JP2006004861A - Heating body and heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability and reliability of a heating body suitable as a heat fixing device loaded on an image forming device. <P>SOLUTION: For the heating body 20 equipped with a base plate 20a, and a heating resistor 20b fitted along a length direction of the base plate, used for a heating device for heating an object for heating, a plurality of heating resistors 20b-1-1, 20b-1-2 and 20b-2-1, 20b-2-2 are arranged in nearly symmetry with nearly a center C in a short-side direction of the base plate as a standard, electrodes themselves 22a, 22b, 22c fitted at electric end parts of the first heating resistor and the second heating resistor in a symmetrical position against the standard are to become common electrodes at both ends. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heating body that heats a material to be heated, and a heating apparatus including the heating body, and is particularly suitable as a heating and fixing apparatus mounted on an image forming apparatus such as a copying machine or a laser beam printer. It is a thing.

  For example, in an image forming apparatus such as an electrophotographic copying machine or printer, as one of image heating and fixing apparatuses that thermally fix an unfixed toner image formed and supported on a recording material such as a transfer material or photosensitive paper as a permanent fixed image An on-demand film heating apparatus is known (Patent Document 1).

  This includes a heating body and a film having one surface sliding with the heating body and the other surface being in contact with the recording material and moving together, and the unfixed toner by heat from the heating body through the film. The image is heat-fixed on the recording material.

  In such a film heating type image heating and fixing apparatus, the heating body and the film as a member for conducting the heat of the heating body to the recording material can be reduced in heat capacity. The time can be shortened (quick start).

  In other words, it takes a short time to raise the temperature of the apparatus from the cooled state to a predetermined temperature, and it is not necessary to energize and heat the heating element during standby, and it is possible to pass the paper immediately after turning on the power to the image forming apparatus. The heating element can be sufficiently heated up to a predetermined temperature before the recording material reaches the fixing site (fixing nip portion), thereby reducing power consumption and reducing the temperature increase in the image forming apparatus. Is possible.

  Specifically, a so-called ceramic heater is used as a heating element having a low heat capacity and a high temperature rise. This consists of a ceramic material substrate (eg, alumina / AlN) with electrical insulation, heat resistance, and good thermal conductivity, and a heat generation resistor that generates heat when supplied with power, which is patterned on the substrate by means of printing, baking, etc. It has a primary circuit (hereinafter referred to as an AC line) including a body (for example, silver palladium), supplies power to the heating resistor to generate heat, and has a low heat capacity as a whole and a high temperature rise.

  Further, the heater as the heating body is provided with a heater control system (hereinafter referred to as a DC line) of a secondary system including a temperature detection element (for example, a thermistor), and the heater is controlled by a temperature control unit connected to the DC line. Is controlled to a predetermined set temperature (target temperature), and the power supplied to the heating resistor is controlled.

  However, when the current applied to the heater in the heater control system is controlled by wave number control, the current is turned on and off every half wave, so the voltage fluctuations with respect to other devices connected to the common line of the commercial power supply In particular, flickering called flicker (current fluctuation) occurs in lighting equipment. This flicker becomes conspicuous on the basis that the fluctuation of the current flowing through the lighting device increases as the power consumption of the heater increases. Therefore, the heating resistor is divided into a plurality of pieces to suppress the flicker. ing.

Also, as a safety measure, a safety element such as a thermo switch is inserted in series with the AC line, and this is placed in contact with or close to the heater. The power supply to the body is urgently cut off.
JP-A-63-313182

  However, in recent years, image forming apparatuses have been required to further increase the speed. To cope with this, the maximum power that can be supplied to the heating resistor even at low voltage is increased by reducing the resistance value of the heating resistor of the heater. Is set to

  For this reason, when the heater temperature control section of the heater control system goes out of control, when the heater goes out of control (abnormal temperature rise / overheat), a large amount of power is supplied even with a single heating resistor, resulting in a heavy load on the board. There is a problem that the heater is destroyed before the power is urgently cut off by the operation of the safety element.

  The present invention is a further improvement of a conventional heating body, and provides a heating body that can reduce the load on the substrate during heat generation and can improve durability and reliability, and a heating device including the heating body. It is something to try.

  Typical configurations of the heating body and the heating device according to the present invention are as follows.

