The primary function of the base coat is to promote adhesion between the nail and the coatings that follow. Since it is in immediate contact with the nail, the base coat represents an important opportunity to affect the structure of the nail while providing the primary function of adhesion promoter. With some thought, a number of other functions can be provided. These include the following.
1. Adhesion between layers of delaminated nail. While the primary function of the base coat is to promote adhesion between the nail and the pigmented enamels that follow, it can also promote adhesion between layers of the nail that have become separated. The dorsal layer of the nail often becomes separated from the intermediate layer, causing both discomfort and an unsightly, unkempt appearance. If this delamination is glued, the nail can grow out in a more sound condition, providing both an important benefit to the user and an important claim for the product. The base coat is the logical product to provide this function. Increasing the polymer solids would be one way to accomplish adhesion between the nail and nail enamel while actually gluing layers of nail together, providing a significant multifunctional base coat.
2. Maintenance of nail flexibility by balancing nail moisture. Additional functionality can be developed into the base coat by balancing the permeability of the coating to allow the moisture content of the nail to remain constant. This balance also keeps the nail from becoming too dry and brittle. The moisture passing through the dorsal layer of the nail maintains flexibility that helps prevent broken nails. Most of us have noticed that the nail becomes quite flexible when wet. Trimming nails after bathing is ideal especially for toenails, because the moisture-laden nail is easily trimmed. Conversely, the nail becomes quite brittle when dry. The normal nail passes a considerable amount of moisture, about 1.5 mg of water per square centimeter per hour . If this moisture is not allowed to escape, bonds between the nail and nail enamel are severely weakened. It would be like painting a wet wall with an oil-based paint. When one is formulating a base coat, permeability can be varied by using nitrocellulose as the primary film former and maintaining flexibility by using one of the phthalate esters, which allow good moisture transfer. The modifying resin would be any one of several chosen from Table 1. Permeability is monitored by casting a test film onto a substrate, which allows it | to be conveniently lifted when dry. Teflon is a good choice. The freestanding test film is then tested for permeability by means of Method D1653 of the American ^
Society for Testing and Materials (ASTM). |
3. Strengthening the dorsal layer of the nail by forming a matrix between the calcium in the nail and an active ingredient in the base coat. The dorsal layer of the nail is made up of totally dehydrated cells of hard keratin and contains the highest level of calcium. This calcium can be used to form a reinforcing structure by combining with an active ingredient included there in. See the Busch patents [4,9] for a more complete description of the chemistry between the calcium-containing nail keratin and fluoride compounds. By using a compound such as fluoride to strengthen the nail, the functionality of the base coat is much improved. It will be left to the interested formulator to identify other compounds with similar functionality.
4. Include ridge-filling ingredients, which help create a smooth beautiful manicure. Since the surface of the human fingernail becomes rough and uneven, a ridge-filling claim is important for many users of nail enamel. The problem seems to get worse with age. The choice of filler ingredients is broad, but if you choose a heavy ingredient, a suspending agent will be required. Filler ingredients include those commonly used in makeup and include sericite, talc, mica, quartz, and many others .
5. Provide extra cushioning to protect the nail from impact-type forces. One strategy for formulating a base coat is to increase the polymer solids to improve impact resistance. To this end, more rapidly evaporating solvents are used to reduce the drying time required before additional coats of the manicure are applied.
Summary A base coat formula with multifunctionality can be clearly developed, offering important consumer benefits while providing the marketer with important commercial claims. While the balance of ingredients will be time-consuming to achieve, the benefit to both the consumer and the marketer could well be significant.
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