The construction and public safety industries are constantly looking for means to make substrates, such as roadways, pathways, and other high-use areas, safer for vehicular and human traffic. One developing area is in the application of friction-modifying coatings to surfaces of substrates to help increase their coefficient of friction, thereby reducing slippage and skidding and making them safer for their intended use. In particular, the roadway industry is trying to reduce the number of accidents caused by loss of tire grip on bridges, curves, intersections, and school zones. Speed, tire condition, and weather conditions can all play a role in these accidents; however, studies have found that increasing the coefficient of friction of the roadway through the use of high friction coatings can increase tire grip, regardless of the weather conditions or nature or condition of the tires.
Currently, few surfaces are being treated with friction-modifying coatings. The surfaces that have been coated are typically being done manually. For example, in the case of a two-component epoxy system, the most common type of binder, the process conventionally starts when a laborer opens the spigot of a tote containing a polymer binder resin, adding it manually to a garbage can or similar container. The spigot is closed when the resin reaches a predetermined level in the garbage can. A second spigot on a second tote containing a catalyst hardener is then opened, adding the hardener to the resin until a second, predetermined level is reached in the garbage can. In some instances, five gallon pails of hardener and resin are combined in the garbage can. The resin and hardener are then mixed, using a mixing blade attached to a hand drill.
The mixed polymer binder is then poured out onto the surface to be coated by tipping the garbage can over or dipping smaller buckets into the garbage can and then pouring the composite polymer binder out of the smaller container onto the surface to be coated. The polymer binder is then spread over the surface, using a squeegee or similar device.
Once the polymer binder is on the surface of the substrate, laborers manually shovel a friction-modifying filler onto the binder. Manually operated blowers and similar instruments have also been used to distribute the friction-modifying filler. The most common filler is bauxite which, once applied, partially sinks into the polymer binder. The epoxy, when it has hardened, acts to bind the filler to the substrate, creating a uniform coating. Because the filler is irregularly shaped, typically jagged and protruding from the polymer binder, it acts to increase the friction coefficient of the surface.
There are a number of drawbacks to the conventional method of application described above. For example, conventional methods utilize a multi-part binder which is manually poured, mixed, and applied to the substrate. Combining the multi-part binder is done using a significant amount of human judgment and imprecise measuring techniques, which introduce error into the component mixing ratios. Most multi-part systems have an ideal ratio of resin and catalyst. Too much of either one of these components can detrimentally affect the properties and performance of the hardened product including, but not limited to, durability, degradation, filler binding, ductility, and frictional properties.
Furthermore, the conventionally practiced method of coating preparation utilizes manual mixing of the components. There is the potential for the components not to be mixed adequately, resulting in pockets of polymer binder wherein the ratio of resin to hardener is not optimal. This variability can ultimately affect the quality of the binder, adhesion to filler, the degree of curing and/or the curing time.
Additionally, if the mixing time of the binder is too long and the binder starts to cure prior to application on the substrate, it may reduce the spread ability and substrate adhesion as well as filler penetration and adhesion.
Furthermore, in the conventional practice of application, the binder is spread on the surface using a squeegee or the like which results in significant variability in the thickness of the binder across the surface of the substrate. As a result, the binder can be too thick in some places and too thin in others. Thick binder can increase drying times and delay the surface availability. Moreover, it can also diminish the integrity of the coating as well as the performance of the coating if the filler is fully enveloped by the binder and does not stick up from its surface. Similarly, binder that is too thin can reduce the integrity and performance of the binder by not providing enough material to hold the filler in place or adhere it to the substrate.
The way the filler is added to the binder can also influence the quality, performance and integrity of the coating. In the conventional method of application when the filler is shoveled or blown onto the surface of the wet binder, it has the tendency to impact the surface of the binder and displace it away from the impact zone. Thus the filler uniformity and overall coating density can vary significantly. In areas with too much filler, the integrity of the coating can be reduced. In areas with too little filler, the frictional properties of the coating can be reduced.
Therefore, what is needed is a system and method for applying friction-modifying coatings to a surface, such as a roadway, without incurring the many drawbacks discussed above.
USPTO Backgrounds
USPTO Backgrounds