(1) In a heating element that includes a substrate and a heating resistor provided along the longitudinal direction of the substrate and is used in a heating device that heats a material to be heated.
The substrate has a plurality of heating resistors arranged substantially symmetrically with respect to the approximate center in the short direction of the substrate, and the first heating resistor and the first heating resistor that are in a symmetrical positional relationship with respect to the reference. 2. A heating element characterized in that the electrodes provided at the electrical end portions of the two heating resistors are common electrodes at both ends.

(2) A heating body having a substrate and a heating resistor provided along the longitudinal direction of the substrate, a flexible member that moves while contacting the heating body, and sandwiching the flexible member A heating device that includes the heating member and a pressure member that forms a nip portion, and heats the material to be heated while nipping and conveying the nip portion;
The substrate has a plurality of heating resistors arranged substantially symmetrically with respect to the approximate center in the short direction of the substrate, and the first heating resistor and the first heating resistor that are in a symmetrical positional relationship with respect to the reference. The heating device characterized in that the two heating resistors always generate heat simultaneously.

  According to the present invention, each heating resistor having a symmetrical relationship with respect to the approximate center in the short direction of the substrate generates heat substantially symmetrically in the short direction of the substrate, so that the thermal load applied to the substrate can be reduced and thus durable. Improvement in reliability and reliability.

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

(1) Example of Image Forming Apparatus FIG. 1 shows an example of an image forming apparatus provided with an image heat fixing device (hereinafter referred to as a fixing device) as a heating device according to the present invention. The image forming apparatus shown in the figure is a laser beam printer using an electrophotographic process.

  The image forming apparatus includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in the direction of the arrow R1 by a driving unit (not shown).

  Around the photosensitive drum 1, a charging roller (charging device) 2, an exposure unit 3, a developing device 4, a transfer roller (transfer device) 5, and a cleaning device 6 are arranged in that order along the rotation direction. .

  In addition, a sheet feeding cassette 7 in which a sheet-like recording material P such as paper is stored as a material to be heated is disposed below the apparatus main body M, and sequentially from the upstream side along the conveyance path of the recording material P. A paper feed roller 15, a transport roller 8, a top sensor 9, a transport guide 10, a fixing device 11 including a heating body according to the present invention, a transport roller 12, a paper discharge roller 13, and a paper discharge tray 14 are arranged.

  Next, the operation of the image forming apparatus having the above configuration will be described.

  The photosensitive drum 1 that is rotationally driven in the direction of arrow R1 by a driving means (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by a charging roller 2.

  The photosensitive drum 1 after charging is subjected to image exposure L based on the image information by the exposure means 3 such as a laser optical system on the surface, and the charge of the exposed portion is removed to form an electrostatic latent image.

  The electrostatic latent image is developed by the developing device 4. The developing device 4 includes a developing roller 4a. A developing bias is applied to the developing roller 4a, and toner is attached to the electrostatic latent image on the photosensitive drum 1, thereby developing the toner image (a visible image). ).

  The toner image is transferred to the recording material P such as paper by the transfer roller 5. The recording material P is stored in a paper feed cassette 7, fed and transported by a paper feed roller 15 and a transport roller 8, and a transfer nip between the photosensitive drum 1 and the transfer roller 5 via a top sensor 9. It is conveyed to the part. At this time, the leading edge of the recording material P is detected by the top sensor 9 and synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.

  The recording material P carrying the unfixed toner image on the surface by transfer is transported to the fixing device 11 along the transport guide 10, where the unfixed toner image is heated and pressurized and fixed on the surface of the recording material P. . The fixing device 11 will be described in detail later.

  The recording material P after the toner image is fixed is transported and discharged onto a paper discharge tray 14 on the upper surface of the apparatus main body M by the transport roller 12 and discharge roller 13.

  On the other hand, on the photosensitive drum 1 after the transfer of the toner image, the toner remaining on the surface without being transferred to the recording material P (hereinafter referred to as transfer residual toner) is removed by the cleaning blade 6a of the cleaning device 6 for the next image formation. Prepare.

  By repeating the above operation, image formation can be performed one after another.

(2) Fixing device 11
FIG. 2 shows a schematic configuration of the fixing device 11. This figure is a longitudinal sectional view along the conveyance direction (arrow K direction) of the recording material P.

  The fixing device 11 shown in the present embodiment is a pressure roller driving type and film heating type device using a fixing film (fixing belt) as a heating member, and a heater 20 as a heating body for heating toner, A heater holder 22 as a heating member holding member for holding the heater 20, a fixing film (fixing rotating body, heating rotating body) 25 as a flexible member including the heater 20 and the heater holder 22, and a contact with the fixing film 25 The pressure roller 26 as the pressure member, the temperature control means 27 that is a secondary circuit for controlling the temperature of the heater 20, and the rotation control means 28 for controlling the conveyance of the recording material P are used as main constituent members. Yes.

  In the fixing device 11 of this example, a pressure roller 26 is pressed against a heater holder 22 holding the heater 20 with a predetermined pressing force via a cylindrical fixing film 25, and a fixing nip portion is interposed between the heating body 20 and the heater 20. N is formed.

  The pressure roller 26 is rotationally driven in the direction of arrow R26 (counterclockwise) by the rotation control means 28, and the rotational force acts on the film 25 by the sliding frictional force with the outer surface of the fixing film 25 due to the rotation of the pressure roller. The film 25 rotates around the heater holder 22 holding the heater 20 in the direction of arrow R25 (clockwise), and the heater 20 is energized and heated by the temperature control means 27, whereby the heater 20 is heated to a predetermined set temperature (target). Temperature). In this state, the recording material P carrying the unfixed toner image t is nipped and conveyed by the fixing nip portion N, whereby the heat of the heater 20 is applied to the recording material P via the fixing film 25, and the unfixed toner image t Is fixed to the surface of the recording material P by heat. The recording material P that has passed through the fixing nip N is separated from the surface of the fixing film 25 and is discharged.

  In the fixing device 11 of this embodiment, the sheet passing reference of the recording material P is the central portion in the longitudinal direction of each member (direction orthogonal to (intersects with) the conveyance direction K of the recording material P).

  The heater 20 has a resistor pattern (hereinafter referred to as a heating resistor) 20b, which is a primary circuit by thick film printing, for example, as a heating resistor on a heat resistant substrate 20a such as alumina, and the heating resistor. A surface protective layer 20c such as a glass coating layer to be coated is formed. The heater 20 will be described in more detail in the next section (3).

  The heater holder 22 is a member formed in a substantially semicircular saddle shape with a heat-resistant resin, and is attached to the apparatus main body M to support the heater 20 and also serves as a guide member for guiding the rotation of the fixing film 25.

  The fixing film 25 is formed of a heat-resistant resin such as polyimide in a cylindrical shape, and is rotatably fitted to the heater holder 22. The fixing film 25 is pressed against the heater 20 by the pressure roller 26, whereby the back surface of the fixing film 25 is brought into contact with the surface protective layer 20 c of the heater 20.

  The pressure roller 26 is provided with a heat-resistant release layer 26b having elasticity such as silicone rubber on the outer peripheral surface of a metal cored bar 26a. The pressure roller 26 is biased toward the fixing film 25 by a biasing member (not shown) such as a pressure spring, and presses the fixing film 25 against the surface protective layer 20c of the heater 20 by the outer peripheral surface of the release layer 26b. Thus, a fixing nip N is formed between the fixing film 25 and the fixing film 25. If the width (nip width) of the pressure roller 26 in the fixing nip portion N in the rotational direction R26 is a, the nip width a suitably heats and presses the unfixed toner image t on the recording material P. It is set to the extent that can be.

  The rotation control means 28 includes a motor 29 that rotationally drives the pressure roller 26, and a control unit (CPU) 30 that controls the rotation of the motor 29. As the motor 29, for example, a stepping motor or the like can be used, and the pressure roller 26 can be continuously rotated in the direction of the arrow R26, or can be intermittently performed by a predetermined angle. That is, the recording material P can be stepped while the pressure roller 26 is repeatedly rotated and stopped.

(3) Heater (heating body) 20
The configuration of the heater 20 will be described in more detail with reference to FIG.

  FIG. 3 is a schematic plan view of the heater surface side with the surface protective layer 20c removed.

The heater substrate 20a is a horizontally long thin plate member made of a ceramic material such as alumina, aluminum nitride or the like having heat resistance, good thermal conductivity, and electrical insulation.
On the substrate 20a, a plurality of heating resistors 20b are arranged substantially symmetrically with respect to the approximate center in the short direction of the substrate.

  The heating resistor 20b includes a main heating resistor pair 20b-1 and a sub-heating resistor pair 20b-2. The main heating resistor pair includes a first heating resistor (20b-1-1) and a second heating resistor (20b-1-2) that are in a symmetrical positional relationship with respect to the approximate center C in the short side direction of the substrate. )have. The sub heat generating resistor pair includes a first heat generating resistor (20b-2-1) and a second heat generating resistor (20b-2-2) having a symmetrical positional relationship with respect to the substantially center C in the lateral direction of the substrate. )have. The main and sub heating resistor pairs 20b-1 and 20b-2 are each about 5 μm thick on one side of the substrate 20a by using a thick film printing method (screen printing method) and a conductive thick film paste such as Ag / Pd. It is formed by printing and baking at a thickness of. Here, in the substrate width direction (short direction), the heating resistor at the end of the substrate is the main heating resistor, the central heating resistor is the sub heating resistor, and the main / sub heating resistor pair is a plurality of heating resistors. Are connected in parallel. Further, the first heating resistor (20b-1-1) and the second heating resistor (20b-) of the main heating resistor pair having a symmetrical positional relationship with respect to the approximate center C in the short direction of the substrate. The electrodes provided at the electrical end of 1-2) are common electrodes (22a, 22c) at both ends. In the sub-heating resistor pair, the electrodes provided at the electrical ends of the first heating resistor (20b-2-1) and the second heating resistor (20b-2-2) are both common electrodes ( 22b, 22c). The common electrode 22c is also a common electrode for the main heating resistor pair and the sub-heating resistor pair.

  The resistance values of the four heating resistors are each set to 18Ω.

  FIG. 4 shows an example of an electric circuit block diagram of the temperature control means 27 for the heater 20.

  The temperature control means 27 includes a temperature detection element 21, a triac 24 (24a, 24b), a temperature control unit (CPU) 23, and the like. The main feeding electrode 22a and the sub feeding electrode 22b of the main heating resistor pair 20b-1 and the sub heating resistor pair 20b-2 are provided with triacs 24a and 24b for controlling an alternating current supplied from the commercial power supply 34, respectively. It is connected. In addition, a safety element 31 (in this example, a thermal fuse or a thermo switch) 31 that prevents the heater 20 from being overheated is connected in series with the commercial power source 34. The safety element 31 is disposed in contact with the heater 20 or in the vicinity of the heater 20. The temperature control unit 23 controls the timing for turning on / off the triacs 24a and 24b based on the temperature detected by the temperature detecting element 21, and the main heating resistor pair from the main power supply electrode 22a to the common electrode 22c in the triac 24a. The heater 20 is heated to a predetermined temperature (target temperature) by controlling the energization of the sub heating resistor pair 20b-2 from the sub power feeding electrode 22b to the common electrode 22c in the triac 24b. Adjust.

  Next, the resistor structure in the conventional heater 50 will be described. FIG. 12 is a schematic plan view of the heater surface side in the conventional heater 50.

  In the conventional heater 50 shown in FIG. 12, one main heating resistor 50b-1 and sub heating resistor 50-2 are provided on one side of the ceramic substrate 50a on one side and the other side in the short side direction of the substrate. Formed along the longitudinal direction. The main heating resistor 50b-1 is energized from the main feeding electrode 51a to the common electrode 51c, and the sub heating resistor 50b-2 is energized from the sub feeding electrode 51b to the common electrode 51c. Yes. In the figure, 52 is a thermo switch.

  As described above, in the conventional example, the main / sub heat generating resistors 50b-1 and 50b-2 are arranged separately on one end side and the other end side of the substrate 50a in the short-side direction of the substrate.

  On the other hand, in this example, each heating resistor (20b-1-1, 20b-1-2) is provided for the main heating resistor pair (20b-1) and the sub-heating resistor pair (20b-2). And (20b-2-1, 20b-2-2) are arranged on one end side and the other end side in the substrate short direction symmetrical to the center C in the substrate short direction.

