Fixing device and image forming apparatus

Abstract

To provide a fixing device and an image forming apparatus that prevent entry of foreign substances into a slide member of the fixing device to prevent the occurrence of an image defect.SOLUTION: A fixing device for fixing a toner image to a recording material, comprises: a rotatable fixing belt that sandwiches and conveys the recording material with a pressure member and fixes the toner image to the recording material; a slide member on which the fixing belt slides at a position where the fixing belt sandwiches and conveys the recording material; and a lubricant that flows into between the fixing belt and the slide member. The slide member includes projections with which the fixing belt comes into slide contact. A height h from a leading end of the projection at a portion separated from a position where the fixing belt comes into slide contact by 100 μm on the upstream side in a conveyance direction of the recording material, is 35 μm≤h≤100 μm. An image forming apparatus has the fixing device mounted therein.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a fixing device that applies heat and pressure to a toner image on a recording material to fix the toner image on the recording material, and to an image forming apparatus. [Background technology]

[0002] In recent years, the market for on-demand printing has expanded, where commercial printed materials such as catalogs, posters, and pamphlets are printed in the required number of copies, and where various invoices, direct mail, and other printed materials are continuously printed while changing part of the print content for each customer. In addition, there is a demand for faster printing times for electrophotographic image forming apparatuses that handle on-demand printing.

[0003] In order to achieve such high-speed printing, it is necessary to maximize the heating efficiency of the recording material when fixing the toner image to the recording material. Therefore, in order to maximize the heating efficiency, a fixing device with a wide fixing nip (wide nip) has been proposed, which uses a belt member, a backup member (pad), and a pressure member.

[0004] In a fixing device having such a wide nip, in order to ensure excellent image quality on the recording material, it is essential to prevent slippage between the belt member and the recording material in the nip forming portion, and between the pressure member and the recording material.

[0005] That is, the frictional force between the backup member and the inner surface of the belt member must be sufficiently small compared to the frictional force between the recording material and the belt member and the frictional force between the recording material and the pressure member.

[0006] Therefore, in order to reduce the friction between the backup member and the belt member, Patent Document 1 proposes a system in which a sliding member is used between the backup member and the belt member.

[0007] In addition, surface materials and surface shapes of the sliding members have been proposed to minimize the friction coefficient of the sliding member surfaces. For example, in Patent Document 2, a low-friction material is used for the sliding member surface, and the frictional force of the sliding member is reduced by creating an uneven surface shape.

[0008] Moreover, in Patent Document 3, a plurality of projections and recesses are provided on the sliding members inside and outside the nip to reduce the frictional force of the sliding members. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2017-181948 A [Patent Document 2] Patent No. 5119724 [Patent Document 3] JP 2020-52354 A Summary of the Invention [Problem to be solved by the invention]

[0010] In the fixing configuration as described above, if foreign matter enters the uneven protrusions on the sliding member while the fixing device is in operation, the inner surface of the belt can be damaged by the foreign matter, resulting in poor image quality.

[0011] SUMMARY OF THE PRESENT DISCLOSURE ... The present invention has been made in consideration of the above circumstances, and has an object to provide a fixing device and an image forming apparatus which prevent foreign matter from entering the sliding members of the fixing device and prevent the occurrence of image defects. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides a fixing device for fixing a toner image onto a recording material, the fixing device comprising: a rotatable fixing belt which clamps and transports the recording material between itself and a pressure member and fixes the toner image onto the recording material; a sliding member against which the fixing belt slides at a position where the fixing belt clamps and transports the recording material; and a lubricant which flows between the fixing belt and the sliding member, the sliding member having a protrusion against which the fixing belt slides, the protrusion having a height h from the tip of the protrusion at a portion 100 μm upstream in the transport direction of the recording material from the position where the fixing belt slides in such a manner that 35 μm≦h≦100 μm; and an image forming apparatus equipped with the fixing device. Effect of the Invention

