Fixing device, image forming apparatus

Abstract

To solve the problem in which: some arrangements of contacts to ground a fixing film and a pressure roller may increase the potential difference between a contact side and a non-contact side in a longitudinal direction.SOLUTION: A first contact member is arranged in an area close to one end of a first rotating body in a longitudinal direction, and a second contact member is arranged in an area close to the other end of a second rotating body in the longitudinal direction.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a fixing device, and more particularly to a fixing device used in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer. [Background technology]

[0002] Conventionally, a film heating type as shown in Patent Document 1 is known as a fixing device used in an image forming apparatus such as an electrophotographic type. A heating device of the film heating type has a heater having a resistance heating element on a ceramic substrate, a fixing film that is heated and rotated while in contact with the heater, and a pressure roller that forms a nip portion with the heater via the fixing film. In such a configuration, if the fixing film or the pressure roller is charged, there is a risk of electrostatic offset or electrical disturbance of the developer on the recording material. In view of this, Patent Document 1 describes a configuration in which the fixing film and the pressure roller are grounded. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2003-337485 Summary of the Invention [Problem to be solved by the invention]

[0004] However, depending on the arrangement of the contacts for grounding the fixing film and the pressure roller, there is a risk that the potential difference between the contact side and the non-contact side in the longitudinal direction will become large.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to suppress the potential difference in the longitudinal direction. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, a fixing device is provided which has a first rotating body, a heating body, and a substrate on which the heating body is provided, and is equipped with an elongated heater arranged in the internal space of the first rotating body, and a second rotating body, and the first rotating body is sandwiched between the heater and the second rotating body, and an image formed on a recording material is fixed to the recording material by heating it through the first rotating body at a nip portion, the fixing device having a first contact member which contacts the first rotating body and grounds the first rotating body, and a second contact member which contacts the second rotating body and grounds the second rotating body, and is characterized in that, when the direction of the long side of the surface of the substrate on which the heating body is provided is defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction on the surface is defined as the transverse direction, the first contact member is arranged in an area close to one end side of the first rotating body in the longitudinal direction, and the second contact member is arranged in an area close to the other end side of the second rotating body in the longitudinal direction. Effect of the Invention

[0007] According to the present invention, the potential difference in the longitudinal direction can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] Schematic diagram of an image forming apparatus [Diagram 2] Cross-sectional view of the fixing device viewed from the longitudinal direction [Diagram 3] Schematic diagram of an end portion of a fixing device viewed from a paper feed direction [Figure 4] Heater schematic diagram [Diagram 5] FIG. 1 is a diagram showing a contact member according to the present embodiment. [Figure 6] FIG. 1 is a diagram showing a contact member of a comparative example. [Figure 7] FIG. 2 is a diagram showing the surface potential of the fixing film and the pressure roller in the longitudinal direction. [Figure 8] FIG. 1 is a diagram showing a contact member according to the present embodiment. [Figure 9] Enlarged view of contact parts [Figure 10] Cross-sectional view of the fixing device viewed from the longitudinal direction [Figure 11] FIG. 1 is a diagram showing a contact member of a comparative example. [Figure 12] FIG. 2 is a diagram showing the surface potential of the fixing film and the pressure roller in the longitudinal direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention according to the claims, and all of the combinations of features described in the embodiments are not necessarily essential to the solution of the invention. EXAMPLES

[0010] (Image forming device) An image forming apparatus 100 according to the present invention will be described. Fig. 1 is a schematic diagram of the image forming apparatus 100 using electrophotographic recording technology used in this embodiment. The image forming apparatus 100 includes four image forming stations 103Y, 103M, 103C, and 103K arranged in a substantially straight line. Of the four image forming stations 103Y, 103M, 103C, and 103K, 103Y forms a yellow (hereinafter abbreviated as Y) image, 103M forms a magenta (hereinafter abbreviated as M) image, 103C forms a cyan (hereinafter abbreviated as C) image, and 103K forms a black (hereinafter abbreviated as K) image. Each of the image forming stations 103Y, 103M, 103C, and 103K has a photosensitive drum 104Y, 104M, 104C, and 104K as an image carrier, and a charging roller 105Y, 105M, 105C, and 105K as a charging means. Each of the image forming stations 103Y, 103M, 103C, and 103K further has an exposure device 106 as an exposure means, and a developing device 107Y, 107M, 107C, and 107K as a developing means. Each of the image forming stations 103Y, 103M, 103C, and 103K further has a cleaning device 108Y, 108M, 108C, and 108K as a cleaning means.

[0011] When the video controller 130 receives image information from an external device (not shown) such as a host computer, it transmits a print signal to a control means 131, which is, for example, a CPU, and an image forming operation starts. When forming an image, in the image forming station 103Y, the photosensitive drum 104Y is rotated in the direction of the arrow in FIG. 1 by a rotation control section (drive control means) (not shown) in response to a print command. First, the outer peripheral surface (surface) of the photosensitive drum 104Y is uniformly charged by a charging roller 105Y, and the charged surface of the photosensitive drum 104Y is exposed by irradiating it with a laser beam according to image data by an exposure device 106, forming an electrostatic latent image. The electrostatic latent image is visualized by a developing device 107Y using Y toner to become a Y toner image. Through the above steps, a Y toner image is formed on the surface of the photosensitive drum 104Y. A similar image forming process is performed in the image forming stations 103M, 103C and 103K, where an M toner image is formed on the surface of the photosensitive drum 104M, a C toner image is formed on the surface of the photosensitive drum 104C, and a K toner image is formed on the surface of the photosensitive drum 104K.

[0012] The intermediate transfer belt 109, which is provided along the arrangement direction of the image forming stations 103Y, 103M, 103C, and 103K, is stretched by a driving roller 109a, a driven roller 109b, and a driven roller 109c. The driving roller 109a rotates in the direction of the arrow in FIG. 1 in response to a print command by a rotation control unit (drive control means) (not shown). As a result, the intermediate transfer belt 109 is rotated and moved at a predetermined process speed along each of the image forming stations 103Y, 103M, 103C, and 103K. Toner images of each color are sequentially transferred and superimposed on the outer circumferential surface (surface) of the intermediate transfer belt 109 by primary transfer rollers 110Y, 110M, 110C, and 110K, which are arranged opposite the photosensitive drums 104Y, 104M, 104C, and 104K with the intermediate transfer belt 109 sandwiched therebetween. Through the above process, a full-color toner image of four colors is formed on the surface of the intermediate transfer belt 109.

[0013] Residual toner remaining on the surfaces of the photosensitive drums 104Y, 104M, 104C, and 104K after the primary transfer is removed by cleaning blades (not shown) provided in the cleaning devices 108Y, 108M, 108C, and 108K. This prepares the photosensitive drums 104Y, 104M, 104C, and 104K for the next image formation. The above-mentioned photosensitive drum 104, charging roller 105, developing device 107, primary transfer roller 110, and scanner unit (not shown) constitute an image forming section that forms an unfixed image on the recording material P.

[0014] On the other hand, the recording materials P stored in a feed cassette 111 provided at the bottom of the image forming apparatus 100 are separated and fed one by one from the feed cassette 111 by a feed roller 112, and fed to a pair of registration rollers 113. The pair of registration rollers 113 sends the fed recording materials P to a transfer nip portion between the intermediate transfer belt 109 and a secondary transfer roller 114. The secondary transfer roller 114 is disposed so as to face the driven roller 109b with the intermediate transfer belt 109 interposed therebetween. A bias is applied to the secondary transfer roller 114 from a high-voltage power source (not shown) when the recording material P passes through the transfer nip portion. As a result, a full-color toner image is secondarily transferred from the surface of the intermediate transfer belt 109 to the recording material P passing through the transfer nip portion. The recording material P carrying the toner is conveyed to a fixing device 18 equipped with a heating member 31 and a pressure roller 32 as a pressure member. Thereafter, the recording material P is heated and pressurized by utilizing heat from a heater in a fixing device 18 serving as a heating device, and the toner image is heat-fixed onto the recording material P. Then, the recording material P is discharged by a discharge roller 129 from the fixing device 18 to a discharge tray 115 outside the image forming apparatus 100. Residual toner remaining on the surface of the intermediate transfer belt 109 after the secondary transfer is removed by an intermediate transfer belt cleaning device 116. This prepares the intermediate transfer belt 109 for the next image formation.

[0015] The image forming apparatus described above is a representative example of a tandem type color laser printer that transfers two or more color toners onto a recording material via an intermediate transfer belt to form an image. However, the application of the present invention is not limited to this, and it may also be a direct transfer type that transfers two or more color toners onto a recording material. It is also possible to apply the present invention to a monochrome laser printer that uses a single monochrome toner.

[0016] (Fixing device) 2 is a cross-sectional view of the fixing device 18 viewed from the longitudinal direction, and FIG. 3 is a schematic diagram of an end of the fixing device 18 viewed from the paper feed direction. The fixing device 18 includes a flexible fixing film 36 as a first rotating body, a heater 37 disposed in the internal space of the fixing film 36, and a pressure roller 32 as a second rotating body that forms a nip portion N with the heater 37 via the fixing film 36. The direction of the long side of the elongated heater 37 in FIG. 2 is also referred to as the longitudinal direction (front-rear direction in FIG. 2), and the direction of the short side of the heater 37 perpendicular to the longitudinal direction is also referred to as the transverse direction (left-right direction in FIG. 2). Furthermore, the thickness direction of the heater 37 perpendicular to the longitudinal direction and the transverse direction is also referred to as the thickness direction (up-down direction in FIG. 2).

[0017] The heating member 31 is a film unit including a flexible cylindrical fixing film 36. The heating member 31 and the pressure roller 32 are disposed approximately parallel between the left and right side plates 34 of the device frame 33, with the heater 37 facing the pressure roller 32 with the fixing film 36 interposed therebetween.

[0018] The pressure roller 32 has a core 32a, an elastic layer 32b formed on the outside of the core 32a, and a release layer 32c formed on the outside of the elastic layer 32b. The elastic layer 32b is made of a material formed by foaming silicone rubber, fluororubber, or the like. The release layer 32c is made of a material such as PFA, PTFE, or FEP.

[0019] In this embodiment, the pressure roller 32 is formed by foaming a silicone rubber layer 32b of about 3.5 mm thick as a non-conductive elastic layer by injection molding on a core metal 32a made of stainless steel with an outer diameter of 11 mm. Furthermore, the outside of the non-conductive elastic layer is covered with a conductive PFA resin tube 32c of about 20 μm thick. The outer diameter of the pressure roller 32 is 18 mm. The hardness of this pressure roller 32 is preferably in the range of 40° to 50° from the viewpoint of securing the nip portion N and durability at a load of 9.8 N using an ASKER-C hardness meter. In this embodiment, it is adjusted to 45°. The length of the elastic layer of the pressure roller 32 in the longitudinal direction is 226 mm. The surface resistance value of the surface layer of the pressure roller 32 in the longitudinal direction is 5.0 MΩ or less when measured by applying 250 V with a HIOKI digital mega-Ω high tester over a measurement width of 220 mm that ensures at least a width in a direction perpendicular to the conveying direction of the LTR paper.

[0020] 3, the pressure roller 32 is rotatably supported between device frame side plates 34 via bearing members 35 at both longitudinal ends of the core metal 32a. A drive gear G is fixed to one end of the pressure roller core metal 32a. A rotational force is transmitted from a drive source (not shown) to the drive gear G, and the pressure roller 32 is driven to rotate.

[0021] 2 includes a fixing film 36, a heater 37 disposed in the internal space of the fixing film 36, a heater holder 38 that supports the heater 37, and a heat equalizing plate 39 that equalizes the heat of the heater. The heating member 31 further includes a metal pressure stay 41 that reinforces the heater holder 38, and flanges 42 and 43 that restrict the movement of the fixing film 36 in the longitudinal direction.

[0022] The fixing film 36 is a cylindrical flexible member having a base layer 36a, an elastic layer 36b formed on the outside of the base layer, and a release layer 36c formed on the outside of the elastic layer as a surface layer. The surface resistance value in the longitudinal direction of the base layer 36a is 154.0 MΩ or less when measured by applying 250 V with a HIOKI digital mega-Ω high tester over a measurement width of 220 mm, which ensures at least a width in a direction perpendicular to the conveyance direction of the LTR paper.

[0023] The fixing film 36 in this embodiment has an inner diameter of 18 mm, and uses a polyimide base material with a thickness of 60 μm as the base layer 36a. Also, conductive silicone rubber with a thickness of about 150 μm is used as the elastic layer 36b. Also, a conductive PFA resin tube with a thickness of 15 μm is used as the release layer 36c. As shown in FIG. 2, the heater holder 38 has a cross section with a substantially semicircular trough shape, is a member having rigidity, heat resistance, and heat insulation properties, and is formed of a liquid crystal polymer in this embodiment. The heater holder 38 is capable of supporting the inner surface of the fixing film 36 fitted onto the heater holder 38, and holding the heater 37.

[0024] 4 is a schematic diagram of the heater 37. The heater 37 has a substrate 37a made of ceramic such as alumina or aluminum nitride, on which a heating element 37b made of a silver-palladium alloy or the like is formed by screen printing or the like. Furthermore, an electrical contact portion 37c made of silver or the like is connected to the heating element 37b. In this embodiment, two heating elements 37b are connected in series, and the resistance value of the two heating elements is 18 Ω. Furthermore, a glass coat 37d is formed as a protective layer on the heating element 37b to protect the heating element 37b and improve the sliding property with the fixing film 36.

[0025] The heater 37 is supported on the seat of the heater holder 38 and is disposed along the fixing film 36. The substrate 37a of the heater 37 is a rectangular parallelepiped with a longitudinal length of 270 mm, a lateral length of 5.8 mm, and a thickness of 1.0 mm, and is made of alumina. The heating element 37b is connected in series at the longitudinal end by the conductor 37e. The heating element 37b has a longitudinal length of 222 mm and a lateral length of 0.9 mm. The lateral positions of the heating elements 37b are located 0.7 mm from the lateral ends of the ceramic substrate 37a on both the upstream and downstream sides, and are formed at positions symmetrical with respect to the lateral center. The inner surface of the fixing film 36 is coated with heat-resistant grease, and the grease improves the sliding properties between the heater 37 and the heater holder 38 and the inner surface of the fixing film 36.

[0026] The pressure stay 41 is U-shaped and is a member that is long in the longitudinal direction. The pressure stay 41 supports the heater holder 38, thereby increasing the bending rigidity of the heating member 31. The pressure stay 41 of this embodiment is formed by bending stainless steel having a plate thickness of 1.6 mm.

[0027] The flanges 42, 43 hold both longitudinal ends of the pressure stay 41. The flanges 42, 43 are engaged with vertical grooves formed in the left and right side plates 34 of the device frame 33. In this embodiment, the flanges 42, 43 are made of a liquid crystal polymer resin.

[0028] 3, the pressure spring 46 is disposed between the pressure portions 42b of the left and right flanges 42, 43 and the pressure arm 45. When the pressure spring 46 presses the left and right flanges 42, 43, the heater 37 is pressed against the pressure roller 32 via the pressure stay 41 and the heater holder 38, sandwiching the fixing film 36. In this embodiment, the total pressure between the fixing film 36 and the pressure roller 32 is 180 N. As a result, the heater 37 forms a nip portion N of about 6 mm with the pressure roller 32, against the elasticity of the pressure roller 32, via the fixing film 36.

[0029] When a rotational force is transmitted from a drive source (not shown) to the drive gear G of the pressure roller 32, the pressure roller 32 is driven to rotate at a predetermined speed in the clockwise direction in FIG. 2. In this embodiment, the rotational speed of the pressure roller 32 is controlled so that the conveying speed of the recording material P is 100 mm / sec. As the pressure roller 32 is driven to rotate, the fixing film 36 also rotates in the counterclockwise direction in FIG. 2 due to the frictional force acting between the pressure roller 32 and the fixing film 36 at the nip portion N. As a result, the fixing film 36 slides in contact with the heater 37 at the nip portion N, and rotates counterclockwise around the outer periphery of the heater holder 38 in response to the rotation of the pressure roller 32.

[0030] The fixing film 36 rotates, power is supplied to the heater 37, and when the temperature detected by the thermistor (not shown) of the heater 37 reaches the target temperature, the recording material P is conveyed to the nip portion N. The fixing inlet guide 30 guides the recording material P carrying the unfixed toner image t toward the nip portion N.

[0031] When the recording material P carrying the unfixed toner image t is transported to the nip portion N, the surface of the recording material P carrying the toner image t comes into contact with the fixing film 36 at the nip portion N, and the recording material P is sandwiched and transported through the nip portion N as the fixing film 36 rotates. During this transport process, the unfixed toner image t on the recording material P is heated and pressed by the fixing film 36 and the pressure roller 32, and is fixed. The recording material P that has passed through the nip portion N is curvature-separated from the surface of the fixing film 36. Then, it is discharged outside the machine by a pair of discharge rollers (not shown). The maximum paper feed width of the fixing device in this embodiment is 216 mm, and LTR size recording material P can be printed at a speed of 20 PPM.

[0032] The contact members 60 and 61 of this embodiment will be described with reference to Figures 5(a) and (b). Figure 5(a) is a layout diagram of the contact members 60 and 61 in the longitudinal direction of the fixing film and the pressure roller. Figure 5(b) is a diagram showing the contact state of the contact members 60 and 61 on the surfaces of the fixing film and the pressure roller.

[0033] The hatched portion shown in FIG. 5(a) indicates an area where the maximum size recording material P conveyed based on the center is passed in the longitudinal direction of the nip portion N (hereinafter, also referred to as the paper passing area). In this embodiment, the area on one end side of the paper passing area in the longitudinal direction is also referred to as area R1, and the area on the other end side is also referred to as area R2. The contact member 60 is a contact for grounding the fixing film 36, and is arranged in area R1 in the longitudinal direction. The contact member 61 is a contact for grounding the pressure roller 32, and is arranged in area R2 in the longitudinal direction. In this embodiment, the contact member 60 is arranged at a position distance L1 from the conveyance reference, and the contact member 61 is arranged at a position distance L2 from the conveyance reference. Note that the contact members are arranged so that the distance L1=the distance L2 as an example here, but this is not limited thereto, and the contact members may be arranged in area R1 on one end side in the longitudinal direction and area R2 on the other end side.

[0034] Here, the recording material P is conveyed based on the center as an example, but is not limited to this. For example, when the recording material P is conveyed based on one side, the center of the fixing film 36 in the longitudinal direction may be used as the reference. In this case, the contact member 60 is disposed at a position distance L1 from the center of the fixing film 36, and the contact member 61 is disposed at a position distance L2 from the center of the fixing film 36. Similarly, the contact members are disposed so that the distance L1=the distance L2 as an example, but are not limited to this, and the contact members may be disposed in an area R1 on one end side in the longitudinal direction and an area R2 on the other end side.

[0035] The contact member 60 is made of a conductive heat-resistant resin, and in this embodiment, it is a 60 μm thick polyimide film with carbon dispersed therein, shaped to be 22 mm×6.55 mm. The contact state between the contact member 60 and the fixing film 36 is shown in FIG. 5(b). The long side of the polyimide film as the contact member 60 is arranged on the outer surface (outer peripheral surface) of the fixing film 36 so as to be parallel to the rotation direction of the fixing film 36 and to contact with the fixing film 36 in the forward direction with a contact pressure of 0.0148 to 0.0235 N. As for the grounding condition, the contact member 60 is connected to a parallel circuit of a capacitor 63 and a diode 64 via a 1.5 MΩ resistor 62 and is grounded to the grounding part. This is to prevent electrostatic offset and banding that occurs when the AC voltage vibration driving the heater 37 of the fixing device is superimposed on the DC voltage of the transfer nip portion via the recording material P.

[0036] The contact member 61 is a contact member made of metal, and in this embodiment, it is made of SUS with a thickness of 0.12 mm and has a shape of 25 mm x 7.00 mm. The contact state between the contact member 61 and the pressure roller 32 is shown in FIG. 5(b). The SUS long side of the contact member 61 is arranged on the outer surface (outer peripheral surface) of the pressure roller 32 so as to be parallel to the rotation direction of the pressure roller 32 and to contact with the pressure roller 32 in the forward direction with a contact pressure of 0.245 to 0.343 N. The grounding condition is that the contact member is grounded to the ground part via a resistor 65 of 1 GΩ. This is to prevent offset and peeling discharge due to charging, and to prevent leakage of the transfer current.

[0037] 6 is a diagram showing a comparative example, in which two contact members are arranged in the same region on one end side in the longitudinal direction.

[0038] 7 is a graph showing the surface potential in the longitudinal direction of the fixing film 36 and pressure roller 32 of this embodiment and the comparative example. The vertical axis indicates the potential, and the horizontal axis indicates the longitudinal position of the fixing film 36 and pressure roller 32, with point A indicating the contact position of contact member 60 and point B indicating the contact position of contact member 61. The plots in the figure indicate the potential at contact positions A and B, and the approximation lines are indicated by solid and dashed lines.

[0039] As shown in the graph of Fig. 7, the surface potential of the fixing film 36 in the longitudinal direction of this embodiment has a gradient of about -80 to -85V near the contact member 60 (plot ● in the figure) and -170 to -175V on the non-contact side where the contact member 60 is not arranged. The surface potential of the pressure roller 32 in the longitudinal direction has a gradient of about 15V near the contact member 61 (plot ◯ in the figure) and 110V on the non-contact side where the contact member 61 is not arranged. The potential difference between the fixing film 36 and the pressure roller 32 is about 190V in the longitudinal direction. It can be seen that the variation in the potential difference between the fixing film 36 and the pressure roller 32 is suppressed over the entire longitudinal area.

[0040] Next, the surface potential of the fixing film 36 of the comparative example has a gradient of about -80 to -85V near the contact member 60 (plot ■ in the figure) and -170 to -175V on the non-contact side where the contact member 60 is not arranged. Also, the surface potential in the longitudinal direction of the pressure roller 32 has a gradient of about 10V near the contact member 61 (plot □ in the figure) and 115V on the non-contact side where the contact member 61 is not arranged. Therefore, the potential difference between the fixing film 36 and the pressure roller 32 is about 95V on the contact side where the contact members 60 and 61 are arranged (point A in the figure), while it is about 285V on the non-contact side where the contact members 60 and 61 are not arranged (point B in the figure). In other words, the potential difference between the fixing film 36 and the pressure roller 32 varies depending on the region in the longitudinal direction.

[0041] When the unfixed toner image t was fixed to the recording material P in this state, scattering of the image occurred near the non-contact side (point B side in the figure) in the comparative example when a halftone image was formed. This is because the potential difference on the non-contact side became large, and the surface potential of the fixing film 36 became greater than the surface potential of the pressure roller 32 which tries to hold the negative polarity toner image t on the recording material P on the recording material P. This caused a repulsive force to be generated against the toner image t on the recording material P, causing scattering.

[0042] In this embodiment, the variation in the potential difference in the entire longitudinal area of ​​the fixing film 36 and the pressure roller 32 was suppressed compared to the comparative example. As a result, the occurrence of image scattering due to the potential difference was also suppressed. This is because the contact member 60 for grounding the fixing film 36 is arranged in the region R1 on one end side in the longitudinal direction, and the contact member 61 for grounding the pressure roller 32 is arranged in the region R2 on the other end side in the longitudinal direction. As a result, the gradient of the surface potential of the fixing film 36 from the contact portion to the non-contact portion and the gradient of the surface potential of the pressure roller 32 from the non-contact portion to the contact portion in the longitudinal direction can be made uniform. Therefore, the surface potential difference between the fixing film 36 and the pressure roller 32 can be made uniform.

[0043] In this way, the contact member 60 for grounding the fixing film 36 is disposed in the region R1 on one end side in the longitudinal direction, and the contact member 61 for grounding the pressure roller 32 is disposed in the region R2 on the other end side in the longitudinal direction. Therefore, the potential difference between the fixing film 36 and the pressure roller 32 in the longitudinal direction can be suppressed. EXAMPLES

[0044] In the previous Example 1, a configuration was described in which the contact member 60 contacts the surface of the fixing film 36. In the present Example, a configuration will be described in which the contact member 60 contacts the inner circumferential surface of the fixing film 36. Note that the same reference numerals are used for the same configurations as those in the previous first embodiment, such as the image forming apparatus 100, and detailed description thereof will be omitted here.

[0045] FIG. 8 is a diagram showing the arrangement of the contact member 600 and the contact member 61 in this embodiment. In FIG. 8, the contact member 600 for grounding the fixing film 36 is arranged in the region R1 in the longitudinal direction as in the previous embodiment 1. The contact member 61 for grounding the pressure roller 32 is arranged in the region R2 in the longitudinal direction. The contact member 600 is arranged at a distance L1 from the conveyance center, and the contact member 61 is arranged at a distance L2 from the conveyance center. Here, the contact members are arranged so that the distance L1 is equal to the distance L2 as an example, but the arrangement is not limited thereto, and the contact members may be arranged in the region R1 on one end side in the longitudinal direction and the region R2 on the other end side.

[0046] FIG. 9 is an enlarged view of the contact member 600, and FIG. 10 is a cross-sectional view seen from the direction of the arrow in FIG. 9. The contact member 600 contacts the fixing film 36 from the inner peripheral surface of the fixing film 36. As in the first embodiment, the contact member 600 is a polyimide film having a thickness of 60 μm, a height of 22 mm, and a width of 6.55 mm, in which carbon is dispersed. The fixing film 36 is a cylindrical flexible member having a base layer 36a, an elastic layer 36b formed on the outside of the base layer, and a release layer 36c formed on the outside of the elastic layer. The surface resistance value of the base layer 36a in the longitudinal direction is 154.0 MΩ or less when measured by applying 250 V with a HIOKI digital mega-Ω high tester.

[0047] The contact member 600 and the fixing film 36 are contacted in the internal space of the fixing film 36 so that the long side of the polyimide film is parallel to the rotation direction of the fixing film 36 and in the forward direction with a contact pressure of 0.0148 to 0.0235 N. The grounding conditions are to prevent electrostatic offset and banding that occurs when the AC voltage vibration driving the heater 37 of the fixing device is superimposed on the DC voltage of the transfer nip portion via the recording material P.

[0048] Since the contact member 600 is in contact with the inner circumferential surface of the fixing film 36, it does not have to be disposed in a region on the one end side of the paper passing region in the longitudinal direction. In other words, as long as it is disposed on the one end side of the center reference in the longitudinal direction, it may be within the paper passing region. This is because the contact member 600 is in contact with the inner circumferential surface of the fixing film 36. As a result, even if a jam occurs in the fixing device or toner adheres to the surface of the fixing film 36 due to image offset or the like, it is possible to prevent the adhered toner from soiling the surface of the contact member 600. As a result, even if the contact member 600 is disposed within the paper passing region, it is possible to suppress contact failure due to the adhered toner and damage to the fixing film due to the toner adhered to the contact member 600.

[0049] 11 is a diagram showing a comparative example, in which two contact members are arranged in the same region on one end side in the longitudinal direction.

[0050] 12 is a graph showing the surface potential in the longitudinal direction of the fixing film 36 and the pressure roller 32 of this embodiment and the comparative example. The vertical axis indicates the potential, and the horizontal axis indicates the longitudinal position of the fixing film 36 and the pressure roller 32, with point A indicating the contact position of the contact member 600 and point B indicating the contact position of the contact member 61. The plots in the figure indicate the potential at the contact positions A and B, and the approximation lines are indicated by the solid line and the dashed line.

[0051] As shown in the graph of Fig. 12, the surface potential in the longitudinal direction of the fixing film 36 of this embodiment has a gradient of about -50 to -55V near the contact member 600 (plot ● in the figure) and -145 to -150V on the non-contact side where the contact member 600 is not arranged. The surface potential in the longitudinal direction of the pressure roller 32 has a gradient of about 15V near the contact member 61 (plot ◯ in the figure) and 110V on the non-contact side where the contact member 61 is not arranged. The potential difference between the fixing film 36 and the pressure roller 32 is about 160V in the longitudinal direction. It can be seen that the variation in the potential difference between the fixing film 36 and the pressure roller 32 is suppressed over the entire longitudinal region.

[0052] Next, the surface potential of the fixing film 36 of the comparative example has a gradient of about -50 to -55V near the contact member 600 (plot ■ in the figure) and -145 to -150V on the non-contact side where the contact member 600 is not arranged. Also, the surface potential in the longitudinal direction of the pressure roller 32 has a gradient of about 10V near the contact member 61 (plot □ in the figure) and 115V on the non-contact side where the contact member 61 is not arranged. Therefore, the potential difference between the fixing film 36 and the pressure roller 32 is about 65V on the contact side where the contact members 600 and 61 are arranged (point A in the figure), while it is about 265V on the non-contact side where the contact members 600 and 61 are not arranged (point B in the figure). In other words, the potential difference between the fixing film 36 and the pressure roller 32 varies depending on the region in the longitudinal direction.

[0053] When the unfixed toner image t was fixed to the recording material P in this state, scattering of the image occurred near the non-contact side (point B in the figure) in the comparative example when a halftone image was formed. This is because the potential difference on the non-contact side became large, and the surface potential of the fixing film 36 became greater than the surface potential of the pressure roller 32 which tries to hold the negative polarity toner image t on the recording material P on the recording material P. This caused a repulsive force to be generated against the toner image t on the recording material P, causing scattering.

[0054] In this embodiment, the variation in the potential difference in the entire longitudinal area of ​​the fixing film 36 and the pressure roller 32 can be suppressed compared to the comparative example. As a result, the occurrence of image scattering due to the potential difference can also be suppressed. This is because the contact member 600 for grounding the fixing film 36 is arranged in the region R1 on one end side in the longitudinal direction, and the contact member 61 for grounding the pressure roller 32 is arranged in the region R2 on the other end side in the longitudinal direction. As a result, the gradient of the surface potential of the fixing film 36 from the contact portion to the non-contact portion and the gradient of the surface potential of the pressure roller 32 from the non-contact portion to the contact portion can be made uniform in the longitudinal direction. Therefore, the surface potential difference between the fixing film 36 and the pressure roller 32 can be made uniform.

[0055] In this way, the contact member 600 for grounding the fixing film 36 is disposed in the region R1 on one end side in the longitudinal direction, and the contact member 61 for grounding the pressure roller 32 is disposed in the region R2 on the other end side in the longitudinal direction. Therefore, the potential difference between the fixing film 36 and the pressure roller 32 in the longitudinal direction can be suppressed. [Explanation of symbols]

[0056] 32 Pressure roller 36 Fixing film 60, 61, 600 Contact parts

Claims

1. A first rotating body; an elongated heater having a heating element and a substrate on which the heating element is provided, the elongated heater being disposed in an internal space of the first rotating body; a second rotating body, the first rotating body being sandwiched between the heater and the second rotating body, and an image formed on a recording material is fixed to the recording material by heating the recording material at a nip portion via the first rotating body, a first contact member that contacts the first rotating body and grounds the first rotating body; a second contact member that contacts the second rotating body and grounds the second rotating body, When the direction of the long side of the surface of the substrate on which the heating element is provided is defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction of the surface is defined as the short side direction, A fixing device characterized in that the first contact member is arranged in an area close to one end side of the first rotating body in the longitudinal direction, and the second contact member is arranged in an area close to the other end side of the second rotating body in the longitudinal direction.

2. 2. The fixing device according to claim 1, wherein the first contact member is in contact with an outer circumferential surface of the first rotating body.

3. 2. The fixing device according to claim 1, wherein the first contact member is in contact with an inner circumferential surface of the first rotating body.

4. 2. The fixing device according to claim 1, wherein the second contact member is in contact with an outer circumferential surface of the second rotating body.

5. In the longitudinal direction, when a region where a recording material of a maximum size conveyed to the nip portion passes through the nip portion is defined as a first region, and a region where the recording material does not pass through the nip portion is defined as a second region, the first contact member is disposed in the second region on the one end side, The fixing device according to claim 2 , wherein the second contact member is disposed in the second region on the other end side.

6. In the longitudinal direction, when a region where a recording material of a maximum size conveyed to the nip portion passes through the nip portion is defined as a first region, and a region where the recording material does not pass through the nip portion is defined as a second region, the first contact member is disposed in the first region on the one end side, 4. The fixing device according to claim 3, wherein the second contact member is disposed in the second region on the other end side.

7. In the longitudinal direction, a distance from a conveyance reference of the recording material conveyed to the nip portion to the first contact member is a first distance, and a distance from the conveyance reference to the second contact member is a second distance, 2. The fixing device according to claim 1, wherein the first distance and the second distance are equal.

8. In the longitudinal direction, a first distance is from a center of the first rotating body to the first contact member, and a second distance is from the center to the second contact member; 2. The fixing device according to claim 1, wherein the first distance and the second distance are equal.

9. the first contact member is grounded via a first resistor and a capacitor; 2. The fixing device according to claim 1, wherein the second contact member is grounded via a second resistor.

10. the first rotating body is a film, the second rotating body is a pressure roller, 2. The fixing device according to claim 1, wherein the heater is disposed in an internal space of the film, the film is sandwiched between the heater and the pressure roller, and the image formed on the recording material is heated through the film in the nip portion.

11. The film has a base layer and a surface layer serving as a release layer on the base layer, 11. The fixing device according to claim 10, wherein the surface resistance of the base layer is 154.0 MΩ or less.

12. the pressure roller has an elastic layer and a surface layer serving as a release layer on the elastic layer, 11. The fixing device according to claim 10, wherein the surface resistance of the surface layer is 5.0 M[Omega] or less.

13. an image forming means for forming an image on a recording material; 2. An image forming apparatus comprising: the fixing device according to claim 1 for fixing an image formed on a recording material.

Images