JP2005062603A - Fixing device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem that in an electro-photographic image forming device provided with a heating device in which a conductive path is constituted so that an electric current is made to flow through a recording material P from a fixing film 4 when a bias is applied to the fixing film, for preventing a tailing phenomenon of an image, since the resistance of the recording material is high when the recording material P is dry and the current is small, and a large current will flow if it absorbs moisture and the resistance becomes low, on the other hand, the larger the current value is, the worse an offset caused by the bias to the fixing film becomes, the tailing phenomenon becomes worse if a large current is prevented from flowing by lowering the bias value to prevent such an offset, . <P>SOLUTION: The current value is so controlled as to prevent too much current from flowing by putting a current limiter 1 circuit in the electric conductive path. Thus, in the recording material P with resistance lowered by moisture absorption or the like, a critical offset is prevented from occurring by inhibiting an unnecessarily large current from flowing while securing a minimum current value indispensable for preventing the tailing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device for fixing an unfixed toner image on a recording material, and an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile machine using the fixing device.

  2. Description of the Related Art Conventionally, fixing devices are used for fixing toner images formed on recording materials in image forming apparatuses such as electrophotographic copying machines, printers, and facsimiles.

  FIG. 10 is a schematic configuration diagram showing main components (near the electrophotographic process unit) of an image forming apparatus using an electrophotographic process. Hereinafter, the electrophotographic process will be briefly described with reference to FIG.

  The photosensitive drum 11 rotates in the direction of the arrow in the figure, and its surface is uniformly charged by applying a bias generated by the power supply 70 to the charging roller 12. The laser emitted and deflected by the laser exposure device 13 is irradiated onto the photosensitive drum 11 via the reflection mirror 14 to form an invisible electrostatic latent image.

  The toner container 15 is filled with toner T as a developer, and an appropriate amount of the toner is extracted by the rotation of the developing roller 16 and is appropriately charged by the developing blade 17.

  The charged toner receives an electrostatic force and adheres to the electrostatic latent image on the photosensitive drum 11 to form a visible toner image. The toner image is electrostatically transferred onto the recording material P by applying an optimum bias having a polarity opposite to that of the charged toner to the transfer roller 18 by the power source 70 ′.

  The untransferred toner remaining on the photosensitive drum 11 without being transferred is accommodated in the waste toner container 20 by the cleaning blade 19, and the photosensitive drum 11 whose surface has been cleaned repeatedly enters the next image forming process.

  Further, the recording material P on which the toner image is formed is heated and pressurized by the fixing device 2, and the toner image is fixed semi-permanently on the recording material.

  When fixing the toner image, the fixing nip reaches a temperature of less than 200 ° C. at the time of fixing, and the moisture contained in the recording material constantly evaporates and the vapor is generated during the sheet passing. For this reason, a phenomenon may occur in which a part of the toner image is blown away from the fixing nip to the upstream side in the conveyance direction due to the generation of water vapor in the vicinity of the heating body. The toner blown off by the steam is shifted by about 0.1 to 1 mm on the upstream side in the transport direction, and the image appears to have a tail, which causes a whisker-like image defect called tailing. This phenomenon is particularly noticeable in horizontal line images.

  In order to prevent this tailing, for example, as described in Patent Document 1 below, the fixing roller side is grounded, and a voltage is applied to the electrode in contact with the recording material P, so that the recording material is placed between the fixing roller and the electrode. A method has been devised in which a current is passed through.

  Further, in Patent Document 2 below, in a fixing device using a film heating method, a voltage is applied to the fixing film, and an electrode contacting the back surface of the recording material is grounded, and a current is supplied from the fixing film using the recording material as a conduction path. A flow method has also been proposed.

  FIG. 11 is a schematic configuration diagram showing an example of such a film heating type fixing device.

  In the fixing device 2, reference numeral 6 denotes a heat-resistant film guide member having a substantially semicircular cross section, and 5 denotes a flat ceramic heater (heating) having a low heat capacity disposed along the longitudinal center of the lower surface of the film guide member 6. Body) 4 is a heat-resistant resin cylindrical (endless) thin film (fixing film) loosely fitted to the film guide member 6 to which the ceramic heater 5 is attached, and 3 is the film guide member 6. The pressure roller is arranged on the lower side and is always pushed up and biased by pressure means such as a push-up spring and presses against the ceramic heater 5 with the film 4 interposed therebetween. That is, the ceramic heater 5 and the pressure roller 3 are pressed against each other with the film 4 interposed therebetween to form a fixing nip portion N.

  A voltage of −600 V is applied to the fixing film 4 from a high voltage power source 7 via a brush or the like.

  The paper discharge roller pair 8 is electrically conductive and is directly grounded from the core of the paper discharge roller.

  The ceramic heater 5 is energized by an energization system (not shown) to generate heat, and is controlled to a predetermined fixing temperature by a temperature control system (not shown).

  The pressure roller 3 is rotationally driven at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow by a drive unit (not shown). The cylindrical film 4 is brought into close contact with the lower surface of the ceramic heater 5 at the fixing nip portion N by the rotational friction force by the rotational driving of the pressure roller 3, and the outer circumference of the film guide member 6 is indicated by an arrow while sliding on the heater surface. It is rotationally driven at a predetermined peripheral speed in the clockwise direction.

  The recording material P which has received the image transfer and is conveyed to the fixing device 2 is guided by the inlet side guide 23, and the temperature-controlled ceramic heater 5 and the cylindrical nip portion of the fixing nip portion N of the rotary pressure roller 3 are driven to rotate. The film enters between the film 4 and the pressure roller 3, is in close contact with the lower surface of the ceramic heater 5 through the film 4, and passes through the fixing nip N while being overlapped with the film 4.

  In the process of passing through the fixing nip N, the unfixed toner image on the recording material P is heated by receiving the heat of the ceramic heater 5 through the film 4 and the image is heated and fixed.

  The recording material P that has passed through the fixing nip N is separated from the surface of the rotating film 4 and is output to the outside of the apparatus via the paper discharge guide 24 and the paper discharge roller 8.

  At this time, when the recording material P comes into contact with the paper discharge roller 8, a current conduction path from the fixing film 4 through the recording material P to the paper discharge roller 8 and then to the ground is formed. Current flows. Then, a force that strongly holds the toner on the recording material P acts between the fixing film 4 and the recording material P, and the toner can be prevented from being blown off by water vapor.

Further, in this configuration, since the current flows only when the recording material straddles the contact member and the fixing nip and does not flow when the recording material does not straddle, the surface release layer is deteriorated by applying a voltage to the fixing film. Can be reduced.
JP-A-8-272245 JP-A-11-202657

  In the above conventional fixing device, since the recording material is used as a current conduction path, the value of the flowing current varies greatly depending on the resistance value of the recording material. For example, when the moisture content of a recording material such as paper is high in a high humidity environment, the resistance value of the recording material is low, so that the current value increases accordingly, and if the resistance value of the recording material is high in a low humidity environment, it is almost Current stops flowing.

  By the way, the tailing phenomenon in which the toner is blown away by water vapor becomes more conspicuous as the paper contains more water, and conversely, if the paper is dried, there is no generation of water vapor, so that it is hardly noticeable. On the other hand, in the configuration in which the recording material as described above is used as the current conduction path, the force for pressing the toner onto the recording material increases as the current value flowing through the conduction path increases. Become.

  Therefore, the change in the current value due to the resistance of the recording material as described above has an ideal effect on the relationship between the moisture content of the paper and the current value. That is, when the amount of moisture in the paper is large, a large amount of current flows and the effect of preventing tailing is enhanced. Conversely, when the amount of moisture in the paper is small, the amount of current is small, but since the occurrence of tailing is slight, Don't be.

  However, the resistance value of the recording material is not determined only by the moisture content of the recording material, but also depends on the material of the recording material. In addition, if too much current flows, there is a problem that the offset deteriorates.

  Although the mechanism that deteriorates the offset by increasing the current flowing through the conduction path has not yet been completely clarified, it is considered that there is the following possibility.

  The current flows from the ground to the fixing film through the recording material. The direction of the current induces a positive charge having a polarity opposite to that of the toner on the back surface of the recording material, and holds the toner on the recording material. However, if this current value is too large, the negatively charged toner will be reversed and charged, and it will be easy to adhere to the fixing film to which a negative bias is applied from the power source. . Although the charge amount of the toner varies, the reversal from the toner having a particularly small charge amount to the above-described plus occurs. Therefore, the offset becomes worse as the current increases.

  Therefore, in the conventional fixing device, since the current flows as the recording material absorbs moisture and the resistance decreases, there arises a problem that the offset level may be deteriorated in an excessively high humidity environment.

  Accordingly, an object of the present invention is to provide a fixing device and an image forming apparatus capable of solving the above technical problems, effectively preventing tailing and preventing offset deterioration.

  The fixing device according to the present invention includes a rotating member that contacts unfixed toner carried on a sheet-like recording material, a pressure member that forms a nip for sandwiching the rotating member and the recording material, and the nip A heating member that supplies heat to the recording material via a rotating member, an abutting member that abuts the recording material at a position different from the nip, and the rotating member and the abutting member via the recording material. A voltage generating circuit for generating a voltage to be applied to at least one of the rotating body and the contact member in order to pass a current between the rotating body and the contact member via the recording material. And a limiting circuit that limits a flowing current.

  The image forming apparatus according to the present invention includes an image forming unit that forms a toner image on a sheet-shaped recording material, and a fixing unit that fixes an unfixed toner image formed on the recording material, The fixing unit includes a rotating body that contacts the unfixed toner carried on the recording material, a pressure member that forms a nip for sandwiching the rotating body and the recording material, and the nip through the rotating body. A heating body that supplies heat to the recording material, a contact member that contacts the recording material at a position different from the nip, and a current to flow between the rotating body and the contact member via the recording material. A voltage generation circuit for generating a voltage to be applied to at least one of the rotating body and the contact member, and a restriction for limiting a current flowing between the rotating body and the contact member via the recording material And a circuit.

  Preferably, the voltage generation circuit applies a voltage to the rotating body, and the contact member is grounded via a current upper limit circuit.

  Preferably, a voltage is applied to the contact member, and the rotating body is grounded via a current upper limit circuit.

  According to the present invention, a voltage is applied to at least one of a rotating member such as a fixing film or a fixing roller and an abutting member for a recording material such as a conductive paper discharge roller or a guide, so that the recording material is In the fixing device in which a current flows between the two through the recording material by passing, a current limiter for limiting an upper limit value of the current is disposed between a conduction path from a power source to which a voltage is applied to the ground.

  With such a configuration, when a current flows from the fixing film or the fixing roller through the recording material, a voltage drop occurs between the film or the fixing roller and the recording material, and the generated electric field functions as a toner holding force. The toner holding force overcomes the pressure of the vapor generated at the fixing nip and prevents toner scattering called tailing. On the other hand, even if the recording material resistance is low, the current limiter increases the value above a certain value. Since no current flows, offset deterioration caused by excessive current flow can be prevented.

  In this configuration, since the current flows only when the recording material straddles the contact member and the fixing nip and does not flow when the recording material does not straddle, the surface release caused by applying a voltage to the fixing roller or the fixing film is performed. Deterioration of the layer can be reduced.

(Example 1)
FIG. 1 is a schematic cross-sectional view of a film heating type fixing device showing an example of an embodiment of the present invention. First, the configuration of a fixing device as an example of an embodiment of the present invention will be described with reference to FIG.

  The heating element 5 is supported by heat insulation along the length of the lower surface of the film guide 6. The fixing film 4 is a cylindrical heat-resistant film that is externally fitted to a film guide 6 to which a heating body 5 is attached.

  The pressure roller 3 forms a pressure nip (fixing nip) N by sandwiching the film 4 with the heating body 5 with a predetermined contact pressure by a pressure mechanism (not shown) and rotationally drives the film 4. It also serves as a driving roller. The rotational force acts on the film 4 by the frictional force between the outer surface of the roller and the outer surface of the film due to the rotational driving of the pressure roller 3, and the film 4 slides in pressure contact with the surface of the heating element 5 in the clockwise direction indicated by the arrow. Driven by rotation.

  The film guide 6 is made of PPS (polyphenylene sulfide), PAI (polyamideimide), PI (polyimide), PEEK (polyetheretherketone), high heat resistant resin such as liquid crystal polymer, and these resins and ceramics, metal, glass, etc. The composite material can be used.

  The heating body 5 includes an elongate heat-resistant / insulating / high-heat-conducting heater substrate 5a having a direction perpendicular to the conveying direction of the fixing film 4 or the recording material P as the material to be heated, and the substrate 5a. The heating heating element surface formed with the energization heating resistor 5b, the power supply electrode (not shown) of the energization heating resistor 5b, and the energization heating resistor 5b formed at the center in the lateral direction on the surface side of the substrate Is a linear heating element (ceramic heater) having a low heat capacity as a whole, comprising a heat-resistant overcoat layer 5c that protects the substrate, a temperature detection element 10 such as a thermistor for detecting the temperature of the heating element, and the like. .

  The heater substrate 5a is, for example, ceramic having a thickness of 1 mm, a width of 10 mm, and a length of 240 mm, such as alumina or aluminum nitride. The energization heating resistor 5b is formed by, for example, applying an electric resistance material such as Ag / Pd (silver palladium), RuO2, Ta2N to a linear or narrow strip having a thickness of about 10 μm and a width of 1 to 3 mm by screen printing or the like. Formed.

  The power feeding electrode is a screen printing pattern layer such as Ag. The overcoat layer 5c is a heat-resistant glass layer having a thickness of about 10 μm, for example.

  When the heating element 5 is supplied with power to an electrode (not shown) of the energization heating resistor 5b, the energization heating resistor 5b generates heat over the entire length and quickly rises in temperature. The temperature rise is detected by the temperature detection element 10, and energization of the heating resistor 5b is controlled so that the temperature of the temperature detection element 10 is maintained at a predetermined set temperature during image heating.

  That is, the output signal of the temperature detection element 10 is input to the CPU 28 via the A / D converter 27. Based on this input signal, the CPU 28 controls the power supplied to the heating resistor 5b of the heating element 5 as the heating element via the AC driver 29, and adjusts the temperature of the heating element 5 to a predetermined temperature. .

  As control of the heating operation of the heating element 5 by the CPU 28, in addition to the control of switching the amplitude or period of the AC bias energized to the heating resistor 5b in accordance with the detection temperature of the temperature detection element 10, any arbitrary fixed time In other words, control of adjusting the energization amount from the external power source to the heating resistor 5b, so-called phase control or wave number control is performed. In particular, the wave number control has an advantage that the noise accompanying the energization is less than that of the phase control. Therefore, in the heating apparatus of this embodiment, the wave number is controlled as the heating operation of the heating element 5. Control is adopted.

  The fixing film 4 has a heat resistance, releasability, strength, durability, and flexibility of a film thickness of 100 μm or less, preferably 70 μm or less and 20 μm or more in order to reduce heat capacity and improve quick start performance. It is a layer film. The fixing film 4 has a three-layer structure, and a base layer 41, a primer layer 42, and a surface release layer 43 are formed in this order from the inside.

  The base layer 41 is a layer that bears mechanical characteristics such as torsional strength and smoothness of the fixing film 4, and is formed, for example, by molding polyimide, polyamideimide, PEEK, PES, PPS or the like into a cylindrical shape with a thickness of 50 μm.

  The conductive primer layer 42 is a layer for ensuring adhesion between the polyimide of the base layer 41 and the surface layer 43 and for transmitting an applied bias to the entire fixing film 4. The conductive layer is exposed at the end of the film as a power feeding portion. A bias is applied from the power source 7 by bringing a conductive brush or the like into contact therewith.

  The bias applied by the high voltage power supply 7 has the same polarity as the charged charge of the toner. In the present embodiment, since the toner exhibits a negative charge polarity, the voltage applied to the fixing film 4 is also negative and is −600V.

Since the surface release layer 43 is resistant to rubbing against the recording material and has high release properties so that the toner does not adhere to it, PTFE, PFA, FEP, etc. having a thickness of 10 to 20 μm and good release properties. 1 × 10 ⁸ Ωcm to 1 × 10 ¹⁴ Ωcm by dispersing electronically conductive carbon black, ionic conductive organic phosphorus salt, antimony pentoxide, K ₄ TiF ₆ or the like as a resistance value adjusting agent. It has a relatively high resistance and is designed to have an optimum resistance value and film thickness so as not to cause various image defects.

  The pressure roller 3 as a pressure member covers a cored bar 3a made of aluminum, cast iron or the like with a heat-resistant insulating elastic body 3b such as silicone rubber, and further has a releasability from toner as a surface layer 3c. Fluorine resin or the like is coated or molded into a tube shape.

  The surface layer 3c is electrically floated.

  A paper discharge roller 8 is in pressure contact with the paper discharge roller 9 to form a paper discharge roller pair.

  The paper discharge roller 8 is a recording material discharge means located downstream of the fixing nip N, and has a function as an electrode by making it electrically conductive. The high heat resistant material is formed with a roller portion 8b in which carbon is dispersed. The roller portion 8b needs to have sufficient electrical conductivity. However, if the amount of carbon is increased too much, the surface property of the roller will drop and problems such as toner contamination will occur, so the mixing ratio of carbon and silicone rubber is 1: 1. It is said.

  The paper discharge roller core 8a is grounded via the current limiter 1 through a conduction path.

  In the above configuration, after the rotation driving of the pressure roller 3 is started and the heating body 5 rises to a predetermined temperature, the recording material P conveyed from the image forming unit (not shown) to the fixing device 2 is supplied with the entrance guide 23. Is introduced between the fixing film 4 and the pressure roller 3 in the fixing nip portion N and is nipped and conveyed together with the fixing film 4, whereby the heat of the heating body 5 is transferred via the fixing film 2 to the recording material P. And the unfixed visible image T on the recording material P is heat-fixed on the recording material P surface.

  At this time, before the recording material P passes the position of the paper discharge roller 8, even if a bias of −600 V is applied to the fixing film, no current flows because there is no conduction path. Eventually, the recording material P is guided by the paper discharge guide 24, and when the leading end reaches the paper discharge roller 8, the recording material P, the paper discharge roller portion 8b, the cored bar 8a, the current limiter 1, and the ground are arranged in this order from the fixing film 4. A conduction path can be created.

  Therefore, a negative charge is transmitted from the fixing film 4 to the recording material P by the bias applied to the fixing film 4, and flows from the paper discharge roller 8 to the ground via the current limiter 1.

  When a conduction path is formed and a current flows, in the surface release layer 43 of the fixing film 4, between the inner surface side in contact with the primer layer 42 and the surface side in contact with the recording material P at the fixing nip portion N. Thus, a voltage due to a voltage drop is generated, and an electric field generated by this voltage generates a binding force acting on the toner T having a negative charge in the surface direction of the recording material P. The toner T is pressed against the recording material by this restraining force to prevent tailing. The restraining force increases as the resistance value of the surface release layer 43 increases and as the flowing current increases.

  Even if the resistance value of the surface release layer 43 is low, the current value increases. However, since the voltage generated in the surface release layer decreases, the anti-tailing effect does not increase but rather decreases. Therefore, in order to prevent tailing, the applied voltage must be set in consideration of the balance between the resistance value of the surface release layer 43 and the flowing current. In this embodiment, the applied voltage is set to -600V.

  At this time, what affects the current value is the resistance value of the recording material P in addition to the applied voltage and the resistance value of the surface release layer 43. The higher the resistance value of the recording material, the smaller the current value. For this reason, the above setting is based on a recording material in which the resistance value is not low and current is relatively difficult to flow, so that tailing can be prevented. Therefore, when the resistance value of the recording material is lower, more current flows and the tailing prevention effect is enhanced. On the other hand, when the current flows too much, the offset is deteriorated as described above.

  In terms of preventing tailing due to an increase in current, if the current value reaches a certain level, the moisture content of the recording material increases and the amount of water vapor increases. Pulling can be prevented. Therefore, in this embodiment, the current limiter 1 is arranged in the conduction path, and it is prevented that the current flows more than necessary and the offset is deteriorated.

  In this embodiment, the current limiter 1 flows as it is up to 5 μA and operates when it exceeds 5 μA.

  FIG. 2 shows an example of the circuit configuration of the current limiter 1.

  R1, R2, and R3 are resistors, Tr1 and Tr2 are transistors, Vs, Vp, and Vbe2 are voltages at their respective locations, and I is a current.

  R1 is set to satisfy Vs> Vbe2 (≈0.7) when I ≧ 5 μA.

  Normally, when I ≦ 5 μA, Tr1 is turned on and current I flows through the resistor R1.

  When I> 5 μA, Vs becomes equal to or higher than Vbe2, Tr2 is turned on, Tr1 is turned off, current I does not flow, and instead a constant current of 5 μA is drawn (the inside of the wavy line is a constant current circuit).

  When Vs ≦ Vbe2 because Tr1 is turned off, Tr2 is turned off, Tr1 is turned on again, and current I flows.

  By repeating the above operation, a circuit that does not flow a current of 5 μA or more is obtained.

  In the present embodiment, the surface of the pressure roller 3 is a float, and the only one that reliably acts as a conduction path is through the current limiter, and the current value can always be controlled to 5 μA or less.

  The current limiter 1 is disposed between the paper discharge roller 8 as a contact electrode and the ground, but may be disposed between the power source 7 and the fixing film 4 as shown in FIG.

  In this embodiment, a conductive paper discharge roller is also used as a contact electrode to form a conduction path. However, as shown in FIG. 4, the paper discharge port is molded with a conductive member such as a resin in which metal or carbon is dispersed. It is also possible to dispose the paper discharge guide 24 and use it as a contact electrode.

  Alternatively, as shown in FIG. 5, a conductive bra 25 in which conductive fibers are implanted on an aluminum substrate is arranged at the paper discharge port so that the tips of the conductive fibers rub against the recording material P. The effect is obtained. When the contact electrode is arranged on the paper discharge side, since the toner on the recording material P has already been fixed, the contact with the recording material is not limited to the back surface but may be the surface carrying the toner.

  Further, the contact electrode may not be on the paper discharge side but on the entrance side in front of the fixing nip N.

  As shown in FIG. 6, if a conductive member is used for the entrance guide 23 for introducing the recording material P into the fixing nip N and is brought into contact with the recording material P, the recording material P, the entrance guide 23, the current from the fixing film 4. A current can flow through the limiter 1 and the ground path to prevent tailing and to prevent offset.

  Further, a conductive brush may be arranged on the entrance side as in the paper discharge side, so that the contact between the recording material P and the contact electrode can be made more reliable.

(Example 2)
In this embodiment, a bias is applied from a power source 7 ′ to a paper discharge roller 8 as a contact electrode, and the fixing film 4 is grounded via the current limiter 1.

  FIG. 7 is a schematic diagram thereof. The same reference numerals are assigned to configurations common to the first embodiment.

  A bias is applied to the paper discharge roller to the paper discharge roller core 8a, and when the conductive roller portion 8b contacts the recording material P, a current flows.

  When a bias is applied to the contact electrode side as in the present embodiment, the polarity of the applied voltage is opposite to that in the first embodiment in order to keep the toner on the recording material P in the same direction as the first embodiment. It must have the opposite polarity to the charged charge of the toner. Therefore, since toner having a negatively charged polarity is used, +600 V is applied in this embodiment. By applying a positive polarity voltage, positive charges flow in the order of the cored bar 8a, the paper discharge roller unit 8b, the recording material P, the fixing film 4, the current limiter 1, and the ground, and in the surface release layer 43 of the fixing film. Due to the generated voltage drop, the toner is strongly pressed onto the recording material P, and tailing can be prevented.

  Needless to say, the contact electrode is not limited to the paper discharge roller as in the first embodiment, and a conductive guide or a conductive brush may be used. Further, the position of the contact electrode as viewed from the fixing nip N is effective on both the paper discharge side and the entrance side.

(Example 3)
A schematic diagram of the fixing device of this embodiment is shown in FIG.

  In this embodiment, a negative polarity bias is applied to the fixing film 4 from the power source 7, and a positive polarity bias is applied to the paper discharge roller 8 as a contact electrode by the power source 7 ′.

  Although the current limiter 1 is disposed between the paper discharge roller 8 and the power source 7 ′, it may be between the fixing film 4 and the power source 7.

  Thus, by applying a bias to both the fixing film 4 and the paper discharge roller 8, each applied voltage can be reduced. In this embodiment, the voltage applied to the fixing film 4 is −300 V, and the paper discharge roller 8. The voltage applied to is + 300V. Of course, this value can be set arbitrarily.

  Further, when voltage is applied from two places as in the present embodiment, the power source can be easily shared with the power source used for other members of the image forming apparatus. For example, when the power source applied to the fixing film 4 is shared with charging, if the voltage used for charging is −500 V, this is applied to the fixing film 4 as it is, and +100 V is added to the amount that is insufficient to prevent tailing. A configuration in which power is applied to the paper discharge roller by a power source can be considered. If the configuration of this embodiment is used, each voltage value can be set flexibly as necessary, so that the cost and size of the apparatus can be easily reduced.

Example 4
FIG. 9 shows a roller type fixing device according to an embodiment of the present invention.

Reference numeral 32 denotes a halogen heater lamp having a heating body therein, which generates heat from the inside of the fixing roller 31 that is a rotating body and raises the temperature of the fixing roller 31 to a temperature suitable for fixing. The fixing roller 31 is provided with a conductive rubber layer on an aluminum tube (core metal) having an outer diameter of 30 mm and a wall thickness of 3 mm, and a release layer having a thickness of 10 μm or more and 100 μm or less formed of a fluororesin such as PFA. Yes. The resistivity of the release layer of the fixing roller 31 is 1 × 10 ⁹ Ωcm or more and 1 × 10 ¹⁴ Ωcm or less. The insulation of the release layer on the surface layer of the fixing roller 31 should be as high as possible, and film uniformity is also required so that the leakage current does not increase due to defects such as pinholes.

  However, it is effective to increase the film thickness in order to ensure insulation and reduce pinhole defects, but the heat transfer ability to the recording material P is reduced, so that the fixing property is deteriorated.

  Therefore, it is important to select a film thickness at which the leakage current is reduced as much as possible within the range satisfying the fixability.

  The pressure roller 3 is pressed against the fixing roller 31 by a pressing means (not shown) to form a nip, and the recording material P is nipped and conveyed by the rotation of the fixing roller 31. As in the first embodiment, the paper discharge roller 8 includes a cored bar 8a and a roller part 8b in which carbon is dispersed in a high heat-resistant material such as silicone rubber around the cored bar 8a. Is grounded through. Since a bias having the same polarity as the charging polarity of the toner is applied to the aluminum tube of the fixing roller 31 by the high-voltage power supply 7, the mechanism for generating the binding force acting on the toner is the same as that shown in the first embodiment. .

  Current flows from the aluminum tube of the fixing roller 31 to the conductive rubber layer, the release layer, the recording material P, the paper discharge roller 8, the current limiter 1, and the ground, and an electric field generated between the recording material P and the conductive rubber layer. By increasing the strength, the binding force acting on the toner can be increased.

  Also in the fixing device of this embodiment, a current flows by the passage of the recording material P to prevent tailing, and when the resistance of the recording material is low, the current value is limited by the current limiter 1 to prevent an offset.

1 is a diagram illustrating a fixing device according to a first embodiment of the present invention. FIG. It is a figure explaining an example of the circuit of the current limiter of this invention. 1 is a diagram illustrating a fixing device according to a first embodiment of the present invention. FIG. 1 is a diagram illustrating a fixing device according to a first embodiment of the present invention. FIG. 1 is a diagram illustrating a fixing device according to a first embodiment of the present invention. FIG. 1 is a diagram illustrating a fixing device according to a first embodiment of the present invention. FIG. It is a figure explaining the fixing device of the 2nd example of the present invention. It is a figure explaining the fixing device of the 3rd example of the present invention. It is a figure explaining the fixing device of the 4th example of the present invention. FIG. 2 is a diagram illustrating main components of an image forming apparatus using an electrophotographic process. It is a figure explaining the conventional fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current limiter 2 Fixing device 3 Pressure roller 4 Fixing film 5 Heating body 6 Film guide 7 Power supply 8 Paper discharge roller 9 Paper discharge roller 10 Temperature detection element 11 Photosensitive drum 12 Charging roller 13 Laser exposure device 14 Reflection mirror 15 Toner container 16 Developing roller 17 Developing blade 18 Transfer roller 19 Cleaning blade 20 Waste toner container 23 Entrance guide 24 Paper discharge guide 25 Conductive brush 31 Fixing roller 32 Halogen heater N Nip T Toner P Recording material

Claims (6)

A rotating body in contact with unfixed toner carried on a sheet-like recording material;
A pressure member that forms a nip for sandwiching the rotating body and the recording material;
A heating body for supplying heat to the recording material through the rotating body at the nip;
A contact member that contacts the recording material at a position different from the nip;
A voltage generating circuit for generating a voltage to be applied to at least one of the rotating body and the contact member so that a current flows between the rotating body and the contact member via the recording material;
A fixing device comprising: a limiting circuit configured to limit a current flowing between the rotating body and the contact member via the recording material.   The fixing device according to claim 1, wherein the voltage generation circuit applies a voltage to the rotating body, and the contact member is grounded via a current upper limit circuit.   The fixing device according to claim 1, wherein the voltage generation circuit applies a voltage to the contact member, and the rotating body is grounded via a current upper limit circuit. Image forming means for forming a toner image on a sheet-like recording material;
Fixing means for fixing the formed unfixed toner image on the recording material,
The fixing means is
A rotating body in contact with the unfixed toner carried on the recording material;
A pressure member that forms a nip for sandwiching the rotating body and the recording material;
A heating body for supplying heat to the recording material through the rotating body at the nip;
A contact member that contacts the recording material at a position different from the nip;
A voltage generating circuit for generating a voltage to be applied to at least one of the rotating body and the contact member so that a current flows between the rotating body and the contact member via the recording material;
An image forming apparatus comprising: a limiting circuit that limits a current flowing between the rotating body and the contact member via the recording material.   The image forming apparatus according to claim 5, wherein the voltage generation circuit applies a voltage to the rotating body, and the contact member is grounded via the limiting circuit.   The fixing device according to claim 5, wherein the voltage generation circuit applies a voltage to the contact member, and the rotating body is grounded via the limiting circuit.

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