JP2009186941A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus suppressing soiling of a transfer member due to toner, in the case of performing a process to supply a toner image to a cleaning member so as to maintain lubricity between the cleaning member and an image carrier. <P>SOLUTION: The image forming apparatus includes: the image carrier 1; the transfer member 5; a power source 51 for applying a transfer voltage to the transfer member 5; the cleaning member 7a; and a fixing device 6. The image forming apparatus performs an operation to form, in addition to an output image I to be fixed to the transfer material P, a toner supply image S for supplying the toner to a cleaning section C on the image carrier, make the toner supply image S pass through a transfer section N and supply the toner supply image S to the cleaning section C. The toner supply image S forming area on the image carrier 1 is set in a position where the image carrier 1 passes through the transfer section N while the transfer material P passes through the transfer section N in the moving direction of the image carrier 1, and also, where the output image I is not formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer or a copier using an electrophotographic system, which forms an image by transferring and fixing a toner image formed on an image carrier onto a transfer material.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system such as a printer, a toner image is formed on a rotating electrophotographic photosensitive member (photosensitive member) as an image carrier, and the photosensitive member is formed on a transfer material such as paper. Transfer the upper toner image. The transfer of the toner image from the photoconductor to the transfer material is performed electrostatically by applying a predetermined voltage to a transfer member that presses against the surface of the photoconductor to form a transfer portion. In the process of repeating the above process, it is necessary to remove the transfer residual toner remaining on the photosensitive member without being transferred to the transfer material. The photoreceptor is generally a rotatable drum, and the transfer member is generally a rotatable roller (transfer roller).

  As a means for removing the transfer residual toner remaining on the photosensitive member after the transfer process, there is a method of scraping with a fur brush or a blade as a cleaning member. From the standpoint of productivity, cost, and performance, a cleaning blade (elastic blade) made of an elastic material such as polyurethane rubber has become the mainstream as a cleaning member. The cleaning blade is usually pressed against the surface of the photosensitive member so that the free end faces the upstream side of the photosensitive member surface in the counter direction with respect to the moving direction of the photosensitive member surface, that is, the support portion. Are arranged. If the cleaning blade is placed in direct contact with the photoconductor and rotated, the cohesive force of the cleaning blade is large, and the tip of the cleaning blade may be caught in the photoconductor and bend. Therefore, in a cleaning device using a cleaning blade, a lubricant is often applied to the cleaning blade.

  By making contact between the rotating photoconductor and the cleaning blade so that no gap is always generated, the transfer residual toner on the photoconductor is cleaned almost 100%. However, the lubricant applied to the cleaning blade may be unevenly coated in a very small range or may be gradually peeled off due to paper passing. Therefore, a phenomenon (stick-slip phenomenon) in which the edge portion at the tip of the cleaning blade is caught in the photosensitive member and immediately restored may be repeated. Then, the contact between the photosensitive member and the edge of the tip of the cleaning blade becomes unstable, and a gap of several μm to several tens of μm may be generated. Eventually, the toner is removed from the gap, and problems due to poor cleaning such as contamination of the charging member and a decrease in image quality are likely to occur. In particular, when the particle size distribution of the toner is not uniform, the toner having a small particle size tends to slip through the gap. Alternatively, spherical polymerized toner or the like can easily pass through even a relatively small gap due to good releasability of the toner, causing a cleaning failure.

  On the other hand, when used over a long period of time, foreign matter such as paper dust or dust carried from the paper as the transfer material is sandwiched between the cleaning blade and the photoconductor, and cleaning is performed when these foreign matter accumulates more than a certain amount. It becomes easy to cause a defect. Also in this case, the frictional resistance between the photosensitive member and the cleaning blade is greatly involved. The smaller the frictional resistance is, the wider the allowable range of foreign matters is, and the cleaning property is maintained well.

  In order to deal with these problems, in general, the cleaning blade and the photoconductor are selected so that the friction resistance between them is as low as possible, the contact pressure of the cleaning blade and This is done by adjusting the contact angle as appropriate.

  However, if this is still insufficient, a means for supplying lubricating particles for suppressing frictional resistance may be provided as represented by Patent Document 1.

As a method for realizing the same effect at a lower cost, a method represented by Patent Document 2 has been proposed and put into practical use. In other words, the toner image formed on the photoconductor is held between the cleaning blade and the photoconductor while the image is not formed (that is, the period during which no transfer material is present in the transfer portion). It is sent to (cleaning part) and functions as lubricating particles. Thereby, the frictional force is suppressed and the cleaning failure is suppressed. The toner image formed on the photoconductor for feeding between the cleaning blade and the photoconductor is a belt-like image (black belt image) continuous in the longitudinal direction (rotation axis direction) of the photoconductor.
JP 11-288194 A JP 2005-148303 A

  However, the above-described method of supplying the black belt image formed on the photoconductor to the position of the cleaning blade at the timing when the transfer material does not exist in the transfer portion has the following problems.

