JP6741369B2 - Intermediate coating composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to an intermediate coating composition capable of obtaining a multilayer coating film having excellent chipping resistance, finished appearance and adhesion.

A multi-layered coating film is formed on a material to be coated on a metal such as an automobile body in order to impart anticorrosion and aesthetics. Generally, in automobile coating, an intermediate coating is applied to a material coated with an undercoating coating that imparts anticorrosion properties, and in the case of metallic coating color, heat curing is applied on the intermediate coating. A multi-layer coating film is formed by applying a heat-curable topcoat clear coat paint on top of the base coat paint and applying a thermosetting top coat clear coat paint thereon without baking, and simultaneously baking and curing the base coat and the clear coat. Further, in the case of solid coating color, a multilayer coating film is formed by coating a thermosetting type solid top coating composition on the intermediate coating film and baking and curing it.

In particular, the lower half of the car body is hit by flying stones etc. while driving, the coating film is damaged and peels off, the steel plate substrate is exposed, and as a result, rust occurs on the exposed part, so such a problem It is required to be a multi-layer coating film having excellent resistance to chipping (chipping resistance), and in a total coating film consisting of an undercoating film, an intermediate coating film and a top coating film, the chipping resistance is mainly the intermediate coating film. It is common to give the function to.

For example, in Patent Document 1, (i) a coconut oil-modified alkyd resin having a number average molecular weight of 1500 to 5000, a hydroxyl value of 60 to 120, an acid value of 15 or less, and an oil length of 3 to 15%, 45 to 75% by weight, ( ii) 20-48% by weight of a cross-linking agent composed of a methylol-imino group-type melamine resin and a non-yellowing type block polyisocyanate, and a weight ratio of the two is (50:50-90:10), and (iii) an epoxy-modified polyester. Disclosed is an automotive coating composition containing a binder component composed of 2 to 7% by weight of a resin.

Moreover, in patent document 2, the amount of hydroxyl groups is 2.0-10.0 mol/kg resin, the number average molecular weight is 300-1500, the weight average molecular weight is 300-3000, and the weight average molecular weight/number. A polyester oligomer having an average molecular weight of 1.0 to 2.0, a lactone modification amount of 31 to 85%, and an aliphatic hydrocarbon group having 4 to 22 carbon atoms which is not derived from lactone, and the above hydroxyl group-containing polyester A low-solvent type resin composition is disclosed, which contains a curing agent that reacts with the hydroxyl group of the oligomer and has an organic solvent amount of 5 to 40%.

Japanese Unexamined Patent Publication No. 10-030075 JP, 8-020745, A

However, when the coating composition for automobiles of Patent Document 1 is applied as an intermediate coating composition in a multilayer coating film of an automobile body, flexibility is insufficiently imparted, and thus the resulting multilayer coating film is resistant to chipping. There was a case where the sex was insufficient.

Further, when the low solvent type resin composition of Patent Document 2 is applied as an intermediate coating composition for a multilayer coating film of an automobile body, the polyester oligomer has a low molecular weight, and therefore the multilayer coating film is subjected to a load such as a water resistance load. In some cases, the adhesion was inadequate when was added.

An object of the present invention is to provide an intermediate coating composition capable of obtaining a multilayer coating film which is excellent in chipping resistance and finished appearance, and is also excellent in coating properties such as adhesion.

As a result of repeated intensive studies, the present inventors have found that a lactone-modified polyester resin, a melamine resin, and a composition containing a pyrazole-blocked polyisocyanate compound as an essential component as a resin component have a lactone-modified amount and a molecular weight of the lactone-modified polyester resin. It has been found that the above-mentioned problems can be solved by a coating composition in which the ratio of the melamine resin and the pyrazole-blocked polyisocyanate is within the specific range, and the present invention has been completed.

That is, the present invention is
(A) Lactone modified amount of 12 to 25% by mass, hydroxyl group-containing polyester resin having a number average molecular weight of 1500 to 2200, (B) melamine resin, (C) pyrazole block polyisocyanate compound, and (D) pigment An intermediate coating composition containing
The intermediate coating composition, wherein the use ratio of the melamine resin (B) and the pyrazole block polyisocyanate compound (C) is 10/30 to 20/15 (melamine resin/pyrazole block polyisocyanate compound) in terms of solid content. It is related to the thing.

Furthermore, the present invention relates to a method for forming a multilayer coating film, which comprises coating the above intermediate coating composition.

The intermediate coating composition of the present invention has a hydroxyl group-containing polyester resin having a specific molecular weight range lactone-modified in a specific range amount as a base resin, and a melamine resin and a pyrazole block polyisocyanate compound as a crosslinking agent in a ratio within a specific range. It is an intermediate coating composition whose main feature is to contain.

The lactone-modified polyester resin, which is the base resin, has a sharper molecular weight distribution compared to the unmodified product, is reduced in low-molecular-weight components that negatively affect the coating performance, and is a resin in which flexibility is imparted by the lactone component, Suitable for both improved chipping resistance and improved coating performance such as adhesion. Further, by using a melamine resin and a blocked polyisocyanate compound in combination as a cross-linking agent, compared to melamine resin alone, due to the characteristics of the polyisocyanate compound, reduction of internal stress of the coating film caused by the curing reaction, in the cured coating film By introducing urethane cross-linking, the chipping resistance can be improved. Furthermore, since the blocking agent for the polyisocyanate compound is pyrazole, which is excellent in curability at a relatively low temperature, the coating performance such as adhesion can be improved.

As described above, according to the intermediate coating composition of the present invention, it is possible to obtain a multilayer coating film having excellent chipping resistance and finished appearance, and excellent coating film performance such as adhesion.

Hereinafter, the intermediate coating composition of the present invention (hereinafter, also simply referred to as "present coating") will be described in detail.

The intermediate coating composition of the present invention,
A coating composition containing (A) a hydroxyl group-containing polyester resin, (B) a melamine resin, (C) a pyrazole-blocked polyisocyanate compound, and (D) a pigment.

<Hydroxyl group-containing polyester resin (A)>
The hydroxyl group-containing polyester resin (A) is a polyester resin having a hydroxyl group modified with a lactone compound.

The hydroxyl group-containing polyester resin can be generally produced by an esterification reaction or a transesterification reaction between a polybasic acid component and a polyhydric alcohol component, and specifically, for example, a carboxyl group in the polybasic acid component. It can be produced by setting the equivalent ratio (COOH/OH) of the hydroxyl groups in the polyhydric alcohol component to less than 1 and carrying out the esterification reaction in a state where there are more hydroxyl groups than carboxyl groups.

Generally, a lactone-modified hydroxyl group-containing polyester resin is usually obtained by polycondensing a polyhydric alcohol with a polybasic acid or an anhydride thereof (by an ester reaction), adding a required amount of a lactone compound to the polyester resin, and heating the polyester resin. Can be obtained. The lactone component is introduced into the polyester resin by the ring opening of the lactone compound and the reaction with the hydroxyl group of the polyester resin.

Polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, trimethylene glycol, tetramethylene glycol, 2,3-dimethyl. Trimethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 3-methyl-1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,6-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 3-methyl-4,5- Pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, hydrogenated bisphenol A , Hydrogenated bisphenol F, spiroglycol, dihydroxymethyltricyclodecane, hydroxyalkylated bisphenol A, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, 2,2-dimethyl-3 -Hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, N,N-bis-(2-hydroxyethyl)dimethylhydanton, polytetra Glycols such as methylene ether glycol, hydroxypivalic acid neopentyl glycol ester, polylactone diols obtained by adding lactones such as ε-caprolactone to these glycols, polyester diols such as bis(hydroxyethyl) terephthalate,
3 such as polycaprolactone polyol, glycerin, diglycerin, triglycerin, sorbitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, mannitol, tris-(hydroxyethyl)isocyanate Polyols of valency or higher,
And hydroxycarboxylic acids such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolpentanoic acid, 2,2-dimethylolhexanoic acid, and 2,2-dimethyloloctanoic acid. Mention may be made of acids. Also, two or more of the above polyhydric alcohols can be used in combination.

Examples of the polybasic acid or its anhydride include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methylhexahydrophthalic acid and methyltetrahydroanhydride. Phthalic acid, hymic acid anhydride, trimellitic acid, trimellitic acid anhydride, hexahydrotrimellitic acid, pyromellitic acid, pyromellitic acid anhydride, isophthalic acid, hexahydroisophthalic acid, terephthalic acid, hexahydroterephthalic acid, maleic acid, Maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, lactic acid, dodecenylsuccinic acid, dodecenylsuccinic anhydride, cyclohexane-1,4-dicarboxylic acid, endoic anhydride, naphthalene Examples thereof include dicarboxylic acid, 4,4-diphenyldicarboxylic acid, diphenylmethane-4,4′-dicarboxylic acid and het acid. Moreover, these 2 or more types can also be used in combination.

Examples of the lactone compound include ε-caprolactone, γ-caprolactone, β-propiolactone, γ-butyrolactone, δ-caprolactone, δ-valerolactone, γ-valerolactone, γ-nonanoic lactone, and δ-dodecanolactone. Can be mentioned. These can be used alone or in combination of two or more. Among these, ε-caprolactone can be preferably used from the viewpoint of reactivity and the like. The lactone compounds may be used alone or in combination of two or more.

The lactone modification amount (mass% of the lactone compound in the constituent component of the modified polyester resin (A)) is 12 to 25 mass%, particularly 15 to 25 mass%, and more particularly 18 to 23 mass%. It is preferably within. If it is less than 12% by mass, it may be difficult to obtain a coating film excellent in chipping resistance due to lack of flexibility of the coating film. If it exceeds 25% by mass, the lactone-modified portion becomes a plasticizer-like component and the coating film hardness may be reduced, resulting in a reduction in coating film performance.

The number average molecular weight of the hydroxyl group-containing polyester resin (A) is 1500 to 2200, preferably 1500 to 2100, and more preferably 1700 to 2100. When the number average molecular weight is less than 1,500, the cohesive force of the coating film is reduced, and thus the coating film performance such as chipping resistance may be reduced. If it exceeds 2200, the finish may be deteriorated due to the deterioration of flowability.

