JP2007079380A - Charging member evaluation method, charging member, charging device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging member evaluation method capable of exactly evaluating whether a charging member can prevent such an excessive current that the limit of an electric source is actuated for a defective part from flowing even when there is the defective part in a member to be charged. <P>SOLUTION: A charging roller 12 is pivotally supported and is brought into contact with a roller-shaped metal electrode 31. The metal electrode 31 is rotated in the arrow direction R1 in the figure by an unillustrated motor, etc. and the charging roller 12 is synchronously rotated with the metal electrode 31. A direct current bias is applied from an electric source 32 to the charging roller 12 and a waveform of current flowing through the charging roller 12 during rotation upon the bias application is measured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for evaluating a roller-shaped charging member that charges a member to be charged. The present invention also relates to a roller-shaped charging member for charging a member to be charged, a charging device, and an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus that forms a latent image on a latent image carrier uniformly charged by a charging device by optical writing or the like, and then attaches toner as an image forming material to the latent image to obtain a visible image. Is widely known. Further, as a charging device mounted on this type of image forming apparatus, a charging roller, which is a charging member to which a charging bias is applied from a power source, is rotated while being in contact with the image carrier to uniformly charge the image carrier. A roller contact type is known. Also, a non-contact roller system that uniformly charges the image carrier by the discharge from the discharge part while maintaining a predetermined charging gap between the discharge part such as a conductive rubber layer in the charging roller and the image carrier. Are also known. The roller non-contact type is more stable than the roller contact type because the transfer of toner from the image carrier to the charging roller is less and it is difficult to fix the toner to the roller surface. Can be maintained.

  A small hole (hereinafter referred to as pinhole) on the surface of the image carrier due to some impact applied to the surface of the image carrier or discharge concentrated on one point on the surface of the image carrier due to foreign matter entering the charged area. May occur. If there is a defect such as a pinhole on the surface of the image carrier, overcurrent flows into the defect when the defect passes through the charging roller. At this time, if the charging roller is made of a material such as a metal having a low resistance, high conductivity, and easy current flow, a large current flows into the defective portion. At this time, if the power supply for applying the charging bias to the charging member is provided with a limit for protecting the power supply, this limit works and the voltage drops. Even if no limit is provided, the power supply capacity is insufficient and the voltage drops. When such a voltage drop occurs, the surface of the image carrier cannot be sufficiently charged. As a result, the potential of the image carrier background becomes low after the defective portion of the image carrier passes through the charging roller until the voltage recovers, and the toner adheres to this background as well. A band-like abnormal image extending in the scanning line direction is generated. Further, as a result of a large current flowing through the charging roller and the image carrier, there is a problem that the image carrier and the charging roller are damaged.

Patent Documents 1 to 4 describe a charging roller in which a conductive metal is provided with a resistive layer having a volume resistivity of 10 ⁶ to 10 ⁹ [Ωcm] on a cored bar. As described above, if the resistance layer is provided on the charging roller, it becomes difficult for the current to flow, and when the defective portion passes through the charging roller, an excessive current flows to the defective portion so that the limit of the power supply works. Can be suppressed. As a result, it is possible to suppress the occurrence of a belt-like abnormal image without a voltage drop. In addition, since a large current does not flow through the charging roller and the photoconductor, damage to the photoconductor and the charging roller can be suppressed.

Japanese Patent Laid-Open No. 5-273841 JP 2001-337515 A JP 2004-264724 A JP 2004-219539 A

When the volume resistivity of a part of the charging roller and the volume resistivity of the material of the resistance layer are measured and the volume resistivity of the charging roller is 10 ⁶ to 10 ⁹ [Ωcm], it is evaluated as a good product and image formation is performed. It is possible to attach it to the device. However, depending on the manufacturing method and the like, when the charging roller is viewed in the cross section in the axial direction, the flow of current differs in each part of the circumference, and there may be a part that flows extremely easily. Therefore, only by measuring the volume resistivity of a part of the charging roller or the volume resistivity of the material of the resistance layer, it cannot be determined whether or not there is a portion where the current easily flows in the charging roller.
Therefore, when the charging roller is viewed in an axial cross section, the volume resistivity of each part of the circumference is measured, and if the volume resistivity of the charging roller in each part of the circumference is 10 ⁶ to 10 ⁹ [Ωcm]. I tried to rate it as good. However, even if the volume resistivity of the charging roller in each part of the circumference is 10 ⁶ to 10 ⁹ [Ωcm], an excessive current may flow to the defective part of the image carrier so that the power source limit acts. there were. This is because the electric capacity C inherent to the charging roller differs depending on the manufacturing method and material of the charging roller, and the ease of current flow to the image carrier varies even with the same volume resistivity. It is done. That is, since the electric capacity C can be expressed as C = Q (charge) / V (voltage), the current flowing through the charging roller can be expressed as I = C × (dV / dt).

The volume resistivity of the charging roller is measured by contacting the charging roller and the metal electrode, and with the charging roller stopped, a current that connects the voltage application portion of the charging member to the contact portion of the metal electrode flows. After passing a current through the part for a long time, the volume resistance value is obtained based on the current value. In other words, the volume resistivity is measured after flowing a current for a long time, accumulating charges corresponding to the electric capacity, and eliminating the influence of the electric capacity component of the charging roller. For this reason, in the method of measuring the volume resistivity, it is impossible to see the ease of current flow of the charging roller including the influence of the capacitance component. Therefore, even if a charging roller having a volume resistivity of 10 ⁶ to 10 ⁹ [Ωcm] is attached to the apparatus in each part of the circumference, an excessive current is applied so that a power source limit acts on a defective portion of the image carrier. As a result, the above-described belt-like abnormal image, the image carrier, and the charging roller are damaged.

  The present invention has been made in view of the above problems, and the purpose of the present invention is to prevent an excessive current from flowing so that a power source limit acts on the defective portion even if the charged member has a defective portion. It is an object to provide a charging member evaluation method capable of accurately evaluating whether or not a charging member is used. Another object of the present invention is to provide a charging member, a charging device, and an image forming apparatus in which an excessive current does not flow so that a power source limit is applied to the defective portion even if there is a defective portion of the member to be charged.

