LOW VOC, ISOCYANATE BASED AQUEOUS CURABLE COMPOSITIONS

Abstract: Provided is a low volatile organic content (VOC), isocyanate based curable oil-in-water emulsion of a polyisocyanate cross-linker and a surface active isocyanate reactive material in an aqueous medium, and a process for the preparation thereof. Also provided is a water-in-oil intermediate product to which an aqueous medium can be added to produce the curable oil-in-water emulsions. Such curable emulsions are particularly suited for use in coatings applications.

Description: LOW VOC, ISOCYANATE BASED AQUEOUS CURABLE COMPOSITIONS BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to low volatile organi .c compound (VOC) content, isocyanate based curable oil-in-water emulsions of a polyisocyanate crosslinker and a surface active isocyanate reactive material in an aqueous medium. The present invention also relates to methods for preparing such curable compositions as well as various end uses thereof, and a water-in-oil emulsion precursor suitable for use in preparing such curable compositions. Description of the Related Art Isocyanate crosslin ed systems are in general well known. As an example, polyuretiiane films can be formed from coating compositions based upon polyols and polyisocyanate crosslinking agents. Polyurethane coatings can be formulated to provide fast curing characteristics, as well as a desirable combination of abrasion resistance, flexibility, adhesion, chemical resistance and appearance characteristics in the resulting films. Due to the reactivity of isocyanates with active hydrogen containing compounds, including water, polyurethane coatings have historically been formulated as two component organic solvent based systems. One-component systems, both organic solvent based and aterbo ne (see GB 1530021 and GB 1530022), have also been formulated by blocking of the isocyanate groups via well-known blocking agents. Despite the excellent films which can be achieved with some of these systems, and particularly the two-component organic solvent based systems, the coatings industry is under great pressure to reduce the environmentally undesirable emission of VOC'S, which includes the organic solvent media as well as the common isocyanate blocking agents. One means of doing so, of course, would be to exchange some or all of me liquid organic solvent medium with water. Unfortunately, the switch from organic solvents to water is neither a simple nor straightforward matter, particularly in the case of common isocyanate crosslinkers which are not only reactive with water, but are also hydrophobic and nondispersible. Several approaches to lowering the VOC of polyurethane coatings arc discussed N.T. Cullen, "Low- VOC Polyurethane Coatings: Current Successes and Promising Developments," American Pain. &. Coatings Journal. August 19, 1991, pp. 44-49 and 64. One such approach has been to preform a water-dispersible film-forming polyurethane polymer by reacting a polyisocyanate with a hydrophilic reactive component, then dispersing the so-preformed hydrophilic polymer in water. A variation on this approach disclosed in GB1162409 is to preform the polyurethane polymer in situ in the aqueous medium with the aid of non-reactive surfactants. A still further variation on this approach is described in EP-A-0369389, in which a lower molecular weight water-dispersible prepolymer containing residual isocyanate functionality is first formed by reaction of a mixture of isocyanates with a polyol chain containing hydrophilic groups, after which the prepolymer is dispersed in water and chain extended or crosslinked. Upon application of these preformed polymer systems to a substrate, films are formed primarily via physical drying mechanisms due to evaporation of the liquid medium (water). While such preformed polyurethane systems can significantly reduce emitted VOC'S, they often can suffer from application and stability problems. In addition, films produced from such systems can suffer from poor water resistance due to the hydrophilic nature of the preformed polymers or surfactants remaining after cure. In another approach disclosed in GB-A2018796 and US4663377, an emulsifiable polyisocyanate mixture comprising (a) a hydrophilic isocyanate functional oligomer and (b) a polyisocyanate, is produced by partially reacting a polyisocyanate with, for example, a hydrophilic polyether alcohol. Curable coating and adhesive compositions can be formed by combining these polyisocyanate emulsions with separate aqueous resins. The emulsifiable polyisocyanate mixtures of these references, however, suffer from low isocyanate content which results from the destruction of some of the isocyanate groups when the polyisocyanate is allowed to partially react with the polyether, as well as the destruction of some of the isocyanate groups due to the reaction with water upon and after emulsiflcation. Predictably, a low isocyanate content would severely reduce the ability of these polyisocyanate mixtures to function as efficient crosslinkers in coating compositions. In addition, these polyisocyanate emulsions suffer from stability problems due to the reaction of isocyanate groups with water, particularly those on the hydrophilic component (a). In a similar approach disclosed in US5202377, an emulsifiable polyisocyanate mixture comprising (a) a hydrophilic tertiary isocyanate functional oligomer and (b) a polyisocyanate having tertiary isocyanate groups, is produced by partially reacting a polyisocyanate containing tertiary isocyanate groups with a hydrophilic polyether. Coating compositions can be formed by combining (i) these polyisocyanate emulsions with (ii) separate aqueous solutions, emulsions or dispersions of film-forming polymers containing isocyanate-reactive functionality. These emulsifiable mixtures are said to produce more stable emulsions than those of US4663377 due to the lower reactivity of tertiary isocyanate groups. Despite the lower reactivity of the tertiary isocyanate groups, coatings produced from these emulsions may still suffer from low isocyanate content as well as stability problems. Still another approach to reducing the VOC of isocyanate crosslinked systems is found in US5075370. This reference generically discloses an aqueous coating composition comprising an aqueous solution and/or dispersion of a surface active isocyanate reactive resin (anionic olefinic polyol) into which a specific relatively low viscosity liquid unblocked polyisocyanate crosslinker is emulsified. The disclosed aqueous coating compositions are produced by emulsifying die isocyanate crosslinker into the aqueous solution and/or dispersion of the isocyanate reactive resin to produce an oil-in-water emulsion. It has, however, been found that, when systems were prepared in accordance with the teachings of US507 370 (emulsiflcation of the isocyanate into the aqueous resin solution/dispersion), the isocyanates do not properly incorporate into the resin solution/dispersion nor is an acceptable emulsion produced. After a short period of time a two phase system results, and films obtained from such systems display poor appearance characteristics, are hazy, contain microblisters, and have little or no gloss. A solution to many of the problems associated with the systems disclosed in US5075370 has been described in US5466745. This patent teaches a curable aqueous oil-in water emulsion prepared by admixing an aqueous medium with a non-aqueous, emulsifiable composition comprising an unblocked polyisocyanate crosslinking agent and a surface active isocyanate reactive material. While excellent stability and ultimate film properties can be achieved with the systems of this patent, viscosity and mixing constraints of the emulsifiable composition may require the addition of diluents prior to admixture with the aqueous medium, thereby undesirably increasing the VOC of me final formulated composition. All of the aforementioned references are incorporated herein for all purposes as if fully set forth. It would, therefore, be highly desirable to achieve the excellent stability and film properties of the systems of US5466745, but at overall lower VOC contents of 2.1 lbs/gal (252 g/1) or less. 15 SUMMARY OF THE INVENTION It has surprisingly been discovered that low VOC, isocyanate based aqueous curable compositions can be readily achieved when die primary components of _ _ the systems described in US5466745 - the aqueous medium, isocyanate crosslinking agent (containing at least two reactive isocyanate groups, and which in and of itself is substantially hydrophobic and non-dispersible in water) and surface active isocyanate reactive material - are formulated according to a process which, in accordance with a first aspect of the present invention, comprises the steps of: 25 (1) admixing (a) an unblocked isocyanate crosslinking agent containing at least two reactive isocyanate groups and being in and of itself substantially hydrophobic and non-dispersible in water, with (b) a mixture of (bl) a surface active isocyanate reactive material and (b2) an aqueous 0 medium, wherein in the mixture (b) the surface active isocyanate