JP5626795B2 - Multi-layer coating formation method - Google Patents

Description

  The present invention relates to a method capable of forming a multilayer coating film having excellent chipping resistance by a 3-coat 1-bake method, and a coated article formed by the method.

  Conventionally, as a method of forming a coating film on an automobile body, an electrodeposition coating is applied to an object to be coated and heat-cured, and then “intermediate coating coating → baking curing → base coating coating coating → clear coating coating → baking curing” A method of forming a multilayer coating film by a three-coat two-bake method in which “is sequentially performed” is widely adopted.

  On the other hand, from the viewpoint of energy saving, the baking and curing process after painting of the intermediate coating is omitted, and “3 coating 1 bake” is performed in which “intermediate coating painting → base coat coating painting → clear coating painting → baking curing” is performed sequentially. A method is being considered.

  However, in the 3-coat 1-bake method, since the intermediate coating film and the base coating film are likely to be mixed, the smoothness and sharpness of the resulting coating film are reduced, or the curing agent is transferred between the coating films. There are problems such as a drop in chipping resistance, which is presumed to be caused by a change in the curing balance accompanying this.

  For example, in Patent Document 1, in the case of the 3-coat 1-bake method, the intermediate coating composition contains a specific polyester resin and a specific curing agent, and smoothness, sharpness, and chipping resistance are solved. In addition, it is described that a coating film excellent in water resistance can be obtained.

WO2007 / 126107 Publication

  However, even in the coating film obtained in Patent Document 1, chipping resistance may be insufficient particularly when the first colored coating film is thin.

  The present invention has been made in consideration of these points, and a multi-layer having excellent chipping resistance in a three-coat one-bake coating method using a first colored paint, a second colored paint, and a clear paint. It aims at providing the article coated by the multilayer coating-film formation method which can form a coating film, and this multilayer coating-film formation method.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have made a three-coat one-bake multi-layer coating in which a first colored paint, a second colored paint, and a clear paint are sequentially coated on an object to be coated. In the film forming method, when a colored paint containing a specific hydroxyl group-containing urethane resin and a curing agent is used as the first colored paint, it is found that a multilayer coating film having excellent chipping resistance can be formed. It came to be completed.

That is, this invention provides the article | item which has the coating film formed by the following multilayer coating-film formation methods and this multilayer coating-film formation method.
1.
The following steps (1) to (4):
(1) A hydroxyl group-containing urethane obtained by reacting a polyisocyanate compound (b) with a polyol component (a) comprising a cyclic polyol compound (a1) having a nurate structure and another polyol compound (a2) on a substrate. Applying the first colored paint (X) containing the resin (U) and the curing agent (C) to form an uncured first colored coating film;
(2) A step of coating the second colored paint (Y) on the uncured colored coating film obtained in the step (1) to form an uncured second colored coating film,
(3) A step of coating the clear paint (Z) on the uncured second colored coating film obtained in the step (2) to form an uncured clear coating film, and (4) Step (1) A step of simultaneously curing these three coating films by heating the uncured first colored coating film, the uncured second colored coating film and the uncured clear coating film formed in (3),
A method for forming a multilayer coating film comprising sequentially performing the steps.
2.
Item 2. The method for forming a multilayer coating film according to Item 1, wherein the cyclic polyol compound (a1) having a nurate structure is tris (hydroxyalkyl) isocyanurate.
3.
The other polyol compound (a2) is a polyether diol compound (a2-1-1) represented by the following general formula (1) and a polycarbonate diol compound (a2-1-2) represented by the following general formula (2) Item 3. The method for forming a multilayer coating film according to Item 1 or 2, which contains at least one diol compound (a2-1).

[In Formula (1), R ¹ represents an alkylene group having 3 or more carbon atoms, and m represents an integer of 2 to 100. Each R ¹ in m repeating units may be the same or different from each other. ]

Wherein (2), represents a plurality of ^{R 2} each independently having 3 or more alkylene group having a carbon, n is an integer of 2 to 100. ]
4).
The content ratio C _{a1 of the} cyclic polyol compound (a1) having a nurate structure relative to the total amount of the polyol component (a) is in the range of ₁ to 75 mol%, and the diol compound (a2-1 relative to the total amount of the polyol component (a) ) Content ratio C _a2-1 is in the range of 10 to 99 mol%, and the ratio C _a1 / C _{a2-1 of} C _a1 and C _a2-1 is in the range of 1/99 to 75/25. Item 4. The method for forming a multilayer coating film according to Item 3 above.
5.
Item 5. The method for forming a multilayer coating film according to any one of Items 1 to 4, wherein the polyisocyanate compound (b) is an alicyclic diisocyanate.
6).
Item 6. The method for forming a multilayer coating film according to any one of Items 1 to 5, wherein the hydroxyl value of the hydroxyl group-containing urethane resin (U) is in the range of 1 to 100 mgKOH / g.
7).
Item 7. The method for forming a multilayer coating film according to any one of Items 1 to 6, wherein the curing agent (C) is a blocked polyisocyanate compound.
8).
Item 8. The method for forming a multilayer coating film according to any one of Items 1 to 7, wherein the first colored paint (X) contains an epoxy resin.
9.
The method for forming a multilayer coating film according to any one of the above items 1 to 8, wherein the first colored coating film has a thickness of 2 to 15 µm when the first colored paint (X) is applied and cured. .
10.
Item 10. The method for forming a multilayer coating film according to any one of Items 1 to 9, wherein the second colored paint (Y) is applied without preheating after the first colored paint (X) is applied.
11.
Item | item which has the coating film formed by the multilayer coating-film formation method of any one of said items 1-10.

  According to the multilayer coating film forming method of the present invention, in the three-coat one-bake method using the first colored paint, the second colored paint, and the clear paint, the specific hydroxyl group-containing urethane is used as the first colored paint. A multilayer coating film having excellent chipping resistance can be formed by using a colored paint containing a resin and a curing agent.

  Hereinafter, the multilayer coating film forming method of the present invention will be described in more detail.

Process (1)
In step (1) of the method for forming a multilayer coating film of the present invention, the first colored paint (X) is applied onto the article to be coated.

  Although it does not specifically limit as said to-be-coated article, For example, the outer plate | board part of automobile bodies, such as a passenger car, a truck, a motorcycle, and a bus | bath, automobile parts, the outer-plate part of a rail vehicle, a road sign, a guardrail, etc. can be mentioned. . Of these, the outer plate of the automobile body and the automobile parts are preferable. Among these, a hood portion and a roof portion of an automobile body that require excellent smoothness are preferable.

  The material of these objects to be coated is not particularly limited. For example, metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel and zinc alloy (for example, Zn-Al, Zn-Ni and Zn-Fe) plated steel; polyethylene resin, polypropylene resin, Resin such as acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin and epoxy resin, and various plastic materials such as FRP; inorganic materials such as cement and concrete Can be mentioned. Of these, metal materials and plastic materials are preferable, and metal materials are particularly preferable.

  The article to be coated may be one obtained by subjecting the metal surface of the metal material or a vehicle body formed from the metal material to surface treatment such as phosphate treatment, chromate treatment, and complex oxide treatment. What formed the coating film on it may be used.

  As a coated object subjected to coating film formation, a surface treatment was applied to the substrate as necessary, an undercoat film was formed thereon, and an intermediate coat film was formed on the undercoat film The thing etc. can be mentioned. In particular, it is preferable that the base material is subjected to a surface treatment as necessary, and an electrodeposition coating is applied thereon to form an undercoat film. As the electrodeposition paint, a cationic electrodeposition paint is preferable.

First colored paint (X)
The first colored paint (X) is a hydroxyl group-containing urethane resin obtained by a reaction between a polyol component (a) comprising a cyclic polyol compound (a1) having a nurate structure and other polyol compounds (a2) and a polyisocyanate compound (b). A coating composition containing (U) and a curing agent (C).
[Hydroxyl-containing urethane resin (U)]
The hydroxyl group-containing urethane resin (U) is obtained by reacting a polyol component (a) composed of a cyclic polyol compound (a1) having a nurate structure and another polyol compound (a2) with a polyisocyanate compound (b).
[Polyol component (a)]
The polyol component (a) is composed of a cyclic polyol compound (a1) having the following nurate structure and another polyol compound (a2).
[Cyclic polyol compound having a nurate structure (a1)]
Examples of the cyclic polyol compound (a1) having a nurate structure include tris (hydroxyalkyl) isocyanurate such as tris (hydroxyethyl) isocyanurate, tris (hydroxypropyl) isocyanurate and tris (hydroxybutyl) isocyanurate, the tris Ε-caprolactone modified form of (hydroxyalkyl) isocyanurate, tris (hydroxyethyl) isocyanurate, diol compound and dicarboxylic acid, and the hydroxyl group in tris (hydroxyethyl) isocyanurate and diol compound is converted to a carboxyl group in dicarboxylic acid. Esterified tris (hydroxyethyl) isocyanurate obtained by reacting in excess, and polyisocyanate compound having nurate structure and diolization And things, hydroxyl groups in the diol compound is the reaction product obtained by reacting with excess state to isocyanate groups in the polyisocyanate compounds and the like having a isocyanurate structure. These can be used alone or in combination of two or more.

  Among these, from the viewpoint of chipping resistance and water resistance of the obtained coating film, tris (2-hydroxyethyl) isocyanurate and ε-caprolactone modified form of tris (2-hydroxyethyl) isocyanurate are preferable. 2-Hydroxyethyl) isocyanurate is more preferred.

In addition, from the viewpoint of chipping resistance and water resistance of the resulting coating film, the content ratio C _a1 of the cyclic polyol compound (a1) having the nurate structure relative to the total amount of the polyol component (a) is in the range of ₁ to 75 mol%. It is preferable that it is in the range of 10 to 65 mol%, more preferably in the range of 20 to 60 mol%, and particularly preferably in the range of 40 to 50 mol%.
[Other polyol compounds (a2)]
The other polyol compound (a2) is a polyol compound other than the cyclic polyol compound (a1) having the nurate structure.

  Examples of the other polyol compound (a2) include polyether polyol, polycarbonate polyol, polyester polyol, polyether ester polyol, polyalkylene polyol, and polyacryl polyol. These can be used alone or in combination of two or more.