In the present specification, the average molecular weight of the resin is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatograph (hereinafter, simply abbreviated as GPC). As GPC, "HLC8120GPC" (manufactured by Tosoh Corporation) was used. As the column, 4 columns of "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (both manufactured by Tosoh Corporation, trade names) are used, and a mobile phase is used. Tetrahydrofuran, measurement temperature; 40° C., flow rate; 1 cc/min, detector; RI;

The hydroxyl value of the hydroxyl group-containing polyester resin (A) is preferably 50 to 200 mgKOH/g, particularly 60 to 180 mgKOH/g, and particularly preferably 70 to 150 mgKOH/g. When the hydroxyl value of the hydroxyl group-containing polyester resin (A) is less than 50 mgKOH/g, the reactivity of the resin may be lowered and the resulting coating film may have insufficient chipping resistance. Further, when the hydroxyl value of the hydroxyl group-containing polyester resin (A) exceeds 200 mgKOH/g, the molecular weight of the resin becomes small and the coating film performance may deteriorate.

The acid value of the hydroxyl group-containing polyester resin (A) is preferably in the range of 2 to 50 mgKOH/g, particularly 3 to 45 mgKOH/g, and especially 4 to 40 mgKOH/g. When the acid value of the hydroxyl group-containing polyester resin (A) is less than 2 mgKOH/g, the curability of the coating film may be insufficient. When the acid value of the hydroxyl group-containing polyester resin (A) exceeds 50 mgKOH/g, it may be difficult to synthesize the resin.

Further, the hydroxyl group-containing polyester resin (A) can be modified with a fatty acid, a monoepoxy compound or the like, if necessary, during the preparation of the polyester resin or after the esterification reaction. Examples of the fatty acid include coconut oil fatty acid, cottonseed oil fatty acid, hempseed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil. Examples of the monoepoxy compound include α-olefin epoxides such as propylene oxide and butylene oxide, “CARDURA E10P” (trade name, manufactured by HEXION Specialty Chemicals, Inc., synthetic). Examples thereof include monoepoxy compounds such as glycidyl ester of highly branched saturated fatty acid).

When the hydroxyl group-containing polyester resin (A) is used as the modified resin, the modified amount is preferably up to about 30 mass% with respect to the total amount of the polyester resin.

Further, the hydroxyl group-containing polyester resin (A) may be a resin partially reacted with a monobasic acid such as benzoic acid.

When a carboxyl group is introduced into the hydroxyl group-containing polyester resin (A), it can be introduced, for example, by adding an acid anhydride to the hydroxyl group-containing polyester resin and half-esterifying.

The intermediate coating composition of the present invention may contain, as a base resin, resins other than the above-mentioned hydroxyl group-containing polyester resin (A), which are usually used in coating applications, if necessary. Specific examples thereof include polyester resins other than the hydroxyl group-containing polyester resin (A) having a crosslinkable functional group such as a hydroxyl group, acrylic resins, alkyd resins, and urethane resins.

<Melamine resin (B)>
In the intermediate coating composition of the present invention, the melamine resin (B) is a crosslinking agent component, and as the melamine resin (B), a partially methylolated melamine resin or a complete methylol obtained by a reaction between a melamine component and an aldehyde component is used. Melamine resin can be used. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like.

Further, the methylol group of the methylolated melamine resin may be partially or completely etherified with an appropriate alcohol. Examples of the alcohol used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethyl-1-butanol, 2-ethyl-1. -Hexanol and the like can be mentioned.

Examples of the melamine resin (B) include a methyletherified melamine resin obtained by partially or completely etherifying a methylol group of a partially or completely methylolated melamine resin, or a methylol group of a partially or completely methylolated melamine resin with butyl alcohol. Butyl etherified melamine resin partially or completely etherified with a methyl-butyl mixed etherified melamine resin partially or completely etherified with a methyl alcohol and a butyl alcohol. A methyl-butyl mixed etherified melamine resin is more preferable.

The weight average molecular weight of the melamine resin (B) is preferably 400 to 6,000, more preferably 500 to 4,000, and even more preferably 600 to 3,000.

A commercially available product can be used as the melamine resin (B). Examples of commercial product names include "Cymel 202", "Cymel 203", "Cymel 204", "Cymel 211", "Cymel 212", "Cymel 238", "Cymel 251", "Cymel 253", "Cymel 254", "Cymel 303", "Cymel 323", "Cymel 324", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 370", "Cymel 380", "Cymel 385", "Cymel 1156", "Cymel 1158", "Cymel 1116", "Cymel 1130" (all manufactured by Nippon Cytec Industries, Ltd.); "Regimin 735", "Regimin 740", "Regimin 741", "Regimin 745", "Regimin 746", "Regimin 747" (above, manufactured by Monsanto); "Uban 120", "Uban 20HS", "Uban 20SE", "Uban 2021", "Uban 2028", "Uban 28-60" (above , Manufactured by Mitsui Chemicals, Inc.); “Sumimar M55”, “Sumimar M30W”, “Sumimar M50W” (above, manufactured by Sumitomo Chemical Co., Ltd.); and the like.

<Pyrazole Block Polyisocyanate Compound (C)>
In the intermediate coating composition of the present invention, the pyrazole-blocked polyisocyanate compound (C) is a crosslinking agent component, and is a compound obtained by blocking the free isocyanate groups of the polyisocyanate compound with the pyrazole compound as a blocking agent.

When the blocked polyisocyanate compound is heated to, for example, 100° C. or higher, preferably 130° C. or higher, the isocyanate group is regenerated and can easily react with the reactive group.

The polyisocyanate compound is a compound having two or more isocyanate groups in one molecule.

Specific examples of the polyisocyanate compound include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates.

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

Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (conventional name: Isophorone diisocyanate), 4,4′-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane( Conventional name: hydrogenated xylylene diisocyanate) or a mixture thereof, alicyclic diisocyanates such as norbornane diisocyanate, for example, 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3 -Isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo( 2.2.1) Heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2 -Isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl) -Bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)-heptane, 6- Examples thereof include alicyclic triisocyanates such as (2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

Examples of the araliphatic polyisocyanate include 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω′-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis( Aroaliphatic diisocyanates such as 1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylenediisocyanate) or a mixture thereof, for example, araliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene. Etc. can be mentioned.

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

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

Examples of the pyrazole compound that is a blocking agent include 3,5-dimethylpyrazole, 3-methylpyrazole, 4-nitro-3,5-dimethylpyrazole, and 4-bromo-3,5-dimethylpyrazole. Among these, the preferable pyrazole compound is 3,5-dimethylpyrazole.

As the block polyisocyanate compound of the intermediate coating composition of the present invention, a block polyisocyanate compound having a compound other than pyrazole as a blocking agent can also be used if necessary.

Examples of the blocking agent other than the pyrazole compound include phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, methyl hydroxybenzoate and the like; ε-caprolactam, δ- Valerolactam, γ-butyrolactam, β-propiolactam and other lactams; methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol and other aliphatic alcohols; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, Ether system such as ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, methoxymethanol; benzyl alcohol; glycolic acid; glycolic acid esters such as methyl glycolate, ethyl glycolate and butyl glycolate; lactic acid Lactic acid esters such as methyl lactate, ethyl lactate, and butyl lactate; alcohol-based compounds such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; formamide oxime, acetamide oxime, acetoxime, methyl ethyl keto. Oxime such as oxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime; active methylene such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, Mercaptan-based compounds such as t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol; acid amide-based compounds such as acetanilide, acetaniside, acetotoluide, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide; Imide type such as succinimide, phthalic acid imide, and maleic acid imide; amine type such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylphenylamine; imidazole, An imidazole system such as 2-ethylimidazole; Urea such as urea, thiourea, ethylene urea, ethylene thiourea and diphenyl urea; carbamate ester such as phenyl N-phenylcarbamate; imine such as ethylene imine and propylene imine; sodium bisulfite, potassium bisulfite etc. Examples of the blocking agent include sulfite-based blocking agents.

In the intermediate coating composition of the present invention, the use ratio of the melamine resin (B) and the pyrazole block polyisocyanate compound (C) is 10/30 to 20/15 (melamine resin/pyrazole block polyisocyanate compound) in terms of solid content ratio, In particular, it is preferably within the range of 12/25 to 19/16, more preferably 15/20 to 18/18. When the ratio of the pyrazole block polyisocyanate compound is less than 20/15, the chipping resistance may be poor because the number of urethane bonds produced by the crosslinking reaction is small. Further, when the ratio of the pyrazole block polyisocyanate compound is more than 10/30, the number of urethane bonds generated by the crosslinking reaction is increased, so that a soft coating film is formed, so that workability such as polishing is deteriorated. There is a case.

In the intermediate coating composition of the present invention, the ratio of the hydroxyl group-containing polyester resin (A) and the cross-linking agent component (the total of the (B) component and the (C) component) is such that the hydroxyl group-containing polyester resin The polyester resin (A) is 50 to 80% by mass, particularly 55 to 75% by mass, and the crosslinking agent component (the total of the (B) component and the (C) component) is 20 to 50% by mass, particularly 25 to 45% by mass. It is preferably within the range from the viewpoint of chipping resistance and finished appearance.

In the intermediate coating composition of the present invention, a cross-linking agent other than the melamine resin (B) and the pyrazole-blocked polyisocyanate compound (C) can also be used if necessary. Specific examples include urea resins, polyhydrazide compounds, polysemicarbazide compounds, carbodiimide group-containing compounds, oxazoline group-containing compounds, epoxy compounds, and polycarboxylic acids. The cross-linking agents that can be used if necessary may be used alone or in combination of two or more kinds.

<Pigment (D)>
As the pigment (D), a pigment usually used in paints can be used. Specifically, coloring pigments such as titanium dioxide, zinc white, carbon black, phthalocyanine blue, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, slene-based pigments, perylene pigments; clay, kaolin , Extenders such as barita, barium sulfate, barium carbonate, calcium carbonate, silica, alumina white, and talc; and bright pigments such as aluminum flakes and mica flakes can be preferably used.

