CA1158105A - Process for making microcapsules and resulting product - Google Patents

Abstract

PROCESS FOR MAKING MICROCAPSULES
AND RESULTING PRODUCT

ABSTRACT OF THE DISCLOSURE

Oil-containing microcapsules are produced by emulsify-ing an oily solution of isocyanatoamidine products into an aqueous solution of emulsifier to form oil-in-water emul-sion. The reactive isocyanatoamidine products are subse-quently hydrolyzed into an impermeable capsule wall.

Description

115810~
PROCESS FOR M~ING MICROCAPSULES
AMD RESULTING PRODUCT

BACKGROUND OF THE INVENTION
In a typical carbonless paper form, the back side of the top sheet has a coating of microscopic capsules contain-ing colorless chromogens or color precursor in the oil.
This top sheet is called CB paper, for coated back. The bottom sheet is the receiving sheet, which is coated with a color developer. It is designated as CF paper, for coated front. The intermediate plies have color developer coating on the front sides and microcapsules coated on the back sides. These sheets are called CFB. A self-contained paper has both the color developer and microcapsules coated on the same side of the web. When the CB and CF coatings are arranged in a manner of facing each other, a typing or writing pressure from the top side of CB paper will produce images on the CF surface. Similarly, images will also appear on all CF sides in a multiform set of CB, CFB's and CF papers. A self-contained paper will develop images in situ upon the rupture of microcapsules by a typing or writing pressure.
Two principal techniques for the production of micro-capsules have been used since the microencapsulation tech-nology was introduced in the 1950's. Numerous patents have revealed in-depth details in this field. The first method is the phase separation of film-forming materials from the continuous phase by the coacervation process. It involves the deposit of colloidal materials, such as gelatin and gum arabic, around the oil droplets, followed by hardening with formaldehyde as taught in U.S. Patent No. 2,800,457 (1957).
Many other patents also disclose that aqueous solutions of hydrophilic colloids may be coacervated by adding various substances, such as inorganic salts and oppositely charged colloids, to the solutions. However, this process has a number of disadvantages in commercial production of the coacervates. It requires careful control of the cooling temperature over a long period of time for the colloids to deposit around oil droplets and continuous adjustment of pH-value for the system. Undesired agglomeration of micro-. . .
.

1 15811)S
capsules usually occurred during the subsequent hardening reaction with aldehyde. The polynuclear cluster of micro-capsules makes it very difficult to produce sharp images in the carbonless papers copying system.
Another method is the interfacial polymerization of two direct-reacting intermediates around minute oil droplets.
Generally, one reacting intermediate is dissolved in a hydrophobic liquid and the second intermediate is present in a hydrophilic liquid. In some cases, both reacting interme-diates may be included in a hydrophobic liquid phase which is emulsified into an immiscible hydrophilic liquid.
Polycondensation is then promoted by catalysts or heat so that the intermediates react with each other to yield a solid product as the skin at the interface of minute oil droplets. Typical examples of such condensates are poly-amide, polyester, polyurethanes, polyurea, and the like.
This interfacial polymerization requires proper selection of intermediates.
Inasmuch as this invention deals with polyisocyanates which have been used in microencapsulation before, their roles may be classified as follows:

1. Re-enforcement of the primary capsule wall.

The capsule wall formed by the coacervation process is normally swollen due to the moisture sensitivity of gelatin material. This primary wall is somewhat perme-able, allowing the capsule core material to escape over a period of time. Thus, polyisocyanates have been used to alleviate such deficiency for the wall of hydrophobic polymers as disclosed in U.S. Patent No. 3,660,304, the wall formed by complex coacervation as disclosed in U.S. Patent No. 3,897,361, and the wall formed by the phase separation of poly(ethylene-co-vinyl acetate) as disclosed in U.S.
Patent No. 3,674,704.

2. Polymerization in the oil phase.

U.S. Patent Nos. 3,726,804 and 3,796,669 disclose the production of microcapsules by dissolving film-forming materials in an oily liquid to be encapsulated, which then 1 1581()~
polymerize by itself or react with another film-forming material to produce a water-insoluble, high molecular weight material. The temperature of the system is raised to cause the deposit of such high molecular weight product on the surface of minute oil droplets.

