JP2625245B2 - Developing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used for a printer, an electrophotographic copying machine or the like, and more specifically, to a developing device formed on an image carrier such as a photosensitive drum. The present invention relates to a developing device for developing the latent image thus formed with a one-component developer.

(Prior Art) In an image forming apparatus such as a copying machine or a printer, a latent image formed on an image carrier such as a photosensitive drum is developed by a developing device. In the developing device, as a developer for developing the latent image, a two-component developer having a toner and a carrier,
Alternatively, a one-component developer not using a carrier is used. Recently, the mixing ratio of carrier and toner (toner concentration ratio)
A developing device using a one-component developer that does not require adjustment of the toner and is not affected by the deterioration of the carrier has attracted attention.

A developing device using a one-component developer has, for example, a developing roller that transports a developer charged to a predetermined polarity. While the developer is being conveyed by the developing roller, the amount of conveyance is regulated by a blade formed of an elastic body such as rubber, thereby forming a thin layer of the developer on the peripheral surface of the developing roller. Is done. When the thin layer of the developer formed on the peripheral surface of the developing roller reaches a position facing the photosensitive drum, the developer transfers only to a latent image portion formed on the photosensitive drum, and the latent image Is developed by the developer.

In such a developing device using a one-component developer, the latent image on the photosensitive drum may not be reliably developed unless a thin layer of the developer is uniformly formed on the peripheral surface of the developing roller. .

As described above, the amount of the developer conveyed on the peripheral surface of the developing roller is usually regulated by the blade pressed against the peripheral surface of the developing roller, and the developer is conveyed to the peripheral surface of the developing roller. To form a thin layer. The blade is disposed so as to contact almost the entire area in the axial direction of the developing roller, but the blade is brought into contact with the peripheral surface of the developing roller with a uniform pressure over almost the entire area in the axial direction of the developing roller. It is not easy. In particular, recently, as the image forming apparatus itself has been downsized, the diameter of the developing roller has become
It is not easy to uniformly press the blade on the peripheral surface of such a small-diameter developing roller over almost the entire area in the axial direction. Therefore, a developer layer having a uniform thickness cannot be formed on the peripheral surface of the developing roller. If the thickness of the developer layer formed on the peripheral surface of the developing roller is not uniform, the latent image on the photosensitive drum is not developed with a uniform density.

To solve such a problem, for example, Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 179473 discloses a developing device in which a mesh member is pressed against a developing roller and a developer is passed through each mesh of the mesh member to form a thin layer of the developer on the peripheral surface of the developing roller. It has been disclosed.

(Problem to be Solved by the Invention) In the developing device disclosed in the publication, a developing roller is disposed in an opening formed in a housing containing a developer, and is pressed against the developing roller. The mesh member covers the opening of the housing.
For this reason, the developer may pass through a part of the mesh member that is not pressed against the developing roller, and the developer may be scattered outside the housing.

The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to prevent the developer from being scattered out of the housing from the through-hole of the porous thin plate pressed against the peripheral surface of the developer carrier,
An object of the present invention is to provide a developing device capable of forming a uniform thin layer of developer on the peripheral surface of the developer carrier.

(Means for Solving the Problems) A developing device of the present invention has an opening facing an image carrier, and a housing in which a one-component developer charged to a predetermined polarity is accommodated. Is arranged in the opening of the housing so as to be in contact with or separated from the image carrier, and
a developer carrier having a surface roughness of m, and for transporting the developer to a region facing the image carrier, and sliding over a predetermined circumferential length on a peripheral surface of the developer carrier which is located inside the housing. A conductive porous thin plate, which is disposed so as to be in contact with and covers the opening of the housing, and has a large number of through holes through which a developer can pass, and a porous thin plate in the housing. A developer supply means for supplying the developer in the housing to the porous thin plate, and applying a bias voltage having the same polarity as the charged polarity of the developer to the porous thin plate; A voltage applying means, wherein the voltage applying means is a voltage applying means for applying a bias potential between the developer carrying member and the porous thin plate, whereby the above object is achieved. Is achieved.