  That is, when the black belt image passes through the transfer member, the transfer member may be soiled. In order to reduce the contamination of the transfer member as much as possible, a bias (hereinafter referred to as “transfer cleaning bias”) having the same polarity as the normal charging polarity of the toner is transferred at the timing when the toner of the black belt image passes through the transfer portion. Apply to member. Alternatively, by separately providing a cleaning time and applying a transfer cleaning bias to the transfer member to remove dirt, the toner adhering to the transfer member is reduced.

  However, a small amount of toner charged to a polarity opposite to the normal charging polarity may remain attached to the transfer member, or the toner may physically adhere to the surface of the transfer member and remain. In particular, in a configuration in which foaming rubber or the like is used for the elastic layer of the transfer roller as a transfer member, the toner often enters and remains in the foam cell.

  On the other hand, the more frequently the process of supplying toner to the cleaning blade, the better the cleaning performance of the photoreceptor can be maintained. However, if the frequency is too high, the toner removed from the photoreceptor by the cleaning blade and collected in the collected toner container increases, and the amount of toner consumed also increases. Therefore, the process is generally performed at a frequency of about once every several tens of sheets. However, even with such a frequency, the toner contamination gradually accumulates on the transfer member by passing about several thousand sheets. The accumulation of toner contamination leads to an increase in the electrical resistance value of the transfer member. When the electrical resistance value of the transfer member increases, in cases where a high-resistance transfer material is passed in a low-temperature, low-humidity environment, the transfer current may be insufficient, or the charge may not be uniformly applied to the paper. This causes image defects such as transfer defects and transfer unevenness. Also, if the amount of accumulated toner stains on the transfer member is large, there may be a problem that the back surface of the subsequent transfer material is stained. In particular, when cardboard or envelopes are used, the pressure that the transfer material receives at the transfer nip increases, and the back surface of the transfer material tends to become dirty due to the pressure.

  Accordingly, an object of the present invention is to suppress contamination of the transfer member due to the toner in the process of supplying the toner of the toner image to the cleaning member in order to maintain the lubricity between the cleaning member and the image carrier. An image forming apparatus is provided.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a movable image carrier that carries a toner image, and a transfer portion formed in contact with the image carrier, and passes through the transfer portion as the image carrier moves. A transfer member for transferring a toner image onto the transfer material from the image carrier; a power source for applying a voltage for the transfer to the transfer member; and a downstream side of the transfer unit in the moving direction of the image carrier. A cleaning member is formed in contact with the image carrier, a cleaning member for removing toner from the image carrier in the cleaning unit, and a fixing for fixing the toner image transferred on the transfer material to the transfer material A toner supply image for supplying toner to the cleaning unit on the image carrier separately from the output image to be fixed to the transfer material. the image The region on the image carrier that forms the toner supply image is moved in the moving direction of the image carrier, and the transfer material is transferred to the transfer portion. An image forming apparatus, wherein the image forming apparatus is set to a position where the output image is not formed while passing through the transfer portion while passing through the portion.

  According to the present invention, when the step of supplying the toner of the toner image to the cleaning member is performed in order to maintain the lubricity between the cleaning member and the image carrier, the transfer member can be prevented from being contaminated by the toner.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
(1) Image Forming Apparatus First, the overall configuration of an embodiment of an image forming apparatus according to the present invention will be described.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present exemplary embodiment. In this embodiment, the image forming apparatus 100 is an electrophotographic laser beam printer.

  The image forming apparatus 100 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as a movable image carrier that carries a toner image. The photosensitive drum 1 is made of a photosensitive material such as OPC (organic photoconductor), amorphous Se, or amorphous Si formed on a cylindrical tube such as aluminum or nickel. In this embodiment, the photosensitive drum 1 is an OPC photosensitive member having a negative charging characteristic.

  Around the photosensitive drum 1, there are a charging roller 2 as a charging means, an exposure device (laser scanner) 3 as an exposure means, a developing device 4 as a developing means, a transfer roller 5 constituting a transfer means, and a cleaning as a cleaning means. A device 7 and the like are arranged. The transfer roller 5 contacts the photosensitive drum 1 to form a transfer nip (transfer portion) N, and a toner image is transferred from the photosensitive drum 1 onto the transfer material P passing through the transfer nip N as the photosensitive drum 1 moves. It is a transfer member comprised with the rotary body for making it transfer.

  In this embodiment, the photosensitive drum 1, the charging roller 2 as a process unit that acts on the photosensitive drum 1, the developing device 4, and the cleaning device 7 are integrally formed into a cartridge to constitute a process cartridge 10. The process cartridge 10 is detachable from the main body of the image forming apparatus 100.

  In the image forming operation, the photosensitive drum 1 is rotationally driven in the illustrated arrow R1 direction (clockwise), and first, the surface thereof is uniformly charged to a predetermined negative potential by the charging roller 2. Next, the surface of the charged photosensitive drum 1 is subjected to scanning exposure with a laser beam L from the exposure device 3 that is ON / OFF controlled according to image information. As a result, an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. This electrostatic latent image is formed when the absolute value of the potential of the exposed portion becomes lower than the absolute value of the charging potential.