In order to achieve the above object, the invention according to claim 1 is a method in which a roller-shaped charging member for charging a member to be charged is brought into contact with a metal electrode, the charging member is rotated, and a voltage is applied to the charging member. At this time, the quality of the charging member is evaluated from the value of the current flowing through the charging member.
In the charging member evaluation method according to claim 1, when the current value I flowing through the charging member and the voltage applied to the charging member are V, the current value I is I ≦ 3.1. × 10 ⁻¹⁰ × V ^2.4
In this case, the charging member is evaluated as a non-defective product.
According to a third aspect of the present invention, in the charging member evaluation method according to the second aspect, a current value I flowing through the charging member is I ≧ 5.0 × 10 ⁻¹¹ × V ^2.4.
In this case, the charging member is evaluated as a non-defective product.
According to a fourth aspect of the present invention, in the charging member evaluation method according to the first aspect, the current value I flowing through the charging member, the dynamic resistance value R calculated from the voltage V applied to the charging member, V, The relationship between the voltage applied to the charging member and V is R ≧ 3.2 × 10 ⁹ × V ^−1.4
In this case, the charging member is evaluated as a non-defective product.
According to a fifth aspect of the present invention, in the charging member evaluation method according to the fourth aspect, the dynamic resistance value R is R ≦ 2.0 × 10 ¹⁰ × V ^−1.4.
In this case, the charging member is evaluated as a non-defective product.
According to a sixth aspect of the present invention, in the charging member evaluation method according to any one of the first to fifth aspects, the rotation speed of the charging member is 47 [mm / s] or more.
According to a seventh aspect of the present invention, in a roller-shaped charging member that discharges to the surface of the member to be charged and charges the surface of the member to be charged, the charging member is brought into contact with the metal electrode, the charging member is rotated and the charging member is rotated. When a voltage is applied to the charging member, the current value flowing through the charging member at that time is I, and the voltage applied to the charging member is V, the current value I is 5.0 × 10 ⁻¹¹ × V ^2.4 ≦ I ≦ 3.1 × 10 ⁻¹⁰ × V ^2.4
A charging member characterized by being configured as follows.
According to the eighth aspect of the present invention, in the roller-shaped charging member that discharges to the surface of the member to be charged and charges the surface of the member to be charged, the charging member is brought into contact with the metal electrode, the charging member is rotated and the charging member is rotated. When a voltage is applied to the charging member, the dynamic resistance value R calculated from the current value flowing through the charging member at that time, and the voltage applied to the charging member is V, the dynamic resistance value R is 3.2 × 10. ⁹ × V ^−1.4 ≦ R ≦ 2.0 × 10 ¹⁰ × V ^−1.4
It is comprised so that it may become.
The invention of claim 9 is a charging device comprising a charging member disposed opposite to the image carrier, and discharging the charging member to charge the surface of the image carrier. 7 or 8 charging members are used.
According to a tenth aspect of the present invention, in the charging device of the ninth aspect, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging member.
The invention of claim 11 is characterized in that, in the charging device of claim 10, the peak-to-peak voltage of the AC voltage applied to the charging member is set to at least twice the charging start voltage of the image carrier. It is.
According to a twelfth aspect of the present invention, in the charging device according to any of the ninth to eleventh aspects, a gap forming member for forming a gap is provided between the charging member and the image carrier. is there.
According to a thirteenth aspect of the present invention, in the charging device of the twelfth aspect, a gap between the charging member and the image carrier is set to 1 to 100 [μm].
According to a fourteenth aspect of the present invention, in the charging device according to the twelfth or thirteenth aspect, a gap between the charging member and the image carrier is made larger than a toner particle size.
The invention of claim 15 is characterized in that, in the charging device of any of claims 9 to 14, a cleaning member for cleaning the surface of the charging member is provided.
According to a sixteenth aspect of the present invention, in the charging device according to the fifteenth aspect, the cleaning member has a blade shape.
According to a seventeenth aspect of the present invention, in the charging device according to the fifteenth aspect, the cleaning member has a brush shape.
According to an eighteenth aspect of the present invention, in the charging device according to the fifteenth aspect, the cleaning member has a roller shape.
According to a nineteenth aspect of the present invention, in the charging device according to the eighteenth aspect, the cleaning member is a melamine resin foam.
According to a twentieth aspect of the present invention, in the charging device according to any one of the seventeenth to nineteenth aspects, the cleaning member is rotatably supported.
The invention according to claim 21 is the charging device according to any one of claims 9 to 20, wherein the charging member is provided on a conductive base, a resistance layer on an outer periphery of the base, and an outer periphery of the resistance layer. The surface layer has a base material and a conductive agent dispersed in the base material.
According to a twenty-second aspect of the present invention, in the charging device of the twenty-first aspect, the volume resistivity of the surface layer is set higher than the volume resistivity of the resistive layer.
According to a twenty-third aspect of the present invention, in an image forming apparatus comprising an image carrier and a charging device for charging the image carrier, the charging device according to any one of the ninth to twenty-second aspects is used as the charging device. It is characterized by this.
According to a twenty-fourth aspect of the invention, in the image forming apparatus of the twenty-third aspect, the image carrier has a surface layer containing a filler.
According to a twenty-fifth aspect of the present invention, in the image forming apparatus of the twenty-third or twenty-fourth aspect, the charging device and the image carrier are provided in a process cartridge that is integrated and detachable from the main body. It is characterized by being.
According to a twenty-sixth aspect of the present invention, in the image forming apparatus of the twenty-fifth aspect, a cleaning device is provided in the process cartridge for cleaning the transfer residual toner adhering to the image carrier.
According to a twenty-seventh aspect of the present invention, there is provided an image forming apparatus according to the twenty-sixth aspect, wherein a plurality of the image carriers are provided, toner images of different colors are formed on the plurality of image carriers, and the toner images of different colors are formed. It is characterized in that a color image is obtained by superposing them on a transfer body in order.

According to invention of Claim 1 thru | or 6, a contact part with a metal electrode changes by rotating a charging member. Therefore, if the charging member is rotated once or more, it is possible to detect from the current value the ease of current flow in each part of the circumference when the charging member is viewed in the axial cross section. As a result, it can be determined whether or not there is a portion where the current easily flows in the charging member, and whether the charging member may cause an excessive current to flow to the defective portion of the member to be charged, so that the power source limit works. You can evaluate whether or not. As a result, if the charging roller evaluated according to this evaluation method is incorporated in the apparatus, the voltage of the power source does not drop and a belt-like abnormal image does not occur.
Moreover, the time which contacts a metal electrode can be made small by rotating a charging member. Therefore, the current does not flow for a long period of time so that a charge corresponding to the electric capacity is accumulated in the portion where the current of the charging member connecting the portion to which the voltage of the charging member is applied and the metal electrode and the contact portion flows. Thereby, the value of the current flowing through the charging member including the influence of the capacitance component and the volume resistivity can be measured. That is, it is possible to detect the ease of current flow of the charging member including the influence of the capacitance component and the volume resistivity. Therefore, it is possible to accurately evaluate the easiness of the current flow of the charging member as compared with the case of determining the easiness of the flow of the charging member only from the volume resistivity of the charging member. Accordingly, it is possible to accurately evaluate whether or not the charging member is easy to flow a current so that an excessive current flows as the power source limit is applied to the defective portion of the member to be charged. Incorporation of the charging member into the apparatus can be suppressed. As a result, if the charging roller evaluated according to this evaluation method is incorporated in the apparatus, the voltage of the power source does not drop and a belt-like abnormal image does not occur.

  Further, according to the seventh to twenty-seventh aspects of the present invention, an excessive current does not flow so that the power source limit is applied to the defective portion of the member to be charged. As a result, it is possible to suppress a problem that the voltage of the power source drops and the charged object surface cannot be sufficiently charged.

  Hereinafter, a method for evaluating the charging roller according to the present embodiment will be described. First, a configuration of an image forming apparatus on which a charging roller that is a charging member evaluated in the present embodiment is mounted will be described.

  FIG. 1 is a schematic configuration diagram illustrating a first embodiment of an image forming apparatus. The image forming apparatus shown in FIG. 1 is configured as a copier, a printer, a facsimile, or a multifunction machine having at least two of these functions. This image forming apparatus is a member to be charged in a main body casing (not shown), and a photosensitive member 1 as an image carrier is arranged and rotated in the clockwise direction in FIG. 1, and its surface moves in the direction of arrow A. The photoreceptor 1 is composed of a photoreceptor in which a photosensitive layer 3 is laminated on the outer peripheral surface of a drum-shaped conductive base 2. The photosensitive member may be a belt-shaped photosensitive member that is driven by being wound around a plurality of rollers, or a drum-shaped or belt-shaped photosensitive member made of a dielectric. Around the photosensitive member 1, a charging device 5, a laser writing unit 6, a developing device 7, a transfer device 8, an auxiliary cleaning device 9, and a cleaning device 10 are arranged.

  The developing device 7 includes a developing roller 11 that conveys the developer while being carried. As the developer, for example, a dry developer having a toner and a carrier, or a one-component developer having no carrier can be used. A developing device using a liquid developer can also be employed. The developing roller 11 is driven to rotate, the developer is carried on the peripheral surface of the transport roller, and transported to the developing area between the developing roller 11 and the photosensitive member 1, and the toner of the developer becomes an electrostatic latent image. The electrostatic latent image is electrostatically transferred, and the electrostatic latent image is visualized as a toner image.

