JPH06266266A - Image forming device - Google Patents

Abstract

PURPOSE:To form a good image without leaving residual toners on the surface of a photoreceptor by changing the cleaning period in response to the toner quantity, and making sufficient cleaning when a toner image has a toner quantity larger than the average toner quantity. CONSTITUTION:When a photoreceptor 1 is rotated and a conducting cylinder 22 is rotated in the opposite direction, magnetic grains 21 are magnetically connected by the magnetic lines of force of a magnet 23 to form a magnetic brush 20A, the photosensitive layer of the photoreceptor 1 is rubbed, and residual toners T are collected, sucked, and attracted by the high-potential bias voltage with a recovery roller 27. When a toner image having the record dot number more than that of the average toner image, e.g. an image having many black solid portions, is written on an image writing device A, the record dot number information is sent to a control means 103 from a CPU 100. If the record dot number is higher than the specified value, the start of the next image forming process is delayed, the conducting cylinder 22 is rotated during this period, and the residual toners T are removed from the inside of the magnetic brush 20A and the surface of the photoreceptor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in an image forming apparatus such as an electrophotographic copying machine, removes and cleans toner remaining on the surface of an image forming body which is an electrostatic charge carrier, and evenly forms the image forming body. The present invention relates to a charging and cleaning device using a magnetic brush for charging.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a corona charger has generally been used for charging an image forming body. This corona charger applies a high voltage of several KV to the discharge wire to generate a strong electric field around the discharge wire for gas discharge, and to adsorb the charge ions generated at that time to the image forming body. Is charged.

Since the corona charger used in such a conventional image forming apparatus can be charged without mechanical contact with the image forming body, the image forming body is not damaged during charging. Have advantages. However, since this corona charger uses a high voltage, there is a risk of electric shock or leakage, and ozone generated by gas discharge is harmful to humans, which shortens the life of the image forming body. Had. In addition, the charging potential of the corona charger is unstable because it is strongly influenced by temperature and humidity. Furthermore, the corona charger requires a high voltage to obtain the charging potential, and thus the communication terminal and the information processing device are required. As a result, it is a major drawback when using an electrophotographic image forming apparatus.

Many drawbacks of such corona chargers are:
The cause is that gas discharge is involved in charging.

Therefore, a cylinder containing a magnet roll is used as a charging device capable of charging the image forming body without performing high-voltage discharge like a corona charger and without mechanically damaging the image forming body. A charging device that forms a magnetic brush by adsorbing magnetic particles on it and is charged by rubbing the surface of an image forming body with this magnetic brush is disclosed in JP-A-53-133569. There is.

Further, in Japanese Patent Application Laid-Open No. 4-13464, a cylinder provided rotatably around the outer circumference of a magnet roll having magnetic poles and a magnetic brush composed of a magnetic particle layer adhered to the cylinder portion is described as an image forming member. By moving and sliding contact relative to the moving direction and applying a bias voltage to the cylinder, the transfer residual toner adhering to the image forming body is removed and the image forming body is charged. There is disclosed a means for charging and cleaning by superimposing an AC bias voltage on the bias voltage applied by.

[0007]

As described above, the means for charging and cleaning using the magnetic brush does not generate ozone, can perform stable and uniform charging, and can perform efficient cleaning. be able to. On the other hand, when a large number of toner images formed on the image forming body, for example, toner images other than normal characters, such as black images or bold characters, are formed on the image forming body after transferring the toner image to the transfer paper. Residual toner is generated.

Further, even if the charging and the exposure for the next image formation are carried out, the residual toner interferes with the charging so that the charging cannot be sufficiently carried out, and the underexposure also occurs, so that an accurate toner image cannot be formed. There is.

The present invention is a means specifically conceived to remedy the above-mentioned drawbacks. That is, in the case where the toner image is an image having a larger amount than the average toner amount due to the number of recorded dots in the image information at the time of forming the image, the cleaning time is changed according to the toner amount, and after performing a sufficient cleaning operation, the next image The purpose is to be formed.

