JPH0814743B2 - Fixing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fixing device that heats and pressurizes an object to be fixed while conveying the object to be fixed.

(Prior Art) Conventionally, as the fixing device of this type, the following devices are often used. This is a fixing roller in which a mold-releasing coating made of fluorine resin or the like is provided on the peripheral surface of a metal cylindrical core metal, and a pressure roller having an elastic layer on the surface and being pressed and driven by the fixing roller. A heating source for heating the fixing roller from the inner peripheral surface of the fixing roller, a temperature detecting element for detecting the temperature on the peripheral surface of the fixing roller, and a driving source for rotationally driving the fixing roller. Normally, the surface temperature of the fixing roller at the time of fixing is set to a temperature T _{2 of} 185 ° C., for example, as shown in FIG. The temperature is kept constant by controlling the power supply. The surface temperature of the fixing roller is set to a temperature T ₁ lower than the temperature T ₂ at the time of fixing except at the time of fixing after the power-on t ₁ . Then, when the fixing operation is started t ₂ , the drive source of the fixing roller is activated and the surface temperature of the fixing roller is switched to T ₂ . After that, the transfer material carrying the unfixed image passes while being pinched and conveyed between the fixing roller and the pressure roller (t ₃ → t ₄ ).
Then, after the transfer material has been heated and pressed to be fixed and the transfer material has passed, the driving of the fixing roller is stopped and the surface temperature of the fixing roller is switched to T ₁ .

However, in this case, a certain waiting time is required until the fixing roller is heated by the heating source and reaches a predetermined temperature during standby or fixing, and the time required for fixing becomes long. 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 the power supply capacity during use is limited, for example, the power of the fixing device is preferably 1.3 KW or less. Therefore, it is difficult to increase the heating value of the heating source, and this method has a limit.

Therefore, it has been proposed to reduce the waiting time by reducing the outer diameter, the 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 a conventional technique has the following problems. That is, when the outer diameter, the inner thickness, etc. of the fixing roller are reduced, the fixing roller is likely to be deformed such as bending due to the pressure contact force with the pressure roll, and this tendency is remarkable because the Young's modulus becomes small at high temperature. Become. by the way,
In the case of the prior art, as shown in FIG. 5, after a predetermined time elapses from the time t ₄ when the fixing of the transfer material is completed, a time t _{6 is} passed.
In addition, stop the drive of the fixing roller and set the temperature at the same time.
Switching from T ₂ to T ₁ . Therefore, even when off the power supply to the heating source of the fixing roller at the time of t _6, the escape of heat from the roller inner surface and the heat transfer to the roller surface is delayed, the O connexion pressure roller to stop the fixing roller Is less,
As shown in FIG. 6, the surface temperature of the fixing roller becomes significantly higher (overshoots) than the normal fixing temperature T ₂ . Moreover, since the fixing roller is stopped at this point in time, the temperature decrease rate is small, and the fixing roller is pressed at a high temperature for a long period of time. There is a problem that wrinkles and the like occur.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to prevent the occurrence of overshoot of the surface temperature of the fixing roller that causes permanent deformation, thereby preventing It is an object of the present invention to provide a fixing device that can reduce permanent deformation and maintain excellent fixing performance for a long period of time.

(Means for Solving Problems) In order to achieve the above object, the present invention provides a fixing roller, a pressure roller that contacts the fixing roller, a heater that heats the fixing roller, and a surface temperature of the fixing roller. The temperature detection means for detecting the temperature and the control means for controlling the energization of the heater so that the temperature detected by the temperature detection means maintains a predetermined set temperature. In a fixing device whose energization is controlled to maintain a set temperature lower than the preset time, when the set temperature is switched from the set temperature for fixing to the set temperature for standby after the fixing is completed, the preset time after the set temperature is switched After that, the fixing roller and the pressure roller stop rotating.

(Example) Below, this invention is demonstrated based on the Example shown in figure.

FIG. 1 is a schematic vertical sectional view showing an embodiment of the fixing device according to the present invention. In the figure, 1 is a fixing roller, 2 is a metallic thin cylindrical core metal, 3 is a release material layer made of fluororesin or the like coated on the outer peripheral surface of the core metal 4, 4 is a heater as a heating source, 5 is a pressure roller that is pressed against the fixing roller 1,
Reference numeral 7 is a metal cylindrical core metal, and 6 is a heat resistant elastic layer made of silicon rubber or the like. Further, 8 is a temperature detecting element such as a thermistor for detecting the surface temperature of the fixing roller 1, 9
Is a sheet discharge detecting element for detecting the discharge of the transfer material P, 10 is an inlet guide, 11 is a sheet discharge guide, and 25 and 26 are heat insulating walls for suppressing heat radiation from the fixing roller 1 and the pressure roller 5. Then, the transfer material P on which the toner image T is transferred is transferred to the entrance guide 10
Through the fixing roller 1 and the pressure roller 5,
It is fixed by being heated and pressed while being nipped and conveyed by both rollers 1, 5.