  The transfer device 8 is constituted by a transfer roller to which a transfer voltage having a polarity opposite to the charging polarity of the toner on the photosensitive member 1 is applied. The transfer device includes a transfer brush, a transfer blade, or a corona discharger having a corona wire. Etc. can also be used. Further, instead of directly transferring the toner image on the photosensitive member to the transfer material P as the final recording medium, the toner image on the image carrier is transferred onto a transfer material made of an intermediate transfer member, and the toner image is transferred to the transfer material P. It can also be configured to transfer to the final recording medium.

  The auxiliary cleaning device 9 is configured by a roller shape, a brush shape, or the like, and the cleaning device 10 is configured by a cleaning blade. The cleaning device 10 may be a roller shape or a brush shape. Further, it is possible to clean the transfer residual toner by controlling the charge of the transfer residual toner by applying a voltage to one or both of the cleaning device 10 and the auxiliary cleaning device 9. Further, the cleaning property may be improved by applying a lubricant to the auxiliary cleaning device 9.

  In the image forming apparatus having the above configuration, the surface of the photoreceptor 1 is charged to a predetermined polarity by a charging device 5 described later during an image forming operation. The surface of the photosensitive member 1 charged by the charging device 5 is irradiated with light-modulated laser light L emitted from a laser writing unit 6 which is an example of an exposure device, whereby an electrostatic latent image is formed on the surface of the photosensitive member 1. It is formed. Next, the electrostatic latent image is visualized as a toner image by toner charged to a predetermined polarity when passing through the developing device 7. On the other hand, a transfer material P made of transfer paper, for example, is fed at a predetermined timing from a paper feeding device (not shown) between the transfer device 8 and the photoconductor 1 facing the photoconductor 1. The toner image formed thereon is electrostatically transferred onto the transfer material P. The transfer material P onto which the toner image has been transferred continues to pass through a fixing device (not shown). At this time, the toner image is fixed on the transfer material P by the action of heat and pressure. The transfer material P that has passed through the fixing device is discharged to a paper discharge unit (not shown). A part of the transfer residual toner that is not transferred to the transfer material P and remains on the surface of the photoreceptor 1 is removed by the auxiliary cleaning device 9, and the rest is removed by the cleaning device 10.

  The charging device 5 has a charging member surface that moves, in the illustrated example, a charging roller 12 that is a charging member disposed opposite to the surface of the photosensitive member 1, and a cleaning member 13 that cleans the outer peripheral surface of the charging roller 12. ing. The cleaning member 13 is rotatably mounted on the casing 17 of the charging device 5, and abuts against the outer peripheral surface of the charging roller 12 by the weight of the cleaning member 13 itself. The cleaning member 13 removes fine particles such as dust and fine particles such as toner adhering to the surface of the charging roller 12, thereby suppressing the electric field from concentrating on the fine particles on the surface of the charging roller 12 and causing abnormal discharge. can do. Further, since the cleaning member 13 is rotatably attached to the casing of the charging device 11, the fine particles removed from the charging roller 12 are uniformly attached to the outer peripheral surface of the cleaning roller by rotating the cleaning member 13. . As a result, the cleaning performance can be maintained over a long period of time as compared with the case where the cleaning member 13 is fixedly fixed and only a specific portion of the cleaning member 13 is always in contact with the charging roller 12. The cleaning roller is preferably made of a melamine resin foam. The foam formed of melamine resin has a hard reticulated fiber. Therefore, the deposit on the charging roller 12 can be easily scraped off or hooked off, and the cleaning performance is excellent. Further, since the melamine resin foam has a relatively fragile property, the contact surface peels off due to the frictional force with the charging roller 12. At this time, deposits such as toner held in the pores of the foam are also peeled off. As a result, a fresh surface is always in contact with the charging roller 12, and good cleaning performance can be maintained. Further, the cleaning member 13 can be omitted if necessary. Also, the cleaning member can be shaped like a brush or a blade depending on the situation.

  Next, the charging roller 12 will be described. FIG. 2 is a cross-sectional view of the charging roller 12, and FIG. 3 is a view showing the charging roller 12 and the photoreceptor 1.

As shown in FIG. 2, the charging roller 12 has a conductive core bar 15 formed in a columnar shape and a volume resistivity of 10 ⁵ to 10 ¹⁰ [Ω · cm] laminated on the outer peripheral surface of the core bar. The charging roller 12 has a semiconductive property. The middle resistance layer 16 has a thickness of about 1 to 2 [mm] and a volume resistivity of about 10 ⁵ to 10 ⁹ Ω · cm, and a thickness of about 10 [μm]. The volume resistivity is set to about 10 ⁶ to 10 ¹⁰ [Ω · cm], and is similar to the surface layer 16b laminated on the outer periphery of the resistance layer 16a.

  The volume resistivity of the surface layer 16b is preferably slightly higher than the volume resistivity of the resistance layer 16a. If the resistance of the surface layer 16b is low, the surface resistivity of the surface layer 16b is reduced, a current path is also formed on the surface of the charging roller, current flows in the axial direction of the charging roller 12, and the discharge energy is made uniform in the gap. There is a risk that it will not be. As a result, discharge concentration occurs, and streamer discharge may occur. By making the volume resistivity of the surface layer 8 higher than the volume resistivity of the resistance layer 16a, it is possible to prevent the formation of a current path in the surface direction of the charging roller 12, uniform discharge, and occurrence of abnormal discharge. Can be prevented.

The metal core 15 is, for example, a metal material having high rigidity and conductivity such as stainless steel or aluminum having a diameter of about 8 to 20 [mm], or 1 × 10 ³ [Ω · cm] or less, preferably 1 × 10. ^It is composed of a highly rigid conductive resin having a volume resistivity of ² [Ω · cm] or less.

  The resistance layer 16a is composed of a base material and a conductive agent dispersed therein. As the base material, a rubber material such as ethylene-propylene-diene rubber (EPDM), urethane rubber, silicone rubber, epichlorohydrin rubber or the like is used. it can. In the proximity charging system, olefin resins such as polyethylene (PE) and polypropylene (PP), styrene resins such as polystyrene (PS) and copolymers thereof (AS, ABS), polymethyl methacrylate (PMMA), and the like. General-purpose resins with good processability such as acrylic resins such as

  Examples of the conductive agent for the resistance layer 16a include alkali metal salts such as lithium peroxide, perchlorates such as sodium perchlorate, quaternary ammonium salts such as tetrabutylammonium salts, and ionic conductives such as polymer-type conductive agents. An agent can be used. Carbon black such as ketjen black and acetylene black can also be used.

  The surface layer 16b can also be made of a material in which a conductive agent is dispersed in a base material. As the base material, suitable materials such as a fluororesin, a silicone resin, an acrylic resin, a polyamide resin, a polyester resin, a polyvinyl butyral resin, and a polyurethane resin can be used. Materials can be used. In particular, it is preferable to select a material to which the toner is difficult to adhere.

  As the conductive material of the surface layer 16b, a conductive agent made of carbon black such as ketjen black or acetylene black, a metal oxide such as indium oxide or tin oxide, or other appropriate conductive agent can be used.

  In the above, the middle resistance layer 16 is composed of the resistance layer 16a and the surface layer 16b, but may be composed of one layer of the resistance layer 16a. However, by providing the surface layer 16b, it is possible to improve the discharge stability and protect the charging roller 12. Moreover, it is desirable for the surface layer to contain a conductive agent in the base material. As a result, even when the environment becomes a low humidity environment or a high humidity environment, the electron conductive surface layer 16b prevents moisture from entering and exiting the inside of the charging roller, so that the resistance fluctuation of the charging roller 12 can be suppressed. As a result, even if the environment changes, the fluctuation of the charged potential on the surface of the photoreceptor can be reduced, and the discharge stability can be improved.

