JP2005042001A - Coating composition, method for forming coated film, and coated article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating composition for providing a coated film having excellent hardness of the coated film (polishing resistance), attachability in recoating, gasohol resistance and moisture resistance; and to provide a coating method. <P>SOLUTION: The final coating composition comprises (a) a main ingredient consisting essentially of a polyol resin having 40-300 mg-KOH/g hydroxyl value, and (b) an isocyanate compound as a curing agent. The curing agent (b) contains 10-75 mass% diisocyanate compound having a urethodione bond, 25-90 mass% compound of a tetramer or a higher oligomer of hexamethylenediisocyanate and/or 5-90 mass% compound of a trimer or a higher oligomer of isophoronediisocyanate, regulated so that the molar ratio (NCO/OH) of the hydroxy group of the main agent (a) to the free isocyanate group of the curing agent (b) is 0.6-3.5. The coating method uses the final coating composition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, a one-part base paint and a two-part clear paint are sequentially applied and baked and dried at a temperature of 65 ° C. or higher to provide excellent recoat adhesion, coating film hardness, gas hole resistance, and moisture resistance. The present invention relates to a coating composition, a coating film forming method and a coated article for obtaining a film.

  Conventionally, the outer panels of automobiles, motorcycles, electrical products, etc., where cosmetic appearance is important, have been finished with a thermosetting paint that forms an excellent coating film such as smoothness, sharpness, and weather resistance. The coating method consists of a one-coat one-bake method in which a thermosetting enamel paint containing a color pigment and a metallic pigment is blended and heat-cured, and a thermosetting clear paint without heating after the thermosetting enamel paint is applied. There is a 2-coat 1-bake method in which the two coating films are cured simultaneously by coating (wet on wet). In particular, the two-coat one-bake method using a two-pack type clear paint has a high-class feeling and good coating film quality, and is currently mainstream.

In automobile paints, there are many kinds in small quantities due to the tendency of users to make multiple colors. Thermosetting enamel-based paints containing colored pigments and metallic pigments are one-pack type with excellent paint stability and easy handling. Paint type is mainstream. And as a method to improve production efficiency, only the surface layer of the coating film is polished with an abrasive to remove dust, scum, etc. of automobile paint (polishing), or the inside of the coating film is polished (sanding), and then The above-mentioned one-component base paint and two-component clear paint are repainted (recoated) on the part.
Further, there is a demand for a lower baking drying temperature for simultaneously curing the two coating films.

  In the two-coat one-bake method using a combination of a low-temperature curing type one-component base paint and a two-component clear paint, which are currently mainstream, recoat adhesion is a problem. With recoating, a one-component base paint and a two-component clear paint are sequentially applied and baked and dried. Again, this cured coating is a specification in which a one-component base paint and a two-component clear paint are sequentially applied and baked and dried. In order to overcome this problem, the adhesion is improved by applying a primer for recoating onto the clear coating film which has been baked and dried, thereby solving the problem. However, from the viewpoint of productivity and process shortening, there is a demand for a solution by a coating film forming method that does not use a recoat primer. For example, the addition of a low-temperature dissociation-type blocked isocyanate to a one-component solvent-based paint has been proposed (Patent Document 1), but recoating adhesion was insufficient when baking at a low temperature of 90 ° C. or lower.

  On the other hand, a reduction in the amount of solvent is required from the viewpoint of the global environment. Corresponding to this, the base paint that discharges the largest amount of solvent is being made water-based. There is a need for a coating method using a combination of a paint and a two-component clear paint. However, the two-coat one-bake method using a low-temperature curing type one-component water-based base paint and two-component clear paint does not provide sufficient moisture resistance and gas hole resistance of the coating film, and is agglomerated in the base coating film. There was a drawback that it was easy to break. This drawback is due to the difficulty in finding a curing agent that reacts with the hydroxyl groups of the resin at low temperatures while maintaining the stability of water-based paints against water, which is a solvent. Therefore, simultaneous hardening of both the base coat and the clear coat by the polyisocyanate compound contained in the two-component clear coating as the top coat without adding a curing agent to the aqueous base coat has been proposed (Patent Document 2, 3). However, when drying at a low temperature of 100 ° C. or less, water is difficult to evaporate and remains in the coating film, thereby reducing the cohesive strength of the coating film. Further, the remaining water inhibits simultaneous curing of both coating films by the polyisocyanate compound. Furthermore, since the base coat does not contain a curing agent, the absolute amount of the curing agent is insufficient, and there is a drawback that the physical properties of the coating film such as water resistance are deteriorated. Further, the recoat adhesion was insufficient. The polyisocyanate compound contained in the two-component clear coating is a one-component solution that has been repainted with a pre-painted two-component clear cured coating film in which free NCO has been deactivated by water remaining in the one-component aqueous base layer. This is thought to be because it is difficult to develop chemical bonds near the interface of the water base layer.

  In addition, as a method for reducing the amount of solvent from the viewpoint of the global environment, it is also required to make the clear coating highly solid in parallel with the water-based base coat. (Patent Documents 4 and 5). For example, Patent Document 4 states that “a polyisocyanate compound obtained from hexamethylene diisocyanate, which has a viscosity of less than 1,400 mPa · s / 25 ° C. in a state substantially free of hexamethylene diisocyanate monomer and solvent. And a curing agent for a two-component polyurethane resin mainly composed of a polyisocyanate compound having a uretdione dimer content of more than 10% and an isocyanurate cyclic trimer content of less than 60%, and the same The paint that was found is listed. However, in order to make the curing agent have a low viscosity, the polyisocyanate compound should have a large proportion of a trimer or smaller molecular weight. Moreover, when the ratio of the dimer and the isocyanurate trimer by the hexamethylene diisocyanate in a hardening | curing agent increases, coating-film hardness and reactivity will fall. In particular, when the number of dimers is increased, there is a drawback that sufficient coating film hardness cannot be obtained. For example, in a production system for automobile coating, since the coating film is polished immediately after baking, the coating film cannot be polished if the coating film hardness immediately after baking is soft, and the productivity is hindered. In other words, in the case of Patent Document 4, since it is intended for high solid paint applications, there are limitations on viscosity, and the molecular weight of the isocyanurate used is limited.

  Patent Document 5 states that “a polyisocyanate obtained from hexamethylene diisocyanate, having a viscosity of 30 to 500 mPa · s at 25 ° C. in a state substantially free of a solvent and hexamethylene diisocyanate, The total content of the isomer and the isocyanate trimer is 50% by weight or more, the content of the linear uretdione of the trimer or more is 30% by weight or less, and the content of the isocyanurate of 5 or more is 20% by weight or less. A polyisocyanate composition having a group content of 22% by weight or more and 25% by weight or less is described. However, as in Patent Document 4, the polyisocyanate compound must have a large proportion of a trimer or smaller molecular weight. Moreover, when the ratio of the dimer and the isocyanurate trimer by the hexamethylene diisocyanate in a hardening | curing agent increases, coating-film hardness and reactivity will fall. In particular, when the number of dimers is increased, there is a drawback that sufficient coating film hardness cannot be obtained. For example, in a production system for automobile painting, since the coating film is polished immediately after baking, the coating film cannot be polished if the coating film hardness immediately after baking is soft, and productivity is hindered. In other words, similar to Patent Document 4, Patent Document 5 is also intended for high solid paint applications, and has a limitation in viscosity, limiting the molecular weight of the isocyanurate used.

