JP2012189749A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of increasing the durability of a belt more than before by suppressing reduction in mechanical strength of a resistance heating element layer, and an image forming device using the fixing device.SOLUTION: There is provided a fixing device using an endless belt 51 having a resistance heating element layer 512, in which the belt 51 has a first and second electrode layers D1 and D2 which are laminated so as to interposed the entire area of a part corresponding to a sheet passing area R1 of at least a recording sheet of the resistance heating element layer 512 and is configured to supply power to the resistance heating element layer 512 through the first and second electrode layers D1 and D2.

Description

  The present invention relates to a fixing device and an image forming apparatus using the fixing device, and more particularly to a technique for improving durability of the belt in a fixing device using a belt having a resistance heating element layer.

In recent years, a fixing device using a belt having a layer of a resistance heating element that generates Joule heat has been used as a fixing device of an image forming apparatus such as a printer or a copying machine.
Patent Document 1 includes a recording sheet having an endless belt having a resistance heating element layer and a pressure roller that presses the circumferential surface of the belt to form a nip portion, and an unfixed image is formed in the nip portion. A fixing device that passes the paper and heat-fixes is disclosed. The belt is provided with electrode layers at both ends in the width direction (rotating axis direction), and power from an external power source is supplied to the resistance heating element layer via the electrode layers at both ends. .

  Patent Document 1 discloses a technique in which such a resistance heating element layer is configured by dispersing conductive fillers in a heat-resistant insulating resin. In such a resistance heating element layer, the electric resistivity [Ω · m] per unit volume can be adjusted by changing the amount (volume content) of the conductive filler in the insulating resin, and the desired heat generation. The electrical resistance value [Ω] is set to obtain the quantity.

JP 2009-109997 A

Incidentally, the amount of heat generated by the resistance heating element layer is inversely proportional to the electrical resistance value when the supply voltage is the same. Moreover, the electrical resistance value of the resistance heating element layer is proportional to the electrical resistivity and the energization distance.
In the conventional fixing device, there are electrode layers at both ends of the belt in the width direction, and the current supplied to the resistance heating element layer flows in the belt width direction. Therefore, the energizing distance is required to be longer than the maximum sheet passing width of the recording sheet and becomes longer. ing. For this reason, in order to obtain an electric resistance value at which a desired calorific value can be obtained, the electric resistivity per unit volume must be lowered, and thus the volume content of the conductive filler is increased. In this case, if the volume content of the conductive filler becomes too high, the mechanical strength of the resistance heating element layer decreases and becomes brittle, which causes a problem that the durability of the belt decreases.

  The present invention has been made in view of the above-described problems, and a fixing device capable of suppressing a decrease in mechanical strength of the resistance heating element layer and improving the durability of the belt as compared with the related art. An object of the present invention is to provide an image forming apparatus using a fixing device.

  In order to achieve the above object, a fixing device according to the present invention forms a nip portion by pressing a pressure member on the peripheral surface of an endless belt having a resistance heating element layer, and an unfixed image is formed in the nip portion. In the fixing device, the formed recording sheet is passed and thermally fixed, and the belt is laminated so as to sandwich at least the entire portion of the resistance heating layer corresponding to the sheet passing area of the recording sheet. And a second electrode layer, and is configured to supply power to the resistance heating layer through the first and second electrode layers.

According to the fixing device having the above-described configuration, the first and second electrode layers are laminated so as to sandwich the resistance heating element layer, and energized in the thickness direction of the resistance heating element layer. Compared to the conventional fixing device that is energized in the width direction, the energization distance can be significantly shortened.
As a result, if the electric resistance value of the resistance heating element layer is the same, the electric resistance per unit volume can be increased as much as the energization distance is significantly shorter than the conventional one. When the conductive filler is dispersed in the heat-resistant insulating resin, the volume content of the conductive filler can be kept low. As a result, a decrease in mechanical strength of the resistance heating element layer can be suppressed, and therefore the durability of the belt can be enhanced as compared with the conventional case.

Here, the resistance heating layer is preferably made of a heat-resistant insulating resin and a conductive filler dispersed in the insulating resin.
In addition, at both ends in the width direction of the belt, it is preferable that an end portion of at least one of the first and second electrode layers is formed so as to recede from an end portion of the resistance heating element layer. . This is to secure the creeping distance of the resistance heating element layer between the first electrode layer and the second electrode layer, thereby suppressing the current flowing on the creeping surface (surface) of the resistance heating element layer. Because it can be done. This creepage distance is preferably 5 [mm] or more.

  Further, here, the first and second power supply members for supplying power in contact with the respective non-sheet passing region portions of the first and second electrode layers are provided, and the first power supply member and the second electrode layer are provided. Preferably, the arrangement positions of the first and second power supply members are determined so that the spatial distance between the second power supply member and the first electrode layer is equal to or greater than a predetermined value. This is to prevent discharge from occurring between the first power supply member and the second electrode layer and between the second power supply member and the first electrode layer. The predetermined value here, that is, the spatial distance is preferably 4 [mm] or more.

  Further, from the viewpoint of ease of attachment of the power supply member, when the belt is formed with the resistance heating element layer sandwiched between the outer peripheral side of the belt as the first electrode layer and the inner peripheral side of the belt as the second electrode layer, At least one end of the electrode layer in the width direction of the belt extends outward in the belt width direction from each end of the resistance heating element layer and the first electrode layer, and the outer peripheral surface of the portion is exposed. Preferably, the second power supply member is disposed so as to contact the exposed outer peripheral surface of the second electrode layer, and the first power supply member contacts the outer peripheral surface of the first electrode layer. .

