JP2003021950A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the prevention of the lowering of the performance of a contact electrifying member compatible with the prolongation of the life of a body to be electrified in a tandem drum type image forming device. SOLUTION: This image forming device has a plurality of image forming units Y, M, C and K where an electrifying member 2 to which voltage is applied is made to abut on the body to be electrified 1 so as to electrify the body 1, the electrostatic latent image of image information is formed on the electrified surface of the body 1, and the electrostatic latent image formed on the body 1 is made visualizable as a toner image by a developing device, and the toner images formed by the respective image forming units Y, M, C and K are successively transferred to material to be transferred 6 so as to form an image. In a state where image forming processing is performed in at least one of the image forming units Y, M, C and K, the body to be electrified in the image forming unit for which the image forming processing is not performed is processed to be electrified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention charges a charged member by bringing a charging member to which a voltage is applied into contact with the charged member.
An electrostatic latent image of image information is formed on the charge-treated surface of the charged body,
Having a plurality of image forming units that visualize the electrostatic latent image formed on the charged body as a toner image by the developing device,
By sequentially transferring the toner image formed by each image forming unit onto the transfer material, a full-color image,
The present invention relates to a so-called tandem drum type image forming apparatus that forms images such as multicolor images and multiple images.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic or electrostatic recording type image forming apparatus, a member to be charged (image carrier) such as an electrophotographic photosensitive member or an electrostatic recording dielectric is subjected to a charging process (including a destaticizing process). A corona charger was often used as a means for doing this.

This is because a corona charger is disposed so as not to contact a member to be charged and the surface of the member to be charged is exposed to a discharge corona generated by the corona charger so that the surface of the member to be charged is charged to a predetermined polarity and potential. It is a thing.

In recent years, a contact charging device (direct charging device) has been put into practical use because it has advantages such as low ozone and low power over a corona charger.

The contact charging device is a device in which a charging member to which a voltage is applied is brought into contact with an object to be charged (hereinafter referred to as a photoconductor) to charge the surface of the photoconductor to a predetermined polarity and potential.

A magnetic brush charging device using a magnetic brush as a contact charging member is preferably used from the viewpoint of charging and contact stability. In this magnetic brush charging device, a magnetic brush charging member is configured by magnetically restraining conductive magnetic particles as a magnetic brush directly on a magnet or on a sleeve containing the magnet, and the magnetic brush is charged. The photoreceptor is charged by contacting the body surface while stopping or rotating and applying a voltage thereto.

In magnetic brush charging, a charge injection layer is provided on the surface of the photoconductor, and a charge member to which a voltage is applied is brought into contact with the photoconductor to inject charges into the charge injection layer so that the surface of the photoconductor has a predetermined polarity. The injection charging method that charges the potential is
Regardless of whether or not the AC bias (alternating voltage) is superposed on the charging member, it is possible to obtain the surface potential of the photoconductor that is substantially equal to the applied DC bias (DC voltage).

Further, since this magnetic brush charging device also has a function as a cleaning device for collecting the transfer residual toner on the photoconductor after the transfer, it is possible to omit a dedicated cleaning device.

As described above, the magnetic brush charging device does not utilize the discharge phenomenon in which the photosensitive member is charged by using the corona charger, and the cleaning device for collecting the transfer residual toner on the surface of the photosensitive member. Since it is not necessary to separately provide the photosensitive member, the deterioration of the photosensitive member due to discharge and the abrasion of the surface layer by the cleaning device are small, and as a result, the service life of the photosensitive member can be extended.

Next, the full-color or multi-color image forming apparatus using the electrophotographic system or the electrostatic recording system can be classified into two types according to the image forming method.

