IL30513A - Microencapsulation process and pressure sensitive transfer sheets coated with the capsules obtained - Google Patents

Description

nT73pnon moiaaa o^Bison MICROENCABSULATION PROCESS AND PRESSURE SENSITIVE TRANSFER SHEETS COATED WITH THE CAPSULES OBTAINED M2671+ This invention relates to the microencapsulation of oils. More specifically, this invention pertains to processes for encapsulating minute oil droplets, to microcapsules produced thereby, and to the use thereof in pressure-responsive, transfer-copy systems.

For about the last ten years, microcapsules containing both liquid and solid nucleus materials have found widespread acceptance in a variety of commercial applications. For example, one of the most widespread uses has been in the art of transfer-copy systems wherein minute droplets of a colorless dye intermediate dispersed or dissolved in an oil are encapsulated and coated onto a transfer sheet. The dye intermediate is thereafter transferred to a copy sheet by rupturing said capsules. The underlying copy sheet has an adsorbent coating thereon containing a material which will react with the' dye intermediate- causing a visible colored mark at point where the microcapsules have been ruptured and the dye transferred. Other recent applications in which microcapsules have been used extensively are in adhesives and adhesive tapes, fertilizers, pharmaceuticals, foods and cosmetics. In the majority of these applications, microencapsulation involves the "coacervation" phenomenon.

Coacervation is the term applied to the ability of a number of aqueous solutions of colloids, to separate into two liquid layers, one rich in colloid solute and the other poor in colloid solute. Factors which influence this liquid-liquid phase separation are: (a) the colloid concentration, (b) the solvent of the system, (c) the temperature, (d) the addition of another polyelectrolyte, and (e) the addition of a simple electrolyte to the solution.

A unique property of coacervation systems is the fact that the solvent components of the two phases are the same chemical species. This is a major distinguishing characteristic of coacervates as compared to two phase systems involving two immiscible liquids. Thus, a colloidal solute particle migrating across the interface of a two-phase coacer vate system finds itself in essentially the same environment on either side of the interface. From the viewpoint of composition, the difference between the two phases is a differ-? ence; in concentration of solute species. Structurally, the two phases differ in that the colloidal solute of the colloid poor phase is randomly oriented and the colloidal solute of the coacervate or colloid-rich phase shows a great deal of order. In all cases where coacervation has been observed, the solute species are geometrically anisotropic particles.

Coacervation can be of two general types. The first is called "simple" or "salt" coacervation where liquid phase separation occurs by the addition of a simple electrolyte to a colloidal solution. The second is termed "complex" coacervation where phase separation occurs by the addition of a second colloidal species to a first colloidal solution, the particles of the two dispersed colloids being oppositely charged. Generally, materials capable of exhibiting an electric charge in solution (i.e. materials which possess an ionizable group) are coacervatable. Such materials include natural and synthetic micromolecular species such as gelatin, acacia, tragacanth, styrene-maleic anhydride copolymers, methyl vinyl ether-maleic anhydride copolymers, polymeth-acrylic acid, and the like.

With both simple and complex coacervate systems, a necessary precondition for coacervation is the reduction of the charge density of the colloidal species. In the case of simple coacervation, this reduction of the charge density along with partial desolvation of the colloidal species is similar to that preceding the flocculation or precipitation of a colloid with the addition of a simple electrolyte since it is known that the addition of more electrolyte to a simple coacervate leads to a shrinking of the colloid-rich layer and the subsequent precipitation of the colloidal species. This same reduction of charge density along with partial desolva-tion of the colloidal species which precedes the precipitation of two oppositely charged colloids from solution may also be regarded to be the cause for the phase separation in a complex coacervate system. However, while the reduction of the charge density is a necessary precondition for coacervation, it is oftentimes not sufficient for coacervation. In other words, the reduction of the charge density on the colloidal particles must alter or modify the solute-solute inter-; actions to such an extent that the colloidal particles will tend to aggregate and form a distinct, continuous liquid phase rather than a flocculant or a solid phase. This tendency is attributable to both coulombic and long-range Van der Waal's interactions of large aggregates in solution. Thus, in both "simple" and "complex" coacervation, two-solution phase formation begins with the colloidal species aggregating to form submicroscopic clustersj these clusters coalesce to form microscopic droplets. Further coalescense produces microscopic droplets which tend to separate into a continuous phase. This phase appears as a top of bottom layer depending upon the relative density of the two layers.

