JP3332835B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus having a charging member to which a voltage is applied and which can contact the image carrier to charge the image carrier, such as the printer.

[0002]

2. Description of the Related Art FIG. 9 is a schematic view showing an example of a transfer type electrophotographic apparatus (copier, printer, facsimile, etc.) as a conventional example of an image forming apparatus.

Reference numeral 101 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier, which is rotated at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow.

[0004] In the course of rotation of the photosensitive drum 101, the entire surface of the photosensitive drum 101 is subjected to pre-exposure by an pre-exposure device (eraser lamp) 102, and the electrical memory remaining in the previous image forming process is erased. Table 103
And then uniformly charged with a predetermined polarity and potential, and then image exposure means (not shown)
Upon receiving image exposure L by a laser beam scanning exposure unit, the uniformly charged surface is selectively neutralized (or attenuated in potential) corresponding to the exposed image pattern, thereby forming an electrostatic latent image. Then, the formed electrostatic latent image is developed as a toner image by a toner developing device 104 as a developing unit.

On the other hand, a transfer material (transfer paper) P as a recording medium is fed between a photosensitive drum 101 and a transfer corona charger 105 as transfer means at a predetermined control timing from a paper feed mechanism (not shown). The toner image on the surface of the photosensitive drum 101 is electrostatically transferred to the front surface of the transfer material P by charging the back surface of the transfer material P with a polarity opposite to that of the toner.

Next, the transfer material P is supplied to the separation corona charger 106.
Thus, the toner image is electrostatically separated from the surface of the rotating photosensitive drum 101, is introduced into a fixing device (not shown), undergoes a fixing process of a toner image, and is output as an image formed product (copy, print).

After the transfer of the toner image onto the transfer material P, the surface of the photosensitive drum 101 is cleaned by a cleaning device (cleaner) 107.
The toner is cleaned by receiving the transfer residual toner, and is repeatedly used for image formation.

In the above, a photoreceptor as an image carrier,
There are various configurations and methods for each means and device for an image forming process such as charging, exposure, development, transfer, fixing, and cleaning.

For example, as the charging means 103, a corona charger has been widely used conventionally. In this method, a corona charger is disposed opposite to a photosensitive drum in a non-contact manner, and the surface of the photosensitive drum is exposed to the corona discharged from the corona charger to charge the photosensitive drum surface to a predetermined polarity and potential.

Recently, a contact-type charging device has been put into practical use because it has advantages such as low ozone and low power as compared with the non-contact type corona charger. In this method, a contact charging member to which a voltage is applied is brought into contact with a photosensitive drum as a member to be charged, and the surface of the photosensitive drum is charged to a predetermined polarity and potential.

As the contact charging member, a magnetic brush contact charging member having a magnetic brush portion in which magnetic particles are magnetically constrained, and the magnetic brush portion is brought into contact with the photosensitive drum is preferably used from the viewpoint of charging contact stability. ing.

The magnetic brush contact charging member is formed by magnetically constraining conductive magnetic particles directly on a magnet or on a sleeve containing a magnet to form a magnetic brush portion. Then, the magnetic brush unit is brought into contact with the photosensitive drum, and a voltage is applied to the photosensitive brush to start charging the photosensitive drum.

Further, a brush provided with conductive fibers in the form of a brush (fur brush member contact charging member) or a conductive rubber roller (charging roller) formed of conductive rubber in a roll shape is also preferably used as the contact charging member. ing.

In particular, using such a contact charging member, a photosensitive drum of a photosensitive drum as a member to be charged has a surface layer (charge injection layer) in which conductive fine particles are dispersed on a normal organic photosensitive member. When an amorphous silicon photoreceptor is used, it is possible to obtain a charging potential on the photoreceptor surface substantially equivalent to a DC component of a bias applied to the contact charging member (Japanese Patent Application Laid-Open No. 6-3921).

Such a charging method (charging of a member to be charged by direct injection of charges) is referred to as "injection charging". If this injection charging is used, the charging of the member to be charged does not use a discharge phenomenon that is performed using a corona charger.
Complete ozone-less and low power consumption type charging becomes possible,
It is getting attention.

In recent years, such image forming apparatuses have been miniaturized. However, as described above, charging, exposure, development,
Each means of image forming process such as transfer / fixing / cleaning
Just reducing the size of each device has limited the overall miniaturization of the image forming apparatus.

As described above, the photosensitive drum 101 after the transfer
The upper transfer residual toner is collected by the cleaner 107 to become waste toner, but it is preferable that this waste toner does not come out from the viewpoint of environmental protection. Therefore, the above cleaner 1
07, the transfer residual toner on the photosensitive drum 101 is removed from the photosensitive drum 101 by “developing simultaneous cleaning” by the developing device 104, and is collected by the developing device 104.
An image forming apparatus of a “cleanerless system” having an apparatus configuration for reuse has also appeared.

Simultaneous development cleaning refers to a fog removal bias (a potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive drum) at the time of development after the next step. This is a method of recovering by taking a potential difference Vback). According to this method, since the transfer residual toner is collected in the developing device 104 and used in the subsequent process, waste toner can be eliminated, and troublesome maintenance can be reduced. In addition, the cleaner-less system has a great advantage in terms of space, and can greatly reduce the size of the image forming apparatus.

[0019]

One of the problems in the contact charging device is that the contact charging member in contact with the member to be charged picks up dirt and foreign matter on the surface of the member to be charged and becomes contaminated by the accumulation thereof. If the contact member is easily contaminated (deterioration of the contact charging member) and becomes in an unacceptable contaminated state, the member to be charged cannot be charged to a desired potential or uneven charging occurs, resulting in a decrease in charging ability.