  Next, the electrostatic latent image on the photosensitive drum 1 is developed (visualized) by supplying toner by the developing device 4. As a developing method, a jumping developing method, a two-component developing method, an FEED developing method, or the like is used, and image exposure and reversal development are often used in combination. In this embodiment, a jumping development method is used. In this embodiment, the normal charging polarity of the toner as the developer used in the developing device 4 is negative, and development is performed by image exposure and reversal development. That is, the electrostatic latent image is developed as a toner image by attaching a toner charged to the same polarity as the charging polarity of the photosensitive drum 1 to a portion where the charge is attenuated by exposure on the uniformly charged photosensitive drum 1. Is done.

  In the present embodiment, a bias voltage in which an AC voltage and a DC voltage are superimposed is applied to the developing device 4 from a developing bias power supply 41 (FIG. 10) as a developing voltage output means during the developing process. More specifically, the developing bias is applied to a developing member (developer carrier) that transports toner to the photosensitive drum 1 provided in the developing device 4. Then, due to the potential difference between the image portion on the photosensitive drum 1 and the potential of the DC component of the developing voltage, the toner charged negatively in the developing device 4 is transferred from the developing device 4 to the electrostatic latent image on the photosensitive drum 1. To do.

  The toner image formed on the photosensitive drum 1 is transferred onto a transfer material (recording material) P by the action of the transfer roller 5. The transfer roller 5 is pressed against the surface of the photosensitive drum 1 to form a transfer nip N. The transfer material P is conveyed to the transfer nip N at a predetermined timing. Here, the leading edge of the transfer material P is detected by the top sensor 8 provided in the transfer path of the transfer material P so that the image forming position of the toner image on the photosensitive drum 1 matches the writing position of the leading edge of the transfer material P. Detected and timed. The transfer material P conveyed at a predetermined timing is nipped and conveyed by the photosensitive drum 1 and the transfer roller 5 with a constant pressure. The transfer roller 5 is connected to a transfer bias power source 51 (FIG. 10) as transfer voltage output means for applying a transfer voltage to the transfer roller 5. In the transfer process, a bias voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the transfer roller 5 from the transfer bias power source 51. As a result, the toner image is electrostatically transferred from the photosensitive drum 1 onto the transfer material P.

  The transfer material P onto which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and conveyed to a heat fixing device 6 as a fixing unit. In the heat fixing device 6, the toner image on the transfer material 1 is fixed on the transfer material P by the action of heat and pressure.

  On the other hand, untransferred toner remaining on the photosensitive drum 1 without being transferred onto the transfer material P during the transfer process is scraped off from the surface of the photosensitive drum 1 by a cleaning blade 7a as a cleaning member provided in the cleaning device 7. Removed. The toner removed by the cleaning blade 7a is collected in a collected toner container 7c provided in the cleaning device 7. Details of the operation of the cleaning blade 7a will be described later. After the cleaning process is completed, the charging process of the surface of the photosensitive drum 1 is started again.

  Further, a paper discharge sensor 9 is provided in the heat fixing device 6 so that when the transfer material P is clogged between the top sensor 8 and the paper discharge sensor 9, it can be detected. It has become.

(2) Cleaning Blade FIG. 2 shows the configuration of the cleaning blade used in this embodiment.

  The cleaning blade 7 a is a cleaning member that contacts the photosensitive drum 1 downstream of the transfer nip N in the moving direction of the photosensitive drum 1 to form a cleaning portion C, and removes toner from the photosensitive drum 1 in the cleaning portion C. is there.

  As shown in FIG. 2, in this embodiment, the cleaning blade 7a has a blade (plate) shape with a width W of about 10 mm and a length L of about 240 mm. Here, the length L is a dimension in the longitudinal direction (rotational axis direction) of the photosensitive drum 1, and the width W is a dimension in a direction orthogonal to the direction of the length L. The cleaning blade 7a has one end 7a1 held by a support member 7b, and an edge (hereinafter referred to as “contact edge”) 7a3 of the other end (hereinafter referred to as “free end”) 7a3 is photosensitive. The drum 1 is in contact with the surface of the photosensitive drum 1 along the longitudinal direction. The cleaning blade 7a is sensitive to the counter direction with respect to the moving direction of the surface of the photosensitive drum 1, that is, the free end 7a2 faces the upstream side of the moving direction of the surface of the photosensitive drum 1 with respect to the support portion by the support member 7b. It is disposed in pressure contact with the surface of the drum 1. A contact portion between the cleaning blade 7 a and the surface of the photosensitive drum 1 is a cleaning portion C.

  Examples of the material of the cleaning blade 7a include elastic bodies such as polyurethane rubber, neoprene rubber, chloroprene rubber, silicone rubber, or fluororubber, but polyurethane rubber excellent in cleaning property and durability is often used. In this embodiment, a cleaning blade 7a made of polyurethane rubber is used.

