JP2005173283A - Proximity electrifying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proximity electrifying device, by which a contribution can be made to the longer life of an electrostatic latent image carrier using a proximity electrifying system of averting the problems of a contact electrifying system, and also electrification can be stably performed, its potential can be controlled with simplicity and high accuracy and ozone generation can be drastically reduced and which is easily manufactured and which itself has high durability. <P>SOLUTION: In the proximity electrifying device for electrifying the image carrier by applying a voltage to an electrifying member arranged in proximity to the image carrier, the electrifying member is a roller member equipped with a conductive member of a cylindrical or columnar shape, a resistance layer of a volume resistivity 105 to 1,012 Ωcm and a resin layer dispersed with conductive particulates covering its surface. The roller member is contactless with the image carrier and has the proximal spacing of 5 to 150 μm and a magnetic substance is used as a conductive material for the resistance layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a proximity charging device applicable to an image forming apparatus such as an electrophotographic copying machine, the same printer, or an electrostatic recording apparatus.

  Conventionally, a corona charger (corona discharger) has been widely used as a charging device that uniformly charges (including static elimination processing) an electrostatic latent image carrier to a desired polarity and potential.

  The corona charger is a non-contact type charging device, and includes a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and is disposed in a non-contact manner with the discharge opening facing the image carrier that is an image carrier. The image carrier surface is charged to a predetermined potential by exposing the image carrier surface to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode.

  In recent years, as a charging device for an electrostatic latent image carrier or the like, many contact charging devices have been proposed and already put into practical use because they have advantages such as low ozone and low power compared to a corona charger.

  In such a contact charging system charging device, the charging member to be brought into contact with the image carrier has various forms such as a roller type (charging roller), a fur brush type, a magnetic brush type, a blade type (charging blade), There are also various improvement proposals.

  The contact charging device directly contacts the surface of the image carrier with a charging member (conductive member) to which a DC voltage or a superimposed voltage of a DC voltage and an AC voltage is applied by a power supply device. Then, the surface of the image carrier is charged to a predetermined potential.

  The contact charging method is characterized in that the power supply voltage can be reduced, the generation of corona products such as ozone is very small, the configuration is simple, and the size and cost of the apparatus can be reduced.

  FIG. 2 is a schematic configuration diagram of an example of an image forming apparatus employing a contact charging device as a uniform charging unit for the image carrier.

  In FIG. 2, when a copy start signal is input, the photosensitive member 1, which is an organic photosensitive member (OPC), is rotated in the direction of the arrow, and after being uniformly discharged by the pre-exposure lamp 8, a predetermined potential is supplied by the charger 3. Are uniformly charged. Here, the photosensitive member 1 is a rotating drum type electrophotographic photosensitive member, and is rotationally driven at a process speed (peripheral speed) of 100 mm / sec in the clockwise direction indicated by an arrow A.

  The charger 3 is a charging roller as a charging member. The resistance is adjusted to a conductive core bar (shaft bar) 3a made of iron, stainless steel or the like, and EPDM, urethane, BR, silicone rubber, IR, etc. located on the outer side. Therefore, the outer layer 3b is made of a rubber material in which a conductive material such as carbon black or metal oxide is dispersed. The charging roller 3 has a predetermined pressing force on the surface of the photosensitive drum 1 by an urging means (not shown) substantially parallel to the bus bar of the photosensitive drum 1 in a state where both ends of the core metal 3a are rotatably supported. They are in contact with each other and are driven to rotate as the photosensitive drum 1 rotates.

  Further, a pad, a brush, or the like is in contact as a cleaning member (not shown) in order to remove or disperse toner and toner external additives adhering to the surface of the charging roller 3. A superposed voltage of, for example, a DC voltage and an AC voltage having a peak-to-peak voltage more than twice the charging start voltage of the photosensitive layer of the photosensitive drum from a charging bias power source S1 (not shown) with respect to the charging roller 3 It is applied to the charging roller 3 through a sliding contact electrode (not shown) brought into contact with the end of the core bar 3a. A voltage is applied to the peripheral surface of the photosensitive drum 1 and the charging roller 3 in contact with the drum surface is uniformly charged to a predetermined potential and polarity by a contact charging method.

