CA2107957A1

CA2107957A1 - Two component water reducible chemical resistant coating

Info

Publication number: CA2107957A1
Application number: CA 2107957
Authority: CA
Inventors: Kurt E. Best; David C. Mcclurg; Leon N. Boretzky
Original assignee: Individual
Current assignee: Bayer Corp
Priority date: 1992-10-16
Filing date: 1993-10-07
Publication date: 1994-04-17
Also published as: MX9306334A

Abstract

TWO COMPONENT WATER REDUCIBLE CHEMICAL RESISTANT COATING
ABSTRACT OF THE DISCLOSURE
A two-component chemical resistant, water-reducible coating composition characterized by a VOC level of less than 240 g/l which is the reaction product of (a) an aqueous dispersion of a hydroxy functional polyurethane with an average functionality if at least 1 and a total urethane plus urea group content of from about 9 to about 20% by weight and (b) an aliphatic isocyanate that has been modified by reaction with an amount of monofunctional polyether sufficient to make the isocyanate dispersible in water formed when (a) and (b) are reacted in amounts such that the NCO/OH ratio is from about 0.8:1 to about 10:1.

Description

2~ ~79.37 ` Mo3864 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 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 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 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 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 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 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' 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~

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 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 -14^
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~

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 .~:
, 2 ~ 7 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 21~9~7 1~-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 2 ~ r~ 7 -19~
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 ' 21~7~ ~

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 oxide of 83:17) and having a molecular weight of approximately 2250.

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 ~, .
, : ,~

- 2 10 ~ 7 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 -~3-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 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.

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 -?4-20X ~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 .

2 1 ~

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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-28^

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.

: ~ Mo3864 ` ~

Claims

1. A two-component chemical resistant, water-reducible coating composition characterized by a VOC level of less than 240 9/1 which is the reaction product of a) an aqueous dispersion of a hydroxy functional polyurethane with an average functionality of at least 1 and a urethane and urea group content of from about 9 to about 20% by weight and b) an aliphatic isocyanate that has been modified by reaction with an amount of monofunctional polyether sufficient to make the isocyanate dispersible in water formed when the first and second components are reacted in amounts such that the NCO/OH ratio is from about 0.8:1 to about 10:1 in water.

2. The coating of Claim 1 in which the hydroxy functional polyurethane dispersion is made by reacting a diisocyanate with a low molecular weight isocyanate-reactive compound containing at least two hydroxyl groups.

3. The coating of Claim 1 in which b) is a hexamethlyene diisocyanate trimer which has been modified with a monofunctional polyether.

4. The coating of Claim 1 in which a) further includes at least one pigment.

5. The coating of Claim 1 in which a) further includes a mixture of a chrome green oxide pigment, a cobalt spinel pigment and a magnesium ferrite pigment.

6. The coating of Claim 5 in which the pigment mixture includes (a) from 45 to 55% by weight, based on total pigment mixture, of chrome green oxide, (b) from 30 to 40% by weight, based on total pigment mixture, of cobalt spinel and (c) from 5 to 25% by weight, based on total pigment mixture, of magnesium ferrite.

7. The coating of Claim 6 in which the pigment mixture is made up of (a) approximately 51.4% by weight of green chrome oxide, (b) approximately 34.5% by weight of cobalt spinel and (c) approximately 14.1% by weight of magnesium ferrite.

8. A process for the production of the coating of Claim 1 comprising:
(a) combining 1) an aqueous dispersion of a hydroxy functional polyurethane with an average functionality of at least 1 and a urethane content of from about to about 20% by weight, 2) a surfactant, 3) a wetting agent and 4) a fluoroaliphatic ester, (b) milling the combination of materials from (a) until the desired Hegman value is achieved, (c) blending under mild agitation with the milled mixture of (b) a blend of 5) an aliphatic isocyanate that has been modified by reaction with an amount of monofunctional polyether sufficient to disperse the isocyanate in water having an isocyanate content of from about 17.2 to about 19.2% by weight, and 6) an organic solvent and (d) adding water to the resultant composition to achieve the desired viscosity.

9. The process of Claim 8 in which a mixture of pigments is incorporated into the milled mixture of (b) prior to blending in accordance with step (c).