JPH0634132B2 - Heat fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a heat fixing device that heat-fixes an unfixed image, powder, or unfixed material such as a capsule resin onto a support material such as a sheet, cloth, or recording material. The present invention also relates to a heat fixing device which is effective for improving the functions of the main body of a copying machine, a printing machine, a printer, a multi-function machine or the like in which the apparatus is incorporated.

(Prior Art) Conventionally, this type of heat fixing device has been widely used in printers and the like, and generally, a supporting member is passed between a pair of fixing rollers.

The fixing roller pair is provided with a heater for heating, and has a temperature of 160 ° C or higher.
The temperature is adjusted to about 200 ° C., and at the same time, the pressure is applied to each other by the pressure means.

In recent years, the fixing process is required to be fast and reliable.
However, when attempting continuous heat fixing at a high speed, in addition to fixing defects and offsets, conveyance defects (paper jams and paper winding) may occur. This is because the amount of heat required to achieve heat fixing between the fixing rollers is not given to the unfixed body and the support material.

That is, when the roller surface temperature decreases due to the continuous support material and unfixed body, the fixing roller continues to be heated by the heater, but since the heat absorbed by the support material and unfixed body is larger, the fixing roller surface temperature is It is greatly reduced, and fixing failure occurs.

With respect to this problem, as disclosed in Japanese Patent Laid-Open Nos. 50-56949 and 52-92521, it is possible to raise the surface temperature of the fixing roller during copying, that is, during fixing processing, according to a copy signal. Proposed.

However, if the surface temperature of the fixing roller is excessively increased, a high temperature offset may occur in the initial stage, or a large temperature change may be given to the fixing roller itself to shorten the life. further,
With 100 (V), 15 (A) rated machines, if there is little power that can be distributed to the fixing device because there are members that consume a lot of power during copying, the surface of the fixing roller can be heated to a sufficient temperature. There is also a problem that speedup cannot be achieved. Further, the replenishment of the amount of heat may not be sufficiently achieved in some cases due to the response delay due to the core metal forming the fixing roller, the offset prevention layer, and the like, which is not sufficient.

(Objective) The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a heat fixing device capable of preventing a fixing failure in continuous fixing and stably performing a fixing process.

(Summary of the Invention) In order to achieve this object, the present invention provides a fixing roller pair according to a decrease in the surface temperature of the fixing roller associated with heat fixing so as to prevent fixing failure between fixing rollers during continuous fixing processing. It is characterized in that it has control means for changing the pressure contact state between the fixing rollers to increase the total pressure applied between the pair of fixing rollers.

(Description of Examples and Effects) Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view of an embodiment of the present invention, showing most of the sectional view. FIG. 1 shows an example in which the present invention is applied to a fixing device of an image forming apparatus such as electrophotography.

Reference numeral 1 denotes a fixing roller having two heaters H incorporated therein, which has a release layer 3 mainly formed of thin tetrafluoroethylene resin on a cylindrical core metal 2. A pressure roller 4 is in pressure contact with the fixing roller 1. The pressure roller 4 has an elastic layer 6 mainly formed of relatively thick silicon rubber on a cylindrical core metal 5. The entire diameter of the fixing roller 1 is larger than that of the pressure roller 4. Incidentally, P is a paper, which is guided between the pair of rollers by a conveying means such as a conveying belt 24 and a guide 18 while supporting a toner image T formed by a predetermined image forming method. The toner image T is fused to the paper P while being nipped and conveyed by the roller pair.

The fixing roller 1 is rotatably supported via a bearing on a side plate fixed to a device (not shown), and given a predetermined driving force from a driving motor 25 shown. The pressure roller 2 is fixed because its rotation center shaft 7 is rotatably supported via a bearing by a stay 9 that engages with a support shaft 8 fixed to the apparatus and is rotatable about the shaft 8. The roller 1 is pressed and driven to rotate.

In this example, the pressure control mechanism for moving the pressure roller 2 with respect to the fixing roller 1 uses the displacement member 15 made of a shape memory alloy having a thermal transformation point. The displacement member 15 in the fixed support container 16 has a transformation point at about 65 ° C., and exhibits a rectangular shape (the upper end is at position 15B in the drawing) shown by a broken line in the drawing at a temperature higher than 65 ° C., It exhibits a long shape shown by a solid line at a temperature lower than 65 ° C. The displacing member 15 is located outside the heat insulating covers 21 and 23 provided to prevent heat radiation from the fixing roller 1 and the pressure roller 4, respectively. Since this position is under the ambient temperature of the fixing device and is normally in the passage of the heat exhausted by the fan 22 in the copying machine, it shows a temperature of 65 ° C. or higher in the fixing enabled state. Therefore, since the displacement member is at a temperature equal to or higher than the transformation point, it is at position 15B, and the pressure roller 4 is at the lowered position B with respect to the fixing roller 1 as shown by the broken line. After this, continuous copying is done,
When the heat of the fixing roller 1 is taken by the paper P, the toner image T, and the pressure roller 2 and the risk of defective fixing increases, the heat released from the fixing roller 1 to the air is significantly reduced.
The displacement member 15 is exposed to an ambient temperature of 65 ° C. or lower. Therefore, at this time, the displacing member 15 has an elongated shape as shown by the solid line, and the pressure roller 4 is at the raised position A with respect to the fixing roller 1 as shown by the solid line.