[0013] According to the present invention, it is possible to provide a fixing device and an image forming apparatus that prevent foreign matter from entering the sliding members of the fixing device and prevent the occurrence of image defects. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic front sectional view of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] 2 is a schematic front cross-sectional view of the fixing device of FIG. 1 according to the first embodiment of the present invention; [Diagram 3] 3 is a detailed view of a sliding member in the fixing device of FIG. 2 according to the first embodiment of the present invention. [Figure 4] 3 is an enlarged front sectional view of a fixing belt and a sliding member in the fixing device of FIG. 2 according to the first embodiment of the present invention. [Diagram 5] 5A to 5C are schematic diagrams illustrating the intrusion of foreign matter into a sliding member according to the first embodiment of the present invention and the resulting image defects. [Figure 6] 3 is an enlarged front sectional view of the vicinity of a tip of one protrusion of the sliding member according to the first embodiment of the present invention. FIG. [Figure 7] 4 is a graph showing the height from the tip of a projection of a projection of the sliding member according to the first embodiment of the present invention. [Figure 8]11 is a table showing the results of an investigation into the state of intrusion of foreign matter when the height from the tip of the projection of the sliding member according to the first embodiment of the present invention is changed. [Figure 9] 11 is a table showing the results of an investigation into the state of foreign matter intrusion when the viscosity of the lubricant of the fixing belt and the paper conveying speed are changed according to the second embodiment of the present invention; [Figure 10] 13A and 13B are explanatory views illustrating a state in which the sliding layer of the protruding portion in the slide member according to the third embodiment of the present invention is worn away. [Figure 11] 13A to 13C are detailed views of the configuration of a sliding member and the arrangement of protrusions according to the third embodiment of the present invention. [Figure 12] 13 is a graph showing the height from the tip of a projection of a sliding member according to a third embodiment of the present invention. [Figure 13] 13 is a table showing the results of an investigation into the wear state of the sliding layer of the protrusions when the height from the tip of the protrusions of the slide member according to the third embodiment of the present invention is changed. [Figure 14] 13 is a graph showing the results of an investigation into the recovery rate of the thickness of the lubricant at the tip of the projections when the interval between the projections of the sliding member according to the fourth embodiment of the present invention is changed. [Figure 15] 13 is an explanatory diagram showing the relationship between the positional relationship of the sliding member with respect to the pressure roller and the contact pressure with the fixing belt according to the fifth embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In the following embodiments, a full-color image forming apparatus using an electrophotographic method having multiple photosensitive drums will be described as an example, but the present invention is not limited to this and can be applied to image forming apparatuses of various methods, monochrome image forming apparatuses, etc. In addition, the components described in the following embodiments are merely examples, and various conditions such as the configuration, function, dimensions, materials, shape, and relative arrangement of the apparatus to which the present invention is applied can be appropriately modified or changed within the scope of the gist of the present invention, and are not limited to the following embodiments.

[0016] [First embodiment] FIG. 1 is a schematic front sectional view of a full-color image forming apparatus according to a first embodiment of the present invention.

[0017] In FIG. 1, an image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus main body 3. The image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus main body 3.

[0018] The image reading unit 2 reads an original placed on a glass platen 21. Light emitted from a light source 22 is reflected by the original and forms an image on a CCD sensor 24 via an optical system member 23 such as a lens. The optical system unit consisting of the light source 22, optical system member 23, and CCD sensor 24 scans in the direction of arrow E, and the CCD sensor 24 converts the original into an image signal of an electric signal data string for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and the control unit 30 performs image processing in accordance with each image forming unit described later. The control unit 30 also receives external inputs as image signals from an external host device such as a print server.

[0019] The image forming apparatus main body 3 includes a plurality of image forming sections Pa, Pb, Pc, and Pd, and each image forming section forms an image based on the image signal described above.

[0020] Specifically, first, an image signal is converted into a PWM (pulse width modulation) laser beam by a control unit 30. A polygon scanner 31 serves as an exposure device, and scans with a laser beam according to the image signal. Then, the laser beam is irradiated onto photosensitive drums 200a-200d serving as image carriers in the image forming units Pa-Pd.

[0021] Note that Pa is a yellow (Y) image forming section, Pb is a magenta (M) image forming section, Pc is a cyan (C) image forming section, and Pd is a black (Bk) image forming section, which form images of the corresponding color. Note that image forming sections Pa to Pd have the same configuration, so the configuration of the Y image forming section Pa will be described below, and the configurations of the other image forming sections will be omitted by assigning the same numbers as the components of the Y image forming section Pa to the components corresponding to the Y image forming section Pa, and by replacing the suffix "a" in the numbers of the components of the Y image forming section Pa with b to d.

[0022] In the Y image forming station Pa, reference numeral 200a denotes a photosensitive drum, on whose surface a toner image is formed based on an image signal, as will be described below.

[0023] Reference numeral 201a denotes a primary charger, which charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential, by a laser beam from a polygon scanner 31. Reference numeral 202a denotes a developer, which develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. Reference numeral 203a denotes a transfer roller, which discharges electricity from the rear surface of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, thereby transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0024] The toner image on the intermediate transfer belt 204 is conveyed to the next image forming section, where the toner images of each color formed in each image forming section are transferred in the order of Y, M, C, and Bk, so that four color images are superimposed on the surface. The toner image that has passed through the Bk image forming section Pd is secondarily transferred to paper as a recording material in a secondary transfer section formed of a pair of secondary transfer rollers 205 and 206 by applying a secondary transfer electric field of opposite polarity to the toner image on the intermediate transfer belt 204. Paper fed from paper feed cassette 8 or 9 waits at registration section 208, and then the timing is controlled to align the position of the toner image on the intermediate transfer belt with the paper, and the paper is conveyed from registration section 208.

