JPH08305190A - Heater assembly, heating device and image forming device - Google Patents

Abstract

PURPOSE: To ensure safety by allowing stress due to a thermal expanding quantity caused in a heater at the runaway time of the heater so as to become maximum on a brittle part, thereby surely interrupting energization off. CONSTITUTION: The heater 4 is embedded in a long sideways groove 3a provided on a back surface of the heater holder 3, and held by the heater holder 3 by adhering the bottom surface of the groove 3a and the heater rear side to adhering point parts on plural sections with a certain interval along the longitudinal direction of the heater. Then, the brittle part 4P being a section where stress is concentrated at the runaway time of the heater 4 is provided on the heater substrate being at a part where the heater crack is caused, and the stress caused by the thermal expansion shifting quantity caused in the heater 4 at the runaway time of the heater is made so as to become maximum on the brittle part 4P. As a result, at the runaway time of the heater 4, the stress is concentrated on the brittle part 4P, the heater 4 is surely broken sideways, from the brittle part 4P, the conduction heating resistor 4C is interrupted, and thus the energization to the heater 4 is interrupted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a heater assembly comprising a substrate, a heater having an energization heat-generating resistor provided on the substrate as a basic component, and a heater holder holding the heater, and the heater assembly. The present invention relates to the above heating device and an image forming apparatus including the heating device as an image heating and fixing device.

[0002]

2. Description of the Related Art As a heating device for a material to be heated, for example, JP-A-63-313182 and JP-A-1-26367.
No. 9, JP-A-2-157878, JP-A-4-
Film heating type heating devices are known from JP-A-44075-44083 and the like.

In this heating device, a material to be heated is brought into close contact with a heating body via a heat-resistant film material, and the heating body and the heat-resistant film material are moved relatively to each other so that heat of the heating body is covered via the heat-resistant film material. An image heating and fixing device in an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile, that is, an electrophotographic, electrostatic recording,
Directly on the surface of the recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, printing paper, etc.) by using a toner made of heat-meltable resin by an appropriate image forming process means such as magnetic recording. The unfixed toner image corresponding to the target image information formed by the indirect (transfer) method can be utilized as a means for performing heat fixing processing as a permanently fixed image on the surface of the recording material carrying the image.

Such a film heating type heating device can use a low heat capacity heating body (thermal head) that quickly raises temperature and a thin heat-resistant film material, thus saving power and shortening wait time. (Quick start property) is possible, and the temperature rise inside the image forming apparatus such as the image forming apparatus can be reduced, which is effective.

The heating element is basically composed of a heat-resistant and insulating ceramic substrate and an energization heating resistor formed on the substrate through printing and firing, and heat is generated by supplying power to the energization heating resistor. A so-called ceramic heater is used.

The heater has a low heat capacity and a rapid temperature rise, and the temperature control system including a temperature detecting element controls the electric power supplied to the energizing heating resistor to control the temperature to a predetermined operating temperature.

Further, a safety device such as a temperature fuse is provided so that when the heater temperature exceeds the upper limit temperature of use, the safety device is actuated to interrupt the energization of the energization heat generating resistor.

[0008]

However, due to a malfunction or failure of the temperature control system or the safety device, a delay in the operation of the safety device due to the rapid temperature rise of the ceramic heater, etc., the energization of the energization heating resistor does not stop ( Runaway of electricity), excessive temperature rise of heater (heat runaway of heater, abnormal temperature rise of heater) and smoking
It is possible that a fire may occur.

Therefore, the present invention ensures that the electric power supply to the heater is surely cut off before smoke or ignition occurs even if a safety device such as a thermal fuse does not operate or there is a time lag in operation during thermal runaway of the heater. The purpose is to ensure safety.

[0010]

SUMMARY OF THE INVENTION The present invention is a heater assembly, a heating device, and an image forming apparatus having the following features.

(1) A substrate, and a heater having a heating resistor, which is a basic component, which generates heat when electricity is applied to the substrate,
An assembly with a heater holder that holds the heater, wherein the substrate is provided with a fragile portion, and the heater is used in the heater holder so that the stress due to the amount of thermal expansion displacement generated in the heater during thermal runaway of the heater becomes maximum at the fragile portion. A heater assembly, wherein the heater assembly is held by the.

(2) The heater is provided by being held by the heater holder in a state where the heater portion near the fragile portion is abutted against the convex portion provided on the heater holder side. Heater assembly.

(3) The positional relationship between the adhesive application position for adhering and holding the heater to the heater holder and the convex portion is such that the convex portion is between the adhesive application positions. The heater assembly as described in (2) above.

(4) A substrate, and a heater having as a basic component a heating resistor provided on the substrate to generate heat when energized.
A heater assembly that holds the heater, wherein the heater holder has a heater abutting point with which the heater that has been thermally expanded abuts during thermal runaway of the heater.

(5) The heater assembly according to (4), characterized in that a fragile portion is provided in the heater portion near the heater portion that abuts the abutting point on the heater holder side due to thermal expansion during thermal runaway of the heater.

