| PATENT ASSIGNEE'S COUNTRY | USA |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 26.12.2000 |
| PATENT TITLE |
Interpenetrating networks of polymers |
| PATENT ABSTRACT |
A process for producing a coating compositions having superior solvent resistance and film hardness comprising an interpenetrating network of a polyurethane component and a functionalized waterborne polymer, wherein the polyurethane component is prepared in the presence of the functionalized waterborne polymer and said polyurethane component and said waterborne polymer are crosslinked directly or indirectly via the chain extender. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | June 23, 1998 |
| PATENT REFERENCES CITED |
A. Patsis, H. X. Xiao, K. C. Frisch, and S. Al-Khatib; "Ionomer/Semi-IPN Coatings from Polyurethanes and Vinyl Chloride Copolymers" --Journal of Coatings Technology; Dec. 1986; vol. 58, pp. 41-47. M. Tehranisa, R. A. Ryntz, H. X. Xiao, P. I. Kordomenos, and K. C. Frisch; "Urethane Acrylic Interpenetrating Polymer Networks (IPNs) For Coating Applications" --Journal of Coatings Technology; Mar. 1987; vol. 59--pp. 43-49. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A process for producing a coating composition, which process comprises: a) preparing a functionalized polyurethane prepolymer; b) dispersing said polyurethane prepolymer in water to form a polyurethane prepolymer dispersion; c) adding at least one functionalized waterborne polymer to said polyurethane prepolymer dispersion, wherein said functionalized waterborne polymer contains at least one functional group that is reactive with the functional group of the polyurethane prepolymer; d) chain extending said polyurethane prepolymer with a chain extender in the presence of said waterborne polymer; and e) crosslinking said functionalized waterborne polymer with said chain extender. 2. The process of claim 1 wherein said functionalized polyurethane prepolymer contains at least one functional group selected from the group consisting of isocyanate, hydroxy, acetoacetoxy, n-methylol and mercaptan. 3. The process of claim 1 wherein said functionalized waterborne polymer contains at least one functional group selected from the group consisting of amine, hydroxy, mercaptan, isocyanate, epoxy, anhydride and acetoacetoxy. 4. The process of claim 1 wherein said waterborne polymer is selected from the group consisting of latex emulsions, acrylic polymers, water-reducible alkyds, alkyd emulsions, alkyd-acrylic hybrid polymer dispersions, polyurethane dispersions, polyurethane-acrylic dispersions, fluoropolymer emulsions, polyester emulsions, silicone emulsions, polyethylene emulsions, polypropylene dispersions, polyamide dispersions, epoxy dispersion, epoxy-acrylic dispersions, water dispersible or emulsifiable polyisocyanates and mixtures thereof. 5. The process of claim 1 wherein said polyurethane prepolymer and/or said waterborne polymer contain functional groups that crosslink upon film formation and exposure to ambient conditions. 6. The process of claim 5 wherein said functional groups are derived from reaction with a compound selected from the group consisting of fatty amines, allyl amines, diallyl amines, ethoxylated allyl amines, ethoxylated allyl alcohols, fatty alcohols, allyl alcohols, trimethylol propane mono- and di-allyl ether, hydroxy ethyl acrylate, hydroxy ethyl methacrylate, mono- and di-glycerides obtained by alcoholysis of drying oils with polyols or the reaction of drying fatty acids with polyols, acetoacetate-containing materials, anhydride-functional drying oils, trialkoxysilane, epoxy-functional oils, amine functional alkoxysilanes, isocyanate functional alkoxy silanes and epoxy functional alkoxy silanes. 7. The process of claim 1 wherein said chain extender is selected from the group consisting of polyols, amino alcohols, primary or secondary aliphatic, alicyclic, aromatic and heterocyclic amines, amine functional silanes, amine functional silicones, polyisocyanates and polyaldehydes. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION This invention relates to a method of making an interpenetrating network of waterborne polymers and the coating compositions produced from such interpenetrating networks. The invention involves coreacting a waterborne polyurethane component and a functionalized waterborne polymer component wherein the functional groups of the waterborne polymer react directly with the functional groups of the polyurethane component or react indirectly with the polyurethane component via the functional groups of the chain extender. Alternatively, the polyurethane component reacts with a chain extender and the functionalized waterborne polymer component independently reacts with a chain extender that may be the same or different than the chain extender which reacts with the polyurethane prepolymer to create an interpenetrating polymer network. Coatings produced from the interpenetrating networks of the present invention possess superior solvent resistance and film hardness and are particularly useful as high performance industrial coatings. Other methods of producing interpenetrating polymer networks involve dispersing polymerizable monomers in a polyurethane dispersion and then polymerizing the monomers in the presence of the polyurethane. U.S. Pat. No. 4,198,330 discloses a method for making a stable aqueous dispersion of polymeric material which comprises: (a) producing an isocyanate-terminated polyurethane prepolymer in the presence of an inert liquid polymerizable ethylenically unsaturated monomer material as a solvent or diluent; (b) dispersing the resulting product in water; (c) chain-extending the prepolymer in the resulting aqueous dispersion; and (d) subjecting the resulting aqueous dispersion to vinyl addition polymerization conditions to polymerize the monomer material in-situ. The polymerizable ethylenically unsaturated monomers must be inert to the prepolymer-forming reaction; that is, they must be devoid of groups interfering with or reactive with the primary isocyanate and active hydrogen-containing reactants. Thus, the monomers should be devoid of --NCO groups and active hydrogen-containing groups such as --OH. U.S. Pat. No. 4,730,021 discloses a process for preparing aqueous dispersion of urethane-acrylate graft copolymers comprising (a) reacting a polymerizable acrylate with a diisocyanate to produce a monoacrylated diisocyanate adduct; (b) reacting the adduct of (a) and other polyisocyanates with an organic compound containing at least one active hydrogen atom and a group which is capable of forming a salt group to form a prepolymer; (c) neutralizing the prepolymer and dispersing it in water, immediately followed by chain extending the prepolymer to obtain a chain extended acrylated urethane polymer dispersion. U.S. Pat. No. 5,173,526 discloses a method for making an aqueous polyurethane-vinyl polymer dispersion which comprises: (a) forming a carboxy-containing, water dispersible, isocyanate terminated polyurethane prepolymer; (b) adding a vinyl monomer composition which includes a polyethylenically unsaturated monomer to the prepolymer/monomer mixture; (c) adding a tertiary amine to the prepolymer/monomer mixture; (d) dispersing the prepolymer/monomer mixture in water; (e) adding an oil soluble free radical initiator and a chain-extender to the aqueous dispersion; and (f) polymerizing the vinyl monomer and completing chain extension of the prepolymer by heating the aqueous dispersion. Suitable vinyl monomers include ethylenically-unsaturated hydrocarbons, esters and ethers, especially esters of acrylic and methacrylic acids, esters of vinyl alcohol and styrene. SUMMARY OF THE INVENTION The present invention comprises a polymer network, also referred to herein as an "interpenetrating network" or "IPN" comprising at least two components; a polyurethane component and a functionalized waterborne polymer component, wherein the polyurethane component is at least partially prepared in the presence of the functionalized waterborne polymer component, and wherein the waterborne component contains functional groups that allow the polyurethane component and waterborne polymer component to coreact in situ either directly or indirectly, or to react with chain extender in situ. Additionally, the polyurethane and/or the waterborne polymer components can contain functional groups that allow it to cure or crosslink with itself or with the other component, upon application to the substrate. While there are a number of different variations and preferred embodiments to the present invention, central to the success of the invention is the preparation of two components, a waterborne polymer component and a polyurethane component. In one embodiment, the polyurethane is prepared as a prepolymer which is neutralized and dispersed into a latex polymer composition and is subsequently chain extended in the presence of functionalized waterborne polymer component. The