JP2003208048A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device in which fixability is improved by preventing a toner image (toner) on a transfer material from entering the fibers of the transfer material during fixing. <P>SOLUTION: The image forming device fixes a toner image on a transfer material by having an endless belt member, a first roller member which stretches the belt member on the side which is downstream in the direction of the rotation of the belt member, a second roller which stretches the belt member on the side which is upstream in the direction of the rotation of the belt member, and a third roller member which abuts on the first roller member with the belt member between them. In the image forming device, a heat nip is formed between the third roller member and the belt member. Also, a fixing bias composed of an AC voltage for generating an AC electric field is applied between the third roller and the transfer material, on the transfer material entrance side of the heat nip. <P>COPYRIGHT: (C)2003,JPO

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 having a belt-type fixing device used for image formation such as a copying machine, a printer, and a fax machine, and more particularly, it uses a toner having a small particle diameter as a developer to improve the fixing property. The present invention relates to a good image forming apparatus.

[0002]

2. Description of the Related Art Recently, with the advent of the information age, demand for office machines such as copiers, printers and facsimiles has increased rapidly, and now, the speed of copiers, image quality and pollution-free. Characteristics such as conversion have been requested. Further, as colorization of copiers and the like has become widespread, improvement of characteristics such as high speed, high image quality, and pollution-free has become more important issues.

In order to improve the image quality of the copying machine and the like, it is necessary to improve the characteristics of the toner, and it is particularly important to reduce the particle size and use a toner having a sharp particle size distribution. I understand. Such a small particle size toner can be obtained by classifying a crude toner into the above particle size range even by the conventional pulverization and granulation method, but a large amount of the toner is removed in the classifying step, so that the yield is low and the productivity is high. There was a problem that was bad. Therefore, in recent years, a polymerized granulated toner obtained by polymerizing by a suspension polymerization method or an emulsion polymerization method has been developed and is about to be put into practical use, and a method of forming an image using a small particle diameter toner is disclosed in, for example, Japanese Patent Laid-Open No. 5-127420
Japanese Patent Laid-Open No. 11-167226 and Japanese Patent Laid-Open No. 11-167226. Further, as a two-component developer using such a small particle size toner, toner particles having a particle size of 7 μm or less are used as the toner, and a corresponding carrier having a particle size of 5 μm is used.
Carrier particles having a particle size of 0 μm or less are usually used for obtaining good developability.

On the other hand, conventionally, a copying machine, a printer, a FAX
As a fixing device used in an electrophotographic image forming apparatus such as a heat generating rubber roller having an elastic layer and maintained at a predetermined temperature, and a pressure rubber roller having an elastic layer in pressure contact with the heat generating rubber roller. A heat roller fixing method is widely used in which a transfer material on which an unfixed toner image is formed is heated while being nipped and conveyed.

However, in this type of device, since the heat capacity of the heat-generating rubber roller is large, the warming-up time becomes long, the temperature inside the elastic layer becomes high, and the life of the heat-generating rubber roller is shortened.

Further, many color images have large solid areas, and many solid images other than black also have uneven gloss. When a hard roller is used as the heat generating rubber roller and the pressure rubber roller, a transfer material (recording paper)
There is a problem that the image quality is deteriorated due to uneven glossiness depending on the unevenness of the toner layer.

In order to solve these problems, an endless belt member (fixing belt) is used, the fixing belt is stretched by a plurality of roller members, and a heating element for heating the fixing belt is provided inside. A heat generating roller that faces the fixing belt and a roller member that faces the heat generating roller sandwiching the fixing belt are provided, and the fixing belt and the roller member heated by the heat generating roller cause the fixing belt to rotate upstream of the roller member in the rotation direction of the fixing belt. A fixing system for fixing the toner image on the recording paper at a heating nip portion provided on the side is disclosed in Japanese Patent Laid-Open No. 10-3197.
No. 72 publication and the like.

Further, in the above fixing device, for the purpose of preventing electrostatic offset and improving the fixing property, the heat generating roller is grounded and is composed of a DC voltage having a polarity opposite to the toner polarity used for the roller member facing the heat generating roller. Applying a fixing bias to form an electric field in the direction that attracts the toner image (toner) to the recording paper, or ground the roller member (earth)
However, the technique of forming an electric field in the direction in which the toner image (toner) is pressed against the recording paper is often applied by applying a fixing bias composed of a DC voltage of the same polarity as the toner polarity used on the heat roller facing the roller member. Are known.

[0009]

However, in the above-mentioned fixing device, when a toner having a small particle size is used, the toner particles are so small that the toner image is transferred between the fibers of the recording paper when the toner image is transferred onto the recording paper. Is likely to enter, and heat and pressure are less likely to be transmitted to the entered toner during fixing, which causes a problem that the fixability of the toner image is deteriorated.
A fixing bias with the opposite polarity to the toner used is applied from the back side of the recording paper to form an electric field in the direction that attracts the toner image (toner) to the recording paper, or a fixing bias with the same polarity as the toner used is used on the recording paper. When an electric field is formed in the direction in which the toner image (toner) is pressed against the recording paper by applying it from the surface side of the toner, the toner further gets into the fiber, which has the opposite effect, and causes uneven fixing. There is a problem that the fixing property such as unevenness of gloss and gloss is further deteriorated.

The present invention solves the above-mentioned problems and prevents the toner image (toner) on the transfer material from entering the fibers of the transfer material at the time of fixing to improve the fixability. The purpose is to provide a device.

[0011]

The above object is to provide an image forming apparatus in which a toner image using a small particle diameter toner having a mass average particle diameter of 3 to 7 μm is transferred onto a transfer material and then fixed by a fixing device. The fixing device includes an endless belt member, a first roller member that stretches the belt member on the downstream side in the rotation direction of the belt member, and the belt member on the upstream side in the rotation direction of the belt member. And a third roller member that is in contact with the first roller member sandwiching the belt member, and fixes the toner image on the transfer material. A heating nip portion is formed between the roller member and the belt member, and an AC electric field is formed between the third roller member and the transfer material on the transfer material entrance side of the heating nip portion. A fuser consisting of an AC voltage It is achieved by an image forming apparatus and applying the astigmatism.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. Note that the description in this section does not limit the technical scope of the claims or the meaning of terms. Further, the following affirmative description in the embodiments of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

An image forming process and each mechanism of an embodiment of an image forming apparatus using the fixing device according to the present invention will be described with reference to FIGS. 1 to 4. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus using a fixing device according to the present invention.
FIG. 4 is a diagram showing an example of a unit that forms an electric field between a third roller member and a transfer material in a fixing device and a heating nip portion of the fixing device. FIG. 3 shows a projected image of polymerized toner particles. FIG. 4 is a diagram showing another example of means for forming an electric field between the third roller member and the transfer material in the fixing device of FIG.

