JP2005092146A - Image forming apparatus, electrifying member, electrifying device, cleaning means and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of an abnormal image by preventing the electrification defect of an image carrier and the staining of an electrifying member at the time of restartup after jam processing and to prolong the lifetime of the image carrier by reducing the amount of wear of the image carrier. <P>SOLUTION: The image forming apparatus is equipped with an electrifying means 3, a developing means 5, an electrostatic cleaning means 7, and protective film forming means 41 and 42. In the above apparatus which passes the toner remaining on the image carrier after being removed by the electrostatic cleaning means through the electrifying member, then recovers the toner by the developing means, at the time of restarting up after the image formation operation is stopped en route, the bias of the polarity reverse from the electrifying polarity of the toner and below the discharge threshold is applied to the electrifying member in a prescribed time by the electrifying bias power sources 25 and 26 and thereafter only the protective film forming means is operated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer. More specifically, the present invention relates to a charging unit that charges an image carrier and an electrostatic latent image formed by exposure to the image carrier charged by the charging unit. Abnormal processing in an image forming apparatus including at least an exposure unit that forms an image, a developing unit that develops the electrostatic latent image, a transfer unit that transfers the developed image, and a cleaning unit that collects transfer residual toner ( The present invention relates to an improvement of the jam processing method.

In the electrophotographic image forming apparatus, as shown in FIG. 15, the image carrier 102 is uniformly charged by the charging unit 103, and then optical image information such as original reflected light is irradiated by the writing unit 104. An electrostatic latent image is formed on the image carrier, the electrostatic latent image is developed with toner from the developing unit 105, the toner image is transferred onto the transfer paper 101 by the transfer unit 106, and then the fixing unit. The image is formed by fixing by 110. The surface of the image carrier after the toner image is transferred is cleaned by the cleaning unit 107, and residual toner, paper dust, and the like are removed. Thereafter, the surface of the image carrier is neutralized by the neutralizing means 108.
Recently, as a charging means, a charging roller system is frequently used in place of a corona discharger having many problems such as ozone generation. By the way, the life of the charging roller is affected by charging roller contamination caused by toner or paper dust. In particular, when a brush roller is used as the cleaning means disposed on the upstream side of the charging roller, the ratio of the toner reaching the charging roller in the event of an abnormality such as a jam is greater than that of the cleaning blade. When a large amount of untransferred toner needs to be cleaned due to the occurrence of a jam or the like, a large amount of residual toner that cannot be completely cleaned may adhere to the charging roller. Become. Therefore, in order to extend the life of the charging roller, it is necessary to improve the processing at the time of abnormality such as a jam.
In addition, it has been found that the wear amount of the image carrier is particularly large when a voltage obtained by superimposing an AC voltage on a DC voltage (hereinafter referred to as a superimposed voltage) is applied to the charging roller. On the other hand, if the protective film is applied to the image carrier using the protective film forming means, the amount of wear during charging is reduced. However, when an abnormality such as a jam occurs, the protective film is peeled off and the wear amount of the image carrier increases, so that the protective effect of the protective film is reduced.
Next, conventional charging means, cleaning means, and protective film forming means will be described.
[Conventional charging means]

Conventionally, it is known to form an electrostatic latent image on an image carrier by charging the image carrier and selectively erasing or reducing the charge range and charge amount by exposure. Conventionally, as charging means for charging the image bearing member, those utilizing corona discharge have been the mainstream. However, the charging means using the corona discharge has a problem that a large amount of ozone is generated, and a high voltage power source for applying a high voltage of 5 to 10 kV is necessary to perform the corona discharge. It has been difficult to reduce the cost of the image forming apparatus.
Therefore, in recent years, many contact-type charging units that contact a charging member with an image carrier without using corona discharge have been proposed as charging units that can be employed in an image forming apparatus. This contact-type charging unit eliminates many of the problems of the charging unit using corona discharge, but also causes problems such as the generation of abnormal images called image flow and increased wear on the image carrier. ing. In addition, when alternating current is used as the applied voltage, noise is also a problem. In addition, since the charging means rubs toner or paper dust between the image carrier (photosensitive member) and the charging member, contamination is promoted, and contamination due to the contamination is also a problem. In order to solve such problems, Japanese Patent Application Laid-Open No. 10-312098 discloses that the charging voltage is controlled by using an auxiliary charging member and a charging member, thereby preventing the charging means from being contaminated by toner, paper dust, or the like. In addition, the occurrence of abnormal images called positive ghosts in the cleanerless system is prevented.
[Conventional cleaning means]

Conventionally, the cleaning method of an image forming apparatus in the electrophotographic method is mainly a cleaning method using a blade, and there are a large number of image forming apparatuses having cleaning means only for the blade. In addition, some high-speed machines have a cleaning brush provided upstream of the blade in order to avoid a state in which a large amount of toner is partially attached.
However, the above-described cleaning method / means has a problem that the recently developed spherical (polymerized) toner having a circularity of 0.90 or more, particularly 0.96 or more and less than 1.00, cannot be sufficiently cleaned. . However, some short-life image forming apparatuses can be cleaned by devising the toner and blade. In addition, since the spherical (polymerized) toner has a high transfer rate and a small amount of untransferred toner, there is an image forming apparatus in which a developing unit also serves as a cleaning unit without a dedicated cleaning unit. That is, there is also known an image forming apparatus in which toner that has not been transferred and remains on the photosensitive member is passed through a charging unit without being cleaned and then electrostatically attracted and collected by a developing unit.
In addition, the polarity control means provided on the upstream side of the cleaning means has been found in old type image forming apparatuses, but is rarely found recently. One of the reasons is that the technology of the cleaning means is improved and the polarity control means is not necessary, and the cost is reduced. Among the above-mentioned blades provided on the upstream side of the blade, there is one in which a voltage is applied to the brush and also serves as a polarity control means, but the number is small. However, many image forming apparatuses that do not have the cleaning unit described above have a polarity control unit.
[Conventional protective film forming means by applying lubricant]

