Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A~L~OUS BRANCHED POLYMER DISPERSANT FOR HYDROPHOBIC
MATERIALS
TECHNICAL FIELD
This invention relates to improved waterborne dispersions containing
an aqueous branched polymer dispersant and a dispersed hydrophobic material.
BACKGROUND OF THE INVENTION
Waterborne coating compositions are widely used to coat automobiles
l0 and trucks since these compositions have substantially reduced VOC
(volatile organic
content) and meet with stringent pollution regulations. Typically, these
coating
contain a latex as the main film forming component, a crosslinking agent, and
other
non-latex resins, additives and pigments. The latex to keep it dispersed in an
aqueous
medium can contain surfactant, and/or the latex polymer contains anionic or
cationic
groups which when formed into a salt with an acid used for cationic groups or
a base
used for anionic groups. The presence of surfactant, cationic or anionic
constituents in
a finished formed from such a coating composition cause defects such as water
spotting, poor resistance to humidity and increase acid etching caused by acid
rain and
the finish has poor resistance to exterior weathering. To improve such defects
in a
coating, hydrophobic constituents can be added to the coating composition such
as
hydrophobic melamine crosslinking resins and hydrophobic polymers. However,
these
hydrophobic constituents are very difficult to disperse in an aqueous medium.
Water dispersible polymers that are used as dispersants for pigments
and used to form pigment dispersions for formulating waterborne coating
2 5 compositions are known in the art and may be considered as a dispersant
for such
hydrophobic materials. U.S. Patent 5,231,131, issued July 27, 1993 to Chu et
al
shows aqueous graft polymer pigment dispersants in which the side chains of
the graft
copolymer contain carboxyl groups that are neutralized with an inorganic base
or an
amine. While these graft copolymers are used as dispersants for pigments,
relatively
3 0 large amounts of polymerized ethylenically unsaturated acid monomers are
present in
the side chains of the graft copolymer to provide water dispersibility but the
presence
of these acid groups in the graft copolymer makes a coating formed with such a
copolymer sensitive to water and would not be suitable for dispersing
hydrophobic
materials in a coating.
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2
A polymer dispersant is needed that will adequately disperse
hydrophobic components used in coating compositions such as crosslinking
agents like
melamine crossIinking agents, hydrophobic polymers like acrylic polymers and
polyesters and mixtures of such components and the polymeric dispersant
contains
relatively small amounts of polymerized acid monomers. When dispersion of such
a
polymer is formulated into a waterborne coating composition, a finish is
formed that is
free from the undesirable effects of exposure to water and weathering.
SUMMARY OF THE INVENTION
A waterbased dispersion usefi~l for forming aqueous coating
compositions containing dispersed hydrophobic material, an aqueous carrier
and a branched polymer dispersant (binder);
the branched polymer has a weight average molecular weight of about
5,000 - 100,000 and contains 20-80% by weight of a hydrophilic backbone and
correspondingly 80-20% by weight of macromonomer side chains; wherein
the backbone of the branched polymer is of polymerized ethylenically
unsaturated monomers and 2-30% by weight, based on the weight of the
backbone of polymerized ethylenically unsaturated monomers having an acid-
fimctional group; and wherein at least I O% of the acid-functional goups are
2 o neutralized with an amine or an inorganic base and is hydrophilic in
comparison
to the side chains; and
the side chains are of macromonomers of polymerized ethylenically
unsaturated monomers that are polymerized into the backbone via an
ethylenically unsaturated group and the macromonomers have a weight
average molecular weight of about 1,000-30,000 and
wherein the weight ratio of hydrophobic material to binder is about
1/100 - 200/100;
DETAILED DESCRIPTION OF THE INVENTION
3 0 The novel dispersion of this invention of a hydrophobic material
dispersed by the branched polymer is stable and in general is non flocculated
or
agglomerated and is compatible with a variety of polymeric film forming
binders that
are conventionally used in waterborne coating compositions and in particular
compatible with acrylic polymers that are used in waterborne coatings. The
branched
polymer dispersant upon curing of the coating composition into which it has
been
incorporated reacts with other film forming components of the coating
composition
and becomes part of the film and does not cause deterioration of the film upon
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3
weathering as may occur if it remained an unreacted component of the film.
Also,
since the branched polymer is an excellent dispersant, the ratio of polymer to
hydrophobic component being dispersed is less than used with conventional
dispersants. Further, the branched polymers allow for the use of higher
molecular
weight polymers that have a lower viscosity in comparison to linear polymers
of the
same composition that have the same molecular weight. The acid content of the
backbone of the branch polymer can readily be adjusted to maximize dispersion
properties of the polymer without increasing molecular weight and not detract
from
the performance properties of a coating composition into which a dispersion of
this
to polymer has been incorporated. Finishes of aqueous coatings formulated with
dispersions containing these branched polymers are hard, water and humidity
resistant.