  When the photosensitive drum 1 rotates in a state where the contact edge 7a3 of the cleaning blade 7a is in contact with the surface of the photosensitive drum 1, the transfer residual toner on the surface of the photosensitive drum 1 or the surface of the photosensitive drum 1 such as paper dust. The foreign matter adhering to the surface is scraped off by the cleaning blade 7a. The transfer residual toner and foreign matter scraped off are accumulated in the collected toner container 7c by being naturally dropped.

  Further, in order to reduce the sliding resistance between the surface of the photosensitive drum 1 and the cleaning blade 7a, a lubricant (lubricating layer) 7d may be applied in the vicinity of the contact edge 7a3 (FIG. 3). As the lubricant 7d, a fluorine compound such as polyvinylidene fluoride (PVDF) or fluorinated graphite having a lower resistance can be used. Alternatively, the lubricant 7d can be obtained by applying and drying a solution in which a solid lubricant such as silicone-based fine particles or molybdenum disulfide is dispersed in a solvent such as ethyl alcohol.

  Even if such a lubricant 7d is applied, the frictional resistance in the longitudinal direction becomes non-uniform due to uneven application, or the lubricant 7d is partially peeled off together with the paper passing as shown in FIG. Thereby, lubricity is impaired, and the contact edge 7a3 may cause stick slip while vibrating as indicated by an arrow in FIG.

  That is, as shown in FIG. 3, a gap of several μm to several tens of μm is generated on the contact surface between the cleaning blade 7a and the photosensitive drum 1 at the moment when stick slip occurs. Through such a gap, a toner having a small particle diameter or a spherical toner excellent in lubricity slips through. This slipped toner T may adhere to the charging roller 2 and cause charging failure. Further, the slipped toner T may be transferred to the transfer material P during the next transfer process while adhering to the photosensitive drum 1, and may become noticeable as streak-like stains. These phenomena are collectively referred to as poor cleaning.

  In particular, when foreign matter such as paper dust accumulates between the cleaning blade 7a and the surface of the photosensitive drum 1, there is always a gap, which may lead to more advanced cleaning failure.

(3) Cleaning Method of the Present Example As a means for suppressing the above-described cleaning failure, a toner image pattern (toner supply image) formed on the photosensitive drum 1 is transferred onto the transfer material P as shown in FIG. So as not to be transferred to the cleaning blade 7a, it is periodically supplied in the vicinity of the contact edge 7a3 of the cleaning blade 7a. As will be described in detail later, the toner supply image is typically formed over substantially the entire area of the photosensitive drum 1 in the longitudinal direction. Then, the toner particles T of the toner supply image are caused to function as a lubricant.

  As a result, the slidability between the cleaning blade 7a and the surface of the photosensitive drum 1 is substantially the entire region in the longitudinal direction of the cleaning portion C (the direction along the longitudinal direction of the photosensitive drum 1) where the cleaning blade 7a and the photosensitive drum 1 are in contact. It becomes possible to make it uniform over the range. Accordingly, the adhesion between the cleaning blade 7a and the surface of the photosensitive drum 1 is improved, and defective cleaning can be suppressed. In particular, in a normal image forming operation, both end portions in the longitudinal direction of the photosensitive drum 1 have many blank portions and areas where no image exists, so that there is little residual toner and sliding resistance between the photosensitive drum 1 and the cleaning blade 7a. Tends to increase and cleaning defects are likely to occur. By supplying toner particles as a lubricant to the cleaning blade 7a over substantially the entire length in the longitudinal direction of the cleaning portion C as described above, it is possible to effectively suppress the occurrence of defective cleaning. Such a process of feeding toner particles as a lubricant to the vicinity of the blade is referred to as a “toner supply process”.

  Here, in the conventional method, as shown in FIG. 5, the toner supply process is performed at a timing when the transfer material P does not exist in the transfer nip N, that is, between the paper, during the pre-rotation, and the post-rotation. The sheet interval is a period between transfer materials in continuous image formation for a plurality of transfer materials. Further, the pre-rotation and the post-rotation are periods of a preparation operation involving the rotation of the photosensitive drum 1 before and after the image forming operation, respectively. That is, in the conventional method, in the toner supply process, the toner supply image is transferred to the photosensitive drum 1 while the transfer material P passes through the transfer portion N in the moving direction of the surface of the photosensitive drum 1. It was formed in a region other than the region above 1. However, in such a conventional method, toner contamination may accumulate on the transfer roller 5.

  That is, as shown in FIG. 5, conventionally, in order to reduce the contamination of the transfer roller 5, the transfer cleaning bias having the same polarity as the normal charging polarity of the toner at the timing when the toner supply image S passes through the transfer nip N. Is applied to the transfer roller 5. However, a small amount of toner charged to a polarity opposite to the normal charging polarity may remain attached to the transfer roller 5 or may be physically adsorbed on the surface of the transfer roller 5. As the toner supply process is performed by using the image forming apparatus, toner contamination may gradually accumulate on the transfer roller 5.

  Therefore, in this embodiment, the image forming apparatus 100 performs the toner supply process as follows.

