Slitting & Rewinding High-speed rewinding of thin films
Kevin Gourlay from Rotoflex says that modern inspection rewinders solve the process issues that are inherent when running film materials
T
he use of film substrates for labelling applications continues to increase. They are at the centre of several
popular product labelling and decoration techniques such as clear (no-label-look) pressure-sensitive labels, shrink films, and in-mold labels. Film materials pose a higher level of processing
challenges for narrow-web converters versus traditional paper substrates. Tension, static, and web guiding are some of the more important parameters that need to be controlled. These challenges are made even more difficult by the fairly recent (and successful) trends to down gauge substrates and liners. Film materials can be a special challenge in the
finishing department when operating inspection rewinders. These machines typically provide three functions: slitting, inspection, and rewinding, and since they represent the last value-added processing before product is shipped to customers, there is a lot riding on rewinder performance. Much has been done in recent years to make
sure inspection rewinders are up to the challenge, especially when it comes to processing film materials. As an example, Rotoflex’s VLI line of inspection rewinders has been specially designed to process films and other tension-sensitive materials. Where just 10 years ago 800 fpm was considered fast, these machines can run at speeds up to 2,000 fpm. Market requirements are also driving the need for wider machines, now available at 28 inches. This allows narrow-web converters to expand their capabilities by moving into the mid-market, which includes both labels and packaging products. The key technology that has supported these performance gains in high-speed rewinding of
28 October 2016
thin films is the use of servo drives. Servos are required to maintain proper tension when running the wide range of thin film materials at these elevated speeds. And tension is just one component of what is really motion control.
WEB PROCESSING The growing range of film materials used in labels and packaging has driven improvements in slitting systems themselves. Understanding that different materials will interact differently with the available cutting systems (crush, shear, or razor slitting), converters need the flexibility to easily select and engage the slitting option that will provide the best solution for their application. Modern rewind systems are built for easy set up and quick changeovers, so systems such as the Rotoflex VLI use a common housing with quick-change cartridges providing the desired slitting method. Tension control provides the most significant
challenge for high-speed rewinding of film materials. Films are stretchable materials and have to be handled very carefully throughout the entire inspection rewind process. Two factors that can have a detrimental effect on
tension in high-speed rewinding are the buildup of both static and air pockets throughout the process. The challenge is to reduce the static and get air out and away from the film as fast as possible. The use of fluted idler rolls and layon rollers
(also called ironing rollers) are used on high-speed rewinders to dissipate and remove air build up before it can cause a problem. Fluted idler rollers have effectively replaced spiral idlers, which had provided a sufficient solution when rewinders were running thicker films at slower speeds. Layon rollers have been in use for many years and when located at the rewind section they do an effective
job of getting air away from the film.
INSPECTION: IT’S ALL ABOUT DATA Modern inspection systems for printing and converting include impressive capabilities for 100 per cent inspection of printed webs, full width at commercial running speeds. The trend has been, and will continue to be, to move the inspection onto the printing press. Roll mapping is a means to communicate the
location of defects within individual rolls coming off printing presses. Mark Andy uses this functionality with its Rotoflex line of inspection rewinders. Defect information for each roll is incorporated into a file, which is used to automatically stop the rewinder when necessary to remove defective product from that specific roll. While there has been a lot of focus in the past
10 years on refining the pressroom to reduce waste, the finishing department is beginning to get more and more attention. There is no use making gains in waste reduction in the pressroom only to lose it in finishing. In addition, later this year, all Rotoflex rewinders will be WiFi-enabled for easy, remote access of live, real-time data.
WHAT THE FUTURE HOLDS Tremendous progress has been made in recent years on the productivity and effectiveness of inspection rewind systems, especially used for high-speed processing of films. Data collection and analysis will be the next frontier that helps drive improvements on the bottom line. Many companies offer good presses and rewinders; the key will be what value-added features are available that give customers an advantage.
uwww.rotoflex.com www.convertermag.co.uk
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