Note: Descriptions are shown in the official language in which they were submitted.
21 6~335
DESCRIPTION
PROCESS FOR FORMING OVERCOAT
TECHNICAL FIELD
The present invention relates to a novel
overcoating process wherein a base coat and a clear coat
are formed by the two-coat one-bake method.
BACKGROUND ART
Motor vehicle outer panels and the like are
overcoated often by the so-called two-coat one-bake
method wherein a base coat composition and a clear coat
composition are applied to the substrate wet-on-wet and
then cured at the same time by heating.
As clear coat compositions for use in the two-
coat one-bake method, thermosetting coating compositions
are generally used which consist primarily of an acrylic
resin or like hydroxyl-containing resin and a melamine
resin.
However, air pollution due to sulfur oxides,
nitrogen oxides, etc. has become aggravated on a global
scale in recent years to produce an acid rain, which has
developed a new drawback in the overcoat formed on motor
vehicle outer panels by the two-coat one-bake method
using the clear coat composition, i.e., susceptibility to
etching, whitening or staining. It is urgently required
to obviate this drawback. The overcoat has another
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drawback in that the surface thereof is subject to
scratches, for example, when the motor vehicle is washed.
On the other hand, a two-coat one-bake coating
process is also proposed with use of a clear coat
S composition which comprises an epoxy- and hydroxyl-
containing resin and a cyclic anhydride serving as a
crosslinking agent (U.S. Patents No. 4,732,790 and No.
4,732,791). This coating process gives coatings that
have inferior scratch resistance and do not always have
satisfactory acid resistance.
The present invention provides a novel two-coat
one-bake coating process for forming overcoats that are
free of the foregoing deficiencies of the prior art and
form overcoats that have excellent acid and scratch
resistance.
SUMMARY OF THE INVENTION
The present invention provides a process for
forming an overcoat by the two-coat one-bake method
wherein a base coat composition and a clear coat
composition are applied to a substrat~ wet-on-wet and
thereafter cured at the same time by heating, the process
being characterized in that the base coat composition is
a coating composition consisting primarily of a hydroxyl-
containing resin, an amino resin, a pigment and an
organic solvent, the clear coat composition being a
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coating composition comprising:
(A) at least one resin selected from the group
consisting of (i) a resin having at least one epoxy group
and at least one hydroxyl group in the molecule, (ii) a
resin mixture of (ii-l) a resin having at least two epoxy
groups in the molecule and (ii-2) a resin having at least
two hydroxyl groups in the molecule, (iii) a resin having
at least two epoxy groups in the molecule, and (iv) an
any mixture thereof,
(B) a crosslinking agent comprising a compound having
at least two noncyclic acid anhydride groups and
represented by the formula
O O ~ O O\
Il 11 11 11
R- C -O -C - -R'- C -O-C n R (I)
wherein R is a monovalent hydrocarbon group having 2 to 5
carbon atoms, R' is a bivalent hydrocarbon group having 2
to 50 carbon atoms, the hydrocarbon groups R and R'
containing or not containing an ether linkage, urethane
linkage or ester linkage, and n is an integer of 1 to
500, and
(C) a curing catalyst.
DETAILED DESCRIPTION OF THE INVENTION
Intensive research has been conducted to
overcome the deficiencies of the prior art and it has
been found that cured coatings which have excellent acid
2 1 63335
and scratch resistance are obtained by conducting the
two-coat one-bake method using as a clear coat
composition a coating composition comprising an epoxy- or
epoxy- and hydroxyl-containing resin, a crosslinking
agent which is a compound having noncyclic acid anhydride
groups and represented by the formula (I), and a curing
catalyst.
The substrates to be overcoated by the process
of the invention include those of various metals and
plastics. Preferably, the substrate has its surface
treated by a usual chemical conversion process before
coating. Examples of such substrates are outer panels of
motor vehicles, outer panels of household electric
devices, outer panels of office machines, building
materials, etc.
Further preferably, the substrate is coated
with a primer coating composition, or with a primer
coating composition and an intermediate coating
composition before overcoating. Examples of useful
primer coating cGmpositions are organic solvent or water
based compositions and powder compositions which can be
cured by crosslinking or dried at room temperature and
which consist primarily of an epoxy resin, alkyd resin,
vinyl resin or the like. Electrophoretic coating
compositions are suitable as such compositions for
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substrates of metals. Examples of useful intermediate
coating compositions are organic solvent or water based
compositions which can be cured by crosslinking or dried
at room temperature and which consist primarily of an
alkyd resin, polyester resin or acrylic resin.
The base coat and clear top coat compositions
to be used in the present process will be described
below.
The base coat composition is a liquid coating
composition comprising a hydroxyl-containing resin, amino
resin, pigment and organic solvent.
More specifically, useful hydroxyl-cont~ining
resins are those having hydroxyl attached to the end
and/or side chain of the skeleton of a base resin such as
polyester resin, acrylic resin, polyurethane resin, epoxy
resin or the like. Examples of such resins are hydroxyl-
containing acrylic resins consisting essentially of a
hydroxyl-containing vinyl monomer (such as hydroxyethyl
acrylate, hydroxyethyl methacrylate, hydroxypropyl
acrylate or hydroxypropyl methacrylate) and further
comprising, when required, a vinyl monomer
copolymerizable with the monomer; resins obtained by the
addition of a compound having two hydroxyl groups (such
as ethylene glycol or diethylene glycol) with a
polyurethane resin having a free isocyanate group by
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urethanization; polyether polyols, etc.
Among these hydroxyl-containing resins,
preferred acrylic resins are those having a number
average molecular weight of about 2000 to about 100000,
more preferably about 4000 to about 60000, an acid value
of 0 to 50 mg/KOH, more preferably 10 to 25 mg/KOH, and a
hydroxyl value of 20 to 200 mg/KOH, more preferably 30 to
150 mg/KOH. Preferred polyester resins are those having
a number average molecular weight of about 500 to about
10000, more preferably about 1000 to about 5000, an acid
value of 0 to 50 mg/KOH, more preferably 5 to 25 mg/KOH,
and a hydroxyl value of 20 to 200 mg/KOH, more preferably
30 to 150 mg/KOH. Especially when the acid value is
adjusted to the above range, the base coat composition is
given improved curability.
Also usable as hydroxyl-containing resins in
the base coat composition are the above-mentioned
hydroxyl-containing resins as modified with a vinyl
compound. Examples of useful modified resins are (1)
those prepared by reacting a carboxyl- or isocyanate-
containing vinyl resin with the hydroxyl-containing
resin, (2) those prepared by reacting an epoxy-containing
vinyl resin with the hydroxyl-containing resin (which
preferably has carboxyl also), (3) those prepared by
modifying the hydroxyl-containing resin with a drying oil
- 21 633~5
fatty acid or incorporating carboxyl into the resin, then
reacting the resin with glycidyl (meth)acrylate to
introduce a radically polymerizable unsaturated group
thereinto and thereafter reacting the resulting resin
with a vinyl monomer by radical polymerization, and (4)
those in the form of a nonaqueous dispersion and prepared
by polymerizing a vinyl monomer in the presence of the
hydroxyl-containing resin as a dispersion stabilizer in
an organic solvent which dissolves the monomer and the
stabilizer but will not dissolve the resulting polymer.
The amino resin is used as a crosslinking agent
for the hydroxyl-cont~ining resin, and is, for example, a
methylolated amino resin which is obtained by the
reaction of an aldehyde compound with an amino compound
such as melamine, urea, benzogll~n~mine, acetogu~n~mine,
sterogll~n~mine, spirogll~n~mine or dicyandiamide.
Examples of useful aldehyde compounds are formaldehyde,
p-formaldehyde, acetaldehyde, benzaldehyde and the like.
The methylolated amino resin as etherified with
a suitable monohydric alcohol is also desirable to use.