(6) A fragile portion is provided in the heater portion near the heater portion where stress is generated by hitting an abutting point on the heater holder side due to thermal expansion during thermal runaway of the heater. The heater assembly described.

(7) The heater holding portion of the heater holder is characterized in that it has a gap between it and the outer peripheral portion of the heater so that the position of the stress applied to the heater during thermal expansion of the heater can be specified. The heater assembly according to any one of (1) to (6).

(8) The gap portion is a gap amount that can specify the position of stress applied to the heater with respect to the amount of heater thermal expansion displacement at that temperature when the heater exceeds the upper limit temperature (7). ) Heater assembly.

(9) The fragile portion is a portion that causes stress concentration such as through holes and notch scratches (1)
The heater assembly as described in any one of (8) to (8).

(10) Any one of (1) to (9), wherein the heater is a ceramic heater having a ceramic substrate and a heating resistor that is provided on the substrate and generates heat when energized. The heater assembly according to one.

(11) The heater according to any one of (1) to (10), characterized in that the heater has an electrical contact for supplying electric power to the heating resistor and a temperature detecting means. assembly.

(12) A heating device comprising the heater assembly described in any one of (1) to (11) above.

(13) A heating device in which a material to be heated is brought into close contact with a heater of a heater assembly through a film, and the heater and the film are relatively moved to apply heat from the heater to the material to be heated through the film. A heating device, wherein the heater assembly is the heater assembly according to any one of (1) to (11).

(14) The heating device according to (13), further comprising a pressing member that sandwiches the film between the heater and the heater to form a nip portion.

(15) The heating device according to any one of (12) to (14), which is an image heating fixing device.

(16) An image forming apparatus having an image forming means for forming an unfixed image on a recording material and a heat fixing means for heating and fixing the unfixed image on the recording material. An image forming apparatus, which is the heating device according to any one of 12) to 15).

[0027]

[Action]

a) In the present invention, at the time of thermal runaway of the heater, even if a safety device such as a thermal fuse does not operate or there is a time lag in the operation, the heat generation resistance at a desired predetermined portion of the heater is increased before the heater smokes or ignites. The heater cracks including the wire breakage of the body are surely caused to stop the power supply to the heater, and the safety is surely ensured.

B) The present invention utilizes the amount of thermal expansion displacement or stress of the heater due to a rapid temperature rise during thermal runaway of the heater to cause cracks including disconnection of the energization heating resistor in the heater itself, and The heater crack is surely caused at a desired predetermined portion of the heater.

C) That is, a fragile portion (stress concentrated portion, through hole, notch scratch, etc.) is provided as a portion where stress concentration occurs in a portion of the heater substrate where the heater is to be cracked, and the heater is heated during thermal runaway. By arranging the heater on the heater holder so that the stress due to the amount of thermal expansion displacement generated on the heater becomes maximum at the fragile portion, the stress due to the amount of thermal expansion displacement of the heater is concentrated on the fragile portion during thermal runaway of the heater. Then, the heater is surely broken from the fragile portion. That is, the heater crack position can be specified to the fragile portion.

In this case ,. The heater portion in the vicinity of the fragile portion is abutted against a convex portion provided on the heater holder side, and the heater is held by being attached to the heater holder. The positional relationship between the application position of the adhesive for holding and holding the heater on the heater holder and the projection is such that the projection is between the application positions of the adhesive. A certain amount of gap is provided between the heater holder and the heater holder so that the thermally expanded heater does not hit the heater holder so that unnecessary stress is not applied to the heater portion other than the fragile portion. When the heater exceeds the upper limit temperature of the heater, the gap is set to be larger than the amount of thermal expansion displacement of the heater at that temperature, so that the amount of thermal expansion displacement of the heater during thermal runaway of the heater is set. It is possible to more reliably concentrate the stress due to the fragile portion and to more reliably break the heater from the fragile portion.

D) Further, by providing the heater holder with a heater abutment point against which the heater that thermally expands during thermal runaway of the heater, a crack is reliably generated in the heater near the heater abutment point during thermal runaway of the heater. You can That is, the heater crack position can be specified.

In this case ,. A fragile portion is provided in the heater portion near the heater portion that abuts the abutting point on the heater holder side due to thermal expansion during thermal runaway of the heater, where stress concentration occurs. A fragile part is provided in the heater part near the heater part where stress is generated by hitting an abutting point on the heater holder side due to thermal expansion during thermal runaway of the heater. The heater holder part of the heater holder has a gap such that the outer peripheral part of a specific portion of the heater holder does not abut against the heater holder when the heater thermally expands. The fragile portion can be cracked more reliably.

[0033]

【Example】

<Example 1> (Figs. 1 to 4) (1) Example of heating device (Fig. 1) Fig. 1 is a schematic configuration diagram of an example of a heating device. The heating device A of this example is disclosed in JP-A-4-44075-44083 and 4-
This is a so-called tensionless type device disclosed in Japanese Unexamined Patent Publication Nos. 204980-204984, and is used as an image heating fixing device in an image forming apparatus such as a copying machine or an LBP.

Reference numeral 1 denotes a cylindrical fixing film (heat resistant film), which is loosely fitted around the outer periphery of a heater holder (heater holding member) 3 having a heater 4 held on its lower surface. Reference numeral 4 is a pressure roller which sandwiches the film 1 and is in pressure contact with the lower surface of the heater 4. N is a fixing nip portion (pressing nip portion) formed between the heater 4 and the pressure roller 2 with the film 1 interposed therebetween.

The cylindrical heat-resistant film 1 has a total thickness of 100 μm or less in order to reduce the heat capacity and improve the quick start property, and in this embodiment, 50 μm to 70 μm.
A single layer or composite total film with heat resistance, releasability, strength and durability of about m is used. For example, a polyimide (PI) film whose surface is coated with a fluororesin such as PTFE having good toner releasability.

The heater holder 3 is a horizontally elongated (vertical direction in the drawing) gutter-shaped member having a substantially semicircular cross section, and also serves as a rotation guide member for the cylindrical film 1 fitted onto the heater holder 3. It is a heat-resistant member made of curable resin.

As will be described later, the heater 4 is basically composed of a horizontally elongated ceramic substrate and a heating resistor formed on the surface of the substrate along the length of the substrate, and is supplied with electric power to the heating resistor. The heat is quickly generated and the temperature is raised, and the temperature control system controls the temperature to a predetermined fixing temperature. The heater 4 is fitted in a groove formed along the length of the lower surface of the heater holder 3 along the length thereof, and is adhered and held by a heat resistant adhesive.

The pressure roller 2 includes a core metal 2b and the core metal 2b.
And a heat resistant rubber 2a such as silicon rubber provided concentrically with the rubber. Both ends of the cored bar 2b are rotatably supported and retained.

The heater assemblies 3 and 4 to which the cylindrical film 1 is fitted and the pressure roller 2 are pressed against each other against the elasticity of the heat resistant rubber 2a of the pressure roller by an unillustrated biasing spring member. The film 1 is sandwiched between the heater 4 and the pressure roller 2
Are pressed against each other with a predetermined pressing force (4 to 10 kg) to form a fixing nip portion N having a predetermined width.

The pressure roller 2 is rotationally driven in the counterclockwise direction at a predetermined peripheral speed by a gear or the like by a drive unit (not shown). The roller 2 and the film 1 are driven by the rotation of the pressure roller 2.
A rotational force acts on the film 1 due to the frictional force with the outer surface of the heater 1, and the film 1 is rotationally driven in the clockwise direction of the arrow around the outer circumference of the heater holder 3 while sliding in contact with the lower surface of the heater 4. In order to reduce the sliding resistance between the inner surface of the film 1 and the lower surface of the heater with which it makes contact and sliding, it is advisable to interpose a lubricant such as heat resistant grease therebetween.

The film 1 is rotated by the rotation of the pressure roller 2 and the fixing nip portion N is heated in a state where the heater 4 has risen to a predetermined fixing temperature and is temperature-controlled.
A sheet (recording material as a material to be heated) P having an unfixed toner image t is introduced between the rotary pressure roller 2 and the rotating film 1 with the toner image bearing surface side thereof being the film 1 side. By being nipped and conveyed with the fixing nip portion N together with 1, the heat of the heater 4 is applied to the sheet via the film 1, and the toner image t is heated and fixed on the sheet surface. The sheet P passing through the fixing nip portion N is separated from the surface of the film 1 and conveyed.

In the apparatus A of this example, only the nip portion N and the film portion in the contact portion area between the outer surface of the heater holder and the film upstream of the nip portion N in the film rotation direction are driven when the film 1 is rotationally driven. Tension acts,
Tension does not act on most of the rest of the film. Therefore, when the film 1 is rotationally driven, the lateral displacement force along the length of the heater holder 3 is small, and the lateral displacement regulation means for the film 1 or the film lateral control means can be simplified. For example, the deviation control means of the film 1 can be a simple one such as a flange member that receives the end of the film, and the film deviation control means can be omitted to reduce the size and cost of the apparatus.

(2) Heater 4 and its energization system (FIGS. 2 and 3) FIG. 2 (a) is a plan view of the ceramic heater 4 (the side on which the inner surface of the film 1 contacts and slides, hereinafter referred to as the heater surface side). ) And (b) are rear views (the surface opposite to the heater surface side,
Hereinafter referred to as the heater back side). FIG. 3 is an exploded perspective view of the device schematically showing the energization path.

The heater 4 has a heat resistant and insulating ceramic substrate 4a and a heating resistor (thin film heating resistor portion) 4c provided on the substrate surface as basic components.

The ceramic substrate 4a is made of, for example, Al ₂ O.
₃ (alumina), AlN (aluminum nitride), SiC
Etc., for example, thickness 0.6 mm, width 10 mm, length 240
It is a member with mm heat resistance, electrical insulation, good thermal conductivity and low heat capacity.

The heating resistor 4c is formed on the ceramic substrate 4
a along the length of the substrate on the surface side of a, for example, Ag / Pb, R
It is formed by applying an electric resistance material such as uO ₂ or Ta ₂ N in a linear or strip pattern having a width of 1 to 3 mm and a thickness of several tens of μm by screen printing and firing.
It can also be formed by vapor deposition, sputtering or the like.

