JP2013054163A - Fixation device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a resistance heating element layer from being damaged by a spark.SOLUTION: A pressure roller 32 is crimped onto the outer peripheral surface of a heating belt 31 on which a resistance heating element layer 31a is provided along the whole circumference to form a fixation nip. Power incoming layers 31d are provided along the whole circumference at both end parts in the direction orthogonal to a rotation direction in the heating belt 31. On the outer peripheral surface of each power incoming layer 31d, a power feeding member 37 is slide contacted. The power feeding members 37 feed power to the resistance heating element layer 31a via the power incoming layers 31d. The slide contact face of the power feeding member 37 is formed into an arc shape that is equal to or smaller than the outer diameter of the power incoming layer 31d when the heating belt 31 is under a non-pressure state, and the central angle of the arc shape is larger than 180°.

Description

  The present invention relates to a fixing device that performs thermal fixing of an unfixed image using a resistance heating element layer that generates Joule heat by power feeding.

In an electrophotographic image forming apparatus such as a printer or a copying machine, a toner image corresponding to image data is transferred to a recording sheet such as plain paper or an OHP sheet, and then fixed by a fixing device. In the fixing device, the toner image on the recording sheet is heated and pressed against the recording sheet to be fixed on the recording sheet.
As a fixing device of an image forming apparatus, a configuration using a heating belt provided with a resistance heating element layer that generates heat when energized is known. In such a fixing device, since the heat capacity of the heating belt is small, the warm-up time can be shortened, and the heat generating heating belt can be raised to the fixing temperature in a short time. In addition, since the heat capacity of the heating belt is small, it can be maintained at a predetermined fixing temperature with a low amount of power, and power consumption can be reduced.

In Patent Documents 1 and 2, a power receiving layer in a conductive state with respect to the resistance heating element layer is provided at each end on both sides in the axial direction of the cylindrical fixing film incorporating the resistance heating element layer in the circumferential direction of the fixing film. And a fixing device provided so that the conductive portion brushes are in sliding contact with the respective power receiving layers.
In the fixing devices disclosed in Patent Documents 1 and 2, electric power is supplied to the respective conductive portion brushes, and the electric power supplied to the conductive portion brushes is resistance through the respective power receiving layers that are in the sliding contact state. Supplied to the heating layer. Thereby, the resistance heating element layer generates heat.

JP-A-8-137304 JP-A-8-202183

  In the fixing devices disclosed in Patent Documents 1 and 2 described above, the conductive portion brush is configured in an arc shape along the circumferential movement direction of each power receiving layer, and the center angle of the arc shape is more than 180 °. It is a small angle. The fixing film that moves around has flexibility, and the fixing film that moves around due to the vibration of the gear when the power from the drive source is transmitted through the gear or the like is removed from the arc-shaped conductive part brush. There is a risk of displacement or deformation in the direction of separation.

Depending on the displacement or deformation of the fixing film, the conductive portion brush may not come into contact with the power receiving layer, and a potential difference between the conductive portion brush and the power receiving layer may occur, and spark may occur. When the spark is generated, a part of the surface of the power receiving layer is damaged by the heat of the spark, and the resistance heating element layer in a conductive state with the power receiving layer may be damaged.
The present invention has been made in view of such problems, and its purpose is to prevent the occurrence of sparks between the power receiving layer provided in the resistance heating element layer and the power feeding member, and to prevent resistance. An object of the present invention is to provide a fixing device that prevents the heating element layer from being damaged and an image forming apparatus including the fixing device.

  In order to achieve the above object, the fixing device according to the present invention has a fixing nip formed by pressing a pressure member against a heating rotator provided with a resistance heating element layer on the entire periphery, and an unfixed image. A fixing device that heat-fixes the recording sheet on which the recording sheet is formed by passing the recording sheet through the fixing nip, in a circumferential direction in a conductive state with the resistance heating element layer at both ends in the axial direction of the heating rotator. A pair of power receiving layers provided along the power supply member disposed in sliding contact with the outer peripheral surface of each power receiving layer, and the power supply member has a sliding contact surface with the power receiving layer. The heating rotator is formed in an arc shape having a diameter equal to or smaller than the outer diameter of the power receiving layer when in a non-pressed state, and the central angle of the arc shape is larger than 180 °. Features.

  An image forming apparatus according to the present invention includes the fixing device.

  In the fixing device according to the present invention, the power receiving layer provided at both ends of the resistance heating element layer in the rotational axis direction of the resistance heating element layer is deformed with respect to the power supply member by the circumferential movement of the heating rotation element provided with the resistance heating element layer. Alternatively, even when the power receiving layer is displaced, the outer peripheral surface of the power receiving layer is kept in contact with the arc-shaped sliding contact surface of the power supply member at any position in the circumferential direction. Thereby, there is no possibility that a spark occurs between the power supply member and the power receiving layer, and therefore it is possible to prevent the resistance heating element layer from being damaged.

Preferably, the width of the power feeding member in the axial direction is constant throughout.
Preferably, the width in the axial direction of the power supply member is shorter than the central portion in the circumferential direction at any one end.
Preferably, the power supply member is disposed so that a central position in the axial direction of the power feeding member coincides with a central position in the axial direction of the power receiving layer.

