JPH0762268A - Primer-coated steel plate and primer composition to be used therefor - Google Patents

Abstract

PURPOSE:To obtain a primer-coated steel plate producible by a plating line and having excellent corrosion resistance and adhesivity to a top-coating layer. CONSTITUTION:This primer composition for the primer-coating of a steel plate contains (A) a styrene-containing acrylic copolymer emulsion containing maleinized polybutadiene as an emulsifier, (B) a colloidal silica having particle diameter of <=100mum and (C) a rust-preventive agent as essential components. The amount of the component C is <=40 pts.wt. based on 100 pts.wt. of A+B. This primer-coated steel plate is produced by forming a chromate-treated layer on a steel plate plated with zinc or a zinc alloy to apply 10-200mg/m<2> of chromium in terms of metallic chromium and forming a film of the above primer composition on the chromate-treated layer to a dried film thickness of 1-10mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primer composition for a primer-coated steel sheet and a coated steel sheet thereof, and more specifically, a water-dispersible primer coating composition which forms a film having excellent corrosion resistance and topcoat adhesion and coating thereof. It relates to a steel plate.

[0002]

2. Description of the Related Art Coating on steel plates, which are building materials such as wall materials and shutter materials, is performed by forming a galvanized steel sheet or a zinc alloy-based galvanized steel sheet that has been subjected to a chemical conversion process, and then applying it at room temperature to dry it at room temperature. It has been practiced to apply the undercoat paint and the top paint after a few days. This way,
It takes a lot of time and effort for the craftsmen to paint, which not only makes the painting cost enormous, but also depends on the weather, so it is difficult to obtain a stable product in terms of quality. In order to solve this problem, some primer steel sheets pre-coated with a coil coat primer have been put into practical use. However, the primer is solvent type and the baking temperature is as high as 180 ° C or higher. After being wound up, it is necessary to paint and bake using a coil coating line, which leaves problems in terms of work and cost.

[0003]

In view of the above points, the present invention is capable of forming a film in a plating production line, that is, a film can be formed by baking in an aqueous system at a low temperature for a short time, and the adhesion to an overcoat film and An object of the present invention is to obtain a primer composition for a primer steel sheet capable of forming a coating film excellent in corrosion resistance and a primer-coated steel sheet coated with the primer.

[0004]

Therefore, the present inventor has made it possible for an end user to directly apply a top coat, and also has excellent corrosion resistance, and a primer which can be produced in a chemical conversion treatment step or a step subsequent to the chemical conversion treatment in a plating production line. As a result of earnest research to develop a coated steel sheet, a chromate treatment layer was formed on the surface of zinc or zinc-based plated steel sheet,
The above-mentioned object can be achieved by forming a specific acrylic copolymer emulsion, a colloidal silica having a particle size of 100 μm or less, and a coating material containing a rust preventive agent as a main component in a dry coating film thickness of 1 to 10 μm. The present invention has been completed and the present invention has been completed.

That is, the present invention is, firstly, (A) an acrylic copolymer emulsion containing maleated polybutadiene as an emulsifier and styrene as an essential component, (B).
Colloidal silica having a particle diameter of 100 μm or less and (C) a rust preventive agent are essential components, and the amount of the (C) component is 40 parts by weight or less based on 100 parts by weight of the sum of the (A) component and the (B) component. A primer composition for a steel sheet coated with a primer is provided.

Secondly, according to the present invention, a chromate-treated layer having a chromium deposition amount of 10 to 200 mg / m ² in terms of metallic chromium is formed on the surface of a galvanized steel sheet or a zinc alloy-based plated steel sheet, and a chromate treatment layer is formed thereon. The present invention provides a primer steel sheet characterized in that a film of the primer composition for a steel sheet coated with a primer is formed to have a dry coating film thickness of 1 to 10 µm.

[0007]

The acrylic copolymer emulsion [component (A)] used in the primer composition of the present invention has a number average molecular weight of about 300 to about 40,000 as an emulsifier.
Emulsion polymerization of styrene and acrylic monomers by a known method using a neutralization product of maleated polybutadiene having an acid value of about 20 to about 350, which is an addition reaction product of polybutadiene with maleic acid or maleic anhydride. It is obtained by doing.

