JP2007133024A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of more effectively suppressing a developer or an external additive from being welded to a developer layer thickness regulating member. <P>SOLUTION: The image forming apparatus 100 has: an image carrier 1; a developing means 4 equipped with a developer carrier 41 and the developer layer thickness regulating member 43; a first voltage applying means 21 for applying voltage to the developer carrier 41; and a second voltage applying means 22 for applying voltage to the developer layer thickness regulating member 43. The first voltage applying means 21 and the second voltage applying means 22 respectively change the voltage applied to the developer carrier 41 and the developer layer thickness regulating member 43 in a reverse direction so as to provide a potential difference between the developer carrier 41 and the developer layer thickness regulating member 43 so that electric field in the reverse direction to that when an image is formed may be formed when an image is not formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using an electrophotographic system or an electrostatic recording apparatus.

  Conventionally, in an image forming apparatus using, for example, an electrophotographic system, the surface of an electrophotographic photosensitive member (photosensitive member) that is an image carrier is charged by a charging unit. Thereafter, the surface of the photoconductor is irradiated with light, whereby an electrostatic image (latent image) is formed on the surface of the photoconductor. This electrostatic image is developed as a toner image by the developer toner supplied from the developing device. This toner image is transferred from a photosensitive member to a transfer material (recording paper, OHP sheet, cloth, etc.) by a transfer unit, and then subjected to a fixing process by a fixing unit.

  Development methods for converting an electrostatic image into a toner image are roughly classified into a one-component development method and a two-component development method. In the one-component development method, a one-component developer substantially consisting only of resin toner particles (toner) is used as a developer. On the other hand, in the two-component development method, a two-component developer mainly including resin toner particles (toner) and magnetic carrier particles (carrier) is used. In both the one-component developer and the two-component developer, an external additive (auxiliary particle) may be added to the toner particles in order to stabilize the chargeability of the toner or adjust the fluidity.

  The one-component development method includes a magnetic one-component development method using a magnetic one-component developer containing a magnetic material and a non-magnetic one-component development method using a non-magnetic one-component developer containing no magnetic material.

  The developing method using a non-magnetic one-component developer does not require a magnetic material for the developer, and simplification and miniaturization of the apparatus are easy. The developing method using a non-magnetic one-component developer is easy to apply to a full-color image forming apparatus because of its good color.

  For example, as shown in FIG. 2, the developing device 4 using the non-magnetic one-component developing system has a developing roller 41 as a developer carrier. Further, the developing device 4 has a developing blade 43 as a non-magnetic one-component developer coated on the developing roller 41, that is, a developer layer thickness regulating member that frictionally charges while regulating the thickness of the toner. Further, the developing device 4 includes a supply roller 42 as a developer supply member that supplies toner to the developing roller 41. The developing device 4 combines a developing frame 45 (developing chamber) for supporting the developing means such as the developing roller 41, the supply roller 42, and the developing blade 43, and a toner container 46 as a developer storage unit. Configured.

  The toner sent from the toner container 46 is supplied to the developing roller 41 by the supply roller 42. The toner carried on the developing roller 41 is regulated in layer thickness by the developing blade 43 in contact with the developing roller 41 and charged to a predetermined polarity, for example, negative polarity by frictional charging.

  Then, a developing bias is applied to the developing roller 41 by a developing bias power source 21 as a developing voltage applying means, and a portion of the developing roller 41 and the photoconductor is close to or in contact with each other (developing region). A toner image is formed by supplying toner onto the body.

  The toner that has not been used for developing the electrostatic image on the photosensitive member on the developing roller 43 is peeled off from the developing roller 41 by the supply roller 42. The toner thus peeled off is accommodated in the developing device 4 and used again.

  However, by repeating the developing operation as described above many times, vertical streak-like defects may occur on the image. This is considered to be because toner or an external additive attached to the developing blade 43 gradually adheres to the developing blade 43 at the contact portion between the developing roller 41 and the developing blade 43. That is, it is considered that this is because the toner or external additive fused to the developing blade 43 hinders the formation of a uniform toner coating in the longitudinal direction of the developing roller 41. This external additive is added in addition to the toner particles in order to stabilize the chargeability of the toner and adjust the fluidity.

  In order to prevent the toner or the external additive from being fused to the developing blade 43, there is the following method. At the time of image formation, a bias having a higher absolute value in the same polarity direction than the developing bias applied to the developing roller 41 (hereinafter referred to as “blade bias”) is applied to the developing blade 43 by the blade bias power supply 22 as a regulating member voltage applying means. ") Is applied. That is, a potential difference that forms an electric field that moves a substance (toner or external additive) charged to the same polarity as the normal charging polarity of the toner in the direction away from the developing blade 43 between the developing roller 41 and the developing blade 43. Is provided. Thus, a substance (toner or external additive) charged with the same polarity as the normal charging polarity of the toner is prevented from adhering to the developing blade 43.

  As a method for applying the blade bias, there are typically the following two methods depending on the state of the toner and the configuration of the developing roller 41 and the developing blade 43.

(1) During image formation: The same potential as the developing bias, or a relatively small potential difference between the developing roller 41 and a high potential in the same polarity direction as the developing bias.
During non-image formation: A potential difference higher than that during image formation is provided between the developing blade 43 and the developing roller 41 as a high potential in the same polarity direction as the developing bias.

  That is, if a large potential difference is provided between the developing blade 43 and the developing roller 41 during image formation, toner tribo (charged charge amount per unit weight) unevenness and toner coat unevenness occur in the longitudinal direction of the developing roller 41. It becomes easy to do. Then, uneven density tends to occur on the image. However, if a large potential difference is not provided between the developing blade 43 and the developing roller 41 during image formation, toner or an external additive may adhere to the developing blade 43 due to a mirroring force or the like. Therefore, a larger potential difference is provided during non-image formation than during image formation.

