JP2000019870A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the leak of the transfer charge of recording material, to prevent offset or tailing from occurring and to prevent peeling offset by making a diode element intervene between the conductive member of a fixing member and ground and arranging the conductive member in a grounded state near a fixing nip. SOLUTION: A fixing film 13 is constituted of a film base layer 13a, a conductive primer layer 13b and a mold releasable layer 13c in order from the inside to the outside. The layer 13b is grounded through a diode 19c[a]. Desirably, an annular exposed part (a) which is not coated with the layer 13c is provided on the layer 13b, and a conductive brush 19a is made to abut on the part (a) and connected to the ground through the diode 19b[b]. The conductive member 16a is disposed in a fixing and paper ejecting guide 16 on a downstream side from the fixing nip part N so that the charge having a reverse polarity to electrostatically charged toner may be charged to the back surface of recording material by the potential of the induced fixing film 13 and electric field between the ground and the member 16a[c].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus employing an image forming process such as an electrophotographic system or an electrostatic recording system. An unfixed image (toner image, charged colored fine powder image) of target image information formed and carried on a transfer method or a direct method on an electrostatic recording paper or the like is fixed as a fixed image (including a hypothetical fixing process). It relates to a fixing device.

More specifically, the unfixed image is fixed on the recording material by passing the recording material on which the unfixed image is formed through a fixing nip portion, which is a mutual press contact portion between the fixing member and the pressing member. The present invention relates to a fixing device that performs heat fixing, heat pressure fixing, or pressure fixing as an image, and an image forming apparatus including the fixing device.

[0003]

2. Description of the Related Art Conventionally, a heat roller type device has been widely used as a fixing device provided in an image forming apparatus.
In recent years, a film heating system has been put to practical use.

A) Fixing device of the heat roller type FIG. 6 is a schematic structural diagram of an example of the fixing device. It has a fixing roller (heat roller, heat roller) 40 as a fixing member and a pressing roller 50 as a pressing member, which are rotated while being pressed against each other.
The recording material P, on which an unfixed image is formed and carried, is introduced into the fixing nip N, which is a press-contact nip, and the fixing nip N is passed through the fixing nip N. In this method, an unfixed image is fixed by heat and pressure on a recording material surface as a permanent fixed image under pressure.

A fixing roller 40 as a fixing member has a hollow metal core 42 made of aluminum or the like, and a release layer 43 covering the outer peripheral surface thereof. A lamp 41 is provided,
The halogen lamp 41 generates heat by energization from a power supply (not shown), and the heat heats the hollow metal core 42 from the inside, so that the surface temperature of the fixing roller 40 is a predetermined fixing sufficient for melting the toner on the recording material. In order to maintain the temperature, the energization of the halogen lamp 41 is controlled on / off by a temperature control system including a thermistor 44 as a temperature detecting unit which is brought into contact with the surface of the fixing roller 40 to control the temperature.

The releasing layer 43 on the outer peripheral surface of the fixing roller is for fixing the toner on the recording material P onto the recording material without offsetting the recording material P, and is a polytetrafluoroethylene exhibiting excellent performance of releasing the toner. Ethylene (PTFE), perfluoroalkoxytetrafluoroethylene copolymer (PF
A) layers such as fluororesins. The release layer 43 is formed in a tube shape, or is formed by electrostatic spraying, dipping coating, or the like.

Further, in order to prevent offset caused by charging-up of the surface of the fixing roller due to conveyance of the recording material P, an electronic conductive substance (conductive filler, conductive member) is mixed into the release layer 43. Some are dispersed.

Further, the hollow metal core 4 of the fixing roller 40
Numeral 2 is electrically connected to ground to prevent charge-up on the surface of the fixing roller.

A pressure roller 50 as a pressure member presses the fixing roller 40 at both ends in the longitudinal direction of the roller by a pressure spring (not shown) to pinch and convey the recording material. The pressure roller 50 includes a cored bar 51, a silicone rubber elastic layer or a silicone rubber foamed sponge elastic layer 52 formed concentrically and integrally with the outer peripheral portion of the cored bar 51 in a roller shape, and further covers the outer peripheral surface thereof. This is an elastic roller having the released release layer 53. The releasable layer 53 is formed by forming PTFE, PFA, FEP, or the like into a tube or coating the same as the fixing roller 40.

A nip portion N having a sufficient nip width can be formed between the fixing roller 40 and the pressure roller 50 by the elasticity of the elastic pressure roller. The upper toner image can be fixed by heating from the fixing roller 40.

B) Fixing device of film heating system This is disclosed, for example, in JP-A-63-313182, JP-A-2-15778, and 4-44075 to 440.
No. 83, No. 4-204980-2044984, etc., and a fixedly supported heating element, a heat-resistant film (fixing film) sliding on the heating element, and a heating element sandwiching this film A pressure member that forms a fixing nip portion that is a pressure contact nip portion between the heating member and the heating member to heat and control the temperature to a predetermined temperature. The recording material on which the formed image is formed and carried is introduced, and the fixing nip is passed through the fixing nip together with the fixing film, so that the image is not fixed by the heat from the heating body through the fixing film and the pressing force of the fixing nip. The image is fixed by heat and pressure on the recording material surface as a permanent fixed image.

In such a film heating type fixing device, a linear heating element having a low heat capacity such as a so-called ceramic heater can be used as a heating element, and a thin film having a low heat capacity can be used as a fixing film. Since the temperature of the body rises and the fixing nip can quickly rise to a predetermined temperature, power consumption can be suppressed to a minimum without supplying power to the heating body during power standby (power-on heating). Even if the recording material is passed immediately, the heating element can be heated to a predetermined temperature by the time the recording material reaches the fixing nip portion, which is a fixing portion, and other contact heating methods such as a heat roller method can be used. Compared to the fixing device, it is possible to save power and shorten the wait time (quick start property), and it is possible to configure an on-demand fixing device.

The fixing film is constituted by a cylindrical member or an endless belt-shaped member, which is used by rotating the fixing film, or is constituted by a roll-wrapped end web member, which is used by traveling. be able to.

