JP5617287B2 - Fixing apparatus and image forming apparatus - Google Patents

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 is established by a process in which the transferred image is transferred onto a recording paper (also referred to as a paper or a recording medium) by a transfer device to carry the image, and a 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.

  The fixing device is premised on the passage of various recording media. For example, a recording medium smaller than the heat generation width in the axial direction of the heating means of the fixing member may be passed. In this case, the non-sheet passing area of the fixing member is deprived of heat by the recording medium as it is. Because it is not, it will be excessive heat.

  Therefore, in Patent Document 8, heat sources (halogen heaters, planar heating elements, electromagnetic induction heating means (IH), etc.) each having different heat generation distributions in the sheet width direction are arranged as heating means, and recording is performed. An invention is disclosed in which an increase in the end temperature of the fixing member is prevented by supplying power only to a heat source suitable for the sheet passing width of the medium. However, since the heat generation width can be changed only by the number of arranged heat sources, it is insufficient as a capacity for dealing with the size of the recording medium.

  In Patent Document 7, a plurality of resistance heating elements are arranged side by side in the axial direction of the fixing belt, and the heat generation is controlled independently for each resistance heating element, so that the heat generation distribution in the axial direction of the fixing belt is variable. However, this invention is also difficult to flexibly cope with recording media of various sizes. Further, since the resistance heating element is made of a metal foil, the degree of freedom for adjusting the temperature distribution in the fixing belt is narrow. That is, it is difficult to superimpose adjacent resistance heating elements, and since they are arranged apart from each other at a certain interval, heating of the boundary portion is insufficient, and the temperature distribution in the axial direction of the fixing belt Became non-uniform and was not preferable. In addition, even if adjacent resistance heating elements can be overlapped with each other, the overlapping portions are arranged because the resistance heating elements are arranged with a minute gap so as not to be pressed against the inner peripheral surface of the fixing belt. However, the contact with the fixing belt becomes uneven and the contact with the fixing belt becomes uneven, which is inconvenient for uniform heating of the fixing belt.

  The present invention has been made in view of the above problems in the prior art, and a fixing device that appropriately heats a fixing member corresponding to recording media of various sizes by a sheet heating element and an image including the fixing device. An object is to provide a forming apparatus.

The present invention provided to solve the above problems is as follows.
[1] A fixing member (fixing sleeve 21) of a rotating endless belt, a pressure member (pressure roller 31) in contact with the outer peripheral surface of the fixing member, and an inner peripheral side of the fixing member, A contact member (contact member 26) that forms a nip by contacting the pressure member via a fixing member, and is disposed on or in close proximity to the fixing member on the inner peripheral side of the fixing member; A heating sheet (heating sheet 22s) that heats the fixing member directly or indirectly and has a resistance heating layer (resistance heating layer 22b) formed on an insulating base layer (base layer 22a). A planar heating element that supplies electric power to the resistance heating layer, and has three or more electrode terminals (electrode terminals 22e) arranged so that the energization distance in the resistance heating layer is adjustable. A planar heating element 22) and an inner periphery of the fixing member; A heating element support member (heating element support member 23) which is disposed so as to sandwich the planar heating element between the fixing member and the fixing member and supports the planar heating element at a predetermined position; and the planar heating element A heat generation width adjusting mechanism that connects any two electrode terminals of the three or more electrode terminals (electrode terminal 22e) and a power source so as to be able to supply power, and changes the heat generation width in the axial direction of the fixing member of the heat generation sheet. Part (heat generation width adjustment mechanism part 32), and the heat generation width adjustment mechanism part supplies power from the power source to the electrode terminals at respective positions in the axial direction corresponding to the three or more electrode terminals. A rotating shaft member provided with a power supply terminal for performing the operation, wherein the power supply terminal is provided including ones having different positions in the circumferential direction of the rotary shaft member, and the rotating shaft member is disposed at a predetermined rotational position. So that two of the three or more electrode terminals Fixing apparatus characterized by connecting the a terminal power feeding capable (fixing device 20, FIGS. 7-8).
[2 ] The fixing device according to [1 ], wherein the heat generation width adjustment mechanism section changes a heat generation width of the heat generation sheet in accordance with a size of a recording medium to be passed.
[ 3 ] The fixing device according to [1] or [2] , wherein the resistance heating layer in the heating sheet is formed by dispersing conductive particles in a heat resistant resin.
[ 4 ] An image forming apparatus (image forming apparatus 1, FIG. 11), comprising the fixing device according to any one of [1] to [ 3 ].

