JP3259585B2 - Organic composite coated steel sheet with excellent rust resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite coated steel sheet suitable for an automobile body and having excellent rust resistance.

[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 salts for preventing road freezing sprayed in winter has become a major social problem. For this reason, there is an increasing tendency to use a surface-treated steel sheet having excellent corrosion resistance in place of a conventional cold-rolled steel sheet as one of the measures for preventing rust of an automobile body.

[0003] As such a surface-treated steel sheet, for example, Japanese Patent Application Laid-Open No. Hei 4-322277 has excellent corrosion resistance in which a Zn-based plated steel sheet has a chromate film on the surface and an organic resin film having a thickness of about 1 µm on the surface. Organic composite coated steel sheets have been proposed. The organic composite coated steel sheet disclosed in Japanese Patent Application Laid-Open No. Hei 4-322277 contains a water-based resin containing a general blocked isocyanate as a hardener, and also contains SiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , and Fe ₃ O _4. , Mg
1 selected from O, ZrO ₂ , SnO ₂ and Al ₂ O ₃
By applying and drying an aqueous solution containing at least one kind of water-dispersed sol, a resin film having excellent corrosion resistance, weldability and adhesion is obtained.

[0004]

On the other hand, recently, corrosion resistance in an environment in which iron rust coexists in a corrosive environment (hereinafter referred to as rust resistance) has begun to be a problem (CAMP-ISIJ vo).
l.5 (1992), p.1693). That is, it has been pointed out that when the organic composite coated steel sheet is used in such an environment, iron rust adheres to the surface of the resin film, thereby deteriorating the excellent corrosion resistance inherent in the organic composite coated steel sheet. However, it has been found that the above-mentioned organic composite coated steel sheet disclosed in Japanese Patent Application Laid-Open No. 4-322777 cannot necessarily exhibit sufficient performance with respect to this rust resistance. This is considered to be because the hardening agent was not added as an essential component to the organic coating of the coated steel sheet, and even if it was added, a sufficient crosslink density was not obtained with a known hardening agent.

[0005] A known document, "GALVATECH '92, p.3
72 '' describes that when the crosslinking agent density is reduced by reducing the amount of the curing agent in the resin film, the rust resistance of the organic composite coated steel sheet is reduced. No specific measures are taken to improve it. In view of such a situation, an object of the present invention is to provide an organic composite coated steel sheet having excellent properties such as corrosion resistance (perforation resistance) and paint adhesion, as well as excellent rust resistance.

[0006]

Means for Solving the Problems The organic composite coated steel sheet of the present invention has been intensively studied by the present inventors to achieve the above object, and as a result, a hardening agent is required to improve the rust resistance. It has been found that the two conditions of using silica and a sparingly soluble chromate in combination as a rust-preventive additive are extremely effective as a rust-preventive additive. That is, the organic composite coated steel sheet of the present invention has the following configuration.

(1) A chromate film having an adhesion amount of 5 to 200 mg / m ^{2 in} terms of metallic chromium is formed on the surface of a Zn-based plated steel sheet, and an ethylene-acrylic acid copolymer resin, styrene-acrylic acid Copolymer resin, selected from polyacrylic acid and its copolymer resin, polyacrylate and its copolymer resin, polymethacrylic acid and its copolymer resin, polymethacrylic ester and its copolymer resin For 100 parts by weight (solid content) of one or more aqueous dispersion type resins [A] obtained,
It contains 5-80 parts by weight (solid content) of a polyfunctional polyisocyanate compound [B] having at least 6 isocyanate groups in the molecule, and further contains a rust preventive additive [C] ([A]
+ [B]) / [C] in a weight ratio of 90/10 to 40/60.
An organic composite coated steel sheet having excellent rust resistance, characterized in that a resin film having a dry film thickness of 0.2 to 3.0 [mu] m was formed by adhering a water-based coating composition containing the same.

(2) In the organic composite coated steel sheet of the above (1), the rust preventive additive [C] constituting the resin film is Cr
₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, ZrO ₂ , Sn
An organic composite coated steel sheet having excellent rust resistance, comprising one or more selected from water-dispersed sols of O ₂ and Al ₂ O ₃ , silica, and poorly soluble chromate. (3) In the organic composite coated steel sheet of the above (1), the rust-preventive additive [C] constituting the resin film is silica having the following weight ratio and an organic compound having excellent rust resistance, which is a hardly soluble chromate. Composite coated steel sheet. Silica / poorly soluble chromate = 35/5/1/39

(4) In the organic composite coated steel sheet according to the above (1) to (3), the polyfunctional polyisocyanate compound [B] is a polyfunctional hexamethylene diisocyanate having at least six isocyanate groups in one molecule. Organic composite coated steel sheet with excellent rust resistance.