FIG. 7 is a schematic model diagram of an example of the fixing device. The apparatus of this example is disclosed in Japanese Patent Application Laid-Open No. 4-44075-4.
This is a so-called tensionless type device disclosed in JP-A Nos. 4083, 4-204980-204498 and the like. That is, a cylindrical (endless) fixing film is used, and at least a part of the circumference of the film is tension-free (in a state where tension is not applied), and the film is pressed with a pressure roller (a pressure rotating body). The roller is driven to rotate by the rotational driving force of a pressing roller and a backup roller.

Reference numeral 60 denotes a fixing film assembly serving as a fixing member, and a heating member (heater, hereinafter referred to as a heater).
61, a stay holder (support) 62, a cylindrical fixing film (heat-resistant thin film) 63 and the like. The heater 61 is generally a low-heat-capacity ceramic heater, and is a horizontally long member whose longitudinal direction is orthogonal to the recording material P conveying direction. The stay holder 62 is a heater support and a film inner surface guide member. The heater 61 is fitted and fixedly supported in a groove formed along the longitudinal direction of the stay holder at a substantially central portion of the lower surface of the stay holder 62. The cylindrical fixing film 63 is loosely fitted to a stay holder 62 fixedly supporting the heater 61.

The fixing member 60 is disposed above the pressing roller 50 as a pressing member with the heater 61 facing downward, and the heater 61 and the pressing roller 5
0 is pressed against the elasticity of the pressure roller 50 with the fixing film 63 interposed therebetween. N is a fixing nip formed between the heater 61 and the pressure roller 50 with the fixing film 63 interposed therebetween.

The pressure roller 50 is driven to rotate in a counterclockwise direction indicated by an arrow by a driving means (not shown). This pressure roller 5
0 at the fixing nip portion N
Rotational force acts on the fixing film 63 by the frictional force between the fixing film 63 and the outer surface of the fixing film 63, and the film 63 slides in close contact with the heater 61, and moves clockwise as indicated by the arrow in the arrow direction.
It is driven to rotate around the outside. The stay holder 62 functions to facilitate the rotational movement of the fixing film 63.

When the rotation peripheral speed of the fixing film 63 is stabilized by the rotation of the pressure roller 50 and the temperature of the heater 61 is raised to a predetermined temperature and the temperature is controlled, the fixing film 63 of the fixing nip N and the pressure roller 50 are adjusted. The recording material P carrying the unfixed toner image is introduced with the toner image carrying surface side toward the fixing film 63.

The recording material P which has entered the fixing nip N is heated by the heater 6 via the fixing film 63 in the fixing nip N.
1 and moves through the fixing nip portion N together with the fixing film 63. In the moving passage process, the heat of the heater 61 is applied to the recording material P via the fixing film 63, and the toner image is heated and fixed on the surface of the recording material P.

The recording material P that has passed through the fixing nip N is separated from the surface of the fixing film 63 and conveyed.

In general, a ceramic heater is used as the heater 61 as a heating member. For example, a silver palladium (Ag / Ag / Ag / Ag) layer is formed on the surface of the ceramic substrate (the surface facing the fixing film 63) having electrical insulation, good thermal conductivity, and low heat capacity such as alumina along the substrate length (the direction perpendicular to the drawing). P
d) A heat-generating resistor layer such as Ta ₂ N is formed by screen printing or the like, and the surface on which the current-generating resistor layer is formed is covered with a thin glass protective layer. In the ceramic heater 61, when current is applied to the energized heating resistor layer, the energized heating resistor layer generates heat, and the entire heater including the ceramic substrate / glass protection layer rapidly rises in temperature. When the temperature of the heater 61 rises, the temperature detecting means 64 installed on the back of the heater 61
And is fed back to the power supply control unit (not shown). The power supply control unit controls power supply to the power supply heating layer so that the heater temperature detected by the temperature detection unit 64 is maintained at a predetermined substantially constant temperature (fixing temperature). That is, the heater 61 is heated and adjusted to a predetermined fixing temperature.

In order to efficiently apply the heat of the heater 61 to the recording material P as the material to be heated through the fixing film at the fixing nip N, the fixing film 63 has a very small total thickness of 20 to 70 μm. ing. As shown in the schematic diagram of the layer structure in FIG. 10, generally, it has a three-layer structure of a film base layer 63 a, a conductive primer layer 63 b, and a release layer 63 c, and the film base layer 63 a side is a side that slides in contact with the heater 61. And the release layer 63c side is the side in contact with the recording material P or the pressure roller 50.

The film base layer 63a maintains mechanical strength such as tear strength of the entire fixing film, and is made of polyimide, polyamideimide, PEEK, or the like having high insulation properties, and has heat resistance and high elasticity. 15 ~ 60μm thickness
It is formed in the degree.

The conductive primer layer 63b has a thickness of 2 to 6 μm.
It is formed of a thin layer of about m, and is electrically connected to the ground in order to prevent charge-up of the entire fixing film.

The release layer 63c is a layer for preventing toner offset with respect to the fixing film.
Fluorine such as FA, PTFE, FEP, etc.
It is formed by coating to a certain extent.

As in the case of the fixing roller 40 in the fixing device of the heat roller type, in order to reduce charge-up on the surface of the fixing film 63 and prevent electrostatic offset, a specific resistance is provided in the release layer 63c. Is 10 ³ Ωcm-10
A conductive member (conductive substance) such as carbon black of about ⁶ Ωcm is mixed.

The stay holder 62 is formed of, for example, a heat-resistant plastic member, and holds the heater 61 and also serves as a conveyance guide for the fixing film 63. Therefore, in order to enhance the slidability with the fixing film 63, the fixing film 63 and the heater 61 or the stay holder 6
A highly heat-resistant grease or the like is interposed between the outer peripheral surfaces of the two.

The pressing roller 50 as a pressing member is the pressing roller 5 in the above-described fixing device of the heat roller type.
It has the same configuration as 0.

As described above, in the conventional heat roller type or film heating type fixing device, the surface layer of the fixing roller 40 as a fixing member or the fixing film 63 of the fixing film assembly is formed of a fluororesin having good releasability. , Relatively low resistance (specific resistance of 10 ³ Ωcm to 10 ⁶ Ωcm
) Of an electronic conductive material (conductive filler, conductive member), and the uniform dispersion of the conductive material 63d as shown in the model diagram of FIG. 11 results in the release layer 63c (43).
Was formed inside.

