JPH10293497A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the degree of the curling of an ejected paper sheet, to prevent a deterioration in the elastic body of a pressure roller and to prolong the life of the bearing of the pressure roller by enabling the switching of the press-contact load of the pressure roller on a heating roller, in two normal and light press-contact stages. SOLUTION: In a fixing device, the pressure roller 20 is in a separated state from the heating roller 10, during the time when power is turned off, that is, stopping. Then, in a state where the power is turned on, the pressure roller 20 is in a press-contact state with the heating roller 10 and at this time, the fixing device is structured so that the press-contact load can be switched in two normal and light load stages. In other words, during warming up or standing by, a spring receiving arm 53 is lowered and the press-contact load of the pressure roller 20 on the heating roller 10 is a light one. During a fixing operation, the spring receiving arm is raised and the press-contact load of the pressure roller 20 on the heating roller is a normal one. Thus, the occurrence of the curling of the sheet can be prevented and the deterioration/deformation life of an elastic body layer and the life of the bearing, in the pressure roller 20 can be prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for use in an electrophotographic image forming apparatus and the like, and a heating roller for heating and fixing an unfixed toner image carried on a sheet;
The present invention relates to a structure of a heat roller fixing device provided with a pressure roller for pressing the unfixed toner image bearing surface of the sheet on the peripheral surface of the heat roller.

[0002]

2. Description of the Related Art FIG. 4 shows a general structure of a heat roller fixing device for heating and fixing a sheet P carrying an unfixed toner image on an upper surface. The heating roller 10 is a hollow metal cylinder 12 having a heater 11 using, for example, a halogen lamp as a heat source, and its outer periphery is covered with a thin layer, for example, a surface layer 13 using a fluororesin tube. The pressure roller 20, which is pressed against the rotating heating roller 10 and is driven to rotate, has a sponge-like elastic layer 22 on the outer periphery of a metal core 21, and further has a thin outer surface layer such as a fluororesin tube. 23.
The temperature of the surface of the heating roller 10 is detected by a temperature sensor (not shown).
The temperature is controlled at about 00 ° C. so that the fixing is appropriate.

The sheet P conveyed along the guide plate portion 31 is heated and fixed at a pressure contact portion between the heating roller 10 and the pressure roller 20, and is separated and fixed from the roller surface by separation claw portions 32a and 32b. It is discharged out of the device. The discharged sheet P is curled downward. This is because there is a temperature difference between the surface temperature of the heating roller 10 as the upper roller and the surface temperature of the pressure roller 20 as the lower roller, and the sheet surface of the sheet P is heated to a higher temperature during fixing than the sheet back surface. As a result, while the front surface is rapidly dried, the back surface is gradually dried, and the fibers (of the sheet P) on the back surface are curled downward due to greater shrinkage of the fibers on the back surface. When the curl generated on the sheet P is strong (the radius of curvature is small), the phenomenon that the fixed sheet P is wound around the pressure roller 20 occurs, or even if the sheet P is separated, There are many problems such as a shortage of conveyance (jam) before the sheet P is ejected outside the apparatus, and the sheets P ejected one after another in a full shape even when ejected outside the apparatus are not properly stacked in a stacked state. It will be.

The present inventors have determined the relationship between the temperature difference between the heating roller 10 and the pressure roller 20 and the curl amount. The temperature of the heating roller 10 is controlled at 200 ° C., and the water content is 9.4 to 9.6.
% Of A4 size commonly used copy paper (55%).
FIG. 5 shows the relationship between the surface temperature of the pressure roller 20 and the curl amount of the paper (kg paper). The curl amount is obtained by placing the copy paper immediately after fixing with the curl direction upward on a flat plate, measuring the lifted heights of the four corners in mm, and taking the average value. Pressure roller 2
The smaller the temperature difference from 0, the smaller the curl amount. In the graph, the forward set and the reverse set are classified based on the mounting state (the state of the front and back) of a large number of copy sheets loaded in the sheet cassette. In this graph, the curl amount tends to be larger when the reverse set is performed. This is because the reverse set sheet has a history of curling downward more easily than the normal set sheet. Reducing the temperature difference between the pressure roller 20 and the pressure roller 20 is a condition for reducing the curl amount.

Many proposals have been made to heat the pressure roller 20 to a temperature close to the surface temperature of the heating roller 10 to perform fixing. There is a proposal to provide a heat source inside the pressure roller 20, but the pressure roller 20 has a sponge-like elastic layer 22 and has poor thermal conductivity and a large thermal gradient. Requires a lot of time, and the temperature inside the pressure roller 20 becomes abnormally high. On the other hand, the pressure roller 20
It has been proposed to heat the pressure roller surface from outside. However, in this case, a heating means for heating the surface of the pressure roller is required, and it is necessary to control the temperature of the surface of the pressure roller.

