There are many methods with various reliability and using range to measure whiteness. Especially in recent years, with the extensive use of fluorescent optical whitener, the determination of whiteness becomes more complicated. The testing of whiteness can generally be divided into two categories: one is to test the reflectance of each wavelength by the spectrophotometric detector and calculate the L value, a value and b value using a computer, and then get the whiteness value by the whiteness formulas. At present, there are many formulas for calculating whiteness, but there are some defects existing. It is difficult to find a formula for calculating whiteness exactly in accordance with the actual situation. Another type of measurement is using the whiteness meter, which is usually express the whiteness value by reflectance at a specific wavelength. Take type ZBD whiteness meter as an example, if the specific wavelength light is measured by making it through the filter and the wavelength is less than 500nm, which means the light irradiated to the sample is not just the blue light, but also purple light, So the whiteness measurement can, therefore, be carried out with samples of fluorescent optical whitener. In the test, the instrument was adjusted with a standard white plate, and then test the relative whiteness of the sample.
1. ZBD type whiteness instrument
2. Operation process
Cut the sample cloth with 12cm×24cm size without being treated by fluorescent optical whitener, fold into 5cm × 5cm, 8 layers (thin fabric with 18cm × 24cm size, and fold into 5cm × 5cm, 12 layers), test the whiteness in whiteness meter, and test three times in different parts with uniform direction, and take the average value.
Other instruments that can be measured or measured to calculate whiteness can be used. The data obtained are not necessarily consistent, but the data measured by the same instrument can still be used as the whiteness, and when the whiteness data is reported, the instrument type shall be indicated.
The folding layers of the fabric should be same
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