JP4870458B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device that develops an electrostatic latent image formed on a photoreceptor with a developer, and an image forming apparatus having the developing device.

  2. Description of the Related Art Conventionally, an electrophotographic recording type image forming apparatus that forms a developer image on a recording medium by thermocompression bonding is known. In this type of image forming apparatus, a charging unit that uniformly charges the surface of the photoreceptor, an exposure unit that exposes the surface of the photoreceptor to form an electrostatic latent image, and a developer (hereinafter referred to as toner) on the electrostatic latent image. .) Is applied to the developing roller, the toner is charged and transported to the developing roller, the developing roller forms a uniform toner layer on the developing roller, and the toner developed on the photosensitive member is used as a medium. The image forming apparatus includes a developing device provided with a transfer portion for transferring and a cleaning portion for collecting toner remaining on the photoreceptor without being transferred.

  As this developing device, there is a developing device of a contact developing system in which a photosensitive member and a developing roller are provided in pressure contact (for example, see Patent Document 1). In such a developing device, as shown in FIG. 1, a developing device having a shape in which the outer diameter at the end of the developing roller is smaller than the outer diameter at the center of the developing roller 104 is used. As a result, the developing device obtains a uniform stress at the pressure contact portion between the developing roller 104 and the photosensitive member 101 as shown in FIG.

JP 2001-350351 A

As described above, the developing roller 104 as shown in FIG. 1 used in the contact developing method including the developing device described in Patent Document 1 has a uniform pressure across the entire surface in the axial direction with respect to the photoreceptor 101. It has become. In this case, since the pressure is uniform in the axial direction, the pressure at which the developing roller 104 and the photosensitive member 101 are pressed is equalized, and the pressure per unit area is reduced. As a result, the toner leaks from between the photoreceptor 101 and the developing roller 104 to the outside of the developing device. As a result, there is a problem in that the toner falls on the recording medium and the formed image is defective due to toner leakage.

SUMMARY An advantage of some aspects of the invention is that it provides a developing device and an image forming apparatus capable of preventing toner as a developer from leaking between a photosensitive member and a developing roller to the outside of the developing device.

The developing device of the present invention is a developing device for developing an electrostatic latent image formed on an image carrier with a developer, and rotates around a developing shaft having an elastic layer formed of an elastic body on the surface, A developing roller that supplies the developer to the image carrier that is in contact; a developing blade that is in contact with the elastic layer of the developing roller and regulates the layer thickness of the developer; and an end of the elastic layer of the developing roller An elastic layer of the developing roller, an outer diameter φc at the center of the elastic layer of the developing roller, an outer diameter φr at both ends of the elastic layer of the developing roller, The relationship between the outer diameter φt at a predetermined position between the end of the developer adhesion region where the developer adheres on the elastic layer of the developing roller and the end of the elastic layer is φc> φt, and , Φr> φt, and φt + 0.5 × (φc−φt) ≦ The shape is such that φr ≦ φt + 2 × (φc−φt).

According to the developing device of the present invention, the shape of the elastic layer of the developing roller provided includes the outer diameter φc at the center of the elastic layer of the developing roller, the outer diameter φr of the end of the elastic layer of the developing roller, and the developer is developed. The relationship between the outer diameter φt at a predetermined position between the end of the developer adhesion region adhering to the elastic layer of the roller and the end of the elastic layer satisfies φc> φt and φr> φt, φt + 0.5 × (φc−φt) ≦ φr ≦ φt + 2 × (φc−φt) is satisfied. As a result, the pressure applied to the photoconductor at the end portion of the elastic layer of the developing roller is higher than the pressure applied to the photoconductor inside the end portion. Therefore, it is possible to prevent toner from leaking between the photosensitive member and the developing roller. Thereby, it is possible to provide a developing device for forming better image quality.

The developing device of the present invention is a developing device that develops an electrostatic latent image formed on a photoreceptor with a developer, and rotates about a developing shaft having an elastic layer formed of an elastic body on the surface. And a developing roller that supplies the developer to the contacted photoreceptor and has a gear at one end of the developing shaft, and a developing blade that contacts the elastic layer of the developing roller and regulates the layer thickness of the developer. , and a seal member provided at a position to abut against an end of the elastic layer of the developing roller, the elastic layer of the developing roller, and φc of the outer diameter of the elastic layer center of the developing roller, the developer Of the end portions of the adhesion region, the outer diameter φg of one end portion on the side having the gear, the outer diameter φh of the other end portion of the developer adhesion region on the opposite side of the one end portion, and the developing roller The relationship between the outer diameter φr at both ends of the elastic layer is φc ≧ φg> φh And characterized in that it is a shape that satisfies the φr>φg> φh.

According to the developing device of the present invention, the shape of the elastic layer of the developing roller provided includes the outer diameter φc at the center of the elastic layer and the outer diameter φg at one end on the side having the gear among the ends of the developer adhesion region. And the relationship between the outer diameter φh of the other end of the developer adhesion region opposite to the one end and the outer diameter φr of both ends of the elastic layer is φc ≧ φg> φh and φr>φg> φh Try to meet. As a result, the pressure applied to the photoconductor at the end portion of the elastic layer of the developing roller is higher than the pressure applied to the photoconductor inside the end portion.
Therefore, it is possible to prevent toner from leaking between the photosensitive member and the developing roller. Thereby, it is possible to provide a developing device for forming better image quality.

According to the image forming apparatus of the present invention, the above-described developing device is provided. Accordingly, it is possible to provide an image forming apparatus that can prevent leakage of the developer and can form better image quality.

In the developing device and the image forming apparatus of the present invention, the pressure on the photoconductor at the end of the elastic layer of the developing roller is higher than the pressure on the photoconductor inside the end. Therefore, it is possible to prevent toner from leaking between the photosensitive member and the developing roller, and it is possible to form a better image quality.

  The developing device and image forming apparatus of the present invention will be described below with reference to the drawings. The developing device and the image forming apparatus of the present invention are not limited to the following descriptions, and can be appropriately changed without departing from the gist of the present invention.