[0025] The toner image transferred onto the paper is fixed to the paper by a fixing device G, which also serves as an image heating device, and the paper with the toner image fixed by the fixing device G passes through the fixing device G, after which it is discharged outside the machine and loaded onto the paper output tray 7.

[0026] On the other hand, in the case of a double-sided JOB, once the transfer and fixing of the toner image on the first side (first surface) of the image formation is completed, the fixed paper is turned over through an inversion section provided inside the image forming device, and the toner image is transferred and fixed to the second side (second surface) of the image formation, after which the paper is ejected outside the machine and loaded onto the output tray 7.

[0027] Next, the configuration of the fixing device G in FIG. 1 will be described in detail.

[0028] Fig. 2 is a schematic front cross-sectional view showing the overall configuration of the fixing device G in Fig. 1. In the following figures, the direction of the arrow X indicates the conveyance direction of the recording material (not shown in the figure), the direction of the arrow Y indicates the width direction of the recording material, and the direction of the arrow Z indicates the pressure direction of the fixing belt. Also, the dotted line part is an enlarged view of the nip part N.

[0029] In FIG. 2, the fixing device G is a belt heating type fixing device, and includes a fixing belt 301 as an endless rotatable heating rotor, a pressure pad 303 for supporting the fixing member, a stay 302 for supporting the pressure pad 303, a sliding member 304 arranged to cover the pressure pad 303, a heating roller 307, and a pressure roller 305 as a pressure rotor that faces the fixing belt 301 and forms a nip portion N together with the fixing belt 301.

[0030] The fixing belt 301 has thermal conductivity, heat resistance, etc., and is a thin cylindrical shape. In this embodiment, as shown in the enlarged view of the dotted line, the fixing belt 301 has a three-layer structure including a base layer 301a, an elastic layer 301b formed on the outer periphery of the base layer 301a, and a release layer 301c formed on the outer periphery of the elastic layer 301b. The base layer 301a is 80 μm thick and made of polyimide resin (PI), the elastic layer 301b is 300 μm thick and made of silicone rubber, and the release layer 301c is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 301 is stretched by a pressure pad 303 and a heating roller 307. The fixing belt 301 has an outer diameter of 150 mm.

[0031] The pressure pad 303 is pressed against the fixing belt 301 by a pressure roller 305 as a pressure contact member, with the fixing belt 301 sandwiched therebetween. LCP (liquid crystal polymer) resin is used as the material of the pressure pad 303. A sliding member 304 is interposed between the pressure pad 303 and the fixing belt 301.

[0032] 3 shows a detailed configuration of the sliding member 304. Fig. 3(A) is a cross-sectional view of the sliding member 304 in the recording material conveying direction, and Fig. 3(B) is a view of the sliding member 304 viewed from the contact surface side with the fixing belt 301.

[0033] In FIG. 3, the sliding member 304 of this embodiment is composed of a base layer 304a, a protrusion 304b, and a sliding layer 304c, as shown in FIG. 3(A). The base layer 304a only needs to have sufficient heat resistance and strength. The material is preferably SUS, copper, aluminum, engineering plastics (PI, PEEK, LCP, etc.). In this embodiment, SUS with a thickness of 1.3 mm is used. The sliding member 304 has a flat top surface and cylindrical protrusions 304b. The sliding layer 304c is preferably provided with a material (fluorine coating, PTFE, PFA, etc.) for realizing low friction. In this embodiment, it is coated with PTFE (polytetrafluoroethylene) with a thickness of 20 μm.

[0034] In FIG. 2, a lubricant is further applied to the inner surface of the fixing belt 301, so that the fixing belt 301 slides smoothly against the sliding member 304. Silicone oil is used as the lubricant. A stay 302 is used to supplement the strength of the pressure pad 303. In this embodiment, the sliding layer 304c is provided on the base material layer 304a, but an adhesive layer may be provided between the base material layer 304a and the sliding layer 304c. By using an adhesive layer in this way, it is possible to develop good adhesive strength between the base material layer a and the sliding layer c when a metal material such as SUS, copper, or aluminum is used as the material of the base material layer 304a.