(2) During image formation: A relatively large electric difference is provided between the developing roller 41 and a high potential in the same polarity direction as the developing bias.
During non-image formation: an electric field that moves a substance having a polarity opposite to the normal charging polarity of the toner in a direction away from the developing blade 43 between the developing roller 41 and the developing blade 43 as a potential in a direction opposite to the developing bias. Form.

  In this method, a substance charged to a polarity opposite to the normal charging polarity of the toner is easily attached to the developing blade 43 during image formation. As a result, the material may be fused to the developing blade 43. In order to prevent such adhesion of substances, a potential difference is provided between the developing blade 43 and the developing roller 41 so that an electric field in the opposite direction to that during image formation is generated during non-image formation. Examples of the material charged to a polarity opposite to the normal charging polarity of the toner include a toner (reversal toner) charged to a polarity opposite to the normal charging polarity and an external additive.

As a method of providing a potential difference between the developing roller 41 and the developing blade 43 during non-image formation, for example, there are methods disclosed in Patent Document 1 and Patent Document 2.
JP 2002-365858 A Japanese Patent Laid-Open No. 2004-054172

  However, in recent years, image forming apparatuses are required to have high speed and long life. For example, in order to extend the life of the developing device, it may be desired to reduce the number of rotations other than the rotation time during the developing operation of the developing roller. Therefore, it is preferable to shorten the operation during non-image formation as much as possible. As a result, there is a case where the time for providing the potential difference between the developing roller and the developing blade becomes insufficient during non-image formation as described above, and the effect cannot be obtained.

  In order to reduce the cost, it may be desired that the bias power supply itself for the developing bias and the blade bias be made inexpensive. However, an inexpensive bias power supply has drawbacks such as a shortage of high-voltage output and a rise time of the high-voltage output. As a result, it becomes difficult to provide an effective potential difference within the non-image forming time, and the toner or the external additive is easily fused to the developing blade.

  An object of the present invention is to provide an image forming apparatus that can more effectively suppress the fusion of a developer and an external additive to a developer layer thickness regulating member.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier on which an electrostatic image is formed on the surface, and a developer attached to the surface of the image carrier in accordance with the electrostatic image formed on the surface of the image carrier. Development means for forming a developer image, the developer carrying body for conveying the developer to the image carrying body, the developer on the developer carrying body being regulated, and the developer carrying body A developer layer thickness regulating member for triboelectrically charging the developer to a predetermined polarity, and a first voltage applying unit for applying a voltage to the developer carrier. And a second voltage applying means for applying a voltage to the developer layer thickness regulating member, wherein the first voltage applying means and the second voltage applying means are respectively configured to carry the developer. The voltage applied to the body and the developer layer thickness regulating member is changed in the reverse direction, and during non-image formation The time imaging is an image forming apparatus, characterized in that a potential difference between said developer carrying member a developer layer thickness regulating member so as to form an electric field in the opposite direction.

  According to the present invention, it is possible to more effectively suppress the fusion of the developer and the external additive to the developer layer thickness regulating member.

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

Example 1
[Image forming apparatus]
First, an overall configuration and operation of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIG. The image forming apparatus 100 according to the present embodiment forms a full color image on a transfer material (recording paper, OHP sheet, cloth, etc.) S using an electrophotographic method in accordance with an image information signal, and can output the full color laser beam. It is a printer. The image information is sent from a personal computer, a document reading device, or the like that is communicably connected to the image forming apparatus main body (apparatus main body) 10.

  The image forming apparatus 100 according to the present exemplary embodiment is an inline type image forming apparatus that is preferable from the viewpoints of speeding up, color image clarity, and the like. In an inline image forming apparatus, a plurality of image forming units are arranged in series. In this embodiment, the image forming apparatus 100 includes first, second, third, and fourth image forming units (image forming units) PY, PM, PC, and PK as image forming units. The first to fourth image forming units PY, PM, PC, and PK respectively form yellow (Y), magenta (M), cyan (C), and black (K) images. In this embodiment, each of the image forming units PY, PM, PC, and PK adopts a non-magnetic one-component contact developing method using a negatively charged non-magnetic one-component developer as a developing method.

  The image forming units PY, PM, PC, and PK have substantially the same configuration except that the color of the image to be formed is different. Therefore, in the following, when there is no particular need to distinguish, the subscripts Y, M, C, and K given to the reference numerals to indicate that they are elements provided for any color are omitted and are generally described. To do.

  The image forming unit P includes a cylindrical photosensitive member (photosensitive drum) 1 as an image carrier. 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 (image writing means), a developing device 4, a transfer roller 5, and a cleaning device 6 as a cleaning means. Has been placed. The cleaning device 6 as a cleaning unit includes a cleaning blade 61 as a cleaning member, and a storage unit 62 that stores waste toner collected from the photosensitive drum 1 by the cleaning blade.

  In addition, a belt that moves endlessly as a transfer material carrier, that is, a conveyance belt 7 is disposed facing the photosensitive drum 1 of each image forming portion P. The transfer roller 5 is disposed opposite to the photosensitive drum 1 via the conveyance belt 7, and the conveyance belt 7 contacts the photosensitive drum 1 at the position of each transfer roller 5 to form a transfer portion (transfer nip) N. Yes.

  Further, a transfer material supply unit 8 and a fixing device 9 as fixing means are arranged in the apparatus main body 10.