  Among these, it is preferable to use polyether polyol and / or polycarbonate polyol from the viewpoint of water resistance of the resulting coating film.

  Examples of the polyether polyol include polymers or copolymers of alkylene oxides (for example, ethylene oxide, propylene oxide and butylene oxide), polymers or copolymers of heterocyclic ethers (for example, tetrahydrofuran), and the like. Examples thereof include copolymers of alkylene oxide and heterocyclic ether. These can be used alone or in combination of two or more.

  Specific examples of the polyether polyol include, for example, polyethylene glycol, polypropylene glycol, polyethylene-polypropylene glycol (block or random copolymer), polyethylene-tetramethylene glycol (block or random copolymer), polytetramethylene ether glycol. And polyoxyalkylene glycols such as polyhexamethylene ether glycol and polyhydric alcohols such as glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol and 1,2,4-butanetriol as initiators, Examples include compounds obtained by adding alkylene oxide (for example, ethylene oxide, propylene oxide, butylene oxide, etc.) to the initiator. These can be used alone or in combination of two or more.

  As said polycarbonate polyol, the polycarbonate polyol obtained by reaction with carbonic acid derivatives, such as diphenyl carbonate, dimethyl carbonate, and phosgene, and a polyol can be used, for example.

  Examples of the polyol include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 3- Methylpentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2-methyl-1,3-propanediol, 2-methyl-1,5-pentanediol, bisphenol A, Diols such as hydrogenated bisphenol A, trimethylolpropane and cyclohexanedimethanol, and trimethylolmethane, trimethylolethane, trimethylolpropane, trimethylolbutane, glycerin, 1,2,6-hexanetriol, trieta Amines, cyclohexane-1,2,3-trimethanol, cyclohexane-1,2,4-trimethanol, cyclohexane-1,3,5-trimethanol, reaction products of monoethanolamine and glycidol and pentaerythritol And triols. These can be used alone or in combination of two or more.

  As the polyol, it is preferable to use a diol. Examples of the diol include 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, and 2-methyl-1,5-pentanediol from the viewpoint of chipping resistance of the resulting coating film. Preferably mentioned. Among these, 1,6-hexanediol is preferable.

  A commercially available product can be used as the polycarbonate polyol. Examples of commercially available products include “T-5650J” (diol components: 1,6-hexanediol and 1,5-pentanediol), “T-4671”, and “T-4672” (all manufactured by Asahi Kasei Chemicals Corporation). Diol components: 1,6-hexanediol and 1,4-butanediol) and “UM-CARB90” (diol components: 1,6-hexanediol and 1,4-cyclohexanedimethanol) and UH manufactured by Ube Industries, Ltd. -CARB200 "(diol component: 1,6-hexanediol) and the like.

  Among these, from the viewpoint of water resistance of the resulting coating film, the other polyol compound (a2) is a polyether diol compound (a2-1-1) represented by the following general formula (1) and the following general formula (2). It is preferable to contain at least one diol compound (a2-1) of the polycarbonate diol compound (a2-1-2) represented by Especially, the said polycarbonate diol compound (a2-1-2) is more preferable from a viewpoint of the chipping resistance of the coating film formed.

In formula (1), R ¹ represents an alkylene group having 3 or more carbon atoms. R ¹ has 3 or more carbon atoms, preferably 3 to 6 and more preferably 4 to 5. m represents an integer of 2 to 100, preferably 4 to 80, and more preferably 8 to 40. Each R ¹ in the m repeating units may be the same or different from each other.

In Formula (2), a plurality of R ² each independently represents an alkylene group having 3 or more carbon atoms. R ² has 3 or more carbon atoms, preferably 3 to 22, more preferably 4 to 9, and still more preferably 6 to 9. n represents an integer of 2 to 100, preferably 4 to 80, and more preferably 8 to 40.

  Examples of the polyether diol compound (a2-1-1) include polyoxypropylene glycol, polytetramethylene ether glycol, polypentamethylene ether glycol, and polyhexamethylene ether glycol. These can be used alone or in combination of two or more. Of these, polytetramethylene ether glycol is preferable.

  As the polyether diol compound (a2-1-1), a commercially available product can be used. Examples of commercially available products include “New Pole PP-1000” and “New Pole PP-2000” manufactured by Sanyo Kasei Co., Ltd., “PTMG650”, “PTMG1000”, “PTMG1500”, “PTMG2000” and “PTMG2000” manufactured by Mitsubishi Chemical Corporation. PTMG3000 "and" POLYTHF1000S "manufactured by BASF-Japan can be used.

Further, from the viewpoint of chipping resistance and water resistance of the resulting coating film, the content ratio C _a2-1-1 of the polyether diol compound (a2-1-1) with respect to the total amount of the polyol component (a) is 10 to 10. It is preferably in the range of 99 mol%, more preferably in the range of 20 to 90 mol%, further preferably in the range of 30 to 80 mol%, and in the range of 40 to 70 mol%. Particularly preferred.

Further, from the viewpoint of chipping resistance and water resistance of the resulting coating film, the content ratio C _{a1 of the} cyclic polyol compound (a1) having a nurate structure with respect to the total amount of the polyol component (a) and the total amount of the polyol component (a) The ratio C _a1 / C _a2-1-1 with the content ratio C _a2-1-1 of the polyether diol compound (a2-1-1) _relative to the ratio is within the range of 1/99 to 75/25. Preferably, it is in the range of 10/90 to 70/30, more preferably in the range of 15/85 to 60/40, and in the range of 30/70 to 45/55. Particularly preferred.

  The hydroxyl value of the polyether diol compound (a2-1-1) is preferably in the range of 10 to 180 mgKOH / g, preferably in the range of 30 to 150 mgKOH / g, from the viewpoint of water resistance of the resulting coating film. It is more preferable that it is in the range of 50 to 120 mgKOH / g.

  The number average molecular weight of the polyether diol compound (a2-1-1) is within the range of 400 to 10,000 from the viewpoint of chipping resistance, smoothness and water resistance of the coating film obtained. Preferably, it is in the range of 500 to 5,000, more preferably in the range of 700 to 2,500, and particularly preferably in the range of 800 to 1,500.

  In addition, in this specification, the number average molecular weight and the weight average molecular weight are the retention time (retention capacity) measured using a gel permeation chromatograph (GPC), and the retention time of standard polystyrene having a known molecular weight measured under the same conditions. (Retention capacity) is a value obtained by converting to the molecular weight of 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” are used as columns. ”And“ TSKgel G-2000HXL ”(trade names, all manufactured by Tosoh Corporation), a differential refractometer is used as a detector, mobile phase: dimethyl sulfoxide, measurement temperature: 40 ° C., flow rate It can be measured under the condition of 1 mL / min.

  As the polycarbonate diol compound (a2-1-2), for example, a polycarbonate diol obtained by a reaction of a carbonic acid derivative such as diphenyl carbonate, dimethyl carbonate and phosgene with a diol having an alkylene group having 3 or more carbon atoms is used. be able to.

  Examples of the diol having an alkylene group having 3 or more carbon atoms include 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 3-methylpentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,5-pentanediol and the like Can be mentioned. These can be used alone or in combination of two or more.

  Of these, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol and 2-methyl-1,5-pentanediol are preferred from the viewpoint of chipping resistance of the resulting coating film. , 6-hexanediol is more preferred.

  A commercial item can be used as said polycarbonate diol compound (a2-1-2). Examples of commercially available products include “T-5650J”, “T-4671” and “T-4672” manufactured by Asahi Kasei Chemicals Corporation, and “UH-CARB50”, “UH-CARB100”, “UH-” manufactured by Ube Industries, Ltd. CARB200 "," UH-CARB300 ", etc. can be mentioned.

In addition, from the viewpoint of chipping resistance and water resistance of the obtained coating film, the content ratio C _a2-1-2 of the polycarbonate diol compound (a2-1-2) with respect to the total amount of the polyol component (a) is 10 to 99 mol. %, Preferably in the range of 20-90 mol%, more preferably in the range of 30-80 mol%, particularly preferably in the range of 40-70 mol%. preferable.

Further, from the viewpoint of chipping resistance and water resistance of the resulting coating film, the content ratio C _{a1 of the} cyclic polyol compound (a1) having a nurate structure relative to the total amount of the polyol component (a) and the total amount of the polyol component (a) The ratio C _a1 / C _{a2-1-2 to} the content ratio C _a2-1-2 of the polycarbonate diol compound (a2-1-2) is preferably in the range of 1/99 to 75/25, More preferably within the range of 10/90 to 70/30, still more preferably within the range of 15/85 to 60/40, and particularly preferably within the range of 30/70 to 45/55. .

  The hydroxyl value of the polycarbonate diol compound (a2-1-2) is preferably in the range of 10 to 240 mgKOH / g, and in the range of 30 to 150 mgKOH / g, from the viewpoint of water resistance of the resulting coating film. More preferably, it is more preferably in the range of 50 to 120 mg KOH / g.

  The number average molecular weight of the polycarbonate diol compound (a2-1-2) is preferably in the range of 400 to 10,000 from the viewpoints of chipping resistance, smoothness and water resistance of the resulting coating film. , More preferably in the range of 500 to 5,000, still more preferably in the range of 800 to 3,500, and particularly preferably in the range of 1,500 to 2,500.

Further, when the polyether diol compound (a2-1-1) and the polycarbonate diol compound (a2-1-2) are used in combination as the diol compound (a2-1), the chipping resistance and water resistance of the resulting coating film are obtained. In view of the above, the content ratio C _a2-1 of the diol compound (a2-1) with respect to the total amount of the polyol component (a) is preferably in the range of 10 to 99 mol%, and in the range of 20 to 90 mol%. More preferably, it is more preferably in the range of 30 to 80 mol%, and particularly preferably in the range of 40 to 70 mol%.

Further, from the viewpoint of chipping resistance and water resistance of the resulting coating film, the content ratio C _{a1 of the} cyclic polyol compound (a1) having the nurate structure to the total amount of the polyol component (a) and the total amount of the polyol component (a) The ratio C _a1 / C _a2-1 to the content ratio C _a2-1 of the diol compound (a2-1) with respect to is preferably in the range of 1/99 to 75/25, 10/90 to 70 / More preferably, it is within the range of 30, more preferably within the range of 15/85 to 60/40, and particularly preferably within the range of 30/70 to 45/55.
[Polyisocyanate compound (b)]
The polyisocyanate compound (b) is a compound having at least two isocyanate groups in one molecule. Examples of the polyisocyanate compound (b) include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates and aromatic polyisocyanates, and derivatives of these polyisocyanates. These can be used alone or in combination of two or more.

  Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3. Aliphatic diisocyanates such as butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate and methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate) and 2 , 6-Diisocyanatohexanoic acid 2-isocyanatoethyl, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane and 2,5,7-trimethyl-1,8-diisocyanato-5 -Aliphatic triisocyanates such as isocyanatomethyloctane.

  Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name) : Isophorone diisocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis (isocyanatomethyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or Mixtures thereof, alicyclic diisocyanates such as methylenebis (1,4-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI) and norbornane diisocyanate and 1,3,5-triisocyanate Socyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3 -Isocyanatopropyl) -2,6-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo ( 2.2.1) Heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanate) Natoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanate Tomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane and 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) Alicyclic triisocyanates such as heptane.

  Examples of the araliphatic polyisocyanate include methylene bis (1,4-phenylene) diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω′-diisocyanato- Aromatic aliphatic diisocyanates such as 1,4-diethylbenzene and 1,3- or 1,4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof and 1,3 , 5-triisocyanatomethylbenzene and other araliphatic triisocyanates.

  Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, or a mixture thereof. Aromatic diisocyanates such as 4,4′-toluidine diisocyanate and 4,4′-diphenyl ether diisocyanate, triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene and 2 And aromatic triisocyanates such as 4,4′-diphenylmethane-2,2 ′, 5,5′-tetraisocyanate and the like.

  Examples of the polyisocyanate derivative include dimer, trimer, biuret, allophanate, uretdione, uretoimine, isocyanurate, oxadiazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI) of the polyisocyanate compound. And crude TDI.

The polyisocyanate compound (b) is preferably an alicyclic diisocyanate or a derivative of the alicyclic diisocyanate from the viewpoint of chipping resistance, water resistance, smoothness and sharpness of the resulting coating film. Diisocyanate is more preferred.
[Method for producing hydroxyl group-containing urethane resin (U)]
The hydroxyl group-containing urethane resin (U) is obtained by reacting a polyol component (a) composed of the cyclic polyol compound (a1) having the nurate structure and the other polyol compound (a2) with the polyisocyanate compound (b).

  Specifically, for example, in the polyol component (a) and the polyisocyanate compound (b), the hydroxyl group in the polyol component (a) is excessive with respect to the isocyanate group in the polyisocyanate compound (b). It can obtain by making it react.

  The blending ratio of the polyol component (a) and the polyisocyanate compound (b) is determined from the number of moles of hydroxyl groups in the polyol component (a) and the polyhydric acid from the viewpoint of chipping resistance, smoothness and water resistance of the resulting coating film. The ratio OH / NCO with the number of moles of isocyanate groups in the isocyanate compound (b) is preferably adjusted to be in the range of 51/49 to 80/20, and in the range of 53/47 to 70/30. Is more preferable, and the range of 55/45 to 65/35 is more preferable.

  The reaction of the polyol component (a) and the polyisocyanate compound (b) can be performed by a conventionally known method. Specifically, for example, the polyol component (a) and the polyisocyanate compound (b) are preferably 10 to 170 ° C., more preferably 20 by using an organic solvent inert to a hydroxyl group and an isocyanate group as a reaction solvent. The reaction can be carried out at a temperature in the range of ˜150 ° C., preferably for 1 to 24 hours, more preferably in the range of 2 to 8 hours.

  Examples of the reaction solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, N-methylpyrrolidone, toluene, and xylene. These can be used alone or in combination of two or more.

  In the above reaction, a catalyst, a reaction terminator, a chain extender and the like can be used as necessary.

  Examples of the catalyst include salts of metals such as dibutyltin dilaurate, dioctyltin dilaurate, lead octylate and tetra n-butyl titanate with organic and inorganic acids, organic metal derivatives, organic amines such as triethylamine, and diazabicyclone. Examples include decene catalysts. These can be used alone or in combination of two or more.

  As the reaction terminator, for example, monofunctional compounds such as monoalcohols and monoamines, and compounds having two types of functional groups having different reactivities with respect to isocyanate can be used.

  Specific examples of the reaction terminator include monoalcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol and tert-butyl alcohol, monoethylamine, n- Examples thereof include monoamines such as propylamine, diethylamine, di-n-propylamine and di-n-butylamine, and alkanolamines such as monoethanolamine and diethanolamine. These can be used alone or in combination of two or more.

  Of these, alkanolamines are preferable in that the reaction can be easily controlled. Moreover, the said reaction terminator can be used in order to adjust the number average molecular weight of a hydroxyl-containing urethane resin (U).

  As the chain extender, for example, water and polyamine can be used.

  Examples of the polyamine include aliphatic polyamines such as ethylenediamine, N-hydroxyethylethylenediamine, tetramethylenediamine, hexamethylenediamine and diethylenetriamine, 4,4′-diaminodicyclohexylmethane, 1,4-diaminocyclohexane and isophoronediamine. Aliphatic polyamines having aromatic rings such as alicyclic polyamines, xylylenediamine and tetramethylxylylenediamine, aromatic polyamines such as 4,4′-diaminodiphenylmethane, tolylenediamine and phenylenediamine, and hydrazine, carbodihydrazide, adipine And hydrazines such as acid dihydrazide, sebacic acid dihydrazide and phthalic acid dihydrazide. These can be used alone or in combination of two or more.

  In addition, the hydroxyl group-containing urethane resin (U) preferably has a hydroxyl value in the range of 1 to 100 mgKOH / g, from the viewpoint of chipping resistance, smoothness and water resistance of the obtained coating film, and 10 to 80 mgKOH / g. More preferably, it is in the range of g, more preferably in the range of 20 to 50 mgKOH / g.

  The hydroxyl group-containing urethane resin (U) preferably has a weight average molecular weight in the range of 5,000 to 100,000 from the viewpoints of chipping resistance, smoothness and water resistance of the resulting coating film. More preferably, it is within the range of 20,000 to 70,000, and even more preferably within the range of 30,000 to 50,000.

The hydroxyl group-containing urethane resin (U) preferably has a number average molecular weight in the range of 2,000 to 20,000 from the viewpoints of chipping resistance, smoothness and water resistance of the resulting coating film. More preferably within the range of 4,000 to 16,000, still more preferably within the range of 5,000 to 12,000, and particularly preferably within the range of 6,000 to 9,900. .
[Curing agent (C)]
The curing agent (C) is a compound capable of curing the coating composition of the present invention by reacting with the functional group in the hydroxyl group-containing urethane resin (U). The functional group in the hydroxyl group-containing urethane resin (U) that reacts with the curing agent (C) is preferably a hydroxyl group.

  Examples of the curing agent (C) include polyisocyanate compounds, blocked polyisocyanate compounds, amino resins, epoxy group-containing compounds, carboxyl group-containing compounds, and carbodiimide group-containing compounds. These can be used alone or in combination of two or more.

  Among these, a polyisocyanate compound, a blocked polyisocyanate compound and an amino resin that can react with a hydroxyl group in the hydroxyl group-containing urethane resin (U) are preferable. From the viewpoint of chipping resistance of the resulting coating film, the polyisocyanate compound and / or A blocked polyisocyanate compound is more preferable, and a blocked polyisocyanate compound is more particularly preferable from the viewpoint of the storage stability of the coating material and the ease of coating work.

  The polyisocyanate compound is a compound having at least two isocyanate groups in one molecule. Specifically, for example, the polyisocyanate compound described in the description of the polyisocyanate compound (b) can be used. Especially, the polyisocyanate compound which has an isocyanurate structure from a smooth viewpoint of the coating film obtained is preferable.

  The blocked polyisocyanate compound is a compound obtained by blocking the isocyanate group of the polyisocyanate compound with a blocking agent. The blocked polyisocyanate compound is preferably a compound obtained by blocking a polyisocyanate compound having an isocyanurate structure with a blocking agent from the viewpoint of the smoothness of the resulting coating film.

  Examples of the blocking agent include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate, ε-caprolactam, δ-valerolactam, Lactams such as γ-butyrolactam and β-propiolactam, aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol and lauryl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl Ethers such as ether, propylene glycol monomethyl ether and methoxymethanol, benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, di Alcohols such as acetone alcohol, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate, oximes such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime and cyclohexane oxime, dimethyl malonate, and malon Active methylene systems such as diethyl acid, ethyl acetoacetate, methyl acetoacetate and acetylacetone , Mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol and ethylthiophenol, acetanilide, acetanisidide, acetolide, acrylamide, methacrylamide, acetic acid amide Acid amides such as stearamide and benzamide; imides such as succinimide, phthalimide and maleic imide, diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, di Amines such as butylamine and butylphenylamine, and imidazoles such as imidazole and 2-ethylimidazole Urea, thiourea, ethylene urea, urea such as ethylene thiourea and diphenyl urea, carbamate esters such as phenyl N-phenylcarbamate, imine such as ethyleneimine and propyleneimine, sodium bisulfite and heavy Examples thereof include sulfite-based compounds such as potassium sulfite and azole-based compounds.

  Examples of the azole compounds include pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3, Pyrazole or pyrazole derivatives such as 5-dimethylpyrazole and 3-methyl-5-phenylpyrazole, imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole and 2-phenylimidazole, and 2-methylimidazoline And imidazoline derivatives such as 2-phenylimidazoline. These can be used alone or in combination of two or more.

  The blocking agent is preferably an oxime-based blocking agent, an active methylene-based blocking agent, and a pyrazole or a pyrazole derivative, particularly an active methylene-based blocking agent, from the viewpoint of improving chipping resistance and smoothness of the resulting coating film. preferable.

  Examples of the blocking agent also include hydroxycarboxylic acids having one or more hydroxyl groups and one or more carboxyl groups, such as hydroxypivalic acid and dimethylolpropionic acid.

  In the multilayer coating film forming method of the present invention, when the first colored paint (X) contains the polyisocyanate compound and / or the blocked polyisocyanate compound as the curing agent (C), the chipping resistance is excellent. The following reason is guessed as a reason which can form a coating film.

