JP5153249B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a function of forming an image on a recording material such as a sheet.

  In an image forming apparatus (image recording apparatus) using an image forming process such as an electrophotographic system or an electrostatic recording system, an image forming operation is performed as follows. First, an electrostatic latent image is formed on a photosensitive drum or the like as an image carrier, and the latent image is developed with a developer (toner) and visualized as a toner image. This toner image is formed on a recording material such as paper. Transcribed. Thereafter, the recording material onto which the toner image has been transferred passes through a nip formed by a fixing roller and a pressure roller provided in the fixing device, whereby the toner image is heated and fixed on the recording material as a permanent image. .

  FIG. 10 is a schematic side view of a main part showing a typical example of such an image forming apparatus.

The surface of the photosensitive drum 101 that extends in the direction perpendicular to the drawing (paper surface) shown in FIG. 10 and rotates in the direction of the arrow is uniformly charged by a charging roller 102 connected to a high-voltage power supply. Then, a laser beam L modulated by an image signal is applied to the charged surface of the photosensitive drum 101 by the laser scanner 3 to form an electrostatic latent image. Toner is supplied from the developing device 104 to the latent image and becomes a toner image and arrives at the transfer nip portion _NT .

The transfer nip portion _NT is composed of a nip portion between the photosensitive drum 101 and the conductive transfer roller 105 in contact with the photosensitive drum 101. Recording is performed in accordance with the timing at which the toner image portion on the photosensitive drum 101 arrives at the transfer nip portion _NT. The material P is supplied and passes through the nip portion. At this time, a transfer bias is applied to the transfer roller 105 by the high voltage power source 106, and the toner image on the photosensitive drum 101 side is transferred to the recording material P. Thereafter, the recording material P carrying the toner image leaves the transfer nip portion _NT and is conveyed to the fixing device 109.

  In recent years, there has been proposed a film heating type fixing device using a fixing method that suppresses power consumption as much as possible without supplying power to the fixing device particularly during standby (see, for example, Patent Documents 1 to 4).

Such a fixing device 109 includes a heater (heating body) 122 and a heat resistant film (fixing film) 123 that slides on the heater 122 as a fixing body. The fixing device 109, a pressure member has a pressure member forming a fixing nip portion N _F pressed against a heater 122 (pressure roller) 124 via the film 123. Then, the fixing device 109, between the film 123 and the pressure member 124 of the fixing nip portion N _F, the recording material on which an unfixed image is formed is nipped and conveyed. In this, the fixing device 109, the pressure of the heat the fixing nip portion N _F from the heater 122 is applied through the film 123, is fixed as a permanent image unfixed image on a recording material.

  Such a film heating type fixing device can use a low heat capacity linear heating element as a heater and a thin film with a low heat capacity as a heater, so that it can save power and shorten the wait time (quick start). is there.

In this type of film fixing and heating type fixing device, the following are known as driving methods for the fixing film. That is, a system is known in which a fixing film is conveyed between a pressure roller and a heater as a pressure member while applying tension using a dedicated conveyance roller and a driven roller for film conveyance. In addition, a tensionless system is known in which a cylindrical fixing film is driven by a conveying force of a pressure roller by rotationally driving a pressure roller as a pressure member.

The former has the advantage that the transportability of the fixing film can be increased, and the latter has the advantage that the apparatus configuration can be simplified and a low-cost apparatus can be realized.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP-A-9-274343

  One of the problems in fixing is the offset phenomenon. This is a phenomenon in which a part of the toner adheres to a fixing body that contacts during fixing and causes an image defect.

  Although these reasons are various, one of the biggest causes is an electrostatic force exerted on the toner from the rotating body. In some cases, the pressure member that contacts the back surface of the recording material carrying an unfixed toner image on the front surface is charged to a negative high potential by continuously conveying the recording material. In such a case, there is a concern that an offset phenomenon may occur due to electrostatic repulsion between the pressure member and the negatively charged toner.

  In order to prevent this offset phenomenon, it is preferable that the fixing body has the same polarity as the toner and the pressure body has a different polarity from the toner.

  However, for example, when paper left in a low-temperature and low-humidity environment or paper with high resistance is passed, the fixing body may be positively charged and the pressure body may be negatively charged. This situation is disadvantageous for the offset phenomenon when the toner is negatively charged.

  In particular, in the case of a pressurizing member composed of an insulating silicone rubber for the base layer and a fluororesin and an insulating material for the surface layer, the pressure may rise to about −several kV due to frictional charging with the recording material. In such a case, if the unfixed toner is negatively charged as described above, the toner moves against the surface of the negatively charged pressure member and moves to the fixing member, so-called electrostatic offset. There was a concern that it would easily occur.

  Therefore, a method for increasing the electrostatic adhesion force of the toner to the recording material has been proposed.

  One is a method in which a bias voltage is applied to a pressure roller core metal, which is a pressure body, by a high voltage power source to induce a charge having a polarity opposite to that of the toner to attract and fix the toner to a recording material.

  However, with this method, if the roller layer is thick and a high resistance material such as silicone rubber, the effect of canceling the charge on the surface of the pressure roller is low, there is a concern that the efficiency is poor, and the cost is increased by using a high voltage power source. There were concerns about circuit complexity.

  In addition, a method has been proposed in which a bias voltage is applied to the fixing member by a high-voltage power source to induce a charge having the same polarity as the toner and the toner is suppressed by a repulsive electric field. There is concern about the complexity of the circuit.

  Therefore, the surface potential of the pressure roller is reduced to a predetermined low potential that does not cause an offset by making a neutralizing brush, a neutralizing needle, etc. face the surface of the pressure roller, which is a pressure body, as a neutralizing means and neutralizing the surface charge. A technique for reducing this value has been proposed. However, even with this method, depending on the type of the pressure roller member and the recording material, there may be a case where the phenomenon of causing image defects on the recording material cannot be completely prevented.

  Further, as in Patent Document 5, the recording material conveyance path is made a conductive member, and the conveyance path and the pressure roller neutralizing needle are connected to be grounded via a rectifying element in a direction to keep the same polarity as the recording material. This type is also introduced.

  However, in this configuration, there is almost no overcharged charge on the back surface of the recording material when the recording material reaches the conveyance path. For this reason, less charge flows into the conveyance path, and the negative charge is removed from the pressure roller charged with a large potential in the opposite polarity to the recording material, and the positive charge is charged to have the same polarity as the recording material. It is difficult to change the potential.

  The present invention has been made in view of the circumstances as described above, and a phenomenon in which a part of unfixed developer transferred to a recording material adheres to a fixing body at the time of fixing and causes an image defect is simplified. The object is to prevent the cost effectively and more effectively with the configuration.

In order to achieve the above object, the present invention provides:
An image bearing member for bearing an unfixed toner image, and charging the recording material the toner and opposite polarity, and an image forming unit having a transfer member onto a recording medium an unfixed toner image on said image bearing member,
A first fixing member that contacts an unfixed toner image at the time of fixing and a nip portion are formed together with the first fixing member, and a surface that contacts the recording material is charged with the same polarity as the toner by friction with the recording material. has a second fixing member, and a fixing unit for fixing an unfixed toner image to the heated recording material while conveying the recording material on which an unfixed toner image is formed by the nip portion,
A first charge eliminating member that neutralizes the recording material charged by the transfer member until the recording material onto which the unfixed toner image has been transferred reaches the nip portion;
A second static elimination member that neutralizes the surface of the second fixing member;
In an image forming apparatus having
A conductive path electrically connecting the first charge removal member and the second charge removal member, the potential of the recording material charged to the opposite polarity to the toner, and the second charge charged to the same polarity as the toner; The surface of the second fixing member is neutralized by a current flowing through the conduction path by a potential difference between the surface potential of the fixing member and the surface of the fixing member .

  According to the present invention, a phenomenon in which a part of unfixed developer transferred to a recording material adheres to a fixing body at the time of fixing and causes image defects can be achieved with a simple configuration at low cost and more effectively. It becomes possible to prevent.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

  First, an image forming apparatus according to a first embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an electrophotographic laser beam printer A as an image forming apparatus according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 3 denotes a laser scanner, and the intensity of the laser light L applied to the photosensitive drum 1 as an image carrier is modulated based on an image signal sent from an external device to a laser beam printer.

  Further, the surface of the photosensitive drum 1 that exposes the laser beam L is uniformly negatively charged by the charging roller 2, and the negative charge disappears in the portion irradiated with the laser beam L on the photosensitive drum 1, so that the image A potential difference occurs in the shape, and an electrostatic latent image is formed.

  This electrostatic latent image is conveyed to the opposing portion of the developing device 4 and the photosensitive drum 1 by the rotation of the photosensitive drum 1 (rotation in the direction indicated by the arrow in FIG. 1). Development is performed sequentially with a negatively charged toner as a developer.

The toner image developed by the developing device 4 (developer image formed on the image carrier) is transferred to the recording material P sent to the transfer nip portion _NT from the feeding device 10 as the recording material supply means. The images are sequentially transferred by the roller 5.

Reference numeral 6 denotes a DC high voltage generator as a transfer voltage application unit that generates a positive transfer voltage to be applied to the transfer roller 5, and reference numeral 7 denotes a transfer voltage controller that controls the DC high voltage generator 6. At the time of transfer, the recording material P on which the toner image has been transferred at the transfer nip portion _NT is subjected to a photosensitive drum while an excessive positive charge charged on the back of the paper is removed by a transfer neutralizing needle (static neutralizing member) 11 as a recording material neutralizing means. It separates with 1 rotation. Here, the back side of the paper means the back side (back side) of the surface of the recording material P on which the toner image is transferred. Then, the toner is sent to a fixing device (fixing device) 9 through a conveyance path 12. The transfer static elimination needle 11 is provided in the conveyance path along which the recording material is conveyed, and performs neutralization of the recording material P conveyed along the conveyance path.

  The conveyance path 12 is configured by forming a resin rib on the entire surface or a portion where the recording material comes into contact with a convex rib extending in the conveyance direction, and a portion of the convex rib is made of metal. In this embodiment, a metal convex rib (metal part, sheet metal part) is used to prevent the conveyance path from being charged and the conveyance of the recording material from becoming unstable due to the electrostatic force or from disturbing the toner image due to the electrostatic force. Is provided with a transport path.

  Next, the configuration of the fixing device 9 will be described.

  FIG. 2 is a cross-sectional view showing a schematic configuration of a main part (photosensitive drum 1, transfer roller 5, transfer charge eliminating needle 11, fixing device 9 and the like) of the laser beam printer A. The fixing device 9 is a so-called tensionless type of a film heating method and a pressure body driving method.

  The fixing device 9 includes a film inner surface guide member 21 and a heater 22. Here, the film inner surface guide member 21 has heat resistance and rigidity. The heater 22 is fixed to the lower surface of the film inner surface guide member 21 shown in FIG. 2 by being fitted into a concave groove provided along the longitudinal direction of the film inner surface guide member 21, and generates heat when energized. The film inner surface guide member 21 in which the heater 22 is fitted has a fixing film 23 made of a cylindrical heat-resistant resin having an outer peripheral length of about 57 mm as a fixing body. Here, the longitudinal direction refers to a direction orthogonal to the recording material conveyance direction in which the recording material is conveyed, and the short direction refers to the recording material conveyance direction.

The heater 22 includes, for example, a substrate, a resistance heating element, a heat-resistant overcoat layer, a power supply electrode at a longitudinal end of the resistance heating element, and a linear heating element. Here, the substrate is a heat-resistant, insulating, and heat-conductive substrate that is provided in an elongated shape along the longitudinal direction (elongated with the bus-line direction of the fixing film 23 as the longitudinal direction). The resistance heating element is formed and formed along the longitudinal direction of the substrate at the center in the short direction on the surface side of the substrate. The overcoat layer is a heat resistant layer for protecting the surface of the heating body on which the resistance heating element is formed.
Further, the linear heating body is composed of a temperature measuring element such as a thermistor which is disposed on the back side of the substrate and detects the temperature of the heating body.

  3A and 3B are diagrams showing a schematic configuration of the fixing film 23, where FIG. 3A is a sectional view and FIG. 3B is a plan view.

  The fixing film 23 is composed of, for example, three layers. As shown in FIG. 3, the base layer 31 includes a polyimide layer having a thickness of 50 microns, a conductive adhesive layer 32 having a thickness of several microns, and a fluororesin having a thickness of several microns. A top layer 33 is applied. The inner peripheral length of the fixing film 23 is 3 mm larger than the outer peripheral length of the film inner surface guide member 21 including the heater 22, and the fixing film 23 has a margin in the peripheral length with respect to the film inner surface guide member 21 including the heater 22. It is loosely fitted outside.

  The fixing film 23 is grounded through a diode D1 as a rectifying element so as to have the same polarity as the toner in order to prevent electrostatic adhesion of negatively charged toner. The diode D1 has an anode side as a fixing film side and a cathode side as a ground side.

  Further, the fixing device 9 includes a pressure roller (pressure contact roller, drive roller) 24 as a pressure body (pressure rotary body). A fixing film 23 is sandwiched between the pressure roller 24 and the film inner surface guide member 21 including the heater 22.

  The pressure roller 24 includes a cored bar 25 and an elastic layer 26 formed by foaming a heat-resistant rubber such as silicone rubber or fluororubber, or silicone rubber formed concentrically and integrally on the cored bar 25. The surface layer is a rotating body made of PFA which is a fluororesin. Here, PFA is a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer.

The pressure roller 24 of the present embodiment has an outer diameter of φ18 mm, the core metal is iron, and the core metal diameter is φ11 mm. A silicone rubber foam is used as the elastic layer 26, the elastic layer has a thickness of t = 3.5 mm, and the surface layer is covered with a PFA tube. The pressure roller 24 is arranged such that both ends of the cored bar 25 are rotatably (rotatably) supported by bearings between side plates on the front side and the back side of the apparatus chassis via bearing members. Then, the pressure roller 24 and the film inner surface guide member 21, each other is fixed so as to be pressed to form a fixing nip portion N _F.

  The pressure roller 24 is driven to rotate at a predetermined peripheral speed by the rotation control unit 8.

Between the outer peripheral surface of the fixing film 23 of the pressure roller 24 by the rotation of the pressure roller 24, the pressure contact frictional force in the fixing nip N _F, the rotational force acts on the cylindrical fixing film 23. As a result, the fixing film 23 is driven to rotate on the outer periphery of the film inner surface guide member 21 while the inner surface of the fixing film 23 slides in close contact with the contact surface (downward surface in FIG. 2) of the heater 22.

In a state where the heater 22 is temperature control rising to a predetermined temperature by heating by being energized, the recording material P, while being bearing an unfixed toner image T, the fixing of the fixing nip portion N _F It is introduced between the film 23 and the pressure roller 24.

Then, at the fixing nip portion N _F, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing film 23, the recording material P is nipped and conveyed to fixing nip portion N _F with the fixing film 23. In this nipping and conveying process, the heat of the heater 22 is applied to the recording material P through the fixing film 23, and the unfixed toner image T on the recording material P is heated and pressed on the recording material P to be melt-fixed. Is done. The recording material P passed through the fixing nip portion N _F is the curvature separated from the fixing film 23.

  Here, in the laser beam printer A that performs the above-described operation, there is a concern that the following problems may occur.

When the recording material P carrying the unfixed toner image T on the surface is continuously conveyed, the pressure roller 24 may be negatively charged due to friction between the recording material P and the pressure roller 24. In particular, it is prominent when paper left in a low-temperature and low-humidity environment or paper with high resistance is passed. This phenomenon, when the recording material P bearing the unfixed toner image T on the surface passes through the fixing nip portion N _F, the toner T charged negatively is negative charge and electrostatic repulsion of the pressure roller 24, The toner T may adhere to the fixing film 23 without being fixed on the recording material P. In this case, the fixing film 23 is round, the toner T when adhered toner T enters the fixing nip N _F again deposited on the recording material P, there is a possibility that the offset phenomenon.

In this embodiment, the surface of the pressure roller 24 is made of PFA which is a fluororesin. Therefore, the recording material P bearing the unfixed toner image T is negatively charged on the surface, passes through the fixing nip portion N _F of the pressure roller 24 and the fixing film 23, the surface potential of the pressure roller 24 is particularly Largely negatively charged.

  For example, if the process speed is 100 millimeters per second, LTR size paper is used as a recording material, and processing is performed at a speed of 16 sheets per minute, depending on the type of recording material, if about 50 sheets are continuously fed, about -3 kV to -6 kV The pressure roller 24 is charged up to.

  Therefore, in this embodiment, the following configuration is adopted.

  FIG. 4 is a diagram for explaining the characteristic configuration of the present embodiment. The main parts of the laser beam printer A of the present embodiment (photosensitive drum 1, transfer roller 5, transfer charge eliminating needle 11, fixing device 9). And the like.

  A pressure roller static elimination needle (static elimination member) 14 as a pressure body static elimination means is fixed to the feeding guide 27 so that the tip of the pressure roller static elimination needle 14 has a certain distance from the surface of the pressure roller 24. Is arranged. In this embodiment, the distance between the surface of the pressure roller 24 and the tip of the pressure roller neutralizing needle 14 is 1 mm.

  In the present embodiment, as a characteristic configuration of the present embodiment, a conduction path (first conduction path) 13 that electrically connects the pressure roller neutralization needle 14 and the transfer neutralization needle 11 is provided. .

  Since the recording material P is positively charged and the pressure roller 24 is negatively charged, the recording material P that is overcharged positively immediately after the transfer is attracted to the negative polarity of the pressure roller 24 by the transfer static elimination needle 11. Positive charges are removed. The removed positive charge passes through the conduction path 13 and is discharged from the pressure roller neutralizing needle 14 onto the surface of the pressure roller 24, and the positive charge is charged on the surface of the pressure roller 24.

  Negative charges on the surface of the pressure roller 24 are removed by being attracted to the positive polarity because the recording material P is positively charged.

  The removed negative charges are discharged from the transfer charge eliminating needle 11 to the recording material P through the conduction path 13.

  Usually, when the surface potential of the pressure roller 24 is compared with the absolute value of the potential of the recording material P before passing through the transfer static elimination needle 11, the surface of the pressure roller 24 is positive because the recording material P is larger. Although it becomes polar or approaches as much as possible, it becomes possible to maintain a positive potential on the recording material P.

  The offset was confirmed using the above configuration, and the surface potential of the pressure roller 24, the paper back potential before passing through the transfer charge removal needle 11, and the paper back potential after passing through the transfer charge removal needle 11 were measured.

<Experimental conditions>
・ Environment: Temperature 15 ℃, humidity 10%
Image forming apparatus body: LTR size paper, 16 ppm (page per minute), electrophotographic image forming apparatus Paper passing paper: FoxRiveBond 90 g / m ² , paper left in the above environment for 7 days Paper passing mode: 50 continuous sheets

  In Comparative Example 1, the transfer static elimination needle 11 was grounded, the pressure roller neutralization needle 14 was not provided, and the grounding was made via a cored bar. The surface of the fixing film 23 was grounded via a diode as a rectifying element. In the diode, the fixing film 23 side is the anode side, and the ground side is the cathode side.

  In Comparative Example 2, the transfer static elimination needle 11 was grounded, and the pressure roller static elimination needle 14 was also grounded. The surface of the fixing film 23 was grounded via a diode as a rectifying element. In the diode, the fixing film 23 side is the anode side, and the ground side is the cathode side.

  In Comparative Example 3, the transfer static elimination needle 11 is grounded, and the pressure roller static elimination needle 14 is connected to the metal portion of the conveyance rib portion below the recording material conveyance portion and is grounded. The surface of the fixing film 23 was grounded via a diode as a rectifying element. In the diode, the fixing film 23 side is the anode side, and the ground side is the cathode side.

  Table 1 shows the results of measuring the offset of the 50th sheet, the surface potential of the pressure roller 24, the paper back potential before passing through the transfer static elimination needle 11, and the paper back potential after passing through the transfer static elimination needle 11. As a result of the offset, ◯ is an OK level, Δ is an acceptable level, and x is an NG level.

  As for Comparative Example 1, the offset is x and the level is NG. This is because the surface of the pressure roller 24 is charged to −6800 V by frictional charging with the paper.

  Further, since there is no means for removing the charged electric charge, the minus potential becomes very high. The negatively charged toner on the paper repels by electrostatic force and adheres to the fixing film 23 side, resulting in a bad offset phenomenon.

Regarding Comparative Example 2, Δ is an acceptable level, but a slight offset occurs. This is because the surface potential of the pressure roller 24 is charged to -2800V. Although the negative charge has been removed by the pressure roller neutralizing needle 14, it can be seen that complete removal is not possible with the grounding type of the pressure roller neutralizing needle 14.

  Regarding the comparative example 3, it is NG level by x. This is because the surface potential of the pressure roller 24 is charged to -4200V. The pressure roller neutralizing needle 14 is connected to the metal part of the transport path 12, and a minute positive charge flowing into the metal part of the transport path 12 is charged on the surface of the pressure roller 24, and the negative charge generated by frictional charging They cancel each other and the negative potential becomes a little smaller. However, since the supply amount of the positive charge is very small, the negative charge of the pressure roller 24 is not removed and the potential remains negatively large.

  Further, when the recording material passes through the metal portion of the transport path 12, the excess charge is removed upstream by the transfer static elimination needle 11, so that the plus charge flowing in the metal portion of the transport path 12 is also small. For this reason, the positive charge supplied to the surface of the pressure roller 24 also becomes very small.

  As for Example 1, the offset is ◯ and the level is OK. This is because the surface potential of the pressure roller 24 is +200 V, and the negatively charged toner is attracted by the electrostatic force from the pressure roller 24 onto the recording material, so that the toner is not offset on the fixing film 23 side. Can also be completely prevented.

  In the first embodiment, the transfer static elimination needle 11 is only connected to the pressure roller static elimination needle 14. However, the charge on the back of the paper after passing from the passage before the transfer static elimination needle 11 has changed, and the excess of the back of the paper is present. It can be seen that the positive charges are well removed. This is because the positive charge removed by the transfer charge removal needle 11 is transmitted through the conduction path 13 and supplied and charged from the pressure roller charge removal needle 14 to the pressure roller 24. The pressure roller 24 is largely negatively charged, but the potential on the back of the paper is much larger and positively charged. As a result, the potential can be held on the positive side.

  As described above, according to the present embodiment, the transfer charge eliminating needle 11 and the pressure roller charge eliminating needle 14 after the transfer are connected by the conduction path 13, so that the excess plus charge eliminated by the transfer charge eliminating needle 11 can be reduced. It becomes possible to positively charge the pressure roller 24 from the pressure roller neutralizing needle 14. As a result, the potential of the pressure roller 24 can be made close to the same polarity as that of the recording material P, so that the offset can be prevented without electrostatically repelling the toner image on the recording material.

  That is, it is possible to more effectively prevent an offset phenomenon in which a part of the toner adheres to the contact fixing film 23 and causes an image defect during fixing.

  In addition, since the above configuration can be achieved without using a high-voltage power supply, it is inexpensive and simplification of the circuit (simplification of the configuration) can be achieved.

  The second embodiment of the present invention will be described below.

  FIG. 5 is a schematic cross-sectional view showing the main part of the image forming apparatus according to the present embodiment, and is a diagram for explaining the configuration of the fixing device. In the present embodiment, the different constituent parts from those of the first embodiment will be described, and the description of the same constituent parts as those in the first embodiment will be omitted.

  In the present embodiment, the second rectifying element is provided so that the conduction path 13 connecting the transfer charge eliminating needle 11 and the pressure roller charge eliminating needle 14 described in the first embodiment can be maintained at the same polarity as the recording material P. It is set as the structure which earth | grounds via the diode D2.

  In this embodiment, as shown in FIG. 5, the conduction path 13 is grounded via a diode D2 having a withstand voltage of 3 KV. The diode D2 is connected so that the ground side is the anode side, the conduction path 13 side is the cathode side, and the conduction path 13 side is held on the plus side having the same polarity as the recording material P.

  By adopting such a configuration, it is possible to obtain the same effect as that described in the first embodiment. Further, the conduction path 13 is grounded via the diode D2 so that the potential of the same polarity as that of the recording material P can be maintained, so that the fixing film 23 has the same polarity as the toner and the pressure roller 24 has the same polarity as the recording material P. Can be maintained stably. For this reason, the offset phenomenon can be more effectively prevented.

  Further, in the laser beam printer A, the positive charge is not supplied from the transfer static elimination needle 11 in the pre-rotation, post-rotation, and idle rotation states such as between sheets, and the surface of the pressure roller 24 is negative due to friction with the fixing film 23. May be charged. According to the present embodiment, even in such a case, there is an effect that negative charges are removed from the surface of the pressure roller 24 through the static elimination needle.

  Furthermore, since the conduction path 13 is grounded via the diode D2, excessive charges do not accumulate on the conduction path 13 and the charge removal needle (transfer charge removal needle 11 and pressure roller charge removal needle 14).

  Accordingly, it is possible to suppress the occurrence of electrical noise due to the discharge of charges at a place other than on the static elimination needle, and the occurrence of problems such as malfunction of the image forming apparatus main body due to the occurrence of this noise.

  Example 3 of the present invention will be described below.

  FIG. 6 is a schematic cross-sectional view showing the main part of the image forming apparatus according to the present embodiment, and is a view for explaining the configuration of the fixing device. In the present embodiment, the different constituent parts from those of the first embodiment will be described, and the description of the same constituent parts as those in the first embodiment will be omitted.

  In the present embodiment, the conduction path 13 connecting the transfer neutralizing needle 11 and the pressure roller neutralizing needle 14 described in the first embodiment is configured to be grounded via a resistor.

  In the present embodiment, as shown in FIG. 6, the conduction path 13 is grounded via a resistor R1. In this embodiment, the resistor R1 is a 100 MΩ resistor.

  By adopting such a configuration, it is possible to obtain the same effect as that described in the first embodiment.

  Furthermore, since the conduction path 13 is grounded via the resistor R1, excessive charges do not accumulate on the conduction path 13 or the charge removal needle (the transfer charge removal needle 11 and the pressure roller charge removal needle 14). Accordingly, it is possible to suppress the occurrence of electrical noise due to discharge at a place other than on the static elimination needle, and the occurrence of problems such as malfunction of the image forming apparatus main body due to the occurrence of this noise.

  The fourth embodiment of the present invention will be described below.

  FIG. 7 is a schematic cross-sectional view showing the main part of the image forming apparatus according to the present embodiment, and is a view for explaining the configuration of the fixing device. In the present embodiment, the different constituent parts from those of the first embodiment will be described, and the description of the same constituent parts as those in the first embodiment will be omitted.

  In this embodiment, the first fixing film 23 (surface) has the same polarity as that of the toner in the conduction path 13 connecting the transfer discharging needle 11 and the pressure roller discharging needle 14 described in the first embodiment. A diode D1 as a rectifying element is connected.

  That is, in this embodiment, in order to make the fixing film 23 have the same polarity as the toner, the conduction path (second path) for electrically connecting the fixing film 23 to the conduction path 13 via the diode D1 as the first rectifying element. A conduction path) K1 is provided.

  In this embodiment, the diode D1 has a withstand voltage of 3 kV. Further, in the diode D1, in order to make the fixing film 23 have the same polarity as the toner, the fixing film 23 side is the anode side, and the conduction path 13 side is the cathode side.

  With this configuration, the negative charge removed from the surface of the pressure roller 24 is directed to the back side of the recording material P or the fixing film 23 side, and the negative charge is more effectively used from the viewpoint of preventing offset. It becomes possible to do.

  While confirming the offset using the configuration of the present embodiment, the surface potential of the pressure roller 24, the paper back potential before passing through the transfer static elimination needle 11, the paper back potential after passing through the transfer static elimination needle 11, and the fixing film 23 The upper surface potential was measured.

<Experimental conditions>
・ Environment: Temperature 15 ℃, humidity 10%
-Image forming apparatus main body: LTR size paper, 16 ppm, electrophotographic image forming apparatus- Paper passing: Fox River Bond, 90 g / m ² , paper left in the above environment for 7 days- Paper passing mode: 50 continuous sheets

  In Comparative Example 1, the transfer static elimination needle 11 was grounded, the pressure roller neutralization needle 14 was not provided, and the grounding was made via a cored bar. The surface of the fixing film 23 was grounded via a diode as a rectifying element. In the diode, the fixing film 23 side is the anode side, and the ground side is the cathode side.

  In Comparative Example 2, the transfer static elimination needle 11 was grounded, and the pressure roller static elimination needle 14 was also grounded. The surface of the fixing film 23 was grounded via a diode as a rectifying element. In the diode, the fixing film 23 side is the anode side, and the ground side is the cathode side.

  In Comparative Example 3, the transfer static elimination needle 11 is grounded, and the pressure roller static elimination needle 14 is connected to the metal portion of the conveyance rib portion below the recording material conveyance portion and is grounded. The surface of the fixing film 23 was grounded via a diode as a rectifying element. In the diode, the fixing film 23 side is the anode side, and the ground side is the cathode side.

  Table 2 shows the results of measuring the offset of the 50th sheet, the surface potential of the pressure roller 24, the paper back potential before passing through the transfer static elimination needle 11, and the paper back potential after passing through the transfer static elimination needle 11. As a result of the offset, ◯ is an OK level, Δ is an acceptable level, and x is an NG level.

  Example 1, offset level of Comparative Examples 1 to 3, surface potential of 50th pressure roller 24, paper back potential before passing through 50th transfer charge eliminating needle 11, after passing 50th transfer charge eliminating needle 11 The result of the paper back potential is as described in Example 1 above. Therefore, only the surface potential on the 50th fixing film 23 will be described here.

  With respect to Example 1 and Comparative Examples 1 to 3, the surface potential of the fixing film 23 is 0V. This is because the surface of the fixing film 23 is charged with a positive charge flowing from the surface of the recording material, but can flow to the ground via the diode and can hold 0V.

  In this embodiment, the surface potential of the 50th pressure roller 24 and the paper back potential before passing through the 50th transfer charge eliminating needle 11 are the same as in the first embodiment. The paper back potential after passing through the 50th transfer charge eliminating needle 11 is slightly higher in the present embodiment than in the first embodiment.

  This is because the negative charge on the surface of the pressure roller 24 is also directed to the fixing film 23 side, so that the negative charge toward the back of the paper is slightly reduced, and the paper back potential after passing through the static elimination needle is slightly increased. However, the paper back potential after passing through the 50th transfer charge elimination needle 11 is at a level that does not cause any problem at the magnitude of the result shown in Table 2 and does not disturb the image.

  In this embodiment, the surface potential on the fixing film 23 is −300 V, the same polarity as that of the negatively charged toner on the surface of the pressure roller 24, and electrostatic repulsive force is generated. Will not stick to.

  This is because the negative charge charged on the surface of the pressure roller 24 is charged on the fixing film 23 via the diode D1. That is, since the charge having the same polarity as that of the toner is charged on the fixing film 23, it is possible to increase the potential difference on the side where electrostatic offset is prevented. Therefore, the electrostatic offset margin is further increased as compared with the first embodiment. Will spread.

  As described above, in this embodiment, the conduction path K1 (path from the conduction path 13 to the surface of the fixing film 23 or the vicinity thereof) that electrically connects the fixing film 23 and the conduction path 13 is provided. Further, a diode D1 is provided in the conduction path K1 so as to hold the charge having the same polarity as that of the toner on the recording material P and not to hold the charge having a different polarity. As a result, the phenomenon in which the surface of the fixing film 23 caused by frictional charging or the like is charged to a polarity different from that of the toner is more effectively suppressed, and the offset phenomenon in which a part of the toner adheres to the fixing body is more effectively prevented. be able to.

  The fifth embodiment of the present invention will be described below.

  FIG. 8 is a schematic cross-sectional view showing the main part of the image forming apparatus according to the present embodiment, and is a view for explaining the configuration of the fixing device. In the present embodiment, different components from those of the first, second, and fourth embodiments will be described, and the description of the same components as those of the first, second, and fourth embodiments will be omitted.

  In this embodiment, in order to make the fixing film 23 (surface) the same polarity as the toner, the fixing film 23 is electrically connected to the conduction path 13 described in the first embodiment via the diode D1 as the first rectifying element. It is set as the structure provided with the conduction | electrical_connection path (2nd conduction | electrical_connection path) K1 connected to. Further, the conduction path 13 is grounded via a diode D2 as a second rectifying element so as to have the same polarity as the recording material P.

  In this embodiment, the diode D1 has a withstand voltage of 3 kV. Further, in order to make the fixing film 23 have the same polarity as the toner, in the diode D1, the fixing film 23 side is set as the anode side, and the conduction path 13 side is set as the cathode side. The conduction path 13 is grounded via a diode D2 having a withstand voltage of 3 KV. The diode D2 is connected so that the ground side is the anode side, the conduction path 13 side is the cathode side, and the conduction path 13 side is held on the plus side having the same polarity as the recording material P.

  By adopting such a configuration, it is possible to obtain the same effects as those described in the first and fourth embodiments. Further, the negative charge removed from the surface of the pressure roller 24 is directed to the back side of the recording material P or the fixing film 23 side, and the negative charge can be used more effectively from the viewpoint of preventing offset.

  Further, in the laser beam printer A, the positive charge is not supplied from the transfer static elimination needle 11 in the pre-rotation, post-rotation, and idle rotation states such as between sheets, and the surface of the pressure roller 24 is negative due to friction with the fixing film 23. May be charged. According to the present embodiment, even in such a case, there is an effect that negative charges are removed from the surface of the pressure roller 24 through the static elimination needle.

  Furthermore, since the conduction path 13 is grounded via the diode D2, excessive charges do not accumulate on the conduction path 13 and the charge removal needle (transfer charge removal needle 11 and pressure roller charge removal needle 14). Accordingly, it is possible to suppress the occurrence of electrical noise due to discharge at a place other than on the static elimination needle, and the occurrence of problems such as malfunction of the image forming apparatus main body due to the occurrence of this noise.

  The sixth embodiment of the present invention will be described below.

  FIG. 9 is a schematic cross-sectional view showing the main part of the image forming apparatus according to the present embodiment, and is a view for explaining the configuration of the fixing device. In the present embodiment, different components from those of the first, third, and fourth embodiments will be described, and the description of the same components as those of the first, third, and fourth embodiments will be omitted.

  In this embodiment, in order to make the fixing film 23 (surface) the same polarity as the toner, the fixing film 23 is electrically connected to the conduction path 13 described in the first embodiment via the diode D1 as the first rectifying element. It is set as the structure provided with the conduction | electrical_connection path (2nd conduction | electrical_connection path) K1 connected to. Further, the conduction path 13 is configured to be grounded via a resistor R1.

  In this embodiment, the diode D1 has a withstand voltage of 3 kV. Further, in order to make the fixing film 23 have the same polarity as the toner, the fixing film 23 side is set as the anode side, and the conduction path 13 side is set as the cathode side. The conduction path 13 is grounded through a 100 MΩ resistor R1.

  By adopting such a configuration, it is possible to obtain the same effects as those described in the first and fourth embodiments. Further, the negative charge removed from the surface of the pressure roller 24 is directed to the back side of the recording material P or the fixing film 23 side, and the negative charge can be used more effectively from the viewpoint of preventing offset.

  Furthermore, since grounding is performed via the resistor R1, excessive electric charge does not accumulate on the conduction path 13 or the charge eliminating needle. Accordingly, it is possible to suppress the occurrence of electrical noise due to discharge at a place other than on the static elimination needle, and the occurrence of problems such as malfunction of the image forming apparatus main body due to the occurrence of this noise.

1 is a schematic configuration diagram illustrating an image forming apparatus according to Embodiment 1. FIG. 1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to Embodiment 1. FIG. 1 is a schematic configuration diagram of a fixing film according to Example 1. FIG. 1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to Embodiment 1. FIG. FIG. 3 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a second embodiment. FIG. 9 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a third embodiment. FIG. 9 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a fourth embodiment. FIG. 10 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a fifth embodiment. FIG. 10 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a sixth embodiment. 1 is a schematic configuration diagram of a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 9 Fixing device 11 Transfer static elimination needle 13 Conduction path 14 Pressure roller static elimination needle 23 Fixing film 24 Pressure roller A Laser beam printer N _F Fixing nip part P Recording material T Toner

Claims (6)

An image bearing member for bearing an unfixed toner image, and charging the recording material the toner and opposite polarity, and an image forming unit having a transfer member onto a recording medium an unfixed toner image on said image bearing member,
A first fixing member that contacts an unfixed toner image at the time of fixing and a nip portion are formed together with the first fixing member, and a surface that contacts the recording material is charged with the same polarity as the toner by friction with the recording material. has a second fixing member, and a fixing unit for fixing an unfixed toner image to the heated recording material while conveying the recording material on which an unfixed toner image is formed by the nip portion,
A first charge eliminating member that neutralizes the recording material charged by the transfer member until the recording material onto which the unfixed toner image has been transferred reaches the nip portion;
A second static elimination member that neutralizes the surface of the second fixing member;
In an image forming apparatus having
A conductive path electrically connecting the first charge removal member and the second charge removal member, the potential of the recording material charged to the opposite polarity to the toner, and the second charge charged to the same polarity as the toner; An image forming apparatus , wherein a current flows through the conduction path due to a potential difference between a surface potential of a fixing member and a surface of the second fixing member . The image forming apparatus according to claim 1, wherein a surface layer of the second fixing member is made of a fluororesin. The first charge eliminating member is provided to face a surface opposite to a surface on which an unfixed toner image is formed in a recording material charged by the transfer member. The image forming apparatus according to 2. 4. The device according to claim 1, wherein the second charge eliminating member is provided so as to face the surface of the second fixing member that contacts the recording material in a non-contact manner. 5. The image forming apparatus described. As the unfixed toner and the opposite polarity charge is held in the conduction path, said conductive path, in any one of claims 1-4, characterized in that it is grounded through a rectifier element The image forming apparatus described. The conducting path, the image forming apparatus according to any one of claims 1-4, characterized in that via a resistor connected to ground.

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