- October 01, 2000, Claudia Hine, Senior Editor
Conductive or nonconductive? That is the question, and it's the premiere question when it comes to choosing a corona treater, says Ron Seaman, VP, Corotec Corp. (corotec.com), Farmington, CT.
A covered roll treater is recommended whenever the application does not call for treating conductive substrates such as metallized material, explains Charles Ballard, product manager at Pillar Technologies (pillartech.com), Hartland, WI. A bare roll treater is used whenever the application calls for treating conductive substrates such as foils, metallized materials, or a laminate that contains one of those. Bare roll treaters also can be used to treat nonconductive substrates—coated papers, plastic films—but the covered roll system is the most efficient way to handle the job, according to Seaman.
Ballard says, "The basic difference between the various technologies for surface treatment of flat substrates is the location of the dielectric, which is placed between the electrode and the ground roller and acts as a buffer."
Universal systems, which have a dielectric covering on both the treater roll and on the electrode, also are recommended for treating conductive substrates. "This is referred to as double dielectric, which produces a very soft corona," says Ballard.
David Markgraf, senior VP, sales and marketing, Enercon Industries Corp. (enerconind.com), Menomonee Falls, WI, explains that several different types of dielectrics are available, including silicone rubber, hypalon rubber, epoxy, and ceramic. He says, "Ceramic is the most expensive, but it lasts the longest, and if you take good care of it, it should last indefinitely."
As you change dielectric, roll diameters change also. For instance, notes Markgraf, if you go with silicone, you need a very large roll diameter so the silicone has a chance to cool before it comes under the corona again. "With the ceramic, you have a small diameter because it's so strong."
But what if your answer to that premiere question—conductive or nonconductive—is "both"?
"When you look at running both conductive and nonconductive," says Seaman, "convertible is the most efficient way to go." In a convertible treating station, there is one metal electrode, one ceramic-covered electrode, and a selector switch. "In a one-second changeover, you can pick electrode A or electrode B, so that you have the most efficient electrode to do the job."
If your operation requires interrupted treatment, Markgraf recommends the covered roll system with metal electrode segments. "If you have a 60-inch-wide web and you're going to slit the web and make it into bags, you have a section that needs to be heat sealed. You don't want to treat that section, so you can raise the segments up so there won't be any treatment in the center."
On a fully segmented electrode, Seaman says, "The segments are one inch wide going across the web. You just pick them up or slide them down. Now you can focus the treatment in lanes on the web."
Because converters need systems that are compact and easy to install and operate, manufacturers have responded with corona treaters that are available in a unitized format. Says Ballard, "The narrow web unit incorporates a built-in power supply versus the stand-alone systems previously offered, eliminating the need for costly high-voltage wiring."
"The treating station and power supply are built as one component," adds Seaman, "so that you take one piece out of the box, mount it, run your power cord to it, and you're ready to treat." A unitized format, up to 10kW of output power, now is available for wide web applications.
Suppliers are working to develop plasma treater systems that will create the corona in gases other than air. Instead of having air between the electrode and the web, helium or nitrogen is introduced, so that when the corona is created, it's created in the gap of that gas. This reportedly would give better properties to the treated film and provide a longer lasting treatment—and it won't create ozone.
To provide R&D labs with more capabilities, sheet treaters are available so scientists can treat a swatch of material eight-and-a-half by eleven inches. Seaman explains, "Labs are becoming much more capable of creating a process and being able to transfer that process with all the data required out to a production environment. It's been a breath of fresh air for the people setting up the process."