Further, a fixing roller 40 as a fixing member
By electrically grounding the conductive hollow core metal 42 and the conductive primer layer 63b of the fixing film 63, the charging roller 40 or the surface of the fixing film 63 is prevented from being charged up, and offset is prevented. I was

[0031]

However, in the case of the above-described fixing device, the surface potential of the fixing roller 40 or the fixing film 63 increases depending on the amount of the conductive substance mixed into the surface layer of the fixing roller 40 or the fixing film 63. Differently, it was difficult to determine the optimal amount of conductive material to resolve all offset and image disturbances.

For example, the above-described carbon black having a small specific resistance is applied to the fixing roller 40 or the fixing film 63.
When the release layer 43 or 63c mixed in a large amount in the fluororesin layer which is the surface layer of the above, it is easy to prevent the charge-up of the surface of the fixing film 63 or the fixing roller 40 due to the conveyance of the recording material. However, on the other hand, the transfer charge holding the toner image on the recording material is caused by the conductive primer layer 63b of the fixing film 63 and the conductive hollow core of the fixing roller 40 due to the conductive substance in the release layer. It is easy to leak to 42. In particular, when a recording material having a small surface resistance is used, the amount of the conductive material is microscopically large, and the transfer charge on the recording material is substantially reduced from the point at which the transfer charge easily leaks. It leaks to gold 42. As a result, the toner image on the recording material is no longer electrostatically held on the recording material,
Offset is likely to occur due to a decrease in the toner suction force on the recording material.

Further, the toner image is easily scattered by an external force due to a decrease in the charge held on the recording material. For example, when a recording material having a large amount of moisture absorption is fixed by heating, the toner image is ejected from the recording material. The so-called “tailing” of scattering the toner image in the direction opposite to the recording material conveyance direction by the water vapor may occur.

On the other hand, when the amount of the conductive substance dispersed in the release layers 63c and 43 is reduced in order to prevent the transfer charge leakage as described above, the conductive material is uniformly dispersed in the release layer. It is more difficult to disperse the conductive material, and the surface of the release layer is locally charged up in a portion where the conductive material is sparse, which may result in offset.
For example, when the dried recording material is peeled off from the fixing nip and conveyed, the recording material is printed on the surface of the fixing roller 40 and the fixing film 63 when the rear end of the recording material is discharged from the fixing nip. The portion corresponding to the rear end of the material is charged up linearly. If the toner image on the subsequent recording material is fixed while this potential is maintained, a so-called “peeling offset” occurs in which the image on the subsequent recording material corresponding to the charged-up position is removed. is there.

Therefore, when a conductive material such as carbon black having a specific resistance of about 10 ³ Ω to 10 ⁶ Ω is mixed into the release layer, the surface resistance of the release layer depends on the amount of the conductive substance mixed. Values and volume resistance values change extremely, it has been difficult to stably produce a release layer having appropriate resistance characteristics to prevent the above-described leak type offset and offset due to charge-up.

In a durability test in which a recording material was heated and fixed by a heating and fixing device in many cases, the state of the release layer differs depending on the durability due to wear of the surface of the fixing member. It was difficult to maintain the electrical state of the release layer.

From the above, it has been difficult to completely prevent all offsets and tailings due to leaks of transfer charges and offsets due to charge-up.

Further, in the case of the above-mentioned particulate conductive material such as carbon black, the smaller the particle size, the larger the surface energy, and secondary aggregation is likely to occur. difficult.

The present invention has been proposed in view of the above,
In this type of fixing device, it is possible to prevent a transfer charge of a recording material from leaking through a release layer which is a surface layer of a fixing member such as a fixing roller or a fixing film, thereby preventing occurrence of offset and tailing. It is another object of the present invention to suppress charge-up potential, remove a local charge on the surface of a release layer of a fixing member via a recording material, and obtain a good image in which peeling offset is prevented.

[0040]

According to the present invention, there is provided a fixing device and an image forming apparatus having the following constitution.

(1) The recording material on which the unfixed image is formed is
In a fixing device for fixing the unfixed image on a recording material by passing the fixing member through a fixing nip that is a mutual pressure contact portion between the fixing member and the pressing member, a diode element is provided between the conductive member of the fixing member and ground. And a conductive member in a grounded state is disposed near the fixing nip.

(2) A fixing device according to (1), wherein a conductive member is provided on the downstream side of the fixing nip in the recording material conveying direction, and the conductive member contacts the conveyed recording material. apparatus.

(3) The fixing device according to (1) or (2), wherein a diode element is interposed between the conductive member of the pressing member and ground.

(4) A conductive member is provided downstream of the fixing nip in the recording material conveyance direction, and the conductive member is grounded via a bias applying device. The fixing device according to any one of 3).

(5) A conductive member is provided on the downstream side of the fixing nip in the recording material conveying direction, and the conductive member is grounded via a bias applying device, and according to the conveying position of the recording material. The fixing device according to any one of (1) to (4), wherein an applied bias by the bias applying device changes.

(6) The fixing device according to any one of (1) to (5), which is a heat fixing device.

(7) The fixing device according to any one of (1) to (6), wherein the fixing member is a fixing film in a film heating type fixing device.

(8) The fixing device according to any one of (1) to (6), wherein the fixing member is a fixing roller in a fixing roller heating type fixing device.

(9) The fixing device according to any one of (1) to (6), which is a pressure fixing device.

(10) An image forming apparatus comprising the fixing device according to any one of (1) to (9).

<Operation> More specifically, the unfixed image is formed on the recording material by passing the recording material on which the unfixed image is formed through a fixing nip portion between the fixing member and the pressing member. In a fixing device for fixing a recording medium such as a fixing roller or a fixing film as a fixing member, a small amount of a conductive substance is mixed so that the volume resistance becomes 10 ⁸ Ωcm or more. Formed from film. In addition, the thickness of the release layer is set to 8 μm or more and 18 μm or less so as to maintain sufficient performance against scraping due to durability. In addition, a conductive member of a fixing member (such as a conductive hollow core of a fixing roller or a conductive primer layer of a fixing film) is grounded so that a charge having the same polarity as the potential of the toner charged in the image forming portion is induced. Through a diode between them. Also,
A conductive member is disposed on the back side of the recording material near the fixing nip, and charges having a polarity different from that of the toner are injected into the recording material. Further, the charge of the peeling discharge when the recording material is discharged from the fixing nip is discharged from the conductive member immediately after the fixing nip to the ground.