Examples of monohydric alcohols usable for the
etherification are methyl alcohol, ethyl alcohol,
n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
isobutyl alcohol, 2-ethylbutanol, 2-ethylhexanol, etc.
For the etherification, all or some of the methylol
- 21 63335
groups are etherified.
Especially preferable as the amino resin for
use in the base coat composition of the invention is a
hexaalkoxymethylmelamine wherein one to five, preferably
two to four, of the alkoxymethyl groups attached to the
nitrogen atoms thereof are substituted with a methylol
group and/or hydrogen atom. In other words, suitable as
the amino resin is a mono- or poly-nuclear compound of
triazine rings which has at least one to five methylol
groups and/or imino groups per molecule.
It is suitable that the amino resin to be used
have a weight average molecular weight of about 500 to
about 10000, preferably 1000 to 6000.
The pigment is used chiefly to color the base
coat to be formed. Examples of useful pigments are usual
coloring pigments and metallic pigments for coating
compositions. More specific examples of coloring
pigments are organic pigments including quinacridone red
and like quinacridone pigments, Pigment Red and like azo
pigments, phthalocyanine blue, phthalocyanine green and
like phthalocyanine pigments, etc,; and inorganic
pigments such as titanium oxide, carbon black and red
iron oxide. Metallic pigments give a glossy metallic
appearance to the coating. Suitable examples of such
pigments are flaky particles of aluminum, nickel, copper,
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brass, colored mica, mica, micalike iron oxide, etc. One
or at least two pigments are usable which are selected
from among these coloring pigments and metallic pigments.
The organic solvent is preferably one capable
of dissolving or dispersing the hydroxyl-containing resin
and amino resin. Examples of such solvents are xylene,
toluene and like aromatic hydrocarbons; ethyl acetate,
propyl acetate, butyl acetate and like esters; acetone,
methyl ethyl ketone and like ketones; ethylene glycol,
cellosolve, butyl cellosolve, cellosolve acetate and like
ethers; etc. One or at least two of these solvents are
usable.
The proportions of the foregoing components to
be mixed into the base coat composition of the invention
can be determined as desired according to the
contemplated purpose. For example, the proportions of
the hydroxyl-containing resin and the amino resin are
preferably about 50 to about 90 wt. %, more preferably 60
to 80 wt. %, of the hydroxyl-containing resin and about
10 to about 50 wt. %, more preferably 40 to 2~ wt. %, of
the amino resin, based on the combined amount of the two
components. To be suitable, the coloring pigment is used
in an amount of about 1 to about 50 parts by weight per
100 parts by weight of the combined amount of the two
components. The organic solvent is used in such an
21 63335
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amount that the solids content of the base coat
composition come to about 10 to about 50 wt. %.
The base coat composition used in the invention
may contain a non-aqueous polymer dispersion (hereinafter
S referred to as NAD) in addition to the hydroxyl-
cont~ining resin and the amino resin used as the main
resin components.
Addition of the NAD can give the base coat
composition of high solid content and significantly
improved strike-in resistance and metallic pigment
orientation, capable of forming a cured film free of
mottling. The preferable proportion of the NAD is 5-70%
by weight, particularly 5-30% by weight based on the
total weight (solid content) of the resin components
including the NAD.
The NAD is preparèd by polymerizing an
ethylenically unsaturated monomer or monomers in a non-
aqueons organic solvent such as low-solbility parameter
organic solvent (e.g. aliphatic hydrocarbon) or high-
solbility parameter organic solvent (e.g. ester, keton,
alcohol) in the presence of a dispersion stabilizer resin
such as alkyd resin, acryl resin, graft polymer of poly
12-hydroxystearic acid and acryl resin, cellulose
derivative or the like.
The ethylenically unsaturated monomers to be
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used in preparation of the NAD are not specifically
limited and include various monomers insofar as they are
radically polymerizable unsaturated monomers. Typical
examples of useful monomers are as follows:
(a) C1-C18 alkyl (meth)acrylate such as methyl
(meth)acrylate, ethyl (meth)acrylate, propyl
(meth)acrylate, isopropyl (meth)acrylate, butyl
(meth)acrylate, hexyl (meth)acrylate, octyl
(meth)acrylate, and the like; glycidyl (meth)acrylate;
C2-C8 alkenyl (meth)acrylate such as allyl (meth)acrylate
and the like; C2-C8 hydroxyalkyl (meth)acrylate such as
2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl
(meth)acrylate and like;
(b) vinyl aromatic compounds such as styrene,
a-methylstyrene, vinyltoluene, p-chlorostyrene, vinyl-
pyridine and the like;
(c) a,~-ethylenically unsaturated acids such as acrylic
acid, methacrylic acid, itaconic acid and the like;
(d) multifunctional unsaturated monomers useful for
interparticle crosslinking such as divinyl benzene,
ethylene glycol diacrylate or dimethacrylate;
(e) siloxy-containing unsaturated monomers such as
(meth)acryloxypropyltriethoxysilane;
(f) others including acrylonitrile, methacrylonitrile,
methyl isopropenyl ketone, vinyl acetate;
21 63335
Of these monomers, preferable are a monomer or
a mixture of monomers containing at least about 40~ by
weight of acrylate or methacrylate.
The polymer particles of the NAD may be
obtained in a crosslinked or non-crosslinked form in the
dispersion. The particle size of the polymer particles is
generally in the range of about 0.1 to about 2.0 ~m.
When required, the base coat composition may
have other components incorporated therein, such as
pigment dispersant, fine pigment particles, ultraviolet
absorber, surface conditioning agent, curing catalyst,
cellulose acetate or derivatives thereof and other
additives for coating compositions.
The clear coat composition to be used in the
process of the invention is a coating composition for
forming a transparent coating over the wet surface of the
base coat composition (uncured coating) as applied to a
substrate. The clear coat composition comprises the
resin (A), crosslinking agent (B) and curing catalyst
(C).
These components will be described in detail
below.
The component (A) is at least one resin
selected from the group consisting of (i) a resin having
at least one epoxy group and at least one hydroxyl group
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in the molecule, (ii) a resin mixture of a resin having
at least two epoxy groups in the molecule and a resin
having at least two hydroxyl groups in the molecule,
(iii) a resin having at least two epoxy groups in the
molecule, and (iv) an any mixture thereof.
Preferred examples of resins (i) having at
least one epoxy group and at least one hydroxyl group in
the molecule are those having at least one epoxy group
and at least one hydroxyl group attached to the end
and/or side chain of the skeleton of a base resin such as
a polyester resin, acrylic resin, polyurethane resin or
epoxy resin. These examples include hydroxyl-containing
bisphenol-type epoxy resins; acrylic resins consisting
essentially of a glycidyl-containing vinyl monomer (such
as glycidyl acrylate, glycidyl methacrylate,
3,4-epoxycyclohexylmethyl acrylate or 3,4-epoxycyclo-
hexylmethyl methacrylate) and a hydroxyl-cont~ining vinyl
monomer (such as hydroxyethyl acrylate, hydroxyethyl
methacrylate, hydroxypropyl acrylate or hydroxypropyl
methacrylate), and when required, further comprising a
vinyl monomer copolymerizable with these monomers; resins
obtained by the addition of a compound having hydroxyl
and glycidyl (such as glycidol) and a compound having two
hydroxyl groups (such as ethylene glycol or diethylene
glycol) to a polyurethane resin having free isocyanate by
21 63335
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urethanization; etc.
It is required that the resin (i) have at least
one epoxy group and at least one hydroxyl group in the
molecule, the number of these groups being preferably 2
to 50. An amino, amide or like functional group may be
present conjointly with these groups. The resin (i) is
preferably about 300 to about 100000, more preferably
about 4000 to about 50000, in number average molecular
weight (as determined by GPC).
The resin mixture (ii) is composed of a resin
(ii-l) having at least two epoxy groups in the molecule
and a resin (ii-2) having at least two hydroxyl groups in
the molecule. These component resins are as follows.
