JP3433889B2 - Fixing device, image forming apparatus, and image forming method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic recording apparatus such as a copying machine, a fax machine or an electrophotographic printer, which heats an image formed of a heat-fusible toner formed on a surface of a recording material such as paper, The present invention relates to a fixing device that fixes a permanent fixed image on the surface of a recording material, an image forming apparatus including the fixing device, and an image forming method using the fixing device.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, toner electrostatically transferred from a photoconductor onto paper is easily peeled off. Therefore, it is possible to permanently fix the toner to paper by heating or pressurizing the toner. Will be needed. This step is called the fixing process. There are various fixing methods, but the heat roller fixing method is most widely used because of its high thermal efficiency and safety. In this heat roller fixing method, two rollers are brought into pressure contact with each other, at least one of the rollers is heated, and an unfixed toner image support (paper, OHP sheet, etc.) is passed through the pressure contact portion (nip portion). In this method, the unfixed toner is heated and fixed on the support.

When heating one of the two rollers,
The roller that heats up is called the fixing roller, and the other roller is called the pressure roller. A heat source such as a halogen lamp or an electric heater is built in the fixing roller so as to extend in the axial direction of the fixing roller. Further, a temperature sensor is attached to the outer peripheral surface of the fixing roller, and the amount of electric power supplied to the heat source is controlled so that the temperature of the nip portion is maintained at a temperature suitable for fixing.

In recent years, in the fixing device of the heat roller fixing system,
In order to save energy, it has been attempted to reduce the heat capacity of the fixing roller and the pressure roller to shorten the startup time until the temperature reaches the set temperature. However, in this case, the ratio of the heat capacity of the fixing roller and the pressure roller to the heat capacity of the support on which the toner image is placed (hereinafter referred to as "paper") becomes small, so that one sheet of paper is fixed. Since a sufficient amount of heat cannot be stored in the fixing roller and the pressure roller, there is a problem that fixing failure occurs due to a temperature decrease in the latter half of the sheet or in repeat copying.

If it is attempted to prevent this fixing failure by raising the set temperature of the fixing roller, the temperature of the first half of the paper rises too much, so that the toner melts too much and adheres to the fixing roller, causing the surface of the paper to melt. A problem (hot offset) that pollutes will occur.

A means for eliminating the above-mentioned problems is disclosed in Japanese Patent Laid-Open Publication No. HEI-6.
-75504, JP-A-6-130843 and JP-A-5-281875.
In the fixing device described in Japanese Patent Application Laid-Open No. 6-75504, when a low-temperature sheet passes through the nip portion, the surface temperature of the fixing roller is high in the first half of the sheet and decreases toward the latter half. The fixing temperature is prevented from being different between the first half side and the second half side of the sheet passing through the nip portion. That is, in this fixing roller, the roller surface temperature is detected and the roller heating amount by the heater is controlled to increase the heat generation amount of the heater when fixing the second half of the paper so that the fixing roller temperature becomes constant. I have to.

In the fixing device described in Japanese Patent Laid-Open No. 6-130843, a heat conduction roller is provided inside the fixing roller, and the outer periphery of this roller is brought into contact with the inner peripheral surface of the fixing roller to heat the nip portion. By increasing the supply amount, the temperature drop at the nip portion is prevented.

The fixing device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-281875 does not prevent the fixing temperature from being different within one sheet, but is intended to prevent a temperature decrease during repeat copying. That is, in this fixing device, the fixing roller temperature when the leading edge of the paper reaches the nip portion,
The temperature of the fixing roller when the trailing end passes through the nip portion is measured, and the control temperature of the fixing roller is corrected to the temperature obtained by adding the temperature difference to the reference control temperature based on the temperature difference.

[0009]

However, in the above-mentioned prior art, when the temperature of the fixing roller is changed, the power consumption always changes. Even if an attempt is made to predict the amount of temperature decrease and to determine the amount of increase in the amount of heat generated by the heater, it is difficult to properly predict the amount of temperature decrease because the amount of temperature decrease differs depending on the type of paper, initial temperature, moisture content, etc. is there.

Further, in the method of providing a heat conduction roller inside the fixing roller to increase the heat supply amount to the nip portion, there is a thermal resistance between the fixing roller and the heat conduction roller, so that the heat supply amount that can be increased is limited. Therefore, it is doubtful that sufficient effect can be obtained when the paper is thick or high-speed copying is performed.

Further, a method of changing the set temperature of the fixing roller by measuring the temperature when the leading edge of the paper reaches the nip portion and the temperature of the fixing roller when the trailing edge passes through the nip portion, There is a problem that the mechanism becomes complicated, such as a means for detecting that the leading edge or the trailing edge of the paper has reached the nip portion.