  Since the affinity between the nurate structure in the cyclic polyol compound (a1) having a nurate structure and the polyisocyanate compound and the blocked polyisocyanate compound is high, the polyol component (a ) And a curing agent (C) comprising a polyisocyanate compound and / or a blocked polyisocyanate compound is highly compatible with the hydroxyl group-containing urethane resin (U) and cured. The urethane bond formed by the reaction with the agent (C) is present relatively uniformly in the cured coating film, so that flexibility is imparted to the entire cured coating film and a coating film with excellent chipping resistance is formed. It is guessed.

  Examples of the amino resin include a partially methylolated amino resin or a completely methylolated amino resin obtained by a reaction between an amino component and an aldehyde component.

  Examples of the amino component include melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, and dicyandiamide.

  Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, and the like.

  Moreover, what methylated the methylol group of the said partial methylolation amino resin partially or completely with suitable alcohol can also be used.

  Examples of the alcohol used for the etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol and 2-ethylhexanol.

  As the amino resin, a melamine resin is preferable. In particular, methyl ether melamine resins in which methylol groups of partially or fully methylolated melamine resins are partially or completely etherified with methyl alcohol, methylol groups of partially or fully methylolated melamine resins are partially or completely with butyl alcohol. Preferred is a methyl-butyl mixed etherified melamine resin in which a methylol group of a partially or fully methylolated melamine resin and a partially or fully methylolated melamine resin are partially or completely etherified with methyl alcohol and butyl alcohol. Etherified melamine resins are more preferred.

  The melamine resin preferably has a weight average molecular weight of 400 to 6,000, more preferably 800 to 5,000, still more preferably 1,000 to 4,000, Most preferably, it is 200-3,000.

  A commercially available product can be used as the melamine resin. Examples of commercially available product names include “Cymel 202”, “Cymel 203”, “Cymel 238”, “Cymel 251”, “Cymel 303”, “Cymel 323”, “Cymel 324”, “Cymel 325”, “Cymel 327”, “Cymel 350”, “Cymel 385”, “Cymel 1156”, “Cymel 1158”, “Cymel 1116”, “Cymel 1130” (above, made by Nippon Cytec Industries, Inc.), “Uban 120”, “ “Uban 20HS”, “Uban 20SE60”, “Uban 2021”, “Uban 2028”, “Uban 28-60” (manufactured by Mitsui Chemicals, Inc.), and the like.

  When a melamine resin is used as the curing agent (C), for example, sulfonic acids such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid and dinonylnaphthalenesulfonic acid, monobutyl phosphoric acid, dibutyl phosphoric acid, mono 2-ethylhexyl phosphoric acid Further, alkyl phosphate esters such as di-2-ethylhexyl phosphate, salts of these acids with amine compounds, and the like can be used as catalysts.

  In the multilayer coating film forming method of the present invention, the blending ratio of the hydroxyl group-containing urethane resin (U) and the curing agent (C) in the first colored paint (X) is from the viewpoint of improving the chipping resistance and water resistance of the coating film. Based on the total amount of the two, the hydroxyl group-containing urethane resin (U) is preferably 30 to 95% by mass, more preferably 40 to 90% by mass, and further preferably 50 to 80% by mass. preferable. Moreover, it is preferable that a hardening | curing agent (C) is 5-70 mass%, It is more preferable that it is 10-60 mass%, It is further more preferable that it is about 20-50 mass%.

  Moreover, in the multilayer coating film forming method of the present invention, the first colored paint (X) further contains a pigment.

  Examples of the pigment include a color pigment, an extender pigment, and a glitter pigment. The pigments can be used alone or in combination of two or more.

  When 1st colored coating material (X) contains the said pigment, the compounding quantity of this pigment is 10 to 10 on the basis of 100 mass parts of total solid content of the said hydroxyl-containing urethane resin (U) and a hardening | curing agent (C). It is preferably within the range of 120 parts by mass, more preferably within the range of 30 to 90 parts by mass, and even more preferably within the range of 40 to 75 parts by mass.

  Examples of the color pigment include titanium oxide, zinc white, carbon black (including conductive carbon black), molybdenum red, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, and isoindoline pigment. And selenium pigments, perylene pigments, dioxazine pigments and diketopyrrolopyrrole pigments. These can be used alone or in combination of two or more. Of these, titanium oxide and carbon black are preferable.

  When the first colored paint (X) contains the colored pigment, the blending amount of the colored pigment is based on 100 parts by mass of the total solid content of the hydroxyl group-containing urethane resin (U) and the curing agent (C). It is preferably within the range of 0.01 to 120 parts by mass, more preferably within the range of 1 to 90 parts by mass, and even more preferably within the range of 10 to 75 parts by mass.

  Examples of the extender pigment include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica and alumina white. These can be used alone or in combination of two or more. Among these, from the viewpoint of chipping resistance of the obtained coating film, barium sulfate and talc are preferable, and talc is more preferable.

  When the first colored paint (X) contains the extender, the amount of the extender is based on 100 parts by mass of the total solid content of the hydroxyl group-containing urethane resin (U) and the curing agent (C). It is preferably within the range of 0.1 to 50 parts by mass, more preferably within the range of 1 to 30 parts by mass, and even more preferably within the range of 5 to 20 parts by mass.

  Specific examples of the bright pigment include non-leafing type or leafing type aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, glass flakes, aluminum oxide, mica, titanium oxide, and oxide. Examples thereof include aluminum oxide coated with iron and mica coated with titanium oxide or iron oxide. Of these, aluminum is preferable.

  The glitter pigment is preferably flake shaped. Further, the longitudinal dimension of the glitter pigment is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 40 μm. The thickness of the glitter pigment is preferably in the range of 0.001 to 5 μm, and more preferably in the range of 0.01 to 2 μm.

  When the first colored paint (X) contains the glitter pigment, the blend amount of the glitter pigment is based on 100 parts by mass of the total solid content of the hydroxyl group-containing urethane resin (U) and the curing agent (C). 1 to 40 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 5 to 15 parts by mass.

  The first colored paint (X) may further contain a curing catalyst, a resin other than the hydroxyl group-containing urethane resin (U), hollow particles, elastomer particles, and other paint additives as required. .

  Examples of the curing catalyst include tin octylate, dibutyltin diacetate, dibutyltin di (2-ethylhexanoate), dibutyltin dilaurate, dioctyltin diacetate, dioctyltin di (2-ethylhexanoate), Dibutyltin oxide, dioctyltin oxide, dibutyltin fatty acid salt, lead 2-ethylhexanoate, zinc octylate, zinc naphthenate, zinc fatty acids, cobalt naphthenate, calcium octylate, copper naphthenate and tetra (2-ethylhexyl) Examples include organometallic compounds such as titanate, tertiary amines, and phosphoric acid compounds. These can be used alone or in combination of two or more.

  When 1st coloring paint (X) contains the said curing catalyst, the compounding quantity of this curing catalyst is 0 on the basis of 100 mass parts of total solid content of a hydroxyl-containing urethane resin (U) and a hardening | curing agent (C). It is preferably within the range of 0.001 to 5 parts by mass, more preferably within the range of 0.003 to 3 parts by mass, and even more preferably within the range of 0.005 to 1 part by mass.

  As the resin other than the hydroxyl group-containing urethane resin (U), for example, an epoxy resin, an acrylic resin, a polyester resin, and a polyolefin resin can be used.

  Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, hydrogenated bisphenol A type epoxy resin, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, Propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, hexahydrophthalic acid diglycidyl ester, glycerin polyglycidyl ether, di Glycerin polyglycidyl ether and polyglycerin polyglycidyl ether And the like aliphatic epoxy resin. These can be used alone or in combination of two or more.

  In the multilayer coating film forming method of the present invention, the first colored paint (X) preferably contains the epoxy resin from the viewpoint of water resistance and chipping resistance of the formed coating film.

  Examples of commercially available epoxy resins include “jER828”, “jER828”, “jER828EL”, “jER828XA”, “jER834” (manufactured by Japan Epoxy Resin Co., Ltd.), “EPICLON840”, “EPICLON840-S”, “EPICLON 850”, “EPICLON 850-S”, “EPICLON 850-CRP”, “EPICLON 850-LC” (manufactured by DIC), “Epototo YD-127”, “Epototo YD-128” (manufactured by Toto Kasei) Bisphenol A type epoxy resins such as “Lika Resin BPO-20E” and “Lika Resin BEO-60E” (manufactured by Shin Nippon Chemical Co., Ltd.), “jER806”, “jER807” (manufactured by Japan Epoxy Resin), “EPICLON83” ”,“ EPICLON 830-S ”,“ EPICLON 835 ”(manufactured by DIC) and“ Epototo YDF-170 ”(manufactured by Tohto Kasei), etc .;“ jER152 ”(manufactured by Japan Epoxy Resin), etc. Novolak-type epoxy resin, “jERYX8000”, “jERYX8034” (manufactured by Japan Epoxy Resin Co., Ltd.), “Epototo ST-3000” (manufactured by Tohto Kasei Co., Ltd.), “Rikaresin HBE-100” (manufactured by Shin Nippon Rika Co., Ltd.) Hydrogenated bisphenol A type epoxy resins such as Denacol EX-252 "(manufactured by Nagase ChemteX Corporation) and" SR-HBA "(manufactured by Sakamoto Pharmaceutical Co., Ltd.) and" YED205 "," YED216M "," YED216D "( Above, Japan Epoxy Resin Co., Ltd.), “Epoto "YH-300", "Epototo YH-301", "Epototo YH-315", "Epototo YH-324", "Epototo YH-325" (above, manufactured by Tohto Kasei Co., Ltd.), "Denacol EX-211", "Denacol “EX-212”, “Denacol EX-212L”, “Denacol EX-214L”, “Denacol EX-216L”, “Denacol EX-313”, “Denacol EX-314”, “Denacol EX-321”, “Denacol EX” -321L "," Denacol EX-411 "," Denacol EX-421 "," Denacol EX-512 "," Denacol EX-521 "," Denacol EX-611 "," Denacol EX-612 "," Denacol EX- 614 "," Denacol EX-614B "," Denacol EX-622 "," "Denacol EX-810", "Denacol EX-811", "Denacol EX-850", "Denacol EX-850L", "Denacol EX-851", "Denacol EX-821", "Denacol EX-830", "Denacol EX-832, Denacol EX-841, Denacol EX-861, Denacol EX-911, Denacol EX-941, Denacol EX-920, Denacol EX-931 (above, Nagase Chem) Manufactured by Tex Corporation), "SR-NPG", "SR-16H", "SR-16HL", "SR-TMP", "SR-PG", "SR-TPG", "SR-4PG", "SR- 2EG "," SR-8EG "," SR-8EGS "," SR-GLG "," SR-DGE "," SR-DGE "," SR- GL "," SR-4GLS "and" SR-SEP "(or, BanHajime manufactured Yakuhin Kogyo Co., Ltd.) aliphatic epoxy resins such as are exemplified.