Stated more specifically, the resin (ii-l)
having at least two epoxy groups in the molecule is a
resin having at least two epoxy groups attached to the
end and/or side chain of the skeleton of a base resin
such as epoxy resin, polyester resin, acrylic resin or
polyurethane resin. The resin is free from hydroxyl.
Examples of such resins are bisphenol-type or novolak-
type epoxy resins; acrylic resins consisting essentially
of a glycidyl-containing vinyl monomer (such as glycidyl
acrylate, glycidyl methacrylate,
3,4-epoxycyclohexylmethyl acrylate or 3,4-epoxycyclo-
hexylmethyl methacrylate), and when required, further
2 1 63335
comprising a vinyl monomer copolymerizable with themonomer; resins prepared by the addition of a compound
having hydroxyl and glycidyl, such as glycidol, to a
polyurethane resin having free isocyanate by
urethanization; and phenoxy resins.
Although it is required that the resin (ii-1)
have at least two, preferably 2 to 50, epoxy groups in
the molecule, the resin may contain a functional group,
such as amino or amide, conjointly with the epoxy groups.
The component (ii-1) is preferably about 300 to about
100000, more preferably about 3000 to about 50000, in
number average molecular weight (as determined by GPC).
Specifically stated, the resin (ii-2) having at
least two hydroxyl groups in the molecule is a resin
which has at least two hydroxyl groups attached to the
end and/or side chain of the skeleton of a base resin
such as polyester resin, acrylic resin, polyurethane
resin or epoxy resin, and which is free from epoxy.
Examples of useful resins (ii-2) are hydroxyl-containing
acrylic resins consisting essentially of a hydroxyl-
containing vinyl monomer (such as hydroxyethyl acrylate,
hydroxyethyl methacrylate, hydroxypropyl acrylate or
hydroxypropyl methacrylate), and when required, further
comprising a vinyl monomer copolymerizable with the
monomer; resins prepared by the addition of a compound
2 1 63335
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having two hydroxyl groups (such as ethylene glycol or
diethylene glycol) to a polyurethane resin having free
isocyanate by urethanization; polyether polyols; etc.
Although it is required that the resin (ii-2)
have at least two, preferably 2 to 50, hydroxyl groups in
the molecule, the resin may further have a functional
group, such as amino or amide, conjointly with the
hydroxyl groups. The component (ii-2) is preferably
about 300 to about 100000, more preferably about 5000 to
about 50000, in number average molecular weight (as
determined by GPC).
The proportions of the resin (ii-1) and the
resin (ii-2) are not limited specifically but can be
determined as desired according to the purpose.
Preferably about 10 to about 90 wt. %, more preferably 30
to 70 wt. %, of the resin (ii-1) is usually mixed with
about 90 to about 10 wt. %, more preferably 70 to 30 wt.
%, of the resin (ii-2) based on the combined weight of
the two components.
The resin (iii) having at least two epoxy
groups in the molecule is the same as the resin (ii-1).
The crosslinking agent (B) to be admixed with
the component (A) for use in the clear coat composition
of the invention is a compound having at least two
noncyclic acid anhydride group and represented by the
21 63335
following formula.
O O O O~
Il 11 11 11
R- C -O-C - -R'- C -O -C n R (I)
wherein R, R' and n are as defined above.
This compound can be prepared easily, for
example, by reacting a monocarboxylic acid having one
carboxyl group in the molecule with a dicarboxylic acid
having two carboxyl groups in the molecule for
dehydration.
Examples of useful monocarboxylic acids are
benzoic acid, methylbenzoic acid, p-tert-butylbenzoic
acid and like aromatic monocarboxylic acids; formic acid,
acetic acid, propionic acid, butyric acid, caproic acid,
caprylic acid, pelargonic acid, isononanoic acid, capric
acid, undecanoic acid, lauric acid, myristic acid,
palmitic acid, stearic acid, cyclohexanecarboxylic acid,
9-decenoic acid, oleic acid, eleostearic acid, elaidic
acid, brassidic acid, linoleic acid, linolenic acid and
like saturated or unsaturated aliphatic monocarboxylic
acids or alicyclic monocarboxylic acids; etc. Also
usable as monocarboxylic acids are coconut oil fatty
acid, soybean oil fatty acid, dehydrated castor oil fatty
acid, linseed oil fatty acid, safflower oil fatty acid
and the like. These examples are usable singly, or at
2 1 63335
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least two of them can be used in combination.
Examples of useful dicarboxylic acids are
terephthalic acid, isophthalic acid, phthalic acid,
naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic
acid, diphenylmethane-4,4'-dicarboxylic acid and like
aromatic dicarboxylic acids; hexahydroisophthalic acid,
hexahydroterephthalic acid, hexahydrophthalic acid and
like alicyclic dicarboxylic acids; adipic acid, sebacic
acid, suberic acid, succinic acid, glutaric acid, maleic
acid, chloromaleic acid, fumaric acid, dodecanoic diacid,
pimelic acid, azelaic acid, itaconic acid, citraconic
acid, dimer acid and like aliphatic acids; etc. One of
these acids is usable, or at least two of them can be
used in combination.
Among these dicarboxylic acids, those wherein
the carboxylic groups are attached to adjacent carbon
atoms readily undergo a self-cyclization reaction and
encounter difficulty in giving the desired crosslinking
agent, so that it is desirable not to use them singly.
Such dicarboxylic acids are phthalic acid,
hexahydrophthalic acid, tetrahydrophthalic acid, succinic
acid, maleic acid, chloromaleic acid, etc.
The dehydration reaction between the two
components can be conducted at about 80 to about 200C.
To promote this reaction, it is desirable to use a
21 63335
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dehydrating agent such as acetic anhydride, acetic acid
chloride or phosphorus pentoxide. Although not limited
specifically, the amount of the agent to be used is
preferably about 2 to about 200 parts by weight per 100
parts by weight of the combined amount of the two
components calculated as solids. The reaction ratio of
the two components is variable within a range permitting
no free carboxyl group to remain in the product as
represented by the formula (I). Stated specifically, it
is desirable to use about 0.5 to about 250 moles of the
dicarboxylic acid per mole of the monocarboxylic acid.
Further some or all of the carboxylic groups of
the two components may be converted, for example, to an
acid chloride, alkali metal salt or amine salt (primary,
secondary, tertiary or quaternary), followed by a
desalting reaction to form acid anhydride groups.
With reference to the formula (I), R and R' are
each a hydrocarbon group which has 2 to 50 carbon atoms
and which may contain an ether linkage, urethane linkage
or ester linkage. The hydrocarbon group is introduced
into the compound (I) by using the mono-carboxylic acid
and dicarboxylic acid.
An ether linkage is introduced into R', for
example, by converting the hydroxyl groups at the
respective ends of a dihydric alcohol as (poly)etherified
2 1 63335
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to carboxyl groups by oxidation to obtain a dicarboxylic
acid polyether having one carboxyl group at each end, and
substituting the polyether for a portion or the whole of
the dicarboxylic acid or a modified product thereof. On
the other hand, an ether linkage is introduced into R,
for example, by converting only one hydroxyl group of the
(poly)etherified dihydric alcohol to a carboxyl group,
with a monohydric alcohol etherified with the other
hydroxyl group, to obtain a monocarboxylic acid
containing an ether linkage, substituting this acid for a
portion or the whole of the monocarboxylic acid to be -
used and conducting the same reaction as described above.
The presence of the ether linkage results in the
advantage that the coating obtained on curing can be
given high resistance to chemicals.
The dihydric alcohol to be (poly)etherified is
a compound having two hydroxyl groups in the molecule.
