US3830750A

US3830750A - Encapsulating substantially soluble portion of core material in substantially soluble shell material of different solubility

Info

Publication number: US3830750A
Application number: US00214031A
Authority: US
Inventors: R Wellman
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1971-12-30
Filing date: 1971-12-30
Publication date: 1974-08-20
Anticipated expiration: 1991-08-20
Also published as: GB1411954A; ES410224A1; DE2255102A1; BE793246A; CA983328A; FR2165941B1; IT973317B; FR2165941A1; JPS4890977A; NL7217788A; BR7208781D0; AU5063372A

Abstract

ENCAPSULATION OF LIQUID, SEMISOLID, OR SOLID CORE MATERIALS IN SHELL MATERIAL BY ATOMIZING AND DRYING A SINGLE PHASE SOLUTION OF CORE AND SHELL MATERIALS. IN ONE SYSTEM MENT USING A MUTUAL SOLVENT-PREFERENTIAL SOLVENT SYSTEM OF CHLOROMERIC AND ISOPROPANOL, THE CORE MATERIAL IS THE POLYMERIC REACTION PRODUCT OF ISOPROPYLIDENEDIPHENOXYPROPANOL AND ADIPIC ACID, AND THE WALL MATERIAL IS THE REACTION PRODUCT OF A DIMER ACID WITH A LINEAR DIAMINE. IN OTHER EMBODIMENT USING A MUTUAL SOLVENT-MUTUAL NONSOLVENT SYSTEM OF CHLOROFORM AND HEPTANE, THE CORE MATERIAL IS THE POLYMERIC REACTION PRODUCT OF ISOPROPYLIDENEDIHENOXYPROPANOL AND ADIPIC ACID, AND THE WALL MATERIAL IS POLYSTYRENE. THE CORE OR SHELL, OR BOTH, MAY BE PIGMENTED OR DYED. THE CAPSULES PRODUCED HAVE NUMEROUS USES INCLUDING THEIR USE AS AN ELECTROSTATOGRAPHIC TONER.

Description

Aug. 20, 1974 R.- a. WELLMAN A 3,830,750 PROCESS ENCAPSULATING' SUBSTANTIALLY SOLUBLE PORTION OF CORE MATERIAL IN SUBSTANTIALLY SOLUBLE SHELL HATIRIAL OF DIFFERENT SOLUBILITY Filed Dec. 30, 1.911

ETHYL ALCOHOL /?\CORE MATERIAL l ACETONE I 7' I I METHYL ETHYL l KETONE I A v SHELL MATERIAL P 4 I 1C I CHLOROFORM SOLVE NT- RICH PHASE wALL PHASE coma PHASE FIG. 2

nited States Patent US. Cl. 252-316 2 Claims ABSTRACT OF THE DISCLOSURE Encapsulation of liquid, semisolid, or solid core materials in shell material by atomizing and drying a single phase solution of core and shell materials. In one system ment using a mutual solvent-preferential solvent system of chloroform and isopropanol, the core material is the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid, and the wall material is the reaction product of a dimer acid with a linear diamine. In another embodiment using a mutual solvent-mutual nonsolvent system of chloroform and heptane, the core material is the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid, and the wall material is polystyrene. The core or shell, or both, may be pigmented 0r dyed. The capsules produced have numerous uses including their use as an electrostatographic toner.

BACKGROUND OF THE INVENTION This invention relates to a process for the encapsulation of liquid, semisolid, and solid core materials, and more particularly to the process of encapsulating core materials in a shell material by atomizing and drying a single phase solution of core and shell materials.

For purposes of illustration, this invention is described in relation to the preparation of electrostatographic developing materials and in particular with respect to toner materials. The formation and development of images on the surface of photoconductor material by electrostatic means is well known. The basic electrostatographic imaging process, as taught by C. F. Carlson in US. Pat. 2,2997,691, involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material referred to in the art as toner. The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently afiixed to the support surface as by heat. Instead of latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a light and shadow image, one may form the latent image by directly charging the layer in image configuration. The powder image may be fixed to the photoconductive layer if elimination of the powder image transfer step is desired. Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing steps.

Several methods are known for applying the electroscopic particles to the electrostatic latent image to be developed. One development method, as disclosed by E. N. Wise in US. Pat. 2,618,552, is known as cascade development. In this method, a developer material comprising relatively large carrier particles having finely divided toner 7 3,830,750 Patented Aug. 20, 1974 C&

particles electrostatically coated thereon is conveyed to and rolled or cascaded across the electrostatic latent image bearing surface. The composition of the carrier particles is so selected as to triboelectrically charge the toner particles to the desired polarity. As the mixture cascades or rolls across the image bearing surface, the toner particles are electrostatically deposited and secured to the charged portion of the latent image and are not deposited on the uncharged or background portions of the image. Most of the toner particles accidentally deposited in the background are removed by the rolling carrier, due apparently, to the greater electrostatic attraction between the toner and the carrier than between the toner and the discharged background. The carrier and excess toner are then recycled. This technique is extremely good for the development of line copy images.

Another method of developing electrostatic latent images is the magnetic brush process as disclosed, for example, in US. Pat. 2,874,063. In this method, a developer material containing toner and magnetic carrier particles are carried by a magnet. The magnetic field of the magnet causes alignment of the magnetic carrier into a brushlike configuration. This magnetic brush is engaged with the electrostatic image bearing surface and the toner particles are drawn from the brush to the latent image by electrostatic attraction.

Still another technique for developing electrostatic latent images is the powder cloud process as disclosed, for example, by C. F. Carlson in US. Pat. 2,221,776. In this method, a developer material comprising electrically charged toner particles in a gaseous fluid is passed adjacent the surface bearing the electrostatic latent image. The toner particles are drawn by electrostatic attraction from the gas to the latent image. This process is particularly useful in continuous tone development. Other development methods such as touchdown development as disclosed by R. W. Gundlach in US. Pat. 3,166,432 may be used where suitable.

The toner particles are usually thermoplastic resins selected to have melting points significantly above any ambient temperatures that might be encountered during electrostatic deposition and these are fixed to the image substrate in most cases by radiant heat. In addition to the developing powder or toner materials described in US. Pat. 2,297,691, a number of additional toner materials have been developed especially for use in the newer development techniques including the cascade technique described above. Generally speaking, these new toner materials have comprised various improved resins mixed with different pigments such as carbon black. Some exemplary patents along this line include US. Pat. 2,659,670 to Copley which describes a toner resin of rosin-modified phenolformaldehyde, U.S. Reissue 25,136 to Carlson which describes an electrostatographic toner employing a resin of polymerized styrene and US. Pat. 3,079,342 to Insalaco describing a plasticized copolymer resin in which the comonomers are styrene and a methacrylate selected from the group of butyl, isobutyl, ethyl, propyl, and isopropyl.

In the past, these toners have generally been prepared by thoroughly mixing a heat softened resin and colorant to form a uniform dispersion as by blending these ingredients in a rubber mill or the like and then pulverizing this material after cooling to form it into small particles. Most frequently, this comminution of the colored resin has been made by jet pulverization of the material. Although this technique of toner manufacture has produced some very excellent toner, it does tend to have certain shortcomings. For example, it generally produces a rather wide range of particle sizes in the toner particles. Although the average particle size of toner made according to this technique generally ranges between about 5 and 10 microns, individual particles ranging from submicron in size to above microns are not infrequently produced. In addition, due to cleavage through carbon black agglomerates, these jetted toners usually contain some free carbon black particles. Further, this technique of toner production imposes certain limitations upon the material selected for the toner because the colored resin must be sufficiently friable so'that it can be pulverized at an economically feasible rate of production. The problem which arises from this requirement is that when the colored resin is sufiiciently friable for really high speed pulverizing, it tends to form even a wider range of particle sizes during pulverization including relatively large percentages of fines and is frequently subject to even further pulverization or powdering when it is employed for developing in electrostatographic imaging apparatus. All other requirements of electrostatographic developers or toners including the requirements that they be stable in storage, nonagglomerative, have the proper triboelectric properties for developing and have a low melting point for heat fusing are only compounded by the additional requirements imposed by this toner forming process. Some developer ma terials, though possessing desirable properties such as proper triboelectric characteristics, are unsuitable because they tend to cake, bridge and agglomerate during handling and storage. The tendency of toner particles to adhere to imaging surfaces may be aggravated when the toner surfaces are rough and irregular. The flow characteristics of many toners are adversely affected when relative humidity is high. The triboelectric characteristics are adversely affected when the relative humidity is either high or low. For example, the triboelectric values of some toner particles fluctuate with changes in relative humidity and are not desirable for employment in electrostatographic imaging systems, particularly in automatic machines which require toners having stable and predictable triboelectric values. Another factor alfecting the stability of toner triboelectric properties is the susceptibility of toner particles to toner impaction. When toner particles are employed in automatic machines and recycled through many cycles, the many collisions which occur between the toner particles, carrier particles, and other surfaces in the machine cause the toner particles carried on the surface of the carrier particles to be welded or otherwise forced into the carrier particles. The gradual accumulation of permanently attached toner marterial on the surface of the carrier particles causes a change in the triboelectric value of the carrier particles and directly contributes to the degradation of copy quality by eventual destruction of the toner carrying capacity of the carrier.

