JP2013061608A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device enabling stable fixing processing for a long time even by using a planar heating body, and an image forming device equipped with the fixing device.SOLUTION: A fixing device includes: a fixing sleeve 21; a pressurizing roller 31; an abutting member 26 disposed on an inner peripheral side of the fixing sleeve 21, and abutting on the pressurizing roller 31 through the fixing sleeve 21 to form a nip portion; a planar heating body 22 having a heating surface contacted with an inner peripheral surface of the fixing sleeve 21, and heating the fixing sleeve 21; a heating body supporting member 23 for supporting the planar heating body 22 by clipping the planar heating body 22 between the fixing sleeve 21 and the heating body supporting member 23 from the inner peripheral side of the fixing sleeve 21; and a core holding member 28 for holding the abutting member 26 and the heating body supporting member 23. In an area 22h for supporting the heating surface of the planar heating body 22 of the heating body supporting member 23, when assuming the thickness of a part having the thinnest wall thickness as t, the linear expansion coefficient of the heating body supporting member 23 as α, a cylinder inner diameter of the fixing sleeve 21 as R, and the linear expansion coefficient of the fixing sleeve 21 as β, an expression αt≥βR is satisfied.

Description

  The present invention relates to a fixing device using a sheet heating element and an image forming apparatus such as a FAX, a printer, a copying machine, or a complex machine using an electrophotographic method, an electrostatic recording method, or the like equipped with the fixing device. is there.

  Conventionally, various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copying machines and printers, and are well known in the art. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. This process is established by a process in which the transferred image is transferred onto a recording paper by a transfer device to carry the image, and the toner image on the recording paper is fixed by a fixing device using pressure or heat.

  In this fixing device, a fixing member and a pressure member constituted by opposing rollers or belts or a combination thereof are arranged so as to contact each other to form a nip portion, and a recording sheet is sandwiched in the nip portion, Heat and pressure are applied to fix the toner image on the recording paper.

  As an example of the fixing device, a technique using a fixing belt stretched around a plurality of roller members as a fixing member is known (for example, see Patent Document 1). An apparatus using such a fixing belt is provided in a fixing belt (endless belt) as a fixing member, a plurality of roller members that stretch and support the fixing belt, and one of the plurality of roller members. And a heater, a pressure roller (pressure member), and the like. The heater heats the fixing belt via the roller member. Then, the toner image on the recording medium conveyed toward the nip formed between the fixing belt and the pressure roller is fixed on the recording medium by receiving heat and pressure at the nip. Belt fixing method).

Further, in the fixing device used in the image forming apparatus described above, there is a fixing device having a fixing member that is in sliding contact with the inner surface of a fixing member that is a rotating body.
For example, in Patent Document 2, a fixing nip portion is formed by sandwiching a heat-resistant film (fixing film) between a ceramic heater as a heating element and a pressure roller as a pressure member. A recording material on which an unfixed toner image to be image-fixed is formed and supported is introduced between the film and the pressure roller, and is nipped and conveyed together with the film. A film heating type fixing device is disclosed in which an unfixed toner image is fixed to a surface of a recording material by a pressure applied to a recording material through a fixing nip portion. This film heating type fixing device can be configured as an on-demand type device using a ceramic heater and a member having a low heat capacity as a film, and energizes the ceramic heater as a heat source only when the image forming apparatus performs image formation. Thus, it is only necessary to generate heat at a predetermined fixing temperature, the waiting time from the power-on of the image forming apparatus to the image forming executable state is short (quick start property), and the power consumption during standby is greatly reduced ( There are advantages such as power saving).

  In Patent Documents 3 and 4, a rotatable heat-fixing roll whose surface is elastically deformed, an endless belt (pressure belt) that can run while being in contact with the heat-fixing roll, and a non-rotation inside the endless belt The endless belt is placed in pressure contact with the heat fixing roll, a belt nip is provided between the endless belt and the heat fixing roll to allow recording paper to pass, and the surface of the heat fixing roll is elastic. A pressure belt type image fixing device having a pressure pad to be deformed has been proposed. According to this fixing method, the lower pressure member is used as a belt, and the contact area between the paper and the roll is widened to greatly improve the heat conduction efficiency, and it is possible to reduce the energy consumption and at the same time realize the miniaturization. It has become.

  However, although the fixing device described in Patent Document 1 described above is suitable for speeding up the device as compared with a device using a fixing roller, it is a warm-up time (a time required to reach a printable temperature). In addition, there is a limit to shortening the first print time (the time from when a print request is received until the print operation is performed and the paper discharge is completed).

On the other hand, the fixing device described in Patent Document 2 can reduce the warm-up time and the first print time by reducing the heat capacity, and also reduce the size of the device. However, the fixing device described in Patent Document 2 has a problem of durability and a problem of belt temperature stability. In other words, the wear resistance due to sliding between the ceramic heater, which is a heat source, and the inner surface of the belt is inadequate, and the surface that repeats continuous friction is roughened when operated for a long time, increasing the frictional resistance and making the belt run unstable. Or, a phenomenon such as an increase in the driving torque of the fixing device occurs, and as a result, the transfer paper forming the image slips and the image shifts, or the stress on the driving gear increases, causing damage to the gear. (Problem 1).
In the film heating type fixing device, since the belt is locally heated at the nip portion, when the rotating belt returns to the nip entrance, the belt temperature becomes the coldest state (especially at high speed rotation). , There was a problem that fixing failure was likely to occur (Problem 2).

  On the other hand, in Patent Document 3, a glass fiber sheet (PTFE-impregnated glass cloth) impregnated with PTFE as a low friction sheet (sheet-like sliding material) on the surface layer of the pressure pad is used, and the slidability of the belt inner surface and the fixing member is improved. Means for improving the problem are disclosed. However, such a pressure belt type fixing device (Patent Documents 3 and 4) has a problem that it takes a long time to warm up because the heat capacity of the fixing roller is large and the temperature rise is slow. (Problem 3).

  With respect to the above problems 1 to 3, in Patent Documents 5 and 6, a substantially pipe-shaped counter member (metal thermal conductor) disposed on the inner peripheral side of the endless fixing belt, and the counter member By providing a resistance heating element such as a ceramic heater that is disposed on the inner peripheral side and heats the opposing member, the entire fixing belt can be warmed, the warm-up time and the first print time can be shortened, and There has been proposed a fixing device that can solve the shortage of heat during high-speed rotation. However, this method is not sufficient in terms of shortening the warm-up time and the first print time because the heat of the resistance heating element is transmitted to the fixing belt through the opposing member (metal heat conductor).

  On the other hand, in Patent Document 7, an endless fixing belt, a pressure roller that presses against the fixing belt and forms a nip portion on which a recording medium is conveyed, and an inner peripheral surface side of the fixing belt are fixed. And a resistance heating element that heats the fixing belt, and a fixing device is proposed in which the resistance heating element is arranged with a small gap so as not to come into pressure contact with the inner peripheral surface of the fixing belt. . As a result, even when the warm-up time and the first print time are shortened and the apparatus is speeded up, it is possible to prevent problems such as defective fixing and wear and damage of the fixing member and the resistance heating element. It is supposed to be.

  However, in the fixing device described in Patent Document 7, stress due to rotation and vibration of the pressure roller repeatedly acts on the resistance heating element, and the resistance heating element is repeatedly bent. Since the body is made of a metal material, the fixing belt may not be appropriately heated due to fatigue breakage caused by repeated bending.

