JPH09329986A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the use of a low-capacity heat source as a second heat means by keeping the temperatures of developer and sheet carried to a fixing part high. SOLUTION: A transfer belt 16 is supported by a drive roller 18, a first heat roller 20 with heater, and a tension roller 22, and a part of the belt, extending from the drive roller 18 to the tension roller 22, is in contact with a photoreceptor 12 in a primary transfer area 24. To a sheet 70 supplied to the secondary transfer area 34 a toner image is transferred from the transfer belt 16 and fixed. The sheet 70 is carried to a fixing area 36 by being attracted by the carrying belt 28. Then, in the fixing area 36, the toner image and sheet 70 are heated again by third and fourth heat rollers 32 and 38, respectively, so that the toner image melts by the heat. Also, the toner image which has melted by the force of the contact between the third heat roller 32 and forth heat roller 38 is fixed to the sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for transferring and fixing a developer on a sheet in an image forming apparatus such as an electrophotographic copying machine or a printer.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, as a method of transferring a developer held on an image carrier to a sheet, the developer is transferred to the sheet based on an electrostatic attraction force between the developer and the sheet. Electrostatic transfer method of adsorbing onto the sheet, thermal transfer method of heating the developer on the image carrier to temporarily fix it to the sheet, simultaneous transfer fixing of heating and melting the developer on the image carrier to permanently fix it on the sheet The scheme is known.

[0003]

However, in the electrostatic transfer system, the transfer efficiency of the developer is not necessarily high, and a large amount of the developer remains on the image bearing member. Therefore, there is also a mechanism for removing this residual developer. You will need it. Further, although the thermal transfer method has an advantage of high transfer efficiency, the temporarily fixed developer must be conveyed to the fixing device to be melted and fixed, and the developer and the sheet that have been cooled during the conveyance must be reused. It has to be heated, and there is a problem of poor thermal efficiency. further,
Since the temperature required for transfer and the temperature required for fixing are different, it is difficult to simultaneously perform transfer and fixing to a satisfactory level in the simultaneous transfer and fixing method.

[0004]

Therefore, the present invention adopts the thermal transfer method among the above three transfer methods, and
The sheet and the developer transferred to the sheet are conveyed to the fixing device without being cooled, so that the fixing process can be performed with high heat efficiency.The transfer unit transfers the developer from the image carrier to the sheet, and then the fixing unit. An image forming apparatus for fixing the developer to a sheet by means of an endless belt, a first roller arranged inside the belt for pressing the belt against an image carrier by the transfer section, and the transfer section. First heating means for heating the developer to fix it to the sheet, a second roller arranged inside the belt for supporting the belt together with the first roller, and a developer for the fixing section. Second heating means for heating and fixing the sheet onto the sheet, and driving means for rotationally moving the belt to convey the sheet from the transfer section to the fixing section are provided.

[0005]

In the image forming apparatus described above, the developer on the image carrier is transferred to the sheet by the heat applied from the first heating means and the contact force between the first roller and the image carrier at the transfer portion. Transcribed. At this point, the developer is not melted but is fixed on the sheet. Further, heat is applied to the belt at the transfer section, and the belt conveys the sheet to the fixing section while keeping the developer and the sheet at a high temperature. Next, in the fixing section, heat is applied to the developer and the sheet again by the second heating means, whereby the developer is melted and fixed on the sheet. Here, since the developer and the sheet conveyed to the fixing unit are kept at a high temperature, it is not necessary to apply much heat to the developer and the sheet from the second heating means. Therefore, a low-capacity heat source can be used as the second heating means.

[0006]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a first embodiment of an image forming apparatus according to the present invention. In this image forming apparatus 10, a charging device, an exposing device, a developing device and the like (not shown) are arranged around a cylindrical photosensitive member 12 which is an electrostatic latent image carrier.

The intermediate transfer device 14 includes an endless image carrier, that is, a transfer belt 16. This transfer belt 16
As, a semiconductive base layer in which a heat-resistant resin layer made of a resin such as polyimide, polyamideimide, polyetherimide, polyethersulfone, or polyetheretherketone and a conductive layer containing carbon are stacked, a silicone resin, and a fluororesin. A laminated film composed of a coating layer having releasability such as is preferably used. Here, the semiconductivity means a resistivity of 10 ⁷ to 10 ¹⁰ Ω · m, and the insulating property means a resistivity of 10 ¹¹ Ω · m or more. The transfer belt 16 is supported by three rollers, that is, a driving roller 18, a first heating roller 20 having a heater, and a tension roller 22,
The belt portion extending from the drive roller 18 to the tension roller 22 is in contact with the photoconductor 12 in the primary transfer area 24.