  On the other hand, from the viewpoint of miniaturization, when the belt has the first electrode layer on the outer peripheral side of the resistance heating element layer and the second electrode layer on the inner peripheral side of the belt, the following two configurations are provided. Any one of the configurations is preferable. One is a configuration in which the first power supply member is disposed in contact with the outer peripheral surface of the first electrode layer and the second power supply member is in contact with the inner peripheral surface of the second electrode layer. The other is that at least one end of the first electrode layer in the width direction of the belt extends outward in the belt width direction from each end of the resistance heating element layer and the second electrode layer. The first power supply member is in contact with the exposed inner peripheral surface of the first electrode layer, and the second power supply member is on the inner peripheral surface of the second electrode layer. It is the structure arrange | positioned so that it may contact | connect.

  Here, it is preferable that the first power feeding member is disposed at one end in the width direction of the belt, and the second power feeding member is disposed at the opposite end. . This is because an electric potential gradient is generated somewhat inside the electrode layer, and therefore, the current distribution flowing through the resistance heating element layer is larger than when both the first and second power supply members are arranged at one end in the belt width direction. This is because it can be made uniform.

The insulating resin for the resistance heating element layer is preferably a polyimide resin. This is because the polyimide resin is superior in terms of heat resistance and pressure resistance.
Further, the invention of the present application may be an image forming apparatus provided with the fixing device having the above-described configuration, whereby the same effect as that of the fixing device having the above-described configuration can be obtained.

1 is a schematic diagram illustrating a configuration of a printer according to a first embodiment of the present invention. FIG. 2 is a perspective view illustrating a configuration of a main part of a fixing unit in the printer. FIG. 3 is a cross-sectional view seen from the Y ′ direction when the fixing device of FIG. 2 is cut along a virtual plane V. FIG. 3 is a partial cross-sectional view for explaining a laminated structure of a fixing belt. FIG. 6 is a diagram comparing energization distance, energization cross-sectional area, and electrical resistivity of a resistance heating element layer of a fixing belt in the fixing unit of the present embodiment and a conventional fixing device. (A) is a schematic side view which shows the structure of the principal part of the fixing part which concerns on the 2nd Embodiment of this invention, (b) is for demonstrating the laminated structure of the fixing belt which a fixing part has It is a fragmentary sectional view. (A) is a schematic side view which shows the structure of the principal part of the fixing part which concerns on the 3rd Embodiment of this invention, (b) is for demonstrating the laminated structure of the fixing belt which a fixing part has. It is a fragmentary sectional view. (A) is a schematic side view which shows the structure of the principal part of the fixing part which concerns on the 4th Embodiment of this invention, (b) is for demonstrating the laminated structure of the supporting member which a fixing part has It is a fragmentary sectional view.

<First Embodiment>
Hereinafter, a first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings by taking a tandem type full color printer (hereinafter simply referred to as “printer”) as an example.
<Overall configuration of printer>
FIG. 1 is a schematic diagram illustrating a configuration of a printer.

  As shown in FIG. 1, the printer 1 includes an image process unit 3, a paper feed unit 4, a fixing unit 5, and a control unit 60. When the printer 1 is connected to a network (for example, a LAN) and receives a print job execution instruction from an external terminal device (not shown), each of the colors of yellow, magenta, cyan, and black is received based on the instruction. After a toner image is formed and these are multiplex-transferred to form a full-color image, a printing process on a recording sheet is executed.

Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.
The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K corresponding to each of Y to K colors, an optical unit 10, an intermediate transfer belt 11, and the like.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the drum 31Y. The other image forming units 3M to 3K have the same configuration as the image forming unit 3Y, and the reference numerals are omitted in FIG.

The intermediate transfer belt 11 is an endless belt, and is stretched around the driving roller 12 and the driven roller 13 to circulate in the direction of arrow A.
The optical unit 10 includes a light emitting element such as a laser diode, emits laser light H for forming images of Y to K colors by a drive signal from the control unit 60, and exposes and scans the photosensitive drums 31Y to 31K.

By this exposure scanning, electrostatic latent images are formed on the photosensitive drums 31Y to 31K charged by the chargers 32Y to 32K.
The electrostatic latent images are developed by developing units 33Y to 33K, and Y to K color toner images are formed on the photosensitive drums 31Y to 31K.
Each of the formed toner images is primarily transferred onto the intermediate transfer belt 11 by an electrostatic force generated by a voltage applied to the primary transfer rollers 34Y to 34K. At this time, the image forming operation in the image forming units 3Y, 3M, 3C, and 3K is performed by the intermediate transfer belt 11 so that the toner images of the respective colors are transferred to the same position on the intermediate transfer belt 11 that is traveling. It is executed with the timing shifted from the upstream side to the downstream side.

After the primary transfer, the toner image on the intermediate transfer belt 11 is collectively transferred onto the recording sheet S conveyed from the paper feeding unit 4 by the electrostatic force generated by the voltage applied to the secondary transfer roller 45. Is done.
The paper feeding unit 4 stores the recording sheet S, the feeding roller 42 that feeds the recording sheet S in the paper feeding cassette 41 one by one onto the conveying path 43, and the fed recording sheet S to the secondary. A timing roller pair 44 and the like for taking the timing of sending to the transfer position 46 are provided. The recording sheet S is conveyed from the paper feeding unit 4 to the secondary transfer position 46 in accordance with the timing of the toner image on the intermediate transfer belt 11.

The recording sheet S on which the toner image (unfixed image) is formed by the secondary transfer is further conveyed to the fixing unit 5. In the fixing unit 5, the toner image on the recording sheet S is heated and pressurized to be thermally fixed. Thereafter, the recording sheet S is discharged onto the discharge tray 72 by the discharge roller pair 71.
The control unit 60 controls the operations of the image processing unit 3, the paper feeding unit 4, and the fixing unit 5.
<Configuration of fixing unit>
Next, the configuration of the fixing unit 5 will be described with reference to FIGS. 2 and 3.