Therefore, an object of the present invention is to cause a partial decrease in the temperature of the paper at the nip portion between the fixing roller and the pressure roller (a partial decrease in the temperature of the nip portion due to heat being taken by the paper). It is an object of the present invention to provide a fixing device capable of preventing fixing failure during copying. It is an object of the present invention to provide a fixing device that can obtain a uniform fixing function over the entire surface of the paper even when the paper size is random. Further, the object of the present invention is to
An object is to provide an image forming apparatus including the fixing device. A further object of the present invention is to provide an image forming method using the above fixing device.

[0013]

In order to achieve the above object, the fixing device of the present invention comprises a metal outer cylinder and an inner cylinder which are concentrically arranged to form a pressure roller. A switch mechanism is formed by the inner cylinder, and a predetermined control device is operated by this switch mechanism to make the fixing efficiency uniform over the entire surface of the paper.

According to a first aspect of the present invention, there is provided a fixing device including a fixing roller containing a heat source, and a pressure roller installed so as to be in pressure contact with the fixing roller and rotating in cooperation with the rotation of the fixing roller. In a fixing device that allows a sheet to pass between the fixing roller and the pressure roller while being pressed and heated, in the pressure roller, an outer cylinder made of metal and an inner cylinder made of metal are concentric with each other. The outer peripheral surface of the outer cylinder is coated with a heat-resistant film to form the outer peripheral surface of the pressure roller, and the gap between the outer cylinder and the inner cylinder is filled with a gas having a positive coefficient of thermal expansion. To form a gas-filled chamber, the inner cylinder is filled with gas or solid with a positive coefficient of thermal expansion, and the temperature of the surface of the pressure roller during fixing causes the temperature of the surface of the pressure roller to drop. Part moves to the inner cylinder side, the outer cylinder contacts the inner cylinder, and the switch action occurs. Characterized in that way the.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the heat source of the fixing roller and the outer cylinder and the inner cylinder of the pressure roller are connected to the temperature control device, and the temperature control device is activated by the switch action. The temperature of the fixing roller is appropriately raised by controlling the heat source via the heat source.

According to a third aspect of the present invention, in the fixing device of the first aspect, the rotation driving mechanism for the fixing roller and the outer cylinder and the inner cylinder are connected to the rotation speed control device, and the rotation speed control device is activated by the switch action. The rotation driving mechanism of the fixing roller is controlled via the control unit to appropriately reduce the rotation speed of the fixing roller.

According to a fourth aspect of the present invention, in the fixing device according to the first aspect, the inner cylinder of the pressure roller is filled with a gas having a positive coefficient of thermal expansion, and the inner cylinder is communicated with an automatic opening / closing valve. The drive part of the on-off valve and the outer cylinder and the inner cylinder are connected to the on-off valve control device, and the drive part of the automatic on-off valve is controlled by the switch action through the on-off valve control device to control the inside cylinder of the pressure roller. It is characterized in that an appropriate amount of the gas is discharged.

According to a fifth aspect of the present invention, there is provided the fixing device according to the first aspect, wherein the switch action increases the pressure contact force between the fixing roller and the pressure roller.

An electrophotographic image forming apparatus according to a sixth aspect of the present invention includes the fixing device according to any one of the first to fifth aspects.

An image forming method according to a seventh aspect is characterized in that an electrophotographic image is formed by the fixing device according to any one of the first to fifth aspects.

Embodiment 1 (Claim 1) FIG. 1 is a schematic perspective view showing a main structure of a fixing device. In the figure, reference numeral 1 is a heat source for heating the fixing roller 2. The heat source 1 is composed of a halogen lamp or the like, and is disposed in the axial direction of the fixing roller 2 with a length substantially equal to the entire length thereof, so that the inner surface of the fixing roller 2 can be uniformly heated in the axial direction. A pressure roller 3 is pressed against the fixing roller 2 by a pressure contact mechanism (not shown). The surface layer of the fixing roller 2 is made of a smooth material such as Teflon (fluorine resin) so that the toner does not adhere thereto, and the part other than the surface layer is made of aluminum so that the heat from the heat source can be quickly transmitted. However, the material is not limited to aluminum, and another material may be used as long as it has a high thermal conductivity and a hardness that does not cause axial deformation.

