One-pack coating composition and coating method using the same

A one-pack coating composition is disclosed. The composition comprises (A) an oligomer or polymer containing an acid anhydride group, a blocked hydroxyl group and an epoxy group as indispensable functional groups in the same or different molecules, (B) a heat-potential curing catalyst which comprises a complex of an organometallic compound and an electron-donating compound or an onium salt and which exhibits its activity upon heating, (C) an ultraviolet absorber comprising a triazine or oxalic anilide, and (D) a hindered amine light stabilizer having a piperidine ring of the following structure: ##STR1## wherein R represents R.sup.1 --CO--, a C.sub.2 to C.sub.20 alkyl group or R.sup.1 --O-- (R.sup.1 being a C.sub.2 to C.sub.20 alkyl group), and R.sup.2, R.sup.3, R.sup.4 and R.sup.5 independently from each other represent a C.sub.1 to C.sub.3 alkyl group, or a phenolic antioxidant. A method for coating using this coating composition is also disclosed.

BACKGROUND OF THE INVENTION
 The present invention relates to a one-pack coating composition for coating
 motor cars and the like. In particular, the present invention relates to a
 one-pack coating composition having an excellent io storability, being
 capable of forming a coating free from unnecessary coloring and having an
 excellent weather resistance.
 A curing resin composition having a siloxy group, an acid anhydride group,
 an epoxy group and an alkoxysilyl group as main functional groups is well
 known as a one-pack coating composition excellent in acid resistance and
 resin stability [see, for example, Japanese Patent Unexamined Published
 Application (hereinafter referred to as "J. P. KOKAI") No. Hei 3-172318].
 A curing catalyst for accelerating the curing reaction of the carboxyl
 group derived from an acid anhydride and an epoxy group is usually used
 for such a curable resin composition to accelerate the curing reaction of
 the oligomer or polymer having the above-described functional groups.
 However, when such a curing catalyst is previously incorporated into the
 paint composition, problems are caused. Specifically, the carboxyl group
 is formed from the acid anhydride group by water (moisture) in air during
 the storage to cause the curing reaction with the epoxy group; the curing
 reaction of the acid anhydride group and the epoxy group proceeds; the
 carboxyl group thus formed acts as the catalyst to remove the blocking
 group from the blocked hydroxyl group; and the viscosity of the coating
 composition gradually increases during the storage. Therefore, recently, a
 so-called heat-potential curing catalyst which dissociates upon heating to
 act as a curing catalyst has come to be used (see, for example, J. P.
 KOKAI No. Hei 5-271526).
 On the other hand, it is well known that a light stabilizer, antioxidant,
 ultraviolet absorber, etc. are incorporated into the coating composition
 for the purpose of improving the weather resistance thereof.
 However, it has been found that, when the light stabilizer, antioxicant,
 ultraviolet absorber, etc. are incorporated into the coating composition
 containing the heat-potential catalyst, the composition cannot be used as
 a one-pack coating composition, since the viscosity of the coating
 composition is gradually increased during the storage or an unnecessary
 coloring of the coating film is caused depending on the kind of these
 additives to be used.
 SUMMARY OF THE INVENTION
 Therefore, the object of the present invention is to provide a one-pack
 coating composition having an excellent storability, being capable of
 forming a coating free from unnecessary coloring and having an excellent
 weather resistance.
 After intensive investigations made for the purpose of attaining the
 above-described object, the inventors have found that a one-pack coating
 composition having a remarkably improved storability, being capable of
 forming a coating free from unnecessary coloring and having an excellent
 weather resistance can be surely obtained by incorporating a specific
 ultraviolet absorber and a specific light stabilizer and/or antioxidant
 into a coating composition comprising an oligomer or polymer (hereinafter
 referred to as "resin", if necessary) containing an acid anhydride group,
 a blocked hydroxyl group and an epoxy group as indispensable functional
 groups. The present invention has been completed on the basis of this
 finding.
 Namely, the present invention relates to:
 1. a one-pack coating composition comprising:
 (A) an oligomer or polymer containing an acid anhydride group, a blocked
 hydroxyl group and an epoxy group as indispensable functional groups in
 the same or different molecules,
 (B) a heat-potential catalyst which comprises a complex of an
 organometallic compound and an electron-donating compound or an onium salt
 and which exhibits its activity upon heating,
 (C) an ultraviolet absorber comprising a triazine or oxanilide, and
 (D) a hindered amine light stabilizer having a piperidine ring of the
 following structure:
 ##STR2##
 wherein R represents R.sup.1 --CO--, a C.sub.2 to C.sub.20 alkyl group or
 R.sup.1 --O-- (R.sup.1 being a C.sub.2 to C.sub.20 alkyl group), and
 R.sup.2, R.sup.3, R.sup.4 and R.sup.5 independently from each other
 represent a C.sub.1 to C.sub.3 alkyl group, or a phenolic antioxidant,
 2. a coating method comprising coating the one-pack coating composition set
 forth in above item 1 to the surface of a substrate and curing the
 resultant coating by heat, to form a coating on the surface of the
 substrate, and
 3. a coating method comprising coating the one-pack coating composition set
 forth in above item 1 to the surface of a substrate at 30 to 80.degree. C.
 DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The acid anhydride group in the present invention is a functional group of
 the formula: --CO--O--CO--.
 The blocked hydroxyl group in the present invention is a hydroxyl group
 blocked with a blocking agent. The blocked hydroxyl groups include, for
 example, hydroxyl groups blocked with the following blocking groups:
 [1] Silyl Blocking Groups:
 The silyl blocking groups are, for example, those of the following formula
 (1):
 ##STR3##
 wherein R.sup.1 to R.sup.3 independently from each other represent an alkyl
 group or aryl group. The alkyl group includes linear or branched alkyl
 groups having 1 to 10 carbon atoms and is particularly preferably lower
 alkyl groups having 1 to 8 carbon atoms such as methyl, ethyl, propyl,
 butyl, s-butyl, t-butyl, pentyl and hexyl groups. The aryl group is, for
 example, phenyl, naphthyl and indenyl groups which may have a substituent.
 Among them, a phenyl group is particularly preferred.
 The silyl blocking groups of the formula (1) include, for example,
 trimethylsilyl, diethylmethylsilyl, ethyldimethylsilyl,
 butyldimethylsilyl, butylmethylethylsilyl, phenyldimethylsilyl,
 phenyldiethylsilyl, diphenylmethylsilyl and diphenylethylsilyl groups. The
 smaller the molecular weight of R.sup.1 to R.sup.3, the better, since the
 groups having a smaller molecular weight is easily dissociated at a low
 temperature and has excellent curing properties.
 Silane halides are usable as preferred blocking agents capable of forming
 the silyl blocking groups. The halogen atoms contained in the silane
 halides include a chlorine atom, a bromine atom, etc. Examples of the
 blocking agents include trimethylsilyl chloride, diethylmethylsilyl
 chloride, ethyldimethylsilyl chloride, butyldimethylsilyl bromide and
 butylmethylethylsilyl bromide.
 [2] Vinyl (thio)Ether Blocking Groups:
 The vinyl (thio)ether blocking groups are, for example, those of the
 following formula (2):
 ##STR4##
 wherein R.sup.1, R.sup.2 and R.sup.3 independently from each other
 represent a hydrogen group or a hydrocarbon group having 1 to 18 carbon
 atoms, R.sup.4 represents a hydrocarbon group having 1 to 18 carbon atoms,
 Y represents an oxygen or sulfur atom, and R.sup.3 and R.sup.4 may be
 bonded together to form a heterocyclic ring containing Y as a hetero atom.
 The hydrocarbon groups in the above formula include, for example, alkyl,
 cycloalkyl and aryl groups. The alkyl groups are particularly preferably
 lower alkyl groups having 1 to 8 carbon atoms such as methyl, ethyl,
 propyl, butyl, s-butyl, t-butyl, pentyl and hexyl groups. The cycloalkyl
 groups are, for example, cyclopentyl and cyclohexyl groups. The aryl
 groups include substituted or unsubstituted phenyl, naphthyl and
 anthracene groups. The phenyl group is particularly preferred.
 The vinyl (thio)ether blocking group can be formed by reacting an aliphatic
 vinyl (thio)ether or cyclic vinyl (thio)ether with a hydroxyl group of a
 carboxyl group. The aliphatic vinyl ethers include, for example, methyl
 vinyl ether, ethyl vinyl ether, isopropyl vinyl ether, n-propyl vinyl
 ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether and cyclohexyl vinyl
 ether, as well as corresponding vinyl thioethers. The cyclic vinyl ethers
 include, for example, 2,3-dihydrofuran, 3,4-dihydrofuran,
 2,3-dihydro-2H-pyran, 3,4-dihydro-2H-pyran,
 3,4-dihydro-2-methoxy-2H-pyran, 3,4-dihydro-4,4-dimethyl-2H-pyrane-2-on,
 3,4-dihydro-2-ethoxy-2H-pyran and sodium
 3,4-dihydro-2H-pyran-2-carboxylate.
 The epoxy groups used in the present invention include non-alicyclic epoxy
 groups and alicyclic epoxy groups. The non-alicyclic epoxy groups include,
 for example, those having an epoxy bond formed with an oxygen atom between
 carbon atoms of alkyl groups such as 1,2-epoxy and 1,3-epoxy groups. The
 alicyclic epoxy groups are those having an epoxy bond formed with an
 oxygen atom between carbon atoms adjacent to each other in a five-membered
 or six-membered ring (including a crosslinked hydrocarbon). The
 non-alicyclic epoxy group is practically preferred to the alicyclic epoxy
 group.
 The resins (oligomers or polymers) used in the present invention are not
 particularly limited so far as they have the above-described functional
 groups. Examples of the resins include vinyl oligomers and polymers and
 polyester oligomers or polymers. From the viewpoint of easiness of the
 production of the resin, the vinyl-polymerized oligomers and polymers are
 particularly preferred. The description will be given with reference to
 mainly the vinyl oligomers and polymers (hereinafter referred to as "vinyl
 oligomers" collectively).
 The vinyl oligomers may contain the above-described acid anhydride group, a
 blocked hydroxyl group and an epoxy group in either the same molecule or
 different molecules.
 The vinyl oligomers have a number-average molecular weight (Mn) of usually
 600 to 20,000, preferably 800 to 10,000. When the number-average molecular
 weight is below 600, the oligomers having no functional group in the
 molecule are partially formed to make the crosslinking insufficient and
 also to make the gasoline resistance and scuff resistance insufficient. On
 the contrary, when the number-average molecular weight is above 20,000,
 the viscosity becomes too high, a larger amount of the solvent is
 necessitated and the formation of the thick film becomes difficult.
 The amount of the functional groups in the vinyl oligomer is usually 1 to 5
 mol/kg-resin, preferably 2 to 4 mol/kg-resin. When it is below 1
 mol/kg-resin, the crosslinking density is lowered to reduce the scuff
 resistance and gasoline resistance. On the contrary, when the amount of
 the functional groups is above 5 mol/kg-resin, the crosslinking density
 becomes too high, the weather resistance is lowered and the coating is
 easily cracked unfavorably.
 The vinyl oligomers are obtained by polymerizing or copolymerizing a
 monomer having a radical-polymerizable unsaturated bonding group. For
 example, when the vinyl oligomers synthesized from acrylic acid or
 methacrylic acid monomer, the products are acrylic oligomers. The monomers
 can be polymerized by a well known, ordinary technique such as an ion
 polymerization technique, e. g., anion or cation polymerization technique,
 or radical polymerization technique. In the present invention, the radical
 polymerization technique is preferred from the viewpoint of the easiness.
 However, in producing a vinyl oligomer having a low molecular weight,
 another polymerization technique such as a technique wherein
 mercaptoethanol, thioglycerol, a mercaptan such as laurylmercaptan or a
 chain transfer agent is used, a technique wherein the reaction is
 conducted at a temperature of as high as 140 to 180.degree. C. or a
 technique wherein the reaction is conducted while the monomer
 concentration is kept low can be employed.
 The radical polymerization is desirably conducted in a solution. The
 solvent used for the radical solution polymerization is any solvent
 ordinarily used for the polymerization of a polymerizable vinyl monomer
 such as acryl monomers. Examples of such solvents include toluene, xylene,
 butyl acetate, methyl ethyl ketone, methyl isobutyl ketone and Solvesso (a
 product of Exxon Corporation).
 The radical reaction initiator used for the radical solution polymerization
 can be any of reaction initiators ordinarily used for the radical
 polymerization. Examples of the reaction initiators include peroxides such
 as benzoyl peroxide, lauroyl peroxide, t-butyl hydroperoxide, di-t-butyl
 hydroperoxide and t-butyl peroxy-2-ethylhexanoate; and azo compounds such
 as azobisvaleronitrile, azobisisobutyronitrile and
 azobis(2-methylpropionitrile).
 The radical-polymerizable unsaturated bonding groups are preferably, for
 example, radical-polymerizable vinyl bonds of the formula:
 CHR.sup.1.dbd.CR.sup.2 -- wherein R.sup.1 and R.sup.2 each represent a
 hydrogen atom, alkyl group or single bond. The alkyl groups herein include
 linear or branched alkyl groups and they are preferably those having 1 to
 20 carbon atoms such as methyl, ethyl, propyl and butyl groups.
 As the vinyl-polymerizable monomers having an acid anhydride group, those
 having the acid anhydride group and the above-described
 radical-polymerizable unsaturated bonding group are preferably used. The
 monomers having the acid anhydride group and the above-described
 radical-polymerizable unsaturated bonding group include, for example,
 those obtained by condensing a monomer capable of forming an acid
 anhydride group in the molecule such as maleic anhydride or itaconic
 anhydride or a monomer having a radical-polymerizable unsaturated bond and
 a carboxyl group in the molecule with a compound having a carboxyl group
 in the molecule by a dehydration reaction or dealcoholization reaction.
 The compounds having a carboxyl group in the molecule are those having or
 not having a radical-polymerizable unsaturated bond in the molecule. Such
 monomers are those obtained by condensing methacrylic anhydride or
 monoester of a divalent polybasic acid such as a monoalkyl maleate or
 monoalkyl itaconate by the dealcoholization reaction.
 The monomers having a blocked hydroxyl group are preferably
 vinyl-polymerizable monomers having the blocked hydroxyl group and the
 above-described radical-polymerizable unsaturated bonding group.
 The vinyl-polymerizable monomers having the blocked hydroxyl group and the
 radical-polymerizable unsaturated bonding group are, for example, those of
 the following formula (3):
 ##STR5##
 wherein R.sup.1 represents a hydrogen atom or a methyl group, R.sup.2
 represents a divalent alkylene group, Y represents --COO--, --CO--,
 --NHCO--, --O-- or single bond, and X represents the above-described
 blocked hydroxyl group.
 The divalent alkylene groups herein include, for example, linear or
 branched alkylene groups having 1 to 18 carbon atoms such as methylene,
 ethylene, propylene, butylene, hexylene, heptylene, octylene, nonylene,
 decylene, undecylene, dodecylene and tridecylene groups.
 Such monomers may be those obtained by blocking a hydroxyl group-containing
 vinyl-polymerizable monomer, which has been obtained by modifying a
 vinyl-polymerizable monomer of the above formula (3) wherein X represents
 a hydroxyl group with a lactone, with the above-described blocking agent.
 Examples of the modified blocked hydroxyl group-containing
 vinyl-polymerizable monomers include those of the following formula:
 ##STR6##
 wherein R.sup.1, R.sub.2 and Y are as defined above, Z represents a
 blocking group derived from the blocking agent, m is, for example, 1 to 6
 and n is, for example, 3 to 7.
 Preferred examples of the blocked hydroxyl group-containing
 vinyl-polymerizable monomers include trimethylsiloxyethyl (meth)acrylate,
 3-trimethylsiloxypropyl (meth)acrylate and 4-trimethylsiloxybutyl (meth)
 acrylate. Examples of the lactone-modified blocked hydroxyl
 group-containing vinyl-polymerizable monomers include those obtained by
 blocking a lactone-modified hydroxyl group-containing vinyl-polymerizable
 monomer selected from among Placcel FM-1, FM-2, FM-3, FM-4, FM-5, FA-1,
 FA-2, FA-3, FA-4 and FA-5 (products of Daicel Chemical Industries, Ltd.).
 "FM" indicates lactone-modified hydroxyl group-containing
 vinyl-polymerizable monomers of methacrylate type and "FA" indicates those
 of acrylate type. The numerals indicate the amount of added
 .epsilon.-caprolactone. For example, FA-1 indicates a hydroxyl
 group-containing vinyl-polymerizable monomer containing one molecule of
 .epsilon.-caprolactone added thereto.
 As the monomers having an epoxy group, those having the epoxy group and the
 above-described radical-polymerizable unsaturated bonding group are
 preferably used.
 The monomers having the epoxy group and the above-described
 radical-polymerizable unsaturated bonding group include, for example,
 epoxy group-containing monomers such as glycidyl (meth)acrylate and
 3,4-epoxycyclohexyl (meth)acrylate.
 In the synthesis of the vinyl oligomers, vinyl-polymerizable monomers other
 than those described above are also usable. Examples of the
 vinyl-polymerizable monomers include the following compounds:
 (1) Acrylic or Methacrylic Esters:
 For example, alkyl (C.sub.1 to C.sub.18) acrylates and methacrylates such
 as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate,
 butyl acrylate, hexyl acrylate, 2-hexyl acrylate, octyl acrylate, lauryl
 acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate,
 isopropyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-hexyl
 methacrylate, octyl methacrylate and lauryl methacrylate; alkoxyalkyl
 (C.sub.2 to C.sub.18) acrylates and methacrylates such as methoxybutyl
 acrylate, methoxybutyl methacrylate, methoxyethyl acrylate, methoxyethyl
 methacrylate, ethoxybutyl acrylate and ethoxybutyl methacrylate; and
 alkenyI (C.sub.2 to C.sub.8) acrylates and methacrylates such as allyl
 acrylate and allyl methacrylate; and alkenyloxyalkyl (C.sub.3 to C.sub.18)
 acrylates and methacrylates such as allyloxyethyl acrylate and
 allyloxyethyl methacrylate.
 (2) Vinyl Compounds:
 For example, styrene, .alpha.-methylstyrene, vinyl acetate,
 hexafluoropropylene, tetrafluoropropylene, vinyltoluene and
 p-chlorostyrene.
 (3) Polyolefin Compounds:
 For example, butadiene, isoprene and chloroprene.
 (4) Allyl Ethers:
 For example, hydroxyethyl allyl ether.
 (5) Others:
 For example, methacrylamide, acrylamide, diacrylamide, dimethacrylamide,
 acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, vinyl
 acetate, vinyl propionate, vinyl pivalate, N,N-dialkylaminoalkyl
 (meth)acrylates, phosphoric acid group-containing (meth)acrylates such as
 phosphonoxyethyl (meth)acrylate, perfluorovinyl ethers such as
 trifluoromethyl vinyl ether, and vinyl ethers such as hydroxyethyl vinyl
 ether and hydroxybutyl vinyl ether.
 The vinyl oligomer contained in the one-pack coating composition of the
 present invention may contain a hydrolyzable silyl group in addition to
 the acid anhydride group and/or blocked hydroxyl group and/or epoxy group.
 The hydrolyzable silyl group is hydrolyzed in the presence of water and
 preferably a dissociation catalyst such as phosphoric acid, a carboxylic
 acid, dibutyltin dilaurate, dimethyltin dichloride or dibutyltin dimaleate
 to form a silanol group, which then reacts with a hydroxyl group formed by
 removal of the blocking group to form an Si--O bond. Further, the two
 silanol groups thus formed react with each other to form an Si--O--Si
 group. When the coating contains the Si--O bond or Si--O--Si bond, its
 strength and flexibility are increased.
 Preferred hydrolyzable silyl groups are, for example, those of the
 following formula:
 ##STR7##
 wherein R.sup.1 and R.sup.2 may be the same or different from each other
 and represent a hydroxyl group, an alkyl group, an alkoxy group, an
 --NR.sup.1 R.sup.2 group (R.sup.1 and R.sup.2 being an alkyl or aryl
 group), an --NR.sup.1 COR.sup.2 group (R.sup.1 and R.sup.2 being an alkyl
 or aryl group), a --COR.sup.1 group (R.sup.1 being an alkyl or aryl
 group), a --OCOR.sup.1 group (R.sup.1 being an alkyl or aryl group), an
 aryl group, an --ONR.sup.1 R.sup.2 group (R.sup.1 and R.sup.2 being an
 alkyl or aryl group), or an --ONCR.sup.1 R.sup.2 group (R.sup.1 and
 R.sup.2 being an alkyl or aryl group), and R.sup.3 represents an alkyl
 group, an --NR.sup.1 R.sup.2 group (R.sup.1 and R.sup.2 being an alkyl or
 aryl group), a --COR.sup.1 group (R.sup.1 being an alkyl or aryl group),
 an aryl group or an --NR.sup.1 R.sup.2 group (R.sup.1 and R.sup.2 being an
 alkyl or aryl group).
 The alkyl groups in the above formula are linear or branched alkyl groups
 having 1 to 10 carbon atoms, such as methyl, ethyl, propyl, isopropyl,
 butyl, isobutyl, s-butyl, t-butyl and pentyl groups. The alkoxy groups are
 those wherein the alkyl group is the same as the above-described alkyl
 group. The aryl groups particularly include substituted or unsubstituted
 phenyl groups, the substituents including halogen atoms, alkyl groups and
 alkoxy groups. The halogen atoms as the substituent include fluorine,
 chlorine, bromine and iodine atoms. The alkyl groups as the substituents
 include linear or branched alkyl groups having 1 to 10 carbon atoms such
 as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl and
 pentyl groups. The alkoxy groups as the substituent are those wherein the
 alkyl group is the same as the above-described alkyl group. Preferred
 substituents are, for example, halogen atoms such as fluorine atom, and
 lower alkyl groups having 1 to 5 carbon atoms.
 The vinyl-polymerizable monomers having the hydrolyzable silyl group and
 usable as the starting material for the vinyl oligomer containing the
 hydrolyzable silyl group are preferably those having the above-described
 hydrolyzable silyl group and the radical-polymerizable unsaturated bonding
 group.
 The vinyl-polymerizable monomers containing the hydrolyzable silyl group
 are, for example, those of the above formula (3) wherein X represents a
 hydrolyzable silyl group.
 Examples of the vinyl-polymerizable monomers containing the hydrolyzable
 silyl group as represented by the above formula include
 .gamma.-(meth)acryloyloxypropyltrimethoxysilane,
 .gamma.-(meth)acryloyloxypropyltriethoxysilane,
 .gamma.-(meth)acryloyloxypropyltripropoxysilane,
 .gamma.-(meth)acryloyloxypropylmethyldimethoxysilane,
 .gamma.-(meth)acryloyloxypropylmethyldiethoxysilane,
 .gamma.-(meth)acryloyloxypropylmethyldipropoxysilane,
 .gamma.-(meth)acryloyloxybutylphenyldimetoxysilane,
 .gamma.-(meth)acryloyloxyphenyldiethoxysilane,
 .gamma.-(meth)acryloyloxyphenyldipropoxysilane,
 .gamma.-(meth)acryloyloxypropyldimethylmethoxysilane,
 .gamma.-(meth)acryloylpropyldimethylmethoxysilane,
 .gamma.-(meth)acryloylpropylphenylmethylmethoxysilane and
 .gamma.-(meth)acryloyloxypropylphenylmethylethoxysilane.
 The number of the functional groups contained in the resin molecule used in
 the present invention varies depending on the molecular weight of the
 resin, and is preferably 1 to 5, more preferably 2 to 4. When the number
 of the functional groups is below 1, the strength of the coating film is
 poor unfavorably. On the contrary, when it is above 5, the viscosity
 becomes too high, and the coating is shrunk on curing, is easily cracked
 or becomes fragile unfavorably.
 The amount of the acid anhydride group is usually 0.3 to 4.0 mol/kg-resin,
 preferably 0.7 to 3.0 mol/kg-resin. When it is below 0.3 mol/kg-resin, the
 solvent resistance and scuff resistance become poor. On the contrary, when
 it is above 4.0 mol/kg-resin, the crosslinking density becomes too high
 and the coating becomes brittle.
 The amount of the blocked hydroxyl group is usually 0.3 to 3.0
 mol/kg-resin, preferably 0.7 to 2.0 mol/kg-resin. When it is below 0.3
 mol/kg-resin, the crosslinking density cannot be increased and the
 properties of the coating are insufficient. On the contrary, when it is
 above 3.0 mol/kg-resin, the amount of the remaining hydroxyl group is
 increased to make the water resistance or the like insufficient.
 The amount of the epoxy group is usually 0.3 to 4.0 mol/kg-resin,
 preferably 0.7 to 3.0 mol/kg-resin. When it is below 0.3 mol/kg-resin, the
 scuff resistance and solvent resistance are reduced unfavorably. On the
 contrary, when it is above 4.0 mol/kg-resin, the crosslinking density
 becomes too high and the coating becomes brittle unfavorably.
 The amount of the hydrolyzable silyl group, used if necessary, is 0.2 to
 3.0 mol/kg-resin, preferably 0.5 to 2.0 mol/kg-resin. When it is above 3.0
 mol/kg-resin, the crosslinking density becomes too high and the coating
 becomes brittle unfavorably.
 The heat-potential curing catalyst (B) contained in the one-pack coating
 composition of the present invention comprises a complex of an organometal
 compound and an electron-donating compound or an onium salt.
 The organometallic compounds used for forming the heat-potential curing
 catalyst (B) include, for example, those of the following formula (6):
EQU (R.sup.1).sub.n -M (6)
 wherein R.sup.1 represents a group selected from alkyl, aryl, alkoxy and
 acyloxy groups having 1 to 20 carbon atoms and a carbonyl group adjacent
 to an active methylene group. Examples of the alkyl groups include methyl,
 ethyl, propyl, n-butyl, s-butyl, t-butyl, n-heptyl and s-heptyl groups.
 Examples of the aryl groups include phenyl, naphthyl and anthracene
 groups. The alkoxy groups include those having the above-described alkyl
 groups. Examples of the acyloxy groups include acetyloxy, propanoyloxy and
 butanoyloxy groups. The carbonyl groups adjacent to the active methylene
 groups include, for example, methylcarbonylmethyl and phenylcarbonylmethyl
 groups.
 M represents Mg, Al, Ca, Sn or Pb, or a transition metal atom of the Groups
 3A through 7A, 8, 1B and 2B among the fourth to sixth periods transition
 metal elements, and n represents an integer of 1 to 6.
 M is particularly preferably Ca, Sn, Pb, Zn or Co among them.
 Examples of the organometallic compounds include aluminum acetylacetonate,
 iron acetylacetonate, zinc acetylacetonate, zirconium acetylacetonate,
 dibutyltin acetyl acetonate, dibutyltin dilaurate, dioctyltin ester
 maleate, magnesium naphthenate, calcium naphthenate, manganese
 naphthenate, iron naphthenate, cobalt naphthenate, copper naphthenate,
 zinc naphthenate, zirconium naphthenate, lead naphthenate, calcium
 octylate, manganese octylate, iron octylate, cobalt octylate, zinc
 octylate, zirconium octylate, tin octylate, lead octylate, zinc laurate,
 magnesium stearate, aluminum stearate, calcium stearate, cobalt stearate,
 zinc stearate and lead stearate. Preferred organometallic compounds are,
 for example, zinc acetylacetonate, dibutyltin acetylacetonate, dibutyltin
 dilaurate, dioctyltin ester maleate, calcium naphthenate, cobalt
 naphthenate, zinc naphthenate, lead naphthenate, calcium octylate, cobalt
 octylate, zinc octylate, tin octylate, zinc laurate, calcium stearate,
 cobalt stearate, zinc stearate and lead stearate.
 The electron-donating compounds include, for example, amide compounds,
 sulfoxide compounds, ether compounds, thioether compounds, phosphoric
 ester compounds, boric ester compounds, carboxylic ester compounds,
 carbonic ester compounds, tertiary amine compounds and alkylphosphine
 compounds. Examples of the electron-donating compounds include amide
 compounds such as N, N-dimethylacetamide, N-methylpyrrolidone and
 hexamethylphosphoric triamide; sulfoxide compounds such as dimethyl
 sulfoxide; ether compounds such as diethyl ether and tetrahydrofuran;
 phosphoric ester compounds such as trimethylphoshoric acid,
 triethylphosphoric acid and tributylphosphoric acid; boric acid compounds
 such as trimethylboric acid; carboxylic ester compounds such as ethyl
 acetate and butyl acetate; carbonic ester compounds such as ethylene
 carbonate; tertiary amines such as triethylamine, pyridine,
 N-methylmorpholine, N-methylpyrrolidone, N-methylpiperidine and
 N-methylimidazole; and trialkylphosphines such as triethylphosphine and
 tributylphosphine. These electron-donating compounds are usable either
 singly or in the form of a mixture of two or more of them.
 The heat-potential curing catalyst comprises the above-described
 organometallic compound and electron-donating compound. The molar ratio of
 the active hydrogen-free electron-donating compound to the unoccupied
 orbital of the organometallic compound is preferably in the range of 0.1
 to 4, particularly 0.5 to 2.0. When the molar ratio is below 0.1, the
 catalytic activity of the organometallic compound might not be
 sufficiently controlled during the storage and, on the contrary, when it
 is above 4, the catalytic activity might be difficultly exhibited when it
 is heated. The organometallic compound may be previously mixed with the
 active hydrogen-free electron-donating compound in a suitable solvent to
 form a complex or, alternatively, they are independently mixed in the
 coating composition to form the complex in the composition.
 The heat-potential curing catalyst is used in a catalytic amount which is
 usually 0.001 to 10% by weight, preferably 0.005 to 5% by weight, based on
 the whole resin (oligomer or polymer). When the amount of this catalyst is
 insufficient, the curing properties of the coating become poor and, on the
 contrary, when it is excessive, water resistance of the coating is reduced
 and yellowed by heat to deteriorate the properties of the coating
 unfavorably.
 The heat-potential curing catalyst, which comprises an onium salt, is
 preferably one of ammonium salts, phosphonium salts and sulfonium salts of
 the following formulae:
EQU (R).sub.4 N.sup.+ X.sup.- (7)
EQU (R).sub.4 P.sup.+ X.sup.- (8)
EQU (R).sub.3 S.sup.+ X.sup.- (9)
 wherein R's may be the same or different from each other and represent an
 alkyl or aryl group having 1 to 20 carbon atoms, and X is, for example,
 PF.sub.6.sup.-, SbF.sub.6.sup.-, BF.sub.4, SbCl.sub.6.sup.-,
 HSO.sub.4.sup.-, p-CH.sub.3 C.sub.6 H.sub.4 SO.sub.3, CH.sub.3 COO.sup.-
 or a halogen.
 The alkyl groups are substituted or unsubstituted alkyl groups such as
 methyl, ethyl, propyl, butyl, s-butyl, t-butyl, pentyl, hexyl, heptyl,
 octyl, nonyl, decyl, undecyl, dodecyl, tridecyl and tetradecyl groups. The
 aryl groups include substituted or unsubstituted phenyl, naphthyl and
 anthracene groups. Among them, a phenyl group is particularly preferred.
 Preferred substituents are, for example, halogen atoms such as fluorine
 atom and lower alkyl groups having 1 to 5 carbon atoms.
 Examples of the ammonium, phosphonium and sulfonium salts include
 tetrabutylammonium tetrafluoroborate, tetrabutylammonium
 hexafluorophosphate, tetrabutylammonium hydrogen sulfate,
 tetraethylammonium tetrafluoroborate, tetraethylammonium
 p-toluenesulfonate, and Opton CP 66 (a product of Asahi Denka Kogyo K. K.)
 and Sun-aid SIL 100 (both of them are sulfonium salts having
 SbF.sub.6.sup.- as the counter anion).
 The heat-potential curing catalyst comprising the above-described onium
 salt is used in an amount of usually 0.001 to 10% by weight, preferably
 0.005 to 5% by weight, based on the whole resin (oligomer or polymer).
 When the amount of the salt is excessive, the water resistance and acid
 resistance are reduced and the appearance of the coating is deteriorated
 unfavorably.
 The heat-potential curing catalyst exhibits its catalytic activity for the
 curing reaction upon heating at a temperature in the range of 60 to
 200.degree. C. for about 2 minutes to 1 hour.
 The ultraviolet absorber (C) used for forming the coating composition of
 the present invention comprises a triazine or oxalic acid anilide. By
 using such a specific ultraviolet absorber, the storability of the coating
 composition can be secured. When an ultraviolet absorber other than that
 described above, such as a benzotriazole ultraviolet absorber (e. g.
 Tinuvin 900 or 384), is used, the composition is colored blue during the
 storage and forms a bluish coating to cause a problem of quality. On the
 other hand, the triazine ultraviolet absorber is free from the coloring
 problem and is capable of improving the storability of the coating
 composition.
 The triazine ultraviolet absorber is not particularly limited so far as it
 has a triazine ring in the molecular structure. Preferred triazine
 ultraviolet absorbers are, for example, those having a structure of the
 following formula (10):
 ##STR8##
 wherein R.sup.1 represents an alkyl or alkoxyalkyl group, R.sup.2 and
 R.sup.3 each represent a lower alkyl group having 1 to 5 carbon atoms, and
 1, m and n each represent an integer of 0 to 2.
 Preferred examples of the triazine ultraviolet absorbers of the above
 formula (10) include those of the following formula (11):
 ##STR9##
 wherein R.sup.1 represents an alkyl group having 1 to 10 carbon atoms or an
 alkyl group substituted with an alkoxy group of the formula:
 (CH.sub.2).sub.n CH.sub.3 (n being an integer of 1 to 10). The alkyl
 groups include, for example, methyl, ethyl, propyl, butyl, s-butyl,
 t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and
 tridecyl groups. The compounds of the above formula (10) are, for example,
 those wherein R.sup.1 represents i-C.sub.8 H.sub.17 or CH.sub.3 CH.sub.2
 CH.sub.2 OCH.sub.2 CH.sub.2 CH.sub.2 group.
 The oxalic anilide ultraviolet absorbers are not particularly limited so
 far as the molecule thereof has an oxalic anilide structure of the
 following formula (12):
 ##STR10##
 wherein R.sup.1 represents a substituted or unsubstituted alkyl group
 having 1 to 15 carbon atoms such as methyl, ethyl, propyl, butyl, s-butyl,
 t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,
 tridecyl or tetradecyl group.
 Examples of the oxalic anilide ultraviolet absorbers having the structure
 shown above are those given below:
 ##STR11##
 wherein R is preferably an ethyl or dodecyl group.
 The ultraviolet absorber is used in an amount of usually 0.01 to 10%,
 preferably 0.1 to 5%, based on the solid content of the resin composition.
