CA1108944A - Capsule manufacture - Google Patents

Abstract

CAPSULE MANUFACTURE

Abstract of the Disclosure A process is disclosed for performing encapsulation, en masse, by an in situ polymerization reaction to yield capsule wall material. The polymerization includes a reaction between urea and formaldehyde or polycondensation of monomeric or low molecular weight polymers of dimethylol urea or methylated dimethylol urea in an aqueous vehicle and the reaction is conducted in the presence of negatively-charged, carboxyl-substituted, linear aliphatic hydro-carbon polyelectrolyte material dissolved in the vehicle. Liquid-liquid phase separation is accomplished and maintained by increase in the molecular weight of the resulting condensation polymer with-out further dilution of the manufacturing vehicle. The negatively-charged polyelectrolyte material is required and has an apparent effect of controlling or modifying the polymerization reaction.
The disclosed encapsulation process permits manufacture of micro-capsules in concentrations of capsule to capsule manufacturing vehicle higher than previously possible.

Description

ACKG~UND OF THE I~ JTION
Field of the Ir~ention - This ir~ention pertains to a process for ~anufacturing minute capsules, en masse, in a liquid manufacturing vehicle The process involves liquid-liquid phase separation of a relatively concen-trated solution of polymeric material to be used in the formation of walls ~or the minute capsules En masse processes for the manufacture of microcapsules have general-ly required large amounts of liquid rnanufacturing vehicle and have generally resulted in lc~-yields of capsules. An encapsulating systern and process ~hich utilizes relatively small amounts of Iranufacturing vehicle to genexate relatively large amounts of Tnicrocapsules w~uld be valuable from several viewpoints. For e~ample, costs of transporting the capsule product, as manufactured, woul~ be reduced because the product contains less vehicle. As another exa~ple, in the case where the capsule product is to be coated to a dried film on a sheet substrate coating costs are reduced because there is less liquid vehicle to be rern~ved from the substrate.
Many cc~b~inations of ~aterials have keen used in the past in search of compositions which yiela certain physical characteristîcs in capsule walls or ~hich permit performing the éncapsulating process under certain desired or xequired conditions. As examples of desirable capsule character-lstics, sm~ll size, ~,permeability of capsule walls or aiffusion and strength of capsule walls to withstand norrnal handling forces can be mentioned. As exa~ples of desira~le process cond;tions, relatively high pH, relatively short tLmes, and relatively hîgh yield and concentration are ~mportant.
It is, therefore, an object of the present invention to provide a capsule manufacturing prw ess wherein cap~ules are procluced in high yield and in increased concentration. It is, additionally~ an ob]ect of the invention to provide a process whîch requires a relatively short time for co~pletion and whîch utilizes process conditions of increased convenience.

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i It is, further, an object of the present invention to provide a process for manufacturing microcapsules, which microcapsules have capsule walls of increased impermeability. Additionally, it is an object of this invention to provide a process for manufac turing very small capsules having predominantly single-particle capsule core entities.
Specifically, it is an object of this invention to provide an encapsulating process wherein the capsule wall materia1 com-prises a polymer formed from a urea-formaldehyde, dimethylol urea or methylated dimethylol urea starting material wherein said wall material is generated by an in situ condensation reaction. It is, further, an object of this invention to provide such capsule wall material by an improved condensation reaction conducted in the presence of a negatively-charged, carboxyl-substituted, linear aliphatic hydrocarbon polyelectrolyte material dissolved in the capsule manufacturing vehicle.
Description of the Prior Art - South African Patent No 62/939 .
issued March 6, 1972 and corresponding in most respects to United States Patent No. 3,516,941, discloses a preparation of microcap-sules by in situ polymerization of amides or amines and aldehydes.
There is no disclosure of the use of a negatively-charged poly-electrolyte material to modify or otherwise affect the polymeriza-tion reaction or product. U.S. 3,516,941 contains disclosure of detrimental effects found in such encapsulating processes when certain wetting agents are used.
United States Patent No. 3,755,190 issued August 28, 1973 dissloses a microencapsulating process wherein the capsule wall material is polyhydroxy phenolic/aldehyde polymeric material gene-rated in the presence of poly(vinyl alcohol).
United States Patent No. 3,726,803 issued April lO, 1973 discloses microcapsules having a composite capsule wall structure of hydrophilic palymeric material interspersed by a hydrophobic polymeric material. The hydrophobic polymeric mater;al is dis-closed to be an in situ-generated condensate of a polyhydro~y phenolic material and an aldehyde.
United States Patent No. 3,016,308 issued January 9, 1962 disclosés encapsulation by continued polymerization of urea/formal-dehyde resin dissolved in an aqueous manufacturing vehicle with a polymeric wetting agent. The process utilizes urea/formaldehyde resin as starting material and a slight amount of wettlng a~ent to maintain an emulsion during the continued polymerization.

SUMMARY OF THE INVE~ITIO~I

The condensation polymer generated in an aqueous capsule manu-facturing vehicle utilizing urea and formaldehyde, dimethylol urea (DMU) or menthylated dimethylol urea (MDMU) as the starting material, results, without more, in brittle films of capsu1e wall material. The polymeric material generated from an aqueous solu-tion of said starting materials to give a molecular weight adequate for phase separation has a tendency to separate from solution as a crystalline, nugget-like, solid. Such a precipitous phase separa-tion can be controlled to yield a liquid separated phase relatively concentrated in the polymeric material, but the control involves frequent and critical dilutions to maintain proper polymer concen-trations. An encapsulating process utilizing the generation of, for example, urea/formaldehyde and step-wise and continual dilution of the manufacturing vehicle does yield capsules of quality adequate for many intended uses despite the frangible and fragile nature of the capsule wall material.
While dilution of the manufacturing vehicle in previously~
developed encapsulating processes which utilize urea/formaldehyde polymer generation is required to alleviate the formation of solid nuggets of polymeric material, dilution is also required to main-tain the encapsulating system at a workable viscosity. Urea/formal-dehyde polymeric material possesses some desirable qualities for use in microcapsule wall material; but previously-disclosed pro-cesses have required substantial improvement for generating the polymeric material in commercially-acceptable quantity and quality in the context of microcapsule manufacture.
The process of the present invention provides for the manufac-ture of capsule walls from the polymerization of urea and formal-dehyde, dimethylol urea or methylated dimethylol urea with the benefits of a well-formed condensation polymer but without the disadvantages of required dilution and nugget formation, which has plagued prior processes. In regard to these matters of dilu-tion and nugget formation, it is important to note that the encap-sulating process of the present invention is conducted effectively and preferably at capsule concentrations higher than previously believed possible. Moreover, at those higher capsule concentra-tions, in the present process, the system viscosity remains within effective and operable liquid limits.

