JPH04316074A - Thermal fixing device - Google Patents

Abstract

PURPOSE:To provide a thermal fixing device capable of preventing an electrostatic offset, without causing the scattering of an image. CONSTITUTION:The core metal 1A of a fixing roller 1 is grounded, and a high voltage power source 3 is connected to the core metal 2C of a pressure roller 2. Then, the electrostatic capacity of the surface layer 2A of the pressure roller 2 is set at >=0.5pF/cm and <=6.4pF/cm per unit length in the roller shaft direction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device that fixes an unfixed image by passing a recording material carrying an unfixed image between a fixing roller and a pressure roller and applying heat and pressure. Alternatively, the present invention relates to a heat fixing device used in the field of fixing technology in electrostatic recording devices.

0002

2. Description of the Related Art FIG. 17 shows a conventional fixing device. Figure 17
18 is a fixing roller, and a fluororesin layer is provided on the outer surface of a hollow aluminum core metal. A halogen heater 11 serving as heating means is disposed inside the fixing roller 18, and heats the fixing roller 18. Also,
A pressure roller 19 having an elastic layer 19A made of low temperature vulcanizable silicone rubber (LTV) or the like on a core bar 19B is disposed below the fixing roller 18 so as to be in pressure contact with the fixing roller 18. The roller pair of the fixing roller 18 and the pressure roller 19 conveys the recording material 22 carrying the toner image 21 by rotating with each other while pinching and heating the recording material 22 at a pressure contact portion (hereinafter referred to as a nip portion). The toner image 21 is fixed. However, some of the toner may not be fixed and may be transferred to the fixing roller 18 side, and transferred again to the subsequent recording material, staining the image. This is a phenomenon called electrostatic offset, and when charged toner enters the pressure contact portion of a pair of rollers, for example, due to charge-up due to friction of the pressure roller 19, the toner is held in the direction of the recording material. The force is transferred to the fixing roller 18 side by receiving a force from an electric field in the opposite direction.

Conventionally, as a means for preventing this electrostatic offset, a silicone oil coating/cleaning member 20 has been disposed above the fixing roller 18. The cleaning member 20 includes a cleaning member 20A made of heat-resistant felt impregnated with silicone oil, which is attached to a holder 2.
It is supported by 0B and pressed against the fixing roller 18.

However, with recent demands for smaller machines and easier maintenance, a fixing device that prevents electrostatic offset without using the cleaning member 20 has become necessary.

Therefore, as shown in FIG. 18, a bias is applied to the fixing roller 18 through a sliding contact (not shown) by a high-voltage power source 23 serving as a voltage applying means, and the pressure roller 1
A device has been proposed that provides a sufficient potential difference to 9. According to this device, an electric field is generated in a direction that presses the toner toward the recording material, thereby preventing electrostatic offset.

As another device, as shown in FIG. 19, a conductive silicone rubber layer 24B and an insulating fluororesin layer 24A are provided on a core bar 24C of a pressure roller 24, and a bias is applied to the core bar 24C. A device was proposed to do this. According to this device, an electric field is generated that attracts the toner to the recording material, and electrostatic offset is prevented.

[0007]

[Problems to be Solved by the Invention] However, in the above conventional example, a strong electric field is required to prevent offset in various cases such as environmental changes and different types of recording materials. Naturally, a strong level of bias is required.

Two problems that may occur at this time are scattering and leakage of the toner image before fixing. Scattering of an unfixed toner image is a phenomenon in which when an excessive bias is applied to the fixing roller or the pressure roller, the unfixed image is disturbed by the strong electric field just before the nip portion. Specifically, when a bias is applied to the fixing roller side, the toner becomes a scattering image (scattering in the opposite direction to the recording material traveling direction) due to the repulsive force from the fixing roller side, and the pressure When a bias is applied to the roller side, this is a phenomenon in which a scattering image (scattering toward the advancing side with respect to the recording material advancing direction) occurs in the toner due to the attractive force from the pressure roller side.

Next, regarding leakage, when excessive bias is applied, dielectric breakdown occurs between other parts, resulting in damage to the leakage point, and even when bias is applied, it is difficult to prevent offset. This is a phenomenon in which the necessary potential cannot be obtained. In particular, when applying bias to the fixing roller side, if a leak occurs with the thermistor (not shown) installed to detect the temperature of the fixing roller, it may even damage the controller side. It was a matter of getting it.

