JP2006251221A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus which prevents a photoreceptor from being flawed by a carrier in a transfer section. <P>SOLUTION: During recovery of the carrier, a development device 38 makes the carrier electrostatically stick to a photoreceptor drum 28. The carrier rotates and moves together with the photoreceptor drum 28 and is held between the photoreceptor drum 28 and an intermediate transfer belt 24 in a primary transfer section 31. At this time, the intermediate transfer belt 24 is elastically deformed with respect to the carrier to reducer the pressing force via the carrier to the photoreceptor drum 28. The carrier past the primary transfer section 31 is removed from the photoreceptor drum 28 by a cleaner 32. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that performs development using a two-component developer in which two components of a toner and a carrier are mixed.

  In an image forming apparatus, there is a case where a carrier is attached to a photosensitive member and collected in order to eliminate the need for collecting the old two-component developer (for example, see Patent Document 1). In such an image forming apparatus, the carrier rotates together with the photosensitive member and is collected by the cleaning device.

In such a conventional image forming apparatus, the photoconductor may be damaged by the carrier at the transfer portion where the photoconductor and the transfer body abut.
JP 2002-31954 A

  In view of the above facts, an object of the present invention is to provide an image forming apparatus in which a photoconductor is not damaged by a carrier at a transfer portion.

  The image forming apparatus according to the first aspect of the present invention is formed on the photosensitive member using a two-component developer in which an electrostatic latent image is formed and a rotationally driven photosensitive member and a toner and a carrier are mixed. The electrostatic latent image is developed with the toner, the developing means for electrostatically attaching the carrier to the photoconductor when collecting the carrier, the cleaning means for removing the carrier attached to the photoconductor, and the photosensitive A transfer body that contacts the body and a transfer portion to transfer a toner image on the photosensitive body, and that is elastically deformable with respect to the carrier attached to the photosensitive body and reduces a pressing force to the photosensitive body; It is characterized by having.

  In the image forming apparatus according to the first aspect of the present invention, the developing unit causes the carrier to electrostatically adhere to the photosensitive member when the carrier is recovered. The carrier rotates together with the photoconductor, and is sandwiched between the photoconductor and the transfer body at the transfer portion. At this time, the transfer body is elastically deformed with respect to the carrier, and the pressing force to the photoconductor through the carrier is lowered. The carrier that has passed through the transfer portion is removed from the photoreceptor by the cleaning means.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the transfer member is driven by a rotational drive of the photosensitive member.

  In the image forming apparatus according to the second aspect of the present invention, the transfer member is driven by the rotation of the photosensitive member, and the photosensitive member, the carrier, and the transfer member move at the same speed.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the transfer member is an endless transfer belt, and tension is applied by a support member on an inner peripheral side, and the endless transfer member is provided. In the transfer belt, the belt base is made of vulcanized rubber or thermoplastic elastomer, and the tension F applied in a state of being supported from the inner peripheral side is 19.6 N / m ≦ F ≦ 98.0 N / m. Features.

  According to the image forming apparatus of the present invention described in claim 3, the endless transfer belt as a transfer body has a belt base material made of vulcanized rubber or thermoplastic elastomer, and 19.6 N / m ≦ F ≦ 98.0 N. The photoconductor is pressed at the transfer portion by being wound with a tension F of / m and rotating.

  The image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the third aspect, wherein the endless transfer belt has a hardness Hs of 40 ≦ Hs ≦ 90 (former JIS A-K6301). And

  According to the image forming apparatus of the present invention described in claim 4, the endless transfer belt has a hardness Hs of 40 ≦ Hs ≦ 90 (former JIS A-K6301), and the transfer portion is in contact with the carrier. Fully elastically deformed.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect, the surface of the photoconductor has a Vickers hardness C of 50 Hv ≦ C ≦ 200 Hv. .

  According to the image forming apparatus of the present invention, the Vickers hardness C on the surface of the photoconductor is 50 Hv ≦ C ≦ 200 Hv, and the photoconductor is not damaged by a slight load by the carrier.

  As described above, according to the image forming apparatus of the present invention, there is an excellent effect that the photosensitive member is not damaged by the carrier at the transfer portion.

  An embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus 10 is a so-called tandem type image forming apparatus.

  A paper tray 12 is disposed below the image forming apparatus 10. A conveyance path 14 is formed on the sheet discharge side of the sheet tray 12, and serves as a sheet path that reaches the discharge port 20 through the secondary transfer unit 16 and the fixing unit 18. A discharge tray 22 is provided outside the discharge port 20.

