JP2012173465A - Fixation device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the longevity of a fixing belt in a resistance heating fixation device.SOLUTION: A fixation device allows a pressure roller 160 to press a pressing roller 150 through a fixation belt 154 from the outside of the fixation belt 154, the pressing roller 150 being movably inserted inside a rotation path of the endless fixation belt 154 including a resistance heating layer, thereby forming a fixation nip N between a surface of the fixation belt 154 and the pressure roller 160. The fixation device also allows the resistance heating layer to generate heat to perform a heat fixation of an unfixed image by letting a sheet having an unfixed image formed thereon through the fixation nip N. The fixation device has a constitution to supply electric power to the resistance heating layer by contacting a power supply member 170 with a pair of annular electrode layers 154e provided to have a sheet feeding area therebetween on an outer peripheral surface of the fixation belt 154. The power supply member 170 is provided in a more upstream side than the fixation nip N in the rotation direction of the fixation belt 154 and in a position where a part of the fixation part 154 from the fixation nip N to a contact position with the power supply member 170 is allowed to be in close contact with the pressing roller 150.

Description

  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 including a resistance heating layer and an electrode layer for supplying power thereto, the life of the fixing belt is extended. It is about technology to plan.

In recent years, an image forming apparatus such as a printer has been proposed that employs a fixing device using a fixing belt including a resistance heating layer from the viewpoint of energy saving as compared with a fixing device using a halogen heater as a heat source. (For example, Patent Document 1)
FIG. 8 is a schematic perspective view showing a configuration example of such a fixing device 500.
As shown in the figure, the fixing device 500 includes a fixing belt 554, a pressure roller 550, a pressure roller 560, a pair of power supply rollers 570 connected to an AC power source, and the like.

The fixing belt 554 is a cylindrical elastically deformable belt including a resistance heating layer 554b, and has an electrode 554e formed on the resistance heating layer 554b at the outer periphery of both ends in the width direction (Y-axis direction). It is.
The pressing roller 550 is covered with an elastic layer 552 on the surface of the cored bar 551, and is loosely inserted inside the rotation path of the fixing belt 554.

The pressure roller 560 is disposed outside the circulation path of the fixing belt 554 and presses the pressing roller 550 via the fixing belt 554 to form a fixing nip 530.
Further, the pressure roller 560 receives a driving force from a driving motor (not shown) and rotates in the direction of arrow P in FIG. When this driving force is transmitted to the pressing roller 550 via the fixing belt 554, the fixing belt 554 and the pressing roller 550 are driven to rotate in the direction of arrow Q in FIG.

The pair of power supply rollers 570 is configured to come into contact with the electrode 554e of the fixing belt 554 from the outside of the circulation path of the fixing belt 554 and press it downward in the figure, thereby the resistance heating layer of the fixing belt 554. Power is supplied to 554b.
In the above configuration, when electric power is supplied to the electrode 554e via the power supply roller 570 while the fixing belt 554 is driven to rotate, the electrode 554e has a much smaller electric resistance than the resistance heating layer 554b. Since the voltage drop at the electrode 554e is negligible, the current flows in the entire circumferential direction of the electrode 554e, and the current in the Y-axis direction flows through the entire resistance heating layer 554b to generate heat.

Since the direction of the current I is periodically reversed, the direction of the current I in FIG. 8 exemplifies a state in a certain moment.
At this time, the fixing belt 554 is not in contact with other members except for the portion pressed against the fixing nip 530 and the power supply roller 570, and heat does not easily escape to the surroundings. The temperature of the area is efficiently raised, and when the toner image formed on the recording sheet (not shown) passes through the fixing nip 530, it is heated and pressurized to be thermally fixed to the recording sheet.

JP 2009-109997 A JP-A-9-16013 JP-A-8-202183 JP-A-8-272250

  However, when the pressure roller 560 is rotationally driven in a state of being pressed against the pressure roller 550 via the fixing belt 554, the fixing belt 554 is deformed into an elliptical shape and is generated between the fixing belt 554 and the power supply roller 570. Due to the influence of friction or the like, the running state of the fixing belt 554 becomes unstable, and the running locus of the slack portion generated in the fixing belt 554 varies (hereinafter referred to as “ripple phenomenon”).

