JPH05216362A - Fixing unit - Google Patents

Abstract

PURPOSE:To prevent a bias voltage applied on a first roller from leaking to a second roller by constituting the abutting area of a member being in contact with the first roller and abrading its surface, out of the paper passing region of an image supporting material, so as not to overlap with the abutting area of the low resistance area part of the second roller. CONSTITUTION:A spacer 21 for maintaining a gap with high accuracy between a fixing roller 1 and a temperature sensing element 20, is provided, the temperature sensing element 20 is held by the spacer 21 and it is pressed by a spring 22 fixed on a fixing device frame. Then, the spacer 21 is abutted on the fixing roller 1, out of the paper passing region of the fixing roller 1, and a dimension in the longitudinal direction of a conductive pressure roller 3 is regulated so that it is provided at the position more inside than the abutting end of the spacer 21 and the fixing roller 1. Since such a constitution is adopted, even if a prescribed region on the PFA tube 131 of the fixing roller 1 has a scratch caused by durable abrasion, the bias voltage applied on the core metal 17 of the fixing roller 1 is prevented from leaking to the conductive pressurizing roller 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or an electrophotographic printer to fix an unfixed image by pressure or heat and pressure.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view of a conventional heat roller type fixing device.

The fixing roller 1 comprises a heater 2 such as a halogen lamp inside a hollow cored bar made of aluminum, iron or the like.
The heater 2 heats the fixing roller 1. The pressure roller 3 is composed of a cored bar 4 made of iron, stainless steel or the like, and the outer periphery of the cored bar 4 is covered with an elastic body 5 having releasability such as silicone rubber. The fixing roller 1 and the pressure roller 3 are brought into contact with each other with a predetermined pressure by an urging means such as a spring (not shown), and are rotationally driven in the arrow direction.

A temperature sensitive element 6 such as a thermistor which is in contact with the surface of the fixing roller 1 detects the surface temperature of the fixing roller 1.
The temperature control circuit controls the energization of the heater 2 according to the temperature detected by the temperature sensitive element 6, and the surface temperature of the fixing roller 1 is automatically controlled to a predetermined thermal fixing temperature. The separation claw 7 for separating the transfer material P from the surface of the fixing roller 1 is arranged such that the tip edge portion is in contact with the surface of the fixing roller 1 with an appropriate pressing force. The cleaning member 8 such as a felt brought into pressure contact with the surface of the fixing roller 1 is the toner t attached to the surface of the fixing roller 1.
Wipe off c and paper dust. The bottom plate 9 made of a metal material of the fixing device covers and fixes the lower side of the fixing device. The transfer material entrance guide 10 is formed by bending the bottom plate 9 upward and mounting and supporting it on the front wall thereof. In addition, the transfer material exit roller 11
a and 11b are attached so as to be rotationally driven in the direction of the arrow in the figure. The transfer material P that has entered the fixing device through the entrance guide 10 comes into pressure contact with each other and enters the nip portion between the fixing roller 1 and the pressure roller 3 which are rotationally driven,
It passes as the rollers 1 and 3 rotate. In the process of passing through the nip, the unfixed toner image ta on the transfer material P is fixed as a permanently fixed image tb by heat and pressure.

The transfer material P, which has passed through the nip portion of the rollers 1 and 3 and has undergone image fixing, has its leading end separated from the surface of the fixing roller 1 by the separating claw 7, and the exit guide 11 and the exit roller 11 are provided.
It is discharged to the outside of the fixing device through a and 11b.

In the fixing process, the fixing roller 1 directly heats and presses the unfixed toner image ta to soften it and fix it to the transfer material P. However, a part of the toner image adheres to the surface of the fixing roller (hereinafter referred to as offset). May be written).
Such offset toner tc is fixed on an improper place of the transfer material P as it rotates, and the transfer material P is soiled, or the back side of the transfer material P accumulated on the pressure roller 3 is soiled or separated. To make it difficult. There are two main causes of the offset, that is, the physical binding force between the toner and the roller and the electrostatic force. The offset caused by the former is effective by increasing the smoothness of the roller surface or decreasing the surface energy. Specifically, as a material having such properties, PTF
Fluorine resins such as E and PFA can be used, but these fluorine resins are also excellent in heat resistance, abrasion resistance and corrosion resistance required as a coating material for the fixing roller. On the other hand, the latter electrostatic force acts on the toner, which is charged powder, in the electric field created by the fixing roller, pressure roller, and transfer material that are charged by friction and peeling. When the repulsive force between the roller and the transfer material acts strongly, a significant offset often occurs.