Other techniques of toner production are known even including spray drying toner from a dyed resin solution as described in US. Pat. 2,357,809 to Carlson. Even though this technique can produce small, well shaped particles, some particles tend to bleed dye and to be unstable under the influences of light, heat and/or handling. Since toners are subjected to many of these influences before, during, or after imaging, they are not always acceptable for all uses.

Further, a method of toner production by spray drying a low melting point resin dissolved in a solvent, and thereafter spray drying the resulting particles dispersed in a solution of a second shell forming resin dissolved in a solvent which is a nonsolvent for the low melting point resin to form encapsulated toner particles is disclosed in US. Pat. 3,338,991 to Insalaco. However, even though this technique can produce encapsulated toner materials, it is a multistep process, it is time consuming, it requires several handling procedures and containers and it requires the use of different solvents. In addition, a tacky core or a liquid cannot be collected, and the second solvent must not swell the core.

The difiicult part of most encapsulation procedures is to prevent agglomeration at some point in the process. Agglomeration during storage or spraying of the dryer feed materials is a major problem in previously known spray drying encapsulation methods. Elimination of these problems will permit wide latitude in the choice of materials, solvents, temperature range, material concentrations, and enable selection of conditions for most core and wall combinations. The difliculty or impossibility of producing very small microcapsules of a desired size and with a relatively narrow size distribution is also a major limitation of previously known encapsulation methods. Further, the production of an encapsulated electrostatographic toner material which can be pressure fixed is advantageous since unencapsulated materials which undergo cold flow tend to form tacky images on the copy sheet which often oifset to other adjacent sheets. Toner particles containing unencapsulated materials which undergo cold flow tend to bridge, cake and block during production and in the shipping container as well as in the electrostatographic imaging machine. Also, the toner material should be capable of accepting a charge of the correct polarity such as when brought into rubbing contact with the surface of carrier materials in cascade, magnetic brush or touchdown development systems. Some toner materials which possess many properties which would be desirable in electrostatographic toners dispense poorly and cannot be used in automatic copying and duplicating machines. Other toners dispense well but form images which are characterized by low density, poor resolution, or high background. Further, some toners are unsuitable for processes where electrostatic transfer is employed.

In general, the term phase separation as employed herein means the separation of a liquid phase or a solid phase from a liquid phase. A useful form of liquid phase separation from aqueous media is known as coacervation and is exemplified in US. Pats. 2,800,457 and 2,800,458 to Green. In US. Pat. 2,800,458 the method of making capsules involves an undesirably large number of steps of (1) preparing an emulsion with a gellable colloid material, (2) inducing coacervation by addition of an aqueous salt solution at a temperature above the melting point of the colloid material, (3) gelling the colloid by pouring the coacervate mixture into a cool salt solution, (4) washing with water and filtering to remove the salt, (5) hardening the filter cake with an aqueous solution of formaldehyde, (6) washing with water and filtering to remove residual formaldehyde, and (7) adjusting the water concentration or removing the residual fluid if desired. There is a further disadvantage in that control of particle size distribution is extremely difficult. Also, many microencapsulation processes are limited to production of particle size to about 40 microns and greater in average particle diameter. Prior phase separation encapsulation processes in liquid media avoid this lower limit, but control of the particle size requires the same, and additional, balancing of conditions as for the prevention of agglomeration.

Spherical particles are desirable for many applications. Spray drying and some other encapsulation processes produce spherical particles. Most other toner production processes result in irregularly shaped particles as in the processes which require the grinding or pulverizing of an agglomerated mass. Since previously known encapsulation processes are deficient in one or more respects, there is a continuing need for an improved encapsulation process.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a method for overcoming the above noted deficiencies.

It is another object of this invention to provide a method for encapsulation which is continuous.

It is another object of this invention to provide a method for encapsulation which is simple, efficient, and one step.

It is another object of this invention to provide a method for encapsulation which avoids problems of agglomeration.

It is another object of this invention to provide a method for encapsulation of particles which avoid problems of caking, bridging, and blocking.

It is another object of this invention to provide a method for encapsulation of 'a liquid, semisolid, or solid core material.

It is another object of this invention to provide a method for encapsulaiton which is capable of producing very small microcapsules of a desired size and controlled size distribution.

It is another object of this invention to provide a method for forming encapsulated particles suitable for use as an electrostato graphic toner.

It is another object of this invention to provide a method for the production of encapsulated particles having stable electrostatographic properties.

It is another object of this invention to provide a method for encapsulaiton of toner particles which have a low melting point.

It is another object of this invention to provide a method for encapsulation of toner particles which avoid dispensing and impaction problems in electrostatographic imaging systems.

It is another object of this invention to provide a method of encapsulation to produce toner particles which are capable of producing high density, excellent resolution, and low background electrostatographic images.

It is another object of this invention to provide an encapsulation method superior to those of known encapsulation processes.

The above objects and others are accomplished by providing a method for the encapsulation of liquid, semisolid, and solid core materials in a shell material during a single step atomizing and spray drying process of a single phase solution of core and shell materials.

A process has now been found for encapsulating the substantially soluble portion of a core material in the substantially soluble poriton of a shell material having different solubility than the core material comprising dissolving the core material and the shell material in at least one relatively volatile solvent to form a solution, substantially simultaneously forming small individual droplets of the solution, removing at least a portion of the solvent from each individual droplet by evaporation thereby increasing the concentration of the dissolved core material and the shell material whereby substantially all of the core material preferentially phase separates as a solvent poor phase, and removing additional solvent from each droplet whereby the shell material deposits around the core material to form substantially dry, small spherical particles comprising the core material encapsulated with the shell material.

Basically, the technique of this invention comprises in selection of the ingredients, including the solvent or mixture of solvents, so that the change in concentration of solvent or solvents and dissolved materials during drying, and in some cases the change in pH or temperature of the atomized solution, will cause the core material to phase separate as a solvent poor, high surface tension phase in a solution of shell material. The solution of shell material will thereafter surround and encapsulate the core phase and ultimately form a substantially dry solid cap sule shell upon evaporation of the solvent while the particles are airborne. The separated core material phase and the separated shell material phase may be solvent poor phases and not solvent free phases. The thus produced encapsulated product can be collected in dry, free flowing form by any conventional or suitable means.

The desired core and wall materials may be selected first on the basis of desired capsule properties. The solvent or mixture of solvents may then be selected to give the desired encapsulation. This selection is made on the basis of core and wall material solubility and solvent volatility. After the desired core and wall materials have been selected, initial experiments may be run to determine the general solubility characteristics of the materials. 'Once these general characteristics have been established, potential solvent combinations are selected and investigated in greater detail by determining solvent ratios at the cloud point. In the simpler cases, the preliminary experiments are sufficient to permit selection of a suitable solvent system. However, the procedure used for these simple cases is best understood if viewed as a simplified version of the procedure used for more complex cases where either the mutual solubility of core and wall materials is limited or difiiculty is encountered in finding conditions for phase separation of the core without also precipitating the wall material. For more complex cases, use is made of a solubility area plot. On a plot with the coordigates of solubility parameter and hydrogen bonding parameter, an area is outlined enclosing solvents in which the core and wall materials are soluble. Two dimensional plots can be used for simplicity but possible polarity effects should be borne in mind. The solubility area is determined by titrating a solution of the core and wall materials with a nonsolvent and taking the cloud point as the limit of the solubility area. Use is made of the fact that both parameters can be calculated for the mixture by the equation, shown for solubility parameter only;

where X 0'; are the volume fraction and solubility parameter of solvent and a is the solubility parameter for the mixture.

Plotting the solubility areas of both wall and core material on the same plot, and assuming no interaction, the initial solution should lie within the overlap of the two areas. Further, the solvent composition should be such that as the solvent mixture evaporates, the two parameters will be moved in a direction that will lead to a point within the solubility area of the wall material but outside the area for the core material. This point should be reached While the solution of wall material is still fluid enough to permit formation of a unified core phase it this is desired. In practice, the assumption of no significant interaction between core and wall materials should be checked by making cloud point determinations on mixed solutions. Also the cloud point will change to some extent with core and wall material concentration and therefore concentration limits should be fixed.

An example of a solubility area plot is shown in FIG. 1 with points for some solvents inserted. In FIG. 1, the solvent selected would correspond approximately to point A and could be a 1/ 1 by volume mixture of methyl ethyl ketone and heptane. Additional experiments would then be made to determine if core and wall materials interaction caused any important changes in solubilities and to determine the properties and composition of the phases formed on evaporation of solvent. With the suggested solvent system and assuming no interaction effects, solvent evaporation would cause the parameters to shift from point A along the dotted line toward point D (pure heptane). At point B, phase separation of the core material would start and, with further evaporation, at point C, the Wall material would commence to phase separate and three phases (excluding any solid pigment, etc.) will form asshown in FIG. 2. Additional solvent removal will cause complete phase separation of the wall material, then removal of the solvent phase by evaporation and lastly complete drying and hardening of the capsules.