The branched polymer used to formulate the dispersion of this
invention is prepared from a macromonomer which forms the side chains of the
branched polymer and comprises polymerized alpha-beta ethylenically
unsaturated
monomers and has one terminal ethylenically unsaturated moiety and has a
weight
average molecular weight (MVO of 1,000-30,000, preferably 6,000 to 15,000.
About
20-80% (by weight), preferably 30-70%, of the macromonomer is copolymerized
with
80-20%, preferably 70-30%, of a blend of other alpha, beta-ethylenically
unsaturated
monomers which form the backbone of the branched polymer, at least 2%,
preferably
2 0 2-30% by weight, most preferably 3-15%, of the alpha, beta ethylenically
unsaturated
monomers of the backbone have carboxylic acid functionality, to form a
branched
polymer with a MW of 5,000-100,000, preferably 5,000-40,000, which after
neutralizing with an amine or other neutralizing agent can be dispersed in
water.
All molecular weights herein are determined by GPC (gel permeation
2 5 chromatography) using a polystyrene standard.
It has been found that improved aqueous or waterborne coating
compositions are obtained by using these branched polymers as dispersants for
hydrophobic materials such as certain crosslinking agents and hydrophobic
polymers.
These coating compositions also contain a film forming binder usually an
acrylic
3 0 polymer. Such compositions have the advantage of providing excellent
coating
properties desirable for automotive finishes.
The side chains of the branched polymer are hydrophobic relative to the
backbone and therefore contain less than 1% by weight , preferably essentially
zero
percent by weight, based on the weight of the branched polymer, of polymerized
3 5 ethylenically unsaturated acid-functional monomers which are listed
hereinafter. The
side chains contain polymerized hydrophobic monomers such as alkyl
methacrylates
and acrylates, cycloaliphatic methacrylates and acrylates and aryl
methacrylates and
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acrylates and styrene as are listed hereinafter and also may contain up to 30%
by
weight, based on the weight of the branched polymer, of polymerized
ethylenically
unsaturated non-hydrophobic monomers which may contain functional groups.
Examples of such monomers are hydroxy ethyl acrylate, hydroxy ethyl
methacrylate,
acrylamide, nitro phenol acrylate, nitro phenol methacrylate, phthalimido
methyl
acrylate, phthalimido methacrylate, acryloamido propane sulfonic acid, and
mixtures
thereof.
The acrylic macromonomer may be prepared using a free radical
initiator in a solvent with a Co (II) or Co (~ chelate chain transfer agent.
The backbone of the branched polymer contains at least 2 percent by
weight of an acid functional (neutralized) monomer as, e.g., acrylic acid,
methacrylic
acid, malefic acid, itaconic acid and the like. Methacrylic and acrylic acid
are
preferred. Other acids that can be used are ethylenically unsaturated
sulfonic, sulfinic,
phosphoric or phosphoric acid and esters thereof; typically, styrene sulfonic
acid,
acrylamido methyl propane sulfonic acid, vinyl phosphoric or phosphoric acid
and its
esters and the like also can be used.
The backbone of the branched polymer preferably contains 2-30% by
weight methacrylic acid or acrylic acid and preferably, 3 to 1 S% by weight
and has a
MW of 1,000-70,000. The acid functional groups on the branched polymer are
2 0 neutralized with an inorganic base or an amine. The backbone is thus
relatively
hydrophilic in comparison to the side chains and the branched polymer keeps
the
hydrophobic constituents well dispersed in the resulting coating composition.
Of
course, relative hydrophobicity or hydrophilicity of the backbone and side
chains of the
branched polymer could be further adjusted by varying the percent of acid
and/or
2 5 hydroxy functional monomers versus more hydrophobic monomers such as 2-
ethyl
hexyl methacrylate.
In one preferred embodiments, the branched polymer contains overall
(including both backbone and macromonomer arms) about 0 to 40, preferably 5 to
40,
and more preferably 10 to 30, percent of hydroxy functional acrylic monomers
as, e.g.,
3 0 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl
acrylate, 2-
hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate
and the
like. These hydroxy groups can be used for crosslinking in addition to the
acid
groups. Hydroxy groups are not necessary when acid groups are the only
crosslinking functionality on the copolymer. Hydroxy groups are necessary when
the
3 5 cross-linking agent of the coating composition is a melamine or a blocked
polyisocyanate.
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As indicated earlier, the branched polymer comprises macromonomer
side chains attached to a polymeric backbone. Each macromonomer ideally
contains a
single terminal ethylenically unsaturated group which is polymerized into the
backbone
of the branched polymer and typically contains polymerized monomers of
styrene,
5 esters and/or nitriles and/or amides of methacrylic or acrylic acid or
mixtures of these
monomers.
Other polymerized ethylenically unsaturated monomers can be present
in the macromonomer and backbone, for example (but not limited to), acrylic
and
methacrylic acid esters of straight-chain or branched monoalcohols of 1 to 20
carbon
to atoms. Alkyl acrylates and methacrylates having 1-12 carbons in the alkyl
group can
be used such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl
acrylate,
butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethyl hexyl acrylate, nonyl
acrylate,
lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate,
isopropyl
methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-
ethyl
hexyl methacrylate, nonyl methacrylate, lauryl methacrylate and the like can
be used.
Cycloaliphatic acrylates methacrylates can be used such as trimethylcyclohexyl
acrylate, t-butyl cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl
methacrylate,
2-ethylhexyl methacrylate, and the like. Aryl acrylates and methacrylates such
as
benzyl acrylate and benzyl methacrylate also can be used.
2 0 Ethylenically unsaturated monomers containing hydroxy functionality
include hydroxy alkyl acrylates and hydroxy alkyl methacrylates, wherein the
alkyl has
1 to 12 carbon atoms. Suitable monomers include hydroxy ethyl acrylate,
hydroxy
propyl acrylate, hydroxy isopropyl acrylate, hydroxy butyl acrylate, hydroxy
ethyl
methacrylate, hydroxy propyl methacrylate, hydroxy isopropyl methacrylate,
hydroxy
2 5 butyl methacrylate, and the like, and mixtures thereof.
Suitable other olefinically unsaturated comonomers include:
acrylamide and methacrylamide and derivatives as allcoxy methyl (meth)
acrylamide
monomers, such as methacrylamide, N-isobutoxymethyl methacrylamide, and N-
methylol methacrylamide; malefic, itaconic and fumaric anhydride and its half
and
3 o diesters; vinyl aromatics such as styrene, alpha methyl styrene and vinyl
toluene; and
polyethylene glycol monoacrylates and monomethacrylates.
The above monomers also can be used in the backbone of the branched
polymer.
The branched polymer may be prepared by polymerizing ethylenically
3 5 unsaturated monomers in the presence of macromonomers each having a
terminal
ethylene unsaturation. The resulting branched polymer can be envisioned as
being
composed of a backbone having a plurality of macromonomer "arms" attached
thereto.
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In the present composition, both the macromonomer arms and the backbone may
have
reactive functionality capable of reacting with a crosslinking compound or
polymer,
although it is optional to have such reactive functionality only or
essentially only or
substantially only on the backbone.
It is to be understood that the backbone or macromonomers referred
to as having functionality may be part of a mixture of macromonomers of which
a
portion do not have any functionality or variable amounts of functionality. It
is also
understood that, in preparing any backbone or macromonomers, there is a normal
distribution of functionality.
to To ensure that the resulting macromonomer only has one terminal
ethylenically unsaturated group which will polymerize with the backbone
monomers to
form the branched polymer, the macromonomer is polymerized by using a
catalytic
chain transfer agent. Typically, in the first step of the process for
preparing the
macromonomer, the monomers are blended with an inert organic solvent which is
water miscible or water dispersible and a cobalt chain transfer agent and
heated usually
to the reflux temperature of the reaction mixture. In subsequent steps
additional
monomers and cobalt catalyst and conventional polymerization catalyst are
added and
polymerization is continued until a macromonomer is formed of the desired
molecular
weight.
2 o Preferred cobalt chain transfer agents or catalysts are described in US
Patent 4,680,352 to Janowicz et al and US Patent 4,722,984 to Janowicz. Most
preferred are pentacyanocobaltate (II), diaquabis(borondifluorodimethyl-
glyoximato)
cobaltate(II) and diaquabis(borondifluorophenyl glyoximato} cobaltate (11).
Cobalt
(III) versions of these catalysts are also preferred. Typically these chain
transfer
2 5 agents are used at concentrations of about 5-1000 ppm based on the
monomers used.
The macromonomer is preferably formed in a solvent or solvent blend
using a free radical initiator and a Co (11) or (III) chelate chain transfer
agent.
Examples of solvents are aromatics, aliphatics, ketones, glycol ethers,
acetates,
alcohols as, e.g., methyl ethyl ketone, isopropyl alcohol, n-butyl glycol
ether, n-butyl
3 o diethylene glycol ether, propylene glycol methyl ether acetate, propylene
glycol methyl
ether, and N-butanol.
