JP6204301B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image.

  In an image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic system, a developing device supplies toner to an electrostatic latent image formed on a photosensitive drum to develop the electrostatic latent image. Thus, a toner image is formed on the photosensitive drum. The developing device includes a developing roller (developer carrier) that is rotatably supported by a housing. The developing roller is disposed on the photosensitive drum with a predetermined gap, and carries a developer containing at least toner on the peripheral surface. Patent Document 1 discloses a developing roller disposed to face a photosensitive drum. Further, a technique in which a resin layer is provided on the surface of the developing roller is disclosed. A dipping method (a dipping method or a dipping method) is disclosed in which a developing roller is manufactured by dipping a base tube of a developing roller in a resin solution in which a resin material is previously dissolved.

JP 2009-300677 A

  As described above, when the developing roller is rotatably supported by the housing, the gap between the developing roller and the photosensitive drum may fluctuate and image defects may occur.

  The present invention has been made to solve the above-described problems, and provides an image forming apparatus in which image defects are less likely to occur due to a change in the interval between the developer carrier and the image carrier. With the goal.

  An image forming apparatus according to an aspect of the present invention includes an image carrier that rotates around an axis and forms an electrostatic latent image on a surface thereof, and a developing device that is disposed to face the image carrier. The developing device includes a housing and a shaft portion, is disposed at a distance from the image carrier, is supported by the housing so as to be rotatable around the shaft portion, and carries a developer on a peripheral surface thereof. A developer carrying member that is disposed on one end side in the axial direction of the developer carrying member, a drive transmission unit that transmits a rotational driving force to the developer carrying member, the peripheral surface of the developer carrying member, and the A regulating member that regulates an interval between the surface of the image carrier and the surface of the image carrier, and the developer carrier includes a cylindrical first substrate, and a first surface layer formed on the first substrate. The image carrier includes a cylindrical second base material, and a second surface layer formed on the second base material. By the immersion method in which the first base material and the second base material are immersed in a predetermined immersion tank so that the axial direction of the developer carrier and the image carrier is along the vertical direction, the first surface layer and the image carrier A second surface layer is formed, and the lower end side of the developer carrier and the image carrier when immersed is disposed opposite to the other end side of the axial direction opposite to the drive transmission unit. It is characterized by being.

  According to this configuration, the developer carrying member of the developing device is disposed at a distance from the image carrying member and is supported by the housing so as to be rotatable around the shaft portion. A developer is carried on the peripheral surface of the developer carrying member. A drive transmission unit disposed on one end side in the axial direction of the developer carrier transmits a rotational driving force to the developer carrier. In the developer carrying member, on one end side in the axial direction where the drive transmission unit is disposed, the drive transmission unit regulates the shaft unit, so that the position of the shaft unit is easily stabilized. Accordingly, the distance between the peripheral surface on one end side of the developer carrier and the surface of the image carrier is stably maintained by the regulating member. On the other hand, on the other end side of the developer carrying member in the axial direction opposite to the drive transmission portion, the shaft portion is not regulated by the drive transmission portion, and therefore the position of the shaft portion is likely to vary. As a result, the distance between the peripheral surface on the other end of the developer carrying member and the surface of the image carrying member is partially widened, and image defects corresponding to the rotation pitch of the developer carrying member are likely to occur. Even in such a case, according to the above configuration, the lower ends of the developer carrier and the image carrier when immersed are opposed to each other on the other end side opposite to the drive transmission unit in the axial direction. Are arranged. A portion where the first surface layer and the second surface layer are partially thick is partially formed on the lower end side during immersion. Therefore, on the other end side of the developer carrier, the distance between the peripheral surface on the other end side of the developer carrier and the surface of the image carrier is set to be partially narrow. For this reason, fluctuations in image density due to the rotation of the developer carrier are suppressed.

  In the above configuration, the drive transmission portion is connected to the first gear fixed to the shaft portion of the developer carrier and the first gear, and the second gear transmits rotational driving force to the first gear. It is preferable that a pressing force in a direction in which the developer carrier approaches the image carrier is applied to the developer carrier by meshing of the first gear and the second gear.

  According to this configuration, on one end side in the axial direction of the developer carrier, the peripheral surface of the developer carrier and the surface of the image carrier are interposed by the engagement of the first gear and the second gear via the restriction member. The interval of is stably maintained. On the other hand, on the other end side in the axial direction of the developer carrier, the pressing force due to the meshing of the first gear and the second gear is difficult to reach. However, the lower end sides of the developer carrying member and the image carrying member when immersed are arranged opposite to each other on the other end side opposite to the drive transmission unit in the axial direction. For this reason, the occurrence of image defects due to the rotation of the developer carrier is suppressed.

  In the above configuration, the image forming apparatus further includes a support frame that rotatably supports the image carrier, and the restricting member is a cylindrical member that is pivotally supported by the shaft portion, and a circumferential surface of the cylindrical member is the image. It is desirable that the distance between the peripheral surface of the developer carrier and the surface of the image carrier is regulated by contacting the surface of the carrier or the support frame.

  According to this configuration, the interval between the peripheral surface of the developer carrier and the surface of the image carrier is regulated by the regulation member made of a cylindrical member.

  In the above configuration, the first base material is made of aluminum, the developer carrier further includes a first oxide layer formed on a surface of the first base material, and the first surface layer includes the first surface layer. It is desirable that it be formed on the surface of one oxide layer.

  According to this configuration, the first oxide layer is formed on the first base material made of aluminum, whereby the adhesion force of the first surface layer to the first base material is increased. As a result, peeling of the first surface layer is suppressed.

  In the above configuration, the second base material is made of aluminum, the image carrier further includes a second oxide layer formed on a surface of the second base material, and the second surface layer is the second surface layer. It is desirable that it be formed on the surface of the oxide layer.