Although in the example only two materials are present, the procedure may be used for combinations of several materials. With more than one soluble core and wall material, the parameters for the solvent used should lie in a region where all the materials overlap and all of the core materials should start to phase separate before any of the wall materials. Thus, in the example shown, one could have additional core materials with cloud points between points A and B and additional wall materials with cloud points between C and D. All of the materials for a given phase, for example, all of the core materials, should be compatible with each other or else a segregated core, or wall may be formed.

In one embodiment, encapsulated particles are formed by selection of components in a single phase solution wherein all of the substantially soluble portion of core and shell materials are dissolved in a single solvent system to permit sequential phase separation of the core and shell materials during a drying process. For the single solvent system, advantage is taken of the differential solubilities and polymer incompatibility of different core and shell materials so that the core material phase separates at a higher solvent concentration than is required to phase separate the wall material when solvent is removed. In this embodiment, the solvent system remains as a mutual solvent for the core and wall material all during drying and phase separation is caused by polymer incompatibility. Polymers are incompatible, as employed herein, when they are not miscible in each other in a mutual solvent system. That is, by decreasing the concentration of the solvent system, one polymer material phase separates before the other polymer material. In this embodiment, phase separation by polymer incompatibility combined with decreased solubility may also be employed. In addition, the materials need not be polymers, but other core materials and film forming shell materials may be employed. Further, in this embodiment a single solvent may be used, but it also includes mixtures of solvents which may be used to advantage with particular core and wall materials. When employing a single solvent, the system should be such that partial removal of the solvent causes the core material to preferentially phase separate and further removal of the solvent causes the shell material to deposit around the core material thus forming the Wall. When employing miscible multisolvents in a system, the system should be such that partial removal by vaporization of each solvent in the ratio they are removed causes phase separation of less soluble core material and further solvent removal causes the more soluble shell material to form around the core material thus forming the wall.

In another embodiment, encapsulated particles are formed by selection of components in a single phase solution wherein all of the substantially soluble portions of core and shell materials are dissolved in a mixture of two solvents and wherein one of the two solvents is a nonsolvent for the core material and is capable of being sufiiciently concentrated by evaporation during a drying process to cause phase separation of the core material prior to deposition of the shell material. In this embodiment, the solvent system becomes a nonsolvent for the core material but remains a solvent for the wall material during a drying process. This embodiment may also be considered a mutual solvent/preferential solvent system and includes any such system in which the wall material remains in solution. A solvent system which comprises of chloroform and isopropanol wherein the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid is the core material and the reaction product of a dimer acid with a linear diamine (e.g., Emerez 1540, available from Emery Industries, Incorporated) is the wall material are dissolved is an example of this embodiment.

In another embodiment, encapsulated particles are formed by selection of components in a single phase solution wherein all of the substantially soluble portions of core and wall materials are dissolved in a mutual solvent mixture and wherein the solvent mixture becomes a nonsolvent first for the core material and later a nonsolvent for the wall material during a drying process. This embodiment may be considered a mutual solvent/mutual nonsolvent system and includes any such system in which three phases; core forming phase, wall forming phase, and solvent phase coexist during the final stages of drying. A solvent system comprising chloroform and heptane wherein the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid is the potential core material, and polystyrene is the potential shell material are dissolved is an example of this embodiment. In the three previous embodiments, the solvent system in the feed solution is initially a mutual solvent for the core and wall materials. Where a mixture of solvents is employed, the change in concentration of the more volatile solvent causes phase separation of the core material to precede deposition of the wall material.

In another embodiment, encapsulated particles are formed by selection of components in a single phase solution wherein all of the substantially soluble portions of core and shell materials are dissolved in a solvent systern as to permit sequential phase separation of the core and shell materials during a drying process by a change in pH of the solution. By way of illustration, a single phase solution of the core and shell materials is prepared and then spray dried so that the relatively volatile solvent system is evaporated forming dry, finely divided encapsulated particles. However, if water soluble materials are employed and the core material is only soluble at a high pH, by spray drying an ammoniacal or alkaline solution of the core and wall materials the volatilization and evaporation of ammonia or other alkaline material results in a lower pH causing phase separation of the core material with sequential phase separation of the wall material forming dry, finely divided encaspulated particles.

In another embodiment, enacapsulated particles are formed by selection of components in a single phase solution wherein all of the substantially soluble portions of core and shell materials are dissolved in a solvent system as to permit sequential phase separation of the core and shell materials during a drying process by cooling of the solution, with or without vacuum, during drying. For example, the core material can be made to phase separate by cooling during spray drying, with or without vacuum, where the droplet temperature is lower than the feed temperature and is controlled by controlling the pressure and temperature of the inlet air or other drying gas and the solvent vapor concentration.

When a product having single cores is desired, the core materials and solvents should be selected to ensure that the core phase will have an appreciably higher surface tension than the wall phase. In addition, the system should be such that the core phase forms while the remaining solution bearing the wall phase is sufficiently fluid to permit movement and coalescence of the separate particles of core phase which form initially.

Any suitable solvent system may be employed in the process of this invention, with the main considerations being the solubility of all the substantially soluble portions of the core and shell materials in such solvent or mixture of solvents and the evaporation characteristics of the solvent or mixture of solvents such as as to permit sequential phase separation of the core and shell materials during a drying process. Typical solvents include water, benzene, chlorobenzene, methanol, ethanol, propanol, isopropanol, butanol, chloroform, methyl ethyl ketone, ethyl acetate, heptane, hexane, cyclohexane, ethylene dichloride, methylene chloride, tetrahydrofuran, acetone, dimethylformamide, dichloromethane, alkanes, and those having a boiling point from about 0 C. to about 200 C. Generally, the suitable amount of solvent and nonsolvent materials for the control of sequential phase separation may be readily determined beforehand by determining the relative solubilities of the core and shell materials in the solvent system in View of suitable temperature considerations. The temperature considerations include those temperatures at which a solution of a suitable concentration of the core and shell materials can be obtained in the solvent system. Thus, many compositions are operable at room temperature by mere adjustment of the solvent system concentration.

Any suitable liquid, semisolid, or solid material soluble in the same solvent or mixture of solvents as the shell material may be employed as the core material for the encapsulated product of the process of this invention. Typical liquid core materials include water, oils, low molecular weight polymers such as polyesters (e.g., Co- Rezyn 3, available from Interplastic Corporation), Polyester based urethane polymers (e.g., Formrez P-910, available from Witco Chemical Corporation) epoxidized bisphenol A acrylate (e.g., Epocryl U-12, available from Shell Chemical Company), the reaction product of dimerized linoleic acid with diamines or polyamines (e.g., Versamid 115 and 140 available from General Mills Chemical Division), polyamides (e.g., Polyamide 315, 235 and 340, available from Union Carbide Corporation), polybutadiene (e.g., Poly BD, a hydroxy terminated polybutadiene liquid resin available from Sinclair Petrochemicals, Incorporated), silicone gums (e.g., W 981 from Union Carbide), copolyesters of phthalic acid and an alkyl dicarboxylic acid condensed with an alkyl diol (e.g., Santicizers 405 and 411, available from Monsanto Chemical Company), and mixtures thereof. Typical semisolid core materials include polyesters (e.g., Epon 872, available from Shell Chemical Company), polyester based urethane polymers (e.g., Formrez P314, P2l1 and MG4 available from Witco Chemical Corporation), epoxidized phenolformaldehyde resin (e.g., Epoxy- Novolak ERLB-0449, available from Union Carbide Corporation), polyisobutylene (e.g., OppanolB10, available from Badische Anilin & Soda Fabrik, West Ger- .many), the reaction product of dimerized linoleic acid with diamines or polyamines (e.g., Versamid 100, available from General Mills Chemical Division), and mixtures thereof. Typical solid core materials polyurethane elastomers (e.g., Estane 5701, 5702, 5710, and 5714 available from B. F. Goodrich Company), polyester based alkyd resins, polyester based urethane polymers (e.g., Formrez P-4l0, P'610, and L72, available from Witco Chemical Corporation), polyamides such as the reaction products of dimerized linoleic acid with diamines or polyamines (e.g., Varsamids 712, 948, and 950, available from General Mills Chemical Divsion), the reaction products of dimer acids with linear diamines (e.g., Emerez 1530, 1538 and 1540, available from Emery Industries, Incorporated), ester gums such as rosin esters and modified rosin esters, polyvinylacetate, the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid, the polymeric reaction product of isopropylidenediphenoxypropanol and sebacic acid, C di-urea, polyacetaldehyde, styrene butadiene block copolymers (e.g., Kraton 4113, available from Shell Chemical Company), and mixtures thereof.

