Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-07-25
2003-07-08
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C430S122520, C399S262000
Reexamination Certificate
active
06589701
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a toner for use in electrophotography, an image forming method for visualizing an electrostatic image and toner jetting; an image forming method using the toner, and a process cartridge including the toner.
Hitherto, various electrophotographic processes have been disclosed in U.S. Pat. Nos. 2,297,691; 3,666,363: 4,071,361; etc. In these processes, an electrostatic latent image is formed on a photoconductive layer by irradiating a light image corresponding to an original, and a toner is attached onto the latent image to develop the electrostatic image. Subsequently, the resultant toner image is transferred onto a transfer(-receiving) material such as paper, via or without via an intermediate transfer member, and then fixed, e.g., by heating, pressing, or heating and pressing, to obtain a copy or a print. The toner remaining on the photosensitive member is cleaned by various methods, and the above steps are repeated for a subsequent image forming cycle.
Japanese Laid-Open Patent Application (JP-A) 55-18656 has proposed a jumping developing method wherein a magnetic toner is applied in a very small thickness onto a sleeve, triboelectrically charged and brought to a proximity to an electrostatic image to effect the development. This method is advantageous in that a sufficient triboelectrification becomes possible by application of the magnetic toner in a very small thickness layer on the sleeve to increase the opportunity of contact between the sleeve and the toner.
However, the developing method using an insulating magnetic toner involves an unstable factor associated with the use of such an insulating magnetic toner. More specifically, insulating magnetic toner particles contain a substantial amount of fine powdery magnetic material, and a portion of the magnetic material is isolated from or exposed to the surfaces of the toner particles, thus affecting the flowability and triboelectric chargeability of the magnetic toner to consequently change or deteriorate the various performances, inclusive of developing performance and continuous image forming performances. These difficulties are presumably caused by the presence at the magnetic toner particle surfaces of fine particles of magnetic material having a lower resistivity than the resin constituting the toner. The toner chargeability also greatly affects the developing performance and transferability, thus also deeply affecting the resultant image quality. For this reason, a magnetic toner capable of stably attaining a high charge is seriously demanded.
Further, in recent years, apparatus utilizing electrophotography have been used not only as copying machines for reproducing originals but also for printers for computers and facsimile apparatus. Accordingly, electrophotographic apparatus are required to be smaller in size and weight and to exhibit higher speed and reliability, so that they are required to be composed of simpler components. Consequently, a toner is required to exhibit higher performances, failure of which makes impossible the realization of an excellent image forming apparatus.
JP-A 7-230182 and JP-A 8-286421 have proposed external addition of magnetic material powder for stabilizing the chargeability. This allows the provision of a toner showing a stable chargeability and high cleanability, but the toner is liable to be attached to a contact charging member which is frequently included in a high-speed printer of a simple structure.
Further, after a transfer step of transferring a toner image from a photosensitive member to a transfer(-receiving) material, a portion of toner (residual toner) remains on the photosensitive member without being transferred. The residual toner has to be cleaned from the photosensitive member in order to continuously obtain good toner images in a continuous copying or printing. The recovered residual toner is stored in a vessel in the image forming machine or a recovery box and then discharged as a waste toner or recycled.
In order to obviate the occurrence of waste toner, the image forming apparatus has to be equipped with a recycle mechanism. Such a recycle system to be placed in the apparatus has to be a large-scale one for complying with multiplicity of function, high-speed and high image quality required of copying machines, printers and facsimile apparatus demanded on the market, thus resulting in a larger apparatus which is against the demand for a smaller apparatus in the market. This problem is also encountered also in the case of storing the waste toner in a vessel or a recovery box disposed in the apparatus or in a system including a waste toner recovery unit integral with the photosensitive member.
In order to alleviate the problem, the rate or efficiency of transfer at the time of transferring a toner image from a photosensitive member to a transfer material has to be increased.
JP-A 9-26672 has proposed a toner containing a transfer efficiency-improving agent having an average particle size of 0.1-3 &mgr;m and hydrophobic silica fine powder having a BET specific surface area of 50-300 m
2
/g, so that the toner is provided with a reduced volume resistivity and a thin layer of the transfer efficiency-improving agent is formed on the photosensitive member, to increases the transfer efficiency. However, a toner produced through the pulverization process is caused to have a generally broad particle size distribution, so that it is difficult to uniformly increase the transfer efficiency of all the toner particles, thus leaving a room for further improvement.
For improving the transfer efficiency, there has been known a method of forming a toner, of which the shape is made closer to a sphere. Examples thereof may include production methods by spraying toner particle formation, dissolution with a solution and polymerization as disclosed in JP-A 3-84558, JP-A 3-229268, JP-A 4-1766 and JP-A 4-102862. However, these toner production methods require a large production apparatus, and the resultant sphere-like toner particles are liable to cause a problem of cleaning failure because of their spherical shape.
In a conventional toner production process including a pulverization step, toner ingredients including a binder resin for ensuring toner fixation onto a transfer material, a colorant or magnetic material for providing a toner and a charge control agent for imparting a chargeability to toner particles are dry-blended and melt-kneaded by a kneading apparatus, such as a roll mill or an extruder, and, after being cooled and solidified, the kneaded product is pulverized by a pulverizing apparatus, such as a jet stream-type pulverizer or a mechanical impingement-type pulverizer, followed by classification by means of a pneumatic classifier, to obtain toner particles, which are optionally further blended with a flowability improver and a lubricant externally added thereto. In order to provide a two-component developer, the toner may be blended with a magnetic carrier.
An example of such a process for producing toner particles is illustrated by a flow chart shown in FIG.
7
.
A coarsely pulverized material is continuously or successively fed to a first classification means, from which a coarse powder fraction principally comprising particles beyond a prescribed particle size range is sent to a pulverization means for pulverization and then recycled to the first classification means.
The other fine powder fraction principal comprising particles within the prescribed particle size range and particles below the prescribed particle size range is supplied to a second classification means and separated thereby into medium powder principally comprising particles within the prescribed particle size range, fine powder principally comprising particles below the prescribed particle size range and coarse powder principally comprising particles above the prescribed particle size range.
As the pulverization means, various pulverizers are used, and for pulverization of a coarsely pulverized toner product principally comprising a b
Hiratsuka Kaori
Nakanishi Tsuneo
Okubo Nobuyuki
Onuma Tsutomu
Yamazaki Katsuhisa
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