JP2005265964A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformly bring a charging device into contact with an image carrier, without damaging the image carrier and to stably charge the image carrier to prescribed potential evenly, regardless of the environmental fluctuations. <P>SOLUTION: The circumferential speed of the leading edge of a conductive sheet 36 is higher than that of a photoreceptor. A curved fold (drape) is formed in a direction crossing with the shaft direction of a shaft 34 on the sheet 36. Thus, the contact probability (contact area) of the sheet 36 with the photoreceptor drum becomes high. Then, the surface area thereof is increased as a whole due to the fold (drape). Since the contact probability (contact area) thereof with residual toner is high, the history (pattern) of the residual toner is eliminated, and performance for temporarily holding the toner, having a reverse polarity and performance to electrify it to a positive polarity are improved. Since the contact probability (contact area) thereof with the photoreceptor drum is high, performance for charging the photoreceptor drum is also high. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus to which a known electrophotographic process is applied forms an image on a recording medium by the following process.

  While rotating an electrophotographic photosensitive member (hereinafter referred to as a photosensitive member), the photosensitive member is uniformly charged to a predetermined potential by a charging unit. The charged photoconductor is exposed by an exposure means to form a latent image. This latent image is developed by developing means to form a toner image on the photoreceptor. The toner image is transferred to a recording medium by a transfer unit, and the toner image is fixed to the recording medium by a fixing unit. Further, before charging by the charging unit, residual toner after transfer is removed by the cleaning unit.

  As a charging means, there is a system in which a charging member is brought into contact with the photosensitive member, a charging bias is applied to the charging member, and the surface of the photosensitive member is charged to a predetermined potential. As a charging member, there is a method of using a so-called fur brush in which conductive fibers are formed in a brush shape.

  Further, as a cleaning means for removing residual toner after transfer, in a system in which development and residual toner collection are simultaneously performed in the developing means without providing a special cleaning mechanism, the rotation of the photosensitive member of the main charger is performed. An auxiliary charger is provided on the upstream side in the direction. With this auxiliary charger, the residual toner after transfer is charged to facilitate recovery by the developing means, and the history (pattern) of residual toner after transfer is recorded. It has been scattered and solved. Some auxiliary chargers in such a system use a fur brush. (For example, Patent Document 1 and Patent Document 2).

Furthermore, in the system in which development and recovery of residual toner are performed simultaneously in the developing means, only the main charger is provided without providing the auxiliary charger, and the above-described residual toner charging and history are eliminated with this main charger. A method that also serves as such has been proposed. Some of such main chargers use a fur brush. (For example, refer to Patent Document 3).
Japanese Unexamined Patent Publication No. 09-211978 JP 2001-215798 A Japanese Patent Laid-Open No. 10-01845

  In order to improve the performance of the main charger and auxiliary charger (such as charging of the photoconductor and residual toner), the fur brush fibers are made more rigid and the contact pressure to the photoconductor is increased. And want to contact the photoreceptor uniformly and stably.

  However, if the contact pressure of the fur brush to the photosensitive member is too high, the surface of the photosensitive member is easily damaged, and the life of the photosensitive member is shortened. In addition, since the toner is pressed strongly against the photosensitive member at the tip of the fur brush, so-called toner filming, in which a toner component is thinly adhered to the surface of the photosensitive member, is likely to occur.

  However, if the fur brush fibers are softened by lowering their rigidity, the contact with the photoconductor becomes non-uniform, which affects the performance of the main charger and auxiliary charger. Further, the fiber tends to sag (permanent deformation), and the contact with the photoreceptor is also non-uniform.

  In addition, since the problem arises when the contact pressure on the photoconductor is too strong or too weak, the fur brush needs to be attached to the photoconductor with high accuracy.

  Furthermore, the amount of adsorbed water adhering to the fiber surface increases in a high temperature and high humidity environment. When the amount of adsorbed water increases, a phenomenon of charge injection to the photoconductor occurs, and the photoconductor is charged without going through a discharge phenomenon, so that the photoconductor is excessively charged. As a result, an abnormal image is generated. Also, the residual toner is not normally charged.

  The present invention has been made to solve the above-described problems. The charger is uniformly brought into contact with the image carrier without damaging the image carrier, and the image carrier is predetermined regardless of environmental changes. The purpose is to uniformly and stably charge the potential.

  The image forming apparatus according to claim 1, a rotating image carrier, a charger that contacts the image carrier and charges the image carrier to a predetermined potential, and a rotating unit that rotates the charger. A latent image forming unit that forms a latent image on the image carrier after charging; a developing unit that develops the latent image to form a toner image on the image carrier; and the toner image on the image carrier. In the image forming apparatus, the charger is attached to a rotation shaft whose axial direction is the same direction as the rotation axis direction of the image carrier, and an outer peripheral surface of the rotation shaft. A plurality of conductive sheets formed, and the conductive sheets are formed with pleats that are curved in a direction intersecting the axial direction of the rotation shaft.

