JPH05289594A - Magnetic brush cleaning device - Google Patents

Abstract

PURPOSE:To obtain a magnetic brush cleaning device having high cleaning efficiency capable of removing residual toner from the surface of an image carrier even when toner having small particle diameter is used. CONSTITUTION:As to the magnetic brush cleaning device removing the residual toner on the photosensitive drum after an electrostatic latent image formed on the photosensitive drum is developed and a visible image formed is transferred to a recording material, a voltage means 16 and 17 impressing a voltage in which an AC component is superposed on 0-300V DC bias voltage between the photosensitive drum and a magnetic brush sleeve 11 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a cleaning device such as an electrophotographic copying machine or an electrostatic recording device, and more particularly, to an improvement of a magnetic brush cleaning device for removing toner remaining on an image carrier by using a magnetic brush. Regarding

[0002]

2. Description of the Related Art In a transfer type electrophotographic copying machine, a cleaning device for removing toner remaining on an image carrier is required in order to prepare for the next development after transferring a toner image on a transfer paper. As one of the cleaning means, there is one that uses a magnetic brush.

However, the magnetic brush cleaning means has the following problems.

First, as a first problem, the magnetic brush cleaning means has an advantage that the surface of the image bearing member is less likely to be scratched because the force of rubbing the surface of the image bearing member is weaker than that of the conventional blade cleaning means. However, it also has a drawback that it is difficult to completely remove the residual toner.

In order to solve this problem, a magnetic brush cleaning device in which a DC and AC bias is applied between the image carrier and the magnetic brush sleeve is disclosed in Japanese Patent Publication No. 1-59587.
It is disclosed in the publication.

According to the magnetic brush cleaning device,
Since the cleaning is performed by using the electric Coulomb force in addition to the mechanical rubbing force, a higher cleaning effect can be achieved as compared with the conventional magnetic brush cleaning device.

However, in order to obtain a high-quality electrophotographic image, when a small particle size toner, particularly a spherical toner having a particle size of 7 μm or less is used, even if the magnetic brush cleaning device is used, the image carrier surface It was difficult to completely remove the toner remaining in the toner. Therefore, it has been desired to develop a cleaning device that has a sufficient effect in reducing the particle size of toner, which is expected to continue to increase in the future.

Next, the second problem of the magnetic brush cleaning means is that the cleaning of the cleaning means becomes complicated.

For example, in an electrophotographic copying apparatus in which the process of rotating the image carrier a plurality of times to superimpose the toner is carried out, if the cleaning member constantly rubs the image carrier, a visible image before transfer is also formed. It is inconvenient because it has been swept away. Therefore, conventionally, the sleeve forming the magnetic brush is configured to be movable, and the distance between the sleeve and the image carrier is changed to switch between pressing and releasing the spikes of the magnetic brush against the image carrier.

However, according to such a switching means,
Each time the cleaning means is released, the distance between the magnetic brush sleeve and the image carrier changes during cleaning, which may cause cleaning failure. Therefore, in order to always maintain the distance with a constant accuracy, the cleaning device releasing device itself becomes complicated, and the maintainability,
It is not preferable in various points such as size and price of the electrophotographic apparatus.

[0011]

SUMMARY OF THE INVENTION The present invention has been completed on the basis of a study on the cleaning properties and cleaning conditions for small particle size toners and the design and trial production of an experimental apparatus. A magnetic brush cleaning device having a high cleaning effect capable of removing the residual toner from the surface of the image bearing member even in the case of being present,
An object of the present invention is to provide a device capable of releasing pressure contact of a magnetic brush with an image bearing member by a simple mechanism when cleaning is not performed.

[0012]

According to a first aspect of the present invention, the electrostatic latent image formed on the image bearing member is developed, and the formed visible image is transferred onto a recording material, and then the residual image on the image bearing member is retained. In a magnetic brush cleaning device for removing toner, insulating magnetic particles are used, and a voltage obtained by superimposing an AC component on a DC bias voltage of 0 to 300 V having a polarity opposite to that of toner charging is applied between the image carrier and the magnetic brush sleeve. A magnetic brush cleaning device characterized by being provided with a power supply means for applying to the magnetic latent image, and a second invention to develop an electrostatic latent image formed on an image carrier and transfer the formed visible image to a recording material. Then, in the magnetic brush cleaning device for removing the residual toner on the image carrier, the conveyance of the magnetic particles constituting the magnetic brush is controlled by a magnet having a polarity different from that of the magnet in the magnetic brush sleeve. That the magnetic brush cleaning apparatus characterized in that a magnetic brush control means, being able to achieve the above object the configuration.

