Electrophotography – Image formation – Development
Reexamination Certificate
2001-10-15
2003-10-21
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Development
C399S274000
Reexamination Certificate
active
06636717
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a developing device for developing an electrostatic image formed on an image bearing member with a developer, and the developing device is preferably used in an image forming apparatus of the electrophotographic type, the electrostatic recording type or like type.
2. Description of the Related Art
As the electrophotographic method, there are known a number of methods as described in U.S. Pat. No. 2,297,691, Japanese Patent Publication (Koukoku) No. 42-23910 and Japanese Patent Publication (Koukoku) No. 43-24748, and generally, by the utilization of a photoconductive material and by various means, an electrical latent image is formed on the surface of a photosensitive member which is a latent image bearing member, and then the latent image is visualized as a toner image by the use of a toner which is a developer, and as required, the toner image is transferred to a transfer material which is a recording medium such as paper, whereafter the transfer material is subjected to the fixing process by heating or solvent vapor or the like to thereby obtain a copy.
There are also known various methods of visualizing an electrical latent image by the use of a toner, and as developing methods, there are known a number of developing methods such as a magnetic brush developing method, a powder cloud method, a fur brush developing method and a liquid developing method.
In these developing methods, particularly magnetic brush development, cascade development, liquid development, etc. using a developer consisting chiefly of a toner and a carrier are widely put into practical use. Any of these methods is an excellent method which can obtain good images relatively stably, while on the other hand, they have common disadvantages peculiar to a two-component developer such as the deterioration of the carrier and the fluctuation of the mixing ratio of the toner and the carrier.
In order to avoid such disadvantages, various developing methods using a mono-component developer consisting of only a toner (hereinafter referred to as the mono-component developing method) have been proposed. For example, in U.S. Pat. No. 3,909,258, there is proposed a method of developing by the use of a magnetic toner having electrical conductivity. This is to cause a sleeve which is a cylindrical and electrically conductive developer carrying member having magnetism therein to carry a magnetic toner thereon, and bring the magnetic toner into contact with an electrostatic latent image which is a latent image on a latent image bearing member to thereby develop the latent image. At this time, in a developing area which is a portion in which the latent image bearing member and the sleeve are opposed to each other, an electrically conducting path is formed between the surface of the latent image bearing member and the surface of the sleeve by toner particles, and charges are directed from the sleeve to the toner particles via this electrically conducting path, and the toner particles adhere to the electrostatic latent image by the Coulomb's force between the sleeve and the electrostatic latent image on the latent image bearing member, whereby the electrostatic latent image is developed. This developing method using the magnetic toner having electrical conductivity is an excellent method avoiding the problems peculiar to the conventional two-component developing method, while on the other hand, it has the disadvantage that since the toner is electrically conductive, it is difficult to finally electrostatically transfer the toner image from the latent image bearing member to a recording medium such as plain paper after the electrostatic latent image has been visualized as a toner image.
In order to solve this problem, as a developing method using a high-resistance toner capable of electrostatically transferring a toner image from a latent image bearing member to a recording medium, Japanese Patent Application Laid-Open No. 52-94140 shows a developing method utilizing the dielectric polarization of toner particles. Such a method, however, has the disadvantages that essentially the developing speed is low and the density of the toner image by development is not sufficiently obtained, and has been difficult in practical use. As another method using a high-resistance magnetic toner, there is known a method in which toner particles are triboelectrically charged by the friction between toner particles and the friction between the toner particles and a sleeve, and the toner particles are brought into contact with a latent image bearing member to thereby develop a latent image on the latent image bearing member. These methods, however, have the disadvantage that the frequency of the contact between the toner particles and the sleeve or the like is small and triboelectric charging is liable to become insufficient, or when the Coulomb's force between the toner particles and the sleeve is strong, the toner particles are liable to cohere on the sleeve, and it is pointed out that these methods have many difficulties in practical use.
In contrast, in Japanese Patent Application Laid-Open No. 54-43036, there is proposed a novel developing method which has eliminated the above-noted disadvantage. This is to apply a toner very thinly onto a sleeve, and triboelectrically charge the toner, and then make the toner very proximate to an electrostatic latent image under the action of a magnetic field and oppose the toner to the electrostatic latent image without bringing the toner into contact with the electrostatic latent image, and develop the electrostatic latent image.
According to the method, it is made possible to adopt a construction of applying a magnetic toner very thinly onto the sleeve to thereby increase the frequency of contact between the magnetic toner and the sleeve, and induce in the toner a triboelectric charge amount necessary to be used for development.
According to our investigation of the imparting of charges to the toner in the mono-component developing process, it has been found that the behavior of the toner in the charge-imparted portion is as follows.
FIG. 4
of the accompanying drawings shows an example of a developing device using the magnetic toner.
Such a developing device, as shown in
FIG. 4
, is provided with a developing sleeve
101
which is a developer carrying member disposed for rotation in the direction of arrow and using a nonmagnetic member, a permanent magnet
101
b
fixed to the interior of the developing sleeve
101
, a magnetic blade
202
which is developer regulating means using a magnetic member, a developing container
103
for containing a magnetic toner therein, and a conveying member
104
.
The magnetic blade
202
is disposed so that the distance thereof to the developing sleeve
101
may be a constant value W. Generally, it is often the case that the distance W is set to a value within the range of 100 &mgr;m-1 mm.
In the developing device shown in
FIG. 4
, the developing sleeve
101
is coated with a thin layer of magnetic toner T, as shown in
FIG. 6
of the accompanying drawings. The layer thickness of this toner layer is determined by the position of a cut line L shown in FIG.
6
.
According to our investigation, it has been found that when the magnetic toner T passes between the developing sleeve
101
and the magnetic blade
202
, charges are imparted to the magnetic toner T. Also, it has been found that the behavior of the magnetic toner T during that time is as follows.
As shown in
FIG. 5
of the accompanying drawings, supposing planes perpendicular to a straight line linking the developing sleeve
101
and the magnetic blade
202
together, and defining a plane near to the magnetic blade
202
as S
1
, and a plane near to the developing sleeve
101
as S
2
, the magnetic flux density on the plane S
1
is greater than the magnetic flux density on the plane S
2
because generally the width of the magnetic blade
202
is made narrow as compared with the width of the permanent magnet
101
b.
Accordin
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