Any suitable material soluble in the same solvent or mixture of solvents as the core material may be employed as the shell material for the encapsulated product of the process of this invention. The shell material may be a homopolymer, a copolymer of two or more monomers or a terpolymer. Typical shell materials include polystyrene (e.g., PS-2, Styron 666 and 678 available from Dow Chemical Company; Lustrex 99, available from Monsanto Chemical Company), copolymers of styrenemethacrylates and styrene-acrylates, polycarbonates (e.g., Lexan 101, a poly-(4,4-dioxydiphenyl-2,2'-propane carbonate) available from General Electric Company), polyethers, low molecular weight polyethylenes, polyesters such as polymeric acrylic and methacrylic esters, fumarate polyester resins (e.g., Atlac Bisphenol A, available from Atlas Chemical Company), Dion-Iso polyester resins available from Diamond Shamrock Chemical Company, Krumbharr polyester resins (e.g., K-2200 and K-l979, available from Lawter Chemicals, Incorporated), polyamides such as the reaction product from terephthalic acid and alkyl substituted hexamethylene diamine (e.g., Trogamid T, available from Dynamit Nobel Sales Corporation), the reaction products of dimerized linoleic acid with diamines or polyamides (e.g., Versamid 712, 948 and 950, available from General Mills Chemical Division), the reaction products of dimer acids with linear diamines (e.g., Emerez 1530, 1538, 1540, and 1580 available from Emery Industries, Incorporated), naturally occurring materials such as gelatin, zein, gum arabic and the like, and mixtures thereof.

In the preparation of electrostatographic toner materials, although any one of many known resinous developing materials which are electroscopic in nature and which form coherent spheres when they come out of solution may be used to form the shell materials solution, it has generally been found that electrically insulating, water insoluble thermoplastic or thermosetting, synthetic polymer resins in thermoplastic stage form toners having many highly desirable properties, especially for use in automatic copying machines Where heat fusing is employed to fix the toner image to the copy sheet. In the event that the final toner is to be employed in a process which uses other toner image fixing techniques, the resins employed may be modified accordingly. Thus, for example, where the toner image is fixed by solvent vapor fusing as described in U.S. Pat. 2,776,907 to Carlson, or by the application of an adhesive overcoating or as in pressure fixing, the core and shell materials employed need not necessarily be soften-able at relatively low temperatures. Since, as described above in the introductory description of the process, the core and shell materials are first placed in solution, a consideration to be observed in this selection of the core and shell materials is that they be mutually soluble in a solvent or mixture of solvents and thus, many thermoplastic or thermosetting resins in thermoplastic stage can be used. In the preparation of electrostatographic toners, shell material resins containing a relatively high percent-age of a styrene resin have demonstrated to provide good image quality. The styrene resin may be a homopolymer of styrene or styrene homologues or copolymers of styrene with other monomers containing a single methylene group attached to a carbon atom by a double bond. Thus, typical monomeric materials which may be copolymerized with styrene by addition polymerization include: p-chlorostyrene; vinyl naphthalene; ethylenically unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vlnyl butyrate and the like; esters of alpha-methylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methylalpha-chloracrylate, methyl methacrylate, and the like; acrylonitrile, methacrylonitile, acrylamide, vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, and the like; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone and the like; vinylidene halides such as vinylidene chloride, vinylidene chlorofluoride and the like; and N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N- vinyl pyrrolidene and the like; and mixtures thereof. The styrene resins may also be formed by the polymerization of mixtures of two or more of these unsaturated monomeric materials with a styrene monomer.

For an electrostatographic toner, the shell material of the encapsulated toner should have a blocking temperature of at least about F. When the encapsulated toner is characterized by a blocking temperature less than about 100 F., the toner particles tend to agglomerate during storage and machine operation and also form undesirable films on the surface of reusable photoreceptors which adversely afiect image quality. It is to be understood that the specific formulas given for units contained in the shell material resins of this invention represent the vast majority of the units present, but do not exclude the presence ethyl methacrylate, butyl methacrylate of other monomeric units or reactants than those which have been shown.

The ratio of core and shell materials to the solvent system generally may be any practical dilution. Thus, the dissolved solids content of the solution may be approximately from about 0.5 percent to about 50.0 percent by weight based on the solution but this may also vary, a general limitation being phase separation of the core material and another being practicality of the solute concentration.

The ratio of shell material to core material may be any suitable value and generally is varied with the thickness, strength, porosity, and solubility characteristics of shell desired. Thus, generally, the ratio of shell material to core material may be between about 99 parts by weight of shell material to about 1 part by weight of core material and about 1 part by weight of shell material to about 99 parts by weight of core material. However, the preferred range is between a ratio of about 7 parts by weight of shell material to about 1 part by weight of core material and about 1 part by weight of shell material to about 7 parts by weight of core material as encapsulated particles having the best surface characteristics are obtained. In general, the thickness of the shell material can be controlled by the ratio of the amount of core material to be encapsulated to the amount of shell material. Thus, if a thicker shell layer is desired, more shell material should be used since the ratio of shell to core material remains constant during the process of this invention. In addition, the size of the encapsulated particle also affects the shell thickness since the smaller the particle, the smaller the shell thickness at a constant core to shell ratio.

The solubilities of the core and shell materials that may be employed by the method of this invention may vary considerably in a selected solvent system. For example, completely hydrolyzed styrene-maleic anhydride polymer is about 2.0 percent by weight soluble in water but at least about 20.0 percent by weight soluble in a 50:50 volume mixture of methanol and water. Thus, solutions of the desired core and shell materials can be prepared in relatively dilute or in concentrated form in water alone or by choice of solvent, or mixtures thereof, depending upon the relative solubilities of the materials employed. Further, the concentration of core and shell materials can be increased by the addition of a solubilizing agent, e.g., another hydrophilic'liquid such as methanol or ethanol.

The core or shell, or both the core and shell materials may be pigmented or dyed, or pigmented and dyed by addition of suitable pigment or dye or both pigment and dye to the solution of core and shell materials. The pigment or dye, or pigment and dye, in many cases can be concentrated in the core or in the shell material or at the interface between the core and shell material by proper selection of colorant and solution system having the desired surface, interaction, and solubility properties. Thus, a dye will generally be concentrated in the phase, core or wall, in which it is soluble. The solubilities obtaining during the encapsulation could conceivably force the dye elsewhere but this would be a special case. For example, a dye soluble in the core material, insoluble in the shell material and soluble in the solvent phase, after phase separation of the wall, would probably be concentrated on the exterior of the capsules. In some cases, dyes will form separate phases like pigment particles because of insufficient solubility in the core and wall materials, that is where the dye is soluble in the solution but has little or no solubility in either core or wall material after removal of the solvent. In these cases, the solubility of the dye in the core and wall material rich, but still fluid, phases will control where the dye particles are concentrated in the dry capsule.

A pigment will generally be concentrated in the core or wall material which preferentially adsorbs on the pigment from solution. With most carbon blacks, and probably most pigments, the tendency to absorb will increase with increased polarity and hydrogen bonding of the polymer. Also the material which is separating as a solvent poor phase is more likely to be absorbed. Thus, in the system employing the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid as the core material and polystyrene as the wall material with carbon black as the colorant, all three factors favor absorption of the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid, therefore the carbon black concentrates in the core phase. With polyisobutylene as the core material and poly-(4,4-dioxydiphenyl- 2,2'-propane carbonate) as the wall material, the polyisobutylene has little tendency to be adsorbed even as a solvent poor phase and the carbon black remains suspended in the solution of wall material to be deposited in the capsule wall. Surfactants and stabilizers, including materials added for other reasons such as core plasticizers, may change the adsorption characteristics and therefore result in the pigment being concentrated in a different phase.

Any suitable pigment or dye or pigment and dye may be employed as the colorant for the encapsulated particles. Electrostatographic toner colorants are well known and include, for example, carbon black, nigrosine dye, aniline blue, Calco Oil Blue, chrome yellow, chrome green, ultramarine blue, cobalt blue, DuPont Oil Red, benzidine yellow, Quinoline Yellow, methylene blue chloride, phthalocyanine blue or green, Malachite Green Oxalate, lamp black, Rose Bengal, and mixtures thereof. The pigment or dye, or pigment and dye, should be present in the toner in a sutficient quantity to render it highly colored so that it will form a clearly visible image on a recording member. Thus, for example, where conventional electrostatographic copies of typed documents are desired, the toner may comprise a black pigment such as carbon black or a black dye such as Amaplast Black dye, available from National Aniline Products, Incorporated. Preferably, the pigment is employed in an amount from about 3 percent to about 20- percent by weight based on the total weight of the colored toner because better images are obtained. If the toner colorant employed is a dye, substantially smaller quantities of colorant may be used.