FIGS. 9A and 9B are diagrams showing a slightly exaggerated appearance of the wavy phenomenon in the fixing belt 554.
As shown in FIG. 9A, the power supply roller 570 is normally urged in the direction of the pressure roller 550 by a compression spring 571 or the like, and the pressure roller 550 is moved over the rising portion 554a of the slack portion. 9B, when the movement of the fixing belt 554 is delayed, the feeding roller 570, the fixing belt 554, and the like, as shown in FIG. A gap S is generated between the two.

At this time, due to the potential difference between the power supply roller 570 and the fixing belt 554, spark discharge occurs in the gap S, and a small hole is formed on the surface of the fixing belt 554, so that the life of the fixing belt 554 is shortened.
The present invention has been made in view of the above-described problems, and includes a fixing belt in which a resistance heating layer and an electrode for supplying power are formed, and a pressing roller is provided on the inner side of the circulation path of the fixing belt. It is an object of the invention to extend the life of a fixing belt in a resistance heating type fixing device and an image forming apparatus that are loosely inserted.

  In order to achieve the above object, a fixing device according to the present invention includes a first roller that is loosely inserted into the inside of a circulation path of an endless belt including a resistance heating layer. By pressing with a roller, a fixing nip is formed between the belt surface and the second roller, and the resistance heating layer is heated while the belt is circulated, whereby a sheet on which an unfixed image is formed is formed. A fixing device for thermally fixing the unfixed image through the fixing nip, wherein a power feeding member is attached to a pair of annular electrodes provided across a sheet passing area on the outer peripheral surface of the belt. A power supply member configured to supply power to the resistance heating layer, wherein the power supply member is located upstream of the fixing nip in the circumferential direction of the belt, and the belt portion extending from the fixing nip to the contact position. , Belt lap In, and being provided on the possible locations it is brought into close contact with the first roller.

  With the above configuration, when the belt is to be pulled to the fixing nip side by the rotation of the first and second rollers, a tension is generated due to the frictional force generated by the contact between the belt and the power supply member. Is pressed against the circumferential surface of the first roller so that the belt can be brought into close contact with the circumferential surface of the first roller, and the belt traveling path from the fixing nip to the contact position with the power supply member is stabilized. Does not occur.

For this reason, a gap is generated between the power supply member and the belt, so that the discharge is suppressed, and the life of the belt can be extended.
Further, a line segment connecting the end of the fixing nip side of the contact surface of the power supply member in the belt circumferential direction and the center of the first roller and a line segment connecting the rotation centers of the first and second rollers are formed. It is desirable that the position where the power feeding member is disposed is determined so that the angle is 80 ° or less in the direction opposite to the circumferential direction of the belt.

Furthermore, the angle is preferably in the range of 30 ° or more and 60 ° or less.
The power supply member is preferably in a block shape.
Note that the present invention may be an image forming apparatus including the fixing device.

1 is a schematic diagram for explaining a configuration of a tandem type color printer which is an example of an image forming apparatus including a fixing device according to an embodiment of the present invention. FIG. 2 is a partially cutaway perspective view showing a configuration of the fixing device. FIG. 2 is a cross-sectional view showing a laminated structure of a fixing belt of the fixing device. It is sectional drawing of the said fixing device. FIG. 5 is a diagram showing a running state of the fixing belt in a configuration in which the power supply member is disposed downstream of the fixing nip N in the circumferential direction of the fixing belt. It is a figure which shows the driving | running | working state for a moment with a fixing belt when the arrangement | positioning position of an electric power feeding member is changed further downstream. FIG. 6 is a diagram illustrating a result of obtaining a variation rate of a resistance value during driving of a belt between an electrode layer and a power supply member by changing a position where a power supply member of the fixing belt is disposed. FIG. 10 is a perspective view of a fixing device in a conventional image forming apparatus. (A) And (b) is a figure which shows the condition where the running locus | trajectory of the slack part of a fixing belt is fluctuating in the conventional fixing device.

Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings.
<Configuration of image forming apparatus>
FIG. 1 is a schematic diagram for explaining a configuration of a tandem type color printer (hereinafter simply referred to as “printer”) which is an example of an image forming apparatus including a fixing device according to an embodiment of the present invention.

  As shown in the figure, the printer 1 includes an image processing unit 3, a paper feeding unit 4, a fixing unit 5, and a control unit 60. The printer 1 is connected to a network (for example, a LAN) and is connected to an external terminal device (not connected). When a print job execution instruction is received from (shown), a toner image composed of yellow, magenta, cyan, and black is formed based on the instruction, and a full-color image is formed by multiple transfer of these.

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.
<Image process part>
The image processing unit 3 includes image forming units 30Y, 30M, 30C, and 30K corresponding to each of Y to K colors, an optical unit 10, an intermediate transfer belt 11, and the like.

  The image forming unit 30Y includes a photosensitive drum 31Y, a charger 32Y disposed around the photosensitive drum 31Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like. A Y-color toner image is formed on the drum 31Y. The other image forming units 30M to 30K have the same configuration as the image forming unit 30Y, and the reference numerals are not shown in the figure.

The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is rotationally driven in the direction of arrow A.
The optical unit 10 includes a light emitting element such as a laser diode, emits a laser beam L for forming an image 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. Each electrostatic latent image is formed by superimposing Y to K color toner images on the photosensitive drums 31Y to 31K obtained by developing by the developing units 33Y to 33K at the same position on the intermediate transfer belt 11. The timing is shifted so that the primary transfer is performed.

The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 11 by the electrostatic force acting on the primary transfer rollers 34Y to 34K to form a full-color toner image, and further move toward the secondary transfer position 46.
On the other hand, the paper feed unit 4 includes a paper feed cassette 41 that stores the recording sheets S, a feed roller 42 that feeds the recording sheets S in the paper feed cassette 41 one by one onto the transport path 43, and a fed recording sheet S. Are provided with a timing roller pair 44 for taking the timing of feeding the toner to the secondary transfer position 46, and the recording sheet S is transferred from the paper feeding unit 4 to the secondary transfer position in accordance with the movement timing of the toner image on the intermediate transfer belt 11. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet S by the action of the secondary transfer roller 45.

The recording sheet S that has passed the secondary transfer position 46 is conveyed to the fixing unit 5, and the toner image (unfixed image) on the recording sheet S is fixed to the recording sheet S by heating and pressurization in the fixing unit 5. Thereafter, the sheet is discharged onto the discharge tray 72 via the discharge roller pair 71.
<Configuration of fixing unit>
FIG. 2 is a partial cross-sectional perspective view showing the configuration of the fixing unit 5.

As shown in the figure, the fixing unit 5 includes a fixing belt 154, a pressure roller 150, a pressure roller 160, and a power supply member 170.
The pressure roller 150 is loosely inserted into the fixing belt 154, and the pressure roller 150 and the pressure roller 160 are arranged in parallel. The pressure roller 160 is pressed by a biasing mechanism (not shown) via the fixing belt 154. By energizing the roller 150, a fixing nip is formed between the fixing belt 154 and the pressure roller 160, and the toner image formed on the recording sheet S when the recording sheet S passes through the fixing nip. Is fixed by melting and pressing.

Hereinafter, the configuration of each part of the fixing unit 5 will be described in detail.
<Configuration of pressure roller>
The pressing roller 150 is rotationally driven in the direction of arrow C by a driving mechanism (not shown) and presses the pressing roller 150 from the outside of the fixing belt 154 via the fixing belt 154.
As a result, the fixing belt 154 and the pressing roller 150 are driven to rotate in the direction of arrow D.

As shown in FIG. 2, the pressure roller 160 includes a cored bar 161 and an elastic body layer 162 that covers a portion excluding both ends of the cored bar 161.
The metal core 161 is rotationally driven by a drive mechanism (not shown), and is a solid shaft made of, for example, aluminum, iron, stainless steel or the like and having an outer diameter of 30 mm.
Instead of such a solid shaft, a hollow shaft having a thickness of 0.1 mm to 10 mm, or a structure having a reinforcing rib having a Y-shaped cross section inside the hollow portion may be used.