[0010]

In order to achieve the above-mentioned object, the present invention comprises, as a first aspect, at least a developing means, a transfer means, and a means for both charging and cleaning centering on an image carrier. In the image forming apparatus, when the toner of the toner image formed on the surface of the image bearing member by the developing unit is larger than the average toner amount, the unit that performs both charging and cleaning before the next image formation is adjusted according to the toner amount. The toner amount is determined by the number of recording dots at the time of image formation.

[0011]

EXAMPLES First, the particle size of the magnetic particles used in the present invention will be described. Generally, when the average particle size of the magnetic particles is large,
Since the state of the magnetic brush formed on the carrier is rough, even if the magnetic brush is charged while being vibrated by the electric field, unevenness is likely to appear on the magnetic brush, which causes a problem of uneven charging. To solve this problem, the average particle size of the carrier particles should be reduced. As a result of experiments, the effect begins to appear when the average particle size is 100 μm or less, and particularly when the average particle size is 70 μm or less, the above-mentioned problem occurs substantially. It turned out to be gone. 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 prominent at 30 μm or less.

From the above, the average particle size of the magnetic particles is
It is preferably 100 μm or less, particularly preferably 70 μm or less and 30 μm or more. The strength of magnetization is 20 to 200 emu / g
Those of are preferably used.

Such magnetic particles can be used as a magnetic substance in the same manner as in conventional magnetic carrier particles, such as metals such as iron, chromium, nickel and cobalt, or their compounds and alloys such as iron tetroxide and γ-oxidation. Ferric iron, chromium dioxide, oxide magazine, ferrite, manganese-copper alloy,
The surface of the ferromagnetic particles or the 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. Alternatively, the particles obtained by making the resin containing the magnetic fine particles dispersed therein are subjected to particle size selection by a conventionally known average particle size selection means.

The formation of spherical magnetic particles is
The particle layer formed on the carrier is uniform, and a high bias voltage can be uniformly applied to the carrier. That is, the fact that the magnetic particles are spherical means that (1) the magnetic particles are generally easily magnetized and adsorbed in the long-axis direction, but due to the spherical shape, the directionality is lost, and therefore, the layer is uniformly formed and localized. (2) Higher resistance of magnetic particles eliminates the edge part seen in conventional particles, and concentration of electric field on the edge part occurs. As a result, there is an effect that even if a high bias voltage is applied to the magnetic particle carrying carrier, the surface of the image carrier is uniformly discharged and charging unevenness does not occur. As the spherical particles having the above effects, it is preferable to form chargeable magnetic particles such that the carrier particles have a resistivity of 10 ⁵ Ω · cm or more, particularly 10 ¹² Ω · cm or less. The resistivity after tapping putting particles in a container having a sectional area of 0.50 cm ^2, a load of 1 kg / cm ² on packed particles, the 1000V / cm between the load and a bottom electrode It is a value obtained by reading the current value when a voltage that causes an electric field is applied.If this resistivity is low, charges are injected into the magnetic particles when a bias voltage is applied to the carrier, and the image bearing The magnetic particles are likely to adhere to the body surface, or the breakdown of the bias voltage is likely to occur. If the resistivity is high, charge injection is not performed and charging is not performed.

In summary, the magnetic particles are spherical so that at least the ratio of the major axis to the minor axis is 3 times or less, and there are no protrusions such as needles and edges, and the resistivity is high. 10 ⁵ Ω
-It is a proper condition that it is not less than cm and preferably not more 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 material fine particle dispersion system, the fine particles of the magnetic material should be used as much as possible, and the spheroidizing treatment should be performed after the formation of the dispersed resin particles. It is manufactured by applying or by having dispersed resin particles by a spray drying method.

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

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 having a particle layer formed on the surface thereof. 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 in a wavy shape, 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 thereof is sufficiently covered by the wavy undulation so as not to cause any 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 conveying direction by the rotation of the sleeve may be the same direction or the opposite direction. However, when considering the cleaning property, the cleaning property in the opposite direction is superior to that in the same direction. However, it is not limited thereto.