FIG. 2 is a perspective view showing the configuration of the main part of the fixing unit 5, and FIG. 3 is a cross-sectional view seen from the Y ′ direction when cut along the virtual plane V of FIG.
The fixing unit 5 includes an endless fixing belt 51 having a resistance heating element layer, a pressure roller 52 loosely fitted inside the fixing belt 51, a pressure roller 53 disposed outside the fixing belt 51, and fixing. Power supply members 54a and 54b for supplying power to the belt 51 and urging portions 56a and 56b are provided. In the fixing unit 5, the pressure roller 53 is pressed against the pressure roller 52 via the fixing belt 51, and a fixing nip N (see FIG. 3) is formed between the fixing belt 51 and the pressure roller 53. ing.

  The pressure roller 53 is rotationally driven through a power transmission mechanism such as a gear gear or a belt using a motor (not shown) as a power source. The pressure roller 52 and the fixing belt 51 are driven to rotate by the rotation of the pressure roller 53 and are interlocked with each other. The pressure roller 53 rotates in the direction of arrow C, and the pressing roller 52 and the fixing belt 51 rotate in the direction of arrow B, respectively. 2 is a plane orthogonal to the virtual axis J of the rotation center (hereinafter referred to as the rotation axis J) when the fixing belt 51 is rotationally driven.

Hereinafter, each component in the fixing unit 5 will be described in detail.
(Pressing roller)
The pressing roller 52 is formed by forming an elastic layer 522 around a long and cylindrical cored bar 521.
The cored bar 521 is made of, for example, aluminum, iron, stainless steel, and the like, and at both axial ends thereof, shaft portions 521a, which are rotatably supported by bearing portions of the fixing portion 5 provided in a housing (not shown). 521b. The elastic layer 522 is made of a material having high heat resistance and high heat insulation, such as a foamed elastic body such as silicone rubber or fluororubber. By providing the elastic layer 522, the pressing roller 52 and the fixing belt 51 are in elastic contact so that the contact pressure is not biased as much as possible and the contact state is improved. Further, since the elastic layer 522 also functions as a heat insulating material, heat generated in the fixing belt 51 can be suppressed from being radiated through the pressing roller 52. The thickness of the elastic layer 522 is preferably 1 to 20 [mm].

Here, the outer diameter of the core metal 521 (excluding the shaft portions 521a and 521b) is about 18 [mm], and the thickness of the elastic layer 522 is about 5 [mm]. The inner diameter of the fixing belt 51 is set to be smaller than 30 [mm]. Further, the length of the pressing roller 52 excluding the shaft portions 521 a and 521 b is equal to the width dimension of the fixing belt 51.
(Pressure roller)
In the pressure roller 53, an elastic layer 532 and a release layer 533 are laminated in this order around a long and cylindrical cored bar 531.

  The metal core 531 is made of, for example, aluminum, iron, stainless steel, and the like, and shaft portions 531a, which are rotatably supported by bearing portions provided in a housing (not shown) of the fixing unit 5 at both axial ends thereof. 531b. The elastic layer 532 is made of, for example, silicone rubber, and the release layer 533 is made of, for example, a fluorine resin such as PFA. By providing the elastic layer 532, the pressure roller 53 and the fixing belt 51 are in elastic contact so that the contact pressure is as small as possible and the contact state is improved. The thickness of the elastic layer 532 is preferably 1 to 20 [mm], and the thickness of the release layer 533 is preferably 10 to 50 [μm].

Here, the outer diameter of the core metal 531 (excluding the shaft portions 531a and 531b) is about 30 [mm], and the thickness of the elastic layer 532 is about 3 [mm]. Further, the length excluding the shaft portions 531a and 531b of the pressure roller 53 is larger than the width of the sheet passing region R1 through which the recording sheet S of the fixing belt 51 is passed, and at both ends of the fixing belt 51. The size is set to 330 [mm] so as not to contact the first and second electrode layers D1 and D2.
(Power supply member)
The power feeding members 54a and 54b are block-like carbon brushes, and are made of a material such as copper graphite or carbon graphite having slidability and conductivity. The power supply members 54a and 54b are electrically connected to the power source 500 through lead wires 55, respectively.

  The power supply member 54a is held so as to be movable in the direction of arrow E (see FIG. 3) by a guide member (not shown), and is urged toward the fixing belt 51 by the urging portion 56a. As a result, the power supply member 54a is brought into sliding contact with the first electrode layer D1 of the fixing belt 51. The power supply member 54b is also held in the same manner, and is urged toward the fixing belt 51 by the urging portion 56b and is slidably contacted with the second electrode layer D2.

The sizes of the power supply members 54a and 54b are set to, for example, 10 [mm] in the vertical direction (Y-axis direction), 5 [mm] in the horizontal direction (X-axis direction), and 11 [mm] in the height (Z-axis direction). .
The power source 500 is, for example, a household power source having a voltage of 100 [V] and a frequency of 50 [Hz] or 60 [Hz]. Note that a known relay (relay switch) (not shown) that performs ON / OFF control of power supply based on an input signal from the control unit 60 is inserted into the lead wire 55.
(Energizing Department)
As shown in FIG. 3, the urging portion 56 a includes a base 57 and a compression coil spring 58 having one end attached to the base 57. The base 57 is attached to a housing or frame (not shown) of the fixing unit 5, and a compression coil spring 58 is inserted between the base 57 and the power supply member 54 a in a compressed state.

  Note that, inside the fixing belt 51, the pressing roller 52 functions as a support member that contacts and supports the inner peripheral surface of the fixing belt 51. Accordingly, the fixing belt 51 is sandwiched between the power supply member 54a and the pressing roller 52. Here, the biasing direction E by the compression coil spring 58 is a direction toward the center G side in the radial direction of the pressing roller 52, and as much as possible, the bias of the contact pressure between the power supply member and the belt is eliminated. It tries to prevent partial wear.

The urging portion 56b is similarly configured. Therefore, the power supply member 54b is also urged by the compression coil spring of the urging portion 56b, and the fixing belt 51 is sandwiched between the urged power supply member 54b and the pressing roller 52. .
(Fixing belt)
FIG. 4 is a partial cross-sectional view of the fixing belt 51 when cut in the direction of the rotation axis J (see FIG. 2) in order to explain the structure of the fixing belt 51.