Examples of such alcohols are ethylene glycol, propylene
glycol, diethylene glycol, trimethylene glycol,
tetraethylene glycol, triethylene glycol, dipropylene
glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol,
1,2-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol,
1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol,
2,3-dimethyltrimethylene glycol, tetramethylene glycol,
3-methyl-4,3-pentanediol, 3-methyl-4,5-pentanediol,
2 1 63335
2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol,
1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol,
1,4-cyclohexanedimethanol, neopentyl glycol, bisphenol A,
etc. One of these alcohols is usable, or at least two of
them can be used in combination.
The polyetherified product can be obtained by
subjecting the dihydric alcohol and an alkylene oxide,
such as ethylene oxide, propylene oxide or butylene
oxide, to an addition reaction.
The monohydric alcohol to be used for forming
the group R containing an ether linkage is a compound
having one hydroxyl group in the molecule. Examples of
such compounds are methyl alcohol, ethyl alcohol, propyl
alcohol, butyl alcohol, ethyl butanol, benzyl alcohol,
lauryl alcohol, stearyl alcohol, ethylene glycol
monomethyl ether, ethylene glycol monoethyl ether,
diethylene glycol monomethyl ether, diethylene glycol
monoethyl ether, diethylene glycol monobutyl ether and
the like. These compounds are usable singly, or at least
two of them can be used in combination.
To introduce a urethane linkage into the group
R or R' of the formula (I), a polyurethane having an
isocyanate group at each of opposite ends is used which
is obtained by subjecting a diisocyanate compound and a
dihydric alcohol to a urethanization reaction. More
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specifically, a urethane linkage can be introduced into
the group R' by reacting a compound having both hydroxyl
and carboxyl in the molecule with the two isocyanate
groups of the polyurethane for urethanization to
introduce a carboxyl group into each end, and
substituting the resulting compound for a portion or the
whole of the dicarboxylic acid. Further a urethane
linkage can be introduced into the group R by adding a
monohydric alcohol to one of the isocyanate groups of the
polyurethane, adding a compound having both hydroxyl and
carboxyl in the molecule to the other isocyanate group by
a urethanization reaction to obtain a monocarboxylic
acid, and substituting the acid for a portion or the
whole of the monocarboxylic acid stated previously. The
presence of the urethane linkage results in the advantage
that the coating obtained on curing has high hardness,
elasticity and high resistance to water and to chemicals.
The diisocyanate compound mentioned above is a
compound having two isocyanate groups in the molecule.
Exemplary of such compounds are hexamethylene
diisocyanate, trimethylhexamethylene diisocyanate and
like aliphatic compounds, hydrogenated xylylene
diisocyanate, isophorone diisocyanate, cyclohexane
diisocyanate and like alicyclic compounds, tolylene
diisocyanate, diphenylmethane diisocyanate and like
2 1 63335
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aromatic compounds. Examples of compounds having both
hydroxyl and carboxyl are lactic acid, p-hydroxybenzoic
acid, dimethylolpropionic acid, hydroxypivalic acid,
ricinoleic acid, 12-hydroxystearic acid, etc. Examples
of dihydric alcohols and monohydric alcohols usable are
those already mentioned.
An ester linkage can be readily introduced into
the group R or R' of the formula (I), for example, by
subjecting a monocarboxylic acid having one carboxylic
group in the molecule and a low-molecular-weight
polyester having two carboxyl groups in the molecule to a
dehydration reaction. The presence of an ester linkage
entails the advantage of giving a noncrystalline compound
which is highly compatible with other resins, permitting
the resulting composition to form cured coatings of
remarkably improved flexibility and elongation.
Examples of monocarboxylic acids useful for the
reaction are aliphatic monocarboxylic acids, alicyclic
monocarboxylic acids, coconut oil fatty acid, etc.
previously mentioned. Also usable are adducts of a
monohydric alcohol with a cyclic acid anhydride. Among
these, benzoic acid, isononanoic acid, coconut oil fatty
acid and the like are desirable to use.
The low-molecular-weight polyester (up to about
2000, preferably lS0 to 1000, in number average molecular
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weight) having two carboxyl groups in the molecule can be
easily prepared, for example, from a dicarboxylic acid
and a glycol. Preferred polyesters are those invariably
having carboxyl groups and an ester linkage in the
S molecule and free from other functional groups and
linkages.
The dicarboxylic acid to be used in this case
is a compound having two carboxyl groups in the molecule
or an acid anhydride thereof. Examples of such acids
include those previously mentioned, i.e., aromatic
dicarboxylic acids or acid anhydrides thereof; alicyclic
dicarboxylic acids or acid anhydrides thereof; and
aliphatic dicarboxylic acids or acid anhydrides thereof.
Among these, preferable to use is one selected from among
phthalic anhydride, adipic acid, succinic acid, sebacic
acid, etc.
The glycol to be used in this case is a
compound having two hydroxyl groups in the molecule.
Examples of such compounds are the dihydric alcohols
previously mentioned. Among these, preferable to use is
one selected from among neopentyl glycol, 1,6-
hexanediol, 1,4-butanediol, etc.
The esterification reaction between the
dicarboxylic acid and the glycol can be carried out by a
known process. The reaction ratio of the two components
2 1 63335
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is variable within such a range that the resulting
polyester has two carboxyl groups in total at the
respective ends or side chains. More specifically, it is
suitable to use about 1.2 to about 2 moles of
dicarboxylic acid per mole of glycol.
Instead of using the dicarboxylic acid and the
glycol for preparing the low-molecular-weight polyester,
it is also possible to use a lactone, such as
-caprolactone, and the above-mentioned compound having
both hydroxyl and carboxyl.
The component (B) of the formula (I) wherein an
ester linkage is introduced into R or R' is prepared by
subjecting the monocarboxylic acid stated above and the
polyester having two carboxyl groups in the molecule to a
dehydration reaction. This dehydration reaction can be
conducted at about 80 to about 300 C. To promote this
reaction, it is desirable to use a dehydrating agent such
as acetic anhydride, acetic acid chloride or phosphorus
pentoxide. The amount of the agent to be used, although
not limited specifically, is preferably about 2 to about
200 parts by weight per 100 parts by weight of the
combined amount of the two components calculated as
solids. The reaction ratio between the two components is
in such a range that no free carboxyl group remains in
the resulting product as shown in the formula (I). More
2 1 63335
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specifically, it is desired to use about 0.5 to about 250
moles of the polyester having two carboxyl groups per
mole of the monocarboxylic acid. Also in this case, some
or all of the carboxyl groups of the two components may
be converted, for example, to an acid chloride, alkali
metal salt or amine salt (primary, secondary, tertiary or
quaternary), followed by a desalting reaction to prepare
acid anhydride groups.
The component (B), which is a crosslinking
agent, has noncyclic acid anhydride groups and a number
average molecular weight which is preferably about 100 to
about 50000, more preferably in the range of 300 to
lO000, although not limited specifically. The number of
acid anhydride groups in the molecule is at least two,
more preferably about 2 to about 50, to be suitable.
The curing catalyst (C) is incorporated into
the clear coat composition for use in the present
invention so as to effect a promoted reaction between the
functional groups in the component (A) ard the component
(B) (e.g., epoxy groups/hydroxyl groups, acid anhydride
groups/epoxy groups, acid anhydride groups/ hydroxyl
groups/epoxy groups, etc.). Curing catalysts (c) usable
are those already known. Examples of such catalysts
include triethylamine, tripropylamine, tributylamine and
like tertiary amines; amine salts of organic acids;
21 63335
sodium hydroxide and like alkali metal hydroxides; alkali
metal salts of organic acids; calcium hydroxide and like
alkaline earth metal hydroxides; alkaline earth metal
salts of organic acids; tetramethylammonium,
tetraethylammonium, tetrapropylammonium,
tetrabutylammonium, dimethyldiethylammonium and like
quaternary ammoniums and quaternary ammonium salts
thereof with chlorine, bromine or the like;
benzyltriphenylphosphonium chloride,
tetraphenylphosphonium bromide, ethyltriphenylphosphonium
bromide, ethyltriphenylphosphonium iodide,
tetrabutylphosphonium chloride, tetrabutylphosphonium
bromide and like quaternary phosphonium salts; esters of
a sulfonic acid, such as benzenesulfonic acid or
dodecylbenzenesulfonic acid, and an alcohol, such as
propanol or butanol; esters of such a sulfonic acid and
an epoxy-containing compound; phosphoric acid mono- or
di-esters; esters of phosphoric acid and an
epoxy-containing compound, etc.
