JP6044081B2 - Charging device and image forming apparatus - Google Patents

Description

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

  The charging device of Patent Document 1 has a configuration in which a conductive base material, a resistance layer, an insulating layer, and a conductive layer are sequentially arranged from the side far from the opposing image carrier. An opening is formed in the conductive layer, and a region limiting portion surrounding the periphery of the opening is provided in the insulating layer. A part of the charged particles generated by the discharge in the region limiting unit moves through the conductive layer in the direction of the image carrier due to a potential difference between the conductive layer and the image carrier. As a result, the image carrier is charged.

JP 2011-69879 A

  An object of the present invention is to obtain a charging device and an image forming apparatus capable of suppressing excessive discharge at an end portion in the arrangement direction of through holes in a configuration having a plurality of through holes in which discharge is performed.

  According to a first aspect of the present invention, there is provided a charging device in which a first electrode and the first electrode are disposed to face each other via an insulator, and a plurality of through holes are formed with the insulator toward the first electrode. A discharge portion where discharge is performed between the first electrode and the hole wall of the through hole of the second electrode, and a contact side opposite to the insulator side of the first electrode The voltage can be applied between the first electrode and the through hole of the second electrode by applying a voltage to the voltage application unit to which a voltage is applied, and the voltage application unit and the second electrode. A voltage applying means for generating a potential difference between the second electrode and the member to be charged, so as to cause a potential difference between the second electrode and the member to be charged. Among the plurality of through-holes formed, end through-holes formed at end portions in the arrangement direction of the plurality of through-holes Discharge, having a discharge limiting means for hard to occur in comparison with the discharge in the inner through-hole formed inside the end portion through-hole in 該配 column that.

  The charging device according to claim 2 of the present invention is characterized in that the discharge limiting means has an electric resistance from a contact surface of the first electrode with the voltage application portion to a discharge surface exposed in the through hole, as the end portion. The through hole is configured to be larger than the inner through hole.

  The charging device according to claim 3 of the present invention is configured such that the discharge limiting unit forms the end through hole of the second electrode in a region outside the end of the voltage application unit. Yes.

  In the charging device according to a fourth aspect of the present invention, the discharge limiting means is configured such that the thickness of the end portion of the first electrode in the arrangement direction is larger than the thickness of the central portion.

  In the charging device according to claim 5 of the present invention, the discharge limiting means is configured such that the electrical resistivity of the region facing the end through hole of the first electrode is greater than the electrical resistivity of the region facing the inner through hole. Is also made higher.

  The charging device according to claim 6 of the present invention is such that the discharge limiting means makes the discharge distance between the first electrode and the second electrode longer than the inner through hole in the end through hole. It is configured.

  The charging device according to claim 7 of the present invention is configured such that the discharge limiting means makes the diameter of the end through hole larger than the diameter of the inner through hole.

  The charging device according to claim 8 of the present invention is configured such that the discharge limiting means makes the diameter of the end through hole of the second electrode larger than the diameter of the end through hole of the insulator. ing.

  The charging device according to claim 9 of the present invention is configured such that the discharge limiting means makes the thickness of the end portion of the insulator in the arrangement direction thicker than the thickness of the central portion.

  An image forming apparatus according to a tenth aspect of the present invention is any one of the first to ninth aspects, wherein the image holding body as the charged body provided rotatably and the outer peripheral surface of the image holding body are charged. 2. The charging device according to claim 1, an exposure unit that exposes an outer peripheral surface of the charged image carrier to form a latent image, and a developing unit that develops the latent image with a developer to form a developer image. And transfer means for transferring the developer image developed by the developing means to a recording medium.

  According to the first aspect of the present invention, in the configuration having a plurality of through-holes in which discharge is performed, excessive discharge at the end portion in the arrangement direction of the through-holes can be suppressed as compared with a configuration having no discharge limiting means. .

  According to the second aspect of the present invention, the charging device can be easily manufactured as compared with the structure in which the structure from the first electrode to the second electrode is changed to suppress excessive discharge at the end.

  The invention according to claim 3 makes it easier to manufacture the charging device as compared with the structure in which the structure from the first electrode to the second electrode is changed to suppress excessive discharge at the end.

  According to the invention of claim 4, the charging device can be easily manufactured as compared with the structure in which the structure from the first electrode to the second electrode is changed to suppress excessive discharge at the end.

  According to the fifth aspect of the present invention, the charging device can be easily manufactured as compared with the structure in which the structure from the first electrode to the second electrode is changed to suppress excessive discharge at the end.

  According to the sixth aspect of the present invention, the discharge state can be easily adjusted as compared with the case where the structure of the voltage application portion or the first electrode is changed to suppress excessive discharge at the end portion.

  According to the seventh aspect of the present invention, the charging device can be easily manufactured as compared with the configuration in which the diameter of the through hole is not changed.

  The invention according to claim 8 facilitates the manufacture of the charging device as compared with the configuration in which the diameter of the through hole is not changed.

  According to the ninth aspect of the present invention, the discharge state can be easily adjusted as compared with the case where the structure of the voltage application portion or the first electrode is changed to suppress excessive discharge at the end portion.

  According to the tenth aspect of the present invention, image unevenness, which is a difference in image density between the central portion and the end portion of the image forming region, can be reduced as compared with the configuration in which the discharge limiting unit is not provided. Furthermore, electrode life can be extended by suppressing excessive discharge.

1 is an overall configuration diagram of an image forming apparatus according to a first embodiment of the present invention. 1A is an overall configuration diagram of a charging device according to a first embodiment of the present invention. FIG. (B) It is explanatory drawing which shows the internal structure of the charging device which concerns on 1st Embodiment of this invention. (A) It is the bottom view which looked at the charging device which concerns on 1st Embodiment of this invention from the photoreceptor side. (B) It is explanatory drawing which shows the bottom face and longitudinal cross-section (AA ') of the charging device which concerns on 1st Embodiment of this invention. FIG. 3 is a schematic diagram illustrating a state where the outer peripheral surface of the photoreceptor is charged by the charging device according to the first embodiment of the present invention. (A) It is a schematic diagram which shows the magnitude | size of the electric current which flows into a resistance layer at the time of discharge in the charging device which concerns on 1st Embodiment of this invention. (B) It is a schematic diagram which shows the magnitude | size of the electric current which flows into a resistance layer at the time of discharge in the charging device of a comparative example. It is explanatory drawing which shows the bottom face and longitudinal cross-section (BB ') of the charging device which concerns on 2nd Embodiment of this invention. (A) It is a schematic diagram which shows the state in which the outer peripheral surface of a photoreceptor is charged by the charging device which concerns on 2nd Embodiment of this invention. (B) It is a schematic diagram which shows the magnitude | size of the electric current which flows into a resistance layer at the time of discharge in the charging device which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the bottom face and longitudinal cross-section (CC ') of the charging device which concerns on 3rd Embodiment of this invention. (A) It is a schematic diagram which shows the state in which the outer peripheral surface of a photoreceptor is charged by the charging device which concerns on 3rd Embodiment of this invention. (B) It is a schematic diagram which shows the magnitude | size of the electric current which flows into a 1st resistance layer and a 2nd resistance layer at the time of discharge in the charging device which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows the bottom face and longitudinal cross-section (DD ') of the charging device which concerns on 4th Embodiment of this invention. (A) It is a schematic diagram which shows the state in which the outer peripheral surface of a photoreceptor is charged by the charging device which concerns on 4th Embodiment of this invention. (B) It is a schematic diagram which shows the magnitude | size of the electric current which flows into a resistance layer at the time of discharge in the charging device which concerns on 4th Embodiment of this invention. It is explanatory drawing which shows the bottom face and longitudinal cross-section (EE ') of the charging device which concerns on 5th Embodiment of this invention. (A) It is a schematic diagram which shows the state in which the outer peripheral surface of a photoreceptor is charged by the charging device which concerns on 5th Embodiment of this invention. (B) It is a schematic diagram which shows the magnitude | size of the electric current which flows into a resistance layer at the time of discharge in the charging device which concerns on 5th Embodiment of this invention. It is explanatory drawing which shows the bottom face and longitudinal cross-section (FF ') of the charging device which concerns on 6th Embodiment of this invention. (A) It is a schematic diagram which shows the state in which the outer peripheral surface of a photoreceptor is charged by the charging device which concerns on 6th Embodiment of this invention. (B) It is a schematic diagram which shows the magnitude | size of the electric current which flows into a resistance layer at the time of discharge in the charging device which concerns on 6th Embodiment of this invention. It is explanatory drawing which shows the longitudinal cross-section of the charging device as another modification of this invention.

(First embodiment)
An example of a charging device and an image forming apparatus according to the first embodiment of the present invention will be described.

