JPH07254478A - Flat heater and fixing device and image forming device - Google Patents

Abstract

PURPOSE:To provide a flat heater in which a thermistor can be easily mounted on a heater base board and a temperature can be accurately and speedily detected with high accuracy. CONSTITUTION:A belt-like resistance heating element 2 is installed on the surface 1A side of a base board 1 composed of a heat resistance-electric insulating material, and a tip-shaped thermistor 5 to detect a temperature of the heating element 2 is installed on the reverse 1B side. In the thermistor 5, a temperature sensing part 5b and terminal parts 5c are formed on one surface side of a base body 5a, and the other surface side of the base body 5a is situated on the board 1 side. The terminal parts 5c are connected to wiring conductors 6 formed on the reverse side of the board 1. This flat heater H, a fixing device mounted with this heater H and an image forming device by this fixing device are constituted. Thereby, a temperature can be adjusted with high accuracy, and the thermistor can be easily installed on the board, and since the jointing becomes the large area over the whole single surface, fixing strength is improved, so that thermorunaway of the heater is not caused due to thermistor separation.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art For example, in an electronic copying machine, a copy sheet on which a toner image is formed is passed while being pinched between a fixing plate heater and a pressure roller, and the heat of the heater causes the copy sheet to remain on the copy sheet. The toner is heated to melt and fix.

A cross section of the fixing plate heater is shown in FIG.
Shown in. The heater H includes silver-palladium alloy (Ag.Pd) powder and the like on the surface side 1A of the elongated heat-resistant and electrically insulating substrate 1 made of alumina (Al ₂ O ₃ ) ceramics, glass powder (inorganic binder), A paste prepared by kneading with an organic binder is applied by printing and firing to form a strip-shaped thick film resistance heating element 2, and silver (Ag) or silver-platinum (Ag) is formed on both ends of the resistance heating element 2. -Pt) alloy or silver-palladium alloy (Ag-Pd) is used to form a film of a good electric conductor to form a power supply terminal portion (not shown), and the surface of the resistance heating element 2 is made of glass. It is covered with an overcoat layer 4 to improve mechanical strength such as abrasion resistance and impact resistance, protect against corrosion from sulfidation and oxidation, and electrically insulate the pressure roller of a copying machine. .

On the rear surface side 1B of the heater H, which is opposite to the front surface side 1A on which the resistance heating element 2 is formed, a chip shape (having no lead wire) as a temperature detecting element of the resistance heating element 2 is provided. Therefore, a thermistor 5 of a disc type is also attached. Reference numerals 6 and 6 in the figure denote silver (Ag) or silver / platinum (Ag) formed on the back surface 1B of the substrate 1.
-A pair of wiring conductors made of a film of a good conductor such as a Pt) alloy or a silver-palladium (Ag-Pd) alloy.

Further, the thermistor 5 having the above-mentioned chip shape (which is also called a disk shape because it has no lead wire) is shown in FIG.
The configuration is as shown in. In FIG. 4, 5a is a flat plate-shaped substrate made of alumina (Al ₂ O ₃ ) ceramics,
Reference numeral b denotes a temperature sensitive portion 5c formed of a thin film formed by mixing oxides of manganese (Mn), cobalt (Co), nickel (Ni), etc. formed in the central portion on one surface of the base 5a,
Reference numeral 5c is an electrode portion composed of a platinum (Pt) layer or the like formed on both ends of the temperature sensitive portion 5b so as to be connected to the temperature sensitive portion 5b. Also,
Reference numeral 5d is an overcoat layer made of silicon oxide (SiO ₂ ) that covers the temperature sensitive portion 5b. (Note that the films formed on the substrate 1 and the base body 5a are thin films as compared with the substrate 1 and the base body 5a, but they are exaggeratedly drawn thick in the drawing.) Such a thermistor 5 is temperature-sensitive. With the part 5b facing the back surface 1B of the substrate 1, both electrode parts 5c and 5c are organically bonded to the wiring conductors 6 and 6 by silver (Ag) or an alloy powder of silver-palladium (Ag-Pd). Bonding is performed via the conductive adhesive 7 mixed with the agent.

In the fixing device of the copying machine, the plate heater and the pressure roller are arranged in parallel to face each other, and a roller portion formed of a heat resistant elastic material is provided on the surface of the pressure roller having a rotating shaft. The overcoat layer 4 of the plate-shaped heater is lightly contacted directly or indirectly. Then, when the copy sheet is supplied between the plate-shaped heater H and the pressure roller, the copy sheet is pressure-fed while sliding on the overcoat layer 4 of the heater H by the rotation of the pressure roller, and the heater H during this period. The toner on the copy paper is heated and fixed by the heat of.

