sign in sign up
<<
Home , Sesamex

O USOO5332584A United States Patent (19) 11) Patent Number: 5,332,584 Scher et al. 45 Date of Patent: k Jul. 26, 1994

54) MICROCAPSULES 4,221,710 9/1980 Hoshi et al...... 264/4.7 X (75) Inventors: Herbert B. Scher, Moraga; Marius 4,223,023. 2,3-1980 Ea.Rai - - - - - a a a -a - 428/402.214. i. Rodson, El Cerrito, both of Calif. 4,576,891 3/1986 Adair et al...... 428/402.21 X 73 Assignee: Zeneca Inc., Wilmington, Del. 4,956,1295,160,529 11/19929/1990 Scher et al...... 264/4.771/118 * Notice: The portion of the term of this patent subsequent to Sep. 11, 2007 has been OTHER PUBLICATIONS disclaimed. Nylen et al.: Modern Surface Coatings, Interscience (21) Appl. No.: 803,870 Publishers, New York, (1965), pp. 190-193. 22 Filed: Dec. 9, 1991 Primary Examiner-Richard D. Lovering Attorney, Agent, or Firm-Joel G. Ackerman Related U.S. Application Data 57 ABSTRACT 63 Continuation of Ser. No.a 540,560,- Jun. 20, 1990, aban- A process is disclosed forf the microencapsulation of a g 3. "Yes i. NR substantially water-insoluble liquid material within a tion-in-pfS.N.366. No porous shell to effect a slow rate of release of said mate doned, which is a continuation-in-part of Ser. No. rial through said shell which comprises (a) providing an 499,973, Jun. 1, 1983, abandoned, which is a continua- organic Solution comprising said material and an etheri tion-in-part of Ser. No. 201,686, Oct. 30, 1980, aban- fied urea-formaldehyde prepolymer dissolved therein in doned. which from about 50% to about 98% of the methylol

51) Int. Cl.5Vak ea e o a no ooooooo so A01N 25/28:9 AON 37/18: groups of said prepolymer have been etherified with a B01J 13/18 C4-C10 alcohol; (b) creating an emulsion of said organic 52) U.S. Cl 424/408; 71/DEG. : solution in an continuous phase aqueous solution com Ohio Yaake ou o aw o a o on a a o 0 0 e o 0 & 8 s> & 4 so a us a so 9 • as prising water and a surfaceactive agent, wherein said 26/2: 2.78.7. emulsion comprises discrete droplets of said organic 58) Field of Search 264/4.3, 4.33, 4.7: solution dispersed in said continuous phase aqueous o solution, there being formed thereby an interface be 428/402.21; 424/40s:ARE's tween the discrete droplets of organic solution and the surrounding continuous phase aqueous solution; and (c) 56 References Cited causing in situ self-condensation and curing of said urea U.S. PATENT DOCUMENTS formaldehyde prepolymers in the organic phase of said discrete droplets adjacent to said interface by simulta 3,016,308 1/1963 Macaulay ------264/4.6 X neously heating said emulsion tO a temperature between 3,074,845 1/1963 Geary ...... 424/19 about 20 C. to about 100 C., and adding to said emul 3:63 Slyay .... 427 s: sion an acidifying agent and maintaining said emulsion 35ió941 6/1970 Mason. ... 264747 X at a pH of between about 0 to about 4 for a sufficient 3,686,015 8/1972 Powell et al.. ... 264/4.3 X period of time to allow substantial completion of in situ 4,001,140 1/1977 Foris et al...... 264/4.7 x condensation of said resin prepolymers to convert the 4,073,968 2/1978 Miyamoto et al...... 427/54 liquid droplets of said organic solution to capsules con 4,087,376 5/1978 Foris et al...... 264/4.7 X sisting of solid permeable polymer shells enclosing said 4,089,802 5/1978 Foris et al...... 264/4.7 X liquid material.

2: $3. Siaka 223: Also disclosed are the microcapsules formed by the 4,157,983 6/1979 Golden ...... 264/467 x above-described process. 4,219,604 8/1980 Kakimi et al...... 428/307 4,219,631 8/1980 Hunsucker et al...... 525/398 15 Claims, No Drawings 5,332,584 1. 2 is released into the aqueous phase (the continuous phase MCROCAPSULES of the emulsion), and the film-forming materials accu mulate at the interface and polymerize. This is a continuation of Ser. No. 07/540,560, filed Olefin polymerization using a peroxide catalyst is Jun. 20, 1990 now abandonment which in turn is a con described in Japanese patent publication No. 9168/1961, tinuation of application Ser. No. 07/151,048, filed Feb. whereby an oil-insoluble polymer is formed at the sur 1, 1988 “now U.S. Pat. No. 4,956,129'; which in turn is faces of oil drops. a continuation-in-part application of Ser. No. 595,136, British Patent Nos. 952,807 and 965,074 describe a filed Mar. 30, 1984, now abandoned; which in turn is a process whereby a solid such as wax or a thermoplastic continuation-in-part application of Ser. No. 499,973, 10 resin is melted, dispersed and cooled to form an encap filed Jun. 1, 1983, now abandoned; which in turn is a sulating film around liquid droplets. continuation-in-part application of Ser. No. 201,686, U.S. Pat. No. 3,111,407 (Lindquist et al., Nov. 19, filed Oct. 30, 1980, now abandoned. 1963) describes a spray drying method which forms BACKGROUND OF THE INVENTION encapsulated droplets at the instant of atomization. 15 These processes vary in terms of equipment expense, A. Field of the Invention energy requirements, ease of controlling the microcap This invention relates to microcapsules and to a pro sule size, the need for extra reagents such as catalysts cess for their production. In particular, this invention and settling agents, and percent microcapsule phase. It relates to encapsulated droplets of a liquid material is therefore an object of the present invention to pro which is substantially insoluble in water, where the 20 vide a simple, inexpensive method for producing micro encapsulating agent is a film formed from a modified capsules of uniform and readily controlled size, which urea-formaldehyde aldehyde polymer. are suitable for use without further treatment. Other B. Description of the Prior Art objects of the invention will be apparent from the foll The use of membranes, coatings, and capsules for the lowing description. controlled release of liquid materials is well known in 25 the art of both agricultural and non-agricultural chemi SUMMARY OF THE INVENTION cals. In