Further, the thickness of the particle layer formed on the carrier is preferably such that the particle is sufficiently scraped off by the regulation plate to form a uniform layer, and the carrier and the image carrier are separated from each other. The gap is preferably 100 to 5000 μm. If the surface gap between the carrier and the image carrier becomes too narrower than 100 μm, it will be difficult to form the magnetic brush ears that uniformly charge the surface, and sufficient magnetic particles will be supplied to the charging section. It becomes impossible to perform stable charging, and if the gap exceeds 5000 μm, the particle layer becomes rough and uneven charging is likely to occur.
In addition, the charge injection effect is reduced, and sufficient charging cannot be obtained. In this way, when the gap between the carrier and the image carrier becomes extremely large, the thickness of the particle layer on the carrier cannot be adjusted appropriately, but the gap is 100 to 5000.
In the range of μm, the particle layer can be formed to have an appropriate thickness. This is because it is possible to prevent the occurrence of sweeps due to the rubbing of the magnetic brush.

Further, in the present invention, the residual toner adhering to the image carrier is removed by rubbing the magnetic brush, but the present invention is a cleaning device suitable for a regular image forming apparatus in which positive development is carried out. is there. For example, in an image forming apparatus in which the image carrier is positively charged, positive development is performed with negatively charged toner. Therefore, when negatively charged toner particles are used as the magnetic particles, the toner adheres to the magnetic particles of the magnetic brush during rubbing, and the toner is collected from the image carrier.

When toner is mixed in the charging magnetic brush,
The resistance of the magnetic brush increases and the charging ability decreases. Therefore, the magnetic brush that has finished rubbing against the image carrier is brought into contact with a collecting roller to which a positive DC bias having a higher potential than the charging bias is applied to collect the toner in the magnetic brush into the collected toner. Is possible.

The present invention is also a cleaning device suitable for a reversal image forming apparatus in which reversal development is performed. For example, in an image forming apparatus in which the image carrier is positively charged, reversal development is performed by the positively charged toner. Therefore, if you use positive magnetic particles as magnetic particles,
Toner adheres to the magnetic particles of the magnetic brush during rubbing,
The toner is collected from the image carrier. At this time, since the voltage applied to the magnetic brush and the toner polarity match, even if some of the toner adheres to the photoconductor, the toner polarity does not change, and therefore the image formation is not adversely affected.
However, if toner is mixed in the charged magnetic brush,
The resistance of the magnetic brush increases and the charging ability decreases. Therefore, the magnetic brush that has more surely rubbed the image bearing member is brought into contact with the collecting roller to which a positive or negative DC bias lower than the charging bias is applied to collect the toner in the magnetic brush. It is preferable to recover it.

The structure of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the outline of the configuration of an image forming apparatus provided with a charging and cleaning device of the present invention.

In FIG. 1, reference numeral 1 denotes a drum-shaped photosensitive member which is an image forming member rotating in the direction of the arrow (clockwise), and a charging / cleaning device 20, a developing device 30, and a developing device 30, which will be described later, are provided on the peripheral portion thereof.
A pre-transfer charger 13, a transfer belt 50 and the like are provided.

The photosensitive member 1 has a photosensitive layer 1A, as shown in FIG.
High γ consisting of the intermediate layer 1B and the grounded conductive support 1C
It is a photoconductor. The thickness of the photosensitive layer 1A is about 5 to 100 μm, preferably 10 to 50 μm. As the photoreceptor 1, a drum-shaped conductive support 1C made of aluminum is used, and an intermediate layer 1B having a thickness of 0.1 μm and made of an ethylene-vinyl acetate copolymer is formed on the support 1C, and on the intermediate layer 1B. It is configured by providing a photosensitive layer 1A having a film thickness of 35 μm.