[0035] In addition, in this embodiment, a configuration is adopted in which the sliding member 304 is fixed to the pressure pad 303. For example, a configuration is adopted in which both ends of the sliding member 304 in the direction of the arrow Y (the recording material width direction) are fixed to the pressure pad 303 with screws or the like. Although not shown here, the sliding member 304 may be integrated with the pressure pad 303.

[0036] The heating roller 307 is a stainless steel pipe having a thickness of 1 mm, and has a halogen heater 306 disposed therein as a heat source, and is capable of generating heat up to a predetermined temperature.

[0037] Heating roller 307 has a rotation center at one end or near the center, and generates a tension difference between the front and rear by rotating relative to fixing belt 301, thereby controlling the position in the main scanning direction of fixing belt 310. In addition, this heating roller 307 is biased by a spring supported by the frame of a heating unit (not shown), and also serves as a tension roller that applies a predetermined tension to fixing belt 301.

[0038] The pressure roller 305 is a roller in which an elastic layer 305b is formed on the outer periphery of a core metal shaft 305c, and a release layer 305a is formed on the outer periphery of the elastic layer 305b, as shown in the enlarged view of the dotted line. The core metal shaft 305c is made of a SUS member having a diameter of 72 mm, the elastic layer 305b is made of conductive silicone rubber having a thickness of 8 mm, and the release layer 305a is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin having a thickness of 100 μm. The pressure roller 305 is axially supported by a fixing frame (not shown) of the fixing device G, and a gear is fixed to one end of the pressure roller 305, which is connected to a drive source (not shown) via the gear and rotated.

[0039] In the nip portion N formed between the fixing belt 301 and the pressure roller 305, the toner image is heated while the recording material carrying the toner image is sandwiched and conveyed. In this way, the fixing device G fixes the toner image to the recording material while sandwiching and conveying the recording material. Therefore, the nip portion N needs to have both the function of applying heat and pressure and the function of conveying the recording material. The pressure roller 305 is pressed against the pressure pad 303 via the fixing belt 301 by a driving source (not shown). The pressure force (NF) in the nip portion N during printing is 1600 N, and the width of the nip portion N in the direction of the arrow X (paper conveyance direction) is set to 24.5 mm, and the width in the direction of the arrow Y (paper width direction) is set to 326 mm.

[0040] Next, the sliding layer 304c of the sliding member 304 when the fixing device G is driven will be described.

[0041] FIG. 4 is an enlarged front cross-sectional view of the fixing belt 301 and the sliding member 304 of the fixing device G.

[0042] In FIG. 4, when the fixing device G is driven, the fixing belt 301 moves relative to the sliding member 304 in the direction of the arrow L in the figure, whereby the sliding layer 304c of the sliding member 304 rubs against the base layer 301a of the fixing belt 301.

[0043] 5A and 5B are schematic diagrams for explaining the intrusion of foreign matter into the sliding member 304 and the resulting image defects. FIG. 5A shows a state in which a foreign matter D has intruded into one of the protrusions 304b of the sliding member 304 and has become entangled with the tip of the protrusion 304b. When the foreign matter D becomes entangled with the tip of the protrusion 304b, the entangled foreign matter D damages the inner surface of the fixing belt 301, lowering the pressure applied to the toner and reducing the gloss. Such locally low gloss areas may affect the image as gloss streaks as shown in FIG. 5B. Therefore, in order to prevent such image defects, it is important to prevent foreign matter from entering the protrusions of the sliding member 304.

[0044] Figure 6 is an enlarged front cross-sectional view of the vicinity of the tip of one of the protrusions 304b of the sliding member 304, with Figure 6(A) showing the shape of the tip of the protrusion 304b with a gentle incline, and Figure 6(B) showing the shape of the tip of the protrusion 304b with a steep incline.

[0045] If the tip of the protrusion 304b of the sliding member 304 has a gentle inclination, when the lubricant O on the inner surface of the fixing belt 301 flows into the protrusion 304b, a buoyant force F is generated on the sliding member 304, and a gap is created between the protrusion 304b of the sliding member 304 and the base layer 301a of the fixing belt 301 (=wedge effect). If a foreign object D flows in under this condition, the foreign object D will enter the protrusion tip of the protrusion 304b.

[0046] On the other hand, when the tip of protrusion 304b of sliding member 304 has a steep inclination, the amount of lubricant O on the inner surface of fixing belt 301 flowing into protrusion 304b is small and the buoyancy F generated on sliding member 304 is small, so that protrusion 304b of sliding member 304 and base layer 301a of fixing belt 301 are in contact with each other, thereby preventing foreign matter D from entering the protrusion tip of protrusion 304b.

