JP6489812B2 - Image heating device - Google Patents

Description

  The present invention relates to an image heating apparatus provided in an image forming apparatus using an electrophotographic system.

  As a fixing device (image heating device) mounted in an electrophotographic image forming apparatus such as a copying machine or a printer, a film heating type is known. This type of fixing device includes a heater having a heating resistor on a ceramic substrate, a fixing film that moves while in contact with the heater, and a pressure roller that forms a heater and a nip portion through the fixing film. doing. The recording material carrying the unfixed toner image is heated while being nipped and conveyed at the nip portion of the fixing device, whereby the toner image is fixed on the recording material.

  FIG. 10 is a schematic cross-sectional view of a conventional film type fixing device. 203 is a ceramic heater, 204 is a heat-resistant resin heater holder, 201 is a fixing film, and 202 is a pressure roller. The fixing device is required to avoid the so-called “heater crack at the time of abnormal temperature rise” in which a substrate of the heater 203 (hereinafter referred to as a heater substrate) breaks when a power supply circuit that supplies power to the heater 203 is abnormal. When a triac or relay used in the power supply circuit fails, the primary current may be supplied to the heater 203 without being controlled. In this case, an abnormal temperature rise occurs in the heater 203 and an excessive thermal stress is applied, which may cause the heater 203 to crack and become unusable. Alternatively, an abnormal temperature rise may occur in the heater 203 and mechanical stress due to melting of the heater holder that supports the heater 203 may be applied to the heater substrate, causing the heater 203 to break and become unusable.

In order to avoid this “heater crack at the time of abnormal temperature rise”, a configuration in which a temperature sensing element 205 is provided to cut off the primary current has been conventionally known. The primary current when flowing into the heater 203, abnormal Atsushi Nobori in the heater 203 occurs before the cracked by thermal stress or mechanical stress, temperature sensing element 205 to cut off power supply to the heating resistor It is a configuration that operates. In this configuration, it is required that the temperature sensitive element 205 always operates before the thermal stress or mechanical stress applied to the heater 203 reaches the bending limit of the heater 203.

Patent Document 1 discloses a configuration in which a heater holder 204 is provided with a hole for fitting a temperature sensing element, and the temperature sensing element 205 is pressed and held in the heater direction by a pressure spring 206 fixed to a support member 207. Yes.

JP 2007-058190 A

However, when the temperature sensing element 205 is pressed by the spring 206, the operation time of the temperature sensing element 205 may not be stable in the configuration in which the spring is supported by the resin member. This will be described with reference to FIG.
11A and 11B are schematic cross-sectional views showing the configuration around the heater 203 of the conventional fixing device. FIG. 11A shows a state in which the image forming apparatus is operating normally, and FIG. A state when the support member 207, which is a resin member, is in a molten state after being heated is shown. In addition, FIG. 11 is a figure upside down with respect to FIG.

As shown in FIG. 11B, when the heater 203 abnormally increases in temperature and reaches the melting point of the resin material constituting the support member 207, the molten resin is applied to the surface of the temperature sensitive element 205 as shown in FIG. May come into contact. When the area where the resin comes into contact with the surface of the temperature sensing element 205 increases, the heat of the temperature sensing element 205 diffuses into the resin and the temperature rise is hindered. When the temperature rise is hindered, the operation of the temperature sensing element 205 is delayed, the thermal stress and mechanical stress applied to the heater 203 may exceed the bending limit of the heater 203, and a heater crack may occur. When a heater crack occurs, the heater 203 becomes unusable and there is a concern that the recyclability is lowered. Further, in the power supply circuit of the image forming apparatus, a sufficient distance cannot be secured to ensure electrical insulation between the portion to which the primary voltage is applied and the secondary side circuit or the GND portion. There is also a concern that will be destroyed and repair costs will increase.

  As means for avoiding this problem, it is possible to reduce the pressure applied to form the fixing nip N and reduce the mechanical stress applied to the heater 203. However, if the applied pressure is reduced, the fixing nip N is reduced, so that the heat on the toner image on the recording material is insufficient, and fixing failure may occur in a low temperature environment or the like. In recent years, there has been a demand for further speeding up of the image forming apparatus. In order to meet the demand, it is necessary to increase the pressure in order to supply heat to the toner image on the recording material in a short time. . Under such circumstances, there is a need for a fixing device that can prevent heater cracking during abnormal temperature rise.

An object of the present invention is to provide an image heating apparatus that can more effectively prevent a heater crack when an abnormal temperature rise occurs by stabilizing the operation of a temperature sensing element.

In order to achieve the above object, the image heating apparatus of the present invention comprises:
An image heating apparatus for heating a toner image formed on a recording material,
A tubular film,
A pressure member in contact with the outer surface of the film;
A heater that generates heat by feeding power, and contacts the inner surface of the film, and is pressed against the pressure member via the film, whereby the recording material is sandwiched and conveyed between the film and the pressure member. A heater for forming a nip portion,
A temperature sensing element that shuts off power supply to the heater when the temperature of the heater reaches a predetermined abnormal temperature;
A first support member for supporting the temperature sensitive element;
A second support member for supporting the first support member;
An urging member that presses the second support member to press the temperature sensitive element toward the heater;
With
The first support member is made of a material having a higher melting point than the second support member , and when viewed from the pressing direction in which the temperature sensing element is pressed against the heater, the first support member is , being larger than the contact portion that contacts the first support member of the second support member.

According to the present invention, by stabilizing the operation of the temperature sensing element, it is possible to more effectively prevent heater cracking when an abnormal temperature rise occurs.

1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. Schematic diagram explaining the structure of the ceramic heater The perspective view of the member arrange | positioned inside the fixing film in Example 1 Schematic cross-sectional view of the vicinity of the thermal fuse arrangement position of the fixing device according to the first embodiment. Schematic sectional view of the vicinity of the position where the thermal fuse is arranged in a modification of the first embodiment Explanatory drawing of power supply circuit PS which applies electric power to the heater in Example 1 The perspective view of the member arrange | positioned inside the fixing film in Example 2. Schematic sectional view of the vicinity of the thermal fuse arrangement position of the fixing device according to the second embodiment. Schematic sectional view showing a schematic configuration of a conventional fixing device Explanatory drawing of the temperature sensor holding structure of a conventional fixing device

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[Example 1]
(1-1) Description of Entire Image Forming Apparatus FIG. 1 is a schematic sectional view showing a schematic configuration of an example of an image forming apparatus in which an image heating apparatus according to an embodiment of the present invention is mounted as a fixing device. This image forming apparatus is a laser beam printer using an electrophotographic process, and transports a recording material by aligning the center of the recording material with the center reference of the recording material transport path in a direction orthogonal to the recording material transport direction. It has become. The image forming apparatus includes an image forming unit A that forms an unfixed toner image (image) on a recording material P, and a fixing unit that fixes an unfixed toner image formed on the recording material on a recording material (hereinafter referred to as a fixing device (hereinafter referred to as a fixing device)). (Image heating device)) C) and the like.

  In the image forming unit A, 7 is a process cartridge. The process cartridge 7 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier, a charging roller (charging means) 2, a developing device (developing means) 4, and a cleaning blade (cleaning means). 6 is integrated into a cartridge. The process cartridge 7 is detachably attached to the image forming apparatus main body B constituting the housing of the image forming apparatus.

  In this image forming apparatus, the photosensitive drum 1 rotates in a direction indicated by an arrow at a predetermined peripheral speed (process speed) in response to a print command output from an external device such as a host computer or a terminal on a network. Yes. During this rotation process, the outer peripheral surface (outer surface) of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2. The uniformly charged surface of the surface of the photosensitive drum 1 is scanned and exposed by a laser beam L that is output from a laser scanner unit (exposure means) 3 and modulated (ON / OFF controlled) in accordance with image information from an external device. Made. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1.

  The electrostatic latent image is developed with toner by the developing roller 4a of the developing device 4 and visualized as a toner image. As a development method, a jumping development method, a two-component development method, a FEED development method, or the like is used, and is often used in combination with image exposure and reversal development.

On the other hand, the recording materials P stacked and stored in the paper feeding cassette 13 are fed one by one by the rotation of the feeding roller 9 and conveyed to the registration roller pair 10 through the first sheet path 11. The recording material P is sent out by the registration roller pair 10 to the transfer nip Tn formed by the surface of the photosensitive drum 1 and the outer peripheral surface (surface) of the transfer roller 5 through the second sheet path 12 at a predetermined conveyance timing. The recording material P is nipped between the surface of the photosensitive drum 1 and the surface of the transfer roller 5 at the transfer nip portion Tn, and is conveyed (nipped and conveyed) to that state. In this conveyance process, a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 5. As a result, the toner image on the surface of the photosensitive drum 1 is electrostatically transferred onto the recording material P at the transfer nip Tn, whereby the recording material P carries an unfixed toner image.

  The recording material P carrying an unfixed toner image (toner image) is separated from the surface of the photosensitive drum 1 and discharged from the transfer nip portion Tn, and through the third sheet path 14, the fixing nip portion (nip portion) N of the fixing device C. To be introduced. When the recording material P passes through the fixing nip portion N, the unfixed toner image is fixed on the recording material P. The recording material P exiting the fixing device C is conveyed to the discharge roller pair 8 through the fourth sheet path 15. The discharge roller pair 8 conveys the recording material P and discharges it onto the discharge tray 16. The surface of the photosensitive drum 1 after separation of the recording material P is cleaned by removing residual toner and the like by the cleaning blade 6, and the photosensitive drum 1 is used for the next image formation.

(1-2) Fixing device (image heating device) C
In the following description, with respect to the fixing device and members constituting the fixing device, the longitudinal direction refers to 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 longitudinal width refers to the dimension in the longitudinal direction. The short width is a dimension in the short direction.

  FIG. 2 is a schematic cross-sectional view illustrating a schematic configuration of the fixing device C according to the present embodiment. The fixing device C is a film heating type fixing device. A fixing device C according to the present embodiment includes a flexible heat-resistant cylindrical fixing film (fixing member) 201, a pressure roller (pressure member) 202, a ceramic heater (heating body) 203, A heater holder (support member) 204, a metal stay (rigid member) 211, and the like are included. The fixing film 201, the pressure roller 202, the ceramic heater (hereinafter referred to as a heater) 203, the heater holder 204, and the metal stay 211 are all members that are long in the longitudinal direction.

  The heater holder 204 is formed in a substantially semicircular arc shaped cross section with a resin material having high heat resistance such as PPS (polyphenylene sulfide) or LCP (liquid crystal polymer). The heater holder 204 supports the heater 203 by a groove 204a formed along the longitudinal direction at the center of the lower surface of the heater holder 204 in the short direction. The heater holder 204 is configured to guide the fixing film 202 to rotate while maintaining an appropriate shape by the outer arc guide surfaces 204b on both sides in the short direction of the heater holder 204.

  The metal stay 211 is formed in a substantially inverted U-shaped cross section that is narrower than the short width of the heater holder 204 by using a predetermined metal material having rigidity. The metal stay 211 is disposed on the upper surface in the short direction of the heater holder 204 so that the center in the short direction of the metal stay 211 matches the center in the short direction of the heater holder 204.

  A fixing film 201 is loosely fitted on the outer periphery of the heater holder 204 that supports the heater 203 and is provided with the rigid stay 211. As the fixing film 201, a surface excellent in releasability of fluororesin or the like on the outer peripheral surface of a cylindrical base layer (not shown) made of a resin material such as thin polyimide or PEEK, or a metal material such as SUS or nickel What provided the layer (release layer) is used.

The heat capacity of the fixing film 201 is very small as compared with a fixing roller used in a conventional heat roller type fixing device. Therefore, by supplying electric power to the heater 203, it is possible to raise the temperature of the fixing nip N, which will be described later, in a very short time. Accordingly, it is possible to start up the fixing device C without waiting time and obtain a fixed image quickly when necessary.

  The heater 203 will be described with reference to FIG. FIG. 3 is a schematic diagram illustrating the configuration of the heater 203. As shown in FIG. 3, the heater 203 has an elongated heater substrate 203a made of ceramic such as alumina or aluminum nitride. On the surface of the heater substrate 203a facing the inner peripheral surface (inner surface) of the fixing film 201, two thin heating resistors 203b made of silver / palladium alloy or the like along the longitudinal direction of the heater substrate 203a are screened. It is formed by printing or the like.

  In this embodiment, an alumina substrate having a thickness of 1 mm and a length in the short direction of 6.0 mm is used as the heater substrate 203a. Two Ag / Pd (silver palladium) pastes are formed on the surface of the alumina substrate along the longitudinal direction of the alumina substrate, and these are used as the heating resistor 203b. The width of the heating resistor 203b in the short direction is 1.0 mm, and is formed at a position 0.3 mm inside from the short end of the heater substrate 203a.

  Furthermore, on one end side in the longitudinal direction of the surface of the heater substrate 203a, two power supply electrodes 203c electrically connected individually to the two heating resistors 203b are formed by screen printing or the like with silver or the like. On the other end side in the longitudinal direction of the surface of the heater substrate 203a, a conductive portion 203d electrically connected to the two heating resistors 203b is formed by silver or the like by screen printing or the like.

  In this embodiment, Ag paste is applied and baked on one end in the longitudinal direction of the surface of the heater substrate 203a to form two power supply electrodes 203c, and Ag paste is applied and baked on the other end in the longitudinal direction. 203d is formed. The two heating resistors 203b are connected in series with the conductive portion 203d. The total resistance of the two heating resistors 203b connected in series was measured and found to be 15Ω.

  Further, a glass coat (protective layer) 203e is formed on the surface of the heater substrate 203a so as to cover the two heating resistors 203b, a part of the two power supply electrodes 203c, and the conductive portion 203d. The glass coat 203e prevents the two heating resistors 203b, a part of the two feeding electrodes 203c and the conductive portion 203d from being damaged by sliding with the inner surface of the fixing film 201, and also the surface of the heater substrate 203a and the fixing film. The slidability with the inner surface of 201 is ensured.

  The pressure roller 202 has a metal core 202a made of iron, aluminum, or the like. An elastic layer 202b made of silicone rubber, silicone sponge, or the like is formed on the outer peripheral surface between shafts (not shown) at both ends in the longitudinal direction of the cored bar 202a. Further, a fluororesin is formed on the outer peripheral surface of the elastic layer 202b. A release layer 202c made of, for example, is formed.

  The pressure roller 202 is supported such that shafts at both ends in the longitudinal direction of the cored bar 202a of the pressure roller 202 are rotatably supported by side plates on both sides in the longitudinal direction of an apparatus frame (not shown) of the fixing device C via bearings. Has been. Above the pressure roller 202, a heater holder 204 is disposed so that the outer peripheral surface (front surface) of the pressure roller 202 and the outer peripheral surface (front surface) of the fixing film 201 face each other. The heater holder 204 is supported such that both ends in the longitudinal direction of the heater holder 204 are movable in the radial direction of the pressure roller 202 on the side plates on both sides in the longitudinal direction of the apparatus frame of the fixing device C.

Both ends in the longitudinal direction of the metal stay 211 disposed on the upper surface in the short direction of the heater holder 204 are perpendicular to the generatrix direction of the fixing film 201 with a predetermined pressure by a pressure member (not shown) such as a pressure spring. Pressurized in the direction. The metal stay 211 presses the surface of the fixing film 201 against the surface of the pressure roller 202 via the heater holder 204. Thus, the elastic layer 202b of the pressure roller 202 is crushed, and a fixing nip portion (nip portion) N having a predetermined short width necessary for fixing the toner image is formed between the surface of the pressure roller 202 and the surface of the fixing film 201. Yes.

Referring to FIGS. 4 and 5, will be explained in the holding structure of the serving temperature sensing element temperature fuse 205. FIG. 4 is a perspective view of members disposed inside the fixing film 201, and FIG. 5 is a schematic cross-sectional view in which the configuration in the vicinity of the position where the thermal fuse 205 is disposed in the fixing device according to the present embodiment is cut in the longitudinal direction. . Note that FIG. 5 is a diagram that is upside down with respect to FIGS. 1 and 2, and in a normal installation state of the image forming apparatus, the direction from the top to the bottom of FIGS. In many cases, the direction from the bottom of 5 toward the top is the direction of gravity.

  As shown in FIG. 4, the heater holder 204 is provided with two holes 204 c 1 and 204 c 2 that penetrate in the thickness direction of the heater 203. A thermistor (temperature detection member) 212 is accommodated in the hole 204c1, and the thermistor 212 is supported so as to come into contact with the back surface of the heater 203 by a locking portion (not shown) provided in the hole 204c1. . On the other hand, a thermal fuse 205 is accommodated in the hole 204c2. The thermal fuse 205 is fitted into the hole 204c2 of the heater holder 204, and is pressed and held by a pressure spring (hereinafter referred to as a fuse spring) 210 in the direction of the heater 203 via the fuse holder 209 and the fuse stay 208.

  A method for attaching the thermal fuse 205 will be described. The fuse holder 209 (second support member) is provided with engagement protrusions 209 d at the front and rear along the wiring direction of the thermal fuse 205. An engagement hole portion 205a that loosely fits with the engagement protrusion 209d is formed in a joint portion where a lead wire and a bundled wire (not shown) of the thermal fuse 205 are crimped and electrically connected. The terminal 205b is prevented from coming off, and the engagement hole 205a is fitted into the engagement protrusion 209d in a loosely fitted state, and the engagement protrusion 205a is allowed to move in the axial direction.

  As shown in FIG. 5, the fuse holder 209 is pressed in a direction toward the heater 203 by a fuse spring 210 (biasing member) supported between the fuse holder 209 and the metal stay 211. The fuse holder 209 is provided with a protruding portion 209a (contact portion, second protruding portion) for sandwiching the fuse stay 208 (first support member) with the thermal fuse 205. The pressing force by the pressure spring 210 is transmitted from the protrusion 209a to the fuse stay 208, and the fuse holder 209 is sandwiched between the thermal fuse 205 and the back surface of the heater 203.

  The material for forming the fuse holder 209 is preferably a resin material having a small heat capacity and a low heat transfer rate. This is to prevent heat non-uniformity in the longitudinal direction of the fixing device C due to the heat of the heater 203 being transferred to the fuse holder 209 via the thermal fuse 205 during printing. The smaller the amount of heat or heat released by the fuse holder 209 from the heater 203, the more uniform the longitudinal heat distribution of the fixing device at the time of printing, and it is possible to obtain an output with no unevenness in fixing properties and gloss. In this example, PPS (polyphenylene sulfide), which is a heat-resistant resin material having a melting point of about 290 ° C., was used.

  For example, if a metal material having a high melting point is used as the material for forming the fuse holder 209, melting can be prevented at abnormal temperature rise, and even if the temperature fuse 205 is directly supported, the contact area at abnormal temperature rise is large. There is no increase. However, if the fuse holder 209 is made of a metal material, the heat capacity and heat dissipation increase, and the temperature rise of the thermal fuse 205 is hindered. Therefore, the thermal fuse 205 needs to be supported via a fuse stay 208 that is a separate member from the fuse holder 209.

Further, the fuse stay 208 covers the fuse holder protrusion 209a and plays a role of shielding the molten resin when the fuse holder 209 is melted when the temperature rises abnormally. Even at a temperature at which the fuse holder 209 melts and deforms, it is necessary to have heat resistance capable of maintaining the shape, and therefore, it is formed of a metal material having a sufficiently higher melting point than the resin material used for the fuse holder 209. Is preferred. Moreover, it is preferable to form a continuous surface that shields the molten resin. That is, the fuse stay 208 may have a shape that shields between the protrusion 209a and the thermal fuse 205 so that a facing region is not formed between the protrusion 209a and the thermal fuse 205. In the present embodiment, the entire fuse stay 208 is a plate-like member that is larger than the protrusion 209a in the projected shape of the thermal fuse 205 in the pressing direction with respect to the heater 203. However, as long as the pressed surface in contact with the protruding portion 209a in the fuse stay 208 is configured to be larger than the protruding portion 209a, other configurations may be employed as appropriate. In other words, the protrusion 209 a may be included in the fuse stay 208 in the projected shape in the pressing direction.

  In this embodiment, the fuse stay 208 is a SUS plate having a thickness of 0.3 mm and 6 mm square. The fuse stay 208 is made of a SUS material having a melting point of about 1400 ° C., and is made into a thin sheet shape, thereby shielding the molten resin while minimizing the heat capacity and the heat radiation area. Note that the surface on which the fuse stay 208 covers the fuse holder protrusion 209a does not necessarily need to be a flat surface as long as it is formed of a continuous surface without holes so that the molten resin can be shielded.

  FIG. 6 is a schematic cross-sectional view of the vicinity of the thermal fuse arrangement position in a modification of the present embodiment. In this modification, a SUS plate molded in a continuous plane is bent, and a fuse stay 208 having two protruding portions 208 c that are convex toward the thermal fuse 205 is used. The fuse stay 208 is in contact with the fuse holder projection 209a at the flat portion 208d, and transmits the pressing force to the thermal fuse 205 at the projection 208c. In this modification, while supporting the thermal fuse 205 with a minimum contact area, the molten resin is shielded when the temperature is raised. That is, in this embodiment, in the projected shape, the entire area of the protrusion 209a contacts the fuse stay 208, but may not be in contact with a part of the area as in this modification. Such a configuration is not particularly limited as long as a gap is partially formed between the protruding portion 209a and the fuse stay 208 and between the fuse stay 208 and the thermal fuse 205. In this modification, the region of the projection 208c that faces the projection 209a functions as a separation portion that separates the projection 209a and the fuse stay 208, and the region that faces the thermal fuse 205 is the region of the present invention. It functions as a first protrusion.

  The thermal fuse 205 will be described. The thermal fuse 205 is an overheat protection component (temperature sensing element) that senses abnormal heat generation of the heater 203 and shuts off a primary circuit of a power supply circuit PS described later when the heater 203 is abnormally heated. In this embodiment, a thermal fuse D226 manufactured by Takara Shosha was used. The thermal fuse 205 is mounted with a fuse element (not shown) that melts at a predetermined temperature in a cylindrical metal casing that constitutes the outer cover of the thermal fuse 205. This fuse element is connected to the primary circuit. The temperature fuse 205 is configured to shut off the primary circuit by fusing the fuse element when the temperature rises abnormally. The predetermined abnormal temperature that triggers the operation of the thermal fuse 205 is appropriately set according to the device configuration and the like.

  The size of the thermal fuse 205 in this embodiment is such that the longitudinal width of the portion that can contact the back surface of the heater 203 of the metal casing is about 10 mm, and the short width of the metal casing 205a is about 4 mm. Thermal conductive grease (for example, SC-102 manufactured by Toray Dow Corning Co., Ltd., thermal conductivity: 2.45 W / mK) is applied between the thermal fuse 205 and the heater 203, or a heat transfer sheet member such as a metal plate (non-conductive). (Shown) may be installed.

  FIG. 7 is an explanatory diagram of a power supply circuit PS that applies power to the heater 203. In FIG. 7, reference numeral 100 denotes a temperature control unit comprising a CPU and a memory such as ROM and RAM. Reference numeral 102 denotes a commercial AC power supply (hereinafter referred to as AC power supply). Reference numeral 101 denotes a triac (power supply control circuit). The power supply circuit PS includes an AC power source 102, a thermal fuse 205, a triac 101, one power supply electrode 203c, one heat generating resistor 203b, a conductive portion 203d, the other heat generating resistor 203b, the other power supply electrode 203c, and the like connected in series. Primary circuit. Although not shown in the figure, a relay for turning on / off the triac 101 is connected to the primary circuit. The power supply circuit PS includes a secondary circuit in which the temperature control unit 100, one thermistor contact 212s, the thermistor 212, the other thermistor contact 212s, and the like are connected in series.

  The temperature control unit 100 controls the drive of the triac 101 based on the temperature information of the heater 203 detected by the thermistor 212, and the power to the heating resistor so as to maintain the temperature of the heater 203 at a predetermined fixing temperature (target temperature). The supply is controlled. As power supply control to the heating resistor 203b by the temperature control unit 100, zero cross wave number control for controlling execution and stop of energization for each half wave of the power waveform, and control of the phase angle for energizing for each half wave of the power waveform A multi-stage power control method such as phase control is used.

(1-3) Operation of Fixing Device C The operation of the fixing device C will be described with reference to FIG. A drive control unit (not shown) rotates and drives a drive motor (not shown) in response to a print command. The rotation of the output shaft of the drive motor is transmitted to a drive gear (not shown) provided at the longitudinal end of the shaft core 202a of the pressure roller 202, whereby the pressure roller 202 is rotated in a predetermined direction in the arrow direction. Rotates at speed (process speed). The rotation of the pressure roller 202 is transmitted to the surface of the fixing film 201 by the frictional force between the surface of the pressure roller 202 and the surface of the fixing film 201 in the fixing nip portion N. As a result, the fixing film 201 rotates (moves) in the direction of the arrow following the rotation of the pressure roller 202 while the inner surface of the fixing film 201 is in contact with the glass coat 203e of the ceramic heater 203 and both ends of the lower surface of the heater holder 204. )

  With reference to FIG. 7, temperature control during operation of the fixing device C will be described. The temperature control unit 100 turns on the triac 101 in response to the print command. As a result, the heating resistor 203b of the heater 203 is energized from the AC power supply 102 via the power supply terminal 203c. Then, the heating resistor 203b rapidly rises in temperature, and the heater 203 heats the fixing film 201 from the inner surface side of the fixing film 201. The temperature of the heater 203 is detected by the thermistor 212. The temperature control unit 100 takes in the temperature information from the thermistor 212 and controls the triac 101 so as to maintain the temperature of the heater 203 at a predetermined fixing temperature (target temperature) based on this temperature information.

  As shown in FIG. 2, the recording material P carrying the toner image (image) T in a state where the pressure roller 202 is rotated and the temperature of the heater 203 is maintained at a predetermined fixing temperature, The paper is fed (introduced) to the fixing nip N in an upward direction. The recording material P is nipped between the surface of the fixing film 201 and the surface of the pressure roller 202 at the fixing nip portion N, and is conveyed in that state (nipping conveyance). In this conveyance process, the toner image T is melted by receiving heat from the fixing film 201, and the toner image T is fixed on the recording material by receiving the pressure of the fixing nip N. The recording material P on which the toner image T is fixed is discharged from the fixing nip N while being separated from the surface of the fixing film 201.

(1-4) Forced Abnormal Temperature Raising Test of Fixing Device C In order to confirm what behavior the fixing device C of this embodiment shows when it is in an abnormal temperature rising state, a fixing nip N is formed. Three levels of 150N, 180N, and 200N were prepared for the applied pressure, and a forced abnormal temperature increase test was performed at each applied pressure.

  When the temperature rises abnormally, the largest thermal stress is applied to the heater 203 when the maximum power that can be supplied to the image forming apparatus is continuously supplied to the fixing device C. Therefore, assuming a double failure of the triac short and the relay short in the primary circuit of the power supply circuit PS, a primary circuit in which the triac 101 and the relay are short-circuited so that a voltage of 120 V is directly input to the heater 203 is manufactured. Connect to an outlet not shown. At this time, since the resistance value of the heating resistor 203b of the heater 203 is 15Ω, 960 W of power is input to the heater 203. This primary circuit is directly connected to the heater 203 of the fixing device C of the image forming apparatus, and it is measured how long a heater crack occurs after the power supply is connected.

  Furthermore, the thermal fuse 205 was disconnected from the primary circuit. A separate low-voltage power supply is prepared, a voltage of several volts is applied to the thermal fuse 205, and the current flowing through the thermal fuse 205 is monitored. When the thermal fuse 205 is blown, the current from the low voltage power source is cut off. For this reason, the time until the thermal fuse 205 operates by measuring the time until the current flowing through the thermal fuse 205 is cut off by simultaneously applying the primary current and energizing the thermal fuse 205 from the low-voltage power supply. Can also be measured separately. This makes it possible to verify whether or not the thermal fuse 205 is surely blown before the heater 203 cracks when an abnormal temperature rise occurs in the heater 203 due to a failure of the primary circuit during actual use.

When the forced abnormal temperature rise test was performed once for each applied pressure, the thermal fuse 205 operated before the heater 203 cracked in any of the tests. At this time, Table 1 shows the results of measuring the time from the start of energization to the heater 203 to the operation of the thermal fuse 205 and the time that the heater 203 breaks.
(Table 1)

  The thermal fuse 205 operates in the order of 7 seconds at any applied pressure. On the other hand, the heater cracking time was shorter as the applied pressure increased. Even at the pressure 220N with the shortest heater cracking time, the thermal fuse 205 was operated before the heater 203 cracked.

  The melting point of PPS used for the fuse holder 209 is 290 ° C., and the melting point of SUS used for the fuse stay 208 is about 1400 ° C. The thermal fuse 205 used in this example operates at 228 ° C., but under the condition where the temperature is rapidly increased with the maximum power as in this test, the temperature of the fuse holder protrusion 209a is transiently above the temperature fuse operating temperature. As the temperature rises, the fuse holder protrusion 209a melts and deforms. In the present embodiment, the fuse stay 208 shields the molten resin and maintains the shape of the temperature fuse 205 support portion, so that the temperature rise of the temperature fuse 205 is not hindered and the energization to the heater 203 is quickly cut off. It became possible.

Assuming the state of the fuse stay 208 and the fuse holder 209 during the operation of the thermal fuse 205, the heater 203 was energized with a power of 960 W for 8.0 seconds using the fixing device of this embodiment. When the fixing device after the energization was disassembled and investigated, the shape of the fuse stay 208 after the energization did not change, and the molten resin was shielded by the fuse stay 208, and the contact area for supporting the thermal fuse 205 was before the energization. Was maintained. Therefore, the fixing device of this embodiment operates the thermal fuse 205 quickly by maintaining the shape of the thermal fuse 205 support portion while shielding the molten resin by the fuse stay 208, and the heater at the time of abnormal temperature rise It can be seen that cracking can be avoided.

(Comparative example)
The fixing device of the comparative example with respect to the present embodiment has a configuration in which the fuse stay 208 is removed from the configuration of the fixing device of the present embodiment. That is, in the fixing device of the comparative example, the thermal fuse 205 is sandwiched between the protrusion 209 a provided in the fuse holder 209 and the back surface of the heater 203. Except for this configuration, the fixing device of the comparative example has the same configuration as the fixing device C of the present embodiment.

Using the fixing device of the comparative example, an abnormal temperature increase test at each applied pressure was performed once. As a result, although the thermal fuse 205 operated before the heater 203 cracked at the applied pressures 180N and 200N, the heater 203 cracked before the thermal fuse 205 operated at 220N. Table 2 shows the results of measuring the time from the start of energization to the heater 203 to the time when the thermal fuse 205 is blown, and the time that the heater 203 breaks. (Table 2)

  Although the time until the heater cracked at the pressure 220N was 9.9 seconds, which was not significantly different from that of the fixing device C of this embodiment, the time until the thermal fuse 205 was operated was 10.5 seconds. Results were slower than 7.7 seconds of composition.

  The reason why the operating time of the thermal fuse 205 is delayed in the comparative example as compared with the present embodiment is that the protrusion 209a is melted and deformed to increase the contact area with the surface of the thermal fuse 205. As in this example, using the fixing device of this comparative example, the heater 203 was energized with 960 W of power for 8.0 seconds to conduct a disassembly investigation. In the fixing device of this comparative example, the protruding portion 209a was melted and deformed, the metal housing portion of the thermal fuse 205 was buried in the protruding portion 209a by about 1 mm, and about 30% of the surface area was in contact with the molten resin. By increasing the contact area with the surface of the thermal fuse 205, the heat of the thermal fuse 205 is diffused and the temperature rise is inhibited, and the operation of the thermal fuse 205 is delayed. For this reason, in the fixing device of this comparative example, if the pressure is set to 220 N, heater cracking occurs when the temperature rises abnormally. Therefore, it is desirable to set a smaller pressure, that is, it is difficult to set a large pressure. I understand that. Therefore, it is difficult to increase the nip portion and increase the speed of the fixing process.

  As described above, in the fixing device C of the present embodiment, the fuse stay 208 sandwiched between the thermal fuse 205 and the fuse holder 209 shields the molten resin in the fuse holder 209 from the thermal fuse 205 when the temperature rises abnormally. . As a result, the shape of the support portion of the thermal fuse 205 is maintained and the heat of the thermal fuse 205 is suppressed from diffusing to other components, so that the temperature rise of the thermal fuse 205 can be accelerated. Since the temperature fuse 205 is heated quickly, the power supply to the heater 203 can be cut off earlier, and even when the pressure applied to the fixing nip N is large, cracking of the heater can be avoided, and the high speed of the image forming apparatus can be avoided. Can be achieved. The temperature sensitive element used in the present invention is not limited to the above thermal fuse, and other elements may be used as long as they can exhibit an equivalent function. Further, in this embodiment, a spring-like pressurizing spring is used as an urging member for generating an urging force that presses the temperature-sensitive element against the heater. May be used.

[Example 2]
(2-1) Fixing device (image heating device) C
A second embodiment of the present invention will be described with reference to FIGS. In this embodiment, the shapes of the fuse stay 308 and the fuse holder 309 are different from those of the fuse stay 208 and the fuse holder 209 of the first embodiment. Other configurations are the same as those in the first embodiment, and the same components are denoted by the same reference numerals and the description thereof is omitted.

FIG. 8 is a perspective view of members disposed inside the fixing film 201 in the fixing device C according to the second embodiment. FIG. 9 is a longitudinal view of the configuration near the position where the thermal fuse 205 is disposed in the fixing device C according to the second embodiment. It is the typical sectional view cut in the direction. The fuse stay 3 08 in this embodiment is formed into a U-shape in which a sheet metal having a thickness of 0.3 mm, a width of 6 mm, and a length of 10 mm is bent perpendicularly in the direction opposite to the pressing direction at the positions of the longitudinal end portions of 2 mm. Has been. In the fuse holder 309 in this embodiment, the protrusion 209a that supports the fuse stay 308 in the fuse pressing direction is not provided, and the protrusion 309b that supports the fuse stay 308 in the longitudinal direction is provided as the second protrusion. The protrusions 309b abut against the special surfaces of both end portions (third projecting portions) of the fuse stay 308 so as to restrict movement of the fuse stay 308 in the longitudinal direction (direction orthogonal to the pressing direction). Similar to the first embodiment, the thermal fuse 205 is fitted into the hole 204c2 of the heater holder 204, and is pressed and held by the pressure spring 210 through the fuse holder 309 and the fuse stay 308 toward the heater 203.

  The fuse holder 309 is pressed toward the heater 203 by the pressure spring 210 supported by the metal stay 211. In this embodiment, the fuse holder 309 supports the fuse stay end surface 308a (the tip of the third protrusion) with the fuse holder flat surface portion 309c. The pressing force by the pressure spring 210 is transmitted from the fuse holder flat surface portion 309c to the fuse stay end surface 308a, and the fuse stay flat surface portion 308b presses the thermal fuse 205 against the back surface of the heater 203. At this time, a gap G is formed on the back surface (fuse holder 309 side) of the fuse stay flat portion 308b.

  In this embodiment, the heat diffused from the thermal fuse 205 to the fuse holder 309 via the fuse stay 308 at the time of abnormal temperature rise is reduced. The heat of the thermal fuse 205 is transmitted to the fuse stay flat portion 308b, and is transmitted from the fuse stay end surface 308a to the fuse holder 309. Further, the heat transferred from the fuse stay 308 to the fuse holder 309 is easily transferred between the flat portion 309c having a larger pressing force and lower contact thermal resistance than the side surface of the fuse holder protrusion 309b. Therefore, it is desirable that the contact portion between the fuse stay 308 and the fuse holder 309 is separated (separated) from the contact portion between the thermal fuse 205, which is a heat source, and the fuse stay 308, and has a small pressing contact area.

  The fuse stay 308 in this embodiment forms a gap G to isolate the flat portion 308 b that is a contact portion with the thermal fuse 205 from the fuse holder 309. Further, the contact area with the fuse holder 309 is minimized by using the end surface 308a as the pressing contact portion with the fuse holder 309. In addition, the fuse stay flat surface portion 308b forms a continuous surface, covers the fuse holder protrusion 309b on the back surface, and plays a role of preventing the fuse 205 from coming into contact with the fuse holder 309 when it melts.

(2-2) Forced Abnormal Temperature Raising Test of Fixing Device C What behavior the fixing device C of this embodiment shows when it is in an abnormal temperature rising state is determined by the same method as in Example 1 A temperature rise test was conducted. Three pressure levels of 200N, 220N, and 250N were prepared for forming the fixing nip N, and an abnormal temperature rise test was performed at each pressure force.

When the forced abnormal temperature rise test was performed once for each applied pressure, the thermal fuse 205 operated before the heater 203 cracked in any of the tests. Table 3 shows the results of measuring the time from the start of energization to the heater 203 until the thermal fuse 205 is blown, and the time that the heater 203 is broken.
(Table 3)

  Although the heater cracking time was accelerated to 8.2 seconds at a pressurizing pressure of 250 N, the thermal fuse 205 operated in the range of 6 seconds at any pressurizing force. In this embodiment, it is possible to operate the thermal fuse 205 earlier than the first embodiment by reducing the diffusion of the heat of the thermal fuse 205 to the fuse holder 309.

  The fuse stay 308 in this embodiment forms a gap G between the fuse holder 309 and the flat portion 308 b that is a contact portion with the thermal fuse 205 is isolated from the fuse holder 309. Thereby, the thermal diffusion from the back surface of the fuse stay flat portion 308b to the fuse holder 309 is suppressed. Further, the area of the pressing contact portion is minimized by contacting the fuse holder 309 with the end face 308a. Thereby, the heat transmitted from the fuse stay flat surface portion 308b in the longitudinal direction is suppressed from being transmitted and diffused at the contact portion with the fuse holder flat surface portion 309c. As a result, it is possible to prevent the heat of the thermal fuse 205 from diffusing into the fuse holder 309 and promote the temperature rise of the thermal fuse 205. For this reason, in the fixing device of the present embodiment, even in the configuration of the pressure force 250N that is the strictest against cracking of the heater 203, the thermal fuse 205 operates before the heater 203 breaks, and the heater cracking can be avoided. Recognize.

  As described above, in the fixing device C of this embodiment, the gap G is provided between the back surface of the fuse stay flat portion 308 b that supports the thermal fuse 205 and the fuse holder 309. By providing the gap G and reducing the contact area between the back surface of the fuse stay flat portion 308 b and the fuse holder 309, it is possible to reduce the diffusion of heat from the thermal fuse 205 to the fuse holder 309. In this embodiment, the thermal diffusion of the thermal fuse 205 is further reduced, and the time until the thermal fuse 205 is operated is shortened, so that the heater cracks also in the fixing device that forms the fixing nip N with a larger applied pressure. It is possible to avoid it.

  In addition, you may combine each structure of said each Example as much as possible.

  DESCRIPTION OF SYMBOLS 201 ... Fixing film, 202 ... Pressure roller (pressure member), 203 ... Heater, 204 ... Heater holder, 205 ... Thermal fuse (temperature sensing element), 208 ... Fuse stay (first support member), 209 ... Fuse holder ( (Second support member), 210 ... fuse spring (biasing member)

Claims (11)

An image heating apparatus for heating a toner image formed on a recording material,
A tubular film,
A pressure member in contact with the outer surface of the film;
A heater that generates heat by feeding power, and contacts the inner surface of the film, and is pressed against the pressure member via the film, whereby the recording material is sandwiched and conveyed between the film and the pressure member. A heater for forming a nip portion,
A temperature sensing element that shuts off power supply to the heater when the temperature of the heater reaches a predetermined abnormal temperature;
A first support member for supporting the temperature sensitive element;
A second support member for supporting the first support member;
An urging member that presses the second support member to press the temperature sensitive element toward the heater;
With
The first support member is made of a material having a higher melting point than the second support member , and when viewed from the pressing direction in which the temperature sensing element is pressed against the heater, the first support member is an image heating apparatus characterized by greater than the contact portion that contacts the first support member of the second support member. The first support member is made of metal,
The image heating apparatus according to claim 1, wherein the second support member is made of resin. Said first support member, before Ki押 when viewed from pressure direction, An apparatus according to claim 1 or 2 characterized in that it is a large plate-shaped member than the contact portion. Said contact portion, said when viewed from the pressing direction, An apparatus according to any one of claims 1 to 3, the total area is equal to or in contact with the first support member. Said first support member, Oite between a plurality of the contact portions, according to any one of claims 1 to 3, characterized in that it has a separating portion for separating from the second supporting member Image heating device. Said first support member has a front first protrusion protruding in Ki押 pressure direction, claim 1, characterized in that for pressing the temperature sensitive device to the heater by the first projecting portion The image heating apparatus according to any one of 5 . Said first support member, An apparatus according to claim 3 or 4, wherein the is a plate-like member having a first protrusion which is configured by bending in a convex shape in the pressing direction. The contact portion, An apparatus according to any one of claims 1 to 7, characterized in that a second protrusion protruding in front Ki押 pressure direction in the second support member. The image heating apparatus according to claim 8 , wherein a tip of the second projecting portion is in contact with the first support member in the pressing direction. Said first support member has a front third protrusion protruding in a direction opposite to the Ki押 pressure direction, claims, characterized in that it is pressed by the second supporting member at the distal end of the third projecting portion Item 4. The image heating apparatus according to any one of Items 1 to 3 . The image heating apparatus according to claim 10 , wherein the third projecting portion abuts on the contact portion in a direction orthogonal to the pressing direction.