JP3697023B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, a first image carrier (charged body) such as an electrophotographic photosensitive member or an electrostatic recording dielectric is set to a predetermined polarity and potential, such as a transfer type electrophotographic apparatus and an electrostatic recording apparatus. Charging means for uniformly charging, electrostatic latent image forming means for forming an electrostatic latent image on the charged image bearing member surface, developing means for developing the electrostatic latent image as a toner image, and the toner image on paper The image forming apparatus includes an image forming process unit including a transfer unit that transfers the image to a second image carrier, and the first image carrier relates to an image forming apparatus that repeatedly performs image formation.
[0002]
More specifically, toner particles (transfer residual toner) remaining on the first image carrier after the toner image of the first image carrier is transferred to the second image carrier by the transfer unit are collected in the developing unit. So-called cleaner-less, in which a dedicated cleaning means for removing the transfer residual toner on the surface of the first image carrier is omitted between the transfer means and the charging means. The present invention relates to an image forming apparatus of a system.
[0003]
[Prior art]
FIG. 9 is a schematic configuration diagram of an example of a transfer type electrophotographic apparatus (copier, printer, facsimile, etc.) as a conventional example of an image forming apparatus.
[0004]
Reference numeral 101 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as a first image carrier, which is rotationally driven at a predetermined peripheral speed (process speed) in the clockwise direction of an arrow.
[0005]
The photosensitive drum 101 is subjected to a uniform charging process with a predetermined polarity and potential by the charging means 102 during its rotation. The charging means 102 is a charging roller which is a contact charging member in this example. S 1 is a charging bias application power source for the charging roller 102. Next, an image exposure L by an image exposure means (not shown) (projection exposure means for a document image, laser scanning exposure means, etc.) is received. As a result, the uniformly charged surface of the photosensitive drum 101 is selectively neutralized (or potential attenuated) corresponding to the exposure image pattern, and an electrostatic latent image is formed on the surface of the photosensitive drum 101.
[0006]
The electrostatic latent image is developed as a toner image by the developing means 103. Reference numeral 103a denotes a developing member (developer carrying or conveying member such as a developing roller or a developing sleeve), and S2 denotes a developing bias application power source for the developing member 103a.
[0007]
On the other hand, a transfer material (transfer paper) P as a second image carrier is fed from a paper feed mechanism unit (not shown) to a transfer unit between the photosensitive drum 101 and the transfer unit 104 at a predetermined control timing. Then, the toner image on the surface side of the photosensitive drum 101 is sequentially transferred onto the surface of the sheet transfer material P. The transfer means 104 is a transfer roller in this example. S 3 is a power supply for applying a transfer bias to the transfer roller 104.
[0008]
Next, the transfer material P is separated from the surface of the rotating photosensitive drum 101 and introduced into a fixing means (not shown), undergoes a toner image fixing process, and is output as an image formed product (copy, print).
[0009]
The surface of the photosensitive drum 101 after the transfer of the toner image onto the transfer material P is cleaned by removing the transfer residual toner by a cleaning means (cleaner) 105 and repeatedly used for image formation.
[0010]
1) Contact charging device
In the image forming apparatus as described above, the photosensitive drum 101 as the first image carrier, and various means and devices 102 to 105 for the image forming process such as charging, exposure, development, transfer, cleaning, and fixing are various. There are methods and configurations.
[0011]
For example, a corona charger has been generally used as the charging means 102 for uniformly charging the surface of the photosensitive drum 101 as the first image carrier to a predetermined polarity and potential. This is because a corona charger is disposed in contact with the photosensitive drum in a non-contact manner, and the surface of the photosensitive drum is exposed to a corona shower generated from a corona charger to which a high voltage is applied, so that the surface of the rotating photosensitive drum has a predetermined polarity. It is charged to a potential.
[0012]
In recent years, contact charging devices have been put into practical use because they have advantages such as low ozone and low power over corona chargers.
[0013]
In the contact charging device, a conductive member whose resistance value has been adjusted is disposed as a contact charging member (contact charging means) in contact with an object to be charged, and a predetermined voltage (charging bias) is applied to the contact charging member. The charged object surface is charged to a predetermined polarity and potential.
[0014]
The contact charging member includes a roller type in which conductive rubber is rolled (charging roller, conductive rubber roller), a blade type in which conductive rubber is in a blade shape (charging blade), and a magnetic brush type (magnetic brush) using magnetic particles. Various types such as a charger and a fur brush type (fur brush charger) in which conductive fibers are formed in a brush shape are preferably used.
[0015]
A magnetic brush charger is one in which conductive magnetic particles are magnetically constrained and held as a magnetic brush directly on a magnet or on a sleeve containing the magnet, and the magnetic brush portion of the magnetic particles is stopped or The surface to be charged is brought into contact with the surface to be charged while being rotated, and a voltage is applied to the surface to be charged, so that the surface to be charged is contact-charged.
[0016]
There are a DC bias application method in which the charging bias applied to the contact charging member is only a DC voltage, and an AC bias application method in which an oscillation voltage having a DC bias component and an alternating bias component is used.
[0017]
2) Injection charging
Contact charging includes a system in which charging by a discharge phenomenon is dominant as disclosed in Japanese Patent Publication No. 3-52058 and the like, and a direct charge of a surface to be charged as disclosed in Japanese Patent Laid-Open No. 6-3921 and the like. There is a system (charge injection charging system) in which charging by injection (charging) is dominant.
[0018]
The charge injection charging method uses a contact charging member as described above, and has a surface layer in which conductive fine particles are dispersed on a normal organic photoconductor in the case of an image bearing member, which is charge-chargeable as an object to be charged. By using a photoconductor, an amorphous silicon photoconductor, or the like, it is possible to obtain a charged potential on the surface of the member to be charged that is substantially equal to the direct current component of the bias applied to the contact charging member.
[0019]
This charge injection charging method does not use a discharge phenomenon in which charging to the body of the object is performed using a corona charger, so the applied charging bias required for charging is equal to the desired surface potential of the body to be charged. Therefore, it has been attracting attention because it is possible to achieve complete ozone-less and low-power consumption charging without generation of ozone.
[0020]
3) Cleanerless system
As an image forming apparatus, an apparatus of a cleanerless system (cleanerless process) has been proposed from the viewpoints of ecology, downsizing and cost reduction of the apparatus.
[0021]
This cleaner-less system image forming apparatus omits the exclusive cleaning device 105 that is disposed between the transfer unit 104 and the charging unit 102 and removes transfer residual toner from the surface of the image carrier 101 after transfer. The transfer residual toner remaining on the surface of the subsequent image carrier 101 is the DC voltage (development bias) applied to the developing member 103a of the developing unit and the surface potential of the image carrier 101 at the development unit 103 during the subsequent development. It is removed and collected by a fog removal potential difference Vback which is a potential difference between them (so-called simultaneous development cleaning), and has the following advantages.
[0022]
(1). By omitting the provision of the dedicated cleaning device 105, there is a great space advantage, and the image forming apparatus can be reduced in size and cost.
