JP7809296B2 - Multi-layer coating - Google Patents

Description

The present invention relates to a multi-layer coating film.

Patent Document 1 discloses a paint containing a metal sulfate and at least one metal powder selected from the group consisting of zinc and zinc alloys.

Japanese Patent Application Laid-Open No. 2021-167379

Patent Document 1 discloses a paint that combines a zinc-rich paint with a metal sulfate, but its corrosion resistance is insufficient.

The objective of the present invention is to provide a multi-layer coating film with excellent corrosion resistance.

The present invention provides the following aspects.
[1]
A metal substrate,
an anti-rust coating film formed on the substrate from an anti-rust coating composition containing zinc particles and a binder;
a primer coating film formed on the anticorrosive coating film from a primer coating composition,
The primer coating composition comprises:
an epoxy resin (a);
a polyamine (b);
Powder (c),
The powder (c) has a solubility of 0.1 g or more in 100 g of water at 5°C and contains a metal sulfate (c-1) that elutes polyvalent metal cations upon dissolution in water.
[2]
The multi-layer coating film according to [1] above, wherein the content of the metal sulfate (c-1) is 0.05% by mass or more and 20% by mass or less of the solid content of the primer coating composition.
[3]
The multilayer coating film according to [1] or [2] above, wherein the metal sulfate (c-1) contains at least one selected from the group consisting of nickel sulfate, aluminum sulfate, magnesium sulfate, zinc sulfate, cobalt sulfate, chromium sulfate, copper sulfate, titanium sulfate, tin sulfate, zirconium sulfate, vanadium sulfate, and manganese sulfate.
[4]
The multi-layer coating film of the above [1] or [2], wherein the powder (c) further contains a white zinc compound (c-2) that dissolves in 100 g of water at a pH greater than 5.0 and at 20°C in an amount of 0.005 g or less and in 100 g of water at a pH of 5.0 or less and at 20°C in an amount of 0.05 g or more.
[5]
The multi-layer coating film of [4] above, wherein the content of the zinc compound (c-2) is 5% by mass or more and 60% by mass or less of the solid content of the primer coating composition.
[6]
The multi-layer coating film according to the above [4], wherein the zinc compound (c-2) comprises at least one selected from the group consisting of zinc oxide, zinc hydroxide and zinc carbonate.
[7]
The multilayer coating film according to the above [1] or [2], wherein the powder (c) further contains an alkaline earth metal compound (c-3) which is at least one of an alkaline earth metal oxide and an alkaline earth metal hydroxide.
[8]
The multi-layer coating film of [7] above, wherein the content of the alkaline earth metal compound (c-3) is 0.05 mass% or more and 20 mass% or less of the solid content of the primer coating composition.
[9]
The multi-layer coating film according to [7] above, wherein the alkaline earth metal compound (c-3) contains at least one selected from the group consisting of calcium oxide, calcium hydroxide, barium oxide, and barium hydroxide.
[10]
The multi-layer coating film according to the above [1] or [2], wherein the content of the zinc particles is 40% by mass or more and 95% by mass or less of the solid content of the anticorrosive coating composition.

The present invention provides a multi-layer coating film with excellent corrosion resistance.

[Multi-layer coating]
The multilayer coating film according to the present disclosure comprises an anti-rust coating film formed on an object to be coated from an anti-rust coating composition, and a primer coating film formed on the anti-rust coating film from a primer coating composition.

The anti-corrosion coating composition used in this disclosure contains zinc particles and a binder.

The primer coating composition used in this disclosure contains an epoxy resin (a), a polyamine (b), and a powder (c). The powder (c) contains a metal sulfate (c-1) that dissolves in 100 g of water at 5°C in an amount of 0.1 g or more and releases polyvalent metal cations upon dissolution in water.

Metal sulfate (c-1) dissolves in water, eluting polyvalent metal ions and sulfate ions. Metal sulfate (c-1) dissolved by rain or seawater splashes penetrates into the anti-corrosion coating. As a result, the polyvalent metal cations (hereinafter referred to as polyvalent cations) eluted from metal sulfate (c-1) form a dense, electrochemically stable rust layer in the presence of iron ions generated from the metal substrate. This rust layer has the ability (blocking properties) to prevent further corrosion factors (e.g., water, oxygen, chloride ions) from reaching the surface of the metal substrate. This improves the corrosion protection of the multi-layer coating.

Sulfate ions eluted from the metal sulfate (c-1) also penetrate the anti-rust coating and come into contact with zinc. The action of these sulfate ions and the generation of hydrogen ions through the hydrolysis of metal ions dissolves the zinc contained in the anti-rust coating, producing zinc ions. The zinc ions react with chloride ions (contained in airborne salt, rainwater, or rust on the substrate surface, which promote corrosion) and trap the chloride ions. The reaction between zinc ions and chloride ions produces, for example, basic zinc chloride. Reaction products such as basic zinc chloride form a water-stable coating (hereinafter referred to as the anti-rust layer). The penetration of sulfate ions into the anti-rust coating proceeds gradually. Furthermore, the presence of the anti-rust coating makes it difficult for sulfate ions to come into contact with the metal substrate. Therefore, the anti-rust layer forms before the metal substrate is corroded by sulfate ions.

Zinc-rich paints generally contain a high concentration of zinc particles and form a porous coating. When metal sulfates are blended into zinc-rich paint to form a coating, as in Patent Document 1, the metal sulfates are washed away by rain or other factors before the top layer of the coating is formed. The amount of leaching increases because the coating is porous. As a result, the effect of the metal sulfates (the improved barrier properties achieved by the formation of the rust layer mentioned above) cannot be fully realized.

In addition, when metal sulfates are added to zinc-rich paint, the eluted sulfate ions act directly on the metal substrate. As a result, corrosion of the metal substrate (the formation of red rust) by the sulfate ions progresses before the anti-rust layer is formed.

The present disclosure layers a primer coating containing a metal sulfate on a rust-preventive coating containing zinc particles. This allows the metal sulfate to fully exert its effects. The multi-layer coating of the present disclosure has excellent corrosion protection because it can form a rust layer and a rust-preventive layer in a corrosive environment.

Hereinafter, epoxy equivalent weight is determined based on the solids mass. Epoxy equivalent weight is determined in accordance with JIS K 7236:2001.

The weight average molecular weight is measured by gel permeation chromatography (GPC).

The active hydrogen equivalent of a polyamine is determined based on the mass of solids. The active hydrogen equivalent of a polyamine is determined in accordance with JIS K 7237:1995.