The elastic body layer 162 is a cylindrical body made of silicone rubber, and the thickness is desirably 1 mm or more and 20 mm or less.
In the present embodiment, the elastic layer 162 has a thickness of 3 mm and an outer diameter of 36 mm.
The length of the elastic body layer 162 in the Y-axis direction is 374 mm.
<Pressing roller>
As shown in FIG. 2, the pressing roller 150 is formed by forming an elastic layer 152 around a long and cylindrical cored bar 151.

The cored bar 151 is a solid shaft made of, for example, aluminum, iron, stainless steel or the like, and has an outer diameter of 20 mm. Both end portions in the axial direction are freely rotatable on a bearing portion of a main body side frame of the fixing unit 5 (not shown). Is pivotally supported.
Instead of such a solid shaft, a hollow shaft having a thickness of 0.1 mm to 10 mm, or a structure having a reinforcing rib having a Y-shaped cross section inside the hollow may be used.

The elastic layer 152 is made of a material having high heat resistance and high heat insulation, for example, a foamed elastic body such as silicone rubber or fluorine rubber, and has a thickness of 1 mm to 20 mm. , 20 mm or more and 100 mm or less, but here it is set to 30 mm.
The length of the elastic layer 152 in the Y-axis direction is 374 mm.

Of course, the length of the elastic layer 152 in the Y-axis direction is set to be larger than the maximum sheet passing width of the recording sheet S.
The hardness of the elastic layer 152 is set to be smaller than the hardness of the elastic layer 162 of the pressure roller 160, and the elastic layer 152 is mainly elastically deformed in the nip portion N.
<Fixing belt>
FIG. 3 is a partial cross-sectional view showing a laminated structure of the fixing belt 51.

Although the drawing focuses on one end of the fixing belt 51 in the roller axis direction, the fixing belt 51 has the same configuration at the other end.
Further, in the same figure, the thickness is slightly exaggerated for easy understanding, and the dimensions of each member do not necessarily correspond to the dimensions exemplified below.
The fixing belt 154 is an elastically deformable endless belt having a laminated structure. As shown in the figure, a resistance heating layer 154b is laminated on the outer peripheral surface of the insulating layer 154a, and the resistance heating layer 154b Electrode layers 154e are stacked on both ends of the outer peripheral surface in the Y-axis direction.

Further, an elastic layer 154c and a release layer 154d are laminated in this order on the outer peripheral surface of the resistance heating layer 154b where the electrode layer 154e is not laminated.
Hereinafter, each layer constituting the fixing belt 154 will be described in detail.
The insulating layer 154a is made of any material having no electrical conductivity, for example, PI (polyimide), PPS (Poly (phenylene sulfide)), PEEK (polyetheretherketone), etc., and its thickness is about 50 μm, and is in the Y-axis direction. The length of is 374 mm.

The resistance heating layer 154b is a cylindrical heating element that generates Joule heat when current flows due to a potential difference at both ends in the Y-axis direction.
More specifically, the resistance heating layer 154b has a thickness of 5 μm or more and 100 μm or less, and one or more kinds of conductive fillers having different electrical resistivity are uniformly dispersed in PI (polyimide) resin. Become.

The length of the resistance heating layer 154b in the Y-axis direction is 374 mm, which is the same as that of the insulating layer 154a.
In addition, PPS, PEEK, and the like can be used as a base material (hereinafter referred to as “base material”) used for the resistance heating layer 154b.
Here, as the conductive filler, metal powder such as Ag, Cu, Al, Mg and Ni, or carbon compound powder such as graphite, carbon black, carbon nanofiber and carbon nanotube, or silver iodide, copper iodide. Examples thereof include high ionic conductors in inorganic compounds, and the shape thereof is preferably fibrous to increase the probability of contact between the conductive fillers per unit content.

In the present embodiment, a conductive filler having a fibrous shape, for example, Ni, is uniformly dispersed in the base material.
Here, the volume resistivity of the resistance heating layer 154b is desirably about 10 × 10 ^ −6 to 1.0 × 10 ^ −2 Ω · m. Further, in the specification of the fixing unit 5 in the present embodiment, It is desirable to set the volume resistivity to 1.0 × 10 ^ −5 to 5.0 × 10 ^ −3 Ω · m.