agriculture, controlled-release techniques have It has now been discovered that a liquid material improved the efficiency of herbicides, , fun which is substantially insoluble in water can be micro gicides, bactericides, and fertilizers. Non-agricultural encapsulated within a porous shell by a process which uses include encapsulated dyes, inks, pharmaceuticals, 30 comprises: flavoring agents, and fragrances. (a) providing an organic solution comprising said The most common forms of controlled-release mate material and an etherified urea-formaldehyde prepoly rials are coated droplets or microcapsules, coated solids mer dissolved therein in which from about 50% to including both porous and non-porous particles, and about 98% of the methylol groups of said prepolymer coated aggregates of solid particles. In some instances, a 35 have been etherified with a C4-C10 alcohol; water-soluble encapsulating film is desired, which re (b) creating an emulsion of said organic solution in an leases the encapsulated material when the capsule is continuous phase aqueous solution comprising water placed in contact with water. Other coatings are de and a surface-active agent, wherein said emulsion com signed to release the entrapped material when the coat prises discrete droplets of said organic solution dis ing is ruptured by external force. persed in said continuous phase aqueous solution, there Still further coatings are porous in nature and release being formed thereby an interface between the discrete the entrapped material to the surrounding medium at a droplets of organic solution and the surrounding contin slow rate by diffusion through the pores. In addition to uous phase aqueous solution; and providing controlled release, such coatings also serve to (c) causing in situ self-condensation and curing of said facilitate the dispersion of water-immiscible liquids into 45 unreaformaldehyde prepolymers in the organic phase of water and water-containing media such as wet soil. said discrete droplets adjacent to said interface by si Droplets encapsulated in this manner are particularly multaneously heating said emulsion to a temperature useful in agriculture, where water from irrigation, rain, between about 20° C. to about 100 C., and adding to and water sprays is frequently present. A variety of said emulsion an acidifying agent and maintaining said processes for producing such capsules is known. 50 emulsion at a pH of between about 0 to about 4 for a In one process, the capsules are formed by phase sufficient period of time to allow substantial completion separation from an aqueous solution through the coac of in situ condensation of said resin prepolymers to ervation of a hydrophilic colloid sol. This is described . convert the liquid droplets of said organic solution to in U.S. Pat. Nos. 2,800,457 (Green et al., Jul. 23, 1957) capsules consisting of solid permeable polymer shells and 2,800,458 (Green, Jul. 23, 1957). 55 enclosing said liquid material. An interfacial polymerization process is disclosed in Microcapsules formed by this process are capable of U.S. Pat. Nos. 4,046,741 (Scher, Sep. 6, 1977) and effecting a slow rate of release of the encapsulated liq 4,140,516 (Scher, Feb. 20, 1979), whereby the film uid by diffusion through the shell to the surrounding forming reactants are dissolved in the hydrophobic medium. The present invention resides in both the pro liquid which is dispersed in water, the reaction occur cess described above and the microcapsules thus ring at the interface when the phases are placed in formed. contact as an emulsion. A further interfacial polymerization process is de DESCRIPTION OF THE PREFERRED scribed in U.S. Pat. No. 3,726,804 (Matsukawa et al., EMBODIMENTS Apr. 10, 1973) whereby all the film-forming ingredients 65 The present invention can be readily adapted to ac initially reside in hydrophobic droplets which also con commodate variations in the materials used, the kind of tain a low boiling or polar solvent in addition to the product desired, and economic factors in general. As material to be encapsulated. Upon heating, the solvent the following indicates, both essential and optional fea 5,332,584 3 4. tures of the process and the product thereof can be varied over a wide range. INSECTICIDES S-tert-butylthiomethyl O,O-diethyl phosphorodithioate A. Core Liquid () It is essential that the organic solution which forms 5 O,O-diethyl-O-4-methylsulphinylphenyl phosphorothi. the interior of the capsules (i.e., the core liquid) be sub oate (fensulfothion) stantially insoluble in water. Preferably, its solubility O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl under ambient conditions is approximately 5000 parts phosphorothioate () per million (ppm) by weight or less. The organic solu O,O-diethyl S-2-ethylthioethyl phosphorodithioate (di tion may consist of a single liquid material or one or O sulfoton) more active liquid or solid materials dissolved in an S-chloromethyl O,O-diethyl phosphorodithioate inert solvent which has at most a slight solubility in (chlormephos) water. In the latter case, the liquid or solid solute must O-ethyl S.S.-dipropyl phosphorodithioate (ethopro reside preferentially in the organic phase when the two phos) phases are in equilibrium. 