JP5804876B2 - Image heating device - Google Patents

Description

  The present invention relates to an image heating apparatus suitable for use as a fixing device (fixing device) mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  As a fixing device (fixing device) mounted on an electrophotographic copying machine or printer, a film heating type fixing device is known. This film heating type fixing device includes a heater having a heating resistor that generates heat upon energization on a ceramic heater substrate, a cylindrical fixing film that rotates while in contact with the heater, and a heater and a nip through the fixing film. A pressure roller for forming the portion. The recording material carrying the unfixed toner image is heated while being nipped and conveyed at the nip portion, whereby the toner image on the recording material is heated and fixed to the recording material.

  This type of fixing device has an advantage that the time for starting energization of the heater and raising the temperature to the fixable temperature is short. Therefore, a printer equipped with this fixing device can shorten the time (FPOT: First Print Out Time) from when a print command is input until the first image is output. This type of fixing device also has an advantage that power consumption during standby for waiting for a print command is small.

  By the way, when a small-size recording material is continuously printed at the same print interval as a large-size recording material in a printer equipped with a fixing device using a fixing film, an area where the recording material of the heater does not pass (non-sheet passing area) is excessive. It is known that the temperature rises. When the non-sheet passing region of the heater is excessively heated, members such as a heater holder and a pressure roller that support the heater may be damaged by heat.

  In particular, when a thick recording material (thick paper, envelope, etc.) with a width smaller than the maximum size is double-fed and passed (introduced) through the nip, the area where the recording material passes through the nip (paper passing area) A lot of heat is lost to the recording material. Moreover, since the temperature control is performed based on the output of the temperature measuring element provided in the sheet passing area, a large amount of electric power is supplied to the heater. On the other hand, in the non-sheet passing area of the nip portion, the recording material is not deprived of heat, so the temperature becomes very high (temperature rise of the non-sheet passing portion), and the members such as the heater holder and the pressure roller that support the heater are damaged by the heat. there is a possibility.

  Therefore, a printer equipped with a film heating type fixing device has a control to widen the print interval when continuously printing on a small size recording material than when continuously printing on a large size recording material. The excessive temperature rise is suppressed.

  However, the control for extending the print interval is to reduce the number of output sheets per unit time, and it is desired to suppress the number of output sheets per unit time to the same level or slightly less than in the case of a large size recording material.

  In order to prevent the temperature rise at the non-sheet passing portion of the nip portion, the following method has been proposed.

  One is to provide heat generation patterns along the longitudinal direction of the heater substrate on both sides of the heater substrate, make one heat generation pattern shorter than the other heat generation pattern, and energize the shorter heat generation pattern when passing small-size paper. Thus, a method for preventing the non-sheet passing portion temperature rise has been proposed. Hereinafter, it is referred to as a heat generation pattern for small-size paper. Also, a method has been proposed in which not only two but also heat generation patterns corresponding to the widths of various small size papers are provided, and the heat generation patterns to be energized are selected according to the paper widths of the small size papers to be passed (patent Reference 1).

  As another countermeasure, a method of using a material having a negative TCR (resistance temperature characteristic) such as graphite for the heat generation pattern can be considered. However, since the negative resistance material generally has a very high volume resistance, it is necessary to increase the thickness and width of the heat generation pattern in order to obtain a desired resistance value, which increases the cost. As a solution to this problem, a method has been proposed in which the heat generation patterns formed on both sides of the heater substrate are connected in parallel to facilitate the formation of a heat generation pattern having a negative characteristic of the TCR and to prevent the temperature rise of the non-sheet passing portion. (See Patent Document 2).

  In addition, since the resistance value decreases as the temperature rises by making the TCR of the heat generation pattern negative, the temperature rises instantaneously if the resistance heating element continues to be heated due to thermal runaway during an abnormality. was there. As a countermeasure against this thermal runaway, a heat generation pattern is formed on both sides of the heater substrate, the TCR of one heat generation pattern is made positive, the other heat generation pattern is made a negative TCR, and the respective heat generation patterns are connected in series and driven. . Furthermore, by configuring the resistance value in each heat generation pattern and the absolute value of TCR to be the same, the series combined resistance can suppress changes due to temperature, and it is possible to suppress the occurrence of rapid temperature rise. The method which becomes is proposed (refer patent document 3).

JP 2003-337484 A JP 2008-268730 A JP 2008-268729 A

  The film heating type fixing device can improve the productivity of small-size recording materials by reducing both heater cracking and shortening the heater start-up time when power is continuously applied to the heat generation pattern due to thermal runaway. It is hoped that Here, the heater start-up time is a period from when power is supplied to the heater until the heater reaches a predetermined fixing temperature.

  An object of the present invention is to provide an image heating apparatus capable of both suppressing cracking of a heating element due to thermal runaway and shortening the start-up time of the heating element and improving the productivity of a small size recording material. is there.

  The configuration of the image heating apparatus according to the present invention for achieving the above object is provided along the longitudinal direction of the substrate on the substrate, one surface of the substrate, and the other surface opposite to the one surface. A heating member having an energization heating resistor, a flexible member that moves in contact with the heating member, and a backup member that forms a nip portion with the heating member via the flexible member. In the image heating apparatus that heats the image on the recording material while nipping and conveying the recording material at the nip, one of the energization heating resistors provided on the one surface and the other surface of the substrate The heating resistor is shorter than the other heating resistor, the shorter heating resistor has a positive resistance temperature characteristic, and the longer heating resistor has a resistance temperature characteristic of zero or negative, The shorter heating resistor and the longer heating resistor When an image on a recording material is heated using the shorter heating resistor connected in parallel, energization of the shorter heating resistor and the longer heating resistor until a predetermined heating temperature is reached. It is characterized by performing.

  According to the present invention, it is possible to provide an image heating apparatus capable of both suppressing cracking of a heating element due to thermal runaway and shortening the start-up time of the heating element and improving the productivity of a small-size recording material. it can.

1 is a schematic configuration diagram of an example of an image forming apparatus. FIG. 3 is a schematic cross-sectional side view of a fixing device. 2 is a schematic configuration diagram of a front surface side and a back surface side of the heater according to Example 1. FIG. FIG. 3 is a diagram illustrating a configuration of a heater drive control circuit according to the first embodiment. It is the heat-generation distribution figure of the longitudinal direction of each heat-generation pattern of the surface side of a heater which concerns on Example 1, and a back surface side. It is a figure showing transition of the emitted-heat amount of the heat generation pattern for small size of the heater which concerns on Example 1. FIG. It is a figure showing the temperature transition of the heater board | substrate of the heater which concerns on Example 1. FIG. It is the longitudinal cross-sectional view of the center of the transversal direction of the heater which concerns on Example 2, and the structure schematic diagram of the surface side and back surface side of the heater. It is the heat-generation distribution figure of the longitudinal direction of each heat-generation pattern of the surface side of a heater which concerns on Example 2, and a back surface side. FIG. 6 is a diagram illustrating a configuration of a heater drive control circuit according to a second embodiment. It is the longitudinal cross-sectional view of the center of the transversal direction of the heater which concerns on Example 3, and the structure schematic diagram of the surface side and back surface side of the heater. It is the heat-generation distribution figure of the longitudinal direction of each heat-generation pattern of the surface side of a heater which concerns on Example 3, and a back surface side. FIG. 6 is a diagram illustrating a configuration of a heater drive control circuit according to a second embodiment.