  FIG. 5A shows the thermal stress when the main resistor pair 20b-1 is energized, and FIG. 5B shows the thermal stress when the sub resistor pair 20b-2 is energized. ) Each shows a heater sectional view and thermal stress distribution of the conventional example and this example.

  5A and 5B, when this example and the conventional example are compared, in the conventional example, a large thermal stress is applied particularly at the substrate edge portion on the heat generation side (one end side and the other end side in the substrate width direction). However, it can be seen that the stress in the edge portion is reduced in this embodiment. That is, the thermal stress generated in the substrate edge portion is smaller in this embodiment. Therefore, a load applied to the edge portion of the substrate due to thermal stress can be reduced.

  Further, FIG. 6 shows the time for the heater to break down and the time for the safety element to operate when each heating resistor runs away.

  Originally, when the safety element 31 is activated, the energization of the main / sub heat generating resistors 20b-1 and 20b-2 is stopped, but in this experiment, the main / sub heat generating resistors 20b-1 and 20b-2 and the safety element 31 are connected. Since they are connected separately, power is supplied to the main and sub heating resistors 20b-1 and 20b-2 until the heater 20 is destroyed even if the safety element 31 is activated.

  As shown in FIG. 6, in the conventional heating resistor arrangement, the heater was destroyed in 3.5 seconds before the safety element was activated during the thermal runaway of the main heating resistor. It can be seen that the safety element is activated (5.8 seconds) before 10 seconds). The same result is obtained when the sub-heating resistor is out of control.

  Therefore, even when the heater 20 is in a thermal runaway (abnormal temperature rise or overheating) during the thermal runaway of the temperature control unit 23, it is not destroyed. Therefore, the durability and reliability of the heater 20 can be improved.

  The actions and effects of the heater 20 shown in FIG. 3 are also achieved by the configuration of the heater 20 shown in FIGS.

  FIGS. 7A to 7C are plan model diagrams on the heater surface side in a state where the surface protective layer is removed. Note that members that are the same as those shown in FIG. 3 are given the same reference numerals, and description thereof will be omitted.

  In (A), the heating resistor 20b is composed of two energized heating resistors, a main heating resistor pair 20b-1 (20b-1-1, 20b-1-2) and a sub-heating resistor 20b-3. ing. The sub heat generating resistor 20b-3 is a short substrate that is symmetrical with respect to the center C in the short direction of the substrate between the main heat generating resistors (20b-1-1, 20b-1-2) of the main heat generating resistor pair. It is arranged in the approximate center of the direction. The sub-heating resistor 20b-3 has a sub-feeding electrode 22d as a common electrode at the electrical end of the main heating resistor pair 20b-1 on the main feeding electrode 22a side. In the heater 20 shown in (A), the temperature control means 27 of FIG. 4 can be used as a secondary system circuit.

  In the heater 20 of (A), the main heating resistor resistance value is 14.5Ω / sub heating resistor resistance value is 23Ω, and the power ratio of the main heating resistor / sub heating resistor is set to about 3: 2. Yes. Here, in order to make up for the power shortage such as low temperature environment, the total power of the main heating resistor pair 20b-1 and the sub heating resistor 20b-3 must be secured, so the power of the sub heating resistor is reduced. Therefore, it is necessary to increase the power of the main heating resistor.

  FIG. 8 shows the heater destruction time, safety element operation time, and margin under the same conditions. When the resistance value of the main / sub heating resistor was 1: 1, there was not enough margin when the sub heating resistor was out of control (0.4 seconds), but the main heating resistor resistance value / sub By optimizing the resistance value of the heating resistor to 2: 3, that is, the power ratio of 3: 2, the margin of the main heating resistor is slightly reduced (3.6 seconds) during the thermal runaway, but the heat of the sub-heating resistor is reduced. A sufficient margin (2.8 seconds) can be secured during runaway. Of course, the proper distribution varies depending on the substrate width, thickness, input voltage, and the like.