In an image forming apparatus using a contact charging device as a charging means for an image carrier such as a photoreceptor, an image forming apparatus having a dedicated cleaner for removing transfer residual toner on the image carrier after transfer. Even so, while the image formation is repeated, toner particles and so-called external additives such as silica contained in the developer, which somewhat pass through the cleaner, are moved to the position of the contact charging member by the continuous movement of the image carrier. The contact charging member is liable to be contaminated because it is carried and adheres to and mixes with the contact charging member and accumulates.

Normally, the electric resistance of toner particles and silica is considerably higher than the resistance of the charging member. Therefore, if such toner particles or silica adhere or mix into the contact charging member, the contact member becomes contaminated more than allowable. In this case, the resistance of the entire or a part of the contact charging member increases, so that the image carrier cannot be charged to a desired potential, or charging unevenness occurs, and an image defect occurs.

The toner contamination of such a contact charging member,
The occurrence of image defects due to the above-mentioned problem is caused by the above-described “cleanerless method” which uses a contact charging means as a charging means for the photoconductor and does not have a dedicated cleaner for removing transfer residual toner on the image carrier after transfer. This is particularly noticeable in the image forming apparatus of the “system”.

That is, in the case of the image forming apparatus of the cleanerless system, the untransferred toner on the image carrier after the transfer is carried to the position of the contact charging member by the continuous movement of the image carrier, so that the contact charging member is moved. This is because the contact charging member is quickly and excessively contaminated with toner.

On the other hand, in recent years, copiers and printers have been introduced into offices and the like, and an image forming apparatus with high efficiency, that is, an image forming apparatus in which operations other than the printing operation are completed in as short a time as possible is desired. In particular, when the number of prints (job length) of one job (from the start of the image forming apparatus to the end of the predetermined continuous operation) is small, the request is high because the next job is waiting.

Therefore, when the job length is short, the time other than the printing operation is shortened as much as possible, and the deterioration of the contact charging member, that is, the occurrence of poor charging or uneven charging due to the contamination of the contact charging member due to durability is prevented. It is an object of the present invention to stably maintain a good contact charging capability over a long period of time and, in an image forming apparatus, to stably maintain a good quality image output for a long period of time.

[0026]

According to the present invention, there is provided an image bearing member for carrying a toner image, a charging member to which the image bearing member is charged and which can be brought into contact with the image bearing member for charging the image bearing member.
An image having a cleaning sequence for cleaning the charging member before at least the charging member starts charging for image formation of the image carrier, or after ending the charging for image formation of the image carrier. The forming apparatus includes an accumulating unit that accumulates the amount of toner consumed in the job. The necessary cleaning time obtained from the accumulated value of the accumulating unit and a cleaning permission determined based on at least one continuous image formation number of the job. The cleaning time is compared with the cleaning time, and if the required cleaning time is within the cleaning permitted time, the cleaning is performed for the required cleaning time, and if the required cleaning time exceeds the cleaning permitted time, the cleaning is performed for the cleaning permitted time. An image forming apparatus.

[0027]

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (FIGS. 1 to 4) (1) Schematic Configuration of Example of Image Forming Apparatus (FIG. 1) FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. . The image forming apparatus of the present embodiment is a laser beam printer using a transfer type electrophotographic process.

A is a laser beam printer, and B is an image reading device (image scanner) mounted on the printer.

A) Image reading device B In the image reading device B, reference numeral 31 denotes a platen glass fixedly arranged on the upper surface of the device, and is placed on the upper surface of the platen glass with the original G to be copied facing downward. Then, a document pressure plate (not shown) is placed over the document and set.

Reference numeral 32 denotes an image reading unit provided with a document irradiation lamp 32a, a short focus lens array 32b, a CCD sensor 32c, and the like. When a copy button (not shown) is pressed, the unit 32 opens the platen glass 3.
1 is moved forward from the home position indicated by the solid line on the left side of the glass to the right side along the lower surface of the glass, and is driven backward when the predetermined forward end point is reached, and the first home position indicated by the solid line Is returned to.

In the forward drive process of the unit 32,
The downward image surface of the set original G on the original platen glass 31 is sequentially illuminated and scanned from the left side to the right side by the original irradiation lamp 32a of the unit 32, and the original surface reflected light of the illumination scanning light is a short focal length lens. An image is incident on the CCD sensor 32c by the array 32b.

The CCD sensor 32c includes a light receiving section, a transfer section,
It consists of an output unit. The light signal is converted to a charge signal in the CCD light receiving unit, and is sequentially transferred to the output unit in synchronization with the clock pulse in the transfer unit. The analog signal thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to the printer A.

That is, the image information of the document G is photoelectrically read by the image reading device B as a time-series electric digital pixel signal (image signal).

B) Printer A In the printer A, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as an image carrier. The photosensitive drum 1 of this example has a negatively charged O
It is a PC photoreceptor. This photoreceptor 1 will be described later (2)
It will be described in detail in the section.

The photosensitive drum 1 has a predetermined peripheral speed in the counterclockwise direction indicated by an arrow around the center support shaft, and in this example, the rotational speed is 100 mm.
/ Sec, and during the rotation process, in the case of this example, the charging means 2 receives a uniform charging process of negative polarity.

The charging means 2 in this embodiment is a contact charging type magnetic brush charging device. The charging device 2 will be described later in detail in (3).

The uniformly charged surface of the rotating photosensitive drum 1 is modulated in accordance with the image signal output from the laser scanning unit (laser scanner) 3 and sent from the image reading device B to the printer A. The scanning exposure L is performed by the laser light, and the document G photoelectrically read by the image reading device B is formed on the surface of the rotating photosensitive drum 1.
The electrostatic latent images corresponding to the image information are sequentially formed.

