JP2006184373A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of restraining the deterioration in image quality occurring because residual toner after transfer passes through a latent image forming area in the midst of forming a latent image. <P>SOLUTION: The residual toner after transfer remaining on the surface of a photoreceptor 1 without being electrostatically transferred to an intermediate transfer belt 10 in a primary transfer nip is temporarily held by a blade 13 before reaching the latent image forming area. When the residual toner after transfer passes through the latent image forming area, it is restored to the surface of the photoreceptor from the blade again in timing in which write-in is not performed on the surface of the photoreceptor by an exposure device 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

  In this type of image forming apparatus, a transfer electric field is formed between the latent image carrier and the transferred material that moves while contacting the latent image carrier, so that the toner image on the latent image carrier is transferred onto the transferred material. Some employ an electrostatic transfer system that transfers to the surface. In such an apparatus, residual toner remains on the surface of the latent image carrier after transfer. If the latent image carrier surface portion is subjected to the next image forming process without the transfer residual toner being removed, charging failure such as uneven charging occurs on the latent image carrier surface portion, and the image quality deteriorates. Cause. Therefore, conventionally, a cleaning device is provided at a position facing the surface of the latent image carrier from the transfer region to the charging region to remove the transfer residual toner. Such a cleaning device includes a waste toner tank that stores transfer residual toner collected from the surface of the latent image carrier, a recycled toner transport passage that transports the transfer residual toner to reuse the collected transfer residual toner, and the like. Space to provide is required. This increases the size of the image forming apparatus.

  For example, there is an image forming apparatus disclosed in Patent Document 1 that can cope with the problem of enlargement of the apparatus. This image forming apparatus employs a system (hereinafter referred to as “developer recovery system”) that collects the transfer residual toner remaining on the surface of the latent image carrier using a developing device. In this developing device collection method, since the transfer residual toner is collected by a developing device installed for a purpose other than cleaning, it is not necessary to separately provide the waste toner tank and the recycled toner conveyance path as described above. Therefore, if this developer collection system is adopted, it can greatly contribute to the downsizing of the apparatus.

  Japanese Patent Application Laid-Open No. 2005-228561 describes an embodiment in which charging is performed by bringing a charging roller into contact with a latent image carrier as a charging device mounted on an image forming apparatus of a developing device collection type. Conventionally, the surface of the latent image carrier is uniformly charged by a contact / proximity charging method in which a charging member such as a charging roller is brought into contact with or close to the surface, and by a corona charger or the like. Charged charger charging methods are known. However, in the charger charging method, it is necessary to generate a large amount of discharge in order to bring the surface of the latent image carrier to a desired potential. Therefore, a large amount of discharge products such as ozone and NOx are generated, which causes environmental problems. is there. On the other hand, the contact / proximity charging method is advantageous in terms of the environment because it generates less discharge than the charger charging method. Therefore, according to the image forming apparatus described in the above-described embodiment, it is considered that the effect that the generation amount of the discharge product is small and the environment is advantageous can be obtained while the apparatus is downsized.

  However, in such an image forming apparatus using both the developer collection method and the contact / proximity charging method, the transfer residual toner, the charging member, and the like are transferred while the transfer residual toner on the latent image carrier is conveyed to the development region. Will be in contact with or close to each other. Therefore, transfer residual toner may adhere to the charging member. If the transfer residual toner adheres to the charging member, uniform charge is prevented by the attached transfer residual toner, and the surface potential of the latent image carrier cannot be set to a desired potential, or charging failure such as uneven charging occurs. . As a result, there has been a problem that image density is deteriorated and background stains occur, resulting in image quality deterioration. This problem is not limited to the case of adopting the developing device collection method, and can similarly occur if the transfer residual toner is transported to the contact area with the charging member without being removed from the latent image carrier. Is.

  In the patent document 2, the present applicant has proposed an image forming apparatus that can solve the above problems. In this image forming apparatus, among the transfer residual toner remaining on the surface of the latent image carrier after the transfer, a reversely charged toner having a polarity opposite to that of the normally charged toner charged to the same polarity as the charging bias is applied. Is collected from the surface of the latent image carrier and held by a temporary holding means such as a brush member. By collecting and holding the reversely charged toner in this way, it is possible to prevent the reversely charged toner from adhering to the charging member. Then, the held reversely charged toner is returned to the surface of the latent image carrier at a predetermined timing such as after the completion of one image formation and before the next image formation. The reversely charged toner returned to the latent image carrier in this way is collected by the developing device, or transferred to a transfer target or a transport member for transporting the transfer target. According to this apparatus, while the returned reversely charged toner passes through the charging region, the application of the charging bias is stopped or the charging member is separated from the latent image carrier. There is no adhesion.

Japanese Patent No. 3091323 JP 2004-93849 A

  On the other hand, the normally charged toner of the transfer residual toner has the same polarity as the charging bias, and therefore does not adhere to the charging member even when the charging bias is applied during image formation. For this reason, the normally charged toner of the transfer residual toner is not collected by the temporary holding means such as a brush member to which a bias having the same polarity as the charging bias is applied. Accordingly, during the next image forming process, the charging member and the latent image forming unit pass through a region (hereinafter referred to as a latent image forming region) facing each other and are collected by the developing device or transferred to a transfer target. However, when a latent image is formed on the surface of the latent image carrier by the latent image forming means while the normally charged toner is attached to the surface of the latent image carrier, the portion where the toner is attached or the portion that is shaded by the toner is Not exposed. As a result, there may be a problem that white spots occur in the solid image portion.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image that can suppress deterioration in image quality caused by a transfer residual toner passing through a latent image forming area during formation of a latent image. A forming apparatus is provided.

