JP2006259411A - Image forming apparatus and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure conduction of development free of scumming of one isolated pixel by ET development. <P>SOLUTION: The image forming apparatus is equipped with an image carrier 1 to which an electrostatic latent image is formed, and a toner carrying member 1 which carries a toner to an area facing the image carrier 1 by a phase shift electric field formed by a voltage of an (n) phase applied to a plurality of electrodes 102. The image carrier 1 has a charge generating layer and a charge transfer layer. When the charge generating layer exists in the inside, the thickness of the charge transfer layer, defined as tg (μm), and the resolution, defined as r (dpi), satisfies the relation tg≤8,400/r+13. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and a process cartridge, and more particularly to an image forming apparatus and a process cartridge for developing an electrostatic latent image by transferring powder by a traveling wave electric field.

  As various image forming apparatuses such as printers, facsimiles, copying machines, plotters, printer / fax / copier multifunction machines, etc., the image carrier is charged to form an electrostatic latent image, and the electrostatic latent image is colored. The powder (hereinafter referred to as “toner” or “toner particles”) is developed and developed, and the toner image is recorded on a recording medium (including a transfer material, paper, recording paper, intermediate transfer member, etc.). An image forming apparatus using an electrophotographic process for transferring is known.

In such an image forming apparatus, as described in Patent Document 1, by forming a traveling wave electric field by applying a multiphase voltage to a plurality of electrodes arranged at a predetermined interval, In a developing device that includes developer transport means for transporting the developer, and in which the development transport means is disposed in a development region facing an image carrier that bears an electrostatic latent image on the surface thereof, the development transport means includes: A plurality of electrodes are arranged in an endless loop, and the plurality of electrodes are divided into a plurality of units and provided with means for controlling voltage application for each unit, and a multiphase voltage is applied to each unit. Some are configured to be possible.
Japanese Patent No. 3530124

In addition, as described in Patent Documents 2 and 3, the present applicant is a phenomenon including horizontal movement (conveyance) and vertical movement (hopping) of powder due to electrostatic force. There has been proposed a developing device using a developing system that utilizes a phenomenon in which a powder jumps on the surface of a member by a phase-shift electric field with a component in a traveling direction. The developing device is a developing device for developing a latent image on an image carrier by depositing powder on the image carrier, and is a traveling wave electric field that is disposed opposite the image carrier and moves the powder. A conveying member having a plurality of electrodes for generating the toner.Powder is directed toward the image carrier with respect to the image portion of the latent image, and the powder is directed to the non-image portion on the electrode of the conveying member. An n-phase potential that forms an electric field in a direction toward the opposite side of the image carrier is applied.
JP 2004-198675 A JP 2002-258601 A

As described in Patent Document 4, as an image forming apparatus, a superimposed voltage of DC and AC is applied between an image carrier and a developing roller, so that the developing roller does not contact the image carrier. Developing by a so-called jumping development method for transferring toner, as described in Patent Documents 5 and 6, using an electrostatic transport substrate, transports the toner to a position facing the image carrier and vibrates. The toner is floated and smoked, and the toner is separated from the transport surface by the suction force generated between the image carrier and the toner is attached to the surface of the image carrier. Some use curtains.
JP-A-9-329947 Japanese Patent Publication No. 5-31146 Japanese Patent Publication No. 5-31147 JP-A-3-21967

As for the developing bias of the developing device, as described in Patent Document 10, a capacitor C1 and a resistor R connected in parallel to the output side of the bias power supply are inserted in series to reduce the peak-to-peak voltage of the developing bias. There is an image forming apparatus in which a variable capacitor C3 is inserted in parallel with the capacitance C2 and is changed according to a change in the capacitance C2 between the image carrier and the developer carrier.
Japanese Patent No. 3376199

  By the way, the present and future problems in an image forming apparatus using an electrophotographic process are how to satisfy image quality, cost, and environment. In terms of image quality, when forming a color image, it is how to develop a single isolated dot of 1200 dpi having a diameter of only about 30 μm, and preferably it is also developed without background stains. In terms of cost, when considering a personal laser printer, it is important to reduce the total cost including not only the single unit cost of the developer and developer but also the maintenance and final disposal costs. Furthermore, in terms of the environment, it is particularly important to prevent the toner that is a fine powder from being scattered inside and outside the apparatus.

  The powder jumps on the surface of the electrostatic transfer member, which has already been proposed in the above-mentioned Patent Document 2 related to the applicant's application, with a component in the traveling direction by a phase-shift electric field (traveling wave electric field) (hopping). ) EH development utilizing phenomenon (EH: Electrostatic transport & Hopping) is a one-way development method that is non-contact with the image carrier, and is an extremely excellent development method that enables low-voltage development.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and a process cartridge that perform development of an isolated pixel by EH development and development without background contamination in the image forming apparatus using the electrophotographic process.

  In order to solve the above-described problems, an image forming apparatus according to the present invention is a plurality of image forming apparatuses that are developed by attaching toner to a latent image formed on an image carrier and arranged side by side at a predetermined interval. A toner conveying member that conveys toner to a region facing the image carrier by a conveyance electric field formed by applying a multiphase voltage to the electrode, and the image carrier has a charge generation layer and a charge transfer layer; When the charge generation layer is inside, the thickness tg (μm) of the charge transfer layer satisfies the equation of tg ≦ 8400 / r + 13 when the resolving power is r (dpi).

  Here, the difference between the image portion potential of the latent image and the background portion potential is preferably 300 V or less.

  A process cartridge according to the present invention includes at least an image carrier and a developing unit that develops toner by attaching a toner to a latent image formed on the image carrier, and is a process that is detachable from the main body of the image forming apparatus. In the cartridge, the developing means is a toner conveying member that conveys toner to a region facing the image carrier by a conveying electric field formed by applying a multiphase voltage to a plurality of electrodes arranged side by side at a predetermined interval. When the image carrier has a charge generation layer and a charge transfer layer, and the charge generation layer is inside, the thickness tg (μm) of the charge transfer layer is tg when the resolution is r (dpi). ≦ 8400 / r + 13 was satisfied.

  According to the image forming apparatus and the process cartridge according to the present invention, a multi-phase voltage is applied to a plurality of electrodes arranged side by side at a predetermined interval, so that a transfer electric field formed in a region facing the image carrier. When the toner carrying member for carrying the toner is provided, and the image carrier has a charge generation layer and a charge transfer layer, and the charge generation layer is inside, the thickness tg (μm) of the charge transfer layer determines the resolving power r ( dpi), the structure satisfying the equation of tg ≦ 8400 / r + 13 is satisfied, so that it is possible to perform clear development up to one isolated pixel without background smearing.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of a first embodiment of an image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a developing device portion of the image forming apparatus.
The developing device is a developing device using a two-component developer composed of a magnetic carrier and a non-magnetic toner, and a developing electric field is generated by applying a multiphase voltage to a plurality of electrodes arranged at a predetermined interval. A toner conveying member 2 formed in a roller shape for conveying toner to a region facing the image carrier 1 on which an electrostatic latent image is formed, and the toner conveying member 2 facing the toner conveying member 2 with respect to the toner conveying member 2 A developer carrier 3 serving as a toner supply means for supplying the toner, and a developer accommodating portion 4 for accommodating the toner and magnetic carrier supplied by the developer carrier 3. In this case, the toner conveying member 2 is disposed so as to face the image carrier 1 and the developer carrier 3 in a region opposite to the radial direction. The toner conveying member 2 does not rotate, and the toner is conveyed on the outer peripheral surface in the direction of the arrow by a conveying electric field (phase-shift electric field). On the other hand, the developer carrier 3 rotates in the direction indicated by the arrow.

  The developer accommodating portion 4 is divided into two chambers, and each chamber communicates with a developer passage (not shown) at both ends in the developing device. A two-component developer is accommodated in the developer accommodating portion 4 and is conveyed through the developer accommodating portion 4 while being agitated by the agitating / conveying screws 5A and 5B in the respective chambers.

  Further, the developer container 4 is provided with a toner supply port 6 for supplying developer from a toner container (not shown). The developer container 4 is provided with a toner concentration sensor (not shown) that detects the magnetic permeability of the developer, and detects the developer concentration. When the toner concentration in the developer accommodating portion 4 decreases, the toner is replenished from the toner replenishing port 6 to the developer accommodating portion 4.

  The developer carrier 3 is disposed in a region of the developer container 4 that faces the agitating and conveying screw 5A. A fixed magnet is disposed inside the developer carrier 3, and the developer in the developer container 4 is pumped up to the surface of the developer carrier 3 by the rotation and magnetic force of the developer carrier 3.

  Further, the developer is placed in a region facing the developer carrier 3 on the downstream side in the rotation direction (arrow direction) of the developer carrier 3 from the developer pumping region and upstream from the region facing the toner conveying member 2. A layer regulating member 7 is provided, and the developer pumped in the pumping area is regulated to a certain amount of developer layer thickness. The developer passing through the developer layer regulating member 7 is transported to a region facing the toner transport member 2 as the developer carrier 3 rotates.