There is known a technique for improving the life and image quality by forming a protective film made of a lubricant or the like on an image bearing member (photosensitive member) (for example, Japanese Patent Application Laid-Open No. 2002-244516 (Ricoh)). JP 2002-156877 (Ricoh), JP 2002-55580 (Canon), JP 2002-244487 (Canon)). The purpose of applying the lubricant includes (1) preventing the occurrence of filming (fusing), and (2) improving the transfer efficiency and preventing the cleaning failure by making the coefficient. it can.
In each of these conventional examples, the problem is solved by applying a lubricant on the photoreceptor to reduce the coefficient of friction. Further, in order to extend the life of the charging member and the photosensitive member, a non-contact charging device is used, and inorganic fine particles are dispersed in the photosensitive layer of the photosensitive member, and zinc stearate or the like is applied as a lubricant. Abrasion is improved (Japanese Patent Laid-Open No. 2002-229227).
Next, as a technique relating to cleaning of the charging roller, Japanese Patent Application Laid-Open No. 7-128954 “Image Forming Apparatus and Method for Uniform Charging” (Ricoh Co., Ltd.) discloses an extremely stable and uniform image that does not generate an abnormal image over a long period. In order to enable proper charging, the image forming number counting unit for counting the number of image forming times, and the cleaning member is kept away from the surface of the charging roller until the count value reaches a predetermined value. A control device that drives the cleaning member moving mechanism after the count value reaches a predetermined value to bring the cleaning member into contact with the surface of the charging roller, and at an initial stage where no toner adheres to the surface A technique that prevents the cleaning member from coming into contact with the charging roller to prevent the occurrence of abnormal images caused by scratches on the surface. There has been disclosed. In addition, it is also disclosed that a similar effect is obtained by uniformly adhering toner to the surface of the charging roller in advance and covering the surface.
However, when a cleaning brush is used to remove toner from the photosensitive member, a small amount of toner remains on the photosensitive member and always adheres to the charging roller, so that a mechanism for separating the cleaning member of the charging roller is not necessary. Further, toner adhesion to the charging roller causes deterioration in image quality and should be avoided. Therefore, this conventional example has no room to be applied to an image forming apparatus using a cleaning brush (fur brush) as a toner removing means for the photosensitive member.

Next, as a technique related to a processing method at the time of restart at the time of jam processing, Japanese Patent Application Laid-Open No. 2001-188454 “Image forming apparatus” (Canon Inc.) discloses that a post-jam processing in an image forming apparatus of a simultaneous development cleaning method. In order to prevent charging failure of the photosensitive drum and contamination of the charging member at the time of restart, first, at restart after jam processing at the time of jamming, the charging roller has the same polarity as the toner charging polarity and below the discharge threshold value. A bias is applied for a predetermined time. Thereafter, a bias having the same polarity as the charging polarity of the toner and not less than the discharge threshold is applied to the charging roller. As a result, even when a large amount of untransferred toner on the photosensitive drum enters the transfer roller, it is possible to apply a bias that biases the untransferred toner from the charging roller side to the photosensitive drum side. It is disclosed that it can be recovered satisfactorily and the charging failure of the photosensitive drum and the contamination of the charging roller can be prevented.
In the above conventional example, a voltage having the same polarity as the charging polarity of the toner is applied to the charging roller. However, if the jam detection is delayed, a situation in which the toner that has passed the transfer is included is generated, and the toner has a normal charging polarity. In this state, not only the toner but also the reverse polarity or uncharged toner is mixed. In addition, the untransferred toner includes toner that is reversely charged and uncharged toner that is hardly charged. Therefore, when a voltage having the same polarity as the charging polarity of the toner is applied to the charging roller, the above-described reversely charged or uncharged toner adheres and the contamination cannot be prevented.
Japanese Patent Laid-Open No. 10-312098 JP 2002-244516 A JP 2002-156877 A JP 2002-55580 A JP 2002-244487 A JP 2002-229227 A Japanese Patent Laid-Open No. 7-128954 JP 2001-188454 A

  The present invention has been made in view of the above, and in the image forming apparatus, the charging failure of the image carrier and the contamination of the charging member at the time of restart after jamming are prevented, and the occurrence of abnormal images is suppressed. An object is to reduce the amount of wear of the image carrier and to extend the life of the image carrier.

In order to achieve the above object, the invention of claim 1 is directed to an image carrier, a charging means for uniformly charging the surface of the image carrier by a charging member disposed opposite to the surface of the image carrier, An exposure unit that exposes the surface of the image carrier in accordance with image information to form an electrostatic latent image; a developing unit that develops a toner image by attaching toner to the electrostatic latent image; Transfer means for transferring the toner image onto a transfer material, electrostatic cleaning means for removing residual toner on the image carrier, and protective film forming means for forming a protective film on the image carrier. In the image forming apparatus in which the toner remaining on the image carrier after being removed by the electrostatic cleaning unit is passed through the charging member and then collected by the developing unit, a charging bias is applied to the charging member. The charging member and the image A charging bias power source that charges the surface of the image carrier by discharging between the holding member and a control unit that controls the charging bias power source. The control unit stops the image forming operation halfway. After the restart, after applying a bias having a polarity opposite to the charging polarity of the toner and below the discharge threshold to the charging member by the charging bias power source for a predetermined time, only the protective film forming means is operated, A bias having the same polarity as the charging polarity of the toner and a discharge threshold value or more is applied.
According to the present invention, it is possible to prevent the charging member from being stained, thereby suppressing the occurrence of abnormal images, and by forming the protective film for the image carrier, it is possible to extend the life of the charging member and the image carrier. Become.

