MXPA99008440A - Polyurethane latexes, processes for preparing them and polymers prepared therewith - Google Patents

Abstract

Disclosed are stable aqueous polyurethane latexes prepared from prepolymer formulations including a polyisocyanate component and polyol component, wherein from 5 to 40 percent of the weight of the polyol component is ethylene oxide in the form of ethylene oxide applied as an end cap onto a propylene oxide or higher oxyalkylene polyoxyalkylene polyol, and no more than 45 percent of the weight of polyol component is ethylene oxide. These latexes are prepared without the use of organic solvents.

Description

POLYURETHANE LATEX, PROCESSES FOR ITS PREPARATION. AND POLYMERS PREPARED WITH THEMSELVES This invention relates to polyurethane latexes, to processes for their preparation, and to polymers prepared therewith. This invention relates particularly to stable polyurethane polymer latexes. It is known that latex polymers are useful in many applications, such as paints, sealants, and films. Polyurethane latexes are used less widely, due to the difficulties inherent in the preparation of stable aqueous polyurethane latexes. For example, polyurethane formulation components such as polyisocyanates can be reactive with water. The polyurethane prepolymers useful for forming latexes are often not low viscosity liquids under ambient conditions. These and other properties can make the polyurethane latexes unstable, that is, they form a dispersion that separates from the continuous aqueous phase of the latex, which is often not desirable in an industrial field. A solution to at least some of the problems of preparing polyurethane latexes is to use a solvent / water based process, where the solvent is optionally removed before being used in the final application. For example, a polyurethane can be prepared by processes such as: 1) dissolving a polyurethane in an organic solvent, 2) emulsifying the solution in water, and 3) removing the solvent. These processes are disclosed in the Patents of the United States of North America Nos. 3,360,599; 3,503,917; 4,123,403; and 5,037,864. Unfortunately, the processes to remove the solvent are often not completely efficient, and leave behind traces of solvents in the latex, which are released later in latex applications, and also the removal of the solvent is an additional cost. In other situations, unstable latexes are tolerated. A polyurethane latex that is described as being useful for the preparation of films is disclosed in British Patent Number GB 1,432,112. In it, a latex is prepared which is allowed to separate into a thixotropic layer and a "serum", wherein the thixotropic layer has a solids concentration of 30 to 50 percent. It would be desirable in the art to prepare polyurethane latexes that are stable. It would also be desirable in the art to prepare polyurethane latexes that are stable without resorting to the use of organic solvents, such as toluene, acetone, and the like. In one aspect, the present invention is a process for the preparation of a stable polyurethane latex, which comprises mixing a polyurethane prepolymer with water, a surfactant, and a chain extender under conditions sufficient to disperse the reaction product of the prepolymer. and the chain extender, for the purpose of forming a latex, wherein: (i) the prepolymer is prepared from a prepolymer formulation including a polyisocyanate component and a polyol component. (ii) from 5 to 40 percent of the weight of the polyol component is ethylene oxide in the form of ethylene oxide applied as an end cap on a propylene oxide or a higher oxyalkylene-polyoxyalkylene polyol, and (iii) no more than 45 percent by 5 percent of the weight of the polyol component is ethylene oxide. In another aspect, the present invention is a stable polyurethane latex prepared by a process for the preparation of a stable polyurethane latex, which comprises mixing a polyurethane prepolymer with water, a surfactant, and / or a chain extender under conditions sufficient to dispersing the reaction product of the prepolymer and the chain extender, in order to form a latex, wherein: (i) the prepolymer is prepared from a prepolymer formulation including a polyisocyanate component and a polyol component, ( ii) from 5 to 40 percent of the weight of the polyol component is ethylene oxide in the form of ethylene oxide applied as an end cap on a propylene oxide or a higher oxyalkylene-polyoxyalkylene polyol, and (iii) not more than 45 percent of the weight of the polyol component is ethylene oxide. 2C In yet another aspect, the present invention is a substrate coated with polyurethane polymer prepared by a process comprising the steps of: (1) mixing a polyurethane prepolymer with water, a surfactant ,. and a chain extender under conditions sufficient to disperse the reaction product of the Zz prepolymer and the chain extender, in order to form a latex, wherein: (i) the prepolymer is prepared from a prepolymer formulation including a polyisocyanate component and a polyol component, (ii) from 5 to 40 weight percent of the polyol component is ethylene oxide in the form of ethylene oxide applied as an end cap on a propylene oxide or a higher polyoxyalkylene-polyoxyalkylene polyol, and (iii) not more than 45 percent of the weight of the polyol component is ethylene oxide, (2) applying the latex to a substrate, and (3) dehydrating the latex to form a coating. Another aspect of the present invention is a stable polyurethane latex that does not contain organic solvents, which comprises: (1) a continuous aqueous phase; and dispersed therein: (2) from 0.1 to 10.0 weight percent of an anionic surfactant; and (3) a polymer comprising the reaction product of: (i) a polyol component of poly (propylene oxide) capped with ethylene oxide, having a molecular weight of 1,500 to 6,000, wherein from 5 to 40 percent of the weight of the polyol component is ethylene oxide, (ii) a polyether monol having an ethylene oxide content greater than 40 weight percent, (iii) a diol having a molecular weight of 30 to 500 , (iv) an aromatic polyisocyanate, and (v) a diamine, water, or a combination thereof. In one embodiment of the present invention, a polyurethane latex is formed. For the purposes of the present invention, the term "polyurethane" is defined to include the compounds known in the art as "polyureas". The terms polyurea and polyurethane are well known in the art of preparing polymers, but for clarity, these terms are defined as follows. A "polyurethane" is a polymer that has a structure similar to that of a polymer prepared by the reaction of a polyisocyanate and a poly-alcohol. A "polyurea" is a polymer that has a structure similar to that of a polymer prepared by the reaction of a polyisocyanate with a polyamine. Furthermore, it is recognized in the technique of the preparation of polyurethanes, that any material may have some different bonds from the aforementioned primary bond. For example, a polyurethane prepared using a base polyol, but also an amine chain extender, would have some urea bonds, but it would still be a polyurethane. In the same way, a polyurea prepared using a polyamine base, but also using a glycol chain extender, would have some urethane bonds, but it would still be a polyurea, but it can also be referred to herein as a polyurethane. The polymers of the