Although the proportions of the resin (A) and
the crosslinking agent (B) for use in the clear coat
composition of the present invention can be determined as
desired according to the purpose, it is desired to use
about 1 to about 1000 parts by weight, preferably 10 to
200 parts by weight, of the component (B) per 100 parts
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by weight of the component (A).
Further it is suitable to use about 0.01 to
about 10 parts by weight of the curing catalyst (C) per
100 parts by weight of the combined amount of the two
components (A) and (B) calculated as solids.
The clear coat composition for use in the
process of the invention consists essentially of the
resin (A), crosslinking agent (B) and curing catalyst
(C). When needed, organic solvents, ultraviolet
absorbers, photostabilizers, pigments, flowability
adjusting agents, particulate polymers and other
additives for coating compositions can be admixed with
the composition.
Among these, examples of useful ultraviolet
absorbers are ethanediamide N-(2-ethoxyphenyl)-N'-(4-
isododecylphenyl) and like oxalic acid anilide compounds;
2,2'-[hexamethylenebis
(2,2,6,6-tetramethyl-4-piperidinyl)-
imino]bis(4,6-diallylamino-1,3,5-triazine) and like
triazine compounds; ~,4-dihydroxybenzophenone,
2-hydroxy-4-methoxybenzophenone and like benzophenone
compounds; 2-(2'-hydroxy-5'-methylphenyl)benzotriazole
and like benzotriazole compounds; etc. Examples of useful
photostabilizers are bis(1,2,2,6,6-pentamethyl-
4-piperidyl)sebacate and like hindered amine compounds;
2 1 63335
8-(acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-
triazaspiro(4,5)decane-2,4-dione and like hindered amide
compounds, etc. Presence of the ultraviolet absorber and
photostabilizer affords greatly improved weather
resistance.
To be suitable,the ultraviolet absorber and the
photostabilizer are each used in an amount of about 0.1
to about 5 parts by weight, preferably 0.5 to 3 parts by
weight, per 100 parts by weight of the combined amount of
solids of the two components (A) and (B).
The clear coat composition is usable in the
form of a powder coating composition which is completely
or almost free from solvent, whereas it is generally
desirable to dissolve or disperse the components in an
organic solvent to prepare a liquid composition for
application.
The organic solvent to be used can be selected
as desired according to the purpose. Examples of useful
solvents are toluene, xylene, hexane, heptane and like
hydrocarbons; methyl ethyl ketone, methyl isobutyl ketone
and like ketones; ethyl acetate, propyl acetate, butyl
acetate and like esters; propanol, butanol and like
alcohols; methyl cellosolve, buty cellosove, methyl
carbinol, butyl carbinol, diethylene glycol dimethyl
ether and like ethers; etc. These solvents are usable
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singly, or at least two of them can be used.
The amount of organic solvent to be used in the
clear coat composition is so adjusted that the
composition to be applied has a solids content of about
30 to 70 wt. %, preferably 40 to 65 wt. %.
The two-coat one-bake overcoating process of
the present invention is practiced by applying the base
coat composition and the clear coat composition to a
substrate and curing the applied compositions in the
following manner.
The method of applying the base coat
composition is not limited specifically but various known
methods are usable. Preferably the composition is
applied by electrostatic coating, air spray coating,
electrostatic air spray coating, electrostatic rotational
atomization coating or like method. To be suitable, the
thickness of the coating as cured is about 10 to about 50
~m, preferably about lO to about 25 ~m. The base coat
composition applied is dried at room temperature or at a
temperature of up to about 100 C when so required, and
further coated with the clear coat composition. The
clear coat composition can be applied by the same method
as the base coat composition. It is suitable that the
thickness of the coating as cured is about 20 to about
120 ~m, preferably about 30 to about 70 ~m. The two
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compositions applied are thereafter heated usually at
about 120 to about 180 C for about 20 to about 60
minutes, whereby the two coatings are cured at the same
time by crosslinking.
The two-coat one-bake overcoating process of
the present invention employs as a clear coat composition
a coating composition comprising an epoxy- or epoxy- and
hydroxyl-containing resin, a crosslinking agent having
noncyclic acid anhydride groups and a curing catalyst.
The use of this composition gives cured coatings which
are excellent in acid resistance, scratch resistance,
weather resistance, chipping resistance,
distinctness-of-image gloss, etc.
BEST MODE OF CARRYING OUT THE INVENTION
The present invention will be described in
greater detail with reference to the following
preparation examples, examples and comparative examples,
in which the parts and percentages are by weight as a
rule.
Preparation of Base Coat Compositions
Preparation Example 1
In 100 parts (solids) of a composition
comprising 75 parts (solids) of a hydroxyl-containing
acrylic resin and 25 parts (solids) of a melamine resin
were dispersed by mixing 7.7 parts of "4919" (brand name,
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metallic pigment paste having a solids content of 65% and
manufactured by Toyo Aluminium K.K.), 2 parts of "Aerosil
#200" (brand name, silica powder manufactured by Nippon
Aerosil Co., Ltd.) and 1 part of "BENTONE #27- (brand
name, organic bentonite manufactured by NL Chemical Co.).
The dispersion was ad~usted to a coating viscosity of 15
seconds (Ford Cup #4/25C) with a solvent mixture
(toluene/xylene/butyl cellosolve = 1/1/1 in weight ratio)
to obtain a silver metallic base coat composition 1. The
weight solids at spray is 23%.
The hydroxyl-containing acrylic resin used
was a copolymer comprising methyl methacrylate, ethyl
methacrylate, butyl methacrylate, hydroxyethyl
methacrylate and acrylic acid and having a number
average molecular weight of about 30000, a hydroxyl
value of 100 and an acid value of 15. The melamine
resin was a compound having 2.5 butoxymethyl groups,
0.2 imino group, 1.4 methylol groups and 1.9 methylene
linkage per triazine ring on the average, and having
a weight average molecular weight of about 3500.
Preparation Example 2
In 100 parts (solids) of a composition
comprising 80 parts (solids) of a hydroxyl-containing
polyester resin and 20 parts (solids) of a melamine
resin were dispersed by mixing 5.4 parts of 4919" (brand
2 1 63335
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name, metallic pigment paste having a solids content of
65% and manufactured by Toyo Aluminium K.K.), 2 parts of
"Aerosil #200" (brand name, silica powder manufactured by
Nippon Aerosil Co., Ltd.) and 1 part of "BENTONE #27"
(brand name, organic bentonite manufactured by NL
Chemical Co.). The dispersion was adjusted to a coating
viscosity of 15 seconds (Ford Cup #4/25C) with a solvent
mixture (toluene/xylene = 1/1 in weight ratio) to obtain
a silver metallic base coat composition 2. The weight
solids at spray is 33~.
The hydroxyl-cont~ining polyester resin used
was a resin prepared by reacting phthalic anhydride,
hexahydrophthalic anhydride, adipic acid, trimethylol-
propane and neopentyl glycol and having a number average
molecular weight of about 3000, a hydroxyl value of 60
and an acid value of 15. The melamine resin was a
compound having 2.7 butoxymethyl groups, 0.6 imino group,
1.5 methylol groups and 1.7 methylene linkages per
triazine ring on the average, and having a weight average
molecular weight of about 1800.