When a pigment is employed as a colorant for toner particles, the technique of this invention comprises in dispersing an insoluble pigment by severe agitation in a solution of the desired core and shell materials followed by drying under controlled conditions so that part of the relatively volatile solvent is driven off and the core material preferentially phase separates forming finely divided particles and further removal of the solvent causes the shell material to phase separate around the core material thus forming the wall. Substantially no free pigment is produced by the process since the pigment may be found in the core or wall material or at the interface between the core and wall material. Obviously, the pigment need not necessarily be included in both the core and the wall of the particle, but instead, may be included in only one of these or neither. Further, since it is desirable that the core material phase separate to form a continuous inner matrix, the pigment concentration is preferably low if the pigment is to form part of the core. Likewise, if the pigment is to form part of the shell, the pigment concentration is preferably not so high as to inhibit the formation of an impermeable shell or otherwise adversely affect the integrity of the shell. Since the encapsulated toner particles will generally be produced in sizes ranging from about 0.5 to about 35 microns, the pigment should preferably have a diameter of less than about 0.1 micron and wherever possible should be smaller as this not only contributes to the uniformity of end product coloration, but also tends to create a more stable suspension of the pigment prior to drying. In any event, the diameter of the pigment particle or other insoluble material should be about 75 percent by volume of the core diameter as a 13 maximum for satisfactory encapsulation. There are simple relationships between particle diameter, core diameter, and wall thickness. In particular, the wall thickness is directly proportional to the particle diameter. Taking r as the core material to wall material volume ratio, X as the volume fraction of core material, d and d as the capsule diameter and the core diameter respectively, V and V as the total volume and core volume respectively, and W as the wall thickness; the wall thickness may be calculated as follows:

Thus, for a one to one core material to wall material volume ratio, W is equal to (d/2)(10.794) which is approximately equal to 0.1d. Commercially available carbon black pigments ranging in size from about 200 millimicrons in diameter down to about 20 millimicrons in average diameter are used to good effect in the formation of spray dried toners as described more fully in the examples which follow. By solubility or sorption considerations, the colorant may be directed to deposit in the core or shell material as disclosed above.

By controlling the amount of core and shell materials in solution, the particle size and amount of colorant in solution or suspension, and the size of the droplets formed in the drying process, the size of the final encapsulated particle produced after drying is completed may be controlled. For example, changing the atomizing spray speed without changing the solution concentration alters the particle size. This result is achieved because the amount of liquid solvent driven off by evaporation in each droplet of the same size will be substantially equal, thus leaving substantially an equal weight of core material and shell material to form the final encapsulated particle.

Generally, three methods of atomization are commonly employed in the industry; pressure nozzles, two-fluid nozzles, and centrifugal or spinning disks. For numerous applications in spray drying, centrifugal disk atomizers rarely plug, erosion is seldom serious and even when it does ocur, it seldom changes the operating characteristics of the atomizer, and a gravity or low pressure feed can usually be employed. Changes in particle size from the atomizer caused by changes in feed-stock characteristics or production rates can usually be compensated for by a change in disk speed. Power costs, particularly in comparison with two-fluid atomizers, are generally low. Therefore, this method of atomizaton, which is particularly suited to slurries, sludges, and high viscosity, thixotropic materials is employed in many commercial spray dryers available to the process industries. In general, the operation of centrifugal disks depends upon feeding a liquid, or semiliquid, to a rotating element from which it is thrown in a radical direction by centrifugal force. The high velocity of the liquid leaving the rotor plus the fact that it is diverging promotes disintegration of the liquid into small drops.

Spray drying is the preferred unit operation capable of performing the one step encapsulation process of this invention. Depending on the solvent or mixture of solvents employed, heating or cooling may or may not be required and any suitable atomization technique can be used to encapsulate core material within wall material. By way of illustration, a single phase solution of the core and shell materials is prepared wherein all of the substantially soluble portions of core and shell materials are in solution and then spray dried so that the relatively volatile solvent or mixture of solvents is volatilized and evaporated forming dry, finely divided encapsulated particles. Since the core material preferentially phase separates out of the spray dried solution in any one droplet to form the core 14 particle, the shell material will sequentially deposit around and encapsulate the core material.

In some cases, where the shell material may have a tendency to form separate homogeneous solid shell particles, such tendency may be reduced by changing the solvent system to alter the surface tension relationship and viscosities of the core material phase and the shell material phase so as to obtain a continuous shell-forming material solution around the core material. Thus, the encapsulation method of this invention is capable of producing large quantities of encapsulated material in the average size particle range of about 0.5 to about 1000 microns. Generally, the unit employed for atomizing and drying is a spray drier, for example, such as manufactured by the Bowen Engineering Corporation, North Branch, NJ. This unit is a laboratory size conical drier with concurrent air flow and has an interchangeable atomizing head mounted near the top of the drying chamber and fitted inside the drying air distributor ring. The atomizer most widely used in the following examples is of the spinning disk variety. This type of atomizer is preferred where, as here, a suspended pigment may be included in the liquid being atomized since other atomizing devices frequently erode during atomization under high speed friction with these solids.

Once the solution has been atomized to the proper droplet size, it moves through the drying air in the spray drying chamber until the solvent is driven off by evaporation leaving the core and shell materials in the form of a single spherically shaped particle with the core material encapsulated by the shell material. This evaporation is hastened by the high surface to mass ratio of the atomized droplets and the drying air. The time during which these droplets are held in suspension in the drying air is referred to as the dwell time. The maintenance of correct drying air temperature is important toefiective operation of the system because the drying air is required to drive off the solvent or mixture of solvents in each droplet by evaporation during the dwell time, while at the same time the particles must be cool enough as they leave the drying air chamber so that they are not tacky enough to stick to the sides of the collecting apparatus or to agglomerate in the collecting device. It is generally found that with most of the desirable encapsulated toner particles obtained this result may be achieved by maintaining an input drying air temperature which is just above the minimum required to effect evaporation of the solvent during the dwell time. This result is produced with polymer-solvent systems because evaporation of the solvent after the droplets make initial contact with the heated air tends to cool the droplets so that they are no longer tacky as they leave the drying chamber even when the initial drying air temperature would make them tacky. If one of the less voltatile solvents is employed, this result sometimes requires a longer dwell time for the droplets or the use of smaller droplets with higher solids concentrations so that the solvents will dry oif faster even with lower temperatures in the drying chamber. With most of the conventional thermoplastic resins which are employed in toners and which are intended for heat fusing or pressure fixing in electrostatographic imaging processes, the problem of excessive tack in toner particles leaving the drying chamber may be avoided by keeping the existing air at about F. for polystyrene shells or lower depending on the softening temperature of the resin. Where for some reason, a resin is employed which becomes tacky at low temperatures, for example, relatively close to room temperature, or where dwell time in the drying air chamber is so short as to require higher than average entry air temperatures, it may 'be desirable to quench the dried toner particles as they leave the drying chamber with a stream of cold air to reduce their taekiness and prevent their agglomeration and sticking in the collector. This step, however, is unusual and is not required with most of the conventional materials. The output of the spray drier is collected in a cyclone-type collector from which the final dried particles may be taken at the end of the process or continuously.

Further, it has also been found that in the practice of this invention, a vacuum may be employed as Well as any process which can vaporize a solution with or without the application of heat depending upon the volatility of the solvent system.

In accordance with the present invention, it is possible to microencapsulate a core material in a shell material by atomizing and drying a solution containing core and shell materials without any preliminary processing. This method can be used to microencapsulate a wide variety of shell materials by selecting the proper solvent or mixture of solvents. The method can be used with core materials which are normally liquid, semiliquid or solid and also where the core material comprises more than one substance and the shell material comprises more than one substance.

The invention is especially advantageous where the principal core and shell materials have similar solubilities, for example, where both are hydrophobic and mutually soluble in certain solvents. As discussed above, in U.S. Pat. 3,338,991 to Insalaco, encapsulation there requires the use of different solvents, that is, a solvent for the shell forming resin which is a nonsolvent for the core material. Also, in U.S. Pats. 2,800,457 and 2,800,458 to Green, the core and shell materials may not have similar solubilities or be mutually soluble in certain solvents. In a microencapsulation embodiment of this invention, the core and shell materials are in a homogeneous solution until after the solution is micronized and formed into droplets in the drying chamber. Therefore, there is no possibility of agglomeration occurring during storage or micronization of the dryer feed material. Also in accordance with the present invention, there is provided an improved method for the encapsulation of electrostatographic developer materials which is greatly simplified and is capable of producing electrostatographic toner particles with improved uniformity of particle size. In addition, it has been found that this method of electrostatographic toner production is capable of forming encapsulated electrostatographic toner of extremely small particle size. Both the uniformity of particle size and the fineness of particle size which may be achieved by this method of encapsulation have gone to produce encapsulated toners with extremely high resolution capabilities and which may be used in virtually any electrostatographic technique including those described above. The ultimate resolution capability of any electrostatographic imaging system is lmited by the largest toner particles which are included in the batch of electrostatographic toner being utilized to develop the electrostatic latent image regardless of the particular development technique employed. Thus, even when an optical system and electrostatographic plate are capable of producing extremely high resolution electrostatic latent images, the overall system resolution is destroyed if the latent image is developed with an electro statographic toner containing particles of a size substantially larger than the dimensions of any part of the latent image. Toner material produced according to these processes have been found to have a unique spherical shape with greatly enhanced developing capabilities especially in cascade systems Where the developer rolls across the plate during development. Accordingly, the encapsulation method of this invention is superior in many other respects for the production of high resolution electrostatographic toner. It provides economic efiiciency and simplicity in the production of encapsulated toners in a single step operation accomplishing the same result as in a conventional multistep, time consuming encapsulation process. It avoids agglomeration problems common to previously known encapsulation processes. It removes the restrictions imposed on the manufacture of toner materials by the pulverizing particle forming process. It is capable of producing extremely small particle size electrostatographic toner. Further, it significantly narrows the particle size range of the toner produced, thus, significantly reducing or completely eliminating any random particles of much larger than average size which might be included in an electrostatographic toner produced by conventional techniques. In addition, it permits the production of an electrostatographic toner which contains a liquid or tacky material which normally cannot be employed in conventional homogeneous toner particles.

This encapsulation method is applicable to any system where the core and shell materials can be made to phase separate sequentially from solution and to any application of microencapsulation where small particles such as are produced by spray drying are desired. The average size and the size distribution of the microcapsules can be varied by changing the atomizer and drying conditions in the same way, and over the same size range, as these are varied in atomizing and drying a solution with a single solute. Further, the process of this invention enables the production of encapsulated particles having various shell materials, for example, of a hydrophobic, lipophilic, or lipophobic nature.

The process of the present invention is particularly advantageous for the making of solid coated toner material which is in an extremely fine state of subdivision, for example, from about 0.5 to about 35 microns in diameter. The particular particle size is not critical to the process of the invention, but is determined by the use to which the coated particle is to be employed. For example, a micronized powder or finely dispersed liquid on the order of about 0.5 to about 10 micron size is desirable for vitamins and other food supplements, for substances to be incorporated into cosmetic formulations and for insecticides. A powdered material up to about 200 micron size is a desirable size for rodenticides.

The encapsulated products of the present invention find applications due to their unique properties in the formulation of compositions for widely diversified fields of use. In the cosmetic field, products such as soap bars, lotions and creams can be formulated containing encapsulated water soluble ingredients which would be unstable or incompatible in unencapsulated form in the presence of other ingredients of the particular formulation. For example, since certain antibacterials such as the chlorinated phenols and neomycin sulfate are incompatible on prolonged contact with soap, the present invention makes possible the formulation of a soap bar containing both of these ingredients.

In the agricultural field, encapsulated food supplements and medicaments can be advantageously formulated. For example, water soluble fertilizers such as ammonium nitrate, urea and superphosphate can be encapsulated for application to the soil when a slow release or extended action is desirable, e.g., where rapid release would burn the vegetation. For the control of pests, encapsulated insecticides can be deposited on vegetation or in the soil without harm to the vegetation; moreover, the insecticide is not dissolved and washed away by moisture or rain, thereby allowing the insecticide to remain where deposited until ingested by the insect. Antihelmintic agents such as piperazine phosphate or citrate, and methyl rosaniline chloride when encapsulated can be incorporated into feed material for domestic animals, the encapsulated antihelmintic thereby being tasteless in the feed and also protected from decomposition during storage of the feed. Rodenticides such as calcium cyanide, thallium sulfate and sodium fluoroacetate, which are unstable in the presence of moisture or have an odor or taste repellent to the rodent are advantageously encapsulated.

Vitamins, minerals, amino acids and other food supplements, when encapsulated can be incorporated in animal feeds and be protected from decomposition during storage periods from such adverse conditions as air, moisture, and incompatible ingredients in the feed composition itself.

17 In a similar manner, food supplements can be incorporated in compositions for human use.

The present invention finds application in medical treat ment of both animals and humans. Medicaments can be encapsulated by this method of the present invention to give a sustained release upon ingestion with resultant sustained therapeutic action. Coatings which will not dissolve in the stomach can be formulated to overcome the problem of gastric irritation or nausea caused by such medicaments as emetine hydrochloride, quinacrine hydrochloride and para-amino-salicylic acid. Similarly, medicaments such as penicillin and certain glandular extracts which are inactivated by the acid condition or enzymes encountered in the stomach are advantageously encapsulated DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples further define, describe and compare exemplary methods of preparing the encapsulated materials of the present invention. Parts and percentages are by weight unless otherwise indicated. The examples, other than the control examples, are intended to illustrate the various preferred embodiments of the present invention.

In the following examples, the term stick point means the temperature at which a material adheres to a metallic substrate; for example, a continuous line of sample is equilibrated on a K-ofier Hot Bench about 12 hours and then gently brushed away. The stick point is the lowest temperature at which the sample sticks to the metallic plate of the hot bench. Likewise, the term blocking tests refers to tests usually conducted on small open dishes of toner material at specific temperature conditions. The blocking temperature is determined as the lowest temperature to which the toner has been subjected for a period of equilibration and the crusty mass produced can no longer be easily broken down to the original particles. Also the term geometric standard deviation is the deviation encountered in a particle size analysis measured as the ratio of the particle diameter which accounts for 84% of the sample to the particle diameter at 50% of the sample.

Example I -A solution of about 90 grams of a polystyrene and about 180 gram-s of the reaction product of isopropylidenediphenoxypropanol and adipic acid having an average molecular weight of 4400 is prepared in a mixture of chloroform and heptane (121.3 chloroformzheptane volume ratio). A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 1.5 percent polystyrene, about 3.0 percent reaction product of isopropylidenediphenoxypropanol and adipic acid, about 0.5 percent carbon black, and about 95.0 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated, laboratory model 30 inch diameter spray dryer with a spinning disk atomizer operating at about 30,000 r.p.m. and a feed rate of about 100 ml./ minute. Drying air inlet temperature is about 110 F. and outlet air temperature is about 95 F. The dry product is a powder of about 10.6 micron diameter volume average particle size with a geometric standard deviation of about 1.51. Electron microscope examination of embedded and microtoned particles shows the individual particles to be primarily spherical and to have a pigmented core surrounded by a clear shell. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is polystyrene and the core principally the reaction product of isopropylidenediphenoxypropanol and adipic acid.

Example II A solution of about 94.9 grams of a polystyrene and about 142.3 grams of the reaction product of isopropylidenediphenoxypropanol and sebacic acid having an average molecular -Weight of 5650 is prepared in a mixture of cyclohex-ane and ethylene dichloride (2211.0 cyclohexane:ethylene dichloride volume ratio). -A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 1.4 percent polystyrene, about 2.0 percent reaction product of isopropylidenediphenoxypropanol and sebacic acid, about 0.2 percent carbon black, and about 96.4 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated laboratory model 30 inch diameter spray dryer with a spinning disk atomizer operating at about 50,000 r.p.m. and a feed rate of about 200 ml./minute. Drying air inlet temperature is about 135 -F. and outlet air temperature is about F. The dry product is a powder of about 7.9 micron diameter volume average particle size with a geometric standard deviation of about 1.75. Electron microscope examination shows the individual particles to be primarily spherical and to have a pigmented core surrounded by a clear shell. Stick point, blocking tests, and examination of crushed particles With the scanning electron microscope all indicate that the shell is polystyrene and the core principally the reaction product of isopropylidenediphenoxypropanol and sebacic acid.

Example III A solution of about 8716 grams of a polystyrene and about 8716 grams of the reaction product of isopropyl-idenediphenoxypropanol and adipic acid having an average molecular Weight of 9655 is prepared in a mixture of chloroform and heptane (121.3 chloroformzheptane volume ratio). A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 4.8 percent polystyrene, about 4.8 percent reaction product of isopropylidenediphenoxypropanol and adipic acid, about 0.5 percent carbon black, and about 89.9 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated, five foot diameter spray dryer with a spinning disk atomizer operating at about 21,000 r.p.m. and a feed rate of about 530 -ml./minute. Drying air inlet temperature is about 135 F. and outlet air temperature is about F. The dry product is a powder of about 14.7 micron diameter volume aver-age particle size with a geometric standard deviation of about 1.52. Electron microscope examination shows the individual particles to be primarily spherical and to have a pigmented core surrounded by a clear shell. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is polystyrene and the core principally the reaction product of isopropylidenediphen-- oxypropanol and adipic acid.

Example IV A solution of about 431 grams of a polystyrene and about 431 grams of the reaction product of isopropylidenediphenoxypropanol and adipic acid having an average molecular weight of 8560 is prepared in a mixture of chloroform and heptane (1:1.3 chloroformzhept-ane volume ratio). A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 4.8 percent polystyrene, about 4.8 percent reaction product of isopropylidenediphenoxyprop-anol and adipic acid, about 0.5 percent carbon black, and about 89.9 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated, laboratory model 30 inch diameter spray dryer with a spinning disk atomizer operating at about 50,000 r.p.m. and a feed rate of about 200 ml./minute. Drying air inlet temperature is about 157 F. and outlet air temperature is about 134 F. The dry product is a powder of about 14.1 micron diameter volume average particle size with a geometric standard deviation of about 1.56. Electron microscope examination shows the individual particles to be primarily spherical and to have a pigmented core surrounded by a clear shell. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is polystyrene and the core principally the reaction product of isopropylidenediphenoxypropanol and adipic acid.

