Process of microencapsulation and products thereof

This invention relates to a process for making microscopic size capsules from an emulsion having an inner oily or hydrophobic phase (material to be encapsulated) and an outer hardenable hydrophilic phase. The process is characterized by the step of contacting said emulsion with a break-up fluid capable of dividing said emulsion into substantially separate capsules having an inner hydrophobic phase and an outer hardenable hydrophilic phase; and then hardening the hydrophilic phase of said capsules to form microscopic size capsules or microencapsulations. The separated capsules can contain clusters of capsules, or they may be made as separate, individual capsules. In the preferred embodiment, the break-up fluid contains a surfactant capable of enhancing the break-up function of the fluid so that the separated capsules are predominately individual capsules. This invention also relates to microscopic size capsules formed by this process.

Microencapsulation provides a means of packaging, separating or storing 
materials on a microscopic scale. Minute particles or droplets of almost 
any material can be encased by an impervious capsule wall and thus 
isolated. The contents of a capsule can be made available by mechanical 
rupture of the capsule wall, by disintegration by electrical or chemical 
means or by a leeching action carried out in an appropriate liquid 
environment. Alternately the capsule can be employed to permanently 
contain its contents without rupture. This is advantageous, for example, 
where suspended in the contained liquid are color-coded micromagnets, said 
micromagnets being magnetically orientable and therefore capable of 
presenting selected colors to the viewer. 
Microencapsulation has been applied to describe particle coating processes 
producing capsules of minute size, for example, varying in size from a few 
microns in diameter to 2000.mu. or larger. 
Microencapsulation has been practiced for many years, for example, as 
dosage forms for drugs, to "lock-in" flavors and essences, in National 
Cash Register Company's NCR (no carbon required) paper, etc. The pressure 
of type striking the NCR paper ruptures the capsules and allows reaction 
to take place producing a resulting image. 
One well known method of microencapsulation is coacervation which involves: 
(a) establishment of a three-phase system with a liquid vehicle as the 
continuous phase, and coating material and material to be coated as the 
dispersed phases; 
(b) deposition of liquid polymeric material around the material to be 
coated; 
(c) hardening of the polymer coating material. 
I have now discovered a process of microencapsulation which comprises 
preparing an emulsion having an inner oily or hydrophobic phase 
(containing the material to be encapsulated) and an outer hardenable 
hydrophilic phase and then contacting said emulsion with a break-up fluid 
capable of dividing said emulsion in substantial separate capsules having 
an inner hydrophobic phase and an outer hardenable hydrophilic phase and 
then hardening the hydrophilic phase of said capsule to form the 
microencapsulate. In the preferred embodiment, the break-up fluid contains 
a surfactant capable of enhancing the break-up function of the fluid so 
that the separated capsules contain predominately sole capsules rather 
than clusters of capsules. 
In this application, by an individual capsule is meant a capsule having a 
sole hydrophobic droplet. By a cluster of capsules is meant a capsule 
having a plurality of hydrophobic droplets. The ratio of individual 
capsules to clusters can be varied by the use of various solvents and 
mixtures of solvents alone or in combination with surfactants. I have 
obtained substantially 100% individual capsules as well as substantially 
100% clusters. 
The present invention may be summarized as follows: 
I. Preparation of emulsion 
(1) inner oily or hydrophobic phase of material to be encapsulated; 
(2) hardenable outer continuous hydrophilic phase. 
II. Contact I with break-up fluid yielding 
(1) individual capsules or small clusters of capsules; 
(2) where the break-up fluid contains surfactant, clusters of capsules are 
minimized. 
III. Harden outer layer of II to form hardened capsules.

The drawings show single capsules but a plurality of capsules are generally 
used. The shell is the hardened outer hydrophilic phase. 
The following examples, in which all proportions are given by weight unless 
otherwise noted, will serve to illustrate but not limit the invention. 
Microscopic capsules containing mineral oil were rapidly and relatively 
inexpensively made as follows: 
EMULSIFICATION 
First the hydrophilic phase containing an aqueous gelatin solution was 
prepared by dissolving, at about 120.degree. F., 50 parts 275 bloom 
strength pork gelatin with 12 parts sorbitol in 290 parts distilled water. 
