Fixing apparatus and image forming apparatus

Abstract

Ensure the surface of the pressure roller is thoroughly discharged of static electricity. [Solution] The pressure roller 31 has a conductive surface layer 34 formed on the main part of the roller so as to contact the surface of the fixing belt 21 at the nip portion N, and a conductive, grounded gear-shaped member 65 (annular member) is installed on the core metal 32 (shaft portion) of the pressure roller 31 so as to have at least a part of it along the end face of the main part of the roller. The conductive surface layer 34 has a folded portion 34a formed at the widthwise end on the side where the gear-shaped member 65 is installed, which is folded from the roller surface side toward the roller central axis side so as to form part or all of the end face of the main part of the roller. Part or all of the folded portion 34a is in contact with the end face of the gear-shaped member 65.

Description

Technical Field

[0001] The present invention relates to a fixing device that heats and fixes a toner image carried on the surface of a sheet, and an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine including the same.

Background Art

[0002] Conventionally, in a fixing device installed in an image forming apparatus such as a copying machine or a printer, a technique for discharging a pressure roller is known in order to prevent the occurrence of abnormal images such as electrostatic offset (see, for example, Patent Document 1).

[0003] On the other hand, Patent Document 1 discloses a technique of installing a conductive rubber ring for discharging a fixing belt or a pressure roller on a shaft portion at a widthwise end of the pressure roller.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional fixing device, the surface of the pressure roller was not sufficiently discharged, and the occurrence of abnormal images such as electrostatic offset could not be sufficiently reduced.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a fixing device and an image forming apparatus capable of sufficiently discharging the surface of a pressure roller.

Means for Solving the Problems

[0006] The fixing device according to the present invention includes a fixing rotating body heated by a heat source, and a pressure roller that forms a nip portion through which a sheet is conveyed by being pressed against the fixing rotating body. The pressure roller is formed on a roller main body so as to contact the surface of the fixing rotating body at the nip portion, and includes a conductive surface layer having conductivity, and an annular member that is installed on a shaft portion of the pressure roller so that at least a part thereof extends along an end surface of the roller main body and has conductivity and is grounded. The conductive surface layer has a folded portion at the widthwise end on the side where the annular member is installed, which is folded from the roller surface side toward the roller central axis so as to form part or all of the end face of the main part of the roller, and part or all of the folded portion is in contact with the end face of the annular member. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a fixing device and an image forming apparatus that can sufficiently remove static electricity from the surface of a pressure roller. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a diagram showing the configuration of the fixing device. [Figure 3] This is a top view of the fixing device as seen in the width direction. [Figure 4] This is a schematic side view showing the anchoring belt and guide member in the width direction. [Figure 5] This is a cross-sectional view showing a fixing device connected to the earth path. [Figure 6] This is a cross-sectional view showing the widthwise end of the main part of the fixing device. [Figure 7] This is a cross-sectional view showing the widthwise end of a pressure roller, as a modified example 1. [Figure 8] This is a cross-sectional view showing the widthwise end of a pressure roller as an example. [Figure 9] This is a cross-sectional view showing the widthwise end of a pressure roller, as a modified example 2. [Figure 10] This is a side view showing the arrangement of the folded portion at the end face of the pressure roller, as an example of modification 3. [Figure 11] This is a cross-sectional view showing the widthwise end of a pressure roller, as a modified example 4. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for carrying out this invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be simplified or omitted as appropriate.

[0010] First, Figure 1 will explain the overall configuration and operation of the image forming apparatus 100. In Figure 1, 100 represents a small printer as an image forming apparatus, 1 represents a photosensitive drum on which a toner image is formed, 6 represents a process cartridge that integrates the photosensitive drum 1, a charging roller 4, a developing device 5, and a cleaning device 2, and 7 represents an exposure device (writing unit) that irradiates the photosensitive drum 1 with exposure light L based on image information input from an input device such as a personal computer. Furthermore, 9 is a transfer roller that transfers the toner image supported on the surface of the photoreceptor drum 1 to the sheet P which is transported to the transfer nip section (transfer position), 12 is a paper feed device (paper feed cassette) in which the sheet P such as paper is stored, 16 is a register roller (timing roller) that transports the sheet P toward the transfer nip section where the photoreceptor drum 1 and the transfer roller 9 come into contact, and 20 is a fixing device that fixes the unfixed image on the sheet P.

[0011] Here, a charging roller 4, a developing device 5, a cleaning device 2, and other components are arranged around the photoreceptor drum 1. These components (photoreceptor drum 1, charging roller 4, developing device 5, and cleaning device 2) are integrated as a process cartridge 6 and are installed in a detachable (replaceable) manner on the image forming apparatus body 100 (apparatus body). The process cartridge 6 is mainly removed from the image forming apparatus body 100 by the user and replaced with a new one when it reaches a predetermined replacement cycle.

[0012] Referring to Figure 1, the operation of the image forming apparatus 100 during normal image forming will be described. First, when image information is transmitted from an input device such as a personal computer to the exposure device 7 of the image forming apparatus 100, the exposure device 7 emits exposure light L (laser light) based on that image information toward the surface of the photoreceptor drum 1. Meanwhile, the photoreceptor drum 1 is driven by a drive motor installed in the image forming apparatus body 100 and rotates in the direction of the arrow (clockwise). First, the surface of the photoreceptor drum 1 is uniformly charged at the position opposite the charging roller 4 (this is the charging process). In this way, a charge potential (approximately -900V) is formed on the photoreceptor drum 1. Subsequently, the charged surface of the photoreceptor drum 1 reaches the irradiation position of the exposure light L. Then, the potential of the part irradiated by the exposure light L becomes the latent image potential (approximately 0 to -100V), and an electrostatic latent image is formed on the surface of the photoreceptor drum 1 (this is the exposure process).

