JP2010164758A - Developing roller and image forming apparatus - Google Patents

Abstract

A developing roller is provided that is less likely to leak.
A developing roller 3 according to the present invention has a groove portion 371 periodically formed on the surface, a shaft 30a capable of carrying toner inside the groove portion 371, and a shaft 30a following the groove portion 371 and covering the shaft 30a. And a covering material 30b made of a heat-shrinkable tube having a conductivity lower than that of the shaft 30a. Since the covering material 30b is made of a heat-shrinkable tube, the shaft 30a can be covered with a uniform thickness. Since the covering material 30b has a lower electrical conductivity than the shaft 30a, leakage is prevented.
[Selection] Figure 4

Description

  The present invention relates to a developing roller and an image forming apparatus.

  Conventionally, electrophotographic image forming apparatuses such as copying machines and printers are known. An electrophotographic image forming apparatus includes a photosensitive drum and a charging device that charges the surface of the photosensitive drum, a writing device that forms a latent image on the charged photosensitive drum, and a development that attaches toner to the photosensitive drum corresponding to the latent image. And a transfer device for transferring the toner adhering to the photosensitive drum.

  The developing device includes a developing roller that rotates close to the surface of the photosensitive drum, a regulation blade that charges the toner and uniformly adheres the toner to the surface of the developing roller. When the developing roller rotates, a part of the developing roller surface sequentially approaches the photosensitive drum surface. The toner on the surface of the developing roller adjacent to the surface of the photosensitive drum flies by the electric field between the developing roller and the photosensitive drum and adheres to the photosensitive drum.

  The surface of the developing roller is provided with irregularities so that the toner can be carried satisfactorily. As one of the methods for providing the unevenness, a method of blasting the surface of the developing roller is known. Concavities and convexities formed by the blasting process are disadvantageous in that they are easily worn by contact with the regulating blade, and the chargeability tends to be uneven. As a technique for solving such inconvenience, a technique described in Patent Document 1 can be cited.

  In the image forming apparatus disclosed in Patent Document 1, a plurality of grooves are periodically formed on the surface of the developing roller by rolling, and toner can be carried inside the grooves. Compared with the unevenness by the blast treatment, the structure between the groove portions of the developing roller has no sharp structure, and the abrasion resistance of the developing roller is remarkably improved.

JP 2008-116543 A

If a developing roller having grooves formed by rolling is used, the life of the developing device can be extended, but leaks easily occur between the developing roller and the photosensitive drum. This is considered to be due to the periodic existence of edges due to the grooves and the large area on the convex portion between the grooves. In the leak portion, the electric field between the developing roller and the photosensitive drum becomes weak, and the toner cannot be satisfactorily adhered to the photosensitive drum.
SUMMARY An advantage of some aspects of the invention is that it provides a developing roller that is less likely to leak.

  In the developing roller of the present invention, a groove is periodically formed on the surface, a shaft capable of carrying toner inside the groove, and the shaft is covered following the groove and has lower conductivity than the shaft. And a covering material made of a heat-shrinkable tube.

  In this way, since the shaft is covered with the covering material made of a material having lower conductivity than the shaft, the leakage between the shaft and the photosensitive drum is remarkably reduced. Further, since the covering material is made of a heat shrinkable tube, the shaft can be covered with a uniform thickness. Therefore, a desired electric field can be applied between the developing roller and the photosensitive drum, and the toner can be satisfactorily adhered to the photosensitive drum. Therefore, it is possible to form a high quality image.

  Further, since the shaft does not come into direct contact with the regulating blade or the like, the shaft itself does not wear with the use of the developing roller. Therefore, when the covering material is worn, the developing roller can be regenerated by replacing the covering material, and the developing roller can be easily regenerated at a lower cost than when the shaft itself is worn.

Moreover, it is preferable that the groove is formed by rolling.
In this way, unlike the blasting process, a sharp-shaped structure is not formed between the groove portions of the shaft. Accordingly, there is no sharp shape on the surface of the covering material covering the shaft following the shaft surface, and the wear resistance of the developing roller can be remarkably improved.

