Fixing device and image forming apparatus

Abstract

To provide a fixing device that can prevent deformation of a fixing belt that rotates along a slide surface having slits formed therein.SOLUTION: A fixing device 7 comprises: a fixing belt 20 that is formed into a cylindrical shape and heats toner on a sheet P; a pressure roller 21 that forms a pressure area N with the fixing belt 20, and applies pressure to the toner on the sheet P passing through the pressure area N while rotating around an axis; and a heater holder 22 that is provided inside the fixing belt 20, has slide surfaces 26, 27 in contact with an inner peripheral surface 20A of the fixing belt 20 with lubricant therebetween, and holds a heater 23 that heats the fixing belt 20. A plurality of slits 31, 32 formed to be recessed in the slide surfaces 26, 27 are arranged side by side in an axial direction on slide surfaces 31, 32 corresponding to ranges excluding the pressure area N, and guide the movement of lubricant directed from the upstream to the downstream in a rotation direction of the fixing belt 20. The fixing belt 20 has hardness capable of regulating deformation in which the fixing belt falls into the slits 31, 32.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a medium and an image forming apparatus. [Background technology]

[0002] A fixing device is known that includes a fixing belt and a pressure roller that contacts the fixing belt to form a nip (see Patent Document 1). A nip forming member is disposed inside the fixing belt, and a lubricant is applied between the inner peripheral surface of the fixing belt and the sliding surface of the nip forming member. The sliding surface of the nip forming member has multiple inclined grooves that transfer the lubricant toward the center in the axial direction (width direction). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-5047 Summary of the Invention [Problem to be solved by the invention]

[0004] In the fixing device described above, the sliding surface has an uneven shape formed by alternating inclined grooves and non-inclined areas in the axial direction. When the fixing belt is made of a soft material, it tends to fall into the inclined grooves (slits), resulting in wavy deformation in the axial direction along the uneven shape formed on the sliding surface. The lubricant does not adhere uniformly to the inner peripheral surface of the wavy fixing belt, which can increase friction between the fixing belt and the sliding surface. Furthermore, with a wavy fixing belt, the pressure at the nip portion becomes uneven in the axial direction, which can result in uneven fixing of the image on the paper. This can result in poor image quality, such as streaks (stripes) appearing in the image fixed on the paper.

[0005] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that can suppress deformation of a fixing belt that rotates along a sliding surface on which slits are formed. [Means for solving the problem]

[0006] The fixing device of the present invention comprises a fixing belt formed in a cylindrical shape and rotating around its axis to heat toner on a medium; a pressure member that forms a pressure area between the fixing belt and the pressure member and pressurizes the toner on the medium as it passes through the pressure area while rotating around its axis; and a holder that is provided inside the fixing belt and has a sliding surface that contacts the inner surface of the fixing belt via a lubricant, and holds a heater that heats the fixing belt. A plurality of slits formed to be recessed in the sliding surface are aligned axially on the sliding surface corresponding to the range excluding the pressure area, and guide the movement of the lubricant from upstream to downstream in the rotation direction of the fixing belt, and the fixing belt has a hardness that can prevent it from deforming into the slits.

[0007] In this case, it is preferable that the fixing belt has a Young's modulus of hardness of 7 GPa or more.

[0008] In this case, the Young's modulus of the fixing belt correlates with the groove width of the slit, and when the fixing belt has a Young's modulus of hardness of 10 GPa or less, the groove width is preferably set to 1.0 to 3.0 mm.

[0009] The image forming apparatus of the present invention includes any one of the fixing devices described above. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress deformation of the fixing belt that rotates along the sliding surface on which the slits are formed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram (side view) showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 1 is a front view showing a fixing device according to an embodiment of the present invention. [Figure 5] FIG. 2 is a rear view showing the fixing device according to the embodiment of the present invention. [Figure 6] 10 is a table showing the results of an experiment to confirm the influence of the Young's modulus of the fixing belt on the fixed image on the paper in the fixing device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that Fr, Rr, L, R, U, and D in the drawings represent front, rear, left, right, top, and bottom. The front-to-back direction (passing direction), left-to-right direction (axial direction), and up-to-down direction are perpendicular to one another. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention. Furthermore, the terms "upstream," "downstream," and similar terms refer to "upstream" and "downstream" in the passing direction (transport direction) of paper P (medium), as well as similar concepts. Note that the dimensions and angles of components in each drawing are not accurate and are shown schematically for the purpose of explanation.

