A process for manufacturing minute capsules

Method for making small capsules Förfarande för framställning av smä kapslar

This invention relates to a process for the manufacture of small capsules having a melamine-formaldehyde hydropolymeric wall. The capsules are specifically, but not exclusively, intended for use in pressure sensitive deinking systems.

U.S. Patent 2,730,456 describes a pressure sensitive de-icing system, commonly referred to as a manifold copying system. This series of copying system comprises an upper sheet, the lower surface of which is coated with microcapsules containing a solution of a colorless chromogenic substance, and a lower sheet, the upper surface of which is coated with a color-generating coreactant, e.g.

acid clay, phenolic resin or certain organic salts. When more than two layers are required in the recording material to achieve a higher copy number, a number of intermediate sheets are also used, the lower surface of each of which is coated with microcapsules containing a colorless chromogenic substance and the upper surface with a color-developing coreactant. The pressure applied to the sheets by hand or typing breaks the microcapsules, thus releasing a solution of the chromogenic substance on the next reactant on the lower sheet, thus creating a chemical reaction that develops the color of the chromogenic substance.

Another type of pressure sensitive deinking system is known as a self-contained system and is described in U.S. Patents 2,730,457 and 4,197,346. Microcapsules containing a solution of a chromogenic agent and a coreactant are coated on the same surface of a sheet of paper. The pressure applied to the sheet by hand or typing causes the capsules to break and release a chromogenic substance, which then reacts with the coreactant on the sheet to produce color.

Strict requirements have been placed on the properties of the microcapsules used in the pressure-sensitive quenching systems described above. To achieve an optimal icing system. Such properties include the strength of the capsules, the range of color distribution, and the uniformity (impermeability) of the walls.

Several methods have been proposed for the preparation of microcapsules with all or part of the melamine formaldehyde polymeric material. For example, in a U.S. patent

0 U.S. Pat. No. 4,015,823 describes a process for encapsulating a chromogenic substance for the preparation of microcapsules, in which the wall of the capsules is prepared by acid catalysis of a water-soluble urea formaldehyde precondensate and a water-soluble melamine formaldehyde condensate in the presence of a water-soluble polymer.

U.S. Patent 4,100,103 describes an encapsulation process by in situ reaction of melamine and formaldehyde and / or polymerization of a monomeric methylol melamine or etherified methylol melamine or a low molecular weight polymer thereof in the presence of one of a number of specific, negatively charged, carboxylated substituents.

U.S. Patent 4,233,178 describes an encapsulation process in which a dispersion of a desired capsule core material is formed in an aqueous solution of a styrene maleic anhydride copolymer polyelectrolyte, melamine formaldehyde precondensate is added, and the mixture is heated to form microcapsule walls.

The method described in U.S. Patent 4,100,103 has been successfully used on a commercial scale to encapsulate solutions of chromogenic agents for use in pressure sensitive stiffening papers.

Preferred polyelectrolyte materials are hydrolyzed maleic anhydride copolymers disclosed in the process of U.S. Patent 4,100,103, the most preferred of which is poly (ethylene-co-maleic anhydride) (hereinafter EMA) due to its commercial availability and its properties for the encapsulation process.

The price of EMÄ has recently risen rapidly, correspondingly raising the price of microcapsules made by the method in which EMÄ forms a polyelectrolyte. In terms of price and availability, poly (acrylic acid) (hereafter PAA) is a logical substitute for EMA as a polyelectrolyte. Although microcapsules made by the process of U.S. Patent 4,100,103 in which PAA forms a polyelectrolyte are commercially useful in pressure sensitive copying papers , they do not have the optimum balance of properties obtained with EMA.

One function of the polyelectrolyte of U.S. Patent 4,100,103 is to actively participate in the polymerization reaction of the starting materials used to form the condensation polymer that forms the capsule walls. Under equivalent reaction conditions, the use of PAA results in a slower formation of capsule walls than when EMA is used.