incorporation of functional groups on both of the polyurethane component or the waterborne polymer component enable the components to crosslink in situ during the preparation of the interpentrating network. The waterborne polymer component may contain functional groups such as amino, hydroxy or mercaptan to react directly with the isocyanate functionality of the polyurethane prepolymer or to react with a polyisocyanate chain extender. Alternatively, the waterborne component may contain functional groups such as isocyanate, epoxy, acetoacetoxy, carbonate or anhydride to react to an amine functional chain extender. The polymer network produced by the process of the present invention contain interpenetrating networks of two or more polymers and some graft copolymers. The polymer network, and coatings containing the polymer network, produced by the present invention have particular utility as a high performance industrial coating and can be applied to substrates which include various kinds of metal, wood, concrete, cement, brick, plastic, leather and vinyl. DETAILED DESCRIPTION OF THE INVENTION The compositions of this invention are polymer systems comprising a polyurethane component and at least one functionalized waterborne polymer component, wherein the polyurethane component and functionalized waterborne component are coreacted to produce a final polymer network that is highly integrated and which has performance characteristics better than a mere physical blend of the individual components. Coating compositions containing the interpenetrating networks of the present invention exhibit superior film properties such as improved MEK resistance, film hardness, water and alkali resistance and flexibility. In a preferred embodiment, an isocyanate terminated polyurethane prepolymer is first prepared and dispersed in water. The polyurethane prepolymer dispersion is then mixed with the waterborne polymer component and chain extended in the presence of the waterborne polymer component. The waterborne polymer component contains functional groups which are reactive with the NCO groups of the polyurethane prepolymer or the functional groups of the chain extender. The functionalized waterborne polymer component may contain latex polymers, water-reducible alkyds, alkyd emulsions, acrylic polymers, alkyd-acrylic hybrid polymer dispersions, polyester emulsions, fluoropolymer emulsions, polyurethane-acrylic dispersions, silicone emulsions, epoxy dispersions, epoxy-acrylic dispersions, water dispersible or emulsifiable polyisocyanates, polyethylene emulsions, polyurethane dispersions, polyamide dispersions and mixtures thereof. The functional groups of the waterborne polymer may include amine, hydroxy, mercaptan, isocyanate, epoxy, anhydride and/or acetoacetate groups. The polyurethane prepolymer may contain isocyanate, hydroxy, acetoacetoxy, carboxy, mercapto or n-methylol functional groups. In addition to the coreaction of the polyurethane component and the waterborne polymer component and/or the coreaction of either or both the polyurethane component and the waterborne component with the chain extender, depending on the functionalities present on each component, the components can further crosslink (either individually or together) after application of the coating composition to the substrate. The composition of the present invention may contain two or more functionalized waterborne components, such as, for example, a latex and a silicone emulsion. Other waterborne polymer components may include, for example, a combination of a latex and a water-reducible alkyd, or an epoxy dispersion and a silicone emulsion. The process of the present invention is an effective way to intimately combine different waterborne polymers to obtain coating films having the property advantages of the different polymers. It is also an effective way to increase the compatibility of the different waterborne polymers. The process of the present invention produces coating compositions having a high solids content. Polyurethane Component As described above, the polyurethane component is generally prepared as a prepolymer that is dispersed in the waterborne polymer component whereafter it is further reacted to produce the final product of this invention. The polyurethane prepolymer is preferably prepared from ingredients that produce a predominantly linear prepolymer, that is, a prepolymer prepared from substantially difunctional reactants. However, branched prepolymers