The polybutadiene is generally 1,
Examples thereof include those having a 2-vinyl type, 1,4-trans type or 1,4-cis type structure, or a partial mixture of these structures. The molecular weight of polybutadiene is about 300
If it does not reach the above value, it does not act as a polymeric emulsifier, while if it exceeds about 40,000, the maleation reaction is difficult. Further, if the acid value of maleated polybutadiene is less than 20, it is difficult to form an emulsion, while if it exceeds 350, the compatibility with the produced polymer becomes poor.

Acrylic monomers used for emulsion polymerization are, for example, those represented by the general formula

[0010]

[Chemical 1]

(In the formula, R ₁ represents a hydrogen atom or a methyl group, R ₂ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an alicyclic group or an aromatic group, or a hydroxy group having 1 to 8 carbon atoms. Acrylic acid, methacrylic acid, acrylic acid ester or methacrylic acid ester represented by (representing an alkyl group). Representative monomers include, for example, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl. Methacrylate, lauryl methacrylate, 2-
Examples include hydroxyethyl acrylate and 2-hydroxyethyl methacrylate.

The amount of styrene used in combination with the acrylic monomer is in the range of 20 to 40% by weight based on the total amount of the monomers, and the glass transition of the organic resin can be achieved by using styrene in this range. The temperature can be raised moderately, and in general, it is possible to impart excellent corrosion resistance so that the film having a high glass transition temperature has excellent corrosion resistance in relation to the physical properties of the organic resin film and the corrosion resistance.

Next, the colloidal silica [component (B)] used in the composition of the present invention has a particle size of 100 μm.
In the following, the range of 10 to 50 μm is particularly preferable,
What is usually supplied as an aqueous dispersion can be used as it is. If the particle size is too small, it will be difficult to produce a uniform primer composition because the stability of the dispersed state will be low, and if a large particle size exceeding 100 μm is used, the total amount of silica particles blended will be small. Since the surface area is relatively small, the interaction with the acrylic copolymer emulsion is small, and the mechanical properties such as flexibility and impact resistance are insufficient when a dried / cured film is formed.

Colloidal silica having a particle size within the above range is
Either the acidic side or the basic side can be used in the state of the aqueous dispersion. That is, as the acidic colloidal silica, for example, commercially available non-stabilized silica (pH 3 to 4) can be used. On the other hand, as the colloidal silica on the basic side, there is silica (pH 8.4 to 10) stabilized by the addition of a trace amount of alkali metal ion, ammonium ion or amine.

In the composition of the present invention, the mixing ratio of the component (A) and the component (B) is not particularly limited, but the component (A) / component (B) is 90 / in the solid content weight ratio. 1
It is preferably in the range of 0 to 50/50 from the viewpoint of corrosion resistance and adhesion of the top coat.

The components (A) and (B) may be a simple mixture, or an organic-inorganic composite obtained by complexing the components (A) and (B) in the presence of trialkoxysilane. It may be a body resin. The organic-inorganic composite resin is a composite resin prepared by mixing and dispersing an acrylic copolymer emulsion and colloidal silica, mixing trialkoxysilane with stirring, and aging at room temperature, preferably at 10 ° C. or higher. But you can
In order to obtain a tough film, it is desirable to continuously heat the mixed solution at a temperature of 50 ° C. or higher and a boiling point (usually about 105 to 110 ° C.), specifically 50 to 90 ° C. The three components are sufficiently bonded to each other. Although the viscosity of the mixed solution gradually increases as the heating is continued, it finally becomes almost constant and no change is observed. Therefore, the heating may be stopped at that time as the end point. Usually, it takes 0.5 to 5 hours to reach the end point.

Typical examples of the above trialkoxysilanes include divinyldimethoxysilane and divinyldi-β.
-Methoxyethoxysilane, di (γ-glycidoxypropyl) dimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ
-Glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, β-
(3,4-Epoxycyclohexyl) ethyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl) γ-
Examples thereof include aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane.