15 O,O-diethyl S-ethylthiomethyl phosphorodithioate A wide variety of liquids can be encapsulated by the () present process. The most useful liquids are those which O-(4-bromo-2-chlorophenyl) O-ethyl S-propyl phos do not react with either the prepolymer, the acid used in phorodithioate (prophenofos) the self-condensation wall-forming step, or any of the S-1,2-di(ethoxycarbonyl)ethyl O,O-dimethyl phos other components in the system. Thus, any nonreactive 20 phorodithioate () liquid which will diffuse through the shell membrane is O,O,O',O'-tetraethyl S,S'-methylene di(phosphorodi suitable. The liquid can be a single chemical compound thioate) () or a mixture of two or more compounds. It can diffuse O-(4-bromo-2,5-dichlorophenyl) O,O-diethyl phos into water, soil, air, or any other surrounding medium. phorothioate (bromophosethyl) Liquids suitable for encapsulation include chemical 25 S-4-chlorophenylthiomethyl O,O-diethyl phosphorodi biological agents such as herbicides, insecticides, fungi thioate () cides, nematocides, bactericides, rodenticides, mollus 2-chloro-1-(2,4-dichlorophenyl) vinyl diethyl phosphate cides, acaricides, larvicides, animal, insect, and bird (chlorphenvinphos) repellents, plant growth regulators, fertilizers, phero O-2,5-dichloro-4-(methylthio)phenyl O,O-diethyl phos mones, sex lures and attractants, and flavor and odor 30 phorodithioate (chlorthiophos) compositions. The microcapsules of the present inven O-4-cyanophenyl O,O-dimethyl phosphorothioate tion are particularly well adapted to pesticides, includ () ing thiocarbamates, dithiocarbamates, acetamides, ani O,O-dimethyl O-2-methylthioethyl phosphorothioate lides, sulfonamides, triazines, organophosphorus com (denephion) pounds, and . The following are examples of 35 O,O-diethyl O-2-ethylthioethyl phosphorothioate such compounds, followed in parentheses by their com (demeton) mon names where available: O-2,4-dichlorophenyl O,O-diethyl phosphorothioate (dichlorofenthion) HERBICIDES O-2,4-dichlorophenyl O-ethyl phenylphosphonothioate S-ethyl-N-cyclohexyl-N-ethylthiocarbamate (cycloate) 40 (EPBP) S-ethyl hexahydro-1H-azepine-1-carbothioate (moli O,O-diethyl O-5-phenylisoxazol-3-yl phosphorothioate nate) () S-2,3-dichloroallyl di-isopropylthiocarbamate (di 1,3-di(methoxycarbonyl)-1-propen-2-yl dimethyl phos allate) phate S-2,3,3-trichloroallyl di-isopropylthiocarbamate (tri- 45 S.S'-(1,4-dioxane-2,3-diyl) O,O,O',O'-tetraethyl di(- allate) phosphorodithioate) () S-ethyl dipropylthiocarbamate (EPTC) O,O-dimethyl-O-4-nitro-m-tolyl phosphorothioate S-4-chlorobenzyl diethylthiocarbamate (benthiocarb) () S-ethyl diisobutylthiocarbamate (butylate) O,O-dimethyl O-4-methylthio-m-tolyl phosphorothio S-benzyl di-sec-butylthiocarbamate 50 ate () S-propyl dipropylthiocarbamate (vernolate) O-(5-chloro-1-isopropyl-1,2,4-triazol-3-yl) O,O-diethyl S-propylbutylethylthiocarbamate (pebulate) phosphorothioate (isazophos) N,N-diallylchloroacetamide (allidochlor) S-2-isopropylthioethyl O,O-dimethyl phosphorodithio a-chloro-6'-ethyl-N-(2-methoxy-1-methylethyl)- ate (isothioate) acetanilide (metolachlor) 55 4-(methylthio)phenyl dipropyl phosphate (propaphos) N-butoxymethyl-a-chloro-2',6'-diethylacetanilide 1,2-dibromo-2,2-dichloroethyl dimethyl phosphate (na (butachlor) led) S-(O,O-diisopropyl phosphorodithioate) ester of N-(2- O,O-diethyl al-cyanobenzylideneamino-oxyphosphono mercaptoethyl)benzenesulfonamide () thioate () N-benzyl-N-isopropyltrimethylacetamide (butam) 60 O,O-diethyl O-4-nitrophenyl phosphorothioate (para 2-chloroallyl diethyldithiocarbamate (CDEC) thion) 2-sec-butyl-4,6-dinitrophenol (dinoseb) O-2-diethylamino-6-methylpyrimidin-4-yl O,O-diethyl 2,6-dinitro-N,N-dipropylcumidine (isopropalin) phosphorothioate (pirimiphos-ethyl) N-(cyclopropylmethyl)-a,a,-trifluoro-2,6-dinitro-N- O-2-diethylamino-6-methylpyrimidin-4-yl propyl-p-toluidine (profluralin) 65 dimethyl phosphorothioate (pirimiphos-methyl) 2-(1,2-dimethylpropylamino)-4-ethylamino-6-meth (E)-O-2-isopropoxycarbonyl-1-methylvinyl O-methyl ylthio-1,3,5-triazine (dimethametryn) ethylphosphoramidothioate (propetamphos) 2-ethyl-5-methyl-5-(2-methylbenzyloxy)-1,3-dioxane O,O,O',O'-tetraethyldithiopyrophosphate (sulfotep) 5,332,584 5 6 O,O,O'O'-tetramethyl O,O'-thiodi-p-phenylene diphos One can broaden the variety of crops on which cer phorothioate (temephos) tain pesticides, particularly herbicides, can be effec S-2-ethylthioethyl O,O-dimethyl phosphorodithioate tively used by including an antidote in the composition. (thiometon) The antidote helps to protect the crop from injury by O,O-diethyl O-1-phenyl-1,2,4-triazol-3-yl phosphoro the herbicide, without appreciable effect on the potency thioate (triazophos) of the herbicide against the undesired weed species. The O-ethyl O-2,4,5-trichlorophenyl ethylphosphonothioate antidote thus renders the herbicide more selective in its () action. Useful antidotes include acetamides such as (-)-3-allyl-2-methyl-4-oxocyclopent-2-enyl (h)-cis, N,N-diallyl-2,2-dichloroacetamide and N,N-diallyl-2- trans-chrysanthemate (allethrin) 10 chloroacetamide, oxazolidines such as 2,2,5-trimethyl (-)-3-allyl-2-methyl-4-oxocyclopent-2-enyl (+)-trans N-dichloroacetyl oxazolidine and 2,2-spirocyclohexyl chrysanthemate () N-dichloroacetyl oxazolidine, and 1,8-naphthalic anhy 3-phenoxybenzyl (-)-cis,trans-chrysanthemate (phe dride. For maximum effect, the antidote is present in the nothrin) composition in a non-phytotoxic, antidotally effective 2-(2-butoxyethoxy)ethyl thiocyanate 15 amount. By "nonphytotoxic' is meant an amount which isobornyl thiocyanoacetate (terpinyl thiocyanoacetate) causes at most minor injury to the crop. By “antidotally carbon disulfide effective' is meant an amount which substantially de 2-(4-tert-butylphenoxy)cyclohexyl prop-2-ynyl sulphite creases the extent of injury caused by the pesticide to (propargite) the crop. The preferred weight ratio of pesticide to 4,6-dinitro-6-octylphenyl crotonates (dinocap) 20 antidote is about 0.1:1 to about 30:1. The most preferred ethyl 4,4'-dichlorobenzilate (chlorobenzilate) range for this ratio is about 3:1 to about 20:1. The utility of many pesticides can also be broadened DEFOLIANTS by the inclusion of synergists in the pesticide composi S.S.S-tributyl phosphorotrithioate tion. Synergists are compounds which have little or no tributyl phosphorotrithioite (merphos) 25 pesticidal activity of their own, but when combined with a pesticide produce a combination with a potency FUNGICIDES significantly greater than the additive sum of the poten copper naphthenates cies of the compounds applied individually. Useful syn 5-ethoxy-3-trichloromethyl-1,2,4-thiadiazole ergists include 5-1-2-(2-ethoxyethoxy)ethoxy-ethoxy 30 1,3-benzodioxole (sesamex), 1,4-di-(1,3-benzodioxol-5- (etridiazole) yl)tetrahydrofuro 3,4-c) furan (sesamin), 1-methyl-2- O-ethyl S.S.-diphenyl phosphorodithioate (edifenphos) (3,4-methylenedioxyphenyl)ethyl octyl sulphoxide INSECT REPELLENTS (sulfoxide), and 5-2-(2-butoxyethoxy)ethoxymethyl-6- 6-butoxycarbonyl-2,3-dihydro-2,2-dimethylpyran-4-one propyl-1,3-benzodioxole (). When (butopyronoxyl) 35 included, synergists are present in effective amounts, N,N-diethyl-m-toluamide (deet) i.e., at any pesticide-to-synergist ratio at which a syner dibytyl phthalate gistic effect is observed. This ratio varies widely from dibutyl succinate one combination to the next. 1,5a,6,9,9a,9b-hexahydro-4a(4H)-dibenzofurancarbox 40 B. Prepolymer aldehyde dipropyl pyridine-2,5-dicarboxylate Prepolymers suitable to the present invention are Of the many different types of core liquids useful in partially etherified urea-formaldehyde prepolymers the present composition, pesticides are preferred, and with a high solubility in the the organic phase and a low certain classes of pesticides are particularly preferred. solubility in water. In its non-etherified form, the pre One such class is that of substituted thiocarbamates, 45 polymer contains a large number of methylol groups, particularly those of the formula -CH2OH, in its molecular structure. Etherification is the replacement of the hydroxyl hydrogens with alkyl O groups, and is achieved by condensation of the prepoly mer with an alcohol. When the alkyl groups comprise 50 four carbon atoms or more and they have replaced more than about 50% of the hydroxyl hydrogen atoms on the prepolymer molecule, the prepolymer becomes in which R is selected from the group consisting of soluble in the organic phase. Complete etherification is C1-C6 alkyl, C2-C6 alkenyl, and C7-C9 phenylalkyl, and to be avoided, however, since hydroxyl groups are is optionally substituted with up to three groups se 55 needed for the in situ self-condensation polymerization lected from halogen and nitro; and R2 and R3 are either which occurs in the wall-forming step. Therefore, the independently C1-C6 alkyl or Cs-C7 cycloalkyl, or con prepolymers useful in the present invention are those in jointly form C4-C7 alkylene. The terms “alkyl,” “alke which from about 50% to about 98% of the hydroxyl nyl,” and “alkylene' are intended to include both hydrogen atoms have been replaced by alkyl groups of straight-chain and branched-chain groups, and all car 4 to 10 carbon atoms each. In preferred practice, about bon atom ranges are intended to be inclusive of the 70% to about 90% of the groups have been etherified upper and lower limits stated. More preferred thiocar with a C4-C6 alcohol. Both straight-chain and bamates are those in which R1 is C2-C4 alkyl and R2 and branched-chain alcohols are useful in the present inven R3 either independently form C2-C4 alkyl or conjointly tion, and all carbon atom ranges quoted herein are to be form hexamethylene. The most preferred are those in 65 inclusive of their upper and lower limits. which R, R2, and R3 are all independently C2-C4 alkyl. Etherified urea-formaldehyde prepolymers are com Thiocarbamates are particularly useful as preemergence mercially available as solutions in alcohol or in a mix and postemergence herbicides. ture of alcohol and xylene. The alcohol used as the 5,332,584 7 8 solvent is normally identical to that used as the etherify ing agent. Those in most common use are n-butanol and C. Optional Additives iso-butanol. The degree of etherification (butylation) in Optional additives include solvents, polymerization these commercial products ranges between 70% and catalysts, and wall-modifying agents. 90%, and the solution contains from 50% to 85 by Solvents provide a means for controlling the wall weight of prepolymer. Minor amounts of free formalde forming reaction. As explained in Section E below, the reaction occurs when protons come in contact with the hyde are also frequently present. These solutions are urea-formaldehyde prepolymer. The organic phase typically sold as cross-linking agents for alkyd resins must be sufficiently hydrophilic to attract protons to the and used primarily for the formulation of coating and 10 interface from the bulk of the aqueous phase, yet suffi finishing products such as paints and lacquers. ciently hydrophobic to prevent large amounts of pro Urea-formaldehyde prepolymers which have not tons from crossing the interface and causing polymeri been etherified are also available commercially, either zation to occur throughout the bulk of the droplet. An in aqueous solutions or as water-dissolvable solids, for appropriately selected solvent added to the organic use as adhesives. These can be etherified by condensa 15 phase can correct the character of the organic phase to tion with the desired alcohol in a weakly acidic alcohol achieve these results. Clearly, the need for a solvent and solution. The water of condensation is distilled off as an the type of solvent needed-hydrophobic or hydro azeotrope with the alcohol until the desired degree of philic-depends on the nature of the liquid core mate condensation (etherification) has been reached. rial. Aliphatic and alicyclic solvents are examples of Urea-formaldehyde prepolymers themselves can be hydrophobic solvents, and alcohols and ketones are prepared by known techniques, notably the base-cat examples of hydrophilic solvents. The amount of sol alyzed reaction between urea and formaldehyde in vent can be varied as needed to achieve the desired water at a weight ratio of 0.6 to 1.3 parts formaldehyde results. to one part urea by weight (1.2:1 to 2.6:1 on a molar Catalysts capable of enhancing the wall-forming re basis), at a pH of 7.5 to 11.0 and a temperature of 50° C. 25 action can be placed in either the aqueous or organic to 