The solids content of a paint composition is the total content of the paint composition excluding volatile components (typically, solvents). The solids concentration of a paint composition can be calculated from the residue when the paint composition is heated to 140°C in accordance with JIS K 5601-1-2 Heat Residue Measurement Method.

The resin solids content of the primer coating composition is the solids content of the epoxy resin (a), polyamine (b), and other primer resin components contained in the primer coating composition.

(Primer coating composition)
The primer coating composition may be a two-component type consisting of a base agent containing an epoxy resin (a) and a curing agent containing a polyamine (b). The powder (c) may be contained in the base agent, the curing agent, or both. The powder (c) may be contained in the base agent.

Epoxy resin (a)
The epoxy resin (a) is a coating film-forming component that undergoes a crosslinking reaction with the polyamine (b) to form a cured coating film.

Epoxy resin (a) is not particularly limited. Examples of epoxy resin (a) include aromatic epoxy resins such as bisphenol-type, novolac-type, biphenyl-type, and naphthalene-type; and aliphatic epoxy resins such as dicyclopentadiene-type and glycidyl ethers of polyhydric alcohols. These may be used alone or in combination of two or more. Epoxy resin (a) may be a modified version of the above epoxy resin. In terms of moisture resistance and toughness, it may be an aromatic epoxy resin or a novolac-type epoxy resin.

Examples of bisphenol-type epoxy resins include bisphenol A, bisphenol F, bisphenol S, bisphenol AD, diglycidyl ethers of alkylene oxide adducts of these bisphenol-type epoxy resins, and hydrogenated bisphenol-type resins in which hydrogen has been added to these bisphenol-type epoxy resins. These can be used alone or in combination of two or more.

Novolac epoxy resins include, for example, phenol novolac, cresol novolac, and bisphenol A novolac. These may be used alone or in combination of two or more.

Examples of biphenyl-, naphthalene-, and dicyclopentadiene-type resins include resins in which one or more glycidyl ether groups are substituted at any position on biphenyl, naphthalene, or dicyclopentadiene.

The solid content of the epoxy resin (a) is, for example, 15% by mass or more and 60% by mass or less of the solid content of the anticorrosion coating composition. When the content of the epoxy resin (a) is 15% by mass or more, curability can be improved. When the content of the epoxy resin (a) is 60% by mass or less, the relative proportion of pigment in the coating film increases, thereby improving hiding power. The content of the epoxy resin (a) may be 20% by mass or more, or may be 25% by mass or more. The content of the epoxy resin (a) may be 50% by mass or less, or may be 40% by mass or less.

The weight-average molecular weight of epoxy resin (a) is not particularly limited. The weight-average molecular weight of epoxy resin (a) may be 6,500 or more and 12,000 or less, in order to enhance curability (particularly curability at low temperatures of 5°C or less). The weight-average molecular weight of epoxy resin (a) may be 8,500 or more. The weight-average molecular weight of epoxy resin (a) may be 11,000 or less.

The epoxy equivalent of epoxy resin (a) is not particularly limited. The epoxy equivalent of epoxy resin (a) may be 1000 g/eq or more and 1200 g/eq or less, in order to enhance curing properties at low temperatures. The epoxy equivalent of epoxy resin (a) may be 1010 g/eq or more.

Commercially available novolac-type epoxy resins (a) include, for example, "EPICLON 5970-60" (phenol novolac-type epoxy resin, weight-average molecular weight 9900, epoxy equivalent of 1000 g/eq or more, manufactured by DIC Corporation). Commercially available bisphenol A-type epoxy resins (a) include, for example, "EPICLON 1040-70X" (bisphenol A-type epoxy resin, epoxy equivalent of 1300 g/eq, manufactured by DIC Corporation).

Polyamine (b)
The polyamine (b) is a curing component that undergoes a crosslinking reaction with the epoxy resin (a) to form a cured coating film.

The polyamine (b) is not particularly limited. The polyamine (b) may be an alicyclic polyamine (b-1) having a cyclic aliphatic hydrocarbon group to which an amino group is bonded, or a non-alicyclic polyamine (b-2) having no cyclic aliphatic hydrocarbon group to which an amino group is bonded, or may contain both. The combined use of an alicyclic polyamine (b-1) and a non-alicyclic polyamine (b-2) tends to suppress dissolution and lifting of the primer coating film when another coating film is layered on top of the primer coating film formed from the primer coating composition.

Examples of alicyclic polyamines (b-1) include 1,4-cyclohexanediamine, 4,4'-methylenebiscyclohexylamine, 4,4'-isopropylidenebiscyclohexylamine, norbornadiamine, bis(aminomethyl)cyclohexane, diaminodicyclohexylmethane, isophoronediamine, menthenediamine (MDA), and 1,3-bis(aminomethyl)cyclohexane. These may be used alone or in combination of two or more.

The active hydrogen equivalent of the alicyclic polyamine (b-1) is, for example, 30 g/eq or more and 150 g/eq or less. When the active hydrogen equivalent of the alicyclic polyamine (b-1) is 30 g/eq or more, curability can be improved. When the active hydrogen equivalent of the alicyclic polyamine (b-1) is 150 g/eq or less, barrier properties can be improved. The active hydrogen equivalent of the alicyclic polyamine (b-1) may be 32 g/eq or more, or 33 g/eq or more. The active hydrogen equivalent of the alicyclic polyamine (b-1) may be 100 g/eq or less, or 50 g/eq or less.

Examples of non-alicyclic polyamines (b-2) include linear aliphatic polyamines, polyamines having an aromatic ring to which an amino group is bonded (aromatic polyamines), and polyamines having a heterocyclic ring to which an amino group is bonded (heterocyclic polyamines). These may be used alone or in combination of two or more.

Examples of linear aliphatic polyamines include alkylene polyamines and polyalkylene polyamines. Alkylene polyamines are represented, for example, by the formula H ₂ N—R ¹ —NH ₂ (wherein R ¹ is a divalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with one or more hydrocarbon groups having 1 to 10 carbon atoms, and which may be branched). Examples of alkylene polyamines include methylene diamine, ethylene diamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, and 1,10-diaminodecane. Examples of polyalkylene polyamines include diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, and hexamethylene tetramine. These may be used alone or in combination of two or more.

Examples of chain aliphatic polyamines include tetra(aminomethyl)methane, tetrakis(2-aminoethylaminomethyl)methane, 1,3-bis(2'-aminoethylamino)propane, triethylene-bis(trimethylene)hexamine, bis(3-aminoethyl)amine, and bishexamethylenetriamine [H ₂ N(CH ₂ ) ₆ NH(CH ₂ ) ₆ NH ₂ ]. These may be used alone or in combination of two or more.