Preparation Example 3
A Silver colored basecoat compositon 3 was
prepared by mixing the following components.
Solution (Part) Solids (Part)
Polyester Resin (PE-1) 227.2 181.7
Melamine Resin (MF-l) 131.8 112.0
NAD Resin (N-l) 222.~ 100.1
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Tinuvin 328 (1) Solution
in Xylene 16.0 4.0
Aluminum Paste (2)61.0 37.8
Black Dispersion (3)9.3 3.2
Indofast Violet Dispersion (4) 4.5 1.6
Titanium Dioxide Dispersion (5) 1.2 1.0
Methanol 26.8
Xylene 83.4
Solvesso 150 Solvent (6) 27.8
PE-l is a 80% solid solution in 1/1 xylene and
methylethyl ketone of a polyester prepared from
neopentyl glycol, trimethylol propane, 1,6-
hexane diol, phthalic acid, adipic acid and
dodecanedioic acid. It has an acid value of
10-15, a hydroxyl value of 150 and a viscosity
of X (Gardner Holdt).
MF-l is a melamine-formaldehyde-butanol condensation
product with four combined formaldehyde and 2.2
combined butanol per melamine and a degree of
polymerization of 1.9. It is 85% solids in
butanol.
N-1 is a 45% solids nonaqueous dispersion resin
solution which has a core (23%) of crosslinked
methyl methacrylate stabilized with a solution
acrylic resin (22%).
(l) A product of Ciba-Geigy Corporation.
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(2) A 62% solids dispersion of Silberline SS5245 aluminum
flake (Trade name of Silverline Co., Ltd.).
(3) 26% Dispersing resin, 8% carbon black.
(4) 6% Dioxazine Violet pigment, 30% dispersing resin.
(5) 67% Titanium Dioxide, 10% dispersing resin.
(6) Trade name of ESSO Oil Co., Ltd.
This basecoat is reduced with Solvesso 100
solvent (Trade name of ESSO Oil Co., Ltd.) to 20 seconds
#4 Ford Cup Viscosity. The weight solids at spray is
40%-
Preparation of Clear Coat comPositions
Preparation of Resins (A)
Preparation Example 4
(A~ Epoxy- and hydroxyl-containing resin
An acrylic resin solution containing 50 wt.%
of solids (solvent: xylol) was prepared from 1
mole of glycidyl methacrylate, 1 mole of
2-hydroxyethyl acrylate and 5.2 moles of n-butyl
methacrylate. The acrylic resin was about 5000 in
number average molecular weight and contained
about 5 epoxy groups per molecule and about 5
hydroxyl groups per molecule.
Preparation Example 5
(A-2): Epoxy- and hydroxyl-containing resin
An acrylic resin solution containing 50 wt.%
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of solids (solvent: xylol) was prepared from 3 moles of
glycidyl methacrylate, 1 mole of hydroxypropyl
methacrylate, 2 moles of styrene and 1 mole of n-butyl
acrylate. The acrylic resin was about 5000 in number
average molecular weight and contained about 15 epoxy
groups in the molecule and about 5 hydroxyl groups in the
molecule.
Preparation Example 6
(A-3): Epoxy-containing resin
An acrylic resin solution containing 50 wt.% of
solids (solvent: xylol) was prepared from 2 moles of
3,4-epoxycyclohexylmethyl methacrylate and 4.2 moles
of n-butyl methacrylate. The acrylic resin was about
6000 in number average molecular weight and contained
about 12 epoxy groups in the molecule.
Preparation Example 7
(A-4): Epoxy-containing resin
An acrylic resin solution containing 50 wt. %
of solids was prepared by reacting monomers, i.e., 2
moles of glycidyl methacrylate and 5 moles of n-butyl
methacrylate, in xylol. The acrylic resin was about
20000 in number average molecular weight and contained
about 40 epoxy groups in the molecule.
Preparation Example 8
25 (A-5 ): Epoxy-containing resin
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A solution acrylic resin was prepared by adding
the following components
Styrene 28 parts
Butyl Methacrylate 32 parts
Glycidyl Methacrylate40 parts
75% t-butyl Peracetate3.6 parts
over a 5 hour period to 44 parts of refluxing
xylene in a stirred reactor. 0.4 Parts additional
peracetate was added over the next 30 minutes. The
resultant resin solution had a Gardner-Holdt viscosity of
Z2+, a solids content of 70.4% and a number average
molecular weight of 6100 by GPC.
Preparation Example 9
tA-6): Epoxy-containing resin
According to the procedure described for (A-5),
the following ingredients
Styrene 25 parts
Butyl Methacrylate 20 parts
Cyclohexyl Methacrylate15 parts
Glycidyl Methacrylate40 parts
75% t-butyl Peracetate5.5 parts
were processed to yield a resin with 69.9%
solids, Z viscosity and number average molecular weight
of 3800.
Preparation Example 10
(A-7): Hydroxyl-containing resin
An acrylic resin solution containing 50 wt. %
of solids (solvent: xylol ) was prepared from 2 moles
of 2-hydroxyethyl acrylate and 5.4 moles of n-butyl
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methacrylate. The acrylic resin was about 6000 in number
average molecular weight and contained about 12 hydroxyl
groups in the molecule.
Preparation of Crosslinkinq Aqents (B)
Preparation Example 11
(B~ Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 6 carbon atoms and R'
is a bivalent hydrocarbon group with 4 carbon atoms, with
about 6 noncyclic acid anhydride groups present in the
molecule
A crosslinking agent (B-1) was prepared by
mixing together 5 moles of adipic acid, 2 moles of
benzoic acid and 10 moles of acetic anhydride, reacting
the monomers at 140C while removing acetic acid as a
by-product, heating the mixture to 160C when acetic acid
ceased flowing out and removing an excess of acetic
anhydride to terminate the reaction. The agent was P in
Gardner viscosity (20C) and about 800 in number average
molecular weight as determined by GPC (gel permeation
chromatography).
Preparation Example 12
(B-2): Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 6 carbon atoms and R'
is a bivalent hydrocarbon group with 7 or 4 carbon atoms,
with about 20 noncyclic acid anhydride groups present in
2 1 63335
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the molecule
Azelaic acid (9 moles), 10 moles of ammonium
adipate and 2 moles of benzoic acid chloride-were mixed
together, and the mixture was reacted at a temperature of
up to 20C for 1 hour. Ammonium chloride formed as a
by-product was removed to obtain a crosslinking agent
(B-2). The agent was Zl in Gardner viscosity and about
1400 in number average molecular weight as determined by
GPC.
Preparation Example 13
(B-3): Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 6 carbon atoms
and R' is a bivalent hydrocarbon group cont~ining
an ether linkage and having 4 carbon atoms,
with about 21 noncyclic acid anhydride groups
present in the molecule
A crosslinking agent (B-3) was prepared by
mixing together 20 moles of a compound represented by
the formula HOOC-CH2CH2-O-CH2CH2-COOH, 2 moles of benzoic
acid and 40 moles of acetic anhydride, reacting the
mixture at 140C while removing acetic acid as a
by-product, heating the mixture to 160C when acetic acid
ceased flowing out and removing an excess of acetic
anhydride to terminate the reaction. The agent was Z in
Gardner viscosity (20 C) and about 1400 in number
21 63335
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average molecular weight as determined by GPC.
Preparation Example 14
(B-4): Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 8 carbon atoms and R'
is a bivalent hydrocarbon group containing a urethane
linkage and having 22 carbon atoms, with about 11
noncyclic acid anhydride groups present in the molecule
A crosslinking agent (B-4) was prepared by
mixing together 10 moles of a compound represented by the
formula
5 10 ICl I C6H12- I- C- O - C5H10CH
O H H O
2 moles of isononanoic acid and 20 moles of acetic
anhydride, heating the mixture at 140C while removing
acetic acid as a by-product, heating the mixture to 160C
when acetic acid ceased flowing out and removing an
excess of acetic anhydride to terminate the reaction.