The fixing device 26 has a transfer function of transferring the toner on the transfer belt 16 to a sheet, a conveying function of conveying the sheet on which the toner is transferred, and a fixing function of permanently fixing the transferred toner to the sheet. These three functions are continuously performed by using the endless conveyor belt 28. The conveyor belt 28 is a belt having a thickness of 100 μm or less which is excellent in heat resistance, releasability, and durability, and is made of polyimide, polyamideimide, polyetherimide, polyethersulfone, polyetheretherketone, silicone resin,
A single layer film made of fluororesin, or a film base made of these materials.
A laminated film provided with a coating layer of m is preferably used.
The transport belt 28 may be insulative or may be semi-conductive by dispersing carbon. In this embodiment, the insulative belt is used for the purpose of surely electrostatically adsorbing and transporting the sheet. Are using.

The conveyor belt 28 has a heater 2
Supported by two heating rollers, that is, a second heating roller 30 and a third heating roller 32, and a tension roller 33.
A predetermined tension is applied by. The transport belt portion supported by the second heating roller 30 is in contact with the transfer belt 16 supported by the first heating roller 20 in the secondary transfer area 34. Further, the transport belt portion supported by the third heating roller 32 is in contact with the fourth heating roller 38 having a heater in the fixing area 36.

A sheet charger 40 that applies a charge having the same polarity as the charging polarity of toner to the back surface of the sheet on the sheet entrance side of the secondary transfer area 34, and the outer peripheral surface of the conveyor belt 28 that enters the secondary transfer area 34 (that is, A belt charger 42 that applies a charge having a polarity opposite to the toner charging polarity to the sheet contact surface) and DC power sources 44 and 46 that apply predetermined currents to the chargers 40 and 42, respectively.

As described above, the fixing device 26 of the present embodiment uses the insulative conveyance belt 28 for the purpose of electrostatically adsorbing the sheet, but excessive charges are accumulated in the insulative sheet. May occur. Therefore, in order to erase electric charges from the conveyor belt 28 that has passed through the fixing area 36, chargers 48 and 50 are provided inside and outside the conveyor belt 28, and these chargers 48 and 50 are respectively AC power sources 52.
Connected to Further, in order to surely separate the sheet electrostatically attracted to the conveyor belt 28, a separation claw 54 is provided for separating the sheet having passed through the fixing area 36 from the conveyor belt 28.

In addition, the fixing device 26 includes a fixing area 3
A cleaner 56 is provided for cleaning the outer peripheral surface of the conveyor belt 28 that has passed through 6. Further, since the cleaner 56 is on the heating roller 32, the toner can be scraped off in a molten state, and the cleaning property is good.

It should be noted that the two heating rollers 32 and 38 in the fixing area 36 are so arranged that the pressure contact force between the two heating rollers 20 and 30 in the secondary transfer area 34 is about 20 to 100 kgf at the support portions at both ends thereof. It is preferable to set the pressure contact force of 2 to about 20 kgf at both end supporting portions. Further, the heating rollers 30, 32, 38 have a diameter of 5
It is preferable to use a roller having an outer diameter of about 60 mm provided with a rubber layer of 1 to 2 mm on the outer peripheral surface of a metal roller of 8 to 59 mm.

Further, as described above, the heating rollers 30, 3
The fixing device 26 including the reference numerals 2, 38 and the conveyor belt 28 is unitized so that it can be integrally replaced.

In the image forming apparatus having the above structure, a toner image is formed around the photoconductor 12 rotating in the direction of arrow 58 based on the well-known electrophotographic image forming process. In the intermediate transfer device 14, the transfer belt 16 rotates in the direction of arrow 60 based on the rotation of the drive roller 18, and the toner image is transferred to the outer peripheral surface of the transfer belt 16 in the primary transfer area 24. In addition, it is preferable to adopt an electrostatic transfer method for the transfer here.

