JP2011203336A - Charging device, cartridge for image forming apparatus, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging device capable of inhibiting salt from being formed on an image holding body, a cartridge for an image forming apparatus, and an image forming apparatus.SOLUTION: An applied voltage setting part 106 sets, in response to a result of comparison by a current comparison part 104, voltage (V) applied by a first voltage application part 90 and voltage (V) applied by a second voltage application part 92 so that current (I) to charge the image holding body 44 may agree with current (I) corresponding to target charging potential (V) of the image holding body 44 and voltage (V) to be applied to a conductive layer 78 (second electrode) may be smaller (absolute value of negative voltage may be larger) than the target charging potential (V) of the image holding body 44.

Description

  The present invention relates to a charging device, an image forming apparatus cartridge, and an image forming apparatus.

  As one of charging methods for an image carrier of an image forming apparatus, there is a method using a scorotron charging method using corona discharge. In this method, the object to be charged is charged in a non-contact manner. As another charging method, there is a method using a charging roll method in which a discharge is generated in a minute gap generated between a semiconductive charging roll and an image carrier so as to perform charging treatment.

  In Patent Document 1, a grid electrode is arranged so as to be substantially parallel to a member to be charged, a voltage slightly lower than a target charging potential is applied to the grid electrode, and ozone is applied between the grid electrode and the member to be charged. Disclosed is an ozoneless non-contact charging method and apparatus for applying a voltage that generates an electric field that generates an electron doubling action between a corona discharge electrode and a grid electrode.

Japanese Patent Laid-Open No. 7-271153

  An object of the present invention is to provide a charging device, an image forming apparatus cartridge, and an image forming apparatus that can suppress the formation of a salt that is an ionic compound on an object to be charged.

  The invention according to claim 1 is characterized in that the first electrode, the second electrode disposed closer to the member to be charged than the first electrode, and the electric potential lower than the charged potential of the member to be charged. And a control unit that controls a voltage applied to the second electrode.

  The invention according to claim 2 further includes a current detection unit that detects a current flowing through the first electrode and the second electrode, and the control unit is configured based on a detection result of the detection unit. The charging device according to claim 1, wherein a voltage applied to the second electrode is controlled.

  According to a third aspect of the present invention, the control unit controls a voltage applied to the second electrode so that a potential difference between the second electrode and the charged potential of the member to be charged is 20 V or more and 100 V or less. The charging device according to claim 1.

  A fourth aspect of the present invention is the charging device according to any one of the first to third aspects, wherein the second electrode is disposed such that a distance from the charged body is 300 μm or more and 2 mm or less.

  The invention according to claim 5 further includes an insulator between the first electrode and the second electrode, and the second electrode includes the first electrode, the insulator, and the first electrode. An opening opening in a first direction in which two electrodes are arranged, and the insulator is open in a direction continuous with the opening and continuous with the opening, and is perpendicular to the first direction. 5. The charging device according to claim 1, further comprising an area restriction unit that is a restricted space in the second direction.

  An invention according to claim 6 is an image holding member as a member to be charged, and a charging device according to any one of claims 1 to 5, which is arranged in a non-contact manner with respect to the image holding member, and charges the image holding member. And a developing device that develops a latent image formed by exposure on the image carrier charged by the charging device with a developer.

  An invention according to claim 7 is an image carrier as a member to be charged, and a charging device according to any one of claims 1 to 5, which is arranged in a non-contact manner with respect to the image carrier and charges the image carrier. A developing device that develops a latent image formed by exposure on the image carrier charged by the charging device with a developer, a transfer unit that transfers an image developed by the developing device to a recording medium, and And an image forming apparatus having fixing means for fixing the image transferred onto the recording medium by the transferring means.

  According to the first aspect of the present invention, there is provided a charging device capable of suppressing the formation of a salt which is an ionic compound on the object to be charged, as compared with the case where this configuration is not provided. be able to.

  According to the invention according to claim 2, in addition to the effect of the present invention according to claim 1 or 2, in comparison with the case without this configuration, in response to environmental fluctuations and individual differences of charged bodies, The voltage to be applied can be controlled with high accuracy.

  According to the invention according to claim 3, in addition to the effect of the invention according to any one of claims 1 to 3, the first electrode and the second electrode are disposed on the side closer to the member to be charged. As compared with the case where the potential difference between one of the potentials and the charged potential of the charged object to be charged is not 20 V or more and 100 V or less, a charging device that can uniformly charge the object to be charged can be provided.

  According to the invention according to claim 4, in addition to the effect of the invention according to any one of claims 1 to 4, the first electrode and the second electrode are disposed on the side closer to the member to be charged. Compared with the case where either one is not arranged so that the distance to the charged body is 300 μm or more and 2 mm or less, ions of one polarity are charged on the charged body side while charging the charged body efficiently. It is possible to provide a charging device capable of suppressing the movement of the charging device.

  According to the invention which concerns on Claim 5, compared with the case where it does not have this structure, it can suppress that the salt which is an ionic compound is formed on a to-be-charged body, suppressing ozone generation amount. A charging device can be provided.

  According to the invention of claim 6, it is possible to provide an image forming cartridge capable of suppressing the formation of a salt which is an ionic compound on the image holding member as compared with the case where this configuration is not provided. Can do.

