During the processing of a material, a measurement of a cleanliness (quantity of contaminant) of a surface of the material may be required. For example, when painting, priming, or sealing a surface, verification of an adequate surface cleanliness is useful to ensure adequate adhesion between the paint, primer or sealant and the surface. Regulatory imposed reductions in the amount of solvents that can be used in applying paints, primers and sealants may require that a surface be cleaned to a higher standard than heretofore required. That is, the new regulatory mandated high-solids materials that are used in the painting, priming and sealing operations are more sensitive to surface contaminants than the old high-solvent systems. Because the solvents help clean the surface, the reduction in the amount of solvents that are used require that a cleanliness of the surface being painted, primed or sealed be verified to a lower level (or quantity) of contaminants than has previously been required.
Additionally, the acceptable amount of a contaminant on the surface may be different for different contaminants. That is, the type of contaminant that maybe found on the surface may vary and may have different properties such that the quantity of solvents that are used in the painting, priming, and sealing operations may be able to remove more or less of the specific contaminant. For example, in the commercial aircraft industry, various contaminants can be found on the exterior surface or skin of the aircraft that is to be painted, primed or sealed. Such contaminants include silicone oil, hydrocarbon oil, temporary protective coating (TPC) residue, aqueous cleaners, fluorocarbons, synthetic oils, long chain alcohols, and cutting oils. Silicone oil is a chain of silicon and oxygen atoms with alternating atoms for each element. The silicone oil is typically used as a lubricant or a releasing agent. Hydrocarbon oil is a chain with a carbon atom backbone and either hydrogen or simple side chains from each carbon atom. Hydrocarbon oil has multiple uses such as a lubricant or a fuel. The TPC is a polymeric material of various chemical compositions that is put onto aircraft to protect the aluminum skin during the manufacturing process. Aqueous cleaners are mostly soap and water with various formulations for the soap. These cleaners sometimes have some organic solvent in them as well to make them clean more efficiently. Fluorocarbons are made up primarily of carbon and fluorine atoms with various arrangements and side chains. They are often used as a lubricants and in refrigeration or cooling systems. Synthetic oil is a long chain ester that is typically used as a lubricant. Long chain alcohols are hydrocarbon chains with an alcohol group on one end. Long chain alcohols are drilling lubricants and fastener lubricants. Cutting oils are hydrocarbon lubricants that are often used with an emulsifier so they can be diluted with water to help cool the cutting or drilling process.
If the surface is not cleaned to the required level of cleanliness, the paint, primer or sealant applied to the surface may not properly adhere. The effects of too high of a contaminant level can show up immediately, for example in the form of bubbling and/or blistering, or can show up later, for example in the form of premature failure or wearing of the paint, primer or sealant on the surface. When the surface contaminant causes failure of the paint, primer or sealant, the surface is reworked to remove the defective layer of paint, primer or sealant and to clean the surface to the required level prior to painting, priming or sealing the surface again. Additionally, the new coating will need to be worked into the old coating to provide a desired appearance. The reworking of the surface increases the time spent painting, priming or sealing the surface and increases the cost. The re-work process also generates an additional waste disposal problem in many cases.
Thus, it is desirable to provide a quantitative measure of surface cleanliness prior to performing the painting, priming or sealing operation. Additionally, because the level of a contaminant that is acceptable can differ based upon the particular contaminant, it is also desirable to be able to quantitatively measure a specific contaminant on a surface to be processed.