FIG. 2 is a cross-sectional view of the main part of the fixing device in the vicinity of the central portion in the longitudinal direction, and FIG. 3 is an enlarged view of part A of FIG. The pressure roller 3 includes a heat-resistant film 4a and a metal layer (outer cylinder) 8 inward from the surface layer thereof.
a, outer chamber (gas filling chamber) 7, metal layer (inner cylinder) 8
b, the inner chamber (gas filling chamber) 6 is formed in this order. A columnar spacer 9 is provided in the gap between the inner chamber 6 and the outer chamber 7. The spacer 9 is preferably made of soft and elastic sponge or the like. The metal layers 8a and 8b are provided close to each other. The heat resistant film 4 is preferably polyimide or the like. The inner chamber 6 and the outer chamber 7 are filled with a gas having a positive coefficient of thermal expansion (the volume increases as the temperature rises). The laminated structure of the heat resistant film 4a and the metal layer 8a, or the heat resistant film 4b and the metal layer 8b can be obtained by subjecting the heat resistant film to, for example, a sputtering process.

The operation of this fixing device will be described.
When the temperature of the fixing roller 2 is the temperature at the time of fixing (without paper), and the pressure roller 3 is in pressure contact with the fixing roller 2, the gas in each of the chambers 6 and 7 is the most expanded, and at this time The heat resistant films 4a and 4b are set to be the most tensioned (the tension is maximum). During the repeat copy, heat is taken by the paper and the temperature of the pressure roller 3 gradually decreases. The temperature decrease amount is larger in the outer chamber 7 than in the inner chamber 6, the outer chamber 7 contracts, and the fixing roller 2 and the pressure roller 3 are in pressure contact (and the metal layers 8a and 8b are close to each other). Therefore, at this pressure contact portion (nip portion), the metal layers 8a and 8b contact each other as shown in FIG.

Therefore, the contact between the metal layers 8a and 8b
By utilizing the non-contact action as a switch, that is, by constructing a switch by combining the metal layers 8a and 8b, it is possible to start or end various control operations by detecting the actual temperature decrease of the nip portion. You can In the portion where the spacer 9 is provided, the metal layers 8a and 8
If b remains in non-contact, but does not become non-contact for a certain period of time, it is considered that the metal layers 8a and 8b are in contact, and the operation of this fixing device is controlled. Figure 5
It is a flowchart which shows the method of this control.

Embodiment 2 (Claim 2) FIG. 6 is a cross-sectional view of a fixing device. With this fixing device,
As in the first embodiment, the temperature of the fixing roller 2 is the temperature at the time of fixing (without paper), and the pressure roller 3 is the fixing roller 2.
The gas in each of the chambers 6 and 7 is the most expanded when it is pressed against, and the heat resistant films 4a and 4b are made to be the most expanded at this time.

At the time of repeat copying, heat is taken by the paper and the temperature of the pressure roller 3 gradually decreases. When the surface temperature of the pressure roller 3 decreases, the metal layers 8a and 8b come into contact with each other.
Therefore, by utilizing this contact action as a switch, the control circuit that raises the temperature of the heating source of the fixing roller 2 is operated to prevent cold offset caused by the decrease in the surface temperature of the pressure roller 3. it can. According to this fixing device, the heating source of the fixing roller 2 can be controlled by detecting the actual nip temperature. FIG. 7 is a flowchart showing this control method.

Embodiment 3 (Claim 3) FIG. 8 is a transverse sectional view of a fixing device. With this fixing device,
As in the first embodiment, the temperature of the fixing roller 2 is the temperature at the time of fixing (without paper), and the pressure roller 3 is the fixing roller 2.
The gas in each of the chambers 6 and 7 is the most expanded when it is pressed against, and the heat resistant films 4a and 4b are made to be the most expanded at this time.

At the time of repeat copying, heat is taken by the paper and the temperature of the pressure roller 3 gradually decreases. When the surface temperature of the pressure roller 3 decreases, the metal layers 8a and 8b come into contact with each other.
Therefore, by utilizing this contact action as a switch, the control circuit for reducing the rotation speed of the fixing roller 2 (and the pressure roller) is operated. As a result, the nip time of these rollers becomes long, and cold offset due to a decrease in the surface temperature of the pressure roller 3 can be prevented. According to this fixing device, the rotational speeds of the fixing roller 2 and the pressure roller 3 can be controlled by the actual nip temperature. Note that the heat source 1 performs normal temperature control. FIG. 9 is a flowchart showing this control method.