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, Additionally, the process of the presenk invention results in the manufacture of capsule walls which are relatively imperme-able and strong, particularly as compared to the capsule walls of urea/formaldehyde polymer made in accordance with previous-known processes.
A system component material specially utilized in -the present process, which material is believed to be required -for realizing any and all of the benefits described herein, is a negatively-charged polymeric polyelectrolyte material having a linear ali-phatic hydrocarbon backbone with an average of about two carboxyl (or anhydride) groups for every four to six backbone carbon atoms.
Use of the proper kind and amount of this system modifier is necessary to permit the manufacture of microcapsules having urea/
formaldehyde, DMU or MDMU wall material in a high capsule concentra-tion, a low vehicle viscosity, and at a benefically high pH
condition.
Poly(vinyl alcohol) has been used, previously, as a supporting polymer in generation of certain, specific, condensation polymers in processes of microencapsulation. The condensation polymer in those processes is a product of an aldehyde and polyhydroxy phenolic materials having at least two phenolic hydroxy groups.
However, poly(vinyl alcohol) is disclosed as the only eligible supporting polymer and only phenolic materials having at least two phenolic hydroxy groups are disclosed to be used as coreactants for the aldehyde.
The present invention provides means to use urea/formaldehyde, dimethylol urea or methylated dimethylol urea as starting materials to form condensation polymers as capsule walls and to obtain the benefits therefrom without the previously-disclosed disadvantages.
The dimethylol urea or methylated dimethylol urea starting materials can be used in the monomeric form or as a low molecular weight polymer thereof, and reference thereto in the present appli-cation includes all of these forms. The system modifier of this invention, in some respects, shares similarities with the poly (vinyl alcohol) supporting polymer discussed above. The system modifier of this invention is, however, required to hàve a carboxyl negative charge in aqueous solution; and even more specifically, only certain carboxyl-substituted materials have been found eligi-ble. While the inventors do not believe that the system modifier forms any strong complex or substantial combination with the start-ing materials prior to polymerization, it is believed that the ~' modifier interferes, in sorne manner, with the po'lymerization reac-tion. The mechanism of the interference is not understood, but the effect of the interference is to permit manufacture of micro-capsules, en masse by in situ polymerization at a surprisingly high concentration with surprisingly low viscosity 1n the manufac-turing vehicle.
The system modifier is not included in the Finished capsu1e walls in appreciable amounts. The system modifier takes some active part in the resulting polymerization reaction as is evidenc~
ed by reduced viscosity of the system at increased polymer concen-tration and increased efficiency of the polymerizing component materials with increased optimum pH of polymerization. Neverthe-less the finished capsule walls retain only a minor residua1 amount of the system modifier. To be effective, the system modifer must be included in the encapsulating system before the commencement of the polycondensation reaction. The characteristic brittleness of the resulting polymeric capsule wall material is alleviated somewhat by that residue of modifier; and the effect, in most cases, is a fortuitous benefit.
Examples of eligible carboxyl group system modifiers include hydrolyzed maleic anhydride copolymers~ which are preferred, such as poly(ethylene-co-maleic anhydride) (EMA), poly(methyl vinyl ether-co-maleic anhydride) (P\JMMA), poly(propylene-co-maleic-anhydride) (PMA), poly(isobutylene-co-maleic anhydride) (iBMA), poly(butadiene-co-maleic anhydride) (BMA), poly(vinyl acetate-co-maleic anhydride) (PV~MA), and the like; and polyacrylates, such as poly(acrylic acid), and the like.
In further regard to the preferred system modifiers, there appears to be a molecular weight range within which the best results are obtained. Eligible system modifiers permit and main-tain the encapsulating system of polymerizing urea and formaldehyde DMU or MDMU at reasonably low and workable viscosities. Negatively charged materials which would otherwise be eligible as system modi-fiers, are ineligible at molecular weights which are too low.
Inexplicably, system modifier materials below a certain molecular weight cause the system to thicken and gel, while materia'ls of an adequately high molecular weight maintain the system viscosity at an acceptable low 'level. The viscosity effect is not under-stood, and no explanation is offered, for the low viscosity using high molecular weight system modi~'iers and the high viscosity using low melecular weight system modifier materials. The critical mole-cular weight is not represented by a sharp change from eligibil-ity to ineligibility but by a transition From preferred to viscous to gelled as the molecular weiyht is decreased. The critical low molecular weight appears, also, to vary somewhat with different kinds of the elgible system modifier materials. For example, pre-ferred poly(ethylene-co-maleic anhydride) should have a mo'lecular weight above about 1000; poly(methylvinylether-co-maleic anhydride) above about 250,000; poly(acrylic acid) about about 20,000.
Material contained within the capsule walls formed in accor-dance with this invention, i.e., the capsular internal phase or capsule core material, is relatively unimportant to the practice of the invention and can be any material which is substantially water-insoluble and which does not interact with the intended cap-sule wall material, or with other encapsulating-system components, to the detriment of the process. A few of the materials which can be utilized as capsule internal phases include, among a multi-tude of others: water-insoluble or substantially water-insoluble liquid such as olive oil, fish oils, vegetable oils, sperm oil, mineral oil, xylene, toluene, kerosene, chlorinated biphenyl, and methyl salicylate; similar substantially water-insoluble materials of a solid but meltable nature such as naphthalene and cocoa butter; water-insoluble metallic oxides and salts; fibrous materials, such as cellulose or asbestos; water-insoluble synthetic polymeric materials; minerals; pigments; glasses; elemental materials including solids, liquids and gases; flavors, fragrances;
reactants; biocidal compositions; physiological compositions; ferti-lizer compositions; and the like.
The process of this invention specifically and preferably includes as one embodiment the steps of establishing an aqueous, single-phase, solution of the system modi-Fier and urea into which is dispersed the intended capsule core material (substantially insoluble in the solution and substantially chemically unreactive with any of the solutes). The dispersing forces are maintained, formaldehyde is added to the system and, on reaction between the urea and the formaldehyde, a urea/formaldehyde polymeric material separates from the solution as a liquid so'lution phase, in its own right, relatively high concentrated in urea/formaldehyde. The separated liquid phase containing urea/formaldehyde wets and en wraps particles of the dispersed capsule core material to yie'ld liquid walled embryonic capsules. Continued reaction oF the urea/
formaldehyde material, preferably with agitation such as s-tirring, yields solid and substantilly water-insoluble capsule walls. Agi-tation is not required for the condensation reaction to proceed.