  Further, it is preferable that a recess is formed outside the region where the toner is carried in the axial direction of the shaft, and the covering material is continuously provided to the inside of the recess in the axial direction of the shaft. . In this case, it is preferable that a pressing portion for pressing the covering material into the recess is provided.

  If the recessed part is formed in the edge part of a shaft, a coating | covering material will become difficult to shift | deviate in the axial direction of a shaft because a coating | coated material will be caught in a recessed part. Therefore, the sag of the coating material due to the shift of the coating material in the axial direction of the shaft can be reduced, and the coating material is prevented from peeling from the shaft due to the sag of the coating material. Further, the coating material is difficult to peel from the shaft due to the frictional force between the side wall of the recess and the coating material. In this way, the coating material is prevented from peeling off from the shaft, so that the electric field between the developing roller and the photosensitive drum is prevented from being distorted at the peeling portion, and the toner can be satisfactorily adhered to the photosensitive drum. become.

  If the pressing portion is provided in the concave portion, the coating material is pressed into the concave portion by the pressing portion, so that the coating material is prevented from peeling off from the shaft with use of the developing roller. Moreover, if the pressing part is provided in the recessed part, it will become difficult to shift | deviate in the axial direction of a shaft because a pressing part is caught in a recessed part.

Further, it is preferable that the dimension of the groove is selected based on the particle diameter of the toner and the thickness of the covering material.
In this way, the inner dimension of the groove portion on the surface of the developing roller can be defined by the dimension of the groove portion of the shaft, and the inner dimension of the groove portion on the surface of the developing roller can correspond to the toner particle size with high accuracy. it can. Therefore, it is possible to favorably carry the toner on the surface of the developing roller, and it is possible to form a high quality image.

An image forming apparatus according to the present invention includes a developing device including the developing roller according to the present invention.
Since the developing device including the developing roller of the present invention can develop a latent image satisfactorily and has a long life, the image forming apparatus of the present invention has a high quality. An image can be formed and has a long life.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of a printer including the developing roller of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration of a developing device including the developing roller of the present invention. It is a perspective view which shows schematic structure of the developing roller of 1st Embodiment. (A) of the developing roller of 1st Embodiment is sectional drawing, (b) is an enlarged view. (A) of the developing roller of 2nd Embodiment is a perspective view, (b) is sectional drawing. (A) is sectional drawing of 3rd Embodiment, (b) is sectional drawing of 4th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the technical scope of the present invention is not limited to the following embodiments. Various modifications are possible without departing from the gist of the present invention. Note that in the drawings used for description, in order to clearly show characteristic portions, the dimensions and scales of the structures in the drawings may be different from the actual structures. In addition, in the embodiment, the same components are illustrated with the same reference numerals, and detailed description thereof may be omitted.

  FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a printer 1 (image forming apparatus) according to the present invention. As shown in FIG. 1, the printer 1 has a photoconductor 110 that rotates in the direction of the arrow shown in FIG. 1 (clockwise in FIG. 1). In the printer 1, a charging unit 120, an exposure unit 130, a developing unit 140, a primary transfer unit 150 and an intermediate transfer body 160, and a cleaning unit 170 are sequentially arranged around the photoconductor 110 along the rotation direction. . The printer 1 has a paper feed tray 180 that feeds a recording medium P1 such as paper at the bottom of FIG. The recording medium P1 is conveyed by a paper feed roller 181 and a registration roller 182. A secondary transfer unit 183 and a fixing unit 184 are sequentially disposed downstream in the conveyance direction of the recording medium P1.

  The photoreceptor 110 has a cylindrical conductive substrate and a photosensitive layer formed on the outer peripheral surface thereof, and is rotatable around the central axis. The charging unit 120 is a device that uniformly charges the surface of the photoconductor 110 by corona charging or the like. The exposure unit 130 writes (forms) an electrostatic latent image by irradiating the photosensitive member 120 with a laser based on image information supplied from a signal source such as a personal computer (not shown).

  The developing unit 140 is a device that visualizes (develops) the latent image as a toner image on the photoconductor 110. Around the central axis 140a of the developing unit 140, holding portions 141 to 144 are provided. The developing devices 2a to 2d are detachably held by the holding units 141 to 144, respectively. The developing devices 2a to 2d correspond to black, magenta, cyan, and yellow colors, respectively. The detailed configuration of the developing devices 2a to 2d will be described later.

  The developing unit 140 generally operates as follows. The developing unit 140 rotates the holding units 141 to 144 around the central axis 140a. With the rotation of the holding units 141 to 144, the developing devices 2a to 2d rotate around the central axis 140a while maintaining their relative positions. In this way, the developing unit 140 selectively causes the developing devices 2a to 2d to face the photoconductor 110 in correspondence with the latent image. The developing devices 2 a to 2 d facing the photoconductor 110 form toner images by attaching toner of each color in a pattern corresponding to the latent image on the surface of the photoconductor 110.

The primary transfer unit 150 is a device that transfers the toner image formed on the photoconductor 110 to the intermediate transfer body 160.
The intermediate transfer body 160 is an endless belt, and is driven to rotate in the direction of the arrow shown in FIG. On the intermediate transfer body 160, a toner image of one or more of black, magenta, cyan, and yellow is transferred. For example, when a full-color image is formed, four color toner images of black, magenta, cyan, and yellow are sequentially transferred to form a full-color toner image.

The secondary transfer unit 183 is a device that transfers a single-color or full-color toner image formed on the intermediate transfer body 160 to a recording medium P1 such as paper, film, or cloth.
The fixing unit 184 is a device that fuses the toner image to the recording medium P1 and fixes it as a permanent image by heating and pressing the recording medium P1 that has received the transfer of the toner image.

  The cleaning unit 170 is a device that removes toner remaining on the photoconductor 110 after the toner image on the photoconductor 110 is transferred onto the intermediate transfer body 160. The cleaning unit 170 has a rubber cleaning blade 171 that contacts the surface of the photoconductor 110 between the primary transfer unit 150 and the charging unit 120. A cleaning blade 171 contacts the surface of the photoconductor 110 and scrapes off the remaining toner.

  Next, the developing devices 2a to 2d of the developing unit 140 will be described in detail. The developing devices 2a to 2d have almost the same configuration. Here, the configuration of the developing device 2a will be described, and the detailed description of the configurations of the developing devices 2b to 2d will be omitted.

  FIG. 2 is a schematic cross-sectional view showing a schematic configuration of the developing device according to the present invention. As shown in FIG. 2, the developing device 2 a has a housing 21. The housing 21 can store the toner T in a storage portion 22 that is an internal space thereof. The accommodating part 22 has an opening leading to the outside. A toner supply roller 23 is rotatably supported in the vicinity of the opening inside the housing portion 22. The developing roller 3 is rotatably supported near the opening outside the housing portion 22.

  When the inside of the accommodating portion 22 is the starting point in the rotation direction of the developing roller 3, the regulating blade 24 is disposed in contact with a part of the developing roller 3 in the vicinity of the opening of the accommodating portion 22 on the downstream side in the rotating direction. . A seal member 25 is disposed in contact with a part of the developing roller 3 in the vicinity of the opening of the housing portion 22 on the upstream side in the rotation direction.

  The developing roller 3 is an application of the present invention, and the detailed structure thereof will be described later. The surface of the developing roller 3 faces the surface of the photoconductor 110 in a non-contact manner. The developing roller 3 can carry the toner T on its surface. An electric field can be applied between the developing roller 3 and the photoconductor 110. The toner T is made of, for example, a resin such as polyester, and is made by adhering fine particles such as a pigment and a charge control material to a granular body having chargeability. The particle diameter of the toner T is, for example, about 7 ± 3 μm.

  The toner supply roller 23 is made of polyurethane foam or the like, and is pressed against the developing roller 3 while being elastically deformed (compressed). As the developing roller 3 rotates, the toner supply roller 23 rotates and the toner is supplied to the developing roller 3.

  The regulating blade 24 regulates the thickness of the toner T on the surface of the developing roller 3 and imparts an electric charge to the toner T. The regulating blade 24 includes a rubber part 241 that contacts the developing roller 3 along the axial direction of the developing roller 3 and a rubber support part 242 that supports the rubber part 241.

  The rubber part 241 is composed mainly of silicon rubber, urethane rubber or the like. The end of the rubber part 241 on the inner side of the housing part 22 is separated from the surface of the developing roller 3 at the edge. The rubber portion 241 is in contact with the developing roller 3 at a portion on the outer side of the housing portion 22 with respect to the end edge. Thus, the edge of the rubber part 241 is prevented from being caught in the rotation of the developing roller 3.

  The rubber support portion 242 is made of an elastic thin plate such as phosphor bronze or stainless steel. The rubber support portion 242 is provided by biasing the rubber portion 241 toward the developing roller 3. One end of the rubber support portion 242 is fixed to the blade support metal plate 27. The blade support sheet metal 27 is attached to the housing 21. A blade back member 26 is provided on the side of the regulating blade 24 opposite to the developing roller 3. The blade back member 26 prevents the toner T from entering between the rubber support portion 242 and the housing 21. The rubber part 241 is pressed against the developing roller 3 by the rubber support part 242 and the blade back member 26.

  The opening of the housing portion 22 is generally closed by the developing roller 3. In the portion along the axial direction of the developing roller 3, the accommodating portion 22 is sealed on the upstream side in the rotational direction by a seal member 25, and is sealed on the downstream side in the rotational direction by a regulating blade 24. The opening of the accommodating portion 22 is sealed by a seal member (not shown) at a portion along the circumferential direction of the developing roller 3. The seal members are disposed at both end portions of the developing roller 3 and are provided in contact with the end portions of the developing roller 3. In this way, the housing portion 22 is sealed so that toner does not leak from the inside to the outside.

The developing device 2a configured as described above generally operates as follows.
The developing roller 3 rotates corresponding to the photoconductor 110. Then, the toner supply roller 23 rotates in conjunction with the developing roller 3 and the toner T is supplied to the surface of the developing roller 3. The toner T on the surface of the developing roller 3 has an excessive thickness portion scraped off by the regulating blade 24 and is charged by friction with the regulating blade 24.

  The charged toner T flies from the surface of the developing roller 3 to the surface of the photosensitive member 110 due to an electric field between the developing roller 3 and the photosensitive member 110. Since the intensity of the electric field between the developing roller 3 and the photoconductor 110 has a distribution corresponding to the pattern of the latent image, the toner T flies in a pattern corresponding to the latent image and adheres to the surface of the photoconductor 110. . As a result, a toner image corresponding to the latent image is formed (developed) on the surface of the photoreceptor 110.

[First Embodiment]
Next, a first embodiment of the developing roller 3 will be described with reference to FIGS. 3 and 4A and 4B. FIG. 3 is a perspective view showing a schematic configuration of the developing roller 3. 4A is a cross-sectional view of the developing roller 3 on the surface including the line CC ′ in FIG. 3, and FIG. 4B is an enlarged view of the surface of the developing roller 3 in the central region 34. In FIG.4 (b), a part of coating | covering material is fractured | ruptured and the surface layer is shown typically.

  As shown in FIG. 3, the developing roller 3 has a substantially cylindrical shape with the C-C ′ line as the central axis. The developing roller 3 includes a main portion 31 and sub-portions 32 and 33 provided at both ends of the main portion 31 in the axial direction. The main part 31 and the sub parts 32 and 33 are both substantially cylindrical, and the diameter of the main part 31 is larger than the diameter of the sub parts 32 and 33. The main portion 31 is a portion that carries toner when the developing roller 3 is used. The sub portions 32 and 33 are portions that support the main portion 31 when the developing roller 3 is manufactured or used. Here, the sub-parts 32 and 33 are formed integrally with the main part 31.

  In the main portion 31, the central region 34 in the axial direction is a region for carrying toner, and the peripheral regions 35 and 36 at both ends in the axial direction are regions where the seal member 28 abuts. The central region 34 is provided with a plurality of toner carrying grooves 37 capable of carrying toner. The toner carrying groove 37 is provided in a spiral shape from one end to the other end in the axial direction of the main portion 31. The toner carrying groove 37 includes two groove groups twisted in opposite directions starting from one end of the main portion 31. Each of the two groove groups is constituted by a plurality of toner carrying grooves 37 arranged at substantially equal intervals in the axial direction. The surface area 38 surrounded by the two toner carrying grooves 37 constituting one of the two groove groups and the two toner carrying grooves 37 constituting the other is directly on the regulating blade 24 or indirectly via the toner. It is the part that is rubbed.

  As shown in FIG. 4A, the developing roller 3 includes a shaft 30a and a covering material 30b. The shaft 30a is formed using a columnar member made of an aluminum alloy, an iron alloy, or the like as a base material. The shaft 30a has a plurality of groove portions 371 formed on the surface of a base material by rolling. According to the rolling process, the shape and position of the groove 371 can be made highly accurate. Both end portions of the shaft 30a in the axial direction are regions where the groove portion 371 is not formed. In the developing device 2a shown in FIG. 2, the seal member 28 is a member that closes the gap between the inside and the outside of the housing portion 22 at both ends in the axial direction of the developing roller 3. The peripheral regions 35 and 36 have almost no unevenness because the groove 371 is not formed. Therefore, the inside of the accommodating part 22 can be favorably sealed by the seal member 28.

  The covering material 30b is provided such that the covering material 30b follows and contacts the bottom surface 372 of the groove portion 371, the side surface 373 of the groove portion 371, and the top surface 381 between the two groove portions 371. Here, the covering material 30 b is continuously provided so as to cover both ends of the main portion 31. The covering material 30b is formed of a substantially cylindrical heat-shrinkable tube made of a conductive material or an insulating material whose conductivity is lower than that of the shaft 30a. Examples of the material for the heat-shrinkable tube include conductive rubber and conductive resin. Specific examples of the heat-shrinkable tube include a conductive super teletube (manufactured by Teijin Chemicals).

  When a heat shrinkable tube made of an insulating material is employed, the material and thickness of the heat shrinkable tube may be selected so that toner can be carried in the toner carrying groove 37. To explain based on a simple model, the centrifugal force acting on the toner when the developing roller 3 rotates is the mass of the toner, the rotating speed of the developing roller 3, and the central axis of the developing roller 3 to the toner in the toner carrying groove 37. It is determined by distance. The electrostatic force that attracts the toner to the developing roller 3 is determined by the potential of the shaft 30a, the charge amount of the toner, the thickness of the covering material 30b, the dielectric constant of the covering material 30b, and the like. If the electrostatic force is equal to or greater than the centrifugal force, the toner can be held in the toner carrying groove 37. Since the thickness of the covering material 30b and the dielectric constant of the covering material 30b are determined by the material and thickness of the heat shrinkable tube, the toner can be carried in the toner carrying groove 37 by selecting these.

  As shown in FIG. 4B, the two groove groups are substantially orthogonal to each other in a state where the surface of the main portion 31 is developed in a planar shape, and the planar shape of the surface region 38 is substantially a square. The distance from the top surface of the surface region 38 to the bottom surface of the toner carrying groove 37 (see FIG. 4A), that is, the depth of the toner carrying groove 37 is larger than the volume average particle diameter of the toner. The covering material 30 b covers the bottom surface 372 and the top surface 381 with a substantially uniform thickness, and the depth of the toner carrying groove 37 is substantially equal to the depth from the top surface 381 to the bottom surface 372. The width of the toner carrying groove 37 is narrower than the width of the groove portion 371 by a dimension corresponding to the thickness of the covering material 30b. In the present embodiment, dimensions such as the width and depth of the groove 371 are selected in consideration of the thickness of the covering material. As described above, the groove portion 371 has high precision in size and position by rolling, and the covering material 30b is formed in accordance with the surface shape of the shaft 30a. Therefore, the dimension of the toner carrying groove 37 becomes high accuracy, and the toner can be carried well in the toner carrying groove 37.

  As an example of the manufacturing method of the developing roller 3, the following methods are mentioned. The shaft 30a in which the groove portion 371 is formed is inserted into the heat shrinkable tube. Subsequently, the developing roller 3 is obtained by heating and shrinking the heat shrinkable tube. When the pressure inside the cylinder of the heat-shrinkable tube is made lower than the pressure outside the cylinder when the heat-shrinkable tube is heated, the gas between the heat-shrinkable tube and the shaft 30a is exhausted through the groove 371. Thereby, a heat contraction tube can be made to follow the groove part 371 of the shaft 30a favorably. As a method for making the pressure inside the cylinder lower than the pressure outside the cylinder, there are a method of reducing the pressure inside the cylinder, a method of increasing the pressure outside the cylinder, a method using these methods together, and the like. The method of pressurizing the pressure outside the cylinder can be performed by increasing the atmospheric pressure outside the cylinder or pressing the outside of the cylinder with a compressible elastic member.

  In the case of employing a heat shrinkable tube made of an insulating material, the following method can be cited as an example of a method for manufacturing the developing roller 3. For example, a heat shrinkable tube made of a polyimide precursor is prepared. By adjusting the degree of polymerization of the polyimide precursor, the heat-shrinkable tube can be molded while being adjusted to a deformable hardness. By covering the shaft 30a with such a heat-shrinkable tube and increasing the polymerization degree of the polyimide precursor by heating or the like, it is possible to form the strong covering material 30b while following the groove portion 371.

  In the developing roller 3 configured as described above, the conductivity of the covering material 30b is lower than the conductivity of the shaft 30a. Therefore, the leak between the shaft 30 a and the photoconductor 110 is remarkably reduced, and a desired electric field can be applied between the developing roller 3 and the photoconductor 110. Therefore, the toner can be satisfactorily adhered to the photosensitive drum, and a high-quality image can be formed.

Moreover, since the coating | covering material 30b consists of a heat-shrinkable tube, it is possible to coat | cover the shaft 30a with uniform thickness.
For example, when a coating film is formed on the surface of the shaft by painting or the like, the outer surface of the shaft is curved and the coating material flows, making it difficult to make the thickness of the coating film uniform in the direction of gravity. Further, the coating material flows from the convex portion (for example, on the top surface 381) of the shaft surface to the concave portion (for example, in the groove portion 371), whereby the thickness of the coating film is likely to be thinner on the convex portion than in the concave portion. Then, although the convex part is a part closer to the photosensitive drum than the concave part, since the non-peritoneum on the convex part is relatively thin, the effect of preventing leakage is reduced. The concave portion is a portion where the toner is carried, but since the coating film in the concave portion is relatively thick, the force for electrostatically adsorbing the toner is weakened, and the toner cannot be favorably carried.
As described above, according to the present embodiment, since the thickness of the covering material 30b is uniform, the leakage can be reduced and the toner can be favorably carried. Therefore, the toner can be satisfactorily adhered to the photosensitive drum, and a high-quality image can be formed.

  Since the shaft 30a is not in direct contact with the regulating blade 24 and the like, the shaft 30a itself is not worn with the use of the developing roller 3. When the covering material 30b is worn, the developing roller 3 can be regenerated by replacing the covering material 30b. Therefore, the necessity for regenerating the shaft 30a is reduced as compared with the case where the covering material 30b is not provided, and the developing roller 3 can be easily regenerated at a low cost.

[Second Embodiment]
Next, a second embodiment of the developing roller of the present invention will be described. The second embodiment is different from the first embodiment in that a recess is formed outside the region where the toner is carried, and the covering material extends to the recess in the axial direction of the shaft.

  FIG. 5A is a perspective view illustrating a schematic configuration of the developing roller 4 of the second embodiment, and FIG. 5B schematically illustrates a cross-sectional structure of the developing roller 4 on a plane passing through the central axis of the developing roller 4. FIG. As shown in FIG. 5A, the peripheral regions 35 and 36 of the developing roller 4 are provided with recesses 41 and 42, respectively. The concave portions 41 and 42 are provided along the circumferential direction of the main portion 31.

  As shown in FIG. 5B, the recesses 41 and 42 are formed deeper than the toner carrying groove 37. In the present embodiment, the recesses 41 and 42 are provided on the outer side in the axial direction with respect to the portion where the developing roller 4 contacts the seal member 28, so that toner does not enter the recesses 41 and 42 during use. . The covering material 30 b extends to the both ends of the main portion 31 while following and abutting the side and bottom surfaces of the recesses 41 and 42.

  In the developing roller 4 configured as described above, the covering material 30b is caught on the side surfaces of the recesses 41 and 42, thereby preventing the axial displacement of the covering material 30b. Since the recesses 41 and 42 are formed deeper than the toner carrying groove 37, the anchoring effect can be more effectively generated in the coating material 30b than in the toner carrying groove 37, and the coating material 30b is peeled off from the shaft 30a. Is prevented.

  The concave portions 41 and 42 may be disposed on the inner side in the axial direction with respect to the portion where the developing roller 4 contacts the seal member 28. In addition, a plurality of at least one of the recesses 41 and 42 may be provided.

[Third Embodiment]
Next, a third embodiment of the developing roller of the present invention will be described. The third embodiment is different from the second embodiment in that a pressing portion that presses the covering material is provided inside the recess.

  FIG. 6A is a diagram schematically showing a cross-sectional structure of the developing roller 5 of the third embodiment. As shown in FIG. 6 (a), inside the recesses 41 and 42, pressing portions 51 and 52 are provided in contact with the covering material 30b, respectively. The pressing portions 51 and 52 of the present embodiment are ring-shaped made of an elastic material such as rubber. The pressing portions 51 and 52 are attached to the concave portions 41 and 42 by exerting tension by extension or the like. The covering material 30 b is pressed to the inside of the recesses 41 and 42 by the force by which the pressing parts 51 and 52 contract.

In the developing roller 5 having the above-described configuration, the covering material 30b is pressed by the pressing portions 51 and 52, and the covering material 30b is prevented from being peeled off from the shaft 30a or shifted in the axial direction. Moreover, since the press parts 51 and 52 are arrange | positioned in the recessed parts 41 and 42, it is also prevented that the press parts 51 and 52 slip | deviate to an axial direction. Thereby, the press parts 51 and 52 can be functioned favorably.
[Fourth Embodiment]
Next, a fourth embodiment of the developing roller of the present invention will be described. The fourth embodiment differs from the third embodiment in that the pressing portion is embedded in the entire inside of the recess, and the pressing portion also serves as the seal member 28.

  FIG. 6B is a diagram schematically illustrating a cross-sectional structure of the developing roller 6 according to the fourth embodiment. As shown in FIG. 6B, the recesses 41 and 42 of the present embodiment are provided in almost the entire peripheral regions 35 and 36. Pressing portions 61 and 62 are embedded in the recesses 41 and 42, respectively. The pressing portions 61 and 62 are made of a compressible material such as foamed urethane or bulk rubber. The thickness of the pressing parts 61 and 62 is selected such that the pressing parts 61 and 62 are compressed in contact with the housing 21 (see FIG. 2) side of the developing device 2a. When the pressing portions 61 and 62 are compressed, the covering material 30b is pressed against the shaft 30a by a repulsive force.

  In the developing roller 6 having the above configuration, the covering material 30b is pressed by the pressing portions 61 and 62, and the covering material 30b is prevented from being peeled off or shifted. Moreover, since the press parts 61 and 62 are arrange | positioned in the recessed parts 41 and 42, the shift | offset | difference of the press parts 51 and 52 is also prevented.

DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2a, 2b, 2c, 2d ... Developing device, 3, 4, 5, 6 ... Developing roller, 30a ... Shaft, 30b ... Coating material, 371 ... groove part, 41, 42 ... concave part, 51, 52, 61, 62 ... pressing part

Claims (6)

A groove that is periodically formed on the surface and capable of carrying toner inside the groove;
A developing roller comprising: a coating material made of a heat-shrinkable tube that covers the shaft following the groove and has a lower electrical conductivity than the shaft.   The developing roller according to claim 1, wherein the groove is formed by a rolling process.   A recess is formed outside the region where the toner is carried in the axial direction of the shaft, and the covering material is continuously provided to the inside of the recess in the axial direction of the shaft. The developing roller according to claim 1 or 2.   The developing roller according to claim 3, wherein a pressing portion that presses the covering material into the concave portion is provided.   The developing roller according to claim 1, wherein the size of the groove is selected based on a particle size of the toner and a thickness of the covering material.   An image forming apparatus comprising the developing device including the developing roller according to claim 1.

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