JP2013250535A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the thermal destruction of a fixing device when using a member having a small heat capacity such as a fixing belt by preventing the abnormal overheat of the member used for fixation.SOLUTION: The fixing device includes: an endless flexible fixing belt 21; a nip forming member 22 disposed inside the flexible fixing belt 21; a support member 23 supporting the nip forming member 22; a pipe-like heat conductor 25 which is wound on an outer surface, so as to form the flexible fixing belt 21 like a loop, in which the nip forming member 22 and the support member 23 are disposed, which is heated by a heat source 24 below the support member 23, to heat the flexible fixing belt 21; and an opposite rotary body 26 coming into contact with the nip forming member 22 across the flexible fixing belt 21, to form a nip part between the opposite rotary body 26 and the flexible fixing belt 21. A deformation suppression member 27 is provided in the pipe-like heat conductor 25, the deformation suppression member 27 which is disposed in a position opposite to the heat source 24 and is with a gap for contacting when the pipe-like heat conductor 25 is thermally deformed, between the inner surface of the pipe-like heat conductor 25 and the deformation suppression member 27.

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a belt fixing mechanism using a belt as a fixing member.

  As is well known, in an electrophotographic image forming apparatus, an electrostatic latent image formed on a photoreceptor, which is a latent image carrier, is subjected to visible image processing with toner, and the toner image is a recording medium such as recording paper. Then, a fixing process is performed in which heat and pressure are applied after the image is transferred to the image, and a copy output is obtained.

As one of the fixing methods used in the image forming apparatus, there is a heat roller fixing method using a fixing roller and a pressure roller that are opposed to each other across a conveyance path of a recording paper.
In this system, the toner image is melted and permeated by heat and pressure by the clamping action between the heat from the heat source provided in the fixing roller and the pressure roller.
In the heat roller fixing method, it takes time to rise to the fixing temperature due to the large heat capacity of the roller.

Therefore, a belt fixing method using a belt having a smaller heat capacity than a roller is known as a configuration for improving the rising of the fixing temperature (for example, Patent Document 1).
FIG. 5 is a diagram showing the configuration of the fixing device disclosed in Patent Document 1, and the configuration will be described as follows.
In FIG. 5, the fixing device A is configured to include a fixing roller B on one side and a pressure roller C on the other side across the conveyance path of the transfer paper S.
A fixing belt E is wound around the fixing roller B between the fixing roller B and a heating roller D disposed at a position different from the fixing roller B. The fixing belt E is applied with tension by the tension roller F. It moves in conjunction with the rotation of the fixing roller B.

A heater D1 is disposed inside the heating roller D, and the temperature of the fixing belt E heated by the heater D1 is controlled by a thermistor G in contact with the belt surface.
Each of these rollers is disposed in the housing 1A of the fixing device A, and the transfer sheet S is heated when passing through a fixing nip formed at a position where the fixing roller B and the pressure roller C are in contact with each other. -The toner image is fixed under pressure.
After the fixing, the transfer sheet S is discharged after its discharge direction is regulated by a separation claw H located behind the fixing nip.

Further, as another example of the above-described belt heating method, a configuration in which the belt is heated facing the fixing nip has been proposed (for example, Patent Document 2).
FIG. 6 is a diagram showing this configuration, in which the fixing device includes a fixing belt E, a metal heat conductor J provided inside the fixing belt E, a heat source K, and the fixing belt E. And a pressure roller L that forms a nip in contact with the metal heat conductor J, and performs a fixing process by heating and pressing a transfer paper (not shown) that is a fixing material passing through the nip. .
In the configuration described above, the metal heat conductor J is a pipe member that is heated by the heat source K, the metal heat conductor J is fixed, and the fixing belt E is movable relative to the metal heat conductor J. The metal heat conductor J and the pressure roller L are pressed against each other via the fixing belt E to form the nip and guide the movement of the fixing belt E.
In the above configuration, unlike the roller, by using the heat capacity, the rise to the fixing temperature can be accelerated, and accordingly, power saving can be achieved.

