JP2019159143A - Fixation device and image formation device - Google Patents

Abstract

To appropriately inhibit generation of electrostatic off set in a heating member.SOLUTION: A fixation device 7 comprises: a heating member 31 that has a conductive core grid 31A and an insulation layer 31B provided around the core grid 31A, and heats unfixed toner on a medium S while rotating; a pressurizing member 32 that forms a pressurizing area N2 together with the heating member 31 while rotating, and pressurizes the medium S passing through the pressurizing area N2; and a functional member 35 including a first element D1 connected between the core grid 31A and ground G, and when a potential difference between the core grid 31A and a surface of the insulation layer 31B is less than a first threshold, blocking current flowing between the ground G and the heating member 31 toward a first direction for storing charge with reversed-polarity of the toner in the insulation layer 31B, and a second element D2 connected between the core grid 31A and ground G, and when a potential difference between the core grid 31A and a surface of the insulation layer 31B is less than a second threshold, blocking current flowing between the ground G and the heating member 31 toward a second direction opposite the first direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device and an image forming apparatus for fixing toner on a medium.

  An electrophotographic image forming apparatus such as a copying machine or a printer includes a heating roller type or film heating type fixing device that fixes a toner image on a recording medium such as paper. The heating roller type fixing device has a simple configuration and can achieve high speed. On the other hand, the film heating type fixing device can realize energy saving. The heating member and the pressure member provided in the fixing device have a surface material made of a fluororesin or the like, thereby ensuring sheet releasability.

  Since the fluororesin is insulative, it is difficult for the charge to attenuate once charged. Therefore, when a fluororesin is applied to a heating member or a pressure member, it may cause electrostatic offset. Therefore, when applying an insulating fluororesin to a heating member or a pressure member, the potential difference between the heating member and the pressure member is established by grounding the heating member or the pressure member via a functional member such as a Zener diode. It has been proposed to stabilize.

  As a specific example, in a configuration employing image formation with positively charged toner, in order to suppress negative charging of the heating member, the cathode of the Zener diode is connected to the heating member side and the anode is connected to the ground side. Has been proposed.

  For example, in a fixing device disclosed in Patent Document 1, a resistor and a constant voltage diode are connected in series between a fixing roller (heating member) and a ground, and between the pressure roller (pressure member) and the ground. In addition, a resistor and a constant voltage diode are connected in series. When the toner carried on the paper is negatively charged, the anode of the constant voltage diode connected to the fixing roller is connected to the fixing roller, and the cathode of the constant voltage diode connected to the pressure roller is pressurized The structure connected to the roller side is adopted.

JP 2006-300701 A

  However, according to the technique of Patent Document 1, electrostatic offset may occur due to induction charging of the heating member due to negative charging of the paper.

  In addition, as described above, the insulating layer constituting the surface material of the heating member has a property that the charged electric charge accumulates without losing, so the cored bar and the insulating layer of the heating member that is a conductor are like a capacitor. May behave. When positively charged toner is used, the transfer roller that transfers the toner image to the paper applies a negative charge to the paper, so that the negative charge is charged from the negatively charged paper to the insulating layer of the heating member. In particular, when the paper is water-containing paper, the resistance value of the paper becomes low, and thus the negative charge applied to the heating member increases.

  After the trailing edge of the paper leaves the transfer roller, the negative charge is no longer applied to the paper, so the electrostatic attraction between the toner and the paper is reduced. When the negative charge charged in the insulating layer of the heating member is discharged, the positively charged toner may adhere to the surface of the heating member and cause an electrostatic offset.

  In order to reduce the amount of charge accumulated in the heating member and prevent electrostatic offset, a configuration has already been proposed in which a functional member having a polarity only in one direction, such as a Zener diode, is connected to the core of the heating member. Yes. However, in the above configuration, there is a possibility that an electrostatic offset occurs when a reverse polarity charging phenomenon occurs.

  In view of the above circumstances, an object of the present invention is to appropriately suppress the occurrence of electrostatic offset in a fixing device.

  The fixing device according to the present invention includes a conductive cored bar and an insulating layer provided around the cored bar, a heating member that heats unfixed toner on the medium while rotating, and the heating while rotating. A pressure member that forms a pressure region together with the member, pressurizes the medium passing through the pressure region, and is connected between the core metal and the ground, and a potential difference between the core metal and the surface of the insulating layer A first element that cuts off a current flowing between the ground and the heating member in a first direction in which charges having a polarity opposite to that of the toner are accumulated in the insulating layer when When the potential difference between the metal core and the surface of the insulating layer is less than a second threshold value, the metal core is connected between the metal core and the ground, and the second metal direction is opposite to the first direction. A second element that blocks a current flowing between a ground and the heating member; A functional member having, characterized in that it comprises a.

  Preferably, in the above-described fixing device, the first element is a first Zener diode, the second element is a second Zener diode, and the first threshold is a Zener voltage of the first Zener diode; The second threshold value is a Zener voltage of the second Zener diode, and the cathode of the first Zener diode and the cathode of the second Zener diode are opposed to each other.

  Preferably, in the fixing device described above, the toner is positively charged, the anode of the first Zener diode is connected to the core metal side, and the anode of the second Zener diode is connected to the ground side. Is done.

  An image forming apparatus according to the present invention includes the above-described fixing device.

  According to the present invention, it is possible to appropriately suppress the occurrence of electrostatic offset in the fixing device.

1 is a cross-sectional view illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The front side of the sheet of FIG. 1 or the like is the front, and in each figure, “L” indicates “left”, “R” indicates “right”, “U” indicates “up”, and “D”. Indicates “below”.

1. Overall Configuration of Image Forming Apparatus The overall configuration of the image forming apparatus 1 will be described with reference to FIG. The image forming apparatus 1 of the present embodiment is a color printer that fixes a color toner image to a sheet S. FIG. 1 is a cross-sectional view schematically showing the internal structure of the image forming apparatus 1.

  The image forming apparatus 1 includes an apparatus main body 2 that forms a substantially rectangular parallelepiped appearance. A paper feed cassette 3 that stores paper sheets S is detachably provided at the lower portion of the apparatus main body 2. A paper discharge tray 4 is provided on the upper surface of the apparatus main body 2. The sheet S as an example of the medium is not limited to paper but may be a resin sheet or the like.

  The image forming apparatus 1 includes a paper feeding device 5, an image forming device 6, and a fixing device 7 inside the apparatus main body 2. The paper feeding device 5 is provided at the upstream end of the conveyance path 8 extending from the paper feeding cassette 3 to the paper discharge tray 4. The fixing device 7 is provided on the downstream side of the conveying path 8, and the image forming device 6 is provided between the paper feeding device 5 and the fixing device 7 in the conveying path 8.

  The image forming device 6 includes four toner containers 10, an intermediate transfer belt 11, four drum units 12, and an optical scanning device 13. The four toner containers 10 contain toners (developers) of four colors (yellow, magenta, cyan, black). The intermediate transfer belt 11 rotates counterclockwise in FIG. Each drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, a primary transfer roller 17, and a cleaning device 18. Each primary transfer roller 17 is provided so as to sandwich the intermediate transfer belt 11 between the photosensitive drum 14.

  A secondary transfer roller 19 is in contact with the right side of the intermediate transfer belt 11 to form a transfer nip N1. The secondary transfer roller 19 applies a negative bias from the print back side of the sheet S to electrically transfer the positively charged toner onto the sheet S when the sheet S passes.

2. Image Forming Process The image forming apparatus 1 forms an image on the sheet S according to the following procedure. Each charging device 15 charges the surface of the photosensitive drum 14. Each photosensitive drum 14 receives scanning light emitted from the optical scanning device 13 and carries an electrostatic latent image. Each developing device 16 develops the electrostatic latent image on the photosensitive drum 14 into a toner image using the toner supplied from the toner container 10. Each primary transfer roller 17 primarily transfers the toner image on the photosensitive drum 14 to the rotating intermediate transfer belt 11. The intermediate transfer belt 11 carries a full-color toner image obtained by superimposing four color toner images while rotating.

  The sheet S is sent out from the paper feeding cassette 3 to the conveyance path 8 by the paper feeding device 5. The secondary transfer roller 19 secondarily transfers the toner image on the intermediate transfer belt 11 to the sheet S that passes through the transfer nip N1. The fixing device 7 heat-fixes the unfixed toner image passing through the fixing nip N2 (pressure area) on the sheet S. Thereafter, the sheet S is discharged to the paper discharge tray 4. Each cleaning device 18 removes the toner remaining on the photosensitive drum 14.

3. FIG. 2 is a cross-sectional view schematically showing the detailed structure of the fixing device 7. The fixing device 7 includes a heating roller 31 (heating member), a pressure roller 32 (pressure member), a housing 33, a heat source 34, and a functional member 35.

  The heating roller 31 is a substantially cylindrical member that is long in the front-rear direction (rotational axis direction). The heating roller 31 includes a conductive core 31A made of a metal such as aluminum or iron, and an insulating layer 31B made of a fluororesin such as PFA having an insulating property. The heating roller 31 is a heating member that heats the sheet S on which the unfixed toner image is formed while rotating around its rotation axis.

  In order to improve the releasability of the sheet S, it is preferable that a fluororesin with less additive (for example, a pure fluororesin to which no additive is added) is used to form the insulating layer 31B. The insulating layer 31B is a PFA tube having a thickness of several tens of μm (for example, 50 μm) to several hundreds of μm (for example, 300 μm). The insulating layer 31B is a dielectric, and the capacitance of the heating roller 31 increases as the thickness of the insulating layer 31B increases. The primer layer formed between the cored bar 31A and the insulating layer 31B is preferably configured to have a thickness of several μm to several tens of μm by adding an additive containing metal such as aluminum.

  The cored bar 31A is connected to the ground G via the functional member 35 (that is, grounded). The surface of the insulating layer 31B accumulates negative charge due to contact with the sheet S in which negative charge is accumulated, and the inner periphery (core metal 31A side) of the insulating layer 31B is positive with respect to the surface of the insulating layer 31B. Become sexual. Thus, the heating roller 31 functions as a capacitor that accumulates electric charges by having a potential difference between the core metal 31A and the surface of the insulating layer 31B.

  The insulating layer 31B may be made of only a fluororesin, or an elastic layer made of silicone rubber having an insulating layer and laminated on the outer peripheral surface of the cored bar 31A, and an insulating PFA or the like. And a release layer that is made of a fluororesin and covers the elastic layer.

  The pressure roller 32 is a substantially cylindrical member that is long in the front-rear direction (rotational axis direction), like the heating roller 31. The pressure roller 32 includes a cylindrical cored bar 32A, an elastic layer 32B laminated on the outer peripheral surface of the cored bar 32A, and a release layer 32C that covers the elastic layer 32B. For example, the core metal 32A is made of a metal such as stainless steel (SUS) or aluminum, the elastic layer 32B is made of silicone rubber, and the release layer 32C is made of a fluororesin such as PFA.

  The pressure roller 32 is urged by a spring (not shown) and pressed against the heating roller 31, and a fixing nip N <b> 2 is formed between the heating roller 31 and the pressure roller 32. The pressure roller 32 is connected to a drive source such as a motor via a drive gear attached to the rear end thereof, and is rotationally driven by the drive source. It is rotationally driven by a drive source such as a motor (not shown). The heating roller 31 is driven to rotate by a pressure roller 32.

  The pressure roller 32 is a pressure member that forms a fixing nip N2 together with the heating roller 31 and presses the sheet S passing through the fixing nip N2 while rotating around its rotation axis. The melted toner is pressed onto the sheet S by being pressed by the heating roller 31.

  The housing 33 is a housing that houses the heating roller 31 and the pressure roller 32, and is formed in a substantially box shape that is long in the front-rear direction. The housing 33 is made of a conductive material such as metal, for example. The housing 33 includes a paper feed port 33A that is opened at the substantially horizontal center of the lower surface, and a paper discharge port 33B that is opened at the substantially horizontal center of the upper surface. The conveyance path 8 of the sheet S passes through the housing 33 through the paper feed port 33A and the paper discharge port 33B.

  The heat source 34 is composed of, for example, a halogen heater or a ceramic heater, and is provided in the internal space of the heating roller 31. The heat source 34 generates heat by power supplied from a power source (not shown) and heats the heating roller 31.

  The functional member 35 is provided between the cored bar 31A of the heating roller 31 and the ground G (grounding). The functional member 35 includes a first Zener diode D1 disposed on the core metal 31A side and a second Zener diode D2 disposed on the ground G side. The cathode of the first Zener diode D1 and the cathode of the second Zener diode D2 are opposed to each other. That is, the functional member 35 has an electrical positive / negative bipolar function.

  The first Zener diode D1 is grounded in the first direction in which charges having a polarity opposite to that of the toner are accumulated in the insulating layer 31B when the potential difference Δ between the core metal 31A and the surface of the insulating layer 31B is less than the first threshold value. It is comprised so that the electric current which flows between G and the heating roller 31 may be interrupted | blocked. The first threshold corresponds to the Zener voltage of the first Zener diode D1.

  In the present embodiment in which the positively charged toner is transferred to the sheet S, the first Zener diode D1 allows a current from the heating roller 31 to the ground G and has a potential difference Δ between the core metal 31A and the surface of the insulating layer 31B. Is configured to allow the current from the ground G to the heating roller 31 when the potential difference Δ is equal to or greater than the first threshold. The That is, the anode of the first Zener diode D1 is connected to the cored bar 31A side, and the cathode is connected to the ground G side.

  When the potential difference Δ between the core metal 31A and the surface of the insulating layer 31B is less than the second threshold value, the second Zener diode D2 has the ground G and the heating roller 31 in the second direction opposite to the first direction. It is comprised so that the electric current which flows between may be interrupted. The second threshold corresponds to the Zener voltage of the second Zener diode D2.

  In the present embodiment in which the positively charged toner is transferred to the sheet S, the second Zener diode D2 allows a current from the ground G to the heating roller 31, and a potential difference Δ between the core metal 31A and the surface of the insulating layer 31B. Is configured to allow the current from the heating roller 31 to the ground G when the potential difference Δ is equal to or greater than the second threshold. The That is, the anode of the second Zener diode D2 is connected to the ground G side, and the cathode is connected to the cored bar 31A side.

  It is preferable that the Zener voltage of each Zener diode D is individually set in the range of several hundreds V (for example, 500 V) to several kV (for example, 2 kV). It is preferable that the Zener voltage of each Zener diode D is set according to the charging property of the fixing system including the fixing device 7 (for example, the electrostatic capacity of the heating roller 31). Further, it is more preferable that the Zener voltage is set in consideration of the influence of the process (transfer process) before the fixing process.

4). Technical Effects of the Present Embodiment As described above, according to the configuration according to the present embodiment, the fixing device 7 includes the conductive core 31A and the insulating layer 31B provided around the core 31A, and rotates. A heating roller 31 that heats unfixed toner on the sheet S while rotating, a pressure roller 32 that forms a fixing nip N2 together with the heating roller 31 while rotating, and pressurizes the sheet S that passes through the fixing nip N2, and a core When the potential difference Δ between the metal core 31A and the surface of the insulating layer 31B is less than the first threshold value and is connected between the gold 31A and the ground G, a first charge is accumulated in the insulating layer 31B. The first element D1 that cuts off the current flowing between the ground G and the heating roller 31 in the direction, and is connected between the core metal 31A and the ground G, and the potential difference between the core metal 31A and the surface of the insulating layer 31B. Δ is second A functional member 35 having a second element D2 that cuts off a current flowing between the ground G and the heating roller 31 in a second direction opposite to the first direction when the value is less than the value. Prepare. According to the above configuration, the electric current flowing between the ground G and the heating roller 31 is interrupted, so that the potential difference Δ between the core metal 31A and the surface of the insulating layer 31B can be suppressed low. The occurrence of offset is appropriately suppressed.

  In particular, since the functional member 35 connected to the heating roller 31 includes the first element D1 and the second element D2 having polarities opposite to each other, the function of the positive and negative polarities is realized in the functional member 35. . Therefore, it is possible to suppress both positive charge and negative charge in the heating roller 31. As a result, the occurrence of electrostatic offset in the fixing device 7 is appropriately suppressed.

  The first element D1 is the first Zener diode D1, the second element D2 is the second Zener diode D2, the first threshold is the Zener voltage of the first Zener diode D1, and the second threshold is the second Zener. According to the configuration of the Zener voltage of the diode D2 and the cathode of the first Zener diode D1 and the cathode of the second Zener diode D2 facing each other, the functional member 35 can be realized with a simple configuration.

  Further, according to the configuration in which the toner is positively charged, the anode of the first Zener diode D1 is connected to the cored bar 31A side, and the anode of the second Zener diode D2 is connected to the ground G side. 35 can be realized with a simple configuration.

  Further, according to the above configuration, the image forming apparatus 1 including the fixing device 7 is provided.

5). Modifications The above-described embodiment can be variously modified. The modification of embodiment is shown below. Two or more aspects arbitrarily selected from the embodiments and modifications can be appropriately combined as long as they do not contradict each other.

  In the above description of the embodiment, positively charged toner is used in the image forming apparatus 1, but negatively charged toner may be used. In the configuration using the negatively charged toner, it is preferable that the secondary transfer roller 19 applies a positive bias to the sheet S.

  In the above description of the embodiment, a halogen lamp is employed as the heat source 34, but any heating member may be employed. For example, an IH heating unit that heats the heating roller 31 from the outside may be employed as the heat source 34. The IH heat generating unit is provided on the opposite side of the fixing nip N2. The IH heat generating unit includes a plurality of IH coils supported by a substantially semi-cylindrical holder. The plurality of IH coils are covered with an arch core formed of a ferromagnetic material such as ferrite. Each IH coil receives a supply of electric power from a power source (not shown) to generate a high frequency magnetic field to heat the heating roller 31.

  In the above description of the embodiment, the case where the image forming apparatus 1 of the present invention is a color printer is shown as an example. However, the present invention is not limited to this. The invention may be applied.

  The description of the above embodiment shows one aspect of the temperature detection device, the fixing device, and the image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above embodiment. Absent.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 7 Fixing apparatus 31 Heating roller (heating member)
31A Metal core 31B Insulating layer 32 Pressure roller (Pressure member)
35 Functional Member D1 First Zener Diode (First Element)
D2 Second Zener diode (second element)
G ground S sheet (medium)

Claims (4)

A heating member that has a conductive mandrel and an insulating layer provided around the mandrel, and heats unfixed toner on the medium while rotating;
A pressure member that forms a pressure region together with the heating member while rotating and pressurizes the medium passing through the pressure region;
The first metal is connected between the metal core and the ground, and stores a charge having a polarity opposite to that of the toner in the insulating layer when a potential difference between the metal core and the surface of the insulating layer is less than a first threshold value. A first element that cuts off a current flowing between the ground and the heating member in a direction, and is connected between the core metal and the ground, and a potential difference between the core metal and the surface of the insulating layer is A functional member having a second element that cuts off a current flowing between the ground and the heating member in a second direction opposite to the first direction when less than two threshold values; A fixing device comprising: a fixing device; The first element is a first Zener diode, the second element is a second Zener diode;
The first threshold is a Zener voltage of the first Zener diode, and the second threshold is a Zener voltage of the second Zener diode;
The fixing device according to claim 1, wherein a cathode of the first Zener diode and a cathode of the second Zener diode are opposed to each other. The toner is positively charged,
The fixing device according to claim 2, wherein an anode of the first Zener diode is connected to the core metal side, and an anode of the second Zener diode is connected to the ground side.   An image forming apparatus comprising the fixing device according to claim 1.

Images