  According to this configuration, the adhesion of the second surface layer to the second substrate is increased by forming the second oxide layer on the second substrate made of aluminum. As a result, the peeling of the second surface layer is further suppressed.

  According to the present invention, there is provided an image forming apparatus in which an image defect is less likely to occur due to a change in the distance between the developer carrier and the image carrier.

1 is a cross-sectional view illustrating an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view of a developing device according to an embodiment of the present invention. Schematic diagram (A) showing the relationship between the lengths in the axial direction of the image carrier and the developer carrier according to the embodiment of the present invention, and the state of the film thickness at the ends of the image carrier and the developer carrier. It is a typical sectional view (B) shown. 5 is graphs (A) and (B) showing the distribution of the film thickness in the axial direction of the developer bearing member according to the embodiment of the present invention. 1 is a schematic plan view of a developing device according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be applied to an image forming apparatus employing an electrophotographic system, such as a copier, a printer, a facsimile machine, and a multifunction machine having these functions.

  FIG. 1 is a front sectional view showing the structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 includes an apparatus main body 11 including an image forming unit 12, a fixing device 13, a paper feeding unit 14, a paper discharging unit 15, a document reading unit 16, and the like.

  The apparatus main body 11 includes a lower main body 111, an upper main body 112 disposed opposite to the lower main body 111, and a connecting portion 113 interposed between the upper main body 112 and the lower main body 111. . The connecting portion 113 is a structure for connecting the sheet discharge portion 15 between the lower main body 111 and the upper main body 112 and is erected from the left and rear portions of the lower main body 111. It has an L shape in plan view. The upper body 112 is supported on the upper end portion of the connecting portion 113.

  The lower main body 111 includes the image forming unit 12, the fixing device 13, and the paper feeding unit 14, and the upper main body 112 is mounted with the document reading unit 16.

  The image forming unit 12 executes an image forming operation for forming a toner image on the paper P fed from the paper feeding unit 14. The image forming unit 12 uses a yellow unit 12Y using a yellow toner, a magenta unit 12M using a magenta toner, and a cyan toner, which are sequentially arranged horizontally from the upstream side to the downstream side. A cyan unit 12C, a black unit 12Bk using black toner, an intermediate transfer belt 125 stretched between a plurality of rollers such as a driving roller 125A so as to be able to run endlessly in the sub-scanning direction in image formation, and an intermediate transfer A secondary transfer roller 196 that contacts the outer peripheral surface of the belt 125 and a belt cleaning device 198 are provided.

  Each color unit of the image forming unit 12 includes a photosensitive drum 121 (image carrier), a developing device 122 that supplies toner (developer) to the photosensitive drum 121, and a toner cartridge (not shown) that contains toner. The charging device 123 and the drum cleaning device 127 are integrally provided. An exposure device 124 for exposing each photosensitive drum 121 is horizontally disposed below the adjacent developing device 122.

  The photosensitive drum 121 has a cylindrical shape and is rotated around an axis. The photosensitive drum 121 carries a toner image in which an electrostatic latent image is formed on its peripheral surface and the electrostatic latent image is made visible by toner. In this embodiment, the photoreceptor drum 121 is a known organic (OPC) photoreceptor, and a charge generation layer, a charge transport layer, and the like are formed on the surface by the same dipping method as the developing roller 83 described later. As shown in FIG. 1, the photosensitive drum 121 is supported by a drum unit 12H (support frame) so as to be rotatable around a predetermined axis. The drum unit 12 is detachable from the lower housing 111.

  The developing device 122 is disposed to face the photosensitive drum 121. The developing device 122 supplies toner to the electrostatic latent image on the peripheral surface of the photoconductive drum 121 rotating in the direction of the arrow and stacks the toner, and the toner corresponding to the image data is formed on the peripheral surface of the photoconductive drum 121. Form an image. Each developing device 122 is appropriately supplied with toner from the toner cartridge.

  The charging device 123 is provided at a position directly below each photosensitive drum 121. The charging device 123 uniformly charges the peripheral surface of each photosensitive drum 121.

  The exposure device 124 is provided below each charging device 123. The exposure device 124 irradiates the peripheral surface of the charged photosensitive drum 121 with laser light corresponding to each color based on image data input from a computer or the like or image data acquired by the document reading unit 16, and each photosensitive member. An electrostatic latent image is formed on the peripheral surface of the drum 121. The exposure device 124 irradiates the laser beam in accordance with a preset exposure light quantity in order to form a predetermined latent image potential on the photosensitive drum 121. The drum cleaning device 127 is provided at the left position of each photoconductive drum 121 and removes residual toner on the peripheral surface of the photoconductive drum 121 for cleaning. The charging device 123 and the drum cleaning device 127 are integrally provided in the drum unit 12H.

  The intermediate transfer belt 125 is an endless belt, and is a conductive soft belt having a laminated structure including a base layer, an elastic layer, and a coat layer. The intermediate transfer belt 125 is wound around a plurality of stretching rollers arranged in a substantially horizontal direction above the image forming unit 12. The tension roller is disposed in the vicinity of the fixing device 13 and drives the intermediate transfer belt 125 to rotate, and the driven roller 125E rotates at a predetermined interval in the horizontal direction with respect to the drive roller 125A. ,including. The intermediate transfer belt 125 is driven to rotate clockwise in FIG. 1 by applying a rotational driving force to the driving roller 125A.

  A secondary transfer bias application unit (not shown) is electrically connected to the secondary transfer roller 196. The toner image formed on the intermediate transfer belt 125 is transferred to the paper P conveyed from the lower conveying roller pair 192 by a transfer bias applied between the secondary transfer roller 196 and the driving roller 125A. The belt cleaning device 198 is disposed to face the driven roller 125E via the intermediate transfer belt 125.