reactive material (bl) is water-dispersible, in proportions and under conditions to produce a substantially homogenous curable water-in-oil emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less; then 3 5 (ϋ) admixing the curable water-in-oil emulsion from step (i) with an aqueous medium in proportions and under conditions to produce a substantially homogenous oil-in-water emulsion of me surface active isocyanate reactive material and the isocyanate crosslinking agent in water, the oil- in-water emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less. 5 The present invention also relates to the precursor curable water-in-oil emulsion resulting from step (i). Specifically, this curable water-in-oil emulsion comprises a substantially homogenous emulsion of water in a substantially homogenous mixture of (bl) a surface active isocyanate reactive material which is water-dispersible, 0 and (a) an unblocked isocyanate crosslinking agent containing at least two reactive isocyanate groups and being in and of itself substantially hydrophobic and non- dispersible in water, the curable water-in-oil emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less, more preferably about 2.0 lbs/gal (240 g/1) or less, and 5 especially about 1.9 lbs/gal (228 g/1) or less. The present invention further relates to the substantially homogenous, curable oil-in-water emulsion prepared by the above process, and an aqueous curable composition based on this substantially homogenous, curable oil-in-water emulsion, Q possessing a VOC content of about 2.1 lbs/gal (252 g/1) or less, more preferably about 2.0 lbs/gal (240 g/1) or less, and especially about 1.9 lbs/gal (228 g/1) or less. VOC content, for the purposes of the present invention, is measured in accordance with United States Environmental Protection Agency Method 24. Optionally, such curable water-in-oil emulsions and the curable oil-in- 5 water emulsions derived therefrom may also comprise one or more of a neutralizing agent for rendering the surface active isocyanate material water-dispersible, a relatively minor amount (at most) of an organic solvent, a cure catalyst, and other well known auxiliaries and additives suited for the particular end use, to the extent that such optional 0 components do not raise the VOC content above the aforementioned level. As wi the curable oil-in-water emulsions of previously incorporated US5466745, the curable oil-in-water emulsions of e present invention, prepared by the process of the present invention, are substantially homogeneous; on standing, they do not separate into two phases and have a relatively long pot life before gelation; when cured, films obtained from curable oil-in-water emulsions prepared in accordance with the present invention have excellent physical and appearance characteristics; and, furthermore, by proper selection, of the emulsion components, films can be obtained which possess outstanding clarity and gloss, and contain minimal or no microblisters. A particular advantage of the present invention over the teaching of US5466745, as discussed above, is that systems having very low VOC contents can be more readily and easily formulated. These and other features and advantages of the present invention will be more readily understood by those skilled in the art from a reading of the following detailed description. TOT Aπ n-n DESCRIPTION OF THE PREFERRED EMBODIMENTS The Unblocked Polvisocvanate Crosslinking Agent Polyisocyanate crosslinking agents are generally well known in the art and have been extensively used in coating compositions in a monomenc, oligomeric and/or polymeric form. To function as an effective crosslinking agent, the polyisocyanate must have at least two reactive isocyanate groups. As suitable polyisocyanate crosslinking agents for use in the present invention may be mentioned any liquid or solid organic polyisocyanate containing at least two reactive isocyanate groups. In addition, such polyisocyanate crosslinking agents should in and of themselves be substantially hydrophobic and non-dispersible in water. Suitable polyisocyanate crosslinking agents may contain aliphatically, cycloaliphaticaliy, araiiphatically and/or aromatically bound isocyanate groups. Mixtures of polyisocyanates are also suitable. Particularly preferred are those polyisocyanates containing aliphatically, cycloaliphaticaliy and/or araiiphatically bound polyisocyanates including, but not limited to, the following specific examples: hexamethylene dϋsocyanatc; 2,2,4-trimethylhexametbylene diisocyanate; 2,4,4-trimethylhexamethylene diisocyanate; meta-α.α.α.α'-tetramethylxylylenediisocyanate (commercially available under die trade designation m-TMXDI™ aliphatic isocyanate from Cytec Industries Inc., West Paterson. New Jersey); para-α,o,α,α'-tetramethylxylylenediisocyanate; l-isocyanato-3,3,5- trimethyl-5-isocyanatomethyl cyclohexane (isophorone diisocyanate, abbreviated as IPDI); bis(4-isocyanatocyclohexyl)meuτane (hydrogenated MDI); biuret derivatives of various diisocyanates including, for example, hexa ethylene diisocyanate (commercially available under the trade designation Desmodur ® N of Bayer Corp., Pittsburgh, Pennsylvania); uretdione derivatives of various diisocyanates including, for example, hexamethylene diisocyanate and IPDI; isocyanurate derivatives of various diisocyanates including, for example, hexamethylene diisocyanate (commercially available under the trade designation Desmodur N 3390 of Bayer Corp., Pittsburgh, Pennsylvania) and IPDI (commercially available under the trade designation IPDI T 1890 polyisocyanate of Huls America, Inc., Piscataway, N.J.); and urethane adducts of diisocyanates with polyols such as, for example, e ylene glycol, propylene glycol, neopentyl glycol, trimemylolpropane, pentaerythritol and the like, as well as oligomeric and polymeric polyors. The preferred polyisocyanate crosslinking agents are those having at least one non-primary isocyanate group. Also preferred are the urethane dϋsocyanate/polyol adducts, more preferably those having an NCO content of at least 10 weight percent (on a 100% solids basis), and especially tfiose wherein the diisocyanate contains at least one non-primary isocyanate group. Particularly preferred are such urethane adducts having an average NCO functionality of greater tihan 2, and especially the dusocyamte/trimethylolpropane adducts. An especially preferred example of such is the 3:1 meta-α,α,α,o;'-terramethylxylylenediisocyaιιate/trimethylolpropane adduct commercially available under the trade designation CYTHANE ® 3174 aliphatic polyisocyanate of Cytec Industries Inc., West Paterson, New Jersey, which has the following properties: Non-Volatiles (% by weight) 74 +/- 1.0 NCO Content (% by weight on Solution) 10.2 +/- 0.5 Solvent Butyl Acetate. Another preferred example of a 3:1 meta- ,o:, ',α' tetramethylxylyieπedϋsocyanate/trimethylolpropane adduct has the following properties: Non-Volatiles (% by weight) 72 NCO Content (% by weight on Solution) 9.6 Solvent (90:10) Methyl Amyl Ketone/ Acetone. Another example of a diisocyanate/trixnethylolpropane adduct is a 3:1 IPDJytrimethylolpropane adduct commercially available under the trade designation SPENLITE ® 25-A4-60 aliphatic urethane prepolymer of Reichhold Chemicals, Research Triangle Park, North Carolina. The Surface Active Isocyanate Reactive Material The surface active isocyanate reactive material contains both (i) functionality capable of reacting with isocyanate groups, as well as (ii) hydropl ilizing functionality capable of rendering the surface active isocyanate reactive material water dispersible. In this manner, in the ultimate curable oil-in-water emulsions the reactive material acts as a surfactant for emulsifying the isocyanate crosslinkers and crther hydrophobic components. In the final film the surface active material is incorporated into the crosslinked network by virtue of its reactivity with the isocyanate crosslinkers, leading to improved water resistance. The preferred surface active isocyanate reactive material is polymeric in nature, with the hydrophilizing groups and isocyanate reactive functionality being incorporated into the polymer via appropriate monomer selection and or subsequent modification, as exemplified by a number of the previously incorporated references. As examples of such may be mentioned olefmic copolymers based on carboxyfunctioπal emylenically unsaturated monomers and hydroxyfunctional ethylenically unsaturated monomers; polyesters based on polybasic carboxylic acids and polyhydric alcohols; polyurethanes based on polyisocyanates, polyhydric alcohols and hydroxy acids; polyepoxy esters; and me like. Especially preferred for use in the present invention are the olefmic copolymers. Isocyanate reactive functionality, as utilized herein, refers to functionality which is reactive with isocyanate groups under cure conditions of the curable emulsions. Such isocyanate reactive functionality is generally well known to those skilled in die relevant art and includes, most commonly, active hydrogen containing functionality such as hydroxyl and amino groups. Hydroxyl is typically utilized as the