According to a second aspect of the present invention, there is provided an image carrier, a charging unit that uniformly charges the surface of the image carrier by a charging member disposed in contact with and in close contact with the surface of the image carrier, and the charged member after charging. An exposure unit that exposes the surface of the image carrier according to image information to form an electrostatic latent image, a developing unit that attaches toner to the electrostatic latent image and develops it as a toner image, and an image on the image carrier Transfer means for transferring a toner image onto a transfer material, electrostatic cleaning means for removing residual toner on the image carrier, and protective film forming means for forming a protective film on the image carrier, In an image forming apparatus in which toner remaining on the image bearing member after being removed by an electrostatic cleaning unit is collected by the developing unit after passing through the charging member, a charging bias is applied to the charging member to Between the charging member and the image carrier. A charging bias power source that charges the surface of the image bearing member by discharging with the control unit, and a control unit that controls the charging bias power source, the control unit restarting after the image forming operation is stopped halfway Sometimes, the charging bias power source applies a bias opposite to the charging polarity of the toner and below the discharge threshold to the charging member for a predetermined time, and then operates only the protective film forming means, and then the charging polarity of the toner. And a bias having a polarity equal to or higher than the discharge threshold is applied.
According to the present invention, in the image forming apparatus in which the image carrier and the charging member are arranged close to each other in a non-contact state, it is possible to prevent the charging member from being stained, thereby suppressing the occurrence of an abnormal image and the image carrier. By forming the protective film, the life of the charging member and the image carrier can be extended.
According to a third aspect of the present invention, the charging member according to the first or second aspect includes a shaft portion and a main body portion that covers the shaft portion, and corresponds to outside the image forming area of the image carrier. A spacer member is provided on the outer periphery of the main body, and a gap is formed between the image carrier and the charging member.
According to the present invention, it is possible to create a dischargeable minute gap between the charging roller and the image carrier that does not cause abnormal discharge, and the image carrier can be uniformly charged.

According to a fourth aspect of the present invention, in the third aspect, the spacer member has contractility.
According to the present invention, similarly to the third aspect, it is possible to create a dischargeable minute gap between the charging roller and the image carrier that does not cause abnormal discharge, and the image carrier can be uniformly charged. Furthermore, it is possible to suppress the gap from being shaken due to vibration or the like.
According to a fifth aspect of the present invention, a charging means includes the charging member according to the third or fourth aspect.
According to a sixth aspect of the present invention, the cleaning means according to the first or second aspect of the invention is a fur brush that also serves as the protective film forming means, and the protective agent is a fur brush. The fur brush supplies the protective agent to the image carrier while cleaning the surface of the image carrier.
As the image forming apparatus is further downsized, it is difficult to install both a cleaning fur brush and a fur brush to which a protective agent is applied. In the present invention, space saving can be achieved by combining the fur brush for cleaning and the fur brush for applying the protective agent. While maintaining both the functions of cleaning and applying a protective agent, it is possible to save space and save resources by reducing parts.
The cleaning means according to the invention of claim 7 is characterized in that the protective agent is solidified in a block shape.
When the protective agent is in a liquid state, the operability is poor, but the operability and design freedom can be improved by solidification.

In the image forming apparatus according to the eighth aspect of the invention, the toner is a toner for developing an electrostatic latent image containing at least a binder resin, a colorant, and a wax component, and has a circularity of 0.96 or more. It is characterized by.
The pulverized toner has a wider particle size distribution and a wider charge amount distribution than a polymerized toner having excellent circularity. In addition, there is a problem in that pulverized toner having a charged polarity of opposite polarity or uncharged is included and a large amount of toner remains after transfer. By using a polymerized toner having a circularity of 0.96 or more, the amount of residual toner is reduced and the residual cleaning toner is reduced. That is, the amount of toner that reaches the charging portion can be reduced. That is, by using a polymerized toner having a new circularity of 0.96 or more, the amount of toner reaching the charging portion can be reduced, and the charging roller can be reduced in dirt.
A process cartridge according to a ninth aspect of the invention is characterized in that the image carrier and the charging member according to the first to fourth aspects are formed at least integrally.
If the image carrier and the charging device (member) are not integrated, it may be difficult to maintain the gap between the image carrier and the charging member. Also, in terms of serviceability, there are problems that it takes time for services such as replacement or that the image carrier is damaged during service. According to the present invention, the gap between the image carrier and the charging member can be easily maintained, and the serviceability is improved.

  According to the present invention, when a non-blade means such as a fur brush is used as the image carrier cleaning means, it is possible to prevent a problem that residual toner that has passed through the cleaning means adheres to the charging member. It is assumed that the toner passing through the charging member is electrostatically attracted and collected by the developing means. In the present invention, in particular, charging failure of the image bearing member and contamination of the charging member at the time of restart after jamming are prevented, the occurrence of abnormal images is suppressed, and the amount of wear of the image bearing member is reduced. Long life can be achieved.