Japanese Patent Application Laid-Open Nos. 1-234877 and 1-2
39579, JP-A-3-138681, JP-A-7-
Japanese Patent Publication No. 114295 discloses a technique of preheating the surface of the pressure roller by rotating the pressure roller while pressing it against the heating roller during standby.

[0007]

However, these publications do not disclose any pressure bonding force of the pressure roller to the heating roller. Further, if the pressing pressure of the pressure roller to the heating roller is applied as it is when the fixing of the fixing device is stopped, the elastic layer of the pressure roller remains deformed, which causes incomplete fixing and causes a long time. Since the elastic body is exposed to a high temperature, there is a problem that the deterioration is accelerated and the life of the roller bearing is shortened. The present invention reduces the amount of curl of a sheet discharged after completion of fixing and reduces the pressure load of the pressing roller against the heating roller at the time of fixing stop and standby to prevent deterioration of the elastic body of the pressing roller. It is another object of the present invention to provide a fixing device in which the life of the bearing of the pressure roller is improved.

[0008]

An object of the present invention is to provide a fixing device including a heating roller having a built-in heater, and a pressure roller capable of pressing and releasing the heating roller.
The pressure load of the pressure roller against the heating roller can be switched between normal and light pressure by two stages.

In a preferred embodiment of the fixing device, the pressing load is a light pressing pressure during warm-up or standby, and is switched to a regular load during a fixing operation.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of an embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a partial sectional view showing an example of the structure of the fixing device of the present invention. In the figure, reference numerals 10 and 20 denote a heating roller and a pressure roller, which are a pair of fixing rotating bodies,
Denotes a cleaning roller, and 16 denotes an oil application roller.

A heating heater 11 such as a halogen lamp is provided on the inner core of the heating roller 10. The ambient temperature of the heating roller 10 is detected by a temperature sensor such as a thermistor (not shown), and is controlled by the detection signal to be maintained within a predetermined temperature range.

The heating roller 10 is a hard roller having an outer diameter of 60 mm having a surface layer 13 in which the outer periphery of a thin metal cylinder 12 is coated with a fluororesin of 30 μm.

The pressure roller 20 is provided with an elastic layer 22 made of an elastic material such as rubber having a rubber thickness of 10 mm and a rubber hardness of Asker C55 degrees around a cored bar 21. This is a soft roller having an outer diameter of 65 mm and having a surface layer 23 coated or coated with a fluororesin.

At the time of fixing, the pressure roller 20 is pressed against the heating roller 10 at 90 kgf by a spring 54 which is an urging member which will be described later, and forms a pressure-bonded portion N on the pressure-bonded surface by elastic deformation of the elastic layer 22. At this time, the length of the pressure-bonded portion N varies depending on the surface pressure and the hardness of the roller surface, but is approximately 10.5 m.
m. The heating roller 10 has a peripheral speed of 350 to 410
(Mm / sec), rotate counterclockwise,
No. 0 is pressed against the heating roller 10 and is driven to rotate.

The cleaning roller 15 is a heating roller 10
The cleaning roller 15 is made of a material that is non-absorbable with respect to oil, such as foamed silicone rubber, for example. If an absorbent material is used, the collected absorbed oil will be discharged, resulting in uneven oil.
Therefore, a non-absorbable material is used for the cleaning roller 15, and the variation in the amount of applied oil is suppressed. In addition, in order to improve the performance of removing foreign matter such as toner, the releasability is low.
Further, a roller having a small heat capacity is selected and used so as not to absorb the heat from the heating roller 10.
Is pressed against the heating roller 10 and is driven to rotate.

The oil application roller 16 is an oil application roller that applies the release oil to the peripheral surface of the heating roller 10 cleaned by the cleaning roller 15. The oil application roller 16 always contacts the heating roller 10, It rotates following the rotation of 10. Oil application roller 1
In addition to the oil that oozes and replenishes from the inside, oil replenishment may be performed from the outer periphery by an oil replenishment pad. With this configuration, the sheet P, which is the toner image carrier to be fixed, is prevented from being stained, and the sheet P is easily separated from the heating roller 10. The cleaning roller 15 is disposed upstream of the oil application roller 16 with respect to the rotation direction of the heating roller 10 as shown in FIG. 1, and the cleaning roller 15 is disposed before the toner adhered to the heating roller 10 adheres to the oil application roller 16. It is configured to remove by. 31 is a guide plate provided above and below the entrance of the fixing device for the sheet P, and 32a and 32b are separation claws respectively provided on the heating roller 10 and the pressure roller 20 to prevent the sheet P from winding. The separation claw 32a is not in contact with the peripheral surface of the heating roller 10 by the urging force of a tension spring (not shown), and the separation claw 32b is lightly pressed against the peripheral surface of the pressure roller 20.