isocyanate reactive functionality in coatings and is preferred for use in die present invention. Hydrophilizing functionality is also generally well known to those skilled in e relevant art and includes, most commonly, anion generating, cation generating and hydrophilic non-ionic functionality. By anion generating and cation generating is meant functionality such as carboxyl (anion generating) or amino (cation generating) which, when appropriately neutralized, becomes hydrophilic in nature. Hydrophilic non-ionic functionality is, in and of itself, hydrophilic in nature. The amount of hydrophilizing functionality present in the isocyanate reactive material should, upon at least partial neutralization of the anion generating or cation generating groups (if present), be sufficient to render d e isocyanate reactive material water-dispersible. Besides the aforementioned carboxyl groups, other examples of suitable groups which generate anions upon neutralization include sulfonic and phosphoric groups. Besides the aforementioned amino groups (substituted and unsubstituted), other examples of suitable groups which generate cations upon neutralization may be mentioned substituted and unsubstituted sulphonate groups, and substituted and unsubstituted phosphite groups. As examples of suitable hydrophilic non-ionic functionality may be mentioned amine oxide, phosphine oxide, alkyl or aryl phosphate, and polyether (polyethylene oxide). Preferred hydrophilizing groups for most applications are those which generate anions upon neutralization and, particularly, the carboxyl and sulfonic groups. Especially preferred are carboxyl groups. When coating compositions are formulated from the oil-in-water emulsions of the present invention, it is especially preferred that the polyisocyanate crosslinker and the surface active isocyanate reactive material comprise the primary film-foπning components of die coating. In such a case, the surface active isocyanate reactive material preferably possesses die following characteristics: a number average molecular weight (Mn) of from about 1000 to about 50000, and more preferably from about 1000 to about 12000; an acid number of from about 15 to about 150 mg KOH/G resin, more preferably from about 20 to about 70 mg KOH/G resin, and especially from about 20 to about 35 mg KOH/G resin; and an amount of hydroxyl groups of from about 2.5 weight percent to about 6 weight percent, more preferably from about 3 weight percent to about 5 weight percent, and especially from about 3.5% to about 4.5 weight percent (1 00% solids basis). In addition, die isocyanate reactive material should have a relatively low glass transition temperature (Tg) of 25 β C or less depending upon certain desired cure/drying characteristics. For example, for ambient cure systems the surface active isocyanate reactive material should have a low Tg of preferably below 0°C to increase reactivity with the isocyanate crosslinking agent. Where fast physical drying characteristics are important, higher Tg materials may be used. Particularly preferred surface active isocyanate reactive materials comprise copolymers of (meth)acrylic acid, hydroxyalkyl (meth)acrylates and, optionally, other free-radically polymerizable monomers which, when polymerized, meet me above characteristics. As exemplified by the previously incorporated references, production of such copolymers is well-known to those skilled in die relevant art and need not be discussed further. For coating applications such as automotive refinish, which require me combination of short dry times along with the development of early hardness and solvent resistance, it was found that a longer chain hydroxyalkyl (meth)acrylate such as 4- hydroxybutyl (me )acrylate is preferred. An specially preferred combination is die use of a long chain hydroxyalkyl (meth)acrylate and a crosslinker based on a tertiary polyisocyanate crosslinker. While a faster and more complete cure may be expected wim a more flexible hydroxyl chain, e development of early dry time under ambient conditions, and hardness under forced dry conditions is surprising. Incorporation of 5- 20 wt %, preferably about 10 wt.%, styrene into a surface active acrylic polyol based on 2-hydroxyethyl (metiι)acrylate also improves the dry time and early hardness of me system. Again, benefits of shorter dry time under ambient conditions and early hardness development under forced dry conditions were unanticipated. These improvements may be related to die fact that the introduction of styrene provides a smaller particle size distribution of the curable emulsion. Particle size was shown to effect the dry times of coatings prepared from surface active polyols based on (meth)acrylic monomers. In comparison, achieving the same properties of short dry time and early hardness by increasing die glass transition temperature of the (meth)acrylic based polyol can led to coating which do not develop complete solvent resistance. In particular, it has been found that the addition of styrene provides beneficial results when die polyol (i.e. the surface reactive isocyanate reactive material) has a hydroxyl content of less tiian about 1.8 wt.% (85% solids) and a Tg of less tiian about 15 β C. It should be noted that, for applications such as electrodeposition, the common hydrophilizing functionality is cation generating. Especially preferred in this case are amino groups, and similar constraints to those set forth above (with d e exception of acid number being exchanged for amine equivalency) would apply to die surface active isocyanate reactive materials utilized in forming curable emulsions for this application. Although the polyisocyanate crosslinker and die surface active isocyanate . . . reactive material can be present in me water-in-od and oil-in-water emulsions m varying amounts, when tiiese components comprise the primary ium-forming components of a subsequently formed coating, it is preferred that tiiey be present in die emulsions in amounts such that the NCO:OH reactive functionality ratio is in the range of from about 0.5:1 to about 2:1, and especially in the range of from about 0.8:1 to about 1.2:1. Optional Ingredients As indicated earlier, the emulsifiable compositions may also comprise additional ingredients such as, for example, neutralizing agents for rendering me surface active isocyanate material water-dispersible, cure catalysts and relatively minor amounts of an organic solvent. When an anion generating group is present on the isocyanate reactive material, any base may be used as the neutralizing agent to produce an anionic surface active material. Normally, a base capable of converting a carboxyl group to a carboxylate anion is used as the neutralizing agent, including organic and inorganic bases such as sodium and potassium hydroxide, sodium and potassium carbonate, and amines such as ammonia, primary, secondary and tertiary amines. Tertiary amines and ammonia are preferred, and particularly tertiary amines such as triemyl amine. Similarly, when a cation generating group is present on the isocyanate reactive material, any acid may be used as the neutralizing agent to produce a cationic surface active material. As discussed in further detail below, when utilized die neutralizing agents may be present at any stage of die process, for example, as a component of the aqueous medium or as a part of d e surface active isocyanate reactive material (preneutralization). In any case, die total amount of neutralizing agent (when present) must at least be sufficient to render die surface active isocyanate reactive material water dispersible. The level of neutralization can have an effect on the particle size distribution of d e final oil-in-water curable emulsion. Generally speaking, die small particle size oil-in-water emulsions tend to give faster dry times. For more hydrophilic polyols, typically tiiσse with higher hydroxyl contents (greater than or equal to about 1.8 wt.