[0013]

EXAMPLES The present invention will be described in detail based on examples.

FIG. 1 is a sectional view showing the schematic arrangement of an electrophotographic copying machine according to an embodiment of the present invention. In the electrophotographic copying machine shown in the figure, the photosensitive drum 7, which is an image carrier, uses a conductive non-magnetic material such as aluminum as a support, and its surface is mirror-finished to form selenium or an organic optical semiconductor. Is formed by vapor deposition or coating, and is rotated clockwise in the figure.

First, the image light 2 modulated on the basis of the original image from the exposure device is irradiated and exposed on the photosensitive drum 7, and the surface of the photosensitive drum 7 uniformly charged by the charger 1 is electrostatically charged. A latent image is formed. The electrostatic latent image is developed by the developing device 3
Of the four developing units provided inside, first, the reverse developing is performed by the first developing unit (A) having the yellow developer,
A yellow toner image is formed on the photosensitive drum 7.
The photosensitive drum 7 rotates once as it is, and when the electrostatic latent image again reaches the position of the developing device 3, reversal development is performed by the second developing device (B) having a magenta color developer. , The magenta toner image is superimposed on the yellow toner image. Similarly, when the photosensitive drum 7 is rotated once, a cyan toner image is generated by the third developing device (C) having a cyan developer, and then a fourth toner image having a black developer is obtained.
A black toner image is superposed by the developing device (D),
Eventually, a toner image in which toners of four colors are superposed is formed on the surface of the photosensitive drum 7. However, the present invention is not limited to this.

The toner image in which the above four colors are superposed on the recording paper in the paper feeding cassette 9 fed by the paper feeding roller 10 so that the leading edge of the toner image coincides with the timing and speed of reaching the transfer device 4. , Is transferred by the transfer device 4. At this time, 60 to 90% of the toner forming the toner image is transferred to the recording paper, but 5 to 20% remains as the residual toner while being attached to the photosensitive drum 7.

For the residual toner, the recording paper is the photosensitive drum 7
Then, after being charged by the charger 26, it is photo-electrified by the uniform exposure lamp (charge-eliminating lamp) 27, and then it is adsorbed by the magnetic brush of the magnetic brush cleaning device 8 and removed from the photoconductor drum 7. On the other hand, the recording paper separated from the photoconductor drum 7 by the separator 5 after the transfer is conveyed to the fixing device 6, and the transferred original image is fixed.

Next, FIG. 2 is a vertical sectional side view of an essential part showing an example of the cleaning device of the present invention.

After being charged by the charger 26, the toner to be cleaned is subjected to photo-static elimination by the static elimination lamp 27.
As a result, the charges on the surface of the photoconductor are removed, and the potential of the toner remains mainly.

On the surface of the magnetic brush sleeve 11 made of a conductive non-magnetic material, a magnetic brush made of carriers which are magnetic particles is formed by the magnetic fields of the plurality of magnets 12 held by the magnet holding roller 13. Here, the magnet 12 has one magnetic pole facing the inner surface of the sleeve 11 as shown in the drawing, and the magnetic poles adjacent to each other in the circumferential direction have different magnetisms. Further, in the figure, only one of the plurality of magnets 12 is provided so as to be closest to the surface of the photosensitive drum 7, but the present invention is not limited to this. In order to improve the cleaning effect, a plurality of magnets may be installed at the position closest to the surface of the photosensitive drum 7.

The ears of the magnetic brush formed on the sleeve 11 rotate clockwise in accordance with the rotation of the sleeve 11 and rub against the surface of the photosensitive drum 7 to clean residual toner, paper dust and the like.

