EP0543630A2

EP0543630A2 - Developing apparatus

Info

Publication number: EP0543630A2
Application number: EP92310508A
Authority: EP
Inventors: Takashi Ito; Takeshi 509 Nichimo-Hiyoshi Dai 5 Corporasu Hori
Original assignee: Mita Industrial Co Ltd
Current assignee: Kyocera Mita Industrial Co Ltd
Priority date: 1991-11-22
Filing date: 1992-11-18
Publication date: 1993-05-26
Also published as: EP0543630A3

Abstract

A developing apparatus for one-component type developing agent comprising a developing agent carrier sleeve which holds and carries a developing agent that is electrically charged to a predetermined polarity by utilizing the electric attractive force, and a rotary fur brush (15) which feeds the developing agent onto said sleeve, and wherein a charging plate (20) is so provided as to come in contact with the fur brush (15). The resilient restoring force of the brush (15) that is deflected upon coming in press-contact with the charging plate (20) causes the developing agent to fly and to be fed onto the sleeve. At the same time, electric charging of the developing agent is effectively promoted, and the electrically non-charged developing agent is effectively suppressed from being fed onto the sleeve.

Description

Background of the Invention

1. Field of the Invention

The present invention relates to a developing apparatus which uses a one-component type developing agent for electrophotography. More specifically, the invention relates to a developing apparatus equipped with a developing agent carrier sleeve of the type which holds and carried the developing agent to a developing zone by utilizing the electric attractive force.

2. Description of the Prior Art

In an electrophotographic apparatus such as a copying machine, in general, an electrostatic latent image formed on the surface of a photosensitive material is developed by using a developing agent which is composed of an electroscopic toner in order to obtain a toner image which is visualized from said latent image. The developing apparatus which effects such a developing is equipped with a developing agent carrier sleeve which is rotationally driven, and the toner that is electrically charged by the friction of the sleeve is carried to the developing zone to develop the image.
A known developing apparatus of this kind can be represented by the one of the type in which a bias voltage is applied to the sleeve, and the developing agent, i.e., the electrically charged toner is held and carried by utilizing the electric attractive force. In the apparatus of this type, provision is made of a rotary fur brush in addition to the developing agent carrier sleeve, and the developing agent (toner) is aggitated by the fur brush to electrically charge it by friction.
In the above-mentioned developing apparatus, however, problems remain in that the toner is not electrically charged by friction to a sufficient degree and the electrically non-charged toner exists in large amounts. When the electrically non-charged toner is carried by the developing agent carrier sleeve to the developing zone, there develop such inconveniences as scattering of toner and fogging.

Summary of the Invention

The object of the present invention, therefore, is to provide a developing apparatus equipped with a developing agent carrier sleeve of the type which holds and carriers an electrically charged toner to the developing zone by utilizing the electric attractive force, wherein the toner is electrically charged effectively by friction, and is effectively fed onto the sleeve.
According to the present invention, there is provided a developing apparatus for one-component type developing agent comprising a developing agent carrier sleeve of the rotationally driven type which holds and carries a developing agent that is electrically charged to a predetermined polarity by utilizing the electric attractive force, and a rotary member having a flexible brush on the surface thereof which frictionally aggitates the developing agent and feeds the developing agent onto said sleeve, wherein said rotary member is provided without being contacted to said developing agent carrier sleeve, a charging plate that is electrically charged to the same polarity as the electrically charged polarity of said developing agent is provided at a position where it comes in contact with the brush on the surface of said rotary member, said brush comes in contact with the charging plate and is deflected accompanying the turn of said rotary member, and the developing agent is caused to fly by the restoring force thereof and is fed onto the developing agent carrier sleeve.
According to the present invention, furthermore, there is provided a developing apparatus for one-component type developing agent comprising a developing agent carrier sleeve of the rotationally driven type which holds and carries a developing agent that is electrically charged to a predetermined polarity by utilizing the electric attractive force, and a rotary member having a flexible brush on the surface thereof which frictionally aggitates the developing agent and feeds the developing agent onto said sleeve, wherein said rotary member is so provided that said brush on the surface of said rotary member comes in contact with the surface of said developing agent carrier sleeve, a charging plate that is electrically charged to the same polarity as the electrically charged polarity of said developing agent is provided at a position where it comes in contact with the brush, said brush comes in contact with the charging plate and is deflected accompanying the turn of said rotary member, and the developing agent is caused to fly by the restoring force thereof and is fed onto the developing agent carrier sleeve.
That is, according to the present invention, the charging plate having an electric charge of the same polarity as the electric charge possessed by the developing agent is provided in contact with the rotary member such as a fur brush in order to electrically charge the developing agent by bringing the charging plate into pressed contact therewith in addition to frictionally charging the developing agent by said rotary member. This makes it possible to effectively suppress the occurrence of electrically non-charged toner. Moreover, the electrically charged toner can be effectively fed onto the sleeve by utilizing the repulsive force of the brush or the like on the rotary member that is in contact with the charging plate.

