Corrosion of Paint
229
7.6.3.5 Other Treatments
Procedures have been developed specifically for plastic processing to overcome the low surface activity of many of these materials. Prior removal of
surface contamination by solvent or detergent cleaning is necessary in most
cases to achieve optimum results.
Primers.
•
The application of a primer coating is used to develop better adhesion of the final coating to the plastic substrate. A variety
of chemical types can be used as primers, including urethane polymers, silicones, nitriles, phenolics, vinyls, or isocyanates. The primer
is applied to the surface as soon as possible after other surface preparation procedures have been completed in order to protect the surface from recontamination.
Flame treatment.
•
The surface of many plastics, such as acetals, polyolefins, fluoropolymers, and polycarbonates, are oxidized by the
impingement of a flame. The oxidation provides a higher level of
surface energy and better film adhesion. This process is particularly
effective on complex shapes and molded parts. Superheated air at
1000°F (538°C) is just as effective.
Exposure to UV radiation.
•
An ionized or highly polar surface results
after exposure to high-intensity UV radiation.
Drying.
•
Over-drying can be effective on plastic formulations that
absorb atmospheric moisture.
Plasma treatment.
•
Plasma treatments are effective for most plastics.
Parts are exposed to gases such as neon, helium, oxygen, and moisture vapor, which are ionized by radio-frequency or microwave
discharge. Although very effective in improving surface conditions
that promote better film adhesion, this process is limited to smaller
components and parts because of equipment size.
Corona discharge.
•
Surface tension can be improved by passing film or
thin-gauge plastics between two electrodes. This treatment is suitable for high-speed operations.
7.7 Application of Coatings
Over the years there have been many changes in the formulation of coatings that have affected the methods by which they are applied to a substrate.
Several of these changes have resulted from governmental regulations.
The Occupational Safety and Health Administration (OSHA) and the Toxic
Substances Control Act (TSCA) regulate the environment in the workplace
229
7.6.3.5 Other Treatments
Procedures have been developed specifically for plastic processing to overcome the low surface activity of many of these materials. Prior removal of
surface contamination by solvent or detergent cleaning is necessary in most
cases to achieve optimum results.
Primers.
•
The application of a primer coating is used to develop better adhesion of the final coating to the plastic substrate. A variety
of chemical types can be used as primers, including urethane polymers, silicones, nitriles, phenolics, vinyls, or isocyanates. The primer
is applied to the surface as soon as possible after other surface preparation procedures have been completed in order to protect the surface from recontamination.
Flame treatment.
•
The surface of many plastics, such as acetals, polyolefins, fluoropolymers, and polycarbonates, are oxidized by the
impingement of a flame. The oxidation provides a higher level of
surface energy and better film adhesion. This process is particularly
effective on complex shapes and molded parts. Superheated air at
1000°F (538°C) is just as effective.
Exposure to UV radiation.
•
An ionized or highly polar surface results
after exposure to high-intensity UV radiation.
Drying.
•
Over-drying can be effective on plastic formulations that
absorb atmospheric moisture.
Plasma treatment.
•
Plasma treatments are effective for most plastics.
Parts are exposed to gases such as neon, helium, oxygen, and moisture vapor, which are ionized by radio-frequency or microwave
discharge. Although very effective in improving surface conditions
that promote better film adhesion, this process is limited to smaller
components and parts because of equipment size.
Corona discharge.
•
Surface tension can be improved by passing film or
thin-gauge plastics between two electrodes. This treatment is suitable for high-speed operations.
7.7 Application of Coatings
Over the years there have been many changes in the formulation of coatings that have affected the methods by which they are applied to a substrate.
Several of these changes have resulted from governmental regulations.
The Occupational Safety and Health Administration (OSHA) and the Toxic
Substances Control Act (TSCA) regulate the environment in the workplace