Referring to FIGS. 1 to 4, as shown in FIG. 1, a color image forming apparatus using the fixing device according to the present invention has a black, cyan, magenta and yellow color along the moving direction of the transfer material. An image forming unit for forming a color toner image is arranged, and the color toner images formed on the image forming bodies of the respective image forming units are superimposed and transferred onto the transfer material (recording paper) conveyed by the transfer material conveying means. It is a match.

In the figure, four sets for forming images for each color of yellow (Y), magenta (M), cyan (C) and black (K) are provided on the peripheral portion of the transfer belt 14A which is a transfer material transfer means. Process unit 100 of Y, M, C with respect to the rotation direction of the conveyor belt 14A indicated by the arrow
And K in this order.

The four process units 100 have a common structure, and each of them has a photosensitive drum 10 as an image forming body and a scorotron charger 11 as a charging means.
An exposure optical system 12 as an image writing unit, a developing device 13 as a developing unit, and a photoconductor cleaning device 19 as an image forming member cleaning unit.

The photosensitive drum 10, which is an image forming body, has a transparent conductive layer and an organic photosensitive layer on the outer periphery of a cylindrical substrate formed of a transparent member such as glass or a transparent acrylic resin. (OPC) photoconductor layer is formed.

The photosensitive drum 10 is rotated clockwise by the power from a drive source (not shown) or by being driven by the conveyor belt 14A while the transparent conductive layer is grounded.

Scorotron charger 11 as charging means
Are attached in close proximity to the photoconductor drum 10 in a direction orthogonal to the moving direction of the photoconductor drum 10 (direction perpendicular to the paper surface in the figure). Scorotron charger 11
Is equipped with a control grid held at a predetermined potential with respect to the organic photoconductor layer of the photoconductor drum 10 and a discharge wire as a corona discharge electrode. (Negative charging) to give a uniform potential to the photoconductor drum 10.

The exposure optical system 12 as an image writing means,
A linear exposure element in which a plurality of LEDs (light emitting diodes) as light emitting elements for image exposure light are arranged in an array in parallel with the axis of the photoconductor drum 10 for each color and a SELFOC lens as an equal magnification imaging element (Registered trademark) is configured as an exposure unit attached to a holder, and the exposure optical system 12 for each color is attached to a cylindrical holder 20 as an exposure optical system holding member and integrally exposed. It is housed inside the body of the body drum 10. The exposure optical system 12 performs image processing based on the image data of each color sent from a separate computer (not shown) and stored in the memory, and then exposes the uniformly charged photoconductor drum 10 from the back side. (Image writing)
Then, a latent image is formed on the photosensitive drum 10.

The developing device 13 as a developing means has two components of each color of yellow (Y), magenta (M), cyan (C) or black (K) charged to the same polarity as the charging polarity of the photosensitive drum 10. Developer (may be a one-component developer)
Respectively, and has a thickness of 0.5 to 1 mm and an outer diameter of 1
Developing roller 13 which is a developer carrier made of non-magnetic stainless steel or aluminum having a cylindrical shape of 5 to 25 mm
a. The developing roller 13a is kept in non-contact with the photosensitive drum 10 with a predetermined gap, for example, 100 to 1000 μm, by an abutting roller (not shown) so that the developing roller 13a rotates in the forward direction of the rotation direction of the photosensitive drum 10. At the time of development, a DC bias voltage having the same polarity as the toner (negative polarity in this embodiment) or a developing bias voltage for superimposing an AC voltage on a DC voltage is applied to the developing roller 13a, whereby the photosensitive drum Non-contact reversal development is performed on the exposed portion on 10.

Conveyor belt 14A as a transfer material conveying means
Has a volume resistivity of 10 ⁸ to 10 ¹⁵ Ω · cm and a surface resistivity of 1
0 ^8-10 was ¹⁵ Omega / □ endless belt, for example modified polyimide, thermal curing polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, thickness 0 the conductive material is dispersed in engineering plastics nylon alloy or the like. A seamless belt having a two-layer structure, in which a semi-conductive film substrate having a thickness of 1 to 0.5 mm is coated with fluorine to a thickness of 5 to 50 μm as a toner filming preventing layer, preferably. In addition to this, a semi-conductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber, urethane rubber or the like can be used as the base body of the transport belt 14A. The transport belt 14A is circumscribed and stretched around the drive roller 14d, the driven roller 14e, the backup roller 14j, and the tension roller 14k.

The image forming process (image forming process) will be described below. When the image recording is started, the drive roller 14d is rotated by the start of the drive motor of the transfer material conveying means (not shown), and the conveying belt 14A is rotated in the direction shown by the arrow in the figure.

The yellow (Y) process unit 1
In 00, the Y photoconductor drum 10 is rotated in the direction shown by the arrow in the figure by the start of the photoconductor drive motor (not shown), and Y
Y photoconductor drum 1 by the scorotron charger 11
A potential is applied to 0. After a potential is applied to the Y photoconductor drum 10, the Y exposure optical system 12 performs exposure (image writing) with a first color signal, that is, an electric signal corresponding to Y image data, and the Y photoconductor drum 10 is exposed. An electrostatic latent image corresponding to a yellow (Y) image is formed on the body drum 10.
The latent image is reversely developed by the Y developing device 13 in a contact or non-contact state, and a yellow (Y) toner image is formed on the Y photoconductor drum 10.

On the other hand, in parallel with the formation of the Y toner image on the Y photoconductor drum 10, the recording paper P is sent out from the paper feed cassette 15 as a transfer material accommodating means by the sending roller, and the feeding roller is operated. After that, it is conveyed to the timing roller 16 as a transfer material feeding means. Furthermore, recording paper P
Is sent from the timing roller 16 in synchronism with the Y toner image formed on the Y photoconductor drum 10, and is attracted to the transport belt 14A by the charging of the paper charger 150 as the transfer material charging means. And then the conveyor belt 14A
Is carried to the Y transfer area.