  FIG. 6 is a schematic diagram in the vicinity of the transfer nip N in the toner supply process according to this embodiment. That is, in the toner supply process, an operation for forming a toner supply image S for supplying toner to the cleaning unit C on the photosensitive drum 1 is performed separately from the output image I to be fixed to the transfer material P. In the toner supply step, an operation of supplying the toner supply image S to the cleaning unit C through the transfer nip N is performed. In particular, in this embodiment, an area on the photosensitive drum 1 where the toner supply image S is formed passes through the transfer nip N while the transfer material P passes through the transfer nip N in the moving direction of the photosensitive drum 1. In addition, the position is set at a position where the output image I is not formed. The toner of the toner supply image S is supplied to the cleaning blade 7a and used as a lubricant.

  Specifically, as shown in FIG. 6, an area on the photosensitive drum 1 corresponding to a margin at the rear end in the conveyance direction of the transfer material P can be used as the area for forming the toner supply image S. Similarly, an area on the photosensitive drum 1 corresponding to a margin at the front end of the transfer material P in the conveyance direction can be used as the formation area of the toner supply image S.

  In other words, in a normal image forming operation, the output image I is placed on the photosensitive drum 1 so as to be located inside the transfer material P with respect to the moving direction of the transfer material P passing through the transfer nip N and the respective ends in the direction orthogonal thereto. Form. In this case, on the image transfer surface of the transfer material P, a predetermined region (blank space) where an image cannot be formed on the inner side from each of the front end, rear end, left end, and right end in the moving direction of the transfer material P. In other words, a so-called “bordered image” is formed. In general, margins are provided for the front end portion, the rear end portion, the left end portion, and the right end portion of the transfer material P in the moving direction, but at least one of the margins may not be provided.

  When such a margin is provided, it is preferable to form a toner supply image in a region on the photosensitive drum 1 corresponding to the margin at the front end in the conveyance direction of the transfer material P or the margin at the rear end in the same direction. As a result, as will be described in detail later, a continuous belt-like toner supply image can be easily formed over substantially the entire longitudinal direction of the photosensitive drum 1.

  Further, based on the image information received by the image forming apparatus 100, a portion where the output image I does not exist in the range of the transfer material P is specified, and a toner supply image is formed in an area on the photosensitive drum 1 of the portion. be able to. For example, if there is an area where there is no output image I in the direction perpendicular to the transfer direction of the transfer material P, the area is used to supply a continuous belt-like toner over substantially the entire longitudinal direction of the photosensitive drum 1. An image can be formed. This method is particularly effective when there is no margin at the front end in the conveyance direction of the transfer material P and / or no margin at the rear end in the same direction.

  Thus, preferably, in this embodiment, the toner supply image S is formed on the photosensitive drum 1 in an area where the transfer image nip N is in contact with the transfer P and where the output image I is not formed. .

  Next, bias control applied to the transfer roller 5 in this embodiment will be described.

  First, as shown in FIG. 6, when the output image I, which is a normal image pattern, is transferred onto the transfer material P, a predetermined polarity (positive polarity in this embodiment) opposite to the normal charging polarity of the toner is used. A transfer bias during printing is applied to the transfer roller 5. That is, at the time of the transfer process, an electric field is formed in the transfer nip N in a direction in which the toner charged with the normal charging polarity is directed from the photosensitive drum 1 side to the transfer roller 5 side (transfer material P side).

  On the other hand, at the timing when the toner supply image S passes through the transfer nip N, the transfer bias is turned off, or more preferably the same polarity as the normal charging polarity of the toner (in this embodiment, the negative polarity). ) Is applied to the transfer roller 5. That is, when the toner supply image S is passed through the transfer nip N, the toner charged in the normal charging polarity is transferred to the transfer nip N from the transfer roller 5 side (transfer material P side) toward the photosensitive drum 1 side. An electric field is formed. Thereby, the toner of the toner supply image S on the photosensitive drum 1 is prevented from being transferred onto the transfer material P as much as possible.

  As described above, in this embodiment, the transfer bias power supply 51 includes the first voltage output unit that outputs a voltage having the same polarity as the normal charging polarity of the toner to the transfer roller 5, and the normal charging polarity of the toner. Has a second voltage output unit that outputs a voltage of reverse polarity to the transfer roller 5.

  5 and 6 is a transfer bias when the toner is transferred from the photosensitive drum 1 onto the transfer material P, and has a polarity opposite to the normal charging polarity of the toner. 5 and 6 is the same polarity as the transfer bias during printing, but the absolute value is set smaller than the transfer bias during printing, and there is no transfer material P in the transfer nip N. Is a bias applied to. Application of the bias during standby is optional.

  Next, the size and pattern of the toner supply image in this embodiment will be described.