present invention are prepared by applying a latex to a substrate. The latex can be applied by painting or spraying. For the purposes of the present invention, the paint is defined as applying a material, such as a polyurethane latex, to a brush or other applicator, and then depositing the polyurethane latex on a substrate, or alternatively, the material is It can be grouped on a substrate, and then spread on the substrate using a brush or other extender element. Also, for the purposes of the present invention, spraying is defined as the application of a material, such as a polyurethane latex, by atomizing the material, and ejecting the atomized material on the substrate. Another process useful with the present invention for applying a polyurethane latex to a substrate is immersion. In an immersion process, a substrate is lowered into a latex pond, and then removed. The latex that is retained on the substrate can be left to dry as is, or can be extended further to make a more uniform application. Parts of the substrate can be masked to prevent the polyurethane latex from reaching the entire surface of the submerged substrate. Still another process to apply a latex to a substrate, useful with the present invention, is the application by means of a transfer process. In a transfer process, a polyurethane latex is applied to a material that has very little ability to adhere to the polymer that forms on dehydration. This "transfer" material is put in contact with another substrate 2: having a higher adhesive affinity for the polymer. The transfer material is removed, and the polymer is retained on the substrate. Although the above processes for applying a latex to a substrate are preferred, any process that an ordinary expert in this field knows to be useful for ;; applying a polyurethane latex to a substrate, with the present invention. One advantage of using latex systems to prepare polymers is the simplicity of using latexes. In contrast, the use of systems A + B (ie, systems in which a polyisocyanate is reacted with a polyol to prepare a polyurethane) can be demanding, requiring considerable experience to prepare articles in a safe and economical manner. Since an A + B system has a reaction profile, the process for preparing an article of manufacture with an A + B system will often include the steps that allow the forming polymer to react for a sufficient time and under appropriate conditions to prepare a polymer with the properties required for the intended application. In striking contrast to the use of an A + B system, in one application of the present invention, the polyurethane polymer is already completely formed in the latex. The polyurethane latex can be applied to a substrate, and can be dried as quickly or as slowly as desirable in the application, and under conditions limited only by the tolerances of the polymer and the substrate. Since the polyurethane polymer is completely formed, there is very little chance that a worker will come into contact with any reactive raw material. Another advantage of the present invention over an A + B system is that the viscosity of a latex of the present invention is very easily adjusted. The common means of adjusting the viscosity of liquid systems, either by varying the temperature or solvent concentration of a system, is largely unavailable with a polyurethane system A + B. Since an A + B system has a reactivity profile, anything that is done to adjust the viscosity of the system, such as increasing the temperature, could cause the polymer to form prematurely, for example, inside a mixing head, with undesired results. In the same way, the addition of a solvent to a polyurethane formulation, possibly would cause a change to the physical properties of any polymer prepared with it. With a polyurethane latex of the present invention, the latex temperatures and latex solids concentrations can be varied to adjust the viscosity of the latex. Special additives such as thixotropes can also be added to the latexes of the present invention. After being applied, a polyurethane latex of the present invention is dried to produce a polymer. Any means can be used to dry the polyurethane latex that ordinary experts in the field know is useful. For example, the polyurethane latex coating can be air dried under ambient conditions, or it can be dried at elevated temperatures, optionally in reduced humidity or with forced air. The two considerations in the choice of drying conditions for the present invention are: 1) not to exceed the temperature tolerance of the polyurethane polymer or the support, and 2) not remove the water from the latex so quickly that the film is interrupted to bubble formation, unless a bubble finish is desired. Any drying conditions can be used, optionally with additional drying aids, such as forced air, which those of ordinary skill in the field of coating substrates with polyurethane latexes know to be useful with the present invention. In one embodiment, the polyurethane latexes of the present invention are prepared by emulsifying a prepolymer in a continuous aqueous phase, and then mixing the prepolymer with a chain extender. In another embodiment, chain extension and water emulsification are presented in a single step, where the chain extender is also water. In any case, there are two discernible formulations. One formulation is the prepolymer having at least one polyisocyanate component and one polyol component. A second formulation is the latex formulation that includes at least one prepolymer and one chain extender. In the process of the present invention, a polyurethane prepolymer formulation and a surfactant with water are emulsified. The surfactant may be present in an amount from 0.1 percent to 10 percent of the solids content of the latex. Preferably, the surfactant is present in an amount of 1 to 5 percent of the solids content of the latex. The surfactant may be ionic or non-ionic. If it is nonionic, preferably the surfactant is an ethoxylated alcohol, an ethoxylated fatty acid, a sorbitan derivative, a lanolin derivative, an ethoxylated nonylphenol, or an alkoxylated polysiloxane. Preferably, the surfactant is an ionic surfactant that does not react in any significant way with the isocyanate groups, and more preferably the surfactant is an anionic surfactant. Suitable classes of surfactants include, but are not restricted to, sulfates of ethoxylated phenols such as poly (oxy-1, 2-ethanediyl) alpha- (nonylphenyl) omega-hydroxy sulfate ammonium salt.; alkali metal fatty acid salts such as alkali metal oleates and stearates; alkali metal lauryl sulfates, quaternary ammonium surfactants; alkali metal alkylbenzene sulphonates such as branched and linear sodium dodecylbenzene sulfonates; anionic fluorocarbon surfactants such as perfluoroalkyl alkali metal sulfonates; trialkine amine salts of dodecylbenzenesulfonic acid; ammonium salts of dodecylbenzenesulfonic acid; lauryl sulfates of trialkanol amine; lauryl ammonium sulfates; lauryl sulfates of trialkine amine; lauryl ammonium sulphonates: alkali metal lauryl sulphonates; lauryl sulphonates of trialcanolic amine; lauryl sulphonates of trialkine amine; amine oxide lauryldimethyl; alkali metal salt of di (sulfonic acid) of dodecyldiphenyl oxide; dicalkaline amine salts of di (sulfonic acid) dodecyldiphenyl oxide; trialkylene amine