Aromatic polyamines include, for example, bis(aminoalkyl)benzenes, bis(aminoalkyl)naphthalenes, and compounds having two or more primary amino groups bonded to a benzene ring. Examples of aromatic polyamines include bis(cyanoethyl)diethylenetriamine, o-xylylenediamine, m-xylylenediamine (MXDA), p-xylylenediamine, phenylenediamine, naphthylenediamine, diaminodiphenylmethane, diaminodiethylphenylmethane, 2,2-bis(4-aminophenyl)propane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenyl sulfone, 2,2'-dimethyl-4,4'-diaminodiphenylmethane, 2,4'-diaminobiphenyl, 2,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, bis(aminomethyl)naphthalene, and bis(aminoethyl)naphthalene. These may be used alone or in combination of two or more.

Examples of heterocyclic polyamines include N-methylpiperazine [CH ₃ -N(CH ₂ CH ₂ ) ₂ NH], morpholine [HN(CH ₂ CH ₂ ) ₂ O], 1,4-bis-(8-aminopropyl)-piperazine, piperazine-1,4-diazacycloheptane, 1-(2'-aminoethylpiperazine), 1-[2'-(2''-aminoethylamino)ethyl]piperazine, 1,11-diazacycloeicosane, and 1,15-diazacyclooctacosane. These may be used alone or in combination of two or more.

The active hydrogen equivalent of the non-alicyclic polyamine (b-2) is, for example, 30 g/eq or more and 550 g/eq or less. The active hydrogen equivalent of the non-alicyclic polyamine (b-2) may be 32 g/eq or more, or 35 g/eq or more. The active hydrogen equivalent of the non-alicyclic polyamine (b-2) may be 250 g/eq or less, 100 g/eq or less, or 50 g/eq or less.

The solids content of polyamine (b) is, for example, 1% by mass or more and 15% by mass or less of the solids content of the anticorrosion coating composition. When the polyamine (b) content is 1% by mass or more, curability can be improved. When the polyamine (b) content is 15% by mass or less, barrier properties can be improved. The polyamine (b) content may be 1.1% by mass or more, or 1.2% by mass or more. The polyamine (b) content may be 10% by mass or less, 5.0% by mass or less, or 2.0% by mass or less.

The solids content of the alicyclic polyamine (b-1) is, for example, 0.5% by mass or more and 10% by mass or less of the solids content of the anticorrosion coating composition. When the alicyclic polyamine (b-1) content is 0.5% by mass or more, curing properties can be improved, particularly at low temperatures. When the alicyclic polyamine (b-1) content is 10% by mass or less, the tackiness of the resulting coating film can be reduced and the treadability can be improved. The alicyclic polyamine (b-1) content may be 0.65% by mass or more, or 0.8% by mass or more. The alicyclic polyamine (b-1) content may be 6.0% by mass or less, 4.0% by mass or less, or 2.0% by mass or less. Treadability refers to the ability of a coating film to resist shoe marks and minimize peeling when a worker walks on the coating film.

The solids content of the non-alicyclic polyamine (b-2) is, for example, 0% by mass or more and 10% by mass or less of the solids content of the anticorrosion coating composition. When the content of the non-alicyclic polyamine (b-2) is 10% by mass or less, the tackiness of the resulting coating film at low temperatures is reduced, and the treadability can be improved. The content of the non-alicyclic polyamine (b-2) may be 0.1% by mass or more, or 0.3% by mass or more. The content of the non-alicyclic polyamine (b-2) may be 6.0% by mass or less, 3.0% by mass or less, or 1.0% by mass or less.

(Alkylphenol)
The curing agent may further include an alkylphenol, which further improves curability (especially low-temperature curability).

Examples of alkylphenols include monohydric phenols such as methylphenol (o-, m-, p-cresol), ethylphenol, butylphenol, tert-butylphenol, octylphenol, nonylphenol, dodecylphenol, and dinonylphenol. These may be used alone or in combination of two or more. The alkyl group of the alkylphenol may have, for example, 1 to 10 carbon atoms. The number of carbon atoms may be 5 or less.

The alkylphenol solids content is, for example, 0.05% by mass or more and 5.0% by mass or less of the solids content of the anticorrosion coating composition. The alkylphenol content may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more. The alkylphenol content may be 3.0% by mass or less, 2.0% by mass or less, or 1.0% by mass or less.

・Powder (c)
The powder (c) functions as a rust inhibitor. By using the specific metal sulfate (c-1), excellent corrosion prevention properties can be obtained as described above.

The average particle size of powder (c) is, for example, 0.1 μm or more and 40 μm or less. The average particle size of powder (c) may be 5 μm or more. The average particle size of powder (c) may be 20 μm or less.

The average particle size of powder (c) is calculated as follows. A composition containing epoxy resin (a), polyamine (b), and metal sulfate (c-1) in a specified ratio is applied to a polished steel plate to form a dry coating film of 100 μm or more, and then dried. The cross section of the resulting coating film in the thickness direction is observed using a scanning electron microscope (SEM). The maximum diameter in a specific direction of 200 particles of metal sulfate (c-1) observed in the image is measured, and the average value is calculated. This average value is the average particle size of metal sulfate (c-1). The average particle sizes of zinc particles, zinc compound (c-2), and alkaline earth metal compound (c-3), described below, can be calculated in the same manner.

Metal sulfate (c-1)
The metal sulfate (c-1) has a dissolution amount of 0.1 g or more in 100 g of water at 5° C. The metal sulfate (c-1) is easily soluble in water even in a low-temperature environment, and therefore can promote the formation of a rust-preventive layer. The dissolution amount of the metal sulfate (c-1) may be 5.0 g or more, or may be 10.0 g or more.

Metal sulfate (c-1) is a salt of a polyvalent metal cation and a sulfate ion. Examples of metals that make up metal sulfate (c-1) include alkaline earth metals, transition metals, and post-transition metals. These generate polyvalent metal cations. These can be used alone or in combination of two or more.

Alkaline earth metals are elements of Group 2 of the periodic table. A specific example of the alkaline earth metal constituting the metal sulfate (c-1) is magnesium (Mg ) .

Transition metals are metallic elements that exist between groups 3 and 11 in the periodic table. Specific examples of transition metals include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), and hassium (Hs).

Post-transition metals are metallic elements found in the P-block of the periodic table. Specific examples of post-transition metals include aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), lead (Pb), bismuth (Bi), polonium (Po), and astatine (At).

