Plastic Bag Production

The continuing trend that favours plastic bags and sacks at the expense of paper continues. This growth is attributable to the demand for pre-made bags as an alternative to rigid containers, and to the use of plastic bags in industrial and agricultural bag applications, such as fertilisers and seeds.

Bjorn Olesen of Danarota Technic A/S, the European Division of Montalvo, notes that this market is vibrant in both the United States and Europe. In the U.S the plastic bag sector employs 42,600 people spread over 500 companies. In 1999 alone this sector accounted for nearly $8 billion worth of products.

In many European countries the plastic bags are manufactured and flexo printed in-house by specialist trade-houses and converters. These producers face a number of challenges, not least of which is that they have to produce a just-in-time product, to exacting standard, and often on thinner gauge, potentially problematic materials.

Furthermore, marketers increasingly demand that the surface of the bag incorporates a sales message printed in vibrant colours with sharp images to reinforce brand image and to encourage repeat purchase.

To lower costs and increase productivity while producing a high quality product is central to commercial viability. However, in a sector where profit margins are low (typically 4%) and where much capital investment is on hold due to the global economic downturn the converter is looking at various areas to improve bottom line performance. One of the least expensive methods to improve performance and profitability is to retrofit new generation control systems.

A precision tension control system can enable the converter to obtain better control of the many processing variables that affect performance and profitability. Retrofitting a Montalvo tension control system can improve machine product throughput while reducing the waste associated with many of the inconsistencies that plague output.

Montalvo systems, in some case, have also improved the performance of newly purchased presses, coaters and laminators; those supplied by OEMs with inferior performing web control components.

Montalvo’s systems, which are comprised of load cells, brakes/clutches, safety chucks, web guides, tension controllers and dancer controllers’ address the following problems: web breaks and wrap around driven rolls (caused by slack webs); loss of colour-to-colour registration while running at speed, splicing or changing speed; deformation of the web on account of wrinkling; print length variations; interleaving of slit webs; web shifts side-to-side; variations in coating thicknesses; unwind or rewind core crushing; reduction in machine speed because of web handling difficulties; high waste, and an inability to run a wide range of web thicknesses, widths and materials.

New equipment introduced in 2002 by Montalvo and designed for applications where top-flight performance is required includes the X-3100ce tension controller. This controller, which is ideal for use on the new breed of faster presses and web-based converting machines, as well as for retrofitting applications, features ‘progressive’ PID control and includes digital parameter handling for closed loop control. This advanced analogue controller includes on-board industry standard PC/PLC communication and can be used in unwind or rewind positions with input signals from any of Montalvo’s strain gauge load cells.

Montalvo’s tension control equipment is employed on a wide range of equipment, from extrusion lines to flexographic presses, and from slitters to rewinding equipment.

In a recent application at a plastic bag printer/converter in Sweden Montalvo systems have been installed to improve the performance of a W + H 6-colour flexographic press. The equipment, which included load cells and a variety of other components, has proved to be a competitively priced solution. This package of equipment has improved print quality and given a better roll quality.

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