Here, a DC bias for adsorbing the toner on the surface of the photosensitive drum 7 to the sleeve 11 and an oscillating electric field are applied to the toner on the surface of the photosensitive drum 7 between the photosensitive drum 7 and the sleeve 11. AC bias is applied by the DC bias power source 16 and the AC bias power source 17 which are power source means, and the residual toner on the surface of the photosensitive drum 7 is adsorbed to the sleeve 11.

The residual toner adsorbed on the sleeve 11 is adsorbed on a toner recovery roller 14 made of the same material as the sleeve 11 and applied with a recovery DC bias by a recovery DC bias power source 18. This toner collecting roller 14 is
A blade 15 is provided which is pressed against the roller surface while having an opposite direction to the roller surface transfer direction. The blade 15 is made of a material having an appropriate elasticity, for example, made of a hard resin, sweeps the toner adsorbed on the surface of the roller 14, and the swept toner is collected by the toner collecting screw 25. The potential difference between the collecting DC bias and the cleaning DC bias is set so that the toner moves in the direction in which the toner moves to the collecting roller 14.

The charging by the charger 26 before cleaning is the same as the toner polarity at the time of development to improve the cleaning property. Considering the photo-electrification of the photoconductor, the reversal development method is preferable because it matches the charging polarity of the toner and the charging polarity of the photoconductor.

In regular development, it is preferable to use a photoreceptor capable of bipolar charging and perform charging opposite to the charging during image formation.
As a result, it is possible to perform the light elimination and to erase the charges of the photoconductor.

On the other hand, above the sleeve 11 in FIG. 2, a magnetic brush control magnet 19 having a magnetic pole different from that of the closest magnet 12 is provided so as to be rotatable in the direction of the arrow by a shaft 20. A partition wall 21 is provided between the brush control magnet 19 and the sleeve 11 so that the carrier does not directly adhere to the magnetic brush control magnet 19. When the surface of the photosensitive drum 7 needs to be cleaned, the magnetic brush control magnet 19 is in the position shown by the broken line in FIG. 2, and the carrier constituting the magnetic brush is conveyed clockwise as the sleeve 11 rotates. Perform cleaning. However, when cleaning is not required, the magnetic brush control magnet 19 is moved to the position shown by the solid line by the magnet control means (not shown). At this time, the carrier is the magnetic brush control magnet 19
The conveyance is stopped by the opposing magnetic field between the magnet 12 and the magnet 12, so that the magnetic brush does not rub the surface of the photosensitive drum 7 for cleaning.

In addition, a magnetic material may be used in place of the magnetic brush control magnet 19, and if an electromagnet is used, control relating to the release of the cleaning means is performed only by the supply of electric power to the electromagnet. Because you can
The release device is more simplified.

Furthermore, in order to improve the cleaning property, it is often the case that a high AC bias is applied, or the linear velocity ratio of the cleaning agent to the sleeve drum and the conveying amount are increased, so that the carrier is often transferred to the photosensitive drum 7. It causes adhesion. Therefore, depending on the cleaning conditions, the carrier attached to the photosensitive drum 7 must be collected after cleaning. Therefore, it is preferable to provide carrier recovery means for recovering the carrier with a sleeve, a magnetic roller, or the like and reusing it as a magnetic brush, downstream in the rotational direction of the photosensitive drum 7. In the embodiment of FIG. 2, the carrier collection sleeve 2
2. It has a carrier scraping blade 23, and a carrier collecting means composed of a carrier carrying screw 24 for returning the carrier collected in a carrier tank (not shown). An AC component may be superimposed on the bias from the bias power source 28, but the DC component is 0 to ± 100 V.
Is applied. This collects the carrier by magnetic force without leaving unnecessary toner and carrier on the photoconductor.

Next, the magnetic particles forming the preferable magnetic brush and the cleaning conditions by the apparatus of this embodiment will be described.

First, the particle size of the magnetic particles will be described. Generally, when the average particle size of the magnetic particles is large, (a) the magnetic brush formed on the carrier is in a rough state, so even when charged while being vibrated by the electric field, unevenness is likely to appear on the magnetic brush. , The problem of uneven cleaning occurs. To solve this problem, the average particle size of the carrier particles should be reduced, and as a result of the experiment, the effect begins to appear when the average particle size is 150 μm or less, and particularly when it becomes 100 μm or less, (a)
It turns out that the problem of does not occur. However, if the particles are too fine, they tend to adhere to the surface of the image carrier or become easily scattered during charging. These phenomena are related to the strength of the magnetic field acting on the particles and the strength of the magnetization of the particles thereby, but generally, the average particle size of the particles becomes remarkable when it is 30 μm or less. The strength of the magnetization is 20 to 20.
Those of 0 emu / g are preferably used.

