Document ID: EPA-R07-OAR-2018-0642-0003
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2018-10-02T04:00Z

Justifications for Exemptions from Construction Permitting
                   567 IAC 22.1(2) "x" through "hh"

bb. Powder coating operations 
Powder coating is popular finishing technology used to apply a decorative and/or functional organic film to a variety of products used by industry and consumers. The technology offers the following economic, environmental, health & safety, and performance benefits over liquid coating:

 Powder is immediately ready for use.  Powder coating is applied in a dry form (powder coating consists of finely ground particles of pigment, resin and additives).  This avoids many of the variables associated with the preparation and application of liquid coatings.
   
 No solvents.  Unlike liquid coatings, powder coating does not contain solvents.  In addition, no solvents are used in the application process or for equipment cleaning. Consequently, no volatile organic compounds (VOCs) or Hazardous Air Pollutants (HAPs) are emitted during application and maintenance of application equipment.   
   
 Reduced fire risk.  Again, because no solvents are used, powder coating presents benefits in regard to regulatory health & safety concerns and insurance premiums.
   
 Reduced operator health risks and exposure.  Although respirable particulates remain a concern with powder coating, it removes many of the health and safety concerns common to liquid coatings (e.g., inhalation of solvent vapor, respirable particulates, dermal exposure to solvents, and greatly reduced risk of fire).  
   
 Ease of application, high utilization potential, and easy housekeeping.  Because powder coating is easy to apply, facilities realize fewer finishing defects and less rework.  This equates to reduced waste and pollution prevention.  Powder coating overspray can also be collected, reclaimed and reused to achieve utilization efficiencies in excess of 95 percent.  Additionally, equipment and application areas are easily cleaned using simple cleaning tools (e.g., compressed air, squeegee, broom or vacuum).   

As a result, it's the fastest-growing finishing technology in North America, representing over 10% of all industrial finishing applications[1].  

Process Overview

Powder used for the process consists of finely ground particles comprised of thermoplastic (e.g., nylon, PVC, polypropylene, polyethylene) or thermoset (epoxy, acrylic, polyester, hybrid and polyurethane) coating materials. Upon heating, thermoplastic powders melt and flow onto the substrate while retaining their original chemical composition.  Thermoset powders, however, simultaneously melt, flow, and polymerize through a cross-linking chemical reaction to form a high molecular weight decorative/protective film.    

For electrostatic spray application, most commercial powders are manufactured with a particle size between 10 and 100 microns[2].  Deviating from this particle size range may result in poor electrostatic deposition, appearance problems, and poor coating performance.  Figure bb/cc-1 illustrates a typical particle size distribution for a pigmented epoxy coating.    

                                       
Figure bb/cc-1.  Typical particle size distribution for a pigmented epoxy powder.

Application Equipment.  Powder coatings are typically sprayed onto the substrate or applied using a fluidized bed.  The electrostatic spray process, however, is most common application method because it's more versatile, efficient, and provides better control.  Spray application is typically an electrostatic process where powder is pneumatically conveyed to a powder coating spray gun (automatic or manually operated).  The powder particles are then charged by the spray gun through corona or tribo charging.  Charged powder particles are then sprayed toward a grounded, conductive work piece.  The charged particles are electrostatically attracted to the work piece, causing them to deposit and adhere to the substrate in a relatively efficient manner.

Powder coating may also be sprayed onto a pre-heated substrate with or without the use of electrostatics.  As powder particles come into contact with the heated substrate they fuse to the surface.  This method of application is often used on low or non-conductive substrates such as glass, ceramics, or medium density fiberboard.     It's also used when high film builds are required.   

Like spray application, fluidized bed operations can used electrostatic charging or pre-heated parts for powder deposition onto the substrate.   Powder is loaded into container equipped with a porous plate above an air plenum chamber.  Compressed air is then supplied to the air plenum where it percolates through the porous plate and fluidizes the powder (i.e., it causes the powder to behave more like a fluid).  Objects to be coated are passed through the fluidized powder (for powder deposition) and then proceed to the cure oven.

Powder Spray Booth.  Powder spray booths are used to contain and collect overspray from a powder coating spray process.  Spray booths are designed to protect the operator (by drawing overspray away) and prevent powder from reaching potentially explosive concentrations in the booth.   Typically, powder booths are equipped with highly efficient cartridge, cyclone or combination cartridge-cyclone collection systems to separate powder from air.  Figures bb/cc-2 and bb/cc-3 illustrate the types of powder coating spray booths often found at powder coating facilities.  As most powder coating booths re-circulate air back into the plant (rather than exhausting outdoors), systems are specifically designed to ensure the air returned to the plant is as clean as possible.  As shown in Figure bb/cc-2, powder-laden air is drawn through the booth to one or more cartridge filters (i.e., the primary filters).  Cartridges are typically constructed of cellulose or synthetic (typically polyester) filter media to separate powder from air.  Cartridge filters used for this application typically have removal efficiencies in excess of 99.99%.  

                                 Final Filters
                                 Final Filters
 Primary   
 Filters
 Primary   
 Filters
Figure bb/cc-2.  Schematic diagram of air flow through a cartridge system powder booth.
                                       
Figure bb/cc-3.  Schematic diagram of air flow through a powder booth equipped with a 
                     combination cyclone-cartridge system.

Air passing through the primary filters is then routed to a final filtration stage (see Figure bb/cc-2).  Documentation obtained on the efficiency of these final filters indicates they are 95% efficient with respect to 0.3 micron particles (based on dioctylphalate [D.O.P.] aerosol testing.  In addition, based on ASHRAE Standard 52-76 test procedures using AC Fine Test Dust[a], these final filters will capture 100% of the powder fed to them.  

Rationale for Exemption

As environmental regulations should promote environmentally-friendly technologies through reduced regulatory burden, it is proposed that powder coating operations performed using generally accepted industry practices and equipment be exempt from air construction permitting.  Based on information presented above, powder coating offers significant environmental and safety benefits over more traditional liquid spray finishing processes.  Additionally, the environmental impact of powder coating is negligible when applied and processed under generally accepted industry practices.  Therefore, in order to promote powder coating as an environmentally-preferred surface coating technology and acknowledge its environmental benefit, powder coating operations using industry-accepted practices and equipment should be exempt.

References

1  Powder Coating Institute (www.powdercoating.org).

2  Interpon Powder Coatings (November 1999) Complete Guide to Powder Coatings. 34pp.

[a]  -  AC Fine Dust Test consists of: 39% of 0 to5 micron particles; 18% of 5 to 10 micron particles; 16% of 10 to 20 micron particles; 18% of 20 to 40 micron particles; and 9% of 40 to 80 micron particles.