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It is important to note that: (a) after makeup of the system and commencement of the capsule-wall-forming condensation reaction, there is no dilution step in the process; (b) the presence of the system modifier permits generation o~ a high concentration of urea/
formaldehyde polymer at a relatively low viscosity; (c) the result-ing high concentration-low viscosity system permits liquid phase separation and subsequent polymerization to a solid tu produce capsules, en masse, in a, by volume~ concentration in the manu-facturing vehicle not before possible.
More specifically the present invention involves a process for manufacturing minute capsules, en masse, in an aqueous manufactur-ing vehicle, comprising the steps of establishing an agitating aqueous system including urea, formaldehyde, a system modifier material in an amount sufficient to modify -the polymerization of the urea with formaldehyde so as to permit formation of urea-formaldehyde polymeric capsular walls, said system modifier material being selected from the group consisting of poly(ethylene-co-maleic anhydride), poly(methyl vinyl ether-co-maleic anhydride), poly(acrylic acid), poly(propylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(butadiene-co-maleic anhydride) and poly(vinyl acetate-co-maleic anhydride), and particles of an intended capsule core material substantially insoluble in the system, in which agitating system the modifier material is present prior to the addition of said particles, and polycondensing the urea and formaldehyde to form a condensation polymer resulting in liquid-liquid phase separation of the urea/formaldehyde polymerization product above a molecular weight to be soluble in the system and continued reaction of the separated liquid urea/formaldehyde polymerization product to give solid capsule wall material individually surrounding particles of the dispersed intended capsule core.
Alternatively, the various system components can be combined in any desired order with only the limitation that the system modi-fier must be present in the system at the time that the polymeriza-tion reaction begins. The capsule core material can be dispersed in the system at any time before the separated liquid phase of polymeric material becomes solid or is so polymerized that dis-persed capsule core particles are not enwrapped by the resulting polymer.

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The polymerization reaction, even as altered by the system modifier, is a condensation conducted in an acid med-ium The con-densation can be accomplished in an aqueous system haviny a pH
of about O to 7, the time and temperature requirements being vari-able to optimize the reaction. As an effect of the system modifier and its relation to the condensation, the preferred pH of operation of this invention is from 2.5 to 5.0 and the most preferred pH
is 3.5.
As to the relative amounts of urea and formaldehyde which should be used, it has been found that the molar ratio of formalde-hyde to urea must be at least 1.6, and is preferably from 1.6 to about 3.
After the reaction has progressed to the point where the capsule walls have been solidified and, in that respect, the capsule manufacture is completed, the capsules can be separated from the manufacturing vehic'le by filtering and washed with water.
The capsule walls can then be dried by placing the capsules in a forced air dryer. It should be understood, however, that the capsules need not have dried wa'lls or even be separated from the liquid vehicle prior to their use. It is desired or required for some intended purpose, the capsule product of this invention can be supplied as a slurry of capsules in a liquid carrier, either the manufacturing vehicle or not, such as for use in a paper-coating composition, a paint, an insecticide composition, or the like, ~' such uses being previously taught in the prior art.
Individual capsules prepared by the present invention are substantially spherical and can be manufactured having diameters of less than l micron to about lOO microns, the preferred size range being from about l to about 50 microns, in diameter. The capsule product of this invention can be made to take the form either of individual capsules with each entity having, as an in-ternal phase, one particle of capsule core material or of aggre-gates of individual capsu'le with each aggregate entity having several particles of capsule core material. Capsule aggregates can be made in sizes from a few m1crons in diameter to several hundred microns in diameter depending upon the size and state of the included core material.

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DESCRIPTION OF THE PREFERRED EMeODIMENTS
-Unless otherwise specified, all percentage and part designa-tions indicate percent and parts, by weight; and all temperature designations indicate degrees Centigrade. All solutions, unless otherwise designated, are aqueous solutions.