  Here, a supply bias is applied to the developer carrier 3 by the first voltage application unit 11. Further, as will be described later, a voltage is applied to the toner conveying roller by the second voltage applying unit 12.

  As a result, in the region where the developer carrier 3 and the toner carrying roller face each other, an electric field is generated between the toner carrying roller and the developer carrier 3 by the first and second voltage applying units 11 and 12. Under the electrostatic force from the electric field, the toner dissociates from the carrier and moves to the surface of the toner transport roller 2. The toner that has reached the surface of the toner transport member 2 is transported (moved) while hopping on the surface of the toner transport member 2 by the transport electric field formed by the voltage applied by the second voltage applying unit 12.

  Next, the toner conveyed by the conveyance electric field to the area facing the latent image carrier 1 is applied onto the latent image carrier 1 by the developing electric field between the toner conveyance member 2 and the image portion on the latent image carrier 1. The latent image on the latent image carrier 1 is moved to be visualized (developed).

  As described above, in the developing device using the two-component developer composed of the magnetic carrier and the nonmagnetic toner, the toner is charged by the contact friction with the carrier, so that the charging is stabilized. In addition, since a large amount of toner is supplied during development, it is suitable for high-speed development. Therefore, by using the two-component developer, a large amount of stably charged toner can be supplied to the toner conveying member.

Here, the distance between the image carrier 1 and the toner conveying member 2 is G (μm), the width of the electrode of the toner conveying member 2 is W1 (μm), and the distance between the electrodes of the toner conveying member 2 is W2 (μm). , The distance G between the image carrier 1 and the toner conveying member 2 satisfies the equation G ≧ (W2 + 0.5W1) × 3 ^1/2 . Further, when the diameter of the isolated minimum pixel is Dmin (μm) and the maximum electric field in the conveying direction formed by the toner conveying member 2 is Ehmax (V / μm), the distance between the image carrier 1 and the toner conveying member 2 The distance G also satisfies the following equation: G ≦ Dmin + 150 (Ehmax) ^1/2 . As a result, it is possible to carry out clean development of an isolated dot without any background contamination.

  The image carrier 1 has a charge generation layer and a charge transfer layer, the charge generation layer is inside, and the thickness tg (μm) of the charge transfer layer is tg when the resolving power is r (dpi). ≦ 8400 / r + 13 is satisfied. As a result, it is possible to reliably develop up to one isolated pixel without background contamination.

Next, another example of the first embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of a developing device portion of the image forming apparatus.
This developing device is a developing device that uses a one-component developer made of non-magnetic toner, and is a toner conveying member formed in a roller shape that conveys toner to a region facing the image carrier 1 on which an electrostatic latent image is formed. 2, a developer carrying member 13 that is a toner supply unit that faces the toner carrying member 2 and supplies toner to the toner carrying member 2, and a developer that contains the toner to be supplied by the developer carrying member 13 And an accommodating portion 14. In this case, the toner conveying member 2 is disposed so as to face the image carrier 1 and the developer carrier 3 in a region opposite to the radial direction. The toner conveying member 2 does not rotate, and the toner is conveyed on the outer peripheral surface in the direction of the arrow by a conveying electric field (phase-shift electric field). On the other hand, the developer carrier 13 rotates in the direction indicated by the arrow.

  The developer accommodating portion 14 includes toner replenishing rollers 15A and 15B, and the toner is pumped onto the developer carrying member 13 by electrostatic force due to frictional charging by the toner replenishing roller 15A and the developer carrying member 13 or the like. Then, the toner on the developer carrier 13 is thinned by the developer layer regulating member 7 and conveyed to a region facing the toner conveying member 2 as the developer carrier 13 rotates.

  Again, a supply bias is applied to the developer carrier 13 by the first voltage application means 11. In addition, a voltage is applied to the electrode of the toner conveying member 2 by the second voltage applying unit 12 as will be described later.

  As a result, in the region where the developer carrying member 13 and the toner carrying member 2 face each other, an electric field is generated between the toner carrying member 2 and the developer carrying member 13 by the first and second voltage applying units 11 and 12. Yes. Under the electrostatic force from the electric field, the toner dissociates from the surface of the developer carrier 13 and moves to the surface of the toner conveying member 2. The toner that has reached the surface of the toner transport member 2 is transported while hopping on the surface of the toner transport member 2 by the transport electric field formed by the voltage applied by the second voltage applying unit 12.

  Then, the toner conveyed to the area facing the latent image carrier 1 by the conveyance electric field is transferred onto the latent image carrier 1 by the developing electric field between the toner conveying member 2 and the image portion on the latent image carrier 1. The latent image on the latent image carrier 1 is moved to be visualized (developed).

  Thus, a one-component developer made of toner can also be used as the developer. In the case of a two-component developer, due to the rotation of the developer carrier and the impact of the magnetic spikes colliding with the toner conveying member, a part of the carrier forming the magnetic spikes is cut and moved to the toner conveying member, There is a risk of adhering to the surface of the toner conveying member. On the other hand, in the case of a one-component developer, no carrier is used, so that the problem of carrier adhesion to the surface of the toner conveying member does not occur. In the case of a one-component developer, the developer container has a simple configuration. Therefore, the developing device can be reduced in size and cost.

Here again, the distance between the image carrier 1 and the toner conveying member 2 is G (μm), the width of the electrode of the toner conveying member 2 is W1 (μm), and the distance between the electrodes of the toner conveying member 2 is W2 (μm). , The distance G between the image carrier 1 and the toner conveying member 2 satisfies the equation G ≧ (W2 + 0.5W1) × 3 ^1/2 . Further, when the diameter of the isolated minimum pixel is Dmin (μm) and the maximum electric field in the conveying direction formed by the toner conveying member 2 is Ehmax (V / μm), the distance between the image carrier 1 and the toner conveying member 2 The distance G also satisfies the following equation: G ≦ Dmin + 150 (Ehmax) ^1/2 . As a result, it is possible to carry out clean development of an isolated dot without any background contamination.

  The image carrier 1 has a charge generation layer and a charge transfer layer, the charge generation layer is inside, and the thickness tg (μm) of the charge transfer layer is tg when the resolving power is r (dpi). ≦ 8400 / r + 13 is satisfied. As a result, it is possible to reliably develop up to one isolated pixel without background contamination.

Here, details of the toner conveying member 2 will be described with reference to FIG. FIG. 3 is an enlarged sectional view of the surface of the toner conveying member 2 on the image carrier 1 side.
The toner conveying member 2 includes a plurality of electrodes 102, 102, 102... Arranged on a support substrate 101 as a set with a predetermined interval along the toner moving direction. A surface protective layer 103 made of an inorganic or organic insulating material, which becomes an insulating electrostatic transfer surface forming member for forming the surface 103a and serves as a protective film covering the surface of the electrode 102, is laminated.

As the support substrate 101, a substrate made of an insulating material such as a glass substrate, a resin substrate, or a ceramic substrate, or a substrate made of a conductive material such as SUS, an insulating film such as SiO ₂ is formed, a polyimide film, or the like A substrate made of a flexible and deformable material can be used.

  The electrode 102 is formed by depositing a conductive material such as Al or Ni—Cr on the support substrate 101 with a thickness of 0.1 to 10 μm, preferably 0.5 to 2.0 μm, and using a photolithography technique or the like. It is formed by patterning into the required electrode shape. The width (electrode width) W1 of the plurality of electrodes 102 in the toner conveyance direction is set to be 1 to 20 times the average particle diameter of the powder to be moved, and the average of the toner to which the pitch p of the electrodes 102 and 102 is also moved. It is 1 to 20 times the particle size (see FIG. 4).

As the surface protective layer 103, for example, SiO ₂ , TiO ₂ , TiO ₄ , SiON, BN, TiN, Ta ₂ O _{5 and the} like are formed to a thickness of 0.5 to 10 μm, preferably 0.5 to 3 μm. Formed. In addition, inorganic nitride compounds such as SiN, Bn, and W can be used. In particular, since the charge amount of the charged toner tends to decrease in the middle of conveyance when the surface hydroxyl groups increase, inorganic nitride compounds with few surface hydroxyl groups (SiOH, silatol groups) are preferable.

  In FIG. 3, lines extending from the respective electrodes 102 represent conductive lines for applying a voltage to the respective electrodes 102, and only the portions indicated by black circles among the overlapping portions of the respective lines are electrically connected. This part is electrically insulated. To each electrode 102, drive voltages V11 to V13 and V21 to V23 having different n phases are applied from the voltage application means (drive circuit) 104 on the main body side. In this embodiment, a case where a three-phase drive voltage is applied (n = 3) will be described. However, the present invention is an arbitrary case where the multiphase (n-phase) satisfies n> 2 as long as the toner is conveyed. It is applicable to the natural number n.

  Each electrode 102 of the toner conveying member 2 is connected to one of the contacts S11, S12, S13, S21, S22, and S23 on the developing device 10 side, and each of the contacts S11, S12, S13, S21, S22, and S23. When the developing device 10 is mounted on the main body of the image forming apparatus, it is connected to the voltage application means 22 on the main body side that applies the drive waveforms V11, V12, V13, V21, V22, and V23, respectively.