In the intermediate coating composition of the present invention, the pigment (D) can be mixed in the coating as powder, but the pigment is mixed with and dispersed in a part of the resin component to prepare a pigment dispersion in advance, It can also be made into a coating material by mixing with the remaining resin components and other components. In the preparation of the pigment dispersion, a conventional paint additive such as a defoaming agent, a dispersant, and a surface conditioner can be used if necessary. As the pigment (D), powder having an average particle diameter of 0.01 μm to 6 μm is preferably used in consideration of dispersibility.

From the viewpoint of chipping resistance and finished appearance, the content of the pigment (D) is preferably in the range of 20 to 60%, particularly 30 to 55%, in terms of PWC (pigment weight concentration Pigment Weight Content).

In the intermediate coating composition of the present invention, a curing catalyst can be used from the viewpoint of improving curability. As the curing catalyst, among the above-mentioned crosslinking agent components, for the melamine resin (B), sulfonic acids such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, and dinonylnaphthalenesulfonic acid; among the sulfonic acid and amine Sodium salt; a neutralized salt of a phosphoric acid ester compound and an amine can be used.

Among the above-mentioned crosslinking agent components, an organometallic compound such as an organotin compound can be used for the pyrazole blocked polyisocyanate compound (C).

Specifically, for example, tin octylate, dibutyltin di(2-ethylhexanoate), dioctyltin di(2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyltin. Oxides, organic metal catalysts such as zinc 2-ethylhexanoate and zinc octylate, tertiary amines and the like can be mentioned.

Among the above, a zinc catalyst can be preferably used especially from the viewpoint of the finished appearance.

The curing catalyst can be used alone or in combination of two or more kinds. The amount of the curing catalyst varies depending on its type, but is usually 0.1 to 0.5% by mass, particularly 0.2 to 0.1% by mass based on the total solid content of the components (A), (B) and (C). It is preferably about 0.5% by mass.

When using the intermediate coating composition of the present invention, a solvent such as water and/or an organic solvent may be added and diluted as necessary to adjust the viscosity to an appropriate value.

In the intermediate coating composition of the present invention, when water is used as a solvent, the hydroxyl group-containing polyester resin (A) is neutralized with a neutralizing agent such as a basic compound in order to facilitate dissolution and dispersion in water. Is preferred.

Examples of the neutralizing agent include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide and barium hydroxide; ammonia; ethylamine, propylamine, butylamine, Primary monoamine compounds such as cyclohexylamine, monoethanolamine, isopropanolamine, neopentanolamine, 2-aminopropanol, 3-aminopropanol, 2-amino-2-methylpropanol; diethylamine, dibutylamine, diethanolamine, diamine Secondary monoamine compounds such as propylamine, diisopropanolamine, N-methylethanolamine, N-ethylethanolamine, N-methylisopropanolamine; triethylamine, tributylamine, dimethylethanolamine, diethylethanolamine, methyldiethanolamine, dimethylamino Examples include tertiary monoamine compounds such as ethanol and triethanolamine; polyamine compounds such as ethylenediamine, diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, and methylaminopropylamine; pyridine; morpholine.

Examples of the organic solvent include hydrocarbon solvents such as hexane, heptane, xylene, and toluene; esters such as ethyl acetate and butyl acetate; ether solvents such as ethylene glycol monomethyl ether; alcohol solvents such as ethanol, propanol, and 2-ethylhexyl alcohol. Ketones such as methyl ethyl ketone and methyl isobutyl ketone; aromatic hydrocarbons such as Swazol 310 and Swazol 1000 (manufactured by Cosmo Oil Co., Ltd.); aliphatic hydrocarbons, alicyclic hydrocarbons, amides, etc. The organic solvent used in the coating composition can be used. The organic solvent may be used alone or in combination of two or more kinds.

The content of the solvent in the intermediate coating composition of the present invention is usually 20 to 50% by mass, and preferably about 25 to 45% by mass.

Furthermore, in the intermediate coating composition of the present invention, if necessary, a pigment dispersant, an antifoaming agent, an antioxidant, an ultraviolet absorber, a light stabilizer, and a surface modifier which are usually used in the coating composition are used. Various additives such as a gloss adjuster can be appropriately used.

The intermediate coating composition of the present invention can be prepared by mixing and dispersing the above-mentioned components. The solid content content during coating is preferably adjusted in the range of 45 to 75% by mass, particularly 50 to 70% by mass.

The intermediate coating composition of the present invention, after adjusting to a viscosity suitable for coating, by a known method such as rotary atomization coating, air spray, airless spray, if necessary, can be applied, coating, From the viewpoint of the smoothness and finish of the coating film, the film thickness can be 10 to 40 μm, preferably 25 to 40 μm based on the cured coating film.

The intermediate coating film obtained by applying the intermediate coating composition of the present invention is usually cured at a temperature of about 120°C to about 180°C, preferably 130 to 170°C, more preferably 135 to 165°C. You can

In addition, before the heat-curing, if necessary, an interval of about 1 to 60 minutes may be provided at room temperature, or preheating may be performed at about 40 to 110°C for about 1 to 30 minutes.

In the intermediate coating composition of the present invention, from the viewpoint of chipping resistance, the elongation at break of the formed intermediate coating film at 20° C. is 20 to 100%, particularly 23 to 95%, and more particularly 27 to 90. %, Young's modulus is 500 to 1500 MPa, particularly 600 to 1500 MPa, more particularly 800 to 1400 MPa, and breaking stress is preferably 20 to 35 MPa, particularly 23 to 35 MPa, and more preferably 25 to 33 MPa. ..

In addition, the said physical-property value is a physical-property value of the intermediate coating film which was hardened|cured on the heating conditions which the film thickness of an intermediate coating film is 50 micrometers, and 140 degreeC x 18 minutes keeps twice.

Since the intermediate coating composition of the present invention can obtain a multilayer coating film excellent in finished appearance such as coating performance such as chipping resistance and water resistance and coating surface smoothness, for example, for building materials, construction It is suitable for use as an intermediate coating composition for automobiles, automobiles, etc., especially for automobile bodies.

<Coating object>
The object to be coated is not particularly limited, but examples thereof include cold rolled steel sheets, galvanized steel sheets, zinc alloy plated steel sheets, steel sheets such as stainless steel sheets and tin plated steel sheets, metal materials such as aluminum sheets and aluminum alloy sheets; polyethylene resin. , Polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin and other resins, various plastic materials such as FRP; concrete surface, mortar surface , Slate board, roof tile, PC board, ALC board, cement, cement calcium silicate board, ceramics, tile, glass, wood, stone material, coated surface and the like are preferable. Of these, metal materials and plastic materials are preferable.
Further, it may be a vehicle body, a building material, or the like of various vehicles such as automobiles, two-wheeled vehicles, and containers formed by these.

Further, the article to be coated may be a metal surface of a metal substrate or the above-mentioned vehicle body, which has been subjected to a surface treatment such as a phosphate treatment, a chromate treatment or a complex oxide treatment.

Further, these objects to be coated may have been previously undercoated (for example, cationic electrodeposition coating). As the undercoat, those which have been electrodeposited are preferable, and among them, car bodies on which an undercoat coating film is formed by a cationic electrodeposition coating are particularly preferable.

The material of the article to be coated forming the automobile body is not particularly limited. For example, metal materials such as iron, aluminum, aluminum alloy, brass, copper, tin plate, stainless steel, galvanized steel, zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel, tin-plated steel, etc. Can be mentioned.

The intermediate coating composition of the present invention is applied to the article to be coated (in the article to be coated, in particular, a metal material such as a steel plate, and more particularly, a material on which an undercoat coating film is further formed by an electrodeposition coating (particularly an automobile body)). It can be particularly preferably used as an intermediate coating composition for forming an intermediate coating of a multilayer coating composed of an intermediate coating/base coating/clear coating.

<Base coating>
The base coating film is formed by applying the base coating material on the intermediate coating film formed by applying the intermediate coating material. The intermediate coating film may be an uncured coating film by omitting baking and heating curing in order to shorten the process in recent years. Further, due to the recent demand for VOC reduction, a water-based base paint is currently applied as a base paint, particularly in the coating of automobile bodies.

The water-based base coating material is a coating material that imparts a design property to the formed multilayer coating film and improves the design property and the feeling of depth by being laminated with the intermediate coating film.

Regarding the water-based base paint, first, a case will be described in which the above-mentioned base coating film is a solid film whose color appearance does not change depending on the observation angle. In this case, the base coating film can be formed by applying an aqueous color base paint.

Aqueous color base paints usually contain color pigments. Specific examples of the color pigment include azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindoline pigments, and isoindolinone pigments. Organic pigments such as pigments, metal chelate azo pigments, phthalocyanine pigments, indanthrone pigments, dioxazine pigments, slene pigments and indigo pigments; metal oxide pigments such as titanium oxide pigments and carbon black pigments. These can be used alone or in combination of two or more.

In the present invention, the blending amount of the color pigment in the water-based color base paint is usually 0.01 to 150% by mass, particularly 0, relative to the total resin solid content in the water-based color base paint from the viewpoint of the brightness of the multilayer coating film. It is preferably in the range of 0.05 to 120% by mass. The coloring pigment that can be mixed in the water-based color base paint can be mixed in the paint as a powder, but the coloring pigment is mixed and dispersed with a part of the resin composition to prepare a pigment dispersion in advance, and the remaining resin is used. It can also be made into a coating material by mixing it with other components and other components. In the preparation of the pigment dispersion, a conventional paint additive such as a defoaming agent, a dispersant, and a surface conditioner can be used if necessary.

The water-based color base paint can usually contain a resin component as a vehicle. As the resin component, specifically, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, or a urethane resin having a crosslinkable functional group such as a hydroxyl group, a melamine resin, a urea resin, a polyisocyanate compound (block body) is used. (Including also) and the like in combination with a cross-linking agent, and these are used by being dissolved or dispersed in a solvent such as an organic solvent and/or water.