Example 1 In this preferred example, negatively-charged poly(ethylene-co-maleic anhydride) is used to modify a urea/formaldehyde encapsulat-ing system to yield capsules in the size range of 1 to 15 microns.
The capsule contents comprise an oily solution of colorable dye materials for use in carbonless copying paper, as will be described below in relation to testing the capsule product of this example.
The capsule contents is termed the "internal phase" herein; A
suitable poly(ethylene-co-maleic anhydride) includes approximately equimolar ethylene and maleic anhydride and has a molecular weight of about 75,000 to 90,000 such as, for example, the product sold by Monsanto Chemical Company, St. Louis, Missouri, under the trade-mark "EMA-31".
Into a blending vessel having about a one liter capacity and equipped for agitation and heating are placed: 100 grams of a 10 percent aqueous solution of hydrolyzed poly(ethylene-co-maleic anhydride) as the system modifier; 10 grams of urea; 1 gram of resorcinol; and 200 grams of water, as the manufacturing vehicle.
The pH is adjusted to 3.5 using 20 percent aqueous sodium hydr-oxide; and 200 milliliters of internal phase is emulsified into the manufacturing vehicle to yield mobile internal phase droplets of an average size of less than about 10 microns in a single-phase solution of the manufacturing vehicle. Twenty-five grams of form-alin (37 percent aqueous formaldehyde solution) is added to the system. The agitation is maintained, the system is heated to about 55 degrees, and under continued agitation, the temperature is main-tained for about two hours and then permitted to decrease to ambient (about 25 degrees).

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This example utilizes a molar ratio o-f formaldehyde/urea of about 1.9 and contains about 6 percent of urea and forma'ldehyde and 3 percent of system modifier in the manufacturing vehicle (excluding consideration of the internal phase). The capsules of oily dye solution are uniformly in a sizè range of abouk 1 to 15 microns and represent more than 40 percent, by volume, of the encapsulating system. The oily dye solution comprises 3,3-bis-(4-dimethylaminophenyl)-6-dimethylaminophthalide (commonly known as Crystal Violet Lactone) and 3,3-bis-(1-ethyl-2-methyl-indol-3-y'l)-phthalide (sometimes known as Indolyl Red) in a mixture of solvents including a benzylated ethyl benzene and a relative'ly high-boiling hydrocarbon oil, such as one having a distillation range of 400-500 degrees Fahrenheit.
The capsule product from this example will be compared, below, with capsule products from the next two examples.

Example 2 This example is identical with Example 1 w-ith the exception that the system modifier is omitted from the manufacturing vehicle.
The initial manufacturing vehicle composition is 10 grams of urea, 1 gram of resorcinol, and 300 grams of water and the materials and the procedure are otherwise unchanged. It should be noted that the colorable dye material encapsu'lated in this series of examples reacts to yield a colored reaction product and thereby becomes iricreasingly so'luble in the manufacturing vehicle below a pH of about 2.7. To prevent such coloration of the dye, the system pH is kept above pH 2.7 and is preferably maintained at about 3.5.
This example also utilizes a molar ratio of formaldehyde/urea of about 1.9 and contains about 6 percent of urea and formaldehyde in the manufacturing vehicle. The capsule materials in this ex-ample represent more than 40 percent, by volume, of encapsula-ting system although the internal phase droplet size varies considerably (from about 5 up to as much as 300 microns) due to a lack of sta-bility in the emulsification. It is noted that most of the capsule materials are not utilized;--the internal phase being unaccep-tably encapsulated and nuggets and so'lid partic'les of urea/formaldehyde polymer existing free in the system.

Cl Example 3 This example is identical with Example l with the exception that poly(vinyl alcohol) is substituted for the negatively-charged, poly(ethylene-co-maleic anhydride). While the poly(vinyl alcohol) does appear to serve as an effective emulsifier or protective colloid to permit control of dispersed droplet size, it has no effect or perhaps even an adverse effect on the condensation re-action. Capsules are not formed in this example although the system evidences a large amount of undeposited solid material which result from the urea/formaldehyde reaction and is unuseable as capsule wall material.

Example ~

This example is identical with Example l with the exception that poly(acrylic acid) is substituted for the poly(ethy1ene-co-maleic anhydride). Poly(acrylic acid) is among the eligible system modifiers in providing the beneficial effect on the urea/formalde-hyde condensation. Control of the capsule size range has been found to be more difficult using poly(acrylic acid), but the capsule quality is comparable with that of Example l. The capsules range in size from about l to lOO microns. A suitable poly(acrylic acid) may have an average molecular weight of more than about 150,000 and less than about 300,000 such as, for example, the pro-duct sold by Rohm and Haas Company, Philadelphia, Pennsylvania, under the trademark "Acrysol A-3".
Because the size of capsules made in the above examples is so small and because the intended capsule use is in carbonless copying papers, the capsules of the above examples are tested by methods which relate to effectiveness in a copying paper use.
As a general description, the capsules are coated onto a sheet termed a "CB Sheet" (sheet with Coated Back) and are tested in conjunction with a standardized sheet termed a "CF Sheet" (sheet with Coated Front). The coating of the CB Sheet includes about 75 percent capsules, 18 percent wheat starch, and 7 percent of gum binder such as, for example, the hydroxyethylether of corn starch or other water-soluble starch derivatives; and is made up by combining lOO parts of aqueous capsule slurry having 40 percent capsules, 125 parts of water, lO parts of wheat starch and ~0 parts of a lO percent aqueous solution of the gum binder--all adjusted .

to about pH 9. The coating is cask usiny a wire-wound rod designed to lay a 20 pounds per ream (3300 square feet) wet film coating.
The coating of an exemplary CF Sheet includes a metal-modified phenolic resin reactive with the dyes, kaolin clay and other addi-tives and a binder material. A CF Sheet is described in U.S.
Patent 3,732,120.
When a CB sheet and a CF Sheet are placed in coated face-to-coated face relation and pressure is applied, capsules of the CB
Sheet rupture and capsule-contained material is transferred to and reacted with the acid component of the CF Sheet to yield a color. A test associated with such capsule rupture and color forma-tion it Typewriter Intensity (TI) and TI values indicate ratios of reflectances--the reflectances of marks produced on the CF Sheet by a typewriter striking two sheets together versus the paper's background reflectance. A high value indicates little color development and a low value indicates good color development.