By this displacement of the displacement member 15, the position of the stay 9 is also displaced from the broken line to the solid line, and the rotation of the pressure roller 4 is guaranteed. Incidentally, 7B indicates the lowered position of the rotation center shaft 7.

Reference numeral 11 denotes a central control means, which controls means 12 for controlling energization of the heater H in accordance with the output from the contact type sensor 10 in order to maintain the surface temperature of the fixing roller 1 at a set temperature.

With the above configuration, the decrease in the fixing temperature that causes the fixing failure can be compensated by the increase in the pressure that is highly responsive, and the stable fixing without the fixing failure can be performed even in the continuous fixing process.

When the pressure contact state is changed as described above, if the paper P or the toner image T is present between the fixing roller and the pressure roller, the peripheral speed of the fixing roller may change, which may cause a jam or an image disturbance. This can be prevented by using a direct current (DC) motor as the drive motor. Therefore, in the present invention, the use of the DC motor as the drive motor has a further effect.

When the ambient temperature at which the displacement member 15 is installed does not show the change as in the above example, means for switching the temperature condition between a higher temperature and a lower temperature with the transformation point as a boundary is required.
FIG. 1 also shows an example of the configuration in that case.

A heating heater 17 is provided inside the fixed support container 16 to heat the periphery of the displacement member 15. 14 is a heater 17
Means for controlling the heat generation of the displacement member 15 and the temperature of the displacement member 15,
You may have a cooling means which is not shown in figure as needed. When the signal 13 indicating continuous recording and fixing is input, the central control means 11 detects the temperature change from the sensor 10 and calculates the fixing failure occurrence timing due to the decrease of the surface temperature of the fixing roller 1 and Heater 1 before the time required
7 is cut off, and the temperature of the displacing member 15 is lowered from 65 ° C. or higher to 65 ° C. or lower at least at this generation time so that the solid member has a long shape. In this way, the position of the displacement member 15 is at an appropriate position. Needless to say, when the shape memory of the displacement member is reversed, the temperature condition is also reversed. However, it is preferable to determine the position of the displacing member and the ambient conditions so that the temperature control means 14 and the heater 17 are not provided and a simple structure can be obtained.

FIG. 2 shows an essential part of an example of the pressure control means using a cam mechanism instead of the displacement member 15 described above, but it is assumed that the configuration shown in FIG. 1 is used for other configurations. The cam 18 has an engaging portion 18b that is a short distance from the center of rotation 19 and an engaging portion 18a that is a long distance from the rotational center 19 through a rotation angle of 180 degrees, and when displacement is required by the driving means 20, the surface of the fixing roller is formed. It is rotated according to the temperature. When the fixing roller 1 indicates the normal fixing temperature, the engaging portion 18b is brought into contact with the stay,
When the temperature is dangerous, the engaging portion 18a may be controlled to abut on the stay.

Here, a conventional problem will be briefly described with reference to FIGS. 3 to 5 in order to clarify the advantages of the present invention.

FIG. 3 shows the surface temperatures of the fixing roller and the pressure roller,
It is represented for the period from the start of heating to the fixing process. FIG. 4 shows the overall change of the embodiment of FIG. 1 for compensating for the deterioration of the fixing property during continuous copying by changing the surface temperature of the fixing roller and the temperature of the shape memory alloy displacement member with respect to the number of copies and the nip width of the fixing roller and the pressure roller. It is a representation. FIG. 5 is a relative comparison diagram of a conventional fixing property change and the present invention to show the effect of the present invention.

Currently, we are aiming to save energy, especially for medium- and high-speed machines. Therefore, the power consumption of the fixing device is designed to be reduced as much as possible. Therefore, when continuous sheet feeding is performed, the fixing roller surface temperature T cannot be maintained even if the fixing heater is continuously turned on during that period, and the fixing temperature decreases as shown in FIG. The fixability at that time deteriorates as shown by the broken line curve in FIG. This fixability is a relative evaluation value when the image after fixing is viewed as a weight ratio before and after rubbing with paper. If the fixability is 0.8 or less and the fixing is defective,
Conventionally, fixing failure occurs in about 10 to 30 sheets, though it depends on the set temperature and the fixing speed.

Briefly, the fixing property depends on the surface temperature of the fixing roller pair and the pressure contact force and pressure contact width between the roller pair.