% based on 85% solids) and higher glass transition (Tg) temperatures (greater tiian about 15 β C), a reduced level of neutralization can improve die compatibilization and give die desired smaller particle size distribution. For more hydrophobic polyols, decreasing neutralization can be expected to increase die particle size of die oil-in-water emulsion. In particular, it is desirable to decreased neutralization to about 30% to about 60% , preferably about 40% to about 50%. An indication of particle size can be obtained by observing die appearance of die oil-in-water emulsion. A bluish opalescence appearance indicates a desired particle size distribution. As die appearance becomes more milky it indicates a less desirable particle size distribution. Water-in-oil curable emulsions witii a median particle size less than 0.2 microns are preferred, /38230 especially preferred emulsions have median particle size between 0.11 and 0.16 microns. Cure catalysts for isocyanates are well known to those skilled in die relevant coatings art. Preferred are organometallic catalysts and, particularly, organotin compounds such as dibutyltin di-2-etirylhexoate, dibutyltin diisooctyl maleate, dibenzyltin di-2-ethylhexoate, dibutyltin dilaurate, dimethyltin dilauratc, tctrabutyl diacetoxy distannoxane, tetramethyl diacetoxy distannoxane, tetrapropyl diacetoxy distannoxane, dibutyltin dichloride, and die like. A preferred catalyst for tertiary polyisocyanates is a dimettryltin dicarboxylate sold under die trade name Fo rez ® UL 28, Witco Corporation. Any organic solvents present in die emulsifiable compositions are generally those present in the various components. For example, many coatings components are not commercially available on a 100% solids basis but are rather a somewhat lower solids content in an appropriate solvent as required to achieve a particular viscosity suitable for mixing. Preferably, no otiier organic solvent (otiier than as contained in die components themselves) is or need be added to achieve acceptable rcsult$ - Depending on their end use, the emulsions of de present invention may also comprise otiier well known auxiliaries and additives. Those typically utilized in the coatings industry include, for example, foam inhibitors, leveling aids, pigments, pigment dispersing aids, dyes, UV absorbers (including hydroxy aryl triazine types (such as CYAGARD* UV-1164 of Cytec Industries Inc.), benzotriazole types (such as CYAGARD* UV-2337 of Cytec Industries Inc.) and benzophenone types), heat stabilizers, otiier stabilizing additives such as antioxidants, hindered amine light stabilizers (such as Sanduvor™ 3055 and 3058 f Clariant) and die like. These optional ingredients are in general well-known to those skilled in the relevant art, as exemplified in die many previously incorporated references, and reference may be had thereto for further details. Reference may specifically be had to US4426471, US4344876, US4619956, US5106891, US5322868, US5461151. EP-A- 0434608, EP-A-0444323 and EP-A-0704437, all of which are incorporated by reference herein as if fully set forth, for detailed discussions of die stabilization of coatings and other curable compositions widi UV absorbers, hindered amine light stabilizers and or other types of light stabilizers. Process for Preparing the Curable Emulsions and the Curable Emulsions So Prepared As mentioned above, die process for preparing a low VOC, isocyanate based aqueous curable compositions in accordance whh the present invention comprises me steps of: (0 admixing (a) an unblocked isocyanate crosslinking agent containing at least two reactive isocyanate groups and being in and of itself substantially hydrophobic and non-dispersible in water, widi (b) a mixture of (bl) a surface active isocyanate reactive material and (b2) an aqueous medium, wherein in die mixture (b) die surface active isocyanate reactive material (bl) is water-dispersible, in proportions and under conditions to produce a substantially homogenous curable water-in-oil emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less; then (ii) admixing die curable water-in-oil emulsion from step (i) with an aqueous medium in proportions and under conditions to produce a substantially homogenous oil-in- water emulsion of die surface active isocyanate reactive material and the isocyanate crosslinking agent in the aqueous medium, the oil-in-water emulsion having a VOC content of about 2.1 lbs gal (252 g/1) or less. Preferably, the water-in-oil and oil-in-water emulsions from steps (i) and (ii), respectively, have VOC contents of about 2.0 lbs/gal (240 g/1) or less, and especially about 1.9 lbs/gal (228 g/1) or less. As is evident, a key aspect to obtaining improved results is to first prepare a water-in-oil emulsion of the components, men add additional aqueous medium until phase inversion occurs. Additional aqueous medium can tiien be added to adjust the resulting oil-in-water emulsions to die desired solids content and viscosity as appropriate for a chosen end use. The admixing can be accomplished by any number of well known techniques, but preferably by: (i) adding die aqueous medium, ehher continuously or in portions, to die surface active isocyanate reactive material to produce a substantially homogenous mixture (wherein in the mixture the surface active isocyanate reactive material is water dispersible by appropriate content of non- ionic and/or neutralized ionic hydrophilizing functionality); (ib) adding die isocyanate crosslinking agent, either continuously or in portions, to die mixture from (ia) in the desired proportions and under conditions (e.g., stirring at ambient temperature) so diat a water-in-oil emulsion is produced; (iia) adding additional aqueous medium, either continuously or in portions, to die water-in-oil emulsions from (ib) in an amount and under conditions (e.g., stirring at ambient temperature) until phase inversion occurs; men (iib) adding additional aqueous medium, either continuously or in portions, to die oil-in-water emulsions from (iia) in amounts and under conditions (e.g., stirring at ambient temperature) to achieve the desired solids content and viscosity. In the aforementioned procedure, die neutralizing agent (if utilized) may ¬ be used to preneutralize die surface active isocyanate reactive material (which is preferred), and/or may be present as a part of the aqueous medium to neutralize during the initial mixing step (ia). In eiύier case, sufficient neutralizing agent should be present in total in order to render die surface active isocyanate reactive material water- dispersible. The aqueous medium may comprise solely water or may, as indicated above, comprises other components such as die neutralizing agent. Otiier than die neutralizing agent, die aqueous medium may also include any one of a number of other auxiliaries and additives common to the end use, as well as minor amounts (at most) of water-miscible organic solvents to ease emulsiflcation or adjust viscosity, although this is not preferred. It is preferred mat any such additional ingredients be incorporated along with die surface active isocyanate reactive material and isocyanate crosslinking agent; in odier words, it is preferred diat die aqueous medium comprise solely water, or comprise water and a neutralizing agent. Most preferably, the aqueous medium is just water. As indicated above, in step (i) die aqueous medium and surface active isocyanate reactive material are mixed, followed by die isocyanate crosslinking agent, in proportions and under conditions to achieve a water-in-oil emulsion. The amount of each component required to achieve a water-in-oil emulsion, of course, will vary depending on a number of factors recognizable by ύiose of ordinary skill in the relevant art. One important factor is die hydrophilicity/lipophilicity of die non-water components of die emulsion and the relationship diat tins has to die amount of water diat can be present in die system before phase inversion occurs. It is, however, well within die abilities of die skilled person to determine by routine metiiods the phase inversion point of a formulated system and die amount of water which die system can tolerate prior to the onset of phase instability. Preferably, and typically, die water-in-oil emulsion will comprise up to about 50% by weight water, and more preferably from about 35% to about 45% by weight water. From the determination of the phase inversion point of the formulated system, the skilled person is then readily apprised of die amount of additional aqueous medium diat needs to be added in step (ii) to achieve phase inversion. Further, based on a particular chosen end use, the skilled person can readily adjust die solids/water content of die od-in-water emulsions to those required far diat end use. Via die above procedure, substantially homogenous, curable, oil-in-water emulsions can be produced which may find use in a variety of fields including, for example, coatings and adhesives applications. Coating Compositions A primary utility of the curable oil-in-water emulsions of die present invention is in e coatings industry, for example, in automotive original equipment manufacturing (OEM), industrial maintenance, electrodeposition and, particularly, ambient temperature cure automotive refinish applications. They are also usable in architectural, coil, can, plastic and wood coating applications. The curable emulsions may be utilized in clearcoat applications, or may contain a pigment for otiier applications. For coatings applications, typical solids contents generally range from about 20% to about 75% by weight solids, but preferably are in die range of from about 30% to about 55% by weight solids, depending on the mediod of application chosen. For die purpose of the present invention, solids content is determined in accordance with ASTM D4713 (method B). An especially preferred application for tiiese curable emulsions is as an ambient temp 'erature cure, automotive refinish clearcoat. Coatings obtained from these curable emulsions may be applied to a variety of substrates in any desirable manner, such as by roller coating, spraying, brushing, sprinkling, flow coating, dipping, electrostatic spraying and electrophoresis. A preferred method of application is by spraying, and one skilled in die relevant art can formulate aqueous coating compositions so as to be spray applicable (e.g., witii an appropriate spray viscosity) as indicated above. Depending on die ultimate end use, coatings may be formulated as ambient or elevated temperature cure systems. For example, for refinish coatings applications the coatings will be formulated for ambient cure (ahhough they may in fact be cured at elevated temperatures), whereas for automotive original equipment manufacturing (OEM) applications the coatings will be formulated for cure at elevated temperatures of, typically, 125 β C. Ahhough die present invention is described with reference to certain preferred embodiments, it is apparent that variations or modifications tiiereof may be made by ύiose skilled in the art without departing from the scope of tins invention as defined by the appended claims. Example 1. Production of Low VOC Surface Active Isocyanate Reactive Material 2-Heptanone (MAK Solvent), 98% (71.1 g) was added to a 500 niilliliter reactor equipped with a stirrer, a reflux condenser, and a thermocouple under a blanket of nitrogen and heated with oil to 148 -150 * C. A monomer feed mixture (393.9 grams total) consisting of butyl acrylate (50.34 wt %). 