Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2000-12-21
2003-01-07
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S110400
Reexamination Certificate
active
06503681
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a toner for developing electrostatic images using an electrophotographic image forming device such as a copying machine, a printer or a facsimile machine.
In a dry copying method, an electrostatic latent image on a photosensitive medium is developed with a toner composed of a binder and a coloring agent. The developed toner image is transferred to a transfer member such as paper and fixed there.
With recent development of digital copying machines and laser printers, there is an increasing demand for a developer capable of giving high quality images. While the current level for high quality images is 300 dpi, it is well expected that higher quality as high as 480 psi or, further, 600 psi, will be required in the near future.
In this circumstance, production of fine particle toner will be of very importance for obtaining high quality images. With a decrease of the particle size of toner, however, agglomeration and deposition of toner particles are apt to occur. As a consequence, there are caused a number of problems such as failure of supplying toner from a toner storage section to an image developing section and failure of transferring toner from the image development section to the electrostatic image bearing surface.
Toner is generally produced by first blending raw material ingredients thereof such as a binder and a coloring agent. The mixture is then kneaded with a kneader such as an extruder at a temperature higher than the melting point of the binder. The kneaded mixture is extruded into a plate, solidified and then pulverized. The pulverization generally includes a series of coarse pulverization, medium pulverization and fine pulverization.
One known pulverization method includes a first step in which a solidified toner composition is coarsely pulverized with a hammer crusher, a second step in which the coarsely pulverized product is pulverized into a medium size with an impact-type pulverizer, and a third step in which the product in the second step is finely pulverized with a jet mill using an air jet method.
The product obtained with the known method has a small average particle diameter. However, because of a large content (15-50% based on the total number of particles) of excessively fine particles, the toner causes a problem of background stains in the produced images. Thus, in order to remove such excessively fine particles, it is necessary to conduct an additional treatment so that the production efficiency is lowered. The conventional method has an additional disadvantage because the third step consumes great energy and requires high production costs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process which can produce toner capable of forming high quality toner images.
Another object of the present invention is to provide an economically acceptable process which can produce, with reduced energy for pulverization, toner having suitable particle size characteristics and a suitable particle shape.
It is a further object of the present invention to provide a process of the above-mentioned type which can produce toner having a reduced content of excessively fine particles.
In accordance with the present invention, there is provided a process for the production of a toner for developing electrostatic images, comprising:
a first pulverizing step wherein a toner composition comprising a binder and a coloring agent is pulverized with a first pulverizer to obtain preliminarily pulverized particles having a weight average particle diameter of 20-100 &mgr;m and containing no more than 50% by weight of particles having roundness of 0.90 or less; and
a second pulverizing step wherein the preliminarily pulverized particles are finely pulverized with a second pulverizer to obtain finely pulverized particles having a weight average particle diameter of 5-13 &mgr;m and containing no more than 30% by weight of particles having roundness of 0.90 or less and no more than 15%, based on the total number of particles of the finely pulverized particles, of particles having a particle diameter of 5 &mgr;m or less.
In the present specification and appended claims, the terms “WEIGHT AVERAGE PARTICLE DIAMETER”, “ROUNDNESS”, “ACTUAL LOAD POWER FOR PULVERIZATION” and “PULVERIZATION BY IMPACT AND SHEARING FORCES” are intended to refer as follows.
WEIGHT AVERAGE PARTICLE DIAMETER:
The particle diameter distribution of the toner is measured with a Coulter Multisizer II (manufactured by Coulter Electronics, Inc.). As an electrolytic solution for measurement, an aqueous 1% by weight NaCl solution of first-grade sodium chloride is used. A dispersant (0.5-5 ml of a salt of alkylbenzenesulfonic acid) is added to 10 to 15 ml of the above electrolytic solution, to which 2 to 20 mg of a sample to be measured are added. The resulting mixture is subjected to a dispersing treatment for about 1-3 minute to about 3 minutes in an ultrasonic dispersing machine. The electrolytic solution (100-200 ml) is taken in another vessel, to which a predetermined amount of the dispersed sample is added. Using an aperture of 100 &mgr;m in the above particle size distribution measuring device, the particle size distribution is measured on the basis of the particle number with the Coulter counter for particles having a diameter in the range of 2-40 &mgr;m. The number and weight particle distribution are calculated. The weight average diameter of the toner is determined from that weight distribution. The median value of each channel is used as the representative of that channel.
ROUNDNESS:
Roundness of toner is defined by the following formula:
Roundness
=
4
π
A
/
B
2
wherein A represents an area of a projected image of a toner particle and B represents a peripheral length of the projected image. Roundness is measured with a flow-type particle image analyzer FPIA-1000 (manufactured by Toa Medical Electronics Co., Ltd.). The roundness becomes nearer to 1 as the contour of the particle becomes smoother and the particle becomes more spherical. Average roundness is an average of the measured values for 7000 to 13000 toner particles.
ACTUAL LOAD POWER FOR PULVERIZATION:
Actual load power is defined by the following formula:
Actual load power =
P
f
−P
0
wherein P
f
represents load power (kW·h/kg) required for pulverizing a raw material feed and P
0
represents load power required for operation with no raw material feed.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
For the production of a toner according to the present invention, a composition containing a binder and a coloring agent is first provided. Any conventional binder may be used for the purpose of the present invention. Examples of the binder include a polyester resin; a hydrogenated petroleum resin; a styrene resin such as polystyrene, poly(p-chlorostyrene), poly(vinyltoluene), a styrene-p-chlorostyrene copolymer, a styrene-propylene copolymer, a styrene-vinyltoluene copolymer, a styrene-vinylnaphthalene copolymer, a styrene-methyl acrylate copolymer, a styrene-octyl acrylate copolymer, a styrene-methyl methacrylate copolymer, a styrene-ethyl methacrylate copolymer, a styrene-butyl methacrylate copolymer, a styrene-methyl a-chloromethacrylate copolymer, a styrene-acrylonitrile copolymer, a styrene-vinyl methyl ketone copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, a styrene-acrylonitrile-indene terpolymer, a styrene-maleic acid copolymer or a styrene-maleate copolymer; poly(methyl methacrylate); poly(butyl methacrylate); poly(vinyl chloride); poly(vinyl acetate); polyethylene; polypropylene, polyester; polyurethane; polyamide; an epoxy resin; poly(vinyl butyral); poly(vinyl acetal); poly(acrylic acid); rosin; modified rosin; a terpene resin; an aliphatic or alicyclic hydrocarbon resin; chlorinated paraffin; or paraffi
Ito Ryoichi
Iwamoto Yasuaki
Izu Mitsuyoshi
Makino Nobuyasu
Miyamoto Tomotsugu
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