[0047] Therefore, in order to prevent the intrusion of foreign matter, it is effective to form the protrusion shape of the protrusion portion 304b of the sliding member 304 such that the inclination of the protrusion tip is steep.

[0048] Therefore, a method for examining the effect of the configuration of the protrusions 304b of the sliding member 304 according to this embodiment that is effective in preventing the intrusion of foreign matter and the results thereof will be described.

[0049] A plurality of levels of sliding members in which the projection shape of the projection portion 304b of the sliding member 304 is changed are prepared.

[0050] As shown in FIG. 7, the protrusion shape of the protrusion 304b is such that the height h from the tip of the protrusion 304b at part B, which is 100 μm upstream in the paper transport direction from the position of contact part A where the base layer 301a of the fixing belt 301 slides against the protrusion 304b, is 10 μm to 120 μm.

[0051] Then, these sliding members 304 were sequentially replaced in the fixing device G, and a black solid image was printed on a plain paper to check whether or not a defective image occurred. 2 The paper transport speed v was set to 435 mm / s.

[0052] Next, the results of the study will be explained using the table in FIG.

[0053] It was found that in conditions 1-1 and 1-2, streaks occurred in the image, and the inner surface of fixing belt 301 was damaged by foreign matter that had entered the tip of protrusion 304b. In condition 1-3, slight streaks occurred in the image, and in conditions 1-4 to 1-9, no streaks were observed in the image, and no damage was observed on the inner surface of fixing belt 301. This is thought to be because the gap between the tip of protrusion 304b and base layer 301a of fixing belt 301 changes due to the influence of the wedge effect described above, and when the gap becomes larger than the size of the foreign matter, the foreign matter enters.

[0054] Furthermore, when the sliding member 304 after the image printing was observed, no change was observed compared to before printing under conditions 1-1 to 1-8, but under condition 1-9, it was confirmed that the sliding layer 304c at the tip of the protrusion of the protrusion 304b of the sliding member 304 had peeled off. This is considered to be because the inclination of the protrusion tip of the protrusion 304b became too large, reducing the inflow of lubricant, and the lubricant at the contact surface between the tip of the protrusion 304b and the base layer 301a of the fixing belt 301 was depleted.

[0055] Therefore, by setting the shape of the protrusion 304b to 35 μm≦h≦100 μm, it is possible to maintain durability and prevent the occurrence of image defects.

[0056] Second Embodiment Next, in order to prevent the intrusion of smaller foreign matter, the shape of the protrusions 304b is set to 35 μm≦h≦100 μm as described above, and the viscosity η [mm 2 The effects of the paper transport speed v [mm / s] and the image transfer speed v [mm / s] were examined.

[0057] Generally, the greater the viscosity η of the lubricant used on the inner surface of the fixing belt 301 x the paper transport speed v, the easier it is for the lubricant to penetrate between the protrusion 304b of the sliding member 304 and the base layer 301a of the fixing belt 301, making it easier for a gap to form, and therefore making it easier for foreign matter to enter due to the wedge effect described above.

[0058] Therefore, a method for examining the effect of viscosity η of the lubricant used on the inner surface of fixing belt 301 according to this embodiment, which is effective in preventing the intrusion of smaller foreign matter, multiplied by paper conveying speed v, and the results thereof will be described.

[0059] In this embodiment, the viscosity η of the lubricant used on the inner surface of the fixing belt 301 is 300 to 3000 mm. 2 We prepared several levels of lubricant with a paper feed speed v of 50 to 435 mm / s and checked the state of the image when the paper feed speed v was changed in the range of 50 to 435 mm / s.

[0060] In order to make it easier to check the influence of foreign matter, a solid black image was printed on coated paper, on which image defects are easily noticeable, and the image was checked. Note that the shape of the protrusion 304b was a sliding member with the above-mentioned h=40 μm.

[0061] Next, the results of the study will be explained with reference to the table in FIG.

[0062] Under conditions 2-1 to 2-3, slight streaks were observed in the image, but no damage was observed on the inner surface of fixing belt 301. This is because minute foreign matter that would not have an effect on plain paper had entered the tip of protrusion 304b. It is believed that the glossiness increased at the location where the pressure was locally increased due to the entry of the foreign matter, which appeared in the image as gloss streaks. Under conditions 2-4 to 2-6, no streaks were observed in the image, and no damage was observed on the inner surface of fixing belt 301.

[0063] Therefore, the viscosity η [mm 2 / s] and paper transport speed v [mm / s], η×v≦2×10 5 mm 3 / s 2 By doing so, it is possible to further improve the accuracy of preventing image defects.