When a full-color image is formed by the image forming apparatus, four color toner images of yellow, magenta, cyan and black are superposed on the transfer belt 16 and then collectively transferred to a sheet. Therefore, the heating rollers 20 and 30 need to be separated from each other while the four color toner images are superimposed, and for example, the heating roller 30 can be moved downward.

On the other hand, in the fixing device 26, the transfer belt 16
The conveyor belt 28 rotates in the direction of the arrow 62 due to the friction between the second and fourth heating rollers 30, 32, 38.
And tension roller 33 have arrows 62, 64, 6 respectively.
It rotates in 6, 68 directions. Also, the second to fourth heating rollers 3
0, 32, 38 are heated together with the first heating roller 20,
The conveyor belt 28 that contacts these heating rollers is heated. Further, an electric charge having a polarity opposite to the toner charging polarity is applied to the outer peripheral surface of the conveyor belt 28 that has passed the facing portion of the belt charger 42.

The sheet fed from a sheet supply unit (not shown) is first charged with a charge having the same polarity as the toner charging polarity on the back surface thereof by the sheet charger 40. Then, the transfer belt 1 is attached to the sheet 70 supplied to the secondary transfer area 34.
The toner image is transferred from 6 and fixed. The sheet 70 that has passed through the secondary transfer area 34 is attracted by the charge of the toner charging polarity applied to the back surface thereof and the charge of the opposite polarity to the toner charging polarity applied to the surface of the transport belt 28.
It comes into close contact with the conveyor belt 28. When the sheet after transfer is conveyed to the fixing unit, if the sheet is charged to the same polarity as the toner, the toner scatters due to the repulsive action of the charged electric charge of the toner and the electric charge applied to the sheet during the conveyance. Although the image may be disturbed, this is not the case in the present embodiment because the toner is fixed to the sheet 70 in the transfer area 34. Further, in this embodiment, since the sheet before transfer has the same polarity as the toner, it is possible to prevent the toner from scattering immediately before the transfer. In other words, the sheet charger 40 uses the sheet 7
It also serves as a charger that attracts 0 to the conveyor belt 28 and a charger that prevents toner from scattering before transfer.

The sheet 70 to which the toner image has been transferred is conveyed toward the fixing area 36 while being adsorbed and held by the conveyor belt 28 and while maintaining the temperature by the heat of the conveyor belt 28. Next, in the fixing area 36, the toner image and the sheet 70 are heated again by the third and fourth heating rollers 32 and 38, and the toner image is melted by this heat. Further, the fused toner image is fixed on the sheet based on the contact force between the third heating roller 32 and the fourth heating roller 38.

The sheet 7 that has passed through the fixing area 36
0 is separated from the conveyor belt 28 by the separation claw 54.
On the other hand, the transport belt 28 that has passed through the fixing area 36 is cleaned by the cleaner 56, and then the charges are erased by the chargers 48 and 50. The cleaner 56 is the heating roller 3
Since they are opposed to each other, foreign matter (for example, toner) attached to the conveyor belt 28 can be efficiently removed.

The heating temperature in the secondary transfer area 34 (transfer temperature) and the heating temperature in the fixing area 36 (fixing temperature) are 120 to 150 ° C. and 140 to 160 ° C., respectively, when using toner for CF70 manufactured by Minolta. Set to. When using other toner, the transfer temperature is 10
It is possible to set the temperature to 0 to 150 ° C. and the fixing temperature to 130 to 180 ° C., but there is a considerable restriction on the selection of the toner.

The tension roller 22 can also be used as meandering correction means by moving one end of the tension roller 22 back and forth or outside the conveyor belt 28 so that it can be tilted. In this case, the meandering of the conveyor belt 28 and the inclination of the tension roller 22 may be mechanically interlocked, or the amount of meandering may be detected by a sensor and the roller may be inclined by a driving unit such as a motor.

Further, it is preferable that the outer peripheral surfaces of the heating rollers 20 and 38 facing the surface of the sheet 70 in contact with the toner image are covered with an elastic material such as rubber to prevent the toner image from being crushed. Similarly, the outer peripheral surfaces of the heating rollers 30 and 32 facing the back surface of the sheet 70 may be covered with an elastic material such as rubber. Such a configuration is suitable for an image forming apparatus that collectively transfers toner of four colors of yellow, magenta, cyan, and black, which are superposed on an intermediate transfer member, onto a sheet. The reason is that the superposed toner images are raised, and in order to uniformly and sufficiently heat the toner images, it is effective to cover the toner images with the elastic material as described above.