Brief Description of the Drawings

Fig. 1 is a diagram illustrating the structure of a developing apparatus according to the present invention;
Fig. 2 is a diagram illustrating another embodiment of the developing apparatus according to the present invention; and
Fig. 3 is a diagram illustrating the toner charging effect by applying a voltage to the charging plate in the developing apparatus of the present invention.

Detailed Description of the Invention

The invention will now be described by way of embodiments in conjunction with the accompanying drawings.
In Fig. 1 which illustrates a developing apparatus of the present invention, a developing agent carrier sleeve 2 of the rotationally driven type is provided in a developing vessel 1, a hopper 3 for replenishing the developing agent is provided at an upper portion of the developing vessel 1, and an electroscopic toner 4 that is known per se, is replenished from the hopper 3. The toner 4 is frictionally charged into a predetermined polarity by being aggitated by a fur brush 15 that will be described later.
The developing agent carrier sleeve 2 is provided with an electret layer 30 having an electric charge of a polarity opposite to that of the electric charge possessed by the toner 4. The electrically charged toner 4 is held and carried by utilizing the electrostatic attractive force. A thickness-adjusting blade 6 is provided over the sleeve 2 maintaining a suitable gap, and is so adjusted that the electrically charged toner 4 carried by the sleeve 2 will have a predetermined thickness.
In the developing apparatus as shown in Fig. 1, the developing agent carrier sleeve 2 is so provided as to be opposed to a photosensitive drum 11 which has a photosensitive layer 10, and an electrostatic latent image formed on the photosensitive layer 10 is developed by the electrically charged toner 4 that is carried by the sleeve 2. In the drawing in this case, the photosensitive drum 11 and the developing agent carrier sleeve 2 are rotated in the forward directions. They, however, may be rotated in the opposite directions. Moreover, the developing may be carried out in a so-called contacting manner or non-contacting manner.
In this apparatus, the electret layer 30 can be formed by using any high molecular material provided it is capable of developing permanent electric polarization. In general, there can be used an olefin-type resin such as a polyethylene, a polypropylene, an ethylene-butene copolymer, an ionically crosslinked olefin copolymer or an ethylene-acrylic copolymer; a fluorine-containing resin such as a vinyl polyfluoride, a vinylidene polyfluoride, a vinyl fluoride/vinylidene fluoride copolymer, an ethylene tetrafluoride resin (PTFE), an ethylene tetrafluoride-perfluoroalkoxyethylene copolymer resin (PFA resin), or an ethylene tetrafluoride-propylene hexafluoride copolymer resin (FEP resin); a chlorine-containing resin such as a vinyl polychloride or a chlorinated polyolefin; a thermoplastic polyester such as a polyethylene terephthalate, a polyethylene naphthalate or a polybutylene terephthalate; a polyamide such as nylon 6, nylon 12, nylon 6,6, nylon 6,10; or a variety of acrylic resins, which are used in a single kind or in a combination of two or more kinds. Among them, it is preferred to use fluorine-containing resins such as PTFE resin, PFA resin, PFE resin and like resins, since they preserve electric charge well and exhibit durability. The electret can be formed by any known method such as thermal electret-forming method, electric electret-forming method, radiant-ray electret-forming method or optical electret-forming method depending upon the kind of high molecular material that is used. The thermal electret-forming method or the electric electret-forming method can be advantageously adopted for the high molecular materials and, particularly, for the fluorine-containing resin.
The density of electric charge on the surface of the electret layer 30 is set to such a degree that a sufficiently large electric attractive force acts upon the electrically charged toner 4. Usually, however, the density of electric charge is so set that the surface potential (absolute value) of the electret layer 30 is smaller than the surface potential (absolute value) of the photosensitive layer 10. When they are equal to each other or have an opposite relationship, the electric attractive force acting between the sleeve 2 (electret layer 30) and the electrically charged toner 4 becomes so great that the electrostatic latent image formed on the photosensitive layer 10 cannot be effectively developed.
The thickness of the electret layer 30 is usually set to be from 10 to 500 µm.
In the developing apparatus of the present invention, a rotary fur brush 15 is provided maintaining such a relation in position that it does not come into contact with the electret layer 30. The rotary fur brush 15 frictionally charges the toner 4 by aggitation and feeds the electrically charged toner 4 onto the sleeve 2 (electret layer 30). The fur brush 15 can be rotated in any direction. Generally, however, the fur brush 15 is better rotated in the same direction as the direction in which the sleeve 2 rotates.