Reference numeral 4b denotes a first electrode pattern (AC contact) provided on the surface portion on the left end side in the longitudinal direction of the ceramic substrate 4a, which is electrically connected to the left end portion of the heating resistor pattern 4c.

Reference numeral 4d denotes a conductive path pattern provided on the surface side of the ceramic substrate 4a substantially in parallel with the heating resistor pattern 4c, and its right end is electrically connected to the right end of the heating resistor pattern 4c. There is.

4h and 4o are third and fourth electrode patterns (DC contacts) provided on the surface portion of the ceramic substrate 4a on the right end side in the longitudinal direction.

The front side of the ceramic substrate 4a has the first and third sides.
-Except for the fourth electrode pattern portions 4b, 4h, and 4o, it is covered with a heat-resistant protective layer such as a thin glass layer, but is omitted in the figure.

On the back side of the ceramic substrate 4a, 4
g is a second electrode pattern (AC contact) provided near the right end in the longitudinal direction of the substrate, and 4f is this second electrode pattern 4g.
Is a conductive path pattern provided by extending to a position substantially the same as the left end of the conductive path pattern 4d on the substrate surface side.

The left end which is the free end of the conductive path pattern 4d on the front side of the ceramic substrate 4a and the left end which is the free end of the conductive path pattern 4f on the back side of the ceramic substrate 4a are the ceramic substrate. Electrical connection is established through a current-carrying through-hole portion 4e which penetrates the thickness of 4a.

Therefore, a series circuit pattern (primary side circuit) of the first electrode pattern 4b → the heating resistor pattern 4c → the conductive path pattern 4d → the through hole portion 4e for conduction → the conductive path pattern 4f → the second electrode pattern 4g. ) Is configured.

4j and 4m are fifth and sixth electrode patterns provided on the back surface portion of the ceramic substrate 4c on the right end side in the longitudinal direction, and 4k and 4l are the fifth and sixth electrode patterns 4.
j · 4m is a conductive path pattern provided by extending leftward in the longitudinal direction of the back surface of the ceramic substrate.

Reference numeral 5 denotes the above-mentioned substantially parallel conductive path patterns 4l and 4
A temperature detecting element such as a thermistor or a temperature sensitive resistor, which is electrically connected between the left end portions which are the free end portions of m and fixed to the back surface of the ceramic substrate 4c with a conductive adhesive.

The third electrode pattern 4h on the front surface side of the substrate, the fifth electrode pattern 4h on the rear surface side of the substrate, and similarly the fourth electrode pattern 4o and the sixth electrode pattern 4m penetrate the thickness of the ceramic substrate 4a. Electrical connection is established through the current-carrying through holes 4i and 4n. The temperature measuring element 5 and its conducting portion are through holes 4i, 4n and 3
0 mm or more apart.

Therefore, the third electrode pattern 4h → the through hole portion 4i for energization → the fifth electrode pattern 4j → the conductive path pattern 4k → the temperature measuring element 5 → the conductive path pattern 4l → the sixth
Electrode pattern 4m → current-carrying through hole 4n → 4th
Electrode pattern 4o series circuit pattern (secondary side circuit)
Is configured.

The above electrode patterns 4b, 4g, 4h, 4
o ・ 4j ・ 4m, and conductive path pattern 4d ・ 4f ・ 4k
4l is formed by pattern-coating a conductive material such as Ag (silver) paste by screen printing and firing.

The heater surface on which the heating resistor pattern 4c and the conductive path pattern 4d are formed and provided is heat-resistant glass except for the first, third and fourth electrode patterns 4b, 4h and 4o for surface protection. Etc., but the protective layer is omitted in the figure.

1 including the above-mentioned heating resistor pattern 4c
The first and second electrode patterns 4b and 4g (AC
The power supply connectors 6 and 7 are respectively connected to the contact points,
The AC voltage is applied from the power source S. That is, electric power is supplied to the energized heating element pattern 4c, and the energized heating element generates heat over its entire length, so that the heater 4 is heated. Heater 4
Has a low heat capacity as a whole, so it rises rapidly,
Raise the temperature.

Further, the third and fourth electrode patterns 4h and 4h of the secondary side circuit including the temperature measuring element (thermistor) 5 described above.
A connector (not shown) leading to the control circuit 9 is connected to the (DC contact). The temperature rise of the heater 4 is detected by the temperature detecting element 5 and the control circuit 9, and the heating resistor pattern 4 on the primary circuit side is maintained so that the temperature of the heater 4 is maintained at a predetermined fixing temperature.
The power supply to a is controlled by the control circuit 9 to control the temperature of the heater 4. For power control, for example, AC voltage on / off control and phase control are used.

Reference numeral 8 is a temperature fuse as a safety device, which is connected in series to the power supply system for the primary side circuit and is provided in contact with the back surface of the heater 4. When the temperature of the heater exceeds the operating temperature, the temperature fuse 8 operates to urgently cut off the power supply to the heating resistor 4c.

