Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1996-03-14
2001-03-27
Dawson, Robert (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C523S435000, C523S461000, C525S100000, C525S107000, C525S408000, C525S438000
Reexamination Certificate
active
06207235
ABSTRACT:
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:
wherein R represents R
1
—CO—, a C
2
to C
20
alkyl group or R
1
—O— (R
1
being a C
2
to C
20
alkyl group), and R
2
, R
3
, R
4
and R
5
independently from each other represent a C
1
to C
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° 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):
wherein R
1
to R
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
1
to R
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):
wherein R
1
, R
2
and R
3
independently from each other represent a hydrogen group or a hydrocarbon group having 1 to 18 carbon atoms, R
4
represents a hydrocarbon group having 1 to 18 carbon atoms, Y represents an oxygen or sulfur atom, and R
3
and R
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 inve
Koga Kazuhi
Kubota Hiroshi
Marutani Yoshiaki
Ohsawa Mika
Uemura Hiroyuki
Aylward D.
Dawson Robert
Fleit Martin
Mazda Motor Corporation
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