JP2003270987A - Belt fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt fixing device which can prevent the coiling round tendency of a fixing belt spread on a plurality of rolls, and can suppress the wrinkling of the belt caused by thermal shrinkage accompanying heating and cooling and which can obtain a uniform color image having excellent glossiness when a recording medium is released from the belt. <P>SOLUTION: The belt fixing device includes a first and second drive rolls 71 and 72 which are rotationally driven, the rotating endless fixing belt 70 spread on a plurality of rotating rolls 71, 72 and 73 including the first and second drive rolls, and a cooling member 76 which is provided between the first drive roll 71 and one rotating roll 72 adjacent to a downstream side in the rotating direction of the fixing belt 70 from the first drive roll 71, and cools the fixing belt 70 from the inside. The circumferential speed of the second drive roll 72 is set to be higher than that of the first drive roll 71. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device of an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, and a composite machine of these, and more specifically,
The present invention relates to an improvement of a fixing device using a fixing belt.

[0002]

2. Description of the Related Art With the widespread use of full-color copying machines and printers in recent years, higher quality and higher gloss images are required. From such a requirement, for example, in JP-A-64-35452 and JP-A-5-216322, a color formed of a thermoplastic resin of the same quality is formed on the surface of a recording medium provided with a transparent resin layer formed of a thermoplastic resin. A method of transferring a toner, heating and fusing the toner to form a color image is disclosed.

A belt fixing method has been proposed as a fixing method suitable for the above-described high gloss image forming method. In such a fixing device, a heat-resistant film is pressed and heated on a recording medium carrying an unfixed toner image with a heating roll and a pressure roll, conveyed in a state of being in close contact with a belt, and cooled by a cooling member, and then the recording medium is transferred. It is configured to peel off. As a result, the toner image is embedded in the transparent resin layer, and the transparent resin layer and the toner image on the surface of the recording medium are solidified according to the belt surface shape, so that the entire recording medium surface becomes a smooth surface and has excellent gloss. You can get a good color image.

Conventionally, in such a belt fixing device, one of a plurality of rolls around which an endless fixing belt is stretched is rotationally driven by a drive source such as a motor and wound around the drive roll. The fixing belt is driven to rotate by the frictional force with the back surface of the fixing belt. Therefore, in order to drive the fixing belt in a stable state,
It is necessary to introduce a predetermined tension to the fixing belt to increase the pressure contact force with the drive roll. In particular, when the fixing belt and the recording medium are nipped and conveyed between the two rolls, the load on the belt driving becomes large, and therefore the tension applied to the fixing needs to be large.

Further, in the belt fixing device in which the fixing belt is heated and pressed in the nip portion between the heating roll and the pressure roll and cooled in the cooling portion, the fixing belt heated in the fixing nip portion is rapidly cooled by the cooling member. Due to the cooling, there is a problem that the fixing belt contracts and wrinkles occur. FIG. 6 is a schematic view showing the state of this wrinkle. The occurrence of this wrinkle weakens the adhesion between the cooling member located on the downstream side of the fixing unit and the belt, and deteriorates the cooling efficiency of the belt and the recording medium in close contact with the belt. However, there is a problem in that gloss unevenness occurs in the surface due to insufficient cooling.

Therefore, in order to drive the fixing belt in a stable state, a large tension is introduced to the fixing belt to further increase the pressure contact force between the belt and the driving roll, or to increase the angle at which the fixing belt is wound around the driving roller. However, measures such as increasing the contact area have been adopted.

[0007]

However, in such a belt fixing device, when the belt is in a state where a large tension is applied even when the belt fixing device is not in operation, the portion wound around the rolls. The wrap around will be attached. That is, the deformed curvature remains on the belt. Such deformation hinders stable driving of the belt and fixing of the toner image. Since the transparent resin layer and the toner image on the surface of the recording medium are solidified following the belt surface shape,
If the deformed curve remains on the belt, there is a possibility that it may be directly reflected on the surface of the recording medium as a replica.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent the fixing belt stretched around a plurality of rolls from being wound around and to prevent wrinkles and waviness. The fixing belt is driven in a stable state to provide a fixed image without uneven color or uneven gloss.

