JP2002175872A - Heating body, heating-fixing device and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent toners at a level which cannot be seen (covered toners), which cannot be fixed on recording materials being transferred, accumulated and stuck on an end part of a pressure roller from a fixing roller or a film, and causing stains on images or causing the recording materials to be wound on the pressure roller, while it is difficult to fix covered toners at an end part (margin part) of the recording materials having the maximum width capable of passing, due to the differences in heating/heat radiation situations and due to the differences in bearing pressure at the central part and the end part. SOLUTION: In the present invention, heat capacity and also a calorific value are set so as to become larger at the end part than at those at the central part of resistor exothermic body pattern in a direction orthogonal to the advancing direction of the recording materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element for heating a recording material in order to improve the surface properties of the recording material, such as wrinkling and polishing, and to use the heating element on a recording material as a heat source. The present invention relates to a heat fixing device that heats and fixes a formed unfixed toner image to a recording material, and an image forming apparatus to which the heat fixing device is applied, such as an electrophotographic copying machine and a laser beam printer.

[0002]

2. Description of the Related Art As a conventional heat fixing device, a heat roller type and an on-demand type are known. The heat roller method uses a recording material in a press nip (fixing nip) between a heating roller (fixing roller) maintained at a predetermined heating temperature by a built-in heat source such as a halogen heater and an elastic pressing roller pressed against the heating roller. Is introduced and conveyed, whereby the unfixed toner image on the recording material surface is heated and fixed on the recording material surface by the heat of the heating roller.

[0003] Of the above-mentioned fixing roller and pressure roller, the fixing roller which comes into contact with the surface of the recording material is a cylindrical roller whose surface is made of a material having good releasability. The unfixed toner image on the recording material is heated by the heater. On the other hand, the pressure roller in contact with the back surface of the recording material is configured by providing an elastic layer on a cored bar, and applies an appropriate pressure to the toner layer.

The on-demand type heat fixing device eliminates the disadvantages of the heat roller type with large energy loss and enables quick start and power saving. This on-demand type heat fixing device uses a heater such as ceramic and a thin film such as polyimide as a substitute for the halogen heater and the fixing roller in the heat roller system to reduce the heat capacity. This solves the problem of heat loss.

[0005] In such an on-demand type heat fixing device, since the heat capacity is small and the temperature responsiveness is good, it is not necessary to preheat the heat fixing device, and fine temperature control is possible. 0FF for energizing the fixing device
You can now.

[0006]

However, the above-mentioned 2)
In any of the two fixing methods, unevenness occurs in the balance between heat generation and heat radiation in a direction perpendicular to the recording material conveyance direction of the heat fixing device (hereinafter referred to as the longitudinal direction), and the longitudinal distribution of the thermal equilibrium temperature is not constant. More specifically, since the ambient temperature is lower at both ends during operation of the apparatus than at the center, the rate of heat radiation at both ends is greater than at the center, and the heating element and the pressure roller The thermal equilibrium temperature of the pressure contact portion is high at the center and low at both ends. In addition, the temporal change of the temperature drop after the operation of the apparatus is different between the center and the end. Further, near the end of the heat fixing device, the pressure contact force between the heating body and the pressure roller was reduced.

As described above, the difference between the heating / radiating conditions at the center and the end of the heat fixing device, the difference in the surface pressure, and the recent miniaturization design of the device are prompt. In addition, it has been difficult to fix an invisible level of toner (fogging toner) from a fixing roller or a film to the recording material at an end portion (margin portion) of the maximum width recording material that can pass. For this reason, the fog toner that cannot be fixed on the recording material is eventually transferred from the fixing roller or the film onto the end of the pressure roller, and adheres. Then, there is a problem that the fogging toner is subsequently peeled off and appears as an image stain, or the recording material is wound around the pressure roller by the attraction force of the fused fogging toner.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and has been made to reduce the temperature difference in the direction (longitudinal direction) perpendicular to the recording material conveyance direction and to reduce the temperature of the recording material. By increasing the relative pressing force at the left and right ends with respect to the central part, heatability of the entire length is ensured, and by increasing the heat capacity of the ends of the heating body, the heating element that suppresses heat radiation at the ends of the heating element The purpose is to gain.

