JP5196884B2 - Image heating apparatus and heater used in the image heating apparatus - Google Patents

Description

  The present invention relates to a heating body suitable for use in a heat fixing apparatus mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, and an image heating apparatus having the heating body.

  As an image heating apparatus mounted on an electrophotographic copying machine or printer, there is a film heating type heat fixing apparatus. The fixing device includes a heater having a heating resistor on a ceramic substrate, a thin cylindrical film that moves while in contact with the heater, a pressure roller that forms a nip portion with the heater via the film, Have Patent Documents 1 and 2 describe this type of fixing device. The recording material carrying the unfixed toner image is heated while being nipped and conveyed by the nip portion of the fixing device, and the toner image is heated and fixed on the recording material. This fixing device has an advantage that it takes a short time to start energization of the heater and raise the temperature to a fixing possible temperature. Therefore, a printer equipped with this fixing device can shorten the time (first printout time (FPOT)) 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.

  In recent years, there has been a demand for speeding up and colorization of image forming apparatuses. Along with this, a larger electric power must be supplied to the heater of the fixing device. When the electric power supplied to the heater is increased, the control for controlling the electric power supply to the heater becomes impossible. Therefore, the problem that the heater breaks when a large electric power is continuously applied to the heater becomes apparent. The cause of the heater cracking is the thermal stress generated when the heater becomes hot. In addition, heater cracking occurs when the heating resistor is around 1000 ° C.

Patent Document 3 discloses a technique that can reduce the occurrence of thermal stress cracking due to leakage between a plurality of heating resistors due to the application of excess current to the heater. The heater disclosed in Patent Document 3 is provided with a plurality of heating resistors that are provided along the longitudinal direction of the substrate and generate heat by energization in parallel in the lateral direction of the substrate, and one end and the other end of the plurality of heating resistors. The conductor part is connected to each. The plurality of heating resistors and the conductor are covered with an insulating layer so as to form gaps between the plurality of heating resistors and the conductor in the longitudinal direction of the substrate.
JP-A-4-44075 JP-A-4-204984 JP 2006-179303 A

The present invention is a further development of the above prior art. The object of the present invention is that when a heater having a high resistance region having a resistance value higher than that of the central portion is used at both ends in the longitudinal direction of the substrate, a runaway in which a current continues to flow through the heater occurs. Another object of the present invention is to provide an image heating apparatus capable of preventing cracking of the heater and a heater used in the image heating apparatus .

In order to achieve the above object, the image heating apparatus according to the present invention includes a cylindrical film, a heater that comes into contact with the inner surface of the film and generates heat when energized, and a nip portion is formed through the film together with the heater. And a safety element that cuts off power to the heater when the temperature of the heater exceeds a predetermined temperature, and the heater includes an elongated substrate and a longitudinal direction of the substrate. A heating resistor formed on the substrate in a pattern that is long and folded at the end in the longitudinal direction of the substrate, and provided at the end on the same side in the longitudinal direction of the substrate, and feeds the heating resistor And a protective layer covering the heating resistor, and the protective layer has a gap across the longitudinal direction of the substrate between the folded heating resistors. Established In the image heating apparatus for transporting a recording material carrying a toner image at the nip portion and heating the toner image, the heating resistor of the heater has a resistance value higher than that of a central portion at both ends in the longitudinal direction of the substrate. Only the part covering the high resistance region on the side close to the power supply contact among the portions covering the high resistance region at both ends of the protective layer of the heater. It is characterized in that the thickness is thicker than the portion covering the central portion.
In order to achieve the above object, the heater according to the present invention is formed on the substrate in a pattern that is elongated along the longitudinal direction of the substrate and is folded at the longitudinal end of the substrate. A heating resistor provided on the same end in the longitudinal direction of the substrate, and two power supply contacts for supplying power to the heating resistor, and a protective layer covering the heating resistor. In the heater in which the protective layer is provided with a gap between the folded heating resistors in the longitudinal direction of the substrate, the heating resistors are disposed at both ends in the longitudinal direction of the substrate. Only the portion that covers the high resistance region on the side close to the feeding contact among the portions that cover the high resistance region at both ends of the protective layer has a high resistance region that has a higher resistance value than the center portion, A portion covering the central portion of the heating resistor Rimoatsumi is characterized by a thick.

According to the present invention, when a heater having a high resistance region having a resistance value higher than that of the central portion at both ends in the longitudinal direction of the substrate is used, a runaway in which current continues to flow through the heater occurs. In addition, it is possible to provide an image heating apparatus that can prevent cracking of the heater and a heater used in the image heating apparatus .

  The present invention will be described with reference to the drawings.

(1) Overall Configuration of Image Forming Apparatus FIG. 6 is a structural model diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention can be mounted as a heat fixing apparatus. This image forming apparatus is an electrophotographic monochrome laser beam printer.

  Reference numeral 21 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) as an image carrier, which is rotated in a direction of an arrow at a predetermined peripheral speed (process speed). First, the outer peripheral surface (surface) of the photosensitive drum 21 is uniformly charged to a predetermined polarity and potential by a charging roller 22 as a charging device.