  Moreover, the epoxy resin preferably has an epoxy equivalent in the range of 110 to 500, and in the range of 130 to 350, from the viewpoint of chipping resistance, water resistance and smoothness of the coating film to be formed. Is more preferable, and it is still more preferable that it exists in the range of 150-250.

  The epoxy resin preferably has a number average molecular weight in the range of 170 to 2,800, and in the range of 200 to 800, from the viewpoint of chipping resistance, water resistance and smoothness of the coating film to be formed. It is more preferable that it is in the range of 300 to 500. The epoxy resin preferably has a hydroxyl group from the viewpoint of chipping resistance and water resistance of the coating film to be formed.

  When 1st coloring paint (X) contains the said epoxy resin, the compounding quantity of this epoxy resin is 0 on the basis of 100 mass parts of total solid content of a hydroxyl-containing urethane resin (U) and a hardening | curing agent (C). 0.1 to 50 parts by mass is preferable, 1 to 30 parts by mass is more preferable, and 2 to 20 parts by mass is even more preferable.

  Examples of the acrylic resin include a carboxyl group-containing polymerizable unsaturated monomer such as (meth) acrylic acid, a hydroxyl group-containing polymerizable unsaturated monomer such as 2-hydroxyethyl (meth) acrylate, and other polymerizable unsaturated monomers. Examples thereof include an acrylic resin obtained by copolymerization in the presence of a radical polymerization initiator.

  The weight average molecular weight of the acrylic resin is preferably in the range of 1,000 to 1,000,000, and more preferably in the range of 1,500 to 100,000. The acid value is preferably in the range of 5 to 150 mgKOH / g, and more preferably in the range of 10 to 75 mgKOH / g. Furthermore, the hydroxyl value is preferably in the range of 10 to 160 mgKOH / g, and more preferably in the range of 30 to 120 mgKOH / g.

  When 1st colored coating material (X) contains the said acrylic resin, the compounding quantity of this acrylic resin is 0 on the basis of 100 mass parts of total solid content of a hydroxyl-containing urethane resin (U) and a hardening | curing agent (C). 0.1 to 50 parts by mass is preferable, 1 to 30 parts by mass is more preferable, and 2 to 20 parts by mass is even more preferable.

  Examples of the polyester resin include polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, 1,6-hexanediol, trimethylolpropane, and pentaerythritol, and adipic acid, isophthalic acid, terephthalic acid, and phthalic anhydride. Examples thereof include polyester resins obtained by a condensation reaction with polyvalent carboxylic acid components such as acid, hexahydrophthalic anhydride and trimellitic anhydride.

  The weight average molecular weight of the polyester resin is preferably in the range of 1,000 to 100,000, and more preferably in the range of 1,500 to 70,000. The acid value is preferably in the range of 1 to 100 mgKOH / g, and more preferably in the range of 5 to 50 mgKOH / g. Furthermore, the hydroxyl value is preferably in the range of 10 to 160 mgKOH / g, and more preferably in the range of 30 to 120 mgKOH / g.

  When 1st coloring paint (X) contains the said polyester resin, the compounding quantity of this polyester resin is 0 on the basis of 100 mass parts of total solid content of a hydroxyl-containing urethane resin (U) and a hardening | curing agent (C). 0.1 to 50 parts by mass is preferable, 1 to 30 parts by mass is more preferable, and 2 to 20 parts by mass is even more preferable.

  Examples of the polyolefin resin include a radical homopolymer or copolymer of at least one olefin selected from ethylene, propylene, butene, methylbutene, and isoprene, and the olefin and vinyl acetate, butadiene, and acrylic acid. And radical copolymers with polymerizable unsaturated monomers such as esters and methacrylates.

  When the first colored paint (X) contains the polyolefin resin, the blending amount of the polyolefin resin is 0 based on 100 parts by mass of the total solid content of the hydroxyl group-containing urethane resin (U) and the curing agent (C). 0.1 to 50 parts by mass is preferable, 1 to 30 parts by mass is more preferable, and 2 to 20 parts by mass is even more preferable.

  As the paint additive, for example, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a thickener, a rust preventive agent, a surface conditioner, a pigment dispersant and the like can be used.

  The first colored paint (X) includes the hydroxyl group-containing urethane resin (U) and the curing agent (C), and, if necessary, a resin other than the pigment, the curing catalyst, and the hydroxyl group-containing urethane resin (U), and other paints. Additives and the like can be adjusted by mixing and dispersing in a solvent by a known method.

  As the solvent, both water and an organic solvent can be used. Examples of the organic solvent include xylene, toluene, cyclohexanone, hexane, pentane, isopropanol, 1-butanol, 1-octanol, 2-ethyl-1-hexanol, benzyl alcohol, butyl acetate, acetone, methyl ethyl ketone, and methyl isobutyl ketone. Is mentioned. These can be used alone or in admixture of two or more.

  The solid content of the first colored paint (X) is usually preferably 5 to 70% by mass, more preferably 10 to 60% by mass, and still more preferably 15 to 50% by mass.

  The first colored paint (X) can be applied onto the cured electrodeposition coating film by a method known per se, for example, air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, etc. At this time, electrostatic application may be performed. Of these, methods such as air spray coating and rotary atomization coating are preferred.

  When air spray coating, airless spray coating, or rotary atomization coating is performed, the viscosity of the first colored paint (X) is adjusted to a viscosity range suitable for the coating, usually Ford Cup No. In the three viscometer, it is preferable to adjust appropriately using a solvent such as an organic solvent so that the viscosity range is 20 to 15 seconds for 21 to 21 seconds, preferably about 17 to 19 seconds.

  The upper limit of the film thickness when the first colored paint (X) is cured is preferably 15 μm or less and more preferably 13 μm or less from the viewpoint of smoothness and sharpness. On the other hand, about a minimum, 2 micrometers or more are preferable from a viewpoint of chipping resistance and a weather resistance, and 4 micrometers or more are preferable. Among these, the film thickness is preferably 5 to 10 μm from the viewpoint of obtaining a coating film having a good balance of chipping resistance, weather resistance, smoothness and sharpness. The first colored coating film formed by the first colored paint (X) has excellent chipping resistance even when coated with a relatively thin film thickness.

  The desired film thickness can be obtained by controlling the coating amount of the first colored paint (X).

  After applying the first colored paint (X), an interval of 1 to 2 minutes may be provided at room temperature before applying the second colored coating film. Or you may perform preheating, an air blow, etc. on the heating conditions which a coating film does not harden | cure substantially. The preheating temperature is preferably 40 to 100 ° C, more preferably 50 to 90 ° C, and still more preferably 60 to 80 ° C. The preheating time is preferably 30 seconds to 15 minutes, more preferably 1 to 10 minutes, and even more preferably 2 to 5 minutes. Moreover, the said air blow can be normally performed by spraying the air heated to the normal temperature or the temperature of 25-80 degreeC on the coating surface of the to-be-coated article for 30 seconds-15 minutes.

  Since the multi-layer coating film forming method of the present invention can form a first colored coating film having excellent chipping resistance, the coating thickness of the first colored coating material (X) is thinner than that of the conventional 3-coat 1-bake method. Even if the above preheating (preheating), air blowing, etc. are not performed, sagging and mixed layers are hardly generated after the second colored paint (Y) is applied, and smoothness, sharpness, and chipping resistance are prevented. It is possible to form a multilayer coating film excellent in the above. For this reason, from the viewpoint of energy saving, the multilayer coating film forming method of the present invention may not include the heating step between the first colored paint (X) and the second colored paint (Y). preferable.

Step (2)
On the uncured coating film of the first colored paint (X) formed in the step (1) described above (hereinafter sometimes referred to as “first colored paint film”), the second colored paint (Y) Is applied to form an uncured second colored coating film.

  The second colored paint (Y) may be in any form of a water-based paint and an organic solvent-type paint. In the present specification, the water-based paint is a term contrasted with an organic solvent-type paint, and generally, a binder component, a pigment, and the like are dispersed and dispersed in water or a medium containing water as a main component (aqueous medium). Means a dissolved paint. The second colored paint (Y) is preferably an aqueous paint from the viewpoint of reducing environmental burden. When the coating composition of the present invention is a water-based coating, the content of water in the coating composition is preferably about 10 to 90% by mass, more preferably about 20 to 80% by mass, and about 30 to 70% by mass. Is more preferable.

  The second colored paint (Y) is generally intended to give an excellent appearance to the object to be coated. For example, a binder component composed of a base resin and a crosslinking agent may be added to the pigment and the like as necessary. It is possible to use a paint which is dissolved or dispersed in a solvent together with the above additives.

  Examples of the base resin include acrylic resins, polyester resins, alkyd resins, urethane resins, and epoxy resins having a crosslinkable functional group such as a carboxyl group and a hydroxyl group. The crosslinking agent is blocked. Examples thereof may include polyisocyanate compounds, melamine resins, urea resins and the like. Among these, from the viewpoints of the appearance and water resistance of the obtained multilayer coating film, a thermosetting water-based paint using a hydroxyl group-containing resin as a base resin and a melamine resin as a crosslinking agent can be suitably used.

A pigment can be further blended in the second colored paint (Y) as necessary.
As the pigment, a bright pigment, a colored pigment, an extender pigment and the like can be used. Especially, it is preferable that a 2nd colored coating material (Y) contains a luster pigment and / or a color pigment as at least 1 type of the said pigment.