Hereinafter, the present invention will be described in detail based on an embodiment in which the present invention is applied to an electrophotographic image forming apparatus (hereinafter referred to as a copying machine).
FIG. 1 is a schematic configuration diagram of an image forming unit of a copying machine according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of an image forming unit of a color image copying machine that directly transfers to a recording sheet. FIG. 3 is a schematic diagram showing a peripheral member of the charging member and a configuration for applying a bias to the charging member. FIG. 4 is a diagram showing an overall configuration of a general black-and-white image copying machine. FIG. 5 is a schematic explanatory view of a color image copying machine as in FIG. 3, but uses an intermediate transfer member 27, and once images of each color are superimposed on the intermediate transfer member, they are transferred to a recording sheet. It is configured to do. FIG. 6 is a modification of FIG.
In FIG. 1, FIG. 2, FIG. 4, FIG. 5, and FIG. 6, parts common to the respective image forming units 1 are described with the same reference numerals in principle. The image forming unit 1 includes an image carrier 2 which is a drum-shaped photoconductor, a charging roller 3 as a charging unit (charging member), an exposure unit 4, a developing unit 5, a transfer unit 6, a separating unit 14, a fixing unit ( A heating roller 11, a pressure roller 12), a cleaning means (electrostatic cleaning means) 7, a static elimination means 8 and the like are provided. Further, the tandem type shown in FIGS. 2, 5, and 6 is provided with a recording paper conveying belt 16 stretched between a plurality of image carriers. Further, a cleaning brush 20 is attached to the charging roller 3. The cleaning means 7 in FIGS. 1, 2, 5, and 6 is provided with a fur brush 41 for applying a cleaning fur brush 13 and a protective agent 42 in the casing. The fur brush 41 and the protective agent 42 constitute protective film forming means.

In FIG. 3, the charging roller 3 is disposed opposite to the image carrier 2 with a small gap G of about 10 to 100 μm. Normally, the charging roller 3 is arranged with a gear or the like and rotates in the clockwise direction opposite to the image carrier 2 as shown in the figure, but it may be rotated counterclockwise. The rotation speed of the charging roller is usually the same as the linear rotation speed of the image carrier 2, but it may be faster. Care must be taken when slowing down since charging may become unstable. A cleaning brush 20 is disposed in proximity to the charging roller 2, and dirt such as toner on the charging roller is removed by a hair tip of the cleaning brush 20. Some contact-type charging rollers apply only a DC voltage, but non-contact charging rollers usually apply an AC voltage superimposed on a DC voltage.
In this example, the AC power source 25 and the DC power source 26 constitute a charging bias power source that applies a charging bias to the charging roller 3 and charges the surface of the image carrier by discharge between the charging roller 3 and the image carrier 2. The charging bias power source is controlled by the control means.
The characteristic configuration of the present invention is that when the control unit is restarted after the image forming operation is stopped halfway due to the occurrence of a jam or the like, the charging roller 3 is charged to the charging roller 3 by the charging bias power sources 25 and 26 and the polarity opposite to the charging polarity of the toner In addition, after applying a bias below the discharge threshold for a predetermined time, only the protective film forming means 41 and 42 are operated. Thereafter, when the image forming process is continued (restarted), only the protective film forming unit is operated, and then a bias having the same polarity as the normal charging polarity of the toner and higher than the discharge threshold is applied.

FIG. 4 is an overall view (cross-sectional view) of the monochrome image forming apparatus according to the embodiment of the present invention. The image forming apparatus shown here has an image carrier 2 in the main body of the image forming apparatus. The image carrier 2 is a drum-like photosensitive member having a photosensitive layer formed on the outer peripheral surface of a cylindrical conductive base. The image carrier 2 is an endless belt-shaped image carrier that is wound around a plurality of rollers and rotated. It can also be used.
The image carrier 2 shown in FIG. 4 is rotated in the clockwise direction during the image forming operation. At this time, the image carrier is charged to a predetermined polarity by the charging means 3. The image carrier 2 charged by the charging unit 3 is irradiated with light-modulated laser light emitted from a laser writing unit 4 which is an example of an exposure unit, whereby an electrostatic latent image is formed on the image carrier. The In the example shown in the figure, the absolute value of the potential of the surface portion of the image carrier irradiated with the laser beam decreases, and this becomes an electrostatic latent image (image portion), and the absolute value of the potential is not irradiated with the laser beam. The part kept high becomes the background part. Next, the electrostatic latent image is visualized as a toner image by toner charged to a predetermined polarity when passing through the developing means 5. An exposure unit having an LED array, an exposure unit that illuminates a document surface and forms an image of the document image on an image carrier can also be used.
On the other hand, a transfer material 15 made of, for example, transfer (recording) paper is sent out from the paper feeding means 17, and the transfer material 15 is placed between the transfer means 6 and the image carrier 2 facing the image carrier 2. It is sent at the timing. At this time, the toner image formed on the image carrier is electrostatically transferred onto the transfer material. The transfer material 15 onto which the toner image has been transferred continues to pass through the fixing means 10, and at this time, the toner image is fixed on the transfer material by the action of heat and pressure. The transfer material that has passed through the fixing unit 10 is discharged to a paper discharge unit. Untransferred toner remaining on the surface of the image carrier without being transferred to the transfer material is removed by the cleaning means 7. In the figure, the fixing unit 10 shows the configuration of the two rollers 11 and 12, but there is no problem with other configurations such as a belt and a roller.

