JP2000321901A - Thermal fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal fixing device by which a pressure member is prevented from being soiled by a recording material using calcium carbonate and tailing offset or peeling offset is reduced. SOLUTION: A fixing member 13 is provided with a fluororesin layer 13b to which conductivity is imparted as the surface layer thereof and a conductive layer 13a as the lower layer thereof. Then, bias voltage whose polarity is identical to toner is applied between the layer 13a and ground or a self-bias element 19b is made to intervene between them. Besides, a conductive member brought into contact with the recording material in order to form a circuit in which a current flows with respect to a ground part through the recording material P from a fixing member is arranged before or behind a fixing nip part. Then, a resistance between the conductive member and the ground is controlled by ionic conduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention employs an image forming process such as an electrophotographic system or an electrostatic recording system, and transfers the image onto a recording material (transfer material, printing paper, photosensitive paper, electrostatic recording paper, etc.). TECHNICAL FIELD The present invention relates to a heat fixing device that heat-fixes an unfixed toner image formed and supported on a recording material by a method or a direct method as a fixed image, and an image forming apparatus to which the heat fixing device is applied.

[0002]

2. Description of the Related Art In a conventional heat fixing apparatus of this type, a recording material P carrying an unfixed toner image passes through a fixing nip formed by a fixing roller and a pressure roller which are pressed against each other and rotated. By so doing, a so-called heating roller type fixing device for fixing an unfixed toner image as a permanent image on the recording material P is widely used because of its high thermal efficiency and high safety.

FIG. 8 is a block diagram showing this heating roller type fixing device. In FIG. 8, reference numeral 40 denotes a fixing roller provided with a heating means, and a halogen lamp 41 is disposed inside a hollow aluminum core 42. A sufficient heating is performed to melt the toner on the recording material P from the inside of the hollow cored bar 42 by supplying power from a power supply (not shown). Further, in order to fix the toner on the recording material P without offsetting the toner on the recording material P, polytetrafluoroethylene (PTFE), A release layer 43 such as a fluoroalkoxytetrafluoroethylene copolymer (PFA) is formed. The release layer 43 is formed in a tubular shape, or is formed by electrostatic coating, spray coating, dip coating, or the like.

In some cases, a conductive material such as carbon black is mixed in the release layer in order to prevent offset caused by charging up of the surface of the fixing roller due to conveyance of the recording material P. Further, the fixing roller 40
The hollow metal core 42 is electrically connected to ground to prevent charge-up on the surface of the fixing roller. The thermistor 44 is in contact with the surface of the fixing roller 40, detects the temperature of the fixing roller surface, and turns on the power supply to the halogen lamp so as to heat the toner image on the recording material P at an appropriate temperature. / OFF control.

On the other hand, a pressing roller 50 presses the fixing roller 40 at both ends in the longitudinal direction of the roller with a pressing spring (not shown) to pinch and convey the recording material P. The pressure roller 50 has an elastic layer formed of silicone rubber or a sponge elastic layer 52 formed by foaming silicone rubber on the outside of the cored bar 51, and further has a PTFE, PFA, FEP or the like similar to the fixing roller 40 on the outside thereof. Mold layer 53
Is formed into a tube or by coating.

Accordingly, a sufficient nip width can be formed between the two rollers due to the elasticity of the pressure roller 50. The unfixed toner image on the recording material P nipped and conveyed in the fixing nip portion can be fixed by heating from the fixing roller 40.

In particular, a method in which power is not supplied to the heat fixing device during standby and power consumption is kept as low as possible, more specifically, a toner on the recording material P via a thin film between a heater and a pressure roller. One example of a film heating device for fixing an image is disclosed in JP-A-63-313182 and JP-A-2-2-1.
It has been proposed in JP-A-57878, JP-A-4-44075, JP-A-4-204980 and the like.

FIG. 9 is a schematic diagram showing the configuration of a heating and fixing apparatus using this film heating method. In FIG. 9, a heating member (heater, hereinafter referred to as a heater) 61 fixedly supported by a stay holder (support) 62. Then, a nip portion (fixing nip portion) having a predetermined nip width (fixing nip portion) having a predetermined nip width is formed on the heater 61 with a heat-resistant thin film (hereinafter, referred to as a fixing film) 63 interposed therebetween by pressing means (not shown). Elastic pressure roller 50.

The heater 61 is heated and adjusted to a predetermined temperature by energization. The fixing film 63 is conveyed and moved in the direction of the arrow while being in close contact with and sliding on the surface of the heater 61 at the fixing nip portion by a driving means (not shown) or the rotational force of the pressure roller 50. Alternatively, it is a rolled end web member.

When the heater 61 is heated and controlled to a predetermined temperature, and the fixing film 63 is conveyed in the direction of the arrow, the unfixed toner is fixed between the fixing film 63 in the fixing nip and the pressure roller 50. When the recording material P on which an image is formed and supported is introduced, the recording material P is brought into close contact with the surface of the fixing film 63 and is conveyed while nipping the fixing nip together with the fixing film.

In the fixing nip portion, the recording material / unfixed toner image is heated by the heater 61 via the fixing film 63, and the unfixed toner image is heated and fixed on the recording material. The recording material P that has passed through the fixing nip is a fixing film 6
3 and is transported. 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). A heating and heating resistor layer such as Pd) • Ta ₂ N is formed by screen printing or the like, and the surface on which the heating resistor layer is formed is covered with a thin glass protective layer.

In the ceramic heater 61, when a current is applied to the current-carrying resistance layer, the current-carrying resistance layer generates heat, and the entire heater including the ceramic substrate and the glass protective layer rapidly rises in temperature. The temperature rise of the ceramic heater 61 is detected by a temperature detecting means 64 provided on the back of the heater, and is fed back to a power supply control unit (not shown). The power supply control unit controls power supply to the power supply heat generating resistance 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 ceramic heater 61 is heated and adjusted to a predetermined fixing temperature.
The fixing film 63 has a heater 61 at a fixing nip portion.
In order to efficiently apply heat to the recording material,
It is formed as very thin as μm.

The fixing film 63 comprises a film base layer 63
a, a conductive primer layer 63b, and a release layer 63c. The film base layer 63a is on the heater side, and the release layer 63c is on the pressure roller side. The film base layer 63a is made of highly insulating polyimide, polyamide imide, PEEK, or the like, and has heat resistance and high elasticity.
It is formed with a thickness of about 15 to 60 μm.

The mechanical strength such as the tear strength of the entire fixing film 63 is maintained by the film base layer 63a. The conductive primer layer 63b is formed of a thin layer having a thickness of about 2 to 6 μm, and is electrically connected to the ground in order to prevent charge-up of the entire fixing film. The releasable layer 63c is a layer for preventing toner offset with respect to the fixing film 63.
It is formed by coating a fluororesin such as FE or FEP to a thickness of about 5 to 10 μm.

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 62
Grease or the like having a high heat resistance is interposed between the outer peripheral surfaces of the above. The pressing member 50 has the same configuration as the above-described pressing roller.

[0016]

However, in the above-mentioned conventional heat fixing device, the surface potential varies greatly depending on the amount of the conductive member mixed in the fixing roller or the fixing film, and all offset and image disturbances are solved. It was difficult to determine the optimal amount of the conductive member. For example, when the fluororesin layer, which is the surface layer of the fixing roller or the fixing film, has a low resistance, the transfer charge on the recording material almost leaks to the conductive primer layer or the conductive hollow core.

As a result, the unfixed 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. In addition, the unfixed toner image is easily scattered by an external force due to a reduction in the charge held on the recording material. For example, when a recording material having a large amount of moisture absorption is heated and fixed, it is ejected from the recording material. The unfixed toner image may be scattered in the direction opposite to the recording material conveyance direction by the water vapor (hereinafter, referred to as tailing).

On the other hand, if the resistance of the release layer is increased in order to prevent the leakage of the transfer charge as described above, the surface of the release layer is charged up, and as a result, offset may occur. is there. For example, when the dried recording material is peeled off from the fixing nip and conveyed, when the rear end of the recording material is discharged from the nip, a portion corresponding to the rear end of the recording material has a line on the surface of the heating member. It charges up like a letter. If the toner image on the succeeding recording material is fixed while maintaining this potential, an offset (hereinafter referred to as a peeling offset) occurs in which the image on the subsequent recording material corresponding to the charged-up position is peeled off. May be.

