JP2020192516A - Bilayer coated film formation method - Google Patents

Abstract

To provide a bilayer coated film formation method by wet-on-wet coating which is excellent in corrosion prevention, weather resistance and finishing appearance and has good productivity.SOLUTION: A bilayer coated film formation method coats a primer coating composition containing an epoxy resin, an alicyclic hydrocarbon resin and a polyisocyanate compound and a top base coating composition and a top clear coating composition which contain an acrylic resin and a polyisocyanate compound as a common component in this order on a coated matter by wet-on-wet coating, and simultaneously cures the obtained bilayer coated film of three layers.SELECTED DRAWING: None

Description

In the present invention, an undercoat coating film is formed on an object to be coated, a topcoat base coating film is formed on the uncured undercoat coating film, and a topcoat clear coating film is further formed on the uncured topcoat base coating film. The present invention relates to a multi-layer coating film forming method in which three layers of coating films are cured at the same time, and a coated article having excellent finished appearance and weather resistance obtained by using the method.

In the coating of construction machinery such as bulldozers, hydraulic excavators, wheel loaders, or industrial machinery, as a method capable of suitably providing a multi-layer coating film having excellent corrosion resistance and weather resistance on an object to be coated, for example, a patent. Document 1 is a wet-on-wet coating method, wherein the undercoat coating composition contains an acrylic resin, an epoxy resin, an isocyanate compound and a surface conditioner, and the topcoat coating composition is an acrylic resin and an isocyanate. It contains a compound and a surface conditioner, and is a value obtained by subtracting the surface tension value (γ ₂ ) of the top coat composition from the surface tension value (γ ₁ ) of the undercoat coating composition Δγ (γ ₁ −γ). ₂ ) is −2 to 8 mN / m, and a method for forming a multi-layer coating film is disclosed, wherein the undercoat coating composition and the topcoat coating composition have a lamella length of 4 mm or less.

However, the method for forming a multi-layer coating film described in Patent Document 1 improves productivity by shortening the coating process and obtains a coating film having excellent corrosion resistance, but is inferior in terms of improvement in finished appearance and weather resistance. In some cases it would be sufficient.

Japanese Patent No. 5324715

The present invention solves the above-mentioned problems of the prior art, and specifically, a method for forming a multi-layer coating film by wet-on-wet coating, which has excellent corrosion resistance, weather resistance, finished appearance, and good productivity. The challenge is to provide.

As a result of diligent research to solve the above problems, the present inventors have made a common component of an undercoat coating composition containing an epoxy resin, an alicyclic hydrocarbon resin, and a polyisocyanate compound, an acrylic resin, and a polyisocyanate compound. The topcoat base coating composition and the topcoat clear coating composition contained in the above are coated on the object to be coated in order by wet-on-wet, and the obtained three-layer multi-layer coating is simultaneously cured by a multi-layer coating formation method. For example, they have found that the above problems can be solved, and have completed the present invention.

That is, the present invention
1. 1. An undercoat coating composition containing an epoxy resin, an alicyclic hydrocarbon resin, and a polyisocyanate compound is coated on an object to be coated to form an uncured undercoat coating, and the uncured undercoat coating is coated. A topcoat base coating composition containing an acrylic resin and a polyisocyanate compound is applied to form an uncured topcoat base coating, and the acrylic resin, the polyisocyanate compound, A topcoat clear coating composition containing a rheology control agent and an ultraviolet absorber and having a coating film having a film thickness of 30 μm as a cured coating film and having a light transmittance of 50% or more at a wavelength of 380 nm to 780 nm. To form an uncured topcoat clear coating, and simultaneously cure the uncured undercoat, topcoat base coating and topcoat clear coating to form a multi-layer coating. Forming method,
2. 2. Item 2. The method for forming a multi-layer coating film according to Item 1, wherein the epoxy resin of the undercoat coating composition is at least one selected from a fatty acid-modified epoxy resin, an amine-modified epoxy resin, and a fatty acid amine-modified epoxy resin.
3. 3. Item 3. The method for forming a multi-layer coating film according to Item 1 or 2, wherein the polyisocyanate compound of the undercoat coating composition is a urethane-modified polyisocyanate compound.
4. The method for forming a multilayer coating film according to any one of Items 1 to 3 above, wherein the topcoat clear coating composition contains 1 to 20% by mass of an extender pigment with respect to the total solid content of the acrylic resin and the polyisocyanate compound. ,
5. Item 3. The method for forming a multi-layer coating film according to Item 4, wherein the extender pigment is barium sulfate having an average particle diameter of 1.0 μm or less.
6. The method for forming a multi-layer coating film according to any one of Items 1 to 5 above, wherein the topcoat clear coating composition contains 1 to 10% by mass of a coloring pigment with respect to the total solid content of the acrylic resin and the polyisocyanate compound. ,
7. The present invention relates to a construction machine or an industrial machine painted by using the method for forming a multi-layer coating film according to any one of the above items 1 to 6.

According to the present invention, an uncured undercoat coating film is formed by the undercoat coating composition, a topcoat base coating film by the topcoat base coating composition is formed on the uncured undercoat coating film, and the uncured topcoat base coating film is formed. Corrosion resistance and weather resistance are achieved by a multi-layer coating film forming method, so-called wet-on-wet coating, in which a top-coat clear coating film is formed on the top-coat clear coating composition and the obtained three-layer multi-layer coating film is simultaneously cured. In addition, it is possible to provide a coated article having an excellent finished appearance with good productivity (productivity comparable to that of a two-coat specification consisting of a two-layer multi-layer coating film).

In the present invention, an undercoat coating composition containing an epoxy resin, an alicyclic hydrocarbon resin, and a polyisocyanate compound is coated on an object to be coated to form an uncured undercoat coating, and the uncured undercoat is formed. A topcoat base coating composition containing an acrylic resin and a polyisocyanate compound is coated on the undercoat coating to form an uncured topcoat base coating, and the acrylic resin, on the uncured topcoat base coating. A topcoat containing a polyisocyanate compound, a rheology control agent, and an ultraviolet absorber, and having a coating film having a film thickness of 30 μm as a cured coating film and having a light transmittance of 50% or more at a wavelength of 380 nm to 780 nm. The clear coating composition is applied to form an uncured topcoat clear coating, and the uncured undercoat, topcoat base coating and topcoat clear coating are simultaneously cured to form a multi-layer coating. The present invention relates to a method for forming a multi-layer coating film and a coated article.

Hereinafter, the method for forming a multi-layer coating film of the present invention (hereinafter, may be referred to as “the present method”) will be described in detail.

Undercoat coating composition The undercoat coating composition is a composition containing an epoxy resin, an alicyclic hydrocarbon resin, and a polyisocyanate compound.

Epoxy resin The epoxy resin is preferably an aromatic epoxy resin obtained by reacting a polyphenol compound with epihalohydrin.

Examples of the polyphenol compound used for forming the aromatic epoxy resin include bis (4-hydroxyphenyl) -2,2-propane [bisphenol A] and bis (4-hydroxyphenyl) methane [bisphenol F]. ], Bis (4-hydroxycyclohexyl) methane [hydrogenated bisphenol F], 2,2-bis (4-hydroxycyclohexyl) propane [hydrogenated bisphenol A], 4,4'-dihydroxybenzophenone, bis (4-hydroxyphenyl) ) -1,1-Ethan, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-3-tert-butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) Examples thereof include methane, tetra (4-hydroxyphenyl) -1,1,2,2-ethane, 4,4'-dihydroxydiphenylsulfone, phenol novolac, cresol novolac and the like.

Further, as the epoxy resin obtained by the reaction of the polyphenol compound and epichlorohydrin, an epoxy resin derived from bisphenol A can be preferably used.

As the epoxy resin, a modified epoxy resin can be preferably used. Examples of the modified epoxy resin include fatty acid-modified epoxy resin, amine-modified epoxy resin, fatty acid amine-modified epoxy resin, urethane-modified epoxy resin, acrylic-modified epoxy resin, polyester-modified epoxy resin and the like.

