Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-05-01
2004-06-01
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111350, C430S111400, C430S111410
Reexamination Certificate
active
06743558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carrier for electrophotographic developer, a developer using the carrier, a container for the developer, an image forming apparatus using the developer, an image forming method using the same and a preparation method of the carrier.
2. Description of the Related Art
There are proposed two developing methods in electrophotography; a so-called one-component developing method using one-component developer comprising merely toner as a main ingredient, and a two-component developing method using two-component developer comprising a mixture of a carrier made from materials such as glass beads, magnetic carrier, or those coated by resinous or other coatings, and a toner.
Two-component developing method is advantageous in comparison with one-component developing method, because it uses carrier which has large surface area causing good enough triboelectric-charge for toner, thereby charge of the toner is made stable, holding high quality in images for a long period of developing time. And as the two-component developing method shows a high ability in the supply of the toner to the developing area, there are many incidences having been employed particularly in high-speed apparatuses.
In digital electrophotographic system comprising steps of forming latent electrostatic images onto a photosensitive member by laser beam-irradiation and the like then developing the latent images, two-component developing method usable above characteristics is also being widely used.
Recently, size reduction and condensed distribution of dot units for latent image (pixcel units) have been designed to satisfy the requirements for improving the resolution degree, reproducibility of highlight image and faithful color-imaging. In, particular, important concern in the field is the achievement of developing system, which enables a faithful development of those latent images (dots composing each image). Therefore, many proposals were made from both points of processing means and developer (toner and carrier). As the processing means, a restriction of development gap and a slenderization of the layers composing photosensitive member are effective, however there are still remaining problems with regard to the processing means that the processing cost is increased as a result of such improvements, and sufficient reliability is not yet achieved, and the like.
On the other hand, with regard to developer, the dot reproducibility is considerably improved by use of small size of toner. However, problems are occurred with developer including small size of toners, such as a stain (or, in other word smear) in background area is generated, optical density in image is declined and others. And, in case of toner having small size which is used for full-color image, resins having a low softening-temperature are generally used which, in comparison with black toner, increase a spent amount on the surface of carrier, and degrade the quality of developer by time lapse and show a tendency apt to toner-scattering and to stain background area.
Various proposals for use of small size carriers are also proposed. For example, Japanese Patent No. 2832013 discloses a developing method for reversal development of a latent electrostatic image formed on a latent image-bearing member having organic photo-conductive layer, using magnetic brash of two-component developer which is held on a developer-bearing member and contains a toner capable of being charged in the same polarity as that of the latent image and a carrier; with imposing biased electric field having alter current component and direct current component, wherein the carrier is a carrier including ferrite core-material particles, the core-material particles are being coated with a electric insulating-resin and having a weight-average diameter ranging from 30 to 65 &mgr;m after coated with the resin, and the core-material particles have, at their surfaces, small bores of 1500 Å to 30000 Å in average size.
And Japanese Patent No. 3029180 discloses a carrier for electrophotographic developer using carrier particles, wherein the carrier particles have a size ranging from 15 to 45 &mgr;m in 50%-average diameter(D
50
) (the D
50
presents a particles amount summed up every ingredient divisions by size till becomes to 50%), the content of smaller carrier particles less than 22 &mgr;m in size ranges from 1 to 20%, the content of small carrier particles less than 16 &mgr;m in size is not higher than 3%, the content of large carrier particles more than or equal to 62 &mgr;m in size ranges from 2 to 15%, the content of larger carrier particles more than 88 &mgr;m in size is not higher than 2%, and the carrier satisfies a ratio(S
1
/S
2
) of surface area(S
1
) measured by air-permeation method in comparison with surface area(S
2
), a range represented by;
1.2≦(S
1
/S
2
)≦2.0
where the S
2
represents surface area(S
2
) calculated from following Equation 1;
S
2
=(6/&rgr;·D
50
)×10
4
Equation 1
(where, the &rgr; is specific gravity of the carrier).
Further, Japanese Unexamined Patent Publication of Tokkai Hei 10-198077 discloses a carrier for developer used for developing electrostatic latent image, wherein a 50%-average diameter(D
50
) in volumetric average diameter of the carrier ranges from 30 to 80 &mgr;m , a ratio(D
50
/D
10
) of the D
50
for a 10%-average diameter(D
10
) in volumetric average diameter of the carrier is 1.8 or less, a ratio (D
90
/D
50
) of a 90%-average diameter(D
90
) in volumetric average diameter of the carrier for the 50%-average diameter (D
50
) in volumetric average diameter of the carrier is 1.8 or less, the magnetic moment (at 1 kilo Oe of magnetic field) of the carrier ranges from 52 to 65 emu/g.
By the use of this kind of carriers having small diameter gives following benefits;
(1) Surface area per unit volume is large, therefore they can give good enough triboelectric-charge for each toner, and scarcely yield toners which have a low level of electric-charge and reverse polarity-charge too, accordingly, scattering of toner particles at the periphery of dot for image-forming and smear (blurring) in background area are few, thus dot reproducibility is excellent;
(2) Due to the nature of large surface area per unit volume and scarce to generate the smear in background area, a low level of average electric-charge in toner is allowable to use, notwithstanding, a high optical density of image is obtained, thus carrier of small diameter is capable to compensate the shortcomings which are caused by use of stall size of toner, hence is effective for driving out the advantages of small size of toner;
(3) As small diameter of carrier forms a dense magnetic brush and the head of the formed magnetic brush has an excellent fluidity, accordingly the trace drawn by dragging of the head of the magnetic brush on image is hardly imprinted.
However, carriers of small diameter in prior arts have a important problem that they are apt to deposit themselves on surfaces contacted with the developer, thus brings flaws on photosensitive member or fixing roller, therefore was difficult to utilize in practical.
With regard to carriers of small diameter, we, the inventor, have investigated diameters of carriers deposited on the surfaces of photosensitive member, and found out the facts that, out of used original carrier having a size-distribution, the smaller size of carrier particles show a tendency apt to deposit on the surface of photosensitive member preferentially, and the deposited ratio of smaller size of particles less than 22 &mgr;m diameter was overwhelmingly much in all deposited particles.
Accordingly, the first object of the present invention is to provide a carrier for electrophotographic developer and a developer using the same which are able to produce high quality of image-reproductions having an excellent dot-reproducibility, an excellent highlight-reproducibility, a high optical density of image, and showing a scarce or devoid of smear in backgro
Kotsugai Akihiro
Takahashi Hiroaki
Yamaguchi Kimitoshi
Yamashita Masahide
Chapman Mark A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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