[0023]
(2). The transfer residual toner collected by the developing means 103 is used again contributing to the development, so there is no waste toner (ecology).
[0024]
(3). Since there is no cleaning device 105, the surface of the image carrier is damaged by the rubbing between the cleaning element 105a such as a cleaning blade and the image carrier 101 in some cases, and the charge injection layer in the case of a charge injection chargeable image carrier. There is no damage.
[0025]
[Problems to be solved by the invention]
However, in the image forming apparatus using the contact charging method for charging the first image carrier, the cleaning unit is not provided, and the transfer residual toner is simultaneously collected by the developing unit (cleanerless system). When the image formation is repeated, since the transfer residual toner cannot be collected by the developing unit, a so-called “positive ghost” in which the previous image remains thin has occurred.
[0026]
This positive ghost cannot charge the image carrier portion below the transfer residual toner when the transfer residual toner on the first image carrier passes through the position of the contact charging member. This phenomenon occurs because the potential difference (Vback) for collecting the charge cannot be secured, and becomes more conspicuous when the contact charging member is contaminated.
[0027]
Therefore, when the first image carrier is charged by the contact charging member, the portion of the image carrier below the transfer residual toner is also charged. Therefore, the transfer residual toner is peeled off from the image carrier at the time of charging and is returned to the image carrier after charging. It is important to collect by developing means.
[0028]
In addition, since the toner particles usually have a relatively high electrical resistance against the contamination of the contact charging member, the toner particles are mixed into the contact charging member and can be sufficiently discharged to the image carrier. If not, the resistance of the entire or part of the contact charging member increases, and the image carrier cannot be charged to a desired potential, or uneven charging occurs, resulting in an image defect.
[0029]
The present invention has been proposed in view of the above, and relates to an improvement in transfer efficiency and contact charging for an image forming apparatus of a contact charging method / cleanerless system, particularly an image forming apparatus using a magnetic brush charger as a contact charging member. An object of the present invention is to provide a device capable of maintaining a good image output without image defects such as positive ghost for a long period of time by preventing resistance increase due to contamination of a magnetic brush charger as a member. To do.
[0030]
[Means for Solving the Problems]
The present invention is an image forming apparatus having the following configuration.
[0031]
  (1) Charging means for charging the first image carrier, latent image forming means for forming an electrostatic latent image on the charging surface of the first image carrier, and developing the electrostatic latent image as a toner image And a transfer means for transferring the toner image to the second image carrier, the developing means having the first image carrier after the toner image is transferred to the second image carrier. In the image forming apparatus that also serves as a cleaning unit that collects toner particles remaining on the upper transfer, and the first image carrier is repeatedly used for image formation.
  The charging means is a contact charging means for charging magnetic particles by bringing them into contact with the image carrier as a magnetic brush by the magnetic force of the magnetic field generating means,
  An image forming apparatus comprising supply means for supplying nonmagnetic conductive particles having an average particle size smaller than the average particle size of the magnetic particles to the magnetic brush.
[0032]
  (2)The conductive particles supplied to the magnetic brush have an average particle size of 10 nm or more (1)The image forming apparatus described.
[0033]
  (3)The volume resistance of the conductive particles supplied to the magnetic brush is less than or equal to the volume resistance of the magnetic particles of the contact charging means (1)Or (2)The image forming apparatus described in 1.
[0035]
  (4)The conductive particles supplied to the magnetic brush are white-based (1) to(3)The image forming apparatus according to any one of the above.
[0036]
  (5)The first image carrier has a resistance 10 on the surface.⁹-10¹⁴It has a layer made of a material of Ω · cm (1) to(4)The image forming apparatus according to any one of the above.
[0037]
  (6)The first image bearing member has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles.(5)The image forming apparatus according to any one of the above.
[0038]
  (7)The conductive fine particles are SnO.₂It is characterized by(6)The image forming apparatus described in 1.
[0039]
  (8)The first image carrier comprises a surface layer having amorphous silicon (1) to (1)(7)The image forming apparatus according to any one of the above.
[0040]
  (9)The bias applied to the contact charging means is a bias in which an alternating voltage is superimposed on a DC voltage (1) to (1)(8)The image forming apparatus according to any one of the above.
[0041]
  (10)The developing means is a contact development system in which toner development of an electrostatic latent image is performed in a state where the developer is in contact with the first image carrier (1) to (1).(9)The image forming apparatus according to any one of the above.
[0042]
  (11)The latent image forming means is an image exposure means for the charged surface of the first image carrier (1) to (1)(10)The image forming apparatus according to any one of the above.
[0043]
<Operation>
By supplying conductive particles to a contact charging member (magnetic brush charger) using magnetic particles, the magnetic binding force of the magnet in the charger is weaker than the magnetic particles in the magnetic brush charger (non-magnetic) In this case, there is no magnetic binding force), and the conductive particles are separated from the charger side little by little and supplied onto the first image carrier. For this reason, when image formation is repeated, the first image carrier is thinly covered with the conductive particles.
[0044]
In this way, the conductive particles cover the first image carrier, whereby the contact state force between the first image carrier surface and the toner image formed on the image carrier surface is weakened. By increasing the transfer efficiency of the toner image to the second image carrier at the part, it is possible to reduce the amount of untransferred toner conveyed to the magnetic brush charger side after transfer.
[0045]
In addition, the contact state force between the first image carrier surface and the transfer residual toner on the image carrier surface is also weakened, and the transfer residual in the charging portion which is the contact portion between the magnetic brush charger and the first image carrier. Disturbance and movement of the magnetic brush portion by rubbing of the toner, and peeling from the first image carrier surface side to the magnetic brush portion side of the magnetic brush charger (temporary transfer residual toner to the magnetic brush charger side) (Recovery) is easy.
[0046]
Thus, since the conductive particles are present on the magnetic brush portion of the magnetic brush charger and the first image carrier, the amount of residual toner is small, and charge injection into the conductive particles is performed. Since the lower surface of the image carrier is sufficiently charged, the occurrence of positive ghost can be prevented.
[0047]
Further, by supplying conductive particles to the magnetic brush portion of the magnetic brush charger, resin components such as toner and the first image carrier and external additives are added to the charging magnetic particles constituting the magnetic brush portion. The entire or part of the magnetic brush charger in the case where the agent or the like is fused, or the transfer toner is mixed in the magnetic brush part and cannot be discharged onto the first image carrier. As a result, it is possible to prevent the charging ability from being lowered due to an increase in resistance, and the durability is greatly improved.
[0048]
More preferably, the charging bias applied to the magnetic brush charger as the contact charging member is an oscillating voltage (alternating voltage) to increase the toner peeling force during charging and maintain the charging property for a longer period. become able to.
[0049]
In this manner, in the image forming apparatus in which the developing unit also serves as a unit for collecting the transfer residual toner, by supplying the conductive particles to the magnetic brush charging unit that is a contact charging member, the transfer efficiency is improved and the resistance of the magnetic brush charging unit is increased. Can be prevented and a good image can be obtained over a long period of time.
[0050]
DETAILED DESCRIPTION OF THE INVENTION
<Example 1> (FIGS. 1 to 5)
FIG. 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 model diagram of a main part thereof.
[0051]
The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process, a contact charging method using a magnetic brush charger, a reversal developing method, and a cleanerless system.
[0052]
In FIG. 1, A is a printer main body, and B is an image reader (image reading apparatus) mounted and installed thereon.
[0053]
(1) Image reader B
In the image reader B, reference numeral 10 denotes a fixed document table (transparent plate such as glass), and the document G is placed on the upper surface of the document table 10 with the surface on which the document G is to be copied facing down. Set with a crimping plate.
[0054]
An image reading unit 9 is provided with a document irradiation lamp 9a, a short focus lens array 9b, a CCD sensor 9c, and the like. When a copy start signal is input, the unit 9 is driven forward along the lower surface of the document table from the home position on the left side of the document table to the right side on the lower side of the document table 10 to obtain a predetermined forward movement end point. When it reaches, it is driven backward and returned to the initial home position.
[0055]
In the forward drive process of the unit 9, the downward image surface of the set original G on the platen 10 is illuminated and scanned sequentially from the left side to the right side by the document irradiation lamp 9 a of the unit 9. Is reflected on the CCD sensor 9c by the short focus lens array 9b.
[0056]
The CCD sensor 9c includes a light receiving unit, a transfer unit, and an output unit. The optical signal is converted into a charge signal in the CCD light receiving unit, and sequentially transferred to the output unit in synchronization with the clock pulse in the transfer unit. The charge signal is converted into a voltage signal in the output unit, amplified and reduced in impedance, and output. The analog signal thus obtained is subjected to known image processing, converted into a digital signal, and sent to the printer main body A.
[0057]
That is, the image information of the original G is photoelectrically read by the image reader B as a time series electric digital pixel signal (image signal).
[0058]
(2) Printer body A
a) 1 is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as a first image carrier. The photosensitive drum 1 is rotationally driven in a clockwise direction a indicated by an arrow with a predetermined peripheral speed (process speed) around a central support shaft. The photoconductor drum 1 of this example is a charge injection / negative charge organic photoconductor having a diameter of about 30 mm, and is driven to rotate at a peripheral speed of 100 mm / sec. The layer structure of the photosensitive drum 1 will be described in detail in section (3) below.
[0059]
b) The outer peripheral surface of the photosensitive drum 1 is uniformly primary charged to approximately -650 V by a magnetic brush charger 3 as a contact charging member (contact charging means) during the rotation process.
[0060]
Reference numeral 31 denotes a conductive particle supply means for the magnetic brush charger 3. The configurations of the magnetic brush charger 3 and the conductive particle supply means 31 will be described in detail in the section (4) below.
[0061]
c) The uniformly charged surface of the rotating photosensitive drum 1 was modulated by the laser exposure means (laser scanner) 2 in accordance with the image signal sent from the image reader B side to the printer main body A side. By performing scanning exposure with the laser light L, an electrostatic latent image corresponding to the image information of the original G photoelectrically read by the image reader B is sequentially formed on the surface of the rotating photosensitive drum 1.
[0062]
The laser exposure unit 2 includes a solid-state laser element 2a, a rotating polygon mirror (polygon mirror) 2b, an f-θ lens group 2c, a deflection mirror 2d, and the like. On / off emission control of the solid state laser element 2a is performed at a predetermined timing by a light emission signal generator (not shown) based on the input image signal. Laser light emitted from the solid-state laser element 2a is converted into a substantially parallel light beam by a collimator lens system, scanned by a rotating polygon mirror 2b that rotates at high speed, and photosensitized via an f-θ lens group 2c and a deflection mirror 2d. A spot image is formed on the body drum 1.
[0063]
By such laser beam scanning, an exposure distribution corresponding to one image scan is formed on the surface of the photosensitive drum 1, and further sub-scanning by rotating the photosensitive drum 1 according to the image signal on the rotating photosensitive drum surface. Exposure distribution is obtained. That is, the rotating photosensitive drum 1 is scanned by scanning the light of the solid laser element 2a whose ON / OFF light emission is controlled according to the image signal by the rotating polygon mirror 2b which rotates at high speed on the uniformly charged surface of the rotating photosensitive drum 1. On one surface, electrostatic latent images corresponding to the scanning exposure pattern are sequentially formed. That is, on the surface of the rotating photosensitive drum 1, the potential of the exposed portion irradiated with the laser light drops (bright portion potential), and the exposure pattern is formed by contrast with the potential of the non-exposed portion (dark portion potential) that was not irradiated. Corresponding electrostatic latent images are formed.
[0064]
d) The electrostatic latent image formed on the surface of the rotating photosensitive drum 1 is reversely developed in this example as a toner image by the developing device 4 in this case. The configuration of the developing device 4 will be described in detail in section (5) below.
[0065]
e) On the other hand, the transfer material P as the second image carrier that is stacked and stored in the paper feed cassette 5 is fed out and fed by the paper feed roller 5a, and a predetermined control timing is given by the registration roller 5b. Are fed to a transfer portion 7e which is a contact nip portion between the photosensitive drum 1 and the transfer device 7 as a transfer means, and the toner image on the surface of the photosensitive drum 1 is electrostatically transferred onto the transfer material P surface.
[0066]
The transfer device 7 in this example is a belt transfer device. The transfer device 7 will be described in detail in section (6) below.
[0067]
f) The transfer material P that has received the transfer of the toner image through the transfer portion 7e is sequentially separated from the surface of the photosensitive drum 1 and is conveyed and introduced to the fixing device 6, where the toner image is thermally fixed and copied or printed. Are discharged to the paper discharge tray 8.
[0068]
g) The printer main body A of this example is not provided with a dedicated cleaning device (cleaner) for removing the transfer residual toner remaining on the surface of the rotating photosensitive drum 1 after the transfer of the toner image to the transfer material P, and the developing device 4 And a cleaner-less system that also serves as a cleaning means for collecting untransferred toner remaining on the surface of the photosensitive drum 1. This will be described in detail in section (7) below.
[0069]
(3) Photosensitive drum 1
As the photosensitive drum 1 as the first image bearing member, a commonly used organic photosensitive member or the like can be used. Preferably, the resistance is 10% on the organic photosensitive member.⁹ -10¹⁴Using a surface layer with a material of Ω · cm or a surface layer with amorphous silicon such as an amorphous silicon photoreceptor can realize charge injection charging, prevent ozone generation, and consume power. It is effective in reducing. In addition, the chargeability can be improved.
[0070]
The photoreceptor drum 1 in this example is an organic photoreceptor having charge injection chargeability and negative chargeability. As shown in the layer configuration model diagram of FIG. 3, the following is formed on an aluminum drum substrate (aluminum substrate) 1a having a diameter of 30 mm. The first to fifth layers 1b to 1f are provided in order from the bottom.