  The image forming apparatus of the present invention is an image forming apparatus provided with a developing device that develops an electrostatic latent image formed on a photosensitive drum as a photosensitive member with toner as a developer. In particular, this image forming apparatus includes a developing roller that adheres toner to the photosensitive drum by rotating opposite to the peripheral surface of the photosensitive drum, and a conveying roller that conveys the toner to the developing roller. It is provided with a developing device that satisfies the conditions found as a result of extensive research by the applicant.

[Embodiment 1]
First, the image forming apparatus of the present invention will be described. FIG. 3 is a side sectional view for explaining the structure of the image forming apparatus, and FIG. 4 is a side sectional view for explaining the structure of the developing device in the image forming apparatus. As shown in FIG. 3, the image forming apparatus includes a paper cassette 91 that stores paper as a recording medium on which no image is formed. The paper stored in the paper cassette 91 is fed out as the hopping roller 92 rotates, and further, registration rollers 96 and 97 and pinch rollers 93 and 95 disposed downstream of the hopping roller 92. Is rotated in the direction of the arrow in FIG. 3 at a predetermined timing in accordance with the rotation.

  Further, the image forming apparatus is provided with a developing device 10. The developing device 10 forms an image using toner on a sheet. Specifically, the developing device 10 charges the photosensitive drum 1 as an image carrier on which an electrostatic latent image is formed by the exposure device 3 provided on the image forming apparatus side, and the surface of the photosensitive drum 1. The charging roller 2, the developing roller 4 that develops the electrostatic latent image formed on the surface of the photosensitive drum 1 with toner, the conveying roller 5 that conveys the toner supplied to the developing roller 4, and the developing roller 4. A developing blade 6 that forms a toner layer of a certain thickness from the toner, and a cleaning device 8 that cleans and collects the toner remaining on the surface of the photosensitive drum 1 without being transferred onto the paper. The exposure device 3 provided on the image forming apparatus side selectively exposes the surface of the photosensitive drum 1 by irradiating light on the basis of print data received from an external device via an interface unit (not shown). An electrostatic latent image is formed on the surface of 1. The transfer roller 7 provided on the image forming apparatus side transfers a toner image obtained by visualizing the electrostatic latent image on the photosensitive drum 1 with toner onto a sheet. The photosensitive drum 1, the charging roller 2, and the transfer roller 7 are configured to be rotationally driven by a motor (not shown), a gear that transmits driving, or the like. The exposure device 3, the developing roller 4, and a motor (not shown) are connected to a power source and a control unit (not shown), respectively.

  Such a developing device 10 charges the surface of the photosensitive drum 1 to a uniform voltage by a charging roller 2 to which a predetermined voltage is applied by a power source (not shown) under the control of a control unit (not shown). When the charged surface reaches the vicinity of the exposure device 3 as the photosensitive drum 1 rotates, the photosensitive drum 1 is irradiated with light modulated by the exposure device 3 to electrostatic latent image. Form an image. The developing device 10 generates a toner image by attaching the toner supplied from the developing roller 4 to the formed electrostatic latent image.

  The toner image developed by the developing device 10 faces the surface of the photosensitive drum 1 with the surface on which the toner image is generated as the photosensitive drum 1 rotates under the control of a control unit (not shown). While reaching the vicinity of the arranged transfer roller 7, the sheet is conveyed between the photosensitive drum 1 and the transfer roller 7, and is transferred onto the sheet by the transfer roller 7. At this time, a predetermined voltage is applied to the transfer roller 7 by a power source (not shown).

  When the transfer is completed, the developing device 10 cleans the toner remaining on each surface of the photosensitive drum 1 by the cleaning device 8 under the control of a control unit (not shown). In the image forming apparatus, the developing device 10 having such a configuration forms an image on a sheet to form an image. In the image forming apparatus, the sheet is conveyed to the fixing device 98.

  Further, the image forming apparatus includes a fixing device 98 downstream of the developing device 10. The fixing device 98 includes a fixing roller having an elastic member on the outer surface of the roller, and a pressure roller that presses the sheet together with the fixing roller. The pressure roller is disposed so as to be in contact with the fixing roller so as to form a nip portion that sandwiches the sheet. In addition, a heater or a halogen lamp that generates heat or emits light from a power source (not shown) is embedded in the fixing roller. In the fixing device 98, the fixing roller is heated by energizing these heaters or causing a halogen lamp to emit light under the control of a control unit (not shown). Such a fixing device 98 rotates the fixing roller and the pressure roller to pass the paper through the nip portion, and heats and presses the paper to melt the toner on the paper and heat-fix the toner image. Let In the image forming apparatus, when the fixing device 98 fixes the image on the sheet, the sheet is conveyed to the outside according to the rotation of the discharge roller 99 and is discharged to the outside. Load it on the stacker.

  The image forming apparatus described above has been described as including one developing device 10, but the present invention is not limited to this. For example, cyan (C), magenta (M), yellow (Y), black (K) The developing devices corresponding to each of the four color toners may be arranged along the transfer belt in this order from the paper supply side to the paper discharge side. In this case, the developing device 10 corresponding to the toner of each color can form a color image by transferring the toner image of each color based on the control of a control unit (not shown).

  Next, the developing device 10 provided in the image forming apparatus will be described. As described above, the developing device 10 includes the photosensitive drum 1, the charging roller 2, the developing roller 4, the conveying roller 5, the developing blade 6, and the cleaning device 8. FIG. 5 is a layout diagram for explaining the relationship among the developing roller 4, the photosensitive drum 1, and the conveying roller 5, and FIG. 6 is a diagram illustrating the external shape of the developing roller 4.

