 |
Description  |
|
|
BACKGROUND OF THE INVENTION
This invention relates to a method of forming multilayer coatings having
metallic glamor.
The exterior of automobile bodies, for example, is finished with a metallic
base coating and a clear top coating formed on the base coating for
decorative and protective purposes. For higher productivity, the clear top
coating is conventionally applied on the base coating wet-on-wet and cured
simultaneously with the base coating. This method is highly suitable for
in-line coating operation in the automobile industry and gives a high
grade finish in terms of appearance, weatherability, solvent and chemical
resistances, discoloring resistance and the like.
In order to achieve excellent appearance, particularly excellent metallic
glamor, it is imperative that the top coat applied on the base coat
wet-on-wet does not cause intermixing of the two layers which, if it
occurs, greatly impairs the orientation of metallic flakes and the
metallic glamor. For this reason, attempts have been made to decrease the
compatibility between the base coat and the top coat by, for example,
using a resin having a higher molecular weight for the base coat than for
that of the top coat or by using different resins for different coats such
as the combination of acrylic top coat/polyester or cellulose acetate
butyrate base coat. The compatibility between the uncured two coats may
also be decreased by modifying the coating conditions thereof. This
technique includes two-stage application of the base coat, prolonged rest
intervals between application steps, elevation of the viscosity the of
base coat relative to the top coat and the like. However, none of these
known attempts is completely satisfactory. The use of high molecular
weight resins requires a decrease in their solid contents at the time of
application. When different resins are used for different coats, the
adhesion between different coats is decreased. Modification of coating
conditions increases the number of steps and the length of time required
for the overall coating operation.
One approach for improving aesthetic properties of multicoat system is to
provide a relatively thick top coat on the base coat. In a two coat system
comprising a base coat containing aluminum flakes of 10 to 50 .mu.m size,
large aluminum flakes often protrude above the base coat surface. The
clear top coat therefore must have a film thickness sufficient to
compensate for these protrusions. However, with conventional top coat
compositions, the film thickness is limited to only 20-30 .mu.m with a
single coating operation, or 40-45 .mu.m with two coating operations. This
is because conventional coating compositions tend to excessively run with
an increase of the amount applied per unit area. Thick top coats may be
provided by multiple coating operations. However, this technique is less
efficient and requires an extensive modification of existing production
lines.
Recently, with the objective of economizing natural resources and energy
and because of the requirements for pollution control, much research has
been conducted with the objective of for increasing the nonvolatile
contents of coating materials. High-solids coating systems are generally
formulated by lowering the molecular weight of vehicle resins but this
technique, when applied to two coat systems to be applied wet-on-wet,
presents several serious problems, such as poor metallic flake
orientation, intermixing, poor gloss, excessive run and the like. Another
approach would be to incorporate a non-aqueous resin dispersion into the
system. However, experiments have shown that this method suffers from the
above-mentioned problems because the increase in viscosity after
application takes too long time.
We have already proposed in Japanese Laid Open Patent Application No.
60-94175 published May 27, 1985 to incorporate internally crosslinked
polymer microgel particles of 0.01 to 10 .mu.m size into both the base
coat and top coat compositions. By incorporating the polymer microgel
particles, the composition exhibits a yield point such that when a shear
force above the yield point is exerted, the composition may be easily
fluidized. Once deposited on a substrate, the composition exhibits a high
structural viscosity. For this reason, migration of metal flakes in the
base coat due to the convection of solvent, intermixing of the two coats
and run are prevented, thereby ensuring an excellent finish having
improved gloss and other aethetic properties even when the top coat is
applied wet-on-wet in a relatively large film thickness.
When relatively low molecular weight resins are used as a vehicles resin in
the above multilayer coating system for achieving high solid contents, an
acid catalyst is required for accelerating the curing reaction thereof
because such vehicle resins are generally less reactive with a
cross-linker than higher molecular weight resins.
The use of such acid catalyst is often undesirable because it tends to
impair the storage life of the coating compositions. When used
excessively, the acid catalyst remains in the finished coating and
adversely affects the quality of the finished coating.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of forming a
multilayer metallic coating utilizing a high-solids coating system
containing low molecular weight vehicle resins, polymer microgel particles
and cross-linker without compromising the quality of finished coating and
the storage life of the coating system.
The present invention relates to a method of forming a multilayer metallic
coating on a substrate which comprises the steps of applying a base
coating composition containing a metallic pigment on said substrate,
applying a clear top coating composition onto the base coating wet-on-wet,
and curing both coatings simultanesouly.
According to the present invention, said base coating composition
comprises:
(a) a film-forming, low molecular weight-polymer having a plurality of
cross-linkable functional groups,
(b) a crosslinker for said film-forming polymer,
(c) a volatile organic liquid diluent,
(d) internally crosslinked polymer microparticles which are insoluble in
the mixture of (a), (b) and (c) but stably dispersible in said mixture,
(e) an organic acid catalyst capable of accelerating a crosslinking
reaction between (a) and (b), the organic acid catalyst being masked with
an organic base, and
(f) a metallic pigment.
The clear top coating composition comprises:
(a') a film-forming, low molecular weight-acrylic polymer having a
plurality of crosslinkable functional groups,
(b) a crosslinker for said film-forming polymer,
(c) a volatile organic liquid diluent,
(d) internally crosslinked polymer microparticles which are insoluble in
the mixture of (a'), (b) and (c) but stably dispersible in said mixture,
and
(e) an organic acid catalyst capable of accelerating a crosslinking
reaction between (a') and (b), the organic acid catalyst being masked with
an organic base.
According to the present invention, the use of low molecular weight-vehicle
resins in combination with polymer microgel particles both in the base and
top coating compositions makes high solids formulations compatible with
improved workability thereof. Furthermore, a high crosslinking density
sufficient to give a finished coating having excellent film properties may
be obtained by the use of the organic acid catalyst masked with an organic
base without affecting the stability of coating compositions upon storage.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(a) Film-forming polymer used in the base coating
Any conventional polymer having a relatively low molecular weight and a
plurality of crosslinkable functional groups such as hydroxyl and carboxyl
groups may be employed in the base coating composition. Examples thereof
include acrylic resins, alkyd resins and polyester resins having such
functional groups and a number average molecular weight of 1,000 to 4,000.
These resins preferably have a hydroxyl number of 60 to 200 and an acid
number of 5 to 30.
The term "polyester resin" refers to one which is conventionally used in
the coating industry and which consists essentially of a condensate of a
polyhydric alcohol and a polycarboxylic acid. Also included in this term
are alkyd resins modified with higher fatty acid groups derived from
natural or synthetic drying, semi-drying or non-drying oils. These
polyester resins must have, as hereinbefore described, acid and hydroxyl
numbers of a suitable range.
Examples of polyhydric alcohols which may be employed in the synthesis of
polyester resins include ethylene glycol, propylene glycol, butylene
glycol, 1,6-hexylene glycol, neopentyl glycol, glycerol,
trimethylolpropane, trimethylolethane, pentaerythritol,
di-pentaerythritol, tri-pentaerythritol, hexanetriol, oligomers of styrene
and allyl alcohol (e.g. one commercially available from Monsanto Chemical
Company under the name of HJ 100), polyether polyols derived from
trimethylolpropane and ethylene oxide and/or propylene oxide (e.g. one
commercially available under the name of Niax Triol) and the like.
Examples of polycarboxylic acids include succinic, adipic, azelaic,
sebacic, maleic, fumaric, muconic, itaconic, phthalic, isophthalic,
terephthalic, trimellitic, pyromellitic acids and their acid anhydrides.
Examples of oils from which higher fatty acids are derived include linseed
oil, soybean oil, tall oil, dehydrated castor oil, fish oil, tung oil,
saflower oil, sunflower oil and cotton seed oil. Preferably the oil length
of oil-modified alkyd resins does not exceed 50%. In order to give an
internal plasticity, polyester resins may include a monocarboxylic acid
such as a C.sub.4 -C.sub.20 saturated aliphatic monocarboxylic acid,
benzoic acid, p-tert.-butyl-benzoic acid and abietic acid.
