JP6740044B2 - Conductive elastic member and image heating device - Google Patents

Description

The present invention relates to a conductive elastic member used in an image heating device and an image heating device. This image heating device can be used as a fixing device or the like in an image forming apparatus such as a copying machine such as an electrophotographic system, a printer, a fax machine, or a multi-function machine thereof.

Conventionally, in the image forming apparatus as described above, the unfixed toner image formed and carried on the recording material (hereinafter, referred to as paper or paper) is heated by the image forming process unit so as to correspond to the target image information. A film heating type device has been put into practical use as a fixing device for fixing.

In this fixing device, a fixing film (hereinafter, referred to as a film) as a heating member is pressed and closely attached to a heater (heating body) by a pressure member to run. Then, the paper is introduced into a pressure contact nip portion (fixing nip portion) formed by a heater and a pressure member with the film sandwiched between them, and the paper is brought into close contact with the film and passed through the fixing nip portion together with the film. Thereby, the heat of the heater is applied to the paper through the film to heat and fix the unfixed toner image on the paper surface.

In a film heating type fixing device, particularly when a dry paper having high electric resistance is passed through, the film surface may be charged with a polarity opposite to that of the toner due to friction between the paper and the film. At this time, when the paper carrying the toner image is passed, the electrostatic holding force of the paper against the toner is reduced, so that a phenomenon (electrostatic offset) in which the unfixed toner is transferred to the film side may occur.

In order to prevent this electrostatic offset, Patent Document 1 discloses a conductive elastic body (conductive elastic body) provided on a core metal of a pressure roller as a driving rotary member by exposing a conductive surface in a part of the film. (Member), the film and the pressure roller are brought into contact with each other at a pressure contact nip portion. Then, a structure is disclosed in which the surface of the film is prevented from being charged by dropping the core metal to the ground.

JP-A-6-202509

In recent years, downsizing of image forming apparatuses has been desired. However, in the fixing device as described above, since the elastic layer of the pressure roller and the conductive elastic body are arranged on the same core metal, the pressure roller is further reduced in size and energy saving. If the outer diameter of is reduced, the following problems occur.

That is, in reducing the outer diameter of the pressure roller, it is relatively easy to adjust the hardness of the elastic layer of the pressure roller to a low level to obtain the necessary nip width. However, when the conductive elastic body is solid, it is not easy to reduce the hardness because the amount is adjusted from the viewpoint of the amount and strength of the conductive filler for imparting conductivity.

When the conductive elastic body has a high hardness relative to the hardness of the pressure roller and is pressed and brought into close contact with the heating member side, a non-uniform contact state is formed in the longitudinal direction, and in the vicinity of the side where the conductive elastic body is mounted. Since the contact pressure at the nip portion is insufficient, it causes fixing failure.

On the other hand, although it is possible to reduce the hardness by using a foam such as conductive sponge rubber as the conductive elastic body and adjusting the foam diameter, the following points are required for a solid conductive elastic body. It doesn't reach.

First, when fixing to the core metal of the pressure roller, in the case of a solid conductive elastic body, optimize the outer diameter of the core metal of the installation portion of the conductive elastic body and the inner diameter of the conductive elastic body to tighten. It can be fixed by setting. However, on the other hand, a foam such as a conductive sponge rubber does not have a sufficient tightening force for fixing, and therefore adhesion is required for fixing with a core metal. At this time, since it is necessary to fix the conductive material after securing it, a conductive adhesive material is required, which leads to an increase in cost.

In addition, the function of this member is to secure and maintain conductivity, but if a foam is used, contact with an adjacent member and maintenance of conductivity will be limited to the wall portion of the foamed cell, so that conduction failure will occur. It tends to occur.

Further, since the foamed material is likely to be plastically strained (set), if the foamed material is left pressed for a long time in the fixing nip portion, the nip portion is unlikely to return to a perfect circular shape, which causes poor conduction.

It is an object of the present invention to solve the above-mentioned problems and further reduce the size and energy consumption of an image heating apparatus of this type, and at the same time, to secure stable fixability without image defects. A member and an image heating device are provided.

A typical configuration of the conductive elastic member according to the present invention for achieving the above object is to have a rotating body that has a conductive surface along at least a part of the circumferential direction and that heats a recording material carrying an image. A cored bar and an elastic layer formed in the shape of a roller around the cored bar, wherein the rotary member and the elastic member are pressed against each other against the elasticity of the elastic layer to contact the rotary member, and Used by being fitted to the cored bar in an image forming apparatus having an elastic roller forming a nip part for nipping and transporting a material, the nip part can be rotated together with the cored bar against the elasticity against the elasticity. Another annular conductive elastic member is characterized in that a plurality of through holes are provided in the annular surface in parallel with the thickness direction and in the circumferential direction of the annular surface.

Further, a typical configuration of the image heating apparatus according to the present invention for achieving the above-mentioned object is a rotating body that heats a recording material carrying an image, a cored bar and a roller-shaped outer periphery of the cored bar. An elastic roller that forms a nip portion between the rotating body and the rotating body by applying pressure against the elasticity of the elastic layer and contacting the rotating body. An image heating device for sandwiching and heating a recording material carrying a toner image, wherein the rotating body has a conductive surface along at least part of a circumferential direction, and the core has the nip portion. At an annular conductive elastic member which is in contact with the conductive surface and can rotate together with the cored bar against elasticity, the conductive elastic member being parallel to the annular surface in the thickness direction and having a circumference of the annular surface. A plurality of through holes are provided in the direction.