(overall structure)
FIG. 1 shows an image forming apparatus 10 as an example of the first embodiment. In the following description, the vertical direction of the image forming apparatus 10 is referred to as the V direction, the horizontal direction is referred to as the H direction, and the depth direction perpendicular to the V direction and the H direction is referred to as the Z direction. In addition, left and right indicate left and right when the image forming apparatus 10 is viewed from the front.

  The image forming apparatus 10 has a housing 12 as an apparatus main body. Then, the image forming apparatus 10 includes the sheet storage unit 14 that stores the recording sheet P and the recording sheet P supplied from the sheet storage unit 14 from the lower side to the upper side in the V direction inside the housing 12. An image forming unit 20 that forms a toner image T as an example of a developer image, a fixing unit 40 that fixes the toner image T to the recording paper P, and a recording paper P on which the toner image T is fixed 12B, and a control unit 30 that controls the operation of each unit of the image forming apparatus 10. Further, on the left side in the housing 12, a conveyance path 16 through which the recording sheet P is conveyed from the sheet storage unit 14 to the discharge unit 50 in the V direction is provided. A pair of and a plurality of transport rolls are arranged on the transport path 16, but the illustration is omitted.

  The paper storage unit 14 is provided with a first storage unit 14A and a second storage unit 14B that store recording papers P of different sizes side by side in the V direction. The first storage portion 14 </ b> A and the second storage portion 14 </ b> B are provided with a delivery roll 15 that feeds the stored recording paper P to the transport path 16. A pair of transport rolls 17 that transport the recording paper P one by one are provided downstream of the feed roll 15 in the transport path 16. Further, the recording paper P is stopped at one end downstream of the transport roll 17 in the transport direction of the recording paper P in the transport path 16 and at a timing determined between a photosensitive member 22 and a transfer roll 32 described later. A positioning roll 18 for feeding the recording paper P is provided.

  The image forming unit 20 includes a photosensitive member 22 as an example of a charged member and an image holding member that are rotatably provided, a charging device 100 that charges an outer peripheral surface of the photosensitive member 22, and a charged photosensitive member 22. The latent image is developed with an exposure unit 24 as an example of an exposure unit that exposes the outer peripheral surface of the photosensitive member 22 to form a latent image (not shown) and the stored developer G, and the developer image is formed on the outer peripheral surface of the photoreceptor 22. A developing unit 26 as an example of a developing unit that forms the image, a transfer roll 32 as an example of a transfer unit that transfers a developer image developed by the developing unit 26 to a recording paper P as an example of a recording medium, and after transfer And a cleaning roll 34 for cleaning the outer peripheral surface of the photosensitive member 22.

  The photoconductor 22 is a cylindrical body that is rotatably provided in the + R direction (clockwise direction in the drawing) with the Z direction as an axial direction. The photoconductor 22 is positioned + R from the charging device 100 at a position facing the outer peripheral surface of the photoconductor 22. An exposure unit 24, a developing unit 26, a transfer roll 32, and a cleaning roll 34 are arranged in order in the direction. The photoconductor 22 is grounded.

  The exposure unit 24 includes a semiconductor laser (not shown), an f-θ lens, a polygon mirror, an imaging lens, and a plurality of mirrors. Then, the exposure unit 24 deflects and scans the laser beam BM emitted from the semiconductor laser based on the image signal with a polygon mirror, and irradiates (exposes) the outer peripheral surface of the charged photoreceptor 22 to form an electrostatic latent image. It comes to form. Note that the exposure unit 24 is not limited to the method of scanning the laser beam BM with a polygon mirror, but may be configured of an LED (Light Emitting Diode) method.

  The developing unit 26 includes a box-shaped unit main body 26A having an opening formed in a part thereof, and a developing roll 26B provided in the opening of the unit main body 26A so as to be rotatable about the Z direction as an axial direction. Yes. The developing roll 26B has a configuration in which a plurality of magnetic poles that generate magnetic force are arranged in a rotating cylindrical sleeve. A developer G is accommodated in the unit main body 26A. As the developer G, for example, a two-component developer containing toner and a magnetic carrier (not shown) is used.

  The transfer roll 32 is applied with a voltage having a polarity opposite to the polarity of the toner of the developer G from a voltage application unit (not shown). The toner image T on the photoconductor 22 is transferred onto the recording paper P conveyed through the conveyance path 16 by the potential difference between the grounded photoconductor 22 and the transfer roll 32.

  As an example, the cleaning roll 34 is configured by a brush roll that comes into contact with the outer peripheral surface of the photoreceptor 22. The cleaning roll 34 scrapes off toner remaining on the outer peripheral surface of the photosensitive member 22 and collects it in a main body (not shown).

  On the other hand, the fixing unit 40 has a heat source (for example, a halogen lamp) provided therein and heats the toner on the recording paper P, and a pressure roll 44 that presses the recording paper P toward the fixing roll 42. have. In the fixing unit 40, when the recording paper P passes through the contact portion between the fixing roll 42 and the pressure roll 44, the toner is melted and solidified, and the toner image T is fixed on the recording paper P.

  The discharge unit 50 includes a pair of discharge rollers 52 that are rotatably provided, and the recording paper P on which the toner image T has been fixed passes through the opening 12A formed in the case 12 and the case. 12 is discharged to the upper surface 12B.

(Main part configuration)
Next, the charging device 100 according to the first embodiment will be described.

  As illustrated in FIG. 2A, the charging device 100 includes a counter electrode unit 110 that faces the outer peripheral surface of the photoconductor 22, and a voltage application unit 112 as an example of a voltage application unit that applies a voltage to the counter electrode unit 110. And a discharge limiting unit 130 as an example of a discharge limiting unit that limits partial discharge of the counter electrode unit 110.

  The counter electrode unit 110 includes a power feeding layer 102 as an example of a voltage application unit and a resistance layer 104 as an example of a first electrode in the radial direction of the photoconductor 22 and in order from the far side to the near side with respect to the photoconductor 22. The insulating layer 106 as an example of an insulator and the conductive layer 108 as an example of a second electrode are formed in a laminated plate shape. The resistance layer 104, the insulating layer 106, and the conductive layer 108 constitute a discharge unit 120. The voltage application unit 112 is electrically connected to the power feeding layer 102 and the conductive layer 108, and applies a voltage to the power feeding layer 102 and the conductive layer 108.

  In the following description, the stacking direction (the radial direction of the photoconductor 22) from the conductive layer 108 toward the resistance layer 104 (power feeding layer 102) is described as the Z direction, and the rotation axis direction of the photoconductor 22 is described as the X direction. A direction orthogonal to the X direction and the Z direction is referred to as a Y direction.

  The power supply layer 102 is in contact with the side of the resistance layer 104 opposite to the insulating layer 106, and a voltage is applied by the voltage application unit 112. The power supply layer 102 is made of, for example, stainless steel, aluminum, a copper alloy, an alloy thereof, or a metal such as iron that has been subjected to a surface treatment such as chromium or nickel. In the present embodiment, as an example, the power feeding layer 102 is made of stainless steel.

  As the resistance layer 104, a resin material or a rubber material in which conductive particles or semiconductive particles are dispersed is used. For example, resin materials include polyester resin, acrylic resin, melamine resin, epoxy resin, urethane resin, silicon resin, urea resin, polyamide resin, polyimide resin, polycarbonate resin, styrene resin, ethylene resin, and synthetic resins thereof. used. Examples of rubber materials include ethylene-propylene rubber, polybutadiene, natural rubber, polyisobutylene, chloroprene rubber, silicon rubber, urethane rubber, epichlorohydrin rubber, fluorosilicone rubber, ethylene oxide rubber, foamed materials obtained by foaming these, A mixed mixed substrate 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 These materials such as an ionic compound such as a quaternary ammonium salt may be used alone or in combination of two or more.

Here, as a material for forming the resistance layer 104, a material having a volume resistivity in the range of 1 × 10 ⁶ Ωcm to 1 × 10 ¹⁰ Ωcm is used. This is because if the volume resistivity of the resistance layer 104 is greater than 1 × 10 ¹⁰ Ωcm, the discharge between the electrodes tends to be insufficient, and sporadic discharge occurs in the through-holes 114 to be described later which are discharge spaces. This is because stable discharge may not be achieved. If the volume resistivity of the resistance layer 104 is smaller than 1 × 10 ⁶ Ωcm, the function of limiting the discharge current by resistance (hereinafter referred to as a discharge current limiting effect) cannot be obtained sufficiently, and the through hole 114 Discharge concentrates locally on the discharge surface 104B (see FIG. 2B) of the resistance layer 104 facing (exposed to the through hole 114), and the discharge current becomes unstable or excessive. This is because rapid deterioration or a short circuit of the resistance layer 104 may be caused.