  The image forming apparatus according to claim 1, wherein the charger has a rotation shaft whose axial direction is the same as the rotation axis direction of the image carrier, and a plurality of conductive sheets attached to the outer peripheral surface of the rotation shaft; It consists of Then, the charger is rotated by a rotating means, and a plurality of conductive sheets are continuously brought into contact with the image carrier to charge the image carrier to a predetermined potential.

  A latent image is formed on the charged image carrier by a latent image forming unit, and the latent image is developed by a developing unit to form a toner image on the image carrier. The toner image formed on the image carrier is transferred to a recording medium by a transfer unit.

  Now, the conductive sheet is formed with pleats that curve in a direction intersecting the axial direction of the rotation axis. Therefore, the contact probability (contact area) of the conductive sheet increases with respect to the image carrier. Therefore, the image carrier is uniformly and stably charged.

  Also, in order to bring the conductive sheet into contact with the image carrier more uniformly and stably, it is desirable to make the conductive sheet strongly contact the image carrier. For this reason, for example, the rigidity of the conductive sheet is increased, and the rotational axis is positioned so that the conductive sheet and the image carrier are in contact with each other, that is, the amount of biting between the conductive sheet and the image carrier increases. Install as follows.

  Thus, even if the conductive sheet is brought into strong contact with the image carrier, the contact area between the conductive sheet and the image carrier is large, so the contact pressure does not increase. Therefore, the surface of the image carrier is hardly damaged. Further, since the residual toner remaining on the image carrier is not strongly pressed against the image carrier, so-called toner filming in which the toner component is thinly adhered to the surface of the image carrier is less likely to occur.

  In addition, for example, compared to a fur brush, the conductive sheet has a very small surface area, so that the amount of adsorbed water adhering to the surface of the conductive sheet is very small even in a high temperature and high humidity environment. Therefore, the charge injection phenomenon to the image carrier due to the adsorbed water does not occur. Therefore, the image carrier is excessively charged by the injection of charges without going through the discharge phenomenon, and as a result, no abnormal image is generated. Therefore, the image carrier is uniformly and stably charged regardless of environmental conditions.

  The image forming apparatus according to claim 2, a rotating image carrier, a charger that contacts the carrier and charges the image carrier to a predetermined potential, and a rotating unit that rotates the charger. A latent image forming unit that forms a latent image on the image carrier after charging; a developing unit that develops the latent image to form a toner image on the image carrier; and the toner image on the image carrier. And a transfer unit that transfers to a recording medium. The charger includes a rotation shaft having an axial direction that is the same as the rotation axis direction of the image carrier, and a radial extension from the rotation shaft. And a plurality of conductive blades.

  The image forming apparatus according to claim 2, wherein the charger has a rotation shaft whose axial direction is the same as the rotation axis direction of the image carrier, and a plurality of conductive blades projecting radially from the rotation shaft; It consists of The charger is rotated by a rotating means, and a plurality of conductive blades are continuously brought into contact with the image carrier to be charged to a predetermined potential.

  As described above, since the plurality of conductive blades are in continuous contact with the image carrier, the image carrier is uniformly and stably charged as in the first aspect.

  Even if the conductive blade is brought into strong contact with the image carrier, the contact area between the conductive blade and the image carrier is large, so the contact pressure does not increase. Accordingly, the surface of the image carrier is hardly damaged. In addition, toner filming hardly occurs.

  In addition, even in a high temperature and high humidity environment, the surface area is very small, and there is little adhesion of adsorbed water to the surface of the conductive blade, so that an abnormal image does not occur due to the charge injection phenomenon to the image carrier. .

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the cross section of the conductive blade is a quadrangle and the tip is an R shape.

  In the image forming apparatus according to the third aspect, since the tip of the conductive blade of the charger has an R shape, the tip has no corner. Therefore, the surface of the image carrier is not damaged more.

  Further, if there is a corner, an abnormal discharge in which the discharge concentrates at the corner occurs, and as a result, an abnormal image is generated. However, since the tip portion has an R shape and there is no portion where the discharge is concentrated, a different image due to abnormal discharge does not occur.

  According to a fourth aspect of the present invention, in the configuration according to any one of the first to third aspects, the image forming apparatus according to the fourth aspect is different from the charger according to any one of the first to third aspects. It is characterized by comprising another charger for charging the image carrier.

  According to a fourth aspect of the present invention, in addition to the charger according to any one of the first to third aspects, the image forming apparatus includes another charger that charges the image carrier. That is, since the image carrier is charged stepwise by a plurality of chargers, the image carrier is more uniformly charged.

  Other chargers do not depend on the method (contact method or non-contact method) or configuration. It is sufficient if the image carrier can be charged.

  The image forming apparatus according to claim 5 is the configuration according to any one of claims 1 to 4, wherein the charger can apply a voltage having a polarity opposite to a predetermined potential of the image carrier. It is characterized by being.