In the fixing device of the present invention, when the power is turned off, the pressure roller 20 is separated from the heating roller 10, and when the power is turned on, the pressure roller 20 is pressed against the heating roller 10. However, this crimping load can be switched between a normal load and a light load in two stages. One embodiment of this structure will be described.

Reference numeral 40 denotes a pressure changing means which can change the pressure load of the pressure roller 20 against the heating roller 10;
Is a rotating board provided rotatably around a support shaft 42 implanted on the side wall of the apparatus, 43 is a stopper pin implanted on the rotating board 41, and 44 is a lifting member fixed on the side wall of the apparatus. A plunger type solenoid 44a is a solenoid 44
, 45 is a tension spring that acts on the rotating substrate 41 in the downward direction, 46 and 47 are pins planted on the side wall of the device, and pin 46 is a pin that locks one end of the tension spring 45.
The pin 47 is a stopper pin for stopping the clockwise rotation of the rotary substrate 41 when the distal end portion 41a abuts when the rotary substrate 41 is pulled down by the tension spring 45. Reference numeral 51 denotes an operation plate which is provided rotatably about a support shaft 52 implanted on a side wall of the apparatus and supports bearing portions at both ends of the core metal 21 of the pressure roller 20. A spring receiving arm rotatably provided around the provided support shaft 56, a compression spring 54 provided between the distal end portion 51 a of the operation plate 51 and the spring receiving arm 53, and 55 a 180 ° by a rotating member such as a motor. This is an eccentric cam which rotates one by one and rotates to a position shown by a solid line or a two-dot chain line shown in the figure. The rotating board 41 and the operating plate 51 are provided symmetrically at both ends of the pressure roller 20. However, when the two operating plates 51 at both ends are integrally formed of a rigid material, the rotating board 41 and the operating plate 51 are provided. The part attached to it can be provided only at one end to simplify the structure.

Next, the operation of the pressure changing means 40 will be described with reference to FIG.
This will be described below.

When the power of the image forming apparatus having the fixing device is turned on, the solenoid 44 is energized. This energization causes the solenoid 44 to suck the plunger 44a against the force of the tension spring 45 until the flange portion abuts on the solenoid 44 main body, and the pressing roller 20 shown in FIG. Pull up to the pressed state. During warm-up or standby of the image forming apparatus, the eccentric cam 55 is controlled by the control of a control unit (not shown).
It stops at the position shown by the dotted line. Accordingly, the spring receiving arm 53 is in a state of being lowered downward as indicated by a two-dot chain line in FIG.
The crimping load to 0 becomes a light load state. When image formation is started and the fixing operation of the fixing device is performed, the eccentric cam 55 is rotated to the position shown by the solid line under the control of the control unit, and the spring receiving arm 5 is rotated.
3 is in a state of rising upward as shown by a solid line in the figure, and the compression spring 54 is compressed and
Is in a regular load state which is larger than the light load state. When the power is turned off, the energization of the solenoid 44 is also turned off, and the solenoid 44 releases the plunger 44a. To be reduced to As a result, the pins 43 provided on the rotating board 41 push down the distal end 51a of the operation plate 51. Therefore, the operation plate 51
The bearing of the pressure roller 20 is pushed down with the rotation of the pressure roller 20 in the counterclockwise direction, and the pressure roller 20 is separated from the heating roller 10. As a result, while the power supply of the image forming apparatus is OFF, the pressure load of the pressure roller 20 to the heating roller 10 becomes zero, so that the deformation of the pressure roller 20 is avoided, and the life of the bearing is further extended. can do.

After the plunger 44a is attracted to the solenoid 44 by energization, the latch member is operated to hold the plunger 44a in the sucked state.
When the signal to turn off the power to the power supply 4 and turn off the power is generated, the latch member is released and the tension spring 45 is turned off.
The power is turned off after the rotating substrate 41 is pulled down by
Is preferably provided. This can prevent unnecessary consumption of power and unnecessary heat generation due to energization.

As a result of a test conducted by the present inventors, in the above-mentioned fixing device, in order to perform complete fixing, a pressure roller 20 is required.
It was found that the pressure applied to the heating roller 10 (the sum of the loads at both ends of the pressure roller 20) should be 90 kgf.
Further, when the surface temperature of the heating roller 10 reaches 200 ° by normal warm-up, the pressure load is 5 to 20 k so that the surface temperature of the pressure roller 20 becomes 150 to 160 °.
It has been found that it suffices to be in a state in which the driven rotation is performed between gf.

When the pressure load is 90 kgf, the life of the elastic body and the bearing of the pressure roller 20 is 350,000 copies, but the pressure load during warm-up and standby is 15 kg.
At f, the life was found to be extended to 450,000 copies.

In the case of the present invention, the surface temperature of the pressure roller 20 when continuous copying is performed is deprived of heat by the sheet P, which is a toner image carrier, and the initial temperature as shown in the graph of FIG. The temperature gradually decreases from 160 ° C. However, it has been found that the curl reduction effect of the sheet P is sufficient up to several hundred copies from the start of copying. The graph of FIG. 3 is a graph at the time of continuous copying, and when there is a pause in the middle, the surface temperature of the pressure roller 20 returns to 160 ° C.

From the above test results, in the fixing device of this embodiment, the pressure load of the pressure roller 20 against the heating roller 10 is 90 kgf for the normal load during the fixing operation, and 20 kgf or less for the light load during the standby state, preferably. It is appropriate to set it to 5 to 15 kgf. However, this value is a value experimentally obtained by the fixing device.

FIG. 2 is a flowchart showing an example of control by a control unit (not shown) of the pressure load of the pressing roller 20 to the heating roller 10 of the fixing device during image formation in the image forming apparatus having the fixing device of the present invention. That is, when the power supply of the image forming apparatus is turned on, the solenoid 44 shown in FIG. 1 is energized and the rotating board 41 of the pressure changing means 40 is pulled upward in FIG. Is rotated. Accordingly, the pressure roller 20 is pressed against the heating roller 10 and the pressure load is reduced. In this state, warm-up is performed and a copy standby state is set (S1). Next, when the copy start button of the operation unit of the image forming apparatus is pressed and turned on (S2),
It is checked whether the surface temperature of the heating roller 10 has reached a predetermined temperature (190 to 200 ° in this embodiment) (S3). When the temperature has reached the predetermined temperature, the eccentric cam 55 is rotated to the position shown by the solid line, and the pressure load of the pressure roller 20 to the heating roller 10 becomes a regular pressure load (S4), and at the same time, the image formation is started (S4). S5). The control unit checks the end of the fixing operation based on the image forming process and signals from various sensors (S6). If the fixing is completed, the eccentric cam 55 is rotated to the position indicated by the two-dot chain line and the pressure roller 20 is rotated.
Is brought into a standby state (S7) after returning to the light load state, and returns to (S1) to wait for the next copy.

[0028]

According to the fixing device of the present invention, since the pressure load of the pressing roller against the heating roller can be changed, the temperature difference between the front and back of the sheet as the toner image carrier can be eliminated with a simple structure, and the curl of the sheet can be eliminated. It is possible to prevent the occurrence of an accident such as a jam, and to provide a fixing device having a longer life due to the deterioration and deformation of the elastic layer of the pressure roller and the life of the bearing because the load is light during standby. Was.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view illustrating an example of a configuration of a fixing device of the present invention.

FIG. 2 is a flowchart illustrating an example of control of a pressure load of a pressure roller.

FIG. 3 is a graph showing the relationship between the surface temperature of a pressure roller and the number of copies.

FIG. 4 is a cross-sectional view illustrating a general configuration of a heat roller fixing device.

FIG. 5 is a graph showing the relationship between the surface temperature difference between the heating and pressing rollers and the curl amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Heat roller 11 Heater 20 Pressure roller 22 Elastic layer 23 Surface layer 40 Pressure change means 41 Rotating substrate 42 Support shaft 43 Stopper pin 44 Solenoid 51 Operating plate 52 Support shaft 53 Spring receiving arm 55 Eccentric cam N Nip part P sheet (toner image carrier)

Claims (2)

[Claims] 1. A fixing device comprising: a heating roller having a built-in heater; and a pressing roller capable of pressing and releasing the heating roller, wherein a pressing load of the pressing roller to the heating roller is normal and A fixing device wherein two-stage switching of light pressure bonding is enabled. 2. The fixing device according to claim 1, wherein the pressure load is a light pressure load during warm-up or standby, and is switched to a normal load during a fixing operation.