(3) Safety measures during thermal runaway of the heater 4 (FIG. 4) In the present embodiment, when the heater 4 runs thermal runaway, the safety device 8 such as a thermal fuse does not operate or there is a time lag in operation. However, by utilizing the amount of thermal expansion displacement or stress of the heater based on the rapid temperature rise during the thermal runaway of the heater, the energization heating resistor 4c of the heater at a desired predetermined part of the heater is used before the heater smokes or ignites. This is to ensure the safety by surely causing the heater to crack including the disconnection and cutting off the power supply to the heater.

That is, in this embodiment, as shown in FIG. 4, a fragile portion 4p (stress concentration portion) as a location where stress concentration is caused is provided in a portion of the heater substrate where the heater is to be cracked, and when the heater is in a thermal runaway state. The heater 4 was attached to the heater holder 2 so that the stress due to the thermal expansion displacement generated in the heater was maximized at the fragile portion 4p.

In the present embodiment, the fragile portion 4p is a through hole portion provided in the heater substrate portion near the conducting through hole portion 4e of the primary circuit.

As a result, during thermal runaway of the heater, stress due to the amount of thermal expansion of the heater concentrates on the fragile portion 4p, and the heater 4 is reliably laterally cracked from the fragile portion 4p and the energization heating resistor 4c is generated. The wire is broken and the heater is de-energized.

As shown in FIG. 4 (a), the heater 4 is fitted into a horizontally elongated groove 3a provided on the lower surface of the heater holder 3 as shown in FIG. 4 (b), and the bottom surface of this groove 3a and the heater back surface are aligned with the heater length. The heater holder 3 holds them by adhering them at a plurality of adhering point portions that are spaced apart from each other. In (a), 3b shows the adhesion points of the plurality of places.

Numeral 3c is a gap portion which is provided between the side surface of the heater 4 and the inner wall of the horizontally long groove 3a for fitting in order to reduce the amount of thermal expansion displacement of the heater 4. In the heater 4, the gap portion 3c of the heater holder 3 is a portion where the amount of thermal expansion displacement of the portion other than the through hole portion 4p as the fragile portion is maximum.
On the other hand, it is adhered in the groove 3a of the heater holder 3 so as to come to a position with a certain amount of gap. Also, the groove 3 of the heater 4
a side surface of the heater is abutted against the protruding portion 3d so that the through hole portion 4p as a weak portion is located at one position of the protruding portions 3d provided at intervals along the length of the inner wall on the one longitudinal side of a. It adheres in the groove 3a. Further, the convex portion 3d is arranged so as to be located between the bonding points 3b for bonding the back surface of the heater 4 and the bottom surface of the groove 3a. The presence of the gap 3c makes it possible to prevent the heater 4 from expanding due to expansion and displacement during thermal runaway, stressing the portions other than the fragile portion 4p, and preventing the heater from cracking in the portions other than the fragile portion 4p. The gap portion 3c and the gap amount are obtained by starting energization of the heater, determining the displacement of the temperature-controlled heater surface at an arbitrary point, and approximating the maximum moment and stress applied.

With such a configuration, the heater 4 does not crack when used at a normal heating temperature (temperature change below the upper limit temperature of use), but when the heater is in thermal runaway, the temperature fuse Even if the safety device 8 does not operate or there is a time lag in operation, the heater 4 emits smoke.
Before igniting, the heater lateral cracks including the disconnection of the energization heating resistor 4c are surely generated in the fragile portion 4p which is a desirable portion of the preset heater, and the energization to the heater is interrupted to ensure the safety. it can.

<Embodiment 2> (FIG. 5) FIGS. 5A and 5B show the structure of the present embodiment.
In comparison with FIG. 4 of the first embodiment, the configuration is the same as that of FIG. 4 except that only one protrusion 3d corresponds to the weakened portion 4p of the heater 4.

That is, the portion of the heater 4 other than the fragile portion 4p is bonded so that the portion where the amount of thermal expansion displacement is maximum is located at a position having a certain amount of gap with respect to the gap 3c of the heater holder 3. The heater 4 at the position of the convex portion 3d.
There is no change in abutting and adhering so that the fragile portion 4p comes. Further, there is no change in the structure in which the convex portion 3d is located between the adhesive application portions 3b for fixing the heater 4 to the heater holder 3.

As shown in FIG. 5, the location of the convex portion 3d is limited to the position of the fragile portion 4p. With this configuration, the stress applied to the heater portion other than the fragile portion 4p can be further alleviated, and the heater cracks in the heater portion other than the fragile portion 4p can be further prevented, and the thermal runaway of the heater 4 can be reliably performed. It is possible to cause lateral cracking of the heater from the fragile portion 4p.

<Third Embodiment> (FIG. 6) FIG. 6 shows the structure of the present embodiment.

The heater 4 is fixed or simply fitted in the groove 3a of the heater holder 3 with a heat-resistant adhesive of silicon rubber type.

Heater fitting groove 3a on the heater holder 3 side
The concave shape of the heater 4 is such that the first electrode pattern 4b side (AC contact side, heater left end side) of the heater 4 has a gap w1 of about 0.5 mm with respect to the outer shape of the heater 4, and the third and fourth electrode pattern sides. (DC contact side, heater right end side) holds a gap w2 of about 2 mm. The point 3e at which the gap is switched from the AC side to the DC side is near the AC side through hole portion 4p provided as the fragile portion of the heater 4.