In recent years, the use of calcium carbonate as a filler for paper as a recording material has been increasing. This calcium carbonate has a property of being strongly charged to a positive polarity, and easily adheres electrically to a fixing roller, a film, or a pressure roller. Alternatively, the problem of sticking to the surface of the pressure roller tends to occur. There is a problem that this phenomenon becomes remarkable particularly in a low humidity environment where static electricity is easily generated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a heat fixing device in which a recording material using calcium carbonate is prevented from being stained by a pressurizing member, and tailing offset and peeling offset are reduced. The purpose is to:

It is another object of the present invention to provide an image forming apparatus which performs a high quality image forming operation by applying the heat fixing device.

[0022]

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

(1) The unfixed toner image is recorded by passing the recording material on which the unfixed toner image is formed through a fixing nip maintained at a predetermined temperature between the fixing member and the pressing member. In a heat fixing device for fixing a permanent image on a material, the fixing member has a fluororesin layer provided with conductivity on a surface layer, has a conductive layer below it, and has a conductive layer and a ground. A bias voltage having the same polarity as that of the toner is applied therebetween, or a self-bias element is interposed therebetween, and a circuit is formed after or before the fixing nip portion, in which a current flows from the fixing member to the ground portion via the recording material. A heat-fixing device, wherein a conductive member is provided in contact with the recording material, and a resistance between the conductive member and the ground is controlled by ionic conductivity.

(2) The heat fixing device according to (1), wherein a conductive member is provided in contact with the recording material conveyed downstream of the fixing nip portion.

(3) The heat fixing device according to claim 1, wherein the conductive member is formed of an ionic conductive member having a resistance value that varies according to ambient temperature or humidity.

(4) The heat fixing device according to claim 1, wherein the conductive member is grounded via an ionic conductive member having a resistance value that varies according to the ambient temperature or humidity.

(5) An image forming apparatus comprising: an image forming means for forming and carrying an unfixed toner image on a recording material; and a heat fixing means for heating and fixing the unfixed toner image formed and carried on the recording material to the recording material. 5. An image forming apparatus, wherein the heat fixing unit is the heat fixing device according to claim 1.

[0028]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1 FIG. 1 shows the configuration of the heat fixing device 6 according to the present invention. In the first embodiment, a description is given of a heat fixing device using a fixing film, but a heat fixing device using a fixing roller may be used.
In FIG. 1, the fixing member 10 includes the following members. Reference numeral 13 denotes a fixing film having a small heat capacity, a polyimide, polyamideimide, PEEK, PPS, PFA, PTFE, and FEP having a total thickness of 100 μm or less and having heat resistance and thermoplasticity to enable quick start.
And the like as a base layer.

Further, a fixing film having sufficient strength and excellent durability for constituting a heat fixing device having a long service life is required to have a total thickness of 20 μm or more. Therefore,
The total thickness of the fixing film 13 is 20 μm or more and 100
μm or less is optimal. Furthermore, in order to prevent offset and to ensure the separation of the recording material, PFA, PTF
A heat-resistant resin such as E or FEP having good releasability is mixed or coated alone. The configuration around the fixing film, which is a main part of the first embodiment, will be described later in detail.

Numeral 11 denotes a heating heater provided inside the fixing film 13, which heats a fixing nip for melting and fixing an unfixed toner image on a recording material.
The heater 11 is provided on the surface of a highly insulating ceramic substrate such as alumina along the longitudinal direction, for example, with Ag / Pd.
(Silver palladium), RuO ₂ , Ta ₂ N, etc., a current-generating resistance layer is screen-printed or the like to a thickness of about 10 μm and a width of
A current-carrying heating member formed by coating in a linear or narrow band shape of about 5 mm. A temperature detecting element 1 such as a thermistor for detecting the temperature of the ceramic substrate, which has been heated in accordance with the heat generated by the heat-generating resistance layer,
4 are provided.

By appropriately controlling the duty ratio, the wave number, and the like of the voltage applied from the electrode (not shown) at the longitudinal end to the energized heating resistor layer in accordance with the detection signal of the temperature detecting element 14, The heating temperature necessary for fixing the unfixed toner image on the recording material is maintained while keeping the temperature of the regulated temperature in the fixing nip substantially constant. DC conduction from the temperature detection element 14 to a temperature control unit (not shown) is achieved by a connector (not shown) via a DC conduction unit (not shown) and a DC electrode unit. In addition, 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.