Further, when the volume resistivity of the resistance layer 104 is in the range of 1 × 10 ⁷ Ωcm to 1 × 10 ⁹ Ωcm, the volume resistivity is out of the range of 1 × 10 ⁷ Ωcm to 1 × 10 ⁹ Ωcm. Compared to the case, more stable discharge continues in the through hole 114.

  Furthermore, the resistance layer 104 is formed with a film thickness of 10 μm or more. Only from the viewpoint of obtaining the effect of limiting the discharge current by the resistance of the resistance layer 104, by selecting a material having a low film thickness and a high resistivity, it is calculated by (volume low efficiency × resistance layer thickness / unit area). The resistance value of the resistance layer 104 may be adjusted. However, if the film thickness is smaller than 10 μm, the withstand voltage against voltage application is reduced, and the frequency of the resistance layer 104 short-circuiting during discharge increases. As an example, when the film thickness is formed in a range of 100 μm or more, a sufficient withstand voltage is obtained, and the temporal stability against high voltage application is ensured.

In addition, the resistance layer 104 satisfies the above-described optimal range of volume resistivity (electrical resistivity) of 1 × 10 ⁷ Ωcm or more and 1 × 10 ⁹ Ωcm or less, and the optimal range of film thickness of 100 μm or more, while in the film thickness direction. If the resistance value is adjusted to be in the range of 1 × 10 ⁸ Ω to 1 × 10 ¹¹ Ω, both the effect of limiting the discharge current due to the resistance component and the stability over time due to securing the film thickness are compatible. The resistance value in the film thickness direction is a value obtained by volume resistivity × thickness / area of the resistance layer 104, and the area is an area of a circle having a diameter of 100 μm.

In this embodiment, as an example, the resistance layer 104 is made of 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.

In the case where the insulating layer 106 is a solid material having a volume resistivity of 1 × 10 ¹² Ωcm or higher, the resistance layer 104 and the conductive layer 108 when a high voltage is applied are compared with the case where the resistivity is smaller than 1 × 10 ¹² Ωcm. The through hole 114 is stably held without being deformed over time.

  The insulating layer 106 is formed within a range of 4 μm to 200 μm in thickness. In this embodiment, since the through hole 114 penetrates the insulating layer 106, the film thickness of the insulating layer 106 corresponds to the distance between the resistance layer 104 and the conductive layer 108, that is, the discharge distance. Here, when the thickness of the insulating layer 106 is 200 μm or less, the discharge is easily maintained. When the insulating layer 106 has a film thickness of 4 μm or more and a discharge distance sufficiently larger than the mean free path of electrons in the air (about 0.1 μm), the number of ionizations in the through hole 114 is ensured, and discharge is generated. It becomes easier to sustain.

  Furthermore, according to Paschen's law which defines the discharge start voltage between parallel flat plates in air and at 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 106 is less than 4 μm.

  In this embodiment, as an example, the insulating layer 106 is made of a glass epoxy material having a thickness of 100 μm.

The conductive layer 108 is disposed so as to face the resistance layer 104 and the insulating layer 106 and has a volume resistivity of 1 × 10 ⁻¹ Ωcm or less. In addition, the conductive layer 108 is formed within a thickness range of 1 μm to 50 μm. This is because when the film thickness is larger than 50 μm, the extraction efficiency of charged particles E (see FIG. 2B) from the through-hole 114 to the photosensitive member 22 does not sufficiently increase, and when the film thickness is smaller than 1 μm. This is because the electrode is easily deteriorated by energization during discharge. Note that as a material of the conductive layer 108, a metal that is hardly contaminated with a 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.

  In the present embodiment, as an example, the conductive layer 108 is made of copper having a thickness of 18 μm formed by plating.

  As shown in FIG. 2B, the insulating layer 106 and the conductive layer 108 have through-holes 114 penetrating in the Z direction and having a circular cross section when viewed in the Z direction, spaced apart in the X direction and the Y direction. A plurality are formed. In FIG. 2A, as an example, 20 through holes 114 in the X direction and 4 through holes 114 are shown, but the number of through holes 114 is not limited to this.

  As shown in FIG. 2B, a portion exposed in the through hole 114 of the resistance layer 104 is a discharge surface 104B where discharge is performed. The through-hole 114 has a hole wall 106A that is an inner wall of the insulating layer 106 and a hole wall 108A that is an inner wall of the conductive layer 108. In the discharge unit 120, discharge is performed between the discharge surface 104 </ b> B of the resistance layer 104 and the hole wall 108 </ b> A of the through hole 114 of the conductive layer 108.

  The through hole 114 is formed with a hole diameter in the range of 4 μm to 200 μm. If the hole diameter is larger than 200 μm, the electric field strength at the opening of the conductive layer 108 (periphery of the through-hole 114) and its periphery may be several times greater than the electric field strength at the center of the hole. It is obtained by electric field analysis calculation. In this case, the electric field distribution in the through-hole 114 becomes non-uniform and the discharge concentrates on the peripheral edge of the through-hole 114. As a result, the discharge becomes unstable, the amount of ozone generation increases, or the resistance layer 104 is short-circuited. Sometimes. Moreover, when the hole diameter of the through-hole 114 is smaller than 4 micrometers, the discharge generation amount per one through-hole 114 becomes small. For this reason, in order to more efficiently charge the photosensitive member 22 to a target potential, the hole diameter is preferably set to 4 μm or more.

  When the hole diameter of the through hole 114 is 200 μm or less, the equipotential surface is formed so as to be approximately parallel to the insulating layer 106, so that the electric field distribution in the through hole 114 becomes uniform and covers the entire area of the through hole 114. And stable discharge is likely to occur.

  On the other hand, the voltage application unit 112 is connected to the power supply layer 102 and the conductive layer 108, and includes a first power source 112 </ b> A connected between the power supply layer 102 and the conductive layer 108, and the conductive layer 108 and the photosensitive member 22. And a second power source 112B connected therebetween. Specifically, the voltage application unit 112 applies a voltage from the first power source 112A and the second power source 112B to the power feeding layer 102 and the conductive layer 108, and the resistance layer 104 and the hole wall 108A in the through hole 114 of the conductive layer 108 A potential difference ΔV1 is generated between the conductive layer 108 and the photoconductor 22 so that the potential difference ΔV1 that can be discharged is generated and the charged particles E generated by the discharge are moved to the photoconductor 22. Yes.

  Here, since the through hole 114 is opened toward the outer peripheral surface of the photoconductor 22, a part of the charged particles E generated by the discharge is caused by a potential difference ΔV 2 between the conductive layer 108 and the photoconductor 22. Then, it passes through the conductive layer 108 and moves to the outer peripheral surface of the photoreceptor 22. As described above, the charging device 100 is configured to charge the photosensitive member 22 by the charged particles E being moved by the electric field (electric field drift). Note that the conductive layer 108 has a function of adjusting the electric field intensity for the charged particles E to move to the photoconductor 22 by the applied voltage, and adjusting the charging potential of the photoconductor 22.

  In the charging device 100, the voltage applied to the resistance layer 104 and the conductive layer 108 is basically a DC voltage. The electric potential of the conductive layer 108 on the side close to the photoconductor 22 is set to be approximately the same as the preset charging potential of the photoconductor 22. The voltage applied to the resistance layer 104 is, for example, a voltage increased by about 1.2 kV with respect to the voltage applied to the conductive layer 108 so that a discharge occurs between the resistance layer 104 and the conductive layer 108. It has become.

  Further, since the charging device 100 is configured to charge the photoconductor 22 by the electric field drift of the charged particles E, the gap between the conductive layer 108 and the photoconductor 22 is generated between the conductive layer 108 and the photoconductor 22. It is not a distance. As an example, the distance between the conductive layer 108 and the photosensitive member 22 is set in the range of 300 μm to 2 mm, and is 500 μm in this embodiment.

  Next, the discharge limiting unit 130 will be described.

  3A and 3B, the discharge limiting portion 130 is a discharge in the end through hole 114B formed at the end of the plurality of through holes 114 in the hole arrangement direction (X direction or Y direction). Is an example of a structure that makes it less likely to occur compared to the discharge in the inner through hole 114A formed inside the end through hole 114B in the arrangement direction. The discharge limiting unit 130 sets the electrical resistance from the contact surface 104A of the resistance layer 104 with the power feeding layer 102 to the discharge surface 104B exposed to the through hole 114 to be larger in the end through hole 114B than in the inner through hole 114A. It is configured.

  As shown in FIG. 3A, when the counter electrode portion 110 is viewed from the conductive layer 108 side, the length in the X direction (longitudinal direction) of the resistance layer 104, the insulating layer 106, and the conductive layer 108 is X1, Y direction. The length in the (short direction) is Y1. The length of the power feeding layer 102 in the X direction (longitudinal direction) is X2 (<X1), and the length in the Y direction (short direction) is Y2 (<Y1).

  As shown in FIGS. 3A and 3B, the power feeding layer 102 is formed in a rectangular shape like the resistance layer 104, the insulating layer 106, and the conductive layer 108. As an example, similarly, the end surface 102A of the power feeding layer 102 is disposed at an intermediate position (on the boundary line K indicated by a broken line) between the inner through hole 114A and the end through hole 114B in the X direction and the Y direction. . That is, the end surface 102A of the power supply layer 102 in the X direction and the Y direction is located on the resistance layer 104 at a position corresponding to an intermediate position between the inner through hole 114A and the end through hole 114B in the plan view of the counter electrode unit 110. The plurality of inner through holes 114A are formed inside the boundary line K corresponding to the outer shape of the power supply layer 102, and the plurality of end through holes 114B are formed outside the boundary line K.

  As described above, the discharge limiting unit 130 according to the first embodiment, as an example, places the end through hole 114B of the conductive layer 108 in a region outside the end (end surface 102A) of the power supply layer 102 (FIG. 3B). It is configured by forming in the area of width ΔX1 indicated by shading.

(Comparative example)
FIG. 5B shows a charging device 300 of a comparative example. The charging device 300 of the comparative example has a configuration in which the end surface 102A of the power supply layer 102 extends to the end surface 104C of the resistance layer 104 in the charging device 100 of the first embodiment (see FIG. 5A). Other configurations are the same as those of the charging device 100.

  In the charging device 300 of the comparative example, when discharge is performed in the inner through hole 114A where the electrodes (discharge surfaces 104B) adjacent on both sides in the hole arrangement direction are discharged, the current I1 that flows to the resistance layer 104 directly below the power supply layer 102 (Thick arrow) and current I2 (thin arrow) that flows from other than directly below flow. In addition, the thickness of the arrow represents the magnitude of the current. The sneaking current I2 has a current amount shared with the adjacent electrode (here, the left adjacent inner through hole 114A (not shown) and the discharge surface 104B of the end through hole 114B).

  Further, in the charging device 300 of the comparative example, when the discharge is performed in the end through hole 114B where there is no electrode adjacent on both sides in the hole arrangement direction (the discharge surface 104B is only on one side), the power supply layer is formed on the resistance layer 104. A current I1 directed immediately below 102 and currents I2 and I3 flowing from other than directly below flow. The current I2 has a smaller current value than the current I1 by sharing with the inner through hole 114A on one side (one side) in the hole arrangement direction, but the current I3 has a through hole (discharge) on the other side in the hole arrangement direction. Since there is no surface 104B), there is no sharing, and the current value is about the same as the current I1 flowing through the resistance layer 104 immediately below the power feeding layer 102. That is, I3> I2.

  As described above, in the charging device 300 of the comparative example, the value of the current flowing through the resistance layer at the portion corresponding to the end through hole 114B is excessive as compared with the value of the current flowing through the resistance layer 104 at the portion corresponding to the inner through hole 114A. Thus, excessive discharge is performed. Then, the usable period of the resistance layer 104 and the conductive layer 108 at the end portion where the discharge amount is large is shortened.

(Function)
Next, the operation of the first embodiment will be described.

  As shown in FIG. 2B, in the charging device 100, a voltage is applied to the power feeding layer 102 and the conductive layer 108 by the voltage application unit 112, so that the potential difference between the resistance layer 104 and the conductive layer 108 is ΔV1. The potential difference between the layer 108 and the photoreceptor 22 is ΔV2.

  Subsequently, as shown in FIG. 4, in the charging device 100, discharge (indicated by an arrow D) occurs between the resistance layer 104 (discharge surface 104 </ b> B) and the hole wall 108 </ b> A of the conductive layer 108, and the charged particles E are generated. Generated. The generated charged particles E move to the outer peripheral surface of the photoconductor 22 by the action of an electric field generated by the potential difference ΔV2 between the conductive layer 108 and the photoconductor 22 (see FIG. 2B). In this way, the outer peripheral surface of the photoreceptor 22 is charged.

  Here, as shown in FIG. 5A, in the charging device 100, when the discharge is performed in the inner through hole 114A where the electrodes (discharge surfaces 104B) adjacent on both sides in the hole arrangement direction are discharged, Then, a current I1 (thick arrow) heading directly below the power feeding layer 102 and a current I2 (thin arrow) that flows from other than directly below flow. The flowing current I2 is shared with the adjacent electrode (here, the discharge surface 104B of the inner through hole 114A and the end through hole 114B).

  Further, in the charging device 100, when the discharge is performed in the end through hole 114B where there is no electrode adjacent on both sides in the hole arrangement direction (the discharge surface 104B is only on one side), the power supply layer 102 is formed on the resistance layer 104. No. For this reason (because there is the discharge limiting portion 130), the sneaking current I2 flows through the resistance layer 104 on the end through hole 114B. Here, the current I2 has a smaller current value than the current I3 (see FIG. 5B). For this reason, compared with the charging device 300 of the comparative example (see FIG. 5B), the charging device 100 has a reduced discharge amount at a portion corresponding to the end through hole 114B, and corresponds to the end through hole 114B. The amount of discharge in the part is a value close to the amount of discharge in the part corresponding to the inner through hole 114A. That is, in the charging device 100, excessive discharge in the end through hole 114B is suppressed. The usable period of the resistance layer 104 and the conductive layer 108 is longer than that in the comparative example.

  Further, in the charging device 100, it is only necessary to form the power feeding layer 102 having a smaller area compared to the resistance layer 104. Becomes easy.

  In addition, in the image forming apparatus 10 shown in FIG. 1, since excessive discharge at the end in the longitudinal direction in the charging device 100 (see FIG. 2A) is suppressed, the end in the axial direction of the charged photosensitive member 22 is suppressed. It is possible to suppress the decrease in the amount of the developer deposited on the surface. As a result, image unevenness, which is a difference in image density between the center portion and the end portion in the width direction (direction intersecting the transport direction) in the image forming region, is reduced compared to a configuration that does not include the discharge limiting unit 130. The

  In the description of the discharge limiting portion 130 described above, the arrangement direction of the through holes 114 (the inner through holes 114A and the end through holes 114B) is the X direction, but the same effect can be obtained in the Y direction. . For this reason, description of the Y direction in the discharge limiting unit 130 is omitted. In addition, the description in the Y direction is also omitted for the discharge limiting unit in other embodiments hereinafter.

(Second Embodiment)
Next, an example of a charging device and an image forming apparatus according to the second embodiment of the present invention will be described. Note that the same reference numerals as those in the first embodiment are given to the same members and parts as those in the first embodiment described above, and the description thereof is omitted.

  FIG. 6 shows a charging device 140 according to the second embodiment. The charging device 140 is provided with a discharge limiting unit 150 as an example of a discharge limiting unit in place of the discharge limiting unit 130 in the above-described charging device 100 (see FIG. 2A). Since the other parts except the discharge limiting unit 150 have the same configuration as the charging device 100, the description thereof is omitted.

  The charging device 140 includes a counter electrode unit 152, and the counter electrode unit 152 is a power supply layer 154 as an example of a voltage application unit from the far side to the near side with respect to the photoreceptor 22 (see FIG. 1). In addition, a resistance layer 156 as an example of the first electrode, an insulating layer 106, and a conductive layer 108 are stacked. The resistance layer 156, the insulating layer 106, and the conductive layer 108 constitute a discharge portion 142. Note that the power feeding layer 154 is made of the same material as that of the power feeding layer 102 (see FIG. 2A), and the resistance layer 156 is made of the same material as that of the resistance layer 104 (see FIG. 2A). Yes.

  The discharge limiting portion 150 is configured such that the electrical resistance from the contact surface 156D of the resistance layer 156 with the power feeding layer 154 to the discharge surface 156E exposed to the through hole 114 is larger in the end through hole 114B than in the inner through hole 114A. ing. A voltage application unit 112 (see FIG. 2A) is connected to the power feeding layer 154 and the conductive layer 108.

  The power feeding layer 154 has a central portion 154A where the inner through hole 114A is disposed and an outer peripheral portion 154B where the end through hole 114B is disposed, with the boundary line K as a boundary. Further, in the power feeding layer 154, the thickness in the Z direction of the central portion 154A is larger than the thickness in the Z direction of the outer peripheral portion 154B in the arrangement direction (X direction or Y direction) of the inner through holes 114A and the end through holes 114B. It is thicker on the lower side by d1, and an L-shaped step portion 154C is formed.

