JP2009204679A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of problems such as cleaning failure, filming, blade noise and blade buckling and to eliminate problems of transfer of a magnetic carrier to a transfer device, an intermediate transfer body or the like in an image forming apparatus equipped with a cleaning means (6) with a cleaning blade system and a developing device with a system of gradually automatically exchanging a developer in a developing means (4). <P>SOLUTION: The image forming apparatus includes: a developer replenishing means (4g) replenishing a replenisher developer to a developing means (4); a developer discharging means (4f) discharging a two-component developer from the developing means; a developer conveying means (10) conveying the two-component developer discharged from the developing means to a cleaning means (6); and a cleaning assisting means (6c) that is disposed in an upstream side along the rotation direction of an image carrier than a cleaning blade (6a) in the cleaning means and abuts on the surface of the image carrier (1) while carrying the two-component developer conveyed by the developer conveying means to the cleaning means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic system or an electrostatic recording system. More specifically, the present invention relates to an image forming apparatus using a cleaning blade system as a cleaning means for removing toner from the surface of an image carrier for forming an image, such as an electrophotographic photosensitive member or an electrostatic recording dielectric.

  Conventionally, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an electrostatic latent image formed on the surface of a traveling image carrier is developed as a toner image by a developing unit, and the toner image is used as a transfer material. Transcribed. The residual toner remaining on the surface of the image carrier without being transferred to the transfer material is removed and collected by the cleaning device.

  As a cleaning device, for example, a cleaning blade method that scrapes toner by bringing a blade made of an elastic body such as rubber into contact with the surface of an image carrier as described in Patent Document 1 is widely used. This is because the structure of the cleaning device is very simple and small, and is advantageous from the viewpoint of cost.

  In a cleaning apparatus having a cleaning blade, a system in which the blade is pressed against the surface of the traveling image carrier from the counter direction is the mainstream. The mechanism of the cleaning action in this method is considered to be due to the so-called Stick-Slip motion as described in, for example, cited document 2. That is, the blade is brought into pressure contact with the surface of the image carrier with a force (0.049 to 0.392 N / cm (5 to 40 gf / cm)) necessary for removing the residual toner on the surface of the image carrier. By this pressure contact, the blade edge portion that is in close contact with the surface of the image carrier is first deformed in the advancing direction of the image carrier (shear deformation, compression) at the contact portion between the blade edge and the image carrier by the frictional force acting on the contact portion. Deform. Then, the energy accumulated in the blade edge portion accompanying the stress acts as a restoring force (repulsive elastic force) and returns to the original state.

  Therefore, the cleaning ability is determined by the vibration motion by the energy accumulated in the blade edge portion, that is, the amplitude and frequency of the stick-slip motion of the blade edge portion. More ideally, for example, in the case of a cylindrical image carrier (such as a photosensitive drum), it is preferable that the vibration motion of the blade edge portion be limited to the tangential plane of the cylinder.

  Here, the amplitude and frequency of the Stick-Slip motion are determined as follows. That is, the coefficient of friction between the blade edge and the surface of the image bearing member, the shape of the blade (blade thickness / free length), the material properties of the blade (Young's modulus, Poisson's ratio, modulus (stress-strain curve)), etc. Is determined by adjusting.

  By the way, in such an image forming apparatus, when image formation is repeated, charge generation caused by ozone generated when the surface of an image carrier (hereinafter referred to as a photosensitive drum) is charged by a charging device. There is a risk that objects adhere to the surface of the photosensitive drum. Further, there is a possibility that toner resin, external additives, and the like that pass through the blade may adhere to the surface of the photosensitive drum.

  As described above, the discharge product, toner resin, or the like adheres to the surface of the photosensitive drum, thereby increasing the friction coefficient of the surface of the photosensitive drum, and accompanyingly, the frictional force of the contact portion between the photosensitive drum and the blade edge portion also increases. When the frictional force of the blade edge portion is increased, the followability of the blade edge portion to the photosensitive drum surface is deteriorated. For this reason, there is a possibility of causing problems such as poor cleaning in which the transfer residual toner slips through the blade edge portion, and filming that is rubbed against the surface of the photosensitive drum when the transfer residual toner or external additive slips through the blade edge portion.

  Further, if the frictional force of the blade edge portion becomes too large, there is a risk of causing blade squealing due to abnormal vibration of the blade edge portion, or blade turning that the blade edge portion reverses along the rotation direction of the photosensitive drum. These problems are not limited to defective output images, and may damage the image forming apparatus itself.

  Therefore, as a method for solving this problem, a method of providing a rotatable resin brush roller in contact with the photosensitive drum on the upstream side of the cleaning blade in the moving direction of the photosensitive drum has been proposed as described in Patent Document 3.

  Further, as described in Cited Document 4, a method of providing a rotatable magnetic brush roller in contact with the photosensitive drum on the upstream side of the cleaning blade in the moving direction of the photosensitive drum has been proposed.

  By providing such a brush roller, it is possible to expect a polishing effect on the surface of the photosensitive drum, and it is possible to remove charged products, toner resin, and the like temporarily attached to the surface of the photosensitive drum, as well as the blade edge portion. An increase in frictional force can be suppressed.

  However, in the method in which the brush roller is provided in contact with the photosensitive drum, with the use of the apparatus, the polishing ability of the brush roller on the surface of the photosensitive drum decreases due to the fall of the brush, permanent deformation, or deterioration of the magnetic particles. It is not a fundamental solution for reducing frictional forces.

Therefore, as a method for solving this problem, there is a method described in Patent Document 5. That is, it has a mechanism for replenishing the developing device with a developer composed of a magnetic carrier and toner and discharging excess developer in the developing device. Then, the magnetic carrier is discharged onto the photosensitive drum at a timing other than image formation, and is collected by a cleaning device having a magnetic brush roller. By using this method, a relatively new magnetic carrier can always be supplied to the magnetic brush roller, and the polishing ability of the magnetic brush roller on the photosensitive drum can be maintained over a long period of time.
Japanese Patent Publication No. 06-012475 JP-A-11-174922 JP 2000-75755 A JP-A-10-143039 JP 2003-330270 A

  However, as disclosed in Patent Document 5, in the method of discharging the magnetic carrier in the developing device to the surface of the photosensitive drum, a part of the magnetic carrier discharged on the photosensitive drum can be transferred to, for example, a transfer device or an intermediate transfer member. There is sex.

  The present invention has been made in view of such technical problems, and is intended to improve an image forming apparatus having a cleaning device of a cleaning blade type and a developing device of a method of gradually and automatically changing the developer in the developing device. It is concerned. The purpose is to prevent the occurrence of such problems as poor cleaning, filming, blade squealing, blade turning, etc., in the cleaning blade type cleaning device. Another object of the present invention is to solve the problem of transfer of magnetic carriers to a transfer device, an intermediate transfer member, etc., and to effectively use the developer discharged from the developing device.

A typical configuration of the image forming apparatus according to the present invention for achieving the above object is as follows:
Rotating image carrier for forming an image, charging means for charging the surface of the image carrier, and image information writing for forming an electrostatic latent image on the image carrier charged by the charging means Means for developing the electrostatic latent image formed on the image carrier by supplying the toner with a two-component developer made of toner and a magnetic carrier, and transferring the visualized toner image to a transfer material. In the image forming apparatus, the image forming apparatus includes: a transfer unit that transfers to the surface; and a cleaning unit that includes a cleaning blade for removing the toner remaining on the surface of the image carrier after transfer.
Developer replenishing means for replenishing the developer for replenishment in which toner and magnetic carrier are mixed to the developing means;
Developer discharging means for discharging the two-component developer from the developing means;
Developer conveying means for conveying the two-component developer discharged from the developing means to the cleaning means;
In the cleaning unit, the image carrier (1) is disposed upstream of the cleaning blade in the rotation direction of the image carrier and carries the two-component developer conveyed to the cleaning unit by the developer conveyance unit. Cleaning auxiliary means abutting the surface of
An image forming apparatus comprising:

  According to the present invention, it is possible to prevent problems such as defective cleaning, filming, blade squealing, blade turning, and the like from occurring in a cleaning blade type cleaning device. Further, it is possible to solve the problem of transfer of the magnetic carrier to the transfer device, the intermediate transfer member, and the like, and to effectively use the developer discharged from the developing device.

