 also shows poorly soluble chromates. Tables 5 to 8 show the constitutions of the organic composite coated steel sheets prepared as described above and the evaluation results of their corrosion resistance (outer surface rust resistance), image clarity, paint adhesion, and weldability. The evaluation method of each characteristic is as follows.

(A) Corrosion resistance (external rust resistance) The test material was electrodeposited with U-600 manufactured by Nippon Paint Co., Ltd. (2
5 μ) and then KPX-3 manufactured by Kansai Paint Co., Ltd.
Intermediate coating (30μ) with 6 and Kansai Paint Co., Ltd.
Top coat coating (35 µ) was performed using Ruga Gabe B-531 manufactured by Mitsubishi. A cross-cut was put on these test pieces with a cutter knife, and [salt spray test: 10 minutes → drying: 155 minutes →
Wet test ・ 75 minutes → dry ・ 160 minutes → wet test ・ 80
Min.] As one cycle for 300 cycles, and the corrosion resistance (outer surface rust resistance) was evaluated by the swelling width of corrosion from the cross cut portion. The evaluation criteria are as follows. ◎: Less than 2 mm ○: 2 mm or more and less than 4 mm △: 4 mm or more, less than 6 mm ×: 6 mm or more

(B) Image clarity test material was subjected to the same electrodeposition coating, intermediate coating and top coating as in the above (a), and the image clarity measuring device (ICM-
2DP) and the image sharpness C when a 0.5 mm slit was used. The evaluation criteria are as follows. ◎: 80 or more ○: less than 80, 75 or more Δ: less than 75, 70 or more ×: less than 70

(C) Paint Adhesion The test materials were subjected to the same electrodeposition coating, intermediate coating and top coating as in the above (a), and these test pieces were immersed in ion-exchanged water at 40 ° C. for 240 hours. Then remove the test piece,
After leaving it at room temperature for 24 hours, 100 cross-cuts were cut on the coating film at intervals of 2 mm, the adhesive tape was adhered and peeled off, and the peeling rate of the coating film was evaluated. The evaluation criteria are as follows. ◎: No peeling ○: Less than 3% △: 3% or more, less than 10% ×: 10% or more

(D) Weldability CF type electrode, applied pressure: 200 kgf, energization time: 10 cycles / 50 Hz, welding current: 10 kA, a continuous dotability test was conducted and evaluated by the number of continuous dots. The evaluation criteria are as follows. ◎: 5000 points or more ○: 4000 points or more and less than 5000 points △: 3000 points or more and less than 4000 points ×: less than 3000 points

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

[0059]

[Table 7]

[0060]

[Table 8]

* 1 From: Example of the present invention Ratio: Comparative example * 2 See Table 1 * 3 Chromate adhesion amount converted to metallic chromium * 4 See Table 2 * 5 See Table 3 * 6 See Table 4 * 7 Nonvolatile content weight ratio * 8 Nonvolatile content weight ratio

[0062]

As described above, according to the present invention, by using a specific block urethane-modified epoxy resin for the organic coating of the organic composite coated steel sheet, it has excellent external surface rust resistance and sharpness. Moreover, since it is also excellent in paint adhesion and weldability, it is extremely useful as a surface-treated steel sheet for automobiles and home appliances.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C09D 5/08 PPX 6904-4J PPY 6904-4J C23C 22/24 8417-4K C25D 3/22 8414- 4K // C09D 163/00 PJM 8416-4J 175/04 PHP 8620-4J (72) Inventor Toyofumi Watanabe 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Yoshio Kikuta Chiba 1900 Togo, Mobara-shi, Mie Prefecture Within Mitsui Toatsu Chemical Co., Ltd. (72) Inventor Kimio Kobori, 1900 Togo, Mobara-shi, Chiba Prefecture In-house Mitsui Toatsu Chemistry Co., Ltd. (72) Hideaki Ogata 1900 Togo, Mobara-shi, Chiba Prefecture Mitsui Higashi Pressure Chemical Co., Ltd.

Claims (8)

[Claims] 1. A surface of a zinc-based plated steel sheet has a chromium layer having a deposition amount of 10 to 200 mg / m ^{2 in} terms of metallic chromium as a first layer, and an epoxy resin and a polyfunctional resin as a second layer above the chromium layer. Modified epoxy resin (A) consisting of amine
On the other hand, a block urethane (B) consisting of polyol, polyisocyanate and a blocking agent is A / B = 95 /
The block urethane-modified epoxy resin mixed in the ratio of 5 to 50/50 (weight ratio) has a rust preventive additive of block urethane modified epoxy resin / rust preventive additive = 90/10 to 40
Thickness of 0.2 to 2 μm added at a ratio of 60/60 (weight ratio)
An organic composite-coated steel sheet having an organic film of m and excellent in external surface rust resistance and image clarity. 2. The organic composite-coated steel sheet excellent in external surface rust resistance and image clarity according to claim 1, wherein the rust preventive additive constituting the organic film is silica. 3. The organic composite coated steel sheet excellent in external surface rust resistance and image clarity according to claim 1, wherein the rust preventive additive constituting the organic film is a poorly soluble chromate. 4. The excellent rust resistance and sharpness on the outer surface according to claim 1, wherein the rust preventive additive constituting the organic film is silica and a sparingly soluble chromate in the following proportions (weight ratio). Organic composite coated steel sheet. Silica / Slightly soluble chromate = 90/10 to 10/90 5. A chromate solution is applied to the surface of a zinc-based plated steel sheet and subjected to a chromate treatment of drying without washing with water, and then a modified epoxy resin (A) comprising an epoxy resin and a polyfunctional amine is obtained. On the other hand, a block urethane-modified epoxy resin in which a block urethane (B) composed of polyol, polyisocyanate and a blocking agent is mixed at a ratio of A / B = 95/5 to 50/50 (weight ratio of nonvolatile content), A coating composition in which a rust preventive additive is added in a ratio of block urethane modified epoxy resin / rust preventive additive = 90/10 to 40/60 (weight ratio of non-volatile content), and baking treatment is performed. The method for producing an organic composite-coated steel sheet excellent in external surface rust resistance and image clarity according to claim 1. 6. The method for producing an organic composite coated steel sheet excellent in external surface rust resistance and image clarity according to claim 5, wherein the rust preventive additive constituting the coating composition is silica. 7. The method for producing an organic composite-coated steel sheet excellent in external surface rust resistance and sharpness according to claim 5, wherein the rust preventive additive constituting the coating composition is a poorly soluble chromate. 8. The outer surface rust resistance and image clarity according to claim 5, wherein the rust-preventive additive constituting the coating composition is silica and a sparingly soluble chromate in the following proportions (weight ratio). Manufacturing method of organic composite coated steel sheet. Silica / Slightly soluble chromate = 90/10 to 10/90