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FLEXO Magazine : January 2013
cate with other IT systems. An on-the-fly system is arguably the most effective and reliable means of guaranteeing print quality: it takes consistently accurate measurements without loss of performance throughout the production run, for 100 percent of the printed run, not just at the end of each roll. TARGETING ACTION The most objective way of describing color is measur- ing spectral response, expressed in L*a*b* values. While a hand-held spectrophotometer may be capable of taking a few readings during the course of a production run, an in-line sys- tem can take readings from multiple image targets, continu- ously, and from anywhere across the printed web. It enables reaching color targets and taking remedial action faster. Inspection camera resolutions are typically 250 dpi, although a maximum of 2,500 dpi is possible. Cameras must detect defects from < 0.1 to 0.2 mm across the web, and from 0.15 to 0.35 mm in the printing direction. Cross-substrate resolution is critical to detect common defects, like long, thin streaks. Lighting is used to illuminate the target areas and ensure the substrate image is captured under suitable, uniform conditions. Three solid-state, temperature-controlled LED lamps provide a constant illumination level on the substrate’s target inspection area: a high-intensity top light for non-reflective and non-trans- parent surfaces; a low-intensity foil light for reflective surfaces and inks; and a back light, both illuminating and providing contrast for transparent or semi-transparent substrates. A web stabilizer provides stable, accurate on-the-fly color measuring on unsupported, transparent and opaque films and paper. It comprises a flat-top, low-friction platform with two BCRA (British Ceramic Research Association) tiles: one black, measuring substrate opacity, and one white, measuring color. Thanks to software advancements, on-the-fly high-definition viewing of dot-profiles is possible. Images are captured at up to 2,500 dpi and made available to the operator via the user inter- face. As a result, a host of defects, common to central-impres- sion flexo, such as pinholing, bridging, doughnuts and halos, can be identified and remedied without production stops. Some in-line controls enable ‘Golden Template Compari- son’, where every printed repeat is compared to a fixed-refer- ence master image. Such a comparison provides assurance against slow-growing defects, such as register, streaking and color changes. Furthermore, the software is capable of compensating for stretching and web movements during the production run. PDF verification makes structural comparisons between the golden template and the customer-approved digital artwork file. The operator is thus alerted to set-up or plating errors without the need for visual checks. This also resolves the problem of inspecting packages that include multi-language information or different alphabets. PLANT-WIDE INTEGRATION The software allows inspection and color measurement equipment to be fully integrated with the press and commu- nicate with the company ’s IT network. A waste management system provides a data connection between the inspection system and slitter/rewinder equipment for fast, precise, ta- gless marking, removal of defective material and splicing. A central repository audits, stores and generates reports of both current and historical data, enabling performance analysis and defect traceability. It also stores job settings, including golden templates, simplifying setup times. The latest color measurement systems can exchange data with ink formulation software. Color deviations are relayed to the ink formulation software, via .CxF file, resulting in auto- matic ink recipe changes. The modern in-line, spectrophotometric, integrated color measurement and inspection system is an essential factor in an industry where getting perfect results first time, every time is not a luxury, but a given. n About the Author: Randy Freeman is vice president and gen- eral manager of packaging at QuadTech, a leading innovator of advanced color and inspection technology for the pack- aging, commercial offset and newspaper printing industries. Since its establishment in 1979, the company has been developing complete, on-the-fly image-based solutions that inspect, measure color and make adjust- ments across the entire substrate throughout the printrun. www.flexography.org january 2013 FLEXO 51 a web stabilizer provides stable, accurate on-the-fly color measuring on unsupported, transparent and opaque films and paper. QuadTech inspection system.