[0010]

[Function] A resin film formed as a second layer on a chromate film formed on the surface of a zinc-based plated steel sheet suppresses excessive elution of hexavalent chromate ions in the chromate film into a corrosive environment. In the present invention, it is formed by reacting a polyfunctional polyisocyanate compound having at least six isocyanate groups in one molecule with a water-based resin as a curing agent. A conventional organic composite coating is formed by the action of a high cross-linking density resin coating and the rust preventive additive added in a specific ratio in the resin coating (particularly, synergistic action when silica and sparingly soluble chromate are added in combination). Compared to steel plates, it has significantly improved rust resistance.

The details of the present invention and the reasons for the limitation will be described below. As the base zinc-coated steel sheet, a zinc-coated steel sheet, a Zn-Ni alloy-coated steel sheet, a Zn-Fe alloy-coated steel sheet, a Zn-Mn alloy-coated steel sheet, a Zn-Al alloy-coated steel sheet, a Zn-Cr alloy-coated steel sheet, Zn -Co
-Cr alloy-plated steel sheet, Zn-Cr-Ni alloy-plated steel sheet, Zn-Cr-Fe alloy-plated steel sheet, and zinc-based composite coated steel sheet in which metal oxide, hardly soluble chromate, polymer, etc. are dispersedly coated Can be mentioned. 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 the above plating. As a plating method, any method that can be performed among an electrolysis method, a melting method, and a gas phase method can be adopted.
From the selectivity of the base cold-rolled steel sheet, the electrolytic method is advantageous.

The chromate film formed on the surface of the galvanized steel sheet suppresses corrosion of the galvanized steel sheet by a self-repairing action of chromate ions of hexavalent chromium. If the amount of the chromate film is less than 5 mg / m ^{2 in} terms of chromium metal, sufficient corrosion resistance cannot be expected, while if it exceeds 200 mg / m ² , the weldability is deteriorated. For this reason, the adhesion amount of the chromate film is 5 to 200 mg / m ^{2 in} terms of metal chromium. Further, in order to satisfy even higher corrosion resistance and weldability, the content is preferably in the range of ²⁰ to 100 mg / m ^{2 in} terms of chromium metal. As a chromate treatment for forming the chromate film, any of a reaction type, an electrolytic type, and a coating type can be applied. From the viewpoint of corrosion resistance, a coating type containing a large amount of hexavalent chromium chromate ions in the chromate film is preferable.

[0013] The coating type chromate treatment comprises a treatment solution containing a partially reduced aqueous solution of chromic acid as a main component and, if necessary, one or more of the following components added thereto. And dried without washing. Water-soluble or water-dispersible organic resins such as acrylic resins and polyester resins Colloids and / or powders of oxides such as silica, alumina, titania, zirconia, and zinc oxide Acids such as molybdic acid, tungstic acid, and vanadic acid Or its salts Phosphoric acid such as phosphoric acid and polyphosphoric acid Zirconium fluoride, silicide fluoride, fluoride such as titanium fluoride Metal ion such as zinc ion Conductive fine powder such as iron phosphide, antimony-doped tin oxide Hydrogen fluoride Silane coupling agent In the application type chromate treatment, the treatment liquid is usually applied by a roll coater method, but after applying by a dipping method or a spray method, it is also possible to adjust the application amount by an air knife method or a roll drawing method. .

As the base resin used in the present invention, ethylene-acrylic acid copolymer resin, styrene-acrylic acid copolymer resin, polyacrylic acid and its copolymer resin, polyacrylic ester and its copolymer resin, One or two selected from polymethacrylic acid and its copolymer resin, polymethacrylic acid ester and its copolymer resin
An aqueous resin dispersion of more than one type of resin can be used. The ratio of the monomer having an OH group to each of these resins is 5 to 40%, the ratio of the monomer having a COOH group is 2 to 20%, and (weight of monomer having an OH group / C
An aqueous resin dispersion polymerized so that the weight of the monomer having an OOH group) = 0.5 to 16 can also be used.

In the present invention, a curing agent is added as an essential component to the above water-dispersible resin [A], and a specific polyfunctional polyisocyanate compound [B] is added as the curing agent. A urethanization reaction takes place between isocyanate groups in the polyisocyanate.

The polyisocyanate compound used as a hardening agent in the resin film of the present invention has at least six isocyanate groups in one molecule (even if these isocyanate groups are blocked) for the purpose of improving rust resistance. (Good). That is, a monoisocyanate compound having one isocyanate group in one molecule or a diisocyanate compound having two isocyanate groups in one molecule cannot sufficiently impart rust resistance to the resin film. On the other hand, in the present invention, a polyfunctional polyisocyanate compound having three or more isocyanate groups in one molecule, more preferably four or more, and still more preferably a polyfunctional polyisocyanate compound having six or more isocyanate groups, It has been found that rust resistance, which is far superior to monoisocyanate compounds and diisocyanate compounds, can be imparted.