1 is a schematic diagram illustrating a configuration of a printer that is an example of an image forming apparatus including a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic perspective view for explaining a configuration of a main part in a fixing device provided in the printer. FIG. 3 is a schematic cross-sectional view for explaining the configuration of the fixing device. FIG. 3 is a schematic cross-sectional view along an axial direction that is a direction orthogonal to a circumferential movement direction of a heating belt provided in the fixing device, and corresponds to a cross section along line YY in FIG. 2. FIG. 4 is a perspective view of a power supply member provided in the fixing device. It is a table | surface which shows the conditions and result of the experiment conducted in order to verify the effect in the fixing device of this invention. (A) And (b) is a perspective view which shows the other example of an electric power feeding member, respectively. FIG. 9 is a schematic cross-sectional view for explaining a modification of the fixing device in the embodiment of the present invention. FIG. 10 is a schematic cross-sectional view for explaining still another modification of the fixing device in the embodiment of the present invention.

Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described.
<Schematic configuration of image forming apparatus>
FIG. 1 is a schematic diagram illustrating a configuration of a printer which is an example of an image forming apparatus provided with a fixing device according to an embodiment of the present invention. This printer forms a monochrome toner image on a recording sheet such as plain paper or an OHP sheet.

The printer shown in FIG. 1 includes a photosensitive drum 11 that is rotationally driven in a direction indicated by an arrow A, and a toner image is formed on the recording sheet S around the photosensitive drum 11 by electrophotography. The charging device 12, the exposure device 13, the developing device 14, and the transfer roller 15 are provided in the order along the rotation direction of the photosensitive drum 11.
The surface of the photosensitive drum 11 in a rotating state is charged to a predetermined potential by the charging device 12 after the residual charge is removed by the static eliminator 18 disposed on the upstream side of the charging device 12. Thereafter, the surface of the photosensitive drum 11 is exposed by the laser light L emitted from the exposure device 13. The exposure device 13 is provided with a laser diode that irradiates a laser beam L. The laser diode is driven by a control unit (not shown) based on image data input from an external device to irradiate the laser beam L. .

  On the surface of the photosensitive drum 11, an electrostatic latent image is formed by exposure of the laser light L emitted from the exposure device 13. A developing device 14 that develops an electrostatic latent image on the surface of the photoconductive drum 11 faces the surface of the photoconductive drum 11 on the downstream side in the rotation direction from the position where the laser light L is irradiated on the photoconductive drum 11. Is provided. The electrostatic latent image formed on the surface of the photosensitive drum 11 is developed with toner by the developing device 14 and visualized as a toner image.

  Below the photosensitive drum 11, a recording sheet cassette 21 capable of storing a plurality of recording sheets S such as plain paper and OHP sheets is provided, and the recording sheet S stored in the recording sheet cassette 21 is fed. Rolls out one by one by the roller 22. The recording sheet S fed out from the recording sheet cassette 21 is conveyed toward the photosensitive drum 11 by the timing roller pair 23.

  A transfer roller 15 that rotates in the direction of arrow B is provided on the side of the photosensitive drum 11 in a state of being pressed against the photosensitive drum 11, and a transfer nip portion is provided between the transfer roller 15 and the photosensitive drum 11. Is formed. The recording sheet S fed out from the recording sheet cassette 21 is conveyed to the transfer nip portion by the timing roller pair 23 and passes through the transfer nip portion.

  While the recording sheet S passes through the transfer nip portion, the toner image formed on the photosensitive drum 11 is transferred onto the recording sheet S by the action of the transfer electric field generated by the transfer voltage applied to the transfer roller 15. Is done. The recording sheet S to which the toner image has been transferred is peeled off from the photosensitive drum 11 by the peeling claw 16 and conveyed to a fixing device 30 provided above the transfer roller 15. The residual toner remaining on the photosensitive drum 11 is removed from the surface of the photosensitive drum 11 by the cleaning member 17.

<Configuration of fixing device>
FIG. 2 is a schematic perspective view for explaining the configuration of the main part of the fixing device 30, and FIG. 3 is a cross-sectional view of the fixing device 30. In the fixing device 30, as shown in FIG. 1, the recording sheet passes from the bottom to the top, but in FIG. 2, the recording sheet passes in a direction orthogonal to the paper surface. The fixing device 30 is shown in FIG.

As shown in FIGS. 2 and 3, the fixing device 30 includes a pressure roller 32 as a pressure member, and a cylindrical heating arranged so as to be rotatable (circular movement) while being pressed against the pressure roller 32. A belt 31 and a pressing roller 33 disposed inside the rotation area (circulation movement area) of the heating belt 31 so as to be pressed against the inner peripheral surface of the heating belt 31 are provided.
The heating belt 31 is a heating rotator that rotates while being pressed against the pressure roller 32, and includes a resistance heating element layer 31a (see FIG. 4) that generates heat when supplied with power.

For example, the length of the heating belt 31 in the direction (axial direction) orthogonal to the circumferential movement direction is slightly longer than the axial length of the outer peripheral surface of the pressure roller 32. The axes of the heating belt 31 and the pressure roller 32 are parallel to each other. A specific configuration of the heating belt 31 will be described later.
The pressing roller 33 provided in the circumferential movement region of the heating belt 31 includes a cored bar 33b provided in the shaft center part, and a cylindrical pressing roller main body 33a laminated on the outer peripheral surface of the cored bar 33b over the entire circumference. have. The cored bar 33b has shaft portions 33c that protrude outward from both end surfaces on both sides in the axial direction of the pressing roller main body portion 33a.