Acrylic polymers which may be used in the base coating composition include
those conventionally used in the coating industry and consisting
essentially of copolymers of a mixture of a alkyl ester of acrylic or
methacrylic acid and a comonomer having a crosslinkable functional group
optionally containing an ethylenically unsaturated comonomer other than
the former two monomers.
Examples of preferable alkyl (metha)acrylates include methyl
(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl
(meth)acrylate and 2-ethylhexyl (meth)acrylate.
Examples of monomers having a cross-linkable group include acrylic acid,
methacrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl
(meth)acrylate, N-butoxymethyl(meth)acrylamide, glycidyl (meth)acrylate
and the like.
Examples of other monomers which may be optionally present in the monomer
mixture include vinyl acetate, acrylonitrile, styrene, vinyl toluene and
the like.
The monomer mixture may be polymerized by any known method such as solution
polymerization, non-aqueous dispersion polymerization or bulk
polymerization. The emulsion polymerization followed by solvent
substitution may also employed.
(a') Acrylic film-forming polymer used in the top coating
Acrylic polymers which may be used in the clear top coating composition may
be the same as the hereinbefore discussed acrylic polymers used in the
base coating. They must have, of course, a sufficient number of functional
groups such as hydroxyl and carboxyl groups available for the reaction
with a crosslinker. They preferably have a number average molecular weight
of 1,000 to 4,000, a hydroxyl number of 60 to 200 and an acid number of 5
to 30.
(b) Crosslinker
Crosslinkers which may be used in the base and top coatings include
aminoplast resins, i.e. condensates of formaldehyde and a nitrogen
compound such as urea, thiourea, melamine, benzoguanamine and the like.
C.sub.1 -C.sub.4 alkyl ethers of these condensates may also be used.
Melamine-based aminoplast resins are preferable.
(c) Organic liquid diluent
The organic liquid diluent used in the base and top coating compositions
may be any conventional solvent used in the coating industry for
dissolving vehicle resins. Examples thereof include aliphatic hydrocarbons
such as hexane, heptane; aromatic hydrocarbons such as toluene and xylene;
various petroleum fractions having a suitable boiling point range; esters
such as butyl acetate, ethylene glycol diacetate and 2-ethoxyethyl
acetate; ketones such as acetone, methyl ethyl ketone and methyl isobutyl
ketone; alcohols such as butanol; and mixtures of these solvents.
The resin (a) or (a') may be present in the mixture of the organic liquid
diluent and the crosslinker in the form of a solution or a stable
dispersion.
(d) Internally crosslinked polymer microgels
The microgel particles incorporated into the coating system of this
invention should be internally cross-linked so as to be not soluble but
stably dispersible in the coating system and have a microscopic average
size. Several method are known to produce microgel particles. One such
method commonly referred to as the non-aqueous dispersion (NAD) method
comprises polymerizing a mixture of ethylenically unsaturated comonomers
including at least one cross-linking comonomer in an organic liquid in
which the mixture is soluble but the polymer is insoluble such as
aliphatic hydrocarbons to form a non-aqueous dispersion of a cross-linked
copolymer.
Alternatively, the microgel particles may be prepared by
emulsion-polymerizing a mixture of ethylenically unsaturated comonomers
including at least one cross-linking comonomer in an aqueous medium by a
conventional method, and then removing water from the emulsion by, for
example, solvent substitution, centrifugation, filtering or drying.
One such method is disclosed in U.S. Pat. No. 4,530,946 assigned to the
assignee of the present application, the disclosure of which is
incorporated herein by reference.
Examples of ethylenically unsaturated comonomers used for the production of
microgels include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl
(meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,
styrene, .alpha.-methylstyrene, vinyltoluene, t-butylstyrene, ethylene,
propylene, vinyl acetate, vinyl propionate, acrylonitrile,
methacrylonitrile, dimethylaminoethyl (meth)acrylate and the like. Two or
more comonomers may be combined.
Cross-linking comonomers include a monomer having at least two
ethylenically unsaturated bonds in the molecule and the combination of two
different monomers having mutually reactive groups.