In the Y transfer area, the Y toner on the Y photoconductor drum 10 is transferred by the transfer roller 14C as the Y transfer means to which the voltage having the opposite polarity (positive polarity in this embodiment) to the toner is applied. The image is transferred onto the recording paper P.

Simultaneously with or slightly after the operation of the Y process unit 100, in the magenta (M) process unit 100, the M photoconductor drum 10 is rotated in the direction shown by the arrow in the figure, and the M scorotron charger is installed. A potential is applied by the charging action of 11 and the M exposure optical system 12 exposes (image-writes) the second color signal, that is, an electric signal corresponding to image data of magenta (M) on the M photoconductor drum 10. And an electrostatic latent image is formed on the surface of the electrostatic latent image.
A magenta (M) toner image is formed on the photosensitive drum 10 of FIG.

In parallel with the formation of the M toner image on the M photosensitive drum 10, the recording paper P carrying the yellow (Y) toner image is conveyed to the M transfer area by the conveying belt 14A. In the M transfer area, the M transfer roller 14C transfers the M toner image formed on the M photoconductor drum 10 onto the recording paper P carrying the M toner image. A color toner image in which Y and M are superposed is formed on.

By the same process, the cyan (C) toner image and the black (K) toner image are sequentially transferred in a superposed manner, and the Y, M, C, and K superposed color images are superposed on the recording paper P. A toner image is formed.

The recording paper P on which the superimposed color toner images have been transferred is a paper separation static eliminator 14 as a transfer material separating means.
It is separated from the conveyor belt 14A by h and is conveyed to the fixing device 17 described later in detail.

After the superimposed color toner images on the recording paper P are fixed in the fixing device 17, the recording paper P is discharged to the tray on the upper part of the device through the paper discharge roller 18.

[0032] During the image formation in the above, 52.3~63.9kg / m ² (1000 sheets) about thin and 64.0~81.4kg / m ² as a recording paper (1000)
Plain paper or 83.0 to 130.0 kg / m ² (10
(00 sheets) thick paper with a linear velocity of 80-350 mm
It is preferable to set the temperature to about 5 sec / sec and the environmental conditions to set the temperature to about 5 to 35 ° C. and the humidity to about 15 to 85%. The fixing temperature is preferably set to about 150 to 180 ° C.

The toner remaining on the peripheral surface of the photoconductor drum 10 after the transfer is cleaned by the photoconductor cleaning device 19 as an image forming member cleaning means, and the next image forming cycle is started.

As shown in FIG. 2, the fixing device 17 of the present invention uses the fixing belt 27 as the endless belt member and the pressure roller 17b as the first roller member.
The tension roller 17c is used as the second roller member, and
The heat generating roller 17a is used as the roller member of
The pressure roller 1 is provided on the downstream side in the rotation direction of the fixing belt 27.
The fixing belt 27 is stretched by 7b, and the fixing belt 2 is also stretched.
7, the fixing roller 27c stretches the fixing belt 27 on the upstream side in the rotation direction, and the tension roller 17d applies tension to the fixing belt 27 to stretch the fixing belt 27, and the fixing belt 27 is sandwiched and pressed. The pressure roller 1 is provided with a heat roller 17a that is in contact with the roller 17b and has a halogen lamp HLa as a heat generator inside.
A wide heating nip portion Na of about 8 to 15 mm is formed between 7b and the heat roller 17a, and the toner image on the recording paper P is fixed by applying heat and pressure through the heating nip portion Na. is there. Also, the fixing belt 27
A fixing belt cleaning roller TR1 is provided so as to face the tension roller 17c with the fixing roller 17c interposed therebetween to apply oil to the fixing belt 27 and clean the oil. The fixing temperature of the fixing device 17 is set to about 150 to 180 ° C., and the toner image (color toner image) on the recording paper P is fixed.

The fixing belt 27 has an inner diameter of about 60 to 150 mm and a thickness of about 20 to 80 .mu.m, for example, a metal belt using a nickel electroformed belt and having a thickness of about 30 to 200 .mu.m on the outer side (outer peripheral surface). A layer coated with insulating silicon rubber with a thickness of 30 on the surface as a release layer.
Fluorine resin (PFA) coating of about 50 μm is used.

The heat generating roller 17a is made of, for example, an aluminum material or a stainless steel material, and has a cylindrical metal pipe 171a having a wall thickness of about 1 to 3 mm, and the outer peripheral surface of the metal pipe 171a is made of, for example, a silicon material. (Thickness) 1 to 4 mm thick with rubber hardness of 10 Hs to 40 Hs (JIS, A
Rubber roller layer 1 composed of a soft rubber layer having a rubber hardness)
72a and 5 to 20 μm on the surface of the rubber roller layer 172a
And a release layer 173a that has been subjected to a fluororesin (PFA) coating process to a degree, and is configured as a soft roller having an outer diameter of about 30 to 50 mm. The color toner image of the superposed color toner images is favorably fixed by the heat generating roller 17a having the function of the soft roller. The rubber roller layer 172a of the heat generating roller 17a has a rubber hardness of 30H, which also serves to form a monochrome image.
You may use the thing of about s-60Hs (JIS, A rubber hardness). Further, a temperature sensor TS1 that is in contact or non-contact with the heat generating roller 17a is provided to control the temperature of the heat generating roller 17a.

The fixing belt cleaning roller TR1
A roller member obtained by winding a felt member impregnated with oil around a cylindrical aluminum pipe or paper tube is used as the fixing belt cleaning roller TR1.
The oil on 7 is applied and cleaned at the same time.

As the pressure roller 17b, one having an outer diameter of about 20 to 30 mm in which the outer peripheral surface of a metal tube or metal rod is coated with silicon rubber or Teflon (R) or the like is used. Further, instead of the pressure roller 17b as the first roller member, the above-mentioned heat generating roller 17a including the halogen lamp HLa may be used if necessary.

The tension roller 17c has an outer diameter of 20 to 30 m.
A metal tube or metal rod of about m is used. A metal tube or a metal rod whose outer peripheral surface is coated with silicon rubber or Teflon (R) may be used.