Japanese Patent Laid-Open No. 2002-119911 JP-A 61-209070 Japanese Patent Laid-Open No. 10-13136 JP-A-5-32759 JP-A-7-304836

  The present invention eliminates the various disadvantages of the above-mentioned prior art of the two-pack type clear paint when the two-coat one-bake method is applied by combining the one-part base paint and the two-part clear paint. When film hardness is obtained and baked and dried at a temperature of 65 ° C. or higher, it is particularly excellent in recoat adhesion of the coating film. When using a solvent-based base paint as a base paint, a water-based base paint is used. However, it is an object to provide a top coating composition excellent in moisture resistance and gas hole resistance of a coating film, a coating film forming method using the top coating composition, and a coated article coated by the coating film forming method And

  The present inventor has intensively studied to solve the above problems. As a result, paying attention to the drying property and curability of tetramethylene or higher hexamethylene diisocyanate and trimer or higher isophorone diisocyanate in the curing agent, a polyol resin having a hydroxyl value of 40 to 300 mgKOH / g In a top coating composition comprising a main component as a main component and an isocyanate compound containing a uretdione bond as a curing agent, a specific amount of an isocyanate compound containing a uretdione bond and a tetramer or more hexamethylene diisocyanate in the curing agent It has been found that the above problems can be solved by using a curing agent containing a compound or / and a trimer or higher isophorone diisocyanate compound, and the present invention has been completed.

  That is, the present invention is a coating composition comprising a main component (a) having a hydroxyl value of 40 to 300 mg KOH / g as a main component and an isocyanate compound as a curing agent (b), wherein the curing agent (b) At least 10 to 75% by mass of an isocyanate compound having a uretdione bond and 25 to 90% by mass of a tetramethylene or more hexamethylene diisocyanate compound, and / or 5 to 90% by mass of a trimer or more of an isophorone diisocyanate compound. A top coating composition in which the molar ratio (NCO / OH) of the free isocyanate group of the curing agent (b) to the hydroxyl group of the main agent (a) is 0.6 to 3.5 is provided.

  The present invention also provides a top coating composition in which the isocyanate compound having a uretdione bond is a hexamethylene diisocyanate compound represented by the general formula (1) (Chemical Formula 1).

（式中、ｍは０〜１の整数である）

(Where m is an integer from 0 to 1)

  In the present invention, a one-component aqueous base paint containing a hydroxyl group-containing resin, a color pigment, a metallic pigment or a pearl pigment is applied to a thickness of 8 to 30 μm based on a dry coating film, and then wetted on the coated surface. A coating film characterized in that, in an on-wet state, the top coating composition of the present invention is applied to a thickness of 20 to 60 μm based on a dry coating film, and both coating films are simultaneously baked and cured at a temperature of 65 ° C. or more. A forming method is provided.

  In the present invention, a one-component solvent-based base paint containing a hydroxyl group-containing resin, a color pigment, a metallic pigment or a pearl pigment is applied to a thickness of 8 to 50 μm based on a dry coating film, and then applied to the coated surface. A coating film forming method characterized in that, in a wet-on-wet state, the top coating composition of the present invention is applied to a thickness of 20 to 60 μm based on a dry coating film, and is simultaneously baked and cured at a temperature of 65 ° C. or higher. provide.

  The present invention also provides a coated article coated with the coating film forming method of the present invention using the coating composition of the present invention.

  Using the top coating composition of the present invention, when a two-coat one-bake method is applied using a combination of a one-component base paint and a two-component clear paint, an excellent coating film hardness is obtained, which is 65 ° C. or higher. By baking and drying at temperature, it is particularly excellent in recoat adhesion of the coating film, and not only when using a solvent-based base paint as a base paint, but also with moisture resistance and gas hole resistance even when using a water-based base paint. An excellent coating film is obtained.

In the top coating composition of the present invention, examples of the polyol resin as the main agent (a) include various polyol resins. One type of polyol resin may be used, or two or more types may be combined.
The polyol resin as the main agent (a) is preferably a polyol resin having a hydroxyl value of 40 to 300 mgKOH / g, preferably a hydroxyl value of 80 to 180 mgKOH / g. When the polyol resin has a hydroxyl value of less than 40 mgKOH / g, the resulting coating film has insufficient crosslinking density, and when it exceeds 300 mgKOH / g, the structure of the coating film becomes too dense. The shrinkage stress becomes large and cannot be relaxed, and cracks and the like are likely to occur in the coating film.

Examples of the main component (a) polyol resin include acrylic polyol and polyester polyol.
When the polyol resin of the main agent (a) is an acrylic polyol, other copolymerizable polymerizable unsaturated monomers and / or acrylic esters are used based on the polymerizable unsaturated monomers containing the following hydroxyl groups. It can be obtained by polymerization or copolymerization.

  Examples of the polymerizable unsaturated monomer containing a hydroxyl group include hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, 1,4-butanediol monomethacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 1 , 4-butanediol monoacrylate and the like. Further, the C1-C18 alkyl alcohol forming the acrylic ester may be any alcohol having a linear, branched, or cyclic alkyl group. These may be used alone or in combination of two or more.

  Other copolymerizable unsaturated monomers that can be copolymerized include, for example, phosmer (trade name, manufactured by Unichemical Co., Ltd.), glycidyl methacrylate, glycidyl acrylate, allyl methacrylate, allyl acrylate, and 3,4-epoxycyclohexyl. Methyl methacrylate, 3,4-epoxycyclohexylmethyl acrylate, phenyl methacrylate, phenyl acrylate, α-methylstyrene, p-vinyltoluene, methacrylamide, acrylamide, N, N-dimethylmethacrylamide, N, N-dimethylacrylamide, Acrylic acid-2,2,6,6-tetramethyl-4-piperidyl, ethyl vinyl ether, isopropyl vinyl ether, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl Aliphatic vinyl ether compounds such as nyl ether and cyclohexyl vinyl ether, 2,3-dihydrofuran, 3,4-dihydro-2H-pyran, trimethoxysilylpropyl methacrylate, maleic anhydride, itaconic anhydride, maleic esters, fumarate Acid esters, styrene, acrylonitrile, methacrylonitrile, 2-hydroxyethyl crotonic acid, 2-hydroxypropyl crotonic acid, 3-hydroxypropyl crotonic acid, 3-hydroxybutyl crotonic acid, 4-hydroxybutyl crotonic acid, crotonic acid 5 -Allyl group-containing compounds such as hydroxypentyl, 6-hydroxyhexyl crotonate, allyl alcohol, allyl glycidyl ether, croton such as methyl crotonate, ethyl crotonate, propyl crotonate Acid alkyl ester, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl stearate and other aliphatic carboxylic acid vinyl esters, cyclohexane carboxylate vinyl And an aromatic carboxylic acid vinyl ester such as vinyl benzoate, vinyl benzoate, vinyl cinnamate and vinyl tert-butyl benzoate. These may be used alone or in combination of two or more.