As shown in FIG. 4, the fixing belt 51 includes an insulating layer 511, a second electrode layer D2, a resistance heating element layer 512, a first electrode layer D1, an elastic layer 513, and a release layer 514 in this order. It has a laminated structure.
The insulating layer 511 is a layer that insulates the surface of the first electrode layer D1 opposite to the resistance heating element layer 512 and secures the strength of the belt. The insulating layer 511 also has a function of suppressing heat generated in the resistance heating element layer 512 from being thermally conducted to the pressure roller 52 inside the belt via the second electrode layer D2. As a constituent material of such an insulating layer 511, for example, a heat-resistant insulating resin such as PI (polyimide), PPS (polyphenylene sulfide), PEEK (polyether ether ketone), or the like can be used.

  The resistance heating element layer 512 is a layer that receives power supply and generates Joule heat, and is configured by uniformly dispersing a conductive filler in a heat-resistant insulating resin. In such a resistance heating element layer 512, the electrical resistivity per unit volume can be adjusted by changing the volume content of the conductive filler in the insulating resin, and an electrical resistance value at which a desired heating value can be obtained. Is set to

  PI, PPS, PEEK, or the like can be used as a heat-resistant insulating resin constituting the resistance heating element layer 512. It is preferable to use PI which is most excellent in terms of heat resistance and pressure resistance. Therefore, PI is used in this embodiment. In addition, as the conductive filler, metal powder such as silver, copper, aluminum, magnesium and nickel, carbon compound powder such as graphite, carbon black, carbon nanotube, carbon nanofiber, and carbon microcoil, and two of them A mixture of the above can be used. The shape of the conductive filler is preferably fibrous, flaky or spherical. The size of the conductive filler is preferably about 0.01 to 10 [μm] in average particle diameter, and in the case of a fibrous shape, the fiber length is preferably about 0.1 to 30 [μm].

The elastic layer 513 is made of a heat-resistant, elastic, and insulating rubber material or resin material such as silicone rubber. By providing the elastic layer 513, it is possible to prevent the toner image from being crushed or the toner image from being melted non-uniformly, thereby preventing the occurrence of image noise.
The release layer 514 is a layer for enhancing the releasability from the recording sheet S after fixing, and is made of an insulating resin having heat resistance and excellent releasability. As the insulating resin, for example, a fluororesin such as PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer) can be used.

The first and second electrode layers D1 and D2 are formed using a metal material such as copper, aluminum, nickel, brass, phosphor bronze, or the like. In the present embodiment, nickel having excellent oxidation resistance, heat resistance, and good conductivity is used.
The layers 511 to 514, D1 and D2 are formed in the entire area of the sheet passing area R1 of the fixing belt 51 and the non-sheet passing areas R2 and R3 on both sides of the sheet passing area R1 in the belt width direction (rotation axis J direction in FIG. 2). Each is formed over at least a part.

  Of these, the first electrode layer D1 has one end D1a (non-sheet passing region R2 side) in the belt width direction extending outward in the belt width direction from each end of the elastic layer 513 and the release layer 514. Thus, a part of the outer peripheral surface D1c of the first electrode layer D1 is exposed. The power feeding member 54a is in sliding contact with the exposed portion of the outer peripheral surface D1c. The second electrode layer D2 has the other end D2b (non-sheet passing region R3 side) in the belt width direction extending outward in the belt width direction from the end 512b of the resistance heating element layer 512. A part of the outer peripheral surface D2c of the electrode layer D2 is exposed. The power supply member 54b is in sliding contact with the exposed portion of the outer peripheral surface D2c. The electric power from the power source 500 (see FIG. 2) is supplied to the resistance heating element layer 512 via the power supply members 54a and 54b and the first and second electrode layers D1 and D2, and the thickness direction of the resistance heating element layer 512 is increased. The current flows through T.

  Note that both end portions D1a and D1b of the first electrode layer D1 recede inward in the belt width direction from both end portions 512a and 512b of the resistance heating element layer 512, respectively. This is to ensure the creepage distances α1 and α2 of the resistance heating element layer 512 between the first electrode layer D1 and the second electrode layer D2 to be equal to or greater than a predetermined value, and thereby the resistance heating element layer 512. The current flowing through the creeping surface (surface) is suppressed. In addition, for example, it is possible to suppress the occurrence of leakage current between the first electrode layer D1 and the second electrode layer D2 due to, for example, dust that includes moisture on the creeping surface. The creepage distances α1 and α2 here are preferably 5 [mm] or more.

In addition, the end portion D1b of the first electrode layer D1 is retracted in this manner, and the arrangement position of the power supply member 54b is adjusted, whereby the spatial distance β between the first electrode layer D1 and the power supply member 54b is set to a predetermined value. The above is secured. This prevents discharge from occurring between the first electrode layer D1 and the power supply member 54b. The spatial distance β here is preferably 4 [mm] or more.
In addition, since the resistance heating element layer 512 and the first electrode layer D1 are interposed between the second electrode layer D2 and the power supply member 54a, no discharge is generated, so it is necessary to consider the spatial distance. There is no.

The thickness of each said layer is uniform over the perimeter. Specifically, the insulating layer 511 is 5 to 100 [μm], the resistance heating element layer 512 is 5 to 100 [μm], the elastic layer 513 is 10 to 800 [μm], and the release layer 514 is 5 to 100 [μm]. The first and second electrode layers D1 and D2 are 5 to 50 [μm].
The width dimension of the fixing belt 51 is set to 378 [mm] in consideration of the widths of the sheet passing area R1 and the non-sheet passing areas R2 and R3 of the recording sheet S. For example, the width of the sheet passing region R1 is set to be slightly larger than the maximum sheet passing width (A3 lengthwise). The inner diameter of the fixing belt 51 is set to 30 [mm].