salts of di (sulfonic acid) of dodecyldifenic oxide: ammonium salts of d i (sulphonic acid) of dodecyldiphenyl oxide; alkylphenol polyethoxylate; polyoxyethylene / polyoxypropylene block copolymers; polyoxyethylene / polyoxybutylene block copolymers; and alkali metal soaps of modified resins. Particularly preferred surfactants are the trialkaline amine salt of dodecylbenzenesulfonic acid, the trietanolic amine salt of dodecylbenzenesulfonic acid, the sodium salt of dodecylbenzenesulfonic acid; and trietanolic amine lauryl sulfate. The polyurethane latexes of the present invention are prepared using polyurethane formulations that include a polyisocyanate component and an isocyanate-reactive component, also known as a material or polyol containing active hydrogen. The term "polyurethane" is not limited to these polymers, which include only polyurethane bonds. It is well understood by ordinary experts in the field of polyurethane preparation that polyurethanes also include polymers containing halofanate, biuret, carbodiimide, oxazolinyl, isocyanurate, uretidinedione, urea, and other linkages in addition to urethane. In a similar way, polyureas can also have these bonds. A polyurethane prepolymer useful with the present invention can be an isocyanate-terminated prepolymer. The polymer of a latex formed by mixing a prepolymer with a chain extender and water, can be an isocyanate terminated polymer, an active hydrogen-terminated polymer, or the reaction product of a mixture of a polyisocyanate and a component that react with polyisocyanate, and a chain extender, in almost stoichiometric concentrations. The prepolymer can be formed by reacting the components of a prepolymer formulation including a polyisocyanate component and an active hydrogen component. The latex is formed by the reaction of a prepolymer and a chain extender in a continuous aqueous phase. Optionally, the prepolymer can be formulated to react where the water of the continuous aqueous phase is a minor, major, or exclusive chain extender. The polyisocyanate component of the prepolymer formulations of the present invention can conveniently be selected from organic polyisocyanates, modified polyisocyanates, isocyanate-based prepolymers, and mixtures thereof. These may include aliphatic and cycloaliphatic isocyanates, but aromatic isocyanates, and especially multifunctional aromatics, are preferred. The preferred polyisocyanates are 2,4- and 2,6-toluene diisocyanate, and the corresponding isomeric mixtures; 4, 4'-, 2, 4'- and 2, 2'-diphenylmethane diisocyanate and the corresponding isomeric mixtures; mixtures of 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanates and PMID polyphenylenepolymethylene polyisocyanates; and mixtures of PMDI and toluene diisocyanates. Also useful for the preparation of the polyurethanes of the present invention are aliphatic and cycloaliphatic isocyanate compounds, such as 1,6-hexamethylene diisocyanate.; 1-isocyanate, 3,5,5-trimethyl-1-3-isocyanato-methylcyclohexane: 2,4- and 2,6-hexahydrotoluene-diisocyanate, as well as the corresponding isomeric mixtures; 4,4'-, 2,2'- and 2,4-dicyclohexylmethanediisocyanate, as well as the corresponding isomeric mixtures. 1,3-Tetramethylene-n-diisocyanate can also be used with the present invention. Also suitable for the polyisocyanate component of the formulations of the present invention are so-called modified multifunctional isocyanates, ie, products obtained by chemical reactions of the above diisocyanates and / or polyisocyanates. Examples are polyisocyanates containing esters, ureas, biurets, halofanates, and preferably carbodiimides and / or uretonyamines; diisocyanates or polyisocyanates containing c isocyanurate and / or urethane group. Liquid polyisocyanates containing carbodiimide groups, uretonimine groups, and / or isocyanurate rings, having isocyanate group (NCO) contents of 10 to 40 weight percent, more preferably 20 to 35 po> may also be used. ri cent in weight. These include, for example, polyisocyanates based on 4,4'-, 2,4'-, and / or 2,2'-diphenylmethanediisocyanate and the corresponding isomeric mixtures, 2,4- and / or 2,6-toluene diisocyanate and the corresponding isomer mixtures mixtures of diphenylmethane diisocyanates and PMDI, and mixtures of toluene diisocyanates and PMDI and / or diphenylmethane diisocyanates. Suitable prepolymers for use as the polyisocyanate component of the prepolymer formulations of the present invention are prepolymers having NCO contents of 2 to 40 weight percent, more preferably 4 to 30 weight percent. These prepolymers are prepared by reacting the di- and / or polyisocyanates with materials including diols and triols of lower molecular weight, but they can also be prepared with multivalent active hydrogen compounds such as di- and tri-amines and di- and tri-thiols. The individual examples are aromatic polyisocyanates containing urethane groups, which preferably have NCO contents of 5 to 40 weight percent, more preferably 20 to 35 weight percent, obtained by the reaction of diisocyanates and / or polyisocyanates with, for example, lower molecular weight diols, triols, oxyalkylene glycols, dioxyalkylene glycols, or polyoxyalkylene glycols having molecular weights up to 800. These polyols can be used singly or in mixtures as di- and / or polyoxyalkylene glycols. For example, diethylene glycols, dipropylene glycols, polyoxyethylene glycols, ethylene glycols can be used. propylene glycols, butylene glycols, polyoxypropylene glycols, and polyoxypropylene polyoxyethylene glycols. Polyester polyols can also be used, as well as alkyl diols such as butane diol. Other useful diols include bishydroxyethyl- or bishydroxypropyl bisphenol A, cyclohexanedimethanol, and even bishydroxyethylhydroquinone. They are particularly useful as the component of: - polyisocyanate of the prepohmeric formulations of the present invention: (i) polyisocyanates having an NCO content of 8 to 40 weight percent, containing carbodiimide groups and / or urethane groups, from of 4,4'-diphenylmethane diisocyanate or a mixture of 4,4'- and 2,4'-diphenylmethanediisocyanates; (ii) prepolymers containing NCO groups, having an NCO content of 2 to 35 weight percent, based on the weight of the prepolymer, prepared by the reaction of polyols, having a functionality of preferably 1.75 to 4, and a molecular weight of 800 to 15,000 with 4,4'-diphenylmethane diisocyanate, or with a mixture of 4,4'- and 2,4'-diphenylmethanediisocyanates and mixtures of (i) and (i); and (iii) 2,4- and 2,6-toluene diisocyanate and the corresponding isomer mixtures. PMDI can also be used in any of its forms, and is preferred. In this case, it preferably has an equivalent weight between 125 and 300, more preferably 130 to 175, and an average functionality greater than 1.5. An average functionality of 1.75 to 3.5 is more preferred. The viscosity of the polyisocyanate component is preferably 25 to 5,000 centipoise (cPs) (0.025 to 5 Pa »s), but values of 100 to 100 cPs are preferred at 25 ° C (0.1 to 1 Pa» s) for ease of processing. Similar viscosities are preferred where alternative polyisocyanate components are selected. Still preferably, the polyisocyanate component of the formulations of the present invention is selected from the group consisting of MDI, PMDI, an MDI prepolymer, a PMDI prepolymer. a modified MDI, and mixtures thereof.

