JP2023056470A - Image forming apparatus - Google Patents

Abstract

To suppress ununiformity in electrification, while suppressing generation of corona products due to discharge and a change in quality of the surface of a photoconductor drum in an electrification configuration for directly injecting electric charges to the surface of the photoconductor drum.SOLUTION: An image forming apparatus has: an electrification brush that electrifies a surface of a photoconductor drum in a first electrifying unit that is in contact with a support and the surface of the photoconductor drum having a surface layer on its surface; a developing member that supplies developer to the surface of the photoconductor drum in an opposite part opposite to the surface of the photoconductor drum; and an electrifying roller that, in the direction of rotation of the photoconductor drum, electrifies the surface of the photoconductor drum electrified by the electrifying brush on a downstream of the first electrifying unit and on an upstream of the opposite part. A surface of the photoconductor drum has a volume resistivity of 1.0×109 Ω cm or more and 1.0×1014 Ω cm. The control unit performs control so that a second potential difference formed between the electrifying roller and the surface of the photoconductor drum electrified by the electrifying brush becomes equal to or more than a discharge start voltage.SELECTED DRAWING: Figure 1

Description

The present invention relates to image forming apparatuses such as laser printers, copiers, facsimiles, etc. that use an electrophotographic recording method.

2. Description of the Related Art Conventionally, in an electrophotographic or electrostatic recording image forming apparatus, a corona charger has been used as a charging means for a photosensitive drum such as an electrophotographic photosensitive member or an electrostatic recording dielectric. In recent years, due to advantages such as low ozone and low power consumption, a contact charging type apparatus has been put into practical use, in which a charging member to which a voltage is applied is brought into contact with the photosensitive drum to charge the photosensitive drum.

In particular, a roller charging system using a charging roller as a charging member is preferably used from the viewpoint of charging stability. In a roller charging type contact charging device, an elastic roller having medium resistance as a charging member is brought into pressure contact with a photosensitive drum, and a voltage is applied to the roller to charge the photosensitive drum. Specifically, since charging is performed by discharging from the charging member to the photosensitive drum, charging is started by applying a voltage equal to or higher than a certain threshold voltage according to Paschen's law.

As an example, when charging is performed by pressing a charging roller against an OPC photoreceptor having a photosensitive layer with a thickness of 25 μm as a photosensitive drum, as shown in FIG. When a voltage of about 550 V or more is applied to the photoreceptor, the surface potential of the photoreceptor begins to rise. After that, the surface potential of the photosensitive member increases linearly with a slope of 1 with respect to the applied voltage. Hereinafter, this threshold voltage is defined as the charging start voltage Vth.

That is, in order to obtain the dark area potential Vd, which is the surface potential of the photosensitive member required for electrophotography, the charging roller requires a direct current (DC) voltage of Vd+Vth or higher. A contact charging method in which only a DC voltage is applied to the contact charging member to charge the photosensitive drum is called a "contact DC charging method."

Compared to the corona charging method, the contact DC charging method can reduce discharge products including ozone. discharge products are generated. In addition, the discharge phenomenon causes deterioration of the surface of the photosensitive drum. The surface of the photosensitive drum, which is affected by the discharge product or changed in properties, has a low resistance, especially in a high-temperature, high-humidity environment. is sometimes difficult.

In order to solve this problem, it is common to scrape off the discharge products and the altered surface of the photosensitive drum at the same time by continuing printing while gradually scraping the surface of the photosensitive drum and the altered surface of the photosensitive drum. used for Specifically, the surface of the photosensitive drum is scraped off by a cleaning blade for cleaning the developer remaining on the surface of the photosensitive drum arranged in contact with the photosensitive drum, a charging member, or a developing roller. However, in recent years, the life of the photosensitive drum has become longer, and it has become difficult to continue scraping the surface of the photosensitive drum throughout the life.

For this reason, Japanese Patent Laid-Open No. 2002-300000 discloses a charging method that does not involve a discharge phenomenon as a countermeasure against deterioration of the discharge product and the surface of the photosensitive drum that does not depend on scraping of the surface of the photosensitive drum. Japanese Unexamined Patent Application Publication No. 2002-100003 proposes a method of providing a charge injection layer on the outermost surface of a photosensitive drum and charging the photosensitive drum by directly injecting charges from a charging brush.

In this configuration, unlike conventional charging using discharge, the charging member directly contacts the photosensitive drum in an ohmic manner and charges are injected, thereby suppressing the generation of discharge products and deterioration of the surface of the photosensitive drum due to discharge. be able to.

JP-A-7-5748

However, Patent Document 1 has the following problems. In the configuration disclosed in Patent Document 1, only the portion where the charging member and the photosensitive drum are in direct contact can be charged. It has to come into contact with the drum. In addition, the number of contact points is increased by rotating the photosensitive drum in the opposite direction at twice the speed. As a result, charging failure due to scratches on the surface of the photosensitive drum, peeling of the conductive coating of the charging brush of the charging brush roller, or developer remaining on the photosensitive drum without being transferred adheres to the charging brush roller. In some cases, the charge injection was insufficient.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress non-uniform charging while suppressing generation of discharge products due to discharge and deterioration of the surface of the photosensitive drum in a charging configuration in which charges are directly injected into the surface of the photosensitive drum. .

As described above, the present invention provides a rotatable photosensitive drum, the photosensitive drum having a support and a surface layer on the surface thereof, a first charging portion being in contact with the surface of the photosensitive drum, and the first a first charging member that charges the surface of the photosensitive drum in a charging portion; a developing member that supplies developer to the surface of the photosensitive drum in a facing portion facing the surface of the photosensitive drum; and rotation of the photosensitive drum. In the direction, the surface of the photosensitive drum charged by the first charging member in the second charging section facing the surface of the photosensitive drum downstream of the first charging section and upstream of the facing section. a second charging member that charges; a first charging voltage applying section that applies a first charging voltage to the first charging member; and a second charging member that applies a second charging voltage to the second charging member. and a control section for controlling the first charging voltage applying section and the second charging voltage applying section, wherein the volume resistivity of the surface layer of the photosensitive drum is 1.5. 0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less, and the controller controls the surface of the photosensitive drum charged by the first charging member and the second charging member. The second charging voltage applied to the second charging voltage applying section is controlled such that the second potential difference formed between the two is equal to or higher than the discharge start voltage.

As described above, according to the present invention, in a charging configuration in which charges are directly injected into the surface of a photosensitive drum, generation of discharge products due to discharge and deterioration of the surface of the photosensitive drum are suppressed, and non-uniform charging is suppressed. can do.

1 is a schematic cross-sectional view of an image forming apparatus and a process cartridge in Example 1. FIG. 1 is a schematic diagram of a layer structure of a photosensitive drum in Example 1. FIG. 4 is a control block diagram in Embodiment 1. FIG. 4 is another configuration example of the first charging member in Example 1. FIG. FIG. 4 is an explanatory diagram of a discharge start voltage for forming a surface potential of a photosensitive drum in Example 1; FIG. 4 is an explanatory diagram of a discharge start voltage for forming a surface potential of a photosensitive drum in Example 1; 3 is a configuration example in which a cleaning member for cleaning the photosensitive drum in Example 1 is added. FIG. 10 is another configuration example of the photosensitive drum and the developing member in Example 2. FIG. FIG. 11 is another configuration example of the charging roller in Example 3. FIG. FIG. 11 is a relational diagram of longitudinal widths of constituent members in Example 4; 1 is a STEM image showing an example of niobium-containing titanium oxide used in Examples. It is a schematic diagram showing an example of niobium-containing titanium oxide used in Examples.

BEST MODE FOR CARRYING OUT THE INVENTION A mode for carrying out the present invention will be exemplarily described in detail below based on an embodiment with reference to the drawings. However, the dimensions, materials, shapes and relative arrangement of the components described in this embodiment should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

1. 1. Image Forming Apparatus FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus 1 according to the first embodiment. The image forming apparatus 1 is a monochrome printer that forms an image on a recording material based on image information input from an external device. Recording materials include paper such as plain paper and thick paper, plastic films such as sheets for overhead projectors, special-shaped sheets such as envelopes and index paper, and various sheet materials of different materials such as cloth.

The image forming apparatus 1 has an image forming section 10 for forming a toner image on a recording material P, as shown in FIG. Further, it has a feeding section 60 that feeds the recording material P to the image forming section 10, a fixing section 70 that fixes the toner image formed by the image forming section 10 onto the recording material P, and a discharge roller pair 80. are doing.

The image forming section 10 has a scanner unit 11, an electrophotographic process cartridge 20, and a transfer roller 12 for transferring the toner image formed on the photosensitive drum 21 of the process cartridge 20 onto the recording material P. . A detailed view of the process cartridge 20 is shown in FIG. 1(b). The process cartridge 20 has a photosensitive drum 21 and a developing device 30 including a charging brush 22 arranged around the photosensitive drum 21 , a charging roller 23 , a pre-exposure device 24 and a developing roller 31 .

The photosensitive drum 21 is a cylindrical photosensitive member, and has a charge injection function on its outermost surface. A photosensitive drum 21 as an image bearing member is rotationally driven in a predetermined direction (clockwise direction in FIG. 1B) at a predetermined process speed by a motor (not shown).

The image forming apparatus of this embodiment has a printing speed of 30 sheets per minute when A4 size paper is continuously fed, and the peripheral surface of the photosensitive drum 21 rotates at 170 mm/sec.

The charging brush 22 and the charging roller 23 contact the photosensitive drum 21 with a predetermined pressing force, and two charging high voltage power supplies (first charging voltage applying section E4 and second charging voltage applying section E1) output different voltages. to apply a desired charging voltage. Here, the first charging voltage applying section E4 is a brush voltage applying section (brush power supply) that applies the first charging voltage to the charging brush 22, and the second charging voltage applying section E1 applies the second charging voltage to the charging roller 23. is a roller voltage applying section (charging power supply) that applies a charging voltage of . By applying a voltage to them, the surface of the photosensitive drum 21 is uniformly charged to a predetermined potential. In this embodiment, the photosensitive drum 21 is negatively charged by the charging brush 22 and the charging roller 23 . The pre-exposure device 24 removes the surface potential of the photosensitive drum 21 before it enters the charging section for stable charging by the charging brush 22 and charging roller 23 . In this embodiment, the charging brush 22 charges the photosensitive drum 21 mainly by direct charge injection, and the charging roller 23 charges the photosensitive drum 21 mainly by discharging.

The charging of the photosensitive drum 21 by the charging brush 22 and the charging roller 23 will be described later.

The scanner unit 11 serving as an exposure unit scans and exposes the surface of the photosensitive drum 21 by irradiating the photosensitive drum 21 with laser light L corresponding to image information input from an external device using a polygon mirror. By this exposure, an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 21 . Note that the scanner unit 11 is not limited to a laser scanner device, and for example, an LED exposure device having an LED array in which a plurality of LEDs are arranged along the longitudinal direction of the photosensitive drum 21 may be employed.

Next, the process cartridge 20 will be explained. The process cartridge 20 shown in detail in FIG. 1B has a developing device 30 . The developing device 30 includes a developing roller 31 as a developer carrying member that carries developer, a developing container 32 as a frame of the developing device 30 , and a supply roller 33 capable of supplying developer to the developing roller 31 . I have. The developing roller 31 and the supply roller 33 are rotatably supported by the developer container 32 . Further, the developing roller 31 is arranged at the opening of the developing container 32 so as to face the photosensitive drum 21 . The supply roller 33 is rotatably in contact with the development roller 31 , and the toner as the developer contained in the development container 32 is applied to the surface of the development roller 31 by the supply roller 33 .

The developing device 30 of this embodiment uses a contact developing method as a developing method. That is, the toner layer carried on the developing roller 31 contacts the photosensitive drum 21 in a developing portion (developing area) where the photosensitive drum 21 and the developing roller 31 face each other. A development voltage is applied to the development roller 31 by a development high-voltage power supply E2, which is a development voltage application section. Under the condition that the developing voltage is applied, the toner carried by the developing roller 31 is transferred from the developing roller 31 to the surface of the photosensitive drum 21 according to the potential distribution on the surface of the photosensitive drum 21, so that the electrostatic latent image is transformed into a toner image. developed into an image. In this example, the development voltage was -350V. Note that this embodiment employs a reversal development method. That is, after the surface of the photosensitive drum 21 is charged in the charging process, the surface of the photosensitive drum 21 is exposed in the exposure process, and the toner adheres to the exposed area, which is the surface of the photosensitive drum 21 whose charge amount is attenuated. A toner image is formed.

Further, in this embodiment, toner having a particle size of 6 μm and a normal charging polarity of negative polarity is used. As an example of the toner, a polymerized toner produced by a polymerization method is used. The toner is a so-called non-magnetic one-component developer that does not contain a magnetic component and is carried on the developing roller 31 mainly by an intermolecular force or an electrostatic force (mirror image force).

