Chemical surface treatments, effects

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

D. Hawke and K. Gaw, "Effects of Chemical Surface Treatments on the Performance of an Automotive Paint System on Die Cast Magnesium," Paper 920074, Society of Automotive Engineers International Congress and Exposition, Detroit, Mich., 1992. 

Paper Friction In addition to the effect on toner fix, organic components in plain uncoated papers intended for electrophotography have other important characteristics that should be evaluated for proper machine performance. For example, chemical surface treatments tend to impact the friction characteristics. Synthetic sizes, when surface applied, may significantly decrease the overall paper-paper friction level (Figure 11), and the static friction peak or resistance towards initial movement is not developed (Figure 12). 

Yip, J., Chan, K., Sin, K.M., Lau, K.S., 2002a. Study of physico-chemical surface treatments on dyeing properties of polyamides, part 1 effect of tetrafluoromethane low temperature plasma. Color. Technol. 118, 26-30. 

If a chemical surface treatment in required, the process must be monitored for proper sequence, bath temperature, solution concentration, and contaminants. If sand- or grit-blasting is employed, the abrasive must be changed regularly. Fresh solvents for cleaning should he on hand. Checks should be made to determine if cloths or solvent containers have become contaminated. The specific surface preparation used can be checked for effectiveness by the water-break-free test. After the final treatment step, the substrate surface is checked for its ability to form a continuous film of water when deionized water droplets are applied to the surface. After the surface treatment has been found to be adequate, precautions must be taken to assure that the substrates are kept clean and dry until the bonding operation. The adhesive or primer should be appUed to the treated surface as quickly as possible. 

The importance of a clean surface for painting is paramount (see Engineering surfaces of metals). For metallic substrates, either mechanical or chemical surface treatment is almost always needed to remove surface contamination and promote adhesion. Chemical pre-treatment of metals prior to painting is an effective method of surface conversion that can provide both corrosion resistance and improved paint adhesion. For ferrous metals, the most common chemical pre-treatment is a phosphate for aluminium (and many other non-ferrous metals), the most effective pre-treatment is chromate. Metals must first be cleaned with an alkaline cleaner and then rinsed before they can be converted chemically in an immersion bath or by spray. 

The coating stage impacts significantly the strength of glass fibers and their surface properties. The effect of chemical surface treatment has been proved to enhance the strength of glass fibers by as much as 20 %. 

Generally considered to be almost impossible to stick unless given very aggressive chemical surface treatment under industrial control, it has been claimed recently that a simple primer treatment is effective ... 

Ion implantation (qv) has a large (10 K/s) effective quench rate (64). This surface treatment technique allows a wide variety of atomic species to be introduced into the surface. Sputtering and evaporation methods are other very slow approaches to making amorphous films, atom by atom. The processes involve deposition of a vapor onto a cold substrate. The buildup rate (20 p.m/h) is also sensitive to deposition conditions, including the presence of impurity atoms which can faciUtate the formation of an amorphous stmcture. An approach used for metal—metalloid amorphous alloys is chemical deposition and electro deposition. 

Surface treatments of carbon fibers can in general be classified into oxidative and non-oxidative treatments. Oxidative treatments are further divided into dry oxidation in the presence of gases, plasma etching and wet oxidation the last of which is carried out chemically or electrolytically. Deposition of more active forms of carbon, such as the highly effective whiskerization, plasma polymerization and grafting of polymers are among the non-oxidative treatments of carbon fiber surfaces. 

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