[0013] An image forming apparatus 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (side view) showing the image forming apparatus 1.

[0014] The image forming apparatus 1 is an electrophotographic printer. The image forming apparatus 1 has an apparatus main body 2 that has a substantially rectangular parallelepiped appearance. A paper feed cassette 3 that stores, for example, paper P (medium) is detachably provided at the bottom of the apparatus main body 2. A paper output tray 4 is provided on the top surface of the apparatus main body 2. Note that the paper P, which is an example of a medium, is not limited to being made of paper, and may be a resin sheet or the like.

[0015] The image forming apparatus 1 includes a paper feeder 5, an imaging device 6, and a fixing device 7. The paper feeder 5 is provided at the upstream end of a transport path 9A that extends from the paper feed cassette 3 to the paper output tray 4, and sends out paper P stored in the paper feed cassette 3 one sheet at a time to the transport path 9A. The imaging device 6 is provided in the middle of the transport path 9A, and forms a toner image on the transported paper P. The fixing device 7 is provided downstream of the transport path 9A, and thermally fixes the toner image to the paper P.

[0016] The conveying path 9A is provided with a pair of registration rollers 10A that temporarily block the conveyed paper P to correct (skew correct) the inclination of the paper P. Below the conveying path 9A, a reversing conveying path 9B is provided that branches off on the downstream side of the conveying path 9A and merges with the upstream side of the conveying path 9A. The reversing conveying path 9B is provided with a plurality of pairs of conveying rollers 10B that convey the paper P.

[0017] The image forming device 6 includes a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is located at the upper front of the device main body 2 and contains, for example, black toner (developer). The drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape and is driven to rotate about its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged around the photosensitive drum 14 in the order of the image formation process. The transfer roller 17 contacts the photosensitive drum 14 from below to form a transfer nip. The optical scanning device 13 is located above the photosensitive drum 14 and emits scanning light toward the surface of the photosensitive drum 14.

[0018] [Image formation processing] A description will be given of the operation of the image forming apparatus 1. A control device (not shown) that controls the image forming apparatus 1 performs image formation processing as follows based on image data input from an external terminal.

[0019] The charging device 15 charges the surface of the photosensitive drum 14, and the optical scanning device 13 emits scanning light based on image data to form an electrostatic latent image on the photosensitive drum 14. The developing device 16 develops a toner image on the photosensitive drum 14 using toner supplied from the toner container 11. The paper feeder 5 feeds paper P one sheet at a time from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew-corrected by a pair of registration rollers 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photosensitive drum 14 to the surface of the paper P as it passes through the transfer nip. The fixing device 7 thermally fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fixing device 7 is discharged to the paper output tray 4.

[0020] In the case of double-sided printing, the paper P that has passed through the fixing device 7 switches back at the downstream end of the conveying path 9A and is sent to the reverse conveying path 9B. The paper P is conveyed by the conveying roller pair 10B, returned from the reverse conveying path 9B to the conveying path 9A again, and after skew correction by the registration roller pair 10A, is sent to the transfer nip. Thereafter, the toner image is transferred onto the paper P and thermally fixed, and the double-sided printed paper P is discharged onto the paper output tray 4.

[0021] [Fixing device] The fixing device 7 will be described in detail with reference to Figures 2 and 3. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a cross-sectional view taken along line III-III in Figure 2.

[0022] The fixing device 7 includes a fixing belt 20, a pressure roller 21, a heater holder 22, and a heater 23. The fixing belt 20 and the pressure roller 21 are supported by a frame (not shown), which is fixed to the device body 2. The heater holder 22 is provided inside the fixing belt 20, and the heater 23 is held by the heater holder 22 (see FIG. 3).