  Further, depending on the design conditions, the heating resistor 20b may be composed of three or more energized heating resistors. An example is shown in (B). The heating resistor 20b includes three energizing heating resistors, a main heating resistor pair 20b-1, a first sub-heating resistor pair 20b-2, and a second sub-heating resistor pair 20b-4. . The first heat generating resistor 20b-4-1 and the second heat generating resistor 20b-4-2 constituting the second sub heat generating resistor pair 20b-4 are composed of a first sub heat generating resistor (20b-2-1). , 20b-2-2) are arranged on one end side and the other end side in the substrate short direction symmetrical to the center C in the short direction of the substrate. Each heating resistor (20b-4-1, 20b-4-2) has a sub-feeding electrode 22e as a common electrode at the electrical end of the first sub-heating resistor pair 20b-2 on the main feeding electrode 22b side. Have.

  In the heater 20 shown in (B), for example, the temperature control means 27 shown in FIG. 9 can be used as the secondary system circuit. Note that members that are the same as those shown in FIG. 4 are given the same reference numerals, and descriptions thereof are omitted.

  In the main heating resistor pair 20b-1 and the first and second sub-heating resistor pairs 20b-2 and 20b-4, the main feeding electrode 22a and the sub feeding electrodes 22b and 22e are supplied with an alternating current from the commercial power source 34. Triacs 24a, 24b, and 24c for controlling are connected to each other. Further, the common electrode 22c is connected to a commercial power supply 34 via a safety element (in this example, a temperature fuse or a thermo switch) 31 that prevents an excessive temperature rise of the heater 20. The safety element 31 is disposed in contact with the heater 20 or in the vicinity of the heater 20. The temperature control unit 23 controls the timing for turning ON / OFF the triacs 24a, 24b, and 24c based on the temperature detected by the temperature detection element 21. The energization of the main heating resistor pair 20b-1 from the main feeding electrode 22a to the common electrode 22c is controlled by the triac 24a, and the sub heating resistor pair 20b-2 from the sub feeding electrode 22b to the common electrode 22c is controlled by the triac 24b. The heater 20 is adjusted to a predetermined temperature (target temperature) by controlling the energization to the sub-heating resistor pair 20b-4 from the sub power feeding electrode 22e to the common electrode 22c by the triac 24c.

  Also in the heater 20 shown in (B), the main sub-resistors 20b-1, 20b-2, and 20b-4 of the main resistor pair, the first, and the second sub-resistor pairs are approximately centered in the short direction of the substrate. Since it is arranged on one end side and the other end side in the short side direction of the substrate that is symmetrical with respect to C, the load applied to the edge portion of the substrate due to thermal stress can be reduced. Even if the heater 20 runs out of heat, it does not break.

  In the heater 20 shown in (A), a linear main heating resistor / sub-heating resistor 20b-3 having a constant heating resistor width is used as the energization heating resistor of the heating resistor 20b. The sub-heating resistor is not limited to this, and a tapered main / sub-heating resistor may be used. An example is shown in (C).

  In (C), each of the main heating resistors (20b-1-1, 20b-1-2) is shaped so as to widen the heating resistor width from the vicinity of the longitudinal center to the end portion, and the sub-heating resistor 20b-3. Is formed in a shape that narrows the heat generation width in multiple steps from the vicinity of the longitudinal center to the end. Also in this case, the main heating resistor (20b-1-1, 20b-1-2) and the sub-heating resistor 20b-3 are each in the substrate short direction symmetrical with respect to the center C in the short direction of the substrate. Arranged at approximately the center.

  According to the present embodiment, the fixing device 11 is unable to control the energization of the heater 20 for some reason, and power is continuously supplied to the heating resistor 20b of the AC line (primary system circuit). Does not break even when a thermal runaway (abnormal temperature rise or overheating) occurs.

  Moreover, since the heater 20 does not break down due to thermal runaway, the safety element 31 such as a temperature fuse / thermo switch intervened in series with the AC line is activated, the AC line is opened, and the power supply to the heating resistor 20b is urgently cut off. Then, the thermal runaway of the heater 20 is stopped.

(Second embodiment)
In the present embodiment, an example of a heater in which a main heating resistor pair as a heating resistor and a sub heating resistor are arranged on both front and back surfaces of a ceramic substrate is shown. The same members as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 10 shows an example of the heater according to this example. (A) is a plane model view of the heater surface side from which the surface protective layer is removed, (B) is an enlarged sectional view taken along line II of (A), and (C) is an enlarged sectional view taken along line II-II.

