A Study of Energy Savings In Corona Treatment of Packaging Films

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Depending on the type of film you are running and the current coating on your corona roll, switching to a Glassed Steel Treater Roll can reduce energy consumption by up to 50% while maintaining the same dyne level.

Glassed Steel Treater Rolls have been installed on all types of lines running many different substrates including polypropylene, polyester and polyethylene. In each of these installations, the manufacturer reports that they have consistently experienced a reduction of the power necessary to achieve and maintain a corona discharge while maintaining their desired treatment levels. Alternatively, some manufacturers have chosen to increase line speeds and maintain power settings at their current levels achieving significant increases in efficiency.

Energy Efficiency Study at ExxonMobil Films
A recent investment by the New York State Energy Research and Development Authority (NYSERDA) funded a multi-client study of the electrical energy utilization of the corona treatment process. The purpose of the study was to detail the energy saving (up to 50% reported) previously found with replacement glass coated dielectric rolls used in corona treaters. During the study, an approximate 27% reduction in electrical energy use was found for treating polypropylene packaging films when compared to a conventional ceramic-coated dielectric roll. The decrease in power utilization results in an improved film treatment process, delivering comparable treatment levels at lower power settings.

Based on the findings, a Glassed Steel Treater Roll can be used to lower energy costs or, conversely, to improve productivity by permitting higher line speeds through the treater.

Films were made and treated on the ExxonMobil line at three power levels using both the ceramic and glass treater rolls. Treatment levels were determined by measuring the receding contact angle of water against the film surface. The results for homopolymer propylene films are shown in Figure 2 and clearly show an improved wettability for the films (lower contact angle) at all power levels for the glass-covered treater roll relative to the ceramic-covered roll.

Corona treatment is a process where high frequency electrical energy is used to create a corona discharge in a narrow gap. This gap is formed between a conductive metal (usually aluminum) bar and a grounded nonconductive roll, (Figure 1). This forms a capacitive circuit where the electrical energy is dissipated in the gap as an electrical discharge, and is converted into gas plasma (called a barrier discharge) by ionizing the nitrogen/oxygen blend of the air. In the treatment process the film is passed over the surface of the roll and into the plasma discharge where it is bombarded by electrons, ozone and gas ions. The film surface is chemically modified (oxidized) as the electrons impact the polymer surface. The oxidation process removes hydrogen ions from the polymer and produces free radicals on or near the film surface. The free radicals react with oxygen, or moisture in the atmosphere, creating an oxygen radical which then gives an oxygen function on the film surface.

In essence, the glass coating permits a higher number of surface reactive sites to be produced by electron bombardment at any given power level by increasing the capacitance of the roll surface (its ability to accept charge). Because the treatment level depends on the total number of reactive sites produced, it is possible to achieve the proper number of oxidized sites on the film surface with lower power levels when using the glass covering.

Talk to Empire Treater Rolls today about how a Glassed Steel Treater Roll might help your company save energy, reduce waste and improve the quality of your film treatment.