Further, by using the heating element as a heat source, it is possible to suppress the occurrence of toner stains on the pressure roller and toner grain stains on the recording material due to poor fixing of the fog toner. The aim is to obtain a device.

It is another object of the present invention to provide an image forming apparatus capable of forming a high-quality image free from toner contamination by applying the heat fixing device.

[0011]

According to the present invention, there is provided a heating element, a heat fixing device, and an image forming apparatus having the following constitution.

(1) A heating element comprising a resistance heating element pattern and a power supply electrode pattern formed on one side of a substrate, and a surface protective layer covering the resistance heating element pattern.
A heating element characterized in that both the heat capacity and the amount of heat generated at the end portion of the resistance heating element pattern in the direction orthogonal to the traveling direction of the recording material are larger at the end than at the center.

(2) The film thickness of the surface protective layer is maximum at a portion corresponding to both ends of the maximum width recording material that can pass, and thinner at a center portion than at an end portion. Heating body.

(3) The film thickness of the surface protective layer is constant in the longitudinal direction, and a portion corresponding to both ends of the maximum width recording material that can pass is provided on the substrate surface opposite to the surface on which the resistance heating element pattern is formed. (1) A thickened portion is formed.
The heating element according to the above.

(4) Any one of (1) to (3)
A film supporting member that holds a heating body according to the above and supports a film so as to move along the heating body, and a pressing member that presses the film against the heating body and sandwiches and conveys a recording material together with the film. A heat fixing device, comprising:

(5) In the heat fixing device described in (4), after the pressing portion is heated to a temperature equal to or higher than the melting point of the toner while the driving is stopped at the end of the fixing operation, and is driven in the non-heated state at the start of the next fixing operation. A heating fixing device for starting a heating driving operation.

(6) An image forming means having an image forming means for forming and carrying an unfixed toner image on a recording material, and a heat fixing means for heating and fixing the unfixed toner image formed and carried on the recording material to the recording material. In the image forming apparatus, the heat fixing unit is the heat fixing device described in (4) or (5).

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic plan view of one end side (near an end on a heating surface side) of a heating body 10 according to the present invention, and FIG. ). The heater 10 includes a heater substrate 12 and the heater substrate 1.
2 and 13a and 13b, which are formed on one side, and the resistance heating element patterns 13a and 13b.
3b, a surface protection layer 11 coated with 3b, power supply electrode patterns 31 and 32 for the resistance heating element patterns 13a and 13b, and the like.

The heater substrate 12 has a horizontally long and thin shape whose longitudinal direction is perpendicular to the conveying / moving direction A of the recording material P. For example, the length is 270 mm and the width is 7.78 mm.
A ceramic substrate of 0.635 mm in thickness, such as alumina, having heat resistance, electrical insulation, and low heat capacity.

The surface protective layer 11 is made of a resistance heating element 13a.1
3b, it is necessary to use a glass film excellent in smoothness, heat resistance, electrical insulation, and heat conductivity because it is necessary to smoothly slide the inner surface of the heat resistant film 15 described later.

For example, in the case where the LTR width is the maximum width that can pass, as shown in FIG. 2, the thickness of the heating element protection layer 11 near the end of the heating element is larger than the inside thereof. Here, as an example, the end portion film thickness Ds is 75 μm,
The thickness Dc on the inner side is set to 50 μm, and a gradient is gradually provided at the boundary. The value of the end portion film thickness Ds is not limited to this, and 10 μm ≦ Ds−Dc ≦ 200.
What is necessary is just to form so as to satisfy μm.

Also, as shown in FIG. 1, by setting the partial resistances of the resistance heating elements 13a and 13b in the thick portion to be higher than those in the other portions, the amount of heat generated at the end portion is smaller than that at the center portion. Let me do more. Here, the heat value at the center is set to 1 and the heat value at the end is set to 1.2. If the value of the calorific value at the end is too large, stress is accumulated in the heating element 10 itself, so that it is desirable that the calorific value does not exceed 1,5 times the calorific value at the central portion. Further, the longitudinal length L of the portion where the film thickness is increased and the calorific value is increased is set to 10 mm here. This length L is assumed to cover the margin of the maximum sheet passing width. The resistance heating elements 13a and 13b and the heating element protective layer 11 are formed by screen printing on a ceramic substrate in a paste form, and sequentially fired. The heating element 10 described above can be formed by adjusting the shape and thickness of the screen and the number of coating and firing steps.

FIG. 3 is a schematic cross-sectional view of a model configuration of a heating and fixing apparatus based on a film heating method using the heating element 10 of the present invention shown in FIGS. 1 and 2 as a heat source. The heat fixing device of the present embodiment is of a pressure roller driving type, and presses the film supporting means 16 holding the heating body 10 to the pressure roller 17 with a predetermined suppression pressure via the cylindrical heat-resistant film 15. As a result, a fixing nip N is formed between the heating element 10 and the heating element 10.

A rotational force acts on the heat-resistant film due to a frictional force between the pressure roller and the outer surface of the heat-resistant film 15 due to the rotational drive of the pressure roller 17, and the heat-resistant film 15 holds the heating element 10. The outer periphery of the film supporting means 16 is rotated in the direction of arrow A (the width direction of the heating body 10). The drive motor 19 of the pressure roller 17 is controlled by the CPU 20 of the motor control means 18.

The electric heating of the heating element 10 can be appropriately controlled by the temperature control means 21. The temperature control means 21 has a temperature control element 14 (hereinafter, referred to as a “thermistor”) attached to the back surface of the heating element 10 with the side of the heating element 10 on which the heating elements 13a and 13b are formed as the heating element surface. CPU for inputting temperature information to be detected
23, and a triac 22 controlled by the CPU 23 to adjust the power supply to the heating element 10 from the power supply 24.

The heat-resistant film 15 is rotated by the rotation of the pressure roller 17, and the energization of the heating element 10 is controlled by the temperature control means 21.
0 rises to a predetermined temperature. In this elevated temperature state, the recording material P carrying the unfixed toner image T enters the fixing nip portion N between the heat-resistant film 15 and the pressure roller 17, so that the heat of the heating element 10 is reduced. Heat resistant film 15
And the unfixed toner image T is melted and thermally fixed on the recording material surface. The recording material P that has passed through the fixing nip N is conveyed after being separated from the surface of the heat-resistant film 15 by a curvature.

FIG. 5 is a diagram showing a longitudinal temperature distribution of the recording material P in the fixing nip portion N when the toner T is fixed on the recording material P having the maximum width that can be passed by using the heat fixing device according to the present embodiment. FIG. 4 schematically shows the surface pressure distribution in the fixing nip portion N in the longitudinal direction. During the operation of the fixing device, the heat radiation state around the central portion of the device and the peripheral portion of the device are different. However, since the calorific value at the edge portion is larger than that at the central portion, the recording material P is transferred to the fixing portion. The temperature distribution in the longitudinal direction when it reached was almost constant. Also, regarding the surface pressure distribution, by increasing the film thickness at the end of the heating body, the pressure loss near the end of the press contact portion is covered, so that the surface pressure becomes almost constant in the longitudinal direction, and the maximum width of the recording paper is Uniform fixability can be obtained.

FIG. 6 shows a temporal change in the temperature of the fixing nip portion N in the image forming apparatus provided with the fixing device according to the present embodiment when intermittent printing of 2 sheets / 10 minutes is continued. And the end was measured. When the heat fixing device of the present embodiment is used, the heat capacity of the longitudinal end portion is larger than that of the central portion, and the heat radiation near the end portion is suppressed, so that the temperature drop from the end of the fixing operation to the next printing is the center. It became almost equal in the part and the end. In other words, regardless of whether the heat fixing device is operating or stopped, the fixing nip portion N
Was able to substantially eliminate the temperature difference in the longitudinal direction. In other words, uniform fixing properties can be obtained over the entire maximum width recording paper regardless of the state of the heat fixing device.

As described above, as in the first embodiment, the thickness of the surface protective layer of the heating element 10 in the heat fixing device is set to the maximum thickness at the portion covering the margin of the maximum width recording paper. By adopting a configuration in which the thickness of the inner side is reduced, the difference between the central part and the end part in the longitudinal temperature distribution and the surface pressure distribution of the fixing nip does not occur at any time and when the heat fixing device is operated. It is possible to obtain a substantially uniform fixing property over the entire recording paper, and it is possible to suppress the above-described problem of toner contamination of the pressure roller due to poor fixing of fog toner and further, generation of toner particle contamination on the paper. did it. (Comparative Example) The configuration of the heat fixing device in this comparative example is the same as that of the first embodiment except for the configuration of the heating element 100 in the heat fixing device. In the configuration of the heating element 100 in this comparative example, as shown in FIGS. 7 and 8, the partial resistances of the resistance heating elements 130a and 130b applied on the ceramic substrate 120 are equal over the entire length. That is, the amount of heat generated in the longitudinal direction is constant. The thickness of the heating element protection layer 110 for protecting the resistance heating elements 130a and 130b is also equal over the entire length.

FIGS. 9 and 10 show the temperature distribution and the surface pressure distribution in the longitudinal direction, respectively, when the fixing device in this comparative example is operated to pinch and convey the maximum width recording material P that can pass. According to FIG. 9, the heat generation amount is equal in the longitudinal direction, and at the same time, with respect to the distribution of the heat radiation from the heat fixing device, the heat radiation is larger at the end portion than at the central portion in the longitudinal direction. Since a difference occurs in the temperature distribution, the temperature of the end portion of the maximum width recording material P is lower than that of the central portion in the longitudinal direction.

According to FIG. 10, in the surface pressure distribution,
At the end of the recording paper P, a decrease in surface pressure is observed. This is because the elastic force of the pressure roller 17 is weaker near the end face than at the center. Therefore, the maximum width recording paper P has insufficient fixability of the toner (fogging toner) near the left and right margins.

FIG. 11 is a graph showing the change over time in the temperature of the fixing nip portion N when the intermittent printing of 2 sheets / 10 minutes is continued in the conventional image forming apparatus having the heat fixing device in this comparative example. It was measured for the center and the edge. When the apparatus of this comparative example is used, the fixing nip N
Because the amount of heat radiation is greater at the end than at the center in the longitudinal direction, the difference in temperature drop after the end of the fixing operation as well as at the end of the fixing operation is widened between the center and the end, not only during the operation of the heat fixing device. Are also different in the temperature of the fixing nip portion N in FIG. Therefore, as the intermittent printing is continued, the temperature difference between the center portion and the end portion is generated. That is, not only is the fogging toner insufficiently fixed in the left and right margins of the maximum width recording paper at the time of the first printing, but also the end fixing property is deteriorated as the intermittent printing is continued.

As described above, when the conventional heat fixing device as in the present comparative example is used, toner fouling of the pressure roller occurs due to poor fixing of fog toner, thereby causing image fouling and recording material. Wrapping problem occurs.

(Embodiment 2) FIG. 12 is a longitudinal sectional view (near an end portion) of a heating body 10 used in a heat fixing apparatus according to Embodiment 2. The configuration of the heat fixing device in the second embodiment is the same as that of the first embodiment except for the configuration of the heating element 10 used as a heat source. The configuration of the heating element 10 according to the present embodiment is exactly the same as that of the first embodiment in that the amount of heat generated at the end is larger than that at the center.
The thickness of the heating element protection layer 11 for protecting the heating element 13b is equal over the entire length. However, the layer 30 is provided on the back surface of the ceramic substrate 12, that is, on the surface opposite to the surface on which the resistance heating elements 13a and 13b are printed, at a portion corresponding to the end of the heating element.

The layer 30 may be a film made of glass, but is desirably a member having heat resistance and elasticity such as polyimide. The thickness of the layer 30 is 10 μm or more and 200 μm.
It is desirable if it is within. If it is too small, the effect will be weak,
If it is too large, stress will be applied to the heating element itself.
By using the heating element 10 as in the second embodiment as a heat source of the heat fixing device, the same operation and effect as in the first embodiment can be obtained.

(Embodiment 3) In the third embodiment, in the heat fixing device used in the first or second embodiment, a sequence for cleaning the pressure roller 17 for each print is provided. The above-described cleaning sequence will be briefly described. At the end of the fixing operation, the fixing nip portion N is heated to a temperature equal to or higher than the melting point of the toner in the driving stop state, and is driven in the non-heating state at the start of the next fixing operation. In this embodiment, the heating temperature and the heating time, which are the parameters of the sequence, are set to 200 ° C. and 5 seconds, respectively.

According to this sequence, a very small amount of toner adhering to the surface of the pressure roller can be moved to the next recording material at an invisible level. However, when such control is performed, if the temperature condition and the surface pressure condition are different between the central portion and the end portion of the pressure roller 17, a difference occurs in the cleaning performance.

In this embodiment, Embodiment 1 or Embodiment 2
The above-mentioned cleaning performance is uniform in the longitudinal direction because there is no difference in the temperature and the surface pressure between the center and the end under any conditions. Becomes That is, by using the heat fixing device as in the present embodiment, it is possible to suppress the contamination of the pressure roller and the occurrence of various problems due to the contamination for a long time.

(Embodiment 4) FIG. 13 is a block diagram of an image forming apparatus to which the heat fixing device of the present invention is applied. FIG.
In the figure, reference numeral 51 denotes a photosensitive drum on which a photosensitive material such as OPC, amorphous Se, amorphous Si or the like is formed on a cylindrical base such as aluminum or nickel. The photosensitive drum 51 is driven to rotate in the direction of the arrow,
First, the surface is uniformly charged by a charging roller 52 as a charging device.

Next, the charged surface of the photosensitive drum 51 is irradiated with a laser beam 53 controlled to be ON or OFF in accordance with image information.
Is performed to form an electrostatic latent image. This electrostatic latent image is developed and visualized by the developing device 54. As a development method, a jumping development method, a two-component development method, or the like is used, and image exposure and reversal development are often used in combination.

The visualized unfixed toner image is transferred from the photosensitive drum 51 onto the recording material P conveyed at a predetermined timing by a transfer roller as a transfer device. Here, the sensor 58 detects the leading end of the recording material so that the image forming position of the unfixed toner image on the photosensitive drum 51 matches the writing start position of the leading end of the recording material, and adjusts the timing. The recording material P conveyed at a predetermined timing is
The photosensitive drum 51 and the transfer roller 55 are nipped and conveyed at a constant pressure. The recording material P on which the unfixed toner image is transferred
Is transported to the heat fixing device 56 according to the present invention, and the unfixed toner image is fixed on the recording material P as a permanent image by passing through the heat fixing device 56. On the other hand, the transfer residual toner remaining on the photosensitive drum 51 is removed from the surface of the photosensitive drum 51 by the cleaning device 57.

[0043]

As described above, according to the present invention,
By increasing the heat capacity, the surface pressure, and the calorific value of the end portion of the resistive heating element pattern in the direction perpendicular to the recording material traveling direction from the central portion, the temperature condition and the pressure condition are always the same as the central portion. Therefore, there is an effect that uniform heating performance can be obtained in the longitudinal direction.

Further, the thickness of the surface protective layer covering the resistive heating element pattern is set to be the maximum thickness at the end portions corresponding to the both ends of the maximum width recording material that can pass, the center portion is made thinner than the end portions, and the longitudinal end portions are formed. Since the calorific value of the part is made larger than that of the central part, the pressure condition can be made uniform in the longitudinal direction with a simple structure.

The thickness of the surface protective layer covering the resistance heating element pattern is constant in the longitudinal direction, and is opposite to the surface on which the resistance heating element pattern is formed at portions corresponding to both ends of the maximum width recording material that can pass. Because a thickened part was formed on the substrate surface of
With a simple configuration, there is an effect that the pressure condition can be made uniform in the longitudinal direction.

Further, a film supporting member for holding a heating body of the present invention and supporting a film so as to move along the heating body, and pressing the film against the heating body to sandwich and transport the recording material together with the film. With the pressure member, the fixing property at the end of the maximum width recording paper that can pass,
In particular, the present invention provides a heat fixing device capable of securing sufficient fixing property for fogging toner in a margin portion and obtaining uniform performance in a longitudinal direction even in a sequence of self-cleaning a pressure roller. There is an effect that can be done.

Further, the pressure contact portion is heated to a temperature equal to or higher than the melting point of the toner when the driving is stopped at the end of the fixing operation, and the heating driving operation is started after the non-heated driving at the start of the next fixing operation. There is an effect that contamination of the pressure roller can be prevented, and problems such as toner particle contamination on the paper and wrapping of the paper due to the contamination can be prevented.

Further, since the heat fixing device of the present invention is applied as a heat fixing means for heating and fixing an unfixed toner image on a recording material, a high quality image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of one end of a heating element according to a first embodiment.

FIG. 2 is a schematic cross-sectional view of the heating body in the longitudinal direction.

FIG. 3 is a schematic cross-sectional view of a configuration model of a heat fixing device using a heating element as a heat source according to the present invention.

FIG. 4 is a longitudinal temperature distribution diagram of a fixing nip portion when an LTR width is passed in Example 1.

FIG. 5 is a distribution diagram of a longitudinal surface pressure of a fixing nip at the time of LTR transmission paper in Example 1.

FIG. 6 is a graph showing a temporal change in nip temperature during intermittent printing using the heat fixing device according to the first exemplary embodiment.

FIG. 7 is a schematic plan view of one end of a heating element in a comparative example.

FIG. 8 is a schematic sectional view in the longitudinal direction of the heating element.

FIG. 9 is a diagram illustrating a longitudinal temperature distribution of a fixing nip portion when an LTR width is passed in a comparative example.

FIG. 10 is a view showing a distribution of a longitudinal surface pressure of a fixing nip portion when an LTR width is passed in a comparative example.

FIG. 11 is a graph showing the change over time in the nip temperature during intermittent printing using the fixing device of the comparative example.

FIG. 12 is a schematic plan view of one end of a heating element according to the second embodiment.

FIG. 13 is a schematic diagram of an image forming apparatus to which a heat fixing device using a heating element as a heat source according to the present invention is applied;

[Explanation of symbols]

Reference Signs List 10: heating element, 11: heating element surface protective layer, 12: heating element substrate, 13: resistance heating element, 13a / 13b: reciprocating resistance heating element, 14: temperature sensing element, 15: heat resistant film, 1
6 film support means, 17 pressure roller, 18 rotation control means, 19 motor, 20 CP for motor control
U, 21: temperature control means, 22: triac, 23 ...
CPU for temperature control, 30: belonging to the back end of the heating element, 51: photosensitive drum, 52: charging roller, 53: laser beam, 5
4: developing device, 55: transfer roller, 56: heat fixing device, 57: cleaning device T: toner, P: recording material, N: fixing nip portion, A: recording material conveyance direction

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H033 AA09 BA25 BB18 BB22 BB28 BB33 BE03 CA07 CA20 CA28 CA32 CA48 3K034 AA04 AA10 AA16 AA23 AA34 AA37 BB06 BB14 BC12 CA32 DA05 HA01 HA10 JA10 3K058 AA61 CE06 3K092 PP18 QA05 QB30 QB59 QB76 QC25 RF03 RF11 RF17 RF22 TT30 UA06 VV22

Claims (6)

[Claims] 1. A heating element having a resistance heating element pattern and a power supply electrode pattern formed on one surface side of a substrate, and a surface protection layer covering the resistance heating element pattern, wherein the heating element has a direction perpendicular to a traveling direction of a recording material. A heating element, wherein both the heat capacity and the amount of heat generated at an end of the resistance heating element pattern are larger than those at a center thereof. 2. The surface protection layer according to claim 1, wherein the film thickness of the surface protective layer is the maximum thickness at both ends of the maximum width recording material that can pass, and the center portion is thinner than the end portions. Heating body. 3. The film thickness of the surface protective layer is constant in the longitudinal direction, and is increased on the substrate surface opposite to the surface on which the resistive heating element pattern is formed at portions corresponding to both ends of the maximum width recording material that can pass therethrough. The heating element according to claim 1, wherein a thick portion is formed. 4. One of claims 1 to 3
A film supporting member for holding a heating body according to the above item and supporting a film so as to move along the heating body, and a pressing member for pressing the film against the heating body and holding and conveying a recording material together with the film. A heat fixing device, comprising: 5. The heat fixing device according to claim 4, wherein
A heating and fixing device characterized in that the press-contact portion is heated to a temperature equal to or higher than the melting point of the toner when the driving operation is stopped at the end of the fixing operation, and is driven in the non-heating state at the start of the next fixing operation, and then the heating driving operation is started. 6. An image forming apparatus comprising: an image forming unit for forming and supporting an unfixed toner image on a recording material; and a heat fixing unit for heating and fixing the unfixed toner image formed and supported on the recording material to the recording material. 6. The image forming apparatus according to claim 1, wherein the heat fixing unit is the heat fixing device according to claim 4.