粒子の表面改質とその効果

Abstract

粒子の表面改質には化学的，物理的，あるいは機械的方法があり，さらに材料特性 (有機/無機) や処理工程 (湿式/乾式) の違いによって，その手法は多様化している．これらの中で，樹脂粒子への超微粒子の外添，すなわちトナー粒子の複合化は，主に機械的方法が採用されている．外添剤は，粒子の付着，流動性などの制御のために使用されており，これらの特性は外添剤の種類と添加条件に大きく依存することが知られている．本稿では，粒子の表面改質および複合化技術の概要を記したのち，特性の僅かな違いを検出して多面的に評価する方法，すなわち，平均値あるいは代表値ではなく，データの統計分布やプロファイルを用いる方法を解説する．付着性の評価では気流法を取りあげ，外添状態，粒子の初期電荷，外部電場の影響を説明するとともに，トナー・キャリア間の付着強度分布も紹介する．流動性の評価では振動細管法を取りあげ，外添剤の大きさ，添加量，添加状態，樹脂粒子の形状よって流動性プロファイルが変化することを示す.

There are many methods to modify the surface of particles, e.g., chemical, physical, and mechanical treatments;in addition, according to the different properties of materials (organic/inorganic) and the processes used (wet/dry), these methods become more diversified. Among these methods, surface modification based on externally adding ultrafine particles to resin particles--i.e. forming toner composites--is carried out mainly by mechanical treatment. The external additives are used to control particle adhesion, flowability, and so forth. It is known that these properties strongly depend on the type of the external additives and its treatment conditions. The techniques for surface modification and the formation of composite particles are summarized in this article. Then, experimental methods to detect slight differences in the aforementioned properties and to allow a multifaceted evaluation are described, where statistical distributions or profiles of the data are used for the evaluation instead of average or representative values. The airflow method is specifically introduced to evaluate the adhesive properties. The effects of the state of the external additives, the initial charge of the particles, and the external electric field on particle adhesion are demonstrated;in addition, the results of the distribution of adhesive strength between the toner and carrier are provided. The vibrating tube method is introduced to evaluate flowability, showing that the flowability profile varies according to the size of the external additives, their amount, the treatment condition, and the shape of the resin particles.