Peroxy- and azo-initiators (0.5-5% weight, based on the weight of the
monomer) can be used in the synthesis of the macromonomers in the presence of
2-
5,000 ppm (on total monomer) or Co (II) chelate in the temperature range
between
35 70-160°C, more preferably azo-type initiators as, e.g., 2,2'-azobis
(2,4
dimethylpentane nitrite), 2,2'-azobis (2-methylpropane nitrite), 2,2'-azobis
(2-
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methylbutane nitrite), 1,1'-azo (cyclohexane carbonitrile) and 4,4'-azobis (4-
cyanopentanoic) acid.
After the macromonomer is formed as described above, solvent is
optionally stripped off and the backbone monomers are added to the
macromonomer
along with additional solvent and polymerization catalyst. Any of the
aforementioned
azo-type catalysts can be used as can other suitable catalysts such as
peroxides and
hydroperoxides. Typical of such catalysts are di-tertiarybutyl peroxide, di-
cumyl
peroxide, tertiary amyl peroxide, cumene hydroperoxide, di(n-propyl)
peroxydicarbonate, peresters such as amyl peroxyacetate and the like.
Commercially
to available peroxy type initiators include, e.g., t-butyl peroxide or
Triganox~ B from
AKZO, t-butyl peracetate or Triganox~ FC50 from AKZO, t-butyl perbenzoate or
Triganox~ C from AKZO, and t-butyl perpivalate or Triganox~ 25 C-75 from AKZO.
Polymerization is continued at or below the reflux temperature of the
reaction mixture until a branched polymer is formed of the desired molecular
weight.
Typical solvents that can be used to form the macromonomer or the
branched polymer are ketones such as methyl ethyl ketone, isobutyl ketone,
ethyl amyl
ketone, acetone, alcohols such as methanol, ethanol, isopropanol, esters such
as ethyl
acetate, glycols such as ethylene glycol, propylene glycol, ethers such as
tetrahydrofuran, ethylene glycol mono butyl ether and the like.
2 0 In the synthesis of the macromonomer and/or the branched polymer
small amounts of difunctional alpha-beta unsaturated compounds can be used as,
e.g.,
ethylene glycol dimethacrylate or hexane diol diacryIate.
After the branched polymer is formed, it is neutralized with an amine or
an inorganic base such as ammonium hydroxide or sodium hydroxide and then
water is
2 5 added to form a dispersion. Typical amines that can be used include AMP {2-
amino-2-
methyl-1-propanol), dimethyl-AMP, amino methyl propanol, amino ethyl propanol,
dimethyl ethanol amine, triethylamine and the like. One preferred amine is
amino
methyl propanol and the preferred inorganic base is ammonium hydroxide.
The conversion into a water dispersion may be accomplished preferably
3 o by stripping our 30 to 60% of the solvent followed by admixing with an
organic amine
or ammonia and diluting with water, or by admixing with a solution of water
and
amine after the solvent stripping. Alternatively, the branched polymer
solution, after
stripping, can be stirred slowly into a solution of water and the amine. The
degree of
neutralization of the dispersion can be from 10 to 150% of the total amount of
acid
3 5 groups, preferably from 40-100%. The final pH of the dispersion can
accordingly be
about 4-10, preferably 7-9. The solvents can be stripped-off eventually
afterwards.
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The overall branched polymer water borne dispersion should be
characterized by an acid value of from 5 to about 150 (mg KOH/g resin solids),
more
preferably from 10 to about 70 and still more preferably from 15 to about 35,
and an
hydroxyl number of about 0 to about 250 (mg KOH/g resin solids), more
preferably
from 40 to 150.
Particularly useful branched polymers include the following:
a branched polymer having a backbone of polymerized acrylate or
methacrylate monomers, styrene monomers, methacrylic or acrylic acid monomers,
and hydroxy-functional acrylate or methacrylate monomers, and side chains of a
l0 macromonomer having a weight average molecular weight of about 2,000-30,000
and
containing about 50% by weight, based on the weight of the backbone, of
polymerized
alkyl methacrylate or acrylate monomers, hydroxy-functional acrylate or
methacrylate
monomers and 2-30 % by weight, based on the weight of the backbone, of
polymerized methacrylic acid or acrylic acid.
a branched polymer having the above backbone of side chains
comprising polymerized methyl methacrylate, butyl acrylate, methacrylic acid,
styrene,
and hydroxyethyl acrylate.
a branched polymer having the above backbone and macromonomers
comprising polymerized 2-ethylhexyl acrylate, butyl methacrylate, and
hydroxyethyl
2 o methacrylate.
a branched polymer having the above backbone and macromonomers of
isobutyl methacrylate, 2 ethyl hexyl methacrylate and hydroxy ethyl
methacrylate.
The branched polymer is used as a dispersing resin to form an aqueous
2 5 dispersion of a wide variety of hydrophobic materials that are commonly
used in
waterborne coating compositions. Typical hydrophobic materials include
hydrophobic
melamine resins, hydrophobic polyesters, hydrophobic acrylic polymers,
hydrophobic
polyurethanes, blocked organic polyisocyanates and mixtures of any of the
above.