The amount of trialkoxysilane used in the case of forming a composite is the sum of the above components (A) and (B) 10
It is usually used in the range of 1 to 5 parts by weight with respect to 0 parts by weight.

In the composition of the present invention, the above-mentioned component (A)
In addition to the component (B) and the component (B), a rust preventive [component (C)] is used as an essential component. Examples of the rust preventive include those listed below. Hexavalent chromium compound : chromic anhydride (CrO ₃ ), lithium chromate (Li ₂ CrO ₄ .2H ₂ O), sodium chromate (Na ₂ CrO ₄ .10H ₂ O), potassium chromate (K ₂ CrO ₄ ). , Ammonium chromate ((N
H _{4) 2} CrO _4), sodium dichromate (Na ₂ C
r ₂ O ₇・ 2H ₂ O), potassium dichromate (K ₂ Cr
₂ O ₇ ), ammonium dichromate ((NH ₄ ) ₂ Cr
₂ O ₇ ), strontium chromate (SrCrO ₄ ),
Barium chromate (BaCrO ₄ ), lead chromate (Pb
CrO _4), calcium chromate (CaCrO _4), basic zinc chromate (ZnCrO ₄ · 4Zn (OH)
₂ ), basic potassium potassium chromate (K ₂ O ・ 4ZnO
・ 4CrO ₃ · 3H ₂ O), red silicochromate (SiO ₂ · PbCrO ₄ ), etc.

Chromium Chromate Compound : Chromate chromate is a complex compound of hexavalent chromium and trivalent chromium. The method for producing such a compound is not particularly limited, and the above hexavalent chromium compound may be a monohydric alcohol such as methanol or ethanol; a polyhydric alcohol such as sorbitol, ethylene glycol or glycerin; hydroquinone or catechol. Aromatic polyhydric alcohols; saccharides such as starch, sucrose, glucose; aldehydes such as formalin; hydrogen peroxide, inorganic compounds such as hydrazine, and other oxidative decomposition products. The amount of these reducing agents used is stoichiometrically determined according to the desired amount of hexavalent chromium in chromium chromate, and the reduction reaction can be carried out by heating.

The phosphate-based compound lead phosphate, aluminum phosphate, calcium phosphate, silicon phosphate, condensed phosphoric acid salts molybdate compound zinc molybdate, calcium molybdate, zinc molybdate calcium, zinc molybdate potassium borate Salt compounds Barium metaborate, calcium borate Other iron oxides, calcium complex, cyanamide zinc calcium, ion exchange silica

The amount of the above-mentioned rust preventive agent (C) in the composition of the present invention is 40 parts by weight based on 100 parts by weight of the sum of the specific acrylic copolymer emulsion component (A) and colloidal silica component (B). Parts or less, preferably 5 to 30 parts by weight. If the blending amount exceeds 40 parts by weight, the workability is lowered and the water resistance of the coating is lowered, which may cause the formation of blisters. In the composition of the present invention,
In addition to the above-mentioned essential components (A), (B) and (C), the following substances can be used in combination as necessary to improve lubricity, electrical conductivity, corrosion resistance and adhesion of top coating.

That is, a lubricity imparting agent may be added to the composition of the present invention in order to impart lubricity. A high melting point polyolefin wax having a melting point of 70 ° C. or higher is effective as the lubricity imparting agent. The polyolefin wax may be any wax as long as it is a wax composed of a polymer of an olefinic hydrocarbon such as polyethylene, polypropylene or polybutene, or a combination thereof. The polyolefin wax having a melting point of 70 ° C. or higher usually has a weight average molecular weight of about 500 to 20,000. Further, a fluorine resin, for example, a resin such as polytetrafluoroethylene resin, polyhexafluoropropylene resin, or polyvinylidene fluoride may be used in combination with the above polyolefin wax.

Further, a conductive substance may be mixed in the composition of the present invention to impart conductivity. As a result, the electric weldability and the grounding property of the coating can be improved. Examples of such conductive substances include zinc, aluminum, iron, cobalt, nickel, manganese, chromium,
Metal powders such as molybdenum, tungsten, copper, lead and tin, and alloy powders thereof, aluminum-doped zinc oxide powder, tin oxide-titanium oxide, tin oxide-barium sulfate,
Examples thereof include semiconductor oxides such as nickel oxide-alumina.