Among polyfunctional polyisocyanate compounds having 6 or more isocyanate groups in one molecule (hexafunctional polyisocyanate compound), a polyfunctional hexamethylene diisocyanate is particularly effective for rust resistance since it is resistant to rust. . The polyfunctional polyisocyanate compound used in the present invention may be a mixture of homologous compounds having different numbers of isocyanate groups in one molecule. Further, two or more of the above polyfunctional polyisocyanate compounds may be used in combination.

Examples of such a polyfunctional polyisocyanate compound having three or more isocyanate groups in one molecule include a compound having three or more isocyanate groups in one molecule and an isocyanate compound having at least two isocyanate groups. Is reacted with a polyhydric alcohol, or a compound such as a buret type adduct thereof or an isocyanuric ring type adduct thereof. For example, triphenylmethane-4,4 ', 4 "-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,4
Polyisocyanate compounds having three or more isocyanate groups such as 6-triisocyanatotoluene, 4,4'-dimethyldiphenylmethane-2,2 ', 5,5'-tetraisocyanate; ethylene glycol, propylene glycol, 1,4 An adduct obtained by reacting a polyisocyanate compound in such an amount that an isocyanate group becomes excessive with respect to a hydroxyl group of a polyol such as butylene glycol, polyalkylene glycol, trimethylolpropane, and hexanetriol; hexamethylene diisocyanate, isophorone diisocyanate, Burette type adducts such as diisocyanate, xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate) or There are Soshianuru ring type adducts.

In the adduct obtained by reacting an amount of the polyisocyanate compound in which the amount of the isocyanate group becomes excessive with respect to the hydroxyl group of the polyol, the polyisocyanate compound may be a polyisocyanate compound having three or more isocyanate groups. Aliphatic diisocyanate compounds such as hexamethylene diisocyanate, 1,4-tetramethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; isophorone diisocyanate, 4,4'-methylene bis (cyclohexyl isocyanate), methylcyclohexane-
2,4- (or -2,6-) diisocyanate, 1,3
An alicyclic diisocyanate compound such as-(or 1,4-) di (isocyanatomethyl) cyclohexane; and xylylene diisocyanate, tolylene diisocyanate, m
Aromatic diisocyanate compounds such as-(or p-) phenylene diisocyanate, diphenylmethane diisocyanate, bis (4-isocyanatophenyl) sulfone and the like can be mentioned.

In order to stably store a resin composition for forming a film, it is necessary to protect isocyanate as a curing agent. As this method, a protection method in which a protective group (blocking agent) is eliminated during heat curing and an isocyanate group is regenerated can be employed. Examples of the protective agent (blocking agent) include: (1) aliphatic monoalcohols such as methanol, ethanol, propanol, butanol, and octyl alcohol; and (2) monoethers of ethylene glycol and / or diethylene glycol, for example, methyl and ethyl. Monoethers such as, propyl (n-, iso) and butyl (n-, iso, sec); (3) aromatic alcohols such as phenol and cresol; (4) oximes such as acetoxime and methyl ethyl ketone oxime. By reacting one or more kinds with the isocyanate compound, an isocyanate compound protected stably at least at room temperature is obtained.

The polyfunctional polyisocyanate compound as such a curing agent is used in an amount of 5 to 80 parts by weight (solid content), preferably 100 parts by weight (solid content) of the aqueous dispersion type resin [A] as the base resin. It is blended in a ratio of 10 to 50 parts by weight. If the amount of the curing agent is less than 5 parts by weight, the crosslinked density of the formed film becomes insufficient and the effect of improving rust resistance is small. On the other hand, if the amount is more than 80 parts by weight, the unreacted residual isocyanate absorbs water and not only has no effect on the rust resistance and also impairs the corrosion resistance (perforation resistance) and adhesion.

Further, a phenol resin as a crosslinking agent,
An alkyl etherified amino resin obtained by reacting a monohydric alcohol having 1 to 5 carbon atoms with a part or all of a methylol compound obtained by reacting formaldehyde with at least one selected from melamine, urea and benzoguanamine, You may use together with the said polyfunctional polyisocyanate compound.

The resin is sufficiently cross-linked with the above-mentioned cross-linking agent. However, in order to further increase the low-temperature cross-linking property, it is desirable to use a known curing promoting catalyst. As the curing promoting catalyst, for example, N-ethylmorpholine, dibutyltin dilaurate, cobalt naphthenate, stannous chloride, zinc naphthenate, bismuth nitrate and the like can be used. Also, with the aim of slightly improving physical properties such as adhesion,
Known resins such as acrylic, alkyd, and polyester can also be added to the resin composition. Further, in order to slightly improve physical properties such as adhesion, a known resin such as acryl, alkyd, or polyester can be used in combination with the resin composition.

In the present invention, the rust preventive additive [C] is contained in the resin film.
The rust preventive additive [C] is 2 mμ.
Cr ₂ O ₃ , Fe ₂ O ₃ , F having a particle size of about
One or more of water-dispersed sols of e ₃ O ₄ , MgO, ZrO ₂ , SnO ₂ , and Al ₂ O ₃ , silica, and hardly soluble chromates can be used alone or in combination. Cr ₂
O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, ZrO ₂ , Sn
The aqueous dispersion sol of O ₂ , Al ₂ O ₃ , and SiO ₂ is stably dispersed in the water-based coating composition, and is uniformly dispersed in the coating to improve the corrosion resistance. As the silica, silica sol or other fumed silica can be used. These silicas have the effect of accelerating the generation of basic zinc chloride, which is effective in suppressing corrosion among the corrosion products of galvanized steel sheets. It is presumed that the anticorrosion effect is exhibited by functioning as a film-forming corrosion inhibitor.

Specific examples of silica that can be used include dry silica (for example, AEROS manufactured by Nippon Aerosil Co., Ltd.).
IL 130, AEROSIL 200, AEROSIL
300, AEROSIL 380, sedimentation wet silica (for example, T-32 (S), K-4 manufactured by Tokuyama Soda Co., Ltd.)
1, F-80, etc.), gel-process wet silica (for example, Syloid 244, Syloid 1 manufactured by Fuji Devison Chemical Co., Ltd.)
50, thyroid 72, thyroid 65, SHIELD
EX etc.). Further, two or more kinds of the above-mentioned silicas can be used as a mixture.

The sparingly soluble chromate salt added to the organic film is dissolved in a very small amount in a corrosive environment to form
It is thought to release chromic ions of valence and suppress corrosion of the zinc-based plated steel sheet by the same mechanism as the chromate film. Barium chromate (BaCrO ₄ ), strontium chromate (SrCrO ₄ ), calcium chromate (CaCr)
O _4), chromic acid zinc (ZnCrO ₄ · 4Zn (O
H) ₂ ), potassium zinc chromate (K ₂ O.4ZnO.4)
Fine powders such as CrO ₃ .3H ₂ O) and lead chromate (PbCrO ₄ ) can be used. It is also possible to use a mixture of two or more of the hardly soluble chromates described above. 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-healing effect by chromate ions over a long period of time. Further, from the viewpoint of minimizing the elution of water-soluble chromium from the organic film in the pretreatment step of coating the automobile, barium chromate having low solubility in water is preferable.

In the present invention, by synthesizing silica and a sparingly soluble chromate salt in a specific ratio in the above-mentioned resin composition comprising the specific base resin and the polyfunctional polyisocyanate compound, a synergistic effect of both anticorrosive effects can be obtained. By effect
The most excellent rust resistance can be realized. That is, the weight ratio of the silica and the sparingly soluble chromate to the nonvolatile content is as follows: (aqueous dispersion type resin [A] + polyfunctional polyisocyanate compound [B]) / (silica + poorly soluble chromate = 90 /
The most excellent corrosion resistance can be obtained when it is blended in a ratio of 10/40/60 silica / poorly soluble chromate = 35/5/1/39. Here, when (aqueous dispersion type resin [A] + polyfunctional polyisocyanate compound [B]) / (silica + poorly soluble chromate) exceeds 90/10, the anticorrosive effect of silica and the sparingly soluble chromate is reduced. Not sufficiently exhibited, resulting in poor rust resistance. On the other hand, when the ratio is less than 40/60, the effect of the aqueous dispersion type resin as a binder becomes insufficient, and the adhesiveness of the paint is deteriorated. Further, if the ratio of silica / slightly soluble chromate exceeds 35/5, or if it is less than 1/39, the synergistic effect becomes insufficient, and the rust resistance of the resin slightly deteriorates.

As described above, silica suppresses corrosion caused by rust due to the effect of promoting the formation of stable corrosion products, while sparingly soluble chromate removes defective portions of the organic film formed by rust. It repairs by the effect of hexavalent chromate ions. By using silica and sparingly soluble chromate, which have different mechanisms of inhibiting corrosion due to rust, excellent rust resistance is obtained for the first time. That was achieved.

FIG. 1 shows that an organic resin (No. 2 in Table 2) comprising the above-mentioned specific base resin and an isophorone diisocyanate-based hexafunctional polyisocyanate compound was prepared by changing the ratio of silica and a sparingly soluble chromate to the organic resin. Corrosion resistance (evaluation after 200 cycles of puncture resistance test) and rust resistance (Rust resistance test 7)
Evaluation after the cycle) and the weight ratio of silica / poorly soluble chromate are shown. According to this, when the weight ratio of silica / poorly soluble chromate exceeds 35/5, the rust resistance deteriorates, whereas when it is less than 1/39, the normal unpainted corrosion resistance (perforation resistance) deteriorates. I do. Therefore, the mixing ratio of silica / poorly soluble chromate is preferably 35/5 to 1/39, and especially when emphasis is placed on rust resistance due to rust resistance.
It is understood that the range of 20 to 1/39 is preferable to be in the range of 20/20 to 5/35 in order to further obtain the most excellent corrosion resistance (rust resistance and puncture resistance). . FIG. 2 shows the relationship between the rust resistance and the weight ratio of silica / poorly soluble chromate when a conventional diisocyanate compound (HMDI) is used as a curing agent for comparison. From FIGS. 1 and 2, it can be seen that the present invention has been achieved for the first time by the synergistic effect of the combination of the polyfunctional polyisocyanate compound, the specific ratio of silica and the sparingly soluble chromate.

Further, FIG. 4 shows the unpainted corrosion resistance (a puncture resistance test 2) when a hexamethylene diisocyanate-based hexafunctional polyisocyanate compound was used as a curing agent.
The relationship between the rust resistance (evaluation after 00 cycles) and rust resistance (evaluation after 15 cycles of rust resistance test) and the weight ratio of silica / poorly soluble chromate is shown. According to this,
As in the case of using the isophorone diisocyanate-based hexafunctional polyisocyanate compound, the compounding ratio of silica / slightly soluble chromate is preferably 35/5 to 1/39. Is 20/20 to 1/3
In order to obtain the most excellent corrosion resistance (wet rust resistance and puncture resistance), it is 20/20 to 20.
It turns out that it is preferable to set it in the range of 5/35.

Further, embodiments described later (for example, No.
74 and No. 77)).
When a hexamethylene diisocyanate-based hexafunctional polyisocyanate compound is compared with an isophorone diisocyanate-based hexafunctional polyisocyanate compound,
When the compounding ratio of the hardly soluble chromate is the same, the use of a hexamethylene diisocyanate-based hexafunctional polyisocyanate compound provides more excellent rust resistance.

In the present invention, the above-mentioned silica and sparingly soluble chromate salt are the main additive components in the resin composition. In addition, silane coupling agents, coloring pigments (for example, condensed polycyclic Organic pigments, phthalocyanine organic pigments, etc.), coloring dyes (eg, azo dyes, azo metal complex dyes, etc.), rust-preventive pigments (eg, aluminum trihydrogen diphosphate, aluminum phosphomolybdate, zinc phosphate, etc.) ), A conductive pigment (for example, iron phosphide, antimony-doped tin oxide, etc.), a surfactant, and the like. In addition, workability can be improved by adding at least one of the following lubricants. Polyolefin wax (polyethylene wax, polypropylene wax, etc.) Fluororesin (ethylene tetrafluoride resin, ethylene tetrafluoride-hexafluoropropylene copolymer resin, ethylene fluoride
(Perfluoroalkyl vinyl ether copolymer resin, ethylene tetrafluoride-ethylene copolymer resin, ethylene trifluoride ethylene resin, vinylidene fluoride resin, etc.) Graphite Molybdenum disulfide Boron nitride You may.

The above-mentioned organic film is coated on the chromate film in an amount of 0.2 to 3.0 μm, preferably 0.5 to 2.0 μm.
m. If the film thickness is less than 0.2 μm, sufficient rust resistance cannot be obtained, while 3.0 μm
If it exceeds, weldability (particularly continuous hitting property) is reduced. FIG.
The results of examining the relationship between the thickness of the organic film and the spot weldability (continuous spotting property) are shown in FIG. According to this, the film thickness is 3.
It can be seen that when the thickness exceeds 0 μm, the spot weldability decreases.

As a method for applying the above-mentioned coating composition to a galvanized steel sheet, the coating composition is usually applied by a roll coater method. However, after applying by a dipping method or a spraying method, an air knife method or a roll drawing method is applied. Can also adjust the amount of application. Further, as a heat treatment method after applying the coating composition, a hot blast furnace, a high-frequency induction heating furnace, an infrared furnace, or the like can be used. The heat treatment is performed at an ultimate plate temperature of 80 to 250 ° C, preferably 100 to 200 ° C.
It is desirable to perform within the range. Further, when the present invention is applied to a BH steel sheet, a heat treatment at 150 ° C. or less is desirable. The steel sheet of the present invention has a great feature that it is obtained by such low-temperature baking.