Typical hydrophobic melamines include partially or fully alkylated
30 melamine formaldehyde resins having 1-4 carbon atoms in the alkylated group
and that
can be monomeric or polymeric having a degree of polymerization of about 1-3.
Typical alcohols that are used to alkylate these melamines are methanol,
ethanol,
propanol, butanol, isobutanol and the like. Typical commercially available
melamine
resins are as follows: "Cymel" 373, "Cymel" 385, "Resimine" 745, BM 7512 from
35 Monsanto Corporation, HM 2608 from Monsanto Corporation, and BM 9539 from
Monsanto Corporation.
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Typical hydrophobic acrylic resins comprise polymers of alkyl
methacrylates and acrylate, hydroxy alkyl acrylates and methacrylates and
styrene such
as a polymer of styrene, butyl methacrylate, butyl acrylate and hydroxy propyl
acrylate.
Typical hydrophobic polyester resins are the esterification product of an
aromatic dicarboxylic acid or an anhydride thereof and a polyol such as a
polyester of
phthalic anhydride, isophathalic acid, neopentyl glycol and trimethylol
propane.
Typical blocked organic polyisocyanates that can be used are aliphatic
polyisocyanates, aromatic polyisocyanate, cycloaliphatic polyisocyanates
blocked with
alcohols, ketimines, oximes and the like.
Typical hydrophobic polyurethanes include hydrophobic polyesters
reacted with a polyisocyanate, hydrophobic acrylic polymers having reactive
hydroxyl
groups reacted with a polyisocyanate.
Cellulose acetate butyrate polymers such as CAB's from Eastman
Chemical Company can be dispersed in aqueous compositions with the branched
polymer and formulated into a waterborne coating composition.
The preferred method for forming the waterborne dispersion of this
invention is to add with agitation the hydrophobic material to be dispersed to
a solvent
solution of the branched polymer before it is neutralized and dispersed in
water and the
neutralizing agent of amine or base is added with agitation. Water then is
added and
2 o mixed in to form the aqueous dispersion. The resulting dispersion has a
yield stress of
about 0-1,000 Pa (Pascals), a low (20 sec-1) shear viscosity of about 100-
10,000 m
Pas (milli Pascal seconds) and a high shear (1000 sec -1) viscosity of about
10-1,000
m Pas measured on a Rotvfisco viscometer.
An alternative method for forming the water bore dispersion of this
invention is to neutralized the branched polymer with amine or base and add
water
with constant agitation and the hydrophobic material to be dispersed to form a
dispersion.
Waterborne coatings in which the dispersions of the present invention
are used may optionally contain a latex of an acrylic-based polymer. These
latexes are
3 o stable dispersions in water, typically as a dispersed latex polymer has an
average
particle size diameter of 10 nm to 1 micron, preferably 20 to 400 nm. These
coating
compositions contain about 10-70%, more typically 15-50% by weight of binder,
and
about 30-90%, more typically 50-85% by weight, of an aqueous carrier. The
carrier is
at least 50% water, preferably 75 to 95% water. Suitable waterborne coatings
are
3 5 prepared by blending other useful components in accordance with normal
paint
formulation techniques.
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To form a coating composition which will crosslink under elevated
baking temperatures of about 60-180°C for abut 5-60 minutes, about 10
to 40~/0,
preferably 15 to 30% by weight, based on the weight of the binder, of a water-
soluble
water dispersible alkylated melamine formaldehyde crosslinking agent having 1-
4
5 carbon atoms on the alkylated group can be used or a dispersion of a
hydrophobic
alkylated melamine formaldehyde resin of this invention can be used. These
crosslinking agents are generally partially alkylated melamine formaldehyde
compounds and may be monomeric or polymeric as described above.
These coating compositions containing a melamine crosslinking agent
io preferably contain about 0.1 to 1.0%, based on the weight of a binder, of a
strong acid
catalyst or a salt thereof to lower curing temperatures and time. Paratoluene
sutfonic
acid is a preferred catalyst or its ammonium salt. Other catalysts that can be
used are
dodecyl benzene sulfonic acid, phosphoric acid and amine or ammonium salts of
these
acids.
Although the dispersion of this invention is aqueous, a solvent can be
utilized, preferably in minimal amounts, to facilitate formulation and
application of the
coating compositions formulated with these dispersions. An organic solvent is
utilized
which is compatible with the components of the composition.
In addition, coating composition utilizing the dispersion of the present
2 o invention may contain a variety of other optional ingredients, including
pigments,
fillers, plasticizers, antioxidants, surfactants and flow control agents.
Typical pigments that are used are metallic oxides such as titanium
dioxide, iron oxides of various colors, zinc oxide, carbon black, filler
pigments such as
talc, china clay, barytes, carbonates, silicates and a wide variety of organic
colored
2 5 pigments such as quinacridones, copper phthalocyanines, perylenes, azo
pigments,
indanthrone blues, carbazoles such as carbazole violet, isoindolinones,
isoindolones,
thioindigo reds, benzimilazolinones, and metallic flake pigments such as
aluminum
flake, nickel flake, pearlescent pigments and the like.
To improve weatherability of a finish formed from such coating
3 o compositions, an ultraviolet light stabilizer or a combination of
ultraviolet light
stabilizers can be added in the amount of about 0.1-5% by weight, based on the
weight
of the binder. The stabilizer may be added for example to a dispersion of this
invention containing hydrophobic material or may be added directly to the
coating
composition or to pigment dispersions used to formulate the coating
composition.
3 5 Such stabilizers include ultraviolet light absorbers, screeners,
quenchers, and specific
hindered amine light stabilizers. Also, an anitoxidant can be added, in the
about 0.1-
5% by weight, based on the weight of the binder.
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Typical ultraviolet light stabilizers that are useful include
benzophenones, triazoles, triazines, benzoates, hindered amines and mixtures
thereof.
Specific examples of ultraviolet stabilizers are disclosed in U.S. Patent
4,591,533, the
entire disclosure of which is incorporated herein by reference.
Such coating composition may also include conventional formulation
additives such as flow control agents, for example, "Resiflow" S
(polybutylacrylate),
BYK 320 and 325 (high molecular weight polyacrylates); rheology control
agents,
such as fumed silica and thickeners such as the Acrylsol~ copolymers from Rohm
&
Haas.
l0 Coating compositions formulated with the dispersion of this invention
have excellent adhesion to a variety of metallic or non-metallic substrates,
such as
previously painted substrates, cold rolled steel, phosphatized steel, and
steel coated
with conventional primers by electrodeposition. These coating composition can
be
used to coat plastic substrates such as polyester reinforced fiberglass,
reaction
injection-molded urethanes and partially crystalline polyamides. These coating
compositions may be used a pigmented monocoats, as clear coats, as the
pigmented
base coat of a clear coatJbase coat or as both the clear coat and the base
coat.
Coating compositions formulated with the dispersion of this invention
can be applied by conventional techniques such as spraying, electrostatic
spraying,
2 o dipping, brushing, flowcoating and the Like. The preferred techniques are
spraying and
electrostatic spraying. In OEM applications, the composition is typically
baked at
100-150°C for about 15-30 minutes to form a coating about 0.1-3.0 mils
thick. When
the composition is used as a clearcoat, it is applied over the color coat
which may be
dried to a tack-free state and cured or preferably flash dried for a short
period before
the clearcoat is applied. The color coat/clearcoat finish is then baked as
mentioned
above to provide a dried and cured finish. The present invention is also
applicable to
non-baking refinish systems, as will be readily appreciated by those skilled
in the art.
It is customary to apply a clear topcoat over a basecoat by means of a
"wet-on-wet" application, i.e., the topcoat is applied to the basecoat without
curing or
3 o completely drying the basecoat. The coated substrate is then heated for a
predetermined time period to allow simultaneous curing of the base and clear
coats.
The following Examples illustrate the invention. All parts and
percentages are on a weight basis unless otherwise indicated. All molecular
weights
disclosed herein are determined by GPC (gel permeation chromatography) using a
3 5 polystyrene standard.
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EXAMPLE 1
A branched polymer was prepared by first preparing a macromonomer
and then polymerizing the macromonomer with monomers that form the backbone of
the branched polymer. A dispersion was then prepared from the branched
polymer.
Preparation of the macromonomer
A macromonomer of 5% IBMA (isobutyl methacrylate), 20% HEMA
(hydroxyethyl methacrylate), and 75% 2F.,HMA (2-ethyl hexyl methacrylate), for
use in
a preparing a branched polymer was prepared as follows: to a 2-liter flask
fitted with
an agitator, condenser, heating mantle, nitrogen inlet, thermocouple and an
addition
port was added 15.25 g of IBMA monomer, 228.94 g of 2-EHMA monomer, 61.078
of HEMA monomer and 251.3 g of propylene glycol monomethyl ether. The mixture
was agitated and heated to reflux (128 - 135 °C) under nitrogen. To
this was then
added, as a shot, a pre-mix of a solution of 0.5 g of Vazo~ 88 initiator [ 1,1
azobis(cyanocyclohexane)]. I3.8 g of propylene glycol monomethyl ether and
26.1 g
of a 0.17% solution of bis(boron difluoro diphenyl glyoximato) cobaltate(II)
in ethyl
acetate. This was followed by the addition of a pre-mix of a solution of 22.87
g of
IBMA monomer, 343.42 g of 2-EHMA monomer, 91.61 g of HEMA monomer, 2 g of
Vazo~ 88 initiator, 10.0 g of ethyl acetate, 70.6 g of propylene glycol
monomethyl
ether over 240 minutes while maintaining a reflux temperature. (I 16-
122° C).