Among the above-mentioned modified epoxy resins, a fatty acid-modified epoxy resin, an amine-modified epoxy resin, and a fatty acid amine-modified epoxy resin can be preferably used.

Examples of commercially available products of these epoxy resins include Araquid 9201N, Araquid 9203N, Araquid 9205, Araquid 9208, Modepix 401 (manufactured by Arakawa Chemical Industries, Ltd., trade name), EPICLON H-405-40, EPICLON H-. 304-40, EPICLON H-403-45, EPICLON H-408-40 (above, manufactured by DIC Corporation, trade name), Epomic R140, Epomic R301, Epomic R304, Epomic R307, Epomic U466BT60, Epomic U455CT60, Epomic U452CT60, Epokey 811, Epokey 872, Epokey 891, (above, Mitsui Chemicals, Inc., trade name) and the like can be mentioned.

From the viewpoint of adhesiveness, the epoxy resin preferably has a hydroxyl value in the range of 50 to 300 mgKOH / g, particularly 50 to 250 mgKOH / g, and more particularly preferably 50 to 200 mgKOH / g.

From the viewpoint of finished appearance and hardness, the epoxy resin preferably has a weight average molecular weight of 10,000 or more, more preferably in the range of 1000 to 20000, and even more preferably in the range of 1000 to 15000.

The number average molecular weight or weight average molecular weight in the specification of the present invention is a value obtained by converting the number average molecular weight or weight average molecular weight measured by gel permeation chromatography (GPC) with reference to the molecular weight of standard polystyrene. .. Specifically, "HLC8120GPC" (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph, and "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and "TSKgel G-2500HXL" are used as columns. It can be measured under the conditions of mobile phase tetrahydrofuran, measurement temperature 40 ° C., flow velocity 1 mL / min and detector RI using four "TSKgel G-2000HXL" (trade name, all manufactured by Tosoh Corporation).

Alicyclic hydrocarbon resin The alicyclic hydrocarbon resin is a hydrocarbon resin having a cyclic hydrocarbon group in the polymer chain. Specific examples thereof include cyclic olefins, that is, homopolymers or copolymers of norbornene-based monomers. These alicyclic hydrocarbon resins can be used alone or in combination of two or more.

By using the epoxy resin and the alicyclic hydrocarbon resin in combination, the quick-drying property of the undercoat coating composition can be improved.

The cyclic olefin is not particularly limited, and for example, norbornene, methanooctahydronaphthalene, dimethanooctahydronaphthalene, dimethanododecahydroanthracene, dimethanodecahydroanthracene, trimenododecahydroanthracene, dicyclopentadiene, 2,3 -Dihydrocyclopentadiene, methanooctahydrobenzoinden, dimethanooctahydrobenzoinden, methanodecahydrobenzoinden, dimethanodecahydrobenzoinden, methanooctahydrofluorene, dimethanooctahydrofluorene and their substitutes. Can be done. These cyclic olefins can be used alone or in combination of two or more.

The substituent in the above-mentioned substituent such as norbornene is not particularly limited, and for example, a known hydrocarbon group or polar group such as an alkyl group, an alkylidene group, an aryl group, a cyano group, an alkoxycarbonyl group, a pyridyl group or a halogen atom can be used. Can be mentioned. These substituents can be used alone or in combination of two or more.

As the alicyclic hydrocarbon resin, a commercially available product can be used. Specific examples thereof include the product name "Arton" series manufactured by JSR Corporation, the product name "Zeonoa" series manufactured by Zeon Corporation, and the "Quinton" series.

Polyisocyanate compound As the polyisocyanate compound, a known polyisocyanate compound usually used for producing a polyurethane resin can be used. Specific examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates.

Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, and 1,3-. Alibo diisocyanates such as butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, such as lysine ester triisocyanate, 1,4,8- Triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1, Examples thereof include aliphatic triisocyanates such as 8-diisocyanato-5-isocyanatomethyloctane.

Examples of the alicyclic polyisocyanate include 1,3-cyclopentenediisocyanate, 1,4-cyclohexanediisocyanate, 1,3-cyclohexanediisocyanate, and 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate (common name:: Isophorone diisocyanate), 4,4'-methylenebis (cyclohexylisocyanate), methyl-2,4-cyclohexanediisocyanate, methyl-2,6-cyclohexanediisocyanate, 1,3- or 1,4-bis (isocyanatomethyl) cyclohexane (isocyanatomethyl) Common name: hydrogenated xylylene diisocyanate) or a mixture thereof, alicyclic diisocyanate such as norbornenan diisocyanate, for example, 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2- (3) -Isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2,6-di (isocyanatomethyl) -bicyclo ( 2.2.1) Heptane, 3- (3-isocyanatopropyl) -2.5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2 -Isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -Bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane, 6- Examples thereof include alicyclic triisocyanates such as (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane.

Examples of the aromatic aliphatic polyisocyanate include 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis (). Arophilic aliphatic diisocyanates such as 1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof, for example, aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene. And so on.

Examples of the aromatic polyisocyanate include m-phenylenediocyanate, p-phenylenediocyanate, 4,4'-diphenyldiisocyanate, 1,5-naphthalenediisocyanate, 2,4'-or 4,4'-diphenylmethane diisocyanate or a mixture thereof. , 2,4- or 2,6-tolylene diisocyanate or a mixture thereof, aromatic diisocyanates such as 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, for example, triphenylmethane-4,4', 4 ''-Aromatic triisocyanates such as triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, such as diphenylmethane-2,2', 5,5'-tetraisocyanate. Aromatic tetraisocyanates and the like can be mentioned.

Examples of the polyisocyanate derivative include dimer, trimmer, biuret, allophanate, carbodiimide, uretdione, uretoimine, isocyanurate, oxadiazine trione, and polymethylene polyphenyl polyisocyanate (crude MDI, polypeptide) of the above-mentioned polyisocyanate compounds. MDI) and crude TDI can be mentioned.

From the viewpoint of corrosion resistance and weather resistance, the polyisocyanate compound is preferably an aliphatic polyisocyanate compound, an alicyclic polyisocyanate compound, or a derivative thereof.

As the polyisocyanate compound in the undercoat coating composition, a modified product of the polyisocyanate compound can be preferably used from the viewpoint of reactivity.

Specific examples of the modified product of the polyisocyanate compound include modified MDI (urethane-modified MDI, carbodiimide-modified MDI, trihydrocarbyl phosphate-modified MDI), urethane-modified TDI, biuret-modified HDI, isocyanurate-modified HDI, and isocyanurate-modified IPDI. And the like; modified products of polyisocyanate compounds such as, and mixtures of two or more of these [for example, combined use of modified MDI and urethane-modified TDI (isocyanate group-containing prepolymer)] and the like.

Among the modified products of the polyisocyanate compound, urethane-modified polyisocyanate compounds, specifically, urethane-modified MDI and urethane-modified TDI can be preferably used.

Examples of commercially available products of such polyisocyanate compounds include Takenate D-165N and Takenate D-102 (manufactured by Mitsui Chemicals, Inc.).

Based on the total solid content of the epoxy resin and the polyisocyanate compound, the epoxy resin is 60 to 90 parts by mass, particularly 65 to 85 parts by mass, and the polyisocyanate compound is 10 to 40 parts by mass, particularly 15 to 50 parts by mass. The range is preferably in the range of 35 parts by mass from the viewpoint of finished appearance and corrosion resistance.

Further, in the undercoat coating composition, the epoxy resin is 30 to 90% by mass, particularly 40 to 80% by mass, based on the total solid content of the epoxy resin, the alicyclic hydrocarbon resin and the polyisocyanate compound, and the alicyclic hydrocarbon is used. The hydrogen resin is preferably in the range of 1 to 50% by mass, particularly 10 to 50% by mass, and the polyisocyanate compound is preferably in the range of 1 to 30% by mass, particularly 10 to 30% by mass.