For the image forming apparatus using the fixing device described above, it is preferable to use a two-component developer containing a non-magnetic polymerized toner and a small particle diameter magnetic carrier. Average particle size is 20-50μ
A two-component developer containing a carrier of m and a non-magnetic polymerized toner having a mass average particle diameter in the range of 3 to 7 μm is preferable.

Details of the small particle size polymerized toner (small particle size toner) and the carrier used in the two-component developer will be described below.

First, the polymerized toner used in the present invention will be described with reference to FIG. FIG. 3A is an explanatory diagram showing a projected image of polymerized toner particles without corners.
(B) and (C) are explanatory views showing projected images of polymerized toner particles each having corners.

The polymerized toner used in the present invention is
(1) Toner particles having a shape factor in the range of 1.2 to 1.6 are 65% by number or more, and the variation coefficient of the shape factor is 16
% Of polymerized toner particles,
(2) toner particles having a coefficient of variation of 16% or less and a coefficient of number variation of 27% or less in a number particle size distribution, (3) a ratio of polymerized toner particles having no corners of 50 It is preferable that the toner particles are composed of toner particles of which content is at least%, or a combination thereof.

In the present invention, the shape factor of the polymerized toner is represented by the following formula and represents the degree of roundness of the polymerized toner particles.

Shape factor = ((maximum diameter / 2) ² × π) / projected area Here, the maximum diameter means the parallel line when a projected image of toner particles on a plane is sandwiched by two parallel lines. Refers to the width of the particles at which the interval is maximum. The projected area means the area of the projected image of the toner particles on the plane.

In the present invention, this shape factor is determined by taking a photograph of the toner particles magnified 2000 times with a scanning electron microscope, and then using the photograph, "SCANNING" is taken.
It was measured by analyzing a photographic image using "IMAGE ANALYZER" (manufactured by JEOL Ltd.). At this time, the shape factor of the present invention was measured by the above calculation formula using 100 toner particles.

In the polymerized toner used in the present invention, the number of toner particles having the shape factor in the range of 1.2 to 1.6 is preferably 65% by number or more, more preferably 70% by number or more. .

When the toner having the shape factor in the range of 1.2 to 1.6 is 65% by number or more, the triboelectric chargeability with carrier particles becomes more uniform,
Accumulation of excessively charged toner can be reduced, and toner can be more smoothly conveyed by carrier particles, so that problems such as development ghosts are less likely to occur. Further, the toner particles are less likely to be crushed, the contamination of the charging member (charging device) is reduced, and the charging property of the toner can be stabilized.

The method of controlling the shape factor is not particularly limited. For example, a method of spraying toner particles in a hot air stream, a method of repeatedly applying mechanical energy by impact force in a gas phase in a gas phase, or a method of adding a toner to a solvent that does not dissolve toner to give a swirling flow, etc. According to the method described above, a toner having a shape factor of 1.2 to 1.6 is prepared, and this is added to a normal toner so as to be within the range of the present invention, and then adjusted. Also, controlling the overall shape at the stage of adjusting the so-called polymerization method toner,
There is a method in which a toner whose shape factor is adjusted to 1.2 to 1.6 is similarly added to an ordinary toner to prepare.

The variation coefficient of the shape factor of the polymerized toner preferably used in the present invention is calculated from the following formula.

Coefficient of variation = (S / K) × 100 (%) In the formula, S represents the standard deviation of the shape factors of 100 toner particles, and K represents the average value of the shape factors.

In the polymerized toner used in the present invention, the variation coefficient of the shape factor is preferably 16% or less, more preferably 14% or less. When the variation coefficient of the shape factor is 16% or less, the voids of the transferred toner layer are reduced, the fixability is improved, and the offset is less likely to occur. In addition, the charge amount distribution becomes sharp and the image quality is improved.

In order to uniformly control the shape factor of the toner and the variation coefficient of the shape factor without extremely lot-to-lot variation, the toner is formed in the steps of polymerizing, fusing and controlling the shape of resin particles (polymer particles). An appropriate process end time may be determined while monitoring the characteristics of certain toner particles (colored particles).

The monitoring means that a measuring device is installed in-line and the process condition is controlled based on the measurement result. That is, in the case of a polymerization toner in which measurement of a shape or the like is incorporated inline, for example, a resin toner is formed by associating or fusing resin particles in an aqueous medium, the shape and the particle size are measured while performing sequential sampling in the steps such as fusing. Is measured, and the reaction is stopped when the desired shape is obtained.

The monitoring method is not particularly limited, but a flow type particle image analyzer FPIA-
2000 (manufactured by Toa Medical Electronics Co., Ltd.) can be used. This device is suitable because the shape can be monitored by performing image processing in real time while passing the sample liquid. That is, a pump or the like is used from the reaction field to constantly monitor and measure the shape and the like, and the reaction is stopped when the desired shape or the like is obtained.

The number particle size distribution and number variation coefficient of the polymerized toner used in the present invention are measured by Coulter Counter TA-II or Coulter Multisizer (manufactured by Coulter Co.). In the present invention, a Coulter Multisizer was used, and an interface (manufactured by Nikkaki Co., Ltd.) for outputting the particle size distribution and a personal computer were connected and used. The aperture used in the Coulter Multisizer was 100 μm, and the volume and number of 2 μm or larger toners were measured to calculate the particle size distribution and mass average particle size. The number particle size distribution represents the relative frequency of toner particles with respect to the particle size, and the mass average particle size represents the median diameter in the number particle size distribution. The number variation coefficient in the number particle size distribution of the toner is calculated from the following formula.

Number variation coefficient = (S / Dn) × 100
(%) In the formula, S represents the standard deviation in the number particle size distribution,
Dn indicates a mass average particle diameter (μm).

In the polymerized toner used in the present invention, the number variation coefficient is preferably 27% or less, more preferably 25% or less. When the number variation coefficient is 27% or less, the voids of the transferred toner layer are reduced, the fixing property is improved, and the offset hardly occurs. Further, the charge amount distribution becomes sharp, the transfer efficiency is improved, and the image quality is improved.

The method of controlling the number variation coefficient is not particularly limited. For example, a method of classifying toner particles by wind force can be used, but classification in a liquid is effective for reducing the number variation coefficient. As a method of classifying in this liquid, there is a method of controlling the number of revolutions and separately collecting and preparing toner particles according to the difference in sedimentation speed caused by the difference in toner particle diameter.