  As shown in FIG. 5, the photosensitive drum 1 includes a conductive base layer made of aluminum or the like and a photosensitive layer 11 made of an organic photosensitive member. The photosensitive drum 1 is fixed to both ends of the frame of the developing device 10 so as to be rotatable about a fixed shaft as a central axis. At one end portion of the fixed shaft, a photoconductor gear 12 for rotating the photoconductor drum 1 is provided. The photoconductor gear 12 and a developing gear 42 of the developing roller 4 described below mesh with each other. The photosensitive drum 1 is fixed on the shaft so as to fit. The photosensitive drum 1 is an electrostatic latent image carrier and is configured to be able to store electric charges on the surface thereof. The charges stored on the surface are configured such that the charges on the surface can be removed by exposure with the exposure apparatus 3. The photosensitive drum 1 forms a toner image by attaching toner as a developer to the electrostatic latent image formed on the surface thereof.

  In the charging roller 2, semiconductive rubber such as epichlorohydrin rubber is formed in a roll shape on a conductive metal shaft. The charging roller 2 is rotatably fixed to the frame of the developing device 10 so as to be in contact with the surface of the photosensitive drum 1 at a constant pressure upstream of the developing roller 4 of the photosensitive drum 1 with a constant pressure. . The charging roller 2 charges the photosensitive drum 1 by applying a predetermined positive voltage or negative voltage to the photosensitive drum 1.

  The cleaning device 8 is made of a predetermined elastic body, and a developing device so that one end of the cleaning device 8 is in contact with the surface of the photosensitive drum 1 at a constant pressure upstream of the charging roller 2 of the photosensitive drum 1 with a constant pressure. It is fixed to 10 frames. The cleaning device 8 cleans the photosensitive drum 1 by scraping off the toner remaining on the surface of the photosensitive drum 1.

  The exposure device 3 is disposed above the photosensitive drum 1. The exposure device 3 irradiates the surface of the photosensitive drum 1 with the image-modulated light from the direction of the arrow, and forms an electrostatic latent image on the photosensitive drum 1. As such an exposure apparatus 3, for example, an arbitrary one such as a combination of a LED (Light Emitting Diode) array and a so-called lens array, a combination of a laser and an image forming optical system, or the like can be applied. it can.

  In the transport roller 5, a foamed elastic layer 51 is formed on a conductive metal transport shaft 53 to improve toner transport. The transport roller 5 is rotatably fixed to the frame of the developing device 10 so as to come into contact with the surface of the developing roller 4 at a constant pressure upstream of the photosensitive drum 1 of the developing roller 4. For the foamed elastic layer 51, materials such as silicone rubber and urethane rubber can be used. Further, the outer diameter Ψs of the metal conveying shaft 53 is, for example, 15.30 mm at least in a portion where the foamed elastic layer 51 is present, and has a uniform shape in the axial direction. A conveyance gear 52 is provided at one end of the conveyance shaft 53. The transport gear 52 does not mesh with the developing gear 42 described below. In the portion where the foamed elastic layer 51 is not provided, the outer diameters may be different sizes. A predetermined positive voltage or negative voltage is applied to the transport roller 5. The supply roller 4 supplies the toner supplied from the toner cartridge to the toner tank to the developing roller 4.

  The toner cartridge is detachably disposed on the upper portion of the frame of the developing device 10 so as to be above the conveyance roller 5. The toner cartridge stores toner as a developer and supplies the stored toner to a toner tank below the toner cartridge. The toner in the toner tank may be, for example, a pulverized toner having a mean particle size of 8.0 μm, a suspension polymerization toner, or an emulsion polymerization toner. It is conveyed to the developing roller 4 by the conveying roller 5.

  The developing blade 6 is formed by bending a plate-like elastic member having a uniform thickness, such as plate-like stainless steel, into an L shape. The developing blade 6 is in contact with the surface of the developing roller 4 at the edge portion bent in an L-shape on the upstream side of the developing roller 4 from the contact portion between the developing roller 4 and the photosensitive drum 1. It is fixed to the frame of the developing device 10 via a holder. The developing blade 6 scrapes off the toner conveyed from the conveying roller 5 on the surface of the developing roller 4 and regulates the thickness of the toner layer formed on the surface of the developing roller 4.

  The developing blade 6 can use a stainless plate, a rubber material, or the like. When a rubber material is used, it is preferable that the rubber material is attached to a plate-like elastic member, and the rubber material portion is pressed against the developing roller 4 to be installed.

  In the photosensitive drum 1, a photosensitive layer 11 is formed on a peripheral surface of a raw tube (not shown), and a photosensitive gear 12 is attached to one end of the raw tube. The outer diameter φk of the photosensitive drum 1 is 30.00 mm, for example, and has a uniform shape in the axial direction. The photosensitive drum 1 is placed in pressure contact with a developing roller 4 described below, and the photosensitive gear 12 and the developing gear 42 are engaged with each other. The photosensitive drum 1 and the developing roller 4 are installed so that the force of pressure contact is 100 μm between the developing roller 4 and the photosensitive drum 1. This NIP amount causes the developing shaft 43 of the developing roller 4 to bend, so that the distance between the center of the photosensitive drum 1 and the centers of both ends of the developing shaft 43 in the axial direction of the developing roller 4 is L, the developing roller Assuming that the outer diameter φt of the end portion T of the developer adhesion region P of 4 is NIP amount = (φk + φt) / 2−L.

  A toner image is formed on the photosensitive drum 1 by supplying toner to the formed electrostatic latent image by the developing roller 4. The area where the electrostatic latent image for forming the toner image is formed is a so-called print area at the central portion excluding a predetermined area at the end of the photosensitive drum 1. The developing roller 4 has a region in contact with the print region, and toner is attached to this region. This area is a developer adhesion area P.

  As shown in FIG. 6, the developing roller 4 includes an elastic layer 41 formed of a semiconductive rubber such as urethane rubber or silicone on a cylindrical conductive metal developing shaft 43 having an outer diameter of 10.00 mm. Is wound. The elastic layer 41 may have a single-layer structure of these materials, but may have a multilayer structure or a structure having a resin coat layer on the surface.

