Definition
Powder whiteness meter is a specialized optical instrument used to measure the whiteness of powder materials. It quantifies the visual whiteness of powders by simulating the human eye's perception of white luster. In industrial production and quality control, whiteness is often used as one of the key indicators to evaluate the appearance quality of powders, and is widely used in many non-medical fields.
Principle
The measurement principle of powder whiteness meter is based on the theory of colorimeter and light reflection. Instruments typically use diffuse illumination and vertical reception geometry to illuminate the sample surface using a standard light source. The detector receives the visible light spectrum reflected from the sample and simulates the visual characteristics of the human eye through a built-in spectral response function. The instrument converts the spectral data into specific whiteness values according to the whiteness formula specified by the relevant standards. Common whiteness calculation formulas are based on the CIE color space, such as the Hunter whiteness formula: WH = 100 - [(100 - L)2 + a2 + b2]1/2, where L represents luminosity, and a and b represent chromaticity coordinates. Different standards may adopt different formula systems.
Measurement method
The instrument needs to be calibrated before measurement, usually using a standard whiteboard for zero point and range calibration. Sample preparation should ensure that the powder is evenly filled, the surface is flat, and the thickness meets the requirements of light penetration. The powder to be tested is placed in a sample cup and a sample is used to make a specimen with a smooth surface. Place the specimen at the measuring port, start the measurement program, and the instrument automatically reads and displays the whiteness value. To reduce error, it is often recommended to average multiple measurements of the same sample. During the measurement process, attention should be paid to the stability of ambient light to avoid vibration.
Influencing factors
The whiteness measurement results of powder are affected by a variety of factors. The characteristics of the sample itself, such as particle size, distribution, shape, and surface structure, affect the scattering and reflection of light, which in turn changes the whiteness reading. Inconsistencies between the tightness of sample preparation and surface flatness can lead to reduced measurement repeatability. Instrument factors include light source stability, detector sensitivity, and aging of the optical system. Environmental conditions such as temperature and humidity may affect the physical state of some powders. Operational specifications, such as calibration frequency, sample cup cleanliness, and measurement pressure control, are also important aspects of data reliability.
Application:
Powder whiteness meters have application value in many industrial fields. In the paper industry, it is used to measure the whiteness of fillers such as calcium carbonate and kaolin to control the appearance of paper. In the coating and pigment industry, it is used to evaluate the whiteness performance of white pigments such as titanium dioxide and Lide powder and various fillers. In the field of ceramics and building materials, it is used to detect the whiteness of raw materials such as glaze, ceramic blank, cement, talcum powder, etc. In the plastics and chemical industry, it is used to monitor the color quality of powder raw materials such as resins and additives. In addition, it is also used in food additives (such as powdered sugar, starch), daily chemicals (such as laundry detergent) and other industries for color control of related products.
Selection
The selection of powder whiteness time should comprehensively consider the technical parameters and actual needs. The measurement geometry of the instrument should meet the requirements of the standards followed. The spectral response function needs to match the whiteness formula standard used by the target industry, such as CIE, ASTM, ISO or GB. The measured pore size should be adapted to common sample sizes. Instrument repeatability and bench-to-bench differences are key indicators of performance stability. Whether the user interface is user-friendly and whether the data storage and management functions meet the daily workload also needs to be evaluated. In addition, it is necessary to consider the calibration convenience of the instrument, maintenance costs, and the technical support capabilities of the supplier. It is recommended that users make a comprehensive selection based on their main powder type, quality standards to follow, and laboratory routine testing throughput.