JP2003122151A - Thermal fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent image even when the printing speed is made higher by making the restraint of a toner's backward scattering phenomenon compatible with the prevention of the adhesion of calcium carbonate to the surface of a rotating body coming into contact with the unfixed image surface of recording material, in a thermal fixing device which has the rotating body 34 equipped with a heating source 33 and coming into contact with the unfixed image surface of the recording material P and a pressurizing member 32 coming into press-contact with the surface of the rotating body, and where the recording material P on which an unfixed image T is formed is introduced and made to pass through the press-contact nip part N of the pressure member with the rotating body so that the unfixed image is fixed on the recording material as a permanent image Ta. SOLUTION: This thermal fixing device is characterized in having an electrode 41 coming into contact with the recording material P and a means 43 applying bias having the same polarity to the electrode 41 and the pressure member 32 at least while the recording material P passes through the press- contact nip part N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic type, electrostatic recording type, magnetic recording type image forming apparatus,
An unfixed image (unfixed toner image) formed and carried on a recording material (transfer material sheet, electrostatic recording material, electrofax paper, printing paper, etc.) by a transfer method or a direct method is heated as a permanently fixed image on the recording material. The present invention relates to a fixing device for fixing.

[0002]

2. Description of the Related Art Conventionally, most of the above-mentioned image forming apparatuses such as copying machines and printers use a contact heating type heat roller system or an energy saving type film heating system as a fixing device which has good thermal efficiency and safety. It is adopted.

(A) Heat roller system As shown in FIG. 8, a heat roller system fixing device includes a heating roller 31 (hereinafter referred to as a fixing roller) as a heating rotator having a halogen heater 37 therein, and a fixing device. Roller 31
The pressure roller 32, which is in pressure contact with the pressure roller 32 as a pressure rotating body, has a basic configuration. By rotating the pair of rollers and introducing and conveying the recording material P carrying the unfixed image (toner image) T to the pressure contact nip portion N (hereinafter, fixing nip portion) formed by the pair of rollers, This is a device that heat-pressure-fixes the unfixed image T on the recording material P as a permanently fixed image Ta by heat from the fixing roller 31 and pressing force of the fixing nip portion N.

(B) Film heating system On the other hand, in the film heating type fixing device, as shown in FIG. 7, a heating member (hereinafter, heater) 33 is provided with a heat-resistant film 34 (hereinafter, fixing film) as a heating rotary member. ) Is brought into close contact with a pressure roller 32 as a pressure rotator and slidably conveyed, and an unfixed image T is applied to a fixing nip portion N formed by the heater 33 and the pressure roller 32 with the fixing film 34 interposed therebetween. By introducing the carried recording material P and conveying it together with the fixing film 34, the heat from the heater 33 applied through the fixing film 34 and the pressing force of the fixing nip portion N
This is a device for fixing the unfixed image T to the recording material P as a permanently fixed image Ta by heat and pressure.

The former (A) is often used for a large machine having a relatively high speed, and the latter (B) is often used for a small machine having a relatively low speed.

In recent years, image forming apparatuses such as electrophotographic printers using the above fixing device have been strongly required to have higher printing speed as well as improved image quality. In order to realize the high speed, the output of the main motor is increased to increase the rotation speed of the pressure roller 32, the fixing film 34, etc., and the staying time in the fixing nip portion N is shortened by the high speed. In order to supply sufficient heat energy to P, it is necessary to improve the fixing temperature, increase the fixing nip, and improve the thermal conductivity of the heater substrate and the fixing film 34.

However, by carrying out these improvements, adverse effects are likely to occur in the fixing nip portion N. For example, in the case of the film heating type fixing device shown in FIG. 7, just before the recording material introducing portion of the fixing nip portion N, the unfixed toner T on the recording material P is partially moved in the recording material conveying direction like Tb. A phenomenon in which the toner is scattered to the upstream side (hereinafter, rearward toner scattering phenomenon) occurs, and the higher the printing speed, the worse the rearward toner scattering phenomenon Tb.

As a mechanism for generating the rearward toner scattering phenomenon Tb, the water contained in the recording material P becomes steam due to the heating in the fixing nip portion N, but when the fixing temperature is increased as the speed is increased, the amount of steam generated is also increased. As a result, the amount of water vapor that has sought to escape is strongly blown out in the front-back direction of the fixing nip portion N. At the same time, since the conveying speed of the recording material P is also high, the unfixed toner T on the recording material P at the recording material introducing portion of the fixing nip portion N has the speed of the steam ejected from the fixing nip portion N to the recording material P. Since the steam is blown at a wind speed that combines the transport speeds, the recording material P
It is considered that a part of the unfixed toner image T, which has a weak adhesive force to, and is easily affected by the steam flow, is blown off by the wind pressure of the steam. This rear toner scattering phenomenon Tb largely depends on the electric resistance, surface property, etc. of the recording material P, but is most likely to occur especially in a toner image having a pattern perpendicular to the recording material conveyance direction such as a horizontal line.

As a countermeasure against this phenomenon, a method of increasing the electrostatic adhesive force of the unfixed toner image T to the recording material P has been attempted. For example, as shown in FIG. 6, in a film heating type fixing device, a bias power supply unit 43 and an electrode 42 such as a conductive brush are provided on the conductive layer portion of a fixing film 34 including a release layer, a conductive layer and a base material layer from the surface. Through the charging polarity of the toner T (in this example, negative polarity)
A predetermined amount of bias having the same polarity as that of (hereinafter, fixing bias) is applied, the release layer on the surface of the pressure roller 32 is sandwiched, and the toner T on the recording material P is generated by the repulsive electric field from the printing surface side by the action of the electric field. A method of holding down is used.

In order to further enhance the effect, as shown in FIG. 5, an electrode 41 such as a grounded conductive brush is provided on the downstream side of the fixing nip portion N in the recording material conveying direction, and the recording material after passing through the fixing nip portion is provided. Recording is performed by applying a fixing bias of the same polarity as that of the toner T to the fixing film 34 in a predetermined amount in the same manner as in the above-described system by adopting a configuration in which the electrode 41 is in contact with the back surface which is the side opposite to the printing surface side of P. Electrode 41 through resistance of material P
A method of inducing a charge having a polarity opposite to that of the bias applied from the ground portion of the recording material P on the back surface of the printing surface of the recording material P and attracting and fixing the toner T having a polarity opposite to the recording material P by the induced charge is used.

[0011]

However, depending on the type of the recording material P, there are recording materials containing calcium carbonate having a strong positive polarity as a filling amount. In the case of a conventional system using a toner of negative polarity, since a fixing bias of negative polarity is applied to hold the surface of the fixing film at a negative potential, calcium carbonate may adhere to the surface of the fixing film. In particular, when a strong negative bias is applied as the fixing bias and the surface potential of the fixing film is maintained at the strong negative potential, the adhesion easily occurs. The adhesion causes deterioration of the releasability of the fixing film and toner adhesion due to electrostatic adsorption, and then the toner is transferred and accumulated on the surface of the pressure roller, and finally on the back side of the printing surface of the recording material. There is a possibility that it will be discharged as toner stains and cause an image problem.

Further, as the printing speed is increased, the amount of bias applied to the recording material required to suppress the rear toner scattering phenomenon Tb is also increased. However, each of the release film of the fixing film and the pressure roller that forms an electric field by applying a bias,
Since both are thin film layers, the withstand voltage against bias is low. Therefore, excessive application of bias exceeding withstand voltage is
There is a possibility that an electric field between the fixing film and the pressure roller may be destroyed by a leak, causing an image defect.

The above-mentioned problems are common to the heat roller type fixing device.