  In this embodiment, the photosensitive drum 1, the charging roller 2, the developing device 4 and the cleaning device 6 are integrated as a process cartridge 50 and can be attached to and detached from the apparatus main body 10. The process cartridge 50 is detachably mounted on the apparatus main body 10 via mounting means 12 such as a mounting guide and a positioning member provided in the apparatus main body 10.

  More specifically, in this embodiment, the process cartridge 50 includes a developing unit 51 including the developing device 4 and a drum unit 52 including the photosensitive drum 1, the charging roller 2, and the cleaning device 6. The developing unit 51 and the drum unit 52 are integrated to form a process cartridge 50.

  The process cartridge 50 can be easily detached from the apparatus main body 10. The process cartridge 50 can be replaced with the developing unit 51 and the drum unit 52 as consumables when the toner is exhausted or when the photosensitive drum 1 is consumed. Thereby, the convenience of the user in the maintenance of the image forming apparatus is improved.

  In the present embodiment, the first, second, third, and fourth process cartridges 50Y, 50M, 50C, and 50K are arranged in the horizontal direction along the conveyance direction of the transfer material S by the conveyance belt 7 in the apparatus main body 10. Are arranged in a direction intersecting with (substantially vertical in this embodiment).

  At the time of image formation, the photosensitive drum 1 is rotationally driven in a direction indicated by an arrow R1 in the drawing by a driving unit (not shown). The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity / potential (in this embodiment, −650 V, which is negative polarity) by the charging roller 2. At this time, a charging bias output from a charging bias power source (not shown) as a charging voltage applying unit is applied to the charging roller 2.

  The surface of the charged photosensitive drum 1 is irradiated with light L in accordance with the separation color image pattern corresponding to each image forming portion P from the exposure device 3. As a result, an electrostatic image (latent image) is formed on the photosensitive drum 1. The latent image formed on the photosensitive drum 1 is visualized as a toner image by the developing device 4.

  The toner image formed on the photosensitive drum 1 is transferred to the transfer material S carried on the conveyance belt 7 by the action of the transfer roller 5 in the transfer portion N. The conveyor belt 7 moves in the direction of the arrow R4 in the drawing at substantially the same speed as the photosensitive drum 1. At this time, the transfer roller 5 rotating in the direction of the arrow in the figure has a normal charging polarity (negative polarity in this embodiment) of the toner output from a transfer bias power source (not shown) as transfer voltage application means. A reverse polarity bias is applied.

  The transfer material S is fed from the transfer material supply unit 8 at a predetermined timing and is carried on the transport belt 7. That is, in the transfer material supply unit 8, the transfer material S stored in the transfer material cassette 81 is sent out by the feed roller 82. Next, the transfer material S is conveyed by the registration roller 83 in synchronization with the formation of the toner image on the photosensitive drum 1 and is carried on the conveying belt 7.

  Untransferred toner remaining on the photosensitive drum 1 without being transferred during the transfer process of the toner image onto the transfer material S is scraped off by the cleaning blade 61 and collected in the storage unit 62. As a result, the photosensitive drum 1 is cleaned and again subjected to the image forming operation.

  For example, when a full-color image is formed, the above-described operation is performed in the first, second, third, and fourth image forming units PY, PM, PC, and PK, and the transfer material carried on the conveyance belt 7 is performed. On S, a multiple toner image is formed by superimposing four color toner images.

  Thereafter, the transfer material S is separated from the conveyance belt 7 and conveyed to the fixing device 9. After the unfixed image on the transfer material S is fixed by the fixing device 9, the transfer material S is carried out to the discharge tray 11 at the upper part of the apparatus body 10. Thus, image formation is completed.

  Note that by forming an image using only an image forming unit for a desired color, it is possible to form a single color or a multicolor image by combining any one of a plurality of colors.

[Developer]
Next, the configuration of the developing device (developing unit) 4 in this embodiment will be further described with reference to FIG.

  The developing device 4 has a developing roller 41 as a developer carrier. The developing device 4 includes a developing blade 43 as a developer layer thickness regulating member for friction charging while regulating the thickness of the toner coated on the developing roller 41. Further, the developing device 4 has a supply roller 42 as a developer supply member for supplying toner to the developing roller 41. The developing device 4 combines a developing frame (developing chamber) 45 for supporting the developing means such as the developing roller 41, the supply roller 42, and the developing blade 43, and a toner container 46 as a developer storage unit. Configured.

  The toner sent from the toner container 46 is supplied to the developing roller 41 by the supply roller 42. The toner carried on the developing roller 41 is regulated in layer thickness by the developing blade 43 in contact with the developing roller 41 and charged negatively in this embodiment by frictional charging.

  The developing roller 41 is applied with a developing bias output from a developing bias power source 21 as a developing voltage applying unit (first voltage applying unit). Thus, toner is supplied onto the photosensitive drum 1 in accordance with the electrostatic image at a portion (development area) where the developing roller 41 and the photosensitive drum 1 are in contact with each other, and a toner image is formed on the photosensitive drum 1. .

  After the developing operation for attaching the toner from the developing roller 43 to the electrostatic image on the photosensitive drum 1 is completed, the toner that has not been used for the development is peeled off from the developing roller 41 by the supply roller 42. The toner thus peeled off is accommodated in the developing device 4 and used again as a developer.

  More specifically, in this embodiment, a non-magnetic one-component contact development method is adopted as a development method. The toner container 46 of the developing device 4 is filled with 150 g of a non-magnetic one-component developer whose normal charging polarity is negative, that is, toner.

  The developing roller 41 as a developer carrying member is positioned in an opening 45 a extending in the longitudinal direction of the developing chamber 45 and is rotatably disposed. The developing roller 41 has an opening 45 a that has a half circumferential surface facing the inside of the developing chamber 45 and the other half circumferential surface exposed outside the developing chamber 45. A part of the developing roller 41 exposed outside the developing chamber 45 is in contact with the photosensitive drum 1. In this embodiment, the developing roller 41 contacts the rigid photosensitive drum 1 and supplies toner to the photosensitive drum 1. Therefore, as the developing roller 41, a roller having an elastic body can be suitably used. As the elastic body, a solid rubber single layer or a solid rubber layer coated with a resin coating in consideration of the charge imparting property to the toner can be used. For example, a cylindrical body made of metal such as aluminum, aluminum alloy, or stainless steel can be used as the core metal. Further, as the base layer of the elastic layer, one made of a rubber material such as NBR, EPDM, silicone rubber, urethane rubber or the like can be used. Further, a surface layer made of ether urethane or nylon can be used.

  In this embodiment, the developing roller 41 has a surface movement speed (170 mm / sec) in the direction of arrow R2 in the drawing (the direction of movement in the forward direction with the surface movement direction R1 of the photosensitive drum 1 at the contact portion with the photosensitive drum 1). Rotate at peripheral speed). In this embodiment, the surface of the developing roller 41 has appropriate irregularities in order to carry the toner well. More specifically, in the present embodiment, the developing roller 41 is a SUS (stainless steel) core metal having a diameter of 6 mm, a thickness of 3 mm, and a surface roughness Rz (ten-point average roughness: JIS B 0601). 8 μm NBR (nitrile-butadiene rubber) rubber is provided. In addition, the surface roughness tester “SE-30H” manufactured by Kosaka Laboratory was used for the measurement of the surface roughness.

  A supply roller 42 as a developer supply member rotates in the direction of arrow R3 in the drawing (a direction moving in the direction opposite to the surface movement direction R2 of the developing roller 41 at the contact portion with the developing roller 41). As the supply roller 42, a sponge roller having a diameter of 14 mm in which urethane foam is provided around a cylindrical body of a metal such as aluminum, an aluminum alloy, or stainless steel can be used.

  Toner is supplied from the toner container 46 to the developing chamber 45 by a stirring blade 45 as a developer stirring and conveying member. Then, when the developing roller 41 and the supply roller 42 come into contact with each other and rotate, the toner adheres to the developing roller 41 from the supply roller 42, and the toner is supplied onto the developing roller 41.

  A developing blade 43 as a developer layer thickness regulating member is fixed to the developing chamber 45 by a support plate 44. In this embodiment, as the developing blade 43, a straight-shaped phosphor bronze plate having a spring elasticity and having a thickness of 100 μm, which is a plate-like elastic member, was used. The developing blade 43 is arranged with the free end facing the upstream side in the surface movement direction of the developing roller 41. In the present embodiment, the contact surface of the developing blade 43 with the developing roller 41 was coated with 30 μm of polyamide elastomer (PAE). However, the present invention is not limited to this, and a stainless steel plate may be used instead of the phosphor bronze plate. The PAE coat thickness may be about 10 to 500 μm. Further, the shape of the tip of the plate constituting the developing blade 43 may be L-shaped. Further, nylon or a rubber material may be bonded or coated on the contact surface of the developing blade 43 with the developing roller 41. In this embodiment, the support plate 44 is a sheet metal having a plate thickness of about 1 to 2 mm and a width of a surface that contacts the developing blade 43 of 7 mm. Stainless steel is used as the support plate 44 because there is a risk of developing problems if rust or the like is generated on the support plate 44. The support plate 44 may be plated with nickel or the like.

  The toner supplied onto the developing roller 41 by the supply roller 42 passes through a contact portion between the developing roller 41 and the developing blade 43 as the developing roller 41 rotates. At this time, the toner on the developing roller 41 is regulated to an optimum layer thickness, and in this embodiment, it is triboelectrically charged to a negative polarity.

  The developing blade 43 is applied with a predetermined blade bias output from a blade bias power source 22 as a regulating member voltage applying means (second voltage applying means) at a predetermined timing. The blade bias will be described in detail later.

  In this embodiment, at the time of image formation, a developing bias of −400 V output from the developing bias power source 21 that is a developing bias applying unit is applied to the developing roller 41. Then, the photosensitive drum 1 comes into contact with the developing roller 41. At this time, the surface of the photosensitive drum 1 is charged to −650 V by the charging roller 2, and the electrostatic charge is attenuated by the exposure device 3 to form an electrostatic image. Accordingly, toner is supplied from the developing roller 41 onto the photosensitive drum 1 according to the electrostatic image, and a toner image is formed on the photosensitive drum 1. The developing bias will be described in detail later.

  The developing bias power supply 21 and the blade bias power supply 22 in this embodiment had a rise time per 100 V (time taken to increase the absolute value of the potential) of about 40 ms. Further, the developing bias power source 21 and the blade bias power source 22 in this embodiment had a fall time per 100 V (a time required for lowering the absolute value of the potential) of about 60 ms.

[Development bias and blade bias]
Next, the operation of the developing bias power source 21 and the blade bias power source 22 in this embodiment will be further described.

  One of the objects of the present invention is to extend the life of the developing means and reduce the cost of the voltage applying means, and to fuse substances such as developer and external additives to the developer layer thickness regulating member. It is to suppress wearing. Another object of the present invention is to achieve the above-mentioned object, in particular, both the developer charged in the same polarity as the regular charged polarity of the developer and the material charged in the opposite polarity to the developer layer thickness. It is possible to peel off from the regulating member.