In the image forming apparatus according to claim 5, since the charger can apply a voltage having a polarity opposite to the predetermined potential of the image carrier, for example, residual toner having a polarity opposite to the predetermined potential adheres to the charger. Even if, for example, the reverse polarity residual toner attached to the charger can be removed by applying a reverse polarity voltage to the charger at a predetermined timing such as during non-image formation. The forming apparatus according to any one of claims 1 to 5, further comprising a blade cleaning mechanism that scrapes and collects residual toner on the image carrier with a blade on a downstream side of the charger. It is characterized by not preparing.

  The image forming apparatus according to claim 6 is not provided with a blade cleaning mechanism that scrapes and collects residual toner with a blade on the downstream side of the charger. Therefore, uneven charging due to the influence of residual toner is likely to occur.

  However, since the charger of the image forming apparatus according to any one of claims 1 to 5 is in contact with the plurality of conductive sheets or the plurality of conductive brushes while rotating the image carrier, The contact probability (contact area) with the image carrier is large, and the contact is uniform. In addition, the overall surface area is sufficiently large. Therefore, since the probability of contact with the residual toner (contact area) is large, uneven charging due to the influence of the residual toner is unlikely to occur.

  If the blade cleaning mechanism is not provided, the residual toner is temporarily held on a holding member or the like, and then discharged to the image carrier at a predetermined timing and attached to the intermediate transfer member. There is a method to collect.

  Even in such a case, uneven charging is less likely to occur. Furthermore, the charger according to any one of claims 1 to 5 can be used as a holding member that temporarily holds residual toner.

  According to a seventh aspect of the present invention, there is provided the image forming apparatus according to the sixth aspect, wherein the developing unit also serves as a cleaning unit that collects residual toner on the image carrier.

  In the image forming apparatus according to the seventh aspect, the developing unit also serves as a cleaning unit that collects residual toner on the image carrier.

  Therefore, since development and recovery of residual toner are simultaneously performed in the developing means, there is no need to provide a special cleaning mechanism as a cleaning means for removing residual toner. Therefore, the image forming apparatus is small and low cost. Further, since the residual toner becomes waste toner and is not discarded, the image forming apparatus is excellent from the environmental viewpoint.

  Note that in such a system in which the developing unit also serves as a cleaning unit that collects the residual toner on the image carrier, the residual toner history (pattern) is eliminated, and the residual toner is charged or temporarily collected for collection by the developing unit. An auxiliary charger for holding and the like is necessary.

  However, since the plurality of conductive sheets or the plurality of conductive brushes are in contact with the image carrier while being rotated, the contact probability (contact area) with the image carrier is large, and the contact is made uniformly. In addition, the overall surface area is sufficiently large.

  Therefore, since the contact probability (contact area) with the residual toner is large, it is effective as an auxiliary charger that disperses the contact residual toner to eliminate the history (pattern), charges the residual toner, or temporarily holds the residual toner. It is. Further, since there is no influence of adsorbed water, the residual toner can be stably charged regardless of environmental conditions.

  As described above, according to the present invention, the image carrier can be uniformly and stably maintained at a predetermined potential regardless of environmental conditions without causing damage (scratches, filming, etc.) to the image carrier. The purpose is to be charged.

  Hereinafter, as an example to which the image forming apparatus according to the present invention is applied, a laser printer to which a known electrophotographic process is applied will be described with reference to the drawings. The known electrophotographic process is to transfer a toner image formed on a photoconductor to a recording paper through charging of the photoconductor, formation of a latent image by exposure with a laser, etc., and development of the latent image with toner. A series of processes for recording an image by fixing a toner image on a recording sheet.

  FIG. 1 shows a schematic configuration of a laser printer 11 according to a first embodiment of the present invention. The laser printer 11 forms a toner image based on image information input from an external apparatus by a known electrophotographic process, and records the image on a recording paper P. In the following description, detailed descriptions of those not directly related to the essence of the present invention are omitted.

  First, an outline of the configuration of the laser printer 11 and an outline of a process for forming an image on the recording paper P will be described.

  As shown in FIG. 1, a photosensitive drum 20 is rotatably disposed near the center inside the laser printer 11. The photosensitive drum 20 is rotated in the direction of the arrow K by driving means (not shown).

The surface of the photoconductor drum 20 is disposed in the upper left part of the photoconductor drum 20 divided into four parts. The charging mechanism 30 including the auxiliary charger 32, the main charger 44, and the like provides about −600 V (desired final charging potential V). ₀₂ ) is charged. After charging, exposure is performed by a laser beam LB emitted from an optical scanning device 52 disposed above the photosensitive drum 20, and a latent image corresponding to image information is formed on the surface of the photosensitive drum 20. The developing roller 56 of the developing unit 54 carries toner charged to a predetermined polarity (in this embodiment, -polarity). The latent image formed on the surface of the photoconductive drum 20 is developed by applying a developing bias to the developing roller 56 to become a toner image. Then, the toner image formed on the photosensitive drum 20 is sent to the transfer roller 58.

