JPH06110350A - Roller for fixing and fixing device - Google Patents

Abstract

PURPOSE:To prevent an image from being missed and stained by preventing peeling charging. CONSTITUTION:A nipping part N is formed by making a fixing roller 10 having a core bar 11, and an insulating layer 12 abut on a pressuring roller 20 having a core bar 21, an elastic layer 22, an insulating layer 23 and a conductive coating layer 25. A - (negative) bias voltage is impressed on the core bar 11, so that - (negative) toner T is prevented from offsetting (transfer) on the surface of the fixing roller 10 on the nipping part N. + (positive) peeling charging occurs on a part corresponding to the trailing edge of a transferring material P1 on the surface of the fixing roller when the trailing edge of the transferring material P1 passes through the nipping part N, so that unfixed toner T on succeeding transferring material P2 is apt to offset on the part. Therefore, the peeling charging is prevented by the conductive coating layer 25 and image missing and image stain caused by the offset of the toner to the fixing roller 11 are eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing roller and a fixing device used in an image forming apparatus such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art FIG. 6 shows a cross section of a conventional fixing device 1. The fixing device 1 includes a fixing roller 10 and a pressure roller 20 that are in contact with each other to form a nip portion N (the fixing roller 10 and the pressure roller 20 are referred to as a “fixing roller”. It is a superordinate concept of "fixing roller", and includes, for example, "fixing belt" in addition to "fixing roller") as main constituent members. The fixing roller 10 has a core metal 1 on the inside.
1, and a release layer (insulating layer) 12 made of, for example, a fluororesin such as PFA or PTFE is laminated on the outer periphery thereof, and is rotationally driven in the direction of arrow R1 by a driving device (not shown). On the other hand, the pressure roller 20 has a cored bar 21 at the center.
An elastic layer 22 made of silicon rubber or the like is formed around it, and a release layer (insulating layer) 23 made of a fluororesin such as PFA or PTFE is formed outside the elastic layer 22. Pressure roller 2
0 abuts on the fixing roller 10 through the nip portion N, and is driven to rotate in the direction of arrow R2 as the fixing roller rotates in the direction of arrow R1.

A heater 2 is housed inside the core metal 11 of the fixing roller 10 and heats the fixing roller 10 from the inside. Further, a temperature sensor 3 connected to a temperature adjusting circuit (not shown) is arranged on the outer peripheral surface of the fixing roller 10, and the surface of the fixing roller 10 is substantially constant by the temperature sensor 3 and the temperature adjusting circuit. Is controlled by the temperature of.

The pressure roller 20 is pressed against the fixing roller 10 by a biasing means (not shown). As a result, the pressure roller 20 having the elastic member 22 is dented, and a nip portion N having an appropriate width is formed between the fixing roller 10 and the pressure roller 20.

The toner T is fixed on the transfer material P by the fixing device 1 including the fixing roller 10 and the pressure roller 20. The toner T having a charge is electrostatically transferred onto the transfer material P by a well-known electrophotographic process, that is, a series of processes such as charging, exposure, development, and transfer. The toner T on the transfer material P is not yet fixed in this state. The unfixed toner T is nipped and conveyed in the direction of arrow K1 by the nip portion N, is heated and pressed by the fixing roller 10 and the pressure roller 20 to melt, and is fixed on the transfer material P as a permanent image.

At this time, a voltage having the same polarity as the toner T is applied to the fixing roller 10. A bias power source 5 is connected to the core metal 11 of the fixing roller 10, and the toner T
When the electric charges of − are negative (−) as shown in FIG. 6, the bias power supply 5 applies − (negative) voltage to the core metal 11. As a result, in the nip portion N, a so-called repulsive electric field is formed in which the toner T is electrostatically repelled from the surface of the fixing roller 10, and the toner T on the subsequent transfer material P is offset (fixed) to the fixing roller 10. To prevent metastasis). When the toner T is offset to the fixing roller 10, not only the image on the subsequent transfer material P may be missing, but also an offset phenomenon occurs in which the toner T is further transferred to the transfer material P, and the transfer material P Image is stained.

Since the stronger the repulsive electric field is, the more the toner T can be prevented from being offset from the fixing roller 10, the elastic layer 22 is preferably conductive. As an example, it is preferable that the elastic layer 22 is formed of silicon rubber in which carbon is dispersed.