  According to the seventh aspect of the present invention, it is possible to provide an image forming apparatus capable of suppressing the formation of a salt which is an ionic compound on the image holding member as compared with the case where this configuration is not provided. it can.

1 is a side view showing an image forming apparatus to which an embodiment of the present invention is applied. 1 is a cross-sectional view of a charging device to which an embodiment of the present invention is applied and a diagram illustrating a control structure thereof. It is a figure which shows the lower surface of the charging device with which one Embodiment of this invention is applied. It is a schematic diagram of the movement of the ion of the plasma state which generate | occur | produced in the area | region restriction | limiting part. The measurement result of the volume low efficiency of the resistance layer by an Example is shown. The measurement result of the charging potential by an Example is shown. The measurement result of the discharge current by an Example is shown. The relative comparison result of the ozone amount by an Example is shown. The measurement result of the surface potential by an Example is shown. A current corresponding to the charging potential _{(V 0) (I 0)} , a measured result indicating a relation between the current (I ₁₎ of the differential current detection portion is calculated. The measurement result of the electric current which flows into an image carrier position is shown. The result of the charging stress test by an Example is shown.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an overall configuration of an image forming apparatus 10 as an embodiment of the present invention. The image forming apparatus 10 includes an image forming apparatus main body 12, an image forming unit 14 is mounted inside the image forming apparatus main body 12, and a discharge unit 16 is provided on the upper portion of the image forming apparatus main body 12.

  Under the image forming apparatus main body 12, for example, two-stage sheet feeders 20 and 20 are arranged. A plurality of paper feeding devices can be additionally arranged below the image forming apparatus main body 12.

  Each sheet feeding device 20 includes a sheet feeding device main body 22 and a sheet feeding cassette 24 in which a recording medium is stored. A pickup roll 26 is provided in the upper part near the rear end of the paper feed cassette 24, a retard roll 28 is disposed behind the pickup roll 26, and a feed roll is provided at a position facing the retard roll 28. 30 is arranged.

  The conveyance path 32 is a recording medium path from the feed roll 30 to the discharge port 34, and this conveyance path 32 is in the vicinity of the back side (the left side surface in FIG. 1) of the image forming apparatus main body 12 and feeds the bottom end. From the apparatus 20 to the fixing device 36, there is a portion formed substantially vertically. The fixing device 36 is provided with a heating roller 38 and a pressure roller 40. A transfer roller 42 and an image carrier 44 as a photosensitive member are disposed on the upstream side of the fixing device 36 in the conveyance path 32, and a registration roller 46 is provided on the upstream side of the transfer roller 42 and the image carrier 44. Is arranged. Further, a discharge roll 48 is disposed in the vicinity of the discharge port 34 of the conveyance path 32.

  Therefore, the recording medium fed from the paper feed cassette 24 of the paper feeding device 20 by the pickup roll 26 is turned off by the cooperation of the retard roll 28 and the feed roll 30. In this way, the recording medium at the top of the paper feed cassette 24 is transported to the transport path 32, temporarily stopped by the registration roll 46, and timed, and passes between the transfer roll 42 and the image carrier 44. Thus, the developer image is transferred to the recording medium. The transferred developer image is fixed on the recording medium by the fixing device 36, and is discharged from the discharge port 34 to the discharge unit 16 by the discharge roll 48.

  The image forming unit 14 is, for example, of an electrophotographic type, and the image holding body 44, a charging device 52 that uniformly charges the image holding body 44, and the image holding body charged by the charging device 52 are latently exposed to light. An optical writing device 54 for writing an image, a developing device 56 for visualizing a latent image of the image carrier 44 formed by the optical writing device 54 with a developer, and a developer image by the developing device 56 is transferred to a recording medium. A transfer roller 42, a cleaning device 58 made of, for example, a blade for cleaning the developer remaining on the image carrier 44, and a developer image on the recording medium transferred by the transfer roller 42 Is fixed to the recording medium.

  The process cartridge 60 is obtained by integrating the image carrier 44, the charging device 52, the developing device 56, and the cleaning device 58, and these can be exchanged as a unit. The process cartridge 60 can be taken out from the image forming apparatus main body 12 by opening the discharge unit 16.

Next, the charging device 52 will be described in detail.
2 shows a cross-sectional view of the charging device 52 and its control structure, and FIG. 3 shows the lower surface of the charging device 52 (the surface on the image carrier 44 side). FIG. 4 is a schematic diagram showing the movement of ions in the plasma state generated by the region limiting unit 82.

The charging device 52 has a configuration in which a conductive substrate 72, a resistance layer 74, an insulating layer 76, and a conductive layer 78 are arranged in this order from the side far from the opposing image carrier 44.
The conductive layer 78 is provided with an opening 80, and the insulating layer 76 is provided with a region limiting portion 82 that is a space continuous with the opening 80. The area limiting unit 82 is configured, for example, in a cylindrical shape in which the direction facing the image carrier 44 is open. As described above, the region limiting portion 82 is open in a direction continuous with the opening 80 and is a space limited in a direction perpendicular to the opening.
The resistance layer 74 may be configured as a two-layer structure including a high resistance layer 84 and a resistance adjustment layer 86.

