Whiteness

In the pulp and paper industry, the spectral reflection factor at 457  nm is used to determine the whiteness or degree of whiteness.

For the measurement, the paper sample is illuminated with a xenon gas discharge lamp, which roughly corresponds to illumination with daylight. The choice of the center of gravity of the measurement at 457 nm is due to the physiology of the human eye. Objects with identical remission at 457 nm are perceived differently depending on their color cast. A yellow tinge appears 'darker' than a blue tint. For the optical impression of 'white', the success of a bleaching treatment correlates directly with the reduction in the yellow tinge of paper raw materials such as cellulose or wood pulp . Completely bleached products show an almost pure 'white' with almost no yellow tint.

The measurement method is standardized several times, e.g. B. to DIN 53145-1 and -2, TAPPI T452 and T525 or ISO 2470. Typical whiteness values ​​(also abbreviated to R457) for paper types are around 60% ISO for newsprint, over 80% for copy paper and around 90% for photo paper. When measuring with the UV component of the xenon lamp, values> 100% remission are also possible due to optical brighteners in the paper.

swell

• Paper dictionary , Deutscher Betriebswirte-Verlag, 1999, Vol. 3, 389; ISBN 3-88640-080-8