Substrate Core Thermal Expansion Limits in High Speed Sheetfed Converting Operations
Substrate core thermal expansion limits dictate sheet dimensional stability, requiring precise thermal control to prevent misregister and bimetallic warp.
UV Lamp Infrared Flux
Radiant Emission
Heat energy emitted by ultraviolet lamps alongside the curing light can warm the substrate and cause dimensional instability. Managing the UV lamp infrared flux is essential when curing inks and coatings on heat-sensitive materials like thin plastic films or delicate papers. Excess infrared radiation can cause the substrate to soften, stretch, or warp during the curing process.
Heat Generation
UV curing lamps generate a large amount of infrared light as a byproduct of the electrical arc that produces the ultraviolet light. This infrared energy is absorbed by the substrate, raising its temperature and potentially causing it to expand or distort. In multi-colour printing, this thermal expansion can lead to registration errors if the web is cured between printing stations.
This expansion is especially problematic for thin film substrates, which lose their structural strength when heated and can stretch permanently under the tension of the press.
Cooling Solution
Modern curing systems utilize quartz plates or dichroic reflectors to block or absorb the infrared radiation while letting the UV light pass through. This design minimizes the heat transferred to the web, keeping the substrate cool and stable. Proper maintenance of the cooling system ensures that the lamps operate at the correct temperature and do not overheat the print line.