Fixing apparatus and image forming apparatus

Abstract

This prevents the lubricant applied to the inner surface of the fixing belt from leaking out of the fixing belt. [Solution] A fixing belt 21 is provided, on which a lubricant is applied directly or indirectly to the inner circumferential surface and which is heated by a planar heater 24. A pressure roller 31 is also provided, which forms a nip portion on which the sheet P is conveyed by pressing it against the fixing belt 21. Furthermore, a helical gear 65 (annular member) that rotates together with the pressure roller 31 is installed on the core metal 32 of the pressure roller 31 so as to contact the widthwise end of the fixing belt 21. The helical gear 65 has multiple helical tooth-shaped protrusions 65a formed on its outer circumference, which are inclined with respect to the axial direction and extend over the entire circumferential surface. In addition, when the helical tooth-shaped protrusions 65a rotate together with the pressure roller 31, they are inclined in a direction that applies a thrust force toward the axial center at the contact portion with the fixing belt 21.

Description

Technical Field

[0001] This 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 equipped with 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 of applying a lubricant to the inner peripheral surface of a fixing belt is known in order to reduce wear of the inner peripheral surface of the fixing belt (see, for example, Patent Document 1).

[0003] Specifically, the fixing device of Patent Document 1 has a planar heater (heat source) that is in sliding contact with the inner peripheral surface of the fixing belt, and this planar heater is pressed against a pressure roller (pressure rotating body) through the fixing belt, thereby forming a fixing nip (nip portion) through which the sheet is conveyed. Then, a lubricant is applied to the inner peripheral surface of the fixing belt in order to reduce the sliding resistance between the planar heater and the inner peripheral surface of the fixing belt.

[0004] On the other hand, Patent Document 2 discloses a technique of installing a sawtooth-shaped member that contacts the end of a fixing belt and moves the fixing belt to the other end side (outer side) in the width direction in order to prevent the fixing belt from shifting to one end side in the width direction.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional fixing device, the lubricant applied to the inner peripheral surface of the fixing belt has moved and leaked in the width direction along the nip portion. Then, the lubricant leaked from the fixing belt has adhered to other constituent members and caused abnormalities in the fixed image or soiled the outside of the fixing device.

[0006] This invention was made to solve the above-mentioned problems, and aims to provide a fixing device and an image forming apparatus in which the lubricant applied to the inner circumferential surface of the fixing belt is less likely to leak out of the fixing belt. [Means for solving the problem]

[0007] The fixing device in this invention comprises a fixing belt on which a lubricant is directly or indirectly applied to the inner circumferential surface and heated by a heat source; a pressurizing rotating body that forms a nip portion on which a sheet is conveyed by pressing it against the fixing belt; and an annular member that is installed on the shaft of the pressurizing rotating body so as to contact the widthwise end of the fixing belt and rotates together with the pressurizing rotating body. The annular member has a plurality of serrated protrusions formed on its outer circumference over the entire circumferential area, which are inclined in the direction of the axial direction, and when the serrated protrusions rotate together with the pressurizing rotating body, they are inclined in a direction that applies a thrust force toward the axial center at the contact portion with the fixing belt. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a fixing device and an image forming apparatus in which the lubricant applied to the inner circumferential surface of the fixing belt is less likely to leak out of the fixing belt. [Brief explanation of the drawing]

[0009] [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 front view showing the widthwise end of the main part of the fixing device. [Figure 7]This is a perspective view showing the widthwise end of the main part of the fixing device. [Figure 8] (A) A schematic diagram showing the behavior of the lubricant in the fixing device of the present invention, and (B) A schematic diagram showing the behavior of the lubricant in a fixing device as a comparative example. [Figure 9] This is a schematic diagram showing the tooth-shaped protrusions in a tooth-shaped gear. [Figure 10] This is a schematic diagram showing the tooth-shaped protrusions in a tooth-shaped gear, as an example of modification 1. [Figure 11] This is a cross-sectional view showing a fixing device connected to the earth path, as a modified example (2). [Figure 12] This is a cross-sectional view showing a fixing device connected to the earth path, as a modified example 3. [Modes for carrying out the invention]

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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).

[0014] 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). After that, the surface of the photoreceptor drum 1 after the developing process reaches the transfer nip portion (transfer position) with the transfer roller 9. Then, at the transfer nip portion with the transfer roller 9, a transfer bias (a bias having a polarity different from that of the toner) is applied from the power supply unit to the transfer roller 9, so that the toner image formed on the photoreceptor drum 1 is transferred onto the sheet P conveyed by the resist roller 16 (this is the transfer process).

[0015] Then, the surface of the photoreceptor drum 1 after the transfer process reaches the opposing position with the cleaning device 2. And at this position, the untransferred toner remaining on the photoreceptor drum 1 is mechanically removed by the cleaning blade and recovered into the cleaning device 2 (this is the cleaning process). Thus, a series of image forming processes on the photoreceptor drum 1 is completed.

[0016] On the other 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 paper feeding device 12 is fed by the paper feeding roller 15 toward the conveyance path. After that, the sheet P reaches the position of the resist roller 16. And the sheet P that has reached the position of the resist 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.

[0017] After passing through the position of the transfer nip portion (transfer roller 9), the sheet P after the transfer process 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). The sheet P with the image fixed is discharged from between the fixing belt 21 and the pressure roller 31 (the fixing nip) and then discharged from the image forming apparatus main body 100 and placed on the paper discharge tray. Thus, the series of image formation processes is completed.

[0018] Next, the configuration and operation of the fixing device 20 will be explained using Figures 2 to 7, etc. The fixing device 20 is a device that heats and transports the sheet P (a sheet on which unfixed toner is carried). Referring to Figure 2, etc., the fixing device 20 consists of 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 helical gear 65 as an annular member (see Figures 3, 5, etc.), etc.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.).

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 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 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 helical gear 65 as an annular member, which will be explained in detail later.

[0028] 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).

[0029] 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 anchoring belt 21, as a belt component, has a lubricant applied directly (or indirectly) to its inner circumferential surface and is heated by a planar heater 24, which serves as a heat source. Furthermore, 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.

[0030] 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 helical gear 65, described later, is installed, which is the left side in Figure 5) is formed to protrude one end in the width direction beyond the belt surface layer 21b. This protruding end of the base material layer 21a (belt conductive layer) then comes into direct contact with the helical gear 65, which is an annular member described later (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, which is the axial direction), excluding the contact area between the base layer 21a and the helical gear 65, which will be described later.

[0031] 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). Here, as shown in Figures 5 to 7 and Figure 8(A), the pressure roller 31 (pressure rotating body) of the fixing device 20 in this embodiment is conductive and 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, and a helical gear 65 as a grounded annular member is installed.

[0032] More specifically, as shown in Figures 5 to 7 and Figure 8(A), the helical gear 65 is an annular (donut-shaped) member made of a conductive material, but it is not a perfect annular shape. Instead, multiple helical tooth-shaped protrusions 65a are formed on its outer circumference over the entire circumferential direction. Furthermore, although this annular member has the shape of a gear, the helical gear 65 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 anchoring belt 21, respectively. Furthermore, the annular helical gear 65 also functions as a lubricant leakage prevention member, preventing the lubricant applied to the inner circumferential surface of the anchoring belt 21 from leaking out from the end of the anchoring belt 21. This will be explained in more detail later.

[0033] More specifically, the helical gear 65 (annular member) is made of a conductive rubber material, and multiple helical tooth-shaped protrusions 65a (see Figure 7, etc.) that are inclined with respect to the axial direction are formed on its outer circumference over the entire circumference. These helical tooth-shaped protrusions 65a are configured (designed) in the same way as the helical teeth (teeth) of a so-called helical gear.

[0034] The helical gear 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 helical gear 65 then rotates together with the pressure roller 31 in a predetermined direction (counterclockwise in Figure 2). Referring to Figure 5, in the pressure roller 31, the conductive surface layer 34 is folded radially so that its axial end (widthwise end) follows the end face of the elastic layer 33, in order to ensure a sufficient contact area with the helical gear 65, and the folded portion is in contact with the end face of the helical gear 65.

[0035] Furthermore, in this embodiment, the outer diameter (tip circle diameter) of the helical gear 65 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 helical gear 65 is in contact with the base material layer 21a of the fixing belt 21 (the portion that protrudes to one end in the width direction). In this case, even if the outer diameter (tip circle diameter) of the helical gear 65 is the same as the outer diameter of the main roller portion, the belt surface layer 21b is extremely thin, and the pressure roller 31 presses against the fixing belt 21 in a way that it bites into it, so the helical gear 65 (helical tooth-shaped protrusion 65a) 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 helical gear shape). Therefore, compared to the case where a perfectly annular member is in contact with the base material layer 21a, multiple gear teeth (helical protrusions 65a) arranged in the 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.

[0036] In this embodiment, the helical gear 65 is press-fitted into 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 helical gear 65 in the width direction (axial direction) of the core metal 32, the helical gear 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 helical gear 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 helical gear 65 is properly grounded. Furthermore, the toothed gear 65 is positioned outside the maximum paper feed area M (the widthwise range through which the largest possible sheet P can be transported) of the fixing device 20 (the non-paper feed area). As a result, there is no effect from the toothed gear 65 coming into contact with the fixed image.

[0037] As described above, the fixing device 20 in this embodiment is equipped with a helical gear 65 that functions as a conductive member, thereby ensuring good electrical conductivity between the base layer 21a (belt conductive layer) of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31 and the grounded helical gear 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.

[0038] "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.

[0039] Referring here to Figures 7 and 8(A), etc., in the fixing device 20 of this embodiment, the helical tooth-shaped protrusions 65a (teeth) of the helical tooth gear 65 (annular member) are inclined in a direction that applies thrust force toward the center in the axial direction (left-right direction in Figure 8(A), which is the width direction) at the contact portion with the fixing belt 21 (the contact portion with the base material layer 21a exposed on one end in the width direction) when it rotates together with the pressure roller 31 (pressure rotating body). In other words, referring to Figure 9, when viewed from the base material layer 21a side at the contact point with the base material layer 21a of the helical gear 65, the tooth surface on the downstream side in the rotational direction faces the axial center (right side in Figure 8(A) and Figure 9) rather than the axial outward side (left side in Figure 8(A) and Figure 9), thus acting a force (thrust force) in the direction of the white arrow on the contact point. Therefore, the angle θ (helix angle) that the tooth surface on the downstream side in the rotational direction makes with the axis W extending in the axial direction will be greater than 0 degrees and less than 90 degrees.

[0040] Therefore, the inner circumferential surface portion (one end) of the anchoring belt 21 (base layer 21a) that the helical gear 65 presses against is bitten into by the helical tooth-shaped protrusion 65a (tooth portion), and the shape of the helical tooth-shaped protrusion 65a in the rotating state is reflected (the inner circumferential surface of the base layer 21a protrudes toward the rotation center in a helical tooth shape). As a result, even if the lubricant applied to the inner circumferential surface of the anchoring belt 21 tries to move outward in the width direction along the nip portion (even if it tries to move in the direction of the black arrow in Figure 8(A)), a thrust force (force in the direction of the white arrow) acts within the inner circumferential surface of the belt to push the lubricant toward the center in the width direction. Consequently, the problem of the lubricant applied to the inner circumferential surface of the anchoring belt 21 leaking outward in the width direction is reduced. In other words, as shown in Figure 8(B) as a comparative example, when a spur gear-shaped annular member 165 is pressed against the base material layer 21a, no thrust force acts within the inner circumference of the belt to push the lubricant back towards the center in the width direction. As a result, the lubricant applied to the inner circumference of the fixing belt 21 moves outward in the width direction along the nip portion (moving in the direction of the black arrow in Figure 8(B)), and leaks out to the outside in the width direction. The lubricant that leaks out then leaks in the direction of the white arrow, adhering to other components and causing abnormalities in the fixed image or contaminating the outside of the fixing device. In particular, the spur gear-shaped annular member 165 shown in Figure 8(B) functions as a relay member (conductive member) for the grounding path to ground the base material layer 21a of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31, just like the helical gear 65 in this embodiment. Therefore, if lubricant adheres to the annular member 165, the conductivity with the base material layer 21a and the conductive surface layer 34 will decrease, reducing its original function as a relay member (conductive member), and causing an electrostatic offset in the fixed image. In contrast, when the helical gear 65 in this embodiment is used, the problem of lubricant applied to the inner circumferential surface of the fixing belt 21 leaking outward in the width direction is reduced, making it less likely for the leaked lubricant to adhere to the helical gear 65 and impair its function as a relay member (conductive member).

[0041] As explained earlier, the fixing belt 21 in this embodiment is a two-layer structure in which a belt surface layer 21b is laminated on a base layer 21a. Compared to a three-layer structure in which an elastic layer or the like is formed between the base layer 21a and the belt surface layer 21b, the shape of the helical tooth-shaped protrusions 65a is more easily reflected on the inner circumferential surface of the base layer 21a into which the helical tooth gear 65 is pressed. Therefore, the effect of making it difficult for lubricant to leak outwards in the width direction, as described above, is more easily achieved. Furthermore, in this embodiment, the one end in the width direction where the annular tooth gear 65 is installed is a non-driving side, unlike the other end in the width direction (driving side) where the gear 45 (see Figure 3) that meshes with the drive gear of the drive motor is installed. This side is prone to lubrication flowing from the driving side due to vibrations on the driving side, and leakage outward in the width direction is likely to occur, making the configuration of the present invention useful.

[0042] Referring to Figure 8(A), in this embodiment, the widthwise (axial) position of the widthwise end of the fixing belt 21 and the axial position of the helical tooth-shaped protrusion 65a of the helical tooth gear 65 (annular member) are configured to coincide substantially. In other words, the widthwise end face of the tooth-shaped protrusion 65a is configured to be almost flush with the widthwise end face of the fixing belt 21, neither on the outside nor the inside. This is because if the widthwise end face of the helical tooth-shaped protrusion 65a is located outside the widthwise end face of the anchoring belt 21, the helical tooth gear 65 will be directly heated by the planar heater 24 that extends outside the widthwise end face of the anchoring belt 21, making it prone to thermal damage. Furthermore, if the widthwise end face of the tooth-shaped protrusion 65a is located inward relative to the widthwise end face of the fixing belt 21, the range in which the shape of the tooth-shaped protrusion 65a is reflected on the inner circumferential surface of the base material layer 21a pressed against the tooth-shaped gear 65 will be narrowed, and the effect of preventing lubricant from leaking to the outside of the fixing belt 21 will be reduced.

[0043] Referring to Figure 9, in this embodiment, the helical gear 65 (annular member) is formed such that at least one helical tooth-shaped protrusion 65a is located relative to the nip width Y (the length of the nip in the direction approximately perpendicular to the plane of the paper in Figure 8(A)) at the contact portion with the base material layer 21a. This configuration allows the shape of the tooth-shaped protrusions 65a to be efficiently reflected on the inner circumferential surface of the base layer 21a at the contact point with the tooth-shaped gear 65, making it easier to prevent the lubricant from leaking out to the outside of the fixing belt 21. Referring to Figure 9, in this embodiment, the tooth-shaped protrusion 65a has a flat tooth surface that applies thrust force in the direction of the white arrow at the contact point with the base layer 21a. Therefore, if we let the gear width of the swastika-shaped protrusion 65a (tooth portion) be X and the nip width at the contact portion be Y, then the angle θ that the tooth surface of the swastika-shaped protrusion 65a makes with the axis W is, θ = tan -1 (Y / X) This is the result. Furthermore, by setting the angle θ to be greater than 0 degrees and less than 90 degrees, a thrust force in the direction of the white arrow mentioned above can be applied.

[0044] In this embodiment, it is preferable that the helical gear 65 (annular member) is configured so that the anchoring belt 21 is not moved in the width direction by the thrust force in the direction of the white arrow described above. The thrust force described above is generated when the rotating helical tooth-shaped protrusions 65a press against the base material layer 21a, which may cause the anchoring belt 21 itself to move towards the base material layer 21a. Therefore, it is preferable to set the frictional resistance, contact amount, and helix angle of the helical tooth gear 65 against the base material layer 21a so that the thrust force is limited to an amount that does not cause such belt movement.

[0045] Furthermore, in this embodiment, it is preferable that the fixing belt 21 is formed such that the surface roughness of the inner circumferential surface portion corresponding to the contact portion with the helical gear 65 is rougher than the surface roughness of the other parts of the inner circumferential surface. As explained earlier, the inner circumferential surface portion of the base material layer 21a, which corresponds to the contact area, has a tooth-shaped projection that reflects the shape of the tooth-shaped protrusion 65a. If the surface roughness is rough, the gripping force on the lubricant increases compared to when it is smooth, making it easier for the thrust force described above to return the lubricant to the center in the width direction.

[0046] <Example 1> As shown in Figure 10(A), in the modified example 1 of the helical gear 65, the helical tooth-shaped protrusion 65a has a tooth surface that applies thrust force in the direction of the white arrow at the contact point with the base layer 21a, and this tooth surface is curved rather than flat. In particular, the helical tooth-shaped protrusion 65a shown in Figure 10(A) is formed such that the angle θ that the tooth surface makes with the axis W extending in the axial direction is larger in the middle portion than at the axial end. Specifically, the angle θ is formed to gradually increase from the axial end towards the middle portion. With this configuration, the force pushing the lubricant back in the direction of the white arrow is greatest at the point where the angle θ is large, and at that position, it is possible to block the lubricant from moving outward in the width direction (opposite to the direction of the white arrow) and leaking out. Furthermore, the shape of the serrated projection 65a is not limited to that shown in Figure 9 or Figure 10(A). Any shape that can apply thrust force in the direction of the white arrow is acceptable, for example, a shape in which multiple curved surfaces are joined together as shown in Figure 10(B), or a shape in which multiple planes are joined together as shown in Figure 10(C). In particular, the serrated projection 65a shown in Figure 10(C) is formed such that the angles θ1 to θ3 gradually increase from the axial end to the middle, thus achieving the same effect as that of Figure 10(A).

[0047] <Modification 2> As shown in Figure 11, in the modified example 2, the pressure roller 31 of the fixing device 20 has a helical gear 66 (annular member) installed on one end in the width direction, as well as another helical gear 66 as an annular member installed on the other end in the width direction (the right side in Figure 11). This sawtooth gear 66 on the other end in the width direction also has multiple sawtooth-shaped protrusions formed on its outer circumference, which are inclined with respect to the axial direction, extending over the entire circumference. Furthermore, the helical tooth-shaped protrusions are inclined in a direction that applies a thrust force (a thrust force directed to the left in Figure 11) toward the axial center at the contact point with the anchoring belt (in the example of Figure 11, the contact point with the belt surface layer 21b) during rotation. Therefore, the twisting direction of the helical tooth gear 66 at the other end in the width direction is opposite to the twisting direction of the helical tooth gear 65 at one end in the width direction. Furthermore, this helical gear 66 does not function as a conductive member for grounding the base layer 21a or the conductive surface layer 34, but rather functions solely as a lubricant leakage prevention member to prevent the lubricant applied to the inner circumferential surface of the fixing belt 21 from leaking out from the other end in the width direction of the fixing belt 21. Therefore, it does not need to be made of a conductive material. Even with this configuration, the lubricant applied to the inner circumferential surface of the fixing belt 21 is less likely to leak out of the fixing belt 21.

[0048] <Variation 3> As shown in Figure 12, the fixing device 20 in modified example 3 is equipped with a restricting member 67 that restricts the movement of the fixing belt 21 in the width direction (towards the right of the belt in Figure 12) due to the thrust force of the helical gear 65 (annular member). More specifically, the regulating member 67 is a donut-shaped plate material installed on the core metal 32 (shaft portion) of the pressure roller 31, and its outer diameter is larger than the roller diameter of the pressure roller 31, and it is formed to be in contact with the end face of the fixing belt 21. With this configuration, even if the thrust force exerted by the rotating tooth-shaped protrusions 65a pressing against the base material layer 21a causes the fixing belt 21 itself to move towards the belt in the same direction, the regulating member 67 interferes with the end face of the fixing belt 21, preventing further belt movement. Furthermore, the flange member 42, as explained using Figure 4, can also be given this function as a restricting member.

[0049] As described above, the fixing device 20 in this embodiment is provided with a fixing belt 21 on which a lubricant is directly or indirectly applied to the inner circumferential surface and which is heated by a planar heater 24 (heat source). It is also provided with a pressure roller 31 (pressure rotating body) that forms a nip portion on which the sheet P is conveyed by pressing it against the fixing belt 21. Furthermore, a helical gear 65 (annular member) that rotates together with the pressure roller 31 is installed on the core metal 32 (shaft portion) of the pressure roller 31 so as to contact the widthwise end of the fixing belt 21. The helical gear 65 (annular member) has multiple helical tooth-shaped protrusions 65a formed on its outer circumference over the entire circumferential area, which are inclined with respect to the axial direction. In addition, when the helical tooth-shaped protrusions 65a rotate together with the pressure roller 31, they are inclined in a direction that applies a thrust force toward the axial center at the contact portion with the fixing belt 21. This makes it less likely for the lubricant applied to the inner surface of the fixing belt 21 to leak out of the fixing belt 21.

[0050] 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, 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, in this embodiment, a helical gear 65 was used as the annular member, but the annular member does not necessarily have to be a helical gear. It is sufficient if multiple helical tooth-shaped protrusions are formed on the outer circumference, inclined in the axial direction, and these helical tooth-shaped protrusions are inclined in a direction that applies a thrust force toward the axial center at the contact point with the anchoring belt during rotation. Furthermore, in this embodiment, a planar heater 24, which serves as a heat source, is used as a nip-forming member and is pressed against the pressure roller 31 via the fixing belt 21 to form a nip portion (fixing nip). However, the nip-forming member does not necessarily have to be a heat source. Furthermore, the same effects as those of this embodiment can be obtained in these cases as well.

[0051] 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.

[0052] 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]

[0053] 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, 65 Hex gear (annular member), 65a Lotus tooth-shaped protrusion, 66 Hex gear (annular member), 67 Regulating members, 68 Resistors (electrical resistance components), 100 Image forming apparatus (image forming apparatus main unit), P-sheet (recording medium).

[0054] Furthermore, the embodiments of the present invention can also be, for example, combinations of appendices 1 to 13 as follows. (Note 1) A fixing belt, on which a lubricant is applied directly or indirectly to the inner surface and heated by a heat source, A pressurizing rotating body that forms a nip section on which the sheet is conveyed by pressing it against the fixing belt, An annular member is installed on the shaft of the pressurizing rotating body so as to contact the widthwise end of the fixing belt and rotates together with the pressurizing rotating body, Equipped with, The annular member has multiple saddle-tooth-shaped protrusions formed on its outer circumference, which are inclined in the axial direction, extending over the entire circumference. The fixing device is characterized in that the tooth-shaped protrusions are inclined in a direction that applies a thrust force toward the axial center at the contact portion with the fixing belt when they rotate together with the pressurizing rotating body. (Note 2) The aforementioned fixing belt is A conductive belt layer, An insulating or medium-resistance belt surface layer is directly or indirectly laminated on the belt conductive layer in a widthwise range excluding the contact portion, It is equipped with, The aforementioned pressurized rotating body is A conductive surface layer that contacts the belt surface layer of the fixing rotating body to form the nip portion, The annular member, which is in contact with the belt conductive layer and the conductive surface layer respectively, and is conductive and grounded, The fixing device according to Appendix 1, characterized by comprising the following: (Note 3) The fixing device according to Appendix 1 or Appendix 2, characterized in that the annular member is a helical gear formed of a conductive rubber material. (Note 4) The fixing device according to any one of the appendices 1 to 3, characterized in that the fixing belt is a two-layer structure in which the belt conductive layer is used as the base layer and the belt surface layer is laminated on the base layer. (Note 5) The fixing device according to any one of the appendices 1 to 4, characterized in that the fixing belt is formed such that the surface roughness of the inner circumferential surface portion corresponding to the contact portion is rougher than the surface roughness of the other inner circumferential surface portions. (Note 6) The fixing device according to any one of the appendices 1 to 5, characterized in that the position in the width direction of the widthwise end of the fixing belt and the position in the axial direction of the tooth-shaped protrusion of the annular member are substantially coincide. (Note 7) The fixing device according to any one of the appendices 1 to 6, characterized in that the annular member is formed such that at least one of the hash-tooth-shaped protrusions is located relative to the nip width at the contact portion. (Note 8) The fixing device according to any one of the appendices 1 to 7, characterized in that the tooth-shaped protrusions have tooth surfaces that apply the thrust force at the contact portion that are formed in a planar or curved shape. (Note 9) The fixing device according to Appendix 8, characterized in that the tooth-shaped protrusions are formed such that the angle the tooth surface makes with respect to the axis extending in the axial direction is larger in the middle portion than at the axial end portion. (Note 10) The fixing device according to any one of the appendices 1 to 9, characterized in that it comprises a planar heater as a heat source that contacts the inner circumferential surface of the fixing belt and presses against the pressurizing rotating body via the fixing belt to form the nip portion. (Note 11) The fixing device according to any one of the appendices 1 to 10, characterized in that the annular member is configured so that the fixing belt is not moved in the width direction by the thrust force. (Note 12) The fixing device according to any one of the appendices 1 to 11, further comprising a restricting member for restricting the movement of the fixing belt in the width direction due to the thrust force of the annular member. (Note 13) An image forming apparatus characterized by being equipped with a fixing device as described in any of Appendix 1 to Appendix 12. [Prior art documents] [Patent Documents]

[0055] [Patent Document 1] Japanese Patent Publication No. 2022-145549 [Patent Document 2] Japanese Patent Publication No. 2009-300775

Claims

1. A fixing belt, on which a lubricant is applied directly or indirectly to the inner surface and heated by a heat source, A pressurizing rotating body that forms a nip section on which the sheet is conveyed by pressing it against the fixing belt, An annular member is installed on the shaft of the pressurizing rotating body so as to contact the widthwise end of the fixing belt and rotates together with the pressurizing rotating body, Equipped with, The annular member has multiple saddle-tooth-shaped protrusions formed on its outer circumference, which are inclined in the axial direction, extending over the entire circumference. The fixing device is characterized in that the tooth-shaped protrusions are inclined in a direction that applies a thrust force toward the axial center at the contact portion with the fixing belt when they rotate together with the pressurizing rotating body.

2. The aforementioned fixing belt is A conductive belt layer, An insulating or medium-resistance belt surface layer is directly or indirectly laminated on the belt conductive layer in a widthwise range excluding the contact portion, It is equipped with, The aforementioned pressurized rotating body is A conductive surface layer that contacts the belt surface layer of the fixing rotating body to form the nip portion, The annular member, which is in contact with the belt conductive layer and the conductive surface layer respectively, and is conductive and grounded, The fixing device according to claim 1, characterized by comprising the above.

3. The fixing device according to claim 2, characterized in that the annular member is a helical gear formed of a conductive rubber material.

4. The fixing device according to claim 2, characterized in that the fixing belt is a two-layer structure in which the belt conductive layer is used as the base layer and the belt surface layer is laminated on the base layer.

5. The fixing device according to claim 1 or 2, characterized in that the fixing belt is formed such that the surface roughness of the inner circumferential surface portion corresponding to the contact portion is rougher than the surface roughness of the other inner circumferential surface portions.

6. The fixing device according to claim 1 or 2, characterized in that the position in the width direction of the widthwise end of the fixing belt and the position in the axial direction of the tooth-shaped protrusion of the annular member are substantially the same.

7. The fixing device according to claim 1 or 2, characterized in that the annular member is formed such that at least one of the hash-shaped protrusions is located relative to the nip width at the contact portion.

8. The fixing device according to claim 1 or 2, characterized in that the tooth-shaped protrusions have tooth surfaces that apply the thrust force at the contact portion formed in a planar or curved shape.

9. The fixing device according to claim 8, characterized in that the tooth-shaped protrusions are formed such that the angle the tooth surface makes with respect to the axis extending in the axial direction is larger in the middle portion than in the axial end portion.

10. The fixing device according to claim 1 or 2, further comprising a planar heater as a heat source that contacts the inner circumferential surface of the fixing belt and presses against the pressurizing rotating body via the fixing belt to form the nip portion.

11. The fixing device according to claim 1 or 2, characterized in that the annular member is configured so that the fixing belt is not moved in the width direction by the thrust force.

12. The fixing device according to claim 1 or 2, further comprising a restricting member for restricting the movement of the fixing belt in the width direction due to the thrust force of the annular member.

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

Images