[0009]

That is, according to the present invention, first and second drive rolls which are rotationally driven and a plurality of rotary rolls including the first and second drive rolls are spanned and rotated. An endless fixing belt is provided between the first drive roll and one rotating roll adjacent to the first drive roll on the downstream side in the rotation direction of the fixing belt, and the fixing belt is in contact with the inside to cool the fixing belt. In the belt fixing device having the cooling member, the peripheral speed of the second drive roll is set to be higher than the peripheral speed of the first drive roll. The peripheral speed difference between the first drive roll and the second drive roll may be greater than 0% (for example, 1% or more), particularly preferably 3% or more, and less than 10%. Preferably there is.

Further, as a constitution for giving the peripheral speed difference to the first drive roll and the second drive roll in this way, the first drive roll and the second drive roll are independent drive sources. Although the rotational drive force may be transmitted from the first drive roll and the second drive roll, the rotational drive force is transmitted from the same drive source, and the first drive roll and the second drive roll reach the first drive roll. The peripheral speed difference may be generated by adjusting one drive transmission system and a second drive transmission system from the drive source to the second drive roll.
For example, the drive transmission system is composed of a plurality of rotating gears, and the gear ratio can be changed by adjusting the number of teeth of each gear to cause the peripheral speed difference.

Further, one rotary roll adjacent to the downstream side of the first drive roll in the rotation direction of the fixing belt may or may not be the second drive roll. further,
At least one of the plurality of rotating rolls may be a tension roll that applies tension to the fixing belt. The tension roll is not a drive roll.

Further, there is provided a pressure contact roll which faces the first drive roll and is in pressure contact with the fixing belt sandwiched therebetween, and the recording sheet image surface is applied to the fixing belt at a pressure contact portion between the fixing belt and the pressure contact roll. The recording sheet may be adhered and the recording sheet may be peeled off from the fixing belt at one rotating roll portion adjacent to the downstream side in the rotation direction of the fixing belt from the first driving roll. Further, the recording sheet has a thermoplastic resin layer on the image side thereof.

The frictional force (dynamic frictional force and / or static frictional force) between the second drive roll and the fixing belt is the frictional force (dynamic frictional force and / or static frictional force) between the first drive roll and the fixing belt. Static friction force) or more. Further, the contact area between the second driving roll and the fixing belt can be configured to be smaller than the contact area between the first driving roll and the fixing belt, and specifically, the second The diameter of the drive roll may be smaller than the diameter of the first drive roll.

By adopting such a structure, tension is applied to the fixing belt between the first driving roll and the second driving roll due to the difference in peripheral speed, and wrinkles and wrinkles in the fixing belt are caused. In addition to preventing the occurrence of waviness, the tension due to the difference in peripheral speed of the driving roll is not applied to the belt when the fixing belt is stopped, so that the winding of the belt is prevented.

[0015]

1 is a schematic sectional view of an image forming system to which a fixing device according to the present invention is applied.
As shown in the figure, this image forming system is roughly divided into an image forming apparatus 1 and a secondary fixing unit 2.

The structures and operations of the image forming apparatus 1 and the secondary fixing unit 2 will be described in detail below.

The image forming apparatus 1 is roughly composed of an image forming section, a secondary transfer section, a sheet conveying section, and a primary fixing section. As the image forming unit, the photosensitive drum 1
0, a charging device 11, an exposure unit 12, a rotary developing unit 13, a primary transfer roll, a photoconductor cleaning unit 16, a toner accommodating portion 14 for supplying toner to the developing unit for each color of the rotary developing unit 13, and a photosensitive member. A toner collection box 17 for storing waste toner collected by the body cleaning unit 16 is provided.