In the configuration disclosed in Patent Document 2, a region where the metal heat conductor J and the pressure roller L face each other is set in the fixing nip portion, and the fixing belt E is rotated by the rotation of the pressure roller L in the fixing nip portion. Is dragged and moves on the surface of the metal thermal conductor J.
When the fixing belt E is dragged by the rotational driving of the pressure roller, the tension changes between the inlet side and the outlet side of the fixing nip portion. Looseness tends to occur on the downstream side in the moving direction of the fixing belt E across the fixing nip.

For this reason, in the metal heat conductor J, the contact state with the fixing belt E is different between the fixing nip portion inlet side and the outlet side, so that a temperature difference occurs between the fixing nip portion outlet side and the fixing nip portion inlet side. Become. That is, since the fixing belt which is a heat transfer target is not in contact with the fixing nip portion outlet side, heat transfer to the fixing belt is not performed unlike the fixing nip portion side, so that the temperature of the metal heat conductor J is increased. It rises abnormally.
As a result, when the metal thermal conductor J is thermally deformed in a convex shape at the center in the longitudinal direction where heat dissipation is less than that at the longitudinal ends, a gap is formed between the fixing belts at both longitudinal ends. As described above, there is a problem that abnormal heat generation occurs due to difficulty in heat transfer.

  An object of the present invention is to prevent abnormal overheating of a member used for fixing in view of the problems in the above-described conventional fixing device, in particular, a fixing device using a type in which a fixing belt moves on a member surface facing a pressure roller. An object of the present invention is to provide a fixing device and an image forming apparatus having a configuration capable of preventing thermal destruction of a fixing device when a member having a small heat capacity such as a fixing belt is used.

  In order to achieve this object, the present invention provides a rotatable endless flexible fixing belt, a nip forming member disposed inside the fixing belt, and the nip forming member. A support member that supports the belt on the side opposite to the side facing the belt, and the flexible fixing belt is mounted on an outer surface so as to form a loop, and the nip forming member and the support member are disposed therein. A pipe-shaped heat conductor that heats the flexible fixing belt by being heated by a heat source disposed below the support member; and a fixing belt that is in contact with the nip forming member with the fixing belt interposed therebetween. An opposite rotator that forms a nip portion between the pipe-shaped heat conductor and the pipe-shaped heat conductor between the inner surface of the pipe-shaped heat conductor at a position opposite to the heat source. Can be contacted during thermal deformation of In the fixing device, characterized in that deformation suppressing member disposed to have a such gap is provided.

According to the present invention, the deformation suppressing member that suppresses the thermal deformation of the pipe-shaped heat conductor is provided at a position opposite to the heat source provided inside the pipe-shaped heat conductor. When thermal deformation occurs when a temperature difference occurs between the position facing the heat source in the body and the position opposite to the heat source, in other words, the position far from the heat source, the amount of deformation is deformed between the deformation suppressing member and the pipe shape. It is suppressed by contact with the heat conductor.
As a result, when the temperature difference between the position facing the heat source in the pipe-shaped heat conductor and the position opposite to the heat source becomes large, particularly at the start of heating, the pipe-shaped heat conductor Abnormality due to continued heating of the pipe-shaped heat conductor itself that occurs when the gap is created by preventing the gap from being formed between the pipe-shaped heat conductor and the flexible fixing belt when the thermal deformation becomes large Overheating can be prevented in advance.

1 is a diagram for explaining a configuration of an image forming apparatus using a fixing device according to an embodiment of the present invention. FIG. FIG. 2 is a schematic diagram for explaining a configuration of a fixing device used in the image forming apparatus shown in FIG. 1. FIG. 3 is an arrow view in the direction indicated by reference numerals (3)-(3) in FIG. FIG. 4 is an enlarged view of a part of the configuration shown in FIG. 3. It is a schematic diagram for explaining one of conventional examples of a fixing device using a belt. It is a schematic diagram for explaining another conventional example of a fixing device using a belt.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, and a cleaning device. A backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2M, 2C, and 2K containing replenishing toner are detachably attached to the bottle container 2. A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 that stores paper P as a recording medium, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like are provided. Here, the recording medium includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet and the like in addition to plain paper. Although not shown, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the printer main body.

Next, the configuration of the fixing device 20 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 20 has a loop-like flexible fixing belt 21 (hereinafter referred to as a fixing belt for convenience) and a nip forming member disposed inside the fixing belt 21. 22, a support member 23 that supports the nip forming member 22 on the side opposite to the side facing the fixing belt 21, and the fixing belt 21 is fitted on the outer surface so as to form a loop, and a nip is formed inside. A member 22 and a support member 23 are arranged, and a pipe-like heat conductor 25 that heats the fixing belt 21 by a halogen heater 24 that is a heat source arranged in three quadrants in the loop of the fixing belt 21, and the fixing belt 21. A pressure roller 26 as a counter rotating body that forms a nip portion with the fixing belt by facing the nip forming member 22 across the nip is provided as a main portion. Although not shown, the fixing device 20 is provided with a temperature detection sensor for detecting the surface temperature of the fixing belt 21 and performing heating control.

The fixing belt 21 is a member that is heated by heat transfer when the pipe-shaped heat conductor 25 in which the fixing belt 21 is mounted is heated by the halogen heater 24, and an elastic layer and a release layer are sequentially laminated on the base material. The overall thickness is set to 1 mm or less.
The base material of the fixing belt 21 has a layer thickness of 25 to 35 μm, and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.
The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber.
By providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the nip portion are not formed, and heat is uniformly transmitted to the toner image T on the paper P, so that generation of a scum skin image is suppressed.
The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, and includes PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), PTFE (tetrafluoroethylene resin), polyimide, polyetherimide, It is made of a material such as PES (polyether sulfide).
By providing the release layer, the releasability (peelability) for the toner T (toner image) is secured.
Further, the diameter of the fixing belt 21 is set to be 15 to 120 mm, and is set to 30 mm in this embodiment.

The pipe-shaped heat conductor 25 is made of a metal pipe having high strength and low thermal conductivity, such as stainless steel, heat-resistant rope, nickel, or the like. The thickness as a pipe is set to 0.1 to 0.2 mm.
The nip forming member 22 disposed inside the pipe-shaped heat conductor 25 has a concave curved surface set to R25 to R60 corresponding to the radius of curvature of the pressure roller 26 on the surface facing the pressure roller. Is formed. Thus, a fixing nip portion of the fixing belt 21 that secures a contact area with the pressure roller 26 and moves between these areas is configured.

In the fixing nip portion, the fixing belt 21 is pressed against the nip forming member 22 having a concave shape by the pressure roller 26, so that the fixing belt 21 has a concave shape of the nip forming member 22 in the vicinity of the upstream portion and the downstream portion of the fixing nip portion. Keep the shape along.
In this state, the fixing belt 21 reaches the heating contact portion of the semi-cylindrical pipe-shaped heat conductor 25 heated by the halogen heater 24 that is a heat source, that is, the upstream side of the fixing nip portion in the moving direction of the fixing belt 21. By being in contact with the front surface, the heat is transferred by heat transfer from the pipe-shaped heat conductor 25, and the pipe-shaped heat conductor 25 and the heating element are added on the upstream side and the downstream side across the fixing nip portion in the moving direction of the fixing belt 21. The shape has a slack that does not contact the pressure roller 26.

The support member 23 described above has a reinforcing portion 23A that extends in the radial direction in the loop of the fixing belt 21 from the side opposite to the belt-facing surface of the nip forming member 22, and the pressing load from the pressure roller 26 causes the nip forming member to be pressed. The bending rigidity when acting on 22 is increased.
The support member 23 is also heated when the halogen heater 24 is in operation, but wasteful energy consumption can be suppressed by performing heat insulation or mirror treatment on the surface of the support to prevent heating. .

  The halogen heater 24 used as a heat source is arranged in a three-quadrant position with respect to the reinforcing portion 23A of the support member 23 in the loop of the fixing belt 21, and heats the pipe-shaped heat conductor 25.

  On the other hand, a deformation suppressing member 27 is disposed at a position opposite to the position of the halogen heater 24 in the loop of the fixing belt 21, that is, at a position in two quadrants with respect to the reinforcing portion 23 </ b> A of the support member 23 in the loop.

The reason why the deformation suppressing member 27 is provided is as follows.
In the pipe-shaped heat conductor 25, a temperature gradient is generated between a region facing the halogen heater 24 and a region not facing the halogen heater 24 with the reinforcing portion 23A of the support member 23 as a boundary. Since the heat conductor 25 is heated from a cold state, thermal expansion occurs in a region facing the halogen heater 24 across the reinforcing portion 23A of the support member 23. As a result, in a region not facing the halogen heater 24, Thermal deformation of about 1.5 to 2.0 mm occurs toward the side facing the halogen heater 24 with the cross-sectional center of the pipe-shaped heat conductor 25 as a reference.
Such a phenomenon, that is, thermal deformation, is eliminated by relaxing the temperature gradient by transferring heat to the entire circumferential direction of the pipe-shaped heat conductor 25 as time elapses from the start of heating.

  When the thermal deformation occurs, a gap is generated between the fixing belt 21 and the pipe-shaped heat conductor 25. In the pipe-shaped heat conductor 25, an abnormality in which the temperature rise becomes significant due to the absence of a heat transfer target. A fever occurs. Such abnormal heat generation may cause thermal expansion in the center in the longitudinal direction where the heat radiation efficiency is lower than both ends in the longitudinal direction in the pipe-shaped heat conductor 25, and may cause deformation or breakage of the pipe-shaped heat conductor.

In the present embodiment, by suppressing thermal deformation of the pipe-shaped heat conductor 25, it is always possible to maintain contact with the fixing belt 21 that is a heat transfer target to prevent abnormal heat generation of the pipe-shaped heat conductor 25 itself. It has become.
That is, the deformation suppressing member 27 is disposed at a position opposite to the halogen heater 24 with a gap that can contact the inner surface of the pipe-shaped heat conductor 25 when the pipe-shaped heat conductor 25 is thermally deformed. ing.

  The above-described gap is set to a size that can reduce the amount of deformation when the pipe-shaped heat conductor 25 is thermally deformed, and is set to a range of 0.2 to 0.5 mm.

As shown in FIG. 3, the deformation suppressing member 27 in the present embodiment is configured by a plurality of rib-shaped members arranged along the longitudinal direction of the pipe-shaped heat conductor 25 on the upper surface of the reinforcing portion 23 </ b> A of the support member 23. ing.
The deformation suppressing member 27 made of a rib-shaped member is made of a material having a lower thermal conductivity than the pipe-shaped heat conductor 25. Specifically, the heat conductivity (20 W / m · Polyimide (PI), polyamide imide (PAI), polyethylene terephthalate (PET), liquid crystal having a thermal conductivity lower than (K to 95 W / m · K) (deformation suppressing member 27 <relationship of pipe-shaped thermal conductor 25) A heat resistant resin such as a polymer (LCP) or polyphenylene sulfide (PPS) is used.

  As described above, a plurality of rib-shaped deformation suppressing members 27 are arranged along the longitudinal direction of the pipe-shaped heat conductor 25, and the longitudinal direction thereof is substantially parallel to the moving direction of the fixing belt 21. Is set.

Since the present embodiment is configured as described above, when heating is started in the cold state, if the temperature rise in the region facing the halogen heater 24 in the pipe-shaped heat conductor 25 is started, Due to the expansion, thermal deformation occurs in which the region not facing the halogen heater 24 is displaced toward the thermally expanded region.
At this time, the region of the pipe-shaped heat conductor 25 that does not face the halogen heater 24 abuts against the deformation suppressing member 27, so that further deformation is suppressed.

On the other hand, since the deformation suppression member 27 is a plurality of rib-like members arranged along the longitudinal direction of the pipe-like heat conductor 25, the contact area with the pipe-like heat conductor 25 is reduced. The area from which heat is removed from the heat conductor 25 is reduced, and thereby the temperature unevenness in the longitudinal direction of the pipe heat conductor 25 can be reduced.
In such a configuration, the chance that the fixing belt 21 is separated from the pipe-shaped heat conductor 25 is reduced, and abnormal overheating is prevented by continuing heating to the pipe-shaped heat conductor 25.

Next, another embodiment according to the present invention will be described.
The deformation suppressing member 27 shown in FIG. 2 is a rib-like member, and the end portion on the side facing the pipe-like heat conductor 25 in the longitudinal direction has an R shape (see FIG. 4A). )) Or a triangular shape (see FIG. 4B).

  In the present embodiment, when the pipe-shaped heat conductor 25 and the deformation suppressing member 27 are in contact with each other, the contact surface on the deformation suppressing member 27 side is not surface contact. Generation of temperature unevenness in the longitudinal direction of the conductor 25 can be suppressed.

Further, as described above, the deformation suppressing member 27 described above is not limited to the direction of the rib-shaped longitudinal direction being parallel to the moving direction of the fixing belt 21, and is not limited to the moving direction of the fixing belt 21 as shown in FIG. 3. It is also possible to adopt a configuration in which it is inclined with respect to it.
In this configuration, when the pipe-shaped heat conductor 25 comes into contact with the deformation suppressing member 27, uniform contact is obtained in the lengthwise direction of the pipe-shaped heat conductor 25. Temperature unevenness can be prevented.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Fixing apparatus 21 Fixing belt 22 Nip forming member 23 Support member 23A Reinforcement part 24 Halogen heater 25 Pipe-shaped heat conductor 26 Pressure roller 27 Deformation suppression member

JP 2009-104001 A JP 2009-3410 A

Claims (7)

A rotatable endless flexible fixing belt;
A nip forming member disposed inside the fixing belt;
A support member for supporting the nip forming member on the side opposite to the side facing the flexible fixing belt;
The flexible fixing belt is mounted on the outer surface so as to form a loop, and the nip forming member and the supporting member are disposed inside and heated by a heat source disposed below the supporting member. A pipe-like heat conductor for heating the flexible fixing belt,
An opposing rotating body that forms a nip portion with the fixing belt by contacting the nip forming member with the fixing belt interposed therebetween,
The pipe-shaped heat conductor is disposed at a position opposite to the heat source with a gap that can contact the inner surface of the pipe-shaped heat conductor when the pipe-shaped heat conductor is thermally deformed. A fixing device, further comprising a deformation suppressing member.   2. The gap between the pipe-shaped heat conductor and the deformation suppressing member is set as a gap that can reduce a deformation amount during thermal deformation of the pipe-shaped heat conductor. Fixing device.   2. A plurality of the deformation suppressing members are arranged along a longitudinal direction of the pipe-shaped heat conductor, and a longitudinal direction substantially parallel to a moving direction of the flexible fixing belt is set. Or the fixing device according to 2.   4. The deformation suppressing member according to claim 1, wherein an end of the deformation suppressing member facing the pipe-shaped heat conductor in the longitudinal direction has an R shape or a triangular shape in plan view. The fixing device according to one.   5. The deformation suppressing member according to claim 1, wherein a longitudinal direction inclined with respect to a moving direction of the flexible fixing belt is set in the longitudinal direction. The fixing device described.   6. The deformation suppressing member is made of a material having a low thermal conductivity with respect to the pipe-shaped heat conductor (deformation suppressing member <pipe-shaped heat conductor). The fixing device according to 1.   An image forming apparatus using the fixing device according to claim 1 as a fixing device for fixing a toner image.

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