The conductive substrate 72 (resistive layer 74) and the conductive layer 78 are connected to a first voltage application unit 90 and a second voltage application unit 92 that apply a voltage to each.
When a voltage of a certain level or higher is applied to the conductive base material 72 (resistance layer 74) and the conductive layer 78, the resistance layer 74 (and conductive base material 72) serves as the first electrode and the conductive layer 78 serves as the second electrode. 74, a discharge is generated in the region limiting portion 82 that is surrounded by the insulating layer 76 and the conductive layer 78 and is spatially limited. Since the region limiting unit 82 is spatially limited in the direction parallel to the image carrier 44, the region limiting unit 82 limits the discharge two-dimensionally.

  The discharge generated in the region limiting unit 82 of the charging device 52 (detailed parameters and the like will be described later) of the present embodiment is called glow discharge. The glow discharge is a continuous and uniform discharge phenomenon that occurs in a low pressure of about 1 / 100th of the atmospheric pressure.

Since the area limiting unit 82 is opened in a direction facing the image carrier 44, some of the charged particles (ions) generated by the discharge are electrically conductive layer 78 (second electrode), the image carrier 44, and the like. Is moved to the image carrier 44 side through the opening 80 of the conductive layer 78 (second electrode). That is, the image carrier 44 is charged by ions generated in the region limiting unit 82 drifting in the electric field to the image carrier 44. Drift means the movement of ions by an electric field.
The conductive layer 78 (second electrode) simultaneously functions to adjust the electric field intensity for ions to move to the image carrier 44 by the applied voltage and to adjust the charging potential of the image carrier 44.

If a potential difference in a constant direction is always applied between the conductive layer 78 (second electrode) and the image carrier 44, that is, if the direction of the electric field generated between them is constant, either positive or negative One of the polar ions moves to the image carrier 44 side, and the other polar ion remains on the charger 52 (conductive layer 78) side. In this case, since only ions of one polarity move to the image carrier 44 side, a salt which is an ionic compound is not easily formed on the image carrier 44.
Here, the salt (for example, ammonium salt) formed on the image carrier 44 causes image defects such as image flow. For this reason, making it difficult to form salt on the image carrier 44 prevents image defects.
Note that, as described above, regulating the direction of ion movement according to the polarity of ions may be referred to as an “ion filtering effect” hereinafter.

  FIG. 4 shows a case where the voltage of the conductive layer 78 (second electrode) is always set to be lower than the charged potential of the image carrier 44 (the absolute value of the negative voltage is increased). Yes. In this case, negative ions move to the image carrier 44 side, and positive ions remain on the conductive layer 78 (second electrode) side.

For example, when the positive ion is ammonium ion (NH ₄ ⁺ ) and the negative ion is nitrate ion (NO ₃ ⁻ ) or oxalate ion ((COO) ₂ ²⁻ ), in this embodiment, ammonium nitrate (NH ₄ An ammonium salt such as NO ₃ ) or ammonium oxalate ((NH ₄ ) ₂ (COO) ₂ ) is difficult to be formed in the vicinity of the image carrier 44.

Moreover, as shown in FIG. 2, between the electroconductive base material 72 and the 1st voltage application part 90, and between the conductive layer 78 (2nd electrode) and the 2nd voltage application part 92, respectively. A first current detection unit 94 and a second current detection unit 96 that detect a current flowing through the conductive base material 72 and the conductive layer 78 (second electrode) are provided. Specifically, the first current detection unit 94 detects a current flowing into the conductive base material 72 and the conductive layer 78 (second electrode), and the second current detection unit 96 includes the conductive base material 72 and A current flowing out from the conductive layer 78 (second electrode) is detected.
The voltage applied to the conductive substrate 72 and the conductive layer 78 (second electrode) is controlled by the voltage control unit 100 in the first voltage application unit 90 and the second voltage application unit 92. The first voltage application unit 90 and the second voltage application unit 92 are connected in series, and the second voltage application unit 92 is grounded. For this reason, the voltage applied to the conductive layer 78 (second electrode) by the second voltage application unit 92 indicates a potential difference from the ground.

The voltage control unit 100 includes a difference current calculation unit 102, a current comparison unit 104, and an applied voltage setting unit 106.
Here, the charge amount Q is shown as “Q = ∫Idt” obtained by integrating the current I with the time t. The charge amount Q is indicated as a product “Q = CV” of the capacitance C and the potential V. That is, the relationship “Q = ∫Idt = CV” is established. For this reason, by calculating the electrostatic capacitance C of the image carrier 44 in advance, the target potential (charge potential (V)) of the image carrier 44 moves to the image carrier 44 (image holding). It can be controlled by the current (I) that charges the body 44.

The difference current calculation unit 102 calculates the difference between the current values from the current detection results (current values) of the first current detection unit 94 and the second current detection unit 96. This difference in current value indicates the current value moved to the image carrier 44, that is, the current (I ₁ ) for charging the image carrier 44.

Based on the relationship described above, the current comparison unit 104 calculates the current (I ₀ ) corresponding to the target charging potential (V ₀ ) of the image carrier 44 and the current (I ₁ ) calculated by the difference current calculation unit 102. Compare.

The applied voltage setting unit 106 receives the comparison result of the current comparison unit 104, and the current (I ₁ ) for charging the image carrier 44 corresponds to the current (V ₀ ) corresponding to the target charging potential (V ₀ ) of the image carrier 44. I ₀ ) and the voltage (V ₂ ) applied to the conductive layer 78 (second electrode) is smaller than the target charging potential (V ₀ ) of the image carrier 44 (absolute negative voltage) The voltage (V ₁ ) applied by the first voltage application unit 90 and the voltage (V ₂ ) applied by the second voltage application unit 92 are set so that the value increases.

