JPH0527865B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device used in electrophotographic devices such as copying machines, printers, and facsimile machines, and in particular, develops an electrostatic latent image formed on the surface of a photoreceptor using a one-component toner. Regarding a dry developing device.

2. Description of the Related Art Conventionally, there are two types of dry developing apparatuses for developing electrostatic latent images formed on the surface of a photoreceptor: those using a two-component developer and those using a one-component developer.

The former uses an insulating non-magnetic toner mainly consisting of a resin and a colorant and carrier particles such as glass beads or iron powder, and by stirring and mixing the toner with the carrier particles, the toner has a polarity opposite to that of the electrostatic latent image. The toner is charged by friction and conveyed to the surface of the photoreceptor, and only the toner is attracted to the electrostatic latent image area and visualized.

In this type of development method, only toner is consumed sequentially each time development is performed, so in order to obtain appropriate image quality, it is necessary to replenish the toner quantitatively and keep the mixing ratio constant. Therefore, it was inevitable that the developing device would become more complicated and larger. Furthermore, since the carrier is used repeatedly over a long period of time, image quality deteriorates due to deterioration of the carrier, and the carrier itself needs to be replaced periodically. In particular, replacing the carrier requires removing and disassembling the developing device and cleaning the inside, making maintenance troublesome.

On the other hand, the development method using a one-component developer has various advantages such as eliminating the above-mentioned drawbacks, making the device smaller, and making maintenance easier, so various technologies have been proposed in recent years. There is.

For example, FIG. 1 shows a developing device that uses a high-resistance magnetic toner formed by uniformly dispersing magnetic powder in a resin/colorant, and performs development by conveying the toner toward the electrostatic latent image side using a magnetic brush. To briefly explain its structure, a magnet roller 3 is made up of a cylindrical magnet assembly 1 having a large number of magnetic poles formed on its surface, and a conductive sleeve 2 arranged concentrically around the assembly 1. and a hopper 5 located above the roller 3 and feeding the toner 4 onto the surface of the sleeve 2.
and a frame 6 that surrounds these and is fixedly installed in the device, and the magnet assembly 1 of the magnet roller 3
and conductive sleeve 2 are configured to rotate relative to each other, and the roller 3 is connected to a drum-shaped photoreceptor 7.
placed close to the surface.

In the developing device having such a structure, the toner 4 (magnetic brush 4a) carried in the form of a spike on the conductive sleeve 2 by the magnetic attraction force of the magnet assembly 1 is moved between the magnet assembly 1 and the conductive sleeve 2.
It is conveyed to the photoreceptor 7 side by the relative rotation between
When the magnetic brush 4a approaches and contacts the electrostatic latent image portion 7a, the toner 4 is drawn by the conductive sleeve 2.
A charge having a polarity opposite to that of the latent image charge is applied to the latent image charge, and as a result, the toner 4 adheres to the electrostatic latent image portion 7a of the photoreceptor 7 due to the Coulomb force of the charge and the latent image charge, and development is performed. Become.

Therefore, in such a developing device, a forced toner charging method such as frictional charging in the above-mentioned two-component developing method is not adopted, but the toner is simply charged within the electric field formed between the conductive sleeve 2 and the electrostatic latent image portion 7a. Since the toner 4 is charged in this manner, the developing efficiency inevitably becomes lower than that in the two-component developing method.

For this reason, in conventionally known developing devices, the opposing distance d between the conductive sleeve 2 and the photoreceptor 7 is reduced, a high frequency bias is applied to the magnetic brush 4a, and the resistance value of the toner 4 is reduced. In either method, the basic structure of charging the toner 4 between the conductive sleeve 2 and the photoreceptor 7 is the same. Therefore, it is impossible to significantly improve the developing efficiency, and the toner 4 once attached to the surface of the electrostatic latent image 7a may flow due to the rubbing of the toner 4 on the photoreceptor 7, or the non-electrostatic latent image may The toner 4 may adhere to the image surface, which tends to cause image disturbances, fogging, and the like. Furthermore, it is extremely difficult to keep the facing distance d between the conductive sleeve 2 and the photoreceptor 7 constant from the viewpoint of processing and assembly.
From this point of view as well, the image stability was lacking.