  In Example 1, since the heating resistor 20b is disposed only on the surface of the ceramic substrate (0.6 mm to 2 mm) 21a, the temperature distribution differs between the front and back of the ceramic substrate 21a when the heating resistor 20b suddenly generates heat. As the substrate 21a is warped, thermal stress is generated, and there is a possibility that the surface protective layer 20c or the substrate 20a serving as protective glass may be broken.

  Therefore, the main heating resistor pair 20b-1 and the sub heating resistor 20b-3 are arranged symmetrically on the front and back surfaces of the ceramic substrate 21a. As shown in (A) and (B), each of the main heating resistors 20b-1-1 and 20b-1-2 of the main heating resistor pair 20b-1 is located at a substantially center C in the short-side direction of the substrate. They are arranged on one end side and the other end side in the symmetric substrate short direction. Each of the main heating resistors 20b-1-1 and 20b-1-2 has a main power supply electrode 22a and a common electrode 22c at electrical ends on the front and back surfaces of the substrate 20a. On the other hand, the sub-heating resistor 20b-2 is symmetrical with respect to the center C in the short direction of the substrate between the main heating resistors 20b-1-1 and 20b-1-2 of the main heating resistor pair 20b-1. It is arranged at the approximate center in the short direction of the substrate. The sub-heating resistor 20b-2 has a sub-feeding electrode 22b at the electrical end of the main heating resistor pair 20b-1 on the main feeding electrode 22a side.

  When the main heating resistor 20b-1 and the sub heating resistor 20b-3 on the front and back surfaces are connected in parallel, the electrodes 22a, 22c, and 22b corresponding to the heating resistors are connected to the electrodes 20a, 22c, and 22b via the substrate 20a. Through holes 22a-1, 22c-1, 22b-1 are provided to establish conduction (see (C)), or a connector 40 is employed that allows conduction through the contacts 40a, 40b from the front and back surfaces of the substrate 20a ((D )).

  According to this embodiment, the temperature difference between the front and back surfaces of the substrate 20a becomes substantially equal. Therefore, even when the substrate 20a is made thicker, the temperature distribution is always symmetrical with respect to the substantially center C in the lateral direction of the substrate. The stress cancels and decreases dramatically.

  FIG. 11 shows the result of comparing the thermal stresses of the heater of Example 1 and the heater of Example 2. 11A is a cross-sectional view in the width direction of the heater 20 shown in FIG. 7A of the first embodiment, and FIG. 11B is a cross-sectional view in the width direction of the heater in the second embodiment and in the first and second embodiments. It is a thermal-stress distribution figure of no heater. And (C) shows the time for each heater to break and the time for the safety element to operate when the heating resistor runs away in the heaters of the first and second embodiments.

  In FIG. 5C, the heater destruction time is 9.0 seconds in the second embodiment compared to 8.2 seconds in the first embodiment. The operating time of the safety element is 3.4 seconds in the second embodiment compared to 4.6 seconds in the first embodiment. As a result, the operating margin of the safety element 31 is 5.6 seconds in the second embodiment compared to 3.6 seconds in the first embodiment.

  Therefore, according to the heater of this embodiment, the thermal stress generated in the substrate thickness direction is reduced (there is no non-uniform temperature distribution). The operation time becomes extremely short by being closer to the heating resistor. As a result, a sufficient margin can be secured as compared with the first embodiment. Therefore, the durability and reliability of the heater 20 can also be improved in this embodiment.

  According to the present embodiment, since the heater 20 is not destroyed due to thermal runaway, the safety element 31 such as a temperature fuse / thermo switch intervening in series with the AC line is activated to open the AC line and supply power to the heating resistor 20b. Is cut off urgently, and the thermal runaway of the heater 20 is stopped.

  In the present embodiment, the heater 20 shown in FIG. 7A of the first embodiment has been described as an example of the heater having the configuration in which the heating resistors are arranged as described above on the front and back surfaces of the substrate. A similar configuration can be applied to the heater 20 shown in FIGS. 3 and 7B and 7C.

  As described above, since the heater 20 does not break down due to thermal runaway, it is caused by emergency interruption of power due to the operation of the safety element 31, current leakage of the AC line / DC line, breakage of the earth leakage / temperature control system, the current leakage It is possible to reduce malfunctions of the communication destination computer.

  Furthermore, since the heater 20 is not destroyed even when the maximum power is turned on, the heater heating resistor total resistance value can be set low.