If, prior to the initiation of coacervation, a water-immiscible material , such as an oil is dispersed as minute droplets in an aqueous solution or sol of an encapsulating colloidal material , and then, a simple electrolyte, such as sodium sulfate, or another, oppositely charged colloidal species is added to induce coacervation, the encapsulating colloidal material forms around each oil droplet, thus investing each of said droplets in liquid coating of the coacervated colloid. The liquid coatings which surround the oil droplets must thereafter be hardened to produce solid-walled microcapsules.

In contrast to the present invention, one of the primary disadvantages of the coacervation encapsulation techniques is the fact that critical control over the concentrations of the colloidal material and the coacervation initiator must be maintained. That is, coacervation will occur only within a limited range of pH, colloid concentration and/or electrolyte concentration. For example, in simple coacervation, if a deficiency of, the electrolyte is added, two-phase formation will not occur; whereas, if an excess is added, the colloid will precipitate ■ as a lumpy mass. With complex coacervation systems using a colloid having an iso-electric point, pH is especially important since the pH must be adjusted and maintained at a point where both colloids have opposite charges. In addition, when a gelable colloid, such as gelatin, is used as the encapsulating material, coacervation must take place at a temperature above the gel point of the colloid.

It is therefore, the object of this invention to provide a process for the microencapsulation of oils which is devoid of the coacervation phenomenon and the disadvantages inherent therewith.

It is another object of this invention to provide oil-containing microcapsules without the necessity for a strict control of the pH of the system or the electrical charge on a colloidal species to permit formation of microcapsules.

It is still another object of this invention to provide oil-containing microcapsules without the necessity for a particular electrolytic concentration or a coacervating agent .

It is yet another object of this invention to provide oil-containing microcapsules comprising walls of either nongelable or gelable colloids.

It is another object of this invention to provide a pressure-sensitive and responsive transfer sheet record material comprising a coating of microcapsules applied to one side of a web material, said microcapsules containing a colorless leuco dye intermediate dispersed or dissolved in an oil and said microcapsules having been prepared by the process of this invention.

These and other objects and features of this invention will become apparent from the following description of the invention and the accompanying drawings. ^ The aspects of this invention which are capable of illustration are shown in the accompanying drawings wherein: Figures 1 and 2 are flow diagrams, which outline the steps of alternative encapsulation processes of this invention.

Figure 3 is a cross-sectional view on an enlarged scale of a portion of a transfer sheet embodying the present invention.

According to the present invention, a process is provided for the formation of microcapsules in the absence of coacervation, which process, in general, includes forming a primary oil-in-water emulsion, which emulsion comprises a water-immiscible oily material dispersed in the form of microscopic droplets in a colloidal solution of one or more emulsifying agents, said oily material and said emulsifying agent or agents having about the same hydrophilic-lipophilic balance (HLB), and at least one of the said emulsifying agents possessing groups capable of reacting with a cross-linking or complexing agent to form an impermeable coating around said dispersed microscopic droplet, when the emulsification is complete. A cross-linking or complexing agent is slowly added to the emulsion with brisk agitation, and this is continued until the final microcapsules are formed. The emulsion containing the microcapsules may be directly coated onto a web material, or, alternatively, the microcapsules may be separated from the emulsion by physical means, such as filtration or centrifugation, washed to remove any excess oil and, if desired, the microcapsules may be redispersed in a solution of a binder and coated onto a web material.

By "water immiscible oily materials" is meant lipophilic materials which are preferably liquid, such as oils, which will not mix with water and which are inert with regard to the components of the particular system. Low melting fats and waxes may also be used in this invention. However, oils are the preferred nucleus materials since they do not require temperature maintenance. In certain embodiments of this in- vention, the vapor pressure and viscosity of the oily material are to be considered. For example, in the art of making a transfer sheet record material, a low viscosity-low vapor pressure oil is preferred. The viscosity of the oily medium is a determining factor in the speed with which the markings can be transferred to the copy sheet since low viscosity oils will transfer more quickly than oils of higher viscosity.

The vapor pressure should be sufficiently low to avoid substantial losses of the oil through evaporation during the encapsulation operation. A compromise should, therefore, be made in selecting an oil of medium viscosity which will have a reasonable rate of transfer onto the copy sheet and of reasonably low volatility.