From the above, the average particle size of the magnetic particles is
It is preferably 150 μm or less, particularly preferably 100 μm or less, and 30 μm or more.

Such a magnetic particle is a metal such as iron, chromium, nickel, cobalt or the like, or a compound or alloy thereof, such as iron tetroxide or γ-oxidation, which is the same as in a conventional magnetic carrier particle as a magnetic substance. Ferric iron, chromium dioxide, manganese oxide, ferrite, manganese-copper alloy,
Whether the surface of these ferromagnetic particles or those magnetic particles is coated with a resin such as styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, etc. Alternatively, particles obtained by making a resin containing magnetic fine particles dispersed therein can be obtained by selecting the particle size by a conventionally known average particle size selecting means.

The formation of spherical magnetic particles is
The particle layer formed on the carrier is made uniform, and a high bias voltage can be uniformly applied to the carrier. That is, the fact that the magnetic particles are sphered means that (1) generally, the magnetic particles are easily magnetized and adsorbed in the long-axis direction, but the spheroidization eliminates the directionality thereof, so that the layer is uniformly formed and local layers are formed. It is possible to prevent the occurrence of unevenness in the region of low resistance and layer thickness. (2) With the increase in the resistance of the magnetic particles, there is no edge portion as seen in conventional particles, and the concentration of the electric field on the edge portions does not occur. As a result, even if a high bias voltage is applied to the magnetic particle carrier. Further, the effect of not causing discharge on the surface of the image carrier and causing uneven cleaning is provided. Spherical particles with the above effects have a magnetic particle resistivity of 10 ⁸ Ωcm or more,
It is particularly preferable that insulating magnetic particles are formed to have a resistivity of 10 ¹² Ω · cm. The resistivity, the electric field of 1000V / cm between After tapping putting particles in a container having a sectional area of 0.50 cm ^2, a load of 1Kg / cm ² to packed particles, the load and a bottom electrode Is a value obtained by reading the current value when a voltage is applied.If this resistivity is low, when a bias voltage is applied to the carrier, electric charges are injected into the magnetic particles and the image carrier surface is exposed. The magnetic particles tend to adhere, or the breakdown of the bias voltage easily occurs.

In summary of the above, the magnetic particles are spherical so that the ratio of the major axis to the minor axis is at most 3 times, there is no protrusion such as needles and edges, and the resistivity is 10 ⁸ Ω ・
It is a proper condition that it is not less than cm, preferably not less than 10 ¹² Ω · cm. Then, such spherical magnetic particles should be selected as spherical as possible for the magnetic particles, and in the particles of the magnetic fine particle dispersion system, the spherical particles should be subjected to the spheroidizing treatment after forming the dispersed resin particles by using the fine particles of the magnetic material as much as possible. Or by having dispersed resin particles by a spray drying method or the like.

The above are the conditions for the magnetic particles, and the conditions for the magnetic particle carrier for forming the particle layer and charging the image carrier will be described below.

As the magnetic particle carrier, a carrier capable of applying a bias voltage is used. In particular, it has a structure in which a magnet body having a plurality of magnetic poles is provided inside a sleeve on the surface of which a particle layer is formed. Those are preferably used. In such a carrier, relative rotation with the rotating magnet body causes the particle layer formed on the surface of the sleeve to undulate and move, so that new magnetic particles are supplied one after another, Even if the particle layer on the surface of the sleeve has some non-uniformity of the layer thickness, the effect is sufficiently covered by the wavy undulation so that it is not a practical problem. Then, it is preferable that the transport speed of the magnetic particles by the rotation of the sleeve or the rotation of the magnet body is almost the same as or faster than the moving speed of the image carrier. Further, the transport direction by the rotation of the sleeve is preferably the same direction. Uniformity of charging is better in the same direction than in the opposite direction. However, it is not limited thereto.

