JPH0888076A - Heating body, fixing device and image forming device - Google Patents

Abstract

PURPOSE: To smoothly carry a fixing sheet by laminating an electrical resistance heating material layer in a belt-like over an electric insulating film layer formed over a substrate between paired belt-like conductive material layers. CONSTITUTION: A heating body 1 has an electrical resistance heating material layer 3 formed at the center axis of a slender electric insulating substrate 2. The substrate 2 is in a slender, straight and belt-like. The electrical resistance exothermic material layer 3 is laminated over both paired band shaped conductive material layers 4a and 4b formed in the specified area of the substrate, and an electric insulating material layer 5 formed on the substrate between the paired conductive layers 4a and 4b. The paired belt-like conductive layers 4a and 4b are so formed not to be overlapped with the electric insulating material layer 5 at both sides of the electric insulating material layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element, a fixing device and an image forming apparatus.

[0002]

2. Description of the Related Art In recent years, a heating element for fixing, which uses an electric resistance layer formed by thick film printing on an electrically insulating elongated substrate as disclosed in Japanese Patent Application Laid-Open No. 2-134667, as a heat source. A fixing device and an image forming apparatus using the body have been put into practical use.

Unlike a conventional heat source such as a halogen lamp, this heating element can instantaneously raise the temperature to a predetermined temperature. Therefore, it is not necessary to heat the heating element during standby, and wasteful heat is generated. There is an advantage that power consumption can be greatly reduced by avoiding it.

The above-mentioned heating element forms a strip-shaped resistance heating element in the longitudinal direction of the elongated substrate, and electricity is also applied in this longitudinal direction. In order to obtain a predetermined resistance value, the direction of energization in the longitudinal direction is naturally determined from the conditions such as the material of the electric resistance heating element to be used, the applied voltage, the value of the flowing current and the like.

However, when materials having different resistivities are used, the energization in the longitudinal direction may not be performed, but may be performed in the width direction perpendicular to the longitudinal direction. For example, conventionally, a silver-palladium alloy has been used as an electric resistance heating element material that conducts electricity in the longitudinal direction, whereas a resistance PTC heating element such as barium titanate is used as an electric resistance heating element material that conducts electricity in the width direction. It is possible to use materials with rates higher than one digit.

The inventors of the present invention have invented a heating body that is energized in the width direction based on the above findings. 7 is a plan view thereof, and FIG. 8 is a sectional view taken along line ZZ of FIG. The cross-sectional view is enlarged in the thickness direction, and the features on the shape are exaggerated.

This heating element 71 comprises a strip-shaped electric resistance heating element layer 73 on a long and narrow electrically insulating substrate 72. The electric resistance heating element layer 73 is arranged so that electricity flows between the pair of strip-shaped conductor layers 74a and 74b formed in the longitudinal direction of the substrate 72 so as to be separated from each other with a constant width in a direction perpendicular to the longitudinal direction of the substrate. Both sides of the electric resistance heating element layer 73 along the longitudinal direction are laminated and connected to the pair of strip-shaped conductor layers 74a and 74b. An electrically insulating protective layer 76 is formed on the pair of belt-shaped conductor layers 74a and 74b and the electric resistance heating element layer 73 except for the terminal portions 75a and 75b.

[0008]

However, the portion of the heating element 71 which generates heat is not the entire electric resistance heating element layer 73. Since the electric current flows through the shortest distance between the conductor layers 74a and 74b, the electric current flows in the portion not laminated with the conductor layers 74a and 74b, and the electric current does not flow in the laminated portion. Therefore, only the portions not laminated with the conductor layers 74a and 74b generate heat, and the laminated portions do not generate heat.

On the other hand, as shown in FIG. 8, since the electric resistance heating element layer 73 is formed by the screen printing method, it has a substantially uniform thickness. Therefore, the surface of the electric resistance heating element layer 73 is recessed because the portion not laminated with the conductor layers 74a and 74b becomes higher and the portion not laminated with the conductor layers 74a and 74b becomes lower. Since the conductor layers 74a and 74b have a thickness of about 10 μm, the recesses have substantially the same depth.

For this reason, the surface of the protective layer 76 is also depressed at the portion corresponding to the heat generating portion as compared with the portion corresponding to the non-heat generating portion. As a result, when the fixing sheet is pressed against the heating body via the transport sheet, the pressure in the recessed portion becomes relatively low, and the heat in this portion may not be sufficiently transmitted to the fixing sheet. Therefore, if the pressure applied to the recessed portion is increased, the pressure of the protruding portion of the portion that does not generate heat becomes too high, and it is difficult to convey the fixing paper smoothly, and there is room for improvement in this respect.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heating body in which the dents on the surface of the heating body are reduced, and as a result, the fixing sheet can be conveyed smoothly. Another object of the present invention is to provide a fixing device and an image forming apparatus using this heating body.

[0012]

According to a first aspect of the present invention, there is provided a heating element, which comprises an elongated electrically insulating substrate, a pair of strip-shaped conductor layers formed on the substrate and spaced from each other in a longitudinal direction of the substrate. An electric insulator layer formed on the substrate between the pair of strip-shaped conductor layers, and a central portion is formed on the electric insulator layer,
And a strip-shaped electric resistance heating element layer which is laminated and connected to the pair of strip-shaped conductor layers on both sides in the longitudinal direction.

According to a second aspect of the present invention, there is provided the heating element according to the first aspect, wherein the electric resistance heating element layer contains a PTC heating element as a main component.

The PTC heating element has a resistance temperature coefficient larger than that of a normal resistance heating element. Therefore, when the temperature exceeds a certain temperature, the resistance value suddenly increases and interrupts the current so that the temperature does not rise above a predetermined temperature. A heating element that can be self-controlled. Therefore, the PTC heating element as the main component allows the addition of other substances as long as it has the function of controlling the exothermic temperature.

According to a third aspect of the present invention, there is provided a heating element according to the first or second aspect, which is a multi-layer portion of a conductor layer and an electric resistance heating element layer
The electrical resistance heating element layer is formed on the conductor layer.

A heating element according to a fourth aspect is the heating element according to any one of the first to third aspects, in which a pair of belt-shaped conductor layers and electric resistance heating element layers are covered with an electrically insulating protective layer. It is characterized by being

A heating body according to a fifth aspect is the heating body according to the fourth aspect, in which one end portion in the longitudinal direction of the conductor layer is not covered with a protective layer on the end portion side of the electric resistance heating body layer. It has a region, and this region constitutes a terminal portion to which power is supplied from the outside.

According to a sixth aspect of the heating element of the present invention, in the heating element of the fifth aspect, the terminal portions are formed at two positions for each conductor layer, and are formed side by side at one end of the substrate. Is characterized by.

The fixing device according to claim 7 is the fixing device according to any one of claims 1 to 6.
Any one of the heating bodies, a conveying sheet that conveys the fixing paper in a direction perpendicular to the longitudinal direction of the heating body, and a fixing roller that presses the fixing paper against the heating body with the conveying sheet interposed. It is characterized by

An image forming apparatus according to an eighth aspect includes an apparatus main body,
The fixing device according to claim 7 installed in the main body of the device.

[0021]

According to the heater of the present invention, since the strip-shaped electric resistance heating element layer is laminated on the electric insulator layer formed on the substrate between the pair of strip-shaped conductive layers, The portion of the resistance heating element layer that generates heat between the pair of strip-shaped conductor layers does not become recessed with respect to the portion that is laminated on the conductor layer, or the recess is suppressed small. As a result, when the fixing paper is pressed against the heating element by the fixing roller,
The heat generating part is sufficiently or directly pressed against the fixing paper. Therefore, it is possible to smoothly convey the fixing paper without applying excessive pressure to the fixing paper.

In the heating element of claim 2, in addition to the function of claim 1, the electric resistance heating element layer contains the PTC heating element as a main component, so that the heating temperature can be self-controlled.

According to the heating element of claim 3, in addition to the function of claim 1 or 2, the electric resistance heating element layer is formed on the electric conductor layer in the overlapping portion of the electric conductor layer and the electric resistance heating element layer. Therefore, the boundary of the conductor layer on the central axis side of the substrate, that is, the boundary with the electric insulator layer is covered with the electric resistance heating element layer, and as a result, the step of this boundary portion is less likely to appear on the surface of the heating element. This boundary portion is pressed by the fixing roller because it is close to the heat generating portion of the electric resistance heating element layer, but since the step is reduced, the fixing sheet is conveyed smoothly.

In addition to the effect of any one of claims 1 to 3, the heater according to claim 4 has a pair of belt-shaped conductor layers and an electric resistance heating element layer covered with an electrically insulating protective layer. Therefore, it has excellent wear resistance. Further, since the protective layer reduces a step which is likely to occur at the boundary between the electric resistance heating element layer, the electric insulating layer and the conductor layer, the fixing sheet can be conveyed smoothly.

In addition to the function of claim 4, the heating element of claim 5 has one end portion in the longitudinal direction of the conductor layer which constitutes a terminal portion which is not covered with the protective layer and which is supplied with electric power from the outside. Therefore, the terminal portion can be easily formed.

In the heating element of claim 6, in addition to the function of claim 5, terminal portions are formed at two locations for each conductor layer,
Since they are formed side by side on one end of the substrate,
Power can be supplied from one side of the substrate to the terminal portion.

The fixing device according to claim 7 is the fixing device according to any one of claims 1 to 6.
Since any one of the heating bodies is included, the function of the heating body according to claims 1 to 6 can be directly obtained.

Since the image forming apparatus according to the eighth aspect has the fixing device according to the seventh aspect, the operation of the fixing device according to the seventh aspect can be directly achieved.

[0029]

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

FIG. 1 is a plan view of a heating element 1 according to the first embodiment, FIG. 2 is a sectional view taken along line XX of the fixing heating element shown in FIG. 1, and FIG. 3 is taken along line YY of FIG. FIG. 2 and 3, the scale in the thickness direction is enlarged, and the characteristic portions of the invention are exaggeratedly described, so that the actual shape is not shown.

The heating element 1 is formed by forming an electric resistance heating element layer 3 on a central axis of a slender electrically insulating substrate 2 made of, for example, alumina ceramics. The substrate 2 has a length of about 350 mm, a width of about 20 mm, and a thickness of about 1 mm,
The electric resistance heating element layer 3 has a length of about 325 mm and a width of about 4 m.
m, and a thickness of about 10 μm, which is an elongated linear shape and a strip shape.

The electric resistance heating element layer 3 is mainly composed of a PTC heating element. The PTC heating element is a known material, and in this embodiment, barium titanate (BaTiO 3) is used.
3) is the main component. This barium titanate (Ba
A glass paste mixed with fine particles of TiO3) is applied by screen printing and then fired to form an electric resistance heating element layer 3. Barium titanate (BaTiO
In 3), the resistance value rapidly increases when the temperature exceeds a certain temperature (Curie temperature) due to the composition. Here, the temperature is controlled to about 350 ° C.

The electric resistance heating element layer 3 is not directly formed on the substrate 2, but a pair of strip-shaped conductor layers 4a and 4b formed in a predetermined region of the substrate 2 and a pair of strip-shaped conductor layers. Is laminated on the electric insulator layer 5 formed on the substrate between the conductor layers 4a and 4b. The electrical insulator layer 5 is formed on the central axis of the substrate 2 to have a width of about 2 mm, a thickness of about 10 μm, and a length of 350 mm corresponding to the entire length of the substrate 2.
This electrical insulator layer 5 is formed by applying an electrically insulating glass paste to the above-mentioned predetermined region by a screen printing method and then firing it.

The pair of strip-shaped conductor layers 4a and 4b are formed on both sides of the electric insulator layer 5 so as not to overlap the electric insulator layer 5. Each of the conductor layers 4a and 4b has a width of about 8 mm, a thickness of about 10 μm, and a length of about 344 mm. The two conductor layers 4a and 4b are laterally offset from each other in FIG. 1, and for example, the right end of the conductor layer 4a is the conductor layer 4a.
It is displaced to the left by 5 mm from the right end of b. Similarly, the left end of the conductor layer 4b is displaced to the right by 5 mm from the left end of the conductor layer 4a. The boundaries of the conductor layers 4a and 4b on the central axis side are in contact with both sides of the electric insulator layer 5. This conductor layer 4
Also for a and 4b, the electric resistance heating element layer 3 formed by applying a silver paste to the above-mentioned predetermined area by the screen printing method and then firing the paste is a pair of strip-shaped conductor layers formed in this way. 4a and 4b are laminated on the electric insulator layer 5, and the right end thereof coincides with the right end of the conductor layer 4a and the left end thereof coincides with the left end of the conductor layer 4b. Further, both sides of the electric resistance heating element layer 3 parallel to the central axis of the substrate 2 are layered with the conductor layers 4a and 4b with a width of 1 mm, and are electrically connected.

Electric resistance heating element layer 3 and conductor layer 4a,
A protective layer 7 made of a glass material is laminated on the surface of 4b except for the terminals 6a and 6b. The glass protective layer 7 is also formed by applying the glass protective layer 7 to the predetermined region by screen printing and then firing it. The terminal portion 6a is formed of the conductor layer 4
The portion not covered by the glass protective layer 7 at the left end of a corresponds to the terminal portion 6b, and the portion not covered by the glass protective layer 7 at the right end of the conductor layer 4b corresponds. In FIG. 1, the broken line 7a,
7b represents the boundary between the left end and the right end of the glass protective layer 7.

The heating element 1 having the above structure is incorporated in a fixing device, and the fixing device is incorporated in an image forming apparatus. FIG. 4 is a schematic sectional view of an example of the fixing device 21, and FIG. 5 is a schematic sectional view of an example of the copying machine 31 which is one of the image forming apparatuses.

In the fixing device 21, a fixing roller 22 is arranged so as to face the surface of the heating element 1 on the electric resistance heating element layer 3 side, and a film-like conveying sheet is movably provided between the heating element 1 and the fixing roller 22. 23 is provided. And
The sheet 25 to which the toner 24 is attached is conveyed while being pressed against the heating body 1 and the fixing roller 22 via the conveyance sheet 23, and the toner 24 is melted and fixed by the heating of the heating body 1. In the figure, 26 is a support for the heating element 1, and 27 and 28 are a conveyance guide and a discharge guide for the fixing paper 25.

As is well known, the copying machine 31 includes an image forming section 32 for adhering toner to the electrostatic latent image formed on the photosensitive drum and transferring the toner 24 onto the paper 25 to form a predetermined image. Toner 2 that is equipped with this image
The above-mentioned fixing device 21 for fixing No. 4 is provided.

Next, the operation of the heating element 1, the fixing device 21 and the image forming device 31 will be described.

When a voltage is applied to the terminals 6a and 6b of the fixing heating element 1, a current flows through the electric resistance heating element layer 3 between the conductor layers 4a and 4b in a direction perpendicular to the axial direction of the substrate, and momentarily. Then, the electric resistance heating element layer 3 generates heat. At this time, as shown in FIG. 5, the sheet 25 conveyed after transferring the toner 24 adhering to the electrostatic latent image formed on the photosensitive drum to form a predetermined image receives the heat and is transferred onto the sheet 25. The toner 24 transferred onto the toner is melted and fixed.

Here, in the cross section of the fixing heating element 1, as shown in FIG. 2, the portion of the electric resistance heating element layer 3 is the conductive layer 4a,
It is formed higher than the portion 4b, and the heating portion is not dented like the heating element 71 of FIGS. Therefore, when the fixing roller 22 presses the fixing paper 25,
The pressure of the portion corresponding to the heat generating portion of the electric resistance heating element layer 3 becomes the highest. As a result, the pressure of the fixing roller applied to the fixing paper 25 is effectively concentrated on the heat generating portion of the electric resistance heating element layer 3. Therefore, a sufficient fixing pressure can be obtained with a small pressure, and the fixing paper 25 can be smoothly conveyed without applying a high pressure to an unnecessary portion.

Actually, when the surface of the fixing heating element 1 is measured, the unevenness of about 1 μm in height peculiar to screen printing remains, but the depression of about 10 μm corresponding to the thickness of the conductor layers 4a and 4b is eliminated. It was

Further, since the electric resistance heating element layer 3 has a PTC heating element as a main component, the heating temperature can be controlled by itself. For example, if the width between the conductor layers 4a and 4b and the film thickness of the electric resistance heating element layer 3 are different depending on the location, the electric resistance value is also changed accordingly. Since the current flows through the electric resistance heating element layer 3 between the conductor layers 4a and 4b in the direction perpendicular to the axial direction of the substrate, the current is small in the portion having a high electric resistance value and large in the portion having a low electric resistance value. Therefore, the heat generation temperature also changes depending on the location.

Such a technical problem is that the conductor layer 4a,
Although it can be solved by precisely controlling the width between the 4b and the film thickness of the electric resistance heating element layer 3, the electric resistance heating element layer 3 is formed by the PTC.
When used as a heating element, the electric resistance heating element layer 3 rapidly increases the resistance value depending on the heating temperature. Therefore, the resistance value itself is increased and the current is suppressed before the heating temperature becomes too high. Maintained at exothermic temperature. In this way, uniformity of heat generation distribution is obtained.

Further, since the electric resistance heating element layer 3 can self-control the heat generation temperature, a safety mechanism such as a temperature detection circuit and a current control circuit for preventing abnormal heat generation becomes unnecessary.

Further, in this embodiment, the conductor layers 4a, 4a
Since the electric resistance heating element layer 3 is formed on the electric conductor layers 4a, 4b in the overlapping portion of the electric resistance heating element layer 3b and the electric resistance heating element layer 3, the electric conductor heating layers 4a, 4b on the central axis side of the substrate 2 The boundary, that is, the boundary between the conductor layers 4a and 4b and the electric insulator layer 5 is covered with the electric resistance heating element layer 3. As a result, heating element 1
It becomes difficult for the step of the boundary portion to appear on the surface of the. Since this boundary portion is close to the heat generating portion of the electric resistance heat generating layer 3, it is pressed by the fixing roller, but since the step is reduced, the fixing paper can be conveyed smoothly.

In this embodiment, the conductor layers 4a and 4b are also used.
Since the electric resistance heat generating layer 3 is covered with the electrically insulating protective layer 7, the abrasion resistance is excellent. Further, since the protective layer 7 reduces a step which is likely to occur at the boundary between the electric resistance heating element layer 3, the electric insulating layer 5 and the conductor layers 4a and 4b, the fixing sheet can be conveyed smoothly.

Further, the terminals 6a, 6b of the heating element 1
Has a structure in which one end portion of the conductor layers 4a and 4b in the longitudinal direction is not covered with a protective layer, so that the terminal portion can be easily formed.

FIG. 6 is a plan view showing a second embodiment of the heating element of the present invention. The heating element 11 includes terminal portions 6a and 6b.
However, the feature different from the first embodiment is that they are arranged side by side on the left side of the drawing. As a result, the heating element 11 becomes the substrate 2
Are vertically symmetrical with respect to the central axis along the longitudinal direction of the. Further, the right side of the electric resistance heating element layer 3 is formed shorter than that in the first embodiment, and the right end of the protective layer 7 is formed up to the right end of the substrate 2. Different from body 1. The other parts have the same configuration as the first embodiment, the same components are designated by the same reference numerals, and detailed description thereof will be omitted.

In the heating element 11 of the second embodiment, like the heating element 1 of the first embodiment, the portion of the electric resistance heating element layer 3 is formed higher than the portions of the conductor layers 4a and 4b, and therefore, A sufficient fixing pressure can be obtained with a small pressure, and the fixing paper 25 can be conveyed smoothly without applying a high pressure to unnecessary portions.

In addition, also in this embodiment, since the electric resistance heating element layer 3 contains the PTC heating element as a main component, the above-mentioned effects similar to those of the first embodiment can be obtained such that the heat generation temperature can be self-controlled. .

Furthermore, the heating element 11 of this embodiment has a unique effect that the wiring is easy because the terminal portions 6a and 6b are arranged on one side of the substrate 2, which is a unique effect not found in the first embodiment. .

The present invention is not limited to the above embodiment. For example, the electric resistance heating element layer 3 is not limited to the PTC heating element, but may be a normal resistance heating element material such as silver palladium or ruthenium oxide.

In addition, the electric resistance heating element layer 3 may be formed below the electric conductor layers 4a and 4b in the overlapping portion of the electric conductor heating layers 4a and 4b and the electric resistance heating element layer 3.

Further, an electrically insulating underlayer or the like may be formed under the conductor layers 4a and 4b and the electric insulator layer 5.

[0056]

According to the first aspect of the present invention, the portion of the electric resistance heating element layer where heat is generated between the conductor layers is not dented with respect to the portion laminated on the conductor layer.
Or it can be suppressed. As a result, when the fixing paper is pressed against the heating body by the fixing roller, the heat generating portion is directly or indirectly pressed sufficiently against the fixing paper, and it is not necessary to apply more pressure than necessary, so the fixing paper can be smoothly transported. .

According to the invention of claim 2, in addition to the effect of claim 1, since the electric resistance heating element layer contains the PTC heating element as a main component, the exothermic temperature can be self-controlled and a uniform exothermic distribution can be obtained. Therefore, the fixing performance is improved. In addition, a safety mechanism such as a thermistor is not needed, and the cost can be reduced.

According to the invention of claim 3, in addition to the effect of claim 1 or 2, there is little step difference in the portion corresponding to the boundary between the conductor layer and the electric insulator layer on the central axis side of the substrate on the surface of the heating body. Therefore, the conveyance of the fixing paper becomes smooth.

According to the invention of claim 4, in addition to the effect of any one of claims 1 to 3, since it is covered with an electrically insulating protective layer, it has excellent wear resistance. Further, since the protective layer reduces a step which is likely to occur at the boundary between the electric resistance heating element layer, the electric insulating layer and the conductor layer, the fixing sheet can be conveyed smoothly.

According to the invention of claim 5, in addition to the effect of claim 4, one end portion in the longitudinal direction of the conductor layer constitutes a terminal portion which is not covered with the protective layer and which is fed from the outside. Therefore, the terminal portion can be easily formed.

According to the invention of claim 6, in addition to the effect of claim 5, since the terminal portions are formed side by side, it is possible to supply power from one side of the substrate to the terminal portions.

According to the invention of claim 7, the fixing device has the same effect as that of the invention of any one of claims 1 to 6.

According to the invention of claim 8, the image forming apparatus has the same effect as that of the invention of claim 7.

[Brief description of drawings]

FIG. 1 is a plan view of a heating body according to a first embodiment.

2 is a cross-sectional view of the fixing heating body of FIG. 1 taken along line XX.

FIG. 3 is a cross-sectional view taken along the line YY of FIG.

FIG. 4 is a sectional view showing a first embodiment of the fixing device in the present invention.

FIG. 5 is a sectional view showing a first embodiment of the image forming apparatus according to the present invention.

FIG. 6 is a plan view showing a second embodiment of the heating element according to the present invention.

FIG. 7 is a plan view of a heating body which is a premise of the present invention.

FIG. 8 is a cross-sectional view taken along line ZZ in FIG.

[Explanation of symbols]

1, 11 ... Heating body, 2 ... Substrate, 3 ... Electric resistance heating element, 4a, 4b ... Conductor layer, 5 ... Electrical insulator layer,
6a, 6b ... Terminal part 7 ... Protective layer, 21 ... Fixing device

Claims (8)

[Claims] 1. An elongated electrically insulating substrate; a pair of strip-shaped conductor layers formed on the substrate so as to be separated from each other in the longitudinal direction of the substrate; and on the substrate between the pair of strip-shaped conductor layers. An electrical insulator layer formed on the electrical insulator layer; and a strip-shaped electric resistance heating element having a central portion formed on the electrical insulator layer and having both sides along the longitudinal direction laminated and connected to the pair of strip-shaped conductor layers. A heating element comprising: a layer; 2. The heating element according to claim 1, wherein the electric resistance heating element layer is mainly composed of a PTC heating element. 3. The heating body according to claim 1, wherein the electric resistance heating element layer is formed on the electric conductor layer in a layered portion of the electric conductor layer and the electric resistance heating element layer. . 4. The heating element according to claim 1, wherein a pair of belt-shaped conductor layers and an electric resistance heating element layer are coated with an electrically insulating protective layer. . 5. One end portion of the conductor layer in the longitudinal direction has a region not covered with a protective layer on the end side of the electric resistance heating element layer, and this region is a terminal to which power is supplied from the outside. The heating element according to claim 4, which constitutes a part. 6. The heating element according to claim 5, wherein the terminal portions are formed side by side on one end of the substrate. 7. A heating element according to claim 1, a conveying sheet for conveying a fixing sheet in a direction perpendicular to a longitudinal direction of the heating element, and a fixing sheet for heating the fixing sheet with the conveying sheet interposed therebetween. And a fixing roller that presses against the fixing roller. 8. An image forming apparatus comprising: an apparatus main body; and the fixing device according to claim 7 installed in the apparatus main body.