JPH11202659A - Fixing device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device constituted so that a recording material obtained after a fixing action is executed is surely prevented from being attached to a fixing roll without using a peeling pawl or excessive releasing agent. SOLUTION: The fixing device is provided with the fixing roll 11 and a pressure roll 12 made to press-contact with each other by prescribed pressure. Then, at least either of the rolls 11 and 12 is provided with a heat source. The roll 11 is provided with an inside layer 112 and a surface layer 111 in turn from the center. By passing the recording material holding a toner image on the roll 11 side through a nip part between the rolls 11 and 12, the toner image is fixed on the recording material. The layer 111 of the roll 11 is fitted so as to be freely rotated with respect to the layer 112. Besides, the inside circumferential length of the layer 111 is longer than the outside circumferential length of the layer 112. Then, an auxiliary roll 13 made to press-contact with the roll 11 at a prescribed press-contact part is arranged on a downstream side near the nip part between the rolls 11 and 12 so as to form a deflection part on the downstream side of the nip part of the layer 111 of the roll 11 and on the upstream side of the press-contact part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic image forming apparatus such as a copying machine and a printer, and more particularly, to a fixing device having a fixing roll and a pressure roll pressed against each other at a predetermined pressure. The present invention relates to a fixing device of an image forming apparatus for fixing a toner image to a recording material by passing a recording material holding the toner image through the nip portion.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine or a printer, a toner image formed on a photoreceptor is transferred to a recording material such as a recording paper or an OHP sheet, and the transferred toner image is transferred to the recording material. It is well known that a toner image is fixed to a recording material by the action of heat and pressure to obtain a permanent image by passing the nip between a fixing roll and a pressure roll provided with a heat source of a fixing device together with the recording material, and the like. ing.

In such a fixing device, since the toner on the surface of the recording material is heated and melted on the surface of the fixing roller, the recording material tends to adhere to the fixing roller even after passing through the nip. For this reason, for example,
As described in JP-A-2005-564, a peeling claw is provided downstream near the nip to peel off the recording material adhering to the fixing roller, or as described in JP-A-59-100478. There has been proposed a technique for improving the releasability of a recording material from a fixing roller by using an agent.

However, when the peeling is performed by using the peeling claw, the leading end of the peeling claw comes into contact with the surface of the recording material holding the toner image to be peeled off. In some cases, the peeling nail may come into contact with the toner image to cause an image defect. Also, when a release agent is used, the recording agent is contaminated with the release agent. Particularly, when a toner image is fixed on a transparent sheet for OHP, the release agent adheres to the surface of the transparent sheet, and the light transmission property is increased. Is greatly impaired.

In order to solve these problems, Japanese Patent Laid-Open No.
By defining the surface roughness and glossiness of the fixing roll and the pressure roll as described in JP-A-210329, or by adding a fixing roll to the fixing roll as described in JP-A-8-26916. A technique has been proposed in which a second fixing roll is provided in addition to the pressure roll, and the recording material that has passed through the nip portion between the fixing roll and the pressure roll is pressed against the pressure roll by the second fixing roll to perform fixing. ing. According to these techniques, it is possible to prevent the recording material from adhering to the fixing roll after fixing without using a peeling nail or an excessive release agent.

[0006]

However, in recent years, in addition to the conventional character-centered image, an image such as a photograph or an illustration is often formed. In many cases, an image is requested. These user demands result in an increase in the amount of toner to be fixed to the recording material, and the recording material is more likely to adhere to the fixing roll than ever before due to the large amount of melted toner. In addition, recording materials that the user wants to use are diversified, such as ordinary plain paper, thick paper such as thin paper, postcards, and the like, and the types thereof are continuously expanding. For example, thin paper generally has no "strain" and thus easily adheres to the fixing roller, and thick paper may not be pressed down to the pressure roll side by the technique described in JP-A-8-26916.

The present invention has been made in view of these problems, and an object of the present invention is to provide an image forming apparatus which is advantageous in that the amount of toner, the characteristics of a recording material, and the like are disadvantageous for peeling from a fixing roll. An object of the present invention is to provide a fixing device capable of reliably preventing a recording material after fixing from adhering to a fixing roll without using a peeling nail or an excessive release agent.

[0008]

According to the present invention, there is provided a fixing roll and a pressure roll which are pressed against each other at a predetermined pressure and provided with a heat source on at least one side thereof, and wherein the fixing roll has an inner layer and a surface layer from the center thereof. In a fixing device that fixes the toner image to the recording material by passing the recording material holding the toner image on the fixing roll side to a nip portion between the fixing roll and the pressure roll, the surface layer of the fixing roll has It is rotatably attached to the inner layer, the inner peripheral length of the surface layer is longer than the outer peripheral length of the inner layer, and the fixing roll is pressed against the fixing roll at a predetermined pressure contact portion downstream of the nip portion between the fixing roll and the pressure roll. An auxiliary roll is provided, and a bent portion is formed downstream of the nip portion and upstream of the press contact portion of the surface layer of the fixing roll. By configuring the fixing device in this manner, a bending portion is generated downstream of the nip portion and upstream of the press-contact portion of the surface layer of the fixing roll, so that the recording material passing through the nip portion is surely changed by a large curvature change of the surface layer bending portion. Peeled from the fixing roll surface.

Further, in the present invention, there is provided a regulating means for regulating the rotation speed of the auxiliary roll to be lower than the rotation speed of the fixing roll in order to stably generate the bent portion. With this configuration of the fixing device, frictional resistance is generated between the fixing roll and the auxiliary roll, and a flexure can be stably generated downstream of the nip portion and upstream of the press-contact portion of the surface layer of the fixing roll. .

Further, according to the present invention, there is provided a control means for controlling a rotational speed difference between a fixing roll and an auxiliary roll in order to adjust the size of the bending portion in accordance with the ease of attachment of a recording material to be fixed to the fixing roll. Is provided. By fixing the recording material that easily adheres to the fixing roll by configuring the fixing device in this manner, the rotational speed difference between the fixing roll and the auxiliary roll is increased, the frictional resistance between the two rolls is increased, and the deflection is increased. The recording material is reliably separated from the fixing roll by increasing the size of the portion. On the other hand, when fixing a recording material that is relatively hard to adhere to the fixing roll, the difference in speed between the fixing roll and the auxiliary roll is reduced, the frictional resistance between the two rolls is reduced, and the wear of both rolls due to friction is prevented, and the life is reduced. Can be extended. The ease with which the recording material adheres to the fixing roll depends not only on the characteristics of the recording material itself, such as “strain”, but also on the amount of toner held by the recording material.

Further, the present invention provides a retracting means for pressing the auxiliary roll against the fixing roll when fixing the recording material, and separating the auxiliary roll from the fixing roll when the fixing is completed. By configuring the fixing device in this manner, the time during which friction occurs between the fixing roll and the auxiliary roll can be reduced as much as possible, and the life of both rolls can be extended.

[0012]

Next, preferred embodiments of the present invention will be described based on examples.

FIG. 1 is an explanatory diagram showing a fixing device 1 according to the present embodiment, and FIG. 2 is an explanatory diagram showing an entire image forming apparatus to which the fixing device 1 according to the present embodiment can be applied. is there.

An image forming apparatus to which the fixing device 1 according to this embodiment can be applied is roughly divided into an image forming section 2 for forming a toner image on the surface of a photoreceptor, and an image forming section 2 for holding a toner image formed on the surface of the photoreceptor. An intermediate transfer unit for transferring the recording material to the recording material, a fixing device 1 for fixing the toner image transferred to the recording material, a conveying unit for conveying the recording material from the recording material tray 41 to the intermediate transfer unit and the fixing device 1 at a predetermined timing. Consists of

The image forming section 2 includes a photosensitive drum 20, a charger 21, an exposure unit 22, a developing unit 23, a photosensitive member cleaning device 24, and the like. The intermediate transfer unit is an intermediate transfer belt 30,
Drive roll 31, tension roll 32, primary transfer device 33,
The secondary transfer device 34 includes a transfer roll 341, a backup roll 342, a power supply roll 343, and the like. The transport section includes a recording material tray 41, a pickup roll 42, a transport roll pair 43, a registration roll pair (not shown),
It comprises a conveyor belt 44 device and the like. The configuration and operation of the fixing device 1 will be described later in detail.

The operation of forming a full-color image by such an image forming apparatus will be described. Charger 21
As a result, the surface of the photosensitive drum 20 is charged to a uniform predetermined voltage. Next, a laser beam is applied to the surface of the photoreceptor drum 20 from an exposure unit according to, for example, an image of a black component, and an electrostatic latent image is formed on the drum surface by a potential difference. The electrostatic latent image is developed with toner by the black developing device 23 to become a visible image of black toner. The black toner image moves to a primary transfer position in contact with the intermediate transfer belt 30 as the photosensitive drum 20 rotates. At this time, the black toner is (primarily) transferred to the intermediate transfer belt 30 by the action of the electric field by the primary transfer device 33. Note that the black toner slightly remaining on the surface of the photoconductor without being primary-transferred is cleaned by a downstream drum cleaning device.
Such an image forming process is performed for each color of yellow, magenta, and cyan.

On the other hand, the toner image primarily transferred onto the intermediate transfer belt 30 moves as the belt 30 rotates. At this time, the transfer roll 341 of the secondary transfer device 34 and the belt cleaning device 35 are separated from the intermediate transfer belt 30 until the primary transfer of the final color (for example, cyan) is completed. Therefore, when the black toner image primarily transferred to the intermediate transfer belt 30 reaches the primary transfer position again, a toner image of the next color, for example, a yellow toner image is primarily transferred and superimposed. Further, when the toner image reaches the primary transfer position, the toner images of the mass center and the cyan toner are successively superimposed. After the final color toner image is primarily transferred, the secondary transfer device 34
The transfer roller 341 and the belt cleaning device 35 contact the intermediate transfer belt 30.

The recording material held in the recording material tray 41 includes a pickup roll 42 and a transport roll pair 43.
, The toner images of all colors are superimposed on the intermediate transfer belt 30 and the nip is released from the registration roll pair at the timing when the toner images reach the secondary transfer position, and the recording material is moved to the secondary transfer position. Transported to Therefore, the toner images of all colors are transferred (secondarily) to the recording material by the action of the electric field supplied from the power supply roll 343, and the recording material holds a full-color toner image on the surface. The recording material is conveyed to the fixing device 1 by the conveyance belt 44, and the full-color toner image becomes a permanent image by the action of heat and pressure, is fixed on the recording material, and the image formation is completed.

The image forming apparatus to which the fixing device 1 according to the present invention can be applied is not limited to such an image forming apparatus. For example, an image forming apparatus having no intermediate transfer belt 30 or a photosensitive member having a belt-like shape is used. The present invention can be applied to a device that forms an image by an electrophotographic method, such as a device having a drum-like intermediate transfer member, a device having a rotary developing device 23, and a device having a transfer device not in contact with an image carrier.

Here, the fixing device 1 according to the present embodiment is pressed against each other at a predetermined pressure, and heat sources 113 and 12 are provided respectively.
4, a fixing roll 11 and a pressure roll 12 provided with
The fixing roll 11 is moved from its center to the inner layer 112 and the surface layer 1.
A fixing device that fixes the toner image to the recording material by passing the recording material holding the toner image on the side of the fixing roll 11 through a nip portion between the fixing roll 11 and the pressure roll 12. And the surface layer 1 of the fixing roll 11
11 is rotatably attached to the inner layer 112, the inner peripheral length of the surface layer 111 is longer than the outer peripheral length of the inner layer 112, and the fixing roll 11 is located near the nip portion between the fixing roll 11 and the pressure roll 12. Is provided with an auxiliary roll 13 to be brought into pressure contact with the surface layer 111 of FIG.

The fixing roll 11 has a surface layer 111 composed of a polyimide substrate coated with a fluororesin from the outside, and an elastic layer 11 composed of silicone rubber.
2a (inner layer 112), a core layer 112b (inner layer 112) made of aluminum, and a halogen lamp as a heat source 113 in a hollow portion of the core layer 112b. 112), that is, the elastic layer 112a (the inner layer 11
2) is not bonded.

FIG. 3 is a diagram showing the fixing roll 11 in more detail. FIG. 3A shows the inner layer 112, and FIG. 3B shows the surface layer 111. The radius R _i and inner surface layer 111 circumferential radius R _o of the inner layer 112 periphery, R _i
< _Ro . Note that the radius R _{i of the} outer circumference of the inner layer 112 and the radius R _{o of the} inner circumference of the surface layer 111 refer to a relationship between the respective radii in a state where the auxiliary roll 13 is pressed against the fixing roll 11. For example, the surface layer 11 of the fixing roll 11
When the auxiliary roller 13 is formed of an elastic member, the auxiliary roller 13 is separated from the fixing roller 11 in a state where R
also becomes _i = R _o, elongation surface layer 111 in a state of being pressed, may be in relationship R _i <R _o. The surface layer 11
If the radius _{Ro of the} inner circumference is too short, it is difficult to form a flexure, and if it is too long, there is a problem that it is difficult to form a stable flexure. Therefore, the surface layer 111
The length of the inner radius R _o is 1.1R _i <R _o <1.4R _i
It is preferred that

The pressure roll 12 has a surface layer 121 composed of a PFA tube, an elastic layer 122 composed of silicon rubber, a core layer 123 composed of aluminum, and a hollow part in the core layer 123 from outside. A halogen lamp is provided as the heat source 124. In addition,
In this embodiment, both the fixing roll 11 and the pressure roll 12 have the heat sources 113 and 124, but they may be provided in either one.

The auxiliary roll 13 is composed of a surface layer 131 made of a PFA tube, a core layer 132 made of aluminum, and a hollow portion inside the auxiliary roll 13 from the outside. If the radius r of the auxiliary roll 13 is too large, it is difficult to provide the auxiliary roll 13 near the exit of the nip between the fixing roll 11 and the pressure roll 12, and if the radius r is too small, the amount of deflection of the auxiliary roll 13 is reduced. There is a problem that becomes large. Therefore,
The radius r of the auxiliary roll 13 is 0.2R _o <r <0.4R _o
It is preferred that Further, the position where the auxiliary roll 13 and the fixing roll 11 are pressed against each other is downstream of the vicinity of the nip between the fixing roll 11 and the pressure roll 12, but if the auxiliary roll 13 is too close to the nip, it is necessary to reduce the diameter of the auxiliary roll 13. There is a problem that if it is too far from the nip portion, the bending portion will not be stable and undulation will occur. Accordingly, the nip portion between the fixing roll 11 and the pressure roll 12 and the pressure contact portion between the auxiliary roll 13 and the fixing roll 11 are formed at a center angle α facing the center of the cross section of the fixing roll 11.
Is preferably 45 ° <α <65 °.

The fixing roll 11 and the pressure roll 12 are vertically opposed to each other, and the auxiliary roll 13 and the fixing roll 11 are pressed against each other at a pressure contact portion having a center angle α = 45 °, and are attached to a support frame of the fixing device 1 (not shown). Both ends of the fixing roll 11, the pressure roll 12, and the auxiliary roll 13 are rotatably supported by bearings. The pressing roller is pressed against the fixing roller by a spring or the like in order to press the conveyed recording material against the fixing roller with a predetermined pressure. The fixing roll 11 and the pressure roll 12 are configured to be rotationally driven by a drive source (not shown), and the auxiliary roll 13 pressed against the fixing roll 11 is configured to rotate following the fixing roll 11. Have been.

The operation of the fixing device 1 will be described.
Before the recording material holding the toner image on its surface is conveyed, the fixing roll 11 and the pressing roll 12 are driven to rotate by a driving source (not shown), and the auxiliary roll 13 which is in pressure contact with the fixing roll 11 is Follow the rotation. Here, since the auxiliary roll 13 itself does not directly obtain rotational drive from the drive source, there is some rotational resistance in the rotation of the auxiliary roll 13, and the rotation starts momentarily after the rotation of the fixing roll 11. I do. Then, the surface layer 111 of the fixing roll 11 is located downstream of the nip portion between the fixing roll 11 and the pressure roll 12 due to the rotation of the auxiliary roll 13 being delayed as compared with the fixing roll 11, and 1
A bent portion is formed upstream near the pressure contact portion with the third member. After that, since the rotation speeds of the fixing roll 11 and the auxiliary roll 13 are substantially the same, the once formed bent portion continues to exist thereafter.

After such a flexure is formed, the preceding recording material enters the nip between the fixing roll 11 and the pressure roll 12. The toner image that has entered the nip portion is a heat source 11
The toner is melted and fixed by the heat from the rollers 3 and 124 and the pressure between the rolls to form a permanent image on the recording material. The recording material that has passed through the nip reaches the bending portion, but the fixing roll 1
The surface layer 111 has a very large curvature change, in other words, a curved surface with a very small radius of curvature at its bend. Even if a large amount of toner melts at the nip, it acts like a kind of adhesive. Even if a weakly stiff recording material such as thin paper is used, the recording material is reliably peeled off the surface of the fixing roll 11 on the curved surface having the small radius of curvature, and the recording material is conveyed to an appropriate conveyance path. .

[0027]

Second Embodiment A fixing device 1 according to a second embodiment is similar to the fixing device 1 according to the first embodiment.
In addition to the configuration of the fixing device 1 described in the first embodiment, the rotational speed of the auxiliary roll 13 is set to be smaller than that of the fixing device 11 in order to stably generate the above-described flexure. A regulating means 14 for regulating the rotation speed lower than the rotation speed, and a rotation of the fixing roll 11 and the auxiliary roll 13 for adjusting the size of the bending portion in accordance with the ease of adhesion of the recording material to be fixed to the fixing roll 11. Control means 15 for controlling the speed difference, and retraction means 16 for pressing the auxiliary roll 13 against the fixing roll 11 when fixing the recording material, and separating the auxiliary roll 13 from the fixing roll 11 when the fixing is completed. is there.

FIG. 4 is a block diagram illustrating a control system of the auxiliary roll 13 of the fixing device 1 according to the present embodiment. Auxiliary roll 1 of fixing device 1 according to the present embodiment
Control 3 controls the rotation speed of the auxiliary roll 13 by the regulating means 14 and the control means 15 (hereinafter, referred to as control means 3).
There is a type that controls the contact / separation of the auxiliary roll 13 from the fixing roll 11 by the retracting means 16 (hereinafter, referred to as a “second control”).

First, the first control will be described. This control contradicts demands to form a stable flexure to reliably prevent the recording material from adhering to the fixing roll 11 and to reduce wear of the fixing roll 11 and the auxiliary roll 13 to extend their life. This is done in order to achieve a balance. That is, as in the first embodiment, the auxiliary roll 1
In the method of causing the fixing roller 3 to follow the rotation of the fixing roll 11, there is a possibility that the bending portion may not be formed stably in the vicinity of the press-contact portion between the auxiliary roll 13 and the fixing roll 11 due to some disturbance, for example, vibration of the image forming apparatus. . Further, if the rotation of the auxiliary roll 13 is completely stopped, for example, it is possible to stably form a bent portion upstream in the vicinity of the pressure contact portion, but the friction between the fixing roll 11 and the auxiliary roll 13 increases, and the friction between the fixing roll 11 and the auxiliary roll 13 increases. However, their life may be shortened. On the other hand, the ease with which the recording material adheres to the fixing roll 11 depends on the amount of toner held by the recording material, the characteristics of the recording material such as straining, and the like. In consideration of these circumstances, the first control stably forms a flexible portion that can reliably peel off the recording material attached to the fixing roll 11, and extends the life of the fixing roll 11 and the auxiliary roll 13 as much as possible. The purpose is to do so.

Next, means for realizing the first control will be described. FIG. 5 shows the restricting means 14 of the fixing device 1 according to the present embodiment. In the present embodiment, the fixing device 14 includes a stepping motor 141, an eccentric cam 142, a spring 143, and a brake shoe 144. Stepping motor 14
1 slightly rotates, the stepping motor 141
The eccentric cam 142 fixed to the shaft also rotates and presses the brake shoe 144 against the inner surface of the hollow portion of the auxiliary roll 13 via the spring 162 to apply a rotational load to the auxiliary roll 13. Auxiliary roll 13 without direct drive source
Is slipped at the pressure contact portion with the fixing roll 11, and the rotation speed of the auxiliary roll 13 is lower than the rotation speed of the fixing roll 11. As a result, it is possible to stably form the bent portion upstream near the pressure contact portion.

The control means 15 is constituted by an electronic circuit, a microprocessor, or the like, and includes information on the amount of toner of an image formed from various sensors provided in the image forming apparatus, information on the quality of the recording material, and the like. Receiving
A control signal is transmitted to the regulating means 14.

The operation of these regulating means 14 and control means 15 will be described with reference to FIG. FIG. 6A shows the fixing roll 11 and the auxiliary roll 13 for a normal image.
Since the regulating means 14 applies a predetermined rotational load to the auxiliary roll 13, the rotational speed of the auxiliary roll 13 is lower than the rotational speed of the fixing roll 11, and the predetermined rotational speed is stably provided upstream near the pressure contact portion. It forms a flexure. Next, information on image formation in a situation where the recording material easily adheres to the fixing roll 11, for example, information on forming a full-color and photographic image on a thin paper recording material is sent from various sensors of the image forming apparatus to the control unit 15. Assume that it has been sent. Then, the control means 15 transmits a control signal to the regulating means 14, and more specifically, drives the stepping motor 141 so as to rotate the eccentric cam 142 to further press the brake shoe 144 against the hollow inner surface of the auxiliary roll 13. The rotational load applied to the roll 13 is increased. Then, the rotation speed of the auxiliary roll 13 becomes slower than the rotation speed of the fixing roll 11, the difference between the rotation speeds of the two rolls becomes large, and the flexure formed near the press contact portion and upstream becomes large (FIG. 6 ( b)). Then, the recording material is fixed to the fixing roll 1 in the bending portion.
1 and the recording material is further removed from the fixing roll 1
The peeling can be surely performed even in a situation where it easily adheres to the substrate 1.

The recording material to be fixed next is plain paper,
It is assumed that information that the amount of toner is also a normal amount is transmitted from various sensors of the image forming apparatus to the control unit 15. Then, the control means 15 transmits a control signal to the regulating means 14, and specifically, rotates the eccentric cam 142 to press the brake shoe 14 pressed against the hollow inner surface of the auxiliary roll 13.
Then, the stepping motor 141 is driven so as to separate the roller 4 slightly, and the rotational load applied to the auxiliary roll 13 is reduced.
Then, the difference in rotational speed between the two rolls is reduced, the frictional resistance between the two rolls is reduced, wear can be prevented, and the life of the two rolls can be extended.

Next, the second control will be described. The purpose of this control is to separate the fixing roll 11 and the auxiliary roll 13 until the recording material actually enters the fixing device 1, prevent friction between the two rolls, and extend their life as much as possible.

FIG. 7 is an explanatory diagram showing the retracting means 16 for performing the second control and the operation thereof. The retracting means 16 includes a solenoid 161 and a spring 162 attached to the bearing of the auxiliary roll 13 and a switch device 163 for supplying / stopping power to the solenoid 161.
Consists of As shown in FIG.
When power is not supplied to the
The auxiliary roll 13 is in pressure contact with the fixing roll 11 by the elastic force of. However, when power is supplied to the solenoid 161 as shown in FIG. 7B, the shaft of the solenoid 161 is pulled into the body of the solenoid 161 against the elastic force of the spring 162.
1 and the auxiliary roll 13 are separated from each other.

The retracting means 16 is provided by a main controller (not shown) of the image forming apparatus or the like to fix the recording material fixing device 1.
Power is supplied / stopped to the solenoid 161 at the passage timing to press / separate the auxiliary roll 13 and the timing will be described with reference to FIG.

FIG. 8 shows the fixing roll 11 and the pressure roll 12
, The presence or absence of a recording material in the nip portion, and the respective timings of pressing / separating the auxiliary roll 13. First, the time t when the recording material reaches the nip
At time t1 before time 3, rotation of the fixing roll 11 and the pressure roll 12 starts. This is to keep the temperature of the roll surface constant before the recording material reaches the nip portion, or to apply the release agent evenly if the roll surface has a release agent. Thereafter, at time t2, the supply of power to the solenoid 161 is stopped, and by time t3, the auxiliary roll 13 is pressed against the fixing roll 11 by the elastic force of the spring 162.
By the operation of 5, a flexure portion is formed stably in the vicinity of the press contact portion and upstream. Thereafter, the first recording material passes through the nip portion (time t3 to t4), and the second recording material passes through the nip portion (time t5 to t6). After a while after the two sheets of recording material have passed through the nip portion, more precisely, after the rear end of the recording material has passed through the bending portion, the rotation of the fixing roll 11 and the pressure roll 12 is stopped at time t7. Then, electric power is supplied to the solenoid 161 to separate the auxiliary roll 13 from the fixing roll 11.

[0038]

As described in detail above, according to the first aspect of the present invention, the fixing after the fixing is surely performed by the bending portion of the fixing roll surface layer without using a peeling nail or an excessive release agent. The recording material can be peeled from the fixing roll,
Neither the peeling nail is caught on the toner image and an image defect is generated nor the image is smeared by a large amount of the release agent.

According to the second aspect of the present invention, since a bent portion can be stably generated in the surface layer of the fixing roll, the recording material after fixing can be more reliably peeled off from the fixing roll.

According to the third aspect of the present invention, even in the case of a recording material which easily adheres to the fixing roll, the recording material can be surely peeled off from the fixing roll, and in the case of a recording material which does not easily adhere to the fixing roll. Can reduce the frictional resistance between the fixing roll and the auxiliary roll and extend the wear life of both rolls.

According to the fourth aspect of the invention, when the recording material is not fixed, the fixing roll and the auxiliary roll are separated from each other, so that the frictional resistance between the two rolls is reduced and the resistance between the two rolls is reduced. Wear life can be extended.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an entire fixing device 1 according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an entire image forming apparatus to which the fixing device 1 can be applied;

FIG. 3 is an explanatory diagram illustrating a fixing roll 11 of the fixing device 1;

FIG. 4 is a block diagram illustrating a control system of the fixing device 1 according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram illustrating a regulating unit 14 of the fixing device 1 according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a bending portion when the rotation speed of the auxiliary roll 13 is controlled by a control unit 15 and a regulating unit 14.

FIG. 7 is an explanatory diagram illustrating a retracting unit 16 of the fixing device 1 according to the embodiment of the present invention.

FIG. 8 is a timing chart for explaining the operation of the retracting means 16;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fixing device, 11 ... Fixing roll, 111 ... Surface layer, 1
Reference numeral 12: internal layer, 113, 124: heat source, 12: pressure roll, 13: auxiliary roll, 14: regulating means, 15: control means, 16: retract means

Claims (4)

[Claims] An image forming apparatus comprising: a fixing roll having a heat source and a pressure roll provided on at least one side thereof at a predetermined pressure; and a fixing roll having an inner layer and a surface layer from the center thereof to fix a toner image. In a fixing device for fixing the toner image to the recording material by passing the recording material held on the roll side to the nip portion between the fixing roll and the pressure roll, the surface layer of the fixing roll is rotatable with respect to the inner layer. An auxiliary roll that is attached, the inner peripheral length of the surface layer is longer than the outer peripheral length of the inner layer, and an auxiliary roll is provided downstream of the nip between the fixing roll and the pressure roll near the fixing roll at a predetermined pressure contact portion. A fixing device, wherein a bending portion is generated downstream of the nip portion and upstream of the pressure contact portion of the surface layer. 2. The fixing device according to claim 1, further comprising a regulating unit that regulates the rotation speed of the auxiliary roll to be lower than the rotation speed of the fixing roll in order to stably generate the bent portion. 3. A control means for controlling a rotation speed difference between a fixing roll and an auxiliary roll in order to adjust the size of the flexible portion in accordance with the ease with which a recording material to be fixed adheres to the fixing roll. The fixing device according to claim 2, wherein: 4. The fixing device according to claim 1, further comprising a retracting means for pressing the auxiliary roll against the fixing roll when fixing the recording material, and separating the auxiliary roll from the fixing roll when fixing is completed. 3. The fixing device according to claim 1.