JP2002229368A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing paper jamming in the device by improving the peeling property of recording paper from a fixing roller while securing stable fixing performance even under a condition that the recording paper passes through at high speed, and easily realizing the miniaturization and the reduction of the cost. SOLUTION: In this fixing device, a toner image is fixed on the recording paper by making the recording paper press-contact with the fixing roller 31 and pass between 1st and 2nd pressure rollers 33 and 35 provided on an upstream side and a downstream side in a paper passing direction. When the hardness of the outer periphery parts of the fixing roller, the 1st pressure roller and the 2nd pressure roller is defined as U0, U1 and U2, respectively, U1<U0<U2 is held. When the press-contact force of the 1st pressure roller is defined as W1 and that of the 2nd pressure roller is defined as W2, W1<W2 is held. When the thickness of the rubber material layer 58 of the fixing roller is defined as T0, that of the rubber material layer 59 of the 1st pressure roller is defined as T1 and that of the rubber material layer 60 of the 2nd pressure roller is defined as T2, T1>T0>T2 is held.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fixing device mounted on an electrophotographic image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile or a multifunction machine having these functions.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a facsimile, a printer, or the like, after a photosensitive member as an image carrier is charged, an original image is directly exposed by an exposure device, or laser scanning is performed. Optical writing is performed according to an image signal by an optical system or an LED optical writing optical system to form an electrostatic latent image on the outer peripheral surface of the photoconductor, and the electrostatic latent image is developed by a developing device to form a toner. An image is formed, and this toner image is transferred to recording paper. Then, the recording paper after the transfer is transported to a fixing device, and the toner image is fixed on the recording paper by the fixing device to obtain an image. In a color image forming apparatus, a process from optical writing to photoreceptor to development is sequentially performed for each color, toner images of a plurality of colors are formed on an intermediate transfer body, and then transferred collectively to recording paper. The transfer paper is conveyed to a fixing device to fix a color toner image on the recording paper, thereby obtaining a color image.

A fixing device in this type of image forming apparatus is configured such that a recording sheet on which a toner image is transferred is passed between a fixing roller having a built-in heater and a pressure roller provided in pressure contact with the fixing roller. The toner image is heated and pressed to fix it on recording paper. The fixing roller and the pressure roller each have an outer peripheral portion formed of a rubber layer, and the rubber layers of the outer peripheral portion of the fixing roller and the pressing roller are pressed against each other to form a nip portion, thereby achieving stable fixing strength. At the same time, the contact time between the recording paper and the fixing roller is made as long as possible.

Further, by setting the hardness of the rubber layer of the fixing roller to be smaller than that of the pressing roller, the rubber layer of the fixing roller is compressed by the pressing roller at the nip between the fixing roller and the pressing roller. A concave portion is formed in the outer peripheral portion of the fixing roller, and the recording paper is passed along the concave portion, thereby improving the releasability of the recording paper from the fixing roller.

In the fixing device described in JP-A-8-160789, a plurality of nip portions are formed by pressing a plurality of pressure rollers against a fixing roller, so that the contact time between the recording paper and the fixing roller is increased. , So that a stable fixing strength can be maintained even when the recording paper passing speed is high.

[0006]

In the conventional fixing device described above, in order to increase the nip width between the fixing roller and the pressure roller as much as possible, the diameter of the fixing roller and the pressure roller must be increased, It is necessary to reduce the hardness and the thickness of the rubber layer of the roller to increase the pressing force between the two rollers. This increases the size and cost of the fixing device,
There is also a problem that permanent deformation occurs in the rubber layer of each roller.

Further, in order to improve the releasability of the recording paper from the fixing roller, the rubber layer of the fixing roller is compressed and dented by the pressing roller. The thickness needs to be sufficiently large and the hardness must be low. As a result, in addition to the above issues,
There is a problem in that the amount of heat generated by the heater required to heat the surface temperature of the fixing roller to the fixing temperature increases, thereby increasing power consumption.

Further, in the apparatus configuration described in the above publication, since a plurality of pressure rollers are used, there is a problem that the fixing device becomes large and the cost increases.

Further, in the apparatus configuration described in the above publication, after the recording paper passes between the fixing roller and the first pressure roller on the upstream side in the paper passing direction, the recording paper passes between the fixing roller and the second pressure roller on the downstream side in the paper passing direction. Paper jam is likely to occur due to the wraparound of the first pressure roller without entering the paper. Even if the paper jam does not occur, the recording paper that has passed between the fixing roller and the first pressure roller is once peeled off from the fixing roller, and at this time, the insufficiently-fixed toner is peeled off from the recording paper and is separated from the recording paper. And the toner is again pressed between the fixing roller and the second pressure roller in that state, so that the peeled toner is re-transferred to the recording paper, so that a double image is likely to occur. is there.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is intended to peel off a recording sheet from a fixing roller while ensuring stable fixing performance even under conditions where the recording sheet passes at a high speed. It is an object of the present invention to provide a fixing device capable of preventing paper jam in the apparatus by improving the easiness of the fixing apparatus and easily reducing the size and the cost.