  Next, image information is written and exposed to the charged surface of the photosensitive drum 21 by a laser scanner 23 as an exposure means. That is, the laser scanner 23 exposes the uniformly charged surface of the surface of the photosensitive drum 21 with the laser beam L that is ON / OFF controlled (modulated) according to the time-series electric digital image signal of the image information. As a result, the exposed portion potential of the uniformly charged surface on the surface of the photosensitive drum 21 is attenuated, and an electrostatic latent image of image information is formed on the surface of the photosensitive drum 21. The electrostatic latent image is developed and visualized as a toner image by attaching toner (developer) to the electrostatic latent image by the developing device 24. The visualized toner image is transferred onto the recording material P from the surface of the photosensitive drum 21 at a transfer nip T between the surface of the photosensitive drum 21 and a transfer roller 26 as a transfer means that contacts the surface of the photosensitive drum 21. . That is, the recording material P is nipped and conveyed to the transfer nip T by the registration roller 25a so that the image forming position of the toner image on the surface of the photosensitive drum 21 and the writing position of the leading end of the recording material P are matched. The recording material P is nipped and conveyed by the photosensitive drum 21 and the transfer roller 26 at the transfer nip T. During the conveyance process, a transfer bias is applied to the transfer roller 26, and the toner image on the surface of the photosensitive drum 21 is transferred onto the recording material P by the transfer bias.

The recording material P that has passed through the transfer nip T is separated from the surface of the photosensitive drum 21, and is transported to the fixing device 27 by the transport belt 25b through the entrance guide 25c. The fixing device 27 heat-fixes the unfixed toner image formed and supported on the recording material P on the recording material . The recording material P is discharged onto a discharge tray by a discharge roller (not shown).

  The transfer residual toner remaining on the surface of the photosensitive drum 21 after separation of the recording material is removed by a cleaning blade 28a provided in the cleaning unit 28, and the surface of the photosensitive drum 21 is used for the next image formation.

  Reference numeral 25 denotes a conveying means. The conveying means 25 includes a registration roller 25a, a conveying belt 25b, an entrance guide 25c, a discharge roller, and the like.

(2) Fixing device 27
In the following description, regarding the fixing device and the members constituting the fixing device, the longitudinal direction is 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 width is a dimension in the short direction. The thickness direction is a direction orthogonal to the recording material conveyance direction and the longitudinal direction on the surface of the recording material. The thickness is a dimension in the thickness direction.

2-1) Overall Configuration of Fixing Device 27 FIG. 4 is a schematic cross-sectional view of an example of the fixing device 27. The fixing device 27 is a film heating type fixing device.

The fixing device 27 shown in the present embodiment includes a heater 1 as a heating element, a heater holder 2 as a holding member that holds the heater 1, and a support stay 3 for pressurizing the holder 2. The fixing device 27 includes a flexible endless fixing film (cylindrical film) 4 as a flexible member, and a pressure roller 6 as a pressure member. The heater 1, the holder 2, the stay 3, the film 4 and the pressure roller 6 are all elongated members in the longitudinal direction.

  The film 4 includes an endless base layer (not shown), a conductive primer layer (not shown) provided on the outer periphery of the base layer, and a release layer (not shown) provided on the outer periphery of the primer layer. And having. For the base layer, polyimide, polyamide, PEEK or the like having high insulating properties is used. The base layer has high heat resistance and is formed with a thickness of about 15 to 60 microns. The base layer maintains the mechanical strength such as the tear strength of the entire film 4. In this embodiment, a polyimide endless film having a thickness of 50 μm is used as the base layer. The primer layer is formed by dipping a mixture of a polyamide resin and a fluororesin dispersion. The primer layer has a thickness of about 2 to 6 μm. The primer layer is a layer for ensuring the adhesive strength between the base layer and the release layer. The releasable layer is provided by a method of forming a fluororesin such as PTFE or PFA by dipping or covering the base layer with a pre-formed fluororesin tube. The reason why the fluororesin is used is to ensure the releasability with the toner and to prevent the surface of the film 4 from being soiled by the adhesion of the toner or the like. Therefore, a material other than a fluororesin may be used as long as the above object can be achieved. In this example, a dispersion obtained by dispersing 30% by weight of titanium oxide in an aqueous dispersion in which PTFE and PFA are mixed at a ratio of 7: 3 is formed by dipping coating.

  The holder 2 is a molded product formed of a heat-resistant liquid crystal polymer resin into a bowl shape having a substantially semicircular cross section. An inverted concave groove 2a is formed along the longitudinal direction on the lower surface of the holder 2, and the heater 1 is fixedly supported in the groove 2a. The film 4 is loosely fitted on the holder 2 supporting the heater 1. Therefore, the holder 2 serves not only to support the heater 1 but also to guide the film 4. In this example, DuPont Zenite 7755 (trade name) was used as the liquid crystal polymer. The maximum usable temperature (heat resistant temperature) of Zenite 7755 is about 270 ° C.

  The stay 3 is a member for pressurizing the holder 2 inside the film 4. The stay 3 is formed of a metal such as iron in a substantially inverted U shape in cross section, and is fixed to the center of the holder 2 in the short direction.

