Method and apparatus for image developing capable of...

Electrophotography – Image formation – Development

Reexamination Certificate

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Details

C399S274000

Reexamination Certificate

active

06775506

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Application
The present application relates to a method and apparatus for image developing, and more particularly to a method and apparatus for image developing which is capable of effectively forming an even development agent layer on a development agent carrying member.
2. Description of the Background
Generally, development apparatuses that develop an electrostatic latent image formed on an image carrying member can be classified into two types. One type develops an electrostatic latent image formed on an image carrying member with a development roller which is brought into contact with the image carrying member. This type is called a contact development apparatus and its development method is referred to as a contact development method. The other type develops an electrostatic latent image formed on an image carrying member with a development roller brought into proximity to the image carrying member. This type is called a non-contact development apparatus and its development method is referred to as a non-contact development method. It is extremely important for both types of the development apparatuses to stably maintain the relative conditions of the development roller and the image carrying member so as to reproduce a superior quality image.
The contact development apparatus, for example, includes a development roller, a toner supplying roller, and a development blade, as important elements. The development roller develops an electrostatic latent image formed on the image carrying member. The toner supplying roller supplies toner to the development roller. The development blade regulates the toner carrier on the development roller into a thin layer having a predetermined thickness. The development roller is held in contact with the image carrying member under a predetermined pressure applied by an elastic member such as a coil spring.
The development agent used for the development of an electrostatic latent image on the image carrying member can also be classified into two types. One type is referred to as a two component development agent that includes toner and carriers. The other type is referred to as a single component development agent that includes toner. The development method using the two component development agent can reproduce a superior quality image in a relatively stable manner but has disadvantages relating to the carriers. For example, the carriers are prone to be degraded over time and a mixture ratio of the toner and the carriers is varied. In addition, the development apparatus using the two component development agent tends to be a relatively large-sized machine. In order to avoid these disadvantages of the two component development agent, it is more convenient to employ the development method that uses the single component development agent.
In the development method using the single component development agent, however, the development roller needs to be held in contact evenly with the image carrying member in a stable manner. Otherwise, the amount of toner supplied to the image carrying member is unstable, which may cause problematic phenomena such as an uneven density on a formed image or a dirty background.
To reproduce a superior quality image, it is required that the development agent carried on the development roller is made into a thin layer by regulating the contact of the image carrying member and the development roller in an area where the development process is conducted.
A Published Japanese Unexamined Patent Application, No. 60-103372 (1985), attempts to regulate the toner into a thin layer in an even manner with a development apparatus using a roll-shaped toner layer regulating member that includes a roll-shaped rubber surface having hardness in a range of 10 degrees to 40 degrees according to the JIS-A (Japanese Industrial Standard-A). However, it is apparent that this structure is not sufficient to succeed in the attempt. In fact, when a polyurethane rubber of hardness in the range of 10 degrees to 40 degrees JIS-A is used for the toner layer regulating member, it is not possible to form an even and thin toner layer because a friction coefficient of such toner layer regulating member is relatively high.
A Published Japanese Unexamined Patent Application, No. 10-104945 (1998), attempts to form an even toner layer and to accelerate toner charging. This attempt uses a roll-shaped toner layer regulating member having a surface roughness R
z
in a range of from 2 &mgr;m to 100 &mgr;m, and produces an effect of a vibrating electric field by applying a voltage overlaid with an AC (alternating current) bias to the development roller. This attempt, however, is not practical since it has problematic disadvantages. For example, it requires a coating on the surface of the toner layer regulating member with uniform toner particles and a matrix resin because of the surface roughness R
z
. Also, this attempt requires a complex configuration which leads to a relatively high manufacturing cost since it uses an AC power source.
FIG. 26
shows a prior art development apparatus that uses a single component development agent. In this prior art development apparatus, a roller-like-shaped development agent carrying member
301
and a roller-like-shaped development agent supplying member
302
are rotated so that development agent contained in a hopper
304
built in a development case
303
is supplied and the development agent is carried on the circumferential surface of the development agent carrying member
301
. The development agent carried is formed into a thin layer by a development agent regulating member
305
and is then attracted to an image carrying member (not shown) so that a latent image formed on the image carrying member is developed into a visual image.
The development agent regulating member
305
has, in many cases, a blade-like shape, as shown in
FIG. 26
, and brings its edge into contact with the development agent carrying member
301
so as to regulate a thickness of the development agent carried. A development agent regulating member including a layer of an elastic substance such as a urethane rubber is applied to a case in which the development agent carrying member includes a hard roller made of a metal or plastic. A metallic development agent regulating member is applied to a case in which the development agent carrying member includes an elastic roller made of rubber.
In a development apparatus using the above blade-shaped development agent regulating member
305
, the development agent is subjected to a friction charging process in a nip band region formed between the development agent carrying member and the development agent regulating member. However, the surface of the development agent is prone to be worn over time because of the friction charging process and therefore the charge capacity of the development agent is reduced. As a result, the charge amount on the development agent is reduced which causes problematic phenomena such as a dirty background, failed development of fine dots, etc.
Also, the development agent is prone to melt in the nip band region due to heating caused through the friction charging process. When the melted development agent fixes on the development agent regulating member, it causes a line mark on the development agent carrying member. This causes a problematic white line mark on a recording sheet, as a result.
In addition, foreign substances such as dust particles are prone to be lodged between the development agent carrying member and the development agent regulating member and such lodged foreign substances may cause the above-described white line marks on a recording sheet. A cause of this is in a structure in which the blade-shaped development agent regulating member
305
is fixed with its base edge to the development case
303
such that the top edge thereof contacts the circumferential surface of the development agent carrying member
301
under pressure.
The above-described problems, in many cases, occur in a relatively short time period a

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