[0011]

The present invention has the following configuration to achieve the above object. According to the present invention, a recording paper on which a toner image has been transferred is brought into pressure contact with one fixing roller having a built-in heater and two pressure rollers provided on the upstream side and the downstream side in the paper passing direction by pressing the fixing roller against the fixing roller. In the fixing device that heats and presses the toner image to fix it on the recording paper, the hardness of the outer peripheral portion of the fixing roller is U0, and the outer peripheral portion of the pressing roller on the upstream side in the paper passing direction is When the hardness is U1 and the hardness of the outer peripheral portion of the pressure roller on the downstream side in the paper passing direction is U2, the condition of U1 <U0 <U2 is satisfied.

The pressing force of the pressing roller on the upstream side in the sheet passing direction with respect to the fixing roller is W1, and the pressing force of the pressing roller on the downstream side in the sheet passing direction with respect to the fixing roller is W1.
When 2, it is desirable to satisfy the condition of W1 <W2.

The fixing roller and the pressing roller have outer peripheral portions formed of a rubber material layer, the thickness of the rubber material layer of the fixing roller is T0, and the rubber material of the pressing roller on the upstream side in the paper passing direction. Assuming that the thickness of the layer is T1 and the thickness of the rubber layer of the pressure roller on the downstream side in the paper passing direction is T2, it is desirable that the condition of T1>T0> T2 is satisfied.

The outer peripheral portion of the pressure roller on the upstream side in the paper passing direction may be formed of a soft material layer, and the outer peripheral portion of the pressure roller on the downstream side in the paper passing direction may be formed of a hard material layer.

When the outer diameter of the fixing roller is D0 and the outer diameter of the pressure roller on the downstream side in the paper passing direction is D2,
It is desirable to satisfy the condition of D2 <D0.

When the outer diameter of the fixing roller is D0, the outer diameter of the pressure roller on the upstream side in the paper passing direction is D1, and the outer diameter of the pressure roller on the downstream side in the paper passing direction is D2, ≧ D
It is desirable that the condition of 0/2 and D2 ≧ D0 / 2 be satisfied.

It is preferable that the rotational driving force applied to the pressure roller on the downstream side in the paper passing direction is sequentially transmitted to the fixing roller and the pressure roller on the upstream side in the paper passing direction.

Further, a paper feeder for passing a recording sheet between the pressure roller on the upstream side in the paper passing direction and the pressure roller on the downstream side in the paper passing direction in a state of being in contact with the outer peripheral surface of the fixing roller. It is desirable to provide a guide member.

It is preferable that the paper passing guide member has an elastic sheet that is in pressure contact with the fixing roller, and a low friction material layer is formed on a surface of the elastic sheet that is in contact with the fixing roller.

Further, instead of providing the paper passing guide member between the two pressure rollers, an endless paper passing guide belt may be stretched between the two pressure rollers.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 illustrates the configuration of a printer including a fixing device according to the present invention. This printer 1
Reference numeral 00 denotes a color printer that forms a color image on recording paper (sheet) in accordance with image data received from an external device such as a personal computer, and includes an optical unit 1, a color developing device 2, a photoconductor unit (photoconductor belt unit). 3, a charging device 4, a photoreceptor cleaner unit 5, an intermediate transfer unit 6, a transfer belt cleaner unit 7, a fixing device 8, a paper feed tray 9, a paper discharge tray 10, and a paper transport path L.

The photoreceptor unit 3 is disposed substantially at the center of the printer 100. The photoreceptor unit 3 is an endless photoreceptor belt 13 serving as an electrostatic latent image carrier, a driving roller 14 for driving while supporting the belt, and a driven roller. And a roller 15.

The photoreceptor belt 13 is stretched between a driving roller 14 and a driven roller 15, and is driven in the direction of arrow A (sub-scanning direction) in FIG. . The charging device 3 is a charger-type charger for uniformly charging the surface of the photoreceptor belt 13 to a predetermined potential. The photoreceptor cleaner unit 5 is for removing and collecting toner remaining on the surface of the photoreceptor belt 13 after image transfer.

The optical unit 1 includes a laser device (not shown) for emitting a laser beam while modulating the intensity thereof in accordance with image data from an image processing unit (not shown), and a high-speed rotation of the laser beam from the laser device. A light deflector 11 that scans in the main scanning direction by being reflected by a polygon mirror,
And a reflection mirror 12 for reflecting the laser light from the photoreceptor belt 1 toward the photoreceptor belt 13.
An electrostatic latent image corresponding to the image data is written on the surface of No. 3.

The image data handled by the printer 100 of this embodiment is obtained by separating the image to be formed on the recording paper into four components of black (K), cyan (C), magenta (M), and yellow (Y). Image data. When forming a color image, the image processing unit supplies the image data for these four colors to the optical unit 1 for each color in one electrostatic latent image writing process. The optical unit 1 sequentially forms an electrostatic latent image for each color on the surface of the photoreceptor belt 13 in accordance with the image data of each color provided from the image processing unit.