[0023] <Fixing belt> The fixing belt 20 is an endless belt formed in a generally cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of a heat-resistant and flexible material (polymer resin, metal, or a combination of polymer resin and metal). A pair of holding members 24 (see FIG. 2) is inserted into both left and right ends of the fixing belt 20. The pair of holding members 24 guide the fixing belt 20 to rotate around its axis while maintaining its generally cylindrical shape. The fixing belt 20 is supported by a frame (not shown) via the pair of holding members 24.

[0024] <Pressure roller> The pressure roller 21, which is an example of a pressure member, is formed in a generally cylindrical shape that is long in the left-right direction. The pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on the outer circumferential surface of the metal core 21A (see FIG. 3). A drive motor M is connected to the left end of the core 21A via a gear train (not shown) (see FIG. 2). The pressure roller 21 contacts the fixing belt 20 from below, forming a pressure region N between the pressure roller 21 and the fixing belt 20. The pressure region N refers to the region extending from an upstream position where the pressure is 0 Pa, through a position where the pressure is applied, to a downstream position where the pressure returns to 0 Pa.

[0025] <Heater holder> As shown in FIG. 3, heater holder 22 (holder) is supported by support member 25 on the inside of fixing belt 20. Support member 25 is formed of a metal material such as stainless steel in a generally rectangular cylindrical shape that is long in the left-right direction (axial direction), and is installed between a pair of holding members 24. Heater holder 22 is fixed to the lower part of support member 25. Heater holder 22 is formed of, for example, a heat-resistant and abrasion-resistant synthetic resin in a generally semi-cylindrical shape that is long in the left-right direction. Heater holder 22 is in contact with the lower side (the pressure region N side) of inner circumferential surface 20A of fixing belt 20.

[0026] <Heater> The heater 23 is formed in a generally rectangular plate shape that is long in the left-right direction, and is fixed (held) on the lower surface of the heater holder 22. The heater 23 has a heating resistor (not shown) stacked on a substrate, and generates heat when electricity is passed through the heating resistor. The heater 23 brings the heating resistor into contact with the inner circumferential surface 20A of the fixing belt 20 at a position corresponding to the pressure region N.

[0027] The frame supporting the fixing belt 20 and other components is provided with a temperature sensor (not shown) for detecting the surface temperature of the fixing belt 20. The drive motor M, heater 23, temperature sensor, and other components are electrically connected to a control device of the image forming apparatus 1 via various drive circuits (not shown) and are appropriately controlled.

[0028] [Function of the fixing device] Here, the operation (fixing process) of the fixing device 7 will be described. The pressure roller 21 rotates by receiving the driving force of the drive motor M, and the fixing belt 20 rotates following the rotation of the pressure roller 21 (see the arrow in FIG. 3). The heater 23 heats the fixing belt 20. The control device receives a detection signal from the temperature sensor and starts the image forming process already described while controlling the heater 23 to maintain a preset temperature.

[0029] The paper P onto which the toner image has been transferred enters the pressure area N. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressure area N while rotating around its axis. The pressure roller 21 pressurizes the toner on the paper P as it passes through the pressure area N while rotating around its axis. This fixes the toner image to the paper P, forming a fixed image on the paper P. The paper P with the fixed image is then discharged onto the paper output tray 4.

[0030] [Heater holder details] 3, heater holder 22 has sliding surfaces 26 and 27 that contact inner circumferential surface 20A of fixing belt 20 on the upstream and downstream sides of a portion that holds heater 23 (a position corresponding to pressure region N). For ease of explanation, in this specification, sliding surface 26 located upstream of pressure region N will be referred to as the "first sliding surface 26," sliding surface 27 located downstream of pressure region N will be referred to as the "second sliding surface 27," and in explanations common to first sliding surface 26 and second sliding surface 27, they will be simply referred to as the "sliding surfaces 26 and 27."

