When light irradiates the sample, part of the light is reflected on the surface of the sample, part is absorbed, and part passes through the sample. The light transmitted through the sample is divided into two parts: parallel transmitted light and scattered transmitted light. Transparency refers to the degree to which a single-layer sample reflects the image of the covered object, expressed in percentage (%).
(1) Transparency test method
The test was carried out according to the national standard GB 2679.1 "Determination of Paper Transparency". This method is suitable for the determination of the transparency of undyed translucent paper, tracing paper, etc. The specific test steps include the following points.
① Choose a 45°/0° reflectance photometer that meets the requirements of GB 2679.1, and a standard whiteboard with a reflectivity of 84% ± 1% for light waves with a dominant wavelength of 457nm and a standard blackboard with a reflectivity of less than 0.5%.
② Calibrate the instrument with white and black standard plates respectively. It should be noted that the compensation current and dark current of the instrument need to be adjusted with a standard white board and a standard black board before each test. For continuous testing, the instrument should be adjusted again after testing several samples.
③Sample collection and processing. Sampling according to GB 450, cut a 50mm×70mm sample, the long side of the sample is the longitudinal direction, and there are 3 pieces on the front and back sides. According to the requirements of GB 10739, carry out temperature and humidity pretreatment on the samples.
④ Place the single-layer sample flatly backed by a white standard plate and clamp it to the sample hole of the instrument. The long side of the sample is parallel to the incident direction of light, that is, parallel to the front-to-back direction of the instrument, and measure its reflectance Rw.
⑤Put the same single-layer sample flatly backed by a black standard plate and clamp it on the sample hole of the instrument. The long side of the sample is parallel to the front and back direction of the instrument , and measure its reflectance Ro.
⑥ Calculation transparency
(2) Opacity test method
The opacity of paper can be measured by testing instruments such as opacity meter, photometer or Whiteness Meter, and the opacity meter mainly measures the size of parallel transmitted light. The specific test method for paper opacity using an opacity meter is: first, take a sample according to GB450, cut a 50mm × 70mm sample, the long side of the sample is longitudinal, 5 pieces on the front and back, and test the sample according to the requirements of GB 10739 Perform temperature and humidity preconditioning. Then stack several samples until opaque, clamp them flat on the test hole (the long side of the sample is parallel to the front and back direction of the instrument), and then use a green filter to measure the reflectance Rw. Then place a single sample on a black standard plate, and measure the reflectance Ro with a green filter.
The opacity of the paper is:
