JP2000305388A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can obtain a stable fixed image by restraining such a phenomenon that toner is scattered backward or toner offset even when high-speed operation is contrived, and an image forming device using the same. SOLUTION: In this fixing device provided with a rotating body having a heating source and a pressure member forming a press-contact part with the surface of the rotating body recording material is carried while it is held in the press-contact part and a toner image electrostatically stuck and formed on the surface of the recording material is thermally fixed on the recording material. The device is provided with an electrifying means (corotron electrifier) 10 electrifying the surface of the rotating body to the same polarity as the toner. Thereby, since an action to electrostatically press or attract the toner image on the recording material comes about, the excellent fixed image without toner scattering backward is obtained even when recording speed is made high and the pressure of water vapor gets high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device and an image forming apparatus, and more particularly, to an electrophotographic printer, a copying machine, a facsimile, and the like.

[0002]

2. Description of the Related Art Conventionally, in an apparatus such as a printer, a copying machine, a facsimile or the like using an electrophotographic system, a toner charged in a developing section is electrostatically adhered to a photoreceptor surface on which an electrostatic latent image is formed. Then, in the transfer section, a charge having a polarity opposite to that of the charged toner is applied to the back surface of the recording material to transfer the toner image on the photoconductor surface onto the recording material, and then the unfixed toner image on the recording material is fixed. An image is formed by a process of melting by heating and permanently fixing the recording material on a recording material.

[0003] In these processes, as an image fixing method, a contact heating type fixing device having good thermal efficiency and safety is widely known. In recent years, in particular, from the viewpoint of promoting energy saving, a conventional halogen heater has been used. As a method that has a higher roller heat transfer efficiency and a faster apparatus start-up than a heat roller method that uses a cylindrical metal containing a fixing roller as a fixing roller, a film heating method that heats through a film with a small heat capacity attracts attention. And JP-A-63-3131.
No. 82, JP-A-2-15778, 4-44075
44083, 4-204980-204498, and the like.

[0004] The structure of the film heating and fixing device includes a method of transporting the film between the pressure roller while applying tension using a transport roller and a driven roller dedicated to transport the film, and a method of adding a cylindrical film. There is a method of driving with a conveying force of a pressure roller. The former has an advantage that film transportability can be enhanced, and the latter has an advantage that a configuration can be simplified and a low-cost fixing device can be realized.

FIG. 2A shows a specific example of the cross-sectional structure of the latter film-fixing device driven by a pressure roller. In FIG. 1, a recording material 8 on which an image is formed by an unfixed toner 9 has a release roller 4a and a heat-resistant rubber layer 4b. And a metal stay 5 on the fixing side pressed by a pressing means (not shown) provided on the upper fixing frame 6 to a total pressure of about 4 to 15 kgf and applied by a frictional force acting on the interface. It is conveyed along a fixing entrance guide 7 to a nip portion between the cylindrical fixing film 3 which is rotated and conveyed along a heater holder 2 also serving as a film guide member with the rotation of the pressure roller, and is heated by the heater 1 via the fixing film 3. The paper is pressed and fixed, and is discharged along the discharge guide 7 '.

At this time, the fixing film 3 has a thickness of 100 μm or less, more preferably 40 μm or less and 20 μm or less, in order to reduce the heat capacity and improve the quick start property.
PTFE and PF that combine the above heat resistance, release properties and durability
A, a single-layer film of PPS or a PT with a conductive primer layer 3b sandwiched on the surface of a base film 3c of polyimide, polyamideimide, PEEK, PES, etc.
It is composed of a composite layer film in which a release layer 3a made of a fluororesin such as FE, PFA, FEP or the like is coated or formed into a tube. When a fixing film having this three-layer structure is used, FIG. As shown in the drawing, a region where the conductive primer layer is exposed at the end of the fixing film is provided, and a conductive rubber ring 4d is attached to the end of the pressure roller side opposite to the surface of the primer layer via a resistor 4e. The primer layer of the fixing film can be grounded by resistance by inserting the conductive rubber ring into the roller core 4c and pressing the conductive rubber ring against the conductive primer layer. It is configured to make it difficult to cause an adverse electrostatic effect on the charged toner image.

[0007] As described above, various image forming apparatuses such as printers using the above-described fixing device eliminate the need for preheating during standby due to the high heating efficiency and the rising speed, and eliminate the waiting time. It has many advantages, especially since the method of driving a cylindrical film with the conveying force of a pressure roller can be realized at low cost. It is as expected.

In order to realize this high speed, first, naturally, the motor is powered up to increase the rotation speed of the pressure roller and the fixing film, and sufficient heat energy is applied to the paper having a short passage time. In order to supply, it is necessary to make improvements such as setting the fixing temperature higher, expanding the heating area by increasing the pressing force of the pressure roller, and changing the material of the heater substrate and fixing film to one with high thermal conductivity. is there.

However, when such improvements are made, various problems are likely to occur at the same time in the fixing section.

As one of the adverse effects, a phenomenon occurs in which the toner on the recording material is partially blown to the downstream side in the paper transport direction, and this phenomenon becomes worse as the recording speed is increased. (Hereinafter, this phenomenon is referred to as a “rear toner scattering” phenomenon). The following mechanism can be considered as a cause of the occurrence of the “rear toner scattering” phenomenon. That is, since the paper fixed in the fixing unit contains a certain amount of moisture even under a normal environment, steam is generated by heating in the nip during fixing, but the fixing temperature is increased with the speeding up. Then, the generation of the water vapor becomes intense, and the water vapor is strongly blown out in the front-rear direction of the nip in search of an escape place. At this time, since the paper transport speed is also increasing at the same time, water vapor is blown at the nip entrance at a speed obtained by synthesizing the paper transport speed with the steam speed to be blown to the unfixed toner on the paper. It is considered that part of the toner, such as the toner on the image surface layer, which has relatively weak adhesion to the paper and is easily affected by the air current on the surface, is blown backward by the wind pressure in the image. Although this phenomenon is greatly affected by the electrical resistance and surface properties of paper and the type of additive, it is most likely to occur in toner images with a pattern perpendicular to the paper conveyance direction, such as horizontal lines, and recording is performed based on the mechanism. This is a phenomenon that gets worse as the speed increases.

Such a phenomenon occurs even in a conventional heat roller type apparatus when the speed is increased, and as a measure for suppressing such a phenomenon, the thermal condition cannot be relaxed due to the necessity of securing the fixing property. A method for enhancing the electrostatic adhesion of toner to paper has been considered.

For example, in the heat roller method, a bias having the same polarity as that of the toner is applied to the metal portion of the fixing roller, and an electric field is applied across an insulating release layer having a sufficient thickness of 15 μm or more provided on the surface of the metal portion. To press the toner on the paper from the front side by the repulsive electric field, or to induce a potential of the opposite polarity (same polarity as the transfer charge) with the toner on the pressure roller side to increase the adhesion strength of the toner to the paper. A method has been devised to increase the influence, but since there is only the influence of the electric field acting through the insulating layer, the surface of the insulating layer itself is rubbed with the paper that is passed through, the influence of the transfer charge, the polarity included in the paper May be abnormally charged due to factors such as the attachment of an additive (pigment) having, and the effect may be incomplete. In order to alleviate this, a method of making the pressure roller side conductive has been devised, but in order to impart conductivity to the surface of the pressure roller, it is necessary to mix a conductive additive into the surface layer. Since the releasability of the surface is easily lost by the additive, in this case, as a result, stains due to toner adhesion may be induced on the pressure roller side. Further, if a bias is continuously applied to one side of the insulating layer, charges of the opposite polarity supplied from the recording material are injected into the insulating layer in the long term, and finally the electric field is canceled and the surface is removed. The potential approaches 0, and the effect may be lost.

On the other hand, in the fixing method using a fixing film, it is difficult to increase the thickness of the surface layer to 15 μm or more due to the restriction of thermal conductivity. Therefore, even if an insulating material is used, the thickness cannot be sufficiently secured. It was difficult to realize a fixing film completely free from electric leak.

On the other hand, if the insulating layer is made to have a certain degree of conductivity by lowering the insulating property in order to prevent the occurrence of abnormal charging by using the insulating surface layer, the transfer applied to the paper via the surface layer is reduced. Since the charge leaks, the toner splattering phenomenon may appear more strongly due to a decrease in the toner holding power.

Further, in the film fixing method, the amount of deformation of the fixing nip is large, and the escape area of water vapor at the fixing entrance is further narrowed, so that the water vapor is blown out strongly and the improvement effect is sometimes hindered. .

In addition, a method of recharging the back of the paper to the same polarity as the charge polarity of the transfer by a charger before the entrance of the fixing has been devised. However, a charge is applied to the back side of the recording material on which the toner image has been formed once. To apply, it is necessary to recharge the paper in a non-contact manner so that it does not contact the paper surface at least and does not cause paper transport resistance, but the position of the paper being transported is not constant and unstable Therefore, it was difficult to always uniformly recharge the entire back of the paper.

In addition to the above-mentioned adverse effects, a phenomenon called offset, in which the toner on the recording material adheres to the surface of the fixing-side rotating body with an increase in the speed and later transfers to another image area, also tends to be deteriorated. Several mechanisms can be considered as factors for the occurrence of the offset phenomenon and the deterioration of the level. One of the mechanisms is, first of all, a decrease in fixability. This is because simply increasing the speed reduces the time required to pass through the fixing nip, making it difficult to apply a sufficient amount of heat to the recording material. The amount of toner is insufficient, and the molten toner on the surface layer adheres to the fixing rotating body side with the heat source due to the adhesive force. Therefore, an offset due to this factor easily occurs.

Another mechanism is an electrostatic factor. This requires that the surface of the rotating body on the fixing side be designed to have a certain level of resistance in order to prevent leakage of the transfer charge of the recording material. Unnecessary charging occurs on the surface of the fixing-side rotating body when continuous paper is passed, and the polarity becomes offset when the polarity becomes opposite to that of the toner that attracts the toner. If the recording material is high, the separation charge generated when the rear end of the recording material passes through the fixing nip and separates from the surface of the fixing-side rotating body further forms a charged area having a polarity opposite to that of the toner on the surface of the fixing-side rotating body. Therefore, a phenomenon called a peeling offset in which the toner is adsorbed in the next fixing step also occurs.

As another factor of worsening the offset, there is a shortage of transfer charge due to high speed. This occurs when the transfer charge to be applied per unit time on the back surface of the recording material per unit time at the transfer unit cannot catch up due to an increase in the speed of passage of the recording material. However, if it is insufficient, as a result, a sufficient force to hold the toner on the recording material cannot be obtained, and the toner is offset toward the fixing rotating body. In this case, At the same time, the above-mentioned rear toner scattering phenomenon also worsens. If such an offset phenomenon occurs frequently, the toner that has been offset toward the fixing rotation side will eventually accumulate on the pressing member side, causing a new problem of stain on the back surface of the recording material.

[0020]

The problem to be solved by the present invention is that when the speed of the fixing device is increased, adverse effects such as a rear toner scattering phenomenon and an offset of the toner toward the fixing rotating body occur as adverse effects. .

Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide a fixing device capable of obtaining a stable fixed image by suppressing the rear toner scattering phenomenon and toner offset even at high speed, and an image forming apparatus using the same. It is in.

[0022]

Means for Solving the Problems [1]: A rotating body having a heating source, and a pressing member forming a pressure contact portion with the surface of the rotating body, the recording material is held and conveyed to the pressure contact portion. A fixing device for thermally fixing a toner image electrostatically adhered and formed on the recording material surface to the recording material, wherein charging means for charging the surface of the rotating body to the same polarity as the toner is provided. A fixing device.

[2] In the fixing device described in [1],
The fixing device is characterized in that the charging unit is a corotron charger.

[3]: In the fixing device described in [1],
The fixing device is characterized in that the charging unit is a charger that applies a high voltage to a metal member having a needle-like tip.

[4]: In the fixing device according to [1] or [2], a high voltage having an absolute value of 4 kV or more is applied to the charging unit, and a charge generation unit of the charging unit and the surface of the rotating body are connected to each other. Wherein the distance between the fixing devices is 5 mm or more.

[5] In the fixing device described in [1],
The fixing device is characterized in that the charging unit is a contact charger that contacts the surface of the rotating body.

[6] In the fixing device described in [5],
The fixing device according to claim 1, wherein the contact charger also functions as a cleaning unit for cleaning the surface of the rotating body.

[7] The fixing device according to [5] or [6], wherein the contact charger is made of a good heat conductor.

[8] In the fixing device according to any one of [1] to [7], the rotating body has a thickness of 100
A fixing device comprising a heat-resistant film having a thickness of not more than μm.

[0030]

[9]: The fixing device according to [8],
A fixing device, comprising: a high-resistance release layer having a thickness of 15 μm or less as a surface layer of the heat-resistant film; and a conductive layer under the high-resistance release layer. The conductive layer is grounded.

[10]: [8] or

[9] In the fixing device according to any one of [9], the pressing member is a pressing roller that rotates with a driving force, and the heat-resistant resin film is driven and rotated by contact with the pressing member. The fixing device is a film, and the charging unit is a roller charger having a driving force.

[11]: A rotating body having a heating source, and a pressing member forming a press-contact portion with the surface of the rotating body, the recording material is held and conveyed to the press-contact portion, and In a fixing device for thermally fixing a toner image formed electrostatically on a recording material, charging means for charging the surface of the pressing member to a polarity opposite to that of the toner is provided. apparatus.

[12] The fixing device according to [11], wherein the charging means is a corotron charger.

[13] The fixing device according to [12], wherein the charging means is a charger for applying a high voltage to a metal member having a needle-like tip.

[14] In the fixing device according to [12] or [13], a high voltage having an absolute value of 4 kV or more is applied to the charging unit, and a voltage between the charging unit and the pressing member surface is increased. A fixing device having a distance of 5 mm or more.

[15] The fixing device according to the item [11], wherein the charging means is a contact charger in contact with the surface of the pressure member.

[16] The fixing device according to [15], wherein the pressing member is a rotating pressing roller, and the contact charger also functions as a cleaning unit for cleaning the surface of the pressing roller. apparatus.

[17] The fixing device according to [16], wherein the contact charger is formed of a good heat conductor.

[18] The fixing device according to any one of [15] to [17], wherein the contact charger is a roller charger that is driven and rotated by contact with the surface of the pressure roller. Characteristic fixing device.

[19] The fixing device according to any one of [15] to [17], wherein the contact charger is a blade charger that makes a counter contact with the surface of the rotary pressing member. Fixing device.

[20] The fixing device according to any one of [11] to [19], wherein the surface of the pressing member has a high-resistance release layer having a thickness of 50 μm or less, and Has a conductive layer, and the conductive layer is grounded.

[21]: Any one of [1] to [20]
In the fixing device according to the item, as a resistance characteristic of the surface of the rotating body and the pressing member, the back surface of each surface is grounded,
The surface potential after 15 seconds from charging the surface to 400V is 15
A fixing device having a resistance characteristic of remaining 0 V or more, more preferably 300 V or more.

[22]: In an image forming apparatus having an image forming means for forming a toner image on a recording material and a fixing means for heating the toner image and fixing the toner image on the recording material, An image forming apparatus comprising the fixing device according to any one of [1] to [21].

<Operation> According to the present invention, each surface is charged to the same polarity or opposite polarity to the toner by using the charging means provided with the surface of the fixing-side rotating body or the pressing member in the vicinity thereof, thereby fixing. By doing so, an action of electrostatically pressing or attracting the toner image on the recording material occurs, so that even if the recording speed is increased and the pressure of the water vapor is increased, the toner does not scatter backward, and a favorable A fixed image can be obtained.

In addition, since the toner of the same polarity hardly adheres to the surface of the fixing-side rotating body due to the charging, an effect of preventing the excessive adhesion of the toner can be obtained, so that the occurrence of the offset accompanying the high speed operation can be suppressed.

[0046]

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

<First Embodiment> FIG. 1 is a sectional view of a fixing device of an image forming apparatus according to a first embodiment of the present invention. In the present embodiment, the same elements as those of the device shown in FIG.
Repetitive description has been omitted by, for example, attaching the same reference numerals.

In this embodiment, a new shield electrode 10
b and a charging wire 10a are provided on the inner surface of the upper fixing frame, and the fixing film 3 and the charging device 10 are opposed by a distance of about 6 mm between the wires, and -4 kV is applied to the charging wire. The current to about 15
At a flow rate of about 95 mm per second, the film is allowed to stand in a fixing area having a nip width of about 7 mm at a rate of about 95 mm per second in an environment of 23 ° C./65% for 8 hours or more while flowing 0 μA to uniformly charge the fixing film surface. The toner on the paper was fixed by continuously passing the paper on which the rear toner scattering phenomenon, which was absorbed, was relatively likely to occur.

At this time, the toner image pattern is set to 0.1.
Using a horizontal line pattern in which horizontal lines having a width of 2 mm are repeatedly formed at 1 mm intervals, the fixing temperature was set to 200 ° C. as a temperature condition, and the operation was started from a state where the fixing device 10 was completely cooled down to room temperature. As a result, no toner scattering phenomenon was observed in the fixed image, and a good image was obtained.

For comparison, when only the power supply of the charger was turned off under exactly the same conditions as the above-mentioned experimental conditions, the rear toner scattering phenomenon occurred frequently throughout the entire region. It has been found that the occurrence of the splattering phenomenon is greatly suppressed.

Further, the difference in image quality due to ON / OFF of the charger also appears in the offset level when continuous passage of high-resistance paper or rough paper with large irregularities on the surface occurs. ON occurred when the offset occurred
After that, it could be suppressed so that it could not be clearly confirmed.

In this embodiment, as in the conventional example shown in FIG. 2, as the fixing film 3, the thickness of the surface release layer 3a is about 10 μm, and the conductive primer layer 3b is sandwiched thereunder. By using an endless film having a polyimide resin base layer 3c of about 50 μm and grounding the conductive primer layer 3b, the charge generated in the charger 10 is set so as to be efficiently applied to the film surface by the action of an electric field. I have.

The fixing film 3 used in the above configuration
A high-resistance film in which the electrical properties of the release layer 3a are grounded on the back side and charged on the front side to 400 V, and the residual potential after 3 seconds is 300 V or more; Similarly, two types of films having relatively low resistance, in which the residual potential is reduced to about 150 V to 200 V, were used. While the improvement effect was obtained, when the charger was turned off, the level of the rear toner scattering phenomenon was not an acceptable level in any case. (The former high-resistance film, which has poor charge decay characteristics, tends to have a slightly different degree of toner scattering, but the lower resistance film has a lower transfer charge leak and retains toner.) The difference is caused by the further reduction of the force and the greater scattering of the toner.) On the other hand, by using these films, a bias of -600 V is applied to the primer layer as in the conventional countermeasure, and the electric field effect is applied. When the suppression level of the rear toner scattering phenomenon was confirmed, the high resistance film seemed to have a slightly lower degree of scattering, but a sufficient effect was not obtained.

From these results, in particular, in the fixing film system in which it is necessary to make the film thickness thin in order to increase the thermal conductivity, even if a bias is applied to the back surface of the film made of a material having high insulation, the film thickness becomes small. Since charge leakage due to thinness cannot be completely prevented, the effect of suppressing the rear toner scattering phenomenon due to the electric field effect is poor.

On the other hand, in the method in which the film surface is forcibly charged, even if a film having a lower resistance is used, the duration of the effect is sufficiently longer than the time for one rotation of the fixing film 3. Thus, the rear toner scattering phenomenon can be almost completely suppressed.

<Second Embodiment> FIG. 4A is a sectional view of a fixing device of an image forming apparatus according to a second embodiment of the present invention. In FIG. 4A, members having the same numbers as those in FIG. 1A indicate the same components, and the description thereof will not be repeated.

In the present embodiment, a charging sheet metal 11 having a plurality of simple saw blade-shaped charging needles is provided on the inner surface of the upper fixing frame instead of the corotron charger in comparison with the first embodiment. In FIG. 4B, 11a is the front shape of the charging sheet metal 11, 11b is the top shape, 11c
Indicates a side shape.

The charged sheet metal 11 of this embodiment has a thickness of 0.1
mm, needle peaks having a height of about 3 mm are arranged at a pitch of 2 mm on the charging needle part.
It is provided so as to face the film surface at a distance of m.

When -4 kV is applied to the charged sheet metal 11,
As a result of fixing the toner on the paper under the same conditions as in the first embodiment, no scatter of the rear toner was observed in the fixed image, and a good image could be obtained.

For comparison, when only the power supply of the charging sheet metal was turned off under the same conditions as the above experimental conditions, the rear toner scattering phenomenon occurred frequently in the whole area.

As a result, it has been found that even in the configuration of the present embodiment, which is considered to be inferior to the first embodiment in terms of charging uniformity, substantially the same effect can be obtained as a measure for suppressing the rear toner scattering phenomenon. In addition, the same effect as that of the first embodiment was confirmed for the offset.

Further, when the charging sheet metal 11 is used, a material having a relatively high surface resistance of the fixing film 3 to be used,
For example, after the conductive primer layer 3b is grounded and the film surface is charged to 400V, the residual potential after 3 seconds is 30
By using the film surface layer 3a having a voltage of 0 V or more, the amount of consumed current can be reduced by 1/1 compared to the first embodiment.
It can be suppressed to about 0.

On the other hand, after the fixing film 3 is made of a material having a relatively low surface resistance, for example, the back surface of the film is grounded to charge the film surface to 400 V, the residual potential after 3 seconds attenuates to about 150 V to 200 V. By using such a film surface layer, the amount of current consumption during charging increases, but the movement of charges on the film surface is activated, and even if a charged sheet metal 11 having a relatively large needle portion and a small number of needles is used. The charging uniformity on the surface can be improved.

Also, in this configuration, the amount of ozone generated by the corotron as in the first embodiment can be greatly reduced at the same time. There is no need to provide

Third Embodiment FIG. 5 is a sectional view of a fixing device of an image forming apparatus according to a third embodiment of the present invention. In FIG. 5, members having the same numbers as those in FIG. 1 are the same components, and thus the description thereof will not be repeated.

In the present embodiment, the charging roller 1 of the contact charging system is used instead of the corotron charger in the first embodiment.
2 is provided on the inner surface of the upper fixing frame via a pressing means. The charging roller 12 is composed of an elastic layer made of silicon rubber having a volume resistance of 10 ⁵ to 10 ⁸ Ωcm on a conductive core metal, and a resistance layer having a higher resistance value than the elastic layer on its surface. In the embodiment, a driving force for rotating the charging roller itself at a peripheral speed that matches the fixing speed is applied to the charging roller itself so as to realize uniform charging without disturbing the conveyance of the fixing film 3, but rather assisting the conveyance. In addition, a driven roller 12 'is provided on the back side of the opposed film 3, so that the surface of the fixing film 3 is contact-charged while nipping and transporting the fixing film 3 between the two rollers.

At this time, the voltage applied to the charging roller 12 is changed from a DC voltage of about -1 kV to about -2 kV to a DC voltage having a peak-to-peak voltage which is at least twice as large as about -640 V to start charging in order to improve charging uniformity. The voltage is superimposed.

In the above configuration, the toner was fixed on paper under the same conditions as in the first embodiment. As a result, the fixed toner image did not show the rear toner scattering phenomenon, and a good image could be obtained.

For comparison, when only the voltage applied to the charging roller 12 is turned off under the same conditions as the above experimental conditions, the rear toner scattering phenomenon frequently occurs in the entire region, and the rear toner scattering phenomenon also occurs in the configuration of this embodiment. As a control measure, it has been found that an effect almost equivalent to that of the above-described embodiment can be obtained.

In addition, even with respect to the offset, unnecessary charging unevenness such as peeling charging is corrected by the action of the AC bias application, so that the same effect as that of the first embodiment can be confirmed. Further, in the contact charging system such as the charging roller 12, the generation of ozone is almost eliminated. Therefore, in order to remove the ozone generated by the corotron charger as in the first embodiment, a pollution prevention means such as an ozone filter is newly provided. There is no need to provide

<Fourth Embodiment> FIG. 6 is a sectional view of a fixing device of an image forming apparatus according to a fourth embodiment of the present invention. In FIG. 6, members having the same numbers as those in FIG. 5 indicate the same components, and in the present embodiment, a new cleaning means 12 ″ is added to the charging roller 12, and the cleaning method is a blade or brush. In addition to the scraping method using members, any method such as a wiping method using a web is effective, but at this time, at the same time, the releasability of the surface layer of the charging roller is lower than the releasability of the fixing film surface layer. The combination of surface materials is adjusted.

By using such a configuration, even if the unnecessary toner adhered to the fixing film 3 cannot be completely removed only by the electrostatic effect against the offset, the unnecessary toner is removed from the fixing film 3. The toner is transferred to the charging roller side by using the difference, and the toner adhering to the surface of the charging roller can be reliably removed by the cleaning unit, so that more reliable offset prevention performance can be obtained.

<Fifth Embodiment> FIG. 7 is a sectional view of a fixing device of an image forming apparatus according to a fifth embodiment of the present invention. In FIG. 7, the members having the same numbers as those in FIG. 5 are the same components, and thus the description thereof will not be repeated.

In this embodiment, as compared with the third embodiment, the charging roller 12 is provided on the inner surface of the lower fixing frame via a pressing means, and abuts on the surface of the pressing roller to be driven by the rotation of the pressing roller 4. However, the difference is that the surface of the pressure roller is set to be charged to the polarity opposite to that of the toner.

At this time, the voltage applied to the charging roller 12 is obtained by superimposing an AC voltage having a peak-to-peak voltage that is at least twice as large as about 640 V at which charging is started, on a DC voltage of about 1 kV to 2 kV in order to improve charging uniformity. Let me.

In this embodiment, the elastic layer of the pressure roller 4 is made of the conductive silicon rubber layer 4b 'having a volume resistance of about 10 ⁵ Ωcm. And the charge of the charger is efficiently applied to the surface of the pressure roller.

As a result of fixing the toner on the paper under the same conditions as in the embodiment with the above-described configuration, the fixed image did not show the toner scattering phenomenon behind, and a good image could be obtained. For comparison, when only the power supply of the charging roller 12 is turned off under exactly the same conditions as the experimental conditions described above, the rear toner scattering phenomenon frequently occurs in the entire region. It has been found that the same effect as that of the embodiment can be obtained. Unnecessary charging unevenness such as peeling charging is corrected for the offset by the action of the AC bias application, and the same or better effect as in the first embodiment can be confirmed. Further, in the contact charging method such as the charging roller, generation of ozone is almost eliminated, so that a pollution prevention means such as an ozone filter is newly provided in order to remove ozone generated in the corotron charger as in the first embodiment. There is no need to provide.

Also in this configuration, the releasability of the surface layer of the charging roller is set lower than the releasability of the surface layer of the pressure roller, and the cleaning means is provided on the charging roller so that the offset toner is accumulated on the surface of the pressure roller. Therefore, it is also possible to prevent problems such as toner stains on the back of the paper that occur as a result of accumulation.

<Sixth Embodiment> FIG. 8 is a sectional view of a fixing device of an image forming apparatus according to a sixth embodiment of the present invention. 8, the members having the same numbers as those in FIG. 7 indicate the same components.

This embodiment is different from the fifth embodiment in that a rubber blade 13a and its supporting plate 1 are used instead of the charging roller.
The difference is that a charging blade 13 composed of 3b is provided, and other configurations are substantially the same.

Rubber blade 13a of charging blade 13
Is made of silicon rubber having a volume resistance of 10 ⁵ to 10 ⁸ Ωcm, and is brought into contact with the surface of the pressure roller by counter to remove unnecessary toner attached to the surface of the pressure roller so that the contact angle and rubber hardness and pressure are applied. Is set.

To improve the charging uniformity, the charging blade 13
Is applied with a DC voltage of about 1 kV to 2 kV superimposed with an AC voltage having a peak-to-peak voltage that is at least twice as large as about 640 V at which charging starts.

As a result of fixing the toner on the paper under the same conditions as in the first embodiment with the above-described configuration, the fixed image did not show the rear toner scattering phenomenon, and a good image could be obtained. For comparison, when only the power of the charged sheet metal is turned off under the same conditions as the above experimental conditions, the rear toner scattering phenomenon frequently occurs in the entire region. It turned out that the effect almost equivalent to a form was obtained.

In addition, with respect to the offset, unnecessary charging unevenness such as peeling charging is corrected by the action of the AC bias application, so that the same effect as that of the first embodiment or more can be confirmed. Even if the unnecessary toner attached to the pressure roller cannot be completely removed only by the electrostatic effect, the unnecessary toner can be scraped off at the tip of the blade 13, so that more reliable offset and pressure can be obtained. Roller contamination prevention performance can be obtained.

Since the charging blade is also of the contact charging type, there is almost no generation of ozone. In order to remove the ozone generated by the corotron charger as in the first embodiment, a pollution prevention means such as an ozone filter is used. There is no need to provide.

In this embodiment, the charging and cleaning of the pressure roller 4 can be performed simultaneously with a simple configuration without providing a member having a multilayer structure such as a charging roller, a bearing for the roller, and a new cleaning means. It is possible to realize a more reliable countermeasure against rear toner scattering and offset at a lower cost.

In each of the above embodiments, in the configuration using the contact charging means, the heat capacity of the charging means is designed to be as small as possible, so that the excess heat capacity is not applied to the fixing device, and the heating efficiency is reduced. In addition to taking into account the realization of a high fixing device, the core metal of the charging roller and the supporting metal plate of the charging blade are made of aluminum with high thermal conductivity, which enables continuous passage of small size paper. Designed to promote the uniform temperature distribution in the longitudinal direction of the fixing-side rotator and pressure member by making the temperature rise in the non-sheet passing area, which is a problem when paper is made, act to be dispersed in the longitudinal direction. are doing.

<Example of Image Forming Apparatus> FIG. 9 is a schematic structural view of an example of the image forming apparatus. The image forming apparatus of this embodiment is a laser beam printer using an electrophotographic process.

Reference numeral 21 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as a first image carrier.

[0090] The photosensitive drum 21 is rotated at a predetermined peripheral speed (process speed) in the clockwise direction of arrow, uniformly charged to its by During rotation the primary charger 22 of a predetermined negative dark potential V _D Is done.

Reference numeral 23 denotes a laser beam scanner, which is a laser beam L modulated according to a time-series electric digital image signal of target image information input from a host device such as an image reading device, a word processor, and a computer (not shown). To scan and expose the uniformly charged surface of the rotating photosensitive drum 21.

By this laser beam scanning exposure, the exposed portion of the uniformly charged surface of the rotating photosensitive drum 21 has a small potential absolute value and a bright potential _VL .
An electrostatic latent image corresponding to the target image information is formed on one surface.

Next, the latent image is reversal-developed (toner adheres to the laser exposure light potential _VL portion on the surface of the photosensitive drum) with the negatively charged powder toner by the developing device 24 to be visualized as a toner image.

The developing device 24 has a developing sleeve 24a which is driven to rotate. The outer peripheral surface of the developing sleeve is coated with a thin layer of negatively charged toner and faces the surface of the photosensitive drum 21. Value is photosensitive drum 2
Since the developing bias voltage V _DC smaller than the dark potential V _{D and} larger than the bright potential _VL of the latent image on one surface is applied, the toner on the developing sleeve 24 a causes the latent image on the surface of the photosensitive drum 21 to become brighter. The latent image is transferred only to the portion of the potential V _L and the latent image is visualized (reversal development).

On the other hand, the recording material 8 as a second image carrier loaded and set on the paper feed tray 25 is fed out one by one by the driving of the paper feed roller 26, and is conveyed by the conveyance guide 27a and the registration roller. The rotation of the photosensitive drum 21 is synchronized with the rotation of the photosensitive drum 21 via a transfer guide 27b via a transfer guide 27b to a transfer nip portion m, which is a nip portion between the photosensitive drum 21 and a transfer roller 29 in contact with the photosensitive drum 21 and to which a transfer bias is applied. The sheet is fed at an appropriate timing, and the toner image on the surface of the photosensitive drum 21 is sequentially transferred to the surface of the recording material 8.

The recording material 8 that has passed through the transfer nip m is separated from the surface of the rotating photosensitive drum 21 and introduced into the fixing device R shown in the first to sixth embodiments via the conveyance guide 27c, and the toner After receiving the image fixing process, a paper output tray 31 is provided via a paper output roller 30 as an image formed product (print).
Output to

After the separation of the recording material, the surface of the rotating photosensitive drum 11 is cleaned by a cleaning device 32 to remove the residual photosensitive drum surface such as toner remaining after transfer, and is repeatedly used for image formation.

<Others> In the above embodiment, the tensionless film heating apparatus is described. However, the rotating body having the heating source of the present invention is not limited to this, and the endless film may be wound around the heating body or the driving roller. And a metal roller (heat roller) including a heat source such as a halogen heater.

In the film heating method, the heat source is not limited to the ceramic heater, but may be an electromagnetic heating method.

[0100]

As described above, according to the present invention, it is possible to provide a fixing device capable of obtaining a stable fixed image by suppressing a rear toner scattering phenomenon and a toner offset even at a high speed, and an image forming apparatus using the same. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view of a fixing device according to a first embodiment of the present invention.

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

FIG. 3 is an explanatory view of a rear toner scattering mechanism of a conventional example.

FIG. 4 is a sectional view of a fixing device according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a fixing device according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a fixing device according to a fourth embodiment of the present invention.

FIG. 7 is a cross-sectional view of a fixing device according to a fifth embodiment of the present invention.

FIG. 8 is a sectional view of a fixing device according to a sixth embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of an example of an image forming apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 2 Heater holder 3 Fixing film 3a Release layer 3b Conductive primer layer 3c Base layer 4 Pressure roller 4a Release layer 4b Heat resistant rubber layer 4b 'Conductive silicon rubber layer 4c Core 4d Conductive rubber ring 4e Resistance Reference Signs List 5 metal stay 6 fixing unit lower frame 6 fixing upper frame 7 entrance guide 7 'discharge guide 8 recording material 9 unfixed toner 10 corotron charger 10a charging wire 10b shield electrode 11 charged sheet metal 12 charging roller 12' driven roller 12 "cleaning Means 13 Charging blade 13a Rubber blade 13b Support sheet metal

Continued on the front page F term (reference) 2H033 AA09 AA10 AA20 BA13 BB30 BE03 3K058 AA00 BA18 DA05 DA22 GA03 GA06

Claims (22)

[Claims] A rotating member having a heating source; and a pressing member forming a pressure contact portion with the surface of the rotating member. The pressing member causes the recording material to be held and conveyed. A fixing device for thermally fixing a toner image that has been formed and adhered on a recording material, wherein a charging unit that charges the surface of the rotating body to the same polarity as the toner is provided. 2. The fixing device according to claim 1, wherein said charging means is a corotron charger. 3. The fixing device according to claim 1, wherein the charging unit is a charger that applies a high voltage to a metal member having a needle-like tip. 4. The fixing device according to claim 1, wherein a high voltage having an absolute value of 4 kV or more is applied to the charging unit, and a distance between a charge generation unit of the charging unit and the surface of the rotating body is set. A distance of 5 mm or more. 5. The fixing device according to claim 1, wherein the charging unit is a contact charger that contacts the surface of the rotating body. 6. The fixing device according to claim 5, wherein the contact charger also functions as a cleaning unit for cleaning the surface of the rotating body. 7. The fixing device according to claim 5, wherein the contact charger is formed of a good heat conductor. 8. The fixing device according to claim 1, wherein the rotating body is formed of a heat-resistant film having a thickness of 100 μm or less. 9. The fixing device according to claim 8, wherein the heat-resistant film has a high-resistance release layer having a thickness of 15 μm or less on a surface layer thereof, and a conductive layer below the high-release layer. A fixing device. 10. The fixing device according to claim 8, wherein the pressing member is a pressing roller that rotates with a driving force, and the heat-resistant resin film is a pressing roller. A fixing film that is driven and rotated by the contact of the fixing device, and the charging unit is a roller charger having a driving force. 11. A rotator having a heating source, and a pressing member forming a press contact portion with the surface of the rotator, wherein the press contact portion causes a recording material to be held and conveyed, and a static electricity is applied to the surface of the recording material. A fixing device for thermally fixing a toner image that has been formed and adhered on the recording material, wherein a charging unit that charges the surface of the pressing member to a polarity opposite to that of the toner is provided. 12. The fixing device according to claim 11, wherein
The fixing device is characterized in that the charging unit is a corotron charger. 13. The fixing device according to claim 12, wherein
The fixing device is characterized in that the charging unit is a charger that applies a high voltage to a metal member having a needle-like tip. 14. A fixing device according to claim 12, wherein a high voltage having an absolute value of 4 kV or more is applied to said charging means, and a distance between said charging means and said pressing member surface is 5 mm or more. A fixing device characterized by being separated. 15. The fixing device according to claim 11, wherein
The fixing device is characterized in that the charging unit is a contact charger that contacts the surface of the pressure member. 16. The fixing device according to claim 15, wherein
The fixing device according to claim 1, wherein the pressing member is a rotating pressing roller, and the contact charger also functions as a cleaning unit for cleaning the surface of the pressing roller. 17. The fixing device according to claim 16, wherein
The fixing device, wherein the contact charger is formed of a good heat conductor. 18. The fixing device according to claim 15, wherein the contact charger is a roller charger that is driven to rotate by contact with the surface of the pressure roller. apparatus. 19. The fixing device according to claim 15, wherein the contact charger is a blade charger that makes a counter contact with the surface of the rotary pressing member. 20. The fixing device according to claim 11, wherein the surface of the pressing member has a thickness of 5 mm.
A fixing device comprising: a releasable layer having a high resistance of 0 μm or less; and a conductive layer thereunder, wherein the conductive layer is grounded. 21. The fixing device according to claim 1, wherein a back surface of each surface layer is grounded and a surface of the rotation member and the pressing member are grounded as resistance characteristics of the surface layers of the rotating body and the pressing member.
A fixing device having a resistance characteristic in which a surface potential after 3 seconds from charging to 00V remains at 150 V or more, more preferably 300 V or more. 22. An image forming apparatus having an image forming means for forming a toner image on a recording material and a fixing means for heating the toner image to fix the toner image on the recording material, wherein the fixing means is used. An image forming apparatus comprising the fixing device according to any one of 1 to 21.