JP2000131974A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of image defect the staining of a pressure roller, and tailing, etc., caused by a toner offset phenomenon, so that a high definition and high accurate image is formed by sufficiently keeping the electrostatic holding force (restraint) of a toner image on a recording material introduced to a fixing nip part even when it is in a condition where the moisture content of the recording material is large, that is, even when the resistance of the recording material is not considered, and even when toner whose particle size is small is used in such contact heating type as a film heating system and a heat roller system fixing device and the image forming device provided with the same. SOLUTION: A means S4 applying a bias voltage on at least one of a fixing member 23 and a pressure member 24 forming the fixing nip part N where the recording material P electrostatically carrying a developer image (t) is interposed and carried and the image (t) is thermally fixed is provided; an electrode 25 abutting on the recording material so as to make a current by the bias voltage flow through the recording material is provided; and the electrode 25 is grounded, and the weight average particle size of the developer is 3.5 to 7 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an unfixed developer image (developed image) formed on a recording material such as paper by an appropriate image forming process means (image forming means) of a transfer type or a direct type. And an image forming apparatus, such as an electrophotographic copying machine and an electrophotographic printer, provided with the fixing device.

[0002]

2. Description of the Related Art For example, in an image forming apparatus such as a transfer type electrophotographic laser beam printer and a copying machine,
An electrostatic latent image of the target image information is formed on the surface of an electrophotographic photosensitive member, generally a rotating drum type, as an image carrier by a charging unit and an exposing unit, and the electrostatic latent image is formed by a developing unit. It is developed and visualized as a developer image.

[0003] The developer is a heat-fixable, colored, charged fine powder (hereinafter referred to as toner), and is electrostatically attached to an image portion or a non-image portion of an electrostatic latent image on the surface of the photoreceptor (regular toner). (Development or reversal development) The electrostatic latent image is developed and visualized as a toner image.

[0004] The toner image on the photoreceptor surface is transferred onto a recording material (transfer material) by a transfer means. The unfixed toner image transferred from the photoreceptor surface to the recording material surface is constrained on the recording material by electrostatic holding force due to the charge of the toner and the transfer charge applied to the recording material during transfer, and is carried. Is done.

[0005] The recording material to which the toner image has been transferred from the surface of the photoreceptor is introduced into a fixing means having a heating means and subjected to a heat fixing process of the toner image, thereby forming an image formed product (print, copy).
The paper is discharged as

The photoreceptor surface after the transfer of the toner image onto the recording material is cleaned by removing the untransferred toner by the cleaning means, and is repeatedly used for image formation.

As a fixing device for thermally fixing an unfixed toner image formed and carried on a recording material on a recording material, a contact heating type fixing device such as a heat roller type or a film heating type is currently widely used. I have.

In a fixing device of a heat roller type, a recording material carrying an unfixed toner image is introduced into a nip (fixing nip) between a pair of fixing rollers (heat rollers) and a pressure roller which rotate while being pressed against each other. To fix the toner image on the recording material surface with heat and pressure.

A fixing device of a film heating type includes a heating element, a heat-resistant fixing film that slides on the heating element, and a pressure roller that forms a nip (fixing nip) with the heating element via the fixing film. And fixing the toner image to the surface of the recording material by heat and pressure by nipping and conveying the recording material carrying the unfixed toner image in the nip (Japanese Patent Application Laid-Open No. 63-3 / 1988).
No. 13182, JP-A-2-15778, 4-44
075-44083, 4-20498-204498
No.).

[0010] The film heating type fixing device is compared with other contact heating type fixing devices such as a heat roller type.
As a heating element, a ceramic heater or the like having a low heat capacity and a rapid temperature rise can be used, and a thin fixing film can be used as a heat transfer member. Sometimes it is not necessary to apply heating (preheating) to the heating element, and even if the recording material is passed immediately, the heating element can be sufficiently heated to a predetermined temperature before the recording material reaches the fixing nip. In addition, there are advantages that power saving and shortening of wait time (quick start property, on-demand) can be performed, and the temperature rise in the apparatus such as an image forming apparatus can be reduced.

[0011]

As described above, the unfixed toner image transferred from the photosensitive member surface to the recording material surface is recorded by the charge of the toner and the transfer charge applied to the recording material at the time of transfer. The recording material, which is constrained and held by the electrostatic holding force on the material and thus electrostatically carries the toner image, is introduced into the fixing nip portion of the fixing device. In a high-temperature, high-humidity environment, when the moisture content of a recording material such as paper is large, the transfer charge supplied to the back surface of the recording material in the transfer unit is likely to leak along the surface of the recording material by being transmitted, and the recording material is left on the recording material. The electrostatic holding force of the transferred toner image is easily lost.

Then, since the electrostatic charge of the toner image on the recording material is weakened by the leakage of the transfer charge on the back surface of the recording material, the toner image is not fixed on the recording material, and the fixing device of the film heating type is used. In the case of a fixing device of the heat roller type, an offset phenomenon occurs in which the toner adheres to the fixing roller surface, and the toner adhering after one rotation of the fixing film or the fixing roller re-appears on the recording material. An image defect that adheres and is fixed is likely to occur.

Further, the toner adheres to the fixing film or the fixing roller due to the offset phenomenon, and is transferred to the pressing roller pressed against the fixing film or the fixing roller to cause contamination of the pressing roller.

If the moisture content of the recording material is large, the amount of steam generated in the fixing nip increases, and the electrostatic holding force of the toner image on the recording material is weakened. The toner was scattered due to the pressure of the steam.

Further, in recent image forming apparatuses, the resolution has been increased, and accordingly, it has become essential to improve the reproducibility of small dots. For this reason, in order to establish a high-resolution and high-definition developing system, the particle diameter of the toner has been reduced. As the particle size of the toner decreases, the charge per unit mass of toner (Q / M) applied on the developer carrier in the developing means does not change, but the charge per toner particle decreases. . Therefore, in a high-resolution image forming apparatus using a toner having a small particle diameter, the electrostatic holding force of the toner image on the recording material when the moisture content of the recording material is large is further weakened. Such problems of image defects, pressure roller contamination, and tailing due to the toner offset phenomenon have become more prominent.

Accordingly, the present invention relates to a contact heating type fixing device such as a film heating type or a heat roller type, and an image forming apparatus equipped with the fixing device, even when the recording material has a high moisture content, that is, the resistance of the recording material. Even if the toner used is a toner having a small particle diameter, the electrostatic holding force (restriction) of the toner image on the recording material introduced into the fixing nip portion of the fixing device on the recording material is not considered. Force) is sufficiently maintained,
An object of the present invention is to prevent the occurrence of image defects, pressure roller contamination, tailing, and the like due to the toner offset phenomenon as described above, thereby enabling high-quality image formation.

Further, even if the process speed increases,
An object of the present invention is to enable high-quality image formation on a recording material of any size even if the number of parts is reduced.

[0018]

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

(1) A heating element, a film that slides on the heating element, and a pressure rotating body that forms a nip with the heating element through the film, and the developer image is electrostatically charged by the nip In a fixing device for fixing the developer image to the recording material by nipping and transporting the recording material that is carried on the recording material, the developer constituting the developer image has a weight average particle diameter of 3.5 to 7.0.
μm, having means for applying a bias voltage to at least one of the film and the pressurizing rotator, provided with an electrode that is in contact with the recording material so that a current by the bias voltage flows through the recording material, The fixing device, wherein the electrode is grounded.

(2) A fixing rotator and a pressure rotator, at least one of which is heated to form a nip and rotate with each other, and sandwiches and conveys a recording material electrostatically carrying a developer image in the nip. In the fixing device for fixing the developer image to the recording material, the developer constituting the developer image has a weight average particle size of 3.5 to 7.0 μm, and Means for applying a bias voltage to at least one of the pressing rotator is provided, and an electrode is provided in contact with the recording material so that a current by the bias voltage flows through the recording material, and the electrode is grounded. A fixing device characterized by the above-mentioned.

(3) A heating member is included in at least one of the fixing rotating member and the pressing rotating member. (2)
3. The fixing device according to claim 1.

(4) A guide member, which is disposed upstream of the nip in the recording material conveyance direction and guides the recording material electrostatically carrying the developer image to the nip, also serves as the ground electrode. The fixing device according to any one of (1) to (3).

(5) A discharge guide member disposed downstream of the nip in the recording material conveyance direction and for guiding the recording material exiting the nip also serves as the ground electrode. The fixing device according to any one of the above items.

(6) Any one of (1) to (3), wherein at least one of the ground electrodes is arranged on both the upstream side and the downstream side of the nip in the recording material conveyance direction. The fixing device as described in the above.

(7) The fixing device according to any one of (1) to (6), wherein the distance from the nip to the ground electrode is equal to or less than the length of the recording material having the shortest length in the conveyance direction in the conveyance direction. .

(8) The elastic body of the pressing rotator has an electrical insulation property, and a part of the conductive layer of the film is electrically connected to the core of the pressing rotator. The fixing device according to (1), wherein a bias is applied to the conductive layer of the film by supplying power to a core metal of the compression rotator.

(9) A bias is applied to the film, and the film has electrical conductivity from the metal core to the surface of the pressing rotator, and the pressing rotator is a ground electrode. The fixing device according to (1).

(10) The pressure rotating body has electrical conductivity from the core metal to the surface, a bias is applied to the pressure rotating body, and the film is a ground electrode. The fixing device according to (1).

(11) A heating element, a film that slides on the heating element, and a pressure rotating body that forms a nip with the heating element via the film, and the developer image is electrostatically charged by the nip In a fixing device for fixing the developer image to the recording material by nipping and transporting the recording material that is carried on the recording material, the developer constituting the developer image has a weight average particle diameter of 3.5 to 7.0.
0 μm, comprising: an electrode arranged to be in contact with a part of the recording material on the downstream side of the nip in the recording material transport direction; and a means for applying a bias voltage to the electrode. The fixing device according to claim 1, wherein the film is grounded so that a current caused by a bias voltage flows through the recording material and the film.

(12) At least one of which has a fixing rotator and a pressurizing rotator which rotate while forming a nip with each other, and nips and conveys a recording material electrostatically carrying a developer image in the nip. A fixing device for fixing the developer image to the recording material, wherein a developer constituting the developer image has a weight average particle size of 3.5 to 7.0 μm, and the recording material is larger than the nip. An electrode arranged so as to be in contact with a part of the recording material on the downstream side in the transport direction, and means for applying a bias voltage to the electrode, wherein a current due to the bias voltage applied to the electrode is applied to the recording material and the The fixing device according to claim 1, wherein the fixing rotator is grounded so as to flow through the fixing rotator.

(13) A heating member is included in at least one of the fixing rotating member and the pressing rotating member.
The fixing device according to 2).

(14) The fixing device according to (12), wherein a heating element is included in the fixing rotating element.

(15) In an image forming apparatus provided with an image forming means for electrostatically carrying a developer image on a recording material and a fixing means for fixing the developer image on the recording material, the fixing means may be ( An image forming apparatus, which is the fixing device according to any one of (1) to (14).

(16) The image forming means includes at least an image carrier, a latent image forming means for forming an electrostatic latent image on the surface of the image carrier, and a static image formed on the surface of the image carrier. A developing unit for developing and visualizing the electrostatic latent image with a developer; and a transfer unit for transferring the developer image on the surface of the image carrier to a recording material and electrostatically carrying the developer image on the recording material. (1)
The image forming apparatus according to 5).

(17) The developing means includes at least a developer, a developer carrier for carrying the developer and transporting the developer to a development area, and an application amount of the developer in contact with the developer carrier. A developer carrying member for carrying the developer and transporting the developer to the developing area, and developing the electrostatic latent image formed on the image carrier on the developer carrier. The image forming apparatus according to (16), wherein the image forming apparatus is a developing device that applies a bias to develop and visualize the image. <Operation> In other words, for a fixing device of a contact heating type such as a film heating system or a heat roller system, and an image forming apparatus equipped with the fixing device, a recording material electrostatically carrying a developer image is nipped and conveyed. Means for applying a bias voltage to at least one of a fixing member and a pressure member that form a fixing nip portion for thermally fixing the developer image, and apply a bias voltage to the recording material so that a current due to the bias voltage flows through the recording material. The contacting electrode is provided and the electrode is grounded, so that an electric field is generated in the fixing nip portion and in the vicinity of the fixing nip portion in a direction in which the developer image is constrained to the recording material. Due to this restraining force, the developer is pressed against the surface of the recording material, even when the moisture content of the recording material is large, that is, without considering the resistance of the recording material, and even when the toner used is a toner having a small particle diameter. In addition, the electrostatic holding force (restraint force) of the toner image on the recording material introduced into the fixing nip portion of the fixing device on the recording material is sufficiently maintained, and image defects due to the toner offset phenomenon, pressure roller contamination, Occurrence of tailing or the like is prevented, and high-quality and high-definition image formation can be performed.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (FIGS. 1 to 5) (1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 1 denotes a drum type electrophotographic photosensitive member as an image carrier. The photoreceptor 1 is formed by laminating a photoconductive photosensitive layer on the surface of a conductive substrate made of aluminum, and is driven to rotate at a predetermined process speed (peripheral speed) in the clockwise direction of arrow a.

The photosensitive member 1 receives a uniform negative charge by the charging roller 2 during the rotation process.

The charging roller 2 is composed of a cored bar and a medium resistance elastic rubber layer which is coated in a roller shape on the outer periphery of the cored bar. Both ends of the cored bar are rotatable by bearings. 1 and is supported so as to contact the photosensitive member 1.
It rotates following the rotation of. The core of the charging roller 2 is electrically connected to a charging bias applying power source S1 capable of superimposing a DC bias and an AC bias, and a predetermined charging bias is applied to the charging roller 2 via the core. The surface of the photoconductor 1 is contact-charged to a predetermined potential.

Next, on the uniformly charged surface of the photoreceptor 1, a laser modulated by a time-series electric digital image signal of image information sent from a photosensitive video controller (not shown) and outputted from a laser scanner 3 is outputted. Scanning exposure with light L is performed. As a result, an electrostatic latent image of image information is formed on the surface of the rotating photoconductor 1. Reference numeral 4 denotes a mirror which deflects a laser beam L output from the laser scanner 3 to an exposed portion of the photoconductor 1.

Next, the electrostatic latent image on the photoreceptor 1 is reversely developed as a toner image by the reverse developing device 5.

The toner image formed on the surface of the photoreceptor 1 is supplied to the transfer nip T from a paper feeder at a predetermined control timing at a transfer nip T formed by the photoreceptor 1 and the transfer roller 6. The recording material (transfer material) P is sequentially transferred to the fed recording material. The toner image on the photoreceptor 1 is recorded in the transfer nip T by applying a transfer bias having a polarity opposite to the charge polarity of the toner (positive in this embodiment) to the transfer roller 6 from a transfer bias application power source S3. Electrostatic transfer is sequentially performed on the surface of the material P.

Reference numeral 8 denotes a recording material loading cassette mounted on the paper feeding unit, in which the recording material P is loaded and stored. The recording material P in the cassette 8 is separated and fed one by one by a sheet feeding roller 9 and a one-sheet separating member (not shown), and passes through a sheet path 10 including a guide plate, a pair of conveying rollers, and the like, and a transfer nip portion T At a predetermined control timing.

The recording material P to which the toner image has been transferred at the transfer nip portion T is sequentially separated from the surface of the photoreceptor 1 and introduced into the fixing device 20 through the sheet path 11 to heat the toner image by the fixing device. Receive a fixing process.

The image-fixed recording material P exiting the fixing device 20 is discharged through a sheet path 12 to a discharge tray 13 on the upper surface of the printer.

On the other hand, in the transfer nip portion T, a contaminant adhering matter such as transfer residual toner and paper dust remaining on the photosensitive member 1 after the transfer of the toner image to the recording material P (after the recording material separation) is cleaned by the cleaning device 7. Removed by blade 71,
The photoconductor 1 whose surface has been cleaned is repeatedly subjected to image formation.

(2) Developing Device 5 The developing device 5 used in this embodiment is a non-contact developing system (jumping developing system) using a magnetic one-component negative toner.

5a is a developing container, t is a toner as a developer contained in the developing container 5a, 5b is a developing sleeve as a developer carrier, 5c is a fixed magnet roller inserted into the developing sleeve 5b, 5d Is a doctor blade made of urethane rubber as a developer layer thickness regulating member, 5e is a sheet metal supporting the doctor blade, 5f is a toner stirring member, and S2 is a power supply for applying a developing bias to the developing sleeve 5b. The sheet metal 5e is fixed to the inner wall of the developing container 5a, and the doctor blade 5d is fixed to the developing sleeve 5b.
Is in contact with the stomach.

As the toner t, an ultra-fast melting fine particle toner having a weight average particle diameter of 7 μm is used in order to achieve high definition and high image quality.

Here, the weight average particle size of the toner t is determined after measuring the particle size distribution of the toner and calculating the volume distribution and the number distribution. The particle size distribution of the toner is measured using a Coulter Multisizer II (manufactured by Coulter) as follows. That is, an interface (manufactured by Nikkaki) and a PC9801 personal computer (manufactured by NEC) that output the number distribution and volume distribution are connected using a Coulter Multisizer, and a 1% NaCl aqueous solution is prepared using primary grade sodium chloride as an electrolyte. I do. For example,
ISOTON R-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, a surfactant (preferably an alkylbenzene sulfonate) is used as a dispersant in 100 to 150 ml of the electrolytic aqueous solution.
Is added, and 2 to 20 mg of a measurement sample is further added. The electrolyte in which the sample was suspended was treated with an ultrasonic
Then, the volume and the number of toner particles are measured by the Coulter Multisizer using a 100 μm aperture to calculate the volume distribution and the number distribution. Then, the weight average particle size of the toner is determined.

The stirring member 5f rotates in the clockwise direction of the arrow e to stir the toner t in the developing container 5a and to send the toner t toward the developing sleeve 5b.

The developing sleeve 5b is rotatably supported by a bearing (not shown), and is opposed to the photoreceptor 1 in a non-contact manner with a predetermined small spacing (several hundred μm). The developing sleeve 5b receives a rotational drive from the photoreceptor 1 via a gear (not shown) and rotates in a counterclockwise direction indicated by an arrow b.

The toner t contained in the developing container contacts the surface of the developing sleeve 5b in the developing container, and a magnetic adhesion layer of the toner t is formed on the sleeve surface by the magnetic field of the magnet roller 5c in the sleeve.

The magnetic adhesion layer of the toner is used as the developing sleeve 5
The toner is conveyed along with the rotation of b, and passes through a contact portion between the developing sleeve 5b and the doctor blade 5d, whereby the thickness of the magnetic adhesion layer of the toner is regulated to a predetermined thin layer. The doctor blade 5d gives an appropriate tribo to the toner by frictional charging.

The developing sleeve 5 in which the thin toner layer continues
The photosensitive drum 1 is taken out of the developing container by the rotation of b, and is conveyed to a developing area which is a non-contact opposing portion between the photosensitive member 1 and the developing sleeve 5b.

A predetermined developing bias of a DC bias and an AC bias superimposed is applied to the developing sleeve 5b from a developing bias applying power source S2. With this developing bias, the toner of the thin toner layer on the side of the developing sleeve 5b is exposed in the developing area. The latent image surface of the photoreceptor 1 is selectively reversely developed with toner by flying and selectively adhering to the latent image surface of the body 1.

The toner remaining on the surface of the developing sleeve 5b without being used for developing the latent image in the developing area is conveyed again into the developing container 5a by the subsequent rotation of the developing sleeve 5b and returned.

Reference numeral 5g denotes a toner blow-out prevention sheet provided inside the developing container 5a corresponding to a lower portion of the developing sleeve 5b, and prevents toner leakage from a lower portion of the developing sleeve.

The developing sleeve 5b is formed by coating a base tube with a coating material in which carbon is dispersed, and is non-magnetic. The base tube is made of aluminum, stainless steel or the like. The surface of the developing sleeve 5b has a roughness due to the coating of the paint, and the roughness is
It contributes to the toner conveyance of b.

Magnet roller 5 in developing sleeve 5b
c has four magnetic poles S1, S2, N1, and N2.

Of these four magnetic poles, the S1 pole (developing pole) is disposed opposite to the photoreceptor 1, and the toner of the thin toner layer on the side of the developing sleeve 5b in the developing area is When the latent image is developed by flying over the developing sleeve 1, it is necessary for the toner causing fogging to adhere to the developing sleeve 5 b.

S2 is provided on the opposite side of the S1 pole.
And developing the toner t in the developing container 5a with the developing sleeve 5b.
And the toner t is circulated in the vicinity of the rotation of the developing sleeve 5b as the developing sleeve 5b rotates. This circulation is performed by the toner t
Contributes to providing a tribo.

The N1 pole and the N2 pole both contribute to the conveyance of the toner coated on the developing sleeve 5b and the provision of a tribo.

In this embodiment, the magnet roller 5c having the above-mentioned four poles is used. However, the number of poles is not limited to four as long as there are poles that fulfill the above functions.

(3) Fixing Device 20 FIG. 2 is a schematic structural diagram of the fixing device 20 used in this embodiment. The fixing device 20 used in the present embodiment is disclosed in
It is a film heating system using a cylindrical fixing film, a pressure roller driving system, and a tensionless type system disclosed in Japanese Patent Nos. 44075 to 44083.

Reference numeral 21 denotes a ceramic heater serving as a heating member, which is a horizontally long and low heat capacity member whose longitudinal direction is perpendicular to the conveying direction of the recording material P (perpendicular to the drawing). That is, the ceramic heater 21 is a ceramic plate (heater substrate) having electrical insulation, good thermal conductivity, and low heat capacity such as alumina (Al ₂ O ₃ ), aluminum nitride (AlN), and silicon carbide (SiC).
And the heater element layer provided on the ceramic substrate as a basic structure, and the entire heater has a low heat capacity. A power supply (not shown) supplies power to the resistor layer, the resistor generates heat, and the entire heater including the ceramic plate quickly rises in temperature, and a temperature rise characteristic in which the temperature quickly falls when power is cut off. It has a falling characteristic. The energized heating resistor layer is formed by forming a desired pattern of a conductive paste on the surface of the ceramic substrate by screen printing or the like and performing a baking process. An element for detecting the temperature of the heater 21 is provided, and the detected temperature information is input to the power supply control unit, and the power supply to the resistor layer is controlled so that the temperature of the heater 21 is adjusted to a predetermined temperature.

Reference numeral 22 denotes a heater support having a trough-like shape with a substantially semicircular arc in cross section. The heater 21 has a heating surface in a groove 22a provided along the length of the support substantially at the center of the lower surface of the heater support 22. The side is exposed downward and is fitted and fixedly supported. The heater support 22 has heat resistance and electrical insulation,
It is made of a rigid material capable of withstanding a high load, for example, PPS (polyphenylene sulfide), PAI (polyamide imide), PI (polyimide), PEEK (polyether ether ketone), or the like.

Reference numeral 23 denotes a cylindrical heat-resistant fixing film loosely fitted to the heater support 22 supporting the heater 21 as described above. The cylindrical fixing film 23 is, for example, a heat-resistant single-layer or multi-layer film having a thickness of about 40 μm to 100 μm as a whole.

The fixing film 23 in this embodiment has a three-layer structure as shown in the schematic sectional view of FIG. That is, the innermost first layer 23a is a base layer, which is a layer having mechanical properties such as torsional strength and smoothness of the fixing film 23, and is made of a resin such as polyimide.

The next second layer 23b is a conductive primer layer, which is a conductive layer in which conductive particles such as carbon black are dispersed, and is an adhesive for bonding the third layer 23c and the base layer which is the first layer 23a. It also plays the role of drug. The outermost third layer 23c is a top layer and is designed to have an optimum resistance value and film thickness so as not to cause various image defects.

Reference numeral 24 denotes an elastic pressure roller as a pressure rotating body, which covers a metal core made of aluminum, cast iron, or the like with a heat-resistant insulating elastic material such as silicon rubber.
The surface layer of the pressure roller is coated with a fluorine resin or the like having a releasing property from the toner. Both ends of the cored bar are rotatably supported via bearings between the front and rear side plates of the apparatus.

Then, the heater 21 is supported on the lower surface side, and the heater support 22 on which the cylindrical fixing film 23 is fitted.
The heater 21 is positioned above the elastic pressure roller 24 with the portion of the heater 21 facing the upper surface of the elastic pressure roller 24, and the heater support 22 is pressed by the elastic pressure roller 2 by pressing means such as a pressure spring.
4 is held in a state of being pressed against the upper surface with a predetermined pressing force. As a result, a fixing nip portion N having a predetermined width is formed between the lower surface of the heater 21 and the upper surface of the elastic pressure roller 24 with the fixing film 23 interposed therebetween.

The elastic pressure roller 24 is driven to rotate in the counterclockwise direction indicated by the arrow by the driving means M. The rotational force acts on the cylindrical fixing film 23 by the pressing frictional force at the fixing nip portion N between the outer surface of the elastic pressing roller 24 and the outer surface of the fixing film 23 due to the rotational driving of the elastic pressing roller 24. The fixing film 23 has a peripheral speed substantially corresponding to the rotational peripheral speed of the elastic pressure roller 24 in the clockwise direction of the arrow while the inner surface of the fixing film 23 slides in the fixing nip portion N in close contact with the lower surface of the heater 21. The outer circumference is rotated (pressure roller drive system). The heater support 22 holds the heater 21 and also serves as a guide member for promoting smooth rotation of the fixing film 23.

The elastic pressing roller 24 is driven to rotate, and accordingly, the cylindrical fixing film 23 rotates around the heater support 22, and electricity is supplied to the heater 21 to generate the fixing nip N by the heat generated by the heater 21. In a state where the temperature is raised to a predetermined temperature and the temperature is adjusted, the recording material P carrying the unfixed toner image t is introduced into the fixing nip portion N, and the toner image bearing surface side of the recording material P is fixed to the fixing film 23 in the fixing nip portion N. The fixing nip N is conveyed together with the rotating fixing film 23 in close contact with the outer surface of the fixing nip N. In the nipping and conveying process, the heat of the heater 21 is applied to the recording material P via the fixing film 23, and the unfixed toner image t on the recording material P is heated and pressed and fixed. When the recording material P passes through the fixing nip portion N, the recording material P is conveyed with a curvature separated from the outer surface of the rotary fixing film 23.

(4) Means for Preventing Image Defects Due to Toner Offset, Contamination of Pressure Roller, Trailing, etc. As described above, the unfixed toner image transferred from the photosensitive member 1 surface to the recording material P surface side t is carried on the recording material P by being constrained by an electrostatic holding force by the charge of the toner and the transfer charge given to the recording material at the time of transfer, and thus the toner image t is carried electrostatically. The recording material P is introduced into the fixing nip portion N of the fixing device 20. In the fixing device, in a high-temperature and high-humidity environment, when the moisture content of the recording material P such as paper is large, the transfer portion T As a result, the transfer charge supplied to the back surface of the recording material P is easily transmitted along the surface of the recording material and leaks, and the electrostatic holding force of the toner image t transferred and formed on the recording material P is easily lost. The toner image is not fixed to the recording material because the electrostatic charge of the toner image t on the recording material P is weakened by the leakage of the transfer charge on the back surface of the recording material. Causes an offset phenomenon in which toner adheres to the surface of the fixing film 23, and the fixing film 23
In this case, an image defect in which the toner adhered after one rotation of the image is reattached to the recording material P and fixed is likely to occur. In addition, the toner adheres to the fixing film 23 due to the offset phenomenon, and is transferred to the pressing roller 24 pressed against the fixing film 23 to cause contamination of the pressing roller.

If the moisture content of the recording material is large, the amount of steam generated in the fixing nip increases, and the electrostatic holding force of the toner image on the recording material is weakened. The toner was scattered due to the pressure of the steam.

In a high-resolution image forming apparatus using a toner having a small particle diameter, the electrostatic holding force of the toner image on the recording material when the moisture content of the recording material is large becomes weaker. As described above, the problems of image defects, pressure roller contamination, and tailing due to the toner offset phenomenon have become more prominent.

Here, the toner scattering phenomenon called tailing which occurs in the fixing nip portion N will be described with reference to the model diagram of FIG.

A fixing nip N, which is a contact portion between the fixing film 23 and the elastic pressure roller 24,
The temperature has reached a little less than 0 ° C., and while the paper is passing through the fixing nip N, the moisture contained in the recording material P is constantly evaporated, and the vapor 61 is generated. Due to the pressure of the steam 61, the toner image t on the recording material P on the upstream side in the recording material conveyance direction from the fixing nip portion N
Is partially blown off. Blown toner t
“a” is shifted by 0.1 to 1 mm to the upstream side in the recording material conveyance direction, and causes a beard-shaped image defect called tailing since the image appears to be trailing.

In this embodiment, in order to prevent the occurrence of image defects, pressure roller contamination, tailing, etc. due to the toner offset phenomenon as described above, as shown in the model diagram of FIG.
A means (high-voltage power supply) S4 for applying a voltage to the conductive primer layer 21b of the fixing film 23 is provided, and an electrode 25 is provided in contact with the recording material P so that a current by a bias voltage flows through the recording material P. Was grounded.

The conductive primer layer 21b of the fixing film 23
Is supplied with a voltage having the same polarity as the charge of the toner t from the high voltage power supply S4. In the present embodiment, since the toner has a negative charge polarity, the voltage applied to the conductive primer layer 21b of the fixing film 21 is also negative, and is −600V.
It is.

The electrode 25 is disposed on the upstream side of the fixing nip portion N in the recording material conveying direction, and is provided on the aluminum substrate 25a.
The conductive fiber 25b is brushed in a brush shape, and the tip of the brush-like conductive fiber 25b of the electrode 25 is provided on the back surface of the recording material P introduced from the transfer portion T to the fixing nip portion N of the fixing device 20. The parts are arranged so as to contact and rub against the recording material P. Aluminum substrate 25a is electrically grounded.

The conductive fiber 25b is made of a soft material because it does not come into contact with the recording material P and does not become a resistance of the conveyance of the recording material P. In order to increase the toner holding power, a material having a low resistance is required for the conductive fiber 25b of the ground electrode 25. In order to minimize the voltage drop due to the resistance of the recording material P, it is preferable to have a contact point with the recording material P at a position as close as possible to the fixing nip portion N.

FIG. 5 is an electrical equivalent circuit model diagram of the fixing device shown in FIG. A voltage of -V is applied to the conductive primer layer 23b of the fixing film 23 by the high voltage power supply S4. Rfp represents the resistance from the output end of the high voltage power supply S4 to the vicinity of the fixing nip of the conductive primer layer 23b of the fixing film 23. The resistance Rfp includes the contact resistance of the power supply contact to the conductive primer layer 23b of the fixing film 23, the resistance of the conductive primer layer 23b, and the like.

The top layer 23c of the fixing film 23
It is a coating layer having a thickness of about 10 μm in which a fluororesin having a relatively high resistance of about × 10 ⁸ to 1 × 10 ¹³ Ωcm and good releasability is dispersed. Rft represents the resistance of the top layer 23c. The value of the resistance Rft is affected by the material and uniformity of the film of the top layer 23c, that is, the density of pinhole leak, and varies from several kΩ to several hundred MΩ.

In the vicinity of the fixing nip N, the recording material P such as paper is heated, and steam 61 (FIG. 4) is always generated. The fixing nip N can be regarded as a vapor source, and the resistance of the recording material portion Pd in the vicinity of the fixing nip is significantly reduced by water vapor, and becomes negligibly small as compared with other resistances inserted in series on an equivalent circuit. In the area of the recording material portion Pd, it can be regarded as equivalently equivalent.

The volume resistance of the paper increases as the distance from the fixing nip N increases, and the rate of change of the resistance value of the recording material P with respect to the distance is determined by the steam flow from the fixing nip N to the upstream and downstream sides in the recording material conveyance direction. There is a great difference from the difference between the amount and the temperature of the recording material. When the recording material P is slightly away from the fixing nip portion N, the resistance of the recording material P cannot be ignored, and the resistance of the recording material P from the vicinity of the fixing nip portion to the ground electrode 25 is indicated by Rp. The ground electrode 25 is disposed so as to contact the back surface of the surface of the recording material P on which the toner image t is placed. The resistance from the contact of the ground electrode 25 with the recording material P to the ground is represented as Rg.

In this embodiment, V is 600 V, and the voltage applied to the conductive primer layer 23 b of the fixing film 23 is −600 V.

The conductive primer layer 23b of the fixing film 23
When a current flows from the conductive primer layer 23b through the top layer 23c → the recording material P → the ground electrode 25, a voltage is generated across the respective resistors due to a voltage drop. Assuming that a voltage generated between both ends of the resistor Rft is Vft, the conductive primer layer 23b and the equipotential portion Pd of the recording material P
An electric field Eft is generated in the direction shown in FIG. In the present embodiment, since the toner t has a negative charge polarity, the generated electric field Eft causes the toner t to generate a binding force Ft on the recording material P. The toner t is pressed against the surface of the recording material P by the restraining force Ft, thereby preventing fixing defects such as tailing and offset.

There are two methods for increasing the restraining force Ft: a) increasing the absolute value of the voltage V, and b) increasing the relative value of the resistor Rft.

In the method a), when the voltage V is increased, the effect is further increased. However, the electric field applied to the top layer 23c of the fixing film 23 is increased, and deterioration due to dielectric breakdown proceeds. Considering the deterioration, the electric field applied to the fixing film 23 is preferably 1 × 10 ⁸ V / m or less. In this configuration, the effect starts to appear at -200 V, and the deterioration of the fixing film 23 becomes remarkable at 3000 V. Therefore, the applied voltage V is preferably in the range of -200 V to -3000 V.
In this embodiment, the applied voltage is set to -1500V.

The experiment shown in Table 1 was conducted using the above configuration.

Table 1 shows that the electrode 25 was formed using an image forming apparatus having a resolution of 600 dpi and a process speed of 60 mm / s.
In this figure, the tailing phenomenon, the offset phenomenon, and the occurrence state of the contamination of the pressure roller were confirmed in a case where the device was grounded and a case where the device was floated. As a check of image quality, reproducibility of one dot at 600 dpi was checked.

Conditions: Environment: 23 ° C., 60% R.C. H. (Hereinafter referred to as an N / N environment) Recording material: Q / M of toner in plain paper with a moisture content of 7% (developer carrier 5b)
The charge amount per unit mass of toner given above is -13 μC
Comparative Example 1: toner weight average particle diameter 10 μm, electrode 25−
Float Comparative Example 2 Toner weight average particle diameter 10 μm, electrode 25−
Grounding Comparative Example 3 Toner weight average diameter 7 μm, electrode 25−
Float Example 1—Toner weight average particle diameter 7 μm, electrode 25−
ground

[0095]

[Table 1] Table 1 shows the results of durability up to 100,000 sheets.

In Table 1, .largecircle. Indicates an OK level, .DELTA. Indicates a practically acceptable level, and X indicates an NG level.

Regarding Comparative Example 1, tailing occurred first, but it was at a level at which there is no practical problem. Since no bias is applied to the recording material, the toner does not have a holding force on the recording material, and the toner is blown off by the pressure of the vapor or the like generated from the recording material.

However, since the weight average particle size of the toner is large, the absolute number of the toner on the recording material is small, and even if the toner falls on the recording material, it does not reach the NG level.

The film offset occurs from the beginning and becomes NG level. This is because no bias is applied to the recording material and the toner is transferred onto the film because there is no toner holding force.

[0100] Contamination of the pressure roller also occurs around 2,300 sheets, and reaches the NG level. This is because the toner with the film offset transferred to the pressure roller between the papers and adheres, and the lump of the toner removed from the pressure roller appears as a defect on the image.

The reproducibility of one dot is at the NG level. This is because the weight average particle diameter of the toner is large and the amount of charge per toner particle is large, so that the number of toners transferred to a one-dot latent image also decreases. Further, since no bias is applied to the recording material, the toner is slightly broken.
That is, it is disadvantageous to faithfully reproduce one dot.

In Comparative Example 2, no tailing, film offset, or contamination with the pressure roller occurred at all, and it was at the OK level. This is because the bias is applied to the recording material, so that the toner holding force on the recording material is increased, so that the toner does not collapse or transfer to the film.

The reproducibility of one dot is at the NG level. This is because the weight average particle diameter of the toner is large, and the charge density per toner particle is large, so that the number of toners transferred to a one-dot latent image also decreases. That is, it is disadvantageous to faithfully reproduce one dot.

Regarding Comparative Example 3, tailing, film offset, and pressure roller contamination were all at the NG level. This occurs because no bias is applied to the recording material, so that the toner does not have a holding force on the recording material and the toner collapses, or the toner is transferred to a film.

Also, because the weight average particle size of the toner is small, the absolute number of toners on the recording material is large, and many of the toners collapse on the recording material or transfer to the film.

Although the reproducibility of one dot is not perfect, it is at a level that does not cause any problem in practical use. Although the weight average particle size of the toner is small, the amount of charge per toner particle is small and the number of toners transferred to a one-dot latent image is large. However, since no bias is applied to the recording material, the toner slightly collapses.

In Example 1, no tailing, film offset, or contamination with the pressure roller occurred, and the result was at the OK level. This is because a bias is applied to the recording material, so that the holding force of the toner on the recording material is increased, and the toner does not collapse or transfer to the film.

The reproducibility of one dot is also at the OK level. Although the weight average particle size of the toner is small,
The amount of charge per toner particle is small, and the number of toners transferred to a one-dot latent image is large. Since a bias is applied to the recording material, one dot can be faithfully reproduced without the toner being destroyed.

From the results shown in Table 1, it is found that the toner having a weight average particle diameter of 7 μm and a bias applied to the recording material with the electrode 25 grounded satisfying any of tailing, film offset, pressure roller stain, and dot reproducibility. Is applied.

Although the weight average particle diameter of the toner was 7 μm,
Similar results were obtained when the weight-average particle size was 3.5 μm, which is a limit in production, and 5 μm, which is slightly larger than that. That is, when a bias is applied to the recording material with the weight average particle diameter of 3.5 μm to 7 μm and the electrode 25 grounded, tailing, film offset, pressure roller contamination, and one-dot reproducibility can be satisfied.

<Second Embodiment> (FIG. 6) This embodiment is for the case where the fixing device 20 is a heat roller type device.

In FIG. 6, reference numeral 31 denotes a fixing roller as a fixing rotating body, and reference numeral 32 denotes a halogen heater lamp as a heat source inserted and disposed inside the fixing roller. 33
Reference numeral denotes an elastic pressure roller as a pressure rotating body that forms a fixing nip portion N by being in pressure contact with the fixing roller 31. The fixing roller 31 and the elastic pressure roller 33 are driven to rotate in the direction of the arrow. The fixing roller 31 is heated by the heat generated by the internal halogen heater lamp 32, and is controlled to a predetermined temperature by a temperature control system including a temperature detecting unit (not shown).

The unfixed toner image t is heated and fixed on the surface of the recording material P by introducing and transporting the recording material P carrying the unfixed toner image t in the fixing nip N.

The fixing roller 31 comprises a base tube 31a and a release layer 31b provided on the peripheral surface thereof. In this embodiment,
The base tube 31a is an aluminum hollow roller having an outer diameter of 30 mm and a wall thickness of 3 mm. The release layer 31b is a layer of a fluororesin such as PFA having a thickness of 20 to 100 μm. In this embodiment, the release layer 31b has a thickness of 60 μm. Release layer 3
1b is an insulating layer having a resistivity of about 1 × 10 ⁹ to 1 × 10 ¹⁴ Ωcm. In this embodiment, it is 1 × 10 ⁷ Ωcm.

Elastic pressure roller 33 as pressure rotating body
Covers a metal core made of aluminum, cast iron, or the like with a heat-resistant insulating elastic material such as silicon rubber. The surface layer of the pressure roller is coated with a fluorine resin or the like having a releasing property from the toner.

In the present embodiment, in order to prevent image defects due to the toner offset phenomenon, contamination of the pressure roller, tailing, etc., the aluminum tube 3 of the fixing roller 31 is used.
A means (high-voltage power supply) S4 for applying a voltage to 1a is provided, and an electrode 25 is provided in contact with the back surface of the recording material P so that a current by a bias voltage flows through the recording material P.
5 was grounded.

Aluminum tube 31a of fixing roller 31
Is supplied with a voltage having the same polarity as the charge of the toner t from the high voltage power supply S4.

The electrode 25 is provided in the same manner as in the first embodiment.
It is disposed on the upstream side of the fixing nip portion N in the recording material conveyance direction, and is obtained by brushing the aluminum substrate 25a with conductive fibers 25b in a brush shape.

The mechanism for generating the binding force acting on the toner t is the same as that described in the first embodiment. The current flows from the aluminum tube 31a of the fixing roller 31 to the release layer 31b →
It flows from the recording material P to the ground electrode 25. By increasing the strength of the electric field generated between the recording material P and the release layer 31b, it is possible to increase the binding force acting on the toner t.

The insulation of the release layer 31b on the surface of the fixing roller 31 is preferably as high as possible, and uniformity of the film is required so that leakage current is not increased due to defects such as pinholes. It is effective to increase the film thickness in order to secure the insulation degree and reduce the pinhole defects, but the heat transfer ability to the recording material is reduced, so that the fixing property is deteriorated. It is important to select a film thickness that minimizes the leak current as far as the fixing property is satisfied.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. As a result, the same effects as in Table 1 were obtained.

Further, the process speed is increased by a factor of 3 which is three times greater than that in Table 1.
The test was also performed at 80 mm / s. In this case, the same effect was obtained.

That is, the weight average particle size of the toner is 3.5 μm.
When a bias is applied to the recording material with the electrode being grounded, the tailing, the fixing roller offset, the pressure roller contamination, the reproducibility of one dot can be satisfied, and the above effects can be obtained even if the process speed is increased. It is done.

Numeral 24 denotes an elastic pressure roller as a pressure rotating body, which covers a metal core made of aluminum, cast iron or the like with a heat-resistant insulating elastic material such as silicon rubber.
The surface layer of the pressure roller is coated with a fluorine resin or the like having a releasing property from the toner. Both ends of the cored bar are rotatably supported via bearings between the front and rear side plates of the apparatus.

<Third Embodiment> (FIGS. 7 to 10) In this embodiment, in the fixing device 20 of the film heating type of the first embodiment, the recording material conveying direction is higher than the fixing entrance guide, that is, the fixing nip portion. The guide member, which is arranged on the upstream side and guides the recording material P electrostatically carrying the unfixed toner image to the fixing nip portion N, also serves as the ground electrode.

7 and 8, reference numeral 26 denotes the above-mentioned fixing entrance guide. The fixing entrance guide 26 has a volume resistance of 1 × 10 ¹⁰ to 1 × 10 ¹² Ωcm and is grounded. In this embodiment, it is 1 × 10 ¹¹ Ωcm.

The entrance side (recording material entry side) of the fixing entrance guide 26 is inclined upward toward the fixing nip N. When the leading end of the recording material P is guided to the fixing nip N, the entrance guide is formed. First hit the middle of the uphill of 26,
It is guided to the fixing nip portion N along an upward slope.

FIG. 8 shows the state of conveyance of the recording material P. The recording material P is conveyed from the transfer transfer portion T on the upstream side, but before the recording material P enters the fixing nip portion N, the recording material P is slightly bent and becomes a state P2 shown by a solid line in FIG. Once the recording material P enters the fixing nip portion N and the recording material is conveyed in the fixing nip portion N, the recording material conveyance speed in the normal fixing device 20 is usually larger than the recording material conveyance speed in the transfer portion T. 8, the bending of the recording material P is eliminated, and tension is applied to the recording material P between the transfer portion T and the fixing nip portion N, thereby approaching the state of Pl without bending indicated by a broken line in FIG.

FIG. 9 shows the result of monitoring the current flowing through the fixing entrance guide 26 also serving as the ground electrode. A is the moment when the recording material (paper) P enters the fixing nip N,
A current path is formed from the fixing film 23 → the recording material P → the fixing entrance guide 26, and the current flows. The amount of current depends on the contact resistance between the recording material P and the fixing entrance guide 26 if the system is the same.

At the moment when the recording material P enters the fixing nip portion N, the recording material P is in a bent state like the shape of P2 shown by the solid line in FIG. 8, and the fixing entrance guide 26 supports the bending. As described above, the contact area with the back surface of the recording material P increases, and a current flows.

As the conveyance of the recording material P proceeds, the tension is applied to the recording material P between the transfer portion T and the fixing nip portion N, so that the recording material P approaches the state of Pl without bending indicated by a broken line in FIG. Since the recording material P floats from the fixing entrance guide 26, the contact area decreases, so that the current flowing through the fixing entrance guide 26 decreases as indicated by a section BC in FIG.

When the recording material P passes through the transfer portion T and is conveyed only by the fixing nip portion N, the tension of the recording material P between the transfer portion T and the fixing nip portion N is lost again, and the recording material P deflects under its own weight. Then, the state returns to the state of P2 shown by the solid line in FIG. The current flowing through the fixing entrance guide 26 increases as shown in a section CD of FIG.

According to the mechanism of the present invention described in the first embodiment, when the resistance between the recording material P and the ground increases, the holding force acting on the toner relatively decreases. That is, the amount of current flowing through the recording material P fluctuates due to the fluctuation of the contact resistance between the recording material P and the fixing entrance guide 26. The toner holding force decreases as the current decreases, and the toner holding force increases as the current increases. .

FIG. 10 shows the relationship between the resistance value of the fixing entrance guide 26 and the flowing current. When the resistance value of the fixing entrance guide 26 increases, the flowing current decreases. When the voltage applied to the fixing film 23 is −600 V, the effect of preventing the tailing phenomenon is effective when the current is 1 μA or more, and the resistance value of the fixing entrance guide 26 is preferably 400 MΩ or less.

The resistance value from the tip of the fixing entrance guide 26 used in this embodiment to the ground point was 40 MΩ.

If the material of the fixing entrance guide 26 is made of metal, the grounding resistance can be extremely reduced. , The phenomenon that the toner image on the recording material is disturbed easily occurs.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. As a result, the same effects as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
m to 7 μm, the fixing inlet guide 26 is grounded as an electrode,
When a bias is applied to the recording material P, tailing, film offset, pressure roller contamination, and reproducibility of one dot can be satisfied, and the fixing entrance guide 26 also serves as an electrode that contacts the paper P and grounds. Therefore, it is not necessary to provide the recording material guide member and the ground electrode as separate members, which can contribute to a reduction in the number of parts and a reduction in cost.

In the above, the fixing device 20 of the film heating type using the heat resistant film 23 has been described.
In the fixing device 20 of the heat roller type as in the second embodiment, the same effect can be obtained by applying a bias to the fixing roller 31 and imparting conductivity to the fixing inlet guide 26 to ground.

<Fourth Embodiment> (FIG. 11) In this embodiment, in the film heating type fixing device 20 of the first embodiment, the paper discharge guide, that is, the downstream side of the fixing nip portion N in the recording material conveyance direction. And a guide member for smoothly sending out the recording material discharged from the fixing nip portion also serves as the ground electrode. In FIG. 11, reference numeral 27 denotes the above-described paper discharge guide.

According to the mechanism of the present invention described in the first embodiment, by applying a voltage to the fixing film 23 to form a current path flowing from the film to the ground, a binding force to the toner can be generated. . In the third embodiment, the grounding contact with the recording material P is arranged before the recording material P reaches the fixing nip N. However, as in this embodiment, after the recording material P passes through the fixing nip N, the recording material P The same effect can be obtained by providing a contact point with the contact. Further, since the recording material comes into contact with the fixed recording material, the possibility that the toner image on the recording material is disturbed by the contact of the electrodes is reduced.

The surface of the paper ejection guide 27 which is in contact with the recording material P is made of sheet metal, so that the ground resistance between the recording material and the ground becomes almost zero, and the toner binding force increases.

Also, at 3 cm before and after the fixing nip portion N, it is estimated that the amount of water vapor is larger after the fixing nip portion and the surface resistance of the recording material is smaller than before the fixing nip portion. When the ground point is provided after the nip portion, the amount of current flowing increases, and the voltage drop in the top layer 23c of the fixing film 23 increases, so that the toner holding power increases.

Not only the paper ejection guide 27 but also a paper ejection roller disposed downstream of the fixing nip portion N in the recording material conveyance direction.
The same effect can be obtained by making a member that comes into contact with a recording material, such as a paper discharge flapper, provided for switching the paper discharge tray conductive and dropping it to ground.

An effect can be obtained by providing a grounding point in a range where steam generated from the fixing device reaches. When grounding is performed by a fixing entrance guide, a paper discharging guide, a paper discharging roller, or the like, within 3 cm before and after the fixing nip N. It is preferred that

In this embodiment, no current flows through the recording material P and the toner binding force does not work until the leading edge of the recording material touches the paper discharge guide 27. Therefore, it is preferable to arrange a point in contact with the recording material closer to the fixing nip portion N. In this embodiment, the discharge guide 27 is set at a position 2 cm from the fixing nip N in consideration of the above.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. As a result, the same results as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
When the discharge guide 27 is grounded as an electrode and a bias is applied to the recording material P, tailing, film offset, dirt on a pressure roller, and reproducibility of one dot can be satisfied. Since the recording material guide member and the ground electrode do not have to be provided as separate members by also serving as an electrode which comes into contact with the material and grounds, the number of parts can be reduced and the cost can be reduced. Further, the disturbance of the toner image of the image before fixing could be prevented.

In the above, the fixing apparatus 20 of the film heating type using the heat resistant film 23 has been described.
In the fixing device 20 of the heat roller type as in the second embodiment, the bias is applied to the fixing roller 31 to
A similar effect could be obtained by giving conductivity to 7 and grounding it.

<Fifth Embodiment> (FIG. 12) In the present embodiment, in the film heating type fixing device 20 of the first embodiment, as shown in FIG. It also serves as the ground electrode.

In the case of this embodiment, the toner restraining force can be applied from the time when the leading end of the recording material P enters the fixing nip N to the time when the rear end of the recording material P passes through the fixing nip N.

The same experiment as in Table 1 of the first embodiment was performed. As a result, the same results as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
When the electrode is grounded and a bias is applied to the recording material, tailing, film offset, pressure roller contamination, and reproducibility of one dot can be satisfied. Further, both the fixing entrance guide 26 and the discharge guide 27 can be used. Can also serve as an electrode that comes into contact with the recording material P and grounds, so that the guide member and the ground electrode do not need to be separate members, which can contribute to a reduction in the number of parts and a reduction in cost.

Further, it is possible to exert a toner restraining force from the front end to the rear end of the recording material P passing through the fixing nip portion N, to prevent the toner image from being disturbed over the entire image area, and to form a high quality image. It has become possible.

In the above, the fixing device 20 of the film heating type using the heat resistant film 23 has been described.
In the fixing device 20 of the heat roller type as in the second embodiment, the bias is applied to the fixing roller 31 to
A similar effect could be obtained by giving conductivity to 7 and grounding it.

<Sixth Embodiment> A feature of this embodiment is that the ground electrode described in the first to fifth embodiments can be transported in the direction of conveyance of the recording material having the minimum size allowed by the image forming apparatus. The configuration is such that the distance between the fixing nip portion N and the ground point is set within the range.

In the present embodiment, in the configuration from the first embodiment to the fifth embodiment, the installation position of the electrode is two
cm, and the same experiment as in Table 1 of the first example was performed.

A postcard size sheet, which is the minimum usable sheet of the image forming apparatus used in this embodiment, was used. The results were the same as in Table 1.

That is, the weight average particle size of the toner is 3.5 μm.
m to 7 μm, when the electrode is grounded and a bias is applied to the recording material, tailing, film offset or roller offset, pressure roller contamination, 1-dot reproducibility can be satisfied, and any size of recording material can be satisfied. High quality image formation has become possible.

In this embodiment, the electrode is set at 2 cm from the fixing nip. However, the present invention is not limited to this as long as the image forming apparatus is changed or a similar effect is obtained.

<Seventh Embodiment> (FIG. 13) A feature of this embodiment is that the bias applied to the fixing film 23 in the first embodiment is
That is, power is supplied from the four sides.

FIG. 13 shows a structural model of the embodiment. That is, the top layer 23c was eliminated on one end side of the cylindrical fixing film 23, and the annular exposed portion W of the conductive primer layer 32b as an intermediate layer was provided.

On one end side of the elastic pressure roller 24, the conductive rubber ring 2 is positioned corresponding to the annular exposed portion w of the conductive primer layer 32b provided on one end side of the fixing film 23.
4b is provided.

The conductive rubber ring 24b is made of rubber in which conductive particles such as carbon black are dispersed, and has a bamboo ring shape. This conductive rubber ring 24b is fitted and supported on a core metal 24a on one end side of the pressure roller 24,
The inner periphery of the conductive rubber ring 24b is in direct contact with the pressure roller core 24a. The core metal 24a of the pressure roller 24 is made of a material having good conductivity such as aluminum. In an assembled state of the apparatus, the outer peripheral surface of the conductive rubber ring 24b on the pressure roller 24 side and the annular exposed portion W of the conductive primer layer 32b of the cylindrical fixing film 23 are in contact with each other to form electrical contacts. .

The bias of the high voltage power supply S4 is
And applied to the conductive primer layer 23b of the fixing film 23 via the conductive rubber ring 24b.

The elastic roller portion of the pressure roller 24 is formed by coating an elastic material such as silicon rubber with a releasable fluororesin or the like. The recording material is nipped and conveyed between the elastic rubber layer of the pressure roller and the top layer 23c of the fixing film 23.

The higher the resistance value of the top layer 23c of the fixing film 23, the greater the toner binding force, and the greater the effect on tailing.

In order to obtain the effects of the present invention, it is important to provide a potential difference between the recording material and the fixing film. Therefore, the electrical insulation of the silicon rubber in contact with the back surface of the recording material is important. If the distance between the fixing film 23 and the pressure roller core 24a is not more than 1 × 10 ¹⁰ Ω without the conductive rubber ring 24b, the toner binding force is reduced.

In this embodiment, a film having a gap of 1 × 10 ¹¹ Ω between the fixing film 23 and the core 24a of the pressure roller was used.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. As a result, the same results as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
When the electrode is grounded and a bias is applied to the recording material, tailing, film offset, dirt on the pressure roller, and reproducibility of one dot can be satisfied.
By applying a bias to the fixing film 23 from the fourth side, the configuration can be simplified, the number of parts can be reduced, and cost can be reduced, and high-quality image formation can be achieved.

<Eighth Embodiment> (FIG. 14) The feature of this embodiment is that the pressure roller also serves as the electrode grounded in the first embodiment.

That is, in FIG.
Is an aluminum core 24a and an elastic layer 24 made of silicon rubber or the like in which conductive particles provided around the aluminum core 24a are dispersed.
and a conductive release layer 24d as a surface layer provided therearound. There is conductivity from the core metal 24a to the surface layer 24d.

The fixing film 23 and the pressure roller 24 are provided with separate conduction paths. A voltage is applied to the conductive primer layer 23b of the fixing film 23 from the high-voltage power supply S4,
A current path to the ground is formed via the top layer 23c of the fixing film 23, the conductive rubber layers 24d and 24c of the pressure roller 24, and the core 24a.

In the recording material P, an electric field is generated due to a potential difference between the pressure roller surface layer 24c and the fixing film primer layer 23b, and a toner binding force is generated.

As a result, the pressure roller 24 can also serve as a ground electrode, and a bias can be applied to the recording material.

Further, since the electrodes are grounded in the fixing section, it is possible to apply a bias without considering the resistance of the recording material.

Further, since the bias is continuously applied from the leading edge to the trailing edge of the recording material, the binding force of the toner acts on the entire recording material.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. As a result, the same results as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
When the electrode is grounded and a bias is applied to the recording material, tailing, film offset, dirt on the pressure roller, and reproducibility of one dot can be satisfied.
Since the electrode 4 also serves as a ground electrode, a bias can be applied without considering the resistance of the recording material, and high-quality image formation can be performed over the entire image area.

<Ninth Embodiment> (FIG. 15) The feature of this embodiment is that, in the first embodiment, a bias is applied from the pressure roller side, and the fixing film side also serves as a ground electrode. is there.

In FIG. 15, the fixing film 23 is grounded, and a bias is applied to the pressure roller 24 from the high voltage power supply S4.

According to the mechanism of the present invention shown in the first embodiment, not the absolute potential of the pressure roller 24 and the fixing film 23 but the potential difference is a factor that causes the toner binding force. Therefore, the same effect can be obtained not only in a configuration in which a bias is applied to the fixing film and the back surface of the recording material is grounded, but also in a configuration in which a bias is applied to the back surface of the recording material and the fixing film is grounded.

In the case of this embodiment, a voltage is applied to the pressure roller 24, and a current path to the ground is made via the conductive rubber layer of the pressure roller 24 and the top layer 24c of the fixing film 23. An electric field is generated in the recording material due to a potential difference between the surface layer of the pressure roller and the film primer layer, and a toner binding force is generated.

As a result, the fixing film 23 can also serve as a ground electrode, and a bias can be applied to the recording material.

Since the electrodes are grounded at the fixing nip, it is possible to apply a bias without considering the resistance of the recording material.

Further, since the bias is continuously applied from the leading edge to the trailing edge of the recording material, the binding force of the toner acts on the entire area of the recording material.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. As a result, the same results as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
When the electrode is grounded and a bias is applied to the recording material, tailing, film offset, pressure roller contamination, and reproducibility of one dot can be satisfied. Further, since the fixing film also serves as a ground electrode, recording is performed. The bias can be applied without considering the resistance of the material, and high-quality image formation can be performed over the entire image area.

<Tenth Embodiment> (FIG. 16) The feature of this embodiment is that, in the first embodiment, a bias is applied from the back surface of the recording material, and the fixing film also serves as a ground electrode. is there.

According to the mechanism of the present invention shown in the first embodiment, not the absolute potential of the pressure roller and the fixing film but the potential difference is a factor that causes the toner binding force. Therefore, the same effect can be obtained not only in the configuration in which a bias is applied to the fixing film and the back surface of the recording material is grounded, but also in the configuration in which a bias is applied to the back surface of the recording material and the fixing film is grounded.

In this case, since a voltage is applied to the power supply electrode member, toner may adhere to the power supply electrode member. Therefore, it is preferable to arrange the power supply contact point on the recording material after passing through the fixing nip portion. .

In this embodiment, as shown in FIG. 16, the paper discharge guide 27 is used as a power supply section.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. As a result, the same effects as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
When the bias is applied to the recording material, tailing, film offset, pressure roller contamination, and 1-dot reproducibility can be satisfied. Further, the discharge guide is a power supply electrode and the fixing film is grounded. By also using the electrodes, toner contamination of the recording material fixing guide member is prevented, and high-quality image formation is enabled.

<Eleventh Embodiment> The feature of this embodiment is that in the heat roller type fixing device of the second embodiment, a bias is applied from the back side of the recording material and the fixing roller 31 is grounded. This is the point that also serves as an electrode.

More specifically, since the fixing film 23 of the tenth embodiment is merely changed to the fixing roller 31,
The illustration of the apparatus and the description of the configuration are omitted.

The same experiment as in Table 1 of the first embodiment was performed using the above configuration. Process speed tripled to 180m
The experiment was performed at m / s. As a result, the same effects as in Table 1 were obtained.

That is, the weight average particle diameter of the toner is 3.5 μm.
When the electrode is grounded and a bias is applied to the recording material, tailing, film offset, pressure roller contamination, and reproducibility of one dot can be satisfied.
7 (FIG. 16) also serves as a power supply electrode and the fixing roller also serves as a ground electrode, thereby preventing toner contamination of the recording material fixing guide member and enabling high-quality image formation even when the process speed is increased.

<Others> 1) The fixing rotating body and the pressing rotating body are not limited to the roller body.

2) The heating method and heating principle of the fixing member are arbitrary. For example, an external heating method or an electromagnetic induction heating method can be used.

3) The pressure member may be heated.

4) Principle of forming developer image on recording material
The method is arbitrary.

[0204]

As described above, according to the present invention, in a contact heating type fixing device such as a film heating type or a heat roller type, and in an image forming apparatus provided with the fixing device, the recording material has a large moisture content. Even in the state, that is, without considering the resistance of the recording material, and even when the toner used is a toner having a small particle diameter, the toner image on the recording material introduced into the fixing nip portion of the fixing device can be printed on the recording material. , The electrostatic holding force (restraining force) is sufficiently held, and the occurrence of image defects, pressure roller contamination, tailing, etc. due to the toner offset phenomenon is prevented, and high-quality, high-definition image formation becomes possible. .

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram of a fixing device (film heating method).

FIG. 3 is a schematic cross-sectional view showing a layer structure of a fixing film.

FIG. 4 is an explanatory diagram of a generation mechanism of a trailing image.

FIG. 5 is an equivalent circuit diagram of an electric circuit in the apparatus of FIG.

FIG. 6 is a schematic configuration diagram of a fixing device (heat roller type) in a second embodiment.

FIG. 7 is a schematic configuration diagram of a fixing device according to a third embodiment.

FIG. 8 is an explanatory diagram of a slack state and a tension operation state of a recording material.

FIG. 9 illustrates characteristics of a fixing device (part 1).

FIG. 10 illustrates characteristics of a fixing device (part 2).

FIG. 11 is a schematic configuration diagram of a fixing device according to a fourth embodiment.

FIG. 12 is a schematic configuration diagram of a fixing device according to a fifth embodiment.

FIG. 13 is a schematic configuration diagram of a fixing device according to a seventh embodiment.

FIG. 14 is a schematic configuration diagram of a fixing device according to an eighth embodiment.

FIG. 15 is a schematic configuration diagram of a fixing device according to a ninth embodiment.

FIG. 16 is a schematic configuration diagram of a fixing device according to a tenth embodiment.

[Explanation of symbols]

Reference Signs List 20 fixing device (film heating method or heat roller method) 21 heating element (ceramic heater) 22 heater support 23 cylindrical fixing film 24 elastic pressure roller 25 ground electrode 26 fixing entrance guide (also used as ground electrode) 27 paper ejection guide (Also used as ground electrode) N Fixing nip P Recording material t Toner image S4 High voltage power supply 31 Fixing roller 32 Halogen heater lamp 33 Elastic pressure roller

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masahide Hirai 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (Reference) 2H033 AA09 AA10 BA11 BA13 BB30 BE03

Claims (17)

[Claims] 1. A heating body, a film that slides on the heating body, and a pressure rotating body that forms a nip with the heating body via the film, and a developer image is electrostatically formed at the nip. A fixing device for fixing the developer image to the recording material by nipping and transporting the recording material carried on the developer, wherein the developer constituting the developer image has a weight average particle size of 3.5 to 7.0 μm. And a means for applying a bias voltage to at least one of the film and the pressurizing rotator, and an electrode that is in contact with the recording material so that a current due to the bias voltage flows through the recording material. Is a fixing device, which is grounded. 2. A fixing rotating body and a pressing rotating body, at least one of which is heated and rotates while forming a nip with each other,
In the fixing device for fixing the developer image to the recording material by nipping and transporting the recording material electrostatically carrying the developer image in the nip, the developer constituting the developer image may have a weight average particle size. A diameter of 3.5 to 7.0 μm; and a means for applying a bias voltage to at least one of the fixing rotator and the pressing rotator so that a current by the bias voltage flows through the recording material. An electrode is provided in contact with the recording material, and the electrode is grounded. 3. The fixing device according to claim 2, wherein a heating element is included in at least one of the fixing rotator and the pressure rotator. 4. A guide member, which is disposed upstream of the nip in the recording material conveyance direction and guides a recording material electrostatically carrying a developer image to the nip, also serves as the ground electrode. The fixing device according to claim 1. 5. A paper discharge guide member disposed downstream of the nip in a recording material conveyance direction and guiding a recording material exiting the nip also serves as the ground electrode.
4. The fixing device according to any one of claims 1 to 3. 6. The fixing device according to claim 1, wherein at least one of the ground electrodes is disposed on both the upstream side and the downstream side of the nip in the recording material conveyance direction. apparatus. 7. The fixing device according to claim 1, wherein a distance from the nip to the ground electrode is equal to or less than a length of the recording material having the shortest length in the conveyance direction. 8. An elastic body of the pressing rotator has an electrical insulating property, and a part of a conductive layer of the film is electrically connected to a metal core of the pressing rotator. The fixing device according to claim 1, wherein a bias is applied to the conductive layer of the film by supplying power to a core of the rotating body. 9. A bias is applied to the film, and the film has electrical conductivity from a metal core to a surface of the pressure rotating body,
2. The fixing device according to claim 1, wherein the pressing rotator is a ground electrode. 10. The pressure rotating body has electrical conductivity from a metal core to a surface thereof, a bias is applied to the pressure rotating body, and the film is a ground electrode. 3. The fixing device according to claim 1. 11. A heating body, a film sliding on the heating body, and a pressure rotating body for forming a nip with the heating body via the film, wherein the developer image is electrostatically transferred by the nip. A fixing device for fixing the developer image to the recording material by nipping and transporting the recording material carried on the developer, wherein the developer constituting the developer image has a weight average particle size of 3.5 to 7.0 μm. An electrode disposed so as to be in contact with a part of the recording material on the downstream side of the nip in the recording material transport direction, and a unit for applying a bias voltage to the electrode; and a bias voltage applied to the electrode. Wherein the film is grounded so that the electric current flows through the recording material and the film. 12. A printing apparatus, comprising: a fixing rotator and a pressure rotator that are heated and at least one of which forms a nip and rotates, and nips and conveys a recording material that electrostatically carries a developer image in the nip. A fixing device for fixing the developer image to the recording material by using a developer. The developer constituting the developer image has a weight average particle diameter of 3.5 to 7.0 μm, and the recording material is transported more than the nip. An electrode disposed so as to be in contact with a part of the recording material on the downstream side in the direction, and means for applying a bias voltage to the electrode, and a current caused by the bias voltage applied to the electrode is used for the recording material and the fixing device. The fixing device according to claim 1, wherein the fixing rotator is grounded so as to flow through the rotator. 13. The heating device according to claim 1, wherein at least one of the fixing rotator and the pressure rotator includes a heating member.
3. The fixing device according to 2. 14. The fixing device according to claim 12, wherein a heating element is included in the fixing rotating element. 15. An image forming apparatus comprising: image forming means for electrostatically carrying a developer image on a recording material; and fixing means for fixing the developer image to the recording material, wherein the fixing means is provided. 15. An image forming apparatus, which is the fixing device according to any one of 1 to 14. 16. The image forming means includes at least an image carrier, a latent image forming means for forming an electrostatic latent image on a surface of the image carrier, and an electrostatic image formed on the surface of the image carrier. Developing means for developing and visualizing the latent image with a developer, and transferring means for transferring the developer image on the surface of the image carrier to a recording material and electrostatically carrying the developer image on the recording material. Claim 1 characterized by the following:
6. The image forming apparatus according to 5. 17. The developing unit includes: at least a developer; a developer carrier that carries the developer and transports the developer to a development area; and a developing device that abuts on the developer carrier and reduces an amount of the developer applied. A regulating member for regulating, wherein the developer carrying member carries the developer and conveys the developer to the developing area, and a developing bias is applied to the developer carrying member to transfer the electrostatic latent image formed on the image carrying member to the developer carrying member. The image forming apparatus according to claim 16, wherein the image forming apparatus is a developing device that develops and visualizes the image by applying the control signal.