  The metal core 33b of the pressing roller 33 is configured by a metal pipe such as aluminum or iron having a thickness of about 1.0 to 10 mm. The pressing roller main body 33a has an elastic layer made of an elastic material having excellent heat resistance such as silicone rubber and fluororubber. The axial length of the pressing roller body 33 a is substantially equal to the axial length of the heating belt 31.

  The pressure roller 32 pressed against the outer peripheral surface of the heating belt 31 has an elastic layer 32a and a release layer 32b sequentially stacked on the outer peripheral surface of a pipe-shaped cored bar 32c. The diameter (the outer diameter of the pressure roller 32) is about 20 to 100 mm. The cored bar 32c has shaft portions 32d that protrude outward from both end surfaces on both sides in the axial direction of the pressure roller main body portion 32a.

The metal core 32c of the pressure roller 32 is formed of a metal pipe such as aluminum or iron having a thickness of about 1.0 to 10 mm. The elastic layer 32b of the pressure roller 32 is configured to have a thickness of about 1 to 20 mm by a highly heat-resistant elastic body such as silicone rubber or fluororubber.
The release layer 32b of the pressure roller 32 has releasability, and PFA (polytetrafluoroethylene), PTFE (polytetrafluoroethylene (tetrafluoroethylene) resin), ETFE (tetrafluoroethylene / ethylene co-polymer). For example, a thickness of about 5 to 100 μm is formed by a fluorine-based tube such as a polymerized resin), a fluorine-based coating, or the like. The release layer 32b may be conductive.

  The pressure roller 32 is urged toward the heating belt 31 by an urging means (for example, a tension spring) (not shown), and the release layer 32 b of the pressure roller 32 is pressed via the heating belt 31. 33 is pressed against the outer peripheral surface of the pressing roller body 33a. As a result, the heating belt 31 and the pressure roller 32 are in pressure contact with each other. A fixing nip N through which the recording sheet S passes is formed at the pressure contact portion between the heating belt 31 and the pressure roller 32.

  The pressure roller 32 is rotated in a direction indicated by an arrow B in FIG. The heating belt 31 follows the rotation of the pressure roller 32 by the pressure roller 33 being pressed against the inner peripheral surface and the pressure roller 32 is pressed against the outer peripheral surface, and is indicated by an arrow A in FIG. Rotate (turn around) in the direction. Further, the pressing roller 33 rotates in the same direction following the rotation of the heating belt 31.

  The unfixed toner image on the recording sheet S conveyed to the fixing nip N is heated and pressed by the pressure roller 32 and the heating belt 31 while the recording sheet S passes through the fixing nip N. As a result, the image is fixed on the recording sheet S. The recording sheet S that has passed through the fixing nip N is peeled off from the heating belt 31 by the separation claw 35 (see FIG. 1). The recording sheet S peeled from the heating belt 31 is discharged onto a paper discharge tray 19 (see FIG. 1) by a pair of paper discharge rollers 24 (see FIG. 1).

  In the above description, the pressure roller 32 is rotationally driven, but instead of such a configuration, the heating belt 31 and the pressure roller 32 are the pressure roller as a configuration for rotationally driving the pressure roller 33. It is good also as a structure made to follow the rotation of 33 and to rotate. Alternatively, as a configuration in which both the pressure roller 32 and the pressure roller 33 are driven to rotate, the heating belt 31 may be configured to follow both the pressure roller 32 and the pressure roller 33 and rotate.

  4 is a cross-sectional view along an axial direction that is a direction orthogonal to the circumferential movement direction of the heating belt 31, and corresponds to a cross section along line YY in FIG. As shown in FIG. 4, the heating belt 31 has a resistance heating element layer 31a, an elastic layer 31b laminated on the resistance heating element layer 31a, and a release layer 31c laminated on the elastic layer 31b. doing. Each of the resistance heating element layer 31a, the elastic layer 31b, and the release layer 31c has a constant thickness.

The resistance heating element layer 31a generates Joule heat by the current flowing, and the recording sheet S passing through the fixing nip N is heated by the generated Joule heat.
The material constituting the resistance heating element layer 31a is not particularly limited as long as it generates Joule heat by flowing current. For example, a conductive filler is uniformly dispersed in a heat resistant resin. The resistance heating element layer 31a is constituted by the formed molded body, metal or the like.

  When the resistance heating element layer 31a is formed of a molded body in which a conductive filler is uniformly dispersed in a heat resistant resin, the heat resistant resin includes PI (polyimide), PPS (polyphenylene sulfide), PEEK (polyether ether). Ketone) and the like are used. In particular, PI is preferable because of its excellent heat resistance. As the conductive filler, metals such as Ag, Cu, Al, Mg, and Ni, and carbon compounds such as graphite, carbon black, carbon nanofiber, and carbon nanotube are suitable.

