By Pillar Technologies
Although UV and waterbased inks have been used in narrow web printing for some time now, the use of PP, LDPE and metallized substrates have recently become more common. As a result, the need for corona treating equipment on narrow web presses has increased, presenting manufacturers with a series of design challenges.
Similarly, corona treaters have been used on narrow web presses for years but have traditionally been used to assure even treat on pretreated material, requiring low power levels. The use of hard to treat materials, such as high slip LDPE and PP, in conjunction with UV and waterbased inks, are creating the need for higher treat levels, requiring versatile, high powered systems.
Corona Treater Systems
There are two basic types of corona treater stations. One type of system is designed to treat non-conductive materials. This system uses a metal electrode over a dielectrically covered roll.
The other type of system is designed to treat conductive substrates. Early designs used a series of driven covered rotating electrodes placed over a bare grounded roll, enabling the conductive web to be grounded. The newer design is an open style, called bare roll, which extracts the ozone between two fixed ceramic tubes, cooling the electrodes, as well. The ceramic tubes are placed over a bare grounded roll.
Narrow Web Treating Systems
Though both types of systems are used on narrow web presses, the bare roll style (conductive design) has been more popular in recent years. This is primarily due to the compact design and because it can treat both conductive and nonconductive materials, although not as efficiently. The harder to treat materials require higher power levels, making treater versatility more important.
The increase in power has also caused treater stations to become larger. Since space on a narrow web press is very limited the challenge to treater manufacturers recently, has been to develop compact designs which can handle higher power levels and efficiently treat conductive and nonconductive substrates.
In order to improve treat levels, many newer designs incorporate two electrode assemblies. One with a metal electrode and the other with ceramic electrodes. These assemblies are mounted over a ceramic covered roll. The operator then connects the appropriate assembly for the type of substrate.
These designs improve the efficiency of treating nonconductive webs (metal electrode over a ceramic roll), however, the dual dielectric combination (ceramic electrodes and ceramic roll) is less efficient for conductive materials. This style treater station is also fairly large due to the need for two electrode assemblies.
The newer approaches incorporate an open style bare roll design, which employs an electrode magazine and an easy roll change mechanism. The user can quickly change from covered roll to bare roll by changing magazines. This feature also enables the user to treat conductive or nonconductive films efficiently, without having to run with a dual dielectric. In addition, the system is more compact since there is only one electrode assembly.
Most of the newer treater station designs usually offer several other features intended to simplify operation and maintenance. These features may be such things as external gap adjustment knobs, pneumatic mechanisms for simplifying web thread up, access for easy cleaning, quick electrode and roll replacement, the use of ceramic dielectrics to reduce pinholing and easy to replace ground brushes.
Solid state power supplies have proven to be reliable for years, however, they have become more compact recently. In addition, they have increased in frequency, in order to help reduce the required electrode area, enabling the non conductive treater stations to become smaller. They have taken advantage of microprocessors, by becoming capable of being controlled by an external (customer supplied) processor, or can be supplied with their own microprocessor controller. These new microprocessors feature memory for storing common job parameters, watt density control, proportional speed controls and various levels of system diagnostics.
It is clear that in order to keep up with the demands of the narrow web printer, treater companies are going to have to continue to design systems to handle higher power which are even more compact, versatile and easier to use and maintain.