A drum made of aluminum, steel, copper or the like is used as the conductive support 1C.
It may be a belt-shaped one in which a metal layer is laminated or vapor-deposited on a paper plastic film, or a metal belt such as a nickel belt made by an electroforming method. Further, the intermediate layer 1B withstands a high voltage of ± 500 to 2000 V as a photosensitive member, and blocks injection of electrons from the conductive support 1C in the case of positive charging, and obtains excellent light attenuation characteristics due to avalanche phenomenon. As described above, it is desirable that the intermediate layer 1B has a hole mobility, and therefore, the intermediate layer 1B contains 10% by weight or less of the positively chargeable charge transporting substance described in Japanese Patent Application Laid-Open No. 63-44662 previously proposed by the present applicant. It is preferable to add it.

As the intermediate layer 1B, for example, the following resins which are usually used in a photosensitive layer for electrophotography can be used.

(1) Vinyl-based polymers such as polyvinyl alcohol (poval) (2) Nitrogen-containing vinyl polymers such as polyvinylamine (3) Polyether-based polymers such as polyethylene oxide (4) Acrylics such as polyacrylic acid and its salts Acid polymers (5) Methacrylic acid polymers such as polymethacrylic acid and its salts (6) Ether fibrin polymers such as methyl cellulose (7) Polyethyleneimine polymers such as polyethyleneimine (8) Polyalanine and other polypolymers Amino acids (9) Starch acetate such as starch acetate and amine starch, and their derivatives (10) Soluble polymer such as polyamide Nylon soluble in a mixed solvent of water and alcohol The photosensitive layer 1A basically comprises a charge transport material. Without using them together, a phthalocyanine fine particle of 0.1 to 1 μm in diameter made of a photoconductive pigment is mixed with an antioxidant. The coating solution is prepared by mixing and dispersing it in a solvent of under resin to prepare a coating solution, coating the coating solution on the intermediate layer 1B, drying and optionally heat treatment.

When the photoconductive material and the charge transport substance are used in combination, the photoconductive pigment and 1 / of the photoconductive pigment are used.
The photosensitive layer 1A is constituted by dispersing a photoconductive material composed of a small amount of charge-transporting substance of 5 or less, preferably 1/1000 to 1/10 (weight ratio), and an antioxidant in a binder resin.

After reversal development, the toner image remaining after transfer is part of the toner image after the cleaning and charging according to the present invention.
If left over, a photosensitive member having a spectral sensitivity on the long wavelength side is necessary so that the beam from the scanning optical system is not blocked by the color toner image, and an infrared ray transmissive toner is used.

The light attenuation characteristics of the high γ photoconductor of this embodiment will be described below. FIG. 3 is a graph showing the characteristics of the high-γ photoconductor.

In FIG. 3, V ₁ is a charging potential (V), V ₀
Is the initial potential (V) before exposure, L ₁ is the irradiation light amount (μJ / c) of the laser beam required for the initial potential V ₀ to be attenuated to 4/5.
m ² ) and L ₂ represent the irradiation light amount (μJ / cm ² ) of the laser beam required for the initial potential V ₀ to be attenuated to 1/5.

The preferred range of L ₂ / L ₁ is _{0.1 ≦ L 2 / L 1 ≦} 1.5.

In this embodiment, V ₁ = 1000V, V ₀ = 950V,
L ₂ / L ₁ = 1.2. Also, the photoconductor potential of the exposed area is 10
V.

The exposure light attenuation curve of light sensitivity in a position corresponding to the exposure medium term that is attenuated to a half the initial potential V ₀ which is the E _1/2, attenuated the initial potential V ₀ which until 9/10 When the photosensitivity at the position corresponding to the initial stage is E _9/10 , (E _1/2 ) / (E _9/10 ) ≧ 2, preferably (E _1/2 ) / (E _9/10 ) ≧ A photoconductive semiconductor that provides the relationship of 5 is selected. Here, the photosensitivity is defined by the absolute value of the potential decrease amount with respect to the minute light amount.