[Example 1]
(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration schematic diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as a fixing device (fixing device). This image forming apparatus is an electrophotographic laser printer that prints on a recording material by a series of processes such as charging, exposure, development, and transfer in an electrophotographic process.

  In the image forming apparatus shown in the present embodiment, as the recording material conveyance reference, the center in the width direction orthogonal to the recording material conveyance direction of the recording material is matched with the center in the longitudinal direction orthogonal to the recording material conveyance direction of the recording material conveyance path. The central transport standard is used to transport the recording material. The control unit (control unit) 100 executes a predetermined image forming sequence in accordance with a print command input from an external device (not shown) such as a host computer, and performs a predetermined image forming operation according to the image forming sequence. It is. The control unit 100 includes a CPU and a memory such as a ROM and a RAM. The memory stores an image formation sequence, various programs necessary for image formation, and the like.

  The image forming apparatus according to the present exemplary embodiment includes a transport unit that transports a recording material, an image forming unit that forms a toner image (image) on the recording material, and an unfixed toner image (image) formed on the recording material. It has a fixing unit (fixing device) for fixing by heating.

  When the image forming sequence is executed, the transport unit sends out only one sheet of recording material P such as a recording sheet or an OHP sheet stacked in the sheet feeding cassette 101 from the sheet feeding cassette 101 by the pickup roller 102. The recording material P is conveyed toward the registration roller 104 by the paper feed roller 103. Further, the recording material P is conveyed by a registration roller 104 to a transfer nip portion between a photosensitive drum 109 of an image forming unit and a transfer roller 110 as a transfer member at a predetermined timing.

  In the image forming unit, the outer peripheral surface (surface) of the photosensitive drum 109 as an electrophotographic photosensitive member is uniformly charged to a predetermined potential by a charging roller 106 as a charging unit. Then, image exposure based on an image signal output from an external device is performed on the charged surface of the photosensitive drum 109 by a scanner unit 111 as image exposure means.

  That is, the laser light emitted from the laser diode 112 in the scanner unit 111 passes through the rotating polygon mirror 113 and the reflection mirror 114, and on the charging surface of the surface of the photosensitive drum 109, the bus line direction and the circumferential direction of the photosensitive drum 109. Scanned. As a result, a two-dimensional electrostatic latent image (latent image) is formed on the charged surface of the photosensitive drum 109. The latent image formed on the surface of the photosensitive drum 109 is visualized as a toner image by a developing roller 107 as a developing unit.

  The recording material P conveyed to the transfer nip portion is sandwiched between the outer peripheral surface (front surface) of the photosensitive drum 109 and the outer peripheral surface (front surface) of the transfer roller 110 and is transported to the state (nip transport). During the conveyance process of the recording material P, the toner image on the surface of the photosensitive drum 109 is transferred onto the recording material P by the transfer roller 110. Then, the recording material P carrying the toner image is conveyed to a fixing device 115 constituting a fixing unit.

  After the toner image is transferred, the surface of the photosensitive drum 109 is subjected to the next image formation after the transfer residual toner is removed by a cleaner 108 as a cleaning unit.

  In the fixing device 115, heat and pressure are applied to an unfixed toner image carried by the recording material to heat and fix the toner image on the recording material.

  In the conveyance section, the recording material P that has exited the fixing device 115 is discharged onto the discharge tray 118 by the intermediate discharge roller 116 and the discharge roller 117. Thus, a series of printing operations of the image forming apparatus is completed.

  The charging roller 106, the developing roller 107, the cleaner 108, and the photosensitive drum 109 are integrally unitized as a process cartridge 105. The process cartridge 105 is detachably mounted on the image forming apparatus main body constituting the casing of the image forming apparatus. M is a motor, which applies a rotational driving force to the fixing device 115, scanner unit 111, process cartridge 105, pickup roller 102, paper feed roller 103, registration roller 104, intermediate paper discharge roller 116, paper discharge roller 117, and the like. Yes.

(2) Fixing device (image heating device) 115
In the following description, regarding the fixing device and the members constituting the fixing device, the longitudinal direction means a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The length is a dimension in the longitudinal direction. The width is a dimension in the short direction. Regarding the recording material, the width direction means a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The width is a dimension in the width direction.

  FIG. 2 is a schematic cross-sectional side view of the fixing device 115 of this embodiment. The fixing device 115 is a pressure member driving type and tensionless type film heating type fixing device (Japanese Patent Application Laid-Open Nos. 4-44075 to 44083, Japanese Patent Application Laid-Open Nos. 4-20480 to 204484, etc.). FIG. 3 is a schematic configuration diagram of the front surface side and the back surface side of the ceramic heater 203 used in the fixing device 115 of this embodiment.

  The fixing device 115 shown in this embodiment includes a film guide 201 as a guide member, a cylindrical fixing film 202 as a flexible member, and a ceramic heater (hereinafter referred to as a heater) 203 as a heating body. doing. Further, a rigid stay 209 as a pressure member and a pressure roller 210 as a backup member are provided. The heater holder 201, the fixing film 202, the heater 203, the rigid stay 209, and the pressure roller 210 are all members that are long in the longitudinal direction.

  The heater 203 has an elongated heater substrate (substrate) 206 made of alumina, aluminum nitride, or the like, which is a high thermal conductive material. Then, a surface (one surface) on the side where the fixing nip portion N of the heater substrate 206 is formed and a surface (the other surface) opposite to the surface on which the fixing nip portion N is formed, respectively. Each of the energization heating resistors has one heating pattern 207 and 204. Of the heat generation patterns 207 and 204, one heat generation pattern 204 is formed to be shorter than the other heat generation pattern 207. The heat generation patterns 207 and 204 are connected in parallel and driven independently.

  On the surface side of the heater, that is, the surface on which the fixing nip N of the heater substrate 206 is formed (hereinafter referred to as the surface), an electric resistance material such as Ag / Pd is applied in the longitudinal direction of the heater substrate 206 by screen printing or the like. A heat generation pattern 207 is formed along the line. Here, Ag / Pd is silver palladium. The heat generation pattern 207 is arranged so as to be axisymmetric (symmetric) with respect to the center in the longitudinal direction of the heater substrate 206 (a region through which the longitudinal center line CL of the heater substrate 206 passes).

  Similarly, an electrically conductive material such as Ag is applied on the surface of the heater substrate 206 by screen printing or the like to form conductive patterns (feeding electrodes) 326 and 323 at both longitudinal ends of the heat generating pattern 207. . Furthermore, a glass coat layer 208 is formed on the surface of the heater substrate 206 by coating glass or the like as a protective layer on the heat generation pattern 207.