  The width in the longitudinal direction of the photosensitive drum 1 of the toner supply image S is preferably set within the range of the maximum sheet passing width of the image forming apparatus 100. The maximum sheet passing width is the maximum value of the width in the direction (longitudinal direction of the photosensitive drum 1) perpendicular to the transfer direction of the transfer material P that can be used in the image forming apparatus 100. However, the left and right margins of the transfer material P are formed as long as a toner supply image can be formed, and may not be formed, for example, when exposure with a laser scanner mask is impossible. In this case, the width in the longitudinal direction of the toner supply image is set in a range narrower than the maximum sheet passing width. That is, preferably, the toner of the toner supply image is supplied as a lubricant to substantially the entire longitudinal direction of the cleaning unit C, and the same or better effect as compared with the conventional one in terms of maintaining the lubricity between the cleaning blade 7 a and the photosensitive drum 1. If it can be achieved.

  Further, the width of the toner supply image in the transfer direction of the transfer material P and the image pattern may be appropriately adjusted according to the frequency of performing the toner supply process and the lubricity required by the cleaning blade 7a. Naturally, the width of the toner supply image in the conveyance direction of the transfer material P is a margin in which the toner supply image can be formed in the conveyance direction of the transfer material P passing through the transfer nip N when the toner supply process is executed. , Limited by the width of the portion determined from the image information.

  In this embodiment, it is sufficient to form a solid black image (image having a maximum density level) with a width of 2.0 mm in the conveyance direction of the transfer material P for every 50 prints and to perform the toner supply process. Confirmed.

  FIG. 10 shows a schematic control mode of the image forming apparatus 100 of the present embodiment. A controller 11 serving as a control unit included in the image forming apparatus 100 is input from an external device 200 such as a personal computer and processed by the image processing unit 13 according to an image information signal of each unit related to the image forming operation of the image forming apparatus 100. Control the overall operation. For example, the controller 11 controls the ON / OFF timing and output voltage value of the voltage output of the charging bias power supply 21, the developing bias power supply 41 and the transfer bias power supply 51, and the operation timing of the exposure device 3 and the fixing device 6. To control. In particular, in connection with this embodiment, the controller 11 controls the toner supply process. That is, the controller 11 executes the toner supply process at predetermined intervals, and in the toner supply process, in order to form the toner supply image at the predetermined position on the photosensitive drum 1, the charging bias power source 21 and the exposure device 3. The developing bias power supply 41 is controlled. Further, the controller 11 switches the output voltage of the transfer bias power source 51 at the predetermined timing so that the toner supply image S passes through the transfer nip N in the toner supply process. The controller 11 includes an arithmetic control circuit including a control unit, a calculation unit, and a storage unit, and executes the control as described above according to a program and data stored in the memory 12 that is a storage unit.

(4) Comparison with Conventional Example Next, an experiment was conducted to compare the effect of the present example with the conventional example. In accordance with the above conditions, a toner supply step for forming a toner supply image S having a width of 2 mm in the conveyance direction of the transfer material P for every 50 prints was performed according to the following methods (A) and (B).

  (A) In this embodiment, a toner supply image S is formed at a position on the photosensitive drum 1 corresponding to the trailing edge margin of the 50th transfer material P, and the toner supply process is performed.

  (B) As a conventional example, the toner supply process is performed during post-rotation after printing the 50th sheet.

About (A) and (B), a total of 10,000 prints were made as a durability test, and then the following items (i) to (iv) were compared.
(I) Toner stain on transfer roller 5 after passing paper (ii) Increase in electrical resistance of transfer roller 5 due to toner stain on transfer roller 5 (iii) Transferability to high resistance paper due to toner stain on transfer roller 5 ( iv) Back dirt when the envelope passes due to toner dirt on the transfer roller 5

  The increase in electrical resistance of the transfer roller 5 was evaluated by measuring the current that flows when a voltage is applied to the transfer roller 5. When the amount of increase in electrical resistance was small, it was determined that there was no increase in electrical resistance. When an increase in electrical resistance exceeding a predetermined value was observed, it was determined that there was an increase in electrical resistance.

  Note that the envelope was used to check the backside dirt because the pressure that the transfer material P receives at the transfer nip N increases with the thickness of the transfer material P, and this is applied to the back surface of the transfer material P when the transfer roller 5 is dirty. It is because it is easy to adhere and it can evaluate in severe conditions.

  In both cases (A) and (B), when the toner of the toner supply image S passes through the transfer nip N, a negative bias (transfer cleaning bias) of about −1000 V is applied to the transfer roller 5 to transfer the toner. The toner of the toner supply image S is prevented from being attracted to the roller 5 side.

  The results are shown in Table 1 below.

  As apparent from the results shown in Table 1, in the conventional example, an increase in electrical resistance of the transfer roller 5 due to toner contamination was observed, and transfer unevenness was also confirmed in the image.

  On the other hand, in this embodiment, the toner supply image S is formed in a region on the photosensitive drum 1 corresponding to the margin at the rear end in the conveyance direction of the transfer material P. As a result, it is understood that the transfer roller 5 is not soiled, and problems caused by the transfer roller 5 are suppressed.

  In this embodiment, since the transfer cleaning bias is applied to the transfer roller 5 while the toner supply image S passes through the transfer nip N, the margin at the rear end of the transfer material P in the conveyance direction is stained. There is nothing. Therefore, it is possible to effectively keep the slidability between the cleaning blade 7a and the photosensitive drum 1 effectively.