From the viewpoint of solubility, the metal may be magnesium (Mg), aluminum (Al), nickel (Ni), or zinc (Zn). These may be used alone or in combination of two or more.

Examples of metal sulfates (c-1) include nickel sulfate, aluminum sulfate, magnesium sulfate, zinc sulfate, cobalt sulfate, chromium sulfate, copper sulfate, titanium sulfate, tin sulfate, zirconium sulfate, vanadium sulfate, and manganese sulfate. These may be used alone or in combination of two or more.

The content of metal sulfate (c-1) is, for example, 0.05% by mass or more and 20% by mass or less of the solids content of the primer coating composition. When the content of metal sulfate (c-1) is 0.05% by mass or more, the effects of metal sulfate (c-1) are more likely to be exerted. When the content of metal sulfate (c-1) is 20% by mass or less, the barrier properties can be further improved, and the coating film properties are also improved.

The content of metal sulfate (c-1) may be 0.1% by mass or more, 1.0% by mass or more, or 2.0% by mass or more. The content of metal sulfate (c-1) may be 15.0% by mass or less, 12.0% by mass or less, or 10.0% by mass or less.

Zinc compound (c-2)
The powder (c) may contain a zinc compound (c-2), which forms an anti-corrosion layer together with zinc particles in a corrosive environment.

The zinc compound (c-2) may dissolve in 100 g of water at 20°C at a pH greater than 5.0 in an amount of 0.005 g or less, and in 100 g of water at 20°C at a pH of 5.0 or less in an amount of 0.05 g or more. If the amount of zinc compound (c-2) dissolved is low in the neutral to alkaline range, excessive dissolution of the zinc compound (c-2) is suppressed in environments where corrosion is unlikely to progress. On the other hand, if the amount of zinc compound (c-2) dissolved is high in the acidic range, the zinc compound (c-2) dissolves and exerts its effect as the pH decreases due to the dissolution of the metal sulfate (c-1).

The zinc compound (c-2) may be white. A white zinc compound (c-2) can change the color of the primer coating composition from white to a light color, thereby increasing the freedom in color design of the multi-layer coating film. The ability to select the design of the finish coating without being limited by the color of the primer is one of the important appealing points to consumers.

The zinc compound (c-2) may have a solubility of 0.005 g or less in 100 g of water at a pH greater than 5.0 and at 20°C, or a solubility of 0.05 g or more in 100 g of water at a pH of 5.0 or less and at 20°C, and may be white.

Examples of zinc compounds (c-2) include zinc oxide, zinc hydroxide, and zinc carbonate. These may be used alone or in combination of two or more. Zinc compounds (c-2) do not include metallic zinc or zinc alloys.

The content of zinc compound (c-2) is, for example, 5% by mass or more and 60% by mass or less of the solids content of the primer coating composition. When the content of zinc compound (c-2) is 5% by mass or more, the effects of zinc compound (c-2) are more likely to be exerted. When the content of zinc compound (c-2) is 60% by mass or less, film-forming properties are less likely to be impaired.

The content of zinc compound (c-2) may be 5.0% by mass or more, or 10.0% by mass or more. The content of zinc compound (c-2) may be 45.0% by mass or less, or 30.0% by mass or less.

Alkaline earth metal compounds (c-3)
The powder (c) may contain an alkaline earth metal compound (c-3). The alkaline earth metal compound (c-3) is at least one of an oxide and a hydroxide of an alkaline earth metal. The alkaline earth metal compound (c-3) dissolves in water and dissociates into alkaline earth metal ions and their counter ions. The alkaline earth metal ions react with sulfate ions to form a salt that is sparingly soluble in water.

As mentioned above, sulfate ions promote the formation of an anti-corrosion layer, but if they act directly on the substrate, they can promote corrosion of the base substrate. By incorporating alkaline earth metal compound (c-3) together with metal sulfate (c-1), corrosion of the substrate caused by sulfate ions is suppressed, thereby preventing the formation of red rust.

The amount of alkaline earth metal compound (c-3) dissolved is not particularly limited. The amount of alkaline earth metal compound (c-3) dissolved in 100 g of water at 20°C may be 0.05 g or more. The amount of alkaline earth metal compound (c-3) dissolved may be 0.1 g or more, or 1.0 g or more. From the perspective of suppressing the generation of voids in the coating film due to rapid dissolution, the amount of alkaline earth metal compound (c-3) dissolved may be 5.0 g or less, or 4.0 g or less.

The alkaline earth metal constituting the alkaline earth metal compound (c-3) may be any one of calcium (Ca), strontium (Sr), barium (Ba), and radium ( Ra ), and may be at least one selected from the group consisting of Ca, Sr, and Ba.

Specific examples of alkaline earth metal compounds (c-3) include calcium oxide, barium oxide, strontium oxide, calcium hydroxide, barium hydroxide, and strontium hydroxide. The alkaline earth metal compound (c-3) may contain at least one selected from the group consisting of calcium oxide, calcium hydroxide, barium oxide, and barium hydroxide.

The content of alkaline earth metal compound (c-3) is, for example, 0.05% by mass or more and 20% by mass or less of the solids content of the primer coating composition. When the content of alkaline earth metal compound (c-3) is 0.05% by mass or more, the effects of alkaline earth metal compound (c-3) are more likely to be exerted. When the content of alkaline earth metal compound (c-3) is 20% by mass or less, deterioration of the coating film due to an increase in pH is suppressed.

The content of alkaline earth metal compound (c-3) may be 0.1% by mass or more, or 1.0% by mass or more. The content of alkaline earth metal compound (c-3) may be 15.0% by mass or less, 12.0% by mass or less, or 10.0% by mass or less.

The content ratio (c-1/c-3) of the metal sulfate (c-1) to the alkaline earth metal compound (c-3) may be, for example, 0.5 or more and 3.5 or less by mass. This may further improve corrosion resistance. The content ratio (c-1/c-3) may be 0.5 or more, or 1.0 or more. The content ratio (c-1/c-3) may be 3.0 or less, or 2.0 or less.

Other rust inhibitors (c-4)
Powder (c) may contain a rust inhibitor (c-4) other than those described above. The other rust inhibitor (c-4) is not particularly limited, and examples thereof include those commonly used as rust inhibitors. Examples of the other rust inhibitor (c-4) include zinc, zinc alloys, calcium phosphite, aluminum phosphate, zinc phosphate, zinc molybdate, aluminum molybdate, and aluminum powder. These may be used alone or in combination of two or more.