According to the present invention, it is possible to reduce the size of the apparatus and save energy, and also to secure stable fixability without image defects.

Structure explanatory drawing of the pressure roller and the conductive rubber ring of the fixing device in Embodiment 1. Schematic front view of the fixing device in Embodiment 1. Cutaway front view of the device (4)-(4) line cross-sectional schematic view of FIG. Illustration of layer structure of film Schematic diagram of an example of the image forming apparatus Structure explanatory drawing of conductive rubber ring of comparative example The figure which showed the deformation|transformation state of the conductive rubber ring in an Example. The figure which showed the deformation state of the conductive rubber ring in a comparative example. The figure which showed the displacement and stress of the conductive rubber ring in an Example and a comparative example. Diagram showing the difference in contact state caused by the difference in stress applied to the conductive rubber ring

<<Example 1>>
[Image forming device]
FIG. 6 is a schematic configuration diagram of an example of the image forming apparatus 100 in which the image heating device according to the present invention is mounted as the fixing device 113. The image forming apparatus 100 is a monochrome laser printer using an electrophotographic recording technique.

In the image forming apparatus 100, an image forming unit 101 that forms a toner image on a recording material (hereinafter, referred to as a sheet) S includes a drum-type electrophotographic photosensitive member (as an image carrier that is rotationally driven in a direction of an arrow ( Hereinafter, referred to as a drum) 102. Further, the image forming unit 101 is a charging device 103, a laser scanner 104, a developing device 105, a transfer device, which is arranged around the drum 102 in order along the drum rotation direction and serves as an electrophotographic process device that acts on the drum 102. It has a roller 106 and a drum cleaner 107. The laser scanner 104 is an exposure device that irradiates the drum 102 with the laser light L.

Since the electrophotographic forming principle and operation of the toner image on the drum 102 of the image forming unit 101 are well known, the description thereof will be omitted.

The sheet S stacked and contained in the cassette 108 is separated and fed by a sheet feeding roller 109 driven at a predetermined control timing, passes through a conveyance path 110, and a contact portion between the drum 102 and the transfer roller 106. Is transferred to the transfer nip portion 111. The sheet S on which the toner image has been transferred from the drum 102 side in the transfer nip portion 111 is conveyed to the fixing device 113 through the conveyance path 112 and undergoes heat fixing of the toner image. The image-formed sheet S that has exited the fixing device 113 is discharged to the discharge tray 116 by the transport rollers 115 through the transport path 114. A is the paper conveyance direction (recording material conveyance direction).

[Fixing device]
Regarding the fixing device 113 described below, the front side is the entrance side of the paper S, and the back side is the exit side of the paper P. Left and right are left or right when the device 113 is viewed from the front side. In this embodiment, the right side is one end side (driving side) and the left side is the other end side (non-driving side). The upstream side and the downstream side are the upstream side and the downstream side in the sheet conveyance direction A. Further, the axial direction of the pressure roller or the direction parallel thereto is defined as the longitudinal direction, and the direction orthogonal to this is defined as the lateral direction.

The fixing device 113 of this embodiment is a film (belt) heating type image heating device (OMF: on-demand fixing device) for the purpose of shortening the startup time and reducing power consumption. 2 is a schematic front view of the fixing device 113 according to the present embodiment, FIG. 3 is a schematic front view of a cutout of the fixing device 113, and FIG. 4 is an enlarged cross-sectional schematic view taken along the line (4)-(4) of FIG. Is.

The fixing device 113 is roughly divided into a film unit (belt unit) 120, a pressure roller 130 as a drive rotating body having elasticity, and a device frame body (chassis, housing) 140 accommodating them.

The film unit 120 includes a fixing film (hereinafter referred to as a film) 121 that is a flexible endless (cylindrical) rotatable belt that is loosely fitted to an internal assembly (internal member). Have. Inside the film 121, a heater (hereinafter referred to as a heater) 122 as a heating member, a heater holder (hereinafter referred to as a holder) 123 that is a holding member that holds the heater 122, and a stay 124 that supports the holder 123 are provided. It is arranged as an internal assembly.

Each of the heater 122, the holder 123, and the stay 124 is a member whose length is longer than the width (length) of the film 121, and one end side and the other end side respectively project outward from both ends of the film 121. Then, the flange members 125R and 125L on one end side and the other end side are fitted to the outer protruding portions 124a on one end side and the other end side of the stay 124, respectively. The flange members 125R and 125L are molded products made of heat-resistant resin having a symmetrical shape.

The movement of the film 121 in the width direction is restricted by the opposing flange surfaces (collar seats) 125a and 125a of the flange members 125R and 125L fitted to both ends of the stay 124, and the film 121 is loosened to the outside of the internal assemblies 122 to 124. Is fitted on.

(1) Film In the free state, the flexible film 121 in this embodiment has a substantially cylindrical shape (cylindrical shape) due to its elasticity, has an outer diameter of 20 mm, and has a multilayer structure in the thickness direction. ing. FIG. 5 is a schematic diagram of the layer structure of the film 121. As the layer structure, a cylindrical base layer 121a for maintaining the strength of the film 121, a conductive primer layer 121b provided on the outer peripheral surface of the base layer 121a, and a film surface provided on the outer side of the conductive primer layer 121b. And a release layer 121c for reducing dirt adhesion.