  Therefore, in Patent Document 8, a resistance heating layer in which conductive particles are dispersed in a heat-resistant resin and an electrode layer that supplies power to the resistance heating layer are formed on an insulating base layer. A flexible heating sheet (planar heating element) having a predetermined width and length corresponding to the axial direction and the circumferential direction of the fixing member is applied to the inner peripheral surface of the fixing sleeve of the rotating endless belt. A fixing device that heats the fixing sleeve in contact with the fixing sleeve has been proposed. As a result, since the heat capacity of the fixing sleeve and the sheet heating element is small, the warm-up time and the first print time can be shortened while suppressing energy consumption. The heating sheet in the sheet heating element is a resin-based sheet. For this reason, stress resulting from rotation and vibration of the pressure member repeatedly acts on the heat generating sheet, and even if the heat generating sheet is repeatedly bent, fatigue damage does not occur and long-time operation is possible.

  However, in the fixing device described in Patent Document 8, even if the fixing process is started without any problem, a problem that the planar heating element as a heating unit fails during operation thereafter.

  The present invention has been made in view of the above-described problems in the prior art, and provides a fixing device capable of stable fixing processing for a long time even when a planar heating element is used, and an image forming apparatus including the fixing device. The purpose is to do.

  The present invention provided to solve the above problems includes a fixing member (fixing sleeve 21) that is a rotating cylindrical endless belt, and a pressure member (pressure roller 31) that contacts the outer peripheral surface of the fixing member. A contact member (contact member 26) disposed on the inner peripheral side of the fixing member and contacting the pressure member via the fixing member to form a nip portion, and an inner peripheral surface of the fixing member The sheet heating element is supported between the sheet heating element (sheet heating element 22) that heats the fixing member by contacting the heating surface and the fixing member from the inner peripheral side of the fixing member. A heating element support member (heating element support member 23), and a core holding member (core holding member 28) that holds the contact member and the heating element support member inside a cylinder of the fixing member, Of the region of the heating element support member that supports the heating surface of the planar heating element, The thickness of the portion where the thickness of the heating element support member in the radial direction from the rotation center of the fixing member is t, the linear expansion coefficient of the heating element support member is α, and the cylindrical inner diameter of the fixing member is R The fixing device (fixing device 20) is characterized in that αt ≧ βR is satisfied when the linear expansion coefficient of the fixing member is β.

  According to the fixing device of the present invention, even when the fixing member and the heating element support member are thermally expanded during the operation of the apparatus, the formula αt ≧ βR is satisfied, so the heating element support member fixes the entire heating surface of the planar heating element. By supporting the member in close contact with the member, it is possible to prevent overheating of the heating surface of the sheet heating element, and to realize a stable fixing process for a long time.

1 is a cross-sectional view illustrating a configuration of a fixing device according to a first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an axial direction and a circumferential direction of a fixing sleeve. FIG. 2 is a cross-sectional view illustrating a positional relationship among a fixing sleeve, a flange member, and a side plate in the fixing device of FIG. 1. It is sectional drawing which shows the structure of the heat generating sheet used by this invention. It is a perspective view which shows the example which assembled the planar heating element and the heating element support member. It is a perspective view which shows the example which assembled the planar heating element, the heating element support member, and the terminal block stay. It is a perspective view which shows the connection state of the electrode terminal of the planar heating element on the terminal stand stay of FIG. 6, and a feeder. FIG. 2 is a cross-sectional view illustrating a configuration of an internal mechanism unit on a fixing sleeve side in the fixing device of FIG. 1. It is sectional drawing which shows the example (1) of adhesion of the planar heating element to a heating element support member. It is sectional drawing which shows the example (2) of adhesion of the planar heating element to a heating element support member. It is a figure which shows the structural example (1) of the planar heating element used by this invention. It is a top view which shows the structural example (2) of the planar heating element used by this invention. It is a figure which shows the structural example (3) of the planar heating element used by this invention on the upper surface. It is a top view which shows the structural example (4) of the planar heating element used by this invention. FIG. 6 is a cross-sectional view illustrating a configuration of a fixing device according to a second embodiment of the present invention. FIG. 16 is a perspective view illustrating a configuration of a rotation support member used in the fixing device of FIG. 15. FIG. 16 is a schematic diagram illustrating a configuration of an internal mechanism unit on a fixing sleeve side in the fixing device of FIG. 15. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to the present invention.

The configuration of the fixing device according to the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view showing the configuration of the fixing device according to the first embodiment of the present invention.
As shown in FIG. 1, the fixing device 20 includes a fixing member (fixing sleeve 21 (also referred to as a fixing rotating body)) composed of a rotating endless belt, and a pressing member (pressurizing) that contacts the outer peripheral surface of the fixing member. A roller 31 (also referred to as a pressure rotator) and an abutting member (abutting member) that is disposed on the inner peripheral side of the fixing member and forms a nip portion by abutting the pressure member via the fixing member. 26), a planar heating element (planar heating element 22) that is disposed on or in close contact with the fixing member on the inner peripheral side of the fixing member, and directly or indirectly heats the fixing member; A heating element support member (heating element support member 23) disposed on the inner peripheral side of the fixing member so as to sandwich the planar heating element between the fixing member and supporting the planar heating element at a predetermined position; Is provided. At this time, the heat generating surface (heating region 22h, which is a heat generating sheet 22s described later) of the sheet heating element 22 is in contact with the inner peripheral surface of the fixing sleeve 21 and directly heated. FIG. 1 shows a state in which the heat generating surface of the sheet heating element 22 is not generating heat and the fixing device 20 is cooled to about room temperature (cooling state).

  Here, the fixing sleeve 21 is a cylindrical endless belt having a length corresponding to the width of the recording medium P through which the axial direction passes, and having a thickness of, for example, 30 to 50 μm. At least a release layer is formed on a base material made of the above metal material, and the outer diameter is 30 mm. Hereinafter, the pipe longitudinal direction of the fixing sleeve 21 is referred to as an axial direction as shown in FIG. 2A, and the pipe circumferential direction of the fixing sleeve 21 is referred to as a circumferential direction as shown in FIG.

  As a material for forming the base material of the fixing sleeve 21, a metal material having good heat conductivity such as iron, cobalt, nickel, or an alloy thereof can be used. Alternatively, a heat resistant resin may be used.

  The release layer of the fixing sleeve 21 is obtained by coating a fluorine compound such as PFA in a tube shape, and its thickness is 50 μm. The release layer is for enhancing the toner release property on the surface of the fixing sleeve 21 with which the toner image (toner) T on the recording medium P is in direct contact.

  Further, as shown in FIG. 3, both ends of the fixing sleeve 21 are rotatably supported by flange members 30 fixed at predetermined positions on the side plate 42 of the fixing device 20. Specifically, the flange member 30 abuts against the axial end portion of the fixing sleeve 21 and has a flange portion 30b having an axial detent flange surface of the fixing sleeve 21, and a flange surface of the flange portion 30b. A cylindrical portion 30 a, a flange portion 30 b is fixed to the side plate 42 of the fixing device 20, and the cylindrical portion 30 a is inserted into the inner diameter portion of the axial end portion of the fixing sleeve 21. The outer shape (cross-sectional shape) of the cylindrical portion 30 a has a substantially circular shape, preferably a true circular shape, except for the portion corresponding to the contact member 26, and the outer diameter thereof is the same as or slightly smaller than the inner diameter of the fixing sleeve 21. It is getting smaller. As a result, the cylindrical portion 30a inserted into the inner diameter portion at both axial ends of the fixing sleeve 21 holds the fixing sleeve 21 in a circular shape in a rotatable state. Therefore, the center of the circle of the cylindrical portion 30a becomes the rotation center O of the fixing sleeve 21 (FIG. 1).

  The pressure roller 31 is formed by sequentially forming a heat-resistant elastic layer such as silicone rubber (solid rubber) and a release layer on a metal core made of a metal material such as aluminum or copper, and has an outer diameter of 30 mm. It has become. The elastic layer is formed to have a thickness of 2 mm. The release layer is coated with a PFA tube and is formed to have a thickness of 50 μm. Further, a heating element such as a halogen heater may be incorporated in the cored bar as necessary. The pressure roller 31 is pressed against the contact member 26 via the fixing sleeve 21 by a pressing means (not shown), and the pressure contact portion forms a nip portion where the fixing sleeve 21 side is recessed. Then, the recording medium P is conveyed to the nip portion.

