A corona treater temporarily modifies the surface energy of a substrate to make it more compatible with ink, adhesives or coatings. Corona treating is an electronic process that increases the adhesion properties of a substrate.
A corona is generated by applying a high-frequency high-voltage signal to an electrode, which is separated from a grounded surface by an air gap and a dielectric. No current will pass through the air gap until there is enough voltage to affect the electrical breakdown of the air, typically 3,000 to 5,000 volts per millimeter. The corona treatment of the substrate results from the bombardment and penetration of these ions into the molecular structure at the surface of the substrate.
It is the oxidation and polar-group formation in the surface molecules, in conjunction with the etching of the surface from the ion bombardment that induces the increase in surface energy of the treated material.
The introduction of the corona treater has allowed for the expansion in the use of water-based inks, coatings, and adhesives thus replacing their solvent-based counterparts.
Best Management Practices & Pollution Prevention
Catalytic ozone destruction systems
A by-product of corona treatment is ozone. As a rule of thumb, units should be kept to 6 to 10 grams of ozone output per hour per kilowatt of generator power. Production of ozone depends upon ambient dewpoint/dry bulb or the air present in the treater. An increase in dewpoint/dry bulb will reduce ozone production. The concentration of ozone in the exhaust air is approximately 25-30 ppm. The recommended exposure limit of ozone is 0.1ppm (0.1 mg/m3) calculated as an 8 hour time-weighted average concentration. There is also a short-term exposure limit for ozone of 0.3 ppm (0.6mg/m3) calculated as a 15 minute time-weighted average concentration.
Another best practice in terms of preventing ozone pollution involves the application of ozone destruction systems, which eliminates 99.99% of ozone from the exhaust stream from corona treating or other ozone generating processes.
Catalytic ozone destruction systems or decomposers convert ozone (O3) into oxygen (O2). The unit typically consists of a particle filter, pre-filter material, and metal oxide catalyst bed that reduces an input ozone level of up to 150 ppm to less than the OSHA limit of 0.1 ppm at the designated flow rate.
To adequately size a corona treater for a given application, several machine and application variables must be closely studied. Treater suppliers have developed data sheets with line items, which systematically present all of the information that may impact treater system sizing.
For access to vendors who may supply alternative materials and equipment, see the PNEAC Vendor Directory.
On April 15, 2004, the EPA designated "non-attainment" areas throughout the country that exceeded the health-based standards for 8-hour ozone. If your facility is within a county designated as a non-attainment area, an ozone destruction unit may be required. Ozone destruction unit requirements are determined by individual state attainment standards with respect to the National Ambient Air Quality Standards (NAAQS)
Health & Safety
OSHA regulates employee exposure to ozone gas through its Air Contaminants Standard, 29 CFR 1910.1000. The permissible exposure limit (PEL) is listed in Table Z-1 as an 8-hour, time-weighted average value of 0.1 part of ozone per million parts of air (ppm). Rule 29 CFR 1910.1000(e) requires that administrative or engineering controls must first be identified and implemented whenever feasible to achieve compliance with the PEL. When such controls are not feasible to achieve compliance, personal protective equipment, respirators, or any other protective measures shall be used to keep the exposure of employees to ozone gas within the PEL.
A corona treater will neutralize static because the ionization of air creates both positive and negative ions. When plastic film or coated paper is processed, static electricity charges can be generated. It can be generated in the unwind or sheet separation, in the nip of pinch rollers, after contact with coated and uncoated rollers, in the coating head, in the laminator and at the rewind or any other type of material delivery. Static buildup can result in fires within the equipment and create a safety risk to employees.