[0064] Third Embodiment In the first embodiment, the height h of the protrusion 304b of the sliding member 304 is set within a specified range, and in the second embodiment, the viscosity η of the lubricant and the paper conveying speed v are set within a specified range, thereby preventing foreign matter from entering the protrusion 304b of the sliding member 304. However, when the contact pressure between the fixing belt 301 and the protrusion 304b is high, it is necessary to improve durability.

[0065] FIG. 10 is an explanatory diagram illustrating a state in which the sliding layer 304c of the protruding portion 304b of the sliding member 304 is worn away.

[0066] 10, as the printing operation of the image forming apparatus progresses, the sliding layer 304c of the protrusion 304b gradually wears from the state shown in FIG 10(A), and the film thickness of the sliding layer 304c at the tip of the protrusion 304b decreases as shown in FIG 10(B). If the printing operation of the image forming apparatus further progresses and the protrusion 304b becomes exposed as shown in FIG 10(C), and the base layer 301a of the fixing belt 301, which has a larger friction coefficient than the sliding layer 304c, comes into direct contact with the protrusion 304b, the frictional force between the fixing belt 301 and the sliding member 304 increases, increasing the driving torque and reaching the end of the product life.

[0067] Conversely, this wear rate becomes faster if it is made difficult for the lubricant to enter between the protrusions 304b of the sliding member 304 and the base layer 301a of the fixing belt 301 as in the first and second embodiments.

[0068] Therefore, in the configuration of the first embodiment, if the thickness of the lubricant used on the inner surface of the fixing belt 301 at the tip of the protrusion 304b can be sufficiently ensured, the frictional force between the fixing belt 301 and the sliding member 304 can be reduced, the wear rate of the sliding layer 304c can be slowed down, and the durability life can be improved.

[0069] To achieve this, in this embodiment, as shown in Figure 11 (A), the sliding member is divided into two regions, region 701 where the protrusion is located most upstream in the paper transport direction, and region 702 located downstream of region 701. In region 701, protrusion 304b is shaped to prevent the intrusion of foreign matter, and in region 702, protrusion 304b is shaped to ensure the thickness of the lubricant, thereby preventing image defects and improving durability at the same time.

[0070] Therefore, as shown in Fig. 11(A), all the protrusions located in areas 701 and 702 are positioned so that they overlap when projected in the paper transport direction. That is, as shown by the dashed line in Fig. 11(A), protrusion 702a is positioned downstream of protrusion 701a in the paper transport direction. Similarly, protrusion 702b is positioned downstream of protrusion 701b in the paper transport direction.

[0071] This is to prevent a foreign object D from entering a protrusion located in region 702 when the foreign object flows downstream in the paper transport direction by passing beside the protrusion located in region 701 without entering the protrusion located in region 701. If the protrusions are located in places where they do not overlap when projected in the paper transport direction, as shown in Figure 11(b), there is a risk that foreign object D passing beside the protrusion located in region 701 will enter the protrusion located in region 702.

[0072] In this embodiment, the configuration shown in FIG. 11(A) is such that the protrusions located in the area 702 where the intrusion of foreign matter is prevented can have a sufficient thickness of the lubricant used on the inner surface of the fixing belt 301, thereby slowing down the wear rate of the sliding layer 304c.

[0073] In other words, the greater the height h of the protrusion located in region 702, the more difficult it becomes to ensure a sufficient thickness of lubricant at the tip of the protrusion. Therefore, the following study was conducted to determine a protrusion shape that can ensure a sufficient thickness of lubricant.

[0074] A plurality of levels of sliding members in which the projection shapes of the projections 304b of the sliding members 304 located in the regions 701 and 702 are changed are prepared.

[0075] As shown in FIG. 12, the protrusion shape of protrusion 304b located in region 701 has a height h1' from the tip of the protrusion at portion B 100 μm upstream in the paper transport direction from contact portion A with base layer 301a of fixing belt 301, which is 60 μm, which is the range in which foreign matter does not enter as shown in the first embodiment. In contrast, protrusion 304b located in region 702 has a height h2' from the tip of the protrusion at portion B 100 μm upstream in the paper transport direction from contact portion A with base layer 301a of fixing belt 301, which is 2 μm to 35 μm.

[0076] Then, a drive durability test was conducted by sequentially replacing these sliding members 304 with the fixing device G mounted on the image forming apparatus in Fig. 1. The drive durability test was conducted in a mode in which the pressure roller 305 alternately repeated states of contact and non-contact with the fixing belt 301, and the design target time in this mode was 240 hours. If the drive torque exceeded a preset upper limit within the design target time, the drive durability test was terminated, and if the drive torque did not exceed the upper limit within the design target time, the drive durability test was terminated after the design target time had elapsed.

[0077] The upper limit of the drive torque was set at 300 mNm, at which point slippage could cause defective images or damage to the drive gear. 2 / s and the paper transport speed v was set to 435 mm / s.

[0078] Next, the results of the study will be explained with reference to the table in FIG.

[0079] In condition 3-1, the driving torque exceeded the threshold value of 300 mNm within the durability design target time, and when the state of the sliding member 304 was checked, it was observed that the sliding layer 304c at the tip of the protrusion 304b had disappeared. In addition, the inner surface of the base layer 301a of the fixing belt 301 was also severely damaged, which was believed to be due to the protrusion 304b being exposed due to the disappearance of the sliding layer 304c, and excessively rubbing against the inner surface of the fixing belt.

[0080] In condition 3-2, the driving torque did not exceed the threshold value within the durability design target time, but the final torque value was 280 mNm, which was close to the upper limit. At this time, the sliding layer 304c of the sliding member 304 was partially lost, and slight streak-like scratches were confirmed on the inner surface of the fixing belt 301.

[0081] In the cases of Conditions 3-1 and 3-2, it is believed that the height h2' of the tip of the protrusion 304b becomes too small, narrowing the gap between the base layer 301a of the fixing belt 301 and the protrusion 304b, making it difficult for the lubricant to penetrate, causing wear powder to accumulate on the sliding layer 304c, and leading to an increase in torque.

[0082] For conditions 3-3 to 3-5, the final torque value was sufficiently lower than the threshold value, and the sliding layer 304c remained sufficiently. Also, no damage was observed on the inner surface of the fixing belt 301. This is considered to be because the wear rate of the sliding layer 304c was reduced due to the shape of the protrusion tip of the protrusion 304b located in the region 702 having a height h2' that ensures a sufficient lubricant thickness by the wedge effect.

[0083] On the other hand, in condition 3-9, like condition 3-1, the driving torque exceeded the threshold value of 300 mNm within the durability design target time, and the sliding layer 304c at the tip of the protrusion disappeared. This is thought to be because the height h2', which is the inclination of the tip of the protrusion 304b, became large, preventing sufficient flow of lubricant, and the lubricant at the contact surface between the tip of the protrusion 304b and the fixing belt 301 was depleted, resulting in partial contact.

[0084] From the above, by setting the shape of the protrusion 304b located in region 701 to 35 μm≦h1'≦100 μm as shown in the first embodiment, and by setting the shape of the protrusion located in region 702 to 5 μm≦h2'≦30 μm, it is possible to prevent image defects and improve durability at the same time.

[0085] [Fourth embodiment] When the lubricant used on the inner surface of fixing belt 301 passes over protrusions 304b of sliding member 304, the lubricant is scraped off by protrusions 304b, temporarily thinning the thickness of the lubricant. A certain amount of time is required for the thickness of the lubricant scraped off by passing over protrusions 304b to recover to the same level as the initial thickness before it reaches the next protrusion 304b it passes over.

[0086] In the third embodiment, it has been shown that it is possible to prevent image defects and improve durability at the same time. However, in order to further extend the durability life in the future or when the contact pressure with the fixing belt is higher, the time t taken for a paper to travel at a transport speed v [mm / s] over a protrusion interval d [mm] between a protrusion 701a in an area 701 and a protrusion 701b in an area 702 shown in FIG. 11(A) of the third embodiment is shown. d By setting [s] within the specified range, a sufficient thickness of the lubricant can be ensured on the protrusions, and further improvement in the durability of the fixing device can be expected.

[0087] Therefore, in order to investigate the effect on the thickness of the lubricant when the projection interval d is changed, multiple levels of sliding members with projection intervals d of 1 to 4 mm were prepared and the following study was carried out.

[0088] In FIG. 11A, when the thickness of the lubricant flowing into the protrusion 701a located at the most upstream of the nip portion is taken as 100%, the thickness of the lubricant flowing into the next protrusion 702a (=thickness recovery rate) after passing the protrusion 701a was measured. The viscosity η of the lubricant was 1000 mm 2 / s and the paper transport speed v was set to 435 mm / s.

[0089] Next, the results of the study will be explained with reference to the graph in FIG.

[0090] As the projection distance d is increased, the thickness recovery rate increases gradually, and reaches 100% when d = 3.5 mm. Therefore, in order to fully recover the thickness of the lubricant scraped off by the projections, d ≥ 3.5 mm is sufficient.

[0091] Therefore, the time it takes for the paper to move at a conveying speed of v [mm / s] over the protrusion interval d [mm] is t d [s] can be expressed as follows: t d =d / v, v=435mm / s, d≧3.5mm Therefore t d ≧3.5 / 435=0.008s By satisfying the above relationship, image defects can be prevented and durability can be further improved.

[0092] Fifth embodiment In the configuration of the third embodiment, when the state of the sliding member 304 after the durability design target time was checked, it was found that the sliding layer 304c was more worn in the protrusions located in the region 701 than in the protrusions located in the region 702. This is considered to be because the lubricant of the fixing belt 301 is less likely to penetrate into the protrusions located in the region 701 than into the protrusions located in the region 702.

[0093] Therefore, if the pressure applied to the protrusions located in the region 701 can be reduced, the wear rate of the sliding layer 304c will be slowed down, and further improvement in durability can be expected.

[0094] FIG. 15A is a schematic diagram showing the positional relationship between a sliding member 304, a fixing belt 301, and a pressure roller 305 facing the fixing belt 301 in this embodiment.

[0095] In Figure 15 (A), the protrusion located in area 701 contacts only the fixing belt 301 and is provided outside the area pressed against the pressure roller 305, while the protrusion located in area 702 contacts the fixing belt 301 and the pressure roller 305 opposing it via the fixing belt 301, and is provided within the area pressed against the pressure roller 305.

[0096] As a result, as shown in FIG. 15(B), the protrusions located in area 701 can have a smaller contact pressure with fixing belt 301 compared to the protrusions located in area 702, thereby improving durability.

[0097] 15A, among the protrusions located in region 702, those located in region 702' that are not included in the nip forming portion located on the downstream side in the paper transport direction may be in contact with pressure roller 305 that faces it across fixing belt 301. In other words, the protrusions located in region 702' may be included in the nip forming portion.

[0098] Furthermore, since the protrusions located in area 702' do not affect the intrusion of foreign matter, if the protrusions located in area 702' are not in contact with pressure roller 305, the protrusion height of the protrusions located in 702' may be selected from the protrusion height of the protrusions in area 701 or area 702. [Explanation of symbols]

[0099] 1...Image forming device 301...Fuser belt 301a…Base layer 301b...Elastic layer 301c…Release layer 302…Stay 303...Pressure pad 304...Sliding member 304a...Base material layer 304b…Protrusion 304c…Sliding layer 305...Pressure roller 306...Halogen heater 307...Heating roller D...Foreign object G: Fixing device N: Nip section O: Lubricant

Claims

1. A fixing device for fixing a toner image onto a recording material, a rotatable fixing belt that sandwiches and conveys a recording material between itself and a pressure member and fixes a toner image onto the recording material; a sliding member along which the fixing belt slides at a position where the fixing belt nip and conveys the recording material; a lubricant that flows between the fixing belt and the sliding member; having the sliding member includes a protrusion with which the fixing belt slides, a height h of the protrusion from a tip of the protrusion at a portion 100 μm upstream of the position where the fixing belt slides in contact with the protrusion in the recording material transport direction is 35 μm≦h≦100 μm.

2. The viscosity η of the lubricant [mm ２ / s] and the conveying speed v [mm / s] of the recording material are related to each other as follows: η×v≦2×10 ５ mm ３ / s ２ 2. The fixing device according to claim 1,

3. the sliding member includes a first protrusion located in a first region in a recording material transport direction, and a second protrusion located in a second region downstream of the first region in the recording material transport direction, the first protrusion and the second protrusion are disposed at positions where they overlap when projected in a recording material conveying direction, The first protrusion has a height h from a tip of the first protrusion at a portion 100 μm away from the position where the fixing belt slides on the upstream side in the conveying direction of the recording material. １ ', 35μm≦h １ '≦100 μm, The second protrusion has a height h from a tip of the second protrusion at a portion 100 μm away from the position where the fixing belt slides on the upstream side in the conveying direction of the recording material. ２ ', 5μm≦h ２ 2. The fixing device according to claim 1, wherein the thickness is less than or equal to 30 μm.

4. The time t during which the recording material is transported between the first protrusion and the second protrusion ｄ [s] is t ｄ 4. The fixing device according to claim 3, wherein the value is greater than or equal to 0.008 s.

5. a pressing member that presses the fixing belt against the sliding member, the first protrusion of the sliding member is provided outside a region that is pressed against the pressing member, 4. The fixing device according to claim 3, wherein the second protrusion of the sliding member is provided within a region that is in pressure contact with the pressure contact member.

6. 4. The fixing device according to claim 3, wherein the first protrusion of the sliding member has a smaller contact pressure with the fixing belt than the second protrusion of the sliding member.

7. The fixing device according to claim 1 , an image forming section for forming a toner image on a recording material, the toner image being fixed by the fixing device; An image forming apparatus comprising:

Images