The developing device 5 includes four developing devices 16a to 16d which are arranged so as to face the surface of the photosensitive belt 13.
And a cam unit 17 for selectively bringing one of the four developing devices 16a to 16d close to the photoreceptor belt 13. Each of the developing devices 16a to 16d
A toner image is formed by applying cyan, magenta, yellow, and black toners to the electrostatic latent image formed on the surface of the photoreceptor belt 13, respectively.

The cam unit 17 includes the developing units 16a to 16a.
Four detaching cams 17a-1 arranged near the rear of 6d
7d. These four detaching cams 17a to 17
d are eccentrically fixed to a common camshaft 51, and are rotated eccentrically by rotating the camshaft 51 so as to abut and separate from the rear ends of the developing devices 16a to 16d at different timings. It has become. Then, the contact / separation cams 17a to 17d come into contact with each other, so that the developing device 16a
16d are pushed toward the photoreceptor belt 13 so that the developing rollers of the developing units 16a to 16d come into contact with the surface of the photoreceptor belt 13.

That is, the cam unit 17 is
, The four developing devices 16a to 16a
16d can be moved toward the photoreceptor belt 13 so that the developing roller of the developing device can be brought into contact with the surface of the photoreceptor belt 13. Therefore, by switching the rotational position of the cam shaft 51 according to the toner color to be developed, the four developing devices 16a to 16d
Can be selectively and exclusively used to supply toner one by one to the electrostatic latent image formed on the surface of the photoreceptor belt 13 for development.

The intermediate transfer unit 6 includes the photosensitive unit 3
Of the endless intermediate transfer belt 20
, A driving roller 18, a tension roller 19, and a pair of transfer rollers (first transfer rollers) 21a and 21b.

The intermediate transfer belt 20 is stretched over the drive roller 18 and the tension roller 19.
The drive roller 18 is driven in the direction of arrow B in the figure by being rotationally driven. The tension roller 19 is held so as to be movable in the direction of the distance from the drive roller 18, and is constantly urged by a spring SP in a direction for applying tension to the intermediate transfer belt 20, that is, in a direction away from the drive roller 18. This prevents the intermediate transfer belt 20 from slipping between the tension roller 19 and the drive roller 18 and presses the intermediate transfer belt 20 against the photosensitive belt 13 with a pressure of 100 to 300 g.

The transfer rollers 21a and 21b are rotatably supported by the frame of the intermediate transfer unit 6 so as to be located before and after the position where the photosensitive belt 13 and the intermediate transfer belt 20 are in contact with each other. The intermediate transfer belt 20 is stretched in cooperation with the roller 18 and the tension roller 19. The transfer rollers 21a and 21b have a diameter of 8 to 10 m.
m metal roller surface with a conductive elastic material (eg, EPD
M, urethane foam, etc.), and a high voltage (high voltage having a polarity opposite to the charged polarity of the toner) for transferring a toner image to the intermediate transfer belt 20 is applied by the conductive elastic material. The transfer rollers 21 a and 21 b transfer the toner image carried on the surface of the photosensitive belt 13 to the intermediate transfer belt 20 by pressing a part of the intermediate transfer belt 20 against the surface of the photosensitive belt 13.

The intermediate transfer belt 20 is a photosensitive belt 13
Is an intermediate transfer member that temporarily holds toner images of respective colors formed on the surface of the recording medium to transfer the toner images to recording paper, and has a thickness of 100 μm.
Is formed endlessly using a polycarbonate film of A four-color toner image formed on the surface of the photoreceptor belt 13 is sequentially superimposed on the surface of the intermediate transfer belt 20 and transferred to form a color toner image (multicolor toner image).

Then, the color toner image formed on the surface of the intermediate transfer belt 20 is collectively transferred to the recording paper fed from the paper feed tray 9, and the recording paper is conveyed to the fixing device 8 and the color toner is transferred to the fixing device 8. By fixing the image to recording paper,
A color image is formed on the recording paper. Intermediate transfer belt 2
The toner remaining on the surface of the photoreceptor belt 13 without being transferred to 0 is removed and collected by the photoreceptor cleaning unit 5 provided on the upper part of the photoreceptor unit 3.

The paper transport path L is provided for discharging the recording paper on the paper feed tray 9 through the intermediate transfer unit 6 and the fixing device 8 provided at the lower part of the printer 100 and the discharge paper provided at the upper part of the printer 100. It is formed in an L-shape to be transported to the paper tray 10. A pickup roller 22, a registration roller 23, a recording paper transfer roller (second transfer roller) 24, and a transport roller 25 are provided in the middle of the paper transport path L.

The transport roller 25 is a small roller for assisting the recording paper to be transported smoothly. A plurality of the transport rollers 25 are provided along the paper transport path L. The pickup roller 22 is a pickup roller provided near the paper feed tray 9 and for feeding the recording papers placed on the paper feed tray 9 to the paper transport path L one by one.

