Aesthetics of any vehicle is a one of the prime requirements and concerns for any automobile user ranging from the tires to the hood of that vehicle, and other parts as well. For example, the shine and glossy facade of the wheels enhances the overall splendor of an automobile. However, the luster of the wheels shine is dulled by various factors including brake dust, road grime, muddy water, etc. Out of those, brake dust not only deteriorates the glossiness, but also the dusts long term contact augments the corrosion tendencies of the wheel.
Generally, brake dust is a product of wear from the friction between the brake pads and rotors of the vehicle. Brake pads convert the kinetic energy of the car to thermal energy by friction. Two brake pads are contained in the brake caliper with their friction surfaces facing the rotor. When the brakes are hydraulically applied, the caliper clamps or squeezes the two pads together into the spinning rotor to slow/stop the vehicle. When a brake pad is heated by contact with a rotor, it transfers small amounts of friction material to the disc, turning it a dull gray. The brake pad and disc (both now with friction material), then “stick” to each other, providing the friction that stops the vehicle. In order to maintain the original appearance of automobiles, a wide variety of automobile appearance products are used in consumer applications. Specifically, numerous wheel and tire cleaners are commercially available to maintain the appearance of soiled tires, metal or plastic wheels, wheel covers, or hubcaps. These wheel cleaners are typically acidic formulations, with pH ranges from 2 to 4. The extreme acidity of the wheel cleaner is required to effectively remove brake dust, road soil, and grime. These formulations also typically use anionic, amphoteric, or nonionic surfactants to enhance the detergency of the wheel cleaning formulation. The extremely low pH of these formulations makes their compatibility poor with many metallic wheels, and most of these products are devised for use on clear-coated wheels so there is no (or very low) chance of acid corrosion. The compositions must be washed or wiped from the tires and wheels within 15 seconds to one minute to prevent permanent damage to the wheels, and also to facilitate cleaning.
The principle of self-cleaning plays a major role in brake dust repellent coatings. In order to achieve a good self-cleaning and dirt repellent surface, the surface not only has to be very hydrophobic, but also has to have some degree of roughness. A suitable combination of structure and hydrophobic properties does not permit any kind of dust or contaminants, including water, to adhere on the surface.
A number of attempts have been made, as evidenced in the prior art, to obtain a super hydrophobic and antistatic composition. U.S. Pat. No. 7,083,828 to Muller et al. describes a formulation for detachable dirt and water repellent coating which has to be applied at room temperature only. U.S. Patent publication number US 2007/0190308 to Brand et al. discloses the formulation for scratch resistant and self-cleaning protective layer for rims of automobiles, but has the drawback that the formulation requires two layers to achieve the effect, and has to cure at an elevated temperature (up to 200° C.). U.S. patent publication number 2009/0018249 to Kanagasabapathy et al. discloses a coating composition for a hydrophobic self-cleaning effect but has the drawback that the formulation has to be applied on wax surface only. U.S. patent publication number 2004/0213904 to Muller et al. discloses a process for producing a water repellent and dirt detachable surface coating consisting of hydrophobic particles in conjunction with alkyd modified silicone wax in a highly volatile siloxane. The suspension is applied to the surface of an article, and volatile siloxane is evaporated forming a grayish coating. The disadvantage of this coating is hazy layer that is left on the treated surface, and is not suited for cosmetic applications.
Furthermore, there are several published articles which have dealt with elimination of water marks. U.S. Pat. No. 5,759,980 to Russo et al. discloses a coating comprised of silicone based surfactant and a polymer, where the Polymer is used as a binder. However, this coating is hydrophilic in nature and may tend to be removed from the surface by single wipe.
The patent publication number WO 2008/153687 discloses a super hydrophobic coating composition composed of nano silica and an acetone solvent combination for forming a clear coating film for painted surfaces on metal, glass, ceramic, fiberglass, wood, and waxed substrates. A Treated silica particle layer forms a contact angle of 165 degrees and a rolling angle of 2 degrees. Despite various advantages of the composition, it has the disadvantage that its durability against vibration and bond strength with the surface of the substrate, and is not suited for automotive applications.
Thus, there is a need for a cost effective super hydrophobic and antistatic composition that can be successfully used for all kinds of automobile wheels, overcoming the above mentioned problems of the currently available super hydrophobic coating compositions, which reduces the accumulation of dust, soil and grime on vehicle wheels without the use of harsh chemicals.