Slitting is the final step in the production process for most roll stock flexible packaging material and entails that a large “master roll” is cut to its final width. However, slitting is so much more than just a machine with a set of razor blades.
Theoretically, slitting is a simple process. A master roll, typically between 30” and 55” wide, is received from extrusion, printing, or lamination. The film passes through a series of idler rolls and a set of razor blades set up to the final roll width. A photo eye reads the edge of the film or printed eye track to assure the film is slit in register. The outer right and left rolls have a portion of the edge removed as scrap.
A key component of the slitting process is tension control. A roll that is wound too loosely will often have feathered edges and may start to telescope on the packaging line. A roll that is wound too hard may block in the packaging machine and cause web breaks and static build up. Certain applications run best with soft winds and some run better with hard winds. It’s often a fine line between soft and too soft, and hard and too hard. The more cuts taken out of a master typically provides a bigger challenge. Experienced operators and well-maintained equipment are key to preventing issues on the packaging line.
Slitting is also the place in the conversion process where “flags”, or problem areas, from the previous production steps are removed as a last quality control checkpoint. At Multifilm, we run high-speed turret slitters at up to 2,000 feet per minute. A turret slitter is a machine with four rewind shafts that help minimize down-time, allowing for an almost continuous operation. Again, experienced and meticulous operators are key to make sure that all defects are removed, especially when running at such high speed.