  Examples of copolymerizable acrylic esters include, for example, methyl methacrylate, ethyl methacrylate, -n-propyl methacrylate, isopropyl methacrylate, -n-butyl methacrylate, isobutyl methacrylate, and t-butyl methacrylate. , Pentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, adamantyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate , -N-butyl acrylate, isobutyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, acrylic acid Damantyl, dodecyl acrylate, isobornyl acrylate, methacrylic acid, acrylic acid, itaconic acid, mesaconic acid, maleic acid, fumaric acid, ω-carboxy-polycaprolactone (n = 2) monoacrylate (for example, Aronix M-5300 (product) Name, manufactured by Toagosei Chemical Industry Co., Ltd.), monohydroxyethyl acrylate phthalate (for example, Aronix M-5400 (trade name, manufactured by Toagosei Chemical Industry Co., Ltd.)), acrylic acid dimer (for example, Aronix M-) 5600 (trade name, manufactured by Toagosei Chemical Industry Co., Ltd.)). These may be used alone or in combination of two or more.

  Other copolymerizable unsaturated monomers and copolymerizable acrylic esters are not essential components, and are appropriately selected and used as needed according to the substrate and purpose of use in designing the coating film. It is done.

  The method for polymerizing or copolymerizing a polymerizable unsaturated monomer having a hydroxyl group is not particularly limited, and known methods such as solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization, and precipitation polymerization in an organic solvent. Etc. can be used. The polymerization method is not particularly limited, and for example, any of radical polymerization, cationic polymerization, and anionic polymerization can be used. Among these, radical polymerization is preferable from an industrial viewpoint. Examples of the polymerization initiator used in radical polymerization include t-butyl hydroperoxide, cumene hydroperoxide, t-butyl peroxyneodecanate, t-butyl peroxypivalate, t-hexyl peroxy-2- Organic peroxides such as ethyl hexanoate and methyl ethyl ketone peroxide, or 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylpropionitrile) (AIBN), Preferred examples include azo initiators such as 2,2′-azobis (2-methylbutyronitrile). Of course, it is not limited to these. These radical polymerization initiators may be used alone or in combination of two or more.

  The reaction temperature during radical polymerization is generally preferably 60 to 150 ° C. If this temperature is less than 60 ° C., the radical polymerization initiator is difficult to decompose and the reaction does not proceed easily. If it exceeds 150 ° C., even if the radical polymerization initiator is decomposed by heat to generate radicals, The lifetime is short and the growth reaction is difficult to proceed effectively. The polymerization time depends on the polymerization temperature and other conditions and cannot be determined in general, but generally about 2 to 6 hours is sufficient.

  The polyol resin as the main agent (a) is preferably one obtained by addition reaction of a compound capable of addition reaction with a hydroxyl group. Examples of the compound capable of undergoing an addition reaction with a hydroxyl group include lactone compounds and alkylene oxides, with lactone compounds being preferred. Examples of the lactone compound include β-methyl-δ-valerolactone, γ-valerolactone, δ-valerolactone, δ-caprolactone, γ-caprolactone, ε-caprolactone, β-propiolactone, γ-butyrolactone, γ -Nonanoic lactone, (delta) -dodecanolactone, etc. are mentioned, (epsilon) -caprolactone is especially preferable. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and the like. These compounds capable of undergoing an addition reaction with a hydroxyl group may be used singly or in combination of two or more.

  Moreover, when the polyol resin of the main agent (a) is a polyester polyol, it is obtained by reacting a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include phthalic anhydride, tetrahydrophthalic anhydride, Isophthalic acid, maleic anhydride, fumaric acid, trimellitic anhydride, methylenetricyclohexenylcarboxylic anhydride, pyromellitic anhydride, itaconic acid, adipic acid, sebacic acid, azelaic acid, hexahydrophthalic anhydride, hymic anhydride, anhydrous Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, neopentyl glycol, butylene glycol, hexanediol, trimethylolethane, and trimethyloyl. Trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitol and the like. Further, the polyester resin may be modified with a monobasic acid, a fatty acid, an oil component, or the like. Furthermore, the introduction of hydroxyl groups in the polyester resin can be easily performed with, for example, a polyhydric alcohol having three or more hydroxyl groups in one molecule.

  In the present invention, the curing agent (b) in the top coating composition can contain various compounds having two or more free isocyanate groups in the molecule, but has at least 10 to 75% by mass of uretdione bonds. It is characterized by containing 25 to 90% by mass of a tetramer or higher hexamethylene diisocyanate compound and / or 5 to 90% by mass of a trimer or higher isophorone diisocyanate compound.

  The isocyanate compound having a uretdione bond in the curing agent (b) in the top coating composition of the present invention includes an isocyanate having a uretdione bond in the molecule derived from a compound having two or more free isocyanate groups in the molecule. Although it may be a compound, an isocyanate compound having a uretdione bond represented by the general formula (1) (Chemical Formula 2) is preferred.

（式中、ｍは０〜１の整数である。）

(In the formula, m is an integer of 0 to 1.)

  The amount of the isocyanate compound having a uretdione bond is 10 to 75% by mass, preferably 15 to 60% by mass in the curing agent (b). When the isocyanate compound having a uretdione bond in the curing agent (b) is less than 10% by mass, the resulting coating film has insufficient moisture resistance, gas hole resistance and recoat adhesion, and when it exceeds 75% by mass, The residual uretdione bond in the clear coating film increases and the weather resistance decreases.

Since the isocyanate compound having a uretdione bond contained in the curing agent (b) in the top coating composition of the present invention has a long linear shape and has only a bifunctional free NCO in one molecule, It has a lower viscosity than a compound having trifunctional free NCO, and can be transferred relatively easily to the wet coating layer of the base coating that is in contact therewith. The transferred free NCO of the isocyanate compound easily reacts with the hydroxyl group in the base paint. On the other hand, when the uretdione bond is placed in a state in which a large number of hydroxyl groups are present as in the base paint, the decomposition temperature thereof is lowered and the temperature is lowered to the 65 ° C. temperature range. Therefore, the isocyanate compound having a uretdione bond transferred into the base coating is decomposed at a baking temperature of 65 ° C. or higher, and the generated free NCO also reacts with the hydroxyl groups present in the base coating.
That is, the isocyanate compound having a uretdione bond moves into a one-component base coating layer in which a hydroxyl group is present in an equimolar amount or more with respect to free NCO, decomposes at a temperature of 65 ° C. or more, and reacts with the hydroxyl group. In other words, the uretdione bond in the two-pack type clear layer hardly remains decomposed and remains in the normal baking drying temperature region of 65 to 120 ° C.

Thus, the NCO released from the uretdione bond has a thermal potential and does not react with hydroxyl groups and water derived from the resin or solvent in the base paint in the normal baking drying temperature range of 65 to 120 ° C. It can move more uniformly in the base coating layer. As a result, the volatilization of water and solvent is promoted until the temperature of the coating reaches 65 ° C., and after reaching the temperature of 65 ° C. or higher, the uretdione bond is decomposed and the free NCO is removed from the base coating layer. Uniform cross-linking can be formed with the hydroxyl groups therein. Due to these specificities of the isocyanate compound having a uretdione bond, the moisture resistance and gas hole resistance of the coating film can be greatly improved as compared with other polyisocyanates.
In addition, during recoating, the isocyanate compound having an uretdione bond in the clear coating moves to the base coating layer and reacts with the hydroxyl groups in the base coating, thereby improving the cohesive strength of the base coating and being excellent. Recoat adhesion can be obtained.

