NEW SOFT CAPSULE 245 45 E 40 g 35 E 3o • 25 2o 20 30 40 50 60 70 80 Temperature of outer oil phase I øC Figure 5. Effect of outer oil phase temperature on the diameters of microcapsules. Stirring speed (5000 rpm) and composition (Table I) were uniform for each condition. In the experiment at 50øC and 70øC of the outer oil phase, the temperatures of the O/W emulsion-agar mixture were 50 ø and 70øC, respectively. However, in the experiment at 25øC of the outer oil phase, the temperature of the O/W emulsion-agar mixture was 50øC (since the agar gels at approximately 30øC). MEASUREMENT OF AGAR GEL STRENGTH The ratio of internal oil is considered to be an important factor that affects the strength of the microcapsules. Since the direct measurement of the strength of the microcapsules is practically impossible because of their physical size (400 lam), the strength of gels consisting of agar and O/W emulsion was measured instead. To estimate the effect of the ratio of the internal oil components on the strength of the microcapsules, samples containing different ratios of internal oil were prepared. Table II shows the relationship between the breaking intensity, Young's modulus, and the ratios of the internal oil phase. Over the entire range of ratios employed, the breaking intensities were almost constant, and this indicates a small effect of the volume of the internal oil. In contrast, Young's modulus was considerably affected by the ratio of the internal oil (Table II). The value of Young's modulus decreased with increase of the internal oil. The effect of temperature on agar aqueous gel was also studied. Since agar gel has a thermoreversible property, it is anticipated that the strength of the agar gel will deeply depend on the thermal conditions. Thus, aqueous agar gels were prepared to measure their thermorheo- logical properties. A constant concentration of agar (4.7%) in the gel was used in the aqueous phase of the formula shown in Table I, and butylene glycol and HCO-60 were removed to clarify the properties of agar. The rheological properties of the agar gel were measured at various temperatures (25ø- 90øC). The breaking intensity and Young's modulus were plotted against the tempera- ture (Figure 7). Although Young's modulus started to decrease over 70øC, the breaking intensity was constant. The results show that the softening point of agar gel exists between 70 ø and 85øC.

246 JOURNAL OF COSMETIC SCIENCE 450 E =. 400 E 350 ß 300 250 • ' ' • • 20 30 40 50 60 70 8O Temperature of outer oil phase I øC Figure 6. Effect of outer oil phase temperature on the diameter of microcapsules. Stirring speed (250 rpm) and composition (Table I) were uniform for each condition. In the experiment at 50øC and 70øC of the outer oil phase, the temperatures of the O/W emulsion-agar mixture were 50øC and 70øC, respectively. However, in the experiment at 25øC of the outer oil phase, the temperature of the O/W emulsion-agar mixture was 50øC, since the agar gels at approximately 30øC. Table II Composition of Microcapsules Containing Different Volumes of Internal Oil Compounds a* b c d fLiquid paraffin A•Water [HCO-60 (Butylene glycol BfAgar Water A:B 0 11.0 20.0 33.3 0 0.6 1.0 1.7 0 0.6 1.0 1.7 0 7.8 14.0 23.3 4.7 3.8 3.0 1.9 95.3 76.2 61.0 38.1 0:100 20:80 36:64 60:40 Breaking intensity (kg/m 2) 2090 2050 Young's modulus (x 10 -4 N/m 2) 46 29 2O5O 2O4O 22 12 * Internal oil ratios: a, 0% b, 11.0% c, 20.0% d, 33.3%. STABILIZING EFFECT OF MICROENCAPSULATION FOR UNSTABLE REAGENTS The amount of all trans-retinol palmitate remaining in microcapsules was determined to evaluate the stabilization effect of microencapsulation. The formulae are shown in Table Ill, and the time course of the changes in the remaining percentage of all trans-retinol palmitate in microcapsule and in oil solution at 50øC is illustrated in Figure 8. Micro-