In general, the lipophilic mucleus materials can be natural or synthetic oils, fats and waxes or any combination thereof which will meet the requirements of the use for which the microcapsules are intended. Among the materials which can be used are: natural oils, such as cottonseed oil, castor oil, soybean oil, petroleum lubricating oils, fish liver oils, drying oils and essential oilsj synthetic oils, such as methyl salicylate and halogenated biphenyls; low melting fats, such as lard, and liquid or low melting waxes, such as sperm oil and lanolin (wool wax) .

Within the scope of the present invention, the herein-disclosed processes may be used to encapsulate an oil alone, or alternatively, the oil may serve merely as a vehicle for carrying another active ingredient or material. In this latter utility, the active material may be dissolved, dispersed or suspended in the oily material. The processes of this invention can, therefore, be used to encapsulate me- dicines, poisons, foods, cosmetics, adhesives or any other material which finds utility in microcapsular form.

In the preferred utility of this invention, viz., transfer sheet record material, these processes may be used to encapsulate an oily printing ink, such as may be used in smudge-proof typewriter ribbons or carbon papers. In such a use, it has been found expedient to encapsulate a colorless, water-insoluble leuco dye intermediate dissolved in the oil, thus avoiding the necessity of removing the residual colored matter from the external surfaces of the capsules prior to coating as is required in the encapsulation of printing inks. Colorless leuco dye intermediates are wholly conventional in such utilities and are well known in the art. Exemplary of the colorless dye intermediates which have been contemplated for use in this invention are leuco dyes, such as, crystal violet lactone and derivatives of bis(p-dialkylaminoaryl) methane such as disclosed in Kranz' United States Patents Nos. 2,981,733 and 2,981,738 both issued April 25, 196l. These dye intermediates are colorless in an alkaline medium and react to form a visible color in an acidic medium. Thus, when a capsule containing such a compound is ruptured and the compound is discharged onto an adsorbent, acidic electron-acceptor material, such as a paper web coated with an organic or an inorganic acid material, a visible color appears on the adsorbent material at the point of contact.

Inhibitors may optionally be dispersed in the oily material along with the dye intermediates. Such materials are helpful in preventing the light and heat degradation of the intermediates during the encapsulation procedure, especially when elevated temperatures are required, such as when a fat is encapsulated. Inhibitors are also considered to aid in the stabilization of the colored marking on the copy sheet against the effects of the atmosphere. A small amount (generally about 1 to 10% by weight of the dye) of an inhibitor, such as N-phenyl 2-naphthylamine, has been used in the practice of this invention.

The leuco dye intermediates which are mentioned above are, in general, oil soluble. Oils which are inert with respect to the dye and in which the dye has appreciable solubility, e.g. above 0.5 grams of dye per 100 grams of oil, are preferable .

The encapsulating material of this invention which encloses the microscopic oil droplets is an emulsifying agent which broadly, has two main characteristics: (1) it possesses reactive groups capable of reacting with a cross-linking or complexing agent to form an impermeable coating about the microscopic oil droplets; and (2) it has an HLB balance similar to that of the oil employed. The encapsulating material may also be an emulsifying agent which is self-complexing or self cross-linking. In such a case the addition of a different cross-linking or complexing agent is unneccesary. Exemplary of emulsifying agents having the aforesaid characteristics which permit their employment in the instant invention are : naturally-occurring, colloids including gums, proteins and polysaccharides, such as gum tragacanth, guar gums and gelatinj and synthetic materials such as polyvinyl alcohol and copolymers of methyl vinyl ether and maleic anhydride. Suitable copolymers of methyl vinyl ether and maleic anhydride are commercially available from the General Aniline and Film Corporation and are sold under the trademark "Gantrez". These The above list comprises both gellable and non-gellable emulsifying agents, e.g. gelatin and polyvinyl alcohol. Emulsifying agents which are self cross-linking or self-complexing include certain derivatives of guar gum, such as those which are commercially available from Stein, Hall and Company sold under the trademark "Jaguar". These materials are natural hydrophilic colloids that are produced by the extraction of guar gum from the endosperm portion of eyamopsis tetragonal-obus seeds and are comprised of a straight chain mannan made up of many manose and glactose units linked together.