  In this embodiment, the image forming apparatus 100 includes a developing bias power source (first voltage applying unit) 21 that applies a voltage to the developing roller 41 and a blade bias power source (second voltage applying) that applies a voltage to the developing blade 43. Means) 22. Then, the output values of the developing bias power supply 21 and the blade bias power supply 22 are changed between image formation and non-image formation. In this case, the output values of the developing bias power source 21 and the blade bias power source 22 are changed in the reverse direction with reference to the values before the change.

  Here, the time of image formation is a timing corresponding to an image forming area formed on the transfer material S excluding a blank portion. The non-image forming means a blank area on the transfer material S, a rotation before preparation before image formation, a rotation after preparation after completion of image formation, a transfer material at the time of continuous image formation on a plurality of transfer materials S It is a timing other than the time of image formation, such as a time between intervals (hereinafter referred to as “sheet interval”). In the present embodiment, a case will be described in which the bias applied to the developing roller 41 and the developing blade 43 is changed between sheets during continuous image formation on a plurality of transfer materials S. In this embodiment, the time between sheets during the continuous printing operation is about 400 ms.

  In the following description, the potential difference provided between the developing roller 41 and the developing blade 43 so that the blade bias potential is negative with respect to the development bias potential is referred to as negative (minus) potential difference. . That is, in this embodiment, the blade bias potential is higher on the normal charging polarity side of the toner than the development bias potential. A potential difference provided between the developing roller 41 and the developing blade 43 so that the blade bias potential is on the positive side with respect to the developing bias potential is referred to as a positive (plus) potential difference. That is, in this case, in this embodiment, the potential of the developing bias is higher than the potential of the blade bias on the normal charging polarity side of the toner. In addition, regarding the development bias and the blade bias, the potential before the change is a stable value (target value) before the bias value changing operation is started. For the development bias and the blade bias, the potential after the change is a stable value (target value) after the operation of changing the bias value is completed.

  In this embodiment, the operations of the developing bias power source 21 and the blade bias power source 22 are controlled by a controller 13 provided in the apparatus main body 10. The controller 13 may also serve as a control unit (CPU) provided in an engine control unit that comprehensively controls the operation of the image forming apparatus 100. The controller 13 has a built-in storage means or is electrically connected. The controller 13 outputs the outputs of the developing bias power source 21 and the blade bias power source 22 to a predetermined polarity / potential at a predetermined timing according to an image forming operation program (including a developing bias and blade bias control program) stored in the storage unit. To control. As described above, in this embodiment, the controller 13 controls the bias output start / stop by the developing bias power source 21 and the blade bias power source 22 and also has a function of a control unit that controls the bias output value.

  FIG. 3 shows an example of the operation of the developing bias power supply 21 and the blade bias power supply 22. In the example shown in FIG. 3, during non-image formation, the potential of the developing blade 43 is set larger than the potential of the developing roller 41 to the same polarity as the normal charging polarity of the toner. In this case, during non-image formation, an electric field in a direction in which a substance having the same polarity (first polarity) as the normal charging polarity of the toner is moved from the developing blade 43 to the developing roller 41 side is generated by the developing blade 43 and the developing roller 41. Formed between.

  Here, depending on the characteristics of the developing roller 41 and the developing blade 43, the developing blade 43 may be configured to be in edge contact with the developing roller 41. In an extreme example, the tip of the developing blade 43 may have a metal surface due to peeling or scratching of the PAE during the manufacturing stage or the process cartridge 50 assembly stage. In this state, if a large potential difference is provided between the developing roller 41 and the developing blade 43 during image formation, electric field unevenness may occur between the developing roller 41 and the developing blade 43 in the longitudinal direction. As a result, toner tribo unevenness, toner coat unevenness and the like on the developing roller 41 may occur, and density unevenness may occur on the image. Therefore, it is not desirable to provide a large potential difference between the developing roller 41 and the developing blade 43 during image formation.

  Therefore, in order to more effectively prevent toner and external additives from adhering to and accumulating on the developing blade 43, it is effective to provide a larger potential difference between the developing roller 41 and the developing blade 43 during non-image formation. .

  According to the study by the present inventors, in order to effectively prevent the fusion of the toner or the external additive, the absolute value of the potential difference provided between the developing roller 41 and the developing blade 43 during non-image formation is It is preferable that it is 100V or more. In consideration of leakage or discharge from the developing blade 43 to the developing roller 41, the absolute value of this potential difference is preferably 400 V or less. In this embodiment, the surface potential (dark portion potential: non-image portion potential) of the photosensitive drum 1 is −650V. Therefore, it is preferable that the range of the developing bias is −300 V to −600 V so that fogging and the back contamination of the transfer material S due to the fogging do not occur.

  In the example shown in FIG. 3, the output values of the developing bias power source 21 and the blade bias power source 22 are both set to the same potential of −400 V during image formation. Then, after the image formation is completed, the output value of the developing bias power supply 21 is changed from -400 V to -200 V, and at the same time, the output value of the blade bias power supply 22 is changed from -400 V to -600 V. As a result, a potential difference of −400 V is set between the developing roller 41 and the developing blade 43 between the sheets. In this case, the negative toner adhered to the developing blade 43 during image formation can be peeled off. In the example shown in FIG. 3, no potential difference is provided between the developing blade 43 and the developing roller 41 during image formation.

  Thereafter, the output value of the developing bias power source 21 is changed from −200 V to −400 V, and the output value of the blade bias power source 22 is changed from −600 V to −400 V, and image formation is performed again. Thereafter, this operation is repeated.