Monomers having at least two polymerization sites may typically be
represented by esters of a polyhydric alcohol with an ethylenically
unsaturated monocarboxylic acid, esters of an ethylenically unsaturated
monoalcohol with a polycarboxylic acid and aromatic compounds having at
least two vinyl substituents. Specific examples thereof include, ethylene
glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol
dimethacrylate, tetraethylene glycol dimethacrylate, 1,3 butylene glycol
dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane
trimethacrylate, 1,4-butanediol diacrylate, neopentyl glycol diacrylate,
1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol
triacrylate, pentaerythritol tetracrylate, pentaerythritol dimethacrylate,
pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate,
glycerol diacrylate, glycerol allyloxy dimethacrylate,
1,1,1-tris(hydroxymethyl)ethane diacrylate,
1,1,1-tris(hydroxymethyl)ethane triacrylate,
1,1,1-tris(hydroxymethyl)ethane dimethacrylate,
1,1,1-tris(hydroxymethyl)ethane trimethacrylate,
1,1,1-tris(hydroxymethyl)propane diacrylate,
1,1,1-tris(hydroxymethyl)propane triacrylate,
1,1,1-tris(hydroxymethyl)propane dimethacrylate,
1,1,1-tris(hydroxymethyl)propane trimethacrylate, triallyl cyanurate,
triallyl isocyanurate, triallyl trimellitate, diallyl phthalate, diallyl
terephthalate and divinyl benzene.
Combinations of two monomers having mutually reactive groups may be used in
place of, or in addition to monomers having two or more polymerization
sites. For example, monomers having a glycidyl group such as glycidyl
acrylate or methacrylate may be combined with carboxyl group-containing
monomers such as acrylic, methacrylic or crotonic acid. Also, hydroxyl
group-containing monomers such as 2-hydroxethyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol
or methallyl alcohol may be combined with isocyanato group-containing
monomers such as vinyl isocyanate or isopropenyl isocyanate. Other
combination will be apparent to those skilled in the art.
Polymer microgel particles prepared in an aqueous or non-aqueous medium may
be incorporated into the coating composition as such, or they may be
separated from the medium by means of a suitable technique such as
filtration, spray drying or lyophilization optionally followed by milling
to a suitable particle size before incorporating to the coating
composition.
The polymer microgel particles have an average particle size of 0.01 to 10
.mu.m, preferably from 0.02 to 5 .mu.m.
(e) Masked organic acid catalyst
Acrylic and polyester resins having a plurality of crosslinkable functional
groups such as hydroxyl and carboxyl groups are conventionally crosslinked
with a crosslinker such as aminoplast resins in the presence of an acid
catalyst such as dinonylnaphthalenedisulfonic acid, dodecylbenzenesulfonic
acid and p-toluenesulfonic acid.
In the present invention, the acid catalyst takes a masked form with an
organic base. By using such masked acid catalyst, it is possible to obtain
a high crosslinking density sufficient to impart the resulting coating
film with high strength properties even when less reactive, low molecular
weight resins are used. The masked acid catalyst does not affect the
storage stability of the coating compositions containing the same. Also it
minimizes drawbacks of free acid catalyst such as decrease in the quality
of finished coatings when remained therein.
Examples of organic acids include an organic acid, particularly sulfonic
acid having a pKa below 4, e.g. p-toluenesulfonic acid,
dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid,
methanesulfonic acid and the like.
The organic acid should be neutralized or masked with at least 60%
equivalents of an organic base. Examples of organic bases used for this
purpose include secondary or tertiary amines such as dimethylamine,
diethylamine, piperidine, morpholine, diethanolamine, methyl ethanolamine,
triethylamine, triethanolamine, diisopropanolamine, pyridine,
di-2-ethylhexylamine, N,N-dicyclohexylmethylamine,
N,N-dimethylcyclohexylamine,
di-(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate and the like. Among
them, strongly basic amines having a high boiling point (above 150.degree.
C.) such as diisopropanolamine and N,N-dicyclohexylmethylamine are
preferable. They give a high grade appearance to the finished coating.
The organic acid and the masking base may be incorporated as a salt
therebetween or separately.
Coating compositions
The coating compositions used in the present invention may contain, in
addition to hereinbefore described components, other conventional
additives as desired. Examples thereof include viscosity adjusting agents
such as organic montmorillonite and cellulose acetate butyrate, surface
conditioners such as silicones and organic polymers, UV absorbing agents,
hindered amines and hidered phenols.
The base coating composition must contain a metallic pigment such as
aluminum flakes, copper flakes and bronze flakes. The base coating
composition may additionally contain a conventional color pigment.
The ratio of the film-forming resin to the crosslinker in the base and top
coating compositions preferably ranges from 4:6 to 8:2 by weight on dry
basis. If the amount of crosslinker is too small, the resulting cured film
will have poor strength properties. Conversely, excessive amounts of
crosslinker will result in a non-flexible, brittle film.
The proportion of polymer microgel particles in the coating compositions
generally ranges from 1 to 40% by weight of the combined solid contents of
the film-forming polymer and the crosslinker. The desired rheology control
function of the microgel particles cannot be expected when the proportion
thereof is less than the lower limit, while the apperance of multilayer
coating will be degraded at a proportion greater than the upper limit.
The proportion of the amine-masked organic acid catalyst preferably ranges
from 0.01 to 3.0% by weight of the total solid contents of the respective
coating compositions exclusive of pigments. Too small proportions are not
effective to catalize the crosslinking reaction, while too large
proportions will adversely affect the appearance, strength and other
properties of the resulting film.
One of advantages of the coating compositions used in the present invention
resides in the fact that the composition may have a higher nonvolatile
content compared with conventional compositions. For example, conventional
base coating compositions and top coating compositions generally have a
non-volatile content of 23-30% and 38-40% by weight, respectively, whereas
corresponding compositions used in the present invention may have a
nonvolatile content as high as 51-56% and 59-65% by weight, respectively.
This enables to lower their organic solvent content.
The maximum film thickness at which conventional coating compositions may
be applied by spraying without run lies at about 45 .mu.m, whereas the
coating compositions used in the present invention may be applied in a
film thickness as thick as 50-60 .mu.m without run. The weatherability of
the resulting cured film is generally comparable with conventional coating
compositions.
In the coating operation according to the present invention, the base
coating composition is first applied on a substrate which has been
previously given a primer or otherwise surface-treated. The material from
which the substrate is made is not limited to metals used for
manufacturing automobiles such as iron, aluminum and copper but include
ceramics, plastics and other materials provided that they can withstand an
elevated temperature at which the multilayer coating of the present
invention is finally cured. After setting the applied base coating
composition at room or elevated temperature, the clear top coating
composition is applied wet-on-wet followed by setting or preheating. The
multilayer coating so applied consisting of the base and top coating
layers is then cured together simultaneously at an elevated temperature to
give a cured coating having a high grade finish.
The following examples illustrate the invention. All parts and percents
therein are by weight unless otherwise specified.
EXAMPLES
Part I. Preparation of Microgels
Microgel Preparation 1
(a) Preparation of Emulsifier
To a two liter flask having a stirring means, a reflux condenser,
temperature-control means, a nitrogen gas-introducing tube and a decanter
were added 134 parts of N,N-bis(hydroxyethyl)taurine, 130 parts of
neopentyl glycol, 236 parts of azelaic acid, 186 parts of phthalic
anhydride, and 27 parts of xylene. The mixture was refluxed and water was
removed as an azeotropic mixture with xylene. The temperature was raised
to 190.degree. C. over 2 hours and the reaction was continued with
stirring until an acid number of 145 was reached.
The reaction product was cooled to 140.degree. C. and 314 parts of CARDURA
E-10 (glycidyl versatate, Shell Chemical Company) was added dropwise over
30 minutes at 140.degree. C. The reaction was continued for additional two
hours with stirring. A polyester resin having an acid number of 59, a
hydroxyl number of 90 and a number average molecular weight (Mn) of 1054
was obtained.
(b) Preparation of Microgel
To a one liter flask provided with stirring means, cooling means and
temperature-control means were added 282 parts of deionized water, 10
parts of the above-described emulsifier and 0.75 parts of diethanolamine
at 80.degree. C. The mixture was stirred to make a solution. To the
solution was added a solution of 4.5 parts of azobiscyanovaleric acid and
4.3 parts of dimethylethanolamine in 45 parts of deionized water. Then a
monomer mixture consisting of 70.7 parts of methyl methacrylate, 94.2
parts of n-butyl acrylate, 70.7 parts of styrene, 30.0 parts of
2-hydroxyethyl acrylate and 4.5 parts of ethylene glycol dimethacrylate
was added dropwise over 60 minutes. After the addition of monomers, a
solution of 1.5 parts of azobiscyanovaleric acid and 1.4 parts of
dimethylethanolamine in 15 parts of deionized water was added. The mixture
was stirred at 80.degree. C. for 60 minutes to give a polymeric emulsion
having a nonvolatile content of 45%, a pH of 7.2, a viscosity of 92 cps
(25.degree. C.) and a particle size of 0.156 microns.
This emulsion was spray dried to obtain microgel particles having a
particle size of 0.8 microns.
Microgel Preparation 2
The procedure of Microgel Preparation 1 was followed except that the
monomer mixture consisted of 189 parts of methyl methacrylate, 54 parts of
n-butyl acrylate and 27 parts of ethyleneglycol dimethacrylate. Particle
size of spray dried microgel particles was 1.2 .mu.m.
Microgel Preparation 3
The procedure of Microgel Preparation 1 was followed except that the
monomer mixture consisted of 243 parts of n-butyl acrylate and 27 parts of
ethyleneglycol dimethacrylate.
Microgel Preparation 4
The procedure of Microgel Preparation 1 was followed to obtain a microgel
emulsion except that the monomer mixture consisted of 216 parts of
styrene, 27 parts of n-butyl acrylate and 27 parts of ethyleneglycol
dimethacrylate.
The resulting emulsion was converted to a microgel dispersion in xylene by
azeotropic distillation. A microgel dispersion having a microgel content
of 40% was obtained. Particle size was 0.2 .mu.m.
Microgel Preparation 5
To a one liter flask provided with stirring means, cooling means and
temperature-control means were added 232 parts of deionized water, 10
parts of the polyester resin obtained in Microgel Preparation 1 (a) and
0.75 parts of dimethylethanolamine with stirring at 80.degree. C. to make
a solution. To the solution was added a solution of 1.0 part of
azobiscyanovaleric acid and 0.26 parts of dimethylethanolamine in 20 parts
of deionized water. Then a monomer mixture consisting of 108 parts of
methyl methacrylate and 27 parts of ethyleneglycol dimethacrylate was
added dropwise over 60 minutes. After the addition of monomers, a solution
of 0.5 parts of azobiscyanovaleric acid and 0.3 parts of
dimethylethanolamine in 25 parts of deionized water was added. Then a
monomer mixture consisting of 9.5 parts of styrene, 20 parts of methyl
methacrylate, 14 parts of n-butyl acrylate and 6 parts of ethyleneglycol
dimethacrylate was added dropwise over 60 minutes. A solution of 1.5 parts
of azobiscyanovaleric acid and 1.4 parts of dimethylethanolamine in 15
parts of deionized water was added again. The mixture was stirred at
80.degree. C. for 60 minutes to complete the polymerization. A microgel
emulsion having a nonvolatile content of 45%, a pH of 7.2, a viscosity of
105 cps (25.degree. C.) and a particle size of 0.2 .mu.m was obtained.
The emulsion was converted to a microgel dispersion in xylene having a
microgel content of 40% as in Microgel Preparation 4. Particle size in
this dispersion was 0.25 .mu.m.
Microgel Preparation 6 (NAD method)
Step (a)
To a flask having a stirring means, a thermometer and a reflux condenser
were added the following stock materials:
______________________________________
Aliphatic hydrocarbons (b.p. 140-156.degree. C.,
20.016 parts
free from aromatic hydrocarbons)
Methyl methacrylate 1.776 parts
Methacrylic acid 0.036 parts
Azobisisobutyronitrile 0.140 parts
33% solution of graft copolymer
0.662 parts
stabilizer (see below)
______________________________________
The interior of the flask was purged with nitrogen gas and the contents
thereof were maintained at 100.degree. C. for 1 hour to produce a seed
dispersion.
To the flask was added a monomer mixture having the following composition
in portions with stirring at 100.degree. C. over 6 hours.
______________________________________
Methyl methacrylate 32.459 parts
Glycidyl methacrylate 0.331 parts
Methacrylic acid 0.331 parts
Azobisisobutyronitrile 0.203 parts
Dimethylaminoethanol 0.070 parts
33% solution of graft copolymer
6.810 parts
stabilizer (see below)
Aliphatic hydrocarbons (b.p. 140-156.degree. C.)
37.166 parts
______________________________________
The contents of the flask was kept at 100.degree. C. for additional 3 hours
to convert the monomer mixture to insoluble polymer gel particles (18-19%
of total dispersed phase) and uncross-linked polymer particles (19% of
total dispersed phase).
The graft copolymer stabilizer solution used in the above procedure was
prepared by self-condensing 12 hydroxystearic acid to an acid number of
31-34 mg KOH/g (corresponding to a molecular weight from 1650-1800),
reacting the condensate with a stoichiometric amount of glycidyl
methacrylate, and then copolymerizing 3 parts of the resulting unsaturated
ester with 1 part of a 95:5 mixture of methyl methacrylate/acrylic acid.
Step (b)
The same flask as used in Step (a) was charged with 63.853 parts of the
dispersion produced in Step (a) and the content was heated at 115.degree.
C. After purging the interior of the flask with nitrogen gas, a monomer
mixture having the following composition was added in portions with
stirring at 115.degree. C. over 3 hours.
______________________________________
Methyl methacrylate 3.342 parts
Hydroxyethyl acrylate
1.906 parts
Methacrylic acid 0.496 parts
Butyl acrylate 3.691 parts
2-Ethylhexyl acrylate
3.812 parts
Styrene 5.712 parts
Azobisisobutyronitrile
0.906 parts
n-Octylmercaptan 0.847 parts
33% solution of graft copolymer
1.495 parts
stabilizer (see above)
______________________________________
After the completion of the addition, the contents were maintained at
115.degree. C. for additional 2 hours to allow the mixture to fully react.
The resulting product was diluted with 13.940 parts of butyl acetate to
obtain 100 parts of a non-aqueous dispersion having a total film-forming
solid content of 45% and an insoluble polymer microgel content of 27.0%.
The particle size was 0.08 .mu.m.
Part II. Synthesis of Vehicle Resins
Resin Synthesis 1
A reactor provided with a stirrer, reflux condenser, a thermometer, a
nitrogen gas-introducing tube and a drip fannel was charged with 220 parts
of SOLVESSO 100 and heated to 150.degree. C. while introducing nitrogen
gas. To the reactor was added the following monomer mixture (a) over 3
hours at a constant rate.
______________________________________
Monomer Mixture (a)
______________________________________
Ethyl acrylate 307 parts
Ethyl methacrylate 292 parts
2-Hydroxyethyl methacrylate
116 parts
PLACCEL FM-1.sup.1 217 parts
Methacrylic acid 18 parts
2,4-Diphenyl-4-methyl-1-pentene
50 parts
Azobisisobutyronitrile
30 parts
t-Butylperoxy-2-ethylhexanoate
150 parts
______________________________________
.sup.1 Sold by Daicel Chemical Industries, Ltd. A 1:1 adduct of
2hydroxyethyl methacrylate and .epsilon.-caprolactone.
After the addition, the mixture was kept at 150.degree. C. for 30 minutes.
Then 10 parts of t-butylperoxy-2-ethylhexanoate and 30 parts of SOLVESSO
were added dropwise over 1 hour at a constant rate. Then the reaction
mixture was kept at 150.degree. C. for 3 hours and cooled to obtain Resin
Solution A having a nonvolatile content of 80%, an Mn of 1,000 and
viscosity X.
Resin Synthesis 2
To a reactor provided with a stirrer, a thermometer, a water trap and a
nitrogen-gas introducing tube were added 3.69 parts of trimethylolpropane,
17.21 parts of neopentylglycol, 34.39 parts of pivaleic acid
neopentylglycol ester, 22.99 parts of hexahydrophthalic anhydride, 21.72
parts of adipic acid, 0.02 parts of dibutyltin oxide and 2 parts of
xylene. The mixture was reacted at 230.degree. C. under nitrogen gas
current while stirring until an acid number of 10.0 mg KOH/g of solid
content was reached. After cooling, the reaction product was diluted with
21 parts of xylene to obtain Resin Solution B having a nonvolatile content
of 80%, an Mn of 1,200 and viscosity Z 2.
Resin Synthesis 3
The procedure of Resin Synthesis 1 was repeated except that the amount of
5-butylperoxy-2-ethylhexanoate was decreased from 150 parts to 60 parts.
Resin Solution C having a nonvolatile content of 80%, an Mn of 1,800 and
viscosity Z 5 was obtained.
Resin Synthesis 4
The same reactor as used in Resin Synthesis 1 was charged with 400 parts of
xylene and heated to 130.degree. C. while introducing nitrogen gas. To the
reactor was added the following monomer mixture (b) over 3 hours at a
constant rate.
______________________________________
Monomer Mixture (b)
______________________________________
Ethyl acrylate 307 parts
Ethyl methacrylate 292 parts
Styrene 50 parts
2-Hydroxyethyl methacrylate
116 parts
PLACCEL FM-1 217 parts
Methacrylic acid 18 parts
t-Butylperoxy-2-ethylhexanoate
80 parts
______________________________________
After the addition, the mixture was kept at 130.degree. C. for 30 minutes.
Then a mixture of 10 parts of t-butylperoxy2-ethylhexanoate and 10 parts
of xylene was added dropwise over 1 hour at a constant rate. The reaction
mixture was kept at 130.degree. C. for 3 hours and cooled to obtain Resin
Solution D having a nonvolatile content of 70%, an Mn of 4,000 and
viscosity Z 1.
Resin Synthesis 5
The procedure of Resin Synthesis 4 was repeated except that 80 parts of
t-butylperoxy-2-ethylhexanoate were replaced by 30 parts of
azobisisobutylronitrile. Resin Solution E having a nonvolatile content of
70%, an Mn of 4,500 and viscosity Z 3 was obtained.
Resin Synthesis 6
The procedure of Resin Synthesis 1 was followed except that monomer mixture
(a) was replaced by the following monomer mixture (c).
______________________________________
Monomer Mixture (c)
______________________________________
Styrene 200 parts
n-Butyl methacrylate 191 parts
Lauryl methacrylate 246 parts
2-Hydroxyethyl methacrylate
232 parts
Methacrylic acid 31 parts
2,4-Diphenyl-4-methyl-1-pentene
100 parts
Azobisisobutyronitrile
20 parts
t-Butylperoxy-2-ethylhexanoate
60 parts
______________________________________
Resin Solution F having a nonvolatile content of 80%, an Mn of 1,800 and
viscosity Z 5 was obtained.
Resin Synthesis 7
The procedure of Resin Synthesis 6 was repeated except that the amount of
t-butylperoxy-2-ethylhexanoate was increased from 60 parts to 150 parts.
Resin Solution G having a nonvolatile content of 80%, an Mn of 1,000 and
viscosity S was obtained.
Resin Synthesis 8
The procedure of Resin Synthesis 4 was repeated except that the amount of
t-butylperoxy-2-ethylhexanoate was increased from 60 parts to 100 parts.
Resin Solution H having a nonvolatile content of 80%, an Mn of 1,200 and
viscosity Y was obtained.
Resin Synthesis 9
The procedure of Resin Synthesis 4 was repeated except that monomer mixture
(b) was replaced by the following monomer mixture (d).
______________________________________
Monomer Mixture (d)
______________________________________
Styrene 300 parts
n-Butyl methacrylate 191 parts
Lauryl methacrylate 246 parts
2-Hydroxyethyl methacrylate
232 parts
Methacrylic acid 31 parts
t-Butylperoxy-2-ethylhexanoate
100 parts
______________________________________
Resin Solution I having a nonvolatile content of 70%, an Mn of 3,500 and
viscosity Y was obtained.
Resin Synthesis 10
The procedure of Resin Sy | | |