In view of the drawbacks of the prior art, the present invention aims to significantly improve the developing efficiency, and also enables development without rubbing the toner on the surface of the photoreceptor, thereby producing a clear image without image distortion. The purpose of the development device is to provide a developing device that can be used for various purposes, and its features include a photoreceptor drum that carries an electrostatic latent image, and a conductive drum that contacts the photoreceptor drum and rotates at the same circumferential speed. A dry type developing device comprising: a conductive developing roller; and a supply roller, which is located on the flow side in the rotational direction from the developing position of the developing roller and conveys the one-component toner to the developing roller side by magnetic force; The developing roller is formed of an elastic roller having a smooth coating layer on the surface and no magnet inside, while the supply roller includes a magnet assembly and is not in contact with the conductive developing roller. The conductive developing roller is grounded, and a voltage-controllable DC voltage having a polarity opposite to the electrostatic charge on the surface of the photoreceptor drum is applied to the supply roller, so that a The reason is that it is configured to form an electric field.

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows a schematic configuration of a copying machine to which an embodiment of the present invention is applied, in which 7 is a drum-shaped photoreceptor with a photoconductive layer on its surface, and surrounding it are a charging device 8, an exposure device 9, and a developing device. 10, transfer device 11, cleaning device 1
2 etc. are arranged.

In such a copying machine, as is well known, when the photoreceptor 7 rotates clockwise in synchronization with the movement of a document table (not shown), a predetermined charge is first applied by a charging device 8, and then a predetermined charge is applied by an exposure device 9. An electrostatic latent image 7a corresponding to the original image on the original platen is exposed sequentially to the photoreceptor 7.
formed on the surface. This electrostatic latent image 7a is visualized as a toner image by a developing device 10, which will be described in detail later, and reaches a transfer device 11. In the transfer device 11, the toner image is transferred and carried on the transfer paper 13 fed from the paper feeder 14, and then the transfer paper 13 is transferred to the photoreceptor 7.
The image is separated from the image and fixed as a final image by the fixing device 15. On the other hand, the photoreceptor 7 to which the toner image was transferred
After the residual toner 4 is removed by the cleaning device 12, it is ready for the next copying.

Since these copying steps are already well known, detailed explanation will be omitted.

On the other hand, the toner 4 used in the copying machine is a high-resistance magnetic toner having a volume resistivity of at least 10 ¹³ Ωcm or more, such as styrene-acrylic resin, magnetite (magnetic powder), carbon black (which also serves as a coloring agent). Resistance control agent), silica (additive), etc. are kneaded and heated in an appropriate blending ratio, and then pulverized and classified to have an average particle size of 15 to 25 μm.

3 to 4 show a developing device 10 as an embodiment of the present invention used in the copying machine, in which a frame 20
, a developing roller 30 , a supply roller 40 , a cleaning member 50 , and a height regulating member 60 .

The frame body 20 is arranged along the circumferential direction of the photoreceptor 7 over almost the entire length in the longitudinal direction of the photoreceptor 7,
It consists of a cartridge mounting section 21 formed at the top, and a toner storage chamber 22 connected to the mounting section 21 and opened on the side facing the photoreceptor 7.

A toner replenishment cartridge 23 is detachably attached to the cartridge attachment part 21, and by peeling off the sealing member 24 stuck to the bottom surface of the cartridge 23 using a peeling means (not shown), the toner in the cartridge 23 can be removed. flows down along the frame bottom plate 25 and is replenished into the storage chamber 22.

Inside the toner storage chamber 22, the developing roller 30, supply roller 40, and cleaning member 50 are arranged parallel to the rotation axis of the photoreceptor 7, respectively, and above the supply roller 40, a brush height regulating member 60 is arranged so that its lower end 61 are arranged close to the outer peripheral surface of the supply roller 40.