According to the fixing device of the present invention, since the heat generation width of the heat generation sheet can be arbitrarily changed by the heat generation width adjustment mechanism, it is possible to overheat the area where the fixing member is not passing through while ensuring good fixing performance. Temperature can be prevented. Further, it is possible to change the size in accordance with the size of the recording medium to be passed through the area where the heat generating sheet contacts and heats the fixing member.
According to the image forming apparatus of the present invention, since the fixing device of the present invention is provided, the warm-up time and first print time are short, and appropriate image formation is possible even if the size of the recording medium changes.

FIG. 3 is a cross-sectional view illustrating a configuration of a reference example which is a premise of the fixing device according to the present invention. FIG. 3 is a schematic diagram illustrating an axial direction and a circumferential direction of a fixing sleeve. 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 structure of the rotation support member used with the fixing device of FIG. FIG. 2 is a schematic diagram illustrating a configuration of an internal mechanism unit on a fixing sleeve side in the fixing device of FIG. 1. It is a figure which shows the structural example of a heat generating sheet. FIG. 2 is a cross-sectional view illustrating a configuration of a fixing device according to the present invention. It is the schematic which shows the structural example (1) of the heat generation width adjustment mechanism part used with the fixing device which concerns on this invention. It is the schematic which shows the structural example (2) of the heat generation width adjustment mechanism part used with the fixing device which concerns on this invention. It is the schematic which shows the structural example (3) of the heat generation width adjustment mechanism part used with the fixing device which concerns on this invention. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to the present invention.

First, a reference example which is a premise of the fixing device according to the present invention will be described.
FIG. 1 is a cross-sectional view showing a configuration of a reference example which is a premise of a fixing device according to the present invention.
As shown in FIG. 1, the fixing device 50 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 sheet heating element (sheet heating element 22) that is disposed in contact with the fixing member on the inner peripheral side of the fixing member and heats the fixing member, and a sheet heating element on the inner peripheral side of the fixing member. A heating element support member (heating element support member 23) which is disposed so as to sandwich the planar heating element between the fixing member and supports the planar heating element at a predetermined position, and an inner peripheral side of the fixing sleeve 21. A pipe-shaped rotation support member (supporting the rotating fixing sleeve 21 provided) A rolling support member 27), a heat insulating support member (heat insulating support member 29) provided on the H-shaped outer surface of the core holding member 28 so as to be disposed on the inner peripheral side of the rotation support member 27 and downstream of the nip portion, Is provided.

  Here, the fixing sleeve 21 is a pipe-shaped endless belt having a length corresponding to the width of the recording medium P through which the paper is passed in the axial direction and having flexibility, for example, a thickness of 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.

  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.

  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 to 3 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, so that the core holding member 28 does not contact the fixing sleeve 21 at the nip portion. Is arranged.

  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 core holding member 28 holds the end portion of the pipe-shaped rotation support member 27 formed by cutting the pipe peripheral surface in the axial direction before and after the nip portion in the circumferential direction. Holding. Note that both ends of the rotation support member 27 in the axial direction are held by side plates constituting a frame of the fixing device 50.