The conductive filler is preferably fibrous. When the conductive filler is in a fibrous form, compared to the case where the conductive filler is in a shape other than the fibrous form, if the content is the same, the probability that the conductive fillers are in contact with each other increases. It becomes possible to make the whole into a more uniform conductive state.
When the resistance heating element layer 31a is constituted by a molded body in which conductive filler is uniformly dispersed in a heat resistant resin, the electrical resistivity can be adjusted by adjusting the thickness of the resistance heating element layer 31a. The electrical resistivity in this case is usually about 1.0 × 10 ^{−6 to} 9.9 × 10 ⁻³ Ω · m, preferably 1.0 × 10 ^{−5 to} 5.0 × 10 ⁻³ Ω · m. m.

Further, when the resistance heating element layer 31a is made of metal, SUS, Ni—Cr, Ti, Cr, Ti—Al, and the like are preferable. Also in this case, the electrical resistivity of the resistance heating element layer 31a can be adjusted by adjusting the thickness of the resistance heating element layer 31a, and is usually 1.0 × 10 ^{−8 to} 9.9 × 10 ^{−. About 5} Ω · m, preferably about 1.0 × 10 ^{−7 to} 5.0 × 10 ⁻⁶ Ω · m.

For example, when the resistance heating element layer 31a is formed of a molded body of heat resistant resin in which conductive filler is uniformly dispersed, the content of the conductive filler is sequentially changed along the direction of current flow. You may do it. Furthermore, when the resistance heating element layer 31a is a metal and contains about several percent of an additive, the ratio of the additive may be slightly different along the direction of current flow.
The manufacturing method of the resistance heating element layer 31a is arbitrary and is not particularly limited. For example, when the resistance heating element layer 31a is formed of a heat-resistant resin molded body in which conductive filler is uniformly dispersed, it is molded using a mold having a predetermined shape in the same manner as a normal resin molded body. can do. Alternatively, the resistance heating element layer 31a may be manufactured by molding a heat-resistant resin containing a conductive filler into a cylindrical shape having a certain thickness.

The elastic layer 31b is laminated on a region excluding the ends on both sides in the axial direction of the resistance heating element layer 31a, and the release layer 31c is laminated on the entire outer peripheral surface of the elastic layer 31b. The recording sheet S passing through the fixing nip N is pressed against the outer peripheral surface of the release layer 31c laminated on the elastic layer 31b.
The elastic layer 31b is formed with a thickness of about 1 to 20 mm by a highly heat-resistant elastic body such as silicone rubber or fluororubber.

A power receiving layer 31d for receiving a current supplied to the resistance heating element layer 31a from a power supply member 37, which will be described later, is stacked on the respective ends of both sides in the axial direction of the resistance heating element layer 31a. .
The release layer 31c has releasability, such as PFA (polytetrafluoroethylene), PTFE (polytetrafluoroethylene (tetrafluoroethylene) resin), ETFE (tetrafluoroethylene / ethylene copolymer resin), etc. For example, a thickness of about 5 to 100 μm is formed by a fluorine-based tube, a fluorine-based coating, or the like.

  The heating belt 31 has a predetermined rigidity so as to maintain a cylindrical shape with a predetermined diameter in a state in which the pressure roller 32 is not in pressure contact, and can be deformed by the pressure roller 32 being in pressure contact. have. The pressure roller 33 having an elastic layer can also be deformed when the pressure roller 32 is pressed by the heating belt 31. The heating belt 31 is deformed into a state along the outer peripheral surface of the pressure roller 32 following the deformation of the pressure roller 33 caused by the pressure roller 32 being pressed.

  The heating belt 31 is not limited to the three-layer structure of the resistance heating element layer 31a, the elastic layer 31b, and the release layer 31c, and may have at least the resistance heating element layer 31a. For this purpose, the heating belt 31 may have a two-layer structure of a resistance heating element layer 31a and a release layer 31c. Further, a resin layer such as PI or PPS for insulation may be further laminated to have a structure of three or more layers.

  Each of the power receiving layers 31d stacked over the entire circumference on both ends in the axial direction of the resistance heating element layer 31a is in a conductive state with respect to the resistance heating element layer 31a. Each power receiving layer 31d does not need to be in a conductive state over the entire circumference with respect to the resistance heating element layer 31a, and may have a configuration in which it is in a conductive state with the resistance heating element layer 31a in a part of the circumferential direction. Good. However, since it is preferable that the current flows uniformly over the entire circumference of the resistance heating element layer 31a, each power receiving layer 31d is preferably in a conductive state over the entire circumference of the resistance heating element layer 31a.

  Each power receiving layer 31d is made of a conductive material and has a constant thickness and an axial (width direction) length. As the power receiving layer 31d, for example, a metal such as copper (Cu), aluminum (Al), nickel (Ni), stainless steel (SUS), brass, phosphor bronze, etc. can be used. It is desirable to use nickel, stainless steel, aluminum, etc. that are excellent in oxidation resistance.

Since each of the power receiving layers 31d becomes more rigid as it becomes thicker, damage such as breakage is less likely to occur. However, if the rigidity becomes higher, it becomes difficult to be deformed, so that it affects deformation of the elastic layer 31b forming the fixing nip N. May affect. For this reason, the thickness of the power receiving layer 31d is preferably about 10 to 100 μm, more preferably about 30 to 70 μm.
The length of each power receiving layer 31d along the axial direction of the heating belt 31 varies depending on the radius of the outer peripheral surface of the heating belt 31 (the radius of the outer peripheral surface of the power receiving layer 31d), but is usually about 5 to 30 mm. .