Although the elastic layer 22 of the pressure roller 20 is electrically conductive, the insulating layer 23 and the fixing roller 10 on the outside thereof are electrically conductive.
The insulating layer 12 is electrically insulating. These insulating layers 12 and 23 are made of members having a resistivity of 10 ¹² Ω · cm or more, and prevent current leakage when a bias voltage is applied to the cored bar 11 by the bias power source 5.

[0009]

However, according to the above-mentioned conventional example, peeling electrification that weakens the repulsive electric field in the nip portion N occurs, the offset prevention effect of the toner is diminished, and the toner T is fixed to the fixing roller 10. In addition, there is a risk that the image is transferred from the fixing roller 10 to the transfer material P.

That is, when the transfer material P passes through the nip portion N, peeling charging occurs between the insulating layer 12 of the fixing roller 10 and the transfer material P and between the pressure roller 20 and the transfer material P. Immediately after the trailing edge of the transfer material P has passed through the nip portion N, locally occurs remarkably at the portion of each of the rollers 10 and 20 corresponding to this trailing edge. For example, as shown in FIG.
When a negative bias voltage is applied to negative (negative) toner, as shown in FIG.
On the surface of 0, + (positive) peeling electrification occurs in a portion corresponding to the rear end of the transfer material P1 immediately after passing through the nip portion N. This positive charge has the opposite polarity to the negative bias voltage and toner T. Therefore, as shown in FIG. 7B, when the + charged portion of the surface of the fixing roller 10 rotates and reaches the nip portion N, the repulsive electric field is locally attenuated by the + charged portion, and the subsequent transfer material P2. Toner T from above
The toner T may be peeled off and the toner T may be offset (transferred) to the + charged portion of the fixing roller 10. Such peeling charging is likely to occur in a low humidity environment in which the transfer material P has high resistance, and when the fixing roller 10 and the pressure roller 20 are new, that is, the insulating layers 12 and 23 of both rollers 10 and 20 are new. Sometimes it is especially likely to occur.

The offset state of the toner T is shown in FIG.
Shown in (a) and (b). FIG. 8A shows a case where a halftone image is formed on the transfer material P2, and the shaded portion is the toner portion. The toner (X portion) stripped off linearly at a right angle to the conveying direction of the transfer material P2 (direction of arrow K1) is once offset to the fixing roller 10 and then transferred to the transfer material P2.
In the rear part (Y portion), the toner is offset from the fixing roller 10 onto the transfer material P2. X part and Y at this time
The distance L to the section corresponds to the circumference of the fixing roller 10. In the case of halftone, since the amount of toner adhered per unit area is small, a white streak is formed as shown in the figure only when a small amount of toner is offset to the fixing roller 10. On the other hand, FIG. 7B shows a case of a character image. in this case,
Unlike in the case of halftone, even if some toner is peeled off from the image in the X part, characters are not lost, but the toner offset to the fixing roller 10 is the same as in the case of halftone. It is offset again to the Y portion on the transfer material P2 that is behind by the distance L.

As described above, when the peeling charge is generated, the image is defective, or the toner is retransferred to an unnecessary portion to cause an image defect.

Therefore, an object of the present invention is to provide a fixing roller and a fixing device in which a conductive coating layer is provided on the uppermost layer to prevent the occurrence of peeling electrification and prevent image defects. To do.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and forms a nip portion by abutting against a rotating body, and the nip portion transfers unfixed toner. A fixing roller in which toner is fixed on the transfer material by sandwiching and conveying the material has a plurality of concentric layered portions on the surface side, and the uppermost layer on the surface side of these layered portions is electrically conductive. Formed by a conductive coating layer,
By forming at least one layer of the layered portion excluding the conductive coating layer with an insulating layer, the conductive coating layer is held in an electrically floating state with respect to the inside of the insulating layer. It is characterized by that.

Further, the fixing device includes a rotating body according to claim 1, a fixing roller according to claim 1, and a bias power source for applying a bias voltage between the rotating body and the fixing roller.
And a repulsive electric field is formed by the bias power source on the toner on the transfer material passing through the nip portion in a direction in which the toner is pressed against the transfer material.

[0016]

According to the above structure, the fixing device tends to cause local peeling charge on the portion of the fixing roller surface corresponding to the rear end of the transfer material immediately after the transfer material passes through the nip portion. By providing an electrically floating conductive coating layer on the surface of the fixing roller as the uppermost layer, local peeling electrification is prevented.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> The fixing roller according to the present invention refers to a roller used for fixing, specifically, the fixing roller 10 or the pressure roller 20. In the first embodiment, the pressure roller 20 corresponds to the fixing roller in the claims, and the fixing roller 10 corresponds to the rotating body. FIG. 1 illustrates a perspective view of the pressure roller 20.

The pressure roller 20 has a cored bar 21 in the center, the elastic layer 22 on the outer side, and the outermost layer, that is, the uppermost layer on the front side, as in the case of the conventional example shown in FIG. It has an insulating layer 23 as a mold layer. The difference from the conventional example is that a conductive coating layer (hereinafter referred to as “conductive layer”) 25 is formed further outside the insulating layer 23.

The insulating layer (release layer) 23 is made of, for example, a fluororesin such as PTFE or PFA.
It is formed to have a thickness of 20 to 100 μm and a width L2 in the axial direction and has a resistivity of 10 ¹² to 10 ¹⁸ Ω · cm.

In contrast to the lower insulating layer 23, the upper conductive layer 25 is a conductive layer in which a metal oxide powder such as carbon or zinc oxide is dispersed in a fluororesin such as PTFE or PFA, and has a thickness. 10 to 50 μm, resistivity 10 ³
It is about 10 ⁶ Ω · cm. The conductive layer 25 has a width L in the axial direction.
1 is ΔL at both ends than the width L2 of the insulating layer 23.
Only the (insulating region) is set to be short, whereby an electrically insulating state is maintained with respect to the conductive elastic layer 22 on the lower layer side. That is, the conductive layer 25 is electrically floated with respect to the inside of the insulating layer 23. Specifically, the insulating region ΔL may be set to 2 to 10 mm, and the width L1 is set to a value slightly larger than the maximum width of the transfer material P used for image formation. I shall.

The insulating layer 23 and the conductive layer 25 are formed as follows. The insulating layer 23 is obtained by applying a fluororesin powder on the elastic layer 22 by a spraying method or a dipping method, or by coating a tube of fluororesin having an appropriate size. On the insulating layer 23 thus obtained,
A conductive conductive layer 25 can be obtained by applying a mixture of a fluororesin powder and conductivity-imparting particles by a spray method or a dipping method, or coating a fluororesin tube in which the conductivity-imparting particles are dispersed. it can. In order to secure the insulating region ΔL at both ends, in the spraying method or the dipping method, the insulating region ΔL may be masked and the conductive layer 25 may be applied, and when covering the conductive tube, the width of the tube may be reduced. L1 may be shorter than the width L2 of the insulating layer 23 by that amount.

The pressure roller 20 formed as described above is
It is incorporated as a main component of the fixing device 1 shown in FIG. The fixing roller 10 that contacts the pressure roller 20 from above to form the nip portion N is the same as that of the conventional example shown in FIG. That is, it has a core metal 11 to which a bias voltage of the bias power source 5 is applied, and an insulating layer (release layer) 12 formed so as to cover the outside thereof. A heater 2 is provided inside the core 11 to heat the fixing roller 10 from the inside, and the surface of the fixing roller 10 is kept at a predetermined temperature by a temperature sensor 3 for detecting the surface temperature of the fixing roller 10. Trying to maintain.

A diode 6 is connected to the pressure roller 20, and a repulsive electric field is formed in the nip portion N together with the bias power source 5 on the fixing roller 10 side so that the toner T on the transfer material P is fixed. It prevents the surface from being offset.

By the way, if attention is paid only to the offset of the toner to the fixing roller 10, the insulating layer 23 on the pressure roller 20 side is not necessarily provided. However, when a large number of transfer materials P pass through the nip portion N, these transfer materials P
The insulating layer 12 of the fixing roller 10 is worn by the abutting objects such as the temperature sensor 3 and the temperature sensor 3, and finally the cored bar 11 is exposed and comes into direct contact with the pressure roller 20. In this case, a leakage current is generated between the fixing roller 10 and the pressure roller 20, and the repulsive electric field is weakened. In order to prevent this, it is effective and essential to form an insulating layer also on the pressure roller 20 side. Further, even in a new state in which the insulating layer 12 of the fixing roller 10 has not worn yet, if the insulating layer 23 is not present, the charge on the back surface of the transfer material P, which is in contact with the pressure roller 20, becomes conductive. Since the layer 25 leaks to the cored bar 21 via the elastic layer 22 to the ground, the repulsive electric field attracting the toner T to the transfer material P is weakened, and the toner T is electrostatically offset to the fixing roller 10 side. It may cause a malfunction. In any of the above cases, the insulating layer 23 on the pressure roller 20 side effectively prevents the repulsive electric field from weakening.