Another function of the polyelectrolyte is to act as an emulsifier to promote and maintain the separation of individual droplets of the desired capsule core material in the aqueous preparation medium. When PAA is used as a polyelectrolyte, more energy and time is required to emulsify the desired capsule core material, and a poorer droplet size distribution is obtained than when EMA is used. It has now been found that the poorer emulsifying capacity of PAA can be offset by mixing, prior to emulsification, the starting materials (e.g. methylated methylol melamine) used in an in situ polymerization reaction to form a condensation polymer that forms capsule walls. The presence of methylated methylol melamine or a low molecular weight polymer thereof (hereinafter MMM) during the emulsification step of the desired core material may result in premature polymerization of the MMM. This tendency of MMM to react prematurely under these conditions is reduced by raising the pH of the PAA-MMM solution to the highest level at which emulsification of the desired core material can occur. As soon as a satisfactory emulsion of the desired core material has formed, its pH must be lowered in order for the capsule walls to satisfactorily precipitate within a reasonable time. This alternative procedure outlined above has been further modified using the steps of:

(1) forming an aqueous solution of MMM and a portion of PAA at as high a pH as where a satisfactory emulsion can be obtained.

(2) emulsifying the desired capsule core material into an aqueous solution, (3) adding the remainder of the PAA solution at a suitably lower pH so that the resulting mixture is at a pH closer to optimum for polycondensation of MMM, and (4) heating the mixture to MMM. to accelerate the polycondensation and subsequent precipitation of the condensation polymer on the dispersed capsule core material.

It has been found that the end-use properties of microcapsules prepared by the procedure described above in pressure-sensitive waste paper are approximately those obtained when EMA is used as a polyelectrolyte in a simpler and more controllable process.

In addition, it has been found that when the process is performed essentially as described above, but the emulsification step is changed by adding a solution containing one or more specific salts, some or all of the additional PAA solution, the microcapsules formed after MMM polycondensation have improved permeability walls. In addition, the viscosity of the resulting microcapsule slurry is lower than that of the slurry prepared by steps (1) to (4) of the previously described method. The advantages of lower viscosity are easier transportability of the wet capsule slurry and coating of the capsule slurry at higher solids concentrations, with correspondingly less energy required to remove water when drying the coating, and improved permeability provides a longer shelf life for the capsule-coated sheet.

It has also been found that the addition of any of these same salts, prior to polycondensation of the starting material, to methods similar to those generally described in U.S. Patents 4,100,103 and 4,233,178 (using any of the polyelectrolyte described therein) unexpectedly results in improved capsule wall integrity and reduced capsule slurry viscosity.

According to the present invention, there is provided a method of making small capsules comprising the step of forming a dispersion of droplets or particles of substantially water-insoluble capsule core material in an acidic aqueous preparation medium comprising:

(a) a capsule wall precursor selected from melamine and formaldehyde; monomeric methylol melamine or a low molecular weight polymer thereof; monomeric methylated methylol melamine or a low molecular weight polymer thereof; or any combination thereof; and

b) a negatively charged polymeric polyelectrolyte 25 having a straight aliphatic hydrocarbon backbone having an average of two carboxyl groups for each of 4-6 backbone carbons;

wherein the water-soluble capsule wall precursor polycondenses to form a condensation polymer, resulting in

i) the formed condensation polymer with a molecular weight above the molecular weight soluble in the aqueous preparation medium as liquid-liquid phase separations, ii) the extended polycondens of the separated polymerization product6

715 After the foundation, the formation of a solid capsule wall material individually surrounding the particles of dispersed capsule core material, the method being characterized in that said dispersion also contains a salt of a periodic group 1A cation or a tertiary or quaternary ammonium cation and a strong acid anion.

In a preferred embodiment of the method, a solution of a polymeric polyelectrolyte negatively charged in the aqueous preparation medium is first formed, followed by the addition of a capsule wall precursor; then the capsule core material is dispersed in the preparation aqueous medium, and then a salt is added, followed by polycondensation of the capsule wall material.

With the exception of salts added during the manufacture of small capsules, this method is similar to that described in U.S. Patents 4,100,103 and 4,233,178. The agents and procedures generally described in these patents can also be used in this method.

In order to achieve a satisfactory dispersion of the desired capsule core material, the aqueous preparation medium must usually be stirred continuously. The negatively charged polymeric polyelectrolyte should normally be present in the aqueous preparation medium prior to the addition of the substantially water-insoluble capsule core material.

The acidity of the aqueous preparation medium is usually obtained from the carboxyl groups of the polyelectrolyte, so that no additional addition of acid is necessary. However, if desired, the acid may be added as a supplement.

Strong acidic anions can be from inorganic acids, for example chloride, sulphate, phosphate, nitrate or polyphosphate anions, or from strong organic acids, for example citrate, maleate and fumarate anions.

Salts of cationic Group 1A cations and chloride, sulfate, phosphate and nitrate anions are preferred salts. Potassium phosphate is the most preferred salt. The salt may be added as such, but may also be formed in situ by the reaction between a basic salt of a cation of Periodic Group 1A and a strong oxygen. The amount of salt can vary widely, but is preferably used in an amount of about 1 to about 10% by weight based on the weight of the aqueous preparation medium. The upper limit has been chosen for convenience rather than functionality. Quantities of more than 10% by weight can be used, but this does not lead to any further improvements in properties.

The negatively charged polymeric polyelectrolyte may be, for example, poly (ethylene-co-maleic anhydride), poly (methyl vinyl ether-co-maleic anhydride), poly (acrylic acid), poly (propylene-co-maleic anhydride), poly (butadiene-co-maleic anhydride), poly ( vinyl acetate co-maleic anhydride and polystyrene-co-maleic anhydride). The greatest advantages are obtained when the polyelectrolyte material is poly (acrylic acid) or poly (styrene-co-maleic anhydride). The amount of polyelectrolyte material used can vary widely, but is preferably used in an amount of about 0.4 to about 15% by weight, based on the weight of the aqueous preparation medium. The upper limit has been chosen in terms of economy and suitability rather than functionality. Amounts in excess of 15% by weight may well be used, but no further improvements in properties are achieved.

The method operates over a wide temperature range, but a temperature range of about 40 ° C to about 95 ° C is recommended. The most preferred temperature range is from about 50 ° C to about 60 ° C.

The invention will now be described with reference to the following examples, in which:

(a) all parts and percentages are by weight unless otherwise stated;

(b) all solutions, unless otherwise stated, are aqueous solutions,

(c) the capsule core material was a solution of the chromogenic compounds listed in Table I.

Table I

Concentration 1, 7%

0,55%

0,55%

Chromogenic substance

3.3-bis- (p-dimethylaminophenyl) -6-dimethylaminophthalide

2'-Anilino-3'-methyl-6'-diethylaminofluorane

3.3-bis- (1-ethyl-2-methylindol-3-yl) phthalide

The solvent for the solution of chromogenic compounds was a mixture of 65 parts of C 1-4 alkylbenzene and 35 parts of benzylated xylenes.

Example 1 :

A solution of 144 g of 12.5% ​​poly (acrylic acid) with an average molecular weight of less than 300,000 (Acrysol A-5, Rohm & Haas) was partially neutralized with 9.55 g of triisopropanolamine and diluted with water to a total weight of 840 g. . To 805 g of this solution, pH 4.55, was added 115 g of partially methylated methylol melamine resin (Cymel 382, ​​American Cyanamid) to give, with stirring, a clear solution, pH 4.95. 880 990 g of a solution of the chromogenic compounds of Table I were emulsified to give a droplet size range of 1 to 10 microns. A 170 g portion of the previous emulsion was added to each of the three vessels. The vessels were placed in a room temperature water bath and stirred continuously. Alternatively, one of the following was added to each mixable emulsion:

Example Added substance

<td>1A</td><td>30 g</td><td>water</td>

<td>1B</td><td>30 g</td><td>KH₂13.3% solution of PO 2</td>

<td>IC</td><td>30 g 3.5</td><td>a solution containing g of poly (acrylic acid),</td>

having a molecular weight of less than 50,000 (Acrysol A-1, Rohm &amp; Haas), and 0.55 g of KOH.

The water bath was heated to 56 ° C and maintained at this temperature for eight hours to initiate and complete encapsulation. The heating of the bath was then stopped and the batches were continued to stir in a cooling water bath overnight. The next day, 2.2 ml of 28% ammonium hydroxide was added to each batch, sufficient 30% KOH 2 was added to each batch to give a pH of about 9.5, and sufficient water was added to each batch to give a total weight of 217 g each.

The viscosity of each capsule batch was measured with a Brookfield LVF viscometer at 25 ° C, and results were expressed in centipoise units (cps). The shaft speed for all batches was 60 rpm, and for batches 1A and 1C the shaft number was 3 and for batch 1B the shaft number was 1.

The impermeability (or vice versa, permeability 1. permeability) of each batch of capsules was determined by the following procedure:

The following mixture was prepared:

Quantity Substance

100 g capsule slurry g 20% ​​ethoxylated starch binder g wheat starch grains

190 g of water

This mixture was dispersed, coated with a wire-twisted coating rod on a paper base, and the coating was dried for one minute in an oven at 150 ° C to give a dry coating weight of 4 g of dried capsules per square meter. A 58.064 cm (9 sq. Inch) portion of the capsule-coated paper was soaked for 10 minutes in 20 ml of room temperature toluene to extract only the chromogenic material that was not inside the capsules with impermeable walls. The color of the chromogenic substance was developed with stannous chloride, and the amount of color was determined 2 colorimetrically. Another 58.064 cm portion of the same capsule-coated paper was extracted with 100 ml of a solution containing

was three volume percent concentrated hydrochloric acid in methanol. By this procedure, which is carried out at 55 ° C for one hour, all the chromogenic substance can be extracted from the sheet. The amount of color that developed in the presence of hydrochloric acid in this extract was determined colorimetrically. The permeability, expressed as a percentage of the coated capsules, is calculated by the following formula:

Permeability The amount of color in a toluene extract The amount of color in a methanol extract

This method of permeability, or capsule wall integrity, is based on the principle that a room temperature toluene extract removes only the chromogenic substance that is not inside the satisfactory, impermeable capsules. The hot methanol extract destroys all the capsule walls, and removes all the chromogenic substance from the sheet. These permeability results can be used to predict the quality of the capsules, for example the ability of the coated capsules to retain their contents during long storage.

Using the viscosity and permeability procedures described above, the three capsule batches of Example 1 were compared:

Pre-order. added Batch pH capsule final. batch permeability mark poly (axial salt viscosity rylic acid)

<td>1A</td><td> 1,5</td><td>g</td><td>No</td><td> 5,65</td><td>1030 cps</td><td> 34,8%</td>

<td>1B</td><td> 1,5</td><td>g</td><td>4 g</td><td> 5,10</td><td>44 cps</td><td> 3,5%</td>

<td></td><td></td><td></td><td>KH₂PO₄</td><td></td><td></td><td></td>

<td>1C</td><td> 5,0</td><td>g</td><td>No</td><td> 4,90</td><td>1350 cps</td><td> 5,5%</td>

Thus, a batch with a lower than desired permeability (batch 1A) can be brought to a much more favorable permeability range by using additional PAA (batch 1C), but at the expense of increasing the viscosity of the batch. Salt addition (KH₂PO₄) the batch (IB) obtained using has both a very satisfactory permeability value and a very low batch viscosity. Example 2:

The procedure of Example 1 was repeated essentially through the emulsification step using the same relative amounts of the same components. Alternatively, one of the following substances was added to 170 g portions of the resulting emulsion:

Example Added substance

<td>2D</td><td> 30</td><td>g</td><td>KH₂PO₄:of</td><td> 6,7%</td><td>solution</td>

<td>2E</td><td> 30</td><td>g</td><td>KH₂PO₄:of</td><td> 10,0%</td><td>solution</td>

<td>2F</td><td> 30</td><td>g</td><td>KH₂PO₄:of</td><td> 13,3%</td><td>solution</td>

<td>2G</td><td> 30</td><td>g</td><td>KH₂PO₄:of</td><td> 20,0%</td><td>solution</td>

<td>2H</td><td> 30</td><td>g</td><td>solution, acid) a</td><td colspan="2">containing 3.5 g of poly (acrylic (Acrysol A-1)) and 0.27 g of KOHx</td>

After the addition of the above substances, the encapsulation process and the following procedures, including capsule coating, were performed as in Example 1.

Capsule slurry viscosity and permeability tests for coated capsules were performed for each batch of Example 2 using the methods described previously. When measuring the viscosity, an axial speed of 60 rpm was used for all batches, with an axle number of 1, except for batch 2H, where it was 3. The results obtained are shown below:

Example coc. poly added pH encapsulation final. perrreabi (acrylic salt after batch viscity acid) cosity

<td>2D</td><td> 1,5</td><td>g</td><td>2 g kh₂po₄</td><td> 5,15</td><td>61 cps</td><td> 4,2%</td>

<td>2E</td><td> 1,5</td><td>g</td><td>3 g KH P °₄</td><td> 5,10</td><td>49 cps</td><td> 3,7%</td>

<td>2F</td><td> 1,5</td><td>g</td><td>² 4 5 kh₂po₄</td><td> 5,05</td><td>44 cps</td><td> 4,0%</td>

<td>2G</td><td> 1,5</td><td>g</td><td>6 g kh₂po₄</td><td> 5,00</td><td>41 cps</td><td> 3,6%</td>

<td>2H</td><td> 5,0</td><td>g</td><td>No</td><td> 4,60</td><td>1374 cps</td><td> 4,4%</td>

<td colspan="3">Above</td><td>the results are</td><td>as evidence</td><td>that</td><td>joint</td>

preferred batch viscosity and capsule permeability results can be achieved over a wide range of salts.