  The toner transport member 2 transports the toner to the vicinity of the image carrier 1, and transports the toner that has not contributed to the development after passing through the development region (including the recovery region), the latent image of the image carrier 1. It is divided into a development area for forming a toner image by attaching toner to the image.

  The development area exists only in the area close to the image carrier 1, and the conveyance area exists on the circumference of the toner conveyance member 2 and in the entire area other than the development area. In the present invention, an area in which toner can move by a phase-shifting electric field is referred to as an “electrostatic conveyance surface”. In the present embodiment, the entire peripheral surface of the toner conveying member 2 is an electrostatic conveying surface.

  In the transport region, the driving waveforms V11, V12, and V13 are applied to the electrodes 102 by the second voltage applying unit 22, and in the developing region, the driving waveforms V21, V22, and V23 are applied to the electrodes 102 by the second voltage applying unit 22. .

  Therefore, the principle of electrostatic conveyance of toner in the toner conveyance member 2 will be described. By applying an n-phase pulse voltage to the plurality of electrodes 102 of the toner conveying member 2, a phase shift electric field (traveling wave electric field) is generated by the plurality of electrodes 102, and the charged toner on the toner conveying member 2 is charged. Receives a repulsive force and / or a suction force and moves in the transfer direction.

  For example, as shown in FIG. 5, with respect to the plurality of electrodes 102 of the toner conveying member 2, a three-phase pulse of A phase, B phase, and C phase that changes between the ground G (0 V) and a positive voltage +. The drive waveform (voltage) is applied while shifting the timing.

  At this time, as shown in FIG. 6, the negatively charged toner T is present on the toner conveying member 2, and “G”, “G”, “+”, “G” are respectively applied to a plurality of continuous electrodes 102 of the toner conveying member 2. ”And“ G ”are applied (FIG. 5A), the negatively charged toner T is positioned on the“ + ”electrode 102. At the next timing, “+”, “G”, “G”, “+”, and “G” are respectively applied to the plurality of electrodes 102 ((b) in the figure). Since a repulsive force acts between the “G” electrode 102 and an attractive force acts between the “+” electrode 102 on the right side, the negatively charged toner T moves to the “+” electrode 102 side. Further, as shown in FIG. 5C, “G”, “+”, “G”, “G”, and “+” are applied to the plurality of electrodes 102 at the next timing, respectively, and negatively charged toner Similarly, the repulsive force and the attractive force act on T, so the negatively charged toner T further moves to the “+” electrode 102 side.

  This will be described in detail with reference to FIG. 7. As shown in FIG. 7A, the electrodes A to F of the toner conveying member 2 are all 0 V (G) and are negatively charged on the toner conveying member 2. When “+” is applied to the electrodes A and D from the state where the toner T is loaded, as shown in FIG. 5B, the negatively charged toner T is attracted to the electrodes A and D and the electrodes A and D are drawn. Move up. At the next timing, as shown in FIG. 5C, when the electrodes A and D are both “0” and “+” is applied to the electrodes B and E, the toner T on the electrodes A and D is displayed. Receives the repulsive force and the suction force of the electrodes B and E, so that the negatively charged toner T is transferred to the electrode B and the electrode E. Further, at the next timing, as shown in FIG. 4D, when the electrodes B and E are both “0” and “+” is applied to the electrodes C and F, The toner T receives a repulsive force and also receives the suction force of the electrodes C and F, so that the negatively charged toner T is transferred to the electrodes C and F. In this way, the negatively charged toner is sequentially transferred rightward in the drawing by the traveling wave electric field.

  Thus, by applying a multi-phase (n-phase) driving waveform (voltage) whose voltage changes to the plurality of electrodes 102, a traveling wave electric field is generated on the toner conveying member 2, and the negatively charged toner progresses in this manner. Move in the traveling direction of the wave electric field. In the case of positively charged toner, the drive waveform changes in the same direction by reversing the drive waveform change pattern.

Next, an example of the second voltage application unit 22 will be described with reference to FIG.
The voltage applying means 22 generates and outputs a pulse signal from a pulse signal generation circuit 105 that generates and outputs a pulse signal, and generates and outputs pulse voltages V11, V12, and V13, which are drive waveforms, by inputting the pulse signal from the pulse signal generation circuit 105. Waveform amplifiers 106a, 106b, and 106c, and waveform amplifiers 107a, 107b, and 107c that generate and output drive waveforms V21, V22, and V23 by inputting a pulse signal from the pulse signal generation circuit 105 are provided.

  The pulse signal generation circuit 105 receives, for example, logic level input pulses, and includes two sets of pulses that are phase-shifted by 120 °, and switches switching means such as transistors included in the waveform amplifiers 106a to 106c and 107a to 107c in the next stage. It generates and outputs a pulse signal having an output voltage of 10 to 15 V that can be driven to perform switching of 100 V.

  The waveform amplifiers 106a, 106b, and 106c apply three-phase drive waveforms (drive pulses) V11, V12, and V13 to the respective electrodes 102 in the transport area, and the waveform amplifiers 107a, 107b, and 107c correspond to the electrodes in the development area. Three-phase drive waveforms (drive pulses) V21, v22, and V23 are applied to the electrode 102.

  Here, in the transport region of the toner transport member 2, for each electrode 102, as shown in FIG. 9, the application time ta of +100 V for each phase is set to about 33%, which is 1/3 of the repetition period tf. (This is referred to as a “carrier voltage pattern”.) Three-phase drive waveforms (drive pulses) V11, V12, and V13 are applied. This drive waveform is a waveform suitable for high-speed conveyance of toner in the conveyance region.

  In the development region, as shown in FIG. 10 or FIG. 11, the application time ta of +100 V (or −100 V) of each phase is set to about 67%, which is 2/3 of the repetition period tf, for each electrode 102. Three-phase drive waveforms (drive pulses) V21, V22, and V23 that have been set (this is referred to as a “hopping voltage (or development voltage) pattern”) are applied. In the developing region, it is preferable to positively launch toner particles toward the image carrier, and the drive waveform in FIG. 10 is suitable for launching toner particles.

  Further, as the hopping voltage pattern, as shown in FIG. 12, a voltage having a waveform in which a pulse voltage and a DC bias are superimposed can be used. The waveform shown in FIG. 12 is a drive waveform of −50 V to −150 V by biasing a DC voltage of −50 V. In the figure, a relatively positive time is a 33% duty waveform.

  Even when a drive waveform of the development voltage pattern is applied, since the toner is also subjected to a lateral force other than the toner positioned at the center of the 0V electrode, not all the toners are launched at the same time, but move in the horizontal direction. Conversely, even when a drive waveform of a carrier voltage pattern is applied, depending on the position of the toner, there is a toner whose ascending distance is larger than that of being obliquely launched at a large angle and moving horizontally.

  Therefore, the drive waveform pattern applied to each electrode 102 in the transport region is not limited to the transport voltage pattern shown in FIG. 9 described above, and the drive waveform pattern applied to each electrode 102 in the development region 12 is also the above-described diagram. The development voltage pattern shown in FIGS. 10 to 12 is not limited.

  The drive waveform has been described for the case of three phases. When this is generalized to the n phase, the drive waveform is as follows. That is, when an n-phase (n is an integer of 3 or more) pulsed voltage (driving waveform) is applied to each electrode to generate a traveling wave electric field, the voltage application time per phase {repetition period time × By setting the voltage application duty to be less than (n−1) / n}, it is possible to increase the efficiency of conveyance and development. For example, when a three-phase drive waveform is used, the voltage application time ta of each phase is set to less than about 67%, which is 2/3 of the repetitive cycle time tf, and when a four-phase drive waveform is used, It is preferable to set the voltage application time of each phase to less than 75%, which is 3/4 of the repetition cycle time.

  On the other hand, the voltage application duty is preferably set to {repetition cycle time / n} or more. For example, when a three-phase driving waveform is used, it is preferable to set the voltage application time ta of each phase to about 33% or more, which is 1/3 of the repetition cycle time tf.

  That is, between the voltage applied to the target electrode and each voltage applied to the upstream adjacent electrode and the downstream adjacent electrode in the traveling direction, a time is set for the upstream adjacent electrode to repel and the downstream adjacent electrode to be sucked. The efficiency can be improved. In particular, when the driving frequency is high, the initial speed for the toner on the electrode of interest is set by setting it within the range of {repeat cycle time / n} or more and less than {repeat cycle time × (n−1) / n}. It becomes easy to obtain.

  Note that the hopping phenomenon of the ET phenomenon does not occur only by using the electrostatic transport substrate, and the electrode width a of the electrode 102 of the toner transport member 2, the inter-electrode spacing R, the drive waveform (voltage) applied to the electrodes, and This is caused by setting the relationship. This point is as described in detail in Patent Document 2 and the like.

  For example, the electrode width a of the electrode 102 is a width dimension for transporting and hopping at least one toner when the electrode width a is 1 times the toner diameter. The applied electric field is reduced, and the conveyance force and flying force are reduced, which is not sufficient for practical use. In addition, as the electrode width a increases, the electric lines of force incline in the traveling direction (horizontal direction), particularly in the vicinity of the center of the upper surface of the electrode, and a region having a weak vertical electric field is generated. . If the electrode width a is too wide, in an extreme case, the image force, van der Waals force, adsorption force due to moisture, etc. according to the charged charge of the toner will be superior, and toner deposition may occur.

  From the efficiency of conveyance and hopping, if the width is such that about 20 toners are placed on the electrode, adsorption is unlikely to occur, and the conveyance and hopping operations can be efficiently performed with a low voltage drive waveform of about 100V. . If it is wider than that, a region where adsorption occurs partially occurs. For example, when the average particle diameter of the toner is 5 μm, it corresponds to a range of 5 μm to 100 μm.

  A more preferable range of the electrode width a of the electrode 102 is 2 times to 10 times the average particle diameter of the toner in order to drive more efficiently at a low voltage of 100 V or less. By setting the electrode width a within this range, the decrease in electric field strength near the center of the electrode surface can be suppressed to 1/3 or less, and the decrease in hopping efficiency is 10% or less, resulting in a significant decrease in efficiency. Disappears. For example, this corresponds to a range of 10 μm to 50 μm when the average particle diameter of the toner is 5 μm.

  More preferably, the electrode width a is in the range of 2 to 6 times the average particle diameter of the toner. For example, this is a range corresponding to 10 μm to 30 μm when the average particle diameter of the toner is 5 μm. It has been found that efficiency within this range is very good.

  Further, the electric field capable of imparting a force acting on toner conveyance and hopping is 0.5 V / μm or more, the preferred electric field free from the problem of adsorption is 1 V / μm or more, and the more preferable electric field capable of imparting a sufficient force. It has been found that it is in the range of 2 V / μm or more.

  Regarding the electrode interval W2, the electric field strength in the transport direction decreases as the interval increases, so the value corresponding to the range of the electric field strength is the same, and is 1 to 20 times the average particle diameter of the toner, preferably It is 2 times or more and 10 times or less, and more preferably 2 times or more and 6 times or less. The hopping efficiency decreases as the electrode interval W2 increases, but practical hopping efficiency can be obtained up to 20 times the average particle diameter of the toner. If the average particle diameter of the toner exceeds 20 times, the adsorbing force of a large amount of toner cannot be ignored, and toner that does not cause hopping is generated. In this respect as well, the electrode interval W2 is 20 times or less of the average particle diameter of the toner. There is a need to.

  In addition, the conveyance and hopping by the electrode configuration described above can be efficiently performed because the average particle diameter of the toner is 2 to 10 μm, and −3 to −40 μC / g when Q / m is negatively charged. It has been found that it is preferably −10 to −30 μC / g, +3 to +40 μC / g in the case of positive charging, and more preferably +10 to +30 μC / g.

  Furthermore, since the difference between the image portion potential Vi and the non-image portion potential (background portion potential) Vg can be sufficiently developed at 300 V or less, a small and low-cost charger can be used as compared with the conventional development method. There is an advantage that the amount of generated ozone is small. The voltage applied to the electrode 102 of the toner conveying member 2 is formed when the voltage of the component that attracts the toner and the voltage of the component that repels the toner are applied between the adjacent electrodes 102 and 102 of the toner conveying member 22. By setting the voltage so that the maximum value of the electric field in the toner transport direction is 2 V / μm or more, toner can be transported more reliably.

  By the way, in the EH development, the toner is hopped on the toner conveying member 2 so as to make the toner conveying member 2 have an attractive force with respect to the toner, but the toner is simply developed on the toner conveying member 2. If the toner is merely hopped, the certainty that the hopped toner adheres to the latent image on the image carrier 1 is not guaranteed even if the hopped toner has progress toward the image carrier 1.

  Therefore, the relationship between the potential (surface potential) of the latent image on the image carrier 1 and the potential (electric field generated) applied to the toner conveying member 2 is set to a predetermined relationship, that is, the latent image on the image carrier 1 is set. An electric field is generated so that the toner is directed toward the image carrier 1 for the image portion and the toner is not directed toward the image carrier 1 for the non-image portion. As a result, the toner adheres reliably to the image portion of the latent image and the toner does not face the image carrier 1 side to the non-image portion, so that the toner hopped from the toner conveying member 2 is efficient. Therefore, it is possible to prevent scattering and to enable high-quality development without color unevenness by driving at a low voltage.

  As described above, the EH development using the toner hopping phenomenon is the most difficult to develop even when the potential difference of the latent image formed on the image carrier is small, specifically, even when the voltage is 300 V or less. It can develop up to 1 pixel.

  On the other hand, in the conventional dry development system, the potential difference between the image portion and the background portion is required to be at least 400 V, and is usually 500 to 900 V, regardless of whether one-component development or two-component development. For example, the image portion is + 700V and the background portion is + 100V (in the case of regular development). Then, the developing bias voltage applied to the developing roller is set to +400 V in the middle, and the negatively charged toner is peeled off from the surface of the developing roller (one component) or the carrier (two components) by electrostatic force at a potential difference of 300 V from the image portion. Then, the toner image is formed by moving it to the image portion, and with a potential difference of 300 V from the background portion, the toner attached to the background portion is peeled off by an electrostatic force and returned to the developing roller to prevent background contamination.

  As described above, in the conventional development method, the toner strongly adhered to the developing roller, the carrier, or the surface of the photosensitive member by the electrostatic force, the image force, the liquid cross-linking force, and the van der Waals force is peeled off and developed. Therefore, in order to eliminate the background stain, a large potential difference is required between the image portion and the background portion.

  On the other hand, in EH development, the toner is driven up to the vicinity of the image carrier by the electrostatic force from the toner conveying member (hopping), so that the source of the force that peels off the adhered toner from the developing roller and carrier on the image carrier side. There is no need to prepare a large potential difference, and simply form a potential (image potential) that attracts the toner launched to the vicinity of the image carrier and a repulsive potential (background potential, non-image portion potential). It is sufficient to keep it, and its size is possible at 100V as explained below.

  According to the present invention, the potential difference between the image portion and the background portion is 300 V or less, low potential development can be put into practical use, the amount of ozone generated during charging is reduced, and the amount of light such as a laser or LED for image exposure is reduced. The service life is extended and the cost can be reduced. Also, the low writing energy means that writing can be performed at high speed when using a conventional high-energy element, and therefore a laser optical system that requires two or four beams should be one beam. Can greatly reduce costs. Alternatively, with the same optical system, the image forming speed can be significantly increased and the transfer voltage can be lowered, so the amount of ozone generated is reduced, the toner image is less disturbed during transfer, and the electric field applied to the photosensitive layer is reduced. Therefore, a great effect such as extending the life of the photoreceptor can be obtained.

In the following, a description will be given of conditions in which the potential difference between the image portion potential Vi of the latent image and the background portion potential Vg can be set to 300 V or less in the hopping mode EH development, and the isolated minimum one pixel can be firmly developed without background contamination.
First, an outline of the image forming apparatus used here will be described with reference to a schematic explanatory diagram of FIG.

  In this image forming apparatus, for example, an OPC drum 201 having a diameter of 60 mm and a charge transfer layer thickness of 13 μm is charged by a scorotron charger 202 and exposed with a laser beam irradiated from an LD writing unit 203, thereby causing the OPC drum 201. An electrostatic latent image is formed thereon. The surface potential of the OPC drum 201 at this time was measured with a surface potential meter provided at the lower right (not shown) of the OPC drum 201.

  Further, a toner transport substrate 204 constituting a developing device (developing means) is provided immediately below the OPC drum 201. The interval between the OPC drum 201 and the toner conveying member 204 was 300 μm, and the rotational speed of the OPC drum 201 was 200 mm / sec. The toner conveying member 204 has the same configuration as that described in FIG. 3, and the electrode 102 has an electrode width W1 of 30 μm and a pitch p of 60 μm (interelectrode spacing W2 = 30 μm).

  Then, the three-phase voltage as described above is applied to the electrode 102 from the voltage applying means 205 in order to generate a transfer electric field. The applied voltage at this time is a pulse voltage, and a voltage (attraction voltage) Vp that attracts toner relatively and a voltage (repulsion voltage) Vr that repels toner are alternately applied. Here, an example in which the frequency of the applied voltage is 3 kHz and the duty is 50% will be described. The force for electrostatically transporting the toner is determined not by the applied voltage value but by the difference between the suction voltage Vp and the repulsion voltage Vr. Therefore, as long as Vp−Vr is kept constant, the voltages Vp and Vr are changed. However, the toner conveyance state does not change.

  Further, the toner T is supplied from the toner supply device 207 to the toner conveying member 204. The toner supply device 207 includes a stirring screw 208 for stirring the toner and a mesh electrode 209, and a bias voltage obtained by adding the bias voltages by the bias power supply 210 and the bias power supply 211 is applied to the stirring screw 208. The negatively charged toner is supplied to the toner conveying member 204 by applying a bias voltage of the bias power source 210.

  Further, a transfer device 213 constituted by a transfer belt 214 and a transfer bias roller 215 for transferring a toner image formed on the OPC drum 201 to a fed paper (transfer material) is disposed. A cleaning unit 216 for removing the toner remaining on the 201, a neutralizing unit 217 for removing the charge remaining on the OPC drum 201, and the like are arranged.

  Here, all the reversal development in which negatively charged toner adheres to the portion where the negative potential of the latent image is low (the absolute value is small) will be described, but the principle that enables low potential development is also applicable to regular development. Basically the same. The developer used is a two-component developer, the average particle diameter of the toner is 5 to 6 μm, and the average charge amount (specific charge) q / m is about −20 μC / g.

  In the apparatus configured as described above, the voltage applied to the grid of the scorotron charger 202 is changed from −50 V to −500 V, the laser light quantity of the LD writing unit 203 is adjusted, and the dark (background) potential Vd and bright ( Image) The potential Vl was measured. The measurement results are shown in FIG.

  From FIG. 14, it can be seen that in order to set the latent image potential difference Vp to 150 V, for example, with this OPC drum (charge transfer layer 13 μm) 201, the grid voltage Vg should be set to −165 V. At this time, the dark potential Vd is −210V, and the light potential Vl is −60V. Here, since negative-positive (reversal) development is performed with negatively charged toner, the dark potential becomes the background portion potential Vg and the bright potential becomes the image portion potential Vi. The amount of laser light was selected so as not to cause overexposure or underexposure with reference to the obtained toner image.

  The OPC drum 201 having a charge transfer layer of 13 μm is used, the OPC drum peripheral speed is 150 mm / sec, the applied voltage to the electrode of the toner conveying member 204 is −180 V ± 60 V, frequency 3 kHz, duty 50%, latent image potential difference 150 V (dark potential Vd = -210V, bright potential Vl = -60V), and the image evaluation was performed by changing the development gap (distance between the toner conveying member 204 and the OPC drum 201) from 50 μm to 700 μm.

  FIG. 15 shows the solid (large area black image) image (optical reflection) density and background density at this time. Since it cannot be directly measured on the OPC drum 201, the toner image is peeled off from the OPC drum 201 with a transparent weak adhesive tape, and the whole tape is pasted on a white sheet, and X-Rite 938 (trade name) of X-Rite Co., Ltd. Measured with

  From FIG. 15, it can be seen that the image density is as high as 1.4 or more in a wide range from 50 μm to 500 μm, and even if it is wider than that, the image density is 1.2 or more up to 700 μm. That is, in terms of solid image density, the development gap is in a practical range from 50 μm to 500 μm. On the contrary, regarding the background, it can be seen that the practical range is from 100 μm to 700 μm except for the gap of 50 μm.

  Next, one isolated pixel and 3 × 3 pixels were developed with different development gaps, and the dot diameter of the toner image was measured. The result is shown in FIG.

  From FIG. 16, it can be seen that even when one dot is the same, the number of pixels constituting it is different, and when the size is different, the change when the development gap changes is different. That is, large dots (3 × 3 pixels) are not significantly affected by the development gap, and are slightly smaller from 50 μm to 700 μm, whereas in the case of small dots (one isolated pixel), the development gap is small. Very small at 400 μm or more.

In order to clarify the cause, the electric field of the 1-pixel latent image and the 3-pixel latent image was simulated by changing the development gap. This result will be described below.
The simulation was performed by the two-dimensional difference method of the axis object. This calculation method is mathematically two-dimensional with z and r, but because of z-axis symmetry, it is physically a three-dimensional space simulation around the z-axis. The calculation conditions were matched to the experimental conditions. That is, the thickness of the OPC is 13 μm, the surface (solid background) potential is −210 V, the electrode width W1 of the toner conveying member is 30 μm, the pitch p is 60 μm, the applied voltage is −180 V ± 60 V, the OPC drum 201 and the toner conveying member The gap between 204 is 50 μm to 700 μm, the toner particle size is 7 μm, the specific charge is −25 μC / g, and the latent image size is 1 pixel × 1 pixel (diameter 42.3 μm) and 3 pixels × 3 pixels (diameter). 127 μm) (one pixel is 1/600 inch).

  Of these results, FIGS. 17 and 18 show cases where the latent images are 42.3 μm and 127 μm and the gap is 400 μm. 17 is a schematic explanatory view of an electric field (development gap 400 μm) formed by a latent image (upper left) having a diameter of 42.3 μm, and FIG. 18 is an electric field (development gap) formed by a latent image (upper left) having a diameter of 127 μm. 400 μm) is a schematic explanatory view. 17 and 18, the upper elongated band is the OPC 201, and the lower rectangle is the electrode 102 of the toner conveying member 204.

  Here, for example, the toner (not shown) on the electrode 102a to which -240V (repulsive voltage) at the leftmost end (z axis) in each figure is applied is launched by an electrostatic force and flies upward. (Hopping) When the electric field lines emitted from the upper left latent image (image part) are reached, the electric field lines are traced in reverse to arrive at the latent image.

  However, FIG. 17 and FIG. 18 show that there is a great difference in the size of the electric lines of force generated from the 42.3 μm latent image and the 127 μm latent image. Naturally, the width is different, but the height (distance from the OPC surface) is also quite different. The height of the peak of the lines of electric force emitted from the latent image was measured to be 54 μm (FIG. 17) for the 42.3 μm latent image and 131 μm (FIG. 18) for the 127 μm latent image.

  The hopped toner can reach the latent image by flying 400−131 = 269 μm in the 127 μm latent image, but cannot reach the latent image by flying 400−54 = 346 μm in the 42.3 μm latent image. Become.

  This difference was considered to have led to an experimental result that a large dot (3 × 3 pixels 127 μm) latent image could be developed without problems even with a gap of 400 μm, but a small dot (isolated 1 pixel 42.3 μm) latent image could hardly be developed. It is done.

  From this result, it is clear that the development gap must be within the height of the minimum latent image (one isolated pixel) + the toner hopping height.

  Next, the heights of the latent images of 42.3 μm and 127 μm at the gap of 400 μm were 54 μm and 131 μm, respectively, which were almost equal to the diameter of the latent image. In order to evaluate whether the change does not change, the gap G and the size of the latent image were simulated, and the height of the latent image was measured in the same manner. The results are shown in FIG. 19 and FIG.

  From FIGS. 19 and 20, it can be seen that when the development gap is 300 μm or more, the height of the latent image is substantially equal to the diameter of the latent image regardless of the development gap.

  Since the height of the latent image was known, the toner hopping height was next obtained by simulation. When the development gap is 400 μm and the latent image diameter is 42.3 μm, a toner having a diameter of 7 μm and a specific charge of −25 μC / g is applied onto the electrode 102 of the toner conveying member 204 including the z-axis to which a repulsion voltage of −240 V is applied. The highest point was determined from the track. The result is shown in FIG.

In FIG. 21, small square symbols are the results of simulation, and the curve represents the following equation. In the formula, H: toner hopping height (μm), E: horizontal transport electric field = (suction voltage−repulsion voltage) / interelectrode spacing W2 (V / μm).
H = √E × 96 [μm]

  From FIG. 21, the toner hopping height is proportional to the route of the horizontal conveyance electric field (maximum value) obtained by dividing the difference between the toner attraction voltage and the repulsion voltage by the interelectrode spacing W2 at the electrode 102 of the toner conveyance member 204. I understand.

The proportionality constant at this time is “96” in this case, but becomes larger as the particle diameter or specific charge of the toner increases, and decreases as the toner decreases. The range is estimated to be about 1.5 times this constant on the larger side and about half on the smaller side. Therefore, the range of the toner hopping height H can be expressed as the following equation as a function of the horizontal carrying electric field E (maximum value).
50 × √E <H <150 × √E

Thus, the practical upper limit value of the hopping height is 150 times the square root of the horizontal carrier electric field maximum value (V / μm), and the electric field height of the minimum latent image (isolated one pixel) is equal to the diameter of the latent image. Therefore, the upper limit Gmax of the development gap G for developing even one isolated pixel is expressed by the following equation when the diameter (μm) of the minimum isolated pixel is Dmin and the maximum horizontal carrying electric field (V / μm) is Ehmax. It will be decided.
Gmax = Dmin + 150 (Ehmax) ^1/2 [μm]

The upper limit Gmax of the development gap G for developing even one isolated pixel may be equal to or less than this Dmin + 150 (Ehmax) ^1/2 , so the relationship of the upper limit Gmax ≦ Dmin + 150 (Ehmax) ^1/2 of the development gap G is satisfied. Just fill it.

  For example, if the minimum pixel is one dot of 600 dpi, Dmin is 42 μm, the inter-carrier electrode interval W2 is 30 μm, and the potential difference therebetween is 120 V (suction = −120 V, repulsion = −240 V), Ehmax is 4 V / At μm, the development gap upper limit Gmax is 342 μm.

  This result agrees well with the experimental result that one isolated pixel of 600 dpi could be developed with a development gap of 300 μm but could not be developed with 400 μm. The maximum horizontal transfer electric field can be sufficiently up to 10 V / μm depending on the selection of the inter-electrode material of the transfer substrate, and the upper limit of the development gap at that time is 500 μm or more.

Next, the lower limit of the development gap G will be described.
First, FIG. 22 and FIG. 23 show the simulation results of the development space in which the development gap is 50 μm where the background stain is generated and the gap is 100 μm where the background is not generated. The simulation method is exactly the same as in FIG.

  Referring to FIG. 23, it can be seen that the lines of electric force extend from the suction (high) potential (−120V) electrode 102b of the electrode 102 toward the background portion (−210V) of the OPC to cover the background portion. . Since the negatively charged toner receives an electrostatic force in the direction opposite to the lines of electric force, the toner hopped from the second repulsive (low) potential electrode 102a from the right also receives the electrostatic force before the OPC and stalls. Conversely, the toner transport member 204 moves toward the suction electrode 102b. For this reason, scumming does not occur.

  On the other hand, when FIG. 22 is viewed, similarly, the lines of electric force from the suction (high) potential electrode 102b are directed toward the background portion of the OPC, but this line is directly above the repulsive (low) potential electrode 102a. , You can see that it is not on either side. That is, here, since the electric field that pushes the negatively charged toner back to the transport substrate is not formed, soiling has occurred.

  Comparing FIG. 22 and FIG. 23, the electric lines of force generated from the suction (high) potential electrodes on both sides of the repulsion (low) potential electrode enter the background portion of the OPC directly above the repulsion (low) potential electrode. It can be seen that the development gap must be somewhat wide. For the minimum gap, there is no practical problem even if it is calculated by replacing the line of electric force drawn in the curve with a straight line. The gradient is 60 °.

Therefore, with reference to FIG. 24, assuming that the lines of electric force generated from the end of the adjacent attraction (high) potential electrode 102b rise linearly with a gradient of 60 degrees, the tip thereof is repulsive (low ) The gap G entering the background just above the center of the potential electrode 102a is represented by the following formula when the electrode width is W1 (μm) and the distance between the electrodes is W2 (μm) from the triangular formula.
G = (W2 + 0.5W1) × 3 ^1/2 [μm]

In order not to cause background stain, the gap G should be equal to or more than the above (W2 + 0.5W1) × ^3½ , so that the relationship of G = (W2 + 0.5W1) × ^3½ is satisfied. You can do it.

  For example, when W1 = W2 = 30 μm, G = 78 μm. If the gap G is smaller than this value, the electric lines of force emanating from the end of the suction (high) potential electrode next to the left will enter the background just above the center of the repulsion (low) potential electrode, On the contrary, the electric lines of force emitted from the end of the right suction (high) potential electrode hit the OPC on the right side, and as a result, the electric force lines directed to the suction (high) potential electrode are between them. If the toner hopped from the center of the repulsive (low) potential electrode reaches here without encountering an electric field in the reverse direction and becomes soiled, and the gap G is wider than 78 μm, the left and right suction (high) potential electrodes The lines of electric force that are emitted from the surface of the repulsive (low) potential electrode are repelled and bent in front of the surface just above the center of the repulsive (low) potential electrode. Dirt is generated because it receives electrostatic force toward the transfer board. There.

  This result is in good agreement with the experimental result of soiling with a gap of 50 μm and not 100 μm.

  Since the electrode width W1 and the inter-electrode spacing W2 of the toner conveying member 204 can be reduced to about half of 30 μm, the practical minimum development gap is about 40 μm.

  In the above description, the case where the toner conveying member has a flat plate shape has been described. However, the same applies to the case where the toner conveying member 12 is a roll-shaped member as shown in FIG. 1 or FIG.

Accordingly, when the distance between the image carrier and the toner conveying member is G (μm), the width of the electrode of the toner conveying member is W1 (μm), and the distance between the electrodes of the toner conveying member is W2 (μm), the distance When G satisfies the equation G ≧ (W2 + 0.5W1) × 3 ^1/2 , development without background contamination can be performed.

The distance between the image carrier and the toner conveying member is G (μm), the diameter of the isolated minimum pixel is Dmin (μm), and the maximum electric field in the conveying direction formed by the toner conveying member is Ehmax (V / μm). ), The distance G satisfies the following formula: G ≦ Dmin + 150 (Ehmax) ^1/2 , so that one isolated pixel can be developed clearly.

Next, the relationship between the thickness of the charge transfer layer of the image carrier and the resolution r will be described with reference to FIG.
Here, five kinds of OPC drums 201 having the charge transfer layer thicknesses of 13 μm, 15 μm, 18 μm, 23 μm, and 28 μm are prepared and the latent image potential difference is set to 150 V by performing the same experiment as described in FIG. The same development conditions (development gap G between toner transport member 204 and OPC drum 201 is 300 μm, OPC drum peripheral speed is 150 mm / sec, applied voltage to the electrode of toner transport member 204 is −180 V ± 60 V, frequency 3 kHz, Development was performed at a duty of 50%, a latent image potential difference of 150 V (dark potential Vd = −210 V, bright potential Vl = −60 V), and image evaluation was performed.

  In addition to the above-mentioned 600 dpi, this experiment was performed for a resolution (image density) of 1200 dpi and 1800 dpi by replacing the laser optical system. The result is shown in FIG.

  According to this experiment, when an image of 600 dpi was seen, it was found that the image was completely different depending on the thickness of the charge transfer layer. In particular, the difference is conspicuous in an isolated minimum one pixel (600 dpi for writing, and three white pixels are arranged between each black pixel), which is most difficult to develop. That is, when the thickness of the charge transfer layer is 28 μm, the toner is scattered sparsely at the position where an isolated pixel is formed, resulting in a lightly blurred dot image (NG image), whereas the charge transfer layer thickness is Is 13 μm, 15 μm, and 18 μm, the toner is densely concentrated at a predetermined position to form a sharp dot image having a high density. When the charge transfer layer thickness was 23 μm, it was slightly blurred in the middle.

  Next, looking at the 1200 dpi image, this time, if the charge transfer layer thickness that was slightly blurred at 600 dpi is 23 μm, it becomes a low-density blurred dot image (NG), and if the charge transfer layer thickness is 18 μm, , It became a slightly blurred dot.

  Further, looking at an image of 1800 dpi, this time, even when the charge transfer layer thickness is 18 μm, the image is NG, and the dot when the charge transfer layer thickness is 15 μm is slightly blurred, but when the charge transfer layer thickness is 13 μm, As usual, a sharp dot image was obtained at a high density.

  Based on this result, in order to develop a low-potential latent image sharply at a high density up to one isolated minimum pixel, in the case of an image carrier having a charge generation layer inside (lower side), the resolving power is r ( dpi), it was found that the thickness tg of the charge transfer layer must satisfy the equation of tg ≦ 7200 / r + 13 [μm]. More preferably, it satisfies the formula of tg ≦ 7200 / r + 10 [μm].

  As the thickness tg of the charge transfer layer increases, the dot image is blurred and developed because the charges generated in the charge generation layer (in this case, holes) have the same polarity when moving through the charge transfer layer. For this reason, it is considered that the Coulomb repulsions repel each other, and the charge of the outer shell moves while spreading laterally. The thicker the charge transfer layer is, the longer the moving distance is. Therefore, the lateral shift is increased, and the one-pixel latent image is expanded (blurred). In addition, the distribution of holes reaching the surface of the image carrier (OPC) is widened, and as a result, the density is also lowered, so that the depth of the latent dot image is shallow (for example, the hole spreads from dark potential -210V). Otherwise, the light potential that has dropped to -80V will only drop to -100V). As a result, the amount of toner to be developed is reduced and the density is reduced.

  In the conventional development system, for example, the dark potential is as high as -870 V and there is no problem because there is a potential difference of 750 V between the light potential (solidly about -120 V), but EH development used in the present invention is not a problem. However, when the light / dark potential difference is only 150 V, for example, the influence of the toner potential generated in the developed toner cannot be ignored. In particular, in the case of an isolated minimum one pixel, the difference is further reduced to 2/3 to 1/2 of the solid potential difference of 150 V, so that the influence of the toner potential Vt generated from the developed charged toner becomes large.

For example, when the toner charged to −20 μC / g is placed on the surface of the image carrier at a density of 0.5 mg / cm ² that gives a sufficient image density, the potential is the OPC with a charge transfer layer thickness of 13 μm. Although it is −55 V, it reaches −120 V in the OPC having a charge transfer layer thickness of 28 μm. Since the depth of the potential of one isolated minimum pixel is estimated to be about 80 V, the density is reduced by OPC with the thickness of the electric field transfer layer being 28 μm. About half of the required amount of toner adheres to the dot latent image. It is presumed that at that time, the electric field of the latent image almost disappeared and the subsequent toner could not participate in the development.

  On the other hand, in the case of the OPC having a charge transfer layer thickness of 13 μm, even if the necessary toner collects in the latent image dots, there is still a potential difference that can be developed a little, so it is assumed that high density dots have been developed. .

  Moreover, even if the thickness of the charge transfer layer is the same, it is considered that this is because the dot of the minimum isolated one pixel becomes unsharp with a lower density as the resolution is higher. In other words, at 1200 dpi, exposure was performed with a pulse width that is 1/2 of the pulse width at 600 dpi, and at 1800 dpi, exposure was performed at 1/3, but at that time, the peak exposure intensity of one pixel also decreased. It is considered that the latent image became shallow and could not be sufficiently developed.

  That is, in the case of low-potential development, the thickness tg of the charge transfer layer is higher in the density of at least one isolated pixel in relation to the toner potential Vt than in the lateral spread of the hole cloud due to Coulomb repulsion. It should be determined so that it can be developed, and FIG. 25 shows the result.

  As a result, with this image forming apparatus, low-potential development in which the potential difference between the image portion and the background portion is 300 V or less can be put into practical use, the amount of ozone generated during charging is reduced, and the amount of light such as a laser or LED for image exposure is reduced. , The lifetime is extended and the cost can be reduced. In addition, since the writing energy is small, writing can be performed at a high speed. Therefore, the cost can be significantly reduced by using one laser optical system that requires two or four beams. Further, since the transfer voltage can be lowered, the amount of ozone generated is reduced, the toner image is less disturbed at the time of transfer, and the electric field applied to the photosensitive layer is lowered, so that a great effect such as extending the life of the photoreceptor can be expected.

  Furthermore, by setting the development gap appropriately with respect to the strength of the transport electric field determined by the dimension of the transport electrode and the applied voltage, even in EH development which is a low potential development with a small latent image potential difference, there is no background stain. Clean development can be performed up to one isolated pixel. In particular, by using EH development, it is possible to develop a single isolated dot of 1200 dpi having a diameter of only about 30 μm.

Next, an example of a process cartridge according to the present invention and an image forming apparatus according to the present invention including the process cartridge will be described with reference to FIG.
The image forming apparatus includes an image carrier, a charging unit, a developing unit according to the present invention as a developing unit, and an image forming unit including a cleaning unit, black (K), magenta (M), cyan (C), and yellow. (Y) process cartridges 501K, 501M, 501C, and 501Y (hereinafter simply referred to as “process cartridge 501” when not distinguished from each other; the same applies to others), optical writing devices 502K, 502M, Transfer rollers 503Bk, 503Bm, 503Bc, and 503By facing the transfer belt 503A and the process cartridges 501K, 501M, 501C, and 501Y with the conveyance belt 503A interposed therebetween, the fixing device 504, the transfer belt 503A A sheet feeding device 505 that accommodates the material 506. .

  Here, the optical writing devices 502K, 502M, 502C, and 502Y are for writing a latent image on the charged image carrier of the process cartridges 501K, 501M, 501C, and 501Y according to image information, and optical scanning using polygons. Various devices such as devices and LED arrays can be used.

  The conveyance belt 503A is stretched between the conveyance roller 511, the driven roller 512, and the tension rollers 513 and 514, and rotates in the direction indicated by the arrow by the rotation of the conveyance roller 511. Then, an adsorption roller 515 for adsorbing the transfer material 506 onto the conveyance belt 503A is arranged facing the conveyance roller 511, and a toner image is formed on the conveyance belt 503A at the exit side of the conveyance belt 503A. A P sensor 516 for detecting a pattern is arranged.

The transfer rollers 503Bk, 503Bm, 503Bc, and 503By have at least a core metal and a conductive elastic layer covering the core metal, and the conductive elastic layer is an elastic material such as polyurethane rubber or ethylene-propylene-diene polyethylene (EPDM). In addition, an elastic roller in which a conductivity imparting agent such as carbon black, zinc oxide, and tin oxide is blended and dispersed to adjust the electric resistance value (volume resistivity) to a medium resistance of 10 ⁶ to 10 ¹⁰ Ω · cm.

  The fixing device 504 includes a heating roller 504a and a pressure roller 504b facing the heating roller 504a.

  In this image forming apparatus, in a normal image forming operation, the transfer material 506 such as a recording sheet supplied from the paper supply device 505 is a transfer material that is a transfer body when a predetermined voltage is applied to the suction roller 515. It is adsorbed to the conveyance belt 503A. The transfer material 506 moves together with the transfer material conveyance belt 503A while being carried on the transfer material conveyance belt 503A. During the movement, the toner images of the respective colors are sequentially transferred from the process cartridges 501K, 501M, 501C, and 501Y. A color toner image is formed thereon. When the transfer material 506 passes through the conveyance belt 503A and reaches the fixing device 504, the toner image on the transfer material 506 is heated while being sandwiched between the heating roller 504a and the pressure roller 504b to be fixed on the transfer material 506. As a result, a visible image is fixedly formed on the transfer material 506. Thereafter, the transfer material 506 on which the color image is formed is discharged to a paper discharge unit 507 at the top of the apparatus main body 510.

  In the mode in which the color misregistration and toner density of each color toner image are adjusted, a toner image having a predetermined pattern is directly formed on the transfer material conveying belt 503A from the image forming units 501K, 501M, 501C, and 501Y. The toner pattern is detected, and the write timing and development bias are changed based on the detection result, so that an optimum color image can be obtained. The toner pattern on the transfer material conveyance belt 503A is adjusted in the charging polarity by the bias applied to the suction roller 515, and then the process cartridges 501K, 501M, 501C, Collected at 501Y.

Next, the process cartridge 501 according to the present invention will be described with reference to FIG. FIG. 27 is an enlarged explanatory view of the process cartridge.
The process cartridge 501 includes an image carrier 521, a contact charging member 531, the developing device 541 (which may be another developing device) described in the above-described example of the first embodiment, and a cleaning device 551. I have.

  The image carrier 521 is a negatively charged organic photoreceptor, and is provided so as to be rotated in the arrow direction (counterclockwise direction in the drawing) by a rotation driving mechanism (not shown). The contact charging member 531 is a flexible charging roller in which a foamed urethane layer of medium resistance in which a urethane resin, carbon black as conductive particles, a sulfurizing agent, a foaming agent, etc. are formulated in a roller shape is formed on a core metal. is there. The middle resistance layer formed on the core of the contact charging member (charging roller) 531 is not limited to the above urethane foam layer, but is urethane, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber. A rubber material obtained by dispersing a conductive material such as carbon black or metal oxide in order to adjust resistance in (NBR), silicone rubber, isoprene rubber, or the like, or a foamed material thereof can be used.

  The cleaning device 551 includes a cleaning blade 552 that is brought into contact with the rotation direction of the image carrier 521 in the counter direction, a waste toner storage unit 553 that stores the cleaned toner particles as waste toner, and the like.

Next, the operation of the process cartridge 501 configured as described above will be described.
This image forming apparatus is a multifunction machine that can function as a copying machine and a printer. When the image forming apparatus functions as a copying machine, image information read from the scanner is subjected to various processes such as A / D conversion, MTF correction, and gradation processing. The image processing is performed and converted into write data. When functioning as a printer, image information in a format such as a page description language or a bitmap transferred from a computer or the like is subjected to image processing and converted into write data.

  Prior to image formation, the image carrier 521 starts rotating in the direction of the arrow in FIG. 25, that is, in the counterclockwise direction so that the moving speed of the surface becomes a predetermined speed. The charging roller 531 is rotated with respect to the image carrier 521. At this time, a DC voltage of −100 V and an AC voltage of an amplitude of 1200 V and a frequency of 2 kHz are applied to the core of the charging roller 531 from the charging bias application power source, whereby the surface of the image carrier 521 is charged to about −100 V.

  The optical writing device 502 irradiates the charged image carrier 521 with a laser beam 502a in accordance with the writing data. That is, by changing the potential of the image portion by light irradiation, a difference from the potential of the non-image portion not irradiated with light is generated, and an electrostatic latent image is formed by this potential contrast.

  The electrostatic latent image formed on the image carrier 521 by the optical writing device 502 is developed by the developing device 541 according to the present invention, and is visualized on the image carrier 521 as a toner image by adhering toner particles to the image portion. Is done.

  The transfer material 506 is conveyed from the paper feeding device 505 in synchronization with the timing at which the toner image formed on the image carrier 521 arrives at the transfer portion that is the opposite portion between the transfer roller 503B and the image carrier 521. The toner image on the image carrier 521 is transferred to the transfer material 506 by the voltage applied to the transfer roller 503B. The transfer material 506 to which the toner image has been transferred is fixed by the fixing device 504, and a color image is output on the transfer material 506.

  On the other hand, toner remaining on the image carrier 521 without being transferred (transfer residual toner) is cleaned by a cleaning device 551, and the surface of the image carrier 521 after cleaning is used for the next image formation.