  Further, the pressure roller 31 is rotationally driven by a driving mechanism (not shown) while being in pressure contact with the fixing sleeve 21 (rotates in the clockwise direction in FIG. 1), and the fixing sleeve 21 is rotated along with the rotation of the pressure roller 31. It will rotate (rotating counterclockwise in FIG. 1).

  The contact member 26 has a length in the axial direction of the fixing sleeve 21, and at least a portion in pressure contact with the pressure roller 31 through the fixing sleeve 21 is made of an elastic body having heat resistance such as fluorine rubber. In addition, the core holding member 28 is fixed in a state of being held at a predetermined position on the inner peripheral side of the fixing sleeve 21. Further, the portion of the contact portion 26 that contacts the inner peripheral surface of the fixing sleeve 21 is preferably made of a material having excellent sliding properties and wear resistance, such as a Teflon (registered trademark) sheet.

  The core holding member 28 is a rigid member having a length corresponding to the axial length of the fixing sleeve 21 and having an H-shaped cross section. It is arranged at a substantially central portion on the circumferential side.

  The core holding member 28 holds various members arranged on the inner peripheral side of the fixing sleeve 21 at predetermined positions. For example, one of the H-shaped core holding members 28 (the side facing the pressure roller 31). The abutting member 26 is housed and held in the recessed portion of (), and is supported from the side opposite to the nip portion so that the abutting member 26 is not greatly deformed even when pressed by the pressure roller 31. The core holding member 28 holds the contact member 26 so as to slightly protrude from the core holding member 28 toward the pressure roller 31, and the core holding member 28 (or a heating pipe 27 described later) at the nip portion. Is arranged so as not to contact the fixing sleeve 21.

  In addition, a concave portion of the other of the H shapes of the core holding member 28 (the side opposite to the pressure roller 31 side) has a length corresponding to the axial length of the fixing sleeve 21 and has a T-shaped cross section. A terminal block stay 24 having a shape and a power supply line 25 that extends on the terminal block stay 24 and supplies electric power from the outside are housed and held. Further, the heating element support member 23 is held on the H-shaped outer surface of the core holding member 28. In FIG. 1, the heating element support member 23 is held in a region corresponding to a lower half circumference of the fixing sleeve 21 (a half circumference on the entry side of the nip portion). At this time, the heating element support member 23 and the core holding member 28 may be bonded in consideration of assembly. Alternatively, in order to prevent heat transfer from the heating element support member 23 side to the core holding member 28 side, both may be non-bonded.

  The heating element support member 23 supports the planar heating element 22 in order to place the heating surface of the planar heating element 22 in contact with the inner peripheral surface of the fixing sleeve 21. Therefore, the heating element support member 23 has an outer peripheral surface having a predetermined arc length along the inner peripheral surface of the fixing sleeve 21 having a circular cross-sectional shape.

  Further, the radius of the arc in the heating element support member 23, that is, the distance from the rotation center O of the fixing sleeve 21 to the outer peripheral surface of the heating element support member 23 is substantially the same as the inner diameter R of the fixing sleeve 21. As a result, the entire heating surface of the sheet heating element 22 supported by the heating element support member 23 comes into close contact with the inner peripheral surface of the fixing sleeve 21 to efficiently heat the fixing sleeve 21. Note that the radius of the arc in the heating element support member 23 (the distance from the rotation center O of the fixing sleeve 21 to the outer peripheral surface of the heating element support member 23) is, for example, from the rotation center O of the fixing sleeve 21 to the heating element in FIG. This is the total of the distance a (the portion of the core holding member 28) to the support member 23 and the thickness t of the heating element support member 23 in the radial direction of the fixing sleeve 21.

  Further, the heating element support member 23 has heat resistance sufficient to withstand the heat generation of the planar heating element 22 and planar heating without deformation when the rotating fixing sleeve 21 contacts the adjacent planar heating element 22. It is preferable to have strength sufficient to support the body 22 and heat insulation so that the heat of the planar heating element 22 is transmitted to the fixing sleeve 21 side without being transmitted to the core holding member 28 side. -It is preferable to consist of ether-ketone resin (PEEK). When the sheet heating element 22 comes into contact with the inner peripheral surface of the fixing sleeve 21, the force that the rotating fixing sleeve 21 pulls the sheet heating element 22 toward the nip portion acts on the sheet heating element 22. The heating element support member 23 needs to be strong enough to support the planar heating element 22 without being deformed. In this case, polyether ether ketone resin (PEEK) is also preferable. In addition, a separate solid resin member may be provided in the interior of the polyether-ether-ketone resin (PEEK) molded body to improve the rigidity.

  As shown in FIG. 4, the heating surface of the planar heating element 22 includes a resistance heating layer 22b in which conductive particles are dispersed in a heat resistant resin on an insulating base layer 22a, and the resistance heating layer 22b. And an electrode layer 22c for supplying electric power to the fixing sleeve 21. The electrode layer 22c preferably includes a heat generating sheet 22s having a predetermined width and length corresponding to the axial direction and the circumferential direction of the fixing sleeve 21 and exhibiting flexibility. On the base layer 22a, an insulating layer 22d is provided that insulates between the resistance heating layer 22b and an electrode layer 22c of another power feeding system adjacent to the base layer 22a or between an edge portion of the heating sheet 22s and the outside. The planar heating element 22 includes an electrode terminal 22e (not shown, described later) that is connected to the electrode layer 22c at the end of the heating sheet 22s and supplies power supplied from the power supply line 25 to the electrode layer 22c. .

  Further, the thickness of the heat generating sheet 22s is about 0.1 to 1 mm, and is flexible enough to be wound around at least the outer peripheral surface of the heat generating element support member 23.

  Here, the base layer 22a is a thin-film elastic film made of a resin having a certain degree of heat resistance such as PET or polyimide resin, and among these, a film member made of polyimide resin is preferable. Thereby, heat resistance, insulation, and a certain amount of flexibility (flexibility) are provided.

  The resistance heating layer 22b is a conductive thin film in which conductive particles such as carbon particles and metal particles are uniformly dispersed in a heat-resistant resin such as polyimide resin. It is configured to generate heat. Such a resistance heating layer 22b may be formed by applying a coating material in which conductive particles such as carbon particles and metal particles are dispersed in a precursor of a heat resistant resin such as polyimide resin on the base layer 22a.

  The resistance heating layer 22b is formed by first forming a thin conductive layer made of carbon particles or metal particles on the base layer 22a, and then laminating an insulating thin film made of a heat resistant resin such as polyimide resin on the conductive layer. It may be integrated.

  The carbon particles used for the resistance heating layer 22b may be ordinary carbon black powder, but may be carbon nanoparticles composed of at least one of carbon nanofibers, carbon nanotubes, and carbon microcoils.

  Further, the metal particles are particles made of Ag, Al, Ni, etc., and the shape thereof may be granular or may be a filament shape.

  The insulating layer 22d may be formed by applying an insulating material made of the same heat resistant resin as the base layer 22a such as polyimide resin.

  The electrode layer 22c may be formed by applying a conductive paste such as conductive ink or Ag, or may be formed by bonding a metal foil or a metal net.

Since the heat generating sheet 22s constituting the sheet heating element 22 is a thin sheet, its heat capacity is small and rapid heating is possible. The amount of heat generated can be arbitrarily set by the volume resistivity of the resistance heat generating layer 22b. . That is, the heat generation amount can be adjusted by the constituent material, shape, size, dispersion amount, etc. of the conductive particles constituting the resistance heat generation layer 22b. For example, the heat generation amount per unit area is 35 W / cm ² , It is possible to realize the planar heating element 22 that can output about 1200 W of electric power. In this case, the heat generating sheet 22s has a size of about 20 cm in width (axial direction) and 2 cm in length (circumferential direction), for example.

  Further, when a sheet heating element made of a metal filament such as stainless steel is used, the surface of the sheet heating element is uneven due to the presence of the filament. When sliding with the peripheral surface, the surface is easily worn, but the heat generating sheet 22s used in the present invention is flat with no unevenness as described above. Excellent durability against sliding. Furthermore, it is preferable to coat the surface of the resistance heating layer 22b of the heating sheet 22s with a fluororesin because durability against contact with the inner peripheral surface of the fixing sleeve 21 is further improved.

  As the arrangement region of the heat generating sheet 22s on the inner peripheral surface of the fixing sleeve 21, FIG. 1 shows a configuration in which the heat generating sheet 22s is disposed from the position opposite to the nip portion on the inner peripheral surface of the fixing sleeve 21 to the front of the nip portion. However, the present invention is not limited to this. For example, the heat generating sheet 22s may be disposed up to the position of the nip portion, or may be disposed on the entire inner peripheral surface excluding the nip portion of the fixing sleeve 21. .

The fixing device 20 configured as described above operates as follows.
First, when the image forming apparatus receives an output signal (for example, when there is a print request to the image forming apparatus by operation of a user's operation panel or communication from a personal computer), in the fixing device 20, the pressure roller 31 is moved to the fixing sleeve 21. Is pressed by the contact member 26 to form a nip portion.
Next, when the pressure roller 31 is driven to rotate in the clockwise direction in FIG. 1 by a driving device (not shown), the fixing sleeve 21 is also rotated in the clockwise direction. At this time, the sheet heating element 22 is in a state of being in contact with and sliding on the inner peripheral surface of the fixing sleeve 21 while being supported by the heating element support member 23.
In synchronization therewith, electric power is supplied from an external power source or an internal power storage device to a sheet heating element 22 through a feeder line 25 (described later), the heating sheet 22s generates heat, and the fixing sleeve 21 comes into contact with the heating sheet 22s. Therefore, heat is transferred efficiently and heated rapidly. The operation of the driving device and the heating by the planar heating element 22 do not need to be started at the same time, but may be started with a time difference as appropriate.
At this time, it is detected by a temperature detecting means (not shown) arranged in contact or non-contact from the inside of the heating element support member 23 on the upstream side of the nip portion and outside the fixing sleeve 21 or inside the heating sheet 22s. The heating by the planar heating element 22 is controlled so that the nip portion has a predetermined temperature depending on the temperature of the recording medium. After the temperature is raised to a temperature necessary for fixing, the sheet is held and passed through the recording medium P. Is started.

  As described above, in the fixing device of the present invention, the heat capacity of the fixing sleeve 21 and the sheet heating element 22 is small, so that it is possible to shorten the warm-up time and the first print time while saving energy. Further, since the heat generating sheet 22s in the sheet heating element 22 is a resin-based sheet, the stress caused by the rotation and vibration of the pressure roller 31 repeatedly acts on the heat generating sheet 22s, and the heat generating sheet 22s is repeatedly bent. Even if it breaks, it will not be damaged by fatigue and can be operated for a long time.

  When there is no output signal to the image forming apparatus, the pressure roller 31 and the fixing sleeve 21 are normally not rotated and the sheet heating element 22 is not energized in order to reduce power consumption. When re-outputting is to be started (returned), the sheet heating element 22 can be energized even when the pressure roller 31 and the fixing sleeve 21 are not rotated. In this case, the sheet heating element 22 is energized to keep the entire fixing sleeve 21 warm.

By the way, when the fixing process is performed using the fixing device having the configuration shown in FIG. 1, even if the fixing process is started without any problem, a problem that the planar heating element 22 breaks down during the operation thereafter.
The inventors investigated the cause, and when the operation of the fixing device is started, the heat generating surface (heat generating sheet 22s) of the sheet heating element 22 generates heat to heat the fixing sleeve 21. At this time, the fixing sleeve 21 is heated. And the heat generating member support member 23 is thermally expanded, and the difference between the inner diameter of the fixing sleeve 21 and the distance from the rotation center O of the fixing sleeve 21 to the outer peripheral surface of the heat generating member support member 23 increases. It was found that a minute gap was generated between the surface and the heat generating surface of the sheet heating element 22. That is, as a result, the heat transfer from the heat generating surface (heat generating sheet 22s) of the sheet heating element 22 to the fixing sleeve 21 is interrupted, so that the temperature of the heat generating surface (heat generating sheet 22s) of the sheet heating element 22 suddenly increases. As a result, the heat generating sheet 22s broke down due to exceeding its heat resistance temperature.
Based on these findings, the inventors have intensively studied to solve the problem and have arrived at the present invention. That is, the fixing device according to the present invention includes a fixing member (fixing sleeve 21) that is a rotating cylindrical endless belt, a pressure member (pressure roller 31) that contacts the outer peripheral surface of the fixing member, and A contact member (contact member 26) which is disposed on the inner peripheral side of the fixing member and contacts the pressure member via the fixing member to form a nip portion, and a heat generating surface on the inner peripheral surface of the fixing member A sheet heating element (sheet heating element 22) that contacts and heats the fixing member, and a heating element that supports the sheet heating element sandwiched between the fixing member from the inner peripheral side of the fixing member And a core holding member (core holding member) that holds the heating member support member inside the cylinder of the fixing member. A region for supporting the heating surface of the planar heating element of the support member (heating region 22h) ) In the radial direction from the rotation center (rotation center O) of the fixing member to t, and the linear expansion coefficient of the heating element support member is α. When the cylindrical inner diameter of the fixing member is R and the linear expansion coefficient of the fixing member is β, αt ≧ βR is satisfied.
Hereinafter, the formula αt ≧ βR, which is a fundamental part of the present invention, will be described.

First, when the fixing sleeve 21 is heated by the heat generated by the planar heating element 22, it expands thermally. At this time, when the temperature of the fixing sleeve 21 is increased by the temperature ΔT, the outer peripheral length of the fixing sleeve 21 is expressed by the following equation (1).
The outer peripheral length of the fixing sleeve 21 = 2πR + 2πR × β × ΔT (1)
R is a cylindrical inner diameter of the fixing sleeve 21 (a distance from the rotation center O of the fixing sleeve 21 to the inner peripheral surface), and β is a linear expansion coefficient of the fixing sleeve 21.

Therefore, the outer diameter of the thermally expanded fixing sleeve 21 is expressed by the following equation (2).
Inner diameter of fixing sleeve 21 = (2πR + 2πR × β × ΔT) / 2π
= R + R × β × ΔT (2)
Therefore, the increase in the inner diameter of the fixing sleeve 21 due to thermal expansion is (R × β × ΔT).

Further, when the heating element support member 23 is heated by the heat generated by the planar heating element 22, it expands thermally. At this time, assuming that the core holding member 28 does not thermally expand, the distance a from the rotation center O of the fixing sleeve 21 to the outer peripheral surface of the heating element support member 23 does not change the distance a of the core holding member 28, and the heat generation Since the part of the body support member 23 expands, the heating element support member 23 increases by an amount corresponding to the expansion, rather than during cooling. At this time, the smallest increment is the rotation center O of the fixing sleeve 21 in the region 22h (that is, the heating region (heating surface)) of the heating element support member 23 that supports the heating sheet 22s of the planar heating element 22. The thickness of the heating element support member 23 in the radial direction is the thinnest part. As in the case of the fixing sleeve 21, when the temperature of the heating element support member 23 is increased by the temperature ΔT, the outer diameter of the heating element support member 23 that passes from the rotation center O of the fixing sleeve 21 to the position is expressed by the following equation (3). become that way.
Peripheral diameter of the heating element support member 23 = a + t + t × α × ΔT (3)
Note that t is the thickness of the heating element support member 23 in the radial direction from the rotation center O of the fixing sleeve 21 in the region 22h of the heating element support member 23 that supports the heating sheet 22s of the planar heating element 22. The thickness of the thin portion, α, is the linear expansion coefficient of the heating element support member 23.
Therefore, the increase in the outer diameter of the heating element support member 23 due to thermal expansion is (t × α × ΔT).