  Each power receiving layer 31d is formed in advance in a ring shape by electroforming, spatula drawing, press drawing, or the like, and formed integrally when the resistance heating element layer 31a is formed. It is manufactured by, for example, a method in which the resistance heating element layer 31a is bonded to and formed on the outer peripheral surfaces of both ends of the resistance heating element layer 31a. In order to improve the adhesion with the resistance heating element layer 31a, a hole may be provided in a contact portion with the resistance heating element layer 31a by etching, laser drilling, or the like.

Further, each power receiving layer 31d may be formed by Ni plating, Cu plating or the like on the resistance heating element layer 31a formed in a predetermined shape. Further, each power receiving layer 31d may be formed by applying a conductive paste to the outer peripheral surface of the resistance heating element layer 31a.
As shown in FIGS. 2 to 4, a power supply member 37 that supplies current to each power receiving layer 31 d is provided around each power receiving layer 31 d on the opposite side of the pressure roller 32. Each power feeding member 37 has an arc shape along the circumferential direction of the power receiving layer 31d. An alternating current supplied from a commercial AC power supply 34 (see FIG. 2) is supplied to each power supply member 37 via a harness, and an inner peripheral surface that faces each power receiving layer 31d. The alternating current supplied to each power supply member 37 flows through the power receiving layer 31d by slidingly contacting the outer peripheral surface of the power receiving layer 31d.

Each power supply member 37 is configured in the same shape by, for example, conductive brushes obtained by mixing and baking carbon powder and powder such as copper powder. As the conductive brush, copper graphite, carbon graphite or the like is used.
As shown in FIG. 3, each power supply member 37 has an inner peripheral surface (sliding contact surface slidably contacting the outer peripheral surface of the power receiving layer 31d) facing the power receiving layer 31d at a center angle θ larger than 180 °. Thus, it is formed in an arc shape having an opening in a part of the circumferential direction. In the present embodiment, the center angle θ is 190 °.

The inner peripheral surface and the outer peripheral surface of the power supply member 37 each have a constant radius. In the present embodiment, the curvature radius Rk of the inner peripheral surface of the power supply member 37 is equal to the radius Rj of the outer peripheral surface of the power receiving layer 31d in a state where the heating belt 31 is not pressed by the pressure roller 32, and is 20 mm respectively. Yes.
FIG. 5 is a perspective view of the power supply member 37. As shown in FIG. 5, the axial length of the power supply member 37 is a constant length (about 5 to 30 mm) slightly shorter than the power receiving layer 31d.

  Each power supply member 37 is in a plane-symmetrical state with respect to a plane including straight lines connecting the respective axes of the pressure roller 32 and the pressure roller 33 with both ends in the circumferential direction positioned on the pressure roller 32 side. The whole is urged toward the pressure roller 32 along the radial direction. In this case, the power receiving layer 31d is located in the internal space of the power feeding member 37, and the axial center position of the power receiving layer 31d substantially coincides with the axial center position of the inner peripheral surface of the power feeding member 37 in the arc shape. It is in a state (coaxial state).

  When the power feeding member 37 having an inner peripheral surface with a radius Rk equal to the radius Rj of the outer peripheral surface of the power receiving layer 31d is coaxial with the power receiving layer 31d, the entire inner peripheral surface of the power feeding member 37 receives power. The power supply member 37 and the power receiving layer 31d are in a conductive state in contact with the outer peripheral surface of the layer 31d. In this case, the respective ends on both sides in the circumferential direction of the power supply member 37 are in contact with the outer peripheral surface of each power receiving layer 31d at a position on the pressure roller 32 side with respect to the axis of the heating belt 31 (power receiving layer 31d). .

  As shown in FIG. 4, the end portions on both sides in the circumferential direction of the power supply member 37 have the axial center portion (width direction) coincident with the axial direction (width direction) center portion of the outer peripheral surface of the power receiving layer 31d. In this manner, the power receiving layer 31d is in pressure contact with the outer peripheral surface. Thereby, the distribution of the pressure applied to the outer peripheral surface of the power receiving layer 31d from each end portion in the circumferential direction of the power supply member 37 can be prevented from being shifted to either one from the center position in the width direction. As a result, the inner peripheral surface of each end of the power supply member 37 and the outer peripheral surface of the power receiving layer 31d can be stably slidably brought into contact with each other.

  In the fixing device 30 having such a configuration, when a current is supplied to one power supply member 37, a current is supplied from the one power receiving layer 31 d that is in sliding contact with the power supply member 37 to the resistance heating element layer 31 a. The current supplied to the resistance heating element layer 31a flows along the axial direction in the resistance heating element layer 31a, and then flows from the other power reception layer 31d to the other power supply member 37 that is in sliding contact with the power reception layer 31d. In this way, when the current flows through the resistance heating element layer 31a, the resistance heating element layer 31a generates heat.

  The heat generated in the resistance heating element layer 31a is transmitted to the release layer 31c through the elastic layer 31b. The heat transmitted to the release layer 31 c is transmitted to the recording sheet S passing through the fixing nip N, and the toner image on the recording sheet S is melted. The toner image in a molten state is fixed onto the recording sheet S by being pressed onto the recording sheet S by the pressure roller 32.

  The electrical resistivity of the resistance heating element layer 31a is the power supplied to the resistance heating element layer 31a, the applied voltage, the thickness of the resistance heating element layer 31a, the outer diameter and the circumferential length of the heating belt 31, It is arbitrarily set based on the diameter and axial length of the pressing roller 33. For example, resistance heat generation in the heating belt 31 in which the outer diameter and the circumferential length are set by setting the outer diameter and the circumferential length of the heating belt 31 depending on the fixability and durability of the toner image on the recording sheet S, etc. What is necessary is just to set the thickness, electrical resistivity, etc. of the resistance heating element layer 31a so that a predetermined calorific value can be obtained by the body layer 31a.

  The heating belt 31 that is circulated is heated by fluctuations in pressure applied to the heating belt 31 when the recording sheet passes through the fixing nip N, vibrations of a gear that transmits a rotational force for rotating the heating belt 31, and the like. There is a possibility that the rotational movement area of the belt 31 (all of the resistance heating element layer 31a, the elastic layer 31b, and the release layer 31c) is deformed except for a portion located in the fixing nip N. When the resistance heating element layer 31a is deformed, each of the power receiving layers 31d stacked on the resistance heating element layer 31a is not pressed against the pressure roller 32 (see FIG. 2). Attempts to deform following the deformation of the area.

However, even if the orbital movement area of the power receiving layer 31d is about to be deformed, the power receiving layer 31d moves around in a state of being constrained by the inner peripheral surface of the power feeding member 37. The contact state is maintained.
Therefore, the conductive state between the power supply member 37 and the power receiving layer 31d is reliably maintained regardless of which direction the circular movement area of the power receiving layer 31d is displaced. Thereby, generation | occurrence | production of the spark by the electric power feeding member 37 and 31 d of electric power receiving layers becoming a non-contact state can be prevented. As a result, there is no possibility that the power receiving layer 31d is damaged by the spark, and therefore there is no possibility that the resistance heating element layer 31a on which the power receiving layer 31d is laminated is damaged.

If the central angle of the power feeding member 37 is slightly larger than 180 °, the power receiving layer 31d is pressed against the outer peripheral surface of the power receiving layer 31d because both ends of the power receiving layer 31d are in circumferential contact with each other. The layer 31d can be moved around in a constrained state. Therefore, the central angle of the power supply member 37 only needs to be slightly larger than 180 °.
However, if the central angle of the power supply member 37 becomes too large, the sliding resistance between the inner peripheral surface of the power supply member 37 and the outer peripheral surface of the power receiving layer 31d increases, so that wear of the power supply member 37 is promoted and durability is increased. May decrease.

  The radius Rk of the inner peripheral surface of the power supply member 37 is not limited to the configuration equal to the radius Rj of the outer peripheral surface of the power receiving layer 31d, and may be slightly smaller than the radius Rj of the outer peripheral surface of the power receiving layer 31d. When the radius Rk of the inner peripheral surface of the power feeding member 37 is slightly smaller than the radius Rj of the outer peripheral surface of the power receiving layer 31d, the outer peripheral surface of the power receiving layer 31d is on the entire circumference of the inner peripheral surface of the power feeding member 37. The power receiving layer 31d is deformed and circulates in a state in which a part of the power receiving layer 31d protrudes outward from the gap between the ends on both sides in the circumferential direction of the power supply member 37.

  However, even when the radius Rk of the inner peripheral surface of the power feeding member 37 is too small (Rk << Rj) relative to the radius Rj of the outer peripheral surface of the power receiving layer 31d, the power receiving layer with respect to the inner peripheral surface of the power feeding member 37 is also provided. The sliding resistance of the outer peripheral surface of 31d increases, and the durability of the power supply member 37 may be reduced. For this reason, it is preferable that the difference (Rj−Rk) between the radius Rj of the outer peripheral surface of the power receiving layer 31d and the radius Rk of the inner peripheral surface of the power feeding member 37 is small.

From the above, considering the durability of the power supply member 37, the difference (Rj−) between the central angle θ of the power supply member 37, the radius Rj of the outer peripheral surface of the power receiving layer 31d, and the radius Rk of the inner peripheral surface of the power supply member 37. Each of Rk) can be set.
The central angle of the power supply member 37 is preferably 270 ° or less, and more preferably 225 ° or less.

Further, the difference (Rj−Rk) between the radius Rj of the outer peripheral surface of the power receiving layer 31d and the radius Rk of the inner peripheral surface of the power feeding member 37 is 5 mm (of the radius of the power receiving layer 31d), although it depends on the radius of the heating belt 31. 25%) or less, preferably 2 mm (10% of the radius of the power receiving layer 31d) or less.
The width of the power supply member 37 (the length along the axial direction) is not particularly limited, but if the width of the power supply member 37 is shortened at the contact position with the power receiving layer 31d, the power supply member 37 Since the current density supplied to the power receiving layer 31d increases, the power feeding member 37 deteriorates. When a conductive brush is used as the power supply member 37, it is preferable that the current density is 20 A / cm ² or less, although it varies depending on the supplied current, voltage, and the like. In order to obtain such a current density, the width of the power supply member 37 is preferably about 5 to 30 mm, and more preferably about 10 to 20 mm.