  As a result, it is possible to provide an image forming apparatus that can cope with speeding up when the fixing device including the heating body is an image heating and fixing device.

(Other)
a) In the first and second embodiments, the pressure member as the pressure rotating body may be an endless belt body having an elastic member instead of the roller body having the elastic member. Further, for example, the heat capacity may be reduced by using a pressure film unit including an endless belt and a pressure member disclosed in JP-A-2001-228731.

  b) The fixing film as one rotating body can be configured to be driven by stretching the film with a driving roller and a tension roller (film driving system).

  While various examples and embodiments of the present invention have been shown and described above, the spirit and scope of the present invention are not limited to the specific descriptions and figures in the present specification by those skilled in the art. It will be understood that the invention extends to various modifications and changes that are all set forth in the appended claims.

  Examples of embodiments of the present invention are listed below.

  [Embodiment 1] A heating element characterized in that, with respect to the heating resistor, the total heating value is equal and the heating value is gradually increased from the substrate center toward the substrate edge.

  [Embodiment 2] A heating element characterized in that the heating resistors are arranged symmetrically on both sides of the substrate.

Longitudinal sectional view showing schematic configuration of image forming apparatus Longitudinal sectional view showing schematic configuration of fixing device The example of the heater of Example 1, the plane model figure of the heater surface side in the state which removed the surface protective layer Electric circuit block diagram of temperature control means for heater Cross-sectional view in the width direction of the heater of Example 1, and a thermal stress comparison diagram of the heater of Example 1 and the heater of the conventional example The figure which shows the time when the heater which makes each heating resistor same value reaches destruction and the time when the safety element operates Planar model of the heater surface side showing another example of the heater of Example 1, with the surface protective layer removed The figure which shows the time when the heater which makes each exothermic resistance value differ, the time when the heater breaks and the safety element operates Other electric circuit block diagram of temperature control means for heater The example of the heater of Example 2, the plane model figure of the heater surface side of the state which removed the surface protective layer Sectional views in the width direction of the heaters of Example 2 and Example 1 and thermal stress comparison diagrams of these heaters An example of a conventional heater, and a plan view of the heater surface with the surface protective layer removed

Explanation of symbols

20... Heating element (heater)
20a... Substrate 20b... Heating resistor (resistor)
20 b-1... Main heating resistor 20 b-2, 20 b-3, 20 b-4... Sub heating resistor 22 a... Main feeding electrode 22 b.・ Common electrode 21 ... Temperature sensing element (thermistor)
22... Heating element holding member (heater holder)
23 ... CPU
24 ... Triac 25 ... Fixing rotator (fixing film)
26 ··· Pressure member (pressure roller)
27 .... Temperature control means 28 ... Rotation control means 29 ... Motor 30 ... CPU
31... Safety element N... Fixing nip part P.

Claims (5)

In a heating body used in a heating device that has a substrate and a heating resistor provided along the longitudinal direction of the substrate, and heats a material to be heated,
The substrate has a plurality of heating resistors arranged substantially symmetrically with respect to the approximate center in the short direction of the substrate, and the first heating resistor and the first heating resistor that are in a symmetrical positional relationship with respect to the reference. 2. A heating element characterized in that the electrodes provided at the electrical end portions of the two heating resistors are common electrodes at both ends.   The heating body according to claim 1, wherein an electrode provided at one electrical end of all of the heating resistors provided on the substrate is a common electrode. A heating body having a substrate and a heating resistor provided along the longitudinal direction of the substrate, a flexible member that moves while being in contact with the heating body, and the heating body sandwiching the flexible member And a pressure member that forms a nip portion, and a heating device that heats while sandwiching and transporting a material to be heated in the nip portion,
The substrate has a plurality of heating resistors arranged substantially symmetrically with respect to the approximate center in the short direction of the substrate, and the first heating resistor and the first heating resistor that are in a symmetrical positional relationship with respect to the reference. The heating device characterized in that the two heating resistors always generate heat simultaneously.   The heating apparatus according to claim 3, wherein electrodes provided at electrical ends of the first heating resistor and the second heating resistor are common electrodes at both ends.   The heating apparatus according to claim 4, wherein an electrode provided on one electrical end of all the heating resistors provided on the substrate is a common electrode.

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