As the secondary transfer portion, the intermediate transfer belt 2 is used.
0, drive steering roll 21, idle roll 22, backup roll 23, secondary transfer roll 24,
A belt cleaning unit 25 and the like are provided. The paper transport unit includes a paper tray 30, a pickup roll 31, a feed roll pair 32, a transport roll pair 33, a registration roll pair 34, a transport belt 35, a paper chute 36, and a discharge roll pair 37. In addition,
The dotted line in the figure indicates the conveyance path of the paper P. The primary fixing unit includes a heating roll 41 and a pressure roll 42.

Here, as the toner accommodated in the toner accommodating portion 14 and the rotary developing unit 13, an oily component obtained by dissolving and dispersing a binder resin, a colorant, and a release agent in an organic solvent is used in an aqueous medium. The toner is obtained by dispersing and granulating, and contains inorganic fine particles inside the toner. More specifically, the binder resin has an average particle size of 5 μm.
m styrene acrylic is used, and the release agent is 5
About 1% by weight of carnauba wax is used, and as the inorganic fine particles, silicon oxide particles having an average particle size of 40 nm and about 3% by weight are used, but not limited thereto. Further, sheets (recording sheets) P stored in the sheet tray 30 are stored.

The secondary fixing unit 2 is composed of a sheet conveying section and a secondary fixing device 7. The sheet conveying unit includes a movable chute 50, a first discharge roll pair 51, a first discharge tray 61, conveyance roll pairs 52 and 55, and a second discharge roll pair 5.
6 and a second discharge tray 62. Secondary fixing device 7
The configuration will be described later.

Next, the operation of the image forming system shown in FIG. 1 will be described. In this image forming system, the secondary fixing device 7 performs the secondary fixing process when an image having a high glossiness is required, and the secondary fixing device 7 performs when the glossiness is not so required. The secondary fixing process is not performed. Hereinafter, operations for forming a black-and-white character image as an example of an image not requiring a high glossiness and a full-color photographic image as an example of an image having a high glossiness on the paper P will be described.

○ Black and white character image formation First, the monochrome character image forming operation will be described.

The surface of the photosensitive drum 10, which is driven to rotate in the direction of the arrow in the figure, is uniformly charged by the charging device 11. Then, based on the image signal as a character (image processing is performed as necessary) from a computer or the like (not shown), the exposure unit 12 irradiates the surface of the photosensitive drum 10 with laser light. Then, the photosensitive drum 10
A potential difference is generated between the exposed portion and the non-exposed portion on the surface of, and an electrostatic latent image is formed by the potential difference. And
When the electrostatic latent image on the surface of the photoconductor drum 10 faces the rotary developing unit 13, the magnetic brush held by the developing roller of the developing device corresponding to black rubs the electrostatic latent image, and the electrostatic latent image is rubbed. Toner is selectively adhered to the image area.

In this way, the surface of the photosensitive drum 10 is visualized with black toner, that is, the toner image T.
(Bk) is formed. When the toner image T (Bk) reaches a position facing the primary transfer roll 15 as the photosensitive drum 10 rotates, the toner image T (Bk) is electrostatically transferred onto the intermediate transfer belt 20 by the primary transfer electric field formed by the primary transfer roll 15. Transcribed. It should be noted that the slight amount of toner remaining on the surface of the photoconductor drum 10 without being primarily transferred is removed from the surface of the photoconductor drum 10 by the photoconductor cleaning unit 16 and finally collected in the toner collection box 17.

The toner image T (Bk) primarily transferred onto the intermediate transfer belt 20 moves with the rotation of the intermediate transfer belt 20 which is rotationally driven in the direction of the arrow in the figure, and faces the secondary transfer roll 24. At this time, the secondary transfer roll 24 is in pressure contact with the intermediate transfer belt 20.

On the other hand, the paper P stored in the paper tray 30 is picked up by the pickup roll 31 and the feed roll pair 3.
2. The sheets are conveyed one by one through the conveyance rolls 33 and temporarily held (stopped) by the registration roll pair 34. Then, the toner image T (B
The registration roll pair 34 rotates in synchronism with the timing at which k) faces the secondary transfer roll 24, and the paper P held until then is pressed against the secondary transfer roll 24 and the intermediate transfer belt 20. Send in.

Then, the toner image T (Bk) on the intermediate transfer belt 20 is secondarily transferred onto the paper P by the secondary transfer electric field formed by the secondary transfer roll 24. At this time, the toner image T (Bk) is transferred onto the transparent resin layer P2 of the paper P. The slight amount of toner remaining on the surface of the intermediate transfer belt 20 without being secondarily transferred is removed by the belt cleaning unit 25.

The sheet P holding the toner image T (Bk) on its surface reaches the primary fixing section via the conveying belt 35 and the sheet chute 36. Then, when passing through the pressure contact portion between the heating roller 41 and the pressure roller 42 which rotate in pressure contact with each other, the toner image T is caused by the action of heat and pressure.
(Bk) is fixed on the paper P as a permanent image. The sheet P after the primary fixing is conveyed to the outside of the image forming apparatus 1 by the discharge roll pair 37 and is conveyed to the inside of the secondary fixing unit 2.

The sheet P conveyed into the secondary fixing unit 2.
The movable chute 50 selects one of the conveyance paths indicated by the dotted line in the figure, and the first discharge roll 51 discharges it to the first discharge tray 61, and the image forming operation of one black and white character image ends.

Full-Color Photographic Image Formation Next, the operation of full-color photographic image formation will be described.

The surface of the photosensitive drum 10 which is rotationally driven in the direction of the arrow in the figure is uniformly charged by the charging device 11. Then, a laser beam corresponding to yellow is first irradiated onto the surface of the photosensitive drum 10 from the exposure unit 12 based on an image signal as a photograph (image processing is performed as necessary) from a computer (not shown) or the like. Then, a potential difference occurs on the surface of the photoconductor drum 10 between the exposed portion and the non-exposed portion, and an electrostatic latent image is formed by the potential difference. Then, when the electrostatic latent image on the surface of the photoconductor drum 10 faces the rotary developing unit 13, the magnetic brush held by the developing roller of the developing device corresponding to yellow rubs the electrostatic latent image to make it static. Toner is selectively adhered to the latent image area.

In this way, the surface of the photosensitive drum 10 is visualized with yellow toner, that is, the toner image T.
(Y) is formed. When the toner image T (Y) reaches a position facing the primary transfer roll 15 as the photosensitive drum 10 rotates, the toner image T (Y) is electrostatically transferred onto the intermediate transfer belt 20 by the primary transfer electric field formed by the primary transfer roll 15. Transcribed. The toner image T (Y) primarily transferred onto the intermediate transfer belt 20 moves with the rotation of the intermediate transfer belt 20 which is rotationally driven in the direction of the arrow in the figure, and reaches the position facing the primary transfer roll 15 again. At this time, the secondary transfer roll 24 and the belt cleaning unit 25 are separated from the intermediate transfer belt 20.

On the other hand, by the same operation, the photosensitive drum 10
A visible image of magenta toner, that is, a toner image T (M) is formed on the surface. Then, the intermediate transfer belt 20
At the timing when the toner image T (Y) already primary-transferred above reaches the position where it faces the primary transfer roll 15 again, the toner image T (M) on the photosensitive drum 10 also reaches the position where it faces the primary transfer roll 15. The toner image T (M) is superimposed on the toner image T (Y) on the intermediate transfer belt 20 due to the primary transfer electric field formed by the primary transfer roll 15. Similarly, the toner image T (C) of the cyan toner and the toner image T (Bk) of the black toner are superposed one after another, and finally a full-color toner image T (F) is formed on the surface of the intermediate transfer belt 20. After the toner images are superposed, the secondary transfer roll 24 and the belt cleaning unit 25 are brought into contact with the intermediate transfer belt 20.

Then, the paper P stored in the paper tray 30 is conveyed one by one through the pickup roll 31, the feed roll pair 32, and the conveying roll 33, and is temporarily held (stopped) by the registration roll pair 34. It Then, the toner image T on the intermediate transfer belt 20
The registration roll pair 34 rotates in synchronization with the timing when (F) faces the secondary transfer roll 24,
The paper P that has been held until then is sent to the pressure contact portion between the secondary transfer roll 24 and the intermediate transfer belt 20.

Then, the toner image T (F) on the intermediate transfer belt 20 is secondarily transferred onto the paper P by the secondary transfer electric field formed by the secondary transfer roll 24. At this time, the toner image T (F) is transferred onto the transparent resin layer P2 of the paper P. The slight amount of toner remaining on the surface of the intermediate transfer belt 20 without being secondarily transferred is removed by the belt cleaning unit 25.

The paper P holding the toner image T (F) on its surface is conveyed through the conveyor belt 35 and the paper chute 36.
Reach the primary fixing section. The toner image T (F) is caused by the action of heat and pressure when passing through the pressure contact portion between the heating roll 41 and the pressure roll 42 which rotate in pressure contact with each other.
Is fixed as a permanent image on the sheet P. The sheet P after the primary fixing is conveyed to the outside of the image forming apparatus 1 by the discharge roll pair 37 and is conveyed to the inside of the secondary fixing unit 2.

The sheet P conveyed into the secondary fixing unit 2.
Is selected by the movable chute 50 from the other conveying path indicated by the dotted line in the figure, and is conveyed to the secondary fixing device 7 by the pair of conveying rollers 52 and 55. Then, the sheet P is subjected to a fixing process (described later) by the secondary fixing device 7, and the image held on the surface thereof has higher gloss. Then, the paper P discharged from the secondary fixing device 7 is discharged to the second discharge tray 62 by the second discharge roll 56, and the image forming operation of one full-color photographic image is completed.

Hereinafter, the secondary fixing device (belt fixing device) 7
The configuration and the operation thereof will be described as Examples 1 to 3.

Example 1 A secondary fixing device 7 according to the present example has a fixing roll (rotating roll: first drive roll) 71, a peeling roll (rotating roll: second drive roll) 72, a tension roll ( (Rotating roll) 73, fixing belt 70 that is stretched around these rollers 71, 72, 73 to rotate, and fixing roll 71
And a peeling roll 72, and a cooling member 76 for cooling the fixing belt 70 from the inside thereof, and a pressure roll 7 facing the fixing roll 71 and press-contacting the fixing belt 70 with the fixing belt 70 sandwiched therebetween.
5 and. The cooling member 76 is called a heat sink, and is a box-shaped cooling device having a structure in which metal fins having good thermal conductivity are erected inside.

The cross section of the fixing belt 70 comprises a base layer 70A and a releasable surface layer 70B as shown in the figure.
Further, an adhesive layer may be provided between the base layer 70A and the surface layer 70B.

The base layer 70A is required to have heat resistance and mechanical strength, and a metal sheet of nickel, aluminum, stainless steel or the like, or a resin film of PET, PBT, polyester, polyimide, polyimide amide or the like can be used. A conductive powder such as carbon black may be added to and dispersed in the resin to control the volume resistivity.

The base layer 70A has a thickness of 30 to 200 μm.
Is preferably in the range of 40 to 150 μm,
More preferably, the range of 50 to 130 μm is suitable. When the thickness of the base layer 70A is less than 30 μm, the dimensional stability and the strength during heating and cooling are insufficient. On the other hand, when the thickness of the base layer 70A exceeds 200 μm, the specific heat of the fixing belt 70 increases and the amount of heat transfer decreases, leading to a decrease in fixing speed and cycle time.

The surface layer 70B is required to have heat resistance, releasability from a toner and a transparent resin, and stability, and examples thereof include silicone rubber, fluororubber, and fluororesin. The thickness of the surface layer 70B is preferably in the range of 1 to 3000 μm,
More preferably in the range of 5 ~ 300 (mu) m, more preferably 10
A range of up to 100 μm is suitable. When the thickness is less than 1 μm, elasticity is insufficient, fixing problems occur, and durability is insufficient. If it exceeds 3000 μm, the specific heat of the fixing belt 70 increases and the amount of heat transfer decreases, leading to a decrease in fixing speed and cycle time.

In this embodiment, as the fixing belt 70, silicone rubber was coated on a polyimide base layer having a circumference of 164 mmφ × width of 320 mm × thickness of 80 μm with a doctor blade to prepare a fixing belt having a layer thickness of 35 μm. .

The fixing roll 71 has a structure having an elastic layer such as silicone rubber on a metal cored bar. For the metal core, a material such as aluminum or SUS is selected according to the purpose such as thermal conductivity and strength. Considering abrasion with the inner peripheral surface of the belt, it is desirable to tubing or coating the release layer with a fluororesin such as PFA. Pressure roll 75
Also, a halogen lamp for heating is arranged inside, and the same layer structure as that of the fixing roll 71 is taken. The pressure roll 75 is driven by a drive gear of the fixing roll 71 and a connecting gear, and adopts a configuration in which latching / unlatching with the fixing roll 71 is switched by rotation of a cam.

On the surface of the peeling roll 72, the fixing belt 70 is provided.
Silicone rubber is coated to provide friction with the inner surface. A drive gear (not shown) is connected to each of the fixing roll 71 and the peeling roll 72, and a separate drive motor (not shown) is connected to each gear. The peripheral speeds of the fixing roll 71 and the peeling roll 72 can be set separately by the individual motors.

In the belt fixing device 7 according to the present embodiment, the tension roll 73 is pressed against the inner surface of the fixing belt 70 by the spring, whereby a predetermined tension is applied to the fixing belt 70, and the fixing roll 71 and the peeling roll 72 are provided. To drive the fixing belt 70 to rotate.

As the paper P used for forming the full-color photographic image, the following dedicated glossy paper is used. This paper P is composed of a base material PA and an image receiving layer PB made of a thermoplastic resin. The thickness of the base material PA is preferably in the range of 150 to 200 μm in order to obtain a texture equivalent to that of a photographic paper photograph. Image receiving layer PB
Is preferably in the range of 5 to 50 μm, more preferably 1
A range of 0-30 μm is suitable. If the image receiving layer PB is too thin, it becomes difficult to embed the toner sufficiently, and the relief feeling becomes noticeable. When the thickness is more than 50 μm, the image receiving layer PB is easily cracked by stress strain (bending strain) between the base material PA and the image receiving layer PB after fixing. Further, wax may be added to the image receiving layer PB as a release agent.

In this embodiment, as the paper P, the basis weight is 170 g / m.
2. TiO2, ZnO on the front and back of 150μm thick base paper
Apply a coating layer in which a white pigment such as
A coating layer having a thickness of μm was provided to serve as a base material PA, and a coating liquid comprising a polyester resin and carnauba wax was applied on the surface and dried to provide a transparent resin layer PB having a thickness of 15 μm.

When the dedicated glossy paper P carrying the full-color toner image T (F) toner is conveyed, the paper P is nipped between the fixing roll 71 and the pressure roll 75, and the fixing belt 7
After being heated and pressed through 0, the cooling member 76 is cooled and solidified while being in close contact with the surface of the fixing belt 70, and then is peeled from the fixing belt 70 by the waist (rigidity) of the paper P at the peeling roll 72, and a fixed image is obtained. Is created.

By the way, the secondary fixing device 7 according to the present embodiment.
Prevents the fixing belt 70 from being wound around and prevents wrinkles of the fixing belt 70 caused by heat contraction due to heating and cooling, and provides a uniform gloss when the recording medium is peeled from the belt. An excellent color fixed image can be obtained. In order to arrive at such a secondary fixing device 7, some experiments conducted by the inventors will be introduced.

[0052]

[Table 1] Table 1 summarizes the effect of the spring load on the tension roll 73 and the spread of the fixing belt 70 on the image quality. The present inventors changed the spring load applied to the tension roll 73 to leave the fixing belt 70 under tension for 24 hours, and confirmed the degree of winding.
After that, form a uniform halftone image on paper P,
After fixing, the fixing belt 70 was used for fixing, and the reflection (replica) on the image of the winding pattern was observed (Experiment 1).

Next, the running property of the fixing belt 70 was confirmed. The running property of the fixing belt 70 depends on the fixing roll 71.
And the pressure roll 75 are controlled to a predetermined temperature, the fixing belt 70 is orbitally driven while keeping the nip, and the peripheral speed of the peeling roll 72 is changed with respect to the peripheral speed of the fixing roll 71 of 60 mm / sec. While observing the occurrence of belt wrinkles and ripples from the downstream side of the nip to the outlet of the cooling unit, a uniform halftone image is formed on the paper P, and the secondary fixing device 7 fixes the image, and the glossiness of the image Was measured (Experiment 2).

The peripheral speed of the peeling roll 72 is the fixing roll 71.
When the speed is the same as or slower than that, wrinkles as shown in FIG. 6 remarkably occur, and wrinkle marks are seen as a difference in gloss on the image. When the peripheral speed of the peeling roll 72 is set higher than that of the fixing roll 71, the wrinkle generation level sharply decreases, and
With a peripheral speed difference of more than%, wrinkles are almost eliminated. Ten
When the peripheral speed difference was increased to more than 100%, slippage between the fixing roll and the fixing belt started to occur, the running property of the belt became irregular, and the fixing property of the image became uneven.

Experimental results shown in the graph of FIG. 3 were obtained for the in-plane gloss unevenness of the fixed image obtained for each peripheral speed difference. The gloss level is Micro-Gloss Catalog No. 4512 (B
YK-Gardner GmbH) is used, and both the incident angle and the light receiving angle are 2
It was measured at 0 °. In this graph, the vertical axis on the left shows the difference between the maximum and minimum values of the image glossiness measured at 20 points.

When the spring load on the tension roll 73 is increased and the tension of the fixing belt 70 is sufficiently high, the running property of the belt 70 is stable without changing the peripheral speeds of the two driving rolls. As described above, the belt 70 is deformed due to the winding curl when stopped, and the image is reflected in the image. Even when the spring load on the tension roll 73 is reduced and the tension of the belt 70 is kept low, the peripheral speed of the peeling roll 72 is set higher than that of the fixing roll 71, so that the belt tension between the two drive rolls 71, 72 is increased. Heightens and wrinkles and ripples are suppressed. In this embodiment, the peeling roll 7
By setting the peripheral speed of No. 2 to be 3 to 10% faster than the peripheral speed of the fixing roll 71, it was possible to obtain a stable image with less uneven gloss.

Example 2 The secondary fixing device 7 according to the present example includes a fixing roll (rotating roll: first driving roll) 71, a peeling roll (rotating roll) 72, a tension roll (rotating roll) 73, and a driving unit. A roll (rotating roll: second drive roll) 74, a fixing belt 70 spanned by these rolls 71, 72, 73, 74 to rotate, a fixing roll 71, and a peeling roll 72.
And a pressure roller 75 that faces the fixing roller 71 and presses the fixing belt 70 while sandwiching it.

A drive gear and a drive motor are connected to the fixing roll 71 and the drive roll 74, respectively, so that they can be set separately. When the secondary fixing device 7 was attached to the image forming apparatus of FIG. 1 and belt wrinkles and uneven gloss were observed, the secondary fixing device 7 according to the present embodiment was observed.
However, by setting the peripheral speed of the driving roll 74 to be 3 to 10% faster than the peripheral speed of the fixing roll 71, it was possible to obtain a stable image with less unevenness in gloss.

Example 3 In Examples 1 and 2, the first drive roll (fixing roll 7) was used.
1) and the second drive roll (the peeling roll 72 (Example 1) and the drive roll 74 (Example 2) are independently driven by separate drive motors, the fixing roll 71 is driven by one drive motor. It is also possible to employ a configuration in which the driving force is transmitted to the second drive roll by a gear train in which the number of teeth is set in a predetermined relationship by rotating the gear.

