Method for preparing stably dispersed nonaqueous microparticle dispersions

Abstract: A method for preparing polymer microparticles which are stably dispersed in a nonaqueous medium involves: (a) mixing into a nonaqueous medium a polymerizable component at least 20 percent of which is insoluble in the nonaqueous medium, said polymerizable component comprising at least one polymerizable species; (b) subjecting the mixture of (a) to stress sufficient to particulate the mixture; (c) polymerizing the polymerizable component within each particle under conditions sufficient to produce polymer microparticles stably dispersed in the nonaqueous medium, said polymer microparticles being insoluble in the nonaqueous medium and the nonaqueous medium being substantially free of dissolved polymer, said polymer microparticles further characterized in that less than 20 percent of the polymer microparticles have a mean diameter greater than 5 microns.

Description: The present invention relates to methods for preparing nonaqueous, microparticle dispersions. There have been numerous and varied approaches to the preparation of microparticle dispersions in nonaqueous media. Each approach has possessed its own inherent disadvantages, largely stemming from the mode of preparation. For example, difficulties which have been prevalent in prior art modes of preparation are the inability to achieve a dispersion which is uniformly of a small particle size, on the order of less than five µm (microns), preferably less than one µm (micron). In addition, generally because of the large particle size, nonaqueous microparticle dispersions have suffered from the lack of stability especially when the continuous phase is of low viscosity. This typically means that the dispersion either settles upon standing or coagulates and forms large clumps. GB-A-21 57 702 discloses a method for producing polymer microparticles by reacting in dispersed form in a liquid hydrocarbon a preformed isocyanate prepolymer, which contains a segment solvated by the hydrocarbon and a segment insoluble in the hydrocarbon, with an active hydrogen containing compound having a functionality of at least 2 to form the polymer microparticles dispersed in the hydrocarbon. Dispersions with solid contents above 40 percent can be obtained by this method. However, the mean particle size of the dispersions is not sufficiently small in order to be determined by light scattering methods and the dispersions, probably therefore, are not fully satisfactory with respect to stability. The said reference further discloses various other prior art methods for the manufacture of microparticle dispersions or microgels in hydrocarbons or another nonaqueous medium. Such methods are described, e.g., in US-A-3,317,635; US-A-3,717,605; US-A-3,748,294; JOURNAL OF CELLULAR PLASTICS, January/February 1981; and US-A-4,425,438. In accordance with the present invention there is provided a method for preparing polymer particles which are stably dispersed in a nonaqueous medium. The method comprises : (a) mixing into a nonaqueous medium a polymerizable component at least 20 percent of which is insoluble in said nonaqueous medium, said polymerizable component comprising at least one species; (b) subjecting the mixture of (a) to stress in order to particulate the mixture into microparticles which are uniformly of a fine particle size, said stress being sufficient to result in a dispersion such that after polymerization (c) less than 20 percent of the polymer microparticles have a diameter greater than 5 micrometers (5 microns) and the mean diameter of the microparticles ranges from 0.05 micrometers (0.5 microns) to 0.5 micrometers (0.5 microns); with the proviso that a dispersant is present when the polymerizable component is mixed into the nonaqueous medium pursuant to step (a) or is introduced into the medium after the particulation pursuant to step (b); and (c) polymerizing the polymerizable component within each particle under conditions sufficient to produce a stable dispersion of polymer microparticles in the nonaqueous medium, said nonaqueous medium containing no more than 30 percent dissolved polymer, said dispersion having a total solids content from 45 percent to 60 percent, when prepared directly, or from 55 to 75 percent, when concentrated during or after polymerization, and having a Brookfield viscosity, in the absence of a polar solvent and at a solids content of 40 percent, of less than 100 mPas (centipoise), measured at 50 RPM using a number 3 spindle at 25°C. The claimed method for preparing polymer microparticles which are stably dispersed in a nonaqueous medium involves several steps. The first step of the claimed method involves mixing into a nonaqueous medium a polymerizable component. The polymerizable component comprises at least one polymerizable species preferably at least two polymerizable species and moreover at least 20 percent of the polymerizable component is insoluble in the nonaqueous medium. For the purposes of the present application, the term "insoluble" means that the insoluble component is observable as a separate phase. The nonaqueous medium provides the continuous phase of the emulsion or dispersion in which the microparticles are suspended. The nonaqueous medium is one which is inert to the reactants and preferably is non-polar. A wide variety of organic solvents can be utilized. Preferably, a major amount of the nonaqueous medium is made up of an aliphatic solvent