Formation method of multilayer coating film and multilayer coating film

Abstract

To provide a formation method of a multilayer coating film which can improve rust prevention of a coated object, and can suppress swelling of the coating film.SOLUTION: A formation method of a multilayer coating film includes a step of coating an undercoating composition onto a coated object and forming an undercoating film, and a step of coating a top coating composition onto the undercoating film and forming a top coating film, wherein the undercoating composition contains a resin component, a pigment and a solvent, the resin component contains at least of an epoxy resin, an urethane resin and an alkyd resin, the pigment contains magnesium oxide and phosphate as rust preventive pigments, pigment volume concentration (PVC) of the undercoating film is 10 to 70, and pigment volume concentration (PVC) of the rust preventive pigment in the undercoating film is 1 to 50.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for forming a multilayer coating film and a multilayer coating film.

Background Art

[0002] Conventionally, a multilayer coating film for improving rust prevention has been formed on the surface of an object to be coated such as a steel plate. As a multilayer coating film, one having an undercoat film formed of an undercoat paint and a topcoat film formed of a topcoat paint is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Although rust prevention is imparted to an object to be coated on which a multilayer coating film is formed, further improvement in rust prevention and durability has been required. Depending on the use of the object to be coated, a great deal of cost may be incurred when the multilayer coating film is repainted. Therefore, it is preferable to reduce the maintenance cost of the object to be coated by not only imparting rust prevention to the object to be coated but also improving the durability of the multilayer coating film. However, the conventional multilayer coating film has a problem that when the coating film is damaged, swelling of the coating film occurs starting from that portion and the rust prevention property deteriorates.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a method for forming a multilayer coating film that can improve the rust prevention property of an object to be coated and suppress swelling of the coating film.

Means for Solving the Problems

[0006] (1) The present invention relates to a method for forming a multi-layer coating film, which includes a step of coating a primer coating composition on an object to be coated to form a primer coating film, and a step of coating a topcoat coating composition on the upper layer of the primer coating film to form a topcoat coating film. The primer coating composition includes a resin component, a pigment, and a solvent. The resin component includes at least one of an epoxy resin, a urethane resin, and an alkyd resin. The pigment includes magnesium oxide as a rust preventive pigment and a phosphate. The pigment volume concentration (PVC) of the primer coating film is 10 to 70%, and the pigment volume concentration (PVC) of the rust preventive pigment in the primer coating film is 1 to 50%.

[0007] (2) The method for forming a multi-layer coating film according to (1), further including a extender pigment as the pigment.

[0008] (3) The method for forming a multi-layer coating film according to (1) or (2), wherein the topcoat coating composition is any one of a fluorine-based coating composition, a silicon-based coating composition, a urethane-based coating composition, an alkyd-based coating composition, and an epoxy-based coating composition.

[0009] (4) The method for forming a multi-layer coating film according to any one of (1) to (3), further including a step of coating a zinc-rich paint on the object to be coated to form a zinc-rich coating film before the step of forming the primer coating film.

[0010] (5) The method for forming a multi-layer coating film according to any one of (1) to (4), wherein the content ratio of the phosphate to the magnesium oxide in the primer coating film is 0.05 to 20 by mass ratio.

[0011] (6) Further, the present invention relates to a multi-layer coating film including a primer coating film formed on an object to be coated and a topcoat coating film disposed on the upper layer of the primer coating film. The primer coating film includes at least one of an epoxy resin, a urethane resin, and an alkyd resin, magnesium oxide as a rust preventive pigment, and a phosphate. The pigment volume concentration (PVC) of the primer coating film is 10 to 70%, and the pigment volume concentration (PVC) of the rust preventive pigment in the primer coating film is 1 to 50%.

[0012] (7) The undercoat coating film is the multi-layer coating film according to (6), further comprising an extender pigment.

[0013] (8) The topcoat coating film is the multi-layer coating film according to (6) or (7), containing any one of a fluororesin, a silicone resin, a urethane resin, an alkyd resin, and an epoxy resin.

[0014] (9) The multi-layer coating film according to any one of (6) to (8), having a zinc-rich coating film between the object to be coated and the undercoat coating film.