  As described above, according to the present exemplary embodiment, the image forming apparatus 100 performs the toner supply process in order to suppress the cleaning failure caused by the toner slipping through between the photosensitive drum 1 and the cleaning blade 7a. In the toner supply step, the toner supply image S formed along the longitudinal direction of the photosensitive drum 1 on the photosensitive drum 1 is periodically supplied to the cleaning blade 7a, and good cleaning between the cleaning blade 7a and the photosensitive drum 1 is achieved. Maintain sex. In this embodiment, the toner supply image S is passed through the transfer nip N while the transfer material P is present in the transfer nip N in the toner supply process, and the output image I is not formed on the photosensitive drum 1. Form in position. Thereby, it is possible to suppress a problem that the transfer roller 5 is soiled with toner. Further, since the toner contamination of the transfer roller 5 can be suppressed, an increase in the electrical resistance of the transfer roller 5 due to the toner contamination, and further, an image defect and a toner contamination on the back surface of the transfer material P due to the increase in the electrical resistance can be suppressed. Is possible.

  Further, by forming the toner supply image S in the margin at the front end in the conveyance direction of the transfer material P or the margin at the rear end in the same direction without the output image I, a normal print image is not disturbed. While the toner supply image S passes through the transfer nip N, the bias applied to the transfer roller 5 is turned off or a bias having the same polarity as the normal charging polarity of the toner is applied. Accordingly, since the toner can be prevented from being transferred to the transfer material P, the surface of the transfer material P is not soiled by the toner of the toner supply image S.

  As described above, according to the present embodiment, when the process of supplying the toner image to the cleaning blade 7a in order to maintain the lubricity between the cleaning blade 7a and the photosensitive drum 1, the toner of the transfer roller 5 is used. Dirt can be suppressed. Therefore, even if the usage amount of the image forming apparatus 100 increases, a good image can be output.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, the same or corresponding elements as those in the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the pattern of the toner supply image S formed on the photosensitive drum 1 during the toner supply process is different from that of the first embodiment as described below.

  When special paper such as smooth paper, glossy paper, thick paper, and high resistance paper is used as the transfer material P, it may be desirable to suppress the following phenomenon. That is, when a solid black image band is formed as the pattern of the toner supply image S in the toner supply step, the pattern of the toner supply image S is slightly transferred onto the transfer material P even when the transfer cleaning bias is applied. May appear as toner stains.

  Therefore, in this embodiment, the toner supply image S is an image in which the toner amount per unit area is smaller than the image of the maximum density level in the image forming apparatus 100. That is, in this embodiment, as the pattern of the toner supply image S, a halftone image formed by horizontal lines, vertical lines, or isolated dots as shown in FIG. 7 can be used. This makes it difficult to adhere to the transfer material P and makes it less noticeable as dirt. In particular, since the toner supply image S is formed by a set of a plurality of isolated dots, adhesion of the toner to the transfer material P is easily suppressed, and even if a small amount of toner is adhered, it is difficult to stand out. preferable. This is considered due to the following reasons.

  That is, when the toner image formed on the photosensitive drum 1 is viewed in a cross-section, the solid black image has a large amount of applied toner and a high height as shown in FIG. In particular, toner swell is often seen at the edge of the image pattern. Therefore, even when a bias having the same polarity as the normal charging polarity of the toner is applied to the transfer roller 5 when passing through the transfer nip N, the toner in that portion is physically transferred to the transfer material P when the amount of toner is large. May stick to the top. In addition, when using a transfer material P that is easily charged to a polarity opposite to that of the toner by rubbing with a conveyance member of the image forming apparatus 100 during conveyance, such as smooth paper, glossy paper, and high resistance paper, as the transfer material P. In particular, the toner in the portion where the toner amount is large is easily transferred.

  On the other hand, for example, in a halftone image such as an isolated dot, as shown in FIG. 8B, the amount of applied toner and its height are reduced. Therefore, the toner does not easily adhere to the transfer material P, and even if it adheres in a very small amount, it does not stand out as dirt, so there is no problem.

  Note that if the pattern of the toner supply image S is composed of a halftone image, the amount of toner supplied to the cleaning blade 7a may be reduced. However, in this case, the influence can be reduced as much as possible by increasing the width of the pattern in the conveyance direction of the transfer material P as much as possible, or by increasing the frequency of the toner supply process.

  In addition to using the image pattern of the toner supply image S as a halftone image, it is possible to adjust the amount of toner to be reduced by the following method. That is, by adjusting the bias applied in the charging process and the developing process and controlling the potential of the electrostatic latent image formed on the surface of the photosensitive drum 1, the density of the toner supply image S is adjusted to be thin. be able to. As a result, even if the toner supply image S is a solid black image pattern, the amount of applied toner can be adjusted to be small, and the same effect as when a halftone image is obtained by the image pattern can be obtained. Can do.

  More specifically, as shown in FIG. 9, it can be achieved by the following method. That is, the potential applied to the photosensitive drum 1 after exposure is lowered by shifting the voltage applied in the charging process toward the charging polarity (negative polarity in this embodiment) of the toner. Further, the potential difference (development) between the exposure potential (image portion potential) and the development potential is shifted by shifting the DC component (development potential) of the development bias to the polarity opposite to the toner charging polarity (positive polarity in this embodiment). Decrease the contrast. Alternatively, the development contrast can be reduced by reducing the amount of exposure light L by the exposure device 3 by adjusting the pulse signal or the like. That is, the toner image on the photosensitive drum 1 is obtained by transferring the charged toner from the developing member to the photosensitive drum 1 due to the potential difference between the image portion potential on the photosensitive drum 1 and the developing member that supplies toner to the photosensitive drum 1. It is formed by transferring to the image area. The potential difference when forming the toner supply image S can be made smaller than when forming the maximum density image.

  The image density can be lowered by simultaneously controlling the potential of the photosensitive drum 1 as described above while forming the pattern of the toner supply image S with the above-described halftone image such as an isolated dot. Thereby, the effect of suppressing the adhesion of the toner supply image S to the transfer material P and the conspicuousness of the adhered toner can be further enhanced.

  As described above, according to the present embodiment, the same effect as in the first embodiment can be achieved. Furthermore, in the present embodiment, the toner application amount S can be suppressed by setting the pattern of the toner supply image S to a halftone image, particularly a halftone formed of isolated dots. As a result, even when various media such as high resistance paper, thick paper, smooth paper, and glossy paper are used for the transfer material P, the toner of the toner supply image S is prevented from adhering to the surface of the transfer material P and appearing as dirt. can do. Further, when the toner supply image S is formed, the applied amount and height of the toner can also be reduced by controlling the bias applied to the charging unit and the developing unit and reducing the image density. If the use of a halftone image pattern such as an isolated dot and the control of the bias applied to the charging unit and the developing unit are used in combination, the adhesion to the surface of the transfer material P can be further reduced. Therefore, even if the amount of use of the image forming apparatus 100 increases, a cleaning failure does not occur and a good image can be output.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. 1 is a schematic perspective view of a cleaning blade in an embodiment of an image forming apparatus according to the present invention. It is a schematic diagram for demonstrating a stick slip phenomenon. FIG. 6 is a schematic diagram illustrating a state where toner of a toner supply image is supplied to a cleaning blade. It is explanatory drawing for demonstrating the toner supply process of a prior art example. It is explanatory drawing for demonstrating an example of the toner supply process according to this invention. FIG. 6 is a schematic diagram for explaining an example of a toner supply image pattern. FIG. 10 is a schematic diagram for explaining a difference in toner loading amount and height depending on a toner supply image pattern. FIG. 6 is an explanatory diagram for explaining an example of a density setting method for a toner supply image. 1 is a block diagram illustrating an outline of a control mode in an embodiment of an image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Exposure apparatus 4 Developing apparatus 5 Transfer roller 6 Heat-fixing apparatus 7 Cleaning apparatus 7a Cleaning blade I Output image P Transfer material S Toner supply image

Claims (6)

A movable image carrier carrying a toner image;
A transfer member that forms a transfer portion in contact with the image carrier, and that transfers a toner image from the image carrier onto a transfer material that passes through the transfer portion as the image carrier moves;
A power source for applying a voltage for the transfer to the transfer member;
A cleaning member that contacts the image carrier on the downstream side of the transfer unit in the moving direction of the image carrier to form a cleaning unit, and removes toner from the image carrier in the cleaning unit;
A fixing device for fixing the toner image transferred onto the transfer material to the transfer material;
Have
Apart from the output image to be fixed on the transfer material, a toner supply image for supplying toner to the cleaning unit is formed on the image carrier, and the toner supply image passes through the transfer unit. To supply to the cleaning unit,
The region on the image carrier that forms the toner supply image passes through the transfer unit while the transfer material passes through the transfer unit in the moving direction of the image carrier and outputs the toner. An image forming apparatus, wherein the image forming apparatus is set at a position where no image is formed.   The power supply may apply a voltage having a polarity opposite to the voltage for the transfer or no voltage to the transfer member while the toner supply image passes through the transfer portion. The image forming apparatus according to claim 1.   3. An area on the image carrier on which the toner supply image is formed is an area corresponding to a margin at a front end in a conveyance direction of the transfer material or a margin at a rear end in the same direction. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the toner supply image is an image in which a toner amount per unit area is smaller than an image having a maximum density level in the image forming apparatus. apparatus.   The image forming apparatus according to claim 4, wherein the toner supply image is formed by a set of a plurality of isolated dots.   The toner image on the image carrier is charged with the charged toner from the developer member by the potential difference between the potential of the image portion on the image carrier and the developing member that supplies toner to the image carrier. The image formation according to claim 4 or 5, wherein the image forming portion is formed by transferring to an image portion on a body, and the potential difference when forming the toner supply image is smaller than when forming a maximum density image. apparatus.

Images