The toner particles contain multiple waxes to adjust the toner's melting properties during the fusing process and its adhesion to the print medium and fusing roller.

On the surfaces of the toner particles, fine particles made of silica particles having a particle size of submicron order are added for adjusting the fluidity and charging performance of the toner. In this embodiment, the developer is defined as a toner to which fine particles are added.

Although a non-magnetic one-component developer is used as an example in this embodiment, a one-component developer containing a magnetic component may also be used. Alternatively, a two-component developer composed of a non-magnetic toner and a magnetic carrier may be used as the developer. When a developer having magnetism is used, for example, a cylindrical developing sleeve having a magnet arranged inside is used as the developer carrier.

A stirring member 34 as a stirring means is provided inside the developer container 32 . The agitating member 34 is driven and rotated to agitate the toner in the developing container 32 and send the toner toward the developing roller 31 and the supply roller 33 . Further, the stirring member 34 has a role of circulating the toner stripped from the developing roller 31 that is not used for development in the developing container and uniformizing the toner in the developing container.

A developing blade 35 made of a stainless steel plate for regulating the amount of toner carried on the developing roller 31 is arranged at the opening of the developing container 32 where the developing roller 31 is arranged. A voltage whose absolute value is 200 V greater than that of the developing roller 31 is applied to the developing blade 35 from a blade power supply as the developing blade applying section E5. That is, the voltage applied to the developing blade 35 is 200 V higher than the normal polarity of the toner.

The developer supplied to the surface of the developing roller 31 passes through the portion facing the developing blade 35 as the developing roller 31 rotates, and is uniformly formed into a thin layer. At the same time, the toner is directly charged by frictional charging with the developing blade 35 and the potential difference provided between the developing blade 35 and the developing roller 31, and is charged to the negative polarity that is the normal polarity of the toner.

The feeding section 60 has a front door 61 supported by the image forming apparatus 1 so as to be opened and closed, a stacking tray 62 , an intermediate plate 63 , a tray spring 64 , and a pickup roller 65 . The stacking tray 62 constitutes the bottom surface of the storage space for the recording material P that appears when the front door 61 is opened. The tray spring 64 urges the intermediate plate 63 upward to press the recording material P stacked on the intermediate plate 63 against the pickup roller 65 . The front door 61 closes the storage space for the recording material P when closed with respect to the image forming apparatus 1 . Support material P.

The fixing unit 70 is of a thermal fixing type that heats and melts the toner on the recording material to fix the image. The fixing unit 70 includes a fixing film 71 , a fixing heater such as a ceramic heater that heats the fixing film 71 , a thermistor that measures the temperature of the fixing heater, and a pressure roller 72 that presses the fixing film 71 .

In this embodiment, the process cartridge 20 is detachably attachable to the main body of the image forming apparatus. For example, a configuration that does not use a developing cartridge to which the developing device 30 is detachable, a drum cartridge to which the drum unit is detachable, a toner cartridge that externally supplies toner to the developing device 30, or a detachable cartridge may be used.

2. Control Mode FIG. 3 is a schematic block diagram showing a control mode of the main part of the image forming apparatus 1 of this embodiment. A control unit 150 is provided in the image forming apparatus 1 . The control unit 150 includes a CPU 151 as arithmetic control means which is a central element for arithmetic processing, a memory (storage element) 152 such as a ROM and a RAM as a storage means, and various elements connected to the control unit 150. It has an input/output unit (not shown) for controlling transmission and reception of signals. The RAM stores sensor detection results, calculation results, and the like, and the ROM stores control programs, pre-determined data tables, and the like.

The control unit 150 is a control unit that controls the operation of the image forming apparatus 1 in an integrated manner. The control unit 150 controls transmission and reception of various electrical information signals, driving timing, and the like, and executes a predetermined image forming sequence. Each unit of the image forming apparatus 100 is connected to the control unit 150 . For example, in relation to this embodiment, the control unit 150 includes a charging power source E1 as a second charging power source, a developing power source E2, a transfer power source E3, a brush power source E4 as a first charging power source, a blade power source E5, an exposure unit 11, Drive motor 110, pre-exposure device 24, etc. are connected.

3. Image Forming Operation Next, the image forming operation of the image forming apparatus 1 will be described. When an image forming command is input to the image forming apparatus 1 , the image forming process by the image forming section 10 is started based on image information input from an external computer connected to the image forming apparatus 1 . The scanner unit 11 irradiates the photosensitive drum 21 with laser light L based on the input image information. At this time, the photosensitive drum 21 is charged in advance by the charging brush 22 and the charging roller 23 , and an electrostatic latent image is formed on the photosensitive drum 21 by being irradiated with the laser light L. FIG. After that, the electrostatic latent image is developed by the developing roller 31 to form a toner image on the photosensitive drum 21 .

In parallel with the image forming process described above, the pickup roller 65 of the feeding section 60 feeds out the recording material P supported by the front door 61 , the stacking tray 62 and the intermediate plate 63 . The recording material P is fed to the registration roller pair 15 by the pickup roller 65 and hits the nip of the registration roller pair 15 to correct the skew. The registration roller pair 15 is driven in synchronization with the transfer timing of the toner image, and conveys the recording material P toward the transfer nip formed by the transfer roller 12 and the photosensitive drum 21 .

A transfer voltage is applied to the transfer roller 12 as transfer means from a transfer high-voltage power supply E3, and the toner image carried on the photosensitive drum 21 is transferred onto the recording material P conveyed by the registration roller pair 15. FIG. The recording material P to which the toner image has been transferred is conveyed to the fixing section 70, and the toner image is heated and pressed when passing through the nip portion between the fixing film 71 and the pressure roller 72 of the fixing section 70. . As a result, the toner particles are melted and then fixed, whereby the toner image is fixed on the recording material P. As shown in FIG. After passing through the fixing section 70 , the recording material P is discharged outside the image forming apparatus 1 by a discharge roller pair 80 and stacked on a discharge tray 81 .

The ejection tray 81 is inclined upward toward the downstream side in the ejection direction of the recording material, and the trailing edge of the recording material ejected to the ejection tray 81 is aligned by the regulation surface 82 by sliding down the ejection tray 81 . be.

4. Photosensitive Drum Details of the photosensitive drum 21 used in this embodiment will be described below with reference to FIG. 2 as an example.

The photosensitive drum 21 according to the present invention has a charge injection function on the outermost surface.

The photosensitive drum 21 according to the present invention comprises a conductive support 21a, a conductive layer 21b, an undercoat layer 21c, a photosensitive layer comprising two layers of a charge generation layer 21d and a charge transport layer 21e, and a charge injection layer 21f. have The charge injection layer 21f contains conductive particles 21g, and the content of the conductive particles 21g is 5.0% by volume or more and 70.0% by volume or less with respect to the total area of the charge injection layer 21f. Furthermore, the volume resistivity of the charge injection layer 21f is 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less.

If the resistance is less than 1.0×10 ⁹ Ω·cm, the resistance of the charge injection layer 21f is too low to properly form an electrostatic latent image, making it difficult to develop a desired image. On the other hand, if it exceeds 1.0×10 ¹⁴ Ω·cm, the resistance of the charge injection layer 21f is too high, and the charge injection property from the charging brush 22 to the charge injection layer 21f, which is a feature of the present invention, is lowered. It becomes difficult to obtain the discharge suppressing effect of the charging roller 23, which will be described later. A more preferable volume resistivity of the charge injection layer 21f is 1.0×10 ¹¹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less.

In order to satisfy this volume resistivity range, the content of the conductive particles 21g is desirably 5.0% by volume or more and 70.0% by volume or less with respect to the total area of the charge injection layer 21f.

If the content of the conductive particles 21g exceeds 70.0% by volume, the charge injection layer 21f itself becomes brittle, and the surface of the photosensitive drum 21 is likely to be scraped through long-term use. As a result, the charging uniformity of the photosensitive drum 21 is lowered, and image defects tend to occur due to charging defects that occur when the speed is increased. A more preferable content of the conductive particles 21g is 5.0% by volume or more and 40.0% by volume or less.

The volume resistivity of the charge injection layer 21f can be controlled by, for example, the particle size of the conductive particles 21g in addition to the content of the conductive particles 21g. The volume average particle diameter of the conductive particles 21g is preferably 5 nm or more and 300 nm or less, more preferably 40 nm or more and 250 nm or less. When the number average particle diameter of the conductive particles 21g is less than 5 nm, the specific surface area of the conductive particles 21g increases, and moisture adsorption increases in the vicinity of the conductive particles 21g on the surface of the charge injection layer 21f. The volume resistivity of 21f tends to decrease. If the number average particle diameter of the conductive particles 21g exceeds 300 nm, the dispersion of the particles in the charge injection layer 21f is deteriorated and the area of the interface with the binder resin is reduced, resulting in an increase in the resistance at the interface and the charge injection performance. tend to get worse.

Examples of the conductive particles 21g contained in the charge injection layer 21f include metal oxide particles such as titanium oxide, zinc oxide, tin oxide, and indium oxide. When a metal oxide is used as the conductive particles 21g, the metal oxide may be doped with an element such as niobium, phosphorus, or aluminum, or an oxide thereof. Also, the conductive particles 21g may have a layered structure in which the particles are coated with the particles. Particles include titanium oxide, barium sulfate, zinc oxide, and the like. Examples of the coating material include metal oxides such as titanium oxide and tin oxide. In the present invention, titanium oxide is preferable from the viewpoint of charge injection from the charging brush 22 .

Furthermore, when the titanium oxide contains niobium, the charge injection property becomes better, and the charge injection property can be improved with a small amount. A preferable niobium content is preferably 0.5% by mass or more and 15.0% by mass or less, more preferably 2.6% by mass or more and 10.0% by mass, based on the total mass of the niobium-containing titanium oxide particles. It is below.

The niobium-containing titanium oxide particles are preferably anatase-type or rutile-type titanium oxide particles, and more preferably anatase-type titanium oxide particles. By using anatase-type titanium oxide, charge transfer in the charge injection layer 21f is facilitated, so charge injection is improved. More preferred are particles having anatase-type titanium oxide particles and a coating material of titanium oxide containing niobium in the vicinity of the surface. By using the anatase titanium oxide particles containing niobium in the vicinity of the surface, it becomes easier for charges to move in the charge injection layer 21f, and at the same time, the charge injection from the charging brush 22 to the charge injection layer 21f can be enhanced. . Moreover, it is possible to suppress a decrease in the volume resistivity of the charge injection layer 21f. This improves the maintainability of the electrostatic latent image in a high-temperature and high-humidity environment. The anatase-type titanium oxide preferably has a degree of anatase of 90% or more. The metal oxide particles may be doped with atoms such as niobium, phosphorus, aluminum, and oxides thereof, and particularly preferably titanium oxide particles containing niobium and having niobium unevenly distributed near the particle surface. is. The uneven distribution of niobium in the vicinity of the surface enables efficient transfer of charge. More specifically, with respect to the concentration ratio calculated as "niobium atom concentration/titanium atom concentration" at the center of the particle, "niobium atom concentration/titanium Titanium oxide particles having a concentration ratio calculated as "atomic concentration" of 2.0 times or more. The niobium atomic concentration and titanium atomic concentration are obtained by a scanning transmission electron microscope (STEM) connected to an EDS analyzer (energy dispersive X-ray analyzer). FIG. 11 shows an STEM image of an example of the niobium-containing titanium oxide particles used in the examples of the present invention. Although the details will be described later, the niobium-containing titanium oxide particles used in the present examples are produced by coating titanium oxide particles with niobium-containing titanium oxide and then firing the coated titanium oxide particles. Therefore, it is considered that the coated niobium-containing titanium oxide undergoes crystal growth as niobium-doped titanium oxide by so-called anaphylactic growth along the titanium oxide crystals of the particles before coating. The niobium-containing titanium oxide thus produced has a lower density in the vicinity of the surface than that in the center of the particle, and is controlled to have a core-shell-like shape.

A STEM image of FIG. 11 is schematically shown in FIG. In FIG. 12, 41 is the center of the conductive particles, 42 is near the surface of the conductive particles, 43 is the X-ray for analyzing the center of the conductive particles, and 44 is 5% of the primary particle diameter from the surface of the conductive particles. 1 shows an X-ray analyzing the interior.