  On the other hand, a paper feed cassette 60 in which the recording paper P is accommodated is disposed below the laser printer 11. The recording paper P is sent out by the pickup roller 62 and is transported by the transport roller 64. Then, it is sent to the transfer roller 58 by the registration roller 68 at a predetermined timing.

  A voltage having a polarity opposite to the predetermined potential of the toner (in this embodiment, + polarity) is applied to the transfer roller 58, and the toner image on the photosensitive drum 20 is transferred onto the recording paper P. The recording paper P onto which the toner image has been transferred is sent to the fixing device 70. The fixing device 70 fixes the toner image on the recording paper P with heat and pressure. The recording paper P on which the toner image is fixed is discharged to a discharge tray 72 on the left side of the laser printer 11.

  The toner image is not completely transferred onto the recording paper P by the transfer roller 58, and a part of the toner image remains on the photosensitive drum 20 as residual toner. However, in the laser printer 11 of the present embodiment, the developing device 54 is optimized by optimizing the setting condition of the developing bias of the developing roller 56 of the developing device 54 without waiting for a special cleaning mechanism for removing residual toner. Development and collection of residual toner are performed simultaneously.

  Therefore, since no special cleaning mechanism is provided as a cleaning means for removing residual toner, the laser printer 11 is small and low cost. Further, since the residual toner becomes waste toner and is not discarded, the laser printer 11 is excellent in terms of environment.

  Further, there is no neutralizing means such as an erase lamp that neutralizes the surface of the photosensitive drum 20 before it is charged by the charging mechanism 30 to equalize the potential. Therefore, it is further small and low cost.

  Next, the charging mechanism 30 will be described.

  With respect to the rotation direction K of the photosensitive drum 20, the auxiliary charger 32 and the main charger 44 are arranged in order from the upstream side.

  As shown in FIG. 2, the auxiliary charger 32 has a thin conductive sheet 36 on the outer peripheral surface of a metal shaft 34 whose axial direction is the same as the axial direction of the photosensitive drum 20. For example, the conductive sheet 36 is attached with a conductive adhesive so as to be energized.

  The conductive sheet 36 is formed with a fold (drape) that is curved with respect to a direction intersecting the axial direction of the shaft 34. Further, as shown in FIGS. 3A and 3B, a plurality of conductive sheets 36 are attached over the entire circumference of the shaft 34.

  As the conductive sheet 36, the resistance is adjusted by, for example, carbon, an ion conductive agent, etc., for example, urethane, silicon polyester, polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, polyimide, PEN , PEK, PES, PPS, PFA, PVdF, ETFE, CTFE, etc., or silicon rubber, EPDM, ethylene, mixed with conductive powder such as carbon black, metal powder, metal oxide, etc. Synthetic rubbers such as propylene rubber, butyl rubber, acrylic rubber, urethane rubber and nitrile rubber, or polar rubbers such as epichlorohydrin rubber, chloroprene rubber and EPDM rubber can be used. (However, polar rubber and the like have high adhesive strength, so it is necessary to devise a method such as coating the surface with a low adhesion material).

  The conductive sheet 36 may be a woven fabric woven with conductive fibers.

  As shown in FIG. 1, the shaft 34 is rotatably attached to a holding tool (not shown) such that the leading end portion of the conductive sheet 36 contacts the photosensitive drum 20.

  A gear 38 (see FIGS. 2 and 3) is attached to one end of the shaft 34, and is rotated in the direction T <b> 1 by the motor 42 via the transmission gear 40. The peripheral speed at the tip of the conductive sheet 36 is faster than the peripheral speed of the surface of the photosensitive drum 20.

The shaft 34 is connected to an auxiliary charger power supply 84. Then, DC (direct current) -1200 V is applied to the auxiliary charger 32 as the charging bias Vc ₀₁ by the auxiliary charger power source 84.

  1, 2, and 3, each conductive sheet 36 is standing in a direction orthogonal to the axial direction of the shaft 34 for easy understanding, but in reality, each conductive sheet 36 has a stiffness. Because it is small, it usually hangs down due to gravity. However, when the shaft 34 is rotated, the state shown in FIG.

As shown in FIG. 1, the main charger 44 has a resistance of about 1 × on a metal shaft 48 whose axial direction is the same as the axial direction of the photosensitive drum 20 by carbon, an ion conductive agent, or the like. The semiconductive roller is provided with a semiconductive elastic layer 46 adjusted in a range of 10 ⁵ to 1 × 10 ¹² Ω. The shaft 48 is rotatably fixed to a holding tool (not shown) so that the elastic layer 46 is pressed against the photosensitive drum 20 to form a nip. As the photosensitive drum 20 rotates, the main charger 44 also rotates following the direction T2. The shaft 48 is connected to the main charger power source 82. Then, a charging bias Vc _{02 in} which DC (direct current) -600 V is superimposed on AC 1500 V _pp (sine wave, Peak to Peak voltage 1500 V, frequency 1000 Hz) is applied to the main charger 44 by the main charger power source 82.