  Hereinafter, embodiments according to the present invention will be described in more detail with reference to the drawings.

[Example 1]
(1) Overall Schematic Configuration of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of a main part of the image forming apparatus in the present embodiment. This image forming apparatus is an electrophotographic system, an intermediate transfer system, and a 4-color tandem system full-color digital printer. This image forming apparatus can form a four-color full-color image on a recording material P in accordance with electrical image information input from an external host device 200 that is communicably connected to a control circuit unit (control unit) 100. The control circuit unit 100 processes control signals to various process devices and information signals input from various process devices in accordance with control programs and reference tables stored in a memory unit (ROM and RAM), stored data, and the like. Execute image sequence control. The external host device 200 is a personal computer, an image reading device, or the like.

  Y-st, M-st, C-st, and Bk-st are first to fourth image formations arranged in parallel (tandem) in the horizontal direction from the left side to the right side in the drawing in the main body of the image forming apparatus. Part (image forming unit). The first image forming unit Y-st is for forming a yellow (Y) color image, the second image forming unit M-st is for forming a magenta (M) color image, and the third image forming unit C-st is The cyan (C) color image is formed, and the fourth image forming unit Bk-st is for black (Bk) color image formation. Each image forming unit has substantially the same mechanism configuration except that the color of the developer contained in the developing device is different from Y color, M color, C color, and Bk color. FIG. 2 is an enlarged view of one image forming unit (schematic configuration model diagram of main parts).

  Each image forming unit has a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as a rotating image carrier for image formation, and an image forming process means acting on the photosensitive drum. In this embodiment, the image forming process means is the following equipment. That is, a roller charger 2 as a charging means, a laser beam scanner 3 as an image information writing means, a developing device 4 as a developing means, a primary transfer roller 5a as a primary transfer means, and a photosensitive drum cleaning as an image carrier cleaning means. Device 6 or the like.

  The developing device 4 of the first image forming unit Y-st contains a two-component developer composed of Y color toner and a magnetic carrier as a developer. The developing device 4 of the second image forming unit M-st contains a two-component developer composed of M color toner and a magnetic carrier as a developer. The developing device 4 of the third image forming unit C-st contains a two-component developer composed of C-color toner and a magnetic carrier as a developer. The developing device 4 of the fourth image forming unit Bk-st contains a two-component developer composed of Bk toner and a magnetic carrier as a developer.

  Reference numeral 4g denotes a developer cartridge corresponding to each developing device 4, and can be attached to and detached from the main body of the image forming apparatus. The developer cartridge 4g contains a replenishment developer in which toner and a magnetic carrier are mixed. The developer cartridge 4g is a developer replenishing unit that replenishes the developing device 4 with a replenishment developer.

  An intermediate transfer unit 5 is disposed below each image forming unit. This unit 5 has an endless intermediate transfer belt 5b made of a dielectric and having flexibility as an intermediate transfer member (first transfer material). The belt 5b is obtained by adjusting resistance by dispersing carbon in a resin such as polyethylene terephthalate or polyimide. In the present embodiment, the length of the belt 5b in the longitudinal direction is 340 mm. A driving roller 5c, a tension roller 5d, a secondary transfer counter roller 5e, and a belt cleaning device 7 as cleaning means for the belt 5b are provided. The driving roller 5c drives and rotates the belt 5b. The rotation direction of the drive roller 5 c is a direction in which the belt 5 b is rotated in the same direction (forward direction) with respect to the rotation direction of the photosensitive drum 1. The tension roller 5d is adjusted so as to maintain the belt 5b with a constant tension between the driving roller 5c and the secondary transfer counter roller 5e.

  The lower surface of the photosensitive drum 1 of each image forming unit is in contact with the upper surface of the ascending belt portion between the driving roller 5c and the tension roller 5d of the belt 5b. The primary transfer roller 5a of each image forming unit is disposed on the inner side of the belt 5b, and a corresponding photosensitive member is sandwiched between the drive roller 5c and the tension roller 5d of the belt 5b. It is in pressure contact with the lower surface of the drum 1. In each image forming portion, the contact portion between the photosensitive drum 1 and the belt 5b is a primary transfer portion. Further, a secondary transfer roller 5f as a secondary transfer unit is in pressure contact with the secondary transfer counter roller 5e with the belt 5b interposed therebetween. A contact portion between the secondary transfer roller 5f and the belt 5b is a secondary transfer portion.

  The operation for forming a full-color image is as follows. The control circuit unit 100 executes predetermined image formation sequence control based on the image formation start signal. In each image forming unit, the photosensitive drum 1 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined control speed (process speed). The belt 5b is also driven to rotate (run) in the clockwise direction indicated by the arrow X at a speed corresponding to the speed of the photosensitive drum 1. The polygon mirror of each laser scanner 3 is also driven. In synchronization with this drive, the roller charger 2 uniformly charges the surface of the photosensitive drum 1 to a predetermined polarity and potential at a predetermined control timing in each image forming unit (charging process). Then, the Y color component image signal of the full color image is output from the control circuit unit 100 to the laser scanner 3 of the first image forming unit Y-st at a predetermined control timing. An M color component image signal of a full color image is output from the control circuit unit 100 to the laser scanner 3 of the second image forming unit M-st at a predetermined control timing. A C color component image signal of a full color image is output from the control circuit unit 100 to the laser scanner 3 of the third image forming unit C-st at a predetermined control timing. A Bk color component image signal of a full color image is output from the control circuit unit 100 to the laser scanner 3 of the fourth image forming unit Bk-st at a predetermined control timing. Each laser scanner 3 scans and exposes the surface of each photosensitive drum 1 with a laser beam L modulated in accordance with an image signal of each color (exposure process). Charges are neutralized by this exposure, and an electrostatic latent image corresponding to an image signal of a corresponding color is formed on the surface of each photosensitive drum 1. The formed electrostatic latent image is developed as a toner image by the developing device 4 (development process).

  By the electrophotographic image forming process operation as described above, a Y color toner image corresponding to the Y color component of the full color image is formed on the photosensitive drum 1 of the first image forming unit Y-st at a predetermined control timing. An M color toner image corresponding to the M color component of the full color image is formed on the photosensitive drum 1 of the second image forming unit M-st at a predetermined control timing. A C color toner image corresponding to the C color component of the full-color image is formed on the photosensitive drum 1 of the third image forming unit C-st at a predetermined control timing. A Bk color toner image corresponding to the Bk color component of the full color image is formed on the photosensitive drum 1 of the fourth image forming unit Bk-st at a predetermined control timing.

  As described above, the surface of the belt 5b on which the color toner image formed on the photosensitive drum 1 of each image forming unit at a predetermined control timing is rotationally driven and sequentially moves through the primary transfer unit of each image forming unit. Are preliminarily superposed in order and are primarily transferred. In this embodiment, the primary transfer roller 5a is a transfer unit that transfers the toner image on the photosensitive drum 1 to a belt 5b as a first transfer material.

  In this embodiment, the pressing force of the primary transfer roller 5a against the photosensitive drum 1 is 500 gf (= 4.9 N). While the toner image on the photosensitive drum 1 reaches the primary transfer portion, from the power source (not shown) to the primary transfer roller 5a, in this embodiment, the negative polarity that is the normal charging polarity of the toner is defined. A positive primary transfer bias having a reverse polarity is applied. As a result, the toner image on the photosensitive drum 1 is electrostatically transferred onto the belt 5b. In this embodiment, the primary transfer bias is + 500V.

  Thus, a four-color full-color unfixed toner image of Y color + M color + C color + Bk color is synthesized and formed on the belt 5b. The toner image subsequently moves to the secondary transfer portion by the rotation of the belt 5b. Further, the transfer residual toner on the photosensitive drum 1 that has not been transferred onto the belt 5 b in the primary transfer portion of each image forming portion is removed and collected by the photosensitive drum cleaning device 6.

