JP3090998B2 - Fixing device - Google Patents

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 an electrophotographic copying apparatus and an electrostatic information recording apparatus.

[0002]

2. Description of the Related Art Conventionally, a fixing device used in an image forming apparatus such as an electrophotographic copying machine has a structure as shown in FIG.
A heating roller 1 is provided. The heating roller 1 has a hollow metal core 3 made of an aluminum material. Core 3 of heating roller 1
Is provided with a heater 4 inside.

A pressure roller 5 is rotatably pressed against the heating roller 1. The pressure roller 5 has a metal core 6, and the outer peripheral surface of the metal core 6 is covered with an elastic layer 7 having releasability. The pressure roller 5 cooperates with the heating roller 1 to form a nip for nipping and conveying the transfer material P.

Around the heating roller 1, a separation claw 8 for preventing the transfer material P from being wound around the heating roller 1, a temperature detecting element 9 for detecting a surface temperature of the heating roller 1, and an adhesion to the heating roller 1. A felt cleaner 10 for removing the toner and the like is disposed. The temperature detection element 9 outputs a temperature detection signal indicating the surface temperature of the heating roller 1, and the temperature detection signal is output from a temperature control circuit (not shown).
Given to. The temperature control circuit controls the operation of the heater 4 on and off based on the temperature detection signal, and the surface temperature of the heating roller 1 is maintained at a predetermined temperature by the on / off operation of the heater 4.

An entrance guide 11 for guiding the transfer material P to the nip is disposed on the entrance side of the nip between the heating roller 1 and the pressure roller 5. On the other hand, an exit guide 12 for guiding the transfer material P to the outside is disposed on the exit side of the nip portion.

At the time of fixing, the transfer material P on which an unfixed toner image is formed is inserted into a nip between the heating roller 1 and the pressure roller 5. During the passage of the transfer material P through the nip portion, the unfixed toner image on the transfer material P is fused on the transfer material P by heat and pressure, and a permanent image is formed on the transfer material P.
The transfer material P subjected to the fixing process is discharged to the outside while being guided by the exit guide 12.

However, a part of the toner 16 which forms the unfixed toner image on the transfer material P is transferred to the surface of the heating roller 1 (so-called offset phenomenon), and the toner 16 may adhere to the surface of the heating roller 1. . The toner adhered to the surface of the heating roller 1 adheres again to the next transfer material P, and the transfer material P is contaminated by the toner.

As a cause of the occurrence of the offset phenomenon, a physical binding force between the toner 16 and the heating roller 1 and an electrostatic force can be considered. The occurrence of the offset phenomenon due to the physical bonding force between the toner 16 and the heating roller 1 is suppressed by increasing the smoothness of the surface of the heating roller 1.
It can be suppressed by lowering the surface energy of the heating roller 1. Thus, the release layer 2 formed on the surface of the heating roller 1 can suppress the occurrence of the offset phenomenon caused by the physical bonding force between the toner 16 and the heating roller 1.

On the other hand, the electrostatic force that causes the offset phenomenon is caused by the charged powder in an electric field formed by the heating roller 1, the pressure roller 5, the transfer material P, etc., which are charged due to friction, peeling and the like. The electrostatic force acting on the toner 16, the attractive force acting between the toner 16 and the heating roller 1, the repulsive force acting between the toner 16 and the pressure roller 5, or the toner 16 and the transfer material P The toner 16 is transferred to the surface of the heating roller 1 by the repulsive force acting between the two.

In order to suppress the occurrence of the offset phenomenon due to the above-mentioned electric action, a conductive coating layer is formed on the surface of the cored bar 3 of the heating roller 1, and a method for releasing the electrification of the surface of the heating roller 1, There is a method of applying an antistatic agent to the roller 1 to prevent the heating roller 1 from being charged.

[0011]

However, in the former method, the effect of preventing electrification of the heating roller 1 can be obtained by imparting conductivity to the surface of the heating roller 1, but the effect of the repulsive electric field generated by the pressure roller 5 can be obtained. The effects cannot be eliminated,
The occurrence of the offset phenomenon cannot be suppressed.

