OPACITY, Illuminant C, UV adjusted

This test is performed to determine the opacity of paper, solid board or folding board. Measure the luminance factor of a single sheet of the paper over a black cavity and the intrinsic luminance factor of the same paper. The opacity is calculated as the ratio of these two luminance factor values.

Operate the instrument in accordance with ISO 2471 and the manufacturer’s instructions.

Leave the samples exposed for 24 h to 23°C and 50% R.H., according to ISO 187.

Calibrate the instrument according to the instrument maker’s instructions, using a non-fluorescent ISO reference standard of level 3 (IR3). Adjust the UV-content to the C/2° Illuminant/observer.

Each sample pack is made of a pad of paper to be tested and a coloured cover sheet.

Remove the coloured protective sheet from the test piece pad.

Without touching the test area, use the procedure appropriate to the instrument to measure the intrinsic luminance factor R_∞ of the top side of the test piece pad. Read and record the value to the nearest 0,01% of the reflectance factor.

Remove the top test piece from the pad and, with the black cavity backing this single test piece, measure the luminance factor R_o, for the same area of the test piece. Read and record the value to the nearest 0,01% of the luminance factor.

(These two clauses describe the two independent measurements, which are necessary for the determination of opacity. This text is not intended to imply that the two measurements shall necessarily be made in this order. It depends on the software installed to manage the reflectometer.)

Move the measured test piece to the bottom of the pad. Repeat the measurements of R_∞ and R_o, 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 clause implies that measurements of R∞ and Ro shall be made alternately, but this is not an essential requirement of this procedure. The five measurements of R_o may be made before or after the five measurements of R_∞ if such a procedure is preferred, or the measurements may be made alternately.)

Turn the pad upside down and repeat the same procedure for the other side.

Using the corresponding values of R_∞ and R_o, calculate the opacity as (R_o / R_∞) · 100

Report 10 measures of the opacity, their over-all mean and standard deviation calculated to 3 significant figures (results are not reported separately for each side).