  The heating element support member 23 supports the planar heating element 22 in order to place 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 heating element support member 23 has heat resistance sufficient to withstand the heat generation of the sheet heating element 22, and the sheet heating element 22 is not deformed when the rotating fixing sleeve 21 contacts the sheet heating element 22. It is preferable to have strength sufficient to support the heat and heat insulation so that the heat of the sheet heating element 22 is transmitted to the fixing sleeve 21 side without being transmitted to the core holding member 28 side. A molded body is preferred. When the sheet heating element 22 is in contact with the inner peripheral surface of the fixing sleeve 21, the force that the fixing sleeve 21 that rotates rotates pulls the sheet heating element 22 toward the nip portion acts on the sheet heating element 22. Therefore, the heating element support member 23 needs to have sufficient strength to support the planar heating element 22 without being deformed. In this case as well, a polyimide resin foam molded body is suitable. In addition, a solid resin member may be supplementarily provided inside the polyimide resin foam to improve the rigidity.

  As shown in FIG. 3, the sheet 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 power to the resistance heating layer 22b. An electrode layer 22c to be supplied, and has 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 an elastic film made of a resin having a certain degree of heat resistance, such as PET or polyimide resin, and among them, 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.

  In addition, as an arrangement | positioning area | region in the fixing sleeve 21 internal peripheral surface of 22 s of heat_generation | fever sheets, you may arrange | position in arbitrary positions from the position on the inner peripheral surface of the fixing sleeve 21 on the opposite side to the nip part.

  By the way, in the fixing device 50, 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 tensioned side, and the inner peripheral surface of the fixing sleeve 21 is It 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 50 is preferably provided with a rotation support member 27 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.

  The rotation support member 27 has a pipe shape made of, for example, a thin metal such as iron or stainless steel having a thickness of 0.1 to 1 mm, and the outer diameter thereof is about 0.5 to 1 mm in diameter than the inner diameter of the fixing sleeve 21. It is small. Further, on the circumference of the pipe of the rotation support member 27, the inner peripheral surface of the fixing sleeve 21 is in contact with the outer peripheral surface of the rotation support member 27 at least from the position opposite to the nip portion and in the vicinity of the entrance of the nip portion. 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.

  Further, as shown in FIG. 4, the rotation support member 27 is provided with an opening 27a by removing the outer peripheral surface of a certain region on the upstream side of the nip portion. As a result, as shown in FIG. 5, 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 surface of the sheet heating element 22 is the rotation support member 27. The outer peripheral surface of the rotation support member 27 is slightly protruded from the outer peripheral surface of the rotation support member 27, and the planar heating element 22 contacts the inner peripheral surface of the fixing sleeve 21. become.

  Accordingly, the sheet heating element 22 (heating sheet 22s) is supported by the heating element support member 23 and is disposed in contact with the inner peripheral surface of the fixing sleeve 21, so that the fixing sleeve 21 can be efficiently heated. It is.

  As described above, the rotation support member 27 not only ensures the rotational running stability of the fixing sleeve 21 but also the fixing sleeve 21 can be supported by the rigid metal rotation support member 27, so that handling in assembly is easy. It is.

  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 23 is preferably the same foamed molded body of polyimide resin as 23.

  With the above configuration, the fixing device 50 can 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. 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.

  In the fixing device 50, the heat generating sheet 22s has a resistance heat generating layer 22b in each of a plurality of regions partitioned in the axial direction on the main surface of the base layer 22a in order to correspond to various sizes of recording media to be passed. It must be formed so that it can generate heat independently.

  FIG. 6A is a top view illustrating a configuration example 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. 6A, the heat generating sheet 22s is roughly divided into three in the width direction (axial direction) and further divided into two in the length direction (circumferential direction) on its main surface. 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. 6B), (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. 6A, when the electrode terminal 22e1 is energized, it generates heat 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 50, 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.

However, even if the configuration of FIG. 6A is adopted, there are two types of sizes of the recording medium P that can be handled, and it has been difficult to flexibly cope with recording media of various sizes to be passed.
The inventors have intensively studied to solve this problem and have accomplished the present invention.

