This method is suitable for near -white paper samples with or without optical brighteners.
1 definition
(1) Reflection factor R is the ratio of the radiant flux reflected by an object to the radiant flux reflected by a fully reflective diffuser under the same conditions, expressed as a fraction.
(2) Reflection factor R. The reflection factor of a single-layer sample backed with black.
(3) The internal reflection factor R is the reflection factor of the sample when the thickness reaches the reflection factor no longer increases with the thickness increase.
(4) The opacity of the paper, the reflection factor R of a single-layer paper with a black backing: the percentage of the internal reflection factor R of the same sample.
2 instruments
① Reflection photometer.
② Work standard whiteboard.
③Standard black letter. The reflection factor is not more than 0.5%.
3 Preparation of samples
①Sampling according to the standard method.
②Cut out no less than 10 square test pieces of 100 mm×100 mm from the extracted paper. One side of the sample is the longitudinal direction of the paper. They are stacked face up to form a stack, and the total thickness should reach the level where the reflection factor does not increase with the increase of the number of test pieces. The top and bottom of the paper stack are lined with a test piece to protect them from being soiled and exposed to light or heat radiation.
4 Calibration of the instrument
According to the instrument manual, insert corresponding filters into the incident beam and the reflected beam respectively, and turn on the power switch of the instrument.
After preheating according to the specified time, use the working standard white board and standard black tube to calibrate the instrument respectively.
5 Measurement procedure
①Remove the protective layer from the sample stack, and test the internal reflection factor R.. of the top layer of the sample, and the reading is accurate to 0.1%. Remove the top layer of sample and place it on the bottom of the paper stack, repeat the test on the second test piece, and then use the same method to test no less than 5 test pieces in turn. Turn over the paper stack and repeat the above operation to measure the internal reflection factor R of the reverse side of the sample.
② For the test piece whose internal reflection factor R. has been tested, it shall be backed with a single-layer standard black tube. Test the reflection factor R of the front and back of each test piece separately.
6 Calculation of results
Calculate the front and back of the sample R. and R respectively. average of. Use the following formula to calculate the opacity of the obverse and reverse samples, respectively.
If the difference between the front and back measurements is greater than 0.5%, report the opacity and transparency values of the front and back separately. If it is less than 0.5%, report the average of the positive and negative sides, and the reported result is accurate to 0.5%.
Note: Due to the method of calculating the opacity of each test piece separately and the method of calculating the opacity based on the average R0 and R of all test pieces, the difference between the two calculation results is very small and can be ignored. For simplicity, the latter calculation method is adopted.