  As shown in FIG. 7, a seal member 45 is installed at the end of the developing roller 4 so as to press against the peripheral surface of the end and prevent the toner from being placed on the end of the developing roller 4. The seal member 45 may be provided with a Teflon (registered trademark) coat on the surface pressed against the developing roller 4 or may be provided with a felt excellent in toner scraping property. The seal member 45 may have a shape along the peripheral surface of the end of a roller having a width of 5 mm and a length of 14 mm, for example.

  The outer diameter Ψd of the developing shaft 43 at the portion around which the elastic layer 41 is wound may have a shape having a uniform outer diameter of, for example, 10.00 mm in the developer adhesion region P. Although the diameter may be increased, the outer diameter of the developing shaft 43 in the developer adhesion region P is considered in consideration of an increase in load torque while the bending of the developing shaft 43 is reduced. Is more preferably uniform. Further, the developing shaft 43 in the portion where the elastic layer 41 is not wound may be the same as the outer diameter Ψd of the developing shaft 43 in the portion where the elastic layer 41 is wound, and may have a different length. May be.

  A developing gear 42 is attached to one end of the developing shaft 43 around which the elastic layer 41 is wound. The developing roller 4 is rotationally driven by the developing gear 42. The developing roller 4 is applied with a predetermined positive voltage or negative voltage via the developing shaft 43, thereby causing the toner to adhere to a predetermined region on the surface of the elastic layer 41 of the developing roller 4. A uniform toner layer is formed by the developing blade 6 with the adhered toner, the developing roller is rotated, and the toner is supplied to the photosensitive drum 1.

  FIG. 6 is a diagram illustrating an external shape of the developing roller 4 according to the first embodiment. As described above, the developing roller 4 has the elastic layer 41 wound around the circumferential surface of a cylindrical conductive metal shaft 43, for example. The outer diameter of the elastic layer 41 gradually decreases from the central portion C of the elastic layer 41 to both ends T of the developer adhesion region P, and the developer adhesion region from each of both ends R of the elastic layer 41. It has a shape in which the outer diameter gradually decreases toward both end portions T of P. That is, the elastic layer 41 has an outer diameter of the central portion C of the elastic layer 41 as φc, an outer diameter of both ends T of the developer adhesion region P as φt, and an outer diameter of both ends R of the elastic layer 41 as φr. , Φc> φt, and φt <φr. Either φc or φr may be larger or the same size. Thereby, toner leakage from the developing roller 4 can be prevented. The developing roller 4 may have any shape as long as φc> φt and φt <φr are satisfied, and a portion corresponding to the end T of the developer adhesion region P of the elastic layer 41 is constricted. Any shape can be used. The constricted portion of the developing roller 4 described in the present embodiment is an end portion T of the developer adhesion region P. However, the position of the constricted portion is not limited to this, and the end portion of the developer adhesion region P (this embodiment) Between the end T) described in the embodiment and the end of the elastic layer (end R described in the present embodiment).

  FIG. 8 is a cross-sectional view of the developing roller 4 and is an enlarged view of a main part in which the upper half is enlarged from the central axis of the developing roller 4. The relationship among the outer diameters of the central portion C of the elastic layer 41, the end portion T of the developer adhesion region P, and the end portion R of the elastic layer 41 will be described with reference to FIG. As shown in FIG. 8, the developing roller 4 has a smaller outer diameter from the center C of the elastic layer 41 to the end T of the developer adhesion region P, and the end R1 or end R2 of the elastic layer 41 from the end T. It is the shape which enlarges an outer diameter over. Here, as the end portion R of the elastic layer 41, an end portion R1 having an outer diameter smaller than the outer diameter φc of the central portion C of the elastic layer 41 and an outer diameter larger than the outer diameter φc of the central portion C of the elastic layer 41 are used. The end R2 having a diameter is taken as an example. In the figure, D is a line indicating the central axis of the developing roller 4. The outer diameter φc of the central portion C of the elastic layer 41 is twice the length φc ′ from the central axis D to the surface. Further, the outer diameter φt of the end T of the developer adhesion region P is twice the length φt ′ from the central axis D to the surface. The outer diameters φr1 and φr2 of the end R1 or the end R2 of the elastic layer 41 are twice the lengths φr1 ′ and φr2 ′ from the central axis D to the surface, respectively.

  The difference between the outer diameter φc of the central portion C of the elastic layer 41 and the outer diameter φt of the end portion T of the developer adhesion region P is Δφ0 = 2 × φO ′ = φc−φt = (φc′−φt ′) × 2 It is represented by Further, the difference between the outer diameter φt of the end portion T and the outer diameter φr of the end portion R of the elastic layer 41 is represented by φr−φt = (φr′−φt ′) × 2. In the elastic layer 41, the relationship between the outer diameter φc of the central portion C of the elastic layer 41, the outer diameter φt of the end T of the developer adhesion region P, and the outer diameter φr of the end R of the elastic layer 41 is φc> φt, In addition, it is sufficient that the shape satisfies φt <φr. More preferably, the relationship among the outer diameter φc of the central portion C, the outer diameter φt of the end portion T, and the outer diameter φr of the end portion R is 0.5. A shape satisfying × Δφ0 ≦ φr−φt ≦ 2 × Δφ0 is more preferable. Since Δφ0 = φc−φt, 0.5 × (φc−φt) ≦ φr−φt ≦ 2 × (φc−φt), and φt + 0.5 × (φc−φt) ≦ φr ≦ φt + 2 × (φc −φt). Therefore, it is preferable that the outer diameter φr of the end portion R is not less than φt + 0.5 × (φc−φt) and not more than φt + 2 × (φc−φt). By making the outer diameter φr of the end portion R larger than φt + 0.5 × (φc−φt), toner leakage from the developing roller 4 can be prevented. Further, when the outer diameter φr of the end portion R is larger than φt + 2 × (φc−φt), the end portion of the developing blade 6 that is in pressure contact is lifted, so that the toner layer thickness on the developing roller 4 in the developer adhesion region is controlled. Can not do. The end portion R1 and the end portion R2 as an example are both suitable because they are at positions satisfying this φt + 0.5 × (φc−φt) ≦ φr ≦ φt + 2 × (φc−φt). In FIG. 8, the outer diameter φc of the central portion C of the elastic layer 41 and the outer diameter φt of the end portion T of the developer adhesion region P are described as being fixed, but the outer diameter φc and the outer diameter are described. φt can be appropriately changed as necessary, and accordingly, the outer diameter φr of the end portion R of the elastic layer 41 is also changed.