FIG. 5 is a view showing the gear train of the secondary fixing device 7 according to this embodiment. In FIG. 5, 81 is the fixing roll 7.
1 is a drive gear connected to the first drive gear 82, and the second drive roll (peeling roll 72 (Example 1), drive roll 74 (Example) via the first gear 82, the second gear 83, and the third gear 84). The driving force is transmitted to the driven roll gear 85 connected to 2).
A drive motor (not shown) is connected to the drive gear 81.

In this embodiment, the outer diameter of the fixing roll is 50 mm.
In addition, the outer diameter of the second drive roll is 25 mm. Drive gear 81, first gear 82, second gear 83, third gear 84,
Set the number of gears (number of teeth) of the driven roll gear 85 to the specified number of gears (number of teeth).
By doing so, the peripheral speed of the second drive roll could be made higher than the peripheral speed of the fixing roll.

[0062]

[Table 2]

Table 2 summarizes the number of teeth of each gear and the peripheral speed difference between the fixing roll and the second drive roll at that time. In this embodiment, the gear train and the number of gears described above are used.
The peripheral speed of the second drive roll can be arbitrarily set to be higher than the peripheral speed of the fixing roll without being limited to the (number of teeth). When the gear trains of and in Table 2 were used, a stable image with less uneven gloss was obtained as in Example 1.

[0064]

As described above, according to the present invention,
The fixing belt stretched over multiple rolls can be prevented from being twisted, and the wrinkles of the belt caused by heat contraction due to heating and cooling can be suppressed. It is possible to obtain a color image having excellent glossiness. Such effects are
This is most prominent in a fixing method in which a recording medium having a thermoplastic transparent resin layer formed on a substrate is applied and the toner is fixed in the transparent resin.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating an image forming system to which a belt fixing device according to the present invention can be applied.

FIG. 2 is a schematic sectional view of the belt fixing device according to the first embodiment.

FIG. 3 is a graph illustrating the relationship between peripheral speed difference and glossiness.

FIG. 4 is a schematic cross-sectional view of the belt fixing device according to the first exemplary embodiment.

FIG. 5 illustrates a drive transmission system of a belt fixing device according to a third exemplary embodiment.

FIG. 6 is an illustration for explaining wrinkles occurring in a fixing belt of a conventional belt fixing device.

[Explanation of symbols]

7 ... Secondary fixing device (belt fixing device), 70 ... Fixing belt, 71 ... Fixing roll, 72 ... Peeling roll, 73 ... Tension roll, 74 ... Driving roll, 75 ... Pressure roll,
76 ... Cooling member, 81 ... Drive gear, 82 ... First gear, 8
3 ... 2nd gear, 84 ... 3rd gear, 85 ... Driven roll gear

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Claims (5)

[Claims] 1. A first and second drive rolls which are rotationally driven, an endless fixing belt which is stretched around a plurality of rotary rolls including the first and second drive rolls, and is rotated. In a belt fixing device having a driving roll and a cooling member which is provided between the first driving roll and one rotating roll adjacent to the downstream side in the rotation direction of the fixing belt, and which cools the fixing belt from the inside thereof, A belt fixing device, wherein a peripheral speed of the second drive roll is set to be higher than a peripheral speed of the first drive roll. 2. The belt fixing device according to claim 1, wherein a peripheral speed difference between the first drive roll and the second drive roll is 3% or more. 3. The belt fixing device according to claim 1, wherein the peripheral speed difference between the first drive roll and the second drive roll is less than 10%. 4. A pressing roller that faces the first driving roller and presses the fixing belt while sandwiching the fixing belt, and the recording sheet image surface is applied to the fixing belt at a portion where the recording sheet is pressed between the fixing belt and the pressing roller. The belt fixing device according to any one of claims 1 to 3, wherein the recording sheet is adhered and the recording sheet is peeled off from the fixing belt at a portion of one rotating roll that is adjacent to a downstream side in the rotation direction of the fixing belt from the first driving roll. 5. The belt according to claim 1, wherein a frictional force between the second drive roll and the fixing belt is equal to or larger than a frictional force between the first drive roll and the fixing belt. Fixing device.