  An intermediate transfer belt 24 as a transfer member is stretched over a substantially central portion of the image forming apparatus 10, and four image forming portions 26 corresponding to different development colors are provided above the intermediate transfer belt 24. Has been placed.

  As shown in FIG. 2, the image forming unit 26 includes a photosensitive drum 28. The outer periphery of the photosensitive drum 28 is cylindrical, and an electrostatic latent image can be formed on the surface 28A of the outer periphery. The surface 28A of the photosensitive drum 28 preferably has a Vickers hardness C of 50Hv ≦ C ≦ 200Hv. By setting 50Hv ≦ C, the surface 28A of the photosensitive drum 28 is not easily damaged by a slight load (due to a carrier or the like described later). By setting C ≦ 200Hv, special processing on the surface 28A becomes unnecessary. . The photosensitive drum 28 is rotatable about the rotation support shaft 29 and is driven to rotate counterclockwise (arrow R direction) in FIG.

  Around the photosensitive drum 28, the primary transfer roller 30, the cleaner 32 as the cleaning means, the charging roller 34 as the charging means, and the exposure device as the exposure means are arranged in the order of rotation of the photosensitive drum 28 (arrow R direction). 36, a developing device 38 as a developing means is disposed. The surface 28 </ b> A of the photosensitive drum 28 is in contact with the intermediate transfer belt 24 on the downstream side of the developing device 38 in the rotation direction (arrow R direction) of the photosensitive drum 28.

  The charging roller 34 is parallel to the photosensitive drum 28, is in a position where it can contact the photosensitive drum 28, and is rotatable. The charging roller 34 is a conductive roller, and a metal core is covered with an elastic layer made of a synthetic resin. A negative voltage is applied to the core from a power source (not shown). ing. Thereby, in the present embodiment, the charging roller 34 charges the surface potential of the photosensitive drum 28 to −700V.

  An exposure device 36 is disposed on the downstream side of the charging roller 34 with respect to the rotation direction of the photosensitive drum 28 (the direction of the arrow R). The exposure device 36 emits a light beam 36L such as LED light to irradiate the surface 28A (photosensitive layer) of the photoconductive drum 28 with a light image, thereby causing the photoconductive drum 28 charged by the charging roller 34 to be irradiated. An electrostatic latent image is formed by exposure. Here, in the present embodiment, the surface potential in the image portion of the photosensitive member is attenuated to −200 V by LED light or the like.

  A developing device 38 is disposed on the downstream side of the exposure device 36 with respect to the rotation direction of the photosensitive drum 28 (the direction of the arrow R). The developing device 38 includes a developing device cartridge 38A, and the developing device cartridge 38A is filled with a two-component developer 50 in which toner and a carrier are mixed.

  The toner contains at least a binder resin and a colorant, and an external additive is added depending on the purpose. As the carrier, magnetic powder such as iron is applied, and the surface of the magnetic powder may have a resin coating layer. In this embodiment, the carrier has a particle diameter (diameter) A of 20 μm ≦ A ≦ 60 μm. In the developing device cartridge 38A, two stirring screws 38B are provided. The stirring screw 38B stirs the toner and the carrier filled in the developing device cartridge 38A to frictionally charge them and mix them uniformly. It is like that. Thereby, the toner is electrostatically adhered to the carrier.

  When the toner and the carrier are mixed to form the two-component developer 50, if the toner charge amount is too high, the adhesion force of the toner to the carrier becomes too high and the toner is difficult to transfer to the photosensitive drum 28, and the toner This causes a phenomenon that good development cannot be performed. On the other hand, if the charge amount of the toner is too low, the adhesion force of the toner to the carrier is weakened, a toner cloud due to free toner is generated, and the toner adheres to the non-image area that should originally be white at the time of printing, resulting in a high density This causes a problem (fogging). In order to perform good development by transferring the toner, the charge amount of the toner in the two-component developer 50 is preferably 5 to 50 μC / g in absolute value.

  A developing magnet roller 38C is disposed above the agitating screw 38B so as to face the photosensitive drum 28. The developing magnet roller 38C and the photosensitive drum 28 are parallel to each other. The developing magnet roller 38C attracts the carrier of the magnetic powder by magnetic force.

  A developing bias of −550 V is applied to the developing magnet roller 38C during development. In this case, the toner adhering to the carrier on the developing magnet roller 38C is caused by the potential difference (developing potential) between the potential (-200V) at which the photosensitive drum 28 is exposed and the developing bias potential (-550V). Is electrostatically attached to the surface. As a result, the developing device 38 causes the toner to adhere to the electrostatic latent image formed on the photosensitive drum 28 and develops it to form a toner image. On the other hand, the carrier on the developing magnet roller 38C is not attracted to the photosensitive drum 28 because the magnetic force by the developing magnet roller 38C with respect to the carrier is larger than the electrostatic force on the photosensitive drum 28 with respect to the carrier (due to the developing potential).