Printed Character Reflectance TI Background Reflectance X 100 Reflectances of a more-or-less solid block of print made with an upper-case "X" character and of the background paper are measured on an opacimeter within twenty minutes after the print is made, first, using freshly prepared CB Sheet and, then, using CB Sheets aged in an oven at 100 degrees. A small difference be-tween the TI values indicates good capsule quality. After the oven aging, a TI value of 100 indicates complete loss of solvent from the capsules and a TI value less than 70 evidences acceptable capsules for these tests. When an initial TI value is less than 70, a TI value difference between initial and aged samples of less than about 5 is acceptable for these tests; but, of course, a difference of less than 3 is much preferred.

TI

I _ ial Aged (time) ; Example 1 'i8 60 (one day) Example 2 96 100 (one hour) Example 3 81 100 (~ne hour) Example 4 ~7 ~7 (one day) ~'3~

Of course, any convenient and reliab'le method for exhibiting comparative capsule quality can be used. In the above examples, it should be noted that the particular coating formu'lation or coat-ing materials are neither critica'l nor important and can be varied or substituted, as desired or required to fit a particular situa-tion. The resorcinol is not necessary and can be omitted or can be replaced by another material such as orcinol or gallic acid.
If used, the resorcinol or other material can be present in the system in amounts of 5 to 30 percent, or more, based on the free or combined urea in the starting materials.

Example 5 In this example, capsules are prepared at a high capsule solids concentration of more than 60 percent, by volume, capsules in only about 40 percent, by volume, of aqueous manufacturing vehicle. Forty parts of 10 percent aqueous system modifier solu-tion, 20 parts of water, 4 parts of urea, and 90 parts of internal phase are combined under emulsifying agitation similar to that of previous examples. The pH is adjusted to about 3.5, the tempera-ture is raised to about 55 degrees, and the emulsification is con-tinued to a droplet size of less than 10 microns. Ten parts of formalin is then added to the system and stirring is maintained for about three hours. The viscosity of the system increases con-siderably as the urea/formaldehyde polymerization reaction pro-gresses. The viscosity appears to be a function of polymer growth and deposition onto capsule wall, however, because the encapsulat-ing system does not show a tendency to gel so long as the system modifier is used. The system of this example can be permitted to stand without agitation after the -first three hours of reaction;
and the capsules will, nevertheless, remain individual and unagglo-merated. The capsules are easily redispersed after settling in the manufacturing vehicle without agitation.
Results from tests on capsules prepared in this example are set out in the following table. Results are shown for capsules prepared using poly(ethylene-co-maleic anhydride) of two different molecular weights as system modif;ers. The TI test results are identified by system modifier molecular weight.

~i Initial Aged 100 degrees Molecular Weight TI TI (1-3 days) ll week) __ _ 15,000-20,000 56 5~ 5~
75,000-90,ooO 57 59 58 When the high concentration encapsulation is attempted by omitting the system modifier or by replacing the system modifier by a nonionic or a positively charged polymer, no acceptable capsules are produced. For example, when poly(vinyl alcohol~ is used, the results are much like those of Example 3, with the excep-tion that, during the condensation reaction, the viscosity of the system increases so much that it cannot be poured without dilution, even at 55 degrees.

Example 6 In this example, three series of different system modifiers are used in accordance with the procedure generally described in Example 1. When the capsules contain the oily internal phase o~
dye solution described above; and, when the capsule quality is tested as above, the test results are:

System Modifier Initial Aged 100 (one day) -- .
poly~ethylene-co-maleic anhydride) M.W. 75,000-90,000 58 60 15,000-20,000 55 57 5,000-7,0001 55 57 1,500-2,000 54 61 poly~methylvinylether-co-maleic anhydride) M.W. 1,125,000 55 56 750,000 61 62 250,000 64 g4 poly(acrylic acid) M.W. less than 300,000 43 45 less than 15,2 47 47 ~less than 50,000 50 59 To demonstrate flexibility in the amount of system modifier which can be used, only one-half as much is used here as is used in the similar materials of higher molecular weight.

2To demonstrate flexibility in the amount of sytem modifier which can be used, twice as much is used here as is used in the similar materials of higher molecular weight.

Example 7 In the sarne manner as described in Example 1, a system compris-ing 100 grams of a 10 percent aqueous solution of hydrolyzed poly(propylene-co-maleic anhydride) as the system modifier, 10 grams of urea, 1 gram of resorcinol and 200 grams of water is pre-pared. The pH is adjusted to 3.5 with sodium hydroxide, and 180 grams of internal phase as described in Example l is dispersed therein to form an emulsion in the manufacturing vehicle. Twenty-five cc. of 37 percent aqueous formaldehyde solution is added to the system.
Agitation of the system is continued while heating at 55C, and after two hours the system is permitted to cool. Uniform capsules containing said internal phase material are obtained.

Example 8 This example is identical with Example 7 except that lO0 grams of a lO percent aqueous solution of hydrolyzed poly(isobutylene-co-maleic anhydride) is used as the system modifier. Uniform capsules having strong capsule walls are again obtained utilizing the same procedure as described in Example 7.

Example 9 This example is identical with Example 7 except that lO0 grams of a 10 percent aqueous solution of hydrolyzed poly(butadiene-co-maleic anhydride) is used as the system modifier. Satisfactory capsules containing the oily dye solution are again obtained.

Example lO
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Twenty grams of dimethylol urea (DMU) is dissolved in 200 cc. of water by adding 200 cc. of boiling water to the DMU in a beaker equipped with a magnetic stirrer. The solution is cooled to about 45C and then about 2.7 cc. of 20 percent sodium hydr-oxide, lO0 grams of hydrolyzed poly(ethylene-co-maleic anhydride) and l gram of resorcinol are added thereto. The final pH is about C

3.5. A standard internal phase as described in Example 1 in the amount of 180 grams is emulsified into the solution as the capsule core material. The system is then heated to a temperature of 55C
in a water bath. After stirring and heatiny are continued for about two hours, the temperature is permitted to decrease to ambient conditions (about 25C).
The resulting capsules of oily dye solution have a uniform size range of about 1 to 15 microns and represent more than 40 percent, by volume, of the encapsulating system.