In such niobium-containing titanium oxide particles, the niobium/titanium atomic concentration ratio in the vicinity of the particle surface is higher than the niobium/titanium atomic concentration ratio in the center of the particle, and the niobium atoms are unevenly distributed in the vicinity of the particle surface. Specifically, the niobium/titanium atomic concentration ratio within 5% of the maximum diameter of the grain from the surface of the grain is at least 2.0 times the niobium/titanium atomic concentration ratio in the central portion of the grain. When the ratio is 2.0 times or more, charges can easily move in the charge injection layer, and the charge injection property can be improved. If it is less than 2.0 times, it becomes difficult to transfer electric charges.

A detailed manufacturing method of the charge injection layer 21f will be described later.

The configuration of the electrophotographic photoreceptor according to the present invention will be described in detail below.

<Support 21a>
In the electrophotographic photoreceptor according to the present invention, the support 21a is preferably an electrically conductive support. Further, the shape of the support 21a includes a cylindrical shape, a belt shape, a sheet shape, and the like. Among them, a cylindrical support is preferable. Further, the surface of the support 21a may be subjected to an electrochemical treatment such as anodization, blasting, cutting, or the like. As the material of the support 21a, metal, resin, glass, or the like is preferable. Examples of metals include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among them, an aluminum support using aluminum is preferable. In addition, it is preferable to impart conductivity to the resin or glass by treatment such as mixing or coating with a conductive material.

<Conductive Layer 21b>
In the electrophotographic photoreceptor according to the present invention, a conductive layer 21b may be provided on the support 21a. By providing the conductive layer 21b, scratches and irregularities on the surface of the support can be covered, and reflection of light on the surface of the support can be controlled. The conductive layer 21b preferably contains conductive particles and resin. Materials for the conductive particles include metal oxides, metals, and carbon black.

Metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, and bismuth oxide. Metals include aluminum, nickel, iron, nichrome, copper, zinc, silver and the like.

Among these, metal oxides are preferably used as the conductive particles, and titanium oxide, tin oxide, and zinc oxide are particularly preferably used.

When a metal oxide is used as the conductive particles, the surface of the metal oxide may be treated with a silane coupling agent or the like, or the metal oxide may be doped with an element such as phosphorus or aluminum or an oxide thereof.

Also, the conductive particles may have a layered structure including particles and a coating material that coats the particles. Examples of the particles include titanium oxide, barium sulfate, and zinc oxide. Coating materials include metal oxides such as tin oxide.

When metal oxides are used as the conductive particles, the volume average particle diameter is preferably 1 nm or more and 500 nm or less, more preferably 3 nm or more and 400 nm or less.

Examples of resins include polyester resins, polycarbonate resins, polyvinyl acetal resins, acrylic resins, silicone resins, epoxy resins, melamine resins, polyurethane resins, phenol resins, and alkyd resins. In addition, the conductive layer 21b may further contain silicone oil, resin particles, masking agents such as titanium oxide, and the like.

The conductive layer 21b can be formed by preparing a conductive layer coating liquid containing each of the above materials and a solvent, forming this coating film on the support 21a, and drying it. Solvents used in the coating liquid include alcohol solvents, sulfoxide solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents and the like. Examples of the dispersion method for dispersing the conductive particles in the conductive layer coating liquid include methods using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

The average film thickness of the conductive layer 21b is preferably 1 μm or more and 40 μm or less, and particularly preferably 3 μm or more and 30 μm or less.

<Undercoat layer 21c>
In the electrophotographic photoreceptor according to the present invention, an undercoat layer 21c may be provided on the support 21a or the conductive layer 21b. By providing the undercoat layer 21c, the adhesion function between the layers is enhanced, and the charge injection blocking function can be imparted.

The undercoat layer 21c preferably contains a resin. Alternatively, the undercoat layer 21c may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group.

Examples of resins include polyester resins, polycarbonate resins, polyvinyl acetal resins, acrylic resins, epoxy resins, melamine resins, polyurethane resins, phenol resins, polyvinyl phenol resins, alkyd resins, polyvinyl alcohol resins, polyethylene oxide resins, polypropylene oxide resins, and polyamide resins. , polyamic acid resins, polyimide resins, polyamideimide resins, cellulose resins, and the like.

The polymerizable functional group possessed by the monomer having a polymerizable functional group includes an isocyanate group, a blocked isocyanate group, a methylol group, an alkylated methylol group, an epoxy group, a metal alkoxide group, a hydroxyl group, an amino group, a carboxyl group, a thiol group, Carboxylic anhydride groups, carbon-carbon double bond groups, and the like.

In addition, the undercoat layer 21c may further contain an electron transporting substance, metal oxide, metal, conductive polymer, etc. for the purpose of enhancing electrical properties. Among these, electron transport substances and metal oxides are preferably used.

Examples of electron-transporting substances include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, halogenated aryl compounds, silole compounds, and boron-containing compounds. . The undercoat layer 21c may be formed as a cured film by using an electron transporting substance having a polymerizable functional group as the electron transporting substance and copolymerizing it with the above-mentioned monomer having a polymerizable functional group.

Metal oxides include indium tin oxide, tin oxide, indium oxide, titanium oxide, zinc oxide, aluminum oxide, and silicon dioxide. Metals include gold, silver, and aluminum.

The metal oxide particles contained in the undercoat layer 21c may be subjected to surface treatment using a surface treatment agent such as a silane coupling agent.

A common method is used for the surface treatment of the metal oxide particles. Examples include dry methods and wet methods.

In the dry method, an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent was added while stirring the metal oxide particles in a mixer capable of high-speed stirring such as a Henschel mixer, and the particles were uniformly dispersed. Drying is performed later.

In the wet method, the metal oxide particles and the surface treatment agent are stirred in a solvent or dispersed in a sand mill using glass beads or the like. After dispersion, the solvent can be removed by filtration or distillation under reduced pressure. done. After removing the solvent, baking is preferably performed at 100° C. or higher.

The undercoat layer 21c may further contain additives such as metal powders such as aluminum, conductive substances such as carbon black, charge transport substances, metal chelate compounds, organometallic compounds, and other known materials. can be contained.

Examples of charge-transporting substances include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, halogenated aryl compounds, silole compounds, and boron-containing compounds. . The undercoat layer 21c may be formed as a cured film by using a charge-transporting substance having a polymerizable functional group as the charge-transporting substance and copolymerizing it with the above monomer having a polymerizable functional group.

The undercoat layer 21c is formed by preparing a coating liquid for the undercoat layer 21c containing each of the above materials and a solvent, forming this coating film on the support 21a or the conductive layer 21b, and drying and/or curing it. can be formed.

Solvents used in the coating liquid for the undercoat layer 21c include organic solvents such as alcohols, sulfoxides, ketones, ethers, esters, aliphatic halogenated hydrocarbons, and aromatic compounds. In the present invention, it is preferable to use an alcohol-based or ketone-based solvent.

Dispersion methods for preparing the coating liquid for the undercoat layer 21c include methods using a homogenizer, an ultrasonic disperser, a ball mill, a sand mill, a roll mill, a vibration mill, an attritor, and a liquid collision high-speed disperser.

<Photosensitive layer>
The photosensitive layer of the electrophotographic photoreceptor is mainly classified into (1) laminated photosensitive layer and (2) single layer photosensitive layer. (1) The laminated photosensitive layer is a photosensitive layer having a charge generating layer 21d containing a charge generating substance and a charge transporting layer 21e containing a charge transporting substance. (2) The single-layer type photosensitive layer is a photosensitive layer containing both a charge-generating substance and a charge-transporting substance.

(1) Laminated Photosensitive Layer The laminated photosensitive layer has a charge generation layer 21d and a charge transport layer 21e.

(1-1) Charge generation layer 21d
The charge generation layer 21d preferably contains a charge generation substance and a resin.

Examples of charge-generating substances include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among the phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred.

The content of the charge-generating substance in the charge-generating layer 21d is preferably 40% by mass or more and 85% by mass or less, more preferably 60% by mass or more and 80% by mass or less, with respect to the total mass of the charge-generating layer 21d. is more preferred.

Resins include polyester resins, polycarbonate resins, polyvinyl acetal resins, polyvinyl butyral resins, acrylic resins, silicone resins, epoxy resins, melamine resins, polyurethane resins, phenol resins, polyvinyl alcohol resins, cellulose resins, polystyrene resins, and polyvinyl acetate resins. , polyvinyl chloride resin, and the like. Among these, polyvinyl butyral resin is more preferable.

The charge generation layer 21d may further contain additives such as antioxidants and ultraviolet absorbers. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, and the like.

The charge generation layer 21d can be formed by preparing a coating liquid for the charge generation layer 21d containing each of the above materials and a solvent, forming this coating film on the undercoat layer 21c, and drying it. Solvents used in the coating liquid include alcohol solvents, sulfoxide solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents and the like.

The average film thickness of the charge generation layer 21d is preferably 0.1 μm or more and 1 μm or less, more preferably 0.15 μm or more and 0.4 μm or less.

(1-2) Charge transport layer 21e
The charge transport layer 21e preferably contains a charge transport substance and a resin.

Examples of charge-transporting substances include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these substances. . Among these, triarylamine compounds and benzidine compounds are preferred.

The content of the charge transport substance in the charge transport layer 21e is preferably 25% by mass or more and 70% by mass or less, and is 30% by mass or more and 55% by mass or less with respect to the total mass of the charge transport layer 21e. is more preferred.

Examples of resins include polyester resins, polycarbonate resins, acrylic resins, and polystyrene resins. Among these, polycarbonate resins and polyester resins are preferred. A polyarylate resin is particularly preferable as the polyester resin.

The content ratio (mass ratio) of the charge transport substance and the resin is preferably 4:10 to 20:10, more preferably 5:10 to 12:10.

Also, the charge transport layer 21e may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipperiness agents, and abrasion resistance improvers. Specifically, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, boron nitride particles. etc.

The charge-transporting layer 21e can be formed by preparing a coating liquid for the charge-transporting layer 21e containing the above materials and solvent, forming this coating film on the charge-generating layer 21d, and drying it. Solvents used in the coating liquid include alcohol solvents, ketone solvents, ether solvents, ester solvents, and aromatic hydrocarbon solvents. Among these solvents, ether solvents and aromatic hydrocarbon solvents are preferred.

The average film thickness of the charge transport layer 21e is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

(2) Single-layer type photosensitive layer A single-layer type photosensitive layer is formed by preparing a photosensitive layer coating liquid containing a charge generating substance, a charge transporting substance, a resin and a solvent, and forming this coating film on the undercoat layer 21c. , can be formed by drying. The charge-generating substance, charge-transporting substance, and resin are the same as those exemplified in the above “(1) Laminated photosensitive layer”.

<Charge injection layer 21f>
The charge injection layer 21f may contain a polymer of a compound having a polymerizable functional group and a resin.

Examples of polymerizable functional groups include isocyanate groups, blocked isocyanate groups, methylol groups, alkylated methylol groups, epoxy groups, metal alkoxide groups, hydroxyl groups, amino groups, carboxyl groups, thiol groups, carboxylic acid anhydride groups, carbon-carbon double bond groups, alkoxysilyl groups, silanol groups, and the like. A monomer having charge transport ability may be used as the compound having a polymerizable functional group.

Examples of resins include polyester resins, acrylic resins, phenoxy resins, polycarbonate resins, polystyrene resins, phenol resins, melamine resins, and epoxy resins. Among them, acrylic resin is preferable.

The material and particle size of the conductive particles contained in the charge injection layer 21f are as described above. From the viewpoint of dispersibility and liquid stability, it is preferable to treat the surface of the metal oxide with a silane coupling agent or the like.

The charge injection layer 21f may contain additives such as an antioxidant, an ultraviolet absorber, a plasticizer, a leveling agent, a slipping agent, and an abrasion resistance improver. Specifically, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, boron nitride particles. etc.

The charge injection layer 21f can be formed by preparing a coating liquid for the charge injection layer 21f containing each of the above materials and a solvent, forming this coating film on the photosensitive layer, and drying and/or curing it. . Solvents used in the coating liquid include alcohol solvents, ketone solvents, ether solvents, sulfoxide solvents, ester solvents, and aromatic hydrocarbon solvents.

The average film thickness of the charge injection layer 21f is preferably 0.2 μm or more and 5 μm or less, more preferably 0.5 μm or more and 3 μm or less.

In this embodiment, an organic photosensitive drum having an organic photosensitive layer is shown as an example. For example, an inorganic photosensitive drum using amorphous silicon as a photosensitive member, or a material in which a charge generating material and a charge transporting material are mixed. It is also possible to use a single-layer drum as described above coated with

A method for measuring the charge injection layer and the conductive particles of the photosensitive drum according to the present invention will be described below.

