Note: Descriptions are shown in the official language in which they were submitted.
'. ~ ~~3~7635 _
TWO-COMPONENT AQUEOUS POLYURETHANE DISPERSIONS
BACKGROUND OF THE INVENTION
_Field of the Invention
The present invention relates to two-component
aqueous polyurethane dispersions which may be cured at ambient
temperature and to the coatings prepared therefrom which have
excellent hardness, flexibility and solvent resistance.
pescrintion of the Prior Art
Aqueous polyurethane dispersions and their use for
to the production of coatings is known. The dispersions may be
cured at ambient temperature by evaporation of water and
coalescence of the individual polyurethane particles. These
aqueous-based products have been developed in an effort to
reduce the amount of organic solvents which are present in
corresponding solvent-based coating compositions. Even though
the prior art dispersions possess many valuable properties, it
has not been possible to obtain coatings which possess all of
the properties of coatings obtained from solvent-based coating
compositions, especially hardness and solvent resistance.
2o The known aqueous polyurethane dispersions do not
possess the amount of crosslinking which is required to obtain
these properties. One method of increasing the amount of
crosslinking is to blend the polyurethane dispersion with a
water dispersible, blocked polyisocyanate as disclosed in U.S.
Patent 4,098,933. U.S. Patent 4,608,413 discloses the use of
water dispersible, blocked polyisocyanates in combination with
polyurethanes which contain hydroxyl groups as crosslinking
sites. While the systems disclosed in these patents make it
possible to obtain improved hardness and crosslinking, they
3o suffer from the disadvantage that the coating compositions must
Mo3476CIP
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be heated to high temperatures in order to release the blocking
agent and initiate crosslinking. Obviously, these coating
compositions are not suitable for application to substrates
which cannot withstand the unblocking temperature of the
polyisocyanate.
Accordingly, it is an object of the present invention
to provide aqueous polyurethane dispersions which may be cured
at ambient temperature to provide coatings with excellent
hardness, flexibility and solvent resistance.
l0 This object may be achieved in accordance with the
present invention as set forth hereinafter by the use of
two-component coating compositions wherein one component is an
aqueously dispersed, hydroxy functional polyurethane and the
second component is a water dispersible, unblocked
polyisocyanate.
Previously, it was known from U.S. Patent 4,663,377
to modify aqueous polyurethane adhesive dispersions by the
addition of water dispersible, unblocked polyisocyanates.
German Offenlegungsschrift 3,728,140 teaches that an
improvement in the heat activation temperature of the adhesive
dispersions may be obtained by chain extending the polyurethane
with a monoamine containing at least one hydroxyl group.
Neither of these references suggest the use of the aqueous
dispersions as coating compositions. In fact, it is surprising
that the two-component dispersions according to the present
invention can be used to prepare acceptable coatings. It would
be expected that a portion of the isocyanate groups of the
water dispersible polyisocyanate would react with the water
present in the aqueous dispersions instead of the hydroxyl
groups of the polyurethane because the reactivity of isocyanate
groups with water and hydroxyl groups is similar. Because the
isocyanate/water reaction produces carbon dioxide as a
by-product, it would also be expected that some of the carbon
dioxide would be trapped in the form of bubbles within the
resulting coating rendering it unacceptable for further use.
Mo3476CIP
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However, it has surprisingly been found that it is possible to
obtain bubble-free coatings in accordance with the present
invention.
SUMMARY OF THE INVENTION
The present invention relates to a two-component,
aqueous polyurethane coating composition which may be cured at
ambient temperature and which contains
I) a first component based on an aqueously dispersed
polyurethane wherein the polyurethane has
a) an average hydroxy functionality of at least 1.8,
b) a total content of urethane and urea groups,
calculated as -NH-C-0-, of 9 to 20% by weight, based on
the weight of the polyurethane,
c) 0 to 200 milliequivalents of chemically incorporated
anionic groups per 100 g of polyurethane and
d) 0 to 25% by weight, based on the weight of the
polyurethane, of ethylene oxide units incorporated within
terminal and/or lateral polyether chains,
wherein components c) and d) are present in an amount which is
2o sufficient to maintain the polyurethane stably dispersed in
water, and
II) a second component based on a water dispersible
polyisocyanate wherein the polyisocyanate has
a) an isocyanate content of 2 to 30% by weight, based on
the weight of the polyisocyanate,
b) an average functionality of at least 1.8,
c) 0 to 200 milliequivalents of chemically incorporated
anionic groups per 100 g of polyisocyanate and
d) 0 to 25% by weight, based on the weight of the
polyurethane, of ethylene oxide units incorporated within
terminal and/or lateral polyether chains,
wherein components components c) and d) are present in an
amount which is sufficient to maintain the polyisocyanate
stably dispersed in water, and
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components I and II are present in an amount sufficient to
provide an equivalent ratio of isocyanate groups to hydroxyl
groups of 0.8:1 to 6:1.
The present invention is also directed to the
coatings prepared from these coating compositions.
DETAILED DESCRIPTION OF THE INVENTION
The hydroxy functional polyurethanes used in
conjunction with the water dispersible polyisocyanates in
accordance with the present invention have an average hydroxy
functionality of at least 1.8, preferably 1.8 to 8, more
preferably 2 to 6 and most preferably 2.5 to 6; a total content
of urethane and urea groups of 9 to 20~ by weight, preferably
about 10 to 179 by weight; and an average hydroxy equivalent
weight (which may be calculated by an end group analysis) of
about 100 to 5000, preferably 500 to 4000 and more preferably
1000 to 3000.
The hydroxy functional polyurethanes are based on the
reaction product of organic polyisocyanates with a high
molecular weight polyols, optionally low molecular weight,
isocyanate-reactive compounds, and at least one of isocyanate-
reactive compounds which contain anionic or potential anionic
groups and isocyanate-reactive compounds containing nonionic
hydrophilic groups. The reactants and their amounts are
selected to ensure that the resulting polyurethane is hydroxy
functional.
Suitable polyisocyanates for preparing the hydroxy
functional polyurethane include any organic polyisocyanate,
preferably monomeric diisocyanates. Especially preferred are
polyisocyanates, especially diisocyanates, having
aliphatically- and/or cycloaliphatically-bound isocyanate
groups, although polyisocyanates having aromatically-bound
isocyanate groups are not excluded and may be used.
Examples of suitable polyisocyanates which may be
used include ethylene diisocyanate, 1,4-tetramethylene
diisocyanate, 1,6-hexamethylene diisocyanate, 2,4,4-trimethyl-
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1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate,
cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and/or
-1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl
cyclopentane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl
cyclohexane (isophorone diisocyanate or IPDI), 2,4- and/or
2,6-hexahydrotoluylene diisocyanate, 2,4'- and/or
4,4'-dicyclohexylmethane diisocyanate, a,a,a',a'-tetramethyl-
1,3- and/or -1,4-xylylene diisocyanate, 1,3- and 1,4-xylylene
diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl-
l0 cyclohexane, 1,3- and 1,4-phenylene diisocyanate, 2,4- and/or
2,6-toluylene diisocyanate, Biphenyl methane-2,4'- and/or
-4,4'-diisocyanate, naphthalene-1,5-diisocyanate, triphenyl
methane-4,4',4"-triisocyanate, polyphenyl polymethylene
polyisocyanates of the type obtained by condensing aniline with
formaldehyde followed by phosgenation, and mixtures of the
above-mentioned polyisocyanates.
Suitable high molecular weight polyols for preparing
the hydroxy functional polyurethane include those which are
known from polyurethane chemistry and have molecular weights
(Mn) of 400 to 6,000, preferably 400 to 3,000. Examples of the
high molecular weight compounds include:
1) polyhydroxy polyesters which are obtained from
polyhydric, preferably dihydric alcohols to which trihydric
alcohols may be added and polybasic, preferably dibasic
carboxylic acids. Instead of these polycarboxylic acids, the
corresponding carboxylic acid anhydrides or polycarboxylic acid
esters of lower alcohols or mixtures thereof may be used for
preparing the polyesters. The polycarboxylic acids may be
aliphatic, cyclocycloaliphatic, aromatic and/or heterocyclic
and they may be unsaturated and/or substituted, e.g. by halogen
atoms. Examples of these acids include succinic acid, adipic
acid, suberic acid, azelaic acid, sebacic acid, phthalic acid,
isophthalic acid, trimellitic acid, phthalic acid anhydride,
tetrahydropthalic acid anhydride, hexahydrophthalic acid
anhydride, tetrachlorophthalic acid anhydride, endomethylene
Mo3476CIP
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tetrahydrophthalic acid anhydride, glutaric acid anhydride,
malefic acid, malefic acid anhydride, fumaric acid, dimeric and
trimeric fatty acids such as oleic acid (which may be mixed
with monomeric fatty acids), dimethyl terephthalate and
bis-glycol terephthalate. Suitable polyhydric alcohols include
ethylene glycol, 1,2- and 1,3-propylene glycol, 1,3- and
1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl
glycol, diethylene glycol, 2-methyl-1,3-propylene glycol,
2,2-dimethyl-1,3-propylene glycol, the various isomeric
bis-hydroxymethyl cyclohexanes, 2,2,4-trimethyl-1,3-pentane-
diol, glycerine and trimethylol propane.
2) Polylactones generally known from polyurethane
chemistry, e.g., polymers of e-caprolactone initiated with the
above-mentioned polyhydric alcohols.
3) Polycarbonates containing hydroxyl groups such as the
products obtained from reaction of the polyhydric alcohols
previously set forth for preparing the polyhydroxy polyesters
(preferably dihydric alcohols such as 1,3-propanediol,
1,4-butanediol, 1,4-dimethylol cyclohexane, 1,6-hexanediol,
diethylene glycol, triethylene glycol or tetraethylene glycol)
with phosgene, diaryl carbonates such as Biphenyl carbonate or
cyclic carbonates such as ethylene or propylene carbonate.
Also suitable are polyester carbonates obtained by the reaction
of lower molecular weight oligomers of the above-mentioned
polyesters or polylactones with phosgene, diaryl carbonates or
cyclic carbonates.
4) Polyethers include the polymers obtained by the
reaction of starting compounds which contain reactive hydrogen
atoms with alkylene oxides such as propylene oxide, butylene
oxide, styrene oxide, tetrahydrofuran, epichlorohydrin or
mixtures of these alkylene oxides. Certain proportions of
ethylene oxide may also be included, provided the polyether
does not contain more than 10% by weight of ethylene oxide;
however, polyethers which do not contain ethylene oxide are
preferably used. Suitable starting compounds containing at
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least one reactive hydrogen atom include the polyols set forth
as suitable for preparing the polyhydroxy polyesters and, in
addition, water, methanol, ethanol, 1,2,6-hexanetriol,
1,2,4-butanetriol, trimethylol ethane, pentaerythritol,
mannitol, sorbitol, methyl glycoside, sucrose, phenol, isononyl
phenol, resorcinol, hydroquinone and 1,1,1- or 1,1,2-tris-
(hydroxylphenyl)ethane. Polyethers which have been obtained by
the reaction of starting compounds containing amino groups can
also be used, but are less preferred for use in the present
invention. Suitable amine starting compounds include ethylene
diamine, diethylene triamine, triethylene tetraamine,
1,6-hexanediamine, piperazine, 2,5-dimethyl piperazine,
1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, bis(4-amino-
cyclohexyl)methane, bis(4-amino-3-methylcyclohexyl)methane,
1,4-cyclohexanediamine, 1,2-propanediamine, hydrazine,
aminoacid hydrazides, hydrazides of semicarbazido carboxylic
acids, bis-hydrazides and bis-semicarbazides, ammonia,
methylamine, tetramethylenediamine, ethanolamine,
diethanolamine, triethanolamine, aniline, phenylenediamine,
2,4- and 2,6-toluylenediamine, polyphenylene polymethylene
polyamines of the kind obtained by the aniline/formaldehyde
condensation reaction and mixtures thereof. Resinous materials
such as phenol and cresol resins may also be used as the
starting materials. The preferred starting compounds for the
polyethers are those compounds which exclusively contain
hydroxyl groups, while compounds containing tertiary amine
groups are less preferred and compounds containing isocyanate-
reactive-NH groups are much less preferred.
Polyethers modified by vinyl polymers are also suitable
for the process according to the invention. Products of this
kind may be obtained by polymerizing, e.g., styrene and
acrylonitrile in the presence of polyethers (U. S. Patent Nos.
3,383,351; 3,304,273; 3,523,095; and 3,110,695; and German
Patent No. 1,152,536). Also suitable as polyethers are amino
polyethers wherein at least a portion of the hydroxyl groups of
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the previously described polyethers are converted to amino
groups.
5) Polythioethers such as the condensation products
obtained from thiodiglycol on its own and/or with other
glycols, dicarboxylic acids, formaldehyde, amino carboxylic
acids or amino alcohols. The products are either polythio
mixed ethers, polythio ether esters, or polythioether ester
amides, depending on the co-components.
6) Polyacetals including those obtained from the above
l0 mentioned polyhydric alcohols, especially diethylene glycol,
triethylene glycol, 4,4'-dioxyethoxy-diphenyldimethylene,
1,6-hexanediol and formaldehyde. Polyacetals suitable for use
in the invention may also be prepared by the polymerization of
cyclic acetals.
7) Polyether esters containing isocyanate-reactive
groups and known in the art.
8) Polyester amides and polyamides including the
predominantly linear condensates obtained from polyvalent
saturated and unsaturated carboxylic acids or their anhydrides
and polyvalent saturated and unsaturated amino alcohols,
diamines, polyamines, or mixtures thereof.
The preferred high molecular weight isocyanate-
reactive compounds for use in the process according to the
invention are the dihydroxy polyesters, dihydroxy polylactones,
dihydroxy polycarbonates and dihydroxy polyester carbonates.
Suitable low molecular weight isocyanate-reactive
compounds which may optionally be used in accordance with the
present invention have molecular weights of up to about 400 and
functionalities which correspond to those of the hydroxy
functional polyurethanes. Examples include the polyols and
diamines previously set forth for use in the preparation of the
polyhydroxy polyesters and the polyethers and the aminoalcohols
set forth hereinafter.
In order to make the hydroxy functional polyurethanes
water dispersible, it is necessary to chemically incorporate
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hydrophilic groups, i.e., anionic groups, potential anionic groups or
nonionic hydrophilic groups, into the polyisocyanate component. Suitable
hydrophilic components contain at least one isocyanate-reactive group
and at least one hydrophilic group or potential hydrophilic group.
Examples of compounds which may be used to incorporate potential ionic
groups include aliphatic hydroxy carboxylic acids, aliphatic or aromatic
aminocarboxylic acids with primary or secondary amino groups, aliphatic
hydroxy sulfonic acids and aliphatic or aromatic aminosulfonic acids with
primary or secondary amino groups. These acids preferably have
molecular weights below 400. It should be emphasized that the carboxylic
acid groups are not considered to be isocyanate-reactive groups due to
their sluggish reactivity with isocyanates.
The preferred anionic groups for incorporation into the hydroxy
functional polyurethanes in the present invention are carboxylate groups
and these groups may be introduced by using hydroxy-carboxylic acids of
the general formula:
(HO)XQ(COOH)y
wherein
Q represents a straight or branched, hydrocarbon radical
containing 1 to 12 carbon atoms, and
x and y represent values from 1 to 3.
Examples of these hydroxy-carboxylic acids include citric acid and tartaric
acid.
The preferred acids are those of the above-mentioned formula
wherein x = 2 and y = 1. These dihydroxy alkanoic acids are described in
U.S. Patent 3,412,054. The preferred group of dihydroxy alkanoic acids
are the a,a-dimethylol alkanoic acids represented by the structural
formula:
,..~n,.~,...
Mo3476C1 P
CH~,OH
Q'-C-COON
CH20H
-10-
wherein Q' is hydrogen or an alkyl group containing 1 to 8
carbon atoms. The most preferred compound is a,a-dimethylol
propionic acid, i.e, wherein Q' is methyl in the above formula.
The acid groups may be converted into hydrophilic
anionic groups by treatment with a neutralizing agent such as
an alkali metal salt, ammonia or a primary, secondary or
preferably tertiary amine in an amount sufficient to render the
hydroxy functional polyurethanes water dispersible. Suitable
alkali metal salts include sodium hydroxide, potassium
l0 hydroxide, sodium hydride, potassium hydride, sodium carbonate,
potassium carbonate, sodium bicarbonate and potassium
bicarbonate. The use of alkali metal salts as neutralizing
agents is less preferred than the use of volatile organic
compounds such as volatile amines since they lead to reduced
15 resistance to water swell in the coatings produced from the
water dispersible compositions of the present invention.
Therefore, less than 50%, preferably less than 20~o and most
preferably none of the acid groups should be neutralized with
alkali metals.
2p The preferred volatile amines for neutralizing the
acid groups are the tertiary amines, while ammonia and the
primary and secondary amines are less preferred.
Examples of suitable amines include trimethylamine, triethyl-
amine, triisopropylamine, tributylamine, N,N-dimethyl-cyclo-
.25 hexylamine, N,N-dimethylstearylamine, N,N-dimethylaniline,
N-methylmorpholine, N-ethyl-morpholine, N-methylpiperazine,
N-methylpyrrolidine, N-methylpiperidine, N,N-dimethylethanol-
amine, N,N-diethylethanolamine, triethanolamine, N-methyl-
diethanolamine, dimethylaminopropanol, 2-methoxy-ethyldimethyl-
30 amine, N-hydroxyethylpiperazine, 2-(2-dimethylaminoethoxy)-
ethanol and 5-diethylamino-2-pentanone. The most preferred
tertiary amines are those which do not contain isocyanate-
reactive groups as determined by the Zerewitinoff test since
they are capable of reacting with isocyanate groups during the
35 curing of the compositions of the present invention.
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In a preferred embodiment of the present invention
volatile tertiary amines are used so that when the water
dispersible coating composition of the subject application are
cured, the tertiary amine is removed from the coated substrate.
The acid groups may be converted into hydrophilic
anionic groups by treatment with the alkali metal or preferably
the volatile amine either before, during or after their
incorporation into the hydroxy functional polyurethane.
However, it is preferred to neutralize the acid groups after
l0 their incorporation.
The compounds containing lateral or terminal,
hydrophilic ethylene oxide units have at least one, preferably
one, isocyanate-reactive group and are an optional component,
which may be present in an amount sufficient to provide a
content of hydrophilic ethylene oxide units (calculated as
-CH2-CH2-0-) present in lateral or terminal chains of up to 25%
by weight. When compounds containing hydrophilic ethylene
oxide units are used, they are preferably incorporated into the
hydroxy functional polyurethanes in an amount sufficient to
provide a content of hydrophilic ethylene oxide units of
greater than 1% by weight, more preferably greater than 3% by
weight, based on the weight of the hydroxy functional
polyurethane. The preferred upper limit for the hydrophilic
ethylene oxide units is 10% by weight, more preferably 7% by
weight, based on the weight of the hydroxy functional
polyurethane.
Hydrophilic components having terminal or lateral
hydrophilic chains containing ethylene oxide units include
compounds corresponding to the formulas
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H-Z-X-Y-R"
or
R' R'
HOCH-CH2-N-CH2-CH-OH
CO-NH-R-NH-CO-Z-X-Y-R"
wherein
R represents a difunctional radical obtained by removing the
isocyanate groups from a diisocyanate corresponding to those
previously set forth,
R' represents hydrogen or a monovalent hydrocarbon radical
containing from 1 to 8 carbon atoms, preferably hydrogen or a
methyl group,
R" represents a monovalent hydrocarbon radical having from 1 to 12
carbon atoms, preferably an unsubstituted alkyl radical having from
1 to 4 carbon atoms,
X represents the radical obtained by removing the terminal oxygen
atom from a polyalkylene oxide chain having from 5 to 90 chain
members, preferably 20 to 70 chain members, wherein at least
40%, preferably at least 65%, of the chain members comprise
ethylene oxide units and the remainder comprises other alkylene
oxide units such as propylene oxide, butylene oxide or styrene
oxide units, preferably propylene oxide units,
Y represents oxygen or -NR"'- wherein R"' has the same definition as
R" and
Z represents a radical which corresponds to Y, but may additionally
represent -NH-.
The compounds corresponding to the above formulae may be
produced by the methods according to U.S. Patents 3,905,929, 3,920,598
and 4,190,566. The monofunctional hydrophilic
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synthesis components are produced, for example, by alkoxylating
a monofunctional compound such as n-butanol or N-methyl
butylamine, using ethylene oxide and optionally another
alkylene oxide, preferably propylene oxide. The resulting
product may optionally be further modified (although this is
less preferred) by reaction with ammonia to form the
corresponding primary amino polyethers.
The hydroxy functional polyurethanes have a content
of chemically incorporated anionic groups of 0 to 200,
preferably 10 to 200, more preferably 10 to 180 and most
preferably 20 to 100 milliequivalents per 100 g of solids, and
a content of chemically incorporated nonionic groups of 0 to
25~o by weight. When compounds containing hydrophilic ethylene
oxide units are used, they are preferably incorporated into the
hydroxy functional polyurethanes in an amount sufficient to
provide a content of hydrophilic ethylene oxide units of
greater than 1% by weight, more preferably greater than 3% by
weight, based on the weight of the hydroxy functional
polyurethane. The upper limit for the content of the
hydrophilic ethylene oxide units is preferably 10% by weight,
more preferably 7% by weight, based on the weight of the
hydroxy functional polyurethane. The amounts of the anionic
groups and hydrophilic ethylene oxide units must be sufficient
for the hydroxy functional polyurethane to remain stably
dispersed in water.
The hydroxy functional polyurethanes may be produced
according to methods known in the art. For example, the
above-mentioned reaction components may be added in any
sequence. One preferred method comprises mixing all of the
isocyanate-reactive components and subsequently reacting the
mixture with the polyisocyanate. The number of isocyanate-
reactive groups per isocyanate group is maintained at 1.1:1 to
4:1, preferably 1.2:1 to 1.8:1. The mixture is then reacted
until no further NCO groups can be detected. The reaction may
take place in the melt or in the presence of organic solvents.
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Suitable solvents include the water-miscible solvents normally
used in polyurethane chemistry such as esters, ketones,
halogenated hydrocarbons, alkanes and arenes. Low boiling
solvents include those boiling at temperatures in the range of
40° to 90°C such as acetone and methyl ethyl ketone. In
addition, higher boiling solvents such as N-methyl
pyrrolidinone, dimethyl formamide, dimethyl sulfoxide,
propylene glycol monomethyl ether acetate and ethylene glycol
mono(-methyl, -ethyl or -butyl) ether acetate may be utilized.
l0 In another preferred method an NCO terminated
prepolymer is prepared by reacting the polyisocyanate with the
high molecular weight polyol, the isocyanate-reactive compound
containing the hydrophilic or potential hydrophilic group and
optionally a low molecular weight compound containing at least
two isocyanate reactive groups. The NCO prepolymer is then
converted to a hydroxy functional polyurethane by a further
reaction with a primary or secondary rtionoamine containing at
least one hydroxy group. Suitable examples of these monoamines
include ethanolamine, N-methylethanolamine, diethanolamine,
3-amino-1-propanol and 2-amino-2-hydroxymethylpropane-1,3-diol.
In a further preferred method an NCO terminated
prepolymer is prepared as described above. However, instead of
capping the isocyanate groups with a monoamine, the NCO
terminated prepolymer is chain extended with a hydroxy
group-containing polyamine, e.g, N-hydroxyethyl-ethylene
diamine. When this chain extender is used in an amount which
is sufficient to provide an NCO: NH ratio of approximately 1.0,
a chain extended, hydroxy functional polyurethane is obtained
which contains lateral hydroxy groups.
.30 The water dispersible polyisocyanates to be used
according to the invention have an (average) NCO functionality
of at least 1.8, preferably 2 to 8 and more preferably 2.5 to
6, and an NCO content of 2 to 30~°, preferably 10 to 25f°. Their
dispersibility in water is ensured by a sufficient content of
suitable emulsifiers.
Mo3476CIP
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Suitable polyisocyanates for preparing the water
dispersible polyisocyanates include any of the monomeric
diisocyanates or polyisocyanates which have previously been
described as suitable for the preparation of the hydroxy
functional polyurethanes, preferably the monomeric aliphatic
and/or cycloaliphatic diisocyanates. However, it is preferred
to prepare the water dispersible polyisocyanates from
. polyisocyanate adducts containing carbodiimide, uretdione,
biuret, allophanate, urethane or isocyanurate groups, or from
to NCO prepolymers which have been prepared from the previously
described aliphatic and/or cycloaliphatic diisocyanates.
Suitable polyisocyanate adducts include:
1) Isocyanurate group-containing polyisocyanates
prepared from the previously described aliphatic and/or
cycloaliphatic diisocyanates. Particularly preferred are
isocyanato-isocyanurates based on 1,6-diisocyanatohexane and/or
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane
(isophorone diisocyanate or IPDI). The production of these
isocyanurate group-containing polyisocyanates is described, for
example, in DE-PS 2,616,416, EP-OS 3,765, EP-OS 10,589,
EP-OS 47,452, US-PS 4,288,586 and US-PS 4,324,879. The
isocyanato-isocyanurates generally have an average NCO
functionality of 3 to 3.5 and an NCO content of 5 to 30%,
preferably 10 to 25% and most preferably 15 to 25% by weight.
2) Uretdione diisocyanates prepared from the previously
described aliphatic and/or cycloaliphatic diisocyanates. The
uretdione diisocyanates are preferably prepared from
hexamethylene diisocyanate and/or of IPDI. The uretdione
diisocyanates can be used as the sole component for preparing
the water dispersible polyisocyanates or in admixture with
other aliphatic and/or cycloaliphatic polyisocyanates,
particularly the isocyanurate group-containing polyisocyanates
set forth under (1) above.
3) Biuret group-containing polyisocyanates prepared from
the previously described aliphatic and/or cycloaliphatic
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diisocyanates, particularly tris-(6-isocyanatohexyl)-biuret or
mixtures thereof with its higher homologues. The biuret group-
containing polyisocyanates generally have a most preferred NCO
content of 18 to 22% by weight and an average NCO functionality
of 3 to 3.5.
4) Urethane and/or allophanate group-containing poly-
isocyanates prepared from the previously described aliphatic
and/or cycloaliphatic diisocyanates, preferably hexamethylene
diisocyanate or IPDI, by reacting excess quantities of the
diisocyanates with the previously described low molecular
weight polyols, preferably trimethylol propane, glycerine,
1,2-dihydroxy propane or mixtures thereof. The urethane and/or
allophanate group-containing polyisocyanates have a most
preferred NCO content of 12 to 20~ by weight and an (average)
NCO functionality of 2.5 to 3.
5) Oxadiazinetrione group-containing polyisocyanates
prepared from the previously described aliphatic and/or
cycloaliphatic diisocyanates, preferably hexamethylene
diisocyanate.
The materials to be used for the preparation of the
water dispersible NCO prepolymer are the same as those used for
the preparation of the hydroxy functional polyurethane. In
contrast to the hydroxy functional polyurethanes the NCO
prepolymers have terminal isocyanate groups. The type and
proportions of the above-mentioned starting materials are
therefore selected such that the resulting prepolymers have
terminal isocyanate groups.
The NCO prepolymers are less preferred than the
polyisocyanate adducts for use in the preparation of the water
dispersible polyisocyanates because due to their higher
molecular weight they also have a higher viscosity. The higher
viscosity may necessitate the additional use of a solvent in
order to maintain the polyisocyanate stably dispersed in water
after it is blended with the aqueous dispersion of the hydroxy
functional polyurethane.
Mo3476CIP
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Mixtures of the monomeric polyisocyanates, the
polyisocyanate adducts and/or the NCO prepolymers may also be
used for preparing the water dispersible polyisocyanates.
The compounds for providing hydrophilicity to the
water dispersible polyisocyanates are also the same as those
previously described for providing hydrophilicity to the
hydroxy functional polyurethanes. The water dispersible
polyisocyanates are prepared by reacting the polyisocyanates
with the hydrophilic compounds containing isocyanate-reactive
groups, preferably with the monofunctional, nonionic
hydrophilic polyether alcohols, in an amount sufficient to
provide the desired amount of hydrophilic groups at a
temperature of 50 to 130°C.
The water dispersible polyisocyanates have a content
of chemically incorporated nonionic groups of 0 to 25% by
weight, preferably 2 to 25% by weight, more preferably 5 to 20%
by weight and most preferably 7 to 15% by weight of hydrophilic
ethylene oxide units (calculated as -CH2-CH2-0-) incorporated
in lateral or terminal polyether chains, and a content of
chemically incorporated anionic groups of 0 to 200
milliequivalents per 100 g of solids, based on the weight of
the water dispersible polyisocyanate. When anionic groups are
used, they are preferably incorporated into the water
dispersible polyisocyanate in an amount sufficient to provide
an anionic group content of least 10, more preferably at least
20 milliequivalents per 100 g of solids, based on the weight of
the water dispersible polyisocyanate. The upper limit for the
content of the anionic groups is preferably 180, more
preferably 100 milliequivalents per 100 g of solids, based on
the weight of the water dispersible polyisocyanate.
In accordance with a preferred embodiment of the
present invention when the water dispersible polyisocyanate
contains uretdione groups, it does.not also contain chemically
incorporated carboxylate groups to provide hydrophilicity.
Mo3476CIP
i '~~~
-18-
In order to reduce the viscosity of the water
dispersible polyisocyanates an organic solvent such as those
previously described for use with the hydroxy functional
polyurethanes may be added to the water dispersible
polyisocyanate before they are blended with the hydroxy
functional polyurethane. It is also possible to convert the
water dispersible polyisocyanates into aqueous dispersions with
a solids content of 10 to 65% by weight. The production of
these dispersions should take place shortly before the
to dispersed polyisocyanates are blended with the hydroxy
functional polyurethanes.
The water dispersible polyisocyanate should not be
blended with the hydroxy functional polyurethane until it is
time to apply the coating composition to a suitable substrate.
15 As with two component, solvent based coating compositions, the
mixture of the coreactants has a limited useful potlife, which
is dependent upon the reactivity of the coreactants, ratios of
coreactants and catalysts present in the system. When it is
desired to blend the two components, the water dispersible
20 polyisocyanate may simply be added to the water dispersible,
hydroxy functional polyurethane or vice versa with mild
stirring. Methods for blending the two components are known in
the art.
The two components should be blended in amounts
25 sufficient to provide a ratio of isocyanate groups from the
water dispersible polyisocyanate to hydroxy groups of the
hydroxy functional polyurethane of 0.8:1 to 6:1, preferably
about 1.2:1 to 4:1. After the two components have been blended
the coating composition should have a solids content of about 2
30 to 60%a, preferably about 10 to 50% by weight.
The aqueous coating compositions according to the
present invention may be applied to substrates using any of the
various techniques known in the art. In addition, the aqueous
compositions may be blended with other types of resins
35 optionally containing isocyanate-reactive groups or with amine-
Mo3476CIP
CA 02047635 2002-10-21
-19-
or phenol-formaldehyde condensates known in the art. They can
also contain pigments, levelling agents, catalysts, and other
auxiliaries known in the art. Examples of the application
techniques, resins and auxiliaries are set forth in U.S. Patent
4,408,008.
The invention is further illustrated but is not
intended to be limited by the following examples in which all
parts and percentages are by weight unless otherwise specified.
Isocyanate Crosslinker A
l0 To 900 parts of a polyisocyanate containing isocyanurate
groups and prepared from hexamethylene diisocyanate (Oesmodur*
N-3300, available from Mobay Corp.) were added 100.0 parts of a
polyether monohydric alcohol having an OH number of 2b.2 and
prepared from n-butanol, ethylene oxide, and propylene oxide
(molar ratio of ethylene oxide to propylene oxide - 83:17).
The reaction mixture was stirred and heated at 110'C for 1.5
hours.
Solids content - 104X
Viscosity - 3900 (25'C, ~4 spindle, 60 rpm)
2o Isocyanate content - 18.8%
Isocyanate Crosslinker B
The reaction product of 500 parts of the poiyisocyanate
used to prepare Isocyanate Crosslinker A and 26.3 parts of a
polyethylene oxide polyether monohydric alcohol having a
molecular weight of 1210 and initiated with 3-ethyl-3-hydroxy-
methyl-oxetane.
Isocyanate content - 19.5%
xmi
Preparation of Dispersion A
A mixture of 132.8 parts of a polyester diol prepared from
phthalic anhydride and hexanediol (OH number 56), 5.0 parts of
the polyether monohydric alcohol used to prepare Isocyanate
Crosslinker A, 13.4 parts of neopentyiglycoi, 20.6 parts of
a,a dimethylolpropionic acid, and 90 parts of N-methyl-
*trade-mark
Mo3476CIP
-20- ~~~ i 635
pyrrolidinone was heated to 70'C with stirring. To this
mixture, 127.6 parts of 4,4'-dicyclohexylmethane diisocyanate
were added, and the resulting mixture was stirred and heated at
110'C for 1 hour until the theoretical isocyanate content of
3.0 was reached. The reaction was cooled to 70'C, and 15.6
parts of triethylamine were added. After stirring for 15
minutes at 70'C, 17.0 parts of ethanolamine and 50 parts of
N-methylpyrrolidinone were added. After the reaction
exothermed to 92'C, the mixture was cooled to 70'C and stirred
ZO until it was found to be NCO-free by IR. 5.0 parts of the
above polyether monohydric alcohol in 50 parts of
N-methylpyrrolidone were added, and the reaction mixture
stirred for 30 minutes. 391.3 parts of distilled water at 50'C
were added to the mixture and the resulting dispersion was
stirred for one hour.
pH - 9.3
Sol ids - 359:
functionality - 2
Urethane/urea content - 13.09: (calculated as NH-C-0, MW 43)
Two Component Formulation
To 200 parts of Dispersion A were added 40.0 parts of
Isocyanate Crosslinker A (NCO/OH equivalent ratio - 3.0), and
0.12 parts of a 109: aqueous solution of Surfactant A (Silwet*
L-77, available from Union Carbide) and the mixture was stirred
vigorously. Drawdown bars were used to make 6 mil (wet film
thickness, wFT) films on glass plates and 5 mil WFT films on
Bonderite*treated steel panels.
~xamoles 2-6
Dispersions B-F, Compositions
Dispersions B-F were prepared in the same manner as
Dispersion A using the materials and amounts set forth in
*trade-mark
Mo3476CIP
-21-
Table 1.
TABLE 1
Dispersion B C D E F
Polyester A 125.2 56.4 323.8
Polyester B 95.0 56.5
NPG 0.2 28.3 17.1 22.3 31.8
TMP 4.7 4.7 58.6
DMPA 8.3 8.3 8.3 8.3 24.1
NMP 60.0 60.0 60.0 120.0 300.0
HMDI 60.6 107.2 83.9 107.7 261.8
TEA 6.0 6.0 6.0 6.0 17.2
EOA 5.7
DEOA 11.0 9.8 11.0
Distilled 424.0 424.0 424.0 364.0 982.7
.15 Water
% Solids 30 30 30 30 35
pH 9.2 9.0 9.8 9.4 8.1
Functionality 6 4 2 6 6
Urethane/Urea (%) 9.5 16.8 13.1 16.8 12.2
Polyester A - a hexanediol
phthalate, OH number 56.1
Polyester B - a neopentyl glycoladipate, number
OH 56.1
NPG - neopentyl glycol
TMP - trimethylol propane
DMPA - a,a-dimethylolpropioniccid
a
NMP - N-methylpyrrolidinone
HMDI - 4,4'-dicyclohexylmethanediisocyanate
TEA - triethylamine
EOA - ethanolamine
DEOA - diethanolamine
Two Component Formulations
2-6
Two component formulations 2-6 were pared as Example
pre in
1 using the materials and amounts in Table
set forth 2.
Mo3476CIP
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TABLE 2
Example 2 3 4 5 6
Dispersion B C D E F
Amount 75.0 75.0 75.0 75.0 180.0
Isocyanate 19.9 17.7 13.3 19.0 49.6
Crosslinker A
Surfactant A 0.05 0.08 0.08 0.05 0.12
NCO/OH equiv 4 4 3 4 3.6
ratio
l0 Example 7
Preparation of Dispersion G
A mixture of 122.5 parts of a polyester of phthalic
anhydride and hexanediol (OH number 56), 4.0 parts of
neopentylglycol and 8.3 parts of a,a dimethylolpropionic
acid
.15 was heated to 70C with stirring. To this mixture 60.6
parts
of 4,4'-dicyclohexylmethane diisocyanate were added,
and the
resulting mixture was stirred and heated at 105C for
2 hours.
Through the reflux condenser 100 parts of acetone were
added
and the reaction mixture was cooled to 56C. 6.0 parts
of
20 triethylamine were added, followed in 15 minutes by the
dropwise addition of 14.7 parts of diethanolamine. When
the
reaction mixture was NCO-free (as determined by IR),
383.9
parts of distilled water were added with vigorous stirring.
The acetone was immediately removed from the 55C dispersion
25' under reduced pressure.
pH - 8.0
Solids content - 35%
Functionality - 4
Urethane/urea content - 9.5%
30 Two Component Formulation
To 150 parts of Dispersion G were added 46.5 parts of
Isocyanate Crosslinker A (NCO/OH ratio - 3.0) and 0.12
parts of
a 10% aqueous solution of Surfactant A; the mixture was
stirred
vigorously. Drawdown bars were used to make 6 mil WFT
films
Mo3476CIP
-23- ,~~~~~9~
on glass plates and 5 mil WET films on steel panels treated
with Bonderite~chemical compositions available from Parker.
~,xamole 8 tComparison)
Dispersion H
180.0 parts of a polyester of adipic acid and butanediol
(OH number 50) were dehydrated under vacuum at 110°C for 30
minutes with stirring, then cooled to 70°C. After the addition
of 8.0 parts of IPDI and 12.1 parts of HDI, stirring was
continued at 80°C .until a constant isocyanate content of 1.1%
was reached. 400.0 parts of acetone were slowiy added while
maintaining the temperature at 50°C. A solution of 6.5 parts
of the sodium salt of N-(2-aminoethyl)-2-aminoethanesulfonic
acid (45% in water) and 1.1 parts of diethanolamine in 25 parts
of distilled water were stirred into the homogeneous acetone
solution at 50°C. After 7 minutes, the reaction mixture was
dispersed in 286.4 parts distilled water and the acetone was
immediately distilled off.
pH - 7.5
Solids content - 40%
Urethane/urea content - 4.5%
Two Component Formulation
To 75.0 parts of Dispersion H were added 1.4 parts of
Isocyanate Crossiinker B and 0.08 part of a lOX aqueous
solution of Surfactant A (NCO/OH equivalent ratio - 4.0); the
mixture was stirred vigorously. Drawdown bars were used to
make 6 mil WET films on glass and 5 mil WET films on Bonderite
treated steel panels.
Example 9 (Comparison)
Dispersion I
To a stirred mixture at 70°C of 116.4 parts of Formrez
YA-86-1 (available from Witco), 6.1 parts of an anhydrous
polyether of propylene oxide and bisphenol A having an ON
number of 202 (molecular weight 550), 8.2 parts of the
monohydric polyether used to prepare Isocyanate Crosslinker A,
19_4 parts of the sodium sulfonate salt (MW 430) of
Mo3476CIprk
ø.
-24- 2047635
propoxylated 1,4-butanediol (709: solution in toluene) were
added 13.8 parts of HDI and 27.2 parts of IPDI. The reaction
exothermed to 105'C and was maintained at that temperature
until the theoretical isocyanate content of 4.59: was attained.
This mixture was then cooled to 60'C and dispersed into 250.7
parts of distilled water with vigorous agitation. Immediately,
a solution of 2.5 parts of ethylenediamine, 8.2 parts of an
amine-terminated polyether (Jeffamine~ 0-400, available from
Texaco), and 5.1 parts of diethanolamine in 46.3 parts of
distilled water was added dropwise. The dispersion was stirred
at 60'C for 3 hours and then filtered and cooled.
pH - 6.8
viscosity - 100 mPa.S
solids - 40%
urethane/urea content - 8.75X
Two Component Formulation
To 150 parts of Dispersion I were added 31.5 parts of
Isocyanate Crosslinker B (NCO/OH equivalent ratio - 6.0), and
0.12 parts of a 109: aqueous solution of Surfactant A; the
mixture was stirred vigorously. Drawdown bars were used to
make 6 mil WFT films on glass and 5 mil WFT films on Bonderite*
treated steel panels.
All films were cured for 2-3 weeks at ambient temperature
and humidity before testing.
*trade-mark
Mo3476CIP
A
-25-
~047G3~
Two Component Film Evaluation
Example MEK 2x Pendulum Impact Tensile Elongation
Rubs Hardness Dir/Ind (psi)
1 200+ 127 160/160 4483 25
2 200+ 116 160/160 6310 20
3 200+ 148 100/60 8066 10
4 200+ 132 160/160 5762 15
5 200+ 179 160/160 9122 20
6 200+ 116 160/160 6327 25
l0 7 200+ 122 160/160 4745 20
8 (Comp) 30 62 160/1&0 2476 90
9 (Comp) 45 55 160/160 2472 80
Test Methods
Tensile properties were determined according to ASTM D
638 using a Type 4 die on an Instron model 1130. Films
prepared on glass were removed prior to testing.
The Erichsen pendulum hardness was determined on
the films cast onto the Bonderit~ treated steel panels. The
tester was leveled, and the steel panel was placed on the
sample stage. The fulcrum points of the pendulum were lowered
onto the cured film and the pendulum was deflected 6' and
released. The time for the pendulum to damp to a 3' deflection
was recorded.
The MEK double rubs were measured by wetting a cloth with
methylethyl ketone and rubbing the cloth across the coating
until the coating was removed; each back and forth motion
constituting one rub.
The Gardner Impact was determined according to ASTM 0
3029-84, method G.
Although the invention has been described in detail
in the foregoing for the purpose of illustration, it is to be
understood that such detail is solely for that purpose and that
variations can be made therein by those skilled in the art
without departing from the spirit and scope of the invention
except as it may be limited by the claims.
*trade-mark
Mo3476CIP