The thickness of the particle layer formed on the carrier is preferably such that it is sufficiently scraped off by the regulating plate to form a uniform layer, and the gap between the carrier and the image carrier is large. Is preferably 100 to 2000 μm. If the surface gap between the carrier and the image carrier is too narrower than 100 μm, it will be difficult to form the magnetic brush ears for uniform cleaning, and sufficient magnetic particles should be supplied to the cleaning unit. If it becomes impossible to perform stable cleaning, and if the gap becomes much larger than 2000 μm, the particle layer becomes rough and cleaning unevenness easily occurs, and the oscillating electric field effect decreases and sufficient cleaning is not performed. It will not be done. in this way,
When the amount of the gap between the carrier and the image carrier becomes an extreme value, the thickness of the particle layer on the carrier cannot be adjusted appropriately, but when the gap is in the range of 100 to 2000 μm, The thickness of the particle layer can be formed appropriately,
It is possible to prevent the occurrence of sweeps due to the rubbing of the magnetic brush.

It is preferable that the magnetic particles are triboelectrically charged in the opposite polarity to the toner without changing the charging polarity during development of the toner. The recovery function can be improved by the triboelectric charging of the toner. In this case, the charge amount is preferably 5 to 30 μc / g under the condition of 5 parts by weight of toner to 100 parts by weight of magnetic particles.

In this example, cleaning was performed without transferring a solid image by reversal development, and the amount of toner remaining on the photoconductor after cleaning was evaluated for cleaning property by reflection density. An example of preferable cleaning conditions is as follows.

Cleaning conditions Toner: d ₅₀ = 0.5-10 μm (spherical) Carrier: d ₅₀ = 30-100 μm (spherical) Magnetic brush sleeve: Diameter = 20-40 mm Magnetic flux density = 500-1100 Gauss Linear velocity for photosensitive drum Ratio = 0.8 to 3.0 Dsd: 100 to 200 μm (gap between magnetic brush sleeve and photoconductor drum) Magnetic brush sleeve applied voltage: _VDC = 0 to 300 V (polarity opposite to toner) V _pp = 200 to 3500 V (of AC component) Peak-to-peak voltage) f _AC = 0.5 to 10 kHz Transport amount on sleeve: 10 to 200 mg / cm ² [Example 1] FIG. 3 shows the effect of the bias applied to the sleeve 11 on the cleaning property. ..

The horizontal axis shows the DC bias, the vertical axis shows the reflection density of the residual toner after cleaning, and the broken line shows the reflection density when there is no residual toner.

It can be seen that as E _AC (= V _PP / Dsd) is increased, the cleaning property is rapidly improved in the low DC bias region. Further, it is considered that the cleaning is possible around V _DC = 0 because the magnetic particles and the toner particles are triboelectrically charged with each other. On the other hand, at a high DC bias, the light background fog that occurred when the AC bias was insufficient disappears, and the DC bias cleaning area expands. However, it is not clear what causes the cleaning to be defective at a higher DC bias as the AC bias application is stronger. It is considered that the cause is that the toner that has been once cleaned is accumulated in reverse, or that the polarity of the toner changes due to partial discharge.

When the peak-to-peak voltage of the AC bias is changed, there is a cleaning region as shown in FIG. 4 with respect to the DC bias.
The cleaning area is enlarged in the low bias area. The vertical axis of FIG. 4 is the DC bias, and the horizontal axis is the amount E _AC = V _PP / Dsd (volts / mm) obtained by dividing V _PP by Dsd.

From the figure, it was confirmed that when the DC bias was increased, poor cleaning, that is, fog, occurred, and when the DC bias was further increased, the fog became severe. Therefore,
It can be said that the cleaning property is good when the DC bias is 0 to 300V. Such a result has a frequency of 0.5 to 1
Obtained at 0 KHz.

The conditions of V _DC and E _AC are V _DC ≦ 0.05E _AC +150 V _DC ≧ −0.15E _AC +150.

However, the development in this embodiment uses toner particles having the same sign as the charge polarity of the electrostatic latent image, but the present invention is not limited to this, and the charge polarity of the charging surface and the toner having a different sign. What is called normal development in which the particles are attached to the high potential portion may be used.