  The glitter pigment is preferably a flake particle pigment having a light interference effect or a glittering glitter, such as aluminum, vapor-deposited aluminum, copper, zinc, brass, nickel, aluminum oxide, mica, and metal oxide. Examples thereof include coated aluminum oxide, mica coated with metal oxide, mica-like iron oxide, mica-like iron oxide coated with metal iron oxide, glass flakes, and hologram pigment. The above luster pigments can be used alone or in combination of two or more. The longitudinal dimension of the glitter pigment is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 40 μm. The thickness of the glitter pigment is preferably in the range of 0.001 to 5 μm, and more preferably in the range of 0.01 to 2 μm. Further, the blending amount of the glitter pigment is suitably 1 to 50 parts by weight per 100 parts by weight of the solid content of the binder component in the second colored paint (Y). Moreover, an organic solvent and / or water can be used as a solvent, The said component can be mixed and disperse | distributed to this.

  Examples of the color pigment include titanium dioxide, zinc white, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, and selenium (anthraquinone) pigments. Perylene pigments, dioxazine pigments, diketopyrrolopyrrole pigments, and the like. These may be used alone or in combination of two or more.

  When the second colored paint (Y) contains the colored pigment, the amount of the colored pigment is usually 1 on the basis of 100 parts by mass of the solid content of the binder component in the second colored paint (Y). It is suitable that it is in the range of -100 parts by mass, preferably 2-50 parts by mass, more preferably 3-30 parts by mass.

  Examples of the extender pigment include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white. These can be used alone or in combination of two or more.

  When the second colored paint (Y) contains the extender, the amount of the extender is usually 1 to 100 parts by weight based on the solid content of the binder component in the second colored paint (Y). It is suitable to be in the range of 100 parts by weight, preferably 2-50 parts by weight, more preferably 3-30 parts by weight.

  In addition, the second colored paint (Y) may further include a curing catalyst, a thickener, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a plasticizer, an organic solvent, a surface conditioner, an anti-settling agent, etc., as necessary. The usual paint additive can be contained. These paint additives can be used alone or in combination of two or more. As the paint additive, for example, those described in the description of the first colored paint (X) can be used.

  In the method for forming a multilayer coating film of the present invention, the second colored coating material (Y) has a solid content concentration in the range of 18 to 35% by mass. It is preferable from the viewpoint of film quality, more preferably 20 to 30% by mass, still more preferably 23 to 27% by mass.

  The second colored paint (Y) can be applied by a method known per se, for example, an air spray, an airless spray, a rotary atomizing coater, or the like, and electrostatic application may be performed during the application.

  In the multilayer coating film forming method of the present invention, the thickness of the second colored coating film formed by coating the second colored paint (Y) is 5 to 20 μm in thickness when cured. Preferably it is 6-15 micrometers, More preferably, it is the range of 7-13 micrometers of leaves. It is because it is excellent in the external appearance, smoothness, and sharpness of a coating film when it is below an upper limit, and is excellent in color developability and concealment property when it is more than a lower limit.

Step (3)
In the multilayer coating film forming method of the present invention, the clear coating is applied on the coating film of the second colored paint (Y) formed in the step (2) (hereinafter sometimes referred to as “second colored coating film”). Paint (Z) is applied.

  The second colored coating film is preferably subjected to preheating, air blowing, or the like under heating conditions in which the coating film is not substantially cured before the clear paint (Z) is applied. The preheating temperature is preferably 40 to 100 ° C, more preferably 50 to 90 ° C, and still more preferably 60 to 80 ° C. The preheating time is preferably 30 seconds to 15 minutes, more preferably 1 to 10 minutes, and even more preferably 2 to 5 minutes. Moreover, the said air blow can be normally performed by spraying the air heated to the normal temperature or the temperature of 25-80 degreeC on the coating surface of the to-be-coated article for 30 seconds-15 minutes.

  The second colored coating film may have an interval of 1 to 2 minutes at room temperature before the clear paint (Z) is applied.

  Before applying the clear paint (Z), the second colored coating film is subjected to the above preheating, air blowing, or the like, so that the solid content concentration of the coating film is usually 60 to 100% by mass, preferably 70%. It is suitable to adjust so that it may become in the range of -100 mass%, More preferably, it is 80-100 mass%.

  As the clear coating (Z), any known thermosetting clear coating composition for coating automobile bodies can be used. Examples thereof include an organic solvent-type thermosetting coating composition, an aqueous thermosetting coating composition, and a powder thermosetting coating composition containing a base resin having a crosslinkable functional group and a crosslinking agent.

  Examples of the crosslinkable functional group possessed by the base resin include a carboxyl group, a hydroxyl group, an epoxy group, and a silanol group.

  Examples of the base resin include acrylic resin, polyester resin, alkyd resin, urethane resin, epoxy resin, and fluororesin.

  Examples of the crosslinking agent include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

  The clear paint may be a one-component paint or a multi-component paint such as a two-component urethane resin paint.

  Further, the clear coating composition can contain, if necessary, a coloring pigment, a bright pigment, a dye, and the like to such an extent that the transparency is not hindered, and further an extender pigment, an ultraviolet absorber, and a light stabilizer. An antifoaming agent, a thickener, a rust inhibitor, a surface conditioner, and the like can be appropriately contained.

  Examples of the base resin / crosslinking agent combination of the clear coating composition include a carboxyl group-containing resin / epoxy group-containing resin, a hydroxyl group-containing resin / polyisocyanate compound, a hydroxyl group-containing resin / blocked polyisocyanate compound, a hydroxyl group-containing resin / melamine resin, etc. The combination of is preferable.

  The clear paint (Z) can be applied to the coating surface of the second colored paint (Y) by a method known per se, for example, airless spray, air spray, rotary atomizer, etc. Alternatively, electrostatic application may be performed.

  The clear paint (Z) can be applied usually in a range of 10 to 80 μm, preferably 15 to 60 μm, and more preferably 20 to 50 μm in cured film thickness.

  In addition, after applying the clear paint (Z), if necessary, leave an interval of about 1 to 60 minutes at room temperature, or preheat at about 40 to 80 ° C. for about 1 to 60 minutes, or apply an object to be coated. Air blowing can be performed by blowing air heated to a normal temperature or a temperature of 25 to 80 ° C. on the surface for 30 seconds to 15 minutes.

Step (4)
In the method for forming a multilayer coating film of the present invention, the uncured first colored coating film, the uncured second colored coating film and the uncured clear coating film formed in the above steps (1) to (3) At the same time, it is cured by heating.

  The first colored coating film, the second colored coating film, and the clear coating film can be cured by a normal coating film baking means, for example, hot air heating, infrared heating, high-frequency heating, or the like.

  The heating temperature is preferably 80 to 180 ° C, more preferably 100 to 170 ° C, and still more preferably 120 to 160 ° C.

  The heating time is preferably 10 to 60 minutes, and more preferably 15 to 40 minutes. By this heating, a multilayer coating film composed of three layers of the first colored coating film, the second colored coating film, and the clear coating film can be simultaneously cured.

  The multilayer coating film forming method of the present invention is a multilayer coating film excellent in smoothness, sharpness and chipping resistance without preheating the uncured colored coating film obtained in step (1). Can be formed. For this reason, the multilayer coating film forming method of the present invention, for example, applies the first colored paint (X) in the intermediate coating booth, and applies the second colored paint (Y) in the base coat painting booth without performing preheating. It can be suitably used in a 3-coat 1-bake system in which the paint is applied and the clear paint (Z) is applied at the clear paint booth. The coating film formation method in this case can be performed according to the following method I, for example.

Method I
The following steps (1) to (5):
(1) A process of coating a steel sheet with an electrodeposition paint and heat-curing to form a cured electrodeposition coating film,
(2) In the intermediate coating booth, a step of coating the first colored paint (X) on the cured electrodeposition coating film obtained in step (1) to form an uncured intermediate coating film,
(3) In the base coat painting booth, the second colored paint (Y) is applied onto the uncured intermediate coating film without preheating the uncured intermediate coating film obtained in step (2). And forming an uncured base coat film,
(4) In the clear coating booth, a step of coating the clear coating (Z) on the uncured base coat film obtained in step (3) to form an uncured clear coating film, and (5) step A step of simultaneously curing these three coating films by heating the uncured intermediate coating film, the uncured base coating film and the uncured clear coating film formed in (2) to (4),
A method for forming a multilayer coating film comprising sequentially performing the steps.

  The booth is a facility for maintaining the coating environment such as temperature and humidity within a certain range in order to ensure uniform coating quality, and is usually divided according to the type of paint to be painted. In the same booth, the same paint may be applied twice in order to prevent sagging or unevenness of the paint applied to the object. In this case, the first painting is called the first stage painting, and the second painting is called the second stage painting.

In the above method I, the coating thickness of the first colored paint (X) is preferably 2 to 15 μm, preferably 4 to 13 μm, and more preferably 5 to 10 μm as a cured film thickness. The coating thickness of the second colored paint (Y) is preferably 5 to 20 μm, preferably 6 to 15 μm, and more preferably 7 to 13 μm as a cured film thickness.
Moreover, the coating film thickness of the said clear coating composition is 10-80 micrometers as a cured film thickness, Preferably it is 15-60 micrometers, More preferably, it is suitable in the range of 20-50 micrometers.

  In the multilayer coating film forming method of the present invention, the first colored paint (X) is applied at the first stage of the base coat painting booth, and the second colored paint (Y) is applied at the second stage of the base coat painting booth. It can be suitably used in a 3-coat 1-bake system in which a clear paint is applied in a clear coating booth. The coating film formation method in this case can be performed according to the following method II, for example.

Method II
The following steps (1) to (5):
(1) A process of coating a steel sheet with an electrodeposition paint and heat-curing to form a cured electrodeposition coating film,
(2) In the first stage of the base coat painting booth, the first colored paint (X) is coated on the cured electrodeposition coating film obtained in step (1) to form an uncured first base coat coating film. The process of
(3) In the second stage of the base coat painting booth, the second coloring is applied to the uncured first base coat film without preheating the uncured first base coat film obtained in the step (2). Applying the paint (Y) to form an uncured second base coat film;
(4) In the clear coating booth, a step of coating the clear coating (Z) on the uncured second base coat film obtained in the step (3) to form an uncured clear coating film, and (5 ) By heating the uncured first base coat film, the uncured second base coat film and the uncured clear film formed in the steps (2) to (4), these three films are simultaneously formed. Curing,
A method for forming a multilayer coating film comprising sequentially performing the steps.