The charging biases Vc ₀₁ and Vc ₀₂ can apply a voltage of +600.

The auxiliary charger power source 84 and the main charger power source 82 are connected to the control unit 80, and the control unit 80 applies the charging bias voltages Vc ₀₁ and Vc ₀₂ applied to the auxiliary charger 32 and the main charger 44. To control.

  Next, the operation of the laser printer 11 of the present embodiment will be described.

  As described above, the toner image is not completely transferred onto the recording paper P by the transfer roller 58, and a part of the toner image remains on the photosensitive drum 20 as residual toner. Further, in the laser printer 11 of the present embodiment, the developing device 54 develops the image by optimizing the setting condition of the developing bias of the developing roller 56 of the developing device 54 without waiting for a special cleaning mechanism for removing the residual toner. And cleaning is done at the same time.

  Therefore, the residual toner remaining without being transferred is carried to the auxiliary charger 32 as it is. The residual toner forms a history (pattern) corresponding to the toner image before transfer.

  However, when the history (pattern) passes through the auxiliary charger 32, the history (pattern) is scattered and made uniform by the rotating conductive sheet 36, and the history (pattern) is eliminated.

A charging bias Vc ₀₁ (DC-1200 V) is applied to the auxiliary charger 32. Accordingly, among the residual toner, the positive polarity (in this embodiment, the polarity is the same as that of the charging bias Vc ₀₁ ) passes through as it is. Of the residual toner, the residual toner having a reverse polarity (in this embodiment, a positive polarity) or a low charge amount adheres to the conductive sheet 36 of the auxiliary charger 32 and is temporarily held, and then reverts to the positive polarity (-polarity). Charges and adheres to the photosensitive drum 20.

  As described above, the history is eliminated by the auxiliary charger 32, and the residual toner of reverse polarity (+ polarity) is charged to positive polarity (-polarity), and only the residual toner of positive polarity (-polarity) is the main charger. 44.

The photosensitive drum 20 is precharged to a preliminary charging potential V ₀₁ (surface potential after the auxiliary charger), approximately −650 V, by the charging bias Vc ₀₁ (DC-1200 V) of the auxiliary charger 32.

A charging bias Vc ₀₂ (AC 1500 Vpp + DC−600 V) is applied to the main charger 44. As described above, as the residual toner, only the positive (−polar) residual toner is sent by the auxiliary charger 32. Charging bias Vc ₀₂ of the main charger 44, the residual toner having the same polarity as the positive polarity are offset in the DC-600V. Therefore, repulsive force acts between the main charger 44 and the positive residual toner slides through the main charger 44.

Further, the surface of the photosensitive drum 20 is finally uniformly charged to the final charging potential V ₀₂ (about −600 V) by the charging bias Vc ₀₂ (AC 1500 Vpp + DC−600 V) applied to the main charger 44. . Since the residual toner is uniformly dispersed by the auxiliary charger 32 and the history is eliminated, charging unevenness in which the charging potential of the history portion is reduced does not occur. Therefore, an abnormal image (ghost phenomenon) due to charging unevenness does not occur.

  Further, although there is no neutralization means such as an erase lamp for eliminating the charge on the surface of the photosensitive drum 20 before charging by the charging mechanism 30 and making the potential uniform, the auxiliary charger 32 and the main charger 42 are connected to each other. Since charging is performed in stages, the photosensitive drum 20 can be charged uniformly.

  Thereafter, the residual toner passes through the exposed portion of the laser beam LB emitted from the optical scanning device 52.

  As described above, since the history of the residual toner is eliminated by the auxiliary charger 32, the exposure unevenness in which the history portion blocks the exposure does not occur. Therefore, an abnormal image (ghost phenomenon) due to uneven exposure does not occur.

  The positive (-polar) residual toner is sent to the developing unit, and is collected simultaneously with development by optimizing the setting condition of the developing bias of the developing roller 56 of the developing unit 54. As described above, since the residual toner is uniformly charged to the positive polarity by the auxiliary charger 32, it is recovered stably by the developing device 54.

  Of the residual toner remaining without being transferred, the adhesion amount of the reverse polarity (+ polarity) residual toner temporarily held in the auxiliary charger 32 gradually increases, and the performance of the auxiliary charger 32 decreases. Let

  Accordingly, at a predetermined timing such as during non-image formation, the control unit 80 applies a potential of reverse polarity, in this embodiment, +600 V to the auxiliary charger 32, so that the photosensitive drum 20 and the auxiliary charger 32 are connected. The reverse polarity (+ polarity) residual toner is discharged to the photosensitive drum 20 by reversing the direction of the electric field therebetween, and the reverse polarity residual toner adhering to the auxiliary charger 32 is removed.