In the pressure roller 6, an elastic layer 6b made of a silicone rubber layer having a thickness of about 3 mm is formed by injection molding on the outer periphery of a stainless steel round shaft core 6a, and a release layer 6c having a thickness of about 40 μm is formed thereon. A PFA resin tube is coated. In the longitudinal direction of the fixing device 27, both ends of the pressure roller 6 are rotatably held by a pair of side plates (not shown) on the front side and the back side of the device frame F via bearings. . Above the pressure roller 6, the heating assembly 5 including the heater 1, the holder 2, the stay 3, the film 4, and the like is arranged in parallel with the pressure roller 6 with the heater 1 facing downward.
Then, both ends of the stay 3 are urged toward the pressure roller 6 with a pressure of one side 74N (7.5 kgf) and a total pressure 147N (15 kgf) by a pressure mechanism (not shown), whereby the outer peripheral surface of the film 4 ( Surface) is in contact with the outer peripheral surface (surface) of the pressure roller 6. Thus, a nip portion (fixing nip portion) N having a predetermined width necessary for heating and fixing the unfixed toner image carried by the recording material P is formed between the surface of the film 4 and the surface of the pressure roller 2. The pressurization mechanism has a pressure release mechanism, and is configured to release the pressurization and remove the recording material P at the time of jam processing or the like.

  Reference numeral 54 denotes a thermistor as temperature detecting means for detecting the temperature of the heater 1. The thermistor 54 is disposed in contact with the insulating layer 1c that covers the heating resistor 1b provided on the back surface (surface opposite to the nip portion N) of the substrate 1a of the heater 1.

  Reference numeral 57 denotes a thermo switch as a safety element. Similar to the thermistor 54, the thermo switch 57 is disposed on the insulating layer 1c of the heater 1 in contact with the insulating layer 1c.

  FIG. 5 is a circuit diagram of an example of a heater temperature control system.

  The heater temperature control system includes a power supply circuit C1 for supplying power to the heater 1 and a control circuit C2 for controlling power supply to the heater 1. The power supply circuit C1 has a circuit configuration in which an AC power supply 51, a relay 52, a triac (heating body driving means) 53, and the heater 1 are connected in series. The control circuit C2 has a circuit configuration in which a thermistor 54, an A / D converter 55, a CPU (control means) 56, and a triac 53 are connected in series. The relay 52 is connected to the CPU 56 via a thermo switch 57. The relay 52 is opened by a command signal from the CPU 56 and cuts off between the AC power source 51 and the heater 1. The CPU 56 takes in the detected temperature signal (output signal) of the thermistor 54 via the A / D converter 55 and, based on the signal, triac so that the detected temperature of the thermistor 54 maintains a predetermined control temperature (target temperature). 53 is controlled ON / OFF. In this embodiment, the control temperature is 180 ° C., for example. The thermo switch 57 is provided in order to prevent the fixing device 27 from being destroyed due to the continued supply of power without stopping the energization of the heater 1 when the fixing device 27 becomes uncontrollable. . That is, when the temperature of the heater 1 exceeds the control temperature, it operates so as to cut off the power supply to the heater 1. That is, the thermo switch, which is a safety element, operates in response to the heat of the heating body (heater) and cuts off the power supply to the heating resistor.

2-2) Heat Fixing Operation of Fixing Device 27 The pressure roller 6 has a drive gear (not shown) at the end of the core 6a, and the drive gear is rotationally driven by the fixing motor M (FIG. 4). Rotate in the direction of the arrow. When the pressure roller 6 rotates, the surface of the film 4 in contact with the surface of the pressure roller 6 receives a rotational force from the pressure roller 6 through the nip portion N. As a result, the film 4 has the inner peripheral surface (inner surface) of the film 4 in contact with the surface of the substrate 1 a (surface on the nip portion N side) of the heater 1 and the outer peripheral surface of the holder 2, as the pressure roller 6 rotates. Rotate following direction. In order to ensure slidability between the surface of the substrate 1a of the heater 1 and the outer peripheral surface of the holder 2 and the inner surface of the film 4 in the rotating state of the film 4, a lubricant such as grease is applied to the inner surface of the film 4.

  Electric power is supplied from the AC power source 51 to the heating resistor 1 b of the heater 1. As a result, the heating resistor 1b generates heat and the heater 1 rapidly rises in temperature. The thermistor 54 detects the temperature of the heater 1 and outputs it to the CPU 56. The CPU 56 takes in the output signal of the thermistor 54 via the A / D converter 55 and controls the triac 53 on and off based on the signal. Thereby, the electric power supplied from the AC power source 51 to the heating resistor 1b of the heater 1 is controlled, and the temperature of the heater 1 is maintained at a predetermined control temperature. The heat of the heater 1 at that time is used for heating and fixing the unfixed toner image t on the recording material P via the film 4.

  In a state where the rotation of the pressure roller 6 and the film 4 is stable and the temperature of the heater 1 is maintained at a predetermined control temperature, the recording material P carrying the unfixed toner image t is introduced into the nip portion N. . The recording material P is nipped and conveyed by the pressure roller 6 and the film 4 at the nip portion N. In the conveyance process, the recording material P and the toner image t are subjected to a nip pressure corresponding to the pressure mechanism via the pressure roller 6 and the film 4 and also received heat of the heater 1 via the film 4. The toner image t is heated and fixed on the recording material P. The recording material P that has exited the nip N is separated from the surface of the film 4 by the curvature, conveyed by the discharge roller 7, and discharged from the fixing device 27.

(3) Structure of Heater 1 FIG. 1 is a structural model diagram of an example of the heater 1. (A) of FIG. 1 is a figure showing the board | substrate 1a back surface side of the heater 1, (b) is bb arrow sectional drawing of (a), (c) is cc arrow sectional drawing of (a), (D) is the dd arrow cross-sectional enlarged view of (a), (e) is the ee arrow cross-sectional enlarged view of (a).