The undercoat coating composition may contain barium sulfate having an average particle size of 0.01 to 5 μm, preferably 0.05 to 4 μm, and more preferably 0.05 to 3 μm from the viewpoint of finished appearance.

Commercially available products of the above barium sulfate include Varifine BF-20 (manufactured by Sakai Chemical Industry Co., Ltd., trade name, barium sulfate having an average particle diameter of 0.03 μm) and BARIACE B-30 (manufactured by Sakai Chemical Industry Co., Ltd., trade name, average). Barium sulfate having a particle size of 0.3 μm), SPARC W-5HB (manufactured by Sino-Can, trade name, barium sulfate powder, average particle size: 1.6 μm) and the like can be mentioned.

In the present specification, the average particle size is a value obtained by measuring the particle size distribution by the dynamic light scattering method. Specifically, for example, UPA-EX250 (trade name, manufactured by Nikkiso Co., Ltd., particle size distribution measuring device by dynamic light scattering method) can be used for measurement.

When the undercoat coating composition contains barium sulfate, the content of barium sulfate is based on the total solid content of the epoxy resin, alicyclic hydrocarbon resin and polyisocyanate compound from the viewpoint of finished appearance and high solid differentiation. It is preferably 1 to 100% by mass, particularly 5 to 80% by mass, and more preferably 10 to 75% by mass.

The undercoat coating composition may contain a rust preventive pigment for the purpose of improving the corrosion resistance. Specific examples of the rust preventive pigment include zinc oxide, phosphite compounds, phosphate compounds, molybdenate compounds, bismuth compounds, and metal ion exchange silica.

Examples of the phosphite compound include calcium phosphite compounds such as EXPERT NP-1000 and EXPERT NP-1020C, and aluminum phosphite compounds such as EXPERT NP-1100 and EXPERT NP-1102 (any of the EXPERT series). Also manufactured by Toho Pigment Co., Ltd., trade name).

Examples of the phosphate compound include aluminum dihydrogen tripolyphosphate treated with a metal compound. Examples of the metal compounds include zinc, calcium, magnesium, manganese, bismuth, cobalt, tin, zirconium, titanium, strontium, copper, iron, lithium, aluminum, nickel, and sodium chloride, hydroxides, coal oxides, and sulfuric acid. Things can be mentioned.

Commercially available products of aluminum dihydrogen tripolyphosphate treated with the above metal compounds include K-WHITE 140, K-WHITE Ca650, K-WHITE 450H, K-WHITE G-105, K-WHITE 105, and K-WHITE K-82 ( All of them are manufactured by TAYCA Corporation (trade name) and the like.

Examples of commercially available products of the molybdenate-based compounds include LF Bowsei M-PSN, LF Bowsei MC-400WR, LF Bowsei PM-300, PM-308 (all manufactured by Kikuchi Color Co., Ltd., trade names) and the like. Can be done.

Examples of the bismuth compound include bismuth oxide, bismuth hydroxide, basic bismuth carbonate, bismuth nitrate, bismuth silicate, and bismuth organic acid.
Examples of the metal ion-exchanged silica include calcium ion-exchanged silica and magnesium ion-exchanged silica. As these metal ion exchange silicas, phosphoric acid-modified metal ion exchange silicas can also be used.

The calcium ion-exchanged silica is silica fine particles in which calcium ions are introduced into a fine porous silica carrier by ion exchange. Commercially available products of calcium ion exchange silica include SHIELDEX (registered trademark) C303, SHIELDEXAC-3, SHIELDEXC-5 (all manufactured by WR Race & Co.), and silomask 52 (manufactured by Fuji Silysia Chemical Ltd.). And so on.

The magnesium ion-exchanged silica is silica fine particles in which magnesium ions are introduced into a fine porous silica carrier by ion exchange. Examples of commercially available magnesium ion-exchanged silica include silomask 52M (manufactured by Fuji Silysia Chemical Ltd.), Nova Nox ACE-110 (manufactured by SNCZ, France) and the like.

Among the above rust preventive pigments, calcium phosphite is particularly preferable from the viewpoint of finished appearance and corrosion resistance.

When the undercoat coating composition contains a rust preventive pigment, the content of the rust preventive pigment is 1 to 50% by mass, particularly 10 based on the total solid content of the epoxy resin, the alicyclic hydrocarbon resin and the polyisocyanate compound. It is preferably about 40% by mass from the viewpoint of finished appearance and corrosion resistance.

The undercoat coating composition may contain a coloring pigment for the purpose of obtaining a desired color. Specific examples of the coloring pigments include titanium white, zinc molybdenate, calcium molybdenate, carbon black, graphite (graphite), iron black (iron black), dark blue, ultramarine blue, cobalt blue, copper phthalocyanine blue, and indanslon. Blue, Yellow Lead, Synthetic Yellow Iron Oxide, Transparent Bengara, Bismus Vanadate, Titanium Yellow, Zinc Yellow (Zinquero), Monoazo Yellow, Oaker, Disazo, Isoindolinon Yellow, Metallic Salt Azo Yellow, Kinoftalone Yellow, Benz Imidazolone Yellow , Bengara, Monoazo Red, Unsubstituted Kinacridone Red, Azoreki (Mn Salt), Kinacridone Magenda, Ansanthron Orange, Gianthraquinonyl Red, Perylene Maroon, Perylene Red, Diketopyrolopyrrole Chrome Vermillion, Chlorinated Phthalocyanine Green, Bromine Examples thereof include phthalocyanine green, pyrazolone orange, benzimidazolone orange, dioxazine violet, perylene violet and the like.

When the undercoat coating composition is a coloring pigment, the content of the coloring pigment is 1 to 150% by mass, particularly 5 to 130% by mass, based on the total solid content of the epoxy resin, the alicyclic hydrocarbon resin and the polyisocyanate compound. % Is preferable from the viewpoint of the finished appearance.
The undercoat coating composition may contain an extender pigment (excluding barium sulfate having an average particle size of 0.01 to 5 μm), if necessary.

Examples of the extender pigment include clay, silica, barium sulfate (excluding barium sulfate having an average particle size of 0.01 to 5 μm), talc, calcium carbonate, white carbon, diatomaceous earth, magnesium aluminum carbonate flakes, mica flakes and the like. Can be mentioned.

When the undercoat coating composition contains an extender pigment, the content of the extender pigment is 20 to 150% by mass, particularly 40 to 130, based on the total solid content of the epoxy resin, the alicyclic hydrocarbon resin and the polyisocyanate compound. It is preferably mass%, more particularly 50 to 120 mass%, from the viewpoint of water resistance and salt spray resistance.

The undercoat coating composition can preferably contain a silane coupling agent for the purpose of improving corrosion resistance. Examples of the silane coupling agent include γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, and N- (β-aminoethyl). ) -Γ-Aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, N- (β- (N-vinylbenzylaminoethyl) -γ Amino group-containing silane coupling agents such as −aminopropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane; γ-glycidoxypropylmethyldimethoxycisilane, γ-glycidoxypropyltriethoxyxisilane, β-( Propyl group-containing silane coupling agent such as 3,4-epylcyclohexyl) ethyltrimethoxysilane; β-carboxyethylphenylbis (2-methoxyethoxy) silane, N-β- (N-carboxymethylaminoethyl) -γ- Examples thereof include a carboxyl group-containing silane coupling agent such as aminopropyltrimethoxysilane.

Of the above, an amino group-containing silane coupling agent and an epoxy group-containing silane coupling agent are preferable from the viewpoint of improving corrosion resistance. The above silane coupling agents can be used alone or in combination of two or more.

Commercially available silane coupling agents include KBM-402, KBM-403, KBM-502, KBM-503, KBM-603, KBE-903, KBM-603, KBE-602, and KBE-603 (all of which are Shinetsu Silicone). Company-made, product name) and the like.

When the undercoat coating composition contains a silane coupling agent, the content of the silane coupling agent is 0.1 to 10% by mass based on the total solid content of the epoxy resin, the alicyclic hydrocarbon resin and the polyisocyanate compound. %, Especially 0.5 to 7% by mass, and more preferably 0.8 to 3.5% by mass from the viewpoint of corrosion resistance and finished appearance.

The undercoat coating composition may contain a rheology control agent for the purpose of controlling the fluidity of the coating material to improve the finished appearance and coating workability.

Specific examples of the rheology control agent include a structure composed of, for example, clay mineral (for example, metal silicate, montmorolilonite), acrylic resin (for example, a polymer of acrylic acid ester or methacrylic acid ester in the molecule, and an oligomer. (Contains), polyolefins (eg, polyethylene, polypropylene, etc.), amides (higher fatty acid amides, polyamides, oligomers, etc.), polycarboxylic acids (including derivatives having at least two or more carboxyl groups in the molecule), cellulose (including derivatives having at least two or more carboxyl groups in the molecule), cellulose (including derivatives having at least two or more carboxyl groups in the molecule). Urethane (polymers containing urethane structure in the molecule, oligomers, etc.), urea (polymers containing urea structure in the molecule, oligomers, etc.), urethane urea (containing various derivatives such as nitrocellulose, acetylcellulose, cellulose ether, etc.) Polymers, oligomers, etc. that contain urethane and urea structures in the molecule) and the like can be mentioned.

Commercially available rheology control agents include, for example, amide waxes such as Disparon 6900 (manufactured by Kusumoto Kasei Co., Ltd.) and Tixol W300 (Kyoeisha Chemical Co., Ltd.); and polyethylene waxes such as Disparon 4200 (manufactured by Kusumoto Kasei Co., Ltd.). Cellulose-based rheology control agents such as CAB (cellulose acetate butyrate, manufactured by Eastman Chemical Products), HEC (hydroxyethyl cellulose), hydrophobized HEC, CMC (carboxymethyl cellulose); BYK-410, BYK-411 , BYK-420, BYK-425 (all manufactured by Big Chemie Co., Ltd.) and other urethane urea rheology control agents; Fronon SDR-80 (Kyoeisha Chemical Co., Ltd.) and other sulfate ester rheology control agents; A polyolefin-based rheology control agent such as Fronon SA-345HF (Kyoeisha Chemical Co., Ltd.); a higher fatty acid amide-based rheology control agent such as Fronon HR-4AF (Kyoeisha Chemical Co., Ltd.); and the like can be mentioned.

When the undercoat coating composition contains a rheology control agent, the content of the rheology control agent is 0.1 to 20% by mass based on the total solid content of the epoxy resin, the alicyclic hydrocarbon resin and the polyisocyanate compound. In particular, it is preferably in the range of 0.5 to 15% by mass, more particularly 0.8 to 10% by mass, from the viewpoint of finished appearance and coating workability.

The undercoat coating composition further comprises a resin other than the resin such as acrylic resin, a curing agent (excluding the polyisocyanate compound), a curing catalyst such as a tin compound, a pigment dispersant, a surface conditioner, a surfactant, and the like. It can contain an antifoaming agent, a preservative, an antifreeze agent, an ultraviolet absorber, a light stabilizer, an organic solvent and the like.

Since the undercoat coating composition contains a polyisocyanate compound having a free isocyanate group as a constituent component, the cross-linking reaction with the epoxy resin which is the substrate resin proceeds at room temperature. Therefore, the epoxy resin and the alicyclic hydrocarbon It is a two-component paint consisting of a resin-containing main agent and a polyisocyanate compound-containing curing agent. Usually, the main agent and the curing agent are mixed immediately before painting, and a solvent such as an organic solvent is added as necessary. It is preferably used by adjusting the viscosity.

At that time, it is generally preferable that the components used as necessary are blended on the main agent side. Mixing can be performed using, for example, a mixing device such as a disper or a homogenizer.

In the present specification, the "high solid content" means that the coating solid content concentration (solid content concentration at the time of coating; coating NV (nonvolatile content) value) is higher than usual. For example, in the case of an undercoat coating composition, a high solid content means a coating solid content concentration of about 40% by mass or more. The coating solid content concentration of the undercoat coating composition is usually 50 to 80% by mass, particularly preferably 55 to 75% by mass from the viewpoint of achieving both high solid differentiation and a finished appearance.

The solid content can be determined as a heating residue, which is a mass fraction of the residue obtained by evaporation under predetermined conditions, as defined in JIS K5601.

Topcoat base coating composition The topcoat base coating composition is a composition containing an acrylic resin and a polyisocyanate compound.

Acrylic resin Acrylic resin can be produced by copolymerizing a hydroxyl group-containing radically polymerizable unsaturated monomer and other radically polymerizable unsaturated monomer.

Examples of the hydroxyl group-containing radically polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and In addition to this, Praxel FM1, Praxel FM2, Praxel FM3, Praxel FA1, Praxel FA2, Praxel FA3 (all manufactured by Daicel Chemical Co., Ltd., trade name, caprolactone-modified (meth) acrylic acid hydroxyesters) and the like can be mentioned.

In addition, in this specification, "(meth) acrylate" means "acrylate or methacrylate". In addition, "(meth) acryloyl" means "acryloyl or methacryloyl". In addition, "(meth) acrylamide" means "acrylamide or methacrylamide".

Examples of the other radically polymerizable unsaturated monomer include carboxyl group-containing radically polymerizable unsaturated monomers such as acrylate, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid; for example, γ. Acrylamide group-containing unsaturated monomers such as − (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane, vinyltrimethoxysilane Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate C1-C18 alkyl or cycloalkyl esters of (meth) acrylic acid, such as cyclohexyl (meth) acrylate; aromatic vinyl monomers such as styrene; (meth) acrylic acid amide, N, N-dimethylol (meth) acrylamide. , N, N-dimethoxymethyl (meth) acrylamide, N, N-dyn-butoxymethyl (meth) acrylamide, N-methoxymethyl-N-methylol (meth) acrylamide, N-methylol (meth) acrylamide, N-alkoxy Examples thereof include (meth) acrylamide-based monomers such as methyl (meth) acrylamide group-containing unsaturated monomers.

Examples of the N-alkoxymethyl (meth) acrylamide group-containing unsaturated monomer include N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-propoxymethyl (meth) acrylamide, and N-iso. Examples thereof include propoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide, N-hexoxymethyl (meth) acrylamide, N-isohexoxymethyl (meth) acrylamide and the like. ..

The blending ratio of these radically polymerizable unsaturated monomers is 1 to 40% by mass, particularly 5 by mass% of the radically polymerizable unsaturated monomers containing hydroxyl groups, based on the total amount of the constituent radically polymerizable unsaturated monomers. It is preferably in the range of ~ 30% by mass and 60 to 99% by mass of other radically polymerizable unsaturated monomers, particularly 70 to 95% by mass.

For example, the acrylic resin is obtained by mixing the above-mentioned hydroxyl-containing radically polymerizable unsaturated monomer and other radically polymerizable unsaturated monomer, and in the presence of a polymerization initiator and in the presence of an inert gas such as nitrogen. By radical polymerization reaction in an organic solvent maintained at about 50 ° C. to about 300 ° C., preferably about 60 ° C. to 250 ° C. for about 1 hour to about 24 hours, preferably about 2 hours to about 10 hours. Obtainable.

A polyester resin modified acrylic resin modified with a polyester resin can also be used. The polyester resin-modified acrylic resin can be produced by a conventionally known production method. For example, a method of copolymerizing a polyester resin having a polymerizable unsaturated group with an acrylic resin copolymerizable therewith can be used. Can be mentioned. By using a polyester resin-modified acrylic resin in the undercoat coating composition, the finished appearance and corrosion resistance can be improved.

Examples of the organic solvent used in the radical polymerization reaction include alcohols such as n-propanol, isopropanol, n-butanol, t-butyl alcohol, and isobutyl alcohol, ethylene glycol monobutyl ether, methylcarbitol, 2-methoxyethanol, and the like. 2-ethoxyethanol, 2-isopropanol ethanol, 2-butoxyethanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol , Ethers such as propylene glycol monomethyl ether can be preferably used. In addition to these, aromatics such as xylene and toluene, ketones such as acetone, methyl ethyl ketone, 2-pentanone, 2-hexanone, methyl isobutyl ketone, isophorone and cyclohexanone, methyl acetate, ethyl acetate, etc. Esters such as pentyl acetate, 3-methoxybutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate, methyl propionate and ethyl propionate can also be used in combination.