In order to achieve the above object, the invention of claim 1 is characterized in that the surface of the latent image carrier is uniformly charged, and an electrostatic latent image is formed on the surface of the uniformly charged latent image carrier. An image forming apparatus comprising: a latent image forming unit configured to develop; a developing unit configured to perform development by attaching toner to the latent image; and a transfer unit configured to transfer the toner image on the latent image carrier to a transfer material. A temporary holding means for temporarily holding the transfer residual toner before the transfer residual toner remaining on the surface of the latent image carrier after the transfer by the transfer means reaches the charging means; and a transfer residual held by the temporary holding means. Control means for returning the toner to the surface of the latent image carrier again at a predetermined timing; toner recovery means for collecting the transfer residual toner returned to the surface of the latent image carrier by the temporary holding means; and the transfer residual toner Before the toner is collected by the collecting means. Charge injection means for injecting a load, the charge injection means comprising a contact member that comes into contact with the latent image carrier, and the contact surface of the contact member that comes into contact with the latent image carrier is provided with conductive fine particles. It is characterized by using a layer containing.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the contact surface of the contact member has an uneven shape with the conductive fine particles exposed.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the conductive fine particles have a volume resistance value of 1 × 10 ¹⁴ [Ω · cm] or less and an average circularity of SR = 0. It is characterized by being 95-1.00.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the volume resistance of the contact surface of the contact member has a volume resistance value of 1 × 10 ¹³ [Ω · cm] or less. It is characterized by being.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the contact member elastically contacts the latent image carrier.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the contact member is a roller member at a contact position between the roller member and the latent image carrier. The roller member is rotated such that the moving direction of the roller member surface is opposite to the moving direction of the latent image carrier surface or the moving speed of the roller member surface is faster than the moving speed of the latent image carrier surface. A drive means is provided.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the developing means contains a developer composed of a toner and a carrier, and the particle size of the carrier is 40 μm or less. It is characterized by this.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, at least the developing means and the latent image carrier are integrally configured so as to be detachable from the image forming apparatus. The process cartridge is provided.

  According to the first to eighth aspects of the invention, during the operation of the latent image forming unit, the transfer residual toner is temporarily transferred between the transfer unit and the charging unit so that the transfer residual toner does not pass the position facing the latent image forming unit. Temporarily hold by holding means. Then, when the transfer residual toner returned to the latent image carrier from the temporary holding unit passes through a position facing the latent image forming unit, the latent image forming unit is held by the temporary holding unit at a timing at which the latent image forming unit is not operating. The transferred residual toner is returned to the surface of the latent image carrier. Therefore, it is possible to suppress the transfer residual toner from adhering to the surface of the latent image carrier that passes through the latent image forming area during the latent image formation. Further, before the transfer residual toner returned from the temporary holding means to the latent image carrier is recovered by the recovery means, a charge having a predetermined polarity is applied to the transfer residual toner by the charge injection means, and the transfer residual toner is set to the predetermined polarity. Align with the same polarity. As a result, all of the untransferred toner that has reached the collecting means is charged to a predetermined polarity. Therefore, if a bias having a polarity opposite to the predetermined polarity is applied to the collecting unit, the transfer residual toner can be electrostatically collected by the collecting unit. The contact surface of the contact member that contacts the latent image carrier of the charge injection means contains conductive fine particles. For this reason, the volume resistance value of the contact surface of the contact member can be lowered, and the charge can be injected well into the transfer residual toner in contact with the contact surface. Therefore, it is possible to ensure that all of the untransferred toner has a predetermined polarity, and it is possible to increase the absolute value of the charge amount of the untransferred toner whose charge amount has decreased. As a result, it is possible to improve the recoverability of the transfer residual toner of the recovery means. Also, before the transfer residual toner passes through the charging means, the charge injection means applies a charge having the same polarity as the charging bias so that the polarity of the transfer residual toner is the same as the charging bias. The transfer residual toner does not adhere to the charging unit without stopping the charging or separating the charging member from the latent image carrier.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a laser printer according to the present embodiment. This laser printer has four sets of image forming means 1M, 1C, 1Y, 1BK (hereinafter referred to as each image forming unit) for forming images of each color of magenta (M), cyan (C), yellow (Y), and black (BK). The subscripts M, C, Y, and BK of the symbols indicate magenta, cyan, yellow, and black members, respectively, and the moving direction of the transfer paper 100 (see FIG. 2) as a transfer material (see FIG. 2). Arranged in order from the upstream side in the direction of arrow A). Each of the image forming units 1M, 1C, 1Y, and 1BK includes a photoconductor unit having photoconductor drums 11M, 11C, 11Y, and 11BK having a diameter of 30 [mm] as an image carrier, and a developing unit. . The image forming units 1M, 1C, 1Y, and 1BK are arranged so that the rotation axes of the photoconductive drums 11M, 11C, 11Y, and 11BK in each photoconductive unit are parallel to each other and in the transfer paper moving direction. It is set to be arranged at a pitch.

  In addition to the image forming means 1M, 1C, 1Y, and 1BK, the laser printer transfers a transfer material toward the optical writing unit 2, the paper feed cassettes 3 and 4, and a transfer portion that faces each of the photosensitive drums 11. A transfer unit 6 having a transfer belt 60 as a transfer material transport belt for transporting a transfer material, a registration roller 5 comprising a pair of rollers for supplying a transfer paper 100 as a transfer material to the transfer belt 60, a belt fixing type fixing unit 7, A paper discharge tray 8 and a reversing unit 9 are provided. The laser printer also includes a manual feed tray, a toner supply container, a waste toner bottle, a power supply unit, and the like (not shown).

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11M, 11C, 11Y, and 11BK while scanning the laser beam based on image data. To do.

  Also, the alternate long and short dash line in FIG. 1 indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration rollers 5 are provided. The transfer paper 100 is supplied to the transfer belt 60 by the registration roller 5 at a predetermined timing, and is conveyed so as to pass through the transfer portions facing the photoconductive drums 11M, C, Y, and BK. As a result, the toner images on the photoconductive drums 11M, 11C, 11Y, and 11BK formed by the image forming units 1M, 1C, 1Y, and 1BK are sequentially superimposed and transferred onto the transfer paper, and are transferred onto the transfer material. A color image is formed. The transfer paper 100 on which the color image is formed is discharged onto the paper discharge tray 8 after the toner image is fixed by the fixing unit 7.

FIG. 2 is an enlarged view showing a schematic configuration of the magenta image forming means 1M among the image forming means 1M, 1C, 1Y and 1BK. Since the other image forming means 1C, 1Y, and 1BK have the same configuration, their descriptions are omitted.
In FIG. 2, the image forming means 1M includes the photoconductor unit 10M and the developing unit 20M as described above. In addition to the photosensitive drum 11M, the photosensitive unit 10M includes a non-contact type charging roller 15M that uniformly charges the surface of the photosensitive drum. Also provided is a blade 13M as temporary holding means for temporarily holding the transfer residual toner on the surface of the photoreceptor, and a charge injection roller 12M as charge injection means for normally charging the reversely charged toner of the transfer residual toner on the surface of the photoreceptor drum. . The charge injection roller 12M is in contact with the photosensitive drum. A power supply (not shown) for applying a bias is connected to the charge injection roller 12M.

  In the photosensitive unit 10M having the above configuration, the surface of the photosensitive drum 11M is uniformly charged by the charging roller 15M to which a voltage is applied. A DC voltage of −1000 V is applied to the charging roller 15M, and the surface of the photoreceptor is uniformly charged to −400V. By applying a DC voltage to the charging roller 15M, photoconductor filming and ozone deterioration of the photoconductor surface can be suppressed. When the surface of the photosensitive drum 11M is irradiated with the laser beam modulated and deflected by the optical writing unit 2 while being scanned, an electrostatic latent image is formed on the surface of the photosensitive drum 11M. The electrostatic latent image on the photosensitive drum 11M is developed by a developing unit 20M described later to become a magenta toner image. In the transfer portion Pt through which the transfer paper 100 on the transfer belt 60 passes, the toner image on the photosensitive drum 11M is transferred to the transfer paper 100.

  The developing unit 20M uses a two-component developer (hereinafter also simply referred to as “developer”) 28M including a magnetic carrier and negatively charged toner as a developer for developing the electrostatic latent image. . As the toner, known toners such as pulverized toner and polymerized toner can be used. In this embodiment, toner having a particle size of 6 [μm] is used. Further, the developing unit 20M has a developing sleeve 22M having a diameter of 18 [mm] made of a nonmagnetic material as a developer carrying member disposed so as to be partially exposed from the opening on the photosensitive drum side of the developing case 21M. In addition, the magnetic permeability of the developer 28M as a magnet roller (not shown), the conveying screws 23M and 24M, the developing doctor 25M, and the toner concentration sensor (T sensor) is detected as a magnetic field generating means fixedly arranged inside the developing sleeve 22M. A magnetic permeability sensor 26M, a powder pump 27M, and the like. The developing sleeve 22M is applied with a developing bias of −300 [V] in which an AC voltage AC (AC component) is superimposed on a negative DC voltage DC (DC component) by a developing bias power supply (not shown) as a developing electric field forming unit. The developing sleeve 22M is biased to a predetermined voltage with respect to the metal base layer of the photosensitive drum 11M.

  In FIG. 2, the developer 28M accommodated in the developing case 21M is frictionally charged by being agitated and conveyed by the conveying screws 23M and 24M. Then, a part of the developer 28M is carried on the surface of the developing sleeve 22M rotating at 500 [mm / sec], the layer thickness is regulated by the developing doctor 25M, and then the developing facing the photosensitive drum 11M. Transported to position. At the development position, the electrostatic latent image on the photosensitive drum 11M is developed by the charged toner in the developer on the development sleeve 22M.

  Since the toner concentration of the developer 28M in the developing case 21M decreases due to the consumption of the developer accompanying the image formation, a toner cartridge (not used) may be necessary depending on the image area and the detected value (Vt) of the magnetic permeability sensor 26M. The toner is replenished by the powder pump 27M from the figure) and is kept substantially constant. The toner supply is based on the difference ΔT (= Vref−Vt) between the toner density target value (Vref) and Vt, and when ΔT is + (plus), the toner density is considered to be sufficiently high and the toner is not supplied. , ΔT is − (minus), the larger the amount | ΔT |, the larger the toner replenishment amount, and the Vt approaches the value of Vref. Further, process control (for example, a plurality of halftones and solid patterns formed on the photosensitive drum 11M is converted into an adhesion amount by a reflection density sensor once every 10 sheets (about 5 to 200 sheets depending on copy speed or the like) Vref, charging potential, and light quantity are set according to a target setting mode. In order to perform such toner density control, a control unit (not shown) is provided, and this control unit includes a CPU, a ROM, a RAM as a storage unit, an I / O interface, and the like.

  Of the four photosensitive drums 11M, 11C, 11Y, and 11BK, only the BK photosensitive member 11BK on the most downstream side is always in contact with the transfer belt, and the remaining photosensitive drums 11M, 11C and 11Y can contact and separate from the transfer belt.

  Each image forming means 1M, 1C, 1Y, 1BK is formed as a process cartridge and is configured to be detachable from the apparatus main body.

Hereinafter, image formation of the laser printer according to the present embodiment will be described.
A multicolor image forming mode for forming a color image on the transfer paper will be described. The four photosensitive drums 11M, 11C, 11Y, and 11BK are in contact with the transfer belt 60, respectively. The electrostatic adsorption roller 61 applies a charge having the same polarity as the toner to the transfer paper 100, and the transfer paper 100 is adsorbed to the transfer belt 60. As a result, as described above, transfer failure of the toner image due to charge-up of the transfer material can be eliminated.

  The transfer paper 100 is conveyed while adsorbed to the transfer belt 60, and magenta, cyan, and yellow color toner images formed on the upstream color drums 11M, 11C, and 11Y are sequentially superimposed and transferred. The black toner image formed on the BK drum 11BK is superimposed and transferred. The toner image transferred and superimposed on the transfer paper 100 is fixed by the fixing unit 7 to form a permanent full-color image.

  In the single color image forming mode in which, for example, a black single color image is formed on the transfer paper 100, the color drums 11Y, 11C, and 11M are separated from the transfer belt 60 in FIG. Only the BK drum 11BK is brought into contact with the transfer belt 60. The transfer paper 100 is conveyed to the transfer nip of the BK drum 11BK, and after the black toner image is transferred, the transfer paper 100 is fixed by the fixing unit 7 to form a black monochrome image.

  Next, cleaning of transfer residual toner remaining on the surface of the photosensitive drum 1 which is a characteristic part of the present invention will be described. FIG. 3A is a graph showing the charge potential distribution immediately before the transfer of the toner carried on the photosensitive drum 1. FIG. 3B is a graph showing the charge potential distribution of the untransferred toner remaining on the photosensitive drum 1 after the transfer. As shown in FIG. 3A, the charge amount of the toner immediately before the transfer is distributed around -30 [μC / g], and most of the charge is normally charged negatively. On the other hand, the charge amount of the transfer residual toner is distributed around about −2 [μC / g]. Generally, most of the untransferred toner is a toner that cannot be charged as desired by receiving charge injection by a positive bias applied to the primary transfer roller 14. As a result, in the transfer residual toner, there is a reversely charged toner that has been reversed to the positive polarity as indicated by the hatched portion in FIG.

  As described above, the untransferred toner mixed with the reversely charged toner reversed to the positive polarity adheres to the surface of the photoreceptor and passes through the contact area between the charge injection roller 12M and the photoreceptor drum 11M. A DC voltage of about −200 [V] is applied to the charge injection roller 12M from a power supply device (not shown), and the polarity of the positively charged toner adhering to the surface of the photoreceptor is reversed to the negative polarity. Thereby, the polarity of the transfer residual toner on the photosensitive drum 11M that has passed through the charging roller 12M can be uniformly made negative. The voltage applied to the charge injection roller 12M is preferably a DC voltage. When the voltage applied to the charge injection roller 12M is an AC voltage, the transfer residual toner is reversely charged or the photoconductor filming is likely to occur.

  FIG. 4 is a cross-sectional view showing the charge injection roller 12. The charge injection roller 12 has a metal core 12a, an elastic layer 12b covered with the metal core 12a, and an outermost layer 12c as a contact surface covered therewith. A DC voltage of −200 [V] is applied to the metal core 12a by a power source (not shown). The elastic layer 12b is made of an elastic material such as epichrome hydrin rubber, nitrile rubber, chlorobrene rubber, acrylic rubber, or thermoplastic elastomer in which a conductive material such as carbon black is dispersed. By dispersing the conductive material, the entire elastic layer 12b exhibits electrical conductivity, and conducts the cored bar 12a and the outermost layer 12c.

The outermost layer 12c is formed by applying a coating material in which conductive fine particles 12d are dispersed in an organic solvent to the surface of the elastic layer 12b and curing it. Specifically, the coating material is coated on the surface of the elastic layer 12b by spray coating or dipping, and then cured by heat treatment. As the conductive fine particles 12d, for example, a conductive metal oxide such as tin oxide or a material such as carbon black can be used. The conductive fine particles 12d preferably have a resistance of 1 × 10 ¹⁴ [Ω · cm] or less. By applying a coating material in which conductive fine particles 12d are dispersed in an organic solvent to the elastic layer 12b to form the outermost layer 12c, the surface of the charge injection roller 12 has the conductive fine particles 12d as shown in FIG. The irregular shape is exposed from the surface.

  The toner used in the image forming apparatus of the present embodiment is a toner with a high degree of circularity. When the surface of the charge injection roller 12 is flat, the charge injection roller 12 and the transfer residual toner are in point contact as shown in FIG. 5A in the contact area between the charge injection roller 12 and the photosensitive drum 1. The area where charge is injected from the charge injection roller 12 to the untransferred toner T is small. On the other hand, when the conductive fine particles 12d are exposed and the surface of the charge injection roller 12 has a concavo-convex shape as in this embodiment, as shown in FIG. The area where T contacts the surface of the charge injection roller 12 increases. Therefore, more charge is injected into the transfer residual toner than the charge injection roller 12 having a flat surface. Therefore, the transfer residual toner can be surely made negative. The conductive fine particles are preferably spherical, and those having a circularity SR = 0.95 to 1.00 are preferred.

  The average circularity of the conductive fine particles can be measured by, for example, a flow particle image analyzer FPIA-2100 (manufactured by Toa Medical Electronics Co., Ltd.). As a specific measuring method, 0.1 to 0.5 ml of a surfactant, preferably alkylbenzene sulfonate is added as a dispersant to 100 to 150 ml of water from which impure solids have been removed in advance, and further measurement is performed. Add about 0.1-0.5g of sample. The suspension in which the sample is dispersed is subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the shape and distribution of the conductive fine particles are measured with the above apparatus with the dispersion concentration being 3000 to 10,000 / μl. Obtained by.

By setting the circularity SR = 0.95 to 1.00, the surface of the charge injection roller 12 becomes more uneven as compared with the case where the conductive fine particles are needle-shaped or planar, and the contact area with the toner is increased. To do. In the present embodiment, conductive fine particles having a resistance of 1 × 10 ¹¹ [Ω · cm] and a circularity SR = 0.96 are used.

The resistance of the outermost layer of the charge injection roller is preferably 1 × 10 ¹³ [Ω · cm] or less and excellent in conductivity. By setting the outermost layer to 1 × 10 ¹³ [Ω · cm] or less, it is possible to smoothly inject the charge of the transfer residual toner from the outermost layer. Further, since the charge injection roller 12 has the elastic layer 12b, the charge injection roller 12 is bent and contacts the photosensitive drum 11, and the contact area with the photosensitive drum 11 is enlarged. Thereby, charge injection is reliably performed on the toner, and the toner can be favorably charged to a negative polarity. Further, since the charge injection roller 12 is elastically contacted with the photosensitive drum 11, it is possible to suppress the surface of the photosensitive drum from being damaged.

  The charge injection roller 12 is rotated by a driving device (not shown) so that the surface of the charge injection roller 12 is more in contact with the surface of the photoreceptor. Specifically, the charge injection roller 12 is driven to rotate in the direction opposite to the photosensitive drum 11. When the charge injection roller 12 is rotationally driven in the same direction as the photosensitive drum 11, the rotational speed (500 [mm / sec) is more than twice the rotational speed (250 [mm / sec]) of the photosensitive drum 11. ]). Due to the difference in linear velocity between the photosensitive drum 11 and the charge injection roller 12, the transfer residual toner on the photosensitive drum rolls in the contact area between the photosensitive drum 11 and the charge injection roller 12. As a result, the transfer residual toner comes into contact with the charge injection roller 12 on various surfaces, and charges are injected from various surfaces of the transfer residual toner. For this reason, the transfer residual toner can be uniformly charged to a negative polarity. Further, by increasing the speed difference between the photosensitive drum 11 and the charge injection roller 12M, it is possible to increase the probability of contact between the untransferred toner and the uneven portion on the surface of the charge injection roller, and to ensure that the untransferred toner is properly charged It can be.

  In FIG. 2 described above, the transfer residual toner on the photosensitive drum 11M that has passed through the charge injection roller 12M is temporarily held by the blade 13M. The blade 13M is configured to be able to contact and separate from the photosensitive drum, and is separated from the surface of the photosensitive member at a predetermined timing. The blade 13M is in contact with the moving direction of the photosensitive drum in the counter direction. Further, the blade 13M for temporarily holding the transfer residual toner is disposed on the upstream side of the charging roller 15M with respect to the moving direction of the photosensitive drum 11M. In order to prevent the transfer residual toner from passing through the latent image formation area during the latent image formation, a blade for temporarily holding the transfer residual toner may be provided between the charging roller 15M and the latent image formation area. However, if a blade is provided between the charging roller 15M and the latent image forming area, the moving distance until the surface of the photoreceptor is charged and developed correspondingly increases. Then, the potential on the surface of the photoconductor changes by that distance, which may lead to image degradation. As described above, the moving distance of the photosensitive drum until it is charged and developed is minimized by installing the blade 13M on the upstream side of the charging roller 15M with respect to the moving direction of the photosensitive drum 11. And the change in potential on the surface of the photoreceptor can be reduced.

  Further, the blade 13M is provided at a position where the held toner does not fall off due to its own weight. Specifically, as shown in FIG. 6, it is preferable to provide in a region A where the surface of the photoreceptor moves from top to bottom.

  As shown in FIG. 2, when the transfer residual toner held on the blade 13M is a mixture of reversely charged toner and regular charged toner, the reversely charged toner and the positively charged toner are electrostatically combined while holding the blade. May end up. When the combined transfer residual toner is returned to the surface of the photoconductor again at a predetermined timing, a problem occurs that the toner cannot be passed through the gap between the charging roller 15M and the photoconductor drum 11 and caught. Then, a charging failure may occur, leading to image deterioration. On the other hand, in the present embodiment, the polarity of the transfer residual toner is uniformly made negative by the charge injection roller 12M before being temporarily held by the blade 13M. As a result, the transfer residual toner is prevented from being combined while the blade 13M holds the transfer residual toner. Therefore, since the toner returned from the blade 13M to the surface of the photosensitive member again is not caught in the gap between the photosensitive drum and the charging roller 15M, it is possible to suppress charging failure and the like.

The blade 13M is separated at a timing such that a latent image is not formed when the transfer residual toner returned from the blade 13M to the photosensitive drum 11M passes through the latent image formation region. The separation timing will be described later.
The transfer residual toner returned at the above timing is uniformly charged by the charge injection roller 12M, and therefore passes without electrostatically adhering to the charging roller 15M. Then, the transfer residual toner passes through the latent image forming area during the formation of the non-latent image and is conveyed to the developing area opposed to the developing sleeve 22M of the developing device as a collecting unit. A developing bias having a polarity (positive) opposite to that during development is applied to the developing sleeve 22M. Since the transfer residual toner on the photosensitive drum conveyed to the development area is all negatively charged toner by the charge injection roller 12M, it is electrostatically applied to the carrier on the development sleeve to which a positive development bias is applied. Adhere to. The toner adhering to the carrier is collected in the developing device by the developing sleeve. The carrier has a particle size of 35 μm, and a small particle size carrier of 40 μm or less is used. By using a carrier having a small particle diameter of 40 μm or less, the magnetic brush formed on the developing sleeve can be made dense. As a result, the surface can be in close contact with the surface of the photosensitive drum, and the number of times of contact with the surface of the photosensitive member is increased, so that the transfer residual toner can be collected more reliably. Also, the dot reproducibility of the image portion after development can be improved.

  Next, the contact timing of the blade 13M will be described. The blade 13M is normally brought into contact with the photosensitive drum, and the blade 13 is separated from the surface of the photosensitive member at a predetermined timing. FIG. 7 is a flowchart showing the timing of blade contact / separation. In this flowchart, the cleaning mode is executed after an image forming operation is performed a certain number of times. In FIG. 6, the number of sheets to be printed is designated and printing is turned on (S1), and printing is executed (S2). At this time, the number of printed sheets n is counted (S3), and if the cumulative number of printed sheets n is equal to or greater than a certain number A (YES in S4), the cleaning mode is executed (S5). When the cleaning mode is executed, the blade 13 is separated from the photosensitive drum, and the transfer residual toner held by the blade 13 is returned to the surface of the photosensitive drum. Further, the developing bias applied to the developing sleeve 22 is switched to a positive developing bias. Then, the photosensitive drum is rotated, and the returned transfer residual toner is collected by the developing device. When the photosensitive drum rotates a predetermined number of times (one rotation or more), the cleaning mode is terminated. When the cleaning mode ends, the number of prints is reset (S6), and when the designated number of prints is made (YES in S7), the process ends. On the other hand, if the designated number of sheets has not been printed (NO in S7), printing is performed again. If the number of prints is equal to or less than a certain number A (NO in S4), if it is not confirmed whether the designated number of prints has been made (NO in S7), printing is executed again. On the other hand, if the designated number of sheets has been printed, the process ends.

  In the above, the cleaning mode is executed after an image forming operation is performed a certain number of times, and the transfer residual toner held on the blade 13 is collected by the developing device. The timing for executing the cleaning mode is as follows. It is not limited to this. For example, the cleaning mode may be executed when the apparatus is started up or every time the image forming operation is completed, and the transfer residual toner held on the blade 13M may be collected in the developing apparatus.

  In the above embodiment, the transfer residual toner is uniformly negatively charged regular toner by the charge injection roller 12M. However, the present invention is not limited to this, and the transfer residual toner is uniformly reversely charged by the charge injection roller 12M. Also good. In this case, in the cleaning mode, the charging bias applied to the charging roller is turned off so that the reversely charged toner does not adhere to the charging roller. In addition, the developing bias applied to the developing sleeve at this time can be collected by electrostatically attracting the transfer residual toner on the photosensitive drum by applying a negative voltage.

  In the above description, the blade 13M is brought into contact with the photosensitive drum moving direction in the counter direction. However, as shown in FIG. 8, the blade 13M is brought into contact with the photosensitive drum moving direction in the trading direction. May be. When the blade 13M is brought into contact with the photosensitive drum in the counter direction, the transfer residual toner is held in the wedge region between the blade 13M and the photosensitive drum 11M. As a result, the untransferred toner held at the blade tip is pushed to a narrower space by the untransferred toner held thereafter and receives a strong pressure. Then, the transfer residual toner held at the blade tip may be fixed. However, if the blade 13M is brought into contact with the photosensitive drum moving direction in the trading direction, the transfer residual toner is not held in the wedge region between the blade and the photosensitive drum. Therefore, the transfer residual toner held at the tip of the blade is not subjected to strong pressure by the transfer residual toner held thereafter, so that the held transfer residual toner can be prevented from sticking.

In the above description, the temporary holding means for holding the transfer residual toner has a blade shape, but the invention is not limited thereto. For example, a magnetic brush roller 41 as shown in FIG. 9 may be used. By using the magnetic brush roller 41 as the temporary holding means, it is possible to greatly reduce the load torque applied to the driving device of the photosensitive drum 11 as compared with the case where the temporary holding means is a blade.
The magnetic brush roller 41 includes a rotating sleeve 41a and a magnet roller 41b as magnetic field generating means fixedly disposed inside the rotating sleeve 41a. The rotating sleeve 41a is made of a conductive / nonmagnetic material, and has a V-shaped groove with a pitch of 0.8 [mm] and a depth of 0.2 [mm] on the outer peripheral surface thereof. The rotating sleeve 41a is rotated at a higher speed than the photosensitive member 11 in the clockwise direction in the drawing similarly to the photosensitive member 1 by a driving device (not shown). The rotation speed of the rotation sleeve 41a is preferably 1.0 to 3.0 times the rotation speed of the photoreceptor 1, and more preferably set to 1.5 to 2.0 times. Inside the magnet roller 41b, N-pole magnets and S-pole magnets are alternately arranged. Further, the toner holding device 40 includes a casing 46 that houses magnetic particles (carriers) 47.

  The magnetic brush roller 41 has inferior holding ability compared to the blade. For this reason, the magnetic brush roller 41 is driven in the opposite direction with respect to the surface of the photoreceptor 1 to increase the number of times the magnetic brush contacts the transfer residual toner, thereby increasing the holding ability.

  A bias is applied to the magnetic brush roller 41 from either the first power supply 43 or the second power supply 44. Specifically, a changeover switch 45 is provided between the power supplies 43 and 44 and the brush roller 41, and the power supply connected to the brush roller 41 is selected by the operation of the changeover switch 45. The operation of the changeover switch 45 is controlled by the control unit of the printer. In the present embodiment, the first power source 43 applies a holding bias such that the potential of the surface portion of the magnetic brush roller 41 is −50 [V] or more, and the second power source 44 An emission bias is applied such that becomes −350 [V]. Further, the toner holding device 40 includes a blade 42 that regulates the layer thickness of the magnetic brush. The blade 42 is disposed so as to have a gap of 0.6 to 0.8 [mm] with the rotating sleeve. The carrier 47 of the holding device 40 is the same as the carrier accommodated in the developing device 5.

  The carrier 47 accommodated in the casing 46 is carried on the rotating sleeve 41 a and conveyed to the photoreceptor 1. At this time, the carrier 47 is raised by the magnetic field of the magnet roller 41b to form a magnetic brush. In this magnetic brush, the layer thickness is adjusted uniformly by the blade 42 in the axial direction of the rotary sleeve 41a. The magnetic brush slides on the surface of the photoconductor and holds the transfer residual toner attached to the photoconductor. At this time, a holding bias is applied to the magnetic brush from the first power supply unit 43. The holding bias is set to a voltage slightly higher than the photoreceptor surface potential (−50 to −100 V) after transfer. Even if the voltage is sufficiently higher than the surface potential of the photoreceptor after the transfer, the transfer residual toner charged uniformly in the negative polarity by the charge injection roller 12 can be held well, but the charge injection roller can be used when held on the magnetic brush. In some cases, the transfer residual toner charged to a negative polarity at 12 has a reverse polarity. For this reason, the holding bias applied to the magnetic brush is set to a voltage slightly higher than that of the photosensitive drum 11 so that the negative transfer residual toner held on the magnetic brush does not have a reverse polarity.

  As described above, the transfer residual toner held on the magnetic brush is returned to the surface of the photosensitive member at the predetermined timing described above after an image forming operation is performed a certain number of times or when the apparatus is started up. Specifically, the changeover switch 45 is switched from the first power supply unit 43 to the second power supply unit 44 at a predetermined timing, and a discharge bias of −350 V is applied to the magnetic brush roller 41. Then, a potential difference is generated between the photoconductor 11 (about −50 V) and the magnetic brush roller 41 (−350 V). As a result, the transfer residual toner that is normally charged negatively by the charge injection roller 12 is electrostatically adsorbed to the photosensitive member having a higher potential than the magnetic brush. As a result, the untransferred toner held by the magnetic brush is returned to the surface of the photoreceptor again.

  The untransferred toner returned from the magnetic brush roller 41 to the surface of the photosensitive member passes through a contact area with the charging roller 15 and is collected by the developing device 20 as a collecting unit.

  Further, a holding device 50 having a fur brush 51 as shown in FIG. The fur brush 51 of the holding device 50 is formed so that the brush density is relatively low. Thus, if the brush density is low, a sufficient space for holding the transfer residual toner can be secured inside the brush. Therefore, the capacity of accommodating the transfer residual toner is increased, and the frequency of the transfer residual toner discharge process can be reduced. Further, by reducing the brush density, the mechanical holding force when the brush roller 51 holds the transfer residual toner is reduced. As a result, the transfer residual toner discharging step can be executed smoothly.

  The brush roller 51 is rotationally driven by the driving device 52 in the direction of the arrow in the figure. Like the holding device 40 that holds the transfer residual toner with the magnetic brush 41 described above, the brush roller 51 is configured to be biased from either the first power supply 53 or the second power supply 54. For switching between the first power supply 53 and the second power supply 54, the power supply connected to the brush roller 51 can be selected by the operation of the changeover switch 55 as described above.

  The holding device 50 in which the temporary holding means for temporarily holding the transfer residual toner is used as the brush roller 51 performs the transfer operation in the same manner as the holding device 40 in which the temporary holding means for temporarily holding the transfer residual toner is used as the magnetic brush 41. The remaining toner is temporarily held and discharged at a predetermined timing. That is, when the transfer residual toner is held by the brush roller 51, a voltage holding bias slightly higher than the surface potential (−50 to −100 V) of the photoreceptor after the transfer is applied from the first power supply 53, and the brush roller In 51, the transfer residual toner is held. Then, the changeover switch 55 is switched from the first power supply 53 to the second power supply 54 at the predetermined timing described above, and a discharge bias of −350 [V] is applied to the brush roller 51. Then, the transfer residual toner held by the brush roller 51 is moved again to the surface of the photoreceptor and collected by the developing device.

  In the above description, the transfer residual toner returned to the photosensitive member by the temporary holding unit is collected by the developing device, but is not limited thereto. For example, the transfer residual toner returned to the photosensitive member by the temporary holding unit may be transferred to the transfer paper P and collected. In the case of an image forming apparatus including an intermediate transfer belt, the transfer residual toner returned to the photosensitive member by the temporary holding unit may be transferred to the intermediate transfer belt and recovered. In this case, the transfer residual toner transferred to the intermediate transfer belt is collected by the intermediate transfer belt cleaning device.

(1)
As described above, according to the image forming apparatus of the present embodiment, the transfer residual toner remaining on the surface of the photosensitive drum 11 without being electrostatically transferred onto the transfer paper P at the transfer nip before reaching the latent image forming area. Temporarily held by temporary holding means. Then, when the transfer residual toner passes through the latent image forming area, it is returned to the surface of the photosensitive member again at a timing at which writing is not performed on the surface of the photosensitive member by the optical writing unit 2 as a latent image forming unit. This suppresses the transfer residual toner from adhering to the surface of the photoreceptor passing through the latent image forming area during the latent image formation by the optical writing unit 2. Therefore, formation of an unexposed portion due to the transfer residual toner is suppressed. As a result, the occurrence of white spots in the solid image portion is suppressed, and a good image can be obtained. Further, before the transfer residual toner is collected by the charging device, charges are injected into the transfer residual toner by the charge injection means, and the reversely charged transfer residual toner is normally charged. As a result, all the transfer residual toner that reaches the developing means can be normally charged, and if a developing bias having a polarity opposite to that of the normal charge is applied to the developing roller, the transfer residual toner can be collected in the developing device. Furthermore, since the outermost layer as the contact surface of the charge injection roller 12 as the contact member of the charge injection means contains conductive fine particles, the volume resistance of the outermost layer can be kept low. As a result, it is possible to favorably inject the charge into the toner in contact with the outermost layer, and to ensure that the reversely charged toner is a regular charged toner.
(2)
Since the toner of this embodiment uses a nearly spherical toner, when the outermost layer surface of the charge injection roller 12 is a flat surface, the contact area between the outermost layer and the toner is small. On the other hand, according to the image forming apparatus of the present embodiment, the outermost layer surface of the charge injection roller 12 has a concavo-convex shape in which conductive fine particles are exposed, so that the outermost layer is made flat as compared with the flat surface. Thus, the contact area with the toner can be increased. As a result, the amount of charge injected into the toner can be increased as compared with a case where the outermost layer is a flat surface, and the reversely charged toner can be reliably made a regular charged toner.
(3)
Further, according to the image forming apparatus of the present embodiment, the volume resistance of the conductive fine particles is set to 1 × 10 ¹⁴ [Ω · cm] or less, and the average circularity is set to SR = 0.95 to 1.00. Since the volume resistance of the conductive fine particles is 1 × 10 ¹⁴ [Ω · cm] or less, the volume resistance of the outermost layer can be lowered, and the charge can be injected well into the transfer residual toner in contact with the outermost layer. it can. Further, by setting the average circularity of the conductive fine particles to SR = 0.95 to 1.00, the surface of the outermost layer can be made more uneven than the conductive fine particles that are needle-like or flat. . Therefore, the contact area between the outermost layer and the transfer residual toner can be increased, and a large amount of charge can be injected into the transfer residual toner.
(4)
In addition, according to the image forming apparatus of the present embodiment, by setting the volume resistance of the outermost layer to 1 × 10 ¹³ [Ω · cm] or less, it is possible to inject charges well into the transfer residual toner in contact with the outermost layer. Can do.
(5)
Further, according to the image forming apparatus of the present embodiment, the charge injection roller is in elastic contact with the photosensitive drum. Thereby, it is possible to suppress the surface of the photosensitive drum from being damaged by the charge injection roller.
(6)
Further, according to the image forming apparatus of the present embodiment, the movement direction of the surface of the charge injection roller is opposite to the movement direction of the surface of the photosensitive drum at the contact position between the charge injection roller and the photosensitive member, or the surface of the photosensitive drum. The speed of movement of the surface of the charge injection roller is made faster than the speed of movement so that the photosensitive drum and the charge injection roller have a speed difference. As a result, the transfer residual toner rotates in the contact area between the charge injection roller and the photosensitive member, and various surfaces of the transfer residual toner come into contact with the outermost layer of the charge injection roller. As a result, the charge can be uniformly injected into the transfer residual toner, and the transfer residual toner can be uniformly charged.
(7)
Further, according to the image forming apparatus of the present embodiment, the magnetic brush formed on the developing sleeve can be made dense by using a carrier having a small particle diameter of 40 μm or less. As a result, the surface can be in close contact with the surface of the photosensitive drum, and the number of times of contact with the surface of the photosensitive member is increased, so that the transfer residual toner can be collected more reliably. Also, the dot reproducibility of the image portion after development can be improved.
(8)
Further, according to the image forming apparatus of the present embodiment, by forming the image forming process means such as the developing device into a process cartridge, the parts accommodated in the process cartridge reach the end of their life or require maintenance. In this case, the process cartridge can be replaced, and convenience is improved.

1 is a schematic configuration diagram of a laser printer according to an embodiment. The enlarged view which shows schematic structure of a magenta image formation means. FIG. 6A is a graph showing a charge potential distribution immediately before transfer of toner carried on the photosensitive drum. (B) is a graph showing the charge potential distribution of the transfer residual toner remaining on the photosensitive drum after transfer. Sectional drawing of a charge injection roller. (A) is a figure which shows a contact state with the untransferred toner in case the surface of a charge injection roller is a plane. FIG. 6B is a diagram illustrating a contact state with the transfer residual toner when the surface of the charge injection roller is uneven. The figure explaining the position of a braid | blade. It is a flowchart which shows the timing of the contact / separation of a blade. The figure which shows the example which made the braid | blade contact | abut in the trading direction with respect to the photosensitive drum moving direction. The figure which shows the example which used the temporary holding means as the magnetic brush roller. The figure which shows the example which used the temporary holding means as the brush roller.

Explanation of symbols

2 Optical writing unit 3 Paper feed cassette 4 Paper feed cassette 5 Registration roller 6 Transfer unit 7 Fixing unit 8 Paper discharge tray 9 Reversing unit 10M, 10C, 10Y, 10BK Photoconductor unit 10M, 11C, 11Y, 11BK Photoconductor drum 12M Charge injection roller 13M Blade 15M Charging roller 20M Development unit

Claims (8)

A charging means for uniformly charging the surface of the latent image carrier, a latent image forming means for forming an electrostatic latent image on the surface of the latently charged latent image carrier, and a toner attached to the latent image. In an image forming apparatus having a developing unit that performs development and a transfer unit that transfers the toner image on the latent image carrier to a transfer material,
A temporary holding means for temporarily holding the transfer residual toner before the transfer residual toner remaining on the surface of the latent image carrier after the transfer by the transfer means reaches the charging means; and a transfer residual held by the temporary holding means. Control means for returning the toner to the surface of the latent image carrier again at a predetermined timing; toner recovery means for collecting the transfer residual toner returned to the surface of the latent image carrier by the temporary holding means; and the transfer residual toner A charge injection means for injecting charges into the transfer residual toner before being collected by the collection means, and the charge injection means is provided with a contact member that contacts the latent image carrier. An image forming apparatus, wherein the contact surface that contacts the latent image carrier is a layer containing conductive fine particles. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the contact surface of the contact member has a concavo-convex shape in which the conductive fine particles are exposed. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the conductive fine particles have a volume resistivity of 1 × 10 ¹⁴ [Ω · cm] or less and an average circularity of SR = 0.95 to 1.00. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein the volume resistance of the contact surface of the contact member has a volume resistance value of 1 × 10 ¹³ [Ω · cm] or less. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the contact member elastically contacts the latent image carrier. The image forming apparatus according to claim 1,
The contact member is a roller member, and at the contact position between the roller member and the latent image carrier, the moving direction of the roller member surface is opposite to the moving direction of the latent image carrier surface, or An image forming apparatus comprising drive means for rotating the roller member such that the moving speed of the surface of the roller member is faster than the moving speed of the surface of the latent image carrier. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the developing means contains a developer composed of a toner and a carrier, and the particle size of the carrier is 40 μm or less. The image forming apparatus according to claim 1,
An image forming apparatus, comprising: a process cartridge which is configured such that at least the developing unit and the latent image carrier are integrally formed and detachable from the image forming apparatus.

Images