  On the other hand, a recording material (second transfer material) P such as paper is separated and fed from the paper feeding unit 20 at a predetermined control timing. The fed recording material P is conveyed by the conveying roller 22 in the sheet path 21 and is sent toward the registration roller 23. The recording material P is subjected to skew correction by abutting the leading end against the nip portion of the registration roller 23 which has stopped rotating at that time, and forming a loop. Thereafter, the recording material P is introduced into the secondary transfer portion by the registration roller 23 being rotationally driven at a predetermined control timing in synchronization with the toner image on the belt 5b. As a result, the full-color toner image on the belt 5b is secondarily transferred collectively onto the surface of the recording material P. In the present embodiment, the secondary transfer roller 5f is a transfer unit that transfers the toner image on the belt 5b as the first transfer material to the recording material P as the second transfer material.

  The secondary transfer roller 5f is in pressure contact with the secondary transfer counter roller 5e with a predetermined pressing force across the belt 5b. In this embodiment, the pressing force of the secondary transfer roller 5f is 1000 gf (= 9.8 N). ). The recording material P conveyed to the secondary transfer unit is nipped and conveyed between the belt 5b that carries and conveys the toner image and the secondary transfer roller 5f. During the conveyance, a positive secondary transfer bias having a polarity opposite to the negative polarity that is the normal charging polarity of the toner is applied to the secondary transfer roller 5f from the power source (not shown) in this embodiment. The As a result, the four color toner images on the belt 5b are electrostatically transferred onto the recording material P. In this embodiment, the secondary transfer bias is +1.5 kV.

  Then, the recording material P that has undergone the secondary transfer of the toner image is separated from the belt 5b and introduced into a fixing device 8 (for example, a heat roller fixing device). (Copy).

  Further, the secondary transfer residual toner on the belt 5b that has not been transferred onto the recording material P in the secondary transfer portion is removed and collected by the belt cleaning device 7, and the belt 5b is cleaned.

(2) Image carrier 1
In this embodiment, the photosensitive drum 1 as an image carrier is a negatively chargeable organic photoconductor (OPC) having an outer diameter of 30 mm and a process speed of 100 mm / sec centering on a central support shaft (not shown). (Circumferential speed) and is driven to rotate counterclockwise as indicated by the arrow.

  This photosensitive drum 1 is laminated on the surface of an aluminum cylinder (conductive drum base) by functionally separating an undercoat layer for suppressing light interference and improving the adhesion of the upper layer, a charge generation layer and a charge transport layer. The photosensitive layer and the surface layer are coated in order from the bottom.

  The surface layer can be formed by polymerizing or crosslinking a hole transporting compound having a chain polymerizable functional group. As a method of polymerizing or crosslinking, there is a method of irradiating heat, visible light, light such as ultraviolet rays, electron beam or the like. In the photosensitive drum 1 of the present embodiment, a method of irradiating an electron beam capable of producing a surface layer of a very high purity three-dimensional matrix was used.

  The photosensitive drum 1 having the surface layer produced in this way has very excellent wear resistance on the surface of the photosensitive drum.

The characteristic physical quantities possessed by the photosensitive drum 1 will be described below. When the hardness of the photosensitive drum 1 is tested using a Vickers square pyramid diamond indenter under an environment of a temperature of 25 ° C. and a humidity of 50%, the elastic deformation rate when pressed with a load of 6 mN is 45% or more and 65% or less. The universal hardness value (HU) is 150 N / mm ² or more 220 N / mm ² or less.

  Universal hardness value (HU) and elastic deformation rate are microhardness measuring equipment Fischerscope H100V in which continuous hardness is required by applying a continuous load to the indenter and directly reading the indentation depth under the load. (Fischer) can be used for measurement. As the indenter, a Vickers quadrangular pyramid diamond indenter having a facing angle of 136 ° can be used. Specifically, measurement is performed in stages (273 points with a holding time of 0.1 S for each point) up to a final load of 6 mN.

  Since the surface of the photosensitive drum 1 having such a surface layer is very hard as compared with the conventional photosensitive drum, it hardly wears only by rubbing with the cleaning blade. Here, the conventional photosensitive drum is a photosensitive drum having no surface layer cured by electron beam irradiation like the photosensitive drum described in the present embodiment. That is, the photosensitive drum does not have a surface layer or has a surface layer formed by thermal curing, photocuring, or the like, and is a photosensitive drum that is softer and wears much more than the photosensitive drum described in this embodiment. In the conventional photosensitive drum, the surface of the photosensitive drum is worn by the cleaning blade, and at the same time, it is possible to remove deposits such as discharge products and toner resin on the surface of the photosensitive drum. However, the photosensitive drum 1 of Example 1 cannot remove deposits such as discharge products and toner resin, and the frictional force at the edge of the cleaning blade tends to increase greatly.

  FIG. 3 shows the increase or decrease in deposits on the surface of the photosensitive drum due to the use of the conventional photosensitive drum (photosensitive drum A) and the photosensitive drum (photosensitive drum B) of the first embodiment by changing the contact angle of the photosensitive drum. It has been confirmed.

  The conventional photosensitive drum A can be worn on the surface by a cleaning blade and can remove deposits on the surface. Therefore, the contact angle of the photosensitive drum slightly decreases immediately after the start of use, as shown by the circles, but thereafter changes between 90 ° and 100 °.

  On the other hand, the surface of the photosensitive drum according to the first exemplary embodiment cannot be worn by the cleaning blade, and therefore, deposits on the photosensitive drum cannot be removed. For this reason, the contact angle of the photosensitive drum falls to 80 ° or less at an early stage after the start of use, as indicated by the plot of the mark ●.

  When the contact angle of the photosensitive drum is 80 ° or less, for example, when the atmosphere environment in which the image forming apparatus is used is a high humidity environment such as a temperature of 30 ° C. and a relative humidity of 80%, charge generation on the surface of the photosensitive drum is generated. Deposits such as objects contain moisture and reduce resistance. For this reason, the electrostatic latent image formed on the surface of the photosensitive drum cannot be maintained, and there is a risk of causing image drift.

  Here, the contact angle of the photosensitive drum refers to an angle formed between the surface of the photosensitive drum and the liquid surface when a liquid droplet such as pure water having a certain size is brought into contact with the surface of the photosensitive drum. When the contact angle of the photosensitive drum is large, the surface of the photosensitive drum is not easily wetted with water, that is, the water repellency is strong. In Example 1, the contact angle was measured using a contact angle meter CA-DS type (Kyowa Interface Chemical Co., Ltd.).

(3) Charging means 2
In the present embodiment, the charging means 2 for uniformly charging the peripheral surface of the photosensitive drum 1 is a contact charging device (contact charger). This contact charging device in this embodiment is a roller charger using a charging roller (conductive roller) 2a as a contact charging member.

  In this embodiment, the outer diameter of the charging roller 2a is 14.0 mm, and both end portions of the cored bar are rotatably held by the bearing members 2b, and are urged toward the photosensitive drum by the pressing spring 2c. Yes. As a result, the charging roller 2a is brought into pressure contact with the surface of the photosensitive drum 1 with a predetermined pressing force (500 gf (= 4.9 N in the case of the first embodiment)). The charging roller 2 a rotates following the rotation of the photosensitive drum 1.

  A charging bias voltage of a predetermined condition is applied to the core of the charging roller 2a from a power source (not shown), whereby the peripheral surface of the rotating photosensitive drum 1 is contact-charged to a predetermined polarity and potential. . In the present embodiment, the charging bias voltage for the charging roller 2a is an oscillating voltage in which a DC voltage (Vdc) and an AC voltage (Vac) are superimposed. More specifically, DC voltage: −500 V, AC voltage; frequency f1 kHz, peak-to-peak voltage Vpp 1.5 kV, and vibration voltage superimposed with a sine wave, and the peripheral surface of the photosensitive drum 1 is −500 V (dark potential Vd). Are uniformly charged by contact.

