JPH07152268A - Fixing heater and device and image forming device - Google Patents

Abstract

PURPOSE:To provide a heater capable of forcibly stopping the energization of a heater and preventing ignition caused by overheating, when the abnormality occurs in a fixing heater. CONSTITUTION:In the fixing heater H having a resistance heating element 2 of a belt-like thick film formed on the surface of a substrate 1 made of a heat-resistant insulating material, a recessed part 6 is formed on the surface of the substrate 1 and the fixing device uses the fixing heater H. In a normal state, an almost uniform temperature distribution in the longitudinal direction is obtained and when the abnormal state of the overheating, etc., occurs, the substrate 1 of the heater H is broken down to surely disconnect electric circuit. Therefore, forming or burning of expensive OA equipment, etc., by the overheating never happens, so that an accident can be prevented without getting out of control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing heater used for toner fixing of an image forming apparatus such as a copying machine or a facsimile, a fixing apparatus using the fixing heater, and an image forming apparatus.

[0002]

2. Description of the Related Art In an electronic copying machine, for example, a copy sheet on which a toner image is formed is passed while being pinched between a fixing heater and a pressure roller, and the heat of the heater heats the copy sheet to heat the toner. Is welded and fixed.

As the fixing heater, silver-palladium alloy (Ag / Pd) powder or the like is formed on the surface of an elongated heat-resistant / electrically insulating substrate 1 made of alumina ceramics or the like, a glass powder (inorganic binder), an organic material. A paste mixed with a binder is applied by printing and fired to form a strip-shaped thick film resistance heating element, and a film made of a good conductor such as silver (Ag) or platinum (Pt) is formed on both ends of this resistance heating element. To form the power supply terminal portion, and further wear the resistance heating element by covering the surface of this heating element with a glassy overcoat layer,
Those that have increased mechanical strength such as impact and are protected from sulfidation and oxidation have been put into practical use.

In a fixing device of a copying machine, a pressure roller and the fixing heater are arranged in parallel to face each other, and the surface of the pressure roller having a rotating shaft is made of a heat resistant elastic material.
It is designed to rotate while being lightly pressed against the overcoat layer of the fixing heater. Then, when the copy sheet is supplied between the fixing heater and the pressure roller, the copy sheet is conveyed while sliding on the surface of the overcoat layer of the heater by the rotation of the pressure roller, and during this time, the heat of the heater copies the copy sheet. The toner on the paper is heated and fixed.

In this fixing heater, a temperature detecting element such as a thermistor is attached to the surface (rear surface) of the substrate 1 opposite to the surface on which the resistance heating element is formed, and the temperature of the heating element is The detected heater is fed back to the temperature control circuit device to control the electric power applied to the fixing heater, so that the fixing heater maintains a constant temperature.

This fixing heater is mounted on a tray made of plastic and mounted on a copying machine, and the temperature is raised to 180 to 200 ° C. to heat and fix the wax which is the main component of the toner. If control becomes uncontrollable due to mounting failure of the element or failure, malfunction or failure of the temperature control circuit device, SSR (solid state relay) etc. becomes energized and commercial voltage is continuously applied, resulting in overcurrent and resistance. The temperature rises so high that the heating element glows red.

If the red heat of the resistance heating element continues, the plastic tray on which the heater is mounted, the casing of the fixing device, and the copy paper that is transported by being pressed on the heater are burned or ignited. There was a problem.

Therefore, in order to deal with this problem, a through hole is formed in the green sheet when the substrate is formed, or a through hole is formed by laser processing after firing the ceramic, and a crack is generated from this through hole portion when the heater is overheated. It has been practiced to generate this to break the substrate into pieces and cut the resistance heating element. That is, when thermal runaway occurs in the heater, a large stress is generated in the ceramic substrate. However, by forming the through hole in advance, the stress concentrates in the through hole, so that a crack is generated from the through hole portion and the substrate 1 Is designed to destroy.

However, providing such a through hole in the portion where the resistance heating element is formed narrows the width of the heating element.
The resistance value of that part becomes high and the temperature distribution in the longitudinal direction is not uniform and absolutely impossible. Also, even if a through hole is provided in a part other than the part where the resistance heating element is formed, heat generation adjacent to the through hole Since the heat from the body part is prevented from being dispersed to the substrate, the temperature of the heating element is locally increased, and the temperature distribution in the longitudinal direction is not uniform as in the above case.

In consideration of the rising characteristics (temperature rising rate) of the heater substrate, the narrower the width of the substrate, the smaller the heat capacity, which is preferable. Usually, the width of the substrate is as narrow as possible. However, providing a through hole in a portion of the narrow board other than the area where the resistance heating element is formed as described above also causes a decrease in the mechanical strength of the board, and the board is destroyed even in a normal use state. I had to do it.

[0011]

Recently, it has been desired to diversify equipments, etc., and when controlling voltage and current, a complicated circuit may be formed, resulting in an increase in electronic parts, which causes troubles such as accidents. The probability of occurrence is also increasing. Of course, in electrical equipment, various accidents are dealt with, and when these accidents occur, the safety device operates.However, the double and triple safety devices do not work, and other accidents occur. There are also unexpected accidents that extend to the circuit.

For example, in the fixing heater having the through hole as described above, an overcurrent flows, and a thermal fuse or an overcurrent which is inserted in the circuit in series with the heater and arranged on the back surface of the heater is detected and prevented. Although safety measures such as breaking the board and stopping energization when the safety device such as a circuit that does not operate has been achieved, it is said that the temperature distribution of heat generation in the longitudinal direction is not uniform or the mechanical strength of the board decreases. There was a problem.

According to the present invention, in a steady state, the heat generation temperature distribution is uniform, and when an overcurrent flows through the fixing heater and an abnormality occurs, energization of the heater is forcibly stopped and ignition due to overheating is forced. It is an object of the present invention to provide a fixing heater which can be prevented from occurring and a fixing device using this heater.

[0014]

The fixing heater according to claim 1 of the present invention is a fixing heater in which a belt-shaped resistance heating element is formed on the surface of a substrate made of a heat-resistant and electrically insulating material. Is characterized in that a concave portion is formed on the surface thereof.

The fixing heater according to the second aspect of the present invention is characterized in that at least one concave portion on the surface of the substrate is formed in a dot shape or a groove shape.

The fixing heater according to the third aspect of the present invention is characterized in that the concave portion of the surface of the substrate has a cross-sectional area that becomes smaller toward the inside.

A fixing heater according to a fourth aspect of the present invention is characterized in that the concave portion on the surface of the substrate has a corner portion formed on the inner surface.

The fixing heater according to the fifth aspect of the present invention is characterized in that the concave portion formed in the substrate has a thermal strength lower than that of the flat portion.

A fixing device according to a sixth aspect of the present invention is characterized in that the pressure roller and the fixing heater according to the first to fifth aspects are arranged opposite to each other.

An image forming apparatus according to a seventh aspect of the present invention is characterized by including the fixing device according to the sixth aspect.

[0021]

In the substrate on which the strip-shaped resistance heating element is formed, there is no notch for blocking heat conduction in the portion where the heating element is not formed, and the portion along the resistance heating element is uniform.
The resistance heating element has a substantially uniform heating temperature distribution,
In the unlikely event that an overcurrent flows through the resistance heating element, the heating element becomes red-heated and a large stress is generated in the ceramic substrate. The ceramic substrate is destroyed, the energization is forcibly stopped, and ignition from the heater can be prevented.

[0022]

Embodiments of the fixing heater of the present invention will be described below with reference to the drawings. 1 is a top view of the fixing heater H, FIG. 2 is a bottom view, and FIG. 3 is an enlarged cross-sectional view of a portion cut along line XX of FIG. In the figure, 1 is a heat-resistant / electrically insulating material, for example, an alumina ceramic, and has a length of about 3
It is an elongated substrate having a size of 00 mm, a width of about 6 mm, and a thickness of about 1 mm. The reference numeral 2 indicates a length of about 230 mm, a width of about 2 mm, and a thickness of about 10 μm formed on the surface of the substrate 1 along the longitudinal direction.
Band-shaped resistance heating element mainly made of silver-palladium alloy,
Reference numerals 3 and 3 denote power supply terminal portions mainly composed of a wide silver-platinum alloy having a length of about 15 mm and a width of about 6 mm formed in multiple layers at both ends of the resistance heating element 2. Further, 4 is an insulating layer made of PbO-based glass powder or the like which covers a part of the surface of the substrate 1 including the resistance heating element 2, and 5 is almost the substrate 1 excluding the surface of the insulating layer 4 and the terminals 3 and 3. It is a glassy overcoat layer that covers the entire surface, and the insulating layer 4 has higher electrical insulation than the glass of the overcoat layer 5.

Reference numeral 6 denotes a recess formed by cutting out the back surface of the substrate 1, at least one of which is formed. Reference numeral 7 denotes a temperature detecting element, for example, a thermistor, which is connected between wiring conductors 8 of a width of about 1 mm formed of the same material as the power supply conductor 3 on the surface of the substrate 1 opposite to the surface on which the resistance heating element 2 is formed. ing. Reference numerals 9 and 9 denote terminal portions formed at the ends of the wiring conductors 8 and 8.

This fixing heater H uses a substrate 1 having recesses 6, 6, ... Formed on the back surface thereof at the time of molding a plate, and the surface of the substrate 1 having the recesses 6, 6 ,. Form body 2. To form the heating element 2, a conductive paste prepared by kneading a powder of silver-palladium alloy (Ag / Pd), a glass powder (inorganic binder), an organic binder and the like is prepared. Then, this paste is applied by printing on the elongated substrate 1, dried and then baked at about 850 ° C. for about 10 minutes. By this firing, the organic binder contained in the coating material is thermally decomposed, gasified and scattered, and the resistance heating element 2 made of silver / valadium is formed.

Then, a material having a smaller electric resistance value than the resistance heating element 2 such as silver (Ag), a silver-platinum alloy (Ag / Pt), or gold is formed on the front surface of both end portions of the resistance heating element 2 and the back surface of the substrate 1. A thick film of metal paste such as (Au) is printed, dried and then fired to form the power feeding terminal portions 3 and 3 and the terminal portion 9 of the wiring conductor 8.

After that, an insulating paste made of a material such as PbO-based glass powder is thick-film printed so as to cover the strip-shaped thick-film resistance heating element 2 portion and a part of the surface of the substrate 1, followed by drying and firing. The electrically insulating layer 4 is formed.

Next, a glassy overcoat layer is formed so as to cover the surface of the insulating layer 4 and substantially the entire surface of the substrate 1 except the terminals 3 and 3.

The overcoat layer 5 is formed by kneading a PbO-based glass powder containing lead oxide (PbO) as a main component with a vehicle (organic binder) in an organic solvent to form a glass paste. Apply the paste to form a continuous coating film with no gaps. Then, after drying, it is baked at about 850 ° C. for about 10 minutes to have a thickness of 30 μm to 100 μm.
The glass layer has a thickness of μm. This overcoat layer 5 has no unevenness on the surface, and the tip of the glass is gradually thinned so as to bleed at the end of the substrate.

The fixing heater H has a circuit configuration as shown in FIG. 4 and is energized to adjust the heat generation temperature. That is, the commercial power source S is connected to the temperature control circuit T via an SSR (solid state relay) and the heater H
When a current is applied between the terminal portions 3 and 3, a current flows through the resistance heating element 2 to generate heat. The temperature of the substrate 1 also rises due to the heat generated by the resistance heating element 2, and this heat is transmitted to the thermistor 7 attached to the back surface of the substrate 1 to change the resistance value of the thermistor 7. This change in the resistance value of the thermistor 7
It is output from the terminal portions 9 and 9 via 8 and is input to the temperature control circuit T to determine whether or not it is within an appropriate temperature range (= set temperature). When the temperature is lower than the set temperature, the ON signal is output to the SSR, and when the temperature is higher than the set temperature, the OFF signal is output to the SSR.

In this way, the temperature of the resistance heating element 2 is adjusted by controlling the electric power applied to the resistance heating element 2. The temperature control circuit T has been described for the ON / OFF control of the SSR, but other than that, the PWM (Pulse Width)
h Modulation) or a pulse width control method.

When the fixing heater H is energized between the terminal portions 3 and 3 at both ends, a current flows through the resistance heating element 2 and the heating element 2 exhibits a substantially uniform heat generation temperature distribution in the longitudinal direction.
In this heater H, silver / palladium contained in the metal alloy serves as an electrical resistance element, and the resistance value of the heating element 2 is adjusted by the ratio of silver / palladium contained in the resistance paste. In this embodiment, it has a resistance value of about 25 ohms [Ω], and when a voltage of 100 V is applied, a current of about 4 A flows, resulting in a heating value of about 400 W.

Then, normally, as described above, the thermistor 7 provided on the back surface of the substrate 1 detects the temperature of the heater H,
The SSR is controlled to be turned on and off through the temperature control circuit T to control it at a predetermined temperature. When the thermistor 7, the temperature control circuit T, the SSR, and the like fail for some reason and commercial power is continuously applied to the resistance heating element 2, the resistance heating element 2 overheats and becomes red. When this heating element 2 overheats, the substrate 1 on which the resistance heating element 2 is provided also becomes high temperature due to heat conduction, and when thermal stress is generated in the substrate 1, stress concentration occurs in the recesses 6, 6, ... A crack is formed, and this crack propagates into the substrate 1 to destroy the substrate 1 and the strip-shaped resistance heating element 2 on the substrate 1 as well. If the resistance heating element 2 is broken, the electrical connection is broken and the heating element 2
The energization to the fixing heater H is stopped and the fixing heater H is cooled, and it is possible to prevent ignition from the heater H itself or an object related to the heater H.

5 and 6 show an example of a fixing device such as a copying machine or a facsimile in which the fixing heater H is incorporated, and the heater H portion in the drawing is the same as that in FIGS. 1 to 3. The same parts are designated by the same reference numerals and the description thereof will be omitted. C1 is a pressure roller, and a heat-resistant elastic material such as a silicone rubber layer C4 is fitted on the surface of a cylindrical roller body C3 having both ends thereof provided with a rotary shaft C2 protruding therefrom. And
The fixing heater H is juxtaposed to the rotating shaft C2 of the pressure roller C1 and is mounted on the base C6. A heat resistant sheet C7 such as a polyimide resin is wound around the base C6 including the heater H, and the surface of the overcoat layer 5 just above the resistance heating element 2 is the heat resistant sheet C.
It is in pressure contact with the silicone rubber layer C4 of the pressure roller C1 via the pressure roller 7.

In the fixing device, the heater H is energized through the elastic connectors C5 and C5 made of a phosphor bronze plate or the like in contact with the terminal portions 3 and 3, and the heater H is overheated on the overcoat layer 5 of the resistance heating element 2. Of the toner image P between the surface of the heat-resistant sheet C7 and the silicone rubber layer C4.
The copying paper P on which T is formed is fed out in the direction of the arrow in the drawing while being pressed, and the copying paper P is heated by the fixing heater H at this time, whereby the unfixed toner image PT
Is melted and fixed on the copy paper P.

That is, as shown in FIG. 6, the pressure roller C
On the paper input side of No. 1, the unfixed toner image P on the copy paper P
First, T is heated and melted by the heater H via the heat-resistant sheet C7, and at least the surface portion thereof is much higher than the melting point and completely softened and melted. Thereafter, on the paper discharge side of the pressure roller C1, the copy paper P separates from the heater H and the toner image P
T naturally radiates heat and is cooled and solidified again, and the heat-resistant sheet C7 is also separated from the copy sheet P.

In this way, the toner image PT is once completely softened and melted, and then cooled and solidified again on the paper discharge side of the pressure roller C1, so that the toner image PT has a very large condensing force.

Then, the substrate 1 of the fixing heater H is in spite of the occurrence of an abnormality in an electronic component such as a semiconductor constituting the temperature control circuit T and an overcurrent flowing into the fixing heater H.
If a safety device such as a thermal fuse arranged on the back surface of the above does not operate, the resistance heating element 2 and the substrate 1 overheat. When the substrate 1 continues to be overheated, cracks are formed from the recesses 6, 6, ... Formed in the substrate 1 as described above, the substrate 1 made of alumina is disassembled, and the resistance heating element 2 on the substrate 1 continues. The part that has been removed disappears and the electrical connection is completely cut off.

Therefore, heat generation from the resistance heating element 2 is stopped, and an unexpected situation such as ignition from the copying machine can be eliminated.

In the experiments conducted by the present inventors, a resistance heating element 2 having a resistance value of about 25 ohm [Ω] was formed on the substrate 1 in the fixing heater H having the structure shown in FIGS. In between 1
When a rated voltage of 00 V is applied, a current of about 4 A flows to the resistance heating element 2 by the temperature control circuit T, and the surface temperature of the resistance heating element 2 is adjusted to about 180 ° C.

When the applied voltage is further increased and the surface temperature of the substrate 1 reaches about 490 ° C., cracks are generated from the recesses 6, 6, ... Formed in the substrate 1 and the substrate 1 , But the heater H was destroyed.

Of course, in order to generate cracks from the recesses 6, 6, ..., The environmental condition in which the fixing heater H is used, the degree of safety, the strength and distortion amount of the recesses 6, 6 ,.
It goes without saying that the resistance value of the resistance heating element 2 and the like must be thoroughly examined and set.

The present invention is not limited to the above embodiment,
For example, the material of the substrate is not limited to alumina ceramics, but may be other ceramics, glass, or a synthetic resin member having high heat resistance such as polyimide resin.

Further, the concave portion 6 may be formed by providing a convex portion in advance on a die for molding a substrate or may be formed by a laser beam after molding, or by intentionally leaving a thermal strain, the concave portion 6 may be formed in the substrate. The thermal shock strength in the vicinity of the recess may be formed weaker than that in other portions. The surface on which the recess 6 is formed is the substrate 1
Not only the surface on the back side of the sheet but also the surface on which the resistance heating element 2 is provided may be formed on the same surface or on both surfaces when the object to be heated is not affected. As shown, the surface may be on the opposite side corresponding to the position where the resistance heating element 2 is provided, but if it is formed on the edge side of the substrate 1, stress concentrates asymmetrically with respect to the substrate 1, so that the substrate 1 is easily destroyed. It was

Further, the shape and number of the concave portions 6 are not limited to the quadrangular pyramid shape formed in a dot shape, and as shown in FIG. 7, the vertical cross section has a polygonal pyramid shape 6a, a conical shape 6b or an oval shape (not shown). , A triangular shape such that the cross-sectional area thereof becomes smaller toward the inside, or a rectangular shape or the like, or a groove 6c having a triangular pyramid cross section or a groove 6d having a conical cross section as shown in FIG. One or several points (streaks) may be formed continuously or discontinuously in the short side direction, the long side direction, and the indefinite direction.

Further, although the heater has been described as one in which a thermistor is provided on the substrate as a temperature detecting element, the temperature detecting element is not limited to the thermistor, and the temperature detecting element is not directly attached to the substrate but is separately provided in a housing or the like. It is also possible to detect the mounting temperature.

Further, the materials for forming the electric insulation layer and the overcoat layer for covering the resistance heating element and the substrate are not limited to those of the embodiment, and it goes without saying that they can be appropriately selected according to the heating temperature and the situation of use. Nor.

Furthermore, the structure of the terminal portion of the heater and the power supply structure of the fixing device are not limited to those in the embodiment.

Further, in the above-described embodiment of the fixing device, the heat-resistant sheet is interposed around the fixing heater for heater protection and paper feeding, but the resistance of the fixing heater is not limited to such indirect contact. The copy paper may directly contact the heating element surface or the overcoat layer surface.

Furthermore, the fixing heater of the present invention is used for fixing an image forming apparatus such as a copying machine or a facsimile.
It is suitable.

[0050]

According to the present invention having the above-mentioned structure, the temperature distribution is substantially uniform in the longitudinal direction in the steady state, and when the safety device does not operate even when an abnormal state such as overheating occurs,
The circuit of the fixing heater can be destroyed to reliably cut off the electric circuit. Therefore, expensive OA equipment or the like does not smoke or burn due to overheating, and it is possible to prevent accidents before they become serious.

[Brief description of drawings]

FIG. 1 is a top view of a fixing heater showing an embodiment of the present invention.

FIG. 2 is a bottom view of FIG.

FIG. 3 is an enlarged cross-sectional view of a portion cut along line XX in FIG.

FIG. 4 is a circuit diagram showing an embodiment of a temperature control circuit and a temperature control circuit for energizing the fixing heater of the present invention to adjust the temperature.

FIG. 5 is a partial cross-sectional front view of a fixing device showing an embodiment of the present invention.

6 is a cross-sectional view taken along line VV in FIG.

FIG. 7 is an enlarged cross-sectional view of a fixing heater showing another embodiment of the present invention.

FIG. 8 is a bottom view of a fixing heater showing another embodiment of the present invention.

[Explanation of symbols]

 H: Fixing heater 1: Substrate 2: Resistance heating element 3, 3: Power supply terminal portion 4: High resistance electrical insulating layer 5: Overcoat layer 6, 6a to 6b: Recessed portion (dotted) 6c, 6d: Recessed portion (Groove shape) 7: Temperature detection element (thermistor) C1: Pressure roller P: Copy paper

Claims (7)

[Claims] 1. A fixing heater in which a belt-shaped resistance heating element is formed on the surface of a substrate made of a heat-resistant / electrically insulating material, wherein a recess is formed on the surface of the substrate. . 2. The fixing heater according to claim 1, wherein at least one concave portion on the surface of the substrate is formed in a dot shape or a groove shape. 3. The fixing heater according to claim 2, wherein the concave portion of the surface of the substrate has a cross-sectional area that decreases toward the inside. 4. The concave portion on the surface of the substrate has a corner portion formed on an inner surface thereof.
The fixing heater as described in. 5. The fixing heater according to claim 1, wherein the concave portion formed on the substrate has a thermal strength lower than that of the flat portion. 6. A fixing device in which a pressure roller and the fixing heater according to any one of claims 1 to 5 are arranged opposite to each other. 7. An image forming apparatus comprising the fixing device according to claim 6.