Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-01-22
2002-04-09
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C241S029000
Reexamination Certificate
active
06368765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a toner for developing latent electrostatic images. More particularly, the present invention relates to a method for producing toner particles with a minimum amount of excessively fine particles by the application of a reduced energy.
2. Discussion of Background
Image forming apparatus such as an electrophotographic copying machine, printer, and facsimile machine output a recording image in such a manner that latent electrostatic images are formed on a latent-image-bearing member and the latent electrostatic images are developed with a developer into visible images. A dry developer unit employing a powdered toner is widely used in the above-mentioned image forming apparatus.
In line with the development of a digital copying machine and a laser printer, the developer unit is required to produce high quality images. In particular, output of high quality images with a density of 300 dpi has currently become the mainstream in the field of printers. Further advance of the image density to 480 dpi and 600 dpi is expected.
Under such circumstances, severe control for obtaining small toner particle size is inevitable. However, the toner particles with small particle diameters tend to aggregate and adhere to each other, so that such toner particles cannot be easily sent to a development section from a toner replenishment section in the course of development of latent electrostatic images. The toner particles cannot be sufficiently transferred to a photoconductor from the development section, with the result that the image density decreases and defective image transfer easily occurs. Such a phenomenon becomes noticeable as the size of toner particles decreases. In other words, the particle size of the toner for developing latent electrostatic images is required to be smaller, while the toner particles without containing excessively fine particles are expected. Further, from the viewpoint of energy-saving, there is an increasing demand for reduction of energy required to produce the toner particles.
To meet the above-mentioned demands, many proposals are made as shown below.
(1) Japanese Laid-Open Patent Application No. 6-59507
A raw material for toner is ground using a special impact mill to control the particle size distribution of the obtained toner.
(2) Japanese Laid-Open Patent Application No. 5-313414
A raw material for toner is coarsely crushed using a mechanical mill, and the crushed particles are then subjected to fine grinding using a jet mill. In this case, the particle size of the coarse product supplied to the jet mill is controlled in advance to increase the yield.
(3) Japanese Laid-Open Patent Application No. 10-18517
One grinding system including an impact mill and the other grinding system including a mechanical mill are reversibly connected to establish a grinding system. The order of the steps consisting of the two grinding systems may be changed in accordance with the application to improve the production efficiency.
(4) Japanese Patent Publication No. 8-10350
A toner raw material is coarsely crushed, and thereafter the coarse product is subjected to secondary grinding to have a weight mean diameter of 20 to 60 &mgr;m using an impact mill. The ground particles are finally pulverized using a jet mill. According to this method, the content of the particles with a weight mean diameter of 100 &mgr;m or more is controlled to 1 to 20% in the particles obtained by secondary grinding.
(5) Japanese Laid-Open Patent Application No. 7-92728
A magnetic toner is prepared using a binder resin, a magnetic material, and a wax. A mixture of the above-mentioned raw materials is subjected to grinding by use of a mechanical mill to satisfy the relationships of 7 &mgr;m≦D
4
<20 &mgr;m and 1<D
4
/D
1
≦3.5, where D
4
is a weight mean diameter and D
1
is a length base mean diameter. After such mechanical milling, fine pulverizing is carried out by use of an impact mill.
(6) Japanese Laid-Open Patent Application No. 6-186776
A toner raw material is ground using an impact mill which is provided with a grinding section where a stator having numerous wavelike protrusions on the inner surface of the stator and a rotator having numerous wavelike protrusions on the outer surface of the rotator are disposed with a minute gap therebetween. This method aims to reduce the generation of excessively fine particles.
The conventional methods for producing the toner as mentioned above still generate a considerable amount of excessively fine particles. In particular, when fine pulverizing is carried out using a jet mill, an increase in the amount of excessively fine particles is unavoidable.
Therefore, an additional device becomes necessary to remove the excessively fine particles, and the required energy is unfavorably increased.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of the present invention to provide a method of producing a toner for developing latent electrostatic images at a reduced energy, with generation of excessively fine particles being minimized.
The inventors of the present invention have intensively studied a preliminarily ground product (hereinafter referred to as a pre-ground product) in order to solve the above-mentioned problems. As a result, it has been found that a toner can be prepared at a reduced energy with minimum generation of excessively fine particles by specifying a particular particle diameter and particle size distribution in the pre-ground product. The present invention has been accomplished based on the above-mentioned finding.
Namely, the first object of the present invention can be achieved by a method of producing a toner for developing latent electrostatic images, comprising the steps of preliminarily grinding a toner composition comprising at least a binder resin and a coloring agent to prepare a preliminarily ground product, and finely pulverizing the preliminarily ground product using a pulverizer to produce toner particles, wherein the preliminarily ground product satisfies conditions (1) and (2):
D
v
≧D
10
(1)
D
50
<3D
10
(2)
wherein D
v
is a weight mean diameter of the preliminarily ground product, D
10
is a weight mean diameter when the cumulative number of particles reaches 10% at measurement of a cumulative particle distribution, and D
50
is a weight mean diameter when the cumulative number of particles reaches 50% at measurement of the cumulative particle distribution.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A toner is usually prepared by mixing raw materials and fusing and kneading the mixture using an extruder to prepare a toner composition. Thereafter, the toner composition is cooled and pulverized, so that a desired toner is obtained. In the pulverizing process, the toner composition is first subjected to coarse crushing, then secondary grinding, and finally fine pulverizing. Fine toner particles excessively pulverized will cause deposition on the background, while large toner particles not sufficiently ground will induce defective toner image transfer. In other words, the pulverizing process is remarkably important.
The toner composition for use in the present invention comprises at least a binder resin and a coloring agent.
Any conventional resins used as the binder resins are usable.
Examples of the binder resin for use in the toner composition include polystyrene resin, styrene—acrylic acid copolymer, styrene—methacrylic acid copolymer, styrene—acrylate copolymer, styrene—methacrylate copolymer, polyester resin, epoxy resin, polyamide resin, and poly(vinyl acetal) resin.
As the coloring agent for use in the toner, carbon black, benzidine yellow pigment, acetoacetanilide-insoluble azo dye, azomethylene dye, and other conventional coloring agent can be used.
The mixing ratio of the binder resin to the coloring agent is not particularly limited, but is preferably in the range of (80:20) to (99:1), more preferably in the range of (90:10) to (95:5).
When the ratio by weight of the b
Ito Ryoichi
Iwamoto Yasuaki
Izu Mitsuyoshi
Makino Nobuyasu
Miyamoto Tomotsugu
Goodrow John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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