Note: Descriptions are shown in the official language in which they were submitted.
2~ ~79.37
` Mo3864
MD-90-78-CT
TWO COMPONENT WATER REDUCIBLE CHEMICAL RESISTANT COATING
BACKGROUND OF THE INYENTION
The present invention relates to a reactive two-component
water reducible coating which is res;stant to chem;cals and has
low VOC (volatile organic content~ levels.
Chemical resistant coatings are typically made from higher
molecular weight polymers which react to form a film of high
crosslink density. Because high molecular weight polymers are
employed, organic solvents are added to these coatings to
reduce their viscosity and facilita~e their application. One
of the disadvantages of these solvent based coatings is that
the volatile organic solvents present environmental concerns.
It is therefore a major goal in the coatings industry to
develop a water reducible coating with a low Yolatile organic
compound content having good surface characteristics and
excellent chemical resistance.
A coating in which volatile organic solvents are replaced
with water would obviously eliminate these enYironmental
concerns. However, in order to make a water reducible system,
the isocyanate and polyol components must both be water
dispersible. Techniques for making isocyanates water
dispersible are known in the art. See, for example~ U.S.
Patent 4,663,377. Similarly, techniques for making polyols
dispersible in water are also known. See, for example, U.S.
Patent 4,028,313.
SUMMARY OF THE INYENTION
It is an object of the present invent~on to provide a
chemical resistant urethane(urea) coating which is water
reducible.
It is also an object of the present invention to provide a
water reducible two-component polyurethane coating having
excellent surface and chemical resistance characteristics.
35376L~W12~0
. - . ............ , :
, .
2~ ~7~7
--2-
It is another object of the present invention to provide a
water reducible two-component polyurethane soating which meets
the requirements of Military Specifications Mil C-46168D
(2-component ground vehicle topcoat systems), Mil C-53039 ~one
component systems) and Mil Spec 85285 (two-component aircraft
topcoat systems).
These and other objects wh;ch will be apparent to those
skilled in the art are accomplished by reacting a f;rst
component which is an aqueous dispersinn of a hydroxy
functional polyurethane with a second component which is an
aliphatic isocyanate that has been modified with a
monofunctional polyether in amounts such that NCO/OH ratio is
from about 0.8-1 to about 10:1 in water. In a preferred
embodiment of the present invention, pigments which produce a
military camouflage coating are incorporated into the coating.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS OF THE INVENTION
The present invention relates to a two-component
polyurethane coating which is water reducible, has a low
volatile organic compound content and has excellent surface
appearance and chemical resistance. This coating is $ormed by
reacting a first component which is an aqueous dispers;on of a
hydroxy functional polyurethane with a second component which
is an aliphatic polyisocyanate that has been modified with a
monofunctional polyether. In pigmented coatings of the present
invention, 60- gloss values of from about 0.5 to about 90.0
units may be obtained. The coatings of the present invention
have the same film appearance as films made with traditional
solvent borne coatings. The coatings of the present invention
are also characterized by their resistance to harsh chemicals
(such as DS2 and Skydrol) which resistance is comparable to
that obtained with traditional solvent borne coatings.
The hydroxy functional polyurethane which is dispersed in
water may be formed by reacting (a) an organic polyisocyanate
3~ with (b) a h;gh molecular weight polyol, optionally (c) a low
Mo3864
2 1 ~ ~ 9 r3
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molecular weight isocyanate-reactive compound, (d) an
isocyanate-reactive compound containing an anionic or
potentially anionic group and (e) an isDcyanate-reactive
compound containing a nonionic hydrophilic group. Each of the
reactants (a) through (e) is used in an amount such that the
resultant polyurethane is hydroxy functional and water
dispersible. The hydroxy functional polyurethane genera~ly has
an average hydroxyl group functionality of at least 19
preferably from about 1.8 to about 12, more preferably from
lo about 2 to about 6 and most preferably about 4. The total
urethane and urea group content of the polyurethan~ dispersion
is ~enerally from about 9 to about 20% by weight, preferably
from about 10 to about 17% by weight. ThP average hydroxy
equivalent weight of the dispers;on (calculated by end group
analysis3 is generally from about 100 to about 5Q00, preferably
from about 500 to about 4000 and most preferably fro~ about
1000 to about 3000.
Suitable polyisocyanates for preparing the hydroxy
functional polyurethanes include any organic polyisocyanate~
preferably a monomeric di;socyanate. Preferred polyisocyanates
are polyisocyanates (particularly diisocyanates) having
aliphatically and/or cycloaliphatically bound isocyanate
groups. Polyisocyanates having aromatically bound isocyanate
groups may be used but they are not preferred.