First, photoconductors used for image formation are prepared in parallel for each color, and images formed on the respective photoconductors are transferred onto a transfer target (intermediate transfer member or transfer target material such as paper or OHT). The image forming apparatus is a so-called tandem drum type image forming apparatus in which an image is formed by sequentially transferring the image to the image forming apparatus. The other is a so-called one-drum type image forming apparatus in which developing devices for each color are prepared in parallel on one photoconductor, and the photoconductors are developed by the number of colors and sequentially transferred to the transfer target to form an image. Is.

Further, the tandem drum type image forming apparatus is
When forming an image of a single color (mainly black), an image forming unit of a target color (image carrier, charging device, exposure device,
Including a developing device and the like; hereinafter referred to as a process unit), it is roughly divided into two types due to the difference in the control method of the process unit.

One is a type in which a photosensitive member of a process unit that is not used is not rotated when a monochromatic image is formed. In the case of using this system, the photosensitive member of the process unit is in contact with the transfer device in contact with the photosensitive member. In order to prevent a speed difference from occurring and a scratch on the photoconductor or the like, it is necessary to provide a function of separating the photoconductor and the transfer device.

Further, when switching between multi-color and mono-color, the time required for the separating operation is generated, which may have an effect such as a substantial decrease in printing speed.

The other method is to rotate the photoconductor of a process unit which is not used at the time of monochromatic image formation, so that the above-mentioned problem does not occur.

In any of the systems, the process unit which is not used during monochromatic image formation is not subjected to the same charging process as in image formation, thereby preventing meaningless wear of the photoconductor. It is an object.

[0017]

However, in the tandem drum type image forming apparatus in which the above-mentioned contact injection charging method and the method of rotating the photoconductor of the process unit which is not used at the time of monochromatic image formation are combined. , The following problems occurred.

That is, the most commonly used transfer material is neutral paper for copying in copying machines or neutral paper for printers, which contains fillers made of various materials. .

Calcium carbonate is the most used of these fillers, but a small amount of calcium carbonate adheres and accumulates on the photoreceptor due to the contact of the paper with the photoreceptor during image formation. Is generally known.

In the photoconductor having a filler such as calcium carbonate accumulated on the surface thereof, the surface free energy is increased and the adhesion force of the photoconductor is increased, so that dust or magnetic fine powder which comes into contact with the surface of the photoconductor is easily attached.

As a result, in the contact type injection charging system in which the magnetic fine powder is used for charging, the amount of the magnetic particles used for charging attached to the photoconductor and detached from the charging device is apt to increase. As a result, there is a possibility that a problem may occur that the charging property is lowered.

Further, since calcium carbonate accumulated on the surface of the photoconductor binds to water molecules in the air, the surface resistance of the photoconductor is lowered and the electrostatic latent image on the photoconductor is disturbed, which is a problem of so-called image deletion. It tends to occur.

Here, in a normal image forming process, the adhering fillers and the like are removed by scraping the surface of the photoconductor in the charging process and the cleaning process of the photoconductor, which causes a substantial problem. Is extremely small.

However, in the method of rotating the photoconductor of the unused process unit during the formation of a monochromatic image, the photoconductor is not charged to prevent unnecessary wear of the photoconductor. Since it comes into contact with the material to be transferred (paper or the like), the ability to remove the filler and the like adhering to the surface of the photoconductor cannot keep up, and the above-mentioned problems occur.

Therefore, an object of the present invention is to solve the above-mentioned problems in the tandem drum type image forming apparatus, and to prevent the deterioration of the performance of the charging member and to extend the life of the member to be charged.

[0026]

The present invention is an image forming apparatus having the following configuration.

(1) A charging member to which a voltage is applied is brought into contact with the charged body to charge the charged body, and an electrostatic latent image of image information is formed on the charged surface of the charged body. An image is formed by having a plurality of image forming units that visualize the electrostatic latent image formed thereon as a toner image by a developing device, and sequentially transferring the toner image formed by each image forming unit onto a transfer material. 2. Description of the Related Art In an image forming apparatus that performs image formation, in a state in which at least one image forming unit among a plurality of image forming units is performing an image forming process, a charged body of a non-image forming unit is charged. An image forming apparatus, characterized in that:

(2) The image forming apparatus described in (1) is characterized in that an electrostatic latent image is formed by exposing image information on a charged surface of an object to be charged.