The developing roller 30 is composed of a rotating body 31 made of conductive rubber and a conductive coating layer 32 applied to the outer circumferential surface of the rotating body 31, and is arranged so that the outer circumferential surface is in contact with the outer circumferential surface of the photoreceptor 7. At the same time, the developing roller 30 rotates in contact with the rotation of the photoreceptor 7 via a gear (not shown) or the like, that is, the developing roller 30 has the same circumferential speed as the photoreceptor 7 and rotates in the opposite direction. It is configured as follows. Note that the contact with the outer circumferential surface of the photoreceptor 7 may be either contact or elastic pressure contact. The rotating body 31 made of conductive rubber has a volume resistivity value of 10 ¹¹ as electrical resistance.
The value used is less than Ωcm, preferably in the range of 10 ⁵ to 10 ⁹ Ωcm.

Further, since the developing roller 30 is grounded and is electrically conductive as described above, an electric field can be formed between it and the supply roller 40 as described later.

Next, to explain the coat layer 32 in detail, the material of the coat layer 32 is the same as that of the toner 4 in order to reduce the physical adhesive resistance between the two when the coat layer 32 comes into contact with the toner 4. In addition, in order to smoothly form the electric field, the volume resistance value is set to 10 ¹¹ Ωcm similarly to the rotating body 31.
Hereinafter, it is preferably controlled within the range of 10 ⁵ to ^{10 9} Ωcm.

Here, "the same kind as the toner 4" means that the toner 4 is made of a composition material containing at least the same types of the materials constituting the toner 4, such as resin, magnetic powder, colorant, resistance control agent, and additives. refers to something that has been done.
In this embodiment, only the blending ratio of the resistance control agent such as magnetite or carbon black in the materials constituting the toner 4 was changed (increased) to control the volume resistivity within the range of 10 ⁵ to ^{10 9} Ωcm. It is formed by

As the thickness of the coating layer 32 increases, the conductive resistance increases, which is not preferable for toner adhesion and electric field formation as described later. The film is formed to be about 3 to 5 times thicker.

Further, the coating layer 32 may be applied so as to absorb the unevenness on the surface of the rotating body 31 formed of the conductive rubber so that the surface of the developing roller 30 becomes a smooth surface. The coating may be applied by brush coating, dipping or other known coating methods, and may also be baked or electron beam hardened to prevent peeling from the surface of the rotating body 31.

A supply roller 40 is disposed on the upstream side of the photoreceptor 7 contact side of the developing roller 30, that is, on the entrance side of the toner storage chamber, with its outer circumferential surface being close to the outer circumferential surface of the developing roller 30.

The supply roller 40 includes a cylindrical magnet assembly 41 having a large number of magnetic poles formed on its surface, and a conductive sleeve made of a conductive non-magnetic material such as aluminum and arranged concentrically around the assembly 41. 42, the magnet assembly 41 and the conductive sleeve 4
By relatively rotating between the two, the toner 4 (magnetic brush 4a) carried in the form of a spike on the conductive sleeve 42 is conveyed to the developing roller 30 side. Here, "relatively rotating" means that the magnet assembly 41 and/or the conductive sleeve 42 are rotated so that a relative speed is generated between the magnet assembly 41 and the conductive sleeve 42. This refers to the case where there is.

Next, the configuration of the supply roller 40 will be explained in more detail. The supply roller 40 extends from a point near the supply roller 40 of the developing roller 30 (hereinafter referred to as a supply position) to a point of contact with the photoreceptor 7 (hereinafter referred to as a development position). The circumferential length (α) of the photoconductor 7 is arranged so that it is larger than the length (β) from the exposure point where the electrostatic latent image 7a is formed to the development position, and the supply roller 40 and the development position are The facing interval between the rollers 30 is set to about 0.3 mm.

A DC voltage applying means 43 is electrically connected to the supply roller 40, and a DC voltage having a polarity opposite to the electrostatic charge formed on the surface of the photoreceptor 7 is applied to the supply roller 40 by the voltage applying means 43. is applied to generate an electric field of a predetermined strength near the supply position between the conductive developing rollers 30. Further, since the voltage applying means 43 is configured to be voltage controllable, the electric field strength between the rollers 30 and 40 can be freely controlled. Further, a control circuit 44 is interposed between the voltage application means 43 and the roller 40, and the voltage application means 43 is turned off at the same time or immediately after the exposure process by the exposure device 9 is completed.