Particularly when a toner is produced by the suspension polymerization method, a classification operation is indispensable in order to keep the number variation coefficient in the number particle size distribution at 27% or less. In the suspension polymerization method,
Before the polymerization, it is necessary to disperse the polymerizable monomer into an oil droplet having a desired size as a toner in an aqueous medium. That is, the large oil droplets of the polymerizable monomer are repeatedly mechanically sheared by a homomixer or a homogenizer to reduce the oil droplets to the size of toner particles. In the method of different shearing, the number particle size distribution of the obtained oil droplets becomes wide, and therefore,
The toner obtained by polymerizing this also has a wide particle size distribution. For this reason, classification operation is essential.

In the polymerized toner used in the present invention, the non-cornered polymerized toner particles are toner particles having substantially no protrusions on which electric charges are concentrated or protrusions which are easily worn by stress. That is, FIG.
As shown in (A), when the major axis of the toner particle T is L, a circle C having a radius (L / 10) is rolled inside while contacting the inner side at one point with respect to the peripheral line of the toner particle T. In this case, the case where the circle C does not substantially extend to the outside of the toner T is referred to as “a corner-free polymerized toner particle”. The term “when substantially not protruding” means a case where there is one or less protrusions with protruding circles. Further, the “major axis of the polymerized toner particles” refers to the width of the particles in which the distance between the parallel lines is maximum when the projected image of the polymerized toner particles on a plane is sandwiched by two parallel lines. In addition, FIG. 3 (B) and (C)
Shows projected images of polymerized toner particles each having corners.

The corner-free polymerized toner was measured as follows. First, an enlarged photograph of the polymerized toner particles was taken with a scanning electron microscope, and further magnified to 15,000.
A 0x photographic image is obtained. Then, the presence or absence of the above-mentioned corner is measured for this photographic image. This measurement was performed on 100 polymerized toner particles.

In the polymerized toner used in the present invention, the proportion of cornerless polymerized toner particles is preferably 50% by number or more, more preferably 70% by number or more. The percentage of polymerized toner particles without corners is 50% by number
By the above, the generation of fine particles due to stress with the carrier particles is less likely to occur, the adhesion of the carrier particles to the surface of the carrier particles can be prevented from being present excessively large, and to the carrier particles Contamination can be suppressed. In addition, the polymerized toner particles that are easily worn or broken and the polymerized toner particles that have a portion where electric charge is concentrated are reduced, the charge amount distribution becomes sharp, the chargeability is stable, and a high-quality image is stable for a long time. Can be formed as desired.

The method for obtaining a cornerless polymerized toner is not particularly limited. For example, as described above as a method of controlling the shape factor, a method of spraying toner particles in a hot air flow, a method of repeatedly applying mechanical energy due to impact force in a gas phase, or a method of dissolving toner It can be obtained by adding it to a solvent that does not contain it and imparting a swirling flow.

Further, in the polymerization toner formed by associating or fusing resin particles, the surface of the fused particles has many irregularities at the step of stopping the fusion, and the surface is not smooth, but the shape control step Corner-free toner particles can be obtained by appropriately adjusting the conditions such as the temperature, the rotating speed of the stirring blade, and the stirring time. These conditions are
Although it depends on the physical properties of the resin particles, for example, by setting the glass transition temperature of the resin particles or higher to a higher rotation speed, the surface becomes smooth and toner particles without corners can be formed.

The mass average particle diameter of the polymerized toner used in the image forming apparatus of the present invention is 3 to 7 μm.
It is preferable that When the toner particles are formed by a polymerization method, the particle size of the polymerized toner can be controlled by the concentration of the aggregating agent, the addition weight of the organic solvent, the desorption time, and the composition of the polymer itself.

Since the mass average particle diameter of the polymerized toner is 3 to 7 μm, it is possible to reduce the presence of a toner having an excessively large adherence to the carrier or a toner having a low adherence in the fixing step, which is excellent. The developability can be stably obtained over a long period of time, the transfer efficiency is improved, the halftone image quality is improved, and the image quality of fine lines, dots, etc. is improved. Mass average particle size of polymerized toner is 3μ
If it is smaller than m, the image quality is apt to be deteriorated due to fogging, and if it is larger than 7 μm, the characteristic of high image quality becomes thin.

Particles used as a carrier are iron,
Conventionally known magnetic particles such as metals such as ferrite and magnetite and alloys of these metals with metals such as aluminum and lead can be used, and ferrite particles are particularly preferably used. The carrier particles used for the polymerized toner having a small particle diameter of 3 to 7 μm are preferably those having a small particle diameter of 20 to 50 μm as the mass average particle diameter. The mass average particle diameter of carrier particles is typically measured by a laser diffraction type particle size distribution measuring apparatus “HELOS” (sympathic (SY
Manufactured by MATETEC). As the carrier, the above magnetic particles can be used as they are, but a carrier coated with a resin or a so-called resin dispersion type carrier in which magnetic particles are dispersed in a resin is preferable. The resin composition for coating is not particularly limited, but for example, an olefin resin, a styrene resin, a styrene / acrylic resin, a silicon resin, an ester resin, a fluorine-containing polymer resin, or the like is used. The resin for forming the resin-dispersed carrier is not particularly limited, and known ones can be used. For example, styrene / acrylic resin, polyester resin, fluorine resin, phenol resin, etc. can be used. You can When the mass average particle diameter of the carrier is smaller than 20 μm, carrier adhesion is likely to occur, and the carrier is 50 μm.
If it is larger than the above range, deterioration of the image quality such as density unevenness called "crimping" is likely to occur in the image.

In the above structure, as described above at the beginning, when a small particle size toner is used as the toner of the developer,
As shown in FIG. 2, since the toner particle size is small, the recording paper P
When the toner image or the superimposed color toner image is transferred onto the recording paper P, toner (minus polarity in the present embodiment) easily enters between the fibers of the recording paper P.
Since heat and pressure are difficult to be transmitted to the toner that has entered, the fixability of the toner image deteriorates. A fixing bias having a polarity (positive polarity in this embodiment) opposite to that of the toner used in the heating nip portion Na is applied from the back side of the recording paper,
The toner image (toner) is pressed onto the recording paper by forming an electric field in the direction that attracts the toner image (toner) to the recording paper, or applying a fixing bias of the same polarity as the toner used from the surface side of the recording paper. When the electric field is formed in the direction, the toner further penetrates into the fiber, which has the opposite effect, resulting in a problem that the fixing property further deteriorates.