3. Interfacial polymerization (other than with the emulsifier).

A number of patents, such as U.S. Patent Nos.
3,432,327, 3,577,515, 3,886,085, 3,900,669, 4,021,595,

4,046,741, 4,119,565 and 4,120,518 have revealed the forma-tion of microcapsules by the polymerization of polyisocy-anate in the oil phase and a co-reactant, other than the emulsifier or protective colloid, from the outer phase of each oil droplet. The polymerized product precipitates at the interface to form the capsule wall. The co-reactant may be selected from polyamines, polyols, polycarboxylic acids, polythiols, and epoxy compounds. Catalysts are normally needed for the interfacial polymerization. Nevertheless, it is very difficult to attain a complete polymerization because the co-reactant is either dissolved or thoroughly dispersed in the aqueous phase in the resulting coating which will be directly exposed to the users, posing health and ecological problems. For example, polyamines and epoxy compounds have been suggested as carcinogens.

4. Interfacial cross-linking of the emulsifier.

The cross-lin~ing of the emulsifier by polyiso-cyanates at the interface of oil droplets has been disclosed in U.S. Patent Nos. 3,895,074, 4,025,455, 4,107,071 and 4,138,362. Polyisocyanates in the oil phase react with the water-soluble emulsifier to produce a water-insoluble film as the capsule wall. The choice of the cross-linkable polymers, both synthetic and natural, is very critical for this method. The use of catalysts is also suggested.

SUMMARY OF THE INVENTION
The present invention relates to a process for produc-ing microcapsules having a stron~ impermeable shell. More , specifically, it relates to a process for producing oil-containing microcapsules having a shell of hydrolyzed isocyanatoamidine product.
The preparation of simple amidines is well described in the book of "The Chemistry of Amidines and Imidates" by Paul Patai, John Wiley & Sons, Ltd., 1975, and in the Journal of Polymer Science: Macromolecular Reviews, volume 11, pages 93-133, 1976, by Henri Ulrich. However, the present inven-tion involves novel isocyanatoamidines.
The present process utilizes two substantially immisci-ble liquids, one termed oil phase and the other termed aqueous phase, to produce a physical dispersion of oil droplets in a continuous aqueous phase, i.e., an oil-in-water emulsion. The oil phase comprises materials to be encapsulated and isocyanatoamidine product as the wall-forming material in a hydrophobic liquid. The aqueous phase contains a water-soluble emulsifier which acts solely as the protective colloid. The isocyanatoamidine product is then hydrolyzed at the interface of each oil droplet into a strong solid capsule wall which is insoluble in either the oil or water. This simple process does not require pH
adjustment, use of catalysts, addition of polymerization promoters, or further enhancement ~y a secondary cross-linking reaction from the outer phase of capsules.
The present process for making microcapsules provides several unique advantages over the prior art mentioned in the previous section. It has been found that isocyanatoami-dines react with other isocyanates to yield high molecular weight isocyanatoamidine products which are easily hydro-lyzed by water in the continuous phase into an impermeable capsule wall. It i5 a surprising finding that no cross-linking reaction was observed. The hydrolysis is actually independent of the emulsifier used to produce microcapsules as evidenced in Examples 5 and 6. Therefore, the addition of a separate co-reactant in the aqueous phase for inter-facial polymerization reaction is consequently obviated.
The resulting microcapsules are non-agglomerating, mononu-clear, discrete and spherical capsules which offer sharp manifolding when employed in the pressure-sensitive copying system. The particular size may range from about 2 microns to about 100 microns in diameter. More importantly, the -1 1~810~
capsule wall exhibits excellent heat stability and humidity resistance. By the process of this invention, an up to 60%
solid contents of microcapsules emulsion may be produced as compared to about 25% usually obtained by coacervation process. In view of the high heat requirement to dry water-based coatings, the present invention proves to be an energy-saving process.

DETAILED DESCRIPTION

Production of Isocyanatoamidine The initial step in this invention involves the reac-tion of an isocyanate compound and a N,N-disubstituted amide to produce isocyanatoamidine. It is usually accompanied by the loss of carbon dioxide as illustrated below.

