Innovations in Electrostatic Charging Technology – Using the Invisible Force
Most Managers in process industries are familiar with the use of electrostatic discharging to solve problems and maintain process speeds. However, few are aware that innovative electrostatic charging can be a valuable tool to improve product control, increase production speeds and reduce costs. Electrostatic charging generally takes the form of electrostatic pinning and is applied to 4 loose production categories:
b. Paper processing.
c. Print finishing.
Electrostatic charges build up on nonconductive surfaces such as plastics, film or paper. These charged surfaces behave like magnets, with like polarities repelling each other whilst opposites attract. The favourite school demonstration of this principle uses a plastic comb which, when rubbed on a tie will pick up small pieces of paper with ease. These forces of attraction or repulsion are what create most static problems, but they can be easily harnessed to give positive benefits.
Generating controlled electrostatic charges is a relatively simple procedure involving seemingly similar equipment to that used in electrostatic discharging. An electrode is connected to a high voltage generator and positioned near to the material to be charged. However, the voltages used are many times greater than those in discharging and can be made to penetrate the material being charged. However, because charging is a dc, rather than ac process, it generates a specific charge polarity on the surface of the subject material. These qualities of selective polarity and penetration can be used in 2 ways: Firstly, if a charge is directed through a single layer of material at a grounded surface such as a roller, the material will stick to the roller. Secondly, if charging bars of opposite polarity are positioned on either side of a compound web comprising several layers of material, the resulting charges will cause the layers to stick firmly together. These processes are generally known as static pinning, nailing or tacking. Let’s look more closely at each of the four categories to see how the principles of Electrostatic Charging can be used to improve efficiency and running speeds.
Flim Casting Processes
Film is generally hot cast or extruded from a die onto a chill roller. As the film leaves the die and meets the cool roller its width reduces or ‘necks’ due to shrinkage, usually giving a ‘thick edge’. Both the initial shrinkage and trimming the thick edge considerably reduce the film width and generate a substantial amount of waste. Although trimmed waste can normally be recycled, the energy used in melting, casting, cooling and trimming is a total loss. Shrinkage can be substantially reduced by pinning the hot film to the chill roller using an electrostatic charging system. The resulting film has a wider useable section, whilst the reduction in trimmed waste results in overall savings in production costs. This can be applied as either a full width
pinning or, more commonly, as an edge pinning process.
Light films and wide webs can be a nightmare to rewind neatly without wander or “telescoping” on the reel, both of which are generally not acceptable to the next process or the customer. By statically charging the web immediately before the rewind reel, the web is firmly pinned to the reel and cannot wander or telescope.
Far from being the universal problem perceived by many, electrostatic charges can be deliberately induced and controlled to bring positive benefits in improved production enhanced product quality and reduced waste across a range of paper processing and service sectors.
As a manager in a competitive and cost conscious industry, ask yourself if any of the scenarios in this article apply to your operations. If so, you too could benefit from the innovative use of electrostatic charging. Your competitors may well be already reaping the benefits in lower costs, higher quality and quicker product turnaround.
Let electrostatic innovation give your company a marketing edge today by calling Arrowquint Ltd, the UK’s leading electrostatic innovators for print and packaging.
Graham S Dawson FIDiagE
For Arrowquint Ltd.
Tel: 08450 655 455