Certain of the emulsifying agents of the type described above give an acidic solution when dissolved in water. Additionally, the complexing of two emulsifying agents may result in an acidic pH. When such materials are utilized to encapsulate an oily material containing a leuco dye intermediate, a color would ordinarily be produced, since these dye intermediates react in an acid medium. To prevent such premature reaction, a basic species or buffer may be incorporated in the emulsion system (usually in the water) in order to maintain a pH of the system, even when the emulsifying agent or agents do not result in an acid solution, as this will prevent an undesired or premature reaction of the dye intermediate by exposure to atmospheric conditions, e.g. carbon dioxide adsorption from the atmosphere.

Suitable buffer systems include base-inorganic salt combinations, such as sodium hydroxide-sodium borate deca-hydrate, while a preferred buffering agent is sodium carbonate, alone. The amount of buffering agent is comparatively quite small and is only the amount sufficient to prevent a premature acid reaction of the dye intermediate. In general, from 0.05 to 0.1 gram-equivalents of the material per 3 grams of dye such as sodium carbonate will suffice for such purposes. Such a material in the prescribed amounts does not interfere with the color reaction of the dye intermediates once they have been transferred to a copy sheet containing an electron-acceptor adsorbent material. Ordinarily, a buffer system need not be employed when the encapsulated material is not acid reactive.

The cross-linking or complexing agents employed with the aforesaid emulsifying agents are selected from three broad categories: (1) monomeric organic compounds, such as the alde^hydes, e.g. formaldehyde, glyoxal and other formaldehyde donors, trioxane ethanolamine, and ethylene diamine; (2) ordinary inorganic compounds, such as sodium borate and boric acid; and (3) mac omolecular species, such as gelatin, glfum tragacanth, and methylcellulose .

While some of the cross-linking or complexing agents are suitable for use with a plurality -of emulsifying agents, others are not. Thus, the preferred cross-linking or complexing agent-emulsifying agent pairs include: (1) gelatin with an aldehyde, such as formaldehyde; (2) polyvinyl alcohol with sodium borate; (3) copolymers of methyl vinyl ether and maleic anhydride with any one of gelatin, gum tragacanth, ethanolamine, ethylene diamine, polyvinyl alcohol; (4) guar gum derivatives with any one of sodium borate or methylcellulosej (5) self-complexing guar gum derivatives with themselves.

The cross-linking or complexing agent is utilized in amounts sufficient to result in the formation of microcapsules. The relative amounts very with the particular system, and may be easily determined in each case.

As previously mentioned, the selected emulsifying agent or combination of emulsifying agents must have a hydro-phil-lipophil balance (HLB) similar to that of the oil used. Based on experimental data, most of the common oils and emulsifying agents have ascribed HLB values (See Remington1 s Practice of Pharmacy, 11th edition, Mack Publishing Company, 1956, at page 191* the disclosure of which is incorporated herein by reference). Thus, by using these figures, the emulsifying agent or combination of emulsifying agents can be selected to match the HLB value of the particular oil utilized. If the HLB value for the emulsifying agent(s) is dissimilar to that of the oil, an unstable oil-in-water emulsion results and encapsulation is prevented. For example, an emulsifying agent having an HLB value approximating 10 is necessary to form a stable emulsion of light petrolatum in water. As the HLB value for the selected emulsifying agents proceeds downwardly to about 4, this oil-in-water emulsion tends to become more unstable and will ultimately invert to a water-in-oil emulsion.

The HLB of blends of two or more emulsifying agents can be calculated by proportion. However, in such combinations, certain antagonisms are evidenced within single classes of emulsifiers. For example, when an aqueous, colloidal dispersion of pigskin gelatin (at a lowered pH) and agar is prepared, a flocculent precipitate having the nature of a coacervate is formed. This formation can be explained by the phenomenon of coacervation since agar is always a negatively charged colloid and gelatin, at a pH below its isoelectric point (which is about pH 9), is highly positive. It follows, therefore, that the gelatin-agar dispersion will be compatible when in an alkaline medium, i.e., when gelatin is above its iso-electric point. Similarly, gelatin is compatible (for the purposes of this invention) with copolymers of methyl vinyl ether and maleic anhydride, which copolymer formes a negatively charged colloid, when the gelatin is at a pH above its iso-electric point, i.e. a negatively charged colloid.