Further, in the above embodiment, the transfer belt 16
Although the conveyor belt 28 is rotated based on frictional contact with the conveyor belt 28, the conveyor belt 28 may be independently driven by drivingly connecting the second, third, or fourth heating roller to the motor. Good.

Furthermore, although the conveyor belt 28 is made of an insulating material in the above embodiment, it may be made of a semi-conductive material. In this case, the chargers 48 and 50, the AC power supply 52, and the separation claw 54 are unnecessary. However, the suction force of the sheet on the semi-conductive transport belt is lower than that on the insulative transport belt.

Another embodiment of the image forming apparatus according to the present invention will be described below. The same members as those of the image forming apparatus of the first embodiment are designated by the same reference numerals and the description thereof will be omitted. FIG. 2 shows a second embodiment of the image forming apparatus which is a modification of the first embodiment. In this image forming apparatus, the fourth heating roller 3
Instead of 8, a pair of rollers 72 and 74 and a fixing belt 76 supported by these rollers are used, and the fixing belt portion supported between the rollers 72 and 74 is in contact with the conveyor belt 28. At least one of the rollers 72 and 74 is preferably a heating roller having a heater. Further, as the fixing belt 76, it is preferable to use the same heat-resistant film as the transport belt 28. In this embodiment, since the area where the fixing belt 76 and the conveying belt 28 are in contact with each other is long, the sheet 70 and the toner image can be sufficiently heated, which is effective in increasing the speed of the image forming apparatus.

FIG. 3 shows a third embodiment of the image forming apparatus which is a modification of the first embodiment. In this image forming apparatus, a fixing belt 84 supported by a pair of rollers 78 and 80 and a heating device 82 is used in place of the fourth heating roller 38, and the fixing belt portion supported by the heating device 82 is a conveyor belt. 28
Is in contact with Note that the fixing belt 84 is the roller 7
At least one of 8 and 80 may be drivingly connected to a motor so as to be rotationally moved.
It may be rotationally moved based on frictional contact with 8. Further, as the fixing belt, it is preferable to use the same heat-resistant film as the transport belt 28. Further, as the heating device 82, it is preferable to adopt a local heating system having a heater close to the fixing belt 84,
According to this, there is an advantage that the fixing belt 84 can be heated to a required temperature within a short period of time, and ON / OFF of the heater can be adjusted based on the detection result of the temperature detecting means provided immediately before the fixing area 36. is there.

FIG. 4 shows an image forming apparatus according to the fourth embodiment.
This image forming apparatus is a so-called tandem type full-color image forming apparatus. It corresponds to four colors of yellow, magenta, cyan, and black, and four photosensitive bodies 86 and four rollers around which a belt is wound. A belt type intermediate transfer device 88 is provided, and the belt of each intermediate transfer device 88 is in contact with each photoconductor 86 in the primary transfer area 90.
Further, four heating rollers 94 corresponding to each intermediate transfer device 88 are provided inside the conveyance belt 92,
Conveyor belt 92 supported by these heating rollers 94
Are the secondary transfer areas 96 and the intermediate transfer device 88.
Is in contact with the belt. In addition, the tension roller 3
3 has a conveyor belt 92 pressed from the outside toward the inside. In the image forming apparatus thus configured, the toner images of the respective colors formed on the photoconductor 86 by the well-known electrophotographic method are transferred to the belt of the intermediate transfer device 88 in the primary transfer area 90. Next, these toner images are held on the conveyor belt 92 in the secondary transfer area 96 based on the heat of the heating roller 94, and are sequentially thermally transferred to a sheet (not shown) conveyed in the direction of the arrow in the figure. Are superimposed on each other to form a full-color toner image. This full-color toner image is conveyed to the fixing area 36 by the movement of the conveying belt 92 together with the sheet, and the heating rollers 32, 3 are conveyed here.
The heat of 8 melts and is fixed on the sheet. Therefore, the speed of the image forming apparatus can be further increased as compared with the first embodiment. Further, since the toner image is transferred to the sheet after being transferred to the intermediate transfer device 88, as in the above embodiment,
No heat is applied to the photoconductor 86.

