328 JOURNAL OF COSMETIC SCIENCE 10 8 10 • 8 6 B 0 20 40 60 80 0 5 10 15 20 Time / s Spreading value / cm 2 Figure 7. Measurements of oil components using the roller-type probe and its relation with spreading value. The measured friction for pentaerythrityl tetraoctanoate (¸), trioctanoin ('), and dimethyl polysi- loxane ([•) is shown in (A). The relation between the friction and spreading value of oils is shown in (B). 4O Z E 30 o 20 u. 10 A 0 2 4 6 8 10 Time / min z E 12 •- 10 E 8 o 6 • 4 o 2 ._u 0 -B Figure 8. Effect of humectants on friction using the roller-type probe. Moisturizing gels (10 I•l) containing various humectants (shown in Table lI) were measured under a probe load of 0.05 N and with reciprocation at 2.4 cm/s. Friction curves for gels containing 10% glycerol (O), 10% DPG (dipropylene glycol,/•), and 10% BG (1,3-butylene glycol, [•) are shown in (A). The detected friction levels at 10 min are summarized in (B). spread the sample over the sweep area. Differences in the frictional force gradually appeared as the slipping of the roller disappeared over time. At 10 min, the frictional force with the gel containing 10% glycerol was 5-7 times higher than that with the gel containing 10% 1,3-butylene glycol or 10% dipropylene glycol. The gel containing 5 %

330 JOURNAL OF COSMETIC SCIENCE 3O ._o o o I 2 3 4 5 Time I rain Figure 9. Detection of stickiness phenomena of thickeners measured using the roller-type probe. Mois- turizing gels (10 F1) containing various thickeners (0.5%) shown in Table III were measured under a probe load of 0.05 N and with reciprocation at 2.4 cm/s. The closed circle (O) represents the gel containing carbomer the open circle (¸), methyl cellulose the open triangle (/•), carboxymethyl cellulose the open square ([•), xanthan gum. A Figure 10. Observation of the contact region between the roller and the sample stage. Photos were taken at 2 min with a non-sticky sample (A) and a sticky sample (B). The non-sticky sample contained carbomer, while the sticky sample contained xanthan gum as a thickener (Table III). The scale bar indicates 5 mm. To investigate the relationship between the frictional force and the stickiness score obtained by sensory evaluation, various types of commercially available moisturizing creams were used as samples. The initial friction, the maximum friction, and the average friction (0-3, 3-6, and 6-9 min) were used for statistical analysis (Table IV). Contrary to expectation, no correlation was found between stickiness and the friction at the initial stages of the measurements, including the initial value, the maximum value, and the average value over 0-3 minutes. However, a clear correlation was observed between the stickiness after application and the average friction in the mid-to-late stage of the measurements (3-6 and 6-9 min). In addition, these mean values were clearly related to other sensory attributes, including spreading or absorption during application and rich- ness or hydration after application. Since the frictional force reached a constant value at 6 min, the friction at the steady state is considered to provide valuable information for the evaluation of cosmetics. This finding implies the importance of studying