  On the other hand, the reader unit illuminates a document G placed on the document table 10 by scanning the document G while irradiating the document as a unit 9 including a document irradiation lamp, a short focus lens array, and a CCD sensor. The original reflection light of the scanning light is imaged by the short focus lens array and is incident on the CCD sensor. The CCD sensor is composed of 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 obtained analog signal is subjected to known image processing, converted into a digital signal, and sent to the printer unit.

  In the printer unit, the charged surface of the photoreceptor 1 is intensity-modulated in response to the digital signal of the image information output from the laser exposure means 2 including a solid laser element, a polygon mirror that rotates at high speed, and the like. Then, scanning exposure E by the laser beam is performed, and an electrostatic latent image corresponding to the image information of the original image is formed on the peripheral surface of the photoreceptor 1. The electrostatic latent image is developed as a toner image by a developing device 4 using magnetic one-component insulating toner.

  Reference numeral 41 denotes a non-magnetic phenomenon sleeve having a diameter of 16 mm containing a magnet roller 42 (not shown). The phenomenon sleeve 41 is coated with the negative toner, and the distance from the surface of the photoreceptor 1 is fixed to 200 μm. A developing bias voltage is applied to the developing sleeve 41 from a developing bias power source S2 (not shown). The applied voltage is a superposition of a DC voltage of −500 V and a rectangular AC voltage having a frequency of 1.8 MHz and a peak-to-peak voltage of 1.6 kV, and causes a jumping phenomenon between the developing sleeve 41 and the photoreceptor 1.

On the other hand, a transfer material P as a recording material is supplied from the paper supply unit, and a pressure nip portion between the photosensitive member 1 and a medium resistance transfer roller 7 as a contact transfer means brought into contact with the photoconductor 1 with a predetermined pressing force. It is introduced into the (transfer section) T at a predetermined timing. A predetermined transfer bias voltage is applied to the transfer roller 7 from a transfer bias application power source S3 (not shown). In this example, the transfer roller resistance value is 5 × 10 8.
Transferring was performed by applying a DC voltage of +2000 V using an Ω.

  The transfer material P introduced into the transfer portion T is nipped and conveyed by the transfer portion T, and the toner images formed and supported on the surface of the photoreceptor 1 are sequentially transferred to the surface side by electrostatic force and pressing force. It will be done.

  Further, the transfer material P that has received the transfer of the toner image is separated from the surface of the photoconductor 1 and introduced into a fixing device 6 such as a heat fixing system, where the toner image is fixed, and an image formed product (print, copy). Is discharged outside the apparatus.

  However, the following problems can be cited as problems in the case of the contact charging device as described above.

1) Occurrence of “pinhole”:
When a charging roller 3 as a charging member comes into contact with the photosensitive drum 1 as a member to be charged and a voltage is applied, the photosensitive layer of the photosensitive drum 1 may break down and generate pinholes. By this pinhole, it appears as a defect of white spots and black spots on the image.

2) Generation of “charging noise”:
When an AC voltage is applied to the charging roller 3, the charging roller 3 in contact with the photosensitive drum 1 vibrates, so that a so-called “charging sound” is likely to be generated. Although this problem can be improved by making the voltage applied to the charging member only DC, there is another problem that it is difficult to obtain a uniform charged state without unevenness.

3) “Toner smear”:
In the contact charging method or the conventional charging method, the toner or the external additive of the toner adheres to the charging member and fusion occurs, or the toner or the external additive of the toner adhering to the charging member spills off, thereby causing an image. Defects are likely to occur.

4) Occurrence of “charging roller trace”:
A plasticizer oozes out from EPDM or the like constituting the outer layer 3a of the charging roller 3 as a charging member in contact with the photosensitive drum 1 as a member to be charged, and this is on the surface of the photosensitive drum 1 during a period when the drum is stopped. By adhering and transferring to the surface, an image defect called “charging roller trace” may occur.

5) Occurrence of “drum scratches and fusion”:
Since the charging roller 3 as the charging member is in contact with the photosensitive drum 1 as the member to be charged, the photosensitive drum 1 is likely to be scratched or fused due to long-term use. The service life is as short as 40,000 sheets.

  The above-mentioned problem is a common problem not only with the charging roller in contact with the member to be charged, but also with other forms such as a blade form and a rod form.

  In order to avoid the above problems, as shown in Patent Document 1 and Patent Document 2, a proximity charging method is proposed in which a charged body and a charging member are not in contact with each other.

In Patent Document 1, the gap between the member to be charged and the charging member is set to 0.01 inch (254 μm) to 0.06 inch (1524 μm).
An electric bias is applied to a roller composed of a resistance layer of 1013 Ω · cm and a protective layer of 1011 to 5 × 1013 Ω · cm. In Patent Document 2, an AC bias is applied by contacting the roller in a non-contact manner. In this case, the gap with the photosensitive member is 5 μm to 300 μm, and 30 μm is most preferable.

US Pat. No. 3,935,517 US Pat. No. 5,146,280

However, in the case of Patent Document 1 that discloses a charging roller configured in a non-contact manner with an image carrier, the gap between the charged body and the charging member is 0.01 inch (254 μm) to 0.06 inch (1524 μm). 109
An electric bias is applied to a roller composed of a resistance layer of 1013 Ω · cm and a protective layer of 1011 to 5 × 1013 Ω · cm, but the charging is unstable when the gap between the charging roller and the image carrier is 254 μm or more. In addition, the amount of current (or applied voltage) required for uniform charging to increase local charge, which is difficult to be charged, increases, and the potential of the image carrier surface due to voltage application at the start of charging is 800 V or more. It cannot be adjusted to a generally target potential of 500 to 700 V, and even the macroscopic photoreceptor potential cannot be adjusted. In addition, there is a drawback that it is difficult to process the rubber layer in close contact with the metal core.

  Further, Patent Document 2 describes a charging device that applies an AC bias by contacting a roller in a non-contact manner, and the gap with the photosensitive member at this time is 5 μm to 300 μm, and is most preferably 30 μm. However, when it is durable with a charging roller having an outer layer such as EPDM, it is about 1k, and toner and toner external additives adhering to the charging member are spilled as a lump as in the conventional contact charging method. Due to this, an image defect occurred. In order to improve this, the surface of the charging roller was provided with a cleaning means such as a pad or brush, and when it was durable, the charging roller was damaged at about 5k sheets, and a streak-like image defect corresponding to the scratch was generated. .

Furthermore, in order to avoid the problems of the proximity charging method, a cylindrical conductive member as a proximity charging method and a volume specific resistance 105 covering the surface thereof are used.
Although a roller member having a resistance layer of 1012 Ω · cm is in non-contact with the photoreceptor and has a closest distance of 5 to 150 μm, the resistance layer uses a magnetic material as a conductive material. If a magnetic material with a large particle size is exposed on the surface according to the particle size distribution of the magnetic material or the state of dispersion in the resin, the exposed magnetic material will be overcharged, resulting in poor charging as a white spot on the image There has occurred.

  Therefore, the object of the present invention is to use the proximity charging method that avoids the problems of the contact charging method, can contribute to the extension of the life of the electrostatic latent image carrier, and can be stably charged. In addition, it is an object of the present invention to provide a proximity charging device that can easily control the electric potential with high accuracy, can extremely reduce the generation of ozone, is easy to produce, and has high durability itself.

  Another object of the present invention is to provide a high-performance proximity charging device that does not cause image defects caused by adhesion of toner or toner external additives to a charging member.

In order to achieve the above object, the invention described in claim 1 is a proximity charging device for charging a charging member disposed in proximity to the image carrier by applying a voltage to the charging member. Is a cylindrical conductive member and a volume resistivity 105
A roller member having a resistance layer of 1012 Ω · cm and a resin layer in which conductive fine particles covering the surface are dispersed, the roller member being in non-contact with the image carrier and having a closest distance of 5 to 150 μm The resistance layer uses a magnetic material as a conductive material.

  According to a second aspect of the present invention, in the first aspect of the present invention, the magnetic material is a ferrite-based material, an alnico-based material, or a neodymium-based material.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the resistance layer or resistor of the roller is EEA resin (ethylene ethyl acrylate), POM resin (polyacetal), PA resin (nylon, polyamide), It has PBT resin (polybutylene terephthalate) and PPS resin (polyphenylene sulfide).

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the conductive fine particles include conductive zinc oxide, conductive titanium oxide, Al, Au, Cu, Ag, Co, i, It is at least one selected from Fe, carbon black, ITO, tin oxide, indium oxide, indium, and barium sulfate.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the resin layer contains at least one selected from polyamide, epoxy, ethylene-vinyl acetate copolymer, and phenol resin. It is characterized by that.

  According to a sixth aspect of the present invention, in any of the first to fifth aspects of the present invention, the roller member is driven to rotate as the image carrier moves.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to fifth aspects, the roller member has a moving speed of the surface of the roller member and a moving speed of the surface of the image carrier in the same direction or in opposite directions. And is driven to rotate at a relative speed difference.

  The invention according to claim 8 is characterized in that, in the invention according to any one of claims 1 to 7, a cleaning member for cleaning the roller member is provided in the vicinity of the roller member.

  According to the present invention, the proximity charging method that avoids the problems of the contact charging method can be used to contribute to the extension of the life of the electrostatic latent image carrier, the charging can be performed stably, and It is possible to provide a proximity charging device that can easily control the potential with high accuracy, can extremely reduce the generation of ozone, is easy to produce, and has high durability itself.

  Further, it is possible to provide a high-performance proximity charging device that does not cause image defects due to adhesion of toner and toner external additives to the charging member.

  EXAMPLES Hereinafter, although a manufacture example and an Example demonstrate this invention concretely, this does not limit this invention at all.

[Example 1]
FIG. 1 is a schematic sectional view of an image forming apparatus, and FIGS. 3A and 3B are a schematic view of a non-contact roller charging device and an enlarged view of the surface of the non-contact roller. Since the configuration and operation of the charger 30 are the same as those of the conventional example, description thereof is omitted.

1 and 3, a charger 30 is a charging roller as a charging member, and a cylindrical or columnar conductive member 30 a such as iron or stainless steel, and a volume specific resistance 105.
A resistance layer 30b having a resistance of 1012 Ω · cm and a surface layer having a volume resistivity of 105 to 1012 Ω · cm covering the surface thereof are provided. The charging roller 30 is disposed in the direction of the generatrix of the photosensitive drum 1 and is in contact with the photosensitive drum 1 As a result, resin layers 30c (or resin tapes) are provided at both ends so that the proximity gap with the surface of the photosensitive drum 1 becomes a predetermined amount d, and is driven as the photosensitive drum 1 rotates.

  The resistance layer 30b is made of an EEA resin (ethylene ethyl acrylate), POM resin (polyacetal), PA resin (nylon, polyamide), PBT resin (polybutylene terephthalate), PPS resin (polyphenylene sulfide), etc. It contains Alnico and neodymium magnetic materials and is produced as a plastic roller by an injection molding method.

The surface layer 30d can be easily formed by a conductive layer obtained by dispersing and applying conductive fine particles in a polymer binder, and is suitable for forming a homogeneous surface. The primary particle size of the conductive fine particles used at this time is 100 nm or less, more preferably 50 nm or less. As conductive fine particles, conductive zinc oxide, conductive titanium oxide, Al, Au, Cu, Ag, Co, Ni, Fe, carbon black, ITO, tin oxide, indium oxide, indium, etc. are used, and these are insulated. The surface of the fine particles may be coated. The content of the conductive fine particles is used so that the volume resistance is sufficiently low, and is preferably added so as to have a resistance of 1 × 10 10 Ω · cm or less. More preferably 1 × 10 8
Used at Ω · cm or less.

  The roller charger 30 is applied with an oscillating voltage obtained by superimposing an AC voltage on a DC voltage from a charging bias voltage application power source S1 (a voltage whose voltage value periodically changes with time). Uniformly charged. The applied voltage to the charging roller 30 is preferably, for example, an oscillating voltage in which an alternating voltage having a peak-to-peak voltage more than twice the charging start voltage of the photosensitive drum and a direct current voltage are superimposed. The waveform of the oscillating voltage is not limited to a sine wave, but may be a rectangular wave, a triangular wave, a pulse wave, or a direct current.

  Next, the proximity roller charger 3 used in this embodiment will be described. The proximity gap between the charging roller 30 and the surface of the photosensitive drum 1 is 50 μm.

<Comparative Example 1>
As the resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Mn—Zn—Fr (average particle size 25 μm, volume resistivity 1.5 × 10 4
Ω · cm, content 90 wt%), and formed by injection molding so that the thickness of the resistance layer 30b is 2 mm on the surface of a φ12 stainless steel rod as the conductive member 30a at a molding density of 3.8 g / cm 3. A charging roller 30 having an outer diameter φ16 was used. The volume resistivity of the resistance layer 30b is 2 × 10 4.
It was Ω · cm.

Using this charging roller 30, when image output evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) superimposed on a DC voltage of -700 V, sandy fog or leak marks were generated. Stable charging conditions could not be found. The charging roller has a resistance value of 4 × 103.
Ω.

<Comparative example 2>
As the resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Mn—Zn—Fr (average particle size 25 μm, volume resistivity 1.5 × 10 4
Ω · cm, content 90 wt%), and formed by injection molding so that the thickness of the resistance layer 30b is 4 mm on the surface of a φ8 stainless steel rod as the conductive member 30a at a molding density of 3.8 g / cm 3. A charging roller 30 having an outer diameter φ16 was used. The volume resistivity of the resistance layer 30b is 2 × 10 4.
It was Ω · cm.

Using this charging roller 30, when image output evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of −700 V, sandy fog and leak marks were generated and stable. The charged area could not be found. The resistance value of the charging roller is 8 × 103.
Ω.

<Comparative Example 3>
As the resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Mn—Zn—Fr (average particle size 25 μm, volume resistivity 1.5 × 10 4
Ω · cm) and Ni—Zn—Fr (average particle size 30 μm, volume resistivity 3 × 10 7 Ω · cm), compounding ratio 2: 1, content 90 wt%, molding density 3.5 g / cm 3
Thus, the charging roller 30 having an outer diameter of φ16, which was injection-formed so that the thickness of the resistance layer 30b was 2 mm on the surface of a φ12 stainless steel rod, was used as the conductive member 30a. The volume resistivity of the resistance layer 30b is 1.5 × 10 5.
Ω · cm.

Using this charging roller 30, image evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of -700 V. Sand cover at 1.7 kVpp or less. Leakage traces occurred at 2 kVpp or higher, but a stable charged region could be found at 1.7 kVpp to 2.1 kVpp. The charging roller has a resistance value of 3 × 104.
Ω.

<Comparative example 4>
As the resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Mn—Zn—Fr (average particle size 25 μm, volume resistivity 1.5 × 10 4
Ω · cm) and Ni—Zn—Fr (average particle size 30 μm, volume resistivity 3 × 10 7 Ω · cm), compounding ratio 1: 1, content 90 wt%, molding density 3.5 g / cm 3
Thus, the charging roller 30 having an outer diameter of φ16, which was injection-formed so that the thickness of the resistance layer 30b was 2 mm on the surface of a φ12 stainless steel rod, was used as the conductive member 30a. The volume resistivity of the resistance layer 30b is 1 × 10 6.
Ω · cm.

Using this charging roller 30, image evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of −700 V. Sand cover at 1.7 kVpp or less. Leakage traces occurred at 5 kVpp or higher, but a stable charged region could be found at 1.7 kVpp to 2.5 kVpp. The resistance value of this charging roller is 2 × 10 5
Ω.

<Comparative Example 5>
As the resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Mn—Zn—Fr (average particle size 25 μm, volume resistivity 1.5 × 10 4
Ω · cm) and Ni—Zn—Fr (average particle size 30 μm, volume resistivity 3 × 10 7 Ω · cm), compounding ratio 1: 2, content 90 wt%, molding density 3.5 g / cm 3
Thus, the charging roller 30 having an outer diameter of φ16, which was injection-formed so that the thickness of the resistance layer 30b was 2 mm on the surface of a φ12 stainless steel rod, was used as the conductive member 30a. The volume resistivity of the resistance layer 30b is 5 × 10 6.
Ω · cm.

Using this charging roller 30, when image output evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of −700 V, sand fogging occurred at 2.1 kVpp or less. However, a stable charged region could be found at 2.2 kVVpp or higher. The resistance value of this charging roller is 1 × 10 6.
Ω.

<Comparative Example 6>
As resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Ni—Zn—Fr (average particle size 30 μm, volume resistivity 3 × 10 7
Ω · cm, content 90 wt%), and formed by injection molding so that the thickness of the resistance layer 30b is 2 mm on the surface of a φ12 stainless steel rod as the conductive member 30a at a molding density of 4 g / cm 3. The charging roller 30 was used. The volume resistivity of the resistance layer 30b is 2 × 10 7
It was Ω · cm.

Using this charging roller 30, image evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of −700 V. Sand fogging occurred at 2.3 kVpp or less. However, it was possible to find a stable charged region at 2.4 kVpp or higher. The resistance value of this charging roller is 4 × 10 6.
Ω.

<Comparative Example 7>
As the resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Mn—Mg—Zn—Fr (average particle size 25 μm, volume resistivity 5 × 10 8
Ω · cm, content 90 wt%), and formed by injection molding so that the thickness of the resistance layer 30 b is 2 mm on the surface of a φ12 stainless steel rod as the conductive member 30 a with a molding density of 3.7 g / cm 3. A charging roller 30 having a diameter of φ16 was used. The volume resistivity of the resistance layer 30b is 1.5 × 10 8.
It was Ω · cm.

Using this charging roller 30, when image output evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of -700 V, it was stable at 2.5 kVpp or more without sand cover. However, since the resistance is high, in order to obtain a desired charging potential, it is necessary to adjust the DC voltage so that the required charging potential is obtained by taking the correspondence of the charging potential to the DC voltage. there were. The resistance value of the charging roller is 3 × 10 7
Ω.

<Comparative Example 8>
As the resistance layer 30b, 6 nylon as the PA resin, ferrite magnetic powder as the filler, Mn—Mg—Zn—Fr (average particle size 25 μm, volume resistivity 5 × 10 8
Ω · cm, content 90 wt%), injection molding so that the thickness of the resistance layer 30b is 0.5 mm on the surface of a φ12 stainless steel rod as the conductive member 30a with a molding density of 3.7 g / cm 3. The charging roller 30 having an outer diameter of φ16 was used. The volume resistivity of the resistance layer 30b is 3.5 × 10 7.
It was Ω · cm.

Using this charging roller 30, when image output evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of -700 V, it was stable at 2.5 kVpp or more without sand cover. However, since the resistance is high, in order to obtain a desired charging potential, it is necessary to adjust the DC voltage so that the required charging potential is obtained by taking the correspondence of the charging potential to the DC voltage. there were. The resistance value of this charging roller is 7 × 10 6
Ω.

<Comparative Example 9>
As the resistance layer 30b, 6 nylon as PA resin, ferrite magnetic powder as filler, Mn—Mg—Zn—Fr (average particle size 25 μm, volume resistivity 5 × 10 8
Ω · cm, content 85 wt%), and formed by injection molding so that the thickness of the resistance layer 30b is 2 mm on the surface of a φ12 stainless steel rod as the conductive member 30a at a molding density of 4 g / cm 3. A charging roller 30 having a diameter of 16 was used. The volume specific resistance of the resistance layer 30b was 2 × 10 10 Ω · cm.

Using this charging roller 30, when image output evaluation was performed while switching the peak-to-peak voltage of an AC voltage (sine wave, frequency 1.8 kHz) to a DC voltage of -700 V, it was stable at 2.5 kVpp or more without sand cover. However, since the resistance is high, in order to obtain a desired charging potential, it is necessary to adjust the DC voltage so that the required charging potential is obtained by taking the correspondence of the charging potential to the DC voltage. there were. The resistance value of the charging roller is 3 × 10 7
Ω (same as Comparative Example 7).

  FIG. 4 is a graph showing the above comparative example, in which a region where a good image is obtained is plotted in the relationship between the AC voltage and the resistance value of the charging roller 30.

  In FIG. 4, a straight line A (AC voltage lower limit) and a curve α from the sand cover are a curve β for the leak trace, a straight line B (charge roller resistance lower limit) for the region where the discharge is unstable, and feedback is required. Straight lines C (charging roller resistance value upper limit) are set.

  On the other hand, when a feedback system having an internal potential sensor that measures the relationship of the surface potential to the DC voltage applied to the charging roller 30 is employed, the volume resistivity can be controlled to 1 × 10 12 Ω · cm.

  Further, the thickness of the charging roller 30 is 100 μm or more to stabilize the discharge even if the resistance is adjusted in the region shown in FIG. It goes without saying that good charging becomes possible if the thickness is controlled so as to fall within this range.

  In the comparative example, only the case where 6 nylon is used as the resin material has been described. However, EEA resin (ethylene ethyl acrylate), POM resin (polyacetal), PA resin (nylon, polyamide), PBT resin (polybutylene terephthalate), Similar results were obtained when a resin such as PPS resin (polyphenylene sulfide) was used.

  The content of the magnetic material as the filler is preferably large in consideration of the uniform dispersibility in the resistance layer 30b. In addition, although the cost is increased, there is an effect even when an alnico or neodymium magnetic material is used.

  On the other hand, Table 1 summarizes the experimental results when the charging roller used in Comparative Example 4 was used and the gap d between the charging roller 30 and the photosensitive drum 1 was changed from 1 μm to 250 μm.

1) Image:
If the gap d is up to 150 μm, charging is performed normally and a good image is obtained. When the gap is larger than 200 μm, discharge is possible, but a uniform discharge state cannot be maintained, resulting in an abnormal image. In Table 1, ◯ indicates that the image is good, Δ indicates that the image is partially defective, and X indicates that the image is defective.

2) Pinhole:
When the gap d is 1 to 3 μm, a part of the irregularities on the surface of the resistance layer 30b comes into contact with the surface of the photosensitive drum 1, so that a “pinhole” occurs due to dielectric breakdown of the photosensitive layer when a voltage is applied. Then, since the resistance layer 30b does not come into contact with the photosensitive drum 1, "pinholes" due to dielectric breakdown did not occur. In Table 1, ◯ indicates that “pinholes” have occurred, Δ indicates that some have occurred, and × indicates that they have occurred.

3) Charging sound:
When the gap d is 1 to 3 μm, a part of the unevenness on the surface of the resistance layer 30b is in contact with the surface of the photosensitive drum 1, so that “charging noise” is generated when voltage is applied. Since it is no longer in contact with the photosensitive drum 1, “charging noise” does not occur. In Table 1, “◯” indicates that “charging noise” does not occur, “Δ” slightly occurs, and “×” indicates that it occurs.

４）ホワイトスポット：
次に、比較例４で使用した帯電ローラでは表面に粒径の大きい磁性体が露出していた部分に対応してホワイトスポットが発生したが、この帯電ローラ上に、表面層３０ｄとしてフェノール樹脂（商品名: プライオーフェン、大日本インキ化学工業（株）製）１６７部をメチルセロソルブ１００部に溶解したものへ導電性硫酸バリウム超微粒子２００部及び平均粒径２μｍのシリコーン樹脂粒子３部を分散したものを浸せきコーティング法により塗工し、乾燥後の膜厚が１５μｍの導電層を形成することによって、磁性体の露出を抑え、且つ、より微粒子の導電材料とすることにより、ホワイトスポットの発生を抑えることができた。

4) White spot:
Next, in the charging roller used in Comparative Example 4, a white spot was generated corresponding to a portion where a magnetic material having a large particle size was exposed on the surface. A phenol resin (surface layer 30d) was formed on the charging roller. (Product name: PRIOFEN, manufactured by Dainippon Ink & Chemicals, Inc.) 167 parts dissolved in 100 parts of methyl cellosolve 200 parts of conductive barium sulfate ultrafine particles and 3 parts of silicone resin particles having an average particle diameter of 2 μm were dispersed. By applying a dip coating method and forming a conductive layer with a film thickness of 15 μm after drying, the exposure of the magnetic material is suppressed, and the generation of white spots can be achieved by using a finer conductive material. I was able to suppress it.

  As described above, as a proximity charging method, a charging roller having a resistance layer with a volume specific resistance of 105 to 1012 Ω · cm is set to a gap d of 5 to 150 μm with the photosensitive drum, and the toner or toner external additive attached to the charging roller surface Use with a pad, fixed brush, reciprocating fixed brush, fur brush as a cleaning means to clean the battery, and even if it is durable for 500,000 sheets, the thermosetting resin will not cause any damage to the charging roller Good results were obtained.

  Here, barium sulfate is used as the conductive fine particles and phenol resin is used as the surface layer resin. However, conductive zinc oxide, conductive titanium oxide, Al, Au, Cu, Ag, Co, Ni, Fe, carbon black, ITO The same effect was obtained even when a conductive material such as tin oxide, indium oxide, or indium and a curable resin such as polyamide, epoxy, or ethylene-vinyl acetate copolymer were used.

[Example 2]
The same effect can be obtained even if the charging roller used in the above embodiment is driven to rotate.

In FIG. 5, a charger 30 ′ is a charging roller as a charging member, and includes a cylindrical or columnar conductive member 30 a such as iron or stainless steel, and a volume specific resistance 105.
A resistance layer 30b having a resistance of 1012 Ω · cm and a surface layer 30d having a volume resistivity of 105 to 1012 Ω · cm covering the surface of the resistance layer 30b. It is supported by a ball bearing provided inside the roller 30′c. When the abutting roller 30′c is brought into contact with the photosensitive drum 1, the proximity gap with the surface of the photosensitive drum 1 becomes a predetermined amount d. As such, it can be rotationally driven.

  6A and 6B show the surface potential of the photosensitive drum 1 when the charging roller 30 'is rotated and when the charging roller 30' is not rotated. FIG. 6A shows a case where a high voltage is applied while driving the roller at 100 mm / sec (equivalent to the driven). On the other hand, FIG. 6B shows the case where the charging roller 30 is rotationally driven at 80 mm / sec in the direction opposite to that of the photosensitive drum 1 and a high voltage is applied in the same manner.

  As can be seen from both figures, when the charging roller 30 is rotationally driven in the reverse direction (FIG. 6B), it can be seen that the drum surface potential is stable and charging is performed stably. On the other hand, when the charging roller 30 ′ is rotated under the same conditions as the driven rotation (FIG. 6A), it can be seen that the drum surface potential is uneven. This unevenness is caused by a change in the interval between the photosensitive drum 1 and the charging roller 30 ′ at each pitch due to the shake of the photosensitive drum 1 and the charging roller 30 ′.

  When the charging roller 30 ′ is rotated so as to have a peripheral speed difference in order to improve the white spot in this way, the fluctuation of the interval between the photosensitive drum 1 and the charging roller 30 ′ is smoothed by the rotation of the charging roller 30, There is another effect that charging is stabilized.

  The present invention is highly applicable to a proximity charging device applicable to an image forming apparatus such as an electrophotographic copying machine, a printer, or an electrostatic recording apparatus.

1 is a schematic configuration diagram of an image forming apparatus when the present invention is applied to an electrophotographic system. FIG. 10 is a schematic diagram of a configuration of an image forming apparatus according to a conventional example. It is a schematic diagram of a roller charging device. It is a figure which shows the application range shown by the comparative example of this invention. It is a schematic diagram of a roller charging device. It is a figure which shows the change of the charging potential by the presence or absence of a circumferential speed difference.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Laser exposure means 3,30 Roller charger 3a, 30a Core metal 3b, 30b Resistive layer 30c Resin layer for ensuring a clearance 4 Developer 6 Fixing device 7 Transfer roller 8 Pre-exposure lamp

Claims (8)

In a proximity charging device for charging the image image carrier by applying a voltage to a charging member disposed close to the image carrier,
The charging member is a roller member including a cylindrical or columnar conductive member, a resistance layer having a volume resistivity of 105 to 1012 Ω · cm, and a resin layer in which conductive fine particles are dispersed covering the surface. A proximity charging device, wherein the roller member is in non-contact with the image carrier and has a closest distance of 5 to 150 μm, and the resistance layer uses a magnetic material as a conductive material.   The proximity charging device according to claim 1, wherein the magnetic body is a ferrite-based, alnico-based, or neodymium-based material.   The roller resistance layer or resistor has EEA resin (ethylene ethyl acrylate), POM resin (polyacetal), PA resin (nylon, polyamide), PBT resin (polybutylene terephthalate), PPS resin (polyphenylene sulfide). The proximity charging device according to claim 1 or 2, characterized in that:   The conductive fine particles are at least one selected from conductive zinc oxide, conductive titanium oxide, Al, Au, Cu, Ag, Co, i, Fe, carbon black, ITO, tin oxide, indium oxide, indium, and barium sulfate. The proximity charging device according to claim 1, wherein the proximity charging device is a single charging device.   The proximity charging device according to claim 1, wherein the resin layer contains at least one selected from polyamide, epoxy, ethylene-vinyl acetate copolymer, and phenol resin.   The proximity charging device according to claim 1, wherein the roller member is driven to rotate as the image carrier moves.   6. The roller member according to claim 1, wherein the roller member is rotationally driven with a relative speed difference between the moving speed of the surface of the roller member and the moving speed of the surface of the image carrier in the same direction or in the opposite direction. The proximity charging device according to claim 1.   The proximity charging device according to claim 1, further comprising a cleaning member that cleans the roller member in the vicinity of the roller member.

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