(3) The image forming apparatus according to (1) or (2), wherein the charging member of the image forming unit is a magnetic brush type charging member made of conductive magnetic particles.

(4) The image according to any one of (1) to (3), wherein the charging member of the image forming unit also functions as a cleaning device for collecting the transfer residual toner on the member to be charged. Forming equipment.

(5) In a state in which at least one image forming unit among the plurality of image forming units is performing the image forming process, the charging to be performed on the charged body of the image forming unit which is not performing the image forming process. The image forming apparatus according to any one of (1) to (4), wherein the processing is performed only with an AC electric field.

(6) The member to be charged is the photosensitive layer and the resistor 10 ⁹
The image forming apparatus according to any one of (1) to (5), which has a surface layer composed of a resin and conductive fine particles of 10 ¹⁴ Ω · cm.

(7) The image forming apparatus according to (6), wherein the conductive particles are SnO ₂ .

<Operation> In the present invention, the image forming process is not performed in the state where the image forming process is performed in at least one of the plurality of image forming units of the tandem drum type image forming apparatus. By charging the member to be charged of the image forming unit, in particular, by charging only the AC electric field to the member to be charged, the member to be charged of the image forming unit is not subjected to the image forming process. By removing the transferred filler from the transferred material that accumulates on the surface of the charged body while preventing an increase in the amount of abrasion of the charged body, it is possible to achieve both prevention of performance deterioration of the charging member and extension of the life of the charged body. Is.

In the magnetic brush type charging system, a charging process is performed by applying a DC voltage superimposed on an AC electric field to a rotating magnetic brush charging member during normal image formation, but this DC voltage should not be superimposed. Thus, it is possible to remove the deposits accumulated on the surface of the charged body while suppressing the wear of the charged body to the minimum.

[0036]

1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention, and FIG. 2 is an enlarged schematic diagram of one of a plurality of image forming units.

The image forming apparatus of this example is an LED printer using a transfer type electrophotographic process, and has four cleaner-less type image forming units (hereinafter, process unit) for four colors of yellow, magenta, cyan and black. Y), M, C, and K are arranged in parallel,
It is a tandem drum type printer.

(1) Printer body The four process units Y, M, C and K for yellow, magenta, cyan and black all have the same construction.

In each of the process units Y, M, C and K, 1 is a rotary drum type electrophotographic photosensitive member which is an image bearing member as a member to be charged. In this example, OP with a diameter of 30 mm
Using C photoconductor, 100 mm / s in the clockwise direction shown by the arrow
It is rotationally driven at a process speed (peripheral speed) of ec. The layer structure of the photoconductor 1 will be described in detail in item (2).

Reference numeral 2 denotes a magnetic brush charging member (magnetic brush type charging device) for uniformly charging the peripheral surface of the photoconductor 1 to a predetermined polarity and potential, and for temporarily transferring transfer residual toner on the photoconductor surface. It is a sleeve type magnetic brush charging member that is physically collected and then discharged. The magnetic brush charging member 2 will be described in detail in section (3).

A predetermined charging bias DC + AC is applied to the sleeve of the magnetic brush charging member 2 from the charging bias applying power source E1 at the time of image formation, and the outer peripheral surface of the rotary photosensitive member 1 is charged substantially uniformly by charge injection charging. To be done.

Image exposure is performed on the charged surface of the rotating photoconductor 1 in accordance with the time series electric digital pixel signals of the target image information output from the image exposure device 3, in this example, the LED array. An electrostatic latent image corresponding to the target image information is formed on the peripheral surface of 1.