(4) Image information writing means 3
In this embodiment, the image information writing means 3 for forming an electrostatic latent image on the charged photosensitive drum surface is an exposure device. The exposure apparatus 3 is a laser beam scanner using a semiconductor laser. The scanner 3 outputs laser light modulated in accordance with an image signal input from the control circuit unit 100, and laser scanning exposure L (image exposure) is performed on the uniformly charged surface of the rotating photosensitive drum 1 at an exposure position. To do. The laser scanning exposure L lowers the potential of the photosensitive drum surface irradiated with the laser light, so that electrostatic latent images corresponding to the scanned and exposed image information are sequentially formed on the rotating photosensitive drum surface. Go.

(5) Developing means 4
In this embodiment, a developing device (developing device) as a developing unit that supplies developer (toner) to the electrostatic latent image formed on the photosensitive drum 1 to visualize the electrostatic latent image uses a two-component developer. It is a developing device. The developing device 4 contains a two-component developer composed of a non-magnetic toner and a magnetic carrier, and the mixing ratio of the toner and the magnetic carrier is approximately 9: 1 by weight. This ratio should be appropriately adjusted according to the charge amount of the toner, the carrier particle size, etc., and does not necessarily have to follow this value.

  The developing container 4a of the developing device 4 has an opening in a developing region facing the photosensitive drum 1, and a developing sleeve 4b is rotatably disposed so as to be partially exposed to the opening. The developing sleeve 4b is disposed in close proximity to the photosensitive drum 1 with the closest distance (referred to as SD gap) to the photosensitive drum 1 being 350 μm. A facing portion between the photosensitive drum 1 and the developing sleeve 4b is a developing portion.

  A part of the two-component developer in the developing container 4a is attracted and held on the outer peripheral surface of the developing sleeve 4b as a magnetic brush layer by the magnetic force of the magnet 4c in the developing sleeve 4b. Then, the magnetic brush layer is transported as the developing sleeve 4b rotates, and is layered to a predetermined thin layer by the developer coating blade 4d, and comes into contact with the surface of the photosensitive drum 1 at the developing portion to make the surface of the photosensitive drum 1 Rub moderately. A predetermined developing bias is applied to the developing sleeve 4b from a power source (not shown). In this embodiment, the developing bias voltage for the developing sleeve 4b is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, it is an oscillating voltage in which a DC voltage; -350V and an AC voltage; a rectangular wave with a frequency of f8.0 kHz and a peak-to-peak voltage of 1.8 kV are superimposed.

  Thus, the toner in the developer coated as a thin layer on the outer peripheral surface of the rotating developing sleeve 4b and transported to the developing unit is selectively corresponding to the electrostatic latent image on the surface of the photosensitive drum by the electric field due to the developing bias. As a result, the electrostatic latent image is developed as a toner image. In the case of this embodiment, toner adheres to the exposed bright portion of the photosensitive drum surface and the electrostatic latent image is reversely developed.

  The magnetic brush layer of the developer after developing the electrostatic latent image is transported back into the developing container 4a by the subsequent rotation of the developing sleeve 4b, peeled off from the surface of the developing sleeve, and collected. A magnetic brush layer of a two-component developer is newly formed on the surface of the developing sleeve.

In the developing container 4a, there are two first developer circulating screws 4e-1 (side closer to the developing sleeve 4b) parallel to the longitudinal direction of the developing container (longitudinal direction of the photosensitive drum) and the second developer circulating screw. 4e-2 (the side far from the developing sleeve 4b) is disposed. Hereinafter, the first developer circulating screw 4e-1 is referred to as a developing screw, and the second developer circulating screw 4e-2 is referred to as a stirring screw. In this embodiment, both the developing screw 4e-1 and the stirring screw 4e-2 are used. A central shaft having a diameter of 7 mm and an outer diameter of 14 mm was used.

  FIG. 4 is a longitudinal plan view of the developing device 4. The developer in the developing container 4a is mixed and stirred by circulating in the developing container 4a in the longitudinal direction of the developing container 4a by the rotation of the developing screw 4e-1 and the stirring screw 4e-2. In this embodiment, the developer circulation direction is the direction from the front side to the back side in the direction perpendicular to the drawing in FIG. 2 on the developing screw 4e-1 side (the direction from right to left in FIG. 4). In the stirring screw 4e-2 side, the direction is from the back side to the near side in the direction perpendicular to the drawing in FIG. 2 (the direction from left to right in FIG. 4). 2 and 4, the developer in the developing container 4a is omitted from the drawing. In FIG. 2, T1 indicates the upper surface level of the developer stored in the developing container 4a.

  When the developer cartridge 4g as a developer replenishing unit for the developing device 4 is mounted on the image forming apparatus main body, the developer replenishing port 4h of the developer cartridge 4g is on the upper surface side of the developing container 4a of the developing device 4. Corresponding to the developer inlet 4k provided in FIG.

  The developer cartridge 4g contains a mixture of toner and magnetic carrier as a replenishment developer. The control circuit 100 controls the rotation of the replenishing screw 4i provided in the developer cartridge 4g so as to supplement the toner consumed by the image formation for the two-component developer in the developing container 4a. Due to the rotation of the replenishing screw 4i, a timely and appropriate amount of replenishing developer from the developer replenishing port 4h of the developer cartridge 4g drops into the developing container 4a through the developer replenishing port 4h and the developer inlet 4k. To be replenished. The developer replenished into the developing container 4a from the developer cartridge 4g is mixed and stirred by the rotation of the stirring screw 4e-2 and the developing screw 4e-1 with the two-component developer in the developing container 4a.

  The mixing ratio of the toner for replenishment developer accommodated in the developer cartridge 4g and the magnetic carrier is about 9: 1 by weight, but is not particularly limited to this value. That is, the toner amount is overwhelmingly larger than the mixing ratio of the two-component developer toner and the magnetic carrier in the developing container 4a, and considering the volume ratio, it is considered that a small amount of magnetic carrier is mixed in the toner. You can also. That is, when the toner consumed by image formation is supplemented to the two-component developer in the developing container 4a, a small amount of magnetic carrier is gradually replenished. If the ratio of the magnetic carrier of the developer to be replenished increases, the same amount of toner replenishment increases the amount of replacement of the magnetic carrier described later, and the developer in the developer container 4a approaches a fresh state. Carrier consumption increases. Accordingly, the mixing ratio between the toner of the replenishment developer accommodated in the developer cartridge 4g and the magnetic carrier may be separately determined depending on the image quality performance and running cost required by the specifications of the image forming apparatus. preferable.

  The replenishment amount of the replenishment developer accommodated in the developer cartridge 4g is roughly determined by the rotational speed of the replenishment screw 4i, and this rotational speed is determined by the toner replenishment amount control means 4j (FIG. 4). As the toner replenishment amount control means 4j, various means such as those for optically detecting the toner density of the developer and those for developing the reference latent image on the photosensitive drum 1 to detect the density of the toner image are used. obtain. In this embodiment, as the toner replenishment amount control means 4j, a method of magnetically detecting the toner concentration of the developer in the developing container 4a is adopted. The reason for adopting this method is that this method is superior in cost and stability compared to other methods, but there is no significant difference in other methods.

  Detection information of the toner replenishment amount control means 4j is input to the control circuit unit 100. The control circuit unit 100 controls the rotation of the replenishing screw 4i based on the input information, and replenishes the developer container 4a with a suitable and appropriate amount of replenishing developer from the developer replenishing port 4h of the developer cartridge 4g. By supplying the developer, the toner concentration (mixing ratio of the toner and the magnetic carrier) of the two-component developer in the developing container 4a is maintained in a substantially constant state. When it is detected that the developer for replenishment in the developer cartridge 4g runs out, the control circuit unit 100 displays on the display unit (not shown) a message prompting the user to replace the developer cartridge 4g with a new one.

  Next, the two-component developer used in this embodiment will be described.