Next, regarding the operation of the pressure roller 20 and the fixing device 1, the − (negative) toner T on the transfer material P is transferred to the transfer material P.
An example will be described in which the image is fixed on the first and P2. When the fixing roller 10 is rotationally driven in the direction of arrow R1, the pressure roller 20
Is driven to rotate in the direction of arrow R2, and at this time both rollers 10,
A nip portion N is formed between 20. When a negative (-) bias voltage is applied to the cored bar 11 of the fixing roller 10 by the bias power source 5, the cored bar 11 of the fixing roller 10 and the cored bar 21 of the pressure roller 20 in the nip portion N are connected. Generates a repulsive electric field in the direction of pressing the negative toner T to the transfer material P1 side. Due to this repulsive electric field, the toner T on the transfer material P1 is fixed on the transfer material P1 without being offset on the surface of the fixing roller 10 and becomes a permanent image.

By the way, in the conventional example, immediately after the rear end of the transfer material P1 passes through the nip portion N, the surface of the fixing roller 10 corresponding to the rear end is locally charged to + (positive) (peeling charging). Then, when this portion reaches the nip portion N as the fixing roller 10 rotates, the repulsive electric field is weakened when the toner T on the subsequent transfer material P2 is fixed, and the toner T is offset to the fixing roller 10. I was promoting it.

However, in the present invention, the fixing roller 1
Even if the portion of 0 corresponding to the rear end of the transfer material P1 is locally charged to +, this charging immediately flows to the conductive layer 25 of the pressure roller 20 and is eliminated. Therefore, peeling charging does not occur, and the toner T on the subsequent transfer material P2 does not offset on the fixing roller 10. That is,
The toner T on the subsequent transfer material P2 is offset on the fixing roller 10 and the image on the transfer material P2 is missing, or the toner T offset on the fixing roller 10 is offset on the image again and the image is stained. There is no such thing. <Embodiment 2> FIG. 3 shows Embodiment 2 of the fixing device 1 according to the present invention. In the second embodiment, the fixing belt 30 is used instead of the fixing roller 10. The fixing belt 30 includes a resin film 31 such as polyimide having a thickness of 30 to 100 μm.
And a conductive layer 12 also serving as an adhesive layer having a thickness of 5 to 10 μm and an insulating layer 33 made of a fluororesin such as PTFE or PFA having a thickness of 5 to 30 μm. The fixing belt 30 is stretched around the plate-shaped heater 7 and the driving rollers 9 and 9. The fixing belt 30 is rotationally driven in the direction of the arrow R1 by the rotation of the driving roller 9 and also has a nip portion N between itself and the fixing roller 20. Is formed. Since the fixing belt 30 is formed to be very thin as described above, it is possible to use a heater having a small heat capacity, and by turning the temperature sensor 3 on and off, the fixing belt 30 can be fixed almost instantly. The belt 30 can be raised to a predetermined temperature. Therefore, the energy-saving type fixing device 1 can be configured as a whole.

The conductive layer 32 of the fixing belt 30 is grounded via the diode 10, and together with the diode 6 connected to the cored bar 21 of the pressure roller 20, the transfer material P is placed in the nip portion N. A repulsive electric field in the direction in which the upper toner T is pressed against the transfer material P is formed to prevent the toner T from being offset to the transfer belt 30. Also in this embodiment, immediately after the transfer material P has passed through the nip portion N, the conductive layer 25 on the pressure roller 20 side is replaced with the insulating layer 3 on the transfer belt 30 side.
By making contact with the transfer material P, peeling charging by the rear end of the transfer material P is prevented, and toner on the subsequent transfer material P is prevented from being offset on the surface of the transfer belt 30.

For the purpose of saving energy as in the second embodiment, it is preferable that the elastic layer 22 of the pressure roller 20 is made of a conductive sponge to reduce heat escape. <Third Embodiment> FIGS. 4 and 5 show a third embodiment of the present invention. 1 and 2 show an example in which the conductive layer 25 is provided on the pressure roller 20 side and the pressure roller 20 is incorporated in the fixing device 1, whereas the fixing roller 1 is shown in FIG.
An example of a fixing device 1 in which a conductive layer 13 is provided on the 0 side and the fixing roller 10 is incorporated is illustrated.

As shown in FIG. 4, the fixing roller 10 of the present embodiment is such that the outer periphery of the insulating layer 12 covering the outer periphery of the cored bar 11 is further covered with the conductive layer 13. As a manufacturing method,
This is almost the same as when the conductive layer 25 is formed on the pressure roller 20 of Example 1, and is formed by firing the conductive layer 13 on the insulating layer 12. From the left and right ends of the conductive layer 13, the lower layer is formed. The insulating layer 12 is exposed by a length ΔL to form an insulating region. As a result, when the core bar 11 is energized, the conductive layer 13 is not energized and the electrically floating state is maintained.

According to the present embodiment, since the conductive layer 13 is provided on the surface of the fixing roller 10, the surface potential of the fixing roller 10 does not locally take a value different from other portions, and the transfer material P is not formed.
When the sheet comes out of the nip portion N, strong peeling charge does not occur in the portion of the fixing roller 10 corresponding to the rear end of the transfer material P. Therefore, the offset in which the toner T on the transfer material P is transferred to the fixing roller 10 does not occur. further,
In the nip portion N, the conductive layer 13 acts as a float electrode, an electric potential intermediate between the toner T adhesion portion and the non-image portion is induced therein, and as a result, the toner T repels from the conductive layer 13. There is also an effect of preventing an electrostatic offset by generating an electric field.

As described above in Examples 1 to 3, the conductive layer for preventing peeling electrification may be provided on the pressure roller 20 side (Examples 1 and 2). It may be provided on the fixing roller 10 side (Example 3). Further, the rotating body with which the pressure roller 20 as a fixing roller contacts is not limited to the fixing roller 10, but the fixing belt 30
(Example 2) may be sufficient.

[0033]

As described above, according to the present invention,
In the fixing roller, the outermost outermost layer of the insulating layer is formed of a conductive coating layer, so that it is possible to prevent local peeling and charging which occurs when the trailing end of the transfer material passes through the nip portion. .

The fixing device provided with such a fixing roller prevents the toner from being offset to the fixing roller by the peeling electrification and further from being offset from the fixing roller onto the transfer material. It is possible to effectively prevent chipping of the image and stain of the image.

[Brief description of drawings]

FIG. 1 is a perspective view showing a pressure roller according to a first embodiment of the present invention.

FIG. 2 is a vertical sectional view of the fixing device.

FIG. 3 is a vertical cross-sectional view of a fixing device according to a second exemplary embodiment that uses a fixing belt.

FIG. 4 is a perspective view of a main part of a fixing roller according to a third exemplary embodiment.

FIG. 5 is a vertical sectional view of the fixing device.

FIG. 6 is a vertical cross-sectional view of a conventional fixing device.

FIG. 7A is a diagram showing how peeling charging occurs due to a trailing end of a preceding transfer material. FIG. 6B is a diagram showing how toner is offset by peeling charging.

8A and 8B are diagrams showing image defects (offset images) caused by peeling electrification.

[Explanation of symbols]

 1 Fixing Device 5 Bias Power Supply 10 Rotating Body (Fixing Roller) 20 Fixing Roller (Pressing Roller) 23 Insulating Layer (Release Layer) 25 Conductive Coating Layer (Conductive Layer) N Nip Part P Transfer Material T Toner

Claims (2)

[Claims] 1. A fixing method in which a nip portion is formed in contact with a rotating body, and a transfer material carrying an unfixed toner is nipped and conveyed by the nip portion to fix the toner on the transfer material. The roller for use has a plurality of concentric layered portions on the front surface side, and the uppermost layer on the front surface side of these layered portions is formed by a conductive coating layer, and among the layered portions excluding the conductive coating layer. A fixing roller, wherein at least one layer is formed of an insulating layer, and the conductive coating layer is held inside the insulating layer so as to be in an electrically floating state. 2. The rotating body according to claim 1, the fixing roller according to claim 1, and a bias power supply for applying a bias voltage between the rotating body and the fixing roller, the bias power supply, A fixing device, wherein a repulsive electric field is formed in a direction in which the toner is pressed against the transfer material, with respect to the toner on the transfer material passing through the nip portion.