  The resistance layer 156 has a central portion 156A where the inner through hole 114A is disposed and an outer peripheral portion 156B where the end through hole 114B is disposed with the boundary line K as a boundary. Further, the resistance layer 156 has a thickness in the Z direction of the outer peripheral portion 156B that is larger than the thickness of the central portion 156A in the Z direction in the arrangement direction (X direction or Y direction) of the inner through hole 114A and the end through hole 114B. It is thicker on the upper side by d1, and an L-shaped step 156C is formed. Then, in the cross section along the XZ plane of the counter electrode portion 152, the stepped portion 154C of the power feeding layer 154 and the stepped portion 156C of the resistance layer 156 are stacked.

  The thickness d1 is such that the current flowing through the central portion 156A corresponding to the one inner through hole 114A during discharge and the current flowing through the outer peripheral portion 156B corresponding to the one end through hole 114B during discharge are approximately the same. The thickness is set in advance so that the current value is obtained.

(Function)
Next, the operation of the second embodiment will be described.

  In the charging device 140, a voltage is applied to the power feeding layer 154 and the conductive layer 108 by the voltage application unit 112 (see FIG. 2A), and a potential difference between the resistance layer 156 and the conductive layer 108 is ΔV1 (see FIG. B)), the potential difference between the conductive layer 108 and the photosensitive member 22 is ΔV2 (see FIG. 2B).

  Subsequently, as shown in FIG. 7A, in the charging device 140, a discharge (indicated by an arrow D) is generated between the resistance layer 156 (discharge surface 156E) and the hole wall 108A of the conductive layer 108, and the charging device 140 is charged. Particles E are generated. The generated charged particles E move to the outer peripheral surface of the photoconductor 22 by the action of an electric field generated by the potential difference ΔV2 between the conductive layer 108 and the photoconductor 22 (see FIG. 2B). In this way, the outer peripheral surface of the photoreceptor 22 is charged.

  Here, as shown in FIG. 7B, in the charging device 140, when the discharge is performed in the inner through hole 114A having the adjacent electrodes (discharge surfaces 156E) on both sides in the hole arrangement direction, A current I1 directed directly below the power supply layer 154 and a current I2 sneaking from other than directly below flow through the central portion 156A. Then, the sneaking current I2 is shared with the adjacent electrode (here, the inner through hole 114A and the end through hole 114B).

  Further, in the charging device 140, when the discharge is performed in the end through hole 114B where there is no adjacent electrode on both sides in the hole arrangement direction (the discharge surface 156E is only on one side), the thickness of the outer peripheral portion 156B of the resistance layer 156 is Since it is thicker than the thickness of the central portion 156A (because there is the discharge limiting portion 150), currents I2, I1 ', and I2' flow through the resistance layer 156 (outer peripheral portion 156B) on the end through hole 114B. .

  Here, the currents I1 ′ and I2 ′ have smaller current values than the currents I1 and I3 (see FIG. 5B). For this reason, compared with the charging device 300 of the comparative example (see FIG. 5B), the charging device 140 has a reduced discharge amount at a portion corresponding to the end through hole 114B and corresponds to the end through hole 114B. The amount of discharge in the part is a value close to the amount of discharge in the part corresponding to the inner through hole 114A. That is, in the charging device 140, excessive discharge in the end through hole 114B is suppressed. The usable period of the resistance layer 156 and the conductive layer 108 is longer than that in the comparative example.

  Further, in the charging device 140, the outer peripheral portion 156B of the resistance layer 156 only needs to be thickened, and the power feeding layer 154 only needs to be formed so as to cover the resistance layer 156. Therefore, the structure from the resistance layer 156 to the conductive layer 108 is sufficient. As compared with the configuration in which the charging device 140 is changed, the charging device 140 can be easily manufactured.

  In addition, in the image forming apparatus 10 having the charging device 140 (see FIG. 1), excessive discharge at the end portion in the longitudinal direction of the charging device 140 is suppressed, so that the charged photosensitive member 22 at the end portion in the axial direction is suppressed. It is possible to suppress a decrease in the amount of developer attached. As a result, image unevenness, which is a difference in image density between the central portion and the end portion in the width direction (direction intersecting the transport direction) in the image forming region, is reduced as compared with a configuration that does not include the discharge limiting unit 150. The

(Third embodiment)
Next, an example of a charging device and an image forming apparatus according to the third embodiment of the present invention will be described. Note that the same reference numerals as those in the first embodiment are given to the same members and parts as those in the first embodiment described above, and the description thereof is omitted.

  FIG. 8 shows a charging device 160 of the third embodiment. The charging device 160 is provided with a discharge limiting unit 170 as an example of a discharge limiting unit in place of the discharge limiting unit 130 in the above-described charging device 100 (see FIG. 2A). Since the other parts except the discharge limiting unit 170 have the same configuration as the charging device 100, description thereof will be omitted.

  The charging device 160 has a counter electrode part 172. The counter electrode part 172 is an example of the power supply layer 102 and the first electrode from the far side to the near side with respect to the photoreceptor 22 (see FIG. 1). The first resistance layer 174 and the second resistance layer 175, the insulating layer 106, and the conductive layer 108 are stacked. The first discharge layer 162 is configured by the first resistance layer 174, the insulating layer 106, and the conductive layer 108, and the second discharge unit 164 is configured by the second resistance layer 175, the insulating layer 106, and the conductive layer 108. Yes.

  The discharge limiting unit 170 determines the electrical resistance from the contact surface 175B with the power supply layer 102 in the second resistance layer 175 to the discharge surface 175A exposed in the end through hole 114B with the contact with the power supply layer 102 in the first resistance layer 174. The electrical resistance from the surface 174B to the discharge surface 174A exposed to the inner through hole 114A is set to be larger. A voltage application unit 112 (see FIG. 2A) is connected to the power feeding layer 102 and the conductive layer 108.

  The first resistance layer 174 has a structure in which the outer side of the boundary line K in the resistance layer 104 (see FIG. 3A) is removed, and the material and thickness are the same as those of the resistance layer 104. Further, the discharge surface 174A of the first resistance layer 174 is exposed to the inner through hole 114A.

  The second resistance layer 175 has the same thickness as the first resistance layer 174 and is provided outside the boundary line K of the first resistance layer 174 in the X direction and the Y direction. The discharge surface 175A is exposed to the end through hole 114B while being sandwiched. The second resistance layer 175 has a current that is approximately equal to the current that flows through a portion corresponding to one inner through hole 114A during discharge and the current that flows through a portion corresponding to one end through hole 114B during discharge. The volume resistivity (electric resistivity) of the region facing the end through hole 114B of the second resistance layer 175 is set to be higher than the volume resistivity (electric resistivity) of the first resistance layer 174 so as to be a value. Has been.

(Function)
Next, the operation of the third embodiment will be described.

  In the charging device 160, a voltage is applied to the power feeding layer 102 and the conductive layer 108 by the voltage application unit 112 (see FIG. 2A), and the first resistance layer 174, the second resistance layer 175, and the conductive layer 108 are connected. Is equal to ΔV1 (see FIG. 2B), and the potential difference between the conductive layer 108 and the photosensitive member 22 is ΔV2 (see FIG. 2B).

  Subsequently, as shown in FIG. 9A, in the charging device 160, the discharge surface 174A of the first resistance layer 174 and the hole wall 108A of the conductive layer 108, and the discharge surface 175A of the second resistance layer 175 Discharge (indicated by arrow D) occurs between the hole wall 108A of the conductive layer 108 and charged particles E are generated. The generated charged particles E move to the outer peripheral surface of the photoconductor 22 by the action of an electric field generated by the potential difference ΔV2 between the conductive layer 108 and the photoconductor 22 (see FIG. 2B). In this way, the outer peripheral surface of the photoreceptor 22 is charged.

  Here, as shown in FIG. 9B, in the charging device 160, when the discharge is performed in the inner through hole 114A having the electrodes (discharge surfaces 174A) adjacent on both sides in the hole arrangement direction, the first resistance layer In 174, a current I1 directed directly below the power feeding layer 102 and a current I2 flowing from other than directly below flow. The sneaking current I2 is shared with the adjacent electrodes (here, the discharge surface 174A of the inner through hole 114A and the discharge surface 175A of the end through hole 114B).

  Further, in the charging device 160, when the discharge is performed in the end through hole 114B where there is no adjacent electrode on both sides in the hole arrangement direction (the discharge surface 175A is only on one side), the volume resistivity of the second resistance layer 175 is Since it is higher than the volume resistivity of the first resistance layer 174 (because there is the discharge limiting portion 170), currents I4, I5, and I6 flow through the second resistance layer 175 on the end through hole 114B.