In the latter method, when an image is formed on the back surface of the transfer material that has passed through the nip portion between the heating roller 1 and the pressure roller 5, the antistatic agent attached to the back surface of the transfer material is exposed to light. It adheres to the drum, and the development and charging of the photosensitive drum are prevented by the adhesion of the antistatic agent. As a result, a good image cannot be formed. Further, in order to maintain the antistatic effect of the heating roller 1, continuous application of an antistatic agent is required, and the antistatic effect of the heating roller 1 is maintained, that is, the effect of suppressing the occurrence of the offset phenomenon (hereinafter, referred to as the following). It is difficult to maintain the "offset suppression effect").

An object of the present invention is to provide a fixing device capable of maintaining the offset suppressing effect.

[0014]

According to the present invention, the object is to provide a fixing roller, a conductive elastic layer on a cored bar, and a cover.
Pressing to form a nip with the above fixing roller with a surface insulating layer
Voltage for applying voltage to the roller and the core of the pressure roller
And an unfixed image on the recording material at the nip.
The recording material is pinched and conveyed so as to be in contact with the above-mentioned fixing roller.
In the fixing device fixed onto the recording material Chakuzo, the fixing
The roller is achieved by having a conductive layer on the surface .

[0015]

In the fixing device of the present invention, the pressure roller has an elastic layer having conductivity and an insulating layer formed on the surface of the elastic layer. During fixing, above the pressure roller bias voltage is applied, the nip portion and the electric field in the vicinity between the pressure roller and the fixing roller <br/> is formed.
Charges of the conductive layer of the fixing roller is released, the constant
The charging of the surface of the application roller is reduced, and the potential of the transfer material inserted into the nip is stabilized.

In the nip portion and the vicinity thereof, the developer charged to a predetermined polarity by the electric field is fixed as described above.
Wear rollers and force is generated to separate from one of the pressure roller, the amount of the developer adheres to the fixing roller or the pressure roller for forming an unfixed developer image on the transfer material becomes very small, The occurrence of the offset phenomenon due to the electric action is suppressed. In addition, the charging of the fixing roller surface is reduced, and the potential of the transfer material inserted into the nip is stabilized, so that the offset suppressing effect is maintained.

[0017]

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

FIG. 1 is a structural view showing a main part of an embodiment of the fixing device of the present invention, and FIG. 2 is a cross-sectional view partially showing a pressure roller used in the fixing device of FIG.

The fixing apparatus, as shown in FIG. 1, the fixing low
And a heating roller 1 as a heating roller. The heating roller 1 is composed of a hollow metal core 3 whose outer peripheral surface is covered with a release layer 2. In the present embodiment, the release layer 2 is made of PFA made conductive by dispersion of a conductive substance such as carbon, and has a thickness of 30 μm. If a release layer having a very small volume resistance value is formed, charges may escape from the transfer material in an unlimited manner in a high-humidity environment and may cause adverse effects such as poor fixing. For this purpose, the release layer 2 is preferably formed of a conductive PFA tube having a volume resistance of 104 to 1011 Ωcm. The core metal 3 is formed of a hollow cylindrical member made of an aluminum material. A heater 4 is arranged inside the core metal 3 of the heating roller 1.

A pressure roller 5 is rotatably pressed against the heating roller 1. The pressure roller 5 has a core 6 as shown in FIGS. 1 and 2, and the outer peripheral surface of the core 6 is covered with an elastic layer 7. The volume resistance value of the elastic layer 7 is set to 10
⁵ Ωcm or less, pressure roller 5 surface (10 cm ² ) and core metal 6
Is preferably 10 ¹¹ Ω (when 500 V is applied) or less. In this embodiment, the elastic layer 7 is made of a conductive silicon sponge material, and its hardness (Asker C hardness) is 21 degrees. The volume resistance of the elastic layer 7 is 10 ² to 10 ⁴ Ωcm.

The surface of the elastic layer 7 is covered with an insulating layer 13,
A conductive primer layer 14 is formed between the insulating layer 13 and the elastic layer 7. Note that it is preferable that the volume resistance value of the insulating layer 13 be 10 ¹⁴ Ωcm or more and the withstand voltage thereof be 1 KV or more. In this embodiment, the insulating layer 13 is made of PF
It is made of an A-tube and has a thickness of 30 μm.
The resistance between the surface of the heating roller 1 and the metal core 6 shows a value of 10 ¹⁴ Ω or more (when 500 V is applied), and its dielectric strength is 2K.
V is shown. The insulating layer 13 having high insulating properties and pressure resistance is obtained by forming the core 6 into a tube.

The pressure roller 5 cooperates with the heating roller 1 to form a nip portion for pressing and transferring the transfer material P.

Around the heating roller 1, a temperature detecting element (not shown) for detecting the surface temperature of the heating roller 1, a separating claw (not shown), a cleaner (not shown), and the like are arranged.

A bias voltage is applied to the metal core 6 of the pressure roller 5, and the bias voltage is generated from a power supply 15.
On the other hand, the core metal 3 of the heating roller 1 is grounded.
The bias voltage applied to the pressure roller 5 has a polarity opposite to the charging polarity of the toner forming the toner image on the transfer material P.

Next, the fixing operation for the transfer material P on which the unfixed toner image is formed will be described. The unfixed toner image on the transfer material P is a toner 1 charged to a negative polarity.
6.

At the time of fixing, a bias voltage is applied to the metal core 6 of the pressure roller 5. A potential difference is generated between the pressure roller 5 and the heating roller 1, and an electric field is formed in the nip portion and its vicinity by the potential difference. Since the surface of the pressure roller 5 is covered with the insulating layer 13, no current flows toward the transfer material P, so that a high bias voltage can be applied with a small current without lowering the voltage. Therefore, the current capacity of the power supply 15 can be reduced, and the bias voltage can be stably supplied.

Next, the transfer material P on which the unfixed toner image is formed is inserted into the nip. Since the conductive release layer 2 is formed on the surface of the heating roller 1, the charge on the surface of the heating roller 1 is released, so that the charge on the surface of the heating roller 1 is reduced and the heating roller 1 is inserted into the nip portion. The potential of the transferred transfer material P is stabilized.

While the transfer material P is passing through the nip portion, the unfixed toner image on the transfer material P is fused on the transfer material P by heat and pressure. Heating roller 1 with negative toner 16
Since a force for separating from the surface is generated, the negative toner 16 that forms an unfixed toner image on the transfer material P is
Is very small, and the occurrence of the offset phenomenon due to the electric action is suppressed. Also,
The release layer 2 formed on the surface of the heating roller 1 suppresses the occurrence of the offset phenomenon caused by the physical bonding force between the toner 16 and the heating roller 1. Therefore, the next transfer material is not contaminated by the offset toner, the charging of the surface of the heating roller 1 is reduced, and the potential of the transfer material P inserted into the nip portion is stabilized. Thus, the offset suppression effect is maintained.

Further, since the bias voltage is applied to the pressure roller 5, no discharge occurs to the temperature detecting element facing the heating roller 1, and the temperature detecting element is not damaged by the discharge.

Further, since there is no need to apply an antistatic agent to the heating roller 1, contamination of the transfer material due to the antistatic agent,
Deterioration of the chargeability is eliminated.

When images are formed on both sides of the transfer material P,
Since the insulating layer 13 of the pressure roller 5 has releasability, the offset toner does not adhere to the surface of the pressure roller 5, so that the transfer material can be reliably prevented from being contaminated by the offset toner.

Next, a paper passing test for the fixing device will be described. The number of sheets in the paper passing test is 1000 sheets. The unfixed toner image on the transfer material P used in the paper passing test is formed from the toner 16 charged to a negative polarity. The bias voltage applied from the power supply 15 to the metal core 6 of the pressure roller 5 is + 500V.

In the paper passing test, the presence or absence of the adhesion of the offset toner was observed on 1,000 transfer materials.
It is confirmed that the number of transfer materials contaminated by the offset toner is 0, and it can be seen that the offset suppressing effect is continuously obtained. In order to confirm the evaluation by the paper-passing test, a paper-passing test was performed without driving the power supply 15, and in the test, contamination of the transfer material by the toner was confirmed from the first transfer material.

Next, another fixing device will be described. FIG. 3 is a configuration diagram showing a main part of another embodiment of the fixing device of the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 3, another fixing device is configured such that a heating roller 1 made of a hollow metal core 3 whose outer peripheral surface is covered with a release layer 2 is rotatably pressed against the heating roller 1. And a pressure roller 5. The pressure roller 5 has a core 6 made of iron, and the outer peripheral surface of the core 6 is covered with an elastic layer 7. A release layer 13 is formed on the surface of the elastic layer 7.

The core 3 of the heating roller 1 is grounded via a rectifying element 17. The rectifying element 17 is connected to the metal core 3 so that charges having the same polarity as the toner can move from the ground side toward the release layer 2. Core 6 of pressure roller 5
, A bias voltage from the power supply 15 is applied.

The rectifying element 17 uses the charge of the transfer material P (charge in the transfer step and the peeling step from the transfer area, contact before and after the nip portion, and charge generated by the peeling charge) as an electromotive force to the core metal 3 to generate toner. Provides polar charge. The rectifying element 17 causes the heating roller 1 to
And the self-bias effect is obtained. When a negative charge is easily applied to the heating roller 1 by the transfer material P, the occurrence of the offset phenomenon can be reliably prevented, and the offset suppressing effect can be maintained.

The maximum value of the potential applied to the metal core 3 of the heating roller 1 by this self-bias effect is
Is equal to the reverse breakdown voltage. Therefore, the maximum potential difference between the heating roller 1 and the metal core 6 of the pressure roller 5 is set to promote the electrification of the heating roller 1 and prevent breakage due to discharge of the temperature detecting element and the like around the heating roller 1. It is preferable to select the rectifying element 17 so as to be 3 KV or less.

The electric field generated between the heating roller 1 and the pressure roller 5 is enhanced by the self-bias effect.

Next, another fixing device will be described. FIG. 4 is a configuration diagram showing a main part of still another embodiment of the fixing device of the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

Still another fixing device is provided with a rectifying element 18 for connecting the metal core 6 of the pressure roller 5 and the power supply 15 as shown in FIG. The rectifying element 18 is connected to the metal core 6 of the pressure roller 5 so that electric charges having a polarity opposite to the polarity of the toner can move from the power supply 15 toward the release layer 2.

A self-biasing effect is obtained by the rectifying element 18, and the electric field generated between the heating roller 1 and the pressure roller 5 is strengthened by the self-biasing effect.

When a positive charge is easily applied to the heating roller 1 by the transfer material P, the occurrence of the offset phenomenon can be reliably prevented, and the effect of suppressing the offset can be maintained.

In this embodiment, the core metal 3 of the heating roller 1 is directly grounded.
Can be grounded via a rectifying element. The rectifying element is a rectifying element for moving charges having the same polarity as the toner to the release layer 2 from the ground side.

[0045]

As described above, according to the fixing device of the present invention , a voltage is applied to the pressing roller and the fixing roller is fixed.
The roller surface is a conductive layer, so that the fixing roller and pressure roller
A stable electric field can be formed between
It can be prevented well .

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a main part of an embodiment of a fixing device according to the present invention.

FIG. 2 is a cross-sectional view partially showing a pressure roller used in the fixing device of FIG. 1;

FIG. 3 is a configuration diagram showing a main part of another embodiment of the fixing device of the present invention.

FIG. 4 is a configuration diagram showing a main part of still another embodiment of the fixing device of the present invention.

FIG. 5 is a configuration diagram illustrating a conventional fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating roller 2 Release layer 5 Pressure roller 7 Elastic layer 13 Insulating layer 15 Power supply 16 Toner 17, 18 Rectifier

Continuation of the front page (72) Inventor Hideo Nanataki 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-3-189673 (JP, A) JP-A-3-217885 (JP, A) Japanese Utility Model 63-92369 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/20

Claims (1)

(57) [Claims] 1. A fixing roller and a conductive elastic material on a cored bar.
Forming a nip with the above fixing roller with a layer and a surface insulating layer
Voltage applied to the pressure roller and the core metal of the pressure roller
And a voltage applying means for applying the voltage to the recording material at the nip.
Nipping and transporting the recording material so that the fixed image contacts the fixing roller
In the fixing device fix the feed Shi unfixed image on a recording material,
The fixing device according to claim 1, wherein the fixing roller has a conductive layer on a surface .