  As shown in FIG. 3, the charging roller 12 faces the photoconductor 1 and extends parallel to the photoconductor 1. At both ends in the axial direction of the charging roller 12, spacers 14 serving as gap forming members are provided at positions corresponding to the non-image forming area Y on the axial direction end side from the image forming area X of the photoreceptor 1. The spacer 14 comes into contact with the non-image forming area of the photoreceptor 1, and the charging roller 3 a rotates with the photoreceptor 1. The spacer 14 forms a predetermined gap G between the image forming area of the photoreceptor 1 and the charging roller 3a in a non-contact state. The spacer 14 is made of an insulating material or a tape having a volume resistivity equal to or higher than that of the resistance layer 7 of the charging roller, and is affixed to the charging roller 14.

  The material of the tape constituting the spacer 14 includes metals such as aluminum, iron and nickel and oxides thereof, metal alloys such as Fe—Ni alloy, stainless steel, Co—Al alloy, Ni steel, duralumin, monel and inconel, Olefin resins such as polyethylene (PE) and polypropylene (PP), polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polytetrafluoroethylene (PTFE), and copolymers thereof (for example, PFA, FEP) ) And the like, and polyimide resins. In particular, it is preferable to use a material having high releasability that is difficult to fix the toner. When a conductive material is used as the tape, the surface of the tape is insulated from the photosensitive member by coating an insulating layer or a half resistor layer on the surface thereof.

  Both ends of the cored bar 6 of the charging roller are rotatably supported by bearings 18 respectively. Each bearing 18 is slidably fitted in a long hole 17b provided in the side plate 17a of the casing 17 of the charging device 5 in a direction in which it is in contact with or separated from the photosensitive member. Further, the bearing 18 is pressurized toward the surface of the photoreceptor 1 by a compression spring 19 as a pressurizing unit. The pressing force of the compression spring 20 is preferably set to a magnitude that causes the charging roller 12 to rotate at a substantially constant speed when the photosensitive member 1 is driven to rotate. As a result, the spacer 14 is pressed against the surface of the photoreceptor 1 with a predetermined pressure, and the charging roller 12 can follow the photoreceptor 1 well. In addition, the minute gap G can be maintained with high accuracy. Further, the charging roller may be rotationally driven by a driving motor (not shown).

  A power source 20 is electrically connected to the cored bar 6 of the charging roller 12, and a predetermined charging bias is applied to the charging roller 12. As a result, a discharge is generated in the gap between the charging member 2 and the surface of the image carrier, and at least the image forming region X of the image carrier 5 is charged to a predetermined polarity.

  As the charging bias, only a DC voltage may be used, but one in which an AC voltage is superimposed on a DC voltage is more preferable. When the electric resistance of the middle resistance layer 16 constituted by the resistance layer 16a and the surface layer 16b of the charging roller 12 is non-uniform, when only a DC voltage is applied to the charging roller 12, the charging potential of the photoreceptor 1 becomes non-uniform. However, if a charging bias in which an AC voltage is superimposed on a DC voltage is applied to the charging roller 12, the charging roller surface potential becomes the same, the discharge becomes stable, and the surface of the photoreceptor can be uniformly charged. At that time, it is particularly preferable to set the peak-to-peak voltage of the AC voltage applied to the charging roller 12 to a value that is at least twice the charging start voltage of the photoreceptor. In this way, even if the discharge from the photosensitive member to the charging roller 12, that is, reverse discharge occurs and the electric resistance of the middle resistance layer 16 of the charging roller 12 becomes nonuniform, the effect of AC voltage makes it The body 1 can be uniformly charged in a more stable state. The charging start voltage is an absolute value of a voltage when the surface of the photosensitive member starts to be charged when only a DC voltage is applied to the charging roller and the absolute value of the applied voltage is gradually increased. Further, as the DC voltage, a constant current controlled DC voltage can be used as necessary.

Next, the minute gap G between the photosensitive member and the charging roller will be described.
When the minute gap G is larger than the optimum value, the frequency of occurrence of the image flow phenomenon increases. This is considered to be because when the minute gap G is widened, the voltage necessary for generating the discharge increases and the ionization space due to the discharge increases. The relationship between the minute gap and the discharge voltage can be explained by Pasche's law. In particular, when the gap is in a certain range, the discharge start voltage Vth (V) and the gap d (μm) are expressed as “Vth = 6.2 × d + 312”. , 40 ≦ d ≦ 120 (μm) ”. From this equation, it can be seen that the wider the minute gap G, the higher the voltage for causing discharge. The fact that discharge occurs at a high voltage means that the energy at the time of occurrence of discharge is large and many molecules can be ionized, so that more discharge products that are the cause of image flow are generated. In addition, when the minute gap G is wide, the gap distance from the charging roller 12 to the photosensitive member 1 is increased, and the space region in which the discharge starts from the charging roller 12 and reaches the photosensitive member 1 is increased. As a result, the number of molecules to be ionized increases, and it is considered that more discharge products are generated. However, if the minute gap G is zero, the air flow in the image forming apparatus stays at the contact portion between the image carrier 5 and the charging member 2, so the concentration of the discharge product in the vicinity of the contact portion. As a result, the amount of discharge products deposited on the surface of the image carrier increases.

  For this reason, it is preferable to set the minute gap G between the charging roller 12 and the photosensitive member 1 to 1 to 100 [μm]. By setting the minute gap G between the charging roller 12 and the photosensitive member 1 to 1 to 100 [μm], the amount of discharge products adhering to the image carrier can be reduced, and the spot-like shape is reduced. It is possible to prevent the occurrence of abnormal images and image flow.

  The minute gap G between the charging roller 12 and the photosensitive member 1 is preferably set to be at least larger than the toner particle size. This is due to the following reason. In some cases, a slight amount of toner that cannot be removed by the cleaning device 11 enters the minute gap G between the charging roller 12 and the photosensitive member 1. At this time, if the minute gap G is narrower than the particle size of the toner, the toner forcibly tries to pass through the minute gap G. Therefore, stress is generated in the toner, and the toner is softened or melted by heat, and the surface of the charging roller. There is a risk of fusion. This is because the charging roller portion where the toner is fused is likely to cause abnormal discharge. Therefore, by setting the minute gap G to a value larger than the toner particle size, the toner that has passed through the cleaning device 11 passes through the minute gap G as it is, and the toner is fused to the surface of the charging roller 12. Absent. As a result, the occurrence of abnormal discharge due to toner fusion can be prevented.

  Further, when a two-component developer is used in the developing device 7, the carrier adheres to the surface of the photoreceptor, and this may pass through the cleaning device 11 and reach the minute gap G. At this time, if the minute gap G is narrower than the particle size of the carrier, the carrier forcibly passes through the gap G. Generally, since the carrier is made of a hard material such as iron powder, when the carrier passes through the minute gap G, the surface of the charging roller 12 or the surface of the photosensitive member is scratched, pinholes, etc., and a point-like abnormal image or band This may cause abnormal images and damage to members. Therefore, it is preferable to set the minute gap G to a value larger than the particle diameter of the developer carrier. By doing so, it is possible to prevent the above-described problems from occurring and to uniformly charge the image carrier.

  Further, the spacer 14 is made of a tape and wound around the charging roller 12 to form a minute gap G between the charging roller 12 and the photosensitive member 1. A minute gap G may be formed between the body 1 and the body 1. For example, as shown in FIG. 4, the gap member G may be formed between the charging roller 12 and the photoreceptor 1 by providing a cap-like spacer member 23 at both ends of the cored bar 6. .

  The photoreceptor 1 is preferably configured as a photoreceptor having an amorphous silicon surface layer. Since the surface of such a photoconductor can be finished very smoothly, it is possible to effectively suppress fluctuations in the size of the microgap G when the photoconductor 1 is rotated, and the size of the microgap G is the size of the photoconductor. Fluctuation in the circumferential direction can be suppressed. Further, when the photoreceptor 1 is configured as a photoreceptor having a surface layer in which a filler such as alumina powder of 0.1 μm or less is dispersed, for example, the surface hardness is increased and the wear resistance is improved. The service life can be greatly extended.

  Further, the charging device 5, the cleaning device 10, the auxiliary cleaning device 9, and the like have a contact member that contacts the photoconductor 1. The image forming apparatus shown in FIG. 1 is configured such that a cleaning device 10 having a contact member, an auxiliary cleaning device 9 and the like can be attached to and detached from the image forming apparatus main body separately from the charging device 12. However, with this configuration, when the cleaning device 10 having the contact member and the auxiliary cleaning device 9 are attached / detached, these contact members move while being in contact with the photosensitive member 1, so that a large external force is applied to the photosensitive member, and the photosensitive member There is a possibility that the minute gap G between the body and the charging roller 12 may fluctuate. Therefore, as shown in FIG. 5, the charging device 5, the cleaning device 10, and the auxiliary cleaning device 9 may be configured as an integrated unit 24. Further, the photosensitive member 1 is rotatably assembled to the unit 24, and the unit 24 has a function as a process cartridge. The unit 24 is configured to be detachable from the main body of the image forming apparatus. As a result, the charging roller 12 and the photoreceptor 1 can be attached to and detached from the image forming apparatus main body with the minute gap G kept constant. In addition, since the cleaning device 10 having the contact member and the auxiliary cleaning device 9 can be attached and detached together with the charging device 12 and the photosensitive member, it is possible to prevent a problem that the size of the minute gap G greatly fluctuates. .

Also, the charging roller evaluated in this embodiment can be mounted on the color image forming apparatus shown in FIG.
The image forming apparatus shown in FIG. 6 includes image forming units C1 to C4 for forming toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (BK). Yes. Further, it has an intermediate transfer belt 90 that is wound around a plurality of rollers and is rotationally driven in the direction of an arrow, and a toner image is transferred from the image forming portions C1 to C4. The toner image formed on the intermediate transfer belt 90 is a recording medium that is disposed opposite to the roller 113 via the intermediate transfer belt 90 and is brought into contact with the intermediate transfer belt 90 with a predetermined nip pressure. A secondary transfer roller 120 for transferring to P is also provided. As shown in FIG. 6, the image forming units C1 to C4 are arranged in series around the intermediate transfer belt 90, and the intermediate transfer belt 90 is rotationally driven in the direction of the arrow. The yellow toner image, the magenta toner image, the cyan toner image, and the black toner image formed by the image forming units C1 to C4 are sequentially transferred onto the intermediate transfer belt 90. On the other hand, the recording paper P is conveyed from the paper feeding device (not shown) between the intermediate transfer belt 90 and the secondary transfer roller 120 at a predetermined timing from the direction of the arrow F. At this time, the toner images of the respective colors formed on the intermediate transfer belt 90 are electrostatically collectively transferred onto the recording paper P. The recording paper P on which the toner image of each color is transferred is heated and pressurized by a fixing device (not shown), and the toner image is fixed on the recording paper P. Thereafter, the recording paper fixed by a fixing device (not shown) is discharged from a paper discharge unit (not shown). The color image forming apparatus of FIG. 6 also includes the above-described charging device.

Next, a charging roller evaluation method, which is a feature of the present embodiment, will be described.
A small hole (hereinafter referred to as a pinhole) is generated on the surface of the photoconductor due to the discharge being concentrated on one point on the surface of the photoconductor due to an impact applied to the surface of the photoconductor or a foreign substance entering the charged region. There is a case. If there is a defective portion such as a pinhole on the surface of the photosensitive member, when the defective portion passes through the charging roller, discharge concentrates on the defective portion, and an overcurrent flows into the defective portion. At this time, if the charging roller is made of a material with low resistance that allows current to flow, a large current will flow into the defective part, and the power capacity of the power supply and the limit for power protection will work, causing the voltage to drop. End up. If the voltage drops, the surface of the photoreceptor cannot be sufficiently charged. As a result, the potential of the photosensitive member background portion is lowered, and toner adheres to the background portion, resulting in a band-like abnormal image extending in the main scanning line direction.

For this reason, for example, a medium resistance layer having a volume resistivity of 10 ⁵ to 10 ¹⁰ [Ωcm] is provided to make it difficult for a current to flow as a semiconductive charging roller and to prevent a large current from flowing into a defective portion. I am doing so. However, even if the volume resistivity is specified, variation in charging roller manufacturing causes variations in volume resistivity and capacitance on the circumference of the charging roller, and the ease of current flow can be reduced. It will be different on the circumference. As a result, when a portion that easily flows on the circumference of the charging roller opposes the defective portion of the photosensitive member, a large current flows into the defective portion as described above, causing a voltage drop and a belt-like abnormal image.
Therefore, in this embodiment, the easiness of current flow in each part of the circumference of the charging roller is measured, and whether or not the charging roller is likely to generate a belt-like abnormal image is evaluated based on the measurement result. . This will be specifically described below.

  FIG. 7 is a cross-sectional view of a measuring device 30 that measures the ease of current flow, which is a characteristic value of the charging roller 12. As shown in FIG. 7, the charging roller 12 is rotatably supported and is in contact with the roller-shaped metal electrode 31. The metal electrode 31 is rotatably supported and grounded. The metal electrode 31 is rotated in the direction of arrow R1 in the figure by a motor (not shown). The charging roller 12 is rotated at the same speed as the metal electrode 31 in the direction of the arrow R2 in the figure by the rotation of the metal electrode 31. The rotation speed of the metal electrode is set to 47 to 120 [mm / s]. If it exceeds 120 [mm / s], the load on the motor increases and the motor may be damaged. On the other hand, if it is less than 47 [mm / s], a large current flows in a constant place for a long period of time, so that the charging roller may be deteriorated. On the other hand, if it is less than 47 [mm / s], a current flows for a long time in a portion where the current flows in the charging roller, so that the electric charge corresponding to the electric capacity of the charging roller is accumulated, and the electric capacity component of the charging roller is affected. This is because it does not appear effectively in the measurement result.

  A grounded external power source 32 is electrically connected to the charging roller 12, and a DC bias is applied from the power source 32 to the charging roller 12. In the circuit, a current waveform measuring device 33 such as an oscilloscope is provided, and the current waveform flowing through the rotating charging roller 12 during bias application is measured. In the current waveform measuring device 33, the period of the current waveform appears according to the rotation period of the charging roller 12. Therefore, the current value is measured for at least one cycle of the current waveform (one rotation of the charging roller 12). Then, an average value of the current values measured for one cycle or more is calculated, and it is evaluated from the average value of the current values whether the charging roller is likely to generate a belt-like abnormal image. In addition, the dynamic resistance may be calculated from the average value of the current, and it may be evaluated whether or not the charging roller is likely to generate a belt-like abnormal image from the dynamic resistance.

  Next, with respect to nine charging rollers (No. 1 to No. 9) made of the same material and manufacturing method using the measuring device 30 of FIG. 7, the relationship between the average value I of the current values and the applied voltage V and The relationship between the dynamic resistance value R and the applied voltage V was examined. The results are shown in FIGS. At this time, the measurement environment was a temperature of 20 [° C.] and a humidity of 45 [RH%].

As shown in FIG. 8 and FIG. 9, it can be seen that there is variation in the ease of current flow and the dynamic resistance value even with charging rollers formed of the same material and manufacturing method. And No. 1, no. 2, no. 5, no. 6, no. No belt-like abnormal image was produced for the 8-electric roller. 3, no. 4, no. 7, no. For the charging roller No. 9, a belt-like abnormal image was generated. From this result and the relationship between the average value of the current value and the applied voltage shown in FIG. 8, the boundary value indicating whether or not the charging roller is likely to cause an abnormal image can be expressed as follows.

The right side of Equation 1 is a curve indicated by line A in FIG. 8, and the relationship between current value I and voltage value V is higher than this line A (I = 3.1 × 10 ⁻¹⁰ × V ^2.4 ). When there is a defective portion of the photosensitive member, current exceeding the allowable capacity of the power source flows through the defective portion, the voltage drops, and a belt-like abnormal image is generated. On the other hand, in the charging roller in which the relationship between the current value I and the voltage value V is below the line A, even if there is a defective portion of the photosensitive member, current exceeding the allowable capacity of the power source does not flow into the defective portion. . As a result, no voltage drop occurs and no band-like abnormal image occurs. Further, if the relationship between the current value I and the voltage value V is less than the curve (I = 5.0 × 10 ⁻¹¹ × V ^2.4 ) shown by the line B in FIG. 8, the resistance of the charging roller becomes too high. As a result, the surface of the photoconductor could not be sufficiently charged, and the background of the image was stained. In other words, when the value of the current flowing through the charging roller is within the range of the following expression, the surface of the photoreceptor can be sufficiently charged without causing a band-like abnormal image.

In Equation 2, the boundary value is set with respect to the current value I flowing through the charging roller, but when set with respect to the dynamic resistance value R of the charging roller, the following is obtained.

The curve indicated by the dotted line A in FIG. 9 is the lower limit value (R = 3.2 × 10 ⁹ × V ^−1.4 ) of the dynamic resistance, and the relationship between the dynamic resistance value R and the voltage value V is this dotted line. In the charging roller below A, when there is a defective portion of the photoreceptor, a current exceeding the allowable capacity of the power source flows through the defective portion, the voltage drops, and a belt-like abnormal image is generated. Is. On the other hand, in the charging roller in which the relationship between the current value I and the voltage value V is above the dotted line A, a current exceeding the allowable capacity of the power source does not flow to the defective portion. As a result, no voltage drop occurs and no band-like abnormal image occurs. A charging roller in which the relationship between the dynamic resistance value R and the voltage value V exceeds the curve (R = 2.0 × 10 ¹⁰ × V ^−1.4 ) indicated by the dotted line B in FIG. Becomes too high, the surface of the photoconductor cannot be sufficiently charged, and the background of the image is stained. Accordingly, when the dynamic resistance value R flowing through the charging roller is within the range of the above formula, the surface of the photoreceptor can be sufficiently charged without causing a band-like abnormal image.

  Next, a verification test was conducted to determine whether the above formula could be applied even if the material of the charging roller was changed and the material changed. The charging roller used for the verification test will be described below.

[Charging roller A]
The charging roller A is prepared as follows. An ion conductive polymer compound (IRGASTAT P18, Ciba Specialty) containing a polyether ester amide component in 100 parts by weight of ABS resin (GR-0500, manufactured by Denki Kagaku Kogyo) on a core metal made of stainless steel having a diameter of 8 [mm]. A composition containing 60 parts by weight of Chemicals) was coated by injection molding to form a resistance layer. The volume resistivity of the resistance layer was 1 × 10 ⁶ [Ωcm]. Next, a resin composition composed of an acrylic silicon resin (3000 VH-P, manufactured by Kawakami Paint Co., Ltd.), an isocyanate curing agent, and tin oxide (60% by weight based on the total solid content) is applied to the surface, and about By forming a surface layer having a thickness of 10 μm, a charging roller A having a diameter of 12 mm was obtained.

[Charging roller B]
The charging roller B is produced as follows. A rubber layer composed of 100 parts by weight of epichlorohydrin rubber (Epichromer CG, manufactured by Daiso Corporation) and 4 parts by weight of ammonium perchlorate is coated on a metal core made of stainless steel having a diameter of 8 [mm] by injection molding to form a coating layer. This was vulcanized to form a resistance layer. Next, on the surface of the resistance layer, a resin composition comprising a polyvinyl butyral resin (Denkabutyral 3000-K, manufactured by Denki Kagaku Kogyo Co., Ltd.), an isocyanate curing agent and tin oxide (60% by weight with respect to the total solid content). The charging roller B having a diameter of 12 [mm] was obtained by coating to form a surface layer having a thickness of about 10 μm.

[Charging roller C]
The charging roller C is produced as follows. An ion conductive polymer compound (IRGASTAT P18, Ciba Specialty) containing a polyether ester amide component in 100 parts by weight of ABS resin (GR-0500, manufactured by Denki Kagaku Kogyo) on a core metal made of stainless steel having a diameter of 8 [mm]. A composition containing 80 parts by weight of Chemicals (volume resistance 1 × 10 6 Ωcm) was coated by injection molding to form a resistance layer. Next, a resin composition composed of an acrylic silicon resin (3000 VH-P, manufactured by Kawakami Paint Co., Ltd.), an isocyanate curing agent, and tin oxide (60% by weight based on the total solid content) is applied to the surface, and about By forming a surface layer having a thickness of 10 [μm], a charging roller C having a diameter of 12 [mm] was obtained.

[Charging roller D]
The charging roller D is produced as follows. An ion conductive polymer compound (IRGASTAT P18, Ciba) containing a polyetheresteramide component in 100 parts by weight of ABS resin (GR-0500, manufactured by Denki Kagaku Kogyo) on a metal core made of stainless steel having a diameter of 8 [mm]. A composition containing 10 parts by weight of Specialty Chemicals) was coated by injection molding to form a resistance layer. The volume resistivity of the resistance layer at this time was (volume resistance 1 × 10 ⁶ [Ωcm]). Next, a resin composition composed of an acrylic silicon resin (3000 VH-P, manufactured by Kawakami Paint Co., Ltd.), an isocyanate curing agent, and tin oxide (60% by weight based on the total solid content) is applied to the surface, and about By forming a protective layer having a thickness of 10 [μm], a charging roller D having a diameter of 12 [mm] was obtained.

[Charging roller E]
The charging roller E is produced as follows. 10 parts by weight of conductive carbon black (manufactured by Ketjen Black EC, Ketjen Black International Co., Ltd.), 100 parts by weight of ABS resin (GR-0500, manufactured by Denki Kagaku Kogyo Co., Ltd.) The composition containing was coated by injection molding to form a resistance layer. Next, a resin composition composed of polyamide resin (Daiamide T-171, manufactured by Daicel Huls) and carbon black (10% by weight with respect to the total solid content) was applied to the surface, and a thickness of about 10 [μm] was applied. By forming the surface layer, a charging roller E having a diameter of 12 [mm] was obtained.

[Measurement of dynamic resistance]
Next, measurement of the dynamic resistance value R in this verification test will be described. As a device for measuring the dynamic resistance value R, a photoreceptor unit that integrally supports a photoreceptor and a charging roller of a Ricoh printer Ipsio Color 8150 (direct transfer type full-color printer) is used. The above-prepared charging rollers A to E were mounted as charging rollers of this printer, and an aluminum base tube having a diameter of 30 mm serving as a base of a photoreceptor used in the printer was mounted as the metal electrode 1. The arrangement relationship between the metal electrode and the charging roller is basically the same as in FIG. 3, but in this measurement, no spacer is provided on the charging roller, and the surface layer 8 of the charging roller 2 is brought into contact with the metal electrode 1 by the compression spring 20. Yes. When the metal electrode 1 is rotated by the motor, the charging member 2 rotates with the metal electrode 1 and rotates at a substantially constant speed. The motor was driven by rotating a metal electrode having a diameter of 30 [mm] at a speed of 30 rpm (47.1 [mm / s]). Further, an oscilloscope (Tektronix TDS-3012B) was used as a current waveform measuring device. A direct current voltage was applied from an external power source, and the dynamic resistance value (voltage / current) was measured from the average value of the current flowing for two cycles of the rotating charging roller. Measurement was performed at two points of applied voltage -350 and -500 (V).