As described above, by maintaining the resistance of the surface layer of the fixing member at a predetermined value or more, it is possible to prevent the transfer charge of the recording material from leaking through the release layer which is the surface layer of the fixing member, and to have the same polarity as the toner. Inducing a potential on the conductive member of the fixing member prevents the toner from being offset to the fixing member. In addition, by injecting charges of a polarity different from that of the toner on the back surface of the recording material by a conductive member provided near the fixing nip, the electrostatic holding force of the toner on the recording material is increased, and offset and tailing are prevented. In addition, the separation discharge when the rearmost end of the recording material is discharged from the fixing nip is released to the ground, thereby preventing a part of the fixing member from being locally charged, thereby preventing a peeling offset.

As described above, it is no longer necessary to control the production in a severe region where the surface resistance and the volume resistance of the release layer are extremely changed with respect to the amount of the conductive substance mixed as in the prior art.

Further, since a small amount of a conductive substance is mixed in the release layer, even if the release layer is scraped to some extent due to durability,
It is possible to prevent offset and tailing due to leakage of the transfer charge of the recording material, thereby forming a fixing member having excellent durability. Further, a good image can be obtained in which offset due to leakage, tailing, and peeling offset due to charge-up are prevented without severe management of the surface layer of the fixing member.

[0055]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (FIGS. 1 to 3) (1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier. OP
A photosensitive material layer of C, amorphous Se, amorphous Si or the like is formed on a cylindrical conductive substrate of aluminum or nickel. The photosensitive drum 1 is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed).

In the process of rotating the photosensitive drum 1, first,
The surface is uniformly charged to a predetermined polarity and potential by a charging roller 2 as a charging device.

Next, a laser beam scanning exposure 3 corresponding to a target image information pattern is received by a laser scanner (not shown) as an exposure device. As a result, an electrostatic latent image corresponding to the target image information pattern is formed on the surface of the rotating photosensitive drum 1.

The laser scanner outputs a laser beam whose ON / OFF is controlled in accordance with a time-series electric digital pixel signal of a target image information pattern sent from an external device such as a host computer, and rotates with the laser beam. The uniformly charged surface of the photosensitive drum 1 is exposed by scanning.

The electrostatic latent image formed on the surface of the rotating photosensitive drum 1 is visualized by developing the toner in the developing device 4. Development methods include a jumping development method, a two-component development method, and F
An EED development method or the like is used, and a combination of image exposure and reversal development is often used.

The toner image formed on the surface of the rotating photosensitive drum 1 is transferred to a transfer nip portion T formed by the photosensitive drum 1 and a transfer roller 5 as a transfer device brought into contact with the photosensitive drum 1 at a constant pressure. The image is sequentially transferred to a recording material (transfer material) P fed from a paper supply unit (not shown) to the transfer nip portion T at a predetermined control timing.

A predetermined transfer bias is applied to the transfer roller 5 from a power supply (not shown) at a predetermined control timing, and the toner image on the surface of the photosensitive drum 1 is nipped and conveyed by the action of the transfer bias. Are sequentially transferred to the recording material P surface.

Reference numeral 8 denotes a sensor for detecting the leading end of the recording material P conveyed from the paper feeding unit to the transfer nip T. The position of the toner image on the photosensitive drum 1 and the starting position of the leading end of the recording material P are determined. The leading edge of the recording material P is detected by the sensor 8 so as to match, and the timing is adjusted.

The recording material P that has received the transfer of the toner image at the transfer nip portion T and passed through the transfer nip portion T is separated from the surface of the rotating photosensitive drum 1 and is conveyed to the fixing device 6, where the toner image is converted into a permanent image. Be established.

On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

(2) Fixing Device 6 The fixing device 6 in this example is a film using a cylindrical fixing film disclosed in Japanese Patent Application Laid-Open No. 4-44075-44083, similarly to the fixing device of FIG. It is a heating type, pressure roller drive type, and tensionless type heat fixing device. FIG. 2 is a schematic cross-sectional view of the device 6.

Reference numerals 10 and 20 denote a fixing member and a pressure member which are in contact with each other to form a fixing nip N.

The fixing member 10 comprises a heating element 11, a heat insulating stay holder 12, a fixing film 13, and the like. The pressure member 20 is an elastic pressure roller.

The heating element 11 is a thin and horizontally long ceramic heater (hereinafter abbreviated as a heater).

The heat insulating stay holder 12 is a member that holds the heater 11 and prevents heat radiation in the direction opposite to the nip.
It is formed of a liquid crystal polymer, a phenol resin, PPS, PEEK, or the like. The heat-insulating stay holder 12 of this example is a member having a substantially semicircular trough-shaped cross section, heat resistance, electrical insulation, and high withstand load. The front surface side is downwardly exposed and fitted and fixedly supported in a groove portion provided along the longitudinal direction of the member.

The fixing film 13 is a cylindrical heat-resistant film, which is loosely fitted to the heat-insulating stay holder 12 including the heater 11 with a margin in the circumferential length. The fixing film 13 is supported from the inside.

The fixing film 13 has a small heat capacity, and has a total thickness of 100 to enable quick start.
Heat-resistant, thermoplastic polyimide, polyamideimide, PEEK, PES, PPS, P
It is a film based on FA, PTFE, FEP or the like. In addition, a film having sufficient strength to constitute a long-life heat fixing device and having excellent durability has a total thickness of 2 mm.
A thickness of 0 μm or more is required. Therefore, fixing film 1
The total thickness of 3 is optimally 20 μm or more and 100 μm or less. Further, in order to prevent offset and ensure the separating property of the recording material, the surface layer is coated with a heat-resistant resin having good releasability, such as PFA, PTFE, FEP, or silicone resin, or coated alone. The configuration of the fixing film 13, particularly, the details of the release layer according to this embodiment will be described later.

The elastic pressure roller 20 as a pressure member is
A core metal 21 and an elastic layer 22 formed by foaming heat-resistant rubber such as silicon rubber or fluorine rubber or silicon rubber on the outside of the core metal 21, and PFA, PRF
A release layer 23 such as E or FEP may be formed.