The agent was in the form of a white solid. When the
product was made into a solution containing about 90
wt. % of solids with methyl ethyl ~etone, the solution
was Z3 in Gardner viscosity (20C) and about 2500
in number average molecular weight as determined by
GPC.
Preparation Example 15
(B-5): Compound of the formula (I) wherein R is a mono-
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valent hydrocarbon group with 18 carbon atoms and R' is a
bivalent hydrocarbon group with 4 carbon atoms, with
about 11 noncyclic acid anhydride groups present in the
molecule
Ten moles of adipic acid was heated to 400C,
and water flowing out was removed, whereupon 2 moles of
dehydrated castor oil fatty acid was added to the
reaction mixture, followed by a further reaction at 200C
for 4 hours to obtain a crosslinking agent (B-5).
The agent was N in Gardner viscosity (20C) and about
2000 in number average molecular weight as determined by
GPC.
Preparation Example 16
(B-6): Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 6 carbon atoms and R'
is a bivalent hydrocarbon group containing an ester
linkage and having 40 carbon atoms, with about 2
noncyclic acid anhydride groups present in the molecule
A crosslinking agent (B-6) was obtained by
preparing a linear polyes~er resin (about 960 in number
average molecular weight) having terminal carboxyl and
comprising 5 moles of adipic acid and 4 moles of
neopentyl glycol, mixing 2 moles of benzoic acid and 3
moles of acetic anhydride with the resin, reacting the
mixture at 140C while removing acetic acid as a
21 63335
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by-product, heating the mixture to 160C when acetic acid
ceased flowing out and removing an excess of acetic
anhydride to terminate the reaction. The agent was K in
Gardner viscosity (20C) and about 350 in number average
molecular weight as determined by GPC.
Preparation Example 17
(B-7): Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 8 carbon atoms and R'
is a bivalent hydrocarbon group containing an ester
linkage and having 42 carbon atoms, with about 6
noncyclic acid anhydride groups present in the molecule
A crosslinking agent (B-7) was obtained by
preparing a linear polyester resin having terminal
carboxyl and comprising 20 moles of phthalic anhydride
and 15 moles of 1,6-hexanediol, mi xi ng 2 moles of
isononanoic acid and 10 moles of acetic anhydride with
the resin and reacting the mixture in the same manner as
in preparing the agent (B-6). The agent was Z in Gardner
viscosity and about 2000 in number average molecular
weight.
Preparation Example 18
(B-8): Compound of the formula (I) wherein R is a mono-
valent hydrocarbon group with 12 carbon atoms and R' is a
bivalent hydrocarbon group containing an ester linkage
and having 40 carbon atoms, with about ll noncyclic acid
21 63335
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anhydride groups in the molecule
A crosslinking agent (B-8) was obtained by
mixing 2 moles of coconut oil fatty acid and 15 moles of
acetic anhydride with 10 moles of a linear polyester
having a molecular weight of 1000 and terminal carboxyl
and prepared by reacting ~-caprolactone with lactic acid,
and reacting the mixture in the same manner as in
preparing the agent (B-6). The agent was S in Gardner
viscosity and about 3000 in number average molecular
weight as determined by GPC.
Preparation Example 19
(B-9): Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 8 carbon atoms and R'
is a bivalent hydrocarbon group with 7-or 4 carbon atoms,
with about 6 noncylic acid anhydride groups present in
the molecule
Two moles of isononanoic acid, 3 mole of
azelaic acid, 2 moles of adipic acid and 12 moles of
acetic anhydride were mixed and heated to 135C and held
for two hours. The mixture was heated from 140C to
160C over a one hour period distilling off products of
condensation. The mix was held at 160C until
distillation ceased and then vacuum was applied to the
reactor gradually distilling off more condensation
product. When the vacuum was reduced to 160 mmHg, the
2 1 63335
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reaction was halted and cooled to 100C where the vacuum
was broken by allowing the entrance of dry nitrogen.
The resultant product was dissolved in
propylene glycol monomethyl ether acetate to achieve 80%
polyanhydride solution. The solution viscosity was B on
the Gardner-Holdt scale. The material had a number
average molecular weight of 9S0 by GPC.
Preparation Example 20
(B-10): Compound of the formula (I) wherein R is a
monovalent hydrocarbon group with 8 carbon atoms and R~
is a bivalent hydrocarbon group with 7 or 4 carbon atoms,
with about 6 noncylic acid anhydride groups present in
the molecule
Using the same procedure as (B-9), 2 moles of
isononanoic acid, S moles of adipic acid and 5 moles of
azelaic acid were reacted with 22 moles of acetic
anhydride. The solution, at 80% in propylene glycol
monomethyl ehter acetate had a Gardner-Holdt viscosity of
F. The material had a number average molecular weight of
~0 2500 by GPC.
Preparation of Clear Coat Compositions
Preparation Example 21
The resins (A) obtained in Preparation Examples
4 to 10, the crosslinking agents (B) obtained in
Preparation Examples 11 to 20, curing catalysts (C) and
2 1 63335
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ultraviolet absorbers (D) were mixed together in
specified combinations and in specified proportions as
listed in Table 1 below. Clear coat compositions a to h
were prepared from the respective mixtures by adjusting
each mixture to a solids content of about 40 wt.% with an
organic solvent mixture (xylol/ "Solvesso #150" (brand
name, aromatic hydrocarbon solvent manufactured by Esso
Oil Co., Ltd.) = 1/1 in weight ratio).
Table 1
ClearResin (A) Crosslinking Curing Ultraviolet
coatagent 'B) catalyst (C) absorber (D)
comp
kind Amount kind Amount kind Amount kind Amount
a (A-1) 100 (B-1) 20 (C-1) 2 (D-l) 2
b (A-2) 100 (B-2) 30 (C-l) 2 (D-l) 2
c (A-3) 40 (B-3) 40 (C-l) 2 (D-l) 2 r~
(A-7) 60
d (A-4) 60 (B-4) 50 (C-2) 2 (D-2) 2
(A-7) 40 W
e (A-l) 50 (B-5) 100 (C-2) 2 (D-2) 2 ~n
(A-7) 50
f (A-2) 100 (B-6) 70 (C-3) 2 (D-3) 2
g (A-3) 100 (B-7) 80 (C-3) 2 (D-3) 2
h (A-4) 100 (B-8) 100 (C-3) 2 (D-3) 2
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The amounts, components (C) and components (D)
listed in Table 1 are as follows.
1) The amounts are all in parts by weight, calculated as
solids.
2) The symbols identifying the respective curing
catalysts (C) stand for the following.
(C~ Tetramethylammonium chloride
(C-2): Tributylamine
(C-3): Benzyltriphenylphosphonium chloride
3) The symbols identifying the respective ultraviolet
absorbers stand for the following.
(D-1): Ethanediamide N-(2-ethoxyphenyl)-N'-
(4-isododecylphenyl)
(D-2): 2,4-Dihydroxybenzophenone
(D-3): 2-(2'-hydroxy-5'-methylphenyl)benzotriazole
Preparation Example 22
The following ingredients were well mixed to
obtain clear coat composition (i).
Solution (Part) Solids (Part)
Epoxy Acrylic Resin (A-5)98.3 68.8
Poly Anhydride Resin (B-9) 39.0 31.2
Polybutyl Acrylate 0.3 0.15
20% Tetrabutyl Phosphonium
Chloride 5.0 1.0
Tinuvin 384 (1) 2.0 2.0
Tinuvin 123 (2) 1.0 1.0
Trimethyl Ortho Acetate5.0
Ethyl Ethoxy Propionate15.0
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(1) An ultraviolet absorber, product of Ciba-Geigy
Corporation.
(2) A light stabilizer, product of Ciba-Geigy
Corporation.
This clearcoat solution had a solids content of
53.5% at 28 sec. #4 Ford Cup viscosity.
