JP2009053507A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control fixing operation so that image quality may be stably kept excellent even in long-term use depending on prolongation of a life. <P>SOLUTION: The fixing device includes a heating heater base 31, a heater holder 32 holding the heating heater base 31, a fixing film 40 sliding on the heating heater base 31 and having a conductive inner surface, and a pressure roller 20 pressured against the heating heater base 31 through the fixing film 40 and forming a fixing nip part F, and thermally fixes recording material carrying a toner image by the fixing nip part F. The heater holder 32 has a contact surface for regulating the rotational locus of the fixing film 40. The fixing device has a conduction member 50 to the fixing film 40 on the contact surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device in an image forming apparatus that employs an image forming process such as an electrophotographic system or an electrostatic recording system. In particular, the image forming process section heat-fixes the unfixed toner image of the image information formed and supported on a recording material (transfer material, printing paper, photosensitive paper, electrostatic recording paper, etc.) by a transfer method or a direct method as a fixed image. The present invention relates to a fixing device.

  Conventionally, a so-called heat roller type fixing device has been widely used as a fixing device provided in an image forming apparatus employing an electrophotographic method, an electrostatic recording method, or the like. Recently, film heating type fixing devices have been widely used. The film heating type fixing device has many advantages over the conventional heat roller type fixing device due to its high heating efficiency and rising speed.

  As a film heating type fixing, there is a method in which a conducting member is brought into contact with the inner surface of the fixing film to be grounded to GND (see, for example, Patent Document 1). This conducting member is a member in which a contact member such as a carbon chip is disposed at the tip of a plate spring such as SUS having elasticity, and this is brought into contact with the inner surface of the film and grounded to the GND, whereby the surface potential of the film is increased. I have control.

JP 2005-166299 A

  However, when the heating device of this power feeding method is used at higher speed and longer life, the inner surface of the fixing film slides with the heater and is scraped. As a result, the inner surface of the film becomes rough, the conductive member and the inner surface of the film are scraped off, and the rotation trajectory of the film becomes unstable. Due to these causes, the contact state between the conductive member and the inner surface of the film becomes unstable. Thereby, there is a possibility that the surface potential of the fixing film cannot be sufficiently controlled. Further, when the conductive member and the inner surface of the film are in poor contact, noise is likely to occur. Then, this noise reaches the main body control system of the image forming apparatus. This may cause a problem such as malfunction or stop of the image forming apparatus.

  For this reason, in a heating device using a fixing film composed of a conductive base layer that has a high speed and a long life, a stable contact state between the inner surface of the fixing film and the conductive member is maintained, and the surface potential of the fixing film is stabilized. It was desired to be controlled.

  An object of the present invention is to control the fixing operation so that the image quality is stably and satisfactorily maintained even in a long-term use due to a long life.

A typical configuration according to the present invention for achieving the above object is as follows:
A heating body, a heating body holding member that holds the heating body, an endless belt that slides on the heating body and has an inner surface that is electrically conductive, and is pressurized against the heating body via the endless belt And a pressure member that forms a fixing nip portion.
In a fixing device that heats and fixes a recording material carrying a toner image at the fixing nip portion,
The heating body holding member has a contact surface for regulating the rotation trajectory of the endless belt,
The contact surface has an electrical contact with the endless belt.

  Since the present invention has the above-described configuration, it is possible to control the fixing operation so that the image quality is stably and satisfactorily maintained even in the long-term use due to the long life.

[First Embodiment]
The first embodiment according to the present invention will be described below.

(Image forming device)
First, an image forming apparatus having a fixing device will be described. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to the first embodiment. As shown in FIG. 1, the image forming apparatus includes a sheet feeding device including a feeding tray 81, a sheet stacking table 82, and a feeding roller 83.

  In the sheet feeding apparatus, the recording material P stacked on the sheet stacking table 82 in the feeding tray 81 is picked up one by one from the uppermost recording material by the feeding roller 83. Thereafter, the recording material P is conveyed by a conveying roller 84 and a conveying roller 85 to a registration portion including a registration roller 86 and a registration roller 87, and the conveying direction is aligned. Thereafter, the sheet is fed to the image forming unit.

  The image forming unit includes a photosensitive drum 88 as an image carrier, a charger for charging the photosensitive drum, a developing unit for developing the electrostatic latent image on the photosensitive drum with toner, and residual toner on the photosensitive drum. It has process means such as a cleaner for removing and storing. These process means are configured as a unit as a toner cartridge 89.

  The laser scanner unit 90 is constituted by unitizing a polyhedral mirror 91, a polyhedral mirror rotating motor, a laser unit, and the like.

  Laser light L based on image information is emitted from the laser scanner unit 90. Then, an electrostatic latent image based on the image information is formed on the photosensitive drum 88 by electrophotography. This electrostatic latent image is developed with toner as a developer by a developing means. The developed toner image is transferred onto the recording material P conveyed from the photosensitive drum 88 by the transfer roller 92.

  After the transfer of the toner image, the recording material P is conveyed to a fixing device including a heating member 30, a fixing film (endless belt) 40, and a pressure roller 20. In the fixing device, the transferred toner image is heated and fixed.

  Thereafter, the recording material P is discharged onto a discharge tray 95 by a discharge unit including an intermediate discharge roller 93, a discharge roller 94, and the like.

  Further, a cooling fan 96 is attached to the side surface of the main body of the image forming apparatus for cooling a temperature rising portion such as an image forming unit in the apparatus or an electrical board. Thus, the outside air is taken into the machine by appropriately rotating the fan, and the machine is cooled. Further, in the vicinity of the cooling fan 96, temperature detecting means 97 such as a thermistor is attached. As a result, when air outside the apparatus is taken in by the cooling fan 96, the temperature of the environment in which the image forming apparatus is installed is detected and fed back to the temperature control sequence of the fixing device based on the detection result.

(Fixing device)
Next, a configuration of a fixing device that heats and fixes an unfixed toner image on a recording material as a permanent image on the recording material will be described. 2A and 2B are schematic sectional views of the fixing device. FIG. 2A is an overall schematic sectional view of the fixing device, and FIG. 2B is an enlarged sectional view of the fixing film.

  The fixing device in this embodiment is a film heating type fixing device using a fixing film 40 in which an elastic layer is formed on a cylindrical thin metal base layer. FIG. 2A relates to the first embodiment. A schematic sectional view is shown.

  As described above, the recording material P is developed and transferred by the image forming unit composed of the photosensitive drum, the transfer roller, and the like, and then is sent to the heating and fixing unit. Guided to the fixing nip F formed by the pressure roller 20. Heat fixing is performed at the fixing nip portion F, and the paper is conveyed to the discharge unit described above.

  The fixing device includes a cylindrical fixing film 40 and a pressure roller 20 as a pressure member. In addition, a heater (heating body) 31 constituting the heating member 30, a metal U-shaped synthetic pressure stay 35 having a downward cross section, and a heat-resistant and rigid heater holder having a substantially semicircular arc-shaped cross section. (Heating body holding member) 32 is provided.

(Fixing film 40)
As shown in FIG. 2B, the fixing film 40 includes a release layer 41, an elastic layer 42, and a base layer 43. The inner surface of the fixing film 40 that slides on the heater base 31 is conductive.

  The base layer 43 is made conductive by mixing a conductive filler such as carbon with a heat-resistant resin such as polyimide, polyamideimide, PEEK, etc. to form a thin-walled flexible endless belt. Here, it is preferable to use a thin metal such as SUS or Ni having higher thermal conductivity as the base layer.

  The elastic layer 42 is formed on the base layer 43 with silicone rubber or the like. Due to the presence of the elastic layer 42, heat can be uniformly applied by enclosing the toner on the recording material. For this reason, it is necessary for suppressing the roughness in a halftone image and obtaining uniform and sufficient fixing properties. As the thickness of the elastic layer 42 increases, the toner on the recording material can be wrapped and fixed uniformly (wrapping effect). However, if it is too thick, the heat capacity becomes too large and the rise of the fixing film 40 is delayed, and the on-demand characteristic peculiar to the film heating method is lowered. Therefore, the thickness of the elastic layer 42 is 30 μm or more and 500 μm or less, preferably 100 μm or more and 300 μm or less. The higher the thermal conductivity of the elastic layer 42, the better. It is preferably 0.2 W / m · K or more, particularly preferably 0.8 W / m · K or more. It is preferable to adjust the thermal conductivity filler such as ZnO and AlN mixed in the silicone rubber so as to achieve such thermal conductivity.

  The release layer 41 is configured on the elastic layer. The release layer 41 is formed of a fluorine resin such as purple alloalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP). The release layer 41 may be a tube coated or a surface coated with a paint. The release layer 41 is more durable when it is covered with a tube.

  In the fixing film 40, the outer diameter of the fixing film 40 is preferably smaller because the heat capacity can be suppressed. However, if the outer diameter is made too small, the fixing nip portion F becomes thin, so it cannot be made extremely small. Regarding the thickness of the elastic layer 42, as described above, if it is too thin, the enveloping effect is reduced, and if it is too thick, the heat capacity increases and the rise is delayed, so an appropriate thickness is required.

  Therefore, the fixing film 40 in the present embodiment has a heat capacity reduced to improve quick start properties, and the thickness of the substrate 43 such as polyimide or SUS is 100 μm or less, preferably 70 μm so as to satisfy the mechanical strength. Below, it is 20 μm or more. And the internal diameter of the base material 43 shall be 16-30 mm.

  The thickness of the elastic layer 42 is preferably 30 to 500 μm, preferably 50 to 300 μm, considering the wrapping effect. As the release layer 41, it is preferable to form a fluororesin layer with a thickness of about 1 μm to 50 μm.

(Pressure roller 20)
As shown in FIG. 2A, the pressure roller 20 is configured by stacking a core shaft portion 23, an elastic layer 22, and a release layer 21 from the inner surface side.

  The core shaft portion 23 is made of aluminum or iron. Alternatively, a ceramic porous body having high strength, low heat capacity, and high heat insulating effect may be used for the core shaft portion 23.

  The elastic layer 22 is formed outside the core shaft portion 23.

  Examples of the elastic layer 22 include an elastic layer 22 (solid rubber layer) made of silicone rubber. In order to have a heat insulating effect, an elastic layer 22 (sponge layer) formed by foaming silicone rubber may be used. Further, a hollow filler may be formed in the silicone rubber layer in order to have a more heat insulating effect. Furthermore, it is good also as the elastic layer 22 (bubble rubber layer) which has the porous formed by adding a water absorbing polymer and water.

  Here, when the heat capacity of the pressure roller 20 is large and the thermal conductivity is as large as possible, heat is easily absorbed from the surface of the fixing film. As a result, the surface temperature of the fixing film is hardly increased. For this reason, a material having a low heat capacity, a low thermal conductivity and a high heat insulating effect is more advantageous for the rise time of the fixing film surface temperature.

  However, when used in a color image forming apparatus or a high-speed machine, the supply of heat from the pressure roller 20 is necessary to improve gloss and fixability. For this reason, it is preferable that the heat capacity and heat conductivity of the pressure roller 20 be high to some extent, and it is necessary to determine the heat capacity and heat conductivity of the pressure roller 20 in consideration of the speed of the image forming apparatus used.

  Here, the solid rubber of the silicone rubber has a thermal conductivity of 0.25 to 0.29 W / m · K, and the sponge rubber and bubble rubber have 0.11 to 0.16 W / m / K. Rubber shows about half the value of solid rubber. The specific gravity related to the heat capacity is 1.05 to 1.30 for solid rubber and about 0.75 to 0.85 for sponge rubber and bubble rubber.

  In this embodiment, in order to use the image forming apparatus at a high speed, it is necessary to form an appropriate width of the fixing nip F and to secure a certain heat capacity. Therefore, the elastic layer 22 was formed using solid rubber having a thickness of 3 mm, and the pressure roller 20 having an outer diameter of 30 mm was used.

  The release layer 21 is formed on the elastic layer 22. The release layer 21 is made of a fluororesin such as purple alloalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP), or the like. The release layer 21 may be a tube coated or a surface coated with a paint, but a tube is preferable because of its excellent durability.

(Heating member 30)
The heating member 30 used in the present embodiment is a plate-like heating element that rapidly heats while sliding on the inner surface of the fixing film 40. The heating member 30 includes a heater substrate 31, a heater holder 32, a temperature detection element 33, a temperature detection means 34, and a synthetic pressure stay 35.

The heater base 31 is formed of an insulating ceramic substrate such as alumina or aluminum nitride, or a heat resistant resin substrate such as polyimide, PPS, or liquid crystal polymer. Along the longitudinal direction on the surface, for example, a conductive or heat-resistant resistance layer such as Ag / Pd (silver palladium), RuO ₂ , Ta ₂ N is formed into a linear or thin strip having a thickness of about 10 μm and a width of about 1 to 5 mm by screen printing. It is formed by coating. A protective sliding layer may be provided on the pressure roller side (surface side) of the heater base 31 so as to protect the energization heat generating resistance layer of the heater base within a range that does not impair the thermal efficiency. However, it is preferable that the thickness of the protective sliding layer is sufficiently thin and the surface property is improved.

  Examples thereof include perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP), and ethylenetetrafluoroethylene resin (ETFE). In addition, there are some which coat a single or mixed fluororesin layer such as polychlorotrifluoroethylene resin (CTEF), polyvinylidene fluoride (PVDF) and the like. Further, a dry sliding lubricant made of graphite, diamond-like carbon (DLC), molybdenum disulfide, or the like, or a protective sliding layer such as a glass coat can be considered. When using aluminum nitride or the like having good thermal conductivity as the heater base 31, the energization heating resistance layer is formed on the opposite side (back side) to the pressure roller 20 with respect to the heater base 31. There may be.

  The heater holder 32 holds the heater base 31. It is formed of a heat resistant resin such as liquid crystal polymer, phenol resin, PPS, PEEK, and the lower the thermal conductivity, the higher the thermal efficiency when heating the inner surface of the fixing film. Therefore, a hollow filler such as a glass balloon or a silica balloon may be included in the resin layer.

  The shape of the heater holder 32 will be described with reference to FIG. FIG. 3 is an enlarged cross-sectional view of the heating member.

  As shown in FIG. 3, the heater holder 32 is provided with an upstream jaw 321 and a downstream jaw 322 (protruding shape portion) on the upstream and downstream sides of the heater base 31, respectively. The upstream jaw 321 and the downstream jaw 322 protrude so as to sandwich the heater base 31 on the upstream and downstream sides of the heater base 31 in the recording material conveyance direction. The upper and lower jaws 321 and 322 protrude from the surface of the heater base 31 being held toward the pressure roller 20 while contacting the rotation locus of the fixing film 40 upstream and downstream of the fixing nip F. regulate. Here, the surface of the heater holder 32 that contacts the fixing film 40 is referred to as a contact surface.

  In this manner, the inner surfaces of the fixing film are prevented from being scraped by the edge of the heater base 31 by forming the jaws 321 and 322 having a shape protruding in the upstream and downstream of the fixing nip portion F in the sheet conveying direction. Further, the sliding grease applied to the surface of the heater base 31 is maintained in the fixing nip portion F on the inner surface of the fixing film 40. Thus, the presence of the upper and lower jaws 321 and 322 prevents the grease from circulating.

  The temperature detector 34 is a thermistor or the like for detecting the heater heater back surface temperature, and is disposed on the heater heater 31 back surface. The temperature detection means 34 makes the back surface temperature of the heater base 31 detected by the temperature detection element 33 constant by an energization control circuit (not shown). Specifically, the duty ratio and wave number of the voltage applied to the energization heating resistor layer of the heater base 31 are appropriately controlled. Further, the temperature detecting means 34 is not limited to the back surface of the heater base 31 but may be elastically brought into contact with the inner surface of the film, such as with a leaf spring such as SUS.

  The temperature detection element 33 is a thermo switch, a temperature fuse, or the like disposed on the back surface of the heater base 31. The temperature detecting means 34 such as a thermo protector is connected in series with the energization heating resistor layer by an energization circuit (not shown). As a result, when the heater base becomes in a runaway state due to a failure of the temperature detection element 33 or the like, the temperature detection means 34 detects an abnormal temperature rise of the heater base 31 and shuts down the energization to the energization heating resistor layer. It is a configuration.

  The synthetic pressurizing stay 35 is inserted into the heater holder 32 and has a U-shaped shape with a metal cross section downward.

  From the above members, the film unit is configured by loosely fitting the fixing film 40 to the heater holder 32. This film unit is arranged in parallel to the pressure roller 20 so that the heater surface faces the pressure roller 20 side. Then, both end portions of the combined pressure stay 35 are urged in the axial direction of the pressure roller 20 by pressure means (not shown).

  As a result, the surface of the heater base 31 is brought into pressure contact with the pressure roller 20 via the fixing film 40, and the fixing nip having a predetermined width required for heat fixing between the fixing film 40 and the pressure roller 20 by the applied pressure. Part F is formed.

  The core shaft portion 23 of the pressure roller 20 is rotatably held by bearings or the like (not shown) at both ends in the longitudinal direction. A driving gear is disposed at the tip of the core shaft at one end in the longitudinal direction of the pressure roller 20. With this configuration, driving from a drive transmission mechanism (not shown) rotationally drives the pressure roller 20. Then, the fixing film 40 in pressure contact with the pressure roller 20 is rotated by the heating member 30 following the pressure roller 20.

  As described above, the recording material P is introduced into the fixing nip portion F formed between the fixing film 40 and the pressure roller 20 in a state where the fixing film 40 is heated by the heating member 30 as a heating source. An unfixed toner image is formed on the recording material P, and the unfixed toner image is fixed to the recording material P by the pressure and heat applied in the fixing nip F.

(Conductive member 50)
The position of the conductive member 50 as an electrical contact will be described. FIG. 4 is an explanatory diagram of the heating member 30 in the first embodiment.

  As shown in FIG. 4, the conducting member 50 is disposed at the center in the longitudinal direction of the upstream jaw 321 of the heater holder 32 corresponding to the center reference in the conveyance direction of the recording material P. The conducting member 50 has a SUS plate and a contact member. The synthetic pressure stay 35 is electrically connected and fixed.

  The jaws 321 and 322 of the heater holder 32 are shaped to contact and regulate the rotation locus of the fixing film 40. For this reason, the conductive member 50 disposed on the upstream jaw 321 of the heater holder 32 always rubs stably against the inner surface of the fixing film. As a result, the fixing film 40 is electrically connected to the metal stay 35.

  The combined pressure stay 35 is connected to a high voltage power source that applies a negative bias having the same polarity as the toner. For this reason, the surface potential of the fixing film 40 is controlled to be negative. Since the surface of the fixing film 40 is negatively charged, the toner on the recording material P before fixing that enters the fixing device is electrostatically prevented from transferring to the fixing film 40. For this reason, it is possible to prevent the toner from being offset to the fixing film 40, and it is possible to prevent the occurrence of gloss unevenness and image defects.

  The synthetic pressure stay 35 is grounded through a diode, and the inner surface of the fixing film 40 is electrically grounded. As a result, the film surface can be prevented from being charged, and the toner image on the recording material P before fixing can be prevented from having an electrostatic influence. Note that at a high fixing speed, a more stable image can be obtained by controlling the surface of the fixing film 40 to the same polarity as the toner.

  Thus, in the present embodiment, the conduction member 50 that applies a bias to the inner surface of the film is disposed on the upstream jaw 321 of the heater holder 32. The heater holder 32 forcibly regulates the rotation locus of the fixing film 40 by contacting the fixing film 40. For this reason, the conducting member 50 disposed in the heater holder 32 comes into stable contact with the rotating film 40. Further, by suppressing the contact failure between the conductive member 50 and the inner surface of the film, no adverse effect on the main body control system due to the contact failure is generated.

  In addition, as described above, even in the metal fixing film 40 that has the rubber layer (elastic layer) 42 on the surface and hardly conducts from the surface side, according to the configuration of the conducting member 50 of this embodiment, conduction is ensured. Can be taken. Further, by using the metal synthetic pressure stay 35 as a part of the electric circuit, no new wiring is required. For this reason, the diameter of the fixing film 40 can be reduced.

〔Example〕
In order to confirm the above, an example in the fixing device of this embodiment will be described. FIG. 5 is a chart showing results of examples according to the first embodiment. FIG. 7 is a diagram for explaining the structure of a comparative example (conventional example) in comparison with the example.

  In this embodiment, continuous image formation of 400,000 sheets is performed, and the fixed image at that time has a defect such as a tail, an image defect such as an offset, an adverse effect on the main body signal system due to an electric contact defect, etc. Confirmed no. FIG. 5 shows the result of adverse effects on the image level and the main body signal system.

In this example, the test environment is a normal temperature and humidity environment of 23 ° C. and 50% RH. The recording material used was XEROX 4024 (LTR size, basis weight 75 g / m ² ) as plain paper, and 400,000 sheets were continuously fed.

  In FIG. 5, the meanings of the symbols are as follows. As an image level, ○: Good with no image defect. Δ: Image is defective, but practically acceptable. ×: Image is defective and impractical. These are shown in three stages.

  Moreover, as an adverse effect on the main body signal system, there is no: no adverse effect on the main body signal system. Yes: The main unit signal system was adversely affected and the main unit malfunctioned. These are shown in two stages.

  As shown in FIG. 5, in this embodiment, there was no image defect from the initial stage until the 200,000th sheet, which was good. Some tailing and offset occurred from around 300,000 sheets, but the image level was acceptable up to 400,000 continuous sheets. On the other hand, in the comparative example, the image level was good from the initial stage up to 50,000 sheets, but some tailing and offset occurred on the 100,000th sheet, and many image defects occurred on the 300,000th sheet. It became impossible to use.

  One possible cause of image failure is that the contact state between the conductive member 50 and the inner surface of the fixing film is unstable. Another cause is deterioration of the film. This is because as the durability progresses, the release layer 41 on the surface of the fixing film 40 is scraped by friction with the recording material, the pressure roller 20, etc., and the surface property deteriorates, so that the release property deteriorates. This is because an image defect such as an offset occurs.

  Further, regarding the adverse effects on the main body signal system, in this embodiment, no problem occurred through 400,000 continuous sheets. On the other hand, in the comparative example, the problem that the image forming apparatus malfunctioned from about 300,000 sheets began to occur.

  These results will be described in detail with reference to FIGS.

  First, as shown in FIG. 7, the conductive member 50 of the comparative example has a carbon chip disposed as a contact member 52 at the tip of an elastic SUS plate 51. The conducting member 50 is slid elastically on the inner surface of the film.

  In the initial stage of paper passing, the inner surface of the film 40 was not scraped, and the film itself rotated stably. Therefore, the contact member 52 can stably come into contact with the inner surface of the film, and the occurrence of tailing and offset can be suppressed by stabilizing the film surface potential. However, as the continuous paper feed proceeds, the inner surface of the film is damaged or the rotation of the film becomes unstable. For this reason, the contact state between the conducting member and the film inner surface becomes unstable. As a result, the film surface potential could not be controlled, and tailing and offset occurred. Further, when the conductive member 50 and the film inner surface are in poor contact, noise is likely to occur. Then, when this noise reaches the main body control system of the image forming apparatus, problems such as malfunction or stop of the image forming apparatus have occurred.

  On the other hand, in the example of this embodiment, the conductive member 50 that applies a bias to the inner surface of the film 40 on the upstream jaw 321 of the heater holder 32 that forcibly regulates the rotation locus of the film 40 by contact. Is arranged. For this reason, even if 400,000 sheets of continuous paper are passed, the inner surface of the film 40 is scraped and the rotation of the film 40 becomes unstable. You are in contact. Therefore, the conducting member 50 can be stably brought into contact with the inner surface of the film 40, and the surface potential of the film 40 can be controlled. Therefore, even if 400,000 continuous sheets were passed, the tailing and offset levels were within the allowable range. In addition, there was no adverse effect on the main body control system due to poor contact between the conductive member 50 and the inner surface of the film.

  As described above, in the present embodiment, the conductive member 50 that applies a bias to the inner surface of the film 40 whose inner surface is conductive is disposed on the upstream jaw 321 of the heater holder 32 that regulates the rotation trajectory of the film 40. To do.

  For this reason, even if the rotation of the film becomes unstable due to long-term durability or the inner surface of the film is scraped and roughened, the inner surface of the film 40 always has the upstream jaw 321 in which the conductive member 50 is disposed. In contact with. For this reason, the conducting member 50 can be stably brought into contact with the inner surface of the film 40, and the surface potential of the film 40 can be stably controlled. Accordingly, it is possible to prevent deterioration in image quality due to offset, tailing, and pressure roller contamination of a fixed image until a long lifetime is reached.

  Further, stable contact between the conductive member 50 and the inner surface of the film 40 is maintained. For this reason, noise due to poor contact does not occur, and adverse effects such as malfunctions to the main body control system due to this noise do not occur.

[Second Embodiment]
A second embodiment will be described with reference to FIG. FIG. 6 is an explanatory diagram of the heating member 30 according to the second embodiment.

  When the fixing device of the first embodiment is used in a monochrome image forming apparatus or a low-speed color image forming apparatus, a good image can be obtained without any problem. However, when used in a higher-speed color image forming apparatus, a slight temperature difference on the surface of the fixing film 40 may cause the fixing to be uneven and may cause uneven gloss.

  In the first embodiment, the conductive member 50 of the upstream jaw 321 of the heater holder is disposed within the image printing range. Here, since the thermal conductivity and heat capacity of the conductive member 50 and the surrounding heater holder 32 are different, unevenness occurs in the surface temperature of the fixing film, and the trace of the conductive member 50 appears as gloss unevenness in the image on the recording material. There is a possibility that.

  In the fixing device of the present embodiment, the image forming apparatus used is an A4 machine. For this reason, the maximum width in which paper can be passed (recording material conveyance) is the LTR size. Considering this, the conductive member 50 is disposed in a non-sheet passing region inside the both ends of the fixing film 40 and outside the LTR size in the longitudinal direction of the upstream jaw 321 of the heater holder.

  As shown in FIG. 6, in the present embodiment, in the longitudinal direction of the heater base 31, the conduction member 50 is formed on the contact surface of the heater holder 32 outside the image forming region and inside the end portion of the fixing film 40. Arranged. As a result, even if the fixing device of this embodiment is used in a high-speed color image forming apparatus sensitive to heat distribution, a good fixed image can be obtained without causing image defects such as uneven gloss.

[Other Embodiments]
In the above-described embodiment, only one conductive member 50 is disposed on one side of the upstream jaw 321 of the heater holder 32. However, the present invention is not limited to this. For example, by disposing another conductive member 50 on the opposite side, it is possible to further stabilize the contact between the conductive member 50 and the inner surface of the fixing film.

  Moreover, although the dimension was specifically illustrated in the above-mentioned embodiment, it is not restricted to this.

1 is a schematic sectional view of an image forming apparatus according to a first embodiment. 1 is a schematic cross-sectional view of a fixing device according to a first embodiment. The expanded sectional view of the heating member concerning a 1st embodiment. Explanatory drawing of the heating member which concerns on 1st Embodiment. The graph which shows the result of the Example which concerns on 1st Embodiment. Explanatory drawing of the heating member which concerns on 2nd Embodiment. The figure explaining the structure of the comparative example (conventional example) for contrast with an Example.

Explanation of symbols

F: Fixing nip portion, L: Laser light, P: Recording material, 20 ... Pressure roller, 21 ... Release layer, 22 ... Elastic layer, 23 ... Core shaft portion, 30 ... Heating member, 31 ... Heater heater base, 32 ... Heater holder, 33 ... Temperature sensing element, 34 ... Temperature sensing means, 35 ... Synthetic pressure stay, 40 ... Fixing film, 41 ... Release layer, 42 ... Elastic layer, 43 ... Base layer, 50 ... Conducting member, 81 ... Feeding tray, 82 ... Sheet stacker, 83 ... Feeding roller, 84 ... Conveying roller, 85 ... Conveying roller, 86 ... Registration roller, 87 ... Registration roller, 88 ... Photoconductor drum, 89 ... Toner cartridge, 90 ... Laser scanner unit, 91 ... polyhedral mirror, 92 ... transfer roller, 93 ... intermediate discharge roller, 94 ... discharge roller, 95 ... discharge tray, 96 ... cooling fan, 97 ... temperature detection means, 321 ... upstream jaw, 322 ... downstream jaw

Claims (3)

A heating body, a heating body holding member that holds the heating body, an endless belt that slides on the heating body and has an inner surface that is electrically conductive, and is pressurized against the heating body via the endless belt A fixing member that heats and fixes a recording material carrying a toner image at the fixing nip portion.
The heating body holding member has a contact surface for regulating the rotation trajectory of the endless belt,
A fixing device having an electrical contact with the endless belt on the contact surface. The contact surface of the heating body holding member has a protruding shape portion that protrudes and sandwiches the heating body in the recording material conveyance direction upstream and downstream,
The fixing device according to claim 1, wherein the electrical contact is disposed in the protruding shape portion.   The electrical contact is disposed on the contact surface outside the image forming region and inside the end of the endless belt in the longitudinal direction of the heating body holding member. The fixing device according to claim 2.

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