2-hydrθxyemyl actylate (21.96 wt %), methyl mediacrylate (21.30 wt %), acrylic acid (6.41 wt %) was prepared and charged to a graduated cylinder attached to a feed pump. Di-tertiary amyl peroxide (d-t-APO) (21.9 grams total) was charged to a feed pump. Catalyst feed (1.6 g.) was added over diirteen minutes before die addition of monomer. Using a piston metering pump, die monomer was added to die reactor over five hours and eight minutes. During ύϋs time die reaction temperature reached a maximum of 152 "C. The total reaction time was six hours and fifteen minutes. After the addition of all die monomer feed, 0.2 g. of catalyst was fed over an additional nineteen minutes. The reactor was heated and stirred at 146- 150 'C for an additional thirty five minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 84.4 weight percent. The relative number average molecular weight of die polymer solution was 3300; a polydispersity index of 3.2 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperature of a dried film was determined to be -6'C via differential scanning calorimetry. The acidity was calculated to be 42 mg. of KOH per gram of solution; die hydroxy concentration was calculated to be 2.60 weight percent. Production Of Water Dispersible Isocyanate Reactive Material by Preneutraliziiig Acrylic Before Adding Water To 100 grams of the above acrylic add 6.64 grams of trieωylamine, 99% and mix well. Add 71 grams of water and mix until dissolved. The theoretical non volatiles equals 47.6 weight percent solids. The theoretical weight percent water is 40.00. The theoretical weight percent solvent, including 3.6% triethylamine, is 12.4. The calculated acidity is 3.6 mg. of KOH per gram of solution; die calculated hydroxyl concentration is 1.5 weight percent. Example 2. Production of Low VOC Styrenic Surface Active Isocyanate Reactive Material 2-Heptanone (MAK Solvent), 98% (71.7 g) was added to a 500 milliliter reactor equipped with a stirrer, a reflux condenser, and a thermocouple under a blanket of nitrogen and heated with an oil batii to 148 -151 * C. A monomer feed mixture (395.8 grams total) consisting of styrene (10.00 wt%), butyl acrylate (50.00 wt %), 2-hydroxyethyl acrylate (21.96 wt %), methyl meihacrylate (11.63 wt %), acrylic acid (6.41 wt %) was prepared. The monomer feed was charged to a graduated cylinder attached to a feed pump. Di-tertiary amyl peroxide (d-t-APO) (15.56 grams total) was charged to a feed pump. Catalyst feed (1.2 g.) was added over thirteen minutes before die addition of monomer. Using a piston metering pump, die monomer was added to die reactor over five hours and two minutes. During tins time die reaction temperature reached a maximum of 151'C. The total reaction time was six hours and two minutes. 0 After die addition of all die monomer feed, 0.8 g. of catalyst was fed over an additional seventeen minutes. The reactor was heated and stirred at 146- 150 * C for an additional thirty minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 84.1 weight percent. The relative number average molecular weight of 5 the polymer solution was 4400; a polydispersity index of 6.7 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperamre of a dried film was determined to be 0.3" C via differential scanning calorimetry. The acidity was calculated to be 42 mg. of KOH per gram of Q solution; die hydroxy concentration was calculated to be 2.59 weight percent. Production Of Water Dispersible Styrenic Isocyanate Reactive Material by Preneutralization Acrylic before adding Water To 100 grams of the above acrylic add 6.51 grams.of triedrylamine, 99% 5 and mix well. Add 71.01 grams of water and mix until dissolved. The tiieoretical weight percent solids, equals 47.38. The theoretical weight percent water is 40.00. The theoretical weight percent solvent, including 3.63% triemylamine, is 12.62. The calculated acidity is 3.6 mg. of KOH per gram of solution; the calculated hydroxyl 0 concentration is 1.5 weight percent. Example 3. Production of Low VOC Surface Active Isocyanate Reactive Material Using 4-Hydroxy Butyl Acrylate 5 2-Heptanone (MAK Solvent), 98% (71.7 g) was added to a 500 milliliter reactor equipped with a stirrer, a reflux condenser, and a uiermocouple under a blanket of nitrogen and heated witii an oil batii to 148 -151 * C. A monomer feed mixture (387.1 grams total) consisting of butyl acrylate (40.81 wt %), 4-hydroxybutyl acrylate (27.88 wt %), methyl mediacrylate (24.90 wt %), acrylic acid (6.41 wt %) was prepared. The monomer feed was charged to a graduated cylinder attached to a feed pump. Di-tertiary amyl peroxide (d-t-APO) (22.3 grams total) was charged to a feed pump. Catalyst feed (1.6 g.) was added over thirteen minutes before die addition of monomer. Using a piston metering pump, die monomer was added to die reactor over five hours and twenty two minutes. During tins time the reaction temperature reached a maximum of 151 'C. The total reaction time was six hours and two minutes. After the addition of all die monomer feed, 0.8 g. of catalyst was fed over an additional thirteen minutes. The reactor was heated and stirred at 149-150 "C for an additional fourteen minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 15 82.5 weight percent. The relative number average molecular weight of die polymer solution was 3680; a polydispersity index of 9.7 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperamre of a dried film was determined to be -8.0' C via differential scanning 2 o calorimetry. The acidity was calculated to be 41 mg. of KOH per gram of solution; the hydroxy concentration was calculated to be 2.55 weight percent. Production Of Water Dispersible Longer Chain Isocyanate Reactive Material by Preneutralization Acrytic Before Adding Water 25 To 100 grams of die above acrylic add 6.39 grams of triediylamine, 99% and mix well. Add 71.0 grams of DI water to die neutralized acrylic and mix until dissolved. The tiieoretical weight percent solids, equals 46.51. The theoretical weight percent water is 40.00. The tiieoretical weight percent solvent, including 3.62% 30 triediylamine, is 13.49. The calculated acidity is 3.5 mg. of KOH per gram of solution; the calculated hydroxyl concentration is 1.4 weight percent. 35 Example 4. Concurrent addition of amiπe and water for neutralization The procedure described in Example 1 is repeated to produce a similar low VOC surface active isocyanate reactive material. Production Of Water Dispersible Isocyanate Reactive Material by Neutralization In water To 100 grams of die above acrylic add 6.67 grams of 99% triediylamine, in 71.1 grams of water and mix well. The tiieoretical non volatile, or weight percent solids, equals 48.49. The theoretical weight percent water is 40.00. The ϋieoretical weight percent solvent, including 3.72% trie ylaniine, is 11.51. The calculated acidity is 3.6 mg. of KOH per gram of solution; de calculated hydroxyl concentration is 1.5 weight percent. Example 5. Production of Low VOC Surface Active Isocyanate Reactive Material With Higher Hydroxy and Higher Glass Transition Temperature and Lower Acidity 2-Heptanone (MAK Solvent), 98% (71.1 g) was added to a 500 milliliter reactor equipped whh a stirrer, a reflux condenser, and a thermocouple under a blanket of nitrogen and heated with oil to 148 -150'C. A monomer feed mixture (396.8 grams total) consisting of butyl acrylate (21.99 wt %), 2-hydroxyedιyl acrylate (32.04 wt %), metiiyl metiiacrylate (43.00 wt %), acrylic acid (2.96 wt %) was prepared and charged to a graduated cylinder attached to a feed pump. Di-tertiary amyl peroxide (d-t-APO) (21.3 grams total) was charged to a metering pump for controlled addition during die reaction . The d-t-APO is die free radical initiator for the polymerization. A portion of this catalyst feed (1.4 g.) was added over thirteen minutes before die addition of monomer. Using a piston metering pump, the monomer was added to die reactor over five hours and four