For the electrostatic latent image, a developer prepared by mixing toner particles and magnetic particles (development carrier) in a fixed ratio was used.
4a, which is developed as a toner image by the component contact developing device 4, is a non-magnetic developing sleeve having a diameter of 16 mm and containing a magnet 4b. This developing sleeve is coated with the toner particles and the developing carrier to form a toner image on the surface of the photoreceptor. With the distance fixed at 500 μm, the photoconductor 1 is reversely rotated at the same speed and the developing bias voltage DC + AC is applied to the sleeve 4a from the developing bias applying power source E2. In this example,
Using a DC voltage of -500V and a rectangular AC voltage with a frequency of 2 kHz and a peak-to-peak voltage of 1.5 kV superimposed,
Development is performed between the sleeve 4a and the photoconductor 1. That is, the negatively charged toner carried by the developing sleeve 4a is attached to the image portion of the latent image by an electric field to perform reverse development.

The two-component developer used in this example is a toner particle in which titanium oxide having an average particle diameter of 20 nm is externally added by 1% by weight to a negatively charged toner having an average particle diameter of 6 μm produced by a pulverizing method. As the developing carrier, a magnetic carrier having a saturation magnetization of 205 emu / cm ^{3 and} an average particle diameter of 35 μm was used. A mixture of this toner and carrier in a weight ratio of 6:94 was used as a developer.

In each of the four process units Y, M, C, and K, the color of the toner image developed by the developing device 4 is yellow in the process unit Y, magenta in the process unit M, and process unit C. Is cyan and process unit K is black.

At the time of forming a full-color image, the image forming process is performed among the above-mentioned four process units Y, M, C and K under a predetermined connection sequence control, and the yellow component of the full-color image is formed in the process unit Y. A pattern image, a magenta component pattern image in the process unit M, a cyan component pattern image in the process unit C, and a black component pattern image in the process unit K are formed.

At the time of forming an image of a single black color, only the process unit K performs the image forming process, and the other process units Y, M and C do not perform the image forming process. However, the photoconductor 1 is rotationally driven, and the charging process for the photoconductor 1 is performed in a predetermined manner as described later.

The transfer roller 5b is brought into contact with the photosensitive member 1 of each of the process units Y, M, C, and K with a predetermined pressing force via the endless transfer belt 5a to form a transfer portion. The endless transfer belt 5a has a driving roller 5c and a turn roller 5d in which the transfer belt 5a is suspended and stretched.
Is driven to rotate in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed.

Transfer target material 6 fed from a sheet feeding unit (not shown)
Is introduced from the process unit Y side onto the ascending side belt of the transfer belt 5a at a predetermined control timing, and the transfer portions of the process units Y, M, C, and K are sequentially sandwiched and conveyed.

A predetermined transfer bias voltage DC is applied from the transfer bias applying power source E3 to the transfer roller 5b.
In this example, the transfer roller 5b had a resistance value of 5 × 10 ⁸ Ω measured by a roller resistance meter when 100 V was applied, and a DC voltage of +2 kV was applied. The transfer material 6 introduced into the transfer portion is nipped and conveyed at the transfer portion, and the toner images formed and carried on the surface of the rotary photoconductor 1 are sequentially transferred to the surface side thereof by electrostatic force and pressing force. Go. The material 6 to which the toner image has been transferred is separated from the surface of the photoconductor 1 and conveyed to the transfer portion of the next process unit.

When a full-color image is formed, the transferred material 6
Are sequentially conveyed through the transfer parts of the process units Y, M, C, and K, so that the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image, which are the color component pattern images of the full-color image, are transferred. The four toner images are sequentially superposed and transferred, and a full-color toner image is synthetically formed on the transferred material 6.

The material to be transferred 6 passes through the transfer portion of the last process unit K, is conveyed to a fixing device 7 composed of an upper heating roller 7a and a lower heating roller 7b, is subjected to a fixing process, and is subjected to a print image. Is output as.