In the present invention as described already, a distinguished feature resides in that the charging plate 20 is so provided as to come in contact with the fur brush 15. The charging plate 20 is electrically charged to the same polarity as that of the electrically charged toner 4. As the charging plate 20 comes into contact with the brush 15, the electrically charged toner 4 flies due to electric repulsive force from the charging plate 20 and the resilient restoring force of the brush 15, and is fed onto the developing sleeve 2 by which it is held, carried and is used for effecting the developing. Due to the press contact of the charging plate 20, furthermore, the toner 4 is more strongly charged by friction and whereby the occurrence of electrically non-charged toner is effectively suppressed. The charging plate 20 is installed at such a position that causes the electrically charged toner 4 to effectively fly onto the developing sleeve 2.
The charging plate 20 will be made of an electrically conducting plate such as a metal plate and is impressed with a bias voltage from, for example, a bias power source 31, so that the metal plate is electrically charged to the same polarity as that of the toner 4. In this case, the bias power source may be made up of a DC power source only or may be made up of a combination of a DC power source and an AC power source in order to apply an alternating voltage that is shifted to the same polarity as the toner 4. It is preferred that the bias voltage applied to the charging plate 20 is usually greater than 100 volts and, particularly, greater than 200 volts (in an absolute value). When the applied voltage is too small, it becomes difficult to electrically charge the toner to a sufficient degree.
In the above-mentioned developing apparatus, the electrically charged toner is carried to the developing zone by forming the electret layer 30 on the developing sleeve 2. According to the present invention, however, the electrically charged toner can be carried even without using the electret layer 30. An embodiment of this case is shown in Fig. 2.
In the apparatus of Fig. 2, provision is made of a bias power source 40 instead of forming the electret layer 30 on the developing sleeve 2, and a bias voltage of a polarity opposite to the electrically charged toner 4 is applied to the sleeve 2 in order to hold and carry the electrically charged toner 4 by the sleeve 2. in this apparatus, in particular, the fur brush 15 is provided in contact with the sleeve 2 in order to effect the electric charging by friction and to remove the unused toner remaining on the sleeve 2. That is, when the electret layer is provided, it is not desired to bring the fur brush into contact with the sleeve 2 since it damages the electret layer. It is therefore difficult to effectively remove the remaining toner. With the apparatus of Fig. 2, however, it is allowed to effectively remove the remaining tower. Even in this apparatus, the fur brush 15 may be provided without being contacted to the fur brush 15, as a matter of course.
In the aforementioned developing apparatuses shown in Figs. 1 and 2, the fur brush 15 is used as a member for feeding the toner onto the sleeve 2. It, however, is also allowable to use the one having resiliency which deflects when it comes in contact with the charging plate 20 but produces a repulsive force when it returns to the ordinary condition to fly the toner, such as the one which has a flexible plastic tape or the like in the form of a duster on the surface of a rotary member, in place of using the fur brush.
Furthermore, the toner used as a developing agent in the present invention is a non-magnetic toner which is basically obtained by blending a resin medium for fixing which is known per se such as a styrene-type resin, acrylic resin, or a styrene-acrylic resin with widely known blending agents for toner such as a coloring agent, an electric charge controlling agent and like agents. It is desired that the toner has a volume resistivity of from 1 x 10⁸ to 3 x 10⁹ Ω -cm, and particularly from 2 x 10⁸ to 8 x 10⁸ Ω -cm, and its dielectric constant should lie within a range of from 2.5 to 4.5, and particularly from 3.0 to 4.0. The resins for fixing and the blending agents for toner should be so selected and used that the above-mentioned properties are obtained.
The toner particles should have a median size based on the volume of from 8 to 14 µm and, particularly, from 10 to 12 µm as measured by using the Coulter counter. Moreover, the toner particles may have either an amorphous shape as prepared by the melt kneading-pulverization method or a spherical shape as prepared by the dispersion or suspension polymerization method.

Example

By using the developing apparatus of Fig. 1, the toner was fed onto the electret sleeve under the following conditions while changing the bias voltage applied to the charging plate.

Toner

Composition:: Styrene-acrylic copolymer resin
(88% by weight)
Carbon (9% by weight)
Wax (2% by weight)
Electric charge controlling agent
(0.8% by weight)
Silica (0.1% by weight)
Alumina (0.1% by weight)

Charging plate

Material: copper
Thickness: 0.4 mm

Electret sleeve

Electret material: FEP
Thickness of electret layer: 100 µm
Surface potential: 200 V
Sleeve diameter: 10
Number of revolutions: 57 rpm

Fur brush

Material: nylon
Diameter: 20
Number of revolutions: 40 rpm
Thickness of toner layer on the sleeve: 75 µm
The toner was fed under the above-mentioned conditions, and the potential of the toner layer on the sleeve was measured for every bias voltage that was applied in order to find an average amount of electric charge per a toner particle in compliance with the following formula, $Average amount of electric charge per a toner particle = \frac{Potential of toner layer x 2ε₀ε x Volume of a toner particle}{Toner rate x (Thickness of toner layer)²}$

wherein:

ε₀:: Dielectric constant in vacuum
ε:: Specific inductivity of the toner

The above results are shown in Fig. 3 from which it will be recognized that the charging plate makes it possible to electrically charge the toner particles effectively.

Claims

A developing apparatus for one-component type developing agent comprising a developing agent carrier sleeve of the rotationally driven type which holds and carries a developing agent that is electrically charged to a predetermined polarity by utilizing the electric attractive force, and a rotary member having a flexible brush on the surface thereof which frictionally aggitates the developing agent and feeds the developing agent onto said sleeve, wherein said rotary member is provided without being contacted to said developing agent carrier sleeve, a charging plate that is electrically charged to the same polarity as the electrically charged polarity of said developing agent is provided at a position where it comes in contact with the brush on the surface of said rotary member, said brush comes in contact with the charging plate and is deflected accompanying the turn of said rotary member, and the developing agent is caused to fly by the restoring force thereof and is fed onto the developing agent carrier sleeve.
A developing apparatus according to claim 1, wherein said developing agent carrier sleeve has a high molecular electret layer on the surface thereof.
A developing apparatus according to claim 1, wherein a metal plate is use as said charging plate, and a bias voltage is applied to said metal plate.
A developing apparatus according to claim 3, wherein a bias voltage of greater than 100 V (absolute value) is applied to said metal plate.
A developing apparatus for one-component type developing agent comprising a developing agent carrier sleeve of the rotationally driven type which holds and carries a developing agent that is electrically charged to a predetermined polarity by utilizing the electric attractive force, and a rotary member having a flexible brush on the surface thereof which frictionally aggitates the developing agent and feeds the developing agent onto said sleeve, wherein said rotary member is so provided that said brush on the surface of said rotary member comes in contact with the surface of said developing agent carrier sleeve, a charging plate that is electrically charged to the same polarity as the electrically charged polarity of said developing agent is provided at a position where it comes in contact with the brush, said brush comes in contact with the charging plate and is deflected accompanying the turn of said rotary member, and the developing agent is caused to fly by the restoring force thereof and is fed onto the developing agent carrier sleeve.
A developing apparatus according to claim 5, wherein a metal plate is used as said charging plate, and a bias voltage is applied to said metal plate.
A developing apparatus according to claim 6, wherein a bias voltage of greater than 100 V (absolute value) is applied to said metal plate.