In order to solve this problem, as shown in FIG. 2, an electric field is formed between the heating roller 17a and the recording paper P via the fixing belt 27 on the side of the heating nip Na where the recording paper P enters. As a means for doing, the thickness is 1 to 3 m.
m, width 5-10 mm, depth A-3 size width (2
97 mm) corresponding to the electrode plate DPa made of a metal plate of aluminum or stainless steel, and facing the heat generating roller 17a grounded (grounded), as shown by the thick line arrow in FIG. Voltage is 1 to 4 kV
Fixing bias VTa composed of AC voltage AC1 of about _PP
Is applied to form an alternating electric field (oscillating electric field) Ea. As described above, by applying the fixing bias VTa of the AC voltage AC1 to the entrance side of the recording paper P in the heating nip portion Na to form the AC electric field Ea, even when the toner having a small particle size is used, at the time of fixing. An oscillating electric field is applied to the toner contained between the fibers of the recording paper P, and the toner contained between the fibers of the recording paper P easily comes out to the surface of the recording paper P, so that heat and pressure are applied to the toner. It is easy to convey, and the fixing properties such as uneven fixing and uneven gloss can be improved.

As the fixing bias VTa, as shown in FIG. 2, it is superimposed on the AC voltage AC1 on the electrode plate DPa, and has the same polarity as that of the toner to be used (negative polarity in this embodiment), for example, −. A DC voltage E1 of about 100 to −400 V is applied from the back side of the recording paper P via the fixing belt 27, and a DC electric field in the direction of separating the toner (toner image) from the recording paper P as shown by a dotted arrow in the figure. E
form c. Thereby, at the time of fixing, the heat generation roller 17a
Paper P in the heating nip portion Na between the fixing belt 27 and the fixing belt 27.
An electric field is applied in a direction in which the toner image (toner) is separated from the recording paper P at the entrance portion of, and the toner that has entered the fibers of the recording paper P appears on the surface of the recording paper P.
Heat and pressure are easily transmitted to the toner, and an image having good fixing properties such as uneven fixing and uneven gloss can be obtained. Further, since the electric field is not formed in the heating nip portion Na on the downstream side of the entrance portion of the recording paper P, the fixing is sufficiently performed in that portion,
There is no electrostatic offset. At this time, the electrode plate DPa is grounded, and a bias having a polarity opposite to that of the toner used in the heat roller 17a (plus polarity in the present embodiment) is applied to transfer the toner image (toner) on the recording paper P to the recording paper P. The same effect may be obtained by forming an electric field that draws out from the fibers.

Further, as shown by the alternate long and short dash line in FIG. 2, on the downstream side of the heating nip portion Na, it faces the heat generating roller 17a which is grounded (earth), and has a polarity opposite to that of the toner used for the pressure roller 17b ( In the present embodiment, a positive polarity), and a DC voltage E of about +100 to +400 V, for example.
A fixing bias VTb composed of 2 is applied from the front side of the recording paper P via the fixing belt 27, and toner (toner image) is provided between the heat roller 17a and the pressure roller 17b as indicated by the white arrow in the figure. ) May be formed on the recording paper P to form a DC electric field Eb. As a result, in addition to improving the fixability, the effect of preventing electrostatic offset is further achieved. At this time, the pressure roller 17b is grounded,
A bias having the same polarity as the toner used in the heat roller 17a (negative polarity in this embodiment) is applied to form an electric field that presses the toner image (toner) on the recording paper P into the fibers of the recording paper P. However, the same effect may be obtained.

As shown in FIG. 4, instead of the electrode plate DPa described with reference to FIG. 2, a fixing belt 27 is used as a means for forming an electric field between the heating roller 17a and the recording paper P. Between the heat roller 17a and the recording paper P,
Outer diameter is 5-10 mm, width is A-3 size width (297 m
m) An electrode roller DRa made of a metal pipe of aluminum or stainless steel equivalent to the recording paper P in the heating nip portion Na.
Is provided on the entry side of the electrode roller DRa, as shown by a thick arrow in FIG.
Fixing bias VTa composed of AC voltage AC1 of about _PP
May be applied to form an AC electric field (oscillating electric field) Ea. In this way, the recording paper P of the heating nip portion Na is
By applying the fixing bias VTa consisting of the AC voltage AC1 on the entrance side of the above, the AC electric field Ea is formed, so that even when the small particle size toner is used, the toner enters between the fibers of the recording paper P at the time of fixing. When the oscillating electric field is applied to the toner, the toner contained between the fibers of the recording paper P becomes the recording paper P.
The heat and pressure are easily transmitted to the toner, and the fixing property such as uneven fixing and uneven gloss can be improved. Further, the width of the heating nip portion Na can be widened by the electrode roller DRa, and the fixing property can be further improved.

Further, as the fixing bias VTa, as shown in FIG.
A DC voltage E1 having the same polarity as that of the toner used in the above (negative polarity in the present embodiment), for example, about −100 to −400 V is applied from the back side of the recording paper P via the fixing belt 27, and a dotted arrow in FIG. As shown by, the DC electric field Ec may be formed in the direction of separating the toner (toner image) from the recording paper P. As a result, at the time of fixing, an electric field is applied in a direction in which the toner image (toner) is separated from the recording paper P at the entrance portion of the recording paper P in the heating nip portion Na between the heat generating roller 17a and the fixing belt 27, and the recording paper is fed. Since the toner that has entered the fibers of P comes out on the surface of the recording paper P, heat and pressure are easily transmitted to the toner, and an image with good fixability such as uneven fixing and uneven gloss can be obtained. Further, since the electric field is not formed on the downstream side of the entrance portion of the recording paper P in the heating nip portion Na, the fixing is sufficiently performed in that portion, and the electrostatic offset does not occur. At this time, the electrode plate DPa is grounded, and a bias having a polarity opposite to that of the toner used in the heat roller 17a (plus polarity in the present embodiment) is applied to transfer the toner image (toner) on the recording paper P to the recording paper P. The same effect may be obtained by forming an electric field that draws out from the fibers.