In the case where the HLB balance of the oily material has to be matched by a combination of two or more emulsifying agents, it is only necessary that at least one of the emulsifying agents be capable of cross-linking or complexing with the added cross-linking or complexing agent.

Figures 1 and 2 of the attached drawings illustrate two processes for the microencapsulation of oily materials. In the process shown in the flow sheet of Figure 1, a primary oil-in-water emulsion is prepared by dissolving the emulsifying agent or combination of agents with the desired HLB value in the oily material and subsequently added water to emulsify.

The water may be added to the emulsifying agent-oil mixture either quickly or slowly with agitation. If the water is added slowly to the oil phase containing the emulsifying agent or agents, a water-in-oil emulsion formed, which eventually is inverted to an oil-in-water emulsion with the further addition of water. Such an inversion step results in a more stable emulsion with some systems, e.g. a methyl cellulose-guar gum derivative system.

The ultimate size of the microcapsules is dependent upon the speed of the mixing during the emulsification process. Higher mixing speeds will break up the oil phase of the emulsion into smaller droplets and thereby produce smaller capsules. In some instances, such as when a water-insoluble leuco dye intermediate is dissolved in the oily material and the resulting microcapsules are to be utilized in producing transfer sheet record material, the smaller capsules are preferred since they can be packed more closely in each other When the capsules are closely packed, a more uniform marking results (i.e. less discontinuity is obtained) when the microcapsules are ruptured. Microcapsules having diameters ranging from 0.1 to several hundred microns can be produced by the process of this invention. However, capsules having diameters in the range of 0.5 to 5·0 microns are preferred for transfer copy systems.

The temperature of emulsification may be varied over a broad range. The temperature must be kept above the gelling point of the emulsifying agent or agents only if a gelable emulsifying agent is used. Therefore, when a non-gelable emulsifying agent is used, e.g. polyvinyl alcohol, the temperature during emulsification can be varied appreciab ly without altering the final desired results. Of course, such variation must be kept within reasonable limits, so as not to influence the solubilities of the emulsifying agent, encapsulated material, e.g. a dye intermediate, etc., to an undue extent.

Subseuqent to the emulsification process, the cross linking or complexing agent is added to the oil-in-water emul sion, slowly, and with brisk agitation to form the final microcapsules. Agitation may be achieved by means of a high speed mixer or impeller, by ultrasonic waves or by other conventional means.

If the emulsifying agent is of the self-complexing variety, e.g. a self-complexing guar gum derivative, the cross-linking or complexing agent comprises the same material as the emulsifying agent.

Alternatively, the emulsion containing the microcapsules may be either coated directly onto a web material and dried or the microcapsules may be separated from the emul sion by some physical means such as filtration or centrifuga-tionj washed to remove any excess oilj redispersed in a solution of a binders coated onto a web material and dried.

Suitable binders include methyl cellulose, starch, casein, polyvinyl alcohol, synthetic latex, and styrene-butadiene rubber. Alternatively, materials such as urea-formaldehyde or melamine-formaldehyde condensates may be employed.

In the encapsulation process illustrated in Figure 2, the oil-in-water emulsion is prepared by dissolving the emulsifying agent (or agents) with the proper HLB in water and subsequently adding the oily material to the water solution with agitation until complete emulsification has occurred. The emulsion may then be diluted with water to give the desired viscosity suitable for coating. Care must be taken not to utilize too large an excess of water when a transfer copy system is desired or the concentration of microcapsules will be reduced and the intensity of the markings produced will be lowered since there will be fewer capsules per unit area to be broken. Capsule diameters suitable for transfer copy systems, i.e. within the 0.5 to 5·0 micron range, are likewise obtainable by the process of Figure 2 by adding cross-linking or complexing agents with agitation as previous ly described.

Figure 3 represents a cross-sectional view of a portion of a transfer sheet record material according to the practice of the present invention wherein a paper web material 10 contains a substantially uniform coating of microcapsules 12, each of which invests an oil which contains a colorless leuco dye intermediate. The binding agent used to secure the microcapsular coating to the paper web is not shown.