[Image Evaluation]
The image was evaluated as follows. One of the charging rollers A to E and a photoconductor with a pinhole formed therein were mounted on a modified Ricoh printer Ipsio Color 8150, and 5,000 continuous images were output and image evaluation was performed. When outputting an image, a standard printer spacer is attached to the charging roller, and the proximity charging method is adopted. The photoconductor with the pinhole opened is pressed against the photoconductor for the printer with a conical indenter with a tip angle of 60 ° with a load of 95 g by a micro hardness tester (3M-2 manufactured by Taiyo Tester). A pinhole was created. The charging method was an AC / DC superposition method, and the charging conditions were a peak-to-peak voltage: 2.0 kV, a frequency: 1.35 kHz, and a DC component voltage: −800 [V]. The measurement environment was set to temperature: 20 [° C.] and humidity: 45 [% RH].
The image was evaluated by visual comparison with an evaluation sample. Evaluation items are abnormal images and image quality. The image quality was evaluated in four stages: “4: no problem”, “3: almost no problem”, “2: a little problem”, and “1: a problem”.

The results are shown below.

In addition, the lower limit value of the dynamic resistance R at −350 [V] obtained from the above formula 3 is 9.6 × 10 ⁵ [Ω], and the upper limit value is 5.48 × 10 ⁶ [Ω]. It is. Further, the lower limit value of the dynamic resistance R at −500 [V] is 5.3 × 10 ⁵ [Ω], and the upper limit value is 3.33 × 10 ⁶ [Ω].

  As can be seen from Table 1, with respect to the charging roller A and the charging roller B that are within the range of both -350 [V] and -500 [V], the band-like image and the background stain of the non-image portion are generated. The image quality was almost satisfactory. On the other hand, in both of −350 [V] and −500 [V], the dynamic resistance value is equal to or lower than the lower limit of Equation 3, and the belt-like abnormal image is generated in the charging roller C and the charging roller E. There was a problem with the image quality. Further, the charging roller D in which both of −350 [V] and −500 [V] exceeded the upper limit of the number 3 caused the soiling of the non-image area, resulting in a problem in image quality.

  Thus, even if there is a difference in the blending amount and material of the resistance layer, if the dynamic resistance value R is in the range of the above formula 3, a belt-like abnormal image or non-image portion ground stains may occur. It can be seen that a charging roller having no toner can be provided.

(1)
As described above, according to the charging device of this embodiment, it is accurately determined whether or not the charging roller is easy to flow a current so that an excessive current flows so that a power source limit is applied to a defective portion of the photosensitive member as a member to be charged. Can be evaluated.
(2)
Further, when the current value I flowing through the charging roller is I ≦ 3.1 × 10 ⁻¹⁰ × V ^2.4 , the charging roller is evaluated as a non-defective product. As a result, if a charging roller evaluated as a non-defective product is incorporated in the apparatus, an excessive current will not flow to the extent that the power source limit is applied to the defective portion of the photoreceptor.
(3)
Further, when the current value I flowing through the charging roller is I ≧ 5.0 × 10 ⁻¹¹ × V ^2.4 , the charging roller is evaluated as a non-defective product. Thus, if a charging roller evaluated as a good product is incorporated into the apparatus, the surface of the member to be charged can be charged satisfactorily.
(4)
When the dynamic resistance value R calculated from the current value I flowing through the charging roller is R ≧ 3.2 × 10 ⁹ × V− ^1.4 , the charging member is evaluated as a non-defective product. If the charging roller evaluated as a non-defective product is incorporated in the apparatus, an excessive current will not flow to the extent that the power source limit is applied to the defective portion of the photoreceptor.
(5)
When the dynamic resistance value R calculated from the current value I flowing through the charging roller is R ≦ 2.0 × 10 ¹⁰ × V− ^1.4 , the charging roller is evaluated as a non-defective product. If the charging roller evaluated as a good product is incorporated in the apparatus, the surface of the member to be charged can be charged satisfactorily.
(6)
The rotation speed of the charging roller is 47 [mm / s] or more. If the rotation speed of the charging roller is 47 [mm / s] or less, an excessive current will flow on the surface of the charging roller in contact with the electrode member for a long period of time, and the charging roller may be damaged. If the rotation speed of the charging roller is set to 47 [mm / s] or less, electric charge corresponding to the electric capacity is accumulated in the current measuring portion of the charging roller, and it becomes impossible to detect the ease of current flow including the electric capacity. End up. By setting it as 47 [mm / s] or more, it is possible to suppress an excessive current from flowing on the surface of the charging roller in contact with the electrode member for a long period of time, and to prevent the charging roller from being damaged. Further, the charge accumulated in the charging roller flows to the electrode, and it is possible to detect the ease of current flow including the electric capacity.
(7)
Further, by using a charging roller having a current value I flowing through the charging roller of 5.0 × 10 ⁻¹¹ × V ^2.4 ≦ I ≦ 3.1 × 10 ⁻¹⁰ × V ^2.4 , defects in the photoconductor Excessive current does not flow so that the limit of the power supply works on the part. As a result, a drop in the voltage value of the power source is suppressed, and the surface of the photoreceptor can be charged satisfactorily.
(8)
In addition, a charging roller having a dynamic resistance value calculated from the current value flowing through the charging roller of 3.2 × 10 ⁹ × V ^−1.4 ≦ R ≦ 2.0 × 10 ¹⁰ × V ^−1.4 is used. Thus, an excessive current does not flow to the extent that the power source limit acts on the defective portion of the photoreceptor. As a result, a drop in the voltage value of the power source is suppressed, and the surface of the photoreceptor can be charged satisfactorily.
(9)
In addition, since the charging device according to the present embodiment uses the charging roller (7) or (8), the photosensitive member can be charged satisfactorily.
(10)
Further, according to the charging device of the present embodiment, since a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging roller, gap fluctuations, charging rollers, and photoconductors are compared with those that apply only a DC voltage. Even if there is some variation in resistance, a stable discharge amount can be obtained and the surface of the photoreceptor can be uniformly charged.
(11)
In addition, since the peak-to-peak voltage of the AC voltage applied to the charging roller is set to be twice or more the charging start voltage of the photosensitive member, a discharge from the photosensitive member to the charging roller 12, that is, a reverse discharge occurs, and Even if the resistance becomes nonuniform, the smoothing effect of the AC voltage works well, and the photoreceptor can be uniformly charged more stably.
(12)
In addition, since a spacer is provided as a gap forming member and a gap is formed between the charging roller and the photosensitive member, it is possible to suppress foreign matter adhering to the surface of the charged body from adhering to the charging roller. In addition, the discharge generation material does not stay, the adhesion of the discharge generation material to the surface of the photoreceptor can be suppressed, and the image flow can be suppressed.
(13)
Further, by setting the gap between the charging roller and the photosensitive member to 1 to 100 [μm], it is possible to reduce the amount of discharge products adhering to the image carrier, It is possible to prevent the occurrence of image flow.
(14)
In addition, since the gap between the charging roller and the photosensitive member is made larger than the toner particle size, it is possible to suppress the toner from adhering to the charging roller and to suppress the deterioration of the charging performance.
(15)
In addition, by providing a cleaning member for cleaning the surface of the charging roller, the charging roller can be prevented from being contaminated with foreign matters such as toner and paper powder, and the charging performance can be maintained for a long time.
(16)
In addition, by making the cleaning member into a blade shape, the surface of the charging roller can be satisfactorily removed.
(17)
Further, even if the cleaning member has a brush shape, the surface of the charging roller can be satisfactorily removed.
(18)
Furthermore, even if the cleaning member is formed in a roller shape, the surface of the charging roller can be satisfactorily removed.
(19)
Moreover, favorable cleaning performance can be maintained by using a roller-shaped cleaning member as a melamine resin foam.
(20)
In addition, by making the roller-shaped and brush-shaped cleaning member rotatable, foreign matter removed from the charging roller can be uniformly attached to the outer peripheral surface of the cleaning member. Accordingly, the cleaning performance can be maintained for a long period of time as compared with the case where the cleaning member is fixedly fixed and only a specific portion of the cleaning member is always in contact with the charging roller.
(21)
The charging roller includes a conductive substrate, a resistance layer on the outer periphery of the substrate, and a surface layer on the outer periphery of the resistance layer. The surface layer has a base material and a conductive agent dispersed in the base material. is doing. As a result, even when the environment becomes a low humidity environment or a high humidity environment, the electron conductive surface layer 16b prevents moisture from entering and exiting the inside of the charging roller, so that the resistance fluctuation of the charging roller 12 can be suppressed. As a result, even if the environment changes, the fluctuation of the charged potential on the surface of the photoreceptor can be reduced, and the discharge stability can be improved.
(22)
Further, when the resistance of the surface layer 16b is low, the surface resistivity of the surface layer 16b is lowered, a current path is formed also on the surface of the charging roller, and current flows in the axial direction of the charging roller 12, thereby discharging energy into the gap. There is a risk that it will not be uniform. As a result, discharge concentration occurs, and streamer discharge may occur. By making the volume resistivity of the surface layer 8 higher than the volume resistivity of the resistance layer 16a, it is possible to prevent the formation of a current path in the surface direction of the charging roller 12, uniform discharge, and occurrence of abnormal discharge. Can be prevented.
(23)
In addition, since the image forming apparatus of the present embodiment uses the charging device having the feature points shown in the above (9) to (22), even if there is a defective portion on the surface of the photoreceptor, a belt-like abnormal image is generated. It does not occur.
(24)
Further, since the photoconductor has a surface layer containing a filler, the surface hardness is increased, the wear resistance is improved, and the life of the photoconductor can be greatly extended.
(25)
In addition, the charging device and the photosensitive member are provided in a process cartridge that is integrated and detachable from the main body. Thus, the process cartridge can be detached from the apparatus main body while the gap between the photosensitive member and the charging roller is maintained. Therefore, since the gap with the charging roller photoconductor does not change by attaching or detaching the process cartridge, it is possible to suppress problems such as an increase in the gap and an increase in discharge products.
(26)
Further, since the cleaning device having a contact member that contacts the photosensitive member is also provided in the process cartridge, the charging device and the photosensitive member can be attached and detached together, and the size of the minute gap G greatly varies. We can prevent trouble.
(27)
A color image can be obtained by providing a plurality of photoconductors, forming toner images of different colors on each of the photoconductors, and sequentially superimposing the toner images of different colors on the transfer body.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus. Sectional drawing of a charging roller. The figure which showed the charging roller and the photoreceptor. The figure which shows the example which made the spacer member the cap shape. FIG. 3 is a diagram illustrating a process cartridge in which a charging device, a cleaning device, an auxiliary cleaning device, and a photoconductor are integrated. FIG. 2 is a main part configuration diagram of a color image forming apparatus. The figure which shows a measuring apparatus. The figure which shows the relationship between an applied voltage and a measurement current. The figure which shows the relationship between an applied voltage and dynamic resistance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 5 Charging device 9 Auxiliary cleaning device 10 Cleaning device 12 Charging roller 13 Cleaning member