The toner is composed of colored resin particles containing an additive such as a binder resin, a colorant, other charge control agents, and wax. In addition, inorganic oxide fine particles such as colloidal silica and titania are externally added to the surface of the colored resin fine particles as necessary for improving fluidity and adjusting the charge amount. In the toner of Example 1, the binder resin is a polyester resin, the resistance value is about 10 ¹⁴ Ωcm, and the volume average particle diameter D ₄ is about 6.0 μm.

The volume average particle diameter D ₄ of the toner, using a Coulter counter Model TA-II (manufactured by Coulter Electronics, Inc.). As a measuring method, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an electrolytic solution composed of 1% NaCl aqueous solution prepared using primary sodium chloride, and further measured. Add 2-20 mg of sample. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes. Using a Coulter counter TA-II, a toner volume of 2 μm or more is measured using a 100 μm aperture. Thus, the volume distribution is calculated, and the median diameter of 50% volume is defined as the volume average particle diameter from the measurement result.

As the magnetic carrier, for example, surface-oxidized or non-oxidized iron, nickel, cobalt, manganese, chromium, rare earth and other metals and their alloys, or oxide ferrite can be preferably used. The production method is not particularly limited. The resistance value of the magnetic carrier in Example 1 is 10 ¹⁰ Ωcm (10 ⁸ Ωcm to 10 ¹² Ωcm), the amount of magnetization is 200 emu / cc (100 emu / cc to 300 emu / cc), and the number average particle diameter is about 35 μm (see FIG. 5).

  The volume average particle size of the magnetic carrier is obtained by dividing the range of particle size of 0.5 to 200 μm by 32 logarithm on the basis of the number of particles using a flow type particle image analyzer FPIA 3000 (manufactured by Sysmex Corporation). taking measurement. Then, from the measurement result, the median diameter of 50% is used as the number average particle diameter.

In addition, the resistance value of the magnetic carrier is determined by using a sandwich type cell having a measurement electrode area of 10 cm ² and a distance between electrodes of 0.4 cm, applying a load of 1 kg to one electrode, and applying a voltage E (V / cm between both electrodes). ) Was used to measure the resistance value of the magnetic carrier.

  As shown in FIGS. 2 and 4, a developer discharge port 4f as a developer discharge means is provided on the wall surface of the developer container 4a in the vicinity of the stirring screw 4e-2. The developer containing the magnetic carrier which is contained in the developing container 4a and deteriorated due to the toner resin adhering to the surface by repeating the image formation is discharged out of the developing device 4 through the developer discharge port 4f. When the developer is replenished from the developer cartridge 4g into the developer container 4a and the upper surface level T1 of the developer in the developer container rises, the developer is discharged from the developer discharge port 4f. This is done by overflowing the developer out of the developer container from the developer discharge port 4f. The amount of the developer discharged is set to be approximately the same as the new developer replenished from the developer cartridge 4g into the developing container 4a.

(6) Image carrier cleaning means 6
The photosensitive drum cleaning device 6 as a cleaning unit for removing toner remaining on the surface of the photosensitive drum after the primary transfer of the toner image to the belt 5b is a blade cleaning type device using a cleaning blade 6a as a cleaning member.

  The blade 6a is a plate-like member made of urethane rubber, and the blade 6a is attached to the cleaning container 6i by a support member 6h. The blade 6a abuts the edge portion on the surface of the photosensitive drum so as to be a counter with respect to the drum rotation direction, and is scraped off when the transfer residual toner on the photosensitive drum reaches the edge portion of the blade 6a.

  Here, as a setting condition for contacting the blade 6a to the surface of the photosensitive drum, in this embodiment, the blade 6a having a free length of 10 mm and a plate thickness of 2 mm is applied with a contact pressure of 500 gf (= 4. 9N), the contact angle is set to 30 °.

(7) Photosensitive drum polishing mechanism Next, the photosensitive drum polishing mechanism which is the most characteristic part in this embodiment will be described. The photosensitive drum polishing mechanism introduces the developer discharged through the developer discharge port 4f of the developing device 4 into the photosensitive drum cleaning device 6, and uses the magnetic carrier contained in the developer as an abrasive for the photosensitive drum 1. It is what you use. The developer discharge port 4f is developer discharge means for discharging the two-component developer stored in the apparatus from the developing device 4.

  As shown in the model diagram of FIG. 2, the developer discharge port 4 f provided in the developing device 4 and the discharged developer supply port 6 f provided in the cleaning device 6 are communicated with each other by a discharged developer transport pipe 10. The discharged developer transport pipe 10 is developer transport means for transporting the two-component developer discharged from the developer discharge port 4 f of the developing device 4 to the cleaning device 6. A discharged developer transport screw 10 a having flexibility (flexible) is inserted into the pipe 10. The screw 10a is rotationally driven by a driving means (not shown) in a direction in which the developer in the pipe 10 is conveyed from the developing device 4 side to the cleaning device 6 side. Of the developer in the developer container 4a, the developer discharged to the outside of the developer container 4a through the developer discharge port 4f enters the pipe 10, and the pipe 10 is rotated in the direction of arrow Y by the rotation of the screw 10a. It is conveyed and eventually reaches the cleaning device 6. In this example, a spring screw having an outer diameter of 14 mm was used as the screw 10a.

  Here, the conveyance speed by the screw 10a of the developer discharged to the pipe 10 outside the developer container 4a through the developer discharge port 4f is based on the image ratio of the image formed by the image forming apparatus in this embodiment. Variable control. Specifically, the control circuit unit 100 decreases the conveyance speed when the image ratio is low, and increases the conveyance speed as the image ratio increases. The reason for this is that when the image ratio is high, the amount of developer fed from the developing device 4 side to the cleaning device 6 side increases. Therefore, the developer in the cleaning device 6 becomes excessive, and the developer may overflow in the cleaning device 6. On the other hand, when the image ratio is low, the amount of developer sent from the developing device 4 side to the cleaning device 6 side decreases. For this reason, the developer in the cleaning device 6 becomes insufficient, and there is a possibility that a magnetic carrier for polishing the photosensitive drum 1 described below is depleted. Therefore, the developer can be stably supplied to the cleaning device 6 by adjusting the conveying speed of the screw 10a according to the image ratio and using the pipe 10 as a developer buffer.

  2 and 6, the developer conveyed from the developing device 4 side to the cleaning device 6 side by the screw 10a of the pipe 10 is taken into the cleaning container 6i of the cleaning device 6 through the discharged developer supply port 6f.

  The developer taken in the cleaning container 6i is uniformly distributed in the cleaning container 6i in the cleaning container longitudinal direction by the developer equalizing screw 6d disposed in the cleaning container longitudinal direction (longitudinal direction of the photosensitive drum). It is conveyed to become. At the same time, the developer in the cleaning container 6i is supplied to a cleaning auxiliary brush roller 6c comprising a rotatable brush roller as a cleaning auxiliary means. Developer uniformizing screw 6d conveys the two-component developer conveyed to the cleaning device 6 in the longitudinal direction of the cleaning device and also supplies the developer uniformly to the longitudinal direction of the cleaning auxiliary brush roller 6c. It is.

  In this embodiment, the developer transport direction by the developer uniformizing screw 6d is the direction from the front side to the back side in the direction perpendicular to the drawing in FIG. 6A (from the left in FIG. 6B). Direction to the right). That is, it is the direction from the position of the discharged developer supply port 6f provided at the front end of the cleaning device 6 toward the back end. In this embodiment, the developer uniformizing screw 6d has a central axis diameter of 7 mm and an outer diameter of 14 mm.

  The cleaning auxiliary brush roller 6c is in contact with the photosensitive drum 1 with a constant intrusion amount in the cleaning container 6i on the upstream side in the rotational direction of the photosensitive drum (upstream side in the rotational direction of the image carrier) with respect to the cleaning blade 6a. It is arranged. The auxiliary cleaning brush roller 6c carries a magnetic carrier in the developer supplied by the developer uniformizing screw 6d, and is driven in a direction opposite to the rotation direction of the photosensitive drum 1 at a contact portion with the photosensitive drum 1. It is rotationally driven by (not shown).

  As described above, the cleaning auxiliary brush roller 6c carries the magnetic carrier, rotates, and rubs against the surface of the photosensitive drum, thereby charging products, toner resin, external additives, and the like attached on the photosensitive drum. It has a role to polish and remove.

  Here, the cleaning auxiliary brush roller 6c weaves fibers (threads) that form a brush into a base cloth on a flat plate, and then cuts into an appropriate size and winds it around a metal core in a spiral shape to form a roller shape. Finished fabric-type brush roller.

  There are various types of materials for the fibers (threads) forming the brush of the brush roller, such as nylon, polyethylene terephthalate, polyimide, rayon, triacetate, and cupra. In this example, nylon was selected from the viewpoint of cost. In this embodiment, the length (pile length) of the fibers (threads) forming the brush of the cleaning auxiliary brush roller 6c is 5 mm, and the core metal thickness is 6 mm. Therefore, the outer diameter of the cleaning auxiliary brush roller 6c is It was 16 mm. The penetration amount of the cleaning auxiliary brush roller 6c into the photosensitive drum 1 was 1.5 mm.

  The following 1) and 2) are important conditions for maintaining the ability of the cleaning auxiliary brush roller 6c to carry the magnetic carrier and to polish the surface of the photosensitive drum.

1) Conditions for the magnetic carrier that actually plays the role of polishing the surface of the photosensitive drum 2) Fiber (thread) conditions for forming the brush of the auxiliary cleaning brush roller 6c to enable the magnetic carrier to be supported sufficiently and sufficiently First, the conditions of 1) magnetic carrier will be described. The number average particle diameter of the magnetic carrier was about 35 μm in Example 1 as described above (see FIG. 5).

  The number average particle diameter of the magnetic carrier is determined by the following matters, for example. When it is stirred together with the toner in the developing device 4, it has a surface area that can maintain a sufficient charge imparting ability for the newly replenished toner, and is sufficiently due to the magnetic force of the magnet 4 c in the developing sleeve 4 b. For example, the size has a magnetization amount to be restrained.

  Depending on the number average particle diameter of the magnetic carrier, the ability of the magnetic carrier to polish the surface of the photosensitive drum does not change greatly directly. However, for example, when the number average particle diameter of the magnetic carrier exceeds 50 μm, there is a possibility that the magnetic carrier cannot be sufficiently carried on the cleaning auxiliary brush roller 6c.

  As a condition of the magnetic carrier that greatly affects the ability of the magnetic carrier to polish the surface of the photosensitive drum, there is unevenness on the surface of the magnetic carrier. FIG. 7 shows a model diagram of the surface of the magnetic carrier. It can be seen that the surface of the magnetic carrier of (a) has larger irregularities than the surface of the magnetic carrier of (b). A typical magnetic carrier includes a core made of a magnetic material and a coat layer (having a thickness of about 0.2 μm) formed to cover the core surface. The role of the coat layer is to prevent adhesion of toner resin and external additives, to maintain the ability to impart charge to the toner, to adjust the resistance of the magnetic carrier, and to improve the releasability from the toner. In order to improve the releasability from the toner, a method of adding inorganic fine particles of several tens of nanometers to the coat layer is often used, and the magnetic carrier surface shown in FIGS. 7A and 7B is used. The unevenness of is different because the particle size and amount of the inorganic fine particles added to the coating layer are different.

  FIG. 8 shows the relationship between the unevenness of the magnetic carrier surface and the polishing ability of the photosensitive drum surface.

  In this example, the change in the contact angle on the surface of the photosensitive drum was measured as a method for evaluating the polishing ability of the magnetic carrier. FIG. 8A shows a change in contact angle with use of the photosensitive drum 1. In general, the contact angle of the photosensitive drum 1 often changes within a certain range after greatly changing immediately after the start of use. Therefore, as a numerical value indicating the polishing ability of the magnetic carrier, a difference value between an initial contact angle on the surface of the photosensitive drum and a stable contact angle after use was used.

  FIG. 8B shows the relationship between the unevenness (center line average roughness; Ra) of the magnetic carrier surface and the polishing ability (contact angle difference value) of the magnetic carrier. Here, the tapping mode, which is one of the functions of the scanning probe microscope D3100 (manufactured by Bieco), was used to measure the unevenness (centerline average roughness; Ra) on the surface of the magnetic carrier. Specifically, a 10 μm square region on the surface of the magnetic carrier is measured, and the center line average roughness (Ra) within the measurement range is calculated. This work is measured for about 10 magnetic carriers arbitrarily selected, and the center line average roughness (Ra) calculated by each measurement is averaged again to obtain the center line average roughness (Ra) of the magnetic carrier. It was.

  From the result of FIG. 8B, in order to maintain the ability of the magnetic carrier to polish the photosensitive drum surface, it is desirable that the center line average roughness (Ra) of the magnetic carrier is in the range of 20 nm to 160 nm. . From this result, the polishing ability of the magnetic carrier greatly depends on the unevenness on the surface of the magnetic carrier, and in fact, the unevenness on the surface of the magnetic carrier makes contact with and rubs against the surface of the photosensitive drum, thereby exhibiting the effect of the abrasive. it seems to do.

  Therefore, with a magnetic carrier with small irregularities such that the center line average roughness (Ra) is 10 nm, the polishing effect due to the irregularities on the surface of the magnetic carrier cannot be expected. On the contrary, it is considered that the polishing effect is lowered in a magnetic carrier with large unevenness having a center line average roughness (Ra) of 180 nm because the frequency of unevenness on the surface of the magnetic carrier is less in contact with the surface of the photosensitive drum.

  In Example 1, the centerline average roughness (Ra) of the magnetic carrier was 80 nm (the magnetic carrier shown in FIG. 7A).

  Incidentally, in a conventional image forming apparatus having a photosensitive drum, the surface of the photosensitive drum may be damaged due to the magnetic carrier being sandwiched between the contact portions of the photosensitive drum and the cleaning blade. However, since the photosensitive drum 1 used in this embodiment has a hard protective layer on the surface of the photosensitive drum, the above-described scratch does not occur.

  Next, the conditions of the fibers (threads) forming the brush of the cleaning auxiliary brush roller 6c of 2) will be described.

  The conditions required for the fibers (threads) forming the brush of the auxiliary cleaning brush roller 6c include that the magnetic carrier that actually polishes the surface of the photosensitive drum is sufficiently supported, and the magnetic carrier that is supported on the brush with a certain force. It is required to press against the surface of the photosensitive drum. In order to satisfy these two conditions, in the first embodiment, the thickness of the fibers (threads) forming the brush of the auxiliary cleaning brush roller 6c and the flocking density were adjusted and optimized.

  FIG. 9A is a model diagram when a magnetic carrier is supported by the cleaning auxiliary brush roller 6c, and FIG. 9B is a model diagram when the magnetic carrier is supported by a magnet roller formed of a rotatable sleeve containing a magnet. Show.

  In the case of (b), the chain made of the magnetic carrier carried by the magnet roller is bent by the shearing force from the photosensitive drum 1 at the portion in contact with the photosensitive drum 1, so that the photosensitive drum 1 of the magnetic carrier. The contact pressure with respect to becomes small. In order to solve this problem, it is conceivable to increase the magnetic force of the magnetic pole of the magnet roller facing the photosensitive drum 1 or to increase the amount of magnetization of the magnetic carrier. However, if these values are increased, the magnetic carrier may stay at the contact portion with the photosensitive drum 1 and overflow. In particular, when the amount of magnetization of the magnetic carrier is changed, when the toner is developed on the electrostatic latent image formed on the surface of the photosensitive drum by the developing device 4, the electrostatic latent image or the toner is developed by the chain of the magnetic carrier. The image may be disturbed, and the image quality as an output product may be deteriorated.

  On the other hand, in the case of (a), the following matters are possible by adjusting the thickness of the fibers (threads) forming the brush of the auxiliary cleaning brush roller 6c and the flocking density. That is, it is possible to realize a necessary and sufficient contact force for carrying the necessary and sufficient magnetic carrier on the brush of the cleaning auxiliary brush roller 6c and for the magnetic carrier to exhibit the polishing ability with respect to the surface of the photosensitive drum.

  In the present embodiment, as described above, nylon is used as the material of the fibers (threads) forming the brush of the cleaning auxiliary brush roller 6c from the viewpoint of cost. Here, the Young's modulus of nylon is 300 kgf / mm (2.94 kN / mm).

  FIG. 10 shows the relationship between the thickness of the fibers (threads) forming the brush of the auxiliary cleaning brush roller 6c and the flocking density and the polishing ability (contact angle difference value) to the photosensitive drum 1 when the magnetic carrier is carried. It is shown.

  (A) shows the relationship between the thickness of the fibers (threads) forming the brush and the polishing ability (difference value of the contact angle). The thickness of the fibers (threads) of the brush is 3 to 10 deniers. It can be seen that good polishing ability is exhibited within the range. Here, when the thickness of the brush fibers (threads) is smaller than 3.0 denier, it is considered that the magnetic carrier cannot give sufficient contact force to the surface of the photosensitive drum in order to exhibit the polishing ability. It is done. On the other hand, when the thickness of the fiber (thread) of the brush is larger than 10 denier, it is considered that the magnetic carrier cannot be sufficiently supported. In Example 1, a 4-denier fiber (thread) forming the brush was used.

(B) shows the relationship between the flocking density of the fibers (threads) forming the brush and the polishing ability (difference value of the contact angle), and the flocking density of the fibers (threads) of the brush is 15k / cm. ^It can be seen that good polishing ability is exhibited within the range of ² to 40 k pieces / cm ² . Here, when the flock density of the fibers (threads) of the brush is less than 15 k pieces / cm ² , the magnetic carrier cannot give sufficient contact force to the surface of the photosensitive drum in order to exhibit the polishing ability. Conceivable. On the other hand, when the flock density of the fibers (threads) of the brush is higher than 40 k pieces / cm ² , it is considered that the magnetic carrier cannot be sufficiently supported. In the present Example 1, the thing of 25k piece / cm < ² > was used as the flocking density of the fiber (thread) which forms a brush.

  2 and 6, 6e is a recovery member (scraper) for recovering the magnetic carrier carried on the cleaning auxiliary brush roller 6c, which is a polyethylene terephthalate plate having a thickness of 1.0 mm. The length of the recovery member 6e is longer than the cleaning auxiliary brush roller 6c, and is in contact with the entire length of the cleaning auxiliary brush roller 6c at a constant angle with an intrusion amount of about 2.5 mm.

  The magnetic carrier recovered from the surface of the cleaning auxiliary brush roller 6c by the recovery member 6e, together with the transfer residual toner recovered from the photosensitive drum 1 by the blade 6a, passes through the cleaning container 6 from the front side by the developer recovery screw 6b. It is conveyed to the side. Then, the toner is discharged out of the cleaning container 6 through a collected toner discharge port 6 g provided on the back side of the cleaning container 6. The developer discharged from the collected toner discharge port 6g is collected in a developer collection box (not shown) provided separately in the image forming apparatus.

  Here, the transport direction of the developer by the developer recovery screw 6b is the same as the transport direction of the developer uniformizing screw 6d in the first embodiment, and the transport speed of the developer by the developer recovery screw 6b is as follows. It was faster than the conveying speed of the developer uniformizing screw 6d. This is because the developer transported by the developer recovery screw 6b is added to the developer introduced into the photosensitive drum cleaning device 6 from the discharged developer replenishing port 6f, and the transfer residual toner recovered from the photosensitive drum by the blade 6a. It is for conveying. By making the developer transport speed by the developer recovery screw 6b faster than the developer uniformizing screw 6d, it is possible to prevent the developer from being excessively accumulated in the photosensitive drum cleaning device 6. In this embodiment, the developer collecting screw 6b has a central axis diameter of 7 mm and an outer diameter of 14 mm.

  FIG. 11 shows the increase or decrease in the amount of deposits on the surface of the photosensitive drum that accompanies the use of the photosensitive drum polishing mechanism described above, based on the change in the contact angle of the photosensitive drum 1.

  The plots marked with ● are obtained when the photosensitive drum 1 having the hard protective layer described above is used in an image forming apparatus that does not have a polishing mechanism using a magnetic carrier as in this embodiment. In this case, since the surface of the photosensitive drum cannot be sufficiently worn, deposits on the photosensitive drum cannot be removed, and the contact angle of the photosensitive drum 1 drops to 80 ° or less at an early stage after the start of use. It will end up.

  On the other hand, the circled plots are those used in the image forming apparatus having the polishing mechanism of this embodiment. Since the surface of the photosensitive drum can be polished by the photosensitive drum polishing mechanism described above and the deposits on the photosensitive drum can be removed, the contact angle of the photosensitive drum 1 changes between 100 ° and 110 °. .

  As described above, the image forming apparatus having the cleaning device of the cleaning blade type and the developing device of the method of gradually automatically changing the developer in the developing device is improved. That is, discharge products, toner resin, and the like adhere to the surface of the photosensitive drum, and the frictional force at the contact portion between the photosensitive drum 1 and the blade 6a increases, resulting in poor cleaning, filming, blade squealing, blade turning, etc. Can be prevented from occurring.

  Further, there is no problem that the magnetic carrier is transferred to the transfer device, the intermediate transfer member, etc., and the developer discharged from the developing device can be used effectively, and a highly stable and low-cost image forming apparatus can be provided. It becomes possible.

  The photosensitive drum 1 shown in the first embodiment is not limited to an organic photoreceptor (OPC) having a hard protective layer, and an inorganic photoreceptor in which the material of the outermost layer of the photosensitive drum 1 is amorphous silicon. May be used.

  Further, the cleaning auxiliary brush roller 6c shown in the present embodiment is not limited to the brush roller, and may be a porous sponge roller as shown in FIG. In FIG. 12, the cleaning auxiliary sponge roller 6c has many holes of about 60 μm that are slightly larger than the number average particle diameter of the magnetic carrier. The surface of the photosensitive drum 1 can be polished by carrying a magnetic carrier in this hole and abutting and rubbing against the surface of the photosensitive drum.

  Furthermore, the cleaning auxiliary brush roller 6c shown in this embodiment is not limited to the brush roller, but is a rotatable magnet roller comprising a rotatable sleeve containing a magnet as shown in FIG. There may be. In FIG. 13, the cleaning auxiliary magnet roller 6 c can carry the magnetic carrier by the magnetic force of the magnet contained therein, and can polish the surface of the photosensitive drum by abutting and rubbing against the surface of the photosensitive drum. .

[Example 2]
Next, a description will be given of a second embodiment of the image forming apparatus according to the present invention. The basic configuration of the image forming apparatus of the second embodiment is the same as that of the first embodiment, and the description of the common configuration is omitted, and the characteristic part of the second embodiment will be described with reference to FIG.

  In the second embodiment, in the cleaning device 6, the developer introduced into the cleaning container 6i from the discharged developer supply port 6f is transported and supplied to the cleaning auxiliary brush roller 6c so as to be uniform in the longitudinal direction. Therefore, the developer uniformizing screw 6d is not provided.

  The cleaning auxiliary brush roller 6c has a function of carrying a developer in the longitudinal direction of the roller, as well as a function of carrying a magnetic carrier to polish the surface of the photosensitive drum. The transport direction of the developer by the cleaning auxiliary brush roller 6c is the same as the transport direction of the developer uniformizing screw 6d of the first embodiment.

  FIG. 14B shows a schematic configuration of the auxiliary cleaning brush roller 6c used in the second embodiment. The cleaning auxiliary brush roller 6c is obtained by winding the brush shown in the first embodiment in a spiral shape at regular intervals, and the outer diameter of the brush portion of the cleaning auxiliary brush roller 6c is 16 mm. Further, a screw for transporting the developer is provided on one end face of the brush portion, and a screw having a central axis diameter of 6 mm and an outer diameter of 12 mm was used.

  In the case of the configuration of the second embodiment, the same effect as that of the first embodiment can be obtained, and space can be saved as compared with the first embodiment.

[Example 3]
Next, a description will be given of an embodiment 3 of the image forming apparatus according to the present invention. The basic configuration of the image forming apparatus of the second embodiment is the same as that of the first embodiment, and the description of the common configuration is omitted, and the characteristic part of the second embodiment will be described with reference to FIG.

  The third embodiment is characterized in that the developer discharged from the developing device 4 of one image forming unit is supplied to the cleaning device 6 of the adjacent image forming unit.

  In FIG. 15, the configurations of the first to fourth image forming units Y-st, M-st, C-st, and M-st are exactly the same as those shown in the first embodiment.

  The discharged developer replenishing port 6f of the cleaning device 6 of the first image forming unit Y-st and the developer discharging port 4f of the developing device 4 of the second image forming unit M-st are pipes 10 as developer conveying means. Have been contacted through. The discharged developer replenishing port 6f of the cleaning device 6 of the second image forming unit M-st and the developer discharging port 4f of the developing device 4 of the third image forming unit C-st are pipes 10 as developer conveying means. Have been contacted through. The discharged developer replenishing port 6f of the cleaning device 6 of the third image forming unit C-st and the developer discharging port 4f of the developing device 4 of the fourth image forming unit Bk-st are pipes 10 as developer conveying means. Have been contacted through. The discharged developer replenishing port 6f of the cleaning device 6 of the fourth image forming unit Bk-st and the developer discharging port 4f of the developing device 4 of the first image forming unit Y-st serve as developer conveying means. Communication is made via a pipe 10.

  Accordingly, the developer is conveyed from the developing device 4 of the adjacent second image forming unit M-st to the cleaning device 6 of the first image forming unit Y-st. The developer is conveyed from the developing device 4 of the adjacent third image forming unit C-st to the cleaning device 6 of the second image forming unit M-st. The developer is conveyed from the developing device 4 of the adjacent fourth image forming unit Bk-st to the cleaning device 6 of the third image forming unit C-st. Then, the developer is conveyed from the developing device 4 of the first image forming unit Y-st to the cleaning device 6 of the fourth image forming unit Bk-st.

  Also in the case of the configuration of the third embodiment, the same effects as those of the first and second embodiments can be obtained, and the developer conveying means can be greatly reduced as compared with the first and second embodiments. Space can be achieved.

[Others]
1) In the above embodiments, a tandem type image forming apparatus having a plurality of image forming units has been described as an example. However, the present invention can be applied to a single color image forming apparatus having one image forming unit. is there.

  2) The image forming apparatus may be configured not to use an intermediate transfer member.

  3) The image carrier and the image forming process are not limited to the electrophotographic photosensitive member and the electrophotographic image forming process. The present invention can also be effectively applied to an image forming apparatus using an electrostatic recording dielectric and an electrostatic recording image forming process, a magnetic recording magnetic material and a magnetic recording image forming process, or the like.

1 is a schematic configuration diagram of a main part of an image forming apparatus in Embodiment 1. FIG. FIG. 2 is an enlarged view (schematic configuration model diagram of a main part) of one image forming unit in the image forming apparatus of FIG. 1. Relationship between the conventional photosensitive drum (photosensitive drum A) and the photosensitive drum of Example 1 (photosensitive drum B), in which the increase or decrease in deposits on the surface of the photosensitive drum due to use was confirmed by the change in the contact angle of the photosensitive drum It is. It is a vertical plane model view of the developing device. It is a related figure which shows the particle size distribution of a magnetic carrier. (A) is a model figure which shows the cross-sectional structure of a cleaning apparatus, (b) is a cross-sectional model figure which follows the (b)-(b) line | wire in (a). (A) And (b) is a model figure which shows the unevenness | corrugation on the surface of a magnetic carrier, respectively. FIG. 6 is a relationship diagram illustrating a relationship between the center line average roughness Ra of the surface of the magnetic carrier and the polishing ability of the magnetic carrier with respect to the photosensitive drum. It is a model for demonstrating the difference between a brush roller type cleaning auxiliary means and a magnet roller type cleaning auxiliary means. FIG. 5 is a relationship diagram illustrating a relationship between the thickness of fibers (threads) forming a brush and the polishing ability of a magnetic carrier with respect to a photosensitive drum of a cleaning auxiliary unit including a brush roller. FIG. 6 is a relationship diagram showing a change in the contact angle of pure water on the surface of the photosensitive drum accompanying use of the photosensitive drum. (A) is a model figure which shows the cross-sectional structure of the cleaning apparatus at the time of using a sponge roller as a cleaning assistance means, (b) is a model figure which shows schematic structure of the cleaning assistance means which consists of sponge rollers. It is a model figure which shows the cross-sectional structure of the cleaning apparatus at the time of using a magnet roller as a cleaning auxiliary means. (A) is a model figure which shows the cross-sectional structure of the cleaning apparatus which concerns on Example 2, (b) is a model figure which shows schematic structure of the cleaning assistance means used. FIG. 6 is a model diagram illustrating a schematic configuration of an image forming apparatus according to a third embodiment.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging means 3 Laser unit (information writing means)
4 developing means 4a developing container 4b developing sleeve 4c magnet roller 4d developer coating blade 4e developer circulating screw 4f developer discharge port 5a primary transfer roller 5b intermediate transfer belt 5f secondary transfer roller 6 photosensitive drum cleaning means 6a cleaning blade 6b Developer recovery screw 6c Cleaning assisting means 6d Developer uniformizing screw 6e Recovery member 6f Discharged developer supply port 6f
6 g Collected toner discharge port 7 Intermediate transfer belt cleaning device 8 Fixing device 10 Discharged developer conveying means P Recording material

Claims (9)

Rotating image carrier for forming an image, charging means for charging the surface of the image carrier, and image information writing for forming an electrostatic latent image on the image carrier charged by the charging means Means for developing the electrostatic latent image formed on the image carrier by supplying the toner with a two-component developer made of toner and a magnetic carrier, and transferring the visualized toner image to a transfer material. In the image forming apparatus, the image forming apparatus includes: a transfer unit that transfers to the surface; and a cleaning unit that includes a cleaning blade for removing the toner remaining on the surface of the image carrier after transfer.
Developer replenishing means for replenishing the developer for replenishment in which toner and magnetic carrier are mixed to the developing means;
Developer discharging means for discharging the two-component developer from the developing means;
Developer conveying means for conveying the two-component developer discharged from the developing means to the cleaning means;
The cleaning unit is disposed upstream of the cleaning blade in the rotation direction of the image carrier in the cleaning unit, and carries the two-component developer transported to the cleaning unit by the developer transport unit and carries the surface of the image carrier. Cleaning auxiliary means abutting on
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the cleaning auxiliary means is a rotatable brush roller.   Developer transport means for transporting the two-component developer transported to the cleaning means by the developer transport means in the longitudinal direction of the cleaning means and uniformly supplying the two-component developer in the longitudinal direction of the cleaning auxiliary means; The image forming apparatus according to claim 1, wherein the image forming apparatus is provided in the cleaning unit.   The image forming apparatus according to claim 2, wherein the thickness of the fiber forming the brush roller is in the range of 3 to 10 denier. 5. The image forming apparatus according to claim 2, wherein a flocking density of fibers forming the brush roller is in a range of 15 k / cm ² to 40 k / cm ² .   6. The image forming apparatus according to claim 1, wherein the center line average roughness of the surface of the magnetic carrier is in the range of 20 nm to 160 nm. When the hardness of the image carrier is tested using a Vickers square pyramid diamond indenter under an environment of a temperature of 25 ° C. and a humidity of 50%, the elastic deformation rate when pressed with a load of 6 mN is 45% to 65%. The image forming apparatus according to claim 1, wherein a universal hardness value is 150 N / mm ² or more and 220 N / mm ² or less.   8. The image forming apparatus according to claim 1, wherein the cleaning assisting unit is a rotatable sponge roller.   The image forming apparatus according to claim 1, wherein the cleaning assisting unit is a rotatable magnet roller.