The yellowness index is used to characterize the degree of yellowishness of a white sample, which can be transparent or opaque. The yellowness index and the degree of yellowing observed under sunlight can be well matched, so it can evaluate the quality and aging degree of plastics. Yellowness index calculation formula: YI=100(1.28X-1.06Z)/Y. In the formula, X, Y, and Z are the tristimulus values representing the color of the material measured by a Colorimeter, a Colorimeter or a Spectrophotometer under a standard C light source. Spectrophotometer series CS-580, CS-600, CS-610, CS-650, CS-660 can all test the degree of yellowing.
At the request of a customer of a transparent plastic sheet manufacturer, the customer sent a plastic sheet sample and asked to use an instrument to test the yellowing degree of the sample. The following specifically introduces how to test the yellowing degree of transparent plastic sheets.
Measuring instrument: CS-600 Spectrophotometer
Measuring conditions: Standard C light source: color temperature is 6774K, composed of A light source (gas-filled spiral tungsten lamp with a color temperature of 2856K, its light color is yellowish) and a cover C-type DG liquid filter, the light color is equivalent to the sky with clouds Light.
Observer Angle: 2°
Measuring range: suitable for yellowness index test method of colorless transparent, translucent and near white opaque plastics. It is suitable for plate, sheet, film, powder and granular samples, not for plastics containing fluorescent substances.
Test steps:
Step 1: Prepare the instrument and three samples of the transparent plastic sheet to be tested (as shown in Figure 2), from left to right are samples 1, 2, and 3, sample 1 is the plastic sheet before aging, and sample 2 is the aging 12 After 24 hours, sample 3 is after aging for 24 hours;
Step 2: Calibrate the instrument and perform black and white calibration on the instrument;
Step 3: After the black and white calibration is completed, use the Up and Down selection keys to select, and press the "Enter" key to enter the "Measurement Settings" page. Select YI, that is, yellowness in the display setting, select C light source in the light source selection, and then select "Observer" through the Up and Down keys, and press the "Enter" key to enter the observer selection page, and select the observer angle of 2°;
Step 4: After the measurement conditions are set, the test can be started. When testing the yellowness of transparent plastic sheets, you need to pick up the sample and put it in the air. There is no need to place an object on the bottom of the sample. After picking up the sample, directly align the test hole of the instrument with the sample to be tested. Press the "Print" button to position the measurement area first. Press the "Test" button again, and the measurement will be completed after the "beep" sound, and the test results can be viewed;
Step 5: Repeat the measurement step to measure the other two samples respectively, and the degree of yellowing can be directly measured.
After the measurement is completed, △YI represents the difference in yellowness index. From the measurement results, it can be seen intuitively that the longer the aging time, the higher the aging degree of the sample, and the greater the yellowing value. The Spectrophotometer can quickly and conveniently measure the yellowness index and yellowing degree of transparent plastic sheets through simple manual operations, which can fully meet the requirements of manufacturers for product quality inspection.