  Of the other essential components in the curing agent (b) according to the present invention, the tetramethylene or higher hexamethylene diisocyanate compound is desirably contained in the curing agent (b) in an amount of 25 to 90% by mass. More preferably, the pentamethylene or higher hexamethylene diisocyanate compound is contained in an amount of 25 to 90% by mass, and particularly preferably 30 to 60% by mass. If the tetramethylene or higher hexamethylene diisocyanate in the curing agent (b) is less than 25% by mass, the resulting coating film has insufficient hardness and does not satisfy the polishing properties. If it exceeds 90% by mass, uretdione The amount of the isocyanate compound having a bond is insufficient, and the recoat adhesion becomes insufficient.

  Also, the trimer or higher isophorone diisocyanate compound is preferably contained in the curing agent (b) in an amount of 5 to 90% by mass, more preferably 10 to 60% by mass. When the content of the trimer or higher component in the isocyanate curing agent (b) is less than 5% by mass, the resulting coating film has insufficient hardness and it is difficult to satisfy the polishing property. When the content exceeds 90% by mass, the uretdione bond The amount of the isocyanate compound having a shortage is insufficient, and the recoat adhesion becomes insufficient.

  Thus, since the coating system is polished immediately after baking, the production system in automobile painting must ensure a certain level of coating film hardness, and if the coating film hardness immediately after baking is soft, Although there was a problem that polishing could not be performed, the curing agent (b) in the top coating composition of the present invention had a predetermined amount of tetramer or higher hexamethylene disissocyanate compound and / or trimer or higher. Since it contains an isophorone diisocyanate compound, the hardness of the top coat film and the reaction rate with the hydroxyl groups in the top coat paint increased, and the baking temperature in the simultaneous curing system of the paint film by the wet-on-wet method could be lowered. .

  As described above, a base coating is obtained by using a predetermined amount of a dimeric isocyanate compound having a uretdione bond in combination with a predetermined amount of a higher molecular weight isocyanate compound in the curing agent (b). It is possible to achieve both recoat adhesion and clear coating film hardness by shifting to a film.

  The other isocyanate compound contained in the curing agent (b) may be a compound having two or more free isocyanate groups in the molecule, and specifically, tolylene diisocyanate, 4,4′-diphenylmethane. Diisocyanate, xylylene diisocyanate, metaxylylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, hydrogenated 4,4′-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, tolylene diisocyanate (3 mol) and trimethylolpropane (1 mol) adduct, polymer of tolylene diisocyanate, hexamethylene diisocyanate (3 mol) and toluene Adduct of methylolpropane (1 mol), reaction product of hexamethylene diisocyanate and water, isocyanurate of hexamethylene diisocyanate, adduct of xylylene diisocyanate (3 mol) and trimethylolpropane (1 mol), tri One or more selected from the adducts of diisocyanate (3 mol) and hexamethylene diisocyanate (2 mol) and isocyanurate of isophorone diisocyanate can be used, of which hexamethylene has excellent weather resistance. Non-yellowing types such as diisocyanate isocyanate and isophorone diisocyanate isocyanate are preferred. Among these isocyanate compounds, those having relatively high volatility are preferably 1% or less in the curing agent (b) in view of their toxicity and the like.

In the overcoating composition of the present invention, the preferred blending ratio of the polyol resin of the main agent (a) and the isocyanate curing agent (b) is determined according to the hydroxyl group contained in the main agent (a) and the free isocyanate group of the curing agent (b). The molar ratio (NCO / OH) is 0.6 to 3.5, more preferably 0.8 to 3.0, and still more preferably 1.1 to 2.5.
When the molar ratio of the free isocyanate group to the hydroxyl group is less than 0.6 or more than 3.5, there are hydroxyl groups and isocyanate groups that remain partially unreacted, the crosslink density of the clear coating film becomes sparse, and moisture resistance The gas hole resistance tends to decrease. In addition, since both the main component (a) and the isocyanate curing agent (b) may react and crosslink at room temperature, it is preferable to separate them in advance and mix them immediately before use.

It is preferable to use a curing reaction catalyst in the top coating composition of the present invention.
Examples of the curing reaction catalyst include tin compounds and zinc compounds. Examples of the tin compound include tin halides such as tin chloride and tin bromide, and organic tin compounds such as dibutyltin diacetate and dibutyltin dilaurate. Examples of the zinc compound include zinc chloride and zinc bromide. Examples include zinc salts of organic acids such as zinc halide, zinc octylate, and zinc laurate. One kind of tin compound or zinc compound as a curing reaction catalyst may be used, or two or more kinds may be used in combination, or may be used in combination with another curing reaction catalyst. The curing reaction catalyst is preferably used in a proportion of 0.01 to 5% by mass with respect to the total nonvolatile content in the coating composition. If this amount is less than 0.01% by mass, the effect of accelerating the curing reaction may not be sufficiently exerted. If it exceeds 5% by mass, the moisture resistance of the coating film decreases, and as a result the weather resistance of the coating film It may cause a decrease in sex and the like. From the viewpoint of the balance between the curing speed and the physical properties of the coating film, the more preferable amount of the curing reaction catalyst is in the range of 0.01 to 2% by mass with respect to the total nonvolatile content in the coating composition.

  The top coating composition of the present invention may contain an organic solvent, a color pigment, and / or various additives, for example, an ultraviolet absorber, a light stabilizer, an antioxidant, a surfactant, a leveling agent, and an antifoaming agent as necessary. Agents, and rheology modifiers such as polyethylene wax, polyamide wax, and internally crosslinked resin fine particles can be blended.

The organic solvent of the top coating composition of the present invention is not particularly limited as long as each component can be dissolved, and examples thereof include fats such as n-hexane, n-heptane, and n-octane. Aromatic hydrocarbons such as benzene, toluene and xylene, halogenated hydrocarbons such as chloroform and carbon tetrachloride, alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol and n-butyl alcohol , Ethers such as dibutyl ether, tetrahydrofuran and 1,4-dioxane, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters such as ethyl acetate, n-propyl acetate and n-butyl acetate. Further, a solvent obtained by adding a soluble amount of water to these organic solvents and mixing them may be used as the solvent. These solvents may be used alone or in combination of two or more.
The mixing method of each component, the addition method of the organic solvent, the color pigment and various additives are not particularly limited, and can be performed by various methods, and the mixing order and the addition order can be performed in various orders. it can.

Next, the one-component base paint before applying the top coating composition of the present invention will be described.
The one-pack type water-based base paint is a paint that is applied prior to the two-part clear paint, and contains water as a main solvent or dispersion medium and a hydroxyl group-containing resin, a color pigment, a metallic pigment, or a pearl pigment. The one-part solvent-based paint is a paint that is applied prior to the two-part clear paint. The solvent is the main solvent or dispersion medium, and a hydroxyl group-containing resin, a color pigment, a metallic pigment, or a pearl pigment is blended. Become. The basic structure of the hydroxyl group-containing resin in the one-component base paint is, for example, an acrylic resin, a polyester resin, a polyurethane resin, a chlorinated polyolefin-modified acrylic resin, a polycaprolactone-modified acrylic resin, a modified acrylic resin such as a urethane-modified acrylic resin, chlorinated Examples thereof include modified polyester resins such as polyolefin polyester resin, polycaprolactone-modified polyester resin, urethane-modified polyester resin, and the like. These may be used alone or in combination of two or more. Introduce a group.