  When the width of the power feeding member 37 is constant throughout, the sliding contact position with the outer peripheral surface of the power receiving layer 31d is changed by applying a force that deforms the power receiving layer 31d with respect to the power feeding member 37. Even so, since the current density of the current supplied from the power supply member 37 to the power receiving layer 31d does not change, wear of the power supply member 37 becomes uniform, and contact unevenness due to durability can be suppressed.

Next, an experiment conducted for verifying the effect of the fixing device of the present invention will be described.
2 to 5, the fixing operation for the recording sheet S is performed five times (fixing operation for five recording sheets), and is generated between the power supply member 37 and the power receiving layer 31 d. It was verified whether or not the resistance heating element layer 31a was damaged by the spark.
In this case, as described above, the radius Rj of the outer peripheral surface of the power receiving layer 31d is 20 mm, and the radius Rk of the inner peripheral surface of the power supply member 37 is also 20 mm. Further, the inner peripheral surface of the power supply member 37 (sliding contact surface with the outer peripheral surface of the power receiving layer 31d) has an arc shape with a central angle of 190 °.

In such a fixing device 30, even when the fixing operation was executed five times, the resistance heating element layer 31 a was not damaged by the spark even once (this is expressed as “0/5”, the same applies hereinafter). The conditions and results in this case are shown as Experiment No. 4 (No. 4) in the table of FIG.
Even when only the radius Rk of the inner peripheral surface of the power supply member 37 is changed to 18 mm and 19 mm shorter than the radius Rj of the outer peripheral surface of the power receiving layer 31d, depending on the execution of the fixing operation five times, The resistance heating element layer 31a was never damaged ("0/5"). The conditions and results in these cases are shown as Experiment No. 5 (No. 5) and Experiment No. 6 (No. 6) in the table of FIG.

For comparison, only the center angle of the power supply member 37 having an arc shape was changed to 90 °, 145 °, and 180 °, respectively. In this case, the power feeding member 37 is biased with respect to the power receiving layer 31 d, and the outer peripheral surface of the power receiving layer 31 d is in contact with the circumferential center position of the power feeding member 37. Under these conditions, five fixing operations were performed.
When the central angle of the power supply member 37 was 90 °, the resistance heating element layer 31a was damaged by the spark in each of the five fixing operations (“5/5”). When the central angle of the power supply member 37 was 145 °, the resistance heating element layer 31a was damaged three times by sparks (“3/5”). Further, when the central angle of the power supply member 37 was 180 °, the resistance heating element layer 31a was damaged once by spark (“1/5”). The respective conditions and results are shown as Experiment No. 1 (No. 1), Experiment No. 2 (No. 2), and Experiment No. 3 (No. 3) in the table of FIG.

Further, for comparison, only the radius of the inner peripheral surface of the power supply member 37 was changed to 21 mm and 22 mm, which were larger than the radius (20 mm) of the power receiving layer 31d, and the fixing operation was performed five times. In this case, since the power feeding member 37 is urged with respect to the power receiving layer 31 d, the outer peripheral surface of the power receiving layer 31 d is in contact with the circumferential center position of the power feeding member 37.
When the radius of the inner peripheral surface of the power supply member 37 is 21 mm, the resistance heating element layer 31a is damaged once by the execution of the fixing operation five times (“1/5”). In this case, the resistance heating element layer 31a was damaged twice by the spark ("2/5"). The respective conditions and results are shown as experiment number 7 (No. 7) and experiment number 8 (No. 8) in the table of FIG.

  As described above, when the radius of curvature of the inner peripheral surface of the power feeding member 37 is larger than the radius of the power receiving layer 31d, a state in which the outer peripheral surface of the power receiving layer 31d does not contact the inner peripheral surface of the power feeding member 37 appears. It is considered that the heating element layer 31a was damaged by the spark (No. 7 and No. 8). Further, even when the central angle of the arc-shaped power supply member 37 is 180 ° or less, a state in which the outer peripheral surface of the power receiving layer 31d does not contact the inner peripheral surface of the power supply member 37 appears, and the resistance heating element layer 31a is caused by the spark. It is thought that it was damaged (No.1-No.3).

  On the other hand, when the radius Rk of the inner peripheral surface of the power feeding member 37 is equal to or less than the radius Rj of the power receiving layer 31d and the center angle of the arc-shaped power feeding member 37 satisfies the condition of 190 ° (No .4 to No. 6), as described above, the feeding member 37 and the power receiving layer 31d are not brought into a non-contact state during the circular movement of the heating belt 31, and the resistance heating element layer 31a is damaged by the spark. It is thought that it did not occur. As described above, it was proved that, when the above-described conditions are satisfied, the resistance heating element layer 31a can be prevented from being damaged by the spark while maintaining the conductive state between the power supply member 37 and the power receiving layer 31d during the fixing operation. .

<Modification>
Note that the power supply member 37 does not need to have a constant width as a whole. For example, as shown in FIG. 7A, the width gradually increases as it approaches one end from the center in the circumferential direction. It is good also as a structure where becomes small. In addition, the width is not limited to a configuration in which the width gradually decreases from the central portion in the circumferential direction to the entire one end portion, but as shown in FIG. It is good also as a structure where a width | variety becomes small sequentially as it approaches the said edge part only in one edge part.