or mixture of aliphatic solvents. Examples of suitable nonaqueous media are hydrocarbons such as acyclic aliphatic hydrocarbons having from 4 to 30 carbon atoms and which are saturated such as N-pentane, N-hexane, N-heptane and N-octane; and cyclic hydrocarbons such cyclohexane and methyl cyclohexane. Also, minor amounts of aromatic hydrocarbons such as xylene and toluene as well as other solvents including ketone solvents and ester solvents can be present. The preferred media are the acyclic aliphatic hydrocarbons. The liquid hydrocarbon may be a mixture of such materials and would include such commercially available products as mineral spirits and solvent naphtha. If the polymerizable component is too viscous, for example a Brookfield viscosity greater than 2,000 mPas (20 poise) measured at 50 RPM using a number 3 spindle at 25°C or a Z Gardner Holdt viscosity, then a polar solvent such as N-methyl-2-pyrrolidone or acetonitrile can be used to dilute the polymerizable component. This is desirable from the standpoint that a less viscous polymerizable component requires less energy to particulate into small particles during the emulsification. However, the use of excessive amounts of polar solvents is not preferred because of the tendency of the polymerizable component to form a macrogel instead of discrete polymeric microparticles. It should be understood that the polar solvent can be inert to the reactants or it can be a reactive diluent such as, for example, N-vinyl pyrrolidone. One can prepare the claimed nonaqueous dispersions initially at low solids and then concentrate to high solids by distillation. In such an instance, a combination of a low boiling solvent (boiling point less than 100°C) and high boiling solvent (boiling point greater than 150°C) is preferred. As was mentioned above, at least 20 percent of the polymerizable component is insoluble in the nonaqueous medium. Generally, fewer difficulties are encountered when the majority of the polymerizable component is insoluble in the nonaqueous medium. The polymerizable component comprises at least one polymerizable species preferably at least two polymerizable species. The polymerizable species are materials which contain functionality which is capable of reacting and polymerizing to form a polymer. At least one of the reactant species and preferably all, should be insoluble in the nonaqueous medium. The reactants can be monomeric materials, oligomers or polymers. Examples of polymerizable species or reactants include active hydrogen containing materials such as, for example, polyester polyols, polyether polyols, and polyurethane polyols which are reacted with a polyisocyanate. When the polymerizable component comprises as reactants such an active hydrogen containing material and a polyisocyanate, the resultant polymer is a polyurethane microparticle dispersion. In the present invention where the expression "polyurethane" is used, not only polyurethanes from the reaction of polyisocyanates and polyols is intended but also mixed poly(urethane-ureas) and polyureas. Also, reaction products obtained from the reaction of polyisothiocyanates with active hydrogen containing compounds are intended. The polymerizable component can also comprise as polymerizable species an aminoplast resin reacted with a polyol such as those which have been listed above. In one embodiment a nonaqueous microparticle dispersion can be prepared by self-condensing one or more aminoplast resins. If desired water can also be added and it will react with the aminoplast during polymerization. Each of these materials is discussed in detail below. Although a variety of materials are disclosed, fewer difficulties are encountered in the claimed method of preparation when the materials chosen are insoluble in the nonaqueous medium. In a preferred embodiment, the polymerizable species are an amine and a polyisocyanate. The amine can be generated by the reaction of water with the polyisocyanate. The resultant product is a polyurea microparticle dispersion. The particles can be crosslinked or uncrosslinked. Examples of polyether polyols are polyalkylene ether polyols which include those having the following structural formula: where the substituent R is hydrogen or lower alkyl containing from 1 to 5 carbon atoms including mixed substituents, and n is typically from 2 to 6 and m is from 2 to 100 or even higher. Included are poly(oxytetramethylene) glycols, poly(oxyethylene) glycols, poly(oxy-1,2-propylene) glycols and the reaction products of ethylene glycol with a mixture of 1,2-propylene oxide, ethylene oxide and alkyl glycidyl ethers. Also useful are polyether polyols formed from oxyalkylation of various polyols, for example, glycols such as ethylene glycol, 1,6-hexanediol, Bisphenol A, or other higher polyols, such as trimethylolpropane, pentaerythritol. Polyols of higher functionality which can be utilized as indicated can be made, for instance, by oxyalkylation of compounds such as sorbitol or sucrose. One commonly utilized oxyalkylation method is by reacting a polyol with an alkylene oxide, for example, ethylene or propylene oxide, in the presence of an acidic or basic catalyst. In addition to the high molecular weight polyols mentioned above, mixtures of both high molecular weight and low molecular weight polyols can be used. Among the low molecular weight polyols are diols, which are preferred, and triols such as aliphatic polyols including alkylene polyols containing