The heater 1 shown in the present embodiment includes a substrate 1a that is elongated in the longitudinal direction, and a heating resistor 1b that is provided along the longitudinal direction of the substrate 1a and generates heat when energized. The heating resistor 1b includes a first heating resistor 1b-1 and a second heating resistor 1b-2 that are provided in parallel in the short direction of the substrate 1a. The heater 1 includes a conductor portion 1c connected to one end and the other end of the first and second heating resistors 1b-1 and 1b-2, and the first and second heating resistors 1b-1. , 1b-2 and an insulating layer (protective layer) 1d covering the conductor portion 1c. Conductor portion 1c includes an electrode (feed contact) 1c-1, which is connected to a first end of the heating resistor 1b-1, the second heating resistor 1b-2 of the electrodes is connected to one end (power supply Contact) 1c-2. Moreover, the conductor part 1c has the connection part 1c-3 connected to the other end of the 1st heat generating resistor 1b-1, and the other end of the 2nd heat generating resistor 1b-2. The insulating layer 1d includes a first insulating layer 1d-1 covering a part of the first heating resistor 1b-1, the electrode 1c-1, and the connecting portion 1c-3, and a second heating resistor 1b. -2 and the electrode 1c-2 and the second insulating layer 1d-2 covering a part of the connecting portion 1c-3. The insulating layer 1d has a gap (gap) S between the first insulating layer 1d-1 and the second insulating layer 1d-2 along the longitudinal direction.

  In other words, the heater is a heating resistor that is provided along the longitudinal direction of the substrate and generates heat by energization, and is provided in parallel in a short direction perpendicular to the longitudinal direction of the substrate. A heating resistor. Further, the heater includes a conductor portion connected to one end and the other end of each of the plurality of heating resistors in the longitudinal direction of the substrate, and an insulating layer covering the plurality of heating resistors and the conductor portion. Have. The insulating layer has gaps between the plurality of heating resistors and between the conductor portions in the longitudinal direction of the substrate.

  The material of the substrate 1a is an electrically insulating material. As the substrate 1a, an insulating ceramic such as alumina or aluminum nitride, or a substrate provided with an insulating layer by means of applying a glass coat to a metal plate such as SUS can be used. In this embodiment, an aluminum nitride 0.605 mm thick substrate is used as the substrate 1a.

  As the heating resistors 1b-1 and 1b-2, a conductive paste applied on the substrate 1a or a nichrome wire or the like fixed on the substrate 1a by a known method such as adhesion may be used. Further, the heating resistors 1b-1 and 1b-2 do not need to be formed directly on the substrate 1a, and may be, for example, via a glaze layer for preventing diffusion of heat to the substrate 1a. In this embodiment, a conductive paste containing silver / palladium alloy is uniformly applied to the toner image surface side of the recording material P of the substrate 1a by a screen printing method and then baked. Thus, the heating resistors 1b-1 and 1b-2 were formed. The resistance values of the heating resistors 1b-1 and 1b-2 used in this example were 49.7Ω. As a result, the power consumption of the fixing heater 100 when the voltage of 240 V is applied is 1159 W. The width of the longitudinal central portion of the heating resistors 1b-1 and 1b-2 is 1.43 mm. The distance between the heating resistors 1b-1 and 1b-2 in the short direction of the substrate 1a is 1.52 mm.

The heating resistors 1b-1 and 1b-2 each have a region (high resistance region) A1 having a narrower width than the other portions at both longitudinal ends. By forming the narrow region A1 by narrowing the width of the heating resistors 1b-1 and 1b-2, the resistance of the heating resistors 1b-1 and 1b-2 is increased in the region A1, and the same value is obtained. The amount of heat generated when a current flows increases. As a result, in the heating resistors 1b-1 and 1b-2 having the narrow area A1 at the longitudinal end, heat escapes through the substrate 1a toward the longitudinal ends of the heating resistors 1b-1 and 1b-2. To compensate. In the present embodiment, in the heating resistors 1b-1 and 1b-2, the width of the narrow area A1 is narrowed by 5% with respect to the other portions, and the width of the area A1 is 1.359 mm.

  The electrodes 1c-1 and 1c-2 function as contacts for supplying power to the heating resistors 1b-1 and 1b-2. In this example, the silver paste was applied to the film having a thickness of 20 μm uniformly by a screen printing method in the same manner as the heating resistors 1b-1 and 1b-2, and then fired, and then the electrodes 1c-1, 1c-2 was formed. The electrodes 1c-1 and 1c-2 are respectively connected to the corresponding heating resistors 1b-1 and 1b-2 in the longitudinal direction of the substrate 1a. An AC voltage is applied to the heating resistors 1b-1 and 1b-2 through the electrodes 1c-1 and 1c-2.