  Here, as Comparative Example 1, only the output value of the blade bias power source 22 was changed using the developing device 4 having the same basic configuration as that of this embodiment. The blade bias was set so that the potential difference between the developing roller 41 and the developing blade 43 was −400 V between the sheets. The operations of the developing bias power source 21 and the blade bias power source 22 at this time are shown in FIG.

  As described above, in the image forming apparatus 100 of the present embodiment, the development bias power supply 21 and the blade bias power supply 22 have a rise time per 100V of about 40 ms and a fall time per 100V of about 60 ms.

  In the comparative example 1 shown in FIG. 4, since the rise time and the fall time occur, there is almost no time for providing a potential difference of −400 V between the developing roller 41 and the developing blade 43 during non-image formation.

  On the other hand, in the example shown in FIG. 3, by operating the developing bias power source 21 and the blade bias power source 22, about 160 ms can be secured as a time for providing a potential difference of −400 V during non-image formation.

  3 and Comparative Example 1 shown in FIG. 4 were subjected to a comparative durability test at a printing ratio (ratio of the total printing area to the total area of the printing surface) of 5%. As a result, in the image forming apparatus of Comparative Example 1, defects on vertical stripes were sometimes seen on the image from about 3000 sheets. In contrast, in the example shown in FIG. 3, the occurrence of vertical stripes on the image is improved up to 5000 printable sheets of the process cartridge 50.

  As described above, when the developing bias power source 21 and the blade bias power source 22 change the voltages in the opposite directions, the predetermined voltage is applied between the developing roller 41 and the developing blade 41 than when the voltage is changed on either side. Can be provided in a short time. As a result, a sufficient potential difference can be provided even in a short time, and as a result, toner or the like can be prevented from being fused to the developing blade 43 even in a short non-image forming time. Further, by changing the outputs of both the developing bias power source 21 and the blade bias power source 22, an inexpensive power source can be adopted, and the cost of the image forming apparatus can be reduced.

  Incidentally, as shown in FIG. 3, even if a negative potential difference is provided during non-image formation, the toner or the external additive may be fused to the developing blade 43. It has been found that such a phenomenon becomes prominent when an external additive that is charged to the toner with a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is added to the toner. That is, it is considered that the positive external additive is fused to the developing blade 43 in order to apply a negative potential difference during non-image formation. In this case, toner (reversed toner) charged to a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) may be fused to the developing blade 43.

  Accordingly, in this embodiment, in order to prevent the material charged to the same polarity as the normal charging polarity of the toner and the material charged to the opposite polarity to the normal charging polarity of the toner from being fused to the developing blade 43. The following operations are performed.

  At the time of image formation, the potential of the developing blade 43 is set to the plus side with respect to the developing roller 41. That is, a positive potential difference is provided between the developing roller 41 and the developing blade 43 during image formation. Thereby, it is possible to prevent the positive external additive (or reversal toner) from adhering to the developing blade 43 during image formation.

  During non-image formation, the potential of the developing blade 43 is set to the negative side with respect to the developing roller 41. That is, a negative potential difference is provided between the developing roller 41 and the developing blade 43 during non-image formation. Thereby, the negative polarity toner can be peeled off from the developing blade 43 during non-image formation.

  That is, the image forming apparatus 100 of the present embodiment is configured as follows. First, as described above, the image forming apparatus 100 includes a developing bias power source (first voltage applying unit) 21 that applies a voltage to the developing roller 41 and a blade bias power source (second second) that applies a voltage to the developing blade 43. Voltage applying means) 22. Then, the output values of the developing bias power supply 21 and the blade bias power supply 22 are changed between image formation and non-image formation. In that case, the development bias power supply 21 and the blade bias power supply 22 change their output values in the opposite directions with reference to the values before the change. At this time, in particular, the direction of the electric field formed by the potential difference provided between the developing roller 41 and the developing blade 43 is reversed between the image formation and the non-image formation.

  Typically, during non-image formation, the potential of the developing blade 43 is increased to the same polarity as the normal charging polarity of the toner. As a result, during non-image formation, an electric field in the direction in which a substance having the same polarity (first polarity) as the normal charging polarity of the toner is moved from the developing blade 43 to the developing roller 41 is applied to the developing blade 43 and the developing roller 41. Form between.

  Typically, during image formation, the potential of the developing roller 41 is increased to the normal charging polarity side of the toner. Accordingly, an electric field in a direction in which a substance having a polarity opposite to the normal charging polarity of the toner (second polarity) is moved from the developing blade 43 toward the developing roller 41 during image formation (an electric field in a direction opposite to that in non-image formation). ) Between the developing blade 43 and the developing roller 41.

  It is to be noted that the opposite electric field is formed when the electric field in the direction in which the substance having the same polarity as the normal charging polarity of the toner is moved from the developing blade 43 toward the developing roller 41 is formed during non-image formation as in this embodiment. This is more preferable than the case where the toner is prevented from adhering to the transfer material (reverse fogging). Further, as in this embodiment, when an image is formed in such a direction that a substance having a polarity opposite to the normal charging polarity of the toner is moved from the developing blade 43 to the developing roller 41 side, an opposite electric field is formed. It is more preferable in terms of prevention of concentration reduction. However, the present invention is not limited to this, and the electric fields formed between the developing roller 41 and the developing blade 43 at the time of non-image formation and image formation can be reversed from the above cases.

  Also, the absolute value of the potential difference provided between the developing roller 41 and the developing blade 43 during non-image formation should be larger than the absolute value of the potential difference provided between the developing sleeve 41 and the developing blade 43 during image formation. Is preferred. Thus, it is possible to prevent toner tribo unevenness and toner coat unevenness in the longitudinal direction of the developing roller 41 by providing an excessive potential difference between the developing roller 41 and the developing blade 43 during image formation. it can.

  As described above, from the viewpoint of uneven toner tribo and uneven toner coat in the longitudinal direction of the developing roller 41, it is not desirable to increase the potential difference provided between the developing roller 41 and the developing blade 43 during image formation. For example, when the edge portion of the developing blade 43 comes into contact with the developing roller 41 and a metal surface may be formed at the edge portion, the toner tribo unevenness and the toner coat unevenness are caused. There is concern about the occurrence. The absolute value of the potential difference provided between the developing roller 41 and the developing blade 43 during image formation is preferably 100 V or less. The absolute value of the potential difference can be appropriately determined depending on a desired effect by providing the potential difference during image formation, but is greater than 0V, preferably 10V or more, more preferably 50V or more.

  Hereinafter, further details will be described with reference to FIG. FIG. 5 shows operations of the developing bias power source 21 and the blade bias power source 22 in this embodiment.

  In this embodiment, the developing bias power supply 21 applies a developing bias of −500 V to the developing roller 11 at the start of image formation. The blade bias power source 22 applies a blade bias of −400 V to the developing blade 43 at the same time as the developing bias power source 21 applies a bias to the developing roller 41. That is, a potential difference of +100 V is set between the developing roller 41 and the developing blade 43 during image formation. This prevents the positive external additive (or reversal toner) from adhering to the developing blade 43 during image formation.

  After the image formation is completed, the developing bias is changed from -500 V to -300 V, and at the same time, the blade bias is changed from -400 V to -600 V. Thus, a potential difference of −300 V is set between the developing roller 41 and the developing blade 43 between the sheets. As a result, the negative toner adhered to the developing blade 43 during image formation is peeled off.

  Thereafter, the output value of the developing bias power source 21 is changed from −300 V to −500 V, and the output value of the blade bias power source 22 is changed from −600 V to −400 V, and image formation is performed again. Thereafter, this operation is repeated.

  As described above, in this embodiment, a potential difference is provided between the developing roller 41 and the developing blade 43 during image formation. Then, during continuous image formation on a plurality of transfer materials S, the process shifts from one image formation to the previous non-image formation before the next image formation, and from the non-image formation to the next image formation. Sometimes the development bias and the blade bias are changed. At this time, the development bias power supply 21 and the blade bias power supply 22 change their output values in the opposite directions with reference to the values before the change. The direction of the electric field formed by the potential difference provided between the developing roller 41 and the developing blade 43 is reversed between the image formation and the non-image formation. In particular, in this embodiment, the absolute value of the potential difference formed between the developing roller 41 and the developing blade 43 is larger during non-image formation than during image formation.

  Here, as Comparative Example 2, only the output value of the blade bias power source 22 was changed between sheets by using the developing device 4 having the same basic configuration as that of the present example. The blade bias was set so that the potential difference between the developing roller 41 and the developing blade 43 was +100 V during image formation and −300 V between paper. The operations of the developing bias power source 21 and the blade bias power source 22 at this time are shown in FIG.

  In the comparative example 2 shown in FIG. 6, since the rise time and the fall time occur, there is almost no time for providing a potential difference of −300 V between the developing roller 41 and the developing blade 43 during non-image formation.

  On the other hand, as shown in FIG. 5, by operating the developing bias power source 21 and the blade bias power source 22 according to this embodiment, it is possible to secure about 160 ms as a time for providing a potential difference of −300 V during non-image formation.

  Further, using the image forming apparatus of this example and the image forming apparatus of Comparative Example 2, a comparative durability test was performed with a printing ratio (ratio of the total printing area to the total area of the printing surface) of 5%. As a result, in the image forming apparatus of Comparative Example 2, defects on the vertical stripes may be seen on the image from about 2000 sheets. On the other hand, in the image forming apparatus of this embodiment, no vertical streak occurred on the image up to 5000 printable sheets of the process cartridge.

  As described above, according to the present embodiment, when a predetermined potential difference is provided between the developing roller 41 and the developing blade 43 during non-image formation, the developing bias and the blade bias are reversed with respect to the values before the change. Change direction. As a result, a desired potential difference between the developing roller 41 and the developing blade 43 can be provided for a sufficient time during non-image formation, and the entire operation time for providing the potential difference can be kept short. Accordingly, it is possible to reduce the drive time (rotation time) other than the image forming operation of the developing roller 41 and the like, and contribute to extending the life of the developing device 4 and the process cartridge 50. Further, as the blade bias power source 22 and further the developing bias power source 21, an inexpensive power source having a relatively long rise time and fall time can be used. That is, even when such a power supply is used, an effective potential difference can be provided for a sufficient time within the time of non-image formation.

  In particular, according to this embodiment, a potential difference is provided between the developing roller 41 and the developing blade 43 during image formation and non-image formation. At this time, the direction of the electric field formed between the developing blade 43 and the developing roller 41 is reversed between image formation and non-image formation. Accordingly, the negative polarity toner can be peeled off from the developing blade 43 during non-image formation, and the positive external additive (or reversal toner) can be peeled off from the developing blade 43 during image formation. That is, both the material charged to the normal charging polarity of the toner and the material charged to the opposite polarity to the normal charging polarity of the toner are peeled off from the developing blade 43, and these are fused to the developing blade 43. Can be prevented.

  Therefore, according to the present embodiment, it is possible to suppress the occurrence of image defects such as streak-like image defects due to the fusion of the toner and the external additive to the developing blade 43. Further, according to the present embodiment, it is possible to contribute to extending the life of the process cartridge (developing device, image forming apparatus) and reducing the price of the image forming apparatus.