The elastic layer 154c is made of a material having elasticity and heat resistance, such as silicone rubber, and has a thickness of about 200 μm.
The material of the elastic layer 154c may be fluorine rubber or the like in addition to silicone rubber.
The release layer 154d is made of a material having releasability such as fluorine resin such as PTFE or PFA, and has a thickness of 5 μm or more and 100 μm or less.

The electrode layer 154e is formed so as to go around the outer periphery of both ends in the Y-axis direction of the resistance heating layer 154b, and functions as a pair of annular electrodes for supplying power to the resistance heating layer 154b.
In addition, the electrode layer 154e is formed by, for example, using a metal such as Cu, Al, Ni, brass, phosphor bronze, or the like having a lower electrical resistivity than the resistance heating layer 154b on both ends of the outer peripheral surface of the resistance heating layer 154b, or It is formed by performing electroplating or the like.

In addition, a belt-like sheet made of the above-described material may be attached to both ends of the resistance heating layer 154b in the Y-axis direction with the conductive adhesive or the like.
The width of the electrode layer 154e (the length in the Y-axis direction) is 18 mm.
Furthermore, the thickness of the electrode layer 154e is preferably 5 μm or more and 100 μm or less in order to ensure flexibility necessary to follow the deformation of the belt in the fixing nip N while having an appropriate strength. It is set to 20 μm.
<Power supply member>
Returning to FIG. 2, the power supply member 170 is electrically connected to an external AC power supply 180 via a lead wire 175, and is in sliding contact with a pair of electrode layers 154 e described later of the fixing belt 154. It is for supplying power.

The lead wire 175 is connected to an AC power source 180 via a not-shown interrupter (relay switch), and the control unit 60 is based on the surface temperature of the fixing belt 154 detected by a not-shown temperature sensor. The fixing belt 154 is configured to have a predetermined target temperature by ON / OFF control of the breaker.
The power supply member 170 includes a brush portion 171, an elastic member 172, a support plate 173, and a shaft portion 174.

The brush portion 171 is, for example, a block-like conductor having a thickness of 30 mm, a width of 10 mm in the Y-axis direction, and a length of 5 mm in the sliding direction, and has both slidability and conductivity. It is a so-called carbon brush made of such materials.
Occurrence of a problem that a large current flows through the electrode layer 154e to open a hole is not only when a discharge occurs between the power supply member 170 and the electrode layer 154e, but for example, the contact area between the two temporarily becomes extremely small, A case where the current density is locally increased is also conceivable.

As described above, by pressing the block-shaped brush portion 171 against the electrode layer 154e, a large energization area can be ensured, and even when the contact state between the two becomes unstable, the contact area is temporarily reduced. The probability of becoming extremely small can be lowered.
The shaft portion 174 is a conductive shaft made of metal or the like, one end of which is embedded and fixed in the brush portion 171, and the other end is connected to the lead wire 175. Yes.

The support plate 173 is joined to the main body side frame of the fixing portion 5 and has a through hole (not shown), and the shaft portion 174 is slidably inserted into the through hole.
The elastic member 172 is, for example, a compression coil spring, and is interposed between the brush portion 171 and the support plate 173, and presses the brush portion 171 against the outer periphery of the electrode layer 154e as shown in FIG.

FIG. 4 is a view when the cross-sectional portion in FIG. 2 is viewed from the Y direction, and shows the position where the power feeding member 170 is disposed. In this figure, hatching indicating a cross section is intentionally omitted so that the drawing can be easily seen.
As shown in FIG. 4, the power supply member 170 is upstream of the fixing nip N in the circumferential direction of the fixing belt 154 and is in a region in contact with the outer peripheral surface of the fixing belt 154 of the power supply member 170. A line segment L2 connecting the end P2 on the fixing nip side in the circumferential direction (hereinafter referred to as “belt circumferential direction”) and the rotation center O1 of the pressing roller 150 is centered on the rotation center O1 of the pressing roller 150. A straight line L1 connecting the rotation centers O1 and O2 of the pressure roller 150 and the pressure roller 160 is provided within a range M of 80 ° or less in the direction opposite to the rotation direction.