In the above configuration, the energized state when the heater 4 has an abnormal temperature rise due to a failure of the control device or the like will be described. First, when the temperature of the heater 4 gradually rises, the temperature fuse 8 as a safety device rises together with the heater 4, and when the temperature reaches a predetermined temperature, the fuse 8 operates and the heater 4 operates.
Turn off the power supply. However, when power is rapidly supplied to the heater 4, the heater 4 heats up at a very high speed.
For example, the temperature is raised from 50 deg to 100 deg in 1 second. In such a case, the thermal fuse 8 has the heater 4
Even if the operating temperature is greatly exceeded, the energization is not interrupted because the temperature fuse 8 itself has not reached the operating temperature.

At this time, the temperature of the heater 4 suddenly rises, so that a temperature gradient is generated in the ceramic substrate 4a of the heater 4. In this embodiment, the heating resistor 4c is offset from the center of the substrate 4a. The heating resistor 4c side thermally expands, and the heater 4 tries to deform in a bow shape on the heating resistor 4c side as shown in FIG. 6B. That is, the groove 3a of the heater holder 3
When the above-mentioned rapid temperature rise occurs in the heater 4 inside the heater, the heater 4 undergoes bow deformation as shown in FIG.
The side opposite to c hits the inner wall of the groove 3a of the heater holder 3, the heater 4 is relatively pushed out to the heating resistor 4c side, and the heater 4 hits the point 3e.

As a result, stress is applied to the heater 4 from the point 3e, stress is further concentrated in the through hole 4p as a weakened portion of the heater in the vicinity of the point 3e, and the heater 4 is laterally cracked from around the through hole 4p to conduct electricity. The heating resistor 4c is disconnected and the heater is de-energized. Figure 6
In (b) of a, a is a lateral cracking line of the heater 4.

In this embodiment, there is a through hole 4p as a fragile portion of the heater 4, but even in the case of a heater without such a through hole, stress is applied to the heater 4 from the abutting point 3e, so that the vicinity of the point 3e is present. With heater 4
Breaks sideways. In the present embodiment, the heater 4 is provided with the through hole 4p as a fragile portion and the abutting point 3e is provided in the vicinity of the through hole portion 4p, so that the heater 4 is always laterally cracked at the through hole 4p portion during thermal runaway. .

<Fourth Embodiment> (FIG. 7) FIG. 7 shows the structure of the present embodiment.

In this embodiment, the heater abutting point 3e is provided in the groove 3a of the heater holder 3 on the side of the heater 4 opposite to the side of the heating resistor 4c. This point 3e
Is 20 mm or more from the position of the thermistor 5 of the heater,
It is a position closer to the through hole 4p side as the heater fragile portion. DC contact points 4h and 4o from the abutting point 3e
A gap w2 is provided on the heater end surface on the side.

When the heater 4 is thermally deformed during thermal runaway, the heater 4 causes an AC contact portion 4b on the side opposite to the heating resistor 4c and an abutting portion 3e with respect to the inner wall of the groove portion 3 of the heater holder 3. And heating resistor 4 in through hole 4p
The c side abuts, the stress concentrates on the through hole portion 4p, and the heater 4 is laterally cracked a around the through hole portion 4p. Heater holder 3 has DC contacts 4h and 4o on the side of heater 4.
No stress is applied because it does not contact with.

<Fifth Embodiment> (FIG. 8) FIG. 8 shows the structure of the present embodiment.

As shown in FIG. 8, when the heating resistor 4c of the heater 4 is located substantially in the center of the heater substrate 4a in the width direction along the length of the substrate, the heater is heated in the longitudinal direction when the temperature rises abnormally. Thermally expands. In such a case, as shown in FIG. 8, the gap w3 between the heater holder 3 and the AC contact 4b side end of the heater 4 is made small, and the gap w4 between the DC contacts 4h and 4o side end and the heater holder 3 is made large.

When the temperature of the heater 4 rises abnormally, the heater 4
The end of the C contact 4b abuts the heater holder 3. Since the heater 4 is pressed by the pressure roller 2 and the heater holder 3, a restraining force is generated. Therefore, when the temperature rises sharply, the end portion on the side of the AC contact 4b is momentarily heated by the heater holder 3
As a result of the collision with the heater, excessive stress is applied to the end portion on the AC contact 4b side, and the heater 4 still has the through hole 4 as a fragile portion.
Lateral cracks a around p.

<Reference> As a reference, (a) of FIG.
The groove portion 3 having substantially the same outer shape as that of the heater 4 is formed on the heater holder 3.
A is provided, and the heater 4 is fitted and held in the groove 3a.

The outer shape of the heater fitting groove 3a of the heater holder 3 is larger than the outer shape of the heater 4 by 0.5 to 1 mm.

