JP2006091451A - Heat fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably obtain an excellent image while an offset phenomenon and a rear toner scatter phenomenon are balanced well even when a printing speed is made fast. <P>SOLUTION: A rotary body for fixation comprises at least three layers which are a conductive layer with conductivity, an intermediate layer of 1 to 6 μm in film thickness, and a surface layer having lower resistance than the intermediate layer, and a current path passing through a recording material is formed between an electrode A provided in contact with the conductive layer of the rotary body and an electrode B provided outside a press-contact nip part in or without contact with the recording material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat fixing device for fixing toner or the like on a recording material used in an image forming apparatus such as an electrophotographic printer, a copying machine, and an electrostatic recording apparatus.

  Conventionally, many electrophotographic copying machines, printers, etc. have a contact heating type heat roller fixing method with good thermal efficiency and safety as a heat fixing means, and quick start property (on-demand property). It uses an energy-saving film heating method that keeps power consumption as low as possible without supplying power to the equipment.

  A heat roller fixing type heat fixing apparatus includes a heating roller (hereinafter referred to as a fixing roller) as a heating rotating body including a halogen heater therein, and an elastic pressure roller (hereinafter referred to as a pressing rotating body) pressed against the heating roller. , A pressure roller). The pair of rollers is rotated, and a recording material (transfer material sheet / electrostatic recording material) as a heated material in which an unfixed image (toner image) is formed and supported in a fixing nip portion that is a pressure nip portion of the pair of rollers・ Introducing electrofax paper, printing paper, etc.) and nipping and transporting the toner image onto the surface of the recording material as a permanently fixed image by heat from the fixing roller and pressure applied to the fixing nip. is there.

  On the other hand, a film heating type heat fixing device is fixed as proposed in, for example, JP-A-63-313182, JP-A-2-157878, 4-44075-44083, 4-204980-204984, and the like. A heat-resistant film (hereinafter referred to as a fixing film), which is a rotating body for heating, is brought into close contact with a heating member such as a ceramic heater (hereinafter referred to as a heater) with a rotating pressure member (hereinafter referred to as a pressure roller) The recording material carrying the toner image is introduced into the fixing nip portion, which is a pressure nip portion formed by the heating body and the pressure roller with the fixing film interposed therebetween, and is conveyed together with the fixing film. The toner image is fixed to the surface of the recording material as a permanently fixed image by heat and heat applied from a heating body through a fixing film and the pressure applied to the fixing nip portion. That.

  FIG. 2 shows a schematic configuration of an example of a film heating type heat fixing device 11.

  The heating assembly 11a includes a heater 20 as a heating member, a film guide 22 as a guide member that supports the heater, and a flexible rotating body that includes the film guide 22 and is in contact with the heater 20. The assembly includes a cylindrical fixing film 25 and a flange member (not shown) that supports the fixing film 25 at both ends and is fitted to the film guide 22. The heater 20 is a so-called ceramic heater having a horizontally long and thin wall having a direction perpendicular to the conveyance direction (arrow K direction) of the recording material P as a longitudinal direction and a low heat capacity as a whole. The fixing film 25 includes a base layer, a primer layer, and a surface layer from the heater 20 side. The elastic pressure roller 26 as a pressure member includes a cored bar 26a, an elastic layer 26b, and a surface release layer 26c.

  The heater 20 and the pressure roller 26 on the side of the heating assembly 11a are opposed to each other and are pressed against each other with the fixing film 25 interposed therebetween to form a fixing nip portion N. The pressure roller 26 is rotationally driven in a counterclockwise direction indicated by an arrow R26 by a driving unit (not shown). By the rotational driving of the pressure roller 26, a rotational force acts on the fixing film 25 by the frictional force between the pressure roller 26 and the outer surface of the fixing film 25 in the fixing nip portion N, and the inner peripheral surface of the fixing film 25 is fixed to the fixing nip. In the part N, the outer periphery of the film guide 22 is rotated in the clockwise direction indicated by the arrow R25 while sliding closely in contact with the surface of the heater 20 at a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 26.

  Then, a recording material P having an unfixed toner image T formed and supported on the surface is introduced between the fixing film 25 and the pressure roller 26 in the fixing nip portion N, and is nipped and conveyed. In this nipping and conveying process, the unfixed toner image T on the recording material P is heated by the heater 20 through the fixing film 25 in the fixing nip portion N, and is fixed by the pressure of the fixing nip portion N.

  Here, there are the following problems in image quality that occur during fixing in both the heat roller system and the film heating system.

(1) A phenomenon in which the toner T on the recording material P is partially blown to the downstream side in the recording material conveyance direction immediately before the fixing nip introducing portion (hereinafter, rear toner scattering).
(2) A part of the toner T on the recording material P adheres to the fixing film 25 or the fixing roller side without being fixed, and when the portion to which the toner has adhered next contacts the recording material, Image failure (hereinafter referred to as offset) in which the toner on the fixing roller is transferred to the recording material side.
As a countermeasure for suppressing these phenomena, conventionally, a method of increasing the electrostatic adhesion force of the toner T to the recording material P has been tried.

  For example, the film heating type heating and fixing apparatus shown in FIG. 2 will be described as an example. A neutralizing means 33 such as a conductive roller grounded downstream of the fixing nip portion N in the recording material conveyance direction is provided. The discharging means 33 is configured to come into contact with the back side of the printing surface of the recording material P after passing through the fixing nip, and a safety circuit (not shown) is connected to a conductive portion (here, a primer layer) of the fixing film 25 by a bias power source 32. The recording material P is applied with a predetermined amount of a fixing bias having the same polarity as the toner T (minus polarity in this case) while at least the recording material P passes through the fixing nip portion N via the power supply means 31 such as a conductive brush. A charge having a polarity opposite to that of the bias applied from the grounding portion of the static elimination means 33 (here, plus polarity) is induced on the back surface of the printing surface of the recording material P via the resistance of P, and the induced plus charge is reversed. Method for fixing attract the toner T is sex on the recording material P has been conducted.

  The greater the amount of fixing bias applied, the greater the effect for suppressing the back toner scattering phenomenon. On the other hand, if the amount is too large, the offset tends to deteriorate. is there. This is because, due to the application of the fixing bias, a positive current having a polarity opposite to that of the toner T flows from the discharging means 33 through the recording material P to the fixing film 25 side. It is considered that T is inverted by this current and easily adheres to the fixing film 25 side. Therefore, if the fixing bias setting is optimized for the offset phenomenon, the rear toner scattering phenomenon occurs remarkably. On the other hand, if the fixing bias setting is optimized for the rear toner scattering phenomenon, the offset phenomenon occurs remarkably. End up. Therefore, the fixing bias application amount is set to a balanced value between the offset level and the rear toner scattering level.

  In recent years, an image forming apparatus such as an electrophotographic printer using the heat fixing apparatus as described above has been strongly demanded to improve the image quality and increase the printing speed. In order to realize high speed, for example, in the film heating type heat fixing device 11, the output of the main motor is increased to increase the rotation speed of the pressure roller 26, the fixing film 25, etc. In order to supply sufficient heat energy to the recording material P whose residence time has been shortened, the thermal conductivity is increased by increasing the fixing temperature, expanding the fixing nip N, and changing the material of the substrate of the heater 20 and the base layer of the fixing film 25. Improvements such as up are implemented. Specifically, the substrate of the heater 20 is changed from aluminum oxide to aluminum nitride, and the base layer of the fixing film 25 is changed from polyimide to a metal such as SUS to a material having higher thermal conductivity.

However, these improvements for increasing the printing speed increase the amount of heat energy supplied per unit time to the recording material P in the fixing nip N, and also increase the conveying speed of the recording material P. In this direction, the above-described rear toner scattering phenomenon is greatly deteriorated. For this reason, the application amount of the fixing bias necessary for suppressing the rear toner scattering phenomenon has increased, and it has become very difficult to balance the rear toner scattering level and the offset level only by adjusting the application amount of the fixing bias. Further, when a metal base layer is used for the fixing film 25, the base layer becomes a conductor. Therefore, when the resistance unevenness in the release layer is large, the potential leaks from a location where the resistance of the release layer is low toward the base layer that is the conductor. It becomes easy to do. In particular, when the release layer has high resistance and a large fixing bias is applied, the toner T is attracted and fixed to the recording material P at the fixing nip portion N due to the occurrence of a locally low portion in the surface potential of the release layer. Since a portion where charge is not induced partially occurs, as shown in FIG. 8, there is a case where a belt-like portion where the back toner scatters in the direction perpendicular to the conveyance direction of the recording material P is generated as shown in FIG. .
JP 2002-40856 A JP 11-119578 A

  In order to solve such problems, attempts have been made to improve the fixing member configuration in the heat fixing apparatus.

  For example, for the purpose of preventing offset and tailing (backward scattering phenomenon here), medium resistance particles are dispersed in the release layer provided on the conductive layer of the fixing member, and the surface resistance of the release layer is reduced by volume. An example of a fixing device that lowers the resistance is proposed in JP-A-2002-40856. This is because by reducing the surface resistance of the release layer, potential unevenness on the surface of the release layer is eliminated and the potential can be controlled over the entire surface, thereby preventing offset. The volume resistance of the release layer is increased by applying a fixing bias to the fixing roller to generate a current through the recording material from the conveying roller provided to come into contact with the recording material after the fixing nip. In a system in which an electric field is generated between the back surface of the material, the potential difference between the fixing roller and the back surface of the recording material is increased, and the electric field that attracts the toner image to the recording material side also increases, so that tailing can be prevented.

  As another example of the method for lowering the surface resistance of the release layer below the volume resistance, an insulating layer and a middle resistance release layer are provided on the conductive layer of the fixing member, so that unfixed toner is applied on the recording material. Japanese Patent Laid-Open No. 11-119578 proposes an example of a fixing device that prevents offset due to leakage of held charges and offset due to peeling discharge between the fixing member and the recording material after the fixing nip.

  However, the conventional method described above has the following problems.

  In the method in which medium resistance particles are dispersed in the release layer so that the surface resistance of the release layer is lower than the volume resistance, the dispersion state of the medium resistance particles in the release layer is very important. Controlling the dispersion of medium resistance particles, etc. so that the surface resistance and volume resistance fall within the desired range over the entire area, that is, reducing the surface resistance only while keeping the volume resistance high is very important considering mass productivity. Difficult and unrealistic. In particular, the belt-like rear toner scattering phenomenon, which is likely to occur when a conductor is used for the base layer, is difficult to suppress by this method because the unevenness of the volume resistance of the release layer needs to be reduced over the entire area. .

  In addition, a method in which an insulating layer and a middle-resistance release layer are provided on a conductive layer so that the surface resistance of the release layer is lower than the volume resistance is obtained by giving each layer a role on the two conductive layers. Since the resistance is adjusted, it is easy to manage the surface resistance and volume resistance within a desired range over the entire area of the release layer. However, this method prevents the flow of charge from the release layer to the conductive layer by increasing the insulation layer and increasing the pressure resistance so that the charge that holds unfixed toner on the recording material does not leak to the fixing member. Therefore, unlike the conventional example shown in FIG. 2, it is impossible to induce a charge having a polarity opposite to that of the toner on the back surface of the printing surface of the recording material by applying a fixing bias. That is, since it is not possible to introduce a method such as applying a fixing bias to further increase the toner holding force on the recording material, it is difficult to suppress the rear toner scattering phenomenon that deteriorates in proportion to the printing speed. Furthermore, as in this method, if the release layer is provided on the insulating layer and floats, the release layer is charged to the opposite polarity to the toner by repeatedly passing the recording material that has received the transfer electric field. And offset may be worsened.

  Accordingly, the present invention solves the above-described problems, and the object of the present invention is to provide a fixing device that can obtain a good image with a good balance between the offset phenomenon and the rear toner scattering phenomenon even when the printing speed is increased. It is to provide with stable quality.

  In order to solve the above-mentioned problems, the present invention has a rotating body including a heating body and a pressure member that presses the rotating body, and is undecided at a pressing nip portion of the rotating body and the pressing member. In the heat fixing apparatus for fixing the unfixed toner image on the recording material by heating and passing the recording material on which the toner image is formed, the rotating body includes a conductive layer having conductivity from the side of the heating body, a film thickness It consists of at least three layers of an intermediate layer of 1 to 6 μm and a surface layer having a lower resistance than the intermediate layer, an electrode A provided so as to be in contact with the conductive layer of the rotating body, and outside the pressure nip portion. A current path through the recording material is formed between the electrodes B provided in contact or non-contact with the recording material.

  In the invention, it is preferable that the electrode B is a discharging means provided on the downstream side of the pressure nip portion in the recording material conveyance direction.

  In the invention, it is preferable that the electrode B is a power feeding unit that applies a bias having a polarity opposite to that of the toner to the back surface of the printing surface of the recording material immediately before entering the pressure nip portion.

  In the present invention, the conductive layer of the rotating body is a flexible metal cylindrical element tube and has a thickness of 20 to 200 μm.

  In the present invention, the intermediate layer of the rotating body is a primer layer for bonding the conductive layer and the surface layer, and has an insulating property.

  According to the present invention, the surface layer of the rotating body is a release layer whose main component is a fluororesin and the resistance is adjusted by a filler, and the film thickness is 5 to 30 μm.

  Further, the invention is characterized in that the surface layer of the rotating body is provided only on the upper surface of the intermediate layer so as not to directly contact the conductive layer.

  As described above, according to the present invention, even if the printing speed is increased, a good image in which the offset phenomenon and the rear toner scattering phenomenon are balanced can be stably obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(1) Image forming apparatus M
FIG. 1 shows an image forming apparatus provided with a fixing device according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a laser beam printer as an example of an image forming apparatus.

  First, the configuration of a laser beam printer (hereinafter referred to as an image forming apparatus) will be described with reference to FIG.

  The image forming apparatus shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in the direction of the arrow R1 by a driving unit (not shown). Around the photosensitive drum 1, a charging roller (charging device) 2, an exposure unit 3, a developing device 4, a transfer roller (transfer device) 5, and a cleaning device 6 are disposed almost in order along the rotation direction. . A sheet feeding cassette 7 that stores a sheet-like recording material P such as paper is disposed below the apparatus main body M, and the sheet feeding roller 15 is sequentially arranged from the upstream side along the conveyance path of the recording material P. , A transport roller 8, a top sensor 9, a transport guide 10, a fixing device 11 according to the present invention, a paper discharge sensor 16, a transport roller 12, a paper discharge roller 13, and a paper discharge tray 14.

  Next, the operation of the image forming apparatus having the above configuration will be described.

  The photosensitive drum 1 that is rotationally driven in the direction of arrow R1 by a driving means (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by a charging roller 2. The photosensitive drum 1 after charging is subjected to image exposure L based on the image information by the exposure means 3 such as a laser optical system on the surface, and the charge of the exposed portion is removed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 4. The developing device 4 includes a developing roller 4a. A developing bias is applied to the developing roller 4a to attach toner to the electrostatic latent image on the photosensitive drum 1 and develop (develop) it as a toner image. The toner image is transferred to the recording material P such as paper by the transfer roller 5. The recording material P is stored in the paper feed cassette 7, fed by the paper feed roller 15, transported by the transport roller 8, and transferred between the photosensitive drum 1 and the transfer roller 5 via the top sensor 9. It is conveyed to the nip part. At this time, the leading edge of the recording material P is detected by the top sensor 9 and is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.

  The recording material P carrying the unfixed toner image on the surface by transfer is transported to the fixing device 11 along the transport guide 10, where the unfixed toner image is heated and pressurized and fixed on the surface of the recording material P. . The fixing device 11 will be described in detail later. The recording material P after the toner image is fixed is transported by the transport roller 12 and discharged onto the discharge tray 14 on the upper surface of the apparatus main body M by the discharge roller 13.

  On the other hand, after the toner image is transferred, the toner remaining on the surface without being transferred to the recording material P is removed by the cleaning blade 6a of the cleaning device 6 and used for the next image formation.

  By repeating the above operations, image formation can be performed one after another.

(2) Heat fixing device 11
Next, an example of the fixing device 11 according to the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view taken along the conveyance direction (arrow K direction) of the recording material P. A fixing device 11 shown in FIG. 2 is a pressure roller driving type heat fixing device using a flexible endless belt as a fixing film.

  The fixing device 11 includes a ceramic heater (hereinafter referred to as a heater) 20 as a heating body for heating toner, a fixing film 25 as a rotating body including the heater 20, and a pressure member in contact with the fixing film 25. The pressure roller 26 is configured as a main constituent member.

  The heater 20 and the pressure roller 26 are pressed against each other with the fixing film 25 interposed therebetween to form a fixing nip portion N. When the pressure roller 26 is rotationally driven in the counterclockwise direction indicated by the arrow R26, a rotational force acts on the fixing film 25 by the pressure frictional force between the pressure roller 26 and the fixing film 25 at the fixing nip portion N. The fixing film 25 is rotated in the clockwise direction indicated by an arrow R25 while the inner surface of the fixing film 25 slides in close contact with the downward surface of the heater 20.

  In a state where the pressure roller 26 is driven to rotate, the fixing film 25 is driven to rotate, and electric power is supplied to the heater 20 so that the heater 20 is heated to a predetermined temperature. The recording material P carrying the unfixed toner image T is introduced between the fixing film 25 and the pressure roller 26 in the fixing nip N, and the toner image carrying surface side of the recording material P in the fixing nip N is the fixing film 25. The fixing nip portion N is nipped and conveyed together with the fixing film 25 in close contact with the outer surface. In this nipping and conveying process, the heat of the heater 20 is applied to the recording material P through the fixing film 25, and the unfixed toner image T on the recording material P is heated and pressurized on the recording material P to be melted and fixed. . The recording material P that has passed through the fixing nip N is separated from the fixing film 25 by curvature.

(1) Heater 20
The heater 20 as a heating member is formed by sequentially forming a heating element obtained by printing a heating paste on a ceramic substrate and a glass coating layer for ensuring the protection and insulation of the heating element. Heat is generated by supplying a power-controlled AC current. As the material of the ceramic substrate, aluminum nitride, aluminum oxide or the like is used. A temperature control thermistor (temperature detection element) 21 is in contact with the back of the ceramic substrate. The heater 20 is long in the left-right direction perpendicular to the conveyance direction (arrow K direction) of the recording material P, and is longer than the width of the recording material P. The heater 20 is supported by a film guide 22 attached to the apparatus main body M. The film guide 22 is a member formed in a semicircular shape with a heat-resistant resin, and also functions as a guide member for guiding the rotation of the fixing film 25 described later.

(2) Fixing film 25
The endless belt-shaped fixing film 25 is externally fitted to the semicircular arc-shaped film guide 22 that supports the above-described heater 20 in a form (with no tension applied) with a sufficient circumferential length. The fixing film 25 is pressed against the heater 20 by a pressure roller 26 which will be described later, whereby the back surface of the fixing film 25 is brought into contact with the lower surface of the heater 20. The fixing film 25 is configured to rotate in the arrow R25 direction as the recording material P is conveyed in the arrow K direction by the rotation of the pressure roller 26 in the arrow R26 direction. Note that both left and right end portions of the fixing film 25 are regulated by a flange member (not shown) that is fitted to the film guide 22 so that the fixing film 25 does not come off in the longitudinal direction of the heater 20. Further, grease is applied to the inner surface of the fixing film 25 in order to reduce the sliding resistance between the heater 20 and the heater holder 22.

  The fixing film 25 is formed of a cylindrical element tube (base layer) 25a made of pure metal or alloy having heat resistance and high thermal conductivity such as SUS, Al, Ni, Cu, Zn, etc. as shown in the layer configuration model diagram of FIG. This is a metal sleeve whose surface is coated with a release layer 25c in which a filler for resistance adjustment is mixed into PTFE, PFA, FEP or the like via a primer layer 25b. As a coating method, for example, after cleaning the surface of the base layer 25a, the primer layer 25b as an adhesive and then the release layer 25c are dipped.

・ Base layer (cylindrical tube) 25a
The thickness of the base layer 25a is preferably 20 μm or more from the viewpoint of strength and durability, and the film thickness is preferably 200 μm or less in order to reduce the heat capacity and enable quick start. Further, since the base layer 25a is a metal and a conductor, the resistance is very small.

・ Primer layer 25b
The primer layer 25b is adjusted so that the base layer 25a and the release layer 25c are bonded and has an insulating property. However, even though it has insulating properties, it is a layer that is thinly coated by dipping or the like, and therefore it is possible to pass a current between the base layer 25a and the release layer 25c by pinholes due to coating unevenness. Further, the film thickness is 1 μm or more from the viewpoint of coating unevenness and adhesiveness, and the heat capacity is reduced to enable quick start, and the charge can be transferred through the primer layer 25b. The thickness is preferably 6 μm or less so as not to be charged up.

  The primer layer 25b may be adjusted to a high resistance by mixing a resistance adjusting filler. However, in order to make the volume resistance as high as possible as a fixing film and to make the film thickness as thin as possible for quick start characteristics. Is preferably insulative.

