JP2016130302A - Bilayer coated film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated article excellent in finishing property, corrosion resistance, weather resistance and chipping resistance and less inn coated film glossiness difference due to galling temperature by wet-on-wet coating.SOLUTION: There is provided a bilayer coated film forming method by forming an uncured coated film by a primer coating composition (A) on an article to be coated, forming a final coated film by a special final coating composition (B) on the uncured coated film and drying both coated films at same time, where the primer coating composition (A) contains an epoxy resin (a1), 1 to 70 pts.mass of a rust preventive pigment (a2), 40 to 150 pts.mass of a coloring pigment (a3) and 40 to 150 pts.mass of an extender pigment (a4) based on 100 pts.ass of solid component total of the epoxy resin (a1) with total oil absorption amount of the rust preventive pigment (a2), the coloring pigment (a3) and the extender pigment (a4) in a range of 16 to 50 ml per 100 g of solid component total of the epoxy resin (a1).SELECTED DRAWING: None

Description

  The present invention is a method of forming an uncured coating film by a primer coating composition on an object to be coated, applying a wet-on-wet coating composition on the uncured coating film, and using the method. Further, the present invention relates to a coated article having excellent finish, corrosion resistance, weather resistance, and chipping resistance, and having little difference in coating film glossiness due to baking temperature.

  Wet that can shorten the process by applying the primer coating composition on the object to be coated, then applying the top coating composition without drying the primer coating composition, and then drying the two types of coatings simultaneously. There is a painting method called on-wet.

Recently, a wet-on-wet coating method has been used in the painting of construction machines or industrial machines such as bulldozers, hydraulic excavators, and wheel loaders in order to shorten the process. However, the wet-on-wet coating method for construction machines or industrial machines has the following problems 1 to 3.
1. When the coating film is dried, the heat capacity of the object to be coated is large and the heat of the drying furnace is not sufficiently transmitted, and the curability of the coating film is not sufficient. For this reason, it is not easy to obtain a coated article with a finish difference, anticorrosion property, and a difference in coating film glossiness due to the baking temperature by a wet-on-wet coating method with few drying steps.
2. Since construction machines or industrial machines have many vertical parts, the uncured coating film may sag by wet-on-wet coating, and the finish is not stable depending on the parts.
3. Since construction machines or industrial machines are used outdoors, there are problems such as requiring coating film hardness, corrosion resistance, and weather resistance.

  Patent Document 1 discloses a wet-on-wet coating method in which 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. A value obtained by subtracting the surface tension value (γ2) of the top coating composition from the surface tension value (γ1) of the undercoat coating composition. Is disclosed in which 2 is 8 to 8 mN / m.

  Patent Document 2 discloses a coating film forming method characterized in that, in addition to the conditions of Patent Document 1, the undercoat film and the topcoat film have a lamella length of 4 mm or less.

  However, the coated article obtained by the coating film forming method described in Patent Documents 1 and 2 has any finish difference, corrosion resistance, weather resistance, chipping resistance, and small coating film gloss difference due to baking temperature. Insufficient and improved.

International Publication No. 2013/24784 Pamphlet JP 2014-151257 A

  The problem to be solved by the present invention is to form an uncured coating film by a primer coating composition on an object to be coated, form an upper coating film on the uncured coating film, and dry both coating films simultaneously. An object of the present invention is to provide a coated article that is excellent in finish, corrosion resistance, weather resistance, and chipping resistance by a method for forming a multi-layer coating film, and has little difference in coating film glossiness due to baking temperature.

  As a result of intensive studies, the present inventors have found that the above problems can be solved, and have completed the present invention.

That is, the present invention
1. An uncured coating film by the primer coating composition (A) is formed on the object to be coated, and an overcoating film by the top coating composition (B) is formed on the uncured coating film. A method for forming a multilayer coating film to be dried,
The primer coating composition (A) is a composition containing an epoxy resin (a1), a rust preventive pigment (a2), a color pigment (a3) and an extender pigment (a4), and is a solid of the epoxy resin (a1) 1 to 70 parts by mass of the rust preventive pigment (a2), 40 to 150 parts by mass of the coloring pigment (a3), and 40 to 150 parts by mass of the extender pigment (a4) based on 100 parts by mass in total, and The total oil absorption of the rust preventive pigment (a2), the colored pigment (a3) and the extender pigment (a4) per 100 g of the solid content of the epoxy resin (a1) in the primer coating composition (A) is 16 to 50 ml. A coating composition that is in the range of
The top coating composition (B) is a composition containing an acrylic resin (b1), a polyisocyanate compound (b2), and barium sulfate (b3) having an average particle size of 0.01 to 5.0 μm, and the acrylic resin 60 to 90 parts by mass of acrylic resin (b1) and 10 to 40 parts by mass of polyisocyanate compound (b2) based on 100 parts by mass of the total solid content of (b1) and polyisocyanate compound (b2) And 1 to 50 parts by mass of barium sulfate (b3),
Multilayer coating film forming method,
2. The multilayer according to item 1, wherein the primer coating composition (A) contains 0.1 to 10 parts by mass of the silane coupling agent (a5) based on 100 parts by mass of the total solid content of the epoxy resin (a1). Coating film forming method,
3. 1 item | term in which a primer coating composition (A) contains 0.1-30 mass parts of talc as at least one part of extender pigment (a4) on the basis of 100 mass parts total of solid content of an epoxy resin (a1), or The method for forming a multilayer coating film according to Item 2,
4). Item 1-3, wherein the top coating composition (B) contains 0.1 to 30 parts by mass of a polyether polyol, based on 100 parts by mass of the total solid content of the acrylic resin (b1) and the polyisocyanate compound (b2). The multilayer coating-film formation method of any one of these.

According to the present invention, an uncured coating film is formed by a primer coating composition, a top coating film is formed on the uncured coating film, and both coating films are dried simultaneously, so-called wet coating. By on-wetting, it is possible to provide a coated article that is excellent in all of finish properties, corrosion resistance, weather resistance, chipping resistance, and that there is little difference in coating film glossiness due to baking temperature.
Furthermore, a coated article with a small difference in gloss of the coating film can be obtained without being affected by variations in the shape of the object to be coated, the coating interval between the base coating and the top coating, and the variation in the coating temperature.

  In the present invention, an uncured coating film by a specific primer coating composition (A) is formed on an object to be coated, and a top coating film by a specific top coating composition (B) is formed on the uncured coating film. The present invention relates to a multilayer coating film forming method for forming and drying both coating films simultaneously, and a coated article. Details will be described below.

Primer paint composition (A)
The primer coating composition (A) is a composition containing an epoxy resin (a1), a rust preventive pigment (a2), a color pigment (a3) and an extender pigment (a4), and the solid content of the epoxy resin (a1) 1 to 70 parts by mass of the rust preventive pigment (a2), 40 to 150 parts by mass of the color pigment (a3) and 40 to 150 parts by mass of the extender pigment (a4) based on 100 parts by mass in total, and a primer The total oil absorption of the rust preventive pigment (a2), the colored pigment (a3) and the extender pigment (a4) per 100 g of the solid content of the epoxy resin (a1) in the coating composition (A) is 16 to 50 ml. It is the coating composition which is the range.

