Electrophotography – Image formation – Development
Reexamination Certificate
2000-08-28
2002-05-28
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Development
C399S274000
Reexamination Certificate
active
06397031
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a development apparatus used in an image forming apparatus such as an electrographic apparatus or an electrostatic recording apparatus.
2. Related Background Art
In the past, as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Post-Examination Publication No. 42-23910 and Japanese Patent Post-Examination Publication No. 43-24748, various methods are well-known, such as electrophotography. In general, an electrostatic latent image is formed on a photosensitive member formed from photoconductive material by various means, and then the latent image is developed by using toner as a toner image, which is in turn transferred onto a transfer material, such as paper. The toner image transferred to the transfer material is fixed to the transfer material by heating or solvent vapor, thereby obtaining a copy (reproduction).
As a developing method, various methods in which an electrical latent image is visualized by using two-component developer mainly including toner and carrier are already known. For example, there are various developing methods such as a magnetic brush developing method as disclosed in U.S. Pat. No. 2,874,063, a powder cloud method, a fur brush developing method, a liquid developing method and the like.
The magnetic brush method and liquid developing method using the two-component developer have widely been put to practical use since a good image can be obtained relatively stably. However, since both methods utilize the developer obtained by mixing the toner and the carrier, they have disadvantages such as deterioration of the carrier, variation in mixing ratio between the toner and the carrier, complication of the apparatus, scattering of the toner and/or uneven streak due to the presence of the carrier.
In order to eliminate such disadvantages, various developing methods using one-component developer (one-component toner) consisting of toner alone have been proposed. For example, U.S. Pat. No. 3,909,258 discloses a developing method using magnetic toner having electrical conductivity. In this method, conductive magnetic toner is carried on a cylindrical developing sleeve having a magnet therein, and, development is effected by contacting the developing sleeve with the latent image. During the development, in a developing portion where the developing sleeve is opposed to a photosensitive member, a conductive path is formed between the surface of the photosensitive member and the surface of the developing sleeve by toner particles so that charges are directed from the developing sleeve to the toner particles through the conductive path, with the result that the toner particles are adhered to an imaged portion by a Coulomb force between the imaged portion of the latent image and the toner particles, thereby developing the latent image.
Although the developing method using the conductive magnetic toner can eliminate the problems regarding the conventional two-component developing methods, since the toner is conductive, it has a disadvantage that it is difficult to electrostatically transfer the developed image from the photosensitive member to an ultimate support member such as a plain paper.
In order to eliminate this disadvantage, a developing method using high-resistance magnetic toner capable of being transferred electrostatically is disclosed in Japanese Patent Application Laid-open No. 52-94140 as a developing method utilizing dielectric polarization of toner particles. However, this method has a disadvantage that adequate density of the developed image cannot be obtained because the developing speed is essentially low, and, thus, it is difficult to put this method to practical use.
As another method using high-resistance magnetic toner, a developing method in which toner particles are frictionally charged by friction between the toner particles and friction between the toner particle and the developing sleeve and the development is effected by contacting the charged toner particles with the photosensitive member is known. However, it has been pointed out that this method has a disadvantage that poor frictional charging may occur because of small number of contacts between the toner particles and a friction member or the toner particles are apt to be aggregated on the developing sleeve if the Coulomb force between the charged toner particles and the developing sleeve, and it is practically difficult to realize this method.
On the other hand, in Japanese Patent Application Laid-open No. 54-43036, a new developing method eliminating the above-mentioned disadvantages has been proposed. In this method, magnetic toner is coated on a developing sleeve as a very thin layer and is frictionally charged and then a latent image is developed under a magnetic field by approaching the toner layer to the latent image without contacting with the latter.
According to this method, by coating the magnetic toner as the very thin layer, the chance for contact between the magnetic toner and the developing sleeve is increased thereby to permit the frictional charges required for development to be applied to the toner.
FIG. 5
shows an example of a magnetic one-component developing apparatus. As shown in
FIG. 5
, the developing apparatus comprises a developing container
10
containing magnetic one-component toner as developer, which container including a developing. sleeve
1
, a permanent magnet
1
a
, two large and small toner conveying members
4
and a magnetic blade
11
. The developing sleeve
1
is formed from a non-magnetic member and is disposed within an opening portion opposed to a photosensitive drum
100
as an image bearing member for rotation in a direction shown by the arrow B
2
, and the permanent magnet
1
a
has a roller shape and is disposed within the developing sleeve in a non-rotation manner.
The magnetic toner in the developing container
10
is conveyed to the developing sleeve
1
by the conveying members
4
and is borne on the surface of the developing sleeve
1
by a magnetic force of the magnet
1
a
and then is conveyed to a developing portion opposed to the photosensitive drum
100
as the developing sleeve
1
is rotated. On the way of the conveyance, the toner is regulated by the magnetic blade
11
spaced apart from the developing sleeve
1
by a distance W, with the result that a thin toner layer is coated on the developing sleeve
1
. The distance W is generally selected to be 100 &mgr;m to 1 mm.
A thickness of the toner layer coated on the developing sleeve
1
is determined by a position of a cut line L shown in FIG.
7
. According to the inventors' investigation, it was found that performance of the magnet toner will be as follows when the magnetic toner passes between the developing sleeve
1
and the magnetic blade
11
.
As shown in
FIG. 6
, when planes perpendicular to a straight line connecting between the developing sleeve
1
and the magnetic blade
11
are considered and it is assumed that a plane near the magnetic blade is S
1
and a plane near the developing sleeve
1
is S
2
, since a width of the magnetic blade
11
is generally selected to be smaller than a width of the magnet
1
a
, when magnetic flux densities on the planes S
1
, S
2
are considered, the magnetic flux density on the plane S
1
becomes greater than that on the plane S
2
. Accordingly, the magnetic toner on the developing sleeve
1
is subjected to a magnetic force directed toward a direction shown by the arrows, i.e., toward the magnetic blade
11
between the developing sleeve
1
and the magnetic blade
11
, with the result that, as shown in
FIG. 7
, the magnetic toner particles t are interconnected between the developing sleeve
1
and the magnetic blade
11
thereby to form chains (or ears) as shown by “B”.
Application of charges to the magnetic toner particles t is effected with respect to end (developing sleeve
1
side) toner particles t
1
by contact between the end toner particles t
1
in the chains B and the developing sleeve
1
. Further, the charges are appl
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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