  At this time, the main charger 44 also applies a reverse-polarity charging bias to prevent residual toner of reverse polarity (+ polarity) from adhering to the main charger 44.

  The residual toner having the reverse polarity (+ polarity) is sent to the developing unit, and the setting condition of the developing bias of the developing roller 56 of the developing device 54 is optimized, and is collected by the developing device 54.

  Now, the peripheral speed of the front end portion of the conductive sheet 36 is faster than the peripheral speed of the photoconductor 20. In addition, as shown in FIG. 2, the conductive sheet 36 is formed with a fold (drape) that is curved in a direction intersecting the axial direction of the shaft 34. Therefore, the contact probability (contact area) with the photosensitive drum 20 is increased. Also, the overall surface area increases due to the draping.

  Therefore, since the probability of contact with the residual toner (contact area) is large, the history (pattern) of the residual toner is eliminated, the performance of temporarily holding the reverse polarity toner and the charging performance to the positive polarity are improved. In addition, since the contact probability (contact area) with the photosensitive drum 20 is large, the performance of precharging the photosensitive drum 20 is also high.

  Further, in order to bring the conductive sheet 36 into contact with the photosensitive drum 20 more uniformly, it is desired that the conductive sheet 36 is brought into strong contact with the photosensitive drum 20. Therefore, the rigidity of the conductive sheet 36 is increased, and the shaft 34 is also in a position where the photosensitive drum 20 and the conductive sheet 36 are in contact with each other, that is, the amount of biting between the conductive sheet 36 and the photosensitive drum 20. It is attached so that becomes large.

  As described above, even if the conductive sheet 36 is brought into strong contact with the photosensitive drum 20, the contact area between the conductive sheet 32 and the photosensitive drum 20 is large, so that the contact pressure does not increase. Therefore, the surface of the photoconductor drum 20 is hardly damaged. In addition, since the residual toner is not strongly pressed against the photosensitive drum 20, so-called toner filming in which the toner component is thinly adhered to the surface of the photosensitive drum 20 hardly occurs. Further, since the amount of biting is large and rough, the mounting accuracy of the shaft 34 may be rough.

  Further, as described above, the conductive sheet 36 has a small stiffness and does not rotate until the state shown in FIG. Therefore, the leading end portion of the conductive sheet 36 is not permanently deformed, and contact with the photosensitive drum 20 is not uneven.

  Furthermore, for example, compared with a fur brush, the conductive sheet 36 has a very small surface area as a whole, and therefore, the amount of adsorbed water adhering to the surface of the conductive sheet 36 is very small even in a high temperature and high humidity environment. Therefore, the charge injection phenomenon to the photosensitive drum 20 due to the adsorbed water does not occur. Therefore, the photosensitive drum 20 is excessively charged by the injection of charges without going through the discharge phenomenon, and as a result, no abnormal image is generated. Residual toner is also uniformly charged on the positive polarity side. That is, it functions as an auxiliary charger regardless of environmental conditions.

  If a charging bias in which DC (direct current) is superimposed on AC (alternating current) is applied to the auxiliary charger, a problem hardly occurs even if a charge injection phenomenon to the photosensitive drum 20 due to adsorbed water occurs. However, if the charging bias is such that DC (direct current) is superimposed on AC (alternating current), the power supply becomes expensive.

  On the other hand, as described above, the auxiliary charger 32 of the present embodiment has very little influence of adsorbed water, so that it is not necessary to superimpose AC (alternating current), and the power supply is low in cost.

  Next, a second embodiment of the image forming apparatus according to the present invention will be described. In addition, the same code | symbol is attached | subjected to the member demonstrated in 1st Embodiment, and the overlapping description is abbreviate | omitted.

  4 and 5 show an auxiliary charger 132 used in the laser printer 12 according to the second embodiment of the present invention. Except for this auxiliary charger 132, the laser printer 12 of the second embodiment has the same configuration as the first laser printer 11 shown in FIG.

  As shown in FIG. 4, the auxiliary charger 132 has a conductive conductive blade 136 (see FIG. 6) on the outer peripheral surface of a metal shaft 134 whose axial direction is the same as the axial direction of the photosensitive drum 20. In addition, a plurality are attached so as to project in the radial direction. The shaft 34 and the conductive blade 136 are fixed with, for example, a conductive adhesive so that current can be passed.

  In addition, as the conductive blade 136, for example, the resistance is adjusted with carbon, an ionic conductive agent, etc. For example, the resistance is adjusted with carbon, ionic conductive agent, etc., for example, urethane, silicon polyester, polyamide, Polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, polyimide, PEN, PEK, PES, PPS, PFA, PVdF, ETFE, CTFE and other conductive materials such as carbon black, metal powder, and metal oxide Synthetic rubber such as silicon rubber, EPDM, ethylene propylene rubber, butyl rubber, acrylic rubber, urethane rubber, nitrile rubber, etc., with mixed resistance, etc., or polarity such as epichlorohydrin rubber, chloroprene rubber, EPDM rubber Use rubber, etc. It can be. (However, polar rubber and the like have high adhesive strength, so it is necessary to devise a method such as coating the surface with a low adhesion material).

