JP2000223244A - Heating body and fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce heat generation in a paper non-passing region and thereby prevent the damage of components such as an offset, a fixing film, a pressing roller and a film guide. SOLUTION: In the front surface side of a ceramic recording material 1 of a heating body A, PTC patterns (positive temperature coefficient characteristic patterns) 3A, 3B each having a length equal to that of a heating element pattern are formed on both sides of the heating element pattern 2A, and a current is carried to the heating element pattern 2A through the PTC patterns 3A, 3B. In the case that the paper passing of a small-sized transferring material is continued, when the temperature of a paper non-passing region is about to exceed 230 deg.C, the resistance in the paper non-passing region is increased nearly tenfold by the PTC patterns 3A, 3B, and the amount of current at both the end parts of the heating element pattern 2A is reduced to 1/10 as much as that of the center, so that the heating value at those parts of the heating element pattern 2A is also reduced to 1/10. As a result, excessive heat feeding in the paper non-passing region is eliminated and the balance with natural heat radiation is established so that the temperature in the paper non-passing region does not rise above 230 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element for fixing a toner image on a transfer material such as paper, and a fixing device having the same.

[0002]

2. Description of the Related Art FIG. 6 is a longitudinal sectional view of a conventional fixing device 20D provided with a conventional heating element D.

In the figure, reference numeral 25 denotes a fixing film, D denotes a heating element, 22 denotes a film guide for supporting the heating element D and guiding the running of the fixing film, and 26 denotes pressing the fixing film against the heating element D to transfer. It is a pressure roller for pressing and transporting the material P.

The fixing film 25 has a diameter of 24 mm and a thickness of 50 mm.
It is obtained by laminating a 4 μm primer and a 10 μm surface layer (Teflon layer) on a μm polyimide.

[0005] The pressure roller 26 is formed by coating a 3.5 mm thick silicone rubber 26b around an aluminum core metal 26a having a diameter of 13mm, covering the surface with a PFA tube, or applying a fluorine resin or fluorine latex. It was done. The temperature of the heating element D is adjusted by turning on / off the triac 24 by the CPU 23 according to the output of the thermistor 6.

FIG. 7 shows a heating element D used in the above-described fixing device 20D. FIGS. 7A, 7B, and 7C are views of a conventional heating element D viewed from below, above, and front, respectively, in this order, that is, a bottom view, a top view, and a front view.

Reference numeral 1 in these figures denotes a ceramic substrate using alumina or aluminum nitride, and a heating element 2D is obtained by alloying silver mixed with palladium, mixing this with a glass paste, and performing screen printing. Is used. In order to supply power to the heating element 2D, a conductor pattern 4 obtained by mixing silver or silver / platinum into a glass paste and performing screen printing.
D is formed. A glass coat 10 is applied to the surface of the heating body D (the lower surface in FIG. 6) in order to improve the slidability and obtain the withstand voltage.

An electrode 5 is formed at an end of the conductor pattern 4D. A thermistor 6 and a conductor pattern 7 for detecting its resistance are formed on the back surface of the ceramic base 1. The conductor pattern 7 is connected to the electrode 9 by a through hole 8.

[0009]

The heating element 2 as described above
When a small transfer material P such as an envelope or a postcard is passed through the fixing device 20D of FIG. 6 using D, heat is consumed by the transfer material P in the non-sheet passing areas at both ends in the longitudinal direction of the heating body D. Since there is no heat, the heat accumulates and the temperature rises, causing problems such as peeling of the coating layer of the silicone rubber or the fluororesin on the surface used in the fixing device 20D and an increase in the compression set. When the coat layer is peeled off, toner accumulates on the surface of the pressure roller 26 to stain the image, or sticks to the paper transfer material P to cause wrapping jam. Also, when the compression set becomes large,
Since the elasticity of the pressure roller 26 is lost and the pressure is not applied periodically, the fixability becomes uneven.

The present invention has been made in view of the above circumstances, and even when a small-sized transfer material is continuously passed, the temperature of the non-sheet passing areas at both ends of the heating body unnecessarily rises. It is an object of the present invention to provide a heating element for preventing the occurrence of a problem and a fixing device provided with the heating element.

[0011]

According to a first aspect of the present invention, there is provided a heat-resistant member having a heating element pattern on at least one surface and a resistance having a positive temperature coefficient characteristic. And a PTC pattern.

According to a second aspect of the present invention, in the heating element of the first aspect, the heating element pattern has a plurality of conduction paths in a longitudinal direction of the plate-shaped heat-resistant member.
A C pattern connects all areas between these conduction paths,
It is characterized by the following.