Acrylic resins and polyester resins can be easily synthesized by known methods. In addition, the introduction of carboxyl groups in the polyester resin can be easily carried out by the combined use of polybasic acids having 3 or more carboxyl groups in one molecule or the addition reaction (half-esterification) of dibasic acids.
The polyurethane resin is a resin having a urethane bond and a hydroxyl group or further a carboxyl group (not containing a free isocyanate group). For example, the polyurethane resin is reacted with an excess polyhydric alcohol and a polyisocyanate compound. Or after reacting a polyhydric alcohol with an excess of a polyisocyanate compound, reacting the remaining free isocyanate with an oxyacid such as dimethylolpropionic acid or diphenolic acid in the resin. Carboxyl groups can be provided.

  The chlorinated polyolefin-modified acrylic resin is obtained by graft polymerization of an acrylic monomer to a chlorinated polyolefin. The chlorinated polyolefin to which the acrylic monomer is graft-polymerized is a polyolefin having a chlorination rate of 50% or less, preferably 10 to 45%, more preferably 20 to 40%. As the chlorinated polyolefin, homopolymers or copolymers of olefins selected from ethylene, propylene, 1-butene, 3-methyl-1-butene, 3-methyl-1-heptene, and the like, and the olefins And a copolymer of vinyl acetate, butadiene, acrylic acid ester, methacrylic acid ester and the like, and chlorination of these is carried out by a conventional method. Specific examples of the chlorinated polyolefin include chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, and chlorinated ethylene-vinyl acetate copolymer.

  The above-mentioned compounds can be used as the acrylic monomer graft-polymerized to chlorinated polyolefin, and these can also be used in combination with a hydroxyl group-containing monomer, carboxyl group-containing monomer, and other vinyl monomers, and all these monomer components are the total amount with chlorinated polyolefin. 90 to 10% by weight, in particular 80 to 30% by weight, based on The introduction of a hydroxyl group into the chlorinated polyolefin is carried out by using a hydroxyl group-containing monomer as an acrylic monomer to be graft polymerized, and the introduction of a carboxyl group is carried out by using the carboxyl group-containing monomer together with an acrylic monomer.

  Examples of the polycaprolactone-modified acrylic resin include a resin obtained by polymerizing an adduct of a hydroxyl group-containing monomer such as 2-hydroxyethyl methacrylate and ε-caprolactone alone or with another unsaturated monomer. The introduction of the carboxyl group is carried out by copolymerizing the adduct with a hydroxyl group-containing monomer and a carboxyl group-containing monomer.

  Examples of the urethane-modified acrylic resin include an acrylic resin obtained by copolymerizing a product obtained by adding a hydroxyl group-containing monomer such as 2-hydroxyethyl methacrylate to an equimolar reaction product of a diisocyanate compound and a monoalcohol, or a hydroxyl group-containing acrylic resin. Examples include acrylic resins in which urethane bonds are introduced by reacting a polyisocyanate compound such as hexamethylene diiososanate or a monoisocyanate compound such as butyl isocyanate.

An example of a caprolactone-modified polyester resin is a resin obtained by reacting a hydroxyl group-containing polyester resin with ε-caprolactone in the presence of a suitable catalyst. Examples of the urethane-modified polyester resin include a polyester resin in which a urethane bond is introduced into a resin by reacting a hydroxyl group in a relatively low molecular weight polyester resin with a polyisocyanate compound such as hexamethylene diisocyanate.
In addition to the hydroxyl group-containing resin of the one-component base paint, a melamine resin, a blocked isocyanate resin, or the like is used as a curing agent.

The one-component solvent-based base paint may be an organic solvent, a color pigment and / or various additives as necessary, for example, an ultraviolet absorber, a light stabilizer, an antioxidant, a surfactant, a leveling agent, an antifoaming agent, Furthermore, rheology modifiers such as polyethylene wax, polyamide wax, and internally crosslinked resin fine particles can be blended.
A one-pack type water-based paint is prepared by dispersing the above resin in water using a dispersant such as an emulsifier, or dispersing the resin in water by emulsion polymerization. Water, a small amount of an organic solvent, and a coloring pigment as necessary , Extender pigments, metallic pigments and the like.

In addition, regarding the one-component water-based base coating, is the water dispersion or water-solubilization of the resin made water-soluble or water-dispersible by neutralizing part or all of the carboxyl groups contained in the resin with a basic compound? Alternatively, the resin is obtained by emulsifying the resin in the presence of a dispersant such as an emulsifier, neutralized or unneutralized, or by dispersing the resin in water using a technique such as emulsion polymerization. As these basic compounds, for example, alkanolamines such as monoethanolamine, diethanolamine and dimethylaminoethanol, alkylamines such as diethylamine and triethylamine, or inorganic alkalis such as potassium hydroxide and sodium hydroxide can be used. Of these, compounds such as tertiary amines are very useful because they can also be used as curing catalysts.
Then, water, a color pigment, a metallic pigment, a water-soluble organic solvent, an extender pigment, and the like are appropriately blended with these water-dispersed or water-soluble aqueous resins (vehicle components) to obtain a one-pack type aqueous base paint.

  In the coating film forming method of the present invention, a one-component water-based or one-component solvent-based base paint containing a hydroxyl group-containing resin, a color pigment, a metallic pigment or a pearl pigment is applied, and then the coated surface is wet-on-wet. The top coating composition of the present invention is applied, and both coating films are simultaneously baked and cured at a temperature of 65 ° C. or more.

  One-part base paints can be applied directly to plastic products, polyolefins such as polyethylene and polypropylene, acrylonitrile-butadiene-styrene copolymers, polycarbonate, nylon, fiber reinforced plastics, polyurethane resins, etc. Alternatively, pre-treatment by toluene degreasing or flame treatment or primer coating is performed in advance, and then coating may be performed. The metal may be coated with a one-component base paint after surface treatment by phosphate treatment, etc., primer coating by an electrodeposition coating, etc. and intermediate coating in advance. In addition, the one-component base paint may be overcoated such as 2 coats or 3 coats.

The coating method of the one-component base coating is not particularly limited, and examples thereof include brush coating, immersion coating, spray coating (including electrostatic coating), roll coating, and anion electrodeposition coating. Among these, in the case of spray coating, it is preferable to adjust the viscosity of the one-component solvent-based base paint to 10 to 20 seconds (Ford Cup # 4/20 ° C.). It is preferable to adjust the viscosity of the one-component water-based base paint to 90 ± 5 mPas / 1000 sec-1 (METTLER RM180 Rheomat manufactured by Rheometric Scientific).
The coating method of the two-component clear paint is not limited and can be performed by the above-described coating method. Examples include brush coating, immersion coating, spray coating (including electrostatic coating), roll coating, and anion electrodeposition coating. Among these, in the case of spray coating, it is preferable to adjust the viscosity of the two-component clear paint to 10 to 30 seconds (Ford Cup # 4/20 ° C.). The coating film thickness is suitably 20 to 60 μm, particularly 30 to 40 μm, based on the dry coating film.

  When a one-component solvent-based coating is used as a base coating and when a one-component water-based coating is used, it is contained in the top coating composition of the present invention due to the influence of water remaining in the base coating film. Since the ease of transfer of an isocyanate compound composed only of uretdione bonds to the base coating is different, a one-part water-based base paint is used as a base paint and a one-part solvent-based base paint is used. Then, the suitable film thickness of the base paint is different.