(Operation) In the developing device of the present invention, the developer is conveyed to the porous thin plate in the housing by the developer supply unit, and the developer passes through the through-hole of the porous thin plate by the pressing of the developer supply unit. I do. The developer that has passed through the porous thin plate is transported by the developer bearing member to a region facing the image bearing member. During the transport, the peripheral portion of the developer bearing member is charged by friction with the porous thin plate. Form a uniform thin layer on the surface. When the thin layer of the developer reaches the region facing the image carrier, the latent image on the image carrier is developed. Since the porous thin plate covers the opening of the housing, and a bias voltage having the same polarity as that of the charged developer is applied, the porous thin plate covering the opening of the housing is removed. The developer does not pass, and there is no possibility that the developer scatters outside the housing.

(Example) Hereinafter, the present invention will be described with reference to examples.

As shown in FIGS. 1 and 2, the developing device of the present invention is disposed so as to face a photosensitive drum 20 as an image carrier. The developing device 10 includes a housing 13 provided with an opening 13a at a portion facing the photosensitive drum, and a developing roller 11 located in the opening 13a of the housing 13. Inside the housing 13, a non-magnetic one-component developer charged negatively by friction is accommodated.

The developing roller 11, for example, on the peripheral surface of the metal shaft 11a,
The urethane rubber 11b is provided, and faces the photosensitive drum 20. In this embodiment, the developing roller
11 is in contact with the photosensitive drum 20.

The peripheral surface of the urethane rubber 11b on the developing roller 11 is 2
The surface roughness is about 20 μm. With the outer peripheral surface of the developing roller 11 having such a surface roughness, the developer that has passed through each mesh of the mesh member 14 has a thickness of 20 to 20 μm on the outer peripheral surface of the developing roller 11 due to its rotation. A thin layer of about 30 μm is formed and transported reliably.

When the developing roller 11 abuts on the photosensitive drum 20 serving as an image carrier as in the present embodiment, the peripheral surface of the developing roller 11 is preferably made of an elastic material such as urethane rubber. .

For example, -1 is attached to the metal shaft 11a of the developing roller 11.
A bias voltage of 00V is applied.

The photosensitive drum 20 is rotated in a direction indicated by an arrow A in FIG. 1, and the developing roller 11 is rotated in a direction indicated by an arrow B in FIG. Is done. Therefore, the peripheral surface of the developing roller 11 is
At a contact portion with the photosensitive drum 20, the peripheral surface of the photosensitive drum 20 is moved in a forward direction.

The opening 13a of the housing 13 is covered with a metal mesh member 14 which is a flexible and conductive porous thin plate having a large number of through holes. The mesh member 14,
Developing roller 11 located in opening 13a of housing 13
Is pressed in contact with the peripheral surface portion of the developing roller 11 in the circumferential direction with respect to the central angle θ of the developing roller 11. The center angle θ is usually set to 180 ° or less. A bias voltage of −300 V having the same polarity as the charged polarity of the developer is applied to the mesh member 14.

As the developer, a toner having a particle size of about 10 μm is generally used. For such a developer, the mesh member has a mesh size of about 40 to 150 μm and a mesh member of about 100 to 400 mesh. used.

The mesh member 14 is fixed along the upper edge of the opening 13a so as to be pressed against the peripheral surface of the developing roller 11 while covering the opening 13a of the housing 13.

In the housing 13, a supply roller 12 as a developer supply unit is provided. This supply roller 12, for example,
Around the metal shaft body 12a, a conductive fur brush 12b having an electric resistance of about 10 ⁴ Ω is provided and configured.
The mesh member 14 pressed against the peripheral surface of the developing roller 11 is pressed toward the developing roller 11. In this embodiment, the diameter of the supply roller 12 is smaller than the diameter of the developing roller 11, and the top is located below the top of the developing roller 11.

The direction of rotation of the supply roller 12 is the same as the direction of rotation of the developing roller 11, as indicated by an arrow C in FIG. 1, and the developer in the housing 13 is supplied to the mesh member 14 by the supply roller 12. Transported to And the supply roller
By being pressed by 12, the developer passes through the mesh of the mesh member 14 and is supplied to the developing roller 11.

