FIXING APPARATUS AND IMAGE FORMING APPARATUS

A fixing apparatus includes first and second rotating members, a heater having a heating element and a substrate, and first and second contact members. A direction of a longer side on a surface of the substrate where the heating element is disposed is a longitudinal direction. A direction intersecting the longitudinal direction is a widthwise direction. The first contact member is disposed in a region outside a region where a maximum size recording material conveyed to a nip portion passes through the nip portion on one end side in the longitudinal direction on an outer circumferential surface of the first rotating member, and the second contact member is disposed in the region outside the region where the maximum size recording material conveyed to the nip portion passes through the nip portion on an other end side in the longitudinal direction on an outer circumferential surface of the second rotating member.

BACKGROUND

Field

The present disclosure relates to a fixing apparatus and, more particularly, to a fixing apparatus used for image forming apparatuses such as electrophotographic copying machines and laser beam printers.

Description of the Related Art

Film-heating processes have been known for a fixing apparatus used for electrophotographic image forming apparatuses. Japanese Patent Application Laid-Open No. 2003-337485 discloses a heating element that heats an object to be heated through at least a thin film, and pressure that presses the object to be heated.

Conventional film-heating type heating apparatuses include a heater having a resistance heating element on a ceramic substrate, a fixing film rotating and being heated while in contact with the heater, and a pressure roller for forming a nip portion with the heater across the fixing film. In such a conventional configuration, when the fixing film and the pressure roller are charged, an electrostatic offset or an electrical disturbance of a developer on a recording material may possibly occur. Here, a fixing film and a pressure roller may be grounded in consideration of an electrical disturbance. However, a difference in potential between the contact and the non-contact sides may increase in the longitudinal direction depending on the arrangement of a contact for grounding the fixing film and a contact for grounding the pressure roller.

SUMMARY

The present disclosure is directed to reducing the difference in potential in the longitudinal direction.

According to an aspect of the present disclosure, a fixing apparatus includes a first rotating member, a heater that is elongate and provided with a heating element and a substrate with the heating element installed on the substrate, and disposed in a space inside the first rotating member, a second rotating member, wherein the first rotating member is pinched by the heater and the second rotating member, and an image formed on a recording material is heated at a nip portion, via the first rotating member, so that the image is fixed to the recording material, a first contact member configured to come into contact with the first rotating member to ground the first rotating member, and a second contact member configured to come into contact with the second rotating member to ground the second rotating member, wherein, in a case where a direction of a longer side on a surface of the substrate where the heating element is disposed is a longitudinal direction and a direction perpendicularly intersecting with the longitudinal direction on the surface of the substrate is a widthwise direction, the first contact member is disposed in a region outside a region where a recording material with a maximum size conveyed to the nip portion passes through the nip portion on one end side in the longitudinal direction on an outer circumferential surface of the first rotating member, and the second contact member is disposed in the region outside the region where the recording material with the maximum size conveyed to the nip portion passes through the nip portion on an other end side in the longitudinal direction on an outer circumferential surface of the second rotating member.

According to the present disclosure, the difference in potential in the longitudinal direction can be reduced.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings. The following exemplary embodiments do not limit the present disclosure within the scope of the appended claims. Not all of the combinations of the features described in the exemplary embodiments are indispensable to the solutions for the present disclosure.

Image Forming Apparatus

A first exemplary embodiment will be described below. An image forming apparatus100according to the present exemplary embodiment will be described below.FIG.1schematically illustrates a configuration of the image forming apparatus100employing an electrophotographic recording technique according to the first exemplary embodiment. The image forming apparatus100includes four different image forming stations103Y,103M,103C, and103K which are approximately linearly disposed. Of the four image forming stations103Y,103M,103C, and103K, the image forming station103Y forms a yellow image, the image forming station103M forms a magenta image, the image forming station103C forms a cyan image, and the image forming station103K forms a black image (hereinafter, yellow, magenta, cyan, and black are referred to as Y, M, C, and K, respectively). The image forming stations103Y,103M,103C, and103K include photosensitive drums104Y,104M,104C, and104K as image carriers, and charge rollers105Y,105M,105C, and105K as charging units, respectively. The image forming stations103Y,103M,103C, and103K further include an exposure apparatus106as an exposure unit, development apparatuses107Y,107M,107C, and107K as developing units, and cleaning apparatuses108Y,108M,108C, and108K as cleaning units, respectively.