[0010] As described above, in a bias application system, it has been difficult to prevent electrostatic offset under various environments without causing the above-mentioned disadvantages.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a heat fixing device that can prevent electrostatic offset without causing image scattering or leakage.

0012

[Means for Solving the Problems] According to the present invention, the above object is achieved by providing a fixing roller having a releasable resin layer on a core metal, a heating means disposed within the core metal, and a fixing roller having a releasing resin layer on the core metal. a pressure roller having an elastic layer on the surface of the fixing roller and disposed in pressure contact with the fixing roller; and voltage application means for applying a predetermined voltage to the core metal of one of the two rollers, the other of the two rollers. This is achieved by setting the composite capacitance between the core metal of the fixing roller and the pressure roller within a predetermined range in a heating fixing device in which the core metal of the fuser roller is grounded without applying voltage. be done.

[0013]

[Function] According to the present invention, by setting the composite capacitance between the core metal of the fixing roller and the core metal of the pressure roller within a predetermined range, the electric field acting on the toner image on the recording material can be reduced to prevent image scattering. It has been found that the offset can be made smaller than the case where the offset occurs and larger than the case where the offset cannot be prevented. therefore,
To surely prevent offset without causing image scattering.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First to third embodiments of the present invention will be explained based on the drawings.

First Embodiment First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 7.

In FIG. 1, 1 is a fixing roller, and a fluororesin layer 1A such as a PFA tube is coated on a core metal 1B with a thickness of 30 μm.
It is formed with a thickness of m. A halogen heater 4 is disposed inside the fixing roller 1, and a pressure roller 2 is disposed below. The pressure roller 2 has a conductive silicone rubber layer 2B having a volume resistance of about 103 Ω·cm formed on a core metal 2C, and a conductive silicone rubber layer 2B having a volume resistance of about 103 Ω·cm.
A PFA tube 2A with a layer thickness of 50 μm is coated on B. The fixing roller 1 side is connected to an earth line 5 via a sliding contact, and the pressure roller 2 side is applied with a bias via a sliding contact by a high voltage power source 3 serving as a voltage applying means.

The most characteristic feature of the apparatus of this embodiment is that the capacitance of the roller itself on the pressure roller 2 side to which the bias is applied is set within a predetermined range. Specifically, the surface layer P
The capacitance of the pressure roller 2 is set by changing the thickness of the FA tube 2A.

[0018] Below, the results of experiments conducted based on the apparatus of this embodiment will be explained.

In this experiment, conductive silicone rubber with a volume resistance of about 103 Ω·cm was used for the pressure roller elastic layer 2B.
By changing the thickness of the PFA tube of the surface layer 2A, the capacitance of the pressure roller itself was changed, and the effect on the electrostatic offset level and image scattering level was investigated. Note that FIG. 2 shows a method for measuring the capacitance of the pressure roller. Pressure is applied to the aluminum core metal 1B of the pressure roller 2 and the fixing roller 1 so that the nip between them is 2 mm, and the LCR meter (AG-4304 manufactured by ANDO, 1KHz
The measurement was performed by connecting a voltage of 1 V (applying 1 V). The axial length of the pressure roller elastic layer at this time was 220 mm. In addition, the capacitance of the three types of pressure rollers in Figures 3 and 4 is P
The thickness of the FA tube is 150μm, 100μm, 20μm
m, 50pF, 100pF, 500pF, respectively.
The value of pF was obtained.

First, FIG. 3 is a diagram showing the relationship between the bias applied to the pressure roller and the electrostatic offset level when the capacitance of the pressure roller is changed. According to the figure, it can be seen that the offset level improves as the bias applied to the pressure roller increases. As the pressure roller capacitance increases, the overall level improves.

On the other hand, FIG. 4 is a diagram showing the relationship between the image scattering level and the bias applied to the pressure roller when the capacitance of the pressure roller is changed. According to the figure, it can be seen that as the bias applied to the pressure roller increases, the level of image scattering worsens. Moreover, it can be seen that the tendency is that the larger the pressure roller capacitance, the worse the level.

From the results shown in FIGS. 3 and 4, in a system where a bias is applied between the fixing roller and the pressure roller, in order to prevent electrostatic offset without causing image scattering, it is necessary to It has been found that it is effective to reduce the capacitance and increase the bias applied to the pressure roller.

The following may be considered as the reason why such a result is obtained.

First, as shown in FIG. 5, between a fixing roller 1 having a release layer on its surface and a pressure roller 2 having an elastic layer, negatively charged toner 7 and a photosensitive drum ( Charge obtained by peeling discharge from (not shown) −Q2
, a recording material P having a charge +Q1 obtained from the transfer means is sandwiched between the back surfaces thereof, a positive bias is applied to the pressure roller core metal, and the fixing roller core metal is connected to ground. Using a fixing device as a model, FIG. 6 shows its equivalent circuit.

FIG. 6 shows a circuit in which the capacitances of the respective elements shown in FIG. 5 are connected in series, and a voltage V is applied to one end of the circuit. In the figure, Cn is the fixing roller capacitance,
Ca is the capacitance of the air gap between the fixing roller and the recording material, Cpa is the capacitance of the recording material, Cb is the capacitance of the air gap between the pressure roller and the recording material, and Cp is the capacitance of the pressure roller. be. On this equivalent circuit, two potentials, V1 and V2, are determined as the potentials acting on the negative toner. V1 represents the potential difference between the surface of the recording material and the surface of the fixing roller, and is most related to electrostatic offset. Further, V2 represents the potential difference between the surface of the recording material and the surface of the pressure roller, and is most related to image scattering (image scattering before fixing). The obtained results are shown below.

[0026]

[Math 1]

[0027]

##EQU00002## In the above equation, V1 is a force that acts in the direction of pressing the toner toward the recording material, so the larger it is, the more effective it is in preventing offset. On the other hand, V2 is a force that acts in the direction of attracting the toner toward the pressure roller, so the larger it is, the more effective it is for offset, but if it is too large, the image will jump forward before it enters the nip, causing problems such as image scattering. This results in the occurrence of In this embodiment, by changing the capacitance Cp of the pressure roller, the combined capacitance C between the fixing roller and the pressure roller core metal is changed, and V1 and V2 are
can be adjusted. Therefore, the main variables in V1 and V2 are the combined capacitance C and the applied bias V.

FIG. 7 shows how these V1 and V2 change when C and V are changed. In the figure, the horizontal axis shows the applied bias V, and the vertical axis shows V1 and V2.
are taken at the same time, and two cases are shown: a case where the electrostatic capacitance C between the core metals is large and a case where it is small. V1MIN shown on the vertical axis is the value at which an offset will occur if the value of V1 becomes lower than this value, and V2
MAX is a value at which image scattering occurs if the value of V2 is higher than this value.

In the figure, when C is large, both the slope and the intercept of V1 and V2 become large from the above-mentioned equations (1) and (2), so they take values as shown by the solid lines in the figure. In this case, in order to eliminate the electrostatic offset, the applied bias V needs to be at least VCB. However, V.C.
Since the value of V2 when B is applied exceeds V2MAX, image scattering occurs, and it is impossible to satisfy both offset prevention and scattering prevention.

On the other hand, if C is small, the above formula ■
, ■ Since both the slope and the intercept of V1 and V2 become small, the values shown by the dashed dotted lines in the figure are taken. At this time,
When applying the minimum necessary bias VCS to eliminate electrostatic offset, the value of V2 is V2
Since it is less than MAX, image scattering will not occur. Therefore, when C is made small, both offset prevention and scattering prevention can be satisfied. The presence of C in this way produces the effect of suppressing the electric field generated by the applied bias.

However, C also has a lower limit. This is due to the following two reasons.

First of all, the fact that C becomes smaller means that V
In order to make V1 more than V1MIN, an excessive V has to be applied. This is because if the required V exceeds the power supply capacity at this time, it will no longer be possible to prevent offset. Second, a smaller C means a smaller capacitance Cp of the pressure roller, and even if a pressure roller with a small Cp receives a slight frictional charge, its surface potential will rise immediately. This is because a so-called charge-up phenomenon occurs, which becomes a cause of offset generation.

From the above, it is considered effective to set the capacitance of the pressure roller within a certain range in a fixing device that applies bias to the pressure roller.

[0034] Now, the optimum range in which the capacitance of the pressure roller should actually be set will be explained.

As shown in FIGS. 3 and 4, the capacitance was adjusted by changing the thickness of the PFA tube layer in the pressure roller. As a result, the measurement method shown in FIG. If you have a configuration that corresponds to the range of 10 pF to 140 pF, and the thickness of the PFA tube is 1 mm (10 pF capacitance) to 80 μm (140 pF capacitance), you can prevent electrostatic offset without causing image scattering. It becomes possible to do so.

Note that the pressure roller capacitance described here is a value measured when the pressure roller elastic body length is 220 mm, so when converted to a unit length value in the roller axial direction, it is as follows.
This means a range of 0.5 pF/cm or more and 6.4 pF/cm or less.

<Second Embodiment> Next, a second embodiment of the present invention will be described based on FIGS. 8 and 9. Note that parts common to the device of the first embodiment are given the same reference numerals, and explanations thereof will be omitted.

FIG. 8 is a diagram showing the configuration of a second embodiment of the present invention. The feature of this embodiment is that the capacitance on the pressure roller side on the bias application side is adjusted by connecting an element having a predetermined capacitance between the pressure roller and the power source.

In FIG. 8, 8 is a member having a predetermined capacitance, such as a high voltage capacitor.

In the first embodiment, in order to obtain the optimum composite capacitance C between the fixing roller and the pressure roller core metal in the pressure roller bias application system, the capacitance Cp of the pressure roller is adjusted by the thickness of the surface PFA tube. It was adjusted by changing. However, the thickness of the PFA tube at that time is
As the capacitance decreases, the thickness increases, which increases the hardness of the pressure roller, and depending on the pressure and temperature control conditions, the conditions for fixing performance may become severe.

Therefore, in this embodiment, in the equivalent circuit diagram shown in FIG. 9, by connecting a capacitor capacitance Cc between the pressure roller capacitance Cp and the power supply V,
A composite capacitance Cp' of Cc and Cp is created, and since the relationship Cp'<Cp holds, the electrostatic capacitance Cp itself of the pressure roller is P
It is possible to obtain the same effect as reducing the capacity by changing the thickness of the FA tube. For example, 50μm PFA
In the case of a pressure roller using a tube, a capacitor with a capacitance in the range of 10 pF to 1000 pF may be used in order to keep the capacitance on the pressure roller side within an appropriate range.

Therefore, according to this embodiment, the connected capacitor has the effect of suppressing the electric field, and the capacitance can be changed without changing the roller configuration such as changing the thickness of the PFA tube layer of the pressure roller. By simply adjusting the predetermined capacity, it is possible to easily adjust the predetermined capacity, and it can be determined independently of the fixing conditions, which has the effect of widening the latitude at the design stage.

<Third Embodiment> Next, a third embodiment of the present invention will be described based on FIGS. 10 to 16. In addition,
The same reference numerals are given to the same parts as in the first embodiment, and the explanation thereof will be omitted.

FIG. 10 is a diagram showing the configuration of a third embodiment of the present invention. In the figure, 1 and 2 are a fixing roller and a pressure roller having the configurations described in the previous embodiment, and 4
is a halogen heater. A high voltage power supply (HV) 10 applies a bias to the fixing roller core metal 1B via a capacitor 9 having a predetermined capacitance, and applies a bias to the fixing roller core metal 1B.
A connection is made from C to ground.

The feature of this embodiment is that in the fixing device that applies a bias to the fixing roller side, the capacitance on the fixing roller side is set within a predetermined range, and in particular, the capacitance is adjusted. Therefore, a capacitor is connected between the fixing roller and the high voltage power supply.

First, when bias is applied to the fixing roller to prevent electrostatic offset, why an appropriate range exists for the capacitance on the fixing roller side will be explained.

FIG. 11 is a model diagram for considering what kind of force acts on the negative toner on the recording material when bias is applied to the fixing roller side, where 1 is the fixing roller and P is the recording material. , 7 is a negative toner, 10 is a high-voltage power supply, and it is assumed that a negative charge -Q2 obtained during peeling from a photosensitive drum (not shown) is present on the recording material. Here, the reason why the pressure roller side is not shown as in the model when bias is applied to the pressure roller shown in FIG. 5 is as follows. When bias is applied to the fixing roller side, even if a potential difference occurs between the fixing roller surface and the pressure roller surface with respect to the recording material surface where toner is present, the distance over which the resulting electric field acts is the fixing roller surface. is very small because it is in contact with the surface of the recording material, whereas
The surface of the pressure roller is large due to the thickness of the recording material, the air gap, etc., and the effect on the toner due to the electric field from the pressure roller side is almost negligible compared to that from the surface of the fixing roller. It's for a reason.

FIG. 12 is an equivalent circuit diagram of the model diagram of FIG. 11. In the figure, Cn is the capacitance of the fixing roller, Ca is the capacitance of the air gap between the fixing roller and the recording material, Cpa is the capacitance of the recording material, and -Q2 is the charge existing on the surface of the recording material. In the following, the potential difference V3 between the surface of the fixing roller and the surface of the recording material is determined as the potential acting on the toner.

[0049]

##EQU00003## In the above equation, the variables that can determine V3 are the applied bias V and the fixing roller electrostatic capacitance Cn.

FIG. 13 is a diagram showing the change in V3 when the fixing roller applied bias V is changed using the above equation. The change in the case is represented by a dashed-dotted line. In addition, in the same figure, V3MAX means that when the potential on the surface of the fixing roller becomes excessive beyond this value, the repulsive force against the toner becomes strong, causing a phenomenon in which the toner scatters to the rear edge of the image before it enters the nip. V3MIN is a potential below which the offset prevention effect is lost. Furthermore, in the case of the fixing roller bias application system, the electric field is larger because the distance at which the potential is generated is shorter than in the pressure roller bias application system, and the influence of the potential is correspondingly greater, so the appropriate range between V3MAX and V3MIN is narrower. It has become.

[0051] Therefore, in order to prevent offset without causing image scattering, these V3MIN and V3MAX
It is necessary to adjust the applied bias V and the fixing roller capacitance Cn so that V3 is within the range. When the possible range of the applied bias V at that time is ΔVB when Cn is large and ΔVS when Cn is small, ΔVB
There is a relationship of <ΔVS.

By the way, considering that the power supply voltage normally fluctuates by about ±15%, ΔVB when Cn is large is the fluctuation range of the power supply for applying bias to the fixing roller (for example, when applying -500V, If the voltage is below 150V, there is a good possibility that the voltage will fall outside the guaranteed performance range. Therefore, the fixing roller electrostatic capacitance Cn must be set to a small value to sufficiently guarantee this area.

However, if the fixing roller capacitance Cn is made extremely small, it will be the same as when applying the pressure roller bias,
In order to obtain sufficient V3 to prevent offset, the applied bias V must be extremely large, and this has the problem that the upper limit is determined by the power supply capacity, so there is also a lower limit for Cn. .

As explained above, in a system that applies bias to the fixing roller, by setting the capacitance on the fixing roller side within a predetermined range, electrostatic offset can be prevented without causing image scattering. can do.

By the way, in order to set the capacitance of the fixing roller to an optimal value, it is possible to set the capacitance to a predetermined value by changing the thickness of the surface PFA tube layer, but for example, in order to increase the capacitance, Making the PFA tube thinner is not desirable in terms of durability, and on the other hand, making the PFA tube thicker in order to reduce the capacity means thickening the layer with poor thermal conductivity, which may worsen the thermal conductivity. There is a possibility that good fixing performance may not be obtained. Therefore, it is not preferable to adjust the capacitance by changing the thickness of the PFA tube.

Therefore, by connecting something with a certain capacitance between the object to which bias is applied (in this case, the fixing roller) and the power source as described in the second embodiment, the capacitance can be increased by the combined capacitance. The method of adjusting will be used in this embodiment as well.

Next, the optimum range in which the capacitance on the fixing roller side should actually be set will be explained.

Therefore, in the configuration shown in FIG. 10, when the capacitor 9 was replaced and the capacitance was changed, the bias applied to the fixing roller was changed and changes in the electrostatic offset level were observed. Note that the electrostatic capacitance on the fixing roller side referred to here means that the fixing roller 1 and the capacitor 9 are connected to each other with conductivity (102
・cm) The value is measured using a single-layer rubber roller 11 as an electrode, pressurized so that the nip between both rollers is 2 mm, installed in a fixing device, and measured with an LCR meter on both cores.

FIG. 15 is a diagram showing the electrostatic offset level for each case. It can be seen that the offset level improves as the capacitance increases and as the applied bias increases.

FIG. 16 is a diagram showing the image scattering level for each case. The capacitance on the fixing roller side shown in FIGS. 15 and 16 is based on a fixing roller surface tube with a thickness of 30 μm and a capacitor of 60 pF and 140 μm.
When pF and 2000 pF are connected, the combined capacitance becomes 50 pF, 100 pF, and 270 pF, respectively.

In addition to the above results, the upper limit of the capacitance was determined by taking into account the variation range of the power supply (normally ±15%), and the lower limit was taken into consideration the charge-up and the upper limit output of the power supply, etc., and the fixing roller side Capacitance is 10pF or more 250p
It was found that F or less is an appropriate range. This value is
For example, the possible capacitance range of a capacitor connected to a fixing roller with a tube thickness of 30 μm is from 10 pF to 12
It is in the range of 00 pF. In addition, this value is 0.5 pF/cm or more when converted to a value per unit length in the roller axial direction.
．． This means that the range is 5 pF/cm or less.

[0062]

[Effects of the Invention] As explained above, according to the present invention,
Since the composite capacitance between the core metal of the fixing roller and the core metal of the pressure roller is set within a predetermined range, electrostatic offset can be prevented without causing problems such as image scattering.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a schematic configuration of a first embodiment of the device of the present invention.

FIG. 2 is a diagram illustrating a method of measuring the capacitance of the pressure roller of the apparatus in FIG. 1;

FIG. 3 is a diagram showing the relationship between the bias applied to the pressure roller of the device shown in FIG. 1 and the offset.

FIG. 4 is a diagram showing the relationship between the bias applied to the pressure roller of the apparatus shown in FIG. 1 and image scattering.

FIG. 5 is a diagram for explaining capacitance in the device of FIG. 1;

FIG. 6 is a diagram showing an equivalent circuit of the device in FIG. 5;

[Figure 7] In the device shown in Figure 1, when the capacitance is changed,
FIG. 3 is a diagram showing the relationship between applied bias and an electric field acting on toner on a recording material.

FIG. 8 is a sectional view showing a schematic configuration of a device according to a second embodiment of the present invention.

FIG. 9 is a diagram showing an equivalent circuit of the device in FIG. 8;

FIG. 10 is a sectional view showing a schematic configuration of a device according to a third embodiment of the present invention.

11 is a diagram for explaining capacitance in the device shown in FIG. 10. FIG.

FIG. 12 is a diagram showing an equivalent circuit of the device shown in FIG. 11;

13 is a diagram showing the relationship between the applied bias and the electric field acting on the toner on the recording material when the capacitance is changed in the apparatus shown in FIG. 10. FIG.

14 is a diagram illustrating a method of measuring capacitance in the device shown in FIG. 10. FIG.

FIG. 15 is a diagram showing the relationship between applied bias and offset of the device in FIG. 10;

16 is a diagram showing the relationship between applied bias and image scattering of the device shown in FIG. 10; FIG.

FIG. 17 is a sectional view showing a schematic configuration of a conventional device including a cleaning member.

FIG. 18 is a sectional view showing a schematic configuration of a conventional device that applies a bias to a fixing roller.

FIG. 19 is a sectional view showing a schematic configuration of a conventional device that applies a bias to a pressure roller.

[Explanation of symbols]

1 Fixing roller 1A　Mold release resin layer (fluororesin layer) 1B　Core metal 2 Pressure roller 2A Elastic layer (surface layer, PFA tube) 2C Core metal 3 Voltage application means (high voltage power supply) 4 Heating means (halogen heater)

Claims (4)

[Claims] 1. A fixing roller having a releasable resin layer on a core metal, a heating means disposed within the core metal, and an elastic layer on the core metal so as to be in pressure contact with the fixing roller. A pressure roller is provided, and voltage applying means applies a predetermined voltage to the core metal of one of the two rollers, and the other core metal is grounded without being applied with voltage. A heat fixing device characterized in that a composite capacitance between the core metal of the fixing roller and the core metal of the pressure roller is set within a predetermined range. 2. The voltage applying means is set to apply a voltage to the core metal of the fixing roller, and the electrostatic capacitance per unit length in the axial direction on the fixing roller side is 0.5 pF/cm or more and 11.5 pF. 2. The heat fixing device according to claim 1, wherein the heat fixing device is set to less than /cm. 3. The voltage applying means is set to apply a voltage to the core metal of the pressure roller, and the capacitance per unit length in the axial direction on the pressure roller side is 0.5 pF/cm or more6. 2. The heat fixing device according to claim 1, wherein the temperature is set to .4 pF/cm or less. [Claim 4] A capacitor is connected between the core metal and the voltage applying means.
The heat fixing device described in .