Therefore, the present invention is to solve the above-mentioned problems in this type of heat fixing device, and its object is to suppress the rear toner scattering phenomenon and to rotate the recording material in contact with the unfixed image surface. It is an object of the present invention to provide a heating and fixing device that can simultaneously prevent the adhesion of calcium carbonate to the body surface and can obtain a good image even when the printing speed is increased.

[0015]

The present invention is a heating and fixing device characterized by the following constitution.

(1) A rotating body provided with a heating source and in contact with the unfixed image surface of the recording material, and a pressure member in pressure contact with the surface of the rotating body. In a heat fixing device for introducing a recording material on which an unfixed image is formed into a pressure nip portion and passing the recording material to fix the unfixed image as a permanent image on the recording material, at least an electrode in contact with the recording material, While the recording material is passing through the pressure contact nip,
A heating and fixing device comprising: the electrode and a means for applying a bias having the same polarity to the pressing member.

(2) A rotary body having a heating source and in contact with the unfixed image surface of the recording material, and a pressure member in pressure contact with the surface of the rotary body. In a heat fixing device for introducing a recording material on which an unfixed image is formed into a pressure nip portion and passing the recording material to fix the unfixed image as a permanent image on the recording material, at least an electrode in contact with the recording material, While the recording material is passing through the pressure contact nip,
A heating and fixing device comprising: the electrode and a unit that applies biases of different polarities to the rotating body.

(3) The electrode is installed on the downstream side of the pressure contact nip portion in the recording material conveying direction and in contact with the back surface of the printing surface of the recording material that has passed through the nip (1). ) Or (2) the heat fixing device.

(4) In any one of (1) to (3), the rotating body is an endless belt having a multilayer structure including a conductive layer and is grounded through the conductive layer. (5) The heat fixing device described in (5), wherein the pressing member is a rotating body composed of a release layer, an elastic layer, and a cored bar in this order from the surface, and a bias is applied through the cored bar. The heat fixing device according to any one of (1) to (4).

(6) The heat fixing device according to (5), wherein the release layer has an insulating property and the elastic layer has a conductive property.

(7) The heat fixing device according to (1), wherein the bias application amount to the electrode is larger than the bias application amount to the pressing member.

(8) The heat fixing device (9) according to (2), wherein the rotating body is an endless belt having a multilayer structure including a conductive layer, and a bias is applied through the conductive layer. The heat fixing device according to (2), wherein the amount of bias applied to the electrode is larger in absolute value than the amount of bias applied to the rotating body.

[Working] In other words, since a bias of reverse polarity to the unfixed image (toner) is positively applied from the electrode to the back side of the printing surface of the recording material, the unfixed image holding force on the recording material increases and The toner scattering phenomenon can be suppressed.
Further, even at the leading edge of the recording material, to which the bias cannot be applied, which corresponds to the distance until the recording material passes through the pressure contact nip portion (fixing nip) and comes into contact with the electrode, the bias of the polarity opposite to that of the unfixed image on the pressing member By applying the voltage, the potential of the surface of the pressure roller is regulated to have a polarity opposite to that of the unfixed image, whereby the unfixed image holding force can be increased from the leading end of the recording material.

On the other hand, when the charging polarity of the unfixed image is negative, a positive current flows from the electrode through the recording material to the rotating body contacting the unfixed image surface of the recording material, and the surface of the rotating body during sheet feeding. Since the potential is kept positive, it is possible to prevent calcium carbonate from adhering to the rotating body from the recording material.

Further, since a bias is directly applied to the recording material from an electrode outside the pressure contact nip portion (fixing nip), and a rotating member is grounded to provide a current path through the recording material, in the conventional method, the inside of the pressure contact nip is It is also possible to apply a high bias at a level that causes leakage, and a good image can be obtained even if the printing speed is increased.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] (1) Example of Image Forming Apparatus FIG. 1 is a schematic diagram of an example of an image forming apparatus. The image forming apparatus 1 of this example is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 11 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed. The photosensitive drum 11 is formed by forming a photosensitive material such as OPC or amorphous silicon on a cylindrical substrate such as aluminum or nickel.

First, the rotating photosensitive drum 11 is
The surface is uniformly charged by a charging roller 12 as a charging device. In this example, it is uniformly charged to a predetermined negative potential.

Next, the uniformly charged surface of the rotating photosensitive drum 11 is exposed to a laser scanner 13 which is an image exposing means.
Scanning exposure is performed by the laser beam L output from the ON / OFF control according to the image information, and an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 11.

This electrostatic latent image is developed (visualized) as a toner image by the developing device 14. As a developing method, a jumping developing method, a two-component developing method, or the like is used, and it is often used in combination with image exposure and reversal developing.

The recording material P is fed from the cassette 21 to the paper feed roller 2
It is taken out by 2 and sent to the registration roller 23. The recording material P is synchronized with the toner image formed on the surface of the photosensitive drum 11 by the registration roller 23,
It is supplied to a transfer nip portion formed by the photosensitive drum 11 and the transfer roller 15. The toner image on the surface of the photosensitive drum 11 and the recording material P in the transfer nip portion may be synchronized with each other by a registration sensor.

At the transfer nip portion, the toner image on the photosensitive drum 11 is transferred onto the recording material P by the action of a transfer bias by a power source (not shown).

The recording material P, which is separated from the surface of the photosensitive drum 11 and holds the unfixed toner image, is conveyed to the heat fixing device 3, and is heated and pressed in the fixing nip portion of the heat fixing device 3 to record the toner image. The image is fixed on the material P, becomes a permanent image, and is discharged out of the apparatus.

On the other hand, the transfer residual toner remaining on the photosensitive drum 11 after the transfer is removed from the surface of the photosensitive drum 11 by the cleaning device 16.

(2) Heat Fixing Device 3 FIG. 2 is a schematic diagram of the heat fixing device 3. The heat fixing device 3 of this embodiment is a film heating type device.

This film heating type heat fixing device 3
Is a tensionless type device described in, for example, JP-A-4-44075 to 44083. Reference numeral 34 denotes an endless belt-shaped flexible heat-resistant film (hereinafter, referred to as a rotating body that contacts the unfixed image surface of the recording material).
Fixing film). Reference numeral 35 is a film guide member having a semicircular cross section, and 33 is a ceramic heater as a heating source, which is fixedly arranged on the lower surface of the film guide member 35 along the length of the member. The fixing film 34 is a film guide member 3 holding a ceramic heater 35.
It is fitted on the outer circumference of the No. 5 with a margin in its circumference (state where no tension is applied). Reference numeral 32 is an elastic pressure roller as a pressure member which is pressed against the lower surface of the ceramic heater 33 through the fixing film 34 to form the fixing nip portion N.

The pressure roller 32 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed by a drive system (not shown). The fixing film 3 is driven by the rotation of the pressure roller 32.
4 rotates around the outer circumference of the film guide member 35 in the clockwise direction of the arrow while sliding in close contact with the lower surface of the ceramic heater 33.

Then, the pressure roller 32 and the fixing film 3
4 is rotated as described above to energize the ceramic heater 33 to raise the temperature of the heater 33, and the temperature of the heater 33 is adjusted to a predetermined fixing temperature by an energization control circuit (not shown) including the heater temperature detection member 36. In this state, the recording material P carrying the unfixed image T is introduced between the fixing film 34 in the fixing nip portion N and the pressure roller 32, and the recording material P is conveyed together with the fixing film 34. The unfixed image T is thermally and pressure-fixed on the recording material P as the permanently fixed image Ta by the heat from the heater 33 and the pressure applied in the fixing nip portion N via the fixing member.

.. Fixing Film 34 The fixing film 34 is made of polyimide, polyamide imide,
PTFE, PF are provided on the surface of a heat-resistant resin film having a low heat capacity such as PEEK and PES via a conductive primer layer.
A composite layer film obtained by coating a release layer in which a conductive member such as carbon black is mixed with A, FEP and the like.

The release layer is designed to have an optimum resistance value so as not to cause various image defects. Further, the fixing film 34 is grounded by exposing the conductive primer layer on a part of the surface of the fixing film and contacting it with a conductive member 42 such as a grounded conductive brush.

The fixing film 34 may be a metal sleeve in which the surface of a thin metal tube made of stainless steel or the like is coated with the release layer via a primer layer. In this case, because of the grounding of the fixing film 34, the metal tube is partially exposed on the surface of the metal sleeve.

.. Ceramic Heater 33 The ceramic heater 33 is formed by sequentially forming a heating element on which a heating paste is printed on a ceramic substrate and a glass coating layer for protecting the heating element and ensuring insulation. Heat is generated by passing a power-controlled AC current. Aluminum nitride, aluminum oxide, or the like is used as the material of the ceramic substrate. A thermistor 36 as a heater temperature detecting member is brought into contact with the back of the ceramic substrate, and a ceramic heater 33 is provided by an energization control circuit including the thermistor 36.
Is controlled to control the heater temperature to a predetermined fixing temperature.

.. Pressure Roller 32 The pressure roller 32 as a pressure member is made of a metal cored bar with a resilient layer of heat-resistant rubber such as silicon rubber or a foam sponge resilient layer sandwiched between PFA, PTFE, and FEP.
The rotating body is composed of an insulating release layer made of fluororesin or the like.

The elastic layer is made conductive by mixing a conductive member such as carbon black in order to suppress charge-up on the surface of the insulating release layer. The core metal of the pressure roller 32 is connected to the bias power source 43. The pressure roller 32 is pressed against the lower surface of the ceramic heater 33 via a fixing film 34 by a spring (not shown) to form a fixing nip portion N. As a form of the pressing member, a rotating belt or the like may be used other than the pressing roller 32 in the present embodiment.

.. A lower surface of the ceramic heater 33 in the lubricant fixing nip portion N, that is, a glass coating layer of the ceramic heater 33,
The back surface (inner peripheral surface) of the fixing film 34, that is, the recording material P
A lubricant is interposed between the surface of the fixing film 34 and the surface on the side opposite to the side in contact with the toner image to stabilize the sliding torque between the fixing film 34 and the ceramic heater 33 in the fixing nip portion N to a low level, The slip between the recording materials P is prevented. As the lubricant, fluorine-based grease (for example,
Product name HP-300 GREASE (Dow Corning) or product name DEMNUM GREASE L-65
(Daikin Industries, Ltd.) and other heat-resistant products are used.

.. Electrode 41 On the downstream side of the fixing nip portion N in the recording material conveyance direction, an electrode 41 such as a conductive brush is provided at a position in contact with the back surface of the printing surface of the recording material P that has passed through the fixing nip portion N. This electrode 41
Is connected to the bias power source 43. The electrode 41
May be provided on the upstream side of the fixing nip portion N in the recording material conveyance direction, but as described later, a bias having a polarity opposite to that of the toner is applied to the electrode 41, and the toner may adhere to the electrode 41. Therefore, it is preferable to provide the fixing nip portion N on the downstream side.

The electrode 41 may be in the form of a roller or a guide as long as it has conductivity.

.. Application of fixing bias From bias power source 43, pressure roller 32 via core metal
Then, a fixing bias having a positive polarity opposite to the toner T (here, a negative polarity toner is used) is applied to the electrode 41. The fixing bias is applied at least while the recording material P is passing through the fixing nip portion N.

.. Suppression of Rearward Toner Scattering Phenomenon Since the fixing film 34 is grounded via a conductive member 42 such as a conductive brush, a positive current circuit flowing from the electrode 41 to the fixing film 34 via the recording material P is formed. By forming this current circuit, the recording material P is transferred from the electrode 41.
Since the positive bias is positively applied to the back surface of the printing surface, the toner holding force on the recording material P is increased, and the rear toner scattering phenomenon can be suppressed.

On the other hand, after the recording material P has passed through the fixing nip portion N,
The fixing bias cannot be applied from the electrode 41 to the recording material P until the electrode 41 comes into contact with the recording material P. Therefore, in order to increase the toner holding force at the leading end of the recording material corresponding to the distance between the fixing nip and the electrode 41, a positive bias is applied to the pressure roller 32 and the pressure roller surface is regulated to a positive potential. The toner holding force can be increased from the leading end of the recording material.

.. Prevention of Calcium Carbonate Adhesion Since a positive current flows from the electrode 41 through the recording material P to the fixing film 34, and the surface potential of the fixing film 34 during paper passing is kept positive, the positive polarity calcium carbonate repels, It is possible to prevent calcium carbonate from adhering to the fixing film 34 side from the recording material P side which is nipped and conveyed in the fixing nip portion N. It should be noted that although the recording material containing a negative polarity filler also depends on the type, it does not adhere because the polarity of the filler itself is not as strong as calcium carbonate.

(3) Comparative Experiment with Conventional Example A case where the fixing device 3 in the present example is used and a negative bias is applied to the fixing film 3 as in the conventional example (FIG. 5).
No. 4 and No. 4, the comparison experiment of the rear toner scattering phenomenon level and calcium carbonate adhesion depending on the fixing bias application amount was performed at different printing speeds (25/35 / 45P).
The results are shown in Table 1. In the table, ○ is OK level, △ is a level that has no practical problem, and × is N.
The rear toner scattering phenomenon indicating the G level is 23 ° C./6.
For plain paper that has been left for 24 hours or more in an environment of 0% RH,
Evaluation was performed by printing a pattern in which lines were arranged in a direction orthogonal to the paper transport direction.

Calcium carbonate adhesion is 15 ° C./10
Evaluation was performed by passing 10,000 character patterns every 2/10 minutes on a paper containing calcium carbonate in an environment of% RH.

[0054]

[Table 1]

As the printing speed increases, the fixing bias amount (absolute value) applied to the recording material P necessary to suppress the rear toner scattering phenomenon increases. Therefore, as shown in Table 1, when a fixing bias commensurate with the print speed was applied to suppress the rear toner scattering, calcium carbonate began to adhere from around 35 PPM in the conventional example, but in the present embodiment, it also adheres at 45 PPM. It was confirmed that there is no.

That is, by adopting a means for suppressing the toner scattering phenomenon by applying a positive current to the recording material P,
Since the surface potential of the fixing film 34 during sheet feeding can be kept positive, it is possible to both suppress the rear toner scattering phenomenon and prevent calcium carbonate from adhering to the fixing film 34.

In this embodiment, the film heating method is explained as an example of the fixing device, but it goes without saying that the same effect can be obtained even if the heat roller fixing method is used.

[Embodiment 2] Next, as Embodiment 2, another example of a fixing bias applying method is shown in FIG. The parts having the same functions as those in the first embodiment described above are designated by the same reference numerals and the description thereof is cited.

(1) Application of Fixing Bias In this embodiment, the fixing bias amount applied to the pressure roller 32 and the fixing bias amount applied to the electrode 41 are set to different values. In order to apply the fixing bias individually, as shown in FIG.
And is provided independently of the electrode application 43b. The bias power source may be common, and resistors having different values may be interposed between the power source and the pressure roller or the electrode 41.

(2) Comparative Experiment with Conventional Example and Example 1 In the case where the above heat fixing device in Example 2 is used,
For the conventional fixing device (FIG. 5) and the heat fixing device of the first embodiment (FIG. 2), the printing speed (45/50/55 PPM) higher than that of the comparative experiment shown in the first embodiment was applied to the rear side by the fixing bias application amount. Table 2 shows the results of a comparative experiment of the toner scattering phenomenon level and the presence / absence of a leak between the fixing film 34 and the pressure roller 32. In the table, “◯” indicates an OK level, “Δ” indicates a level having no practical problem, and “X” indicates an NG level.

The presence or absence of a leak between the fixing film 34 and the pressure roller 32 was evaluated from the printed image together with the measurement of the surface potential of the fixing film 34 or the pressure roller 32.

[0062]

[Table 2]

Further increasing the printing speed further increases the fixing bias amount (absolute value) applied to the recording material P, which is necessary for suppressing the rear toner scattering phenomenon. Therefore, as shown in Table 2, in the conventional example in which the bias is directly applied to the fixing film 34 and in Example 1 in which the bias is directly applied to the pressure roller 32 in addition to the electrode 41, it is necessary to suppress the backward scattering phenomenon at around 50 PPM. Fixing film 3
4 and the pressure resistance of each release layer of the pressure roller 32 (about 1 kV in this embodiment) are exceeded, and therefore the fixing film 34
A leak occurred between the pressure roller 32 and the pressure roller 32, and the scattering of the toner in the rear also became worse.

On the other hand, in this embodiment, the amount of bias applied to the pressure roller 32 is suppressed to +700 V at a level that does not cause a problem with the withstand voltage of the release layer, and the electrode 41 located away from the fixing nip portion N is used. Since a high bias is directly applied to the recording material P, the rear toner scattering phenomenon can be suppressed even at 55 PPM without leakage between the fixing film 34 and the pressure roller 32.

That is, a fixing bias is directly applied to the recording material P from the electrode 41 outside the fixing nip portion N, and the fixing film 34 is grounded to provide a current path through the recording material P. It is possible to apply a high bias that causes a leak in the nip portion N, and it is possible to obtain a good image even if the printing speed is increased.

[Third Embodiment] Next, as a third embodiment, another example of a fixing bias applying method is shown in FIG. The parts having the same functions as those in the first embodiment described above are designated by the same reference numerals and the description thereof is cited.

(1) Application of Fixing Bias In this embodiment, a fixing bias having the same polarity as the toner T is applied to the fixing film 34 from the conductive member 42 such as a conductive brush through the conductive primer layer, and the toner T is applied to the electrode 41. A fixing bias of opposite polarity is applied. In order to apply the biases of different polarities, a bias power source is provided independently for the fixing film application 43a and the electrode application 43b as shown in FIG.

The pressure roller 32 is grounded from the core metal.
It is preferable that the diode 44 is provided between the core metal and the ground to restrict the pressure roller 32 to the opposite polarity to the toner.
It is preferable since the toner holding power on the recording material can be increased.

The application of the negative bias from the fixing film 34 further accelerates the application of the positive bias from the electrode 41 to the back side of the printing surface of the recording material P, and the tip portion of the recording material P to which the bias cannot be applied from the electrode 41 is also a film. Since the toner is pressed against the recording material P by the repulsive electric field from the recording material P, it is possible to suppress the rear toner scattering phenomenon from the front end of the recording material.

On the other hand, in order to prevent the surface potential of the fixing film 34 from being kept negative, the amount of bias applied is an absolute value and the amount of bias applied to the electrode 41 is fixed.
It is also possible to prevent the adhesion of calcium carbonate by setting the amount larger than the amount applied to the.

Further, as in Example 2, the fixing film 3 was used.
Since the high bias can be directly applied to the recording material P from the electrode 41 located at a position away from the fixing nip while the amount of bias applied to the recording medium 4 is suppressed to a level that does not cause a breakdown voltage, the printing speed is high. It is possible to obtain a good image even if it is changed.

[0072]

As described above, according to the present invention, a bias having a polarity opposite to that of the unfixed image is positively applied from the electrodes to the back surface of the printing surface of the recording material, so that the unfixed image holding force on the recording material is increased. It is possible to suppress the rear toner scattering phenomenon. Further, a positive current flows from the electrode through the recording material to the rotating body that contacts the unfixed image surface of the recording material, and the surface potential of the rotating body is kept positive during paper passing, so that adhesion of calcium carbonate can be prevented. . A bias was applied to the recording material directly from the electrode outside the pressure contact nip portion (fixing nip portion), and the rotating body was grounded to provide a current path through the recording material. It is also possible to apply a high bias to the extent that it causes a problem, and a good image can be obtained even if the printing speed is increased.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of the configuration of a heat fixing device according to the first exemplary embodiment.