Further, as shown by the one-dot chain line in FIG. 4, on the downstream side of the heating nip portion Na, it faces the heat-generating roller 17a that is grounded (earth) and has a polarity opposite to that of the toner used for the pressure roller 17b ( In the present embodiment, a positive polarity), and a DC voltage E of about +100 to +400 V, for example.
A fixing bias VTb composed of 2 is applied from the front side of the recording paper P via the fixing belt 27, and toner (toner image) is provided between the heat roller 17a and the pressure roller 17b as indicated by the white arrow in the figure. ) May be formed on the recording paper P to form a DC electric field Eb. As a result, in addition to improving the fixability, the effect of preventing electrostatic offset is further achieved. At this time, the pressure roller 17b is grounded,
A bias having the same polarity as the toner used in the heat roller 17a (negative polarity in this embodiment) is applied to form an electric field that presses the toner image (toner) on the recording paper P into the fibers of the recording paper P. However, the same effect may be obtained.

[0076]

EXAMPLES Example 1 A performance test on fixability was conducted using the image forming apparatus shown in FIG. 1 and the fixing apparatus shown in FIG. The main image forming conditions and the conditions of the fixing device are as follows.

Recording paper P: Plain paper with a paper thickness of 55 kg / m ² Environmental conditions: temperature 25 ° C., humidity 50% Two-component developer: carrier particles having a particle size of 50 μm are used as a carrier, and a particle size is used as a toner. The toner density is adjusted to 6% by mass by using a cyan polymerized toner of 6.5 μm. Photoconductor drum: OPC photoconductor is used Linear velocity: 200 m / sec Fixing device: The belt as described in FIG. 2 as a fixing method. The test was conducted using a fixing device of the type.

The specific configuration is as follows. Electrode plate (means for forming an electric field between the heating roller and the recording paper):
A stainless metal plate having a thickness of 2 mm, a width of 8 mm and a depth of 297 mm was used.

Fixing belt: A metal belt using a nickel electroformed belt having an inner diameter of 100 mm and a thickness of 50 μm as a substrate, the outer surface (outer peripheral surface) of which is coated with an insulating silicone rubber having a thickness of 150 μm, and a release layer. As a thickness of 40 on the surface
The thing which performed the fluororesin (PFA) coating process of μm was used.

Pressure roller 17b: A metal tube or a metal rod having an outer diameter of 20 mm in which the outer peripheral surface is coated with silicon rubber was used.

Stretching roller 17c: A metal tube or metal rod having an outer diameter of 20 mm was used. Heat generating roller 17a: a cylindrical metal pipe having a thickness of 2 mm made of an aluminum material, and a silicon material used for the outer peripheral surface of the metal pipe, having a thickness (thickness) of 3 mm and a rubber hardness of 10 Hs.
(JIS, A rubber hardness) a rubber roller layer made of a rubber layer, and 10 μm of fluororesin (PF) on the surface of the rubber roller layer.
A) A soft release roller having an outer diameter of 40 mm was formed by forming a release layer subjected to a coating process and having a halogen heater inside.

With the above structure, the width of the heating nip portion is 12.
It was 3 mm. The temperature of the heat generating roller was set to 175 ° C.

Under the above set conditions, the heating roller is grounded, the fixing bias is applied to the electrode plate, and the peak-to-peak voltage is 3 k.
As a result of conducting a test by applying an AC voltage of V _PP , the toner that has entered the fibers of the recording paper vibrates and appears on the surface of the recording paper, and the toner has not entered the fibers of the recording paper. Was measured with a microscope, and uneven fixing and uneven gloss were not measured visually, and an image having good fixability was formed.

Further, as a fixing bias to the electrode plate, a DC voltage of −300 V having the same polarity as that of the toner was applied by superimposing it on the above AC voltage, and a test was conducted. As a result, uneven fixing and uneven gloss were visually observed. No measurement was made, and an image having good fixability was formed.

Further, as a result of conducting a test by applying a fixing bias of +200 V having a polarity opposite to that of the toner to the pressure roller, the occurrence of electrostatic offset was not visually measured at all.

Comparative Example 1 Using the image forming apparatus of FIG. 1 and the fixing device of FIG. 2, the image forming conditions and the conditions of the fixing device were set to the same conditions as in Example 1, and an AC voltage was applied to the electrode plate as a fixing bias. As a result of conducting the test without applying the toner, it was measured with a microscope that the toner had entered the fibers of the recording paper, and uneven fixing and uneven gloss were slightly measured with the naked eye. It wasn't good.

Comparative Example 2 Using the image forming apparatus of FIG. 1 and the fixing device of FIG. 2, the image forming conditions and the conditions of the fixing device were set to the same conditions as in Example 1, and the alternating current was applied to the electrode plate as a fixing bias. In addition to applying voltage, it has a polarity of +
As a result of conducting a test by superimposing and applying a DC voltage of 300 V, it was measured with a microscope that more toner entered the fibers of the recording paper, and uneven fixing and uneven gloss were visually measured. The fixability was not good.

(Example 2) A performance test for fixability was conducted using the image forming apparatus of FIG. 1 and the fixing apparatus of FIG. The main image forming conditions and the conditions of the fixing device are as follows.

Recording paper P: 64 kg / m ² (1000 sheets)
Paper thickness of plain paper Environmental conditions: Temperature 25 ° C, humidity 50% Two-component developer: Carrier particles with a particle size of 50 μm are used as a carrier, and cyan polymerized toner with a particle size of 6.5 μm is used as a toner. The toner concentration was adjusted to 6% by mass. Photoconductor drum: OPC photoconductor was used. Linear velocity: 200 m / sec. Fixing device: As a fixing method, a belt type fixing device described in FIG. 4 was used for the test. .

Electrode roller (means for forming an electric field between the heat generating roller and the recording paper): A stainless metal pipe having an outer diameter of 8 mm and a width of 297 mm was used.

Fixing belt: A metal belt using a nickel electroformed belt having an inner diameter of 100 mm and a thickness of 50 μm as a substrate, the outer surface (outer peripheral surface) of which is coated with an insulating silicone rubber having a thickness of 150 μm, and a release layer. As a thickness of 40 on the surface
The thing which performed the fluororesin (PFA) coating process of μm was used.

Pressure roller 17b: A metal tube or metal rod having an outer diameter of 15 mm in which the outer peripheral surface of the metal tube is coated with silicon rubber was used.

Stretching roller 17c: A metal tube or metal rod having an outer diameter of 15 mm was used. Heat generating roller 17a: A cylindrical metal pipe made of an aluminum material and having a thickness of 1.5 mm, and a silicon material on the outer peripheral surface of the metal pipe. The thickness (thickness) is 3 mm and the rubber hardness is 20H.
A rubber roller layer composed of a rubber layer of s (JIS, A rubber hardness), and 10 μm of fluororesin (P
FA) coating release layer was formed, and a soft roller having a halogen heater inside and an outer diameter of 40 mm was used.

With the above construction, the width of the heating nip portion is 11.
It was 5 mm. The temperature of the heat generating roller was set to 175 ° C.

Under the above set conditions, the heating roller is grounded, the fixing bias is applied to the electrode plate, and the peak-to-peak voltage is 3 k.
As a result of conducting a test by applying an AC voltage of V _PP , the toner that has entered the fibers of the recording paper vibrates and appears on the surface of the recording paper, and the toner has not entered the fibers of the recording paper. Was measured with a microscope, and uneven fixing and uneven gloss were not measured visually, and an image having good fixability was formed.

As a fixing bias for the electrode roller,
As a result of conducting a test by applying a DC voltage of −250 V having the same polarity as that of the toner on the above AC voltage, fixing unevenness and gloss unevenness are not visually measured, and an image having good fixing property is formed. Made

Further, as a result of conducting a test by applying a fixing bias of +250 V having a polarity opposite to that of the toner to the pressure roller, the occurrence of electrostatic offset was not visually measured at all.

Comparative Example 3 Using the image forming apparatus of FIG. 1 and the fixing device of FIG. 4, the image forming conditions and the conditions of the fixing device were set to the same conditions as in Example 2, and an AC voltage was applied to the electrode roller as a fixing bias. As a result of conducting the test without applying the toner, it was measured with a microscope that the toner had entered the fibers of the recording paper, and uneven fixing and uneven gloss were slightly measured with the naked eye. It wasn't good.

Comparative Example 4 Using the image forming apparatus of FIG. 1 and the fixing device of FIG. 4, the image forming conditions and the conditions of the fixing device were set to the same conditions as in Example 2, and the above-mentioned AC was used as a fixing bias for the electrode roller. In addition to applying the voltage, a DC voltage of + 300V having the opposite polarity to the toner was superimposed and applied, and as a result of the test, it was measured with a microscope that more toner entered the fibers of the recording paper. In addition, uneven fixing and uneven gloss were visually measured and the fixability was not good.

[0100]

According to the first aspect, the third aspect, or the fourth aspect, a fixing bias composed of an AC voltage for forming an AC electric field is applied on the transfer material entrance side of the heating nip portion even when a small particle size toner is used. By applying an oscillating electric field, the toner contained between the fibers of the transfer material easily comes out to the surface of the transfer material, so heat and pressure are easily transferred to the toner, and uneven fixing and uneven gloss are fixed. It is possible to provide an image forming apparatus that is improved in quality.

According to the second aspect, even when the small particle size toner is used, a direct current electric field which forms a direct current electric field in the direction of separating the small particle size toner from the transfer material is further applied to the fixing bias composed of the AC voltage which forms the AC electric field. By superposing the voltage, the toner contained between the fibers of the transfer material is more likely to come out to the surface of the transfer material, so that heat and pressure are easily transmitted to the toner and the occurrence of electrostatic offset is suppressed. Therefore, it is possible to provide an image forming apparatus in which fixing properties such as uneven fixing and uneven gloss are improved.

According to the present invention, the electrostatic offset prevention effect is further improved by applying a DC voltage that forms a DC electric field in the direction of attracting the toner image to the transfer material on the transfer material discharge side of the heating nip portion. The improvement and the fixability are achieved.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus using a fixing device according to the present invention.

FIG. 2 is a diagram illustrating a fixing device and an example of a unit that forms an electric field between a third roller member and a transfer material in a heating nip portion of the fixing device.

FIG. 3 is a diagram showing a projected image of polymerized toner particles.

FIG. 4 is a view showing another example of means for forming an electric field between a third roller member and a transfer material in the fixing device of FIG.

[Explanation of symbols]

10 Photosensitive drum 11 Scorotron charger 12 Exposure optical system 13 Developer 14A conveyor belt 14C transfer roller 15 paper cassettes 16 Timing roller 17 Fixing device 17a Heat roller 17b Pressure roller 17c tension roller 17d tension roller 27 fixing belt 100 process units AC1 AC voltage DPa electrode plate DRa Electrode roller E1, E2 DC voltage Ea AC electric field Eb, Ec DC electric field HLa halogen lamp Na heating nip P recording paper VTa, VTb Fixing bias

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Akita             2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock             In the company F-term (reference) 2H005 EA05 FB02                 2H033 AA02 AA09 BA08 BA10 BA11                       BA12 BA13 BA58 BB04 BB05                       BB14 BB15 BB28 BB33

Claims (5)

[Claims] 1. An image forming apparatus in which a toner image using a small particle diameter toner having a mass average particle diameter of 3 to 7 μm is transferred onto a transfer material and then fixed by a fixing device, wherein the fixing device is endless. Belt member, a first roller member that stretches the belt member on the downstream side in the rotation direction of the belt member, and a second roller that stretches the belt member on the upstream side in the rotation direction of the belt member. A member and a third roller member that is in contact with the first roller member with the belt member sandwiched therebetween, and fixes a toner image on a transfer material. The third roller member and the belt member A heating nip portion is formed between the transfer roller and the transfer material entrance side of the heating nip portion, and a fixing bias composed of an AC voltage forming an AC electric field is applied between the third roller member and the transfer material. Special to do Image forming apparatus to be used. 2. A direct current voltage forming a direct current electric field in a direction of separating the small particle toner from the transfer material is superposed on a fixing bias composed of an alternating current voltage forming the alternating current electric field. The image forming apparatus according to item 1. 3. The image forming apparatus according to claim 1, wherein the fixing bias is applied to an electrode plate that is in contact with or close to the first roller member via the belt member. 4. The image forming apparatus according to claim 1, wherein the fixing bias is applied to an electrode roller that is in contact with the first roller member via the belt member. 5. A DC electric field is formed between the first roller member and the third roller member on the transfer material discharge side of the heating nip portion in a direction to attract the toner image to the transfer material. 3. A direct current voltage is applied.
The image forming apparatus according to any one of 1 to 4.