  In addition, the first voltage application unit 90 and the second voltage application unit 92 are connected in parallel (that is, any one of these voltage application units 90 and 92 is grounded), and the applied voltage setting unit 106 allows the conductive base material to be connected. The voltage applied to 72 and the conductive layer 78 (second electrode) may be controlled. In this case, the voltage applied to the conductive substrate 70 by the first voltage application unit 90 and the voltage applied to the conductive layer 78 (second electrode) by the second voltage application unit 92 are respectively ground and The potential difference is shown.

Therefore, in this embodiment, the voltage (V ₂ ) applied to the conductive layer 78 (second electrode) by the second voltage application unit 92 at all times is the target charging potential (V ₀ ) of the image carrier 44. Is set to be lower (the absolute value of the negative voltage is larger). Note that, when set in this way, the amount of NH ₄ ⁺ detected on the image holding member 44 was reduced to about 1/10 or less as compared with the case where it was not set in this way. .

The voltage (V ₂ ) applied to the conductive layer 78 (second electrode) has a potential difference of 20 V or more and 100 V or less (20 ≦ V ₀ −V ₂ ≦ 100) from the target charging potential (V ₀ ) of the image carrier 44. ).
If the potential difference between the voltage (V ₂ ) applied to the conductive layer 78 (second electrode) and the charging potential (V ₀ ) of the image carrier 44 is greater than 100 V, the variation increases and the practicality is lacking.
If the potential difference between the voltage (V ₂ ) applied to the conductive layer 78 (second electrode) and the charged potential (V ₀ ) of the image carrier 44 is smaller than 20 V, the ion filtering effect cannot be sufficiently obtained, and the image is retained. An image defect may occur due to the salt formed on the body 44.

  The voltage applied to both electrodes (the resistance layer 74 (first electrode) and the conductive layer 78 (second electrode)) by the first voltage application unit 90 and the second voltage application unit 92 is basically a DC voltage. is there. The voltage applied by the first voltage application unit 90 to the resistance layer 74 (first electrode) is such that the second voltage application unit 92 applies to the conductive layer 78 (second electrode) so that a discharge occurs between both electrodes. For example, the value is about 1.0 to 1.5 kV lower than the applied voltage (the absolute value of the negative voltage is increased).

  As the conductive substrate 72, for example, a metal such as stainless steel, aluminum, a copper alloy, an alloy thereof, or iron subjected to a surface treatment such as chromium or nickel is used.

As a material for forming the resistance layer 74, a material having a volume resistivity in the range of 1 × 10 ⁶ Ωcm to 1 × 10 ¹⁰ Ωcm is used.
If the volume resistivity of the resistance layer 74 is greater than 1 × 10 ¹⁰ Ωcm, discharge between the electrodes tends to be insufficient, and sporadic discharge occurs in the region limiting portion 82 that is a discharge space, resulting in a stable glow discharge. It may not reach.
If the volume resistivity of the resistance layer 74 is smaller than 1 × 10 ⁶ Ωcm, the function of limiting the discharge current due to the resistance (hereinafter sometimes referred to as a discharge current limiting effect) is not sufficiently obtained, and the region limiting portion In some cases, discharge concentrates locally in the surface of the resistance layer 74 facing 82, and the discharge current becomes unstable or excessive, causing rapid deterioration of the material or short-circuiting of the resistance layer 74.

When the volume resistivity of the resistance layer 74 is in the range of 1 × 10 ⁷ Ωcm to 1 × 10 ⁹ Ωcm, the volume resistivity is outside the range of 1 × 10 ⁷ Ωcm to 1 × 10 ⁹ Ωcm In comparison, more stable glow discharge is sustained in the region limiting unit 82.

Further, the resistance layer 74 is formed in a thickness range of 10 μm or more.
From the viewpoint of obtaining the effect of limiting the discharge current by the resistance of the resistance layer 74, by selecting a material having a high resistivity by reducing the thickness of the resistance layer 74 (volume resistivity × resistance layer thickness / unit area). The resistance value of the resistance layer 74 calculated by the above equation may be adjusted. However, if the film thickness is smaller than 10 μm, the withstand voltage against the applied voltage is lowered, and the frequency of the resistance layer 74 being short-circuited during discharge increases.
When the thickness of the resistance layer 74 is formed in a range of 100 μm or more, a sufficient withstand voltage can be obtained and the temporal stability against high voltage application is ensured as compared with the case where the thickness is outside the range of 100 μm or more. Is done.

The resistance layer 74 satisfies the above-described optimal volume resistivity range of 1 × 10 ⁷ Ωcm or more and 1 × 10 ⁹ Ωcm or less and the optimal film thickness range of 100 μm or more, while the resistance value in the film thickness direction (volume resistivity × When the resistance layer thickness / area is determined so that the area is an area of a circle having a diameter of 100 μm) is 1 × 10 ⁸ Ω or more and 1 × 10 ¹¹ Ω or less, the discharge current due to the resistance component The effect of limiting the film thickness and the stability over time due to the ensured film thickness are compatible.

