JP6164021B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus including a transfer roller and a power supply roller that supplies a transfer bias current to a transfer nip via an axis of the transfer roller (see Patent Document 1). An image forming apparatus having a conductive roller including a conductive shaft and a conductive elastic layer provided on the outer periphery of the shaft is known (see Patent Document 2).

JP 2007-256860 A

JP 2003-195601 A

  An object of the present invention is to provide an image forming apparatus capable of achieving a uniform transfer current applied to a recording medium.

  In order to achieve the above object, an image forming apparatus according to claim 1 includes an image carrier that forms a toner image on a surface thereof, a core shaft of an insulator, and an ion conductive material wound around the core shaft. A transfer member that transfers a toner image onto a recording medium; and a power supply member that contacts the transfer member and supplies a transfer current to a sandwiching portion where the image carrier and the transfer member sandwich the recording medium. One of the power supply member and the transfer member has a first shape in which the diameter of the end portion in the longitudinal axis direction is larger than the diameter of the central portion in the longitudinal axis direction, and the other of the power supply member and the transfer member is in the longitudinal axis direction. The central portion has a second shape in which the diameter of the central portion is larger than the diameter of the end portion in the longitudinal axis direction.

  The image processing apparatus according to claim 2 is the image processing apparatus according to claim 1, wherein when the recording medium is a sheet, the transfer member has the first shape, and the power feeding member has the second shape. It is characterized by being.

  An image processing apparatus according to a third aspect is the image processing apparatus according to the first aspect, wherein the recording medium is an intermediate transfer belt.

  The image forming apparatus according to claim 4 includes an image carrier that forms a toner image on a surface thereof, a core shaft of an insulator, and an ion conductive material wound around the core shaft, and the toner image is placed on a recording medium. A transfer member that transfers, and a power supply member that abuts against the transfer member and supplies a transfer current to a sandwiching portion between which the image carrier and the transfer member sandwich the recording medium, and the transfer member uses the recording medium The contact width between the transfer member and the image carrier at the end portion in the longitudinal axis direction of the transfer member is the transfer width at the center portion in the longitudinal axis direction of the transfer member. The contact width between the transfer member and the power supply member at the end in the longitudinal axis direction of the transfer member is larger than the contact width between the member and the image carrier, The contact width between the transfer member and the power supply member Characterized in that is also small.

  According to the first aspect of the present invention, the transfer current applied to the recording medium can be made uniform as compared with the case where the nip width is not uniform in the axial direction and the shaft core is not an insulator.

  According to the invention of claim 2, the transfer current applied to the recording medium can be made uniform while suppressing the occurrence of paper wrinkles.

  According to the third aspect of the present invention, the transfer current applied to the intermediate transfer belt can be made uniform.

  According to the invention of claim 4, the transfer current applied to the recording medium can be made uniform as compared with the case where the nip width is not uniform in the axial direction and the shaft core is not an insulator.

1A is a configuration diagram of an image forming apparatus according to the present embodiment. (B) is a block diagram of a modified example of the image forming apparatus according to the present embodiment. (A) is a diagram showing the positional relationship of a photosensitive drum, a recording medium (paper S or intermediate transfer belt), a transfer roller, and a power supply roller. (B) is a figure which shows the modification of FIG. 2 (A). FIG. 6A is a diagram illustrating a relationship between the contact width of the transfer roller 14a and the photosensitive drum 10 and the contact width of the transfer roller 14a and the power supply roller 15a. (B) is a diagram showing the relationship between the contact width of the transfer roller 14b and the photosensitive drum 10 and the contact width of the transfer roller 14b and the power supply roller 15b. It is a figure which shows the relationship between rotation of a transfer roller, and the flow of electric current (namely, movement of electric charge). (A) is a figure which shows the modification of a transfer roller and a feed roller. FIG. 7B is a diagram illustrating a state in which the transfer roller and the power supply roller according to the modification are pressed against the photosensitive drum side. It is a figure which shows the experimental result of whether a paper wrinkle, a transfer nonuniformity, and the energization resistance rise of a transfer roller generate | occur | produce when each of several sets of a transfer roller and a power feeding roller is used.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1A is a configuration diagram of an image forming apparatus according to the present embodiment.

The image forming apparatus 1 in FIG. 1A is, for example, a printer. The image forming apparatus 1 includes a photosensitive drum 10 as an image carrier, a charging roller 11 that uniformly charges the surface of the photosensitive drum 10, and an exposure device 12 that forms an electrostatic latent image on the photosensitive drum 10. A developing device 13 for forming a toner image corresponding to the electrostatic latent image, a transfer roller 14 as a transfer member for transferring the toner image to a recording medium and conveying the recording medium, and a transfer current to the transfer roller 14 A power supply roller 15 as a power supply member for supplying the toner, a transfer bias power source (that is, a DC power source) 16, and a heating roller 17 and a pressure roller 18 for fixing the toner image on the recording medium to the recording medium. . In addition, the recording medium in FIG.
The photosensitive drum 10 is rotationally driven in the arrow A direction, and the sheet S on which the toner image is formed is conveyed in the arrow B direction. The toner image is negatively charged. A voltage having a polarity opposite to that of the toner image (that is, a positive polarity voltage) is applied to the power supply roller 15.

  FIG. 1B is a configuration diagram of a modification of the image forming apparatus according to the present embodiment.

  The image forming apparatus 2 in FIG. 1B is, for example, a copier or a multifunction machine. Similar to the image forming apparatus 1 in FIG. 1A, the image forming apparatus 2 includes a photosensitive drum 10, a charging roller 11, an exposure device 12, a developing device 13, a transfer roller 14, a power supply roller 15, A transfer bias power source 16, a heating roller 17, and a pressure roller 18 are provided. Further, the image forming apparatus 2 includes a conveyance roller 20 and an intermediate transfer belt 21.

  In the image forming apparatus 2, the toner image on the photosensitive drum 10 is transferred to an intermediate transfer belt 21 as a recording medium. The intermediate transfer belt 21 is stretched around two transport rollers 20 and a heating roller 17. The toner image transferred to the intermediate transfer belt 21 is fixed on the paper S by the heating roller 17 and the pressure roller 18.

  The photosensitive drum 10 is rotationally driven in the arrow A direction, and the sheet S on which the toner image is formed is conveyed in the arrow B direction. The intermediate transfer belt 21 is moved in the direction of arrow C by the transfer roller 14, the transport roller 20, and the heating roller 17.

  FIG. 2A is a diagram illustrating a positional relationship among the photosensitive drum, the recording medium (paper S or intermediate transfer belt), the transfer roller, and the power supply roller. FIG. 2B is a diagram illustrating a modification of FIG. FIG. 3A is a diagram showing the relationship between the contact width of the transfer roller 14a and the photosensitive drum 10 and the contact width of the transfer roller 14a and the power supply roller 15a. FIG. 3B is a diagram illustrating the relationship between the contact width between the transfer roller 14b and the photosensitive drum 10 and the contact width between the transfer roller 14b and the power supply roller 15b.

  2A and 2B, the shapes of the transfer roller 14 and the power supply roller 15 are different. Accordingly, FIG. 2A shows the transfer roller 14 and the power supply roller 15 as the transfer roller 14a and the power supply roller 15a, and FIG. 2B shows the transfer roller 14 and the power supply roller 15 as the transfer roller 14b and the power supply roller 15b. Show.

  The transfer rollers 14a and 14b and the power supply rollers 15a and 15b are pressed against the photosensitive drum 10 by a driving device (not shown), and the toner image on the photosensitive drum 10 is recorded on the recording medium (paper S or intermediate transfer belt 21). Is transcribed.

The transfer rollers 14 a and 14 b are constituted by an insulating core shaft 141 and a semiconductive foam rubber 142. The insulator core shaft 141 is made of, for example, a resin, and the core shaft 141 has a volume resistivity of 1 × 10 ¹⁰ Ω · cm or more. Preferably, the volume specific resistance value of the core shaft 141 is 2 × 10 ¹² Ω · cm or more in order to prevent current from flowing. Specifically, the semiconductive foam rubber 142 is a 7.2 log Ω ion conductive foamed urethane using a quaternary ammonium salt as the ion conductive material. A semiconductive foam rubber 142 is coated around the core shaft 141 of the insulator.

  The transfer rollers 14a and 14b have a function of conveying the recording medium and a function of transferring the toner image on the photosensitive drum 10 to the recording medium. When the recording medium is the paper S, it is important that the paper S is not damaged such as wrinkles. For this reason, when the transfer roller 14 contacts the photosensitive drum 10 via the recording medium (paper S), the contact width of the end portion of the transfer roller 14 in the longitudinal axis direction is the center of the transfer roller 14 in the longitudinal axis direction. It is necessary to make it larger than the contact width of the part. Therefore, as shown in FIG. 2A, the transfer roller 14a is formed in a flare shape in which the diameter of the end portion in the longitudinal axis direction is larger than the diameter of the central portion in the longitudinal axis direction. As a result, a force F1 that pulls the paper S outwards acts on the paper S, and the occurrence of paper wrinkles is suppressed.

  On the other hand, in order to transfer the toner image satisfactorily, it is important to supply the paper S with a uniform density. This is because uneven transfer occurs when uniform charge is not supplied to the paper S.

  When the core shaft 141 of the transfer roller 14a is a conductive core shaft such as metal, the core shaft 141 becomes equipotential when a transfer current is applied from the power supply roller 15a. The core shaft 141 is equipotential regardless of whether the resistance between the power supply roller 15a and the core shaft 141 is uniform or non-uniform. The charge density used for transfer from the core shaft 141 which is equipotential depends on the relationship between the contact width of the transfer roller 14a and the photosensitive drum 10, and the charge density at the end in the longitudinal axis direction of the transfer roller 14 is The charge density in the central portion of the transfer roller 14 in the longitudinal axis direction becomes larger, and the charge density in the longitudinal axis direction of the transfer roller 14 becomes nonuniform.

  Therefore, in this embodiment, the core shaft 141 of the transfer rollers 14a and 14b is made of an insulator. Thereby, it is possible to optimize the resistance from the power supply roller 15a to the contact portion between the transfer roller 14a and the photosensitive drum 10. That is, the charge density at the contact portion between the power supply roller 15a and the transfer roller 14a is directly at the contact portion between the transfer roller 14a and the photosensitive drum 10 (that is, the holding portion where the transfer roller 14a and the photosensitive drum 10 sandwich the recording medium). Will be reflected.

  When the transfer roller 14a of FIG. 2 (A) is used, as shown in FIG. 3 (A), the contact width of the end portion in the longitudinal axis direction of the transfer roller 14a is the central portion of the transfer roller 14a in the longitudinal axis direction. It becomes larger than the contact width. For this reason, the charge density at the end of the transfer roller 14a in the longitudinal axis direction is larger than the charge density at the center of the transfer roller 14a in the longitudinal axis direction.

  In order to supply the paper S with a uniform density, as shown in FIG. 2A, the power supply roller 15a has a crown shape in which the diameter of the central portion in the longitudinal axis direction is larger than the diameter of the end portion in the longitudinal axis direction. Is formed. Thus, when the power supply roller 15a contacts the transfer roller 14a, as shown in FIG. 3A, the contact width of the central portion in the longitudinal axis direction of the power supply roller 15a or the transfer roller 14a is equal to the power supply roller 15a or transfer roller. It becomes larger than the contact width of the end of the roller 14a in the longitudinal axis direction. Therefore, the contact width between the transfer roller 14a and the photosensitive drum 10 and the contact width between the power supply roller 15a and the transfer roller 14a are complementary.

  As described above, the charge density at the contact portion between the power supply roller 15a and the transfer roller 14a increases at the central portion in the longitudinal axis direction of the transfer roller 14a and decreases at the end portion in the longitudinal axis direction of the transfer roller 14a. The contact width between the transfer roller 14a and the photosensitive drum 10 decreases at the central portion of the transfer roller 14a in the longitudinal axis direction and increases at the end portion of the transfer roller 14a in the longitudinal axis direction. For this reason, the charge density at the contact portion between the transfer roller 14a and the photosensitive drum 10 is uniform in the longitudinal axis direction of the transfer roller 14a. Accordingly, the uniform charge is supplied to the paper S. As described above, the transfer roller 14a and the power supply roller 15a in FIG. 2A can suppress paper wrinkles and achieve a uniform transfer effect.

  When the recording medium is the intermediate transfer belt 21, the uniform transfer charge is supplied to the intermediate transfer belt 21 as in the case where the recording medium is the paper S. In the case of FIG. 2A, the generation of paper wrinkles is suppressed by forming the transfer roller 14a in a flare shape. However, when the recording medium is the intermediate transfer belt 21, the intermediate transfer belt 21 is used. Has a constant strength, so there is no need to consider the occurrence of wrinkles.

  The shapes of the transfer roller 14b and the power supply roller 15b shown in FIG. 2B are opposite to the shapes of the transfer roller 14a and the power supply roller 15a shown in FIG. That is, the transfer roller 14b is formed in a crown shape in which the diameter of the central portion in the longitudinal axis direction is larger than the diameter of the end portion in the longitudinal axis direction. The feeding roller 15b is formed in a flare shape in which the diameter of the end portion in the longitudinal axis direction is larger than the diameter of the central portion in the longitudinal axis direction.

  In this case, as shown in FIG. 3B, the contact width between the transfer roller 14b and the photosensitive drum 10 becomes small at the end in the longitudinal axis direction of the transfer roller 14b, and the center in the longitudinal axis direction of the transfer roller 14b. Become bigger in the department. On the other hand, as shown in FIG. 3B, the contact width between the transfer roller 14b and the power supply roller 15b increases at the end portion in the longitudinal axis direction of the transfer roller 14b, and at the center portion in the longitudinal axis direction of the transfer roller 14b. Get smaller. Therefore, the contact width between the transfer roller 14b and the photosensitive drum 10 is complementary to the contact width between the power supply roller 15b and the transfer roller 14b.

  Accordingly, the charge density at the contact portion between the power supply roller 15b and the transfer roller 14b increases at the end portion in the longitudinal axis direction of the transfer roller 14b and decreases at the center portion in the longitudinal axis direction of the transfer roller 14b, but the transfer roller 14b. The contact width between the photosensitive drum 10 and the photosensitive drum 10 decreases at the end portion of the transfer roller 14b in the longitudinal axis direction and increases at the central portion of the transfer roller 14b in the longitudinal axis direction. For this reason, the charge density at the contact portion between the transfer roller 14b and the photosensitive drum 10 is uniform in the longitudinal axis direction of the transfer roller 14b. Therefore, a uniform density charge is supplied to the recording medium.

  Note that when the transfer roller 14b of FIG. 2B is used, a force F2 directed toward the center of the paper S acts on the paper S, so that paper wrinkles are likely to occur. Therefore, when the recording medium is the paper S, it is preferable to employ the transfer roller 14a and the power supply roller 15a shown in FIG. When the recording medium is the intermediate transfer belt 21, the intermediate transfer belt 21 has a certain strength, so that it is not necessary to consider the occurrence of wrinkles. Therefore, when the recording medium is the intermediate transfer belt 21, one of the transfer roller 14a and the power supply roller 15a shown in FIG. 2A and the transfer roller 14b and the power supply roller 15b shown in FIG. do it.

  FIG. 4 is a diagram illustrating the relationship between the rotation of the transfer roller 14a or 14b and the flow of current (that is, charge movement).

  In the initial state, point A indicates a contact portion between the photosensitive drum 10 and the transfer roller 14a or 14b, and point B indicates a contact portion between the power supply roller 15a or 15b and the transfer roller 14a or 14b. In FIG. 4, arrows indicate the flow of current. 4, the current flows from the surface of the transfer roller 14a or 14b to the inside of the transfer roller 14a or 14b at the point B, and at the point A, the surface of the transfer roller 14a or 14b from the inside of the transfer roller 14a or 14b. Current is flowing through. When the transfer roller 14a or 14b is rotated 90 degrees clockwise, the transfer roller 14a or 14b is in a state as shown in the central view of FIG.

  In the right view of FIG. 4 in which the transfer roller 14a or 14b has been rotated 180 degrees, at point A, current flows from the surface of the transfer roller 14a or 14b to the inside of the transfer roller 14a or 14b, and at point B, the transfer roller 14a or 14b. Current flows from the inside to the surface of the transfer roller 14a or 14b.

  When a voltage is applied to the shaft core of the transfer roller 14a or 14b having ionic conductivity as in the prior art, the resistance of the transfer roller 14a or 14b, which is considered to be unevenly distributed, occurs, and the transfer roller 14a or 14b The long-term use of 14b becomes difficult.

  In this embodiment, since the power supply roller 15a or 15b is provided, the direction of the current is automatically switched by the rotation of the transfer roller 14a or 14b even if the insulator core shaft 141 is used. For this reason, the uneven distribution of ions does not occur in the transfer roller 14a or 14b, and an increase in resistance of the transfer roller 14a or 14b is suppressed, so that the transfer roller 14a or 14b can be used for a long period of time.

  FIG. 5A is a diagram illustrating a modification of the transfer roller and the power supply roller. FIG. 5B is a diagram illustrating a state in which the transfer roller and the power supply roller according to the modification are pressed against the photosensitive drum side.

  In FIG. 5A, the transfer roller 14c is a cylindrical transfer roller, and is composed of a core shaft 141 made of an insulator such as resin and a semiconductive foam rubber 142. The power supply roller 15c is a cylindrical power supply roller. That is, the transfer roller 14c and the power supply roller 15c are cylindrical, not flare-shaped or crown-shaped.

  As shown in FIG. 5B, when the transfer roller 14c and the power supply roller 15c are pressed against the photosensitive drum 10, the load is applied to both ends of the core shaft 141, so that the transfer roller 14c bends. At this time, the contact width between the transfer roller 14c and the photosensitive drum 10 increases at the end of the transfer roller 14c in the longitudinal axis direction and decreases at the center of the transfer roller 14c in the longitudinal axis direction. That is, the contact width between the transfer roller 14c and the photosensitive drum 10 has the same relationship as the contact width between the transfer roller 14a and the photosensitive drum 10 in FIG.

  On the other hand, the contact width between the power supply roller 15c and the transfer roller 14c decreases at the end portion in the longitudinal axis direction of the transfer roller 14c, and increases at the center portion in the longitudinal axis direction of the transfer roller 14c. That is, the contact width between the power supply roller 15c and the transfer roller 14c has the same relationship as the contact width between the power supply roller 15a and the transfer roller 14a in FIG. Therefore, even when the cylindrical transfer roller 14c and the cylindrical power supply roller 15c are used, the charge having a uniform density is supplied to the recording medium.

  The present applicant, when using each of the transfer roller 14a and the power supply roller 15a, the transfer roller 14b and the power supply roller 15b, and the transfer roller 14c and the power supply roller 15c, reduces paper wrinkles, transfer unevenness, and current transfer resistance of the transfer roller. It was confirmed by experiment whether an increase occurred. The experimental results are shown in FIG. In the comparative example of FIG. 6, a cylindrical transfer roller and a cylindrical power feeding roller were used. The core shaft of this cylindrical transfer roller was made of stainless steel, and a transfer voltage was applied to the core shaft.

  As shown in FIG. 6, paper wrinkles occurred in the transfer roller 14b and the power supply roller 15b and the comparative example, but no paper wrinkles occurred in the transfer roller 14a and the power supply roller 15a, and the transfer roller 14c and the power supply roller 15c. .

  In the comparative example, transfer unevenness occurred, but transfer unevenness did not occur in the transfer roller 14a and the power supply roller 15a, the transfer roller 14b and the power supply roller 15b, and the transfer roller 14c and the power supply roller 15c.

  Further, in the comparative example, the energization resistance of the transfer roller increased, but the transfer roller 14a and the power supply roller 15a, the transfer roller 14b and the power supply roller 15b, and the transfer roller 14c and the power supply roller 15c are all energized. There was no increase in resistance.

  As described above, according to the present embodiment, the image forming apparatus 1 (or 2) includes the photosensitive drum 10 that forms a toner image on the surface, the insulator core shaft 141, and the core shaft wound around the photoreceptor drum 10. A transfer roller 14a (or 14b) that transfers the toner image onto the recording medium, and a transfer roller 14a (or 14b) that is in contact with the ionic conductive material (ie, semiconductive foam rubber 142). The body drum 10 and the transfer roller 14a (or 14b) are provided with a power supply roller 15a (or 15b) that supplies a transfer current to a sandwiching portion that sandwiches the recording medium, and the power supply roller 15a (or 15b) and the transfer roller 14a (or 14b). Is a flare shape in which the diameter of the end portion in the longitudinal axis direction is larger than the diameter of the central portion in the longitudinal axis direction, and the power supply roller 15a (or 15b) and the transfer roller 14a (or 14b). The other is, the diameter of the central portion in the longitudinal direction is larger crown shape than the diameter of the end portion in the longitudinal axis direction.

  Therefore, the charge density in the sandwiching portion where the photosensitive drum 10 and the transfer roller 14a (or 14b) sandwich the recording medium is uniform in the longitudinal axis direction of the transfer roller 14a (or 14b). Therefore, the transfer current applied to the recording medium can be made uniform.

  In addition, the image forming apparatus 1 (or 2) includes a photosensitive drum 10 that forms a toner image on the surface, an insulating core shaft 141, and an ion conductive material wound around the core shaft (that is, semiconductive foam). A transfer roller 14c for transferring the toner image onto the recording medium, and abutting against the transfer roller 14c, and supplying a transfer current to a sandwiching portion where the photosensitive drum 10 and the transfer roller 14c sandwich the recording medium. When the transfer roller 14c is in contact with the photosensitive drum 10 via the recording medium, the contact width between the transfer roller 14c and the photosensitive drum 10 at the end in the longitudinal axis direction of the transfer roller 14c is as follows. The transfer roller 14c is larger than the contact width between the transfer roller 14c and the photosensitive drum 10 in the central portion of the transfer roller 14c in the longitudinal axis direction, and the transfer roller at the end of the transfer roller 14c in the longitudinal axis direction 14c and the contact width of the feed roller 15c is smaller than the contact width of the transfer roller 14c and the feed roller 15c at the center of the longitudinal axis of the transfer roller 14c.

  Therefore, the charge density in the nipping portion where the photosensitive drum 10 and the transfer roller 14c sandwich the recording medium becomes uniform in the longitudinal axis direction of the transfer roller 14c. Therefore, the transfer current applied to the recording medium can be made uniform.

  Note that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1, 2 Image forming apparatus 10 Photosensitive drum 11 Charging roller 12 Exposure apparatus 13 Developing device 14, 14a, 14b, 14c Transfer roller 15, 15a, 15b, 15c Feeding roller 16 Transfer bias power supply 17 Heating roller 18 Pressure roller 141 Core Shaft 142 Foam rubber

Claims (4)

An image carrier for forming a toner image on the surface;
A transfer member having a core shaft of an insulator and an ion conductive material wound around the core shaft, and transferring the toner image onto a recording medium;
A power supply member that abuts on the transfer member and supplies a transfer current to a sandwiching portion where the image carrier and the transfer member sandwich the recording medium;
One of the power supply member and the transfer member has a first shape in which the diameter of the end portion in the longitudinal axis direction is larger than the diameter of the central portion in the longitudinal axis direction, and the other of the power supply member and the transfer member is the longitudinal axis. An image forming apparatus having a second shape in which the diameter of the central portion in the direction is larger than the diameter of the end portion in the longitudinal axis direction.   2. The image forming apparatus according to claim 1, wherein when the recording medium is a sheet, the transfer member has the first shape and the power supply member has the second shape.   The image forming apparatus according to claim 1, wherein the recording medium is an intermediate transfer belt. An image carrier for forming a toner image on the surface;
A transfer member having a core shaft of an insulator and an ion conductive material wound around the core shaft, and transferring the toner image onto a recording medium;
A power supply member that abuts on the transfer member and supplies a transfer current to a sandwiching portion where the image carrier and the transfer member sandwich the recording medium;
When the transfer member is in contact with the image carrier via the recording medium, the contact width between the transfer member and the image carrier at the end in the longitudinal axis direction of the transfer member is the length of the transfer member. The contact width between the transfer member and the image carrier at the central portion in the axial direction is larger than the contact width between the transfer member and the power feeding member at the end in the longitudinal axis direction of the transfer member. An image forming apparatus, wherein the width is smaller than a contact width between the transfer member and the power supply member at a central portion in a longitudinal axis direction.

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