  The photosensitive drum 1 is driven to rotate clockwise via the developing gear 42 of the developing roller 4, and the surface of the photosensitive drum 1 is charged to, for example, about −600 V by the charging roller 2. Then, the exposure device 3 exposes the photosensitive drum 1, erases the potential on the surface of the photosensitive drum 1 at the irradiated location, and forms an electrostatic latent image on the surface of the photosensitive drum 1.

  The developing roller 4 and the conveying roller 5 are driven counterclockwise by a driving motor (not shown), and the conveying roller 5 conveys the toner to the developing roller 4. This drive motor (not shown) may be provided to drive the photosensitive drum 1. Since the conveyed toner is loosely formed on the developing roller 4, the thickness of the toner layer varies. Therefore, the developing blade 6 scrapes off excess toner on the developing roller 4 by an edge portion bent in an L shape, and forms a uniform toner layer on the developing roller 4. Further, when the toner layer is formed, the toner is frictionally charged by being rubbed against the developing roller 4 and the developing blade 6, and the toner is negatively charged. As for the frictional charging of the toner, the charge amount of the toner increases or decreases according to the pressure between the photosensitive drum 1 and the developing roller 4. When the pressure between the photosensitive drum 1 and the developing roller 4 is increased, the pressure is rubbed strongly and the charge amount of the toner is increased. On the contrary, when the pressure between the photosensitive drum 1 and the developing roller 4 is reduced, the pressure is rubbed weakly and the charge amount of the toner is reduced.

  For example, a voltage of −200 V is applied to the developing roller 4 by a power source (not shown), and a potential difference is generated between the developing roller 4 and the photosensitive drum 1. Due to the potential difference, the toner is developed on the electrostatic latent image on the photosensitive drum 1. The toner developed into the electrostatic latent image is transferred from the surface of the photosensitive drum 1 to the paper by the transfer roller 7. The toner remaining on the surface of the photosensitive drum without being transferred is scraped off by the cleaning device 8. The sheet on which the toner is transferred is fixed with toner as described above, and is discharged to the outside.

  The photosensitive drum 1 and the developing roller 4 are installed by being pushed in with an NIP amount of 100 μm. For this reason, the developing shaft 43 of the developing roller 4 is bent in a direction away from the photosensitive drum 1 at the central portion in the axial direction. Although the developing shaft 43 is separated from the photosensitive drum 1, as described above, the shape of the elastic portion 41 of the developing roller 4 is the outer diameter from the central portion C of the elastic layer 41 to the end portion T of the developer adhesion region P. Therefore, the pressure in contact with the photosensitive drum 1 at the central portion in the axial direction does not decrease and becomes uniform in the axial direction as shown in FIG.

  Further, since the outer diameter φr of the end portion R of the elastic layer 41 is larger than the outer diameter φt of the end portion T of the developer adhesion region P, the pressure pressed against the photosensitive drum 1 at the end portion R of the elastic layer 41 is As shown in FIG. 9, it becomes stronger than the developer adhesion region P. As a result, the relative position between the developing roller 4 and the photosensitive drum 1 is not shifted in the axial direction, and toner can be prevented from leaking between the developing roller 4 and the photosensitive drum 1.

  Therefore, fog measurement is performed on the developing roller in which the outer diameter φc of the central portion C, the outer diameter φr of the end portion R, and the outer diameter φt of the end portion T of the developer adhesion region P are changed. Went. This fogging is a phenomenon that occurs when the toner is charged in the opposite direction, and the toner adheres to the white background of the paper and causes the paper to become dirty.

For the measurement of fog, the developing device 10 is operated based on print data that becomes blank paper, and after the operation, a tape is applied so as to cover a part of the print area of the photosensitive drum 1, and By removing the tape, the fog toner attached to the tape is collected. And this tape is stuck on a pure white paper. For comparison, a tape without fog toner is also stuck on a pure white paper. The L * a * b * color system chromaticity of this tape is measured with a spectrophotometer (Spectrophotometer CM2600d manufactured by Konica Minolta). The position where the tape is applied is the end of the print area of the photosensitive drum 1 and the center of the print area, and the L * a * b * color system chromaticity measured at each position is ΔE = (ΔL ² + Δa ² + Δb ^2). ) Calculate by ^1/2 and measure fog at each position. The results are shown in Table 1 below. The values of the end fog and the central fog describe an average value over time. For the item of toner leakage, 20,000 sheets of A4 size paper (transverse feed) are printed, and it is determined that the toner is dropped on the paper. At this time, the rotational speed of the photosensitive drum 1 was 145 rotations per minute, and the developing roller 17 was 1.24 times the rotational speed of the photosensitive drum 1. Further, the item of the edge adhesion amount is the amount of toner adhered at the edge of the developer adhesion region P on the surface of the developing roller 4 after passing through the developing blade 6, and is 0.6 mg / mm ^2. In the following, it was marked as ◯, and when larger than 0.6 mg / mm ^2, it was marked as x.

  As shown in Table 1, the fog is better as ΔE is smaller, and more preferably ΔE <2.5. Further, in the case of a color image forming apparatus provided with four color toners, it is preferable that ΔE <2.0 for a single color. In order to reduce the variation in fogging between the end portion and the central portion of the printing area, it is preferable that 0.05 mm ≦ Δφ0 from Table 1, and more preferably 0.10 mm ≦ Δφ0. As described above, since toner leakage occurs when φr−φt <0.5 × Δφ0, 0.5 × Δφ0 ≦ φr−φt is preferable.