The content of the rust inhibitor (c-4) other than zinc particles is, for example, 8.0% by mass or less of the solids content of the primer coating composition. The content of the other rust inhibitor (c-4) may be 5.0% by mass or less, 3.0% by mass or less, or 0% by mass.

The zinc particle content is, for example, less than 40% by mass of the solids content of the primer coating composition. To reduce electrical resistance, the zinc particle content may be 20.0% by mass or less, 8.0% by mass or less, 5.0% by mass or less, or 0% by mass.

Pigment The primer coating composition may contain a pigment. Examples of pigments include, without limitation, pigments that are typically incorporated into coating compositions. Examples of pigments include extender pigments and coloring pigments. These may be used alone or in combination of two or more.

Extender pigments include, for example, talc, clay, calcium carbonate, magnesium carbonate, barium sulfate, silicic acid, silicates, aluminum oxide hydrate, calcium sulfate, gypsum, micaceous iron oxide (MIO), glass flake, szolite mica, and clarite mica. These may be used alone or in combination of two or more. The amount of extender pigment is not particularly limited.

Coloring pigments Examples of coloring pigments include titanium oxide, carbon black, white lead, graphite, zinc sulfide, chromium oxide, yellow nickel titanium, yellow chromium titanium, yellow iron oxide, red iron oxide, black iron oxide, phthalocyanine blue, phthalocyanine green, ultramarine blue, quinacridones, and azo-based red and yellow pigments. These may be used alone or in combination of two or more. The content of the coloring pigment is not particularly limited.

The total content of powder (C) and various pigments is, for example, 30% or more and 60% or less in terms of pigment volume concentration (PVC). This ensures hiding power while preventing the occurrence of coating cracks and deterioration of adhesion. PVC is the volume percentage (%) of powder (C) and various pigments out of the total volume of the total resin solids, powder (C), and various pigments in the primer coating composition.

Other Resins The primer coating composition may contain resins other than the epoxy resin (a). Examples of other resins include xylene resins, acrylic resins, and polyester resins. These may be used alone or in combination of two or more.

The primer coating composition may contain a solvent. The content of the solvent is, for example, 5% by mass or more and 50% by mass or less of the total mass of the primer coating composition.

Solvents include those commonly used in the relevant field. Examples of solvents include toluene, xylene, isobutyl alcohol, methyl ethyl ketone, and weak solvents. These may be used alone or in combination of two or more.

The primer coating composition may contain a weak solvent. The content of the weak solvent is, for example, 5% by mass or more and 50% by mass or less of the total mass of the primer coating composition.

Weak solvents are aliphatic hydrocarbon compounds. Examples of weak solvents include single-component solvents such as n-butane, n-hexane, n-heptane, n-octane, isononane, n-decane, n-dodecane, cyclopentane, cyclohexane, and cyclobutane; and mixed solvents such as mineral spirits, white spirits, mineral turpentine, isoparaffin, solvent kerosene, aromatic naphtha, VM&P naphtha, and solvent naphtha.

Commercially available weak solvents include "Solvesso 100," "Solvesso 150," and "Solvesso 200" (all trade names manufactured by Esso Oil Co., Ltd.), "Swasol 310," "Swasol 1000," and "Swasol 1500" (all trade names manufactured by Cosmo Oil Co., Ltd.).

Others The primer coating composition may contain other components, such as a silane coupling agent and various additives.

The silane coupling agent improves adhesion between the corrosion-protective coating and the metal substrate. The silane coupling agent may have at least one of a trimethoxysilyl group and a triethoxysilyl group. The content of the silane coupling agent may be 0.5% by mass or more and 5% by mass or less, based on the total mass of the primer coating composition.

Additives include, for example, anti-sagging agents, anti-settling agents, anti-color separation agents, anti-foaming agents, anti-popping agents, leveling agents, and matting agents. These may be used alone or in combination of two or more.

(Preparation method)
Two-component primer coating compositions are prepared by mixing the base agent, the curing agent, and, if necessary, diluents, etc., by methods known to those skilled in the art. The base agent and the curing agent are usually mixed immediately before use (for example, the composition is used within 60 minutes after mixing the components). Examples of diluents include the same solvents as those listed as being capable of being contained in the base agent.

The base agent is prepared by mixing the above ingredients using the method described above. A commonly used mixing device such as a paint shaker or mixer can be used for mixing. The hardener can be prepared in the same way.

(Anti-rust coating composition)
The anti-corrosion coating composition comprises zinc particles and a binder.

Binder: There are no particular limitations on the binder, and those commonly used in zinc-rich paints can be used. Examples of binders include butyral resin, epoxy resin, alkyl silicate, phenol resin, acrylic resin, polyester resin, and fluororesin. The binder may be butyral resin, epoxy resin (x), alkyl silicate, or may be epoxy resin or alkyl silicate. These may be used alone or in combination of two or more.

Examples of the epoxy resin (x) include those similar to the epoxy resin (a) used in the primer coating composition. Polyamine (y) may be blended together with the epoxy resin (x). Examples of the polyamine (y) include those similar to the polyamine (b) used in the primer coating composition.

Examples of alkyl silicates include tetraalkoxysilanes, alkyltrialkoxysilanes, dialkylalkoxysilanes, and partial condensates thereof. Commercially available partial condensates of tetraalkylsilanes include MKC Silicate MS51 (a condensate of tetraalkoxysilane manufactured by Mitsubishi Chemical Corporation) and Ethyl Silicate 40 (a condensate of tetraethoxysilane manufactured by Colcoat Co., Ltd.).

The solid content of the binder is, for example, 3% by mass or more and 60% by mass or less of the solid content of the anticorrosive coating composition. If the binder content is 5% by mass or more, curability can be improved. If the binder content is 60% by mass or less, the sacrificial corrosion protection function of zinc can be effectively exerted. The binder content may be 5% by mass or more, or may be 10% by mass or more. The binder content may be 50% by mass or less, or may be 40% by mass or less.

Zinc particles: Zinc particles are powders of zinc metal or zinc-based alloys. The shape of the zinc particles is not particularly limited. The zinc particles may be spherical or flake-shaped. A zinc-based alloy is an alloy containing 50% or more by mass of zinc. Examples of zinc alloys include zinc-aluminum alloys and zinc-magnesium alloys.

The zinc particle content is, for example, 40% by mass or more and 95% by mass or less of the solid content of the anti-corrosion coating composition. When the zinc particle content is 40% by mass or more, sacrificial corrosion protection function is likely to be exhibited. When the zinc particle content is 95% by mass or less, film-forming properties are improved. The zinc particle content may be 60% by mass or more, 80% by mass or more, or 85% by mass or more. The zinc particle content may be 93% by mass or less, or 90% by mass or less.

The average particle size of the zinc particles is not particularly limited. The average particle size of the zinc particles is, for example, 1 μm or more and 50 μm or less. This can suppress settling of the zinc particles and improve coating workability. The average particle size of the zinc particles may be 2 μm or more, or 3 μm or more. The average particle size of the zinc particles may be 45 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less.

Commercially available zinc particles include, for example, the zinc powder series manufactured by Toyo Zinc Co., Ltd., the zinc powder series manufactured by UMICORE Co., Ltd., and the zinc powder series manufactured by Nippon Paint Anti-Corrosion Coatings Co., Ltd.

Other Rust Inhibitors The anti-rust coating composition may contain a rust inhibitor other than zinc particles. The other rust inhibitor is not particularly limited, but it is desirable that the anti-rust coating composition does not contain a metal sulfate (c-1). It is desirable that the anti-rust coating composition does not contain a zinc compound (c-2). It is desirable that the anti-rust coating composition does not contain an alkaline earth metal compound (c-3). It is desirable that the anti-rust coating composition does not contain any of the metal sulfate (c-1), zinc compound (c-2), and alkaline earth metal compound (c-3). It is acceptable that the anti-rust coating composition contains the metal sulfate (c-1), zinc compound (c-2), and alkaline earth metal compound (c-3) in an amount of less than 8 mass%, less than 5 mass%, or less than 2 mass% of the solid content of the anti-rust coating composition, respectively.

Examples of rust inhibitors other than zinc particles, metal sulfate (c-1), zinc compound (c-2), and alkaline earth metal compound (c-3) include calcium phosphite, aluminum phosphate, zinc phosphate, zinc molybdate, aluminum molybdate, and aluminum powder. The content of the other rust inhibitor is, for example, 8% by mass or less of the solids content of the rust-preventive coating composition. The content of the other rust inhibitor (c-4) may be 5% by mass or less, 3% by mass or less, or 0% by mass.

Pigment The anticorrosive coating composition may contain a pigment. Examples of pigments include, without limitation, pigments that are typically incorporated into coating compositions. Examples of pigments include the above-mentioned extender pigments and coloring pigments. These may be used alone or in combination of two or more.

The anticorrosive coating composition may contain the above-mentioned solvent. The content of the solvent is, for example, 5% by mass or more and 50% by mass or less of the total mass of the anticorrosive coating composition.

Others The anticorrosive coating composition may contain other components, such as a chelating agent, a silane coupling agent, and various additives.

Additives include, for example, anti-sagging agents, anti-settling agents, anti-color separation agents, anti-foaming agents, anti-popping agents, leveling agents, and matting agents.

(Preparation method)
The anticorrosive coating composition is prepared by mixing the above components and, if necessary, diluents, etc., in the same manner as for the primer coating composition. Examples of diluents include the same solvents as those mentioned above.

(Painting method)
The anti-rust coating composition and the primer coating composition are each applied by a common method such as by brush, roller or spray.

(Anti-rust coating)
The thickness of the anti-rust coating film is not particularly limited and can be appropriately set depending on the type of substrate, application, etc. The dry thickness of the anti-rust coating film is, for example, 30 μm or more and 75 μm or less. The anti-rust coating composition may be applied multiple times to form an anti-rust coating film with a laminated structure.

(Primer coating)
The thickness of the primer coating film is not particularly limited and can be appropriately set depending on the type of substrate, application, etc. The dry film thickness of the primer coating film is, for example, 10 μm or more and 300 μm or less. The primer coating composition may be applied multiple times to form a laminated primer coating film.

(subject to be coated)
The object to be coated with the anticorrosive coating composition (substrate) is not particularly limited as long as corrosion resistance is required. The substrate is typically a metal. Examples of metals include iron, copper, aluminum, tin, zinc, and alloys thereof.

Specific examples of substrates include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-plated steel sheets, zinc-iron alloy-plated steel sheets, zinc-magnesium alloy-plated steel sheets, zinc-aluminum-magnesium alloy-plated steel sheets, aluminum-plated steel sheets, aluminum-silicon alloy-plated steel sheets, and tin-plated steel sheets. More specific examples of substrates include ships, vehicles (e.g., railway cars, large vehicles), aircraft, bridges, offshore structures, plants, tanks (e.g., oil tanks), pipes, steel pipes, cast iron pipes, and other steel structures and buildings.

The substrate may have been subjected to blasting, anti-rust coating, or shop primer coating. The substrate may have a previous coating film (a coating film other than the above-mentioned anti-rust coating film that was formed before the anti-rust coating film was formed). The substrate may have corrosion products on its surface.

(Other coatings)
On the primer coating, other coatings may be formed, such as topcoats and/or functional coatings.

Topcoat paint compositions include, for example, oil-based paints, long-oil phthalic acid resin paints, silicone alkyd resin paints, phenolic resin paints, chlorinated rubber resin paints, epoxy resin paints, modified epoxy resin paints, tar epoxy resin paints, vinyl chloride resin paints, polyurethane resin paints, fluororesin paints, and silicone-modified resin paints. Functional paints include, for example, photocatalytic paints that exhibit self-cleaning properties against pollutants, and antifouling paints that prevent the adhesion of marine organisms, etc.

The present embodiment will be described in more detail below using examples, but the present embodiment is not limited by these examples. In the examples, "parts" and "%" are by weight unless otherwise specified.

[Production Example 1] Production of Epoxy Resin (a-1) 250 g of p-tert-butylphenol novolac resin (trade name: Hitanol #1133, manufactured by Hitachi Chemical Co., Ltd.), 250 g of octylphenol novolac resin (trade name: Hitanol #1501, manufactured by Hitachi Chemical Co., Ltd.), and 2,040 g of epichlorohydrin were charged into a 2-L reactor equipped with a thermometer, a stirrer, and a condenser, and stirred to form a homogeneous solution. Next, 268 g of 48% by mass sodium hydroxide was added dropwise at 60 to 110°C over 2 hours. During this time, the water generated in the system was azeotropically distilled with epichlorohydrin and removed from the system using a water separator, while the epichlorohydrin was refluxed within the system. After completion of the dropwise addition, the mixture was aged at 100 to 120°C for 2 hours, and the reaction was terminated when the theoretical amount of water had flowed out.

150 g of xylene was added to the resulting epichlorohydrin solution of the epoxy compound, and the mixture was washed with a large amount of water. After removing the resulting salt and excess sodium hydroxide, the mixture was neutralized with a 3% by mass aqueous solution of phosphoric acid. The epichlorohydrin and xylene were then distilled off under reduced pressure, and 460 g of a high-boiling paraffin solvent (product name: Swazol 310, manufactured by Cosmo Oil) was added to obtain liquid epoxy resin (a-1) (novolac-type epoxy resin). The epoxy resin (a-1) had a weight-average molecular weight of 6,500, an epoxy equivalent of 1,000 g/eq, and a solids content of 60% by mass.

[Production Example 2] Production of epoxy resin (a-2) A liquid epoxy resin (a-2) (novolac-type epoxy resin) was obtained in the same manner as in Production Example 1, except that 1,440 g of epichlorohydrin was charged. The weight-average molecular weight of the epoxy resin (a-2) was 8,500, the epoxy equivalent was 1,010 g/eq, and the solid content was 60 mass%.

[Production Example 3] Production of epoxy resin (a-3) A liquid epoxy resin (a-3) (novolac-type epoxy resin) was obtained in the same manner as in Production Example 1, except that 900 g of epichlorohydrin was added. The weight-average molecular weight of the epoxy resin (a-3) was 10,000, the epoxy equivalent was 1,020 g/eq, and the solid content was 60 mass%.

[Preparation Examples G1 to G9] Preparation of Antirust Coating Compositions Antirust coating compositions G1 to G9 were prepared by mixing the components according to the formulations shown in Table 1. Details of each component shown in Table 1 are as follows.

Zinc particles : Product name: "Fine particle zinc powder LS-4", manufactured by AS Paint Co., Ltd., average particle size 4 μm
Epoxy resin (x)
・Product name "EPICLON 830", manufactured by DIC, solid content 100% by mass, epoxy equivalent 170g/eq
Polyamine (y)
・Product name: “SUNMIDE #315”, manufactured by Sanwa Chemical Industry Co., Ltd., active hydrogen equivalent: 125 g/eq
Ethyl Silicate
Product name "ES-40", manufactured by Tama Chemical Co., Ltd., alkyl silicate condensate
solvent
- Xylene, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[Preparation Examples I to XVI]
Primer coating compositions I to XVI were prepared by mixing the components according to the formulations shown in Tables 2 and 3. Details of the components shown in Tables 2 and 3 are as follows.

Polyamine (b)
Alicyclic polyamine (b-1): 1,3-bis(aminomethyl)cyclohexane, manufactured by Tokyo Chemical Industry Co., Ltd., active hydrogen equivalent: 34.2 g/eq, weight average molecular weight: 142.24
Non-alicyclic polyamine (b-2): m-xylylenediamine, manufactured by Tokyo Chemical Industry Co., Ltd., active hydrogen equivalent: 35.5 g/eq, weight average molecular weight: 136.19

Alkylphenol /o-tert-butylphenol
Ethyl Silicate
Product name "ES-40", manufactured by Tama Chemical Co., Ltd., alkyl silicate condensate
Weak solvent
Solvesso 100, manufactured by Esso Oil
thickener
Product name: F-9050, manufactured by Kusumoto Chemicals
Antifoaming agents
Product name: Disparlon 1958, manufactured by Kusumoto Chemicals

Metal sulfate (c-1)
The amount dissolved in 100 g of water at 5° C. is shown in parentheses. The average particle size of each metal sulfate (c-1) was 0.1 to 40 μm.
Aluminum sulfate (32.2 g)
Nickel sulfate hexahydrate (39.1 g)
Magnesium sulfate (25.4 g)
Zinc sulfate (44.2 g)

Zinc compound (c-2)
The amounts dissolved in 100 g of water at 20° C. and pH 7.0, and the amounts dissolved in 100 g of water at 20° C. and pH 5.0 are shown in parentheses.
Zinc oxide (0.000394g, >12.5g)

Alkaline earth metal compounds (c-3)
The amount dissolved in 100 g of water at 20°C is shown in parentheses.
Calcium oxide (0.112 g)
Barium oxide (3.48 g)

Other rust inhibitors The amount dissolved in 100 g of water at 20°C is shown in parentheses.
Sodium sulfate (170g)

[Examples 1 to 14, Comparative Examples 1 and 2]
The anti-rust coating composition was applied to a substrate (SS400 grid-blasted steel plate, 70 × 150 × 3 mm) and dried at 23 ° C for 24 hours. Next, a primer coating composition was applied and dried at 23 ° C for 7 days to produce a coated plate having a multi-layer coating film comprising a 70 μm thick anti-rust coating film and a 60 μm thick primer coating film. Primer coating compositions I to XVI and anti-rust coating compositions G1 to G9 were combined as shown in Table 4.

[evaluation]
The multi-layer coating film was evaluated by the following method.

(1) Corrosion resistance 1
Two cuts, each 80 mm long and 0.1 mm wide and deep enough to reach the object to be coated, were made in the multi-layer coating film using a cutter, at a 60° angle to each other in the center of the coating film.

The coated panels were then subjected to 240 cycles of combined cycle corrosion testing (CCT testing) in accordance with JIS K 5600-7-9 Cyclic Corrosion Test (Annex 1 Cycle D).

In the CCT test, one cycle consisted of three steps: (1) spraying a 50±10 g/L sodium chloride aqueous solution in an environment of 30±2°C for 30 minutes, (2) wetting for 1.5 hours in a humid environment of 30±2°C and 95±3% RH, and (3) drying for 2 hours at temperatures of 50±2°C and 30±2°C, respectively.

After the CCT test, the total maximum bulge width (mm) on both sides of the cut was measured. The results are shown in Table 4.

(2) Corrosion resistance 2
Next, the maximum blister width of each multilayer coating film formed with primer coating composition I and anti-rust coating compositions G1 to G9 was used as the reference (100%), and the percentage (%) of the maximum blister width of the multilayer coating film formed with primer coating composition II to XVI and anti-rust coating compositions G1 to G9 was calculated. The percentages (%) of the maximum blister width of the multilayer coating film formed with primer coating composition II and anti-rust coating compositions G1 to G9 were averaged. Similarly, the percentages (%) of the maximum blister width of the multilayer coating film formed with primer coating composition III to XVI and anti-rust coating compositions G1 to G9 were averaged.

The average percentage (%) of the maximum blister width of the composite film formed using primer coating compositions II to XVI relative to the average maximum blister width (100%) of the composite film formed using primer coating composition I was evaluated according to the following criteria. The results are shown in Table 5. The multilayer coating films rated A to D can be evaluated as having corrosion protection. The multilayer coating film of Comparative Example 1 had a large blister width and was inferior in corrosion protection.

(Evaluation criteria)
A: Less than 40% B: 40% or more but less than 65% C: 65% or more but less than 75% D: 75% or more but less than 95% E: 95% or more

[Reference Example] Evaluation of Water Resistance of Antirust Coating Compositions Each of the antirust coating compositions G1 to G9 was applied to a substrate (SS400 grit-blasted steel plate, 70 mm × 150 mm × 3 mm) and then dried at 23°C for 1 week to produce a coated plate having an antirust coating film 30 μm thick.

The coated panels were then placed in a salt spray tester as specified in JIS Z2371 and removed after 72 hours. After the test, the coated panels were visually inspected for the presence or absence of red rust in an area excluding a 1 cm area from the edge. The results are shown in Table 6.

Red rust occurred on panels coated with anti-rust paint composition G9, which contained aluminum sulfate. However, as shown in Tables 4 and 5, high corrosion protection was achieved by applying multiple coats of primer paint compositions II-XII and XIV-XVI.

The present invention includes the following aspects.
[1]
A metal substrate,
an anti-rust coating film formed on the substrate from an anti-rust coating composition containing zinc particles and a binder;
a primer coating film formed on the anticorrosive coating film from a primer coating composition,
The primer coating composition comprises:
an epoxy resin (a);
a polyamine (b);
Powder (c),
The powder (c) has a solubility of 0.1 g or more in 100 g of water at 5°C and contains a metal sulfate (c-1) that elutes polyvalent metal cations upon dissolution in water.
[2]
The multi-layer coating film according to [1] above, wherein the content of the metal sulfate (c-1) is 0.05% by mass or more and 20% by mass or less of the solid content of the primer coating composition.
[3]
The multilayer coating film according to [1] or [2] above, wherein the metal sulfate (c-1) contains at least one selected from the group consisting of nickel sulfate, aluminum sulfate, magnesium sulfate, zinc sulfate, cobalt sulfate, chromium sulfate, copper sulfate, titanium sulfate, tin sulfate, zirconium sulfate, vanadium sulfate, and manganese sulfate.
[4]
The multilayer coating film of any of the above [1] to [3], wherein the powder (c) further contains a white zinc compound (c-2) that dissolves in 100 g of water at a pH greater than 5.0 and at 20°C in an amount of 0.005 g or less, and in 100 g of water at a pH of 5.0 or less and at 20°C in an amount of 0.05 g or more.
[5]
The multi-layer coating film of [4] above, wherein the content of the zinc compound (c-2) is 5% by mass or more and 60% by mass or less of the solid content of the primer coating composition.
[6]
The multi-layer coating film according to the above [4], wherein the zinc compound (c-2) comprises at least one selected from the group consisting of zinc oxide, zinc hydroxide and zinc carbonate.
[7]
The multilayer coating film according to any one of the above [1] to [6], wherein the powder (c) further contains an alkaline earth metal compound (c-3) which is at least one of an alkaline earth metal oxide and an alkaline earth metal hydroxide.
[8]
The multi-layer coating film of [7] above, wherein the content of the alkaline earth metal compound (c-3) is 0.05 mass% or more and 20 mass% or less of the solid content of the primer coating composition.
[9]
The multi-layer coating film according to the above [7], wherein the alkaline earth metal compound (c-3) contains at least one selected from the group consisting of calcium oxide, calcium hydroxide, barium oxide, and barium hydroxide.
[10]
The multilayer coating film according to any one of [1] to [9] above, wherein the content of the zinc particles is 40% by mass or more and 95% by mass or less of the solid content of the anticorrosive coating composition.

The present invention provides a multi-layer coating film with excellent corrosion resistance. Therefore, the multi-layer coating film is particularly suitable as a primer coat for steel materials used in large structures such as plants, bridges, steel towers, and buildings.

Claims (10)

A metal substrate,
an anti-rust coating film formed on the substrate from an anti-rust coating composition containing zinc particles and a binder;
a primer coating film formed on the anticorrosive coating film from a primer coating composition,
The primer coating composition comprises:
an epoxy resin (a);
a polyamine (b);
Powder (c),
The powder (c) has a solubility of 5.0 g or more in 100 g of water at 5°C and contains a metal sulfate (c-1) that elutes polyvalent metal cations upon dissolution in water , and an alkaline earth metal compound (c-3) that is at least one of an alkaline earth metal oxide and an alkaline earth metal hydroxide . The multi-layer coating film according to claim 1, wherein the content of the metal sulfate (c-1) is 0.05% by mass or more and 20% by mass or less of the solid content of the primer coating composition. The multilayer coating film according to claim 1 or 2, wherein the metal sulfate (c-1) includes at least one selected from the group consisting of nickel sulfate, aluminum sulfate, magnesium sulfate, zinc sulfate, cobalt sulfate, chromium sulfate, copper sulfate, titanium sulfate, tin sulfate, zirconium sulfate, vanadium sulfate, and manganese sulfate. The multi-layer coating film according to claim 1 or 2, wherein the powder (c) further contains a white zinc compound (c-2) that dissolves in 100 g of water at a pH greater than 5.0 and at 20°C in an amount of 0.005 g or less, and in 100 g of water at a pH of 5.0 or less and at 20°C in an amount of 0.05 g or more. The multi-layer coating film according to claim 4, wherein the content of the zinc compound (c-2) is 5% by mass or more and 60% by mass or less of the solid content of the primer coating composition. The multi-layer coating film according to claim 4, wherein the zinc compound (c-2) includes at least one selected from the group consisting of zinc oxide, zinc hydroxide, and zinc carbonate. The multilayer coating film according to claim 1 or 2 , wherein the content of the alkaline earth metal compound (c-3) is 0.05 mass% or more and 20 mass% or less of the solid content of the primer coating composition. The multilayer coating film according to claim 1 or 2 , wherein the alkaline earth metal compound (c-3) comprises at least one selected from the group consisting of calcium oxide, calcium hydroxide, barium oxide, and barium hydroxide. The multi-layer coating film according to claim 1 or 2, wherein the content of the zinc particles is 40% by mass or more and 95% by mass or less of the solid content of the anticorrosive coating composition. The multilayer coating film according to claim 1 or 2, wherein the alkaline earth metal constituting the alkaline earth metal compound (c-3) includes at least one selected from the group consisting of calcium, strontium, and barium.