IMPORTANT PARAMETERS FOR PAPER & PAPERBOARD
- Brightness - the percentage of the blue light reflectance from a sample measured at an effective wavelength of 457nm, to provide an indication of the amount of bleaching. Generally the higher the reflectance, the brighter the sample appears.
- Whiteness - the extent that paper diffusely reflects light of all wavelengths throughout the visible spectrum i.e. the magnitude & uniformity of spectral reflectance measured as the percent light reflectance for the whole wavelength range.
- Colour - related to perception and therefore measured or specified in terms of colour space. A commonly used system is the CIE L,a,b system. This is based on the idea of colour opposites. L - measure of whiteness and varies from 100 for perfect white to 0 for perfect black. a - redness to greenness. b - yellowness to blueness.
- Gloss - it is the specular reflection of light, which is reflected at an equal and opposite angle. Normally measured at 75o or 20o. It is advisable to measure high gloss surfaces at 20o. Printed and varnished surfaces are measured at 60o.
- Opacity - the property of a substrate to resist passage of light. Important in book printing where both sides of the paper are printed.
- Printability - the extent to which properties of paper lend themselves to the true reproduction of the original artwork. This is influenced by the printing process and can be evaluated in terms of - dot reproduction, dot gain, print gloss, hue shift and print uniformity.