Hereinafter, the fixing device according to the present invention will be described.
FIG. 7 is a cross-sectional view showing the configuration of the fixing device according to the present invention.
As shown in FIG. 7, the fixing device 20 includes a rotating endless belt fixing member (fixing sleeve 21), a pressure member (pressure roller 31) in contact with the outer peripheral surface of the fixing member, and the fixing member. An abutting member (abutting member 26) which is disposed on the inner peripheral side of the fixing member and abuts against the pressure member via the fixing member to form a nip portion; and the fixing member on the inner peripheral side of the fixing member The fixing member is disposed in contact with or in close proximity, and directly or indirectly heats the fixing member, and one resistance heating layer (resistance heating layer 22b) is formed on the insulating base layer (base layer 22a). A heating sheet (heating sheet 22s) and three or more electrode terminals (electrode terminals 22e) that supply electric power to the resistance heating layer and are arranged so that the energization distance in the resistance heating layer can be adjusted. And a planar heating element (planar heating element) 2) and a heating element support member (heating element support member) which is disposed on the inner peripheral side of the fixing member so as to sandwich the planar heating element between the fixing member and supports the planar heating element at a predetermined position. The member 23) and any two electrode terminals of the three or more electrode terminals of the planar heating element and a power source are connected so as to be able to supply power, and the heat generation width in the axial direction of the fixing member of the heat generating sheet is changed. And a heat generation width adjustment mechanism section (heat generation width adjustment mechanism section 32).

Here, the fixing sleeve 21, the terminal block stay 24, the contact member 26, the rotation support member 27, the core holding member 28, and the pressure roller 31 are the same as those constituting the fixing device 50 shown in FIG. The fixing device 50 is different from the fixing device 50 in that a heating width adjusting mechanism 32 is provided on the terminal block stay 24 instead of the power supply line 25. Further, the heat insulating support member 29 may be omitted or provided.
Hereinafter, the heat generation width adjusting mechanism 32 that forms the basis of the present invention will be described.

  FIG. 8 is a schematic diagram showing a configuration example (1) of the heat generation width adjusting mechanism used in the present invention. Here, only the planar heating element 22 and the heating width adjusting mechanism 32 are conceptually shown.

Here, the basic configuration of the planar heating element 22 is the same as that described above as the planar heating element 22 constituting the fixing device 50, but is different in the following points.
That is, as the heat generating sheet 22s, one resistance heat generating layer 22b having a predetermined width and length corresponding to the axial direction and the circumferential direction of the fixing sleeve 21 is formed on the insulating base layer 22a. Three or more electrode terminals (eight electrode terminals i to viii in FIG. 8) 22e are connected with a predetermined interval in the axial direction at one end in the circumferential direction of the resistance heating layer 22b. In the fixing device 20 of FIG. 7, the heating sheet 22 s of the planar heating element 22 is held on the outer peripheral surface of the heating element holding member 23, and only the plurality of electrode terminals 22 e are axially arranged on the terminal block stay 24. It is fixed at the predetermined interval.

  Further, the heat generation width adjusting mechanism 32 has a rotating shaft member 32 a that is arranged so as to be rotatable in a state where it is in contact with all the electrode terminals 22 e fixed to the terminal block stay 24. The rotary shaft member 32a has three or more power supply electrodes (eight power supply electrodes 1 to 8 in FIG. 8) 32e on the insulating outer peripheral surface which are the same as the number of the electrode terminals 22e. The terminals 22e are arranged at a predetermined interval in the axial direction so as to have a one-to-one correspondence with the terminals 22e and are exposed so as to be in contact with the electrode terminals 22e. The power supply electrode 32e is in a state in which power can be supplied from an external power source to the electrode terminal 22e that is in contact with the power supply electrode 32e.

  For example, when the electrode terminal 22e and the power supply electrode 32e are an odd number, the specific one power supply electrode 32e is always a specific one of the odd number of power supply electrodes 32e. It is preferable to keep the electrode terminal 22e in contact with the remaining power supply electrode 32e on the circumference of the rotary shaft member 32a so that they are positioned at different circumferential angles. Accordingly, when the rotary shaft member 32a is rotated at a predetermined rotation angle, the one specific power supply electrode 32e and one of the remaining power supply electrodes 32e come into contact with the corresponding electrode terminals 22e, and these electrode terminals Power is supplied from 22e.

  Further, when the electrode terminals 22e and the power supply electrodes 32e are an even number, the even number of power supply electrodes 32e are divided into two pairs of power supply electrodes 32e, and the two power supply electrodes 32e of each pair of the rotation shaft member 32a are separated from each other. It is good to arrange | position so that it may become the position of the same circumference angle on a circumference, and may become the position of the circumference angle from which pairs mutually differ. In FIG. 8, four power supply electrode 32e pairs (reference numerals 1 and 8, 2 and 7, 3, and 6, 4 and 5) are provided so as to have a symmetrical positional relationship with respect to the axial center of the rotating shaft member 32a. It is divided into.

  Accordingly, when the rotary shaft member 32a is rotated at a predetermined rotation angle from the reference position with respect to a position in the circumferential direction, any pair of the feed electrodes 32e among the even number of feed electrodes 32e correspond to each other. The electrode terminals 22e to be contacted and power can be supplied from these electrode terminals 22e. For example, in the configuration shown in FIG. 8, the rotation shaft member 32a is rotated at four different rotation angles, and at a certain rotation angle 1, the power supply electrodes 32e with reference numerals 1 and 8 are electrode terminals with reference numerals i and viii. Power is supplied to the resistance heating layer 22b between the electrode terminals 22e of reference numerals i and viii in contact with 22e. In the case of a certain rotation angle 2, the power supply electrode 32e of reference numerals 2 and 7 contacts the electrode terminal 22e of reference numerals ii and vii to supply power to the resistance heating layer 22b between the electrode terminals 22e of reference numerals ii and vii. To do. Further, in the case of a certain rotation angle 3, the feeding electrodes 32e indicated by reference numerals 3 and 6 are brought into contact with the electrode terminals 22e indicated by reference numerals iii and vi to supply power to the resistance heating layer 22b between the electrode terminals 22e indicated by reference numerals iii and vi. To do. Further, in the case of a certain rotation angle 4, the power supply electrodes 32e with the reference numerals 4 and 5 contact the electrode terminals 22e with the reference signs iv and v to supply power to the resistance heating layer 22b between the electrode terminals 22e with the reference signs iv and v. To do.

  As described above, in the heat generation width adjusting mechanism 32, the rotary shaft member 32a is axially rotated by a predetermined rotation angle, and the arbitrary two power supply electrodes 32e among the three or more power supply electrodes 32e are replaced with the planar heating element 22. Any two corresponding electrode terminals 22e in the three or more electrode terminals 22e can be brought into contact with the power supply from the power source. At this time, if the rotation angle of the rotary shaft member 32a is adjusted, the interval between the electrode terminals 22e that allows the resistance heating layer 22b to be energized can be set to an arbitrary interval. As a result, the fixing sleeve 21 of the heating sheet 22s It is possible to change the heat generation width in the axial direction.

  Further, it is preferable that the heat generation width adjustment mechanism unit 32 changes the heat generation width of the heat generation sheet 22s according to the size of the recording medium P to be passed. In the case of FIG. 8, the sheet passing through the recording medium P is based on the axial center. For example, when the minimum size recording medium P to be passed through the fixing device 20 is passed, the rotating shaft member 32a of FIG. It is preferable that power is supplied to the resistance heating layer 22b between the electrode terminals 22e with the signs iv and v in contact with the v electrode terminal 22e. Further, when the maximum size recording medium P to be passed through the fixing device 20 is passed, the rotary shaft member 32a of FIG. It is preferable to supply electric power to the resistance heating layer 22b between the electrode terminals 22e of symbols i and viii in contact with the electrode terminal 22e of viii. As a result, a predetermined area in the axial direction that matches the width of the recording medium P that passes through the heat generating sheet 22s generates heat, and the fixing sleeve 21 can be heated with an appropriate width, and the recording medium that passes through the fixing sleeve 21 passes through. It is possible to prevent an excessive temperature increase in a region outside the width of P.