Epoxy resin (a1)
The epoxy resin (a1) used in the present invention is preferably an aromatic epoxy resin obtained by a reaction between a polyphenol compound and epihalohydrin.

  Examples of the polyphenol compound used for forming the aromatic epoxy resin include bis (4-hydroxyphenyl) -2,2-propane [bisphenol A], 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-ethane, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-3-tert-butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) Methane, tetra (4-hydroxyphenyl) -1,1,2,2-ethane 4,4'-dihydroxydiphenyl sulfone, phenol novolak, and the like cresol novolak.

  Moreover, as an epoxy resin (a1) obtained by reaction of a polyphenol compound and epichlorohydrin, the resin of the following formula induced | guided | derived from bisphenol A is suitable especially.

ここで、ｎ＝０〜８で示されるものが好適である。
かかるエポキシ樹脂（ａ１）の市販品としては、例えば、ｊＥＲ８２８ＥＬ、ｊＥＲ１００１、ｊＥＲ１００２、ｊＥＲ１００３、ｊＥＲ１００４、ｊＥＲ１００７（以上、三菱化学株式会社製、商品名）、ＡＥＲ−６００３、ＡＥＲ−６０７１、ＡＥＲ−６０７２、ＡＥＲ−６０９７、ＡＥＲ−ＥＣＮ１２７３など（以上、旭化成ケミカルズ株式会社、商品名）、ＥＰＩＣＬＯＮ−Ｎ−７４０−８０Ｍ、ＥＰＩＣＬＯＮ−ＦＱ−０６５−Ｐなど（以上、大日本インキ化学工業株式会社、商品名）などが挙げられる。

Here, what is shown by n = 0-8 is suitable.
Examples of such commercially available epoxy resin (a1) include jER828EL, jER1001, jER1002, jER1003, jER1004, jER1007 (above, trade name, manufactured by Mitsubishi Chemical Corporation), AER-6003, AER-6071, AER-6072, AER-6097, AER-ECN1273, etc. (above, Asahi Kasei Chemicals Corporation, trade name), EPICLON-N-740-80M, EPICLON-FQ-065-P, etc. (above, Dainippon Ink Chemical Co., Ltd., trade name) Etc.

  Modified epoxy resins can also be used as the epoxy resin (a1), and examples thereof include urethane-modified epoxy resins, amine-modified epoxy resins, acrylic-modified epoxy resins, polyester-modified epoxy resins, and dimer acid-modified epoxy resins. Examples of commercially available products of these modified epoxy resins include Arachid 9205, Arachid 9208 (above, Arakawa Chemical Industries, Ltd., trade name), EPICLON H-405-40, EPICLON FK753 (above, Dainippon Ink & Chemicals, Inc., Product name), Epokey 803, Epokey 813, Epokey 820-40CX, Epokey 833-40SC (Mitsui Chemicals, Inc., trade name), jER872X75 (Mitsubishi Chemical Corporation, trade name), and the like. The epoxy resin (a1) has an epoxy equivalent of 200 to 2,500, preferably 400 to 2,000, and a number average molecular weight of 400 to 4,000, preferably 800 to 2,500. Is suitable.

  The number average molecular weight or the weight average molecular weight in the specification of the present invention is a value obtained by converting the number average molecular weight or the weight average molecular weight measured using a gel permeation chromatograph (GPC) on the basis of 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 Four “TSKgel G-2000HXL” (trade name, all manufactured by Tosoh Corporation) can be used, and measurement can be performed under conditions of mobile phase tetrahydrofuran, measurement temperature of 40 ° C., flow rate of 1 mL / min, and detector RI.

Antirust pigment (a2)
The primer coating composition (A) contains a rust preventive pigment (a2) for the purpose of improving corrosion resistance. Examples of such a rust preventive pigment (a2) include zinc oxide, phosphite compounds, phosphate compounds, molybdate compounds, bismuth compounds, and metal ion exchange silica.

  Examples of the calcium phosphite compound of the phosphite compound include EXPERT NP-1000 and EXPERT NP-1020C, and examples of the aluminum phosphite compound of the phosphite compound include EXPERT NP-1100, EXPERT NP-1102 (or more, Toho Pigment, trade name) and the like.

  Examples of the phosphate compound include aluminum dihydrogen tripolyphosphate treated with a metal compound. Examples of the metal compound include zinc, calcium, magnesium, manganese, bismuth, cobalt, tin, zirconium, titanium, strontium, copper, iron, lithium, aluminum, nickel, and sodium chloride, hydroxide, carbonate, and sulfuric acid. Thing etc. are mentioned.

  Examples of commercially available phosphate compounds include calcium phosphate-based LF bowsey CP-Z, magnesium phosphate-based LF bowsey MZP-500, and aluminum phosphate-based LF bowsey CRFC-1 (above, manufactured by Kikuchi Color Co., Ltd.). , Product name) and the like.

  Commercial products of aluminum dihydrogen tripolyphosphate treated with the metal compound include K-WHITE 140, K-WHITE Ca650, K-WHITE 450H, K-WHITE G-105, K-WHITE K-105, K-WHITE K- 82 (above, product name, manufactured by Teika).

  As a commercially available product of the molybdate compound, for example, as zinc molybdate, LF bowsei M-PSN; as calcium molybdate, LF bowsey MC-400WR; aluminum molybdate LF bowsei PM-300, PM-308 (above, manufactured by Kikuchi Color Co., Ltd., trade name) and the like.

  Examples of the bismuth compound include bismuth oxide, bismuth hydroxide, basic bismuth carbonate, bismuth nitrate, bismuth silicate, and organic acid bismuth.

  Examples of the metal ion exchange silica include calcium ion exchange silica and magnesium ion exchange silica. These metal ion exchange silicas may be modified with phosphoric acid as necessary to obtain phosphoric acid modified metal ion exchange silica. 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 (Shielddex, registered trademark) C303, SHIELDEXAC-3, SHIELDEXC-5 (all of which are manufactured by WR Grace & Co.), Silo Mask 52 (manufactured by Fuji Silysia). ) And the like.

  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 Silo Mask 52M (manufactured by Fuji Silysia) and Novinox ACE-110 (manufactured by SNCZ, France). Among these rust preventive pigments (a2), aluminum dihydrogen tripolyphosphate treated with a metal compound is preferable in terms of finish and corrosion resistance.

  The blending amount of the rust preventive pigment (a2) in the primer coating composition (A) is 1 to 70 parts by weight of the rust preventive pigment (a2), preferably 100 parts by weight of the solid content of the epoxy resin (a1). 2-40 mass parts, More preferably, it is 5-30 mass parts from the surface of coating-material stability, corrosion resistance, and chipping resistance.

Color pigment (a3)
Examples of the color pigment (a3) include titanium white, zinc molybdate, calcium molybdate, carbon black, graphite (iron), iron black, bitumen, ultramarine blue, cobalt blue, copper phthalocyanine blue, indanthrone blue, Yellow lead, synthetic yellow iron oxide, transparent iron, bismuth vanadate, titanium yellow, zinc yellow (zinc yellow), monoazo yellow, ocher, monoazo yellow, disazo, isoindolinone yellow, metal complex azo yellow, quinophthalone yellow, benzimidazolone Yellow, red, clear red, monoazo red, monoazo red, unsubstituted quinacridone red, azo lake (Mn salt), quinacridone magenta, ansanthrone orange, dianslaquinonyl red, perylene maroon, quina Ridonmazenda, perylene red, diketopyrrolopyrrole chrome vermilion, chlorinated phthalocyanine green, brominated phthalocyanine green, etc.; pyrazolone orange, benzimidazolone orange, dioxazine violet, perylene violet and the like.

  For example, commercially available titanium white products include “Tai Pure R-100”, “Tai Pure R-101”, “Tai Pure R-102”, “Tai Pure R-103”, “Tai Pure R-104”, “Tai Pure R-105”, and “Tai Pure R-108”. "Tai Pure R-900" "Tai Pure R-902" "Tai Pure R-960" "Tai Pure R-706" "Tai Pure R-931 (DuPont, trade name)", "Taipeku CR-93" "Taipeku CR-" 95 ”“ Taipeke CR-97 ”(named Ishihara Sangyo Co., Ltd., trade name),“ JR-301 ”“ JR-403 ”“ JR-405 ”“ JR-600A ”“ JR-605 ”“ JR-600E ”“ JR805 ”,“ JR-806 ”,“ JR-701 ”,“ JR-901 ”(above, Takeka Co., Ltd., trade name) and the like.

  The blending amount of the color pigment (a3) in the primer coating composition (A) is 40 to 150 parts by weight, preferably 45 to 45 parts by weight of the color pigment (a3) based on 100 parts by weight of the solid content of the epoxy resin (a1). 130 parts by mass, and more preferably 50 to 100 parts by mass is preferable from the viewpoint of paint stability, weather resistance, and chipping resistance.

Extender pigment (a4)
Examples of the extender pigment (a4) include clay, silica, barium sulfate, talc, calcium carbonate, white carbon, diatomaceous earth, magnesium aluminum carbonate flakes, and mica flakes.

  The amount of the extender pigment (a4) in the primer coating composition (A) is 40 to 150 parts by mass, preferably 50, based on the total solid content of 100 parts by mass of the epoxy resin (a1). From the standpoint of paint stability, finish, and chipping resistance, it is preferably from -120 parts by mass, more preferably from 55 to 110 parts by mass.

  Moreover, as a commercial item of the said talc, "Simgon" "Talc MS" "MICRO ACE SG-95" "MICRO ACE P-8" "MICRO ACE P-6" "MICRO ACE P-4" "MICRO ACE P-" 3 ”MICRO ACE P-2” “MICRO ACE L-1” “MICRO ACE K-1” “MICRO ACE LG” “MICRO ACE S-3” “NANO ACE D-1000” Company, product name), "P talc" "PH talc" "PS talc" "TTK talc" "TT talc" "T talc" "ST talc" "Hightron" "Hightron A" "Microlite" "Hilac" " Commercial products such as “HIMICRON HE5” (above, Takehara Chemical Co., Ltd., trade name) can be mentioned.

  In particular, based on 100 parts by mass of the solid content of the epoxy resin (a1) in the primer coating composition (A), 0.1 to 30 parts by mass of talc as an at least part of the extender pigment (a4), preferably 3 It is preferable to contain -25 mass parts, More preferably 7-20 mass parts from the surface of finish property and chipping resistance.

  As commercial products of the above-mentioned calcium carbonate, Nanocoat S-25, MC Coat S-10 (above, Maruo Calcium Co., Ltd., trade name), Oak Gloss (manufactured by Nichigo Movinyl), Neolite SS, Neolite SA-200 (above, Takehara Kogyo Co., Ltd., trade name). Examples of commercially available products of barium sulfate include barium sulfate 100 and barita BF-1 (above, manufactured by Sakai Chemical Industry Co., Ltd.).

  Furthermore, the total oil absorption amount of the rust preventive pigment (a2), the colored pigment (a3), and the extender pigment (a4) per 100 g of the total solid content of the epoxy resin (a1) in the primer coating composition (A) ( Note) is 16 to 50 ml, preferably 20 to 43 ml, more preferably 25 to 40 ml. By wet-on-wet coating, a finished article having excellent finish, corrosion resistance, weather resistance and chipping resistance is obtained. It is necessary for this purpose.

(Note) Total oil absorption: Assume that 10 g of pigment X, 20 g of pigment Y, and 30 g of pigment Z are blended with respect to a total solid content of 100 g of the epoxy resin (a1).
When the oil absorption amount of the pigment X (Note 1) is X _S (ml / 100 g), the oil absorption amount of the pigment Y is Y _S (ml / 100 g), and the oil absorption amount of the pigment Z is Z _S (ml / 100 g), The total amount of oil absorption is given by the following formula.
Total oil absorption = [X _S × (10/100)] + [Y _S × (20/100)] + [Z _S × (30/100)]...
(Note 1) Oil absorption amount: The oil absorption amount of each pigment is the oil absorption value (ml / 100 g) determined according to the method described in the oil method (JIS K 5101-13-2).

  In addition, the primer coating composition (A) includes a silane coupling agent (a5), an ultraviolet absorber, a light stabilizer, a rheology control agent, an antifoaming agent, a pigment dispersant, a surface conditioner, an interface as necessary. An activator, a curing agent, a curing catalyst, a thickener, a preservative, an antifreezing agent and the like can be blended.

Silane coupling agent (a5)
In the primer coating composition (A) used in the present invention, a silane coupling agent (a5) can be blended for the purpose of improving the corrosion resistance. Examples of the silane coupling agent (a5) include γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β -Aminoethyl) -γ-aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, N- (β- (N-vinylbenzylaminoethyl) ) -Γ-aminopropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane and other amino group-containing silane coupling agents; γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltriethoxyxysilane, β- (3,4-epoxycyclohexyl) ethyltrime Epoxy group-containing silane coupling agents such as xysilane; carboxyl groups such as β-carboxyethylphenylbis (2-methoxyethoxy) silane, N-β- (N-carboxymethylaminoethyl) -γ-aminopropyltrimethoxysilane Examples include silane coupling agents.

  Among these, amino group-containing silane coupling agents and epoxy group-containing silane coupling agents are desirable for improving corrosion resistance. Moreover, these silane coupling agents may be used independently and may be used together 2 or more types.

  Commercially available silane coupling agents (a5) include KBM-402, KBM-403, KBM-502, KBM-503, KBM-603, KBE-903, KBM-603, KBE-602, KBE-603 ( As mentioned above, the product name of Shin-Etsu Silicone Co., Ltd. can be mentioned.

  When mix | blending a silane coupling agent (a5) in this invention, the compounding ratio of a silane coupling agent (a5) is 0.1-10 mass parts with respect to 100 mass parts of solid content of an epoxy resin (a1). The amount is preferably 0.5 to 5 parts by mass, more preferably 0.8 to 3.5 parts by mass, from the viewpoint of finish and corrosion resistance.

Top coating composition The top coating composition is a composition containing an acrylic resin (b1), a polyisocyanate compound (b2), and barium sulfate (b3) having an average particle size of 0.01 to 5.0 μm, and the acrylic resin The coating composition contains 1 to 50 parts by weight, preferably 5 to 30 parts by weight of barium sulfate (b3), based on 100 parts by weight of the total solid content of (b1) and the polyisocyanate compound (b2).

Acrylic resin (b1)
The said acrylic resin (b1) can be manufactured by copolymerizing the mixture of a hydroxyl-containing radically polymerizable unsaturated monomer (b11) and another radically polymerizable unsaturated monomer (b12).

  Examples of the hydroxyl group-containing radical polymerizable unsaturated monomer (b11) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) ) Acrylate, and in addition to this, Plaxel FM1, Plaxel FM2, Plaxel FM3, Plaxel FA1, Plaxel FA2, Plaxel FA3 (above, trade name, caprolactone-modified (meth) acrylic acid hydroxy esters) manufactured by Daicel Chemical Industries, etc. It is done.

  In the present specification, “(meth) acrylate” means “acrylate or methacrylate”. “(Meth) acryloyl” means “acryloyl or methacryloyl”. “(Meth) acrylamide” means “acrylamide or methacrylamide”.

Examples of the other radical polymerizable unsaturated monomer (b12) include carboxyl group-containing radical polymerizable unsaturated monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid; For example, unsaturated alkoxy-containing unsaturated groups such as γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane, vinyltrimethoxysilane Monomer; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl ( Meta C1-C18 alkyl or cycloalkyl esters of (meth) acrylic acid such as acrylate and cyclohexyl (meth) acrylate; aromatic vinyl monomers such as styrene; (meth) acrylic acid amide and N, N-dimethylol (meth) Acrylamide, N, N-dimethoxymethyl (meth) acrylamide, N, N-di-n-butoxymethyl (meth) acrylamide, N-methoxymethyl-N-methylol (meth) acrylamide, N-methylol (meth) acrylamide,
(Meth) acrylamide monomers such as N-alkoxymethyl (meth) acrylamide group-containing unsaturated monomers represented by the following formula (1);

(In formula (1), R ¹ represents an alkyl group having 1 to 8 carbon atoms, and R ² represents a hydrogen atom or a methyl group)

  Examples of the N-alkoxymethyl (meth) acrylamide group-containing unsaturated monomer represented by the above formula (1) include N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, and N-propoxy. Methyl (meth) acrylamide, N-isopropoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide, N-hexoxymethyl (meth) acrylamide, N-isohexoxymethyl ( Mention may be made of (meth) acrylamide.

  The blending ratio of these radically polymerizable unsaturated monomers is 1 to 40% by mass of the hydroxyl group-containing radically polymerizable unsaturated monomer (b11) based on the total amount of the radically polymerizable unsaturated monomers to be constituted. The content of the other radical polymerizable unsaturated monomer (b12) is preferably 60 to 99% by mass, preferably 70 to 95% by mass.

  The acrylic resin (b1) is a mixture of the above hydroxyl group-containing radical polymerizable unsaturated monomer (b11) and other radical polymerizable unsaturated monomer (b12). For example, in the presence of a polymerization initiator, About 1 hour to about 24 hours, preferably about 2 hours to about about 2 hours in an organic solvent maintained at about 50 ° C. to about 300 ° C., preferably about 60 ° C. to 250 ° C. in the presence of an inert gas such as nitrogen. It can be obtained by a radical polymerization reaction for 10 hours.

  Moreover, the polyester resin modified acrylic resin modified with the polyester resin can be used as a part of the acrylic resin (b1). The polyester resin-modified acrylic resin can be produced by a conventionally known production method, for example, a method by copolymerization of a polyester resin having a polymerizable unsaturated group and a copolymerizable acrylic resin (b1). Can be mentioned. The anticorrosion can be improved by using a polyester resin-modified acrylic resin in the top coating composition (B).

  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, methyl carbitol, 2-methoxyethanol, 2-ethoxyethanol, 2-isopropoxyethanol, 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 this, optionally, for example, aromatics such as xylene and toluene, ketones such as acetone, methyl ethyl ketone, 2-pentanone, 2-hexanone, methyl isobutyl ketone, isophorone, cyclohexanone, methyl acetate, ethyl acetate Further, esters such as pentyl acetate, 3-methoxybutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate, methyl propionate and ethyl propionate can be used in combination.

  Examples of the polymerization initiator used in the radical polymerization reaction include benzoyl peroxide, di-t-butyl hydroperoxide, t-butyl hydroperoxide, cumyl peroxide, cumene hydroperoxide, t-butyl peroxybenzoate, and lauryl peroxide. Examples thereof include oxide, acetyl peroxide, azobisisobutyronitrile, and azobisisobutyronitrile.

  The weight average molecular weight of the obtained acrylic resin (b1) is preferably in the range of 3,000 to 50,000, particularly 4,000 to 15,000, the acid value is in the range of 1 to 20 mgKOH / g, and the hydroxyl value is 40. A range of ˜200 mg KOH / g is suitable.

Polyisocyanate compound (b2)
The polyisocyanate compound (b2) is a compound having two or more free isocyanate groups in one molecule.
As the polyisocyanate compound (b2), those conventionally used for polyurethane production can be used. For example, an aliphatic polyisocyanate compound having 2 to 18 carbon atoms, an alicyclic polyisocyanate compound having 4 to 15 carbon atoms, Aromatic aliphatic polyisocyanate compounds having 8 to 15 carbon atoms, aromatic polyisocyanate compounds having 6 to 20 carbon atoms (excluding carbon in the NCO group, the same shall apply hereinafter) and crude products thereof, modified products of these polyisocyanate compounds, and A mixture of two or more of these is included.

  Specific examples of the aliphatic polyisocyanate compound include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), dodecamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate. Lysine diisocyanate, 2,6-diisocyanatomethyl caproate, bis (2-isocyanatoethyl) fumarate, bis (2-isocyanatoethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexano Eate.

  Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), bis ( 2-isocyanatoethyl) -4-cyclohexene-1,2-dicarboxylate, 2,5- and / or 2,6-norbornane diisocyanate.

  Specific examples of the araliphatic polyisocyanate compound include m- and / or p-xylylene diisocyanate (XDI), α, α, α ′, α′-tetramethylxylylene diisocyanate (TMXDI), and the like.

  Specific examples of the aromatic polyisocyanate compound include 1,3- and / or 1,4-phenylene diisocyanate, 2,4- and / or 2,6-tolylene diisocyanate (TDI), crude TDI, 2,4 '-And / or 4,4'-biphenylmethane diisocyanate (MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl -4,4'-diisocyanatodiphenylmethane, crude MDI, 1,5-naphthylene diisocyanate, 4,4 ', 4 "-triphenylmethane triisocyanate, m- and p-isocyanatophenylsulfonyl isocyanate, and the like. .

  Examples of the modified 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. Modified products of isocyanate; and mixtures of two or more thereof [for example, combined use of modified MDI and urethane-modified TDI (isocyanate group-containing prepolymer)].

  In addition to the polyisocyanate compound, those obtained by blocking the isocyanate group of the polyisocyanate compound with a blocking agent can be used in combination. Examples of the blocking agent include phenols; oximes; lactams; alcohols; mercaptans; pyrazoles; active methylene compounds such as diethyl malonate. When using a block polyisocyanate compound, it is preferable to use a dissociation catalyst of a blocking agent in combination and heat and dry at 80 ° C. or higher, preferably 90 to 180 ° C.

  From the standpoint of corrosion resistance and weather resistance, preferred as the above polyisocyanate compounds are aliphatic polyisocyanate compounds and alicyclic polyisocyanate compounds. The number average molecular weight of the polyisocyanate compound is preferably 3,000 or less, particularly preferably in the range of 100 to 1,500.

  Commercially available products of such polyisocyanate compounds include Bayhydr (TPHLS2550, Sumidur N3300 (manufactured by Sumika Bayer Urethane Co., Ltd.), TPA100 (manufactured by Asahi Kasei Chemicals), BASONAT (manufactured by Asahi Kasei Chemicals Corporation). Bassonate) HI100 (manufactured by BASF Corporation) and the like.

  The acrylic resin (b1) is 60 to 90 parts by mass, preferably 65 to 85 parts by mass, based on the total solid content of 100 parts by mass of the acrylic resin (b1) and the polyisocyanate compound (b2). Isocyanate compound (b2) is in the range of 10 to 40 parts by mass, preferably 15 to 35 parts by mass, from the viewpoint of coating stability and coating film hardness.

Barium sulfate (b3) with an average particle size of 0.01-5 μm
The top coating composition used in the present invention contains barium sulfate (b3) having an average particle size of 0.01 to 5 μm, and preferably an average particle size of 0.05 to 1 μm. (Hereinafter, barium sulfate (b3) having an average particle diameter of 0.01 to 5 μm is simply referred to as barium sulfate (b3)).

  Examples of such commercially available barium sulfate (b3) include Varifine BF-20 (manufactured by Sakai Chemical Industry Co., Ltd., trade name, barium sulfate with an average particle size of 0.03 μm), and BARIACE B-30 (manufactured by Sakai Chemical Industry Co., Ltd.). , Trade name, barium sulfate having an average particle diameter of 0.3 μm), SPARWITE (Spurwite) W-5HB (manufactured by Sino-Can, trade name, barium sulfate powder, average particle diameter: 1.6 μm). In the present specification, the average particle size is measured using UPA-EX250 (trade name, manufactured by Nikkiso Co., Ltd., particle size distribution measuring apparatus by dynamic light scattering method).

  The blending amount of barium sulfate (b3) in the top coating composition (B) is 1 to 50 parts by mass, preferably based on 100 parts by mass in total of the solid contents of the acrylic resin (b1) and the polyisocyanate compound (b2). When the amount is 5 to 45 parts by mass, more preferably 10 to 40 parts by mass, a coating film having good finish, weather resistance, and chipping resistance can be obtained.

Polyether Polyol Polyether polyol can be used in the top coating composition used in the present invention, if necessary, for the purpose of further reducing the difference in coating film gloss due to the baking temperature.

  As said polyether polyol, the compound which alkylene oxide added to active hydrogen containing compounds, such as a polyhydric alcohol, polyhydric phenol, polyhydric carboxylic acids, is mentioned.

  Examples of the active hydrogen-containing compound include water, polyhydric alcohols (ethylene glycol, diethylene glycol, trimethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4 -Dihydric alcohols such as dihydroxymethylcyclohexane and cyclohexylene glycol, glycerin, trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propane Triol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl- 3,4,5-heptanetriol, 2,4-dimethyl- , 3,4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, trihydric alcohols such as trimethylolethane, trimethylolpropane, pentaerythritol, 1 , 2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,4,5-pentanetetrol, 1,3,4,5-hexanetetrol, diglycerin, Tetravalent alcohols such as sorbitan, pentahydric alcohols such as adonitol, arabitol, xylitol, triglycerin, hexavalent alcohols such as dipentaerythritol, sorbitol, mannitol, iditol, inositol, dulcitol, talose, allose, etc., and octavalent alcohols such as sucrose Polyglycerin, etc.); Knols [polyhydric phenols (pyrogallol, hydroquinone, phloroglucin, etc.), bisphenols (bisphenol A, bisphenolsulfone, etc.)]; polycarboxylic acids [aliphatic polycarboxylic acids (succinic acid, adipic acid, etc.), aromatic polycarboxylic acids (Phthalic acid, terephthalic acid, trimellitic acid, etc.)] and the like; and mixtures of two or more thereof.

  Particularly preferred as trihydric or higher alcohols used for forming a polyether polyol having at least 3 or more hydroxyl groups in one molecule are glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitan, sorbitol, etc. It is.

The polyether polyol is usually obtained by subjecting an alkylene oxide to the active hydrogen-containing compound in the presence of an alkali catalyst and subjecting it to an addition reaction at a temperature of 60 to 160 ° C. under normal pressure or pressure. Examples of the alkylene oxide include alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide.
A particularly preferred example of the polyether polyol includes a compound represented by the following formula (1).

(In the formula (1), l, m and n are each independently an integer of 1 or more, and l + m + n = 3 to 15 and each A in (AO) _l , (AO) _m and (AO) _n Are the same or different ethylene groups and / or propylene groups)

  Examples of commercially available polyether polyols include Sannics GP-600, Sannics GP-1000, Exenol 430, Exenol 385SO, Exenol 450ED, Exenol 500ED, Exenol 750ED (above, Asahi Glass Co., Ltd., trade name), Adeka Polyether (Adeka Co., Ltd., trade name), Actcoal T-1000 (Mitsui Chemicals, Inc., trade name), and the like. The number average molecular weight of such polyether polyol is less than 3,000, preferably 90 to 2,000, and more preferably 500 to 1,500.

  When the polyether polyol is blended in the top coating composition (B), the blending amount is 0.1 to 30 on the basis of 100 parts by mass in total of the solid content of the acrylic resin (b1) and the polyisocyanate compound (b2). It is preferable from the point which can obtain the coating film with few coating film glossiness differences by baking temperature that it is the range of a mass part, Preferably it is 1-20 mass parts, More preferably, it is 3-15 mass parts.

  In addition, for the top coating composition (B), coloring pigments, extender pigments, rust preventive pigments, rheology control agents, ultraviolet absorbers, light stabilizers, antifoaming agents, pigment dispersants, surface conditioners are optionally added. , Surfactants, curing catalysts, thickeners, preservatives, antifreeze agents and the like can be blended.

  The said rust preventive pigment can use the said rust preventive pigment (a2), for example, zinc oxide, a phosphite compound, a phosphate compound, etc. are mentioned. As the colored pigment, the pigments exemplified in the colored pigment (a3) can be used, and examples thereof include titanium dioxide, benzimidazolone yellow, and red pepper. As the extender pigment, extender pigments exemplified in the extender pigment (a4) can be used, and examples thereof include talc, barium sulfate, calcium carbonate, and clay.

  The rheology control agent is intended to improve the finish by controlling the fluidity of the paint. As a rheology control agent, clay minerals (for example, metal silicates, montmorillonite), acrylics (for example, those containing a structure composed of polymers or oligomers of acrylic acid esters or methacrylic acid esters in the molecule), polyolefins (for example, , Polyethylene, polypropylene, etc.), amides (higher fatty acid amides, polyamides, oligomers, etc.), polycarboxylic acids (including derivatives having at least two carboxyl groups in the molecule), cellulose (nitrocellulose, acetylcellulose, cellulose ether) And other derivatives), urethane (polymers and oligomers containing a urethane structure in the molecule), urea (polymers and oligomers containing a urea structure in the molecule), urethane urea (urethane structure and urea structure in the molecule) Polymers, oligomers, etc.), and the like, including.

  Examples of commercially available rheology control agents include amide waxes such as Dispalon 6900 (manufactured by Enomoto Kasei Co., Ltd.) and Chixol W300 (Kyoeisha Chemical Co., Ltd.); polyethylene waxes such as Disparon 4200 (manufactured by Enomoto Kasei Co., Ltd.). Cellulose-based rheology control agents such as CAB (cellulose acetate butyrate, Eastman Chemical Products), HEC (hydroxyethylcellulose), hydrophobized HEC, CMC (carboxymethylcellulose); BYK-410, BYK-411 , Urethane urea-based rheology control agents such as BYK-420 and BYK-425 (manufactured by BYK-Chemical Co., Ltd.); sulfate anionic surfactants such as Flownon SDR-80 (Kyoeisha Chemical Co., Ltd.); flow Emission SA-345HF (manufactured by Kyoeisha Chemical Co.) rheology control agents polyolefin such as; Furonon HR-4AF (Kyoeisha Chemical Co.) rheology control agent of higher fatty acid amide-based and the like; and the like.

  In addition, when mix | blending a rheology control agent, the compounding quantity is 0.1-20 mass parts on the basis of 100 mass parts total of solid content of an acrylic resin (b1) and a polyisocyanate compound (b2), Preferably it is 0.00. The range of 5 to 15 parts by mass, and more preferably 0.9 to 5 parts by mass is desirable from the viewpoint of paint stability and finish.

Multilayer coating film forming method The multilayer coating film forming method of the present invention comprises forming an uncured coating film by the primer coating composition (A) on an object to be coated, and forming the uncured coating film on the uncured coating film. In this method, a top coating film is formed from the top coating composition (B), and both coating films are simultaneously dried to form a coating film.

  Examples of the article to be coated include cold-rolled steel sheets, black skin steel sheets, galvannealed steel sheets, and electrogalvanized steel sheets. These may be subjected to shot blasting, surface adjustment, surface treatment, and the like as necessary.

  The primer coating composition (A) is applied by, for example, dip coating, brush coating, roll brush coating, spray coating, roll coating, spin coating, dip coating, bar coating, flow coating, electrostatic coating, airless coating, It can be performed by a coating method such as electrodeposition coating or die coating. The dry film thickness is usually 10 μm to 150 μm, preferably 30 μm to 80 μm.

  After forming the coating film of the primer coating composition (A), setting at room temperature or preheating is performed as necessary.

  Application of the top coating composition (B) onto the uncured coating film by the primer coating composition (A) is, for example, dip coating, brush coating, roll brush coating, spray coating, roll coating, spin coating. , Dip coating, bar coating, flow coating, electrostatic coating, airless coating, electrodeposition coating, die coating, and the like. The dry film thickness is usually in the range of 10 μm to 150 μm, preferably 30 μm to 80 μm. Subsequently, it can dry for 10 to 120 minutes at normal temperature-160 degreeC, Preferably it is 20-90 minutes at 60-120 degreeC, and can obtain a multilayer coating film.

  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, “parts” indicates mass parts, and “%” indicates mass%.

Production of primer coating composition Production Example 1 Primer coating composition no. Production Example 1 According to the following steps 1 to 2, primer coating composition No. 1 was obtained.
Step 1:
50 parts (solid content) of Arachid 9205 (Note 2), 10 parts of zinc oxide (Note 4), 70 parts of Taipure R-902 (Note 6), 40 parts of LAKABAR SF (Note 8), Neolite SA-200 (Note 10) ) To 70 parts, a suitable amount of Swazol 1000 (manufactured by Cosmo Oil Co., Ltd., aromatic hydrocarbon solvent) was added and dispersed with a sand mill to obtain a pigment dispersion paste.
Step 2:
50 parts (solid content) of Arachid 9205 (Note 2) and 1 part of Disparon A 603-20X (Note 15) are blended in the pigment dispersion paste obtained above, and Swazol 1000 (Cosmo Oil Co., Ltd., aromatic Hydrocarbon solvent) is added and stirred, and the solid content is adjusted to obtain primer coating composition No. 70 having a solid content of 70%. 1 was obtained.

Production Examples 2 to 17 Primer paint composition No. 2-No. Production Example 17 In the same manner as in Production Example 1 except that the blending contents shown in Table 1 were used, the primer coating composition No. 2-No. 17 was obtained.

Comparative Production Examples 1 to 9 Primer paint composition No. 18-No. Production Example 26 In the same manner as in Production Example 1 except that the blending contents shown in Table 2 were used, the primer coating composition No. 18-No. 26 was obtained.

(Note 2) Arachide 9205: Arakawa Chemical Co., Ltd., trade name, bisphenol A type epoxy resin, glass transition temperature 84 ° C
(Note 3) Epokey 803: Mitsui Chemicals, trade name, urethane-modified epoxy resin (Note 4) Zinc oxide: Sakai Chemicals, trade name, oil absorption 12 ml / 100 g
(Note 5) K-WHITE 140: Kikuchi Color Co., Ltd., trade name, aluminum dihydrogen tripolyphosphate, oil absorption 32 ml / 100 g
(Note 6) Taipure R-902: DuPont, trade name, titanium white, oil absorption 16ml / 100g
(Note 7) Taipei CR-93: Ishihara Sangyo Co., Ltd., trade name, titanium white, oil absorption 20ml / 100g
(Note 8) LAKABAR SF: LAKAVISUTH, trade name, barium sulfate powder, average particle size 10.4 μm, oil absorption 10 ml / 100 g
(Note 9) Varifine BF-20: manufactured by Sakai Chemical Industry Co., Ltd., trade name, barium sulfate with an average particle size of 0.03 μm, oil absorption 24 ml / 100 g
(Note 10) Neolite SA-200: Takehara Chemical Industry Co., Ltd., trade name, calcium carbonate, oil absorption 32 ml / 100 g
(Note 11) Nanocoat S-25: Maruo Calcium Co., Ltd., trade name, calcium carbonate, oil absorption 23 ml / 100 g
(Note 12) T talc: manufactured by Takehara Chemical Co., Ltd., trade name, talc, average particle size 9.0 μm, oil absorption 27 ml / 100 g
(Note 13) Hilac: manufactured by Takehara Chemical Co., Ltd., trade name, talc, average particle size 7.0 μm, oil absorption 36 ml / 100 g
(Note 14) KBM-403: Shin-Etsu Chemical Co., Ltd., trade name, epoxy group-containing silane coupling agent (Note 15) Disparon A603-20X: Enomoto Kasei Co., Ltd., trade name, thickener (Note 16) Paint stability :
Each primer coating composition was placed in a 250 ml glass container and stored in the dark at 20 ° C. for 24 hours to check the condition.
The symbol indicates that the primer coating composition does not settle.
○ indicates that sedimentation of the primer coating composition is slightly observed, but returns to the original state even with gentle stirring.
Δ indicates slight phase separation of the primer coating composition.
In x, the phase separation of the primer coating composition is remarkably observed.

Production and Production Example 18 of Topcoat Coating Composition Manufacture of Acrylic Resin Solution 28 parts Swazol 1000 (Cosmo Oil Co., Ltd., aromatic hydrocarbon solvent), 85 parts toluene, 41.6 parts styrene, 6.9 n-butyl acrylate Parts, 19 parts isobutyl methacrylate, 15 parts Plaxel FM-3 (Note 17), 17 parts 2-hydroxyethyl methacrylate, 0.5 parts acrylic acid, 8 parts di-tert-butyl hydroperoxide at 110 ° C. under nitrogen gas To obtain an acrylic resin solution. The resin solid content of the obtained acrylic resin solution was an acid value of 3.9 mgKOH / g, a hydroxyl value of 94.9 mgKOH / g, and a weight average molecular weight of 11,000.

(Note 17) Plaxel FM-3: Daicel Chemical Industries, Ltd., trade name, ε-caprolactone-modified vinyl monomer of 2-hydroxyethyl acrylate

Production Example 19 Production of polyester-modified acrylic resin solution (according to JP-A-8-302204)
In a four-necked flask equipped with a stirrer, thermometer, cooling pipe and nitrogen gas introduction pipe, 143 parts of Beccosol P-470-70 (manufactured by DIC, trade name, soybean oil-based long oil alkyd resin), 457 parts of spirit was charged and the temperature was raised to 100 ° C.

  Next, 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 “Solvesso 100”, 10 parts of benzoyl peroxide The resulting mixture was added dropwise over 4 hours.

  The polyester-modified acrylic resin solution was obtained by making it react at the same temperature for 8 hours after completion | finish of dripping. The resin solid content of the polyester-modified acrylic resin solution was an acid value of 2.5 mgKOH / g and a weight average molecular weight of 9,000.

Production Example 20 Top coating composition no. Production Example 1 80 parts (solid content) of the acrylic resin solution obtained in Production Example 18, 12 parts of Taipei CR-93 (Note 7), 12 parts of Hoster Palm Yellow H-3G (Note 18), Varifine BF-20 (Note 19) 15 parts and Bayferrox 4905 (Note 23) 12 parts were blended, and the solid content adjusted with Swazol 1000 (Cosmo Oil Co., Ltd., aromatic hydrocarbon solvent) was charged into a ball mill and stirred for 6 hours. A base paint was obtained by dispersing. Further, immediately before coating, 20 parts (solid content) of Sumijour N3300 (Note 25) were mixed and stirred, and the top coating composition No. 1 was obtained.

Production Examples 21 to 25 Top coating composition No. 2-No. Production Example 6 In the same manner as in Production Example 20 except that the contents of Table 3 were used, the top coating composition No. 2-No. 6 was obtained.

Comparative Production Examples 9 to 14 Top coating composition No. 7-No. Production Example No. 12 The top coating composition No. 12 was prepared in the same manner as in Production Example 20 except that the content of blending shown in Table 4 was used. 7-No. 12 was obtained.

(Note 18) Hoster Palm Yellow H-3G: manufactured by Clariant, trade name, Hansa Yellow yellow pigment (Note 19) Varifine BF-20: trade name, manufactured by Sakai Chemical Industry Co., Ltd., trade name, barium sulfate having an average particle size of 0.03 μm (Note 20) SPARWITE W-5HB: Sino-Can, trade name, barium sulfate having an average particle size of 1.6 μm (Note 21) BARIACE B-30: Sakai Chemical Industry Co., Ltd., trade name, average particle size 0. 3 μm barium sulfate (Note 22) Barium sulfate BA: manufactured by Sakai Chemical Industry Co., Ltd., trade name, barium sulfate, average particle size 6 μm
(Note 23) Bayferrox 4905: Lanxess Corporation, trade name,
Red pigment (Note 24) Actol T-1000: manufactured by Mitsui Chemicals, trade name, polyether polyol, number average molecular weight 1,000
(Note 25) Sumijour N3300: Sumika Bayer Urethane Co., Ltd., trade name,
Isocyanurate of hexamethylene diisocyanate

<Creation of a multilayer coating film-formed coating plate>
Example 1 Multi-layer coating film-forming coating plate No. 1 Preparation of multilayer coating film formation coating board No. 1 by the following process 1-process 3. 1 was obtained.
Step 1: A primer coating composition No. obtained in Production Example 1 was applied to a cold-rolled steel plate (size 0.8 × 70 × 150 mm, Palbond # 3020). No. 1 was applied vertically by spray coating so that the dry film thickness was 45 μm, and set at 25 ° C. for 3 minutes.
Step 2: Next, the top coating composition No. obtained in Production Example 20 was applied onto the primer coating film. No. 1 was used, and vertical coating was performed wet-on-wet by spray coating so that the dry film thickness was 40 μm, thereby forming a top coating film.
Step 3: After setting the coating film obtained in Step 1 to Step 2 at 25 ° C. for 10 minutes, heat drying at 80 ° C. for 30 minutes and further drying at room temperature (20 ° C.) for 72 hours to form a multilayer coating film Forming plate No. 1 was obtained.

Examples 2 to 22 Multi-layer coating film forming coating plate No. 2-No. No. 22 In the same manner as in Example 1, except that the primer coating composition in step 1 and the top coating composition in step 2 were the coatings in Table 5, the multilayer coating film-formed coating plate No. 2-No. 22 was obtained.

Comparative Examples 1 to 16 Multilayer coating film-formed coating plate No. 1 23-No. No. 38 Preparation of the multilayer coating film-forming coating plate No. 1 in the same manner as in Example 1 except that the primer coating composition in step 1 and the top coating composition in step 2 were the coating materials in Table 6. 23-No. 38 was obtained.

Coating Film Performance Test Each multilayer coating film-formed coating plate was used for a coating film performance test according to the test conditions described below. A result is combined with Table 5-Table 6, and is shown.
Moreover, about the test of "film glossiness difference", the difference of the said multilayer coating film formation coating board and the multilayer coating film formation coating board A produced according to the content of (* 32) was calculated | required.

Performance Evaluation (Note 27) Finish: The appearance of the coated surface of the multilayer coating film-formed coated plate obtained by Examples and Comparative Examples was visually evaluated.
○ indicates that there is no problem with smoothness because there is no mixture of the top coat film and the primer paint film, and Δ indicates that the top coat film and the primer paint film are mixed layers, and at least one kind selected from swell, glossy skin and chili skin There is a slight decrease in finish,
In x, the mixed layer of the top coating film and the primer coating film is remarkable, and at least one finish selected from waviness, glossiness, and chile skin is markedly lowered.

(Note 28) Pencil hardness: A multilayer coating film-formed coated plate obtained by Examples and Comparative Examples was applied with a pencil core at an angle of about 45 ° with respect to the test coated plate surface according to JIS K 5600-5-4. The plate was moved forward at a uniform speed by about 10 mm while pressing firmly against the test coating plate surface to such an extent that the core was not broken. The hardness symbol of the hardest pencil that did not tear the coating film was defined as pencil hardness.

(Note 29) Corrosion resistance: Cross-cut scratches were made with a knife on the multilayer coating film-formed coated plates obtained in the Examples and Comparative Examples, and this was subjected to a salt spray resistance test for 120 hours according to JIS Z-2371. Evaluation was made according to the following criteria based on the rust and blister width from the scratch.
◎ indicates that the maximum width of rust and blisters is less than 2 mm (one side) from the cut,
○, the maximum width of rust and blisters is 2mm or more and less than 3mm (one side) from the cut part,
△ indicates that the maximum width of rust and blisters is 3 mm or more and less than 4 mm (one side) from the cut part,
X: The maximum width of rust and blisters is 4 mm or more from the cut part (one side).

(Note 30) Weather resistance: Multi-layer coating film-formed coated plates obtained according to the examples and comparative examples were subjected to a sunshine carbon arc lamp type light resistance and weather resistance test specified in JIS B-7533 with an irradiation time of up to 1, The test was conducted until 200 hours. In the coating film of the test plate, the irradiation time when the gloss retention with respect to the gloss before the test was 80% was measured.
◎ indicates that the gloss retention is 80% or more even when the irradiation time is 1,200 hours. ○ indicates that the irradiation time when the gloss retention is less than 80% is 1,000 hours or more and less than 1200 hours.
Δ is an irradiation time of 800% or more and less than 1,000 hours when the gloss retention is less than 80%,
X: Irradiation time when gloss retention is less than 80% is less than 800 hours

(Note 31) Chipping resistance:
The multilayer coating film-formed coating plate obtained by the example and the comparative example is placed on a specimen holding stand of a chipping test apparatus (manufactured by Suga Test Instruments Co., Ltd., stepping stone testing machine “JA-400 type”) with respect to a stone outlet. The coated surface was fixed at a right angle, and at 20 ° C., 500 g of granite crushed stone No. 6 was sprayed on the coated surface 5 times with compressed air of 0.294 MPa (3 kgf / cm ² ), and then the coated surface was clothed. An adhesive tape (Fuji Kogyo Co., Ltd.) was attached, and after it was peeled off rapidly, the degree of scratches on the coating film was visually observed and evaluated according to the following criteria.
◎ indicates that the size of the scratch is 1.0 mm or less in diameter and the top coating film is partially scratched.
○, the size of the scratch is more than 1.0 mm in diameter and 1.5 mm or less, and the primer coating is partially exposed,
Δ, the size of the scratch exceeds the diameter of 1.5 mm and is 2.0 mm or less, a part of the primer coating is missing, the steel plate is exposed,
In the case of ×, the size of the scratch exceeds 2.0 mm in diameter, and the primer coating film is largely exposed, or the primer coating film is lost and the steel plate is exposed, and the appearance is remarkably impaired.

(Note 32) Difference in coating film gloss:
In the preparation of the above-mentioned “multi-layer coating film-forming plate”, “multi-layer coating film formation” is performed in the same process except that the setting for 3 minutes at 25 ° C. in Step 1 is changed to heat drying at 80 ° C. for 10 minutes. Coated plate A "was obtained.
The glossiness of the “multilayer coating film forming coating plate” and “multilayer coating film forming coating plate A” is determined in accordance with “60 degree specular gloss” of JIS K 5600-4-7 (1999), and the coating films of both coating films are obtained. The difference in glossiness (Δ) was determined.
A: The difference in film glossiness (Δ) between the two coating films is within ± 2.
◯ indicates that the difference in coating film glossiness (Δ) between both coatings exceeds 2 and 5 or less. Δ indicates that the difference in coating film glossiness (Δ) between both coatings exceeds 5 and 10 or less. The difference in coating film glossiness (Δ) exceeds 10.

  By wet-on-wet coating, it is possible to provide a coated article that is excellent in finish, corrosion resistance, weather resistance, and chipping resistance, and has little difference in coating film gloss due to baking temperature.

Claims (4)

An uncured coating film by the primer coating composition (A) is formed on the object to be coated, and an overcoating film by the top coating composition (B) is formed on the uncured coating film. A method for forming a multilayer coating film to be dried,
The primer coating composition (A) is a composition containing an epoxy resin (a1), a rust preventive pigment (a2), a color pigment (a3) and an extender pigment (a4), and is a solid of the epoxy resin (a1) 1 to 70 parts by mass of the rust preventive pigment (a2), 40 to 150 parts by mass of the coloring pigment (a3), and 40 to 150 parts by mass of the extender pigment (a4) based on 100 parts by mass in total, and The total oil absorption of the rust preventive pigment (a2), the colored pigment (a3) and the extender pigment (a4) per 100 g of the solid content of the epoxy resin (a1) in the primer coating composition (A) is 16 to 50 ml. A coating composition that is in the range of
The top coating composition (B) is a composition containing an acrylic resin (b1), a polyisocyanate compound (b2), and barium sulfate (b3) having an average particle size of 0.01 to 5.0 μm, and the acrylic resin 60 to 90 parts by mass of acrylic resin (b1) and 10 to 40 parts by mass of polyisocyanate compound (b2) based on 100 parts by mass of the total solid content of (b1) and polyisocyanate compound (b2) And 1 to 50 parts by mass of barium sulfate (b3),
A method for forming a multilayer coating film.    The primer coating composition (A) contains 0.1 to 10 parts by mass of the silane coupling agent (a5) based on 100 parts by mass of the total solid content of the epoxy resin (a1). A method for forming a multilayer coating film.   The primer coating composition (A) contains 0.1 to 30 parts by mass of talc as at least a part of the extender pigment (a4) based on 100 parts by mass of the total solid content of the epoxy resin (a1). 3. The method for forming a multilayer coating film according to 1 or 2.   The top coating composition (B) contains 0.1 to 30 parts by mass of a polyether polyol based on 100 parts by mass of the total solids of the acrylic resin (b1) and the polyisocyanate compound (b2). The multilayer coating film formation method of any one of -3.