Examples of the polymerization initiator used in the radical polymerization reaction include benzoyl peroxide, di-t-butylhydroperoxide, t-butylhydroperoxide, cumylperoxide, cumenehydroperoxide, t-butylperoxybenzoate, and lauryl. Examples thereof include peroxide, acetyl peroxide, azobisisobutyronitrile, and azobisisobutyronitrile.

The number average molecular weight of the acrylic resin is preferably in the range of 1000 to 3000, particularly 1500 to 2800, the acid value is preferably in the range of 1 to 20 mgKOH / g, and the hydroxyl value is preferably in the range of 40 to 200 mgKOH / g.

The number average molecular weight of the acrylic resin in the topcoat base coating composition is in the range of 1000 to 3000, especially 1500 to 2800, the acid value is in the range of 1 to 20 mgKOH / g, and the hydroxyl value is in the range of 40 to 200 mgKOH / g. It is preferable to have.

Polyisocyanate compound Specific examples of the polyisocyanate compound include the polyisocyanate compound of the undercoat coating composition.

The number average molecular weight of the polyisocyanate compound in the topcoat base coating composition is preferably 3000 or less, particularly preferably in the range of 100 to 1500.

If necessary, an organic tin compound or the like can be used as a curing catalyst for the purpose of improving curability.

The ratio of the acrylic resin to the polyisocyanate compound in the topcoat base coating composition is such that the ratio of the isocyanate group in the polyisocyanate compound to the hydroxyl group in the acrylic resin and the NCO / OH ratio are 0.6 to 1. It is preferably in the range of 8.8, particularly 0.8 to 1.5, from the viewpoint of water resistance and weather resistance.

The topcoat base coating composition can contain a rust preventive pigment, a coloring pigment, an extender pigment (including barium sulfate), a silane coupling agent, and a rheology control agent. Specifically, each of these can contain the ones listed in the above-mentioned undercoat coating composition, and the conditions such as the content can be contained in the same range as the above-mentioned undercoat coating composition.

If necessary, the topcoat base coating composition may further include resins other than acrylic resins such as epoxy resins, curing agents other than polyisocyanate compounds, curing catalysts other than organotin compounds, pigment dispersants, surfactants, defoamers, etc. It can contain a surface conditioner, an ultraviolet absorber, a light stabilizer, a preservative, an antifreeze agent, an organic solvent and the like.

Topcoat Clear Paint Composition The topcoat clear paint composition is a composition containing an acrylic resin, a polyisocyanate compound, a rheology control agent, and an ultraviolet absorber.

The clear coating composition is a coating composition that makes a generally obtained coating film transparent, and an extender pigment, a coloring pigment, and the like can be contained to such an extent that the transparency is not impaired.

Acrylic Resin Specific examples of the acrylic resin include the acrylic resin of the topcoat base coating composition.

The number average molecular weight of the acrylic resin in the topcoat clear paint composition is in the range of 1000 to 3000, especially 1500 to 2800, the acid value is in the range of 1 to 20 mgKOH / g, and the hydroxyl value is in the range of 40 to 200 mgKOH / g. It is preferable to have.

Polyisocyanate compound Specific examples of the polyisocyanate compound include the polyisocyanate compound of the undercoat coating composition.

The number average molecular weight of the polyisocyanate compound in the topcoat clear coating composition is preferably 3000 or less, particularly preferably in the range of 100 to 1500.

If necessary, an organic tin compound or the like can be used as a curing catalyst for the purpose of improving curability.

The ratio of the acrylic resin to the polyisocyanate compound in the topcoat clear coating composition is such that the ratio of the isocyanate group in the polyisocyanate compound to the hydroxyl group in the acrylic resin and the value of the NCO / OH ratio are 0.6 to 1. It is preferably in the range of 8.8, particularly 0.8 to 1.5, from the viewpoint of weather resistance and water resistance.

Rheology control agent Specific examples of the rheology control agent include the rheology control agent of the undercoat coating composition.

The content of the rheology control agent is in the range of 0.1 to 20% by mass, particularly 0.5 to 15% by mass, and more particularly 0.9 to 5% by mass, based on the total solid content of the acrylic resin and the polyisocyanate compound. It is preferable that the content is inside from the viewpoint of paint stability and finished appearance.

Ultraviolet absorber The ultraviolet absorber is a compound that absorbs ultraviolet rays, and is contained for the purpose of suppressing photodegradation of the resin in the coating composition and improving the weather resistance of the coating film.

As the ultraviolet absorber, conventionally known ones can be used, and examples thereof include benzotriazole-based compounds, triazine-based compounds, salicylic acid derivative-based compounds, and benzophenone-based compounds.

Specific examples of benzotriazole compounds include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-t-butylphenyl) benzotriazole, and 2- (2). '-Hydroxy-3', 5'-di-t-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-Hydroxy-3', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3', 5'-di-t-amylphenyl) benzotriazole, 2- (2'-Hydroxy-4'-octoxyphenyl) benzotriazole, 2- {2'-hydroxy-3'-(3 ", 4", 5 ", 6" -tetrahydrophthalimidemethyl) -5'-Methylphenyl} benzotriazole and the like can be mentioned.

Specific examples of triazine compounds include 2,4-bis (2,4-dimethylphenyl) -6- (2-hydroxy-4-isooctyloxyphenyl) -1,3,5-triazine, 2-[. 4 ((2-Hydroxy-3-dodecyloxypropyl) -oxy) -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine, 2- [4 -((2-Hydroxy-3-tridecyloxypropyl) -oxy) -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine, 2-( 2,4-Dihydroxyphenyl) -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine and the like can be mentioned.

Specific examples of the salicylic acid derivative compound include phenylsalicylate, p-octylphenylsalicylate, 4-tert-butylphenylsalicylate and the like.

Specific examples of benzophenone compounds include 4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2 -Hydroxy-4-methoxy-5-sulfobenzophenone trihydrate, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-octadesiloxybenzophenone , Sodium 2,2'-dihydroxy-4,4'-dimethoxy-5-sulfobenzophenone, 2,2', 4,4'-tetrahydroxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 5-chloro-2- Examples thereof include hydroxybenzophenone, resorcinol monobenzoate, 2,4-dibenzoyl resorcinol, 4,6-dibenzoyl resorcinol, hydroxydodecylbenzophenone and the like.

Commercially available products of UV absorbers include, for example, TINUVIN 900, TINUVIN 928, TINUVIN 348-2, TINUVIN 479, TINUVIN 405, TINUVIN 292 (manufactured by BASF, trade name, TINUVIN Chinuvin is a registered trademark), RUVA 93 (Otsuka Chemical Co., Ltd.). HOSTAVIN 3206HP LIQ (manufactured by DuPont, trade name) and the like can be mentioned. The ultraviolet absorber can be used alone or in combination of two or more.

The content of the ultraviolet absorber is in the range of 0.1 to 10% by mass, particularly 0.2 to 8% by mass, and more particularly 0.3 to 5% by mass, based on the total solid content of the acrylic resin and the polyisocyanate compound. It is preferable from the viewpoint of weather resistance and paint stability.

In the topcoat clear coating composition, extender pigments, coloring pigments and the like can be contained to the extent that the transparency is not impaired. Specifically, the topcoat obtained by coating the cured coating film so as to have a film thickness of 30 μm. It can be contained in a range in which the light transmittance of the clear coating film having a wavelength of 380 nm to 780 nm is 50% or more, preferably 60% or more.

The weather resistance and hardness of the coating film obtained by incorporating the extender pigment and the color pigment in the topcoat clear coating composition within the range of the above-mentioned light transmittance can be improved.

When the topcoat clear coating composition contains an extender pigment, it is 1 to 20% by mass, particularly 1 to 10% by mass, based on the total solid content of the acrylic resin and the polyisocyanate compound, although it depends on the type of the extender pigment. Is preferable.

Barium sulfate can be particularly preferably contained as the extender pigment of the topcoat clear coating composition. The average particle size of the barium sulfate is preferably 1.0 μm or less, 0.01 to 0.9 μm, and 0.02 to 0.8 μm from the viewpoint of the finished appearance.

When the topcoat clear coating composition contains a coloring pigment, the content of the coloring pigment varies depending on the type of the coloring pigment, but is 1 to 10% by mass, particularly 1 to 10% by mass, based on the total solid content of the acrylic resin and the polyisocyanate compound. It is preferably 5% by mass.

Further, the topcoat clear coating composition may contain a silane coupling agent for the purpose of improving the weather resistance and hardness of the coating film.

The extender pigment (including barium sulfate), the color pigment, and the silane coupling agent can contain those mentioned in the undercoat coating composition.

If necessary, the topcoat clear paint composition may further include resins other than acrylic resins such as polyester resins and epoxy resins, curing agents other than polyisocyanate compounds, curing catalysts other than organotin compounds, defoaming agents, surface conditioners, and light. It can contain stabilizers, preservatives, antifreezes, organic solvents and the like.

Since the topcoat base coating composition and the topcoat clear coating composition of the method for forming a multi-layer coating film of the present invention both contain a polyisocyanate compound having a free isocyanate group as a constituent component, they are substrate resins at room temperature. Since the cross-linking reaction with the acrylic resin proceeds, it is a two-component paint consisting of a main agent containing an acrylic resin and a curing agent containing a polyisocyanate compound. Normally, the main agent and the curing agent are mixed immediately before painting. It is preferably used by adding a solvent such as an organic solvent as needed to adjust the viscosity.

At that time, in addition to the rheology control agent and the ultraviolet absorber of the topcoat clear coating composition, components used as necessary such as pigments and silane coupling agents are generally preferably blended on the main component side. Mixing can be performed using, for example, a mixing device such as a disper or a homogenizer.

It is also possible to use a method in which the main agent and the curing agent are supplied from the main agent pipe and the curing agent pipe, respectively, mixed immediately before, and then painted after passing through a pipe such as a static mixer.

Multi-layer coating film forming method In the multi-layer coating film forming method of the present invention, an uncured undercoat coating film based on the undercoat coating composition is formed on an object to be coated, and the above-mentioned uncured undercoat coating film is formed. A topcoat base coating film is formed of the topcoat base coating composition, a topcoat clear coating film of the topcoat clear coating composition is formed on the uncured topcoat base coating film, and the three layers of coating films are simultaneously cured. This is a method for forming a multi-layer coating film.

Object to be coated Examples of the object to be coated include metal substrates such as iron, zinc, tin, copper, titanium, tinplate, and galvanized iron. These metal substrates may be plated with zinc, copper, chromium or the like. In particular, examples of the steel sheet that is the iron base material include cold-rolled steel sheets, black-skinned steel sheets, alloyed galvanized steel sheets, and electrogalvanized steel sheets.

Further, shot blasting, surface preparation, and surface treatment using a surface treatment agent such as chromic acid, zinc phosphate, or zirconium salt may be performed.

The method for forming a multi-layer coating film of the present invention can be particularly preferably used for an object to be coated, such as a metal substrate, which has a large heat capacity and does not sufficiently transfer heat to the object to be coated in a heating furnace. Specific examples of such objects to be coated include construction machines (for example, bulldozers, scrapers, hydraulic excavators, excavators, transport machines (trucks, trailers, etc.), cranes / cargo handling machines, and foundation construction machines (diesel hammers). , Hydraulic hammers, etc.), Tunnel construction machines (boring machines, etc.), road rollers, etc.); Light and heavy electrical equipment, agricultural machinery, steel furniture, machine tools, industrial machinery such as large vehicles; However, an object to be coated or the like whose temperature is difficult to raise can be mentioned.

Coating Method The method for coating the undercoat coating composition, the topcoat base coating composition and the topcoat clear coating composition is not particularly limited, and for example, immersion, brush, roller, roll coater, air spray, airless spray, curtain flow coater, roller. Examples of commonly used coating methods such as curtain coaters, die coaters, and electrostatic coatings can be mentioned.

Among these, air spray and airless spray are preferable. These can be appropriately selected according to the use and shape of the object to be coated.

The undercoat coating composition is preferably coated so that the cured film thickness is in the range of 10 to 80 μm, particularly 20 to 60 μm. After forming the uncured undercoat coating, the topcoat base coating composition can be applied (wet-on-wet coating). The coating interval (interval) from the formation of the uncured undercoat coating film to the coating of the topcoat base coating composition is preferably 0 to 60 minutes at room temperature (5 to 35 ° C.) from the viewpoint of work efficiency, and is preferably 1 to 30 minutes. Minutes are more preferred, and 1 to 15 minutes are even more preferred.

Further, if necessary, the undercoat coating film is preheated at a temperature exceeding a general room temperature (for example, 40 to 100 ° C., more preferably 40 to 80 ° C.) for about 1 to 10 minutes to semi-cure the undercoat coating film. It is also possible to coat the topcoat base coating composition in this state.

The topcoat base coating composition is preferably coated so that the cured film thickness is in the range of 10 to 80 μm, particularly 20 to 60 μm. After forming the uncured topcoat base coating, the topcoat clear coating composition can be applied (wet-on-wet coating). The coating interval (interval) from the formation of the uncured topcoat base coating film to the coating of the topcoat clear coating composition is preferably 0 to 60 minutes at room temperature (5 to 35 ° C.) from the viewpoint of work efficiency, and 1 to 1 30 minutes is more preferable, and 1 to 15 minutes is even more preferable.

Further, if necessary, the multi-layer coating film of the undercoat coating film and the topcoat base coating film is prepared at a temperature exceeding a general room temperature (for example, 40 to 100 ° C., more preferably 40 to 80 ° C.) for about 1 minute to 10 minutes. It is also possible to apply the topcoat clear coating composition in a state where the multi-layer coating film of the undercoat coating film and the topcoat base coating film is semi-cured by heating.

The topcoat clear coating composition is preferably coated so that the cured film thickness is in the range of 20 to 80 μm, particularly 30 to 60 μm.

The uncured undercoat film, the uncured topcoat base coating film, and the uncured topcoat clear coating film thus obtained are left at room temperature (5 to 35 ° C.) for 1 to 10 days, or are generally left. By heating (about 20 to 60 minutes) at a temperature exceeding the normal room temperature (for example, 50 to 100 ° C., more preferably 60 to 100 ° C.), the undercoat film, the topcoat base coating film, and the topcoat clear coating film are formed. A multi-layer coating film can be obtained.

From the viewpoint of productivity (working efficiency), it is preferable to obtain a multi-layer coating film by heating and curing at a temperature exceeding a general room temperature.

Hereinafter, the present invention will be described in more detail with reference to Production Examples, Examples and Comparative Examples, but the present invention is not limited thereto. In each example, "part" indicates a mass part and "%" indicates a mass%.

Production Example 1 Production of Acrylic Resin Solution 113 parts of a mixed solvent (xylene / n-butyl alcohol = 80/20) was charged in a reaction vessel and kept at 80 ° C., and the following "mixture" was added dropwise over 4 hours. Then, 8 parts of di-tert-butyl hydroperoxide was added, and the reaction was carried out by holding at 80 ° C. for 3 hours, and further adjusted with a mixed solvent (xylene / n-butyl alcohol = 80/20) to solidify. An acrylic resin solution of 60% by mass was produced. The obtained acrylic resin solution had a hydroxyl value of 94.9 mgKOH / g, an acid value of 3.9 mgKOH / g, and a number average molecular weight of 2,800.

"mixture"
Styrene 41.6 parts n-butyl acrylate 6.9 parts Isobutyl methacrylate 19 parts Caprolactone FM-3 (*) 15 parts 2-Hydroxyethyl methacrylate 17 parts Acrylic acid 0.5 parts (*) Caprolactone FM-3: Daicel Chemical Industry Manufactured by Co., Ltd., trade name, ε-caprolactone-modified vinyl monomer of 2-hydroxyethyl acrylate Production Example 2 Production of polyester-modified acrylic resin solution (according to Reference Example 1 of JP-A-8-302204)
In a four-necked flask equipped with a stirrer, a thermometer, a cooling tube and a nitrogen gas introduction tube, 143 parts of Beckozol P-470-70 (manufactured by DIC, trade name, soybean oil-based long oil alkyd resin), and minerals. 457 parts of the spirit was charged and the temperature was raised to 100 ° C.

Then, from 200 parts of styrene, 489 parts of isobutyl methacrylate, 106 parts of 2-ethylhexyl acrylate, 100 parts of 2-hydroxyethyl methacrylate, 5 parts of methacrylic acid, 200 parts of mineral spirit, 300 parts of "Solbesso 100", and 10 parts of benzoyl peroxide. The mixture was added dropwise over 4 hours.

After the completion of the dropping, the reaction was carried out at the same temperature for 8 hours to obtain a polyester-modified acrylic resin solution having a solid content mass concentration of 50%. The obtained polyester-modified acrylic resin had an acid value of 2.5 mgKOH / g and a number average molecular weight of 2800.

Production Example 3 undercoat paint composition of the coating composition No. Production of Undercoat Coating Composition No. 1 by the following steps 1 and 2. I got 1.

Process 1
40 copies (solid content) of Epomic U466BT60 (Note 1), 60 copies of BLANCE FIXE MICRO (Note 5), 60 copies of TI-SELECT TS-6200 (Note 4), 30 copies of K-WHITE 105 (Note 6), Sunlight An appropriate amount of butyl acetate was added to 80 parts of SL1500 (Note 7) and dispersed by a sand mill to obtain a pigment-dispersed paste.

Process 2
To the pigment dispersion paste obtained above, 40 parts (solid content) of Quinton 1500 (Note 3) and 1.5 parts (solid content) of Disparon A603-20X (Note 8) are blended, and a surface conditioner and defoaming agent are added. The agent was added and stirred, and butyl acetate was added to adjust the solid content. Further, by adding 20 parts (solid content) of Takenate D-102 (Note 9) immediately before painting, the undercoat coating composition No. I got 1.

Production Example 4 Undercoat paint composition No. Production of No. 2 Undercoat coating composition No. 2 was prepared in the same manner as in Production Example 3 (using 40 parts (solid content) of Epomic U452CT60 (Note 2) for the epoxy resin of the pigment dispersion paste) except that the contents were blended in Table 1. I got 2.

Production Example 5 Topcoat Base Paint Composition No. Production of Topcoat Base Paint Composition No. 1 by the following steps 1 to 3. I got 1.

Step 1 50 parts of acrylic resin solution (30 parts of solid content) obtained in Production Example 1, 12 parts of Typake CR-93 (Note 11), 12 parts of Hoster Palm Yellow H-3G (Note 12), Bayferrox 4905 (Note 13) An appropriate amount of 12 parts, 30 parts of Varifine BF-20 (Note 14) and xylene were added and dispersed in a sand mill for 2 hours to obtain a pigment-dispersed paste.

Step 2 The acrylic resin solution obtained in Production Example 1 was added to 50 parts (solid content 30 parts), the pigment dispersion paste obtained in Step 1 was added and stirred, and then the polyester-modified acrylic resin solution obtained in Production Example 2 was added. 30 parts (15 parts of solid content), 1 part of TINUVIN 292 (Note 15), 3 parts of KBM-403 (Note 16), 0.1 part of dibutyltin dilaurate, Disparon 6900-10X (fatty acid amide Kusumoto Kasei Co., Ltd.) ) 1 part (0.1 part of solid content) was added and stirred, and xylene was added to adjust the solid content to obtain a main component of a topcoat base coating composition having a solid content of 60% by mass.

Step 3 Immediately before coating, 41.7 parts (25 parts of solid content) of an ethyl acetate solution of Sumijour N3300 (Note 10) adjusted to 60% was added to the main component of the topcoat base coating composition obtained in the above step 2. Then, the topcoat base coating composition No. I got 1.

Production Example 6 Topcoat Base Paint Composition No. Production of No. 2 The topcoat base coating composition was prepared in the same manner as in Production Example 5 except that the contents of Table 2 were used (50 parts (solid content: 30 parts) of the acrylic resin solution obtained in Production Example 1 was used for the pigment dispersion paste). No. I got 2.

Production Example 7 Production of Topcoat Clear Paint Composition A 125 parts (solid content 75 parts) of acrylic resin solution obtained in Production Example 1, Disparon 6900-10X (Rheology control agent manufactured by Kusumoto Kasei Co., Ltd.) 1 part ( Solid content 0.1 part), TINUVIN 384 (Note 17) 2 parts, TINUVIN 292 (Note 15) 1 part, and dibutyltin dilaurate 0.1 part are mixed and stirred, and Swazole 1000 (manufactured by Cosmo Oil Co., Ltd., aromatic) A base material of the topcoat clear coating composition A was obtained by stirring the mixture in which the solid content was adjusted by adding a group hydrocarbon solvent). Immediately before coating, 25 parts (solid content) of Sumijour N3300 (Note 10) was added, mixed and stirred, and butyl acetate was further added to adjust the viscosity to obtain a topcoat clear coating composition A.

Production Examples 8 to 11 Production of Topcoat Clear Paint Compositions B to E Each topcoat clear paint composition B to E was obtained in the same manner as in Production Example 7 except that the contents were as shown in Table 3.

The coloring pigment and the extender pigment are mixed as a pigment dispersion paste using 50 parts (solid content 30 parts) of the acrylic resin solution obtained in Production Example 1 to produce the main agent of each topcoat clear coating composition. As a result, each topcoat clear coating composition was obtained.

The blending amounts in Tables 1, 2 and 3 are the solid content. In addition, each note in Tables 1, 2 and 3 is as follows.
(Note 1) Epomic U466BT60: Mitsui Kagaku Co., Ltd., trade name, fatty acid amine-modified bisphenol A type epoxy resin, hydroxyl value 108 mgKOH / g, weight average molecular weight 13,000 (Note 2) Epomic U452CT60: Mitsui Kagaku Co., Ltd., product Name, modified bisphenol A type epoxy resin, hydroxyl value 156 mgKOH / g, weight average molecular weight 11,000 (Note 3) Quinton 1500: Nippon Zeon Co., Ltd., trade name, alicyclic hydrocarbon resin (dicyclopentadiene / vinyl acetate) Copolymer)
(Note 4) TI-SELECT TS-6200: Chemers Co., Ltd., trade name, titanium dioxide (Note 5) BLANCE FIXE MICRO: Sachtler Ben Co., Ltd., trade name, barium sulfate, average particle size 0.7 μm, oil absorption 13 ml / 100g
(Note 6) K-WHITE 105: manufactured by TAYCA CORPORATION, product name, aluminum dihydrogen dihydrogen tripolyphosphate (Note 7) Sunlight SL1500: Takehara Chemical Industry Co., Ltd., product name, calcium carbonate, oil absorption 28 ml / 100 g
(Note 8) Disparon A603-20X: Kusumoto Kasei Co., Ltd., trade name, fatty acid amidowax (Note 9) Takenate D-102: Mitsui Chemicals, Inc., trade name, TDI urethane prepolymer (Note 10) Sumijour N- 3300: (Product name, manufactured by Sumika Cobestrourethane, isocyanurate structure-containing polyisocyanate derived from hexamethylene diisocyanate, solid content of about 100%, isocyanate group content of 21.8%
(Note 11) Typake CR-93: Ishihara Sangyo Co., Ltd., trade name, titanium white, oil absorption 20 ml / 100 g
(Note 12) Hoster Palm Yellow H-3G: Clariant, product name, Hansa Yellow pigment (Note 13) Bayferrox 4905: Lanxess Co., Ltd., product name, red pigment (Note 14) Varifine BF-20: Sakai Chemical Manufactured by Kogyo Co., Ltd., trade name, barium sulfate with an average particle size of 0.03 μm, oil absorption 24 ml / 100 g
(Note 15) TINUVIN 292: BASF Corporation, trade name, photostabilizer (Note 16) KBM-403: Shin-Etsu Chemical Co., Ltd., trade name, silane coupling agent containing epoxy group (Note 17) TINUVIN 384: BASF shares Company, product name, UV absorber
Forming a multilayer coating film coated plates Creating Example 1 for forming a multilayer coating film coated plate No. Preparation of No. 1 Multi-layer coating film forming coating plate No. 1 by the following steps 1 to 3. I got 1.

Step 1: Undercoat coating composition No. 2 obtained in Production Example 3 on a zinc phosphate-treated steel sheet (size 70 × 150 × 0.8 mm, Palbond # 144). Using No. 1, spray coating was performed so that the cured film thickness was 30 μm, and the setting was made at 25 ° C. for 3 minutes.

Step 2: Next, on the undercoat coating film, the topcoat base coating composition No. 1 obtained in Production Example 5 was obtained. Using No. 1, wet-on-wet coating was performed by spray coating so that the cured film thickness was 30 μm, and the setting was made at 25 ° C. for 3 minutes.

Step 3: Next, the topcoat clear coating composition obtained in Production Example 7 is wet-on-wet coated on the topcoat base coating film by spray coating so that the cured film thickness becomes 30 μm, and a three-layer multi-layer is applied. A coating film was formed.

Step 4: The multi-layer coating film obtained in steps 1 to 3 was set at 25 ° C. for 10 minutes and then heat-cured at 80 ° C. for 20 minutes to form a multi-layer coating film No. I got 1.

Examples 2 to 4 and Comparative Examples 1 to 3 Multilayer coating film forming coating plate No. Preparation of Examples No. 2 to 7 except that the undercoat coating composition of step 1, the topcoat base coating composition of step 2, and the topcoat clear coating composition of step 3 are the coating compositions shown in Table 4. In the same manner as in No. 1, each multi-layer coating film forming coating plate No. 2-7 were obtained.

In addition, the multi-layer coating film forming coating plate No. of Comparative Example 3 Reference numeral 7 denotes a two-layer multi-layer coating film without a topcoat clear coating film. After the wet-on-wet coating in step 2, the film is set at 25 ° C. for 10 minutes and then heat-cured at 80 ° C. for 20 minutes to form a multi-layer coating film. I got a coated board.

Coating film performance test Each multi-layer coating film-forming coating film was subjected to a coating film performance test according to the test conditions described below. The results are also shown in Table 4.

Clear coating film Light transmittance (%): A topcoat clear coating composition is applied to a smooth PTFE plate as a cured coating film so as to be 30 μm, left in a laboratory at room temperature of about 20 ° C. for 15 minutes, and then dried with warm air. It was dried at 80 ° C. for 20 minutes using a machine to obtain a cured coating film. The obtained coating film was peeled off to prepare a free film, and the light transmittance with a wavelength of 380 nm to 780 nm was measured using a spectrophotometer UV3700 (trade name, manufactured by Shimadzu Corporation), and the average value is shown in Table 4. Indicated.

Initial gloss (finished appearance 60 ° gloss): The glossiness of each multi-layer coating film-forming coating plate was measured according to the mirror surface glossiness (60 degrees) of JIS K5600-4-7 (1999).

Pencil hardness: According to JIS K 5600-5-4, apply the pencil lead to the test coat surface at an angle of about 45 °, and make the test coat surface strong enough not to break the lead. It was moved forward at a uniform speed by about 10 mm while being pressed against. The hardness symbol of the hardest pencil that did not tear the coating film was defined as pencil hardness.

Xenon (weather resistance): For each multi-layer coating plate, use the super xenon weather meter (trade name, manufactured by Suga Test Instruments Co., Ltd.) specified in JIS B 7754, and xenon arc lamp for 1 hour and 42 minutes. After the repeated tests of 1000 hours (500 cycles), 2000 hours (1000 cycles), and 3000 hours (1500 cycles), each copy is taken as one cycle, with 2 hours of irradiation of the lamp and irradiation of the same lamp under 18 minutes of rainfall conditions as one cycle. The accelerated weather resistance was evaluated by measuring the gloss retention rate (GR%) and the color difference (ΔE) with respect to the coated plate (initial coated plate).

Water resistance: The appearance of each multi-layer coating film-forming coating plate after being immersed in warm water at 23 ° C. for 10 days was evaluated according to the following criteria.
⊚: No change in appearance was observed with respect to the coating film before the test ○: Slight gloss, blistering or discoloration was observed with respect to the coating film before the test, but there was a problem when the product was made. No level Δ: Slight gloss, cracks, blisters or discoloration was observed with respect to the coating film before the test, and the product was inferior. ×: Remarkably glossy, cracked, cracked with respect to the coating film before the test. Blisters or discoloration are seen.

Anticorrosion: Cross-cut scratches are made on each multi-layer coating film-forming coated plate to a depth that reaches the steel plate with a knife, and a salt spray resistance test is conducted for 240 hours according to JIS Z-2371. Rust and blistering width from knife scratches Evaluated according to the following criteria.
◎: Maximum width of rust and blisters is less than 2 mm from the cut part (one side)
◯: The maximum width of rust and blisters is 2 mm or more and less than 3 mm (one side) from the cut part.
Δ: The maximum width of rust and blisters is 3 mm or more and less than 4 mm (one side) from the cut part.
×: Maximum width of rust and blisters is 4 mm or more from the cut part (one side)
Productivity: Evaluated according to the following criteria.
⊚: Productivity level equivalent to the 2-coat specification consisting of 2 layers of multi-layer coating film ○: Productivity level comparable to the 2-coat specification consisting of 2 layers of multi-layer coating film

It is possible to provide a wet-on-wet multi-layer coating film forming method having excellent corrosion resistance, weather resistance and finished appearance, and good productivity.

Claims (7)

An undercoat coating composition containing an epoxy resin, an alicyclic hydrocarbon resin, and a polyisocyanate compound is coated on the object to be coated to form an uncured undercoat coating film.
A topcoat base coating composition containing an acrylic resin and a polyisocyanate compound is coated on the uncured undercoat to form an uncured topcoat base coating.
The wavelength of the coating film obtained by containing an acrylic resin, a polyisocyanate compound, a rheology control agent and an ultraviolet absorber on the uncured topcoat base coating film and coating the cured coating film so as to have a film thickness of 30 μm. A topcoat clear coating composition having a light transmittance of 380 nm to 780 nm of 50% or more is applied to form an uncured topcoat clear coating film, and the uncured undercoat coating film, topcoat base coating film and topcoat clear coating film are formed. A method for forming a multi-layer coating film by simultaneously curing the film to form a multi-layer coating film. The method for forming a multilayer coating film according to claim 1, wherein the epoxy resin of the undercoat coating composition is at least one selected from a fatty acid-modified epoxy resin, an amine-modified epoxy resin, and a fatty acid amine-modified epoxy resin. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the polyisocyanate compound of the undercoat coating composition is a urethane-modified polyisocyanate compound. The method for forming a multilayer coating film according to any one of claims 1 to 3, wherein the topcoat clear coating composition contains 1 to 20% by mass of an extender pigment with respect to the total solid content of the acrylic resin and the polyisocyanate compound. .. The method for forming a multi-layer coating film according to claim 4, wherein the extender pigment is barium sulfate having an average particle diameter of 1.0 μm or less. The method for forming a multilayer coating film according to any one of claims 1 to 5, wherein the topcoat clear coating composition contains 1 to 10% by mass of a coloring pigment with respect to the total solid content of the acrylic resin and the polyisocyanate compound. .. A construction machine or an industrial machine painted by using the method for forming a multi-layer coating film according to any one of claims 1 to 6.