  In the painting method of the above method II, different paints are used in the first stage and the second stage, unlike the general two-stage painting in which the same paint is used in the first stage and the second stage of the base coat painting booth. .

  Of the coating methods of Method I and Method II, Method II does not require an intermediate coating booth and has the advantage that energy for adjusting the temperature and humidity of the intermediate coating booth can be reduced.

  Further, the multilayer coating film forming method of the present invention can form a multilayer coating film excellent in smoothness, sharpness and chipping resistance without performing the preheating. For this reason, in the multilayer coating film forming method of the present invention, the first colored paint (X) and the second colored paint (Y) are applied in the same coating booth, so it is difficult to introduce preheating equipment. In the above method II, it can be particularly preferably used.

  Moreover, in the process (4) of the said method II, the said preheating, an air blow, etc. can be performed to the basecoat coating film obtained by the process (2) and (3).

  In the method II, the coating thickness of the first colored paint (X) is preferably 2 to 15 μm, preferably 4 to 13 μm, and more preferably 5 to 10 μm as a cured film thickness. The coating thickness of the second colored paint (Y) is preferably 5 to 20 μm, preferably 6 to 15 μm, and more preferably 7 to 13 μm as a cured film thickness.

  Moreover, the coating film thickness of the said clear coating composition is 10-80 micrometers as a cured film thickness, Preferably it is 15-60 micrometers, More preferably, it is suitable in the range of 20-50 micrometers.

  According to the method for forming a multilayer coating film of the present invention, it is possible to form a multilayer coating film having excellent chipping resistance in a three-coat one-bake coating method. In particular, in the 3-coat 1-bake method in which an intermediate coating (referred to as the first colored coating (X) in the present invention) is applied with a thinner film thickness than that conventionally applied, the chipping resistance is improved. In addition, a multilayer coating film having excellent smoothness and sharpness can be formed.

  In the multilayer coating film forming method of the present invention, a multilayer coating film having excellent chipping resistance can be formed even when the first colored coating (X) is applied with a thinner film thickness than the conventional intermediate coating. As a reason, it is guessed that the softness | flexibility excellent in the coating film in which the said hydroxyl-containing urethane resin (U) is formed is provided.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to only these examples. “Part” and “%” are based on mass. Moreover, the film thickness of a coating film is based on a cured coating film.
[Production of ε-caprolactone modified form of tris (2-hydroxyethyl) isocyanurate]
(Production Example 1)
In a four-necked reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube and a dropping device, 456 parts of “PLACCEL-M” (trade name, manufactured by Daicel Chemical Industries, ε-caprolactone) , 261 parts of tris (2-hydroxyethyl) isocyanurate and 0.03 part of tetrabutyl titanate were charged and heated to 160 ° C. while stirring. The reaction was carried out at the same temperature for about 4 hours to obtain a modified ε-caprolactone of tris (2-hydroxyethyl) isocyanurate.
[Production of hydroxyl group-containing urethane resin (U)]
(Production Example 2)
In a four-necked reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser, nitrogen inlet tube and dropping device, 243 parts of methyl isobutyl ketone and 20 parts of tris (2-hydroxyethyl) isocyanurate (molecular weight 261) "New Pole PP-1000" (trade name, manufactured by Sanyo Kasei Co., Ltd., polypropylene glycol, number average molecular weight 1,000, hydroxyl value 112 mg KOH / g) 102 parts, N-methyl-2-pyrrolidone 24 parts and dibutyltin dilaurate 0 .016 parts were charged and heated to 110 ° C. with stirring. Next, 40 parts of methylenebis (1,4-cyclohexanediyl) diisocyanate was added while maintaining the temperature of the liquid at 110 ° C., and the reaction was continued until the isocyanate value was 1.0 mg NCO / g or less based on the resin solid content. Next, 111 parts of methyl isobutyl ketone was added to obtain a hydroxyl group-containing urethane resin solution (U-1) having a solid content of 30%. The obtained hydroxyl group-containing urethane resin had a hydroxyl value of 44 mgKOH / g, a weight average molecular weight of 20,000, and a number average molecular weight of 5,000.

Moreover, content rate C _a1 of the cyclic polyol compound (a1) having a nurate structure with respect to the total amount of the polyol component (a) in the obtained hydroxyl group-containing urethane resin was calculated as follows.

Number of moles of cyclic polyol compound (a1) having a nurate structure = 20/261 (tris (2-hydroxyethyl) isocyanurate)
≒ 0.0766 [mol]
Number of moles of polyol component (a) = 20/261 (tris (2-hydroxyethyl) isocyanurate) +102/1000 (“Newpol PP-1000”)
≒ 0.0766 + 0.102
= 0.1786 [mol]
Content ratio C _{a1 of the} cyclic polyol compound (a1) having a nurate structure with respect to the total amount of the polyol component (a)
= 0.0766 / 0.1786 × 100
≒ 43 [mol%]
Moreover, content rate C _a2-1 of the diol compound (a2-1) with respect to the total amount of the polyol component (a) in the obtained hydroxyl group-containing urethane resin was calculated as follows.

Total number of moles of diol compound (a2-1) = 102/1000 (“Newpol PP-1000”)
= 0.102 [mol]
Content ratio C _a2-1 of diol compound (a2-1) with respect to the total amount of polyol component (a)
= 0.102 / 0.1786 × 100
≒ 57 [mol%]
Moreover, ratio C _a1 / C _a2-1 of said C _a1 and C _a2-1 of the obtained hydroxyl-containing urethane resin was _43/57 from said calculation value.
(Production Examples 3 to 27)
Except having the composition shown in Table 1 below, the synthesis was performed in the same manner as in Production Example 1 to obtain a hydroxyl group-containing urethane resin solution (U-2) to (U-26) having a solid content of 30%.

Table 1 shows the content ratio C _{a1 of the} cyclic polyol compound (a1) having a nurate structure relative to the total amount of the raw material composition (parts) of the hydroxyl group-containing urethane resin solutions (U-1) to (U-26) and the polyol component (a). , the diol compound to the total amount of polyol component (a) content _{C a2-1} of (a2-1), the _{C a1} and the ratio _C a1 _{/ C a2-1} with _{C a2-1,} hydroxyl value, acid value, weight Average molecular weight and number average molecular weight are shown.

(Note 1) “PTMG-650”: trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, number average molecular weight 650, hydroxyl value 172 mg KOH / g
(Note 2) “PTMG-1000”: trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, number average molecular weight 1,000, hydroxyl value 112 mgKOH / g
(Note 3) “PTMG-2000”: trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, number average molecular weight 2,000, hydroxyl value 56 mgKOH / g
(Note 4) “UH-CARB50”: trade name, manufactured by Ube Industries, polycarbonate diol, number average molecular weight 500, hydroxyl value 224 mgKOH / g
(Note 5) “UH-CARB100”: trade name, manufactured by Ube Industries, polycarbonate diol, number average molecular weight 1,000, hydroxyl value 112 mgKOH / g
(Note 6) “UH-CARB200”: trade name, manufactured by Ube Industries, polycarbonate diol, number average molecular weight 2,000, hydroxyl value 56 mgKOH / g
(Note 7) “UH-CARB300”: trade name, manufactured by Ube Industries, polycarbonate diol, number average molecular weight 3,000, hydroxyl value 37 mgKOH / g
(Note 8) “Kuraray polyol P-510”: trade name, manufactured by Kuraray Co., Ltd., polyester diol, number average molecular weight 500, hydroxyl value 224 mgKOH / g
(Note 9) “Kuraray polyol P-1011”: trade name, manufactured by Kuraray Co., Ltd., polyester diol, number average molecular weight 1,000, hydroxyl value 112 mgKOH / g
(Note 10) “PEG-1000”: trade name, manufactured by Sanyo Kasei Co., Ltd., polyethylene glycol, number average molecular weight 1,000, hydroxyl value 112 mgKOH / g
In Table 1, among the hydroxyl group-containing urethane resin solutions (U-1) to (U-26), the hydroxyl group-containing urethane resin solutions (U-1) to (U-25) are cyclic polyol compounds (a1) having a nurate structure. And a hydroxyl group-containing urethane resin (U) obtained by a reaction between a polyol component (a) comprising the other polyol compound (a2) and the polyisocyanate compound (b).
[Manufacture of coating composition]
(Production Example 28)
83 parts of a hydroxyl group-containing urethane resin solution (U-1) obtained in Production Example 1 (resin solid content 25 parts), 50 parts of “JR-806” (trade name, manufactured by Teica, titanium dioxide pigment), “Carbon MA— 100 parts (trade name, manufactured by Mitsubishi Chemical Corporation, carbon black pigment), 5 parts "MICRO ACE S-3" (trade name, manufactured by Nippon Talc Co., Ltd.) and 15 parts of methyl isobutyl ketone, and then paint A pigment dispersion paste was obtained by dispersing for 30 minutes with a shaker.

  Next, 154 parts of the obtained pigment dispersion paste, 150 parts of the hydroxyl group-containing urethane resin solution (U-1) obtained in Production Example 2 (45 parts of resin solid content), “Desmodule BL3370MPA” (trade name, Sumika Bayer) Urethane, active methylene blocked polyisocyanate compound, solid content 70%) 43 parts (resin solid content 30 parts) and “Denacol EX-252” (trade name, manufactured by Nagase ChemteX, hydrogenated bisphenol A type epoxy resin) 10 parts of epoxy equivalent 213) were mixed uniformly.

Next, methyl isobutyl ketone was added to the resulting mixture, and Ford Cup No. A first colored paint (X-1) having a viscosity of 18 according to 3 was obtained.
(Production Examples 29-58)
In Production Example 28, the first colored paints (X-2) to (X-31) were obtained in the same manner as in Production Example 28 except that the composition was as shown in Table 2 below.