As means for reducing the offset due to such an electric action, the fixing roller surface coating layer is made conductive so as to release the charged electric charge, or an antistatic agent is applied to the surface to prevent the electrostatic charge. There is a way to do it.

Making the surface of the fixing roller electrically conductive has the effect of preventing charging of the fixing roller, but cannot prevent the influence of the repulsive electric field from the pressure roller. Further, in the electrophotographic system, the distance between the transfer and fixing portions is generally shorter than that of the maximum size transfer material, and a lowering of the resistance easily causes a transfer current to flow into the fixing roller and cause a transfer failure.

Further, when the antistatic agent is applied, the antistatic agent adhering to the surface of the transfer material may adhere to the photoconductor to prevent the photosensing phenomenon or the electrification of the photoconductor when the transfer material once passed is re-passed. become. In such a case, a good image cannot be expected. Further, in the case of a system which is applied on the surface, a replenishing member is required to maintain its effect.

Therefore, in recent years, a method of applying a voltage having the same polarity as the toner to the fixing roller to suppress the toner by the action of an electric field has been considered.

As this method, for example, there is a method of applying a bias voltage having the same polarity as the toner to the core metal of the fixing roller 1. However, it is difficult to obtain a sufficient bias effect because the counter electrode is not formed only by applying the bias voltage to the fixing roller 1. Therefore, the applicant of the present invention has previously proposed a method of providing a low resistance layer on the surface of the pressure roller 3 or in the vicinity thereof and using the low resistance layer as an opposing electrode so that the effect of the bias applied to the fixing roller 1 can be sufficiently exerted. (Patent application, Heisei 2.10.9 application).

According to the invention of this application, in order to prevent the bias voltage from leaking from the fixing roller 1 to the pressure roller 3, an adhesive layer 18 is formed on the core metal of the fixing roller 1 as shown in FIG. It is necessary to provide the release layer 13 made of an insulating PFA resin via the above. The release layer 13 has a higher voltage when the film thickness is thicker, but if it is too thick, a sufficient bias effect cannot be obtained. Therefore, the release layer 13
It is necessary to make the film thickness of 20 μm to 80 μm.

[0013]

However, in the above apparatus, when a member that abrades the releasing layer 13 of the fixing roller 1 is in contact with the releasing layer 13, the durability of tens to hundreds of thousands of sheets of paper passing can be obtained. As a result, it was found that the insulation of the release layer 13 is broken and the bias applied to the fixing roller 1 leaks to the conductive pressure roller 3. In particular, if a thermistor, a thermoswitch, or a member that supports them is in contact with the outside of the paper passing area, a leak occurs in the non-paper passing area, so that the fixing roller 1 and the pressure roller 3 are in contact with each other even when the paper is passing. Leaks will not subside as they are. When the fixing bias leaks, an excessive current flows, the bias voltage itself drops, and an electrostatic offset occurs to stain the image, or the separation claw 7
And the cleaning member 8 is contaminated with toner.

[0014]

According to the present invention, a first roller having a cored bar and a surface insulating layer provided on the outer side of the cored bar, a second roller in pressure contact with the first roller, and a first roller are provided. A fixing device having a bias power supply for applying a bias voltage, and nipping and transporting a supporting material supporting an unfixed image by a first roller and a second roller, wherein the second roller is a surface or a surface. In a fixing device having a low resistance layer in the vicinity thereof, a contact area of a member contacting the first roller outside the sheet passing area of the image support material and abrading the surface of the first roller is a low resistance area portion of the second roller. The bias voltage applied to the first roller is set so that it does not overlap with the contact area of the second roller.
This is to prevent leakage to the roller.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a schematic sectional view of a fixing device according to an embodiment of the present invention. In this embodiment, as the fixing roller 1, a cored bar 17 made of aluminum or stainless steel is covered with a pure PFA tube 131 having a thickness of 300 μm. As the coating layer, in addition to such a fluororesin tube, a fluororesin multi-coating treatment, an insulating property as a fluororesin adhesive,
A material having a very high pressure resistance can be used.

The covering layer as an insulating layer has a volume resistance of 10 ¹⁴ Ω.
cm or more, and the withstand voltage is preferably 1 KV or more.

The fixing roller 1 used in this embodiment is 30 μm.
However, the actual resistance between the surface and the cored bar 17 was 10 ¹⁴ Ω or more (when 500 V was applied), and the dielectric strength was 2 KV. The reason why such high insulating property and pressure resistance are exhibited is that the pinhole is not included in the structure by tube molding, and the high insulating property originally possessed by the PFA resin is secured.

In the present embodiment using the fixing roller 1 having such a PFA tube 131 as a coating layer, even if a high voltage is applied to the cored bar 17, no current will flow to the transfer material P, Even if the current capacity of the voltage source 14 is small, the applied voltage does not drop, and a stable voltage can be supplied.

On the other hand, the pressure roller 3 uses a conductive silicone rubber as the conductive elastic material 51 in the surface layer, and the conductive elastic material 51 is grounded. As described above, the pressure roller 3 formed of the conductive elastic material 51 is not charged even when it rubs against the transfer material P and does not exert an electrostatic repulsive force on the toner. is there. The electric resistance of the conductive elastic material 51 for exhibiting such properties is 10 ⁵ Ωcm or less in terms of volume resistance, and 10 ¹¹ Ω between the surface (10 cm ² ) as the actual resistance of the pressure roller 3 and the core metal 4. (5
It is preferable that the applied voltage is 00 V or less). Further, in the case of a device configuration in which a part of the transfer material P enters the fixing device while receiving the transfer operation, if the pressure roller 3 has an extremely low resistance, the transfer material P is infinitely charged in a high humidity environment. Missed. There is a possibility that adverse effects such as transfer failure may occur. Therefore, preferably, the conductive elastic material 51 having a volume resistance of 10 ² to 10 ⁵ Ωcm is used, and the actual resistance of the pressure roller 3 is 10 ³ to 10 ¹¹ Ω.
It is preferable that the pressure roller 3 is configured as follows (hereinafter, the pressure roller 3 having this configuration is referred to as a conductive pressure roller 3).

When a voltage having the same polarity as that of the toner is applied to the fixing roller core bar 17 to suppress the offset, the conductive pressure roller 3 is used in combination to stabilize the potential of the transfer material P and to fix it. The electric potential on the surface of the roller 1 can be suppressed to a minimum, and as a result, a high offset suppressing effect can be maintained even when continuous sheets are passed. As an example,
When a bias of about 500 V to 700 V was applied using a negative toner, good results were obtained.

A gap of 300 μm from the surface of the fixing roller 1.
The temperature sensitive element 20 such as a thermistor which is separated and kept in non-contact is provided with a spacer 21 in order to maintain the gap with high accuracy, and the temperature sensitive element 20 is held by the spacer 21 by a spring 22 fixed to the fixing device frame. The spacer 21 is urged to urge the spacer 21
Is brought into contact with the fixing roller 1. With this configuration, the gap between the temperature sensitive element 20 and the fixing roller 1 can be accurately defined, and accurate temperature detection can be performed. In other words, unless the temperature sensitive element 20 is installed with the fixing roller 1 as a reference, the gap varies greatly and accurate temperature detection is impossible.

Here, as shown in FIG. 2, the spacer 21 is in contact with the paper non-passage area of the fixing roller 1 at both ends thereof. Set the distance between the spacer 21 and the abutting end of the fixing roller 1 to l (el).
1. When the total length of the surface of the fixing roller 1 is l (ell) 3 and the total length of the surface of the conductive pressure roller 3 is l (ell) 2,
1 (L) 3> l (L) 1> l (L) 2. Then, the longitudinal dimension is defined so that the spacer 21 is brought into contact with the fixing roller 1 outside the sheet passing area and the conductive pressure roller 3 is provided inside the contacting end of the spacer 21 and the fixing roller 1. .. With this configuration, even if the area of the shaded area A of the PFA tube 131 of the fixing roller 1 is damaged due to durable wear, the bias voltage applied to the core metal 17 of the fixing roller 1 is the conductive pressure roller. It never leaks to 3.

[Second Embodiment] FIG. 3 is a schematic view showing a second embodiment of the present invention. In the second embodiment, the conductive elastic material 51 of the pressure roller 3 is grounded via the rectifying element 15. As a method of connecting the rectifying element 15, the rectifying element 15 is connected in a direction in which charges having a polarity opposite to that of the toner can move from the ground side to the elastic material. As a result, the pressure roller 3 is biased to a voltage having a polarity opposite to that of the toner, and has an effect of suppressing offset (self-bias effect). Due to this self-bias effect, the maximum value of the potential applied to the core metal 4 of the pressure roller is equal to the reverse withstand voltage of the rectifying element 15, and if the reverse withstand voltage is too high, the charging of the fixing roller 1 is promoted when the charge roller is charged up. In addition, the core metal 17 of the fixing roller and surrounding members may be discharged to cause damage to the members or electromagnetic interference. Therefore, the maximum potential difference between the core metal 4 of the pressure roller and the core metal 17 of the fixing roller is 3K.
It is preferable to select the rectifying element 15 so as to be V or less.