  The material of the insulating layers 1d-1 and 1d-2 is an insulator such as glass or resin. For example, the material of the insulating layers 1d-1 and 1d-2 is insulating glass. The insulating layers 1d-1 and 1d-2 are provided to ensure the withstand voltage of the heating resistors 1b-1 and 1b-2, the electrodes 1c-1 and 1c-2, and the connecting portion 1c-3. In the present embodiment, the heating glass 1c-1, 1b-2, the electrodes 1c-1, 1c-2, and the connecting portion 1c-3 are formed with an insulating glass coating layer having a thickness of 80 μm so as to form the above-described void S. The insulating layers 1d-1 and 1d-2 are provided by performing screen printing so as to cover them. The width of the gap S in the short direction of the substrate 1a is 0.82 mm. Further, the insulating layers 1d-1, 1d-2 are formed on the heating resistors 1b-1, 1b-2 between 35 mm from the electrodes 1c-1, 1c-2 side, which is the highest temperature part where the heater cracks. The insulating layers 1d-1 and 1d-2 have portions T1 and T2 where the thickness is larger than others. That is, each insulating layer has one thicker portion on the heating resistor than the others. The thicker portion of the insulating layer is provided at a place where the heat generation amount of the heating resistor is maximized when the heating resistor is energized in excess of a specified energization amount. In the present embodiment, the thicknesses of the portions T1 and T2 are 240 μm.

  In the heater 1, for example, when power is applied to the electrode 1c-1, a current flows through the path of the heating resistor 1b-1, the connecting portion 1c-3, the heating resistor 1b-2, and the electrode 1c-2 to generate heat. The resistors 1b-1 and 1b-2 generate heat.

(4) Excessive fixing power input test for heater 1 With respect to the heater 1 of this example, effects and verification were performed in a simulation assuming a fixing excessive power input test. As described above, in the heater 1 of this embodiment, the thicknesses of the insulating layers 1d-1 and 1d-2 are set to 80 μm, and the thicknesses of the portions T1 and T2 where the thicknesses of the insulating layers 1d-1 and 1d-2 are larger than the others are set. It is 240 μm.

  FIG. 2 shows the heater of Comparative Example 1 compared with the heater 1 of this example. FIG. 3 shows a heater of Comparative Example 2 compared with the heater 1 of this example. In the heater shown in FIGS. 2 and 3, the same reference numerals are given to members common to the heater 1 of this embodiment, and the description thereof is omitted.

  FIG. 2 is a structural model diagram of the heater 1A of the first comparative example. 2A is a view showing the back side of the substrate 1a of the heater 1A, FIG. 2B is a sectional view taken along the line ff in FIG. 2A, and FIG. 2C is a sectional view taken along the line GG in FIG. (D) is the hh arrow cross-sectional enlarged view of (a). FIG. 3 is a structural model diagram of the heater 1B of Comparative Example 2.

  The heater 1A shown in FIG. 2 is the same as the heater 1 of this embodiment except that the thickness of the region covering the heating resistors 1b-1 and 1b-2 in the insulating layers 1d-1 and 1d-2 is 240 μm. Same configuration.

  (A) of FIG. 3 is a figure showing the board | substrate 1a back surface side of the heater 1B, (b) is the ii arrow sectional drawing of (a), (c) is the j arrow sectional drawing of (a), (D) is the kk arrow cross-sectional enlarged view of (a).

  The heater 1B shown in FIG. 3 is the same as the heater 1 of this embodiment except that the insulating layers 1d-1 and 1d-2 cover the heating resistors 1b-1 and 1b-2 with a thickness of 80 μm. Same configuration.

  As a simulation condition for the heaters 1, 1 A, 1 B, the voltage applied to the heating resistors 1 b-1, 1 b-2 is 10% higher than the rated voltage of 240 V in the highest voltage region in the 200 V range, ie, , About 264V.

  In each of the heaters 1, 1A, 1B, the portion where the heater is cracked has a large potential difference between the heating resistors 1b-1, 1b-2, and the T1, on the side of the electrodes 1c-1, 1c-2 that has the highest temperature. This is the T2 portion. Therefore, the temperature rises of the T1, T2 portions of the heaters 1, 1A, 1B were respectively compared and verified.

4-1) Comparison and verification of T1 and T2 portions in heater 1 and heater 1B In the heater 1B of Comparative Example 2, the heating resistors 1b-1 and 1b-2 in T1 and T2 portions reach 800 ° C. It is 2.64 seconds from the start of power supply. In contrast, in the heater 1 of this embodiment, the heating resistors 1b-1 and 1b-2 in the T1 and T2 portions reach 800 ° C. in 3.00 seconds from the start of power supply. Therefore, the heater 1 of this example was able to extend +0.36 seconds compared to the heater 1B of Comparative Example 2.

4-2) Comparison and verification of T1 and T2 portions in the heater 1 and the heater 1A In the heater 1A of the comparative example 1, since the insulating layers 1d-1 and 1d-2 are as thick as 240 μm, the heating resistor 1b-1, The amount of heat entering the thermo switch 57 from 1b-2 is reduced. Therefore, the operation of the thermo switch 57 is delayed. The heater 1 of this embodiment can solve the problem that the operation of the thermoswitch 57 is delayed because the thickness of the insulating layers 1d-1 and 1d-2 is as thin as 80 μm.