When a video controller130receives image information from an external apparatus (not illustrated) such as a host computer, the video controller130transmits, for example, a print signal to a control unit131as a Central Processing Unit (CPU), so that an image forming operation is started. In image forming, the photosensitive drum104Y of the image forming station103Y is rotated in the direction of the arrow (FIG.1) by a rotation control unit (drive control unit, not illustrated) in response to a printing instruction. Firstly, the outer circumferential surface (front surface) of the photosensitive drum104Y is uniformly charged by the charge roller105Y. When the exposure apparatus106irradiates the charging plane on the surface of the photosensitive drum104Y with a laser beam corresponding to image data, an electrostatic latent image is formed. The development apparatus107Y visualizes the electrostatic latent image by Y toner to form a Y toner image. In the above-described process, a Y toner image is formed on the surface of the photosensitive drum104Y. The image forming stations103M,103C, and103K perform a similar image forming process. As a result, an M toner image is formed on the surface of the photosensitive drum104M, a C toner image is formed on the surface of the photosensitive drum104C, and a K toner image is formed on the surface of the photosensitive drum104K.

An intermediate transfer belt109provided along the arrangement direction of the image forming stations103Y,103M,103C, and103K is stretched by a drive roller109aand driven rollers109band109c.The drive roller109ais rotated in the direction of the arrow inFIG.1by the rotation control unit (drive control unit, not illustrated) in response to a printing instruction. Thus, the intermediate transfer belt109is moved to rotate at a predetermined process speed along the image forming stations103Y,103M,103C, and103K. Toner images of different colors are sequentially transferred onto the outer circumferential surface (front surface) of the intermediate transfer belt109in an overlapped way by primary transfer rollers110Y,110M,110C, and110K disposed to face the photosensitive drums104Y,104M,104C, and104K, respectively, across the intermediate transfer belt109. In the above-described process, a four-color full color toner image is formed on the surface of the intermediate transfer belt109.

After the primary transfer, transfer residual toners remaining on the surface of the photosensitive drums104Y,104M,104C, and104K are removed by cleaning blades (not illustrated) disposed in the cleaning apparatuses108Y,108M,108C, and108K, respectively. The photosensitive drums104Y,104M,104C, and104K prepare for the next image forming. The above-described photosensitive drums104, charge rollers105, development apparatuses107, primary transfer rollers110, and a scanner unit (not illustrated) are included in the image forming units for forming a non-fixed image on a recording material P.

Meanwhile, the recording materials P stacked on a feeding cassette111disposed at the bottom of the image forming apparatus100are separated one by one from the feeding cassette111by a feed roller112and then fed to a registration roller pair113. The registration roller pair113sends out the fed recording material P to a transfer nip portion between the intermediate transfer belt109and a secondary transfer roller114.

The secondary transfer roller114is disposed to face the driven roller109bacross the intermediate transfer belt109. A bias voltage is applied to the secondary transfer roller114from a high-voltage power source (not illustrated) when the recording material P passes through the transfer nip portion. Thus, the full color toner image is secondarily transferred from the surface of the intermediate transfer belt109to the recording material P passing through the transfer nip portion.