[0031] A lubricant (not shown) is applied to the inner circumferential surface 20A of the fixing belt 20, and the sliding surfaces 26 and 27 of the heater holder 22 contact the inner circumferential surface 20A of the fixing belt 20 via the lubricant. The lubricant is a viscous and fluid grease or the like, and reduces frictional resistance between the fixing belt 20 and the heater holder 22. The lubricant moves as the fixing belt 20 rotates, and is known to move toward both outer sides in the axial direction in portions of the fixing belt 20 where the inner circumferential surface 20A of the fixing belt 20 is not in contact with the sliding surfaces 26 and 27. If the lubricant leaks from both axial ends of the fixing belt 20 and the amount of lubricant decreases due to repeated fixing processes, the frictional resistance between the fixing belt 20 and the heater holder 22 increases, which may hinder the smooth rotation of the fixing belt 20.

[0032] Therefore, the fixing device 7 according to this embodiment is provided with a structure that suppresses leakage of the lubricant applied to the inner circumferential surface 20A of the fixing belt 20. The structure that suppresses leakage of the lubricant will be described below with reference to Figs. 3 to 5. Fig. 4 is a front view of the fixing device 7. Fig. 5 is a rear view of the fixing device 7. Note that the fixing belt 20 is not shown in Figs. 4 and 5.

[0033] <Slit> The heater holder 22 has a plurality of slits 31, 32 arranged in the left-right direction (axial direction) on the sliding surfaces 26, 27 corresponding to the area excluding the pressure region N. The plurality of slits 31, 32 are recessed into the sliding surfaces 26, 27, respectively, and guide the movement of the lubricant from upstream to downstream in the rotation direction of the fixing belt 20. For convenience of explanation, in this specification, the slit 31 (see FIG. 4) formed on the sliding surface 26 upstream of the pressure region N will be referred to as the "first slit 31," and the slit 32 (see FIG. 5) formed on the sliding surface 27 downstream of the pressure region N will be referred to as the "second slit 32." In descriptions common to the first slit 31 and the second slit 32, the slits will be simply referred to as the "slits 31, 32." For simplicity of explanation, this specification will mainly focus on one first slit 31 and one second slit 32. Also, as mentioned at the beginning, in this specification, when we simply refer to "upstream" and "downstream," we are referring to the direction in which the paper P passes (the conveying direction), and are distinguished from "upstream" and "downstream" in the rotation direction of the fixing belt 20.

[0034] 4 and 5, the slits 31 and 32 are grooves that extend linearly along the rotation direction of the fixing belt 20. To be precise, the slits 31 and 32 are inclined toward the center in the left-right direction (axial direction) from upstream to downstream in the rotation direction of the fixing belt 20. The inclination angles (absolute values) of the multiple slits 31 and 32 are all the same, and the multiple slits 31 and 32 are arranged symmetrically with respect to the center in the left-right direction as an axis.

[0035] (First slit) As shown in FIGS. 3 and 4, the first slit 31 has a bottom surface 31A and a peripheral wall surface 31B and is recessed into the first sliding surface 26 to form an annular opening edge 31C. The bottom surface 31A and the opening edge 31C have an outer shape that is a substantially parallelogram, and the peripheral wall surface 31B is formed in a substantially rectangular cylindrical shape so as to connect the periphery of the bottom surface 31A and the opening edge 31C. The groove width W1 of the first slit 31 may be, for example, approximately 1.0 to 6.0 mm. The groove width W1 refers to the length of a line segment that intersects the opposing wall surfaces of the peripheral wall surface 31B in the left-right direction (axial direction) (see FIG. 4). The peripheral wall surface 31B forms a step between the bottom surface 31A and the first sliding surface 26. The step may be, for example, approximately 0.5 to 2.0 mm. Of the peripheral wall surface 31B of the first slit 31, the wall surface located downstream in the rotation direction of the fixing belt 20 serves as a blocking portion 41 that restricts the outflow of the lubricant from the first slit 31. The blocking portion 41 is located upstream of the most upstream end of the pressure region N (the portion that holds the heater 23), and a first sliding surface 26 is also formed between the blocking portion 41 and the most upstream end of the pressure region N.