In the present invention, the preferable bias applied to the sleeve 11 is D including the case of reversal development.
C bias is 0 to 300V, AC bias has a frequency of 0.5k
It is 0.2 to 3.0 KV at -10 kHz.

When the carry amount is 10 to 20 mg / cm ² , no large change is observed in the cleaning area, but the cleaning property tends to improve as the carry amount increases.

When the linear velocity ratio of the cleaning agent to the drum is 0.8 to 3.0, the cleaning property is improved by the increase of the transportation speed, but the cleaning property depends on the transportation speed as compared with the AC bias described above. Is less affected, and it is particularly preferable to have a linear velocity ratio of 1.2 to 2.5 times.

In order to clarify the effect of the invention of the present application, comparison with blade cleaning for spherical toner was conducted, and the cleaning dependency on toner particle size was examined. The result is shown in FIG. As a blade to be compared, a cleaning blade made of urethane rubber used in U-BIX8028 manufactured by Konica Corporation is used.

In FIG. 5, the horizontal axis represents the toner particle size and the vertical axis represents the cleaning efficiency. Here, the cleaning efficiency is obtained by calculating the adhesion amount R ₁ of toner before cleaning and the adhesion amount R ₂ of toner after cleaning and substituting into the following equation.

Cleaning efficiency [%] = (R ₁ −R ₂ ) / R ₁ × 100 From FIG. 5, blade cleaning does not provide sufficient cleaning even with a particle size of 10 μm, and the cleaning property is further improved by reducing the particle size. However, it is confirmed that the magnetic brush cleaning can clean spherical toner particles having a particle size of 0.5 to 10 μm.

[0053]

According to the apparatus of the present invention described above, the particle size which cannot be removed by the conventional cleaning apparatus is 0.5 μm.
It has a remarkable effect that the toner having the small particle diameter up to the above can be almost completely removed, and further has an effect that the cleaning device can be released with a simple configuration.

As described above, the present invention was able to achieve the above-mentioned object by the above-mentioned constitution.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of an electrophotographic copying machine that is an embodiment of the present invention.

FIG. 2 is a vertical sectional side view of an essential part showing an example of a cleaning device of the present invention.

FIG. 3 is a diagram showing a result of examining an influence of a sleeve applied bias.

FIG. 4 is a diagram showing a relationship between a sleeve application bias and a cleaning property.

FIG. 5 is a graph showing comparison with blade cleaning and cleaning dependency on toner particle size.

[Explanation of symbols]

 1 Charging Device 2 Image Light 3 Developing Device 4 Transfer Device 5 Separator 6 Fixing Device 7 Photosensitive Drum 8 Magnetic Brush Cleaning Device 9 Paper Feed Cassette 10 Paper Feed Roller 11 Magnetic Brush Sleeve 12 Magnet 13 Magnet Holding Roller 14 Toner Recovery Roller 15 Blade 16 DC bias power supply 17 AC bias power supply 18 Recovery DC bias power supply 19 Magnetic brush control magnet 20 Axis 21 Partition wall 22 Carrier collecting sleeve 23 Carrier scraping blade 24 Carrier conveying screw

Claims (3)

[Claims] 1. A magnetic brush cleaning device for developing an electrostatic latent image formed on an image carrier, transferring the formed visible image to a recording material, and then removing residual toner on the image carrier. In the above-mentioned, a power supply means for applying a voltage in which an AC component is superposed on a DC bias voltage having a polarity opposite to that of the toner charging using an insulating magnetic particle is provided between the image carrier and the magnetic brush sleeve. Magnetic brush cleaning device. 2. The magnetic brush cleaning device according to claim 1, further comprising a collecting unit that is arranged downstream of the image carrier in the rotational direction and collects the carrier attached to the image carrier. 3. A magnetic brush cleaning device for developing an electrostatic latent image formed on an image carrier, transferring the formed visible image to a recording material, and then removing residual toner on the image carrier. 2. The magnetic brush cleaning device according to claim 1, further comprising magnetic brush control means for controlling the transport of the magnetic particles by a magnetic body that produces a pole having a polarity different from that of the magnet in the magnetic brush sleeve.