2 o Following a 30 min. hold period, a pre-mixed solution of 0.4 g of Vazo~ 88
initiator,
4.95 g of ethyl acetate and 18 g of propylene glycol monomethyl ether was
added over
60 rains. while maintaining reflux. The batch was then held at reflux for an
additional
60 rains. at which time a mixture of 0.3 g of t-butyl peroctoate and 33.35 g
of ethyl
acetate were added as a single add and then the reaction mixture was cooled.
The
2 5 macromonomer thus prepared has a number average molecular weight of 5322
and a
weight average molecular weight of about 7627 as determined by GPC, weight
solids
are 61.9% and Gardner viscosity of U. The percent terminal vinyl unsaturation
is
greater than 95 as determined by thermogravimetric analysis.
Preparation of branched pol m~er
3 o To a 2-liter flask fitted with an agitator, condenser, heating mantle,
nitrogen inlet, thermocouple and an addition port was added 305.01 g of the
macromonomer prepared above and 296.06 g of propylene glycol monomethyl ether
and the temperature raised to reflux (110-115° C) under nitrogen. This
was followed
by the addition of a premixed solution of 122.98 g of methyl methacrylate
monomer
3 5 (MMA), 91. I g of styrene monomer (STY), 91.1 g of hydroxy ethyl acrylate
monomer
(IAA), 118.42 g of butyl acrylate monomer (BA), 3 I .88 g methacrylic acid
monomer
(MAA), 8.2 g t-butyl peracetate and 86.54 g butyl acetate over 180 minutes
holding
CA 02321798 2000-08-22
WO 99/45078 PCTNS98/04352
13
temperature at reflux and then cooling the reaction mixture to room
temperature. The
branched polymer has a number average molecular weight of 14,710 and a weight
average molecular weight of 37,190. Weight solids are 53.3% and Gardner
viscosity
is Y. The ration of backbone to macromonomer arms is about 60/40. The
composition of the backbone is MMAJSTYBA/I~A/MAA in the weight ratio of
27/20/26/20/7.
Preparation of waterborne dispersion of branched polymer and
hydrophobic melamine
To a 2-liter flask fitted with an agitator, condenser, heating mantle,
nitrogen inlet, thermocouple and an addition port was added 500 g of branched
polymer prepared above and the temperature raised to distill 133 g of solvent.
The ,
batch was cooled to less than 50° C at which time a 41.95 g of a 30%
solution of
ammonia in water was added to neutralize the acid functionality of the branch
polymer. The batch was agitated for 10 mins. at which time 124.06 g. of a
butylated
melamine resin (BM 7512 from Monsanto Corp.) and 1.5 g heptane were added and
the mixture was agitate for 15 minutes. At this time 588.28 g deionized water
was
slowly added over 60 minutes with good agitation and the resulting dispersion
was
cooled to room temperature. A white, stable dispersion of the branched polymer
and
butylated melamine was obtained having a total weight solids 35% (24.5%
branched
2 o polymer and 10.5% butylated melamine), Gardner viscosity A, pH 8.31 and a
particle
size of 140 nanometers as determined by quasi electric light scattering. No
phase
separation of the butylated melamine was noted on standing at room temperature
over
30 days.
EXAMPLE 2
2 5 Another waterborne dispersion of the branched polymer of Example 1
but with a different butylated melamine was prepared. 133.93 g of hydrophobic
butylated melamine (HNI 2608 from Monsanto) was used. A white, stable
dispersion
of the branched polymer and butylated melamine was obtained having a total
weight
solids 35% (24.5% branched polymer and 10.5% butylated melamine}, Grardner
3 o viscosity A, pH 8.31 and a particle size of 45 nanometers as determined by
quasi
electric light scattering. No phase separation of the butylated melamine was
noted on
standing at room temperature over 30 days.
EXAMPLE 3
A third waterborne dispersion of the branched polymer of Example 1
3 5 and a different butylated melamine was prepared. 110.92 g of hydrophobic
butylated
melamine (BM 9539 from Monsanto) was used. A white, stable dispersion of the
branched polymer and butylated melamine was obtained having a total weight
solids
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WO 99/45078 PCT/US98/04352
14
35% (24.5% branched polymer and 10.5% butylated melamine), Gardner viscosity A
ID, pH 8.2 and a particle size of 116 nanometers as determined by quasi
electric light
scattering. No phase separation of the butylated melamine was noted on
standing at
room temperature over 30 days.