After the gelatin had dissolved, 130 parts methanol was added to the 
solution. Into 100 parts of this gelatin solution was then mixed the 
hydrophobic phase containing 100 parts of a second liquid, which in this 
example is white mineral oil (31 USP, Amoco), and an emulsion was formed 
by agitation, the oil forming droplets in the gelatin solution, and the 
size of the droplets being determined by the time and vigor of the 
agitation. At this stage the emulsion consisted of a two-phase system, the 
polymer wall former, in solution, being the continuous phase and the oil 
droplets suspended therein being the discontinuous phase. 
DISPERSION IN BREAK-UP BATH 
The 200 parts emulsion was then dispersed, by stirring, into 300 parts 
xylol, at about 70.degree. F., the xylol performing as a break-up bath in 
which the continuous phase gelatin solution divided into separate 
spherical and spheroidal capsule shells, each shell containing the oil 
droplet it had carried in the emulsion. A surfactant employed, such as an 
oil detergent containing zinc dialkyldithiophosphate (Texaco Super Motor 
Detergent), in a ratio of about 20 parts mixed with the 300 parts xylol, 
aided in the division of the gelatin phase into separate, individual 
capsules. 
Other surfactants used in varying proportions have been calcium petroleum 
sulfonate (25H, Witco Chemical), Alkylaryl Sulfonamido Ester (Estersulf 
14, Trask Corp.), Sulfated Soya Oil (OY 75, Trask Corp.), or a mixture of 
50% Calcium sulfonate (TLA-414, Texaco) and 50% ashless dispersant 
(TC-9781, Texaco). 
HARDENING 
The xylol break-up bath, together with the now separated, individual 
microscopic capsules dispersed in it, still under stirred agitation, was 
then cooled to about 45.degree. F. to partially congeal the gelatin and 
the capsules were then permitted to settle to the bottom of the bath. 
Excess break-up bath fluid was removed and the remainder, with its 
capsules dispersed therein, was then mixed with about 600 parts of a 
hardening bath, at about 40.degree. F., prepared of, by volume, 200 parts 
anhydrous isopropyl alcohol, 150 parts xylol, and 50 parts steam distilled 
turpentine. Two or three successive washings in the hardening bath were 
usually employed and the now completed microscopic capsules were screened 
out and any hardening bath still coating the walls was removed by air 
drying at room temperature, the relative humidity being kept preferably 
under 40%. 
As microcapsules decrease in size, settling in the bath becomes slower and 
often, therefore, the settling step was eliminated and the entire 
bath-capsule mixture was mixed with a larger quantity of the hardening 
bath. 
The above proportions may be varied and the break-up bath has comprised 
hydrocarbon solvents, both aromatic and aliphatic. Terpenes and 
chlorinated solvents have also been employed. For example, toluene has 
been used with or in place of xylol, and break-up baths have been made of 
275 parts VM & P naptha and 80 parts trichlorethylene; or 275 parts 
turpentine and 50 parts trichlorethylene; or 250 parts mineral spirits 
with 100 parts trichloroethylene. 
Oils have also been used for the break-up bath. Hydrocarbon oils such as 
low viscosity mineral oils have been used as has vegetable oils such as 
corn oil, and these oils blended with hydrocarbon solvents and/or 
terpenes. 
In some break-up baths the capsules retrived consisted of walled clusters, 
single, tiny capsules containing within several smaller capsules. In some, 
especially those in which had been incorporated a surfactant, such as the 
oil detergent mentioned above, the aqueous gelatin solution was divided 
into lone capsules such as those shown in the drawings. 
The temperatures given may also be varied. The temperature of the gelatin 
solution, of course, must be kept above the gel point until the emulsion 
has been dispersed in the break-up bath, and the lowering of the 
temperature of the break-up bath and using a hardening bath at a lowered 
temperature accelerated the hardening of the shell walls and helped to 
prevent agglomeration of the unhardened capsules. Capsules have been 
produced, however, with both baths being at room temperature. 
The capsule wall-forming material may employ a gelatin of higher or lower 
bloom strength than the 275 mentioned and other hydrophilic gellable 
colloids such as gum arabic and agar may be employed, although gelatin is 
preferred. And glycerine has been used as a plasticizer for the gelatin 
instead of sorbitol and capsules have been made with no plasticizer at 
all. Also, ethyl alcohol in place of or with methanol has been used in the 
aqueous gelatin solution, and the gelatin was usually dissolved in the 
water and the alcohol then added. 
