Establishing manufacturing processes, skin effects, texture and preventing problems with stability are all integral in the development and manufacture of cosmetics. The aim of this study was to evaluate the usefulness of rheological measurement in these areas of cosmetic production. Rheological measurement was applied at various stages during the development and manufacture of a bath milk, a skin care product, a cleansing milk and a facial cleansing foam. In the case of the bath milk, we applied mainly flow curves to observe the dispersibility of emulsified particles and to predict its stability. Regarding the skin care product, we investigated the rheological properties of materials on its basic formula to understand their effects on its texture. As for the cleansing milk, we used rheological measurements in order to distinguish the physical properties of formulas with defective texture from those that were acceptable. We then compared the rheological properties of an acceptable formula to those that had been produced by different manufacturing methods. The results of the study showed a significant correlation between the rheological measurement results and that of microscopic observations, sensory evaluations and stability tests. In the case of the facial cleansing foam, we selected a manufacturing machine and process with reference to the rheological measurement results. In conclusion, this study proved that rheology is useful in the development and manufacture of cosmetics.

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It is very important for product engineers in the field of cosmetics and toiletry industry to guarantee consumers to keep the constant quality and feeling of the products during the home use. This study aims at establishing technology for property control of toiletry products containing a long-chain alcohol and surfactants. Internal structure of cosmetic and toiletry products such as a self-assembly comprising cetyltrimethylammonium chloride (C16CA), cetyl alcohol (C16OH) and water was examined by electron microscopy et al. Rheological behaviors of the self-assembly were also observed to clarify the internal structure change during aging. It was confirmed that the self-assembly prepared at higher temperature involves multilamellar vesicles dispersed in continuous phase and also that semi translucent lamella was formed when self-assembly was prepared at room temperature. Phase transition of self-assembly from multilamellar vesicles to lamellae was confirmed on aging. Shear flow tests described showed that self-assembly is shear thinning with a hysteresis at higher shear rate and the maximum apparent viscosity made a steep and linear increase in a few days after preparation, followed by a gradual increase on further aging. Based on the creep test, a mechanical model for self-assembly was presented by 6 elements. The dependence of dynamic modulus (G') and loss modulus (G") on frequency (ω) was obtained. The Cole-Cole plots were combination of 2 arcs, indicating coexistence of 2 different relaxation mechanisms. They are attributed to the formation of the networks of vesicles and of lamellae. The change in the relaxation mechanisms also corresponds to the phase transition in self-assembly. In conclusion, this study unveiled the internal structure of the self-assembly comprising surfactants as a main component and showed its close relation with rheological behaviors.

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The relationships between suspension rheology and its effect of UV-protection for various suspensions were analyzed, such as particle type, particle size, particle surface properties, and type of dispersants. The objective of this study is to achieve the effective UV-protective method by use of the accurate control of suspension rheology. The rheological properties are studied for suspension of ultra-fine TiO₂ dispersed in silicone oil containing polyoxyethylene(POE) -modified silicones as dispersants. The effects of dispersion stability are evaluated through rheological methods and the flocculation mechanisms are discussed as a function of the molecular structures and HLB (Hydrophilic-lipophilic balance) of POE-modified silicones. The UV-protecting ability of suspensions of ultra-fine TiO₂ particles is also discussed in relation to degree of flocculation. Furthermore, the study of rheological behavior is used complex suspensions of TiO₂ and ZnO. The role of dispersants in heterogeneous flocculation behavior will be discussed in relation to their molecular structures to determine the optimum formulation of sunscreen cosmetics with high UV-protecting ability in both UVA and UVB regions. In the various cosmetics fields, the technology which formulates oil-in-water type emulsion containing fine particles in inner oil phase is the most general of them all. That can give the high UV-protection performance, smooth texture like non-powder, and natural color on the skin. The development and the application for this technology are additionally expected in cosmetic industries.

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Cosmetic formulations are composed by various ingredients. In particular, aqueous thickeners play important role in both functional and sensory aspects in formulations. We mention about our attempts to use microgels as intelligent aqueous thickener and to quantify the texture of the cosmetics, by using the rheological properties. Agar microgel dispersion was prepared from agar bulk-gel which was granulated by high-speed mixer (5000 rpm). The inverse microemulsion polymerization system was also studied to create a fine microgel. The thickening effect of the microgel prepared by using the system was higher than that of the agar microgel. The flow characteristic parameters of the microgels were analized by using Herschel-Bulkley equation which is a scaling law model. It was revealed that both the microgels present refresh feeling through power index n in H-B equation. Flow properties of cosmetic lotions, containing various kinds of aqueous thickeners, were studied by creep measurement, and parameters were calculated from their rheological data based on the Nutting equation, which is an empirical equation. There were some correlations among the time dependency parameter α and some sensory evaluation points, assessed by human panels. Simple linear regression analysis revealed that the evaluation scores of slimy feeling, sticky feeling, refresh feeling, and penetrating feeling of the cosmetic lotions were converted to numerical data by the parameter α. This quantification method for the texture of cosmetic products will be a useful tool for efficient development of cosmetic formulations.

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Establishing manufacturing processes, skin effects, texture and preventing problems with stability are all integral in the development and manufacture of cosmetics. The aim of this study was to evaluate the usefulness of rheology in establishing manufacturing processes for cleansing milk. We used rheological measurements in order to distinguish the physical properties of products with defective texture from those that were acceptable. We then compared the rheological properties of an acceptable product to those that had been produced by different manufacturing methods. From a correlation between the rheological properties and the manufacturing methods, we finally identified the factors that caused the product to have defective texture allowing the establishment of a suitable manufacturing process. In conclusion, this study proved that rheological measurement is useful in establishing manufacturing processes for cleansing milk.

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We have been focusing on the normal force difference in the high shear rate region as moisture feel for lipsticks. It is widely known that the use of polymeric materials is effective to increase the normal force. However the control of spinnability has been a problem for ordinary polymers like polyether. A cellulose derivative with low spinnability has been developed. Spinnability and viscoelasticity were evaluated for a polyether (POE) and a long-alkyl acylated cellulose derivative (RCE). Although spinnability was easily evaluated by using the tack mode of rheometer, it was difficult to measure 10 cm or more. Since dynamic moduli of both samples could not be expressed with a single Maxwell mode, one of these samples is shifted by the correspondence of their tan δ. The storage modulus, G', of RCE with low spinnability is greater than that of POE with high spinnability. For the non-linear rheology, we found that the correspondence between the first normal stress coefficient, Ψ₁, and G'/ω² is different between two samples. POE with high spinnability has no correspondence of this relationship.

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The viscosity modifier formulated in the juice part of cosmetic stretchable mask plays critical role in its overall performance. The performance by viscosity modifiers evaluated by rheological measurement is introduced. Several parameters from dynamic visco-elastic measurements which are related to product appearance as SMOT (second moment of truth) are also discussed.

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Rheological characteristics of stringy cosmetic emulsions that contain different ingredients and have different firmness was determined by a stress-controlled rheometer. Although the measurement of steady flow showed the first normal stress difference [N1] increase and viscosity [η] decrease with increase in shearing speed, there was no correlation between both parameters and the sensory evaluation score which indicates the degree of the stringiness. But it was found that new parameter ([N1]/[η]) has a strong correlation with the sensory evaluation score(r > 90) within a range of 300 - 1000S-1.

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