The laser scanning section 3 includes a light emitting signal generator, a solid laser element, a collimator lens system, a rotating polygon mirror (polygon mirror), and the like.

In the case of performing laser scanning exposure L on the surface of the rotating photosensitive drum by the laser scanning unit 3, first, the solid-state laser element is turned on / off at a predetermined timing by a light emission signal generator based on an input image signal. Let it. The laser light emitted from the solid-state laser element is converted into a substantially parallel light beam by a collimator lens system, and further scanned in the direction of the arrow by a rotating polygonal mirror that rotates at a high speed in the counterclockwise direction of the arrow, and by the fθ lens group. An image is formed on the photosensitive drum surface 1 in a spot shape. By such laser light scanning, an exposure distribution for one scan of an image is formed on the photosensitive drum surface 1, and the rotation of the photosensitive drum 1 causes the photosensitive drum surface to scroll by a predetermined amount perpendicular to the scanning direction for each scan. Thus, an exposure distribution according to the image signal is obtained on the rotating photosensitive drum surface.

The electrostatic latent image formed on the surface of the rotating photosensitive drum 1 is sequentially developed as a toner image by the developing device 4 in a reversal manner in the case of this embodiment. The developing device 4 of this embodiment is a two-component contact developing type device. The developing device 4 will be described later in detail in section (4).

On the other hand, the transfer material P as a recording medium stored in the paper feed cassette 5 is fed out one by one by the paper feed roller 5a and fed into the printer A, where the registration roller 5b
Thus, at a predetermined control timing, the sheet is fed to a transfer portion T which is a contact nip portion between the photosensitive drum 1 and a transfer belt type transfer device 6 as a transfer unit.

The toner image on the side of the rotating photosensitive drum 1 is sequentially electrostatically transferred to the surface of the transfer material P fed to the transfer portion T by the transfer charging blade 6 d disposed inside the transfer belt 6. This transfer device 6 will be described later in detail in (5).

The transfer material P, to which the toner image has been transferred through the transfer portion T, is sequentially separated from the surface of the photosensitive drum 1 and is conveyed to the fixing device 8 by the conveying device 7, where the toner image is thermally fixed and copied. Or output as a print.

In this embodiment, a case where a cleanerless system having no cleaner before transfer and before primary charging is applied is shown, but a cleaner for cleaning residual toner after transfer and before primary charge may be provided.

After the transfer of the toner image onto the transfer material P, the transfer residual toner remains on the photosensitive drum 1. These transfer residual toners have both positive and negative polarities due to peeling discharge at the time of transfer. The transfer residual toner having a mixed polarity reaches the magnetic brush charger 20 as a contact charger. Particularly, the transfer residual toner having a positive polarity is collected in the magnetic brush portion 23 of the magnetic brush charger 20, and the magnetic brush The particles become negative due to frictional charging with the particles and are discharged onto the photosensitive drum 1, reach the developing section m of the developing device 4, and are collected by the fog removing electric field during development. Magnetic brush charger 20
Brush charger 2 to improve toner recovery
An alternating electric field is superimposed on the applied DC bias for zero.

When performing continuous copying, the untransferred toner reaches the charger 20 and the charger 20 charges the photosensitive member. The photosensitive member having the untransferred toner is exposed to an image, and A latent image is formed. When the latent image forming area reaches the developing section, a developing electric field for attaching toner from the developing sleeve to a bright part of the latent image is formed, and at the same time, a fogging electric field is formed from the dark part of the latent image to the developing sleeve. Simultaneous development cleaning is performed.

However, of the transfer residual toner, the negative polarity toner having a large charge amount is not recovered by the magnetic brush charger 20, nor is it recovered by the phenomenon device 4, and is again conveyed to the transfer portion T, and is transferred to the transfer material P. The image was transferred and sometimes caused an image defect. In order to prevent this, in this example, the magnetic brush charger 20 (first contact charging member), which is a contact charger, is upstream of the photosensitive drum rotation direction and downstream of the transfer unit T in the rotation direction of the photosensitive drum (magnetic brush). A conductive fiber brush having a bristle length of 6 mm, a penetration amount of about 1 mm, and a contact nip of about 3 mm with the photosensitive drum 1 (between the charger 20 and the transfer portion T) (flocking density 1
100,000 lines / inch ² , resistance value 5 × 10 ⁶ Ω) were provided as the auxiliary member 10 (second contact charging member).

The auxiliary member 10 serving as the second contact charging member is supplied with a power supply S of plus 500 V opposite to the DC charging polarity of the magnetic brush charger 20 serving as the first contact charging member.
4 was applied.

As a result, the transfer residual toner having a particularly large negative charge is primarily captured in the auxiliary member 10,
After being neutralized or charged to the positive electrode, it is sent out onto the photosensitive drum 1 again and collected by the magnetic brush charger 20 or collected by the developing device 4.

(2) Photosensitive Drum 1 (FIG. 2) As the photosensitive drum (photosensitive body) 1 as an image carrier, a commonly used organic photosensitive body or the like can be used.
Further, a photosensitive member using an inorganic semiconductor such as CdS, Si, or Se can also be used. Preferably, when an organic photoreceptor having a surface layer having a material having a resistance of 10 ⁹ to 10 ¹⁴ Ω · cm or an amorphous silicon photoreceptor is used, charge injection charging can be realized and ozone generation can be prevented. , And power consumption. Further, the chargeability can be improved.

