PROCESS FOR PRODUCING TONER FOR ELECTROPHOTOGRAPHY

Abstract

The present invention relates to a process for readily producing a toner for electrophotography which contains toner particles having a small particle size and a narrow particle size distribution, and a toner for electrophotography having a small particle size and a narrow particle size distribution which is produced by the above process. There is provided a process for producing a toner for electrophotography which includes the steps of (A) finely dispersing a resin binder in an aqueous medium in the presence of a nonionic surfactant to prepare a dispersion of resin binder-containing fine particles; (B) aggregating the resin binder-containing fine particles obtained in the step (A) together to prepare a dispersion of mother particles; (C) adding a dispersion of a resin binder-containing fine particles at one time or sequentially in several divided parts to the dispersion of the mother particles obtained in the step (B) to prepare aggregated particles thereof; and (D) coalescing the aggregated particles obtained in the step (C), as well as a toner for electrophotography which is produced by the above process.

Description

Claims

1. A process for producing a toner for electrophotography, comprising the steps of: (A) finely dispersing a resin binder in an aqueous medium in the presence of a nonionic surfactant to prepare a dispersion of resin binder-containing fine particles;(B) aggregating the resin binder-containing fine particles obtained in the step (A) together to prepare a dispersion of mother particles;(C) adding a dispersion of a resin binder-containing fine particles at one time or sequentially in several divided parts to the dispersion of the mother particles obtained in the step (B) to prepare aggregated particles thereof, and(D) coalescing the aggregated particles obtained in the step (C).

2. The process according to claim 1, wherein when adding the dispersion of the resin binder-containing fine particles sequentially in several divided parts to the dispersion of the mother particles in the step (C), the second or subsequent part of the dispersion of the resin binder-containing fine particles is added along with an aggregating agent in which the resin binder-containing fine particles and the aggregating agent are added separately from each other but at the same time, or added alternately.

3. The process according to claim 1, wherein the resin binder contains a polyester.

4. The process according to claim 1, wherein in the step (A), the dispersion of the resin binder-containing fine particles contains a colorant.

5. The process according to claim 1, wherein an amount of the resin binder-containing fine particles added in the step (C) is from 15 to 75% by weight on the basis of a total amount of the resin binder-containing fine particles and the mother particles contained in the dispersion of the mother particles.

6. The process according to claim 1, wherein in the step (C), the dispersion of the resin binder-containing fine particles is added sequentially in 2 to 6 separate parts.

7. The process according to claim 1, wherein when adding the dispersion of the resin binder-containing fine particles sequentially in several divided parts to the dispersion of the mother particles in the step (C), the second or subsequent part of the resin binder-containing fine particles is added along with an aggregating agent.

8. The process according to claim 1, wherein particles of the toner have a volume median particle size (D50) of 1 to 4 μm and a variation coefficient of particle size distribution (CV value) of 23% or less.

9. A toner for electrophotography which is produced by the process as defined in any one of claims 1 to 8.

10. A method of controlling a particle size of a toner for electrophotography, comprising the steps of finely dispersing a resin binder in an aqueous medium in the presence of a nonionic surfactant to prepare a dispersion of resin binder-containing fine particles; aggregating the resin binder-containing fine particles to prepare a dispersion of mother particles; then adding a dispersion of a resin binder-containing fine particles at one time or sequentially in several divided parts to the dispersion of the mother particles to prepare aggregated particles thereof; and coalescing the aggregated particles.