90° C. Etherification is then accomplished as de phase. Catalyst are generally used when the core mate scribed in the preceding paragraph. rial is too hydrophobic, since they serve to attract pro tons toward the organic phase. Any water-soluble cata The degree of etherification can be monitored by the lyst which has a high affinity for the organic phase and quantity of water driven off during the distillation. Al is capable of carrying a proton can be used. Carboxylic though the degree of etherification can be varied over a and sulfonic acids are particularly useful. Examples wide range to accommodate the needs of the reaction include orthochlorobenzoic acid, 2-phenyl-2,2- system, the rate of polymerization in the subsequent dichloroacetic acid, benzoic acid, salicylic acid, p-tol wall-forming step decreases as the degree of etherifica uenesulfonic acid and dodecylbenzene sulfonic acid. tion increases. Too high a degree of etherification, 35 The same catalytic effect can be accomplished by dis therefore, tends to inhibit the progress of the wall for solving salts of these acids in the aqueous or organic mation. However, the water solubility of the prepoly phase and then acidifying the aqueous phase. The acid mer also decreases with increasing degree of etherifica form is produced by ion exchange. tion. Since low water solubility is a desirable feature of Wall-modifying agents serve to modify the character the prepolymer, it is best to avoid too low a degree of 40 of the wall by varying its permeability to the core mate etherification. Thus, the suitable and preferred ranges rial. Suitable wall-modifying agents contain a substan are those stated above. tial number of hydroxyl or mercapto groups capable of The organic solution comprising the core liquid and reacting with the methylol groups on the prepolymer. the etherified prepolymer is most conveniently formed The wall modifier can be used in the organic solution to when the latter is predissolved in a solvent, as it is when 45 add multiple linkages to the methylol groups to increase commercially sold for the coatings and finishings indus the degree of cross-linking, or to exhaust active sites on try. In the absence of such a solvent, there is a high the prepolymer to decrease the degree of cross-linking. degree of hydrogen bonding between the hydroxyl Thus, depending on the kind of modifier used and the groups, and the prepolymer is a waxy solid which is ratio of modifier to prepolymer, the permeability of the difficult to dissolve in the capsule core liquid. Polar 50 wall (and consequently the release rate of the core liq organic solvents are particularly useful for preventing uid) can be either increased or decreased. Castor oil is the hydrogen bonding and dissolving the prepolymer; one example of such an agent. The preferred cross-link examples include alcohols, ketones, esters, and aromat ing wall-modifying agent is pentaerythritol tetrakis ics. When etherifying agents of high chain length are (mercaptopropionate) sold under the tradename Mer used, aliphatics and other non-polar solvents can also be 55 captate Q-43 Ester, by Cincinnati Milacron Chemicals. used. The most useful solvents are the same alcohols Other poly-functional mercaptain esters of a similar used as the etherifying agents, the solution being taken nature can be used. directly from the reaction mixture of the etherification D. Emulsion Formation process. 60 Once the organic solution is formed, an emulsion is The concentration of the prepolymer in the organic formed by dispersing the organic solution in an aqueous phase is not critical to the practice of the invention, but solution comprising water and a surface-active agent. can vary over a wide range depending on the desired The relative quantities of organic and aqueous phases capsule wall strength and the desired quantity of core are not critical to the practice of the invention, and can liquid in the finished capsule. It will be most convenient, 65 vary over a wide range, limited mostly by convenience however, to use an organic phase with a prepolymer and ease of handling. In practical usage, the organic concentration of from about 1% to about 70% on a phase will comprise a maximum of about 55% by vol weight basis, preferably from about 5% to about 50%. ume of the total emulsion and will comprise discrete 5,332,584 10 droplets of organic solution dispersed in the aqueous agitation is generally sufficient to prevent droplet solution. growth throughout the balance of the process. The surface-active agent can be any of the wide vari ety of compounds known to be useful for lowering the E. Wall Formation surface tension of a fluid interface. Nonionic and ani 5 Once the dispersion and desired droplet size are at onic types are both useful. Examples of nonionic agents tained, the system is acidified to a pH of between about are long chain alkyl and mercaptan polyethoxy alco 0 and about 4.0, preferably between about 1.0 and about hols, alkylaryl polyethoxy alcohols, alkylaryl polyether 3.0. This causes the etherified urea-formaldehyde pre alcohols, alkyl polyether alcohols, polyoxyethylene polymer to polymerize by self-condensing in situ and sorbitan fatty acid esters, polyoxyethylene ethers, and 10 form a shell completely enclosing each droplet. Acidifi polyethylene glycol esters with fatty or rosin acids. cation can be accomplished by any suitable means, in Examples of anionic agents are the calcium, amine, cluding adding any acid which is water-soluble, includ alkanolamine, and alkali salts of alkyl and alkylaryl ing formic acid, citric acid, hydrochloric acid, sulfuric sulfonates; vegetable sulfonates; and ethoxylated and acid, phosphoric acid, and the like. Acidification can propoxylated mono- and diethers of phosphoric acid. 15 also be achieved by the use of acidic dispersants or Blends of surface-active agents are also useful. Pre surface-active agents, provided that such components ferred surface-active agents are polyethylene glycol are added to the system after the emulsion has been ethers of linear alcohols and alkali salts of alkyl and formed. alkylaryl sulfonates. As the polymer wall becomes more rigid, contact The quantity of surface-active agent is not critical to 20 between the active groups on the prepolymer becomes increasingly more difficult. Thus, the in situ self-con the invention, and can vary over a wide range. For densation polymerization reaction is self-terminating convenience, the agent generally comprises from about and is generally allowed to run to completion. The 0.1% to about 5.0% by weight of the aqueous phase. reaction can be arrested before completion, however, The agent can be added before or after the emulsion is 25 by raising the pH. In this manner, the wall tightness, formed. rigidity, and permeability can be controlled. This can In some systems, emulsion stability can be enhanced also be accomplished in most cases by a wall modifier as by adding a protective colloid to the aqueous phase. A described above. protective colloid stabilizes a dispersed system against The rate of the in situ self-condensation polymeriza aggregation, flocculation, and coalescence. Many mate 30 tion reaction increases with both acidity and tempera rials are known to function as protective colloids and ture depending upon the pH. The reaction can therefore are available commercially, including polyvinyl alco be conducted anywhere within the range of about 20 hols, alginates, alpha- and gamma-protein, casein, C. to about 100 C., preferably between about 40 C. methyl cellulose, carboxymethyl cellulose, gelatin, and about 70° C. The reaction will generally be com glues, natural gums, polyacids, and starch. The colloid 35 plete within a few hours, although with high acidity and can be added to the aqueous phase prior to the forma high temperature, the reaction can be completed within tion of the emulsion, or to the emulsion itself after it has minutes. been formed. Although the colloid is an optional addi The shell or wall content of the microcapsules com tive, its inclusion in the present system is preferred. prises from about 1 to about 25, preferably from about 5 Polyvinyl alcohol protective colloids are particularly to about 16, most preferably from about 5 to about 10, preferred. weight % of the microcapsule. Additional compounds which serve as protective Once the capsules are formed, they can be stored and colloids are the salts of lignin sulfonate, such as the used as an aqueous dispersion, or filtered and recovered sodium, potassium, magnesium, calcium or ammonium as dried capsules. In either form, the capsules are useful salts. Among commercial lignin sulfonates are Treax (E), 45 and effective in the slow release of the core liquid. Dis LTS, LTK and LTM, respectively, the potassium, mag persions are preferably stabilized by dispersants dis nesium and sodium salts of lignosulfonate (50% aqueous solved in the continuous phase. Since most dispersants solutions), Scott Paper Co., Forest Chemical Products; are more effective in neutral or basic solutions, it is Marasperse CR(R) and Marasperse CBOS-3 (R), sodium preferable to raise the pH of the dispersion once the lignosulfonate, American Can Co.; Polyfon O(E), Poly 50 wall has been formed. This is accomplished by any fon T (R), Reax 88B (R), Reax 85B (R), sodium salts of water-soluble base. Any conventional dispersant can be lignin sulfonate and Reax C-21 (E), calcium salt of lignin used. Typical dispersants include lignin sulfonates, pol sulfonate, Westvaco Polychemicals; Orzan S and Orzan ymeric alkylnaphthalene sulfonates, sodium naphtha A, the sodium and ammonium salts of lignosulfonate, lene sulfonate, polymethylene bis-naphthalene sulfo ITT Rayonier, Inc. 55 nate, and sodium N-methyl-N-(long chain acid) tau The actual quantity of colloid is not critical and any rates. amount which is effective in enhancing the stability of A unique feature of the process of the invention is the emulsion can be used. It is most convenient to use that the solid permeable polymer shells enclosing the between about 0.1% and about 5.0% colloid by weight organic phase droplets are formed by means of conden in terms of the aqueous phase. sation of the urea-formaldehyde prepolymer in the or The droplet size in the emulsion is not critical to the ganic phase adjacent to the interface formed between invention. For greatest utility of the final product, the the organic phase droplets and the aqueous phase solu droplet size will fall in the range of about 0.5 microns to tion. This is a consequence of the urea-formaldehyde about 4000 microns in diameter. The preferred range prepolymers being dissolved in the organic phase. for most pesticidal applications is from about 1 micron 65 The advantages of forming the polymer shells on the to about 100 microns in diameter. The emulsion is pre organic side of the interface are several. The first is that pared by the use of any conventional high shear stirring the process itself is more easily controlled than the prior device. Once the desired droplet size is attained, mild art processes, which involve wall-forming condensation 5,332,584 11 12 in the aqueous phase. When the condensation takes nane (a known insect maturation inhibitor-see U.S. place in the aqueous phase, the wall-forming polymer Pat. No. 4,002,769, issued Jan. 11, 1977, to Schwarz et can deposit upon the walls of the container in which the al.) and 48.0 g of Resimene (R)X-918. The latter is a 70% emulsion is present, on the agitator or any other struc n-butanol solution of a partially butylated ureaformal ture which may be present, in addition to depositing on dehyde prepolymer with a degree of butylation of ap the droplets. In contrast, the wall-forming polymer that proximately 80-90%, a product of Monsanto Plastics condenses on the organic side of the interface does not and Resins Company, Newport Beach, Calif. deposit on any of the container walls or other struc This solution was added to an aqueous solution com tures. prising 168.1 g of water and 1.87 g of Gelvatol 40-20 Additionally, when the condensation takes place in 10 and an emulsion was formed as in Example 1, with the aqueous phase, as in the prior art, a reduced amount droplets ranging in diameter from 1 to 40 microns. To of dispersed organic phase must be used inasmuch as if this emulsion was added 20 g of water containing 1.87 g a higher dispersed organic phase content is utilized, the each of the dispersants Lomar NCO (R) and Darvan (R) dispersion gets too thick and gels, thus effectively pre #2. The former is a product of Diamond Shamrock venting formation of the microcapsules. Condensation 15 Chemical Company, Nopco Division, Morristown, on the organic side of the interface thus allows higher N.J., and is a sodium salt of a condensed mononaphtha dispersed organic phase loading to be obtained because lene sulfonic acid. The latter is a product of R. T. Van a gel is not formed in the aqueous phase. derbilt Company, Inc., Norwalk, Conn., and is com In the examples set forth herein, in which the organic prised of sodium salts of polymerized substituted ben phase contains a pesticide, a higher loading of organic zoic alkyl sufonic acids. A 5% hydrochloric acid solu phase results in a more concentrated pesticide formula tion was added to lower the pH of the emulsion to 2.0 tion. This enables substantial cost savings to be achieved and the temperature was raised to 50° C. with continued in manufacturing, packaging and transportation. stirring for three hours. The resulting dispersion was The following examples are offered as illustrative of then cooled to room temperature and concentrated both the process and product of the present invention, 25 caustic solution was added to raise the pH to 9.0. and are intended neither to define nor limit the inven Microscopic observation of the dispersion revealed tion in any manner. fully formed, discrete capsules as in Example 1. EXAMPLE 1. EXAMPLE 3 An aqueous solution was prepared, comprising 2.0% 30 The organic solution for this example consisted of (weight) Gelvatol (R)40-20 and 0.3% Tergitol(R) 15-S-7, 139.9 g of O-ethyl S-phenyl ethylphosphonodithioate (a with a total solution weight of 300 g. Gelvatol 40-20 is commercial also known by the common a polyvinyl alcohol protective colloid (degree of hydro name “') and 39.9 g of Resimene X-918. This lysis 73-77%), with an average molecular weight of solution was emulsified in an aqueous solution consist about 3000, obtained from Monsanto Company, Indian 35 ing of 200g of water and 2.35 g of Gelvatol 40-20 to a Orchard, Mass. Tergitol 15-S-7 is a nonionic surfactant droplet size of 1 to 40 microns, and 35 g of water con consisting of a polyethylene glycol ether of a linear taining 2.35 g each of the dispersants Lomar NCO and alcohol, obtained from Union Carbide Chemicals and Darvan #2, as well as 2.4 g of p-toluene sulfonic acid, Plastics Company, New York, N.Y. was added. The temperature was raised to 60° C. and In a separate vessel, 100 g of S-ethyl diisobutylthi stirring was continued for three hours. The dispersion ocarbamate (a herbicide known by the common name was then allowed to cool to room temperature and the “butylate”) and 50 g of Beckamine (R) 21-625 were pH was raised to 9.0 with caustic solution. blended into a homogeneous solution. Beckamine Microscopic observation of the dispersion revealed 21-625 is a 70-75% n-butanol solution of a partially fully formed, discrete capsules as in Example 1. butylated ureaformaldehyde prepolymer in which the 45 degree of butylation is approximately 80-90%, obtained EXAMPLE 4 from Reichhold Chemicals, Inc., White Plains, N.Y. The organic solution for this example consisted of 156 The thiocarbamate/prepolymer (organic) solution g of HI-SOL (R) 4-3 and 43.5g of Beckamine 21-625. was added to the aqueous solution and an emulsion was The former is a heavy aromatic naphtha, with boiling formed by means of a high shear stirrer, the organic 50 temperature ranging from 238 C. to 286 C., a product solution forming the dispersed phase with droplets of Ashland Chemical Company, Industrial Chemicals ranging in size from 5 to 40 microns in diameter. While and Solvents Division, Columbus, Ohio. This solution mild agitation was maintained, the pH of the emulsion was emulsified in an aqueous solution consisting of was adjusted to 2.0 with concentrated hydrochloric 194.6 g of water, 3.9 g of Gelvatol 40-20, and 7.8g of acid and the temperature was raised to 50° C. for three 55 Darvan #2, to a droplet size of 1 to 40 microns. The pH hours. The resulting suspension was then allowed to was adjusted to 2.0 with a 5% solution of hydrochloric cool to room temperature and concentrated aqueous acid and the temperature was raised to 50° C. with sodium hydroxide was added to raise the pH to 7.0. continued stirring for three hours. The dispersion was Observation of the suspension under both a labora then allowed to cool to room temperature and the pH tory microscope and an electron microscope revealed 60 was raised to 9.0 with caustic solution. discrete, roughly spherical, fully enclosed capsules with Microscopic observation revealed fully formed, dis smooth-surfaced outer walls. The capsules were about 5 crete capsules as in Example 1. to 40 microns in diameter and although some were touching each other, none were fused together. EXAMPLE 5 65 An aqueous solution consisting of 251.6 g of water, 5 EXAMPLE 2 g of Gelvatol 40-20, and 2.5 g of Tamol(R) SN was An organic solution was prepared, comprising 162.2 heated to 50° C. Tanol SN is a dispersant identified as g of 2-methoxy-9-(p-isopropylphenyl)-2,6-dimethylno a sodium salt of a condensed naphthalene sulfonic acid, 5,332,584 13 14 obtained from Rohm and Haas Company, Philadelphia, persion was then cooled to room temperature and the Pa. To this heated aqueous solution was added an or pH was raised to 7.5 with caustic solution. ganic solution consisting of 173.4 g of S-ethyl diisobu Microscopic observation revealed fully formed, dis tylthiocarbamate (butylate), 7.5 g of N,N-diallyl di crete capsules as in Example 1. chloroacetamide, and 22.5g of Resimene X-918. The EXAMPLE 8 thiocarbamate/acetamide combination is a known her bicide/antidote combination-see U.S. Pat. No. This example demonstrates microcapsule preparation 4,021,224, issued May 3, 1977, to Pallos et al. An emul according to the present invention without the use of a sion was formed by means of a high-speed stirrer as in protective colloid. 