In the fixing device, the plate-shaped heater H detects the temperature of the heating element 2 by the chip-shaped thermistor 5 attached to the back surface 1B of the substrate 1 opposite to the surface on which the resistance heating element 2 is formed. The detected signal is fed back to the temperature control circuit device to control the electric power applied to the plate-shaped heater H to keep the heater H at a constant temperature.

[0008]

However, as described above, both the electrode portions 5c and 5c are placed on the wiring conductors 6 and 6 with the temperature sensing portion 5b of the chip-shaped thermistor 5 facing the back surface side 1B of the substrate 1. However, the following problems may occur when the conductive adhesive 7 is used for bonding.

The chip-shaped thermistor 5 is extremely small (length about 1,6 mm × width about 0.8 mm, thickness about 0.25 mm), and the electrode portion 5c (length about 0.5 mm × width about 0, 8 mm) and the contact area between the wiring conductor 6 and the wiring conductor 6 are small, the joining strength is reduced if the pressure is weak at the time of joining, or if the joining position is slightly displaced.
The thermistor 5 may peel off from the substrate 1 when subjected to vibration or shock when the high temperature state continues for a long time or when the bonding force decreases due to deterioration over time.

The surface of the temperature sensing portion 5b of the thermistor 5 is covered with an overcoat layer 5d for preventing damage and for preventing corrosion and deterioration due to humidity and impure gas.
If the overcoat layer 5d rides on the wiring conductor 6 without contact with c (shown in FIG. 11A), or if the thickness of the overcoat layer 5d is thicker than the wiring conductors 6 and 6, the temperature sensing portion 5 is formed.
In some cases, the terminal portions 5c and 5c on both sides of b cannot contact the wiring conductors 6 and 6 (shown in FIG. 11B), and the electrical connection may become unstable or may not be possible.

When the thermistor 5 is not satisfactorily mounted on the substrate 1 and the connection with the wiring conductor 6 is insufficient as described above, the temperature control of the resistance heating element 2 by the thermistor 5 becomes impossible, A voltage is continuously applied to cause an overcurrent to flow, and the temperature of the substrate 1 becomes high enough to heat it red. If this high temperature state continues, the tray made of plastic on which the plate-shaped heater H is mounted, the casing of the fixing device and the copy paper that is sent by being pressed on the heater H may be burned or ignited. was there.

Further, in such a plate-shaped heater H,
The layer thickness of the overcoat layer 5d of the thermistor 5 is smaller than the film thickness of the wiring conductors 6 and 6, and the substrate 1 and the overcoat layer 5d
If the space 5e between the two is large (shown in FIG. 10), it is difficult to detect the temperature of the substrate 1 accurately and quickly, and there is also a problem that the temperature control cannot be performed with high accuracy.

According to the present invention, a thermistor can be easily mounted on a heater substrate, and a plate-shaped heater capable of accurately and quickly detecting temperature with high accuracy at the time of heat generation, a fixing device having the heater mounted thereon, and the fixing device can be used. It is an object of the present invention to provide an image forming apparatus having the above configuration.

[0014]

The plate heater of the present invention comprises:
A substrate made of a heat-resistant and electrically insulating material, a strip-shaped resistance heating element formed on the front surface side of the substrate, and a chip-shaped thermistor for detecting the temperature of the resistance heating element attached to the back surface side of the substrate. In the chip-shaped thermistor, the temperature sensing portion and the electrode portion are formed on one surface side of the substrate, the other surface side of the substrate is located on the substrate side, and the electrode portion is formed on the back surface side of the substrate. It is characterized by being connected and attached to.

Further, the temperature of the substrate made of a heat-resistant and electrically insulating material, the strip-shaped resistance heating element formed on the front surface side of the substrate, and the temperature of the resistance heating element attached to the back surface side of the substrate are detected. The chip-shaped thermistor has a temperature-sensing part and an electrode part formed on one side of the base, and the other side of the base is attached to the substrate via an electrically insulating, good thermal conductive adhesive. It is characterized in that it is attached and the electrode portion is connected to the wiring conductor formed on the back surface side of the substrate.

The material of the substrate is ceramics, glass or heat-resistant synthetic resin.

Further, it is characterized in that a vitreous overcoat layer is formed to cover the resistance heating element on the front surface side of the substrate.

Further, the present invention is characterized in that a chip-shaped thermistor is attached in the recess formed on the back surface side of the substrate.

Further, the electrode portion of the thermistor is characterized in that it is connected to a wiring conductor formed on the back side of the substrate through a conductive adhesive.

