Importance

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Abstract

A dry toner powder the toner particles of which are triboelectrically negatively charged and are suited for development of an electrostatic charge pattern, wherein said toner particles contain: (1) at least one triboelectrically negatively chargeable thermoplastic resin serving as binder having a volume resistivity of at least 10.sup.13 .OMEGA.-cm, and (2) at least one resistivity lowering substance being an onium compound having a volume resistivity lower than the volume resistivity of said binder, and said toner particles are free from non-resinous charge-controlling agent(s) providing negative triboelectric chargeability, wherein said substance(s) (2) is (are) capable of lowering the volume resistivity of said binder by a factor of at least 3.3 when present in said binder in a concentration of 5% by weight relative to the weight of said binder, and wherein said toner powder containing toner particles including a mixture of said ingredients (1) and (2) under triboelectric charging conditions is capable of obtaining an absolute median (q/d) charge/diameter value (x) lower than 10 fC/10 .mu.m but not lower than 1 fC/10 .mu.m, and said toner powder under the same triboelectric charging conditions but free from said substance(s) (2) then has an absolute median q/d value (x) at least 50% higher than when said substance(s) (2) is (are) present, and wherein the distribution of the charge/diameter values of the individual toner particles is characterized by a coefficient of variation .nu..ltoreq.0.33.

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First Claim