Here, the angle formed by the line segment L1 and the line segment L2 upstream of the fixing nip N in the circumferential direction of the fixing belt 154 is defined as an angle θ1.
Hereinafter, the effectiveness of the arrangement position of the power supply member 170 will be described.
First, as shown in FIG. 5, the inventor of the present application places the power supply member 170 downstream of the fixing nip N in the circumferential direction of the fixing belt 154 and the rotation of the pressing roller 150 and the pressure roller 160. An angle formed by a straight line L1 connecting the centers O1 and O2, and a line segment L3 connecting the end P1 on the fixing nip side in the belt circumferential direction in the region contacting the outer peripheral surface of the fixing belt 154 and the rotation center O1 of the pressing roller 150. In a configuration in which θ2 is about 50 [°], the running state of the fixing belt 154 was confirmed.

This figure is a diagram showing the running state of the fixing belt 154 at this time.
In this configuration, in the fixing belt 154, in the vicinity of the exit of the fixing nip N, the frictional force f1 generated between the fixing belt 154 and the power supply member 170 is opposite to the force f0 that pushes the fixing belt 154 downstream in the circumferential direction. In the meantime, a small slack portion F tends to occur in the fixing belt 154 in the meantime, and this causes a wavy phenomenon.

Therefore, the contact state between the electrode layer 154e and the power supply member 170 becomes unstable, and electric discharge easily occurs between the two, and the life of the fixing belt 154 is shortened.
Furthermore, when the value of the angle θ2 is gradually increased, the state approaches the state of the prior art, and the distance from the downstream side of the nip portion N to the contact position of the power supply member becomes longer, and the amount of slackness at that portion also increases. Thus, the circular orbit becomes unstable, and the undulation phenomenon is more likely to occur, and the contact state between the electrode layer 154e and the power supply member 170 becomes worse.

FIG. 6 shows the value of the angle formed by the straight line CL connecting the center position in the belt circumferential direction in the region of the power supply member 170 contacting the outer peripheral surface of the fixing belt 154 and the rotation center O1 of the pressing roller 150. FIG. 6 is a diagram showing an instantaneous running state of the fixing belt 154 when the
As shown in the figure, slack portions G and J exist on both sides of the power feeding member 170 in the belt circumferential direction, respectively.

When the fixing belt 154 is driven to rotate, the travel locus of the slack portions G and J becomes like the travel locus of the slack portions G ′ and J ′ and is unstable. It is considered that the contact state with the member 170 is not stabilized.
Therefore, as shown in FIG. 4, the inventor places the power supply member 170 upstream of the fixing nip N in the circumferential direction of the fixing belt 154 and the rotation center O1 of the pressing roller 150 and the pressure roller 160. The straight line L1 connecting O2 and the end P2 on the fixing nip side in the belt circumferential direction of the fixing belt 154 in the region contacting the outer peripheral surface of the fixing belt 154 of the power supply member 170 and the rotation center O1 of the pressing roller 150 are connected. The traveling state of the fixing belt 154 was confirmed in a configuration in which the angle θ1 formed by the line segment L2 was 50 [°].

Then, in a state where the fixing belt 154 is driven to rotate, a portion of the fixing belt 154 from the fixing nip N to a position where the power supply member 170 comes into contact with the fixing belt 154 is in close contact with the outer peripheral surface of the pressing roller 150. The contact state between the electrode layer 154e and the power supply member 170 was stable, and no discharge occurred between the two.
This is thought to be due to the following reason. That is, when the fixing belt 154 is pulled into the fixing nip N by the rotation of the pressure roller 150 and the pressure roller 160, the tension is applied to the fixing belt 154 due to the frictional force generated by the contact between the fixing belt 154 and the power supply member 171. As a result, the fixing belt 154 is pressed against and closely contacts the peripheral surface of the pressing roller 150, so that the travel locus of the fixing belt 154 is stable from the fixing nip N to the contact position with the power supply member 171. As a result, no wavy phenomenon occurs. Therefore, there is no room for a gap to be generated between the power supply member 171 and the electrode on the fixing belt 154, and therefore, no spark discharge occurs.

