Reducing Converter Down-Time and Waste: Inline Press Controls
How to achieve quality consistency and implement lean production methods has been a prime concern of flexible packaging printers. Waste reduction is also increasingly an issue as the rising price of raw material puts margins under pressure.
A significant proportion of printing houses use their own means of guaranteeing color for their facilities.In such a situation, it becomes almost impossible to assure the print buyer of predictable quality from one run to the next.
Inline solutions offer the most accurate means of measuring printed work. The latest measurement systems form a closed loop in which targets are reached quickly after production start-up, maintained on-the-fly, and stored for easy job recall, minimizing start-up waste and setup times.
For flexo and gravure printing, an inline inspection and color measurement system comprises a video camera/sensor; a lighting system to illuminate the target areas and ensure the substrate image is captured under suitable, uniform conditions; high-powered software to process the image; and a central data repository to enable at-a-glance viewing of spectral data and communication with other systems within the workflow.
While both hand-held devices and inline systems take accurate, image-based readings to an accuracy of 1∆E, it is only in-line measurement that enables statistical color analysis.
Alternatives to TensionLighting systems provide the versatility for the variety of flexible packaging substrates, including reflective and transparent types. Three lamp varieties are used to illuminate the substrate: a high-intensity top light to illuminate non-reflective and non-transparent surfaces, a low-intensity foil light to illuminate reflective substrates and inks, and a back light to illuminate and provide contrast for transparent or semi-transparent substrates.
White LED temperature-controlled, actively cooled lamps offer longer life and can even be configured to illuminate color in the ultra-violet spectrum. Tension is no longer an obstacle when measuring unsupported substrates thanks to the web stabilizer, which provides a stable, controlled way of taking spectral color measurements on transparent and opaque films, on-the-fly, without risk of corrugation.
The unit features a flat-top, low-friction platform with two BCRA tiles: one to measure substrate opacity, and one for measuring color. A low-pressure area is created between the substrate and the surface of the device, momentarily pulling and stabilizing the web and pulling it to 0.0001” above the tiles. Tile accreditation to national standards makes it possible to know the spectral response and to determine the color and opacity of any material.
Replacing Rolling With FixedThe Golden Template Comparison is a master image that is grabbed by the inspection system when the press is running good copy. Every printed repeat is compared to that original.The Golden Template results in a fixed reference with a stable, repeatable quality and it is more sensitive to slow-growing defects.
There is growing preference among flexible package printers for a fixed – as opposed to a rolling – reference. A rolling reference is where the first image is used to inspect the second image and so on. Subtle color changes or register movement may go undetected from one repeat to the next.
The latest generation inspection equipment is sophisticated and versatile enough to give quality assurance without the costly web stoppages and start-up waste. It means higher productivity as well as consistent quality.
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