The developing means 5 shown in FIG. 4 has a developing case 5a that contains a dry developer, and a developing roller 5b that carries the developer while carrying it. As the developer, for example, a dry developer having a toner and a carrier, or a one-component developer having no carrier can be used. A developing means using a liquid developer can also be employed. The developing roller 5b is rotationally driven in the direction of the arrow. At this time, the developer is carried and conveyed on the peripheral surface of the developing roller, and the toner in the developer carried to the developing area between the developing roller and the image carrier 2 is transferred. The electrostatic latent image is electrostatically transferred to the electrostatic latent image, and the electrostatic latent image is visualized as a toner image.
The transfer means 6 shown in FIG. 4 is constituted by a transfer roller to which a transfer voltage having a polarity opposite to the charging polarity of the toner on the image carrier 2 is applied, and a transfer brush, a transfer blade, or a corona wire having a corona wire. It is also possible to use transfer means comprising a discharger. Further, instead of directly transferring the toner image on the image carrier to a transfer material as a final recording medium, the toner image on the image carrier is transferred onto a transfer material comprising an intermediate transfer member, and the toner image is transferred to the transfer material. It can also be configured to transfer to the final recording medium.
Further, the cleaning means 7 shown in FIG. 4 has a cleaning member 41 made of a fur brush rotatably supported by a cleaning case, and these cleaning members 41 come into contact with the surface of the image carrier. Clean the transfer residual toner that adheres. A protective agent 42 is also in contact with the fur brush 41, and at the same time as cleaning is performed, the protective agent is supplied to the image carrier. The protective material 42 is made of a solid agent, and when the fur brush 41 rotates, the tip thereof scrapes the protective material powder from the protective agent surface.
As the image forming apparatus is further downsized, it is difficult to place both the cleaning fur brush 13 and the fur brush 41 to which the protective agent is applied side by side. In this embodiment, space saving is achieved by combining the fur brush for cleaning and the fur brush for applying the protective agent. Furthermore, it is possible to save space and save resources by reducing parts.
The protective agent 42 is solidified into a block shape such as a rod shape or a box shape. When the protective agent is in a liquid state, the operability is poor. Therefore, the operability can be improved by solidification.
In the image forming apparatus of this example, the image carrier 2, the charging unit 3 for charging the image carrier 2, the exposure unit 4 for exposing the image carrier 2 charged by the charging unit 3 to form an electrostatic latent image, The developing means 5 that visualizes the electrostatic latent image as a toner image, the transfer means 6 that transfers the toner image to a transfer material, and the transfer residual toner that adheres to the surface of the image carrier after the toner image transfer is removed. And a cleaning means 7. Usually, the transfer residual toner is collected by the cleaning means 7, but the toner remaining untransferable by the cleaning means 7 in the case of an abnormality such as a jam is electrostatically collected by the developing means 5 after passing through the charging means 3. Can be removed.

FIG. 7 is a sectional view showing the structure of the charging means (roller) used in the present invention.
As shown in FIG. 4 and the like, the charging unit 3 has a charging member disposed opposite to the surface of the image carrier 2. Although this charging member can be configured in an appropriate form, in the example shown in FIG. 4 and the like, it is configured by a charging roller. As shown in an enlarged view in FIG. 7, the charging roller 3 includes a conductive cored bar (shaft part) 21 formed in a columnar shape, and a cylindrical medium resistance layer 22 fixed to the cored bar 21. And a surface layer 23 laminated on the outer peripheral surface of the resistance layer 22. The middle resistance layer 22 and the surface layer 23 constitute a main body.
The metal core 21 is, for example, a metal material having high rigidity and conductivity, such as stainless steel or aluminum having a diameter of about 4 to 20 mm, or 1 × 10 ³ Ω · cm or less, preferably 1 × 10 ² Ω · cm or less. It is comprised by the highly rigid conductive resin etc. which have the volume resistivity of these. In this example, the core metal 21 constitutes the core shaft of the charging roller.
The volume resistivity of the middle resistance layer 22 is set to 10E + 3 to 10 Ω · cm, t = 1, for example, about 10 ^{4 to} 10 ⁹ Ω · cm, and the thickness thereof is set to, for example, about 1 to 2 mm. The volume resistivity of the surface layer 23 is set to 10E + 3 to 12 Ω · cm, t = 0.01, for example, about 10 ^{6 to} 10 ¹¹ Ω · cm, and the volume resistivity of the surface layer 23 is based on the volume resistivity of the medium resistance layer 22. Is preferably slightly higher. The thickness of the surface layer 23 is, for example, about 10 μm.

Next, FIG. 8 shows a configuration example in which a gap G is formed between the charging roller and the image carrier. By attaching the spacer member 24 over the entire length in the circumferential direction to a region (region corresponding to outside the image forming region of the image carrier) of the outer peripheral surface of the charging roller 3, a minute gap G is formed. Yes. Here, a uniform thickness tape is used as the spacer member 24, but the gap G may be formed by a roller or the like.
According to this, even when an external force such as vibration is applied, the gap between the charging roller and the image carrier is fluctuated and the charge amount and the like can be prevented from varying.
Next, specific examples of materials constituting each part of the charging member 3 are listed.
The middle resistance layer 22 is composed of a base material and a conductive agent dispersed in the base material. Examples of the base material include olefin resins such as polyethylene (PE) and polypropylene (PP), polystyrene (PS), and co-polymers thereof. General-purpose resins having good processability such as styrene resins such as coalesced (AS, ABS) and acrylic resins such as polymethyl methacrylate (PMMA) can be used.
Examples of the conductive agent for the medium resistance layer 22 include alkali metal salts such as lithium peroxide, perchlorates such as sodium perchlorate, quaternary ammonium salts such as tetrabutylammonium salts, and ionic systems such as polymer-type conductive agents. A conductive agent can be used, and carbon black such as ketjen black and acetylene black can also be used.

The surface layer 23 can also be composed of a material in which a conductive agent is dispersed in a base material. As the base material, an appropriate material such as a fluorine resin, a silicone resin, an acrylic resin, a polyamide resin, a polyester resin, a polyvinyl butyral resin, or a polyurethane resin is used. In particular, it is preferable to select a material to which the toner is difficult to fix. As the conductive material constituting the surface layer 23, an electron conductive conductive agent made of carbon black such as ketjen black or acetylene black, a metal oxide such as indium oxide or tin oxide, or other appropriate conductive agent is used. Can do.
Examples of the material of the tape constituting the spacer member 24 include metals such as aluminum, iron, nickel and oxides thereof, metals such as Fe—Ni alloy, stainless steel, Co—Al alloy, Ni—steel, duralumin, monel, and inconel. Alloys, olefin resins such as polyethylene (PE) and polypropylene (PP), polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polytetrafluoroethylene (PTFE), and copolymers thereof (for example, PFA) , FEP) and the like, and polyimide resins. In particular, it is preferable to use a material having high releasability that is difficult to fix the toner. When a conductive material is used for the tape, the surface and the image carrier are insulated by coating the surface with an insulating layer or a half resistor layer. By using a material having contractility (flexibility, elasticity) as the spacer member, it is possible to prevent a minute gap between the image carrier and the image carrier from fluctuating due to vibration, impact, or the like.
However, the constituent materials of the charging roller 3 are not limited to the above materials.

FIG. 9 is a diagram illustrating a discharge start voltage depending on a difference in the value of the gap G, showing a voltage at which a current starts to flow when a DC voltage is applied to the charging roller 3, and a voltage at which the current starts to flow is started. It is called voltage. When the gap between the charging roller and the photoconductor is widened, the discharge start voltage moves to the high voltage side.
FIG. 10 is a flowchart from the start to the end of a print job.
When a print command signal is input in S1, the image forming apparatus performs preparatory rotation before image formation (S2). Thereafter, the image forming operation starts (S3). If no abnormality occurs, the image formation is terminated, the preparatory rotation after the image formation is performed, and the image formation operation is terminated (S4, 5).
If an abnormality occurs in step 4, the cover of the apparatus may be opened during image formation, the power cord may be removed, or the recording paper may stop in the image forming apparatus (this is called a jam). Normally, there is no need to open the cover of the apparatus or unplug the power cord during image formation, so a jam that is a typical example of abnormality will be described below.
During the image forming operation, when a jam is detected by a sensor provided in each part where the recording paper of the image forming apparatus passes, the image forming operation is stopped (S4, 6). Thereafter, when the operator removes the jam, the recovery operation is started (S7, 8, 9).
This recovery operation is an operation when a jam occurs at least with the transfer paper in the vicinity of the image carrier. That is, if only one sheet is printed, this corresponds to the case where the transfer paper jams in the vicinity of the image carrier, and if two or more sheets are printed, one of the transfer papers is in the vicinity of the image carrier. Refers to a case. In addition, when the intermediate transfer belt is used, it indicates a case where a jam occurs at least after the latent image on the image carrier is developed until the cleaning of the image carrier is completed. For example, the recovery operation is not performed in the case of a jam only in the paper feed unit or a jam only in the fixing unit.

The characteristic recovery operation in the present invention is as follows. First, a voltage opposite to the charging polarity of the toner is applied to the cleaning fur brushes 41 and 13. At the same time, a voltage having a polarity opposite to the charging polarity of the toner and lower than the discharge start voltage is applied to the charging roller 3. Thereafter, the image carrier 2 is rotated to clean the untransferred toner or untransferred toner. At this time, no voltage is applied to the transfer unit 6, but at least a voltage is not applied to the developing unit 5, or a voltage that can attract the charged polarity (minus) of regular toner is applied.
By applying a voltage to each means as described above, almost all toner is collected by the cleaning device and the developing machine. Note that a series of these operations may be performed several times in order to ensure the cleaning effect. (The image carrier may be rotated several times.)
Thereafter, the protective agent is applied in a state where no voltage is applied to the developing unit 5 and the transfer unit 6, a voltage equal to or lower than the discharge start voltage is applied to the charging unit 3, and a normal voltage is applied to the cleaning fur brush 41. 42 is applied to the image carrier 2. Also in this case, the protective agent application operation may be performed at least once more in order to ensure the cleaning effect. The series of operations is performed, and the recovery operation is completed.
After completion of the recovery operation, the process returns to the normal flow, and the preparation rotation is performed.

Next, each operation of the recovery operation will be described. Here, the normal charging polarity of the toner is negative charging. By applying a positive voltage having a polarity opposite to the charging polarity of the toner to the cleaning fur brush, the normally negatively charged toner is recovered.
Further, the toner is attached to the charging roller 3 by applying a voltage (positive) opposite to the normal charging polarity (minus) of the toner and a voltage equal to or lower than the discharge start voltage to the charging roller 3. To prevent. That is, when a voltage equal to or higher than the discharge start voltage is applied, a discharge occurs and the charged state of the toner changes. Since most of the negatively charged toner is collected by the cleaning fur brush, most of the toner at the position of the charging roller is positively charged. However, when a voltage equal to or higher than the positive discharge start voltage is applied to the charging roller 3, discharge occurs, and when the toner passes through the discharge region, the toner is positively charged. However, since most of the toner conveyed to the discharge area is positively charged, there are few that change in polarity. In addition, since the charging roller 3 and the toner have the same polarity, the toner does not adhere to the charging roller.
On the other hand, the charging roller 3 is greatly affected by the deterioration of the toner material and the removal of the external toner additive. Occurrence of the above-described change in the toner causes deterioration of toner transportability and charging characteristics, and deterioration of recyclability due to the deterioration. Therefore, it is preferable to apply a voltage that does not cause discharge.