from 2 to 18 carbon atoms. Examples include ethylene glycol, 1,4-butanediol, 1,6-hexanediol; cycloaliphatic polyols such as 1,2-hexanediol and cyclohexanedimethanol. Examples of triols include trimethylolpropane and trimethylolethane. Also useful are polyols containing ether linkages such as diethylene glycol and triethylene glycol. Polyester polyols can be prepared by the polyesterification of an organic polycarboxylic acid or its functional equivalent (e.g., anhydride or ester) with organic polyols and/or an epoxide. Usually, the polycarboxylic acids and polyols are aliphatic or aromatic dibasic acids and diols. The diols which are usually employed in making the polyester include alkylene glycols, such as ethylene glycol, neopentyl glycol and other glycols such as hydrogenated Bisphenol A, cyclohexanediol, cyclohexanedimethanol, caprolactone derived diols, for example, the reaction product of epsilon-caprolactone and ethylene glycol, hydroxy-alkylated bisphenols, polyether glycols, for example, poly(oxytetramethylene) glycol. Polyols of higher functionality can also be used. Examples include trimethylolpropane, trimethylolethane, pentaerythritol, as well as higher molecular weight polyols such as those produced by oxyalkylating lower molecular weight polyols. The acid component of the polyester consists primarily of monomeric carboxylic acids or anhydrides having 2 to 36 carbon atoms per molecule. Among the acids which are useful are phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, decanedioic acid, dodecanedioic acid, and other dicarboxylic acids of varying types. The polyester may include minor amounts of monobasic acid such as benzoic acid, stearic acid, acetic acid, hydroxystearic acid and oleic acid. Also, there may be employed higher polycarboxylic acids such as trimellitic acid and tricarballylic acid. Where acids are referred to above, it is understood that anhydrides of those acids which form anhydrides can be used in place of the acid. Also, lower alkyl esters of the acids such as dimethyl glutarate and dimethyl terephthalate can be used. Besides polyester polyols formed from polybasic acids and polyols, polylactone-type polyesters can also be employed. These products are formed from the reaction of a lactone such as epsiloncaprolactone and a polyol. The product of a lactone with an acid-containing polyol can also be used. In addition to the aforedescribed polyols, polyurethane polyols can also be used. These polyols can be prepared by reacting any of the above-mentioned polyols with a minor amount of organic polyisocyanate (OH/NCO equivalent ratio greater than 1:1) so that terminal hydroxyl groups are present. The organic polyisocyanate can be an aliphatic polyisocyanate, including a cycloaliphatic polyisocyanate or an aromatic polyisocyanate. Useful aliphatic polyisocyanates include aliphatic diisocyanates such as ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 1,6-diisocyanatohexane, 1,4-butylene diisocyanate, lysine diisocyanate, 1,4-methylene bis(cyclohexyl isocyanate) and isophorone diisocyanate. Useful aromatic diisocyanates include the various isomers of toluene diisocyanate, meta-xylene-diisocyanate. and para-xylene-diisocyanate, also 4-chloro-1,3-phenylene diisocyanate, 1,5-tetrahydro-naphthalene diisocyanate, 4,4'-dibenzyl diisocyanate and 1,2,4-benzene triisocyanate can be used. In addition the various isomers of alpha, alpha, alpha'-tetramethyl xylene diisocyanate can be used. Also useful as the polyisocyanate are isocyanurates such as DESMODUR® 3300 from Mobay and biurets of isocyanates such as DESMODUR® N100 from Mobay. Aminoplast resins are based on the addition products of formaldehyde, with amino- or amido-group carrying substance. Condensation products obtained from the reaction of alcohols and formaldehyde with melamine, urea or benzoguanamine are most common and are preferred herein. However, condensation products of other amines and amides can also be employed, for example, aldehyde condensates of triazines, diazines, triazoles, guanidines, guanamines and alkyl- and aryl- substituted derivatives of such compounds, including alkyl- and aryl-substituted melamines. Some examples of such compounds are N,N'-dimethyl urea, benzourea, dicyandiamide, formaguanamine, acetoguanamine, ammeline, 2-chloro-4,6-diamino-1,3,5-triazine, 6-methyl-2,4-diamino-1,3,5-triazine, 3,5-diaminotriazole, triaminopyrimidine, 2-mercapto-4,6-diamino-pyrimidine, 3,4,6-tris(ethylamino)-1,3,5-triazine. While the aldehyde resins contain methylol or similar alkylol groups, and in most instances at least a portion of these alkylol groups are etherified by reaction with an alcohol so long as the alcohol chosen or the degree of etherification does not yield an aminoplast resin with excessive solubility in the solvent used in the nonaqueous medium. Any monohydric alcohol can be employed for this purpose, including such alcohols as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol and others, as well as benzyl alcohol and other aromatic alcohols, cyclic alcohols such as cyclohexanol, monoethers of glycols such as those sold under the trademarks CELLOSOLVE® and CARBITOL®, by Union Carbide and halogen-substituted or other substituted alcohols, such as 3-chloropropanol and butoxyethanol. The preferred aminoplast resins are substantially alkylated with methanol. The proportion of each of the materials which make up the polymerizable component can vary widely depending upon the polymeric structure