JP4750287B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image forming apparatus such as an electrophotographic system or an electrostatic recording system, in which a charging process means for charging an image bearing member is a contact charging apparatus, which is a transfer system and cleanerless.
[0002]
[Prior art]
  (A) Contact charging device
  Conventionally, for example, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric is uniformly charged to a required polarity and potential (including static elimination). The corona charger (corona discharger) was used as the charging device.
[0003]
  The corona charger is a non-contact type charging device, for example, 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 object to be charged. The surface of the object to be charged is charged to a predetermined level by exposing the surface of the object to be charged to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode.
[0004]
  In the contact charging device, a conductive charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type, a blade type or the like is brought into contact with an object to be charged, and a predetermined charging bias is applied to the contact charging member. Thus, the surface of the image carrier is charged to a predetermined polarity and potential.
[0005]
  The contact charging mechanism (charging mechanism, charging principle) has two types of charging mechanisms: a discharge charging mechanism and an injection charging mechanism (direct charging mechanism), and each characteristic depends on which is dominant. appear.
[0006]
  [Discharge charging mechanism]
  This is a mechanism for charging the surface of the member to be charged by a discharge phenomenon that occurs in a minute gap between the contact charging member and the member to be charged.
[0007]
  Since the discharge charging mechanism has a certain discharge threshold between the contact charging member and the member to be charged, it is necessary to apply a voltage larger than the charging potential to the contact charging member. Further, although the generation amount is remarkably smaller than that of the corona charger, it is unavoidable that a discharge product is generated in principle, and thus harmful effects due to active ions such as ozone are unavoidable.
[0008]
  [Injection charging mechanism]
  This is a mechanism for charging the surface of the member to be charged by directly injecting the charge from the contact charging member to the member to be charged. Also called direct charging.
[0009]
  More specifically, a medium-resistance contact charging member comes into contact with the member to be charged, and charges are directly injected into the surface of the member to be charged without going through a discharge phenomenon, that is, basically without using discharge. Therefore, even if the applied voltage to the contact charging member is an applied voltage that is equal to or lower than the discharge threshold, the object to be charged can be charged to a potential corresponding to the applied voltage. Since this injection charging mechanism does not involve the generation of ions, there is no adverse effect caused by the discharge product.
[0010]
  However, since the charging is injection charging, the contact property of the contact charging member to the member to be charged greatly affects the charging property. Therefore, the contact charging member needs to be configured more densely, have a large speed difference from the object to be charged, and must be configured to contact the object to be charged more frequently.
[0011]
  The magnetic brush charging device is a charging means in which the injection charging mechanism is dominant.
[0012]
  In addition, the injection charging mechanism is dominant in the particle charging device disclosed in, for example, Japanese Patent Application Laid-Open No. 10-307454-30759, etc., which is contact-charged through non-magnetic / conductive fine particles (charged particles, charge promoting particles)NaIt is a charging means.
[0013]
  (B) Cleanerless (toner recycling system)
  In a conventional general transfer type image forming apparatus, a transfer residual developer (toner) remaining on an image carrier after transfer is removed from the image carrier surface by a cleaner (cleaning device) to become waste toner. It is desirable that this waste toner does not come out from the viewpoint of environmental protection.
[0014]
  Therefore, the cleaner is eliminated, and the transfer residual developer on the image carrier after transfer is removed from the image carrier by “development simultaneous cleaning” by the developing device, and the cleaner-less image is collected and reused in the developing device. A forming device has also appeared.
[0015]
  Simultaneous development cleaning is a fog removal bias (a difference in fog removal potential, which is the difference between the DC voltage applied to the developing device and the surface potential of the image carrier) when developing on the image carrier after the transfer. Vback). According to this method, the untransferred developer is collected by the developing device and reused in the subsequent steps, so that waste toner can be eliminated and maintenance work can be reduced. Further, the cleanerless has a great advantage in terms of space, and the image forming apparatus can be greatly downsized.
[0016]
  (C) Contact charging, transfer, and cleanerless image forming apparatus
  In a transfer type / cleanerless image forming apparatus, when a contact charging device is adopted as the charging means for the image carrier, the transfer residual in the developing device is caused by the scattering effect of the transfer residual developer by the charging member in contact with the image carrier. Positive ghosts due to poor developer recovery can be suppressed. Since it is cleanerless, there is an advantage that there is no damage to the surface of the image carrier due to the cleaning member that is in contact with and rubs against the surface of the image carrier.
[0017]
  Magnetic brush charging using, as a contact charging member, a magnetic brush charging member having a magnetic brush portion in which conductive magnetic particles are magnetically constrained into a brush shape is preferably used in a cleanerless process.
[0018]
  Further, in the particle charging method disclosed in Japanese Patent Application Laid-Open No. 10-307454-30759 and the like, in which contact charging is performed via charge accelerating particles, the charge accelerating particles are externally added to the developer of the developing device in advance, together with the developer. There is also disclosed a method for realizing a cleanerless process by supplying charging promoting particles to a contact charging member by developing (attaching to an image carrier).
[0019]
[Problems to be solved by the invention]
  In an image forming apparatus of contact charging type / transfer type / cleanerless, the transfer residual developer adhering / mixing (temporarily recovered) to the contact charging member is adjusted to the normal polarity and the contact charging member is changed to the image carrier. The toner is sequentially discharged electrostatically, is carried to the developing unit by the subsequent rotation of the image carrier, and is collected and reused by the developing device through the simultaneous development cleaning.
[0020]
  However, transfer that adheres to and mixes with the contact charging member due to a loss of quantitative balance between the amount of residual developer that adheres to and mixes with the contact charging member and the amount of developer that is electrostatically discharged from the contact charging member. If the remaining developer accumulates and the contact charging member is unacceptably contaminated with the developer, the chargeability is lowered.
[0021]
  Therefore, the applicant previously applied an AC voltage of 5 to 500 Hz in order to positively clean the transfer residual developer adhering to the surface of the contact charging member as described in JP-A-11-149205. The technology to do is proposed. This technology is effective for low-speed printing type devices, but it may not be sufficient for long-term stability, and charging performance may be reduced when performing high-speed printing. .
[0022]
  The present invention relates to a further improvement of this technology, and as a contact charging system, transfer system, and cleanerless image forming apparatus, even if it is durable over a long period of time or in the case of a high-speed printing type apparatus, it is a transfer residual development. It is an object of the present invention to provide an image forming apparatus capable of maintaining good chargeability and image quality by preventing the agent from accumulating unacceptably on the surface of the contact charging member.
[0023]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention is an image forming apparatus having the following configuration.
[0024]
    An image carrier;
  A charging member that contacts the image carrier with a peripheral speed difference to charge the image carrier;
  A developing device for developing the electrostatic latent image formed on the image carrier with a developer;
In an image forming apparatus comprising:
  Non-magnetic conductive particles are carried on the surface of the charging member, and the conductive particles are charged to a polarity opposite to the charging polarity of the developer by rubbing with the developer,
  The developing device can collect the developer remaining on the image carrier,
  During non-image formationThe aboveFor charging member, Charging memberAC bias for cleaningApplied,
  The exchangebiasofThe frequency (Hz = cycle / s),
  Alternating currentBias frequency (Hz = cycle / s)> ([Peripheral speed of image carrier(Mm / s)] ×[bandElectric member peripheral speed (%)] × 10 (cycle)) / ([length of contact portion between image carrier and charging member (mm)] × (100% +[bandElectrical member peripheral speed (%)]))age,
  In addition, the change in potential per unit time when the AC bias increases in the same direction as the polarity of the developer increases in potential per unit time when the amount of change in potential increases in the direction opposite to the polarity of the developer. The waveform is larger than the amountAn image forming apparatus.
[0025]
[0026]
[0027]
[0028]
[0029]
[0030]
[0031]
[0032]
DETAILED DESCRIPTION OF THE INVENTION
  <Reference Example 1>
  Figure 1Reference example2 is a schematic configuration model diagram of the image forming apparatus of FIG.This exampleThe image forming apparatus is a copier or a printer using a transfer type electrophotographic process, an injection charging method using charge accelerating particles, a laser beam scanning exposure method, a reversal development method, a cleanerless process cartridge method.
[0033]
  (1) Description of overall schematic configuration of image forming apparatus
  [Image carrier]
  Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image carrier.This exampleThe image forming apparatus uses reversal development and uses a negative photosensitive member.
[0034]
  This exampleThe photosensitive member 1 is an OPC photosensitive member having a diameter of 30 mm, and is driven to rotate at a peripheral speed (= process speed) of 200 mm / sec in the clockwise direction of an arrow.
[0035]
  [Charge]
  Reference numeral 2 denotes a conductive elastic roller as a contact charging member brought into contact with the photoreceptor 1. The surface of the contact charging member 2 is coated with the charge accelerating particles m in advance. The photoreceptor 1 and the contact charging member 2 have a peripheral speed difference.This exampleThen, the contact charging member 2 is driven at a peripheral speed of 150% in the opposite direction (counter direction) to the rotation direction of the photosensitive member 1 in the charging portion a which is a contact portion with the photosensitive member 1.
[0036]
  Here, driving at a peripheral speed of 150% is a peripheral speed of 300 mm / sec in the facing direction (counter direction). 100% here means that “the speed of the surface of the contact charging member 2” is the same as the “speed of the surface of the photoreceptor 1” (however, the direction is opposite). Therefore, in the case of 150%, it is 300 mm / s at 200 mm / sec × 150%.
[0037]
  A DC voltage of −620 V is applied as a charging bias from the charging bias power source S1 to the contact charging member 2 so that the outer peripheral surface of the photoreceptor 1 is uniformly charged to approximately −600 V during image formation. The charging mechanism is dominated by the injection charging mechanism.
[0038]
  AlsoThis exampleThe applied voltage to the contact charging member 2 is variable between the image forming time and the non-image forming time, and the DC voltage of −620 V is applied as described above during the image forming time. At that time, a rectangular AC wave having a frequency of 600 Hz, a peak-to-peak voltage of 400 V, and a DC component of -620 V is applied.
[0039]
  As will be described later, the charge accelerating particles m are also mixed in the developer 31 of the developing device 3 at a predetermined mixing ratio, and the charge accelerating particles m mixed in the developer 31 adhere to the surface of the photoreceptor 1 during development. Then, it is carried to the charging unit a and supplied.
[0040]
  [Exposure]
  Laser beam scanning exposure L by a laser beam scanner 10 including a laser diode, a polygon mirror, and the like is performed on the charged surface of the photosensitive member 1 in the exposure unit b.
[0041]
  The laser beam scanner 10 outputs a laser beam whose intensity is modulated in accordance with the time-series electric digital pixel signal of the target image information, and performs scanning exposure L on the charged surface of the photoreceptor 1. Thereby, an electrostatic latent image corresponding to the target image information is formed on the outer peripheral surface of the photoreceptor 1.This exampleThen, an electrostatic latent image having an image resolution of 600 dpi is formed.
[0042]
  [Current image]
  The electrostatic latent image is developed as a toner image by the reversing non-contact developing device 3 using a negatively chargeable magnetic one-component insulating toner having an average particle diameter of 6 μm as the developer 31.
[0043]
  Reference numeral 32 denotes a non-magnetic developing sleeve having a diameter of 16 mm containing a magnet 33. The developing sleeve 32 is coated with the developer 31 and the distance from the surface of the photosensitive member 1 is fixed to 500 μm. The developing bias voltage is applied to the developing sleeve 32 from the developing bias power source S2 by rotating at a constant speed. The developer 31 is triboelectrically charged by sliding with the developing elastic blade 34 and has a charge. By applying a predetermined developing bias to the developing sleeve 32, one-component jumping development is performed between the developing sleeve 32 and the photoreceptor 1 in the developing portion c.
[0044]
  As the developing bias, a rectangular AC wave having a frequency of 1.6 kHz, a peak-to-peak voltage of 1.7 kV, and a DC component of −400 V is applied.
[0045]
  [Transfer]
  On the other hand, a transfer material P as a recording material is supplied from a paper supply unit (not shown), and the photosensitive member 1 and a transfer roller 4 with medium resistance as contact transfer means brought into contact with the photoconductor 1 with a predetermined pressing force. Are introduced at a predetermined timing into the transfer part d which is the pressure contact part.
[0046]
  A predetermined transfer bias power source is applied to the transfer roller 4 from a transfer bias application power source S3.This exampleThen, as the transfer roller 4, the roller resistance value = 5 × 10⁸Transferring was performed by applying a DC voltage of +3000 V using an Ω.
[0047]
  The transfer material P introduced into the transfer portion d is transferred to the transfer portion d.PinchingThe developer image formed and supported on the surface of the photosensitive member 1 is transferred onto the surface side in succession by the electrostatic force and the pressing force.
[0048]
  [Fixed]
  The transfer material P that has received the transfer of the developer image is separated from the surface of the photoreceptor 1 and is introduced into a fixing device 5 such as a heat fixing system, where the developer image is fixed, and as an image formed product (print, copy). It is discharged out of the device.
[0049]
  [Cleanerless]
  The transfer residual developer remaining on the surface of the photoconductor 1 after the transfer material is separated is not removed from the surface of the photoconductor 1 by a dedicated cleaning device (cleaner) because the image forming apparatus is cleanerless. As the body 1 rotates, it is carried to the charging part a and adheres to and mixes with the contact charging member 2 (temporary recovery of the transfer residual developer by the contact charging member). Then, the transfer residual developer adhering to and mixed in the contact charging member 2 is adjusted to the normal polarity, and is discharged electrostatically and sequentially from the contact charging member 2 to the photosensitive member 1, and developed by the subsequent rotation of the photosensitive member 1. It is carried to the part c and is collected and reused by the developing device 3 by the simultaneous development cleaning.
[0050]
  [cartridge]
  This exampleThe image forming apparatus is a cartridge-type apparatus in which three process devices including a photosensitive member 1, a contact charging member 2, and a developing device 3 are included in a cartridge C and can be attached to and detached from the main body of the image forming apparatus. However, it is not limited to this. Reference numerals 9 and 9 denote part of the process cartridge attachment / detachment guide / holding member on the image forming apparatus side.
[0051]
  Here, the process cartridge is a cartridge in which a charging unit, a developing unit or a cleaning unit and an image carrier are integrally formed, and the cartridge can be attached to and detached from the image forming apparatus main body. In addition, at least one of the charging unit, the developing unit, and the cleaning unit and the image carrier are integrally formed into a cartridge, and the cartridge can be attached to and detached from the image forming apparatus main body. Further, at least the developing means image carrier is integrally formed into a cartridge, and the cartridge can be attached to and detached from the image forming apparatus main body.
[0052]
  (2) Operation sequence of image forming apparatus
  FIG. 2 is an operation sequence diagram of the image forming apparatus.
[0053]
  1)Pre-multi-rotation process: a starting operation period (starting operation period, warming period) of the image forming apparatus. When the main power switch is turned on, the main motor of the apparatus is driven to rotationally drive the photosensitive member to execute a preparatory operation for a predetermined process device.
[0054]
  2)Pre-rotation step: This is a period during which the pre-printing operation is executed. This pre-rotation process is executed subsequent to the pre-multi-rotation process when a print signal is input during the pre-multi-rotation process. When no print signal is input, the main motor is temporarily stopped after completion of the previous multi-rotation process, and the rotation of the photosensitive member is stopped. The apparatus is kept in a standby state until a print signal is input. . When the print signal is input, the pre-rotation process is executed.
[0055]
  3)Printing process (image forming process, image forming process): When a predetermined pre-rotation process is completed, an image forming process for the rotating photoconductor is subsequently executed, and a developer image formed on the surface of the rotating photoconductor is transferred to a transfer material. Then, the developer image is fixed by the fixing means, and the image formed product is printed out.
[0056]
  In the case of the continuous printing (continuous printing) mode, the above printing process is repeated for a predetermined set number of prints.
[0057]
  4)Inter-sheet process: In the continuous print mode, after the trailing edge of one transfer material passes through the transfer portion, the transfer material is not allowed to pass through the transfer portion until the leading edge of the next transfer material reaches the transfer portion. It is a paper state period.
[0058]
  5)Post-rotation process: This is a period during which a predetermined post-operation is executed by continuing to drive the main motor for a while even after the last transfer material printing process is completed to rotate the photosensitive drum.
[0059]
  6)Standby: When the predetermined post-rotation process is completed, the drive of the main motor is stopped, the rotation of the photosensitive member is stopped, and the apparatus is kept in a standby state until the next print start signal is input.
[0060]
  In the case of printing only one sheet, after the printing is completed, the apparatus goes into a standby state through a post-rotation process.
[0061]
  When a print start signal is input in the standby state, the apparatus shifts to a pre-rotation process.
[0062]
  3)The printing process is the time of image formation,1)Before multi-rotation process,2)Pre-rotation process,4)Inter-paper process,5)The post-rotation process is during non-image formation (non-image formation).
[0063]
  In FIG. 1, reference numeral 100 denotes a control circuit unit that controls all operations of the image forming apparatus.
[0064]
  (3) Contact charging member 2
  This exampleThe conductive elastic roller 2 as a contact charging member is formed by forming a middle resistance layer 22 of rubber or foam on a cored bar 21. The middle resistance layer 22 is made of resin (This exampleAnd urethane), conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and formed on the core metal 21 in a roller shape. Thereafter, the surface was polished.
[0065]
  The resistance value of the contact charging member 2 was measured as follows. That is, the photoreceptor 1 of the image forming apparatus is replaced with an aluminum drum. Thereafter, a voltage of 100 V was applied between the aluminum drum and the contact charging member 2, and the resistance value of the contact charging member 2 was obtained by measuring the current value flowing at that time.
[0066]
  This exampleThe resistance value of the contact charging member 2 used in FIG.⁶Ω. This measurement was performed in an environment of a temperature of 25 ° C. and a humidity of 60%. About this measurement environment,This exampleAnd otherReference Example 2,The same applies to other measurements in the examples.
[0067]
  The average cell diameter on the surface of the contact charging member 2 was 20 μm for each resistance value. The average cell diameter was measured by observation with an optical microscope.
[0068]
  (4) Charge promoting particles m
  This exampleThen, the specific resistance is 10 as the charge promoting particles m.⁷Conductive zinc oxide particles having an Ω · cm and an average particle diameter of 1 μm were used.
[0069]
  The particle size was defined as the average particle size of the aggregates when the particles were configured as aggregates. 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.
[0070]
  Resistance was measured by the tablet method and normalized. Bottom area 2.26cm²A powder sample of about 0.5 g is placed in the cylinder, and 147 N (15 kg) is applied to the upper and lower electrodes. At the same time, a voltage of 100 V is applied to measure the resistance value, and then normalized to calculate the specific resistance. did.
[0071]
  This exampleThe charge-promoting particles m used in 1) are suitably colorless or white particles so as not to interfere with the latent image exposure. Further, the image exposure may be blocked unless the particle size is about ½ or less of the particle size of the developer (toner) 31. So it needs to be smaller.
  As a material for the charge promoting particles m,This exampleIn this example, conductive zinc oxide particles are used. However, the present invention is not limited to this, and various conductive particles such as conductive inorganic particles such as other metal oxides and mixtures with organic substances can be used as the material of the particles.
[0072]
  (5) Developer 31
  This exampleThe developer 31 used in Example 1 contained a binder resin mainly composed of a styrene-acrylic copolymer, 60% by weight of magnetite, and 1% by weight of a metal complex salt of a monoazo dye as a negative charge control material. The rate is about 10¹³An Ω · cm magnetic one-component insulating toner obtained by adding 0.8% of silica fine particles hydrophobized to impart fluidity to the developer by weight is used.
[0073]
  Further, in a comparative example described later, developer A is the developer described above, and developer B is substantially the same as developer A, but the metal complex salt of a monoazo dye that is a negative charge control material is 1.1. The developer was changed to wt%, and the developer C was similarly changed to 0.9 wt%.
[0074]
  The toner 31 as a developer is mixed with the charge promoting particles m, and the amount of the mixing is 2 parts by weight of the charge promoting particles with respect to 100 parts by weight of the developer. However, the mixing amount is not limited to this amount.
[0075]
  This exampleThen, by charging the charge electrifying particles m on the contact charging member 2 in advance, the charging property at the initial stage of use of the apparatus is secured, and the charge promoting particles m are mixed into the developer 31 of the developing device as described above. In addition, the charge accelerating particles m are supplied from the developing device 3 to the contact charging member 2 through the surface of the photoreceptor.
[0076]
  That is, the charge accelerating particles m mixed in the developer 31 in the developing device 3 adhere to the developer 31 and migrate and adhere to the surface of the photoreceptor 1 when developing the electrostatic latent image. In addition, since a negative charge control agent is added to the developer 31, the charge accelerating particles m are frictionally charged against the positive charge and have a positive charge of opposite polarity. Therefore, the charge accelerating particles m in the developer 31 on the developing sleeve 32 are supplied from the developing sleeve 32 to the surface of the photoreceptor 1 due to a potential difference between the developing sleeve 32 and the surface of the photoreceptor 1.
[0077]
  Since the charge accelerating particles m have a charge with a polarity opposite to that of the developer 31, they are not substantially transferred to the transfer material P in the transfer portion d and are carried to the charging portion a, resulting in contact charging. The material 2 is supplied and coated. By supplying and coating the charge accelerating particles m to the contact charging member 2 in this manner, the state where the charge accelerating particles m are always interposed in the charging portion a is maintained, and good chargeability can be obtained.
[0078]
  (6) Cleaning bias application sequence for the contact charging member 2
  This exampleApplies a cleaning bias including an AC bias for cleaning the surface of the contact charging member 2 to the contact charging member 2 during non-image formation, and the cleaning bias frequency (Hz = cycle / s) is
  Cleaning bias frequency (Hz = cycle / s)> ([process speed (mm / s)] × [contact charging member peripheral speed (%)] × 10 (cycle)) / ([contact between image carrier and contact charging member] Part length (mm)] × (100% + [contact charging member peripheral speed (%)]))
  It sets so that it may become.
[0079]
  The cleaning bias application sequence for the contact charging member 2 is the same as the operation sequence of the image forming apparatus described in the item (2).1) ・ 2) ・ 4) ・ 5)It is not necessary to execute at the time of all non-image formation, or at the time of forming one or a plurality of non-images, or at least a predetermined time within one or a plurality of non-image formation It can also be.
[0080]
  This exampleUses a cleaner-less process that does not include a step of cleaning a residual transfer developer remaining on the surface of the photoreceptor 1 after the transfer step. Therefore, the transfer residual developer adheres to the surface of the contact charging member 2 in the charging step. Therefore, as described above, there is a conventional technique in which an AC voltage of 5 to 500 Hz is applied in order to clean the surface of the contact charging member during non-image formation as described in JP-A-11-149205. However, even when this technique is used, the surface of the contact charging member is not sufficiently cleaned when high-speed printing or long-term printing is performed, and the chargeability may be deteriorated.
[0081]
  The reason why the charging property is lowered is that this conventional technique is considered only for low-speed printing, and when high-speed printing is performed, uneven cleaning on the surface of the contact charging member may occur remarkably. A point is mentioned.
[0082]
  In particular,This exampleIn a device having a process speed of about 200 mm / s, when a cleaning bias is applied to the surface of the contact charging member at about 500 Hz, the surface of the contact charging member has “cleaning unevenness corresponding to its frequency”. The charged potential on the surface of the photoreceptor 1 is affected.
[0083]
  The contact charging member 2 forms a contact portion a having a certain length (circumferential length: nip width) n with respect to the surface of the photoreceptor 1. If the “size of cleaning unevenness on the surface of the contact charging member” is sufficiently short with respect to the length n of the contact portion a, charging potential unevenness does not occur on the surface of the photoreceptor. However, when the length of the contact portion a between the contact charging member 2 and the surface of the photoreceptor 1 is not negligible, the contact charging member 2 causes unevenness in the charging performance on the surface of the photosensitive member 1, and as a result, uneven charging occurs on the surface of the photosensitive member 1.
[0084]
  For example, the process speed is 200 mm / sThis exampleIn the case where an AC voltage of 200 Hz is used as the cleaning bias, unevenness on the surface of the contact charging member is
  200 (mm / s) [process speed] × 150% [contact charging member peripheral speed] / 200
(Hz = cycle / s) ≈1.5 (mm / cycle)
It becomes.
[0085]
  This exampleThen, the length n of the contact portion a between the contact charging member 2 and the surface of the photoreceptor 1 is about 2 mm, and the length of the contact charging member 2 that rubs while the surface of the photoreceptor 1 passes through the contact portion a is
  2 (mm) [length n of contact part a] × (100% + 150% [contact charging member peripheral speed])
≒ 5mm
It becomes.
[0086]
  In this case, the length of the contact charging member on which the surface of the photosensitive member 1 rubs is only 5 mm, which is about three times as high as 1.5 mm, which is the size of the cleaning unevenness on the surface of the contact charging member. For this reason, when the surface of the photosensitive member 1 is charged, uneven cleaning on the surface of the contact charging member cannot be ignored, and uniform chargeability cannot be obtained.
[0087]
  This exampleAs a result of an experiment in which the frequency of the cleaning bias was changed using the image forming apparatus, the “size of uneven cleaning on the surface of the contact charging member” was changed to “the length of the contact charging member on which the surface of the photosensitive member 1 rubs”. On the other hand, if the ratio exceeds 1/10, uneven charging occurs.
[0088]
  That is,
  “Size of cleaning unevenness of contact charging member surface” = 200 (mm / s) [process speed] × 150% [contact charging member peripheral speed] / 200 (Hz = cycle / s)
But,
  “Contact charging member length with which the surface of photoconductor 1 rubs” = 2 (mm) [length of contact portion] × (100% + 150% [contact charging member peripheral speed]) / 10 (cycle / s)
It is necessary to be smaller. If you write this in general,
  [Length of contact portion] (mm) × (100% + [contact charging member peripheral speed] (%)) / 10 (cycle / s)> [process speed] (mm / s) × [contact charging member peripheral speed ] (%) / [Cleaning bias frequency] (Hz = cycle / s)
  Because
  Cleaning bias frequency (Hz = cycle / s)> ([process speed (mm / s)] × [contact charging member peripheral speed (%)] × 10 (cycle)) / ([contact between image carrier and contact charging member] Part length (mm)] × (100% + [contact charging member peripheral speed (%)]))
If so, cleaning unevenness on the surface of the contact charging member did not affect the chargeability.
[0089]
  This exampleIf you say
  200 (mm / s) × 150% × 10 (cycle) / (2 (mm) × (100 + 150) (%)) = 600 (Hz = cycle / s)
Therefore, when a frequency of 600 Hz or more was applied as a cleaning bias for the contact charging member 2, a good image without charging unevenness was obtained.
[0090]
  in this way,This exampleIs the frequency of the cleaning bias on the surface of the contact charging member,
  Cleaning bias frequency (Hz = cycle / s)> ([process speed (mm / s)] × [contact charging member peripheral speed (%)] × 10 (cycle)) / ([contact between image carrier and contact charging member] Part length (mm)] × (100% + [contact charging member peripheral speed (%)]))
By setting so as to be, it becomes possible to obtain good chargeability without the cleaning unevenness of the surface of the contact charging member due to the frequency of the cleaning bias affecting the chargeability.
[0091]
  In addition,This exampleThen, the DC value or the like of the cleaning bias applied to the contact charging member 2 is not changed, but the present invention is not limited to this, and the DC value may be changed at the time of the cleaning bias in order to perform stronger cleaning.
[0092]
  <Reference Example 2>
  This reference exampleIsReference example 1In addition to the above characteristics, by changing the development bias in accordance with the cleaning sequence for the contact charging member 2, the contact charging member cleaning bias potential applied to the contact charging member 2 is charged rather than the potential of the development bias. It is characterized by not being lowered with respect to the potential direction.
[0093]
  As a result, the residual transfer developer discharged from the contact charging member 2 can be easily collected in the developing device 3, and at the same time, the developer is developed (attached) from the developing device 3 to the surface of the photosensitive member when the contact charging member cleaning bias is applied. Can be prevented.
[0094]
  In addition,This exampleThe image forming apparatus used in 1 is almost the same as in Example 1, but only the developing bias when performing the cleaning sequence for the contact charging member 2 during non-image formation is different.
[0095]
  That is, the developing bias is changed between image formation and non-image formation, and a rectangular alternating wave having a frequency of 1.6 kHz, a peak-to-peak voltage of 1.7 kV, and a DC component of −450 V is applied during image formation. In non-image formation, a rectangular AC wave having a frequency of 1.6 kHz, a peak-to-peak voltage of 1.7 kV, and a DC component of −300 V is applied.
[0096]
  This exampleThen, for the purpose of cleaning the surface of the contact charging member, a rectangular AC wave having a frequency of 600 Hz, a peak-to-peak voltage of 400 V, and a DC component of −620 V is superimposed on a DC voltage of −620 V with respect to the contact charging member 2 during non-image formation. ing.This exampleSince the injection charging mechanism is used, the surface of the photosensitive member is substantially equal to the potential applied to the contact charging member 2. Therefore, the contact charging member 2This exampleWhen an AC voltage such as a cleaning bias is applied, potential unevenness corresponding to the AC voltage occurs on the surface of the photoreceptor.
[0097]
  For example,This exampleThen, the potential unevenness in each minute region of plus / minus 200V around −620V occurs. That is, the photosensitive member surface potential during application of the contact charging member cleaning bias has potential unevenness in the range of −420 to 820V.
[0098]
  for that reason,This exampleAs shown in FIG. 3, if a rectangular AC wave having a frequency of 1.6 kHz, a peak-to-peak voltage of 1.7 kV, and a DC component of −450 V is applied even during non-image formation, like the developing bias during image formation of Furthermore, since the developing bias is −450 V, the surface potential of the photoconductor 1 is partially −420 V, so that the developer is developed from the developing device 3 on a part of the surface of the photoconductor (see FIG. Have been attached)
[0099]
  for that reason,This exampleThen, by changing the developing bias during application of the contact charging member cleaning bias during non-image formation, the developing bias is changed to a rectangular AC wave having a frequency of 1.6 kHz, a peak-to-peak voltage of 1.7 kV, and a DC component of −300 V. Unnecessary development of the developer from the developing device 3 onto the surface of the photoreceptor can be prevented.
[0100]
  At the same time, by increasing the back contrast potential of the developing bias (difference between the DC value of the photosensitive member surface potential and the developing bias), the transfer residual developer discharged from the contact charging member surface to the photosensitive member 1 surface is increased. Recovery potential can be increased by increasing the potential difference that promotes recovery to the developing device.
[0101]
  With these features, in this example, when the surface of the contact charging member is cleaned, it is possible to efficiently collect the transfer residual developer and prevent the developer from being unnecessarily developed from the developing device. Become.
[0102]
  <Example>
  This embodiment is characterized in that a sawtooth wave having a sharp edge in the charging potential direction is used as a cleaning bias applied to the contact charging member 2 during non-image formation.
[0103]
  Thereby, it is possible to prevent the charge promoting particles m from being excessively discharged when the transfer residual developer is cleaned from the surface of the contact charging member.
[0104]
  The image forming apparatus used in this example isReference example 2And the cleaning bias of the contact charging member is different.
[0105]
  In this embodiment, the applied bias is variable during image formation and non-image formation, a DC voltage of -620 V is applied during image formation, and a frequency of 600 Hz and peak is applied to the contact charging member during non-image formation. A sawtooth alternating current wave having a sharp edge in the charging potential direction with an inter-voltage of 400 V and a DC component of −620 V is applied.
[0106]
  The residual transfer developer adhering to the surface of the contact charging member is negatively charged as the original charge polarity by rubbing against the charge accelerating particles m. Therefore, when the potential of the contact charging member 2 is larger in the charging potential polarity direction than the potential of the surface of the photoreceptor 1, the residual transfer developer is easily discharged from the surface of the contact charging member to the surface of the photoreceptor 1. That is, when the cleaning bias of the contact charging member 2 has a sharp edge in the charging potential direction, the transfer residual developer can be effectively discharged from the surface of the contact charging member.
[0107]
  On the other hand, since the charge accelerating particles m are positively charged with the opposite charge polarity to the residual transfer developer, the potential of the contact charging member 2 is smaller in the direction of the charged potential polarity than the potential of the surface of the photoreceptor 1. It becomes easy to be discharged in case. That is, when the cleaning bias of the contact charging unit 2 has a sharp edge in the direction opposite to the charging potential direction, the charge accelerating particles m are easily discharged from the surface of the contact charging member.
[0108]
  If the charge accelerating particles m are excessively discharged from the surface of the contact charging member, the chargeability is lowered, which is not preferable. Therefore, in this embodiment, as the cleaning bias of the contact charging member 2, the cleaning bias of the contact charging member 2 has a sharp edge in the charging potential direction, and the cleaning bias of the contact charging member has a sharp edge in the direction opposite to the charging potential direction. No sawtooth wave is used.
[0109]
  FIG. 4 shows the cleaning bias of the contact charging member. As shown in FIG. 4, by using such a waveform, the transfer residual developer on the surface of the contact charging member is effectively discharged, and at the same time, the charge promoting particles m are excessively discharged. Can be prevented.
[0110]
  In the present embodiment, the sawtooth wave is used as the cleaning bias of the contact charging member 2, but the present invention is not limited to this, and any other waveform, for example, a sine wave having a different duty, may be used as long as the above two conditions are satisfied. Etc. may be used.
[0111]
  <Others>
  1) The image carrier may be either one having a dominant corona chargeability or one having a dominant injection chargeability.
[0112]
  10 on the surface⁹-10¹⁴By providing a layer made of a material of Ω · cm, the contact injection charging property can be made dominant. For example, it has a photosensitive layer and a surface layer, and the surface layer is SnO.₂And a resin layer (charge injection layer) in which conductive fine particles are dispersed. Even when the charge injection layer is not used, for example, even when the charge transport layer of the photoreceptor is in the above resistance range, the contact injection charging property can be made dominant. The volume resistance of the surface layer is about 10¹³The same effect can be obtained even if an amorphous silicon photoconductor (Ω · cm) is used.
[0113]
  2) The image carrier is not limited to a photoconductor, and may be an electrostatic recording dielectric or the like. In this case, an electrostatic latent image is formed by selectively discharging the uniformly charged magnetic brush contact charging device of the embodiment or the surface of the image carrier by a discharging means such as a discharging needle array or an electron gun.
[0114]
  3)In the above embodiment,Image carrier contact charging device, NonInjection charging device using electrification promoting particles that are magnetic and conductive fine powderIt is.
[0115]
  4) The developing system of the developing device is also arbitrary. In general, the electrostatic latent image is developed by coating a non-magnetic toner on a developer carrying member such as a sleeve with a blade or the like, and magnetic toner on a developer carrying member. A method of developing an electrostatic latent image by coating and transporting by force and applying it in a non-contact state to the image carrier (one-component non-contact development), and coating on the developer carrying member as described above A method of developing an electrostatic latent image by applying toner in contact with an image carrier (one-component contact development) and a developer obtained by mixing a magnetic carrier with toner particles (two-component developer) And a method of developing the electrostatic latent image by conveying it by magnetic force and applying it in contact with the image carrier (two-component contact development), and the developer in a non-contact state with respect to the image carrier. Apply and develop electrostatic latent image It is roughly divided into four types of modulo (two component non-contact development).
[0116]
  5) The transfer unit 4 is not limited to roller transfer, and may be any transfer such as belt transfer, corona discharge transfer, or pressure transfer.
[0117]
  6) An image forming apparatus that uses an intermediate transfer means such as a transfer drum or a transfer belt to form not only a single color image but also a multicolor or full color image by multiple transfer or the like may be used.
[0118]
【The invention's effect】
  As described above, according to the invention, the image forming apparatus of the contact charging system, the transfer system, and the toner recycling system is contaminated by the residual transfer developer.StripEfficiently discharges toner, which is a charging inhibiting factor, from electric members, can maintain good chargeability stably over a long period of time, can execute direct charging and toner recycling system without any problems, and achieve high-quality image formation for a long time Can be maintained over time.In addition, it is possible to prevent the charge accelerating particles m from being excessively discharged when the transfer residual developer is cleaned from the surface of the charging member.
[Brief description of the drawings]
[Figure 1]Reference example 1Schematic model diagram of image forming apparatus
FIG. 2 is an operation sequence of the image forming apparatus.
[Fig. 3]Reference example 2Explanation of contact charging member cleaning bias and development bias
[Fig. 4]ExampleExplanation of contact charging member cleaning bias
[Explanation of symbols]
  1 .... Image carrier (photoconductor) 2..Contact charging member, m..Charge accelerating particles 3 .... developing device 31, ... developer, 4 .... transfer roller, 5 .... fixing device, C・ ・ Process cartridge, 10 ・ ・ Laser scanner, 100 ・ ・ Control circuit

Claims (1)

An image carrier;
A charging member that contacts the image carrier with a peripheral speed difference to charge the image carrier;
A developing device for developing the electrostatic latent image formed on the image carrier with a developer;
In an image forming apparatus comprising:
Non-magnetic conductive particles are carried on the surface of the charging member, and the conductive particles are charged to a polarity opposite to the charging polarity of the developer by rubbing with the developer,
The developing device can collect the developer remaining on the image carrier,
During non-image formation , an AC bias for cleaning the charging member is applied to the charging member ,
The frequency of the AC bias (Hz = cycle / s)
AC bias frequency (Hz = cycle / s)> ([ peripheral speed of the image carrier (mm / s)] × [a static-member peripheral speed (%)] × 10 (cycle )) / ([ the image bearing member charging length of the contact portion of the member (mm)] × (100% + [belt conductive member peripheral speed (%)]) and),
In addition, the change in potential per unit time when the AC bias increases in the same direction as the polarity of the developer increases in potential per unit time when the amount of change in potential increases in the direction opposite to the polarity of the developer. An image forming apparatus having a waveform that is larger than a quantity .