Further, a bias of −400 V, for example, is applied to the developing magnet roller 38C during carrier recovery. In this case, the electrostatic force to the photosensitive drum 28 with respect to the carrier is larger than the magnetic force by the developing magnet roller 38C with respect to the carrier, and the carrier is electrostatically attached to the photosensitive drum 28. (The carrier collection timing may be set automatically by sequence control or based on a command from the user.)
A carrier supply roll 39A and a toner supply roll 39B are disposed above the developing device 38, and a carrier box 40 containing a supply carrier is detachably disposed above the carrier supply roll 39A. Above the supply roll 39B, a toner box 42 containing supply toner is detachably disposed. The carrier in the carrier box 40 is supplied into the developer cartridge 38A by the rotation of the carrier supply roll 39A, and the toner in the toner box 42 is supplied into the developer cartridge 38A by the rotation of the toner supply roll 39B. It has become.

  On the inner peripheral side of the intermediate transfer belt 24 (the lower side in FIG. 2), the intermediate transfer belt 24 is positively charged at a position facing the photosensitive drum 28 so that the outer surface of the intermediate transfer belt 24 is exposed to light. A primary transfer roller 30 for adsorbing toner on the surface 28A of the body drum 28 is provided. The primary transfer roller 30 is formed by forming a urethane foam layer on a metal core, and a primary transfer bias is applied to the primary transfer roller 30. Since the primary transfer roller 30 rotates while applying pressure to the intermediate transfer belt 24, the toner image on the photosensitive drum 28 is transferred to the intermediate transfer belt 24.

  A cleaner 32 is disposed downstream of the primary transfer roller 30 with respect to the rotation direction of the photosensitive drum 28 (in the direction of arrow R). The cleaner 32 includes a cleaner housing 32A that opens to the side facing the photosensitive drum 28, and a cleaning blade 32C is disposed via a blade holder 32B fixed to the cleaner housing 32A. The cleaning blade 32C is made of a plate-like rubber member, and its tip abuts against the surface 28A of the photosensitive drum 28 so as to remove deposits (waste toner, waste carrier, etc.) attached to the photosensitive drum 28. . A spiral auger 32D is provided at the lower portion of the cleaner 32. The spiral auger 32D once receives the deposit removed by the cleaning blade 32C and then discharges it to a collection box (not shown).

  As shown in FIG. 1, the intermediate transfer belt 24 below the image forming unit 26 is an endless belt having elasticity, and includes three tension rollers 44 provided on the inner peripheral side of the intermediate transfer belt 24 and A predetermined tension is applied by being supported by the secondary transfer backup roller 16A of the secondary transfer unit 16, and is in contact with the photosensitive drum 28 and the primary transfer unit 31 (between the primary transfer roller 30 and the photosensitive drum 28). .

  Here, the tension F (see FIG. 3) applied in a state where the intermediate transfer belt 24 is supported from the inner peripheral side is preferably 19.6 N / m ≦ F ≦ 98.0 N / m. By setting this range, the load applied to the photosensitive drum 28 by the carrier 50C (see FIG. 3) in the primary transfer portion 31 is suppressed while ensuring good transferability.

  The intermediate transfer belt 24 is rotated in the clockwise direction (arrow K direction) in FIG. 1 following the rotational driving of the photosensitive drum 28. The toner image on the photosensitive drum 28 is primarily transferred to the intermediate transfer belt 24 by the primary transfer roller 30 in the order of yellow, magenta, cyan, and black, and the intermediate transfer belt 24 transfers the primary transferred toner image. The sheet is conveyed toward the secondary transfer unit 16 while being held.

  As the material of the intermediate transfer belt 24 shown in FIG. 3, an elastically deformable material is applied to the carrier 50 </ b> C attached to the photosensitive drum 28. The intermediate transfer belt 24 preferably has a hardness Hs of 40 ≦ Hs ≦ 90 (former JIS A-K6301). By setting 40 ≦ Hs, the wear resistance can be ensured, and by setting Hs ≦ 90, the primary transfer portion 31 can be sufficiently elastically deformed with respect to the carrier 50C. The Young's modulus Y of the intermediate transfer belt 24 is preferably 30 MPa ≦ Y ≦ 50 MPa.