Even in such a system, the reverse withstand voltage applied to the rectifying element 15 is formed by constructing the relationship between the fixing roller 1, the pressure roller 3 and the spacer 21 as shown in FIG. 2 as in the first embodiment. Can be prevented from leaking to the region A of the fixing roller 1 due to scratches caused by durable wear.

[Third Embodiment] FIG. 4 is a schematic view showing a third embodiment of the present invention. In this third embodiment, the spacer 2
The area B of the pressure roller 3 facing the area A where durable wear occurs due to No. 1 is covered with an insulating thin film (100 μm thick PFA tube as an example). By doing so, even if the insulation on the fixing roller 1 side is broken due to durable wear, no leak occurs between the fixing roller 1 and the pressure roller 3. In addition, since the pressure roller 3 surface is present in the area B even when l (el) 2 in FIG. 4 becomes narrower than the maximum sheet passing width in the longitudinal direction, the transfer material P of the transfer material P is not formed. It does not impair transportability.

In the first to third embodiments described above, an example in which a fixing temperature adjusting element such as a thermistor is used as the temperature sensing element 20 has been described. However, in addition to this, a so-called fixing temperature runaway such as a thermo switch is used. The present invention can be carried out in the same manner even when the preventing means is used in a non-contact manner. As an example,
Bimetal part on the surface of the thermoswitch (drawing omitted)
To the surface of the fixing roller 1 by the spacer 21
When the non-contact state is maintained at the gap of m, the fixing temperature is correctly detected and the limit temperature is detected during runaway, and the same effect as in the above-described embodiment is obtained with respect to the bias voltage leakage prevention during durability. Was given.

[Fourth Embodiment] The present invention works effectively even when there is a member in contact with the fixing roller 1 in the paper passing area. This example will be described below.

In general, the wear promoting member in contact with the fixing roller 1 includes a thermistor for temperature control, a thermoswitch for preventing runaway of the fixing temperature, a separation claw for separating the transfer material P (reference numeral 7 in FIG. 5), and the like. .. Of these, the separation claw 7 is inevitably placed in the paper passing area for that purpose, and the thermistor for temperature control is provided with a protective tape such as Teflon tape on the surface to improve the temperature detection accuracy. It may be placed in contact with 1. In such a case, slight wear may occur due to durability and the fixing bias may partially leak, but within the sheet passing area, the transfer material P is sandwiched between the fixing roller 1 and the pressure roller 3. While
Since the rollers 1 and 3 are insulated from each other and the fixing bias leak does not occur, there is no fear of offset.

As an example, a runaway preventing thermoswitch is supported by the spacer 21 described in the first embodiment and kept in non-contact with the fixing roller 1, and the spacer 21 is fixed outside the paper passing area as shown in FIG. The pressure roller 3 is placed in contact with the roller 1 so as not to overlap with the roller 1, and the temperature sensing element 20, that is, the thermistor, and the separation claw 7 are placed in contact with the fixing roller 1 in the paper passing area. When 200,000 sheets of paper were passed, slight wear occurred in the thermistor contact portion, but no leakage of the fixing bias occurred during the passage of paper, so that offset did not occur.

[0031]

As described above, according to the present invention, the bias voltage of the fixing roller 1 can be prevented from leaking due to durable wear, and a good offset suppressing effect can be maintained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a first embodiment of the present invention.

FIG. 2 is a front view of the first embodiment of the present invention viewed from the sheet passing direction.

FIG. 3 is a vertical sectional view of a second embodiment of the present invention.

FIG. 4 is a front view of the third embodiment of the present invention viewed from the sheet passing direction.

FIG. 5 is a vertical sectional view of a conventional example.

FIG. 6 is a vertical sectional view of a conventional example.

[Explanation of symbols]

1 ... Fusing roller 2 ... Heater 3 ... Pressure roller
13, 131 ··· PFA tube surface 14 · · Bias power supply 16 · · Rectifying element 17 · · Core of fixing roller 20 · · Temperature sensing element 21 · · Spacer member 51 · ·
Conductive elastic material for pressure roller.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasumasa Otsuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takayasu Yukinochi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Hideyuki Yano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hideo Nanaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kazuro Ono 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (1)

[Claims] 1. A first roller having a cored bar and a surface insulating layer provided outside the cored bar, a second roller in pressure contact with the first roller, and a bias power supply for applying a bias voltage to the first roller. And a fixing device for holding and fixing a supporting material supporting an unfixed image by the first roller and the second roller, wherein the second roller has a low resistance layer on the surface or in the vicinity of the surface. In the apparatus, the contact area of the member that contacts the first roller and wears the surface of the first roller outside the sheet passing area of the image support material does not overlap the contact area of the low resistance area portion of the second roller. A fixing device having the above-mentioned configuration.