J. Soc. Cosmet. them., 32, 43-52 (January/February 1981) Techniques for evaluation of nail enamel MITCHELL L. SCHLOSSMAN, Tevco Incorporated, Carlstadt, NJ 07072 Received September 3, 1980. Presented at the Society of Cosmetic Chemists'Annual Scientific Seminar, San Francisco CA, May 15-16, 1980. Synopsis Appraisal of nail enamel entails examination and measurement of several properties. They include flow characteristics, compatibility of constituents during drying, the rate of drying of films, and their resistance to soap and detergents. Nail lacquers should be carefully tested to make sure that they meet the performance specifications which have been set up by both marketing and technical executives. The judicious selection of testing methods and the correct interpretation of data are vitally important to the development of improved nail coating formulations. The performance of a nail enamel and its components is of primary concern to the lacquer chemist, he must prescribe the tests, interpret and refine the data while recognizing their overall significance, and apply conclusions based on the information obtained in the tests. The following physical parameters of nail enamel compositions are examined and measured along with their respective performance characteristics: adhesion, brushability, color and color stability, detergent resistance, drying qualities, durability, film thickness, flexibility, flow, gloss, storage stability, water resistance and wear. INTRODUCTION A recent interview among women readers of SELF Magazine (1), points out that the main factors influencing purchase of nail enamel were pleasing color, protection, wear, shine and ease of application considerations. A laboratory evaluation of experimental formulations will entail the examination of these and other properties. These include flow characteristics, compatibility of constituents during drying, the rate of drying of films, their resistance to soap and detergents, as well as other special performance evaluations. DISCUSSION Nail enamels, prior to release from the manufacturing plant, should undergo rigid control analysis. The following tests should be undertaken on all batches of nail enamels to determine the quality of the product: abrasion resistance, adhesion, application, color, density, drying time, flexibility, flow, gloss, hardness, nonvolatile content or solids, settling, viscosity, water content, water and detergent resistance. 43

44 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ABRASION RESISTANCE Nail coatings come into direct contact with other objects. The abrasion resistance of a coating (its ability to resist mechanical wear) may then largely determine the length of its useful life. Abrasion resistance of a test coating can be evaluated by periodic examinations performed while on the nail. However, the time to produce meaningful results would be excessive and controls difficult to obtain. The use of a Taber Abraser or similar instrument is used to measure abrasion resistance through the action of two resilient abrading wheels which a•e made to rub the coated surface. The nail enamel coating is applied to a special four-inch-square steel panel having a center spindle hold. The panel is placed on a turntable operating at a constant speed. Two abrading wheels, each 3/4 in. wide, are fixed on each side of the spindle and in contact with the coating surface. A load of up to 1000 g may be placed on the wheels in addition to their own 250-g weight. The direction of the abrasion pattern developed by the one wheel is from the outside to the center and by the other wheel from the center of the panel to the outside. A tachometer is provided to count the number of turntable rotations. Between the wheels, a vacuum device acts to remove loose particles abraded from the coating. With wheels of appropriate abrasive capacity in place under a suitable load, the instrument is operated for a specific number of cycles or until a portion of substrate is exposed. Results may be reported either as the number or cycles to failure per mil of film thickness or as the weight loss in milligrams per 1000 cycles. Utimately, any nail enamel must be evaluated on nails for wear resistance. For this evaluation a large panel of subjects is employed. Usually, an experienced manicurist applies both the test lacquer and a control on alternative fingernails of the subjects. The enamels are worn for a test period of one week, and the nails are examined daily and the condition of the lacquer recorded. This test will indicate large differences in wear resistance (2). Small differences may be obtained by using large numbers of subjects and setting up a statistical design of the results. Since the ability to resist mechanical wear may largely determine the length of a nail enamels useful life the aformentioned abrasion resistance evaluations are necessary and somewhat indicative of an enamels integrity. ADHESION An efficient coating, must adhere firmly to the nail surface. A striking color or a superior wear resistant polish is relatively useless unless adequate adhesion between the coating and the nail is achieved. Three methods are generally employed to measure this property. The cellophane tape adhesion test (particularly appealing because of its simplicity) and the use of a Hoffman scratch adhesion unit, which records the grams loading needed to scratch a film coating from the substrate glass plate. In the tape adhesion test, the coating is deeply scribed with a razor blade in the shade of a Greek letter lambda or another figure. This cut is made 1 in. high and 1/2 in. wide at the base. A piece of ordinary 3/4-in. cellophane tape, several inches long, is laid over its entire surface with a hard rubber eraser. A tab large enough to be grasped firmly with the fingers is left well above the figure. The tape is then removed by pulling rapidly and evenly toward the bottom of the test panel. An arbitrary numerical rating from 1 (complete failure) to 10 (perfect adhesion) is assigned to the test film depending on the