A new composite-carrier based on magnetic particles and phenol resin has been developed for long-life electrophotographic developers. The present carrier, composed of core particles and a resin shell, is quite spherical in shape and is characterized by a narrow particle-size distribution (controllable range: 10-200 μm in diameter). The carrier core can either be made up of magnetic fine particles such as ferrites and magnetites, or of non-magnetic particles such as hematites. The content of the core particles can be as high as 90 wt%. The core particles were prepared by dispersing magnetic or non-magnetic fine particles in an aqueous solution of phenol and formaldehyde using ammonium as an initiator. The surface of the core particles was then coated with silicone resin. The composite-carrier thus prepared exhibits an excellent performance in charging and charge-holding properties that greatly exceeds the characteristics of commercial ferrite-carriers.
Toshiyuki Hakata, "New Composite-Carrier for Electrophotographic Developers" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP16), 2000, pp 714 - 716, https://doi.org/10.2352/ISSN.2169-4451.2000.16.1.art00073_2