According to a third aspect of the present invention, in the heating element of the first aspect, the PTC pattern is arranged so as to sandwich the entire conduction path of the heating element pattern.

According to a fourth aspect of the present invention, a heating element pattern and an NTC pattern having a resistance having a negative temperature coefficient characteristic are provided on at least one surface of the plate-shaped heat-resistant member.

According to a fifth aspect of the present invention, in the heating element of the fourth aspect, the NTC patterns are arranged at both ends in the longitudinal direction of the heating element pattern.

According to a sixth aspect of the present invention, there is provided a fixing device including a heating element for heating the unfixed toner carried on the surface of the transfer material to fix the toner on the transfer material, wherein the heating element comprises:
A heating element according to claim 1, 2, 3, 4, or 5.
It is characterized by the following.

[0017]

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

Embodiment 1 FIG. 1 shows an example of a fixing device according to the present invention. Note that FIG.
FIG. 3 is a longitudinal sectional view of a fixing device using the same.

The fixing device 20 shown in FIG. 1 includes a heating element (heater) A, a film guide 25, and a fixing film 25.
And a pressure roller 26.

The heating element A is a plate-shaped member formed to be long in the width direction of the transfer material P. A heating element pattern 2A is provided on the surface (the lower surface in FIG. 1) of the ceramic base material 1, and the heating pattern 2A is further provided. Is covered with a glass coat 10. The purpose of the glass coat 10 is to improve the slidability and obtain the withstand voltage. The heating element A will be described later in detail.

The fixing film 25 has a diameter of 24 mm and a thickness of 5 mm.
4 μm primer and 10 μm on 0 μm polyimide
And a surface layer (Teflon layer) is formed into an endless shape, and is wrapped around the film guide 22. The fixing film 25 is formed by an arrow R26 of a pressure roller 26 described later.
With the rotation in the direction, it is driven to rotate in the direction of arrow R25.

The pressure roller 26 is formed by coating a 3.5 mm-thick silicone rubber 26b around an aluminum core 26a having a diameter of 13 mm, and covering the surface with a PFA tube, or by applying a fluororesin or a fluorine latex. Or something. The pressure roller 26 presses the fixing film 25 against the heater A from below. As a result, a belt-shaped fixing nip portion N having a nip width a is formed between the fixing film 25 and the pressure roller 26. Pressure roller 2
6 is rotationally driven in the direction of arrow R26 by driving means (not shown), whereby the transfer material P
Is transported in the direction of arrow K.

A thermistor 6 serving as a temperature detecting means is attached to the back surface (the upper surface in FIG. 1) of the above-mentioned heating element A.
The temperature is adjusted by turning on / off the triac 24 by the PU 23.

FIGS. 2A, 2B and 2C show the structure of the heating element A. FIG. It is a bottom view, a top view, and a front view in this order. In the following description, the vertical dimension in (a), (b), and (c) is the “length L” of the heating element A (or the ceramic substrate 1), and the horizontal dimension in (a) and (b). Dimensions are "width W" of heating element A (or ceramic substrate 1),
The dimension in the left-right direction in (c) is the “thickness t” of the heating element A.
It is assumed that. Also, the lower surface illustrated in (a) is referred to as “front surface”, and the upper surface illustrated in (b) is referred to as “back surface”.

The heating element A is a long plate-shaped ceramic substrate 1
, A heating element pattern 2A, a PTC pattern 3A, a conductor pattern 4, and an electrode 5.

The ceramic substrate (heat-resistant member) 1 is formed of alumina in the form of a long plate having a length L of 270 mm, a width W of 7.78 mm and a thickness of 0.635 mm.

The heating element pattern (resistance heating element) 2A is formed at the center of the surface side of the ceramic substrate 1 in the width W direction so as to extend in a band shape in the length L direction. The heating element pattern 2A was formed such that the length was 215 mm, the width was 1.5 mm, and the total resistance was 25Ω. Resistance pattern 2A
Is formed by applying a paste material, and this paste material has a positive temperature resistance coefficient of 500 ppm / deg.

The PTC pattern 3A is formed on both sides in the width direction of the heating element pattern 2A and has the same length as the heating element pattern 2A. That is, the PTC pattern 3A
Have a length of 215 mm and a width of 1 mm, and are formed on the left and right sides of the heating element pattern 2A, respectively. The PTC pattern 3A used in the present embodiment has a glass frit and a PTC characteristic such as barium titanate (positive temperature coefficient characteristic of resistance).
And a mixture with an oxide ceramic having the formula: The PTC pattern 3A had a positive temperature coefficient characteristic of 3000 ppm / deg.

The conductive pattern 4 is formed of the respective PTs described above.
It is formed so as to contact the C pattern 3A on the outside. The conductive patterns 4 and 4 have upper portions in FIG. 2A longer than the PTC patterns 3A and 3A, and are connected to the electrodes 4 and 4, respectively.

Electrodes 9 and 9 are also provided below the surface of the ceramic substrate 1 in FIG. These electrodes 9, 9 are connected to conductor patterns 7, 7 on the back side through through holes 8, 8, and these electrodes 7, 7 have a length L walking on the back side of the ceramic substrate 1. A thermistor 6 arranged substantially at the center is connected.

Each of the above-mentioned patterns is formed on the front surface or the back surface of the ceramic substrate 1 by, for example, screen printing.

The portion of the surface of the ceramic substrate 1 which is in contact with the fixing film 25 is coated with glass (not shown) to provide slidability and dielectric strength.

The heating element A having the above-described configuration was incorporated in the fixing device 20 as the above-described heating element A in FIG.

In such a fixing device 20, while maintaining the heating element A at 200 ° C., a width of 100 mm and a length of 240 mm
Were continuously fed at a speed of 8 sheets per minute on a central basis. When paper is passed using the conventional heating element D (see FIG. 7), the temperature gradually increases in a non-paper passing area where no envelope passes. In the experiment, the temperature of the heating body D reached 270 ° C. outside the paper passing area on the tenth sheet. For this reason, the heating element D melts the film guide 22 formed of the liquid crystal polymer, and the nip width a of the fixing nip portion N is reduced at both ends where the envelope does not pass. Further, when the paper is further continuously fed, the difference in thermal expansion of the pressure roller 26 appears as a diameter difference of 0.3 mm (1.5%) between the center and the end, so that the fixing film 25 Twist occurs.

Further, if a coating such as FEP is provided on the surface of the pressure roller 26, melting starts, the film is peeled off, and the releasability is reduced.

On the other hand, when the heating member A of the present embodiment (see FIG. 2) is used, if the non-sheet passing area is going to exceed 230 ° C., the resistance in this area is increased about 10 times. Since the amount of current at both ends is reduced to 1/10 of that at the center, the amount of heat generated in this portion of the heating element pattern 2A is also 1
/ 10. As a result, excessive heat is not supplied in the non-sheet passing area, and natural heat radiation is balanced, so that the temperature does not rise to 230 ° C. or higher. Therefore, the above problem did not occur.

FIG. 5 shows the temperature distribution in the longitudinal direction of the heating element (heater) during the passage of small-size paper between the present embodiment and the conventional example. A broken line X indicates the conventional example, and a solid line Y indicates the present embodiment. Is shown.

In the conventional example, the control temperature is maintained in the small-size paper passing area, but the temperature is raised outside the control temperature. On the other hand, in the present embodiment, it can be seen that the control temperature is maintained outside the small-size sheet passing area.

<Embodiment 2> FIGS. 3 (a), 3 (b),
(C) shows a heating element B according to the second embodiment. It is a bottom view, a top view, and a front view in this order.

In the present embodiment, as shown in these figures, two heating element patterns 2B, 2B are formed on both sides of one PTC pattern 3B, and the conductor patterns 4, 4 Is formed. Other configurations are the same as those in the above-described first embodiment, and a description thereof will not be repeated.

The PTC pattern 3B has the same positive temperature resistance characteristics as that of the first embodiment, and is formed by printing over a width of 1 mm and a length of 215 mm.

The lengths of the heating element patterns 2B and 2B were also 215 mm, and the width was 1.5 mm. Here, it is not always necessary that the two heat generating patterns 2B, 2B have the same width. The resistance value of these heat generating patterns 2B, 2B was set to 25Ω by adding two measured values in the width direction.

However, when the two heating element patterns 2B and 2B are used, the actual heating width of the heating element patterns 2B and 2B is wider than that in the first embodiment. The efficiency of heating the non-heated fixing film 25 and the pressure roller 26 is better than simply expanding the 1.5 mm of the first embodiment to 2 mm. This is presumably because the heating is performed at a position closer to both ends of the nip width a of the formed fixing nip N, so that the temperature distribution in the fixing nip N becomes wider.

As described above, the PTC pattern 3B
Is formed, it is possible to arrange the PTC pattern 3B in a portion where the temperature is highest in the fixing nip portion N. As a result, the conduction in the non-sheet-passing area is reduced as soon as small-sized paper such as an envelope starts to pass, so that the temperature in the non-sheet-passing area can be prevented more quickly.

<Embodiment 3> FIGS. 4 (a), (b),
(C) shows a heating element C according to the third embodiment. It is a bottom view, a top view, and a front view in this order.

In the present embodiment, the first embodiment,
2 uses the positive temperature coefficient characteristic PTC patterns 3A and 3B, while uses the negative temperature coefficient characteristic NTC pattern 3C.

As shown in FIG. 3A, a heating element pattern 2C disposed at the center in the width W direction of the ceramic base 1 is formed.
Along the portion that becomes the non-sheet passing area in the length L direction
TC patterns 3C and 3C are provided.

The heating element pattern 2C has a length of 215 mm and a width of 1.5 mm, and is in contact with the NTC patterns 3C and 3C over a length of 60 mm from both ends. N
The TC patterns 3C, 3C are connected to the electrodes 5, 5 via the conductor patterns 4C, 4C. L1 indicates the width of the minimum sheet passing size on the basis of the center. When passing letter-size paper, use NTC pattern 3
Since the portions C and 3C do not enter the non-sheet passing state, the temperature does not exceed 200 ° C. Therefore, NTC pattern 3
Almost no current flows through C and 3C, conductor pattern 4C,
A current flows from 4C to each end of the heating element pattern 2C. This is because both ends of the heating element pattern 2C are directly connected to the conductor patterns 4C, respectively.

On the other hand, when the above-described envelope is passed, the resistance of the NTC patterns 3C and 3C is reduced, and the resistance of this portion is lower than that of the heating element pattern 2C. Therefore, the current flows to near the center through this part. For this reason, the current at both ends of the heating element pattern 2C is reduced, so that heat generation is suppressed.

In this case, it is possible to prevent the temperature of the non-sheet passing area from rising even for a sheet having a width of 182 mm such as B5. This is because the resistance of the NTC patterns 3C and 3C in the paper passing area does not decrease, so that the NTC patterns 3C and 3C are conducted just outside the paper passing area. This is because the current path moves to the heating element pattern 2C without passing through 3C and 3C.

[0051]

As described above, according to the present invention,
By combining the pattern of the positive temperature coefficient characteristic or the negative temperature coefficient characteristic with a part or all of the heating element, the heat generation in the non-sheet passing area is reduced, and the offset due to high temperature, the fixing film, the pressure roller, the film, etc. Damage to parts such as guides can be prevented.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a fixing device according to a first embodiment.

FIG. 2A is a bottom view of the heating body according to the first embodiment.
(B) is a top view of the heating element of the first embodiment. (C) is a front view of the heating body of Embodiment 1.

FIG. 3A is a bottom view of a heating body according to the second embodiment.
(B) is a top view of the heating element of the second embodiment. (C) is a front view of the heating body of Embodiment 2.

FIG. 4A is a bottom view of a heating element according to the third embodiment.
(B) is a top view of the heating element of the third embodiment. (C) is a front view of the heating body of Embodiment 3.

FIG. 5 is a diagram showing a relationship between a heater length direction position and a heater surface temperature.

FIG. 6 is a longitudinal sectional view of a conventional fixing device.

FIG. 7A is a bottom view of a conventional heating element. (B) is a top view of a conventional heating element. (C) is a front view of the conventional heating body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat resistant member (ceramic base material) 2A, 2B, 2C Heating element pattern 3A, 3B PTC pattern 3C NTC pattern 4, 4C Conductor pattern 6 Thermistor 20 Fixing device 25 Fixing film 26 Pressure roller A, B, C Heating element (Heater ) P transfer material

Claims (6)

[Claims] A PT having a heating element pattern on at least one surface of a plate-shaped heat-resistant member and a resistance having a positive temperature coefficient characteristic.
A heating element comprising a C pattern. 2. The heating element pattern has a plurality of conduction paths in a longitudinal direction of the plate-shaped heat-resistant member,
The heating element according to claim 1, wherein the TC pattern connects the entire area between the conduction paths. 3. The heating element according to claim 1, wherein the PTC pattern is arranged so as to sandwich the entire conduction path of the heating element pattern. 4. An NT having a heating element pattern on at least one surface of a plate-shaped heat-resistant member and a resistance having a negative temperature coefficient characteristic.
A heating element comprising a C pattern. 5. The heating element according to claim 4, wherein the NTC patterns are arranged at both ends in the longitudinal direction of the heating element pattern. 6. A fixing device provided with a heating element for heating an unfixed toner carried on a surface of a transfer material and fixing the toner on the transfer material, wherein the heating element comprises: Or a heating element according to claim 5.