[0036] (Second slit) 3 and 5, the second slit 32 has a shape similar to that of the first slit 31 turned upside down. The second slit 32 has a bottom surface 32A and a peripheral wall surface 32B, and is recessed to form an annular opening edge portion 32C in the second sliding surface 27. The wall surface of the peripheral wall surface 32B located downstream in the rotation direction forms a blocking portion 42. The groove width W2 (see FIG. 5) and step of the second slit 32 are equivalent to the groove width W1 and step of the first slit 31.

[0037] The intervals (centroid distances) between any two adjacent slits 31, 32 inclined in the same direction are generally equal, but may be variable (not shown). For example, the slits 31, 32 may be formed so that the intervals between them gradually (in steps) narrow or widen from the center in the axial direction outward (not shown). Furthermore, the groove widths W1, W2 of the slits 31, 32 are all the same, but may be different. For example, the slits 31, 32 may be formed so that the groove widths W1, W2 gradually narrow or widen from the center in the axial direction outward (not shown).

[0038] [Slit action] The lubricant adhering to the inner circumferential surface 20A of the fixing belt 20 moves downstream in the rotation direction as the fixing belt 20 rotates, and lubricates the fixing belt 20 (inner circumferential surface 20A) sliding against the first sliding surface 26. The lubricant enters the first slit 31 and moves along the first slit 31 toward the center in the axial direction.

[0039] As the rotation of the fixing belt 20 progresses, the lubricant lubricates the fixing belt 20 sliding against the heater 23, and when the fixing belt 20 passes through the pressure region N, the lubricant lubricates the fixing belt 20 sliding against the second sliding surface 27. The lubricant enters the second slit 32 and moves along the second slit 32 toward the center in the axial direction.

[0040] As described above, the slits 31 and 32 are inclined toward the center in the axial direction from upstream to downstream in the rotation direction of the fixing belt 20, so that the lubricant can be moved toward the center in the axial direction of the heater holder 22. This makes it possible to prevent the lubricant from leaking from both outer ends of the fixing belt 20 in the axial direction. Furthermore, the slits 31 and 32 are formed with the blocking portions 41 and 42 on the downstream side in the rotation direction of the fixing belt 20. Therefore, some of the lubricant moving along the slits 31 and 32 overcomes the blocking portions 41 and 42 and flows out, but the remaining lubricant is blocked by the blocking portions 41 and 42 and remains in the slits 31 and 32. This makes it possible to limit the amount of lubricant that flows out from the slits 31 and 32, and to prevent excessive adhesion of the lubricant to the inner circumferential surface 20A of the fixing belt 20.

[0041] On the sliding surfaces 26 and 27, the slits 31 and 32 and areas without slits 31 and 32 (between adjacent slits 31 and 32) are alternately arranged in the axial direction, forming an uneven shape. If the fixing belt 20 were made of a soft material, it would easily fall into the slits 31 and 32 and may deform into a wavy shape in the axial direction along the uneven shape formed on the sliding surfaces 26 and 27. The lubricant may not adhere uniformly to the inner circumferential surface 20A of the fixing belt 20 that has been deformed into a wavy shape, which may increase friction between the fixing belt 20 and the sliding surfaces 26 and 27. Furthermore, in the fixing belt 20 that has been deformed into a wavy shape, the pressure in the pressure region N becomes uneven in the axial direction, which may result in uneven fixing of the image on the paper P in the axial direction. This may result in poor image quality, such as the appearance of streaks (stripes) in the image fixed on the paper P. Furthermore, when the wavy fixing belt 20 rotates, a force acts to move the fixing belt 20 in the axial direction, and the end of the fixing belt 20 may come into contact with the holding member 24 and be damaged.