Example 11 A solution is prepared by combining 50 grams of a 10 percent solution of poly(methyl vinyl ether-co-maleic anhydride) (Gantrez 149), 0.5 gram of resorcinol, approximately 1.4 cc. of 20 percent NaOH and 10 grams of dimethylol urea dissolved in 100 grams of hot (95C) water. The pH is adjusted to 3.5. Ninety grams (100 cc) of standard internal phase as described in Example 1 (Standard IP) is emulsified into the solution, and the emulsion is placed into a water bath maintained at a temperature of 55C.
After 4 hours a draw-down of this emulsion on a CF test strip gave a reflectance value of 63%.
The CF draw-down test is a method of determining capsule wall forrnation. The encapsulation emulsion containing all of the capsule-forming ingredients is coated onto a reactive CF paper.
A color is formed by the reaction of the dye with the CF coating.
Wall formation is demonstrated by the mitiga~ion of the color when the emulsion is coated at a later time and is measured by an opaci-meter to give the reflectance of the coated area.

_xample 12 As described in Example 11, 20 grams of a 25% solution of poly(acrylic acid) (Acrysol A-5), 30 grams of water, 0.5 grams of resorcinol, approximately 1.5 cc. of 20~, NaOH and 10 grams of dimethylol urea d~ssolved in 100 grams of hot (95 C) water are mixed. The pH is adjusted to 3.5. Ninety grams (100 cc.) of Standard IP is emulsified into the solution, and the solution is placed into a water bath maintained at a temperature of 55C.
After 1 hour and 20 minutes, a sample of this ernulsion coated on a CF test strip gave a reflectance value of 61%.

_ample '13 Fifty grams of a 10% solution of poly(propylene~co-maleic anhydride), 0.5 grams oF resorcinol, 1.4 cc. of 20% NaOH and 10 grams of dimethylol urea dissolved in 100 grams of hot (95C) water are mixed to form a solution. The pH is adjusted to 3.5. Ninety grams (100 cc.) of Standard IP is emulsified into the solution, and the solution is placed into a water bath maintained at a tem-perature of 55C.
A-fter 1 hour, a sample of this emulsion coated on a CF test strip gave a reflectance value of 68%.
Example 14 A 10% solution of poly(isobutylene-co-maleic anhydride) is prepared by dissolving the polymer with the aid of NaOH and then treating the resulting solution with a strongly cationic ion ex-change resin (Amberlite* IR 120J. The pH of this solution when diluted with 2 parts of water is 3.5.
Fifty grams of said 10% solution of poly(isobutylene-co-maleic anhydride), G.5 grams of resorcinol and 10 grams of dimethylol urea dissolved in 100 grams of hot (95C) water are mixed. Ninety grams (100 cc) of Standard IP is emulsified into the solution, and the solution is placed into a water bath maintained at a tem-perature of 55C.
After 1 hour, a sample of this emulsion coated on a CF test strip gave a reflectance value of 52%. A samp'le of this emulsion when coated on nonreactive base paper gave a reflectance of 53%.
Example 15 A solution of 38.5 grams of a 13% solution of poly(butadiene-co-maleic anhydride) (Maldene* 285, Borg-Warner Corp.) in water, 0.5 grams of resorcinol, 0.9 cc. of 20% NaOH, 11.5 grams of water and 10 grams of dimethy'lol urea dissolved in 100 grams of hot (95C) water is prepared. The pH is adjusted to 3.5. Ninety grams (100 cc.) of Standard IP is emulsified into the solution, and the solution is p'laced into a water bath maintained at a temperature of 55C.
After 1 hour and 15 minutes, a sample of this emulsion coated on a CF test strlp gave a reflectance va'lue of 62%.

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Example_l_ A solution of 400 grams of water, 200 grams of a 10% aqueous solution of poly(ethylene-co-maleic anhydride) (EMA* 31) and 2 grams of resorcinol is adjusted to a pH of 3.5 with 20% NaOH.
Into this solution is emulsified 400 ml. of Standard IP as describ-ed in Example 1.

Sample A
To a 484 gram portion of the above emulsion, stirring in a 55C water bath, is added a solution of 22.8 grams of methylated dimethylol urea resin (Beetle* 60 Resin, American Cyanamid Co.) and 15.0 grams of water.

Sample B
To a 484 gram portion of the above emulsion, stirring in a 55C water bath, is added a solution of 20.1 grams of methylated dimethylol urea resin (Beetle 65 Resin, American Cyanamid Co.) and 17.7 grams of water.
Samples A and B, along with a batch prepared in accordance with Example 1 hereinabove (Sample C), are left stirring overnight in the water bath. The heat to the water bath is turned off two hours after the reactants have been added.
The three batch samples were tested for degree of encapsula-tion by coating draw-downs of the batches on CF sheets at various time intervals. The following reflectance values were obtained when the batches were tested after stirring overnight (19 hours):

Opacimeter Reading of Draw-Down _n CF
Sample A Sample B Sample C

Batches of Samples A, B and C were also formulated and coated to produce CB sheets successfully.

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e3 Example 17 A solution of 100 grams of water, 50 grams of a 10~ solution of poly(methyl vinyl ether-co-maleic anhydride) ~Gantrez* 16g) and 0.5 gram of resorcinol is adjusted to a pH of 3.5 with 20%
NaOH. Into this solution is emulsified 100 ml of Standard IP.
The emulsion is placed in a 55C water bath, and a solution of 10 grams of methylated dimethylol urea resin (Beetle 65) and 8.9 grams of water is added thereto. The stirring is continued for 19 hours, but the heat is turned off after 3 hours.
The reflectance reading of a draw-down on a CF Sheet after 19 hours was 60.