When the resistance layer 74 has a two-layer structure and the discharge current limiting effect is adjusted, for example, the upper layer (high resistance layer 84) has a volume resistivity of 1 × 10 ⁹ Ωcm and a film thickness of 30 μm to obtain a sufficient discharge current limiting effect. Thus, the lower layer (resistance adjustment layer 86) may have a volume resistivity of 1 × 10 ⁷ Ωcm and a film thickness of 100 μm. Thus, the upper layer (high resistance layer 84) secures the effect of limiting the discharge current due to resistance, and the lower layer (resistance adjustment layer 86) has sufficient thickness from the conductive substrate 72 to improve pressure resistance. By doing so, both the effect of limiting the discharge current and the stability over time are achieved.

  As the resistance layer 74, a resin material or a rubber material in which conductive particles or semiconductive particles are dispersed is used. For example, as a resin material, polyester resin, acrylic resin, melamine resin, epoxy resin, urethane resin, silicon resin, urea resin, polyamide resin, polyimide resin, polycarbonate resin, styrene resin, ethylene resin, or a synthetic resin thereof. used. Rubber materials include ethylene-propylene rubber, polybutadiene, natural rubber, polyisobutylene, chloroprene rubber, silicone rubber, urethane rubber, epichlorohydrin rubber, fluorosilicone rubber, ethylene oxide rubber, foamed materials obtained by firing them, or a mixture of these. A mixed base material is used.

Examples of the conductive particles or semiconductive particles include carbon black, zinc, aluminum, copper, iron, nickel, chromium, titanium, and other metals, ZnO—Al ₂ O ₃ , SnO ₂ —Sb ₂ O ₃ , In ₂ O. _{3 -SnO 2, ZnO-TiO 2} , MgO-Al 2 O 3, FeO-TiO 2, TiO 2, SnO 2, Sb 2 O 3, in 2 O 3, ZnO, and metal oxides such as MgO, 4th An ionic compound such as a quaternary ammonium salt, or a mixture of these materials alone or in combination of two or more thereof is used.

  In addition, the resistance layer 74 is not limited to an organic material such as resin or rubber, but may be composed of semiconductive glass in which conductive particles are dispersed in glass, an aluminum porous anodic oxide film, or the like.

The structure of the region limiting portion 82 that limits the discharge space is determined by the diameter of the hole that penetrates the insulating layer 76 and the conductive layer 78 (second electrode) and the film thickness of the insulating layer 76.
The region limiting portion 82 is formed within a range of a hole diameter of 4 μm or more and 200 μm or less. Here, the hole diameter is the length (diameter) of the region limiting portion 82 in the direction perpendicular to the direction in which the conductive base material 72, the resistance layer 74, the insulating layer 76, and the conductive layer 78 are arranged.

When the hole diameter is larger than 200 μm, the electric field strength at the edge (edge) of the opening 80 of the conductive layer 78 (second electrode) and its peripheral portion is several times larger than the electric field strength at the center of the space in the region limiting portion 82. It is required by general electrostatic field analysis calculation to be larger than twice. If the electric field distribution in the region limiting portion 82 becomes non-uniform and the discharge concentrates on the periphery of the opening 80, the discharge becomes unstable and the amount of ozone generated increases or the resistance layer 74 is short-circuited. There is a case.
When the hole diameter is 200 μm or less, the equipotential surface is formed so as to be approximately parallel to the insulator, the electric field distribution in the region limiting portion 82 becomes uniform, and the glow discharge is stably performed over the entire region limiting portion 82. Is likely to occur.

  When the hole diameter is smaller than 4 μm, the amount of discharge generated per one area limiting portion 82 is reduced. For this reason, in order to more efficiently charge the image carrier 44 to a target potential, the hole diameter is preferably set to 4 μm or more.

  When the hole diameter of the area restricting portion 82 is in the range of 50 μm or more and 150 μm or less, uniform discharge is generated efficiently over the entire area restricting portion 82 compared to the case where the hole diameter is outside the range of 50 μm or more and 150 μm or less. To do.

The material for forming the insulating layer 76 is not limited to an organic material / inorganic material, but a solid material having a volume resistivity of 1 × 10 ¹² Ωcm or more is compared with a case where the volume resistivity is smaller than 1 × 10 ¹² Ωcm. Thus, the insulation between both electrodes (the resistance layer 74 and the conductive layer 78) when a high voltage is applied is excellent, and the shape of the region limiting portion 82 is stably held without being deformed over time.

  The insulating layer 76 is formed within a thickness range of 4 μm to 200 μm. In this embodiment, since the region limiting portion 82 is provided so as to penetrate the insulating layer 76, the film thickness of the insulating layer 76 is the distance between both electrodes (the resistance layer 74 and the conductive layer 78), that is, the discharge. Limit the distance. That is, the thickness of the insulating layer 76 is the length of the region limiting portion 82 in the direction in which the conductive base material 72, the resistance layer 74, the insulating layer 76, and the conductive layer 78 are arranged.

When the thickness of the insulating layer 76 is 200 μm or less and the discharge distance is shortened, local concentration of discharge and rapid increase in discharge current are suppressed, and glow discharge is easily maintained.
If the thickness of the insulating layer 76 is set to 4 μm or more and the discharge distance is sufficiently larger than the mean free path (about 0.1 μm) of electrons in the air, the number of ionizations in the region limiting portion 82 is secured and the discharge is sustained. It becomes easy.

