JP4147047B2 - Charging roller evaluation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present inventionAs a contact charging memberCharging rollerEvaluation methodIt is about.
[0002]
[Prior art]
  In an image forming apparatus such as an electrophotographic system or an electrostatic recording system, charging that uniformly charges an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric, and other charged bodies to a predetermined polarity and potential. As a means, a corona charger that is generally a non-contact type has been used.
[0003]
  This is because a corona charger is disposed in a non-contact manner with the discharge opening facing the non-charged body, and the surface of the charged body is exposed to the corona discharged from the corona charger so that the surface of the charged body has a predetermined polarity and potential. It is to be charged.
[0004]
  In recent years, it has advantages such as low ozone and low power compared to the case of using the above-mentioned non-contact type corona charger. Therefore, a conductive charging member (contact charging member) in which a voltage is applied to the object to be charged. A contact charging type charging device that charges an object to be charged by bringing the object into contact with each other has been put into practical use.
[0005]
  In particular, a roller charging type contact charging device using a conductive roller as a contact charging member is preferably used from the viewpoint of stabilization of charging.
[0006]
  In this method, a conductive elastic roller (hereinafter referred to as a charging roller) is brought into pressure contact with a member to be charged, and a voltage is applied thereto to charge the member to be charged.
[0007]
  Specifically, since charging is performed by discharging from the charging roller to the member to be charged, charging is started by applying a voltage equal to or higher than a certain threshold voltage.
[0008]
  As an example, when charging is performed by pressing the charging roller against an electrophotographic photosensitive member having a thickness of 25 μm as a member to be charged, a voltage of about 600 V is applied to the charging roller. When applied, the surface potential of the photoconductor begins to rise, and thereafter, the photoconductor surface potential increases linearly with a slope with respect to the applied voltage. Hereinafter, this threshold voltage is defined as a discharge start voltage (charging start voltage) Vth.
[0009]
  That is, in order to obtain the photoreceptor surface potential VD required for electrophotography, it is necessary to apply a DC voltage (DC voltage) of VD + Vth to the charging roller.
[0010]
  The contact charging method in which only the DC voltage equal to or higher than the discharge start voltage of the contact charging member and the member to be charged is applied to the contact charging member to charge the member to be charged is referred to as a “DC charging method”.
[0011]
  In addition, there is an “AC charging method” in which a charging target is charged by applying a voltage in which an alternating voltage (AC voltage) is superimposed on a DC voltage to a contact charging member. In this AC charging method, as disclosed in, for example, Japanese Patent Laid-Open No. 63-149669, an AC voltage having a peak-to-peak voltage of 2 × Vth or more is applied to a DC voltage corresponding to a desired surface potential VD to be charged. The superposed oscillating voltage is applied to the contact charging member to charge the object to be charged.
[0012]
  This is intended to smooth the potential by AC, and the surface potential of the photosensitive member as the member to be charged converges to the middle of the peak voltage according to the separation between the contact charging member and the photosensitive member. The AC charging method has disadvantages such as an increase in high-pressure cost and damage (shaving) to the photoreceptor.
[0013]
  Although the DC charging method is excellent in terms of increase in high-voltage cost and damage (scraping) to the photoreceptor, there are disadvantages such as insufficient charging uniformity. This DC charging contact charging device is used as an image carrier. In the transfer type image forming apparatus used as the charging processing means, it is necessary to dispose an image carrier neutralization means (potential control means) such as a pre-exposure device between the transfer part and the charging part of the image carrier. there were.
[0014]
  FIG. 5 shows a schematic model diagram of such an image forming apparatus.
[0015]
  Reference numeral 101 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier (charged member). The photosensitive drum 101 is rotationally driven in a counterclockwise direction indicated by an arrow with a predetermined process speed (circumferential speed).
[0016]
  Reference numeral 102 denotes a charging roller as a contact charging member, which is a conductive / elastic roller. The charging roller 102 is in contact with the photosensitive drum 101 with a predetermined pressing force in parallel with the photosensitive drum 101, and rotates following the rotation of the photosensitive drum 101. A contact portion between the photosensitive drum 101 and the charging roller 102 is a charging portion (charging nip portion) N. By applying a predetermined charging bias to the charging roller 102 from the charging bias application power source S1, the surface of the photosensitive drum 101 is charged to a predetermined polarity and potential. In this example, a DC charging method is used, and the charging bias applied from the power source S1 to the charging roller 102 is only a predetermined DC voltage equal to or higher than the discharge start voltage of the charging roller and the photosensitive drum.
[0017]
  Reference numeral 103 denotes a laser beam scanner as latent image forming means (information writing means, image exposure means). This laser beam scanner includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and an image inputted from a host device (not shown) such as a document reading device, a computer, a word processor, etc. having a photoelectric conversion element such as a CCD. The laser beam L modulated in accordance with the time series electric digital pixel signal of information is emitted, and the uniformly charged surface of the rotating photosensitive drum 101 is subjected to laser beam scanning exposure. By this laser beam scanning exposure, an electrostatic latent image corresponding to the scanning exposure pattern is formed on the peripheral surface of the rotary photosensitive drum 101.
[0018]
  A toner developing device 104 reversely develops or normally develops the electrostatic latent image on the peripheral surface of the rotating photosensitive drum 101 as a toner image in the developing unit D. Reference numeral 104a denotes a developing sleeve (developing roller) which is close to or in contact with the photosensitive drum 101, and a predetermined developing bias is applied from the developing bias applying power source S2.
[0019]
  Reference numeral 105 denotes a conductive / elastic transfer roller as transfer means, which is in contact with the photosensitive drum 101 with a predetermined pressure contact force in parallel with the photosensitive drum 101, and has a peripheral speed substantially the same as the rotational peripheral speed of the photosensitive drum 101. The photosensitive drum 101 rotates in the forward direction. A contact portion between the photosensitive drum 101 and the transfer roller 105 is a transfer portion (transfer nip portion) T. Then, the transfer material P fed from a paper supply unit (not shown) is introduced into the transfer unit T at a predetermined control timing, and the transfer unit T is nipped and conveyed. In the meantime, a predetermined transfer bias having a polarity opposite to the toner charging polarity is applied to the transfer roller 105 from the transfer bias applying power source S3, and the toner image on the photosensitive drum 101 surface side is electrostatically transferred to the transfer material P surface. It will be done.
[0020]
  The transfer material P, which is nipped and conveyed by the transfer unit T and receives the transfer of the toner image, is separated from the surface of the photosensitive drum 101, introduced into an image fixing unit (not shown), and subjected to image fixing processing to be discharged as an image formed product. Is done.
[0021]
  Further, the surface of the photosensitive drum 101 after the transfer of the toner image onto the transfer material P is neutralized by being subjected to the entire exposure by the pre-exposure device 106, and cleaned by the cleaning device 107 after removal of adhering contaminants such as transfer residual toner. And repeatedly used for image formation. The cleaning device 107 is of a blade type in this example, and adhering contaminants such as transfer residual toner on the surface of the photosensitive drum 101 are scraped off by a cleaning blade 107a and stored in a waste toner container.
[0022]
  The pre-exposure device 106 serving as a charge eliminating unit is, for example, an LED array or a fluorescent lamp, and a roller charging method is performed by uniformizing the disturbed surface potential of the surface of the photosensitive drum 101 that has passed through the transfer portion T by charge removal by full exposure. -Used to ensure the uniformity of charging in the DC charging system. The pre-exposure device 106 can be disposed between the cleaning device 107 and the charging roller 102.
[0023]
[Problems to be solved by the invention]
  In the image forming apparatus adopting the roller charging method / DC charging method as described above, when the neutralizing means 106 such as a pre-exposure device is omitted, a low temperature and low humidity environment (L / L environment of 12 to 17 ° C. and 5 to 15%) ), The disturbed surface potential of the surface of the photosensitive drum 101 that has passed through the transfer portion T cannot be made uniform by the charging roller 102, and horizontal streak-like unevenness occurs remarkably when a halftone image is output.
[0024]
  An object of the present invention is to provide a charging roller evaluation method that enables selection of a charging roller having characteristics that do not cause the above problems.
[0025]
[Means for Solving the Problems]
  The present invention is a charging roller evaluation method characterized by the following.
[0026]
  (1)coreAt least elastic material is coated around goldAnd a method for evaluating a charging roller that is in contact with a member to be charged and charges the member to be charged by applying a voltage,The time RT measured in the following (Voltage Response Measuring Method) is the DC current I applied to the charging roller._DCWhen RT = | 10 | ˜ | 30 | μA, time RT ≦ 0.7 ms or lessUse a charging rollerIt is characterized byEvaluation method of charging roller.
  <Voltage response measurement method>
  [A] The measuring device is
    a) a movable conductor;
    b) One side of the charging roller with respect to this movable conductor 4.90 to 7.84 N
        Means for pressing both sides with a force of (500-800 gF);
    c) means for rotationally driving the movable conductor to rotate the charging roller.
    d) a 1 kΩ resistor connected between the movable conductor and ground;
    e) means for applying a constant DC current between the core of the charging roller and the ground;
    f) Between the 1 kΩ resistor, the charging roller and the movable conductor.
        A first voltage Vc to be divided and a second voltage to be divided by the 1 kΩ resistor.
        Recording means for simultaneously measuring the voltage Vr of
Have
  [B] The means for applying the DC constant current has at least a current amplification factor of 200 μA / V, 20 μA / V, a slew rate of 20 V / μsec or more, and an accuracy at the time of voltage amplification of 0.5% (FS).
  [C] The charging roller as the object to be measured was left for 24 hours or more in an environment of a temperature of 12 to 17 ° C. and a humidity of 5 to 15%.
  [D] When the time when the second voltage Vr recorded by the recording means takes the minimum value is 0 ms, the average value of the first voltage Vc in 2 to 4 ms is expressed as V _AVE And the first voltage Vc is V for the first time starting from the time 0 ms. _AVE The time RT is measured.
  (2) The charging roller has a resistance of 10 ⁵ -10 ⁸ The method for evaluating a charging roller according to (1), wherein the charging roller is Ω.
[0027]
[0028]
[0029]
[0030]
[0031]
[0032]
[0033]
[0034]
[0035]
[0036]
[0037]
[0038]
[0039]
[0040]
[0041]
[0042]
[0043]
[0044]
[0045]
[0046]
[0047]
[0048]
[0049]
[0050]
[0051]
  Here, the current amplification factor is the specification (spec) of the high-voltage power supply when the high-voltage power supply (Trek. 610.C) is used as a constant current control circuit. Specifically, for example, “200 μA / V” means that a current of 200 μA is supplied to a 1V input.
[0052]
  The “It mode” is a mode for controlling the current value at the high voltage output terminal when the high voltage power supply is specified as a constant current control circuit.
[0053]
DETAILED DESCRIPTION OF THE INVENTION
  Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0054]
  (1) Overall schematic configuration of image forming apparatus
  FIG. 1 is a schematic structural model diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus according to the present embodiment uses a transfer type electrophotographic process, a roller charging method, a DC charging method, a reversal development method, and a process cartridge method, and does not have a charge eliminating unit or a potential control unit such as a pre-exposure device. It is a printer.
[0055]
  1 is an image carrier(Subject to be charged)The rotary drum type electrophotographic photosensitive member (photosensitive drum) is rotated at a predetermined process speed (circumferential speed) in the counterclockwise direction of the arrow, in this embodiment, 94.2 mm / sec.
[0056]
  The photosensitive drum 1 of this embodiment is an organic photoconductor in which a charge generation layer and a charge transport layer are sequentially laminated on a conductive substrate such as an aluminum drum. The charge transport layer is 15 μm in this embodiment.
[0057]
  The thickness of the charge transport layer is preferably 5 to 20 μm. That is, it is preferably 5 μm or more in terms of preventing current leakage to a minute defect of the photosensitive drum, and 20 μm or less in order to improve charging uniformity by increasing the charge density. The electrostatic capacity is 1cm on the photosensitive drum.²The per-capacitance becomes 100 pF to 600 pF.
[0058]
  Reference numeral 2 denotes a charging roller as a contact charging member. The charging roller 2 of this embodiment has a diameter of φ12, a surface length of 230 mm, 10 mm, and a circumference of a cored bar (conductive shaft) 2a of φ6 and at least an elastic layer 2b.⁵It is an elastic roller with a resistance of Ω.
[0059]
  The layer configuration of the charging roller 2 is arbitrary. For example, the charging roller 2 may have a plurality of layers such as two layers or three layers in which a dielectric layer or a surface layer is further laminated on the outer periphery of the elastic layer 2b.
[0060]
  The charging roller 2 is brought into contact with the photosensitive drum 1 with a predetermined pressing force by a pressing means (not shown) in parallel with the photosensitive drum 1, and rotates following the rotation of the photosensitive drum 1. A contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) N.
[0061]
  The pressing force of the charging roller 2 against the photosensitive drum 1 is constant in the range of 4.90 to 7.84 N (500 to 800 gF) on one side.
[0062]
  By applying a predetermined charging bias to the charging roller 2 from the charging bias application power source S1, the surface of the photosensitive drum 1 is charged to a predetermined polarity and potential. In this embodiment, a DC charging system is used. In this embodiment, a DC voltage of -1250 V is applied from the charging bias application power source S1 to the charging roller 2, and the surface of the photosensitive drum 1 is contact-charged with a charging potential (dark portion potential) of -700V. .
[0063]
  The applied voltage to the charging roller 2 is preferably −1000 V or less in order to improve the charging uniformity by increasing the charge density, and −1500 V or more in terms of preventing current leakage to minute defects on the photosensitive drum.
[0064]
  L is a laser beam output from a laser beam scanner (not shown) serving as a latent image forming unit, and the charged surface of the photosensitive drum 1 is scanned and exposed by this laser beam L. An electrostatic latent image of image information corresponding to the scanning exposure pattern is formed on the peripheral surface of the rotating photosensitive drum 1 by the potential contrast with the dark portion potential portion due to the charged potential (bright portion potential) of the exposed portion being attenuated to -150V. Is done.
[0065]
  Reference numeral 4 denotes a toner developing device. In this embodiment, the electrostatic latent image on the surface of the photosensitive drum 1 is reversely developed in the developing portion D by the developing device. Reference numeral 4a denotes a developing sleeve that is close to or in contact with the photosensitive drum 1, and is rotated at a predetermined peripheral speed in the clockwise direction of an arrow. A proximity portion or a contact portion of the developing sleeve 4a with respect to the surface of the photosensitive drum 1 is a developing portion D.
[0066]
  A doctor blade 4b made of urethane rubber or the like having a proximal end attached to the developing sleeve container 4c is in elastic contact with the developing sleeve 4a, and the layer thickness of the toner on the surface of the developing sleeve 4a is 0.4 to 4 by the doctor blade 4b. 1.0 mg / cm²Is a predetermined value −7 μC / g of a uniform charge amount. t is a developer (toner) stored in the developer container 4d, which is agitated by the agitating member 4e, and a part thereof is supplied to the developing sleeve container 4c and applied to the developing sleeve 4a by the doctor blade 4b. .
[0067]
  Further, a predetermined developing bias, -500 V in this embodiment, is applied to the developing sleeve 4a from the developing bias applying power source S2.
[0068]
  As the developer (toner), magnetic toner, non-magnetic toner, polymerized toner, and pulverized toner can be used.
[0069]
  Reference numeral 5 denotes a conductive / elastic transfer roller as transfer means, which is in contact with the photosensitive drum 1 in parallel with the photosensitive drum 1 with a predetermined pressure contact force, and has a rotational speed substantially equal to the rotational peripheral speed of the photosensitive drum 1. The photosensitive drum 1 rotates in the forward direction. A contact portion between the photosensitive drum 1 and the transfer roller 5 is a transfer portion (transfer nip portion) T. Then, the transfer material P fed from a paper supply unit (not shown) is introduced into the transfer unit T at a predetermined control timing, and the transfer unit T is nipped and conveyed. In the meantime, a predetermined transfer bias having a polarity opposite to the toner charging polarity is applied to the transfer roller 5 from the transfer bias applying power source S3, and the toner image on the photosensitive drum 1 surface side is electrostatically transferred to the transfer material P surface. It will be done.
[0070]
  The transfer material P, which is nipped and conveyed by the transfer unit T and receives the transfer of the toner image, is separated from the surface of the photosensitive drum 1, introduced into an image fixing unit (not shown), subjected to image fixing processing, and discharged as an image formed product. Is done.
[0071]
  In addition, the photosensitive drum 1 surface cleaning device 7 after the transfer of the toner image onto the transfer material P is subjected to removal of adhering contaminants such as transfer residual toner and the like to be cleaned and repeatedly used for image formation. The cleaning device 7 is of a blade type in this embodiment, and adhering contaminants such as transfer residual toner on the surface of the photosensitive drum 1 are scraped off by a cleaning blade 7a and stored in a waste toner container 7b.
[0072]
  In the printer of this embodiment, the four process devices of the photosensitive drum 1, the charging roller 2, the developing device 4, and the cleaning device 7 are collectively a process cartridge PC that can be attached to and detached from the printer main body. The process cartridge PC is mechanically and electrically connected to the printer body by being mounted on the printer body in a predetermined manner.
[0073]
  In the present invention, at least the image carrier and the charging unit are integrally formed into a cartridge, and the process cartridge is detachable from the image forming apparatus main body. One or a plurality of other process devices such as a developing unit and a cleaning unit may be added to form a cartridge integrally, and the cartridge may be detachable from the image forming apparatus main body.
[0074]
  (2) Method for measuring resistance of charging roller 2
  FIG. 2 is a schematic diagram of a measuring apparatus for measuring the resistance of the charging roller 2.
[0075]
  Reference numeral 13 denotes a conductive drum as a movable conductor, which is rotatably supported by a bearing and is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed by a driving means (not shown).
[0076]
  The charging roller 2 as the object to be measured is arranged in parallel with the shaft of the conductive drum 13 by rotatably supporting both ends of the cored bar 2a on a bearing member (not shown), and the conductive drum 13 is pressed by a pressing means (not shown). It is set in pressure contact with a pressing force of 4.90 N (500 gF) on one side with respect to 13 surfaces. The charging roller 2 is driven to rotate the conductive drum 13.
It is driven to rotate.
[0077]
  The cored bar 2a of the charging roller 2 is connected to a direct current power supply (DC power supply) 14, and the conductive drum 13 is connected to the ground of the DC power supply 14 via a carbon resistor (resistor) 15 of 10 kΩ. .
[0078]
  Further, a voltmeter 16 is connected to both ends of the carbon resistor 15 to measure the voltage applied to the carbon resistor 15.
[0079]
  Then, after the above-mentioned apparatus in which the charging roller 2 as a measurement object is set is left in an L / L environment (15 ° C., 10%) for 24 hours or more, the conductive drum 13 is driven at a peripheral speed by a driving means (not shown). It is driven to rotate at 94.2 mm / s. The charging roller 2 is driven to rotate at the same peripheral speed as the conductive drum 13 rotates. A DC constant voltage of −50 V is applied by the DC power source 14. At this time, the voltage Vr divided by the resistor 15 is measured.
[0080]
  Hereinafter, a method for calculating the resistance value of the charging roller 2 will be described. The current I flowing through the system is obtained by Ohm's law.
[0081]
    I = Vr / 10⁴...1)
  A partial pressure Vc to the charging roller 2 is calculated.
[0082]
    Vc = -50-Vr ...2)
  1) and 2)Therefore, the resistance value R of the charging roller 2 is expressed by the equation3)Sought by.
[0083]
    R = (− 50−Vr) / (Vr / 10⁴) ...3)
  The roller resistance is obtained by the measurement method described above.
[0084]
  (3) Method for measuring voltage responsiveness of charging roller 2
  As described above, in a conventional DC charging type image forming apparatus that does not have a charge eliminating unit or a potential control unit such as a pre-exposure device, when a halftone image is output in an L / L environment, the image passes through a transfer unit. The disturbed surface potential of the image bearing member surface cannot be made uniform by the charging roller, and horizontal stripe-like unevenness occurs.
[0085]
  In this embodiment, paying attention to the fact that the amount of discharge current (20 μA) of the charging roller 2 with pre-exposure is significantly different from that without pre-exposure (5 μA), a constant DC current, especially a very small current, is applied. The voltage responsiveness of the charging roller 2 was noted.
[0086]
  FIG. 3 shows a charging roller 2 according to the present invention.Used in the evaluation methodThe schematic of the measuring apparatus for enforcing a voltage responsiveness measuring method is shown.
[0087]
  That is, similar to the resistance measuring device for the charging roller 2 shown in FIG. 2, the bearing is rotatably supported and is driven to rotate at a predetermined peripheral speed in the counterclockwise direction indicated by an arrow by a driving means (not shown). With respect to the conductive drum 13 serving as the conductor, the charging roller 2 serving as the object to be measured is rotatably supported by a bearing member (not shown) at both ends of the cored bar 2a in parallel with the axis of the conductive drum 13. It is arranged and set by pressing with a predetermined pressing force by a pressing means (not shown). The charging roller 2 is driven to rotate as the conductive drum 13 is driven to rotate.
[0088]
  The pressing force of the charging roller 2 against the conductive drum 13 as a movable conductor is constant in the range of 4.90 to 7.84 N (500 to 800 gF) on one side.
[0089]
  In this example, the charging roller is set by pressing with a pressing force of 4.90 N (500 gF) on one side by pressing means (not shown) on both sides of the charging roller.
[0090]
  The cored bar 2a of the charging roller 2 is connected to a direct current power source (DC power source) 14, and the conductive drum 13 is connected to the ground of the DC power source 14 through a carbon resistor (resistor) 17 of 1 kΩ. .
[0091]
  Further, the voltage measuring device 18 is connected so that the behavior of the voltage Vc divided between the charging roller 2 and the conductive drum 13 and the behavior of the voltage Vr divided by the carbon resistor 17 can be monitored simultaneously.
[0092]
  The DC power source 14 in this example is Trek 610C manufactured by Trek Co., Ltd., which has a slew rate of 20 V / μsec or more and an accuracy of voltage amplification of 0.5% (FS), and was measured in the It mode.
[0093]
  Moreover, the voltage measuring device 18 used ORM1200 by Yokogawa Electric Corporation.
[0094]
  Then, after leaving the above-mentioned apparatus in which the charging roller 2 as the measurement object is set in the L / L environment for 24 hours or more, the conductive drum 13 is rotated by a driving means (not shown).
Driven at a speed of 94.2 mm / s.
[0095]
  A DC power source 14 applies a DC constant current of −10 μA to the metal core 2 a of the charging roller 2 and is divided into a voltage Vc divided between the charging roller 2 and the conductive drum 13 and a carbon resistor 17. The behavior of the voltage Vr was simultaneously monitored by the voltage measuring device 18 at a sampling frequency of 20 kHz.
[0096]
  FIG. 4 is obtained by the voltage meter 18.
    A) a voltage Vc divided between the charging roller 2 and the conductive drum 13;
    B) Voltage Vr divided by the carbon resistor 17
It is a waveform.
[0097]
  When the time point A at which the voltage Vr applied to the carbon resistor 17 takes the minimum value is 0, the average value of the voltage Vc divided between the charging roller 2 and the conductive drum 13 in 2 to 4 ms (section B). V_AVEThe voltage Vc divided between the charging roller 2 and the conductive drum 13 starting from time 0 is V for the first time._AVEA time RT (time C) is a value RT indicating responsiveness to the voltage of the charging roller 2.
[0098]
  In this example, for the sake of strictness, the same measurement was performed five times or more, and the average value of the obtained values excluding the maximum value and the minimum value was defined as RT.
[0099]
  Similarly, the time RT was measured for DC constant currents of −20 μA and −30 μA.
[0100]
  (4) Verification
  In the printer of FIG. 1 described above, the L / L environment in the case where the example rollers 1 to 4 and the comparative example rollers 1 to 6 having various resistance values and times RT as shown in Table 1 are used as the charging roller 2. Evaluation of the horizontal streaky unevenness, the current leakage to the minute defect of the photosensitive drum, and the charging ability were performed.
[0101]
  Example rollers 1 to 4 have a plurality of layers such as two or three layers, and materials include epichlorohydrin rubber, urethane rubber, EPDM, and the like, and ion conductive materials are used as conductive materials.
[0102]
  Comparative Example Rollers 1 to 6 have a plurality of layers such as two or three layers, and the materials include NBR, epichlorohydrin rubber, styrene butadiene rubber, EPDM, etc., and the conductive material used is an electronic conductive type. .
[0103]
  The resistance and time RT of each charging roller were measured by the resistance measuring method described in the above item (2) and the voltage responsiveness measuring method described in the item (3).
[0104]
  If the charging ability (convergence potential-potential at the first round of the drum) is ensured to be 20 V or less, there is no problem on the image.
[0105]
  As shown in Table 1, there was no correlation between the charging roller resistance and the horizontal stripe-like unevenness.
[0106]
  The resistance range is 10 to prevent current leakage to a minute defect of the photosensitive drum.⁵10 to ensure Ω or more and charging ability (convergence potential-potential at the first circumference of the drum) 20 V or less.⁸It can be seen that Ω or less is necessary as a charging roller.
[0107]
  As shown in Examples 1 to 4, the relationship between the maximum value of RT and the horizontal streak between the applied currents of −30 to −10 μA was correlated.
[0108]
  If the resistance is lowered as in the comparative example roller 3, the RT decreases, but it is impossible to achieve both current leakage prevention to a minute defect of the photosensitive drum 1.
[0109]
  As shown in Table 1, a good image was obtained with a charging roller having an RT of 0.7 ms or less, and the deterioration of the horizontal stripe was verified by increasing the RT.
[0110]
  As described above, by using the charging roller 2 having an RT of 0.7 ms or less, a uniform halftone image can be obtained even in DC charging without using a neutralizing means such as pre-exposure in an L / L environment. it can.
[0111]
  The RT described in this example is the most severe in the L / L environment. For example, in an environment such as 23 ° C./60% or 32.5 ° C./80%, RT increases and horizontal stripes tend to decrease.
[0112]
[Table 1]
[0113]
  In Table 1, “maximum RT” of “maximum RT (ms) between −30 to −10 μA”
  a) RT as the average value of the numerical values excluding the maximum value and the minimum value among the measured values of 5 times or more when the current applied to the charging roller is “−10 μA”.
  b) RT as an average value of numerical values excluding the maximum value and the minimum value among five or more measured values when the current applied to the charging roller is “−20 μA”.
  c) RT as an average value of numerical values excluding the maximum value and the minimum value among the measured values of 5 times or more in the case of the current “−30 μA” applied to the charging roller.
  It is the largest RT value among the RTs as the average values of the above a), b) and c).Claim 1“RT” in this is this “maximum RT”.
[0114]
  When pre-exposure is specified, a current of about 30 μA flows during image formation. This time is the RT value at the time of 30 μA energization in RT measurement. At this time, no horizontal stripes are generated even with the conventional AC + DC charging roller, and the RT value is 0.7 ms. When pre-exposure is not used (when 10 μA is energized), it becomes 2.7 ms.
[0115]
  In the charging rollers of Examples 1 to 3, a base layer made of urethane foam rubber is provided on the outer periphery of the core metal, and a conductive intermediate layer is formed by extrusion on the outer peripheral surface of the base layer. Is coated.
[0116]
  In the charging rollers of Comparative Examples 1 to 6, a base layer made of a conductive elastic material is provided on the outer periphery of the cored bar, and an intermediate layer to the right of conductivity is formed on the outer periphery of the base layer. The surface layer is coated with.
[0117]
  Materials for the base layer include EPDM (ethylene-propylene-diene copolymer), polybutadiene, natural rubber, polyisoprene, SBR (styrene butadiene rubber), CR (chloroprene), NBR (acrylonitrile butadiene rubber), silicon rubber, urethane Rubbers such as rubber and epichlorohydrin rubber; RB (butaneene resin), SBS (styrene-butadiene-styrene elastomer), etc. are used, and conductive materials to be added are general conductive materials such as titanium oxide, carbon, and conductive tin oxide. It was used.
[0118]
  Materials for the intermediate layer include styrene resin, vinyl chloride resin, olefin resin, polyester resin, polyamide resin, urethane resin, polyethylene, polypropylene, urethane nylon, ABS, EVA, fluororesin, polycarbonate, polystyrene, etc. As the conductive material to be added, a general conductive material such as titanium oxide, carbon, conductive tin oxide or the like was used.
[0119]
  The surface layer was prepared by adding a conductive material to a fluororesin with a roll coater.
[0120]
  (5) Other
  1) The image exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means such as the printer of the embodiment. Capable of forming an electrostatic latent image corresponding to image information, such as normal analog image exposure, exposure means of a light emitting element array such as an LED, and exposure means using a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter. That's fine.
[0121]
  2) The image carrier is not limited to a photoreceptor, and may be an electrostatic recording dielectric or the like. In this case, the dielectric surface is uniformly primary-charged to a predetermined polarity and potential, and is then selectively discharged by a discharging means such as a discharging needle head or an electron gun to form an electrostatic latent image.
[0122]
  3) The electrostatic latent image toner developing means may use a one-component developer or a two-component developer. Regular developing means may be used.
[0123]
  4) The transfer means may be a transfer belt type or the like, or a non-contact type corona charger.
[0124]
  5) The transfer material that receives the transfer of the toner image from the image carrier may be an intermediate transfer member such as a transfer drum or a transfer belt.
[0125]
  6) The image forming apparatus may be a cleaner-less system in which a cleaning device is not provided and the transfer residual toner on the image carrier is simultaneously collected by the developing device.
[0126]
【The invention's effect】
  As described above, the present inventionAccording to the charging roller evaluation method,An image forming apparatus adopting a roller charging system / DC charging system has a simple configuration in which a static elimination unit or a potential control unit such as a pre-exposure apparatus for performing a static elimination process on the surface of an image carrier that has passed through a transfer unit is omitted, and L / L Even in the environment, when charging a halftone image, it is possible to ensure uniform charging performance without unevenness, and at the same time prevent current leakage to the micro defects of the image carrier and charge performance.A charging roller having characteristics can be selected.
[Brief description of the drawings]
FIG. 1 is a schematic configuration model diagram of a main part of an image forming apparatus according to an embodiment.
FIG. 2 is a schematic configuration model diagram of a charging roller resistance measuring device.
FIG. 3 is a schematic configuration model diagram of a charging roller voltage response measuring apparatus.
FIG. 4 is a measurement chart of charging roller voltage response measurement.
FIG. 5 is a schematic configuration model diagram of an example of a DC charging type image forming apparatus having a pre-exposure device.
[Explanation of symbols]
  DESCRIPTION OF SYMBOLS 1,101 ... Photosensitive drum (image carrier), 2,102 ... Charging roller, 103 ... Laser beam scanner, L ... Laser beam, 4,104 ... Developing device, 5,105 ... Transfer roller, 106 ... Pre-exposure device (static elimination means), 7,107 ... Cleaning device, P ... Transfer material, S, S2, S3 ... Bias applied power supply, 13 ... Conductive drum, 14 ... DC power supply, 15 ... 10kΩ carbon resistor, 16 ... Voltmeter, 17 ... 1kΩ carbon resistor, 18 ... Voltage measuring instrument

Claims (2)

At least an elastic member is coated around the core metal, is in contact with the member to be charged, an evaluation method of the charging roller that charges the member to be charged by a voltage is applied, (the voltage response measurement method described below the measured time RT in> direct current _I DC is applied to the charging roller = | 10 | ~ | 30 | when .mu.A, to the charging roller for use charging roller is less time RT ≦ 0.7 ms A method for evaluating a charging roller.
<Voltage response measurement method>
[A] The measuring device is
a) a movable conductor;
b) One side of the charging roller with respect to this movable conductor 4.90 to 7.84 N
Means for pressing both sides with a force of (500-800 gF);
c) means for rotationally driving the movable conductor to rotate the charging roller.
d) a 1 kΩ resistor connected between the movable conductor and ground;
e) means for applying a constant DC current between the core of the charging roller and the ground;
f) a first voltage Vc divided between the 1 kΩ resistor, the charging roller and the movable conductor, and a second voltage divided by the 1 kΩ resistor.
Recording means for simultaneously measuring the voltage Vr of
Have
[B] The means for applying the DC constant current has at least a current amplification factor of 200 μA / V, 20 μA / V, a slew rate of 20 V / μsec or more, and an accuracy at the time of voltage amplification of 0.5% (FS).
[C] The charging roller as the object to be measured is left to stand for 24 hours or more in an environment of a temperature of 12 to 17 ° C. and a humidity of 5 to 15%.
[D] When the time when the second voltage Vr recorded by the recording means takes the minimum value is 0 ms, the average value of the first voltage Vc in 2 to 4 ms is V _AVE , and the time 0 ms The time RT when the first voltage Vc becomes V _AVE for the first time is measured from The charging roller evaluation method according to claim 1, wherein a resistance of the charging roller is 10 ⁵ to 10 ⁸ Ω .