Example 18 A solution of 130 grams of water, 20 grams of a 40% solution of poly(acrylic acid) (Acrysol A-5) and 0.5 gram of resorcinol is adjusted to a pH of 3.5 with 20% NaOH. A Standard IP in the amount of 100 ml. is emulsified therein.
The emulsion is placed in a 55C water bath, and a solution of 10 grams of methylated dimethylol urea resin (Beetle 65) and 8.9 grams of water is added thereto. The stirring is continued for 19 hours, but the heat is turned off after 2-1 hours.
The reflectance reading of a draw-down on a CF Sheet after 19 hours was 74.

Example 19 A solution of 50 grams of a 10% solution of poly(propylene-co-maleic anhydride), 100 grams of water, 10 grams of methylated di-methylol urea resin (Beetle 65, 100% solid), and 0.5 gram of resor-cinol is adjusted to a pH of 3.5 with 20% NaOH. Ninety grams (100 ml.) of Standard IP is emulsified in the solution and the emulsion is placed into a 55C water bath.
After 2 hours, a sample of this emulsion coated on a CF test strip gave a reflectance of 60%. A sample coated on nonreactive paper gave a reflectance of 61%.

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Example 20 A solution of 50 grams oF a 10% solution of poly(isobuty'lene-co-maleic anhydride), lOC grams of water, 10 grams of methylated dimethylol urea resin (Beetle 65) and 0.5 gram of resorcinol is adjusted to a pH of 3.5 with NaOH. Ninety grams (100 ml.) of Standard IP is emulsified in the solution, and the emulsion is placed into a 55C water bath.
After 2 hours, a sample of this emulsion coaked on a CF test strip gave a reflectance of 53%. A sample coated on nonreactive paper showed a reflectance of 54%.

Example 21 A solution of 38.5 grams of a 13% solution of poly(butadiene-co-maleic anhy~ride) (Maldene 285), 101.5 grams of water, 10 grams of methylated dimethylol urea resin (Beet'le 65) and 0.5 gram of resorcinol is adjusted to a pH of 3.5 with NaOH. Ninety grams (100 ml-? of Standard IP is emulsified into this solution, and the emulsion is placed into a 55C water bath.
After 2 hours and 30 minutes, a sample coated on a CF test strip gave a reflectance value of 48%. A samp'le coated on nonreac-tive paper gave a reflectance of 50%.

Example 22 This example demonstrates that encapsulation can be obtained even with no agitation after the ingredients have been combined.
A solution of 100 grams of a 10% solution of poly(ethylene-co-maleic anhydride) (EMA-31), 100 grams of water, 10 grams of urea, and 1 gram of resorcinol is adjusted to a pH of 3.5 with 20% NaOH.
A Standard IP (200 cc.) as described in Example 1 is emulsified into the solution, and 25 cc. of 37'~ formaldehyde solution is added thereto. The emulsion is placed into a 55C water bath without agitation. Capsules are obtained successfully'without any agita-tion or stirring, as the batch does not set up.

Draw-downs on CF sheets show the formation of capsules, the opacimeter reading reaching 60 in approximately one hour.
Example 23 A 10% solution of poly(vinyl acetate-co-maleic anhydride) is prepared by dispersing the polymer in cold water and dissolving it by the addition of 0.4 ml. of 20% NaOH per gram of dry polymer.
Fifty grams of the PVAMA solution, lOO grams of water, 5 grams of urea and 0.5 grams of resorcinol are combined and adjusted to a pH of about 3.6 with NaOH. Ninety grams (lOO ml.) of Standard IP is emulsified into the solution, and 12.5 ml. of 37% aqueous formaldehyde solution is added thereto. The emulsion is placed into a 55C water bath. The heat is turned off after 4 hours, and the emulsion is left in the water bath overnight.
A sample of the resulting emulsion coated on a CF test strip gave an opacimeter reading of 56%. A sample of the emulsion coated on nonreactive paper gave an opacimeter reading of 65~.

The amounts and kinds of encapsulating system materials used in these examples are any of those previously disclosed. The pH
of the encapsulating system can be pH 0-7 and the formaldehyde to urea mole ratio can be from 1.6 to 3. As the pH of the system is increased, it is helpful to increase the temperature of the encapsulating system also. Eligible temperatures of operation range from about 25 to 100 degrees under ambient conditions, about 5Q-55 degrees being preferred.
By adjusting the degree of agitation, if employed, droplets of liquid intended capsule core material can be produced of any size from a few to several hundred microns. Moreover, the amount of intended capsule core material can be altered to change the amount of completed capsule which is internal phase as opposed to capsule wall material. Capsules can generally be made from less than 50 percent internal phase to 95 percent internal phase, or more.
The amount of system modifier in the encapsulating system appears to be important to the practice of this invent10n, with respect to the minimum amount to assure adequate interference with the condensation reaction to form polymer and with respect to the maximum amount as an economic matter. Of course, if the system modifier is present in very high concentrations, the system viscos-ity will be inoperably high. As a general rule, the encapsulating system should include at least abouk 0.75 percent system modifier.
At the other extreme, it must be remembered -that the variety of eligible materials precludes establishment of an exact general maximum due to differences in solution viscosity among the several materials. It can be said that more than 10 percent is seldom used or required. However, amount of system modifier of up to about 15 percent can be employed, if desired.
It may be generally stated that the amount of system modifier material employed is that amount sufficient to modify the polymeri-zation of the urea with formaldehyde~ in one embodiment, or the polymerization of the dimethylol urea or methylated dimethylol urea, in another embodiment of the invention, so as to permit forma-tion of polymeric capsular walls therefrom.
The invention being thus described, it will be obvious that the same may be varied in rnany ways. Such variations are not to be regarded as a departure from the spirit and scope of the inven-tion, and all such modifications are intended to be included within the scope of the following claims.

Gil .. . .

Claims (14)

WHAT IS CLAIMED IS:

1. A process for manufacturing minute capsules, en masse, in an aqueous manufacturing vehicle, comprising the steps of:
(a) Establishing an agitating aqueous system including urea, formaldehyde, a system modifier material in an amount sufficient to modify the poly-merization of the urea with formaldehyde so as to permit formation of urea-formaldehyde polymeric capsular walls, said system modifier material being selected from the group consisting of poly(ethylene-co-maleic anhydride), poly(methyl vinyl ether-co-maleic anhydride), poly(acrylic acid), poly(propylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(butadiene-co-maleic anhydride) and poly(vinyl acetate-co-maleic anhydride), and particles of an intended capsule core material substantially insoluble in the system, in which agitating system the modifier material is present prior to the addition of said particles, and (b) polycondensing the urea and formaldehyde to form a condensation polymer resulting in (i) liquid-liquid phase separation of the urea/formaldehyde polymerization product above a molecular weight to be soluble in the system and (ii)continued reaction of the separated liquid urea/formaldehyde polymerization pro-duct to give solid capsule wall material indivi-dually surrounding particles of the dispersed intended capsule core.

2. The process of claim 1, wherein the aqueous manufactur-ing vehicle is less than 60 percent, by volume, of the system.

3. The process of claim 1, wherein the aqueous manufactur-ing vehicle is less than 50 percent, by volume, of the system.

4. The process of claim 1, wherein the aqueous system includes an additive compound selected from the group consisting resorcinol, orcinol and gallic acid.

5. The process of claim 4, wherein said additive compound is present in the system in an amount of 5 to 30 percent, by weight, of the urea.

6. The process of claim 1, wherein the pH of the aqueous manufacturing vehicle is maintained between 3 and 7 through step (b).

7. The process of claim 1, wherein the amount of modifier material in the system is about 0.75 to about 15 percent, by weight, of the aqueous manufacturing vehicle.

8. The process of claim 1, wherein the aqueous system is heated at a temperature of about 25° to 100°C,

9. A process for manufacturing minute capsules, en masse, in an aqueous manufacturing vehicle, comprising the steps of:

9 (concluded) (a) establishing an agitating single-phase aqueous solution system including urea and a system modifier material in an amount sufficient to modify the polymerization of the urea with formaldehyde so as to permit formation of urea-formaldehyde polymeric capsular walls, said system modifier material being selected from the group consisting of poly(ethylene-co-maleic anhydride), poly(methyl vinyl ether-co-maleic anhydride), poly(acrylic acid), poly(propylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(butadiene-co-maleic anhydride) and poly(vinyl acetate-co-maleic anhydride), (b) dispersing into the solution system particles of an intended capsule core material substantially insoluble in the system, and (c) adding formaldehyde to the system, whereby the urea and formaldehyde react to form a condensation polymer resulting in (i) liquid-liquid phase separation of the urea/
formaldehyde polymerization product above a molecular weight to be soluble in the system and (ii) continued reaction of the separated liquid urea/formaldehyde polymerization product to give solid capsule wall material individually surrounding particles of the dispersed intended capsule core.

10. The process of claim 9, wherein the amount of modifier material in the system is about 0.75 to about 15 percent, by weight, of the aqueous manufacturing vehicle.

11. A process for manufacturing minute capsules, en masse, in an aqueous manufacturing vehicle, comprising the steps of:
(a) establishing an agitating single-phase aqueous solution system including a system modifier material in an amount sufficient to modify the polymerization of the urea with formaldehyde so as to permit formation of the urea-formaldehyde polymeric capsular walls, said system modifier material being selected from the group consisting of poly(ethylene-co-maleic anhydride), poly(methyl vinyl ether-co-maleic anhydride), poly(acrylic acid), poly(propylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(butadiene-co-maleic anhydride), and poly(vinyl acetate-co-maleic anhydride), (b) dissolving urea and formaldehyde in the aqueous system, the urea and the formaldehyde reacting together in the presence of the system modifier to yield a liquid-liquid phase separated polymerization product, and (c) dispensing in the system particles of an intended capsule core material substantially insoluble in the system and substantially unreactive with the components of the system, the dispersed particles being wet and enwrapped by the liquid, phase-separated polymerization product, whereby the urea and formaldehyde further polymerize into solid capsule wall material insoluble in the system.

12. The process of claim 11, wherein the amount of modifier material in the system is about 0.75 to about 15 percent, by weight, of the aqueous manufacturing vehicle.

13. A. process for manufacturing minute capsules, en masse, in an aqueous manufacturing vehicle, comprising the steps of:
(a) establishing an agitating single-phase aqueous solution system including a system modifier material in an amount sufficient to modify the poly-merization of the urea with formaldehyde so as to permit formation of urea-formaldehyde polymeric capsular walls, said system modifier material being selected from the group consisting of poly(ethylene-co-maleic anhydride), poly(methyl vinyl ether-co-maleic anhydride), poly(acrylic acid), poly(propylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(butadiene-co-maleic anhydride) and poly(vinyl acetate-co-maleic anhydride), (b) dispersing in the system particles of an intended capsule core material substantially insoluble in the system and susbstantially unreactive with the components of the system, and (c) adding urea and formaldehyde to the result-ing emulsion, the urea and the formaldehyde react-ing together in the presence of the system modifier to yield a liquid-liquid phase-separated poly-merization product, the dispersed particles being wet and enwrapped by the liquid, phase-separated polymerization product, whereby the urea and formal-dehyde further polymerize into solid capsule wall material insoluble in the system.

14. The process of claim 13, wherein the amount of modifier material in the system is about 0.75 to about 15 percent, by weight, of the aqueous manufacturing vehicle.