(Note 11) "Desmodule BL3175" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., methyl ethyl ketoxime blocked polyisocyanate compound, solid content 75%)
(Note 12) “Sumijour N3300” (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., polyisocyanate compound having an isocyanurate structure, solid content of 100%)
(Note 13) “Cymel 325” (trade name, manufactured by Nippon Cytec Industries, Inc., melamine resin, solid content 80%)
(Note 14) “Denacol EX-931” (trade name, manufactured by Nagase ChemteX Corporation, polypropylene glycol diglycidyl ether, epoxy equivalent 471)
[Coating film forming method]
Using the first colored paints (X-1) to (X-31) obtained in Production Examples 28 to 58, test plates were produced as follows and subjected to an evaluation test.
[Preparation of test article]
A thermosetting epoxy resin-based cationic electrodeposition coating composition (trade name “Electron GT-10”, manufactured by Kansai Paint Co., Ltd.) is applied to a 30 cm × 45 cm zinc phosphate-treated cold rolled steel sheet so as to have a film thickness of 20 μm. Electrodeposition coating was performed and cured by heating at 170 ° C. for 30 minutes to prepare a test article.

Example 1
The first colored paint (X-1) obtained in Production Example 28 is cured on the test object using a rotary atomizing electrostatic coater so that the film thickness becomes 8 μm. The film was electrostatically coated and left for 3 minutes. Next, a top-coated base coat coating composition (trade name “WBC-713T”, manufactured by Kansai Paint Co., Ltd., acrylic resin / amino resin-based aqueous coating composition, hereinafter “second colored coating” (Y-1) ”may be electrostatically coated using a rotary atomizing type electrostatic coating machine so that the film thickness when cured is 9 μm, and after standing for 2 minutes, 80 ° C. For 3 minutes. Next, on the uncured second colored coating film, an acrylic resin-based solvent-type clear coating (trade name “MAGICRON KINO-1210” manufactured by Kansai Paint Co., Ltd., hereinafter referred to as “clear coating (Z-1)” may be used. ) Is electrostatically coated so that the film thickness when cured is 35 μm, left for 7 minutes, and then heated at 140 ° C. for 30 minutes to produce the first colored coating film, the second colored coating film, and the clear coating film. Were simultaneously cured to prepare a test plate.

Examples 2-35, Comparative Example 1
In Example 1, in place of the first colored paint (X-1), any one of the first colored paints shown in Table 3 below was used, and the film thickness when cured became the film thickness shown in Table 3 below. A test plate was prepared in the same manner as in Example 1 except that the coating was applied.

Example 36
The first colored paint (X-3) obtained in Production Example 30 is cured on the test object by using a rotary atomizing electrostatic coater so that the film thickness becomes 8 μm. The film was electrostatically coated and left for 3 minutes. Next, a top-coated base coat coating composition (trade name “TB-516”, manufactured by Kansai Paint Co., Ltd., acrylic resin / amino resin-based organic solvent coating composition, hereinafter referred to as “second coating” on the uncured first colored coating film. The colored paint (sometimes referred to as “Y-2)” was electrostatically coated using a rotary atomizing electrostatic coating machine so that the film thickness when cured was 9 μm, and left for 3 minutes. Next, electrostatic coating was performed so that the film thickness when the clear coating (Z-1) was cured was 35 μm on the uncured second colored coating film, left for 7 minutes, and then heated at 140 ° C. for 30 minutes. Then, a test plate was prepared by simultaneously curing the first colored coating film, the second colored coating film, and the clear coating film.

Example 37
The first colored paint (X-3) obtained in Production Example 30 is cured on the test object by using a rotary atomizing electrostatic coater so that the film thickness becomes 8 μm. The film was electrostatically coated, allowed to stand for 3 minutes, and then preheated at 80 ° C. for 2 minutes. Next, the second colored paint (Y-1) is cured on the uncured first colored coating film using a rotary atomizing type electrostatic coating machine so that the film thickness becomes 9 μm. The coating was electrostatically coated and allowed to stand for 2 minutes, followed by preheating at 80 ° C. for 3 minutes. Next, the uncoated second colored coating film is electrostatically coated so that the film thickness when the clear coating (Z-1) is cured is 35 μm, left for 7 minutes, and then at 140 ° C. for 30 minutes. A test plate was prepared by heating and simultaneously curing the first colored coating film, the second colored coating film and the clear coating film.

Comparative Example 2
The first colored paint (X-31) obtained in Production Example 58 is cured on the test object by using a rotary atomizing electrostatic coater so that the film thickness becomes 8 μm. The film was electrostatically coated, allowed to stand for 3 minutes, and then preheated at 80 ° C. for 2 minutes. Next, the second colored paint (Y-1) is cured on the uncured first colored coating film using a rotary atomizing type electrostatic coating machine so that the film thickness becomes 9 μm. The coating was electrostatically coated and allowed to stand for 2 minutes, followed by preheating at 80 ° C. for 3 minutes. Next, the uncoated second colored coating film is electrostatically coated so that the film thickness when the clear coating (Z-1) is cured is 35 μm, left for 7 minutes, and then at 140 ° C. for 30 minutes. A test plate was prepared by heating and simultaneously curing the first colored coating film, the second colored coating film and the clear coating film.

Evaluation Test Each test plate obtained in Examples 1 to 37 and Comparative Examples 1 and 2 was evaluated by the following test method. The evaluation results are shown in Table 3 below.

(Test method)
Smoothness: Evaluated using the Wc value measured by “Wave Scan DOI” (trade name, manufactured by BYK Gardner). It shows that the smoothness of a coating surface is so high that Wc value is small.

  Vividness: Evaluated using the Wb value measured by “Wave Scan DOI” (trade name, manufactured by BYK Gardner). The smaller the Wb value, the higher the clearness of the coating surface.

Water resistance: After immersing the test plate in warm water of 40 ° C. for 240 hours, pulling up and drying at 20 ° C. for 12 hours, the multi-layer coating film of the test plate was cut into a lattice shape with a cutter so as to reach the substrate, and the size was 2 mm. Make 100 x 2mm gobang eyes. Subsequently, an adhesive cellophane tape was attached to the surface, and the remaining state of the goby eye coating after the tape was rapidly peeled off at 20 ° C. was examined according to the following evaluation criteria. Evaluations A to C indicate pass, and evaluation D indicates failure.
A: 100 Gobang eye coats remain, and no small chipping of the paint film occurs at the cutting edge of the cutter. B: 100 Gobang eye coats remain, but the coating film is small at the cutting edge of the cutter. D: There are 95 to 99 goblet-coated films remaining. D: The remaining number of gobang-coated films is 94 or less. Chipping resistance: Stepping stone tester (trade name “JA-400 type” Suga A test plate was installed on a specimen holder of Tester Co., Ltd., and at −20 ° C., with a compressed air of 0.392 MPa (4 kgf / cm ² ) from a location 30 cm away from the test plate 50 g of granite crushed stone was collided with the test plate at an angle of 30 degrees. Thereafter, the obtained test plate was washed with water and dried, and a cloth adhesive tape (manufactured by Nichiban Co., Ltd.) was attached to the coated surface. And the said tape was peeled, the generation | occurrence | production degree of the crack of a coating film, etc. was observed visually and evaluated.
◎: The electrodeposition surface and the base steel sheet are not exposed. ○: The electrodeposition surface and the base steel sheet are exposed, but the exposed scratch ratio is less than 10%. There are scratches where the steel plate is exposed, and the exposure scratch rate is 10% or more.

Claims (11)

The following steps (1) to (4):
(1) A hydroxyl group-containing urethane obtained by reacting a polyisocyanate compound (b) with a polyol component (a) comprising a cyclic polyol compound (a1) having a nurate structure and another polyol compound (a2) on a substrate. Applying the first colored paint (X) containing the resin (U) and the curing agent (C) to form an uncured first colored coating film;
(2) A step of coating the second colored paint (Y) on the uncured colored coating film obtained in the step (1) to form an uncured second colored coating film,
(3) A step of coating the clear paint (Z) on the uncured second colored coating film obtained in the step (2) to form an uncured clear coating film, and (4) Step (1) A step of simultaneously curing these three coating films by heating the uncured first colored coating film, the uncured second colored coating film and the uncured clear coating film formed in (3),
A method for forming a multilayer coating film comprising sequentially performing the steps.   The method for forming a multilayer coating film according to claim 1, wherein the cyclic polyol compound (a1) having a nurate structure is tris (hydroxyalkyl) isocyanurate. The other polyol compound (a2) is a polyether diol compound (a2-1-1) represented by the following general formula (1) and a polycarbonate diol compound (a2-1-2) represented by the following general formula (2) The method for forming a multilayer coating film according to claim 1, comprising at least one diol compound (a2-1).

[In Formula (1), R ¹ represents an alkylene group having 3 or more carbon atoms, and m represents an integer of 2 to 100. Each R ¹ in m repeating units may be the same or different from each other. ]

Wherein (2), represents a plurality of ^{R 2} each independently having 3 or more alkylene group having a carbon, n is an integer of 2 to 100. ] The content ratio C _{a1 of the} cyclic polyol compound (a1) having a nurate structure relative to the total amount of the polyol component (a) is in the range of ₁ to 75 mol%, and the diol compound (a2-1 relative to the total amount of the polyol component (a) ) Content ratio C _a2-1 is in the range of 10 to 99 mol%, and the ratio C _a1 / C _{a2-1 of} C _a1 and C _a2-1 is in the range of 1/99 to 75/25. The method for forming a multilayer coating film according to claim 3.   The method for forming a multilayer coating film according to any one of claims 1 to 4, wherein the polyisocyanate compound (b) is an alicyclic diisocyanate.   The method for forming a multilayer coating film according to any one of claims 1 to 5, wherein the hydroxyl value of the hydroxyl group-containing urethane resin (U) is in the range of 1 to 100 mgKOH / g.   The method for forming a multilayer coating film according to any one of claims 1 to 6, wherein the curing agent (C) is a blocked polyisocyanate compound.   The method for forming a multilayer coating film according to any one of claims 1 to 7, wherein the first colored paint (X) contains an epoxy resin.   The method for forming a multilayer coating film according to any one of claims 1 to 8, wherein the thickness of the first colored coating film is 2 to 15 µm when the first colored paint (X) is applied and cured. .   The method for forming a multilayer coating film according to any one of claims 1 to 9, wherein the second colored paint (Y) is applied without preheating after the application of the first colored paint (X).   The article | item which has a coating film formed by the multilayer coating-film formation method of any one of Claims 1-10.