  In the heater 1A, the heating resistors 1b-1 and 1b-2 in the T1 and T2 portions reach 800 ° C. in 2.91 seconds from the start of power supply. On the other hand, considering that the heater 1 is 3.00 seconds, the heater 1A is disadvantageous as a heater crack countermeasure. This is because the resistance R of the heating resistors 1b-1 and 1b-2 is R = resistance value at normal temperature × (1 + temperature coefficient × rising temperature of the resistance heating element), and the heater power supply W is W = V × V / R. Therefore, the heater supply power decreases as the temperature rise of the entire heating resistor increases, and the temperature rise in the T1 and T2 portions is reduced. Therefore, the thickness of the insulating layer is partially increased in the entire heating resistor from the heater 1A, which increases the heat capacity by increasing the thickness of the insulating layer of the entire heating resistor and reduces the temperature rise of the entire heating resistor. The heater 1 having a larger thickness is more effective in preventing heater cracking.

  In the heater 1, each insulating layer has one thicker portion on the heating resistor than the others, but the heater 1 is not limited to this. That is, the heater 1 may be configured such that each insulating layer has one or more thicker portions on the heating resistor than the others. In other words, the heater 1 may be configured such that each insulating layer has at least one thicker portion on the heating resistor than the other. In the insulating layer, the portion where the thicker portion is formed may be appropriately determined according to the actual product.

[Example 2]
The heater 1 of the first embodiment is not limited to a fixing device that can be mounted on an electrophotographic monochrome laser printer, but can also be used for a fixing device that can be mounted on an electrophotographic color image forming apparatus. The fixing device will be described below.

  In the present embodiment, members that are the same as those of the fixing device 27 of Embodiment 1 are given the same reference numerals, and description thereof is omitted.

  FIG. 7 is a schematic cross-sectional view of an example of a fixing device that can be mounted on a color image forming apparatus.

The fixing device 31 shown in the present embodiment has the same configuration as the fixing device 27 of the first embodiment except for the following three points. That is, an endless (seamless) fixing belt (cylindrical film) 32 is used as the flexible member, the temperature of the fixing belt 32 is detected by the thermistor 54, and the heater holder 2 has a thermostat. This is the point where the switch 57 is provided. In the fixing device 31, the heater 1 is controlled by a heater temperature control system having the same configuration as that of the first embodiment.

  The fixing belt 32 has an elastic layer (not shown) on the outer periphery of an endless base layer (not shown) having flexibility. The configuration of the fixing belt 32 is disclosed in JP-A-10-10893, JP-A-11-15303, and the like. By using this fixing belt, when the unfixed toner image t carried by the recording material P passes through the nip portion N, the elastic layer can be deformed along the toner layer of the toner image t. Due to the deformation of the elastic layer, the toner image t placed on the recording material P is unevenly formed on the image, and the toner image t can be uniformly heated. Thereby, uniform fixing of the toner image t to the recording material P can be achieved. An image that is uniformly fixed in this manner has no gloss unevenness, and has a feature that the light transmittance of the image is excellent particularly when a color image is fixed on an OHT (transparent sheet for an overhead projector). In the fixing belt 32, a rubber material such as silicone rubber is generally used as a material for the elastic layer.

  However, the thermal conductivity of silicone rubber or the like used for the elastic layer of the fixing belt 32 is not so high. The holder 2 of the heater 1 indicates that the recording material P has passed through the nip portion N between the fixing belt 32 and the pressure roller 6 to take heat from the surface of the fixing belt 32 and the temperature of the surface of the fixing belt 32 has decreased. It is difficult to detect with the thermistor 54 provided on the side surface. The reason is that the thermistor 54 detects that the temperature of the surface of the fixing belt 32 has decreased via the holder 2, and therefore it takes too much time to respond to the temperature decrease of the surface of the fixing belt 32. Therefore, in order to control the temperature of the fixing belt 32 based on the output signal of the thermistor 54, it is necessary to improve the responsiveness of the thermistor 54 to the temperature decrease of the surface of the fixing belt 32.

  Therefore, in the fixing device 31 of this embodiment, in addition to using a metal belt as the base layer of the fixing belt 32, the thermistor 54 is disposed so as to be in contact with the base layer inner surface (metal belt inner peripheral surface) of the fixing belt 32. It is comprised as follows. Thereby, the temperature of the fixing belt 32 can be detected more directly by the thermistor 54.

  However, in the fixing device having the fixing belt 32 using a metal belt as a base layer, when a heater crack occurs, a primary current flows from the metal belt to the control circuit C2 (secondary circuit) via the thermistor, The probability that it leads to destruction of the secondary circuit is increased.

  Therefore, in the fixing device 31 of the present embodiment, even if a heater crack occurs, the primary current does not flow from the metal belt of the fixing belt 32 to the secondary circuit via the thermistor or the like. It is necessary to improve the margin.

  In the fixing device 31 of this embodiment, a thermistor (thermistor element) 54 is attached to the tip of a stainless steel arm 61 held by the holder 2. The arm 61 has elasticity (spring property) so that the thermistor 54 contacts the inner surface of the base layer of the fixing belt 31. Accordingly, even if the behavior of the fixing belt 32 during the rotational operation becomes unstable, the arm 61 swings with respect to the inner surface of the base layer of the fixing belt 32 according to the behavior, and the thermistor 54 is moved to the inner surface of the base layer of the fixing belt 31. It can always be in contact. As a result, even if a heater crack occurs, the primary current can be prevented from flowing from the metal belt of the fixing belt 32 to the secondary circuit via the thermistor 54, and the safety margin can be improved.