  On the other hand, on the back side of the heater, that is, the side opposite to the side where the fixing nip N of the heater substrate 206 is formed (hereinafter referred to as the back side), for example, an electric resistance material such as Ag / Pd is applied by screen printing or the like. A heat generation pattern 204 is formed along the longitudinal direction of the heater substrate. The heat generation pattern 204 is arranged so as to be line symmetric (symmetric) with respect to the center in the longitudinal direction of the heater substrate 206. Similarly, an electrically conductive material such as Ag is applied to the back surface of the heater substrate 206 by screen printing or the like to form conductive patterns (power feeding electrodes) 324 and 325 at one end in the longitudinal direction of the heat generating pattern 204. . Furthermore, a glass coat layer 205 is formed on the back surface of the heater substrate 206 by coating glass or the like as a protective layer on the heat generation pattern 204.

  A temperature detection member 213 that detects the temperature of the heater 203 is disposed on the glass coat layer 205 on the back surface side of the heater 203 so as to face the center in the longitudinal direction of the heat generation pattern 207 in the thickness direction of the heater substrate 206. . The temperature detection member 213 is, for example, a thermistor. The thermistor 213 is pressed against the glass coat layer 205 of the heater 203 with a predetermined pressure by a spring (not shown) or the like. Further, a protective device 214 as an excessive temperature rise prevention unit is disposed on the glass coat layer 205 so as to face the heat generation pattern 204 in the thickness direction of the heater substrate 206. The protection device 214 is, for example, a temperature fuse or a thermo switch.

  The film guide 201 made of heat-resistant resin is formed in a substantially bowl shape in cross section, and guides the inner peripheral surface (inner surface) of the cylindrical fixing film 202 with an arcuate guide surface 201a on the outer side in the short direction. Yes. The heater 203 is supported by a groove 201b provided along the longitudinal direction at the center of the lower surface of the film guide 201 in the short direction. The fixing film 202 is loosely fitted on the outer periphery of the film guide 201 that supports the heater 203. Both ends in the longitudinal direction of the film guide 201 in which the fixing film 202 is loosely fitted are supported by front and rear side plates (not shown) of the apparatus frame of the fixing device 115.

  The fixing film 202 has a base layer (not shown) made of a flexible endless heat-resistant film, and a release layer (not shown) by applying a coating such as a fluororesin to the outer peripheral surface (surface) of the base layer. Is formed.

  The rigid stay 209 is formed in a substantially inverted U shape in cross section, and is disposed along the longitudinal direction at the center of the upper surface of the film guide 201 in the short direction. Both ends of the rigid stay 209 in the longitudinal direction are supported by the front and rear side plates of the apparatus frame.

  The pressure roller 210 is made of a heat-resistant rubber elastic body such as silicon rubber on the outer peripheral surface between the core shaft 211 made of aluminum, iron, stainless steel, or the like and the supported portions at both ends in the longitudinal direction of the core shaft 211. It has a roller-like elastic layer 212 and the like. On the outer peripheral surface of the elastic layer 212, a coating layer in which a fluororesin is dispersed is provided as the release layer 213 for reasons such as transportability of the recording material P and the fixing film 202 and prevention of toner contamination. The pressure roller 210 is disposed below the heater 203 via the fixing film 202, and supported parts at both ends in the longitudinal direction of the cored bar 211 are rotatably supported by a device frame via bearings (not shown). Has been.

  Then, both ends in the longitudinal direction of the rigid stay 209 are urged by a pressure spring (not shown) in a direction perpendicular to the generatrix direction of the outer peripheral surface (surface) of the pressure roller 201. As a result, the film guide 202 is pressed in the same direction, and the heater 20 is pressed against the surface of the pressure roller 201 via the fixing film 202. As a result, the elastic layer 212 of the pressure roller 210 is elastically deformed in the pressure direction of the heater 203 to form a fixing nip portion (nip portion) N having a predetermined width between the surface of the pressure roller 210 and the surface of the fixing film 202.

(3) Heater drive control circuit and resistance temperature characteristic of heat generation pattern FIG. 4 shows the configuration of the heater 203 drive control circuit. In the figure, reference numeral 322 denotes a temperature control unit (hereinafter referred to as a CPU) comprising a CPU and a memory such as a ROM and a RAM. The memory stores various programs required for the small size paper mode, the large size paper mode, and the temperature control of the heater 203. Reference numeral 301 denotes a commercial AC power source connected to the image forming apparatus. The image forming apparatus supplies power from the AC power supply 301 to the heater 203 to cause the heat generation patterns 207 and 204 on the front surface side and the back surface side of the heater 203 to generate heat. The drive control circuit for the heater 203 of this embodiment has two heater drive circuits for independently controlling the power supplied to the heat generation patterns 207 and 204.

  The electric power supplied to the heat generation pattern 207 on the surface side of the heater 203 is controlled by turning on / off the triac 312. The resistors 303 and 304 are bias resistors for the triac 302, and the phototriac coupler 305 is a device for ensuring insulation between the primary and secondary. Then, the triac 302 is turned on by energizing the light emitting diode 305b of the phototriac coupler 305. The resistor 306 is a resistor for limiting the current of the light emitting diode 305 b, and turns on / off the phototriac coupler 305 by the transistor 307. The transistor 307 operates (turns on) in accordance with a heater drive signal (heater drive 1) output from the CPU (temperature control unit) 322 via the resistor 308.

  The electric power supplied to the heat generation pattern 204 on the back side of the heater 203 is controlled by turning on / off the triac 302. The resistors 313 and 314 are bias resistors for the triac 312, and the phototriac coupler 315 is a device for ensuring insulation between the primary and secondary. Then, the triac 312 is turned on by energizing the light emitting diode 315b of the phototriac coupler 315. The resistor 316 is a resistor for limiting the current of the light emitting diode 315b, and turns on / off the phototriac coupler 315 by the transistor 317. The transistor 317 operates (turns on) in accordance with a heater drive signal (heater drive 2) output from the CPU 322 via the resistor 318.

  The temperature detected by the thermistor 213 is detected as an analog signal as a divided voltage between the resistor 321 and the thermistor 213, and the analog signal is converted into a digital signal by an A / D conversion circuit (not shown), and a TH signal is sent to the CPU 322. (Thermistor temperature) is input.

  Based on the temperature detected by the thermistor 213 and the set temperature of the heater 203 (target temperature (heat temperature) set to heat and fix the unfixed toner image on the recording material via the fixing film), the CPU 322, for example, PI The power ratio to be supplied is calculated by the control. Further, it is converted into a control level of a phase angle (phase control) and a wave number (wave number control) corresponding to the power ratio to be supplied, and the CPU 322 outputs a heater drive signal to the transistors 307 and 317 according to the control conditions. In this embodiment, the set temperature of the heater 203 is set to 200 ° C.

  As described above, power supply (energization) to the heat generation patterns 204 and 207 can be controlled independently, and the heat generation ratio of each of the heat generation patterns 204 and 207 is determined by the recording material size to be printed. . Details of this control will be described later.