The elastic pressure roller 20 is held by a bearing member (not shown), and the fixing film 13 is sandwiched between the downward surface of the heater 11 fixed and supported on the lower surface side of the heat insulating stay holder 12. Is sufficiently pressed from both ends in the longitudinal direction to form a fixing nip portion N necessary for heat fixing.

The pressure roller 20 is driven to rotate in a counterclockwise direction indicated by an arrow by a driving unit (not shown) (a rotary member driving system for pressure). A rotational force acts on the fixing film 13 by the frictional contact between the outer surface of the roller 20 and the outer surface of the fixing film 13 at the fixing nip portion N due to the rotational driving of the pressure roller 20, and the fixing film 13 The outer periphery of the heat-insulating stay holder 12 is driven to rotate in the clockwise direction of the arrow at a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 20 while sliding in close contact with the downward surface of the heater 11 in the fixing nip portion N. Become.

In this case, the cylindrical fixing film 13 which is driven to rotate around the outer periphery of the heat insulating stay holder 12 has a fixing free nip portion N and a fixing film portion other than the fixing film portion in the vicinity of the fixing nip portion N. (Not added).

The fixing film 13 has a heater 1 on the inner surface side.
1 and a part of the outer surface of the heat insulating stay holder 12 are rotated while being rubbed, so that the frictional resistance between the heater 11 and the heat insulating stay holder 12 and the fixing film 13 needs to be reduced. Therefore, a small amount of lubricant such as heat-resistant grease is interposed between the surfaces of the heater 11 and the heat insulating stay holder 12. Thus, the fixing film 13 can rotate smoothly.

Thus, the pressure roller 20 is driven to rotate,
Accordingly, the cylindrical fixing film 13 is driven to rotate around the heat insulating stay holder 12,
Is supplied to the fixing nip N due to the heat generated by the heater 11.
In a state where the temperature has risen to a predetermined level and the temperature has been adjusted,
A recording material P having an unfixed toner image formed and carried on the fixing nip portion N is introduced along a heat-resistant fixing entrance guide 15, and the unfixed toner image carrying surface of the recording material P is fixed on the fixing nip portion N by a fixing film. The fixing nip N is conveyed together with the fixing film 13 in close contact with the outer surface of the fixing film 13.

In the process of nipping and transporting the recording material P, the heat of the heater 11 is applied to the recording material via the fixing film 13 so that the unfixed toner image on the recording material P is heat-pressure fixed.

When the recording material P passes through the fixing nip N, the recording material P is separated from the outer surface of the fixing film 13 by a curvature and is guided by a heat-resistant fixing discharge guide 16 to be nipped and conveyed by a discharge roller 17 and a discharge roller 18. The sheet is discharged onto the discharge tray shown in the figure.

(2) Heater 11 The heater 11 (ceramic heater) is made of, for example, Ag / Pd (silver palladium), RuO ₂ , Ta ₂ N on the surface of a highly insulating ceramic substrate such as alumina along the longitudinal direction.
The thickness of the heat-generating resistive layer such as 1
It is a current-carrying heating member formed by coating in a linear or narrow band shape of about 0 μm and a width of about 1 to 5 mm.

A temperature detecting element 14, such as a thermistor, for detecting the temperature of the ceramic substrate raised in accordance with the heat generated by the current-generating resistance layer is provided on the rear surface of the ceramic substrate. By appropriately controlling the duty ratio, the wave number, and the like of the voltage applied from the electrode (not shown) at the end in the longitudinal direction to the energized heating resistor layer in accordance with the signal from the temperature detecting element 14, the fixing nip N The temperature necessary for fixing the toner image on the recording material is maintained while the temperature inside the inside is kept substantially constant.

The DC power supply from the temperature detecting element 14 to the temperature control unit (not shown) is achieved by a connector (not shown) via a DC power supply unit (not shown) and a DC electrode unit. Also,
A protective layer such as a thin glass coat or the like that can withstand rubbing with the fixing film 13 is provided on the surface of the current-carrying resistance layer of the heater 11.

(3) Fixing Film 13 and the Like FIG. 3A is a schematic cross-sectional view showing the layer structure of the fixing film 13. The fixing film 13 includes a film base layer 13a and a conductive primer layer 1 in order from the inside to the outside.
3b, a three-layer laminate including a release layer 13c.

The conductive primer layer 13b has a thickness of 2 to 6
It is formed of a thin layer of about μm.

Here, when the fixing film 13 is made to be entirely insulative, the electrostatic capacity of the film becomes small, and the recording material P charged in the transfer portion of the image forming apparatus forms the fixing nip portion N. By passing through, the surface potentials of the fixing film 13 and the pressure roller 20 increase, causing charge-up. Therefore, the fixing film 13 and the pressure roller 20
During this time, an electric field may be generated to cause an electrostatic offset in the fixing film 13. In order to avoid this, as described above, the primer layer 13 which is an intermediate layer of the fixing film 13 is used.
The primer layer is made conductive by mixing carbon black or the like into b.

Further, the conductive primer layer 13b is grounded via a diode 19b.

A release layer 13c is provided outside the primer layer 13b. The release layer 13c serves as a toner offset prevention layer for the fixing film 13.
It is formed by coating a fluororesin such as PFA, PTFE, FEP or the like having good releasability with a thickness of about 8 to 18 μm by a coating method such as electrostatic spraying or dipping.

In particular, in order to suppress the transfer charge from leaking from the surface of the fixing film 13, a small amount of a conductive substance is mixed into the release layer 13c, and the volume resistance of the release layer 13c is set to 10 ⁸ Ωcm. That is all. In addition, even when the release layer 13c is scraped due to durability, the thickness is 8 μm, which is a sufficient thickness to prevent offset and tailing due to leakage.
The above is required.

Further, as shown in FIG. 3B, an annular exposed portion a which is not covered with the release layer 13c is provided on the above-mentioned conductive primer layer 13b, and amorphous fiber, SUS or the like is provided in this portion. A conductive brush 19a made of a conductive material, and further connected to the ground via a diode 19b. As a result, a potential of the same polarity as that of the toner is induced in the conductive primer layer 13b of the fixing film 13. It should be noted that the figure shows the direction of the diode when the toner is negatively charged in the image forming apparatus. Diode 1 if toner is positively charged
The direction of 9b is reversed.

Further, in this embodiment, as shown in FIG. 3 (c), a charge having a polarity opposite to that of the toner charged on the back surface of the recording material due to the induced electric potential of the fixing film and the electric field between the ground is injected. As a result, the conductive member 16a is provided in the fixing discharge guide 16 downstream of the fixing nip portion N in the recording material conveyance direction (at a position about 5 mm to 20 mm downstream from the fixing nip).
Is arranged. The conductive member 16a is electrically connected to the ground, and when the recording material P is discharged from the fixing nip portion N, the back surface of the recording material contacts the conductive member 16a so that the fixing film 13 and The conductive member 1
A current path occurs between 6a. Thus, since the fixing film 13 is induced to have the same polarity as the toner, a charge having a polarity opposite to that of the toner is injected into the back surface of the recording material via the conductive member 16a.

Further, when the rear end of the recording material P is discharged from the fixing nip portion N, the fixing film 13 is released by peeling discharge.
A local potential (potential of the opposite polarity to the toner)
At the moment when this potential is generated, the local charge on the fixing film 13 flows into the conductive member 16a via the recording material. As a result, no local potential having a polarity opposite to that of the toner remains on the fixing film.

As described above, in the present embodiment, when the recording material is nipped and conveyed into the fixing nip, the conductive member 16 immediately after the fixing nip is formed.
When the recording material comes into contact with a, a charge having a polarity opposite to that of the toner is injected into the back surface of the recording material, so that the electrostatic holding force of the toner image on the recording material increases, and it is possible to prevent offset, tailing, and the like. become.

Here, in the present embodiment, the apparatus in which the grounded conductive member 16a is provided immediately after the fixing nip portion has been described. However, even when the entrance guide 15 and the like immediately before the fixing nip portion are made conductive and grounded, the same applies. Offset and tailing can be prevented.

Further, when the rear end of the recording material P is discharged from the fixing nip portion, local charges on the fixing film caused by peeling discharge escape from the conductive member 16a immediately after the fixing nip portion. No stripping offset due to local charge occurs.

(4) Evaluation In order to confirm the above effects, the following examination was conducted.

The fixing device 6 is configured such that the fixing film 13 has an inner diameter of φ24 and a conductive primer layer 13b in which carbon black is dispersed on the outer surface of a 50 μm-thick polyimide film as a film base layer 13a. One obtained by forming a release layer 13c through a dipping coating and baking process in a mixed solution of PFA and PTFE was used.

The heater 11 used was one in which Ag / Pd was screen-printed as an exothermic resistance layer on an alumina substrate, and a glass protective layer was formed on the surface thereof.

The pressure roller 20 is made of silicone rubber 2
2 having a PFA tube 23 over φ25 was used.

In each of Conventional Examples 1-4, Examples 1-4, and Comparative Examples shown in Tables 1 and 2, the primer layer 13b of all the fixing films 13 was 4 μm, and the surface layer 13c was coated with a fluororesin of 10 μm. Prepared.

Further, a conductive brush made of an amorphous fiber as the conductive member 16a was disposed at a position downstream of the fixing nip portion N so as to be able to rub against the recording material P, and was grounded. For comparison, a comparison was made with and without the conductive brush 16a.

Further, when the conductive primer layer 13b of the fixing film 13 is electrically grounded,
Comparison was also made through the case b.

Evaluation items Evaluation 1: Leak-type offset: 200,000 sheets of recording material were continuously conveyed, and then three sheets of moisture-absorbing recording material having a small surface resistance were conveyed to evaluate the offset.

Evaluation 2: Trailing ... Similar to Evaluation 1 described above,
Using a durable fixing film, three sheets of the absorbed recording material were conveyed to evaluate tailing.

Evaluation 3: Peeling Offset: The peeling offset when a recording material having a high surface resistance was continuously conveyed by double-sided printing was evaluated.

Tables 1 and 2 show the results of the evaluations 1 to 3.
In the table, ○ indicates a satisfactory level, △ indicates an allowable level, and × indicates a poor level.

The volume resistivity of the conventional example shows the result when the volume resistance is changed by varying the amount of the conductive agent in the fluororesin.

[0108]

[Table 1]

[0109]

[Table 2] From the above results, when the release layer 13c of the fixing film 13 is grounded as in the conventional example, and the grounded conductive member 16a is not provided immediately after the fixing nip portion, the release layer 1
It is difficult to prevent all of offset, tailing and stripping offset only by the amount of the conductive substance dispersed in the fluororesin of 3c, and it is almost impossible to satisfy even when a durable fixing film is used. Met. Also, the release layer 13c for balancing all problems.
Since the amount of the conductive material dispersed therein significantly affects the resistance value, the amount of the conductive material must be controlled in a narrow region. For this reason, the productivity of the fixing film has been deteriorated. In addition, since the offset phenomenon has a severe effect on the dispersibility of the conductive material, severe management is required to improve the dispersibility.

On the other hand, in the present embodiment, a potential of the same polarity as that of the toner is induced in the conductive primer layer 13b of the fixing film 13, and the conductive material 16a in the grounded state immediately after the fixing nip portion causes the back of the recording material. Since a charge having a different polarity from that of the toner is injected into the recording material, a sufficient holding force of the toner on the recording material can be secured, and as a result, all of offset, tailing, and stripping offset can be prevented. Further, since the range of allowable volume resistance as the release layer 13c of the fixing film 13 is widened, it is not necessary to strictly control the amount of the conductive substance dispersed. Further, since the volume resistance of the release layer 13c of the fixing film 13 can be set higher than in the past, even if the surface layer of the fixing film is slightly scraped due to durability, the transfer of the recording material can be easily performed as in the conventional example. No charge leaks. Further, a grounded conductive member 16a provided immediately after the fixing nip portion for a local charge-up of the fixing film.
This makes it possible to discharge via the recording material. Therefore, both the leak type offset and tailing and the stripping offset due to the charge up can be performed without deteriorating the productivity of the fixing film.

In this embodiment, a conductive brush having elasticity and flexibility is used as the conductive member 16a immediately after the fixing nip portion. However, a conductive blade is arranged so as not to hinder the conveyance of the recording material. You may. Further, the same effect can be obtained even when the discharge roller 17 and the discharge roller 18 for nipping and conveying the recording material discharged from the fixing nip portion N in FIG.

As a heat fixing device, it is better to use a deformable fixing film shown in this embodiment than to a system using a rigid fixing roller as a fixing member, so that the recording material is applied to the conductive brush 16a immediately after the fixing nip. The fixing device using a fixing film is more suitable because the contact is ensured. This is because the recording material uses a stationary roller.
When a strong external force is applied to the fixing nip by the temperature of the fixing roller and the temperature of the pressure roller, the degree to which the recording material is deformed changes. On the other hand, in a system using a fixing film, a heater 11 as a heating element is used. This is because a stable external force is always applied to the recording material because the surface is horizontal. That is, since the direction of separation of the recording material discharged from the fixing nip is determined by the external force received at the fixing nip, the heat fixing device of the fixing film system to which a stable external force is applied is more stable immediately after the fixing nip. The recording material P can be brought into contact with the conductive member 16a.

<Second Embodiment> (FIG. 4) This embodiment is different from the first embodiment in that the elastic layer of the pressure roller 50 is made conductive, and as shown in FIG. Independent diodes 19b and 19c are connected between the layer 13b and ground, and between the conductive elastic layer 22 (FIG. 2) of the pressure roller 20 and ground. Other configurations of the image forming apparatus and the fixing device are the same as those of the first embodiment.

The diode 19c is connected to the metal core 21 of the pressure roller 20 to connect the conductive elastic layer of the pressure roller 20 to the ground, and has a potential opposite to that of the conductive primer layer 13b of the fixing film 13. In other words, a potential having a polarity opposite to that of the toner charged in the image forming unit is induced in the pressure roller core 21 and the conductive elastic layer 22.

In this way, an electric field is generated that further increases the toner holding force on the recording material P conveyed to the fixing nip N. Therefore, toner offset, tailing,
Since the effect of preventing the stripping offset is higher, there is no stripping offset even when a conductive material such as carbon black is not dispersed in the fluororesin which is the release layer 13c of the fixing film 13, for example. Good images can be obtained. This is a state in which a potential having a polarity opposite to that of toner generated by peeling discharge generated when the rear end of the recording material is discharged from the fixing nip portion cannot be completely removed from the grounded conductive member 16a immediately after the fixing nip portion. In other words, even when a part of the locally charged up portion of the fixing film remains, since the toner holding power of the subsequent recording material is secured, the toner image is heated and fixed without being peeled off. Because it is done.

In order to confirm the above effects, the first embodiment was used.
Was confirmed for the stripping offset.
The amount of the conductive substance dispersed in the release layer 13c of the fixing film 13 was extremely reduced, and the peeling offset at that time was compared. As a comparative example, the case where a diode was interposed between the conductive primer layer and the ground only on the fixing film side shown in Example 1 was compared.

Table 3 shows the results of the evaluation. In addition, when the number of diodes in the table is 1, the diode connection only on the fixing film side shown in the first embodiment is shown, and when the number of diodes is 2, the fixing film 13 and the pressure roller 20 shown in the present embodiment are respectively connected. On the other hand, the case where diodes 19b and 19c are connected is shown. The amount of the conductive agent indicates the amount of a conductive substance contained in the release layer 13c of the fixing film 13. The recording material evaluated for the peeling offset was left for one day in a low-temperature (10 ° C.), low-humidity (10%) environment.

[0118]

[Table 3] From the above results, it can be seen that in the present embodiment, the peeling offset can be prevented without dispersing any conductive substance in the release layer 13c of the fixing film 13. Therefore, the conductive primer layer 13 of the fixing film 13
There is no need to control the conductive material dispersed in b, and the productivity of the fixing film can be further improved. In particular, when the amount of the conductive substance dispersed in the release layer 13c of the fixing film 13 is small, it is difficult to uniformly disperse the conductive substance. In the embodiment, the productivity of the fixing film can be remarkably improved.

<Third Embodiment> (FIG. 5) In the present embodiment, the toner image of the recording material is retained by positively injecting a charge having a polarity opposite to that of the toner into the back surface of the recording material in the first embodiment. As shown in FIG. 5, a bias applying device 30 was interposed between the conductive member 16a immediately after the fixing nip and the ground as shown in FIG. Other configurations of the image forming apparatus and the fixing device are the same as those of the first embodiment.

The bias application device 30 is connected so that a bias having a polarity opposite to that of the toner charged in the image forming unit is applied from the back of the recording material. As a result, an electric field is generated between a potential and a bias having the same polarity as the toner of the fixing film, and charges having a polarity opposite to that of the toner are positively injected into the back surface of the recording material. It is possible to completely prevent problems such as offset and tailing. Further, even when the conductive material is not dispersed in the release layer 13c of the fixing film 13, a sufficient effect for offset and tailing can be obtained.

The sensor 8 for detecting the front end of the recording material shown in FIG. 1 also detects the rear end of the recording material in the same manner, and matches this with the bias application timing by the bias applying device 30. That is, only when the trailing end of the recording material is discharged from the fixing nip N,
Is turned off to ground. Alternatively, an opposite bias (a bias having the same polarity as the toner) is applied.
This is to enhance the effect of preventing the peeling offset by removing the discharge generated when the rear end of the recording material is discharged from the fixing nip N.

As described above, the recording material P is nipped and conveyed to the fixing nip N, and the conductive member 16 immediately after the fixing nip is formed.
a while the recording material P is in contact with the recording material P.
When the charge of the opposite polarity to the toner is injected into the recording material P from the above, and when the trailing end of the recording material P is discharged from the fixing nip portion N, the conductive member 16a is switched to the ground state, or the same polarity as the toner. Is injected into the recording material P from the conductive member 16a. This makes it possible to completely prevent offset, tailing and stripping offset.

Here, at the moment when the recording material P passes through the fixing nip portion N, the bias from the conductive member 16a to the recording material is reversed, ie, to the peeling offset when the bias is switched to the same polarity as the toner. The effect of prevention was confirmed. The release layer 13c of the fixing film 13 was formed of a fluororesin layer containing no conductive substance. Other configurations were the same as the configurations shown in the first and second embodiments.