can be prepared in instances where a higher degree of crosslinking is desired. The polyurethane prepolymer compositions of this invention are generally produced by first reacting an active-hydrogen containing composition with an isocyanate-functional material. The isocyanate-functional material is preferably a diisocyanate-functional material selected from the group of aromatic, cycloaliphatic or aliphatic isocyanates. Examples of suitable isocyanates include 1,6-hexamethylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, isophorone diisocyanate, cyclohexane-1,4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, p-xylylene diisocyanate, meta-1,1,3,3-tetramethylxylylene diisocyanate and mixtures thereof. Small amounts of trifunctional isocyanates such as a trimer of hexamethylene diisocyanate in the form of isocyanurate or biuret and the trimer of isophorone diisocyanate may be used. The isocyanate-functional materials are most preferably diisocyanates selected from the group consisting of 4,4'-dicyclohexylmethane diisocyanate, meta-1,1,3,3-tetramethylxylylene diisocyanate, isophorone diisocyanates and mixtures thereof. Most preferred is a combination of 4,4'-dicyclohexylmethane diisocyanate and meta-1,1,3,3-tetramethylxylylene diisocyanate. As with the active-hydrogen containing materials, a minor percentage of the isocyanate-functional materials can have a functionality greater than two, however, an appreciable percentage of such isocyanate ingredients is not acceptable due to the crosslinking effect and branching of both the intermediate and the final product. When a mixture of two or more isocyanates is used, the ratio of NCO equivalents contributed by the individual isocyanates is not critical. The active-hydrogen containing composition that is reactive with the isocyanate is preferably difunctional with respect to isocyanate groups, that is, they have two active hydrogen atoms as determined by the Zerewitinoff method. Active hydrogens include hydrogen atoms attached to oxygen, nitrogen or sulfur and thus useful compounds include those having at least two of the groups --OH, --SH, --NH and --NH.sub.2. The active-hydrogen containing composition is preferably a diol selected from the group consisting of polyester diols, polyether diols, polyacetal diols, polyamide diols, polyester polyamide diols, poly(alkylene ether) diols, polythioether diols and polycarbonate diols. Suitable polyether diols are, for example, the condensation products of ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran, and their copolymerization, graft or block polymerization products, such as, mixed ethylene oxide, propylene oxide condensates, and the graft polymerization products of the reaction of olefins under high pressure with the mentioned alkylene oxide condensates. Suitable polyethers are prepared by the condensation of the mentioned alkylene oxides with polyhydric alcohols, such as, ethylene glycol, 1,2-propylene glycol and 1,4-butanediol. Suitable polyester diols, polyester amide diols and polyamide diols are preferably saturated and are obtained, for example, from the reaction of saturated or unsaturated polycarboxylic acids with saturated or unsaturated polyhydric alcohols. Suitable carboxylic acids for preparing these compounds include, for example, adipic acid, succinic acid, phthalic acid, terephthalic acid, and maleic acid. Suitable polyhydric alcohols for preparing the polyester diols include, for example, ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, hexanediol, and trimethylolpropane. A suitable amino alcohol for preparing polyester amide diols is, for example, ethanolamine. Suitable diamines for preparing polyesteramide diols and polyamide diols are, for example, ethylene diamine and hexamethylene diamine. Suitable polyacetals can be prepared, for example, from 1,4-butanediol or hexanediol and formaldehyde. Suitable polythioether diols can be prepared, for example, by the condensation of thiodiglycol with ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran. Additional useful diols include Bisphenol A, polybutadiene based diols, polysiloxane based diols, fluorinated diols and mixtures thereof. In addition to the polyols disclosed above, compounds such as diamines, aminoalcohols and mercaptans, are also useful. The most preferred difunctional active-hydrogen containing starting materials are a combination of 1) the polyester diols formed from the reaction of saturated and unsaturated dihydric alcohols such as ethylene glycol, propylene glycol, neopentyl glycol, 1,4-butanediol, 1,4-butenediol, 1,6-hexanediol, furan dimethanol, and cyclohexane dimethanol with saturated and unsaturated polycarboxylic acids such as maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, adipic acid, isophthalic acid, terephthalic acid, phthalic anhydride, dimethyl terephthalate, dimer acids and the like; and 2) a diol containing hydrophilic groups. One such preferred polyester diol is Rucoflex.TM. 1015-120 (a mixture of polyester diols based on neopentyl glycol, hexanediol and adipic acid, commercially available from Ruco Polymer Corporation). A particularly preferred diol containing hydrophilic groups is dimethylolpropionic acid. When used, these two diols are preferably present in percentages such that the Rucoflex.TM. material contributes between about 30% to about 70% of the OH functionality of the total materials. As the examples below demonstrate, a preferred embodiment comprises Rucoflex.TM. 1015-120, trimethylolpropane, dimethylolpropionic acid and cyclohexane dimethanol. Although it is preferred to use difunctional active hydrogen containing compounds, small amounts of tri- and higher functional compounds may be used. Examples of such higher functional compounds include trimethylol propane, pentaerythritol, polyester triols and polyether triols. Large amounts of such higher functional compounds will create a highly crosslinked, non-linear prepolymer in solution. In one preferred embodiment, the polyurethane component contains at least one functional group that enables the polyurethane component to further crosslink (autooxidatively or otherwise) once the composition has been applied to the substrate and is exposed to ambient air drying conditions normally associated with air drying paints. For baked industrial finishes, suitable crosslinkers such as, for example, methoxy melamines, blocked isocyanates, oxazolines and other crosslinkers which can react with the above mentioned groups can be included in the coating composition. For two-part systems, crosslinkers such as, for example, aziridines, carbodiimides, polyisocyanates, epoxy silanes and other crosslinkers which can react with the above mentioned groups can be included in the coating composition. During the preparation of an isocyanate functional polyurethane prepolymer, the preferred ratio of total active-hydrogen containing materials to isocyanate should be such that there is an excess of isocyanate functionality over active-hydrogen functionality. Preferably, the ratio of molar equivalents of NCO to total active-hydrogen should be between about 1.01:1 to about 2.0:1; preferably between about 1.01:1 to about 1.7:1. In order to prepare a hydroxy functional polyrurethane prepolymer, there should be an excess of hydroxy functionality over isocyanate functionality. Optionally, and preferably present during the reaction is up to about 0.06%, preferably between about 0.01% and about 0.04% (by weight based upon total solids of active-hydrogen containing compositions and diisocyanate) of a catalyst such as di-butyl tin dilaurate, tin octoate and the like. To ensure that the polyurethane prepolymer is dispersible in an aqueous media such as a latex media, pendant ionizable groups are incorporated into the prepolymer and then subsequently ionized. Useful ionizable groups include pendant groups such as carboxylate, sulfonate, sulfate, phosphonate and/or phosphate groups located along the polymer backbone. Preferred are carboxylate groups which are derived by preparing the polyurethane prepolymer from an active hydrogen containing composition having a carboxyl group. For example, diols, diamines and difunctional thiols containing a carboxyl group are useful. The preferred carboxy-functional active hydrogen containing composition is dimethylolpropionic acid. The polyurethane prepolymer must contain a sufficient amount of the carboxyl groups which are ionized by neutralization to render the polyurethane prepolymer dispersible. Preferably, between about 1% and about 10% of the polyurethane prepolymer weight solids is contributed by active-hydrogen containing compositions having ionizable groups. The ionizable groups of the polyurethane prepolymer are converted by combining the prepolymer with water containing a tertiary amine. Tertiary amines that may be used include triethylamine, trimethylamine, triisopropyl amine, tributyl amine, triethylene diamine, N,N-dimethyl-cyclohexyl