Claims (27)

  A roller-shaped charging member that charges the member to be charged is brought into contact with the metal electrode, and the charging member is rotated and a voltage is applied to the charging member. The charging member evaluation method characterized by performing. In the charging member evaluation method according to claim 1,
When the current value I flowing through the charging member and the voltage applied to the charging member are V, the current value I is I ≦ 3.1 × 10 ⁻¹⁰ × V ^2.4.
When this is the case, the charging member is evaluated as a non-defective product. In the charging member evaluation method according to claim 2,
The current value I flowing through the charging member is I ≧ 5.0 × 10 ⁻¹¹ × V ^2.4.
The charging member is evaluated as a non-defective product. In the charging member evaluation method according to claim 1,
The relationship between the current value I flowing through the charging member, the dynamic resistance value R calculated from the voltage applied to the charging member V, and the voltage applied to the charging member V is R ≧ 3.2 ×. 10 ⁹ × V ^-1.4
When this is the case, the charging member is evaluated as a non-defective product. In the charging member evaluation method according to claim 4,
The dynamic resistance value R is R ≦ 2.0 × 10 ¹⁰ × V ^−1.4
When this is the case, the charging member is evaluated as a non-defective product. In the charging member evaluation method according to any one of claims 1 to 5,
A charging member evaluation method, wherein a rotation speed of the charging member is 47 [mm / s] or more. In the roller-shaped charging member that discharges to the surface of the member to be charged and charges the surface of the member to be charged,
When the charging member is brought into contact with the metal electrode, the charging member is rotated, and a voltage is applied to the charging member. The current value flowing through the charging member at that time is I, and the voltage applied to the charging member is V. The current value I is 5.0 × 10 ⁻¹¹ × V ^2.4 ≦ I ≦ 3.1 × 10 ⁻¹⁰ × V ^2.4
A charging member characterized by being configured as follows. In the roller-shaped charging member that discharges to the surface of the member to be charged and charges the surface of the member to be charged,
The charging member is brought into contact with the metal electrode, the charging member is rotated, and a voltage is applied to the charging member. At that time, a dynamic resistance value R calculated from a current value flowing through the charging member is applied to the charging member. When the voltage is V, the dynamic resistance value R is 3.2 × 10 ⁹ × V ^−1.4 ≦ R ≦ 2.0 × 10 ¹⁰ × V ^−1.4
A charging member characterized by being configured as follows. A charging device comprising a charging member disposed opposite to an image carrier, and discharging the charging member to charge the image carrying surface;
A charging device using the charging member according to claim 7 or 8 as the charging member. The charging device according to claim 9, wherein
A charging device, wherein a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging member. The charging device according to claim 10.
A charging device characterized in that the peak-to-peak voltage of the AC voltage applied to the charging member is set to be twice or more the charging start voltage of the image carrier. The charging device according to any one of claims 9 to 11,
A charging device comprising a gap forming member for forming a gap between the charging member and the image carrier. The charging device according to claim 12, wherein
A charging device, wherein a gap between the charging member and the image carrier is 1 to 100 [μm]. The charging device according to claim 12 or 13,
A charging device, wherein a gap between the charging member and the image carrier is larger than a toner particle size. The charging device according to any one of claims 9 to 14,
A charging device comprising a cleaning member for cleaning the surface of the charging member. The charging device according to claim 15, wherein
A charging device, wherein the cleaning member has a blade shape. The charging device according to claim 15, wherein
A charging device, wherein the cleaning member has a brush shape. The charging device according to claim 15, wherein
A charging device, wherein the cleaning member has a roller shape. The charging device of claim 18, wherein
A charging device, wherein the cleaning member is a melamine resin foam. The charging device according to any one of claims 17 to 19,
A charging device, wherein the cleaning member is rotatably supported. The charging device according to any one of claims 9 to 20,
The charging member includes a conductive substrate, a resistance layer on the outer periphery of the substrate, and a surface layer on the outer periphery of the resistance layer, and the surface layer is a base material and a conductive agent dispersed in the base material. And a charging device. The charging device of claim 21, wherein
The charging device according to claim 1, wherein the volume resistivity of the surface layer is set higher than the volume resistivity of the resistance layer. In an image forming apparatus comprising an image carrier and a charging device for charging the image carrier,
An image forming apparatus using the charging device according to claim 9 as the charging device. 24. The image forming apparatus according to claim 23.
An image forming apparatus, wherein the image carrier has a surface layer containing a filler. The image forming apparatus according to claim 23 or 24.
An image forming apparatus, wherein the charging device and the image carrier are provided in a process cartridge configured integrally and detachably with respect to the main body. The image forming apparatus according to claim 25.
An image forming apparatus comprising: a cleaning device for cleaning transfer residual toner adhering to the image carrier in the process cartridge. 27. The image forming apparatus according to claim 26.
An image formation comprising: a plurality of the image carriers, and forming a color image on each of the plurality of image carriers, and sequentially superimposing the different color toner images on a transfer member. apparatus.

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