Further, a protective coat layer made of a resin adhesive is formed so as to cover the backside including the thermistor on the backside of the substrate and the connection between the thermistor and the wiring conductor.

Further, a protective coat layer made of a ceramic adhesive is formed so as to cover the backside including the thermistor on the backside of the substrate and the connecting portion between the thermistor and the wiring conductor.

Further, the fixing device of the present invention is characterized in that the pressure roller and the plate heater described above are arranged opposite to each other.

Furthermore, the image forming apparatus of the present invention is characterized by including the fixing device described above.

[0024]

Since the base side of the thermistor, which is opposite to the side on which the temperature sensing portion is formed, faces the substrate side of the heater for joint mounting, even if the positional relationship with the wiring conductor is slightly misaligned during joining. The electrical connection can be made without any problem, and the adhesive can be supplied from above the overlapping portion instead of being interposed between the members at the time of joining, which facilitates the work.

When an electrically insulating and highly heat-conductive adhesive is interposed between the thermistor substrate and the heater substrate, the temperature of the substrate is efficiently and accurately transferred to the temperature sensing portion through the substrate. Therefore, the temperature can be detected accurately and quickly with high accuracy.

Since the thermistor is held on the heater substrate by a plurality of kinds of adhesive layers such as a conductive adhesive, a good thermal conductive adhesive, and a protective coating layer made of an adhesive, the heater is mounted. The thermistor does not fall off while the equipment is operating. In particular, when the protective coating layer is formed of a ceramic adhesive, it has a function of wrapping the thermistor to shield external heat, and highly accurate temperature detection can be performed without being affected by external heat.

[0027]

Embodiments of the plate heater of the present invention will be described below with reference to the drawings. 1 to 4 show a first embodiment of the present invention, FIG. 1 is a top view of a plate heater H used in a fixing device and the like, FIG. 2 is a bottom view, and FIG. 3 is a XX line of FIG. FIG. 4 is an enlarged cross-sectional view of a portion cut along the line, and FIG. 4 is a partial cross-sectional perspective view of a thermistor having a chip shape (also referred to as a disk shape because it has no lead wire). In the figure, 1 is a heat-resistant and electrically insulating material such as alumina (Al ₂ O ₃ ) ceramics, which is an elongated substrate having a length of about 300 mm, a width of about 6 mm, and a thickness of about 0.8 to about 1 mm. 2 is a length of about 2 formed along the longitudinal direction on the front surface side 1A of the substrate 1.
A strip-shaped resistance heating element mainly composed of a silver / palladium (Ag / Pd) alloy or a nickel / tin (Ni / Sn) alloy having a size of 30 mm, a width of about 2 mm and a thickness of about 10 μm, 3 and 3 are the resistance heating elements 2 Approximately 15m in length with multiple layers formed at both ends of
m, wide 6 mm wide silver (Ag), platinum (Pt), gold (Au), silver-platinum (Ag.Pt) alloy, silver-palladium (Ag.Pd) alloy, etc. This is a terminal part for feeding power, which is made of a film.

Reference numeral 4 is the terminal portions 3 and 3 and the substrate 1.
1A on the front surface side of the substrate 1 including the resistance heating element 2 excluding a part of
Is a glassy overcoat layer having a layer thickness of 20 to 100 μm formed by melting glass powder or the like formed so as to cover almost the entire surface.

Reference numerals 6 and 6 in the figure denote silver (Ag), platinum (Pt), gold (Au), silver-platinum (Ag.Pt) alloy and silver-palladium (formed on the back surface 1B of the substrate 1). Ag / P
d) A pair of wiring conductors 6a, 6a mainly composed of an alloy and having a film thickness of 10 to 30 μm, and terminal portions of the wiring conductors 6, 6.

Reference numeral 5 is a temperature detecting element composed of a chip-shaped (there is also referred to as a disk-shaped because it does not have a lead wire) thermistor (for example, a thermistor model number 364FT manufactured by Ishizuka Glass Co., Ltd.), which is enlarged in FIG. The configuration is as shown. In FIG. 4, 5a is alumina (Al ₂ O
₃ ) A flat plate-like substrate 5b made of ceramics and having a thickness of about 250 μm, and 5b are oxides (MnO ₂ , Co, etc.) of manganese, cobalt, nickel or the like formed in the central portion of the substrate 5a.
₃ O _4, NiO) sensing portion formed of a thin film formed by mixing, 5c, 5c are formed by connecting the temperature sensing unit 5b ends platinum (Pt) layer and a gold (Au) thin film made of layer It is an electrode part. Reference numeral 5d denotes a layer thickness of 5 to 30 made of silicon oxide (SiO ₂ ) which is coated to prevent the film forming the temperature sensing portion 5b from being deteriorated in characteristics by atmospheric humidity or impure gas.
It is a μm overcoat layer. (Note that each of the above films,
Although the layers are thin films in comparison with the substrate 1 and the base body 5a, they are exaggeratedly drawn thick in the drawings and are not proportional. ) This chip-shaped thermistor 5 uses an electric resistor having a large negative temperature coefficient, and when the temperature rises, the resistance value greatly decreases, and heat detection for converting the temperature into large and small resistance values. It is a sensor consisting of elements.

In such a thermistor 5, in the state where the base body 5a is between the pair of wiring conductors 6 on the rear surface side 1B of the substrate 1 and the whole one surface on the side where the temperature sensing portion is not formed is in contact with the substrate 1 face-to-face. , Silver (Ag) or silver-palladium (Ag.) From both electrode portions 5c and 5c to the adjacent wiring conductors 6 and 6.
The conductive adhesive 7 in which an alloy powder of Pd) or the like is mixed with an organic adhesive is piled up and joined. Also,
In the figure, 8 is a heat-resisting / electrically-insulating resin such as an epoxy resin, a silicone resin, or a polyimide resin, which is formed by covering the backside including the connection between the thermistor 5 and the wiring conductors 6 around the thermistor 5 part. It is a protective coat layer made of an adhesive.

Next, the production of the plate heater H will be described. First, the resistance heating element 2 is formed on the front surface side 1A of an elongated substrate 1 made of alumina (Al ₂ O ₃ ) ceramics. To form the heating element 2, for example, a conductive paste prepared by kneading a powder of silver-palladium (Ag.Pd) alloy, a glass powder (inorganic binder), an organic adhesive and the like is prepared. Then, this paste is applied as a strip-shaped thick film on the elongated substrate 1, dried, and dried at about 850 ° C. for about 10 minutes.
It is performed by baking for a minute. By this firing, the binder contained in the coating material is thermally decomposed, gasified and scattered, and the resistance heating element 2 made of silver / varadium (Ag / Pd) is formed.

Then, a material having a smaller electric resistance value than that of the resistance heating element 2, for example, a conductive paste of a silver / platinum (Ag / Pt) alloy is thickly formed on the surfaces of both ends of the resistance heating element 2 and the back surface 1B of the substrate 1. A film is printed, applied, dried, and then fired to form terminal portions 3 and 3 for power supply, wiring conductors 6 and 6 and terminal portions 6a and 6a.

After that, the glass-like overcoat layer 4 is formed so as to cover the portion of the resistance heating element 2 of the band-shaped thick film and the surface of the substrate 1. This overcoat layer 4 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, which is thickened. The film is printed to form a continuous coating film without gaps. And
After drying, bake at about 850 ° C for about 10 minutes to obtain a thickness of 2
The glass layer has a thickness of 0 μm to 100 μm.

Then, the thermistor 5 is placed between the pair of wiring conductors 6, 6 formed on the back surface 1B of the substrate 1 in such a manner that one surface of the base 5a is in face-to-face contact with the substrate 1. Then, the respective wiring conductors 6 adjacent to the both electrode portions 5c, 5c,
Conductive adhesive 7 such as polyimide, epoxy, or silicone based on 6 as a filler of alloy powder of silver / palladium (Ag / Pd), etc. (for example, epoxy resin adhesive product number H35-175MP manufactured by Epotek Co., Ltd.) Are piled up and the adhesive 7 is cured to bond them, and the thermistor 5 is attached to the substrate 1. It should be noted that, at the time of this bonding, the work may be performed while pressing the thermistor 5 and the substrate 1 so as to improve the adhesion.

Finally, the overcoat layer 5 of the thermistor 5
d, a heat-resistant and electrically-insulating resin adhesive made of epoxy resin, silicone resin, polyimide resin, etc. is applied so as to cover the surface including the joint portion of both electrode portions 5c, 5c, and the adhesive is cured to protect it. The coat layer 8 is formed.

Such a plate-shaped heater H is incorporated in a device, and is energized by a circuit configuration as shown in FIG. That is, when the commercial power source S is energized between the terminal portions 3 and 3 of the heater H via the SSR (solid state relay) connected to the control terminal of the temperature control circuit T, a current flows through the resistance heating element 2 to generate heat. The temperature of the substrate also rises due to the heat generated by the resistance heating element 2, and this heat is transmitted to the thermistor 5 attached to the rear surface of the substrate, and the resistance value of the thermistor 5 is changed. This change in the resistance value of the thermistor 5 is output from the terminal portion via the wiring conductor formed on the substrate, and this is input to the temperature control circuit T to determine whether it is within an appropriate temperature range (= set temperature). To do. If the above temperature is lower than the set temperature, output an ON signal to the SSR,
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: pulse width control method) or the like.

When the plate-shaped 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. This heater H is made of silver / palladium (A
g · Pd) serves as an electric resistance element, and the resistance value of the heating element 2 is adjusted by the ratio of silver / palladium (Ag · Pd) contained in the resistance paste. In this embodiment, about 2
It has a resistance value of 5 ohms [Ω], a current of about 4 A flows when a voltage of 100 V is applied, and the amount of heat generated is about 400 W.

Then, normally, as described above, the thermistor 5 provided on the back surface side of the substrate 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.

In the case of this embodiment, both the substrate 1 constituting the heater H and the base body 5a constituting the thermistor 5 abutting on the substrate 1 and attached thereto have relatively high thermal conductivity. It is made of alumina (Al ₂ O ₃ ) ceramics, and the surfaces of the substrate 5a are in contact with the substrate 1 because they are relatively flat surfaces and one surface of the substrate 5a is in contact with the substrate 5a well. Can be detected accurately and quickly. In addition, the thermistor 5 is made of the conductive adhesive 7 joined to the wiring conductors 6, 6 and the double adhesive of the synthetic resin adhesive forming the protective coat layer 8 covering the whole of the plate heater H. Since it is adhered to the substrate 1, its fixing strength can be improved. Further, the protective coat layer 8 has a function of enclosing the thermistor 5 and shielding external heat, and can perform highly accurate temperature detection without exerting a thermal influence from the other.

Therefore, the temperature can be adjusted with high accuracy, and the bonding of the thermistor 5 to the substrate 1 becomes a large area over the entire surface, so that the fixing strength is improved and the thermistor 5 is separated from the substrate 1 during use. As a result, a problem such as thermal runaway of the heater H does not occur, and highly accurate temperature detection can be performed.

FIG. 6 shows another embodiment of the present invention,
In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. 3 differs from that shown in FIG. 3 in that the surface opposite to the surface of the base 5a forming the thermistor 5 on which the temperature-sensitive portion is formed has a good heat-conductive adhesive 9 having electrical insulation (for example, epoxy resin adhesive manufactured by Epotek Co., Ltd.). Product number H65-175M
P) is attached between the pair of wiring conductors 6 and 6 on the back surface side 1B of the substrate 1 of the plate-shaped heater H, and both electrode portions 5c and 5c are provided on the wiring conductors 6 and 6 by silver. -To raise the conductive adhesive 7 such as polyimide, epoxy, or silicone-based adhesive (for example, epoxy resin adhesive product number H35-175MP manufactured by Epotek Co., Ltd.) using palladium (Ag / Pd) alloy powder as a filler. Are joined together.

With such a structure, although the flat surfaces are in contact with each other and the hard materials of the ceramics are in contact with each other, a gap may be formed in the contact surfaces, and good heat conduction is achieved between these members. If the conductive adhesive 9 is filled and interposed, the heat transfer property between the members is not impaired, and extremely good heat transfer can be performed, and the temperature of the substrate 1 can be transmitted to the thermistor 5 and detected accurately and quickly. .

Further, the conductive adhesive 7 in which the thermistor 5 is bonded to the wiring conductors 6 in this way, the good heat conductive adhesive 9 covering one surface, and the triple adhesive forming the protective coat layer 8 Since it is fixed to the substrate 1 of the plate-shaped heater H, its strength can be improved, the thermistor 5 does not drop off from the substrate 1 of the plate-shaped heater H, and highly accurate temperature detection can be performed.

FIG. 7 shows another embodiment of the present invention,
In the figure, the same parts as those in FIGS. 3 and 6 are designated by the same reference numerals, and the description thereof will be omitted. The part different from the above embodiment is the substrate 1.
A concave portion 1C is formed on the back surface side 1B, and the thermistor 5 is housed in the concave portion 1C.

With this structure, not only the entire bottom surface of the base body 5a of the thermistor 5 but also the side surface of the base body 5a (in the case of the present embodiment, the base body 5a is a quadrangle;
The surface can also be contacted, so that the heat transfer property is further improved. Therefore, extremely good heat transfer can be performed, and the temperature of the substrate 1 can be detected accurately and quickly. In addition, when attaching the thermistor 5 to the substrate 1, it is possible to accurately and easily perform the operation without shifting the position and improve the fixing strength.

When the thermistor 5 is housed in the recess 1C as described above, the depth of the recess 1C is not such a depth that the base 5a is substantially buried as in the embodiment, but one of the base 5a. It may be filled with a portion, and may not be filled with the good heat conductive adhesive 9 as in the first embodiment.

Next, the fixing device C in which the plate heater H of the above embodiment is mounted and the copying machine P in which the fixing device C is mounted will be described with reference to FIGS. 8 and 9.

FIG. 8 shows an example of a fixing device C such as a copying machine, a printer or a facsimile in which the plate-shaped heater H described in the above embodiment is mounted. The heater H portion in the drawing is the same as that in the above embodiment and is the same. The same reference numerals are given to the parts, and the description thereof will be omitted.

In the figure, 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 rotary shafts C2 protruding from both end surfaces. The plate-shaped heaters H are juxtaposed to the rotation shaft C2 of the pressure roller C1 and attached to the base C5. A heat resistant sheet C6 such as a polyimide resin is wound around the base C5 including the heater H, and the surface of the overcoat layer 4 directly above the resistance heating element 2 is covered with the heat resistant sheet C6. It is in elastic contact with the silicone rubber layer C4 of the pressure roller C1.

Then, in the fixing device C, the plate-shaped heater H
Is energized through a connector (not shown) made of phosphor bronze plate or the like which is in contact with the terminals 3 and 3 and which is provided with elasticity,
The copy paper PA on which the toner image PT is formed is pressed out between the surface of the heat-resistant sheet C6 provided on the overcoat layer 4 of the resistance heating element 2 that has generated heat and the silicone rubber layer C4 while being pressed in the direction of the arrow in the figure. The unfixed toner image PT is melted and fixed on the copy sheet PA by heating the copy sheet PA with the heater H at that time.

That is, on the paper input side of the pressure roller C1, the unfixed toner image PT on the copy paper PA is first heated and melted by the heater H via the heat-resistant sheet C6, and at least the surface portion thereof largely exceeds the melting point and is completely melted. It softens and melts. Thereafter, on the sheet discharge side of the pressure roller C1, the copy sheet PA separates from the heater H, the toner image PT naturally radiates heat, and is cooled and solidified again, and the heat-resistant sheet C6 is also separated from the copy sheet PA.

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

Next, a copying machine P incorporating the fixing device C will be described. In FIG. 9, P1 is a casing of the copying machine P, and P2 is an original placing table made of a transparent member such as glass provided on the upper surface of the casing P1 to reciprocate in the arrow Y direction to scan the original PA1. A lamp L for irradiation is provided above the inside of the casing P1, and the reflected light from the original PA1 irradiated by the lamp L is slit-exposed onto the photosensitive drum P4 by the short-focus small-diameter image forming element array P3. To be done. The photosensitive drum P4 rotates in the arrow direction.

Further, P5 is a charger, which uniformly charges the photosensitive drum P4 coated with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer. On the drum P4 charged by the charger P5, an electrostatic image subjected to image exposure by the imaging element array P3 is formed. This electrostatic image is visualized using a toner made of a resin or the like that softens and melts when heated by the developing device P6.

On the other hand, the copy paper PA stored in the cassette P7 is a pair of conveyance rollers P9 which are rotated in pressure contact with each other in the vertical direction at a timing synchronized with the image on the feeding roller P8 and the photosensitive drum P4. Is sent onto the drum P4. The toner image formed on the photosensitive drum P4 by the transfer discharger P10 is the copy paper P.
Transcribed on A.

After this, the paper PA separated from the drum P4
Is guided to a fixing device C, which will be described later, by a transport guide P11, subjected to heat fixing processing, and then discharged onto a tray P12. After the toner image is transferred, the residual toner on the drum P4 is removed by the cleaner P13.

The fixing device C has an effective length in the direction perpendicular to the moving direction of the copy sheet PA, which corresponds to the width (length) of the maximum size sheet that can be copied by the copying machine P, that is, the width of the maximum size sheet (length). A plate-shaped heater H is arranged by extending a longer resistance heating element 2 and a feed roller C1 is provided opposite to the resistance heating element 2 so as to make a light elastic contact in the extending direction of the resistance heating element 2. Has been. Then, the unfixed toner image on the sheet PA fed between the heater H and the feed roller C1 is melted by receiving heat from the resistance heating element 2, and characters, alphanumeric characters, drawings, etc. are printed on the surface of the sheet PA. Make the duplicated image appear.

Such a copy image by the fixing device C is
The resistance heating element 2 is continuously formed in a slender shape over the length (width) of the maximum size sheet permitted by the copying machine P, a substantially uniform temperature distribution is obtained in the extending direction, and the sheet PA is entirely covered. A clear, high-quality copy with the same contrast without transfer unevenness can be obtained.

Therefore, the fixing device C and the copying machine P incorporating the fixing device C as described above can accurately and promptly detect the heat generation temperature of the heater H and adjust the temperature with high accuracy, and the substrate Since the thermistor 5 is firmly fixed to the substrate 1, the thermistor 5 can be removed from the substrate 1 while the device is operating.
Therefore, the heater H does not run away due to temperature separation, and it is possible to prevent ignition of the heater H itself, the holding member of the heater H, the copy sheet PA, or the like.

The present invention is not limited to the above embodiment,
For example, the material of the substrate of the plate heater is alumina (Al ₂ O
₃ ) Not limited to ceramics, other materials such as ceramics, glass, and synthetic resin members having high heat resistance such as polyimide resin may be used.

Further, the formation of the overcoat layer for covering the resistance heating element and the substrate is not essential, and the material of the glass when forming it is not limited to that of the embodiment, but may be changed depending on the heating temperature and the situation of use. It goes without saying that you can select it appropriately.

The material of the substrate of the chip-shaped thermistor is not limited to alumina (Al ₂ O ₃ ) ceramics, but other materials such as ceramics, glass, silicone, polyimide resin having high heat resistance, or the like can be used. It may be. Further, the material of the temperature sensing portion is also an oxide (MnO ₂ , Co ₃ O ₄ , NiO) of manganese, cobalt, nickel, etc.
Not only a mixture of but also each alone or magnesium,
Oxides such as calcium, barium, titanium, zirconium and aluminum (MgO, CaO, BaO, TiO
₂ , ZrO ₂ , Al ₂ O _3, etc.) may be used alone or as a mixture.

Further, the formation of the overcoat layer covering the temperature sensitive portion is not essential, and the material of the glass when forming it is not limited to that of the embodiment, but may be changed depending on the heat generation temperature of the attached heater. You can choose as appropriate. Further, the conductive adhesive for joining the electrode portion of the thermistor and the wiring conductor of the heater substrate is not limited to those described in the examples, and an epoxy resin adhesive may be a product number XNR5310 manufactured by Nagase Ciba Co., Ltd.
Ablestech Co., Ltd. product number 8700E, Toshiba Silicone Co., Ltd. product number CT262K, etc. are used as silicone resin adhesives. Toshiba Silicone Co., Ltd. product number YE3452uB, TCM5406, TCM5.
417u, TCM5418u, TCM5428u, TC
It may be M5107, TCM5508, TCM5516u, or the like.

The electrically insulating and highly heat-conductive adhesive interposed between the base of the thermistor and the substrate of the heater is not limited to those described in the examples, but the product number CRM-1145 manufactured by Sumitomo Bakelite Co., Ltd., etc. However, the thermal conductivity is 1 × 10 ⁻⁴ to 1 × 10 ⁻² cal / cm · sec · ° C.
If so, there was no problem in practical use.

The formation of the protective coat layer covering the thermistor portion is not essential, but if it is formed, it will be exposed to external impacts on the thermistor portion or adhesion of impurities such as oil from the equipment and impure gas. Can be prevented. Then, the covered portion is not limited to the thermistor portion and the connection portion with the wiring conductor, but the entire back surface side of the substrate (however,
(Excluding the terminal portion). Also, heat resistance to form
The material of the electric insulation material is not limited to the resin adhesive described in the examples, but a ceramic adhesive (for example, "Sumiceram": Asahi Kagaku Kogyo Co., Ltd. product number S-18C-composition: SiO ₂ 25 to 65% by weight). , Al ₂ O ₃ 10-65
%, Mullite 10 to 65% by weight, particle size 40 μm or less), the ceramic adhesive has a function of wrapping the thermistor to shield external heat, and does not exert thermal influence from others and is highly accurate. Can detect temperature. Further, when the substrate is made of ceramics, the coefficient of thermal expansion is close to each other, so that the substrate can be more firmly fixed.

Further, the configuration of the base, the pressure roller and the like to which the plate heater is mounted in the fixing device is not limited to the embodiment. Further, in the embodiment of the fixing device, the heat-resistant sheet is interposed around the base on which the plate heater is mounted for the purpose of protecting the heater and feeding the paper, but the plate heater is not limited to such indirect contact. The copying paper may directly contact the surface of the resistance heating element or the surface of the overcoat layer.

Furthermore, the fixing device of the present invention is not limited to a copying machine, but can be put into practical use by being incorporated in an image forming apparatus of various OA equipment such as a laser printer, another printer or a facsimile.

[0070]

According to the present invention having the above-described structure, both the substrate forming the heater and the base forming the thermistor which is in contact with and attached to the substrate are made of materials having relatively high thermal conductivity. Moreover, since the surfaces of the base body are in contact with the substrate, which are relatively flat surfaces, the heat of the substrate can be well transferred to the base body, and the temperature of the substrate can be detected accurately and quickly. Also, the work of attaching the thermistor to the substrate of the heater is facilitated, and the occurrence of misalignment is reduced and reliable electrical connection can be performed.

Therefore, it becomes possible to adjust the temperature with high accuracy, and the thermistor can be easily attached to the substrate, and the bonding becomes a large area over the entire surface, so that the fixing strength is improved, and the thermistor can be removed from the substrate during use. Does not come off and thermal runaway of the heater does not occur. Further, a thermistor held by a plurality of types of adhesive layers such as a conductive adhesive, a good thermal conductive adhesive, and a protective coat layer made of an adhesive can be particularly firmly fixed. Further, when the protective coating layer is formed of a ceramic adhesive, it has a function of wrapping the thermistor to shield external heat, and highly accurate temperature detection can be performed without being affected by external heat.

[Brief description of drawings]

FIG. 1 is a top view of a plate heater of the present invention.

FIG. 2 is a bottom view of FIG.

FIG. 3 is an enlarged cross-sectional view showing the plate heater of the present invention taken along line XX in FIG.

FIG. 4 is a partially cutaway perspective view of a chip-shaped (disk-shaped) thermistor.

FIG. 5 is a circuit diagram showing an embodiment of a temperature control circuit and a temperature control circuit for energizing the plate heater of the present invention to adjust the temperature.

FIG. 6 is an enlarged cross-sectional view of a plate heater showing another embodiment of the present invention.

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

FIG. 8 is an enlarged cross-sectional view showing a fixing device according to an embodiment of the present invention.

FIG. 9 is a sectional view showing a schematic configuration of a copying machine according to an embodiment of the present invention.

FIG. 10 is an enlarged cross-sectional view showing a conventional plate heater taken along line XX in FIG.

11A and 11B are schematic enlarged transverse sectional views showing a conventional plate heater.

[Explanation of symbols]

 H: Plate heater 1: Substrate 1A: Front side 1B: Back side 1C: Recessed part 2: Resistance heating element 3: Terminal part 4: Overcoat layer 5: Thermistor 5a: Base 5b: Temperature sensing part 5c: Terminal part 5d: Overcoat layer 6: Wiring conductor 7: Conductive adhesive 8: Protective coating layer 9: Electrically insulating and thermally conductive adhesive C: Fixing device C1: Pressure roller C5: Base P: Copy machine PA: Copy paper

Claims (10)

[Claims] 1. A substrate made of a heat-resistant and electrically insulating material;
A strip-shaped resistance heating element formed on the front surface side of the substrate; and a chip-shaped thermistor attached to the back surface side of the substrate for detecting the temperature of the resistance heating element; Is characterized in that the temperature sensing part and the electrode part are formed on one surface side of the substrate, the other surface side of the substrate is located on the substrate side, and the electrode part is connected and attached to the wiring conductor formed on the back surface side of the substrate. Plate heater. 2. A substrate made of a heat-resistant and electrically insulating material;
A strip-shaped resistance heating element formed on the front surface side of the substrate; and a chip-shaped thermistor attached to the back surface side of the substrate for detecting the temperature of the resistance heating element; Has a temperature sensing part and an electrode part formed on one surface side of the base body, and the other surface side of the base body is attached to the substrate through an electrically insulating and highly heat-conductive adhesive and the electrode part is formed on the back surface side of the substrate. A plate-shaped heater characterized by being connected to a wiring conductor. 3. The plate heater according to claim 1, wherein the substrate material is ceramics, glass, or heat-resistant synthetic resin. 4. The plate-shaped heater according to claim 1, further comprising a vitreous overcoat layer which covers the resistance heating element on the front surface side of the substrate. 5. The plate heater according to claim 1, wherein a chip-shaped thermistor is attached in a recess formed on the back surface side of the substrate. 6. The plate according to claim 1, wherein the electrode portion of the thermistor is connected to a wiring conductor formed on the back side of the substrate via a conductive adhesive. Shaped heater. 7. A protective coating layer made of a resin adhesive is formed so as to cover the thermistor on the rear surface side of the substrate and the rear surface side including the connecting portion between the thermistor and the wiring conductor. The plate heater according to claim 6. 8. A protective coat layer made of a ceramic adhesive is formed so as to cover the backside including the thermistor on the backside of the substrate and a connecting portion between the thermistor and a wiring conductor. The plate heater according to any one of claims 2 and 5 to 7. 9. A fixing device in which a pressure roller and the plate heater according to any one of claims 1 to 8 are disposed so as to face each other. 10. An image forming apparatus comprising the fixing device according to claim 9.