  Further, according to Paschen's law that defines the discharge start voltage between parallel flat plates in air and atmospheric pressure, the discharge start voltage becomes the minimum value when the gap is about 4 μm, and the discharge start voltage when the gap becomes narrower than that. Rises. This suggests that discharge is less likely to occur when the thickness of the insulating layer 76 is less than 4 μm.

  When the film thickness of the insulating layer 76 is in the range of 50 μm or more and 150 μm or less, compared to the case where the film thickness is outside the range of 50 μm or more and 150 μm or less, the insulation between electrodes and uniform discharge with respect to high voltage application is achieved. It is kept more stable.

  As a material for forming the conductive layer 78 (second electrode), a material having a volume resistivity of 0.1 Ωcm or less is used.

The conductive layer 78 (second electrode) is formed in a thickness range of 1 μm to 50 μm.
If the thickness of the conductive layer 78 (second electrode) is larger than 50 μm, the extraction efficiency of charged particles from the opening 80 to the image carrier 44 is not sufficiently increased.
When the film thickness of the conductive layer 78 (second electrode) is smaller than 1 μm, the electrode is easily broken by energization during discharge.

  As the material of the conductive layer 78 (second electrode), a metal that is difficult to get dirty with the discharge gas is used. For example, metal materials such as tungsten, molybdenum, carbon, platinum, copper, and aluminum, and materials obtained by performing surface treatment such as gold plating on these metals are used.

The charging device 52 charges the image carrier 44 by the movement (drift) of charged particles due to an electric field, and therefore, between the conductive layer 78 (second electrode) disposed on the side close to the image carrier 44 and the image carrier 44. It is arranged at a position where a distance where no discharge occurs is maintained.
Specifically, the conductive layer 78 (second electrode) of the charging device 52 is disposed so as to be 300 μm or more and 2 mm or less at the closest distance (closest distance) to the image carrier 44.

If the closest distance between the conductive layer 78 (second electrode) and the image carrier 44 is larger than 2 mm, the charging efficiency is deteriorated.
When the closest distance between the conductive layer 78 (second electrode) and the image carrier 44 is smaller than 300 μm, discharge easily occurs between the conductive layer 78 (second electrode) and the image carrier 44, and the image carrier 44. Load. For example, “−2 kV” is applied to the resistance layer 74 (first electrode) and “−750 V” is applied to the conductive layer 78 (second electrode) with respect to the target charged potential “−700 V” of the image carrier 44. In this case, if the closest distance is less than 300 μm, according to the estimation of the discharge start voltage according to Paschen's law, the resistance layer 74 (first electrode) passes through the conductive layer 78 (second electrode) to the image carrier 44. Discharge may occur.
In the region where the closest distance between the conductive layer 78 (second electrode) and the image carrier 44 is smaller than 300 μm, the image carrier 44 is charged and the potential difference with the conductive layer 78 (second electrode) becomes small. In some cases, the ion filtering effect is not sufficiently obtained, and a salt formed in the vicinity of the image carrier 44 may cause an image defect.

Hereinafter, although an example is described, the present invention is not limited to this.
Stainless steel (SUS) is used as the conductive base material 72, and a material having a volume resistivity of 3 × 10 ⁸ Ωcm and a film thickness of 150 μm in which carbon is dispersed in a polyimide resin is used for the resistance layer 74.
FIG. 5 is a result of measuring the volume resistivity of the material used for the resistance layer 74 under the condition of applying a voltage of 250 V for 1 minute using a high resistivity meter Hi-Lester IP (MCP-HT260) and an HRS probe. Although there is an error of about 10% at the maximum, the volume resistivity is about 3 × 10 ⁸ Ωcm. These materials are formed on the conductive substrate 72.

  A glass epoxy material with a film thickness of 100 μm is used for the insulating layer 76, and a conductive layer 78 (second electrode) is laminated on the insulating layer 76 by gold plating a copper foil with a film thickness of 18 μm. The insulating layer 76 and the conductive layer 78 (second electrode) are formed with a cylindrical region limiting portion 82 having a hole diameter of 100 μm penetrating both.

  The insulating layer 76 and the conductive layer 78 are fixed on the resistance layer 74 so that the electrode is formed. The distance A (see FIG. 3) between the adjacent region limiting portions 82 in the axial direction of the image holding member 44 is that the charged particles moved by the electric field from the region limiting portion 82 onto the image holding member 44 cause streaky irregularities in the potential. The distance between the image carrier 44 and the conductive layer 78 (second electrode) is at least equal to or less than the distance so as to be uniform. The number of columns in the rotation direction is adjusted to the number of columns that can ensure the required charging capability according to the process speed.

  In the present embodiment, the region limiting portion 82 which is a discharge space is parallel to the axial direction of the image carrier 44, and is a distance of 300 μm, that is, a pitch of 400 μm (a length obtained by adding a space between the hole limiting and adjacent region limiting portions 82). (Distance B shown in FIG. 3)), a width necessary for charging is formed in a row. In order to improve the charging ability, five similar rows are arranged at intervals of 750 μm in the rotation direction of the image carrier 44.