  According to the fixing unit 5 having the above-described configuration, the first and second electrode layers D1 and D2 of the fixing belt 51 are laminated so as to sandwich the entire region of the resistance heating element layer 512 corresponding to at least the paper passing region R1. Since current flows in the thickness direction T of the resistance heating element layer 512, the energization distance L (see FIG. 4) is significantly shorter than that of the conventional fixing device in which current flows in the belt width direction of the resistance heating element layer. .

  Accordingly, if the electric resistance value of the resistance heating element layer is the same, the electric resistance per unit volume is increased in the resistance heating element layer 512 as the energization distance L is shortened as compared with the conventional fixing device. Can do. Therefore, since the volume content of the conductive filler of the resistance heating element layer 512 can be lowered, it is possible to suppress a decrease in the mechanical strength of the resistance heating element layer 512 due to the volume content of the conductive filler. , It can be prevented from becoming brittle. As a result, the durability of the belt can be increased as compared with the conventional case.

FIG. 5 is a diagram comparing the energization distance, the energization cross-sectional area, and the electrical resistivity of the resistance heating element layer of the fixing belt in the fixing unit 5 (example) of the present embodiment and the conventional fixing device (comparative example). is there.
In this comparison, as shown in FIG. 5, the supply voltage, the resistance heating element layer dimensions (width M1, thickness M2, inner diameter M3), and electrical resistance R are set to the same value. Here, the electric resistance value R is a value (8.5 [Ω]) set so that the power consumption at the supply voltage 100 [V] is about 1180 W.

First, looking at the energization distance L, in the comparative example, the energization distance L is 340 [mm] which is the width M1 of the resistance heating element layer, whereas in the example, the energization distance L is the thickness of the resistance heating element layer. M2 is significantly shorter than 0.04 [mm] (1/8500 of the comparative example).
On the other hand, the energization cross-sectional area S is only 3.8 [mm ² ] in the comparative example, but is extremely large at 32,028 [mm ² ] in the example (8500 times that of the comparative example). Here, the energization cross-sectional area S is obtained by “inner circumference length × thickness M2” in the comparative example using the inner circumference length (= inner diameter M3 × circumference ratio) of the resistance heating element layer. In the example, it is obtained by “inner circumference length × width M1”.

The electrical resistivity ρ per unit volume is obtained using the electrical resistance value R, the energization distance L, and the energization cross section S (ρ = R × (S / L)).
Looking at the electrical resistivity ρ thus obtained, the comparative example is extremely low at 9.4 × 10 ⁻⁵ [Ω · m], whereas in the example, 6.8 × 10 ³ [Ω · m. In contrast, in this comparison, it is about 7 × 10 ⁷ times that of the comparative example. Therefore, in the example, the volume content of the conductive filler of the resistance heating element layer can be greatly reduced as compared with the comparative example, so that it is possible to suppress the decrease in the mechanical strength of the resistance heating element layer and to become brittle. Can be prevented.

  In this case, in order to increase the electrical resistivity ρ, when reducing the volume content of the conductive filler, instead of simply reducing the amount (number) of the conductive filler, the size of the conductive filler is reduced. Therefore, it is desirable to suppress the decrease in the number. This is to prevent the interval between the conductive fillers from becoming too large compared to the conventional case, thereby causing temperature unevenness in the resistance heating element layer and fixing unevenness.

In the present embodiment, since the first and second electrode layers D1 and D2 are made of a metal material and have good thermal conductivity, even if temperature unevenness occurs in the resistance heating element layer 512, Since the first and second electrode layers D1, D2 can alleviate the temperature unevenness, it is possible to suppress the occurrence of fixing unevenness.
<Manufacturing method>
Next, an example of a method for manufacturing the fixing belt 51 provided in the fixing unit 5 of the present embodiment will be described.

Here, the manufacturing process of the resistance heating element layer 512 and the first and second electrode layers D1 and D2 of the fixing belt 51 will be described, and the description of the other processes will be omitted. Here, the intermediate body until the fixing belt 51 is completed is referred to as a “belt intermediate body”. A cylindrical core is fitted into the belt intermediate body until the fixing belt 51 is completed.
(1) First, a nickel layer is formed by electroless plating on the outer peripheral surface of the first belt intermediate (a state where only the insulating layer 511 is formed). Thereafter, a plating process is performed by nickel electroforming until the thickness of the nickel layer becomes, for example, 20 [μm].

In this step, a second belt intermediate body in which the second electrode layer D2 made of a nickel layer is formed on the insulating layer 511 is formed.
Thus, by performing nickel electroforming in addition to electroless plating, the plating process can be performed more efficiently than in the case of electroless plating alone.
(2) Next, a varnish for forming the resistance heating element layer 512 is prepared by uniformly dispersing the PI of the heat-resistant insulating resin, the conductive filler, and the adhesive component such as epoxy.

In this step, the volume content of the conductive filler is calculated so that the electrical resistivity ρ per unit volume of the resistance heating element layer 512 approaches the design value, and the amount of the conductivity that becomes the volume content obtained is calculated. The filler is dispersed.
(3) Thereafter, a resistance heating element layer is formed using a known ring coater type film forming machine.
Specifically, the varnish prepared above is supplied between the cylindrical mold of the film forming machine and the ring coater, and the ring coater is moved upward so that the varnish is placed on the peripheral surface of the cylindrical mold. A coating film is formed and dried to form a resistance heating element layer.

The thickness of the resistance heating element layer can be adjusted by the size of the gap between the cylindrical mold and the ring coater.
Then, the resistance heating layer is removed from the cylindrical mold, cut into a predetermined length, and fitted into the outer side of the second belt intermediate formed in the step (1), whereby the second electrode layer D2. A third belt intermediate body having the resistance heating element layer 512 laminated thereon is completed.

In this case, the length of the resistance heating layer is set to be shorter by the contact portion D2b (FIG. 4) of the power feeding member 54b than the length of the second belt intermediate.
Note that the resistance heating layer 512 may be laminated by forming a coating film of varnish with a ring coater after the second belt intermediate is fitted in advance in the cylindrical mold of the film forming machine.
(4) Next, a part of the outer peripheral surface of the third belt intermediate body on which the resistance heating element layer 512 is formed is masked with a tape or the like.

Here, the exposed region of the outer peripheral surface D2c of the second electrode layer D2 and both end portions 512a and 512b (see FIG. 4) of the resistance heating element layer 512 in the belt width direction are masked. Thus, both end portions D1a and D1b of the first electrode layer D1 formed in the next step are set back from the both end portions 512a and 512b of the resistance heating element layer 512 in the belt width direction.
(5) Then, a nickel layer is formed on the outer peripheral surface of the masked third belt intermediate by electroless plating, and then the thickness of the nickel layer is, for example, 20 [μm] by nickel electroforming. Perform plating.

In this step, a fourth belt intermediate body in which the first electrode layer D1 made of a nickel layer is laminated is formed. Also in this case, the electroless plating is performed first because the resistance heating element layer 512 is not a perfect conductor and is intended to improve the adhesion of plating.
By carrying out the above steps, the resistance heating element layer 512 and the first and second electrode layers D1 and D2 having a uniform thickness can be formed.

Finally, the elastic layer 513 and the release layer 514 are formed on the fourth belt intermediate body, and the fixing belt 51 is completed.
<Second Embodiment>
The fixing unit according to the second embodiment is different from the first embodiment in that one of two power supply members that supply power to the fixing belt is disposed inside the fixing belt.

Since other configurations are basically the same as those of the fixing unit 5 of the first embodiment, the same configurations are denoted by the same reference numerals for the sake of simplicity, and description thereof is omitted.
FIG. 6A is a schematic side view showing the configuration of the main part of the fixing unit 100 according to the second embodiment.
In the fixing unit 100 shown in FIG. 6A, the pressure roller 102 and the power supply member 104 b are arranged inside the fixing belt 110, and the pressure roller 53, the power supply member 104 a and the urging unit 105 are outside the fixing belt 110. Is arranged.

  The outer diameter of the pressing roller 102 is set smaller than that of the pressing roller 52 of the first embodiment in order to secure a space for arranging the power supply member 104 b inside the fixing belt 110. The power supply member 104b is supported by a frame (not shown) or the like so as to be in sliding contact with the inner periphery of the fixing belt 110, and is arranged in the secured space. The other power supply member 104 a is disposed on the opposite side of the power supply member 104 b with the fixing belt 110 interposed therebetween, and is urged (in the direction of arrow E) by the urging unit 105 and is in sliding contact with the outer periphery of the fixing belt 110.

FIG. 6B is a partial cross-sectional view when the fixing belt 110 is cut in the rotation axis direction.
As shown in FIG. 6B, the fixing belt 110 includes an insulating layer 111, a second electrode layer D4, a resistance heating element layer 112, a first electrode layer D3, an elastic layer 113, and a release layer 114 in this order. The fixing belt 51 is the same as the fixing belt 51 of the first embodiment in that the current supplied to the resistance heating element layer 112 flows in the thickness direction T.

The fixing belt 110 is different from the fixing belt 51 of the first embodiment because the feeding member 104b is brought into sliding contact with the inner peripheral surface D4c of the second electrode layer D4, so that the end portion of the insulating layer 111 is changed. 111a (non-sheet passing region R2 side) is retracted inward in the belt width direction from the end D4a of the second electrode layer D4 to expose a part of the inner peripheral surface D4c of the second electrode layer D4. It is only a point.
Also in the present embodiment, since a current flows in the thickness direction T of the resistance heating element layer 112, the energization distance L is significantly shortened compared to the conventional fixing device, and the same effect as that of the first embodiment is obtained. Obtainable.

In this embodiment, since the power supply members 104a and 104b are arranged on the outer peripheral side and the inner peripheral side of the fixing belt 110, as shown in FIG. 6B, the belt width direction (YY ' (Direction), the positions of the power feeding members 104a and 104b can be adjusted. As a result, the width of the fixing belt can be shortened as compared with the case where the power feeding members 54a and 54b are shifted in the belt width direction as in the first embodiment, and thus the fixing unit can be downsized. There are advantages.
<Third Embodiment>
The fixing unit according to the third embodiment is different from the first embodiment in that two power supply members that supply power to the fixing belt are both disposed inside the fixing belt.

Since other configurations are basically the same as those of the fixing unit 5 of the first embodiment, the same configurations are denoted by the same reference numerals for the sake of simplicity, and description thereof is omitted.
FIG. 7A is a schematic side view showing the configuration of the main part of the fixing unit 140 according to the third embodiment.
In the fixing unit 140 shown in FIG. 7A, the pressure roller 142, the power supply members 144 a and 144 b and the urging unit 145 are arranged inside the fixing belt 150, and the pressure roller 53 is arranged outside the fixing belt 150. ing.

  The outer diameter of the pressing roller 142 is set smaller than that of the pressing roller 52 of the first embodiment in order to secure a space for arranging the power feeding members 144a and 144b and the urging portion 145 inside the fixing belt 110. Has been. The power supply members 144 a and 144 b are arranged in the space secured in this way, and are urged (in the direction of arrow E) by the urging unit 145 and are slidably contacted with the inner periphery of the fixing belt 150. The urging unit 145 is supported by a frame (not shown).

FIG. 7B is a partial cross-sectional view when the fixing belt 150 is cut in the rotation axis direction.
As shown in FIG. 7B, the fixing belt 150 includes an insulating layer 151, a second electrode layer D6, a resistance heating element layer 152, a first electrode layer D5, an elastic layer 153, and a release layer 154 in this order. The fixing belt 51 is the same as the fixing belt 51 of the first embodiment in that the current supplied to the resistance heating element layer 152 flows in the thickness direction T.

The fixing belt 150 is different from the fixing belt 51 of the first embodiment in that the power supply member 144a is on the inner peripheral surface D5c of the first electrode layer D5 and the power supply member 144b is on the second electrode layer D6. This is only a point where a part of the inner peripheral surfaces D5c and D6c is exposed to be brought into sliding contact with the inner peripheral surface D6c.
Also in the present embodiment, since a current flows in the thickness direction T of the resistance heating element layer 152, the energization distance L is significantly shortened compared with the conventional fixing device, and the same effect as that of the first embodiment is obtained. Obtainable.

In the present embodiment, since the power supply members 144a and 144b are both arranged inside the fixing belt 110, the fixing unit can be downsized as compared with the case where the power supply member is arranged outside the fixing belt. be able to. In addition, since the foreign matter such as paper dust is relatively small inside the fixing belt compared to the outside of the fixing belt, the foreign matter adheres to the electrode layer, resulting in poor contact between the electrode layer and the power supply member. There is an advantage that the possibility can be reduced.
<Fourth embodiment>
In the fixing unit according to the fourth embodiment, a long support member is disposed inside the fixing belt instead of the pressing roller, and the pressure roller is pressed against the supporting member via the fixing belt. Thus, the third embodiment is different from the third embodiment in that the fixing nip is formed.

Since other configurations are basically the same as those of the fixing unit 140 of the third embodiment, the same configurations are denoted by the same reference numerals for the sake of simplicity, and description thereof is omitted.
FIG. 8A is a schematic side view showing the configuration of the main part of the fixing unit 160 according to the fourth embodiment.
In the fixing unit 160 shown in FIG. 8A, an elongate support member 162, a power supply member 144 a, and a power supply member 144 b (not shown) are arranged inside the fixing belt 150. The support member 162 is formed with an arcuate sliding contact surface 162 c that is in sliding contact with the inner periphery of the fixing belt 150. Further, as shown in FIG. 8B, the support member 162 has notches 162a and 162b formed at both ends in the length direction. A power supply member 144a is disposed at the position of the notch 162a, and is biased (in the direction of arrow E) by a compression coil spring 165 attached to the support member 162. As a result, the power supply member 144a is brought into sliding contact with the inner peripheral surface D5c (see FIG. 7B) of the first electrode layer D5 of the fixing belt 150. The same applies to the notch 162b. A power supply member 144b (not shown) is arranged and is urged by the compression coil spring 165. As a result, the power supply member 144b is brought into sliding contact with the inner peripheral surface D5c (see FIG. 7B) of the first electrode layer D5 of the fixing belt 150.

Also in this embodiment, since the fixing belt 150 of the third embodiment is used and a current flows in the thickness direction T of the resistance heating element layer 152, the energization distance L is significantly larger than that of the conventional fixing device. The effect similar to that of the third embodiment can be obtained.
[Modification]
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

  (1) In the above embodiment, the resistance heating element layer of the fixing belt has been configured to include a heat-resistant insulating resin and a conductive filler uniformly dispersed in the insulating resin. Not what you want. For example, in addition to these, glass fiber, whisker, titanium oxide, potassium titanate, or the like may be used to increase mechanical strength, and aluminum nitride, alumina, or the like is used to increase thermal conductivity. It doesn't matter. Furthermore, an imidizing agent, a coupling agent, a surfactant, an antifoaming agent, or the like may be added to improve production stability.

Moreover, although the structure which uses a metal powder or a carbon compound powder was shown as an electroconductive filler, it is not limited to this, For example, it is good also as a structure using electroconductive particles, such as a metal alloy and an intermetallic compound. It can also be set as the structure which added electroconductive particles, such as a metal alloy and an intermetallic compound, to the metal powder or the carbon compound powder.
The configuration of the resistance heating element layer can be appropriately selected according to the specifications of the fixing belt.

  (2) In the above embodiment, the resistance heating element layer is formed not only in the sheet passing area R1 but also in the non-sheet passing areas R2 and R3 of the fixing belt. Since at least the sheet passing area R1 is sufficient, the non-sheet passing areas R2 and R3 can be configured to have no resistance heating element layer. In this case, heat generation can be suppressed because heat generation in the non-sheet passing regions R2 and R3 of the fixing belt can be suppressed. In this case, however, it is preferable to provide an insulating layer between the first and second electrode layers in the non-sheet passing regions R2 and R3. Thereby, while preventing the discharge between the 1st and 2nd electrode layer, the creeping distance between the 1st and 2nd electrode layer can be ensured more than predetermined value.

(3) In the above embodiment, the first electrode layer and the second electrode layer are composed of the same metal material (nickel). However, the present invention is not limited to this and is composed of different metal materials. You can also
(4) In the above embodiment, the fixing belt has a laminated structure in which the insulating layer, the second electrode layer, the resistance heating element layer, the first electrode layer, the elastic layer, and the release layer are laminated in this order. Although the configuration is shown, it is not limited to this. In the fixing belt, it suffices that at least the entire portion of the resistance heating element layer corresponding to the sheet passing region is laminated so as to be sandwiched between the first and second electrode layers. Accordingly, the configuration of the fixing belt can be appropriately selected.

  For example, if it is possible to ensure insulation from other members, it is not necessary to provide an insulating layer on the fixing belt itself. In this case, the electrode layer of the fixing belt can be formed, for example, by direct plating on a core metal such as SUS. Thus, when plating on the core metal such as SUS, the formed electrode layer can be easily removed by applying a release agent to the core metal in advance.

(5) In the first embodiment, the configuration in which the pressing roller 52 that sandwiches the fixing belt 51 is loosely fitted inside the fixing belt 51 is shown, but the present invention is not limited to this. The configuration may be such that 52 is squeezed and fitted inside the fixing belt 51.
(6) In the above-described embodiment, the configuration using the compression coil spring as the biasing member that biases the power supply member is shown. However, the configuration is not limited to this. For example, the configuration using the leaf spring is used. It is good.

