METHOD FOR FORMING MULTILAYER COATING FILM

Abstract

A method for forming a multilayer coating film is provided. The method includes coating at least one object with an aqueous primer coating composition, an aqueous first colored coating composition, an aqueous second colored coating composition, and a clear coating composition, in that order. The aqueous primer coating composition contains a component (A) which contains a polyolefin resin, a component (B) which contains a polyurethane resin, a curing agent (C) and electrically conductive carbon (D). The aqueous first colored coating composition and aqueous second colored coating composition each contain a core/shell emulsion. The clear coating composition contains a hydroxyl group-containing acrylic resin, a polyisocyanate and a melamine resin. The method improves the appearance, chipping resistance, adhesive properties and low temperature impact properties of a coating film.

Claims

1. A method for forming a multilayer coating film, the method comprising: a step of simultaneously coating a same aqueous primer coating composition on two coated objects, namely a pre-coated steel sheet and a pre-treated plastic base material for a motor vehicle, a step of simultaneously coating a same aqueous first colored coating composition on the primer-coated materials using a wet-on-wet process, a step of simultaneously coating a same aqueous second colored coating composition on the aqueous first colored coating composition-coated materials using the wet-on-wet process, a step of simultaneously coating a same clear coating composition on the aqueous second colored coating composition-coated materials and a step of simultaneously curing the formed multilayer coating film, the method being characterized in that: (1) the aqueous primer coating composition contains: an aqueous polyolefin resin (A) having a melting point of 60-100 C. and a weight average molecular weight in a range of 50,000-250,000, an aqueous polyurethane resin (B) having a glass transition temperature (Tg) of 100 C. to 70 C. and an elongation percentage of 500% or more, a curing agent (C), and electrically conductive carbon (D), (2) the aqueous first colored coating composition and the aqueous second colored coating composition each contain a core shell emulsion having an acrylic resin core and a polyurethane resin shell as a base resin, and (3) the dear coating composition contains a hydroxyl group-containing acrylic resin containing 20 mass % or more of t-butyl methacrylate, a polyisocyanate compound and a melamine resin, and a coating film obtained by curing the clear coating composition has a glass transition temperature (Tg) of 70 C. or higher and an elongation percentage of 3% or less.

2. The method for forming a multilayer coating film as claimed in claim 1, wherein the plastic base material contains at least one type of resin material selected from the group consisting of PP resins, ABS resins, PC resins and ABS/PC resins.

3. The method for forming a multilayer coating film as claimed in claim 1, which is characterized in that a proportion in terms of parts by mass of component (A) and component (B) in the aqueous primer coating composition is 20/80 to 80/20 in terms of resin solid content, a proportion in terms of parts by mass of component (C) and {component (A)+component (B)} is 1/100 to 30/100 in terms of solid content, and furthermore a proportion in terms of parts by mass of component (D) and {component (A)+component (B)+component (C)} is 2/98 to 20/80 in terms of solid content.

4. The method for forming a multilayer coating film as claimed in claim 1, which is characterized in that component (B) in the aqueous primer coating composition is a colloidal dispersion type or emulsion type aqueous polyurethane resin.

5. The method for forming a multilayer coating film as claimed in claim 1, which is characterized in that component (B) in the aqueous primer coating composition is an aqueous polyurethane resin obtained by subjecting a polyurethane, which is obtained by reacting a polyisocyanate with a polyol selected from among a polyester polyol, a polycarbonate polyol and a polyether polyol, to chain extension using a low molecular weight compound having at least 2 active hydrogens in the compound.

Description

WORKING EXAMPLES

[0134] The present invention will now be explained in greater detail through the use of working examples, but is not limited to these working examples. In the working examples, the term parts means parts by mass and use of the symbol % relating to blending quantities and content values means mass %, unless explicitly indicated otherwise.

Production Example 1

Production of Non-Chlorinated Polyolefin Resin Aqueous Dispersion P-1

[0135] A non-chlorinated polyolefin resin aqueous dispersion used in the present invention is produced using the following three-stage process.

(i) First Stage: Production of Non-Chlorinated Polyolefin Resin

[0136] 110 mL of deionized water, 22.2 g of magnesium sulfate heptahydrate and 18.2 g of sulfuric acid were placed in a 1000 mL round-bottomed flask and dissolved under stirring. 16.7 g of commercially available granular montmorillonite was dispersed in this solution, heated to 100 C. and stirred for 2 hours. This dispersion was then cooled to room temperature, the obtained slurry was filtered, and a wet cake was recovered. The recovered cake was re-slurrified with 500 mL of demineralized water in a 1000 mL round-bottomed flask, and then filtered. This procedure was repeated twice. 13.3 g of chemically treated montmorillonite was obtained by drying the ultimately obtained cake overnight at 110 C. in a nitrogen atmosphere. 20 mL of a (0.4 mmol/mL) toluene solution of triethyl aluminum was added to 4.4 g of the obtained chemically treated montmorillonite and stirred for 1 hour at room temperature. 80 mL of toluene was added to this suspension and stirred, after which the supernatant liquid was removed. After repeating this procedure twice, a clay slurry (slurry concentration: 99 mg clay/mL) was obtained by adding toluene.

[0137] A catalyst slurry was obtained by placing 0.2 mmol of triisobutyl aluminum in another flask, adding 19 mL of the obtained clay slurry and a toluene dilution solution of 131 mg (57 mol) of dichloro[dimethylsilylene(cyclopentadienyl)(2,4-dimethyl-4H-5,6,7,8-tetrahydro-1-azulenyl) hafnium and stirring for 10 minutes at room temperature.

[0138] Next, 11 L of toluene, 3.5 mmol of triisobutyl aluminum and 2.64 L of liquid propylene were placed in an induction stirring type autoclave having an internal volume of 24 L. The entire quantity of the catalyst slurry was introduced to the autoclave at room temperature, the temperature was increased to 62 C., and stirring was continued for 2 hours at the same temperature while maintaining the overall pressure at a constant 0.65 MPa during polymerization. Following completion of the stirring, unreacted propylene was purged so as to stop the polymerization. The autoclave was opened, the entire quantity of the toluene solution of the polymer was recovered, and when the solvent and clay residue was removed, 11 kg of an 11.0% toluene solution of a propylene-based polymer was obtained. The weight average molecular weight Mw of the obtained propylene-based polymer was 210,000.

(ii) Second Stage: Production of Maleic Anhydride-Modified Non-Chlorinated Polyolefin Resin

[0139] 200 g of the propylene-based polymer obtained in the first stage described in (i) above and 300 g of toluene were placed in a glass flask fitted with a reflux condenser tube, a thermometer and a stirrer, the inside of the flask was purged with nitrogen, and the temperature was increased to 110 C. After increasing the temperature, 12 g of maleic anhydride was added, 6 g of t-butylperoxyisopropyl monocarbonate (Perbutyl I manufactured by NOF Corp.) was added, and a reaction was carried out by continuing the stirring at the same temperature for a period of 7 hours. Following completion of the reaction, the system was allowed to cool to approximately room temperature, acetone was added, and the thus precipitated polymer was filtered. Furthermore, precipitation with acetone and filtration were repeated, and the ultimately obtained polymer was washed with acetone. A white powdery maleic anhydride-modified polymer was obtained by subjecting the washed polymer to vacuum drying. When this modified polymer was subjected to infrared absorption spectrum analysis, the content of maleic anhydride groups (the graft ratio was 1.3% (0.13 mmol as maleic anhydride groups per 1 g of propylene-based polymer), the weight average molecular weight was 120,000, and the melting point, as measured using a DSC-50 differential scanning calorimeter, was 80 C.

(iii) Third Stage: Production of Aqueous Dispersion of Maleic Anhydride-Modified Non-Chlorinated Polyolefin Resin

[0140] 100 g of the maleic anhydride-modified propylene-based polymer (maleic anhydride group content: 13 mmol) obtained in the second stage described in (ii) above and 250 g of toluene were placed in a glass flask fitted with a reflux condenser tube, a thermometer and a stirrer, the temperature was increased to 110 C., and the materials in the flask were completely dissolved. Next, a solution obtained by dissolving 30 g (30.0 mmol, corresponding to 30 parts by mass relative to 100 parts by mass of the propylene-based polymer) of a poly(oxyethylene/oxypropylene) block copolymer (molecular weight 1000) in 22.5 g of toluene was added to the flask, and a reaction was carried out for 3 hours at 110 C.

[0141] After cooling, 115 g of a yellow polymer was obtained by distilling off the toluene under reduced pressure. When the thus obtained product was subjected to infrared absorption spectrum analysis, a peak at approximately 1784 cm.sup.1, which was attributable to maleic anhydride, had disappeared, and it was confirmed that the maleic anhydride-modified propylene-based polymer was bonded to a polyether. A graft copolymer was formed in which a polyether was graft-bonded to the maleic anhydride-modified propylene-based polymer. 160 g of tetrahydrofuran (THF) was added to 40 g of the obtained modified polymer, and the modified polymer was completely dissolved at 65 C. A semi-transparent pale yellow solution was obtained by adding 200 g of pure water dropwise over a period of 1 hour at the same temperature. Semitransparent pale yellow polyolefin resin aqueous dispersion P-1 was obtained by cooling this solution to 50 C., gradually reducing the pressure by altering the degree of vacuum from 0.03 MPa to 0.0045 MPa, and distilling off THF and water under reduced pressure until the solid resin content reached 30%.

[0142] Moreover, the poly(oxyethylene/oxypropylene) block copolymer used in the present working example had an insoluble component content of 1 mass % or less when dissolved at a concentration of 10 mass % in water at 25 C., and was a hydrophilic polymer.

Production Example 2

Production of Aqueous Primer Coating Composition WP-1

[0143] Aqueous primer coating composition WP-1 was produced by adding 1.66 parts of electrically conductive carbon black Printex XE2B (manufactured by Degussa), 12.55 parts of titanium dioxide JR600-E (manufactured by Tayca Corp.) and 0.93 parts of a pigment dispersing agent Disperbyk 191 (manufactured by BYK Chemie, solid content 98%, acid value 31 mg KOH/g, amine value 20 mg KOH/g) to 26.5 parts of a polyurethane resin Impranil DLU (manufactured by Covestro Japan Ltd., solid resin content 60%, Tg 83 C., elongation percentage 800%), dispersing these components by means of a disperser, adding 21.0 parts of non-chlorinated polyolefin resin aqueous dispersion P-1, 1.5 parts of a curing agent DURANATE WM4 4-L70G (a water-dispersed blocked polyisocyanate compound manufactured by Asahi Kasei Chemicals Corporation, solid resin content 70%), 33.96 parts of deionized water, 0.8 parts of a leveling agent BYK-348 (manufactured by BYK Chemie) and 1.1 parts of a thickening agent Rheovis AS S130 (manufactured by BASF, solid content 30%), mixing in a dissolver and adjusting the pH to 7-8 by means of dimethylethanolamine.

Production Example 3

Production of Aqueous Primer Coating Compositions WP-2 to WP-18

[0144] Aqueous primer coating compositions WP-2 to WP-18 were obtained on the basis of the formulations shown in Table 1, using the same method as that used in Production Example 2.

TABLE-US-00001 TABLE 1 Aqueous primer coating composition WP-1 WP-2 WP-3 WP-4 WP-5 A: Polyolefin Non-chlorinated 21 21 21 21 21 resin polyolefin resin aqueous dispersion P-1 B: Impranil DLU 26.5 Polyurethane Acrit WBR-2181 (*1) 48.18 resin Permarin UA-150 (*2) 53 Ucoat DA-100 (*3) 45.43 Takelac W6061 (*4) 53 Bayhydrol UH2952/1 (*5) Lacstar 5215A (*6) C: Curing Duranate WM44-L70G 1.5 1.5 1.5 1.5 1.5 agent Mycoat 775 (*7) D: Printex XE2B 1.66 1.66 1.66 1.66 1.66 Electrically conductive carbon Titanium JR600-E 12.55 12.55 12.55 12.55 12.55 dioxide Pigment Disperbyk 191 0.93 0.93 0.93 0.93 0.93 dispersing agent Leveling agent BYK-348 0.8 0.8 0.8 0.8 0.8 Thickening Rheovis AS S130 1.1 1.1 1.1 1.1 1.1 agent Deionized water 33.96 12.28 7.46 15.03 7.46 Total 100 100 100 100 100 A: Polyolefin Melting point ( C.) 80 80 80 80 80 resin Weight average 120,000 120,000 120,000 120,000 120,000 molecular weight B: Glass transition 83 89 87 80 78 Polyurethane temperature ( C.) resin Elongation percentage 800 700 600 500 1000 (%) A/B 28/72 28/72 28/72 28/72 28/72 C/(A + B) 5/100 5/100 5/100 5/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 7/93 Aqueous primer coating composition WP-6 WP-7 WP-8 WP-9 A: Polyolefin Non-chlorinated 21 21 21 14.8 resin polyolefin resin aqueous dispersion P-1 B: Impranil DLU 26.5 29.6 Polyurethane Acrit WBR-2181 (*1) resin Permarin UA-150 (*2) Ucoat DA-100 (*3) Takelac W6061 (*4) Bayhydrol UH2952/1 39.75 (*5) Lacstar 5215A (*6) 33.61 C: Curing Duranate WM44-L70G 1.5 1.5 1.5 agent Mycoat 775 (*7) 2 D: Printex XE2B 1.66 1.66 1.66 1.66 Electrically conductive carbon Titanium JR600-E 12.55 12.55 12.55 12.55 dioxide Pigment Disperbyk 191 0.93 0.93 0.93 0.93 dispersing agent Leveling agent BYK-348 0.8 0.8 0.8 0.8 Thickening Rheovis AS S130 1.1 1.1 1.1 1.1 agent Deionized water 20.71 26.85 33.46 37.06 Total 100 100 100 100 A: Polyolefin Melting point ( C.) 80 80 80 80 resin Weight average 120,000 120,000 120,000 120,000 molecular weight B: Glass transition 49 60 83 83 Polyurethane temperature ( C.) resin Elongation percentage 530 250 800 800 (%) A/B 28/72 28/72 28/72 20/80 C/(A + B) 5/100 5/100 6/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 Aqueous primer coating composition WP-10 WP-11 WP-12 WP-13 WP-14 A: Polyolefin Non-chlorinated 29.6 59.2 62.9 21 21 resin polyolefin resin aqueous dispersion P-1 B: Impranil DLU 22.2 7.4 5.55 26.5 26.5 Polyurethane Acrit WBR-2181 (*1) resin Permarin UA-150 (*2) Ucoat DA-100 (*3) Takelac W6061 (*4) Bayhydrol UH2952/1 (*5) Lacstar 5215A (*6) C: Curing Duranate WM44-L70G 1.5 1.5 1.5 0.32 3.1 agent Mycoat 775 (*7) D: Printex XE2B 1.66 1.66 1.66 1.66 1.66 Electrically conductive carbon Titanium JR600-E 12.55 12.55 12.55 12.55 12.55 dioxide Pigment Disperbyk 191 0.93 0.93 0.93 0.93 0.93 dispersing agent Leveling agent BYK-348 0.8 0.8 0.8 0.8 0.8 Thickening Rheovis AS S130 1.1 1.1 1.1 1.1 1.1 agent Deionized water 29.66 14.86 13.01 35.14 32.36 Total 100 100 100 100 100 A: Polyolefin Melting point ( C.) 80 80 80 80 80 resin Weight average 120,000 120,000 120,000 120,000 120,000 molecular weight B: Glass transition 83 83 83 83 83 Polyurethane temperature ( C.) resin Elongation percentage 800 800 800 800 800 (%) A/B 40/60 80/20 85/15 28/72 28/72 C/(A + B) 5/100 5/100 5/100 1/100 10/100 D/(A + B + C) 7/93 7/93 7/93 7/93 7/93 Aqueous primer coating composition WP-15 WP-16 WP-17 WP-18 A: Polyolefin Non-chlorinated 18.3 21 21 21 resin polyolefin resin aqueous dispersion P-1 B: Impranil DLU 21.5 26.5 26.5 26.5 Polyurethane Acrit WBR-2181 (*1) resin Permarin UA-150 (*2) Ucoat DA-100 (*3) Takelac W6061 (*4) Bayhydrol UH2952/1 (*5) Lacstar 5215A (*6) C: Curing Duranate WM44-L70G 7.8 1.5 1.5 1.5 agent Mycoat 775 (*7) D: Printex XE2B 1.66 0.47 3.21 5 Electrically conductive carbon Titanium JR600-E 12.55 3.55 24.27 37.65 dioxide Pigment Disperbyk 191 0.93 0.26 1.8 2.5 dispersing agent Leveling agent BYK-348 0.8 0.8 0.8 0.8 Thickening Rheovis AS S130 1.1 1.1 1.1 1.1 agent Deionized water 25.95 44.82 19.82 3.95 Total 90.59 100 100 100 A: Polyolefin Melting point ( C.) 80 80 80 80 resin Weight average 120,000 120,000 120,000 120,000 molecular weight B: Glass transition 83 83 83 83 Polyurethane temperature ( C.) resin Elongation percentage 800 800 800 800 (%) A/B 30/70 28/72 28/72 28/72 C/(A + B) 30/100 5/100 5/100 5/100 D/(A + B + C) 7/93 2/98 14/86 22/78

[0145] Details of blending components shown in Table 1 are as follows. [0146] (*1) Acrit WBR-2181 (manufactured by Taisei Fine Chemical Co,. Ltd., solid resin content 33%, Tg 89 C., elongation percentage 700%) [0147] (*2) Permarin UA-150 (manufactured by Sanyo Chemical Industries, Ltd., solid resin content 30%, Tg 87 C., elongation percentage 600%) [0148] (*3) Ucoat DA-100 (manufactured by Sanyo Chemical Industries, Ltd., solid resin content 35%, Tg 80 C., elongation percentage 500%) [0149] (*4) Takelac W6061 (manufactured by Mitsui Chemicals, Inc., solid resin content 30%, Tg 78 C., elongation percentage 1000%) [0150] (*5) Bayhydrol UH2952/1 (manufactured by Covestro Japan Ltd., solid resin content 40%, Tg 49 C., elongation percentage 530%) [0151] (*6) Lacstar 5215A (manufactured by DIC Corp., solid resin content 47.3%, Tg 60 C., elongation percentage 250%) [0152] (*7) Mycoat 775 (melamine resin, manufactured by Allnex Japan, Inc., solid resin content 70%)

Production Example 4

Production of Polyester Resin Varnish PA-1

[0153] 54.0 parts of a dimer acid (product name EMPOL 1008, manufactured by Cognis Corporation, number of carbon atoms: 36), 8.0 parts of neopentyl glycol, 17.8 parts of isophthalic acid, 19.4 parts of 1,6-hexane diol and 0.8 parts of trimethylolpropane were placed in a reaction vessel equipped with a reflux condensing tube, to which a reaction water separation tube was fitted, a nitrogen gas introduction device, a thermometer and a stirring device, the temperature was increased to 120 C. so as to dissolve the raw materials, and the temperature was then increased to 160 C. while stirring the contents of the reaction vessel. The temperature was held at 160 C. for 1 hour, and then gradually increased to 230 C. over a period of 5 hours. Polyester resin varnish PA-1, which had a solid resin content of 74.6%, a hydroxyl value of 62 mg KOH/g, an acid value of 4 mg KOH/g and a number average molecular weight of 1800, was obtained by allowing a reaction to continue while maintaining a temperature of 230 C., cooling to a temperature of 80 C. or lower when the resin acid value reached 4 mg KOH/g, and then adding 31.6 parts of methyl ethyl ketone.

Production Example 5

Production of Polyurethane Resin WB-1

[0154] 78.3 parts of polyester resin solution PA-1, 7.8 parts of dimethylolpropionic acid, 1.4 parts of neopentyl glycol and 40.0 parts of methyl ethyl ketone were placed in a reaction vessel equipped with a nitrogen gas introduction device, a thermometer and a stirring device, the temperature was increased to 80 C. while stirring the contents of the reaction vessel, 27.6 parts of isophorone diisocyanate was added, and the components were allowed to react while maintaining a temperature of 80 C. When the isocyanate value reached 0.43 meq/g, 4.8 parts of trimethylolpropane was added, and the reaction was allowed to continue at a temperature of 80 C. In addition, when the isocyanate value reached 0.01 meq/g, 33.3 parts of butyl cellosolve was added and the reaction was terminated. Next, the temperature was increased to 100 C. and methyl ethyl ketone was removed under reduced pressure. Polyurethane resin WB-1, which had a solid resin content of 35.0%, a hydroxyl value of 40 mg KOH/g, an acid value of 35 mg KOH/g and a number average molecular weight of 4900, was obtained by lowering the temperature to 50 C., adding 4.4 parts of dimethylethanolamine so as to neutralize acid groups, and adding 147.9 parts of deionized water.

Production Example 6

Production of Core/Shell Emulsion WC-1

[0155] 46.4 parts of polyurethane resin WB-1 and 33.1 parts of deionized water were placed in a reaction vessel equipped with a nitrogen gas introduction device, a thermometer, an addition funnel and a stirring device, the temperature was increased to 85 C. while stirring the contents of the reaction vessel, and a homogeneous mixture comprising 4.9 parts of styrene, 4.5 parts of methyl methacrylate, 3.9 parts of n-butyl acrylate, 3.0 parts of 2-hydroxyethyl methacrylate, 3.8 parts of propylene glycol monomethyl ether and 0.24 parts of the polymerization initiator t-butylperoxy-2-ethyl hexanoate as dropwise addition components was added dropwise at constant speed over a period of 3.5 hours using the addition funnel. Following completion of the dropwise addition, core/shell emulsion resin WC-1, which had a solid resin content of 32.5%, was obtained by maintaining a temperature of 85 C. for 1 hour, adding a polymerization initiator solution obtained by dissolving 0.03 parts of the polymerization initiator t-butylperoxy-2-ethylhexanoate in 0.14 parts of propylene glycol monomethyl ether as an additional catalyst, and terminating the reaction after maintaining a temperature of 85 C. for a further 1 hour. The acrylic resin of the core had a hydroxyl value of 80 mg KOH/g and an acid value of 0 mg KOH/g.

Production Example 7

Production of Aqueous First Colored Coating Composition WD-1

[0156] Using aqueous polyurethane resin WB-1 as a dispersing resin, a pigment paste was prepared by dispersing 33.8 parts of titanium dioxide (product name Ti-Pure R706, manufactured by DuPont) and 0.4 parts of carbon black (product name MA-100, manufactured by Mitsubishi Chemical Corp.) in a motor mill.

[0157] Next, a resin base was prepared by mixing 25.5 parts of core/shell emulsion WC-1, aqueous polyurethane resin WB-1 and 5.9 parts of an aqueous acrylic resin (product name SETAQUA 6511, manufactured by Nuplex Resins, acid value 8 mg KOH/g, hydroxyl value 138 mg KOH/g, glass transition temperature 12 C., solid resin content 47%) in a dissolver, and this resin base was added to the previously prepared pigment paste and mixed. Finally, aqueous first colored coating composition WD-1 was obtained by adding and mixing 6.6 parts of a polyisocyanate (product name Bayhydur 3100, manufactured by Sumika Bayer Urethane Co., Ltd., solid resin content 100%, NCO content 17.5%). Moreover, the content of aqueous polyurethane resin WB-1 in aqueous first colored coating composition WD-1 was 47.4 parts.

Production Example 8

Production of Aqueous First Colored Coating Composition WD-2

[0158] Aqueous first colored coating composition WD-2 was obtained on the basis of the formulation shown in Table 2, using the same method as that used in Production Example 7.