The registration rollers 23 transfer the recording paper supplied from the paper feed tray 9 to the paper transport path L by the intermediate transfer belt 2.
0 and a roller for temporarily stopping just before the transfer roller 24. Then, the recording paper is fed between the intermediate transfer belt 20 and the transfer roller 24 with good timing according to the rotation of the intermediate transfer belt 20 so that the toner image formed on the surface of the intermediate transfer unit 6 can be transferred to the recording paper. Has a function.

A pre-registration detection switch (not shown) is provided between the pickup roller 22 and the registration roller 23.
Is provided. The pre-registration detection switch detects that the recording paper has passed a predetermined position on the paper transport path L and outputs a predetermined detection signal. Then, the stopped registration roller 23 is driven based on this detection signal, so that the leading end of the printing range of the recording paper is aligned with the leading end of the toner image on the intermediate transfer belt 20 so that the intermediate transfer belt is moved. It is fed between the transfer roller 20 and the transfer roller 24.

The second transfer roller 24 is used for the intermediate transfer belt 2
The recording paper is rotatable with respect to the intermediate transfer belt 20, and rotates while sandwiching the recording paper with the intermediate transfer belt 20. Then, the toner image formed on the intermediate transfer belt 20 is collectively transferred onto a recording sheet by using a voltage of a high-voltage power supply (not shown).

The intermediate transfer belt 20 is not transferred to the recording paper.
The toner remaining on the surface of the transfer belt cleaner unit 7 provided so as to be able to contact and separate from the intermediate transfer belt 20
Removed and collected by

The fixing device 8 includes one fixing roller 31 having a built-in heater 37 (see FIG. 2),
And two pressure rollers 33 and 35 provided on the upstream side and the downstream side in the sheet passing direction by being brought into pressure contact with the fixing roller 31, and the fixing roller 31 and the pressure rollers 33 and 35 rotate with the recording paper therebetween. It has become. Then, the recording paper on which the toner image has been transferred is passed between the fixing roller 31 and the pressure rollers 33 and 35 while being pressed and pressed, so that the toner image on the recording paper is heated and pressed to be fixed on the recording paper. It is configured to be.

The recording paper after fixing is sent out from the fixing device 8 to the paper transport path L, passes through the back side of the cam unit 17, and is discharged onto the paper discharge tray 10 with the image forming surface side facing downward. Paper.

Next, the fixing device 8 will be described in more detail. Hereinafter, the pressure roller on the upstream side (left side in the drawing) in the paper passing direction is referred to as a first pressure roller 33, and the pressure roller on the downstream side (right side in the drawing) in the paper passing direction is referred to as a second pressure roller 35.

FIG. 2 is an enlarged view of a main part of the fixing device 8 according to the first embodiment of the present invention. In the fixing device 8,
In addition to the fixing roller 31, the first pressure roller 33, and the second pressure roller 35 described above, a cleaning roller 32, a thermistor 34, an oil roller 36, a paper guide 38,
A heater control device 52 and the like are provided.

First pressure roller 33, second pressure roller 3
5, the cleaning roller 32, the thermistor 34, the oil roller 36, and the paper guide 38 are pressed against the outer peripheral surface of the fixing roller 31 by the elastic force of the springs 53 to 56, respectively.

The cleaning roller 32 includes the fixing roller 3
1 removes toner and paper dust attached to the outer peripheral surface. The oil supply roller 36 supplies oil to the outer peripheral surface of the fixing roller 31 to form an oil film, and the oil film prevents the toner on the recording paper from fusing to the fixing roller 31 and peeling off from the recording paper. I do.

The thermistor 34 detects the surface temperature of the fixing roller 31. The heater controller 52 controls the power supply to the heater 37 in the fixing roller 31 based on the temperature detected by the thermistor 34 so that the surface temperature of the fixing roller 31 is maintained at a predetermined surface temperature required for fixing. It has become.

The outer peripheral portions of the fixing roller 31, the first pressing roller 33, and the second pressing roller 35
8 to 60. The rubber layer 58 of the fixing roller 31 and the rubber layer 60 of the second pressure roller 35 are formed of solid silicone rubber. First pressure roller 33
The rubber material layer 59 is formed of sponge-like silicon rubber. These rubber material layers 58 to 60 are held by cores 61 to 63 of the rollers 31, 33, and 35, respectively. As the core 61 of the fixing roller 31, an aluminum core having good heat conductivity is used.

The paper guide 38 is connected to the intermediate transfer belt 20.
The unfixed recording paper sent between the fixing roller 31 and the transfer roller 24 is guided to a nip portion between the fixing roller 31 and the first pressure roller 33.