The material of the base layer 21a needs to have heat resistance because it receives the heat of the heater 122, and also needs strength to slide with the heater 122. Therefore, it is preferable to use a metal such as SUS (Stainless Used Steel: stainless steel) or nickel, or a heat resistant resin such as polyimide. Since metal has a higher strength than resin and can be thinned, and has a high thermal conductivity, the heat of the heater 122 is easily transferred to the surface of the film 21. On the other hand, since resin has a smaller specific gravity than metal, it has an advantage that it has a small heat capacity and is easily heated. Further, the resin can be molded at low cost because a thin film can be molded by coating molding.

In this example, a polyimide resin was used as the material of the base layer 121a of the film 121, and a carbon-based filler was added to improve the thermal conductivity and strength. The thinner the base layer 121a, the easier it is to transfer the heat of the heater 122 to the surface of the film 121, but the strength is lowered, so that the thickness is preferably about 20 μm to 100 μm.

The conductive primer layer 121b is made of a polyimide resin or a fluororesin, and carbon or the like is added to reduce the resistance. When the paper is passed through the fixing device 113, a conductive layer exposed portion 121d, which is an exposed portion of the conductive primer layer 121b, which is annularly disposed on the other end side of the film 121, is disposed on the pressure roller 130 side. It is grounded via a ring-shaped conductive rubber ring 135 which is a conductive elastic body. This stabilizes the potential of the film 121. This will be described later.

As the material of the release layer 121c, it is preferable to use a fluororesin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), or tetrafluoroethylene-hexafluoropropylene resin (FEP). In this embodiment, PFA, which has excellent releasability and heat resistance, is used among the fluororesins, the conductive material is dispersed, and the resistance is moderate.

The release layer 121c may be formed by coating a tube, but may be coated on the surface with a paint. In this example, the release layer 121c was formed by a coating excellent in thin molding. The thinner the release layer 121c, the easier it is to transfer the heat of the heater 122 to the surface of the film 121. However, if the release layer 121c is too thin, the durability is lowered.

Since the conductive rubber ring 135 comes into contact with the conductive primer layer 121b for electrical conduction, the release layer 121c is not formed in the longitudinal end 5 mm width on the other end side of the film 121, and the conductive primer layer is formed in the film circumferential direction. 121b forms a conductive layer exposed portion 121d which is annularly exposed.

(2) Heater The heater 122 of the present embodiment is a general heater used in a film heating type heating device, and is one in which a resistance heating element is provided in series on a ceramic substrate.

More specifically, the heater 122 has a heat-resistant insulating substrate having good thermal conductivity such as alumina or aluminum nitride. The surface of this substrate has an electric resistance layer having a thickness of about 10 μm and a width of 1 to 3 mm, which is made of an electric resistance material such as Ag/Pd (silver palladium) and is applied by screen printing or the like. Further, it has a protective layer made of glass or fluororesin coated on the electric resistance layer. A thermistor 126 as a temperature detecting means is arranged on the back surface of the heater 122.

The heater 122 receives power supply from a triac 151 as an energization control unit controlled by a control unit (control circuit unit: CPU) 150 via an electrical connector (not shown) so that a predetermined effective full-length area of the resistance heating element is generated. Generates abrupt heat. The temperature of the heater 122 is sent to the controller 150 as an output signal (temperature detection signal) of the thermistor 126 through the A/D converter 152.

The controller 150 controls the temperature of the heater 122 by controlling the electric power supplied to the heater 122 by the triac 151 by phase control or wave number control based on the temperature detection signal. When the temperature is lower than a predetermined set temperature (target temperature), the heater 122 is heated, and when the temperature is higher than the set temperature, the triac 151 is controlled to lower the temperature, and the heater 122 is kept at the set temperature.

(3) Holder and stay The holder 123 is preferably made of a material having a low heat capacity so that the heat of the heater 122 is not easily taken. In this embodiment, a liquid crystal polymer (LCP) which is a heat resistant resin is used. The holder 123 is supported by an iron stay 124 from the side opposite to the heater 122 in order to have strength.

(4) Pressure roller The pressure roller 130 includes a core metal 131, a heat-resistant elastic layer 132 concentrically and integrally provided around the core metal 131 in a roller shape, and a separation layer formed on the elastic layer 132. The mold layer 133 is used.

The core metal 131 is a metal such as SUS having a diameter of 8.5 mm. The elastic layer 132 is a heat-resistant rubber such as insulating silicone rubber or fluororubber, or an elastic body formed by foaming heat-resistant rubber. The elastic layer 132 can be formed of a sponge-like elastic material having fine pores such as a sponge rubber layer and a foamed rubber layer.

A release layer 133 made of a fluororesin such as PFA, PTFE or FEP is formed on the outer periphery of the elastic layer 132. In this embodiment, as the pressure roller 130, an elastic roller having an outer diameter of the elastic roller portion of 14.0 mm and a hardness of 40° (Asker-C 600 g load) is used.

A drive gear 134 is concentrically and integrally arranged on one end side of the core metal 131 of the pressure roller 130. An annular conductive rubber ring 135, which is a conductive elastic body (conductive elastic member), is fitted to the other end of the core bar 131 so as to be adjacent to the elastic roller portion. The conductive rubber ring 135 will be described later.

(5) Pressure Configuration The film unit 120 and the pressure roller 130 are arranged in parallel with each other and are respectively disposed between the side plates 141L and 141R on one end side and the other end side of the apparatus housing 140. In the film unit 120, the flange members 125R and 125L on one end side and the other end side are positioned and fixed to the side plates 141L and 141R, respectively, and fixedly supported. Therefore, the heater 122, the holder 123, and the stay 124, which are the internal assembly of the film unit 20, are also fixed and supported between the side plates 141L and 141R.

The pressure roller 130 is rotatably supported at one end side and the other end side of the core bar 131 via bearing members 142 with respect to the side plates 141L and 141R. The heater 122 of the film unit 120 faces the pressure roller 130 via the film 121. The bearing members 142 on the one end side and the other end side are engaged with the guide slit portions 142a, 142a formed on the side plates 141R, 141L on the respective sides.

The guide slit portions 142a, 142a respectively slide and guide the bearing member 142 in a direction toward the film unit 120 and a direction away from the film unit 120. Therefore, the pressure roller 130 as a whole has a degree of freedom capable of moving between the side plates 141L and 141R along the guide slit portions 142a and 142a in a direction toward and away from the film unit 120.

A pressure spring 144R is compressed between the bearing member 142 on the one end side and the spring receiving seat 143R on the one end side of the device frame 140. Similarly, a pressure spring 144L is contracted between the bearing member 142 on the other end side and the spring receiving seat 143L on the other end side of the device frame 140.

Due to the compressive reaction force of the pressure springs 144R and 144L, a predetermined equal pressing force acts on the bearing members 142 on the one end side and the other end side. As a result, the pressure roller 130 is urged against the film unit 120, and the pressure roller 130 is pressed against the heater 122 via the film 121 with a predetermined pressing force against the elasticity of the elastic layer 132. Therefore, as shown in FIG. 4, a fixing nip portion B having a predetermined width in the paper transport direction A is formed between the film 121 and the pressure roller 130.

In the fixing device 113 according to the present exemplary embodiment, the heater 121, or the heater 121 and the holder 123 function as a backup member that contacts the inner surface of the film 121.

(6) Fixing Operation The driving force of the motor 153 controlled by the control unit 150 is transmitted to the gear 134 of the pressure roller 130 via the drive transmission unit, so that the pressure roller 130 serves as a drive rotator in FIG. It is rotationally driven in the direction of arrow R130 at a predetermined peripheral speed. Due to the rotation of the pressure roller 130, a rotational force acts on the film 121 by a frictional force with the pressure roller 130 in the fixing nip portion B. As a result, the inner surface of the film 121 slides in close contact with the surface of the heater 121 while being driven to rotate in the direction of the arrow R121 at a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 130.

On the other hand, the heater 122 receives electric power from the triac 151 controlled by the control unit 150 and rapidly generates heat. The temperature of the heater 122 is detected by the thermistor 126, and the detected temperature information is input to the control unit 150. The control unit 150 appropriately controls the current flowing from the triac 151 to the heater 122 according to the detected temperature information to be input, so that the temperature of the heater 122 is raised to a predetermined temperature and the temperature is controlled so that the temperature is maintained. To do.

In this way, the pressure roller 130 is rotationally driven, the film 121 is driven to rotate accordingly, and in the state where the temperature of the heater 122 is adjusted to a predetermined temperature, the unfixed toner image is transferred from the transfer nip portion 111 side. The sheet S carrying t is introduced into the fixing nip portion B. The sheet S is introduced into the fixing nip portion B so that the carrying surface of the toner image t faces the film 121, and is nipped and conveyed. As a result, the unfixed toner image t on the sheet is heated and pressed and fixed as a fixed image. The sheet S that has passed through the fixing nip portion B is separated from the surface of the film 121 by curvature and is discharged and conveyed from the fixing device 113.

In the image forming apparatus 100 and the fixing device 113 according to the present exemplary embodiment, the conveyance of the sheets S of various sizes of large and small is performed based on the so-called center reference of the center of the sheet width. An apparatus configuration may be used in which the sheet is conveyed on the basis of what is called a one-sided reference with one end side of the sheet in the width direction as a reference. In FIG. 2 and FIG. 3, Wmax is the width of the sheet passing (passing) area of the sheet of the maximum width size usable in the apparatus.

(7) Configuration for Grounding the Film Surface As described above, the conductive layer exposed portion (conductive surface) 121d, which is the exposed portion of the conductive primer layer 121b, is arranged annularly in the film circumferential direction on the other end side of the film 121. It is set up. On the side of the pressure roller 130, an annular (ring-shaped or donut-shaped) conductive elastic body (conductive elastic member) is in contact with the conductive layer exposed portion 121d at a position corresponding to the conductive layer exposed portion 121d of the film 121. A conductive rubber ring 135 is provided.

The conductive layer exposed portion 121d on the film 121 side is grounded via the conductive rubber ring 135 on the pressure roller 130 side. As a result, even when a dry sheet having a high electric resistance is passed through, the film potential is stabilized by suppressing the charge on the film surface due to the friction between the sheet S and the film 121.

1A is a front view of the pressure roller 130 in which the conductive rubber ring 135 of the present embodiment is installed on the core metal 131, and FIG. 1B is a schematic configuration diagram of the conductive rubber ring 135 alone.

In this embodiment, the outer diameter D130 of the elastic roller portion of the pressure roller 130 is 14.0 mm in the free state (no-load state). The outer diameter D131 of the core bar 131 is 8.5 mm. The conductive rubber ring 135 is fitted to the core bar 131 so as to be adjacent to the elastic roller portion on the other end side of the core bar 131. The conductive rubber ring 135 is a solid conductive silicone rubber whose resistance is adjusted by mixing carbon black with silicone rubber, and the hardness of the conductive elastic member is 23° (JIS-A).

A knurled shape (uneven shape) 135 a is formed on the outer peripheral surface of the cylinder of the conductive rubber ring 135. The outer diameter D135 is 13.8 mm, the diameter (inner diameter) E135 of the inner hole portion 135b is 7 mm, and the width F135 is 3 mm. Further, a plurality of through holes (lightening holes) 135c are provided in the annular surface (ring-shaped body) between the outer diameter and the inner diameter of the conductive rubber ring 135 in parallel with the thickness direction and in the circumferential direction of the annular surface. ing. In other words, a plurality of through holes (lightening holes) 135c are provided in the annular surface of the conductive rubber ring 135 in the direction parallel to the longitudinal direction of the core bar 131 to be mounted and in the circumferential direction of the core bar 131.

The conductive rubber ring 135 is mounted by fitting the inner hole portion 135b onto the core metal 131. In this case, the inner diameter E135 of the conductive rubber ring 135 is 7 mm, and the outer diameter D131 of the core bar 131 is 8.5 mm. Therefore, the conductive rubber ring 135 is fitted over the core bar 131 with a tightening margin of 1.5 mm with respect to the outer diameter D131 of the core bar 131 on which the conductive rubber ring 135 is installed, which is 8.5 mm. It is installed.

As a result, the conductive rubber ring 135 is secured to be electrically connected to the core bar 131, and the conductive rubber ring 135 is fixed so as to rotate with the rotation of the core bar 131 without being displaced in the longitudinal direction of the core bar 131. It has become. That is, the conductive rubber ring 135 can rotate together with the core metal 131. Here, the effect is not affected whether the conductive rubber ring 135 is mounted in contact with the end surface of the elastic roller portion of the pressure roller 130 or mounted separately.

As described above, the pressure roller 30 is pressed against the film unit 20 by the pressure mechanism, and the fixing nip portion having a predetermined width is provided between the film 121 and the pressure roller 130 against the elasticity of the elastic layer 132. B is formed. At this time, the conductive rubber ring 135 is also compressed and deformed against elasticity at a position facing the conductive layer exposed portion 121d of the film 121, and a nip (hereinafter, referred to as “nip” between the conductive layer exposed portion 121d and the conductive rubber ring 135). A conductive nip portion) C (FIGS. 2 and 3) is formed.

Due to the elasticity of the conductive rubber ring 135 compressed in the conductive nip portion C, the conductive layer exposed portion 121d and the conductive rubber ring 135 come into contact with each other with a constant stress, and electrical conduction is secured between them. Further, the conductive rubber ring 135 is electrically grounded 156 via a metal pressure roller core 131, a diode (commutator) 154, and a security resistor 155.

The toner used in this embodiment is a negative charging toner, and if the surface of the film 121 is positively charged, electrostatic offset is likely to occur due to electrostatic force. Therefore, the diode 154 is arranged so that the charge having the opposite polarity to the charge polarity of the toner is released from the film surface. As described above, the film 121 is grounded 156 via the conductive layer exposed portion 121d, the conductive rubber ring 135, the core bar 131, the diode 154, and the resistor 155, so that a charge having a polarity opposite to that of the toner is accumulated. To prevent that.

At this time, if the resistance value between the conductive layer exposed portion 121d and the core bar 131 exceeds 1 MΩ, the high resistance paper S left in the environment is continuously passed in a low temperature and low humidity environment. In this case, the electric charge accumulated in the film 121 cannot be removed. Therefore, it is known that the electrostatic offset starts to occur. Therefore, when the fixing nip portion B is formed by the pressure contact between the film 121 and the pressure roller 130, it is necessary to maintain the resistance value between the conductive layer exposed portion 114d and the core metal 131 to be 1 MΩ or less.

(8) Experimental example 1
Table 1 shows the contents of the fixing device configuration as a comparative example, which was compared with the configuration of the present embodiment. In the configuration of this embodiment, a pressure roller having an elastic roller portion having an outer diameter D130 of φ14 mm is used as the pressure roller 130, and a conductive rubber ring having a through hole 135c shown in FIG. Is used and is attached to the core 131.

On the other hand, in the configuration studied as the comparative example, a pressure roller having an elastic roller portion having an outer diameter D130 of φ14 mm is used as the pressure roller, and the conductive rubber ring is a conductive rubber ring having no through hole as shown in FIG. It is equipped with 135A. The conductive rubber ring 135A shown in FIG. 7 is the same as the conductive rubber ring 135 shown in FIG. 1B except that it does not have the through hole 135c.

In the fixing device configuration of the present embodiment and the fixing device configuration of the comparative example, the pressure roller 130 is pressed against the film 121 side so that the width of the fixing nip portion B in the sheet conveyance direction A is 6 mm.

By providing the through hole 135c in the conductive rubber ring 135 of the present embodiment, the through hole 135c absorbs the stress, so that the conductive nip portion C can be stably formed, and the offset is prevented and the fixing failure is less likely to occur. It has become a thing.

FIG. 8 is an explanatory view showing a state when a load is applied from the upper surface to the conductive rubber ring 135 provided with the through hole 135c of this embodiment to compressively deform it. The conductive rubber ring 135 of the present embodiment is deformed as shown in (a)→(b)→(c) by being compressed and deformed, and is deformed so that the through hole 135c is crushed according to the load.

FIG. 9 is an explanatory view showing a state in which a conductive rubber ring 135A having no through hole in the comparative example (FIG. 7) is subjected to compression deformation by applying a load from the upper surface. The conductive rubber ring 135A of the comparative example is deformed as (d)→(e)→(f) depending on the load.

FIG. 10 shows changes in stress with respect to displacement of the conductive rubber ring 135 of this example and the conductive rubber ring 135A of the comparative example at this time. The symbols (a) to (f) attached to the respective levels for the displacement on the horizontal axis in FIG. 10 correspond to the symbols showing the state when the conductive rubber ring shown in FIGS. 8 and 9 is compressed and deformed. There is.

The conductive rubber ring 135 of this embodiment absorbs the stress due to the crushing of the through hole 135c when the load is increased to increase the displacement in the order of (a)→(b)→(c). The feature is that there is a region where the change is small.

Hereinafter, an experiment for confirming the effect of the conductive rubber ring 135 of this embodiment will be described. The fixing device configuration shown in Table 1 was evaluated for fixability and electrostatic offset under a low temperature and low humidity (temperature: 15° C., humidity: 10%) environment. As the evaluation paper, Xerox Vitality Multipurpose Paper (Letter size, 20 lb) paper left in this low temperature and low humidity environment for 2 days was used.

1) Fixability was determined by printing 100 sheets of a 5 mm square halftone image as the fixing evaluation image on the above paper continuously. After printing, samples from the 1st to 3rd and 100th samples were extracted from 100 sheets, and the reflection densities before and after rubbing with a nonwoven fabric under a load of 10 g/cm ² were measured by a reflection densitometer (trade name: RD918; manufactured by Gretag Macbeth). If the difference between the reflection densities before and after rubbing with a non-woven fabric is larger than 10%, a practical problem occurs, so 10% or less is marked with ◯, and 10% or more is marked with x.

2) For the electrostatic offset, a halftone image in which an isolated 1 dot of 600 dpi in which offset easily occurs is printed from 5 mm to 20 mm at the front end of the paper was used as an evaluation image. Similarly to the above, 100 sheets of Xerox Vitality Multipurpose Paper (Letter size, 20 lb) were continuously printed, and then the 1st to 3rd sheets and the 100th sheet of samples were extracted and evaluated. The case where stains due to the offset toner did not occur on the solid white paper surface 20 mm or more from the front end of the paper was indicated by ◯, and the case where stains occurred was indicated by x.

The outer diameter D135 of the conductive rubber ring 135 (135A) can be adjusted appropriately with respect to the outer diameter D130 of the elastic roller portion of the pressure roller 130, so that the conductive rubber ring 135 ( Evaluation was performed by shaking the outer diameter D135 of (135A).

The reason why the outer diameter D135 of the conductive rubber ring 135 (135A) affects the fixing property is as follows.

As shown in FIGS. 2 and 3, the elastic layer 132 and the conductive rubber ring 135 of the pressure roller 130 are formed and mounted on the same core metal 131, and the pressure roller 130 presses the film 121 side. Thus, a fixing nip portion B having a width of 6 mm in the paper transport direction A is formed. Therefore, when the outer diameter D135 of the conductive rubber ring 135 is relatively large with respect to the outer diameter D130 of the elastic roller portion of the pressure roller 130, the stress applied to the conductive rubber ring 135 increases. In this case, since the pressure applied to the elastic roller portion of the pressure roller 130 is relatively reduced, the pressurizing force required for fixing in the fixing nip portion B is insufficient and the fixability is deteriorated.

The reason why the outer diameter D135 of the conductive rubber ring 135 affects the electrostatic offset is as follows.

In order to prevent electrostatic offset, in the conductive nip portion C, it is necessary that the conductive rubber ring 135 and the conductive layer exposed portion 121d of the film 121 maintain a contact pressure above a certain level. However, when the outer diameter D135 of the conductive rubber ring 135 is relatively smaller than the outer diameter D130 of the elastic roller portion of the pressure roller 130, the contact pressure between the conductive rubber ring 135 and the conductive layer exposed portion 121d is low. It becomes too much or does not contact. In this case, the conduction between the conductive rubber ring 135 and the conductive layer exposed portion 121d cannot be ensured, and charges are accumulated in the film 121, so that electrostatic offset occurs.

Further, the fixing property and the electrostatic offset are evaluated on the first and the 100th sheets of continuous paper for the following reason. Since the elastic roller portion of the pressure roller 130 is heated during the fixing operation, its outer diameter increases due to thermal expansion, and the thermal expansion of the outer diameter saturates after approximately 100 sheets are continuously fed. On the other hand, since the electric resistance layer is not provided on the heater 122 at the position of the conductive nip portion C where the conductive rubber ring 135 contacts, the thermal expansion of the conductive rubber ring 135 is slight.

The relative relationship between the outer diameter D130 of the pressure roller 130 and the outer diameter D135 of the conductive rubber ring 135 changes as the pressure roller 130 is heated by continuous sheet feeding. The result of the electrical offset will change. It is necessary for the fixing device to have good fixability regardless of the number of printed sheets and in a state where electrostatic offset does not occur. To confirm this, the evaluation of the first to third sheets and the 100th sheet of continuous paper feeding are required. I did.

Table 2 shows the results of the effect confirmation experiment for the conductive rubber rings of the present example and the comparative example described above.

This result will be described with reference to the schematic diagram shown in FIG. 11 showing three contact states caused by the difference in stress applied to the conductive rubber ring 135.

“State A” in FIG. 11 is a diagram schematically showing a state example when an electrostatic offset occurs, and is a state in which the conductive rubber ring 135 and the conductive layer exposed portion 121d are not in contact with each other. As described above, when the conductive rubber ring 135 and the conductive layer exposed portion 121d are not in contact with each other or when the contact pressure is weak, the charge accumulated in the film 121 cannot be removed, so that electrostatic offset occurs. To do.

"State B" is a state in which the conductive rubber ring 135 and the conductive layer exposed portion 121d are in contact with each other with an appropriate contact pressure. At this time, no problem occurs.

“State C” is a diagram schematically showing a state example when the fixing property evaluation result is “X”, and is a state in which the contact pressure between the conductive rubber ring 135 and the conductive layer exposed portion 121d is too high. .. In this case, the pressure in the fixing nip portion B between the elastic roller portion of the pressure roller 130 and the film becomes insufficient, and further, a gap is generated between the pressure roller 130 and the film 121. Therefore, fixing failure occurs.

(Results of this Example)
In this embodiment in which the through hole 135c is provided in the conductive rubber ring 135, the outer diameter D135 of the conductive rubber ring 135 is set to 13.6 to 14.0 mm with respect to the outer diameter D130 of the pressure roller 130: 14 mm. As a result, both good fixability and a state in which no electrostatic offset occurs can be achieved. The pressure roller 130 has an outer diameter D130 of 14 mm, but when compressed and deformed to form the fixing nip portion B, it deforms to a diameter corresponding to an outer diameter of substantially 13.4 mm.

When the diameter D135 is set to 13.6 to 14.0 mm using the conductive rubber ring 135 of this embodiment, the state of "state B" in FIG. 11 is maintained even when the first to 100th sheets are passed. Since it was done, the problem did not occur.

(Results of Comparative Example)
In the conductive rubber ring 135A of the comparative example, for example, when a conductive rubber ring having an outer diameter of 13.2 mm was used, there was no problem for the first to third sheets, but electrostatic offset occurred at the 100th sheet. This is because the outer diameter of the pressure roller 130 was increased due to thermal expansion when the 100th sheet was fixed, although the state of "state B" in FIG. 11 was maintained when the first sheet was fixed. That is, the outer diameter D135 of the conductive rubber ring 135A is relatively smaller than the outer diameter D130 of the pressure roller 130, and the state is the "state A" in FIG.

Further, for example, when the conductive rubber ring 135A having an outer diameter D135 of 13.6 mm was used, the fixing failure occurred in the first to third sheets. This is because the state is “state C” in FIG. 11 from the relationship between the outer diameter of the conductive rubber ring 135A of 13.6 mm and the outer diameter of the pressure roller 130 at the time of pressing (13.4 mm). This is because the pressure roller 130 thermally expands when fixing the 100th sheet in this state, so that the state in which the stress is concentrated on the conductive rubber ring 135A in the "state C" is eliminated and the state is changed to the "state B".

In the conductive rubber ring 135 of the present embodiment, by using a conductive rubber ring having an outer diameter D135 of 13.6 to 14.0 mm, it was possible to obtain a fixed image having no problem in fixing property and offset. On the other hand, in the conductive rubber ring 135A of the comparative example, even if the outer diameter was varied, it was not possible to obtain a level at which no image defect occurred.

In the present embodiment, the example in which the circular through holes 135c are provided on the same circumference has been described, but the same effect can be obtained even if a plurality of through holes 135c having different sizes are provided or holes other than the cylindrical shape. can get.

Further, the through holes 135c can be appropriately arranged, and if the through holes 135c are arranged at a position corresponding to directly below the convex portion of the knurled shape 135a on the surface, the stress receiving portion and the stress absorbing portion become close to each other. It is preferable because it can quickly absorb stress. These can be easily handled by changing the shape of the die when molding the conductive rubber ring.

As the elastic layer 132 of the pressure roller 130, a solid rubber layer, a sponge rubber layer obtained by foaming silicone rubber, a foamed rubber layer in which a hollow filler is dispersed in silicone rubber, and a cured product has a bubble portion, Either is effective. Among them, particularly in the case of a sponge-like elastic layer having fine pores such as a sponge rubber layer and a foam rubber layer, the displacement when pressure is applied to form the fixing nip portion B becomes large, so The conductive rubber ring of the invention is highly effective.

In the above embodiments, the conductive layer exposed portion (conductive surface) 121d is arranged on the other end side of the film 121, but it is not limited to this. The conductive layer exposed portion 121d may be arranged on one end side of the film 121. The conductive layer exposed portion 121d can be provided on at least a part of the film 121 along the circumferential direction.

Further, in the embodiment, the film 121 is configured to be grounded via the conductive rubber ring 135 and the core metal 131. The present embodiment is not limited to this, and the effect of the present embodiment is the same in a configuration in which a voltage having the same polarity as the toner charging polarity is applied to the conductive layer exposed portion 121d of the film 121 via the conductive rubber ring 135 and the core metal 131. That is, an apparatus configuration having a power supply unit (not shown) for applying a voltage having the same polarity as the toner charging polarity to the conductive layer exposed portion 121d of the film 121 via the core metal 131 and the conductive rubber ring 135 may be used.

《Other matters》
(1) The pressure configuration of the film unit 120 and the pressure roller 130 for forming the fixing nip portion B may be a device configuration in which the film unit 120 is pressed against the pressure roller 130. The film unit 120 and the pressure roller 130 may be configured to press each other. That is, the pressure mechanism may be configured to press at least one of the film unit 120 and the pressure roller 130 toward the other.

(2) In the film unit 120, the film 121 is suspended and supported by a plurality of suspension members, and the film 121 is rotated by the pressure roller 130 or a driving rotating body other than the pressure roller 130. Can also

(3) The backup member of the film 21 may be a member other than the heater 22.

(4) The heating means of the film 21 as the rotating body that heats the sheet S carrying the image t is not limited to the heater 22 of the embodiment. Appropriate heating configurations such as an internal heating configuration, an external heating configuration, a contact heating configuration, and a non-contact heating configuration using other heating means such as a halogen heater and an electromagnetic induction coil can be adopted.

(5)) The rotating body that heats the sheet S carrying the image t is not limited to the film form of the embodiment. It may be a roller body.

(6) In the embodiment, as the image heating device, the fixing device for heating and fixing the unfixed toner image formed on the recording material has been described as an example, but the image heating device is not limited to this. The present invention can also be applied to an apparatus (glossiness improving apparatus) for increasing the gloss (glossiness) of an image by reheating a toner image fixed or assumedly attached to a recording material.

(7) The image forming apparatus is not limited to the one that forms a mono-color image as in the embodiment. An image forming apparatus that forms a color image may be used. Further, the image forming apparatus can be implemented in various applications such as a copying machine, a FAX, and a multi-functional machine having a plurality of these functions, in addition to necessary equipment, equipment, and housing structure.

113.. Image heating device (fixing device), 121.. Rotating member (fixing film) for heating the recording material S carrying the image t, 121d.. Conductive surface, 130.. Elastic roller (pressure roller), 131 ..Core bar, 132..Elastic layer, A..Nip portion (fixing nip portion), 135..Conductive elastic member, 135c..Through hole

Claims (10)

A rotating body which has a conductive surface along at least a part of the circumference thereof and which heats a recording material carrying an image, a cored bar, and an elastic layer formed in a roller shape around the cored bar. In an image forming apparatus having an elastic roller that forms a nip portion for nipping and conveying the recording material between the rotating body and the body by pressing against the elasticity of the elastic layer and contacting the core body A ring-shaped conductive elastic member that is attached to and used in contact with the conductive surface against the elasticity in the nip portion and can rotate together with the core metal. A conductive elastic member having a plurality of through holes in the circumferential direction. The conductive elastic member according to claim 1, wherein a concavo-convex shape is formed on the outer peripheral surface, and the through hole is provided corresponding to the convex portion of the concavo-convex shape. A rotating body that heats a recording material carrying an image,
A cored bar and an elastic layer formed in the shape of a roller around the cored bar are provided, and a nip portion is formed between the rotating body and the rotating body by pressurizing and abutting against the elasticity of the elastic layer. An elastic roller to be formed,
An image heating device that nips and conveys a recording material carrying a toner image in the nip portion and heats the recording material,
The rotating body has a conductive surface along at least a part of its circumference,
The core metal has an annular conductive elastic member that is in contact with the conductive surface against the elasticity in the nip portion and is rotatable with the core metal.
The image heating device, wherein the conductive elastic member is provided with a plurality of through holes in parallel with the thickness direction in the annular surface and in the circumferential direction of the annular surface. The image heating device according to claim 3, wherein a concave-convex shape is formed on an outer peripheral surface of the conductive elastic member, and the through hole is provided corresponding to a convex portion of the concave-convex shape. The image heating device according to claim 3 or 4, wherein the elastic layer is formed of a sponge-like elastic material having fine pores. The cored bar is grounded via a commutator arranged so as to release an electric charge having a polarity opposite to the charging polarity of the toner. Image heating device. 7. A power supply unit for applying a voltage having the same polarity as the charging polarity of toner to the conductive surface via the core metal and the conductive elastic member, according to any one of claims 3 to 6. The image heating device described. The rotating body is a flexible tubular film, has a backup member in contact with the inner surface of the film, and the elastic roller contacts the backup member via the film. The image heating device according to any one of claims 3 to 6. 9. The image adding apparatus according to claim 8, wherein the backup member is a heating body that heats the film, and the film slides on the heating body to rotate. The image heating apparatus according to claim 3, wherein the elastic roller is a driving rotating body.