TABLE-US-00002 TABLE 2 Aqueous first colored coating composition WD-1 WD-2 Core/shell emulsion WC-1 (solid resin content 32.5%) 25.5 25.5 Aqueous polyurethane resin WB-1 (solid resin content 47.4 47.4 35.0%) Aqueous acrylic resin (solid resin content 47.0%) 5.9 5.9 Polyisocyanate (*8) 6.6 Polycarbodiimide compound (*9) 12.8 Titanium dioxide (*10) 33.8 32.4 Carbon black (*11) 0.4 0.4 Total 119.6 124.4 Core/shell emulsion 30% 30% Aqueous polyurethane resin 60% 60% Aqueous acrylic resin 10% 10% NCO/OH (molar ratio) 1.0 NCN/COOH (molar ratio) 1.0 P/B 1.0 1.0

Production Example 9

Production of Aqueous Second Colored Coating Composition WE-1

[0159] Using aqueous polyurethane resin WB-1 as a dispersing resin, a pigment paste was prepared by dispersing 4.0 parts of carbon black (product name MA-100, manufactured by Mitsubishi Chemical Corp.) in a motor mill.

[0160] Next, a resin base was prepared by mixing 25.5 parts of core/shell emulsion WC-1, aqueous polyurethane resin WB-1 and 5.9 parts of an aqueous acrylic resin (product name SETAQUA 6511, manufactured by Nuplex Resins, acid value 8 mg KOH/g, hydroxyl value 138 mg KOH/g, glass transition temperature 12 C., solid resin content 47%) in a dissolver, and this resin base was added to the previously prepared pigment paste and mixed. Finally, aqueous second colored coating composition WE-1 was obtained by adding and mixing 16.9 parts of a melamine resin (product name Mycoat 775, manufactured by Allnex Japan, Inc., solid resin content 70%). Moreover, the content of aqueous polyurethane resin WB-1 in aqueous second colored coating composition WE-1 was 47.4 parts.

Production Example 10

Production of Aqueous Second Colored Coating Compositions WE-2 to WE-7

[0161] Aqueous second colored coating compositions WE-2 to WE-7 were obtained on the basis of the formulations shown in Table 3, using the same method as that used in Production Example 9.

TABLE-US-00003 TABLE 3 Aqueous second colored coating composition WE-1 WE-2 WE-3 WE-4 WE-5 WE-6 WE-7 Core/shell emulsion WC-1 (solid resin content 32.5%) 25.5 25.5 25.5 25.5 25.5 25.5 25.5 Aqueous polyurethane resin WB-1 (solid resin content 35.0%) 47.4 47.4 47.4 47.4 47.4 47.4 47.4 Aqueous acrylic resin (solid resin content 47.0%) 5.9 5.9 5.9 5.9 5.9 5.9 5.9 Melamine resin (*7) 16.9 39.5 9.9 4.4 Polyisocyanate (*8) 6.6 Polycarbodiimide compound (*9) 12.8 Carbon black (*11) 4.0 5.0 3.5 3.0 2.5 2.4 2.1 Total 99.7 123.3 92.2 86.2 87.9 94.0 80.9 Core/shell emulsion 30% 30% 30% 30% 30% 30% 30% Aqueous polyurethane resin 60% 60% 60% 60% 60% 60% 60% Aqueous acrylic resin 10% 10% 10% 10% 10% 10% 10% NCO/OH (molar ratio) 1.0 NCN/COOH (molar ratio) 1.0 Base resin/melamine resin (solid content mass ratio) 2.3 1.0 4.0 9.0 P/B 0.1 0.1 0.1 0.1 0.1 0.1 0.1

[0162] Details of blending components shown in Tables 2-3 are as follows. [0163] (*7) Melamine resin (product name Mycoat 775, manufactured by Allnex Japan, Inc., solid resin content 70%) [0164] (*8) Polyisocyanate (product name Bayhydur 3100, manufactured by Sumika Bayer Urethane Co., Ltd., NCO 17.5%) [0165] (*9) Polycarbodiimide (product name Carbodilite V-02-L2, manufactured by Nisshinbo Chemical Inc., NCN 4.15%) (*10) Titanium dioxide (product name Ti-Pure R706, manufactured by DuPont) [0166] (*11) Carbon black (product name MA-100, manufactured by Mitsubishi Chemical Corp.)

Production Example 11

Production of Clear Coating Composition CC-1

(i) Production of Acrylic Resin Solution CA-1 for Clear Coating

[0167] 5 parts of Solvesso 100 was placed in a four-mouthed flask equipped with a thermometer, a reflux condenser, a stirrer and an addition funnel, and the flask was heated and maintained at a temperature of 140 C. while stirring the Solvesso 100 in a nitrogen stream. Next, 7.8 parts of styrene, 0.2 parts of n-butyl methacrylate, 6.3 parts of 2-ethylhexyl acrylate, 1 part of isobutyl methacrylate, 14.1 parts of 2-hydroxyethyl methacrylate, 0.2 parts of hydroxypropyl methacrylate, 4.4 parts of 2-ethylhexyl methacrylate, 6.9 parts of cyclohexyl methacrylate, 0.2 parts of n-butyl acrylate, 0.4 parts of acrylic acid and 20.5 parts of t-butyl methacrylate were homogeneously mixed and used as monomer components added dropwise. Meanwhile, 2 parts of Solvesso 100 was homogeneously mixed under stirring with 3.6 parts of Perbutyl Z (t-butylperoxy benzoate, manufactured by NOF Corp. and used as an initiator component added dropwise. The monomer components added dropwise and initiator component added dropwise were placed in separate addition funnels, and simultaneously added dropwise at the same rate over a period of 4 hours. Following completion of the dropwise addition, the same temperature was maintained for a period of 1 hour, after which a solution obtained by stirring and homogeneously mixing 1 part of Solvesso 100 and 0.1 parts of Perbutyl Z, was separated into several portions, which were added dropwise within a period of 30 minutes. Next, acrylic resin solution CA-was obtained by terminating the reaction once a temperature of 140 C. had been maintained for a further 1 hour and then using 16.1 parts of xylene, 6.4 parts of methoxypropyl acetate and 3.8 parts of butyl acetate as thinning agents. Acrylic resin CA-1 had a solid resin content of 62%, a hydroxyl value of 100 mg KOH/g, an acid value of 5 mg KOH/g and a weight average molecular weight of 3,500.

(ii) Production of Acrylic Resin Solutions CA-2 to CA-4 for Clear Coating

[0168] Acrylic resin solutions CA-2 to CA-4 for clear coating were obtained on the basis of the formulations shown in Table 4, using the same method as that used in Production Example 11 (i).

TABLE-US-00004 TABLE 4 Acrylic resin solution for clear coating CA-1 CA-2 CA-3 CA-4 Styrene 7.8 4.6 9.2 6 n-butyl methacrylate 0.2 1.7 6.2 2-ethylhexyl acrylate 6.3 15.4 Isobutyl methacrylate 1 1.2 11.1 4-hydroxybutyl acrylate 20.9 2-hydroxyethyl methacrylate 14.1 16.8 25.7 Hydroxypropyl methacrylate 0.2 Methyl methacrylate 6 2-ethylhexyl methacrylate 4.4 2.4 20 Cyclohexyl methacrylate 6.9 12 n-Butyl acrylate 0.2 Acrylic acid 0.4 0.9 0.9 0.6 t-butyl methacrylate 20.5 12.1 -caprolactone 11.3 Perbutyl Z 3.7 4.2 4.5 1.2 Xylene 16.1 6.3 7.7 Solvesso 100 8 20.5 7 Methoxypropyl acetate 6.4 31.1 Butyl acetate 3.8 6 26.5 Total 100 100 100 100 Solid resin content (%) 62 63 62 60 Hydroxyl value (mg KOH/g) 100 120 180 140 Acid value (mg KOH/g) 5 4.5 6 3.5 Weight average molecular weight 3500 4500 5500 5500
(iii) Production of Clear Coating Composition CC-1

[0169] 80 parts of acrylic resin solution CA-1 was placed in a vessel equipped with a stirrer, 8 parts of Solvesso 100 (manufactured by Exxon Mobile, aromatic naphtha), 3 parts of xylene, 0.1 parts of BYK-300 (manufactured by BYK, surface modifier, 10 mass % xylene solution), 2.5 parts of Tinuvin 292 (manufactured by Ciba Specialty Chemicals, photostabilizer, 20 mass % xylene solution) and 5 parts of Tinuvin 900 (manufactured by Ciba Specialty Chemicals, ultraviolet radiation absorber, 20 mass % xylene solution) were placed in the vessel in that order while being stirred, and homogeneously mixed. Next, 1 part of Flownon SH-290 (manufactured by Kyoeisha Chemical Co., Ltd., viscosity-adjusting agent, 10 mass % xylene solution), 0.4 parts of Neostann U-100 (manufactured by Johoku Chemical Co., Ltd., isocyanate curing catalyst, 1 mass % xylene solution) and 6 parts of a melamine resin (product name U-VAN225, manufactured by Mitsui Chemicals, Inc., solid resin content 60%) were added in that order while being stirred and then thoroughly stirred so as to obtain a homogeneous mixture. Clear coating composition CC-1 was obtained by charging and stirring 40 parts of Duranate THA-100 (manufactured by Asahi Kasei Corp. HMDI-based nurate type polyisocyanate curing agent, solid resin content 75%, NCO content 23.1%) and 15 parts of a mixed solvent comprising Solvesso 100/butyl acetate/propylene glycol monomethyl ether acetate (blending ratio: 60/20/20) relative to 100 parts of the obtained mixture immediately before use, and stirring until sufficiently homogenized.

(iv) Production of Clear Coating Compositions CC-2 to CC-8

[0170] Clear coating compositions CC-2 to CC-8 were obtained on the basis of the formulations shown in Table 5, using the same method as that used in Production Example 11 (iii).

TABLE-US-00005 TABLE 5 Clear coating composition CC-1 CC-2 CC-3 CC-4 CC-5 CC-6 CC-7 CC-8 Acrylic resin 80 80 80 80 80 solution CA-1 (62%)* Acrylic resin 93.1 solution CA-2 (63%)* Acrylic resin 80.1 solution CA-3 (62%)* Acrylic resin 84.4 solution CA-4 (60%)* Aromatic 8 8 8 8 8 8 8 8 naphtha Xylene 3 3 3 3 3 3 3 3 Surface 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 modifier Photostabilizer 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Ultraviolet 5 5 5 5 5 5 5 5 radiation absorber Viscosity- 1 1 1 1 1 1 1 1 adjusting agent Curing catalyst 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Melamine resin 6 1.5 9 10 Subtotal 106 100 101.5 109 110 113.1 100.1 104.4 Polyisocyanate 40 40 40 40 40 40 40 40 Mixed solvent 15 15 15 15 15 15 15 15 Total 161 155 156.5 164 165 168.1 155.1 159.4 Glass 84 82 82 84 85 66 71 96 transition temperature ( C.) of clear coating film Elongation 2.9 3.5 3.1 2 1.5 5.4 3 1.8 percentage (%) of clear coating film *The numbers in brackets indicate solid resin content

Working Example 1

[0171] A cationic electrodeposition coating material (product name Cathoguard No. 500 manufactured by BASF Japan

[0172] Ltd.) was electrodeposited on a zinc phosphate-treated mild steel sheet so as to have a dried film thickness of 20 m, and then baked for 25 minutes at 175 C. so as to obtain an electrodeposition film sheet used for the present evaluation (hereinafter referred to as the electrodeposited sheet). In addition, a polypropylene base material SP-853 whose surface had been wiped with isopropyl alcohol was used as a plastic base material.

[0173] Aqueous primer coating composition WP-1 was coated on the electrodeposited sheet and the polypropylene base material so as to have a dried film thickness of 6-8 m. The electrodeposited sheet and polypropylene base material were then allowed to stand at room temperature for 5 minutes, after which the first aqueous base coating composition WD-1 was coated so as to have a dried film thickness of 20 m. The electrodeposited sheet and polypropylene base material were then allowed to stand at room temperature for 5 minutes, after which the second aqueous base coating composition WE-1 was coated so as to have a dried film thickness of 12 m. Following the coating, the electrodeposited sheet and polypropylene base material were then allowed to stand at room temperature for 5 minutes, and then pre-heated for 5 minutes at 80 C. After allowing the electrodeposited sheet and polypropylene base material to cool to room temperature, clear coating composition CC-1 was coated so as to have a dried film thickness of 30 m. Following the coating, the electrodeposited sheet and polypropylene base material were then allowed to stand at room temperature for 10 minutes and then baked for 30 minutes at 80 C. so as to obtain evaluation sheets.

[0174] The obtained evaluation sheets were subjected to the following coating film performance evaluations.

(Coating Film Appearance)

[0175] Each obtained evaluation sheet was evaluated visually in terms of coating film appearance according to the following criteria. [0176] : Smoothness, glossiness and clarity all good. [0177] : Smoothness, glossiness or clarity somewhat poor. [0178] : Smoothness, glossiness or clarity extremely poor.

(Adhesive Properties)

[0179] Using a knife, 11 vertical and horizontal cuts were made in each obtained evaluation sheet so as to obtain 100 grid cells measuring 2 mm2 mm, cellophane tape was strongly bonded to the evaluation sheet, and the number of grid cells in which the coating film remained without becoming detached when the cellophane tape was peeled off in a single movement was evaluated according to the following criteria. [0180] : No detachment of coating film (100/100 grid cells). [0181] : Partial detachment of coating film (95-99/100 grid cells). [0182] : Major detachment of coating film (0-94/100 grid cells).

(Moisture Resistance)

[0183] Each obtained evaluation sheet was allowed to stand for 240 hours in a constant-temperature constant-humidity chamber at a temperature of 50 C. and a humidity of 95%. After being allowed to stand in the chamber, the coated sheets were removed from the chamber and investigated in terms of coating film appearance abnormalities and degree of swelling. In addition, 2 hours after removing the sheets from the chamber, the sheets were evaluated in terms of adhesive properties following a moisture resistance test using the same method as that described above for evaluating adhesive properties. Coating film appearance following a moisture resistance test was evaluated according to the following criteria. [0184] : No abnormalities on coating film. [0185] : Minor protrusions or appearance abnormalities on coating film. [0186] : Swelling or significant appearance abnormalities on coating film.

[0187] In addition, adhesive properties following a moisture resistance test were evaluated in the same way as that described above for evaluating adhesive properties.

(Chipping Resistance)

[0188] A test piece-holding stand of a JA-400 gravel chipping test instrument (chipping tester) manufactured by Suga Test Instruments Co., Ltd. was fixed at a right angle to a stone blower port, each of the obtained evaluation sheets was fixed to the test piece-holding stand, 50 g of granite gravel having a grain size of No. 7 was blown at the coating film at 20 C. using 0.4 MPa compressed air, and the degree of chipping of the coating film by the gravel was observed visually and evaluated according to the following criteria. [0189] : The chip size was very small, with defects appearing on the top coat. [0190] : The chip size was small, with aqueous coating materials (the compositions used in the present invention) exposed. [0191] : The chip size was small, but the steel sheet was exposed. [0192] : The chip size was somewhat large, and the steel sheet was significantly exposed.

(Low Temperature Impact Resistance)

[0193] Each evaluation sheet was allowed to stand for 3 hours or more in a constant temperature chamber held in advance at a temperature of 30 C. Within 5 seconds of being removed from the chamber, each evaluation sheet was placed with the coating film facing upwards on a support base of a DuPont impact deformation testing machine specified in JIS K5600 5-3. An impact shaft having a hemispherical tip was placed on the evaluation sheet, after which a weight of 1 kg was dropped onto the impact shaft from a height of 70 cm. A total of three or more tests were carried out, once per evaluation sheet, and cases where 67% or more of the evaluation sheets did not have cracks that passed through the base material and did not undergo coating film detachment were deemed to have withstood the impact. [0194] : 67-100% [0195] : <67%

Working Examples 2-25, Comparative Examples 1-4

[0196] Evaluation sheets were prepared using the aqueous primer coating compositions, aqueous first colored coating compositions, aqueous second colored coating compositions and clear coating compositions shown in Tables 6-7 using the same method as that used in working example 1, and subjected to the coating film performance evaluations. The coating film performance evaluation results are also shown in Tables 6-7.

TABLE-US-00006 TABLE 6 Working Working Working Working Working Example Example Example Example Example 1 2 3 4 5 Aqueous primer coating composition WP-1 WP-2 WP-3 WP-4 WP-5 Aqueous first colored coating composition WD-1 WD-1 WD-1 WD-1 WD-1 Aqueous second colored coating composition WE-1 WE-1 WE-1 WE-1 WE-1 Clear coating composition CC-1 CC-1 CC-1 CC-1 CC-1 Composition of aqueous primer coating A: Polyolefin Melting point ( C.) 80 80 80 80 80 resin Weight average molecular 120,000 120,000 120,000 120,000 120,000 weight B: Polyurethane Glass transition 83 89 87 80 78 resin temperature ( C.) Elongation percentage 800 700 600 500 1000 (%) Composition A/B 28/72 28/72 28/72 28/72 28/72 C/(A + B) 5/100 5/100 5/100 5/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 7/93 Glass transition temperature ( C.) of 84 84 84 84 84 clear coating film Elongation percentage (%) of clear 2.9 2.9 2.9 2.9 2.9 coating film Coating film quality Base material: Coating film appearance Electrodeposited Adhesion sheet Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Base material: Coating film appearance Polypropylene Adhesion Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Working Working Working Working Example Example Example Example 6 7 8 9 Aqueous primer coating composition WP-8 WP-9 WP-10 WP-11 Aqueous first colored coating composition WD-1 WD-1 WD-1 WD-1 Aqueous second colored coating composition WE-1 WE-1 WE-1 WE-1 Clear coating composition CC-1 CC-1 CC-1 CC-1 Composition of aqueous primer coating A: Polyolefin Melting point ( C.) 80 80 80 80 resin Weight average molecular 120,000 120,000 120,000 120,000 weight B: Polyurethane Glass transition 83 83 83 83 resin temperature ( C.) Elongation percentage 800 800 800 800 (%) Composition A/B 28/72 20/80 40/60 80/20 C/(A + B) 6/100 5/100 5/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 Glass transition temperature ( C.) of 84 84 84 84 clear coating film Elongation percentage (%) of clear 2.9 2.9 2.9 2.9 coating film Coating film quality Base material: Coating film appearance Electrodeposited Adhesion sheet Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Base material: Coating film appearance Polypropylene Adhesion Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Working Working Working Working Working Example Example Example Example Example 10 11 12 13 14 Aqueous primer coating composition WP-12 WP-13 WP-14 WP-15 WP-16 Aqueous first colored coating composition WD-1 WD-1 WD-1 WD-1 WD-1 Aqueous second colored coating composition WE-1 WE-1 WE-1 WE-1 WE-1 Clear coating composition CC-1 CC-1 CC-1 CC-1 CC-1 Composition of aqueous primer coating A: Polyolefin Melting point ( C.) 80 80 80 80 80 resin Weight average molecular 120,000 120,000 120,000 120,000 120,000 weight B: Polyurethane Glass transition 83 83 83 83 83 resin temperature ( C.) Elongation percentage (%) 800 800 800 800 800 Composition A/B 85/15 28/72 28/72 30/70 28/72 C/(A + B) 5/100 1/100 10/100 30/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 2/98 Glass transition temperature ( C.) of clear 84 84 84 84 84 coating film Elongation percentage (%) of clear coating 2.9 2.9 2.9 2.9 2.9 film Coating film quality Base material: Coating film appearance Electrodeposited Adhesion sheet Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Base material: Coating film appearance Polypropylene Adhesion Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Working Working Working Working Example Example Example Example 15 16 17 18 Aqueous primer coating composition WP-17 WP-18 WP-1 WP-1 Aqueous first colored coating composition WD-1 WD-1 WD-2 WD-1 Aqueous second colored coating composition WE-1 WE-1 WE-1 WE-2 Clear coating composition CC-1 CC-1 CC-1 CC-1 Composition of aqueous primer coating A: Polyolefin Melting point ( C.) 80 80 80 80 resin Weight average molecular 120,000 120,000 120,000 120,000 weight B: Polyurethane Glass transition 83 83 83 83 resin temperature ( C.) Elongation percentage (%) 800 800 800 800 Composition A/B 28/72 28/72 28/72 28/72 C/(A + B) 5/100 5/100 5/100 5/100 D/(A + B + C) 14/86 22/78 7/93 7/93 Glass transition temperature ( C.) of clear 84 84 84 84 coating film Elongation percentage (%) of clear coating 2.9 2.9 2.9 2.9 film Coating film quality Base material: Coating film appearance Electrodeposited Adhesion sheet Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Base material: Coating film appearance Polypropylene Adhesion Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Working Working Working Working Working Example Example Example Example Example 19 20 21 22 23 Aqueous primer coating composition WP-1 WP-1 WP-1 WP-1 WP-1 Aqueous first colored coating composition WD-1 WD-1 WD-1 WD-1 WD-1 Aqueous second colored coating composition WE-3 WE-4 WE-5 WE-6 WE-7 Clear coating composition CC-1 CC-1 CC-1 CC-1 CC-1 Composition of aqueous primer coating A: Polyolefin Melting point ( C.) 80 80 80 80 80 resin Weight average molecular 120,000 120,000 120,000 120,000 120,000 weight B: Polyurethane Glass transition 83 83 83 83 83 resin temperature ( C.) Elongation percentage (%) 800 800 800 800 800 Composition A/B 28/72 28/72 28/72 28/72 28/72 C/(A + B) 5/100 5/100 5/100 5/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 7/93 Glass transition temperature ( C.) of clear 84 84 84 84 84 coating film Elongation percentage (%) of clear coating 2.9 2.9 2.9 2.9 2.9 film Coating film quality Base material: Coating film appearance Electrodeposited Adhesion sheet Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Base material: Coating film appearance Polypropylene Adhesion Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Working Working Working Working Example Example Example Example 24 25 26 27 Aqueous primer coating composition WP-1 WP-1 WP-1 WP-1 Aqueous first colored coating composition WD-1 WD-1 WD-1 WD-1 Aqueous second colored coating composition WE-1 WE-1 WE-1 WE-1 Clear coating composition CC-4 CC-5 CC-7 CC-8 Composition of aqueous primer coating A: Polyolefin Melting point ( C.) 80 80 80 80 resin Weight average molecular 120,000 120,000 120,000 120,000 weight B: Polyurethane Glass transition 83 83 83 83 resin temperature ( C.) Elongation percentage (%) 800 800 800 800 Composition A/B 28/72 28/72 28/72 28/72 C/(A + B) 5/100 5/100 5/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 Glass transition temperature ( C.) of clear 84 85 71 96 coating film Elongation percentage (%) of clear coating 2 1.5 3 1.8 film Coating film quality Base material: Coating film appearance Electrodeposited Adhesion sheet Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance Base material: Coating film appearance Polypropylene Adhesion Moisture resistance (coating film appearance) Moisture resistance (adhesion) Chipping resistance

TABLE-US-00007 TABLE 7 Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Aqueous primer coating composition WP-6 WP-7 WP-1 WP-1 WP-1 Aqueous first colored coating composition WD-1 WD-1 WD-1 WD-1 WD-1 Aqueous second colored coating composition WE-1 WE-1 WE-1 WE-1 WE-1 Clear coating composition CC-1 CC-1 CC-2 CC-3 CC-6 Composition of aqueous primer coating A: Polyolefin Melting point ( C.) 80 80 80 80 80 resin Weight average 120,000 120,000 120,000 120,000 120,000 molecular weight B: Polyurethane Glass transition 49 60 83 83 83 resin temperature ( C.) Elongation percentage 530 250 800 800 800 (%) Composition A/B 25/75 25/75 28/72 28/72 28/72 C/(A + B) 5/100 5/100 5/100 5/100 5/100 D/(A + B + C) 7/93 7/93 7/93 7/93 7/93 Glass transition temperature ( C.) of 84 84 82 82 66 clear coating film Elongation percentage (%) of clear 2.9 2.9 3.5 3.1 5.4 coating film Coating film quality Base material: Coating film appearance Electrodeposited Adhesion sheet Moisture resistance (coating film appearance) Moisture resistance X (adhesion) Chipping resistance X Base material: Coating film appearance Polypropylene Adhesion Moisture resistance (coating film appearance) Moisture resistance X (adhesion) Chipping resistance X X X X X