Static Controls Take Charge
Although it can't be eliminated, static charge build-up can be monitored, neutralized and otherwise controlled.
By Stanley Weitz, President, Electro-Tech Systems Inc.
Each of the vast number of substrates used in today's package printing and converting applications possesses the ability to produce static electricity when brought in contact with the very equipment used to convert it, making it extremely difficult to support increased printing speeds without sacrificing yields.
Cause and effect
Static electricity is caused by unbalanced molecules. Generally, static electricity occurs at a point where two surfaces touch each other or are separated from one another, throwing molecules out of their natural balance. Additionally, large amounts of energy cause electrons to flow, while heat causes the surface transfer of electrons. Insulating materials compound the problem by giving off electrons easily. This is significant since most papers and films are insulators. Therefore, they cannot replenish or compensate for lost or gained electrons. The resulting charge becomes static, causing static electricity.
Two insulators will stick together, causing jams in printing and converting equipment. The static field can also stick tape systems and attract unwanted debris. The attraction of foreign materials, such as lint and dust, can cause friction and binding. This results in poor product quality, rejects, machine downtime and wear.
Built-in static generators
Package printing operations are plagued by static charge build-up from the very start. Static electricity is immediately generated as the web is pulled into the corona treater by idler, infeed nip and pacing rolls.
The print module itself produces numerous contact points, however, the wetting action of the ink tends to hold down any static build-up. As the web passes through tensioners in back-end operations, such as rewinding, slitting or die-cut and stacking operations, it begins to accumulate a static charge.
If more than one web is being run, extreme electrostatic polarization will take place. Now the multi-web setup acts as a single web bonded together by static electricity. Applying static neutralizers serves only to neutralize the outside surfaces. Therefore, static between the webs remains throughout the entire operation.