  The process cartridges 501K, 501M, 501C, and 501Y for forming these black, magenta, cyan, and yellow toner images are detachable from the image forming apparatus main body 510. That is, as shown in FIG. 28, the process cartridges 501K, 501M, 501C, and 501Y are detachable from the open space when the transfer material transport belt 503A is opened and retracted from the apparatus main body 510. Exchange is possible.

Next, another example of the image forming apparatus according to the present invention provided with the developing device according to the present invention will be described with reference to FIGS. Elements having the same functions as those in FIG. 26 are denoted by the same reference numerals, and the description thereof is omitted unless particularly necessary.
This image forming apparatus includes a belt-like image carrier 561 in which a negatively charged organic photoconductor is configured in a belt shape. The belt-like image carrier 561 is provided between a driving roller 562, a driven roller 563, and a transfer counter roller 564. It is bridged and moved around in the direction of the arrow by a rotary drive mechanism (not shown).

  The belt-like image carrier 561 includes a charging device 565K, 565M, 565C, and 565Y that charges the belt-like image carrier 561, and a development according to the present invention that develops an electrostatic latent image on the belt-like image carrier 561. The developing cartridges 566K, 566M, 566C, and 566Y, which are apparatuses, face each color, and are configured to sequentially superimpose toner images on the image carrier 561 as the image carrier 521 moves. Yes (1 pass color).

  Further, opposed rollers 567K, 567M, 567C, and 567Y are disposed at positions facing the toner conveying member 2 of the developing cartridges 566K, 566M, 566C, and 566Y with the belt-shaped image carrier 561 interposed therebetween. Further, a transfer roller 568 is disposed at a position facing the transfer counter roller 564 with the belt-shaped image carrier 561 interposed therebetween.

  The charging device 565 is for uniformly charging the surface of the image carrier 561, and in this embodiment, a corona charging method is adopted. If non-contact charging means such as corona charging is used, the image carrier 561 can be charged without disturbing the toner image formed by the upstream developing cartridge 566.

  The developing cartridge 566 is a developing device according to the present invention, and is the same as the developing device described in the above embodiment, although the shape is slightly changed. Here, the developing cartridges 566K, 566M, 566C, and 566Y for developing the black, magenta, cyan, and yellow toner images are opened and retracted from the apparatus main body 510 as shown in FIG. It is removable from the open space and can be replaced by the user.

  In this image forming apparatus, the surface of the image carrier 561 is uniformly charged by the charging device 565 during image formation. Even when a toner image is already formed on the image carrier 561, the surface of the image carrier 561 including the toner image is uniformly charged. Next, a light beam corresponding to the image information is emitted from the optical writing device 502. Since the light beam passes between the charging device 565 and the developing cartridge 566, the image carrier 561 that has already been uniformly charged is irradiated with the light beam, and the image carrier, which is a negatively chargeable photoconductor. On the surface of the body 561, the area corresponding to the image portion is neutralized to form a latent image.

  As in the first embodiment, the developing cartridge 566 attaches toner particles to the image portion of the latent image formed on the image carrier 561 and visualizes the latent image as a toner image. The charging, light beam irradiation, and development processes described above are repeated at the portion facing each developing cartridge as described above, and a full-color image in which four color toner images are superimposed on the image carrier 561 is formed.

  On the other hand, the transfer material 506 sent from the paper feeding device 505 is conveyed to a contact portion between the image carrier 561 and the transfer roller 568, and a full color image formed on the image carrier 561 at the contact portion is transferred to the transfer roller 568. The image is transferred onto the transfer material 506 by the voltage applied to. Thereafter, when the transfer material 506 reaches the fixing device 504, the toner image on the transfer material 506 is heated while being sandwiched between the heating roller 504 a and the pressure roller 504 b, thereby being fixed on the transfer material 506, and the transfer material 506. A full color visible image is formed on top.

  Needless to say, the present invention can also be applied to a color image forming apparatus, a monochrome image forming apparatus, and the like using an intermediate transfer belt, a transfer drum, an intermediate transfer drum, and the like.

FIG. 2 is a schematic configuration diagram illustrating an example of a developing device portion of the image forming apparatus according to the first embodiment of the present invention. It is a typical block diagram which shows the other example of the image development apparatus part of the embodiment. FIG. 6 is an explanatory diagram illustrating an example of a toner conveyance member according to the embodiment. FIG. 6 is an explanatory diagram for explaining an electrode arrangement of the toner conveying member. FIG. 6 is an explanatory diagram illustrating an example of a driving waveform for explaining a principle of conveyance by the toner conveying member. FIG. 6 is an explanatory diagram for explaining an example of toner conveyance. FIG. 6 is an explanatory diagram illustrating a specific example of toner conveyance. FIG. 6 is a block diagram illustrating an example of a configuration of a voltage applying unit for the toner conveying member. FIG. 6 is an explanatory diagram illustrating an example of a voltage waveform applied to a transport region of the toner transport member. FIG. 6 is an explanatory diagram illustrating an example of a voltage waveform applied to a developing region of the toner conveying member. FIG. 10 is an explanatory diagram showing another example of a voltage waveform applied to the developing region of the toner conveying member. FIG. 10 is an explanatory diagram illustrating still another example of a voltage waveform applied to the transport region of the toner transport member. It is explanatory drawing with which it uses for description of the apparatus structure used for experiment. It is explanatory drawing which shows the measurement result of the relationship between a grid voltage, a dark potential, a bright potential, and a latent image potential difference. It is explanatory drawing which shows the measurement result of the relationship between the development gap G and optical reflection density. It is explanatory drawing which shows the measurement result of the relationship between the image development gap and the size of the developed dot. It is explanatory drawing with which it uses for description of the electric field which a latent image of diameter 42.3 micrometers forms. It is explanatory drawing with which it uses for description of the electric field which a latent image of 127 micrometers in diameter forms. It is explanatory drawing with which it uses for description of the relationship between the development gap G and latent image height. It is explanatory drawing with which it uses for description of the relationship between a development diameter and latent image height. It is explanatory drawing with which it uses for description of the relationship between the maximum value of a horizontal conveyance electric field, and hopping height. It is explanatory drawing with which it uses for description of the electric field in the image development space corresponding to a background part when development gap G is 50 micrometers. It is explanatory drawing with which it uses for description of the electric field in the development space corresponding to a background part when the development gap G is 100 micrometers. It is explanatory drawing with which it uses for description of an electrode width, the space | interval between electrodes, and the minimum image development gap G. It is explanatory drawing which shows the quality evaluation result of the development dot in the relationship between a writing pixel density and electric charge transfer amount thickness tg. It is a block diagram explaining 2nd Embodiment of the image forming apparatus which concerns on this invention provided with the process cartridge which concerns on this invention. It is explanatory drawing with which it uses for description of the process cartridge. FIG. 3 is an explanatory diagram for explaining the removal and attachment of a process cartridge of the image forming apparatus. It is a block diagram explaining 3rd Embodiment of the image forming apparatus which concerns on this invention provided with the developing cartridge which consists of developing devices based on this invention. FIG. 3 is an explanatory diagram for explaining the attachment / detachment of the developing cartridge of the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image carrier 2 ... Toner conveyance member 3, 13 ... Developer carrier 4 ... Storage part 5A, 5B ... Stir screw 7 ... Developer control member 11 ... First voltage application means 12 ... Second voltage application means 102 ... Electrode 201 ... OPC drum 204 ... Toner transport member (toner transport substrate)
501K, 501M, 501C, 501Y ... Process cartridge 502K, 502M, 502C, 502Y ... Optical writing device 503A ... Transfer material conveying belt 503Bk, 503Bm, 503Bc, 503By ... Transfer roller 504 ... Fixing device 505 ... Paper feed device 506 ... Transfer material 507: Paper discharge unit 521: Image carrier 531 ... Charging device 541 ... Developing device 551 ... Cleaning device 561 ... Image carrier 565K, 565M, 565C, 565Y ... Charging devices 566K, 566M, 566C, 566Y ... Developing cartridge

Claims (3)

In an image forming apparatus that develops a toner by attaching toner to a latent image formed on an image carrier, a transport electric field formed by applying a multiphase voltage to a plurality of electrodes arranged side by side at a predetermined interval A toner transporting member for transporting the toner in a region facing the image carrier, wherein the image carrier has a charge generation layer and a charge transfer layer, and the charge generation layer is located inside the charge transfer layer. When the thickness tg (μm) is r (dpi),
tg ≦ 8400 / r + 13
An image forming apparatus characterized by satisfying the formula:   2. The image forming apparatus according to claim 1, wherein a difference between an image portion potential of the latent image and a background portion potential is 300 V or less. In a process cartridge that includes at least an image carrier and a developing unit that develops toner by attaching the toner to a latent image formed on the image carrier. A toner conveying member configured to convey the toner to a region facing the image carrier by a conveying electric field formed by applying a multiphase voltage to a plurality of electrodes arranged side by side at a predetermined interval; When the carrier has a charge generation layer and a charge transfer layer, and the charge generation layer is inside, when the thickness tg (μm) of the charge transfer layer is r (dpi),
tg ≦ 8400 / r + 13
Process cartridge characterized by satisfying the following formula.

Images