The fixing roller 31 and the first pressure roller 33 are
The unfixed recording paper is conveyed to the second pressure roller 35 side with the nip portion between them. At this time, the toner on the recording paper is fixed on the recording paper by the heat of the fixing roller 31 and the pressure between the rollers 31 and 33. The recording paper that has passed through the nip between the fixing roller 31 and the first pressure roller 33 further enters the nip between the fixing roller 31 and the second pressure roller 35, and
The sheet is conveyed while being heated and pressurized again and sent out of the fixing device 8. By this heating and pressurizing again, the fixation of the toner on the recording paper is ensured.

By the way, the recording paper passing through the nip portion of the two rollers rotating while pressing against each other advances along the shape of the nip portion. Therefore, in order to ensure that the recording paper that has passed through the nip between the fixing roller 31 and the first pressure roller 33 enters the nip between the fixing roller 31 and the second pressure roller 35, the fixing roller 31 It is necessary to prevent the rubber layer 58 from being dented as much as possible by the pressure contact with the first pressure roller 33. That is, the shape of the nip portion between the fixing roller 31 and the first pressure roller 33 is set to be as long as possible in the circumferential direction of the fixing roller 31, and the recording paper exiting the nip portion between them is indicated by an arrow a in FIG. Fixing roller 3
It is necessary to advance to the first pressure roller 35 side without separating from the outer peripheral surface of the fixing roller 31.

If the rubber layer 58 of the fixing roller 31 is greatly depressed due to the pressure contact with the first pressure roller 33, the recording paper exiting the nip between the two will be the first recording paper as shown by the arrow c in FIG. Proceeding in the rotation direction of the pressure roller 33, the possibility that the pressure roller 33 does not enter between the fixing roller 31 and the second pressure roller 35 increases. In such a case, paper jam tends to occur due to the recording paper wrapping around the outer periphery of the first pressure roller 33.

Therefore, in this embodiment, the fixing roller 3
1 so that the rubber material layer 59 of the first pressure roller 33 is depressed by the pressure contact with the rubber material layer 58 of the fixing roller 31.
Is formed of solid, that is, hard silicone rubber, and the rubber material layer 59 of the first pressure roller 33 is formed of sponge-like, that is, soft silicone rubber.

Thus, the rubber material layer 5 of the fixing roller 31
Assuming that the hardness of No. 8 is U0 and the hardness of the rubber material layer 59 of the first pressure roller 33 is U1, the condition of U1 <U0 is satisfied.

In this embodiment, the thickness of the rubber material layer 58 of the fixing roller 31 is set to T0,
Assuming that the thickness of the rubber material layer 59 of No. 3 is T1, the thickness of the rubber material layers 58, 59 of both rollers 31, 33 is set so as to satisfy the condition of T1> T0. Thus, the amount of depression of the rubber material layer 59 of the first pressure roller 33 due to the pressure contact with the fixing roller 31 is surely larger than the amount of depression of the rubber material layer 58 of the fixing roller 31.

On the other hand, the fixing roller 31 and the second pressure roller 3
In the nip portion with No. 5, the recording paper needs to be quickly separated from the fixing roller 31 after fixing and discharged from the fixing device 8.

For this purpose, it is necessary to prevent the second pressure roller 35 from being dented as much as possible by the pressure contact with the fixing roller 31. That is, the shape of the nip portion between the fixing roller 31 and the second pressure roller 35 is set to be as long as possible in the circumferential direction of the second pressure roller 35, and the recording paper exiting from both nip portions is indicated by an arrow in FIG. As shown by b, the fixing roller 31
It is necessary to be able to separate from and proceed.

Therefore, in the present embodiment, the rubber material layer 60 of the second pressure roller 35 is fixed so that the rubber material layer 58 of the fixing roller 31 is depressed by the pressure contact with the second pressure roller 35. The roller 31 is formed of a hard silicone rubber having a higher hardness than the rubber material layer 58.

Thus, the rubber material layer 5 of the fixing roller 31
Assuming that the hardness of No. 8 is U0 and the hardness of the rubber material layer 60 of the second pressure roller 35 is U2, the condition of U2> U0 is satisfied.

Further, in the present embodiment, the thickness of the rubber material layer 58 of the fixing roller 31 is set to T0,
Assuming that the thickness of the rubber material layer 60 of T5 is T2, the thickness of the rubber material layers 58, 60 of both rollers 31, 35 is set so as to satisfy the condition of T0> T2, and the fixing roller 3
Assuming that the outer diameter of No. 1 is D0 and the outer diameter of the second pressure roller 35 is D2, both rollers 3 satisfy the condition of D2 <D0.
The outer diameters D0 and D2 of 1, 35 are set. This allows
Since the amount of depression of the rubber material layer 58 of the fixing roller 31 due to the pressure contact with the second pressure roller 35 is surely larger than the amount of depression of the rubber material layer 60 of the second pressure roller 35, both rollers 31, The recording paper that has exited the nip portion 35 is easily peeled off from the fixing roller 31. Also, the outer diameter D of the second pressure roller 35
Since 2 is small, it is also possible to prevent paper jams due to recording paper wrapping around the outer periphery of the second pressure roller 35.

Further, in order to make the nip width as large as possible in the conventional fixing device, the depression of each roller by the pressing force of the fixing roller and the pressure roller is used. A large pressing force is not required because of the spacing between the pressure rollers, and only a pressing force sufficient to guide the peeling direction of the recording paper may be applied. Therefore, the torque for rotating each roller can be suppressed low, and the stress applied to the fixing unit can be reduced.

The fixing roller 31 and the second pressure roller 3
When the recording paper passes through the nip portion between the fixing roller 31 and the first pressure roller 33, the recording paper must be separated from the fixing roller 31 when the recording paper passes through the nip portion between the fixing roller 31 and the first pressing roller 33. Since there is no need to separate the fixing roller 31 and the first pressing roller 33, an extremely weak pressing force between the fixing roller 31 and the first pressing roller 33 is sufficient.

Therefore, when the pressure contact force between the fixing roller 31 and the second pressure roller 35 is W1 and the pressure contact force between the fixing roller 31 and the second pressure roller 35 is W2, the condition of W1 <W2 is satisfied. Should be set to. Pressing force W2
Is the minimum force required to ensure the releasability of the recording paper from the fixing roller 31, the pressure contact force W1 will be an extremely weak force.

On the other hand, in order to reduce the size of the fixing device 8,
The outer diameters D1, D2 of the first and second pressure rollers 33, 35 are preferably as small as possible. However, if the outer diameter D1 of the first pressure roller 33 is smaller than 1/2 of the outer diameter D0 of the fixing roller 31, The leading edge of the recording paper is the fixing roller 31 and the second pressure roller 3
5 does not smoothly enter the nip portion, which causes a recording paper jam inside the fixing device 8. Therefore, the outer diameter D0 of the fixing roller 31 and the outer diameter D1 of the first pressure roller 33 are set so as to satisfy the condition of D1 ≧ D0 / 2. Experimental results confirming that it is necessary to satisfy this condition are shown in the following table.

[0064]

[Table 1]

When the outer diameter D2 of the second pressure roller 35 is smaller than 1/2 of the outer diameter D0 of the fixing roller 31, the strength of the second pressure roller 35 decreases and the second pressure roller 35 3
5 causes a decrease in the releasability of the recording paper from the fixing roller 31. Therefore, the outer diameter D0 of the fixing roller 31 and the outer diameter D2 of the second pressure roller 35 also need to satisfy the condition of D2 ≧ D0 / 2.

Next, a second embodiment of the present invention will be described. Also in the fixing device 8 of the first embodiment described with reference to FIG. 2, depending on conditions, as shown in FIG. 4, the recording paper P passing between the fixing roller 31 and the first pressure roller 33 is fixed. At this time, the toner T with insufficient fixation is detached from the recording paper P and the fixing roller 3
1 and adheres to another position on the recording paper P, and passes again between the fixing roller 31 and the second pressure roller 35 in this state, so that the separated toner T Double image transfer due to transfer and fixing can occur.

In the fixing device 8 according to the second embodiment, as shown in FIG. 5, the recording paper is applied between the first pressure roller 33 and the second pressure roller 35 around the outer periphery of the fixing roller 31. A paper passing guide member 39 is provided for passing the sheet while contacting the surface. An elastic sheet 41 such as foamed silicone rubber is provided on a surface of the paper passing guide member 39 facing the fixing roller 31.
The low friction material layer 42 is formed on the surface of the elastic sheet 41 by Teflon (registered trademark) coating or the like. The paper passing guide member 39 is urged toward the fixing roller by a spring 40, and both ends of the elastic sheet 41
It is in close contact with the pressure roller 33 and the second pressure roller 35.

Since the paper passing guide member 39 is provided, the recording paper that has passed between the fixing roller 31 and the first pressure roller 33 is temporarily removed from the fixing roller 31 to cause a double image. Occurrence can be reliably prevented. An elastic sheet 41 is provided on a surface of the paper passing guide member 39 facing the fixing roller 31, and a low friction material layer 42 is formed on the surface of the elastic sheet 41. The fixing roller 31 can be smoothly guided between the fixing roller 31 and the second pressure roller 35 in a state where the fixing roller 31 is in contact with the surface, and the fixing roller 31 is not damaged by the contact with the paper passing guide member 39.

FIG. 6 is an enlarged view of a main part of the fixing device 8 according to the third embodiment of the present invention. In this embodiment, an endless paper passing guide belt 46 made of a polyimide material or the like is provided between the first pressure roller 31 and the second pressure roller 35.
To press the outer peripheral surface of the paper passing guide belt 46 against the fixing roller 31. With such a configuration,
It is possible to reliably prevent a problem such as a double image due to the recording paper passing between the fixing roller 31 and the first pressure roller 33 being separated from the fixing roller 31 once.

FIG. 7 is an enlarged view of a main part of a fixing device 8 according to a fourth embodiment of the present invention, and FIG. 8 is a perspective view of the main part.
As shown in the figure, a second pressure roller gear 44 is fixed to the shaft of the second pressure roller 35, and a drive gear 43 is disposed so as to mesh with the second pressure roller gear 44, and a motor gear is meshed with the drive gear 43. 45 are arranged. The motor gear 45 is fixed to a rotating shaft of a motor (not shown).
The rotational driving force of the motor is the motor gear 45 and the driving gear 4
3 to the second pressure roller gear 44.

When the rotational driving force of the motor is transmitted to the second pressure roller gear 44, the second pressure roller 35 is driven to rotate in the direction of arrow A in the figure. And the second pressure roller 35
Is transmitted to the fixing roller 31 by frictional force and the fixing roller 31 rotates, and the rotational force of the fixing roller 31 is transmitted to the first pressure roller 33 by frictional force and the first pressure roller 33 rotates. .

The second pressure roller 35 includes a fixing roller 31,
Of the first pressure roller 33 and the second pressure roller 35, the thickness of the rubber layer is set to be the smallest and the rubber hardness is set to be the highest, so that the roller diameter is unlikely to change due to heat or aging. Since the rotation driving force given to the second pressure roller 35 is sequentially transmitted to the fixing roller 31 and the first pressure roller 33, the transmission of the rotation force is performed by the reduction system. In addition to stabilizing the recording paper conveyance speed, the gears conventionally mounted on the rotating shafts of the fixing roller 31 and the first pressure roller 33 are omitted, and a compact and low-cost fixing device 8 can be realized. .
By providing the paper surface guide member described in the second embodiment, the above-described effects can be obtained.

In the embodiment described above, the second pressure roller 35 has the rubber material layer 60 on the outer peripheral portion, but unlike the other rollers, the second pressure roller 35 is not necessarily formed of the rubber material layer 60. It does not need to be one that satisfies the conditions described above. For example, a core metal such as hollow aluminum whose surface is coated with Teflon may be used.

Although the printer 100 having the intermediate transfer unit 6 has been described as an example, the present invention is naturally applicable to a developing device of a printer configured to directly transfer a toner image from the photosensitive belt 13 to recording paper. It is.

The present invention is naturally applicable not only to a printer but also to a developing device of another image forming apparatus, such as a copying machine, a facsimile, or a multifunction machine having these functions.

[0076]

As described above, according to the present invention, when the hardness of the outer peripheral portions of the fixing roller, the first pressure roller, and the second pressure roller is U0, U1, U2, respectively, U1 <U0.
By satisfying the condition of U2, a large nip portion can be formed as a whole with a relatively small pressing force between the fixing roller and the first and second pressure rollers, so that the torque for rotating each roller can be reduced. In addition, it is possible to provide a small and inexpensive fixing device that can maintain high fixing performance even under conditions where recording paper passes at high speed and can improve the releasability of the recording paper from the fixing roller.

Further, the shape of the nip between the fixing roller and the first pressure roller is made as long as possible in the circumferential direction of the fixing roller, and the recording paper exiting from both nips is peeled off from the outer peripheral surface of the fixing roller. Instead of the nip between the fixing roller and the second pressure roller.
Paper jam of the recording paper can be prevented.

When the pressing force of the first pressure roller and the second pressure roller against the fixing roller is W1 and W2, respectively, the condition of W1 <W2 is satisfied.
The releasability of the recording paper from the fixing roller can be further improved.

The outer peripheral portions of the fixing roller, the first pressure roller, and the second pressure roller are each formed of a rubber layer, and the fixing roller and the rubber layers of the first pressure roller and the second pressure roller are formed. When the thickness is T0, T1, and T2, respectively, by satisfying the condition of T1>T0> T2,
The fixing property can be maintained even when the recording paper is fed at high speed, and the releasability of the recording paper from the fixing roller can be further improved.

Further, since the outer peripheral portion of the first pressure roller is formed of a flexible member and the outer peripheral portion of the second pressure roller is formed of a hard member, the releasability of the recording paper from the fixing roller is further improved. Can be done.

When the outer diameters of the fixing roller and the second pressure roller are D0 and D2, respectively, the condition of D2 <D0 is satisfied, thereby further improving the releasability of the recording paper from the fixing roller. Can be.

When the outer diameters of the fixing roller, the first pressure roller, and the second pressure roller are D0, D1, and D2, respectively, the conditions of D1 ≧ D0 / 2 and D2 ≧ D0 / 2 are satisfied. By satisfying the condition, the releasability of the recording paper from the fixing roller can be further improved, and the size of the apparatus can be reduced.

Further, the configuration is such that the rotational driving force applied to the second pressure roller is sequentially transmitted to the fixing roller and the first pressure roller, so that the transport speed of the recording paper is most stabilized. In addition, power transmission parts such as gears can be reduced, and a compact and low-cost fixing device can be realized.
The force applied to the torque transmitting device can be minimized.

Further, by providing a paper passing guide member between the first pressure roller and the second pressure roller for passing the recording paper in contact with the outer peripheral surface of the fixing roller, the fixing roller and the second pressure roller are provided. It is possible to reliably prevent the occurrence of double image due to the recording paper having passed between the first pressure roller and the recording paper once separating from the fixing roller.