10 The organic solution consisted of 154 g of butylate, the above examples, to a droplet size of 1 to 40 microns. 6.7 g of N,N-diallyl dichloroacetamide, and 47.6 g of The high temperature was maintained and the pH was Resimene X-918 (same ingredients as Example 5). This lowered to 2.0 with 5% hydrochoric acid. After three solution was emulsified in 197.8g of a 4.0% (by weight) hours of additional stirring, the dispersion was cooled to aqueous solution of Darvan #2 to a droplet size of 1 to room temperature and the pH was raised to 9.0 with 15 40 microns. The pH of the dispersion was then adjusted caustic solution. to 2.0 with a 5% solution of hydrochloric acid and the Microscopic observation revealed fully formed, dis temperature was raised to 50 C. with continuous stir crete capsules as in Example 1. ring for three hours. The dispersion was then allowed to EXAMPLE 6 cool to room temperature and the pH was raised to 9.0 with caustic solution. In this example, an additional feature is demon Microscopic observation of the dispersion revealed strated-the inclusion of an organic solvent (kerosene) fully formed, discrete capsules as in Example 1. in the organic phase, the solvent thus becoming part of What is claimed is: the encapsulated liquid. 1. A microcapsule comprising a liquid core material The aqueous solution was prepared with 177.12 g of 25 which is substantially insoluble in water, enclosed water, 2 g of Gelvatol 40-20, and 2 g of Darvan #2. The within a solid permeable shell of self-condensed etheri organic solution was prepared with 132.74 g of S-ethyl fied urea-formaldehyde polymer, said shell comprising hexahydro-1H-azepine-1-carbothioate (a commercial from about 1 to about 25 weight percent of the micro herbicide known by the common name "molinate'), capsule. 2. A microcapsule according to claim 1 wherein the 44.25 g of kerosene, and 35.48 g of Beetle (R) 1050-10. ' liquid core material is a pesticide. The latter is a 60% n-butanol solution of a partially 3. A microcapsule according to claim 2 wherein the butylated urea-formaldehyde prepolymer in which the liquid core material is a herbicide. degree of butylation is approximately 70-90%, obtained 4. A microcapsule according to claim 3 wherein the from American Cyanamide Company, Resins Depart- 35 herbicide is a thiocarbamate herbicide. ment, Wayne, N.J. 5. A microcapsule according to claim 4 wherein the The organic solution was emulsified in the aqueous herbicide is EPTC. solution by means of a high shear stirrer to an average 6. A microcapsule according to claim 4 wherein the droplet diameter of 18 microns, and 19.68 g of water herbicide is butylate. containing 2 g of DAXAD (R) LAA was slowly added, 40 7. A microcapsule according to claim 4 wherein the lowering the pH of the emulsion to 1.7. DAXAD LAA herbicide is molinate. is a dispersant in acidic form, identified as a polymerized 8. A microcapsule according to claim 3 wherein the alkyl naphthalene sulfonic acid, a product of W. R. herbicide is an acetamide herbicide. Grace and Company, Organic Chemicals Division, 9. A microcapsule according to claim 8 wherein the Lexington, Mass. 45 herbicide is metolachlor. The emulsion temperature was then raised to 50 C. 10. A microcapsule according to claim 3 further con for three hours with continued stirring. The dispersion taining an antidote for said herbicide. thus formed was cooled to room temperature and the 11. A microcapsule according to claim 10 wherein pH was raised to 7.5 with caustic solution. the antidote is selected from the group consisting of 50 N,N-diallyl-2,2-dichloroacetamide, N,N-diallyl-2- Microscopic observation revealed fully formed, dis chloroacetamide, 2,2,5-trimethyl-N-dichloroacetylox crete capsules as in Example 1. azolidine, 2,2-spirocyclohexyl-N-dichloroacetylox EXAMPLE 7 azolidine, and 1,8-naphthalic anhydride. In this example, two additional features are demon 12. A microcapsule according to claim 10 wherein 55 the weight ratio of herbicide to antidote is from about strated-the inclusion of kerosene as in Example 6 and 0.1:1 to about 30:1. the addition of a wall-modifying component (castor oil) 13. A microcapsule according to claim 1 wherein the to the prepolymer. shell comprises from about 5 to about 16 weight percent The aqueous solution was prepared with 181.6 g of of the microcapsule. water, 2 g of Gelvatol 40-20, and 2 g of Darvan #2. The 60 14. A microcapsule according to claim 1 wherein the organic solution was prepared with 32.7 g of S-ethyl shell comprises from about 5 to about 10 weight percent hexahydro-1H-azepine-1-carbothioate, 44.25 g of kero of the microcapsule. sene, 22.97g of Beetle 1050-10, and 6.9 g of castor oil. 15. A microcapsule according to claim 1 wherein the An emulsion with an average droplet diameter of 18 urea-formaldehyde polymeric shell or wall of said mi microns was formed, and 20.2 g of water containing 2 g 65 crocapsule is formed from the self-condensation of eth of DAXAD LAA was added, lowering the pH to 1.7. erified urea-formaldehyde prepolymer containing from The emulsion temperature was then raised to 50° C. for about 50% to about 98% etherified methylol groups. three hours with continued stirring. The resulting dis