In any case, the current density supplied from the power supply member 37 to the power receiving layer 31d is preferably 20 A / cm ² or less.
In such a configuration, the sliding resistance with the passive layer 31d can be reduced because the width at one end portion in the circumferential direction of the power supply member 37 is small.
In addition, by disposing one end in the circumferential direction of the power supply member 37 having a small width on the downstream side in the conveyance direction of the recording sheet S in the fixing nip N, the power supply member 37 on the downstream side of the fixing nip N. The sliding resistance between the end of the power receiving layer and the power receiving layer 31d can be reduced. As a result, the power receiving layer 31d smoothly contacts the end portion of the power feeding member 37 located on the downstream side in the conveyance direction of the recording sheet S. Therefore, when the power receiving layer 31d contacts the end portion of the power feeding member 37, both It is possible to suppress the deformation of the power receiving layer 31d due to an increase in the frictional resistance.

In addition, the space around one end of the power supply member 37 whose width is smaller than the central portion in the circumferential direction can be widened so that the power supply member 37 does not interfere with other members around the heating belt 31. It becomes easy to arrange in. Furthermore, since the volume of the power supply member 37 is reduced, the amount of material constituting the power supply member 37 is reduced, and the material cost can be reduced.
Further, the arrangement position of the power supply member 37 is not limited to a configuration in which both end portions in the circumferential direction are positioned on the fixing nip N side so that the distance between both end portions faces the fixing nip N. You may change according to the state of the space in the circumference | surroundings of the both sides of the axial direction of the belt 31. FIG.

  For example, as shown in FIG. 8, a straight line connecting the center in the circumferential direction of the power supply member 37 and the axis of the heating belt 31 is 45 with respect to a line connecting the axes of the pressure roller 32 and the pressing roller 33. It may be configured to be arranged in an inclined state. Further, as shown in FIG. 9, each of the power supply members 37 may be arranged on both sides of the fixing nip N in the axial direction with the fixing nip N interposed therebetween. In any case, useless spaces around both sides of the heating belt 31 in the axial direction can be reduced, and an increase in size of the fixing device can be suppressed.

Further, the power receiving layer 31d is not limited to a configuration in which the power receiving layer 31d is disposed in a stacked state on the resistance heating element layer 31a, and may be in a conductive state with respect to the resistance heating element layer 31a. For this reason, it is good also as a structure which each arrange | positions the receiving layer 31d on the outer side of each edge part of the both sides of the axial direction of the resistance heating element layer 31a.
Further, since the power supply member 37 only needs to have an arcuate inner peripheral surface, the outer peripheral surface does not need to be arcuate and may be configured as a flat surface.

Furthermore, in the above description, a commercial AC power source is used as the power source of the fixing device 30, but a configuration using a DC power source may be used.
Furthermore, the pressure roller 32 is pressed against the heating belt 31 or the pressure roller 33 to form the fixing nip N. However, the pressure means for forming the fixing nip N is limited to the pressure roller 32. For example, a pressure belt may be used, and further, there is no need to rotate like the pressure roller 32 and the pressure belt, and a fixed pressure member or the like may be used. Good.

  The image forming apparatus according to the present invention is not limited to a printer that forms a monochrome image, and may be a color printer. Furthermore, the present invention is not limited to a printer, and can also be applied to a copying machine, an MFP (Multiple Function Peripheral), a FAX, and the like (in either case, either a color image or a monochrome image).

  INDUSTRIAL APPLICABILITY The present invention is useful as a technique for preventing a spark from being generated between a power receiving layer and a power supply member in a fixing device using a heating rotator having a resistance heating element layer that generates heat when a current flows.

DESCRIPTION OF SYMBOLS 30 Fixing device 31 Heating belt 31a Resistance heating element layer 31b Elastic layer 31c Release layer 31d Power receiving layer 32 Pressing roller 33 Pressing roller 34 AC power supply 37 Feeding member

Claims (5)

A pressure member is pressed against a heating rotator provided with a resistance heating element layer on the entire circumference to form a fixing nip, and a recording sheet on which an unfixed image is formed is passed through the fixing nip. A fixing device for heat fixing,
A pair of power receiving layers provided along the circumferential direction in a conductive state with the resistance heating element layer at both ends in the axial direction of the heating rotator,
A power supply member disposed in sliding contact with the outer peripheral surface of each power receiving layer, and
The power feeding member is formed in an arc shape whose sliding contact surface with the power receiving layer is the same as or smaller than the outer diameter of the power receiving layer when the heating rotating body is in a non-pressed state. A fixing device characterized in that the central angle of the shape is larger than 180 °.   The fixing device according to claim 1, wherein an axial width of the power supply member is constant throughout.   The fixing device according to claim 1, wherein a width of the power supply member in an axial direction is shorter than a central portion in a circumferential direction at any one end portion.   The fixing device according to claim 1, wherein a central position in the axial direction of the power supply member is arranged to coincide with a central position in the axial direction of the power receiving layer.   An image forming apparatus comprising the fixing device according to claim 1.

Images