  In the present embodiment, the intermediate transfer belt 24 includes an elastic belt base 24A and a protective layer 24B that covers the surface of the belt base 24A. Here, examples of the material of the belt base material 24A include vulcanized rubber and thermoplastic elastomer. Here, as raw material rubber materials, general diene rubbers such as styrene / butadiene rubber (SBR), polyisoprene rubber (IIR), ethylene / propylene / diene rubber (EPDM), polybutadiene rubber (BR), acrylic rubber ( ACM, ANM), etc., but acrylonitrile butadiene rubber is relatively high in rigidity, has a volume resistivity close to semiconductivity, and has good fluidity in the mold. (NBR), hydrogenated NBR, chloroprene rubber (CR), epichlorohydrin rubber (CO, ECO), polyurethane rubber (PUR) and the like are preferable. On the other hand, polyester-based, polyurethane-based, styrene-butadiene triblock-based, polyolefin-based, etc. are used as the thermoplastic elastomer. When such a thermoplastic elastomer is used, recycling is possible, which is environmentally preferable. Furthermore, the material of the belt base material 24A is not necessarily one type, and two or more types of materials can be blended. For example, a material obtained by blending chloroprene rubber (CR) and EPDM is used. In addition, a conductive filler or an insulating filler can be added to the belt base material 24A to adjust the volume resistivity of the belt base material 24A. As a material of the protective layer 24B, a polyurethane resin, a polyester resin, a polyacrylic resin, or the like is used as a binder, and a predetermined filler, typically, a lubricating filler and a conductive filler are dispersed. The surface roughness Rz (δ) of the coating layer 24B is preferably set to 1.5 to 9 μm or less in consideration of the adhesion to the photosensitive drum and the toner particle size to be used. If the thickness T of the protective layer 24B is larger than necessary, the elastic force of the belt base material 24A is hindered, and the elastic deformation of the carrier 50C attached to the photosensitive drum 28 becomes insufficient.

The intermediate transfer belt 24 presses the photosensitive drum 28 by the pressure of the primary transfer roller 30, and a carrier 50 </ b> C (in this embodiment, a particle diameter ( The pressing force P applied to the photosensitive drum 28 by the intermediate transfer belt 24 when the diameter A) is 20 μm ≦ A ≦ 60 μm is 19.6 N / m ² ≦ P ≦ 49.0 N / m ² . It is preferable. By setting this range, it is possible to ensure transferability while suppressing the load applied to the photosensitive drum 28 by the carrier 50C in the primary transfer portion 31.

  Next, the operation of the above embodiment will be described.

  At the time of printing, as shown in FIG. 1, each photosensitive drum 28 is uniformly charged to −700 V by the charging roller 34 and is exposed by a light beam 36 </ b> L (see FIG. 2) from the exposure device 36. The surface potential in the 28 image portions is attenuated to −200 V, and a latent image is formed. The latent images on the four photosensitive drums 28 are respectively developed by developing devices 38 (developing magnet rollers 38C shown in FIG. 2) by applying a developing bias of −550 V to toner images of respective colors.

  That is, the toner adhering to the carrier on the developing magnet roller 38C shown in FIG. 2 is caused by the potential difference (developing potential) between the potential at which the photosensitive drum 28 is exposed (−200V) and the developing bias potential (−550V). The toner is electrostatically attached to the photosensitive drum 28, whereby toner is attached to the electrostatic latent image formed on the photosensitive drum 28 and developed to form a toner image. On the other hand, the carrier on the developing magnet roller 38C is not attracted to the photosensitive drum 28 because the magnetic force by the developing magnet roller 38C with respect to the carrier is larger than the electrostatic force on the photosensitive drum 28 with respect to the carrier (due to the developing potential).

  In the primary transfer unit 31 shown in FIG. 1, the primary transfer roller 30 rotates while applying pressure to the intermediate transfer belt 24, and a primary transfer bias is applied, so that the intermediate transfer belt 24 has a surface of the photosensitive drum 28. The toner image formed on 28A is transferred. The toner images of the respective colors are sequentially primary transferred and superimposed on the intermediate transfer belt 24 to form a color image.

  The intermediate transfer belt 24 conveys the toner images of four colors while holding them, and the secondary transfer unit 16 transfers the toner images on the intermediate transfer belt 24 to a sheet. The sheet is fixed by the fixing unit 18 and discharged from the discharge port 20 to the discharge tray 22. On the other hand, deposits (waste toner and the like) on the surface 28A of the photosensitive drum 28 that have passed through the primary transfer portion 31 are removed by the cleaner 32.