Example 3:

This example describes how a salt can be formed by an in situ reaction.

The procedure of Example 1 was essentially repeated through the emulsification step using the same relative amounts of the same components. Alternatively, one of the following was added to 170 g of the resulting emulsion.

<td>Example</td><td>Added</td><td>'substance</td>

<td> 31</td><td>30 g of a solution of LiOH.H₂O</td><td>was 2.14 g H 2 PO 2 and 0.95 g</td>

<td>3J</td><td>30 g of a solution with NaOH</td><td>was 2.14 g H 2 PO 2 and 0.9 g</td>

<td>3K</td><td>30 g of a solution with KOH</td><td>was 2.14 g H₃PO₄ and 1.19 g</td>

<td>3L</td><td>30 g of a solution with CsOH</td><td>was 2.14 g H₃PO₄ and 3.14 g</td>

<td>3 M</td><td>30 g of a solution with</td><td>was 2.14 g of II₃PO₄ and 3.32 g</td>

(hoc₂B₄)₃of

<td>3N</td><td>30 g of a solution with</td><td>was 2.14 g H₃PO₄ and 4.70 g</td>

<td></td><td>(HOC₂B₄) ₄noii</td><td></td>

<td> 30</td><td>30 g of a solution with</td><td>was 0.5 g of acetic acid.</td>

After the addition of the above substances, the encapsulation process and the following procedures, including capsule coating, were performed as in Example 1. During the encapsulation step, Example 30 coagulated, resulting in a batch of unsatisfactory capsules, which could not be evaluated in viscosity and permeability tests, respectively.

Capsule slurry viscosity and coated capsule permeability tests were performed for each batch of Examples 3 I-N using the methods previously described. When measuring viscosity, the shaft speed was 60 rpm and the shaft number was 1 for all batches 3 I - N.

The results obtained are shown below:

503

Batch

Example Added salt pH Capsule final batch permeability viscosity

<td></td><td></td><td>after</td><td>ti</td><td></td>

<td> 31</td><td>lithium phosphate</td><td> 5,05</td><td>49 cps</td><td> 4,1%</td>

<td>3J</td><td>sodium phosphate</td><td> 5,10</td><td>52 cps</td><td> 4,2%</td>

<td>3K</td><td>potassium phosphate</td><td> 5,10</td><td>50 cps</td><td> 3,8%</td>

<td>3L</td><td>cesium phosphate</td><td> 5,10</td><td>54 cps</td><td> 3,2%</td>

<td>3M</td><td>tertiary amine phosphate</td><td> 5,15</td><td>43 cps</td><td> 3,4%</td>

<td> 30</td><td>No</td><td> 4,70</td><td>coagulated</td><td> —</td>

<td colspan="3">Previous results show that</td><td>group IA-</td><td>and small</td>

molecular weight, water-soluble tertiary and quaternary amine cations are effective in the practice of this invention. Example 30 shows that the beneficial effects of this invention are not the result of pH adjustment alone. Acetic acid was used in this example because it was difficult to obtain a suitable pH using the strong acid H 2 PO 4. Example 4:

The procedure of Example 1 was essentially repeated through the emulsification step using the same relative amounts of the same components. Alternatively, one of the following was added to 170 g of the resulting emulsion.

Example_Added substance_

4P 30 g 10% KH₂PO₄

4Q 30 g 20% ​​KCl

4R 30 g 10% K „SO.

³ 2 4

4S 30 g 20% ​​KNO₃

4T 30 g of a solution containing 2.5 g of citric acid and 1.0 g of KOH.

For each batch of Example 4, viscosity and coated capsule permeability tests of the capsule slurry were performed using the methods described previously. When measuring viscosity, the shaft speed was 60 rpm and the shaft number was 1 for all batches 4 P to T. The results obtained are shown below.