  The protection device 214 is disposed between the AC power supply 301 and the conductive patterns 325 and 326 of the heater 203. When the heater 203 reaches a thermal runaway and the protection device 214 reaches a predetermined temperature (the temperature at which the heater 203 causes heater cracking), the protection device 214 is opened and the power supply to the heater 203 is cut off.

  FIG. 5 shows the heat generation distribution in the longitudinal direction of the heat generation patterns 207 and 204 on the front side and the back side of the heater 203, respectively. In FIG. 5, hatched portions indicate the heat generation patterns 207 and 204. The heat generation pattern 207 on the heater 203 surface side (film sliding surface side) corresponds to a large-size paper passing area (passage area of a large-size recording material passing through the fixing nip portion). The heat generation pattern 204 on the back surface side (non-film sliding surface side) of the heater 203 corresponds to a small size paper passing area (passage area of a small size recording material passing through the fixing nip portion). Here, the small-size paper passing area corresponds to the width of the recording material having the smallest size among the recording materials that can pass through the fixing nip portion N (can be introduced).

  In this embodiment, the length of the heat generation pattern 204 on the back surface side of the heater 203 is set to 115 mm in order to correspond to a small size recording material (Western envelope No. 2) having a width of 114 mm. Further, the length of the heat generation pattern 207 on the surface side of the heater 203 was set to 222 mm in order to correspond to a large-size recording material (US-LETTER paper) having a width of 216 mm. Here, the reason why the heat generation pattern is made longer than the sheet passing area is to secure the fixing property of the toner image up to the end in the width direction of the recording material. Hereinafter, the heat generation pattern 204 on the back surface side of the heater 203 is referred to as a heat generation pattern 204 for small size paper, and the heat generation pattern 207 on the front surface side of the heater 203 is referred to as a heat generation pattern 207 for large size paper.

  The glass coat layers 208 and 205 on the front side and the back side of the heater 203 are provided to prevent resistance variation due to oxidation of the heat generation patterns 204 and 207 and to ensure insulation between the heat generation pattern 207 and the inner surface of the fixing film 202. It is.

  As shown in FIG. 5, the heat generation amount per unit length in the heat generation pattern 204 for small size paper is set to be equal to the heat generation amount per unit length in the heat generation pattern 207 for large size paper. The resistance value of the heat generating pattern 204 for small size paper was 20Ω, and the TCR (resistance temperature characteristic) was a positive characteristic of about 600 ppm / ° C. On the other hand, the resistance value of the heat generating pattern 207 for large size paper was 10Ω, and the TCR (resistance temperature characteristic) was about 0 ppm / ° C.

  Here, as can be seen from the heat generation distribution of the heat generation pattern 204 for small size paper shown in the same figure, the length of the heat generation pattern 204 for small size paper corresponds to the width of the small size paper to be passed. Therefore, when the thermal runaway of only the small-size paper heat generation pattern 204 occurs, the longitudinal direction both ends of the large-size paper heat generation pattern 207 of the heater substrate 206 and the central portion in the longitudinal direction having the small-size paper heat generation pattern 204. The temperature difference is severe, which is disadvantageous for heater cracking.

  Therefore, in the present invention, the TCR of the heat generating pattern 204 for small-size paper, which is disadvantageous against heater cracking, is made positive so that, for reasons described later, a relatively simple protection such as a thermo switch before the heater cracking occurs. The device 214 can be operated.

  FIG. 6 shows the transition of the amount of heat generated when 100 V is applied to the small-sized heat generation pattern 204 when the TCR is 0 ppm / ° C. or a positive characteristic. As shown in the figure, when power is continuously supplied to the small-sized heat generation pattern 204 due to thermal runaway, the temperature rises rapidly at a TCR of 0 ppm / ° C. Therefore, the time (t0) to reach the heater cracking temperature is not in time for the relatively simple operation timing (t1) of the protection device 214 such as a thermo switch.

  On the other hand, by setting the TCR to a positive characteristic, as shown in the figure, as the temperature of the heat generating pattern 204 for small size rises, the resistance value increases and the time (t2) to reach the heater crack occurrence temperature is 0 ppm / ° C. Compared to the case, it is advantageous for the heater cracking longer. Thereby, generation | occurrence | production of a heater crack can be suppressed.

  FIG. 7 shows the temperature transition of the heater substrate 206 when 100 V is applied only to the heating pattern 204 for small size paper having a TCR of 0 ppm / ° C. In addition, the same figure shows the temperature transition of the heater substrate 206 when 100 V is applied only to the heat generating pattern for a small size having a positive characteristic. Furthermore, the figure shows the temperature transition of the heater substrate 206 when 100 V is applied to both the large-size paper heat generation pattern 207 having a TCR of 0 ppm / ° C. and the small-size paper heat generation pattern 204 having positive characteristics. As shown in the figure, when the TCR is 0 ppm / ° C., the printable temperature arrival time (t4) when the TCR has a positive characteristic is increased compared to the time (t3) when the printable temperature is reached.

  Therefore, it is possible to shorten the print arrival time (t5) by simultaneously energizing the heat generating pattern 204 for small size paper and the heat generating pattern 207 for large size paper at the start-up when printing a small size recording material. . Thereby, the number of processed sheets per unit time when printing a small size recording material, that is, the productivity of the small size recording material can be improved.

  Referring to FIG. 4, the small-size heat generation pattern 204 and the large size of the heater 203 in the fixing device 115 when a small size paper (for example, envelope paper) and a large size paper (for example, A4 paper) are printed by the image forming apparatus. The energization control to the paper heating pattern 207 will be described.

  The CPU 322 determines whether the recording material P is a small size paper or a large size paper based on the print command. When the CPU 322 determines that the recording material is a small size paper, the CPU 322 executes the small size paper mode, and when the CPU 322 determines that the recording material is a large size paper, the CPU 322 executes the large size paper mode.

  In the small size paper mode, when the heater 203 is started up, the CPU 322 turns on the triacs 302 and 312 based on a print command, and power is supplied from the commercial power supply 301 to the heat generating pattern 207 for large size paper and the heat generating pattern 204 for small size paper. To do. At this time, power is supplied to both the heat generating pattern 207 for large size paper and the heat generating pattern 204 for small size paper until the temperature detected by the thermistor 213 reaches about 200 ° C. (set temperature of the heater 203).

  At the time of printing (a period from introduction of small size paper to the fixing nip portion N to discharge), the CPU 322 turns off the triac 312 and applies power only to the heat generation pattern 204 for small size paper. However, when printing very thick recording paper such as envelope paper continuously, heat is rapidly taken away by the recording paper. The TRIAC 312 may be turned on.

  In the large size paper mode, when the heater 203 is started up, the CPU 322 turns on the triacs 302 and 312 based on the print command, and power is supplied from the commercial power supply 301 to the heat generation pattern 207 for large size paper and the heat generation pattern 204 for small size paper. To do. At this time, power is supplied to both the heat generating pattern 207 for large size paper and the heat generating pattern 204 for small size paper until the temperature detected by the thermistor 213 reaches about 200 ° C.