 When the amount of the ultraviolet absorber is below 0.01%, the excellent
 weather resistance of the product cannot be obtained and it is easily
 cracked. On the contrary, the use thereof in an amount of above 5% is
 economically disadvantageous as compared with the effect thereof obtained
 by increasing the amount.
 The photostabilizers (D) used in the present invention are not particularly
 limited so far as they have a piperidine ring of the formula given below,
 and thus various hindered amine photostabilizers are usable. However, a
 hindered amine photostabilizer of the below formula wherein R has less
 than 2 carbon atoms (such as Sanol LS 292) is unusable, since it increases
 the viscosity of the composition.
 Preferred examples of the hindered amine photostabilizers are as follows:
 ##STR12##
 ##STR13##
 The hindered amine photostabilizer is used in an amount of usually 0.01 to
 5%, preferably 0.1 to 3%, based on the solid content of the resin
 composition. When it is below 0.01%, the excellent weather resistance of
 the product cannot be obtained and it is easily cracked. On the contrary,
 the use thereof in an amount of above 5% is economically disadvantageous
 as compared with the effect thereof obtained by increasing the amount.
 The autioxidants (D) used in the present invention are phenolic
 antioxidants.
 The phenolic antioxidants have a phenol group or phenoxy group in the
 molecule. Examples of preferred phenolic antioxidants are as follows:
 ##STR14##
 ##STR15##
 ##STR16##
 The phenolic antioxidant is used in an amount of usually 0.01 to 5%,
 preferably 0.1 to 3%, based on the solid content of the resin composition.
 When it is below 0.01%, the antioxidizing effect cannot be sufficiently
 improved. On the contrary, the use thereof in an amount of above 5% is
 economically disadvantageous as compared with the effect thereof obtained
 by increasing the amount.
 The one-pack coating composition of the present invention is prepared by
 mixing the components. If necessary, the one-pack coating composition of
 the present invention can suitably contain various additives usually used
 in the technical field of painting such as a pigment (for example, a
 coloring pigment or glitter), anti-sagging agent or anti-settling agent,
 levelling agent, defoaming agent, antistatic agent and thinner.
 Preferred pigments or glitters are, for example, titanium oxide, carbon
 black, precipitated barium sulfate, calcium carbonate, talc, kaolin,
 silica, mica, aluminum, red iron oxide, lead chromate, lead molybdate,
 chromiumoxide, cobalt aluminate, azo pigment, phthalocyanine pigment and
 anthraquinone pigment.
 Preferred anti-sagging agents or anti-settling agents are, for example,
 silica, castor oil wax, amide wax, microgel and aluminum acetate.
 Preferred levelling agents are, for example, silicon-containing products
 such as KF 69, KP 321 and KP 301 (products of Shin-Etsu Chemical Co.,
 Ltd.), Modaflow (a product of Mitsubishi Monsanto Chemical Co.), BYK 358
 (a product of BYK Chemie Japan KK) and Diaaid AD 9001 (a product of
 Mitsubishi Rayon Co., Ltd.).
 Preferred thinners are, for example, aromatic compounds such as toluene,
 xylene and ethylbenzene; alcohols such as methanol, ethanol, propanol,
 butanol and isobutanol; ketones such as acetone, methyl isobutyl ketone,
 methyl amyl ketone, cyclohexanone, isophorone and N-methylpyrrolidone;
 ester compounds such as ethyl acetate, butyl acetate and methyl
 cellosolve; and mixtures of them.
 Preferred antistatic agents include, for example, Esocard C 25 (a product
 of Lion Armor).
 The one-pack coating composition of the present invention is particularly
 suitable for use as a clear coating paint for automobiles.
 The one-pack coating composition of the present invention is particularly
 suitable for use as a clear paint for two coating/one baking technique,
 three coating/two baking technique or overcoating. The one-pack coating
 composition of the present invention is usable also as a clear paint to be
 applied by a wet-on-wet coating technique after the application of a
 well-known paint for forming a base coating. The paint for forming the
 base coating is preferably a paint composition containing, for example, a
 hydroxyl group-containing oligomer or polymer (resin) and a melamine
 resin. The base coating paint composition may be of either an organic
 solvent-type or aqueous type.
 In a preferred embodiment of the formation of a coating with the one-pack
 paint composition of the present invention, a predetermined quantity of
 the composition is applied to a substrate, and it is then set (dried) and
 baked.
 The setting (drying) is conducted usually at room temperature or ambient
 temperature for 1 to 30 minutes, preferably 3 to 15 minutes. The baking is
 conducted at 60 to 200.degree. C., preferably 80 to 170.degree. C., for 1
 to 60 minutes, preferably 10 to 40 minutes.
 A coating can be formed while the quantity of the solvent is kept small by
 hot-spraying the one-pack coating composition of the present invention.
 The hot spraying can be conducted by, for example, keeping the temperature
 in a predetermined range which is usually 30 to 80.degree. C., preferably
 35 to 70.degree. C., during the period from the strage of the one-pack
 coating composition in a tank to immediately before the spraying.
 The one-pack coating composition of the present invention is not thickened
 during the storage and, after the application, the curing reaction is
 caused by heating to form the desired coating.