FIG. 2 is a block diagram showing the control system. In the figure, 20 is a CPU as 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 energization of the heater 4, 23 Is an AC power supply for supplying power to the heater 4, 24
Is an operation switch.

In the fixing device having the above structure, the fixing roller is driven and the temperature is controlled as follows. That is, when the power of the copying machine is turned on, t ₁ , COP20
Energizes the heater 4 via the temperature control switch element 22 to heat the fixing roller 1 and control the surface temperature of the fixing roller 1 to the standby temperature T ₁ as shown in FIG. At that time, when the surface temperature of the fixing roller 1 becomes equal to T ₁ , the energization of the heater 4 is turned off. However, due to the delay of heat transfer between the inner peripheral surface and the outer peripheral surface of the roller, As shown in FIG. 4, the surface temperature becomes substantially constant at the temperature T ₁ after being largely overshought. Then time
When the fixing start signal is issued to t ₂ from the operation switch 24,
The CPU 20 controls the surface temperature of the fixing roller 1 to a temperature T ₂ higher than that at the standby time, and the surface temperature of the fixing roller 1 is set to the fourth temperature.
As shown in the figure, the temperature T ₂ becomes almost constant after a slight overshoot. Further, at time t ₂ , the CPU 20 sends a signal to the driving source 21 to start the rotational driving of the fixing roller 1. Heater 4
Since a part of the amount of heat supplied by the pressure roller 5 is taken away by the pressure roller 5, the temperature rising speed of the fixing roller 1 is slightly reduced. However, before the transfer material P actually reaches the fixing device, As shown in Fig. 4, the surface temperature of the fixing roller 1 is T ₂
As described above, good fixing can be performed. The actual fixing process is performed from t ₃ to t ₄ (in the case of the maximum size) as shown in FIGS. 3 and 4.
At the time t ₄ when the transfer material is completely discharged after the fixing process of the maximum size is completed, the CPU 20 changes the set temperature of the fixing roller 1 from T ₂ to T _2.
After changing to ₁ , after continuing the rotation of the fixing roller 1 for a predetermined time (t _{4 to} t ₅ ), the rotation of the roller is stopped at time t ₅ to prepare for the next fixing process.

At this time, since the fixing roller 1 is still rotating at the time t ₄ when the surface temperature of the fixing roller 1 is changed to T ₁ ,
As shown in the figure, due to the heat transfer to the pressure roller 5, the overshoot does not occur and the temperature decrease rate is large, and after the roller rotation stops at the time t ₅ , the temperature decrease rate becomes smaller than that.

Next, the result of an experiment of fixing property using the fixing device according to the present embodiment will be described. The fixing device shown in FIG. 1 was incorporated into a known electrophotographic copying apparatus, and the fixing process was carried out on 5 sheets of A4 size paper at a peripheral speed of the fixing roller of 50 mm / s, and then the temperature was controlled for 2 hours and then naturally cooled. , Left for 24 hours. After that, five fixing processes were performed under the same conditions to check the occurrence of fixing unevenness and wrinkles, and then the fixing device was disassembled, and the fixing roller was left for 48 hours in an environment of a temperature of 23 ° C and a humidity of 60%, and then fixed. The amount of deflection of the roller was measured. As the fixing roller, the outer diameter is 25 mmφ and the wall thickness is
A cylindrical core metal made of Al having a total length of 250 mm of 0.8 mmt, 0.6 mmt and 1.6 mmt and having a 25 μm thick PFA resin coated on the outer peripheral surface was used. As a pressure roller, 10 mmφ S
A silicon rubber layer is provided on the core made of μs to have an outer diameter of 24 mmφ, the rubber hardness is 25 ° (JIS-A), and the total length is 230 nm. The total pressure was about 6kg, and it was supported so that it could be driven to rotate. As the set temperature, the standby temperature T ₁ is 160 ° C and the fixing temperature is 185
° C. On the other hand, as the heater, an 8 mmφ halogen heater made of a transparent quartz tube having an emission length of 220 mm was used, and its rated power was 850 W. The results of the above experiments are shown in Table 1 as the average value of 5 experiments.

In Table 1, in this example, the interval between t ₄ and t ₅ was 5 seconds. At this time, as described above, the overshoot did not occur, and the temperature when the roller was stopped was about 170 ° C. Time t ₅
Is 5 seconds after the time when the trailing edge of the transfer material P is detected by the paper discharge detection element 9 described above. In the present embodiment, the trailing edge of the transfer material P is detected by the paper discharge detection element 9, but this may be set to t ₅ after a predetermined time has elapsed since the leading edge of the transfer material was detected. When the passing size is the length of A4 size paper = 297 mm, the fixing processing time (6 in this embodiment)
You may add 5 seconds to (seconds) and set 11 seconds later. Further, in the present embodiment, the means for predicting the end time of the fixing process may be a predetermined time after another signal, for example, the paper feed signal, and the point is that the end of the fixing process can be surely detected. By the way, when the occurrence of fixing unevenness and wrinkles was examined by the above-mentioned method, no problem was found. In this case, the waiting time from the room temperature of 23 ° C. to the standby temperature T ₁ was about 20 seconds.

Comparative example 1 uses the same fixing roller as that of the present embodiment, and
This is an example of fixing in the sequence shown in the figure.
In this case, one second later than the time t ₄ when it detects the trailing edge of the transfer material
At t ₆ , the roller drive was stopped and the set temperature was changed from T ₂ to T ₁ . As a result, as shown in FIG. 6, overshoot occurs, and the average maximum temperature after the roller stops is 197.
Reached ℃. When the occurrence of fixing unevenness and wrinkles was examined by the same method as in the present embodiment, some fixing unevenness was generated in the advancing direction at the time of fixing, and some areas were poor in fixability. As for wrinkles, wrinkles were formed on 8 of the 25 sheets, which was not practically possible.

Comparative Example 2 shows an example in which the waiting time is shortened by further reducing the thickness of the core metal of the fixing roller, and the waiting time was 16 seconds, which was 4 seconds shorter than that of this embodiment. However, when fixing was performed in the same sequence as in Comparative Example 1, uneven fixing and wrinkling occurred. When the fixing roller of Comparative Example 2 was tested in the same sequence as that of the present embodiment, the temperature when the roller was stopped was about 172 ° C., which was slightly high, and fixing unevenness and wrinkles were slightly generated, resulting in a performance limit of practical use. Seems to be.

Comparative Example 3 is a typical example of a conventional fixing device, and fixing was performed in the sequence shown in FIG. 5 using a fixing roller having a large thickness. In this case, the waiting time was as long as 30 seconds, but uneven fixing and wrinkles did not occur.

The thin fixing roller expressed in the present invention has a roller deflection amount δ of The fixing roller of FIG.

Where, w: Total load l: Roller pressure contact length d ₂ : Outer diameter d ₁ : Inner diameter E: Young's modulus at operating temperature By the way, in the case of δ ≦ 30μ, practical problems did not occur without special sequence consideration as shown in Comparative Example 3. However, it is needless to say that the performance can be further improved by applying the present invention even when δ ≦ 30μ.

(Effects of the Invention) The present invention has the above-described configuration and operation, and by suppressing the occurrence of overshoot of the surface temperature of the fixing roller that causes permanent deformation, the permanent deformation of the fixing roller is reduced and the fixing roller can be used for a long period of time. Therefore, it is possible to provide a fixing device capable of maintaining excellent fixing performance.

[Brief description of drawings]

1 is a schematic sectional view showing an embodiment of a fixing device according to the present invention, FIG. 2 is a block diagram showing a control system, FIG. 3 is a timing chart showing the operation of the control system, and FIG. 4 is a fixing device. FIG. 5 is a graph showing a change in the surface temperature of the roller, FIG. 5 is a timing chart showing the operation of the conventional fixing device, and FIG. 6 is a graph showing the change in the surface temperature of the fixing roller of the conventional example. Explanation of symbols 1 ... Fusing roller, 2 ... Core metal 5 ... Pressure roller, 20 ... CPU

Continuation of the front page (56) Reference JP 56-1073 (JP, A) JP 57-141671 (JP, A) JP 58-52666 (JP, A) JP 58-52669 (JP , A) JP 58-40561 (JP, A) JP 52-62027 (JP, A) JP 61-39073 (JP, A) JP 59-62883 (JP, A) JP 56-1065 (JP, A) JP 56-142563 (JP, A) JP 57-129476 (JP, A) JP 61-175666 (JP, A) JP 58-14850 (JP, A) A) JP-B 57-19428 (JP, B2) JP-B 61-31463 (JP, B2)

Claims (1)

[Claims] 1. A fixing roller, a pressure roller contacting the fixing roller, a heater for heating the fixing roller, a temperature detecting means for detecting the surface temperature of the fixing roller, and a temperature detected by the temperature detecting means is set to a predetermined value. In a fixing device that has a control unit that controls energization to a heater so as to maintain a temperature, and that is energized so that the temperature detected by the temperature detection unit is maintained at a preset temperature lower than that at the time of fixing during standby. When the set temperature is switched from the set temperature at the time of fixing to the set temperature at the time of standby after completion of fixing, the fixing roller and the pressure roller are stopped to rotate after a predetermined time after the set temperature is switched. Fixing device.