Table 4 shows the evaluation results. The switching timing in the table refers to the conductive member 16a immediately after the fixing nip.
The timing at which the bias applied to the recording material is switched is 0 mm at the moment when the recording material leaves the fixing nip, minus is the state in which the recording material is nipped and conveyed to the fixing nip, and plus is when the recording material has left the fixing nip. The numerical values indicate how far the rear end of the recording material is away from the fixing nip discharge port at the timing when the bias is switched. The bias switching is continued until the recording material is completely discharged from the fixing nip. Before the next recording material enters the fixing nip, the original bias application, that is, the bias of the polarity opposite to that of the toner is returned.

[0125]

[Table 4] From the above results, if the bias by the bias applying device 30 is switched immediately before the recording material P is discharged from the fixing nip portion N, the peeling offset can be completely prevented. However, if the timing is too early from the switching timing, the toner holding force of the recording material is lost at the rear end of the recording material, and the recording material may be offset at the rear end.
1 from the moment when the trailing edge of the recording material is discharged from the fixing nip
The switching is preferably performed in a state where the recording material is on the upstream side within a range of 0 mm or less (a state where the recording material is held in the fixing nip portion).

As described above, in the present embodiment, the polarity of the bias applied to the conductive member 16a immediately after the fixing nip portion is switched according to the position of the recording material, so that offset, tailing,
All of the peeling offset can be prevented. In particular,
It is possible to positively inject the charge of the opposite polarity to the toner immediately after the fixing nip in the direction of increasing the holding force of the toner on the recording material, and to positively release the peeling discharge charge at the rear end of the recording material. Even when the resistance of the release layer 13c of the fixing film 13 is high, a good image can be obtained without causing the above problem.

<Others> 1) In the present invention, a film heating type fixing device is
As the driving method of the fixing film, an endless belt-shaped or cylindrical fixing film is used, a driving roller is disposed on the inner peripheral surface side of the film, and the film is tensioned between a plurality of members including the driving roller. And a driving system in which the film is suspended and rotated by a driving roller to drive the film.

Further, an apparatus configuration may be used in which a rolled endless web-shaped fixing film is used, and the film is fed and run.

2) The heating element 11 is not limited to a ceramic heater. For example, an electromagnetic induction heating member such as an iron plate or another heater structure may be used.

The fixing film itself may be provided with an electromagnetic induction heating layer.

3) The fixing device may be of a fixing roller heating type. The fixing roller may generate electromagnetic induction heat.

The fixing device may be of a pressure fixing type or the like.

4) The pressure member need not be a roller.
For example, it may be a rotating belt member.

5) In the present invention, the fixing device is not limited to the heat fixing device of the embodiment, but may be a device for modifying a surface property such as gloss by heating or pressing a recording material carrying an image. A hypothetical wearing device is also included.

6) The principle and process of forming an unfixed toner image on a recording material are arbitrary.

[0136]

As described above, according to the present invention,
A fixing device for fixing the unfixed image on the recording material by passing the recording material on which the unfixed image is formed through a fixing nip portion, which is a mutual pressure contact portion between the fixing member and the pressing member, To prevent the transfer charge of the recording material from leaking through the release layer which is a surface layer of a fixing member such as a fixing member or a fixing film, thereby preventing the occurrence of offset and tailing, and suppressing the charge-up potential. At the same time, it is possible to remove a local charge on the surface of the release layer of the fixing member via the recording material to obtain a good image in which the peeling offset is prevented, and the intended purpose is well achieved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic configuration diagram of a fixing device.

FIG. 3A is a cross-sectional model diagram showing a layer structure of a fixing film, and FIGS.

FIG. 4 is a schematic diagram of a main part of a fixing device according to a second embodiment.

FIG. 5 is a schematic diagram of a main part of a fixing device according to a third embodiment.

FIG. 6 is a schematic configuration diagram of a heat roller type fixing device.

FIG. 7 is a schematic configuration diagram of a film heating type fixing device.

FIG. 8 is a cross-sectional model diagram showing a layer configuration of a fixing film.

FIG. 9 is a schematic cross-sectional view of a release layer in which a conductive material is dispersed.

[Description of Signs] 10: Fixing member (fixing film assembly) 11: Heating element (heater) 12: Heat insulating stay holder 13: Fixing film 13c: Releasable layer 16a: Conductive member 20 ... Pressure member (elastic pressure roller)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masami Takeda 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H027 ED16 ED25 ED26 2H033 BA11 BA13 BD03 BE03

Claims (10)

[Claims] A fixing device that fixes the unfixed image on the recording material by passing the recording material on which the unfixed image is formed through a fixing nip that is a mutual pressure contact portion between the fixing member and the pressing member. 2. The fixing device according to claim 1, wherein a diode element is interposed between the conductive member of the fixing member and ground, and a conductive member in a grounded state is arranged near the fixing nip. 2. The fixing device according to claim 1, wherein a conductive member is provided on the downstream side of the fixing nip in the recording material conveyance direction, and the recording material to be conveyed contacts the conductive member. . 3. A diode element is interposed between the conductive member of the pressing member and ground.
Or the fixing device according to item 2. 4. The apparatus according to claim 1, further comprising a conductive member provided downstream of the fixing nip in the recording material conveyance direction, wherein the conductive member is grounded via a bias applying device. The fixing device according to claim 1. 5. A conductive member is provided downstream of the fixing nip in the recording material transport direction, the conductive member is grounded via a bias applying device, and the conductive member is provided in accordance with the recording material transport position. The fixing device according to claim 1, wherein an applied bias by the bias applying device changes. 6. The fixing device according to claim 1, wherein the fixing device is a heating fixing device. 7. The fixing member according to claim 1, wherein the fixing member is a fixing film in a film heating type fixing device.
7. The fixing device according to any one of items 6 to 6. 8. The fixing device according to claim 1, wherein the fixing member is a fixing roller in a fixing roller heating type fixing device.
7. The fixing device according to any one of items 6 to 6. 9. The fixing device according to claim 1, wherein the fixing device is a pressure fixing device. 10. An image forming apparatus comprising the fixing device according to claim 1. Description: