Patrick Mahoney
Associate Editor
The biggest force in packaging today is sustainability. The word has become a shorthand way of saying, “Do more with less.” In other words, the push is on to package goods with less material and do it while consuming less energy.
An example of how designers are attacking the problem comes from package-equipment maker Lantech in Louisville, Ky. The company devised both a shrink wrapper and a stretch wrapper that manage to use less material while making operations more efficient to boot.
When it comes to shrink wrapping, for example, side-sealing, cross-sealing, and trim-winding operations can cause energywasting downtime while wasting material. The problem is tooling that cuts and seals with the same surface creates a buildup of melted film. This not only results in poor seals and poor shrink but, at some point, the operator must stop the machine for cleaning.
Lantech’s sealing technology separates the cutting and sealing of shrink-wrap film for cross and side seals. This results in cooler sealing surfaces. The trim surface for the side seal uses no heat at all, so the seal head can be threaded and checked “cold.”
The novel rotary side-seal system has a sharpened cutting wheel and a heated fusing wheel mounted next to each other on the same axis. The hardened cutting wheel contacts a similarly hardened backup wheel. Light pressure produces a positive cut.
The shrink-wrapper’s new seal-bar design cuts with one surface, then seals with another. This cooler shrink wrapping eliminates film buildup. A sharp cutting blade clamped in a blade holder with two rounded edges makes up the sealing surfaces. The seal bar contacts a spongy, but firm, backup pad. The bar is configured so its heated, sharp cutting blade cuts through the film a fraction of a second before making the seal. The film never melts, because the sealing surfaces are only heated to the minimum needed to fuse the film (350°F for polyolefin versus 500°F for conventional units that cut and seal with the same surface).
The shrink wrapper borrows technology from the company’s stretch wrapper to control the spool that takes up the trimmedoff film. A feedback system, which controls the trim-winding motor’s torque, detects slack in the trim web and maintains a constant level of tension. That constant level of tension results in a very narrow web of trim.
Shrink-wrapping operators often use a wide web of trim to reduce breakage caused by excess tension at the trim winder. Most trim winders have a friction plate or speed board to control take-up, but friction devices have to be adjusted several times per roll of film to maintain proper tension. Too much tension on the film web can lead to a break, and even the slightest excess tension can make it nearly impossible to remove tightly wound trim from the takeup spool. Reducing this tension produces a narrower web of trim, saving film and making it easier for the operator to remove the scrap from the spool.
The company then turned its attention to stretch wrapping. The RS-6000’s novel all-mechanical design speedily wraps pallets while using 30% less film than ordinary units. The so-called Ring-straddle design wraps 50-gauge film without film breaks and despite any holes that might form in the film. Such holes normally propagate and cause ordinary stretch-wrapping operations to wad up.
The key to the Lantech system is a mechanically synchronized method of paying out the film. Conventional stretch wrappers employ a demand-pull scheme to pull film from the roll as it spins around the pallet. In contrast, Lantech’s machine automatically pays out film as the spool rotates. The film coming off the spool is not under tension. It comes off at the same speed as the speed at which the spool rotates.
Surprisingly, the film spool is not powered by an electric motor. Instead, it is suspended from a ring (part of a mechanical transmission) above the pallet. The spool revolves around the pallet by following a track on the ring.
The SW-3000 Side-Seal Shrink Wrapper separates the cut and seal processes to eliminate film buildup.
The SW-3000 Side-Seal Shrink Wrapper separates the cut and seal processes to eliminate film buildup.
Consistent tunnel-air temperature in the ST-900 Shrink tunnel reduces waste.
Consistent tunnel-air temperature in the ST-900 Shrink tunnel reduces waste.