Infrared and Its Application For Drying Coatings On Webs AIMCAL FALL TECHNICAL CONFERENCE 2005 By: Bob Narang Radiant Energy Systems, Inc. www.radiantenergy.com
Water or solvent based wet coatings applied on webs, are generally dried using three technologies:. Convection such as a hot air impingement or flotation dryer Exhaust Air Plenum Recirc/ Exhaust Heated Supply Air Web Path 2. Conduction oil or steam heated drum Direct Impingement Convection Dryer 3. Infrared or Radiant Heating Heated Drum IR Emitter Web Path Web Path Typical Conduction Heating System Electric/Gas Infrared Heating System
Infrared Drying Theory of Infrared Different types of infrared heaters Applications Advantages and Limitations Acknowledgements
Theory of Infrared Electromagnetic Spectrum showing various types of energy based on wavelength
Infrared Spectrum he Infrared spectrum can be divided into three categories: 1. Short Wave Length 2. Medium Wave Length 3. Long Wave Length
Wien s s Law The peak wave length of emission of an infrared heater can be calculated by Wien s s Law 3 Basic Laws of Radiation λ = C/T λ wavelength in microns C - Constant 2898 T - Source temperature (ºK)
Stefan Boltzman Law W = kt 4 W Emitted Power k - Constant T Source temperature ( K)
Planck s s Law
Spectral Characteristics of Infrared - Absorbed by the object (A) - Reflected by the object (R) - Transmitted through the object (T) A + R + T = 100% of energy received.
Absorption Curves for Different Products
Types of Heaters Short Wavelength Quartz Tube Emitter (T-3 3 lamp) Medium Wavelength Quartz Tube Emitters Medium Wavelength Stamped Foil Type Heaters
Types of Heaters Long Wavelength Infrared Heaters Gas Fired Infrared Heaters
Applications Infrared Air Pre-dryer Infrared Air & Hot Air Dryer on a Coating Line
Applications There are numerous applications where Infrared and Infrared Air Dryers have been successfully used to enhance drying and curing capabilities of coating lines. Listed below are some of the more common and more successful applications: Dry and Pre-Dry Water and Solvent based Pressure Sensitive Adhesives Laminate foam to fabric using web adhesives for automotive and furniture industries Dry and Pre-Dry Water based latex and clay coatings on paper Moisture profiling across the machine direction in paper industry Preheat films for laminating and embossing Dry flexo and gravure printed inks Dry and cure PTFE coatings on fiberglass fabrics Cure Silicone coatings on various substrates Cure PVC coatings on scrim, nonwovens and woven fabrics Dry and cure solvent base resin coatings for electronics industry Cure 100% solids resin coatings on fiberglass for Printed Circuit Boards Pre-Dry, dry and cure coatings on industrial fabrics Dry food, nutraceutical and pharmaceutical coatings on film
Advantages of Infrared Dryers High efficiency conversion of electrical energy into heat fo electrical IR Higher rate of heat transfer Floor space savings due to smaller size Heats only the object without heating the surroundings Easy to zone for uniform heating of the product Faster response to changing process conditions Quick start up and shut down Easy to have cut off zones for narrow widths Ease of control Lower capital and installation cost Can be easily be added to existing conventional dryers to increase line speed Infrared Air dryers suitable for solvent based coatings
Limitations of Infrared Dryers Some coatings may not be able to take advantage of higher rates of heat transfer and may skin and blister Difficult to work with temperature sensitive substrates Scaling up of the heaters is not always straightforward Since IR is basically a surface phenomenon, harder to dry heavier coatings Almost essential to run trials in lab or on the pilot line to confirm design
Acknowledgements Infrared Process Heating Handbook by Industrial Heating Equipment Association Handbook of Industrial Drying by Arun Mujumdar Watlow IR Handbook Phillips Lighting Handbook Litex Infrared Lamps Electric Process Heating by Maurice Orfeuil Hydro Quebec