Optical Measurement
The cumulative surface area of visible ink and contaminant particles remaining on a sheet of deinked paper determines the final optical quality and market value of the recycled pulp. Measuring the speck area using automated scanner-based image analyzers is the standard method for assessing the cleanliness of a processed batch. This metric is expressed in parts per million of the total scanned paper area.
Print Interruption
Residual ink spots can disrupt the appearance of printed graphics and affect the runnability of the paper on high-speed presses. Ink deposits on the paper surface can cause linting and piling on printing blankets, which forces operators to stop the press for cleaning. High speck counts in packaging boards also reduce the visual appeal of brand packaging, making the material unsuitable for premium consumer products.
By monitoring the size and count of these specks, mills can adjust their screening and flotation systems before the paper is wound onto rolls.
Reject Threshold
Recycled pulp grades are classified according to strict limits on contaminant surface area. If the measured value exceeds the threshold established by the buyer, the entire batch may be rejected or downgraded to a lower-value application. This strict quality control helps maintain the commercial viability of recycled packaging and paper boards in demanding print markets.