FIG. 5 shows an image forming apparatus according to the fifth embodiment.
This image forming apparatus is also a tandem type full-color image forming apparatus, and is provided with four photoconductors 100 corresponding to four colors of yellow, magenta, cyan, and black. The intermediate transfer device 102 includes two rollers 104 and 106,
The transfer belt 108 wound around these is provided.
Four photoconductors 100 each in one primary transfer area 110
Is in contact with Then, the toner image of each color formed on each photoconductor 100 is transferred onto the transfer belt 10 in the primary transfer area 110.
8 is transferred and superposed, and is transferred to the conveyor belt 28 in the secondary transfer area 112. According to this image forming apparatus, the structure of the intermediate transfer device is further simplified. Further, since the four color toners are piled up while the transfer belt 108 makes one rotation, the speed of the image forming apparatus can be further increased.

In the conventional tandem type image forming apparatus, the process up to fixing can be performed at high speed by providing a photoconductor for each color and performing parallel processing, but the fixing speed is slow. Therefore, I had no choice but to slow down the system speed. In both the fourth embodiment and the fifth embodiment, since the sheet is conveyed to the fixing unit while maintaining the heat generated by the heating in the transfer unit, the thermal efficiency is high and the high-speed fixing is possible. The effect of speeding up by the processing can be fully utilized.

FIG. 6 shows an image forming apparatus according to the sixth embodiment, in which a plurality of heating lamps 114 are provided so as to face the conveyor belt 28 that has passed through the secondary transfer area 34. In this image forming apparatus, the toner image transferred onto the sheet 70 in the secondary transfer area 34 is heated and melted by the heating lamp 114 and is fixed on the sheet 70. As shown in the drawing, a reflecting plate 116 is provided around the heating lamp 114 except for the portion facing the conveyor belt 28, whereby the heating lamp 114 is provided.
It is desirable to collect the heat of the above toward the conveyor belt 28.
Although not shown, a pressure roller may be provided so as to face the third heating roller 32, so that the fused toner image can be reliably fixed to the sheet 70.

In the image forming apparatus described above, driving is stopped during non-image formation. However, it takes a certain amount of time for the heating roller to rise to the temperature required for transfer and fixing. Therefore, it is necessary to keep the heating roller at a predetermined temperature or higher even when it is not driven. However, if the heating roller is heated in the non-driving state, the temperature unevenness in the non-driving may be maintained as it is until the driving. Therefore, as shown in FIG. It is preferable to preliminarily rotate the belt to eliminate temperature unevenness, and to operate the tension roller to correct the meandering of the belt so that the image forming operation is started when the temperature of the conveyor belt becomes stable. When the four color toner images are overlapped for a long time as in the first and second embodiments, preheating of the conveyor belt may be performed during the operation of transferring the toner images of the respective colors to the intermediate transfer device.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view showing a second embodiment of the image forming apparatus according to the present invention.

FIG. 3 is a schematic sectional view showing a third embodiment of the image forming apparatus according to the present invention.

FIG. 4 is a schematic sectional view showing a fourth embodiment of the image forming apparatus according to the present invention.

FIG. 5 is a schematic sectional view showing a fifth embodiment of the image forming apparatus according to the present invention.

FIG. 6 is a schematic sectional view showing a sixth embodiment of the image forming apparatus according to the present invention.

FIG. 7 is a flowchart of an image forming process including a preheating operation.

[Explanation of symbols]

Reference numeral 10 ... Image forming apparatus, 12 ... Photoconductor, 14 ... Intermediate transfer device, 16 ... Transfer belt, 20 ... First heating roller, 26 ...
Fixing device, 28 ... conveying belt, 30 ... second heating roller,
32 ... Third heating roller, 34 ... Secondary transfer area, 36 ... Fixing area, 38 ... Fourth heating roller.

Claims (1)

[Claims] 1. An image forming apparatus which transfers a developer from an image carrier to a sheet at a transfer section and then fixes the developer on the sheet at a fixing section, comprising: (a) an endless belt;
(B) a first roller which is arranged inside the belt and presses the belt against the image carrier at the transfer section;
First heating means for heating the developer in the transfer portion to fix it to the sheet; and (d) a second roller arranged inside the belt for supporting the belt together with the first roller, e) second heating means for heating the developer in the fixing section to fix it on the sheet; and (f) driving means for rotationally moving the belt to convey the sheet from the transfer section to the fixing section. An image forming apparatus provided with.