  At the time of printing (a period from when the large size paper is introduced to the fixing nip portion N until it is discharged), the CPU 322 turns off the triac 307 and applies power only to the heat generating pattern 207 for large size paper.

(4) Heat Fixing Operation of Fixing Device The control unit 100 rotationally drives the motor M (see FIG. 1) in response to a print command. The rotation of the output shaft of the motor M is transmitted to a drive gear (not shown) provided at the longitudinal end of the cored bar 211 of the pressure roller 210 via a gear train (not shown). As a result, the pressure roller 210 rotates in the arrow direction at a predetermined peripheral speed (process speed). The rotation of the pressure roller 210 is transmitted to the surface of the fixing film 202 by the frictional force between the surface of the pressure roller 210 and the surface of the fixing film 202 at the fixing nip portion N. As a result, the fixing film 202 rotates (moves) in the direction of the arrow following the rotation of the pressure roller 210 while the inner peripheral surface (inner surface) of the fixing film 202 is in contact with the protective layer 208 of the heater 203.

  In the small size paper mode, the CPU 322 outputs a heater drive signal to the transistors 307 and 317, turns on the phototriac couplers 305 and 315, and turns on the triacs 302 and 312. As a result, the small-sized paper heating pattern 204 is energized from the commercial power supply 301 via the conductive patterns 324 and 325, and the large-sized paper heating pattern 207 is energized from the commercial power supply 301 via the conductive patterns 323 and 326. As a result, the heat generating pattern 204 for small size paper and the heat generating pattern 207 for large size paper generate heat, and the heater 203 rapidly rises in temperature.

  Further, the CPU 322 determines whether the temperature of the heater 203 has reached the set temperature based on the TH signal from the thermistor 213. When the temperature of the heater 203 reaches the set temperature, the CPU 322 outputs a heater drive stop signal to the transistor 317, turns off the phototriac coupler 315, and turns off the triac 312. As a result, the power supply to the large-size paper heat generation pattern 207 of the heater 203 is stopped, but the power supply to the small-size paper heat generation pattern 204 is continued. Then, the CPU 322 turns on / off the transistor 307 based on the TH signal from the thermistor 213 so as to maintain the temperature of the heater 203 at the set temperature.

  In a state where the motor M is driven to rotate and the heat generation pattern 204 for small size paper is energized, the small size paper P carrying the unfixed toner image t is introduced into the fixing nip portion N with the toner image carrying surface facing upward. The The small-size paper P is nipped between the surface of the fixing film 202 and the surface of the pressure roller 210 in the fixing nip portion N and is conveyed (nipped and conveyed) to that state. In this conveyance process, the toner image t on the small size paper P is heated and melted by the heater 203 through the fixing film 202 and is heated and fixed on the small size paper P (on the recording material) by the pressure of the fixing nip portion N. The Then, the small size paper P on which the toner image t is heated and fixed is discharged from the fixing nip portion N and conveyed toward the intermediate paper discharge roller 116.

  In the large size paper mode, the CPU 322 outputs a heater drive signal to the transistors 307 and 317, turns on the phototriac couplers 305 and 315, and turns on the triacs 302 and 312. As a result, the small-sized paper heating pattern 204 is energized from the commercial power supply 301 via the conductive patterns 324 and 325, and the large-sized paper heating pattern 207 is energized from the commercial power supply 301 via the conductive patterns 323 and 326. As a result, the heat generating pattern 204 for small size paper and the heat generating pattern 207 for large size paper generate heat, and the heater 203 rapidly rises in temperature.

  Further, the CPU 322 determines whether the temperature of the heater 203 has reached the set temperature based on the TH signal from the thermistor 213. When the temperature of the heater 203 reaches the set temperature, the CPU 322 outputs a heater drive stop signal to the transistor 307, turns off the phototriac coupler 305, and turns off the triac 302. As a result, the power supply to the heat generating pattern 204 for small size paper by the heater 203 is stopped, but the power supply to the heat generating pattern 207 for large size paper is continued. The CPU 322 turns on / off the transistor 315 based on the TH signal from the thermistor 213 so as to maintain the temperature of the heater 203 at the set temperature.

  In a state where the motor M is driven to rotate and the heat generation pattern 204 for large size paper is energized, the large size paper P carrying the unfixed toner image t is introduced into the fixing nip portion N with the toner image carrying surface facing upward. The The large-size paper P is nipped between the surface of the fixing film 202 and the surface of the pressure roller 210 in the fixing nip portion N and is conveyed (nipped and conveyed) to that state. In this conveying process, the toner image t on the large size paper P is heated and melted by the heater 203 via the fixing film 202 and is heated and fixed on the large size paper P (on the recording material) by the pressure of the fixing nip N. The Then, the large size paper P on which the toner image t is heated and fixed is discharged from the fixing nip portion N and conveyed toward the intermediate paper discharge roller 116.

  As described above, the fixing device 115 of the present embodiment can achieve both suppression of heater cracking due to thermal runaway and shortening of heater start-up time, and can improve the productivity of small size paper.

[Example 2]
Another example of the fixing device will be described. The fixing device of the present embodiment has the same configuration as that of the fixing device of the first embodiment except that the configuration of the heater is different.

  The heater used in the fixing device of this embodiment has one heat generation pattern on the back surface of the heater substrate, and has at least one heat generation pattern on the surface of the heater substrate. One heating pattern is made shorter than the other heating pattern, and each heating pattern is connected in parallel and driven independently. Further, the TCR of a short heat generation pattern has a positive characteristic, and the TCR of a long heat generation pattern has a zero or negative characteristic. In this embodiment, three heat generation patterns are provided on the surface of the heater substrate.

  The heater shown in this embodiment includes the shape in the longitudinal direction of the heat generation pattern for small size paper, the number and shape of the heat generation pattern for large size paper, the number of power supply electrodes to the heat generation pattern for large size paper, and the thermistor. The configuration is the same as that of the heater of the first embodiment except that the number of the heaters is different. In the present embodiment, members and portions that are common to the heater of the first embodiment are denoted by the same reference numerals, and the description of the members and portions is omitted.

  FIG. 8 is a longitudinal sectional view of the center of the heater 203 of the present embodiment in the short direction, and a schematic configuration diagram of the front and back surfaces of the heater 203.

  On the surface of the heater substrate 206, a heat generating pattern 709 for large size paper is formed along the longitudinal direction of the heater substrate 206. The large-size paper heating pattern 709 has a width in the short direction of the heater substrate 206 that changes from the longitudinal center of the heater substrate 206 (the region through which the longitudinal centerline CL passes) toward the end in the longitudinal direction. It is composed of different types of heat generation patterns.