In the developing roller 4, if the toner layer thickness on the developing roller 4 is larger than 0.6 mg / mm ^{2, a} printing failure occurs because the toner layer is not thinned. Therefore, the toner layer thickness on the developing roller 4 is preferably 0.6 mg / mm ² or less. However, in the case of 2 × Δφ0 <φr−φt, the end of the developing blade 6 is a free end and thus floats up. Due to the influence, the developing blade 6 at the end T of the developer adhesion region P in the developing roller 4 is also insufficiently pressed against the developing roller 4. For this reason, the toner layer thickness at the end T of the developer adhesion region P on the developing roller 4 cannot be controlled, and printing failure occurs. Therefore, φr−φt ≦ 2 × Δφ0 is preferable.

  Further, even if the pressure distribution between the photosensitive drum 1 and the developing roller 4 is uniform with 0.10 mm ≦ Δφ0, the fog is deteriorated if the pressure is too weak. It is necessary to press the body drum 1 and the developing roller 4 against each other. However, if the pressure of the pressure contact between the photosensitive drum 1 and the developing roller 4 is excessively increased in order to improve fogging, the film thickness of the photosensitive layer 11 on the surface of the photosensitive drum 1 becomes severe, and the photosensitive drum 1 The life of the is shortened.

  Therefore, in the developing roller in which the outer diameter φc of the central portion C of the elastic layer 41 of the developing roller 4, the outer diameter φr of the end portion R, and the outer diameter φt of the end portion T of the developer adhesion region P are changed, A4 size. The thickness of the photosensitive layer 11 after printing 20,000 sheets of paper (transverse feed) was measured. The thickness of the photosensitive layer 11 was measured with a film thickness measuring device (LH-300 manufactured by Kett) based on the raw tube of the photoreceptor 1. This measurement was performed by a high-frequency eddy current method. In the high-frequency eddy current method, an induction coil that has passed a constant high-frequency current is brought close to a metal to generate an eddy current on the metal surface. Since this eddy current changes according to the distance between the induction coil and the metal surface, the voltage applied to both ends of the induction coil changes. This change is read from the current value and converted into a film thickness. As the photosensitive drum 1 used here, a photosensitive drum 1 having a film thickness of 18 μm before printing was used.

  The film thickness of the photosensitive layer 11 is preferably 10 μm or more which does not affect printing. Therefore, from Table 2, it can be said that it is preferable that 1.003 ≦ φc / φt <1.009.

  As described above, the developing roller 4 has the outer diameter φc of the central portion C of the elastic layer 41, the outer diameter φt of the end T of the developer adhesion region P of the developing roller 4, and the end of the elastic layer 41 of the developing roller 4. The image forming apparatus and the developing device of the present invention press-contact the developing roller 4 and the photosensitive drum 1 so that the relationship between R and the outer diameter φr satisfies φc> φt and φr> φt. Even if it is rotated in this state, there is no deviation in the axial direction, and toner leakage from the developing roller 4 can be prevented. Thereby, a good quality image can be formed.

  Further, by forming the developing roller 4 into a shape satisfying φt + 0.5 × (φc−φt) ≦ φr ≦ φt + 2.0 × (φc−φt), the image forming apparatus and the developing apparatus according to the present invention can prevent toner leakage. In addition to this, an image with good fog can be formed. Thereby, a higher quality image can be formed.

  Furthermore, by forming the developing roller 4 into a shape that satisfies 1.003 ≦ φc / φt <1.009, the image forming apparatus and the developing apparatus according to the present invention have a film thickness of the photosensitive layer 11 of the photosensitive drum 1. Therefore, the photosensitive drum 1 has a long life. Therefore, a high-quality image can be formed for a long time.

  The present invention is not limited to the developing roller 4 having the shape described in the first embodiment. For example, a developing roller having a shape as shown in FIG. 10 may be used. The developing roller shown in FIG. 10A may have a shape that increases the outer diameter so as to form an arc shape from the end T of the developer adhesion region to the end R of the elastic layer. Further, as shown in FIG. 10B, the outer diameter may be increased so as to be linear from the end T of the developer adhesion region to the end R of the elastic layer. Further, the developing roller shown in FIG. 10C has a shape that forms an arc shape opposite to that of FIG. 10A from the end T of the developer adhesion region to the end R of the elastic layer. In other words, the outer diameter may be increased. Furthermore, the developing roller shown in FIG. 10 (d) is partially flat from the end T of the developer adhesion region to the end R of the elastic layer, and from the end T to the end R. It may be a shape that increases the outer diameter. Even if it is such a shape, the effect similar to the above can be acquired.

[Embodiment 2]
The image forming apparatus and the developing apparatus described in the second embodiment use developing rollers having different outer diameters at one end on the developing gear side of the elastic layer of the developing roller and the other end. Hereinafter, a developing device and an image forming apparatus using the developing roller will be described with reference to the drawings. However, the same members as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  FIG. 11 is a diagram illustrating an appearance of the developing roller described in the second embodiment. As shown in FIG. 11, the developing roller 4 has an elastic layer 41 wound around a cylindrical conductive metal developing shaft 43 similar to that of the first embodiment. A developing gear 42 is attached to one end of the developing shaft 43 around which the elastic layer 41 is wound. The material of the elastic layer 41 is the same as that of the elastic layer 41 of the first embodiment. The developing roller 4 is rotationally driven by the developing gear 42.

  The elastic layer 41 of the developing roller 4 has a shape in which the outer diameter gradually decreases from the center of the elastic layer 41 to the end of the developer adhesion region, but the developer adhesion region P on the side having the development gear 43. When the size of the outer diameter φg of the end portion G of the toner is compared with the size of the outer diameter φh of the end portion H of the developer adhesion region P on the side opposite to the side having the developing gear 43, there is a shape satisfying φg> φh. is doing. Further, the outer diameter gradually increases from the end G or the end H of the developer adhesion region P to the end R of the elastic layer 41. That is, the elastic layer 41 has the outer diameter of the central portion C of the elastic layer 41 as φc, the outer diameter of the end G on the developing gear 43 side of the developer adhesion region P as φg, and the developer opposite to the end G. When the outer diameter of the end H of the adhesion region P is φh and the outer diameter of the end R of the elastic layer 41 is φr, it has a shape that satisfies φc ≧ φg> φh and φr> φg> φh. . Either φc or φr may be larger or the same size. Thereby, toner leakage from the developing roller 4 can be prevented. The developing roller 4 may have any shape as long as φc ≧ φg> φh and φr> φg> φh.

  The developing roller 4 is disposed so as to mesh the developing gear 42 and the photosensitive gear 12 with the photosensitive drum 1 described in the first embodiment, and the developing roller 4 and the photosensitive drum 1 are pressed against each other. . The developing roller 4 and the photosensitive drum 1 are composed of the elastic layer 41 and the photosensitive layer 11, for example, the outer diameter φr of both ends R of the developing roller 4 is 16.00 mm, and the outer diameter of the photosensitive drum 1 is 30.00 mm. Are arranged so that the NIP amount is 100 μm. At this time, the photosensitive drum 1 and the developing roller 4 are installed so that the central axes are balanced.

  As in the first embodiment, the photosensitive drum 1 is driven to rotate clockwise via the developing gear 42 of the developing roller 4, and the developing roller 4 is driven counterclockwise by a drive motor (not shown). By this driving, the toner is developed with the toner as in the first embodiment, the developed toner is transferred to the paper, and an image is formed on the paper by fixing the toner.

  As the rotational speed of the photosensitive drum and the developing roller increases, the photosensitive gear and the developing gear act in a direction away from each other, and in particular, a phenomenon occurs in which the amount of NIP on the gear side decreases. However, the developing roller 4 is installed so that the central axes of the developing roller 4 and the photosensitive drum 1 are parallel to each other. Further, the outer diameter φg of the end portion G of the elastic layer 41 of the developing roller 4 on the side of the developing gear 41 on the developing gear 41 side is larger than the outer diameter φh of the end portion H opposite to the end portion G. Thereby, the pressure applied to the contact portion between the developing roller 4 on the gear side and the photosensitive drum 1 is increased, and the decrease in the NIP amount caused by the rotation can be prevented.

  As a result, it is possible to prevent the occurrence of fogging caused by a decrease in the amount of NIP on the gear side and the occurrence of a white broach where no toner is developed. In order to prevent the reduction of the NIP amount on the gear side, there is a method in which the relationship between the central axis of the photosensitive drum and the central axis of the developing roller is set closer to the gear side. Since they are not parallel to each other, the jitter is affected. In the present invention, since the central axes are parallel to each other, such jitter is not affected.

  Here, the measurement of fogging with various developing rollers 4 in which the outer diameter φc of the central portion C of the elastic layer 41 and the outer diameter φg of the end portion G on the developing gear 43 side of the developer adhesion region P are changed. The results are shown below. The fog is measured by the same method as in the first embodiment. The fog near the end G on the gear side of the developer adhesion region P, the fog near the end H opposite to the end G, and the elasticity The fog of the central portion C of the layer 41 is measured, and the average value over time is described. The measured outer diameter φh of the end H of each roller is fixed at 16.00 mm, and the rotation speed of the photosensitive drum 1 is 145 rotations per minute. Further, the developing roller 17 has a rotational speed of 1.24 times the rotational speed of the photosensitive drum 1.

  From the above Table 3, it can be seen that the fogging of the end G is improved as the outer diameter φg is reduced. However, it can be seen that the fogging at the central portion C and the fogging at the end H side are deteriorated when φg> φc. On the other hand, if the outer diameter φg of the end G is too large, the pressure between the photosensitive drum 1 and the developing roller 4 is increased, and the force for rubbing the toner is increased, so that the toner is overcharged. This excessive charging of the toner causes scumming. From this result, in addition to the effects of the image forming apparatus and the developing apparatus described in the first embodiment, the elastic layer 41 of the developing roller 4 satisfies φc ≧ φg> φh, so that the developer adhesion region P is fogged. Get better. Further, since the central axes of the photosensitive drum 1 and the developing roller 4 are parallel to each other, a good image without jitter can be formed.

[Embodiment 3]
The image forming apparatus and the developing apparatus described in the third embodiment pay attention to the relationship between the outer diameter of the developing shaft with the developing roller 4 described in the first embodiment and the outer diameter of the conveying shaft of the conveying roller 5. . In the image forming apparatus and the developing apparatus described in the third embodiment, the same members as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, the developing roller 4 and the conveyance roller 5 are made of the same material as in the first embodiment, and are arranged so that the development roller 4 and the conveyance roller 5 are pressed against each other. The developing roller 4 and the photosensitive drum 1 are disposed so as to be in pressure contact with each other. The developing shaft 43 of the developing roller 4 has an outer diameter ψd in the developer adhesion region P that is, for example, 30.00 mm and is uniform in the axial direction.

  A semiconductive foamed elastic layer 51 having an outer diameter φs of 15.30 mm that is constant in the axial direction, for example, is formed on the transport shaft 53 of the transport roller 5. Further, the outer diameter ψs of the conveying shaft 53 is uniform in the axial direction and satisfies ψd> ψs. The conveying roller 5 and the developing roller 4 are in pressure contact with an NIP amount of 1.0 mm, for example.

  As shown in FIG. 5, the developing roller 4 is disposed between the photosensitive drum 1 and the conveying roller 5. Therefore, due to the pressure contact between the photosensitive drum 1 and the developing roller 4, the developing shaft 43 of the developing roller 4 bends in a direction away from the photosensitive drum 1, that is, in a direction approaching the conveying roller 5. Further, since the developing roller 4 has a shape in which the outer diameter φc of the central portion C of the elastic layer 41 is larger than the outer diameter φt of the end portion T of the developer adhesion region P, the pressure distribution between the developing roller 4 and the conveying roller 5. Increases at the center in the axial direction.

  As described above, in the developing roller 4 and the conveying roller 5, the relationship between the outer diameter Ψd of the developing shaft 43 of the developing roller 4 and the outer diameter Ψs of the conveying shaft 53 of the conveying roller 5 is the outer diameter Ψd> Ψs. . Thereby, since the conveyance shaft 53 of the conveyance roller 5 becomes easy to bend, the frictional force with the elastic layer 41 of the developing roller 4 concerning the foaming elastic layer 51 can be reduced.

  If the conveyance shaft of the conveyance roller is less bent than the development shaft of the development roller, the development shaft of the development roller is bent and the foamed elastic layer of the conveyance roller is recessed, and the elastic layer of the development roller and the conveyance roller are foamed. The elastic layer continues to be rubbed strongly. As a result, the foamed elastic layer is worn and it becomes difficult to convey the toner to the developing roller, so that the image transferred to the paper becomes faint. By doing as described above, the foamed elastic layer can be prevented from being worn, so that a good image can be formed on the paper.

  Table 4 below shows the amount of wear of the outer diameter ψs of the conveying shaft 53 of the conveying roller 5 and the foamed elastic layer 51 of the conveying roller 5. This is because the conveyance roller 5 having the conveyance shafts 53 with different outer diameters Ψs is used, and the amount of wear and the shaft at the axial end of the foamed elastic layer 51 after printing 20,000 sheets of A4 size paper (transverse feed). The amount of wear at the center of the direction is measured.

Since the amount of wear is 0.30 mm or more and the printed image is faint, it can be seen that the outer diameter Ψs ≦ 7.0 mm of the conveying shaft 53 is preferable. However, when Ψs = 5.0 mm, the deflection of the conveyance shaft 53 becomes large and the conveyance roller 5 rotates eccentrically, so that the toner conveyance amount changes. For this reason, density unevenness occurs in the horizontal band of the printed image. Therefore, by setting the outer diameter of the conveying shaft 53 of the conveying roller 5 to 5.0 mm <Ψs ≦ 7.0, in addition to the effects of the image forming apparatus and the developing apparatus described in the first embodiment, as described above. A good image without uneven density can be formed.

  Further, the image forming apparatus 1 of the present invention can be applied to a printer, a copying machine, a facsimile, a multifunction printer, and the like using an electrophotographic system.

It is a figure which shows the shape of the developing roller of a conventional developing device, and a photoreceptor. FIG. 2 is a diagram illustrating a pressure at a pressure contact portion between a developing roller and a photoreceptor in FIG. 1. 1 is a side sectional view for explaining the structure of an image forming apparatus of the present invention. FIG. 3 is a side cross-sectional view illustrating the structure of the developing device in the image forming apparatus of the present invention. The relationship among the developing roller, the photosensitive drum, and the conveying roller of the developing device of the present invention will be described. It is a figure which shows the external appearance shape of the developing roller of the developing device of this invention. FIG. It is a figure explaining the developing roller of the developing device of this invention, a photoconductive drum, and a sealing member. It is an expanded sectional view of the principal part of the developing roller of the developing device of the present invention. It is a figure which shows the pressure in the press-contact part of the developing roller and photosensitive drum in FIG. It is a figure which shows the cross-sectional shape of the modification of the developing roller of the developing device of this invention. It is a figure which shows the external appearance shape of the developing roller of the developing device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Exposure apparatus 4 Developing roller 5 Conveying roller 6 Developing blade 7 Transfer roller 8 Cleaning apparatus

Claims (7)

A developing device for developing an electrostatic latent image formed on an image carrier with a developer,
A developing roller that rotates around a developing shaft having an elastic layer formed of an elastic body on the surface and supplies the developer to the image carrier that is in contact with the developing roller;
A developing blade that contacts the elastic layer of the developing roller and regulates the layer thickness of the developer;
A seal member provided at a position in contact with an end of the elastic layer of the developing roller;
The elastic layer of the developing roller is
An outer diameter φc at the center of the elastic layer of the developing roller;
Outer diameter φr at both ends of the elastic layer of the developing roller;
The relationship between the outer diameter φt at a predetermined position between the end of the developer adhesion region where the developer adheres on the elastic layer of the developing roller and the end of the elastic layer is:
φc> φt and φr> φt are satisfied,
Further, the developing device has a shape satisfying φt + 0.5 × (φc−φt) ≦ φr ≦ φt + 2 × (φc−φt).   The developing device according to claim 1, wherein the predetermined position is an end of the developer adhesion region.   The developing device according to claim 1, wherein a minimum outer diameter of the elastic layer is in a developer adhesion region. The elastic layer of the developing roller is
The outer diameter φc at the center of the elastic layer of the developing roller with respect to the outer diameter φt at both ends of the developer adhesion region is a shape satisfying 1.003 ≦ φc / φt <1.009. The developing device according to any one of claims 1 to 3. A developing device for developing an electrostatic latent image formed on a photoreceptor with a developer,
A developing roller that rotates around a developing shaft having an elastic layer formed of an elastic body on a surface thereof, supplies the developer to the photosensitive member that contacts, and includes a gear at one end of the developing shaft;
A developing blade that contacts the elastic layer of the developing roller and regulates the layer thickness of the developer;
A seal member provided at a position in contact with an end of the elastic layer of the developing roller;
The elastic layer of the developing roller is
The outer diameter of the elastic layer center of the developing roller is φc,
Outer diameter φg of one end portion on the side having the gear among the end portions of the developer adhesion region,
An outer diameter φh of the other end portion of the developer adhesion region opposite to the one end portion;
The relationship with the outer diameter φr at both ends of the elastic layer of the developing roller is
A developing device having a shape satisfying φc ≧ φg> φh and φr>φg> φh. A transport roller that rotates around a transport shaft and transports the developer to the developing roller;
6. The outer diameter Ψd of the developing shaft of the developing roller with respect to the outer diameter Ψs of the conveying shaft of the conveying roller is 0.5 <Ψs / Ψd <0.8. The developing device according to claim 1.   7. An image forming apparatus for forming an image on a recording medium, wherein the image forming means for forming an image on the conveyed recording medium has the developing device according to claim 1. An image forming apparatus.