minutes. During this time die reaction temperature reached a ma dmum of 152 'C. The total reaction time was six hours. After the addition of all de monomer feed, 0.82 g. of catalyst was fed over an additional thirteen minutes. The reactor was heated and stirred at 146-150 * C for an additional thirty minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 85.5 weight percent. The relative number average molecular weight of die polymer solution was 2540; a polydispersity index of 2.5 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperature of a dried film was determined to be 10' C via differential scanning calorimetry. The acidity was calculated to be 20 mg. of KOH per gram of solution; th hydroxy concentration was calculated to be 3.85 weight percent. Production Of Water Dispersible Isocyanate Reactive Material by Neutralizing in Water To 100 grams of the above acrylic add 3.05 grams of 99% triediylamine in 68.7 grams of DI water and mix well. The tiieoretical non volatile, or weight percent solids, equals 49.79. The tiieoretical weight percent water is 40.00. The tiieoretical weight percent solvent, including 1.76% triediylamine, is 10.21. The calculated acidity is 1.7 mg. of KOH per gram of solution; die calculated hydroxyl concentration is 2.2 weight percent. Example 6. Production of Low VOC Surface Active Isocyanate Reactive Material Containing Low Hydroxy Content and Low Glass Transition Temperature 2-Heptanone (MAK Solvent), 98% (150 g) was added to a 3 liter jacketed reactor equipped with a stirrer, a reflux condenser, and a thermocouple under a blanket of nitrogen and heated with oil to 148 -150 'C. A monomer feed mixture (2252 grams total) consisting of butyl acrylate (50.33 wt %), 2-hydroxyedιyl acrylate (21.96 wt %), metiryl methacrylate (21.30 wt %), acrylic acid (6.41 wt %) was prepared and MAK solvent was added (250 g). The monomer feed was charged to a graduated cylinder attached to a feed pump. Di-tertiary amyl peroxide (d-t-APO) (115 grams total) was charged to a feed pump. Catalyst feed (9.5 g.) was added over thirteen minutes before the addition of monomer. Using a piston metering pump, the monomer was added to die reactor over four hours and six minutes. During tins time de reaction temperature reached a maT.mi.nfi of 152 'C. The total reaction time was five hours and eleven minutes. After die addition of all the monomer feed, 8 g. of catalyst was fed over an additional twenty-one minutes. The reactor was heated and stirred at 146-150' C for an additional thirty minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 84.4 weight percent. The relative number average molecular weight of the polymer solution was 3840; a polydispersity index of 4.6 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperamre of a dried film was determined to be -7 * C via differential scanning calorimetry. The acidity was calculated to be 42 mg. of KOH per gram of solution; die hydroxy concentration was calculated to be 2.6 weight percent. Production Of Water Dispersible Isocyanate Reactive Material by Preneutralizing Acrylic Before Adding Water To 100 grams of die above acrylic add 6.44 grams' of triediylamine, 99% and mix well. Add 70.96 grams of DI water to die neutralized acrylic. The theoretical non volatile, or weight percent solids, equals 47.58. The theoretical weight percent water is 40.00. The tiieoretical weight percent solvent, including 3.63% triediylamine, is 12.42. The calculated acidity is 3.6 mg. of KOH per gram of solution; the calculated hydroxyl concentration is 1.5 weight percent. Example 7. Production of Low VOC Surface Active Isocyanate Reactive Material Containing Higher Hydroxy and Low Glass Transition Temperature 2-Heptanone (MAK Solvent), 98% (401.1 g) was added to a 3 liter jacketed reactor equipped whn a stirrer, a reflux condenser, and a ώermocouple under a blanket of nitrogen and heated with oil to 148 -150 * C. A monomer feed mixture (2174 grams total) consisting of butyl acrylate (43.20 wt %), 2-hydroxyetiiyl acrylate (32.06 wt %), meuiyl methacrylate (18.36 wt %), acrylic acid (6.41 wt %) was prepared and charged to a graduated cylinder attached to a feed pump. Di-tertiary amyl peroxide (d-t-APO) (96.7 grams total) was charged to a feed pump. Catalyst feed (8.7 g.) was added over sixteen minutes before the addition of monomer. Using a piston metering pump, de monomer was added to die reactor over five hours and thirty three minutes. During this time die reaction temperamre reached a maximum of 15d * C. The total reaction time was six hours and thirty six minutes. After the addition of all die monomer feed, 8.3 g. of catalyst was fed over an additional thirty tiiree minutes. The reactor was heated and stirred at 148-156 * C for an additional thirty minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 83.9 weight percent. The relative number average molecular weight of die polymer solution was 3920; a polydispersity index of 21.4 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperature of a dried film was determined to be -2 * C via differential scanning calorimetry. The acidity was calculated to be 42 mg. of KOH per gram of solution; die hydroxy concentration was calculated to be 3.78 weight percent. Production Of Water Dispersible Isocyanate Reactive Material by Neutralizing in Water at a Lower Percent Neutralization of Carboxylic Acid Groups To 100 grams of die above acrylic add 4.20 grams of 99% triemylamine in 69.47 grams of DI water and mix well. The theoretical non volatile, or weight percent solids, equals 48.30. The tiieoretical weight percent water is 40.00. The theoretical weight percent solvent, including 2.4% triethylamine, is 11.70. The calculated acidity is 10.9 mg. of KOH per gram of solution; die calculated hydroxyl concentration is 2.2 weight percent. Example 8. Production of Low VOC Surface Active Isocyanate Reactive Material Containing Higher Hydroxy and Higher Glass Transition Temperature 2-Heptanone (MAK Solvent), 98% (401.1 g) was added to a 3 liter jacketed reactor equipped widi a stirrer, a reflux condenser, and a thermocouple under a blanket of nitrogen and heated with oil to 148 -150'C. A monomer feed mixture (2182 grams total) consisting of butyl acrylate (24.51 wt %), 2-hydroxyetiiyl acrylate (32.03 wt %), mediyl methacrylate (37.06 wt %), acrylic acid (6.41 wt %) was prepared and charged to a graduated cylinder attached to a feed pump. Di-tertiary a yl peroxide (d-t-APO) (118.7 grams total) was charged to a feed pump. Catalyst feed (8.2 g.) was added over thirteen minutes before die addition of monomer. Using a piston metering pump, die monomer was added to the reactor over five hours and nine minutes. During this time the reaction temperature reached a maximum of 151" C. The total reaction time was six hours and thirty six minutes. After die addition of all die monomer feed, 9.8 g. of catalyst was fed over an additional uϋrty eight minutes. The reactor was heated and stirred at 146-151 "C for an additional tiϋrty six minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 83.9 weight percent. The relative number average molecular weight of die polymer solution was 3590; a polydispersity index of 5.2 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperature of a dried film was determined to be 10' C via differential scanning calorimetry. The acidity was calculated to be 42 mg. of KOH per gram of solution; die hydroxy concentration was calculated to be 3.77 weight percent. 0 Production Of Water Dispersible Isocyanate Reactive Material By Neutralizing in Water at a Lower Percent Neutralization of Carboxylic A d Groups To 100 grams of the above acrylic add 2.6 grams of 99% triediylamine in 5 70.0 grams of DI water and mix well. The theoretical non volatile, or weight percent solids, equals 48.55. The tiieoretical weight percent water is 40.56. The theoretical weight percent solvent, including 2.4% triethylamine, is 10.89. The calculated acidity- is 15.98 mg. of KOH per gram of solution; the calculated hydroxyl concentration is _ 2.19 weight percent. Example 9. Production of Low VOC Surface Active Isocyanate Reactive Material Containing Low Hydroxy and Higher Glass Transition Temperature 2-Heptanone (MAK Solvent), 98% (401.1 g) was added to a 3 liter 5 jacketed reactor equipped with a stirrer, a reflux condenser, and a ύiermocouple under a blanket of nitrogen and heated widi oil to 148 -150 * C. A monomer feed mixture (2151 grams total) consisting of butyl acrylate (31.00 wt %), 2-hydroxyedιyl acrylate (21.5 wt %), methyl methacrylate (40.64 wt %), acrylic acid (6.41 wt %) was prepared and 0 charged to a graduated cylinder attached to a feed pump. Di-tertiary a yl peroxide (d-t-APO) (155.2 grams total) was charged to a feed pump. Catalyst feed (12.3 g.) was added over fifteen minutes before die addition of monomer. Using a piston metering pump, die monomer was added to die reactor over five hours and fifteen minutes. 5 During tins time he reaction temperature reached a maximum of 152 * C. The total reaction time was six hours and forty three minutes. After the addition of all the monomer feed, 14.7 g. of catalyst was fed over an additional tiύrty tiiree mmutes. The reactor was heated and stirred at 146-152 * C for an additional thirty three minutes. The polymer solution was cooled and analyzed. The concentration was determined to be 83.9 weight percent. The relative number average molecular weight of the polymer solution was 2570; a polydispersity index of 3.0 was obtained via high pressure size exclusion chromatography compared against polystyrene standards. The glass transition temperature of a dried film was determined to be 4 * C via differential scanning calorimetry. The acidity was calculated to be 42 mg. of KOH per gram of solution; die hydroxy concentration was calculated to be 2.59 weight percent. Production Of Water Dispersible Isocyanate Reactive Material by Neutralizing in Water at a Lower Percent Neutralization of Carboxylic Acid Groups To 100 grams of die above acrylic add 3.5 grams of 99% triethylamine in 70.0 grams of DI water and mix well. The tiieoretical non volatile, or weight percent solids, equals 48.36. The theoretical weight percent water is 40.00. The tiieoretical weight percent solvent, including 2.0% trtediylamine, is 11.64. The calculated acidity is 13.1 mg. of KOH per gram of solution; the calculated hydroxyl concentration is 1.5 weight percent. Examples 10 to 22. Production of Low VOC Surface Active Isocyanate Reactive Material The procedure of Example 1 was followed to produce low VOC surface active isocyanate reactive materials. But, In these examples die desired attributes of die material were synthesized by variations of the monomer composition and the initiator feed rates. Monomer Compositions Used in Examples 10 to 22. The hydroxy concentration was adjusted by the amount of 2-hydroxycthyl acrylate monomer m die feed. In these examples the 2-hydroxyethyl acrylate monomer was varied between 21.95 to 32.03 weight percent. Thus, die hydroxy concentration varied from 3.2 to 3.8 weight percent. The glass transition was adjusted using botii die butyl acrylate and the methyl methacrylate monomers. In these examples die butyl acrylate was adjusted from 24.42 to 50.33 weight percent of die monomer mixture. In tiiese examples die metiiyl mediacr late was adjusted from 18.36 to 40.65 weight percent of the monomer mixture. Thus, die glass transition temperature varied from - 13 'C to 18 'C via differential scanning calorimetry measurements. The acrylic acid monomer remained the same throughout these examples. The amount of acrylic acid monomer was 6.41 weight percent of the total monomer mixture In Examples 10 to 22 . 0 Free Radical Initiator Quantity Used in Examples 10 to 22 In Examples 10 to 22 the catalyst was varied from 2.9 to 6.3 grams per hundred grams of monomer depending on die desired molecular weight. Thus, die number average molecular weight of die materials varied from 2580 to 4740 and the 5 polydispersity index varied from 2.7 to 9.1 analyzed via high pressure size exclusion chromatography compared against polystyrene standards. Production Of Water Dispersible Isocyanate Reactive Material by Preneutralizing Q Acrylic Before Adding Water in Examples 10 to 22 The procedure of Example 1 was used to produce die water dispersible Isocyanate reactive material show in Table 1 as "Polyol Information", examples numbers 10 to 22. 5 Production of Curable Emulsion A To 11.3 g of surface active isocyanate reactive material produced by d e procedure given in Example 1, were added under stirring, the following components in the listed order to produce a substantially homogeneous water-in-oil emulsifiable 0 composition: 0.43 g of a 10 wt % solution of dibutyltin dilaurate in ureύiane grade propylene glycol monomediyl etiier acetate, and 4.20 g of CYTHANE ® 3174 aliphatic polyisocyanate resin (74 wt % 5 solids in normal butyl acetate). To this emulsifiable composition were added, at room temperature, four portions of water (10.4 g total) widi die resulting mixture being stirred after each addition to give a substantially homogeneous oil-in-water emulsion. Curable emulsion A contained 32 wt % non-volatiles and an NCO/OH equivalent ratio of 1:1. Volatile organic compounds (VOC) were present at a level of not more tiian 2.1 lb/gal as calculated by EPA Mediod 24. Production of Curable Emulsions B through P Curable emulsions B through P were produced in a manner simuar to Curable Emulsion A widi the amount of CYTHANE being adjusted to maintain a 1:1 NCO/OH equivalent ratio. The amount of water added was also adjusted to maintain a workable final viscosity. Typical non-volatile content ranged from 26 to 39 wt %. Drawdowns of Curable Emulsions A-P were made on BONDERTTE ® ED- 5050 cold rolled steel panels, a product of Advanced Coating Technologies, Sourhfield, MI. using a 76 micron wet film thickness wire cator. Wet films of 76 microns thickness corresponding to dry film thickness of 30 to 40 microns were obtained. The films were cured at room temperature to produce high gloss coatings. TABLE 1 PROPERTIES OF ROOM TEMPERATURE CURED COAΗNGS Polyol Information Film Properties after 7 days at 25°C Curable Example Knoop NCO MEK Appearance E ul. No. Tg OH* Mn Hardness reacted resistance A 1 -6 1.5 3300 7.0 90 200+ Clear, no blisters B 10 -13 2.1 2580 8.4 75 20 200+ Clear, no blisters C 11 -7 1.5 3840 9.3 93 200+ Clear, no blisters D 12 -7 2.1 3710 12.6 76 20/200+ Clear, no blisters Dl-LN 7 -2 2.1 3920 10.2 63 30 200+ Clear, no blisters E 13 14 1.5 3000 8.5 76 20/200+ Clear, no blisters F 14 18 2.1 3060 7.9 57 20/200+ Clear, no blisters G 15 15 1.5 4020 12.6 82 10/60 Clear, no blister Gl-LN 9 16 1.5 2574 14.4 61 120 200+ Clear, no blisters H 16 IS 2.1 3830 12.4 53 10/60 Clear, no blisters Hl-LN 8 15 2.1 3590 15.0 46 100/200+ Clear, no blisters I 17 -8 1.8 3100 10.6 67 10/150 Clear, no blisters J 18 15 1.8 2980 9.3 54 10/80 Clear, no blisters K 19 -2 1.8 3050 9.3 62 10/150 Clear, no blisters L 20 11 1.8 3740 10.1 62 10/150 Clear, no blisters M 21 6 1.8 4740 12.4 63 10/150 Clear, no blisters N 22 3 1.8 3550 10.5 61 10/150 Clear, no blisters O 3 -8 1.4 3680 8.9 87 200+ Clear, no blisters P 2 0 l.S 4440 12.8 74 200+ Clear, no blisters * wt % OH in isocyanate reactive polyol at 48% solids after neutralization and water addition Example 23 Curable Compositions Q and R. The use of TJL 28 in place of dibutyltin dilaurate (DBTDL) also provides faster development of solvent resistance under ambient cure conditions. Curable compositions Q and R were prepared as in O and P except diat 0.5 wt % Fomrez ® UL 28 was substituted for DBTDL. Film Cure Schedule: 1 day @ 25'C/50% RH Curable Composition Catalyst MEK double rubs O DBTDL 20/150 Q U 28 10/200+ P DBTDL 10/100 R UL 28 10/200+ Example 24. Demonstration that die particle size distribution of the of oil-in-water curable emulsion as measured by emulsion appearance, influences die dry time of coating Curable Emulsion C, E, and F were prepared to give bluish and milky appearing oil-in- * -.« . , water emuiSUUlS. ølUISll apμcaiaiivc vuuciαica wiui <t IUCUKUI muuc aix s - * s .i. microns for these acryhc polyols, milky appearance correlates widi a median particle size > 0.35 microns. Curable Emulsion Appearance Dry Time (hrs) C Milky 4.25 C Bluish 1.5 E Milky 4.25 E Bluish 1.5 F Milky 4.25 F Bluish 3.0 Example 24. The use of lower percent neutralization of de carboxylic acid groups in d e surface active isocyanate reactive material can produce more desirable smaller particle size oil-in-water emulsions for more hydrophilic polyols. Surface active polyols were prepared as described in Examples 10-22 to produce higher OH, low Tg polyols. These polyols were converted to curable emulsions and compared to die curable emulsion prepared from die more hydrophobic polyol described in Example 1. Curable Emulsion Polyol Tg OH %Neutralization median particle siz Characteristics • c wt% (microns) Hydrophilic -4 2.1 85 0.457 -4 2.1 43 0.198 -8 1.8 85 0.290 -8 1.8 47 0.160 16 1.5 85 130* Comparative example Hydrophobic -8 1.5 85 0.153 -8 1.5 49 0.302 * bimodal particle size distril Example 25. The incorporation of eitiier a more hydrophobic monomer such as styrene in Example 2, or longer chain hydroxyl monomers such as 4-hydroxyburyl acrylate as in Example 3 provides both a faster dry time under ambient conditions and die development of early hardness under forced dry conditions, which can be important if buffing die coating is a key performance attribute. Polvol Characteristic Properties at 40 min/όO'C Hydroxy Tg Mn OH Ambient Cure Knoop MEK Ex. Monomer • c wt % Dry Time (hrs) Hardness resistance l 2-HEA -9 3300 1.5 3.5 1.7 10/60 2 Styrene 0 4440 1.5 1.0 6.6 20/200+ 3 4-HBA -8 3680 1.4 1.5 4.8 30/200+

Claims: WE CLAIM: 1. A process for preparing an isocyanate based, curable oil-in-water emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less, comprising the steps of: (i) admixing (a) an unblocked isocyanate crosslinking agent containing at least two reactive isocyanate groups and being in and of itself substantially hydrophobic and non-dispersible in water, with (b) a . mixture of (bl) a surface active isocyanate reactive material and (b2) an aqueous medium, wherein in die mixture (b) d e surface active isocyanate reactive material (bl) is water-dispersible, in proportions and under conditions to produce a substantially homogenous curable water-in-oil emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less; men (ii) admixing die curable water-in-oil emulsion from step (i) widi an aqueous medium in proportions and under conditions to produce a substantially homogenous oil-in-water emulsion of die surface active isocyanate reactive material and the isocyanate crosslinking agent in water, die oil-in-water emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less. The process of claim 1, wherein die admixing of step (i) comprises: (a) adding the aqueous medium (b2) to the surface active isocyanate reactive material (bl) to produce a substantially homogenous mixture; (b) adding die isocyanate crosslinking agent to die substantially homogenous mixture so that the water-in-oil emulsion is produced; (c) adding an aqueous medium to the water-in-oil emulsion until a phase inversion occurs, forming die oil-in-water emulsion; and (d) adding additional aqueous medium to the oil-in-water emulsion such diat said oil-in-water emulsion has a desired solids content and viscosity. 3. The process of claim 1, which further comprises adding a neutralizing agent. 4. The process of claim 3, wherein said neutralizing agent is added to die aqueous medium (bl) employed in step (a). 5. The process of claim 1, wherein die aqueous medium (b2) comprises water and is added in an amount such diat die water-in-oil emulsion 10 comprises up to about 40% by weight water. 6. The process of claim 5, wherein said water is added in an amount such that die water-in-oil emulsion comprises from about 5% to about 25% by weight 15 water. 7. The process of claim 1, wherein: (a) die unblocked isocyanate crosslinking agent is selected to comprise _ _ aliphatically, cycloaliphaticaliy, araiiphatically or aromatically bound isocyanate groups; and (b) the surface active isocyanate reactive material is selected to comprise a polymeric material. 25 8. The process of claim 7, wherein: (a) the unblocked isocyanate crosslinking agent is selected to comprise a urethane diisσcyanate/polyol adduct having an NCO content of at least 10 weight percent and 30 (b) me surface active isocyanate reactive material (bl) is selected to comprise olefmic copolymers based on carboxyfunctional ethylenically unsaturated monomers and hydroxyfunctional ethylenically unsaturated monomers; polyesters based on polybasic carboxylic acids and polyhydric alcohols; polyuredianes based on 35 polyisocyanates, polyhydric alcohols and hydroxy acids; and polyepoxy esters. 9. A curable water-in-oil emulsion comprising a substantially homogeneous emulsion of water in a substantially homogenous mixture of a surface active isocyanate reactive material which is dispersible in water and an unblocked isocyanate crosslinking agent containing at least two reactive isocyanate groups and being in and of itself substantially hydrophobic and non-dispersible in water, die curable water-in-oil emulsion having a VOC content of about 2.1 lbs/gal (252 g/1) or less. 10. The curable water-in-oil emulsion of claim 9, wherein said water- in-oil emulsion has a VOC content of less tiian about 2.0 lbs/gal. 11. The curable water-in-oil emulsion of claim 9, wherein said water- in-oil emulsion has a VOC content of less tiian about 1.9 lbs/gal. 12. The curable water-in-oil emulsion of claim 9, wherein the unblocked isocyanate crosslinking agent comprises aliphatically, cycloaliphaticaliy, araiiphatically and/or aromatically bound isocyanate groups. 13. The curable water-in-oil emulsion of claim 9, wherein the unblocked isocyanate crosslinking agent comprises a mixture of polyisocyanates. 14. The curable water-in-oil emulsion of claim 9, wherein die unblocked isocyanate crosslinking agent comprises a urediane diisocyanate/polyol adduct. 15. The curable water-in-oil emulsion of claim 14, wherein said urediane diisocyanate/polyol adduct has an NCO content of at least 10 weight percent. 16. The curable water-in-oil emulsion of claim 14, wherein die unblocked isocyanate crosslinking agent comprises a 3:1 meta-α.α.α'.α'- teu-ame y ylylene-diisQcyanate/trimethylolpropane adduct. 17. The curable water-in-oil emulsion of claim 9, wherein die surface active isocyanate reactive material comprises a polymeric material. 18. The curable water-in-oil emulsion of claim 9, wherein die surface active isocyanate reactive material is selected from the group consisting of olefmic copolymers based on carboxyfunctional ethylenically unsaturated monomers and hydroxyfunctional ediyleneically unsaturated monomers; polyesters based on polybasic carboxylic acids and polyhydric alcohols; polyurethanes based on polyisocyanates, polyhydric alcohols and hydroxy acids; and polyepoxy esters. 19. The curable water-in-oil emulsion of claim 9, wherein die surface active isocyanate reactive material comprises: (a) functionality capable of reacting widi isocyanate groups; and (b) hydrophilizing functionality capable of rendering die surface active isocyanate reactive material water dispersible. 20. The curable water-in-oil emulsion of claim 9, wherein die surface active isocyanate reactive material has a number average molecular weight of from about 1000 to about 50,000; an acid number from about 15 to about 150 mg KOH g resin and about 2.5 weight percent to about 6 weight percent hydroxyl groups. 21. The curable water-in-oil emulsion of claim 9, wherein die unblocked isocyanate crosslinking agent and die surface active isocyanate reactive material are present in amounts such diat they have an NCO: OH reactive functionality ratio in the range of 0.5:1 to about 2.1. 22. The process of claim 1, which further comprises: (a) selecting a surface active isocyanate reactive material having a hydroxyl content of at least about 1.8 wt.% (base on 85 wt. % sohds); and (b) at least partially neutralizing the surface active isocyanate reactive material. 23. The process of claim 22, wherein said surface active isocyanate reactive material has a Tg of greater tiian about 15"C. 24. The process of claim 23, wherein said surface active isocyanate reactive material is neutralized to about 30% to about 60%. 25. The process of claim 23, wherein said surface active isocyanate material is neutralized to about 40% to about 50%. 26. The process of claim 1, which further comprises selecting die surface active iisocyanate reactive material which comprises a long chain hydroxyalkyl (meui)acrylate. 27. The process of claim 26, wherein die surface active isocyanate reactive material is selected to comprise 4-hydroxybutyl acrylate. 28. The process of claim 26, wherein said unblocked isocyanate crosslinking agent comprises a tertiary polyisocyanate. 29. The process of claim 1 which further comprises adding styrene to said surface active isocyanate reactive material. 30. The process of claim 28, wherein die styrene is added in amount of about 5 to 20 wt.% of said surface active isocyanate reactive material. 31. The process of claim 28, wherein the styrene is added in amount of about 10 wt.% of said surface active isocyanate reactive material. 32. The process of claim 28, wherein said surface active isocyanate reactive material has a hydroxyl content of less tiian about 1.8 wt.% (based on 85 wt.% solids). 33. The process of claim 28 wherein said surface active isocyanate reactive material has a Tg of less than about 15° C. 34. The curable water-in-oil emulsion of claim 9, wherein the surface active isocyanate reactive material is at least partially neutralized and has a hydroxyl content of at least about 1.8 wt. % (based on 85% solids) and a Tg of greater dian about 15*C. 35. The curable water-in-oil emulsion of claim 33, wherein die surface active isocyanate reactive material is about 30% to about 60% neutralized. 36. The crable water-in-oil emulsion of claim 33, wherein die surface active isocyanate reactive material is from about 40% to about 50% neutralized. 37. The curable water-in-oil emulsion of claim 9, wherein die surface active isocyanante reactive material comprises a long chain hydroxyalkyl meth(acr late). 38. The curable water-in-oil emulsion of claim 36, wherein the surface active isocyanate reactive material comprises 4-hydroxybutyl acrylate. 39. The curable water-in-oil emulsion of claim 9, wherein die surface active isocyanate reactive material further comprises a styrene. 40. The curable water-in-oil emulsion of claim 38, wherein die styrene is present in an amount of from about 5 wt. % to about 20 wt. % of said surface active isocyanate reactive material. 41. The curable water-in-oil emulsion of claim 38, wherein die styrene is present in an amount of about 10 wt. % of said surface active isocyanate reactive material. 42. The curable water-in-oil emulsion of claim 38, wherein die surface active isocyanate reactive material has a hydroxyl content of less than about 1.8 wt.% (based on 85% sohds) and a Tg of less dian about 15 °C. - 3B

Inventors: FIORI DENISE E, FIORI, DENISE, E.
Applicants: CYTEC TECH CORP, CYTEC TECHNOLOGY CORP.
Application year: 1998
Main classification: C08G18
IPC codes: C08G18, C08L75, C09D175