When a one-component solvent-based paint is used, the coating film thickness is suitably 8 to 50 μm, particularly 8 to 30 μm, based on the dry coating film. If it is thicker than 50 μm, the component containing an uretdione bond or the like is not sufficiently transferred to the base coating film, and the recoatability is insufficient.
When a one-component water-based base coating is used, the coating film thickness is suitably 8-30 μm, especially 8-20 μm, based on the dried coating film, and if it is thicker than 30 μm, it becomes a base coating film such as a component having a uretdione bond. Therefore, the recoating property is insufficient.
In any case, when the base coating film has a film thickness of less than 8 μm, the hiding power is insufficient and a desired color tone cannot be obtained.
The coating method of the present invention is applied by wet-on-wet, but before applying the top coat, a process such as forcing hot air is added to accelerate evaporation of the solvent and water. May be.

  The one-pack type base paint in the coating film forming method of the present invention can be applied even when two or more kinds of paints expressing different designs are used. In other words, as long as the film thickness based on the dry coating film of a one-component base coating is within the applicable range, a coating film forming method can be applied in any number of layers with two or more types of coatings expressing different designs in a wet-on-wet state. It is. For example, as a one-component base paint, a color base paint and a mica base paint are applied in a wet-on-wet state, and then the paint composition (A) is applied on the coated surface in a wet-on-wet state. This is a coating film forming method in which baking and curing are simultaneously performed at a temperature of ℃ or higher.

  Examples of the coated article obtained by the present invention include structures, wooden products, metal products, plastic products, rubber products, processed paper, ceramic products, and glass products. More specifically, automobiles, automotive parts (for example, parts such as bodies, bumpers, spoilers, mirrors, wheels, interior materials, etc., of various materials), metal plates such as steel plates, motorcycle parts, motorcycle parts , Road materials (eg, guardrails, traffic signs, noise barriers, etc.), tunnel materials (eg, side walls, etc.), ships, railway vehicles, aircraft, furniture, musical instruments, household appliances, building materials, containers, office supplies, Examples include sports equipment and toys.

Next, the present invention will be described more specifically with reference to examples. In addition, this invention is not restrict | limited at all by these examples.
In addition, the performance of the coating film obtained by the coating composition of this invention was calculated | required as follows.
(1) Cross-cut adhesion test A cross-cut cellophane tape peel test was performed according to JIS K5600-5-6 (1999). 100 grids of 2 mm square were prepared, and the cellophane tape peeling test was carried out three times at the same location, and the number of grids that were not peeled was counted.
(2) Gas hole resistance After coating, baking and drying, a test piece coating film left for 48 hours was immersed in a gas hole obtained by adding 10% by volume of ethanol to regular gasoline for 30 minutes at 20 ° C. Then, the surface state of the test piece was visually observed and evaluated according to the following criteria.
◯: There is almost no change in the gloss and surface state of the test piece coating film compared to before the test.
(Triangle | delta): Compared with before a test, there exists a little change of gloss of a test piece coating film, blistering, and wrinkle generation | occurrence | production.
X: The change of gloss of a test piece coating film, blistering, and wrinkle generation | occurrence | production are remarkable compared with the test front.
(3) Moisture resistance After coating and drying, the substrate left at room temperature for 48 hours is left in an atmosphere of 50 ° C. and 98% humidity for 240 hours and then left at room temperature for 24 hours. The surface condition of the test piece after being allowed to stand at room temperature for 24 hours was evaluated according to the following criteria.
◯: There is almost no change in the gloss and surface state of the test piece coating film compared to before the test.
(Triangle | delta): Compared with before a test, there exists a little change of gloss of a test piece coating film, and blistering (blister).
X: The change of gloss of a test piece coating film and blistering (blister) are conspicuous compared with before the test.
(4) Weather resistance Weather resistance was tested for 2000 hours using a sunshine carbon arc lamp type weather resistance tester (JIS B7753) under conditions of a black panel temperature of 63 ± 3 ° C. and a rainfall time of 12 minutes (60 minutes irradiation). The subsequent color difference ΔE and gloss retention, and cross-cut adhesion test were evaluated.

(5) Recoat adhesion The multi-layer coating film formed in Examples and Comparative Examples is allowed to stand at room temperature for 7 days, and the same paint is repainted on the coated surface under the same film thickness condition and cured at the same baking temperature. Then, after being allowed to stand at room temperature for 3 days, an adhesion test was conducted in the same manner as the cross-cut adhesion test described above.
(6) Coating film hardness After being coated and dried, the substrate is left in a constant temperature room at 20 ° C for 3 hours. Use a hardness standard pencil (JIS S-6006) and hold it at about 45 ° with an instrument or hand. A load was applied so that the core could not be broken at a speed of about 3 mm / sec toward the front, and a length of 10 mm was repeated five times at different locations, and then the state of the scratches on the coating film was examined. When scratches are found in the coating film more than twice out of 5 times, the same test is performed with a pencil whose core hardness is one step lower, and the hardness of the core when the scratches are less than 1 time is determined as the coating film hardness. And In addition, when the scratch observed in the coating film is one in the first five tests, the hardness of the core is increased by one step and the same test is repeated until the scratch becomes twice or more. The hardness one step lower than the hardness is defined as the coating film hardness.
(7) Polishing property The polishing property was evaluated according to the following criteria based on the coating film hardness.
○: Hardness of coating film hardness 4B or more x: Softness of coating film hardness of less than 4B

Production of polyol resin solution (X) -1 and main agent (Y) -1 A four-necked flask equipped with a thermometer, reflux condenser, stirrer, and dropping funnel was charged with 17.1 parts by mass of xylene and 19.0 butyl acetate. A mass part was charged and heated to maintain a reflux state. Thereto, 14.0 parts by mass of 2-hydroxyethyl methacrylate, FM-1D (trade name, manufactured by Daicel Chemical Industries, 1 mol of ε-caprolactone 1 mol addition-modified 2-hydroxyethyl methacrylate), 13.0 parts by mass, meta A mixture prepared by mixing 8.5 parts by mass of 2-ethylhexyl acrylate, 24.5 parts by mass of methyl methacrylate and 3.0 parts by mass of t-butylperoxy-2-ethylhexanoate was added to the reflux state from the dropping funnel. It was dripped over 2 hours, keeping. After the completion of the dropwise addition, the mixture was kept under reflux for 1 hour and then mixed with 0.1 parts by mass of t-butylperoxy-2-ethylhexanoate and 0.8 parts by mass of xylene, and further stirred for 1 hour. Continued. After the completion of polymerization, a resin solution (X) -1 having a nonvolatile content of 60.5% by mass was obtained. The polyol resin (X) -1 had a hydroxyl value of 150 mgKOH / g and a number average molecular weight of 3700.
This polyol solution (X) -1 100.0 parts by mass, dibutyltin dilaurate 0.018 parts by mass, TINUVIN 900 (Ciba Specialty Chemicals Co., Ltd.) 2 parts by mass, TINUVIN 292 (Nippon Ciba Geigy Co., Ltd.) 0.4 parts by mass And main agent (Y) -1.