amine, N,N-dimethylstearyl amine, N,N-dimethyl aniline, N-methylmorpholine, N-ethylmorpholine, N-methylpiperazine, N-methylpyrrolidine, N,N-dimethyl-ethanol amine, N,N-diethyl-ethanol amine, triethanol amine, N-methyldiethanol amine, dimethylaminopropanol, 2-methoxyethyldimethyl amine, N-hydroxyethylpiperazine, 5-diethylamino-2-pentanone and mixtures thereof, and dispersed. The amount of tertiary amine added should be sufficient to neutralize at least about 90% of the ionic groups present in solution. Preferably, the tertiary amine is added in an amount sufficient to neutralize 100% of the ionic groups. Other weak bases may be used to neutralize the ionic groups, but tertiary amines are preferred because they do not react with the free isocyanate groups of the prepolymer. Preparation of the polyurethane prepolymer is typically carried out by charging the active-hydrogen containing composition with the catalyst to a reaction vessel, heating the contents to a temperature of between about 85.degree. C. and about 100.degree. C., and adding, via continuous or stepwise addition over a period of time, preferably between about 0.5 hour to about 1.5 hours, the isocyanate-functional materials. Optionally present can be a solvent such as n-methyl-2-pyrrolidone, dimethyl formamide, methyl ethyl ketone, toluene, and mixtures thereof in an amount ranging up to about 20% by weight based upon the total weight of the materials present in the reaction vessel. After complete addition of the isocyanate materials, the reaction vessel temperature is maintained between about 85.degree. and 100.degree. C. for approximately 3 to 4.5 hours. The residual isocyanate percentage can be measured by any means well known in the art. At this point, the polyurethane prepolymer is now formed and is ready for further reaction according to this invention. The prepolymer is dispersed in water containing a tertiary amine such as, for example, triethylamine, which neutralizes the ionic groups of the prepolymer. Once the polyurethane is dispersed in water, the dispersion is ready for incorporation of the waterborne polymer component. Overall, the weight ratio of polyurethane prepolymer component to waterborne polymer component is generally in the range of about 1:99 to about 99:1, preferably from about 1:4 to about 1:1. In order to chain extend the polyurethane prepolymer, a functional compound capable of chain extending the polyurethane prepolymer such as a polyol, an amino alcohol, a primary or secondary aliphatic, alicyclic, aromatic or heterocyclic amine or diamine, ammonia, an amine functional silicone or amine functional silane, a water dispersible or emulsifiable polyisocyanate, a polyaldehyde or an epoxy silane may be used. Water-soluble chain extenders are preferred. Examples of suitable chain extenders include ethylene diamine, propylene diamine, butylene diamine, hexamethylene diamine, cyclohexylene diamine, piperazine, 2-methyl piperazine, isophorone diamine, phenylene diamine, tolylene diamine, xylylene diamine, hydrazine, dimethylhydrazine, adipic dihydrazide, mono- and diaminioalkoxy silanes, ethylene glycol, di-, tri-, and tetraethylene glycol, propane 1,2-diol, propane 1,3-diol, neopentyl glycol, mixtures thereof, equivalents thereof and the like in an amount sufficient to react with up to at least 90% of the theoretical amount of residual NCO functionality is generally added to the composition for chain extension of the polyurethane. If the polyurethane prepolymer is hydroxy, mercapto, n-methylol or acetoacetoxy functional, water dispersible polyisocyanates can be used as the chain extender. Chain extenders having a functionality greater than two such as, for example, diethylenetriamine, can also be included but should be limited to a small amount to avoid creating a composition that is highly crosslinked. As discussed above, the dispersing media for the polyurethane prepolymer is preferably water to which the waterborne polymer component is subsequently added. It can be a combination of the waterborne polymer component and additional water. Variations on the Polyurethane Structure In one embodiment, the polyurethane component of the present invention contains ingredients that enable it to autooxidatively cure after application to the substrate when exposed to ambient air curing conditions normally associated with architectural paints and coatings. In one embodiment, during or subsequent to the preparation of the polyurethane prepolymer, but prior to the