The light attenuation curve of the photoconductor 1 has a small absolute value of the differential coefficient of the potential characteristic which is the photosensitivity as shown in FIG. 3 when the amount of light is small, and attenuates sharply as the amount of light increases. Specifically, as shown in FIG. 3, the light attenuation curve shows that the sensitivity characteristic is poor and the level is almost flat in the early stage of exposure for a short period L ₁ , but the light attenuation curve is in the middle of the exposure L ₁ to L _2. Over the course of time, the sensitivity becomes extremely high, and the sensitivity becomes extremely high γ, which drops almost linearly. It is considered that the photoreceptor 1 specifically obtains a high γ characteristic by utilizing an avalanche phenomenon under a high charge of +500 to + 2000V. That is, the carriers generated on the surface of the photoconductive pigment in the initial stage of exposure are effectively trapped in the interface layer between the pigment and the coating resin, and the light attenuation is surely controlled. It is understood that a phenomenon occurs. Such a photoconductor has a characteristic that it is not conspicuous on a straight line because recording is performed in a binary manner even if the photoconductor has uneven charging or cleaning failure.

The basic operation of the copy process of this embodiment is as follows.
When a copy start command is sent to the control unit 101 from an operation unit (not shown), the control unit 101 controlled by the CPU 100
The photoconductor 1 starts to rotate in the arrow direction by the drive motor M. As the photoconductor 1 rotates, its peripheral surface is cleaned by the charging / cleaning device 20 and uniformly charged. An image is written on the photoconductor 1 by, for example, a laser beam L from an image writing device A controlled by the CPU 100, and an electrostatic latent image corresponding to the image is formed.

A DC or further AC bias voltage is applied to the developing sleeve 31 of the developing device 30, and non-contact development is performed by a two-component developer which is a developing means to form a toner image. Contact development with a two-component developer or a one-component developer using a contact or non-contact development method may be used.

The toner images thus formed on the peripheral surface of the photoconductor 1 are sent one by one from the sheet feeding cassette (not shown) by the first sheet feeding roller in the transfer section, and the toner image is formed by the second sheet feeding roller 42. It is sent out in time with and is moved in the direction of the arrow.

That is, the toner image is transferred onto the transfer material by bringing the transfer belt 50, which is used as a transfer means, which has been rotated before the start of transfer, into contact with the photosensitive member 1 through the transfer material.

The transfer belt 50 is stretched between a roller 59 and a roller 60, and is rotated in synchronization with the peripheral speed of the photosensitive member 1 by the rotational driving of the roller 60, and the bias roller 58 moves up and down. As a result, the transfer belt 50 is separated from or brought into contact with the photoconductor 1.

As the transfer belt 50, a rubber belt containing a conductive cloth is used as a base, and a high resistance layer or an insulating layer made of an elastic body having a thickness of 0.5 mm is provided on the outer periphery thereof.

The transfer is performed by the bias roller 58, and a transfer potential having a polarity opposite to that of the toner is applied to the bias roller 58 from the bias power source 581 to perform the transfer. The toner attached to the transfer belt 50 is removed and cleaned by the transfer belt cleaning device 53.

The transfer material thus transferred with the toner image is
The toner is separated from the peripheral surface of the photoconductor 1 and conveyed to a fixing unit (not shown), and the toner is melted and fixed by the fixing roller, and then discharged to the outside of the apparatus via the paper discharge roller.

On the other hand, the photosensitive member 1 from which the transfer material has been separated is discharged by the discharging lamp 51 and then charged and cleaned by the charging and cleaning device 20.
The residual toner is removed and cleaned by and the printer waits for the next print.

FIG. 2 is a sectional view showing an embodiment of the charging / cleaning device 20 of the present invention used in the electrostatic recording device of FIG. In FIG. 2, 21 is a magnetic particle, for example, a spherical ferrite particle coated so as to have conductivity is used. In order to perform good charging, the outer shape is spherical and the particle size is adjusted to 50 μm and the specific resistance is set to 10 ⁸ Ω · cm. In addition, it is also possible to use conductive magnetic resin particles obtained by crushing magnetic particles and a resin as the main components after the skillfulness.

22 is a conductive cylinder made of non-magnetic metal,
Reference numeral 23 denotes a columnar magnet (roll) arranged inside the conductive cylinder 22, and this magnet 23 is magnetized so that the S pole and the N pole are arranged in FIG.
22 is rotatable with respect to a fixed magnet 23. Further, the magnet 23 may rotate as a magnetic pole having an equal pole. The magnetic force of the magnet 23 is 600 gauss or more, and the magnetic particles 21 are rotated at a peripheral velocity of 0.2 to 2.0 times in the direction opposite to the moving direction of the photoconductor 1 at the facing position of 50 emu / g.

Gear 22 provided integrally with the conductive cylinder 22
In contrast to 1, it is rotationally driven by the drive motor M1 as shown in FIG. The drive motor M1 is connected to the output device 102 controlled by the CPU 100, and its rotation is controlled via the output device 102 by a control signal from the CPU 100. 1
Reference numeral 03 denotes the CPU 10 for inputting image information such as a document not shown.
It is a control means for controlling the rotation of the conductive cylinder 22 according to the image information.

Reference numeral 24 is a bias power supply for applying a bias voltage between the conductive cylinder 22 and the grounded conductive support 1C, and the conductive cylinder 22 is grounded via the bias power supply 24.

The bias power supply 24 is a power supply for supplying an AC bias voltage in which an AC component is superposed on a DC component set to the same value as the voltage to be charged, and is applied via the protection resistor 24a. The conditions for applying the voltage vary depending on the size of the gap between the conductive cylinder 22 and the photoconductor 1, the charging voltage of the photoconductor 1, etc., but the gap is maintained between 0.1 and 5 mm, and is almost the same as the voltage to be charged. Peak-Peak to the same DC component of 500-1000V
A preferable charging condition could be obtained by supplying an AC bias voltage on which an AC component of 200 to 3500 V was superimposed as a voltage. The frequency is 300H to avoid uneven charging.
_Z to 10 KH _Z is preferred.

The bias power source 24 performs constant voltage control for the DC component and constant current control for the AC component.

Reference numeral 25 denotes a casing forming a storage portion for the magnetic particles 21, the conductive cylinder 22 and the magnet 23 are arranged in the casing 25, and a regulation plate 26 is provided at the outlet of the casing 25. Therefore, the thickness of the layer of the magnetic particles 21 attached to and discharged from the conductive cylinder 22 is regulated according to the set developing gap, and the gap between the photoconductor 1 and the conductive cylinder 22 is regulated. Are connected by 21 layers of magnetic particles whose thickness is regulated. 27 is a collecting roller that collects the toner T by applying a bias voltage having a polarity opposite to the charging of the toner T, 28 is a stirring plate that rotates around a plate member that corrects the bias of the magnetic particles 21, and 29 is collecting A collection blade for scraping off the toner T collected from the roller 27, and a collection screw 91 for carrying the collected toner T to the collection box or the developing device 30.

In the above embodiments, the conductive cylinder is used.
FIG. 5 shows the results of changing the frequency and voltage of the AC voltage component applied to 22.

In FIG. 5, the range shaded by vertical lines is the range where dielectric breakdown is likely to occur, the range shaded by diagonal lines is the range where uneven charging is likely to occur, and the range not shaded is stable. This is a preferable range in which electrostatic charging is obtained. As is clear from FIG. 5, the preferable range changes slightly depending on the change of the AC voltage component. The waveform of the AC voltage component is not limited to a sine wave, and may be a rectangular wave or a triangular wave. Further, in FIG. 5, the low frequency region shaded with dots is a range where uneven charging occurs due to the low frequency.

Next, the charging and cleaning device 20 described above
The operation of will be described.

While rotating the photoconductor 1 in the direction of the arrow, the control unit 101 receiving the control signal from the CPU 100 drives the drive motor M and the gear 221 to move the conductive cylinder 22 in the opposite direction of the arrow to the periphery of the photoconductor 1. When rotated at a peripheral speed of 0.2 to 2.0 times the speed, the layer of magnetic particles 21 is magnetically connected at the position facing the photoconductor 1 on the conductive cylinder 22 by the magnetic lines of force of the magnet 23 to form a kind of brush. That is, a so-called magnetic brush 20A is formed. Then, the magnetic brush 20A is conveyed in the rotating direction of the conductive cylinder 22 and rubs against the photosensitive layer 1A of the photoconductor 1,
The transfer residual toner T attached to A is supplemented. Conductive cylinder 22
Since the AC bias voltage is applied between the photoconductor 1 and the photoconductor 1, electric charges are injected into the photoconductive layer 1A through the conductive magnetic particles 21 to perform charging. In this case, since the bias voltage is an AC bias voltage, extremely stable charging can be performed. At this time, the transfer residual toner T remaining on the photoconductor 1 is electrostatically rubbed against the control unit 101.
Under the control, the magnetic brush 20A is rotated by a certain number of times and is conveyed by being attracted to the magnetic brush 20A, reaches the collecting roller 27, and is attracted by the bias voltage having a higher potential applied to the collecting roller 27 and is transferred to the collecting roller 27. The transfer residual toner T transferred to the collecting roller 27 is scraped off by the collecting blade 29, falls to the bottom of the casing 25, and is conveyed by the collecting screw 91 to the developing device 30 as a collecting box (not shown) or recycled toner.

The above cleaning operation is a case in which an average toner image is formed on the photoconductor 1 and cleaning and charging are performed. For example, a toner image having a larger number of recording dots than the average toner image, for example, a black solid image. When an image with many portions or thick characters is input to the CPU 100 and an image is written by the laser beam L from the image writing device A, the transfer belt 50 and the bias roller 58 shown in FIG. Even if the toner image is transferred onto the surface of the photoconductor 1, a large amount of untransferred toner remains on the surface of the photoconductor 1 and is conveyed to the cleaning device 20. Therefore, when such a toner image having a large number of recording dots is written by the image writing device A, the CPU 100 sends the recording dot number information to the control means 103, and when the number of recording dots is larger than the specified value, the recording is performed. The start of the next image forming process is delayed from when forming a toner image with a small number of dots, during which the conductive cylinder 22 is rotated to substantially completely remove the residual toner in the formed magnetic brush 20A and on the surface of the photoreceptor 1. By doing so, the charging performance is restored.

Therefore, when the number of recorded dots is large, the cleaning device 20 is operated for a certain period of time, and the CPU 100 controls the image formation to be slightly delayed so that the next exposure operation is not started immediately. A bias for charging the surface of the photoconductor 1 can be applied during the cleaning operation.

Further, the time for delaying the next image forming process may not be determined by a specific prescribed value but may be determined continuously in proportion to the dot number information. By doing so, cleaning and charging failure can be prevented.

Transfer is not performed due to a jam or the like,
When a large amount of toner image remains on the surface of the photoconductor 1, a longer delay time is set in order to perform the step of removing the residual toner from the magnetic brush 20A and the photoconductor 1 for a specific long time. Is preferred. As for the delay time, the average of the toner adhesion state after cleaning is directly detected on the surface of the photoconductor 1 by the photosensor P1 shown in FIG. 1, and when the toner adhesion amount is below a certain amount, the next image forming process is started. You may do it.

Alternatively, the average of the toner adhesion amount before the cleaning is started may be detected by the photosensor P2 shown in FIG. 1, and the delay time for the next image forming process may be determined in advance.