Production of polyol resin solution (X) -2 and main agent (Y) -2 A four-necked flask equipped with a thermometer, reflux condenser, stirrer, and dropping funnel was charged with 17.1 parts by mass of xylene and 19.0 butyl acetate. A mass part was charged and heated to maintain a reflux state. Thereto, 18.0 parts by weight of 2-hydroxyethyl methacrylate, 2.0 parts by weight of butyl acrylate, FM-1D (trade name, manufactured by Daicel Chemical Industries, Ltd., 1 mol of ε-caprolactone, addition-modified 2-hydroxy methacrylate) 13.0 parts by mass of ethyl), 8.5 parts by mass of 2-ethylhexyl methacrylate, 18.5 parts by mass of methyl methacrylate, and 3.0 parts by mass of t-butylperoxy-2-ethylhexanoate were mixed. The thing was dripped over 2 hours, maintaining a reflux state from a dropping funnel. After the completion of the dropwise addition, the mixture was kept under reflux for 1 hour and then mixed with 0.1 parts by mass of t-butylperoxy-2-ethylhexanoate and 0.8 parts by mass of xylene, and further stirred for 1 hour. Continued. After the completion of polymerization, a resin solution (X) -2 having a nonvolatile content of 60.5% by mass was obtained. The polyol resin (X) -2 had a hydroxyl value of 183 mgKOH / g and a number average molecular weight of 3400.
This polyol (X) -2 100.0 parts by mass, dibutyltin dilaurate 0.018 parts by mass, TINUVIN 900 (Ciba Specialty Chemicals Co., Ltd.) 2 parts by mass, TINUVIN 292 (Nippon Ciba Geigy Co., Ltd.) 0.4 parts by mass are mixed. Main agent (Y) -2.

Production of Curing Agent (B) Curing agent was Desmodur N3400 (uretdione structure of hexamethylene diisocyanate (HDI) manufactured by Sumika Bayer Urethane Co., Ltd., solid content = 100%, NCO group content = 21.8% ( Resin module)), Desmodur N3300 (Sumika Bayer Urethane Co., Ltd. hexamethylene diisocyanate isocyanurate structure, solid content = 100%, NCO group content = 21.8% (resin content conversion)), Duranate 24A-100 (A bimer structure of hexamethylene diisocyanate manufactured by Asahi Kasei Kogyo Co., Ltd., solid content = 100%, NCO group content = 23.6% (resin content conversion)), Death module Z4470SN (Suika Bayer Urethane Co., Ltd.) ) Isophorone disissocyanate (IPDI) isocyanurate structure, solid content = 70%, NCO group content = 11.9% (resin content conversion)) was used. Moreover, as a result of analyzing the content of the uretdione compound represented by the general formula (1) (chemical formula 3) in each curing agent by an infrared absorption spectrum and a liquid chromatograph (HLC-8020 manufactured by Tosoh Corporation), the general formula (1) The content of the uretdione compound represented by (Chemical Formula 3) was 43% for N3400, 0% for N3300, 6% for 24A-100, and 0% for Z4470SN. Based on this result, each curing agent was mixed and adjusted so that the uretdione compound represented by the general formula (1) (Chemical Formula 3) was in the prescribed amount described in Table 1 (Table 1). Furthermore, the hardening | curing agent used for Example 13 and Comparative Examples 4 and 5 is shown by General formula (1) (chemical formula 3) in N3400 hardening | curing agent using a liquid chromatograph (HLC-8020 by Tosoh Corporation). The uretdione compound is fractionated / adjusted, and the content of the uretdione compound is 70% (b) -6 curing agent, 80% (b) -7 curing agent and 53% (b) -8 curing agent Adjusted. Table 1 (Table 1) shows the compounding amounts of the isocyanate compounds in detail and the free isocyanate content (in terms of resin content) of the curing agents (b) -1 to (b) -8.

（式中、ｍは０〜１の整数である）

(Where m is an integer from 0 to 1)

Manufacture of two-component clear paints Each main agent and NCO / OH (molar ratio) shown in Table 2 (Table 2), Table 3 (Table 3), Table 4 (Table 4), and Table 5 (Table 5) Each curing agent was mixed and the viscosity was adjusted to 13 seconds (Ford Cup # 4/20 ° C.) with an organic solvent (xylene) to obtain a two-component clear paint (Clear A to Clear M).

Preparation of test piece and coating film performance test (Example 1)
A polypropylene (PP) base material (SP850) manufactured by Idemitsu Petrochemical Co., Ltd. was used as an object to be coated, and after degreasing with isopropyl alcohol, a primer (manufactured by NOF BASF Coatings Co., Ltd., trade name “PM1500 Primer”) Was coated so that the dry film thickness was 8 μm, and allowed to stand at room temperature for 10 minutes. Next, a one-component water-based base paint (manufactured by NOF BASF Coatings Co., Ltd., trade name “Aqua BC-3 Silver Metallic”) was applied to a dry film thickness of 10 μm, and 0.6 m / 80 ° C. at 80 ° C. s warm air (humidity of 40% or less) for 2 minutes, and after cooling at room temperature for 3 minutes, clear A was diluted with xylene to a coating viscosity (Ford Cup No. 4, 13 seconds at 20 ° C.) and air sprayed. After coating to a dry film thickness of 35 μm and setting for 10 minutes at room temperature, after the temperature of the object to be coated reaches 80 ° C., keep that temperature for 20 minutes, and bake and dry the test piece. Was made. Moreover, as a test piece for recoating, a one-component water-based base paint (manufactured by NOF BASF Coatings Co., Ltd., trade name “Aqua BC-3 Silver Metallic”) is applied to the test piece so that the dry film thickness becomes 10 μm. Paint, apply 0.6 m / s warm air (humidity 40% or less) at 80 ° C. for 2 minutes, and after 3 minutes of cooling at room temperature, apply clear A as a clear paint with xylene (Ford Cup No. 4, 20 ° C.) After coating with air spray to a dry film thickness of 35 μm and setting for 10 minutes at room temperature, the temperature of the object to be coated reached 80 ° C., and then the temperature was changed to 20 Minutes were kept and baked and dried to obtain test pieces.

(Examples 2-3)
A test piece was prepared in the same manner as in Example 1 except that Clear A in Example 1 was changed to Clear B or Clear C as the clear paint. Similar to Example 1, a recoat test piece was prepared by repeating the same coating process.

(Example 4)
A test piece was prepared in the same manner as in Example 3 except that the film thickness of the water-based base paint of Example 3 was changed to 15 μm. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.

(Example 5)
Instead of the water-based base paint of Example 3, a color base of solvent one-component base paint (manufactured by NOF BASF Coatings Co., Ltd., trade name “PMH120 Silver Metallic”) is applied with a dry film thickness of 30 μm, and warm air is applied. A test piece was prepared in the same manner as in Example 3, except that after leaving for 3 minutes at room temperature without applying, Clear C was applied as a clear paint. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.

(Example 6)
A test piece was prepared in the same manner as in Example 5 except that Clear C in Example 5 was changed to Clear D as the clear paint. Similar to Example 5, a recoat test piece was prepared by repeating the same coating process.

(Example 7)
When a cationic electrodeposition paint (Power Top U-50 manufactured by Nippon Paint Co., Ltd.) is used on a 0.8 mm thick, 10 cm x 35 cm thick dull steel sheet treated with zinc phosphate as an object to be coated, the dry film thickness is 20 μm. Electrodeposition coating was performed, and baking drying was performed at 160 ° C. for 30 minutes. Next, on the obtained electrodeposition coating film, High Epico. 500 N9.0 (Nippon Yushi BASF Coatings epoxy resin paint) was applied so that the dry coating film was 30 μm, and baked and dried at 140 ° C. for 30 minutes. Next, an aqueous one-component base paint (manufactured by NOF BASF Coatings Co., Ltd., trade name “Aqua BC-3 Silver Metallic”) was applied to a dry film thickness of 10 μm, and 0.6 m / 80 at 80 ° C. s Warm air (humidity 40% or less) is applied for 2 minutes, and after 3 minutes of cooling at room temperature, Clear C is diluted with xylene to a coating viscosity (Ford Cup No. 4, 13 seconds at 20 ° C.) as an air spray, and then air sprayed After coating the film to a dry film thickness of 35 μm and setting for 10 minutes at room temperature, keep the temperature at 80 ° C., keep the temperature for 20 minutes, perform baking drying, and test It was a piece. A recoat test piece was also prepared by repeating the same coating process on the test piece.