<Calculation of primary particle size of conductive particles>
First, the entire photosensitive drum was immersed in methyl ethyl ketone (MEK) in a graduated cylinder and irradiated with ultrasonic waves to peel off the resin layer, and then the substrate of the photosensitive drum was taken out. Next, the insoluble matter not dissolved in MEK (the photosensitive layer and the charge injection layer containing conductive particles) was filtered and dried in a vacuum dryer. Furthermore, the obtained solid was suspended in a mixed solvent of tetrahydrofuran (THF)/methylal at a volume ratio of 1:1, and after insoluble matter was filtered off, the filtrate was collected and dried in a vacuum dryer. By this operation, the conductive particles and the resin of the charge injection layer were obtained. Furthermore, the filter cake was heated to 500° C. in an electric furnace so that only the conductive particles were solid, and the conductive particles were recovered. In order to secure the necessary amount of conductive particles for measurement, a plurality of photosensitive drums were subjected to the same treatment.

Part of the collected conductive particles is dispersed in isopropanol (IPA), the dispersion is dropped on a grid mesh with a support film (manufactured by JEOL Ltd., Cu150J), and a scanning transmission electron microscope (JEOL, JEM2800). Observation of the conductive particles was performed in the STEM mode. Observation was performed at a magnification of 500,000 to 1,200,000 times to facilitate calculation of the particle size of the conductive particles, and STEM images of 100 conductive particles were taken. At this time, the acceleration voltage was set to 200 kV, the probe size to 1 nm, and the image size to 1024×1024 pixels. Using the obtained STEM image, the primary particle size was measured with image processing software "Image-Pro Plus (manufactured by Media Cybernetics)". First, using the straight line tool (Straight Line) on the toolbar, select the scale bar displayed at the bottom of the STEM image. If Set Scale is selected from the Analyze menu in that state, a new window opens and the pixel distance of the selected straight line is entered in the Distance in Pixels column. Enter a scale bar value (eg, 100) in the Known Distance column of the window, enter a scale bar unit (eg, nm) in the Unit of Measurement column, and click OK to complete scale setting. Next, using a straight line tool, a straight line was drawn so as to have the maximum diameter of the conductive particles, and the particle diameter was calculated. The same operation was performed for 100 conductive particles, and the number average value of the obtained values (maximum diameter) was taken as the primary particle size of the conductive particles.

<Calculation of niobium atom/titanium atom concentration ratio>
A sample piece of 5 mm square was cut out from the photoreceptor, and cut to a thickness of 200 nm with an ultrasonic ultramicrotome (UC7, Leica) at a cutting speed of 0.6 mm/s to prepare a thin sample. This thin section sample was observed in the STEM mode of a scanning transmission electron microscope (JEOL, JEM2800) connected to an EDS analyzer (energy dispersive X-ray analyzer) at a magnification of 500,000 to 1,200,000 times. gone.

Among the cross sections of the conductive particles observed, a cross section of the conductive particles having a maximum diameter of approximately 0.9 to 1.1 times the primary particle diameter calculated above was selected visually. Subsequently, the spectrum of the constituent elements of the cross section of the selected conductive particles was collected using an EDS analyzer to prepare an EDS mapping image. Spectral collection and analysis were performed using NSS (Thermo Fischer Scientific). The acquisition conditions were an acceleration voltage of 200 kV, a probe size of 1.0 nm or 1.5 nm so that the dead time was between 15 and 30, a mapping resolution of 256×256, and a frame number of 300. EDS mapping images were obtained for 100 cross sections of the conductive particles.

By analyzing the EDS mapping image obtained in this way, the niobium atomic concentration (atomic %) and the titanium atomic concentration (atomic %) in the center of the particle and inside 5% of the maximum diameter of the measured particle from the particle surface Calculate the ratio. Specifically, first, press the NSS "Line extraction" button, draw a straight line so that it becomes the maximum diameter of the particle, and the atomic concentration on the straight line from one surface to the other surface through the inside of the particle (atomic %) information is obtained. If the maximum diameter of the particles obtained at this time was in the range of less than 0.9 times or more than 1.1 times the primary particle diameter calculated above, it was excluded from further analysis. (The following analysis was performed only for particles having a maximum diameter in the range of 0.9 times or more and less than 1.1 times the primary particle diameter.) Read the niobium atomic concentration (atomic %) inside 5% of the maximum diameter. Similarly, the "titanium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface" is obtained. Then, using these values, the "concentration ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured grain from the grain surface" on the grain surfaces on both sides is obtained from the following formula.
Concentration ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface =
(Niobium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface) / (Titanium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface)

Of the two concentration ratios obtained, the smaller one is adopted as the "concentration ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particles from the particle surface" in the present invention.

Further, the niobium atomic concentration (atomic %) and the titanium atomic concentration (atomic %) at the midpoint of the maximum diameter on the straight line are read. Using these values, the "concentration ratio of niobium atoms and titanium atoms in the grain center" is obtained from the following formula.
Concentration ratio of niobium atoms and titanium atoms in the grain center =
(Niobium atomic concentration in the center of the grain (atomic %)) / (Titanium atomic concentration in the central part of the grain (atomic %))

In addition, "concentration ratio calculated by niobium atomic concentration/titanium atomic concentration in 5% of the maximum diameter of the measured particle from the particle surface to the concentration ratio calculated by niobium atomic concentration/titanium atomic concentration in the center of the particle ” is calculated by the following formula.

(concentration ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface)/(concentration ratio of niobium atoms and titanium atoms at the center of the particle)

<Calculation of content of conductive particles>
Next, four sample pieces of 5 mm square were cut out from the photoreceptor, and the charge injection layer was three-dimensionalized to 2 μm×2 μm×2 μm by Slice & View of FIB-SEM. From the difference in FIB-SEM Slice & View contrast, the content of the conductive particles in the total area of the charge injection layer was calculated. The conditions for Slice & View were as follows.
Sample processing for analysis: FIB method Processing and observation device: NVision 40 manufactured by SII/Zeiss
Slice interval: 10 nm
Observation conditions:
Accelerating voltage: 1.0 kV
Sample tilt: 54°
WD: 5mm
Detector: BSE detector Aperture: 60 μm, high current
ABC: ON
Image resolution: 1.25 nm/pixel

The analysis area is 2 μm long×2 μm wide, and the information for each section is integrated to obtain the volume V per 2 μm long×2 μm wide×2 μm thick (8 μm 3 ). The measurement environment is temperature: 23° C., pressure: 1×10 −4 Pa. As a processing and observation device, Strata 400S manufactured by FEI (specimen tilt: 52°) can also be used. Information on each cross section was obtained by image analysis of the area of the specified conductive particles of the present invention. Image analysis was performed using image processing software: Image-Pro Plus manufactured by Media Cybernetics.

Based on the obtained information, in each of the four sample pieces, the volume V of the conductive particles of the present invention in a volume of 2 μm × 2 μm × 2 μm (unit volume: 8 μm) was determined, and the content of the conductive particles [ volume %] (=Vμm3/8μm3×100) was calculated. The average value of the content values of the conductive particles in the four sample pieces was taken as the content [% by volume] of the conductive particles of the present invention in the charge injection layer with respect to the total volume of the charge injection layer.

At this time, all four sample pieces were processed up to the boundary between the charge injection layer and the lower layer to measure the thickness t (cm) of the charge injection layer, and the following <Volume resistance of the charge injection layer of the photoreceptor Method of Measuring Ratio>, the value of the film thickness of the charge injection layer was used to calculate the volume resistivity ρs.

<Method for Measuring Volume Resistivity of Charge Injection Layer>
A pA (picoampere) meter was used to measure the volume resistivity of the present invention.

First, a comb-shaped gold electrode shown in FIG. 4 having an inter-electrode distance (D) of 180 μm and a length (L) of 59 mm was formed on a PET film by vapor deposition, and a charge injection layer having a thickness (T1) of 2 μm was formed thereon. prepare. Next, the DC voltage (I) when a DC voltage (V) of 100 V was applied between the comb-shaped electrodes under the conditions of temperature 23° C./humidity 50% RH and temperature 32.5° C./humidity 80% RH. was measured, and the volume resistivity ρv (Ω·cm) was obtained by the following formula (1).
Volume resistivity ρv (Ω cm) = V (V) × T1 (cm) × L (cm) / {I (A) × D (cm)} (1)

If it is difficult to identify the composition of the conductive particles and binder resin of the charge injection layer, the surface resistivity of the surface of the photosensitive drum is measured and converted into volume resistivity. When measuring the volume resistivity of the charge injection layer coated on the surface of the photoreceptor instead of the charge injection layer alone, measure the surface resistivity of the charge injection layer and convert it to volume resistivity. It is desirable to

In the present invention, the inter-electrode distance (D) of 180 μm and the length (L) of 59 mm shown in FIG. Next, in an environment of temperature 23° C./humidity 50% RH, a DC voltage (I) of 1000 V was applied between the comb-shaped electrodes, and the DC voltage (I) was measured. The surface resistivity ρs of the charge injection layer was calculated from the DC voltage (I).

Furthermore, using the film thickness t (cm) of the charge injection layer measured in <Analysis of Cross Section of Charge Injection Layer of Photosensitive Drum>, the volume resistivity ρv (Ω·cm) was calculated by the following formula (2). .
ρv=ρs×t (2)
(ρv: volume resistivity, ρs: surface resistivity, t: thickness of charge injection layer)

In this measurement, since a very small amount of current is measured, it is preferable to use a device capable of measuring a very small current as the resistance measuring device. For example, picoammeter 4140B manufactured by Hewlett-Packard and the like can be used. It is desirable to select the comb-shaped electrode to be used and the voltage to be applied so that an appropriate SN ratio can be obtained depending on the material and resistance value of the charge injection layer.

<Production Example of Electrophotographic Photoreceptor>
(Titanium oxide production example)
The anatase-type titanium oxide particles, which are the conductive particles according to the present invention, can be produced by a known sulfuric acid method. That is, it is obtained by heating and hydrolyzing a solution containing titanium sulfate and titanyl sulfate to prepare a hydrous titanium dioxide slurry, and then dehydrating and calcining the titanium dioxide slurry.

(Production example of anatase-type titanium oxide particles 1)
The anatase-type titanium oxide of the present invention preferably has a degree of anatase of 90 to 100%. By the above method, anatase-type titanium oxide having a degree of anatase of approximately 100% can be produced. Further, the charge injection layer 21f according to the present invention containing anatase type titanium oxide containing niobium within this range achieves good and stable rectification, and satisfactorily achieves the above-described effects of the present invention. .

Here, the degree of anatase is obtained by measuring the intensity IA of the strongest interference line of anatase (plane index 101) and the intensity IR of the strongest interference line of rutile (plane index 110) in powder X-ray diffraction of titanium oxide, It is a value calculated by the following formula.

Degree of anatase (%) = 100/(1 + 1.265 x IR/IA)
In order to produce a degree of anatase in the range of 90 to 100%, in the production of titanium oxide, a solution containing titanium sulfate and titanyl sulfate as titanium compounds is heated and hydrolyzed to produce anatase with a degree of anatase of almost 100%. type titanium oxide is obtained. Further, if an aqueous solution of titanium tetrachloride is neutralized with an alkali, an anatase-type titanium oxide having a high degree of anatase conversion can be obtained.

In the present invention, the anatase-type titanium oxide particles 1 can be produced by controlling the solution concentration of titanyl sulfate.

<Production of conductive particles>
(Production of conductive particles 1)
100 g of titanium oxide particles 1 were dispersed in water and heated to 60° C. to form a 1 L aqueous suspension. This was mixed with a niobium solution obtained by dissolving 3 g of niobium pentachloride (NbCl ₅ ) in 100 mL of 11.4 mol/L hydrochloric acid, and 600 mL of a titanium sulfate solution containing 33.7 g of titanium as titanium niobate solution ( Mass ratio of niobium and titanium is 1.0/33.7) and 10.7 mol/L sodium hydroxide aqueous solution are added dropwise simultaneously over 3 hours so that the pH of the suspension becomes 2 to 3 ( parallel addition). After completion of dropping, the suspension was filtered, washed and dried at 110° C. for 8 hours. The dried product was subjected to heat treatment (calcination treatment) at 800° C. for 1 hour in an air atmosphere to obtain niobium atom-containing titanium oxide particles 1 in which niobium atoms were unevenly distributed near the surface. Table 1 shows the physical properties of the niobium atom-containing titanium oxide particles 1.

next,
・Niobium-containing titanium oxide particles 1 100.0 parts ・Surface treatment agent 1 (formula (S-1) below) (trade name: KBM-3033, manufactured by Shin-Etsu Chemical Co., Ltd.) 3.0 parts

Toluene 200.0 parts These were mixed, stirred for 4 hours with a stirring device, filtered, washed, and heat-treated at 130° C. for 3 hours to obtain conductive particles 1 . Table 1 shows the physical properties of the conductive particles 1. The niobium atom content in Table 1 is the content of niobium atoms in the conductive particles, and is a value obtained by measurement by an elemental analysis method (XRF) using fluorescent X-rays.