Capsule shell walls have also been made using a copolymer of vinyl acetate 
(Gelva C-5 V-10, Monsanto) which was dissolved 10 parts C-5 V-10 in 98 
parts water and 2 parts 28% ammonia. Five parts of the copolymer solution 
were then mixed with 200 parts of the aqueous gelatin solution. 
In another formulation, an acrylic modified capsule shell wall was formed 
by mixing into 100 parts of the aqueous gelatin solution 10 parts of an 
acrylic emulsion (Rhoplex AC-61, Rohm & Haas) which had been diluted 20 
parts AC-61 to 250 parts water. 
Still another shell wall was made with polyvinyl alcohol (Gelva 20--20, 
Monsanto) dissolved 20 parts PVA in 290 parts water and 130 parts 
methanol, and 10 parts of the PVA solution were mixed with 200 parts of 
the aqueous gelatin solution. 
In each case, the shell wall contained a hydrophilic hardenable colloid 
which is a natural or synthetic polymer or combinations thereof. 
Although it is not a requirement of this invention, cross-linking of the 
capsule wall material may be effected with the use of any suitable 
cross-linking agent such as an aldehyde, for example, by the addition to 
the aqueous wall forming solution of about one part of 37% formaldehyde. 
The use, in the break-up bath of a highly overbased calcium sulfonate 
(such as TLA-414, Texaco) or a magnesium sulfonate (such as 9717, Amoco) 
may be useful in raising the pH of the wall forming material so as to aid 
in cross-linking. 
In addition the hardening bath has employed other alcohols mixed with a 
hydrocarbon and/or a terpene, such as ethyl alcohol or methyl alcohol, 
although isopropyl alcohol is preferred. Hardening baths, for example, 
have been prepared from, by volume, 500 parts toluene with 500 parts 
isopropyl alcohol, and from 500 parts turpentine with 500 parts isopropyl 
alcohol. It was also found that a bath of isobutyl alcohol or n-butyl 
alcohol, without a hydrocarbon or terpene solvent, satisfactorily hardens 
the gelatin walls. Thus, it is not necessary to combine either of these 
alcohols with a hydrocarbon solvent, terpene, or chlorinated solvent 
before mixing them with the break-up bath. 
In accord with this invention, the first step, in which the inner oil or 
hydrophobic phase is emulsified in the wall forming exterior aqueous 
phase, requires substantial immiscibility between the two phases. 
The second step, in which this emulsion is then mixed with the break-up 
bath, requires that the break-up bath be substantially immiscible with the 
polymer wall forming phase. The break-up bath may be, or may be not, 
miscible with the inner hydrophobic phase being encapsulated. 
The third step, in which the hardening bath is introduced into the break-up 
bath, requires that the hardening liquid be substantially miscible with 
the break-up bath. 
Substantial miscibility, here, is meant to indicate the ready blending of 
two or more liquids without the formation, between one of the liquids and 
the other, or others, of a separate phase or emulsion, which emulsion 
would, in that particular step, produce a deleterous effect in that step. 
Substantial immiscibility is meant to indicate the lack of such ready 
blending and thus the formation of an emulsion. 
The hardening liquids, always miscible with the break-up bath, will be, 
either of themselves, or in combination with other liquids, substantially 
immiscible with the wall forming aqueous solvent. For example, isopropyl 
alcohol, while itself miscible with an aqueous solution, when mixed with, 
say, equal parts of xylol forms a liquid substantially immiscible with the 
wall forming solvent. Or, isopropyl alcohol, introduced into a break-up 
bath of xylol, blends and becomes, in situ, substantially immiscible with 
the wall forming solution. Isobutyl alcohol, if used as a hardener, is 
itself, substantially immiscible with the aqueous solvent. 
To further illustrate miscibilities, if mineral oil, say, is chosen for the 
break-up bath, isobutyl alcohol, or normal butyl alcohol, used as a 
hardener, will blend with the mineral oil, with which it is miscible. 
Isopropyl alcohol, alone, however, would not be miscible with the mineral 
oil. A hardening bath employing isopropyl alcohol mixed with, say, an 
equal amount of xylol, is miscible with a mineral oil break-up bath, 
however. 
In summary, the hardening liquid is always miscible with the break-up bath 
and is, either of itself, or in combination with other liquids 
substantially immiscible with the wall forming solvent. While I do not 
wish to be bound by theoretical considerations, hardening is believed to 
be the result of a reaction between the hardening mixture and the wall 
forming polymer, causing it to force out its aqueous solvent into the 
hardening bath. Neither the break-up bath, nor the hardening mixture, 
will, of course, be selected from liquids which would dissolve the wall 
forming polymer. 
Microcapsules have been produced in this manner in sizes from about one 
micron to about 2000.mu.. The desired size of the capsules was achieved by 
selection of the viscosity of the aqueous colloid solution, i.e., the 
proportions and type of the wall forming material to its solvent, and/or 
the time and vigor of agitation used to effect the emulsion. 
Liquids that have been so encapsulated include turpentine, mineral oils, 
vegetable oils, animal oils, liquid polymers (Amoco polybutene, Indopol 
L-14), as well as such solvents as xylol, toluene, and mineral spirits. 
Solids suspended in the encapsulated liquids include pigments, such as 
carbon black, dispersed in linseed oil and turpentine. The capsules 
containing this mixture were coated onto a paper substrate and, upon being 
ruptured, transferred marking to a second paper. 
Other solids suspended in the encapsulated liquid have been color coded 
micromagnets described in my U.S. Pat. No. 3,460,248, No. 3,406,363, and 
No. 3,938,263, said micromagnets being suspended in a thixotropic oil or 
liquid polymer. The capsule walls were transparent and the capsules were 
mixed with a transparent binder which was then coated onto a substrate 
where the binder was permitted to harden either by solvent evaporation or 
by catalytic curing, and the micromagnets, being magnetically orientable, 
could be selectively rotated to present colorful patterns to the viewer. 
These are described and claimed in my application Ser. No. 775,202 filed 
Mar. 7, 1977, now abandoned, and in its continuation-in-part Ser. No. 
777,180 filed Mar. 14, 1977, now abandoned, and in its 
continuation-in-part Ser. No. 872,214 filed Jan. 25, 1978, now pending. 
Said applications Ser. Nos. 775,202, 777,180 and 872,214 are by reference 
incorporated into this application, as if part hereof. 
The present invention can be employed to microencapsulate a wide variety of 
materials. The following are non-limiting illustrations of such materials: 
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adhesives foods perfumes 
blowing agents 
fuels photographic agents 
catalysts inks pigments 
curing agents 
insecticides plasticizers 
detergents leavening agents 
propellants 
drugs metals solvents 
dyes monomers stabilizers 
flavors oils vitamins 
paints 
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As is quite evident other hydrophobic materials, other hardenable 
hydrophilic materials, other break-up fluids and surfactants employed in 
the break-up fluids are known or will be constantly developed which could 
be useful in this invention. It is, therefore, not only impossible to 
attempt a comprehensive catalogue of such components, but to attempt to 
describe the invention in its broader aspects in terms of specific 
chemical names of all components that could be used would be too 
voluminous and unnecessary since one skilled in the art could by following 
the description of the invention herein select useful hydrophobic 
materials, hydrophilic materials, break-up fluids and surfactants employed 
therein. This invention lies in a process of microencapsulation and 
products formed therefrom. Their individual components are important only 
in the sense that they affect such microencapsulation and products 
thereof. To precisely define each possible component and each possible 
variation in preparative techniques in light of the present disclosure 
would merely call for knowledge within the skill of the art in a manner 
analogous to a mechanical engineer who prescribes in the construction of a 
machine the proper materials and the proper dimensions thereof. From the 
description in this specification and with the knowledge of one skilled in 
the art, one will know or deduce with confidence the applicability of 
specific components suitable in this invention. In analogy to the case of 
a machine, wherein the use of certain materials of construction or 
dimensions of parts would lead to no practical or useful result, various 
materials will be rejected as inapplicable while others would be 
operative. One can obviously assume that no one will wish to make a 
useless microencapsulate nor will be misled because it is possible to 
misapply the teachings of the present disclosure to do so. 
Thus, the examples given herein are intended to be illustrative and various 
modifications and changes in the materials and structures may be apparent 
to those skilled in the art without departing from the spirit of this 
invention.