-Release layer 25c
The release layer 25c has a releasability so that toner and paper dust do not adhere, and a resistance is adjusted by mixing a resistance adjusting filler. The resistance value of the fixing film is lower than that of the primer layer 25b described above in order to make the surface resistance lower than the volume resistance. The film thickness is preferably 5 μm or more from the viewpoint of surface wear due to durability, and 20 μm or less in order to reduce the heat capacity and enable quick start.

  Here, the resistance adjusting filler includes, for example, a conductive agent such as carbon black, a charge control agent, a metal oxide, and the like, but any material or shape may be used as long as it can adjust the resistance.

  Further, as shown in FIG. 4, the fixing film 25 exposes a base layer (cylindrical element tube) 25a on a part of the surface of the fixing film and contacts with a power supply means 31 such as a conductive brush in order to apply a fixing bias described later. ing. Furthermore, since the resistance of the release layer 25c is lower than that of the primer layer 25b, only the upper surface portion of the primer layer 25b is provided so that the release layer 25c and the base layer 25a are not in direct contact as shown in FIG. The release layer 25c is coated.

In this embodiment, as an example, the base layer 25a is a SUS film having a thickness of 45 μm, the primer layer 25b is an insulating film having a thickness of 4 μm, and the release layer 25c is a medium resistance film having a thickness of 12 μm. 10 ⁷ Ω and a volume resistance of 10 ¹¹ Ωcm were used.

(3) Pressure roller 26
The pressure roller 26 has an insulating layer made of a fluororesin such as PFA, PTFE, or FEP with an elastic layer 26b of a heat-resistant rubber such as silicone rubber or a foamed sponge elastic layer sandwiched between the outer peripheral surface of a metal cored bar 26a. The fixing film 25 is pressed against the heater 20 from below by the outer peripheral surface of the releasing layer 26c, and a fixing nip portion N is formed between the rotating member and the fixing film 25. . If the width (nip width) in the rotation direction of the pressure roller 26 in the fixing nip portion N is a, the nip width a is such that the toner on the recording material P can be suitably heated and pressed. Is set. In order to suppress the charge-up on the surface of the insulating release layer 26c, it is preferable that the elastic layer 26b is made conductive by mixing a conductive member such as carbon black and the cored bar is grounded.

(4) Static elimination means 33
Static elimination means such as a grounded conductive roller at a position in contact with the back surface of the printing surface of the recording material P that has passed through the fixing nip N on the downstream side in the conveyance direction (arrow K direction) of the recording material P in the fixing nip N. 33 is provided. As a form of the static elimination means 33, if it has electroconductivity, forms, such as a brush and a guide, may be sufficient.

(5) Fixing bias applying means The toner T is brought into contact with the base layer 25a partially exposed on the surface of the fixing film 25 from a bias power source 32 through a safety circuit (not shown) and a power supply means 31 such as a conductive brush. A fixing bias having the same polarity is applied to the fixing film 25. The fixing bias is applied at least while the recording material P is in contact with the fixing film 25.

  Here, since a predetermined potential difference is generated between the static elimination means 33 that is electrically grounded and the voltage applied as a fixing bias to the base layer 25 a of the fixing film 25, the recording material P is separated from the fixing nip portion N. While in contact with the charge eliminating means 33, a current path is formed between the charge eliminating means 33 and the base layer 25 a of the fixing film 25.

(6) Equivalent Circuit FIG. 5 is a diagram showing a main part of the heat fixing device 11 of this embodiment, and fixing when a DC bias having the same polarity as the toner is applied from the bias power source 32 to the base layer 25a of the fixing film 25 This is an example of an equivalent circuit when a recording material P on which a toner image of unfixed toner T is formed enters a nip portion.

  A bias is applied to the base layer 25a of the fixing film 25 by bringing a power supply means 31 such as a conductive brush into contact with the base layer 25a as shown in FIG. 2, and a protective resistance is provided between the output end of the bias power source 32 and the base layer 25a. A resistor R1 is connected. R2 is the contact resistance between the power feeding means 31 and the base layer 25a and the resistance to the vicinity of the fixing nip portion of the base layer 25a. However, since the base layer 25a is a conductor, the resistance of the base layer 25a can be ignored. R3 is the resistance of the primer layer 25b of the fixing film 25, and R4 is the resistance of the release layer 25c.

  In the region of Pn near the fixing nip portion, the recording material P such as paper is heated and water vapor is generated, so that the electrical resistance of the Pn portion is reduced and compared to other resistors connected in series on the equivalent circuit. It becomes so small that it can be ignored, and can be regarded as equipotential in the Pn region. On the other hand, since the moisture content of the paper after passing through the fixing nip is reduced, the resistance value cannot be ignored, and the resistance to the static elimination means 33 that is electrically grounded is R5. Further, the contact resistance with the recording material P of the static elimination means 33 such as a conductive roller and the resistance to the ground as shown in FIG.

  In the equivalent circuit as described above, when the voltage V is applied to the base layer 25a of the fixing film 25 from the bias power source 32, the voltage applied to the base layer 25a of the fixing film 25 near the fixing nip due to the voltage drop due to the resistors R1 and R2. The potential Vn is slightly lower than V. Since the current i flows between the potential Vn of the base layer 25a of the fixing film 25 and the ground potential V0 via the primer layer 25b, the release layer 25c, the recording material P, and the static elimination means 33, the base layer 25a and the recording material An electric field E is generated between the equipotential portions Pn of P. This electric field exerts a binding force F = q · E on the recording material P in proportion to the charge amount q of the toner T on the toner image of the unfixed toner T, so that image defects such as a rear toner scattering phenomenon can be suppressed. It becomes possible.

(7) Suppression of Rear Toner Scattering Phenomenon and Offset Phenomenon As described above, in order to increase the effect of suppressing the rear toner scattering phenomenon, the restraining force F of the toner T on the recording material P may be increased. Since the restraining force F is proportional to the electric field E, the effect of suppressing the rear toner scattering phenomenon can be increased by increasing the combined resistance (R3 + R4) of the primer layer 25b and the release layer 25c.

  On the other hand, in order to suppress the offset phenomenon, as described above, it is important to uniformly control the potential over the entire surface of the release layer 25c. That is, the effect of suppressing the offset phenomenon can be increased by reducing the surface resistance (R4) of the release layer 25c so as to reduce the surface potential unevenness. Further, the resistance R3 of the primer layer 25b should not be too large in order to suppress the offset phenomenon due to the charge-up of the release layer 25c.

  For these reasons, the fixing film 25 in this embodiment has a surface resistance smaller than the volume resistance, that is, the surface potential unevenness is reduced (R4) in a state where the electric field E is increased (R3 is large). Therefore, both the rear toner scattering phenomenon and the offset phenomenon can be suppressed.

  Further, the belt-like rear toner scattering phenomenon as shown in FIG. 8 is also achieved by providing a primer layer 25b (R3) having a lower surface resistance (R4) of the release layer 25c and a higher resistance in the lower layer. Occurrence can be prevented because leakage from the mold layer 25c toward the base layer 25a becomes difficult.

(3) Comparative experiment 1
In this example, the base layer 25a has a SUS film thickness of 45 μm, the primer layer 25b has an insulating film thickness of 4 μm, the release layer 25c has a medium resistance film thickness of 12 μm, a surface resistance of 10 ⁷ Ω, and a volume resistance of 10 ^11. When the fixing film 25 of Ωcm is used, and as a conventional example, the base layer 25a has a SUS film thickness of 45 μm, the primer layer 25b has a resistance of 10 ⁶ Ω of 4 μm, and the release layer 25c has a resistance of 10 ¹¹ Ω of 12 μm. In the case of using the fixing film 25 in which the surface resistance and the volume resistance are not particularly controlled, a comparison experiment was performed to compare the level of the rear toner scattering phenomenon and the offset phenomenon by changing the amount of fixing via applied to the base layer 25a. The results are shown in Table 1, since the image forming apparatus with a process speed of 250 mm / sec was used.

  In the table, ◯ indicates an OK level, Δ indicates a level having no practical problem, and × indicates an NG level. The rear toner splattering phenomenon is caused by printing five patterns with lines arranged in a direction perpendicular to the paper transport direction on plain paper that has been left for 24 hours or more in an environment of 23 ° C / 60% RH. Observe the toner scattering state (including the belt-like rear toner scattering), and the offset phenomenon is normal paper that has been left in a 23 ° C / 60% RH environment for 24 hours or more. Printed 10 sheets of solid white patterns, and evaluated by observing the offset state of the character pattern to the solid white part.

この結果から、定着バイアス印加量を増加することにより、従来例１は後方トナー飛び散り現象は良化する一方、帯状の後方トナー飛び散り現象の発生やオフセット現象の悪化が起こったが、本実施例では後方トナー飛び散り現象が良化するとともに帯状の後方トナー飛び散り現象も発生せず、オフセット現象に対するマージンも拡大したことが確認できた。

From this result, by increasing the fixing bias application amount, the conventional example 1 improved the rear toner scattering phenomenon, while the occurrence of the belt-like rear toner scattering phenomenon and the deterioration of the offset phenomenon occurred. It was confirmed that the rear toner scattering phenomenon was improved, the belt-like rear toner scattering phenomenon did not occur, and the margin for the offset phenomenon was increased.

(4) Comparative experiment 2
Next, in this embodiment, the base layer 25a has an SUS film thickness of 45 [mu] m, the primer layer 25b has an insulating film thickness of 4 [mu] m, and the release layer 25c has an insulating property against the medium resistance film thickness of 12 [mu] m. In the case where only the thickness of the primer layer 25b is changed (6, 7, 10 μm), the amount of fixing via applied to the base layer 25a is changed to compare the level of the rear toner scattering phenomenon and the offset phenomenon, and the process speed Was performed using an image forming apparatus having a thickness of 250 mm / sec.

  In the table, ◯ indicates an OK level, Δ indicates a level having no practical problem, and × indicates an NG level. The rear toner splattering phenomenon is caused by printing five patterns with lines arranged in a direction perpendicular to the paper transport direction on plain paper that has been left for 24 hours or more in an environment of 23 ° C / 60% RH. Observe the toner splattering state on the paper, and the offset phenomenon is 10 sheets of plain paper that is left for 24 hours or more in an environment of 23 ° C / 60% RH, with 100mm at the leading edge and solid white at the trailing edge. It was printed and evaluated by observing the offset state of the character pattern to the solid white part.

この結果から、絶縁性のプライマー層２５ｂの膜厚を厚く、すなわち抵抗を大きくすることにより、後方トナー飛び散り現象の抑制効果は大きくなるが、オフセット現象は悪化することが確認できた。これは、絶縁性のプライマー層２５ｂの膜厚を厚くすることにより、プライマー層２５ｂを介しての電荷の移動がしにくく、転写電界を受けた記録材を繰返し通紙することによって、離型層２５ｃがトナーと逆極性にチャージアップされるため、オフセット現象が悪化してしまうのである。

From this result, it was confirmed that by increasing the film thickness of the insulating primer layer 25b, that is, by increasing the resistance, the effect of suppressing the rear toner scattering phenomenon increases, but the offset phenomenon worsens. This is because by increasing the film thickness of the insulating primer layer 25b, it is difficult for the charge to move through the primer layer 25b, and by repeatedly passing the recording material subjected to the transfer electric field, the release layer Since 25c is charged up to the opposite polarity to the toner, the offset phenomenon becomes worse.

  It was also confirmed that the offset phenomenon worsened as the fixing bias application amount increased. This is because an increase in the amount of bias applied increases the charge of the opposite polarity to the applied bias induced on the surface of the release layer 25c, and as described above, the transfer of charge from the release layer 25c is difficult and the surface potential is increased. Is difficult to attenuate, and the offset phenomenon is worsened.

  From the above, in the present invention, by setting the thickness of the insulating primer layer 25b to 6 μm or less, it is possible to obtain a good image in which the offset phenomenon and the rear toner scattering phenomenon are balanced.

  Next, as a second embodiment, FIG. 6 shows another example of a method of attracting and fixing the toner T to the recording material P by passing an electric current through the recording material P. In addition, the part which has the same function as Example 1 mentioned above uses the same code | symbol, and uses description.

Bias application from the power supply means 41 before the fixing nip N The reverse polarity of the toner T from the bias power source 42 is applied to the back surface of the surface of the recording material P before entering the fixing nip N where the unfixed toner image T is formed. In order to apply a bias having a positive polarity (here, positive polarity), a power feeding unit 41 is provided on the upstream side in the conveyance direction of the recording material in the fixing nip N. If a bias can be applied to the recording material P, the presence or absence of contact with the recording material does not matter, but the unfixed toner image P formed on the recording material P may be disturbed by an impact due to contact with the power supply means. The power supply means 41 such as a non-contact type charging needle shown in FIG.

  Since a bias is applied from the power supply means 41 in front of the fixing nip N, the application of the fixing bias to the fixing film 25 described in the first embodiment is not an essential requirement. Therefore, in this embodiment, it does not matter whether or not a fixing bias is applied to the fixing film 25. However, when the application of the fixing bias is eliminated, the base layer partially exposed on the surface of the fixing film 25 is brought into contact with the static eliminating means 43 such as a grounded conductive brush as shown in FIG. Is electrically grounded.

  Here, since a predetermined potential difference is generated between the base layer of the fixing film 25 that is electrically grounded and the voltage applied as a bias from the power feeding means 41 facing the recording material P, the recording material P is fed. While facing the means 41 and in contact with the fixing nip portion N, a current path is formed between the base layer of the fixing film 25 and the power supply means 41.

Equivalent Circuit FIG. 7 is a diagram showing a main part of the heat fixing device 11 of this embodiment. After the recording material P on which the unfixed toner image T is formed is applied with a bias from the opposing power supply means 41, It is an example of an equivalent circuit when entering the fixing nip portion.

  The bias application to the recording material P is performed in a non-contact manner as shown in FIG. 6 from a bias power source 42 via a power supply means 41 such as a charging needle. R1 is a spatial resistance to the recording material P facing through the power feeding means 41, and R2 is a resistance from the position where the bias is applied from the power feeding means facing the recording material P to the vicinity of the fixing nip portion. In the region of Pn near the fixing nip portion, the recording material P such as paper is heated and water vapor is generated, so that the electrical resistance of the Pn portion is reduced and compared to other resistors connected in series on the equivalent circuit. It becomes so small that it can be ignored, and can be regarded as equipotential in the Pn region.

  R3 is the resistance of the release layer 25c of the fixing film 25, and R4 is the resistance of the primer layer 25b. R5 is the resistance from the vicinity of the fixing nip portion of the base layer 25a to the static elimination means 43, the contact resistance between the base layer 25a and the static elimination means 43, and the resistance to the ground, but the resistance of the base layer 25a is ignored because the base layer 25a is a conductor. it can.

  In the above equivalent circuit, when the voltage V is applied from the bias power source 42 to the back surface of the recording material P, the potential near the fixing nip portion of the recording material P is lower than the applied voltage V due to the voltage drop due to the resistors R1 and R2. Vn. Since the current i flows between the potential Vn of the recording material P and the ground potential V0 via the release layer 25c, the primer layer 25b, the base layer 25a, and the charge removal means 43, the equipotential of the base layer 25a and the recording material P An electric field E is generated between the parts Pn. This electric field exerts a binding force F = q · E on the recording material P in proportion to the charge amount q of the toner T on the toner image of the unfixed toner T, so that image defects such as a rear toner scattering phenomenon can be suppressed. It becomes possible.

O Suppression of rear toner scattering phenomenon and offset phenomenon As described above, in order to increase the suppression effect of the rear toner scattering phenomenon, the restraining force F of the toner T on the recording material P may be increased. Since the binding force F is proportional to the electric field E, the effect of suppressing the rear toner scattering phenomenon can be increased by increasing the combined resistance (R3 + R4) of the release layer 25c and the primer layer 25b.

  On the other hand, in order to suppress the offset phenomenon, as described above, it is important to uniformly control the potential over the entire surface of the release layer 25c. That is, the effect of suppressing the offset phenomenon can be increased by reducing the surface resistance (R3) of the release layer 25c so as to reduce the surface potential unevenness. Further, the resistance R4 of the primer layer 25b must not be too large in order to suppress the offset phenomenon due to the charge-up of the release layer 25c.

  For these reasons, the fixing film 25 in this embodiment has a surface resistance smaller than the volume resistance, that is, the surface potential unevenness is reduced (R3) in a state where the electric field E is large (R4 is large). Therefore, both the rear toner scattering phenomenon and the offset phenomenon can be suppressed.

  Further, the belt-like rear toner scattering phenomenon as shown in FIG. 8 is also achieved by providing a primer layer 25b (R4) having a lower surface resistance (R3) of the release layer 25c and a higher resistance below the release layer 25c. Occurrence can be prevented because leakage from the mold layer 25c toward the base layer 25a becomes difficult.

  That is, in the configuration of the second embodiment, the same effect as that of the first embodiment can be obtained.

  As described above, as described in the first and second embodiments, the bias applying method is different in the heat fixing apparatus in which the current is supplied to the recording material P to attract and fix the toner T to the recording material P. However, if the fixing film of the present invention is used, the image margin against the rear toner scattering phenomenon and the offset phenomenon is enlarged, and a good image with good balance can be obtained.

(Other)
○ The heating and fixing device of the film heating system is a rotating body driving system for pressurization, but an apparatus of a system in which a driving roller is provided on the inner peripheral surface of the endless fixing film and the film is driven while applying tension. It may be an apparatus of a system in which a film is rolled into a web with a roll end and this is driven to travel.

  In the present invention, the heat fixing device is not limited to the film heating method, but the image on the recording material can be transferred by sandwiching and conveying the recording material carrying the image at the nip between the heating member and the pressure member, such as a heat roller method. Any image heating apparatus may be used.

  ○ The heater is not limited to ceramic heaters. For example, an electromagnetic induction heat generating member such as an iron plate may be used. By using an electromagnetic induction heat generating member such as an iron plate as a heater, this is disposed at the position of the fixing nip portion, and a high frequency magnetic field generated by an electromagnetic coil and a magnetic core as an alternating magnetic flux generating means is applied thereto. An apparatus configuration that generates heat can also be used. Also, the film itself as the moving member can be made into an electromagnetic induction heat generating member so as to generate heat by the alternating magnetic flux generating means.

  The heat fixing device of the present invention is not only a fixing device that heat-fixes an unfixed image as a permanent image on a recording material, but also a heating device that presupposes an unfixed image on a recording material, and a recording material carrying an image. A heating device that modifies image surface properties such as gloss by reheating is also included.

  The image forming method of the image forming apparatus is not limited to the electrophotographic method, and may be an electrostatic recording method, a magnetic recording method, or the like, or may be a transfer method or a direct method.

1 is a cross-sectional view of an electrophotographic image forming apparatus in a first embodiment of the present invention. It is sectional drawing of the heat fixing apparatus in 1st Example of this invention. It is a layer structure model figure of the fixing film in the 1st example of the present invention. It is a schematic diagram of the base layer exposure part of the fixing film in 1st Example of this invention. FIG. 3 is an equivalent circuit diagram in the vicinity of the fixing nip portion in the first embodiment of the present invention. It is sectional drawing of the heat fixing apparatus in 2nd Example of this invention. FIG. 6 is an equivalent circuit diagram in the vicinity of a fixing nip portion in a second embodiment of the present invention. 6 is an image of a back toner scattering phenomenon that occurs in a belt shape.

Explanation of symbols

1 Image carrier (drum)
DESCRIPTION OF SYMBOLS 11 Fixing device 20 Heater 21 Thermistor 22 Film guide 25 Fixing film 26 Pressure roller 31, 41 Power supply means 32, 42 Bias power supply 33, 43 Static elimination means N Fixing nip part

Claims (7)

A rotating body including a heating body, and a pressure member that presses the rotating body, and heats a recording material on which an unfixed toner image is formed at a pressure nip portion between the rotating body and the pressing member; In a heat fixing device for fixing the unfixed toner image on a recording material by passing it through,
The rotating body includes at least three layers of a conductive layer having conductivity from the heating body side, an intermediate layer having a thickness of 1 to 6 μm, and a surface layer having a lower resistance than the intermediate layer,
An electrode A provided in contact with the conductive layer of the rotating body;
Between the electrodes B provided in contact or non-contact with the recording material outside the pressure nip portion,
A heat-fixing apparatus, wherein a current path through a recording material is formed.   The heat fixing apparatus according to claim 1, wherein the electrode B is a discharging unit provided on the downstream side of the pressure nip portion in the recording material conveyance direction.   2. The heat fixing device according to claim 1, wherein the electrode B is a power supply unit that applies a bias having a polarity opposite to that of the toner to the back surface of the printing surface of the recording material immediately before entering the pressure nip portion. .   The heat fixing apparatus according to claim 1, wherein the conductive layer of the rotating body is a flexible metal cylindrical element tube and has a thickness of 20 to 200 μm.   The heat fixing apparatus according to claim 1, wherein the intermediate layer of the rotating body is a primer layer that bonds the conductive layer and the surface layer, and has an insulating property.   The heating layer according to claim 1, wherein the surface layer of the rotating body is a release layer whose main component is a fluororesin and the resistance is adjusted by a filler, and the film thickness is 5 to 30 μm. Fixing device.   The heat fixing apparatus according to claim 1, wherein the surface layer of the rotating body is provided only on the upper surface portion of the intermediate layer so as not to directly contact the conductive layer.

Images