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Magnetic toner with negative polarity for developing latent electrostatic images, and image forming apparatus using the same

Image Number 2 for United States Patent #6641969.

A magnetic toner with a negative polarity for developing latent electrostatic images is made of toner particles, each toner particle containing a binder resin, a magnetic powder, and a charge control agent, the surface of the magnetic toner satisfying the relationship of 2.times.10.sup.-7.ltoreq.C/Sw.ltoreq.10.times.10.sup.-7, provided C.ltoreq.8.times.10.sup.-3, wherein C is an amount (g/g) of the charge control agent dissolved in a solvent comprising water and methanol, and Sw is a specific surface area (cm.sup.2 /cm.sup.3) of the toner particles determined from a weight-average particle diameter of the toner particles. An image forming apparatus has an electrostatic image bearing member, and a unit for developing the electrostatic image with the above magnetic toner, the unit having a developer holding member provided with a magnet, and a developer container. A method for measuring the amount of a charge control agent extracted from the surface of magnetic toner particles employs an aqueous alcohol solvent of water and an alcohol.

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