[0042] To address the above-described problem, in the fixing device 7 according to this embodiment, the fixing belt 20 has a hardness that can prevent deformation such as dropping into the slits 31 and 32. Specifically, the fixing belt 20 is formed in a substantially cylindrical shape using a polymer resin such as polyimide or a metal such as nickel or stainless steel, and has a Young's modulus of 7 GPa or more. More specifically, the Young's modulus of the fixing belt 20 is preferably 7.0 GPa or more and 200 GPa or less. The Young's modulus of the material of the fixing belt 20 can be adjusted, for example, by adding an additive during the manufacturing process of the polymer resin or metal.

[0043] Furthermore, it is preferable that the Young's modulus of the fixing belt 20 correlates with the groove widths W1 and W2 of the slits 31 and 32. That is, when the groove widths W1 and W2 of the slits 31 and 32 are narrow (for example, about 1.0 to 3.0 mm), the fixing belt 20 is unlikely to sink into the slits 31 and 32, so the Young's modulus may be set low (for example, about 7 to 10 GPa). On the other hand, when the groove widths W1 and W2 of the slits 31 and 32 are wide (for example, about 3.0 to 6.0 mm), the fixing belt 20 is likely to sink into the slits 31 and 32, so the Young's modulus may be set high (for example, about 10 to 200 GPa).

[0044] The applicant conducted an experiment to confirm the effect of the Young's modulus of the fixing belt 20 on the fixed image on the paper P, with the groove widths W1 and W2 of the slits 31 and 32 set to about 3.0 mm. As a result, as shown in Fig. 6, it was confirmed that when the Young's modulus of the fixing belt 20 was set to 6 GPa, streaks (striped patterns) appeared in the image fixed on the paper P (image evaluation: ×), and when the Young's modulus of the fixing belt 20 was set to 7 GPa or more, streaks (striped patterns) did not appear in the image fixed on the paper P (image evaluation: ◯). The material and Young's modulus of the fixing belt 20 are as shown in Fig. 6.

[0045] In the fixing device 7 according to the present embodiment described above, the fixing belt 20 has a hardness (e.g., a Young's modulus of 7 GPa or more) that prevents the fixing belt 20 from deforming into the slits 31 and 32. This configuration reduces the likelihood of the fixing belt 20 deforming into the slits 31 and 32, thereby preventing the fixing belt 20 from undulating in the axial direction along the unevenness formed on the sliding surfaces 26 and 27. In other words, the deformation of the fixing belt 20 rotating along the sliding surfaces 26 and 27 on which the slits 31 and 32 are formed can be prevented. This allows the lubricant to be applied substantially uniformly to the smooth inner circumferential surface 20A of the fixing belt 20. As a result, an increase in friction between the fixing belt 20 and the heater holder 22 can be prevented, ensuring smooth rotation of the fixing belt 20. Furthermore, because the undulating deformation of the fixing belt 20 is prevented upstream and downstream of the pressure region N, the pressure in the pressure region N can be made substantially uniform in the axial direction. This stabilizes the fixing state of the image on the paper P and prevents image quality defects, such as streaks (stripe patterns) from occurring in the image. Furthermore, since the rotation of the fixing belt 20 makes it difficult for a force to move it in the axial direction to act, the end of the fixing belt 20 is prevented from coming into contact with the holding member 24, and damage to the end of the fixing belt 20 can also be prevented.

[0046] Furthermore, in the fixing device 7 according to this embodiment, the Young's modulus of the fixing belt 20 correlates with the groove widths W1 and W2 of the slits 31 and 32. According to this configuration, when the groove widths W1 and W2 of the slits 31 and 32 are narrow (for example, 1.0 to 3.0 mm), the fixing belt 20 may be made of a flexibly deformable material with a Young's modulus of approximately 7 to 10 GPa. This allows the outer diameter of the fixing belt 20 to be reduced (its curvature to be increased), thereby enabling the fixing device 7 to be made more compact.