  The fixing device 13 includes a heating roller 132 provided with an energization heating element such as a halogen lamp as a heating source, and a pressure roller 134 disposed to face the heating roller 132. The fixing device 13 heats the toner image on the paper P transferred by the image forming unit 12 from the heating roller 132 while the paper P passes through the fixing nip portion between the heating roller 132 and the pressure roller 134. To give a fixing process. The color-printed paper P that has been subjected to the fixing process is discharged toward a paper discharge tray 151 provided at the top of the apparatus main body 11 through a paper discharge conveyance path 194 extending from the top of the fixing device 13. .

  The sheet feeding unit 14 is provided with a manual feed tray 141 that can be freely opened and closed on the right side wall of the apparatus main body 11 in FIG. And. The paper feed cassette 142 accommodates a sheet bundle P1 formed by stacking a plurality of sheets P. A pick-up roller 143 is provided above the paper feed cassette 142, and the pick-up roller 143 feeds the uppermost paper P in the paper bundle P 1 accommodated in the paper feed cassette 142 toward the paper transport path 190. The manual feed tray 141 is a tray that is provided at a lower position on the right surface of the lower main body 111 and feeds paper P one by one toward the image forming unit 12 by manual feed operation.

  A paper conveyance path 190 extending in the vertical direction is formed at the left position of the image forming unit 12. The paper conveyance path 190 is provided with a conveyance roller pair 192 at an appropriate position. The conveyance roller pair 192 directs the paper P fed from the paper supply unit 14 to the secondary transfer nip portion having the secondary transfer roller 196. Transport.

  The paper discharge unit 15 is formed between the lower main body 111 and the upper main body 112. The paper discharge unit 15 includes a paper discharge tray 151 formed on the upper surface of the lower main body 111. The paper discharge tray 151 is a tray from which the paper P on which the toner image is formed by the image forming unit 12 is discharged after the fixing device 13 performs the fixing process.

  The document reading unit 16 includes a contact glass 161 mounted on the upper surface opening of the upper main body 112 for placing a document, an openable / closable document pressing cover 162 for pressing the document placed on the contact glass 161, And a scanning mechanism 163 that scans and reads an image of the document placed on the contact glass 161. The scanning mechanism 163 optically reads an image of an original using an image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), and generates image data. In addition, the apparatus main body 11 has an image processing unit (not shown) that generates an image formation image from the image data.

<Configuration of developing device>
Next, the developing device 122 will be described in detail. FIG. 2 is a cross-sectional view in the vertical and horizontal directions schematically showing the internal structure of the developing device 122. FIG. 3 is a schematic diagram (A) showing the relationship between the lengths of the photosensitive drum 121 and the developing roller 83 in the axial direction according to the present embodiment, and shows the film thickness at both ends of the photosensitive drum 121 and the developing roller 83. It is a typical sectional view (B) shown. FIG. 4 is graphs (A) and (B) showing the distribution of the film thickness in the axial direction of the developing roller 83. FIG. 5 is a schematic plan view of the developing device 122 according to the present embodiment. In FIG. 5, the magnetic roller 82 and the developing roller 83 are shifted to the left for the sake of explanation.

  The developing device 122 according to the present embodiment employs a touch-down developing method including a developing roller 83 and a magnetic roller 82. The developing device 122 includes a developing housing 80 (housing) that defines an internal space of the developing device 122. The developing housing 80 is provided with a developer storing portion 81 for storing a developer including a non-magnetic toner and a magnetic carrier charged to a predetermined polarity. Further, inside the developing housing 80, there are a magnetic roller 82 disposed above the developer reservoir 81, and a developing roller 83 (developer carrier) disposed opposite to the magnetic roller 82 at a position obliquely above the magnetic roller 82. ) And a developer regulating blade 84 disposed opposite to the magnetic roller 82. Further, the developing device 122 includes a driving unit 962 and a developing bias applying unit 88 (FIG. 2).

  Referring to FIGS. 2 and 5, developer storage unit 81 includes two adjacent first developer storage chambers 81 a and second developer storage chambers 81 b that extend in the longitudinal direction of developing device 122. The second developer storage chamber 81 b is disposed to face the magnetic roller 82. The first developer storage chamber 81a and the second developer storage chamber 81b are separated from each other by a partition plate 801 that is integrally formed with the development housing 80 and extends in the longitudinal direction, but at both ends in the longitudinal direction (axial direction). The first communication part 81c and the second communication part 81d communicate with each other. The first developer storage chamber 81a and the second developer storage chamber 81b accommodate a first screw feeder 85 and a second screw feeder 86, respectively, that agitate and convey the developer by rotating around the axis. Although the 1st screw feeder 85 and the 2nd screw feeder 86 are rotationally driven by the drive part 962, the rotation direction is set to the mutually reverse direction. As a result, the developer is circulated and conveyed between the first developer storage chamber 81a and the second developer storage chamber 81b as shown by arrows D1, D3, D2, and D4 in FIG. By this stirring, the toner and the carrier are mixed, and the toner is charged positively, for example. A first screw gear 85G and a second screw gear 86G are fixed to the rear end portions of the first screw feeder 85 and the second screw feeder 86, respectively.

  The magnetic roller 82 is rotatably supported by the developing housing 80 so as to face the developing roller 83 along the longitudinal direction of the developing device 122. The magnetic roller 82 is driven to rotate clockwise in FIG. Inside the magnetic roller 82, a fixed so-called magnet roll (fixed magnet, not shown) is arranged. The magnet roll has a plurality of magnetic poles. In this embodiment, the magnet roll has a drawing pole 821, a regulation pole 822, and a main pole 823. The scooping pole 821 faces the developer storage section 81, the regulation pole 822 faces the developer regulation blade 84, and the main pole 823 faces the developing roller 83.