  One is two heat generation patterns (hereinafter referred to as main heat generation patterns) 700 that are designed so that the width of the heat generation pattern in the short direction is widened from the longitudinal center of the heater substrate 206 toward the end in the longitudinal direction. The other one is a heat generation pattern 701 (hereinafter referred to as a sub heat generation pattern) 701 designed so that the width in the short direction of the heat generation pattern is narrowed from the longitudinal center of the heater substrate 206 toward the end in the longitudinal direction. The sub heat generation pattern 701 is disposed between the two main heat generation patterns 700. A large-size paper heat generation pattern 709 including two main heat generation patterns 700 and one sub heat generation pattern 701 is arranged so as to be line-symmetric with respect to the longitudinal center of the heater substrate 206.

  Further, a common conductive pattern (feeding electrode) 705 of the main heat generation pattern 700 and the sub heat generation pattern 701 is formed on one end of the heater substrate 206 in the longitudinal direction by coating the surface of the heater substrate 206 by screen printing or the like. It is. Similarly, the common conductive pattern (power supply electrode) 703 of the main heat generation pattern 700 and the conductive pattern (power supply electrode) 704 of the sub heat generation pattern 701 are coated by screen printing or the like, and the other end in the longitudinal direction of the heater substrate 206. Is formed.

  On the back surface of the heater substrate 206, a small-size paper heating pattern 702 is formed along the longitudinal direction of the heater substrate 206. The heat generating pattern 702 for small size paper is arranged so as to be line symmetric with respect to the center in the longitudinal direction of the heater substrate 206. In the heat generating pattern 702 for small size paper, the width in the short direction of the heater substrate 206 changes from the center in the longitudinal direction of the heater substrate 206 toward the end in the longitudinal direction. That is, the heat generation pattern is designed such that the width of the heat generation pattern in the short direction is increased stepwise from the longitudinal center of the heater substrate 206 toward the end in the longitudinal direction.

  In addition, conductive patterns (feeding electrodes) 705 and 706 of a small-size paper heating pattern 702 are formed on one end of the heater substrate 206 in the longitudinal direction by coating the back surface of the heater substrate 206 by screen printing or the like. is there. The conductive pattern 705 is electrically connected via a conductive pattern 705 on the surface of the heater substrate 206 and a conductive pattern (not shown) in a through hole provided in the heater substrate 206.

  On the back surface side of the heater 203, a temperature detection member (hereinafter referred to as a central thermistor) 213a is disposed on the glass coat layer 205 so as to face the vicinity of the center in the longitudinal direction of the heat generation pattern 204 in the thickness direction of the heater substrate 206. ing. On the glass coat layer 205, a temperature detection member (hereinafter, referred to as an end thermistor) 213b is disposed so as to face the end in the longitudinal direction of the heat generating pattern 709 for large size paper in the thickness direction of the heater substrate 206. Has been. Furthermore, a protection device 214 is disposed on the glass coat layer 205 so as to face the vicinity of the center in the longitudinal direction of the heat generation pattern 204 in the thickness direction of the heater substrate 206.

  FIG. 9 shows the heat generation distribution in the longitudinal direction in the heat generation pattern 709 for large size paper and the heat generation pattern 702 for small size paper. As shown in the figure, the heat generation pattern 702 for small-size paper is designed so that the resistance value at the center in the longitudinal direction is reduced stepwise with respect to the end in the longitudinal direction. Smaller than. Therefore, when thermal runaway occurs only in the small-size paper heat generation pattern 702, the temperature difference between the longitudinal end portions and the longitudinal center portion of the small-size paper heat generation pattern 702 on the heater substrate 206 is alleviated, and heater cracking occurs. It is advantageous. Thereby, generation | occurrence | production of a heater crack can be suppressed.

  In addition, the two main heat generation patterns 700 of the large-size paper heat generation pattern 709 are designed so that the resistance value of the resistance value at the center in the longitudinal direction is reduced stepwise with respect to the end portions in the longitudinal direction. The calorific value is smaller than the center in the longitudinal direction. Contrary to the two main heat generation patterns 700, the sub heat generation pattern 701 is designed to increase the resistance value of the resistance value at the center in the longitudinal direction stepwise with respect to the end portions in the longitudinal direction. The amount is greater than the center in the longitudinal direction. Therefore, by independently controlling the two main heat generation patterns 700 and the sub heat generation patterns 701, the degree of freedom of temperature controllability of the large size paper heat generation pattern 707 can be improved. Thereby, it is possible to suppress the temperature rise of the non-sheet passing portion for the recording paper whose recording paper width is equal to or larger than the heat generating pattern 204 for small size paper and equal to or smaller than the large size paper passing area (see FIG. 5).

  FIG. 10 shows the configuration of the drive control circuit of the heater 203 of this embodiment. Here, the same reference numerals are assigned to the same circuit configurations as those of the drive control circuit of the heater 203 in the first embodiment, and the description thereof is omitted.

  In this embodiment, the switching between the two main heat generation patterns 700 of the large-size paper heat generation pattern 707 and the sub heat generation pattern 701 is performed by using the bipolar switching relay 707. When printing large-size paper, the main heat generation pattern 700 is switched to, and a print operation is performed by combining the main heat generation pattern 700 and the sub heat generation pattern 701. When printing a small size paper, the print operation is switched to the heat generation pattern 702 for the small size paper, and a printing operation is performed with a combination of the heat generation pattern 702 for the small size paper and the sub heat generation pattern 701. The protection device 214 is disposed between the AC power supply 301 and the conductive pattern 705 of the heater 203.

  Referring to FIG. 10, when the image forming apparatus prints small size paper (for example, envelope paper) and large size paper (for example, A4 paper), heat generation pattern 702 for small size and large size of heater 203 in fixing device 115 are printed. The energization control to the paper heating pattern 709 will be described.

  In the small-size paper mode, the CPU 322 outputs a relay drive signal based on the print command and turns on the transistor 708, thereby turning on the switching relay 707 and connecting the contacts 707a and 707b, thereby generating a heat generation pattern for small-size paper. Switch to 702. When the heater 203 is started up, the CPU 322 outputs a heater drive signal to turn on the triacs 302 and 312, and power is supplied from the commercial power supply 301 to the heat generating pattern 702 for small size paper and the sub heat generating pattern 701. At this time, the CPU 322 takes in the temperature detected by the central thermistor 213a and supplies power to both the sub heat generation pattern 701 and the heat generation pattern 702 for small size paper until the temperature reaches about 200 ° C.

  As described above, the print arrival time can be shortened by simultaneously energizing the heat generating pattern 702 for small size paper and the sub heat generating pattern 701 at the time of starting up when printing a small size recording material. Thereby, the number of processed sheets per unit time when printing a small size recording material, that is, the productivity of the small size recording material can be improved.

  At the time of printing, the CPU 322 turns off the triac 312 and turns on the power only to the heat generation pattern 702 for small size paper. However, when continuously printing thick recording paper such as envelope paper, since the heat is rapidly taken away by the recording paper, the triac 312 is turned on so that the sub heat generation pattern 701 is also energized. You may comprise as follows.

