JPH08185069A - Fixing heater and device, and image forming device - Google Patents

Abstract

PURPOSE: To reduce unevenness in heating and fixing with a simple constitution by providing a pair of electrodes electrically connected to a heating resistor having a nonlinear heat generating region and a thermal diffusion layer formed with an electrical insulating layer on the heating resistor. CONSTITUTION: A PTC heating resistor 15 having a positive temperature coefficient of resistance is laminated on the top surfaces of a pair of the comb-shaped electrodes 13 and 14 and a substrate 12a and energized by a rectangular waveform heat generating part 15a interposed in the gap g0 between the respective comb line projecting parts 13a and 14a of a pair of the comb-shaped electrodes 13 and 14, to generate heat. The heat generating part 15a is meandered like a rectangular wave in a longitudinal direction, to expand a heat generating region. Then, an electrical insulating glass coat 16 as the electrical insulating layer covering the outside surface of the PTC heating resistor 15 is laminated on the substrate surface 12a and further, the thermal diffusion layer is laminated to receive/diffuse the heat from the resistor 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin fixing heater to be used by being attached to small equipment such as office automation equipment, household electric equipment and precision manufacturing equipment, and a copying machine and a facsimile equipped with the fixing heater. The present invention relates to a fixing device used for fixing a toner and an image forming apparatus using the fixing device.

[0002]

2. Description of the Related Art Generally, in an electronic copying machine, a copy sheet on which a toner image is formed is passed between a plate-shaped fixing heater and a pressure roller while directly or indirectly with a heat-resistant sheet interposed therebetween. The toner on the copy paper is heated and melted by the heating of the fixing heater to be fixed.

As a conventional fixing heater of this type, there is one having a structure as shown in FIGS. The fixing heater 1 is formed by laminating a pair of comb-shaped electrodes 3 and 4 made of a good conductor film on a surface 2a of an elongated heat-resistant / electrically insulating substrate 2 made of alumina (Al ₂ O ₃ ) ceramics or the like. There is. These comb-shaped electrodes 3 and 4 have a plurality of rectangular comb-shaped projections 3a and 4a protruding in the longitudinal direction at a predetermined pitch,
These comb-tooth-shaped protrusions 3a and 4a are arranged side by side so as to be engaged with each other with a predetermined gap g therebetween, and the respective rectangular one end portions in the longitudinal direction are formed in the power receiving portions 3b and 4b, and are shown here No power supply connector is electrically connected to receive power.

As shown in FIG. 9, a PTC (Positive Temperature Coefficient) resistance heating element 5 having a positive resistance temperature coefficient is laminated on the upper surfaces of the pair of comb-shaped electrodes 3, 4 and the substrate surface 2a. . Further, the outer surface of the PTC resistance heating element 5 is covered with a surface glass layer 6 having smoothness and electrical insulation, and a copy paper P is slid on the upper surface thereof to heat and fix the toner image on the copy paper P. It is designed to let you.

The PTC resistance heating element 5 has a rectangular wave-shaped heating portion 5a (FIG. 7, FIG. 7) interposed in a gap g between the comb tooth-shaped projections 3a, 4a of the pair of comb-shaped electrodes 3, 4. 8 is indicated by parallel diagonal lines).

The heating portion 5a is a PT having a positive temperature coefficient of resistance.
When the heating current exceeds a predetermined value due to an increase in the passing current, the resistance is increased to suppress the passing current, so that the temperature rise above the predetermined temperature is suppressed. For this reason, it is not necessary to control the temperature of the heat generating portion 5a.
A temperature sensor such as a thermistor that detects the temperature of the device and a temperature control circuit that controls the current flowing to the PTC resistance heating element 5 based on the detection value of this temperature sensor are not necessary, and the number of parts is reduced and the size and weight are reduced. And cost reduction can be achieved together.

[0007]

However, in such a conventional fixing heater 1, since the heating portion 5a of the PTC resistance heating element 5 meanders in a rectangular waveform, as shown in FIG. A portion a having a large heating area due to the long length of the heating portion 5a of the PTC resistance heating element 5 with respect to the sliding direction indicated by the arrow and a portion b having a small heating area due to the short heating length are resistive. Since the heating elements 5 are distributed at a required pitch in the longitudinal direction, the heating time of the copy sheet differs in each part, which causes uneven heating and uneven fixing.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a fixing heater, a fixing device, and an image forming apparatus capable of reducing heating unevenness and fixing unevenness with a simple structure. is there.

[0009]

The present invention is configured as follows in order to solve the above-mentioned problems.

According to a first aspect of the present invention, there is provided a substrate made of a heat-resistant electrically insulating material, a resistance heating element formed on one surface of the substrate and having a non-linear heating area, and the resistance heating element. It is characterized by having a pair of electrodes electrically connected to each other and a heat diffusion layer formed on the resistance heating element with an electric insulating layer interposed therebetween.

Further, in the invention according to claim 2 of the present application, the resistance heating element is formed such that the length of the heating region when viewed from the direction perpendicular to the longitudinal direction is different depending on the position in the longitudinal direction. It is characterized by being done.

Further, the invention according to claim 3 of the present application is
The pair of electrodes is characterized by a pair of comb-shaped electrodes that are arranged side by side so that the plurality of comb-shaped projections are engaged with each other with a required gap therebetween.

Further, the invention according to claim 4 of the present application is characterized in that the resistance heating element comprises a resistance element having a positive temperature coefficient of resistance.

The invention according to claim 5 of the present application is characterized in that the heat diffusion layer is made of a metal layer.

Further, the invention according to claim 6 of the present application is
A substrate made of a heat-resistant electrically insulating material, a pair of comb-shaped electrodes arranged side by side on one surface of the substrate so that a plurality of comb-shaped projections are engaged with each other with a required gap, and one surface of the substrate A resistance heating element that has a positive temperature coefficient of resistance and is laminated over the pair of comb-shaped electrodes, an electric insulating layer that covers the resistance heating element, and heat that is laminated on the electric insulating layer. It is characterized by having a diffusion layer and a surface protective layer covering the thermal diffusion layer.

Furthermore, the invention according to claim 7 of the present application is characterized in that a heat insulating layer is formed between the substrate and the resistance heating element.

The invention according to claim 8 of the present application is characterized in that the fixing heater according to any one of claims 1 to 7 and the pressure roller are arranged to face each other.

Further, the invention according to claim 9 of the present application is
The fixing device according to claim 8 is provided.

[0019]

In the present invention, since the thermal diffusion layer is formed on the resistance heating element such as PTC, the resistance heating element has a non-linear portion in its heating portion due to meandering along the longitudinal direction. Then
Even when heating unevenness is likely to occur, the heat generated from these heat generating portions is diffused by the heat diffusion layer, so that the heating unevenness can be reduced or prevented.

[0020]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 9, the same or corresponding parts are denoted by the same reference numerals, but the dimensions of each part are exaggerated in some cases, and the dimensions are not necessarily proportional,
For example, FIG. 1 is enlarged in the width direction, and FIGS. 2 and 4 are enlarged in the thickness direction of each layer.

FIG. 1 is a plan view showing the surface of an embodiment of a fixing heater according to the present invention, and FIG. 2 is an end view of the section cut along the line II--II in FIG. 1. As shown in these drawings, fixing is performed. Heater 11
Is a heat resistant / electrically insulating material such as alumina (Al ₂
Surface 12 of elongated substrate 12 made of O ₃ ) ceramics
A pair of comb-shaped electrodes 13 and 14 made of a good conductor film on a.
Are stacked. These comb-shaped electrodes 13 and 14 have a plurality of rectangular comb-shaped projections 13a and 14a protruding in the longitudinal direction at a predetermined pitch, and the comb-shaped projections 13a and 14a have a predetermined gap g0. They are placed side by side so that they can be engaged with each other.
b and 14b, and a power feeding connector (not shown) is electrically connected to receive power.

As shown in FIG. 2, a PTC (Positive Temperature Coefficien) having a positive resistance temperature coefficient is formed on the upper surfaces of the pair of comb-shaped electrodes 13 and 14 and the substrate surface 12a.
t) The resistance heating element 15 is laminated. The PTC resistance heating element 15 is composed of a pair of comb-shaped electrodes 13 and 14, and each comb-shaped projection 13 is formed.
A rectangular wave-shaped heat generating portion 15a (indicated by parallel diagonal lines in FIG. 1) interposed in the gap g0 between the a and 14a is energized to generate heat. The heat generating portion 15a is meandered in a rectangular wave shape along the longitudinal direction to enlarge the heat generating region.

The heat generating portion 15a has a positive temperature coefficient of resistance P
Since the TC resistor is used, when the conduction current increases and the heat generation temperature exceeds the predetermined value, the electrical resistance is increased to suppress the conduction current and suppress the temperature rise above the predetermined temperature. For this,
Since the temperature control of the heat generating portion 15a is unnecessary, a temperature sensor such as a thermistor for detecting the temperature of the heat generating portion 15a and the PTC resistance heating element 15 based on the detected value of the temperature sensor.
Since a temperature control circuit for controlling the current passing therethrough is not necessary, it is possible to reduce the number of parts, reduce the size and weight, and reduce the cost.

An electrically insulating glass coat 16 which is an electrically insulating layer for covering the outer surface of the PTC resistance heating element 15 is provided.
Is laminated on the substrate surface 12a, and a heat diffusion layer 17 is further laminated on the electrically insulating glass coat 16 to receive heat from the PTC resistance heating element 15 and diffuse it.

The thermal diffusion layer 17 is laminated on the electrically insulating glass coat 16 by applying a conductive paste such as Ag or Pt by screen printing and firing, and the outer surface of the thermal diffusion layer 17 is made smooth. The copy sheet P is covered with the surface glass coat layer 18 and the copy sheet P is slid on the surface glass coat layer 18 to heat the copy sheet P.
The toner image attached to one surface of the sheet is fixed on the copy sheet P.

Therefore, according to the present embodiment, even if there is uneven heating due to the heating portion 15a of the PTC resistance heating element 15 meandering, the heat from the heating portion 15a is transferred to the heat diffusion layer 1
7, the copying paper P sliding on the upper surface of the surface glass coat layer 18 on the thermal diffusion layer 17 can be heated uniformly, and uneven heating can be effectively prevented. As a result, Thus, it is possible to effectively prevent uneven fixing due to uneven heating.

FIG. 3 shows a fixing heater 2 according to another embodiment of the present invention.
1 is a plan view of the fixing heater 21, in which a pair of comb-shaped electrodes 13 and 14 are laminated on the PTC resistance heating element 15 as shown in the longitudinal sectional view of FIG. It is characterized in that a heat insulating layer 19 is interposed between and the substrate surface 12a.

According to the fixing heater 21, the heat generated by the PTC resistance heating element 15 is transferred to the substrate 12 so that the heat insulating layer 1
Since the heat is insulated by 9, the heat radiation from the back surface of the substrate 12 can be reduced, while the heat generation of the resistance heating element 15 can be efficiently conducted to the surface glass coat layer 18, so that the heating efficiency is improved. be able to. Further, since a temperature sensor such as a thermistor is not provided on the back surface of the substrate 12, it is not necessary for the PTC resistance heating element 15 to transmit the heat generated by the PTC resistance heating element 15 to the substrate 12. The surface glass coat layer 18 may be omitted. In the present invention, the material of the resistance heating element is not limited to the PTC resistor and may be a negative characteristic (NTC) resistor.

FIG. 5 shows the construction of an embodiment of an electronic copying machine 31 which is a kind of image forming apparatus according to the present invention. The copying machine 31 has a casing 32 and a copy sheet P in a cassette 33. And an image forming unit 34 that forms a toner image corresponding to an image of an original document (not shown) and a fixing device 35 that fixes the toner image on the copy sheet P.

The fixing device 35 is constructed, for example, as shown in FIG. 6, and faces the fixing roller 36 to face the fixing heater 1.
The fixing heater 11 is attached to the holder 37.

The holder 3 including the fixing heater 11
A ring-shaped endless heat-resistant sheet 38 such as polyimide resin is wound around the outer periphery of 7, and the upper surface of the surface glass coat layer 18 immediately above the heat diffusion layer 17 of the fixing heater 11 is the heat-resistant sheet 38 in the figure. It is elastically in contact with the silicone rubber layer of the fixing roller 36 through.

Then, the fixing heater 11 is energized through the elastic connector made of phosphor bronze plate or the like in contact with the power receiving portions 13b, 14b of the pair of comb-shaped electrodes 13, 14 to generate heat from the PTC resistance heating element 15. The portion 15a generates heat, and this heat generation is diffused by the thermal diffusion layer 17 and then applied to the surface glass coat layer 18. Therefore, the outer surface of the heat resistant sheet 38 of the surface glass coat layer 18 and the fixing roller 36.
The copying paper P on which the toner image T is formed is heated by the fixing heater 21 between the silicone rubber layer and
The unfixed toner image T can be melted and fixed on the copy paper P.

[0033]

As described above, according to the present invention, since the thermal diffusion layer is formed on the resistance heating element such as PTC, the resistance heating element is meandered along the longitudinal direction, so that the heating portion thereof is formed. In addition, even if there is a non-linear portion and heating unevenness is likely to occur, the heat generation from these heat generating portions is diffused by the heat diffusion layer, so that the heating unevenness can be reduced or prevented.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of a fixing heater according to the present invention.

FIG. 2 is an end view of a cut portion taken along line II-II in FIG.

FIG. 3 is a plan view of a fixing heater according to another embodiment of the present invention.

FIG. 4 is an end view of a cut portion taken along line IV-IV in FIG.

FIG. 5 is an overall configuration diagram of an embodiment of an image forming apparatus according to the present invention.

FIG. 6 is a vertical cross-sectional view of an embodiment of the fixing device shown in FIG.

FIG. 7 is a plan view of an example of a conventional fixing heater.

FIG. 8 is an enlarged view of a heat generating portion of the fixing heater shown in FIG.

FIG. 9 is an end view of a cut portion taken along line IX-IX in FIG. 7.

[Explanation of symbols]

 11, 21 Fixing heater 12 Heat-resistant electrical insulating substrate 12a Surface of heat-resistant electrical insulating substrate 13,14 Pair of comb-shaped electrodes 13a, 14a Comb-shaped protrusions 15 PTC resistance heating element 15a Heating portion 16 Electrical insulating glass coat 17 Heat Diffusion layer 18 Surface glass coat 19 Thermal insulation layer 31 Image forming apparatus 32 Housing 33 Cassette 34 Image forming apparatus main body 35 Fixing device 36 Fixing roller 37 Holder 38 Heat resistant sheet P Copy paper T Toner image

Claims (9)

[Claims] 1. A substrate made of a heat-resistant electrically insulating material, a resistance heating element formed on one surface of the substrate and having a non-linear heating area, and a pair of electrodes electrically connected to the resistance heating element. And a heat diffusion layer formed on the resistance heating element with an electrical insulating layer interposed therebetween, a fixing heater. 2. The resistance heating element is formed so that the length of the heating region when viewed from the direction perpendicular to the longitudinal direction of the resistance heating element is different depending on the position in the longitudinal direction. The fixing heater described. 3. The pair of electrodes comprises a pair of comb-shaped electrodes arranged in parallel so that a plurality of comb-tooth-shaped protrusions are engaged with each other with a required gap therebetween. Fixing heater. 4. The fixing heater according to claim 1, wherein the resistance heating element is a resistance element having a positive temperature coefficient of resistance. 5. The fixing heater according to claim 1, wherein the heat diffusion layer is made of a metal layer. 6. A substrate made of a heat-resistant electrically insulating material, and a pair of comb-shaped electrodes provided on one surface of the substrate so that a plurality of comb-tooth-shaped protrusions are arranged side by side so as to be engaged with each other with a required gap therebetween. A resistance heating element laminated on one surface of the substrate and on the pair of comb-shaped electrodes and having a positive temperature coefficient of resistance; an electric insulating layer covering the resistance heating element; and an electric insulating layer on the electric insulating layer. A fixing heater comprising: a heat diffusion layer laminated on the heat diffusion layer; and a surface protection layer covering the heat diffusion layer. 7. The fixing heater according to claim 1, wherein a heat insulating layer is formed between the substrate and the resistance heating element. 8. A fixing device, wherein the fixing heater according to claim 1 and a pressure roller are arranged so as to face each other. 9. An image forming apparatus comprising the fixing device according to claim 8.