Cutting Die Technology for Ultra-Thin Liners
The use of thinner and thinner substrates is leaving no margin for error in diecutting processes.April 2012 By Steve Lee and Brent Fischmann, RotoMetrics
Spurred by the potential for less waste and increased productivity, the label and packaging industry is moving to implement ultra-thin facestocks and liners. Converters are pursuing the multiple promises of significant waste reduction, better resistance to moisture and humidity for food and beverage applications, and material recyclability. At the same time, brand owners are looking to the combination of new 23 micron/0.00092˝ PET liners with thinner film face materials for label-application technology that enables product differentiation and an enhanced clear film, no-label, or opaque conformable look for high-volume applications.
The transition to 23 micron/0.00092˝ PET liner material—or even thinner (20 micron/0.00075˝)—is also posing new challenges for diecutting. There is literally no room for error cutting to the ultra-thin PET layer. With the ultra-thin liner materials, pressure sensitive diecutting requires separation of the face stock and adhesive while ensuring that the die does not touch the liner or cause a break during automated label dispensing. New flexible die technology has emerged in direct response to the new challenges of film substrates, with suppliers optimizing performance for 20/23/25 micron PET.
As an example, RotoMetrics has introduced the AccuStar™ flexible die for extensible film converting. Given the absolute premium on control of liner strike, the die is machined to a tolerance on total plate height of ±2.5 microns (0.0001˝). Advanced manufacturing technology also delivers narrower blade angles, and laser hardening achieves hardness levels of up to 68 HRC for more durable blades, providing long-lasting performance in high-volume applications.
Along with improved flexible die performance, the exacting requirements of new substrates require greater control of the entire diecutting process, to include high-precision, high-quality magnetic cylinders and die-station components. New technology cylinders are manufactured to guaranteed diameter tolerances of +0.0/–2.5 microns (0.0001˝). Total indicator readings (TIR) are also held to this exacting level. Before converting thin-film liner material, it is strongly recommended that your die system supplier inspects the magnetic cylinder inventory to assure their overall accuracy.
Along with advanced flexible cutting die technology, machine-finished solid rotary tooling remains an industry option to achieve the tight tolerances on blade edge consistency and total height required for 20/23/25 micron PET.
Maintenance is critical
Beyond the cutting dies, care must be taken to maintain overall die station performance. A strong program of preventive maintenance is necessary as you address the converting challenges of thin film liners. In particular, a very smooth anvil surface must be maintained. Work with your die supplier to audit your anvil inventory. At the same time, excessive wear in the die frame slots can mean your anvil and dies are not being held firmly, which can lead to an inconsistent die strike. Similarly, bearers on support rolls and magnetic cylinders or solid dies should be inspected for wear that could affect liner impression.