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 and an image forming apparatus that fix a toner image on a recording material by applying heat and pressure to the recording material. [Background technology]

[0002] In recent years, the market for on-demand printing has expanded, allowing for the printing of commercial printed materials such as catalogs, posters, and pamphlets in the required number of copies, as well as for continuous printing of various invoices, direct mail, and other documents while changing some of the printed content for each customer. Furthermore, there is a demand for faster printing times for electrophotographic image forming devices that handle on-demand printing.

[0003] To achieve such faster printing times, it is necessary to maximize the heating efficiency of the recording material when fixing the toner image to the recording material.To maximize 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 guarantee excellent image quality on the recording material, it is essential to prevent slippage between the belt member and the recording material at 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 frictional force 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] Furthermore, surface materials and surface shapes of the sliding member have been proposed to minimize the coefficient of friction of the surface of the sliding member. For example, in Patent Document 2, a low-friction material is used for the surface of the sliding member, and the frictional force of the sliding member is reduced by creating an uneven surface shape.

[0008] Furthermore, in Patent Document 3, a plurality of uneven shapes 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] Japanese Patent Application Publication No. 2017-181948 [Patent Document 2] Patent No. 5119724 [Patent Document 3] Japanese Patent Publication No. 2020-52354 Summary of the Invention [Problem to be solved by the invention]

[0010] In the fixing configuration described above, if foreign matter enters the uneven protrusions on the sliding member while the fixing device is operating, the foreign matter can damage the inner surface of the belt, resulting in image defects.

[0011] SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and aims 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. [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 on a recording material, the fixing device comprising: a rotatable fixing belt that sandwiches and conveys the recording material between itself and a pressure contact member, and fixes the toner image on the recording material; a sliding member that slides on the inner circumferential surface of the fixing belt at a position where the fixing belt sandwiches and conveys the recording material; and a lubricant that flows between the fixing belt and the sliding member, the sliding member having a protrusion with which the fixing belt slides, the protrusion being 100 mm in diameter and 100 mm in height, the sliding member having a protrusion that is ... a height h from the tip of the protrusion at a portion 100 μm away from the fixing belt on the upstream side in the recording material conveyance direction is 35 μm≦h≦100 μm, the sliding member has a first protrusion located in a first region in the recording material conveyance direction and a second protrusion located in a second region downstream of the first region in the recording material conveyance direction, the first protrusion and the second protrusion are arranged in positions where they overlap when projected in the recording material conveyance direction, and the height h from the tip of the first protrusion at a portion 100 μm away from the position where the fixing belt slides on the fixing belt on the upstream side in the recording material conveyance direction is 35 μm≦h≦100 μm, h 1' is 35μm≦ h 1'≦100 μm, and the height of the second protrusion from the tip of the second protrusion at a portion 100 μm away from the position where the fixing belt slides in contact with the second protrusion on the upstream side in the conveying direction of the recording material. h 2' is 5μm≦ h The present invention provides a fixing device in which 2'≦30 μm and an image forming apparatus equipped with the fixing device. [Effects 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 explanation of the drawings]

[0014] [Figure 1] 1 is a schematic front cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. [Figure 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; [Figure 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 cross-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. FIG. [Figure 5] 5A and 5B 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 cross-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 protrusion of a protrusion of a sliding member according to the first embodiment of the present invention. [Figure 8] 10 is a table showing the results of an investigation into the state of foreign matter intrusion when the height from the tip of the protrusion of the sliding member according to the first embodiment of the present invention is changed. [Figure 9] 10 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 conveyance speed are changed according to the second embodiment of the present invention; [Figure 10] 10A and 10B are explanatory views illustrating a state in which the sliding layer of the protruding portion in the sliding member according to the third embodiment of the present invention is worn away. [Figure 11] 10A and 10B are detailed views of the configuration of a sliding member and the arrangement of protrusions according to a third embodiment of the present invention. [Figure 12] 10 is a graph showing the height from the tip of a protrusion of a sliding member according to a third embodiment of the present invention. [Figure 13] 10 is a table showing the results of examining the wear state of the sliding layer of the protrusions when the height from the tip of the protrusion of the slide member according to the third embodiment of the present invention is changed. [Figure 14] 10 is a graph showing the results of a study on the recovery rate of the thickness of the lubricant at the tip of the projection 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 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 INVENTION

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

[0016] [First embodiment] FIG. 1 is a schematic front cross-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.

[0018] The image reading unit 2 reads a document placed on a document glass table 21. Light emitted from a light source 22 is reflected by the document and forms an image on a CCD sensor 24 via optical elements 23 such as lenses. The optical system unit consisting of the light source 22, optical elements 23, and CCD sensor 24 scans in the direction of arrow E, causing the CCD sensor 24 to convert the document into an image signal consisting of an electrical 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, where it is subjected to image processing in accordance with each image forming unit (described later) by a control unit 30. 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. 31 denotes a polygon scanner serving as an exposure device, which scans with a laser beam corresponding to the image signal. The laser beam is then 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 unit, Pb is a magenta (M) image forming unit, Pc is a cyan (C) image forming unit, and Pd is a black (Bk) image forming unit, each of which forms an image of the corresponding color. Note that image forming units Pa to Pd have the same configuration, so the following will explain the configuration of the Y image forming unit Pa, and the configurations of the other image forming units will be shown by assigning the same numbers as the components of the Y image forming unit Pa to the components corresponding to the Y image forming unit Pa, and by replacing the suffix "a" in the numbers of the components of the Y image forming unit Pa with b to d, and will not be explained again.

[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. A laser beam from the polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. 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 from the back of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, 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 intermediate transfer belt 204 is transported to the next image forming station, where the toner images of each color formed in each image forming station are transferred in the order of Y, M, C, and Bk, forming four-color images superimposed on the surface. The toner image that has passed through Bk image forming station Pd is secondarily transferred to paper as a recording material in a secondary transfer station composed 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 intermediate transfer belt 204. Paper fed from paper feed cassette 8 or 9 waits at registration unit 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 transported from registration unit 208.

[0025] The toner image on the secondary transferred paper is fixed to the paper by a fixing device G, which 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, is then discharged outside the machine, and is stacked on 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 side) of the image formation is completed, the fixed paper is reversed through an inversion section provided inside the image forming device, and the toner image is transferred and fixed to the second side (second side) of the image formation, after which it is ejected outside the machine and stacked on the paper output tray 7.

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

[0028] Figure 2 is a schematic front cross-sectional view showing the overall configuration of the fixing device G in Figure 1. In the following figures, the direction of arrow X indicates the conveyance direction of the recording material (not shown in the figure), the direction of arrow Y indicates the width direction of the recording material, and the direction of arrow Z indicates the pressure direction of the fixing belt. The dotted line portion is an enlarged view of the nip portion 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, and other properties, and is a thin-walled cylindrical shape. In this embodiment, as shown in the enlarged view indicated by the dotted line, the fixing belt 301 has a three-layer structure consisting of 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) fluororesin. The fixing belt 301 is stretched between 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 between them. The pressure pad 303 is made of LCP (liquid crystal polymer) resin. A sliding member 304 is interposed between the pressure pad 303 and the fixing belt 301.

[0032] 3 shows the detailed configuration of the sliding member 304. Fig. 3(A) is a cross-sectional view of the sliding member 304 in the recording material conveyance 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] 3A, the sliding member 304 of this embodiment is composed of a base layer 304a, protrusions 304b, and a sliding layer 304c. The base layer 304a only needs to have sufficient heat resistance and strength. Stainless steel, copper, aluminum, engineering plastics (PI, PEEK, LCP, etc.), etc. are desirable materials. In this embodiment, a 1.3 mm thick stainless steel plate 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.) to achieve low friction. In this embodiment, the sliding layer 304c is coated with a 20 μm thick PTFE (polytetrafluoroethylene) coating.

[0034] In FIG. 2, a lubricant is further applied to the inner surface of fixing belt 301, allowing fixing belt 301 to slide smoothly against sliding member 304. Silicone oil is used as the lubricant. Stay 302 is used to supplement the strength of pressure pad 303. In this embodiment, sliding layer 304c is provided on base material layer 304a, but an adhesive layer may be provided between base material layer 304a and sliding layer 304c. Using an adhesive layer in this manner makes it possible to achieve good adhesive strength between base material layer a and sliding layer c when using a metal material such as SUS, copper, or aluminum for base material layer 304a.

[0035] Furthermore, 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 arrow Y (the recording material width direction) are fixed to the pressure pad 303 with screws or the like. Furthermore, although not shown here, the sliding member 304 may be integral 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, which 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 on the frame of the heating unit (not shown), and also functions as a tension roller that applies a predetermined tension to fixing belt 301.

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

[0039] In the nip 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 transported. In this way, the fixing device G fixes the toner image to the recording material while sandwiching and transporting the recording material. Therefore, the nip N must have both the function of applying heat and pressure and the function of transporting the recording material. A driving source (not shown) presses the pressure roller 305 against the pressure pad 303 via the fixing belt 301. The pressure force (NF) at the nip N during printing is 1600 N, and the width of the nip N in the direction of arrow X (paper transport direction) is set to 24.5 mm, and the width in the direction of 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] 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 illustrating the intrusion of foreign matter into sliding member 304 and the resulting image defects. FIG. 5A shows a state in which foreign matter D has intruded into one of protrusions 304b of sliding member 304 and become entangled at the tip of protrusion 304b. When foreign matter D becomes entangled at the tip of protrusion 304b, the entangled foreign matter D damages the inner surface of fixing belt 301, reducing the pressure applied to the toner and reducing gloss. Such locally low gloss areas can affect the image as gloss streaks as shown in FIG. 5B. Therefore, to prevent such image defects, it is important to prevent foreign matter from entering the protrusions of 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, where Figure 6(A) shows the shape of the tip of the protrusion 304b with a gentle slope, and Figure 6(B) shows the shape of the tip of the protrusion 304b with a steep slope.

[0045] If the tip of protrusion 304b of sliding member 304 is gently inclined, a buoyancy F is generated on sliding member 304 when lubricant O on the inner surface of fixing belt 301 flows into protrusion 304b, and a gap is formed between protrusion 304b of sliding member 304 and base layer 301a of fixing belt 301 (= wedge effect). If foreign matter D flows in under this condition, foreign matter D will enter the tip of protrusion 304b.

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

[0048] Therefore, a method for examining the effect of the configuration of the protrusions 304b of the sliding member 304 according to this embodiment, which 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 with the fixing device G, and a black solid image was printed on plain paper to check whether or not any image defects 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 under conditions 1-1 and 1-2, streaks appeared in the image, and foreign matter that had entered the tip of protrusion 304b had damaged the inner surface of fixing belt 301. Under condition 1-3, slight streaks appeared in the image, and under 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 wedge effect described above, and foreign matter enters when the gap becomes larger than the size of the foreign matter.

[0054] Furthermore, when sliding member 304 was observed after the image was printed, no change was found compared to before printing under conditions 1-1 to 1-8, but under condition 1-9, it was confirmed that sliding layer 304c at the tips of protrusions 304b of sliding member 304 had peeled off. This is thought to be because the inclination of the tips of protrusions 304b became too great, reducing the inflow of lubricant, and causing the lubricant to run out on the contact surface between the tips of protrusions 304b and base layer 301a of fixing belt 301.

[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 protrusion 304b is set to 35 μm≦h≦100 μm as described above, and the viscosity η [mm 2 The influence of the paper transport speed v [mm / s] and the image quality was examined.

[0057] Generally, the greater the viscosity η of the lubricant used on the inner surface of the fixing belt 301 x the paper conveying speed v, the more easily the lubricant penetrates 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 foreign matter can easily enter due to the wedge effect described above.

[0058] Therefore, we will explain the 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.

[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 velocity v of 50 to 435 mm / s and checked the state of the image when the paper transport speed v was changed in the range of 50 to 435 mm / s.

[0060] To make it easier to check the influence of foreign matter, a black solid image was printed on coated paper, on which image defects are more 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 using the table in FIG.

[0062] Under conditions 2-1 to 2-3, slight streaks were observed in the image, but no damage was found on the inner surface of fixing belt 301. This is because tiny foreign matter, small enough not to affect plain paper, had entered the tip of protrusion 304b. It is thought that the gloss increased in areas where pressure was locally increased due to the entry of foreign matter, resulting in gloss streaks appearing in the image. Under conditions 2-4 to 2-6, no streaks were observed in the image, and no damage was found on the inner surface of fixing belt 301.

[0063] Therefore, the viscosity η [mm 2 / s] and paper transport speed v [mm / s], and 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 to prevent 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 protrusion 304b of the sliding member 304 is worn away.

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

[0067] This wear rate is actually increased by making it 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 ensured to be sufficient, 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, and the durability life can be improved.

[0069] To this end, 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, which is 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 achieving both prevention of image defects and improved durability.

[0070] Therefore, as shown in Fig. 11(A), all of 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 foreign matter D from entering the protrusions located in region 702 if the foreign matter flows downstream in the paper conveyance direction, passing beside the protrusions located in region 701, without entering the protrusions located in region 701. If the protrusions are located in places where they do not overlap when projected in the paper conveyance direction, as shown in Figure 11(b), there is a risk that foreign matter D passing beside the protrusions located in region 701 will enter the protrusions 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 are shaped to ensure 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 larger 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 are prepared in which the projection shapes of the projections 304b of the sliding member 304 located in the region 701 and the region 702 are changed.

[0075] As shown in Figure 12, the protrusion shape of protrusion portion 304b located in region 701 has a height h1' of 60 μm from the tip of the protrusion at portion B, which is 100 μm upstream in the paper transport direction from contact portion A with base layer 301a of fixing belt 301, which falls within the range shown in the first embodiment to prevent foreign matter from entering.In contrast, protrusion portion 304b located in region 702 has a height h2' of 2 μm to 35 μm from the tip of the protrusion at portion B, which is 100 μm upstream in the paper transport direction from contact portion A with base layer 301a of fixing belt 301.

[0076] Then, a drive durability test was conducted by sequentially replacing these sliding members 304 in the fixing device G mounted on the image forming apparatus in Figure 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, with the design target time in this mode being 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, which is a value that could cause slippage and 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 using 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 sliding member 304 was checked, it was observed that sliding layer 304c at the tip of protrusion 304b had disappeared. In addition, the inner surface of base layer 301a of fixing belt 301 was also severely damaged, which is thought to be because protrusion 304b was exposed when sliding layer 304c disappeared, and excessive friction occurred on the inner surface of the fixing belt.

[0080] Under condition 3-2, the drive torque did not exceed the threshold value within the durability design target time, but the final torque value was 280 mNm, rising 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 found on the inner surface of the fixing belt 301.

[0081] In the case of conditions 3-1 and 3-2, 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, 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] Under conditions 3-3 to 3-5, the final torque value was sufficiently lower than the threshold value, and sliding layer 304c remained sufficiently intact. Furthermore, no damage was observed on the inner surface of fixing belt 301. This is thought to be because protrusions 304b located in region 702 have a shape with a protrusion tip height h2' that ensures a sufficient lubricant thickness through a wedge effect, thereby reducing the wear rate of sliding layer 304c.

[0083] On the other hand, under condition 3-9, as with condition 3-1, the drive 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. It takes a certain amount of time for the thickness of the lubricant scraped off by passing over protrusions 304b to recover to the same level as the initial thickness before reaching the next protrusion 304b that the lubricant 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] through the protrusion interval d [mm] between the protrusion 701a in the area 701 and the protrusion 701b in the area 702 shown in FIG. 11(A) of the third embodiment is shown. d By setting [s] within the specified range, it is possible to ensure a sufficient thickness of the lubricant on the protrusions, and further improvement in the durability of the fixing device is expected.

[0087] Therefore, in order to investigate the effect on the thickness of the lubricant when the projection interval d is changed, several 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. 11(A), when the thickness of the lubricant flowing into the protrusion 701a located at the most upstream of the nip portion is set to 100%, the thickness of the lubricant flowing into the next protrusion 702a after passing through the protrusion 701a (= thickness recovery rate) 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 using the graph in FIG.

[0090] As the projection distance d increases, the thickness recovery rate gradually increases, reaching 100% when d = 3.5 mm. This means that d ≥ 3.5 mm is sufficient to fully recover the thickness of the lubricant scraped off by the projections.

[0091] Therefore, the time it takes for the paper to travel at a transport 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, it is possible to prevent image defects and further improve durability.

[0092] Fifth Embodiment In the configuration of the third embodiment, when the state of the sliding member 304 after the target durability design time was checked, it was found that the sliding layer 304c was more worn at the protrusions located in the region 701 than at the protrusions located in the region 702. This is thought 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 the sliding member 304, the fixing belt 301, and the 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 located 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 located within the area pressed against the pressure roller 305.

[0096] As a result, as shown in Figure 15(B), the protrusions located in area 701 can reduce the contact pressure with the 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 downstream 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 region 702' do not affect the intrusion of foreign matter, if the protrusions located in region 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 region 701 or region 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...Fusing device N: Nip section O...lubricant

Claims

1. In a fixing device that fixes a toner image on a recording material, a rotatable fixing belt that sandwiches and conveys a recording material between itself and a pressure contact member, and fixes a toner image onto the recording material; a sliding member that slides on an inner circumferential surface of the fixing belt 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; and the sliding member has a protrusion with which the fixing belt slides, the protrusion has a height h of 35 μm≦h≦100 μm from the tip of the protrusion at a position 100 μm away from the position with which the fixing belt slides toward the upstream side in the conveyance direction of the recording material, the sliding member includes a first protrusion located in a first region in the recording material conveyance direction, and a second protrusion located in a second region downstream of the first region in the recording material conveyance direction, the first protrusion and the second protrusion are disposed at positions where they overlap when projected in a recording material conveyance direction, a height h1' of the first protrusion from a tip of the first protrusion at a portion 100 μm away from a position with which the fixing belt slides and is on the upstream side in a recording material conveyance direction is 35 μm≦h1'≦100 μm; The fixing device is characterized in that the height h2' from the tip of the second protrusion at a portion 100 μm upstream of the position where the fixing belt slides in contact with the fixing belt in the conveying direction of the recording material is 5 μm≦h2′≦30 μm.

2. 2. The fixing device according to claim 1, wherein the relationship between the viscosity η [mm 2 / s] of the lubricant and the conveying speed v [mm / s] of the recording material is η×v≦2×10 5 mm 3 / s 2 .

3. 2. The fixing device according to claim 1, wherein the time td [s] during which the recording material is transported between the first protrusion and the second protrusion satisfies td≧0.008 s.

4. the pressing member 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, 2. The fixing device according to claim 1, wherein the second protrusion of the sliding member is provided within a region that is pressed against the pressing member.

5. 2. The fixing device according to claim 1, wherein the first protrusion of the sliding member has a contact pressure with the fixing belt that is smaller than that of the second protrusion of the sliding member.

6. The fixing device according to any one of claims 1 to 5, an image forming unit that forms a toner image fixed by the fixing device on a recording material; An image forming apparatus comprising:

Images