Note that when a DC voltage is applied to the developing roller 30 side, a potential difference is also generated between the surface of the photoreceptor 7 and the developing roller 30. For example, if a DC voltage of opposite polarity to the electrostatic charge is applied, the electrostatic latent The toner 4 also adheres (fogs) to the background portion where the image 7a is not formed, which is undesirable.

The cleaning member 50 is located on the downstream side of the developing position of the developing roller 30, and conductive fibers such as polyester, acrylic, rayon, carbon-containing rayon, nylon, vinylon, etc. are formed into a rotating brush shape around a rotating shaft, or the cleaning member 50 is arranged so that the conductive fibers are formed into a rotating brush shape around a rotating shaft. It is wound to form a rotating roller, and its outer peripheral surface is in contact with the surface of the developing roller 30 between the downstream side of the developing position of the developing roller 30 with the photoreceptor 7 and the supplying position of the supply roller 40. Place it in

The rotation direction and peripheral speed of the cleaning member 50 are set so that the toner 4 remaining on the developing roller 30 is not swept off toward the photoconductor 7 but only toward the supply roller 40. are doing. Specifically, the developing roller 30 is rotated in a direction opposite to the rotating direction of the developing roller 30, and its circumferential speed is configured to be greater than the circumferential speed of the developing roller 30.

The brush height regulating member 60 has a blade shape, and its tip is disposed close to the outer peripheral surface of the supply roller 40 on the upstream side of the supply position, so that the brush height of the magnetic brush 4a can be regulated to a predetermined height.

Next, the operation of the present invention with this configuration will be explained.

First, when the copying machine starts, as the photoreceptor 7 rotates, the developing roller 30, the supply roller 40,
The cleaning members 50 and 50 are rotated in predetermined rotational directions, and a DC voltage is applied to the supply roller 40, and development is performed in the following order.

That is, first, the toner 4 staying in the storage chamber 22 is supported in the shape of a spike (magnetic brush 4a) on the conductive sleeve 42 by the magnetic attraction force of the magnet assembly 41, and then the toner 4 is transferred to the magnet assembly 41. The relative rotation between the conductive sleeves 42 transports the toner 4 to the developing roller 30 side, and while the brush height of the magnetic brush 4a is regulated by the brush height regulating member 60, only an appropriate amount of toner 4 is supplied between the developing rollers 30. approach the position.

A DC voltage having a polarity opposite to that of the electrostatic charge is applied to the supply roller 40, and a conductive developing roller 3 is applied to the supply roller 40.
0 is grounded, an electric field corresponding to the DC voltage is formed between the rollers 30 and 40. On the other hand, since the rollers 30 and 40 are rotating in opposite directions, the rollers 30 and 40 There is a considerable relative rotational speed between the rollers 30 and 40, and therefore the toner 4 guided to the supply position is formed between the rollers 30 and 40 while being rubbed between the rollers 30 and 40. A charge of opposite polarity to the electrostatic charge corresponding to the electric field strength is applied, and a desired amount of toner 4 is transferred to the developing roller 30.
Electrostatic charge adheres to the entire outer circumferential surface of the The toner 4 adhering to the developing roller 30 is conveyed to the photoreceptor 7 side by the rotation of the roller 30 and guided to the developing position.

The amount of toner attached to the developing roller 30, that is, the amount of toner conveyed to the developing position on the photoreceptor 7 side is as follows:
Since it can be freely controlled by changing the DC voltage applied to the supply roller 40, the electrostatic latent image formed on the surface of the photoreceptor 7 can be controlled depending on whether it is an area image or a line image. Even when adjusting the copy density of the latent image area, by manually or automatically changing the DC voltage, the copy density can be easily adjusted and the developing effect can be easily selected depending on the type of image area.

Next, since the toner 4 guided to the development position is charged with a polarity opposite to the electrostatic charge, it comes into contact with the electrostatic latent image 7a on the surface of the photoreceptor 7, thereby causing the electrostatic latent image 7a to come into contact with the electrostatic latent image 7a.
It is attracted to part a and a visible image is formed.