The microencapsulated oils of this invention are suitable for use in the manufacture of transfer sheet record material. More specifically, capsules containing a leuco dye intermediate in the oil are to be coated onto one side of a web material and dried. The coating operation is performed by conventional means, such as by use of an air knife. The capsule coatings are dried at temperatures ranging from about 40 to 75° C. At these temperatures, no appreciable degradation of the capsules, and in particular, the leuco dye intermediate, takes place.

The web material commonly used in transfer sheet record material is paper and is, therefore, preferable in the practice of this invention. However, the microcapsules produced by the herein disclosed processes are also capable of being coated onto other materials such as plastic and fabric or textile webs. When using a web material having a high degree of porosity, it is advisable to pre-coat the web with a material which will reduce seepage of the microcapsular coating through the web. Impregnating the web material with polyvinyl alcohol or a butadiene-styrene latex is the conventional practice for producing an essentially impervious substrate .

Transfer sheets according to the various embodiments of this invention have a pleasant appearance and are almost completely smudge-proof when brought into face-to-face contact with a copy sheet containing a coating of an adsorbent electron-acceptor material. In additipn, they showed a marked improvement over the transfer sheets presently available in commerce . It has been found that coated paper comprising microcapsules which contain a leuco dye intermediate dissolved in the oil and which microcapsules are formed by the process of this invention are extremely stable. For example, exposure of the coated papers to direct sunlight for five hours, to a temperature of 65° C. for ΐβ hours, and to a temperature of βθ° C. for 17 hours in a 90$ relative humidity environment does not alter either the pleasant appearance or the transfer and color-forming properties of the paper.

The following examples illustrate the best modes contemplated for carrying out this invention: EXAMPLE 1 A primary oil-in-water emulsion is formed by adding 50 milliliters of cottonseed oil containing 2 grams of 1- >bis(p-dimethylaminophenyl)methyl7-pyrrolidine (a leuco aura-mine dye intermediate) to ten grams of a purified gelatin having an HLB similar to that of the oil which is dissolved in 100 grams of water containing 5 milliliters 5N Na CX solution (for the prevention of a premature reaction of the dye intermediate) at a temperature of about 50° C, over a period of 20 to 30 minutes. Subsequently, 100 milliliters of a 1M formaldehyde solution in water are slowly added to the emulsion with brisk agitation followed by the addition of 50 milliliters of water. The addition of the formaldehyde results in the formation of well-defined microcapsules.

The microcapsules are then filtered, washed with successive 50 milliliter portions of water, methanol and formalin solution, and redispersed in 100 milliliters of water containing grams of a binding agent comprising methyl cellulose. The solution of methyl cellulose cotaining the microcapsules is coated onto a paper web and dried at 50-600 C.

The following examples illustrate the employment of a non-gelable emulsifying agent in the process of this invention.

EXAMPLE 2 One hundred grams of water, containing 5 grams of polyvinyl alcohol and 5 milliliters of 5N Na CX^ are emulsified with 35 milliliters of cottonseed oil (containing 1 gram of l- bis(p-dimethylaminophenyl)methyl7-pyrrolidine) for a period of 20 to 30 minutes. One hundred and fifty milliliters of a 1M sodium borate decahydrate solution are slowly added to the emulsion with brisk agitation, resulting in the formation of microcapsules which can be seen under an ordinary microscope. The emulsion containing the microcapsules is coated onto a paper web and dried at between 50 and 6o° C.

EXAMPLE Cne hundred grams of water containing 5 grams of methyl cellulose are emulsified with 25 grams of cottonseed, oil (containing 1 gram of l-^bis(p-dimethylaminophenyl)meth-yl7-pyrrolidine) . Ten grams of Gantrez-139 (a copolymer of methyl vinyl ether and maleic anhydride) are added to the emulsion and emulsification is allowed to proceed for an additional 10 to 15 minutes. Subsequently, 10 milliliters of ethylene diamine are slowly added with brisk agitation, resulting in the formation of well-defined microcapsules (seen under an ordinary microscope). The viscosity of the above emulsion, containing the microcapsules is further regulated with additional water (between 50 and 60 milliliters of water) prior to coating the emulsion onto a paper web and dried at about 50 to 60° C.

The following Example illustrates the utilization of the inversion technique in forming a stable oil-in-water emulsion in the process of this invention.

EXAMPLE Eight grams of methyl cellulose are dispersed in 25 milliliters of cottonseed oil (containing l- bis(p-dimethyl-aminophenyl)methyl7-benzotriazole) and this dispersion is emulsified by the slow addition of 100 milliliters of water. The addition of a few milliliters of water (10 to 15) results in a water-in-oil emulsion, which inverts to an oil-in-water emulsion with the further addition of water. Following emulsification, 3 grams of Jaguar-2S1 (a derivative of guar gum) are slowly added to the emulsion with brisk agitation, followed by the addition of 100 ml. of water (containing 0.1 gram-equivalents of a2C03). The addition of the Jaguar results in the formation of well-defined microcapsules (seen under an ordinar microscope evenly dispersed throughout the emulsion. The emulsion containing the microcapsules is subsequently coated onto a paper web and dried at about 50 to 60° C.

EXAMPLE 5 Ten grams of gum arable are dissolved in 100 grams of water and the solution is emulsified with 25 milliliters of soybean oil (containing 1 gram of l-^bis(dimethylamino-phenyl)methyl7-benzotriazole) . Subsequently, 10 grams of Gantrez-139 are added to the emulsion and emulsification is allowed to proceed for 10 to 15 additional minutes. The subsequent addition of 10 milliliters of ethylene diamine slowly and with brisk agitation results in the formation of well-defined microcapsules. The emulsion containing the microcapsules is coated onto a paper web and dried at about 50 to 60° C.

EXAMPLE 6 Into a solution of l80 grams of water (containing 25 grams of Gantrez and enough agCO^ to bring the pH to 8.5, 50 milliters of Arochlor No. 1248 (chlorinated biphenyls) containing 2 grams of l- p-dimethylaminophenyl)methyl7-pyr-rolidine are added and emulsified for approximately 15 to 20 minutes. To the emulsion, 20 milliliters of 10 by weight gelatin in water solution are added slowly and with brisk agitation. The addition of the gelatin solution results in well-defined microcapsules, evenly dispersed throughout the emulsion. The emulsion is subsequently coated onto a paper web and dried at about 50 to 60° C.

EXAMPLE 7 Into 200 grams of water, containing 8 grams of Gantrez-139 and enough a2C0 to bring the pH to 8.5, 50 mil- liliters of castor oil (containing 2 grams of l-,/bis(-dimeth-ylaminophenyl)methyl7-benzotriazole) are added and emulsi.-' fied. Subsequently, 2 grams of gum tragacanth are added to the emulsion with brisk stirring, resulting in the formation of well-defined microcapsules, evenly dispersed throughout the emulsion. The emulsion is coated onto a paper web and dried at about 50 to 60° C.

The following Example illustrates the employment of a self-complexing emulsifying agent in the process of this invention.

EXAMPLE 8 Into a solution of 200 grams of water and 10 grams of Jaguar 315-CM (a self-complexing derivative of guar gum) and 50 milliliters of cottonseed oil (containing 1 gram of l- bis(p-dimethylaminophenyl)methyl7-pyrrolidine) are added and emulsified for approximately 30 minutes with brisk stirring. The emulsion is found to contain microcapsules which are evenly dispersed throughout the emulsion and are visible under an ordinary microscope. The emulsion is subsequently coated onto a paper web and dried at between 50 and 60° C.

In all of the foregoing Examples, the HLB of the particular oil was matched to approximate the emulsifying agents utilized.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore, and as defined in the appended claims.

Claims (1)

1. eth nolamine th l n iam n v 6. A process as defined in Claim 1 wherein the emulsifying agent is a guar gum derivative and the crossr-iinking agent is a member selected from the group consisting of sodium borate and methyl cellulose. 7. A process' as defined in Claim 1 wherein both the emulsifying agent and the complexing agent is a self«r completing guar gum derivative. 8. A process as defined in Claim 1 vherei said oily material contains therein a colorless dye intermediate. 9. A process as defined in Claim 1 wherein the oil-in— water emulsion is prepared by dissolvin the emulsifying agent in the oily material and slowly adding water to initially form a water-in-oil emulsion, which emulsion inverts to a stable oil-in-water emulsion by the further addition of more water. 10. Pressure-rupturable microcapsules made according to the process of Claim I. 11. Pressure- upturable microcapsules made according to the process of Claim 2. 12. A pressure-sensitive transfer sheet record material for use in a transfer-copy system having oh one side thereof a coating of microcapsules as ttorneys or Applicant.