A urethane resin emulsion, an ethylene-based ionomer resin emulsion, an epoxy resin emulsion and the like can be used in combination for improving the corrosion resistance and the adhesion of the top coating material. Furthermore, the composition of the present invention is
Coloring pigments, extender pigments, dyes and the like which are usually used in the field of coating materials can be dispersed in the composition.

The primer composition for a primer-coated steel sheet of the present invention can be applied to cold-rolled steel sheet, galvanized steel sheet, zinc alloy-based steel sheet, aluminum-plated steel sheet, chemical conversion treatment sheet of these steel sheets, etc., but has corrosion resistance. In particular, it is preferable to coat a galvanized steel sheet or a zinc alloy-based galvanized steel sheet on which a specific chromate treatment layer is formed, and the present invention is formed by forming a predetermined film thickness of the composition of the present invention on the treatment layer. It is possible to obtain a primer-coated steel sheet.

In the primer-coated steel sheet of the present invention, the galvanized steel sheet may be either a hot-dip galvanized steel sheet or an electrogalvanized steel sheet, and the zinc alloy-plated steel sheet is iron-zinc, zinc-aluminum, nickel-
Examples include alloy-plated steel sheets such as zinc.

The chromate treatment for forming the chromate treatment layer may be a known chromate treatment such as a reaction type, a coating type or an electrolytic type, but the amount of deposited chromium is 10 to 200 mg / m ² in terms of metallic chromium. It is necessary to form a film. If the amount of adhesion is less than 10 mg / m ² , the corrosion resistance becomes insufficient, and if it exceeds 200 mg / m ² , not only the effect of improving the corrosion resistance corresponding to the amount of adhesion cannot be obtained, but also bending such as deformation of the steel sheet is performed. In that case, cohesive failure of the chromate film is likely to occur. A more preferable amount of the chromate film is 10 to 10 per one side of the steel plate in terms of metal chromium.
It is within the range of 0 mg / m ² .

The specific examples of the chromate treatment liquid for forming the chromate treatment layer are as follows. The composition of the reactive chromate treatment liquid is 1 to 100 g / in terms of metallic chromium.
1 water-soluble chromium compound and 0.2 to 20 g / l sulfuric acid as main components, and the content of trivalent chromium in the total chromium is 50% by weight or less, preferably 20 to 35% by weight. However, if necessary, an appropriate amount of metal ions such as Zn ²⁺ , Co ²⁺ , Fe ^{3+ and the} like and other mineral acids such as phosphoric acid and hydrofluoric acid may be added.

The coating type chromate treatment liquid has a composition similar to that of the above reaction type chromate treatment liquid, and a water-soluble composition containing a large amount of carboxyl groups in the molecule and a composition and phase similar to those of the above reaction type chromate treatment liquid. An example is one in which a soluble organic polymer resin is added to adjust the pH to 2.0 to 3.5. This organic polymer has an average molecular weight of 1,0
It is preferably from 00 to 500,000. The amount added is generally in the range of 0.02 to 30 g / l in terms of resin content.

In the production of the primer-coated steel sheet of the present invention, the chromate-treated layer is air-dried or baked and dried, and then the primer composition of the present invention is applied onto the chromate-treated layer and dried to form a dried film. Can be formed. The thickness of the dry film is 1 to 1
It is in the range of 0 μm, preferably in the range of 3 to 6 μm. 1
If it is less than μm, not only corrosion resistance cannot be expected, but also scratches due to handling cannot be suppressed, which is not preferable. On the other hand, if it exceeds 10 μm, the film peeling easily occurs when subjected to severe processing, which is not preferable.

To form a film of the above primer composition, the above composition is applied by a known coating means such as a roll coater, a curtain flow coater, or a spray, or a chromate-treated galvanized steel sheet or a zinc alloy system is applied to the above composition. After dipping and pulling the plated steel sheet, the amount of adhesion can be controlled by squeezing a roll or blowing air, and then it can be easily dried. Drying is usually performed by heating for about 10 seconds to 90 seconds so that the plate temperature is about 60 ° C. or higher, preferably 80 to 200 ° C., using a hot air oven, a dielectric heating device, or the like.

[0033]

EXAMPLES Examples and comparative examples will be shown below. These examples are for explaining the present invention more specifically, and do not limit the scope of the present invention. “Part”
And "%" are based on weight.

Synthesis Example of Acrylic Copolymer Emulsion Polybutadiene (Molecular weight 1,900, 1,4-cis type 7
2%, 1,4-trans type 27% and 1,2-vinyl type 1%) 150 parts, maleic anhydride 20 parts and xylene 7
After 5 parts were enclosed in an autoclave and purged with nitrogen gas, the mixture was reacted at 190 to 200 ° C. for 5 hours while stirring. After the reaction, the product was washed with water, 60 parts of butyl cellosolve was added, and water was removed by an evaporator to obtain maleated polybutadiene. This product has an acid value of 93 and a concentration of 85.6%.
Met. Then 40 parts of styrene in the autoclave,
Butyl methacrylate 40 parts, ethyl acrylate 20
Parts, 40 parts of the above maleated polybutadiene, 10 parts of 28% ammonia water, 233 parts of water and 0.2 parts of ammonium persulfate are added, and the gas is replaced with nitrogen gas and stirred at 75-8.
Solid content of 35% by heating at 5 ℃ for 2 hours and cooling
To obtain an acrylic copolymer [A] emulsion.

Synthetic Example of Organic-Inorganic Composite Resin 214 parts of acrylic copolymer emulsion (A) liquid having a solid content of 35% synthesized as described above, 1 part of deionized water
61 parts and Snowtex C (manufactured by Nissan Chemical Industries, pH
125 parts of an aqueous colloidal silica dispersion having a particle size of 9 to 10 and a particle size of 10 to 20 μm) are uniformly mixed, and 2 parts of γ-methacryloyloxypropyltrimethoxysilane is added dropwise to the mixture under stirring, and then heated to 85 ° C. And 2 at the same temperature
By reacting for a time, a milky white organic-inorganic composite resin [B] aqueous dispersion having a solid content of about 20% was obtained.

Examples 1 to 11 and Comparative Examples 1 to 9 Hot-dip galvanized steel sheet having a plate thickness of 0.4 mm and a plating amount of 130 g / m ² (abbreviated as “Zn” in Table 1) or a plate thickness of 0.4.
mm, plating amount 90 g / m ² zinc-aluminum alloy (Zn
43.4%, Al 55%, Si 1.6%) A plated steel sheet (abbreviated as "Zn-Al" in Table 1) is subjected to reactive chromate treatment or coating chromate treatment, A chromate-treated layer was formed by drying. Then, on the plated steel sheet having the chromate-treated layer formed thereon, the acrylic copolymer [A] emulsion synthesized in the above-mentioned Synthesis Example, the organic-inorganic composite resin [B] aqueous dispersion, and other surfactants were used as emulsifiers. Acrylic resin [C] emulsion, epoxy resin [D] emulsion, urethane resin [E] emulsion, colloidal silica aqueous dispersion, rust preventive agent and pigments are appropriately dispersed so as to have a solid content shown in Table 1. The blended primer composition was applied by a roll coater so that the dry coating film thickness shown in Table 1 was obtained. Next, each primer-coated steel sheet was prepared by heating the steel sheet in a hot air drying oven for about 15 seconds until the temperature of the steel sheet reached 100 ° C. to dry the coating film. In Table 1, for Example 10, organic-inorganic composite resin [B]
Since () is used, the breakdown of the components is described with ().

In Table 1, the types of colloidal silica and rust preventive are as follows. Type of colloidal silica a: Snowtex C (manufactured by Nissan Chemical Industries, Ltd., particle size 10
20 μm aqueous colloidal silica dispersion) b: Adelite AT-20 (Asahi Denka Kogyo KK, particle size 10)
-20 μm aqueous colloidal silica dispersion) c: Snowtex 20L (Nissan Chemical Co., Ltd., aqueous colloidal silica dispersion having a particle size of about 45 μm) Types of rust preventives I: Strontium chromate, II: Barium chromate III: Condensation Aluminum phosphate, IV: Calcium molybdate V: Sealdex (Fuji Silysia Chemical Ltd., calcium ion exchange silica)

Regarding the primer steel sheets obtained in the above Examples and Comparative Examples, the primer steel sheet alone and a phthalic acid type constantly dry coating (film thickness 35 μm) or aminoalkyd type baking paint (film thickness 35 μm, baking conditions 120 ° C.) were used. -2
The following test was conducted on the top-coated plate coated with 0 minutes). The test results are shown in Table 2 below.

Bending-tape test With the coated surface facing outward, the primer-coated steel sheet was bent 180 degrees so that the inner surface had a radius of curvature of 2 mm, and the cellophane tape was adhered to the coated surface of the bent portion. When the tape was quickly peeled off, cracks on the coated surface of the bent portion and peeling were visually evaluated. A: No cracks or peeling are observed. ◯: Cracks are observed, but peeling is not observed at all. Δ: Peeling less than 10% is recognized. X: Peeling is recognized by 10% or more.

Gobang eyes-tape test 100 pieces of goggles that reach the substrate at 1 mm intervals are made on the coated surface of the top coating plate with a cutter, and a cellophane tape having a width of 25 mm is adhered on the eyes, and a round tip with a diameter of 10 mm is applied. Using a stick or the like, the cellophane tape was rubbed evenly with a uniform force evenly on the area of the scorch, and the tape was quickly peeled off in the direction of 180 degrees, and the presence or absence of peeling was visually inspected. ◎: No peeling at all ○: Peeling is less than 10% △: Peeling is 10 to 50% ×: Peeling is more than 50%

A cross cut reaching the substrate was put under the coated surface of the corrosion resistance test piece with a cutter, and the cross cut was placed in a salt spray tester at an angle of 15 degrees, and after 240 hours, the rust and blister penetration distance from the cross cut ( Evaluate by one side mm). ◎: No blistering or rusting ○: Penetration distance less than 1 mm △: Penetration distance 1-3 mm ×: Penetration distance over 3 mm

A humidity resistance test piece was replaced with a humidity resistance tester (internal temperature 49 ± 1 ° C., relative humidity 9
5% or more) and left for 240 hours, and then evaluated the blister degree of the coated surface according to ASTM standard. ⊚: No abnormalities are observed in the coating film ◯: Blister density is “F” according to ASTM evaluation Δ: Blister density is “M” according to ASTM evaluation ×: Blister density is “D” according to ASTM evaluation

[0043]

As is apparent from the above examples, according to the present invention, a primer composition which can be cured by baking in an aqueous system at a low temperature for a short time is used, so that it can be produced on a plating production line. In addition, it is possible to provide a primer-coated steel sheet having excellent adhesion to a top-coat coating film and corrosion resistance when it is top-coated, and the industrial effect is extremely remarkable.

[0044]

[Table 1]

[0045]

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C23C 22/00 Z

Claims (2)

[Claims] 1. An (A) maleic polybutadiene as an emulsifier, an acrylic copolymer emulsion containing styrene as an essential component, (B) a colloidal silica having a particle diameter of 100 μm or less, and (C) an anticorrosive as an essential component. ,
The amount of component (C) is the sum of component (A) and component (B) 100
40 parts by weight or less based on parts by weight of the primer composition for a primer-coated steel sheet. 2. The amount of chromium deposited on the surface of a galvanized steel sheet or a zinc alloy-based plated steel sheet is 10 to 100 in terms of metallic chromium.
A chromate-treated layer of 200 mg / m ² is formed, on which (A) an acrylic copolymer emulsion containing maleated polybutadiene as an emulsifier and styrene as an essential component, (B) a colloidal silica having a particle diameter of 100 μm or less. And (C) a rust preventive agent as a main component, and the amount of the (C) component is 40 parts by weight or less based on 100 parts by weight of the sum of the (A) component and the (B) component. A primer-coated steel sheet having a dry coating film thickness of 1 to 10 μm.