If the baking temperature is lower than 80 ° C., the crosslinking of the film does not proceed and sufficient corrosion resistance cannot be obtained.
High-temperature baking exceeding 50 ° C. deteriorates corrosion resistance. This is due to the volatilization of water contained in the chromate film component and the hydroxyl group (

Embedded image ) The rapid progress of the dehydration-condensation reaction between the two causes the chromate film to break down due to the occurrence of cracks in the chromate film, and the reduction of hexavalent chromium to proceed to reduce the passivating effect of hexavalent chromium. It is presumed to be due to The car body is subjected to cationic electrodeposition coating, but the chromate film + the organic film has a wet electric resistance of 200.
If it exceeds kΩ / cm ² , there is a problem that the cationic electrodeposition coating is not formed well. Therefore, in the steel sheet of the present invention mainly used for automobile bodies, the wet resistance of the chromate film + resin composition film is 200 kΩ / cm ² or less. It is preferable to form both films so as to keep the film thickness at a minimum.

The present invention includes a steel sheet having the above-described coating structure on both sides or one side. Embodiments of the steel sheet of the present invention include, for example, the following. (1) One side: Plating film-Chromate film-Organic film One surface: Fe surface (2) One surface: Plating film-Chromate film-Organic film One surface: Plating film (3) Both surfaces: Plating film-Chromate film-Organic film The organic composite coated steel sheet of the invention is not limited to automobiles,
It can also be used for home appliances and building materials.

[0037]

EXAMPLES As an organic composite coated steel sheet for an automobile body, a zinc-based coated steel sheet was alkali-degreased, washed with water, dried, subjected to chromate treatment, and then coated with a coating composition using a roll coater and baked. With respect to the obtained organic composite coated steel sheet, each test was performed for resistance to puncture, resistance to rust, paint adhesion and weldability. The results are shown in Tables 5 to 16.
Shown in The manufacturing 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 platings and used as an original plate for processing.
(See Table 1)

(2) Chromate treatment Coating type chromate treatment A chromate treatment solution having the following composition was applied by a roll coater and dried without washing with water. The adhesion amount of the chromate layer was adjusted by changing the peripheral speed ratio between 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)

Electrolytic chromate treatment Chromic anhydride 30 g / l, sulfuric acid 0.2 g / l, bath temperature 40
A cathodic electrolytic treatment was performed on a zinc-based plated steel sheet at a current density of 10 A / dm using a treatment liquid at a temperature of 10 ° C., followed by washing and drying. The adhesion amount of the chromate layer was adjusted by controlling the amount of electricity in the cathodic electrolysis treatment. Reaction type chromate treatment Chromic anhydride 30 g / l, phosphoric acid 10 g / l, NaF
Using a treatment liquid of 0.5 g / l, K ₂ TiF ₆ 4 g / l, and a bath temperature of 60 ° C., the zinc-plated steel sheet was spray-treated, washed with water and dried. The amount of the chromate layer deposited was adjusted by changing the treatment time.

(3) Organic Resin Table 2 shows the organic resins used. The types and synthesis examples of the base resin (aqueous dispersion type resin) and the curing agent (polyisocyanate) shown in the table are shown below. [Base resin] A1: Ethylene-acrylic acid copolymer resin A2: Styrene-acrylic acid co-resin resin A3: Polyacrylic acid resin A4: Polyacrylic ester resin A5: Monomer having OH group is 15%, Ethylene-acrylic acid copolymer copolymerized so that 5% of the monomer having a COOH group and (weight of monomer having an OH group / weight of monomer having a COOH group) = 3 resin

[Curing Agent] (1) Hexafunctional Isocyanate (Curing Agent B1) In a reactor equipped with a thermometer, a stirrer and a reflux condenser with a dropping funnel, 222 parts of isophorone diisocyanate and 34 parts of methyl isobutyl ketone were weighed. After taking and dissolving uniformly, 87 parts of methyl ethyl ketone oxime was dropped from the dropping funnel into the stirred isocyanate solution kept at 70 ° C. for 2 hours. Thereafter, 30.4 parts of sorbitol was added, the temperature was raised to 120 ° C, and the reaction was performed at 120 ° C. Then, an IR measurement of the reaction product was performed,

(Equation 1) No absorption by isocyanate groups was confirmed, and 50.4 parts of butyl cellosolve was added to obtain a curing agent B1. The active ingredient of the curing agent B1 was 80%.

(2) Tetrafunctional Isocyanate (Curing Agent B2) 222 parts of isophorone diisocyanate and 34 parts of methyl isobutyl ketone were weighed and measured in a reactor equipped with a thermometer, a stirrer and a reflux condenser with a dropping funnel. Then, 87 parts of methyl ethyl ketone oxime was dropped from the dropping funnel into the stirred isocyanate solution kept at 70 ° C. for 2 hours. Thereafter, 34 parts of pentaerythritol was added and the temperature was raised to 120 ° C.
Was reacted. Then, an IR measurement of the reaction product was performed,

(Equation 2) No absorption by isocyanate groups was confirmed, and 52 parts of butyl cellosolve was added to obtain a curing agent B2. The active ingredient of this curing agent B2 was 80%.

(3) Trifunctional isocyanate (curing agent B3) Duranate TPA-100 (HMD) was attached to a reactor equipped with a thermometer, a stirrer and a reflux condenser with a dropping funnel.
550 parts of isocyanuric ring type I (manufactured by Asahi Kasei Corporation) and 34 parts of methyl isobutyl ketone are weighed and uniformly dissolved, and then 270 parts of methyl ethyl ketone oxime is stirred at 70 ° C. from the dropping funnel at 70 ° C. The solution was dropped into the solution over 2 hours. Then, an IR measurement of the reaction product was performed,

(Equation 3) No absorption by isocyanate groups was confirmed, and 47 parts of butyl cellosolve was added to obtain a curing agent B3. The active ingredient of this curing agent B3 was 90%.

(4) Bifunctional isocyanate (curing agent B4) Takenate B-870N (MEK oxime block of IPDI; manufactured by Takeda Pharmaceutical Co., Ltd.) was used as the curing agent B4. (5) Hexamethylene diisocyanate hexafunctional isocyanate (curing agent B5) Duranate MF-B80M (HMD
An I-type oxime block of a hexafunctional isocyanate (manufactured by Asahi Kasei Corporation) was used as the curing agent B5.

The evaluation method of each characteristic is as follows. (A) Corrosion resistance test (perforation resistance) After tape-sealing the edge and back surface of the unpainted test piece, a cross cut was made on the lower half surface of the test piece, and the corrosion promotion test of the following composite corrosion test cycle was performed. And the degree of progress of corrosion after 200 cycles. 5% NaCl spraying / 35 ° C (4 hours) ↓ Drying / 60 ° C (2 hours) ↓ 95% RH wet / 50 ° C (4 hours) The evaluation criteria are as follows. ◎: No red rust generated ○ +: Red rust area ratio less than 5% ○: Red rust area ratio 5% or more and less than 10% ○-: Red rust area ratio 10% or more, less than 20% △: Red rust area ratio 20% or more, 50% Less than ×: Red rust area ratio 50% or more

(B) Rust-Resistant Resistance After the edge and the back of the unpainted test piece were tape-sealed, an accelerated corrosion test was performed by the following composite corrosion test cycle in the presence of iron rust. 7 for 1-73
The degree of rust generation after the cycle was measured by using Example No. 74 ~
For 132, the degree of rusting after 15 cycles was evaluated. In the presence of iron rust (* Note) 5% NaCl immersion, 50 ° C (18 hours) ↓ 95% RH wet, 50 ° C (3 hours) ↓ Drying, 60 ° C (3 hours) (* Note) Iron rust supply method: A cold rolled steel sheet having an area of 10 cm ² per liter of salt water was immersed. The evaluation criteria are as follows. ◎: No red rust occurred ○: Red rust area ratio less than 10% ○-: Red rust area ratio 10% or more, less than 20% △: Red rust area ratio 20%, less than 50% ×: Red rust area ratio 50% or more

(C) Paint adhesion After the test piece was degreased with alkali, Nippon Paint Co., Ltd.
At 600, electrodeposition coating (25 μm thickness) was performed, and then overcoating (35 μm thickness) was performed with Luga Bake B-531 manufactured by Kansai Paint Co., Ltd. These tests were immersed in ion exchange water at 40 ° C. for 240 hours. Next, the test piece was taken out and allowed to stand at room temperature for 24 hours. Then, 100 pieces of grids were cut at intervals of 2 mm on the coating film, 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 ○: peeling rate less than 3% △: peeling rate 3% or more and less than 10% ×: peeling rate 10% or more

(D) Weldability A continuous hitting test was carried out with a CF electrode, a pressing force of 200 kgf, an energizing time of 10 cycles / 50 Hz, and a welding current of 10 kA. The evaluation criteria are as follows. ◎: 2000 points or more ○: 1000 points or more and less than 2000 points ×: less than 1000 points

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

[Table 6]

