JPS61148469A - Roller for heat fixation and fixing device with roller for heat fixation - Google Patents

Abstract

PURPOSE:To uniform a heating state by a heat generating layer having temperature self-control function(PTC) characteristics by providing the 1st and the 2nd heating body layers and an electrode couple. CONSTITUTION:Heating layers 4 and 4 are PTC ceramic layers provided as upper layers of an internal surface layer 7 and has lower resistance than the ceramic of the internal surface layer 7. Conductors 5A and 5B are printed alternately inside of this layer at nearly constant intervals. Those conductors 5A and 5B are patterned linearly to the overall length of the heating layers 4 and 4. Then, the conductor 5B and conductor 5A are provided between two conductors 5A and two conductors 5B adjacently in a circumferential direction. Intervals of adjacent conductors 5A and 5B are constant, and intervals of conductors 5A and intervals of conductors 5B are also constant. Thus, the PTC ceramic generates heat uniformly in the lengthwise direction of a roller.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field to which the invention pertains) The present invention relates to a heat fixing roller of a fixing device applied to a recording device such as an electrophotographic copying machine, a printing machine, a printer, or a facsimile.

The present invention relates to a heat fixing roller and a fixing device as a heating means used for fixing an unfixed image.

(Prior Art) A heat fixing roller that has been put to practical use in the past has a temperature sensor on its surface, and its temperature is controlled by switching a halogen heater provided at the center of the roller into a energized state or a non-energized state.

Since this temperature control is quite complicated, Po5itive Temperature, which has a self-temperature control function, is used.
Co-eNcient of resistiv
ity (hereinafter abbreviated as PTC) has been proposed.

U.S. Pat. No. 4,288,155 discloses a heat fixing roller using a semiconductor ceramic having PTC characteristics in the form of a bar. However, since this rod-shaped PTC ceramic is thick, it must be provided at a large distance from the inner peripheral surface of the roller.

Therefore, in the roller disclosed in US Pat. No. 4,268,155, the surface layer of the roller heated by the ceramic has an uneven temperature distribution, resulting in poor fixing.

Therefore, there is a need for a twin-heated fixing roller fixing device that can perform stable fixing without causing fixing defects.

(Object of the Invention) In view of the above-mentioned problems, an object of the present invention is to provide a heat fixing roller that can form a uniform heating state with a heat generating layer having PTC characteristics and has excellent fixing properties.

An object of the present invention is to provide a fixing device having the above heat fixing roller, and other objects will be explained below.

(Structure of the Invention) In order to solve the above-mentioned problems, the present invention provides positive resistance temperature characteristics by firing.
re co-efficient of resis
tivity characteristic). a second heating element layer; provided between the first heating element layer and the second heating element layer;
a pair of electrodes for applying voltage to these heating element layers, the first heating element layer is located outside the second heating element layer, and the resistance of the first heating element layer is equal to the resistance of the corresponding second heating element layer. A heat-fixing roller and a fixing device including the heat-fixing roller are characterized in that the resistance is smaller than that of a heating element layer.

(Embodiments and Overview of the Invention) Embodiments and application examples thereof that meet each object of the present invention will become clear from the description of FIG. 1.

In FIG. 1, numeral 36 indicates a block of image forming means, and the built-in structure shows that various image forming means such as a general facsimile, laser printer, printing machine, etc. are gold-colored.

For convenience, means A to H for forming a visual image by electrophotography are shown as an example of the image forming means 36.

B shows a photosensitive drum having a photosensitive layer as an example of an image carrier. Upon receiving the copy signal, the photosensitive drum B rotates in the direction of the arrow by the driving force of a drive source (not shown), and is pre-neutralized by a pre-static charger (not shown) to become a zero-order photosensitive drum B.
is charged by a primary charger E, and then subjected to secondary charge elimination by a secondary charger H. On the other hand, at the same time, origi
The nal image is scanned by an optical device A including an optical member and an optical member moving means, so that the photosensitive drum B is image-exposed. Then, an electrostatic latent image is formed on the drum B by the next whole surface exposure (not shown). This latent image is developed in the developing device C, becomes a visible image, rotates together with the drum B, and reaches the transfer charger F.

On the other hand, 1, recording material S of different width sizes, and 31 are cassettes 3
From 0.31, the sheets are fed one by one by the conveyance rollers 32 and 33, moved along the guide member 34, and conveyed close to the drum B with timing determined by the registration roller G in order to receive the developed image. . At this time, transfer charger F
As a result, the recording material S, 31 is charged from the back side thereof to a polarity opposite to that of the visible image, whereby the visible image is transferred onto the recording material S, 31. Thereafter, the surface of the photosensitive drum B is cleaned by a cleaning means in preparation for the next copying.

On the other hand, the recording material S reliably carries the visible image T.

Sl is separated from the photosensitive drum B and sent to the fixing device 37.

The heat fixing roller 1 has a configuration described later, and the pressure roller 2
The recording materials S and St are sandwiched and conveyed. At this time, the thermoplastic powder developer (hereinafter referred to as toner) of the developed image in contact with the fixing roller 1 is melted and pressurized, and is heated and fixed onto the recording material.

The pressure roller 2 has a thick coating 43 made of an offset-preventing elastic material such as silicone rubber on the circumferential surface of a rigid metal roll 44 . The fixing roller 1 and the pressure roller 2 are in pressure contact with each other, and the elastic coating 43 is elastically deformed, so that the recording material S
, forming a nip portion for fixing Sl. These rollers 1 and 2 are driven by a motor (not shown) on the main body side of the electrophotographic recording apparatus 3, in which roller 1 is rotated in the direction of the arrow, and roller 2 is driven to rotate by roller 1 due to frictional force. Further, a web 51 for cleaning the surface of the fixing roller 1 is pressed against the circumferential surface of the fixing roller 1 by a pressing roller 38. After cleaning the surface of the fixing roller, the web wound around the shaft 40 is moved to the rotating shaft 39 by the driving force, and is wound around the shaft 39. Zero or more rollers 1, 2, 38 and the shaft 39, 40 have a width is recording material S
, St, and is rotatably supported by the fixing device box body 52. 41 is a separation claw that comes into contact with the fixing roller and separates the recording material from the roller surface; 42 is a separation claw that comes into contact with the fixing roller;
This is the information board near the. Reference numerals 48 and 47 are discharge rollers that discharge the recording material conveyed between the separation claw 41 and the guide plate 42 onto the tray 48.

The fixing device 37 is a pair of rails fixed in the device.
The outer workpiece 52 can be attached to and detached from the device 3 by moving H in one session.

The aforementioned heat fixing roller 1 will be described in detail.

As seen in FIGS. 1 to 4, the roller I has a multilayer construction. 50 is a hollow metal cylindrical roller, which forms the base of the roller l. 49 is a metal cylindrical roller 5
0, electrically insulating the upper PTC ceramic heat generating layer M4 and the PTC ceramic inner layer 7 from the base body of the roller 50. This insulating layer 49 is provided to increase the heat generation efficiency of the upper PTC ceramic layer.

The inner layer 7 is a cylindrical PTC ceramic layer as seen in FIG. 2, and has a joint 6 to form a cylinder. The inner layer 7 has a conductor 8 printed on the entire circumference of both ends.
A and 8B constitute electrodes that receive the applied voltage from the device 3.

The heat generating layer 4 is a cylindrical PTC ceramic layer provided as an upper layer of the inner layer 7, and has a resistance lower than that of the ceramic of the inner layer 7. Conductors 5A are arranged inside this layer 4 at approximately regular intervals.

5B are printed in alternating order. These conductors 5A and 5B form a linear pattern in the longitudinal direction over the entire length of the heat generating layer 4, with a conductor 5B between the two conductors 5A and a conductor 5B between the two conductors 5B.
A are provided so as to be adjacent to each other in the circumferential direction.

The distance between adjacent conductors 5A and 5B is constant, and
The distances between the conductors 5A and 5B are also constant. It is preferable that such line-shaped conductors 5A and 5B with a constant interval be provided in an area at least equal to or larger than the passage area of the recording materials S and Sl.The reason for this is that if the conductor interval is constant, This is because the sandwiched PTC ceramic can generate heat uniformly in the longitudinal direction of the roller.

The conductors 5A and 5B each form an electrode, but the conductor 5A and the conductor 5B have different polarities, so that the conductor 5N gathers the conductor 5A and the conductor 5B' gathers the conductor 5B. These concentrated conductors 5A and 5B' are provided on the left and right sides of both ends of the heat generating layer 4 over the entire inner circumferential surface thereof (see FIG. 2).
A and 8B are joined to form a power feeding mechanism for the roller 1.

The joint portion 6 of the heat generating layer 4 is opposed to the joint portion 6 of the inner layer 7 with a difference of 180° so that the joint portion 6 is not at the same position with respect to the circumference. Not overlapping the joint portions 6 has the effect of increasing the strength of the heat fixing roller. The heat fixing roller then applies a surface release layer 9, for example PFA, to the surface of the heat generating layer 4 to prevent the toner from the image T from fusing.
It has a layer made of a polymer material such as resin, FEP resin, or PTFE resin.

35 is a voltage application device that applies a voltage between all the conductors 5A and 5B to flow current, and a power supply brush 35A to both poles.
, 35B (or power supply filament 35A as shown in Figure 3)
, 35 '). In Figure 2, conductors 8A, 8
Brush 35A for each.

35B is in contact with it.

As mentioned above, the width L0 of the recording material S, the width L+ of the recording material St
Since the roller surface corresponding to (Lo > Ls) is provided with conductors 5A and 5B of different electrodes in order in the circumferential direction, heat generation in the heat generating layer can be performed in the circumferential direction. As a result, when the roller surface temperature in an area corresponding to the width of the recording material decreases, only the area where the temperature has decreased is heated due to the reduced resistance of the PTC ceramic in that area. Therefore, unnecessary temperature rise on the roller surface is prevented, and the roller surface temperature distribution can be made uniform in the axial direction of the roller. Also, conductors 5A and 5B
Making the spacing substantially constant produces more preferable temperature uniformity, and by alternately arranging the conductors 5A and 5B, uniform temperature distribution in the circumferential direction of the roller can be achieved.

Although the first surface layer 9, the insulating layer 49, and the base roller 50 are not shown in FIG. 2, the structure shown in this figure but provided with the surface release layer 9 is also an example of the roller structure of the present invention.
, a longitudinal section of the roller l can be seen from FIG. In addition, in FIG. 3, the power supply filament 3 explained in FIG.
5A and 35B', a heat-insulating electric insulating flange 52 is provided on one end surface of the roller, and an annular assembly is provided on the outer surface of the 7 flange 52 so as to draw a double concentric circle around the axis 54 of the roller 1. It has conductor rails 5A'' and 5B''. Conductors 5A and 5B are electrically connected to the rails 5A'' and 5B'', respectively. Furthermore, in FIG. 3, in addition to the shaft 54 being fixed to the substrate 56 of the device,
Bearing 5 for enabling roller 1 to rotate about shaft 54
3 is provided on the 7 langes 52. filament 35
K.

35B' is connected to the voltage application device 35 and is brought into contact with the rails 5A'' and 5B'' by pressure springs 57, respectively. The width of the tip of the filament 35 of 35g is smaller than the width of the rails 5A'', 5B'', so that the filament 35 stably contacts the rails. Reference numeral 55 denotes a shaft support that accommodates a filament and a pressure spring, and is fixed to the device through a minute gap with respect to the flange 52.

Next, the manufacturing flowchart shown in FIG. 6 will be explained while also explaining FIG. 4.

A solvent 111 and a dispersant 12 are added to a ceramic raw material 10 having a material composition that has one cucumber point by firing,
The ceramic raw material 10 to be subjected to the mixing chamber pulverization step 13 is P
Raw materials for BaTiO3-based ceramics with TC characteristics 10
Additive elements (for example, La, Ce, etc.) are added to BaCO3 and TiO2 to make them semiconductor.

Oxides such as Nb, Ta, Bi, Sb, W, etc.) are added, and components that increase the positive temperature coefficient of resistance (Mn, Fe, etc.) are added.
, Cu, Cr, etc.) and components (Al103+5i02, TiO□) that promote semiconductor formation and adjust grain size.

In this example, the raw materials are mixed to have a composition ratio of 9 parts (or less) of lead titanate to 16 parts of barium titanate to obtain a heat generating layer with a curie point of 100°C to 250°C. I have to.

Here, the solutions include trichlene, alcohol, ethyl acetate, toluene, acetone, and MEK.

Using water etc., as the dispersant 12, fish oil, octylamine, glyceryl monooleate (G17cery1mono)
oleate), glyceryl triolate (Gltce
ryltrioleaLe) etc. are used.

Further, a plasticizer 15 and a binder 16 are added, and the mixture is thoroughly mixed again, pulverized 14L, molded, and dried 17 to produce a green sheet 18. Here, the green sheet contains 10 to 20% of the binder and is flexible. This plasticizer 15 is polyethylene glycol.

Using DBP (dibutyl phthalate), DOP (dioctyl phthalate), 5AIB (isobutyral stearate), glycerin, etc., as the binder 16, cellulose acetate, polyacrylate, PVA (polyvinyl alcohol), PVB (polyvinyl butyral), EVA ( Ethyl vinyl acetate), PVA (polyvinyl acetate), etc. are used. After producing a green sheet 18 with a thickness of 0.5 to 2 mm in this manner, a conductive paste for high temperature sintering, preferably a tungsten powder paste, is applied onto the sheet by a screen self-printing method to form the conductor 5A described above. , 5B, 5A, and 5B' are printed 19 in a comb tooth shape as shown. In the printed state, it is in the form of a sheet as shown by the broken line in FIG. 4, and during printing, it is heated at a much lower temperature of 200°C or less, unlike the high temperature of 500°C to 1500°C, which is the firing temperature of ceramics.

If a green sheet with a conductor pattern printed in this way is arranged so that the conductor is on the inner side, it will become the heat generating layer 4 shown in Fig. 1, and if it is arranged so that the conductor is placed on the front side, it will become the heat generating layer 4 shown in Fig. 4.
It becomes Bg. In any case, the sheet is formed into a cylindrical shape 2
It will be 0.

Next, this sheet is formed into a cylindrical shape 20.

This cylindrical molded product requires no means for applying pressure from the outside, so that the molded product is free from the effects of residual stress, strain, etc.

The binder 16 remaining inside the cylindrical molded product thus formed is heated to be removed (21).

This heating is followed by sintering 22 at a temperature of 200-400°C per hour and about 1300-1400°C in a reducing atmosphere for 2 hours.

Under this high temperature and reducing atmosphere condition, the ceramic contracts and acquires PTC properties. At this time, the patterned conductors 5A, 5B, 5A', and 5B' are also exposed to high temperature at the same time, so the conductors that were unstable due to being printed on the ceramic are tightly fixed to the ceramic during this firing. . If this fired product is cooled at 100 DEG C. to 200 DEG C. per hour, a roller as shown in FIG. 4 will be produced.

In FIG. 1, since the inner layer 7 is included, a ceramic green sheet is prepared for the inner layer 7 in the same manner as the heat generating layer 4 to supplement this manufacturing method.181. , conductor 8A as a pattern electrode
, 8B printed in a line shape on both ends of one side of the sheet 19
As described above, the 9 heat generating layer 4 is connected to the conductors 5A, 5 in advance.
Conductors 8A and 8B of the sheet of inner layer 7 are prepared as sheets with B etc. printed on them, and conductors 5A' and s'
The stacked pairs of sheets are formed into a cylindrical shape 20 so that the sheets on which the conductors 8A and 8B are printed are on the inside, and the seams do not overlap.
do. Thereafter, the heating 21° sintering 22 described above is performed, whereby the heat generating layer 4 and the inner surface layer 7 are formed into a conductive roller shape.

Generally, ceramics shrink when fired, and this partial unevenness in shrinkage causes cracks, uneven quality, and even dimensional unevenness. This uneven local shrinkage is caused by uneven mixing of raw materials, residual stress and strain due to pressure during molding.

Conventionally, cracks and qualitative unevenness occurred during firing, but with this method, there is no influence of external pressure during molding, and as a result, there is no residual stress or strain within the molded product, so cracks are eliminated. The roller can be manufactured without causing any unevenness or quality unevenness.

In this way, a PTC ceramic crawler having PTC characteristics is manufactured. The electrodes are baked into this roller at the same time as the roller is sintered, and there is no need to add electrodes afterwards, so the attachment of electrodes can prevent the occurrence of cracks and dimensional deformation due to thermal shock.

FIG. 2 is a perspective view of another embodiment that can be used as the heat fixing roller of the present invention, and in this case, in this method,
It is possible to produce products with a wall thickness of 0.5mm to about 30mm (the thickness of two 4.7 sheets pasted together). Further, the dimensions after firing are approximately 10 φ rollers with an accuracy of about ±0.3 to 0.5%.

The example shown in Figures 1 and 2 has electrodes (5A, 5
8, 5B, 525') are not exposed, there are no irregularities in the electrode portion, and there is no diffusion of heat into the air due to heat generation from the surface.

FIG. 5 shows the PTC characteristics of row 1 created by this method. This figure shows the temperature change of the resistance according to this embodiment, normalized with reference to the resistance at 25°C. The data in Figure 5 is based on the case where Ba atoms are replaced with 25% by weight of Pb, but in this case, the amount of Pb replaced increases and non-uniformity during firing is likely to occur due to evaporation of Pb. , the smaller the amount of Pb substitution, the better.

By creating PTC ceramic in this way,
Not only is it possible to make thin rollers, but
Rollers with good dimensional accuracy and low distortion can be made by baking electrodes at the same time. This PTC ceramic roller whose surface is coated with a fluororesin is used as a toner image heating and melting member in electrophotography with a bearing at the end. Surface PTFE coat both 2
5±5 final thickness). The results are shown in Table 1.

Table 1 As shown in Table 1, good rise characteristics and temperature distribution were obtained.

In the conventional method, which simply uses a rod-shaped PTC ceramic to heat a roller that is a good heat conductor, the PTC ceramic itself has a temperature of 20%.
Although the temperature can be raised to 180°C in ~30 seconds, it takes 90 to 100 seconds for the surface of the fixing roller to reach approximately 180", and the temperature distribution on the surface is quite uneven, which is difficult to achieve according to the present invention. A big difference was seen.

As explained above, by forming a PTC ceramic raw material into a sheet shape, printing electrodes on its surface, forming it into a cylinder and sintering it to make a PTC ceramic roller, 1. It is possible to prevent cracks without impairing dimensional accuracy. It is now possible to make PTC rollers without causing qualitative unevenness, and PTC ceramic rollers with good heat generation efficiency can be made. 2. By forming the electrodes at the same time as the firing of the ceramic roller, the electrode attachment can be done quickly. 3. It is possible to prevent dimensional deformation and cracks due to thermal shock and provide a low-cost roller. 3. By using it as a heating roller in an electrophotographic fixing device, it is possible to provide a fusing device that has good start-up characteristics and can be quickly started in a short heating time to reach a predetermined temperature.

The above effects are achieved.

Further, as described above, when different electrodes are formed in sequence on the circumferential surface (on either the inner surface or the outer surface) of the roller, a large amount of heat can be generated.

This means that the distance d between each electrode conductor 5A, 5B, the number n of conductors, the parallel length of conductors 5A, 5B, and the resistivity of unit length as O5, the resistance of the layer is R = Os 10X
n, and in order to obtain the total calorific value in IKW, u = 30
Assuming 0 layers and an applied voltage of 100 (V), R=10Ω. In other words, if the above calorific value is given by the above pattern electrode (if given, O8 is 1OΩ/lumen, then dCC10×n=
300 (s-), it is sufficient to set d and n, which has the advantage of simplifying the design and expanding the practical range. Conversely, if the unit resistance, distance d, and number of conductors n are changed, a larger amount of heat generation can be obtained. Therefore, good fixing performance can be expected when an unfixed toner image is fixed.

Even if separate electrodes are provided on the surface and inner surface of this heat generating layer 4 to generate heat, the resistance is R=h b/a (a is the inner diameter of the inner electrode, b is the outer diameter of the outer electrode, and ρ is the unit resistivity of length)
Therefore, if you try to obtain IKW by applying a limited voltage i o o (v), the resistance will be 300v.
, ρ=10Ω/intestine-, and R=lOΩ, then ln b
/a = 200 - b/a = 0200, which makes it impossible to realize, and even if you try to use 1o(v) or 1(v) chisel pressure, b/a = e2. b/a= eO-0
2":1.02, which is impossible or requires an extremely large transformer, which is a big disadvantage in practice.

In the above embodiment, (dXn) is preferably 1B<(dXn)≦42 based on the above formula, and P
The resistance of the TC ceramic is suitably 6Ω to 50Ω, preferably 14Ω or less considering the heat generation of 1.5KW or less and the heat generation at a rise of 700W or more.

Both the inner layer 7 and the heat generating layer R4 are PT as shown in the example in Fig. 1 above.
When using the C heat generating layer, it is advantageous to make the resistance of the heat generating layer 4, which is the outer surface layer, smaller than the resistance of the inner layer 7 in order to shorten the time required for startup, and M#i! This has the effect of preventing heat loss during fixing. Further, by disposing a plurality of PTC heat generating layers, there is an effect that the temperature distribution on the surface of the fixing roller can be made more uniform.

It is preferable to provide a releasable layer on the surface of the heat fixing roller, and the layers 49, 59, 9, which are other components in FIG. 1, may be provided by any method, and the inner layer 49, 50 An electrically insulating layer made of ceramics that provides sufficient strength may also be used.

The heat-fixing roller in the present invention includes a fixing roller that comes into contact with an unfixed toner image, a roller that pinches and conveys a recording material with the fixing roller, a roller that heats the fixing roller, and the like.

Further, the present invention is novel and has sufficient effects not only in a heat-fixing roller but also in a fixing device including a pressure roller used together with the heat-fixing roller.

The voltage applying means 35 may be a device for substantially flowing current, but may be either an alternating current (including a voltage wave meter such as a sine wave, a rectangular wave, a pulse wave, a triangular wave, etc.) or a direct current. In this case, the conductor alternately changes into a positive electrode and a negative electrode, and the expressions in the claims include these.

The above electrode pair is shown as being parallel to the axial direction of the roller, but it may also be spiral-shaped on the inner and outer peripheral surfaces of the roller, or slightly inclined with respect to the axial direction of the roller. Preferably, the spiral electrode pair has a narrowing gap in a direction fairly close to the circumferential direction.

(Effect of 1!11) As described above, the present invention provides a plurality of PTC heat generating layers,
Since the resistance of the outer layer is made smaller than the resistance of the inner layer, it has the advantage of shortening the time required for startup and the effect of preventing heat loss during continuous fixing. Further, by disposing a plurality of PTC heat generating layers, there is an effect that the temperature distribution on the surface of the fixing roller can be made more uniform.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the overall configuration of an embodiment of the present invention, FIG. 2 is a perspective view of an embodiment of the heat fixing roller of FIG. 1, and FIG.
4 is a perspective view of another embodiment of the heat fixing roller, and FIG. 5 is a graph showing a resistance change curve of the heat generating layer of the heat fixing roller of the present invention. FIG. 6 is a detailed explanatory flowchart of the present invention. 1 is a heat fixing roller, 2 is a pressure roller, 4 is a heat generating layer (P
TC ceramic), 7 is the inner layer (PTC ceramic),
5A, 5B, 8A, 8B are conductors, 9 is a surface release layer, 35
49 is an insulating layer, and 50 is a metal cylindrical roller.

Claims (8)

[Claims] (1) Positive resistance temperature characteristics (Positive) due to firing
eTemperature Co-efficient
of resistance characteristics), and a cylindrical first and second heating element layer, which is provided between the first heating element layer and the second heating element layer, and for applying a voltage to these heating element layers. a pair of electrodes, the first heating element layer is located outside the second heating element layer, and the resistance of the first heating element layer is smaller than the resistance of the corresponding second heating element layer. A roller for heating and fixing. (2) The electrode pair has a conductor forming one pole and a conductor forming the other pole alternately on one side of the cylindrical heating element layer, and furthermore, the electrode pair extends over the recording material in the longitudinal direction of the heating element layer. The heat fixing roller according to claim 1, wherein the heat fixing roller is provided with a width greater than or equal to the width. (3) The electrode pair is provided on the first heating element layer before firing, and is fixed to the first heating element layer when the first heating element layer is fired. The heating fixing roller according to item 1 or 2. (4) The heat fixing roller according to claim 1 or 2, wherein the electrode pair is integrated with the heat generating layer before firing the heat generating layer. (5) Positive resistance temperature characteristics (Positive) by firing
eTemperature Co-efficient
of resistance characteristics), and a cylindrical first and second heating element layer, which is provided between the first heating element layer and the second heating element layer, and for applying a voltage to these heating element layers. a heat-fixing roller having a pair of electrodes, the first heating layer is located outside the second heating layer, and the resistance of the first heating layer is greater than the resistance of the corresponding second heating layer. This fixing device is characterized by its small size. (6) The electrode pair has a conductor forming one pole and a conductor forming the other pole alternately on one side of the cylindrical heating element layer, and furthermore, the electrode pair extends over the longitudinal direction of the heating element layer of the recording material. The fixing device according to claim 5, wherein the fixing device is provided with a width greater than or equal to the width. (7) The electrode pair is provided on the first heating element layer before firing, and is fixed to the first heating element layer when the first heating element layer is fired. The fixing device according to item 6 or item 6. (8) The fixing device according to claim 5 or 6, wherein the electrode pair is integrated with the heat generating layer before firing the heat generating layer.