Example Added salt batch pH capsule final. the rigidity of the viscosity ablation was assumed

<td>4P</td><td>potassium phosphate</td><td> 5,10</td><td>46 cps</td><td> 4,6%</td>

<td>4Q</td><td>potassium chloride</td><td> 5,00</td><td>35 cps</td><td> 3,9%</td>

<td>4R</td><td>potassium sulfate</td><td> 5,10</td><td>48 cps</td><td> 4,3%</td>

<td>4S</td><td>potassium nitrate</td><td> 5,10</td><td>49 cps</td><td> 3,8%</td>

<td>4T</td><td>potassium citrate</td><td> 4,90</td><td>24 cps</td><td> 4,6%</td>

<td colspan="2">Previous results</td><td>show</td><td>that salts,</td><td>which contain</td>

common anions of strong inorganic acids, and anions of water-soluble strong organic acids, are effective in the practice of this invention.

Example 5:

The procedure of Example 1 was repeated essentially using the same relative amounts of components throughout the emulsification step, with the exception that the poly (acrylic acid) was replaced by poly (ethylene-co-maleic anhydride, MP about

75 000 - 90 000 (EMA-31, Monsanto Company, St. Louis,

Missouri), with an equal relative weight, and the EMA was partially neutralized with 11.97 g of triisopropanolamine.

170 Alternatively, one of the following substances was added to the g portions of the resulting emulsion:

Example_Added substance

5U 30 g of water

5V 30 g 20% ​​KH₂PO₄

Capsule slurry viscosity and coated capsule permeability tests were performed on the batches of Example 5 using the methods described above. When measuring viscosity, the shaft speed was 60 rpm and the shaft number was 2 for 5U and 1 for 5V. The results obtained are shown below

Example The pH of the added salt batch is final. batch permeabi capsule viscosity after lysis

5U

5V not potassium phosphate

5,05

4,80

220 cps 71 cps

6,6%

3,8%

The foregoing results indicate that, when used with the present invention, a carboxyl group polyelectrolyte other than PAA of U.S. Patent 4,100,103 has a somewhat lower but still significant and unexpected effect on the viscosity and permeability properties of the resulting capsule batch.

Example 6:

The procedure of Example 1 was repeated using essentially the same relative amounts of components throughout the emulsification step, except that poly (acrylic acid) was replaced with poly (styrene-co-maleic anhydride) (hereinafter SMA) (Scripset 520, Monsanto Company, St. Louis, Missouri) with the same relative weight section. SMA was hydrolyzed by mixing in warm water with an added amount of KOH such that the equivalent ratio of potassium ion to SMA carboxylic acid was 0.3: 1. No trisopropanolamine was used in Example 6.

170 Alternatively, one of the following substances was added to g portions of the resulting emulsion.

Example_Added substance

6W 30 g water

6X 30 g 10% KH_ofPO.

Capsule slurry viscosity and coated capsule permeability tests were performed on batches of Example 6 using the methods described previously. When measuring viscosity, the shaft speed was 60 rpm and the shaft number was 2 for batch 6W and 1 for batch 6X. The results obtained are shown below.

Example Added pH of a batch of final batch permeability capsule viscosity after lysis

6W no

6X potassium phosphate

5,95

5,55

332 cps 46 cps

74%

20%

6

The foregoing results indicate that, when applied to the process of the present invention using SMA as a system modifier, there are significant and unexpected beneficial results in the viscosity and permeabilities of the resulting capsule batch.

Example 7:

The procedure of Example 6 was repeated with essentially the same relative amounts of components, except that the partially methylated methylol melamine resin was replaced by the reaction product of melamine and formaldehyde, with an equal relative weight. The reaction product of melamine and formaldehyde was prepared by heating a mixture of 15 g of melamine, 37.5 g of 37% formaldehyde and 52.5 g of water to 76 ° C with stirring until a clear solution (ca.

20 minutes). This solution was then used instead of the Cymel described previously.

170 Alternatively, one of the following substances was added to the portions of the resulting emulsion:

Example_Added substance

7Y 30 g of water

7Z 30 g 10% KH₂PO₄

Capsule permeability tests were performed on the batches of Example 7 using the method previously described. The results obtained are shown below.

Example Added salt after batch pH encapsulation permeability

7Y no 6.15 25.4%

7Z potassium phosphate 5.60 6.1%

The foregoing results indicate that this invention, when applied to the process of U.S. Patent 4,233,178, has significant and advantageous results in the permeability properties of the resulting capsule batch.