[0055]

[Table 7]

[0056]

[Table 8]

[0057]

[Table 9]

[0058]

[Table 10]

[0059]

[Table 11]

[0060]

[Table 12]

[0061]

[Table 13]

[0062]

[Table 14]

[0063]

[Table 15]

[0064]

[Table 16]

* 1 Emission: Example of the present invention, ratio: Comparative example * 2 * 3 Adhesion amount of chromate in terms of metal chrome * 4 No. of organic resin listed in Table 2 * 5 No. of rust preventive additives listed in Table 3. * 6 No. of the hardly soluble chromate described in Table 4. * 7 Weight ratio of non-volatile components (SiO ₂ etc. refers to rust-preventive additives described in Table 3) * 8 Weight ratio of non-volatile components (SiO _2, etc. refers to rust-preventive additives described in Table 3)

As is clear from the above examples, the organic composite coated steel sheet of the present invention exhibits excellent rust resistance. Ma
Example No. 74 and Example No. Comparison of No. 77 shows that the use of a hexamethylene diisocyanate-based hexafunctional polyisocyanate compound as the curing agent provides superior rust resistance, compared to the use of an isophorone diisocyanate-based hexafunctional polyisocyanate compound.

[0067]

The organic composite coated steel sheet of the present invention described above is excellent in rust resistance and puncture resistance, and also excellent in paint adhesion and weldability. Very useful as a steel plate.

[Brief description of the drawings]

FIG. 1 shows the addition of silica and a sparingly soluble chromate to an organic resin composed of a specific base resin defined by the present invention and a polyfunctional polyisocyanate compound (isophorone diisocyanate-based hexafunctional polyisocyanate compound) at different ratios. Weight ratio of silica / sparingly soluble chromate and the usual unpainted corrosion resistance and rust resistance (Rust rust resistance test 7)
Graph showing the relationship with

FIG. 2 shows the weight ratio of silica / slightly soluble chromate and the rust resistance when silica and sparingly soluble chromate are added in a different ratio to an organic resin using a conventional diisocyanate compound as a curing agent. Graph showing the relationship with

FIG. 3 is a graph showing the relationship between the thickness of an organic film and weldability.

FIG. 4 is a graph showing the relationship between the ratio of silica and the sparingly soluble chromate added to an organic resin comprising a specific base resin defined by the present invention and a hexamethylene diisocyanate-based hexafunctional polyisocyanate compound at a different ratio. Graph showing the relationship between the weight ratio of hardly soluble chromate and ordinary unpainted corrosion resistance and rust resistance (evaluation after 15 cycles of rust resistance test).

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B32B 15/08 B32B 15/08 GC23C22 / 24 C23C22 / 24 22/30 22/30 (56) References JP-A-6-235071 ( JP, A) JP-A-4-322771 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/00-7/26 B32B 15/08 C23C 22/24 C23C 22 / 30

Claims (4)

(57) [Claims] 1. A chromate film having an adhesion amount of 5 to 200 mg / m ^{2 in} terms of chromium metal is formed on the surface of a Zn-based plated steel sheet, and an ethylene-acrylic acid copolymer resin and a styrene-acrylic acid Polymer resin, selected from polyacrylic acid and its copolymer resin, polyacrylate and its copolymer resin, polymethacrylic acid and its copolymer resin, polymethacrylic ester and its copolymer resin The polyfunctional polyisocyanate compound [B] having at least 6 isocyanate groups in one molecule is used in an amount of 5 to 80 with respect to 100 parts by weight (solid content) of one or more kinds of the aqueous dispersion type resins [A]. Parts by weight (solid content) and further contains a rust inhibitor [C] ([A]
+ [B]) / [C] in a weight ratio of 90/10 to 40/60.
An organic composite coated steel sheet having excellent rust resistance, characterized in that a resin film having a dry film thickness of 0.2 to 3.0 [mu] m was formed by adhering a water-based coating composition containing the same. 2. A rust preventive additive [C] constituting a resin film.
Are Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, Z
2. The rust-resistant material according to claim 1, comprising one or more selected from water-dispersed sols of rO ₂ , SnO ₂ , and Al ₂ O ₃ , silica, and poorly soluble chromate. Organic composite coated steel sheet. 3. A rust preventive additive [C] constituting a resin film.
2. The organic composite coated steel sheet according to claim 1, which is silica and a sparingly soluble chromate having the following weight ratios. Silica / poorly soluble chromate = 35/5/1/39 4. A polyfunctional polyisocyanate compound [B]
Is a polyfunctional hexamethylene diisocyanate having at least 6 isocyanate groups in one molecule, the organic composite coated steel sheet having excellent rust resistance according to claim 1, 2 or 3.