[0013] Subsequently, the surface of the photoreceptor drum 1, on which the electrostatic latent image has formed, reaches a position opposite the developing device 5. Then, toner is supplied from the developing device 5 onto the photoreceptor drum 1, and the latent image on the photoreceptor drum 1 is developed to form a toner image (this is the developing process). Subsequently, the surface of the photoreceptor drum 1 after the development process reaches the transfer nip (transfer position) with the transfer roller 9. At the transfer nip with the transfer roller 9, a transfer bias (a bias with a different polarity from the toner's polarity) is applied from the power supply unit to the transfer roller 9, thereby transferring the toner image formed on the photoreceptor drum 1 onto the sheet P conveyed by the register roller 16 (this is the transfer process).

[0014] Then, the surface of the photoreceptor drum 1 after the transfer process reaches a position facing the cleaning device 2. At this position, any untransferred toner remaining on the photoreceptor drum 1 is mechanically removed by the cleaning blade and collected in the cleaning device 2 (this is the cleaning process). Thus, the series of image-forming processes on the photoreceptor drum 1 are completed.

[0015] On one hand, the sheet P conveyed to the transfer nip portion between the photoreceptor drum 1 and the transfer roller 9 operates as follows. First, the uppermost sheet P stored in the sheet feeding device 12 is fed by the sheet feeding roller 15 toward the conveyance path. After that, the sheet P reaches the position of the registration roller 16. And the sheet P that has reached the position of the registration roller 16 is conveyed toward the transfer nip portion (the contact position between the transfer roller 9 and the photoreceptor drum 1) while adjusting the timing to align with the image formed on the photoreceptor drum 1.

[0016] Then, after the sheet P passes through the position of the transfer nip portion (transfer roller 9) in the transfer process, it reaches the fixing device 20 through the conveyance path. The sheet P that has reached the fixing device 20 is fed between the fixing belt 21 and the pressure roller 31, and the image is fixed by the heat received from the fixing belt 21 and the pressure received from both members 21 and 22 (this is the fixing process). After the sheet P with the image fixed is sent out from between the fixing belt 21 and the pressure roller 31 (the fixing nip), it is discharged from the image forming apparatus main body 100 and placed on the paper discharge tray. In this way, a series of image forming processes is completed.

[0017] Next, the configuration and operation of the fixing device 20 will be described using FIGS. 2 to 6 and the like. The fixing device 20 is a device that conveys the sheet P (a sheet carrying unfixed toner) while heating it. Referring to FIGS. 2 and the like, the fixing device 20 includes a fixing belt 21 as a fixing rotating body, a planar heater 24 as a heat source (heating means), a holder 23, a stay 30, a thermistor 40, a pressure roller 31 as a pressure rotating body, a gear-shaped member 65 as an annular member (refer to FIGS. 3, FIGS. 5, FIGS. 6, etc.), and the like.

[0018] Here, the fixing belt 21 is an endless belt member that is in contact with the pressure roller 31 and rotates in a driven manner as the pressure roller 31 rotates. The fixing belt 21 is a thin-walled, flexible endless belt that rotates (rotates in a driven manner) in the direction of the arrow in Figure 2 (clockwise). Referring to Figure 5 (not a proportional scale), the fixing belt 21 has a base material layer 21a as a belt conductive layer and an insulating (or medium-resistance) belt surface layer 21b (surface layer) laminated from the inner circumferential surface (the sliding surface with the planar heater 24), and its overall thickness is set to 1 mm or less. The base material layer 21a of the fixing belt 21 has a layer thickness of 30 to 50 μm and is formed from a metal material such as nickel or stainless steel, or a resin material such as polyimide in which carbon is dispersed, and functions as a conductive belt layer. The belt surface layer 21b of the fixing belt 21 has a layer thickness of 5 to 50 μm and is made of an insulating material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyethersulfone). By providing an insulating belt surface layer 21b, release properties (peelability) from the toner (toner image) are ensured. In this embodiment, the belt surface layer 21b is formed from an insulating material, but it can also be formed from a medium-resistance material by dispersing a relatively small amount of carbon in the insulating material described above.

[0019] On the inside (inner circumferential surface) of the fixing belt 21, a planar heater 24, a holder 23, a stay 30, a thermistor 40, etc., are installed. Here, the planar heater 24 is positioned to extend in the width direction (the direction perpendicular to the plane of the paper in Figure 2, the left-right direction in Figures 3 to 6, and synonymous with the "axial direction"). The planar heater 24 presses against the pressure roller 31 via the fixing belt 21 on the inside (inner circumferential surface side) of the fixing belt 21, forming a nip section (fixing nip) through which the sheet P is conveyed. In other words, the planar heater 24 is installed so as to slide against the inner circumferential surface of the fixing belt 21. The planar heater 24 presses against the pressure roller 31 via the fixing belt 21, thereby forming a nip section through which the sheet P is conveyed. In this way, the planar heater 24 functions as a member that forms a nip section (fixing nip) (nip section forming member). Furthermore, the planar heater 24 has a resistive pattern (heat-generating resistor) formed on the portion that slides against the inner circumferential surface of the fixing belt 21. Power is supplied to the resistive pattern from a power supply unit (not shown), and the resistive pattern generates heat due to its resistance, thereby heating the fixing belt 21. In this way, the planar heater 24 also functions as a heat source (heating means) for heating the fixing belt 21.