[0071]
First layer 1b; an undercoat layer, which is a conductive layer having a thickness of 20 μm provided for leveling defects of the drum base 1a.
[0072]
Second layer 1c is a positive charge injection preventing layer, and serves to prevent the positive charge injected from the drum base 1a from canceling the negative charge charged on the surface of the photoreceptor, and is formed by amylan resin and methoxymethylated nylon. 1 × 10⁶ This is a medium resistance layer having a thickness of 1 μm, the resistance of which is adjusted to about Ω · cm.
[0073]
Third layer 1d: a charge generation layer, which generates positive and negative charge pairs upon exposure to a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin.
[0074]
Fourth layer 1e: a charge transport layer, which is a P-type semiconductor in which hydrazone is dispersed in a polycarbonate resin. Therefore, the negative charge charged on the surface of the photoreceptor cannot move through this layer, and only the positive charge generated in the charge generation layer can be transported to the surface of the photoreceptor.
[0075]
Fifth layer 1f; charge injection layer, SnO as conductive fine particles in binder of insulating resin₂ It is a coating layer of a material in which 1 g of ultrafine particles are dispersed. Specifically, SnO having a particle size of 0.03 μm is obtained by reducing the resistance (conducting) by doping an insulating resin with antimony which is a light-transmissive conductive filler.₂ It is a coating layer of a material in which particles are dispersed by 70 weight percent with respect to the resin. The coating solution thus prepared was applied to a thickness of about 3 μm by an appropriate coating method such as a dipping coating method, a spray coating method, a roll coating method, or a beam coating method to form a charge injection layer.
[0076]
(4) Magnetic brush charger 3 and conductive particle supply means 31
a) Magnetic brush charger 3
In this example, the magnetic brush charger 3 as a contact charging member is a sleeve rotation type.
[0077]
As shown in the model diagram of FIG. 2, the magnetic brush charger 3 includes a fixed magnet roller 3a and a non-magnetic sleeve made of aluminum or the like having an outer diameter of 16 mm, which is concentrically and freely fitted around the magnet roller 3a. 3b, a magnetic brush portion 3c of magnetic particles for charging (magnetic carrier) attached and held in a brush shape by the magnetic force of the internal magnet roller 3a on the outer peripheral surface of the sleeve, and the like, which are long in the generatrix direction of the photosensitive drum 1. It is a horizontally long member. A magnet roller 3a is fixedly supported on the housing 3d, and the non-magnetic sleeve 3b is rotationally driven at a predetermined peripheral speed in a clockwise direction b indicated by an arrow (not shown). The layer thickness of the magnetic brush portion 3c of magnetic particles is regulated by the regulating blade 3e.
[0078]
The magnetic brush portion 3c is brought into contact with the surface of the photosensitive drum 1 with a predetermined contact width. The contact portion n1 is a charging portion. In this example, the charging portion n1 formed by bringing the magnetic brush portion 3c into contact with the photosensitive drum 1 is adjusted so that the width thereof is about 6 mm.
[0079]
As described above, the nonmagnetic sleeve 3b is rotated in the clockwise direction indicated by an arrow by a drive system (not shown), that is, in the rotating direction of the photosensitive drum 1 at the charging portion n1 which is the contact portion of the magnetic brush portion 3c with the photosensitive drum 1. On the other hand, it is rotationally driven at a predetermined peripheral speed in the counter direction. In this example, the nonmagnetic sleeve 3b is driven to rotate at 150 mm / sec with respect to the rotational peripheral speed of the photosensitive drum 1 of 100 mm / sec. As the non-magnetic sleeve 3b is driven to rotate, the magnetic brush portion 3c magnetically restrained and held on the outer peripheral surface of the non-magnetic sleeve 3b also rotates in the same direction as the non-magnetic sleeve 3b together with the non-magnetic sleeve 3b. In response to the regulation of the layer thickness, the surface of the photosensitive drum 1 is rubbed at the charging portion n1.
[0080]
A predetermined charging bias is applied to the nonmagnetic sleeve 3b by a charging bias application power source S1. In this example, a DC bias of −650 V is applied to the nonmagnetic sleeve 3b to charge and charge the surface of the rotary photosensitive drum 1 to approximately −650V. By applying a charging voltage to the nonmagnetic sleeve 3b, a charge is applied to the photosensitive drum 1 from the charging magnetic particles constituting the magnetic brush portion 3c, and is charged to a potential corresponding to the charging voltage. As the relative rotational speed of the photosensitive drum 1 and the magnetic brush charger 3 increases, the charging uniformity tends to improve.
[0081]
As the magnetic particles for charging constituting the magnetic brush portion 3c,
An average particle size of 10 to 100 μm,
Saturation magnetization is 20 ~ 250emu / cm^Three ,
Resistance is 1 × 10² ~ 1x10^TenΩ · cm
In consideration of the existence of an insulation defect such as a pinhole in the photosensitive drum 1, the resistance is 1 × 10.⁶ It is preferable to use one having Ω · cm or more.
[0082]
In order to improve the charging performance, it is better to use the one with the smallest possible resistance.
Average particle size 25 μm,
Saturation magnetization 200emu / cm^Three ,
Resistance 5 × 10⁶ Ω · cm
The magnetic particles were used. The charging magnetic particles used in this example are those obtained by adjusting the resistance by oxidizing and reducing the ferrite surface.
[0083]
Here, the resistance value of the magnetic particles for charging has a bottom area of 228 mm.² After putting 2g of magnetic particles in the metal cell, 6.6Kg / cm² And applying a voltage of 100V for measurement.
[0084]
The average particle size of the magnetic particles for charging is indicated by the maximum horizontal chord length, and the measurement method is a microscopic method, randomly selecting 300 or more magnetic particles, measuring the diameter and taking the arithmetic average to obtain the average particle size. It was.
[0085]
A DC magnetization BH characteristic automatic recording device BHH-50 manufactured by Riken Denshi Co., Ltd. can be used for measuring the magnetic characteristics of the magnetic particles for charging. At this time, a cylindrical container having a diameter (inner diameter) of 6.5 mm and a height of 10 mm is filled with magnetic particles with a load of about 2 g weight, and the magnetic particles do not move in the container, and saturation magnetization is obtained from the BH curve. Measure.
[0086]
The magnetic particles for charging consist of a resin carrier formed by dispersing magnets as a magnetic material in the resin to make it conductive, and carbon black dispersed for resistance adjustment, or the surface of magnetite alone such as ferrite is oxidized and reduced. Those having been subjected to resistance adjustment by treatment, or those having the resistance adjusted by coating the surface of a magnetite simple substance such as ferrite with a resin can be used.
[0087]
b) Conductive particle supply means 31
In this example, the conductive particle supply means 31 for the magnetic brush charger 3 is a sponge roller brought into contact with the magnetic brush portion 3c of the magnetic particles of the magnetic brush charger 3.
[0088]
This sponge roller 31 faces the lower opening of the conductive particle hopper 32 provided at the rear of the housing 3d of the magnetic brush charger 3 and is brought into contact with the magnetic brush 3c of the magnetic brush charger 3 to rotate. The bearing is freely supported by the housing 3d. The magnetic brush charger 3 is rotationally driven at a low speed of 10 mm / sec in the counterclockwise direction c indicated by the forward arrow with respect to the rotational direction of the magnetic brush charger 3. m is a conductive particle (conductive particle) accommodated in the conductive particle hopper 32.
[0089]
The sponge roller 31 is in contact with the reservoir of the conductive particles m in the hopper portion 32 at the lower opening of the conductive particle hopper portion 32, and the conductive particles m are applied as a thin layer on the peripheral surface of the sponge roller 31 by the blade 33 as it is driven to rotate. Is done. The conductive particle application surface of the sponge roller 31 comes into contact with the magnetic brush portion 3c of the magnetic brush charger 3, whereby the conductive particles m are supplied to the magnetic brush portion 3c. In this example, 0.05 g of conductive particles m per 100 output sheets are set to be supplied to the magnetic brush portion 3c of the magnetic brush charger 3.
[0090]
In this example, the specific resistance is 10 as the conductive particles m.⁶ Conductive zinc oxide particles having an Ω · cm and an average particle diameter of 3 μm were used.
[0091]
As the material of the conductive particles m, various conductive particles such as conductive inorganic particles such as other metal oxides and mixtures with organic substances can be used.
[0092]
The effect of supplying the conductive particles m to the magnetic brush portion 3c of the magnetic brush charger 3 will be described in detail in section (7) below.
[0093]
Regarding the conductive particles m, since the particle resistance is exchanged through the particles, the specific resistance is preferably less than the resistance of the charging magnetic particles in view of the effect of preventing the resistance value of the charging magnetic particles from increasing. The resistance was measured by the tablet method and normalized. Bottom area 2.26cm² Approximately 0.5 g of a powder sample was placed in the cylinder, and 15 kg of pressure was applied to the upper and lower electrodes. At the same time, a voltage of 100 V was applied to measure the resistance value, and then normalized to calculate the specific resistance.
[0094]
The particle diameter is preferably smaller than the particle diameter (average particle diameter) of the charging magnetic particles, and the lower limit of the particle diameter is 10 nm as long as the particles can be stably obtained.
[0095]
In the present invention, the particle size when the particles are constituted as an aggregate is defined as an average particle size as the aggregate. For the measurement of the particle size, 100 or more samples were extracted from observation with an optical or electron microscope, the volume particle size distribution was calculated with the maximum horizontal chord length, and the 50% average particle size was determined.
[0096]
The conductive particles m are suitably colorless or nearly white particles so as not to interfere with the formation of a latent image by image exposure particularly when used for charging a photoreceptor. Further, when color recording is performed, considering that the conductive particles are transferred from the photosensitive member to the transfer material, it is desirable that the particles are colorless or close to white. In order to prevent light scattering by particles during image exposure, the particle size is desirably equal to or smaller than the constituent pixel size.
[0097]
(5) Developing device 4
Generally, electrostatic latent image development methods are roughly classified into the following four types.
a. Non-magnetic toner is coated on the sleeve with a blade or the like, and the magnetic toner is coated with a magnetic force and conveyed and developed in a non-contact state with respect to the photosensitive drum (one-component non-contact development).
[0098]
b. A method in which the toner coated as described above is developed in contact with the photosensitive drum (one-component contact development).
[0099]
c. A method in which toner particles mixed with a magnetic carrier are used as a developer and are conveyed by magnetic force and developed in contact with a photosensitive drum (two-component contact development).
[0100]
d. A method in which the above two-component developer is developed in a non-contact state (two-component non-contact development).
[0101]
The two-component contact development method c is often used from the viewpoint of high image quality and high stability.
[0102]
The developing device 4 in this example is a two-component contact developing device (two-component magnetic brush developing device). In the model diagram of FIG. 2, reference numeral 41 denotes a developing sleeve that is rotationally driven in a clockwise direction d indicated by an arrow, 42 denotes a magnet roller fixedly arranged in the developing sleeve 41, 43 and 44 denote developer stirring screws, and 45 denotes developer. A regulating blade arranged to form T on the surface of the developing sleeve 41 in a thin layer, 46 is a developing container, and 47 is a replenishing toner hopper.
[0103]
The developing sleeve 41 is disposed so that a region closest to the photosensitive drum 1 is at least about 500 μm at least during development, and a thin layer of the developer T formed on the surface of the developing sleeve 41 is a photosensitive drum. It is set so that development can be performed while being in contact with 1. n2 is a developer contact area (developing portion) with respect to the photosensitive drum 1;
[0104]
As the two-component developer T used in this example, toner particles t are obtained by adding 1.5% by weight of titanium oxide having an average particle diameter of 20 nm to a negatively charged toner having an average particle diameter of 6 μm for development. The magnetic carrier c has a saturation magnetization of 205 emu / cm.^Three A magnetic carrier having an average particle size of 35 μm was used. A mixture of the toner t and the developing magnetic carrier c at a weight ratio of 8:92 was used as the developer T.
[0105]
The toner t in the developer T at this time has a triboelectric charge amount of about −25 × 10^-3c / kg.
[0106]
Here, a measuring method or measuring apparatus for the triboelectric charge amount (tribo charge amount) of the toner will be described with reference to FIG.
[0107]
First, a two-component agent in which toner particles t to be measured for triboelectric charge and magnetic carrier c are mixed at a weight ratio of 5:95 is put into a polyethylene bottle having a capacity of 50 to 100 ml, and is manually put for about 10 to 40 seconds. Shake and take about 0.5 to 1.5 g of the two-component agent, put it in a metal measuring container 52 with an 800 mesh screen 53 and cover it with a metal lid 54.
[0108]
The total weight of the measurement container 52 at this time is measured and is defined as W1 (kg).
[0109]
Next, in the suction machine 51 (at least a part in contact with the measurement container 52 is suctioned), the pressure of the vacuum gauge 55 is set to 250 mmAq by suction from the suction port 57 and adjusting the air volume control valve 56.
[0110]
In this state, the resin is removed by suction for 2 minutes. The potential of the electrometer 59 at this time is set to V (volt). Here, 58 is a capacitor, and the capacity is C (F). Further, the entire weight of the measurement container 52 after the suction is weighed and is defined as W2 (kg).
[0111]
The triboelectric charge amount of the toner is calculated as the following formula.
[0112]
Resin triboelectric charge (c / kg) = C × V × 10^-3/ (W1-W2)
The developing sleeve 41 is driven to rotate at a predetermined peripheral speed in a clockwise direction d indicated by an arrow which is a counter direction with respect to the rotation direction of the photosensitive drum 1 in the developing unit n2. Along with the rotation, the developer T in the developing container 46 is pumped up and transported to the surface of the developing sleeve 41 by the N3 pole of the magnet roller 42, and is disposed perpendicular to the developing sleeve 41 in the transporting process. The layer thickness is regulated by the regulating blade 45, and a thin layer of the developer T is formed on the developing sleeve 41. When the developer formed as a thin layer is conveyed to the developing pole N1 corresponding to the developing portion n2, a spike is formed by the magnetic force. The electrostatic latent image on the surface of the rotary photosensitive drum 1 is developed as a toner image in the developing unit n2 by the toner t in the developer formed in the spike shape. In this example, the electrostatic latent image is reversely developed. ta represents the toner image.
[0113]
The developer thin layer on the developing sleeve 41 that has passed through the developing portion n2 enters the developing container 46 with the subsequent rotation of the developing sleeve 41, and is separated from the developing sleeve 41 by the repulsive magnetic field of N2 pole and N3 pole, and the developing container. It is returned to the developer pool in 46.
[0114]
A DC voltage and an AC voltage are applied to the developing sleeve 41 from the power source S2. In this example,
DC voltage: -480V
AC voltage; Vpp = 1500V, Vf = 3000Hz
Is applied.
[0115]
In general, in the two-component development method, when an AC voltage is applied, the development efficiency increases and the image becomes high-quality, but conversely, there is a risk that fogging easily occurs. For this reason, in general, it is possible to prevent fogging by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1. More specifically, a bias voltage having a potential between the potential of the exposed portion of the photosensitive drum 1 and the potential of the non-exposed portion is applied.
[0116]
This potential difference for preventing fogging is called a fog removal potential (Vback). Due to this potential difference, toner adheres to a non-image area (non-exposed portion) on the surface of the photosensitive drum 1 when developing the surface of the rotating photosensitive drum 1. In addition, the cleanerless system apparatus collects the transfer residual toner on the surface of the photosensitive drum 1 (simultaneous development cleaning).
[0117]
The toner density is monitored by a sensor (not shown) that detects the toner density of the developer T in the developing container 46, and the toner density in the developer T is consumed for developing the latent image. When the density level falls below the toner level, the toner is replenished from the replenishing toner hopper 47 into the developing container 46. By this toner replenishment operation, the toner density of the developer T is always maintained at a predetermined level.
[0118]
(6) Transfer device 7
The transfer device 7 in this example is a belt transfer device, and an endless transfer belt 7a is suspended between the driving roller 7b and the driven roller 7c, and is substantially the same as the rotational peripheral speed of the photosensitive drum 1 in the counterclockwise direction e of the arrow. It is rotated at a peripheral speed. A transfer charging blade 7d is provided inside the endless transfer belt 7a, and a substantially intermediate portion of the belt portion on the ascending side of the belt 7a is brought into contact with the surface of the photosensitive drum 1 with the blade 7d to transfer the transfer portion (transfer nip portion) 7e. Is formed.
[0119]
The transfer material P rides on the upper surface of the ascending belt portion of the belt 7a and is conveyed to the transfer portion 7e. When the leading edge of the transport transfer material P enters the transfer portion 7e, the transfer charging blade 7d is supplied with a predetermined transfer bias from the transfer bias application power source S3, so that the reverse polarity of the toner is charged from the back side of the transfer material P. As a result, the toner images ta on the photosensitive drum 1 are sequentially transferred tb onto the upper surface of the transfer material P.
[0120]
In this example, the belt 7a is made of polyimide resin having a film thickness of 75 μm. The material of the belt 7a is not limited to polyimide resin.NateResins, plastics such as polyethylene terephthalate resin, polyvinylidene fluoride resin, polyethylene naphthalate resin, polyether ether ketone resin, polyether sulfone resin, polyurethane resin, and fluorine-based and silicon-based rubbers can be suitably used. . The thickness is not limited to 75 μm, and a thickness of about 25 to 2000 μm, preferably 50 to 150 μm can be suitably used.
[0121]
Further, the transfer charging blade 7d has a resistance of 1 × 10.^Five ~ 1x10⁷ A plate with a thickness of 2 mm and a length of 306 mm was used. Transfer was performed by applying a bias of +15 μA to the transfer charging blade 7d under constant current control.
[0122]
The toner image ta formed on the photosensitive drum 1 in this way is electrostatically transferred tb onto the transfer material P by the transfer charging blade 7d.
[0123]
The transfer belt 7a also serves as a means for transporting the transfer material P from the transfer portion 7e to the fixing device 6. The transfer material P that has passed through the transfer portion 7e is separated from the surface of the rotating photosensitive drum 1 and fixed on the transfer belt 7a. It is conveyed and introduced into the device 6.
[0124]
(7) Cleanerless system and effect of conductive particles m
The printer A of this example does not include a dedicated cleaning device for removing the transfer residual toner remaining on the surface of the rotating photosensitive drum 1 after the transfer of the toner image to the transfer material P, and the developing device 4 has the photosensitive drum 1. This is a cleaner-less system that also serves as a cleaning means for collecting the residual transfer toner remaining on the surface. In this case, the transfer efficiency is improved to reduce the residual transfer toner, and the magnetic brush charger is contaminated. By preventing the resistance from increasing, it is possible to maintain a good image output without image defects such as positive ghost over a long period of time.
[0125]
This will be described mainly based on the model diagram of FIG. In FIG. 2, the toner t and the conductive particles m are drawn with exaggerated particle sizes with respect to the magnetic particles for charging and the developing carrier for easy understanding.
[0126]
a) Cleanerless system
(1). The untransferred toner tc remaining on the surface of the rotary photosensitive drum 1 after the transfer of the toner image to the transfer material P is a contact portion between the photosensitive drum 1 and the magnetic brush portion 3c of the magnetic brush charger 3 by the subsequent rotation of the photosensitive drum 1. To the charging unit n1.
[0127]
(2). In this charging portion n1, the surface of the photosensitive drum 1 is rubbed by the magnetic brush portion 3c of the magnetic brush charger 3, so that the transfer residual toner tc carried to the charging portion n1 is disturbed on the surface of the photosensitive drum 1.・ The pattern of the transfer remaining when it is moved is scraped, and among the remaining transfer toner tc, the one whose charge polarity is reversed by the peeling discharge during transfer (inverted from negative to positive in this example) is charged. In the portion n1, the surface is moved and mixed from the photosensitive drum 1 surface side to the magnetic brush portion 3c side by the electric attractive force by the charging bias applied to the magnetic brush charger 3, and is temporarily recovered, that is, the photosensitive drum 1 surface. In the charging unit n1, the photosensitive drum surface portion under the untransferred toner is also charged.
[0128]
Among the remaining transfer toner, the toner whose polarity is not reversed has a charging potential generally lower than the charging bias applied to the magnetic brush charger 3, and therefore is not collected by the magnetic brush portion 3c and is not collected by the surface of the photosensitive drum 1. It is disturbed and moved above and passes through the charging part n1.
[0129]
(3). The transfer residual toner having a reversed charge polarity, which is temporarily collected after being transferred / mixed to the magnetic brush portion 3c side of the magnetic brush charger 3, is friction with the charging magnetic particles constituting the magnetic brush layer 3c. The electrification results in a recharged state with a normal charging polarity (negative polarity in this example), and the magnetic brush charger 3 is discharged onto the photosensitive drum 1 by an electric repulsive force due to a charging bias applied.
[0130]
(4). Then, as in (2) above, the untransferred toner whose polarity is not reversed, which has been disturbed and moved on the surface of the photosensitive drum 1 without being collected by the magnetic brush unit 3c in the charging unit n1 and passed through the charging unit n1. (Negative polarity) and the polarity is reversed as in (3) above, so that the charging portion n1 is temporarily recovered by the magnetic brush portion 3c and recharged to the normal charging polarity. Any untransferred toner (negative polarity) discharged to the toner is carried to the developing unit n2 which is the opposing part of the photosensitive drum 1 and the developing sleeve 41 of the developing device 4 by the subsequent rotation of the photosensitive drum 1, and the developing device. 4 is collected at the fog removal potential Vback (development simultaneous cleaning).
[0131]
b) Effects of the conductive particles m
(1). As described above, an appropriate amount of conductive particles m is supplied to the magnetic brush portion 3c of the magnetic brush charger 3 by the conductive particle supply means 31.
[0132]
By supplying an appropriate amount of conductive particles m to the magnetic brush portion 3c of the magnetic brush charger 3, the mixed conductive particles m supplied to the magnetic brush portion 3c are obtained from the charging magnetic particles constituting the magnetic brush portion 3c. However, since the magnetic restraint force by the magnet roller 3a is weak (there is no magnetic restraint force when the conductive particles m are non-magnetic), it is separated little by little from the magnetic brush portion 3c and supplied to the surface of the rotating photosensitive drum 1 little by little. Is done.
[0133]
For this reason, when image formation is repeated, the peripheral surface of the photosensitive drum 1 is thinly covered with the conductive particles m.
[0134]
Thus, when the surface of the photosensitive drum 1 is thinly covered with the conductive particles m, the contact state force between the surface of the photosensitive drum 1 and the toner image ta formed on the surface of the photosensitive drum. Is weakened and the transfer efficiency of the toner image to the transfer material P side at the transfer portion 7e is increased, so that the residual transfer toner tc carried to the magnetic brush charger 3 side can be reduced.
[0135]
Further, the contact state force between the surface of the photosensitive drum 1 and the transfer residual toner tc on the surface of the photosensitive drum is also weakened, and the magnetic brush portion of the transfer residual toner in the charging portion n1 in (2) of the above a). Thus, disturbance and movement due to the rubbing and peeling off from the photosensitive drum 1 surface side to the magnetic brush portion 3c side are facilitated.
[0136]
Thus, since the conductive particles m are present on the magnetic brush portion 3c and the photosensitive drum 1 of the magnetic brush charger 3, the amount of the transfer residual toner tc is small and charge injection to the conductive particles m is performed. By sufficiently charging the photosensitive drum surface portion under the toner, generation of positive ghost can be prevented.
[0137]
(2). Further, by supplying an appropriate amount of conductive particles m to the magnetic brush portion 3c of the magnetic brush charger 3, toner or a photosensitive drum is applied to the charging magnetic particles constituting the magnetic brush portion 3c, the surface of the sleeve 3b, and the like. Such as when resin components such as resin additives and external additives are fused, or when a large amount of untransferred toner is mixed in the magnetic brush portion 3c and cannot be discharged onto the photosensitive drum 1 sufficiently. The effect that the charging ability can be prevented from being lowered due to the entire or partial resistance increase of the charger 3 is obtained, and the durability is greatly improved.
[0138]
FIG. 5 shows the transition of the difference between the saturation potential and the potential that can be charged in the first round (ΔV) with respect to the number of durable sheets. There is a large difference in durability between A when the conductive particles m are supplied and B when the conductive particles m are not supplied. Has occurred.
[0139]
In order to increase the recovery efficiency of the transfer residual toner tc from the photosensitive drum 1 surface side to the magnetic brush charger 3 side, that is, the removal efficiency, the transfer residual toner tc is normally charged between the transfer portion 7e and the magnetic brush charger 3. It is also effective to provide charging means for charging in the opposite polarity.
[0140]
<Example 2> (FIG. 6)
In the first embodiment, the charging bias for the magnetic brush charger 3 is only a DC voltage of −650 V (DC bias application method), but the charging bias applied to the magnetic brush charger 3 is transferred by the charger 3. In order to further improve the recovery efficiency of the remaining toner, that is, the stripping efficiency and the charging uniformity, it is desirable to superimpose an alternating voltage on the DC voltage (AC bias application method).
[0141]
This embodiment is an example of the AC bias application method. That is, in Example 1, the charging bias for the magnetic brush charger 3 is set.
DC voltage: -650V
Alternating voltage: Frequency 1000Hz, amplitude 700V
Is the vibration voltage superimposed. The peripheral surface of the rotating photosensitive drum 1 is charged by contact injection at approximately −650V.
[0142]
Other device configurations and setting conditions are the same as those in the first embodiment.
[0143]
Including an alternating voltage in the charging bias of the magnetic brush charger 3 greatly improves the charging ability ΔV (the difference between the saturation potential and the potential that can be charged in the first week), and in addition, the photosensitive drum in the charging unit n1. The effect of peeling off the untransferred toner during charging from the 1 side to the magnetic brush charger 3 side is greatly enhanced.
[0144]
As an alternating voltage setting condition, an effect can be obtained by setting the frequency to about 200 to 8000 Hz and the amplitude to about 200 to 1500 V.
[0145]
FIG. 6 shows the saturation potential and the potential that can be charged in the first round for the durable number of C when the conductive particles m are supplied to the magnetic brush charger 3 and D when the conductive particles m are not supplied in the case of the above AC bias application method. This is the transition of the difference (ΔV).
[0146]
As can be seen from FIG. 6, in the case of the AC bias application method in which the conductive particles m are supplied to the magnetic brush charger 3 and a charging bias in which an alternating voltage is superimposed is applied, C is almost free from deterioration in charging ability. Chargeability is possible for a long time.
[0147]
<Example 3> (FIGS. 7 and 8)
In the first and second embodiments, the supply of the conductive particles m to the magnetic brush charger 3 is a fixed replenishment method at a rate of 0.05 g per 100 output sheets. The conductive particles m were replenished while changing and adjusting the replenishment amount with time so as to be constant.
[0148]
In this embodiment, as in the first embodiment, a DC bias application method in which the charging bias applied to the magnetic brush charger 3 is only a DC voltage of −650V is adopted.
[0149]
Other device configurations, setting conditions, and the like are the same as those in the first embodiment.
[0150]
FIG. 7 shows the change over time of the replenishment amount (per 100 outputs) of the conductive particles m to the magnetic brush charger 3 in this embodiment. As the endurance progresses, the replenishment amount increases slightly. This is because the magnetic brush charging is caused by contamination of the magnetic brush charger 3 due to fusion of resin components such as toner or adhesion of external additives to the magnetic particles constituting the magnetic brush portion 3c of the magnetic brush charger 3. This corresponds to the increase in resistance of the vessel 3.
[0151]
By performing such conductive particle m-replenishment amount control, as shown in FIG. 8, the difference (ΔV) between the saturation potential and the potential that can be charged in the first round with respect to the durable number is determined as the conductive particle m- of Example 1. It is possible to suppress fluctuations smaller than in the case of quantitative replenishment.
[0152]
<Others>
1) The present invention is not limited to the embodiments 1 to 3 described above, and image formation in which the developing means also serves as a cleaning means for the first image carrier after the toner image is transferred to the second image carrier. The apparatus includes all configurations in which means for supplying the conductive particles m to the contact charging means is provided.
[0153]
2) The surface resistance of the photosensitive member as the first image carrier is 10⁹ -10¹⁴Having a low resistance layer of Ω · cm is desirable from the standpoint of preventing the generation of ozone because charge injection can be realized. However, organic photoreceptors other than those described above are sufficiently effective in preventing the increase in resistance of the charger. It is done.
[0154]
3) As the electrostatic latent image developing method, only the two-component developing method has been described in the first to third embodiments, but other developing methods are also effective. A reversal development method or a regular development method may be used. Preferably, one-component contact development or two-component contact development in which the developer is developed in contact with the photoreceptor is more effective in enhancing the simultaneous recovery effect during development.
[0155]
The toner particles in the developer may be pulverized toner or the like. More preferably, when polymerized toner is used, the above one-component contact development and two-component contact development are of course one-component non-contact. In other development methods such as development and two-component non-contact development, a sufficient recovery effect of the transfer residual toner can be obtained.
[0156]
4) The magnetic brush charger 3 uses a so-called sleeve rotation type charger having a magnet roller 3a-fixed, non-magnetic sleeve 3b-rotation, but is not limited to this charger configuration. System and magnet for rotating roller 3arollerEven in a system in which the magnet roller itself rotates with the configuration of only 3a, the roller surface can be used by conducting a conductive treatment or the like.
[0157]
5) As a waveform of the AC bias component when the charging bias is applied to the magnetic brush charger 3 by the AC bias application method, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. The AC bias includes a rectangular wave voltage formed by, for example, periodically turning on and off a DC power supply. To control the AC bias at this time, the peak-to-peak voltage may be controlled. In this way, the AC bias can be a bias whose voltage value periodically changes.
[0158]
The same applies to the AC bias when an AC bias component is included in the developing bias applied to the developing device.
[0159]
  6) The first image carrier may be predominantly charged by discharge.Yes.
[0160]
7) The first image carrier may be an electrostatic recording dielectric or the like. In this case, the dielectric surface is first charged uniformly to a predetermined polarity and potential, and then the electrostatic latent image corresponding to the target image information is selectively discharged by a discharging means such as a discharging needle head or an electron gun. Write form.
[0161]
8) The transfer method may be roller transfer, blade transfer, corona discharge transfer, or the like. The present invention can be applied not only to the formation of a single color image but also to an image forming apparatus that forms a multicolor or full color image by multiple transfer or the like using an intermediate transfer member such as a transfer drum or a transfer belt.
[0162]
9) Arbitrary process equipment such as the first image carrier 1, charging means 3, developing device 4 and the like is configured to be a process cartridge detachable apparatus configuration that can be detachably attached to the main body of the image forming apparatus. You can also.
[0163]
【The invention's effect】
As described above, according to the present invention, the contact charging method / cleanerless system image forming apparatus, particularly the image forming apparatus using the magnetic brush charger as the contact charging member, is improved in transfer efficiency and is a contact charging member. It is possible to prevent an increase in resistance due to contamination of the magnetic brush charger and to maintain a good image output without image defects such as positive ghost over a long period of time.
[Brief description of the drawings]
FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to a first embodiment.
[Fig. 2] An enlarged model of the main part
FIG. 3 is a model diagram of a layer structure of a photosensitive drum.
FIG. 4 is a diagram for explaining the procedure for measuring the charge amount of toner.
FIG. 5 is a graph showing fluctuations in charging ability accompanying durability of the magnetic brush charger in Example 1.
FIG. 6 is a graph showing a change in charging ability with durability of the magnetic brush charger in Example 2.
7 is a transition graph of the amount of conductive particles replenished in Example 3. FIG.
FIG. 8 is a graph showing fluctuations in charging ability accompanying durability of the magnetic brush charger in Example 3.
FIG. 9 is a schematic configuration diagram of a conventional example of an image forming apparatus.
[Explanation of symbols]
A printer
B Image reader
1 Photosensitive drum (first image carrier)
2 Laser exposure means
3 Magnetic brush charger (contact charging member)
31 Conductive particle supply means (sponge roller)
m conductive particles
5 Paper cassette
6 Fixing device
7 Transfer device
8 Output tray
P transfer material (second image carrier)

Claims (11)

Charging means for charging the first image carrier, latent image forming means for forming an electrostatic latent image on the charging surface of the first image carrier, and developing means for developing the electrostatic latent image as a toner image And transfer means for transferring the toner image to the second image carrier, and the developing means transfers the toner image onto the first image carrier after the toner image is transferred to the second image carrier. In the image forming apparatus that also serves as a cleaning unit that collects remaining toner particles, and the first image carrier is repeatedly used for image formation,
The charging means is a contact charging means for charging the magnetic particles by bringing them into contact with the image carrier as a magnetic brush by the magnetic force of the magnetic field generating means,
An image forming apparatus comprising supply means for supplying nonmagnetic conductive particles having an average particle size smaller than the average particle size of the magnetic particles to the magnetic brush. The image forming apparatus according to claim 1, wherein the conductive particles supplied to the magnetic brush have an average particle diameter of 10 nm or more. The volume resistivity of the conductive particles to be supplied to the magnetic brush, the image forming apparatus according to claim 1 or 2, characterized in that less volume resistivity of the magnetic particles of the contact charging means. The conductive particles are supplied to the magnetic brush image forming apparatus according to any one of claims 1 to 3, characterized in that it is white. The image forming apparatus according to any one of claims 1 to 4, characterized by having a layer made of a material of said first image carrier is resistant to surface 10 ⁹ ~10 ¹⁴ Ω · cm. Said first image bearing member photosensitive layer, and has a surface layer, an image forming apparatus according to any one of claims 1 to 5, characterized in that said surface layer has a resin and conductive fine particles . The image forming apparatus according to claim 6 , wherein the conductive fine particles are SnO ₂ . The image forming apparatus according to any one of claims 1 to 7 wherein the first image bearing member is characterized by comprising a surface layer having an amorphous silicon. The bias applied to the contact charging means, an image forming apparatus according to any one of claims 1 to 8, characterized in that a bias alternating voltage is superimposed on DC voltage. The developing unit is any one of claims 1, wherein the developer is a contact developing method in which toner development of the electrostatic latent image is made in contact with the first image carrier 9 The image forming apparatus described in 1. The latent image forming means image forming apparatus according to any one of claims 1 to 10, characterized in that an image exposure means to the charging surface of the first image bearing member.

Images