JPH10301427A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device where low temperature offsetting caused by the temperature lowering of a center at a printing time is prevented by suppressing overshoot at a pre-rotating time to a minimum. SOLUTION: A pressure roller 3 is arranged so as to be brought into press- contact with a fixing roller 2 having a long straight part A, and a halogen heater 4 is provided at the inside of the fixing roller 2, and also a thermistor 6 detecting the surface temperature of the fixing roller 2 is made to abut on the end part of the fixing roller 2 in a longitudinal direction. The pressure roller 3 is formed so as to make the length B of an elastic layer which is an abutting part on the fixing roller 2 longer than that of the straight part A of the fixing roller 2 so as to constitute the fixing device 1. When the fixing device 1 starts forward multiple rotation, the long pressure roller 3 effectively takes the heat of the fixing roller 2 so as to prevent the overshoot, and temperature adjustment is excellently executed by taking the heat of the end part of the fixing roller 2 during continuous printing, so that the occurrence of the low temperature offsetting is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus using an electrophotographic technique such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art As the network environment using computers has become widespread in recent years and the communication performance of computers, printers, and faxes has improved, it has been desired that image forming apparatuses can print a wide variety of papers in large quantities. It has become.

Conventionally, a heat roller fixing device has been widely used as a heat fixing device in an image forming apparatus for transferring a toner image onto a transfer material such as paper and heating and pressing the toner image to obtain a permanent image. The transfer material is pressed and melted and fixed between the roller and the pressure roller. This type of fixing device has advantages that it can be used widely from low-speed devices to high-speed devices, and that it can cope with a longer life.

FIG. 6 is a schematic diagram showing an example of the above-mentioned conventional fixing device. The fixing roller 10 on the image surface side of the heat roller fixing device is placed on a metal pipe 110 having a straight portion of a predetermined length on a metal pipe 110 having a length of 30 to 100 μm in order to enhance releasability.
The coating layer 120 is formed by coating a fluororesin or applying a primer to cover a fluororesin tube. As the fluororesin used here, for example, PFA and PTFE are used.

[0005] A pressing roller 20 for pressing the surface of the fixing roller 10 having the above-described structure toward the fixing roller 10 from the back side of the transfer material covers a metal core 210 with a rubber layer 220 as an elastic member. Coating layer 2 whose surface is coated with the above fluororesin or with a fluorine resin tube
30 are provided. Normally, pressure roller 2
The length of the rubber layer 220 (elastic member) is set so that the pressing force is uniformly applied in the longitudinal direction of the fixing roller 10.
The fixing roller 10 is formed to be shorter than the length of the straight portion of the fixing roller 10 in contact therewith.

The fixing roller 10 is provided with, for example, one or more halogen heaters 30 as heat sources inside the fixing roller 10 along the rotation axis direction of the fixing roller 10. A thermistor 50 for detecting the surface temperature of the fixing roller is in contact with the end, and the thermistor 50 is connected to a temperature control circuit (not shown). Is controlled so that the surface temperature of the fixing roller 10 can be controlled to a desired constant temperature.

Here, the contact position of the thermistor 50 is preferably set at the center, for example, in the case of center reference sheet passing in order to detect a temperature change of the fixing roller 10 due to sheet passing. However, in the case of a fixing device without a cleaning member, if the thermistor is installed in the image area, toner adheres to the thermistor, causing a flaw of the fixing roller and causing image defects. Therefore, in order to satisfy high-speed and long-life of the apparatus, it is preferable to provide the apparatus in an end non-sheet passing area which does not affect an image. Therefore, the contact position of the thermistor is in the non-sheet passing area at the end, but is preferably in the sheet passing area of the maximum size sheet so that a temperature change due to sheet passing can be detected.

In the above-described fixing device, the time (start-up time) until the fixing device enters the standby state depends on the heat capacity of the fixing roller and the rated output of the heater. In recent years, the start-up time tends to be shortened due to an increase in user needs. However, since the rated output of the heater must be used within the limit of the power required for the entire image forming apparatus, it cannot be excessively increased. Therefore, means for reducing the heat capacity by reducing the thickness of the fixing roller and shortening the startup time are taken. In this case, the metal pipe constituting the fixing roller is often formed of iron or aluminum having a thickness of 3 mm or less.

[0009]

However, in the case where a thin fixing roller is used as described above, a case where a thermistor is provided at the end non-sheet passing area of the fixing roller to control the temperature of one halogen heater. However, the following problem occurs.

A description will be given using a one-component magnetic toner having a temperature range of 170 to 200.degree. C., which shows good fixing, as a toner used for image formation.
If the fixing is performed at a lower temperature, a low-temperature offset occurs, and if the fixing is performed at a temperature exceeding 200 ° C., a high-temperature offset occurs.

FIG. 7 shows the temperature change of the fixing roller surface due to the continuous printing after the power is turned on, and the temperature change of the fixing roller surface when the image forming apparatus immediately starts the printing operation at the same time as the power is turned on will be described. . When the power of the image forming apparatus is turned on, the fixing device warms up (starts up), and activates the halogen heater to increase the surface temperature of the fixing roller. At this time, the rate of temperature rise is higher at the center of the fixing roller than at the end (the position where the thermistor is provided). When the surface temperature of the fixing roller rises and the temperature detected by the thermistor reaches the pre-multi-rotation start temperature S, the fixing roller starts preparing for multi-rotation and prepares for printing while increasing the temperature of the pressure roller that is driven and rotated. When the temperature detected by the thermistor reaches the pre-multi-rotation start temperature S, the temperature at the center is ΔΔ lower than the pre-multi-rotation start temperature S.
Only high temperature.

At the point when the thermistor position reaches the pre-multi-rotation end temperature F, if a print signal is input, the printer enters the printing state as it is. If no print signal is input, the pre-multi-rotation is stopped and the standby state is set. State. As shown in FIG. 7, in the conventional fixing device, when the printing operation is started immediately after the power is turned on, when the thermistor position at the end of the fixing roller reaches the printable temperature,
The temperature at the center is much higher than the temperature at the thermistor position (hereinafter referred to as overshoot), and if printing is performed in that state, a high-temperature offset of the toner occurs (FIG. 7).
(The area indicated by the oblique line X).

The high-temperature offset is a phenomenon in which the toner image on the paper is peeled off and adhered to the fixing roller during paper passing, and an offset is generated at a position corresponding to the length of the fixing roller cycle. This is because as the thickness of the fixing roller becomes thinner, the difference in the rate of temperature rise between the central portion and the end portion at the time of warm-up increases, so that the amount of overshoot tends to increase. Conversely, if the heater is controlled so as not to cause overshoot, when one sheet of paper reaches the fixing device, the temperature at both ends of the paper is low, and a low-temperature offset occurs. The above is the time when the power of the image forming apparatus is turned on. However, even when printing is performed from the standby state, overshoot occurs for the same reason.

Further, if the thermistor is brought into contact with the end of the maximum size paper to be passed through the fixing device so that the abrasion does not affect the image, if the paper is continuously passed, the paper is not passed. Since the temperature at the edge where the temperature does not drop so much can secure the printing temperature, the heater is controlled so that the fixing roller is not heated so much. The temperature drops below (center temperature drop), and in some cases, the fixing temperature cannot be secured. As described above, during continuous paper feeding, the temperature of the image area cannot be controlled well, and there is a problem that a low-temperature offset occurs due to the temperature drop (the area indicated by the oblique line Y in FIG. 7). This central temperature drop is more likely to occur as the paper size decreases, that is, as the paper edge moves away from the thermistor contact position.

Accordingly, the present invention provides a fixing device that detects the temperature in the non-sheet passing area at the end and controls the lighting of the heater, thereby minimizing the overshoot during the pre-rotation and lowering the central temperature during printing. It is an object of the present invention to provide a fixing device which can prevent a low-temperature offset due to the above-described method and can obtain the above-mentioned effect even in a heat fixing unit having a small heat capacity.

[0016]

According to a first aspect of the present invention, an object of the present invention is to provide a thermal fixing device having a long straight portion and fixing a toner image carried on the surface of a transfer material by a nip portion thereof. Means, a pressurizing means having a contact portion abutting on the straight portion and arranged to press against the heat fixing means, a heating means for heating the heat fixing means, and a surface temperature of the heat fixing means. In a fixing device provided with a temperature detecting means for detecting a temperature of the heat fixing means by contacting at a longitudinal end of the heat fixing means for controlling, a length of a contact portion of the pressing means to the heat fixing means is adjusted. Is the same as the length of the longitudinal straight portion of the heat fixing means,
Or more.

Further, according to the second aspect of the present invention, the above object is achieved by using an energized heating element as a heating means, and controlling the light distribution L ₀ at the center of the heat fixing means by the energized heating element and the temperature detecting means. the ratio of the light distribution L _th at the installation position, 0.8 <L _th
/ L ₀ <1.1 is achieved.

According to a third aspect of the present invention, the object is to use a metal pipe having a heating means therein as the heat fixing means of the first and second aspects, Is achieved by making the wall thickness of 3 mm or less.

Further, according to the fourth invention of the present application, the above object is achieved by using a film member having a heating means therein as the heat fixing means of the first and second inventions. You.

That is, according to the first aspect of the present invention, the pressing unit is formed such that the length of the contact portion of the pressing unit is the same as the length of the straight portion of the heat fixing unit. Or, forming the pressing means so that the length of the contact portion of the pressing means is longer than the length of the straight portion of the heat fixing means,
During the pre-rotation, the pressurizing means longer than the straight part of the heat fixing means deprives the heat of the heat fixing means, thereby reducing the variation in the surface temperature of the heat fixing means to prevent the occurrence of high-temperature offset and the heat during continuous printing. By removing heat at the end of the fixing unit, it is possible to prevent the occurrence of low-temperature offset due to a decrease in temperature at the center of the heat fixing unit.

Further, according to the second aspect of the present invention, the light distribution L ₀ at the center of the heat fixing means and the light distribution L at the position where the temperature detecting means is installed by the energizing heating element for heating the heat fixing means. ratio of _th is, by adjusting the light distribution of 0.8 <L _th / L ₀ <a range of 1.1 as the energization heater, the temperature rise of the center and the ends of the thermal fixing means In addition to reducing the difference in rate and suppressing overshoot during pre-rotation, it effectively prevents the occurrence of high-temperature offset, and also allows heat removal at the end of the thermal fixing means during continuous printing so that A low-temperature offset caused by a temperature drop at the center can be effectively prevented.

Further, according to the third invention of the present application, a metal pipe having a thickness of 3 mm provided with a heating means therein is used as the heat fixing means, and a pressing means is applied to the heat fixing means. The length of the contact portion is configured to be equal to or longer than the length of the straight portion in the longitudinal direction of the thermal fixing unit, or the light distribution L ₀ at the center of the thermal fixing unit by the current-generating heating element. and the ratio of the light distribution L _th of a temperature sensing means mounting position, by a range of _{0.8 <L th / L 0 <} 1.1, even in the fixing device using a low thermal fixing unit heat capacity Similarly to the first or second aspect, the difference in the rate of temperature rise between the central portion and the end portion of the heat fixing unit is reduced to suppress overshoot during pre-rotation, and the end portion of the heat fixing unit during continuous printing. To reduce the temperature at the center of the heat fixing means. It is possible to prevent the occurrence of low-temperature offset.

Further, according to the fourth aspect of the present invention, as the heat fixing means, a film member provided with a heating means therein is used, and the length of the abutting portion of the pressing means to the heat fixing means is used. Saga, either the same as the length of the longitudinal straight portion of the heat fixing means, or or configure it to above becomes light distribution L ₀ and the temperature detecting means at the central portion of the thermal fixing means by energization heater the ratio of the light distribution Lth at the installation position, 0.8 <by the scope of the L _th / L ₀ <1.1, the first even in the fixing device using a low thermal fixing unit heat capacity of the film member Alternatively, similarly to the second invention, the difference in the rate of temperature rise between the central portion and the end portion of the heat fixing means is reduced to suppress overshoot at the time of pre-rotation, and the end portion of the heat fixing means during continuous printing is reduced. So that heat can be removed at the center of the heat fixing means. It is possible to prevent the occurrence of low-temperature offset due to temperature decrease.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. Note that the overall operation of the fixing device of the present embodiment is substantially the same as that described in the conventional example, and the description of the overlapping portions will be omitted.

FIG. 1 is a longitudinal sectional view of the fixing device of the present embodiment, showing the positional relationship between the paper passing through the heater and the light distribution of the heater. FIG. 2 is a longitudinal sectional view of the fixing device of the present embodiment. Next, the outline and effects of the fixing device will be described. This fixing device uses, for example, paper up to A3 size as a transfer material,
The paper is transported on the basis of the center, an image is formed on the paper with one-component magnetic toner, and the image is fixed by a fixing device. The transfer material is not limited to paper.

A fixing device 1 shown in FIG. 2 has a long straight portion A and a fixing roller 2 provided as a heat fixing means for fixing a toner image carried on the surface of a transfer material 6 by a nip portion N thereof. A pressure roller 3 provided as pressure means arranged to be in pressure contact with the fixing roller 2, and a halogen which is an energizing heating element provided in the fixing roller 2 as a heating means for heating the fixing roller 2. It comprises a heater 4 and a thermistor 6 which is in contact with the longitudinal end of the fixing roller 2 to control the surface temperature of the fixing roller 2 and is provided as temperature detecting means for detecting the surface temperature.

The fixing roller 2 for fusing and fixing the toner image on the transfer material 7 has, for example, an outer diameter of 30 mm and a thickness of 0.7 m.
m on a surface of a substantially pipe-shaped aluminum core 11 having a thickness of 3 mm.
It is formed by covering a 0 μm PFA tube 12. As shown in FIG. 1, the length of the straight portion A of the fixing roller 2 is, for example, 300 mm, and a sheet (transfer material) up to A3 (297 mm wide) size to be passed.
The upper toner image can be sufficiently fixed. The core metal is not limited to aluminum, and iron or the like may be used.

The pressure roller 3 pressed against the fixing roller 2 is formed, for example, on the surface of an iron core bar 21 having an outer diameter of 15 mm as an elastic layer which is a contact portion that contacts the straight portion of the fixing roller 2. It is formed by covering the silicon rubber 22 with a thickness of 6 mm and covering the outer periphery of the silicone rubber 22 with a PFA tube 23. Pressing means (not shown)
As a result, the fixing nip N through which the transfer material passes can be formed by being pressed against the fixing roller 2 side. As shown in FIG. 1, the length B in the longitudinal direction of the silicone rubber 22 which is the contact portion (elastic layer) of the pressure roller 3 and the PFA tube thereon is 320 mm, and the straight portion A of the fixing roller 2 is By making the length longer than the length, heat is removed from the thermistor position during continuous printing, so that the central temperature can be prevented from lowering. Note that the length B of the pressing roller 3 in the longitudinal direction may be the same value as the length of the straight portion A of the fixing roller 2. Further, the fixing roller 2 and the pressure roller 3 are connected to a driving unit (not shown), and each can be rotated in the direction of the arrow in FIG. 2 by the operation of the driving unit.

Inside the fixing roller 2, as a heating means for heating the fixing roller 2 from the inside, for example, a rated output 10
A 00W halogen heater 4 is provided. Also,
As shown in FIG. 1, the thermistor 6 in contact with the fixing roller 2 is disposed at an end of the straight portion A of the fixing roller 2 and outside the A3-size sheet passing area. The surface temperature of the roller 2 is detected, a detection signal is transmitted to a control circuit (not shown), and the control circuit controls the lighting of the halogen heater 4 based on the detected temperature so that the surface temperature of the fixing roller 2 can be adjusted. It has become.
Since the abutment position of the thermistor 6 is located outside the paper passing area of the A3-size paper, the toner on the paper does not adhere to the thermistor.

When the image forming apparatus receives a print signal while the fixing roller 2 is in a standby state, the fixing roller 2 is driven by the halogen heater 4 until the temperature detected by the thermistor 6 reaches 180 ° C. Is heated, and the fixing roller 2 and the pressure roller 3 are rotated (pre-rotated) in a predetermined direction by a driving unit, so that the fixing roller 2 is rotated.
The fixing roller 2 and the pressure roller 3 are heated to a predetermined temperature by heating the pressure roller that is driven and rotated by the heat of the fixing roller 2. afterwards,
The transfer material 7 on which the unfixed toner 8 is placed is guided by the fixing inlet guide 5 which is arranged on the upstream side in the transport direction of the transfer material 7 and guides the transfer material 7 to the fixing nip N such that the leading end thereof contacts the fixing roller 2. Then, the toner is pressed and heated in the fixing nip N to perform permanent fixing of the toner.

Here, a one-component magnetic toner is used as the toner for forming an image on the transfer material 7, and the one-component magnetic toner has a temperature range of 170 to 200.degree.
Was used. This toner causes low-temperature offset when the fixing roller temperature falls below 170 ° C.
If the temperature exceeds ℃, a high-temperature offset occurs.

In the fixing device of this embodiment, the pressure roller 3
Since the length B of the elastic layer of the fixing roller 2 is longer than the length A of the straight portion of the fixing roller 2, as shown in FIG. 3
Removes heat from the fixing roller 2 in a well-balanced manner, so that overshoot can be prevented when the power is turned on or when the apparatus is started up from the standby state.
During continuous printing rotation, heat is removed from the fixing roller 2 at the position where the thermistor 6 is installed, and the difference between the temperature of the paper passing portion of the fixing roller 2 and the temperature of the end of the fixing roller 2 does not increase. , The temperature at the center of the fixing roller 2 during continuous printing does not become too low, and low-temperature offset can be prevented.

Further, it has been found that by setting the light distribution of the halogen heater 4 as follows, it is possible to effectively prevent the overshoot during the pre-rotation and the temperature drop at the center during the continuous printing. That is, shown in FIG. 1, the intensity of the L _th light distribution at the thermistor location of the fixing roller, when the light distribution of the intensity at the center portion and the L _0, the value obtained by dividing the L ₀ in L _th, The light distribution of the halogen heater 4 is adjusted so that 0.8 <L _th / L ₀ <1.1.
As a result, the temperature is detected in the end non-sheet passing area,
In the fixing device that controls the lighting of the heater, the occurrence of high-temperature offset and low-temperature offset can be more effectively prevented.

In this embodiment, the thickness of the aluminum core is set to 0.7 mm. However, the use of an aluminum core having a thickness of 0.3 mm or less effectively reduces the occurrence of high-temperature offset and low-temperature offset. The effect that it can be prevented can be obtained.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. In the present embodiment, a plurality of halogen heaters as the heating means of the first embodiment are provided. In addition, a plurality of halogen heaters in the fixing roller are provided, and other members of the fixing device, for example, the length of the elastic layer of the pressure roller is changed to a straight length of the fixing roller, except that the temperature of the fixing roller is adjusted by the heaters. The portions are formed longer than the length of the portion, and the operation of each member is the same as in the first embodiment.

As shown in FIG. 4 (a), the light distribution of the halogen heater used in the present embodiment is, for example, a main heater which is convex in the width of the central small size paper (for example, A4 vertical width). 9a (400W) and a sub-heater 9b (400W) convex at both ends. As described above, the advantage of using two heaters is that a temperature distribution suitable for various paper types can be formed by changing the lighting ratio of the main heater and the sub-heater depending on the paper size and paper type. In particular, in the case of a high-speed machine, the temperature range of the high-temperature offset and the low-temperature offset tends to shrink, and in the case of the high-speed machine, it is necessary to finely control the temperature using a plurality of heaters. When a plurality of heaters are used, it is possible to control the temperature difference between the end portion and the center at the time of startup by using such a feature.

In this embodiment, the length of the elastic layer of the pressure roller is formed to be longer than the length of the straight portion of the fixing roller, and as shown in FIG. In the above, when the light distribution of the main heater and the sub-heater are superimposed, the light distribution at the center is L ₀ , and the light distribution at the end thermistor position is L _th, and the value of the ratio between them is 0.8. By adjusting the superimposed light distribution of the two heaters so as to fall within the range of <L _th / L ₀ <1.1, it is possible to more effectively prevent overshoot and a decrease in the central temperature during continuous printing.

On the other hand, when the length of the pressure roller is shorter than the length of the straight portion of the fixing roller as in the conventional case, when the temperature is controlled at the end of the fixing roller, the combination of the main heater and the sub heater is used. In some cases, overshoot or a decrease in the central temperature during continuous printing occurs.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. In the present embodiment, in a film heating type fixing device using a film member as a heat fixing unit, the length of the contact portion of the pressing unit is the same as the length of the straight portion of the heat fixing unit, or It is formed as described above.

The heat fixing means of the fixing device 400 using a film member is a heat-resistant film 500 which is endless belt-shaped and which is long in the direction perpendicular to the transfer material conveying direction. The heating element 520 is covered with the film guide member (stay) 530 in such a manner that the director has a margin, and is in contact with the inner peripheral surface of the heat-resistant film 500 in the film guide member 530. Is provided. The heat-resistant film 50
0 has a film thickness of 100 μm or less in order to reduce the heat capacity and perform a quick start.
Durable polyimide, polyamide, PEEK, PE
Single layer film such as S or PTFE, PFA, FEP
For example, a composite layer film coated with a release layer is used.

The heating element 520 provided in the film guide member 530 includes an energizing heating element (resistance heating element) 520a as a heat source that generates heat by supplying electric power. The body 520 is heated, and the heat of the heating body 520 is transmitted to the transfer material passing through the nip N via the heat-resistant film 500. Note that, for example, a ceramic heater can be used as the electric heating element.

Since the fixing temperature can be determined by detecting the temperature of the current-carrying heating element 520a, a temperature detecting element is arranged on the current-carrying heating element 520a. Since the temperature detecting element has a small heat capacity, the temperature detecting element is provided as much as possible in the non-sheet passing area at the end so as not to cause temperature unevenness in the heating element 520.

The pressing roller 510 arranged as a pressing means is formed by coating a rubber elastic layer and a release layer on a core metal such as iron as in the first embodiment. By the rotation of the roller 510, the heat-resistant film 500 comes into close contact with the surface of the heating element 520 in the clockwise direction indicated by the arrow in FIG. 5, and rotates at a predetermined peripheral speed while sliding on the surface of the heating element 520. I have. Further, a guide member 540 for smoothly feeding the transfer material into the nip portion N of the heat-resistant film 500 is provided.

In the fixing device 400 having the above-described configuration, the power is supplied to the current-carrying heating element 520a of the heating element 520,
In a state where the heating element 520 is heated and the heat-resistant film 500 is rotationally driven, the transfer material and the film are moved when the transfer material enters the nip portion N due to the elastic force generated by the deformation of the elastic layer of the pressure roller 510. The toner image on the transfer material is pressed and melted and fixed by closely passing through the nip portion N.

In the fixing device of this embodiment, the length of the elastic layer of the pressure roller 510 in the longitudinal direction is
30 or longer than the width of the heat-resistant film 500,
It is possible to prevent overshoot and a decrease in the central temperature during continuous printing.

Further, assuming that the intensity of light distribution at the position of the temperature detecting element of the energizing heating element is L _th and the intensity of light distribution at the center of the fixing roller is L ₀ , L ₀ is _subtracted from L _th. value is such that _{0.8 <L th / L 0 <} 1.1, so as to adjust the light distribution of the energization heater, the more effectively the central temperature drop during overshoot or continuous printing This may be prevented.

[0048]

As described above, according to the first aspect of the present invention, in the heat fixing means provided with the temperature detecting means used for temperature control at the end, the abutting portion of the pressing means is provided. By making the length equal to or longer than the length of the straight part of the thermal fixing means, high-temperature offset due to overshoot and low-temperature offset during continuous printing are prevented, and printing after warm-up is performed. Also, good image formation can be performed during continuous printing.

Further, according to the second aspect of the present invention, the light distribution L ₀ at the center of the heat fixing means by the current-carrying heating element is provided.
The value of the ratio of the light distribution L _th at the installation position of the temperature sensing means,
0.8 <by adjusting the light distribution so that the range of L _th / L ₀ <1.1, the rate of temperature rise of the center and the ends of the thermal fixing means are averaged to more effectively High-temperature offset due to overshoot and low-temperature offset during continuous printing can be prevented.

According to the third invention of the present application, a metal pipe having a thickness of 3 mm or less and having a heating means therein is used as the heat fixing means, and the length of the contact portion of the pressure means is reduced by the heat. or the same as the length of the straight portion of the fixing means or the straight portion or longer than, at the installation position of the light distribution L ₀ and the temperature detecting means at the central portion of the thermal fixing means by energization heater in the metal pipe distribution values of the ratio of the light L _th, 0.8 <L _th of
By setting the range of / L ₀ <1.1, it is possible to effectively prevent high-temperature offset due to overshoot and low-temperature offset during continuous printing even when a heat fixing unit having a low heat capacity is used.

According to the fourth aspect of the present invention, the film member provided with the heating means is used as the heat fixing means, and the length of the contact portion of the pressing means is reduced by the straight portion of the heat fixing means. if to the same as the length or or longer than the straight section, the ratio of the light distribution L _th at the installation position of the light distribution L ₀ and the temperature detecting means at the central portion of the thermal fixing means by energization heater By setting the value in the range of 0.8 <L _th / L ₀ <1.1, even when a heat fixing unit having a low heat capacity called a film member is used, high-temperature offset due to overshoot and continuous printing can be effectively performed. Low-temperature offset can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a longitudinal section and a heater light distribution of a fixing device according to a first embodiment.

FIG. 2 is an explanatory longitudinal sectional view of the fixing device according to the first embodiment.

FIG. 3 is a graph showing a temperature change on the surface of a central portion of a fixing roller when continuous printing is performed after power-on by the fixing devices of the first embodiment and a conventional example.

FIGS. 4A and 4B are schematic explanatory diagrams showing heater arrangements and respective light distributions of a fixing device using two halogen heaters according to a second embodiment, and light distributions of two superposed heaters; It is a schematic explanatory drawing (b).

FIG. 5 is an explanatory longitudinal sectional view showing a fixing device using a film member according to a third embodiment.

FIG. 6 is an explanatory longitudinal sectional view showing a conventional heat roller fixing device.

FIG. 7 is a graph showing a temperature change on the surface of a fixing roller when continuous printing is performed after power-on by a conventional fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing apparatus 2 Fixing roller 3 Pressure roller 4 Halogen heater 6 Thermistor

Claims (4)

[Claims] 1. A thermal fixing means having a long straight portion and fixing a toner image carried on the surface of a transfer material by a nip portion thereof, and a contact portion contacting the straight portion and being pressed against the thermal fixing means. Pressurizing means, heating means for heating the heat fixing means, and contact of the heat fixing means at the longitudinal end of the heat fixing means to control the surface temperature of the heat fixing means. In a fixing device provided with a temperature detecting unit for detecting a temperature, a length of a contact portion of the pressing unit to the heat fixing unit is equal to or longer than a length of a longitudinal straight portion of the heat fixing unit. A fixing device, characterized in that: As a heating means wherein the heat fixing means, together with the energization heater is used, the light distribution L _th of the light distribution L ₀ and the temperature detecting means installation position at the center of the thermal fixing means by energization heater the value of the ratio of the is 0.8 <fixing device according to claim 1, in the range of L _th / L ₀ <1.1. 3. The method according to claim 1, wherein a metal pipe having a heating means therein is used as the heat fixing means, and the thickness of the metal pipe is 3 mm or less. Fixing device. 4. A heat-fixing means, wherein a film member having a heating means therein is used, and a length of a contact portion of the pressure means to the heat-fixing means is equal to a length in a longitudinal direction of the heat-fixing means. 3. The fixing device according to claim 1, wherein the length of the fixing unit is equal to or longer than the length of the fixing unit.