Reference numeral 12 denotes a heat insulating stay holder for holding the heating heater 11 and preventing heat radiation in a direction opposite to the fixing nip portion, and includes a liquid crystal polymer, a phenol resin, PPS, P
The fixing film 13 is loosely fitted to the outside with a margin and is rotatably arranged in the direction of the arrow. Further, since the fixing film 13 rotates while rubbing against the internal heater 11 and the heat insulating stay holder 12, it is necessary to reduce the frictional resistance between the heater 11 and the heat insulating stay holder 12 and the fixing film 13. . 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. Thereby, the fixing film 1
3 can rotate smoothly.

The pressing member 20 has a structure in which an elastic layer 22 formed by foaming heat-resistant rubber such as silicone rubber or fluorine rubber or silicone rubber is provided on the outside of the cored bar 21. PFA, PTFE, F on top
A release layer 23 such as EP may be formed. The pressing member 20 is sufficiently pressed from both ends in the longitudinal direction to form a fixing nip required for heat fixing by a pressing means (not shown) in the direction of the fixing member 10. , And is rotationally driven in the direction of the arrow by a rotational drive source (not shown) through a metal core 21. As a result, the fixing film 13 is driven and rotated on the outside of the stay holder 12 in the direction of the arrow in the drawing. Alternatively, a driving roller (not shown) is provided inside the fixing film 13 and the driving roller is rotated to rotate the fixing film 13.

The recording material P is appropriately supplied by a supply unit (not shown), and is fed along a heat-resistant fixing entrance guide 15 into a fixing nip formed by a heating member 10 and a pressing member (pressure roller) 20. Conveyed. Thereafter, the recording material P discharged from the fixing nip portion is supplied to a heat-resistant fixing discharge guide 16.
And is conveyed by being nipped by the discharge roller 17 and the discharge roller 18 and discharged onto a discharge tray (not shown).

Here, the fixing film 1 according to the present invention
FIGS. 2 to 4 show the configuration of No. 3 and the configuration around the fixing film. In FIG. 2, reference numeral 13a denotes a film base layer, and a conductive primer layer 13b is formed on the outside as a thin layer having a thickness of about 2 to 6 μm. Here, when the fixing film 13 is made to be entirely insulative, the fixing film 13 causes charge-up due to frictional charging caused by rubbing with the heater for heating. For this reason, an electric field may be generated between the fixing film 13 and the pressure roller 20 to cause an electrostatic offset on the fixing film 13. To avoid this, as described above, the primer layer 1 which is the intermediate layer of the fixing film 13 is used.
The primer layer is made conductive by mixing carbon black or the like into 3b.

As described later, the conductive primer layer 13b is grounded via a diode 19b. A release layer 13c is provided on the outside of the conductive primer layer 13b. As a toner offset prevention layer for the fixing film 13, PFA and PTF having good release properties are provided.
It is formed by coating a fluororesin such as E or FEP to a thickness of about 8 to 18 μm by a coating method such as electrostatic spraying or dipping. In particular, the surface release layer of the fixing film 13 has a volume resistance of 10 ⁶ Ωcm to 10 ¹² Ωcm for the reason described later.
Ωcm range. Further, even when the release layer is scraped due to durability, a thickness of 8 μm or more is required as a thickness sufficient to prevent offset and tailing due to generation of leak.

Further, as shown in FIG. 4, an exposed portion which is not covered with the release layer 13c is provided at an end of the cylindrical fixing film 13, and the exposed portion is made of amorphous fiber or SUS. The conductive brush 19a is in contact with the conductive primer layer 13b and is connected to the ground via the diode 19b. In the drawing, the direction of the diode 19b when the unfixed toner is negatively charged in the image forming apparatus is shown. When the unfixed toner is positively charged, the direction of the diode 19b is reversed. As a result, a potential of the same polarity as that of the unfixed toner is induced in the conductive primer layer 13b of the fixing film 13.

In the first embodiment, as shown in FIG. 3, the induced electric potential of the fixing film 13 and the electric field between the ground and the electric field flow between the recording material P so that a current flows through the fixing nip downstream of the fixing nip. The discharge roller 17 on the side is made conductive and grounded. As the conductivity imparting means, the discharge roller 17
R, a rubber material having ionic conductivity such as epichlorohydrin rubber alone, or a rubber material having the above rubber material dispersed in a silicone rubber having excellent heat resistance and release properties, or a silicone rubber in the silicone rubber. Using a dispersion of a fluorine-based surfactant, and a core metal 17b
By providing such a rubber layer on the top and grounding via the cored bar 17b, it is possible to flow an electric current through the recording material.

Hereinafter, the operation and effect of each of the above-described members will be described based on the specific first embodiment.

The configuration of the heat fixing device is as follows.
The fixing film 13 is a conductive primer layer 13b in which carbon black is dispersed on the outer surface of a polyimide base layer 13a having a thickness of 50 μm, and a liquid in which carbon black is dispersed in a mixture of PFA and PTFE on the surface. It is assumed that the release layer 13c is formed by applying dipping inside and then firing. At this time,
The thickness of the conductive primer layer 13b is 4 μm,
The thickness of c was 10 μm, and the volume resistance of the release layer 13 c was 10 ⁸ Ωcm.

The heater 11 used was one in which Ag and Pd were screen-printed as heat generating resistance layers on an alumina substrate and a glass layer was formed on the surface thereof. The pressure roller 20 is a 50 μm-thick PFA on silicone rubber 22.
A tube 23 having a rubber thickness of 4 mm and an outer diameter of φ25 was used. As the discharge roller 17, a roller in which polyether-modified silicone oil was dispersed in silicone rubber and the resistance value of which was adjusted to 10 ⁷ Ω at normal temperature and normal humidity (23 ° C., 60%) was used.

When such a heat fixing device was applied to an image forming apparatus having a recording material feeding speed of 100 mm / sec and evaluated, the temperature was from room temperature and normal humidity (about 23 ° C. and about 60%) to high temperature and high humidity (3
There are no problems such as image tailing and offset which are problematic under 0 ° C and about 80%.
About 5%) to low temperature and low humidity (about 15 ° C. and about 10%), which cause problems such as peeling offset, fixing film generated when a recording material containing a large amount of calcium carbonate is passed through, and pressure roller contamination. There was no.

On the other hand, when the discharge roller 17 was simply molded with silicone rubber and used in the above-mentioned heat fixing device, tailing and offset were observed. Therefore, when a material having conductivity (resistance of 10 ⁷ Ω or less) was added by dispersing carbon black in the above silicone rubber, no problem of tailing and offset occurred, but in a low humidity environment. Thus, when the recording material P containing a large amount of calcium carbonate was conveyed, a problem of fouling of the fixing film and the pressure roller occurred.

More specifically, in the heat fixing device of the first embodiment, even if 100,000 sheets of A4 size recording material P having a weight of 80 g / m ² and containing 16 wt% of calcium carbonate pass through 100,000 sheets of the fixing film 13, Although there was no dirt on the pressure roller 20,
In the heat fixing device having the discharge roller 17 using the conductive silicone rubber in which the carbon black is dispersed,
Approximately 20,000 sheets were stained with the pressure roller. When the fixing film 13 was directly grounded without using a diode, about 50,000 sheets were stained with a pressure roller.

It is considered that such an action occurs for the following reasons.

When the recording material P is discharged from the fixing nip portion, the recording material P comes into contact with the conductive discharge roller 17 to form a current circuit between the fixing film 13 and the conductive discharge roller 17. Is done. Since a charge having the same polarity as that of the toner is induced in the fixing film 13 by the diode 19b, a potential difference is generated between the fixing nip portion and the conductive discharge roller, and the fixing nip is applied to the conductive discharge roller 17 via the recording material P from the fixing nip portion. The transfer of electric charge having the same polarity as that of the toner occurs.

As a result, the fixing nip portion potential of the recording material P becomes the same as the fixing film surface potential at the fixing nip portion, but a current flows through the fixing film releasing layer at the fixing nip portion, causing a voltage drop. The potential is lower than the surface potential of the fixing film near the fixing nip where no current flows. As a result, a difference is generated between the potential of the recording material P and the surface potential of the fixing film in the vicinity of the nip portion, and an electric field in the direction of attracting the toner to the recording material P works to prevent phenomena such as tailing and offset.

On the other hand, when no current flows from the fixing nip portion to the conductive member via the recording material P, the recording material potential is the same as the fixing nip portion, and the surface potential of the fixing film near the fixing nip is also reduced. Since no electric field acts between the recording material P and the fixing film 13 at the same potential as above, the effect of preventing tailing and offset does not occur.

The conductive discharge roller 17 of the first embodiment
Has the ionic conductivity, and thus has the low resistance value (10 ⁷ Ω or less) in an environment in which tailing and offset pose a problem, so that the above-described effect is exerted. On the other hand, in a low-humidity environment, a current value does not flow from the fixing film 13 to the conductive discharge roller 17 via the recording material P due to a high resistance value. However, in a low-humidity environment, the resistance of the recording material P is high. Since the recording material P sufficiently retains the charge for retaining the toner in the fixing portion, tailing and offset do not cause a problem.

In order to obtain the above-described functions and effects, if the resistance value of the release layer of the fixing film is extremely low with respect to the recording material P, the amount of current flowing through the fixing nip becomes less than the resistance value of the recording material P. Therefore, the voltage drop in the release layer of the fixing nip becomes negligibly small, the potential difference between the recording material P and the fixing film near the fixing nip becomes small, and tailing and offset prevention effects can be expected. Absent.

On the other hand, when the resistance value of the release layer of the fixing film is high, the above effect can be easily obtained. However, since the peeling offset due to the charge-up described above is easily generated, the release layer is extremely hardened. The resistance cannot be increased. According to the study of the present inventors, an appropriate range of the resistance value of the releasable layer differs depending on the recording material feeding speed of the image forming apparatus, and means for generating a voltage of the same polarity as the toner on the fixing film 13. Although the appropriate range differs depending on whether a self-bias is used or a voltage is applied by a power supply, the release layer resistance value is 10 ⁶ Ωcm to 10 ¹² Ωcm in volume resistance.
The above-mentioned effects can be obtained by appropriately selecting a value between Ωcm and Ωcm.

Further, by imparting ionic conductivity to the discharge roller 17, the resistance of the discharge roller increases in a low humidity environment, and the electric field does not work between the fixing film 13 and the recording material P as described above. Calcium carbonate contained in the recording material is strongly charged to a positive polarity and easily charged. Therefore, if an electric field exists between the recording material P and the fixing film 13 to attract toner (negatively charged in this embodiment) in the direction of the recording material. Calcium carbonate is easily transferred to the fixing film, and then transferred to the pressure roller 20 via the fixing film 13, and the toner slightly offset on the fixing film with the calcium carbonate as a nucleus is transferred onto the fixing film or It sticks on the pressure roller and accumulates due to durability.

In the first embodiment, no electric field acts between the recording material P and the fixing film 13.
The recording material P also has the same potential due to the effect of the potential of the same polarity as the toner generated in the toner 3, so that the recording material P acts to electrically restrain the calcium carbonate, which is the filling amount, and the calcium carbonate is applied to the fixing film 13. The effect that the transfer to the pressure roller 22 becomes difficult occurs, and the fixing film 13 and the pressure roller 2 caused by the recording material P containing a large amount of calcium carbonate are generated.
It is considered that this works effectively as a countermeasure against zero contamination.

In order to obtain such an effect, the
Roller resistance is 10 at normal temperature and humidity ⁶-10⁸Ω, under low humidity
Then 10⁸This is achieved by showing a resistance value of Ω or more. What
Note that the resistance value is 10 mm width metal foil on the outer peripheral surface of the discharge roller.
Roller core metal when a voltage of 200V is applied
Was determined from the value of the current flowing through.

Embodiment 2 Hereinafter, the second embodiment will be described with reference to FIG.
Will be described. The configuration of the entire apparatus is the same as that of the first embodiment.
1 and the configuration in the heat fixing device and the configuration of the fixing film 13 are also the same as those in FIGS. 2 and 3 described in the first embodiment, and therefore description thereof is omitted. In the second embodiment, a configuration is adopted in which a bias voltage is applied to the fixing film 13 from a power supply.

In FIG. 5, reference numeral 19 denotes a power source provided between the fixing film 13 and the ground E, which can be appropriately selected from -200 to -1000 V. In the second embodiment, the power source is -600 V.
Is applied to the conductive primer layer 13b of the fixing film 13. Since the operation and effect of the second embodiment are the same as those of the first embodiment, description thereof will be omitted. However, since a bias voltage is applied to the fixing film 13, the tailing and offset prevention effects are further enhanced, and the image quality is further improved. The configuration is suitable for increasing the speed of the forming apparatus.

As in the first embodiment, the configuration of the heat fixing device is such that the fixing film 13 having an inner diameter of φ24 is used.
The fixing film 13 is dipped in a conductive primer layer 13b in which carbon black is dispersed on the outer surface of a polyimide base layer 13a having a thickness of 50 μm, and the surface thereof is dipped in a liquid in which carbon black is dispersed in a mixture of PFA and PTFE. Thereafter, firing is performed to form the release layer 13c. At this time, the thickness of the conductive primer layer 13b was 4 μm, the thickness of the release layer 13c was 10 μm, and the volume resistance of the release layer 13c was 10 ⁸ Ωcm.

The heating heater 11 used was one in which Ag / Pd was screen-printed as an exothermic resistance layer on an alumina substrate and a glass layer was formed on the surface thereof. The pressure roller 20 used was a silicone rubber covered with a 50 μm thick PFA tube, having a rubber thickness of 4 mm and an outer diameter of φ25. The discharge roller 17 disperses a polyether-modified silicone oil in silicone rubber,
(° C./60%), a roller whose resistance value was adjusted so as to have a resistance value of 10 ⁷ Ω was used.

When such a heat fixing device was applied to an image forming apparatus having a recording material feeding speed of 150 mm / 8 ec and evaluated, the temperature was from room temperature and normal humidity (about 23 ° C. and about 60%) to high temperature and high humidity (3
There are no problems such as image tailing and offset which are problematic under 0 ° C and about 80%.
5%) to low temperature and low humidity (I5 ° C. · 10%), which cause problems such as peeling offset, a fixing film generated when the recording material P containing a large amount of calcium carbonate is passed through, and pressure roller contamination. There was no.

Embodiment 3 The third embodiment will be described below. The overall configuration of the apparatus is the same as that shown in FIG. 1 described in the first embodiment, and the configuration inside the heat fixing device and the configuration of the fixing film 13 are also the same as those shown in FIG.
The description is omitted because it is the same as FIG. In the third embodiment, the ionic conductive discharge roller 1 used in the first and second embodiments uses a conductive member that contacts the back surface of the recording material.
As shown in FIG. 6, a conductive brush 15 is provided on the entrance side of the fixing device in contact with the back surface of the recording material. The conductive brush 15a is grounded by a sheet member 15b having ion conductivity. This sheet member 15b
Is a rubber sheet made of epichlorohydrin rubber or NBR. The rubber sheet may have a resistance value similar to that of the discharge roller 17.

In the above embodiment, the electric field for holding the toner on the recording material between the fixing film 13 and the recording material P does not act until the leading end of the recording material P comes into contact with the discharge roller 17. In the third embodiment, since the conductive brush 15a is also provided before the fixing nip, the action of the electric field can be obtained from the moment when the recording material P enters the fixing nip, and the tail can be obtained over the entire recording material. An image without pulling is obtained. Further, by grounding the conductive brush 15a via the sheet member 15b having ionic conductivity, the range of material selection of the conductive brush 15a to be brought into contact with the recording material P is widened, and the recording is performed as in the third embodiment. It is also possible to use a very soft conductive brush 15a which does not hinder material conveyance.

Embodiment 4 FIG. 7 is a configuration diagram of an image forming apparatus to which the heat fixing device of the present invention is applied. In FIG. 7, reference numeral 1 denotes a photosensitive drum, on which a photosensitive material such as OPC, amorphous Se, amorphous Si or the like is formed on a cylindrical base such as aluminum or nickel.
The photosensitive drum 1 is driven to rotate in the direction of the arrow.
The surface is uniformly charged by a charging roller 2 as a charging device.

Next, the charged surface of the photosensitive drum 1 is subjected to scanning exposure with a laser beam 3 whose ON / OFF is controlled according to image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a developing method, a jumping developing method, a two-component developing method, or the like is used, and a combination of image exposure and reversal developing is often used.

The visualized unfixed toner image is transferred from the photosensitive drum 1 onto the recording material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. Here, the sensor 8 detects the leading end of the recording material so that the image forming position of the unfixed toner image on the photosensitive drum 1 matches the writing start position of the leading end of the recording material, and the timing is adjusted. The recording material P conveyed at a predetermined timing is nipped and conveyed by the photosensitive drum 1 and the transfer roller 5 with a constant pressing force. The recording material P to which the unfixed toner image has been transferred is conveyed to the heat fixing device 6 according to the present invention, and passes through the heat fixing device 6, whereby the unfixed toner image is fixed on the recording material as a permanent image. You. On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed by the cleaning device 7.
As a result, it is removed from the surface of the photosensitive drum 1.

[0066]

As described above, according to the present invention, a recording material on which an unfixed toner image has been formed is passed through a nip maintained at a predetermined temperature between a fixing member and a pressing member. Thereby, in the heat fixing device for fixing the unfixed toner image as a permanent image on a recording material, the fixing member has a fluororesin layer provided with conductivity on the surface layer, and a conductive layer as a lower layer. A bias voltage having the same polarity as the toner is applied or a self-bias element is interposed between the conductive layer and the ground, and after or before the fixing nip, the fixing member is connected to the ground via a recording material. A conductive member is provided in contact with the recording material to form a circuit through which a current flows, and the resistance between the conductive member and the ground is configured to be 10 ⁸ Ω or more depending on the environment. sex Hardly charged up by providing the grant was fluororesin layer, as a result, it is possible to prevent the peeling offset.

At the same time, a bias voltage or a self-bias having the same polarity as the toner on the recording material is generated in the fixing member, and a circuit for flowing a current between the fixing nip portion and the ground via the recording material is formed. An electric field for restraining the toner on the recording material can be generated in the nip portion, and tailing and offset phenomenon due to transfer charge leakage on the recording material can be prevented.

Further, since the resistance value between the conductive member and the ground is controlled by the environment, it is possible to prevent the calcium carbonate, which is a filler in the recording material, from adhering to the fixing member electrostatically, especially in a low humidity environment. As a result, it is possible to obtain a heat fixing device having such an effect that the toner can be prevented from being fixed to the fixing member and the pressing member.

Since this heat fixing device is applied,
The effect of providing a high quality image forming apparatus is obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a heat fixing device according to the present invention.

FIG. 2 is a cross-sectional view of the fixing film according to the first embodiment of the present invention.

FIG. 3 is an enlarged view of a downstream side of a fixing nip according to the first embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of Embodiment 1 of the present invention.

FIG. 5 is a longitudinal sectional view of Embodiment 2 of the present invention.

FIG. 6 is an enlarged view of a downstream side of a fixing nip according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of a heat fixing device according to a conventional example.

FIG. 9 is a configuration diagram of a heat fixing device according to a conventional example.

[Explanation of symbols]

Reference Signs List 1 photosensitive drum (image forming means), 2 charging roller (image forming means), 3 laser beam (image forming means), 4 developing device (image forming means), 5 transfer roller (image forming means), 6 heat fixing device, Reference Signs List 11 heater for heating, 12 heat insulating stay holder, 13 fixing film (fixing member), 13a film base layer, 13b conductive plasma layer, 13c release layer,
20 pressure roller (pressure member), 15a, 18 conductive brush (ion conductive member).

Claims (5)

[Claims] An image forming apparatus comprising: a recording material having an unfixed toner image formed thereon is passed through a fixing nip maintained at a predetermined temperature between a fixing member having a heat source and a pressing member,
In a heat fixing device for fixing the unfixed toner image as a permanent image on a recording material, the fixing member has a fluororesin layer provided with conductivity on a surface layer, and has a conductive layer as a lower layer, A bias voltage having the same polarity as that of the toner is applied or a self-bias element is interposed between the conductive layer and the ground, and a current flows from the fixing member to the ground via a recording material before or after the fixing nip. A conductive member that contacts a recording material in order to form a circuit through which heat flows, and controls the resistance between the conductive member and ground by ionic conduction. 2. The heat fixing device according to claim 1, further comprising a conductive member that contacts a recording material conveyed downstream of the fixing nip portion. 3. The heat fixing device according to claim 1, wherein the conductive member is formed of an ionic conductive member having a resistance value that varies according to ambient temperature or humidity. 4. The heat fixing device according to claim 1, wherein the conductive member is grounded via an ionic conductive member having a resistance value that varies according to ambient temperature or humidity. 5. An image forming apparatus comprising: an image forming unit for forming and supporting an unfixed toner image on a recording material; and a heat fixing unit for heating and fixing the unfixed toner image formed and supported on the recording material to the recording material. 5. The image forming apparatus according to claim 1, wherein the heat fixing unit is the heat fixing device according to claim 1. 6.