desired. Typically the dispersion stabilizer or dispersant which is discussed below is used in an amount of from about 5 percent by weight to about 30 percent by weight, based on the total weight of the solid generating component of the pre-emulsification mixture. The balance is polymerizable component. For the purposes of determining these percentages the solid generating component does not include the inert materials which make up the nonaqueous medium as it has been defined herein. Reactive diluents as they have been defined herein, however, are considered to be solid generating. Once the polymerizable component has been thoroughly mixed with the nonaqueous medium, the mixture is subjected to stress in order to particulate the mixture into microparticles which are uniformly of a fine particle size. The mixture is subjected to stress sufficient to result in a dispersion such that after polymerization less than 20 percent of the polymer microparticles have a diameter greater than 5 microns. The preferred mode of subjecting the mixture of polymerizable component and nonaqueous medium to the appropriate stress is by use of a MICROFLUIDIZER® emulsifier which is available from Microfluidics Corporation in Newton, Massachusetts. The MICROFLUIDIZER® high pressure impingement emulsifier is patented in U.S. patent 4,533,254. The device consists of a high pressure (up to 137,800 kPa (20,000 psi)) pump and an interaction chamber where the emulsification takes place. The pump forces the mixture of reactants in nonaqueous medium into the chamber where it is split into at least two streams which pass at a very high velocity through at least two slits and collide resulting in the particulation of the mixture into small particles. Generally, the reaction mixture is passed through the emulsifier once at a pressure between 34,500 and 103,500 kPa (5,000 and 15,000 psi). Multiple passes result in smaller average particle size and a narrower range for the particle size distribution. When using the aforesaid MICROFLUIDIZER® emulsifier, stress is applied by liquid liquid impingement as has been described. However, it should be understood that if desired, other modes of applying stress to the pre-emulsification mixture can be utilized so long as sufficient stress is applied to achieve the requisite particle size distribution, that is, such that after polymerization less than 20 percent of the polymer microparticles have a diameter greater than 5 micrometer (5 microns). For example, one alternative manner of applying stress would be the use of ultrasonic energy. Stress is defined as force per unit area. Although the precise mechanism by which the MICROFLUIDIZER® emulsifier stresses the pre-emulsification mixture to particulate it is unknown, it is theorized that stress is exerted in more than one manner. It is believed that one manner in which stress is exerted is by shear. Shear means that the force is such that one layer or plane moves parallel to an adjacent, parallel plane. Stress can also be exerted from all sides as a bulk, compression stress. In this instance stress could be exerted without any shear. A further manner of producing intense stress is by cavitation. Cavitation occurs when the pressure within a liquid is reduced enough to cause vaporization. The formation and collapse of the vapor bubbles occurs violently over short time periods and produces intense stress. Although not intending to be bound by theory, it is believed that both shear and cavitation contribute to producing the stress which particulates the pre-emulsification mixture. Once the mixture has been particulated into microparticles, the polymerizable component within each particle is now polymerized under conditions sufficient to produce polymer microparticles which are stably dispersed in the nonaqueous medium. It should be understood that one of the requisite conditions sufficient to achieve the stably dispersed microparticles is the presence in the reaction mixture of a dispersion stabilizer also termed a dispersant. The dispersion stabilizer is preferably present when the polymerizable component is mixed into the nonaqueous medium prior to particulation. Alternatively, the dispersant can be introduced into the medium at a point just after the particulation within the MICROFLUIDIZER® emulsifier. The dispersant, however, is an important part of the polymerizable component necessary to achieve the requisite particle stability. The stabilizer is a material whose role is to prevent the emulsified particles from agglomerating to form larger particles. The same variety of dispersion stabilizers or dispersants which can be utilized during conventional nonaqueous emulsion polymerization are also suitable for this high stress technique. For a detailed listing of several suitable stabilizers see Dowbenko and Hart, "Nonaqueous Dispersions as Vehicles for Polymer Coatings", I&EC Product Research and Development, Vol. 12, March 1973, pages 14 to 20, copyright 1973. A preferred dispersion stabilizer is known as the comb stabilizer. The preparation of the preferred comb type graft dispersant is disclosed in U.S. 3,607,821. It should be understood that in some instances it may be desirable for some of the reactant species to be added after particulation of the remaining reactants and the nonaqueous medium. These reactants can be added either before or during the polymerization. For example, in the preparation of a polyurea directly from amine and polyisocyanate or when water is used initially to react with the polyisocyanate to generate amine, it is preferred that the amine or water be added to the isocyanate functional microparticle dispersion rather than being added prior to particulation. The particulated mixture is then subjected to conditions sufficient to induce polymerization of the polymerizable mixture within the microparticles. The particular conditions will vary depending upon the actual materials being polymerized. For example, for the reaction of aminoplasts with polyols the addition of an acid catalyst and heat is used; for the reaction of polyisocyanates and polyols a catalyst such as dibutyltin dilaurate and heat is used; for vinyl addition polymerization a free radical catalyst is utilized. For example, in the preparation of polyurethanes generally the temperature can vary from about 20°C to about 120°C, preferably 80°C to 100°C. The length of time required to complete polymerization typically varies from about three hours to about 12 hours. Usually, the preparation of a polyurethane microparticle dispersion requires a temperature of about 85°C to 90°C for a period of from about three to about five hours. The progress of the polymerization reaction can be followed by techniques conventionally known to those skilled in the art of polymer chemistry. For example, isocyanate equivalent weight and infrared spectroscopy can be used to follow the polyurethane preparation. For a vinyl addition polymerization one can monitor solids and for an aminoplast polyol reaction one can monitor the amount of distillate being removed (typically water and alcohol and occasionally formaldehyde are removed by distillation). Once the polymerization is complete, the resultant product is a stable dispersion of polymer microparticles in a nonaqueous medium, wherein the polymer is contained within each particle. The nonaqueous medium therefore is substantially free of dissolved polymer since it is essentially self-contained within each microparticle. The resultant polymer microparticles are of course insoluble in the nonaqueous medium. In saying that the nonaqueous medium is substantially free of dissolved polymer, it is intended that the term "substantially free" means that the nonaqueous medium contains no more than 30 percent by weight of dissolved polymer, preferably no more than 15 percent. By "stably dispersed" is meant that the polymer microparticles do not settle upon standing and do not coagulate or flocculate on standing. Typically, when diluted to 50 percent total solids the claimed dispersions do not settle even when aged for one month at room temperature As was stated above, a very important aspect of the polymer microparticle dispersions of the claimed invention is that the particle size is uniformly small, i.e., after polymerization less than 20 percent of the polymer microparticles have a mean diameter which is greater than 5 micrometers (5 microns), more preferably greater than 1 micrometer (1 micron). The mean diameter of the particles after polymerization ranges from about 0.05 micrometers (0.05 microns) to about 0.5 micrometers (0.5 microns). The particle size can be measured with a particle size analyzer such as the Coulter N4 instrument commercially available from Coulter. The instrument comes with detailed instructions for making the particle size measurements. However, breifly, a sample of the nonaqueous dispersion is diluted with heptane until the sample concentration falls within specified limits required by the instrument. The measurement time is 10 minutes. Moreover, generally the microparticle dispersions are characterized by the property that in the absence of a polar solvent, when at a solids content of 40 percent, the Brookfield viscosity is less than 100 mPas (100 centipoise) measured at 50 RPM using a number 3 spindle at 25°C. In a preferred embodiment when one is preparing a polyurethane, when at a solids content of 60 percent the Brookfield viscosity is less than 1,000 mPa·s (1,000 centipoise) measured at 50 RPM using a number 3 spindle at 25°C. It should be understood that the claimed nonaqueous polymer microparticle dispersions can be thixotropic. That is, their viscosity can increase if they are allowed to stand undisturbed. However, upon application of sufficient high shear for a period of time the viscosity will be decreased. The claimed microparticle dispersions are high solids materials of low viscosity. Dispersions can be prepared directly with a total solids content of from 45 percent to 60 percent. They can also be prepared at a lower solids level of 30 to 40 percent total solids and concentrated to a higher level of solids of 55 to 75 percent by stripping. This can even be done during the polymerization. The molecular weight and viscosity of the claimed nonaqueous dispersions are independent of each other. The weight average molecular weight can range from a few hundred to greater than 100,000. The Brookfield viscosity can also vary widely from 100 mPas (one poise) to 10,000 mPas (100 poise), preferably from 100 mPas to 500 mPas (1 to 5 poise) when measured at 25°C using a number 3 spindle at 50 RPM. The microparticle dispersions can be either crosslinked or uncrosslinked. When uncrosslinked the polymer within the microparticles can be either linear or branched. In the preparation of polyurethanes, the use of difunctional polyisocyanates and active hydrogen containing materials results in linear materials. The incorporation of materials of higher functionality leads to branching and/or crosslinking. As is appreciated by those skilled in polymer chemistry, the ratio of the reactants determines the molecular weight, degree of branching and degree of crosslinking. The nonaqueous dispersions of the present invention are very advantageous. They can be used in a variety of protective and decorative coatings including coatings, adhesives, sealants, molding resins, casting resins and free films. As has been mentioned above, they are high solids materials but of a low viscosity. The fact that they are high solids materials is particularly advantageous. Since the claimed dispersions are of high solids they can be utilized in coating applications without significantly increasing the volatile organic content of the composition. In addition, depending upon the active hydrogen containing material the polyurethane microparticles can be tailored so as to result in improved impact resistance, and flexibility of the resultant coating. The following examples are illustrative of the invention. EXAMPLE I This example illustrates the preparation of a nonaqueous, hydroxyl functional polyurethane crosslinked microparticle dispersion. A solution was prepared by mixing the following ingredients in the indicated proportions: The above solution was added while stirring to 4680 grams of a 1:1 mixture of heptane (boiling range of 94°C to 98°C) and ISOPAR® G (commercially available from Exxon and has a boiling range of 156°C to 176°C). Vigorous stirring of the total mixture produced a pre-emulsion which was passed through a MICROFLUIDIZER® M-110 emulsifier at a pressure of 62000 kPa (9000 psi). 2.1 grams of dibutyltin diacetate and 21 grams of triethylamine were added to the resulting emulsion which was then heated at 70°C for nine hours. During the last six hours a vacuum was applied to remove solvent until a final total solids content of 64.0 percent was achieved. The Brookfield viscosity, using a number 2 spindle at 50 rpm, of the opaque, bluish-white product was 340 mPas (340 centipoise). The mean particle size, as measured on a Coulter N4 particle size analyzer, was 249 nanometers (0.249 micrometers) with a standard deviation of 58 nanometers (0.058 micrometers). EXAMPLE II This example illustrates the preparation of an acid-functional crosslinked microparticle dispersion. A mixture was prepared by vigorously mixing together the following ingredients: Ingredients Parts by Weight (grams) acrylic polymer solution 233 FORMREZ® 55-56 330 dispersant of footnote 3 130 acetonitrile 60 ISOPAR® G 1300 The aforesaid mixture was passed through a MICROFLUIDIZER® M-110 emulsifier at 57,200 kPa (8300 psi) and the resulting nonaqueous dispersion was heated at 90°C for 10 hours while distilling off solvent with a nitrogen sparge. The infrared spectrum of a sample of the reaction mixture showed a small amount of anhydride present. After 1 gram of ethylene diamine dissolved in 4 grams of propylene glycol monomethyl ether acetate was added at 60°C, no anhydride was present. Solvent was distilled under reduced pressure at 50°C until a total solids content of 69.5 percent was achieved. The final product had a Brookfield viscosity of 381 mPas (381 centipoise) determined at 50rpm using a number 2 spindle. EXAMPLE III A mixture was prepared by vigorously shaking together the following ingredients: Ingredients Parts by Weight (grams) hydroxyethyl acrylate 95 acrylic acid 5 dispersant of footnote (3) 30 ISOPAR® K 400 The aforesaid mixture was passed through a MICROFLUIDIZER® M-110 emulsifier at a pressure of 60,600 kPa (8800 psi) and 0.5 grams of the free radical polymerization initiator VAZO-67 commercially available from E. I. DuPont deNemours) dissolved in 5 grams of propylene glycol monomethyl ether acetate was added to the dispersion. The microparticle dispersion was slowly heated to 50°C whereupon an exotherm occurred which raised the temperature to 80°C. After allowing the temperature to drop, the reaction was held at 60°C for two hours, at 70°C for two hours and at 80°C for two hours. After cooling, the solids content of the product was found to be 21.4 percent. EXAMPLE IV This Example illustrates the preparation of an acrylate functional polyurethane crosslinked microparticle dispersion. A mixture of the following ingredients was prepared Ingredients Parts by Weight (grams) FORMREZ® 55-56 1000 DESMODUR® N100 95 1,4-butanediol 60 isophorone diisocyanate 360 hydroxyethyl acrylate 190 dispersant of footnote (3) 473 acetonitrile 200 IONOL® 1.9 The above solution was added while stirring vigorously to 3900 grams of ISOPAR® E (aliphatic solvent having boiling range between 116°C and 138°C, commercially available from Exxon). The resulting mixture was passed once through a MICROFLUIDIZER® M-110 emulsifier and then heated at 50°C for 10 hours. Two grams of dibutyltin dilaurate was added and heating was continued for an additional 15 hours until no isocyanate was detectable by infrared spectroscopy. Vacuum distillation of solvent from the emulsion yielded a final total solids content of 62.1 percent and a Brookfield viscosity of 260 centipoise using a number 2 spindle at 50 rpm. EXAMPLE V This example illustrates the preparation of an uncrosslinked linear polyurethane microparticle dispersion. The following ingredients were mixed together to form a solution: Ingredients Parts by Weight (grams) FORMREZ® 55-56 1000 1,4-butanediol 180 trimethylhexamethylene diisocyanate 642 dispersant of footnote (3) 512 N-methyl pyrrolidone 200 A mixture was formed by adding the above solution, while stirring, to 4,000 grams of a solvent mixture consisting of one part of ISOPAR® G and three parts of heptane (boiling range 94°C to 98°C). The mixture was then passed through a MICROFLUIDIZER® M-110 emulsifier at 62,000 kPa (9,000 psi) and 2 grams of dibutyltin diacetate and 20 grams of triethylamine were added to the emulsion. After heating the emulsion for 8 hours at 70°C, the infrared spectrum of a sample of the mixture indicated the presence of isocyanate. The temperature was held at 70°C while 50 grams of a mixture of 4 parts of propylene glycol monomethyl ether acetate and one part of ethylenediamine was added, dropwise, over a period of two hours. After the infrared spectrum of a sample indicated that all of the isocyanate had reacted, the solvent was distilled under vacuum until a final solids content of 57.6 percent was achieved. The Brookfield viscosity at 50 RPM using a number 2 spindle was 370 mPa s (370 centipoise). The mean particle size, measured on a Coulter N4 particle size analyzer was 362 nanometers (0.362 micrometers) with a standard deviation of 230 nanometers (0.230 micrometers) EXAMPLE VI This example illustrates the preparation of a polyester melamine crosslinked microparticle dispersion. A solution was prepared by mixing the following ingredients: Ingredients Parts by Weight (grams) CYMEL® 303 510 polyester polyol 1530 dispersant of footnote (3) 578 dodecylbenzene sulfonic acid (70 percent solution) 28.9 acetonitrile 595 The above mixture was added to 1,496 grams of ISOPAR® K (boiling range 177°C to 197°C, commercially available from Exxon) and 2,550 grams of heptane (boiling range 94°C to 98°C). The total mixture was stirred vigorously to produce a mixture which was passed through a MICROFLUIDIZER® M-110 emulsifier at a pressure of 54,400 kPa (7,900 psi) to produce an opaque, bluish-white emulsion. The emulsion was stirred at 75°C to 100°C for 10 hours under a stream of nitrogen while collecting distillate. Vacuum was applied for six hours at 85°C to remove solvent and achieve a final total solids content of 63 percent. EXAMPLE VII This example illustrates the preparation of a glycoluril-polyol nonaqueous microparticle dispersion. A solution was prepared by stirring together the following ingredients: Ingredients Parts by Weight (grams) CYMEL® 1171 1500 ethylene glycol 375 dodecylbenzene sulfonic acid (70 percent) 53.8 dispersant of footnote (3) 531.3 The solution was added to a stirring mixture of Isopar® K (aliphatic solvent from Exxon having boiling point range of 177°C to 197°C) and 3750g heptane (boiling point range of 94°C to 98°C). The resulting mixture was passed through a MICROFLUIDIZER® M-110 emulsifier to produce a stable, bluish-white emulsion which was then heated at 70°C to 80°C for five hours under a nitrogen sparge. Of 1387 ml of distillate collected, 481ml separated into a lower layer. The emulsion was further condensed by vacuum distillation at 50°C to a total solids content of 51.8 percent. The Brookfield viscosity of the final emulsion was 124 mPas (124 centipoise) at 50 rpm using a number 3 spindle. This dispersion exhibited an increase in viscosity upon standing undisturbed for several days however upon application of high shear the viscosity decreased. EXAMPLE VIII This Example illustrates the preparation of a crosslinked polyurea nonaqueous microparticle dispersion. A mixture was prepared by stirring together the following ingredients: Ingredients Parts by Weight (grams) DESMODUR® N100 1620 dispersant of footnote (3) 448.2 ethyl acetate 540 ISOPAR® E 4050 The mixture was passed through a MICROFLUIDIZER® M-110 emulsifier to produce a bluish-white emulsion. After 75g of water and 3g of dibutyltin dilaurate were added, the emulsion exothermed to 40°C and began to evolve gas. After 20 hours of stirring without external heating, 50g of water was added and the emulsion heated at 50°C for 30 minutes at which point a sample of the reaction mixture examined by infrared spectroscopy indicated the absence of isocyanate. Solvent was removed by vacuum distillation at 50°C until a total solids content of 60.3 percent was achieved. The Brookfield viscosity of the final product was 60 mPas (60 centipoise) using a number 3 spindle at 50 RPM. The particle size distribution was bimodal with about two-thirds of the particles having a diameter of 276 nanometers (0.276 micrometers) with a standard deviation of 90 nanometers (0.090 micrometers) and one-third of the particles having a diameter of 983 nanometers (0.983 micrometers) with a standard deviation of 150 nanometers (0.150 micrometers). EXAMPLE IX This Example illustrates the preparation of an amine functional polyurethane nonaqueous microparticle dispersion. A mixture was prepared by stirring together the following ingredients: Ingredients Parts by Weight (grams) DESMODUR® N100 1330 1,4-butanediol 220.5 acetonitrile 210 dispersant of footnote (3) 474.6 The above solution was added while stirring to 3920g heptane (boiling range of 94°C to 98°C) to produce a pre-emulsion which was passed through a MICROFLUIDIZER® M-110 emulsifier at 51,700 kPa (7500psi). The resulting emulsion was heated to 70°C over a one hour period and then held at that temperature for an additional hour. Then, 156g of dimethylethanolamine was added over a 45 minute period. The temperature was held at 70°C for one hour at