The discharge starting voltage is usually about 600 to 700 V when an OPC photosensitive member and a contact charging roller are used, and is a value as shown in FIG. 9 in the case of a non-contact charging roller. Here, if the voltage actually applied is equal to or less than the discharge start voltage in the non-contact charging roller, the gap between the charging roller and the toner becomes narrow when the toner or the like is between the gap G between the charging roller and the image carrier. As a result, the discharge start voltage decreases and discharge occurs. Therefore, the set value of the voltage not higher than the discharge start voltage applied to the charging roller is preferably set to be equal to or lower than the discharge start voltage in contact charging. More preferably, a value lower by about 200 V than the discharge start voltage in contact charging is better, and further, a value lower by about 400 V than the discharge start voltage in contact charging in consideration of occurrence of discharge due to gap narrowing caused by gap fluctuation. Is better.
For comparison with the case where a positive voltage equal to or higher than the discharge start voltage is applied to the charging roller 3, assuming that a negative voltage is applied to the charging roller, if the toner passes through the discharge region, the toner will have a negative voltage. Something is charged. Since the negatively charged toner is not collected by the developing means, there arises a problem such as staining the transfer means 6 located on the downstream side of the developing means. In addition, since the polarities of the charging roller 3 (minus) and the toner (plus) are different, there is a problem that the toner adheres to the charging roller.
Most of the toner that has passed through the charging roller 3 to which a positive voltage equal to or lower than the discharge start voltage is applied is positively charged, and is sent to the developing means 5 to which a negative voltage is applied. Collected in. However, when the developing means 5 is a contact type one-component development or a two-component magnetic brush development method, the toner is collected also by a rubbing force caused by contact.
Next, when the powder of the protective agent 42 is applied onto the image carrier 2 using the fur brush 41, a voltage equal to or lower than the discharge start voltage is applied to the charging roller 3 for the purpose of preventing toner adhesion. When a voltage equal to or higher than the discharge start voltage is applied, the protective agent adheres to the charging roller due to the discharge, which is intended to prevent it. That is, when a large amount of protective agent adheres to the charging member, uniform charging may be hindered.

Next, FIG. 11 shows a superposition for charging a normal image carrier having a discharge start voltage or higher on a charging member (charging roller) in a state where the protective agent is applied to the image carrier only in one half region as shown in FIG. The result of having experimented by applying a voltage is shown. The experiment was performed with all other developing means removed from the image forming unit.
In the region on the image carrier to which the protective agent was applied, the image carrier was hardly scraped after 200 hours of experiment, but the non-coated region was scraped by about 2.5 μm.
FIG. 13 shows the detailed structure of the cleaning means (cleaning device). The cleaning means 7 constituting the image forming unit shown in FIGS. 4 and 6 has a structure as shown in FIG. 1, 2, and 5, another fur brush 13 is installed, and a protective agent 42 is in contact with the fur brush 41 on the downstream side. A recovery roller 31 is in contact with the fur brush 41 in FIG. 13, and a voltage for recovering the toner 40 attached to the fur brush 41 is applied from the cleaner power source 34. The scraper 31 comes into contact with the collecting roller 31 to remove the toner 40 attached thereto. The toner removed by the scraper 32 is collected by the collection coil 33.

By the way, in the image forming apparatus shown in each of the above embodiments, as shown in FIG. 14, a casing 3A that rotatably supports the charging roller 3 and a cleaning case 7A of the cleaning device 7 are configured as an integrated unit case UC. Then, the image carrier 2 is rotatably assembled to the unit case UC. Thus, an image forming unit (process cartridge P) in which the charging roller 3 and the image carrier 2 are integrally assembled is configured, and the process cartridge P can be attached to and detached from the image forming apparatus main body. It is installed. The charging roller 3 and the image carrier 2 are incorporated in the unit case UC in a state where the minute gap G is kept constant, and the process cartridge P is attached to the main body of the image forming apparatus while keeping the minute gap G constant. It can be attached and detached. For this reason, when the process cartridge P is attached / detached, a problem that the size of the minute gap G largely fluctuates can be prevented. The image carrier 2 and the charging roller 3 may be configured to be separately attached to and detached from the image forming apparatus main body. However, according to this configuration, there is a possibility that the minute gap G 1 changes when the image carrier 2 and the charging roller 3 are attached and detached. There is a risk that uniform charging will not be possible.
In addition to the charging roller 3, the image forming unit and the process cartridge according to this embodiment include contact members (fur brushes 13, 41) that contact the image carrier 2. In the example shown in FIG. 4, as described above, the cleaning case 7A and the charging roller casing 3A are formed as a unit case UC, and the fur brushes 13 and 41 are assembled to the unit case UC. Reference numerals 13 and 41 constitute contact members that contact the image carrier. The contact member may be configured to be attachable to and detachable from the image forming apparatus main body separately from the charging roller 3, but in this case, when the contact member is attached or detached, these members move while being in contact with the image carrier. Therefore, a large external force is applied to the image carrier, which may cause the minute gap G to fluctuate. On the other hand, if the contact member is also a component of the image forming unit and the process cartridge, when the image forming unit is attached to and detached from the main body of the image forming apparatus, the contact member made of the fur brush is also attached and detached. The member does not move relative to the image carrier, and there is no possibility that the minute gap G will fluctuate greatly.

