Electrophotography – Image formation – Development
Reexamination Certificate
1997-11-13
2002-04-30
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
C399S281000, C399S283000
Reexamination Certificate
active
06381434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing apparatus used in image forming apparatus such as electrophotographic apparatus and electrostatic recording apparatus.
2. Related Background Art
There are a lot of conventionally known methods of electrophotography, for example as described in U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910, and Japanese Patent Publication No. 43-24748. In ordinary methods, an electrostatic, latent image is formed on a photosensitive member by various means by the use of a photoelectric substance, the latent image is then developed by toner, a toner image thus obtained is transferred onto a transfer medium such as paper as occasion demands, and thereafter the image transferred is fixed by heating or solvent vapor or the like to obtain a copy.
There are also a variety of developing methods for visualizing the electric, latent image by use of toner. For example, many developing methods are known, including the magnetic brush developing method as described in U.S. Pat. No. 2,874,063, the powder cloud method and fur brush developing method as described in U.S. Pat. No. 2,221,776, and the liquid developing method.
Among these developing methods, the magnetic brush developing method using a two-component developer mainly containing toner and carrier is an excellent method capable of obtaining high-quality images relatively stably and is popularly used in practice. However, the magnetic brush developing method using the two-component developer has drawbacks of deterioration of carrier and variation in mixture ratios of toner and carrier, because it uses the two-component developer. In addition, it requires an agitating member, a toner concentration sensor, and the like to be set in the developing unit in order to overcome the drawbacks. The problem was, therefore, that the developing unit itself became large.
For avoiding this problem, a variety of developing methods using a one-component developer containing only toner have been proposed. For example, U.S. Pat. No. 3,909,258 proposed a method for developing the latent image by use of magnetic toner having the electrically conductive property. This is a method for developing the electrostatic, latent image by supporting the magnetic toner on a cylindrical, conductive sleeve (developing sleeve) having a magnet inside and making the toner contact the latent image. On this occasion, toner particles form conductive paths between the surface of photosensitive member and the surface of developing sleeve in the developing section, the charge is guided via these conductive paths from the developing sleeve to the toner particles, and the toner particles adhere to image portions by Coulomb force with respect to the image portions of the electrostatic, latent image, thereby developing the image. This developing method using the conductive, magnetic toner is an excellent method avoiding the problem in the conventional two-component developing method, but, on the other hand, it has a drawback that, because the toner is electrically conductive, it is difficult to electrostatically transfer the developed toner image from the photosensitive member to a final support member such as plain paper.
For solving this problem, a developing method using high-resistance toner to enable the electrostatic transfer was proposed; for example, Japanese Patent Application Laid-open No. 52-94140 describes a developing method utilizing dielectric polarization of toner particles. This method, however, has such drawbacks that the developing speed is essentially slow, the density of developed image is not sufficient, and so on, and it was not practically applicable. Other known methods using the magnetic toner of high resistance are those for frictionally electrifying the toner particles by friction between toner particles, friction between toner particles and developing sleeve, etc. and making them contact the photosensitive member, thereby developing the electrostatic, latent image. It is, however, pointed out that these methods have such drawbacks that the amount of contact is small between the toner particles and a frictional member, so as to result in insufficient frictional electricity (triboelectricity) and that when the Coulomb force is strong between the charged toner particles and the developing sleeve, the toner particles are likely to aggregate on the developing sleeve, and therefore, they have many difficulties in practical use.
Against it, Japanese Patent Application Laid-open No. 54-43038 proposes a novel developing method eliminating the above drawbacks. This is a method for making an elastic blade of rubber or metal contact the developing sleeve, thereby frictionally electrifying the toner on the developing sleeve and forming a thin layer of the toner thereon, and then bringing it to the very vicinity of the electrostatic, latent image under action of magnetic field to keep the toner layer opposed thereto without contact, thereby developing the latent image. This method increases the chances of contact between the magnetic toner and the developing sleeve by making the very thin coating of magnetic toner, thereby enabling to give the toner an amount of triboelectric charge necessary for development. However, since the magnetic toner includes a magnetic material such as magnetite, this method has problems that it is difficult to apply it to color toner and that it is very difficult to decrease power consumption, because the fixing temperature must be set rather high.
On the other hand, a non-magnetic one-component developing method not using the magnetic toner is proposed and used in practice, as described in Japanese Patent Application Laid-open No. 58-116559. Since this method can be applied to formation of color image and can realize a inexpensive and compact developing apparatus, it is frequently used in developing units of printer or the like.
FIG. 8
shows a developing apparatus using the conventional, non-magnetic one-component developing method. This developing apparatus has a developing sleeve
11
in an opening portion of developing container
13
for accommodating the non-magnetic toner of one-component developer. This developing sleeve
11
is opposed with a predetermined clearance to the photosensitive drum (not illustrated) and is driven to rotate in the direction of the arrow. A toner supply roller
14
is set in contact with the developing sleeve
11
inside the container
13
. The supply roller
14
is constructed in such manner that an elastic member
14
b
of urethane foam or the like covers the outside periphery of core
14
a
of SUS or the like. The supply roller
14
frictionally rotates in the direction of the arrow relative to the developing sleeve
11
, so as to supply the non-magnetic toner in the container
13
to the surface of the developing sleeve
11
to form a coating of toner thereon, and it also scrapes off the residual toner not having contributed to development from the surface of developing sleeve
11
. A regulating blade
12
is in contact with and on an almost top part of developing sleeve
11
. This regulating blade
12
is constructed in such structure that an elastic member
12
b
of urethane rubber or the like is bonded to a surface of elastic support member
12
a
of phosphor bronze or the like on the opposed side to the developing sleeve
11
and the regulating blade
12
functions to form a thin layer of toner by regulating the non-magnetic toner supplied to the surface of developing sleeve
11
and to give the charge to the toner.
By employing the above construction, the non-magnetic one-component developing apparatus well forms the thin layer of non-magnetic toner on the developing sleeve
11
, so that it can well develop the electrostatic, latent image on the photosensitive drum.
However, when the coating of toner was formed on the developing sleeve
11
by frictional rotation of the toner supply roller
14
in contact with the developing sleeve
11
, non-charged toner was often supplied onto the developing
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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