  In the present embodiment, a negatively charged toner having a normal charging polarity and a positive external additive are used. Therefore, at the time of image formation, the developing bias and the blade bias are set so as to provide a positive potential difference in order to prevent the positive external additive from adhering to the developing blade 43. Further, at the time of non-image formation, the developing bias and the blade bias were set so as to provide a negative potential difference in order to prevent negative toner from adhering to the developing blade 43. However, suitable settings for various biases vary depending on the type of toner, the characteristics or configuration of the developing roller 41 and the developing blade 43, and are not limited to those in the present embodiment.

  Further, as described above, the operation of changing the developing bias and the blade bias between the image forming time and the non-image forming time may be performed between the image forming time and the interval between the papers. It may be performed each time image formation is performed on the number of transfer materials S. In this embodiment, the operation of providing a predetermined potential difference between the developing roller 41 and the developing blade 43 is performed at the timing between sheets as in non-image formation. However, the present invention is not limited to this. For example, the developing roller 41 and the developing blade 43 may be used during image formation and rotation before preparation as non-image formation and / or rotation after preparation after image formation. A predetermined potential difference similar to the above may be provided between the two. That is, when shifting from the non-image formation (pre-rotation) to the first image formation, the output values of the developing bias power supply 21 and the blade bias power supply 22 can be changed in opposite directions. Further, when shifting from the last image forming time to the non-image forming time (post-rotation), the output values of the developing bias power source 21 and the blade bias power source 22 can be changed in opposite directions.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned embodiment.

  For example, the image forming apparatus may not be a color image forming apparatus but may be a single color image forming apparatus having a single image forming unit corresponding to one image forming unit in the image forming apparatus of the above embodiment. In the above embodiment, a non-magnetic one-component developer is used as the developer. However, the present invention can be applied to an image forming apparatus using a magnetic one-component developer, and the same effects can be obtained. In the case of using a magnetic one-component developer, the developing device supplies the developer onto the developer carrier by magnetic force. The developer on the developer carrying member is regulated by the developer layer thickness regulating member, and triboelectric charge is applied.

  In the above embodiment, the photosensitive drum 1, the charging roller 2, the developing device 4, and the cleaning device 6 are integrated into a cartridge and are described as process cartridges that can be attached to and detached from the apparatus main body 10. However, the process cartridge is not limited to this, and the image carrier and at least the developing means as the process means acting on the image carrier are integrally formed into a cartridge that can be attached to and detached from the apparatus main body. If it is. In the process cartridge, at least one of a charging unit for charging the image carrier and a cleaning unit for cleaning the image carrier may be integrally formed into a cartridge. Further, the cartridge that can be attached to and detached from the apparatus main body is not limited to the process cartridge described above, and any cartridge that can be attached to and detached from the apparatus main body at least with the developing means formed into a cartridge.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus to which the present invention can be applied. FIG. 2 is a schematic configuration diagram of a developing device provided in the image forming apparatus of FIG. 1. It is a chart figure showing an example of operation of development bias and blade bias. 6 is a chart showing operations of a developing bias and a blade bias in Comparative Example 1. FIG. It is a chart figure showing an example of operation of development bias and blade bias according to the present invention. 10 is a chart showing operations of a developing bias and a blade bias in Comparative Example 2. FIG.

Explanation of symbols

1 Photosensitive drum (image carrier)
4 Developing device 21 Developing bias power source (first voltage applying means)
22 Blade bias power supply (second voltage applying means)
41 Developing roller 43 Developing blade

Claims (6)

An image carrier on which an electrostatic image is formed on the surface;
Development means for forming a developer image by attaching a developer to the surface of the image carrier in accordance with the electrostatic image formed on the surface of the image carrier, wherein the developer is the image carrier. A developer layer thickness regulating member for regulating the developer on the developer carrier and the developer on the developer carrier and frictionally charging the developer to a predetermined polarity between the developer carrier and the developer carrier Developing means comprising:
First voltage applying means for applying a voltage to the developer carrying member;
Second voltage applying means for applying a voltage to the developer layer thickness regulating member;
Have
The first voltage applying unit and the second voltage applying unit change the voltages applied to the developer carrying member and the developer layer thickness regulating member in opposite directions, respectively, so that an image is formed during non-image formation. An image forming apparatus, wherein a potential difference is provided between the developer carrier and the developer layer thickness regulating member so as to form an electric field in a direction opposite to that at the time of formation.   The absolute value of the potential difference provided between the developer carrying member and the developer layer thickness regulating member during non-image formation is provided between the developer carrying member and the developer layer thickness regulating member during image formation. The image forming apparatus according to claim 1, wherein the absolute value of the potential difference is larger.   At the time of non-image formation, an electric field is formed in such a direction that a substance charged with the same polarity as the normal charging polarity of the developer is moved from the developer layer thickness regulating member to the developer carrier. 3. The image according to claim 1, wherein an electric field is formed in a direction in which a substance charged to a polarity opposite to a normal charging polarity is moved from the developer layer thickness regulating member to the developer carrying member. Forming equipment.   The image forming apparatus according to claim 1, wherein at least the developing unit is formed into a cartridge and is detachable from a main body of the image forming apparatus.   The image forming apparatus according to claim 4, wherein the image carrier is integrally formed as a cartridge and is detachable from the main body of the image forming apparatus.   Further, at least one of charging means for charging the image carrier and cleaning means for cleaning the image carrier is integrally formed into a cartridge that can be attached to and detached from the main body of the image forming apparatus. The image forming apparatus according to claim 5, wherein the image forming apparatus is an image forming apparatus.

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