The photosensitive drum 1 used in this embodiment is a negatively charged organic photosensitive member having a charge injection layer provided on the surface thereof. The photosensitive drum 1 is formed on a 30 mm-diameter aluminum drum base (hereinafter referred to as aluminum base). Are provided in order from the bottom. FIG. 2 is a model diagram of the layer structure.

The first layer 12 is a subbing layer, and is a conductive layer having a thickness of 20 μm provided for smoothing out defects or the like of the aluminum base 11.

A second layer 13; a positive charge injection preventing layer, which functions to prevent positive charges injected from the aluminum substrate 11 from canceling out negative charges charged on the surface of the photoreceptor; This is a medium resistance layer having a thickness of 1 μm and a resistance adjusted to about 1 × 10 ⁶ Ω · cm by nylon nylon.

Third layer 14: a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and which generates positive and negative charge pairs upon exposure to light.

Fourth layer 15: a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, negative charges charged on the surface of the photoreceptor cannot move through this layer, and only positive charges generated in the charge generation layer 14 can be transported to the surface of the photoreceptor.

Fifth layer 16: a charge injection layer, which is a coating layer of a material in which ultrafine SnO ₂ particles as conductive particles 16a are dispersed in a binder of an insulating resin. Specifically, a particle diameter of about 0.03 μm obtained by doping an insulating resin with antimony, which is a light-transmitting insulating filler, to reduce the resistance (to make it conductive).
This is a coating layer of a material in which m SnO ₂ particles are dispersed in a resin by 70% by weight.

The coating solution thus prepared was applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coating method, beam coating method, etc. to form a charge injection layer.

The volume resistivity of the charge injection layer (surface layer) is 10
^{It is 12} Ω · cm. By controlling the surface volume resistivity in this way, the direct chargeability is improved and a high-quality image can be obtained. The photoreceptor is not limited to OPC but a-Si
It can also be realized with drums, and can achieve higher durability.

Here, the volume resistivity of the surface layer is measured by arranging metal electrodes at intervals of 200 μm, flowing a preparation liquid of the surface layer between the electrodes to form a film, and applying a voltage of 100 V between the electrodes. Value. Measurements were made at a temperature of 23 ° C and a humidity of 50% RH
Is a value measured under the conditions of

(3) Charging Device 2 (FIG. 3) The charging device 2 in this embodiment is a magnetic brush charging device of a contact charging type. FIG. 3 is a schematic configuration diagram thereof. Reference numeral 20 denotes a magnetic brush charger as a contact charging member disposed in contact with the photosensitive drum 1.

The magnetic brush charger 20 of this embodiment is of a rotary sleeve type, and has a magnet roll 21 fixedly supported in a non-rotating manner and an outer diameter which is rotatably fitted around the outer periphery of the magnet roll in a concentric manner. A 16-mm non-magnetic sleeve (non-magnetic, conductive, charging electrode sleeve) 22;
A magnetic brush portion 23 of conductive magnetic particles (magnetic carrier for charging) and the like formed by being attracted and held on the outer peripheral surface of the non-magnetic sleeve 22 by the magnetic force of the magnet roll 21 inside the sleeve.

The magnetic brush charger 20 is disposed substantially parallel to the photosensitive drum 1 with the magnetic brush portion 23 in contact with the surface of the photosensitive drum 1. In this case, the magnetic brush charger 20 was arranged such that the contact nip width (charging area) n of the magnetic brush portion 23 formed on the photosensitive drum 1 was about 5 mm.

The charging magnetic particles constituting the magnetic brush portion 23 have an average particle diameter of 10 to 100 μm, a saturation magnetization of 20 to 250 emu / cm ³ , and a resistance of 1 × 10 ² to 1.
× is preferred of ^{1010 Ω} · cm. Considering that the photosensitive drum 1 has an insulation defect such as a pinhole, it is preferable to use a photosensitive drum having a resistance of 1 × 10 ⁶ Ω · cm or more. In order to improve the charging performance, it is better to use one having as small a resistance as possible. In this example, magnetic particles having an average particle diameter of 25 μm, a saturation magnetization of 200 emu / cm ³ and a resistance of 5 × 10 ⁶ Ω · cm are used. Was.

The resistance value of the magnetic particles is such that the bottom area is 228 mm.
After placing 2g of the magnetic particles in the ^second metal cell, 6.6kg /
The weight was measured in cm ² and a voltage of 100 V was applied for measurement.

The average particle size of the magnetic particles is represented by the maximum chord length in the horizontal direction, and the measurement was performed by microscopically selecting 300 or more particles at random, measuring the diameter, and taking the arithmetic average.

For the measurement of the magnetic properties of the magnetic particles, a DC magnetization BH characteristic automatic recording apparatus BHH-50 manufactured by Riken Denshi Co., Ltd. can be used. At this time, the diameter (inner diameter) is 6.5 m
m, magnetic particles in a cylindrical container with a height of 10 mm
The filling is carried out at about g weight, and the saturation magnetization is measured from the BH curve while keeping the particles from moving in the container.

As the magnetic particles, a resin carrier formed by dispersing magnetite as a magnetic material in a resin and dispersing carbon black for conductivity and resistance adjustment;
Alternatively, a material in which the surface of a single magnetite such as ferrite is oxidized and reduced to adjust the resistance, or a material in which the surface of a single magnetite such as ferrite is coated with a resin and the resistance is adjusted may be used. In the present embodiment, a ferrite surface whose resistance has been adjusted by oxidizing and reducing is used.

Non-magnetic sleeve 2 of magnetic brush charger 20
Reference numeral 2 denotes a counterclockwise direction of an arrow (counter direction) opposite to the rotation direction of the photosensitive drum 1 in the charging area n, which is 15 with respect to the rotational peripheral speed of the photosensitive drum 1 of 100 mm / sec.
It was rotated at 0 mm / sec.

A predetermined charging bias was applied to the non-magnetic sleeve 22 from the charging bias applying power source S1.

In the present embodiment, the charging conditions are as follows: a constant voltage control of -550 V, a substantially sine-wave DC bias and a frequency of 1 kHz.
z, a voltage with an AC bias superimposed with a peak-to-peak voltage of 700 V was applied.

With the rotation of the non-magnetic sleeve 22, the magnetic brush portion 23 rotates in the same direction and rubs the surface of the photosensitive drum 1 in the charging area n. The photosensitive drum 1 is provided on the photosensitive drum 1, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential.

In the case of this example, as described above, the photosensitive drum 1
Has a charge injection layer 16 on the surface thereof, so that the photosensitive drum 1 is charged by charge injection charging. That is, by applying a predetermined charging bias voltage to the non-magnetic sleeve 22, electric charges are given to the photosensitive drum 1 from the magnetic particles constituting the magnetic brush portion 23,
The surface of the photosensitive drum 1 is charged to a potential corresponding to the charging bias voltage. The non-magnetic sleeve 22 tends to have better charging uniformity as the rotation speed is higher.

Reference numerals 26 to 28 denote bias control systems for changing a voltage value applied to the magnetic brush charger 20 as a contact charging member. This will be described in detail in section (6).

(4) Developing device 4 (FIG. 4) As a toner developing method for an electrostatic latent image, the following a to d are generally used.
Are roughly divided into four types.

A. Non-magnetic toner is coated on the sleeve with a blade or the like, and magnetic toner is coated by magnetic force, transported, and developed in a non-contact state with the photoreceptor (one-component non-contact development). B. A method in which the toner coated as described above is developed in contact with the photoreceptor (one-component contact development). C. A method in which a mixture of toner particles and a magnetic carrier is used as a developer and conveyed by magnetic force to develop in contact with a photoreceptor (two-component contact development). D. Method of Developing the Two-Component Developer in a Non-Contact State (Two-Component Non-Contact Development) Among these, the two-component contact development method of c is often used from the viewpoint of high image quality and high stability. ing.

FIG. 4 shows a schematic configuration of the developing device 4 used in this embodiment. The developing device 4 of the present embodiment uses a mixture of non-magnetic toner particles and magnetic carrier particles as a developer, causes the developer to be held as a magnetic brush layer by a magnetic force on a developer carrying member, and The electrostatic latent image is developed as a toner image by being transported and brought into contact with the surface of the photosensitive drum 1 2
It is a component magnetic brush contact development type device.

Reference numeral 41 denotes a developing container; 42, a developing sleeve as a developer carrier; 43, a magnet roller as a magnetic field generating means fixedly disposed in the developing sleeve 42;
44 is a developer layer thickness regulating blade for forming a thin layer of the developer on the surface of the phenomenon sleeve, 45 is a developer stirring and conveying screw, 46 is a two-component developer housed in the developing container 41, and is a non-magnetic developer. Toner particles t and magnetic carrier particles c
Are mixed.

The developing sleeve 42 has a closest distance (gap) to the photosensitive drum 1 at least at the time of development.
The developer magnetic brush thin layer 46 a carried on the outer surface of the developing sleeve 42 is set to be in contact with the surface of the photosensitive drum 1. The contact nip m between the developer magnetic brush layer 46a and the photosensitive drum 1
Is a development area (developing part).

The developing sleeve 42 is driven at a predetermined rotational speed in the counterclockwise direction indicated by the arrow around the fixedly disposed magnet roller 43 at a predetermined rotational speed, and the developer 46 is applied to the outer surface of the sleeve in the developing container 41 by the magnetic force of the magnet roller 43. A magnetic brush is formed. The developer magnetic brush is sleeve 4
2 is conveyed together with the rotation of the roller 2, and is regulated by the blade 44 so as to be taken out of the developing container as a developer magnetic brush thin layer 46a having a predetermined thickness, conveyed to the developing section, and contacts the surface of the photosensitive drum 1 and continues. The rotation of the sleeve 42 returns the developer to the inside of the developing container 41 and is conveyed again.

That is, first, as the developing sleeve 42 rotates,
Current drawn by the N3 pole of the magnet roller 43
The image agent 46 is S_Two Pole → N₁ In the process of being transported with the poles,
A regulating blade arranged perpendicular to the developing sleeve 42
Is developed on the developing sleeve 42 by the
A thin layer 46a of the agent 46 is formed. Development with thin layer
Agent layer 46a is the main developing pole S of the developing section.₁ Is transported to
Ears are formed by magnetic force. This spike is formed
The electrostatic latent image on the photosensitive drum 1 is formed by the developer layer 46a.
Developed as a toner image, and then N_Three Pole ・ N_TwoPole rebound
Present by magnetic field The developer on the image sleeve 42 is
Returned to 1

A developing bias of a DC voltage (DC) and an alternating voltage (AC, AC voltage) is applied between the developing sleeve 42 and the conductive drum substrate of the photosensitive drum 1 by a developing bias applying power source S2.

In this example, DC voltage: -400 V alternating voltage; amplitude Vpp = 1500 V, frequency Vf = 30
A developing bias of 00 Hz is applied, and the toner t in the developer magnetic brush thin layer 46 a on the developing sleeve 42 side selectively adheres to the electrostatic latent image on the photosensitive drum 1 side in the developing section, so that the electrostatic image becomes a toner image. Developed as

In general, in the two-component developing method, when an alternating voltage is applied, the developing efficiency is increased, and the quality of the image becomes high. On the contrary, there is a risk that fogging is liable to occur. For this reason, fog is generally prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1.

The potential difference for preventing fogging is called a fog removing potential (Vback). This potential difference prevents toner from adhering to a non-image area of the photosensitive drum 1 during development.

The toner concentration (mixing ratio with the carrier) of the developer 46 in the developing container 41 gradually decreases as the toner is consumed for developing the electrostatic latent image. The toner concentration of the developer 46 in the developing container 41 is detected by a detection unit (not shown), and when the toner concentration falls to a predetermined allowable lower limit concentration, the toner replenishing unit 47.
Then, the toner t is supplied to the developer 46 in the developing container 41, and the toner replenishment is controlled so that the toner concentration of the developer 46 in the developing container 41 is always kept within a predetermined allowable range.

[0087] The two-component developer 46 used in the present example is composed of toner particles t;
1% by weight of titanium oxide having an average particle diameter of 20 nm was externally added.
Carrier c; saturation magnetization is 205 emu / cm^Three Average grain
A magnetic carrier having a diameter of 35 μm is mixed at a weight ratio of 6:94.

For the volume average particle diameter of the toner, for example, the one measured by the following measuring method is used.

As a measuring device, Coulter Counter T
A-II type (manufactured by Coulter), number average distribution,
Interface to output volume average distribution (made by Nikkaki)
And a CX-i personal computer (manufactured by Canon Inc.), and the electrolyte is 1% Na using primary sodium chloride.
Prepare C1 aqueous solution.

The measuring method is as follows.
In 150 ml, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant, and 0.5 to 50 mg of a measurement sample is further added.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and the particle size distribution of particles of 2 to 40 μm was measured using the Coulter Counter TA-II with a 100 μm aperture. Is measured to determine the volume distribution. From these determined volume distributions, the volume average particle size of the sample is obtained.

(5) Transfer Device 6 In this embodiment, the transfer device 6 (FIG. 1) is a transfer belt as described above.
Type. Reference numeral 6a denotes an endless transfer belt, which is driven.
It is stretched and suspended between the roller 6b and the driven roller 6c.
The rotation circumference of the photosensitive drum 1 in the forward direction of the rotation direction of the optical drum 1
It is rotated at a peripheral speed substantially equal to the speed. 6d is a transfer belt
6a is a transfer charging blade disposed inside the transfer belt 6a.
Of the ascending belt of the belt 6a against the photosensitive drum 1.
Transfer nick And forming a transfer portion T, and applying a transfer bias.
When a transfer bias is applied from the power source S3, the transfer material
The reverse polarity of the toner is charged from the back surface of P. This
The transfer material P passing through the transfer portion T
-The images are sequentially transferred electrostatically.

In this example, the belt 6a has a thickness of 75
A resin made of a μm polyimide resin was used.

The material of the belt 6a is not limited to a polyimide resin, but may be a polycarbonate resin,
Plastics such as polyethylene terephthalate resin, polyvinylidene fluoride resin, polyethylene naphthalate resin, polyetheretherketone resin, polyethersulfone resin, and polyurethane resin, and fluorine-based and silicon-based rubbers can be suitably used. The thickness is not limited to 75 μm, but is
000 μm, preferably 50 to 150 μm can be suitably used.

The transfer charging blade 6d used had a resistance of 1 × 10 ⁵ to 1 × 10 ⁷ Ω, a plate thickness of 2 mm and a length of 306 mm. This transfer charging blade 6d
Was transferred by applying a bias of +15 μA under constant current control.

(6) Control of bias applied to contact charging member As described above, in the contact charging device, the contact charging member, which is in contact with the member to be charged, picks up dirt and foreign matter on the surface of the member to be charged and accumulates the dirt and foreign matter, thereby causing a contamination state. If the polluted state is more than acceptable, the charged object cannot be charged to a desired potential, or charging unevenness occurs, and charging ability is reduced.

An image forming apparatus using a contact charging device is
Specialized in removing residual toner on the image carrier after transfer.
Forming apparatus having a cleaning device for
Even before image formation is repeated, cleaning
Immediately could not be removed by the device Cleaning equipment
Included in toner particles and developer that slip through at least
So-called external additives such as silica continue to move the image carrier
It is carried to the position of the contact band member and adheres to the contact charging member.
The contact charging member is gradually contaminated by accumulating due to
You. And, when the contamination of the contact charging member becomes more than allowable,
The resistance of all or part of the contact charging member increases.
The image carrier could not be charged to the desired potential
Or uneven charging, resulting in poor image quality.
It will be.

In FIG. 5, the horizontal axis represents the weight ratio of the mixed toner to the magnetic particles for charging in the magnetic brush charger 20 as a contact charger, and the applied DC bias is, for example, −5.
Regarding the photoreceptor potential at 50 V, the solid line indicates that the AC bias Vpp (peak-to-peak value) was 700 V, the one-dot chain line indicates that the AC bias was 400 V, and the dashed line indicates the CD bias. From this, it is understood that, for example, assuming that the potential lowering value due to toner mixing is 60 V, the allowable value of the toner mixing amount increases as the value of Vpp increases. The potential drop allowable value varies depending on developer characteristics, developing conditions, image processing methods, and the like.
When the process conditions were set based on the photoconductor potential when toner was not mixed, the photoconductor potential caused so-called fogging in which unintended toner was developed on a white background portion of an image.

FIG. 6 shows the AC applied to the magnetic brush charger when the weight ratio of the mixed toner to the magnetic particles in the magnetic brush charger 20 is 1% and 0.5%.
When the bias Vpp is set to 400 V, the solid line indicates
7 is a graph showing the weight ratio of the toner remaining in the magnetic brush charger to the time with a wavy line when the voltage is set to 0V.

FIG. 6 shows that after the charging device has finished charging the photosensitive member for image formation (for example, during the post-rotation of the photosensitive member), that is, the trailing end of the image area of the photosensitive member has passed the charging position. Thereafter, the peak-to-peak voltage Vpp applied to the charger for moving the toner from the magnetic brush charger to the photoconductor is 400 V
That is, Vpp is changed to a small value. In other words, when the charging device charges the photoconductor not for image formation (when charging a region that is to be an image area of the photoconductor) than when charging the photoconductor for image formation (when the photoconductor is charged). (When charging the non-image area)
By reducing the peak-to-peak voltage Vpp applied to the charger, the amount of toner remaining on the magnetic brush charger can be quickly reduced to a small value.

Note that the image area is an area in which image formation can be performed on arbitrary image information (the same area as the entire black image area).

The reason why the toner in the charger can be cleaned by reducing Vpp is that the polarity of the toner in the charger becomes the same as that of the toner at the time of development, as described with reference to FIG. This is because the smaller the value of Vpp, the larger the electric field in which the mixed toner moves to the photosensitive member. The same can be said that the larger the amount of mixed toner, the larger the amount of change in the amount of remaining toner. Also in this embodiment, it is possible to set the Vpp of the magnetic brush charger to, for example, only OV, that is, DC at the time of post-rotation. However, when the amount of mixed toner is large, the potential drop is large and fogging occurs in the developing unit. Since the potential becomes the photoconductor potential, it is necessary to change the DC voltage value of the magnetic brush charger or the DC voltage value of the developing bias. For this reason, in the present embodiment, the AC bias V
pp was set to 400V.

FIG. 7 shows the weight ratio of the mixed toner to the magnetic particles in the magnetic brush charger when the integrated value of the image information amount is plotted on the horizontal axis as a substitute numerical value of the toner consumption amount. . However, FIG. 7 shows a case where the above-described cleaning sequence is not used for the magnetic brush charger at the time of post-rotation. In addition, as an integrated value of the image information amount, the image information amount of A4 size and the entire Max density is set to 1
It was shown by the value as follows. This indicates that the amount of toner mixed in the magnetic brush charger has a correlation with the integrated value of image information. Also, A applied to the magnetic brush charger
When the C bias Vpp is 700 V, the allowable toner mixing amount is 1% from FIG. 5 and the integrated image information value is 3 from FIG.
It can be seen that up to 00 is an allowable value. FIG. 6 shows that when the toner mixing amount is 1%, the cleaning time is 10 seconds and the toner mixing amount can be sufficiently reduced. FIG. 8 shows the relationship of the cleaning time with which the amount of mixed toner can be sufficiently reduced with respect to the integrated amount of image information.

The image information integrating means integrates the digital signal described in the image reading device B before transferring it to the printer, for example, and indicates the ratio of the A4 size Max density image information amount to the printer. Not C
It is conceivable that the data is transferred to the PU and the CPU of the printer performs an operation such as integration. In addition, the printer has means for storing image information, and when the image-processed signal is temporarily stored in the storage means, the CPU of the printer can perform calculations such as counting and multiplication.

As means for integrating the toner consumption, instead of using the above-described method using a digital signal, the amount of toner in the developing device is optically detected, magnetic force is detected, The formed toner patch may be detected and integrated in accordance with such a detection signal. In addition, in response to a replenishment signal for replenishing toner to the developing device in accordance with the prediction of the amount of toner in the developing device. May be added.

On the other hand, at the timing when charging can be completed (voltage application is turned off), the developing operation is completed in the developing unit because the developing unit does not develop the potential lowering unit (for example, the rotation of the developer carrier is stopped and the developing bias falls) It is necessary to guarantee the potential until the transfer material ends, but in many cases, the potential can be finished before the transfer material is discharged. In this embodiment, charging can be completed before the transfer material is discharged for about one second. Therefore, even if the post-rotation, which is the cleaning operation of the magnetic brush charging, is performed for about one second before the end of the printer operation, the print end time is not substantially affected. Therefore, as an allowable cleaning time, for example, a job length 1 to 10 sheets is 1 second,
11 to 50 sheets for 2 seconds, 51 to 100 sheets for 3 seconds
Seconds, 1 second is added every 50 sheets, and 401 sheets or more are set to 10 seconds.

The number of copies is the number of copies that the image forming apparatus continuously copies in response to one input of an image formation start signal from outside, and one job is a time during the continuous copy operation. The longer the permissible cleaning time is, the longer the waiting time for starting the next job is. However, in this embodiment, the permissible cleaning time for one copy is increased because the permissible cleaning time is increased as the number of continuous copies increases. , Not so big.

As described above, the allowable cleaning time is determined according to the job length (the number of continuous copies), but the required cleaning time shown in FIG. 9 is calculated from the integrated image information value for one job. If the required cleaning time is within the allowable cleaning time, after the charging of the photoconductor for image formation is completed, the cleaning operation of the charger is executed for the required cleaning time. However, if the required cleaning time exceeds the allowable cleaning time, the cleaning operation is performed for the allowable cleaning time, and the difference is carried over to the next job. That is, the carry-over of the difference is performed by adding the previous cleaning insufficient time to the next cleaning required time or adding the image information integrated amount corresponding to the previous cleaning insufficient time at the time of the next job.

