US 5,489,975 AGranted

Image forming method and apparatus

AssigneeEastman Kodak Company

InventorsJoseph Y. Kaukeinen, Thomas A. Jadwin, Peter S. Alexandrovich, Eric C. Stelter

Life of this patent

Estimating the term…

Loading patent…

Abstract

An electrostatic image on an image member already containing a loose dry first toner image is toned with a second toner, for example, a toner of a second and different color from the first toner image. The toning is accomplished by a developer having a high coercivity permanently magnetized carrier and toner which is moved through a development zone by a rapidly rotating core inside a sleeve on which the developer moves. Pole transitions caused by the rapidly moving core make the high coercivity permanently magnetized carrier move vigorously in a wave motion having alternating crests and troughs. Scavenging of the first toner image is prevented by separating the sleeve from the image member sufficiently that the crests of the developer do not touch the image member during the toning process. An alternating electrical field is applied between the sleeve and the image member to enhance development.

Claims7

Dependent claims

Image forming apparatus comprising:

an image member,
means for forming an electrostatic image on the image member,
a supply of two component developer including charged toner particles and oppositely charged carrier particles, which carrier particles have a coercivity of at least 1,000 gauss when magnetically saturated and exhibiting an induced magnetic moment of at least 20 emu/gm when in an applied field of 1,000 gauss,
an applicator having a rotatable magnetic core having at least eight alternating poles around its periphery and a shell around the core,
means for rotating the core within the shell at a speed of at least 500 revolutions per minute to create a rapidly changing magnetic field on the shell to move the developer in a wave motion having alternating crests and troughs through close proximity with the image member but without the crests of the developer contacting the image member, and
means for applying an alternating electric field of at least 500 volts and 300 Hertz between the image member and the shell.

3 more elements

Dependencies are inferred from the claim text.