The image forming apparatuses shown in FIGS. 1, 2, 4, 5, and 6 each include the charging device 3 and the image carrier 2 configured as described above. If there are irregularities such as large undulations on the surface of the carrier, the size of the minute gap G is likely to fluctuate when the image carrier 2 is rotated even if the above-described configurations are adopted. Therefore, the image carrier 2 is preferably configured as a photoconductor having an amorphous silicon surface layer. Since the surface of the image carrier 2 can be finished very smoothly, it is possible to effectively suppress fluctuations in the size of the minute gap G when the image carrier 2 is rotated. The toner removal effect by the charging device configuration can be made more reliable.
Further, when the image carrier 2 is configured as a photoreceptor having a surface layer in which a filler such as alumina powder of 0.1 μm or less is dispersed, the surface hardness is increased and the wear resistance is improved. The service life can be greatly extended.
As the toner to be used, for example, a toner for developing an electrostatic latent image containing at least a binder resin, a colorant, and a wax component is used, and the circularity is, for example, 0.96 or more.
The pulverized toner has a wider particle size distribution and a wider charge amount distribution than a polymerized toner having excellent circularity. In addition, there is a problem in that pulverized toner having a charged polarity of opposite polarity or uncharged is included and a large amount of toner remains after transfer.
By using a polymerized toner having a circularity of 0.96 or more, it is possible to reduce the amount of transfer residual toner and to reduce cleaning residual toner. That is, the amount of toner reaching the charging unit can be reduced, and contamination of the charging roller can be reduced.
The charging devices having the above-described configurations can be applied to image forming apparatuses other than the types shown in FIGS. For example, as shown in FIGS. 2, 5, and 6, a plurality of, for example, four image carriers 2 on which toner images of different colors are formed are arranged and formed on each image carrier. A color image forming apparatus that sequentially superimposes and transfers a toner image onto a transfer material is well known, but the above-described charging device can be employed to charge each image carrier of the image forming apparatus. .

1 is a schematic configuration diagram of an image forming unit of a copying machine according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of an image forming unit of a color image copying machine that directly transfers to a recording sheet. 1 is a schematic diagram illustrating a configuration for applying a bias to a peripheral member of a charging member and a charging member. The figure which shows the whole structure of the copying machine for general monochrome images. FIG. 2 is a schematic explanatory diagram of a color image copying machine. The figure which shows the modification of FIG. Sectional drawing of an example of a charging roller. FIG. 3 is a diagram illustrating a configuration example of a charging roller according to an example of the present invention. The figure which shows the discharge start voltage. The flowchart for demonstrating the control procedure which concerns on one Embodiment of this invention. The figure explaining the film | membrane scraping amount of an application part and a non-application part. The figure which shows the structural example of the image carrier used for the experiment of FIG. The block diagram of an example of the image formation unit which concerns on one Embodiment of this invention. The block diagram of the image formation unit which concerns on other embodiment of this invention. Explanatory drawing of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming unit, 2 Image carrier, 3 Charging means (charging member), 4 Exposure means, 5 Developing means, 6 Transfer means, 7 Cleaning means, 8 Static elimination means, 10 Fixing means, 11 Fixing roller, 12 Pressure roller , 13 Fur brush (cleaning brush), 14 Separating means, 15 Recording paper, 16 Conveying belt, 20 Cleaning brush, 24 Spacer member, 41 Fur brush (cleaning brush), 42 Solid agent

Claims (9)

An image carrier, a charging unit that uniformly charges the surface of the image carrier by a charging member disposed opposite to the surface of the image carrier, and the surface of the image carrier after charging is exposed according to image information. An exposure unit that forms an electrostatic latent image; a developing unit that develops a toner image by attaching toner to the electrostatic latent image; a transfer unit that transfers a toner image on the image carrier onto a transfer material; An electrostatic cleaning unit that removes residual toner on the image carrier and a protective film forming unit that forms a protective film on the image carrier, and the image carrier after being removed by the electrostatic cleaning unit In the image forming apparatus for collecting the toner remaining on the body by the developing unit after passing through the charging member,
A charging bias power source for charging the surface of the image carrier by applying a charging bias to the charging member and discharging between the charging member and the image carrier, and a control means for controlling the charging bias power source; With
The control means applies a bias having a polarity opposite to the charging polarity of the toner and not more than a discharge threshold to the charging member for a predetermined time by the charging bias power source upon restart after the image forming operation is stopped halfway. An image forming apparatus. An image carrier, charging means for uniformly charging the surface of the image carrier by a charging member disposed in contact with and in close proximity to the surface of the image carrier, and image information on the surface of the image carrier after charging Exposure means for forming an electrostatic latent image by exposure according to the above, developing means for developing a toner image by attaching toner to the electrostatic latent image, and a toner image on the image carrier on the transfer material A transfer means for transferring; an electrostatic cleaning means for removing residual toner on the image carrier; and a protective film forming means for forming a protective film on the image carrier; and removing by the electrostatic cleaning means In the image forming apparatus in which the toner remaining on the image carrier after the toner is passed through the charging member and then collected by the developing unit,
A charging bias power source for charging the surface of the image carrier by applying a charging bias to the charging member and discharging between the charging member and the image carrier, and a control means for controlling the charging bias power source; With
The control means applies a bias having a polarity opposite to the charging polarity of the toner and not more than a discharge threshold to the charging member for a predetermined time by the charging bias power source upon restart after the image forming operation is stopped halfway. And an image forming apparatus using the same.   The charging member according to claim 1 or 2 includes a shaft portion and a body portion that covers the shaft portion, and a spacer member is provided on the outer periphery of the body portion corresponding to the outside of the image forming area of the image carrier. A charging member, wherein a gap is formed between the image carrier and the charging member.   The charging member according to claim 3, wherein the spacer member has contractibility.   A charging device comprising the charging member according to claim 3. The cleaning member constituting the electrostatic cleaning unit according to claim 1 or 2 is a fur brush that also serves as the protective film forming unit, and is installed so that the protective agent contacts the fur brush.
The fur brush supplies a protective agent to the image carrier while cleaning the surface of the image carrier.   The cleaning means according to claim 6, wherein the protective agent is solidified in a block shape.   3. The toner according to claim 1, wherein the toner is a toner for developing an electrostatic latent image containing at least a binder resin, a colorant, and a wax component, and has a circularity of 0.96 or more. Image forming apparatus.   5. A process cartridge for an image forming apparatus, wherein the image carrier and the charging member according to claim 1 are at least integrally formed.

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