(Examples 8 to 9)
A test piece was prepared in the same manner as in Example 3 except that the baking temperature of Example 3 was set to 70 ° C. or 120 ° C. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.

(Example 10)
A test piece was prepared in the same manner as in Example 3 except that the clear C of Example 3 was changed to Clear E as the clear paint. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.
(Example 11)
A test piece was prepared in the same manner as in Example 3 except that Clear C in Example 3 was changed to Clear D. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.

(Example 12)
A test piece was prepared in the same manner as in Example 3 except that Clear C in Example 3 was changed to Clear F as the clear paint. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.

(Example 13)
A test piece was prepared in the same manner as in Example 3 except that Clear C in Example 3 was changed to Clear G. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.

  Although the performance of the obtained coating film of Examples 1-13 is shown in Table 2 (Table 2) and Table 3 (Table 3), in any case, good gas hole resistance, coating film hardness (polishing property), It showed moisture resistance, weather resistance and recoat adhesion.

(Comparative Examples 1-2)
A test piece was prepared in the same manner as in Example 1 except that Clear A in Example 1 was changed to Clear H or Clear I as the clear paint. Similar to Example 1, a recoat test piece was prepared by repeating the same coating process.

(Comparative Example 3)
A test piece was prepared in the same manner as in Example 3 except that the baking temperature in Example 3 was set to 60 ° C. Similar to Example 3, a recoat test piece was prepared by repeating the same coating process.

(Comparative Examples 4-5)
A test piece was prepared in the same manner as in Example 1 except that Clear A in Example 1 was changed to Clear J or Clear K as the clear paint. Similar to Example 1, a recoat test piece was prepared by repeating the same coating process.

(Comparative Example 6)
A test piece was prepared in the same manner as in Example 5 except that Clear C in Example 5 was changed to Clear L as the clear paint. Similar to Example 5, a recoat test piece was prepared by repeating the same coating process.

(Comparative Example 7)
A test piece was prepared in the same manner as in Example 4 except that Clear C in Example 4 was changed to Clear L. A recoat test piece was prepared in the same manner as in Example 4 by repeating the same coating process.

(Comparative Example 8)
A test piece was prepared in the same manner as in Example 1 except that Clear A in Example 1 was changed to Clear L as the clear paint. Similar to Example 1, a recoat test piece was prepared by repeating the same coating process.

(Comparative Example 9)
A test piece was prepared in the same manner as in Example 7 except that Clear A in Example 7 was changed to Clear L as the clear paint. A recoat test piece was prepared in the same manner as in Example 7 by repeating the same coating process.

(Comparative Example 10)
A test piece was prepared in the same manner as in Example 4 except that Clear C in Example 4 was changed to Clear M as the clear paint. A recoat test piece was prepared in the same manner as in Example 4 by repeating the same coating process.

(Comparative Example 11)
A test piece was prepared in the same manner as in Example 1 except that Clear A in Example 1 was changed to Clear M as the clear paint. Similar to Example 1, a recoat test piece was prepared by repeating the same coating process.

(Comparative Example 12)
A test piece was prepared in the same manner as in Example 7 except that Clear A in Example 7 was changed to Clear M as the clear paint. A recoat test piece was prepared in the same manner as in Example 7 by repeating the same coating process.
The coating film performance of the comparative examples is shown in Table 4 (Table 4) and Table 5 (Table 5).

In Comparative Example 1, the NCO / OH molar ratio is 0.5 and there is an excess of unreacted hydroxyl groups, while in Comparative Example 2, the NCO / OH molar ratio is 4.0. In both cases, unreacted free isocyanate groups existed excessively, so that the cross-linking density of the clear coating film became sparse, and the moisture resistance, gas hole resistance, etc. were lowered.
In Comparative Example 3, since the baking temperature was less than 65 ° C., the reaction of the hydroxyl group and the isocyanate group was not sufficiently accelerated, and the moisture resistance, gas hole resistance, recoat adhesion, and coating film hardness (polishing property) were lowered. .
In Comparative Example 4, since the isocyanate compound component of the tetramer or more was less than 25%, the coating film hardness (polishing property) was lowered. In Comparative Example 5, when the content of the general formula (1) in the curing agent exceeds 80%, the weather resistance is lowered, and since the tetramer or more component is less than 25%, the coating film hardness (polishing property) is lowered. did.
In Comparative Examples 6 to 12, since the content of the general formula (1) in the curing agent was less than 10%, all of the gas hole resistance, moisture resistance, and recoat adhesion could not be satisfied.

The top coating composition of the present invention is obtained by combining a one-component base paint and applying it by a two-coat one-bake method, whereby an excellent coating film hardness is obtained, and particularly by baking and drying at a temperature of 65 ° C. or higher. , Excellent recoat adhesion of the paint film, and as a base paint, it is possible to obtain a paint film with excellent moisture resistance and gas hole resistance not only when using a solvent-based base paint but also when using a water-based base paint. It is effectively used for the coating of the outer panels of automobiles, motorcycles, electrical products, etc. where cosmetic appearance is important.

Claims (5)

  A coating composition comprising a main component (a) having a hydroxyl value of 40 to 300 mg KOH / g as a main component and an isocyanate compound as a curing agent (b), and at least a uretdione bond in the curing agent (b). Containing 10 to 75% by mass of an isocyanate compound having 25 to 90% by mass of a tetramer or more of hexamethylene diisocyanate and / or 5 to 90% by mass of a compound of trimer or more of isophorone diisocyanate, The top coating composition whose molar ratio (NCO / OH) of the free isocyanate group of the hardening | curing agent (b) with respect to the hydroxyl group of a) is 0.6-3.5. The top coating composition according to claim 1, wherein the isocyanate compound having a uretdione bond is a hexamethylene diisocyanate compound represented by the general formula (1) (Chemical formula 1).

(Where m is an integer from 0 to 1)   A one-pack type aqueous base paint containing a hydroxyl group-containing resin, a color pigment, a metallic pigment or a pearl pigment is applied to a thickness of 8 to 30 μm based on a dry coating film, and then wet-on-wet on the coated surface. A method for forming a coating film, comprising: coating the top coating composition according to 1 or 2 to a thickness of 20 to 60 μm based on a dry coating film, and simultaneously baking and curing both coating films at a temperature of 65 ° C. or higher. .   A one-component solvent-based base paint containing a hydroxyl group-containing resin, a color pigment, a metallic pigment or a pearl pigment is applied to a thickness of 8 to 50 μm based on a dry coating film, and then the coated surface is wet-on-wet. A coating film forming method comprising coating the top coating composition according to Item 1 or 2 to a thickness of 20 to 60 μm based on a dry coating film, and simultaneously baking and curing at a temperature of 65 ° C. or higher. A coated article coated by the coating film forming method according to claim 3 or 4 using the coating composition according to claim 1 or 2.