Specific examples of polyisocyanates useful in the
production of the hydroxy functional polyurethanes include:
ethylene diisocyanate, 1,4-tetramethylene diisocyanate,
1,6-hexamethylene d~isocyanate, 2,4,4-trimethyl-1,6-hexa- -
methylene diisocyanate, 1,12-dodecane diisocyanate,
cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate,
cyclohexane 1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl
cyclopentane, 1-isocyana~o- 3,3,5-trimethyl-5-isocyanatomethyl
cyclohexane ~isophorone diisocyanate or IPDI), 2,4-hexahydro-
toluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate,
2,4'-dicyclohexylmethane diisocyanate, 4,4'-dicyclohexylmethane
Mo3864
21~79~7
--4--
diisoçyanate, ~ tetramethyl^1,3-xylylene diisocyanate,
~ tetramethyl-1,3-xylylene diisocyanate, 1,3-xylyl~ne
diisocyanate, 1,4-xylylene diisocyanate, i-isocyanato-1-methyl-
4(3)-isocyanatomethyl-cyclohexane, 1,3-phenylene diisocyanate7
1,4-phenylene diisocyanate, 2,4-toluylene diisocyanate,
2,6-tGluylene diisocyanate 9 diphenyl methane-2,4'-diisocyanate,
diphenyl methane-4,4~-d;;socyanate, naphthalene-1,5-
diisocyanàte, triphenyl methane-4,4',4"-triisocyanate,
polyphenyl polymethylene polyisocyanates of the type obtained
o 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~ f
fro~ about 400 to about fi,OOO, preferably from about 400 to
about 3,0~0. Examples of such high molecular weight compounds
include: polyhydroxy polyesters, polylactones, polycarbonates
containing hydroxyl groups, polyethers, polythioethers,
polyacetals, polyether esters, polyester amides and polyamides.
Useful polyhydroxy polyesters may be obtained from
polyhydric (preferably, dihydric) alcohols and polybasic
(preferably, dibasic) carboxylic acids. Instead of the
polybasic carboxylic ac;d, the correspond;ng acid anhydride or
polycarboxylic acid esters of lower alcohols or mixtures
thereof may be used to produce the polyhydroxy polyester.
Suitable polycarboxyl;c acids include aliphatic, cycl~-
aliphat~c, aromatic and/or heterocycl~c acids. These acids may
be saturated or unsaturated. They may also be subst;tuted,
3~ e.g., by halogen atoms. Specific examples of appropriate acids
include: succinie acid, adipic acid, suberie acid, azelaic
acidj sebacic acid, phthalic acid, isophthalic acid,
trimellitic acid, phthalic acid anhydride, tetrahydrophthalic
acid anhydride, hexahydrophthalic acid anhydride, tetrachloro-
Mo3864
210 7 9 ~ ~
phthalic acid anhydride, endomethylene tetrahydrophthalic acid
anhydride, fumaric acid, dimeric and trimeric fatty acids such
as oleic acid (which may be mixed with monomeric fatty acids),
dimethylterephthalate and bis-glycol terephthalate. Suitable
polyhydric alcohols include: ethylene glycol~ 1,2 propylene
glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol9
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 cyclo-
hexanes, 2,2,4-trimethyl-1,3-pentane-d;ol, glycerine and
trimethylol propane.
Polylactones suitable for use in the polyhydroxy
polyurethanes used in the present in~ention are known to those
skilled in the art. Specific examples of such polylactones are
polymers of ~-caprolactone initiated with any of the
above-mentioned polyhydrio alcohols.
Suitable polycarbonates containing hydroxyl groups include
the reaction products of polyhydric aloohols with phosgene,
diaryl carbonates such as diphenyl carbonate or cycl;c
carbonates such as ethylene or propylene carbonate.
Polycarbonates formed from dihydric alcohols such as
1,3-propanediol, 1,4-butanediol, 1,4-dimethylol cyclohexane,
1,6-hexanediol, diethylene glycol, triethylene glycol, or
tetraethylene glycol are particularly preferred. Other
suitable polycarbonates are the polyester carbonates obtained
by reacting of lower molecular weight oligomers of the
above-listed polyesters or polylactones with phosgene, diaryl
carbonates or cyclic carbonates.
Polyethers useful in the production of the polyhydroxy
polyurethanes used in the present invention include those
polymers obtained by reacting starting compounds having
reactive hydrogen atoms with alkylene oxides such as propylene
oxide, butylene oxide, styrene oxide, tetrahydrofuran,
epichlorohydrin or mixtures of these alkylene oxides. Limited
amounts of ethylene oxide may also be included, provided the
Mo3864
~1~7 ~ ~3 ~
polyether contains no more ~han 10% ethylene oxide. Polyethers
in which no ethylene oxide is included are, howeYer, preferred.