  On the other hand, when the carrier is collected before and after printing, a bias of, for example, −400 V is applied to the developing magnet roller 38C shown in FIG. And the carrier is electrostatically attached to the photosensitive drum 28.

  As shown in FIG. 3, the carrier 50 </ b> C rotates together with the photosensitive drum 28 in the drum rotation direction (arrow R direction), and is sandwiched between the photosensitive drum 28 and the intermediate transfer belt 24 in the primary transfer unit 31. . At this time, since the intermediate transfer belt 24 is sufficiently elastically deformed with respect to the carrier 50C, the carrier 50C is temporarily embedded in the intermediate transfer belt 24, and the pressing force P applied to the photosensitive drum 28 via the carrier 50C. And the force with which the carrier 50C rubs the photosensitive drum 28 is reduced. The intermediate transfer belt 24 is driven by the rotation of the photosensitive drum 28, and the photosensitive drum 28, the carrier 50C, and the intermediate transfer belt 24 move at the same speed, so that the friction between the carrier 50C and the photosensitive drum 28 is maintained. Is very small. The carrier 50C that has passed through the primary transfer portion 31 is removed from the photosensitive drum 28 by the cleaner 32 shown in FIG.

  In the above embodiment, a bias of −400 V is applied to the developing magnet roller 38C shown in FIG. 2 at the time of carrier recovery. For example, the bias is applied to the developing magnet roller 38C without applying a bias, etc. It is sufficient that a potential difference capable of transferring and attaching the carrier from the developing device 38 to the photosensitive drum 28 is given.

  In the above embodiment, the carrier is collected before and after printing. However, for example, the carrier may be collected by being attached to the non-image part of the photosensitive drum 28 at the time of printing. Any time may be used as long as the body drum 28 is rotationally driven.

  Further, rollers are arranged on the upstream side and the downstream side adjacent to each primary transfer roller 30 in the above-described embodiment, and the intermediate transfer belt 24 is in contact with the photosensitive drum 28 in a wrap shape between these rollers. Thus, the intermediate transfer belt 24 may be driven by the rotation of the photosensitive drum 28.

  Furthermore, in the above embodiment, the case where the image forming apparatus is a so-called tandem color image forming apparatus has been described as an example, but a so-called four-cycle image forming apparatus or a black and white image forming apparatus (an apparatus that does not perform intermediate transfer) Other image forming apparatuses such as the above may be used.

  In the above-described embodiment, the negatively charged photosensitive drum 28 is used as the photosensitive member. However, another photosensitive drum such as a positively charged photosensitive drum (for example, an amorphous silicon photosensitive member) is used. May be.

1 is a schematic configuration diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating a configuration of an image forming unit according to an embodiment of the present invention. FIG. 6 is a schematic state diagram illustrating a state in which the intermediate transfer belt is elastically deformed with respect to the carrier attached to the photosensitive drum in the embodiment of the present invention.

Explanation of symbols

10 Image forming apparatus 16A Secondary transfer backup roller (support member)
24 Intermediate transfer belt (endless transfer belt (transfer body))
24A belt base material 28 photoconductor drum (photoconductor)
28A Surface 31 Primary transfer part (transfer part)
32 Cleaner (cleaning means)
38 Developing device (developing means)
44 Tension roller (support member)
50 Two-component developer 50C Carrier F Tension

Claims (5)

A photosensitive member on which an electrostatic latent image is formed and driven to rotate;
Using a two-component developer in which a toner and a carrier are mixed, the electrostatic latent image formed on the photoconductor is developed with the toner, and the carrier is electrostatically attached to the photoconductor when the carrier is recovered. Developing means;
Cleaning means for removing the carrier adhering to the photoreceptor;
A transfer member that contacts the photosensitive member at a transfer portion to transfer a toner image on the photosensitive member, and that is elastically deformable with respect to the carrier attached to the photosensitive member and reduces the pressing force to the photosensitive member. When,
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the transfer member is driven by rotation of the photosensitive member.   The transfer body is an endless transfer belt, and tension is applied by a support member on the inner peripheral side, and the endless transfer belt has a belt base material made of vulcanized rubber or a thermoplastic elastomer, from the inner peripheral side. 3. The image forming apparatus according to claim 2, wherein the tension F applied in a supported state is 19.6 N / m ≦ F ≦ 98.0 N / m.   The image forming apparatus according to claim 3, wherein the endless transfer belt has a hardness Hs of 40 ≦ Hs ≦ 90 (former JIS A-K6301).   5. The image forming apparatus according to claim 3, wherein the surface of the photoconductor has a Vickers hardness C of 50 Hv ≦ C ≦ 200 Hv.

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