In the case of such a configuration, the heater holder 3
The outer shape of the heater fitting groove portion 3a is smaller than the thermal deformation amount of the heater, and the heater 4 is immediately abutted against the inner wall portion of the groove portion of the heater holder 3 due to thermal expansion, and stress is applied to the heater 4, so that even in normal use. Sometimes heater cracks are seen, and it is difficult to identify heater cracks.

The heater 4 is provided with a heating resistor 4c on the front surface and a thermistor 5 for detecting the temperature on the back surface, and conductors 4k and 4l for taking out a signal from the thermistor 5 are provided. Since it is not clear where the heater 4 abuts the heater holder 3, if the crack a of the heater 4 occurs on the side where the thermistor 4 is bonded as shown in FIG. 9, the heater surface side as shown in FIG. 9B. Heating resistor 4c
The distance between the heater 4 and the conductors 4k and 4l on the back surface of the heater is t, which is 0.6 mm in this case, by the thickness of the substrate 4a of the heater 4. The heating resistor 4c is connected to an AC power source, and the conductors 4k and 4l are connected to a control board for controlling this device. These distances are designed to always have a predetermined distance in order to guarantee dielectric strength. For example, A
When the C power source is 220 V, the space is 4 mm or more and the creeping surface is 5 mm.
It keeps a distance of more than mm.

However, if the heater cracks as shown in FIG. 9 occur, the distance between the heating resistor 4c and the conductors 4k and 4l becomes 0.6 mm, and in some cases, a leak occurs and smoke or ignition occurs. There was a possibility.

In the case of the present invention, as in Examples 1 to 5, only when the heater 4 is in thermal runaway, lateral cracking of the heater is surely caused at a desired specific portion of the heater 4 to energize the heater. The emergency shutoff can be performed, and the above problems are solved.

<Sixth Embodiment> (FIG. 10) FIGS. 10A to 10C show other structural examples of the film heating type heating device.

In the case of (a), an endless belt-shaped film 1 is suspended and stretched between a heater 4 held by a heater holder 3, a driving roller 21 and a driven roller (tension roller) 22. The drive roller 21 drives the film 1 to rotate. 2 is film 1
It is a pressure roller in which the nip portion N is formed by pressing the lower surface of the heater 4 while sandwiching it.

In the case of (b), the endless belt-shaped film 1 is suspended and stretched between the two members of the heater 4 held by the heater holder 3 and the driving roller 21, and the driving roller 21 rotationally drives the film 1. Is.

In the case of (c), the film 1 is not an endless belt-like one, but a long end film wound in a roll is used.
The heater holder 3 is configured to travel at a predetermined speed to the winding shaft 25 side via the lower surface of the heater 4 held by the heater holder 3.

Also in the heating device having such a configuration, the same structure as in the first to fifth embodiments can be adopted to improve the safety of the heater 4 during thermal runaway.

In the first to fifth embodiments, the fragile portion 4p serving as the stress concentration portion provided in the heater 4 is a through hole. However, this is a cutout portion of the heater, a surface scratch, a thin portion, a narrow portion, The through hole need not be a through hole as long as stress is likely to concentrate, such as a dissimilar material portion.

The present invention is not limited to the ceramic heater as in the embodiments, but can be widely applied to a heater having a substrate and a heating resistor provided on the substrate to generate heat when energized.

The film heating type heating devices of Examples 1 to 6 are not only heat-fixing devices for images, but also, for example, heating a recording material carrying an image to modify surface properties (such as gloss). It can be widely used as a heating device for materials to be heated, such as a heating device, a hypothetical fixing device, a device for heating, drying, and laminating a sheet-shaped material while conveying it. Of course, the heating device of the present invention is not limited to the film heating type device shown in the embodiment.

<Embodiment 7> (FIG. 11) FIG. 11 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this example is a copying machine or printer using a transfer type electrophotographic process.

Reference numeral 31 is a rotary drum type electrophotographic photosensitive member, which is rotationally driven in the clockwise direction of the arrow at a predetermined process speed (peripheral speed).

Reference numeral 32 denotes a contact charging roller as a photosensitive member charging means, to which a predetermined charging bias is applied, and the charging roller 32 uniformly charges the surface of the rotating photosensitive member 31 to a predetermined polarity and potential. It

Exposure of target image information 33 is performed on the charged surface of the rotary photoconductor 31 by an image information exposure means section (slit image forming exposure means for original image, laser beam scanning exposure means, etc.) not shown. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photoconductor 31.

The latent image is developed as a toner image by the toner developing device 34.

The toner image is transferred from a paper feed unit (not shown) to a transfer unit, which is a pressure contact nip between the rotating photoconductor 31 and the transfer roller 35 to which a predetermined transfer bias is applied. The image is transferred onto the transfer material P as the recording material conveyed at the timing.

The transfer material P, which has passed the transfer portion and has received the transfer of the toner image, is separated from the surface of the rotary photosensitive member 31.
When the unfixed toner image is heat-fixed by being conveyed and introduced into the heating device 10 as the image heat-fixing device of FIG.
It is output as a copy or print.

After the transfer of the toner image to the transfer material P, the surface of the rotary photosensitive member 31 is cleaned by the cleaning device 37 to remove residual adhered substances such as transfer residual toner, and is repeatedly used for image formation.

[0108]

As described above, according to the present invention, a heater having a substrate and a heating resistor provided in the substrate to generate heat when energized, a heater including the heater, and the heating device. For an image forming apparatus equipped with an image heating and fixing device, when the heater is in thermal runaway, the heater is energized before the smoke or fire is caused by causing the heater to crack laterally at a desired specific portion of the heater. It is possible to make an emergency cutoff and ensure the safety.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a heating device according to a first embodiment.

FIG. 2 (a) is a plan view of a front surface of a heater, and FIG.
Is a plan view of the back side

FIG. 3 is an exploded perspective view of the apparatus

FIG. 4A is a plan view of a heater fitting groove portion of a heater holder, and FIG. 4B is a plan view of a heater portion with the heater fitted therein.

5A is a plan view of a heater fitting groove portion of a heater holder in the apparatus of the second embodiment, and FIG. 5B is a plan view of a heater portion in which a heater is fitted.

6A is a plan view of a heater portion in a state where a heater is fitted in a heater fitting groove portion of a heater holder in the apparatus of Embodiment 3, and FIG. 6B is a plan view when a heater cracks due to heater thermal runaway.

FIG. 7 is a plan view of a heater portion in a state where a heater crack occurs due to heater thermal runaway in the apparatus according to the fourth embodiment.

FIG. 8 is a plan view of a heater portion in a state where a heater crack occurs due to heater thermal runaway in the apparatus according to the fifth embodiment.

9A and 9B are explanatory views of a reference example.

10 (a), (b), and (c) are schematic views of another example of the configuration of the film heating type heating device.

FIG. 11 is a schematic diagram of an example of an image forming apparatus.

[Explanation of symbols]

A heating device (film heating type image heating and fixing device) 1 heat resistant film 2 pressure roller 2a pressure roller rubber part 2b pressure roller core metal 3 heater holder 4 heater 4d energizing through hole 4p through hole as a weak part 5 temperature measurement Element (Thermistor) 8 Safety device (Thermal fuse)

Claims (16)

[Claims] 1. An assembly of a substrate, a heater, which is a basic constituent body of a heating resistor provided on the substrate and generates heat when energized, and a heater holder holding the heater,
The substrate is provided with a fragile portion, and the heater is held by the heater holder so that the stress due to the thermal expansion displacement amount generated in the heater during thermal runaway of the heater is maximized at the fragile portion. Heater assembly. 2. The heater according to claim 1, wherein the heater is held by the heater holder in a state where the heater portion near the fragile portion is abutted against the convex portion provided on the heater holder side. assembly. 3. The positional relationship between the adhesive application position for adhering and holding the heater to the heater holder and the convex portion is such that the convex portion is located between the adhesive application positions. The heater assembly according to claim 2. 4. An assembly of a substrate, a heater having a heating resistor provided in the substrate as a basic component for generating heat when energized, and a heater holder holding the heater,
A heater assembly characterized in that the heater holder has a point at which the heater abuts against the heater that has been thermally expanded during thermal runaway of the heater. 5. The heater assembly according to claim 4, wherein a fragile portion is provided in a heater portion near a heater portion that abuts against an abutting point on the heater holder side due to thermal expansion during thermal runaway of the heater. 6. The fragile portion is provided in a heater portion near a heater portion where stress is generated by hitting an abutting point on the heater holder side due to thermal expansion during thermal runaway of the heater. Heater assembly. 7. The heater holding portion of the heater holder has a gap portion between the heater holding portion and the outer peripheral portion of the heater so that the position of the stress applied to the heater at the time of thermal expansion of the heater can be specified. The heater assembly according to claim 6. 8. The gap portion is a gap amount capable of specifying the position of stress applied to the heater with respect to the heater thermal expansion displacement amount at that temperature when the heater exceeds the upper limit temperature of use. A heater assembly as described in. 9. The heater assembly according to claim 1, wherein the fragile portion is a portion that causes stress concentration such as through-holes and notch scratches. 10. The ceramic heater according to claim 1, wherein the heater is a ceramic heater including a ceramic substrate and a heating resistor that is provided on the substrate and generates heat when energized. Heater assembly according to item 1. 11. The heater assembly according to claim 1, wherein the heater has an electric contact for supplying electric power to the heating resistor and a temperature detecting means. . 12. A heating device comprising the heater assembly according to any one of claims 1 to 11. 13. A heating device for bringing a material to be heated into close contact with a heater of a heater assembly via a film, and relatively moving the heater and the film to apply heat of the heater to the material to be heated via the film. A heating device, wherein the assembly is the heater assembly according to any one of claims 1 to 11. 14. The heating device according to claim 13, further comprising a pressing member that sandwiches a film between the heater and a heater to form a nip portion. 15. The heating device according to claim 12, wherein the heating device is an image heating fixing device. 16. An image forming apparatus comprising: an image forming means for forming an unfixed image on a recording material; and a heating fixing means for heating and fixing the unfixed image on the recording material. An image forming apparatus comprising the heating device according to any one of claims 12 to 15.