FIG. 3 is a schematic configuration diagram of a heating and fixing device according to a second exemplary embodiment.

FIG. 4 is a schematic configuration diagram of a heating and fixing device according to a third exemplary embodiment.

FIG. 5 is a schematic configuration diagram of a heat fixing device in a conventional example.

FIG. 6 is a schematic configuration diagram of a heat fixing device in a conventional example.

FIG. 7 is a schematic configuration diagram of a heat fixing device in a conventional example.

FIG. 8 is a schematic configuration diagram of a heat fixing device in a conventional example.

[Explanation of symbols]

1 ... Image forming apparatus, 11 ... Photosensitive drum, 12 ...
..Charging rollers, 13 ... Laser scanner, 14
... developing device, 15 ... transfer roller, 16 ... cleaning device, 21 ... cassette, 22 ... paper feeding roller, 23 ... registration roller, 3 ... fixing device, 31 ... ..Fusing rollers, 32 ... Pressure rollers, 3
3 ... Heater, 34 ... Fixing film, 35 ...
Film guide member, 36 ... Thermistor, 37 ...
-Halogen heater, 41 ... Electrode, 42 ... Conductive member, 43 ... Bias power supply, 44 ... Diode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Eiji Uekawa             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Shinji Hashiguchi             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Hiroshi Kataoka             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H033 BA10 BA11 BA12 BA13 BA25                       BB28 BB29 BB30 BE03

Claims (9)

[Claims] 1. A rotating body having a heating source, which is in contact with an unfixed image surface of a recording material, and a pressure member which is in pressure contact with the surface of the rotating body.
Having a pressure contact nip portion between the rotating body and the pressure member,
In a heat fixing device for introducing a recording material on which an unfixed image is formed and passing the recording material to fix the unfixed image as a permanent image on the recording material, an electrode in contact with the recording material and at least the pressure contact of the recording material A heating and fixing device comprising: a means for applying a bias having the same polarity to the electrode and the pressing member while passing through the nip portion. 2. A rotating body provided with a heating source, which is in contact with an unfixed image surface of a recording material, and a pressure member which is in pressure contact with the surface of the rotating body.
Having a pressure contact nip portion between the rotating body and the pressure member,
In a heat fixing device for introducing a recording material on which an unfixed image is formed and passing the recording material to fix the unfixed image as a permanent image on the recording material, an electrode in contact with the recording material and at least the pressure contact of the recording material A heating and fixing device comprising: means for applying biases of different polarities to the electrodes and the rotating body while passing through the nip portion. 3. The electrode is installed on the downstream side of the pressure contact nip portion in the recording material conveyance direction and so as to come into contact with the back surface of the printing surface of the recording material that has passed through the nip. Or the heat fixing device according to 2. 4. The heating according to any one of claims 1 to 3, wherein the rotating body is an endless belt having a multilayer structure including a conductive layer and is grounded via the conductive layer. Fixing device 5. The pressing member is a rotating body composed of a release layer, an elastic layer, and a cored bar in this order from the surface, and a bias is applied through the cored bar. Item 1
5. The heat fixing device according to any one of 4 to 4. 6. The heat fixing device according to claim 5, wherein the release layer has an insulating property and the elastic layer has a conductive property. 7. The heat fixing device according to claim 1, wherein the bias application amount to the electrode is larger than the bias application amount to the pressing member. 8. The heat fixing device according to claim 2, wherein the rotating body is an endless belt having a multilayer structure including a conductive layer, and a bias is applied through the conductive layer. 9. The heat fixing device according to claim 2, wherein the amount of bias applied to the electrode is larger in absolute value than the amount of bias applied to the rotating body.