In the fixing belt 32, a silicone rubber layer is formed as an elastic layer on the outer periphery of a SUS belt formed into a seamless belt shape having a thickness of 50 μm by drawing a SUS base tube by a ring coating method. The outer periphery of the silicone rubber layer is covered with a PFA resin tube having a thickness of 30 μm as a release layer. For the silicone rubber layer, it is desirable to use a material having a high thermal conductivity as much as possible and to reduce the heat capacity of the fixing belt 32 from the viewpoint of temperature rise. In this example, a material having a thermal conductivity of about 1.0 × 10 ⁻³ cal / sec · cm · K and a silicone rubber having a high thermal conductivity were used.

  On the other hand, it is desirable to make the silicone rubber layer of the fixing belt 32 as thick as possible from the viewpoint of image quality, such as OHT permeability and “s” (small gloss unevenness) on the image. It has been found that a silicone rubber layer thickness of 200 μm or more is required to obtain a satisfactory level of image quality. The silicone rubber layer in this example was 250 μm thick.

The heat capacity of the fixing belt 32 thus formed was measured and found to be 2.8 × 10 ⁻² cal / cm ² K (heat capacity per 1 cm ^{2 of the} fixing belt). In general, when the heat capacity of the fixing belt 32 is 1.0 cal / cm ² K or more, the temperature rise becomes dull and the on-demand property is impaired. On the other hand, if it is attempted to be 1.0 × 10 ⁻² cal / cm ² K or less, the silicone rubber layer of the fixing belt 32 has to be extremely thinned. The thickness of the rubber layer necessary for maintaining the image quality cannot be secured. Therefore, it can be seen that the heat capacity of the fixing belt 20 that satisfies both on-demand characteristics and image quality is included in the range of 1.0 × 10 ⁻² cal / cm ² K to 1.0 cal · cm ² K. .

  Further, by providing a fluororesin layer on the surface of the fixing belt 32, the releasability of the surface of the fixing belt 32 is improved, and the toner once adheres to the surface of the fixing belt 32 and then moves to the recording material P again. The offset phenomenon can be prevented.

  Further, when the fluororesin layer on the surface of the fixing belt 32 is a PFA tube, a uniform fluororesin layer can be formed more easily.

  In the fixing device 31 of this embodiment, the thermo switch 57 is not in direct contact with the heater 1 but is provided with insulating layers 1b-1 and 0 of the heater 1 by spacers (not shown) provided integrally with the holder 2. It is arranged so as to face each other with a gap of about 5 mm. That is, a safety element that operates in response to the heat of the heating body and cuts off the power supply to the heating resistor is disposed in the vicinity of the heating body in a non-contact manner.

  FIG. 8 is a structural model diagram of an example of a color image forming apparatus in which the fixing device 31 of this embodiment can be mounted.

  The color image forming apparatus shown in this embodiment is an electrophotographic full-color image forming apparatus. This image forming apparatus has a process speed of 90 mm / sec and the number of printed sheets per minute is 16 US letter size paper. Further, this image forming apparatus takes about 15 seconds from the input of the print command to the output of the first image.

  The image forming apparatus of the present embodiment includes four process cartridges Y, C, M, and K that form yellow, cyan, magenta, and black color toner images. Each of the cartridges Y, C, M, and K supports a photosensitive drum 61 as an image carrier, a charging roller 62 as a charging device, a developing device 63, and a cleaning unit 64 in a single container. Is. Each of the cartridges Y, C, M, and K is detachably attached to the image forming apparatus main body A constituting the housing of the image forming apparatus.

  Yellow toner is stored in the developing device 63 of the yellow cartridge Y, and cyan toner is stored in the developing device 63 of the cyan cartridge C. The developing device 63 of the magenta cartridge M stores magenta toner, and the developing device 63 of the black cartridge K stores black toner.

  Reference numeral 65 denotes a laser scanner (laser scanning exposure optical system) as exposure means. The laser scanner 65 is provided corresponding to each cartridge Y, C, M, and K. The laser scanner 65 forms an electrostatic latent image by exposing the surface of the photosensitive drum 61 of each cartridge Y, C, M, and K.

  In each cartridge Y, C, M, and K, the scanning light based on the image data is exposed from the laser scanner 65 to the surface of the photosensitive drum 61 that is uniformly charged by the charging roller 62, thereby causing the surface of the photosensitive drum 61 to be exposed. An electrostatic latent image corresponding to the scanning exposure image is formed. By setting the developing bias applied from a power source (not shown) to the developing roller 63a provided in the developing means 63 to an appropriate value between the charged potential and the latent image (exposed portion) potential, the negative polarity is obtained. The charged toner is selectively attached to the electrostatic latent image on the surface of the photosensitive drum 61 for development. As a result, a yellow toner image is formed on the photosensitive drum 61 of the cartridge Y, and a cyan toner image is formed on the photosensitive drum 61 of the cyan cartridge C. A magenta toner image is formed on the photosensitive drum 61 of the magenta cartridge M, and a black toner image is formed on the photosensitive drum 61 of the black cartridge K.

  The monochromatic toner image formed on the surface of the photosensitive drum 61 of each of the cartridges Y, C, M, and K is synchronized with the rotation of each photosensitive drum 61 and the outer periphery of an intermediate transfer belt 66 as an intermediate transfer member that rotates at a substantially constant speed. The image is superimposed on the surface (surface) in a predetermined alignment state in order and is primarily transferred. As a result, an unfixed full-color toner image is synthesized and formed on the surface of the intermediate transfer belt 66. The intermediate transfer belt 66 is wound around three rollers, a driving roller 67a, a secondary transfer roller facing roller 67b, and a tension roller 67c, and is driven by the driving roller 67a.

