Controlling Tension Transients in Metallizing and the Subsequent Converting Process

Like so many materials and processes we take for granted today, the development of metalized films came about as a consequence of research and development undertaken and employed during the Second World War. In the case of metalized films, scientists found that cut into narrow strips metalized films when dropped from an aircraft could confuse enemy radar.

Fast forwarding sixty plus years, metalized plastic films and papers play a more peaceful role and are widely used in sectors such as packaging for their visual appeal and functional capabilities. The radiance of metallic and embossed surfaces has long been recognized by brand owners and marketers as a means of conveying prestige and quality, attracting consumer and influencing purchasing decisions. But metalized films and papers don’t just look pretty; they provide a barrier resistance to moisture and gases, thus keeping the product contained in the package fresher longer.

The process of metallization can be undertaken by air-to-air systems or via roll-to-roll systems. The process involves coating a plastic film with an extremely thin metal layer of around 10 to 18 microns, under vacuum conditions, onto the continuously moving web. The success of the process is dependent upon a number of critical factors such as good adhesion to the substrate, uniformity of appearance and precise tension control of the web. Normally metallization is not the final process; subsequent converting operations to produce a saleable product may include cross cutting, varnishing, lamination and printing – all of which are dependent for their success on precision tension control.

Montalvo web control equipment is employed during metallization and the subsequent converting processes. For example, Montalvo’s X-3400ce tension controller, which offers fieldbus communication, web break detection, progressive PID regulation and many other advanced control features, can be used together with tension-sensing load cells (transducers) for the ‘closed loop’ control of tension prior to entering the vacuum zone or chamber.

On entering the chamber the substrate is passed around the processing drum where evaporation and coating takes place. On exit another set of Montalvo load cells (transducers) installed at the rewind zone ensures that the processed web is rewound precisely and evenly, not too soft and not too hard, so as to avoid problems such as telescoping or burst rolls.

These load cells (transducers) have the ability to measure actual tension. The signals provided to the Montalvo controller are evaluated instantly and tension adjusted according to set point.
Montalvo load cells (transducers) offer many advantages. They are of compact design, ruggedly constructed and can be located virtually anywhere there is a roller. Load cells (transducers) are characterized by low hysteresis, high overload capacity and high linear response and they operate over a wide range of tensions. This is made possible by the negligible movement, low inertia, accuracy and sensitivity of the units.

When it comes to undertaking further processing of the metalized films, for example gravure or multi-colour flexographic printing, the load cells (transducers) together with other Montalvo web tension control elements help to reduce waste by ensuring that registration remains within set parameters. They are also an aid to faster production.

Packaging converters sometimes print the reels of pre-metalized materials such as PP in single ply on flexo or gravure presses. An alternative option is to laminate metalized OPP to another film prior to printing. With a substrate such as polyester the tendency is to laminate to the backing film prior to printing, though sometimes metalized polyester is reverse printed prior to laminating. Montalvo equipment has a controlling influence irrespective of the processing options chosen. The line up of Montalvo equipment used to maintain processing integrity includes: pneumatic friction brakes, the D-3400ce dancer roll controller, the DTI-3400ce dancer roll controller with tension indication, and a comprehensive range of load cells (transducers).

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