which time the infrared spectrum of a sample indicated that no isocyanate remained. The dispersion was vacuum distilled at 70° until a final total solids content of 66.3 percent was achieved. EXAMPLE X This Example illustrates the preparation of an isocyanate functional polyurethane nonaqueous microparticle dispersion. A mixture was prepared by stirring together the following ingredients: Ingredients Parts by Weight (grams) polyester polyol 932 DESMODUR® N100 1138 dispersant of footnote (3) 549 The above solution was added while stirring to 4680g of ISOPAR® E to produce a pre-emulsion which was then passed through a MICROFLUIDIZER® M-110 emulsifier. The resulting emulsion was heated at 50°C for about eight hours and then vacuum stripped to a final solids of 65.3 percent. The isocyanate equivalent weight was found by titration to be 24,000. EXAMPLE XI This Example illustrates the preparation of an acid functional polyurethane nonaqueous microparticle dispersion. A solution was prepared by mixing the following ingredients together: Ingredients Parts by Weight (grams) FORMREZ® 55-56 1400 1,4-butanediol 315 DESMODUR® N100 136.5 trimethyl hexamethylene diisocyanate 524.3 methyl hexahydrophthalic anhydride 176.4 dispersant of footnote(3) 711.2 The above solution was added with vigorous stirring to 840g of ISOPAR® K (aliphatic solvent with a boiling point range of 177°C to 197°C commercially available from Exxon) and 3080g heptane (boiling point range 94°C to 98°C) and the resulting pre-emulsion was passed through a MICROFLUIDIZER® M-110 emulsifier at 62,700kPa (9100 psi). Then, 2.8g of dibutyltin diacetate and 28g triethylamine were added to the emulsion which as heated at 70°C for about four hours. After three hours the infrared spectrum of a sample did not show the presence of anhydride functionality and after four hours the infrared spectrum showed that no isocyanate functionality remained. The emulsion was vacuum stripped at 50°C until a final total solids of 64.4 percent was obtained. The acid equivalent weight of the final emulsion was 4,520.

Claims: A method for preparing polymer microparticles which are stably dispersed in a nonaqueous medium, which method comprises: (a) mixing into a nonaqueous medium a polymerizable component at least 20 percent of which is insoluble in said nonaqueous medium, said polymerizable component comprising at least one species; (b) subjecting the mixture of (a) to stress in order to particulate the mixture into microparticles which are uniformly of a fine particle size, said stress being sufficient to result in a dispersion such that after polymerization (c) less than 20 percent of the polymer microparticles have a diameter greater than 5 micrometers (5 microns) and the mean diameter of the microparticles ranges from 0.05 micrometers (0.05 microns) to 0.5 micrometers (0.5 microns); with the proviso that a dispersant is present when the polymerizable component is mixed into the nonaqueous medium pursuant to step (a) or is introduced into the medium after the particulation pursuant to step (b); and (c) polymerizing the polymerizable component within each particle under conditions sufficient to produce a stable dispersion of polymer microparticles in the nonaqueous medium, said nonaqueous medium containing no more than 30 percent dissolved polymer, said dispersion having a total solids content from 45 percent to 60 percent, when prepared directly, or from 55 to 75 percent, when concentrated during or after polymerization, and having a Brookfield viscosity, in the absence of a polar solvent and at a solids content of 40 percent, of less than 100 mPas (centipoise), measured at 50 RPM using a number 3 spindle at 25°C. The method of claim 1 wherein less than 20 percent of the polymer microparticles have a diameter greater than 1 micrometer (1 micron). The method of claims 1 or 2 wherein the stress is applied by liquid-liquid impingement. The method of any of claims 1 to 3 wherein the polymerizable component additionally comprises a polar solvent as diluent which is different from the nonaqueous medium. The method of any of claims 1 to 4 wherein the nonaqueous medium is an aliphatic non-polar solvent. The method of claim 5 wherein the nonaqueous medium is a saturated hydrocarbon having a carbon chain length of from 4 to 30 carbon atoms. The method of any of claims 1 to 6 wherein the polymerizable component comprises an active hydrogen containing material and a polyisocyanate as polymerizable species. The method of any of claims 1 to 6 wherein the polymerizable component comprises as polymerizable species an aminoplast resin and a polyol selected from polyurethane polyols, polyester polyols and polyether polyols. The method of any of claims 1 to 6 wherein the polymerizable component comprises as polymerizable species a polyisocyanate and an amine. The method of any of claims 1 to 9 wherein the nonaqeous medium contains no more than 15 percent of dissolved polymer. The method of any of claims 1 to 10 wherein the polymer microparticles are crosslinked. The method of any of claims 1 to 10 wherein the polymer microparticles are uncrosslinked.

Inventors: FALER DENNIS LEROY, HARTMAN MARVIS EDGAR, MCCOLLUM GREGORY JAMES, O'DWYER JAMES BRENDAN, FALER, DENNIS LEROY, HARTMAN, MARVIS EDGAR, MCCOLLUM, GREGORY JAMES, O'DWYER, JAMES BRENDAN
Applicants: PPG INDUSTRIES INC, PPG INDUSTRIES, INC.
Application year: 1988
Main classification: C08G18
IPC codes: C08G2, C08F2, C08G18, C08G12, C08G85