In the table, A is "the concentration ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface", and B is "the concentration ratio of niobium atoms and titanium atoms in the center of the particle. ”.

(Electrophotographic Photoreceptor Production Example 1)
An aluminum cylinder (JIS-A3003, aluminum alloy) having a diameter of 24 mm and a length of 257.5 mm was used as the support 21a (conductive support).

(Manufacturing Example 1 of Conductive Layer 21b)
Next, the following materials were prepared.
・214 parts of titanium oxide (TiO ₂ ) particles (volume average particle diameter 230 nm) coated with oxygen-deficient tin oxide (SnO ₂ ) as metal oxide particles ・Phenolic resin (monomer of phenolic resin) as binding material / Oligomer) (trade name: Pryofen J-325, manufactured by Dainippon Ink and Chemicals, Inc., resin solid content: 60% by mass) 132 parts 1-methoxy-2-propanol 98 parts as a solvent Placed in a sand mill using 450 parts of 0.8 mm glass beads, and subjected to dispersion treatment under the conditions of rotation speed: 2000 rpm, dispersion treatment time: 4.5 hours, cooling water set temperature: 18 ° C. to obtain a dispersion liquid. . The glass beads were removed from this dispersion with a mesh (opening: 150 μm).

Silicone resin particles (trade name: Tospearl 120, manufactured by Momentive Performance Materials Co., Ltd., average particle size: 2 μm) were added to the resulting dispersion as a surface roughening agent. The amount of the silicone resin particles added was set to 10% by mass with respect to the total mass of the metal oxide particles and the binder material in the dispersion after removing the glass beads. In addition, silicone oil (trade name: SH28PA, manufactured by Dow Corning Toray Co., Ltd.) was added as a leveling agent to 0.01% by mass with respect to the total mass of the metal oxide particles and the binder in the dispersion. ) was added to the dispersion.

Next, methanol and A mixed solvent of 1-methoxy-2-propanol (mass ratio 1:1) was added to the dispersion. After that, a coating liquid for the conductive layer 21b was prepared by stirring.

This coating liquid for the conductive layer 21b was dip-coated on the support 21a and heated at 140° C. for 1 hour to form the conductive layer 21b with a thickness of 30 μm.

(Manufacturing Example 1 of Undercoat Layer 21c)
Next, the following materials were prepared.
・3.11 parts of an electron-transporting substance represented by the following formula (E-1) ・6.49 parts of blocked isocyanate (trade name: Duranate SBB-70P, manufactured by Asahi Kasei Chemicals Co., Ltd.) ・Styrene-acrylic resin (trade name: UC-3920, manufactured by Toagosei) 0.4 parts Silica slurry (product name: IPA-ST-UP, manufactured by Nissan Chemical Industries, solid content concentration: 15% by mass, viscosity: 9 mPa s) 1.8 parts of these , 48 parts of 1-butanol and 24 parts of acetone to prepare a coating solution for the undercoat layer 21c. This coating liquid for the undercoat layer 21c was dip-coated on the conductive layer 21b and heated at 170° C. for 30 minutes to form the undercoat layer 21c with a thickness of 0.7 μm.

Next, in a chart obtained by CuKα characteristic X-ray diffraction, 10 parts of crystalline hydroxygallium phthalocyanine having peaks at positions of 7.5° and 28.4° and polyvinyl butyral resin (trade name: S-Lec BX-1, (manufactured by Sekisui Chemical Co., Ltd.) was prepared.

These were added to 200 parts of cyclohexanone and dispersed for 6 hours with a sand mill apparatus using glass beads with a diameter of 0.9 mm. 150 parts of cyclohexanone and 350 parts of ethyl acetate were further added to dilute the mixture to obtain a coating liquid for the charge generating layer 21d.

The resulting coating solution was dip-coated on the undercoat layer 21c and dried at 95° C. for 10 minutes to form a charge generating layer 21d with a thickness of 0.20 μm.

The X-ray diffraction measurement was performed under the following conditions.

[Powder X-ray diffraction measurement]
Measuring machine used: Rigaku Denki Co., Ltd., X-ray diffractometer RINT-TTRII
X-ray tube: Cu
Tube voltage: 50KV
Tube current: 300mA
Scanning method: 2θ/θ scan Scanning speed: 4.0°/min
Sampling interval: 0.02°
Start angle (2θ): 5.0°
Stop angle (2θ): 40.0°
Attachment: Standard Sample Holder Filter: Not Used Incident Monochrome: Used Counter Monochromator: Not Used Divergence Slit: Open Divergence Longitudinal Limiting Slit: 10.00 mm
Scattering slit: Open Receiving slit: Open flat plate Monochromator: Counter used: Scintillation counter

(Production Example 1 of Photosensitive Layer)
Next, the following materials were prepared.
・6 parts of a charge-transporting substance (hole-transporting substance) represented by the following formula (C-1) ・3 parts of a charge-transporting substance (hole-transporting substance) represented by the following formula (C-2) ・3 parts of the following formula ( 1 part of the charge-transporting material (hole-transporting material) represented by C-3) Polycarbonate (trade name: Iupilon Z400, manufactured by Mitsubishi Engineering-Plastics Co., Ltd.) 10 parts The following formula (C-4) and the following formula Polycarbonate resin (C-5) having a copolymer unit (x/y = 0.95/0.05: viscosity average molecular weight = 20000) 0.02 parts of these, 25 parts of ortho-xylene / 25 parts of methyl benzoate / A coating liquid for the charge transport layer 21e was prepared by dissolving in a mixed solvent of 25 parts of dimethoxymethane. This coating liquid for the charge transport layer 21e was dip-coated on the charge generation layer 21d to form a coating film, and the coating film was dried at 120° C. for 30 minutes to form the charge transport layer 21e having a thickness of 12 μm. .

(Manufacturing Example 1 of Charge Injection Layer 21f)
Next, the following materials were prepared.
- 100.0 parts of a compound represented by the following structural formula (O-1) as a binder resin - 66.7 parts of the surface-treated niobium-containing titanium oxide particles as conductive particles 1, and 100 parts of 1-propanol/ It was mixed with a mixed solvent of 100 parts of cyclohexane and stirred for 6 hours with a stirrer. Thus, a coating liquid for the charge injection layer 21f was prepared.

This coating liquid for the charge injection layer 21f was dip-coated on the charge transport layer 21e to form a coating film, and the obtained coating film was dried at 50° C. for 6 minutes. After that, in a nitrogen atmosphere, the coating film was irradiated with an electron beam for 1.6 seconds while rotating the support 21a (body to be irradiated) at a speed of 300 rpm under the conditions of an acceleration voltage of 70 kV and a beam current of 5.0 mA. The dose at the position of the charge injection layer 21f was 15 kGy.

After that, the temperature of the coating film was raised to 117° C. in a nitrogen atmosphere. The oxygen concentration from the electron beam irradiation to the subsequent heat treatment was 10 ppm.

Next, after the coating film was naturally cooled in the atmosphere until the temperature of the coating film reached 25° C., heat treatment was performed for 1 hour under the condition that the temperature of the coating film reached 120° C. to form a charge injection layer 21f having a thickness of 2 μm. . Thus, the electrophotographic photoreceptor 1 was manufactured.

5. Recovery of Transfer Residual Toner This embodiment employs a so-called cleanerless configuration in which transfer residual toner remaining on the photosensitive drum 21 without being transferred to the recording material P is recovered in the developing device 30 and reused. The transfer residual toner is removed in the following steps. The transfer residual toner includes toner that is positively charged, which is opposite to the normal polarity in this embodiment, and toner that is negatively charged but not sufficiently charged. The surface potential of the photosensitive drum 21 after passing through the transfer section is removed to about 0 V by the pre-exposure device 24, and a large charging voltage is applied to the charging brush 22 on the negative side of the surface of the photosensitive drum 21. . As a result, the charge is injected by the charging brush 22 into the positively charged untransferred toner and the toner that does not have a sufficient negative charge. As a result, the transfer residual toner having sufficient negative charge does not adhere to the charging brush 22 and the charging roller 23 and is conveyed as the photosensitive drum 21 rotates. As a result, the charging brush 22 and the charging roller 23 can maintain good charging performance.

Further, in a state where the toner is deteriorated such as at the end of the product life, or when a large amount of high-quality printed images are output, a large amount of transfer residual toner may rush into the charging brush 22 . At this time, the charging brush 22 may not sufficiently charge the transfer residual toner to a negative polarity in time, and the transfer residual toner may temporarily adhere to the charging brush 22 . As a result, direct injection charging from the charging brush 22 to the photosensitive drum 21 cannot be properly performed, which causes streaks in a halftone image as charging failure.

However, in this embodiment, since uniform charging is performed by the charging roller 23 downstream of the charging brush 22, it is possible to continue outputting a good image even if the transfer residual toner temporarily adheres to the charging brush 22. . Since the charging roller 23 performs charging by non-contact discharge according to Paschen's law, even if some residual toner adheres, the uniform charging property is not affected much.

The transfer residual toner adhering to the surface of the photosensitive drum 21 that has passed through the contact portion with the charging brush 22 and the contact portion with the charging roller 23 reaches the developing portion as the photosensitive drum 21 rotates. Here, the behavior of the transfer residual toner reaching the developing portion will be described separately for the exposed portion and the non-exposed portion of the photosensitive drum 21 . In the non-exposed portion of the photosensitive drum 21 , that is, the dark portion potential Vd portion, the surface potential of the photosensitive drum 21 is higher than the developing voltage applied to the developing roller 31 toward the negative side. Therefore, the untransferred toner having a sufficient negative charge moves to the developing roller 31 by the coulomb force of the electric field and is collected in the developing container 32 . Here, the dark potential portion Vd of the photosensitive drum 21 is not limited to the non-exposed portion. good.

The toner collected in the developing container 32 is stirred and dispersed with the toner in the developing container 32 by the stirring member 34, and is carried by the developing roller 31 to be used again in the developing process.

On the other hand, at the exposed portion Vl of the photosensitive drum 21, the surface potential of the photosensitive drum 21 is smaller than the developing voltage applied to the developing roller 31 to the negative side, so the residual toner is transferred from the photosensitive drum 21 to the developing portion at the developing portion. It remains on the surface of the photosensitive drum 21 without being transferred to the roller 31 . The untransferred toner remaining on the surface of the photosensitive drum 21 is carried by the photosensitive drum 21 together with other toner transferred from the developing roller 31 to the exposure portion, moves to the transfer portion, and is transferred to the recording material P at the transfer portion. .

In this embodiment, Vd is -600V and Vl is -100V. As described above, since the development voltage is −350 V, the potential difference between the dark potential portion Vd of the photosensitive drum 21 that has passed through the contact portion with the charging roller 23 and the development voltage (surface potential of the development roller 31) is A certain back contrast was taken as -200V. The development contrast, which is the potential difference between the exposed portion Vl of the photosensitive drum 21 and the development voltage (the surface potential of the development roller 31), was set to -250V.

6. Charging Configuration In this section, the charging of the photosensitive drum 21 by the charging brush 22 and the charging roller 23, which are features of this embodiment, will be described in detail.

The charging brush 22 charges the photosensitive drum 21 mainly by direct injection charging. Since direct injection charging is charging without discharge, no discharge product is generated. However, since only the portion that is in direct contact with the photosensitive drum 21 can be charged, uneven charging will occur if the charging brush 22 is not in uniform contact with the photosensitive drum 21 . The influence of discharge products will be described later.

The charging roller 23 charges the photosensitive drum 21 mainly by discharging. Discharge occurs at a non-contact location according to Paschen's law, and even a location where the charging roller 23 and the photosensitive drum 21 are not in contact can be charged, so uniform charging is possible.

By providing the charging brush 22 on the upstream side in the rotation direction of the photosensitive drum 21 and the charging roller 23 on the downstream side, discharge products can be suppressed by direct injection charging of the charging brush 22 on the upstream side. Furthermore, it is possible to charge the photosensitive drum 21, uniformly charge the surface of the photosensitive drum 21 by discharging the charging roller 23 on the downstream side, and finish the charging process. The charging brush 22 and charging roller 23 will be described in detail below.

The charging brush 22 contacts the photosensitive drum 21 with a predetermined pressing force. A desired voltage is applied to the charging brush 22 by the charging high-voltage power source E4, and the surface of the photosensitive drum 21 is neutralized to approximately 0 V by the pre-exposure device 24. FIG. The surface of the photosensitive drum 21, which has been neutralized by the pre-exposure device 24, is mainly charged to the negative polarity side, which is the normal polarity side, by direct injection charging. The charging brush 22 is fixed by attaching a 5 mm-wide conductive nylon fiber pile fabric to a stainless steel sheet metal. The conductive nylon fibers have a fineness of 2 denier, a flocking density of 240 fibers/mm ² , and a pile length of 6 mm. The direct injection charging performance of the charging brush 22 improves as the contact area between the charging brush 22 and the photosensitive drum 21 increases. When the same charging brush 22 is compared, the contact area tends to increase as the penetration amount increases, and the direct injection charging property improves. However, if the penetration amount exceeds a certain size, the contact pressure between the charging brush 22 and the photosensitive drum 21 increases, and the charging brush 22 may scratch the photosensitive drum 21 . Further, in this embodiment, a cleanerless configuration is adopted in which no cleaning member is provided for removing the developer remaining on the surface of the photosensitive drum 21 . In a configuration adopting a cleanerless system such as this configuration, if the contact pressure between the charging brush 22 and the photosensitive drum 21 is high, the charging brush 22 dams up the untransferred toner remaining on the photosensitive drum 21 without being transferred. This reduces the direct injection charging functionality of the charging brush 22 . Therefore, the design values of the charging brush 22, such as the flocking density, fineness, pile length, penetration amount, etc., need to be set with a balance between the above point of view and the injection chargeability. The charging brush 22 has a resistance value of 1×10 ⁵ Ω. This resistance value is obtained by converting the value of current flowing when the charging brush 22 is brought into contact with a metal cylinder of the same diameter as the photosensitive drum 21 under the same conditions and a voltage of -100 V is applied. The resistance value of the charging brush 22 can be controlled by changing the material of the conductive fibers of the charging brush 22 to change the resistance of the raw thread. The lower the resistance value, the better the charging performance of the charging brush 22 . However, if the resistance value is too low, a large current locally flows from the charging brush 22 to the photosensitive drum 21, causing a so-called pinhole leak in which dielectric breakdown occurs in the charge injection layer 21f and the charge transport layer 21e. There is In this configuration, the resistance value of the charging brush 22 was 1×10 ⁴ Ω or more, and pinhole leakage could be suppressed. Also, sufficient injection chargeability was exhibited with a resistance of 1×10 ⁸ Ω or less. Therefore, it is preferable that the charging brush 22 has a resistance value of 1×10 ⁴ Ω to 1×10 ⁸ Ω. From the above point of view, the resistance value of the charging brush 22 in this embodiment is set to 1×10 ⁵ Ω.

In this embodiment, a fixed brush type charging member is exemplified, but other configurations may be used as long as they can contact the photosensitive drum 21 and perform injection charging directly. For example, as shown in FIG. 4, a charging brush 123 may be wound around a roller-type core metal 122 and brought into contact with the photosensitive drum 21 while being rotated. In these configurations as well, it is necessary to determine the material of the charging brush 22 and the contact configuration of the charging brush 22 from the viewpoints of pinhole leakage, contact pressure with the photosensitive drum 21, and injection chargeability. Although the brush shape is used in this embodiment, the shape is not limited to the brush.

In this embodiment, a potential of -500 V is applied to the charging brush 22 so that the potential difference between the charging brush 22 and the photosensitive drum 21 is equal to or less than the discharge start voltage of 550 V, and the photosensitive drum 21 is charged by direct charge injection. In this configuration, as described above, the potential of the surface of the photosensitive drum 21 before passing through the contact portion with the charging brush 22 is leveled to about 0 V by the pre-exposure device 24 . Thereby, a potential difference of 500 V can be stably provided between the charging brush 22 and the photosensitive drum 21 . In the configuration without the pre-exposure device 24, the surface potential of the photosensitive drum 21 before passing through the charging brush 22 changes due to various factors such as the voltage applied to the transfer roller 12 and the temperature and humidity of the printing environment. In particular, the absolute value of the voltage (positive polarity) applied to the transfer roller 12 has a large effect, and depending on this value, the surface of the photosensitive drum 21 before passing through the charging brush 22 can be charged positively or negatively. There is also In this case, it is preferable to control the voltage applied to the charging brush 22 so that the potential difference between the charging brush 22 and the photosensitive drum 21 becomes a target value (500 V in this embodiment) according to each situation. Desirable for direct injection charging properties. When the potential difference between the charging brush 22 and the surface of the photosensitive drum 21 exceeds 550 V, discharge starts between the charging brush 22 and the photosensitive drum 21, but charging by direct charge injection also occurs at the same time. Therefore, even if the potential difference between the charging brush 22 and the surface of the photosensitive drum 21 exceeds 550 V, it is possible to reduce the amount of discharge by direct injection charging and reduce the discharge products. However, if the first charging voltage applied to the charging brush 22 exceeds the target potential Vd (−600 V in this embodiment) of the photosensitive drum 21, the charging by the charging brush 22 causes the surface potential of the photosensitive drum 21 to increase. Vd=-600V becomes larger on the negative side. As a result, potential unevenness may occur on the surface of the photosensitive drum 21 after being charged by the charging roller 23 . Therefore, it is desirable that the voltage applied to the charging brush 22 is Vd or less.

Next, the charging roller 23 will be described. The charging roller 23 contacts the photosensitive drum 21 with a predetermined pressing force with respect to the charging brush 22 on the downstream side in the rotation direction of the photosensitive drum 21 .

The charging roller 23 has a multi-layered structure in which a metal core made of stainless steel and having a diameter of 6 mm is used as a support, and the periphery thereof is covered with a plurality of flexible resin layers. In this configuration, the charging roller 23 has a two-layer structure consisting of a base layer that is a first resin layer that covers the metal core and a surface layer that is a second resin layer that covers the base layer. The resin material of the base layer is a conductive hydrin rubber in which conductive carbon is dispersed. In this embodiment, conductive hydrin rubber is used, but any other resin material may be used as long as it is flexible and conductive.

In this embodiment, as described above, the photosensitive drum 21 has the charge injection layer 21f having the charge injection function on the outermost surface. The charging roller 23 has a smaller contact area with the photosensitive drum 21 than the charging brush 22 . Therefore, charging by direct charge injection is generally difficult to occur, but in this embodiment, since the photosensitive drum 21 having the charge injection function is employed, charging by direct charge injection may occur depending on the configuration of the charging roller 23. may occur. Since a charging voltage having an absolute value greater than Vd is applied to the charging roller 23, if the charge is directly injected from the charging roller 23 to the photosensitive drum 21, the surface of the photosensitive drum 21 will be more negative than Vd. It will be charged to a large value. As a result, the corresponding portion is visualized in the image as potential unevenness.

In order to suppress direct injection charging from the charging roller 23 to the photosensitive drum 21, the outermost surface of the charging roller 23 needs to have a high volume resistivity and a small contact area with the photosensitive drum 21. FIG.

Therefore, in this configuration, a high-resistance resin layer having a thickness of about 30 μm and having an appropriate surface Ra is spray-coated on the base layer of the charging roller 23 as a surface layer. By making the outermost surface high resistance, it is possible to suppress the movement of charges from the charging roller 23 to the photosensitive drum 21 . Also, by providing an appropriate surface Ra, the charging roller 23 and the photosensitive drum 21 are in point contact, and the area into which charges are injected can be reduced. In this configuration, a urethane-based resin material was mixed with roughly 50% by weight of roughening particles of a urethane-based material having a particle size of about 20 μm for imparting an appropriate Ra to the surface, to prepare a coating liquid for the surface layer. A surface layer was formed by spray coating the coating solution onto the base layer. The surface layer has a volume resistivity of about 1×10 ¹⁴ Ω·cm and a surface Ra of about 2.0 μm. In this embodiment, the surface layer of the charging roller 23 preferably has a volume resistivity of 1.0×10 ¹² Ω·cm or more and a surface Ra of 0.5 to 3.0 μm.

In the charging roller 23 of this embodiment, it was confirmed that when the potential difference from the photosensitive drum 21 was 550 V or less, which is the discharge start voltage, the charging amount was 0 V, and direct injection charging hardly occurred.

A desired charging voltage is applied to the charging roller 23 by a charging high-voltage power source E1 different from the first charging power source E4 that applies a voltage to the charging brush 22, and the surface of the photosensitive drum 21 is set to a negative target potential mainly by discharging. uniformly charged.

A charging voltage of −1150 V is applied to the charging roller 23 to uniformly charge the surface of the photosensitive drum 21 to −600 V, which is the target Vd value.

7. Influence of Discharge Products on Photosensitive Drum When an image forming operation is performed using the image forming apparatus 1 , discharge produces a small amount of discharge products such as ozone and NOx, which adhere to the surface of the photosensitive drum 21 . I have something to do. The discharge products are scraped off by a member in contact with the photosensitive drum 21, but if the amount of adhered products is larger than the amount of scraped off products, they are gradually accumulated on the surface of the photosensitive drum 21 by repeated image forming operations. When the discharge product adheres to the surface of the photosensitive drum 21, it absorbs moisture and lowers the electrical resistance of the surface of the photosensitive drum 21, thereby lowering the charge retention capacity of the photosensitive drum 21. When a voltage is applied, the photosensitive drum 21 has a lower electric resistance. A charge may be injected into the surface of the drum 1 .

Next, the influence of discharge products on the formation of the surface potential of the photosensitive drum 1 will be described.

FIG. 5 is a graph showing the results of measuring the relationship between the charging voltage applied to the charging roller 23 and the surface potential of the photosensitive drum 21 in a high-temperature and high-humidity environment of 32.5° C. and 80% relative humidity. When the absolute value of the charging voltage is small, the surface potential on the photosensitive drum 21 does not change, but the potential starts to form on the surface of the photosensitive drum 1 from a certain voltage value. This value becomes the discharge start voltage Vth. In this embodiment, -550V is Vth. Vth is determined from the gap between the charging roller 23 and the photosensitive drum 21, the thickness of the photosensitive layer, and the dielectric constant of the photosensitive layer. When a voltage having an absolute value of Vth or more is applied to the charging roller 23 , a discharge phenomenon occurs in the gap based on Paschen's law, and the photosensitive drum 21 is charged.

As in FIG. 5, FIG. 6 shows the charge applied to the charging roller 23 when the photosensitive drum 21 with the discharge products adhered thereto is used in a high-temperature and high-humidity environment of 32.5° C. and 80% relative humidity. 3 shows the results of measuring the relationship between the voltage and the surface potential of the photosensitive drum 21. FIG. Since discharge products absorb moisture in a high-humidity environment, the electrical resistance of the surface of the photosensitive drum 21 tends to decrease. Therefore, unlike the result of FIG. 5 measured in the same environment, it can be seen that a potential starts to be formed even with an applied voltage whose absolute value is smaller than Vth, and a potential of about −50 V is formed by applying Vth. This is because the electrical resistance of the surface of the photosensitive drum 21 to which the discharge products adhere is lowered and injection charging is performed, so that even when a voltage less than Vth is applied, a minute potential is formed. The amount of injection charging depends on the amount of discharge products on the photosensitive drum 21 .

As described above, the electric resistance of the surface of the photosensitive drum 21 is lowered by the discharge products, so that the current flows in the portion where the discharge products adhere more. As a result, an appropriate electrostatic latent image and surface potential cannot be formed on the surface of the photosensitive drum 21, and a phenomenon called image deletion may occur in which the electrostatic latent image is blurred.

8. Effect of Suppressing Image Deletion and Improving Uniformity of Charging In this section, experimental results of image deletion and the effect of improving uniformity of charging according to the configuration of this embodiment will be described.

As described above, the image smearing is caused by a discharge product or a lowered resistance of the deteriorated surface of the photosensitive drum 21, and is remarkably worsened in a high-temperature and high-humidity environment. Therefore, the evaluation of the smeared image and the uniform charging property in this example was carried out in a high-temperature and high-humidity environment of 32.5° C. and 80% humidity.

In this embodiment, the photosensitive drum 21 is rotated by the driving motor 110 at a peripheral velocity of 168 mm/sec. The surface potential of the photosensitive drum 21 after passing through the transfer portion, which is the portion facing the transfer roller 12 of the photosensitive drum 21 , is lowered to about 0 V by the charge removal by the pre-exposure device 24 .

After the surface potential of the photosensitive drum 21 drops to approximately 0 V, the charging brush 22 and charging roller 23 charge the photosensitive drum 21 to Vd again.

At this time, as a charging current for charging the surface of the photosensitive drum 21 to Vd, a current of about 32 μA was required in total for the charging brush 22 and the charging roller 23 .

In this embodiment, by measuring the charging currents flowing through the charging brush 22 and the charging roller 23 respectively, the percentage of the total charge charged by the charging brush 22 and the charging roller 23 was estimated. The charging current flowing through the charging brush 22 is consumed for direct injection charging, and the charging current flowing through the charging roller 23 is consumed for charging by discharging. Therefore, by measuring the charging currents of the charging brush 22 and the charging roller 23, the ratio of the charging amount charged by direct injection charging to the total charging amount can be calculated. Hereinafter, this charge amount ratio will be referred to as a direct injection charge ratio.

In this embodiment, the charging current flowing through the charging brush 22 is 22 μA, the charging current flowing through the charging roller 23 is 10 μA, and a total current of 32 μA flows. It was charged. That is, the direct injection charge ratio is about 69%, and the charge amount due to discharge is reduced to about 31%.

Table 2 summarizes the occurrence levels of image density unevenness and image deletion in this configuration and in the comparative example. For image density unevenness, a halftone image was output, and x was given when there was visible density unevenness. Evaluation of image smearing was carried out under an environment of 32.5° C. temperature and 80% relative humidity. 5,000 sheets of Xerox multipurpose paper (basis weight: 75 g/m ² , LTR size) manufactured by Xerox Co., Ltd. were continuously fed and left for 12 hours, and then halftone images and text images were evaluated.

The printed image is a solid white image, and the level of image smearing is △ when the gradation of the halftone image changes and there is no abnormality in the text, and when both the gradation of the halftone image and the text change. It was evaluated as x.

In this embodiment, the volume resistivity of the outermost surface of the electrophotographic photosensitive member 1 as a drum is 1×10 ¹² Ω·cm, and voltages of −500 V and −1150 V are applied to the charging brush 22 and the charging roller 23, respectively. and the direct injection charging ratio is 69%. At this time, there was no occurrence of image density unevenness and image deletion, and good images could be printed from the initial stage until after 5,000 sheets were fed.

In Comparative Example 1, in the electrophotographic photosensitive member 1, the photosensitive drum 21 did not have the charge injection layer 21f, and the charge transport layer 21e was the outermost layer. ¹⁵ Ω·cm. In Comparative Example 1, even if a voltage of −500 V was applied to the charging brush 22, only about 11 μA of charging current flowed through the photosensitive drum 21, and the direct injection charging ratio was 34%. In this configuration, in order to charge Vd to −600 V, charging by discharging of the charging roller 23 had to be used for the majority, which increased the amount of discharge products generated and deteriorated the surface of the photosensitive drum 21 . Therefore, the level of image deletion after 5,000 sheets of paper in Comparative Example 1 was Δ level at which gradation change occurred in the halftone image.

Comparative Example 2 has a configuration in which the charging brush 22 is not provided and the photosensitive drum 21 is charged only by the charging roller 23 . Since the charging roller 23 has a high resistance and a rough surface structure, even if there is a charge injection layer 21f on the outermost surface of the photosensitive drum 21, charging by direct injection charging is not performed, and the direct injection charging ratio is 0%. Met. Since the charging of the photosensitive drum 21 is entirely performed by discharging, as a result, the amount of discharge products generated increases, and the surface of the photosensitive drum 21 deteriorates. Therefore, the level of image deletion after 5,000 sheets of paper in Comparative Example 2 was x, which affected the text as well.

In Comparative Example 3, the charging roller 23 is not provided, and the surface of the photosensitive drum 21 is charged only by the charging brush 22 . When a voltage of -1050V was applied to the charging brush 22, the surface potential of the photosensitive drum 21 was -600V. The reason why the surface of the photosensitive drum 21 can be charged to the Vd potential with a lower applied voltage than that of the charging roller 23 is that the charging brush 22 charges the photosensitive drum 21 by both charging by direct injection charging and discharging. . Although the direct injection charging ratio at this time cannot be measured, since the discharge starts upstream of the contact portion between the bristles of the charging brush 22 and the photosensitive drum 21 in the rotation direction of the photosensitive drum 21, the photosensitive drum 21 is mainly exposed by the discharge. It is considered that the drum 21 is being charged. Since direct injection charging is performed at the contact portion between the charging brush 22 and the photosensitive drum 21 after discharging, the voltage applied to the charging brush 22 for charging the surface potential of the photosensitive drum 21 to −600 V is −1050 V, and the charging roller 23 The 100 V absolute value was smaller than that. Therefore, it is considered that charging for 100 V was performed by direct injection charging. Therefore, the direct injection charging ratio at this time is expected to be about 17%. In addition, since the contact state between the charging brush 22 and the photosensitive drum 21 is uneven, direct injection charging is likely to occur at locations with a large contact area, and injection charging is not performed at locations that are not in contact. Therefore, even if the average surface potential of the photosensitive drum 21 is -600 V, there are many microscopic potential unevenness, many streaks appear on the halftone image, and the image density unevenness is x. rice field. Since the direct injection charging ratio is expected to be smaller than that of the present embodiment, the level of image smearing was also at the level of .DELTA. where gradation change occurred in the halftone image.

As described above, the first embodiment has the following configuration and features.

It has a rotatable photosensitive drum 21 having a support 21a made of an aluminum cylinder and a charge injection layer 21f as a surface layer on its surface. It has a charging brush 22 which is a first charging member that contacts the surface of the photosensitive drum 21 to form a first charging section and charges the surface of the photosensitive drum 21 in the first charging section. A developing roller 31 serving as a developing member for supplying developer to the surface of the photosensitive drum 21 is provided at a portion facing the surface of the photosensitive drum 21 . The surface of the photosensitive drum 21 charged by the charging brush 22 in the second charging section that faces the surface of the photosensitive drum 21 downstream of the first charging section and upstream of the facing section in the rotation direction of the photosensitive drum 21. It has a charging roller 23 which is a second charging member for charging. It has a first charging voltage applying section E4 that applies a first charging voltage to the charging brush 22 and a second charging voltage applying section E1 that applies a second charging voltage to the charging roller 23. FIG. It has a control section 150 that controls the first charging voltage applying section E4 and the second charging voltage applying section E1. The volume resistivity of the charge injection layer 21f of the photosensitive drum 21 is 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less. The control unit 150 controls the second charging voltage applying unit E1 so that the second potential difference formed between the surface of the photosensitive drum 21 charged by the charging brush 22 and the charging roller 23 is greater than or equal to the discharge start voltage. Control the applied second charging voltage.

A transfer portion facing the photosensitive drum 21 is formed, and a transfer roller 12 is provided for transferring the toner image from the photosensitive drum 21 to the recording material P, which is a transfer target, at the transfer portion. After the toner image formed on the surface of the photosensitive drum 21 is transferred to the recording material P in the transfer section, the toner remaining on the surface of the photosensitive drum 21 is collected by the developing roller 31 .

Also, the charging brush 22 has a fixed brush shape. The charging brush 22 may have a brush roller shape. The charging brush 22 is conductive, and preferably has a resistance value of 1.0×10 ⁴ Ω·cm or more and 1.0×10 ⁸ Ω·cm or less. The controller performs control so that the absolute value of the surface potential of the photosensitive drum 21 formed after the first charging voltage is charged with the second charging voltage is smaller. Furthermore, the first charging voltage applied to the first charging voltage applying section E4 is controlled so that the first potential difference formed between the surface of the photosensitive drum 21 and the charging brush 22 is less than the discharge start voltage. do. The charging current flowing through the charging brush 22 is controlled to be 40% or more of the total value of the charging currents flowing through the charging brush 22 and the charging roller 23 . The charging roller 23 has a roller shape. It is preferable that the volume resistivity of the outermost surface of the charging roller 23 is 1.0×10 ¹² Ω·cm or more. Further, it is preferable that the surface Ra of the outermost surface of the charging roller 23 is 0.5 to 3.0 μm. A surface layer provided on the photosensitive drum 21 is a charge injection layer 21f. The charge injection layer 21f has a structure in which conductive particles are dispersed in a binder resin. The charge injection layer 21f may be composed of amorphous silicon. Conductive fine particles are added to the surface of the developer, and the conductive fine particles may contain phosphorus oxide.

With the above configuration, in a charging configuration in which charges are directly injected into the surface of the photosensitive drum 21, generation of discharge products due to discharge and deterioration of the surface of the photosensitive drum 21 can be suppressed, and non-uniform charging can be suppressed. can.

In the present embodiment, a cleaner-less configuration is adopted in which the residual toner is collected in the developing device 30 and reused. good. FIG. 7 shows a charging configuration in which a cleaning blade 25 is added. Untransferred toner collected by the cleaning blade 25 and foreign matter on the photosensitive drum 21 including paper dust are collected in a collection container 26 installed separately from the developing device 30 .

In this configuration, the foreign matter on the photosensitive drum 21 is cleaned by the cleaning blade 25, so that the deterioration of charging performance caused by the direct injection from the charging brush 22 to the photosensitive drum 21 caused by the adhesion of these foreign matter to the charging brush 22 is suppressed. It has the advantage of being able to

However, a collection container 26 is required to collect foreign matter on the cleaned photosensitive drum 21, and the longer the product life, the larger the space required for the collection container 26. FIG.

A common technique is to use a screw member or the like to transport the foreign matter on the drum collected in the collection container 26 to another collection container provided in the dead space inside the printer main body, thereby reducing the size of the collection container 26. This leads to an increase in the cost of the product itself.

Whether or not to add the cleaning blade 25 is desirably selected from the viewpoint of product life, cost, cartridge size, required direct injection chargeability, and the like.

The second embodiment has a configuration in which the photosensitive drum 21 and the developing roller 31 are arranged in a non-contact manner as shown in FIG. Since the configuration other than the arrangement of the photosensitive drum 21 and the developing roller 31 is the same as that of the first embodiment, detailed description thereof will be omitted.

In the configuration related to this proposal, the volume resistivity of the outermost surface of the photosensitive drum 21 is 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less, which is lower than that of the general photosensitive drum 21 . It has the characteristic that there is

By controlling the outermost surface of the photosensitive drum 21 within this range of volume resistivity, good direct charge injection from the charging brush 22 to the photosensitive drum 21 can be achieved. It can create challenges.

If the volume resistivity of the outermost surface of the photosensitive drum 21 is low, depending on the volume resistivity of the surface of the developing roller 31, the charge on the surface of the photosensitive drum 21 may transfer to the developing roller 31 at the contact portion between the photosensitive drum 21 and the developing roller 31. , and the surface potential of the photosensitive drum 21 may become unstable. As a result, image defects such as density unevenness may occur in the printed image.

In addition, charge transfer also occurs between the photosensitive drum 21 and the toner, which may also cause density unevenness.

By arranging the photosensitive drum 21 and the developing roller 31 in a non-contact manner as shown in FIG. 8, the occurrence of this problem can be suppressed. By maintaining a small gap between the photosensitive drum 21 and the developing roller 31 by a roller regulating member or the like, the photosensitive drum 21 and the developing roller 31 or the photosensitive drum 21 and the toner do not come into physical contact. Therefore, mutual movement of charges is eliminated, and the occurrence of density unevenness can be suppressed.

The size of the minute gap requires an electric field strength necessary for the toner to fly from the developing roller 31 to the printing portion (scanner exposure portion) of the photosensitive drum 21 . In addition to the above-described electric field strength, the electric field strength required to prevent toner from flying to the non-printing portion (scanner non-exposed portion) is within a range that can be maintained between the photosensitive drum 21 and the developing roller 31. It is necessary to be

When a DC electric field is formed between the photosensitive drum 21 and the developing roller 31 as in this embodiment, the minute gap is desirably 10 to 100 μm, more desirably 10 to 50 μm. With this gap amount, it was possible to develop the latent image with the setting value described in the first embodiment, which was the same as in the case of contact.

In the case of providing a minute gap amount, if the size of the gap amount fluctuates in the longitudinal position or in the circumferential position during driving, the electric field intensity of the photosensitive drum 21 and the developing roller 31 will change, thereby affecting the developability. may change, resulting in uneven image density. Therefore, it is required to precisely control the gap amount.

By setting the gap amount between the photosensitive drum 21 and the developing roller 31 sufficiently large with respect to the variation in the gap amount, the influence of the variation in the gap amount on the developability is reduced. In the image forming apparatus of this embodiment, if the gap amount is increased to 150 μm or more, the influence of the gap amount variation on the image is sufficiently reduced.

However, if the gap amount is large, the electric field difference between the photosensitive drum 21 and the developing roller 31 for ensuring the electric field strength required for developing performance becomes very large. It is difficult to charge the common photosensitive drum 21 to a potential necessary for the electric field difference. In addition, when the photosensitive drum 21 is charged with a high charging potential, the amount of discharge increases, and image deletion tends to worsen.

Therefore, when the gap between the photosensitive drum 21 and the developing roller 31 is set to be large to some extent, an AC bias with a large amplitude is applied to the developing roller 31 in addition to the DC bias in order to form the electric field strength necessary for development. A configuration in which high frequencies are superimposed is desirable. Specifically, so-called jumping development is generally used in which the toner on the photosensitive drum 21 is reciprocally moved with respect to the printing portion and the non-printing portion on the photosensitive drum 21 by an AC bias to develop the toner.

When an AC bias having an amplitude for forming an electric field strength necessary for development is superimposed on the developing roller 31, the bias of the developing roller 31 is in a state where the bias is greater on the negative charge side than the potential of the non-printing portion of the photosensitive drum 21, and The state where the potential of the printing portion of the drum 21 is smaller toward the negative charge side than the potential is repeated.

When the bias of the developing roller 31 is greater toward the negative charge side than the potential of the non-printing portion of the photosensitive drum 21, the toner flies (develops) also in the non-printing portion of the photosensitive drum 21, but is more likely to develop in the printing portion. A force that causes the toner to fly (develop) strongly acts. Conversely, when the bias of the developing roller 31 is smaller than the potential of the printing portion of the photosensitive drum 21 toward the negative charge side, the toner from the printing portion of the photosensitive drum 21 also flies onto the developing roller 31 and is peeled off. , a stronger force works to remove the toner from the non-printing portion.

When this cycle is periodically repeated with an alternating current bias, the printing portion on the photosensitive drum 21 eventually becomes advantageous in toner flying (development), and the non-printing portion converges to a state in which toner separation is advantageous. As a result, it becomes possible to form an image according to the latent image on the photosensitive drum 21 . The frequency of the AC bias to be superimposed is generally set within a range sufficient for development and peeling to converge.

For example, under the conditions that the charging potential of the non-printing portion of the photosensitive drum 21 is -600 V, the charging potential of the printing portion is -100 V, the development bias is -350 V, and the rotation speed of the peripheral surface of the drum is 170 mm/sec. do. Under these conditions, when a gap amount of 300 μm is set between the photosensitive drum 21 and the developing roller 31, in addition to the DC bias of −350 V, the AC bias of about 2000 Vp _-p is superimposed on the developing bias at a frequency of about 2500 Hz. Then, it was possible to form an image according to the latent image. Note that _Vpp indicates the absolute value of the difference between the maximum value and the minimum value of the alternating potential of the AC bias.

The gap between the photosensitive drum 21 and the developing roller 31 is preferably between 150 μm and 400 μm. If the gap amount is less than 150 μm, the change in developability due to the variation in the gap amount becomes worse. Conversely, if it is larger than 400 μm, the flying distance of the toner from the developing roller 31 to the photosensitive drum 21 becomes long, and the toner is easily affected by the gradient force created by the latent image, resulting in so-called sweeping and blurring of the image. becomes more likely to occur.

When jumping development is adopted, it is difficult to collect the transfer residual toner by the developing roller 31. Therefore, as shown in FIG. contact is desirable.

Further, during development with an AC bias, if the toner having almost no electric charge is attracted by the charged toner and once reaches the non-printing portion of the photosensitive drum 21, the toner can be peeled off from the drum. However, it continues to remain, resulting in image defects such as so-called fogging.

Therefore, when adopting jumping development, toner containing a magnetic material and a cylindrical developing sleeve with a magnet placed inside are used, so that the uncharged toner is held on the developing sleeve and exposed to light. It is common to use a configuration that does not fly onto the drum 21 .

The third embodiment has a configuration in which the charging roller 223 is arranged in a non-contact manner with the photosensitive drum 21 . Since the configuration other than the configuration of the charging roller 223 is the same as that of the first embodiment, detailed description thereof is omitted.

As shown in FIG. 9, in this embodiment, the charging roller 223 is arranged downstream of the charging brush 22 in the rotation direction of the photosensitive drum 21 . In the present embodiment, unlike the first embodiment, the distance between the surfaces of the photosensitive drum 21 and the charging roller 223 is regulated so as to maintain a gap between the surfaces of the photosensitive drum 21 and the charging roller 223 by, for example, roller-regulating both ends of the charging roller 223 . The separation distance is preferably a distance at which discharge is stably generated, preferably 10 μm to 100 μm. In this embodiment, the separation distance is set to 30 μm.

Discharge according to Paschen's law is possible even if the photosensitive drum 21 and the charging roller 223 are separated from each other. Therefore, in this embodiment, the surface of the photosensitive drum 21 can be uniformly charged by the discharge.

Also in this embodiment, about 66% of the charge amount is charged by direct injection charging by the charging brush 22, so that the amount of discharge by the charging roller 223 can be suppressed, and the deterioration of the discharge product and the surface of the photosensitive drum 21 is prevented. can also be suppressed.

In this embodiment, since the charging roller 223 and the photosensitive drum 21 are not in contact with each other, direct injection charging from the charging roller 223 to the photosensitive drum 21 does not occur regardless of the configuration of the charging roller 223 . Therefore, image density unevenness due to direct injection charging from the charging roller 223 to the photosensitive drum 21 as described in the first embodiment does not occur. Therefore, the volume resistivity and shape of the outermost surface of the charging roller 223 can be selected more freely.

Further, in this embodiment, a so-called cleaner-less configuration is adopted in which the residual toner after transfer is collected in the developing device 30 and reused. It is also possible to suppress discharge defects caused by adhesion to the surface.

In this embodiment, the charging roller 223 is taken as an example of the non-contact charging member, but the configuration is not limited to this as long as uniform charging can be performed. For example, the photosensitive drum 21 may be charged by arranging a metal wire such as tungsten and discharging it. Alternatively, the photosensitive drum 21 may be charged by applying a higher voltage to the charging member 223 to ionize the molecules in the air. In both cases, the amount of discharge products generated by discharge and ionization and the amount of deterioration of the photosensitive drum 21 can be suppressed by directly injecting and charging the photosensitive drum 21 with the charging brush 22 . In a configuration in which a metal wire or the like is used to ionize molecules in the atmosphere, discharge products may adhere to the metal wire side, resulting in a loss of uniform charging. In this case, as is conventionally known, there is no problem if the user attaches a cleaning member for periodically cleaning the wire with a sponge member or the like.

In the fourth embodiment, the longitudinal width of the charging area of the charging brush 22 arranged on the upstream side in the rotation direction of the photosensitive drum 21 is longer than the longitudinal width of the charging area of the charging roller 23 arranged on the downstream side. . In addition, since it is the same as that of Example 1 except the relationship of the longitudinal width of each structural member, detailed description is abbreviate|omitted.

As shown in FIG. 10A, in this embodiment, the longitudinal width of the charge injection layer 21f of the photosensitive drum and the longitudinal width of the charging area of the charging brush 22 are longer than the longitudinal width of the charging area of the charging roller 23. are arranged as Here, the charging area of the charging brush 22 is an area where the charging brush 22 charges the photosensitive drum 21 mainly by direct injection charging, as shown in FIG. It is the place where the pile is in contact with the photosensitive drum 21 . The charging area of the charging roller 23 is an area where the charging roller 23 charges the photosensitive drum 21 mainly by discharging, as shown in FIG. 10C. In other words, it is a region where the photosensitive drum 21 is charged by discharge from the surface of the resin layer of the charging roller 23 and discharge from the side surface of the resin layer of the charging roller 23, which will be described later.

Discharge according to Paschen's law is generated not only from the surface of the resin layer of the charging roller 23 but also from the side surface. The width in which the surface of the photosensitive drum 21 can be charged by the discharge from this side surface is about 500 μm on one side in the longitudinal outer direction from the end of the resin layer of the charging roller 23 . longer than the longitudinal width of the layer. Therefore, it is desirable that the longitudinal width of the charging brush 22 is longer than the longitudinal width of the resin layer of the charging roller 23 by 1 mm or more. In this embodiment, the longitudinal width of the resin layer of the charging roller 23 is set to 229.8 mm, and assembly tolerances including part tolerances of the charging roller 23 and charging brush 22 are set to ±2 mm and ±2.5 mm, respectively. At that time, the longitudinal width of the charging brush 22 was set to 235.3 mm so that the longitudinal width of the charging brush 22 was longer than the longitudinal width of the resin layer of the charging roller 23 by 1 mm.

With this configuration, since the discharge by the charging roller 23 occurs inside the range directly injected and charged by the charging brush 22, the amount of discharge by the charging roller 23 can be suppressed, and the surface of the photosensitive drum 21 caused by the discharge can be reduced even at the ends. deterioration can be suppressed.

Reference Signs List 1 image forming apparatus 21 photosensitive drum 21a support 21f charge injection layer 22 charging brush 23 charging roller 31 developing roller 150 control unit E1 charging voltage power supply E4 brush voltage power supply

Claims (20)

a rotatable photosensitive drum having a support and a surface layer on the surface;
a first charging member that forms a first charging portion in contact with the surface of the photosensitive drum and charges the surface of the photosensitive drum in the first charging portion;
a developing member that supplies developer to the surface of the photosensitive drum at a portion that faces the surface of the photosensitive drum;
The second charging section facing the surface of the photosensitive drum downstream of the first charging section and upstream of the facing section in the rotational direction of the photosensitive drum, and charged by the first charging member. a second charging member that charges the surface of the photosensitive drum;
a first charging voltage applying section that applies a first charging voltage to the first charging member;
a second charging voltage applying unit that applies a second charging voltage to the second charging member;
a control unit that controls the first charging voltage applying unit and the second charging voltage applying unit;
The surface layer of the photosensitive drum has a volume resistivity of 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less,
The control unit controls the second charging member so that a second potential difference formed between the surface of the photosensitive drum charged by the first charging member and the second charging member becomes equal to or higher than a discharge start voltage. and controlling the second charging voltage applied to the charging voltage applying section of the image forming apparatus. 2. An image forming apparatus according to claim 1, wherein said first charging member has a fixed brush shape. 2. An image forming apparatus according to claim 1, wherein said first charging member has a brush roller shape. 4. The image forming apparatus according to claim 1, wherein said first charging member is conductive. 5. The apparatus according to claim 1, wherein the first charging member has a resistance value of 1.0×10 ⁴ Ω·cm or more and 1.0×10 ⁸ Ω·cm or less. Image forming device. 3. The controller controls the surface potential of the photosensitive drum formed after the first charging voltage is charged with the second charging voltage so that the absolute value of the surface potential of the photosensitive drum is smaller than that of the surface potential of the photosensitive drum. 6. The image forming apparatus according to any one of 1 to 5. The controller controls the voltage applied to the first charging voltage applying unit such that a first potential difference formed between the surface of the photosensitive drum and the first charging member is less than a discharge start voltage. 7. The image forming apparatus according to claim 1, wherein the first charging voltage is controlled. The control unit controls the charging current flowing through the first charging member to be 30% or more of the total value of the charging currents flowing through the first charging member and the second charging member. The image forming apparatus according to any one of claims 1 to 7, characterized by: The image forming apparatus according to any one of claims 1 to 8, wherein the second charging member has a roller shape. 10. The image forming apparatus according to claim 1, wherein the outermost surface of the second charging member has a volume resistivity of 1.0×10 ¹² Ω·cm or more. The image forming apparatus according to any one of claims 1 to 10, wherein the surface Ra of the outermost surface of the second charging member is 0.5 to 3.0 µm. The image forming apparatus according to any one of claims 1 to 9, wherein the second charging member is arranged without contact with the photosensitive drum. 13. The image forming apparatus according to claim 1, wherein the surface layer provided on the photosensitive drum is a charge injection layer. 14. The image forming apparatus according to claim 13, wherein the charge injection layer has a structure in which conductive particles are dispersed in a binder resin. 14. The image forming apparatus of claim 13, wherein the charge injection layer is made of amorphous silicon. a transfer member that forms a transfer portion facing the photosensitive drum, and that transfers the toner image from the photosensitive drum to a transfer material at the transfer portion;
After the toner image formed on the surface of the photosensitive drum is transferred to the transfer material in the transfer section, toner remaining on the surface of the photosensitive drum is collected by the developing member. 14. The image forming apparatus according to any one of claims 1 to 13. 14. The apparatus according to any one of claims 1 to 13, wherein the width of the charging area in the longitudinal direction of the first charging member is larger than the width of the charging area in the longitudinal direction of the second charging member. Image forming device. Cleaning for cleaning foreign substances on the photosensitive drum by contacting between the contact portion of the transfer portion and the photosensitive drum and the contact portion of the first charging member and the photosensitive drum on the surface of the photosensitive drum. 14. The image forming apparatus according to any one of claims 1 to 13, comprising a blade. 14. The image forming apparatus according to claim 1, wherein the photosensitive drum and the developing member are arranged in a non-contact manner. A bias obtained by superimposing an AC bias on a DC bias is applied to the developing member, and the AC bias causes the developer on the developing member to reciprocate with respect to the image portion and the non-image portion on the photosensitive drum. 14. The image forming apparatus according to any one of claims 1 to 13, wherein the developer is developed with.

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