Suitable starting compounds having reactive hydrogen atoms
include: the polyols listed above as being suitable for the
produc~ion of polyesters, water, methanol, ethanol, 1,2,6-
hexanetriol, 1,2,4-butanetriol, trimethylol ethane,
pentaerythritol, mannitol, sorbitol, methyl glycoside, sucrose,
phenol, isononyl phenol, resorcinol, hydroquinone,
l,l,l-tris-(hydroxyphenyl) ethane and 1,1,2-tris-(hydroxy-
lo phenyl~ ethane.
Polyethers which have been obta;ned from starting
materials containing amino groups may also be used in the
practice of the present invention but they are not preferred.
Examples of amines which may be used to produce polyethers
include: ethylene diamine, diethylene triamine, triethylene
tetraamine, 1,6-hexanediamine, piperazine, 2,5-dimethyl
piperazine, l-amino-3-aminomethyl-3,5,5-trimethylcyolohexane,
bis(4-amino-cyclohexyl)methane, bis(4-am;no-3-methylcyclo-
hexyl)methane, 1,4-cyclohexanediamine, 1,2-propanediamine,
hydrazine, aminoacid hydrazides, hydrazides of semicarbazido
carboxylic acids, bis-hydrazides, bis-semicarbazides, ammonia,
methylamine, tetramethylenediamine, ethanolamine, diethanol-
amine, triethanolamine, aniline, phenylenediamine, 2,4-
toluylene diamine, 2,6-toluylene diamine, polyphenylene
polymethylene polyamines and mixtures thereof.
Polyethers may also be prepared from resinous startlng
materials such as phenol and cresol resins.
The preferred starting materials for preparation of
polyethers used in the present invention are those compounds
which contain hydroxyl groups exclusively. Compounds having
tertiary amino groups are less preferred and compounds having
isocyanate-reactive-NH groups are even less preferred.
Polyethers modified by vinyl polymers are also suitable
for making the polyhydroxy polyurethanes used in the present
invention. These modified polyethers may be obtained by
Mo3864
2~Q~.9.57
-7--
polymerizing styrene and acry70nitrile in the presence of
polyethers as disclosed for example in U~S. Patents 3,383,351;
3,304,273; 3,523,095 and 3,110,695. Amino polyethers in which
at least a portion of the hydroxyl groups of the polyethers
modified by vinyl groups have been converted to amino groups~
Polythioethers such as the condensation products of
thiodiglycol alone or in combination with other glycols9
dicarboxyl;c acids, formaldehyde, amino carboxylic acids or
am;no alcohols. The products are e;ther polythio m;xed ethers,
polythio ether esters, or polythioether ester amides.
Polyacetals useful in the present ;nvention include those
obtained by reacting formaldehyde with any of the polyhydric
alcohols listed aboYe. DiethylenP glycol, triethylene glycol,
4,4'-dioxyethoxy-diphenyldimethylene and 1,6-hexanediol are
particularly preferred alcohols.
Polyester amides and polyamides including the
predominan~ly linear condensates may be obtained by reacting
polyYalent 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 production of the polyhydroxy
polyurethanes used in the present invention are the d;hydroxy
polyesters, dihydroxy polylactones, dihydroxy polycarbonates
and dihydroxy polyester carbonates.
Suitable low molecular weight isocyanate-reactive
compounds which may optionally be used to produce the
polyhydroxy polyurethane generally have a molecular weight of
up to 400 and functionalities corresponding to those of the
hydroxy functional polyurethane. Examples of such low
molecular weight compounds include the polyols and diamines
described above as being suitable for the production of
polyhydroxy polyesters and polyethers as well as aminoalcohols.
To make the hydroxy functional polyurethanes water
3~ dispersible, it is necessary to chemically incorporate
Mo3864
2~7 ~7
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hydrophilic groups, i.e.~ anionic groups, potential anionic
gr~ups, or nonionic hydrophilic groups into the polyisocyanate
component. Suitable hydrophilic components contain at least
one isocy~nate-reactiYe group and at least one hydrophilic
group or potential hydrophilic group, Examples of compounds
which may bP used to incorporate potential ionic groups include
aliphatic hydroxy carboxylic acids, aliphatic or aromatic
aminocarboxylic acids with primary or secondary amin3 groups,
aliphatic hydroxy sulfonic acids and aliphatic or aromatic
aminosulfonic acids with primary or secondary amino groups.
