JPS62206580A - Fixing device - Google Patents

Abstract

PURPOSE:To shorten the waiting time and reduce permanent deformation of a fixing roll by switching the surface temperature of the fixing roll to a set temperature processing is terminated and stopping the rotation of the roll when a prescribed time elapses thereafter. CONSTITUTION:When a transfer material is ejected completely after the fixing processing is terminated, a CPU20 switches the set temperature of a fixing roll 1 from a temperature T2 higher than a temperature T1 for stand-by to the temperature T1 for stand-by: and when the rotation of the fixing roll 1 is continued for a prescribed time (t4-t5) thereafter, the rotation of the roll is stopped at a time t5 to prepare for the next fixing processing. Since the fixing roll 1 is rotated when the surface temperature of the fixing roll 1 is switched to the temperature T1, overshoot does not occur by heat transmission to a pressure roll 5 and the temperature fall speed is high; and after the rotation of the roll is stopped at the time t5, the temperature fall speed is lower. Thus, the waiting time is shortened and permanent deformation of the fixing roll is reduced to keep a superior fixing capacity for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fixing device that fixes an object by heating and pressurizing it while holding and conveying the object.

(Prior Art) Conventionally, the following types of fixing devices have been widely used as this type of fixing device. This consists of a fixing roller that has a releasable coating made of fluororesin etc. on the circumferential surface of a metal cylindrical core, and a pressure roller that has an elastic layer on its surface and follows the fixing roller in pressure contact. , a heat source that heats the fixing roller from the inner circumferential surface of the fixing roller, a temperature detection element that detects the temperature on the circumferential surface of the fixing roller, and a drive source that rotationally drives the fixing roller. Normally, the surface temperature of the fixing roller during fixing is set to a temperature T2 of, for example, 185°C, as shown in FIG. A constant temperature is maintained by controlling the supply of The surface temperature of the fixing roller is the temperature T at the time of fixing, except when the foot touches the ground after 11 when the power is turned on.
The temperature TI is set to be lower than 2. Then, the fixing operation starts 1. Then, the drive source of the fixing roller is activated, and the narrow surface temperature of the fixing roller is switched to T2.

Thereafter, the transfer material carrying the unfixed image passes between the fixing roller and the pressure roller while being pinched and conveyed (ts→
At step 14), the transfer material is heated and pressurized to be fixed, and after the transfer material has passed, the drive of the fixing roller is stopped and the surface temperature of the fixing roller is switched to Tt.

However, in this case, there is a problem that a certain amount of waiting time is required for the fixing roller to be heated by a heat source and reach a predetermined temperature during standby or fixing, and the time required for fixing becomes longer. There was a point.

In order to solve this problem, it is possible to increase the amount of heat generated by the heating source, but since there are restrictions on the power supply capacity during use, for example, the power for the fixing device must be 1.3□ or less. Although this method is preferable, it is difficult to increase the calorific value of the heating source, and this method has its limitations.

Therefore, it has been proposed to shorten the waiting time by reducing the outer diameter, wall thickness, etc. of the core metal of the fixing roller to reduce the heat capacity of the fixing roller.

(Problems to be Solved by the Invention) However, such prior art has the following problems. In other words, if the outer diameter, wall thickness, etc. of the fixing roller are made smaller, the fixing roller is more likely to undergo deformation such as deflection due to the pressure contact force with the pressure roll, and this tendency becomes more noticeable at high temperatures as the Young's modulus decreases. . By the way, in the case of the prior art, as shown in FIG.
6, the driving of the fixing roller is stopped and the set temperature is changed from T3 to Tt at the same time. Therefore, at time t6, the fixing roller is connected to the heat source 1! Even if it is turned off, there is a delay in heat transfer from the inner surface of the roller to the roller surface, and when the fixing roller stops, less heat escapes to the pressure roller, so the surface temperature of the fixing roller is as shown in Figure 6. As shown, the fixing temperature becomes significantly higher than the normal fixing temperature T2 (overshoots). Moreover, since the fixing roller is stopped at this point, the temperature decrease rate is slow, and the fixing roller is pressurized while being stopped at a high temperature for a long time, which tends to cause permanent deflection, resulting in poor fixing and transfer. There is a problem that wrinkles etc. occur in the material.

The present invention has been made to solve the problems of the prior art described above, and its purpose is to shorten the waiting time without increasing the power supply capacity, and to prevent permanent deformation of the fixing roller. It is an object of the present invention to provide a fixing device that can be made small and maintain excellent fixing performance over a long period of time.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a thin hollow fixing roller, a pressure roller that faces and presses against the fixing roller, and a surface temperature of the fixing roller. and a control means for controlling at least two set temperatures and controlling the rotation of the i-ra, and when the fixing process is completed, the surface temperature of the fixing roller is first switched to a set temperature lower than that during fixing, and then for a predetermined period of time. The roller is configured to stop rotating after the lapse of time.

(Example) The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a schematic vertical sectional view showing an embodiment of a fixing device according to the present invention. In the figure, 1 is a fixing roller, 2 is a metal thin cylindrical core, 3 is a discrete material layer made of fluororesin or the like coated on the outer peripheral surface of the core 2, 4 is a heater as a heating source, 5 is a specific pressure roller that is in pressure contact with the fixing roller l; 7;
6 is a cylindrical metal core, and 6 is a heat-resistant elastic layer made of silicone rubber or the like. Further, 8 is a temperature detection element such as a thermistor that detects the surface temperature of the fixing roller 1, 9 is a paper discharge detection element that detects the discharge of the transfer material P, 10 is an entrance guide, 11 is a paper discharge guide, 25 and 26 is fixing roller 1
and a heat insulating wall that suppresses heat radiation from the pressure roller 5.

The transfer material P onto which the toner image T has been transferred enters between the fixing roller 1 and the pressure roller 5 via the entrance guide 10t, and is nipped and conveyed by both rollers 1 and 5.
It is fixed by heat and pressure treatment.

FIG. 2 is a block diagram of the control system. In the figure,
20 is a CPU as a control means; 21 is a drive source for rotationally driving the fixing roller 1; 22 is a temperature control switch element such as a solid state relay (SSR) for controlling the passage to the heater 4; and 23 is a temperature control switch element for controlling the heater 4. 24 is an operating switch for supplying power to the AC'tM source.

In the above configuration, in the fixing device according to this embodiment, the drive and temperature control of the fixing roller is performed as follows. That is, when the copying machine is turned on, tl, CPU
20 energizes the heater 4 through the temperature control switch element 22t to heat the fixing roller 1 and control the surface temperature of the fixing roller 1 to the standby temperature Tl as shown in FIG. Other than that, when the surface temperature of the fixing roller 1 becomes equal to Tx, the power supply to the heater 4 is turned off, but due to the delay in heat transfer between the inner circumferential surface and the outer circumferential surface of the roller, the surface temperature of the fixing roller 1 decreases. , as shown in Figure 4,
After a large overshoot, the temperature becomes approximately constant at T1. Next, when a fixing start signal is issued from the operation switch 24 at time tJ, the CPU 20 controls the surface temperature of the fixing roller 1 to a temperature T2 higher than that during standby, and the surface temperature of the fixing roller 1 is as shown in FIG. As shown, the temperature remains approximately constant at T2 with a slight overshoot. Further, at time -, the CPU 20 sends a signal to the drive source 21 to start rotating the fixing roller 1. A portion of the heat supplied from the heater 4 is taken away by the pressure roller 5, so the temperature rise rate of the fixing roller 1 is slightly reduced, but the As shown in FIG. 4, since the surface temperature of the fixing roller 1 is 13 or more, good fixing can be performed. The actual fixing process is performed from stl to t4 (in the case of maximum size) as shown in FIGS. 3 and 4. Time t4 when the maximum size fixing process is completed and the discharge of the transfer material is completed.
Then, the CPU 20 changes the set temperature of the fixing roller 1 from T2 to Ts, and then continues the rotation of the fixing roller 1 for a predetermined time Cta~ts). Stop the rotation of the roller and prepare for the next fixing process.

At this time, the surface temperature of the fixing roller is changed to Tx, and at the ninth point t4, while the fixing roller 1 is still rotating, overshoot is prevented by heat transfer to the pressure roller 25, as shown in FIG. The speed of temperature drop is large without causing any problems, and after 9 seconds after the rotation of the rollers stops at time ts, the rate of temperature fall becomes smaller than that.

Next, the results of an experiment on fixing performance using the fixing device according to this embodiment will be explained. The fixing device shown in Fig. Wc1 was incorporated into a known electrophotographic copying machine, and the fixing process was performed on five A4 size papers at a circumferential speed of the fixing roller of 50 wI/s.After that, the temperature was kept on standby for 2 hours, and then naturally cooled. , and left for 24 hours.

After that, five sheets were subjected to the fixing process under the same conditions, and the occurrence of fixing unevenness and wrinkles was examined. After that, the fixing device was disassembled, and the fixing roller was left in an environment with a temperature of 23°C and a humidity of 60% for 48 hours, and then fixed. A friend who measures the amount of deflection of the roller. The fixing roller has an outer diameter of 25 mm and a wall thickness of 0.8 mm.
t, 0.6 ml, 1.6 mt total length 250
The outer peripheral surface of an inner cylindrical core bar made of M was coated with a PFA resin having a thickness of 25 μm. 9. As for the pressure roller, a silicone bim layer is provided on a 10-φ SμS core metal with an outer diameter of 24 wmφ, the Zam hardness is 25° (JIS-A), and the overall length is Using a 230 nm roller, the total pressure is approximately 6 by applying spring pressure to the fixing roller.
They were pressed together at Kf and supported for driven rotation. As the set temperature, the methane pie temperature T1 is 160°C, and the fixing temperature is 185°C.
℃. On the other hand, as a heater, an 8 mφ halogen heater made of a transparent quartz tube with a light emitting length of 220 m was used, and its rated power was 850 W. Table 1 shows the results of the above experiment as the average value of 5 experiments.

Table 1 In Table 1, in this example, the time between t4 and t5 is 5 seconds. At this time, as mentioned above, no overshoot occurs, and the temperature when the roller stops is approximately 170°C. Time 1. 5 seconds after the trailing edge of the transfer material P was detected by the above-mentioned paper ejection detection element 9 from time 9. In this embodiment, the trailing edge of the transfer material P is detected by the discharge detection element 9.
tllt after a predetermined time from when the leading edge of the transfer material is detected.
For example, if the maximum paper passing size is the vertical length of A4 size paper = 297 pieces, then the fixing processing time (
In this embodiment, it may be set after 11 seconds by adding 5 seconds to 6 seconds). Further, in this embodiment, the means for predicting the end point of the fixing process may be a predetermined time after another signal, such as a paper feed signal, as long as it can reliably detect the end of the fixing process.

By the way, we investigated the occurrence of uneven fixing and wrinkles using the method described above, and no problems were found. In this case, the waiting time from the room temperature of 23° C. to the standby temperature T1 is about 20 seconds.

Comparative Example 1 uses the same fixing roller as the present example.
This is an example of nine cases in which fixing is performed in the sequence shown in Figure S. In this case, the trailing edge of the transfer material is detected, and at t6, 91 seconds after time t4, the roller drive is stopped and the set temperature is changed from T8 to Tx. As a result, as shown in FIG. 6, overshoot occurred and the average maximum temperature after the roller stopped reached 197°C. When the occurrence of fixing unevenness and wrinkles was examined using the same method as in this example, some fixing unevenness occurred in the direction of progress during fixing, and some areas had poor fixing performance. Regarding wrinkles, 8 out of 25 sheets had wrinkles, which was practically impossible.

Comparative Example 2 shows an example in which the thickness of the core metal of the fixing roller was further reduced to shorten the waiting time, and the waiting time was 16 seconds, which was 94 seconds shorter than the present example.

However, when fixing was performed in the same sequence as in Comparative Example 1, uneven fixing and wrinkles occurred. When the fixing roller of Comparative Example 2 was tested in the same sequence as this example, the temperature when the roller stopped was approximately 172°C, which was slightly higher.
Some fixation unevenness and wrinkles also occurred, and the performance seems to be at its practical limit.

Comparative Example 3 is an alternative to the conventional fixing device, in which fixing was performed in the sequence shown in FIG. 5 using a thick fixing roller. In this case, although the waiting time was as long as 30 seconds, no fixing unevenness or wrinkles occurred.

Note that the thin fixing roller expressed in the present invention refers to a fixing roller having a deflection amount δ.

Here, W: Total load t: Roller pressure welding length: Moment of inertia of area (=-i-(di' cbs) d2: Outer diameter dl: Inner diameter E: Young's modulus at operating temperature By the way, if δ≦30μ As shown in Comparative Example 3, no practical problem occurred even without special sequence consideration.However, even in the case of δ≦30μ, the performance can be further improved by applying the present invention. Of course.

(Effects of the Invention) The present invention has the above-described configuration and operation, and can shorten the waiting time without increasing the power supply capacity.
Furthermore, it is possible to provide a fixing device that can maintain excellent fixing performance over a long period of time by reducing permanent deformation of the fixing roller.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the fixing device according to the present invention, FIG. 2 is a block diagram showing the control system, FIG. 3 is a timing chart showing the operation of the control system, and FIG. 4 is the fixing device. FIG. 5 is a graph showing changes in the surface temperature of the roller. FIG. 5 is a timing chart showing the operation of the conventional fixing device. The sixth factor is a graph showing changes in the surface temperature of the fixing roller in the conventional example. Explanation of symbols 1...Fixing roller 2...Core metal 5...Pressure roller 20...CPU agent Patent attorney Back
1) Noriyuki -1\Figure 1 Figure 3 Figure 5

Claims (1)

[Claims] A fixing device comprising: a thin hollow fixing roller; a pressure roller that is in opposing pressure contact with the fixing roller; and a control means that controls the surface temperature of the fixing roller to at least two set temperatures and controls the rotation of the roller. When the process is completed, the fixing device first changes the surface temperature of the fixing roller to a set temperature lower than that during fixing, and then stops the rotation of the roller after a predetermined period of time has elapsed.