However, during the job, for example, when the integrated value of the image information amount is calculated for each sheet and exceeds 300, the cleaning operation for 10 seconds is performed before the printing operation of the next transfer material regardless of the number of continuous copies. Then, the operation for printing the remaining transfer material is started. This prevents a potential drop exceeding the fog allowable value. At this time, if the cleaning operation during the job is performed, the integrated value of the image information amount is reset to zero.

When the integrated value of the in-job image information amount is 300,
If the number exceeds the limit, the cleaning operation for a predetermined considerably long time may be performed after the end of the job, regardless of the number of continuous copies, so that the amount of toner in the charging device may be greatly reduced.

In the above example, the magnetic brush charging cleaning sequence is provided after the final print operation of the job has been completed (after the charging of the photosensitive member for image formation has been completed). A cleaning sequence for the previous job can be provided before the charging for image formation of the body is started, that is, before the leading end of the area to be the image area of the photoconductor passes the charging position, or there is continuous printing. In the area corresponding to the space between the transfer material and the next transfer material (the area that should be the non-image area of the photoconductor)
A cleaning operation can also be performed.

FIG. 1 shows an example in which the image of the photoreceptor is transferred to a transfer material such as paper. The image of the photoreceptor is transferred to the intermediate transfer member, and then transferred from the intermediate transfer member to the transfer material. Is also good.

[0113]

As described above, according to the present invention, the deterioration of the contact charging member, that is, the occurrence of poor charging and uneven charging due to durability can be prevented, and a high-quality image free from fogging can be formed in an image forming apparatus for a long time. Over a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment.

FIG. 2 is a schematic diagram of a layer configuration of a photoreceptor.

FIG. 3 is a schematic diagram of a magnetic brush charger and its control system.

FIG. 4 is a structural model diagram of a developing device part.

FIG. 5 is a diagram for explaining a toner mixing amount and a potential drop when different biases are applied to a magnetic brush charger;

FIG. 6 is a diagram for explaining a change in toner mixing amount when different biases are applied to the magnetic brush charger;

FIG. 7 is a diagram for explaining an integrated value of image information and an amount of toner mixed in a magnetic brush charger;

FIG. 8 is a diagram for explaining the amount of toner mixed in the magnetic brush charger and the required cleaning time.

FIG. 9 is a diagram for explaining a conventional example.

[Explanation of symbols]

 Reference Signs List A laser beam printer B image reading device 1 member to be charged 2 contact charging means 20 magnetic brush charger (contact charging member) 4 developing device 6 transfer device 8 fixing device

──────────────────────────────────────────────────続 き Continuing from the front page Examiner Shinichiro Takemura (56) References JP-A-8-110684 (JP, A) JP-A-9-31529 (JP, A) JP-A-7-31530 (JP, A) Japanese Unexamined Patent Publication No. Hei 9-305009 (JP, A) Japanese Patent Laid-Open No. Hei 9-244352 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 G03G 15/00 303 G03G 21/14

Claims (9)

(57) [Claims] 1. An image carrier that carries a toner image, and a charging member to which the image carrier is charged and to which a voltage is applied so that the image carrier can be charged. Before starting charging for image formation of the image carrier, or after ending charging for image formation of the image carrier,
An image forming apparatus including a cleaning sequence for cleaning the charging member, further comprising: an integrating unit configured to integrate a toner consumption amount during a job;
The required cleaning time obtained from the integrated value of the integrating means is compared with a cleaning permission time determined according to the number of continuous image formations of at least one job. An image forming apparatus which performs cleaning for a cleaning time, and performs cleaning for a cleaning permission time when a required cleaning time exceeds a cleaning permission time. 2. When the charging member performs charging for forming an image on the image carrier, a superimposed voltage of an AC voltage and a DC voltage is applied to the charging member. 2. The image forming apparatus according to claim 1, wherein a superimposed voltage of an AC voltage and a DC voltage having a smaller peak-to-peak voltage than the AC voltage or a DC voltage without an AC voltage is applied to the power supply. 3. The image forming apparatus according to claim 1, wherein the cleaning permission time increases as the number of continuous images formed in one job increases. 4. An apparatus according to claim 1, wherein said apparatus has writing means for writing an electrostatic latent image corresponding to image information on said image carrier charged by said charging member, and said integrating means integrates the integrated amount of image information. The image forming apparatus according to claim 1, wherein: 5. The method according to claim 1, wherein when the required cleaning time exceeds the permitted cleaning time, an insufficient cleaning time or an integrated amount of image information corresponding to the insufficient cleaning time is added to the next job. An image forming apparatus according to any one of 1 to 4. 6. If the required cleaning time is longer than the permitted cleaning time and the insufficient cleaning time or the integrated amount of image information corresponding to the required cleaning time reaches a predetermined value, continuous image formation after the end of the job is performed. 5. The image forming apparatus according to claim 1, wherein the cleaning sequence is performed for a predetermined time regardless of the number. 7. When the integrated amount of the image information reaches a predetermined value in the middle of one job, a cleaning sequence for a predetermined time in the middle of the job is performed regardless of the number of continuous image formations. 7. The image forming apparatus according to claim 1, wherein the image forming is performed. 8. The image forming apparatus according to claim 1, further comprising a developing unit configured to form a toner image on the image carrier, and a cleaner that charges the image carrier after the toner image is transferred onto a transfer material and before the charging member charges the image carrier. The image forming apparatus according to claim 1, wherein the developing unit is capable of cleaning residual toner from the image carrier. 9. The image forming apparatus according to claim 1, wherein the charging member includes a magnetic brush that contacts the image carrier, and the toner is moved from the charging member to the image carrier in the cleaning sequence. Any one of the image forming apparatuses.