[0015] (10) The multi-layer coating film according to (6) to (9), wherein the content ratio of the phosphate to the magnesium oxide in the undercoat coating film is 0.05 to 20 by mass ratio. [Advantages of the Invention]

[0016] According to the present invention, it is possible to provide a method for forming a multi-layer coating film that can improve the rust prevention property of an object to be coated and suppress the swelling of the coating film. [Embodiments for Carrying Out the Invention]

[0017] Hereinafter, a method for forming a multi-layer coating film and the multi-layer coating film according to an embodiment of the present invention will be described. The present invention is not limited to the description of the following embodiments.

[0018] [Method for Forming Multi-Layer Coating Film] The method for forming a multi-layer coating film according to the present embodiment includes at least a step of coating an undercoat paint composition on an object to be coated to form an undercoat coating film, and a step of coating a topcoat paint composition on the upper layer of the undercoat coating film to form a topcoat coating film. The method for forming a multi-layer coating film according to the present embodiment may include a step of coating a zinc-rich paint on the object to be coated to form a zinc-rich coating film before the step of forming the undercoat coating film.

[0019] [Object to be Coated] The object to be coated on which a multilayer coating film is formed by the method for forming a multilayer coating film according to this embodiment is not particularly limited, and known metallic materials can be mentioned. Examples of metallic materials include cold-rolled steel materials, hot-rolled steel materials, stainless steel, electro-galvanized steel materials, hot-dip galvanized steel materials, zinc-aluminum alloy-based plated steel materials, zinc-iron alloy-based plated steel materials, zinc-magnesium alloy-based plated steel materials, zinc-aluminum-magnesium alloy-based plated steel materials, aluminum-based plated steel materials, aluminum-silicon alloy-based plated steel materials, tin-based plated steel materials, lead-tin-based plated steel materials, chromium-based plated steel materials, Ni-based plated steel materials, and other metallic steel materials.

[0020] The use of the object to be coated on which the multilayer coating film is formed is not particularly limited, and examples include onshore structures such as bridges, iron towers, and tanks, as well as ships and offshore structures.

[0021] (Step of forming a zinc-rich coating film) The step of forming a zinc-rich coating film is a step of coating a zinc-rich paint on the object to be coated to form a zinc-rich coating film. The step of forming a zinc-rich coating film is performed before the step of forming an undercoat coating film. A zinc-rich paint is a paint composition containing at least zinc powder, a film-forming component (binder), and a solvent. The zinc-rich paint is not particularly limited, and known ones can be used. For example, a water-based zinc-rich paint containing an epoxy resin emulsion as the main agent, a polyamine as the curing agent, and zinc powder, and a solvent-based zinc-rich paint containing an alkyl silicate or an epoxy resin as the binder and zinc powder can be mentioned.

[0022] (Step of forming an undercoat coating film) The step of forming an undercoat coating film is a step of coating an undercoat paint composition on the object to be coated to form an undercoat coating film. The undercoat paint composition is a solvent-based paint composition containing a resin component, a pigment, and a solvent. The undercoat paint composition may be a one-component paint or a two-component paint containing a main agent and a curing agent.

[0023] [Resin component] The resin component contains at least one of an epoxy resin, a urethane resin, and an alkyd resin.

[0024] The epoxy resin as the resin component is a resin having an epoxy group at its terminal, and examples thereof include novolac type epoxy resins and bisphenol type epoxy resins. Examples of the bisphenol type epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, hydrogenated bisphenol F type epoxy resin, bisphenol A propylene oxide addition type epoxy resin, bisphenol F propylene oxide addition type epoxy resin, and the like.

[0025] When an epoxy resin is used as the resin component, it is preferable to use an amine compound as the curing agent. The amine compound is a compound having two or more amino groups in one molecule. Examples of the polyamine include aliphatic polyamines such as ethylenediamine, N-hydroxyethylethylenediamine, tetramethylenediamine, hexamethylenediamine, and diethylenetriamine; alicyclic polyamines such as 4,4'-diaminodicyclohexylmethane, 1,4-diaminocyclohexane, and isophoronediamine; aromatic polyamines such as 4,4'-diaminodiphenylmethane, tolylenediamine, benzidine, and phenylenediamine; aliphatic polyamines having an aromatic ring such as xylylenediamine and tetramethylxylylenediamine; and polyamideamines obtained by the reaction of these polyamines with polymerized fatty acids.

[0026] As the epoxy resin, commercially available products can be used. For example, JER1001 (manufactured by Mitsubishi Chemical Corporation), JER1002 (manufactured by Mitsubishi Chemical Corporation), Epotope YD-011 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), Epotope YD-012 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), Epotope YD-013 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), Epotope YD-014 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), Epotope YD-017 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), Epotope YD-019 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), etc. can be mentioned. Similarly, as examples of commercially available products of amine compounds, ANCAMIDE 2634 (manufactured by Evonik Japan Co., Ltd.), SUNMIDE 2652 (manufactured by Evonik Japan Co., Ltd.), SUNMIDE 175-60 (manufactured by Evonik Japan Co., Ltd.), SUNMIDE 270X (manufactured by Evonik Japan Co., Ltd.), SUNMIDE 305-70X (manufactured by Evonik Japan Co., Ltd.), Vegichem Green V100XB65 (manufactured by Tsukuno Food Industry Co., Ltd.), Vegichem Green V115X70 (manufactured by Tsukuno Food Industry Co., Ltd.), Vegichem Green V240TI50 (manufactured by Tsukuno Food Industry Co., Ltd.), Vegichem Green V270XK70 (manufactured by Tsukuno Food Industry Co., Ltd.), Vegichem Green V280X75 (manufactured by Tsukuno Food Industry Co., Ltd.), etc. can be mentioned.

[0027] The urethane resin as a resin component is a resin having a urethane bond obtained by the reaction of various polyol components such as acrylic polyol, polyester polyol, polyether polyol, and polycarbonate polyol with an isocyanate compound. Examples of the isocyanate compound include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures thereof, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, and mixtures thereof, naphthalene-1,5-diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, xylylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, etc.

[0028] Examples of commercially available products of the above polyol include JER1004 (manufactured by Mitsubishi Chemical Corporation), ACRYDIC 57-168 (manufactured by DIC Corporation), ACRYDIC A-801-P (manufactured by DIC Corporation), ACRYDIC AL-1082 (manufactured by DIC Corporation), ACRYDIC AU-7523 (manufactured by DIC Corporation), and the like. Similarly, examples of commercially available products of the isocyanate compound include Coronate L (manufactured by Tosoh Corporation), Coronate HX (manufactured by Tosoh Corporation), Coronate HK (manufactured by Tosoh Corporation), Coronate 2770 (manufactured by Tosoh Corporation), Coronate 2785 (manufactured by Tosoh Corporation), Desmodur L75 (manufactured by Sumika Covestro Urethane Co., Ltd.), and the like.

[0029] The alkyd resin as a resin component is a resin obtained by condensation polymerization of a polybasic acid component, a polyhydric alcohol component, and an unsaturated fatty acid component. The alkyd resin may be modified with other resins.

[0030] An example of a commercially available product of the above alkyd resin is Acrylic FL-238-N (manufactured by DIC Corporation).

[0031] Examples of the polybasic acid component include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic acid, succinic acid, maleic acid, fumaric acid, adipic acid, itaconic acid, azelaic acid, pyromellitic acid, and acid anhydrides thereof.

[0032] Examples of the polyhydric alcohol component include ethylene glycol, propylene glycol, butanediol, decanediol, diethylene glycol, pentanediol, neopentyl glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and the like.

[0033] Examples of unsaturated fatty acid components include drying oils such as linseed oil, safflower oil, soybean oil, sesame oil, castor oil, perilla oil, corn oil, tall oil, sunflower oil, cottonseed oil, tung oil, dehydrated castor oil, rice bran oil, etc., and fatty acids of semi-drying oils, as well as synthetic unsaturated fatty acids represented by high-oleic fatty acids.

[0034] The content of the resin component is adjusted so that the pigment volume concentration (PVC) of the entire undercoat film described later is 10 to 70%.

[0035] [Pigment] As the pigment, a rust preventive pigment is essentially included. In addition to the above, as the pigment, it is preferable to include an extender pigment. Also, any pigment other than the above, such as a coloring pigment, may be included. The pigment is contained in the undercoat paint composition so that the pigment volume concentration (PVC) of the entire undercoat film is 10 to 70%. The pigment volume concentration (PVC) of the entire undercoat film is preferably 15 to 50%.

[0036] As the rust preventive pigment, magnesium oxide and phosphate are essentially included. By including magnesium oxide as the rust preventive pigment, the pH when magnesium oxide elutes becomes high, so that the rust prevention property can be improved when an iron-based substrate is used as the object to be coated. By including phosphate as the rust preventive pigment, an oxide film is formed on the iron-based substrate when the phosphate elutes, so that the rust prevention property can be improved. As the rust preventive pigment, a rust preventive pigment other than magnesium oxide and phosphate may be included.

[0037] Examples of phosphates include zinc phosphite, calcium phosphite, aluminum phosphite, magnesium phosphite, etc. The content ratio of phosphate to magnesium oxide is preferably 0.05 to 20, more preferably 0.1 to 10 by mass ratio.

[0038] Examples of commercially available magnesium oxide products include Starmag U (manufactured by Sanshi Gypsum Co., Ltd.), Starmag CX (manufactured by Sanshi Gypsum Co., Ltd.), Starmag M (manufactured by Sanshi Gypsum Co., Ltd.), Starmag L (manufactured by Sanshi Gypsum Co., Ltd.), Starmag P (manufactured by Sanshi Gypsum Co., Ltd.), Starmag G (manufactured by Sanshi Gypsum Co., Ltd.), Kyowa Mag 30 (manufactured by Kyowa Chemical Industry Co., Ltd.), Kyowa Mag 150 (manufactured by Kyowa Chemical Industry Co., Ltd.), Kyowa Mag MF30 (manufactured by Kyowa Chemical Industry Co., Ltd.), Kyowa Mag MF150 (manufactured by Kyowa Chemical Industry Co., Ltd.), Pyroquesma 5301 (manufactured by Kyowa Chemical Industry Co., Ltd.), Pyroquesma 3320 (manufactured by Kyowa Chemical Industry Co., Ltd.), RFA-100 (manufactured by Ube Materials Co., Ltd.), RF-70C (manufactured by Ube Materials Co., Ltd.), RF-50 (manufactured by Ube Materials Co., Ltd.), RF-10C (manufactured by Ube Materials Co., Ltd.), RF-10CS (manufactured by Ube Materials Co., Ltd.), and the like.

[0039] Examples of commercially available phosphate products include LF Bousei XP-600 (manufactured by Kikuchi Color Co., Ltd.), LF Bousei MZP-500 (manufactured by Kikuchi Color Co., Ltd.), Protex YM60 (manufactured by Taihei Chemical Industry Co., Ltd.), Protex YM70 (manufactured by Taihei Chemical Industry Co., Ltd.), Protex YM92NS (manufactured by Taihei Chemical Industry Co., Ltd.), Protex YM102NS (manufactured by Taihei Chemical Industry Co., Ltd.), EXPERT NP-1500 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1530 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1600 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1000 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1007 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-102C (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1055C (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1102 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1162 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1802 (manufactured by Toho Pigment Co., Ltd.), EXPERT NP-1902 (manufactured by Toho Pigment Co., Ltd.), and the like.

[0040] Examples of commercially available products of the extender pigment include MS-P (manufactured by Nippon Talc Co., Ltd.), SWE (manufactured by Nippon Talc Co., Ltd.), SSS (manufactured by Nippon Talc Co., Ltd.), RA (manufactured by Nippon Talc Co., Ltd.), PA-OG (manufactured by Nippon Talc Co., Ltd.), RL119 (manufactured by Nippon Talc Co., Ltd.), RL217 (manufactured by Fuji Talc Kogyo Co., Ltd.), RG319 (manufactured by Fuji Talc Kogyo Co., Ltd.), RH415 (manufactured by Fuji Talc Kogyo Co., Ltd.), RS415 (manufactured by Fuji Talc Kogyo Co., Ltd.), RS515 (manufactured by Fuji Talc Kogyo Co., Ltd.), RS613 (manufactured by Fuji Talc Kogyo Co., Ltd.), A-11 (manufactured by Yamaguchi Micca Co., Ltd.), A-21S (manufactured by Yamaguchi Micca Co., Ltd.), AB-25S (manufactured by Yamaguchi Micca Co., Ltd.), J-31M (manufactured by Yamaguchi Micca Co., Ltd.), NK-8G (manufactured by Nippon Koken Kogyo Co., Ltd.), NK-10G (manufactured by Nippon Koken Kogyo Co., Ltd.), NK-20G (manufactured by Nippon Koken Kogyo Co., Ltd.), NK-M (manufactured by Nippon Koken Kogyo Co., Ltd.), R heavy carbonate (manufactured by Maruo Calcium Co., Ltd.), heavy calcium carbonate (manufactured by Maruo Calcium Co., Ltd.), Super S (manufactured by Maruo Calcium Co., Ltd.), Super SS (manufactured by Maruo Calcium Co., Ltd.), Super SSS (manufactured by Maruo Calcium Co., Ltd.), Super 1500 (manufactured by Maruo Calcium Co., Ltd.), Super 2000 (manufactured by Maruo Calcium Co., Ltd.), SL-100 (manufactured by Takehara Chemical Industry Co., Ltd.), SL-300 (manufactured by Takehara Chemical Industry Co., Ltd.), SL-700 (manufactured by Takehara Chemical Industry Co., Ltd.), SL-1000 (manufactured by Takehara Chemical Industry Co., Ltd.), SL-1500 (manufactured by Takehara Chemical Industry Co., Ltd.), SL-2200 (manufactured by Takehara Chemical Industry Co., Ltd.), NN kaolin clay (manufactured by Takehara Chemical Industry Co., Ltd.), ST kaolin clay (manufactured by Takehara Chemical Industry Co., Ltd.), ASP-G92 (manufactured by BASF Japan Ltd.), ASP-200 (manufactured by BASF Japan Ltd.), ASP-170 (manufactured by BASF Japan Ltd.), ASP-400P (manufactured by BASF Japan Ltd.), and the like.

[0041] The rust preventive pigment is contained in the undercoat paint composition such that the pigment volume concentration (PVC) of the rust preventive pigment in the undercoat paint film is 1 to 50%. The pigment volume concentration (PVC) of the rust preventive pigment is preferably 3 to 20%.

[0042] In this specification and the claims, the pigment volume concentration (PVC) means the volume percentage (%) of the pigment in the total solid content of all resin components and all pigments in the coating composition. The pigment volume concentration (PVC) of the rust preventive pigment in the undercoat film means the value obtained by subtracting the pigment volume concentration (PVC) of the pigments other than the rust preventive pigment in the undercoat film from the pigment volume concentration (PVC) of the entire undercoat film.

[0043] When the pigment volume concentration (PVC) of the entire undercoat film is 10 to 70% and the pigment volume concentration (PVC) of the rust preventive pigment in the undercoat film is 1 to 50%, swelling of the undercoat film can be suppressed. The reason for obtaining such an effect will be explained below. Since the pigment volume concentration (PVC) is within the above range, the undercoat film becomes relatively brittle. Therefore, when swelling occurs in the undercoat film, the undercoat film repeatedly swells and breaks in minute regions. Consequently, it is considered that swelling can be suppressed from occurring in large-area units and large peeling can be prevented from occurring at the coating film interface, and as a result, the corrosion resistance (durability of the multi-layer coating film) of the object to be coated can be improved.

[0044] The extender pigment is not particularly limited, and examples thereof include plate-like pigments such as talc and mica, and spherical pigments such as calcium carbonate, clay, and kaolin. By using an extender pigment in combination with the pigment, the cost required for forming the multi-layer coating film can be reduced. The extender pigment is preferably a plate-like pigment such as talc or mica, and more preferably talc. By using a plate-like pigment as the extender pigment, the plate-like pigments are arranged in layers in the undercoat film, and infiltration of moisture and the like can be suppressed. Note that the aspect ratio of the plate-like pigment may be 1 or more (the ratio of the average particle diameter to the average thickness is 1 or more).

[0045] [Solvent] The solvent is not particularly limited and may be a weak solvent or a strong solvent. Examples of the weak solvent include mineral spirit, white spirit, mineral terpene, isoparaffin, solvent naphtha, aromatic naphtha, VM&P naphtha, solvent naphtha, etc. Examples of the strong solvent include aromatic hydrocarbons such as xylene and toluene, esters, ketones, etc.

[0046] (Step of forming the topcoat film) The step of forming the topcoat film is a step of applying a topcoat paint composition on the upper layer of the undercoat film to form a topcoat film. The topcoat paint composition is preferably any one of a fluororesin, a silicone resin, a urethane resin, an alkyd resin, and an epoxy resin.

[0047] The fluorine-based paint composition is a paint composition containing a synthetic resin of a fluorine-containing polymer obtained by polymerizing a fluorine-containing polymerizable monomer. The silicone-based paint composition is a paint composition containing a synthetic resin of a silicon-containing polymer obtained by polymerizing a silicon-containing polymerizable monomer, and examples thereof include a paint composition containing an acrylic silicone resin. The urethane-based paint composition is a paint composition having a synthetic resin of a urethane-containing polymer obtained by polymerizing a urethane-containing polymerizable monomer or a synthetic resin having a urethane bond by polymerization. Further, as the alkyd resin and the epoxy resin, the same configuration as that of the above-described undercoat film can be adopted.

[0048] [Other components] The undercoat paint composition and the topcoat paint composition may contain other components other than those described above as long as the effects of the present invention are not impaired. Examples of the other components include, for example, a combined resin other than those described above, a viscosity modifier, a curing accelerator, an anti-sagging / sedimentation agent, a surface conditioner, a colorant, a color separation inhibitor, an anti-foaming / anti-wicking agent, a leveling agent, etc.

[0049] (Other steps) The method for forming a multi-layer coating film according to this embodiment may include steps other than those described above. For example, after the step of forming a zinc-rich coating film, it may include a step of sealing the voids of the zinc-rich coating film and forming a mist coat layer for preventing foaming. As the paint for mist coating used for forming the mist coat layer, known epoxy paints or the like can be used. When the method for forming a multi-layer coating film according to this embodiment includes the step of forming a mist coat layer, the step of forming the undercoat coating film is to coat the undercoat paint composition on the mist coat layer to form the undercoat coating film.

[0050] The method for forming a multi-layer coating film according to this embodiment may include a step of coating the intermediate coat paint composition on the undercoat coating film to form an intermediate coat coating film after the step of forming the undercoat coating film. The intermediate coat paint composition is not particularly limited, and an acrylic paint composition, an epoxy paint composition, a urethane paint composition can be used. Or, a composition similar to the topcoat paint composition can be used. When the method for forming a multi-layer coating film according to this embodiment includes the step of forming an intermediate coat coating film, the step of forming the topcoat coating film is to coat the topcoat paint composition on the intermediate coat coating film to form the topcoat coating film.

[0051] In each step of the method for forming a multi-layer coating film according to this embodiment, the method of coating each paint composition or paint is not particularly limited, and generally used coating methods can be used. For example, dipping, brushing, roller, roll coater, air spray, airless spray, curtain flow coater, roller curtain coater, die coater, etc. can be mentioned, and these can be appropriately selected according to the type of the object to be coated, the use of the object to be coated, etc.

[0052] In each step of the method for forming a multi-layer coating film according to this embodiment, optionally, it may include a drying step of drying the coating film. The drying of the coating film may be performed by naturally drying the coating film at room temperature for a predetermined time, or may be performed by a known baking method. The drying step may be a step performed for each layer, or may be a step of drying a plurality of layers simultaneously.

