Developer containing magnetic and non-magnetic toner

Claim 1

In a two-component simultaneously consumable, dry-type composite developer which comprises a mixture of magnetic toner particles composed of a dispersion of a powdery magnetic material in an electrically insulating binder resin medium and non-magnetic toner particles composed of a dispersion of a coloring agent in an electrically insulating binder resin medium, the improvement wherein the magnetic toner particles comprise (a) a resin binder medium and (b) 40 to 70% by weight, based on the sum of the binder and powdery magnetic material, of magnetite having a bulk density of at least 0.45 g/ml, a number average maximum size as measured by an electron microscope of at least 0.5 μm and a maximum size/minimum size ratio of from 1.0 to 5.5, the magnetic toner particles have an electrostatic capacitance of 7 to 8.5 pF (picofarad), a dielectric constant of 3.59 to 4.36, and a volume resistivity of 1.2×10 - to about 8.6×10 14 Ω-cm, as determined under conditions of an electrode gap of 0.65 mm, an electrode sectional area of 1.43 cm 2 and an inter-electrode load of 105 g/cm 2 , the non-magnetic toner particles comprise (i) a resin binder medium, (ii) 2 to 10% by weight, based on the resin binder medium, of a pigment, and (iii) a negative charge controlling agent composed of a chromium-, iron- or cobalt-containing complex salt dye, and have an electrostatic capacitance of 6.0 to 8.0 pF and a dielectric constant of 3.08 to 4.10, as determined under said conditions, the magnetic toner particles and the non-magnetic toner particles have a friction chargeability characteristic of the same polarity, and the magnetic toner particles and the non-magnetic toner particles are present in the developer at a weight ratio of from 100:1 to 100:30.