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. 7 by a drive device (not shown), the fixing sleeve 21 is also rotated in the clockwise direction. At this time, the heating sheet 22 s of the sheet heating element 22 is in a state of sliding with respect to the inner peripheral surface of the fixing sleeve 21.
In synchronization therewith, electric power is supplied from the external power source or the internal power storage device to the planar heating element 22 through the heating width adjusting mechanism 32, and the heating sheet 22s generates heat. At this time, the heat generating sheet adjusting unit 32 generates heat at a predetermined width corresponding to the width of the recording medium P to be passed by the heat generating width adjusting mechanism 32, and the fixing sleeve 21 is efficient in an area corresponding to the width from the heat generating sheet 22s. Heat is transferred to and rapidly heated. 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, on the upstream side of the nip portion, the temperature of the nip portion is set to a predetermined temperature by a temperature detected by a temperature detecting means (not shown) arranged in contact with or non-contact with the fixing sleeve 21. Heating control by the sheet heating element 22 is performed. After the temperature is raised to a temperature necessary for fixing, the sheet is held and the sheet feeding of 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. Furthermore, the fixing sleeve 21 is heated only in the area corresponding to the width of the recording medium P scheduled to pass paper, and the excessive temperature rise in the area outside it is prevented.

  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.

  The heat generation width adjusting mechanism used in the present invention is not limited to the heat generation width adjusting mechanism 32 shown in FIG. 9 and 10 show another configuration example of the heat generation width adjustment mechanism used in the present invention.

  FIG. 9 is a schematic view showing a configuration example (2) of the heat generation width adjusting mechanism used in the present invention. Here, only the planar heating element 22 and the heating width adjusting mechanism 33 are conceptually shown.

Here, the basic configuration of the planar heating element 22 is the same as that described above as the planar heating element 22 constituting the fixing device 50, but is different in the following points.
That is, as the heat generating sheet 22s, the resistance heat generating layer 22b having a certain width is formed in a meandering state on the insulating base layer 22a. Three or more electrode terminals (six electrode terminals i to vi in FIG. 9) 22e are connected to each other at a predetermined interval. In the fixing device 20 of FIG. 7, the heating sheet 22 s of the sheet heating element 22 is held on the outer peripheral surface of the heating element holding member 23, and only the plurality of electrode terminals 22 e are fixed on the terminal base stay 24. Each of the plurality of electrode terminals 22e is led out to the outside of the fixing sleeve 21 in one axial direction by a lead wire such as a harness.

  Further, the heat generation width adjusting mechanism 33 has three or more power supply terminals (1 to 3 in FIG. 9) that independently connect the lead wires corresponding to the plurality of electrode terminals 22e drawn to the outside of the fixing sleeve 21. 6 terminals) 33t. In other words, two arbitrarily selected power supply terminals 33t among the three or more power supply terminals 33t are in a state where power can be supplied from an external power source to the electrode terminal 22e to be connected.

  For example, it is assumed that a specific one of the three or more power supply terminals 33t is always in contact with one specific electrode terminal 22e (the electrode terminal 22e of the reference symbol i). In addition, a structure in which an arbitrary power supply terminal 33t can be selected from the remaining power supply terminals 33t, for example, a channel switching structure may be used. As a result, the specific heating electrode 32e and one of the remaining feeding electrodes 32e are selected by the heating width adjusting mechanism 33, and power is supplied from those electrode terminals 22e.

  Thus, for example, in the configuration shown in FIG. 9, the power supply terminal 33 t is selected by switching between five different channels. In the case of a certain channel 1, the power supply terminals 33 t of 1 and 2 are selected, Power is supplied to the resistance heating layer 22b between the i and ii electrode terminals 22e. Further, in the case of a certain channel 2, the power supply terminals 33t with reference numerals 1 and 3 are selected, and power is supplied to the resistance heating layer 22b between the electrode terminals 22e with reference numerals i and iii. In the case of a certain channel 3, the power supply terminals 33 t denoted by reference numerals 1 and 4 are selected to supply power to the resistance heating layer 22 b between the electrode terminals 22 e denoted by reference numerals i and iv. Further, in the case of a certain channel 4, the power supply terminals 33t with reference numerals 1 and 5 are selected and power is supplied to the resistance heating layer 22b between the electrode terminals 22e with reference numerals i and v. Further, in the case of a certain channel 5, the power supply terminals 33t with reference numerals 1 and 6 are selected, and power is supplied to the resistance heating layer 22b between the electrode terminals 22e with reference numerals i and vi.

  As described above, in the heat generation width adjusting mechanism unit 33, any two power supply terminals 33t are selected from the three or more power supply terminals 33t, and the correspondence in the three or more electrode terminals 22e of the planar heat generator 22 is selected. Any two electrode terminals 22e can be brought into contact with a power supply from a power source. At this time, the interval between the electrode terminals 22e through which the resistance heating layer 22b can be energized can be set to an arbitrary interval by the selected channel of the power supply terminal 33t. As a result, the heat generation in the axial direction of the fixing sleeve 21 of the heating sheet 22s. The width can be changed.

  Further, it is preferable that the heat generation width adjustment mechanism unit 33 changes the heat generation width of the heat generation sheet 22s in accordance with the size of the recording medium P to be passed. In the case of FIG. 9, the sheet passing of the recording medium P is based on the right end in the axial view. For example, when the recording medium P of the minimum size to be passed through the fixing device 20 is passed, the channel 1 is set in the heat generation width adjusting mechanism 33 in FIG. , Ii to supply power to the resistance heating layer 22b between the electrode terminals 22e. Further, when the maximum size recording medium P to be passed through the fixing device 20 is passed, the channel 5 is set in the heat generation width adjusting mechanism 33 in FIG. , Vi is preferably supplied to the resistance heating layer 22b between the electrode terminals 22e of vi. As a result, a predetermined area in the axial direction that matches the width of the recording medium P that passes through the heat generating sheet 22s generates heat, and the fixing sleeve 21 can be heated with an appropriate width, and the recording medium that passes through the fixing sleeve 21 passes through. It is possible to prevent an excessive temperature increase in a region outside the width of P.

  FIG. 10 is a schematic view showing a configuration example (3) of the heat generation width adjusting mechanism used in the present invention. Here, only the planar heating element 22 and the heating width adjusting mechanism 34 are conceptually shown.

Here, the basic configuration of the planar heating element 22 is the same as that described above as the planar heating element 22 constituting the fixing device 50, but is different in the following points.
That is, as the heat generating sheet 22s, a resistance heating layer 22b having a certain width (or linear shape) is formed in a meandering manner on the insulating base layer 22a, and one of the resistance heating layers 22b in the circumferential direction is formed. At the end, three or more electrode terminals (11 electrode terminals in FIG. 10) 22e are connected with a predetermined interval in the axial direction. In the fixing device 20 of FIG. 7, the heating sheet 22 s of the planar heating element 22 is held on the outer peripheral surface of the heating element holding member 23, and only the plurality of electrode terminals 22 e are axially arranged on the terminal block stay 24. It is fixed at the predetermined interval.

  Further, the heat generation width adjusting mechanism 34 includes a rotating shaft member 34a having a thread groove formed on the outer peripheral surface thereof and arranged to be rotatable, and one specific electrode terminal 22e among the three or more electrode terminals 22e. (The electrode terminal 22e at the right end in the drawing) is connected to the power supply electrode 34e1 connected to be capable of power supply, and a screw hole that is threaded on the inner periphery is passed through the shaft of the rotary shaft member 34a. And a power supply electrode 34e2 that moves in the axial direction as the motor rotates and contacts any electrode terminal 22e other than the specific one electrode terminal 22e so that power can be supplied.

Thus, when the power supply electrode 34e2 is moved by rotating the rotation shaft member 34a by a predetermined distance from the reference position with respect to a certain position in the axial direction of the rotation shaft member 34a, the power supply electrode 34e2 other than the one specific electrode terminal 22e is moved. Electric power can be supplied from the electrode terminal 22e in contact with an arbitrary electrode terminal 22e and connected to the electrode terminal 22e and the power supply electrode 34e1. The way of selecting the electrode terminal 22e is the same as that shown in FIG.
At this time, the interval between the electrode terminals 22e through which the resistance heating layer 22b can be energized can be set to an arbitrary interval depending on the method of selecting the feeding electrode 34e2, and as a result, the heating sheet 22s in the axial direction of the fixing sleeve 21 can be set. It becomes possible to change the heat generation width.

Further, it is preferable that the heat generation width adjusting mechanism unit 34 changes the heat generation width of the heat generating sheet 22s in accordance with the size of the recording medium P to be passed. In the case of FIG. 10, the sheet passing of the recording medium P is based on the right end in the axial view.
As a result, a predetermined area in the axial direction that matches the width of the recording medium P that passes through the heat generating sheet 22s generates heat, and the fixing sleeve 21 can be heated with an appropriate width, and the recording medium that passes through the fixing sleeve 21 passes through. It is possible to prevent an excessive temperature increase in a region outside the width of P.

Next, the image forming apparatus according to the present invention will be described.
FIG. 11 is an overall configuration diagram showing the configuration of the image forming apparatus according to the present invention.
As shown in FIG. 11, the image forming apparatus 1 is a tandem 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. 11 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 endlessly moved 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. 11, the uppermost recording medium P is fed toward 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, the image forming apparatus according to the present invention includes the fixing device 20 described above, so that the warm-up time and the first print time are short, and appropriate image formation is performed even if the size of the recording medium P changes. On the other hand, it is possible to prevent an excessive temperature rise in the area where the fixing member is not passed.

  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 3 Exposure part 4Y, 4M, 4C, 4K Image formation part 5Y, 5M, 5C, 5K Photosensitive drum 12 Paper feed part 20, 50 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 22s Heating sheet 23 Heating element support member 24 Terminal block stay 25 Feed line 26 Contact member 27 Rotation support member 27a Opening portion 28 Core holding member 29 Heat insulation support Member 31 Pressure roller 32, 33, 34 Heat generation width adjusting mechanism 32a, 34a Rotating shaft member 32e, 34e1, 34e2 Feeding electrode 33t Feeding terminal 75 Charging part 76 Developing part 77 Cleaning part 78 Intermediate transfer belt 79Y, 79M, 79C, 79K First transfer bias roller 80 Intermediate transfer creep 82 Secondary transfer backup roller 83 Cleaning backup roller 84 Tension roller 89 Secondary transfer roller 85 Intermediate transfer unit 97 Paper feed roller 98 Registration roller pair 99 Paper discharge roller pair 100 Stack part 101 Bottle storage part 102Y, 102M, 102C, 102K toner bottle L laser beam 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 2008-310051 A

Claims (4)

A fixing member for a rotating 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;
The fixing member is disposed in contact with or close to the inner peripheral side of the fixing member, and directly or indirectly heats the fixing member, and one resistance heating layer is provided on the insulating base layer. A sheet heating element comprising: a heating sheet formed; and three or more electrode terminals that supply electric power to the resistance heating layer and are arranged such that a conduction distance in the resistance heating layer can be adjusted. When,
A heating element support member disposed on an 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;
A heat generation width adjusting mechanism for connecting any two electrode terminals of three or more electrode terminals of the planar heat generating element and a power source so as to be able to supply power, and changing a heat generation width in the axial direction of the fixing member of the heat generating sheet. And comprising
The heating width adjusting mechanism includes a rotating shaft member provided with a power supply terminal for supplying power from the power source to the electrode terminal at each axial position corresponding to the three or more electrode terminals. ,
The power supply terminal is provided including a different position in the circumferential direction of the rotating shaft member,
A fixing device characterized in that two of the three or more electrode terminals and the power source are connected so as to be able to supply power by setting the rotating shaft member to a predetermined rotational position. The fixing device according to claim 1, wherein the heat generation width adjusting mechanism unit changes a heat generation width of the heat generating sheet in accordance with a size of a recording medium to be passed. The resistance heating layer in the heat generating sheet fixing device according to claim 1 or 2 conductive particles in heat-resistant resin is characterized by comprising dispersed. An image forming apparatus comprising: a fixing device according to any one of claims 1-3.

Images