These ac;ds preferably have molecular weights below 400. It
should be emphasized that the carboxylic acid groups are not
cons;dered 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 inYen~ion are
carboxylate groups and these groups may be introduced by using
hydroxy-carboxylic acids of the general formula:
(HO)xQ(COOH)y
in which
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 in which x = 2 and y = 1. ~hese dihydroxy alkanoic
acids are described in U.S. Patent 3,412,054, herein
incorporated by reference. The preferred group of dihydroxy
3o alkanoic acids are the ~,~-dimethylol alkanoic acids
represented by the structural formula:
C, H20H
Q'-C-COOH
C~20H
Mo3864
21~7~)7
g
in which Q' is hydrogen or an alkyl group containing 1 to 8
carbon atoms. The most preferred compound is ~ dimethylol
propionic acid, iOe, in which Q' is methyl in the above
formula.
The acid groups may be conYerted into hydrophilic anionic
groups by treatment with a neutralizing agent such as an alkalî
metal salt, ammonia or a pr;mary, 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 hydroxide,
sodium hydride, potassium hydride, sodium carbonate, potassium
carbonate, sod;um bicarbonate and potassium bicarbonate. The
use o~ 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 resistance to water
swell in the coatings produced from the water dispersible
compositions of the present invention. Therefore, less than
5~Xo~ preferably less than 20% and most preferably none of the
acid groups should be neutralized with alkali metals.
2~ The preferred volatile amines for neutralizing the acid
groups are the tertiary am;nes, while ammonia and the primary
and secondary amines are less preferred. Examples of suitable
amines include trimethylamine, triethylamine, triisopropyl-
amine, tributylamine, N,N-dimethyl-cyclohexylamine, N,N-
dimethylstearylamine, N,N-dimethylaniline, N-methyl-
morpholine, N-ethyl-morpholine, N-methylpiperazine,
N-methylpyrralidine, N-methylpiperidine, N,N-dimethylethanol-
amine, N,N-diethylethanolamine, triethanolamine, N-methyl-
diethanolamine, dimethylaminopropanol, 2-methoxy-ethyld~methyl-
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 ;socyanate groups during the
curing of the compositions of the present invention.
Mo3864
2 1 ~ 7 9 ~ l
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In a preferred embodiment of the present invention
volatile tertiary amines are used so that when the water
d;spersible coating composition of the subject application are
cured, the tertiary amine ;s removed from the coated substrate
The acid groups may be converted into hydrophilic anion~c
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 neutrali~e the acid groups after
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 -CH~-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 prov;de a
2Q 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 lO~o 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
oompounds corresponding to the formulas
H-Z-X-Y-R"
or
Mo3864
:
2~79~7
~, R'
HOCH-CH2-N-CH2-CH-OH
C0-NH-R-NH-C0-Z-X-Y-R"
in which
R represents a difunctional radical obtained by removing the
isocyanate groups from a di;socyanate corresponding to
those preYiously set f~rth,
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 atoms7 preferably an unsubstituted alkyl
radical having from 1 to 4 carbon atoms,
ls 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, in
which at least 40%, preferably at least 65~o~ of the
cha;n members comprise ethylene oxide units and the
remainder comprises other alkylene ox;de units such as
propylene oxide, butylene oxide or styrene oxide units,
preferably propylene oxide units,
Y represents oxygen or -NR"'- in which R"' has the same
definition as R" and
: 25 Z represents a radical which corresponds to Y, but may
additionally represent -NH-.
The compounds correspQnding to the aboYe formulae may be
produced by the methods according to U.S. Patents 3,905,929,
3,920,598 and 4,190,566 (the disclosures of which are herein
incorporated by reference). The monofunctional hydrophilic
: synthesis components are produced, for example, by alkoxylating
:~ a~monofunctional compound such as n-butanol or N-methyl
butylamine, using ethylene oxide and optisnally another
alkylene oxide, preferably propylene oxide. The resulting
Mo3864
.
,, .
.
~7~
-12-
product may opt;onally be further mod;fied (although th;s is
less preferred3 by reaction w;th ammonla to form the
corresponding primary amino polyethers.
The hydroxy functional polyurethane~ have a content of
chemically incorporated anionir groups of 0 to 200~ preferably
10 to ?00, more preferably 10 to lB0 and most preferably 20 to
100 milliequivalents per 100 9 of solids, and a content of
chemically incorporatPd nonionic groups of O to 25% by weight.
When compounds containing hydrophilic ethylene oxide units are
used, they are preferably incorporated ints the hydroxy
functional polyurethanes in an amount sufflcient to proYide 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 ~ay 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. Suitable solvents include the water-misc;ble
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
Mo3864
.
2~9~7
-13-
ke~one. In addition, higher boiling solvents such as N-methyl
pyrrolidinone, dimethyl formamide, dimethyl sulfoxide,
propylene slycol monomethyl ether acetate and ethylene glycol
~ono(-methyl, -ethyl or -butyl~ ether acetate may be utilized.