Example V A solution of about 2156 grams of a polystyrene and about 2156 grams of the reaction product of isopropylidenediphenoxypropanol and adipic acid having an average molecular weight of 4200 is prepared in a mixture of chloroform and heptane (1:1.3 chloroformzheptane volume ratio). A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 4.8 percent polystyrene, about 4.8 percent reaction product of isopropylidenediphenoxypropanol and adipic acid, about 0.5 percent carbon black, and about 89.9 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated, laboratory model 30 inch diameter spray dryer with a spinning disk atomizer operating at about 50,000 r.p.m. and a feed rate of about 200 ml./minute. Drying air inlet temperature is about 145 F. and outlet air temperature is about 115 F. The dry product is a powder of about 12.9 micron diameter volume average particle size with a geometric standard deviation of about 1.53. Electron microscope examination shows the individual particles to be primarily spherical and to have a pigmented core surrounded by a clear shell. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is polystyrene and the core principally the reaction product of isopropylidenediphenoxypropanol and adipic acid.

Example VI A solution of about 400 grams of a polystyrene and about 400 grams of the reaction product of isopropylidenediphenoxypropanol and adipic acid having an average molecular weight of 6140 is prepared in chloroform. A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 3.4 percent polystyrene, about 3.4 percent reaction product of isopropylidenediphenoxypropanol and acipic acid, about 0.4 percent carbon black, and about 92.8 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated, laboratory model 30 inch diameter spray dryer with a spinning disk atomizer operating at about 50,000 rpm. and a feed rate of about 200 ml./minute. Drying air inlet temperature is about 240 F. and outlet air temperature is about 180 F. The dry product is a powder of about 12.9 micron diameter volume average particle size with a geometric: standard deviation of about 1.65. Electron microscope examination shows the individual particles to be primarily spherical and to have a pigmented core surrounded by a clear shell. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is polystyrene and the core principally the reaction product of isopropylidenediphenoxypropanol and adipic acid.

Example VII A solution of about 442.5 grams of a polystyrene and about 147.5 grams of hydroxy terminated polybutadiene (e.g., P'oly B-D, from Sinclair Petrochemicals, Incorporated) is prepared in a mixture of methylene chloride and acetone (1:1 methylene chloridezacetone). A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 3.4 percent polystyrene, about 1.1 percent of hydroxy terminated polybutadiene, about 0.5 percent carbon black, and about 95.0 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated, five foot diameter spray dryer with a spinning disk atomizer operating at about 21,000 rpm. and a feed rate of about 200 mL/minute. Drying air inlet temperature is about 146 F. and outlet air temperature is about 126 F. The dry product is a powder of about 15.5 micron diameter volume avearge particle size with a geometric standard deviation of about 1.60. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a pigmented shell. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is polystyrene and the core principally hydroxy terminated polybutadiene.

Example VIII A solution of about 200 grams of the reaction product of a dimer acid with a linear diamine (Emerez 1540, from Emery Industries, Incorporated) and about 200 grams of the reaction product of isopropylidenediphenoxypropanol and adipic acid having an average molecular weight of 4400 is prepared in a mixture of chloroform and isopropyl alcohol (1:2 chloroformzisopropyl alcohol volume ratio). A carbon black is dispersed in the solution by severe agitation. The final concentrations are about 4.8 percent reaction product of a dimer acid with a linear diamine, about 4.8 percent reaction product of isopropylidenediphenoxypropanol and adipic acid, about 0.5 percent carbon black, and about 90.0 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering Incorporated, laboratory model 30 inch diameter spray dryer with a spinning disk atomizer operating at about 50,000 rpm. and a feed rate of about 200 ml./minute. Drying air inlet temperature is about 151 F. and outlet air temperature is about 118 F. The dry product is a powder of about 11.6 micron diameter volume average particle size with a geometric standard deviation of about 1.56. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell with both core and shell containing pigment. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is the reaction product of a dimer acid with a linear diamine and the core principally the reaction product of isopropylidenediphenoxypropanol and adipic acid.

Example 1X A solution of about 118.7 grams of a polystyrene and about 118.7 grams of the reaction product of isopropylidenediphenoxypropanol and sebacic acid having an average molecular weight of 5650 is prepared in a mixture of cyclohexane and ethylene dichloride (2.2:1.0 cyclohexanezethylene dichloride) A carbon black is dispersed 111 the solution by severe agitation. The final concentrations are about 1.5 percent polystyrene, about 1.5 percent reaction product of isaopropylidenediphenoxypropanol and sebacic acid, about 0.3 percent carbon black, and about 96.7 percent solvent. The solution, with dispersed carbon black, is spray dried using a Bowen Engineering, Incorporated, five foot diameter spray dryer with a spinning disk atomizer operating at about 50,000 r.p.m. and a feed rate of about 200 ml./ minute. Drying air inlet temperature is about 137 F. and outlet air temperature is about F. The dry product is a powder of about 11.0 micron diameter volume average particle size with a geometric standard deviation of about 1.82. Electron microscope examination shows the individual particles to be primarily spherical and to have a pigmented core surrounded by a clear shell. Stick point, blocking tests, and examination of crushed particles with the scanning electron microscope all indicate that the shell is polystyrene and the core principally the reaction product of isopropylidenediphenoxypropanol and sebacic acid.

Example X A solution of about 10.0 grams of a polystyrene and and about 20.0 grams of a polyurethane elastomer (Estane 5701, from B. F. Goodrich) is prepared in a mixture of tetrahydrofuran and benzene (2:1 tetrahydrofuran: benzene volume ratio). The final concentrations are about 0.3 percent polystyrene, about 0.7 percent polyurethane elastomer, and about 99 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 37,000 r.p.m. and a feed rate of about 55 ml./ minute. Drying air temperature is about 77 F. The dry product is a powder of about 12.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is polystyrene and the core principally polyurethane elastomer.

Example XI A solution of about 15.0 grams of a polystyrene and about 15.0 grams of a polyurethane elastomer (Estane 5710, from B. F. Goodrich) is prepared in a mixture of tetrahydrofuran and benzene (2:1 tetrahydrofuranzbenzene volume ratio). The final concentrations are about 0.5 percent polystyrene, about 0.5 percent polyurethane elastomer, and about 2.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 33,000 r.p.m. and a feed rate of about 33 mL/minute. Drying air inlet temperature is about 104 F. The dry product is a powder of about 13.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is polystyrene and the core principally polyurethane elastomer.

Example XII A solution of about 10.0 grams of a polystyrene and about 20.0 grams of a polyurethane elastomer (Estane 5710, from B. F. Goodrich) is prepared in a mixture of tetrahydrofuran and benzene (2:1 tetrahydrofuranzbenzene volume ratio). The final concentrations are about 0.7 percent polystyrene, about 1.3 percent polyurethane elastomer, and about 98.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 24,000, r.p.m. and a feed rate of about 37 ml./minute. Dying air temperature is about 104 F. The dry product is a powder of about 18.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is polystyrene and the core principally polyurethane elastomer.

Example XIII A solution of about 5.0 grams of a copolymer of styrene and n-butyl methacrylate (about 65/35 percent by weight) and about 10.0 grams of a polyurethane elastomer (Estane 5701, from B. -F. Goodrich) is prepared in a mixture of tetrahydrofuran and benzene (2:1 tetrahydrofuranzbenzene volume ratio). The final concentrations are about 0.3 percent styrene and n-butyl methacrylate copolymer, about 0.7 percent polyurethane elastomer, and about 99.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 24,000 r.p.m. and a feed rate of about 35 mL/minute. Drying air temperature is about 86 F. The dry product is a powder of about 11.0 micron diameter volume av- 22 erage particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is styrene and n-butyl methacrylate copolymer and the core principally polyurethane elastomer.

Example XIV A solution of about 1.1 grams of a copolymer of styrene and n-butyl methacrylate (about 65/35 percent by weight) and about 10.0 grams of a polyurethane elastomer (Estane 5714, from B. F. Goodrich) is prepared in tetrahydrofuran. The final concentrations are about 0.2 percent styrene and n-butyl methacrylate copolymer, about 1.8 percent polyurethane elastomer, and about 98.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 33,000 r.p.m. Drying air inlet temperature is about 77 F. The dry product is a powder of about 9.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is styrene and n-butyl methacrylate copolymer and the core principally polyurethane elastomer.

Example XV A solution of about 1.0 grams of a copolymer of styrene and n-butyl methacrylate (about 65/35 percent by Weight) and about 4.0 grams of a polyurethane elastomer (Estane 5714, from B. F. Goodrich) is prepared in a mixture of tetrahydrofuran and hexane (3:2 tetrahydrofuranzhexane volume ratio). The final concentrations are about 0.2 percent syrene and n-butyl methacrylate copolymer, about 0.8 percent polyurethane elastomer, and about 99.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 33,000 r.p.m. Drying air inlet temperature is about 77 F. The dry product is a powder of about 8.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is styrene and n-butyl methacrylate copolymer and the core principally polyurethane elastomer.

Example XVI A solution of about 2.5 grams of a copolymer of styrene and n-butyl methacrylate (about 65/ 35 percent by weight) and about 5.0 grams of a polyurethane elastomer (Estane 5702, from B. F. Goodrich) is prepared in a mixture of tetrahydrofuran and benzene (3:1 tetrahydrofuran:benzene volume ratio). The final concentrations are about 0.3 percent styrene and n-butyl methacrylate copolymer, about 0.7 percent polyurethane elastomer, and about 99.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a pneumatic atomizer operating at about 40,000 r.p.m. Drying air inlet temperature is about 77 F. The dry product is a powder of about 3.0 micron diameter volume average particle size. 'Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests,

and examination of crushed particles with an optical and Example XVII A solution of about 5.0 grams of poly-(4,4"-dioxyphenyl 2,2 propane carbonate) (Lexan 101, GB. Company) and about 5.0 grams of a polyurethane elastomer (Estane 5701, from B. F. Goodrich) is prepared in a mixture of chloroform and tetrahydrofuran (:1 chloroform:tetrahydrofuran volume ratio). The final concentrations are about 0.5 percent poly-(4,4'-dioxyphenyl-2,2-propane carbonate), about 0.5 percent polyurethane elastomer, and about 99.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 33,000 r.p.m. Drying air inlet temperature is about 70 F. The dry product is a powder of about 11.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is poly- (4,4-dioxyphenyl-2,2'-propane carbonate), and the core principally polyurethane elastomer.

Example XVIII A solution of about 3.0 grams of a poly-(4,4'-dioxyphenyl-2,2-propane carbonate) (Lexan 101, GB. Company), about 10.0 grams of a polyurethane elastomer (Estane 5701, from B. F. Goodrich) is prepared in a mixture of chloroform and tetrahydrofuran (2:1 chloroformttetrahydrofuran volume ratio). The final concentrations are about 0.5 percent poly-(4,4-dioxyphenyl-2,2'- propane carbonate), about 1.5 percent polyurethane elastomer, and about 98.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 33,000 r.p.m. Drying air inlet temperature is about 70 F. The dry product is a powder of about 12.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed par ticles with an optical and a scanning electron microscope all indicate that the shell is poly-(4,4-dioxyphenyl-2,2- propane carbonate) and the core principally polyurethane elastomer.

Example XIX A solution of about 3.5 grams of a polystyrene, about 5.0 grams of a polyurethane elastomer (Estane 5701, from B. F. Goodrich) and about 1.5 grams of a polyester (Epon 872 from Shell Chemical Company) is prepared in a mixture of tetrahydrofuran and benzene (2:1 tetrahydrofuranzbenzene volume ratio). The final concentrations are about 1.7 percent polystyrene, about 2.5 percent polyurethane elastomer, about 0.8 percent of polyester and about 95.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 24,000 r.p.m. and a feed rate of about 15 ml./minute. Drying air temperature is about 96 F. The dry product is a powder of about 10.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is polystyrene and the core principally polyurethane elastomer and polyester.

Example XX A solution of about 6.5 grams of a polystyrene, about 5.0 grams of a polyurethane elastomer (Estane 5701, from B. F. Goodrich) and about 1.5 grams of a polyester (Epon 872 from Shell Chemical Company) is prepared in a mixture of tetrahydrofuran and benzene (2:1 tetrahydrofuranzbenzene volume ratio). The final concentrations are about 0.5 percent polystyrene, about 0.4 percent polyurethane elastomer, about 0.1 percent of polyester and about 99.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 24,000 r.p.m. and a feed rate of about 20 ml./minute. Drying air temperature is about 104 F. The dry product is a powder of about 12.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is polystyrene and the core principally polyurethane elastomer and polyester.

Example XXI A solution of about 5.0 grams of a polystyrene and about 5.0 grams of a C di-urea is prepared in a mixture of benzene and dimethylformamide (9:1 benzene:dimethylforrnamide volume ratio). The final concentrations are about 0.5 percent polystyrene, about 0.5 percent C di-urea, and about 99.0 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 34,000 r.p.m. and a feed rate of about 40 ml./minute. Drying air temperature is about 122 F. The dry product is a powder of about 15.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of eushed particles with an optical and a scanning electron microscope all indicate that the shell is polystyrene and the core principally C di-urea.

Example XXII A solution of about 10.3 grams of a polystyrene and about 1.1 grams of a polyacetaldehyde is prepared in chlorobenzene with a minute quantity of benzophenone. The final concentrations are about 4.5 percent polystyrene, about 0.5 percent polyacetaldehyde., and about percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 24,000 r.p.m. and a feed rate of about 5 ml./minute. Drying air temperature is about 104 F. The dry product is a powder of about 14.0 micron diameter volume average particle size. Electron microscope examination shows the individual particles to he primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is polystyrene and the core principally polyacetaldehyde.

Example XXIII A solution of about 1.0 grams of a copolymer of sty rene and n-butyl methacrylate (about 65/35 percent by weight) and about 5.0 grams of a silicone gum (W 981 from Union Carbide) with about 1 percent benzoyl peroxide is prepared in a mixture of hexane, ethyl acetate, and toluene (50:31:1 hexanezethyl acetateztoluene volume ratio). The final concentrations are about 0.3 percent styrene and n-butyl methacrylate copolymer, about 1.2 percent silicone gum, about 0.01 percent benzoyl peroxide and about 98.5 percent solvent. The solution is spray dried using a laboratory 12 inch diameter spray dryer with a spinning cup atomizer operating at about 33,000 r.p.m. Drying air inlet temperature is about 77 F. Cooling during drying is induced to promote primary separation of the silicone gum core material. Electron microscope examination shows the individual particles to be primarily spherical and to have a core surrounded by a shell. Stick point, blocking tests, and examination of crushed particles with an optical and a scanning electron microscope all indicate that the shell is styrene and n-butyl methacrylate copolymer and the core principally silicone gum.

Although specific materials and conditions are set forth in the above exemplary processes of making the encapsulated materials of this invention, these are merely intended as illustrations of the present invention. There are other wall materials, core materials, solvents, substituents and processes such as those listed above which may be substituted for those in the Examples with similar results.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A process for encapsulating the substantially soluble portion of a core material in a substantially soluble portion of a shell material having a solubility different from said core material comprising:

(a) dissolving said core material and said shell material in a mixture of two solvents to form a singlephase solution of said core material and said shell material wherein one solvent of said mixture of two solvents is a non-solvent for the core material and is capable of being sufiiciently concentrated by evaporation during a drying process to cause phase separation of said core material prior to deposition of said shell material, said solvent mixture remaining a solvent for said shell material during the drying process; said core material comprises the polymeric reaction product of isopropylidenediphenoxypropanol and adipic acid, said shell material comprises the reaction product of a dimer acid and a linear diamine, and said mixture of two solvents comprises chloroform and isopropanol;

(b) forming small individual droplets of said singlephase solution;

(c) removing at least a portion of said mixture of two solvents from said droplets by spray drying said solution whereby said core material and said shell material sequentially phase separate respectively; and

(d) removing additional portions of said mixture of two solvents from said droplets whereby said shell material deposits around said core material to form substantially dry, small spherical particles comprising said core material encapsulated with said shell material.

2. A process for encapsulating the substantially soluble portion of a core material in a substantially soluble portion of a shell material having a solubility different from said core material comprising:

(a) dissolving said core material and shell material in a mutual sol-vent mixture to form a single-phase solution of said core material and said shell material wherein said mutual solvent mixture becomes a nonsolvent first for said core material and subsequently a non-solvent for said shell material during a drying .process wherein a core material forming phase a shell material forming phase, and a solvent phase co-exist during the final stages of said solvent removal, said core material comprises the polymeric reaction product of isopropylidene-diphenoxypropanol and adipic acid, said shell material comprises polystyrene, and said solvent mixture comprises chloroform and heptane;

(b) forming small individual droplets of said singlephase solution;

(c) removing at least a portion of said mutual solvent mixture from said droplets by spray drying said solution whereby said core material and said shell material sequentially phase separate respectively; and

(d) removing additional solvent from said dropletswhereby said shell material deposits around said core material to form substantially dry, small spherical particles comprising said core material encapsulated with said shell material. a

References Cited UNITED STATES PATENTS RICHARD D. LOVERING, Primary Examiner US. Cl. X.R.

106-308 F, 308 M, 308 N; 117-100 A, B, 100 C; 252-621, 363.5, 364; 2644 "M050 UNITED STATES PATENT OFFICE CERTIFICATE" OF CORRECTION t Russell E; Wellman It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Ih the Abstract, line 16, following "one" please delete "system" and substitute therefore, "embodi-".

Column 1-, line 45, following "Pat. and preceding "involves" please delete "2,2997,69l," and substitute therefore, "2, 297, 691,

Signed and sea led this 19th day of November 9W4.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents @3 3 UNITED STATES PATENT OFFICE CERTIFICATE" OF CORRECTION Patent No. 3,830, 750 Dated August 20, 1974 fi fl Russell E. Wellman It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 16, following "one" please delete "system" and substitute therefore, "embodi"..

Column 1, line 45, following "Pat. and preceding "involves" please delete "2,2997,69l," and substitute therefore," 2, 297, 691,

Signed and sealed this 19th day of November 97 (SEAL) Attest: I

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents