Web Cleaning & Static Control
Increasing productivity and reducing downtime with the right web cleaning solution
between blow-and-vacuum and boundary layer solutions. Blow-and-vacuum systems employ air knives on either side of the web to strip the boundary layer and traces of contamination from the web’s surface. The presence of vacuum airflows ensure that turbulent air is captured and removed. Boundary layer systems are a relatively recent
development. High-speed, non-contact rollers rotate at a distance of between 0.5 and 1mm from the surface of the web and in the opposite direction. The roller design is optimised to generate its own high-speed boundary layer, the greater energy of which destroys the boundary layer carried by the incoming web.
CyClean web cleaner F
or label printers, a clean web is a productive web. Contamination is an inevitable by- product of high-speed webs, and so it is
important to have an effective web cleaning system in place to increase productivity. Given that any web cleaning solution will have
to fit into an existing production line, and how type and level of contamination, and reason for web cleaning, will differ in label printing, lots of factors can influence which system will be chosen. This is why it is fundamental to understand the basics of web contamination.
THE KEY CAUSES OF CONTAMINATION Contamination takes on the form of dust, dirt and assorted airborne particles that deposit on the web’s surface during the printing process. There are two main reasons why a web attracts contamination: The boundary layer created by any moving web and the generation of static charges. An effective web cleaning solution must be capable of tackling both. The friction or separation between two objects can lead to the generation of static electricity, creating an electrical charge on the material surface that will attract contamination to the web. The boundary layer is caused by the ambient air that the web drags along when in motion. This movement draws contamination to the substrate, trapping it either beneath the layer — and therefore directly on the web’s surface — or holding it within the layer.
CONTACT OR NON-CONTACT There are two basic web cleaning technologies for breaking the boundary layer on a label converting line: Contact web cleaning and non- contact web cleaning. Contact systems typically incorporate two
types of cleaning methods: Vacuum technology, or adhesive rollers. One employs a low-friction
30 November 2017
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component of the cleaning manifold to make contact with the web, breaking the boundary layer and releasing the contaminants, which are subsequently vacuumed away. Other contact vacuum systems incorporate brushes to free debris before vacuuming. While this approach is effective when large particles need to be removed from heavily contaminated surfaces, it can be too harsh a cleaning method for use on sensitive materials. Systems using adhesive rollers incorporate twin
elastomer rollers, which are in contact with the full width of the web, breaking down the boundary layer and lifting contamination from the web’s surface. This is then transferred to a second roller with a high adhesive mass, which removes debris from the first roller, preventing recontamination. Adhesive-roller systems perform well on small particles (down to as low as 0.5 micron), but are not designed for more demanding applications. The choice of non-contact technologies is
CONTROLLING STATIC A web cleaner alone is not enough to guarantee a spotless web, which is why it must be combined with a static control solution to counter the charges on the web’s surface that also cause contamination. A static charge is typically generated by the separation (such as when the web unwinds) or friction (as the web travels over non-conductive nip rollers, for example) between two objects. Charges can be positive or negative in polarity, with paper usually being positive and film negative. Active static control provides the most effective means of neutralising charges. The technology uses ionisation. A voltage is fed to an array of emitter pins mounted on an ionising bar, creating a high-energy ‘cloud’ of positive and negative ions. Any statically-charged surface, of either polarity, passing close to the cloud, is quickly neutralised.
CONCLUSION A clean web is the key to productivity. Label printers must be able to deliver on this promise and do so profitably. Installing a web cleaning solution can increase the productivity of the converting line and ensure products are processed to a consistent high quality. Arriving at the right choice of web cleaning system, however, means considering a variety of factors, from analysing the source of contamination to understanding how customers’ needs are likely to develop in the future.
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Hyperion 924IPS pulsed DC ionising bar
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