2026 Volume 69 Pages 63-67
Background and Aims: Powder technology plays a crucial role in modern industrial products across diverse fields including pharmaceuticals, cosmetics, food, ceramics, and electronic materials. In electrophotographic technology particularly, the charging characteristics of toner particles have a decisive impact on print quality, making accurate evaluation of particle charging properties essential. The conventional Faraday cage method, which has been widely used, has significant limitations as it only measures the average charge amount of the entire sample and cannot determine the charge distribution of individual particles or the correlation with particle size. This study aims to introduce the particle size and charge distribution analyzer “E-SPART Analyzer®” (EST), which enables charge measurement at the individual particle level to address these challenges, and to demonstrate its measurement principles and applications.
Methods and Results: EST simultaneously measures particle size and charge amount of individual particles using acoustic and electric fields formed within a measurement cell. Particle size measurement utilizes phase lag caused by particle inertia in an acoustic vibration field, while charge measurement employs precise laser Doppler measurement of charged particle deflection phenomena in an electric field. In experiments with two-component toner concentration changes, a clear shift of the charge distribution toward zero was observed as toner concentration increased from 2% to 6%. This is attributed to the relative decrease in triboelectric charging opportunities for individual toner particles due to the increased number of toner particles per carrier. Scatter plot visualization enabled intuitive understanding of the correlation between charge amount and particle size, as well as distribution characteristics, demonstrating the acquisition of detailed charging property information that cannot be obtained through conventional bulk measurements.
Conclusions (Outlooks): EST represents the world’s only individual particle charge measurement technology, having been utilized for over 30 years since its commercial launch in 1987 with more than 100 units sold. Development of next-generation EST is currently underway, featuring significant miniaturization for portability, improved mechanical stability through semiconductor laser adoption, and enhanced measurement accuracy and operability through digitalization. As interest in the impact of particle charging characteristics on product quality continues to grow, the value of precise charging property evaluation technology is expected to increase further, and EST is anticipated to continue contributing to the advancement of powder technology.
https://ror.org/018hwpf05 