The prepolymer formulations of the present invention include a polyol component. The polyfunctional active hydrogen-containing materials useful with the present invention may include materials other than those already described hereinbefore. The active hydrogen-terminated prepolymers useful with the present invention include active hydrogen auxiliaries of the polyisocyanates and polyisocyanate-terminated prepolymers described hereinbefore. The active hydrogen-containing compounds most commonly used in the production of polyurethane, are those compounds that have at least two hydroxyl groups or amine groups. These compounds are referred to herein as polyols. Representatives of suitable polyols are generally known, and are described in publications such as High Polymers, Volume XVI, "Poiyurethanes, Chemistry and Technolgy" by Saunders and Frisch, Interscience Publishers, New York, Volume I, pages 32-42, 44-54 (1962), and Volume II, pages 5-6, 198-199 (1964); Organic Polymer Chemistry by K.J. Saunders, Chapman and Hall, London, pages 323-325 (1973); and Developments in Polyurethanes, Volume I, J.M. Burst, ed., Applied Science Publishers, pages 1-76 (1978). However, any compound containing active hydrogen can be used with the present invention. Examples of these materials include those selected from the following classes of compositions, alone or mixed: (a) alkylene oxide adducts of polyhydroxyalkanes; (b) alkylene oxide adducts of non-reducing sugars and sugar derivatives; (c) alkylene oxide adducts of phosphorus and polyphosphorus acids; and (d) alkylene oxide adducts of polyphenols. Polyols of these types are referred to herein as "base polyols". Examples of the alkylene oxide adducts of polyhydroxyalkanes useful herein are adducts of ethylene glycol, propylene glycol, 1,3-dihydroxypropane, 1,4-dihydroxybutane, and 1,6-dihydroxyethane, glycerol, 1, 2,4-trihydroxybutane, 1, 2,6-trihydroxyhexane, 1,1,1-trimethylol ethane, 1,1,1-trimethylolpropane, pentaerythritol, polycaprolactone, xylitol, arabitol, sorbitol, manitoi, and the like. Preferred as adducts of alkylene oxide of polyhydroxyalkanes are propylene oxide adducts and propylene oxide adducts capped with ethylene oxide of dihydroxy- and trihydroxy-alkanes. Other useful alkylene oxide adducts include adducts of ethylene diamine, glycerin, piperazine, water, ammonia, 1,2,3,4-tetrahydroxybutane, fructose, sucrose, and the like. Also preferred are poly (oxypropylene) glycols, triols, tetroles, and hexols, and any of these which are capped with ethylene oxide. These polyols also include poly (oxypropyleneoxyethylene) polyols. The oxyethylene content should preferably comprise less than 80 weight percent of the total weight of the polyol. and more preferably less than 40 weight percent. The ethylene oxide, when used, may be incorporated in any manner along the polymer chain, for example, as internal blocks, terminal blocks, or randomly distributed blocks, or any combination thereof. Another class of polyols that can be used with the present invention are "copolymer polyols", which are base polyols containing stably dispersed polymers, such as acrylonitrile-styrene copolymers. The production of these copolymer polyols can be from reaction mixtures comprising a variety of other materials, including, for example, catalysts such as azobisisobutyronitrile; copolymer polyol stabilizers; and chain transfer agents, such as isopropanol. Polyester polyols can be used to prepare the polyurethane latexes of the present invention. Polyester polyols are generally characterized by repeating ester units, which may be aromatic and aliphatic, and by the presence of the primary hydroxyl or terminal secondary groups, but any polyester that ends in at least two hydrogen groups may be used. active with the present invention. For example, the reaction product of the transesterification of glycols with polyethylene terephthalate can be used to prepare the latexes of the present invention. Polyamines, amine terminated polyethers, polymercaptans, and other compounds that react with isocyanate are also suitable in the present invention. Compounds containing polyisocyanate polyaddition (PIPA) active hydrogen can be used with the present invention. PIPA compounds are typically the reaction products of TDI and trietanolic amine. A process for the preparation of the PIPA compounds can be found, for example, in U.S. Patent Number 4,374,209, issued to Rowlands. In addition to the polyisocyanates and active hydrogen-containing compounds, the polyurethane formulation useful for the preparation of polyurethane latexes of the present invention may include additional materials called additives. For example, formulations useful with the present invention can include fillers, thixotropic agents, surfactants, catalysts, dispersion aids, crosslinkers. Any additive that an ordinary expert in the field of polyurethane latex preparation knows to be useful can be used., with the present invention. Preferred additives are added either to the polyisocyanate or to the polyol component of the prepolymer formulation, more preferably they are added to the polyol component, but can be added in any manner useful in the formation of a polyurethane latex. Although any of the aforementioned compounds and materials can be used with the prepolymer formulations of the present invention, preferably the primary components of the formulations will include an aromatic polyisocyanate, more preferably MDI, TDI, TMDI, or MDI or TDI prepolymer, as the polyisocyanate component.

Preferably, the polyol component will be a polyol, polyamine, polyol mixture, or mixture of polyamines, wherein the polyol, the polyamine, or the primary component of a mixture of polyols or polyamines, is a polyether having a content of 5 ethylene oxide from 5 to 45 percent, and a molecular weight from 750 to 8,000. From 5 to 40 percent of the weight of the polyol component is in the form of ethylene oxide end cap. The end cap is the term applied to the preparation of a polyether polyol which uses higher alkylene oxides, such as propylene oxide, and then, in a second step, ethylene oxide is applied to the ends of the polyol. This provides advantages, such as a higher primary hydroxyl termination without the highly hydrophilic properties of all ethylene oxide polyols. These polyols with end cap are required for the Polyol component of the prepolymer formulations of the present invention. The polyol component of the prepolymer formulations of the present invention may include the other polyols described hereinbefore, provided that the ?: limitations that the polyol component has an ethylene oxide content of 5 to 45 percent, a molecular weight of 750 to 8,000. and from 5 to 40 percent of the weight of the polyol component is ethylene oxide in the form of ethylene oxide end cap. Preferably, any additional polyols are used in a minor amount. For example, a small amount of a polyester polyol could be added to a polyol end capped with ethylene oxide, and that mixture could be used as the polyol component of a prepolymer formulation of the present invention. The stoichiometry of the prepolymer formulations of the present invention is such that a fully reacted combination of the polyisocyanate component and the polyol component (hereinafter referred to as the NCO content of the prepolymer), preferably will have an NCO content of 10%. percent. Prepolymer formulations having NCO contents of lower prepolymers can be used, but the viscosity of the prepolymer will be higher, which, in turn, may require a rigorous mixing for dispersion of the prepolymer in water. Prepolymer formulations having higher NCO contents of the prepolymer can also be used, but increasing the NCO content of the prepolymer can cause the polymer to coagulate instead of dispersing in water. Preferably, the NCO content of the prepolymer, in the prepolymers of the present invention, is from 6 to 10 percent. Additionally, it is necessary that the latex formulation includes a chain extender. Any chain extender that ordinary experts in the field of polyurethane preparation know to be useful can be used with the present invention. These chain extenders typically have a molecular weight of 30 to 500, and have at least two groups containing active hydrogen. Polyamines are the most preferred chain extenders. Other materials, particularly water, can function to extend the chain length, and thus, are chain extenders for the purposes of the present invention. It is particularly preferred that the chain extender be selected from the group consisting of amine terminated polyethers, such as, for example, Jeffamine D-400 from Huntsman Chemical Company, aminoethylpiperazine, 2-methylpiperazine, 1,5-diamino-3-methylpentane, isophorone thiamine, ethylenic diamine, diethylene triamine, triethylene tetramine, triethylene pentamine, ethanolic amine, lysine in any of its stereoisomeric forms, and salts thereof, hexandiamine, hydrazine, and piperazine. In the practice of the present invention, the chain extender is often used as a solution of the chain extender in water. Although the chain extender of the present invention may be water, preferably it is a diamine. To the extent that a chain extender other than water is used in the formulations of the present invention, it is preferably used in an amount such that the equivalents of the active hydrogens of the chain extender are less than 90 percent of the equivalents of isocyanate represented by the NCO content of the prepolymer. Still more preferably, the chain extender is present in an amount such that the active chain extender hydrogens equivalents are from 80 to 90 percent of the isocyanate equivalents represented by the NCO content of the prepolymer. The mixtures, emulsions, and dispersions of the present invention are all prepared by mixing the liquid components of the prepolymer formulation and a continuous aqueous phase, in the absence of an organic solvent, such as toluene or acetone. There are a variety of mechanical mixing devices and equipment commercially available to perform this mixture. The effectiveness of the mixture can be measured by the size of the particles in average volume of the resulting emulsion. An average particle size of less than 5 microns is an indication that an adequate mixture has been made. More preferably, a particle size in average volume of less than 2.0 microns is desired for the practice of this invention. U.S. Patent No. 5,539,021 to Pate disclosed a means for mixing a polyurethane latex useful with the present invention, but any means for mixing the components of the prepolymer formulation of the present invention that produces a Latex that has a particle size of less than 5 microns. The latexes of the present invention can be prepared with additives included in the latex prepolymer formulations, or latexes themselves. Any useful additive may be used in a latex formulation or in a latex prepolymer formulation or in a polyurethane latex prepolymer formulation, with the present invention. For example, latexes of the present invention can be prepared with a fire retardant material. In one embodiment of the present invention, the latices of the present invention include an inorganic filler. In another embodiment of the present invention, the latexes of the present invention are prepared with a monol as an additive in the latex prepolymer formulation. Where a monol is included in the prepolymer formulation, the monol is preferably a mono-functional hydrophilic polyether having the general formula: H-0- (CH2CH20) n- (CH2CHBO) m-CH2CH2R wherein R is a group free of active hydrogens, and which does not negate the hydrophilicity of the oxyethylene units; B is an alkyl group having from 1 to 8 carbon atoms; n is a number from 5 to 120; m is a number selected such that the weight ratio of the oxyethylene units to the other oxyalkylene groups is from 100: 1 to 40:60. Preferably, R is a low molecular weight alkoxy group, or an aliphatic carboxylic acid ester group of less than 24, preferably less than 20 carbon atoms. The monools described above can be incorporated into the prepolymer as a means to modify the properties of the latex and improve the ease of emulsion formation. When present, the monol is present in an amount of 0.1 to 15 weight percent of the prepolymer formulation, preferably 2 to 5 weight percent of the prepolymer formulation. The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention, and should not be construed in that way. The amounts are in parts by weight or percentages by weight, unless otherwise indicated. The materials used in the examples are as defined below: Polyol 1 is a diol of propylene oxide (PO) capped with 12 percent ethylene oxide (EO), which has an equivalent weight of 1,000 grams / equivalent. Polyol 2 is a propylene oxide diol having an equivalent weight of 1,000 grams / equivalent. Polyol 3 is a triol of propylene oxide capped with 15 percent ethylene oxide with an equivalent weight of 1,650 grams / equivalent. Polyol 4 is a triol of propylene oxide capped with 18 percent ethylene oxide, with an equivalent weight of 1.617 grams / equivalent. Polyol 5 is a diol of propylene oxide capped with 30 percent ethylene oxide, with an equivalent weight of 1,250 grams / equivalent. Monol 1 is a polyoxyethylene monol with a molecular weight of 950, initiated from methanol.

The polyisocyanate is a 50 percent mixture of 2,4'-MDI and 50 percent of 4,4'-MDI. Prepolymer A is prepared by mixing 640 grams (0.396 equivalents) of Polyol 4, and 160 grams (1.28 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 20 percent. Prepolymer B is prepared by mixing 640 grams (0.388 equivalents) of Polyol 3, and 160 grams (1.28 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 20 percent. Prepolymer C is prepared by mixing 94 parts of Prepolymer A with 6 parts of polyisocyanate, which results in a prepolymer having a polyisocyanate content of 25 percent Prepolymer D is prepared by mixing 87.5 parts of Prepolymer A with 12.5 polyisocyanate portions, which results in a prepolymer having a polyisocyanate content of 30 percent. Prepolymer E is prepared by mixing 540 grams (0.327 equivalents) of Polyol 3, and 240 grams (1.92 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 31 per cent.

Prepolymer F is prepared by mixing 480 grams (0.48 equivalents) of Polyol 1 and 320 grams (2.56 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 40 percent. Prepolymer G is prepared by mixing 544 grams (0.544 equivalents) of Polyol 1, and 240 grams (1.92 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 31 percent. Prepolymer H is prepared by mixing 480 grams (0.384 equivalents) of Polyol 5, and 320 grams (2.56 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 40 percent. Comparative Prepolymer I is prepared by mixing 560 grams (0.560 equivalents) of Polyol 2, and 240 grams (1.92 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 30 percent. Prepolymer J is prepared by mixing 560 grams (0.560 equivalents) of Polyol 1, and 240 grams (1.92 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 30 percent.

Comparative Prepolymer K is prepared by mixing 560 grams (0.448 equivalents) of Polyol 5, and 240 grams (1.92 equivalents) of polyisocyanate at 90 ° C for 2 hours, which results in a prepolymer having a polyisocyanate content of 30%. percent. Surfactant is a sodium dodecylbenzenesulfonic acid surfactant sold under the trademark designation RHODACAL DS-10, which is a trade designation of Rhone Poulenc. The Physical Properties Test is done in accordance with ASTM D-1708.

EXAMPLE 1 120 grams of water and 45 grams of a 20 percent blend of surfactant and water are placed in the mixing cup of a WARNING MIXER (WARING is a trade designation of WARING PRODUCTS DIVISION OF DYNAMICS CORPORATION OF AMERICA). Next, 75 grams of Prepolymer B are added to the mixing cup, and mixed for 1 minute to form a prepolymer emulsion. Then, 12.7 grams are added (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine to the emulsion by means of a syringe for a period of 30 seconds, and stirring is continued for an additional 30 seconds to form a latex. Then the latex is filtered through a paint filter, and has a solids content of 35 percent. Part of the filtered latex is applied to a clean glass plate, and allowed to air dry under ambient conditions to form a thin elastomeric film, another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation. The film and the latex are tested by the physical properties, which are mentioned later in the table.

EXAMPLE 2 A filtered latex is prepared in a manner substantially identical to Example 1, with the exception that 189 grams is used instead of 120 grams of water, 36 grams instead of 45 grams of surfactant, Prepolymer A instead of Prepolymer B, and 2.49 grams (0.42 equivalents) of a 50 percent aqueous solution of ethylenic diamine instead of 12.7 grams (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine. Part of the filtered latex is applied to a clean glass plate, and allowed to air dry to form a thin elastomeric film, another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation.

EXAMPLE 3 A filtered latex is prepared in a manner substantially identical to Example 1, with the exception that Prepolymer C is used in place of Prepolymer B. Part of the filtered latex having a solids content of 35 percent is applied to a plate of clean glass, and allowed to air dry to form a thin elastomeric film. Another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation.

EXAMPLE 4 A filtered latex is prepared in a manner substantially identical to Example 1, with the exception that the Prepolymer D in place of Prepolymer B, and 22.4 grams (0.149 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine, instead of 12.7 grams (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine. Part of the filtered latex having a solids content of 35 percent is applied to a clean glass plate and allowed to air dry to form a thin elastomeric film. Another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation.

EXAMPLE 5 A filtered latex is prepared in a manner substantially identical to Example 1, except that Prepolymer E is used instead of Prepolymer B, 122.5 grams instead of 120 grams of water, 35 grams instead of 45 grams of surfactant, and 22.4 grams (0.149 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine instead of 12.7 grams (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine. Part of the filtered latex having a solids content of 35 percent is applied to a clean glass plate and allowed to air dry to form a thin elastomeric film. Another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation.

EXAMPLE 6 A filtered latex is prepared in a manner substantially identical to Example 1, with the exception that 25.5 grams of a 33 percent piperazine solution (0.197 equivalents) are used instead of 12.7 grams (0.08 equivalents) of an aqueous solution of 33 percent 2-methylpiperazine. Part of the filtered latex having a solids content of 35 percent is applied to a clean glass plate and allowed to air dry to form a thin elastomeric film. Another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation.

EXAMPLE 7 A filtered latex is prepared in a manner substantially identical to Example 1, with the exception that 13.1 grams of a 33 percent piperazine solution (0.101 equivalents) are used instead of 12.7 grams (0.08 equivalents) of an aqueous solution of 33 percent 2-methylpiperazine. Part of the filtered latex having a solids content of 35 percent is applied to a clean glass plate and allowed to air dry to form a thin elastomeric film. Another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation. The film and the latex are tested by the physical properties that are mentioned later in the table.

EXAMPLE 8 A filtered latex is prepared in a manner substantially identical to Example 1, with the exception that Prepolymer H is used in place of Prepolymer B. 85 grams instead of 120 grams of water, 35 grams instead of 45 grams of surfactant, and 55.7 grams of a 15 percent piperazine solution (0.194 equivalents) instead of 12.7 grams (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine. Part of the filtered latex having a solids content of 35 percent is applied to a clean glass plate and allowed to air dry to form a thin elastomeric film. Another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation. The film and the latex are tested by the physical properties that are mentioned later in the table.

COMPARATIVE EXAMPLE 9 An attempt is made to prepare a filtered latex in a manner substantially identical to Example 1, with the exception that Comparative Prepolymer I is used in place of Prepolymer B, and 15 grams of a 33 percent piperazine solution (0.116 equivalents) ) instead of 12.7 grams (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine. During the addition of the chain extender, the dispersion coagulates and is useless for another test.

EXAMPLE 10 A filtered latex is prepared in a manner substantially identical to Example 1, with the exception that Prepolymer J is used in place of Prepolymer B, and 15 grams of a 33 percent piperazine solution (0.116 equivalents) instead of 12.7 (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine. Part of the filtered latex having a solids content of 35 percent is applied to a clean glass plate and allowed to air dry to form a thin elastomeric film. Another portion of the latex is retained for observation. After 30 days, the latex is still stable without an observable indication of settling or layered separation.

COMPARATIVE EXAMPLE 11 An attempt is made to prepare a filtered latex substantially identical to that of Example 1, with the exception that Comparative Prepolymer K is used in place of Prepolymer B, no surfactant, 135 grams instead of 120 grams of water, and 17.9 grams of a solution of 33 percent piperazine (0.138 equivalents) instead of 12.7 grams (0.08 equivalents) of a 33 percent aqueous solution of 2-methylpiperazine. During the addition of the chain extender, the dispersion coagulates and is useless for another test.

TABLE EXAMPLE 12 A prepolymer is prepared by mixing 633.5 grams of Polyol 1, 20 grams of Monol 1, 13.5 grams of diethylene glycol, 333 grams of the polyisocyanate, and heating at 70 ° C for 15 hours. 75 grams of the prepolymer are weighed into an 8-ounce glass bottle having an internal diameter of 5.6 centimeters. The bottle is held in place, and an INDCO * mixing blade (4.3 centimeters in diameter) is inserted into the prepolymer, so that the blade is just covered by the liquid. (* INDCO is a commercial designation of INDCO, INC.) Then 26.5 grams of water are fed into the prepoiimer at a rate of 12 grams / minute for 2.25 minutes. A timer is started, and stirring is started at a speed of 3,000 rpm. At 30 seconds, a surfactant (5.2 grams of a 40 percent solution of the lathyric sulfate tepid amine salt in water) is introduced into the water feed for a period of 5 seconds by means of a syringe. After complete addition of water, a 10 percent piperazine solution in water (37.9 grams) is added via syringe. Then the latex with a resulting 55.7 percent solids, is poured into a beaker of 3 plastic springs, covered with aluminum foil, and left stirring gently overnight with a magnetic stirrer. The next day, the latex is filtered through a coarse paint filter, diluted to 45 percent solids, emptied over polypropylene, and allowed to dry under ambient conditions overnight. The resulting film is heated at 90 ° C for 1 hour, resulting in a film with the following tensile properties: 3.318 psi (22.876 kN / m2) of ultimate tensile strength, elongation of 519 percent, Young's modulus of 1,312 psi (9,045 kN / m2). The latex with 55.7 percent filtered solids has an average particle size of 0.7 microns.

EXAMPLE 13 A prepolymer is prepared by mixing 193.2 grams of Polyol 1, 4.3 grams of diethylene glycol, and 102.3 grams of polyisocyanate, and allowing it to react for 16 hours at 75 ° C. The resulting prepolymer has an NCO percentage of 7.34, and a viscosity of 9,300 cPs (9.3 Ns / m2) at 25 ° C, and 40,000 cPs (40 Ns / m ") at 7 ° C. A latex is prepared from the prepolymer, first mixing 12.6 grams of the surfactant, and 50.4 grams of water, to form a 20 percent aqueous surfactant solution, then a mixer is charged with the surfactant premix, 41.7 grams of water, and 100 grams of the prepolymer, and mix at full speed for 1 minute, then add a 7.4-gram piperazine chain extender mixture and 87.9 grams of water for 30 seconds, drip latex into a beaker, and stir until any foam is present. The resulting latex is filtered and tested for its physical properties. The physical properties of latex are: viscosity of 17 cPs (0.017 Ns / m2) at 25 ° C, solids percentage of 40.5, pH of 8.99, and particle size of 0.78 microns. A film is prepared by pouring the latex into an aluminum mold, and allowing it to dry at room temperature overnight. Then the film is heated at 90 ° C for 1 hour. The physical properties of the film are: tensile strength of 5,336 psi (36,790 kN / m2), elongation percentage of 653, tension of 100 percent, traction of 949 psi (6,543 kN / m2), tensile modulus of 6,794 psi (46,843 kN / m2), and a Tg of -38.7 ° C.

Claims (14)

1. A process for the preparation of a stable polyurethane latex, which comprises mixing a polyurethane prepolymer with water, a surfactant, and a chain extender, under conditions sufficient to disperse the reaction product of the prepolymer and the chain extender, with in order to form a latex, wherein: (i) the prepolymer is prepared from a prepolymer formulation including a polyisocyanate component and a polyol component, (i) from 5 to 40 weight percent of the polyol is ethylene oxide in the form of ethylene oxide applied as an end cap on a propylene oxide or a higher oxyalkylene-polyoxyalkylene polyol, and (iii) not more than 45 weight percent of the polyol component is oxide of ethylene. The process of claim 1, wherein the process is carried out in two stages: a first step of mixing a prepolymer with water and a surfactant to form an emulsion, and a second step of mixing the emulsion with a chain extender. 3. The process of claim 1. wherein the chain extender is an amine. 4. The process of claim 3 wherein the amine is a diamine. 5. The process of claim 1, wherein the surfactant is an ionic surfactant. 6. The process of claim 5, wherein the ionic surfactant is an anionic surfactant. 7. The process of claim 1, wherein the process is carried out with the proviso that no organic solvent is used to prepare the latex. 8. The process of claim 1, wherein the chain extender is water. 9. The process of claim 8, wherein the process is performed in one step. The process of claim 1, wherein the polyol component includes a polyoxypropylene diol capped with ethylene oxide having a molecular weight of 1,500 to 6,000, and a polyether monol having an ethylene oxide content greater than 40 percent. The process of claim 10, wherein the polyol component includes a diol having a molecular weight of 30 to 500. 1

2. A stable polyurethane latex prepared by the process of claim 1. 1

3. A substrate coated with polyurethane polymer prepared by a process comprising the steps of: (1) preparing a latex according to the process of claim 1, (2) applying the latex to a substrate, and (3) dehydrating the latex. 1

4. A stable polyurethane latex that does not contain organic solvents, which comprises: (1) a continuous aqueous phase; and dispersed therein: (2) from 0.1 to 10.0 weight percent of an anionic surfactant; and (3) a polymer comprising the reaction product of: (i) a polyol component of poly (propylene oxide) capped with ethylene oxide having a molecular weight of from 1,500 to 6,000, wherein from 5 to 40 weight percent of the polyol component is ethylene oxide, (ii) optionally a polyether monol having an ethylene oxide content greater than 40 weight percent, (iii) optionally, a diol having a molecular weight of from 30 to 500, (iv) an aromatic polyisocyanate, and (v) a diamine, water, or a combination thereof.