Further, by stretching an endless paper passing guide belt between the first pressure roller and the second pressure roller, the recording paper passing between the fixing roller and the first pressure roller is fixed. It is possible to reliably prevent the occurrence of double reflection due to the temporary separation from the roller.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating the configuration of a printer including a fixing device according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of the fixing device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of an operation of the fixing device shown in FIG. 2;

FIG. 4 is a diagram illustrating a case in which a recording sheet that has passed between a fixing roller and a first pressure roller is once peeled off from the fixing roller.
FIG. 4 is an explanatory diagram regarding a mechanism of occurrence of double reflection.

FIG. 5 is an enlarged view of a main part of a fixing device according to a second embodiment of the present invention.

FIG. 6 is an enlarged view of a main part of a fixing device according to a third embodiment of the present invention.

FIG. 7 is an enlarged view of a main part of a fixing device according to a fourth embodiment of the present invention.

8 is a perspective view of a main part of the fixing device shown in FIG.

[Explanation of symbols]

 8 Fixing Device 31 Fixing Roller 33 1st Pressure Roller (Pressure Roller on the Upstream Side in Paper Feeding) 35 2nd Pressure Roller (Pressure Roller on the Downstream Side in Paper Passing) 37 Heater 39 Paper Passing Guide Member 41 Elastic Sheet 42 Low friction material layer 46 Paper passing guide belt 58 Rubber material layer 59 Rubber material layer 60 Rubber material layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H033 AA14 AA16 BA15 BB12 BB30 BB37 BB38 3J103 AA02 AA90 FA07 GA57 GA58 GA60 HA04 HA12 HA53

Claims (10)

[Claims] 1. A recording paper on which a toner image has been transferred is brought into pressure contact with one fixing roller having a built-in heater and two fixing rollers provided on an upstream side and a downstream side in a paper passing direction by pressing the fixing roller. The fixing device fixes the toner image on the recording paper by heating and pressing the toner image by passing the toner image through the gap between the outer peripheral portion of the fixing roller and the outer peripheral portion of the pressing roller on the upstream side in the paper passing direction. Hardness of U
1. The hardness of the outer peripheral portion of the pressure roller on the downstream side in the paper passing direction is U2
Wherein a condition U1 <U0 <U2 is satisfied. 2. The pressure contact force of the pressure roller on the upstream side in the sheet passing direction with respect to the fixing roller is W1, and the pressure contact force of the pressure roller on the downstream side in the sheet passing direction with respect to the fixing roller is W2. 2. The fixing device according to claim 1, wherein a condition W2 is satisfied. 3. An outer peripheral portion of the fixing roller and the pressure roller is made of a rubber material layer, the thickness of the rubber material layer of the fixing roller is T0, and the rubber material layer of the pressure roller on the upstream side in the paper passing direction. The thickness of T
1. The thickness of the rubber material layer of the pressure roller on the downstream side in the paper passing direction is T
3. The fixing device according to claim 1, wherein the condition of T1>T0> T2 is satisfied when 2. 4. An outer peripheral portion of the pressure roller on the upstream side in the paper passing direction is made of a soft material layer, and an outer peripheral portion of the pressure roller on the downstream side in the paper passing direction is made of a hard material layer harder than the soft material layer. The fixing device according to claim 1, wherein: 5. The condition that D2 <D0 is satisfied, where D0 is the outer diameter of the fixing roller, and D2 is the outer diameter of the pressure roller on the downstream side in the paper passing direction. The fixing device according to claim 1. 6. When the outer diameter of the fixing roller is D0, the outer diameter of the pressure roller on the upstream side in the paper passing direction is D1, and the outer diameter of the pressure roller on the downstream side in the paper passing direction is D2, The fixing device according to any one of claims 1 to 4, wherein a condition of? D0 / 2 and D2? D0 / 2 is satisfied. 7. The apparatus according to claim 1, wherein the rotational driving force applied to the pressure roller on the downstream side in the paper passing direction is sequentially transmitted to the fixing roller and the pressure roller on the upstream side in the paper passing direction. The fixing device according to any one of claims 1 to 6. 8. A paper feeder that passes a recording sheet between the pressure roller on the upstream side in the paper passing direction and the pressure roller on the downstream side in the paper passing direction in a state of being in contact with the outer peripheral surface of the fixing roller. The fixing device according to claim 1, further comprising a guide member. 9. An elastic sheet is formed on a surface of the sheet passing guide member facing the fixing roller, and a low friction material layer is formed on a surface of the elastic sheet facing the fixing roller. The fixing device according to claim 8, wherein 10. An endless paper feed guide belt is stretched between the pressure roller on the upstream side in the paper passing direction and the pressure roller on the downstream side in the paper pass direction, and the paper guide guide belt conveys the recording paper. The fixing device according to claim 1, wherein a path is formed.