In another preferred method, an NC0 terminated prepol~mer
is prepared by reacting the polyisocyanate with the high
molecular weight polyol, the isocyanate-react;ve compound
containing the hydrophil;c or potential hydrophilic group and
oot~onally a low molecular we;ght compound conta;n;ng at least
two isocyanate reactive groups. The NC0 prepolymer is then
converted to a hydroxy functional polyurethane by a further
reaction with a pr;mary or secondary monoamine conta;n;ng at
least one hydroxy group. Su;table 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 NC0 terminated
prepolymer is prepared as described above. However, instead of
capping the isocyanate groups with a monoamine, the NC0
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.
The water dispersible polyisocyanates to be used according
to the invention have an (average) NC0 functionality of at
least 1.8, preferably 2 to 8 and more preferably 2.5 to 6, and
an NC0 content of 2 to 30%, preferably 10 to 25%. Their
dispersibility in water is ensured by a sufficient content of
suitable emulsifiers.
Suitable polyisocyanates for preparing the water
dispersible polyi~ocyanates 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
Mo3864
2 ~ 7
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and/or cycloaliphatic d;;socyanates. However, it is preferred
to prepare the water dispers;ble poly;socyanates from
poly;socyanate adducts conta;n;ng carbodiimide, uretdione,
b;uret, allophanate, urethane or ;socyanurate groups, or from
NCO prepolymers wh;ch have been prepared from the previously
descr;bed al;phat;c and/or cycloaliphatic di;socyanates.
Su;table polyisocyanate adducts include:
1) Isocyanurate group~containing polyisocyanates
prepared from the previously described aliphat;c and/or
lo cycloaliphatic diisocyanates. Particularly preferred are
isocyanato-isocyanurates based on 1,6-diisocyanatohexane and/or
1-isocyanato-3,3 7 5-trimethyl-5-isocyanatomethyl-cyclohexane
(isophorone diisocyanate or ~PDI). The production of these
isocyanurate group-containing polyisocyanates is described, for
~5 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,-~24,879. 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 prev;ously
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 polyisocyan~tes prepared from
the previously described aliphatic and/or cycloaliphatic
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
35` of 3 to 3.5.
Mo3864
~7~ 7
.
4) Urethane and/or allophanate group-containing poly-
isocyanates prepared from the previously described aliphatic
and/or cycloaliphatic di;socyanates, preferably hexamethylene
diisocyanate or IPDI~ by reacting excess quantities of the
diisocyanates with the previously described low molecular
we;ght polyols, preferably tr;methylol propane, glycerine,
1,2-d;hydroxy propane or m;xtures thereof. The urethane and~or
allophanate group-conta;n;ng poly;socyanates have a most
preferred NC0 content of 12 to 20% by weight and an (average)
NC0 functionality of 2.5 to 3.
5~ Oxadiazinetrione group-containing polyisocyanates
prepared from the previously described aliphatis and/or
cycloaliphatic diisocyanates, preferably hexamethylene
diisocyan~te.
The materials to be used for the preparation of the water
dispersible NC0 prepolymer are the same as those used for the
preparation of the hydroxy functional polyurethane. In
contrast to the hydroxy functional polyurethanes, the NC0
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 NC0 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.
Mixtures of the monomeric polyisocyanates, the
polyisocyanate adducts and~or the NC0 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
Mo3864
~07~
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previously describe~ for providing hydrophilicity to the
hydroxy functlonal polyurethanes. The water dispersible
polyisocyanates are prepared by reacting the polyisocyanates
with the hydrophilic compounds containing isoçyanate-reac~ive
groups, preferably with the monofunc~ional, nonionic
hydrophilic polyether alcohols, in an amount sufficient to
provide the desired amount o~ hydrophili~ groups at a
temperature of 50 to 130~C.
The water dispersible polyisocyanates have a content of
chem;cally incorporated nonion;c 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
mîlliequivalents per 100 9 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 9 of solids, based on
the weight of the water dispersible polyisocyanate.
In accordance with a preFerred embodiment of the present
invent;on when the water dispersible polyisocyanate contains
uretdione groups, it does not also contain chemically
incorporated carboxylate groups to provide hydrophilicity.
In order to aid in the blending of the water dispersible
polyisocyanates, an organic solvent such as one or more of
~ those preYiously described for use with the hydroxy functional
;~ polyurethanes may be added to the water dispersible
polyisccyanate before blending with the hydroxy functional
polyurethane.
Mo3864
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The water dispersible polyisocyanate should not be blended
with the hydroxy functional polyurethane until it is time to
apply the coating compssition to a suitable substrate. As with
two component, solvent based coating compositions~ the mixture
of the co-reactants has a limited useful potlife, which is
dependent upon the reactivity of the co-reactants9 ratios of
co-reactants and catalysts present in the system. When ;t 1s
desired to blend the two components, the water d;spers;ble
polyisocyanate may simply be added to the water ~ispersible,
lo hydroxy funct;onal polyurethane or vice versa w;th mild
stirring. Methods for blending the two components are known in
the art.
Soatings prepared from the aqueous coating compositions
according to the present invention are distinguished by low
1~ VOCs, excellent hardness, flexibility and solvent resistance,
and an excellent surface appearance. Conventional coatings
have YOCs of about 420 g/l, whereas the coatings of the present
invention have VOCs of less than 240 g/l, preferably less than
200 g/l, and most preferably less than 120 g/l. Conventional
dispersions contain fully reacted polyurethanes in the form of
discrete particles. When these dispersions are applied to a
suitable substrate, coatings are formed by the coalescence of
these particles. In contrast, the two-component aqueous
compositions according to the present invention are not fully
reacted when they are applied to a substrate.
The two components should be blended in amounts 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 10:1, preferably from about
1.2:1 to 4:1. After the two components have been blended, ths
coating composition should have a solids content of about 2 to
60%, preferably about 10 to 50% by weight. Deionized water
may, of course, be added until the desired viscosity is
reached.
Mo3864
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The aqueous coating compositions according to the present
;nvention may be applied to substrates us;ng any of the various
techniques known in the art. In add;tion, the aqueous
compos;tions may be blended with other types of resins
optionally conta;ning isocyanate-react;ve groups or with amine-
or phenol-Formaldehyde condensates known in the art. They can
also contain pigments, levelling agents, catalysts, and other
auxili~ries known in the art. Examples of the application
techniques, resins and auxiliaries are set forth in U.S. Patent
4,408,008, which is herein incorporated by reference.
In preparing coating compositions for military topcoats
having specific gloss, color and infrared reflectance
requirements, pigmentation is preferably adapted to provide a
spectral reflectance similar to the spectral reflectance
profile of, e.g., green vegetation, black or tan. Preferably,
the pigmentation is adapted to provide an IR reflectance within
the spectral reflectance limits set out in M;l-C-85285B Type I
or II, Mil-C-46168D Types II and IV and MIL-C-53039.
In general, any pigment or dye which is typically used to
color or tint paint may be included in the coatings of the
present invention. Examples of suitable reflective pigments
include chromium oxide, cobalt spinel, magnesium ferrites,
carbazole dioxazine violet and titanium dioxide.
The coatings of the present invention are not, however,
limited to military coatings. In non-military applications,
any of the known prime or extender pigments may be employed
where the coating is to be a topcoat. If the coating of the
present invention is to be used as a primer, anticorrosive
pigments would, of course, be used. Suitable pigments include
organic, inorganic, natural and synthetic pigments in
particulate or paste form. It is preferred that the pigment be
pH-basic or neutral. The opt;mum amount of pigment will, of
course, be dependent upon the gloss, color, hiding power and
num~er of coats desired. For example, it is known that a
.
Mo3864
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coating with h;gh gloss w;ll be obtained when a relatively
small amount of pigment is ;ncluded in the coating.
It would also be possible to impart color to the coatings
of the present invention w;th any of the known dyes dispersed
in water or in an organic solvent. The dye or dyes could be
used alone or in combination with one or more pigments.
To obtain a low gloss coating composition, as well as to
maintain a law VOC, low oil adsorption materials9 such as
silicon diox;de, talc or a silane-treated silica (e.g., silicon
dioxide treated with hexamethyldisilazane) may be added to the
coating composition, preferably to the aqueous dispersion of a
hydroxy functional polyurethane from which the coating is
produced.
The liguid carrier of the coating of the present invention
1~ is water, prcferably deionized water. Organic solvents are
often present in small amounts due to the fact that they are
present in mater;als used in the production of the coating,
e.g., as a dispersing agent for a dye or pigmen~. Any of the
known organic solvents could be included in the coatings of the
present invention in relatively small amounts but because these
solvents increase the VOC level of the coating, they are not
preferred.
The coatings of the present invention may be used as
either a topcoat or a primer. These coatings may be applied to
any substrate, particularly sheet metals and vehicle parts, in
any suitable thickness.
The invention is further illustrated but is not intended
to be limited by the following exa~ples in which all parts and
percentages are by weight unless otherwise specified.
EXAMPLES
The coatings of the present invention described in the
Examples given below were evaluated for acid resistance, DS2
Resistance, flexibility, hardness and gloss in accordance with
the procedures described below.
Mo3864
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DS2 Resistance
A half milliliter sample of DS2 agent was placed onto the
surface of a coated panel and allowed to stand for 30 minutes.
The panel was then rinsed with water and examined for
blistering or color change,
Mandrel Bend Test
The coating was tested for flexibility by bending the
coated panel around a one-quarter inch mandrel and examining
for cracking or delamination.
lo Pencil Hardness
Pencil hardness was determined by taking pencils of
increasing hardness (from F to 6H~ and attempting to etch a
scribe mark in the coating. The softest pencil which etched
thè coating is reported as the pencil hardness for the film.
Gloss
Gloss measurements were carried out with a Gardner Gloss
Meter available from the Gardner Instrument Company. Gloss
measurements at a 60~ and 85 incident angle to the coa~ing
were preferably less than 1.0 and 3.5 respectively.
The following materials were used in the Examples more
fully described below:
POLYOL A: a water reducible, hydroxy functional
polyurethane dispersion having a functionality of 4 and a
urethane group content of 5% which is commercially available
under the designation XP7044 fro0 Miles, Inc.
POLYISOCYANATE A: a modified aliphatic having an NCO
content of 17.2% by we;ght which was formed by reacting the
isocyanurate of hexamethylene diisocyanate with 129 gm of
methoxy polyethylene glycol having a molecular weight of
approximately 350.
POLYISOCYANATE B: a modified hexamethylene diisocyanate
having an NCO content of 19.1% by weight formed by reacting the
isocyanurate of hexamethylene diisocyanate with a polyether
monohydric alcohol prepared from n-butanol, ethylene oxide and
propylene oxide (molar ratio of ethylene oxide to propylene
Mo3864
. ~
21~7~j7
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oxide of 83:17) and having a molecular weight of approximately
2250.
EXAMPLE 1
The following materials were oharged into a reaotion
vessel in the relative amounts indicated to form the millbase
from which Component I was subsequently formed:
32.2% by weight (based on the total weight of
millbase) of POLYOL A
2.1% by weight (based on the total weight of
lo millbase) of a 20% carbazole dioxazine v;olet
toner (commercially ava;lable under the name
Indofast violet B-4018 from Miles Inc.)
0.3~ by weight (based on the total weight of
millbase) of an aliphatic alcohol/phosphorus
pentoxide wetting agent (commercially aYailable
under the name Victawet 35-B from Akzo~
0.1% by weight (based on the to$al weight of
millbase) of a mixture of anionic/nonionic
surfactants ~commercially available under the
name Nopco NDW from Henkel)
1.9% by weîght (based on the total weight of
millbase) of a 5% fluoroaliphatic polymeric
ester in deionized water solution (commercially
available under the name FC-430 from 3M).
2~. These materials were mixed for 5 minutes under low
agitation. The following pigments were then added to the
disperser vessel with agitation:
29.8% by weight (based on the total weight of
millbase) green chrome oxide
30. 20.6% by weight (based on the total weight of
millbase) cobalt spinel
: 7.6% by weight (based on the total weight of
millbase) magnesium ferrite
: 4.gX by weight (based on the total weight of
millbase) deionized water.
Mo3864
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The speed of the disperser was then increased to apply
enough shear ~o the mixture ~o ob~ain a Hegman value of a~
leas~ 5.5.
Component I was formed from the aboYe-described millbase
by adding to 22.6% by weight ~based on total weight of
Component I) of the millbase under agitation the following:
23.9% by weight (based on total we;ght of Component I~
POLYOL A
0.08% by weight (based on total weight of Component I)
o . of an al;phatic alcohol/phosphorus pentoxide
wetting agent (co~mercially available under the
name V;ctawet 35-B from Akzo)
0.12% by weight (based on total weight of Component I)
of a mixture of nonionic1anionic surfactants
~commercially available under the name Nopco NDW
from Henkel)
0.02% by weight (based on total we;ght of So~ponent I)
of a petroleum derivative (commercially
available under the name Disperse Ayd W-22 from
Daniel Products)
0.43% by weight (based on total weight of Component I)
of a 5% fluoroaliphatic polymeric ester in
deionized water solution (commercially available
under the name FC-430 from 3M)
2~ ~ 12.82% . by weight (based on total weight of Component I)
of calcined diatomaceous earth
14.2% by weight (based on total weight of Component I)
of hydrous calcium magnesium silicate
3.33% by weight (based on total weight of Component I~
3a. of magnes;um aluminum silicate
22.5% by weight (based on total weight of Component I)
of deionized water.
Mo3864
2~7~7
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This mixture was then milled until a Hegman value of 3.5
was achieved.
Component II was prepared by blending
75~ by weight (based on total weight of Component II) of
POLYIS00YANATE A
25% by weight (based on total weigh~ of Component II~ of
the acetic acid ester solvent which is eommercially
available under the name Exxate 600 frsm Eastman
Chemical Products, Inc.
Component I and Component II were then blended under mild
agitation in quantities such that the NCO:OH ratio was 3.5:1.
The resultant coating composition was then applied to a
zinc phosphate pretreated steel panel or a primed zinc
phosphate pretreated steel panel wh;ch was primed with
MIL-P-53022 pr;mer to a thickness of 2.0 mils ~ 0.2m;ls.
This coating composition had a VOC of 1.54 lb/gal
~185 g/l) and passed the water resitance (ASTM D 1308) and DS2
Resistance (MIL-C-46168D) tests.
EXAMPLE 2
The millbase from which Component I was ~ormed was made by
charging the following materials to a Cowles Dissolver:
10.8X by weight (based on total pa;nt components) of
POLYOL A
1.5% by weight (based on total paint components) of
25.~ deionized water
0.5% by weight (based on total paint components) of
the polymeric hyperd;spersant which is
commercially available under the name Solsperse
20000 from ICI Colors
0.3% by weight (based on total paint components)
calcined calcium carbonate
0.2% by weight (based on total paint components)
polysiloxane emulsifying agent commercially
available under the name ~yk 023 from Byk-Chemie
0.5% by weight (based on total paint components) of a
Mo3864
2 ~ 07 9 ~7
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20X ~arbazolQ dioxazine violet toner
8.4Yo by weight (based on total paint components)
green chrome ox;de
5.3% by weight (based on total paint components)
cobalt spinel
1.5% by weight (based on total paint components)
magnesium ferrite.
These materials were then milled until a Hegman value of
about 6 was achieved.
The following materials were then charged under agitation
to the dissolver containing the above-described millbase to
form Component I:
10.1% by weight (based on total paint components3
POLYOL A
8.2% by weight (based on total paint components) of a
35% high density polyethylene emulsisn which is
commercially available under the name Poly
Emulsion 392N35 from Chemical Corporation of
America
16.5% by weight (based on total paint components) of
deionized water
9.5% by weight (based on total paint components) of
hydrous calcium magnesium silicate
8.570 by weight (based on total paint components) of
calcined diatomaceous earth
1.4% by weight (based on total paint components~
magnesium aluminum silicate.
These materials were then milled until a Hegman value of
3.5 was achieved.
To Component I was added with agitation a mixture of 6.4%
by weight (based on total paint components) of POLYISOCYANATE A
and 2.1% by weight (based on total paint components) of acetic
acid ester solvent which is commercially available under the
name Exxate 600 from Eastman Chemical Products, Inc. ~.3% by
weight of de~onized water (based on total paint components) was
Mo3864
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2 1 ~
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added to the paint m;xture to br;ng the pa;nt to ;ts f;nal
~;scosity of 72 KU (Kreb units3. This paint was then applie~
to a zins phosphate pretreated steel panel. The propert;es of
this pa;nt are reported in Table 1.
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EXAMPLE 3
A high gloss white coating was produced on a sandmill from
the materials described below.
To the sandm;ll was charged:
43% by weight (based on total coating components)
POLYOL A
3.1% by weight (based on total coating components)
calcium carbonate
21.7% by weight (based on total coating components)
lo titanium dioxide
0.3% ~y weight (based on total coating components~
aliphatic alcohol/phosphorus pentoxide wetting
agent which is commercially available under the
name Y ktawet 35-B from Akzo.
?,5% by weight (based on total coating components~ of
a 5% ~uoroaliphatic polymeric ester ;n
deionized water which ester is commercially
available under the name FC-430 from 3M
0.3% by weight (based on total coating components) of
bis(1,2,2,6,6-pentamethyl-4-piperidinyl)
sebacate
5.8% by weight (based on total coating components~ of
deionized water.
These materials were then milled until a Hegman value of 7
was achieved. 10.1% by weight (based on total coa~ing
components) deionized water was then added to form Component I.
13.2% by weight (based on total coating components) of
POLYISOCYANATE A was then added to Component I
and blended until a homogeneous mixture was
obtained. This coating was then applied to a
substrate of primed aluminum at a thickness of
: 1.8-2.3 mils. The properties of this coating
were as follows:
Mo3864
~1~7~7
-2~-
VOC (g/l) 210
YOC (lb/gal~ 1.76
~0 glo~s < 3.5
GE impact at 2 mils 20~
Potli~e ~ 4 hrs.
24 hour immersion
in MIL-L-23699 slight color change
at 250F
24 hour immersion
1~ in MIL-H-83282 slight color change
at 250C
Although the invent;on 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 ~rom the spirit and scope of the in~ention
except as it may be limited by the claims.
2G
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