[0020] Furthermore, in this embodiment, in order to reduce the sliding resistance between the planar heater 24 and the inner surface of the fixing belt 21, a lubricant such as silicone oil or fluorine grease is directly applied to the inner surface of the fixing belt 21. In this embodiment, the lubricant was directly applied to the inner circumferential surface of the fixing belt 21. However, the lubricant can also be applied indirectly to the inner circumferential surface of the fixing belt 21 by applying the lubricant to the sliding contact surface of the planar heater 24, for example. In addition to applying lubricant to the inner surface of the fixing belt 21, the surface of the planar heater 24 can also be covered with a sheet-like member made of a low-friction material such as PTFE or a surface layer can be provided.

[0021] In this embodiment, the planar heater 24 is held by the holder 23 (holding member). The holder 23 has a recess formed therein, into which the planar heater 24 is fitted, thereby holding the planar heater 24 across its width. The holder 23 is held by the stay 30 while holding the planar heater 24. The stay 30, which holds the planar heater 24 and the holder 23, is held by the frame 60 of the fixing device 20 at both ends in the width direction via flange members 42 (see Figure 3, etc.).

[0022] In this way, the fuser belt 21 is directly heated by a planar heater 24 (resistor pattern) installed inside it. Then, heat is applied to the toner image on the sheet P from the surface of the heated fuser belt 21. Here, the output control of the planar heater 24 is performed based on the temperature detection result by the thermistor 40, which is in direct (or indirectly via another component) contact with the planar heater 24. In this embodiment, there is no temperature sensor that directly detects the surface temperature of the fixing belt 21. Instead, the temperature of the planar heater 24 is controlled by the thermistor 40, thereby indirectly controlling the surface temperature (fixing temperature) of the fixing belt 21 to reach a desired temperature.

[0023] Referring to Figure 4, the pair of flange members 42 guide both ends of the fixing belt 21 in the width direction from the inner circumferential surface side so that the fixing belt 21 maintains a substantially cylindrical position. More specifically, the two flange members 42 are made of a heat-resistant resin material or the like, and are held at both ends in the width direction of the frame 60 of the fixing device 20 so as to be slidable in the direction of forming a nip portion (fixing nip). The flange members 42 are provided with a guide portion 42a for holding the fixing belt 21 while maintaining the substantially cylindrical posture of the fixing belt 21, and a stopper portion for restricting the movement of the fixing belt 21 in the width direction (towards the belt), etc. Furthermore, in this embodiment, as shown in Figure 3, the fixing belt 21 (and the planar heater 24 and holder 23) are configured to be pressed against the pressure roller 31 by pressure applied by the pressure lever 52 (pressure mechanism 51) via the flange member 42. Furthermore, the flange members 42 are positioned at both ends in the width direction, within the circumferential range excluding the fixing nip, so as not to interfere with the formation of the fixing nip by the planar heater 24. Furthermore, in this embodiment, the only members that contact the inner circumferential surface of the fixing belt 21 are the flange members 42 that make loose contact at both ends in the width direction and the planar heater 24, and there are no other members (belt guides) that contact the inner circumferential surface and guide the rotation of the fixing belt 21.

[0024] In this embodiment, the stay 30 is installed inside the fixing belt 21 so as to contact the pressure roller 31 via the planar heater 24 (and holder 23) and the fixing belt 21. The stay 30 reinforces the strength of the planar heater 24 (and holder 23) that forms the fixing nip, and is installed on the frame 60 (or holder 23) by screw fastening or the like. Furthermore, the stay 30 contacts the pressure roller 31 via the planar heater 24 (and holder 23) and the fixing belt 21, thereby preventing the planar heater 24 (and holder 23) from deforming significantly in the fixing nip due to the pressure applied by the pressure roller 31. In order to satisfy the above-mentioned function, it is preferable that the stay 30 be made of a metal material with high mechanical strength, such as stainless steel or iron.

[0025] While resin materials and metal materials can be used to form the holder 23, a resin material (such as liquid crystal polymer (LCP), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), polyetheretherketone (PEEK), etc.) is preferred as it has sufficient rigidity to prevent excessive deflection even under pressure from the pressure roller 31, and possesses thermal and heat insulating properties. In this embodiment, liquid crystal polymer (LCP) is used as the material for the holder 23.

[0026] Referring to Figure 2, the pressure roller 31, which acts as a pressurizing rotating body, has an elastic layer 33 and a conductive surface layer 34 sequentially laminated on a core metal 32 which acts as a shaft, and is driven to rotate in a predetermined direction (counterclockwise in Figure 2) by a drive motor 95. The core metal 32 (shaft portion) of the pressure roller 31 is a hollow structure made of a metal material (conductive material). The elastic layer 33 of the pressure roller 31 is made of an insulating material such as foamed silicone rubber, silicone rubber, or fluororubber. The conductive surface layer 34 of the pressure roller 31 is a thin surface layer (release layer) formed by dispersing carbon or the like in PFA, PTFE, etc., and is electrically conductive. In this embodiment, the conductive surface layer 34 is tubular and can be formed by covering the elastic layer 33 with a tube and subjecting it to heat processing or the like. The conductive surface layer 34 will be explained in more detail later with reference to Figure 6, etc. The pressure roller 31 presses against the fixing belt 21 to form a desired nip (fixing nip) between the two components. Also, referring to Figure 3, a gear 45 that meshes with the drive gear of the drive motor is installed on the pressure roller 31, and the pressure roller 31 is rotated in the direction of the arrow in Figure 2 (counterclockwise). Furthermore, both ends of the pressure roller 31 in the width direction are rotatably supported on the frame 60 of the fixing device 20 via bearings. In this embodiment, the fixing device 20 is also equipped with a gear-shaped member 65 as an annular member, which will be explained in detail later.

[0027] The following briefly describes the normal operation of the fixing device 20 configured as described above. When a print command is input to the main unit 100, power is supplied to the planar heater 24, and the drive motor 95 starts rotating the pressure roller 31 in the direction of the arrow in Figure 2. As a result, the fixing belt 21 also rotates in the direction of the arrow in Figure 2 due to the frictional force between the fixing nip and the pressure roller 31. Subsequently, the sheet P is fed from the paper feeder 12, and the unfixed image is placed (transferred) onto the sheet P at the position of the transfer roller 9. The sheet P, on which the unfixed image (toner image) is placed, is guided by an entrance guide plate (not shown) and transported in the direction of arrow Y10 in Figure 2, and is fed into the nip section (fixing nip) of the fixing belt 21 and pressure roller 31, which are in a pressed state. Then, the toner image is fixed to the surface of the sheet P by heating from the fixing belt 21 heated by the planar heater 24, and by the pressing force between the planar heater 24 (and holder 23), reinforced by the stay 30, and the pressure roller 31. After that, the sheet P, which has been fed out from the fixing nip, is transported in the direction of arrow Y11 while being guided by an exit guide plate (not shown).

[0028] The configuration and operation of the characteristic fixing device 20 in the image forming apparatus 100 of this embodiment will be described in detail below. As explained earlier using Figures 2 and 5, the fixing belt 21 is provided with a base layer 21a, which serves as a conductive belt layer. In addition, an insulating belt surface layer 21b (or a belt surface layer with medium resistance) is directly laminated onto the base layer 21a (belt conductive layer) of the fixing belt 21. In other words, the fixing belt 21 in this embodiment has a two-layer structure in which a conductive belt conductive layer is used as a base layer 21a, and an insulating or medium-resistance belt surface layer 21b is laminated on the base layer 21a.

[0029] In particular, in this embodiment, one end of the base material layer 21a (belt conductive layer) in the width direction (the side on which the conductive gear-shaped member 65 (annular member), described later, is installed, which is the left side in Figure 5) is formed to protrude beyond the belt surface layer 21b in the width direction. That is, the base material layer 21a (conductive belt conductive layer) has a portion that is exposed at the width direction end on the side on which the gear-shaped member 65 (annular member) is installed. Then, the base material layer 21a (belt conductive layer) that protrudes from one end in the width direction comes into direct contact with the gear-shaped member 65, which will be described later as an annular member (a contact portion is formed). Therefore, the belt surface layer 21b is laminated on the base layer 21a (belt conductive layer) in the width direction (left-right direction in Figures 5 and 6, and axial direction) excluding the contact area between the base layer 21a and the gear-shaped member 65 described later. In other words, the belt surface layer 21b is directly laminated on the base layer 21a in the width direction excluding the exposed portion of the base layer 21a.

[0030] On the other hand, the pressure roller 31, which acts as a pressurizing rotating body, is provided with a conductive surface layer 34 (which has conductivity) that contacts the belt surface layer 21b of the fixing belt 21 (fixing rotating body) to form a nip portion (fixing nip). The conductive surface layer 34 is formed on the main part of the roller (the part in which the elastic layer 33 and the conductive surface layer 34 are laminated) so as to contact the surface of the fixing belt 21 at the nip portion. Here, as shown in Figures 5 and 6, the pressure roller 31 (pressure rotating body) of the fixing device 20 in this embodiment has a gear-shaped member 65, which is a conductive and grounded annular member, installed on the core metal 32, which is the shaft portion of the pressure roller 31, such that at least a part of the gear-shaped member 65 is along the end face of the main part of the roller (the part in which the elastic layer 33 and conductive surface layer 34 are formed, excluding the ends where only the core metal 32 is exposed). Furthermore, the gear-shaped member 65 (annular member) in this embodiment is in contact with and electrically connected to the exposed portion of the base material layer 21a (belt conductive layer) (the portion where the belt surface layer 21b is not laminated and is exposed on one end in the width direction). Therefore, the gear-shaped member 65 is in contact with and electrically connected to the base material layer 21a (belt conductive layer) and the conductive surface layer 34 of the fixing belt 21, respectively.

[0031] More specifically, as shown in Figures 5 and 6, the gear-shaped member 65 is an annular (donut-shaped) member made of a conductive material, but it is not a perfect annular shape. Instead, multiple spur-tooth-shaped protrusions are formed on its outer circumference along the entire circumference. In other words, the gear-shaped member 65 is formed in a gear shape, similar to a so-called spur gear. However, although this annular gear-shaped member 65 has a gear shape, it does not function as a gear for so-called drive transmission, but rather functions as a conductive member for grounding the base material layer 21a (belt conductive layer) and the conductive surface layer 34 of the fixing belt 21, respectively.

[0032] The gear-shaped member 65 is inserted (installed) into the core metal 32 of the pressure roller 31 (the part that functions as the shaft at the end) so as to contact the base material layer 21a (belt conductive layer) of the fixing belt 21 and the end face of the main part of the pressure roller 31. The gear-shaped member 65 then rotates together with the pressure roller 31 in a predetermined direction (counterclockwise in Figure 2).

[0033] Furthermore, in this embodiment, the gear-shaped member 65 has an outer diameter (tooth tip diameter) that is approximately equal to or slightly larger than the outer diameter of the main roller portion of the pressure roller 31 (the portion on which the elastic layer 33 and conductive surface layer 34 are formed). The teeth of the gear-shaped member 65 are in contact with the base material layer 21a of the fixing belt 21 (the exposed portion of the belt conductive layer). In this case, even if the outer diameter (tooth tip diameter) of the gear-shaped member 65 is the same as the outer diameter of the main part of the roller, the belt surface layer 21b is extremely thin, and the pressure roller 31 presses against the fixing belt 21 so as to bite into it, the gear-shaped member 65 (teeth) comes into contact with the base material layer 21a (belt conductive layer) and becomes electrically conductive. In this embodiment, the annular member that contacts the base material layer 21a (belt conductive layer) of the fixing belt 21 is not a perfectly annular member, but rather a gear-shaped member (in this embodiment, a spur gear shape). Therefore, compared to the case where a perfectly annular member is in contact with the base material layer 21a, multiple gear teeth arranged in a circumferential direction alternately contact the base material layer 21a, reducing contact defects such as uneven contact, and as a result, it becomes possible to ensure good, stable, and relatively large contact pressure for electrical conductivity with the base material layer 21a.

[0034] In this embodiment, the gear-shaped member 65 is press-fitted onto the core metal 32, which serves as the shaft, in order to improve conductivity (electrical connectivity) with the core metal 32. Furthermore, to prevent misalignment of the gear-shaped member 65 in the width direction (axial direction) of the core metal 32, the gear-shaped member 65 can also be bonded and fixed to the core metal 32 via a conductive adhesive. Furthermore, as shown in Figure 5, in this embodiment, the gear-shaped member 65 is grounded via the core metal 32. More specifically, the core metal 32 is connected to the grounding wire (connected to the grounded frame 60) on which the resistor 68 (electrical resistance component) is installed. As a result, the gear-shaped component 65 is properly grounded. Furthermore, the gear-shaped member 65 is positioned outside the maximum paper-feeding area M of the fixing device 20 (the widthwise range through which the largest possible sheet P can be transported passes) (non-paper-feeding area). As a result, there is no influence from the gear-shaped member 65 coming into contact with the fixed image.

[0035] As described above, the fixing device 20 in this embodiment is equipped with a gear-shaped member 65 that functions as a conductive member, thereby ensuring good electrical conductivity between the base material layer 21a (belt conductive layer) of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31 and the grounded gear-shaped member 65. Consequently, charge is less likely to accumulate on the fixing belt 21 and the pressure roller 31, reducing the occurrence of abnormal images such as electrostatic offset due to charge accumulation.

[0036] "Electrostatic offset" is a phenomenon that occurs during the fixing process when toner carried on the sheet P fed into the nip section (fixing nip) electrostatically transfers to and adheres to the surface of the fixing belt 21 (fixing rotating body), and this adhered toner then reattaches to the sheet P as the fixing belt 21 completes one rotation. This transfer of toner to the fuser belt 21 occurs because the surfaces of the fuser belt 21 and the pressure roller 31 each become electrically charged. In particular, the toner used in this embodiment has a negative polarity, and when the fuser belt 21 becomes positively charged and the pressure roller 31 becomes negatively charged, the toner receives an electrostatic repulsive force from the pressure roller 31 side and an electrostatic adsorption force from the fuser belt 21 side, causing it to adhere to the fuser belt 21. In response to this phenomenon, as described above, the fixing device 20 in this embodiment actively removes static electricity from the base layer 21a (belt conductive layer) of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31, so that the surfaces of the fixing belt 21 and the pressure roller 31 are less likely to become charged. Therefore, electrostatic offset is less likely to occur.

[0037] Referring to Figure 6, etc., in the pressure roller 31 of this embodiment, the conductive surface layer 34 has a folded portion 34a formed at the widthwise end (one end in the widthwise direction, which is the left end in Figures 5 and 6) on the side where the gear-shaped member 65 (annular member) is installed. This folded portion 34a is a part that is folded from the roller surface side (outer peripheral surface side) to the roller central axis side (side of the central axis W) so as to form a part or all of the end face of the main part of the pressure roller 31 (the part on which the elastic layer 33 and the conductive surface layer 34 are formed) (including cases where it is formed to appear folded in appearance even if it is not actually folded during the manufacturing process). In particular, the conductive surface layer 34 in this embodiment is tubular in shape and is formed to cover almost the entire outer peripheral surface and end face of the elastic layer 33. Furthermore, the folded portion 34a is configured to be in contact with the end face of the gear-shaped member 65 (annular member). In other words, the conductive surface layer 34 is folded radially so that its widthwise end (axial end) follows the end face of the elastic layer 33, and the folded portion is in contact with the end face of the gear-shaped member 65.

[0038] By bringing the folded portion 34a formed on the conductive surface layer 34 into contact with the end face of the gear-shaped member 65, a sufficient contact area between the conductive surface layer 34 and the gear-shaped member 65 can be secured with a relatively simple configuration without the need for a complex grounding path. Therefore, the surface of the pressure roller 31 (conductive surface layer 34) is sufficiently discharged, and the occurrence of abnormal images such as electrostatic offset is sufficiently reduced.

[0039] <Example 1> As shown in Figure 7, in the fixing device 20 of the modified example 1, the gear-shaped member 65 as an annular member is configured such that, at room temperature, the end face on the side facing the main part of the pressure roller 31 (the part on which the conductive surface layer 34 and elastic layer 33 are formed) has a gap with the end face of the main part of the roller on the outer circumferential side. More specifically, in the modified example 1, the gear-shaped member 65 has a gear width D2 on the outer diameter side that is smaller than the gear width D1 on the inner diameter side (D1 > D2), and is formed in a roughly drum shape. Furthermore, the conductive surface layer 34 of the pressure roller 31 has a folded portion 34a formed on one end in the width direction, and the axial center side of the folded portion 34a is in contact with the inner diameter side of the gear-shaped member 65 (the part with gear width D1), thus providing electrical contact. The reason for forming the gear-shaped member 65 in this way is that, during the fixing process (actual operating conditions) in which the fixing device 20 is used at high temperatures, the gear-shaped member 65 may undergo greater thermal expansion on the outer diameter side than on the inner diameter side. In particular, as shown in Figure 7, in the fixing device 20 of the modified example 1, the gear-shaped member 65 (annular member) is bonded to the core metal 32 (shaft portion) via a conductive adhesive, with its inner circumferential surface serving as the adhesive portion R. As a result, the outer diameter portion expands more than the inner diameter portion portion, where thermal expansion is limited by the adhesive at the adhesive portion R, causing the gear width to become larger than at room temperature. Figure 8 shows a gear-shaped member 65 as a comparative example. In this example, the gear width is constant from the inner diameter side to the outer diameter side at room temperature, but during the fixing process (high temperature), the gear width on the outer diameter side becomes larger than that on the inner diameter side due to thermal expansion. In such a case, the end face of the roller portion of the pressure roller 31 is pressed by the gear-shaped member 65, whose gear width on the outer diameter side has increased due to thermal expansion, causing wrinkles to form at the end of the elastic layer 33 or the end of the conductive surface layer 34 to bulge (see area F enclosed by dashed lines). When this happens, the conductive surface layer 34 and the elastic layer 33 are damaged, reducing the function of the pressure roller 31 as a pressure roller that forms the nip portion N (fixing nip), and making it difficult to make contact with the conductive surface layer 34. In contrast, the fixing device 20 in Modified Example 1 anticipates that the gear width on the outer diameter side of the gear-shaped member 65 will increase due to thermal expansion during the fixing process (at high temperatures) as described above, and therefore sets the gear width D2 on the outer diameter side to be smaller in advance when the temperature is normal (providing a space for the outer diameter side of the gear-shaped member 65 to expand due to thermal expansion). As a result, the problems described using Figure 8 are less likely to occur. Furthermore, in the modified example 1 as well, since a portion of the folded portion 34a (towards the axial center) is configured to contact the end face of the gear-shaped member 65, a sufficient contact area between the conductive surface layer 34 and the gear-shaped member 65 is ensured, making it possible to sufficiently discharge static electricity from the surface (conductive surface layer 34) of the pressure roller 31. In particular, compared to the room temperature shown in Figure 7, the contact area between the conductive surface layer 34 and the gear-shaped member 65 is further increased during the fixing process (at high temperatures) due to thermal expansion on the outer diameter side of the gear-shaped member 65, thus making it easier to exert the static electricity discharge effect described above.

[0040] <Modification 2> As shown in Figure 9(A), the gear-shaped member 65 installed on the pressure roller 31 of the fixing device 20 in modified example 2 is configured, similar to that in Figure 7, such that at room temperature, the end face on the side facing the main part of the pressure roller 31 (the part on which the conductive surface layer 34 and elastic layer 33 are formed) has a gap with the end face of the main part of the roller on the outer circumferential side. However, unlike the roughly drum-shaped one in Figure 7, only the end face facing the main part of the roller has that shape, while the end face on the opposite side (left side in Figure 9(A)) has a straight shape when viewed in cross-section. In another configuration, the gear-shaped member 65 (annular member) shown in Figure 9(B) has a small-diameter portion 65x (formed to be sufficiently smaller than the outer diameter of the pressure roller 31 without contacting the base material layer 21a of the fixing belt 21) formed on the side facing the main roller portion of the pressure roller 31. The end face of this small-diameter portion 65 is in contact with the folded portion 34a of the conductive surface layer 34. Furthermore, in another configuration, the gear-shaped member 65 (annular member) shown in Figure 9(C) is configured such that a notch is formed in the width direction on the outer circumferential surface at room temperature. Specifically, a notch 65z is formed in the center of the gear-shaped member 65 in the gear width direction (axial direction) (in the example of Figure 9(C), this is the side relatively close to the end face of the main roller part of the pressure roller 31) and is sufficiently smaller than the outer diameter of the pressure roller 31 without contacting the base material layer 21a of the fixing belt 21. Furthermore, even when using gear-shaped members 65 as shown in Figures 9(A) to (C), since there is a space for relief when the outer diameter side of the gear-shaped member 65 expands due to thermal expansion, the problem of the end face of the roller portion of the pressure roller 31 being pushed towards the outer diameter side of the gear-shaped member 65 is less likely to occur. As a result, the problem of wrinkles forming at the edges of the elastic layer 33 and the edges of the conductive surface layer 34 bulging are also less likely to occur. Furthermore, in the fixing device 20 as shown in Figures 9(A) to (C), a part or all of the folded portion 34a is configured to contact the end face of the gear-shaped member 65, thereby ensuring a sufficient contact area between the conductive surface layer 34 and the gear-shaped member 65, and enabling sufficient static discharge of the surface (conductive surface layer 34) of the pressure roller 31.

[0041] <Variation 3> As shown in Figure 10(A), in the fixing device 20 of the modified example 3, the folded portion 34a of the conductive surface layer 34 of the pressure roller 31 is divided in the circumferential direction and multiple portions are formed so that they do not overlap with each other. Forming multiple folded portions 34a in the conductive surface layer 34 in this manner is used when performing processes such as bonding the unfolded conductive surface layer 34 onto the elastic layer 33. Specifically, the conductive surface layer 34 shown in Figure 10(A) has two folded portions 34a that are offset by approximately 180 degrees, and are configured so that they do not overlap each other. This configuration ensures good contact (electrical conductivity) between the multiple folded portions 34a and the end face of the gear-shaped member 65. In other words, as shown in Figure 10(B) as a comparative example, if multiple folded portions 34a are formed to overlap each other, a step difference will occur between the overlapping portion and the non-overlapping portion, which may prevent good contact (electrical conductivity) with the end face of the gear-shaped member 65. Furthermore, the folded portion 34a shown in Figure 10(A) is formed with a larger contact area with the end face contact portion 65k of the gear-shaped member 65, in order to increase the contact area with the end face contact portion 65k. Furthermore, in the fixing device 20 of the modified example 3, the folded portion 34a is configured to contact the end face of the gear-shaped member 65, so that a sufficient contact area is secured between the conductive surface layer 34 and the gear-shaped member 65, making it possible to sufficiently discharge static electricity from the surface (conductive surface layer 34) of the pressure roller 31.

[0042] <Modification 4> As shown in Figure 11, in the fixing device 20 of the modified example 4, the folded portion 34a of the conductive surface layer 34 of the pressure roller 31 is configured such that a gap is formed between the roller surface side (the outer peripheral surface side, which is the portion 34a1 enclosed by the dashed line) and the end face of the main part of the roller. In other words, in the modified example 4, the folded portion 34a is not adhered to the end face of the main roller of the pressure roller 31, except for the portion 34a1 enclosed by the dashed line (the portion that forms a gap with respect to the roller end face). The folded portion 34a is adhered to the roller end face and makes contact (electrical connection) with the small diameter portion 65x of the gear-shaped member 65. In other words, in modified example 4, the folded portion 34a is folded from the roller surface side toward the roller central axis side so as to form a part of the end face of the main roller portion of the pressure roller 31 (the part closest to the core metal 32). The gear-shaped member 65 is then installed on the core metal 32 such that a part of it (the part closest to the core metal 32, which is the small diameter portion 65x) is aligned with the end face of the main roller portion of the pressure roller 31. In this way, by leaving a gap in the portion of the folded portion 34a that is close to the outer circumferential surface of the main roller portion, without adhering it to the end face of the main roller portion, it is possible to prevent damage to the fixing belt 21 caused by protrusions (bulges) that may occur when the folded portion 34a is folded vertically from the outer circumferential surface side. Furthermore, in the fixing device 20 of the modified example 4, the folded portion 34a is configured to contact the end face of the gear-shaped member 65, so that a sufficient contact area is secured between the conductive surface layer 34 and the gear-shaped member 65, making it possible to sufficiently discharge static electricity from the surface (conductive surface layer 34) of the pressure roller 31.

[0043] As described above, the fixing device 20 in this embodiment includes a fixing belt 21 (fixing rotating body) heated by a planar heater 24 (heat source), and a pressure roller 31 that forms a nip section N on which the sheet P is conveyed by pressing it against the fixing belt 21. The pressure roller 31 has a conductive surface layer 34 formed on its main body so as to contact the surface of the fixing belt 21 at the nip section N, and a conductive, grounded gear-shaped member 65 (annular member) is installed on the core metal 32 (shaft) of the pressure roller 31 so as to have at least a part of it along the end face of the main body of the roller. The conductive surface layer 34 has a folded portion 34a formed at the widthwise end on the side where the gear-shaped member 65 is installed, which is folded from the roller surface side toward the roller central axis so as to form part or all of the end face of the main body of the roller. Part or all of the folded portion 34a is in contact with the end face of the gear-shaped member 65. This allows the surface of the pressure roller 31 to be sufficiently electrostatically discharged.

[0044] In this embodiment, the present invention was applied to a fixing device 20 using a planar heater 24 as a heat source. However, the fixing device to which the present invention is applied is not limited to this, and the present invention can naturally be applied to fixing devices using heaters or electromagnetic induction coils as heat sources, for example. Furthermore, in this embodiment, the present invention was applied to a fixing device 20 using a fixing belt 21 as the fixing rotating body. However, the fixing device to which the present invention is applied is not limited to this, and the present invention can naturally be applied to fixing devices such as fixing rollers or fixing belts (stretched between multiple roller members) as the fixing rotating body. Furthermore, in this embodiment, a base layer 21a was used as the belt conductive layer formed on the fixing belt 21. However, in the fixing belt 21, a conductive elastic layer and a belt surface layer 21b can be sequentially laminated on the base layer 21a (as a three-layer structure), and the conductive elastic layer can be used as the belt conductive layer. Furthermore, although a gear-shaped member 65 was used as the annular member in this embodiment, the annular member does not necessarily have to be gear-shaped. Also, the annular member does not necessarily have to be a spur gear; for example, it may be a helical gear. Furthermore, in this embodiment, the planar heater 24, which serves as a heat source, is configured to form a nip portion (fixed nip) by being pressed against the pressure roller 31 via the fixing belt 21 as a nip-forming member. However, the nip-forming member does not necessarily have to be a heat source. Furthermore, in this embodiment, the gear-shaped member 65 (annular member) is configured to form an earth path by contacting the folded portion 34a (pressure roller 31) and the base material layer 21a (fixing belt 21), respectively. However, it is also possible to form an earth path by contacting only the folded portion 34a (pressure roller 31) with the gear-shaped member 65 (annular member), and to form a separate earth path with respect to the base material layer 21a (fixing belt 21). Furthermore, the same effects as those of this embodiment can be obtained in these cases as well.

[0045] It is clear that the present invention is not limited to this embodiment, and that this embodiment can be modified as appropriate within the scope of the technical concept of the present invention, in addition to what is suggested here. Furthermore, the number, position, shape, etc. of the constituent members are not limited to this embodiment, and can be set to a number, position, shape, etc. that is suitable for carrying out the present invention.

[0046] In this specification, the term "sheet" is defined to include not only paper but also all sheet-like recording media such as coated paper, label paper, OHP sheets, and film sheets that are transported. [Explanation of symbols]

[0047] 20 Fixing device, 21 Fixing belt (fixing rotating body), 21a Substrate layer (belt conductive layer), 21b Belt surface layer, 24-sided heater (heat source), 31 Pressure roller (pressure rotating body), 32 Core metal (shaft part), 33. Elastic layer (insulating elastic layer), 34 conductive surface layer, 34a Folded section, 65 Gear-shaped member (annular member), 65k end contact part, 65x small diameter section, 65z notch, 68 Resistors (electrical resistance components), 100 Image forming apparatus (image forming apparatus main unit), N Nip section (fixing nip), R adhesive part, P-sheet (recording medium).

[0048] Furthermore, the embodiments of the present invention can also be, for example, combinations of appendices 1 to 11 as follows. (Note 1) A fixing rotating body heated by a heat source, A pressure roller that forms a nip section on which the sheet is conveyed by pressing it against the aforementioned fixing rotating body, Equipped with, The aforementioned pressure roller A conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, and the conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, An annular member that is conductive and grounded is installed on the shaft of the pressure roller such that at least a part of it is along the end face of the main part of the roller, It is equipped with, The conductive surface layer has a folded portion at the widthwise end on the side where the annular member is installed, which is folded from the roller surface side toward the roller central axis so as to form part or all of the end face of the main part of the roller. A fixing device characterized in that part or all of the folded portion contacts the end face of the annular member. (Note 2) The fixing belt of the aforementioned fixing rotating body, A portion is formed at the widthwise end of the side on which the annular member is installed, and a conductive belt conductive layer is formed thereon. An insulating or medium-resistance belt surface layer is directly or indirectly laminated on the belt conductive layer in the width direction, excluding the exposed portion, It is equipped with, The fixing device according to Appendix 1, characterized in that the annular member contacts and conducts electricity with the exposed portion of the belt conductive layer. (Note 3) The fixing device according to Appendix 2, characterized in that the annular member is formed in a gear shape and its teeth contact the exposed portion of the belt conductive layer. (Note 4) The fixing device according to any one of the appendices 1 to 3, characterized in that the annular member is configured such that, at room temperature, the end face on the side facing the main roller portion forms a gap with respect to the end face of the main roller portion on the outer peripheral side. (Note 5) The fixing device according to Appendix 4, characterized in that the annular member is formed in a roughly drum-like shape. (Note 6) The fixing device according to Appendix 4, characterized in that the annular member has a small diameter portion formed on the side facing the main roller portion. (Note 7) The fixing device according to any one of the appendices 1 to 3, characterized in that the annular member is configured such that a notch is formed in the width direction on the outer surface side when at room temperature. (Note 8) The fixing device according to any one of the appendices 1 to 7, characterized in that the annular member has its inner circumferential surface bonded to the shaft portion. (Note 9) The fixing device according to any one of the appendices 1 to 8, characterized in that the aforementioned folded portion is divided in the circumferential direction and formed in multiple sections so as not to overlap with each other. (Note 10) The fixing device according to any one of the appendices 1 to 9, characterized in that the folded portion is configured such that a gap is formed on the roller surface side with respect to the end face of the main part of the roller. (Note 11) An image forming apparatus characterized by being equipped with a fixing device described in any of Appendix 1 to Appendix 10. [Prior art documents] [Patent Documents]

[0049] [Patent Document 1] Japanese Patent Publication No. 2008-268629

Claims

1. A fixing rotating body heated by a heat source, A pressure roller that forms a nip section on which the sheet is conveyed by pressing it against the aforementioned fixing rotating body, Equipped with, The aforementioned pressure roller A conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, and the conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, An annular member that is conductive and grounded is installed on the shaft of the pressure roller such that at least a part of it is along the end face of the main part of the roller, It is equipped with, The conductive surface layer has a folded portion at the widthwise end on the side where the annular member is installed, which is folded from the roller surface side toward the roller central axis so as to form part or all of the end face of the main part of the roller. A fixing device characterized in that part or all of the folded portion contacts the end face of the annular member.

2. The fixing belt of the aforementioned fixing rotating body, A portion is formed at the widthwise end of the side on which the annular member is installed, and a conductive belt conductive layer is formed thereon. An insulating or medium-resistance belt surface layer is directly or indirectly laminated on the belt conductive layer in the width direction, excluding the exposed portion, It is equipped with, The fixing device according to claim 1, characterized in that the annular member contacts and conducts electricity with the exposed portion of the belt conductive layer.

3. The fixing device according to claim 2, characterized in that the annular member is formed in a gear shape and its teeth contact the exposed portion of the belt conductive layer.

4. The fixing device according to claim 1 or 2, characterized in that the annular member is configured such that, at room temperature, the end face on the side facing the main roller portion has a gap formed with respect to the end face of the main roller portion on the outer peripheral side.

5. The fixing device according to claim 4, characterized in that the annular member is formed in a roughly drum shape.

6. The fixing device according to claim 4, characterized in that the annular member has a small diameter portion formed on the side facing the main roller portion.

7. The fixing device according to claim 1 or 2, characterized in that the annular member is configured such that a notch is formed in the width direction on the outer surface side when at room temperature.

8. The fixing device according to claim 1 or 2, characterized in that the inner circumferential surface of the annular member is bonded to the shaft portion.

9. The fixing device according to claim 1 or 2, characterized in that the folded portion is divided in the circumferential direction and formed in multiple locations so as not to overlap with each other.

10. The fixing device according to claim 1 or 2, characterized in that the folded portion is configured such that a gap is formed on the roller surface side with respect to the end face of the main part of the roller.

11. An image forming apparatus characterized by comprising a fixing device according to claim 1 or claim 2.

Images