  In the embodiment having the above-described configuration, the charged potential of the target image carrier 44 is set to “−720 V”, “−2.2 kV” is set to the conductive substrate 72, and the target is set to the conductive layer 78 (second electrode). Of the image carrier 44 when a DC voltage of “−800 V” lower than the charging potential of (−the absolute value of the negative voltage is large) is applied and the image carrier 44 of Φ30 mm is rotated at a process speed of 120 mm / sec. The charging potential (FIG. 6) and the discharge current (FIG. 7) flowing between the conductive substrate 72 and the conductive layer 78 (second electrode) are shown in the graph.

  In the period of 780 ms of the rotation period of the image carrier 44, the unevenness of the charged potential is stable at about Δ10 V or less, and the image carrier 44 is charged to the target charging potential “−720 V”. The discharge current is about 60 μA per 5 cm charge width in the axial direction of the image carrier 44. Since there are about 630 area limiting portions 82 ((charging width 5 cm / pitch 400 μm) × 5 rows) in the range of the charging width 5 cm, the discharge current per area limiting portion 82 is as small as about 0.1 μA. . At this time, the difference in voltage applied between the conductive substrate 72 and the conductive layer 78 (second electrode) is reduced, and the discharge current is set to be as small as possible within a range where the charging capability can be maintained. As the discharge current increases, the amount of ozone generation increases. Therefore, when the discharge current is reduced, the amount of ozone generation is reduced.

FIG. 8 shows the result of a relative comparison of the amount of ozone generated when the configuration of this example and each of the scorotron systems are used under the above charging conditions. Both of these are non-contact charging methods.
When the ozone detection amount after 10 minutes of continuous charging was almost saturated, the ozone generation amount of this example was at least about 1/10 or less of the scorotron. In the charging method using the scorotron, the ozone amount is usually controlled using means such as an ozone filter.
For reference, the figure shows the amount of ozone when a charging roll, which is a contact-type charging means that contacts the image carrier 44, is used.

FIG. 9 shows an average surface potential (charging potential) of the image carrier 44 when the voltage applied to the resistance layer 74 (first electrode) and the conductive layer 78 (second electrode) is changed in the above configuration. Shows fluctuations.
Conditions in which the difference in applied voltage between the resistance layer 74 (first electrode) and the conductive layer 78 (second electrode) is maintained at 1.4 kV (Example 1: first electrode = −2.2 kV, second electrode = −0. 8 kV, Example 2: first electrode = -1.9 kV, second electrode = -0.5 kV), that is, when a sufficient discharge is generated between both electrodes, the conductive layer 78 (second electrode) The applied voltage and the charging potential of the image carrier 44 correspond to each other. Specifically, when the conductive layer 78 (second electrode) increases, the charged potential of the image carrier 44 also increases accordingly.
For this reason, it is shown that the charged particles generated between the electrodes move due to the electric field between the conductive layer 78 (second electrode) and the image carrier 44, and the image carrier 44 is charged.

  In contrast, the condition in which the difference in applied voltage between the resistance layer 74 (first electrode) and the conductive layer 78 (second electrode) is maintained at 0.9 kV (Example 1: first electrode = −1.7 kV · second) Electrode = −0.8 kV, Example 2: first electrode = −1.4 kV, second electrode = −0.5 kV), that is, when almost no discharge is generated between both electrodes, the image carrier 44 is Charged particles necessary for charging are not generated, and the image carrier 44 is not charged.

  As described above, when charged particles sufficient to charge the image carrier 44 are generated by the discharge between the resistance layer 74 (first electrode) and the conductive layer 78 (second electrode), the conductive layer By controlling the voltage applied to the layer 78 (second electrode), the charging potential of the image carrier 44 is controlled.

FIG. 10 shows the charging potential (V ₀ ) and the corresponding current when the difference in applied voltage between the resistance layer 74 (first electrode) and the conductive layer 78 (second electrode) is kept at 1.4 kV in FIG. The relationship between (I ₀ ) and the current (I ₁ ) calculated by the differential current detector 102 is shown.
The current (I ₀ ) is a theoretical value when charging to the charging potential (V ₀ ), and is calculated from the following charging conditions.
・ Process speed 120mm / sec,
-Photoconductor film thickness 29μm,
-Photoconductor relative dielectric constant 3.2,
・ Charge width 5cm
The result of FIG. 10 shows that the second electrode and the second electrode are set so that the current (I ₁ ) matches the previously calculated current (I ₀ ) and the charging potential (V ₀ ) is lower than the voltage of the second electrode. This is a result when the applied voltage of the second electrode is controlled while maintaining the voltage difference of the first electrode at 1.4 kV. The plots of the current (I ₀ ) and the current (I ₁ ) are almost the same, and the control as intended can be performed.

FIG. 11 shows a measurement electrode when a measurement electrode having a diameter of 1 mm is arranged at the position of the image carrier 44 instead of the image carrier 44 and a potential difference is applied between the charging device 52 and the measurement electrode. The result of measuring the flowing current is shown.
As shown in FIG. 11, the detection current of the measurement electrode is proportional to the distance between the charging device 52 and the measurement electrode (distance between the electrodes) and the potential difference between the charging device 52 and the measurement electrode. For this reason, it is shown that the charged particles generated in the charging device 52 drift due to the potential difference between the charging device 52 and the measurement electrode and are observed on the measurement electrode.
Accordingly, it can be said that no discharge is generated between the image carrier 44 (measurement electrode) and the charging device 52, that is, the image carrier 44 is an electrode and no discharge is generated.

