JP2006178119A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of realizing the speeding-up of a fixing stage by making the length of a nip part longer with simple constitution, and of preventing hot offset, and to provide an image forming apparatus. <P>SOLUTION: In the fixing device 11, a toner image T is fixed by supplying a recording medium 21 to which an unfixed toner image T is transferred to a nip part N between a part of the outer peripheral surface 12a of an annular film member 12 made to circulate in a direction A and a pressure roller 13 arranged on the outside of the film member 12, and the film member 12 and the recording medium 21 are separated from each other at a medium separation part on a more downstream side in the direction A than the nip part N, then a backing member 15 supporting the inner periphery 12b side of the film member 12 at the nip part N is formed in surface shape going along the surface 13a of the pressure roller 13. The fixing device 11 is provided with a tubular heating element 16 for heating the film member 12 at a more upstream position in the direction A than the nip part N. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device that is used in an image forming apparatus such as a copying machine or a facsimile machine, and that fixes an unfixed toner image formed on a recording medium by heating and pressing, and an image forming apparatus including the fixing device.

In general, in an image forming apparatus such as a copying machine or a facsimile, a recording medium on which an unfixed toner image is transferred is guided to a fixing device, and the toner image is fixed on the recording medium to form a permanent image.
As such a fixing device, there is known a fixing device including a heating roller maintained at a predetermined temperature and a pressure roller disposed in pressure contact with the heating roller.
In this fixing device, the heating roller is rotated and the pressure roller is driven, and the recording medium onto which the toner image is transferred is sandwiched and conveyed by a nip portion where the fixing roller and the pressure roller are in pressure contact with each other.
The recording medium onto which the toner image has been transferred is fed into the nip portion so that the transfer surface faces the fixing roller, and heated and pressurized while passing through the nip portion, and the toner image melted by heat is applied to the recording medium. It is fixed.

By the way, in image forming apparatuses such as copying machines and facsimiles, there is a strong demand for improvement in printing efficiency. Accordingly, in recent image forming apparatuses, the speed of the image forming process and the speed of the fixing process have been increased. Yes.
However, when the speed of the fixing process is increased, in the fixing device in which the heating roller and the pressure roller described above are in pressure contact with each other, in order to ensure the heating and pressing time of the recording medium to which the toner image is transferred, The length also needs to be increased.
Therefore, the diameters of the heating roller and the pressure roller must be increased, and the heat capacity of the heating roller is increased, and the time required for heating to a predetermined fixing temperature (so-called warm-up time) is increased.

  On the other hand, if a sufficient amount of heat is applied to the recording medium without increasing the length of the nip portion, it is necessary to increase the set temperature of the heating roller, but the power consumption increases and the durability of the heating roller is increased. From the point of view, it is not preferable.

In order to solve the above-described problem, the fixing device described in Patent Document 1 includes a heating unit including a low heat capacity linear heater and a pressure roller, and a substantially flat contact surface formed on the heating unit. The pressure roller is opposed to a film member formed so as to be able to go around.
Thus, a nip portion having a large length is formed at the contact portion between the pressure roller and the film member, and the film member is stretched between the heating means, the drive roller, and the driven roller.
JP-A-9-80941

However, in the fixing device described in Patent Document 1, the heating means is disposed immediately above the nip portion formed at the contact portion between the pressure roller and the film member.
Accordingly, when attention is paid to the temperature distribution of the film member forming the peripheral circuit, the nip portion has the highest temperature.
On the other hand, the recording medium heated and pressurized in the nip part is separated from the film member in the medium separating part on the downstream side in the circumferential direction from the nip part, but the temperature of the recording medium is still considerable in this medium separating part. It is high.
For this reason, when the toner temperature on the recording medium in the medium separating unit exceeds, for example, 200 degrees Celsius, the toner is liquefied to reduce the cohesive force, and the toner image is attached to the film member side. There is a disadvantage that a phenomenon called so-called hot offset occurs.

Further, in the fixing device described in Patent Document 1, a driving roller and a driven roller for rotating the film member are required, which increases the cost of the fixing device.
Furthermore, in the fixing device described in Patent Document 1, the film is protected during transportation, the accuracy and reliability of temperature detection at various parts of the fixing device, and the heating means abnormally generates heat. No particular consideration was given to the provision of failsafe means.

In view of the above problems, an object of the present invention is to provide a fixing device and an image forming apparatus that can remarkably improve printing efficiency with a simple configuration.
Specifically, it is an object of the present invention to provide a fixing device and an image forming apparatus capable of increasing the speed of the fixing process by increasing the length of the nip portion with a simple configuration and preventing hot offset.
Another object of the present invention is to provide a fixing device and an image forming apparatus capable of appropriately protecting a film member during transportation of the fixing device.
Another object of the present invention is to provide a fixing device and an image forming apparatus that can reduce the cost by reducing the number of rollers for rotating the film member.
Another object of the present invention is to provide a fixing device and an image forming apparatus capable of improving the accuracy and reliability of temperature detection at various parts of the fixing device.
It is another object of the present invention to provide a fixing device and an image forming apparatus capable of interrupting energization of the heating means when the heating means abnormally generates heat.

In order to solve the above-described problems, the fixing device according to the present invention is not yet determined in the nip portion between a part of the outer peripheral surface of the film member and the support member disposed outside the film member while rotating the annular film member. The recording medium having the transferred toner image transferred thereon is supplied to fix the toner image, and the film member and the recording medium are separated at the medium separation portion downstream of the nip portion in the circumferential direction. In the fixing device, the backing member that supports the inner peripheral side of the film member in the nip portion is formed in a planar shape along the surface of the support member, and the film is located upstream of the nip portion in the circumferential direction. A heating means for heating the member is provided (claim 1).
According to the present invention, the flexible film member is sandwiched between the backing member formed in a planar shape along the surface of the support member and the support member, so that a large length along the surface of the support member is obtained. A nip portion is formed.
Further, since the heating means for heating the film member is provided on the upstream side of the nip portion in the circumferential direction of the film member, the toner image is sufficiently heated at the initial stage of passing through the nip portion, and more than the nip portion. Further, the temperature of the film member is sufficiently lowered in the medium separation section downstream in the circumferential direction.

In addition, at least one of the support member or the backing member is formed of an elastic material so that the surface facing the nip portion is urged toward at least one of the support member or the backing member toward the other. An urging means for elastically deforming the elastic material may be provided (claim 2).
When the support member or the backing member is elastically deformed, a nip portion having a large length along the surface of the support member is formed.

Further, if the casing that holds the support member is provided with an urging release mechanism that restores elastic deformation of the elastic material (Claim 3), the urging release mechanism is provided when necessary during transportation. The biasing force received by the film member can be released by acting.
In addition, a guide member that supports the film member from the inner peripheral side and curves in a direction away from the support member may be provided at a position downstream of the nip portion in the circumferential direction.
Thereby, a film member is hold | maintained so that rotation is possible by a guide member in the rotation direction downstream rather than a nip part.

The heating member may be provided as a rotatable tubular heating element disposed on the inner peripheral side of the film member.
Thus, the inner peripheral side of the film member is held by the tubular heating element, and heat is quickly transferred from the tubular heating element to the film member.

In addition, the heating member may be placed on the outer peripheral side of the film member, and a film support member may be provided on the inner peripheral side of the film member to bring the heating member into press contact with the film member. 6).
Thereby, heat is directly transferred from the heating member to the film member.

In addition, a contact-type temperature detection sensor for detecting the surface temperature of the tubular heating element may be provided in a non-sheet passing region of the film member that is in contact with the tubular heating element that is out of the recording medium passage portion. ).
As a result, even if dirt is attached to the temperature detection sensor, the paper passing area is not affected.

The backing member may be provided with a temperature detection sensor for detecting the temperature of the nip portion.
Thereby, the temperature of the nip part of a film member is detected directly.

In addition, at least a part of the film member is formed of a transparent material, the first radiation temperature detection sensor for detecting the surface temperature of the film member, and the tubular heating element via the transparent portion of the film member. A second radiation temperature detection sensor for detecting the surface temperature of the tube, and a temperature control unit for controlling the temperature of the tubular heating element based on detection results from both the radiation temperature detection sensors may be provided. ).
Accordingly, the surface temperature of the film member and the surface temperature of the tubular heating element are directly detected in a non-contact manner by the first radiation temperature detection sensor and the second radiation temperature detection sensor.
Further, the temperature detection sensor can be arranged not at the periphery where the tubular heating element and the film member are arranged, but at a position away from them.
Further, in the temperature control unit, energization control of the tubular heating element is performed based on these detection results.

The tubular heating element is attached to a bracket that rotatably supports the tubular heating element via an attachment member, and a power supply contact is in contact with a terminal of the tubular heating element exposed on the outer surface. The member may be formed of a material whose thermal deformation temperature is lower than the ignition temperature of the recording medium.
If the tubular heating element generates heat abnormally for some reason, the heat is transferred to the attachment member, and this attachment member is deformed at a temperature lower than the ignition temperature of the recording medium. Contact with the body terminals will be lost.

  Further, an invention according to claim 11 is an image forming apparatus comprising: a developing device that supplies the recording medium onto which the unfixed toner image is transferred; and the fixing device according to any one of claims 1 to 10. It is.

According to the fixing device of the first aspect, since a nip portion having a large length can be formed between the film member and the outer peripheral surface of the support member with a simple configuration, even if the fixing process is speeded up, Sufficient heat can be applied to the recording medium.
Moreover, in the medium separation part further downstream in the circumferential direction than the nip part, the temperature of the film member is sufficiently lowered, so that hot offset in the medium separation part can be prevented.

  According to the fixing device of the second aspect, the support member or the backing member is elastically deformed, so that a nip portion having a large length is more reliably formed between the film member and the outer peripheral surface of the support member. This can contribute to speeding up the fixing process.

According to the fixing device of the third aspect, the film member can be appropriately protected by releasing the urging force to the film member during transportation.
According to the fixing device of the fourth aspect, it is not necessary to provide a roller for stretching the film member on the downstream side of the backing member in the circumferential direction, so that the cost of the entire fixing device can be reduced.

  According to the fixing device of the fifth aspect, since the film member can be held by the tubular heating element, the film member can be stably circulated and the tubular heating element can be in direct contact with the inner peripheral side of the film member. Therefore, heat can be transferred quickly without heat loss.

  According to the fixing device of the sixth aspect, since it is not necessary to rotate the heating member, it is possible to improve the reliability of the heating member and to transfer heat directly from the heating member to the film member. Heat can be transferred quickly without loss.

  According to the fixing device of the seventh aspect, by disposing a contact-type temperature detection sensor such as a thermistor in a non-sheet-passing region on the film member, dirt that adheres to and accumulates on the surface of the temperature detection sensor. Since it does not reach the paper passing area, it is possible to prevent the recording medium from being contaminated.

  According to the fixing device of the eighth aspect, since the temperature detection sensor provided on the backing member can directly detect the temperature of the nip portion of the film member, there is a separate space for arranging the temperature detection sensor. It becomes unnecessary, and the fixing temperature can be controlled with high accuracy.

According to the fixing device of the ninth aspect, the surface temperature of the film member and the surface temperature of the tubular heating element are directly detected in a non-contact manner by the first radiation temperature detection sensor and the second radiation temperature detection sensor. Therefore, accurate temperature detection can be performed without causing the above-described problem of dirt adhesion.
In addition, the temperature control unit can perform more precise temperature control based on the detected temperature information, and can simplify the peripheral structure.

According to the fixing device of the tenth aspect, even when the tubular heating element generates heat abnormally for some reason, the attachment state between the tubular heating element and the bracket can be released. Heat generation, and the safety of the fixing device can be improved.
According to the image forming apparatus of the eleventh aspect, the fixing process can be speeded up and hot offset can be prevented.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present embodiment. The image forming apparatus 1 includes a developing device 2 and a fixing device 11.
The developing device 2 is a well-known device including at least a photosensitive drum 3, a charging roller 4, an exposure unit 5, a toner image forming unit 6, and a transfer roller 7, and is a recording on which an unfixed toner image T is transferred. In FIG. 1, the medium 21 is conveyed in the C direction and reaches the fixing device 11.

The fixing device 11 is brought into contact with an endless film member 12 that circulates in the A direction in FIG. 1 to form a peripheral circuit, and an outer peripheral surface 12 a of the film member 12, and a spring (biasing means) 14 In FIG. 1, there is provided a rotatable pressure roller (supporting member) 13 that is biased in the direction B, that is, the direction of a backing member 15 described later.
Further, it is made of an elastic material, and is arranged inside the peripheral circuit, and is pressed from the pressure roller 13 through the film member 12, thereby causing a planar sliding contact surface 15 a along the outer peripheral surface 13 a of the pressure roller 13. Is formed between the film member 12 and the pressure roller 13 by sandwiching the film member 12 between the sliding contact surface 15a and the outer peripheral surface 13a. The nip portion N is also formed in a planar shape along the outer peripheral surface 13 a of the pressure roller 13.
In this embodiment, the pressure roller 13 is urged in the direction of the backing member 15 by the spring 14, but the backing member 15 may be urged in the direction of the pressure roller 13. .

A tubular heating element (heating means) 16 that is rotatably driven is provided in the vicinity of the upstream side in the circumferential direction A with respect to the nip portion N. An outer peripheral surface 16 a of the tubular heating element 16 is provided on the film member 12. It contacts with the inner peripheral surface 12b.
In the present embodiment, the contact surface between the outer peripheral surface 16a of the tubular heating element 16 and the inner peripheral surface 12b of the film member 12 is arranged in non-contact with the pressure roller 13.

A thermistor 17 is disposed in contact with a region S2 described later on the outer peripheral surface 12a of the film member 12, and an output signal of the thermistor 17 is input to the control unit 20.
Further, on the downstream side of the backing member 15 in the circumferential direction A, a guide surface 18a is formed which is in sliding contact with the inner circumferential surface 12b of the film member 12 and guides the film member 12 in the circumferential direction A. A member 18 is provided.

  The fixing device 11 is housed in a fixing device housing 19 having an upper frame (bracket) 19a and a lower frame (casing) 19b, and the recording medium 21 onto which the unfixed toner image T is transferred is fixed. After passing through the fixing process in the apparatus 11, it is sandwiched by a pair of discharge rollers 22, 22 and discharged to the outside.

The film member 12 is externally mounted on the tubular heating element 16, the backing member 15, and the guide member 18 to form a peripheral circuit. In the present embodiment, the film member 12 is 2 to 2 times longer than the peripheral circuit length in the non-mounted state. It is a PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin) tube formed in an annular shape having a circumference of about 5 mm and a thickness of about 0.1 mm.
Further, a release coat layer to which a conductive material such as carbon black is added as necessary is formed on the outer peripheral surface 12a and the inner peripheral surface 12b of the film member 12.

  The pressure roller 13 supported so as to be rotatable in the forward counterclockwise direction in the conveyance direction of the recording medium 21 includes a rubber elastic layer having good releasability such as silicone rubber. As described above, the outer peripheral surface 13 a is pressed toward the backing member 15 by the biasing force of the spring 14.

In the present embodiment, the backing member 15 supported by the upper frame 19a is formed of an elastic material such as silicone sponge. In a state where the backing member 15 is not elastically deformed, as shown in FIG. The circumferential direction is the short side, and the long side is formed in a substantially rectangular parallelepiped shape extending in the width direction of the film member 12.
Further, a film tape such as polyimide having high heat resistance and high wear resistance is bonded or wound on the facing surface 15b of the backing member 15 facing the film member 12 as a sliding layer for reducing frictional resistance. The mounted sliding layer 15c is formed, and can be smoothly slidably contacted with the film member 12.
In the state where the backing member 15 is incorporated in the fixing device 11, as shown in FIG. 2B, the opposing surface 15 b of the backing member 15 is elastically deformed by the urging force of the pressure roller 13, Since the planar sliding contact surface 15a along the outer peripheral surface 13a is formed, as described above, the nip portion N formed between the film member 12 and the pressure roller 13 also has a surface shape along the outer peripheral surface 13a. It is said.
Here, the relationship between the dynamic friction coefficient μ1 between the pressure roller 13 and the outer peripheral surface 12a of the film member 12 and the dynamic friction coefficient μ2 between the backing member 15 and the inner peripheral surface 12b of the film member 12 is μ1. > Μ2.
In this embodiment, the backing member 15 is formed of an elastic material, but may be formed of a resin material or the like on which the sliding contact surface 15a is formed in advance.

As shown in FIG. 3A, the tubular heating element 16 disposed in the vicinity of the upstream side in the circumferential direction A from the nip portion N is extended in the direction of the rotation axis L, for example, carbon or nichrome wire. A resistor 31 made of a material, a cylindrical sealing tube 32 made of an insulating material such as a ceramic surrounding the resistor 31, and both ends of the sealing tube 32. Electrode caps (terminals) 33 and 33 that are electrically connected to each other.
The outer peripheral surface of the sealing tube 32 is an outer peripheral surface 16a that is in contact with the inner peripheral surface 12b of the film member 12, as shown in FIG. The tension of the stretched film member 12 acts on the body 16 in the D direction (the backing member 15 side).
Further, both ends of the outer peripheral surface 16a of the tubular heating element 16 are rotatably supported by bearings 34, 34, and bearing holding members 35, 35 for holding the bearings 34, 34 are attached by mounting members 36, 36. It is attached to the upper frame 19a.
In this attached state, the sliding contacts (power supply contacts) 37 and 37 positioned on the upper frame 19a and the electrode caps 33 and 33 can be slidably contacted with each other. Is supplied.
A driving gear 38 connected to a driving means (not shown) is attached to one end of the sealing tube 32 of the tubular heating element 16, whereby the tubular heating element 16 rotates around the rotation axis L. Driven freely.

In the present embodiment, since the tubular heating element 16 is disposed in the vicinity of the nip portion N, the difference between the temperature of the outer peripheral surface 16a of the tubular heating element 16 and the temperature at the nip portion N is relatively small. Even if the tubular heating element 16 is not heated excessively, the temperature of the nip portion N is raised to a predetermined fixing temperature.
Therefore, when the fixing device 11 is operating normally, the heat resistance of the bearing holding members 35 and 35 and the attachment members 36 and 36 is not so required.
Therefore, in the present embodiment, the attachment members 36, 36 are made of, for example, a thermoplastic resin such as a nylon bag or a polycarbonate screw whose softening point is lower than the ignition point of paper as a typical recording medium. As will be described later, a fail-safe means is configured when the tubular heating element 16 is abnormally heated.

Instead of the attachment members 36, 36, the bearing holding members 35, 35 may be directly attached to the upper frame 19a with a metal such as solder whose melting point is lower than the ignition point of the paper.
In FIG. 3B, the portion where the inner peripheral surface 12b of the film member 12 and the tubular heating element 16 are in contact with each other includes a sheet passing area S1 through which the recording medium 21 passes and both ends of the sheet passing area S1. The non-sheet-passing areas S2 and S2 are located in the non-sheet-passing area S2 in order to control the energization of the tubular heating element 16 by observing the temperature of the tubular heating element 16 in one non-sheet-passing area S2. The thermistor 17 is abutted and arranged.

The guide member 18 attached to the upper frame 19a extends in the width direction of the film member 12, and in the present embodiment, as shown in a partially cutaway view in FIG. The first guide part G1 that guides the film member 12 in the left direction in FIG. 4 and the direction in which the film member 12 is separated from the pressure roller 13 from the first guide part G1 are curved. The second guide portion G2 that guides the film member 12 upward, and the third guide portion that is further curved from the second guide portion G2 toward the tubular heating element 16 and guides the film member 12 to the right in FIG. G3.
The surface on which the guide member 18 and the inner peripheral surface 12b of the film member 12 are slidably contacted is a guide surface 18a, and the frictional resistance is reduced on the guide surface 18a in the same manner as the opposing surface 15b of the backing member 15. As a sliding layer, a sliding layer 18b is formed on which a film tape such as polyimide having high heat resistance and high wear resistance is bonded or wound, and can be smoothly slidably contacted with the film member 12. The
Here, the dynamic friction coefficient μ3 between the guide member 18 and the inner peripheral surface 12b of the film member 12 is substantially equal to the dynamic friction coefficient μ2 between the backing member 15 and the inner peripheral surface 12b of the film member 12 described above. The
Therefore, the relationship between the dynamic friction coefficients μ1 and μ3 between the pressure roller 13 and the outer peripheral surface 12a of the film member 12 is μ1> μ3.
In FIG. 4, the film member 12 and the recording medium 21 are separated at a medium separating portion M that is a continuous portion of the first guide portion G <b> 1 and the second guide portion G <b> 2. The radius of curvature r2 from the center of curvature P of M is formed smaller than the radius r1 of the pressure roller 13 (see FIG. 2B).

Next, the fixing operation of the fixing device 11 in the present embodiment will be described.
When the tubular heating element 16 is driven to rotate clockwise in FIG. 1 by the control unit 20, the outer peripheral surface 16 a of the tubular heating element 16, the sliding contact surface 15 a of the backing member 15, and the guide surface of the guide member 18. The film member 12 stretched over 18a is stretched by receiving a biasing force from the pressure roller 13 biased by the spring 14, and starts to circulate in the A direction.

Here, since the backing member 15 and the guide member 18 are respectively provided with the sliding layer 15c and the sliding layer 18b, the film member 12 slides on the surfaces of the sliding layer 15c and the sliding layer 18b. However, it is circulated without generating wrinkles by the urging force from the pressure roller 13.
As described above, the dynamic friction coefficient μ1 between the pressure roller 13 and the outer peripheral surface 12a of the film member 12 and the dynamic friction coefficient μ2 between the backing member 15 and the inner peripheral surface 12b of the film member 12 are as follows. The relationship is μ1> μ2, and the relationship between μ1 and the dynamic friction coefficient μ3 between the guide member 18 and the inner peripheral surface 12b of the film member 12 is also μ1> μ3. No slip occurs between 12 and the pressure roller 13.

Next, the electrode caps 33, 33 of the tubular heating element 16 are energized from the control unit 20 through the sliding contacts 37, 37, whereby the resistor 31 is heated, and this heat is transferred to the sealing tube 32 and It is transmitted to the film member 12.
Since the tubular heating element 16 has a structure in which the resistor 31 is sealed by a cylindrical sealing tube 32 having a small heat capacity, the temperature of the tubular heating element 16 is quickly raised, and accordingly, the film member The temperature of 12 is also quickly raised.

The surface temperature of the tubular heating element 16 is always detected by the thermistor 17 disposed in contact with the non-sheet passing region S2 of the film member 12 described above. Based on this detected temperature, the controller 20 generates the tubular heating element. Energization control to the body 16 is performed.
The thermistor 17 is arranged in the non-sheet passing region S2. The reason that the thermistor 17, which is a contact type temperature detection sensor, is arranged in the sheet feeding region S1, the dust of the recording medium 21 causes dust on the film member 12 and the like. This is because the outer peripheral surface 12a is soiled, and after the dirt is deposited on the tip portion of the thermistor 17, the dirt may adhere to the outer peripheral surface 12a of the film member 12 again.
Here, in the present embodiment, since the tubular heating element 16 is disposed in the vicinity of the nip portion N, the difference between the temperature detected by the thermistor 17 and the temperature in the nip portion N is relatively small.
Therefore, by controlling the surface temperature of the tubular heating element 16 to a desired fixing temperature, the temperature at the nip portion N can be made substantially the desired fixing temperature.

When the surface temperature of the tubular heating element 16 reaches a desired fixing temperature, the recording medium 21 onto which the unfixed toner image T has been transferred is conveyed in the C direction (see FIG. 1) and reaches the fixing device 11, and the film The nip portion N is supplied in close contact with the member 12.
Further, as described above, the dynamic friction coefficient μ1 between the pressure roller 13 and the outer peripheral surface 12a of the film member 12, the dynamic friction coefficient μ2 between the backing member 15 and the inner peripheral surface 12b of the film member 12, and Since the relationship between the dynamic friction coefficient μ3 between the guide member 18 and the inner peripheral surface 12b of the film member 12 is appropriately set, the supplied recording medium 21 is free from surface deviation and wrinkle. 12 is maintained in close contact with the nip portion N while receiving the nip pressure.
In the nip portion N, heat from the film member 12 is transmitted to the recording medium 21, and the toner image T is melted and softened and bonded to the recording medium 21.

Thereafter, in the process where the recording medium 21 that has passed through the nip portion N reaches the medium separation portion M while being in close contact with the film member 12, the melted toner image T is naturally cooled and completely fixed on the recording medium 21. .
In addition, since the radius of curvature r2 of the guide member 18 in the medium separating portion M is smaller than the radius r1 of the pressure roller 13 that is substantially equal to the radius of curvature of the nip portion N, the recording medium 21 is smooth from the film member 12. Separated.
Finally, the recording medium 21 on which the toner image T is completely fixed is sandwiched between the pair of discharge rollers 22 and 22 and discharged to the outside.

Here, when the recording medium 21 is supplied to the nip portion N, the temperature (t) at an arbitrary point on the recording medium 21, the adhesion force (f1) between the recording medium 21 and the toner, the film member 12 and the toner The relationship between the toner adhesion force (f2) and the toner cohesion force (f3) will be described with reference to FIG.
In FIG. 5, in the region where the temperature t is lower than the temperature t1 (cold offset region), the toner is not melted and remains in powder form, so f1 and f3 are smaller than f2, and the toner is on the film member 12 side. A phenomenon called so-called cold offset can occur.
In a region where the temperature t is between the temperatures t1 and t2 (normal fixing region), f1 and f3 are smaller than f2, and the toner adheres to the recording medium 21, so that a normal fixing operation is performed.
When the temperature t becomes higher than t2 and the toner is liquefied and f3 is lowered, a phenomenon called so-called hot offset, in which the toner adheres to the film member 12 side, may occur.

However, in the fixing device 11 of the present embodiment, the temperature of the outer peripheral surface 16a of the tubular heating element 16 is higher than that of other parts, but the recording medium 21 is not separated at this part, and temporarily Even if the temperature of the outer peripheral surface 16a is in the above-described hot offset region, there is no problem, and the toner image T is sufficiently melted and properly fixed at the nip portion N.
Further, since the tubular heating element 16 is disposed upstream of the nip portion N in the circumferential direction A, the medium separating portion M where the recording medium 21 is separated from the film member 12 is separated from the tubular heating element 16. The temperature of the recording medium 21 in the medium separating unit M is the lowest compared with the other parts of the nip N.
Therefore, if the temperature of the recording medium 21 in the medium separating unit M is the temperature of the normal fixing region, the film member 12 and the recording medium 21 are appropriately separated.
Even if the temperature of the recording medium 21 in the medium separation unit M is in the cold offset region described above, the toner image T has already been fixed on the recording medium 21, and f1 and f3 Compared with the powder state, it becomes sufficiently large, and f1>f3> f2, so that the phenomenon that the toner image T adheres to the film member 12 side does not occur.
Therefore, in the fixing device 11 of the present embodiment, the normal fixing region can be substantially enlarged.

In the present embodiment, when the tubular heating element 16 is abnormally heated due to damage of the thermistor 17 or the like, this heat is attached to the attachment member 36 via the bearings 34 and 34 and the bearing holding members 35 and 35. , 36.
When the temperature of the attachment members 36, 36 reaches a softening point temperature lower than the ignition point of the recording medium 21, the attachment members 36, 36 are softened and deformed as shown in FIG.
At this time, since the tension in the D direction from the film member 12 acts on the tubular heating element 16, the tubular heating element 16 is displaced in the D direction from the normal attachment position with the upper frame 19a, and the electrode cap The sliding contact state between 33 and 33 and the sliding contact points 37 and 37 is released, and energization of the tubular heating element 16 from the control unit 20 is stopped.

According to the first embodiment, the film member 12 is urged by the urging force from the pressure roller 13 between the outer peripheral surface 13a of the pressure roller 13 and the sliding contact surface 15a of the backing member 15 made of an elastic material. Because of the clamping, it is possible to form a nip portion N having a large planar shape along the outer peripheral surface 13a without increasing the diameter of the pressure roller 13, and even if the fixing process is speeded up, it is sufficient. Heat can be applied to the recording medium 21.
Further, since the tubular heating element 16 is disposed upstream of the nip portion N in the circumferential direction A, the toner image T is sufficiently heated at the initial stage of passing through the nip portion N, and the circumferential direction A is more than the nip portion N. In the medium separating section M on the downstream side, the temperature of the film member 12 is sufficiently lowered, so that hot offset in the medium separating section M can be prevented.

  The film member 12 is stretched over the backing member 15, the tubular heating element 16, and the guide member 18, stretched by receiving the urging force from the pressure roller 13, and circulated in the A direction. Since it is not necessary to provide a separate roller on the downstream side of the circumferential direction A of the member 15, the cost of the fixing device 11 can be reduced, and the tension of the film member 12 can be minimized. And it is suitable for forming a release layer made of a flexible material on the inner peripheral surface 12b.

Further, since the nip portion N is formed long, the amount of heat to be supplied to the nip portion N can be reduced, and the tubular heating element 16 having a small heat capacity is used as the heating member. The temperature can be raised, and the warm-up time can be shortened.
Further, since the thermistor 17 is arranged in the non-sheet passing region S2, it is possible to prevent dirt from being accumulated at the tip of the thermistor 17.

  Furthermore, even when the tubular heating element 16 abnormally generates heat for some reason, the attachment member 36 is deformed, whereby the energization of the tubular heating element 16 from the control unit 20 is cut off and further heat generation is prevented. Therefore, the fixing device 11 can be provided with fail-safe means.

FIG. 7 shows a second embodiment of the present invention, and the same reference numerals are assigned to parts common to the first embodiment, and description thereof is omitted.
In the fixing device 41 according to the second embodiment, as shown in the schematic configuration diagram of FIG. 7A, the backing guide member 42 is formed by integrally forming the backing member 43 and the guide member 44. This is different from the first embodiment.

  The configuration of the backing guide member 42 will be further described with reference to FIG. 7B. When the backing guide member 42 is incorporated in the fixing device 41, the backing member 43 is added via the film member 12. Since the opposed surface 43a facing the pressure roller 13 is elastically deformed by the urging force of the pressure roller 13 to form a planar sliding contact surface 42a along the outer peripheral surface 13a, as described above, the film member The nip portion N formed between the pressure roller 12 and the pressure roller 13 is also formed into a planar shape along the outer peripheral surface 13a.

The backing member 43 that forms a part of the backing guide member 42 is formed of an elastic material such as silicone sponge. When the backing member 43 is not elastically deformed, the circumferential direction is the short side, and the long side is the film member. 12 is formed in a substantially rectangular parallelepiped shape extending in the width direction, but in the present embodiment, the downstream side in the circumferential direction A from the nip portion N is formed in a shape along the peripheral circuit of the film member 12. Thus, the first guide portion G1 and a part of the second guide portion G2 are formed, and the medium separation portion M is also formed.
In addition, a film tape such as polyimide having high heat resistance and high wear resistance is bonded to the facing surface 43a of the backing member 43 that is in sliding contact with the film member 12 as a sliding layer for reducing frictional resistance. A wound sliding layer 43b is formed.

Further, the guide member 44 that forms a part of the backing guide member 42 has a substantially inverted U shape when viewed from the front as shown in FIG. This is integrated with the member 43, whereby a part of the remaining part of the second guide part G2 and the third guide part G3 are formed.
Further, a film tape such as polyimide having high heat resistance and high wear resistance is bonded or wound on the guide surface 44a of the guide member 44 that is in sliding contact with the film member 12 as a sliding layer for reducing frictional resistance. The mounted sliding layer 44b is formed.
In addition, about each shape of the backing member 43 and the guide member 44 which are integrated, it is not restricted to what is shown by FIG. 7, For example, the 1st guide part G1 and the 2nd guide part G2 by the guide member 44 are used. The third guide part G3 and the medium separation part M may be formed.
The fixing operation of the fixing device 41 is the same as in the first embodiment.

  According to the second embodiment, since the backing member 43 and the guide member 44 are integrated as the backing guide member 42 in addition to the same effects as the first embodiment, the number of parts can be reduced. Since the positional deviation between the backing member 43 and the guide member 44 can be prevented, the film member 12 can be stably circulated.

FIG. 8 shows a third embodiment of the present invention, and the same reference numerals are assigned to parts common to the previous embodiment, and the description thereof is omitted.
In the fixing device 61 of the third embodiment, in addition to the thermistor 17 in the first and second embodiments (hereinafter, referred to as “first thermistor 17” in the present embodiment), a second one. The thermistor 62 is sealed and disposed at a location facing the center of the nip portion N in the arc direction of the nip portion N in the backing member 43, and the outputs of the first thermistor 17 and the second thermistor 62 are sent to the controller 63. The point which was comprised so that it might input is different from 2nd Embodiment.
Since the second thermistor 62 is not in direct sliding contact with the outer peripheral surface 12a of the film member 12, the above-described problem of dirt accumulation does not occur.
Therefore, the position of the second thermistor 62 in the width direction of the film member 12 may be a position corresponding to either the sheet passing area S1 or the non-sheet passing area S2, but the width of the film member 12 with the most rapid temperature drop. It is preferable to arrange in the center of the direction.

In the fixing operation of the fixing device 61, the temperature in the non-sheet passing region S2 of the outer peripheral surface 16a of the tubular heating element 16 is detected by the first thermistor 17, and the film member in the nip portion N is detected by the second thermistor 62. The temperature at the center in the 12 width direction is detected.
Here, since the fixing operation is not performed in the non-sheet passing area S2 where the first thermistor 17 is disposed, the temperature gradient between the sheet passing area S1 and the non-sheet passing area S2 is relatively small.
Therefore, the control unit 63 calculates the temperature difference and the temperature gradient based on the temperatures detected from the first thermistor 17 and the second thermistor 62, and thereby the heat capacity of the film member 12 and the recording medium 21. It is controlled to prevent fixing failure due to the influence of the above.

  According to the third embodiment, since the first thermistor 17 and the second thermistor 62 are provided in addition to the same effects as those of the first and second embodiments, the outer peripheral surface of the tubular heating element 16 is provided. The temperature of 16a and the temperature of the nip portion N can be detected, and temperature control with high accuracy can be performed.

FIG. 9 shows a fourth embodiment of the present invention, and the same reference numerals are assigned to parts common to the previous embodiment, and the description thereof is omitted.
In the fixing device 81 according to the fourth embodiment, instead of the tubular heating element 16 as the heating member in the second embodiment, the fixing device 81 is disposed on the upstream side in the circumferential direction A from the nip portion N. A driving roller 82 that is slidably contacted with the inner peripheral surface 12b and is driven to rotate in a clockwise direction by a driving means (not shown), and disposed opposite to the driving roller 82 with the film member 12 interposed therebetween. The point which is provided with the stationary heating member 83 contact | abutted by this outer peripheral surface 12a is different from 2nd Embodiment.
Further, a pressing force is applied from the driving roller 82 in the direction of the stationary heating member 83 (direction E in FIG. 9) by a pressing means (not shown), and the stationary heating member 83 and the film member 12 are in a pressing contact state. Is done.
Further, the stationary heating member 83 is disposed at a position facing the driving roller 82, and supports a flat plate-like heating element 83a made of carbon, metal oxide or the like formed by thick film printing, and the heating element 83a. It is comprised by the heat generating body support part 83b.
The fixing operation of the fixing device 81 is the same as in the first embodiment.

  According to the fourth embodiment, the heating member is the stationary heating member 83, and it is not necessary to rotate by providing a sliding contact, so that the reliability can be improved and the stationary heating is performed. Since heat is directly transferred from the member 83 to the film member 12, heat loss can be reduced.

FIGS. 10 to 12 show a fifth embodiment of the present invention, and the same reference numerals are assigned to parts common to the previous embodiments, and the description thereof is omitted.
In the fixing device 101 according to the fifth embodiment, as shown in FIGS. 11A to 11C, a substantially central portion of the sheet passing area S <b> 1 of the surface 102 a of the transparent film member 102 is provided at the center. An infrared radiation portion 103a having a high infrared radiation coefficient colored with carbon or the like on the surface 102a of the film member 102, and an infrared non-radiation portion 103b having a low infrared radiation coefficient on which the surface 102a of the film member 102 is exposed have a circumferential direction A. 1st patch part 103 arranged alternately along is formed.
Further, the surface 104a of the tubular heating element 104 is exposed at a position that is substantially in the center of the longitudinal direction of the tubular heating element 104 made of ceramic but does not overlap with the first patch part in the width direction of the film member 102. An infrared radiation portion 105 a having a high infrared radiation coefficient and an infrared non-radiation portion 105 b having a low infrared radiation coefficient in which metal plating or the like is applied to the surface 104 a of the tubular heating element 104 along the circumferential direction of the tubular heating element 104. Alternately arranged second patch portions 105 are formed.

Further, the first radiation temperature detection sensor 106 is disposed so as to face the first patch portion 103 without contacting the film member 102, and the second radiation temperature detection sensor 107 is not contacted with the film member 102. Thus, the second patch portion 105 is disposed so as to face the film member 102.
Further, the thermistor 17 is brought into contact with the non-sheet passing region S <b> 2 of the surface 102 a of the film member 102, and is disposed to face the tubular heating element 104 through the film member 102.
The first radiation temperature detection sensor 106, the second radiation temperature detection sensor 107, and the thermistor 17 are connected to the control unit 108, and the control unit 108 controls energization of the tubular heating element 104. Is called.
As the first radiation temperature detection sensor 106 and the second radiation temperature detection sensor 107, a pyroelectric infrared sensor (for example, RE814S manufactured by Nippon Ceramics Co., Ltd.) is suitable.

The fixing operation of the fixing device 101 will be described in particular with respect to temperature detection and temperature control, which are the features of the present embodiment. When the tubular heating element 104 is rotated by a driving means (not shown), the circulation of the film member 102 is started. When the tubular heating element 104 is energized, the surface temperatures of the surface 104a of the tubular heating element 104 and the surface 102a of the film member 102 are quickly raised.
In the first radiation temperature detection sensor 106 disposed in contact with the first patch portion 103 in a non-contact manner, a continuous change in infrared radiation is detected as the film member 102 circulates. The temperature at the center of the sheet passing area S1 is detected and input to the control unit.
Further, in the second radiation temperature detection sensor 107 arranged to face the second patch portion 105 via the film member 102, when the tubular heating element 104 is rotated, the transparent film member 102 is interposed. Thus, a continuous change in infrared radiation is detected from the second patch unit 104, and the temperature at the center in the longitudinal direction of the tubular heating element 104 is detected from the differential element and input to the control unit.

Further, since the fixing operation is not performed in the non-sheet passing area S2 where the thermistor 17 is disposed, the temperature gradient between the sheet passing area S1 and the non-sheet passing area S2 is relatively small.
Therefore, the calibration of the first radiation temperature detection sensor 106 and the second radiation temperature detection sensor 107 is performed in the control unit 108 based on the temperature detected from the thermistor 17 when no paper is passed.

FIG. 12 is a schematic configuration diagram of the control unit 108. As shown in FIG. 12A, the control unit 108 mainly includes a microprocessor unit 108a, an A / D conversion unit 108b, and an I / O unit. 108c.
The microprocessor unit 108a converts the voltage divided by the thermistor 17 and the resistor R1, the output of the first radiation temperature detection sensor 106, and the output of the second radiation temperature detection sensor 107 into an A / D conversion unit 108b. And calculating each temperature to determine whether or not to energize the tubular heating element 104.
When the tubular heating element 104 is energized, a drive signal to that effect is output to the I / O unit 108c to drive the light emission side of the phototriac PC.
As a result, as shown in FIG. 12B, the light receiving side of the phototriac PC drives the gate of the triac Qt to conduct, and the tubular heating element 104 is energized.

According to the fifth embodiment, in addition to the same effects as those of the first and second embodiments, the non-contact type first radiation temperature detection sensor 106 allows the temperature at the substantially central portion of the sheet passing area S1. Can be detected without causing the problem of dirt accumulation as in the contact-type temperature detection sensor.
In addition, the surface temperature of the tubular heating element 104 can be directly detected by the second radiation temperature detection sensor 107 disposed outside the peripheral circuit of the film member 102.
The thermistor 17 can calibrate the second radiation temperature detection sensor 107.
Accordingly, the control unit 108 appropriately calculates the temperature difference and temperature gradient of each part based on the detection signals from these sensors, thereby preventing the fixing failure due to the influence of the heat capacity of the film member 102 and the recording medium 21. Temperature control can be performed.
Furthermore, since the first radiation temperature detection sensor 106 and the second radiation temperature detection sensor 107 can be arranged apart from the tubular heating element 104 and the film member 102, the peripheral structure can be simplified.

FIG. 13 shows a sixth embodiment of the present invention, and the same reference numerals are assigned to parts common to the previous embodiment, and the description thereof is omitted.
In the fixing device 121 of the sixth embodiment, a hole 19d is provided in the bottom surface 19c of the lower frame 19b, and a part of a rotatable arm member 122 that supports the spring 14 projects into the hole 19d. The arm member 122 is pressed from the outside of the lower frame 19b by the chassis 123 to apply a biasing force to the spring 14.
That is, the arm member 122 includes a hook-shaped spring receiving seat 122a, one end extending from the spring receiving seat 122a, and the other end pivotally supported by the pivot PV, and a spring receiving seat. A stopper portion 122c extending in the opposite direction from the arm portion 122b is provided from 122a, and the spring 14 is disposed so that one end thereof is held by the spring seat 122a and the other end presses the pressure roller 13. Has been.

The operation of the fixing device 121 will be described. When the fixing device 121 is attached to the image forming apparatus side chassis 123 and the fixing process is being performed, the spring seat 122a of the arm member 122 is connected to the stopper surface 123a of the chassis 123. Since the contact is made, the pressure roller 13 receives an urging force from the spring 14 at the urging position X1 in FIG. 13A and presses the film member 12 and the backing guide member 42 in the B direction. As described above, the nip portion N is formed.
On the other hand, when the chassis 123 is removed from the lower frame 19b, the spring seat 122a is separated from the stopper surface 123, and the arm member 122 rotates the pivot PV in the J direction in FIG. The stopper 122c of the arm member 122 is rotated at the center until it contacts the bottom surface 19c of the lower frame 19b.
As a result, the urging force of the spring 14 to the pressure roller 13 is released, the pressure roller 13 is moved to the non-biasing position X2 in FIG. 13B, and the pressure applied to the film member 12 is also released. .
Note that FIG. 13 is an example of a means for releasing the pressure applied to the film member 12, and it goes without saying that various modes can be adopted.

According to the sixth embodiment, the urging force from the pressure roller 13 to the film member 12 is released by leaving the chassis 123 removed from the lower frame 19b during transportation, and the film member. 12 can be appropriately protected, so that the durability and reliability of the fixing device 121 can be improved.
Further, even when a so-called medium jam occurs in which the recording medium 21 is clogged, the recording medium 21 can be easily removed.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 4 is a backing member of the fixing device according to the first embodiment of the present invention, where (a) is a front view when not incorporated into the fixing device, and (b) is a pressure roller incorporated into the fixing device. It is a figure which shows a mode that the pressing force is received from. FIG. 2A is a front view of the tubular heating element of the fixing device according to the first embodiment of the present invention, and FIG. FIG. 3 is a partial cutaway view of a guide member of the fixing device according to the first exemplary embodiment of the present invention. It is a conceptual diagram showing the relationship between the temperature (t) at an arbitrary point on the recording medium, the adhesion between the recording medium and the toner, the adhesion between the film member and the toner, and the cohesion of the toner. It is a figure which shows a mode that the tubular heat generating body of the fixing device of the 1st Embodiment of this invention was shifted from the normal attachment position by the deformation | transformation of an attachment member. FIG. 7 is a diagram illustrating a second embodiment of the present invention, where (a) is a schematic configuration diagram of a fixing device, and (b) is a drawing where a backing guide member is incorporated in the fixing device and a pressing force is applied from a pressure roller. It is a figure which shows a mode that it has received. It is a schematic block diagram of the fixing device of the 3rd Embodiment of this invention. It is a schematic block diagram of the fixing device of the 4th Embodiment of this invention. It is a schematic block diagram of the fixing device of the 5th Embodiment of this invention. It is a figure which shows the structure of the temperature detection part of the 5th Embodiment of this invention, Comprising: (a) is an expanded schematic diagram of a temperature detection part, (b) is the 1st patch part formed in the film member. (C) is a figure which shows the 2nd patch part formed in the tubular heat generating body. It is a schematic block diagram of the control part of the 5th Embodiment of this invention, (a) is the part which drives the light emission side of a photo triac based on a sensor signal, (b) is a tubular heat_generation | fever by driving a triac. It is a figure which shows the part which supplies electricity to a body. FIG. 10 is a schematic configuration diagram of a fixing device according to a sixth embodiment of the present invention, where (a) is a state where the fixing device is attached to an image forming apparatus-side chassis, and (b) is an image forming apparatus side of the fixing device. It is a figure which respectively shows the state removed from the chassis.

Explanation of symbols

1 Image forming device 11, 41, 61, 81, 101, 121 Fixing device 12, 102 Film member 13 Pressure roller (support member) 15, 43 Backing member 16, 104 Tubular heating element 17, 62 Thermistor 18, 44 Guide Member 20, 63, 108 Control unit 33 Electrode cap 36 Mounting member 37 Sliding contact 42 Backing guide member 82 Driving roller 83 Stationary heating member 103 First patch unit 105 Second patch unit 106, 107 Radiation temperature detection sensor 122 Arm member M Medium separation portion N Nip portion S1 Paper passing area S2 Non-paper passing area T Toner image

Claims (11)

While rotating the annular film member, a recording medium on which an unfixed toner image is transferred is supplied to a nip portion between a part of the outer peripheral surface of the film member and a support member arranged outside the film member, In the fixing device that fixes the toner image and separates the film member and the recording medium at a medium separation unit downstream of the nip portion in the circumferential direction.
A backing member for supporting the inner peripheral side of the film member in the nip portion is formed in a planar shape along the surface of the support member, and heating the film member at a position upstream of the nip portion in the circumferential direction. A fixing device is provided.   At least one of the support member or the backing member has a surface facing the nip portion formed of an elastic material, and urges the elastic member toward at least one of the support member or the backing member toward the other. The fixing device according to claim 1, further comprising an urging unit that elastically deforms.   The fixing device according to claim 2, wherein the casing holding the support member is provided with an urging release mechanism that restores elastic deformation of the elastic material.   The guide member which supports the said film member from the inner peripheral side and curves in the direction separated from the said supporting member is provided in the downstream position of the said lap | rotation direction rather than the said nip part. The fixing device according to claim 3.   The fixing device according to claim 1, wherein the heating member is a rotatable tubular heating element disposed on an inner peripheral side of the film member.   The heating member is fixed on the outer peripheral side of the film member, and a film support member is provided on the inner peripheral side of the film member to bring the heating member into a pressed contact state with the film member. The fixing device according to claim 1.   The contact-type temperature detection sensor which detects the surface temperature of the said tubular heating element is provided in the non-paper passing area | region which remove | deviated from the said recording medium passage part in the said film member in contact with the said tubular heating element. Item 6. The fixing device according to Item 5.   The fixing device according to claim 1, wherein the backing member is provided with a temperature detection sensor that detects a temperature of the nip portion.   At least a part of the film member is formed of a transparent material, a first radiation temperature detection sensor that detects a surface temperature of the film member, and a surface temperature of the tubular heating element via the transparent portion of the film member 8. A second radiation temperature detection sensor for detecting the temperature, and a temperature control unit for controlling the temperature of the tubular heating element based on detection results from both the radiation temperature detection sensors. Fixing device.   The tubular heating element is attached to a bracket that rotatably supports the tubular heating element via an attachment member, and a power supply contact is in contact with a terminal of the tubular heating element exposed on the outer surface, the attachment member being The fixing device according to claim 5, wherein the fixing device is formed of a material whose thermal deformation temperature is lower than an ignition temperature of the recording medium. An image forming apparatus comprising: a developing device that supplies the recording medium to which the unfixed toner image is transferred; and the fixing device according to claim 1.

Images