chain extension of the prepolymer in the waterborne polymer component, compositions which attach to the polyurethane backbone can be added to the prepolymer composition. Each of these compositions are reacted directly to the polyurethane backbone but remain unreactive during the chain extension process and also remain unreactive during normal storage of the final product. However, upon application of the product to the substrate and exposure to drying conditions normally associated with air drying paint, these added functionalities autooxidatively cure the polyurethane component. Preferred compositions that allow such post-application crosslinking include active-hydrogen containing compositions that are monofunctional or difunctional with respect to isocyanates. Some of these active-hydrogen containing materials include the fatty amines, allyl amines, diallyl amines, ethoxylated allyl amines, ethoxylated allyl alcohols, fatty alcohols, allyl alcohols, trimethylol propane mono- and di-allyl ether, hydroxy ethyl acrylate, hydroxy ethyl methacrylate, mono- and di-glycerides obtained by alcoholysis of drying oils with polyols or the reaction of drying fatty acids with polyols, acetoacetate-containing materials such as the adduct of trimethylolpropane with t-butyl acetoacetate, direct introduction of acetoacetate functionality onto the polyurethane prepolymer by reaction with t-butyl acetoacetate or diketene and reaction of the backbone with anhydride-functional drying oils. Post-crosslinking functionalities that cure by the condensation mechanism may also be added to the polyurethane polymer backbone, for example, by reacting the isocyanate functional polyurethane prepolymer with an amine functional di- or trialkoxysilane, a diamine functional di- or trialkoxysilane, an isocyanate functional di- or trialkoxysilane or epoxy functional di- or trialkoxy silane. Post-crosslinking functionalities can also be prepared by treating the polyurethane prepolymer with adipic dihydrazide and formaldehyde. Additionally, the polyurethane prepolymer may be modified to include post-crosslinking functionalities by incorporation of epoxy-functional oils, anhydride functional oils, epoxy functional di- or trialkoxysilanes, or amine or diamine functional di- or trialkoxysilanes in the chain extension stage. Aminoplast crosslinkers such as hexamethoxymelamine or those with a high content of N-methylol or imino groups can be added in the chain extension step to introduce crosslinking by condensation. Waterborne Polymer Component Suitable for use as the functionalized waterborne polymer component of the invention are waterborne polymers that contain functional groups which are reactive with the isocyanate, hydroxy, n-methylol, mercapto or acetoacetoxy functionality of the polyurethane prepolymer or the polyamine, polyhydroxy, polyisocyanate or polyanhydride chain extender, as well as the carboxyl groups and any other functional groups on the prepolymer. Such waterborne polymers include latex emulsions, acrylic polymers, polyester emulsions, water-reducible alkyd polymers, alkyd emulsions, alkyd-acrylic hybrid polymer dispersions, fluoropolymer emulsions, silicone emulsions, epoxy dispersions, epoxy-acrylic dispersions, water dispersible or emulsifiable polyisocyanates, polyethylene emulsions, polypropylene emulsions, polyurethane dispersions, polyamide dispersions and polyurethane-acrylic dispersions. These waterborne polymers may contain amine, hydroxy and/or mercaptan functional groups to react with the isocyanate functional groups of an isocyanate functional polyurethane prepolymer or water dispersible polyisocyanate chain extender. The waterborne polymers may also contain isocyanate or anhydride functional groups to react with the hydroxy functional groups of a hydroxy functional polyurethane prepolymer. Alternatively, these waterborne polymers may contain isocyanate, epoxy or acetoacetate groups to react with the amine or hydroxy functional groups of the chain extender to form crosslinked polymer chains of each network intimately associated with one another or become indirectly crosslinked to each other or the polyurethane component through the chain extender. A waterborne polymer useful in the present invention is a conventional latex composition which contains amine, hydroxy or mercaptan functionality to enable the latex to crosslink directly to the isocyanate functionality of the polyurethane prepolymer. If the polyurethane prepolymer is hydroxy