  As shown in FIG. 6, the cross section of the conductive blade 136 has a quadrangular shape, and as shown in FIG. 5, it is attached over the entire circumference of the shaft 134. Further, as shown in FIG. On the other hand, they are arranged alternately (staggered) so that there is no gap.

  The shaft 134 is rotatably attached to a holding tool (not shown) so that the tip of the conductive blade 136 is in contact with the photosensitive drum 20. (See Figure 1). Therefore, there is no portion where the conductive blade 136 does not contact the photosensitive drum 20 when rotated. (However, both end portions of the photosensitive drum 20 are excluded).

  The conductive blade 136 preferably has a width L of about 0.1 mm to 5.0 mm and a thickness D of about 0.1 mm to 1.0 mm. If it is smaller than this, the contact pressure increases, and damage (scratches, toner filming, etc.) to the photosensitive drum 20 increases. On the other hand, if it is larger than this, the surface area becomes small as a whole, and the temporary retention performance and charging performance of the residual toner of reverse polarity will be affected.

  The tip of the conductive blade 136 has an R shape.

As shown in FIG. 4, a gear 138 is attached to the end of the shaft 134 and is rotated in the direction T1 by the motor 42 via the transmission gear 40 as in the first embodiment. (See Figure 1). The peripheral speed at the tip of the conductive blade 136 is faster than the peripheral speed of the surface of the photosensitive drum 20. The shaft 48 is connected to the auxiliary charger power source 84 as in the first embodiment. Then, DC-1200 V is applied to the auxiliary charger 132 as the charging bias Vc ₀₁ by the auxiliary charger power source 84. (See Figure 1).

  Next, the operation of the laser printer 12 of this embodiment will be described.

  Although the laser printer 12 of the second embodiment is rotated, the conductive blade 136 is continuously brought into contact with the photosensitive drum 20 to achieve the same operation as the laser printer 11 of the first embodiment. The following effects are exhibited.

  Since the tip of the conductive blade 136 has an R shape as shown in FIG. 7B, as shown in FIG. 7A, compared to the shape of the blade 500 having a corner 500A at the tip, There is little damage (scratches, toner filming, etc.) to the photosensitive drum 20.

  Furthermore, as shown in FIG. 7A, if there is a corner 500A at the tip, abnormal discharge in which the discharge concentrates on this corner 500A is likely to occur. When an abnormal discharge occurs, the portion where the discharge is concentrated is excessively charged, resulting in an abnormal image. Alternatively, the surface of the photosensitive drum 20 is destroyed due to abnormal discharge.

  On the other hand, as shown in FIG. 7B, when the tip portion of the conductive blade 136 has an R shape, there is no portion where the discharge concentrates, so that no abnormal discharge occurs. Therefore, the problem due to the abnormal discharge described above does not occur.

  The present invention is not limited to the above embodiment.

  For example, in the above embodiment, the auxiliary charging devices 32 and 132 and the main charging device 44 are arranged in the charging mechanism in order from the upstream side with respect to the rotation direction K of the photosensitive drum 20. However, it is not limited to this. For example, the configuration may include a second, third, or more auxiliary charger.

  The main charger 44 is a semiconductive roller, but is not limited thereto. For example, a charger having the same configuration as the auxiliary chargers 32 and 132 may be used, or other contact-type chargers such as a fur brush may be used. Alternatively, a non-contact charger such as a corona charger may be used.

Further, the main charger 44 is not provided, and only one auxiliary charger 32, 132 may be provided. That is, the auxiliary chargers 32 and 132 temporarily hold and charge the reverse polarity toner carried by the auxiliary chargers 32 and 132, and the photosensitive drum 20 carried by the main charger 44 has a predetermined final charging potential V _02. It is good also as a structure which bears both roles.

  In the case of a configuration in which only one auxiliary charger 32, 132 is provided, as described above, the auxiliary charger 32, 132 is not affected by adsorbed water, so there is no need to superimpose AC (alternating current). Therefore, the power source is low cost. Further, there is no resonance sound that causes the photosensitive drum 20 to resonate due to AC (alternating current). Therefore, since it is not necessary to take measures such as attaching a resin or the like to the inner wall of the photosensitive drum 20 in order to suppress the resonance noise, the cost is reduced.

  Further, for example, in the above embodiment, the developing unit 54 is optimized by optimizing the setting condition of the developing bias of the developing roller 56 of the developing unit 54 without waiting for a special cleaning mechanism for removing the residual toner after transfer. The laser printers 11 and 12 are of the type in which the development and the recovery of the residual toner are performed at the same time, but are not limited thereto.

