PREPRINTS OF THE 1998 ANNUAL SCIENTIFIC MEETING 67 ADDITIVES FOR WATER-BASED NAIL POLISH Mitchell Schlossman, Consultant West Orange, New Jersey Introduction and Discussion: There are four components of organic coatings- Binders. Solvents, Pigments, and Additives. Each component serves a different function: Binder- Polymer (resin) and crosslinker both react to form crosslinked networks. Solvent- To provide proper application and alter certain properties. Pigment- To provide color and enhance other properties. Additives- To control application and protective properties. Depending upon the content and binder/solvent make-up, nail polishes are classified into the following three categories: (a) Solvent-Borne- Low solids (binder) content high solvent content high volatile organic content. (b) Water-Borne- Binder/crosslinker dispersed in water low volatile organic content. (c) Latex-Synthesized polymer particles are suspended in water: low volatile organic content. The main types of polymers used in water-based nail polish formulations are Aqueous Polymer Dispersions and Water Soluble Polymers. Aqueous dispersions of water insoluble polymers are frequently prepared by aqueous emulsion polymerization, in which case they are generally described as emulsion polymers or latexes. Such polymers are mainly based on water insoluble comonomers such as methyl methacrylate, butyl acrylate, styrene, vinylidene chloride these polymers have a low degree of water solubility. Water soluble comonomers such as acrylic acid, methacrylic acid, are often present at low concentrations for reason of adhesion, colloidal stability or cross- linkability. Water-soluble polymers that give genuine water solutions over a broad pH range are rarely used as binders for aqueous nail polish because of the obvious problems of water sensitivity of the final product. Even after cross-linking they are rarely .successful in eliminating this problem. Instead, they are often used as additives, chiefly thickeners, colloidal stabilizers and pigrhent dispersants. Main examples are homopolymers of ethylene oxide, acrylic acid, methacrylic acid, polyvinyl alcohol and

68 JOURNAL OF COSMETIC SCIENCE various cellulosics. Frequently the purpose of a given additive is to overcome or alleviate a given difficulty. It is instructive to consider some of the difficulties and to consider the role of the additives. The rheology of aqueous polymer dispersions is less favorable for application than that of more Newtonian polymer solutions. Addition of water-soluble polymers (thickeners) is vital to increase high shear rate viscosity to an acceptable level for application of the nail polish and the low shear rate viscosity necessary to effect the flow and levelling characteristics. Although, the advantages of aqueous nail polishes are well recognized, there are several other difficulties associated with its formulation. An obvious disadvantage is that water has a high latent heat of evaporation (approx. 540 cal/g) therefore, at high temperature, a high-energy input is required to facilitate drying, while at ambient temperature and/or high relative humidities drying is slow. These effects can be alleviated by the use of selected volatile cosolvents. A significant problem encountered is that the surface tension of water (approx. 72 dynes/cm.2) is very high, leading to a number of difficulties, e.g., wetting of most surfaces (especially low energy ones such as nails), crawling, cratering and pigment wetting. The addition of surfactant to aid surface wetting and/or to help stabilize the dispersed component in an aqueous system (polymer and pigments) can itself cause difficulties because such additives are, by necessity, surface active and may cause foam and pinhole formation by stabilizing the water-air interface of entrained air bubbles by increasing surface elasticity and/or surface viscosity. The adhesion strength of the aqueous coating may be adversely effected. In general, it is more difficult to achieve a good pigment dispersion in an aqueous nail polish system than in the case of a corresponding solvent system. The freezing point of water is high compares to most organic solvents therefore, it is frequently necessary to add freezing point depressants to protect the formulations from freezing. Finally, bacterial growth requires an aqueous environment. It is frequently necessary to add a preservative in an aqueous formulation to prevent bacterial growth in the wet formulation, thus further increasing the number of components. Conclusion: It is clear from the foregoing discussion that the formulation of aqueous nail polish is generally more complex than is the case for solvent systems. Many patents have been issued, but to date no major cosmetic firm had entered the marketplace with a water- based product because of these inherent problems.