  In the large size paper mode, the CPU 322 outputs a relay drive stop signal based on the print command and turns off the transistor 708, thereby turning off the switching relay 707 and connecting the contacts 707a and 707c to the main heat generation pattern 700. Switch. When the heater 203 is started up, the CPU 322 outputs a heater drive signal, turns on the triacs 302 and 312, and supplies power to the sub heat generation pattern 701 and the main heat generation pattern 700. At this time, the CPU 322 takes in the temperature detected by the central thermistor 213a and the temperature detected by the end thermistor 213b, and supplies power to both the sub heat generation pattern 701 and the main heat generation pattern 700 until the temperature reaches about 200 ° C. .

  At the time of printing, the CPU 322 controls the energization ratio to the sub heat generation pattern 701 and the main heat generation pattern 700 so as to always maintain a predetermined set temperature based on the temperatures of the central thermistor 213a and the end thermistor 213b.

  In this embodiment, a switching relay 707 is used to switch between the heat generation pattern 702 for small size paper and the main heat generation pattern 700. This is because both the heat generation pattern for small size paper 702 and the main heat generation pattern 700 are heat generation patterns in which the heat generation amount in the central portion in the longitudinal direction is larger than that in both end portions in the longitudinal direction.

  When a thermal runaway occurs in which power is continuously applied to both the small size paper heat generation pattern 702 and the main heat generation pattern 700, the heater cracks compared to the combination of energizing the small size paper heat generation pattern 702 and the sub heat generation pattern 701. Against. However, in this embodiment, since the TCR of the heat generation pattern 702 for small size paper is made to have a positive characteristic, the heat resistance pattern 702 for the small size paper and the sub heat generation pattern 701 are made advantageous for heater cracking due to thermal runaway. It may be configured to switch between.

  Further, a configuration may be adopted in which a triac is connected to each of the two main heat generation patterns 700 and one sub heat generation pattern 701 without using the switching relay 707 to control each heat generation pattern.

  As described above, the fixing device 115 according to the present embodiment can both suppress the cracking of the heater due to thermal runaway and shorten the heater start-up time, and can improve the productivity of small size paper.

[Example 3]
Another example of the fixing device will be described. The fixing device of the present embodiment has the same configuration as that of the fixing device of the first embodiment except that the configuration of the heater is different.

  The heater used in the fixing device of this embodiment has at least one heating pattern on each of the front and back surfaces of the heater substrate, one heating pattern is shorter than the other heating pattern, and each heating pattern is parallel. It is connected to and is driven independently. Further, the TCR of a short heat generation pattern has a positive characteristic, and the TCR of a long heat generation pattern has a zero or negative characteristic. In this embodiment, three heating patterns are provided on the front and back surfaces of the heater substrate.

  The heater shown in the present embodiment has the same configuration as the heater of the second embodiment except that the number of heat generation patterns for small size paper, the shape in the longitudinal direction, and the number of thermistors are different from the heater of the second embodiment. In the present embodiment, members and portions that are common to the heaters of the second embodiment are denoted by the same reference numerals, and the description of the members and portions is omitted.

  FIG. 11 is a longitudinal cross-sectional view of the center of the heater 203 of the present embodiment in the short-side direction, and a schematic configuration diagram of the front and back surfaces of the heater 203.

  On the back surface of the heater substrate 206, a heat generating pattern 1005 for small size paper is formed along the longitudinal direction of the heater substrate 206. In the heat generation pattern 1005 for small size paper, the width in the short direction of the heater substrate 206 changes from the center in the longitudinal direction of the heater substrate 206 (the region through which the longitudinal center line CL passes) toward the end in the longitudinal direction. It is composed of different types of heat generation patterns.

  One is two heat generation patterns 1000 (hereinafter referred to as small-size main heat generation patterns) 1000 that are designed to have a wide width in the short direction of the heat generation pattern from the longitudinal center of the heater substrate 206 to the longitudinal end. is there. The other is a heat generation pattern 1001 (hereinafter referred to as a small size sub heat generation pattern) 1001 in which the width of the heat generation pattern is narrowed from the longitudinal center of the heater substrate 206 toward the end in the longitudinal direction. . The small size sub heat generation pattern 1001 is disposed between the two small size main heat generation patterns 1000. A small-size paper heating pattern 1005 including two small-size main heating patterns 1000 and one sub-heating pattern 1001 is arranged so as to be line-symmetric with respect to the longitudinal center of the heater substrate 206.

  On the back surface of the heater substrate 206, a small-size paper heating pattern 702 is formed along the longitudinal direction of the heater substrate 206. The heat generating pattern 702 for small size paper is arranged so as to be line symmetric with respect to the center in the longitudinal direction of the heater substrate 206. In the heat generating pattern 702 for small size paper, the width in the short direction of the heater substrate 206 changes from the center in the longitudinal direction of the heater substrate 206 toward the end in the longitudinal direction. That is, the heat generation pattern is designed such that the width of the heat generation pattern in the short direction is increased stepwise from the longitudinal center of the heater substrate 206 toward the end in the longitudinal direction.

  A thermistor (hereinafter, referred to as a central thermistor) 213 a is disposed on the back surface side of the heater 203 at a position facing the heat generating pattern 702 for small size paper on the surface of the glass coat layer 205. Further, a thermistor (hereinafter referred to as an end thermistor) 213b is disposed on the surface of the glass coat layer 205 at a position facing the heat generating pattern 709 for large size paper.

  Further, a common conductive pattern (feeding electrode) 1002 of the small main heating pattern 1000 and the small sub heating pattern 1001 is applied to the back surface of the heater substrate 206 by screen printing or the like. It is formed at the end. Similarly, the common conductive pattern (power supply electrode) 1004 of the small main heating pattern 1000 and the conductive pattern (power supply electrode) 1003 of the small size sub heat generation pattern 1001 are coated by screen printing or the like. It is formed at one end in the direction.

  On the back surface side of the heater 203, a temperature detection member (hereinafter referred to as a small size central thermistor) is provided on the glass coat layer 205 so as to face the vicinity of the center in the longitudinal direction of the heat generating pattern 1005 for small size paper in the thickness direction of the heater substrate 206. ) 213a is provided. On the glass coat layer 205, a temperature detection member (hereinafter, referred to as a large size end portion thermistor) 213b is disposed so as to face the longitudinal end portion of the large size heat generation pattern 709 in the thickness direction of the heater substrate 206. Has been. Further, on the glass coat layer 205, a temperature detection member (hereinafter, referred to as a small size end portion thermistor) 213c is provided so as to face the longitudinal end portion of the heat generating pattern 1005 for small size paper in the thickness direction of the heater substrate 206. It is arranged.

  Furthermore, a protective device 214 is disposed on the glass coat layer 205 so as to face the vicinity of the center in the longitudinal direction of the heat generating pattern 1005 for small size paper in the thickness direction of the heater substrate 206.

  FIG. 12 shows the heat generation distribution in the longitudinal direction in the heat generation pattern 709 for large size paper and the heat generation pattern 1005 for small size paper. As shown in the figure, the two small-sized main heat generation patterns 1000 of the heat generation pattern 1005 for small-size paper are designed to gradually reduce the resistance value of the resistance value at the center in the longitudinal direction with respect to the end portion in the longitudinal direction. Therefore, the amount of heat generated at both ends in the longitudinal direction is smaller than the center in the longitudinal direction. Contrary to the two small size main heat generation patterns 1000, the small size sub heat generation pattern 1001 has a design in which the resistance value of the resistance value at the center in the longitudinal direction is increased stepwise with respect to the end portion in the longitudinal direction. The amount of heat generated at both ends is greater than the center in the longitudinal direction. Therefore, the degree of freedom of temperature controllability of the small-size paper heating pattern 1005 can be improved by independently controlling the two small-size main heating patterns 1000 and the small-size sub-heating patterns 1001. Thereby, it is possible to suppress the temperature rise of the non-sheet passing portion for the recording paper whose width is less than or equal to the small size paper passing area (see FIG. 5) of the heat generating pattern 204 for small size paper.

  FIG. 13 shows the configuration of the drive control circuit of the heater 203 of this embodiment. Here, the same reference numerals are given to the same circuit configurations as those of the drive control circuit of the heater 203 in the first and second embodiments, and the description thereof is omitted.

  In this embodiment, the switching between the heat generation pattern 1005 for small size paper and the heat generation pattern 709 for large size paper is performed by using a bipolar switching relay 707. When printing large-size paper, the print pattern is switched to the large-size paper heat generation pattern 709, and the print operation is performed by combining the main heat generation pattern 700 and the sub heat generation pattern 701. When printing small-size paper, the print pattern is switched to the small-size paper heat generation pattern 1005, and the print operation is performed with a combination of the small-size main heat-generation pattern 1000 and the small-size sub-heat-generation pattern 1001.

  Referring to FIG. 13, when the image forming apparatus prints a small size paper (for example, envelope paper) and a large size paper (for example, A4 paper), the heat generation pattern 702 for small size of the heater 203 and the large size in the fixing device 115 are printed. The energization control to the paper heating pattern 709 will be described.

  In the small-size paper mode, the CPU 322 outputs a relay drive signal based on the print command and turns on the transistor 708, thereby turning on the switching relay 707 and connecting the contacts 707a and 707b, thereby generating a heat generation pattern for small-size paper. Switch to 1005. When the heater 203 is started up, the CPU 322 outputs a heater drive signal to turn on the triacs 1200, 1207, and 312 and supply power from the commercial power source to the small size main heat generation pattern 1000, the small size sub heat generation pattern 1001, and the sub heat generation pattern 701. To do. At this time, the CPU 322 takes in the temperature detected by the small size central thermistor 213a and supplies power to the small size main heat generation pattern 1000, the small size sub heat generation pattern 1001, and the sub heat generation pattern 701 until the temperature reaches about 200 ° C.

  As described above, the print arrival time can be shortened by simultaneously energizing the small size main heat generation pattern 1000, the small size sub heat generation pattern 1001, and the sub heat generation pattern 701 at the start-up when printing a small size recording material. Become. Thereby, the number of processed sheets per unit time when printing a small size recording material, that is, the productivity of the small size recording material can be improved.

  At the time of printing, the CPU 322 takes in the temperature detected by the small size center thermistor 213a and the temperature detected by the small size end thermistor 213c. Based on the temperature, the energization ratio to the small size main heat generation pattern 1000 and the small size sub heat generation pattern 1001 is controlled so as to always maintain a predetermined set temperature. However, when a thick recording paper such as envelope paper is continuously printed, the sub heat generation pattern 701 is also energized as a supplement since heat is rapidly taken away by the recording paper.

  In the large size paper mode, the CPU 322 outputs a relay drive stop signal based on the print command and turns off the transistor 708, thereby turning off the switching relay 707 and connecting the contacts 707a and 707c to the main heat generation pattern 700. Switch. When the heater 203 is started up, the CPU 322 outputs a heater drive signal, turns on the triacs 312 and 1241, and supplies power to the sub heat generation pattern 701 and the main heat generation pattern 700. At this time, the CPU 322 takes in the temperature detected by the small size center thermistor 213a and the temperature detected by the large size end thermistor 213b, and both the sub heat generation pattern 701 and the main heat generation pattern 700 until the temperature reaches about 200 ° C. Turn on the power.

  At the time of printing, the CPU 322 controls the energization ratio to the sub heat generation pattern 701 and the main heat generation pattern 700 so as to always maintain a predetermined set temperature based on the temperatures of the small size center thermistor 213a and the large size end thermistor 213b.

  As described above, the fixing device 115 according to the present embodiment can achieve both suppression of heater cracking due to thermal runaway and shortening of the heater start-up time. The productivity of small-size paper can be further improved for recording paper having a width smaller than the paper area.

[Other embodiments]
In the first to third embodiments, the example in which the longer heat generation pattern is disposed on the surface side of the heater and the shorter heat generation pattern is disposed on the surface side has been described. A similar effect can be obtained by arranging a heat generation pattern and arranging the longer heat generation pattern on the surface side.

  In the first to third embodiments, the heat generation amount per unit length of the heater pattern for the small size paper and the heat generation pattern for the large size paper of the heater are made equal, but the heat generation pattern for the small size paper and the heat generation pattern for the large size paper The amount of heat generated by the patterns is not necessarily equal.

  The fixing device 115 according to the first to third embodiments is not limited to use as a device that heat-fixes the unfixed toner image t carried by the recording material P onto the recording material. For example, it can also be used as an image heating apparatus that heats an unfixed toner image to be applied to a recording material, or an image heating apparatus that heats a toner image heated and fixed on a recording material to give glossiness to the surface of the toner image.

115: fixing device, 203: ceramic heater, 202: fixing film, 210: pressure roller, N: fixing nip, P: recording material, 204, 702, 1005: heating pattern for small size paper, 207, 709: large Heat generation pattern for size paper

Claims (4)

A heating body having a substrate, an energization heating resistor provided along a longitudinal direction of the substrate on one surface of the substrate and the other surface opposite to the one surface, and in contact with the heating body; And a backup member that forms a nip portion with the heating body via the flexible member, and the image on the recording material is displayed while the recording material is nipped and conveyed by the nip. In an image heating apparatus for heating,
Of the energization heating resistors provided on the one surface and the other surface of the substrate, one heating resistor is shorter than the other heating resistor, and the shorter heating resistor is a resistor. The temperature characteristic is positive, the longer heating resistor has a resistance temperature characteristic of zero or negative, the shorter heating resistor and the longer heating resistor are connected in parallel, and the shorter heating resistor When heating an image on a recording material using a heating resistor, image heating is performed by energizing the shorter heating resistor and the longer heating resistor until a predetermined heating temperature is reached. apparatus.   2. The image heating apparatus according to claim 1, wherein the shorter heating resistor and the longer heating resistor have the same width in the lateral direction of the substrate.   The image heating apparatus according to claim 1, wherein the shorter heating resistor and the longer heating resistor change widths in a short direction of the substrate.   The image heating apparatus according to claim 1, wherein each of the shorter heating resistor and the longer heating resistor includes at least one heating resistor.