functional, the latex may contain isocyanate or anhydride functionality to react with the hydroxyl groups of the polyurethane prepolymer. In addition, the latex may contain isocyanate or epoxy functionality to react to the carboxyl groups of the polyurethane prepolymer. The functional latex may also crosslink with the polyurethane prepolymer indirectly by reacting with the functional groups of the chain extender. Such useful latexes include those having isocyanate, epoxy or acetoacetoxy, carbonate or anhydride functionality to react with the amine groups of the chain extender. Conventional latex polymers are prepared by polymerizing at least one ethylenically unsaturated monomer in water using surfactants and water soluble initiators. Typical ethylenically unsaturated monomers include vinyl monomers, acrylic monomers, allylic monomers, acrylamide monomers, and mono- and dicarboxylic unsaturated acids. Vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrates, vinyl isopropyl acetates, vinyl neodeconate and similar vinyl esters; vinyl halides include vinyl chloride, vinyl fluoride, and vinylidene chloride; vinyl aromatic hydrocarbons include styrene, .alpha.-methyl styrenes, and similar lower alkyl styrenes. Acrylic monomers include monomers such as lower alkyl esters of acrylic or methacrylic acid having an alkyl ester portion containing between 1 to 12 carbon atoms as well as aromatic derivatives of acrylic and methacrylic acid. Useful acrylic monomers include, for example, acrylic and methacrylic acid, methyl acrylate, and methacrylate, ethyl acrylate and methacrylate, butyl acrylate and methacrylate, propyl acrylate and methacrylate, 2-ethyl hexyl acrylate and methacrylate, cyclohexyl acrylate and methacrylate, decyl acrylate and methacrylate, isodecylacrylate and methacrylate, and benzyl acrylate and methacrylate. Preparation of latex compositions is well-known in the paint and coatings art. Any of the well-known free-radical emulsion polymerization techniques used to formulate latex polymers can be used in the present invention. Isocyanate functional monomers can be prepared by the addition of isophorone diisocyanate with hydroxy ethyl acrylate or methacrylate, or the addition of 4,4'-dicyclohexylmethane diisocyanate or meta-1,1,3,3-tetramethylxylylene diisocyanate with hydroxy ethyl acrylate or methacrylate. Examples of isocyanate functional monomers include meta-isopropenyl-.alpha.,.alpha.-dimethyl isocyanate (m-TMI), para-isopropenyl .alpha.,.alpha.-dimethylbenzyl isocyanate (p-TMI) and isocyantoethyl methacrylate. Isocyanate functional latexes are prepared by reaction of the isocyanate functional monomers with other standard acrylic or vinyl acrylic latex ingredients. Epoxy functional latexes can be produced from monomers which include glycidyl acrylate and methacrylate, n-glycidyl acrylamide and allyl glycidyl ether. Acetoacetoxy functional latexes include those that contain acetoacetoxyethyl methacrylate, acetoacetoxy ethyl acrylate, acetoacetoxypropyl methacrylate, allyl acetoacetate, acetoacetoxybutyl methacrylate, 2,3-di(acetoacetoxy) propyl methacrylate and n-acetoacetyl acrylamide. Hydroxy functional latexes can be produced from polymerizable monomers such as allyl alcohol and hydroxy alkyl acrylates and methacrylates including, for example, hydroxylethyl acrylate and methacrylate, hydroxypropyl acrylate and methacrylate, hydroxybutyl acrylate and methacrylate and mixtures thereof. Carbonate and anhydride functional latexes can be produced from vinyl or allyl carbonates and maleic anhydride. As with the polyurethane component, the waterborne polymer component may contain functionalities that cure after the coating composition has been applied to the substrate. Such post-application crosslinking functionalities include those listed above as variations of the polyurethane structure. Coating Formulas Once dispersed into the dispersing media, the composition can be modified with other standard ingredients commonly used to formulate paints and coatings. For example, the dispersions of this invention can be combined with other ingredients such as pigments, extenders, dispersants, surfactants, colorants, paraffins, waxes, UV light stabilizers, rheology modifiers, mildewcides, biocides, fungicides, and other conventional additives. Colorants and pigment dispersions, when used, are typically added in amounts up to about 15% by volume of the total composition. |
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