Coating application methods electrostatic spraying

A matter of considerable importance in the selection of an application method is its efficiency. Spray techniques are usually inefficient, since many droplets drift past the target and are lost. Even electrostatic spraying can waste as much as 35% of the paint. There is some loss of paint in most methods, but roller coating, curtain coating and electrodeposition are very efficient. Electrodeposition is also a very useful technique where corrosion resistance is important, since it applies a uniform coating over nearly all surfaces of even the most complex-shaped article. 

The most common methods of paint applications are brush and roller, air or airless spray, roll coating, electrostatic spraying, electro deposition, and dip coating. Many factors affect the choice of method to be used for a particular application. These include film thickness, appearance requirements, and operating cost. 

Use of application methods that can use relatively high-viscosity paints is advantageous. Appropriate methods include roller coating, special electrostatic spray equipment, hot-spray techniques, and two-nozzle spray guns. 

In this method, the finish and activator are metered mechanically along separate feed lines and mix only at the instant of application, usually after both materials have left the application equipment. Special twin-feed spray-guns have to be used. The main objections are that sometimes mixing is not efficient enough and faults in the mechanical metering device can lead to insufficient or excess peroxide. If mechanical failure occurs, the defect will probably remain undetected until several objects have been coated and probably ruined. However, the latest equipment is quite good and the method is particularly suited to electrostatic spraying. 

Electrostatic spraying n. Methods of application spraying in which an electrostatic potential is created between the article to be coated and the atomized paint particles. The charged particles of paint are attracted to the article being painted and are then deposited and discharged. The electrostatic potential is used in some processes to aid the atomization of the paint. 

Spraying assures excellent application where selective or spot coating is required and may be easily automated. Spraying can be accomplished by several methods (conventional air assisted, airless spray or electrostatic spray). Sprayed films usually give the best aesthetic appearance to a coated part (no runs, sags or tears). Dry film thickness is easier to control with spraying because adjustments can be made in adhesive dilution, fluid flow. 

The anionic polymerization of lactams represents the only suitable method to prepare powdered PA materials. One advantage here is that the polymerization process is fast, even at temperatures much below than the melting temperature of the synthetized polyamide. Powdered PAs have a number of applications, including flame spraying, electrostatic coating and paste preparation (mainly for cosmetics). 

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