EXAMPLE 4
Prep,~r taa 'on of a branched ~3rmer
To a 5-liter flask fitted with an agitator, condenser, heating mantle,
nitrogen inlet, thermocouple and an addition port was added 1762.0 g of
macromonomer from Example 1 above, 237.96 g of hexanol and the temperature
1o raised to 99-IOI°C under nitrogen. This was followed by the addition
of a premixed
solution of 392.8 g of MMA, 224.5 g of STY, 168.3 g HEA, 224. 5 g of BA, 112.2
g
MAA, 12.4 g of Vazo~88 initiator, 145.9 g of propylene glycol monomethyl ether
and
145.9 g of butyl acetate over 120 min. holding the temperature at 99-
101°C. This was
followed by a hold period of 60 min. at which time the temperature was reduced
to
90°C over a 30 minute period and the reaction mixture was held at this
temperature of
an additional 270 minutes and cooled to room temperature. The number average
molecular weight of the branched polymer was 9080 and the weight average
molecular
weight was 17800. The weight solids are 64.4% and the Gardner viscosity is Z2.
The
composition of the backbone is MMA/STY/I~A/BAJMAA in the weight ratio of
35/20/15/20/10 and the weight ratio of backbone to macromonomer about 40/60.
Preparation of waterborne dispersion of branched polymer and
a water immiscible polyester
To a 2-liter flask fitted with an agitator, condenser, heating mantle,
nitrogen inlet, thermocouple and an addition port was added 300 g of branched
polymer prepared above and the temperature raised to distill 58.3 g of
solvent. The
batch was cooled to less than 80° C at which time a 7.96 g of dimethyl
ethanol amine
and 15.0 g water were added to neutralize the acid functionality of the branch
polymer. The batch was agitated for 1 S rains. at which time 118.4 g. of a
polyester of
a composition of (in equivalents) phthalic anhydride (0.528)/ isophthalic acid
(0.471)/
3 o neopentyl glycol (0.819)/ trimethylol propane (0.057)/ MPDIOL (0.236) diol
from
Arco Chemical. The polyester was a 69.8% solids solution in methyl amyl ketone
and
the polyester has a hydroxyl number of 58, and a number average molecular
weight of
2115 and a weight average molecular weight of 5066. After the polyester was
added
the composition was agitated for 15 minutes and then 840.1 g deionized water
was
slowly added over a 30 minute period with good agitation and the dispersion
was
cooled to room temperature. A white, stable dispersion of the branched polymer
and
the polyester was obtained having a total weight solids 25% (17.5% branched
CA 02321798 2000-08-22
WO 99/45078 PCT/US98/04352
polymer and 7.5% polyester), Gardner viscosity A3, pH 8.6 and a particle size
of 260
nanometers as determined by quasi electric light scattering. No phase
separation of
the polyester was noted on standing at room temperature over 30 days.
EXAMPLE 5
5 Pr~aration of waterborne dispersion of branched polymer and
a water immiscible acrylic ~lymer
To a 2-liter flask fitted with an agitator, condenser, heating mantle,
nitrogen inlet, thermocouple and an addition port was added 300 g of branched
polymer prepared above Example 12 and the temperature raised to distill 58.3 g
of
to solvent. The batch was cooled to less than 80° C at which time a
7.96 g of dimethyl
ethanol amine and 15.0 g water were added to neutralize the acid functionality
of the
branch.polymer. The batch was agitated for 15 rains. at which time 118.4 g. of
an
acrylic polymer of a composition of styreneJbutyl methacrylate/butyl
acrylate/hydroxy
propyl acrylate ( weight ratio of 15/30/17/38), 70% solids in Solvesso TM
(Shell
15 Chemical) and the acrylic polymer has a number average molecular weight
2300 and
weight average molecular weight 6220 was added and the mixture agitated for 15
minutes. and then 840.1g deionized water was slowly added over a 30 minute
period
with good agitation and the dispersion was cooled to room temperature. A
white,
stable dispersion of the branched polymer and the acrylic polymer was obtained
having a total weight solids 25% (17.5% branched polymer and 7.5% polyester),
Gardner viscosity A3, pH 8.68 and a particle size of 133 nanometers as
determined by
quasi electric light scattering. No phase separation of the acrylic polymer
was noted
on standing at room temperature over 30 days.
Various modifications, alterations, additions or substitutions of the
2 5 components of the compositions of this invention will be apparent to those
skilled in
the art without departing from the scope and spirit of this invention. This
invention is
not limited to the illustrative embodiments set forth herein, but rather the
invention is
defined by the following claims.