In the present embodiment, the latent image on the photosensitive drum 20 is developed by a reversal development method implemented in a laser printer or the like. In this embodiment, an organic photoconductor (OPC) is used as the photoconductor drum 20, and a surface potential of -700V is applied. Then, the image is exposed by the laser beam, and the potential of the exposed portion is attenuated, whereby a latent image is formed. A bias voltage of −100 V is applied to the developing roller 11, and the developer conveyed by the developing roller 11 adheres to the latent image portion on the photosensitive drum 20 where the surface potential is attenuated, An image is formed.

In the developing device 10 having such a configuration, the developer supplied into the housing 13 is stirred by the supply roller 12, charged to a negative polarity, and transported to the mesh member 14. Then, when the developer is conveyed by the supply roller 12 and reaches the region facing the developing roller 11, the mesh member 14 is charged to the same polarity as the charged developer. The negatively charged developer is pressed toward the developing roller 11 by being pressed by the supply roller 12, and a mesh member interposed between the supply roller 12 and the developing roller 11. Pass through 14 meshes. The developer that has passed through the mesh member 14 is transported by the developing roller 11 to a region where the developer contacts the photosensitive drum 20. The developer forms a uniform thin layer on the peripheral surface of the urethane rubber 11b of the developing roller 11 while being sufficiently frictionally charged by slidingly contacting the mesh member 14 during the transport. When the thin layer of the developer reaches the contact area of the photosensitive drum 20, the latent image on the photosensitive drum 20 is developed in the area.

Although the mesh member 14 covers the opening 13a of the housing 13, the mesh member 14 is applied with a negative bias voltage having the same polarity as the charged polarity of the developer. The developer in 13 is a mesh member.
Therefore, there is no risk of passing through each mesh of the mesh member. Therefore, the developer in the housing 13 is filled with the mesh member 1 covering the opening 13a in the housing 13.
4, except for the part pressed by the supply roller 12,
There is no risk of passing the developer, and the developer is prevented from scattering outside the housing 13.

The developer conveyed by the developing roller 11 is more reliably frictionally charged by slidingly contacting the peripheral surface of the developing roller 11 and the mesh member 14 pressed against the developing roller 11, but the mesh member 14 Since the roller 11 comes into sliding contact in the circumferential direction for a long time, the developer is reliably frictionally charged.

In this embodiment, a metal mesh member is used as the porous thin plate. However, a metal substrate having a large number of through holes formed by etching or the like may be used.

The supply roller 12 is not limited to the one in which the fur brush 12b is provided on the peripheral surface of the metal shaft 12a, and a sponge roller or the like in which a sponge body is provided on the metal shaft 12a can also be used.

The present invention is also applicable to a developing device in which the developer conveyed on the peripheral surface of the developing roller flies to the photosensitive drum without the developing roller coming into contact with the photosensitive drum. The image carrier is not limited to the photoconductor drum, but may be a belt-shaped photoconductor.

(Effect of the Invention) In the developing device of the present invention, the developer conveyed by the developer carrier is sufficiently triboelectrically charged by the porous thin plate slidably contacting the peripheral surface of the developer carrier. Because of the uniform thin layer, the latent image on the image carrier is developed well. Since the porous thin plate is in a state of covering the opening of the housing in which the developer is stored, and a bias voltage having the same polarity as the charged polarity of the developer is applied,
There is no possibility that the developer is scattered outside the housing through the through hole of the porous thin plate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the developing device of the present invention, and FIG. 2 is a perspective view of a main part thereof. 10 developing device, 11 developing roller, 12 supply roller, 13 housing, 13a opening, 14 mesh member.

Claims (1)

(57) [Claims] An opening facing the image bearing member;
A housing in which a one-component developer charged to a predetermined polarity is accommodated, and which is disposed in an opening of the housing so as to face the image carrier while being in contact with or separated therefrom; 20 μm
A developer carrying member having a surface roughness of not more than 3 and transporting the developer to a region facing the image carrying member, and slidably contacting a peripheral surface of the developer carrying member located inside the housing for a predetermined length in a circumferential direction. A conductive porous thin plate, which is disposed so as to cover the opening of the housing and has a large number of through holes through which the developer can pass, and which is press-contacted with the porous thin plate in the housing. Developer supply means for supplying the developer in the housing to the porous thin plate; and a voltage for applying a bias voltage having the same polarity as the charged polarity of the developer to the porous thin plate. And a voltage applying means for applying a bias potential between the developer carrier and the porous thin plate.