R4-N=C=O
+ N~R4 f \N,R2 c2 N ~3 wherein Rl represents hydrogen or lower alkyl group, such as methyl, ethyl, propyl, and butyl; R2 and R3 represent lower alkyl groups, such as methyl, ethyl, propyl, and butyl; R4 represents an isocyanatoaryl group, such as 3-isocyanatophenyl( ~ ), 2~CO

NCO
4-isocyanato-2-tolyl ( ~ ), 6-isocyanato-2-tolyl ~ ~ ), ....

` ` ~15810S
a-(4'-isocyanatophenyl)- r--\ ~
4-tolyl ( ~ ~12 ~ NCO), CH
a-~4'-isocyanato)-4- ( ~ 1 - {3 NC), cumenyl ~ 1H3 ~ NCO

4-isocyanato-1-naphthyl ( ~ ), and the like; an isocyanatoalkyl group, such as 2-isocyanatopropyl (-CH2CH-NCO), .
2-isocyanatobutyl (-CH2fH-NCO), . 2 3 a-isocyanatohexyl (-CH2CH2CH2CH2CH2CH2-NCO), and the like; and an isocyanatocycloalkyl group, such as NCO

2-isocyanatocyclohexyl ( ~ ), .

4-isocyanatocyclohexyl ( ~ NCO), and the like.
Typical examples of isocyanate compounds are aryl isocyanates, such as 2,4-toluene-diisocyanate, 2,6-toluene-diisocyanate, m-phenvlene diisocyanate, 4,4'-isopropylidene-diphenyldiisocyanate, 3, 3 ~ -dimethY1-4,4~-methY1enediPhenY1-diisocyanate, 4,4'-methylenediphenyldiisocyanate, 1,4-naph-... .

1 0 ~
thyl-diisocyanate, 1,3-xylene-diisocyanate, 1-4-xylene-di-isocyanate, etc.; alkyl isocyanaies, such as propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, hexamethylene-di-isocyanate, etc.; cyclic alkyl isocyanates, such as cyclo-hexyl-1,2-diisocyanate, cyclohexyl-1,4-diisocyanate, etc.;
adduct of isocyanate and hydroxy compounds are also useful.
Typical examples of hydroxy compounds are ethylene glycol, 1,3-propylene glycol, 1,5-pentanediol, 1,6-heptanediol, 2-ethyl-hexane-1,3-diol, hexanetriol, 2-ethyl-2-(hydroxymeth-yl)-1,3-propanediol, pentaneerythritol, sorbitol, and the like.
Suitable amides include N,N-dimethylformamide, N,N-di-ethylformamide, N,N-dipropylformamide, N,N-dibutyl-forma-mide, N,N-dimethylacetamide, N,M-diethylacetamide, N,N-di-propylacetamide, N,N-dibutylacetamide, and N-methyl-2-pyrro-lidone.
The temperatures for carrying out reactions are about 150C for N,N-dialkylformamides, about 80C for N,N-dialkyl-acetamides, and about 230C for N-alkyl-pyrrolidones. The reaction time -for the formation of isocyanatoamidines is about 2 hours to about 30 hours; preferably, about 4 hours to about 20 hours.
The second step in this invention is the reaction of isocyanatoamidine with another isocyanate compound to yield a final isocyanatoamidine product which may be readily hydrolyzed. The reaction temperature may range from about 40C to about 120C for 4 to 10 hours; preferably about 60C
to about 100C for 4 to 6 hours. The molar ratio has been found to be 1 mole of isocyanatoamidine to 1-5 moles of isocyanate compound; preferably, the ratio of 1 to 5.

Solution of IsocYanatoamidine Products The desired weight of isocyanatoamidine product per 100 parts of a hydrophobic liquid (i.e., oil) is generally about 2 to about 15 parts; preferably, about 4 to about 10 parts by weight.
The preferred hydrophobic liquids for this invention are alkylnaphthalenes, terpenes, isopropylbiphenyls, ben-zylated xylenes, ethyldiphenylmethanes, dimethyldiphenyl-ethanes, tributyl phosphate, tricresyl phosphate, and the mixtures of the said oil and kerosene. Suitable co-solvents . ..

ll58ilO5 for dissolving isocyanatoamidine product in the hydrophobic liquid are acetone, methyl ethyl ketone, ethyl acetate, tributyl phosphate, tricresyl phosphate, dioxane, and tetrahydrofuran.

The Aqueous Phase The quantity of the protective colloid for 100 parts by weight of the core material (including the oil and the small amounts of dye and amidine products) is generally between about 0.5 and about 40 parts by weight; preferably, between about 2 and about 30 parts by weight.
Typical examples of protective colloids are carboxy-methyl cellulose, hydroxymethylpropyl cellulose, hydroxy-ethyl cellulose, hydroxypropyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cellulose phthalate, casein, gelatin, starch, benzylated starch, benzylated gelatin, gum arabic, chitosan, gum tragacanth, guar gum, carrageenan, polyvinylalcohol, polyvinylacetate, styrene-maleic anhydride copolymer, methyl vinylether-maleic anhy-dride copolymer, partially hydrolyzed poly(ethylene-co-vinyl acetate), and the like. Other natural and synthetic poly-mers may also be used as protective colloids.

The Hydrolysis Reaction The hydrolysis reaction of isocyanatoamidine product may be conducted at any suitable temperature, for example, between about ambient temperature and about 100C for a period of time of about 1 and 24 hours. Preferably, the temperature is in the range of between about 40C and about 80C for a period of about 1 to 3 hours, yielding carbamic acid which precipitates around the oil droplets to form the capsule wall.
The present invention is further illustrated, but not limited by the following examples.

The purpose of this example is to illustrate the fact that the amidine products are necessary to the practice of the invention -- these products not being achieved in this example.

. ~ , 1 158:10~
A solution of 7.4 grams of 2-ethyl-hexane-1,3-diol in 10 grams of isopropylbiphenyls oil was added drcpwise to a solution of 17.6 grams of TD-80 (mixture of 80% by weight of 2,4- and 20% by weight of 2,6-toluene-diisocyanates, Mobay Chemical Company) in 15 grams of isopropylbiphenyls at about 50C. The temperature was gradually increased to 80C and kept at that temperature for 3~ hours. A viscous solution was obtained.
Three grams of the above product were dissolved in a solution of 1.5 grams of crystal violet lactone in 50 grams of isopropylbiphenyls. The solution was emulsified into 50 grams of 15% benzyl gelatin solution to produce minute oil droplets having about 5 microns in diameter. The emulsion was heated at 60C for 2 hours to complete the microencapsu-lation.
The microcapsules were coated on a paper web to provide a transfer sheet. When this sheet was arranged in a conti-guous juxtaposition with a receiving sheet coated with a phenolic novolak resin, instant blue images were formed on the receiving sheet. A separate transfer sheet was then subjected to an accelerated heat-aging test at 100C for 3 hours for comparison. The aged sheet developed faint and discontinuous images on the receiving sheet, indicating that capsules were imperfect to hold the core material. The ensuing example illustrates the preferred practice where the isocyanate-amide reaction is present.

To ten grams of the viscous product of 2-ethyl-hexane-1,3-diol and TD-80 in Example 1 were added 1.76 grams of N,N-dimethylacetamide. The mixture was heated at 85C for 6 hours. A slow evolution of carbon dioxide was observed during the reaction. Resulting therefrom was a product having at least some proportion of the hetero-cyclic isocy-anatoamidine products inasmuch as the amount of acetamide was greater than the stoichiometric amount.
Three grams of the above product were mixed in a solution of 1.5 grams for crystal violet lactone in 50 grams of isopropylbiphenyls. This resulting solution was encapsu-lated as core material and evaluated according to the procedure of Example 1. The aged transfer sheet showed a l 158105 good capsule wall integrity upon mating with a receiving sheet.

A mixture of 12 grams of ethyl acetate, 27.8 grams of TD-80, and 7.14 grams of 2-ethyl-2-(hydroxymethyl)-1, 3-propanediol was gently refluxed for 3 hours in a 125-ml round-bottomed flask. A viscous solution was produced.
Three grams of the above product were added into a solution of 1.5 grams crystal violet lactone in 50 grams of 10 benzylated xylenes and 0.8 grams of tributyl phosphate.
This solution was emulsified into 50 grams of 15% gelatin (gel strength 135 grams) solution to produce oil droplets having an average particle size of about 5 microns. The emulsion was then heated at about 50C for 3 hours. The resulting microcapsules were coated over a phenolic novolak resin on the receiving sheet. Upon drying the coating in an oven at 80C, the coating turned blue. This indicated that the capsule wall was permeable enough for the dye solution to leach out and react with phenolic novolak resin into a 20 blue color.

In a 125-ml round-bottomed flask, a mixture of 12 grams of ethyl acetate, 27.8 grams of TD-80, and 7.14 grams of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol was gently reflux-ed for 3 hours. While maintaining the temperature at 80C, 2~5 grams of N,N-dimethylacetamide were added. The tempera-ture was maintained at about 80C for 7 hours. Decarboxyla-tion occurred after one hour of heating and subsided toward the end of reaction.
Three grams of the above product were evaluated in the same manner described in Example 3. The final coating remained virtually colorless after drying in an oven of 80C. It showed that the capsule wall was superior to that of Example 3.

The purpose of this experiment was to demonstrate that the capsule wall was formed by the hydrolyzed substance o~
isocyanatoamidine product, regardless of the emulsifiers 115~
used. The volume of oil phase was the same as the volume of aqueous phase for each emulsifier solution.
Oil Phase: A mixture of 8.3 grams of ethyl acetate, 19.3 grams of TD-80, and 4.9 grams of 2-ethyl-2-(hydroxy-methyl)-1,3-propanediol was mildly refluxed for 3 hours.
While maintaining the temperature at 75C, 1.73 grams of N, N-dimethylacetamide were added. Decarboxylation occurred after one hour of heating and subsided in about 7 hours.
Six grams of the above product were dissolved in a mixture of 8 grams tributyl phosphate and 100 grams of isopropyl-biphenyls. Fifteen milliliters aliquot was used for each emulsifier solution.
Aqueous phase: Fifteen milliliters of each emulsifier solution were used.
Concentrations (by weight) are noted individually as follows:
Vinol 540 polyvinylalcohol 6 animal glue - 135 15%
benzylated animal glue - 135 15%
hydroxypropylmethylcellulose 0.936%
Gantrez AN-119 10%
hydroxypropylcellulose (Klucel L) 3.71%
water (control) Each aqueous solution was placed in a glass cylinder (39-mm diameter, 50-mm height) through a pipette. Fifteen milliliters of oil solution were carefully added onto each aqueous solution through another dry pipette to form two distinct layers. Each glass cylinder was tightly covered with a plastic film and immersed about 40-mm into a constant temperature bath at 60C for two`hours. An insoluble film formed at the interface of oil and water layers in each case.
The film was taken out, washed with 60-ml of oil composed of 8 parts of tributyl phosphate and 100 parts of isopropylbiphenyls. The film was further washed with 60-ml of hexane, followed by stirring in distilled water at 60C
for two hours. The insoluble solid was collected by filtra-tion, rinsed with cold distilled water, dried in an oven at 60C, and stored in a dry vial for infrared spectrophoto-metric analysis and elemental analysis. Infrared spectra .
1158~L05 (in Nujol mull) of all seven ~amples were structurally identical using Infrared Spectrophotometer Model 297 of Perkin-Elmer. Again, al] seven samples exhibited the identical chemical composition based on the elemental analyses performed by Micro-Tech Laboratories, Inc., Skokie, Illinois, 60076. Carbon, hydrogen and nitrogen elemental analyses of all emulsifiers are tabulated in Table 1 for comparison. Results for all seven samples are included in Table 2.

Table 1. Elemental Anaylsis of Emulsifiers Emulsifier %C %H %N
Vinol 540 polyvinylalcohol 54.01 9.10 0 animal glue - 135 44.85 6.77 16.45 benzylated animal glue - 135 46.65 5.91 15.26 hydroxypropylmethylcellulose 48.62 7.26 0 Gantrez AN-119 49.32 5.27 0 hydroxypropylcellulose tKlucel L)54.29 8.65 0 .

Table 2. Elemental Analysis of Capsule Walls (Equal Volume) Emulsifier used to obtain Figure capsule wall material %C%H %N
2 Vinol 540 polyvinylalcohol61.29 5.93 11.46 3 animal glue - 135 61.13 5.83 11.14 4 benzylated animal glue - 13561.725.68 11.34 hydroxypropylmethylcellulose 61.30 5.79 11.36 6 Gantrez AN-119 61.50 5.87 11.38 7 hydroxypropylcellulose 61.23 6.09 11.39 (Klucel L) 8 water (control) 61.19 5.80 11.55 The purpose of this experiment was to show that the capsule wall was formed by the hydrolyzed substance of isocyanatoamidine product instead of the cross-linked emulsifier. The amount of oil phase was 10 grams in each 1 15810~
case. The dry weight of each emulsifier was the same in all cases.
Oil phase: Ten grams of oil solution prepared accord-ing to the procedure of Example 5.
Aqueous phase: Fifteen grams of each emulsifier solution listed below were used. The concentration of each aqueous solution was 10% by weight.

animal glue - 135 benzylated animal glue - 135 hydroxypropylcellulose (Klucel L) Gantrez AN-ll9 Vinol 540 polyvinylalcohol (87-89% hydrolysis, med mol wt) Elvanol 70-05 polyvinylalcohol (98-99% hydrolysis) Covol 9700 polyvinylalcohol (87-89% hydrolysis, low mol wt) water (control) The procedure of Example 5 was repeated to obtain dry capsule wall materials. Infrared spectra (in Nujol mull) of all eight samples were virtually identical. The elemental analyses of capsule wall materials also revealed the same chemical constituents as shown in Table 3.

Table 3. Elemental Analysis of Capsule Walls (Equal Weight) Emulsifier used to obtain Figure capsule wall material %C %H %N
9 animal glue - 135 62.18 6.00 11.53 benzylated animal glue - 135 62.76 6.02 11.27 11 hydroxypropylcellulose - 62.26 5.87 11.50 (Klucel L) 12 Gantrez AN-ll9 62.40 6.08 11.53 13 Vinol 540 polyvinylalcohol 62.28 6.10 11.41 14 Elvanol 70-05 polyvinylalcohol 62.06 6.09 11.57 Covol 9700 polyvinylalcohol 62.18 6.11 11.50 16 water (control) 62.20 5.93 11.46 1 158iLOS

In a flask equipped with a drying tube, 16.8 grams of hexamethylene diisocyanate and 11.5 grams of N,N-diethyl-acetamide were heated at 150C for 15 hours. Carbon dioxide was generated as gas bubbles. After the completion of reaction, 67.2 grams of hexamethylene diisocyanate were added into the slightly yellowish solution. Heating was continued at about 150C for an additional 4 hours. The viscous liquid was further added to 26.8 grams of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol and heated for 4 more hours to yield isocyanatoamidine product.
Four grams of the above product were dissolved in 4 grams of tributyl phosphate. This solution was added into a solution of 2 grams of 2-methyl-6-diethylaminofluoran in 50 grams of isopropylnaphthalenes. The resulting solution was emulsified into 50 grams of 15~ benzyl gelatin solution to obtain oil droplets having a particle size of about 3 to about 7 microns. The emulsion was cured at 50C for 4 hours to form impermeable capsule wall.
With the scope of the present invention, the herein disclosed microencapsulation process may be used to encapsu-late printing inks, chemical reagents, pharmaceuticals, fertilizers, fungicides, pesticides, adhesives, poisons, perfumes and chromogenic compounds known in the art of carbonless paper copy system, such as crystal violet lac-tone, benzoyl leuco methylene blue, fluorans, phthalides, leucoauramines, rhodamine B lactams, derivatives of Mich-ler's hydrol, and the like. Thus, the encapsulatable material may be the hydrophobic material itself -- such as aromatic oils, organophosphates, ketone, perfume, adhesive monomer, or liquid solution as in the case of dyes dissolved in the hydrophobic liquid, or solid dispersion such as pigments suspended in the hydrophobic liquid.
While in the foregoing specification a detailed des-cription of the invention has been set down for the purpose of explanation, many variations in the details hereingiven may be made by those skilled in the art without departing from the spirit and scope of the invention.

