Paperboard Substrate Lightfastness Criteria under Accelerated LED Exposure
Substrate lightfastness under retail LED fixtures depends on optical brightener stability, requiring specific 450 nm test criteria to prevent retail chargebacks.
Cartonboard Brightness
Meaning
Optical properties of paper-based packaging materials describe the percentage of blue light reflected from a surface at a specific wavelength of 457 nanometers. High cartonboard brightness indicates a whiter surface that provides greater contrast for printed graphics and brand imagery. This metric is separate from whiteness, which considers the entire visible spectrum rather than just the blue region.
Mills control this property by managing the bleaching process and the addition of minerals like calcium carbonate. The process involves removing lignin from wood fibers and adding fillers that scatter light effectively.
Reflectance Standard
Testing follows the iso 2470 or tappi t452 procedures to ensure that measurements are comparable across different suppliers. A specific level of cartonboard brightness is often mandated in the technical specification of a luxury goods contract. The standard requires the use of a spectrophotometer to isolate the blue light reflectance from other environmental factors.
Consistent reflectance ensures that brand colors appear identical regardless of the mill that produced the raw material.
Supply Consistency
Maintaining a steady level of light reflection prevents variations in the appearance of printed halftone dots. Fluctuations in cartonboard brightness can lead to shifts in the final color of the package, causing issues during the retail display phase. When a shipment falls below the agreed percentage, the ink coverage may appear muddy or the whites may look yellow.
Printers adjust their ink formulations to compensate for these variances, but this adds cost and time to the production cycle.
Margin Impact
Precise specifications for surface reflectance reduce waste during the converting stage. A failure to meet the target leads to the rejection of production lots. Stable material properties allow for faster machine speeds and more predictable results.