Preparation Example 23
The following ingredients were well mixed to
obtain clear coat composition (j).
Solution (Part) Solids (Part)
Epoxy Acrylic Resin (A-6)98.3 68.8
Poly Anhydride Resin (B-10) 31.3 2S.0
Polybutyl Acrylate 0.3 0.2
20% Tetrabutyl Phosphonium
Chloride 4.7 0.94
Tinuvin 384 2.0 2
Tinuvin 123 1.0
Trimethyl Ortho Acetate5.0
Ethyl Ethoxy Propionate15.0
This clearcoat was reduced to a #4 Ford Cup
viscosity of 28 sec. with solvesso 100 solvent. The
weight solids is 56.0%.
Examples 1-8 and Comparative Examples 1-3
"Elecron No. 9400" (b~and name, cationic
electrophoretic coating composition manufactured by
Kansai Paint Co., Ltd.) was electrophoretically applied
to steel panels to a thickness, as cured, of 20 ~m and
heated at 170C for 30 minutes for curing. Subsequently,
"ES Primer Surfacer TP-37" (brand name, intermediate
coating composition manufactured by Kansai Paint Co.,
21 63335
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Ltd.) was sprayed onto the steel panels over the coating
to a thickness, as cured, of 30 ~m and heated at 140 for
30 minutes for curing. The steel panels thus coated were
used as substrates.
Some of the substrates were overcoated by the
two-coat one-bake method wherein the base coat
composition and the clear coat composition prepared in
Preparation Examples were applied wet-on-wet and then
cured by heating.
The same procedure as above was repeated using
different base coat compositions and clear coat
compositions as listed in Table 2 below. The two types
of the coating compositions were applied by the
electrostatic rotational atomization method to form a
base coat and a clear coat having a thickness of about 20
~m and about 35 ~m, respectively, when cured.
Each substrate was allowed to stand at room temperature
for about 5 minutes after the application of the base
coat composition, then coated with the clear coat
composition, heated at 140C for 30 minutes to cure the
compositions at the same time and thereby overcoated.
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Table 2
Example Comp. Ex.
1 2 3 4 5 6 7 8 1 2 3
Base coat 1 1 1 l 2 2 2 2
composition
Clear coat a b c d e f g h X Y Z
composition
The comparative clear coat compositions X, Y
and Z listed in Table 2 are as follows.
The clear coat composition X corresponds to
the clear coat composition a wherein the crosslinking
agent (B-l) is replaced by the same amount of a resin
(22000 in weight average molecular weight) having a
cyclic acid anhydride group and prepared by
copolymerizing n-butyl acrylate, styrene and maleic
anhydride (16% in content).
The clear coat composition Y corresponds to the
clear coat composition a wherein the crosslinking agent
(B-l) is replaced by the same amount of a free
carboxyl-containing resin (22000 in weight average
molecular weight) prepared by copolymerizing n-butyl
acrylate, styrene and maleic acid (16% in content).
The clear coat composition Z corresponds to
the clear coat composition a wherein the crosslinking
agent (B-l) is replaced by the same amount of
methylhexahydrophthalic acid anhydride.
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The cured coatings thus obtained by the two-
coat one-bake method were tested for properties by the
following methods.
Test Methods
Appearance on finishing: The coating was
visually evaluated according to the criteria of: A,
satisfactory in smoothness and gloss; B, slightly poor in
smoothness and gloss; C, very poor in smoothness and
gloss.
Distinctness-of-immage gloss: The coating was
checked for ICM value by an image clarity meter (product
of Suga Shikenki Co., Ltd.). ICM values are in the range
of 0 to 100 (%). ICM values not lower than 80 indicate
an excellent distinctness-of-image gloss.
Acid resistance: A 0.4 ml quantity of 40%
aqueous solution of sulfuric acid was applied dropwise to
the coating, which was then dried at 60C for 15 minutes
with a hot air dryer, thereafter washed with water and
visually evaluated according to the criteria of: A, free
of any whitening, staining or etching; B, slight
whitening, staining or etching; C, marked whitening,
staining or etching.
Solvent resistance: The coating was rubbed with
gauze wet with xylol 10 times and then visually evaluated
according to the criteria of: A, no change; B, noticeable
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scratches; C, noticeable swelling and whitening.
Scratch resistance: A motor vehicle having the
test piece affixed to its roof was washed 5 times by a
car washing machine, "P020FWRC," product of Yasui Sangyo
Co., Ltd., and the coating of the test piece was then
checked and evaluated according to the criteria of: A,
almost free from sratches; B, noticeable sratches; C,
marked sratches.
Weather resistance: Determined by a Q W
accelerated weather test using an accelerated weathering
tester, product of Q Panel Co., Ltd. The coating was
irradiated with W rays at 60C for 16 hours and then
exposed to condensation water at 50C for 9 hours as one
cycle. After repeating this cycle for 3000 hours, the
coating was evaluated according to the criteria of: A,
almost r~ining unchanged in gloss; B, appreciable
reduction in gloss; C, marked reduction in gloss along
with cracking or whitening.
Chipping resistance: The coating was tested by
a QGR gravelometer (product of Q Panel Co., Ltd.). About
100 ml of gravel in the form of crushed stones, 5 to 10
mm in diameter, was forced against the coating at an air
pressure of about 4 kg/cm2 at a temperature of about
-20C at a panel angle of 45 deg. The coating was then
evaluated according to the criteria of: A, slightly
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noticeable flaws due to impact, but no separation of the
intermediate coat; B, an increased number of flaws due to
impact with slightly noticeable separation of the
intermediate coat; C, many flaws due to impact, with
noticeable separation of the intermediate coat.
Adhesion: The coating was checked by a
cross-cut adhesion test. An adhesive cellophane tape was
affixed to the coating having 100 2 x 2 mm squares formed
by cutting and then forcibly peeled off. The number of
squares remaining on the panel was thereafter counted.
The adhesion was evaluated according to the criteria of:
A, at least 95 squares remaining unremoved; B, removal of
6 to 10 squares; C, removal of at least 11 squares.
Table 3 below shows the results.
Table 3
Example Comp. Ex.
1 2 3 4 5 6 7 8 1 2 3
Appearance on A A A A A A A A B B A
finishing
Distinctness-of- 85 84 85 87 84 86 86 85 73 76 80
image gloss
Acid resistance A A A A A A A A B B B ~ C~
Solvent re`sistance A A A A A A A A A A B
Scratch resistance A A A A A A A A C C C ~n
Weather resistance A A A A A A A A A A B
Chipping A A A A A A A A B B B
resistance
Adhesion A A A A A A A A A A A
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Example 9
The solvent based basecoat composition 3 was
sprayed over a primed steel panel to give a cured film
thickness of 20 ~m. Clearcoat composition (i) was
sprayed over the basecoat to give a cured film thickness
of clearcoat of 50 ~m, wet-on-wet, and the panel was
cured for 30 minutes at 140C. The resultant coated
panel had the following properties.
Tukon Hardness 12.6
20 Gloss 85
Distinctness-of-Image gloss 87
Min Spot Temperature (1) 63C
The appearance and hardness are very acceptable
for automotive enamel usage and the acid resistance is
substantially better than currently used acrylic
polyol/melamine crosslinker systems which etched at 45C.
(1) The panel is placed on a gradient oven so
the surface of the panel ranges form 45C
on one end to 90C on the other end. A
row of 10% sulfuric acid spots are placed
on the panel for 30 minutes. The panel is
washed with water and the temperature where
spotting begins is recorded as minimum spot
temperature.
Example 10
The procedure of Example 9 was followed except
that the clear coat composition (j) was used instead of
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the clear coat composition (i). The resultant coated
panel had the following properties.
Tukon Hardness 13.6
20 Gloss . 86
Distinctness-of-Image gloss 87
Min Spot Temperature 64C