  For example, a cleaning mechanism, for example, a cleaning blade is brought into contact with the photosensitive drum 20 (see FIG. 1) between the transfer roller 58 and the charging mechanism 30, and the residual toner after transfer is scraped and removed by the cleaning blade. It may be a configuration.

  Further, for example, in the above-described embodiment, there is no neutralization unit that neutralizes the potential by neutralizing the photosensitive drum 20 before charging by the charging mechanism, but the present invention is not limited to this. For example, a static eliminating unit, for example, an erase lamp is disposed on the photosensitive drum 20 between the transfer roller 58 and the charging mechanism, and the photosensitive drum 20 is exposed to the static electricity by the racer lamp to neutralize the electric potential and then charged. It may be a configuration.

  The image carrier is not limited to an electrophotographic photosensitive member, and may be an electrostatic recording dielectric. In this case, after the surface of the electrostatic recording dielectric is charged to a predetermined potential, a latent image is formed by selectively removing the charge using a charge removal needle head, an electron gun, or the like as latent image forming means.

  Further, the image forming apparatus to which the present invention is applied is not limited to a printer, and may be a copier, a facsimile machine, a multifunction machine, or the like.

It is the figure which showed typically the inside of the laser printer which concerns on the 1st Embodiment of this invention. It is a figure which shows the auxiliary charger of the laser printer which concerns on the 1st Embodiment of this invention. The auxiliary | assistant charger of the laser printer which concerns on the 1st Embodiment of this invention is shown, (A) is the figure seen in the axial direction, (B) is the figure seen in the direction orthogonal to an axial direction. It is a figure which shows the auxiliary charger of the laser printer which concerns on the 2nd Embodiment of this invention. It is the figure which looked at the auxiliary charger of the laser printer which concerns on the 2nd Embodiment of this invention to the axial direction. It is a figure which shows the electroconductive blade of the auxiliary charger of the laser printer which concerns on the 2nd Embodiment of this invention. (A) is a view in which other blades are in contact with the photosensitive drum, and (B) is a diagram showing that the conductive blade of the auxiliary charger of the laser printer according to the second embodiment of the present invention is the photosensitive drum. FIG.

Explanation of symbols

11 Laser printer (image forming device)
12 Laser printer (image forming device)
20 Photosensitive drum (image carrier)
32 Auxiliary charger (charger)
34 Shaft (Rotating shaft)
36 conductive sheet 38 gear (rotating means)
40 Transmission gear (rotating means)
42 Motor (rotating means)
44 Main charger (other charger)
52 Optical scanning device (latent image forming means)
54 Developer (Developing means)
58 Transfer roller (transfer means)
132 Auxiliary charger (charger)
134 Shaft (Rotating shaft)
136 Conductive Blade 138 Gear (Rotating Means)
P Recording paper (recording medium)

Claims (7)

A rotating image carrier;
A charger that contacts the image carrier and charges the image carrier to a predetermined potential;
Rotating means for rotating the charger;
Latent image forming means for forming a latent image on the image carrier after charging;
Developing means for developing the latent image and forming a toner image on the image carrier;
Transfer means for transferring the toner image on the image carrier to a recording medium;
In an image forming apparatus comprising:
The charger is composed of a rotation shaft whose axial direction is the same as the rotation axis direction of the image carrier, and a plurality of conductive sheets attached to the outer peripheral surface of the rotation shaft. The image forming apparatus is characterized in that a fold is formed that curves in a direction intersecting the axial direction of the rotation shaft. A rotating image carrier;
A charger that contacts the carrier and charges the image carrier to a predetermined potential;
Rotating means for rotating the charger;
Latent image forming means for forming a latent image on the image carrier after charging;
Developing means for developing the latent image and forming a toner image on the image carrier;
Transfer means for transferring the toner image on the image carrier to a recording medium;
In an image forming apparatus comprising:
The charger is composed of a rotation shaft whose axial direction is the same as the rotation axis direction of the image carrier, and a plurality of conductive blades projecting radially from the rotation shaft. Image forming apparatus.   The image forming apparatus according to claim 2, wherein a cross section of the conductive blade has a quadrangular shape and a tip end portion has an R shape.   The charging device according to any one of claims 1 to 3, further comprising another charging device that charges the image carrier in addition to the charging device according to any one of claims 1 to 3. 2. The image forming apparatus according to item 1.   The image forming apparatus according to claim 1, wherein the charger is capable of applying a voltage having a polarity opposite to a predetermined potential of the image carrier.   6. The blade cleaning mechanism according to claim 1, further comprising a blade cleaning mechanism that scrapes and collects residual toner on the image carrier with a blade on a downstream side of the charger. The image forming apparatus described.   The image forming apparatus according to claim 6, wherein the developing unit also serves as a cleaning unit that collects residual toner on the image carrier.

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