At the time of forming a black monochromatic image, there is no transfer to the transfer material 6 at the transfer portion of the process units Y, M, and C, and the transfer material 6 transfers the black toner image at the transfer portion of the process unit K. Upon receipt, it is conveyed to the fixing device 7.

In this example, each process unit Y, M,
C and K are cleanerless, and the surface of the photoconductor 1 after the toner image is transferred to the transfer material 6 is cleaned by the magnetic brush charging member 2 which also functions as a cleaning device, after removing adhered contaminants such as residual toner. To be used for image formation.

The transfer residual toner collected from the surface of the photosensitive member 1 to the magnetic brush charging member 2 has a negative charging polarity which is a normal polarity due to friction with the magnetic particles of the magnetic brush and an applied bias to the magnetic brush charging member 2. Is electrostatically ejected from the magnetic brush charging member 2 to the surface of the photoconductor 1 again, and is carried to the developing section by the subsequent rotation of the photoconductor 1 and collected at the same time in the developing device 4 (cleaning at the same time as development). It The toner is taken in by the developing device 4 by a fog removing bias (a fog removing potential difference Vback which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor) during development.

(2) Photoreceptor 1 As the photoreceptor 1, a commonly used organic photoreceptor or the like may be used, but it is desirable to use a material having a resistance of 10 ⁹ to 10 ¹⁴ Ω · cm on the organic photoreceptor. By using one having a surface layer having a charge injection property, charge injection charging can be realized, which is effective in preventing ozone generation and reducing power consumption. In addition, it becomes possible to improve the charging property.

In this example, a negatively charged organic photoreceptor is used.
A photoreceptor 1 having the following five layers, first to fifth layers, provided in this order from the bottom on a drum base made of aluminum having a diameter of 30 mm
It was used by rotating at a rotation speed of 00 mm / sec.

First layer: an undercoat layer having a thickness of 20 μm provided to smooth defects and the like of the aluminum substrate.
Of the conductive layer.

Second layer: a positive charge injection preventing layer, which plays a role of preventing the positive charges injected from the aluminum substrate from canceling out the negative charges charged on the surface of the photoconductor, and the amylan resin and methoxymethylated nylon. By 10 ⁶ Ω
-It is a medium resistance layer with a thickness of 1 μm whose resistance is adjusted to about cm.

Third layer: a charge generation layer, which is exposed to light with a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin to generate positive and negative charge pairs.

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

Fifth layer: a charge injection layer, which is a coating layer of a material in which SnO ₂ ultrafine particles as conductive fine particles are dispersed in a binder of an insulating resin. Specifically, SnO ₂ having a particle size of 0.03 μm, which is obtained by doping an insulating resin with antimony that is a light-transmitting conductive filler to reduce resistance (conductivity).
This is a coating layer of a material in which 70% by weight of particles are dispersed in a resin. The coating solution prepared in this manner is used for dipping coating method, spray coating method, roll coating method,
Thickness of about 3μm by an appropriate coating method such as beam coating
To form a charge injection layer.

(3) Magnetic Brush Charging Member 2 The magnetic brush charging member 2 of this example is a fixed magnet roller 2a having a diameter of 16 mm, and a non-magnetic SUS sleeve 2b rotatably fitted on the magnet roller 2a. Magnetic brush layer 2c of magnetic particles (charging carrier) adhered and held on the outer peripheral surface of the sleeve by the magnetic force of the magnet roller 2a.
It is a sleeve rotation type.

The charge carrier constituting the magnetic brush layer 2c has an average particle size of 10 to 100 μm, a saturation magnetization of 20 to 250 emu / cm ³ , and a resistance of 1 × 10 ² to 1 × 1.
It is preferably 0 ¹⁰ Ω · cm, and 1 × 10 in consideration of the existence of insulation defects such as pinholes in the photoconductor 1.
It is preferable to use one having a resistance of ⁶ Ω · cm or more. Resistance value of the charging carrier, after which the bottom area is placed 2g of the magnetic particles in a metal cell of 228 mm ^2, weighted by 6.6 kg / cm ^2, are measured by applying a voltage of 100 V.

In order to improve the charging performance, it is better to use the one having the smallest possible resistance. Therefore, in this example, the average particle diameter is 25 μm, the saturation magnetization is 200 emu / cm ³ , and the resistance is 5.
A magnetic brush layer 2c was formed by using 40 × 10 ⁶ Ω · cm and magnetically adhering it to the outer peripheral surface of the sleeve 2b by 40 grams.

As the constitution of the charging carrier, a resin carrier formed by dispersing a magnet as a magnetic material in a resin to make it conductive and carbon black dispersed for resistance adjustment, or a surface of a magnetite simple substance such as ferrite is oxidized. There are used those whose resistance is adjusted by reduction treatment, or those whose surface is coated with resin to adjust the resistance.

The magnetic brush layer 2c of the magnetic brush charging member 2 is arranged in contact with the surface of the photosensitive member 1. The width of the contact nip portion (charging nip portion) between the magnetic brush layer 2c and the photoconductor 1 was 6 mm.

At the time of image formation, the charging bias applying power source E1 applies a predetermined charging bias DC to the sleeve 2b.
+ AC is applied to the sleeve 2b in the contact nip portion with the photoconductor 1 in the clockwise direction indicated by the arrow, which is the counter direction (reverse direction) to the rotation direction of the photoconductor 1, and the rotation speed of the photoconductor 1 is 100 mm / sec. On the other hand, the peripheral speed is 150 mm / se
By being driven to rotate by c, the surface of the rotating photoconductor 1 is rubbed by the magnetic brush layer 2c to which a charging bias is applied, and the surface of the photoconductor layer of the photoconductor 1 is uniformly charged by the injection charging method to a desired potential. Primary charging processing is performed.

In the present example, at the time of image formation, it is preferable to apply to the magnetic brush charging member 2 a charging bias in which a rectangular wave AC electric field having a frequency of 500 Hz and a peak-to-peak voltage of 800 V is superimposed on a DC voltage of -700 V. It was possible to obtain a charging property.

(4) Switching Control of Charging Bias In the charging bias applying power source E1, the switch SW is switched to the contact a side by a control circuit (not shown) at the time of image formation, so that a predetermined charging bias DC + AC is applied to the magnetic brush charging member 2. Is applied. Further, by switching the switch SW to the contact b side, only the AC voltage is applied to the magnetic brush charging member 2.

While the image forming process is being performed in at least one of the plurality of process units Y, M, C and K, while contacting the photoconductor 1 of the process unit which is not performing the image forming process. With respect to the magnetic brush charging member 2 that is rotationally driven, the switch SW is switched to the contact b side, and only a rectangular wave AC electric field 800V having a frequency of 500 Hz and a peak-to-peak voltage of 800 V is applied, so that the carbon dioxide accumulated in the photoconductor 1 is stored. It becomes possible to remove deposits such as calcium.

FIG. 3 is a graph in which the horizontal axis represents the number of sheets passed in the process unit Y, and the vertical axis represents the value obtained by the contact angle meter when pure water on the surface of the photosensitive member 1 of the process unit Y is used. Is.

The contact angle meter is one in which a water drop of a predetermined reagent is dropped on the surface of an object and the angle calculated from the angle between the top of the water drop and both ends in contact with the object surface is measured. Is a value that generally indicates the surface free energy of the object, and it can be considered that the surface free energy increases as the contact angle decreases, that is, the adhesive force on the surface increases.

FIG. 3 shows the transition of the contact angle of the photoconductor 1 by dropping a water droplet of 1 μl of pure water on the surface of the photoconductor 1 of the process unit Y for each predetermined number of sheets passed.

A in the graph of FIG. 3 is a DC voltage for each sheet-
Frequency 700Hz, voltage 500Hz, peak-to-peak voltage 80
Charging bias DC + superposed with 0 V rectangular wave AC electric field
When AC is applied to the magnetic brush charging member 2 that is rotationally driven, B is only when the magnetic brush charging member 2 is driven and rotated without charging, C is a rectangular wave AC electric field having a frequency of 500 Hz and a peak-to-peak voltage of 800 V. When the charging bias AC is applied to the magnetic brush charging member 2 that is rotationally driven,
The transition of the contact angle on the surface of each photoconductor is shown.

As can be seen from the graph of FIG. 3, the C photoconductor in which only a predetermined AC electric field is applied to the rotationally driven magnetic brush charging member 2 is higher than the uncharged B photoconductor, and DC and AC It can be seen that the surface contact angle is maintained at about the same level as that of the photoconductor of A to which the bias in which is superimposed is applied.

The surface resistance of each of the photoconductors A, B, and C when the number of sheets passed was 6000 was measured in a high temperature and high humidity environment at room temperature of 30 ° C. and humidity of 80%.
The surface resistance of the photoconductor of B was 1 × 10 ¹¹ Ω · cm or less, whereas the surface resistance of the photoconductors of A and C was 1 × 10 ¹² Ω · cm.
It kept above cm.

When an image was actually formed using the A, B, and C photoconductors, characters of 7-point character size could be output without problems for the A and C photoconductors, whereas the B photoconductor was output. Regarding the body, characters with a character size of 11 points or less were blurred and blurred characters were output.

Next, in FIG. 4, the horizontal axis represents the process unit Y.
Is the number of sheets passed through, and the vertical axis is the photoconductor 1 of A, B, and C.
In the image forming apparatus shown in this embodiment using
This is the amount of magnetic particles that have separated from the magnetic brush charging member 2.

Here, the recovery amount of the magnetic particles depends on the developing device 4
The same charging process as that for image formation was performed in the state where the developer of No. 2 was removed, and the amount adhered to the surface of the developing sleeve 4a by the magnetic force was measured for each predetermined number of sheets of paper to be examined.

As can be seen from the graph of FIG. 4, when the photoconductors of A and C are used, the magnetic brush charging member 2 is 1 / C compared with the case of using the B photoconductor in which no charging bias is applied. It was found that only magnetic particles in an amount of 10 or less were released.

Next, in FIG. 5, the horizontal axis represents the process unit Y.
Is the number of sheets passed through, and the vertical axis is the photoconductor 1 of A, B, and C.
This is a measurement of the amount of abrasion of the resin layer.

As can be seen from the graph of FIG. 5, the abrasion amount of the resin layer of the photoconductor of A applied to the magnetic brush charging member 2 for rotationally driving the charging bias in which the AC electric field is superimposed on the DC electric field is averaged per 10,000 sheets. Is about 1 μm, whereas the abrasion amount of the resin layer of the C photoconductor applied to the magnetic brush charging member 2 that rotationally drives only the AC electric field is 0.01 to 10,000 sheets.
The wear is suppressed to about 1/100 or less, about 0,015 μm.

In this example, the example in which the present invention is applied to the process unit Y has been described, but the same effect can be obtained in any process unit arranged in parallel.

(5) Others 1) The magnetic brush charging member 2 is not limited to the sleeve rotating type of the embodiment, but may be of a type in which magnetic particles are directly adsorbed and held by a magnet roller to rotate the magnet roller, or a non-rotating type. It may be a rotating type.

In the present invention, the contact charging member is not limited to the magnetic brush type.

2) The image exposure device 3 as the information writing means is not limited to the LED array of the embodiment, but may be another digital exposure device such as a laser scanner or a combination device of a light source and a liquid crystal shutter. It may be an analog exposure device such as an image forming / projecting device for a document image.

3) The image carrier is not limited to the photoconductor, but may be an electrostatic recording dielectric or the like. In this case, an electrostatic latent image is formed by selectively removing electricity by using a uniformly charged magnetic brush contact charging device of the embodiment or an image carrier surface as an electricity writing means such as an electricity removal needle array or an electron gun. To do.

4) Each image forming unit (process unit) may be equipped with a cleaning device.

5) The transfer device is not limited to belt transfer, but may be roller transfer, corona discharge transfer, pressure transfer, or the like.

6) An image forming apparatus may be used which forms an image by using an intermediate transfer means such as a transfer drum or a transfer belt.

[0092]

As described above, according to the present invention, an image forming unit that has not been subjected to image forming processing in a state in which at least one of the plurality of image forming units is performing image forming processing. By charging the member to be charged, especially because the charging process is only an AC electric field, it is possible to prevent an increase in the amount of abrasion of the member to be charged in the image forming unit not subjected to the image forming process, and By removing the transferred filler from the transferred material that accumulates on the body surface, it is possible to prevent deterioration of the performance of the charging member and to extend the life of the charged body.

[Brief description of drawings]

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

[Fig. 2] Configuration model diagram of one process unit part

FIG. 3 is a transition correlation diagram of the number of passed sheets and the contact angle on the surface of the photoconductor.

FIG. 4 is a transition correlation diagram of the number of passed sheets and the amount of magnetic particles leaked from the magnetic brush charging member in the developing device.

FIG. 5: Transition correlation diagram between the number of passed sheets and the scraped amount of the photoconductor

[Explanation of symbols]

1 Image bearing member (photoreceptor) 2 Magnetic brush charging member 2a magnet 2b sleeve 2c magnetic particles 3 Image exposure device (LED) 4 Developing device 4a sleeve 4b magnet 5a transfer belt 5b Transfer roller 6 Transfer material 7 Fixing device

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H030 AB02 AD02 AD03 AD17 BB01                       BB21 BB43 BB52 BB71                 2H068 AA05 AA08 CA37 FB13 FC01                       FC15                 2H200 FA02 GA12 GA23 GA31 GA44                       GA47 GB14 GB36 GB37 HA01                       HA21 HA29 HB01 HB12 HB17                       HB48 JA01 JB06 NA03 PA10                       PA21

Claims (7)

[Claims] 1. A charging member, to which a voltage is applied, is brought into contact with a member to be charged to charge the member to be charged, and an electrostatic latent image of image information is formed on the charged surface of the member to be charged. An image is formed by having a plurality of image forming units that visualize the electrostatic latent image formed on the toner image as a toner image by a developing device, and sequentially transferring the toner images formed by each image forming unit onto a transfer material. In the image forming apparatus that performs the image forming process, in a state where at least one image forming unit among the plurality of image forming units is performing the image forming process, the charged body of the image forming unit that is not performing the image forming process is charged. An image forming apparatus characterized by applying. 2. The image forming apparatus according to claim 1, wherein an electrostatic latent image is formed by exposing image information on a charged surface of a body to be charged. 3. The image forming apparatus according to claim 1, wherein the charging member of the image forming unit is a magnetic brush charging member made of conductive magnetic particles. 4. The image forming apparatus according to claim 1, wherein the charging member of the image forming unit also serves as a cleaning device for collecting the transfer residual toner on the charged body. 5. A charging process performed on an object to be charged of an image forming unit that has not been subjected to the image forming process while at least one of the plurality of image forming units is performing the image forming process. Is an alternating electric field only.
The image forming apparatus described in 1. 6. The member to be charged comprises a photosensitive layer and a resistance of 10 ⁹ to 10 ^9.
The image forming apparatus according to claim 1, further comprising a surface layer made of a resin and conductive fine particles of ¹⁴ Ω · cm. 7. The image forming apparatus according to claim 6, wherein the conductive particles are SnO ₂ .