Further, in the water-based color base paint, if necessary, a solvent such as water or an organic solvent, a dispersant, an anti-settling agent, a curing catalyst, a defoaming agent, an antioxidant, an ultraviolet absorber, a surface modifier, a rheology control agent. Various additives such as the above, extender pigments, and the like can be appropriately mixed.

The water-based color base paint is prepared by mixing and dispersing the above-mentioned components. It is preferable to adjust the solid content at the time of coating to 12 to 60% by mass, particularly 15 to 50% by mass based on the coating composition.

Water-based color base paint can be applied by electrostatic coating, air spray, airless spray, etc. after adjusting the viscosity to a suitable level by adding water, organic solvent, etc. Based on the above, it is preferably 5 to 30 μm, particularly 5 to 25 μm, and more preferably 10 to 25 μm from the viewpoint of the smoothness of the coating film.

Next, a case will be described in which the base coating film is a coating film exhibiting a metallic color whose color appearance changes depending on the observation angle. In this case, the base coating film can be formed by applying an aqueous metallic base coating material as the aqueous base coating material.

The aqueous metallic base coating material usually contains a scaly bright pigment for the purpose of imparting a particle feeling to the coating film. As the scaly bright pigment, one kind or a combination of two or more kinds can be appropriately selected and used from the light reflecting pigment and the light interference pigment.

Specific examples of the light-reflecting pigment include aluminum, copper, nickel alloys, scale-like metal pigments such as stainless steel, scale-like metal pigments whose surface is coated with a metal oxide, and chemical adsorption or bonding of a coloring pigment on the surface. Examples thereof include scaly metal pigments and scaly aluminum pigments having an aluminum oxide layer formed by causing an oxidation reaction on the surface. Among them, the scaly aluminum pigment can be preferably used in terms of graininess and finished appearance.

The scaly aluminum pigment is generally produced by crushing and grinding aluminum in a ball mill or an attritor mill in the presence of a grinding medium using a grinding aid. As the grinding aid, higher fatty acids such as oleic acid, stearic acid, isostearic acid, lauric acid, palmitic acid and myristic acid, as well as aliphatic amines, aliphatic amides and aliphatic alcohols can be used. Aliphatic hydrocarbons such as mineral spirits can be used as the grinding liquid medium.

The scaly aluminum pigment can be roughly classified into a leafing type and a non-leafing type depending on the type of the grinding aid. The leafing type, when added to the coating composition, is arranged (leafing) on the surface of the coating film obtained by painting, giving a strong metallic finish, having a heat reflecting action, and exhibiting rust prevention power. Therefore, it is often used for various building materials such as tanks, ducts, pipes and roofing roofing of production facilities. In the present invention, it is possible to use a leafing type scale-like aluminum pigment, but when using this type of scale-like aluminum pigment, depending on the blending amount thereof, in the coating film forming process, a grinding aid Care must be taken because the surface tension may obscure the surface completely and the particle feeling may not appear. From this point, it is preferable to use a non-leafing type scaly aluminum pigment.

Regarding the size of the scale-like aluminum pigment, it is preferable to use one having an average particle size of 8 to 25 μm, particularly 10 to 18 μm in terms of finish appearance of the multilayer coating film, highlight brightness and particle feeling. And the thickness is preferably in the range of 0.2 to 1.0 μm. The particle diameter and the thickness here mean the median diameter of the volume-based particle size distribution measured by a laser diffraction scattering method using a Microtrac particle size distribution measuring device MT3300 (trade name, manufactured by Nikkiso Co., Ltd.).

If the average particle size exceeds the upper limit, the resulting coating film may have an excessive particle feel, which may be unfavorable in terms of design, and if it is less than the lower limit, the particle feel may be insufficient.

In the water-based metallic base paint, a light interference pigment can be used as the scaly bright pigment.

As the light interference pigment, specifically, a pigment obtained by coating a semitransparent base material such as natural mica, artificial mica, alumina flake, silica flake, glass flake with a metal oxide can be used.

The metal oxide-coated mica pigment is a pigment in which a natural mica or an artificial mica is used as a base material and the surface of the base material is coated with a metal oxide. The natural mica is a scale-like base material obtained by crushing ore mica (mica), and the artificial mica is an industrial raw material such as SiO2, MgO, Al203, K2SiF6, Na2SiF6 that is heated and melted at a high temperature of about 1500°C. However, it was synthesized by cooling and crystallization, and it has less impurities and is uniform in size and thickness when compared with natural mica. Specifically, fluorine-based mica (KMg3AlSi3O10F2), potassium tetrasilicon mica (KMg25AlSi4O10F2), sodium tetrasilicon mica (NaMg25AlSi4O10F2), Na-teniolite (NaMg2LiSi4O10F2), LiNa-teniolite (LiNaMg2LiSi4O10F2) and the like are known. Examples of the coated metal oxide include titanium oxide and iron oxide. An interference color can be developed by the coated metal oxide.

The metal oxide-coated alumina flake pigment is a pigment having alumina flake as a base material and the surface of the base material being coated with a metal oxide. Alumina flakes mean scale-shaped (flake-shaped) aluminum oxide, and are colorless and transparent. It does not have to be a single component of aluminum oxide, and may contain an oxide of another metal. Examples of the coated metal oxide include titanium oxide and iron oxide. An interference color can be developed by the coated metal oxide.

The metal oxide-coated silica flake pigment is obtained by coating scaly silica, which is a base material having a smooth surface and a uniform thickness, with a metal oxide having a refractive index different from that of the base material. Examples of the coated metal oxide include titanium oxide and iron oxide. An interference color can be developed by the coated metal oxide.

The metal oxide-coated glass flake pigment is a scale-like glass base material coated with a metal oxide. Since the base material surface is smooth, strong light reflection occurs and a particle feeling is exhibited. Examples of the coated metal oxide include titanium oxide and iron oxide. An interference color can be developed by the coated metal oxide.

The light-interfering pigment may be surface-treated to improve dispersibility, water resistance, chemical resistance, weather resistance and the like.

The size of the above-mentioned light-interfering pigment is 5 in the case of the light-interfering pigment based on natural mica, artificial mica, alumina flakes and silica flakes, from the viewpoint of the finished appearance of the coating film and the feeling of graininess. It is possible to preferably use those having a thickness of -30 μm, particularly 7-25 μm.

In the case of a light-interfering pigment having glass flakes as a base material, those having an average particle size of 15 to 100 μm, particularly 17 to 45 μm can be suitably used from the viewpoint of the particle feeling of the coating film.

The thickness of the light interference pigment is preferably 0.05 to 7.0 μm, more preferably 0.1 to 3 μm.

The particle diameter and the thickness here mean the median diameter of the volume-based particle size distribution measured by a laser diffraction scattering method using a Microtrac particle size distribution measuring device MT3300 (trade name, manufactured by Nikkiso Co., Ltd.).

If the average particle size exceeds the upper limit value, the particle feeling due to the light-interfering pigment of the multilayer coating film may be unfavorable in terms of design, and if it is less than the lower limit value, the particle feeling may be insufficient. ..

The content of the scaly bright pigment in the water-based metallic base coating composition is 0.01 to 25 in total with respect to the total solid content of the resin composition in the coating composition from the viewpoint of the finished appearance and particle appearance of the resulting coating film. It is preferably within the range of mass %, particularly 0.01 to 15 mass %, and more preferably 0.05 to 5 mass %.

The aqueous metallic base paint may contain a coloring pigment for the purpose of finely adjusting the hue and lightness of the resulting coating film. Specific examples of the color pigment include transparent iron oxide pigments, composite oxide pigments such as titanium yellow, titanium oxide pigments containing fine particle titanium oxide, inorganic pigments such as carbon black pigments, and azo pigments. Quinacridone pigment, diketopyrrolopyrrole pigment, perylene pigment, perinone pigment, benzimidazolone pigment, isoindoline pigment, isoindolinone pigment, metal chelate azo pigment, phthalocyanine pigment, indanthrone pigment Examples thereof include organic pigments such as dioxazine-based pigments, slene-based pigments, and indigo-based pigments. These may be used alone or in combination of two or more.

The color pigment can be mixed in the paint as a powder, but the color pigment is mixed and dispersed with a part of the resin composition to prepare a pigment dispersion in advance, and the pigment dispersion is used as the remaining resin component and other components. It can also be made into a paint by mixing with it. In the preparation of the pigment dispersion, a conventional paint additive such as a defoaming agent, a dispersant, and a surface conditioner can be used if necessary.

When a coloring pigment is contained in the water-based metallic base paint, the amount thereof is usually 0.01 to 10 mass with respect to the total amount of the resin composition solids in the paint from the viewpoint of the brightness of the multilayer coating film and the like. %, particularly preferably in the range of 0.01 to 5 mass %.

The aqueous metallic base paint usually contains a resin composition as a vehicle-forming component. Specifically, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, and a urethane resin having a crosslinkable functional group such as a hydroxyl group, and a crosslink of a melamine resin, a urea resin, a polyisocyanate compound (including a block body), etc. There may be mentioned those used in combination with an agent, and these are used by being dissolved or dispersed in an organic solvent and/or a solvent such as water.

Further, the water-based metallic base coating, if necessary, a solvent such as water or an organic solvent, a pigment dispersant, a curing catalyst, a defoaming agent, an antioxidant, an ultraviolet absorber, various additives such as a surface modifier, A gloss adjusting agent, an extender pigment and the like can be appropriately mixed.

The water-based metallic base paint is prepared by mixing and dispersing the above-mentioned components. It is preferable to adjust the solid content at the time of coating to 12 to 60% by mass, particularly 15 to 50% by mass based on the coating composition.

The water-based metallic base coating material can be applied by a known method such as rotary atomization coating, air spraying, airless spraying after adjusting the viscosity suitable for coating by adding water, an organic solvent or the like.

From the viewpoint of the smoothness of the coating film, the coating thickness is preferably 10 to 25 μm based on the cured coating film, more preferably 10 to 20 μm, further preferably 13 to 17 μm. It can be painted within the range.

The water-based paint is a term contrasted with an organic solvent-based paint, and generally, a film-forming resin, a pigment and the like are dispersed and/or dissolved in water or a medium containing water as a main component (aqueous medium). Means paint.

It is preferable that the base resin of the resin composition of the aqueous base paint has an acid group, and in the case of water dispersion, neutralization with a neutralizing agent is carried out in order to facilitate mixing and dispersion in water. It is preferable from the viewpoint of improving the property.

The neutralizing agent is not particularly limited as long as it can neutralize an acid group, and examples thereof include sodium hydroxide, potassium hydroxide, trimethylamine, 2-(dimethylamino)ethanol and 2-amino-2-methyl-. Basic compounds such as 1-propanol, triethylamine and aqueous ammonia can be mentioned.

The base coating film itself obtained by applying the water-based base coating can be cured at a temperature of about 50° C. to about 180° C. in the case of baking drying type, and can be cured at room temperature or forced drying type. Can be usually dried at room temperature to a temperature of about 80° C.

<Clear coating>
On the intermediate coating film formed by applying the intermediate coating composition, a base coating is applied to form a base coating, and a clear coating is applied to form a clear coating.

The clear coating is a coating for forming a clear coating film formed on the uppermost layer of a multilayer coating film to be formed, and imparts functionality such as acid resistance and scratch resistance, and has a finished appearance (smoothness, smoothness, It is a paint that improves gloss.
Normally, the clear paint is applied on the uncured base coating film without curing the base coating film.

The base coating film is preferably subjected to the above-mentioned preheating, air blowing and the like under heating conditions before the coating film is substantially cured before applying the clear coating composition. The preheating temperature is preferably 40 to 100°C, more preferably 50 to 90°C, and further preferably 60 to 80°C. The preheating time is preferably 30 seconds to 15 minutes, more preferably 1 to 10 minutes, and further preferably 2 to 5 minutes. The air blowing can be performed, for example, by blowing air heated to room temperature or a temperature of 25°C to 80°C for 30 seconds to 15 minutes on the coated surface of the object to be coated.

The base coating film is, if necessary, subjected to the above preheating, air blowing, etc. before the clear coating is applied so that the solid content of the coating film is usually 70 to 100% by mass, preferably 80 to 100% by mass. It is more preferable to adjust the content to be within the range of 90 to 100% by mass.

As the clear paint, it is possible to use, for example, one known per se which is usually used in the painting of automobile bodies. Specifically, a hydroxyl group, a carboxyl group, an epoxy group, having a crosslinkable functional group such as a silanol group, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, an epoxy resin, a fluororesin, and a melamine resin, Urea resin, polyisocyanate compound which may be blocked, carboxyl group-containing compound or resin, epoxy group-containing compound or resin or the like organic solvent-based thermosetting coating material containing a crosslinking agent as a resin component, water-based thermosetting coating material, Examples thereof include thermosetting powder coatings.

Among them, a thermosetting coating material containing a carboxyl group-containing resin and an epoxy group containing resin, and a thermosetting coating material containing a hydroxyl group-containing resin and a polyisocyanate compound which may be blocked are preferable.

As the clear paint, a one-pack type paint may be used, or a two-pack type paint such as a two-pack type urethane resin paint may be used.

In addition, the clear paint may contain a coloring pigment, a bright pigment, a dye, etc., if necessary, to the extent that transparency is not impaired, and further, an extender pigment, an ultraviolet absorber, a light stabilizer, and a erasing agent. A foaming agent, a thickener, a rust preventive, a surface conditioner and the like can be appropriately contained.

From the viewpoint of further improving the chipping resistance of the multilayer coating film, a urethane cross-linking type clear coating material containing a hydroxyl group-containing resin and a polyisocyanate compound is preferable, and particularly, a hydroxyl group-containing acrylic resin and a polyisocyanate compound are contained. The clear coating composition can be preferably used.

The hydroxyl group-containing acrylic resin can be produced by copolymerizing the hydroxyl group-containing unsaturated monomer (M-1) and the other copolymerizable unsaturated monomer (M-2) by a conventional method.

The hydroxyl group-containing unsaturated monomer (M-1) is a compound having one hydroxyl group and one unsaturated bond in one molecule, and this hydroxyl group mainly acts as a functional group that reacts with the crosslinking agent. .. As the monomer, specifically, a monoester product of acrylic acid or methacrylic acid and a dihydric alcohol having 2 to 10 carbon atoms is preferable, and for example, 2-hydroxyethyl (meth)acrylate, 2- Examples thereof include hydroxyalkyl(meth)acrylates such as hydroxypropyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, and 4-hydroxybutyl(meth)acrylate. Furthermore, examples of the monomer include ring-opening polymerization adducts of the above-mentioned hydroxyalkyl (meth)acrylate and lactones such as ε-caprolactone. As the hydroxyl group-containing unsaturated monomer (M-1), specifically, for example, "Plaxel FA-1", "Plaxel FA-2", "Plaxel FA-3", "Plaxel FA-4", "Plaxel FA-5", "Plaxel FM-1", "Plaxel FM-2", "Plaxel FM-3", "Plaxel FM-4", "Plaxel FM-5" (all of which are Daicel Chemical Industries, Ltd. Manufactured, trade name) and the like.

The compounding ratio of the hydroxyl group-containing unsaturated monomer (M-1) in the hydroxyl group-containing acrylic resin is in the range of 20 to 50% by mass, particularly 25 to 45% by mass based on the total amount of the monomer mixture. Is preferred.

When the compounding ratio of the hydroxyl group-containing unsaturated monomer (M-1) is less than 20% by mass, the cured coating film may be insufficiently crosslinked and the coating film performance such as scratch resistance may be deteriorated. On the other hand, if it exceeds 50% by mass, the compatibility with other copolymerizable unsaturated monomer (M-2) and the copolymerization reactivity decrease, and further the obtained hydroxyl group-containing acrylic resin and polyisocyanate compound. When the compatibility with (B) decreases, the finished appearance of the coating film may deteriorate.

In addition, in this specification, "(meth)acrylate" means "acrylate or methacrylate."

The other copolymerizable unsaturated monomer (M-2) is a compound having one unsaturated bond in one molecule other than the hydroxyl group-containing unsaturated monomer (M-1), Specific examples are listed below in (1) to (8).

(1) Acid group-containing unsaturated monomer: a compound having at least one acid group and one unsaturated bond in one molecule, and examples thereof include (meth)acrylic acid, crotonic acid, itaconic acid, and maleic acid. Carboxyl group-containing unsaturated monomers such as acids and maleic anhydride; sulfonic acid group-containing unsaturated monomers such as vinyl sulfonic acid and sulfoethyl (meth)acrylate; 2-(meth)acryloyloxyethyl acid phosphate; 2-(meth)acryloyloxypropyl acid phosphate, 2-(meth)acryloyloxy-3-chloropropyl acid phosphate, acidic phosphoric acid ester unsaturated monomers such as 2-methacryloyloxyethylphenylphosphoric acid, etc. be able to. These can be used alone or in combination of two or more. The acid group-containing unsaturated monomer can also act as an internal catalyst when the component (A) undergoes a cross-linking reaction with the cross-linking agent, and the amount used is the total amount of the monomer mixture constituting the hydroxy-containing acrylic resin. Based on the above, it is preferably used within the range of 0.1 to 5% by mass, particularly 0.1 to 3% by mass.

(2) Monoester compound of acrylic acid or methacrylic acid and monohydric alcohol having 1 to 20 carbon atoms: for example, methyl (meth)acrylate, ethyl acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl. (Meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl acrylate (Osaka Organic Chemical Industry) Co., Ltd., trade name), cyclohexyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, adamantyl (meth)acrylate, 3,5-dimethyladamantyl (meth). Acrylate, 3-tetracyclododecyl methacrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, 4-methylcyclohexylmethyl (meth)acrylate, 4-ethylcyclohexylmethyl (meth)acrylate, 4-methoxycyclohexylmethyl (meth) Examples thereof include acrylate, tert-butylcyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, cyclododecyl (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate.

(3) Unsaturated monomer containing alkoxysilane group: for example, vinyltrimethoxysilane, vinyltriethoxysilane, acryloxyethyltrimethoxysilane, methacryloxyethyltrimethoxysilane, acryloxypropyltrimethoxysilane, methacryloxypropyltri. Methoxysilane, acryloxypropyltriethoxysilane, methacryloxypropyltriethoxysilane, vinyltris(β-methoxyethoxy)silane and the like. Of these, preferred alkoxysilane group-containing unsaturated monomers include vinyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and the like.

(4) Aromatic unsaturated monomer: Examples thereof include styrene, α-methylstyrene, vinyltoluene and the like.

(5) Glycidyl group-containing unsaturated monomer: a compound having one glycidyl group and one unsaturated bond in one molecule, and specific examples thereof include glycidyl acrylate and glycidyl methacrylate.

(6) Nitrogen-containing unsaturated monomer: For example, (meth)acrylamide, dimethylacrylamide, N,N-dimethylpropylacrylamide, N-butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetoneacrylamide, Examples thereof include N,N-dimethylaminoethyl (meth)acrylate, vinyl pyridine and vinyl imidazole.

(7) Other vinyl compounds: For example, vinyl acetate, vinyl propionate, vinyl chloride, Verova 9 which is a vinyl ester of versatic acid, Veova 10 (Japan Epoxy Resin) and the like can be mentioned.

(8) Unsaturated bond-containing nitrile compound: Examples thereof include acrylonitrile and methacrylonitrile.

These other copolymerizable unsaturated monomers (M-2) can be used alone or in combination of two or more.

A hydroxyl group-containing acrylic resin can be obtained by copolymerizing a monomer mixture containing the above monomers (M-1) and (M-2).

The copolymerization method for obtaining a hydroxyl group-containing acrylic resin by copolymerizing the above-mentioned monomer mixture is not particularly limited, and a known copolymerization method per se can be used. In the above, a solution polymerization method of carrying out the polymerization in the presence of a polymerization initiator can be preferably used.

Examples of the organic solvent used in the solution polymerization method include aromatic solvents such as toluene, xylene, and Swazol 1000 (trade name, high boiling point petroleum solvent manufactured by Cosmo Oil Co., Ltd.); ethyl acetate, 3-methoxy. Ester solvents such as butyl acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone, propyl propionate, butyl propionate, ethoxyethyl propionate And so on.

These organic solvents may be used alone or in combination of two or more, but from the viewpoint of the solubility of the resin, it is preferable to use a high boiling point ester solvent or ketone solvent. Further, aromatic solvents having a higher boiling point can be used in suitable combination.

Examples of the polymerization initiator that can be used in copolymerization of the hydroxyl group-containing acrylic resin include 2,2′-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, There may be mentioned radical polymerization initiators known per se, such as t-butyl peroctoate and 2,2′-azobis(2-methylbutyronitrile).

The hydroxyl value of the hydroxyl group-containing acrylic resin is preferably in the range of 80 to 200 mgKOH/g, more preferably 100 to 170 mgKOH/g. If the hydroxyl value is less than 80 mgKOH/g, the scratch resistance may be insufficient due to the low crosslink density. If it exceeds 200 mgKOH/g, the water resistance of the coating film may decrease.

The weight average molecular weight of the hydroxyl group-containing acrylic resin is in the range of 2,500 to 40,000, and more preferably 5,000 to 30,000. If the weight average molecular weight is less than 2,500, the coating film performance such as acid resistance may decrease, and if it exceeds 40,000, the smoothness of the coating film may decrease, and thus the finish property may decrease.

The glass transition temperature of the hydroxyl group-containing acrylic resin is preferably -40°C to 85°C, particularly preferably -30°C to 80°C. If the glass transition temperature is less than -40°C, the coating film hardness may be insufficient, and if it exceeds 85°C, the coating surface smoothness of the coating film may deteriorate.

In addition to the hydroxyl group-containing acrylic resin, a hydroxyl group-containing resin such as polyester resin, polyether resin, polyurethane resin or the like, which is usually used for coating materials, can be contained as the base resin, if necessary.

The hydroxyl group-containing acrylic resin may be used alone or in combination of two or more.

The polyisocyanate compound is a compound having two or more free isocyanate groups in one molecule, and those conventionally used for producing polyurethane can be used. For example, aliphatic polyisocyanate, alicyclic polyisocyanate, araliphatic polyisocyanate, aromatic polyisocyanate and derivatives of these polyisocyanates can be mentioned.

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, 2,6-diisocyanatomethylcaproate, for example lysine ester triisocyanate, 1,4,8- Triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1, Examples thereof include aliphatic triisocyanates such as 8-diisocyanato-5-isocyanatomethyloctane.

Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (conventional name: Isophorone diisocyanate), 4,4′-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane( Conventional name: hydrogenated xylylene diisocyanate) or a mixture thereof, alicyclic diisocyanates such as norbornane diisocyanate, for example, 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3 -Isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo( 2.2.1) Heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2 -Isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl) -Bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)-heptane, 6- Examples thereof include alicyclic triisocyanates such as (2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

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

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

Examples of the polyisocyanate derivative include dimer, trimer, biuret, allophanate, carbodiimide, uretdione, uretoimine, isocyanurate, oxadiazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric) of the above polyisocyanate compound. MDI) and crude TDI.

These polyisocyanate compounds may be used alone or in combination of two or more. Of these polyisocyanate compounds, aliphatic diisocyanates and their derivatives can be preferably used from the viewpoint of scratch resistance, weather resistance and the like.

Further, the polyisocyanate compound may be a blocked polyisocyanate compound in which free isocyanate groups are blocked by a blocking agent. When the blocked isocyanate group is heated to the dissociation temperature of the blocking agent, the block is released and the free isocyanate group is regenerated.

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, γ. -Lactams such as butyrolactam and β-propiolactam; glycolic acid; glycolic acid esters such as methyl glycolate, ethyl glycolate and butyl glycolate; lactic acid esters such as lactic acid, methyl lactate, ethyl lactate and butyl lactate; methylol urea , Methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and other alcohols; formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime, and other oximes; Active methylene compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol. , Mercaptans such as ethylthiophenol; acid amides such as acetanilide, acetaniside, acetotoluide, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, benzamide; imides such as succinimide, phthalic acid imide, maleic acid imide; Amine type such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylphenylamine; imidazole type such as imidazole and 2-ethylimidazole; 3,5-dimethylpyrazole etc. Pyrazole type; urea type such as urea, thiourea, ethylene urea, ethylene thiourea, diphenyl urea; carbamate type ester such as phenyl N-phenylcarbamate; imine type such as ethylene imine, propylene imine; sodium bisulfite, bisulfite Blocking agents such as potassium sulfites can be used.

Among them, from the viewpoint of the appearance of the obtained coating film, a pyrazole type and an oxime type can be preferably used, and among them, 3,5-dimethylpyrazole, methylethylketoxime and the like can be preferably used.

Since the hydroxyl group of the hydroxyl group-containing acrylic resin and the isocyanate group of the polyisocyanate compound react even at room temperature (except when it is a block polyisocyanate compound), from the viewpoint of storage stability, the main agent containing the hydroxyl group-containing acrylic resin and polyisocyanate It is preferable that the compound and the compound are separated from each other, and the two are mixed and used immediately before use.

From the viewpoint of curability and scratch resistance of the coating film, the equivalent ratio (NCO/OH) of the hydroxyl group of the hydroxyl group-containing acrylic resin and the isocyanate group of the polyisocyanate compound is 0.6 to 1.4, particularly 0.8 to 1 It is preferably within the range of 0.2.

The clear coating material usually contains an organic solvent in addition to resin components such as a hydroxyl group-containing acrylic resin and a polyisocyanate compound, and further contains a curing catalyst, a pigment, a pigment dispersant, a leveling agent, an ultraviolet absorber, an optical agent, if necessary. A stabilizer, a plasticizer, and the like, which may be used as additives for coating materials usually used in the field of coating materials.

Examples of the curing catalyst include tin octylate, dibutyltin di(2-ethylhexanoate), dioctyltin di(2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyl. Examples thereof include tin oxide, organometallic catalysts such as zinc 2-ethylhexanoate, and tertiary amines.

These compounds described above as the curing catalyst may be used alone or in combination of two or more. The amount of the curing catalyst varies depending on the type, but is usually 0 to 0.2% by mass, preferably 0 to 0.1% by mass, based on the total solid content of the hydroxyl group-containing acrylic resin and the polyisocyanate compound.

Examples of the pigment include titanium oxide, zinc white, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, slene pigment, perylene. Coloring pigments such as pigments; extender pigments such as talc, clay, kaolin, barita, barium sulfate, barium carbonate, calcium carbonate, silica, and alumina white; metallic pigments such as aluminum powder, mica powder, and mica powder coated with titanium oxide. Can be mentioned.

These pigments described above may be used alone or in combination of two or more. The content of the pigment varies depending on its type, but is usually 0 to 20% by mass, preferably about 0 to 10% by mass based on the total solid content of the hydroxyl group-containing acrylic resin and the polyisocyanate compound.

The content of the coloring pigment varies depending on the type, but it can be added to the extent that transparency is not impaired.

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

When an ultraviolet absorber is used, the content of the ultraviolet absorber in the clear coating is usually 0 to 10 parts by mass, particularly 0.2 to 5 parts by mass, based on 100 parts by mass of the total solid content of the resin, and further, It is particularly preferably in the range of 0.3 to 2 parts by mass in terms of weather resistance and yellowing resistance.

As the light stabilizer, conventionally known ones can be used, and examples thereof include a hindered amine light stabilizer.

When a light stabilizer is used, the content of the light stabilizer in the clear coating is usually 0 to 10 parts by mass, particularly 0.2 to 5 parts by mass, based on 100 parts by mass of the resin solid total amount, and further, It is particularly preferably in the range of 0.3 to 2 parts by mass in terms of weather resistance and yellowing resistance.

The method of applying the clear coating material is not particularly limited, but the wet coating film can be formed by a coating method such as air spray coating, airless spray coating, rotary atomization coating, curtain coat coating and the like. These coating methods may be electrostatically applied if necessary. Of these, air spray coating and rotary atomization coating are particularly preferable. The amount of the clear coating applied is usually 10 to 50 μm, preferably 20 to 40 μm as a cured film thickness.

In the case of air spray coating, airless spray coating and rotary atomization coating, the viscosity of the clear coating is set within the viscosity range suitable for the coating, usually Ford Cup #No. In a 4 viscometer, it is preferable to appropriately adjust using a solvent such as an organic solvent so that the viscosity range is about 15 to 60 seconds at 20°C.

Examples of the organic solvent include ester solvents such as ethyl acetate, butyl acetate and ethyl-3-ethoxypropionate, toluene, xylene, aromatic mixed solvents (“Swazol 1000”, “Swazol 1500” (all are Cosmo Petrochemical (Trade name, etc.), etc. can be used, and these can be used individually by 1 type or in combination of 2 or more types.

The clear coating film itself obtained by applying the clear coating composition can be heated and cured at a temperature of room temperature to about 150°C.

In addition, after the clear paint is applied, it may be preheated at room temperature for about 1 to 60 minutes or at 40 to 110° C. for about 1 to 30 minutes, if necessary.

In a multilayer coating consisting of an intermediate coating film, a base coating film and a clear coating film, the clear coating film obtained by applying the clear coating film can usually be heat-cured together with the uncured base coating film. it can.

The above-mentioned heating can be performed by usual heating means for the coating film, for example, hot air heating, infrared heating, high frequency heating and the like. The heating temperature is preferably 60 to 180°C, more preferably 110 to 170°C, and further preferably 130 to 160°C. The heating time is not particularly limited, but is preferably 10 to 90 minutes, more preferably 15 to 60 minutes, still more preferably 15 to 30 minutes.

Preheating may be appropriately performed before heat curing. The temperature of preheating is preferably 40 to 110°C, more preferably 50 to 110°C. The preheating time is preferably 30 seconds to 15 minutes, more preferably 1 to 10 minutes.

The final heating after the clear coating for forming the clear coating which is the uppermost coating is completed to complete the curing of the multilayer coating consisting of the intermediate coating, the base coating and the clear coating.

From the viewpoint of the finished appearance, the multilayer coating film preferably has a thickness of 70 to 120 μm, particularly 80 to 100 μm, based on the cured coating film.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples. In addition, "part" and "%" are based on the mass basis, and the film thickness of the coating film is based on the cured coating film.

The average molecular weight of the resin is measured by GPC using a standard polystyrene calibration curve.

<Production of hydroxyl group-containing polyester resin (A)>
Production example 1
In a reactor equipped with a stirrer, a thermometer, a reaction product water removing device, and a nitrogen gas introducing pipe, 664 parts of isophthalic acid, 496 parts of adipic acid, 237 parts of phthalic anhydride, 788 parts of neopentyl glycol, 341 parts of trimethylolpropane. Was charged and heated to 160° C. with stirring under a nitrogen gas atmosphere. After holding at 160° C. for 1 hour, the generated condensed water was removed and the temperature was raised to 230° C. over 5 hours, and the temperature was kept at the same temperature. When the acid value reached 7 mgKOH/g, the mixture was cooled to 170° C., 490 parts of ε-caprolactone was added, and the mixture was kept at the same temperature for 1 hour. A hydroxyl group-containing polyester resin (A-1) was obtained by diluting with a boiling point aromatic solvent, manufactured by Shell Chemicals Japan. The obtained hydroxyl group-containing polyester resin (A-1) had a lactone modification amount of 18%, a hydroxyl value of 100 mgKOH/g, an acid value of 5.7 mgKOH/g, a number average molecular weight of 2030, and a heating residue of 70%.

Production Examples 2 to 13
In Production Example 1, each hydroxyl group-containing polyester resin (A-2) to (A-13) was obtained by producing in the same manner as in Production Example 1 except that the raw material compound composition was as shown in Table 1. ..

The raw material compound composition in Table 1 is a molar ratio, and the hydroxyl group-containing polyester resins (A-10) to (A-13) are resins for comparative examples.

<Production of intermediate coating composition (X)>
Examples 1-13 and Comparative Examples 1-7
Raw materials having the compositions shown in Table 2 ((A) hydroxyl group-containing polyester resin produced in Production Examples 1 to 13, (B) melamine resin, (C) pyrazole block polyisocyanate compound and (D) pigment were mixed and stirred, Butyl acetate was added to obtain each intermediate coating composition (X1) to (X20) having a viscosity of 30 seconds according to Ford Cup No. 4 at 20° C. The content of each component is a solid content.

The intermediate coating materials (X14) to (X20) are intermediate coating materials for comparative examples.

The raw materials used in Table 2 are as follows.

Melamine resin (B-1): weight average molecular weight 1200, imino group-containing methylbutyl mixed etherified melamine.

Melamine resin (B-2): a weight average molecular weight of 1500 and an imino group-containing butyl etherified melamine.

Blocked polyisocyanate compound (C-1): A compound in which hexamethylene diisocyanate is fully blocked with 3,5-dimethylpyrazole.

Blocked polyisocyanate compound (C-2): a compound in which hexamethylene diisocyanate is fully blocked with diethyl malonate.

Blocked polyisocyanate compound (C-3): a compound in which hexamethylene diisocyanate is fully blocked with methyl ethyl ketoxime.

Pigment (D-1): titanium dioxide, average particle size 0.25 μm.

Pigment (D-2): barium sulfate, average particle size 0.7 μm.

Pigment (D-3): carbon black, average particle size 0.02 μm.

<Manufacture of water-based paint>
Production Example 14
Hydroxyl group-containing acrylic resin dispersion (i) 100 parts (solid content 30 parts), hydroxyl group-containing water-soluble acrylic resin (ii) 73 parts (solid content 40 parts), methyl-butyl mixed etherified melamine resin (solid content 60%, Weight average molecular weight 2,000) 50 parts (solid content 30 parts), aluminum pigment paste "GX-40A" (Asahi Kasei Metals Ltd., metal content 74%) 11 parts, and aluminum pigment paste "MH-8805" (Asahi Kasei). ASE-60 (alkaline swelling thickener, trade name, manufactured by Rohm and Haas Co.), 2-(dimethylamino)ethanol and deionized water are mixed with 10 parts of Metals, 68% metal content. The mixture was added, adjusted, mixed with stirring, and diluted to a viscosity suitable for coating to obtain an aqueous base coating (Y1) having a pH of 8.0 and a coating solid content of 23%.

Hydroxyl group-containing acrylic resin dispersion (i):
130 parts of deionized water in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen introducing pipe and a dropping device, "Aqualon KH-10" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Polyoxy 0.52 parts of ethylene alkyl ether sulfate ester ammonium salt, active ingredient 97%) was charged, and the mixture was stirred and mixed in a nitrogen stream and heated to 80°C. Then, 1% of the total amount of the following monomer emulsion (1) and 5.3 parts of a 6% ammonium persulfate aqueous solution were introduced into the reaction vessel and kept at 80° C. for 15 minutes. Then, the remaining monomer emulsion (1) was added dropwise to the reaction container kept at the same temperature over 3 hours. After completion of dropping, the mixture was aged for 1 hour.

Next, the following monomer emulsion (2) was added dropwise over 1 hour. After aging for 1 hour, 40 parts of a 5% 2-(dimethylamino)ethanol aqueous solution was gradually added to the reaction vessel, cooled to 30° C., and filtered through a 100 mesh nylon cloth to obtain a filtrate having an average particle diameter of 120 nm. (Using a submicron particle size distribution measuring device "COULTER N4 type" (manufactured by Beckman Coulter, Inc.) and diluted with deionized water and measured at 20° C.), a hydroxyl group-containing acrylic resin dispersion having a solid content concentration of 30%. (I) was obtained. The acid value of the obtained hydroxyl group-containing acrylic resin dispersion (i) was 33 mgKOH/g, and the hydroxyl value was 25 mgKOH/g.

Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2.1 parts of methylenebisacrylamide, 2.8 parts of styrene, 16.1 parts of methyl methacrylate, 28 parts of ethyl acrylate and 21 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (1).

Monomer emulsion (2): Deionized water 18 parts, "Aqualon KH-10" 0.31 part, ammonium persulfate 0.03 part, methacrylic acid 5.1 parts, 2-hydroxyethyl acrylate 5.1 parts, styrene 3 Parts, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate and 9 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (2).

Hydroxyl group-containing water-soluble acrylic resin (ii):
After charging 35 parts of propylene glycol monopropyl ether to a flask and heating to 85° C., 30 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 29 parts of n-butyl acrylate, 15 parts of hydroxyethyl acrylate, 6 parts of acrylic acid, propylene glycol. A mixture of 15 parts of monopropyl ether and 2.3 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) was added dropwise to the flask over 4 hours, and the mixture was aged for 1 hour after completion of the addition. Thereafter, a mixture of 10 parts of propylene glycol monopropyl ether and 1 part of 2,2′-azobis(2,4-dimethylvaleronitrile) was added dropwise to the flask over 1 hour, and the mixture was aged for 1 hour after completion of the addition. Further, 7.4 parts of diethanolamine was added to obtain a hydroxyl group-containing water-soluble acrylic resin (ii) having a solid content concentration of 55%, an acid value of 47 mgKOH/g and a hydroxyl value of 72 mgKOH/g.

<Manufacture of clear paint>
Production Example 15
A main agent having 64 parts of a hydroxyl group-containing acrylic resin (iii), 2 parts of UV1164 (manufactured by Ciba-Geigy, UV absorber), and 2 parts of HALS292 (manufactured by Ciba-Geigy, light stabilizer) dissolved in ethyl acetate and cured 36 parts of the agent N-3300 (manufactured by Sumika Bayer Urethane Co., isocyanurate of hexamethylene diisocyanate, solid content 100%, NCO content 21.8%) is mixed by stirring using a disper, and ethyl acetate and acetic acid are used. Dilute with a mixed solvent of butyl (mass ratio 1/1) to Ford Cup #No. A clear paint (Z1) was obtained by adjusting the viscosity of the sample No. 4 at 20° C. for 17 seconds.

Hydroxyl group-containing acrylic resin (iii): A monomer composition having a monomer composition of styrene/cyclohexyl methacrylate/2-ethylhexyl acrylate/2-hydroxyethyl acrylate/acrylic acid=20/26/19/34/1 is prepared, and the monomer composition is prepared. 100 parts of the product was polymerized with 1 part of the polymerization initiator di-t-amyl peroxide to obtain a hydroxyl group-containing acrylic resin (iii). The solid content was 60% by mass (diluting solvent: ethoxyethyl propionate), the weight average molecular weight was 10,000, the hydroxyl value was 164 mgKOH/g, and the acid value was 8 mgKOH/g).

<Creation of test plate>
(Preparation of test object)
"ELECRON GT-10" (trade name, manufactured by Kansai Paint Co., Ltd., a thermosetting epoxy resin-based cationic electrodeposition coating) is electro-deposited on the cold-rolled steel sheet treated with zinc phosphate to a film thickness of 20 µm, It was heated at 170° C. for 30 minutes to be cured to obtain a test article.

The intermediate coating composition (X1) prepared in Example 1 was applied to the test article by electrostatic bell coating so that the cured coating film had a thickness of 35 μm, left for 7 minutes, and then heated at 140° C. for 30 minutes. Cured.

Then, the aqueous base coating material (Y1) obtained in Production Example 14 was applied on the intermediate coating film by electrostatic bell coating so as to have a cured film thickness of 15 μm, and allowed to stand for 5 minutes at 80° C. Preheating was performed for 3 minutes.

Then, the clear coating composition (Z1) prepared in Production Example 15 was electrostatically bell-coated on the uncured base coating film so as to have a cured film thickness of 35 μm, allowed to stand for 7 minutes, and then heated at 140° C. for 30 minutes. A test plate was prepared by heating and curing the multilayer coating film.

Each test plate was produced in the same manner as above except that the intermediate coating composition (X1) was changed to any of the intermediate coatings (X2) to (X20).

Each of the obtained test plates was tested for chipping resistance, finished appearance (smoothness, sharpness) and water-resistant adhesion based on the following test methods and evaluation methods.

The test results are also shown in Table 2.

Chipping resistance: A test plate was installed on a specimen holder of a stepping stone tester JA-400 (chipping tester) manufactured by Suga Test Instruments Co., Ltd., and compressed air of 0.3 MPa from a distance of 35 cm at -20°C. No. 6, crushed stone (200 g) was made to collide with the test plate at an angle of 90 degrees. After that, the obtained test plate is washed with water, dried, and a cloth adhesive tape (manufactured by Nichiban Co., Ltd.) is attached to the coated surface, and after peeling it off, the degree of scratches in the coating film is visually observed. Then, the evaluation was made according to the following criteria.
◎: The size of the scratch is extremely small and the steel plate on the electrodeposition surface or the base material is not exposed. ○: The size of the scratch is small, the steel plate on the electrodeposition surface or the base material is not exposed. △: The size of the scratch is Although it is small, the electrodeposited surface and the base steel plate are exposed. ×: The size of the scratch is quite large, and the base steel plate is also largely exposed.
<Finished appearance (smoothness, sharpness)>
The surface of the multilayer coating film of each test plate was evaluated by visual evaluation in accordance with the following criteria of “⊚”, “◯”, “Δ”, and “x”. ⊚: Good ∘: Slightly good Δ: Slightly inferior ×: Inferior <Water resistance adhesion>
After dipping each test plate at 40° C. for 10 days, the adhesion of the multilayer coating film of each test plate to the test object was measured according to the 2 mm width cross-cut tape method of the former “JIS K5400 paint general test method”. Then, a cross-cut peeling test was performed, and evaluation was made based on the following criteria of "◎", "○", "△", and "x".
⊚: 100 goggles-like coating films remained, and no small borders of the paint film were produced at the edges of the cutter cuts. ○: 100 goggles-like coating films remained, but the coating films were small at the cutting edges of the cutter. Borders are generated. Δ: 90 to 99 pieces of goggles coating film remain ×: 89 or less remaining pieces of goggles coating film

<Production of hydroxyl group-containing polyester resin (A)>
Production Example 16
In a reactor equipped with a stirrer, a thermometer, a reaction product water removing device, and a nitrogen gas introducing pipe, 664 parts of isophthalic acid, 496 parts of adipic acid, 237 parts of phthalic anhydride, 788 parts of neopentyl glycol, 341 parts of trimethylolpropane. Was charged and heated to 160° C. with stirring under a nitrogen gas atmosphere. After holding at 160° C. for 1 hour, the generated condensed water was removed and the temperature was raised to 230° C. over 5 hours, and the temperature was kept at the same temperature. When the acid value reached 7 mgKOH/g, the temperature was cooled to 170° C., 490 parts of ε-caprolactone was added, the mixture was kept at the same temperature for 1 hour, and then 77 parts of trimellitic anhydride was added to this reaction product. The addition reaction was performed at 170° C. for 30 minutes. Then, the mixture was cooled to 50° C. or lower, 0.88 equivalent of 2-(dimethylamino)ethanol was added to the acid group for neutralization, and deionized water was gradually added to give a solid concentration of 40%. , To obtain a hydroxyl group-containing polyester resin (A-14) aqueous dispersion having a pH of 7.5. The hydroxyl group-containing polyester resin (A-14) obtained had a lactone modification amount of 18% by mass, a number average molecular weight of 2074, a hydroxyl value of 89 mgKOH/g, and an acid value of 23 mgKOH/g.

Production Examples 17-28
In Production Example 16, each hydroxyl group-containing polyester resin (A-15) to (A-26) was obtained by producing in the same manner as in Production Example 16 except that the raw material compound composition was as shown in Table 3. ..

In addition, the raw material compound composition in Table 3 is a molar ratio, and the hydroxyl group-containing polyester resins (A-23) to (A-26) are resins for comparative examples.

<Production of hydroxyl group-containing polyester resin other than hydroxyl group-containing polyester resin (A)>
Production Example 29
In a reactor equipped with a stirrer, a thermometer, a reaction product water removing device, and a nitrogen gas introducing pipe, 664 parts of isophthalic acid, 496 parts of adipic acid, 237 parts of phthalic anhydride, 788 parts of neopentyl glycol, 341 parts of trimethylolpropane. Was charged and heated to 160° C. with stirring under a nitrogen gas atmosphere. After holding at 160° C. for 1 hour, the generated condensed water was removed and the temperature was raised to 230° C. over 5 hours, and the temperature was kept at the same temperature. After cooling to 170°C when the acid value reached 7 mgKOH/g, 57 parts of trimellitic anhydride was added to this reaction product, and addition reaction was carried out at 170°C for 30 minutes. Then, the mixture was cooled to 50° C. or lower, 0.88 equivalent of 2-(dimethylamino)ethanol was added to the acid group for neutralization, and deionized water was gradually added to give a solid concentration of 40%. , And a hydroxyl group-containing polyester resin (PE-1) aqueous dispersion having a pH of 7.5 was obtained. The hydroxyl group-containing polyester resin (PE-1) thus obtained had a hydroxyl value of 110 mgKOH/g, an acid value of 22 mgKOH/g, and a number average molecular weight of 1,780.

Example 14
In a stirring and mixing container, 50 parts of the hydroxyl group-containing polyester resin (PE-1) aqueous dispersion obtained in Production Example 29 (resin solid content: 20 parts), the pigment (D-1) (titanium dioxide, average particle size: 0.25 μm). ) 75 parts, 25 parts of the pigment (D-2) (barium sulfate, average particle size 0.7 μm), 0.5 parts of the pigment (D-3) (carbon black, average particle size 0.02 μm) and deionized Water (15 parts) was added, the mixture was mixed uniformly, and 2-(dimethylamino)ethanol was further added to adjust the pH to 8.0. Then, the obtained mixed liquid was put into a wide-mouth glass bottle, glass beads having a diameter of about 1.3 mmφ were added as a dispersion media and the mixture was sealed, and dispersed with a paint shaker for 4 hours to prepare a pigment dispersion paste (P-1). Obtained.
Next, 120.5 parts (solid content) of the obtained pigment dispersion paste (P-1), 40 parts (solid content) of the hydroxyl group-containing polyester resin (A-14) aqueous dispersion obtained in Production Example 16, and the following melamine: 10 parts (solid content) of the resin (B-3), 10 parts (solid content) of the following melamine resin (B-4) and 20 parts (solid content) of the following block polyisocyanate compound (C-4) were uniformly mixed.
Then, 2-(dimethylamino)ethanol and deionized water were added to the obtained mixture, and Ford cup No. 2 at pH 8.0 and 20° C. was added. Thus, an intermediate coating composition (X21) having a viscosity of 35 seconds according to No. 4 was obtained.

Examples 15-25, Comparative Examples 8-13
Each of the intermediate coating compositions (X22) to (X38) was obtained in the same manner as in Example 14, except that the raw material compound composition was as shown in Table 4 below. In addition, the compounding quantity of each component is solid content.

The intermediate coating compositions (X33) to (X38) are intermediate coating compositions for comparative examples.

The raw materials used in Table 4 are as follows.

Melamine resin (B-3): weight average molecular weight 550, methyl etherified melamine Melamine resin (B-4): weight average molecular weight 600, imino group-containing methyl etherified melamine block polyisocyanate compound (C-4): hexamethylene di A water dispersion of a compound in which isocyanate is fully blocked with 3,5-dimethylpyrazole.

<Creation of test plate>
The intermediate coating composition (X21) prepared in Example 14 was applied to the test object by electrostatic bell coating so that the cured coating film had a thickness of 25 μm, left for 5 minutes, and then preheated at 80° C. for 5 minutes. After that, it was heated at 150° C. for 30 minutes to be cured.

Then, the aqueous base coating material (Y1) obtained in Production Example 14 was applied on the intermediate coating film by electrostatic bell coating so as to have a cured film thickness of 15 μm, and allowed to stand for 5 minutes at 80° C. Preheating was performed for 3 minutes.

Then, the clear coating composition (Z1) prepared in Production Example 15 was electrostatically bell-coated on the uncured base coating film so as to have a cured film thickness of 35 μm, allowed to stand for 7 minutes, and then heated at 140° C. for 30 minutes. A test plate was prepared by heating and curing the multilayer coating film.

Each test plate was produced in the same manner as above except that the intermediate coating composition (X21) was changed to any of the intermediate coating compositions (X22) to (X38).

Each of the obtained test plates was tested for chipping resistance, finished appearance (smoothness, sharpness) and water-resistant adhesion based on the above-mentioned test method and evaluation method.

The test results are also shown in Table 4.

Claims (2)

(A) Lactone modified amount of 12 to 25% by mass, hydroxyl group-containing polyester resin having a number average molecular weight of 1500 to 2200, (B) melamine resin, (C) pyrazole block polyisocyanate compound, and (D) pigment An intermediate coating composition containing
The intermediate coating composition, wherein the use ratio of the melamine resin (B) and the pyrazole block polyisocyanate compound (C) is 10/30 to 20/15 (melamine resin/pyrazole block polyisocyanate compound) in terms of solid content. Stuff. For the article to be coated, the following steps (1) to (4),
Step (1): a step of applying an intermediate coating composition (X) to form an intermediate coating film,
Step (2): A step of applying a water-based base coating material (Y) on the intermediate coating film formed in the step (1) to form a base coating film,
Step (3): a step of applying a clear coating (Z) on the base coating film formed in the step (2) to form a clear coating film, and step (4): the steps (1) to (( A method for forming a multilayer coating film, which comprises sequentially performing the step of heating and curing the intermediate coating film, the base coating film and the clear coating film formed in 3),
A method for forming a multilayer coating film, comprising applying the intermediate coating composition according to claim 1 as the intermediate coating composition (X).