.. ,. I

Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for making microcapsules comprising:
dissolving an isocyanatoamidine product in a hydrophobic liquid, said isocyanatoamidine product comprising the reaction product of (A) an isocyanatoamidine having the formula wherein R1 is a member selected from the group consisting of hydrogen and a lower alkyl group, R2 and R3 are members selected from the group consisting of lower alkyl groups, and R4 is a member selected from the group consisting of an isocyanatoaryl group, an isocyanatoalkyl group and an isocyanatocycloalkyl group and (B) an isocyanate, and thereafter introducing the solution thus achieved into an aqueous emulsifier under conditions promotive of hydrolysis of said product to produce an impermeable capsule wall surrounding hydrophobic liquid.

2. The process of claim 1 in which said solution includes a soluble dye ingredient.

3. The process of claim 1 in which said hydrolysis is conducted at a temperature from ambient to about 100°C and for a period of time from about one to 24 hours.

4. The process of claim 3 in which said hydrolysis is conducted at a temperature in the range of about 40°C to about 80°C and for a period of time from about one to about three hours.

5. The process of claim 1 in which said isocyanato-amidine product is the reaction product of an isocyanate and an amide.

6. The process of claim 5 in which the said reaction is carried on for from 2 to 30 hours at a temperature in the range of about 80°C to about 230°C.

7. The process of claim 6 in which the said amide is a member selected from the class consisting of N,N-dialkyl-formamides, N,N-dialkylacetamides and N-alkyl-pyrrolidones, the temperature for carrying out the reaction being about 150°C for N,N-dialkylformamides, about 80°C for N,N-dialkyl-acetamides, and about 230°C for N-alkyl-pyrrolidones.

8. The process of claim 5 in which said isocyanate (B) is present in an amount of from about 1 to about 5 moles per mole of said isocyanatoamidine.

9. The process of claim 8 in which the further reaction is carried out at a temperature in the range of 40°C to about 120°C for about 4 to about 10 hours.

10. The process of claim 1 in which the said isocyana-toamidine product is present in about 2 to about 15 parts by weight to 100 parts by weight by hydrophobic liquid.

11. A process for making microcapsules comprising:
reacting an isocyanate having a radical consisting of a member selected from the group consisting of an isocyanato-aryl group, an isocyanatoalkyl group and an isocyanatocyclo-alkyl group with an amide at a temperature of about 80°C to about 230°C for a time of about 2 hours to 30 hours to produce an isocyanatoamidine, further reacting said isocy-anatoamidine with 1 to 5 moles of free isocyanate to obtain a readily hydrolyzable isocyanatoamidine product, then dissolving said isocyanatoamidine product resulting there-from in a hydrophobic liquid in the ratio of 2 to 15 parts of product to 100 parts of liquid, introducing the solution thus achieved into an aqueous emulsifier under conditions promotive of hydrolysis to produce capsules having a diame-ter of about 2 to about 100 microns and characterized by an impermeable wall surrounding hydrophobic liquid.

12. The process of claim 11 in which the hydrolysis promoting conditions include a temperature in the range of ambient to 100°C and the residence time of hydrophobic liquid in the emulsifier is from about one to about 24 hours.

13. The process of claim 12 in which the hydrolysis temperature is from about 40°C to about 80°C and the hydrolysis time is from about one to about three hours.

14. The process of claim 11 in which the said emulsi-fier is a protective colloid, said capsule including 100 parts by weight of core material and from about 0.5 to about 40 parts by weight of said protective colloid.

15. The process of claim 14 in which the protective colloid is present in an amount of about 2 to about 30 parts by weight.

16. The process of claim 11, wherein said capsules have a diameter of between about 3 to about 7 microns.

17. Microcapsules having impermeable walls consisting essentially of the hydrolyzed reaction product of (A) an isocyanatoamidine having the formula wherein R1 is a member selected from the group consisting of hydrogen and a lower alkyl group, R2 and R3 are members selected from the group consisting of lower alkyl groups, and R4 is a member selected from the group consisting of an isocyanatoaryl group, an isocyanatoalkyl group and an isocyanatocyeloalkyl group and (B) an isocyanate.