Here, the pressure contact width between the roller pair will be examined. In general, when one surface of the pair of fixing rollers is a rubber surface, the pressure contact width when the rubber layer is sufficiently heated and warmed in a normal state is used as a measure of fixability. However, in a state where the rubber layer is not sufficiently warmed up, in particular, the pressure contact width immediately after weight up is narrower than the set standard value. In such a case, if the continuous paper feeding is performed, the surface temperature of the fixing roller is drastically lowered, and accordingly, the fixing property is largely lowered. Such a problem occurs within a short time (about 30 minutes) after the power is turned on, and the pressure roller is not sufficiently warmed up, so that the nip width is narrow at this point. Therefore, in the case where the fixing property is insufficient in practice in the above continuous paper feeding state, it is preferable to increase the pressing force between the roller pair and widen the roller nip width. In particular, during the above short time, the roller deformation or the like does not occur even if the applied pressure is increased, which is preferable.

When continuously viewed, the temperature of the fixing roller pair non-sheet passing area portion or the temperature of the instrument in the paper conveyance path of the paper passing through the fixing roller pair rises. For example, a handle of a paper discharge port, a paper discharge tray, or the like. Except for those mentioned above, the temperature of the appliance, device or its ambient temperature is lowered. This is because the wind is generated inside the machine due to the rotation of the fixing roller pair and the operation of other devices during the paper passing. Alternatively, this is because the exhaust heat fan 22 for preventing the temperature rise inside the machine operates to generate air inside the machine, and the temperature of the apparatus and its atmosphere are lowered. As shown in FIG. 4, continuous copying was started in the morning, the ambient temperature of the shape memory alloy displacement member 15 decreased, and a certain specified temperature (transformation point)
When lowered, the displacement member 15 expands and pushes up the stay 9. As a result, the pressure between the pair of fixing rollers increases and the pressure contact width increases. Therefore, even if the surface temperature of the fixing roller is lowered by continuous copying in the morning, the nip width is increased by the above configuration, and the deterioration of the fixing property can be prevented.

Ti-Ni, Ag-Cd, Au-cd, etc. can be used as the shape memory alloy. The shape memory alloy is not limited to those described above, and any alloy capable of undergoing phase transformation within 0 to 15 ° C may be used. Since the shape memory alloy is bidirectional, it can be used repeatedly.

A specific example will be described below (see FIG. 4).

The surface temperature of the fixing roller is 185 ° C and the nip width of 7.0mm in the morning is continuously copied. Phase transformation occurs when the temperature of the Ti-Ni alloy becomes lower than 68 ° C. The nip width is increased to 8.0mm.

The fixability at this time is shown by the solid curve in FIG. As is clear from this figure, even if continuous copying is performed, good fixing properties can be obtained.

As described above, according to the present invention, it is possible to reliably prevent defective fixing and obtain a stable fixed image. The total amount of pressurization of the present invention means a pressure contact width or a pressure per unit area, and more preferably both.

In the above embodiment, the fixing roller is directly heated and the pressure roller is indirectly heated. However, the present invention includes a method of directly heating both rollers and a heating method opposite to the above embodiment. Therefore, the shortage of the heating amount is compensated by the total amount of pressurization, the quick response is excellent, and the fixing failure is surely prevented with almost no power consumption. The material of the roller pair of the present invention may be either resin or rubber.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an embodiment of the present invention, FIG. 2 is an explanatory view of essential parts of another embodiment in which the pressure control of the embodiment of FIG. 1 is changed, and FIG. 3 is a fixing roller and a pressure roller, respectively. FIG. 4 is a change diagram showing the surface temperature of the sheet against the period from the start of heating to the fixing process.
FIG. 5 is a change diagram showing the overall change of the embodiment by changing the surface temperature of the fixing roller and the temperature of the shape memory alloy displacement member with respect to the number of copies, and the nip width between the fixing roller and the pressure roller.
The figure is a relative comparison diagram of the conventional fixing change and the present invention for showing the effect of the present invention. Reference numeral 1 is a fixing roller, 4 is a pressure roller, 9 is a stay, 10 is a contact type sensor, 11 is a central control means, 12 is an energization control, 13 is a signal indicating continuous recording and fixing, 14 is a temperature control means, and 15 is a displacement. Member, 18 is a cam, 22 is a fan, 25
Is a drive motor and H is a heater.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-79976 (JP, A) JP-A-57-14866 (JP, A) JP-A-58-126558 (P, A) JP-A-57- 169777 (P, A) JP 59-45478 (P, A) JP 61-20074 (P, A) JP 58-150985 (P, A) JP 54-92749 (P, A) Actual Open Sho 59-89364 (JP, U) Actual Open Sho 61-27157 (JP, U)

Claims (1)

[Claims] 1. A heating device comprising: a fixing roller pair; heating means for heating one of the fixing roller pair; a temperature detecting member for detecting a surface temperature of the fixing roller; and pressing means for pressing the fixing roller pair. The fixing device includes a shape memory alloy provided in the pressing means, a heater for heating the shape memory alloy, and a control means for controlling energization of the heater according to the temperature detected by the temperature detection member. The heating and fixing device is characterized in that the pressure applied between the pair of fixing rollers can be changed by controlling the energization of the heater.