  A primary transfer roller 68 is used as a primary transfer unit of the toner image from the surface of the photosensitive drum 61 of each cartridge Y, C, M, and K to the surface of the intermediate transfer belt 66. The primary transfer roller 68 is provided on the inner peripheral surface side of the intermediate transfer belt 66. A primary transfer bias having a polarity opposite to that of the toner is applied to the primary transfer roller 68 by a power source (not shown), so that the surface of the photosensitive drum 61 of each cartridge Y, C, M, and K is transferred from the surface of the intermediate transfer belt 66 to the surface of the intermediate transfer belt 66. The toner image is primarily transferred.

  Transfer residual toner remaining on the surface of the photosensitive drum 61 of each cartridge Y, C, M, and K after the primary transfer of the toner image is removed by a cleaning blade (not shown) provided in the cleaning unit 64. In this embodiment, a urethane blade is used as the cleaning blade.

  In the image forming apparatus of the present embodiment, the above process is performed only for a target color when an image of only a single color is formed (single color mode).

  On the other hand, the recording material P is conveyed from the feeding cassette 70 by the conveying roller 69a. The recording material P is conveyed by a registration roller 69b to a transfer nip T between the intermediate transfer belt 66 and the secondary transfer roller 71 that is wound around the secondary transfer roller facing roller 67b at a predetermined timing. The

  The primary transfer toner image formed on the surface of the intermediate transfer belt 66 is collectively transferred onto the recording material P by a bias having a reverse polarity to the toner applied to the secondary transfer roller 71 by a power source (not shown).

  The transfer residual toner remaining on the surface of the intermediate transfer belt 66 after the secondary transfer of the toner image is removed by a cleaning blade 72 a provided in the intermediate transfer belt cleaning unit 72. In this embodiment, a urethane blade is used as the cleaning blade 72a.

  The toner image transferred onto the recording material P is heated and fixed on the recording material P by passing through the fixing device 31. The recording material P on which the toner image is heat-fixed is discharged to the discharge tray 73 through the discharge passage 69d by the discharge roller 69c.

  Reference numeral 69 denotes a conveying means. The conveying unit 69 includes a conveying roller 69a, a registration roller 69b, a discharge roller 69c, a discharge passage 69d, and the like.

3 is a structural model diagram of an example of a heater of Example 1. FIG. 3 is a structural model diagram of a heater of Comparative Example 1 compared with the heater of Example 1. FIG. FIG. 3 is a structural model diagram of a heater of Comparative Example 2 compared with the heater of Example 1; FIG. 3 is a schematic cross-sectional view of an example of the fixing device according to the first exemplary embodiment. It is a circuit diagram of an example of a heater temperature control system. 1 is a configuration model diagram of an example of an image forming apparatus. FIG. 6 is a cross-sectional model diagram of an example of a fixing device according to a second embodiment. 1 is a configuration model diagram of an example of a color image forming apparatus.

Explanation of symbols

1: heater (heating body), 1a: substrate, 1b-1: first heating resistor, 1b-2: second heating resistor, 1c-1, 1c-2: electrode (conductor portion), 1c- 3: Connecting portion (conductor portion), 1d-1: first insulating layer, 1d-2: second insulating layer, S: gap, T1, T2: portions where the thickness of the insulating layer is larger than others, 4: fixing Film (flexible member), 32: fixing belt (flexible member)

Claims (2)

When the temperature of the cylindrical film, the heater that contacts the inner surface of the film and generates heat by energization, the pressure member that forms a nip portion together with the heater through the film, and the heater exceeds a predetermined temperature A safety element that cuts off the power to the heater,
The heater includes an elongated substrate, a heating resistor formed on the substrate in a pattern that is long along the longitudinal direction of the substrate and folded at the longitudinal end of the substrate, and the longitudinal direction of the substrate. Two power supply contacts for supplying power to the heat generating resistor and a protective layer covering the heat generating resistor, and the protective layer is the folded heat generation. A gap is provided between the resistors over the longitudinal direction of the substrate,
In the image heating apparatus for heating the toner image by transporting the recording material carrying the toner image at the nip portion,
The heating resistor of the heater has a high resistance region having a resistance value higher than that of a central portion at both ends in the longitudinal direction of the substrate, and covers the high resistance region at both ends of the protective layer of the heater Of these, only the portion covering the high resistance region on the side close to the power supply contact is thicker than the portion covering the central portion of the heating resistor. An elongated substrate; a heating resistor formed on the substrate in a pattern that is long along the longitudinal direction of the substrate and folded at the longitudinal end of the substrate; and on the same side in the longitudinal direction of the substrate Two power supply contacts provided at an end for supplying power to the heating resistor, and a protective layer covering the heating resistor, the protective layer between the folded heating resistors In the heater provided with a gap over the longitudinal direction of the substrate,
The heating resistor has a high resistance region having a resistance value higher than that of a central portion at both ends in the longitudinal direction of the substrate, and the power supply contact is included in a portion covering the high resistance region at both ends of the protective layer. Only the portion covering the high resistance region on the near side is thicker than the portion covering the central portion of the heating resistor.