[0047] In the fixing device 7 according to the present embodiment, the slits 31 and 32 are recessed to form the annular opening edges 31C and 32C, but the present invention is not limited to this. For example, in the slits 31 and 32 according to the first modification, the peripheral wall surfaces 31B and 32B may not have a wall surface on the downstream side in the rotation direction of the fixing belt 20, and the downstream ends of the bottom surfaces 31A and 32A may be formed so as to be continuous with the sliding surfaces 26 and 27 without forming a step (not shown).

[0048] Furthermore, in the fixing device 7 according to this embodiment, the multiple slits 31, 32 are inclined at the same angle. Depending on the inclination angle, the lubricant may accumulate excessively in the axial center. Therefore, in the slits 31, 32 according to the second modification, for example, one to three slits 31, 32 near the axial center may be formed parallel to the rotation direction of the fixing belt 20, and the remaining slits 31, 32, excluding these central slits 31, 32, may be inclined toward the axial center from upstream to downstream in the rotation direction of the fixing belt 20 (not shown). Alternatively, in the slits 31, 32 according to the third modification, the inclination angle with respect to the rotation direction of the fixing belt 20 may gradually (stepwise) increase from the center toward both outer sides in the axial direction (not shown). With these configurations, the lubricant can be directed toward the center in the axial direction of the slits 31, 32 located closer to the outside. This prevents the lubricant from accumulating excessively in the axial center while suppressing leakage of the lubricant from both ends of the fixing belt 20 in the axial direction.

[0049] In the fixing device 7 according to the present embodiment (including the first to third modified examples, the same applies hereinafter), the multiple slits 31, 32 are formed on the two sliding surfaces 26, 27, but this is not limiting, and for example, they may be formed on only one of the sliding surfaces 26, 27 (not shown). Also, for example, the slits 31, 32 having annular opening edges 31C, 32C may be formed on the sliding surface 26, and the slits 31, 32 according to the first modified example may be formed on the sliding surface 27, and various types of slits 31, 32 including those according to the first to third modified examples may be freely combined and formed on the sliding surfaces 26, 27 (not shown).

[0050] In the fixing device 7 according to the present embodiment, the slits 31 to 34 are formed linearly, but this is not limiting and they may be curved (not shown). In addition, the slits 31 and 32 may be formed so as to be parallel to the rotation direction of the fixing belt 20 (or the passing direction of the paper P) without being inclined (not shown).

[0051] Furthermore, in the description of the above embodiment, the present invention has been applied to a monochrome image forming device 1 as an example, but this is not limiting and the present invention may also be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

[0052] The above-described embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0053] 1. Image forming device 7 Fixing device 20 Fixing belt 20A inner surface 21 Pressure roller (pressure member) 22 Heater holder (holder) 23 Heater 26 First sliding surface (sliding surface) 27 Second sliding surface (sliding surface) 31 First slit (slit) 32 Second slit (slit) N pressure area P Paper (media W1,W2 Groove width

Claims

1. a fixing belt formed in a cylindrical shape and rotating around its axis to heat the toner on the medium; a pressure member that forms a pressure region between itself and the fixing belt and that pressurizes the toner on the medium that passes through the pressure region while rotating around its axis; a holder that is provided inside the fixing belt, has a sliding surface that contacts the inner circumferential surface of the fixing belt via a lubricant, and holds a heater that heats the fixing belt; a plurality of slits formed in the sliding surface so as to be recessed are arranged in the axial direction on the sliding surface corresponding to an area excluding the pressure region, and guide the movement of the lubricant from upstream to downstream in the rotation direction of the fixing belt; The fixing device is characterized in that the fixing belt has a hardness that can prevent deformation of the fixing belt such that the fixing belt falls into the slit.

2. 2. The fixing device according to claim 1, wherein the fixing belt has a Young's modulus of 7 GPa or more.

3. The fixing device according to claim 2, characterized in that the Young's modulus of the fixing belt is correlated with the groove width of the slit, and when the Young's modulus of the fixing belt has a hardness of 10 GPa or less, the groove width is set to 1.0 to 3.0 mm.

4. 4. An image forming apparatus comprising the fixing device according to claim 1.

Images