Therefore, the inventor tried an experiment as to how much the angle θ1 at which the electrode layer 154e and the power feeding member 170 can stably contact can be increased.
In this experiment, the maximum resistance value between the electrode layer 154e and the power supply member 170 when driving the fixing belt 154 is R1, and the distance between the electrode layer 154e and the power supply member 170 when the fixing belt 154 is stopped. The resistance value of R1 was R2, and the values of R1 and R2 were measured while changing the value of the angle θ1.

Then, by substituting these measured values of R1 and R2 into Equation 2 shown below, the fluctuation rate of the resistance value between the electrode layer 154e and the power supply member 170 (hereinafter referred to as “resistance fluctuation rate”) H [ %].
(Formula 2) H = (R1-R2) / R2 × 100
Here, when the resistance fluctuation rate H [%] is small, it means that the contact state between the electrode layer 154e and the power feeding member 170 is stable, and vice versa. means.

FIG. 7 is a diagram showing the results of the experiment.
The fixing device used in the experiment is basically the same as the fixing unit 5 in the present embodiment, and only the arrangement position of the power supply member is changed.
As shown in the figure, in the range of θ1 from 20 [°] to 80 [°], the resistance fluctuation rate H [%] is a low value of 2% to 4%, and the electrode layer 154e It can be seen that the contact state with the power supply member 170 is stable.

On the other hand, when θ1 exceeds 80 [°], the value of the resistance fluctuation rate H [%] rapidly increases, and the contact state between the electrode layer 154e and the power supply member 170 becomes unstable.
This is because the pulling force of the belt at the nip portion N is dominant when θ1 is in the range of 80 [°] or less, and the inner surface of the pressing roller 150 and the fixing belt 154 are originally not pressed by the power feeding member. Since the distance from the peripheral surface is a short range, the adhesion between the pressing roller 150 and the fixing belt 154 was easy to maintain. However, when θ1 is in the range of 80 [°] to 170 [°], the power feeding member does not press. In this case, the distance between the outer peripheral surface of the pressing roller 150 and the inner peripheral surface of the fixing belt 154 is in an increasing range, and fluctuations in the starting of the flexure portion occurring on the upstream side in the belt circling direction are further increased. This is considered to be because the fixing belt 154 is easily separated from the surface of the pressing roller 150 due to the strong influence.

  For the above reasons, when θ1 is in the range of 20 [°] to 80 [°], from the position where the power supply member 170 contacts the fixing belt 154 to the fixing nip N in the state where the fixing belt 154 is driven in a circular manner. Since the contact state between the fixing belt 154 and the outer peripheral surface of the pressing roller 150 is stably maintained, the contact state between the electrode layer 154e and the power supply member 170 is stabilized, and the life of the fixing belt 154 is extended. Can be achieved.

Furthermore, as shown in the figure, when the value of θ1 is 50 [°], the value of the resistance fluctuation rate H is the lowest, and the change in the fluctuation rate H before and after the angle is also small. Therefore, it is more desirable that the value of θ1 is in the range of 30 [°] or more and 60 [°] or less.
Here, as the value of θ1 approaches 50 [°] from 50 [°], the value of the resistance fluctuation rate H gradually increases because it is easily affected by the deformation of the nip portion N. It is done.

Note that the position where the power supply member 170 is disposed is upstream of the fixing belt 154 in the circumferential direction of the fixing belt 154 and there is no data in which θ1 is less than 20 °. If θ1 is further reduced, the fixing nip N This is because the power supply member 170 interferes.
<Modification>
The present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

(1) In the above embodiment, the fixing belt 154 includes the insulating layer 154a, the resistance heating layer 154b, the elastic layer 154c, the release layer 154d, and the electrode layer 154e. However, at least the resistance heating layer 154b and the electrode layer 154e may be provided.
For example, in a monochrome copying machine, even when the fixing nip width is set smaller than that of a color copying machine, the deterioration of fixing quality is not so noticeable, so the elastic layer 154c in the fixing belt 154 may be omitted. .

(2) Moreover, in the said embodiment, although the electric power feeding member 170 made the block-shaped brush part 171 contact | abut to the electrode layer 154e of the brush part 171, not only this but a brush part depending on the case. Instead of 171, a metal roller may be used to maintain electrical contact with the electrode layer 154 e.
By using the metal roller, the frictional resistance acting on the fixing belt 154 is reduced, and the tension of the fixing belt 154 from the contact position between the power supply member 170 and the fixing belt 154 to the fixing nip N is reduced. It is thought to do.

The tension is considered to contribute to the stabilization of the contact state between the electrode layer 154e and the power supply member 170 by bringing the tension into close contact with the outer peripheral surface of the pressing roller 150. It is desirable to increase the frictional resistance by bringing a leaf spring or the like into contact with the rotating shaft.
(3) Further, as in the above embodiment, the pressure roller 160 is driven to rotate and the pressure roller 150 is driven to rotate. However, the present invention is not limited to this configuration.

For example, the pressure roller 150 may be rotationally driven and the pressure roller 160 may be driven and rotated, or both the pressure roller 150 and the pressure roller 160 may be rotationally driven.
(4) In the above embodiment, the hardness of the elastic layer 152 of the pressure roller 150 is set lower than the hardness of the elastic layer 162 of the pressure roller 160, and deformation at the fixing nip N is mainly performed by pressing. Although it occurs in the elastic layer 152 of the roller 150, the present invention is not limited to this. In some cases, the hardness of the elastic layer 152 may be set higher than the hardness of the elastic layer 162 if the fixing quality does not deteriorate. The elastic layer 152 and the elastic body layer 162 may be set to the same hardness.

  (5) In the above embodiment, an example in which the image forming apparatus according to the present invention is applied to a tandem type color digital printer has been described. However, a monochrome printer or the like may be used. This can be applied to a resistance heating type fixing device in which a pressure roller is loosely inserted in a circulation path of a fixing belt including an electrode layer for the purpose, and an image forming apparatus including the fixing device.

  Further, the contents of the above embodiment and the above modification may be combined.

  In the present invention, the pressure roller is loosely inserted inside the circulation path of the fixing belt including the resistance heating layer and the electrode for supplying power thereto, and the pressure roller passes through the fixing belt from the outside of the circulation path. The present invention can be widely applied to a fixing device and an image forming apparatus that are pressed in a state to form a fixing nip.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 4 Paper feed part 5 Fixing part 10 Optical part 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 30Y, 30M, 30C, 30K Image forming part 31 Photosensitive 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 60 Control Unit 71 Discharge Roller Pair 72 Discharge Tray 150 Press Rollers 151 and 161 Core Metal 152 Elastic Layer 154 Fixing belt 154a Insulating layer 154b Resistance heating layer 154c Elastic layer 154d Release layer 154e Electrode layer 160 Pressure roller 162 Elastic body layer 170 Power supply member 171 Brush portion 172 Elastic member 173 Support plate 174 Shaft portion 175 Lead wire 180 AC power supply

Claims (5)

The first roller loosely inserted inside the endless belt including the resistance heating layer is pressed by the second roller from the outside of the belt through the belt, and the belt surface, the second roller, A fixing nip is formed between the sheet and the belt, and the resistance heating layer is heated while circulating the belt, and the sheet on which the unfixed image is formed is passed through the fixing nip to heat-fix the unfixed image. A fixing device to perform,
A power supply member is brought into contact with a pair of annular electrodes provided across a sheet passing area on the outer peripheral surface of the belt to supply power to the resistance heating layer;
The power supply member is disposed upstream of the fixing nip in the belt rotation direction, and the belt portion extending from the fixing nip to the contact position is in close contact with the first roller during the belt rotation. A fixing device provided at a possible position.   An angle formed by a line segment connecting the end of the fixing nip side of the contact surface of the power supply member with the center of the first roller and a line segment connecting the rotation centers of the first and second rollers. The fixing device according to claim 1, wherein the position where the power supply member is disposed is determined so that the angle is 80 ° or less in a direction opposite to the belt circumferential direction.   The fixing device according to claim 2, wherein the angle is in a range of 30 ° to 60 °.   The fixing device according to claim 1, wherein the power supply member has a block shape.   An image forming apparatus comprising the fixing device according to claim 1.

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