FIG. 12 shows the result of the charging stress test.
For reference, a charging stress test is performed by repeating only charging and discharging of the image carrier using the configuration of the present embodiment and the charging roll method, respectively, and each image carrier subjected to the charging stress test is used for the temperature in the image forming apparatus. The image flow occurrence rate of a sample printed at 28 ° C. and a humidity of 80% is shown. As shown in FIG. 11, the result that the image carrier occurrence rate of the image carrier subjected to the charging test in the configuration of the present embodiment is significantly reduced as compared with the charging roll method.
The conditions for the charging stress test are as follows.
・ Charging potential -700V,
・ Process speed 120mm / sec,
-Voltage application period 500 rotations In addition, a voltage obtained by superimposing a DC component on the AC component shown below was applied to the charging roll.
・ Frequency 950Hz,
DC voltage = -720V,
AC voltage (peak-to-peak voltage) = 1850V: 1.25 times the AC voltage value at which the charging potential is saturated

  The image carrier used in the charging stress test is an organic photoreceptor in which an undercoat layer, a photosensitive layer, and a charge transport layer are laminated in this order on a grounded cylindrical aluminum. The undercoat layer has a thickness of 15 μm and functions to maintain charging characteristics, the photosensitive layer has a thickness of 1 μm or less and has a charge generation function for light having a wavelength of about 800 nm, and the charge transport layer has a thickness of 29 μm and charges generated in the photosensitive layer (holes). ) Are transported in the direction of the photoreceptor surface.

  In addition, the experimental device for the charging stress test this time is composed of only the function of rotating the image carrier, the charging function (this embodiment or charging roll), and the charge eliminating function (charge eliminating lamp), and does not include a cleaning blade. It is configured. An image carrier that has been subjected to a charging stress test is used, and an image forming apparatus is used to confirm the image flow rate, thereby accelerating and confirming the influence of the charging stress exerted on the image carrier by the charger.

In the above embodiment, the voltage (V ₂ ) applied to the conductive layer 78 (second electrode) by the second voltage application unit 92 is always lower than the charging potential (V ₀ ) of the image carrier 44. Although the configuration in which the negative voltage is set to be large has been described, the voltage (V ₂ ) that is always applied to the conductive layer 78 (second electrode) is not limited to this, and the charged potential. (V ₀₎ is higher than may be set (minus the absolute value of the voltage is small.) as.
In this way, by always setting the electric field to be in a certain direction, only either positive or negative ions can move to the image carrier 44 side.

The example in which the charging device of the present invention is applied to the image forming apparatus has been described above. However, the application of the charging device of the present invention is not limited to this, and can be applied to the uses exemplified below.
・ In the manufacturing process of electronic devices, etc., neutralization by applying a charge opposite to the charged charge to neutralize the device so that electrostatic breakdown due to charging of the device does not occur. ・ Surface modification treatment of solid materials (for example, hydrophilization) Treatment and hydrophobic treatment)
・ Sterilization and sterilization in food processing and medical fields

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming apparatus main body 14 Image forming means 20 Paper feed apparatus 32 Conveying path 36 Fixing device 44 Image holding body 52 Charging apparatus 56 Developing apparatus 72 Conductive base material 74 Resistive layer 76 Insulating layer 78 Conductive layer 80 Opening 82 region limiting unit 84 high resistance layer 86 resistance adjustment layer 90 first voltage application unit 92 second voltage application unit 94 first current detection unit 96 second current detection unit 100 voltage control unit 102 differential current calculation unit 104 Current comparison unit 106 Applied voltage setting unit

Claims (7)

A first electrode;
A second electrode disposed closer to the member to be charged than the first electrode;
A control unit that controls a voltage applied to the second electrode so that the potential is lower than a charging potential of the object to be charged;
A charging device. Current detection means for detecting a current flowing through the first electrode and the second electrode;
Further comprising
The charging device according to claim 1, wherein the control unit controls a voltage applied to the second electrode based on a detection result of the detection unit.   3. The charging according to claim 1, wherein the control unit controls a voltage applied to the second electrode so that a potential difference between the second electrode and a charged potential of the charged body is 20 V or more and 100 V or less. apparatus.   4. The charging device according to claim 1, wherein the second electrode is disposed such that a distance from the object to be charged is 300 μm or more and 2 mm or less. 5. An insulator between the first electrode and the second electrode;
Further comprising
The second electrode has an opening that opens to a first direction in which the first electrode, the insulator, and the second electrode are arranged,
The insulator includes a region limiting portion that is a space continuous with the opening and open in a direction continuous with the opening and limited in a second direction perpendicular to the first direction. The charging device according to any one of 1 to 4. An image carrier as a member to be charged;
The charging device according to any one of claims 1 to 5, wherein the charging device is disposed in a non-contact manner with respect to the image carrier and charges the image carrier.
A developing device for developing a latent image formed by exposure on the image carrier charged by the charging device with a developer;
A cartridge for an image forming apparatus. An image carrier as a member to be charged;
The charging device according to any one of claims 1 to 5, wherein the charging device is disposed in a non-contact manner with respect to the image carrier and charges the image carrier.
A developing device for developing a latent image formed by exposure on the image carrier charged by the charging device with a developer;
Transfer means for transferring an image developed by the developing device to a recording medium;
Fixing means for fixing the image transferred on the recording medium by the transfer means to the recording medium;
An image forming apparatus.

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