BS ISO 9416:2017 pdf download – Paper — Determination of light scattering and absorption coefficients (using Kubelka-Munk theory)
6 Sampling and conditioning
If the tests are being made to evaluate a lot of paper or board, the sample should be selected in accordance with ISO 186. If the tests are made on another type of sample, make sure that the test pieces taken are representative of the sample received. Conditioning according to ISO 187 is recommended but not required, but preconditioning with elevated temperatures should not be applied since it might change the optical properties.
7 Preparation of test pieces Avoiding watermarks, dirt and obvious defects, cut rectangular test pieces approximately 75 mm × 150 mm. Assemble at least 10 of the test pieces in a pad with their top sides uppermost; the number of test pieces should be such that doubling the number does not alter the reflectance factor. Protect the pad by placing an additional sheet on both the top and bottom of the pad; avoid contamination and unnecessary exposure to light or heat. Mark the top test piece in one corner to identify the sample and its top side. If the top side can be distinguished from the wire side, it shall be uppermost; if not, as may be the case for papers manufactured on twin-wire machines, ensure that the same side of the sheet is uppermost.
8.1 If the sample contains or may contain a fluorescent whitening agent, check that the 420 nm UV- cut-off filter is in the UVex(420) position.
8.2 Remove the protecting sheets from the test-piece pad. Without touching the test area, use the procedure appropriate to the instrument and the working standard to measure the intrinsic luminance factor R y,∞ of the top side of the test-piece pad. Read and record the value to the nearest 0,01 % of the luminance factor. 8.3 Remove the top test piece from the pad and, with the black cavity backing the test piece, measure the single-sheet luminance factor, R y,0 , for the same area of the test piece. Read and record the value to the nearest 0,01 % of the luminance factor.
8.2 and 8.3 describe the two independent measurements required to calculate the light absorption and scattering coefficients using the Kubelka-Munk theory in Clause 9. This is not intended to imply that the two measurements shall necessarily be made in this order. 8.4 Move the measured test piece to the bottom of the pad. Repeat the measurements of R y,∞ and R y,0 , moving the top test piece to the bottom of the pad after each pair of measurements, until five pairs of measurements have been made. This subclause implies that measurements of R y,∞ and R y,0 shall be made alternately, but this is not an essential requirement of this document. The five measurements of R y,0 may be made before or after the five measurements of R y,∞ if such a procedure is preferred, or the measurements may be made alternately.
8.5 Turn the pad upside down and repeat procedures 8.2 to 8.4 for the other side.
8.6 Determine the grammage of the material according to ISO 536 after conditioning in accordance with ISO 187.
For greater accuracy, the grammage of each individual test piece should be determined.
9 Calculation of results
Calculate the means of R y,∞ and R y,0 for each side of the sample and use these values to calculate the Kubelka-Munk coefficients as in Formulae (1) and (2).
For greater accuracy, if the grammage of each individual test piece is known, calculate s y and k y for each pair of measurements and then calculate the mean values. Calculate these values to the nearest 0,1 m 2 /kg for each set of measurements.
Report the light- scattering coefficient to the nearest whole number. If the light-scattering coefficients for the two sides of the sample do not differ by more than 1,0 m 2 /kg, report the overall average. If the two sides differ by more than 1,0 m 2 /kg, report the average value for each side separately. Similarly, report the light- absorption coefficient to the nearest 0,1 m 2 /kg.