  The magnetic roller 82 magnetically pumps (receives) the developer from the developer reservoir 81 onto its peripheral surface 82A by the magnetic force of the pumping pole 821. The magnetic roller 82 magnetically supports the developer drawn up as a developer layer (magnetic brush layer) on the peripheral surface 82A. The magnetic roller 82 supplies toner to the developing roller 83. As the magnetic roller 82 rotates, the developer is conveyed toward the developer regulating blade 84.

  The developer regulating blade 84 is disposed to face the magnetic roller 82 on the upstream side of the developing roller 83 when viewed from the rotation direction of the magnetic roller 82. The developer regulating blade 84 regulates the layer thickness of the developer magnetically attached to the peripheral surface 82A of the magnetic roller 82. The developer regulating blade 84 forms a regulating gap G having a predetermined size with the peripheral surface 82 </ b> A of the magnetic roller 82. Thereby, a uniform developer layer having a predetermined thickness is formed on the peripheral surface 82A.

  The developing roller 83 is disposed so as to extend along the longitudinal direction of the developing device 122 and in parallel with the magnetic roller 82, and is driven to rotate clockwise in FIG. The developing roller 83 is disposed to face the photosensitive drum 121. The developing roller 83 includes a shaft portion 83J (FIGS. 3A and 5). The shaft portion 83J serves as a rotation shaft in the rotation of the developing roller 83. The developing roller 83 has a cylindrical shape and is supported by the developing housing 80 so as to be rotatable around a shaft portion 83J. The developing roller 83 rotates while being in contact with the developer layer held on the peripheral surface 82A of the magnetic roller 82, and receives the toner from the developer layer to carry the toner layer (developer). Have At the time of development in which the development operation is performed, the development roller 83 supplies the toner of the toner layer to the peripheral surface of the photosensitive drum 121.

  The developing roller 83, the magnetic roller 82, the first screw feeder 85, and the second screw feeder 86 are rotationally driven by a drive unit 962 (FIG. 2). As shown in FIG. 5, a roller gear 83G (first gear) is fixed to the rear end portion of the shaft portion 83J of the developing roller 83. An input gear 82G (second gear) is fixed to the rear end portion of the magnetic roller 82. In FIG. 5, for the sake of explanation, a gap is formed between the roller gear 83G and the input gear 82G. Actually, however, the input gear 82G is connected to the roller gear 83G, and the input gear 82G. Transmits the rotational driving force to the roller gear 83G. The roller gear 83G and the input gear 82G function as a drive transmission unit of the present invention. The drive transmission unit is disposed on one end side in the axial direction of the developing roller 83, and transmits a rotational driving force to the developing roller 83 via the shaft unit 83J.

  The driving unit 962 (FIG. 2) is a motor that generates a rotational driving force. The drive unit 962 is connected to the input gear 82G. The rotational driving force input to the input gear 82G is transmitted to the roller gear 83G and the second screw gear 86G. The roller gear 83G transmits the rotational driving force to the developing roller 83. The second screw gear 86G transmits the rotational driving force to the second screw feeder 86. The second screw gear 86G is further connected to the first screw gear 85G. The first screw gear 85G transmits the rotational driving force to the first screw feeder 85. As a result, the developing roller 83, the magnetic roller 82, the first screw feeder 85, and the second screw feeder 86 are rotated synchronously by the rotational driving force generated by the driving unit 962. In this embodiment, the pressing force in the direction in which the developing roller 83 approaches the photosensitive drum 121 (FIG. 3B, arrow DR in FIG. 5) due to the meshing of the roller gear 83G and the input gear 82G is applied to the developing roller 83. To be granted.

  A gap S (FIG. 2) having a predetermined size is formed between the peripheral surface 83A of the developing roller 83 and the peripheral surface 82A of the magnetic roller 82. The gap S is set to 0.3 mm, for example. The developing roller 83 is disposed so as to face the photosensitive drum 121 through an opening formed in the developing housing 80, and a gap (interval) having a predetermined dimension is also formed between the peripheral surface 83A and the peripheral surface of the photosensitive drum 121. Is formed. In the present embodiment, the gap is set to 0.12 mm.

  The developing bias applying unit 88 (FIG. 2) applies a developing bias in which an AC voltage is superimposed on a DC voltage to the magnetic roller 82 and the developing roller 83. A high AC voltage is applied between the photosensitive drum 121 and the developing roller 83 and between the developing roller 83 and the magnetic roller 82. In particular, toner is supplied from the magnetic roller 82 to the developing roller 83, and further, toner is supplied from the developing roller 83 to the photosensitive drum 121. Therefore, the movement of the toner is compared with known one-component and two-component developing devices. Therefore, a high alternating voltage is applied to the developing roller 83.

  Referring to FIG. 5, the developing device 122 further includes a reverse conveyance unit 86 </ b> A and a developer discharge unit 87. The reverse conveyance unit 86A is a screw blade fixed coaxially with the second screw feeder 86 at the front end portion of the second developer storage chamber 81b. However, the screw blades of the reverse conveying unit 86 </ b> A are arranged in the opposite direction to the screw blades of the second screw feeder 86. 86 A of reverse conveyance parts are arrange | positioned facing the front end side of the 2nd communication part 81d. The reverse conveyance unit 86A rotates integrally with the second screw feeder 86, pushes back the developer conveyed by the second screw feeder 86 in the reverse direction, and partially retains the developer.

  The developer discharge portion 87 communicates with the second developer storage chamber 81b in front of the reverse conveyance portion 86A. The developer discharge portion 87 includes a cylindrical wall portion having a space portion therein, and a discharge screw 87A that rotates in the space portion. The discharge screw 87A is a screw blade fixed on the same axis as the second screw feeder 86. The discharge screw 87A is disposed in the same direction as the screw blades of the second screw feeder 86. When a part of the developer passes over the reverse conveyance portion 86A and flows into the developer discharge portion 87 from the developer retention portion formed by the reverse conveyance portion 86A, the developer is moved forward (arrow of FIG. 5) by the discharge screw 87A. After being conveyed to D5), it is discharged from a discharge port (not shown). As described above, the present embodiment employs trickle technology in which a part of the developer is discharged from the inside of the developing device 122. In addition, in order to supplement the carrier to the developing device 122, the carrier may be accommodated together with the toner in a toner cartridge (not shown), or another carrier supply tank may be provided.

  With reference to FIG. 3A, in the present embodiment, the length of the photosensitive drum 121 in the axial direction is set slightly larger than the length of the developing roller 83 in the axial direction. The developing roller 83 includes a tracking roller 83K. The tracking roller 83K is a cylindrical member that is pivotally supported by the shaft portion 83J of the developing roller 83. The tracking roller 83K is a thin plate-like member having a slight thickness in the axial direction of the developing roller 83. The circumferential surface of the tracking roller 83K is in contact with both ends (exposed portions 121M) of the surface of the photosensitive drum 121, so that the gap (gap) between the peripheral surface 83A (FIG. 2) of the developing roller 83 and the surface of the photosensitive drum 121 is reached. ) Is regulated. In another embodiment, the peripheral surface of the tracking roller 83K abuts on the outer wall of the drum unit 12H (FIG. 1) that rotatably supports the photosensitive drum 121, and the peripheral surface 83A of the developing roller 83 and the photosensitive member. The distance from the surface of the drum 121 may be regulated.

  With reference to FIG. 3B, the developing roller 83 includes a cylindrical sleeve 830 (first base material) and a coat layer 83C (first surface layer) formed on the sleeve 830. The sleeve 830 having a diameter of 12 to 20 mm is mainly used according to the specifications of the developing device 122. The photosensitive drum 121 includes a cylindrical drum base tube 120 (second base material) and a functional layer 120C (second surface layer) formed on the drum base tube 120. It should be noted that the outside of the functional layer 120C in the axial direction, that is, both ends of the photosensitive drum 121 are exposed after the formation of the functional layer 120C and the exposed portion 121M (FIG. A)) is formed. The aforementioned tracking roller 83K is in contact with the exposed portion 121M.

  The sleeve 830 of the developing roller 83 is made of aluminum. The coat layer 83C of the developing roller 83 is formed by the following immersion method. First, the outer peripheral surface of the sleeve 830 is anodized to form an alumite layer (first oxide layer) having a thickness of 10 μm. By forming the oxide layer on the sleeve 830 made of aluminum, the adhesion force of the coat layer 83C to the sleeve 830 is increased. As a result, peeling of the coat layer 83C is suppressed. Thereafter, the surface of the sleeve 830, that is, the surface of the alumite layer is heat-treated at 120 ° C. for 10 minutes or more. This heat treatment is performed in order to intentionally generate a crack in the sleeve 830 in advance in order to suppress the occurrence of a crack in the drying process of the coat layer 83C. The time for the heat treatment is determined in advance, for example, more than the time required for the drying step. The heat treatment is always performed at a constant temperature for a certain time. As a result, almost constant cracks are generated in all the sleeves 830 subjected to the heat treatment. After the heat treatment, a process of forming a coat layer 83C on the alumite layer is performed. Specifically, an alcohol-soluble nylon resin (100 parts by weight) as a binder resin, titanium oxide (50 to 125 parts by weight) as a pigment, and methanol (800 parts by weight) as a dispersion medium have a diameter of 1.0 mm. A mixed solution is prepared by mixing for about 48 hours with a zirconia bead in a ball mill. An alumite-treated sleeve 830 is immersed in the mixed solution for a predetermined time, and then pulled up and dried in a high temperature environment of 130 ° C. for 10 minutes. The sleeve 830 is immersed in the mixed liquid and pulled up so that the cylindrical axial direction is along the vertical direction. At this time, the excess liquid mixture is peeled off by a polytetrafluoroethylene blade. As a result, a sleeve 830 coated with a coat layer 83C having a thickness of 2 μm to 11 μm is manufactured. Thus, before the coating layer 83C is coated, cracks are generated in the alumite layer by heat treatment in advance. For this reason, the conductive agent (pigment) contained in the coat layer 83C is prevented from being unevenly distributed due to the influence of convection generated in the coat layer 83C when the coat layer 83C is dried. As a result, it is possible to form the coat layer 83C in which the conductive material is uniformly dispersed.

  The functional layer 120C of the photosensitive drum 121 is also formed by the dipping method in the same manner as the coat layer 83C. The functional layer 120 </ b> C includes a known charge generation layer and charge transport layer having a function for forming an electrostatic latent image on the surface of the photosensitive drum 121. Note that an alumite layer (second oxide layer) is formed in advance on the surface of the drum base tube 120 made of aluminum, and then a functional layer 120C is formed on the alumite layer. For this reason, the adhesion force of the functional layer 120C to the drum base tube 120 is increased. As a result, peeling of the functional layer 120C is suppressed.

  On the other hand, when the coat layer 83C and the functional layer 120C are formed by the dipping method as described above, the mixed liquid adhering to the surfaces of the sleeve 830 and the drum base tube 120 is likely to sag downward due to the influence of gravity during pulling. For this reason, a roller thick layer portion 83C1 that is a partially thick coat layer 83C is formed on the surface of the sleeve 830 positioned on the lower end side during immersion (FIG. 3B). ). In addition, a roller thin layer portion 83C2, which is a coat layer 83C that is partially thinner than the central portion in the axial direction, is formed on the surface of the sleeve 830 that is positioned on the upper end side when immersed. Similarly, a drum thick layer portion 120C1, which is a functional layer 120C that is partially thicker than the central portion in the axial direction, is formed on the surface of the drum base tube 120 located on the lower end side during immersion. In addition, a drum thin layer portion 120C2, which is a functional layer 120C that is partially thinner than the central portion in the axial direction, is formed on the surface of the drum base tube 120 that is positioned on the upper end side during immersion.

  FIG. 4A shows the distribution of film thickness on the lower end side of the coat layer 83 </ b> C formed on the sleeve 830 of the developing roller 83. On the other hand, FIG. 4B shows the distribution of film thickness on the upper end side of the coat layer 83 </ b> C formed on the sleeve 830. In either case, the horizontal axis indicates the distance from the end of the sleeve 830, and the vertical axis indicates the film thickness corresponding to each position in the axial direction as a difference with respect to the average film thickness of the coat layer 83C. As shown in FIGS. 4A and 4B, the length of the thin portion at the upper end of the coat layer 83C is longer than the length of the thick portion at the lower end. Further, the maximum film thickness decrease (3 μm) at the upper end of the coat layer 83C is a value approximated to the maximum film thickness increase (3.5 μm) at the lower end. Thus, the axial length of the roller thin layer portion 83C2 tends to be longer than the axial length of the roller thick layer portion 83C1 due to the influence of gravity during pulling. Similarly, the axial length of the drum thin layer portion 120C2 tends to be longer than the axial length of the drum thick layer portion 120C1.

  With reference to FIG. 3B and FIG. 5, in the present embodiment, the lower end side when the developing roller 83 and the photosensitive drum 121 are immersed is the other end side opposite to the drive transmission portion 83 </ b> R in the axial direction. They are arranged opposite to each other. That is, as shown in FIG. 3B, the roller thick layer portion 83C1 is disposed to face the drum thick layer portion 120C1, and the drum thin layer portion 120C2 is disposed to face the roller thin layer portion 83C2. In FIG. 5, the thickness and distribution of the coat layer 83C are exaggerated for explanation.

  Referring to FIG. 5, the drive transmission portion 83 </ b> R disposed on the rear end side (one axial end side) of the developing roller 83 transmits a rotational driving force to the developing roller 83. On the rear end side of the developing roller 83, the drive transmission portion 83R regulates the shaft portion 83J, so that the position of the shaft portion 83J is easily stabilized. In particular, as described above, the pressing force in the direction in which the developing roller 83 approaches the photosensitive drum 121 is applied to the developing roller 83 by the meshing of the roller gear 83G and the input gear 82G (arrow DR in FIG. 5). Accordingly, the distance between the peripheral surface 83A (FIG. 2) on the rear end side of the developing roller 83 and the surface of the photosensitive drum 121 is stably maintained by the tracking roller 83K (FIG. 3).

  Of the developing roller 83, the front end side (the other end side in the axial direction) opposite to the drive transmission portion 83 </ b> R is not easily pressed by the meshing between the roller gear 83 </ b> G and the input gear 82 </ b> G. For this reason, since the shaft part 83J is not regulated by the drive transmission part 83R, the position of the shaft part 83J tends to fluctuate. In particular, the shaft 83J of the developing roller 83 is supported by the developing housing 80 via a ball bearing (not shown). Further, the developing roller 83 has an outer periphery touch and eccentricity within a predetermined tolerance range. In addition, the ball bearing also has a predetermined play. For this reason, the gap between the developing roller 83 and the photosensitive drum 121 is likely to fluctuate due to these influences. At this time, if the gap is larger on the front end side of the developing roller 83 than on the rear end side of the developing roller 83, the toner image on the photosensitive drum 121 is reduced in density or according to the rotation pitch of the developing roller 83. Density unevenness occurs.

  On the other hand, in the present embodiment, the lower end side when the developing roller 83 and the photosensitive drum 121 are immersed is arranged opposite to each other on the other end side (front end side) opposite to the drive transmission portion 83R in the axial direction. Yes. On the lower end side at the time of immersion, portions where the thickness of the coat layer 83C and the functional layer 120C are partially thick (the roller thick layer portion 83C1 and the drum thick layer portion 120C1) are formed. Therefore, on the front end side of the developing roller 83, the interval between the circumferential surface 83A of the developing roller 83 and the surface of the photosensitive drum 121 is set to be partially narrow. For this reason, even if there is a region where the circumferential surface 83A of the developing roller 83 and the surface of the photosensitive drum 121 partially expand according to the rotation period of the developing roller 83, the gap on the front end side of both is Widening compared to the gap on the rear end side is suppressed. As a result, it is possible to prevent the toner image from having a density drop and density unevenness corresponding to the rotation pitch of the developing roller 83.

  Furthermore, in this embodiment, the touch-down development method is adopted as described above. In the developing device 122, a magnetic brush composed of toner and carrier is formed on the peripheral surface of the magnetic roller 82. The coat layer 83C of the developing roller 83 may be worn due to the strong scraping force of the magnetic brush. The scraping power of the magnetic brush varies with the toner concentration in the magnetic brush. In particular, when the toner concentration is low and the surface of the carrier is easily exposed, the scraping force of the magnetic brush increases and the wear of the coat layer 83C is promoted. Referring to FIG. 5, the second screw feeder 86 gradually supplies the developer to the magnetic roller 82 while conveying the developer forward. Further, when the toner is consumed in the developing roller 83, the developer having a low toner concentration is collected in the second developer storage chamber 81b as needed. For this reason, in the second developer storage chamber 81b, the toner concentration gradually decreases from the rear end side toward the front end side. That is, in the developer carried on the magnetic roller 82, the toner density is relatively lower on the front side of the magnetic roller 82. Therefore, as described above, an area where the scraping force by the magnetic brush on the magnetic roller 82 is strong (area H in FIG. 5) is generated. Such a phenomenon becomes conspicuous when the image forming apparatus 1 continuously prints a high density image.

  In the present embodiment, as described above, the lower end side when the developing roller 83 is immersed, in which the coating layer 83C is relatively thick, is disposed on the front end side of the developing device 122. Therefore, even when receiving a strong scraping force of the magnetic brush, the front end side coat layer 83C is prevented from being thinner than the rear end side coat layer 83C. Further, the coat layer 83C is prevented from being peeled off by the mechanical force of the magnetic brush. Note that, on the front end side of the magnetic roller 82, the toner density is low, and as a result, the chargeability of the toner tends to be high. As a result, on the front end side of the developing roller 83, the toner is not easily developed on the photosensitive drum 121, and the density is likely to decrease. However, as described above, the gap between the photosensitive drum 121 and the developing roller 83 is set to be partially narrow on the front end side of the developing roller 83, so that the developing action is promoted and density reduction is prevented. .

  In the present embodiment, the developing device 122 includes a developer discharging unit 87. By gradually replacing the developer, particularly the carrier, in the developer reservoir 81, the life of the developer is maintained long. As a result, a stable image is formed over a long period of time. Referring to FIG. 5, the toner concentration is low on the downstream side of the second developer storage chamber 81 b and contains a large amount of carriers, which is desirable for discharging the developer. Most of the developer retention portion K formed by the reverse conveyance portion 86A is conveyed to the first developer storage chamber 81a side via the second communication portion 81d. Further, a part of the developer gets over the reverse conveying portion 86A as described above and is discharged from the developer discharging portion 87.

  Thus, the amount of developer carried on the circumferential surface increases on the front end side of the magnetic roller 82 due to the influence of the staying portion K formed on the downstream side of the second developer storage chamber 81b. As a result, the amount of developer passing through the developer regulating blade 84 (FIG. 2) also increases compared to the rear end side, so that the scraping force of the magnetic brush as described above is likely to further increase. Thus, even when the developer discharge portion 87 is formed on the downstream side of the second developer storage chamber 81b, the lower end side when the developing roller 83 is immersed is arranged on the front end side of the developing device 122. Therefore, thinning of the coat layer 83C is suppressed.

  The image forming apparatus 1 according to each embodiment of the present invention has been described above, but the present invention is not limited to this, and for example, the following modified embodiment can be adopted.

  (1) Although the above embodiment has been described using a full-color machine as the image forming apparatus 1, the present invention is not limited to this. The image forming apparatus 1 may be a monochrome machine that prints monochrome images.

  (2) In the above-described embodiment, the second screw feeder 86 is described as transporting the developer forward from the roller gear 83G side, but the present invention is not limited to this. The second screw feeder 86 may be configured to convey the developer from the front toward the roller gear 83G.

  (3) In the above embodiment, the reverse conveyance unit 86 </ b> A (developer retention unit) has been described in the form of partially retaining the developer in order to discharge the developer from the developer discharge unit 87. The present invention is not limited to this. A bearing portion (not shown) that rotatably supports the second screw feeder 86 is attached to the developing housing 80 at the downstream end of the second screw feeder 86 in the transport direction. 86 A of reverse conveyance parts may retain a developer partially in order to suppress the approach of the developer to said bearing part. Further, the developing device to which the present invention is applied is not limited to the touch-down method. The present invention may be applied to other two-component and one-component developing devices.

Next, preferred modes of the photosensitive drum 121 and the developing roller 83 in the image forming apparatus will be described based on examples. In addition, each subsequent Example was performed on the following experimental conditions.
<Experimental conditions>
Print speed: 30 sheets / min Photoconductor drum 121: OPC drum Peripheral speed of photoconductor drum 121: 180 mm / sec
Developing roller 83: Anodized surface treatment + nylon resin coating Peripheral speed of developing roller 83: Peripheral speed ratio with respect to photosensitive drum 121 (with rotation)
-Peripheral speed of magnetic roller 82: Peripheral speed ratio 1.1 (counter rotation) with respect to developing roller 83
-Gap between the photosensitive drum 121 and the developing roller 83: 0.12 mm
・ Gap between magnetic roller 82 and developing roller 83: 0.3 mm
-Surface potential of the photosensitive drum 31: + 430V (background portion), + 100V (image portion)
Developing bias applied to developing roller 83: AC voltage frequency 3.7 kHz, Duty 27%, Vpp 1500 V, DC voltage 190 V
Development bias applied to the magnetic roller 82: AC voltage frequency 3.7 kHz, Duty 73%, Vpp 650 V, DC voltage 490 V
-Average toner particle size: 6.8 μm (positive charge)

  In Example 1, as in the above-described embodiment, the lower end side when the photosensitive drum 121 and the developing roller 83 are immersed is the front end side of the developing device 122 (the opposite side to the roller gear 83G, hereinafter the reaction driving side). Arranged). In Comparative Example 1, the lower end side when the developing roller 83 is immersed is disposed on the rear end side of the developing device 122 (the roller gear 83G side, hereinafter referred to as the drive side), and the lower end side when the photosensitive drum 121 is immersed is the embodiment. 1 is disposed on the front end side of the developing device 122. Further, in Comparative Example 2, the lower end side when the photosensitive drum 121 and the developing roller 83 are immersed is arranged on the rear end side (drive side) of the developing device 122. Hereinafter, the results of Example 1 are shown in Table 1, the results of Comparative Example 1 are shown in Table 2, and the results of Comparative Example 2 are shown in Table 3. In each experiment, the rotation pitch unevenness of the developing roller 83 in the halftone image is evaluated while the peak-to-peak voltage (Vp-p) of the AC voltage of the developing bias applied to the developing roller 83 is changed. In each table, L indicates that a leak has occurred between the photosensitive drum 121 and the developing roller 83, and ◯ indicates that no rotation pitch unevenness has occurred. Further, Δ indicates that rotational pitch unevenness occurred, and x indicates that rotational pitch unevenness occurred remarkably. Furthermore, the driving side, the center, and the non-driving side in each table indicate the positions of the developing roller 83 in the axial direction.

  As shown in Table 1, in Example 1, good results were obtained in which leakage and rotation pitch unevenness did not occur when the peak-to-peak voltage of the AC voltage was in the range of 1500 V to 1900 V. On the other hand, in Comparative Example 1 shown in Table 2, rotation pitch unevenness occurred on the non-driving side under the condition of a peak-to-peak voltage of 1500V. This is because the roller thin layer portion 83C2 of the coat layer 83C is disposed on the front end side of the developing roller 83, so that the gap between the developing roller 83 and the photosensitive drum 121 is partially expanded, and sufficient toner movement is performed. It was because there was not. Furthermore, in Comparative Example 2 shown in Table 3, for the same reason, the rotational pitch unevenness occurred remarkably on the non-driving side under the condition of a peak-to-peak voltage of 1500V. Further, leakage occurred on the driving side under the condition of a peak-to-peak voltage of 1900V. In Comparative Example 2, the roller thick layer portion 83C1 and the drum thick layer portion 120C1 face each other on the drive side where the position of the shaft portion 83J is easily regulated by the drive transmission portion 83R. For this reason, since the space | interval of the developing roller 83 and the photoconductive drum 121 becomes too close, it becomes easy to generate | occur | produce a leak.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Apparatus main body 12 Image forming part 120 Drum base tube (2nd base material)
120C functional layer (second surface layer)
120C1 drum thick layer portion 120C2 drum thin layer portion 121 photoconductor drum (image carrier)
122 Developing device 12H Drum unit (support frame)
80 Development housing (housing)
81 Developer storage part 82 Magnetic roller 82G Input gear (second gear)
83 Development roller (developer carrier)
830 Sleeve (first base material)
83C Coat layer (first surface layer)
83C1 Roller thick layer part 83C2 Roller thin layer part 83G Roller gear (first gear)
83J Shaft part 83K Tracking roller (regulating member)
83R Drive transmission section 84 Developer regulating blade 85 First screw feeder 86 Second screw feeder 86A Reverse conveying section 87 Developer discharge section

Claims (5)

An image carrier that is rotated about its axis and forms an electrostatic latent image on its surface;
A developing device disposed opposite to the image carrier,
The developing device includes:
A housing;
A shaft portion, disposed at a distance from the image carrier, supported by the housing so as to be rotatable around the shaft portion, carrying a developer on a peripheral surface, and the developer on the image carrier; a developer carrying member for feeding,
A drive transmission unit disposed on one end side in the axial direction of the developer carrier, and transmitting a rotational driving force to the developer carrier;
A regulating member that regulates an interval between the peripheral surface of the developer carrier and the surface of the image carrier;
With
The developer carrier comprises a cylindrical first base material and a first surface layer formed on the first base material,
The image carrier includes a cylindrical second substrate and a second surface layer formed on the second substrate,
By the immersion method in which the first base material and the second base material are immersed in a predetermined immersion tank so that the axial direction of the developer carrier and the image carrier is along the vertical direction, the first surface layer and the image carrier Each of the second surface layers is formed, and the film thickness of the first surface layer on the lower end side during the immersion of the developer carrier is thicker than the central portion in the axial direction, The film thickness of the first surface layer on the upper end side is thinner than the central part in the axial direction, and the film thickness of the second surface layer on the lower end side when the image carrier is immersed is thicker than the central part in the axial direction. The film thickness of the second surface layer on the upper end side during the immersion of the image carrier is thinner than the central portion in the axial direction,
Wherein the lower side to each other at the time of the immersion of the developer carrying member and said image bearing member, and the drive transmission portion of the axial direction in the opposite other end, are arranged opposite each other Rutotomoni, the developing The portion where the film thickness of the first surface layer on the upper end side during the immersion of the agent carrier is thin and the portion where the film thickness of the first surface layer on the lower edge side during the immersion of the developer carrier is thick are An image forming apparatus , wherein the developer carrier is supported by the housing so as to be included in a region where the developer is supplied to the image carrier on the developer carrier . The drive transmission unit is
A first gear fixed to the shaft portion of the developer carrier;
A second gear coupled to the first gear and transmitting a rotational driving force to the first gear;
With
2. The pressing force in a direction in which the developer carrier approaches the image carrier is applied to the developer carrier by the meshing of the first gear and the second gear. Image forming apparatus. A support frame that rotatably supports the image carrier;
The restriction member is a cylindrical member pivotally supported on the shaft portion,
The circumferential surface of the cylindrical member abuts on the surface of the image carrier or the support frame, whereby the distance between the circumferential surface of the developer carrier and the surface of the image carrier is regulated. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The first substrate is made of aluminum,
The developer carrier further comprises a first oxide layer formed on the surface of the first substrate,
The image forming apparatus according to claim 1, wherein the first surface layer is formed on a surface of the first oxide layer. The second substrate is made of aluminum,
The image carrier further comprises a second oxide layer formed on the surface of the second substrate,
The image forming apparatus according to claim 4, wherein the second surface layer is formed on a surface of the second oxide layer.

Images