The recording material P carrying the toner image is conveyed to a fixing apparatus18including a heating member31and a pressure roller32as a pressure member. Subsequently, the recording material P is heated with the heat from a heater and then pressurized in the fixing apparatus18as a heating apparatus. Then, the toner image is heat-fixed onto the recording material P. The recording material P is discharged from the fixing apparatus18to a discharge tray115outside the image forming apparatus100by a discharge roller129. After the secondary transfer, transfer residual toner remaining on the surface of the intermediate transfer belt109is removed by an intermediate transfer belt cleaning apparatus116. Then, the intermediate transfer belt109prepares for the next image forming.

The image forming apparatus100has been described above centering on a tandem type color laser printer that transfers toner of two or more different colors onto a recording material via an intermediate transfer belt, as a typical example. However, the present exemplary embodiment is applicable not only to a tandem type but also to a direct transfer method for transferring toner of two or more different colors onto a recording material. The present exemplary embodiment is also applicable to monochromatic laser printers using monochrome toner.

Fixing Apparatus

FIG.2is a cross-sectional view illustrating the fixing apparatus18viewed from the longitudinal direction, andFIG.3is a schematic view illustrating both ends of the fixing apparatus18viewed from the paper feed direction. The fixing apparatus18includes a flexible fixing film36as a first rotating member, a heater37disposed in a space inside the fixing film36, and a pressure roller32as a second rotating member for forming a nip portion N with the heater37across the fixing film36. Referring toFIG.2, the direction of the longer side of the elongate heater37(direction from the front to the depth sides) is also referred to as a longitudinal direction, the direction of the shorter side of the heater37(horizontal direction) perpendicularly intersecting with the longitudinal direction is also referred to as a widthwise direction, and the direction of the thickness of the heater37(vertical direction) perpendicularly intersecting with the longitudinal and the widthwise directions is also referred to as a thickness direction.

The heating member31is a film unit including a flexible cylindrical fixing film36. The heating member31and the pressure roller32are disposed approximately in parallel between right and left side plates34of an apparatus frame33in a state where the heater37faces the pressure roller32across the fixing film36.

The pressure roller32includes a core32a,an elastic layer32bformed outside the core32a,and a mold release layer32cformed outside the elastic layer32b.The elastic layer32bis made of a material formed by foaming silicone rubber or fluoro rubber. The mold release layer32cis made of perfluoroalkoxy alkane (PFA), polytetrafluoroethylene (PTFE), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP).

According to the present exemplary embodiment, the pressure roller32includes the core32amade of stainless steel having an outer diameter of 11 mm, and the elastic layer32bas a foamed non-conductive elastic layer having a thickness of about 3.5 mm formed on the core32athrough injection molding. The outer surface of the non-conductive elastic layer is coated with a conductive PFA resin tube32chaving a thickness of about 20 μm. The pressure roller32has an outer diameter of 18 mm. The pressure roller32desirably has a hardness of 40 to 50 degrees (measured with an Asker C hardness meter) under a load of 9.8 N from the viewpoint of the formation and durability of the nip portion N. According to the present exemplary embodiment, the hardness is adjusted to 45 degrees. The elastic layer of the pressure roller32has a longitudinal length of 226 mm. The longitudinal surface resistance value of the surface layer of the pressure roller32is set to 5.0 MΩ or less when 250 V is applied by using the Digital Megohm HiTester from HIOKI E.E. CORPORATION with at least a measurement width of 220 mm corresponding to the width of letter (LTR) size paper in the direction perpendicularly intersecting with the conveyance direction.

As illustrated inFIG.3, the pressure roller32is rotatably supported between the side plates34of the apparatus frame33via bearing members35at both longitudinal ends of the core32a.A drive gear G is fixed to one end of the core32aof the pressure roller32. The pressure roller32is driven to rotate by a rotational force transmitted from a driving source (not illustrated) to a drive gear G.

The heating member31illustrated inFIG.2includes a fixing film36, a heater37disposed in the space inside the fixing film36, a heater holder38for supporting the heater37, and a soaking plate39for uniforming the heat of the heater37. The heating member31further includes a metal pressurizing stay41for reinforcing the heater holder38, and flanges42and43for regulating the longitudinal movement of the fixing film36.

The fixing film36is a cylindrical flexible member including a base layer36a,an elastic layer36bformed outside the base layer36a,and a mold release layer36cas the surface layer formed outside the elastic layer36b.The longitudinal surface resistance value of the base layer36ais set to 154.0 MΩ or less when 250 V is applied by using the Digital Megohm HiTester from HIOKI E.E. CORPORATION at least with a measurement width of 220 mm corresponding to the width of LTR size paper in the direction perpendicularly intersecting with the conveyance direction.

According to the present exemplary embodiment, the fixing film36has an inner diameter of 18 mm, and the base layer36ais made of a polyimide base material having a thickness of 60 μm. The elastic layer36bis made of conductive silicone rubber having a thickness of about 150 μm. The mold release layer36cis made of a conductive PFA resin tube having a thickness of 15 μm. As illustrated inFIG.2, the heater holder38is made of a rigid, heat-resistant, and heat-insulating material having a cross-sectional shape of an approximate semicircular gutter. According to the present exemplary embodiment, the heater holder38is made of a liquid crystal polymer. The heater holder38can support the inner surface of the fixing film36externally fit to the heater holder38and hold the heater37.

FIG.4schematically illustrates a configuration of the heater37. The heater37includes a ceramic substrate37amade of alumina or aluminum nitride, and heating elements37bmade of a silver-palladium alloy formed on the substrate37athrough screen printing. The heating elements37bare connected with an electric contact37cmade of silver. According to the present exemplary embodiment, two heating elements37bare connected in series to provide a resistance value of 18 Ω. A glass coat37das a protection layer is formed on the heating elements37bto protect the heating elements37band improve the slidability with the fixing film36.

The heater37is supported by the seat surface of the heater holder38and disposed along the fixing film36. The substrate37aof the heater37is made of alumina and has a shape of a rectangular parallelepiped with a longitudinal length of 270 mm, a widthwise length of 5.8 mm, and a thickness of 1.0 mm in the thickness direction. The heating elements37bare connected in series by a conductor37eat a longitudinal end. Each of the heating elements37bhas a longitudinal length of 222 mm and a widthwise length of 0.9 mm. The widthwise positions of the heating elements37bare 0.7 mm from the widthwise ends of the ceramic substrate37aon both the upstream and the downstream sides, i.e., the heating elements37bare formed at positions symmetric with respect to the widthwise center. A heat-resistant grease is applied to the inner surface of the fixing film36to improve the slidability of the heater37and the heater holder38with the inner surface of the fixing film36.

The pressurizing stay41is U-shaped and extends in the longitudinal direction. The pressurizing stay41supports the heater holder38to improve the bending rigidity of the heating member31. The pressurizing stay41according to the present exemplary embodiment is made of stainless steel having a thickness of 1.6 mm and formed through bending processing.

The flanges42and43support both longitudinal ends of the pressurizing stay41. The flanges42and43are engaged with vertical grooves of the right and left side plates34of the apparatus frame33. According to the present exemplary embodiment, the flanges42and43are made of a liquid crystal polymer resin.

As illustrated inFIG.3, a pressurizing spring46is disposed between a pressure member42band a pressure arm45of each of the right and left flanges42and43. When the right and left flanges42and43are pressed by the pressurizing springs46, the heater37is pressed against the pressure roller32across the fixing film36via the pressurizing stay41and the heater holder38. According to the present exemplary embodiment, the total contact pressure of the fixing film36and the pressure roller32is 180 N. Thus, the heater37forms the nip portion N having a width of about 6 mm together with the pressure roller32against the elasticity of the pressure roller32across the fixing film36.

When the rotational force is transmitted from the driving source (not illustrated) to the drive gear G of the pressure roller32, the pressure roller32is driven to rotate in the clockwise direction inFIG.2at a predetermined speed. According to the present exemplary embodiment, the rotational speed of the pressure roller32is controlled so that the recording material P is conveyed at a conveyance speed of 100 mm/sec. When the pressure roller32is driven to rotate, the fixing film36rotates in the counterclockwise direction inFIG.2by the frictional force acting between the pressure roller32and the fixing film36at the nip portion N. Accordingly, the fixing film36slides in contact with the heater37at the nip portion N, and is driven to rotate in the counterclockwise direction around the heater holder38by the rotation of the pressure roller32.

The fixing film36rotates, and power is supplied to the heater37. When the temperature detected by a thermistor (not illustrated) of the heater37reaches a target temperature, the recording material P is conveyed to the nip portion N. A fixing apparatus entry guide30guides the recording material P with a non-fixed toner image t carried thereon, toward the nip portion N.

When the recording material P with the non-fixed toner image t carried thereon is conveyed to the nip portion N, the surface of the recording material P carrying the toner image t comes into contact with the fixing film36at the nip portion N, and the recording material P is nipped and conveyed at the nip portion N with the rotation of the fixing film36. In this conveyance process, the non-fixed toner image t on the recording material P is heated and pressurized by the fixing film36and the pressure roller32, respectively, to be fixed to the recording material P. When the recording material P passes through the nip portion N, the recording material P is curvature-separated from the surface of the fixing film36. Then, the recording material P is discharged out of the fixing apparatus18by a discharge roller pair (not illustrated). The maximum paper feedable width of the fixing apparatus18according to the present exemplary embodiment is 216 mm, and printing on the recording material P of the LTR size can be performed at a printing speed of 20 prints per minute (PPM).

Contact members60and61according to the present exemplary embodiment will be described below with reference toFIGS.5A and5B.FIG.5Aillustrates arrangements of the contact members60and61on the fixing film36and the pressure roller32, respectively, in the longitudinal direction.FIG.5Billustrates contact states of the contact members60and61on the surfaces of the fixing film36and the pressure roller32, respectively.

Referring toFIG.5A, the shaded portion indicates the longitudinal region of the nip portion N where the recording material P having the maximum size conveyed at a center reference is fed (hereinafter this region is also referred to as a paper feed region). According to the present exemplary embodiment, the region closer to one end side in the longitudinal direction than the paper feed region is referred to as a region R1, and the region closer to the other end side in the longitudinal direction is referred to as a region R2. The contact member60for grounding the fixing film36is disposed in the region R1in the longitudinal direction. The contact member61for grounding the pressure roller32is disposed in the region R2in the longitudinal direction. According to present exemplary embodiment, the contact member60is disposed at the position by a distance L1from a conveyance reference, and the contact member61is disposed at the position by a distance L2from the conveyance reference. Although the contact members60and61are disposed so that the distances L1and L2are equal as an example, the present exemplary embodiment is not limited to this example. A contact member needs to be disposed in each of the region R1on one end side in the longitudinal direction and the region R2on the other end side in the longitudinal direction.

Although the recording material P is conveyed at the center reference as an example, the present exemplary embodiment is not limited to this example. For example, the recording material P is conveyed with reference to one side, the longitudinal center of the fixing film36may be used as a reference. In this case, the contact member60is disposed at the position by the distance L1from the center of the fixing film36, and the contact member61is disposed at the position by the distance L2from the center of the fixing film36. Although the contact members60and61are disposed so that the distances L1and L2are equal as an example, the present exemplary embodiment is not limited to this example. A contact member needs to be disposed in each of the region R1on one end side in the longitudinal direction and the region R2on the other end side in the longitudinal direction.

The contact member60is made of a heat-resistant resin provided with conductivity. According to the present exemplary embodiment, the contact member60is a polyimide film containing distributed carbon and having a thickness of 60 μm and a shape of 22 mm by 6.55 mm. Contact states of the contact member60and the fixing film36are illustrated inFIG.5B.

The polyimide film as the contact member60is disposed on the outer surface (outer circumferential surface) of the fixing film36so that the longer side of the contact member60is parallel to the rotational direction of the fixing film36, and the contact member60comes into contact with the fixing film36with a contact pressure of 0.0148 to 0.0235 N in the forward direction. As a grounding condition, the contact member60is connected with a parallel circuit of a capacitor63and a diode64via a 1.5-MΩ resistor62and grounded to a grounding portion. This configuration is intended to prevent an electrostatic offset or banding that occurs when the alternating current (AC) voltage oscillation driving the heater37of the fixing apparatus18is superimposed on the direct current (DC) voltage at the transfer nip portion across the recording material P.

The contact member61is made of metal. According to the present exemplary embodiment, the contact member61is stainless steel (SUS) having a thickness of 0.12 mm and a shape of 25 mm by 7.00 mm. Contact states of the contact member61and the pressure roller32are illustrated inFIG.5B. The SUS as the contact member61is disposed on the outer surface (outer circumferential surface) of the pressure roller32so that the longer side of the contact member61is parallel to the rotational direction of the pressure roller32, and the contact member61comes into contact with the pressure roller32with a contact pressure of 0.245 to 0.343 N in the forward direction. As a grounding condition, the contact member61is grounded to the grounding portion via a 1-GΩ resistor65. This configuration is intended to prevent an offset due to charging, separating discharge, and a transfer current leakage.

FIG.6illustrates a comparative example. According to the comparative example, two different contact members are disposed in the region on the same one end side in the longitudinal direction.

FIG.7illustrates charts indicating longitudinal surface potentials of the fixing film36and the pressure roller32according to the present exemplary embodiment and the comparative example. The vertical axis denotes the surface potential, the horizontal axis denotes the longitudinal position of the fixing film36and the pressure roller32, a point A denotes the contact position of the contact member60, and a point B denotes the contact position of the contact member61. Referring toFIG.7, the plots denote the potentials at contact positions A and B, and the solid and broken lines denote approximate lines of these potentials.

The charts inFIG.7according to the present exemplary embodiment will be described below. The longitudinal surface potential of the fixing film36has a gradient formed between about −80 to −85 V in the vicinity of the contact member60and −170 to −175 V on the non-contact side where the contact member60is not disposed (plots ●). The longitudinal surface potential of the pressure roller32has a gradient formed between about 15 V in the vicinity of the contact member61and 110 V on the non-contact side where the contact member61is not disposed (plots ○). The potential difference between the fixing film36and the pressure roller32is about 190 V in the longitudinal direction. This means that variations of the potential difference between the fixing film36and the pressure roller32are restricted over the entire longitudinal region.

The charts inFIG.7according to the comparative example will be described below. The surface potential of the fixing film36has a gradient formed between about −80 to −85 V in the vicinity of the contact member60and −170 to −175 V on the non-contact side where the contact member60is not disposed (plots ▪). The longitudinal surface potential of the pressure roller32has a gradient formed between about 10 V in the vicinity of the contact member61and 115 V on the non-contact side where the contact member61is not disposed (plots □). Therefore, the potential difference between the fixing film36and the pressure roller32is about 95 V on the contact side (point A) where the contact members60and61are disposed, and about 285 V on the non-contact side (point B) where the contact members60and61are not disposed. This means that the potential difference between the fixing film36and the pressure roller32varies in the longitudinal region.

According to the comparative example, when the non-fixed toner image t is fixed to the recording material P in this state, image scattering occurs in the vicinity of the non-contact side (point B) in a case of forming a halftone image. This is because the potential difference on the non-contact side increases, and the surface potential of the fixing film36becomes higher than the surface potential of the pressure roller32for retaining the toner image t with the negative polarity on the recording material P to the recording material P. This generates a repulsive force against the toner image t on the recording material P as a cause of image scattering.

The present exemplary embodiment makes it possible to restrain variations of the potential difference between the fixing film36and the pressure roller32over the entire longitudinal region to a further extent than the comparative example. This also enables preventing the generation of image scattering due to the potential difference. The contact member60for grounding the fixing film36is disposed in the region R1on one end side in the longitudinal direction, and the contact member61for grounding the pressure roller32is disposed in the region R2on the other end side in the longitudinal direction. This enables equalizing the longitudinal inclinations of the gradient of the surface potential of the fixing film36from the contact portion to the non-contact portion and the gradient of the surface potential of the pressure roller32from the non-contact portion to the contact portion. This enables providing a uniform surface potential difference between the fixing film36and the pressure roller32.

The contact member60for grounding the fixing film36is disposed in the region R1on one end side in the longitudinal direction, and the contact member61for grounding the pressure roller32is disposed in the region R2on the other end side in the longitudinal direction. This enables restricting variations of the potential difference between the fixing film36and the pressure roller32in the longitudinal direction.

A second exemplary embodiment will be described below. The first exemplary embodiment has been described above centering on a configuration where the contact member60is brought into contact with the surface of the fixing film36. The second exemplary embodiment will be described below centering on a configuration where the contact member60is brought into contact with the inner circumferential surface of the fixing film36. Components of the image forming apparatus100similar to those according to the first exemplary embodiment are assigned the same reference numerals, and redundant descriptions of the similar components will be omitted.

FIG.8illustrates arrangements of a contact member600and the contact member61according to the present exemplary embodiment. Referring toFIG.8, like the first exemplary embodiment, the contact member600for grounding the fixing film36is disposed in the region R1in the longitudinal direction, and the contact member61for grounding the pressure roller32is disposed in the region R2in the longitudinal direction. The contact member600is disposed at the position by a distance L1from a conveyance center, and the contact member61is disposed at the position by a distance L2from the conveyance center. Although the contact members60and61are disposed so that the distances L1and L2are equal as an example, the present exemplary embodiment is not limited to this example. A contact member needs to be disposed in each of the region R1on one end side in the longitudinal direction and the region R2on the other end side in the longitudinal direction.

FIG.9is a partial enlarged view illustrating the contact member600, andFIG.10is a cross-sectional view illustrating the contact member600inFIG.9viewed from the direction of the arrow.

The contact member600is in contact with the fixing film36from the inner circumferential surface of the fixing film36. Like the first exemplary embodiment, the contact member600is a polyimide film containing distributed carbon and having a thickness of 60 μm, a height of 22 mm, and a width of 6.55 mm. The fixing film36is a cylindrical flexible member including a base layer36a,an elastic layer36bformed outside the base layer36a,and a mold release layer36cformed outside the elastic layer36b.The longitudinal surface resistance value of the base layer36ais set to 154.0 MΩ or less when 250 V is applied by using the Digital Megohm HiTester from HIOKI E.E. CORPORATION.

As a method for bringing the contact member600and the fixing film36into contact with each other, the polyimide film as the contact member600is disposed in the space inside the fixing film36so that the longer side of the contact member600is parallel to the rotational direction of the fixing film36, and the contact member600comes into contact with the fixing film36with a contact pressure of 0.0148 to 0.0235 N in the forward direction. This configuration is intended to prevent an electrostatic offset or banding that occurs when the AC voltage oscillation driving the heater37of the fixing apparatus18is superimposed on the DC voltage of the transfer nip portion across the recording material P.

Because the contact member600is in contact with the inner circumferential surface of the fixing film36, the contact member600does not need to be disposed in the region closer to one end side in the longitudinal direction than the paper feed region. This means that the contact member600may be disposed even in the paper feed region as long as it is disposed closer to the one end side in the longitudinal direction than the center reference. This is because the contact member600is in contact with the inner circumferential surface of the fixing film36. Even if a paper jam occurs in the fixing apparatus18or if toner adheres to the surface of the fixing film36because of an image offset, for example, the above-described configuration enables preventing the adhering toner from smearing the surface of the contact member600. Even if the contact member600is disposed in the paper feed region, the above-described configuration enables preventing defective contact and a damage to the fixing film36due to toner adhering to the contact member600.

FIG.11illustrates a comparative example. According to the comparative example, two different contact members are disposed in the region on the same one end side in the longitudinal direction.

FIG.12illustrates charts indicating longitudinal surface potentials on the fixing film36and the pressure roller32according to the present exemplary embodiment and the comparative example. The vertical axis denotes the surface potential, the horizontal axis denotes longitudinal position on the fixing film36and the pressure roller32, a point

A denotes the contact position of the contact member600, and a point B denotes the contact position of the contact member61. Referring toFIG.12, the plots denote the potentials at the contact positions A and B, and the solid and broken lines denote approximate lines of the potentials.

The charts inFIG.12according to the present exemplary embodiment will be described below. The longitudinal surface potential of the fixing film36has a gradient formed between about −50 to −55 V in the vicinity of the contact member600and −145 to −150 V on the non-contact side where the contact member600is not disposed (plots ●). The longitudinal surface potential of the pressure roller32has a gradient formed between about 15 V in the vicinity of the contact member61and 110 V on the non-contact side where the contact member61is not disposed (plots ○). The potential difference between the fixing film36and the pressure roller32is about 160 V in the longitudinal direction. This means that variations of the potential difference between the fixing film36and the pressure roller32are restricted over the entire longitudinal region.

The charts inFIG.12according to the comparative example will be described below. The surface potential of the fixing film36has a gradient formed between about −50 to −55 V in the vicinity of the contact member600and −145 to −150 V on the non-contact side where the contact member600is not disposed (plots ▪). The longitudinal surface potential of the pressure roller32has a gradient formed between about 10 V in the vicinity of the contact member61and 115 V on the non-contact side where the contact member61is not disposed (plots □). Accordingly, the potential difference between the fixing film36and the pressure roller32is about 65 V on the contact side (point A) where the contact members600and61are disposed, and about 265 V on the non-contact side (point B) where the contact members600and61are not disposed. This means that the potential difference between the fixing film36and the pressure roller32varies in the longitudinal region.

According to the comparative example, when the non-fixed toner image t is fixed to the recording material P in this state, image scattering occurs in the vicinity of the non-contact side (point B side) in a case of forming a halftone image.

This is because the potential difference on the non-contact side increases, and the surface potential of the fixing film36becomes higher than the surface potential of the pressure roller32that retains the toner image t with the negative polarity on the recording material P to the recording material P. This generates a repulsive force against the toner image t on the recording material P as a cause of image scattering.

The present exemplary embodiment makes it possible to restrain variations of the potential difference between the fixing film36and the pressure roller32over the entire longitudinal region to a further extent than the comparative example. This also enables preventing the generation of image scattering due to the potential difference. The contact member600for grounding the fixing film36is disposed in the region R1on one end side in the longitudinal direction, and the contact member61for grounding the pressure roller32is disposed in the region R2on the other end side in the longitudinal direction. This enables equalizing the longitudinal inclinations of the gradient of the surface potential of the fixing film36from the contact portion to the non-contact portion and the gradient of the surface potential of the pressure roller32from the non-contact portion to the contact portion. This enables providing a uniform surface potential difference between the fixing film36and the pressure roller32.

The contact member600for grounding the fixing film36is disposed in the region R1on one end side in the longitudinal direction, and the contact member61for grounding the pressure roller32is disposed in the region R2on the other end side in the longitudinal direction. This enables restricting variations of the potential difference between the fixing film36and the pressure roller32in the longitudinal direction.

This application claims the benefit of Japanese Patent Application No. 2023-012440, filed Jan. 31, 2023, which is hereby incorporated by reference herein in its entirety.