When the cleaning device 20 is being cleaned and charged, when the magnetic particles 21 at the tips of the magnetic brush reach the position of the stirring plate 28 and are scraped off and stirred by the stirring plate 28, the magnetic particles 21 of the magnetic brush are It is constantly replaced. Further, as described above, since the toner T mixed in the magnetic particles 21 is immediately collected, it is prevented that the resistance of the magnetic particles 21 becomes high and the charging ability is lowered due to the mixing of the toner T, and it is always stable together with the AC bias voltage. The uniform charging is also performed at the same time.

Further, a toner having a high γ characteristic as in the embodiment shown in FIG. 1 is used, and further, an infrared ray transmissive toner having a light wavelength of 750 mm or more as described in JP-A-2-271371. When T is used, even if some toner T remains, it does not matter if it is not accumulated in one portion. Therefore,
In this embodiment, a good cleaning effect was obtained by the magnetic brush 20A, but even if the toner T was not completely recovered, in the case of reversal image formation using reversal development or the infrared transmissive toner T on the photoconductor 1. Since it has a leveling effect of evenly dispersing, it is an excellent cleaning means. In the present embodiment, non-charging can be performed by setting the DC component of the bias voltage to zero. Further, when the N-S direction of the magnetic pole of the magnet 23 is rotated so as to be parallel to the tangent line of the facing portion of the photoconductor 1, the ears of the magnetic brush are parallel to the tangential direction of the facing portion of the photoconductor 1 due to the horizontal magnetic field. Since the tip of the magnetic brush is separated from the photoconductor, it can be in a non-charged and non-cleaning state.

The charging and cleaning device of the present invention uses a two-component developer for development, for example, when the photoreceptor 1 is positively charged, (a): In the case of positive development, the toner T is negatively charged. .
In this case, magnetic particles are used that negatively charge the toner T by frictional charging. (B): In the case of reversal development, the toner T is positively charged. In this case, if the magnetic particles are those that positively charge the toner T, the same magnetic particles 21 as the carrier of the developer can be used, and the recovery of the toner T can be performed efficiently. It becomes a cleaning device.

[0064]

According to the present invention, since the electric charge is directly injected into the photosensitive member with the above-described structure, the bias voltage can be lowered, the generation of ozone can be prevented, and the bias voltage can be changed to the AC bias voltage. Therefore, it is possible to prevent deterioration of the photoconductor, perform extremely stable and uniform charging, and clean the surface of the photoconductor. Further, in the present invention, after the toner image formed on the photoconductor is transferred to the transfer material, the cleaning device 20 is operated in accordance with the amount of the residual toner remaining on the photoconductor surface to remove the residual toner on the photoconductor surface. Therefore, a good image can be always formed.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an image forming apparatus including a charging and cleaning device of the present invention.

FIG. 2 is a sectional view showing an embodiment of the charging and cleaning device of the present invention.

FIG. 3 is a graph showing characteristics of a high γ photoconductor.

FIG. 4 is a sectional view showing an example of the configuration of a high-γ photoconductor.

FIG. 5 is a charging characteristic diagram when the frequency and voltage of the AC voltage component are changed.

[Explanation of symbols]

 1 Photoreceptor 20 Charging and Cleaning Device 21 Magnetic Particles 22 Conductive Cylinder 23 Magnet 24 Bias Power Supply 25 Casing 26 Regulation Plate 27 Recovery Roller 28 Stirrer Plate 29 Recovery Blade 100 CPU 101 Control Unit 102 Output Device 103 Control Means A Image Writing Device M , M1 Drive motor T Toner P1, P2 Photo sensor

Claims (2)

[Claims] 1. An image forming apparatus comprising at least a developing means, a transfer means, and a means for both charging and cleaning centering on the image carrier, and a toner image formed on the surface of the image carrier by the developing means. An image forming apparatus characterized in that, when the amount of toner is larger than the average amount of toner, the means for both charging and cleaning is operated for a predetermined time according to the amount of toner before the next image formation. 2. The image forming apparatus according to claim 1, wherein the toner amount is determined by the number of recording dots when forming an image.