Here, in the present invention, the outer diameter increase (t × α × ΔT) of the heating element support member 23 due to thermal expansion is equal to or greater than the inner diameter increase (R × β × ΔT) of the fixing sleeve 21 due to thermal expansion, It shall satisfy the following formula (4).
αt ≧ βR (4)

  As a result, even when the fixing sleeve 21 and the heating element support member 23 are thermally expanded during operation of the apparatus, at least from the inner diameter of the fixing sleeve 21 and the rotation center O of the fixing sleeve 21 to the outer peripheral surface of the heating element support member 23 than during cooling. Therefore, the difference between the distance and the heat generating surface of the fixing sleeve 21 and the heat generating surface of the sheet heating element 22 can be prevented from being generated and the two can be brought into close contact with each other. Further, heat can be efficiently transmitted from the heat generating surface (heat generating sheet 22s) of the sheet heating element 22 to the fixing sleeve 21, and overheating of the heat generating sheet 22s can be prevented. Therefore, the fixing device 20 can perform a long-time stable fixing process.

In order to satisfy Equation (4), in the fixing device 20, it is preferable to select materials for the fixing sleeve 21 and the heating element support member 23 and set their respective thermal expansion coefficients to appropriate values. For example, the material constituting the fixing sleeve 21 (in this case, the base material) is nickel (thermal expansion coefficient: 1.37 × 10 ⁻⁵ / ° C.), and the material constituting the heating element support member 23 is polyether ether. A ketone resin (linear expansion coefficient: 4.8 × 10 ⁻⁵ / ° C.) is used.
Alternatively, in order to satisfy the formula (4), in the fixing device 20, the thickness t of the heating element support member 23 and the cylindrical inner diameter R of the fixing sleeve 21 may be adjusted.

Next, assembly on the fixing sleeve 21 side in the fixing device 20 is performed, for example, according to the following procedure.
(S11) First, the heating sheet 22s of the planar heating element 22 is attached along the outer peripheral surface of the heating element support member 23 with an adhesive (FIG. 5). At this time, it is desirable to use an adhesive having a low thermal conductivity in order to prevent heat from flowing to the heating element support member 23.

  At this time, all of the plurality of electrode terminals 22e (electrode terminals 22e1, 22e2) connected to the electrode layer 22c are provided at one end of the heat generating sheet 22s corresponding to the circumferential direction of the fixing sleeve 21. In FIG. 5, on one side of the heat generating sheet 22 s corresponding to the circumferential direction of the fixing sleeve 21 (end opposite to the pressure roller 31 (nip part) side) (end side), One electrode terminal 22e1, 22e2 is provided at each of both ends corresponding to the axial direction of the fixing sleeve 21.

  This is for the following reason. That is, the sheet heating element 22 is provided with at least two electrode terminals 22e for supplying power to the resistance heating layer 22b. For example, two electrode terminals 22e are provided at both ends of the heating sheet 22s. When provided one by one, it is necessary to connect a power harness or the like required for power supply to the electrode terminals 22e at both ends. At this time, the heat generating sheet 22s itself is a thin film, and since the rigidity of the heat generating sheet 22s itself is low, it is necessary to provide a terminal block for connecting a power supply harness at both ends of the heat generating sheet 22s, which increases the size of the apparatus. Therefore, in the present invention, the size of the apparatus is reduced by providing the electrode terminal 22e collectively at one end of the heat generating sheet 22s and supplying power.

  Although it is conceivable to arrange the electrode terminal 22e at the end of the heat generating sheet 22s corresponding to the axial direction of the fixing sleeve 21, when the heat generating sheet 22s is attached along the outer peripheral surface of the heat generating member support member 23, The electrode terminal 22e also bends, and the electrode part for supplying power causes inconveniences such as deformation at the time of screw fastening, complication of the terminal member, and deterioration in assembling property. Therefore, in the present invention, a plurality of electrode terminals 22e are arranged at one end of the heat generating sheet 22s corresponding to the circumferential direction of the fixing sleeve 21, and thereby the heat generating sheet 22s along the outer peripheral surface of the heat generating member support member 23. Even when affixed, the electrode terminal 22e is not curved and good assemblability is realized.

(S12) Next, the heating sheet 22s in the vicinity of the electrode terminal 22e is bent along the edge of the heating element support member 23 so that the electrode terminal 22e faces the center side of the circular fixing sleeve 21, and then the electrode terminal 22e1. , 22e2 are connected and fixed to the feeder line 25 on the terminal block stay 24 (FIGS. 6 and 7). The connection and fixing of the electrode terminals 22e1 and 22e2 on the terminal block stay 24 may be performed by screw fastening as shown in FIG. Further, a fixing terminal 22f extending for fixing the heat generating sheet 22s is provided from the central portion of the end where the electrode terminal 22e of the heat generating sheet 22s is provided, and the fixing terminal 22f is also screwed to the terminal base stay 24. And fix.

(S13) Next, the core holding member 28 is mounted so that the terminal block stay 24 is accommodated in one recessed portion of the H shape, and the contact member 26 is mounted in the other recessed portion of the H shape. Thus, the internal mechanism portion on the fixing sleeve 21 side is completed (FIG. 8).
Finally, the internal mechanism is inserted into the inner peripheral side of the fixing sleeve 21 and arranged as shown in FIG. 1 to complete the assembly of the fixing device 20 on the fixing sleeve 21 side.

  In the case of non-adhesion where the heating element support member 23 and the heating sheet 22s are not fixed with an adhesive or the like, the electrode terminal 22e and the fixed terminal 22f located on the opposite side of the nip portion in the heating sheet 22s are connected to the terminal base stay 24 The fixing sleeve 21 is rotated so that the heat generating sheet 22s is pulled from the fixed side to the nip portion side, whereby the heat generating sheet 22s is moved to the inner periphery of the heat generating member support member 23 and the fixing sleeve 21. The fixing sleeve 21 comes into contact with the surface stably in a state of being sandwiched between the fixing sleeve 21 and the fixing sleeve 21 can be efficiently heated.

  However, in a state where the heat generating sheet 22s is not bonded to the heat generating member supporting member 23, the heat generating sheet 22s moves so as to be lifted when the fixing sleeve 21 is rotated reversely during jam processing or the like. The position may be shifted. As the heat generating sheet 22s moves, the electrode terminal 22e may be twisted or deformed to be damaged. Therefore, in order to prevent the positional deviation of the heat generating sheet 22s, it is preferable that the heat generating sheet 22s is bonded and fixed to the heat generator support member 23.

  At this time, if the entire surface of the heat generating sheet 22s is bonded, the heat generated by the heat generating sheet 22s is not preferable because it easily moves to the heat generating member support member 23, and out of both ends corresponding to the axial direction of the fixing sleeve 21. It is preferable that only the area where the recording medium P does not pass, that is, the non-sheet passing area (surface) is bonded to the heating element support member 23. Accordingly, the positional deviation of the heat generating sheet 22s is prevented, and the paper passing area of the heat generating sheet 22s (here, the area through which the maximum size of the recording medium P used (the maximum paper passing area) passes) is a heating element. Since it is in a floating state without being bonded to the support member 23, there is no heat transfer from the sheet passing area of the heat generating sheet 22s to the heat generating element support member 23, and the heat generated in the sheet passing area of the heat generating sheet 22s is efficiently fixed. It can be used for heating the sleeve 21.

  The heat generating sheet 22s may be bonded using a coating-type liquid adhesive, but a tape-shaped adhesive member having adhesiveness or tackiness on both sides made of a heat-resistant acrylic material or silicone material. (Double-sided tape) may be used. This not only facilitates the attachment of the sheet heating element 22 (heating sheet 22s) to the heating element support member 23, but also allows the sheet heating surface to be removed simply by removing the double-sided tape when an abnormality occurs in the sheet heating element 22. It becomes the structure which can replace | exchange the heating element 22 and becomes excellent in maintainability.

  At this time, if the double-sided tape is simply sandwiched between the heat generating sheet 22s and the heat generating member support member 23, the surface of the heat generating sheet 22s is bonded to the surface of the fixing sleeve 21 with the double-sided tape. As a result, the sheet heating region 22 (heat generating sheet 22s) does not uniformly contact the fixing sleeve 21 in the sheet passing region, and the heating efficiency is lowered and the temperature distribution in the axial direction is not uniform.

  Therefore, it is preferable to reduce the thickness of the heat generating sheet 22s where the double-sided tape is attached in the planar heating element 22 by the thickness of the double-sided tape. That is, since the double-sided tape has a certain thickness (for example, 0.1 mm), as shown in FIG. 9, as shown in FIG. A recess extending in the circumferential direction at a depth corresponding to the thickness of 22t is provided, and a double-sided tape 22t is bonded to the recess, and then the heating sheet 22s is placed at a predetermined position of the heating element support member 23 via the double-sided tape 22t. Try to adhere. Thus, when the heat generating sheet 22s is bonded to the heat generating member support member 23, the surface of the heat generating sheet 22s on the side of the fixing sleeve 21 becomes flat in the axial direction of the fixing sleeve 21, and the sheet heat generating element 22 (heat generating) Since the sheet 22s) uniformly contacts the fixing sleeve 21, the temperature distribution in the axial direction of the fixing sleeve 21 can be made uniform with good heating efficiency.

  Alternatively, as shown in FIG. 10, it is preferable that the thickness of the double-sided tape 22t is recessed at a position corresponding to the non-sheet passing region of the heat generating sheet 22s of the heat generating member support member 23. That is, the recesses extending in the circumferential direction at a depth corresponding to the thickness of the double-sided tape 22t are provided at positions corresponding to the non-sheet passing regions of the heat generating sheet 22s at both end portions in the axial direction of the heat generating member support member 23, The double-sided tape 22t is bonded to the recess, and then the heating sheet 22s is bonded to the heating element support member 23 in that state via the double-sided tape 22t. Also by this, the surface of the heat generating sheet 22s on the side of the fixing sleeve 21 becomes flat in the axial direction of the fixing sleeve 21, and the planar heat generating element 22 (heat generating sheet 22s) uniformly contacts the fixing sleeve 21 in the sheet passing region. The temperature distribution in the axial direction of the fixing sleeve 21 can be made uniform with good heating efficiency.

Next, a detailed configuration of the heat generating sheet 22s in the sheet heating element 22 used in the present invention will be described.
That is, the heat generating sheet 22s may have the resistance heat generating layer 22b formed on the entire main surface of the base layer 22a or a certain region, but in each of a plurality of regions arbitrarily divided on the main surface of the base layer 22a. The resistance heating layer 22b is preferably formed so as to be able to generate heat independently. An example of the configuration is shown in FIGS.

  FIG. 11A is a top view showing a configuration example (1) of the planar heating element 22. Here, a state in which the planar heating element 22 is unfolded on a flat surface and viewed from above is shown before being attached to the heating element support member 23. Further, the horizontal direction in the figure is the width direction corresponding to the axial direction of the fixing sleeve 21, and the vertical direction is the length direction corresponding to the circumferential direction of the fixing sleeve 21.

  In FIG. 11A, the heat generating sheet 22s is roughly divided into three in the width direction (axial direction) on the main surface, and six divided regions are further divided into two in the length direction (circumferential direction). ing. Here, when the six divided regions are viewed as a matrix matrix in which the length direction (circumferential direction) includes row components and the width direction (axial direction) includes column components (FIG. 11B), (1,2) A resistance heating layer 22b1 having a predetermined width and length is formed in a divided region of the component (a region corresponding to the central portion in the axial direction of the fixing sleeve 21), and a divided region of the (2, 1) component and the (2, 3) component. A resistance heating layer 22b2 having a predetermined width and length is formed in each of the regions corresponding to both axial ends of the fixing sleeve 21.

  In addition, an electrode layer 22c connected to the resistance heating layer 22b1 is formed in the divided region of the (1,1) component and the (1,3) component, and each of the electrode layers 22c has a heating sheet 22s. An electrode terminal 22e1 extending from one side (lower side in the figure) is provided to form a first heat generating circuit.

  In addition, an electrode layer 22c that connects the two resistance heating layers 22b2 is formed in the (2, 2) component divided region, and the length direction of the heating sheet 22s ( The electrode layer 22c extending in the circumferential direction and extending toward the one side (the lower side in the figure) is connected, and each electrode layer 22c has an electrode terminal 22e2 extending from the one side of the heat generating sheet 22s. A second heat generation circuit is formed.

  In addition, an insulating layer 22d is provided between the first heat generating circuit and the second heat generating circuit to prevent short circuit therebetween.

  In the sheet heating element 22 having the configuration shown in FIG. 11A, when energized from the electrode terminal 22e1, heat is generated as Joule heat due to the internal resistance of the resistance heating layer 22b1, and the electrode layer 22c does not generate heat due to low resistance. Only the divided region of the (1, 2) component of the heat generating sheet 22s generates heat, and the central portion in the axial direction of the fixing sleeve 21 can be heated.

  Further, when energized from the electrode terminal 22e2, heat is generated as Joule heat due to the internal resistance of the resistance heating layer 22b2, and the electrode layer 22c does not generate heat due to low resistance. Therefore, the (2, 1) component and (2 3) Only the divided region of the component generates heat, and both axial end portions of the fixing sleeve 21 can be heated.

  Therefore, when a small size (narrow width) recording medium P is passed through the fixing device 20, only the electrode terminal 22e1 is energized to heat only the central portion in the axial direction of the fixing sleeve 21 and to widen the width. When the recording medium P is passed, the electrode terminals 22e1 and 22e2 are energized to heat the entire width in the axial direction of the fixing sleeve 21, thereby suppressing the energy consumption and appropriately depending on the width of the recording medium P. Fixing is possible. Further, since the amount of heat generated by the sheet heating element 22 can be controlled in accordance with the size of the recording medium P, the temperature of the non-sheet passing portion does not rise excessively even if small size paper is continuously fed. It is possible to prevent the device from being stopped for protection and the productivity from being lowered. Further, by providing the positional relationship of the different heat generating portions with the integrated planar heat generating element 22, a heat generating element having a smaller temperature deviation in the axial direction than that formed by a separate heat generating element can be obtained.

  In addition, in the heat generating sheet 22s, the heat generation amount tends to decrease due to the outflow of heat to the insulating layer 22d and the electrode layer 22c having a relatively high thermal conductivity at the ends of the respective resistance heat generating layers 22b1 and 22b2. It is in. Therefore, as shown in FIG. 11A, in the width direction (axial direction) of the heat generating sheet 22s, the boundary between the central resistance heating layer 22b1 and the resistance heating layer 22b2 at the end is the same surface. When the currents 22e1 and 22e2 were energized, the temperature distribution in the axial direction of the fixing sleeve 21 caused a temperature drop at the boundary between the resistance heating layer 22b1 and the resistance heating layer 22b2, and an abnormal image such as a fixing failure was generated. Therefore, it is preferable to adopt the configuration shown in FIG. 12 or 13 to improve this problem.

FIG. 12 is a top view showing a configuration example (2) of the planar heating element 22.
The basic configuration of the planar heating element 22 shown in FIG. 12 is the same as that shown in FIG. 11A, but the resistance heating layer 22b1 and the resistance heating layer 22b2 are partially in the width direction of the heating sheet 22s. The difference is that they overlap in the (axial direction) to form an overlap region. Thereby, it is possible to prevent a temperature drop at the boundary between the resistance heating layer 22b1 and the resistance heating layer 22b2 when the electrode terminals 22e1 and 22e2 are energized.

FIG. 13 is a top view showing a configuration example (3) of the planar heating element 22.
The basic configuration of the planar heating element 22 shown in FIG. 13 is the same as that shown in FIG. 12, but in the overlapping region of the resistance heating layer 22b1 and the resistance heating layer 22b2, each of the resistance heating layers 22b1 and 22b2 and electrodes The difference is that the boundary line with the layer 22c is inclined in different directions with respect to the length direction (circumferential direction) to adjust the overlapping amount of the resistance heating layers 22b1 and 22b2.

  This is because the area ratio of the overlapping regions of the resistance heating layers 22b1 and 22b2 is constant in the width direction (axial direction) in the configuration of FIG. 12, and the variation in the amount of heat generation increases as the overlapping width varies. However, in the configuration of FIG. 13, the area ratio in the overlapping region of the resistance heating layers 22b1 and 22b2 changes at a constant rate in the width direction (axial direction) to reduce the influence of adjustment of the heat generation distribution and component variations. Thus, the temperature uniformity in the entire axial direction is improved, and the problems caused by the configuration of FIG. 12 are improved.

  In the heat generating sheet 22s having the configuration shown in FIGS. 11 to 13 as described above, only the regions corresponding to the resistance heating layers 22b1 and 22b2 on the main surface of the base layer 22a are exposed to form the resistance heating layers 22b1 and 22b2 by coating. Next, an insulating layer 22d made of only a heat-resistant resin is formed by application in a state where only the region corresponding to the insulating layer 22d is exposed, then only the region corresponding to the electrode layer 22c is exposed, and a conductive paste is applied to expose the electrode layer 22c. This is possible by forming Therefore, the resistance heating layers 22b1 and 22b2 having an arbitrary shape can be formed by adjusting the exposed shape of the region corresponding to the resistance heating layers 22b1 and 22b2.

  Further, the sheet heating element 22 used in the present invention is formed by laminating a plurality of heating sheets 22s, and the heating sheets 22s are formed in any region on the main surface of each base layer 22a in a resistance heating layer 22b. Are preferably formed so that they can generate heat independently. FIG. 14 shows a specific configuration thereof.

FIG. 14 is an exploded perspective view showing a configuration example (4) of the planar heating element 22.
In FIG. 14, a sheet heating element 22 is formed by laminating a first heating sheet 22s, an insulating sheet made of an insulating layer 22d, and a second heating sheet 22s in this order from the top.

  Here, the main surface of the first heat generating sheet 22s is divided into three in the width direction (axial direction), the resistance heat generating layer 22b1 is formed in the central divided region, and the resistance is formed in each of the divided regions on both sides thereof. An electrode layer 22c connected to the heat generating layer 22b1 is formed. The main surface of the second heat generating sheet 22s is divided into five in the width direction (axial direction), and the resistance heat generating layer 22b2 is formed in the second and fourth divided regions in the width direction (axial direction). An electrode layer 22c connected to the resistance heating layer 22b2 is formed in each of the remaining divided regions.

  The first heat generating sheet 22s and the second heat generating sheet 22s are stacked with an insulating sheet made of an insulating layer 22d interposed therebetween, and an independent first heat generating circuit is formed on the first heat generating sheet 22s. An independent second heat generating circuit is formed on the second heat generating sheet 22s.

  As a result, when the first heat generating circuit is energized, heat is generated as Joule heat by the internal resistance of the resistance heat generating layer 22b1, and only the central region in the width direction (axial direction) of the first heat generating sheet 22s generates heat. The central portion of the sleeve 21 in the axial direction can be heated. When the second heat generating circuit is energized, heat is generated as Joule heat by the internal resistance of the resistance heat generating layer 22b2, and only the both end regions in the width direction (axial direction) of the second heat generating sheet 22s generate heat. Both axial ends of the sleeve 21 can be heated.

  Like the planar heating element 22 shown in FIGS. 11 to 13, the area of the entire planar heating element 22 is increased in order to secure a necessary amount of heat when it is divided up to the length direction (circumferential direction), In some cases, the fixing sleeve 21 having a small diameter cannot be used. Therefore, as shown in FIG. 14, the heat generation sheets 22 s having different heat generation portions are stacked in the thickness direction of the sheet heating element 22, thereby different heat generation distributions as in the sheet heating element 22 illustrated in FIGS. 11 to 13. It is possible to achieve a high output while saving space (reducing the size) while realizing the planar heating element 22 that can be obtained.

  By the way, in the fixing device 20, during rotation, the fixing roller 21 is pulled by the pressure roller 31 at the nip portion, so that the fixing sleeve 21 on the upstream side of the nip portion becomes a tension side to which tension is applied, and the inner peripheral surface of the fixing sleeve 21 is The sheet heating member 22 slides on the sheet heating element 22 while being in pressure contact with the heating element support member 23. On the other hand, the tension is not applied to the fixing sleeve 21 on the downstream side of the nip portion, and the fixing sleeve 21 is in a relaxed state. If an attempt is made to increase the speed of the apparatus in this state, the fixing sleeve 21 on the downstream side of the nip portion. As a result, the degree of slackening of the fixing sleeve 21 becomes serious, and the rotational running stability of the fixing sleeve 21 is hindered.

  Therefore, the fixing device 20 of the present invention preferably includes a rotation support member that supports the rotation state of the fixing sleeve 21 on the inner peripheral side of the fixing sleeve 21 and at least on the downstream side of the nip portion.

FIG. 15 is a cross-sectional view showing the configuration of the fixing device according to the second embodiment of the present invention.
The fixing device 20 shown in FIG. 15 has the same basic configuration as that shown in FIG. 1, but includes a pipe-shaped rotation support member 27 provided on the inner peripheral side of the fixing sleeve 21 and the inner periphery of the rotation support member 27. This is different in that a heat insulating support member 29 is provided on the H-shaped outer surface of the core holding member 28 so as to be disposed on the downstream side of the nip portion.

  Here, the rotation support member 27 is, for example, in the shape of a pipe made of a thin metal such as iron or stainless steel having a thickness of 0.1 to 1 mm, and the outer diameter thereof is 0.5 mm larger than the inner diameter of the fixing sleeve 21. It is about 1 mm smaller. Further, the nip portion side is cut and opened in the axial direction on the outer peripheral surface of the rotation support member 27, and the end portion thereof is folded into the core holding member 28 side so as not to contact the nip portion. In addition, the cylindrical portion 30a of the flange member 30 is inserted into the inner diameter portion of both ends of the rotation support member 27 in the axial direction, and the outer shape (cross-sectional shape) of the rotation support member 27 is. It is held in a substantially circular shape along the outer shape of the cylindrical portion 30a. Also in this case, the center of the circle of the cylindrical portion 30 a becomes the rotation center O of the fixing sleeve 21.

  The heat insulating support member 29 has a heat resistance sufficient to withstand the heat of the fixing sleeve 21 via the rotation support member 27 and a heat outflow (loss) from the rotation support member 27 in contact with the fixing sleeve 21 on the exit side of the nip portion. It has a heat insulating property to prevent, and a strength sufficient to support the rotating support member 27 so that the rotating fixing sleeve 21 does not deform when it contacts the rotating support member 27, and a heating element support member It is preferably made of the same polyether ether ketone resin (PEEK) as 23.

  Further, as shown in FIG. 16, the rotation support member 27 is provided with an opening 27a by removing an outer peripheral surface of a certain region on the upstream side of the nip portion. Accordingly, as shown in FIG. 17, when the internal mechanism portion of the fixing sleeve 21 is configured, the entire surface of the sheet heating element 22 is exposed from the opening 27a, and the sheet heating element 22 is exposed to the fixing sleeve. It comes to contact | abut to the internal peripheral surface of 21. FIG.

The fixing device 20 shown in FIG. 15 also satisfies the above formula (4).
Thereby, the fixing device 20 of the second embodiment shown in FIG. 15 is similar to the fixing device 20 (FIG. 1) of the first embodiment, and the fixing sleeve 21 and the heating element support member during the operation of the device. The thermal expansion of the fixing sleeve 21 does not increase the difference between the inner diameter of the fixing sleeve 21 and the distance from the rotation center O of the fixing sleeve 21 to the outer peripheral surface of the heating element support member 23 at least as compared with cooling. Since it is possible to prevent a minute gap from being generated between the inner peripheral surface of the sheet and the heat generating surface of the sheet heating element 22 and to bring them into close contact with each other, it is possible to prevent overheating of the heat generating sheet 22s. Therefore, the fixing device 20 can perform a long-time stable fixing process.

  Also in the fixing device 20 shown in FIG. 15, as in the fixing device 20 (FIG. 1) of the first embodiment, the warm-up time and the first print time can be shortened while saving energy. Further, since the heat generating sheet 22s in the sheet heating element 22 is a resin-based sheet, the stress caused by the rotation and vibration of the pressure roller 31 repeatedly acts on the heat generating sheet 22s, and the heat generating sheet 22s is repeatedly bent. Even if it breaks, it will not be damaged by fatigue and can be operated for a long time. Further, in the sheet heating element 22, heat is generated at different heating portions in the axial direction of the fixing sleeve 21, so that efficient temperature control can be performed according to the size of the recording medium P to be passed. In addition to this, by providing the rotation support member 27 (the heat insulation support member 29 as necessary), the rotational running stability of the fixing sleeve 21 can be improved, and the speed can be increased. Further, the heat support in the axial direction of the fixing sleeve 21 in the rotation support member 27 can assist the temperature uniformity in the axial direction of the fixing sleeve 21, so that it is possible to cope with a higher speed apparatus. Become.

Next, the image forming apparatus according to the present invention will be described.
FIG. 18 is an overall configuration diagram showing the configuration of the image forming apparatus according to the present invention.
As shown in FIG. 18, the image forming apparatus 1 is a tandem type color printer. Four bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing.
An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge eliminating unit (not shown), and the like are disposed. Then, an image forming process (charging process, exposure process, development process, transfer process, cleaning process) is performed on each of the photoconductive drums 5Y, 5M, 5C, and 5K. An image of each color is formed on 5K.

The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in a clockwise direction in FIG. 18 by a drive motor (not shown). Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (a charging process).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and electrostatic latent images corresponding to the respective colors are formed by exposure scanning at this position. (It is an exposure process.)

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing device 76, and the electrostatic latent image is developed at this position to form toner images of each color (developing process). .)
Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions, the photoconductive drums 5Y, 5M. The toner images on 5C and 5K are transferred onto the intermediate transfer belt 78 (this is a primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. 77 is mechanically collected by a cleaning blade (cleaning process).
Finally, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. The
Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 78 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 78.
Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. , Etc. The intermediate transfer belt 78 is stretched and supported by the three rollers 82 to 84, and is moved endlessly in the direction of the arrow in FIG.

The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, thereby forming primary transfer nips. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.
The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78.

Thereafter, the intermediate transfer belt 78 onto which the toner images of the respective colors are transferred in an overlapping manner reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78.
Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip is transported from the paper feeding unit 12 disposed below the apparatus main body 1 via the paper feeding roller 97 and the registration roller pair 98. It is a thing.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is rotated counterclockwise in FIG. 18, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 20. At this position, the color image transferred to the surface is fixed on the recording medium P by heat and pressure generated by the fixing sleeve 21 and the pressure roller 31.
Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The transferred P discharged from the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

  As described above, since the image forming apparatus of the present invention includes the fixing device 20 described above, stable image formation can be performed for a long time. In addition, the warm-up time and the first print time are short, and even if the size of the recording medium P changes, it is possible to form an appropriate image while suppressing energy consumption. Can be prevented.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus main body 3 Exposure part 4Y, 4M, 4C, 4K Image formation part 5Y, 5M, 5C, 5K Photosensitive drum 12 Paper feed part 20 Fixing device 21 Fixing sleeve 22 Planar heating element 22a Base layer 22b, 22b1, 22b2 Resistance heating layer 22c Electrode layer 22d Insulating layer 22e, 22e1, 22e2 Electrode terminal 22f Fixed terminal 22h Heating area (heating surface)
22s Heat generation sheet 22t Double-sided tape (adhesive member)
DESCRIPTION OF SYMBOLS 23 Heat generating body support member 24 Terminal block stay 25 Power supply line 26 Contact member 27 Rotation support member 27a Opening part 28 Core holding member 29 Heat insulation support member 30 Flange member 30a Cylindrical part 30b Flange part 31 Pressure roller 42 Side plate 75 Charging part 76 Developing unit 77 Cleaning unit 78 Intermediate transfer belt 79Y, 79M, 79C, 79K First transfer bias roller 80 Intermediate transfer cleaning unit 82 Secondary transfer backup roller 83 Cleaning backup roller 84 Tension roller 85 Intermediate transfer unit 97 Paper feed roller 98 Registration roller Pair 99 Discharge roller pair 100 Stack section 101 Bottle storage section 102Y, 102M, 102C, 102K Toner bottle L Laser light P Recording medium T Toner

Japanese Patent Laid-Open No. 11-2982 JP-A-4-44075 JP-A-8-262903 Japanese Patent Laid-Open No. 10-213984 JP 2007-334205 A JP 2008-154822 A JP 2008-216928 A JP 2011-133839 A

Claims (4)

A fixing member that is a rotating cylindrical endless belt;
A pressure member in contact with the outer peripheral surface of the fixing member;
An abutting member disposed on an inner peripheral side of the fixing member and abutting the pressure member via the fixing member to form a nip portion;
A sheet heating element that heats the fixing member by contacting the heating surface with the inner peripheral surface of the fixing member;
A heating element support member that supports the sheet heating element sandwiched between the fixing member and the inner periphery of the fixing member; and
A core holding member that holds the contact member and the heating element support member inside a cylinder of the fixing member;
With
Of the region of the heating element support member that supports the heating surface of the planar heating element, the thickness of the portion where the thickness of the heating element support member in the radial direction from the rotation center of the fixing member is the smallest is t, A fixing device, wherein αt ≧ βR is satisfied, where α is a linear expansion coefficient of the heating element support member, R is a cylindrical inner diameter of the fixing member, and β is a linear expansion coefficient of the fixing member.   The heating surface of the planar heating element includes a resistance heating layer in which conductive particles are dispersed in a heat-resistant resin on an insulating base layer, and an electrode layer that supplies power to the resistance heating layer. The fixing device according to claim 1, wherein the fixing device is a heat generating sheet that is formed and has a predetermined width and length corresponding to an axial direction and a circumferential direction of the fixing member and exhibits flexibility.   The fixing device according to claim 1, further comprising a rotation support member that supports a rotation state of the fixing member on an inner peripheral side of the fixing member. An image forming apparatus comprising the fixing device according to claim 1.