At this time, since the photoreceptor 7 and the developing roller 30 are rotating at the same circumferential speed while being in rolling contact with each other, the toner 4 can be developed without being rubbed against the photoreceptor 7. It is possible to obtain extremely clear images without image disturbances (shifts or blurring) caused by mechanical abrasion, which are the drawbacks of conventional one-component development systems.

In particular, in this embodiment, since the surface layer of the developing roller 30 is formed of a conductive rubber-like rotating body 31 with the coating layer 32 in between, the developing roller 30 is pressed against the surface of the photoreceptor 7 (elastically The developing efficiency is further improved.

Further, the development is not performed by applying an electric charge by mechanical friction as in the conventional one-component development method, but by applying an electric charge to the toner 4 forcibly charged at the supply position between the supply roller 40 and the developing roller 30. Photoreceptor 7
The electrostatic latent image area is electrically attracted and
Because it is attached, the development efficiency is extremely high.

For example, print density indicated by reflected optical density is
In order to increase the voltage to 1.4 or higher, the surface potential of the photoreceptor 7 must be set to 1000 V in the conventionally known one-component development method.
However, in this example, even if the surface potential of the photoreceptor 7 was lowered to 400V, it was possible to maintain a printing density of 1.4 or more.

Furthermore, in this embodiment, the developing roller 30
The rotating body 31 made of conductive rubber and the toner 4
Since a low-resistance conductive coating layer 32 made of the same material as the toner 4 is interposed between the toner 4 and the toner 4, the surface energy between the developing roller 30 surface and the toner 4 can be reduced, and the toner 4 can be roller 30
It becomes easy to transfer (suction adhesion) from the photoreceptor 7 to the photoreceptor 7, and the image clarity on the surface of the photoreceptor 7 improves. Furthermore, the presence of the coating layer 32 can prevent the toner 4 from adhering to the surface of the developing roller 30, thereby preventing irregularities in the developing conditions due to time-series resistance changes and variations on the surface of the developing roller 30 caused by the adhesion of the toner 4. It is possible to stabilize the image and prevent image unevenness.

The developing roller 30 that has passed the developing position further rotates and reaches the cleaning member 50. Since the cleaning member 50 rotates while being rubbed against the surface of the developing roller 30, the toner 4 remaining on the developing roller 30 is surely swept away toward the supply roller 40 side. At this time, in this embodiment, since the surface of the developing roller 30 is coated with a conductive coating layer 32 made of the same material as the toner 4, the toner 4 can be more easily swept away.

In this way, the cleaning member 50 is attached to the developing roller 30 between the downstream side of the developing position and the supply position.
Because it is placed in contact with the surface, the developing roller 3
The surface of the roller 0 can always be kept clean in preparation for the next charging, and as a result, the electric field strength between the supply roller 40 and the developing roller 30 is always constant, and charging is repeatedly performed between the rollers 30 and 40. Even if the toner 4 is mixed, the amount of toner 4 adhering to the developing roller 30 does not fluctuate, and stable image formation is possible.

Further, the cleaning member 50 sweeps off the toner 4 only toward the supply roller 40 side without sweeping it toward the photoconductor 7 side. This prevents excess toner 4 from adhering to the area and prevents image distortion.

Further, since the cleaning member 50 is made of a conductive material, it is possible to remove the charge on the toner 4 during the cleaning process, and no problem will occur during the next reuse.

Thereafter, development is carried out while repeating the above-mentioned actions.

At the end of development, the exposure device 9
At the same time or immediately after the exposure process ends, the voltage application means 43 is turned off and the supply roller 40
Stop applying the DC voltage to both rollers 3.
The supply of toner 4 to the developing roller 30 is stopped by cutting off the electric field between 0 and 40, and the developing roller 30 is rotated so that no toner other than toner 4 necessary for development is placed on the developing roller 30. The rearmost electrostatic latent image 7a formed at the end point of the exposure process
After developing the developed visible image, the toner at the rear end adhering to the developing roller 30 is transferred to the developing position, i.e., until the developed visible image is transferred or the final step is performed, i.e., the final image is formed. The toner 4 passes through the contact position of the photoreceptor 7 and is further swept away by the cleaning member 50 on the downstream side, and the machine is stopped with no toner 4 attached to the surface of the developing roller 30.

In this embodiment, the circumferential length (α) from the supply position of the developing roller 30 to the developing position where it contacts the photoreceptor 7 is longer than the exposure point where the electrostatic latent image 7a is formed on the photoreceptor 7. Since it is configured to be longer than the length (β) to the developing position, the toner is formed at the end of the exposure process before the last toner adhering to the developing roller 30 passes through the developing position. The rearmost electrostatic latent image 7a passed through the development position, and the above operation is smoothly achieved.

As described above, according to the present invention, the toner is forcibly charged by forming an electric field between the supply roller and the developing roller, the charged toner is attached to the outer peripheral surface of the developing roller, and the developing roller is connected to the photoreceptor. Since development is performed while rotating in contact or close proximity, development efficiency can be greatly improved.

In particular, the present invention completely eliminates the difficulty of setting the facing distance between the developing roller and the photoreceptor by rotating the developing roller while rolling it into contact with the photoreceptor, and also enables development at a low voltage. Furthermore, it becomes possible to form a clear image without blurring, that is, to form a clear image with the potential of the photoreceptor unchanged.

Further, in the present invention, since the conductive developing roller is formed of an elastic roller having a smooth coating layer on the surface and no magnet inside, smooth rolling contact is possible.

Furthermore, in the present invention, since the electric field between the two rollers is formed using a DC voltage, by changing the DC voltage, the copy density can be adjusted and the image area (area image,
The development effect can be easily selected depending on the type of line image).

In particular, the amount of toner attached to the developing roller, that is, the amount of toner conveyed to the developing position on the photoreceptor side, can be freely controlled by changing the DC voltage applied to the supply roller. Depending on whether the electrostatic latent image formed on the surface is an area image or a line image, or when adjusting the copy density of the latent image area, it is easy to adjust the copy density of the latent image area by manually or automatically changing the DC voltage. It is possible to easily adjust copy density and select development effects depending on the type of image area.

Note that when a DC voltage is applied to the developing roller side, a potential difference is also generated between the surface of the photoreceptor and the developing roller. For example, if a DC voltage of opposite polarity to the electrostatic charge is applied, an electrostatic latent image is formed. Toner also adheres (fogging) to the background areas that are not colored, which is not desirable, but this does not occur in the present invention.

Furthermore, since the developing efficiency of the present invention is improved as described above, it is possible to obtain a printing density higher than that of the conventional technology even if the surface potential of the photoreceptor is significantly lowered, and as a result, the photoconductive layer formed on the surface of the photoreceptor is It has various advantages such as being able to use various photoconductive semiconductors without being limited by the material used.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a developing device using a conventionally known single-component toner. 2 to 4 show embodiments of the present invention, FIG. 2 is a schematic explanatory diagram of a copying machine to which a developing device according to the present embodiment is applied, and FIG. 3 is a sectional view of the developing device, and FIG. FIG. 4 is an explanatory diagram showing the state of adhesion of toner.

Claims (1)

[Scope of Claims] 1. A photosensitive drum carrying an electrostatic latent image, a conductive developing roller that contacts the photosensitive drum and rotates at the same circumferential speed, and a direction of rotation from the developing position of the developing roller. A dry developing device comprising a supply roller located on the upstream side and configured to convey one-component toner to the developing roller side by magnetic force, the conductive developing roller having a smooth coating layer on its surface; The supply roller is formed of an elastic roller having no magnet inside, and the supply roller is formed of a non-magnetic roller that includes a magnet assembly and faces the conductive developing roller in a non-contact state, and The conductive developing roller is grounded, and a voltage controllable DC voltage having a polarity opposite to the electrostatic charge on the surface of the photoreceptor drum is applied to the supply roller to form an electric field between the two rollers. A dry developing device.