(7) In the said embodiment, the magnitude | size, shape, arrangement | positioning, etc. of an electric power feeding member are not limited. It is only necessary to maintain good contact between the power supply member and the electrode layer of the fixing belt, and the size, shape, arrangement, and the like of the power supply member can be appropriately selected according to the specifications of the fixing unit.
For example, when a current is supplied from the power supply member to the electrode layer of the fixing belt, a potential gradient is generated in the electrode layer. Therefore, the power supply member is connected to both ends in the belt width direction as in the first embodiment. Compared with the configuration in which the power feeding member is disposed only at one end in the belt width direction as in the second embodiment, the configuration disposed in each can make the current distribution flowing through the resistance heating element layer uniform. This is preferable in this respect because temperature unevenness can be suppressed.

(8) In the above embodiment, a tandem full-color printer has been described as the image forming apparatus. However, the scope of the present invention is not limited to this, and a copying machine having a fixing unit using a resistance heating element, The present invention can be applied to a facsimile machine, a printer, and the like.
Further, the contents of the above-described embodiment and modification examples may be combined as much as possible.
(9) In the first embodiment, the method for manufacturing the fixing belt 51 provided in the fixing unit 5 has been described. However, the method for manufacturing the fixing belt is not particularly limited. For example, in forming the first and second electrode layers D1 and D2, a nickel foil may be adhered with a conductive adhesive, or nickel may be applied in an ink form or a paste form.

  The manufacturing method can be appropriately selected according to the specification or application of the fixing belt.

  The present invention relates to a fixing device and an image forming apparatus using the fixing device, and in particular, in a fixing device using a belt having a resistance heating element layer, can be used as a technique for improving the durability of the belt.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3 Image forming part 4 Paper feed part 5 Fixing part 10 Optical part 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 31 Photoreceptor drum 32 Charger 33 Developer 34 Primary transfer roller 35 Cleaner 41 Paper feed cassette 42 Roller 43 Conveying path 44 Timing roller pair 45 Secondary transfer roller 46 Secondary transfer position 51 Fixing belt 52 Pressing roller 53 Pressure roller 54a Power supply member (first power supply member)
54b Power supply member (second power supply member)
56a, 56b Energizing section 60 Control section 71 Discharge roller pair 72 Discharge tray 100, 140, 160 Fixing section 104a, 104b Power supply member 110, 150 Fixing belt 112, 152 Resistance heating element layer 144a, 144b Power supply member 162 Support member 500 Power supply 511 Insulating layer 512 Resistance heating element layer 512a, 512b End (resistance heating element layer)
513 Elastic layer 514 Release layer R1 Paper passing area R2, R3 Non-paper passing area D1, D3, D5 First electrode layer D1a, D1b End (first electrode layer)
D1c Outer peripheral surface (first electrode layer)
D2, D4, D6 Second electrode layer D2b End (second electrode layer)
D2c outer peripheral surface (second electrode layer)

Claims (12)

A fixing device that forms a nip portion by pressing a pressing member on the peripheral surface of an endless belt having a resistance heating element layer, and passes a recording sheet on which an unfixed image is formed in the nip portion to thermally fix the nip portion. Because
The belt has first and second electrode layers stacked so as to sandwich at least the entire portion of the resistance heating layer corresponding to the sheet passing area of the recording sheet,
The fixing device is configured to supply power to the resistance heating layer via the first and second electrode layers. The fixing device according to claim 1, wherein the resistance heating layer includes a heat-resistant insulating resin and a conductive filler dispersed in the insulating resin. At both ends in the width direction of the belt, an end of at least one of the first and second electrode layers is formed so as to recede from an end of the resistance heating element layer. The fixing device according to claim 1, wherein the fixing device is a fixing device. The fixing device according to claim 3, wherein a creepage distance between the first and second electrode layers is 5 [mm] or more at both ends in the width direction of the belt. Comprising first and second power supply members for supplying power in contact with the respective non-sheet passing regions of the first and second electrode layers;
The first and second power feeds so that the spatial distance between the first power feed member and the second electrode layer and the spatial distance between the second power feed member and the first electrode layer are equal to or greater than a predetermined value, respectively. The fixing device according to claim 1, wherein an arrangement position of the member is determined. The fixing device according to claim 5, wherein the predetermined value is 4 mm or more. In the belt, when the outer peripheral side of the belt sandwiches the resistance heating element layer is the first electrode layer, and the inner peripheral side of the belt is the second electrode layer,
At least one end portion of the second electrode layer in the width direction of the belt extends outward in the belt width direction from each end portion of the resistance heating element layer and the first electrode layer, and an outer periphery of the portion. The surface is exposed,
The second power supply member is disposed so as to be in contact with the exposed outer peripheral surface of the second electrode layer, and the first power supply member is in contact with an outer peripheral surface of the first electrode layer. The fixing device according to claim 5, wherein the fixing device is a fixing device. In the belt, when the outer peripheral side of the belt sandwiches the resistance heating element layer is the first electrode layer, and the inner peripheral side of the belt is the second electrode layer,
The first power supply member is disposed so as to contact an outer peripheral surface of the first electrode layer, and the second power supply member is disposed so as to contact an inner peripheral surface of the second electrode layer. Item 7. The fixing device according to Item 5 or 6. In the belt, when the outer peripheral side of the belt sandwiches the resistance heating element layer is the first electrode layer, and the inner peripheral side of the belt is the second electrode layer,
At least one end of the first electrode layer in the width direction of the belt extends outward in the belt width direction from each end of the resistance heating element layer and the second electrode layer, The peripheral surface is exposed,
The first power supply member is disposed so as to be in contact with the exposed inner peripheral surface of the first electrode layer, and the second power supply member is in contact with an inner peripheral surface of the second electrode layer. The fixing device according to claim 5, wherein the fixing device is provided. The first power supply member is disposed at one end of the belt in the width direction, and the second power supply member is disposed at the opposite end. The fixing device according to claim 5. The fixing device according to claim 1, wherein the insulating resin of the resistance heating element layer is a polyimide resin.   An image forming apparatus comprising the fixing device according to claim 1.

Images