  Here, the current I5 is slightly smaller than the current I2, the current I4 is slightly smaller than the current I1, and the current I6 is smaller than the current I3 (see FIG. 5B). For this reason, compared with the charging device 300 of the comparative example (see FIG. 5B), the charging device 160 has a reduced discharge amount at a portion corresponding to the end through hole 114B, and corresponds to the end through hole 114B. The amount of discharge in the part is a value close to the amount of discharge in the part corresponding to the inner through hole 114A. That is, in the charging device 160, excessive discharge in the end through hole 114B is suppressed. The usable period of the resistance layer 174 and the conductive layer 108 is longer than that in the comparative example.

  Further, in the charging device 160, the second resistance layer 175 only needs to be disposed outside the first resistance layer 174, so that the structure from the first resistance layer 174 and the second resistance layer 175 to the conductive layer 108 is changed. Compared to the above, the manufacturing of the charging device 160 is facilitated.

  In addition, in the image forming apparatus 10 having the charging device 160 (see FIG. 1), excessive discharge at the end portion in the longitudinal direction of the charging device 160 is suppressed, so that the axial end portion of the charged photoreceptor 22 is suppressed. It is possible to suppress a decrease in the adhesion amount of the developer. As a result, image unevenness, which is a difference in image density between the central portion and the end portion in the width direction (direction intersecting the transport direction) in the image forming region, is reduced as compared with a configuration that does not include the discharge limiting portion 170. The

(Fourth embodiment)
Next, an example of a charging device and an image forming apparatus according to the fourth embodiment of the present invention will be described. Note that the same reference numerals as those in the first embodiment are given to the same members and parts as those in the first embodiment described above, and the description thereof is omitted.

  FIG. 10 shows a charging device 180 according to the fourth embodiment. The charging device 180 is provided with a discharge limiting unit 190 as an example of a discharge limiting unit in place of the discharge limiting unit 130 in the above-described charging device 100 (see FIG. 2A). Since the other parts except the discharge limiting unit 190 have the same configuration as the charging device 100, description thereof is omitted.

  The charging device 180 includes a counter electrode portion 192. The counter electrode portion 192 is insulated from the power supply layer 102, the resistance layer 104, and the insulating layer from the far side to the near side with respect to the photosensitive member 22 (see FIG. 1). The layer 106 and the conductive layer 108 are stacked. In addition, a voltage application unit 112 (see FIG. 2A) is connected to the power feeding layer 102 and the conductive layer 108.

  The discharge limiting unit 190 sets the discharge distance between the resistance layer 104 and the conductive layer 108 in the end through hole 194 formed at the end in the arrangement direction (X direction or Y direction) more than the inner through hole 114A. It is configured to be long. Specifically, the discharge limiting portion 190 is configured by making the diameter D2 of the end through hole 194 larger than the diameter D1 of the inner through hole 114A. The diameter D2 of the end through-hole 194 has a current flowing through the resistance layer 104 corresponding to the one inner through-hole 114A and a current flowing through the resistance layer 104 corresponding to the one end through-hole 194. The size is set so that the current value is about the same.

  Since the diameter D2 of the end through hole 194 is larger than the diameter D1 of the inner through hole 114A, the edge of the end through hole 194 has an edge of the inner through hole 114A with respect to the boundary line K set in the first embodiment. Located closer to the edge. The distance from the center position (not shown) of the end through hole 194 to the boundary line K is the same as the distance from the center position (not shown) of the inner through hole 114A to the boundary line K.

(Function)
Next, the operation of the fourth embodiment will be described.

  In the charging device 180, a voltage is applied to the power feeding layer 102 and the conductive layer 108 by the voltage application unit 112 (see FIG. 2A), and the potential difference between the resistance layer 104 and the conductive layer 108 is ΔV1 (see FIG. B)), the potential difference between the conductive layer 108 and the photosensitive member 22 is ΔV2 (see FIG. 2B).

  Subsequently, as shown in FIG. 11A, in the charging device 180, discharge (indicated by an arrow D) is generated between the discharge surface 104B of the resistance layer 104 and the hole wall 108A of the conductive layer 108 in the inner through hole 114A. And discharge (indicated by an arrow Da) occurs between the discharge surface 104B of the resistance layer 104 and the hole wall 108B of the conductive layer 108 in the end through hole 194. Thereby, charged particles E are generated. The generated charged particles E move to the outer peripheral surface of the photoconductor 22 by the action of an electric field generated by the potential difference ΔV2 between the conductive layer 108 and the photoconductor 22 (see FIG. 2B). In this way, the outer peripheral surface of the photoreceptor 22 is charged.

  Here, as shown in FIG. 11B, in the charging device 180, when the discharge is performed in the inner through hole 114A having the adjacent electrodes (discharge surface 104B) on both sides in the hole arrangement direction, Then, a current I1 directed directly below the power feeding layer 102 and a current I2 flowing from other than directly below flow. Then, the sneaking current I2 is shared with the adjacent electrode (here, the inner through hole 114A and the discharge surface 104B of the end through hole 194).

  Further, in the charging device 180, when discharge is performed in the end through hole 194 that has no adjacent electrodes on both sides in the hole arrangement direction (the discharge surface 104B is only on one side), the diameter D2 of the end through hole 194 is set to the inner side. Since it is larger than the diameter D1 of the through hole 114A (because there is the discharge limiting portion 190), currents I2, I7, and I8 flow through the resistance layer 104 on the end through hole 194.

  Here, the current I7 is slightly smaller than the current I1, and the current I8 is smaller than the current I3 (see FIG. 5B). For this reason, compared with the charging device 300 of the comparative example (see FIG. 5B), the charging device 180 has a reduced discharge amount at a portion corresponding to the end through hole 194 and corresponds to the end through hole 194. The amount of discharge in the part is a value close to the amount of discharge in the part corresponding to the inner through hole 114A. That is, in the charging device 180, excessive discharge in the end through hole 194 is suppressed. The usable period of the resistance layer 104 and the conductive layer 108 is longer than that in the comparative example.

  Further, in the charging device 180, since the discharge limiting portion 190 is provided on the side closer to the photoreceptor 22 (see FIG. 11A), the power feeding layer 102 or the resistance layer 104 on the side far from the photoreceptor 22 is changed. As a result, the discharge state can be easily adjusted as compared with one that suppresses excessive discharge at the end.

  Further, in the charging device 180, when there is an existing counter electrode part in which the inner through hole and the end through hole are formed with the same diameter, it is only necessary to enlarge the diameter of the end through hole. Not only can the electrode portion be diverted, but also the charging device 180 can be easily manufactured.

  In addition, in the image forming apparatus 10 having the charging device 180 (see FIG. 1), excessive discharge at the end portion in the longitudinal direction of the charging device 180 is suppressed, so that the axial end portion of the charged photoreceptor 22 is suppressed. It is possible to suppress a decrease in the amount of developer attached. As a result, image unevenness, which is a difference in image density between the center portion and the end portion in the width direction (direction intersecting the transport direction) in the image forming region, is reduced as compared with a configuration that does not include the discharge limiting unit 190. The

(Fifth embodiment)
Next, an example of a charging device and an image forming apparatus according to the fifth embodiment of the present invention will be described. Note that the same reference numerals as those in the first embodiment are given to the same members and parts as those in the first embodiment described above, and the description thereof is omitted.

  FIG. 12 shows a charging device 200 according to the fifth embodiment. The charging device 200 is provided with a discharge limiting unit 210 as an example of a discharge limiting unit in place of the discharge limiting unit 130 in the above-described charging device 100 (see FIG. 2A). Since the other parts except the discharge limiting unit 210 have the same configuration as the charging device 100, the description thereof is omitted.

  The charging device 200 includes a counter electrode portion 212. The counter electrode portion 212 is insulated from the power supply layer 102, the resistance layer 104, and the insulating layer from the far side to the near side with respect to the photosensitive member 22 (see FIG. 1). The layer 106 and the conductive layer 108 are stacked. A voltage application unit 112 (see FIG. 2A) is connected to the power feeding layer 102 and the conductive layer 108.

  The discharge limiting unit 210 sets the discharge distance between the resistance layer 104 and the conductive layer 108 in the end through hole 214 formed at the end in the arrangement direction (X direction or Y direction) more than the inner through hole 114A. It is configured to be long.

  Specifically, the discharge limiting portion 210 has an end through-hole 214 composed of a first through-hole 214A formed in the insulating layer 106 and a second through-hole 214B formed in the conductive layer 108. Yes. The discharge limiting unit 210 is configured by making the diameter D3 of the second through hole 214B of the conductive layer 108 larger than the diameter D1 of the first through hole 214A of the insulating layer 106. The diameter D3 of the second through hole 214B is such that the current flowing through the resistance layer 104 corresponding to one inner through hole 114A and the current flowing through the resistance layer 104 corresponding to one end through hole 214 are: The size is set so that the current value is about the same.

  Since the diameter D3 of the second through hole 214B is larger than the diameter D1 of the inner through hole 114A, the edge of the end through hole 214 has an edge of the inner through hole 114A with respect to the boundary line K set in the first embodiment. Located closer to the edge. The distance from the center position (not shown) of the end through hole 214 to the boundary line K is the same as the distance from the center position (not shown) of the inner through hole 114A to the boundary line K.

(Function)
Next, the operation of the fifth embodiment will be described.

  In the charging device 200, a voltage is applied to the power feeding layer 102 and the conductive layer 108 by the voltage application unit 112 (see FIG. 2A), and a potential difference between the resistance layer 104 and the conductive layer 108 is ΔV1 (see FIG. B)), the potential difference between the conductive layer 108 and the photosensitive member 22 is ΔV2 (see FIG. 2B).

  Subsequently, as shown in FIG. 13A, in the charging device 200, discharge (indicated by an arrow D) occurs between the discharge surface 104B of the resistance layer 104 and the hole wall 108A of the conductive layer 108 in the inner through hole 114A. And discharge (indicated by an arrow Db) occurs between the discharge surface 104B of the resistance layer 104 and the hole wall 108B of the conductive layer 108 in the end through-hole 214. Thereby, charged particles E are generated. The generated charged particles E move to the outer peripheral surface of the photoconductor 22 by the action of an electric field generated by the potential difference ΔV2 between the conductive layer 108 and the photoconductor 22 (see FIG. 2B). In this way, the outer peripheral surface of the photoreceptor 22 is charged.

  Here, as shown in FIG. 13B, in the charging device 200, when the discharge is performed in the inner through hole 114A having the electrodes (discharge surfaces 104B) adjacent on both sides in the hole arrangement direction, Then, a current I1 directed directly below the power feeding layer 102 and a current I2 flowing from other than directly below flow. The flowing current I2 is shared with the adjacent electrode (here, the discharge surface 104B of the inner through hole 114A and the end through hole 214).

  Further, in the charging device 200, when discharge is performed in the end through-hole 214 where there is no electrode adjacent on both sides in the hole arrangement direction (the discharge surface 104B is only on one side), the second through-hole of the end through-hole 214 is used. Since the diameter D3 (see FIG. 13A) of 214B is larger than the diameter D1 (see FIG. 13A) of the inner through-hole 114A (because there is the discharge restricting portion 210), the end through-hole 214 is provided. In the upper resistance layer 104, currents I2, I9, and I10 flow.

  Here, the current I9 is slightly smaller than the current I1, and the current I10 is smaller than the current I3 (see FIG. 5B). For this reason, compared with the charging device 300 of the comparative example (see FIG. 5B), the charging device 200 has a reduced discharge amount at a portion corresponding to the end through hole 214 and corresponds to the end through hole 214. The amount of discharge in the part is a value close to the amount of discharge in the part corresponding to the inner through hole 114A. That is, in the charging device 200, excessive discharge in the end through hole 214 is suppressed. The usable period of the resistance layer 104 and the conductive layer 108 is longer than that in the comparative example.

  Further, in the charging device 200, since the discharge limiting portion 210 is provided on the side close to the photoreceptor 22 (see FIG. 13A), the power feeding layer 102 or the resistance layer 104 on the side far from the photoreceptor 22 is changed. As a result, the discharge state can be easily adjusted as compared with one that suppresses excessive discharge at the end.

  Furthermore, in the charging device 200, when there is an existing counter electrode part in which the inner through hole and the end through hole are formed with the same diameter, it is only necessary to increase the diameter of the end through hole on the conductive layer 108 side. Therefore, not only the existing counter electrode part can be used, but also the charging device 200 can be easily manufactured.

  In addition, in the image forming apparatus 10 having the charging device 200 (see FIG. 1), excessive discharge at the end portion in the longitudinal direction of the charging device 200 is suppressed, so that the axial end portion of the charged photoreceptor 22 is suppressed. It is possible to suppress a decrease in the adhesion amount of the developer. As a result, image unevenness, which is a difference in image density between the center portion and the end portion in the width direction (direction intersecting the conveyance direction) in the image forming region, is reduced as compared with the configuration in which the discharge restriction unit 210 is not provided. The

(Sixth embodiment)
Next, an example of a charging device and an image forming apparatus according to the sixth embodiment of the present invention will be described. Note that the same reference numerals as those in the first embodiment are given to the same members and parts as those in the first embodiment described above, and the description thereof is omitted.

  FIG. 14 shows a charging device 220 of the sixth embodiment. The charging device 220 is provided with a discharge limiting unit 230 as an example of a discharge limiting unit in place of the discharge limiting unit 130 in the above-described charging device 100 (see FIG. 2A). Since the other parts except the discharge limiting unit 230 have the same configuration as the charging device 100, the description thereof is omitted.

  The charging device 220 includes a counter electrode portion 232, and the counter electrode portion 232 is an example of the power supply layer 102 and the first electrode from the far side to the near side with respect to the photoreceptor 22 (see FIG. 1). The resistance layer 234, the insulating layer 236 as an example of an insulator, and the conductive layer 108 are stacked. The resistance layer 234, the insulating layer 236, and the conductive layer 108 constitute the discharge portion 222. In addition, a voltage application unit 112 (see FIG. 2A) is connected to the power feeding layer 102 and the conductive layer 108. The resistance layer 234 is formed using a material similar to that of the resistance layer 104 (see FIG. 2A), and the insulating layer 236 is formed using a material similar to that of the insulating layer 106 (see FIG. 2A). Yes.

  The discharge limiting unit 230 sets the discharge distance between the resistance layer 234 and the conductive layer 108 in the end through hole 114B formed at the end in the arrangement direction (X direction or Y direction) more than the inner through hole 114A. It is configured to be long. Specifically, the discharge limiting portion 230 is configured by making the thickness of the end portion 236B of the insulating layer 236 in the arrangement direction thicker by d2 than the thickness of the central portion 236A.

  The resistance layer 234 has a central portion 234A where the inner through hole 114A is disposed and an outer peripheral portion 234B where the end through hole 114B is disposed with the boundary line K as a boundary. In addition, the resistance layer 234 has an L-shape in which the thickness in the Z direction of the central portion 234A and the thickness in the Z direction of the outer peripheral portion 234B are the same in the arrangement direction of the inner through holes 114A and the end through holes 114B. Step portions 234C and 234E are formed. That is, the outer peripheral portion 234B has a shape in which the thickness d2 is cut into the power feeding layer 102 as compared with the central portion 234A.

  The insulating layer 236 has a central portion 236A where the inner through hole 114A is disposed and an outer peripheral portion 236B where the end through hole 114B is disposed with the boundary line K as a boundary. Further, in the arrangement direction of the inner through hole 114A and the end through hole 114B, the insulating layer 236 has a thickness in the Z direction of the outer peripheral part 236B that is thicker than the thickness of the central part 236A in the Z direction by a thickness d2. In addition, an L-shaped step portion 236C is formed. In the cross section along the XZ plane of the counter electrode part 232, the stepped part 234C of the resistance layer 234 and the stepped part 236C of the insulating layer 236 are stacked in contact with each other.

  The thickness d2 is such that the current flowing through the central portion 234A corresponding to the one inner through-hole 114A during discharge and the current flowing through the outer peripheral portion 234B corresponding to the one end through-hole 114B during discharge are comparable. The thickness is set in advance so that the current value is obtained.

(Function)
Next, the operation of the sixth embodiment will be described.

  In the charging device 220, a voltage is applied to the power feeding layer 102 and the conductive layer 108 by the voltage application unit 112 (see FIG. 2A), and a potential difference between the resistance layer 234 and the conductive layer 108 is ΔV1 (see FIG. B)), the potential difference between the conductive layer 108 and the photosensitive member 22 is ΔV2 (see FIG. 2B).

  Subsequently, as shown in FIG. 15A, in the charging device 220, discharge (indicated by an arrow D) occurs between the discharge surface 234D of the resistance layer 234 and the hole wall 108A of the conductive layer 108 in the inner through hole 114A. And discharge (indicated by an arrow Dc) occurs between the discharge surface 234D of the resistance layer 234 and the hole wall 108B of the conductive layer 108 in the end through hole 114B. Thereby, charged particles E are generated. The generated charged particles E move to the outer peripheral surface of the photoconductor 22 by the action of an electric field generated by the potential difference ΔV2 between the conductive layer 108 and the photoconductor 22 (see FIG. 2B). In this way, the outer peripheral surface of the photoreceptor 22 is charged.

  Here, as shown in FIG. 15B, in the charging device 220, when the discharge is performed in the inner through hole 114A having the adjacent electrodes (discharge surface 234D) on both sides in the hole arrangement direction, Then, a current I1 directed directly below the power feeding layer 102 and a current I2 flowing from other than directly below flow. The flowing current I2 is shared with the adjacent electrode (here, the discharge surface 234D of the inner through hole 114A and the end through hole 114B).

  Further, in the charging device 220, when the discharge is performed in the end through hole 114B where there is no adjacent electrode on both sides in the hole arrangement direction (the discharge surface 234D is only on one side), the thickness of the outer peripheral portion 236B of the insulating layer 236 is Since it is thicker than the thickness of the central portion 236A (because there is the discharge limiting portion 230), currents I2, I1, and I11 flow through the resistance layer 234 (outer peripheral portion 234B) on the end through hole 114B.

  Here, the current I11 has a smaller current value than the current I3 (see FIG. 5B). For this reason, compared with the charging device 300 of the comparative example (see FIG. 5B), the charging device 220 has a reduced discharge amount at a portion corresponding to the end through hole 114B and corresponds to the end through hole 114B. The amount of discharge in the part is a value close to the amount of discharge in the part corresponding to the inner through hole 114A. That is, in the charging device 220, excessive discharge in the end through hole 114B is suppressed.

  Further, in the charging device 220, since the discharge limiting portion 190 is provided on the side closer to the photoreceptor 22 (see FIG. 15A), the power feeding layer 102 or the resistance layer 104 on the side far from the photoreceptor 22 is changed. As a result, the discharge state can be easily adjusted as compared with one that suppresses excessive discharge at the end.

  Further, in the image forming apparatus 10 having the charging device 220 (see FIG. 1), excessive discharge at the end portion in the longitudinal direction of the charging device 220 is suppressed, so that development at the axial end portion of the charged photoconductor 22 is performed. It is suppressed that the adhesion amount of an agent decreases. As a result, image unevenness, which is a difference in image density between the central portion and the end portion in the width direction (direction intersecting the transport direction) in the image forming region, is reduced as compared with a configuration that does not include the discharge limiting unit 230. The

  In addition, this invention is not limited to said embodiment.

  As shown in FIG. 16, a charging device 240 having a discharge limiting unit 250 as an example of a discharge limiting unit that combines the first to sixth embodiments may be used. In addition, the same code | symbol as 1st Embodiment to 6th Embodiment is provided to the fundamentally same member and site | part as 1st Embodiment mentioned above to 6th Embodiment, and the description is abbreviate | omitted.

  The charging device 240 has a counter electrode part 252, and the counter electrode part 252 is formed with a central part 252 </ b> A in which the inner through hole 114 </ b> A is formed and an end through hole 254 with the boundary line K as a boundary. And the outer peripheral portion 252B. In the central portion 252A, a power feeding layer 102, a resistance layer 104 having a thickness d3, an insulating layer 236 having a thickness d4, and a conductive layer 108 are stacked in this order from the side far from the photoreceptor 22 in the Z direction. In the outer peripheral portion 252B, a second resistance layer 175 having a thickness d5 (> d3), an insulating layer 236 having a thickness d6 (> d4), and a conductive layer 108 are stacked in this order from the side far from the photoreceptor 22 in the Z direction. Has been.

  The diameter of the inner through hole 114A is D1, and the end through hole 254 includes a first through hole 254A having a diameter D4 (> D1) formed in the insulating layer 236 and a diameter D5 formed in the conductive layer 108. (> D4) second through hole 254B. Thus, you may suppress the excessive discharge in the edge part through-hole 254 using the discharge limiting part 250 which combined 1st Embodiment to 6th Embodiment.

Alternatively, the resistance layer 104 may be two layers in the Z direction, and a two-layer structure of a high resistance layer and a resistance adjustment layer may be used. For example, the high resistance layer (upper layer) has a volume resistivity of 1 × 10 ⁹ Ωcm and a film thickness of 30 μm, and the resistance adjustment layer (lower layer) has a volume resistivity of 1 × 10 ⁷ Ωcm and a film thickness of 100 μm. In this way, while ensuring the discharge limiting effect due to resistance in the high resistance layer, by increasing the thickness from the power feeding layer 102 and improving the pressure resistance, both the discharging current limiting effect and the stability over time are compatible. . The resistance layer 104 is not limited to organic materials such as resin and rubber, but may be composed of semiconductive glass in which conductive particles are dispersed in glass or an aluminum porous anodic oxide film.

  Furthermore, it is good also as a structure which combined the discharge limiting part of X direction and the discharge limiting part of Y direction about each edge part through-hole (114B etc.) arrange | positioned at four corners.

10 Image forming apparatus 22 Photosensitive member (an example of a charged member and an image holding member)
24 exposure unit (an example of exposure means)
26 Developing unit (an example of developing means)
32 Transfer roll (an example of transfer means)
100 Charging device 102 Power feeding layer (an example of a voltage application unit)
104 Resistive layer (example of first electrode)
104A Contact surface 104B Discharge surface 106 Insulating layer (an example of an insulator)
108 conductive layer (example of second electrode)
108A Hole wall 112 Voltage application part (an example of voltage application means)
114 through-hole 114A inner through-hole 114B end through-hole 120 discharge part 130 discharge restriction part (an example of discharge restriction means)
140 Charging device 142 Discharge unit 150 Discharge limiting unit (an example of discharge limiting means)
154 Feed layer (an example of a voltage application unit)
156 Resistance layer (example of first electrode)
160 Charging device 162 First discharge unit 164 Second discharge unit 170 Discharge limiting unit (an example of discharge limiting means)
174 First resistance layer (an example of the first electrode)
175 Second resistance layer (example of first electrode)
180 Charging device 190 Discharge limiting unit (an example of discharge limiting means)
194 End through-hole 200 Charging device 210 Discharge limiting unit (an example of discharge limiting means)
214 End through-hole 220 Charging device 222 Discharge unit 230 Discharge limiting unit (an example of discharge limiting means)
234 Resistance layer (example of first electrode)
236 Insulating layer (an example of an insulator)
240 Charging device 250 Discharge limiting unit (an example of discharge limiting means)
254 End through-hole E Charge G Developer T Toner image (Example of developer image)

Claims (10)

A first electrode; and a second electrode disposed opposite to the first electrode through an insulator and having a plurality of through holes formed with the insulator toward the first electrode. And a discharge part in which discharge is performed between the hole wall of the through hole of the second electrode,
A voltage application unit that is in contact with a side opposite to the insulator side of the first electrode and to which a voltage is applied;
By applying a voltage to the voltage application section and the second electrode, a potential difference that can be discharged is generated between the first electrode and the through hole of the second electrode, and the electric charge generated by the discharge Voltage applying means for generating a potential difference between the second electrode and the charged body so that the electrode moves to the charged body;
Out of the plurality of through holes formed in the second electrode, the discharge in the end through holes formed at the end portions in the arrangement direction of the plurality of through holes is more than in the arrangement direction than the end through holes. A discharge limiting means that makes it less likely to occur compared to the discharge in the inner through-hole formed inside;
A charging device.   The discharge limiting unit is configured such that an electrical resistance from a contact surface of the first electrode with the voltage application unit to a discharge surface exposed to the through hole is larger in the end through hole than in the inner through hole. The charging device according to claim 1.   The charging device according to claim 2, wherein the discharge limiting unit is configured by forming the end through hole of the second electrode in a region outside the end of the voltage application unit.   4. The charging device according to claim 2, wherein the discharge limiting unit is configured by making a thickness of an end portion of the first electrode in the arrangement direction thicker than a thickness of a central portion.   The discharge limiting means is configured by making the electrical resistivity of the region facing the end through hole of the first electrode higher than the electrical resistivity of the region facing the inner through hole. The charging device according to claim 4.   6. The discharge limiting device according to claim 1, wherein a discharge distance between the first electrode and the second electrode is longer than the inner through hole in the end through hole. The charging device according to any one of the above.   The charging device according to claim 6, wherein the discharge limiting unit is configured by making a diameter of the end through hole larger than a diameter of the inner through hole.   The said discharge limiting means is comprised by making the diameter of the said edge part through-hole of the said 2nd electrode larger than the diameter of the said edge part through-hole of the said insulator. Charging device.   9. The charging device according to claim 6, wherein the discharge limiting unit is configured by making an end portion of the insulator in the arrangement direction thicker than a thickness of a central portion. . An image holding body as the charged body provided rotatably;
The charging device according to any one of claims 1 to 9, wherein the outer peripheral surface of the image carrier is charged.
Exposure means for exposing the outer peripheral surface of the charged image carrier to form a latent image;
Developing means for developing the latent image with a developer to form a developer image;
Transfer means for transferring the developer image developed by the developing means to a recording medium;
An image forming apparatus.

Images