[0053] [Multi-layer coating film] The multi-layer coating film according to this embodiment is formed on an object to be coated by the method for forming the multi-layer coating film, and essentially includes the undercoat coating film and the topcoat coating film. In addition to the above, the multi-layer coating film according to this embodiment may have a zinc-rich coating film, a mist coat layer, and an intermediate layer. The order in which these are arranged on the object to be coated is, from the object to be coated side toward the upper layer side, in the order of zinc-rich coating film, mist coat layer, undercoat coating film, intermediate coat coating film, and topcoat coating film.

[0054] The zinc-rich coating film is formed by the zinc-rich paint. It is preferable that the mist coat layer is formed on the zinc-rich coating film.

[0055] The undercoat coating film is formed by the undercoat coating composition, and essentially includes at least one of an epoxy resin, a urethane resin, and an alkyd resin, magnesium oxide as a rust preventive pigment, and a phosphate. The content ratio of the phosphate to magnesium oxide is preferably 0.05 to 20 in terms of mass ratio, and more preferably 0.1 to 10. The undercoat paint preferably contains the extender pigment. The pigment volume concentration (PVC) of the entire undercoat coating film is 10 to 70%, and the pigment volume concentration (PVC) of the rust preventive pigment in the undercoat coating film is 1 to 50%. The pigment volume concentration (PVC) of the entire undercoat coating film is preferably 15 to 50, and the pigment volume concentration (PVC) of the rust preventive pigment is preferably 3 to 20%.

[0056] The film thickness of the undercoat coating film is preferably, for example, 30 μm to 1 mm.

[0057] The intermediate coat coating film is formed by the intermediate coat coating composition.

[0058] The topcoat coating film is formed by the topcoat coating composition, and preferably contains any one of a fluorine-based resin, a silicon-based resin, a urethane-based resin, an alkyd-based resin, and an epoxy-based resin.

[0059] The multilayer coating film according to this embodiment may contain layers other than the above, as long as the effects of the present invention are not impaired.

Examples

[0060] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0061] [Preparation of Undercoat Paint Composition] <Examples 1 to 13, Comparative Examples 1 to 6> The components were blended so as to have the amounts shown in Tables 1 and 2 below, and the undercoat paint compositions according to each example and comparative example were prepared. In the case of a two-component type paint, the resin component, rust preventive pigment, and extender pigment are included in the main agent. The resin amount in this case indicates the solid content (resin amount) of the solution after mixing the main agent resin and the curing agent. Only phosphates and magnesium oxide (RF-10CS manufactured by Ube Materials Co., Ltd.) were used as the rust preventive pigment. The details of the materials shown in Tables 1 and 2 are shown below.

[0062] (Resin Component) A1: Epoxy (main agent) (JER1001 (manufactured by Mitsubishi Chemical Corporation)) / Amine (curing agent) (SUNMIDE 270X (manufactured by Evonik Japan Co., Ltd.)) two-component type paint composition (specific gravity: 1.08) A2: Polyol (main agent) (JER1004 (manufactured by Mitsubishi Chemical Corporation)) / Isocyanate (curing agent) (Coronate L (manufactured by Tosoh Corporation)) two-component type paint composition (specific gravity: 1.18) A3: Alkyd resin (Acrylic FL-238-N (manufactured by DIC Corporation)) (specific gravity: 0.93)

[0063] (Phosphate) B1: Calcium phosphite (EXPERT NP-1000 (manufactured by Toho Pigment Co., Ltd.)) (specific gravity: 3.1) B2: Zinc phosphite (EXPERT NP-1500 (manufactured by Toho Pigment Co., Ltd.)) (specific gravity: 3.5)

[0064] (Extender Pigment) C1: Talc (manufactured by Nippon Talc Co., Ltd.) (specific gravity: 2.7) C2: Calcium carbonate (heavy calcium carbonate (manufactured by Maruo Calcium Co., Ltd.)) (specific gravity: 2.7)

[0065]

Table 1

[0066]

Table 2

[0067] [Corrosion resistance test for combined cycles (CCT)] The undercoat paint compositions according to the above-prepared respective examples and comparative examples were spray-coated on a test panel (150×70×3.2 mm, blast steel plate) specified in JIS K 5551 7.17 so that the dry film thickness became 120 μm, cured at 23°C for 7 days, and test panels according to the respective examples and comparative examples were obtained. After irradiating the painted surface of the test panel with a xenon lamp for 60 hours, cross-cut scratches reaching the base material were made in the coating film, and a CCT test was conducted. In the CCT test, first, a 0.5% NaCl aqueous solution kept at 30°C was sprayed for 0.5 hour. Next, the test panel was left standing in a humid atmosphere at a relative humidity of 95% and 30°C for 1.5 hours. Next, the test panel was dried at a temperature of 50°C for 2 hours. Next, the test panel was left standing at a temperature of 30°C for 2 hours. The above was taken as one cycle and repeated 56 cycles (14 days). Then, the maximum value of the swelling width (one side) of the coating film from the cross-cut scratches was measured, and evaluation was conducted according to the following evaluation criteria. The results are shown in Table 1 and Table 2.

[0068] 4: Swelling width of the coating film is less than 0.5 mm 3: Swelling width of the coating film is 0.5 mm or more and less than 0.8 mm 2: Swelling width of the coating film is 0.8 mm or more and less than 1.0 mm 1: Swelling width of the coating film is 1.0 mm or more

[0069] As shown in Table 1, it was confirmed that the undercoat paint composition according to each example had a smaller swelling width of the coating film compared to the undercoat paint composition according to each comparative example, and as a result, it was possible to impart favorable rust prevention properties to the object to be coated.

Claims

1. A method for forming a multi-layer coating film, comprising the steps of applying an undercoat coating composition onto a substrate to form an undercoat coating film, and applying a topcoat coating composition onto the undercoat coating film to form a topcoat coating film, The undercoat paint composition includes a resin component, a pigment, and a solvent, The resin component includes at least one of an epoxy resin, a urethane resin, and an alkyd resin, The pigment includes magnesium oxide as an anti-rust pigment, and a phosphate; The method for forming a multi-layer coating film, wherein the pigment volume concentration (PVC) of the undercoat coating film is 10 to 70%, and the pigment volume concentration (PVC) of the anti-rust pigment in the undercoat coating film is 1 to 50%.

2. 2. The method for forming a multi-layer coating film according to claim 1, wherein the pigment further comprises an extender pigment.

3. The method for forming a multilayer coating film according to claim 1 or 2, wherein the topcoat coating composition is any one of a fluorine-based coating composition, a silicon-based coating composition, a urethane-based coating composition, an alkyd-based coating composition, and an epoxy-based coating composition.

4. 3. The method for forming a multi-layer coating film according to claim 1 or 2, further comprising a step of applying a zinc-rich paint onto the substrate to form a zinc-rich coating film prior to the step of forming the undercoat coating film.

5. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the content ratio of the phosphate to the magnesium oxide in the undercoat coating film is 0.05 to 20 by mass ratio.

6. A multi-layer coating film formed on a substrate, the multi-layer coating film including an undercoat coating film and a topcoat coating film disposed on the upper layer of the undercoat coating film, The undercoat coating film contains at least one of an epoxy resin, a urethane resin, and an alkyd resin, and magnesium oxide and a phosphate as rust-preventive pigments; A multi-layer coating film, wherein the pigment volume concentration (PVC) of the undercoat coating film is 10 to 70%, and the pigment volume concentration (PVC) of the anti-rust pigment in the undercoat coating film is 1 to 50%.

7. The multi-layer coating film according to claim 6 , wherein the undercoat coating film further comprises an extender pigment.

8. The multi-layer coating film according to claim 6 or 7, wherein the topcoat coating film contains any one of a fluorine-based resin, a silicone-based resin, a urethane-based resin, an alkyd-based resin, and an epoxy-based resin.

9. 8. The multi-layer coating film according to claim 6 or 7, further comprising a zinc-rich coating film between the substrate and the undercoat coating film.

10. The content ratio of the phosphate to the magnesium oxide in the undercoat coating film is 0.05 to 20 by mass ratio, and the multilayer coating film according to claim 6 or 7.

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