Embodiment 4 (Claim 4) FIG. 10 is a cross-sectional view of a fixing device. 11A is a side view showing a mounting mode of the automatic opening / closing valve 10, FIG. 11B is a front view showing a mounting portion of the automatic opening / closing valve 10, and 11 is a gas discharge port. In this fixing device, an automatic opening / closing valve 10 such as an electromagnetic valve is provided in communication with the chamber 6 inside the pressure roller 3, and the automatic opening / closing valve 10 is slightly opened by contact with the metal layers 8a and 8b. To do. That is, as in the first embodiment, the temperature of the fixing roller 2 is the temperature at the time of fixing (without paper), and when the pressure roller 3 is in pressure contact with the fixing roller 2, the gas in each chamber 6, 7 is the most. It is expanded, and at this time, the heat resistant films 4a and 4b are made to be the most stretched.

At the time of repeat copying, heat is taken by the paper and the temperature of the pressure roller 3 gradually decreases. When the surface temperature of the pressure roller 3 decreases, the metal layers 8a and 8b come into contact with each other.
Therefore, by utilizing this contact action as a switch, the automatic opening / closing valve 10 is slightly opened, and the gas in the inner chamber 6 is slightly discharged through the discharge port 11. As a result, the nip width between the fixing roller 2 and the pressure roller 3 is widened, so that the nip time is extended, and cold offset due to the decrease in the surface temperature of the pressure roller 3 can be prevented.
According to this fixing device, the nip time can be controlled by the actual temperature of the nip portion. Metal layers 8a and 8b
When the gas is separated, the gas discharged in the above amount is discharged into the gas discharge port 1
We will start from 1. The heat source 1 performs normal temperature control. FIG. 12 is a flowchart showing the above control method.

Embodiment 5 (Claim 5) FIG. 13 is a cross-sectional view of a fixing device. In this fixing device, as in the first embodiment, the temperature of the fixing roller 2 is the temperature at the time of fixing (without paper), and when the pressure roller 3 is in pressure contact with the fixing roller 2, The gas is most expanded, and the heat resistant films 4a and 4b are made to be the most expanded at this time.

At the time of repeat copy, heat is taken by the paper and the temperature of the pressure roller 3 gradually decreases. When the surface temperature of the pressure roller 3 decreases, the metal layers 8a and 8b come into contact with each other.
Therefore, by utilizing this contact action as a switch, the control circuit for increasing the pressure contact force (nip pressure) between the fixing roller 2 and the pressure roller 3 is operated to increase the nip pressure. As a result, it is possible to prevent cold offset caused by a decrease in the surface temperature of the pressure roller 3. According to this fixing device, the nip pressure between the fixing roller 2 and the pressure roller 3 can be controlled by the actual temperature of the nip portion. In order to increase the nip pressure, a method of introducing gas into the chambers 6 and 7 inside and outside the pressure roller 3 can be adopted. Note that the heat source 1 performs normal temperature control. FIG. 14 is a flowchart showing the above control method.

[0033]

As is apparent from the above description, according to the present invention, the following operational effects can be obtained. (1) When the temperature of the surface of the pressure roller at the time of fixing the fixing device of claim 1 is lowered, the outer cylinder pressure contact portion by the fixing roller is displaced to the inner cylinder side, and the outer cylinder is brought into contact with and electrically connected to the inner cylinder so that the switch action is performed. Since the switch action is used to appropriately control the operation of the fixing roller and / or the pressure roller, it is possible to partially reduce the paper temperature at the nip portion between the fixing roller and the pressure roller. It is possible to prevent defective fixing due to repeat copying. In particular, the present invention can provide a fixing device that can obtain a uniform fixing function over the entire surface of the paper even when the paper size is random.

(2) Fixing device of claim 2 In claim 1, the heat source of the fixing roller, the outer cylinder and the inner cylinder are connected to a temperature control device, and the temperature of the heat source is passed through the temperature control device by the switch action. Therefore, it is possible to automatically prevent the fixing failure at the time of repeat copying with a simple configuration.

(3) Fixing device according to claim 3 In claim 1, the rotation driving mechanism of the fixing roller, the outer cylinder and the inner cylinder are connected to the rotation speed control device, and the switch action causes the rotation speed control device to intervene. By controlling the rotation driving mechanism to appropriately reduce the rotation speeds of the fixing roller and the pressure roller, the same effect as that of the fixing device according to the second aspect can be obtained.

(4) Fixing device of claim 4 In claim 1, the inner cylinder of the pressure roller is filled with gas having a positive coefficient of thermal expansion, and the inside of the inner cylinder is communicated with an automatic opening / closing valve to automatically open / close the same. The drive unit of the valve and the outer cylinder and the inner cylinder are communicated to the on-off valve control device, and the drive unit of the automatic on-off valve is controlled by the switch action via the on-off valve control device to control the inside of the inner cylinder of the pressure roller. Since I tried to expel an appropriate amount of gas,
The same effect as the fixing device according to the second aspect can be obtained.

(5) Fixing device according to claim 5 In claim 1, since the pressure contact force between the fixing roller and the pressure roller is increased by the switch action, the same effect as the fixing device according to claim 2 is obtained. can get.

(6) An image forming apparatus according to claim 6, claim 7
The image forming method is configured to form an electrophotographic image by the fixing device according to any one of claims 1 to 5, so that an image having uniform fixing characteristics can be stably formed during repeat copying. Can be formed.

[Brief description of drawings]

FIG. 1 is a schematic perspective view illustrating a configuration of a fixing device according to a first exemplary embodiment.

2 is a cross-sectional view of FIG.

FIG. 3 is an enlarged view of part A of FIG.

FIG. 4 is a cross-sectional view illustrating the operation of the fixing device in FIG.

FIG. 5 is a flowchart illustrating an operation of the fixing device in FIG.

FIG. 6 is a transverse cross-sectional view showing the configuration and operation of the fixing device according to the second embodiment.

FIG. 7 is a flowchart illustrating the operation of the fixing device in FIG.

FIG. 8 is a transverse cross-sectional view showing the configuration and action of the fixing device according to the third embodiment.

9 is a flowchart illustrating the operation of the fixing device in FIG.

FIG. 10 is a transverse cross-sectional view showing the configuration and operation of the fixing device according to the fourth embodiment.

11 is a side view showing the manner of mounting the automatic opening / closing valve to the pressure roller in the fixing device of FIG.
FIG. 3B is a front view showing a part of the fixing device.

FIG. 12 is a flowchart illustrating an operation of the fixing device in FIG.

FIG. 13 is a lateral cross-sectional view showing the configuration and action of the fixing device according to the fifth embodiment.

FIG. 14 is a flowchart illustrating an operation of the fixing device in FIG.

[Explanation of symbols]

1 heat source 2 fixing roller 3 pressure roller 4a, 4b heat resistant film 6 Inside room (gas filling room) 7 Outside room (gas filling room) 8a Outer cylinder (metal layer) 8b Inner cylinder (metal layer) 9 spacers 10 Automatic open / close valve (solenoid valve) 11 gas outlet

Claims (7)

(57) [Claims] 1. A fixing roller having a built-in heat source, and a pressure roller that is installed so as to be in pressure contact with the fixing roller and that rotates in cooperation with the rotation of the fixing roller. In a fixing device that passes through a pressure roller while heating the pressure roller, a metal outer cylinder and a metal inner cylinder are concentrically provided at appropriate intervals from each other. A heat-resistant film is attached to the outer peripheral surface of the cylinder to form the outer peripheral surface of the pressure roller, and a gas having a positive coefficient of thermal expansion is filled in the gap between the outer cylinder and the inner cylinder to form a gas filling chamber. , The inner cylinder is filled with gas or solid with a positive coefficient of thermal expansion, and the temperature of the surface of the pressure roller during fixing lowers the outer cylinder pressure contact part of the pressure roller by the fixing roller to the inner cylinder side. , The outer cylinder comes into contact with the inner cylinder so that a switch action occurs. Fixing device. 2. A heat source for a fixing roller according to claim 1,
An outer cylinder and an inner cylinder of the pressure roller are connected to a temperature control device, and the temperature of the fixing roller is appropriately raised by controlling the heat source via the temperature control device by the switch action. Fixing device. 3. The rotation driving mechanism of the fixing roller, the outer cylinder and the inner cylinder of the fixing roller are connected to a rotation speed control device, and the rotation operation mechanism of the fixing roller is operated by the switch action via the rotation speed control device. Is controlled to appropriately reduce the rotation speed of the fixing roller. 4. The automatic cylinder according to claim 1, wherein the inner cylinder of the pressure roller is filled with gas having a positive coefficient of thermal expansion, and the inside of the inner cylinder is communicated with the automatic opening / closing valve. Connecting the cylinder and the inner cylinder to the on-off valve control device, and controlling the drive unit of the automatic on-off valve via the on-off valve control device by the switch action to discharge an appropriate amount of gas in the inner cylinder of the pressure roller. Fixing device characterized by. 5. The fixing device according to claim 1, wherein the contact pressure between the fixing roller and the pressure roller is increased by the switch action. 6. An electrophotographic image forming apparatus comprising the fixing device according to any one of claims 1 to 5. 7. An image forming method, comprising forming an electrophotographic image by the fixing device according to claim 1. Description: