JP2009063815A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image heating device reducing nonuniform heat generation in a widthwise cross-section perpendicular to the lengthwise direction of a substrate in a heater in which the entire narrow long substrate generates heat by supply of electric power. <P>SOLUTION: The image heating device includes: the heater 1 which generates heat by supply of power; power supply members 3a and 3b for supplying power to the heater; a back-up member 40 which forms a nip part N together with the heater. The image heater heats an image t held on a recording material P in the nip part. This heater 2 has the substrate 2 which is a narrow, long substrate formed along the lengthwise direction of the backup member and generates heat over the entire substrate by supply of power. The substrate is made of a material with the characteristic in which a resistance decreases as the temperature of the heat generated in the substrate increases, so as to extend to the outside of both the lengthwise ends of the back-up member. The power supply members are disposed in contact with the substrate on the outside of both the lengthwise ends of the back-up member. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  As an image heating device (fixing device) mounted on an image forming apparatus such as an electrophotographic copying machine or a printer, there is a film heating type. A film heating type fixing device includes a heater having a heating element on a ceramic substrate, a flexible member that moves while contacting the heater, and a heater and a nip portion that are formed via the flexible member. And a pressure roller. The recording material carrying the unfixed toner image is heated while being nipped and conveyed by the nip portion of the fixing device, whereby the toner image on the recording material is heated and fixed on the recording material. This fixing device has an advantage that it takes a short time to start energizing the heater and raise the temperature to a fixable temperature. Therefore, the printer equipped with this fixing device can shorten the time (FPOT: First Print Out Time) until the first image is output after the print command is input. In addition, this fixing device has an advantage that power consumption during standby waiting for a print command is small.

  By the way, when a small-sized recording material is continuously printed at the same print interval as a large-sized recording material with a printer equipped with a fixing device using a flexible member, the area where the recording material of the heater does not pass (non-sheet passing area) Is known to overheat. If the non-sheet passing area of the heater is excessively heated, the holder and the pressure roller that hold the heater may be damaged by heat. Therefore, a printer equipped with a fixing device that forms a fixing nip portion with a heater and a pressure roller through a flexible member, when continuously printing on a small size recording material, when printing continuously on a large size recording material Control is performed to widen the print interval. Thereby, the excessive temperature rise in the non-sheet passing area of the heater is suppressed.

  Therefore, as a heater used in the above-described fixing device, a resistance temperature characteristic having a resistance temperature coefficient (NTC: Negative Temperature Coefficient) in which the resistance value decreases as the temperature rises is considered. If the heater has NTC characteristics, the resistance value of the non-sheet passing area is lowered even if the non-sheet passing area is excessively heated, so that excessive temperature rise in the non-sheet passing area, that is, so-called non-sheet passing portion temperature increase can be suppressed. This is the idea.

  In a heater having a heating element on a ceramic substrate, a heater can be obtained by screen-printing a paste-like electric resistor having NTC characteristics on the ceramic substrate as a heating element and performing a firing process (patent) Reference 1).

On the other hand, a heating element having NTC characteristics generally has high resistance, and cannot take advantage of the above-described fixing device, which requires a short time to start energizing the heater and raise the temperature to a fixable temperature. . Therefore, a material having NTC characteristics may be used after being processed into a long and narrow substrate shape. Patent Document 2 describes a carbon heater. In this way, by using a material having NTC characteristics in a bulk state, the total resistance as a heater can be reduced, and the rise to the fixable temperature and the rise of the non-sheet passing portion at the time of small size continuous printing are possible. It becomes possible to achieve both temperature suppression.
JP 06-019347 A JP 2006-154802 A

  A bulk heater in which a long and narrow substrate is integrally formed of a material having NTC characteristics is provided in the fixing device, and power is supplied to both ends in the longitudinal direction of the substrate. In that case, heat generation unevenness is more likely to occur in the cross section in the short direction of the substrate than when the fixing device is provided with a bulk heater in which an elongated substrate is integrally formed of a material having PTC characteristics.

  The bulk heater with PTC characteristics increases the resistance of the heat generating part in the substrate and suppresses the heat generation, and the current flows to the part where the temperature is low and the resistance is low. become.

  On the other hand, a bulk heater having an NTC characteristic has a tendency that when the substrate generates heat, the resistance of the heated portion decreases and the portion where the resistance decreases further tends to generate heat. It is hard to become like. In particular, the shortest distance between the electrodes in the longitudinal direction of the substrate is most likely to generate heat, and other short cross-sectional portions of the substrate are less likely to generate heat. As a result, even if the heat generation unevenness of the substrate, especially when the heat generation unevenness in the recording material conveyance direction, that is, the heat generation unevenness of the cross section in the short direction of the substrate is large, the stress stress of the substrate is increased by the increase of the thermal stress on the substrate May occur.

  Therefore, in the NTC characteristic bulk heater, if the width in the short direction of the substrate is widened in order to suppress the occurrence of stress breakdown of the substrate, the region corresponding to the entire recording material conveyance width in the longitudinal direction of the substrate does not generate sufficient heat. For this reason, the amount of heat transferred to the recording material does not increase, and the effect of improving the heat fixing property cannot be obtained sufficiently, which causes the fixing failure of the unfixed toner image.

  An object of the present invention is to provide an image heating apparatus capable of reducing heat generation unevenness in a cross-sectional portion in a short direction perpendicular to the longitudinal direction of a substrate in a heater that generates heat by energizing the entire elongated substrate.

  A configuration for achieving the above object includes a heater that generates heat when energized, a power supply member that energizes the heater, and a backup member that forms a nip portion together with the heater, and a recording material is carried by the nip portion. In the image heating apparatus for heating an image to be heated, the heater is an elongated substrate formed along the longitudinal direction of the backup member, and the substrate has a substrate that generates heat when energized. It is formed to the outside of both ends in the longitudinal direction of the backup member by a material whose resistance decreases as the heating temperature of the substrate rises, and the power supply member is connected to the substrate outside the both ends of the backup member in the longitudinal direction. It is characterized by being in contact.

  In addition, a configuration for achieving the above object includes a heater that generates heat when energized, a power supply member that energizes the heater, a flexible member that moves while being in contact with the heater, and the flexible member. An image heating apparatus that includes the heater and a backup member that forms a nip portion, and heats an image while sandwiching and conveying a recording material that carries an image at the nip portion, wherein the heater is a longitudinal direction of the backup member And the substrate is such that the entire substrate generates heat when energized, and the backup member is made of a material whose resistance decreases as the heating temperature of the substrate increases. The power supply member is in contact with the substrate outside the both ends in the longitudinal direction of the backup member.

  ADVANTAGE OF THE INVENTION According to this invention, the image heating apparatus which can reduce the heat_generation | fever unevenness of the cross-sectional part of the transversal direction orthogonal to the longitudinal direction of a board | substrate in the heater which the whole elongate board | substrate generates heat | fever by electricity supply can be provided.

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

[Example 1]
Hereinafter, the present invention will be described in detail with reference to the drawings.

(1) Example of Image Forming Apparatus FIG. 1 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 an image heating fixing apparatus (fixing device). This image forming apparatus is an electrophotographic laser beam printer.

  Reference numeral 11 denotes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. For example, an organic photosensitive drum in which a photosensitive layer such as an organic photoconductor is formed on the outer peripheral surface of a conductive drum base such as aluminum.

  Reference numeral 12 denotes a charging roller as charging means. The charging roller 12 uniformly charges the outer peripheral surface (surface) of the photosensitive drum to a predetermined polarity and potential.

  Reference numeral 10 denotes a laser exposure apparatus. The laser exposure apparatus 10 outputs a laser beam L modulated in accordance with image information input from an external device such as an image scanner or a computer (not shown). This laser beam scans and exposes the uniformly charged surface on the surface of the photosensitive drum 11. This scanning exposure attenuates or eliminates the charge in the exposed bright portion of the photosensitive drum surface, and an electrostatic latent image corresponding to the image information is formed on the photosensitive drum surface.

  Reference numeral 13 denotes a developing device as developing means. The developing device 13 includes a developing roller 13a. The roller 13a visualizes the electrostatic latent image on the surface of the photosensitive drum 11 as a toner image (developed image) with toner (developer).

  Reference numeral 17 denotes a paper feed cassette in which recording materials (transfer materials) P are stacked and stored. Based on the paper feed start signal, the paper feed roller 18 is rotated and the recording materials P in the paper feed cassette 17 are separated and fed one by one. The fed recording material P is conveyed to a registration roller pair 21 through a sheet path 20 by a conveyance roller 19. Then, the registration roller pair 21 is introduced into the transfer portion T, which is a contact nip portion between the photosensitive drum 11 and the transfer roller 16, at a predetermined control timing.

  The recording material P introduced into the transfer portion T is nipped and conveyed by the transfer portion T, and during that time, the toner image on the surface of the photosensitive drum 11 is electrostatically transferred sequentially onto the recording material P surface by the transfer roller 16.

  The recording material P that has received the transfer of the toner image at the transfer portion T is separated from the surface of the photosensitive drum 11 and then conveyed to the fixing device 22 where it undergoes a heat fixing process for the toner image.

  On the other hand, the surface of the photosensitive drum 11 after separation of the recording material (after transfer of the toner image to the recording material) is cleaned by the cleaning blade 14a of the cleaning device 14 to remove the adhering matter such as residual toner and paper dust, and repeatedly To be used for image formation.

  The recording material P that has passed through the fixing device 22 is sent to the paper discharge roller 24 by the transport roller 23. The paper is discharged onto a paper discharge tray 25 on the upper surface of the printer by the paper discharge roller 24.

  The printer according to the present embodiment includes a process cartridge 15 that can be attached to and detached from the printer body in a batch with respect to four process devices including a photosensitive drum 11, a charging roller 12, a developing device 13, and a cleaning device 14. It is configured as.

(2) Fixing device (image heating device) 22
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 length is a dimension in the longitudinal direction. The width is a dimension in the short direction.

  FIG. 2 is a cross-sectional configuration model diagram of an example of the fixing device 22. FIG. 3 is a longitudinal sectional configuration model diagram of the fixing device 22. FIG. 4 is a view of the fixing device 22 as viewed from the recording material introduction side. The fixing device 22 is a tensionless type film heating type image heating device disclosed in Japanese Patent Application Laid-Open Nos. 4-44075 to 44083, Japanese Patent Application Laid-Open No. 4-20420 to 204984, and the like.

  The tensionless type film heating type image heating apparatus uses an endless belt-shaped or cylindrical heat-resistant film as a flexible member. The film is an apparatus in which at least a part of the circumference of the film is always tension free, and the film is rotationally driven by the rotational driving force of the pressure member.

  Reference numeral 32 denotes a stay as a heating body supporting member / film guide member. This stay 32 is a horizontally long rigid member made of heat-resistant resin that is long in the longitudinal direction, and is formed in a substantially semicircular saddle shape in cross section. In this embodiment, a highly heat-resistant liquid crystal polymer is used as the material (material) of the stay 32. Both ends of the stay 32 are held by side plates of an apparatus frame (not shown).

  Reference numeral 1 denotes a heater as a heating body, which is fitted in a groove 32 a provided on the lower surface of the stay 32 along the longitudinal direction of the stay 32. The heater 1 will be described in detail in the next section (3).

  Reference numeral 33 denotes a cylindrical film having excellent heat resistance as a flexible member. The film 33 is loosely fitted on the outer periphery of the stay 32. The film 33 has a total thickness of about 100 μm or less in order to reduce the heat capacity and improve the quick start property. As a specific example of the film 33, a single layer of PTFE, PFA, FEP having heat resistance, releasability, strength, durability and the like can be used. Alternatively, a composite layer film in which PTFE, PFA, FEP or the like is coated on the outer peripheral surface of polyimide, polyamideimide, PEEK, PES, PPS or the like can be used. In this example, a film having a thickness of 60 μm obtained by coating a 10 μm thick PTFE on a 50 μm thick polyimide film was used as the film 33. The inner peripheral surface side of the film 33 is coated with grease in order to improve slidability.

  Reference numeral 40 denotes an elastic pressure roller as a backup member. The pressure roller 40 has an insulating property such as a silicone solid rubber or a silicone sponge rubber as an elastic layer on a metal shaft 41 made of a metal such as iron or aluminum, or a conductivity obtained by dispersing a conductive agent. The elastic layer 42 is formed. A fluororesin layer is formed thereon as the release layer 43. The pressure roller 40 is a horizontally long member that is long in the longitudinal direction, and both longitudinal ends of the cored bar 41 are rotatably held on the side plate of the apparatus frame via bearing members (not shown). . The pressure roller 40 is pressed by a pressure spring (not shown) so that the outer peripheral surface (surface) of the pressure roller 40 is in contact with the outer peripheral surface (surface) of the film 33 with a pressure of about 127 N (13 kgf). Has been. That is, a predetermined pressure is applied between the heater 1 and the pressure roller 40 (precisely between the stay 32 holding the heater 1 and the pressure roller 40), so that the space between the heater 1 and the pressure roller 40 is increased. A nip portion (fixing nip portion) N having a predetermined width is formed with the film 33 interposed therebetween. That is, the pressure roller as a backup member forms a nip portion together with the heater 1. The dimensions of the elastic layer 42 of the pressure roller 40 are a length of 230 mm, an outer diameter of φ25, and a wall thickness of 3 mm.

  When the driving force of the rotation driving mechanism M is transmitted to the driving gear G provided at the end of the metal core 41 of the pressure roller 40, the pressure roller 40 is rotated at a predetermined peripheral speed in the arrow direction. Due to the rotation of the pressure roller 40, a rotational force acts on the film 33 by the frictional force between the surface of the pressure roller 40 and the surface of the film 33 at the nip portion N. The inner surface of the film 33 is in contact with the surface of the heater 1 (the surface of the substrate 2 described later) in the nip portion N and slides around the stay 32 in the direction of the arrow substantially the same as the rotational speed of the pressure roller 40. Followed by speed. The stay 32 also serves as a guide member for the film 33 that is driven to rotate.

  The recording material P carrying the toner image t between the film 33 and the pressure roller 40 in a state where the temperature of the heater 1 rises to a predetermined fixing temperature and the rotational peripheral speed of the film 33 is steady is fixed to the fixing inlet guide 45. Introduced along. Then, when the recording material P is nipped and conveyed together with the film 33 at the nip portion N, the heat of the heater 1 is applied to the recording material P through the film 33 and an unfixed toner image t on the recording material P is recorded. Heat-fixed on the surface of the material P. The recording material P that has passed through the nip portion N is separated from the surface of the film 33 and conveyed to the conveying roller 23.

(3) Heating body (heater) 1
5A is an explanatory diagram of the configuration of the heater 1, the temperature control system, the power supply members 3a and 3b, and the recording material conveyance reference, and FIG. 5B is a diagram illustrating the contact state between the substrate 2 of the heater 1 and the power supply member 3a. It is.

  The heater 1 has an elongated substrate 2 in the longitudinal direction. As the substrate 2, a conductive ceramic mainly composed of β-type (cubic) SiC was used. Specifically, manufactured by Bridgestone Corporation, trade name: Pure Beta-R, volume resistance value: about 0.1 Ω · cm by four-probe method, resistance temperature coefficient from around room temperature (25 ° C), substrate A material of −3000 ppm / K was used in the range up to 300 ° C., which is the maximum temperature reached. The dimensions of the substrate 2 are a thickness of 1 mm, a width of 6 mm, and a length of 250 mm. Accordingly, the substrate 2 is formed longer than the elastic layer 42 of the pressure roller 40 that forms the nip portion N with the pressure roller 40. That is, the substrate is formed up to the outside of the pressure roller as a backup member (outside from both end faces in the longitudinal direction of the pressure roller). Hereinafter, in the longitudinal direction of the substrate 2, a region outside the both end surfaces of the pressure roller 40 in the longitudinal direction of the substrate 2 is referred to as a heater longitudinal nip outer region.

  Reference numerals 3 a and 3 b denote power supply members held at both ends in the longitudinal direction of the stay 32. As the power supply members 3a and 3b, a bent SUS plate is brought into contact with the back surface of the substrate 2 opposite to the surface (film sliding surface) of the substrate 2 in the region outside the heater longitudinal nip. That is, the power supply member is in contact with the substrate at the outer sides in the longitudinal direction of the pressure roller as the backup member (outside the both ends in the longitudinal direction of the elastic layer).

  When the heater 1 is energized from the commercial power source (AC power source) 54 through the AC power source control circuit (triac) 53 to the power supply members 3a and 3b, the entire substrate 2 generates heat and quickly rises in temperature. That is, the heater 1 is energized through the path of the AC power source 54 → the power supply member 3 a → the substrate 2 → the power supply member 3 b, and the substrate 2 generates heat. A thermistor 50 as temperature detecting means is disposed on the back surface opposite to the front surface (film sliding surface) of the substrate 2. The thermistor 50 detects the temperature state of the heater 1. The temperature information of the thermistor 50 is taken into the control circuit (CPU) 52 as the control means through the A / D converter 51. The CPU 52 controls the power supply to the heater 1 by performing phase control, wave number control, etc. on the AC voltage supplied from the triac 53 to the heater 1 based on the temperature information from the thermistor 50, thereby controlling the heater 1 to a predetermined fixing temperature (target Temperature).

  Here, the paper width is a recording material dimension in a direction orthogonal to the recording material conveyance direction X on the surface of the recording material P. In the printer of this embodiment, the center in the width direction of the recording material is used as a transport reference, and the center in the longitudinal direction of the heater 1 of the fixing device 22 is a transport reference for recording materials P of various sizes. In FIG. 5A, O is the recording material conveyance reference line (virtual line). A is a sheet passing portion (maximum sheet passing area) of a recording material having a fixed maximum sheet width that can be used in this printer, and is equal to the length of the substrate 2 of the heater 1. B is a sheet passing portion (minimum sheet passing area) of a recording material having a fixed minimum sheet width that can be used in the printer. C is a non-sheet passing portion (non-sheet passing region) generated in the nip portion N in the longitudinal direction of the heater 1 when a recording material (small size paper) having a smaller paper width than the recording material having the maximum paper width is passed. The area width of the non-sheet passing portion C varies depending on the size of the sheet width of the small size sheet that has been passed.

  The thermistor 50 for detecting the temperature of the heater 1 is provided in a minimum sheet passing area that is a recording material passing area, that is, an area corresponding to the sheet passing portion B, regardless of whether a recording material having a large or small paper width is passed. Yes. The reason why SiC is used as the material (material) of the substrate 2 of the heater 1 is that the resistance value decreases as the temperature rises, that is, the NTC (Negative Temperature Coefficient) characteristic is used, and the non-sheet-passing portion C of the heater 1 is excessive. This is to suppress the temperature rise. Therefore, the substrate has a characteristic that the resistance decreases as the heating temperature of the substrate increases in a temperature range below the maximum substrate temperature.

  Next, the reason why the excessive temperature rise in the non-sheet passing portion C can be reduced by using the heater 1 made of the NTC characteristic substrate 2 will be described with reference to FIG.

FIG. 6 is a model diagram of the heater 1. When the current flowing through the heater substrate 2 is I, the resistance value of the sheet passing portion of the heater 1 is R1, and the resistance value of one side of the non-sheet passing portion is R2, the heating value W1 of the sheet passing portion is I ² · R1. The calorific value W2 of the non-sheet passing portion is I ² · R2. For the sake of simplicity, the position where R1 = 2 × R2 in a state where the recording material P is not passed (introduced) into the nip portion N, that is, the length of the non-sheet passing portion (the length of the non-sheet passing portion on both sides). Let us consider dividing the paper passing portion and the non-paper passing portion at a position where (sum) is equal to the length of the paper passing portion. Here, in a state where the recording material P is not passed through the nip portion N, the resistance value per unit length of the substrate 2 is uniform throughout the heater 1.

  Consider a case where small-size paper is passed through a fixing device equipped with a heater formed by integrally molding a substrate having the same dimensions as the substrate 2 made of a material having PTC (Positive Temperature Coefficient) characteristics. Since the film heated by the heater comes into contact with the small size paper, the heat of the sheet passing portion is taken by the width of the small size paper. The temperature of the sheet passing portion is detected by a thermistor, and energization control is performed based on the temperature information of the thermistor so that the temperature of the sheet passing portion does not decrease. For this reason, the non-sheet passing portion where the heat is not taken away by the small size paper becomes higher in temperature than the sheet passing portion. In this case, since the resistance value per unit length of the non-sheet passing portion is higher than the resistance value per unit length of the sheet passing portion due to the PTC characteristic, the heat generation amount W2 of the non-sheet passing portion on one side is the sheet passing portion. It becomes larger than the calorific value W1. That is, the amount of heat generated per unit length of the non-sheet passing portion is larger than that of the sheet passing portion. Further, since the temperature rises as the heat generation amount increases, the resistance further increases and the heat generation amount further increases.

  On the other hand, in the heater 1 having the NTC characteristic as in this embodiment, when small-size paper is passed, the resistance value is lower when the temperature is higher, so the resistance value per unit length of the non-sheet passing portion. Becomes lower than the resistance value per unit length of the sheet passing portion. Therefore, the heat generation amount W2 of the non-sheet passing portion on one side is smaller than the heat generation amount W1 of the sheet passing portion. That is, the heat generation amount per unit length of the non-sheet passing portion is smaller than that of the sheet passing portion. For this reason, heat generation at the non-sheet passing portion can be suppressed as compared with a heater having PTC characteristics.

  For the reasons described above, the NTC characteristic heater 1 can keep the temperature of the non-sheet passing portion low when passing small size paper.

In this embodiment, the material of the substrate 2 of the heater 1 is a SiC sintered body. Although SiC differs depending on the firing conditions, generally it has a large negative resistance temperature coefficient at 400 ° C. or lower, so that the temperature rise of the non-sheet passing portion of the heater 1, so-called non-sheet passing portion temperature rise is greatly increased. Can be reduced. In addition to SiC, it is also possible to use other ceramic heating elements mainly composed of LaCrO ₃ or the like as the material of the substrate 2. In a bulk heater in which a substrate is integrally molded with such a ceramic heating element, the entire substrate can generate heat.

(4) Description of Heat Generation Unevenness FIG. 7 is an explanatory view of a fixing device of a comparative example for explaining the characteristic part of the fixing device 22 of this embodiment.

  The fixing device 22 shown in the comparative example has the same configuration as the fixing device 22 of this embodiment, except that the length of the elastic layer 42 of the pressure roller 40 is set to the same length as the length of the substrate 2 of the heater 1. It is as.

  In FIG. 7, (a) is an explanatory view of the longitudinal ends of the substrate 2 and the pressure roller 40 of the heater 1 and the power supply member 2a. (B) is a diagram showing the relationship between the longitudinal end of the substrate 2 of the heater 1 and the power supply member 2a. (C) is a figure showing the temperature distribution of the line AB cross section (cross section 1) of the longitudinal direction edge part of the board | substrate 2 of the heater 1 of (a). (D) is a figure showing the temperature distribution of the line CD cross section (cross section 2) of the longitudinal direction edge part of the board | substrate 2 of the heater 1 of (b).

  In the fixing device 22 of the comparative example, when paper is passed through the nip portion N and energization is performed between the power supply members 3a and 3b at both ends in the longitudinal direction of the substrate 2 of the heater 1, (c) and (d) The temperature distribution is as shown in section 1 and section 2, respectively. The temperature distributions shown in (c) and (d) are respectively started by a printer equipped with the fixing device 22 of the comparative example, and energized while the temperature of the substrate 2 of the heater 1 of the fixing device 22 is controlled, This is a temperature distribution measured immediately before the paper is passed through the nip portion N.

  The temperature distribution in the sectional view 1 is a result of measurement using thermocouples installed on the A-side surface (back surface) and the B-side surface (front surface) of the substrate 2, respectively. In the temperature distribution of the cross-sectional view 1, the temperature on the A side surface of the substrate 2 was observed to be higher than that on the B side surface.

  The temperature distribution in the sectional view 2 is a result of temperature measurement by thermocouples installed at five locations on the surface in the short direction of the substrate 2. In the temperature distribution of the sectional view 2, it can be seen that there is a heat generation peak in the region corresponding to the contact portion in contact with the power supply member 3 a in the short direction of the substrate 2, that is, in the central portion in the short direction of the substrate 2. However, it can be seen that heat is not sufficiently generated in the regions other than the both ends in the short direction of the substrate 2 and the region corresponding to the contact portion. This corresponds to a portion where a current flows as a result of a current flowing locally between the power supply members 3a and 3b at both ends in the longitudinal direction of the substrate 2 at the shortest distance (a contact portion in contact with the power supply member 3a). This is a phenomenon that occurs because only the (region) is generating heat.

  Thus, if only local heat generation occurs in the short direction of the substrate 2, that is, the recording material conveyance direction X, stress breakdown of the substrate 2 may occur due to an increase in thermal stress on the substrate 2 due to heat generation. . In addition, a reduction in the amount of heat transferred to the recording material P may cause a heat fixing defect of the toner image t. In order to prevent this, it is necessary to make the temperature distribution in the short direction of the substrate 2 in the nip portion N uniform.

  FIG. 8 is an explanatory diagram of a characteristic part of the fixing device 22 of this embodiment. 8A shows the length relationship between the substrate 2 of the heater 1 and the elastic layer 42 of the pressure roller 30, the temperature distribution in the longitudinal direction of the substrate 2 of the heater 1, and the longitudinal direction of the substrate 2 of the heater 1. It is a figure showing resistance distribution. (B) is a figure showing resistance distribution of the longitudinal direction of the board | substrate 2 of (a). (C) is a figure showing the temperature distribution of the longitudinal direction edge part of the board | substrate 2 of the heater 1 of (a). (D) is a figure showing the temperature distribution of the edge part of the transversal direction of the board | substrate 2 of the heater 1 of (a). (C) and (d) represent the temperature distribution measured on the substrate 2 at the same location and under the same conditions as the line AB cross section and the line CD cross section of FIG.

  As shown in FIG. 8A, the area outside the heater longitudinal nip of the substrate 2 (both ends in the longitudinal direction of the substrate 2, 10 mm each) is larger than the area inside the nip N. The elastic layer 42 does not exist. Accordingly, since the heat capacity of the area outside the heater longitudinal nip of the substrate 2 is small because the pressure roller 40 does not exist, the temperature of the substrate 2 becomes higher than that of the nip portion N. Actually, the temperatures of the area outside the heater longitudinal nip and the area inside the nip portion N of the substrate 2 were measured. As a result, the temperature in the region outside the heater longitudinal nip of the substrate 2 is about 200 to 300 ° C. with about 0 to 500 continuous sheets passing, and the substrate temperature in the region within the nip N of the substrate 2 during image heating. Was about 150 ° C. Since the substrate 2 has the NTC characteristic, the resistance at the location where the temperature is increased as shown in FIG. The resistance in the area outside the heater longitudinal nip of the substrate 2 is smaller than the resistance in the area in the nip portion N of the substrate 2. For this reason, the current supplied from the power supply members 3 a and 3 b is once diffused in the entire region in the short-side cross section in the region outside the heater longitudinal nip of the substrate 2 and then energized to the region in the nip N portion of the substrate 2. . As a result, as shown in FIGS. 8C and 8D, the temperature distribution can uniformly generate heat in the short direction of the substrate 2. Therefore, unevenness in heat generation in the short-side direction of the substrate in the region outside the nip portion N of the substrate 2 and the region in the nip N can be reduced.

[Example 2]
Another example of the fixing device according to the present invention will be described.

  FIG. 9 is an explanatory diagram of another example of the characteristic part of the fixing device 22 of the present embodiment.

  The fixing device 22 shown in the present embodiment is the same as that of the first embodiment except that the power supply members 3a and 3b are brought into contact with the longitudinal end faces 2a and 2b of the substrate 2 in the region outside the heater longitudinal nip of the substrate 2 of the heater 1. The configuration is the same as that of the fixing device 22.

[Example 3]
Another example of the fixing device according to the present invention will be described.

  FIG. 10 is an explanatory diagram of another example of the characteristic part of the fixing device 22 of the present embodiment.

  The fixing device 22 shown in the present embodiment has the same configuration as the fixing device 22 of the first embodiment, except that the power supply members 3a and 3b are brought into contact with the back surface of the substrate 2 in the heater longitudinal nip region of the substrate 2 of the heater 1. It is as.

[Example 4]
Another example of the fixing device according to the present invention will be described.

  FIG. 11 is an explanatory diagram of another example of the characteristic part of the fixing device 22 of the present embodiment.

  Also in each of the fixing devices 22 of Examples 2 to 4, the current supplied from the power supply members 3a and 3b is once diffused in the entire region in the short-side cross section in the region outside the heater longitudinal nip of the substrate 2, and then the substrate 2 The region in the nip portion N is energized. Therefore, the fixing devices 22 of the above-described Embodiments 2 to 4 can obtain the same operational effects as the fixing device 22 of the Embodiment 1.

  In each of the fixing devices 22 of Examples 1 to 4, the resistance temperature coefficient of the substrate 2 of the heater 1 is set to −3000 ppm / K in the temperature range from room temperature to the maximum substrate reaching temperature. The temperature coefficient is not particularly concerned. By comparison with other fixing devices (not shown) of the comparative example, if it is −1000 ppm / K, there is no uneven heat generation in the nip portion as well, and the same effects as those of the fixing devices 22 of the first to fourth embodiments are obtained. Is obtained. Therefore, it is preferable that the resistance temperature coefficient of the substrate 2 of the heater 1 is larger than −1000 ppm / K. Below this value, heat unevenness begins to occur slightly, but the same effect can be obtained. That is, the heater substrate only needs to have a negative resistance temperature coefficient of 1000 ppm / K or more in a temperature range below the maximum substrate temperature.

[Other]
1) In the first to fourth embodiments, the fixing device 22 having the configuration in which the nip portion N is formed by the heater 1 and the pressure roller 40 with the film 33 interposed therebetween is described. However, the fixing device 22 is not limited thereto. That is, as another example of the fixing device 22, a device having a configuration in which the nip portion N is formed by the heater 1 and the pressure roller 40 without providing the film 33 may be used. Even in the fixing device having such a configuration, the same operational effects as those of the fixing device 22 of each embodiment can be obtained.

  2) In each of the embodiments, the example in which the fixing device 22 is mounted on the printer that transports the recording material based on the central reference has been described. However, the fixing device 22 may be mounted on the printer that transports the recording material based on the one-side reference. .

  3) The image heating apparatus of the present invention is not limited to the heat fixing apparatus of each embodiment, but an image heating apparatus that heats a recording material carrying an image to improve surface properties such as gloss, an image heating apparatus that is supposed to be worn, It can be used as a means / apparatus for heat-treating a recording material carrying an image widely.

Configuration model diagram of an example of an image forming apparatus Cross-sectional configuration model diagram of an example of a fixing device according to Embodiment 1 Fig. 3 is a longitudinal sectional configuration model diagram of a fixing device according to the first embodiment. FIG. 3 is a diagram of the fixing device according to the first exemplary embodiment viewed from the recording material introduction side (A) is explanatory drawing of the structure of a heater, a temperature control system, a power feeding member, and a recording material conveyance reference | standard, (b) is a figure showing the contact state of the board | substrate of a heater and a power feeding member. Model diagram of heater Explanatory drawing of the fixing apparatus of the comparative example for demonstrating the characterizing part of the fixing apparatus which concerns on Example 1. FIG. Explanatory drawing of the characteristic part of the fixing apparatus which concerns on Example 1. FIG. Explanatory drawing of the characteristic part of the fixing apparatus which concerns on Example 2. FIG. Explanatory drawing of the characteristic part of the fixing device which concerns on Example 3. FIG. Explanatory drawing of the characteristic part of the fixing apparatus which concerns on Example 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heater, 2 ... Substrate, 3a, 3b ... Feeding member, 33 ... Film, 40 ... Elastic pressure roller, N ... Nip part, P ... Recording material

Claims (3)

In an image heating apparatus that has a heater that generates heat by energization, a power supply member that energizes the heater, and a backup member that forms a nip portion together with the heater, and heats an image carried by a recording material in the nip portion.
The heater is an elongated substrate formed along the longitudinal direction of the backup member, and has a substrate that generates heat as a whole when energized. The substrate increases with an increase in the heat generation temperature of the substrate. The image is characterized in that it is formed to the outside of both ends in the longitudinal direction of the backup member by a material having a characteristic of decreasing resistance, and the power supply member is in contact with the substrate outside the both ends in the longitudinal direction of the backup member. Heating device. A heater that generates heat when energized; a power supply member that energizes the heater; a flexible member that moves while in contact with the heater; a backup member that forms the nip and the heater across the flexible member; An image heating apparatus that heats an image while sandwiching and conveying a recording material that carries an image at the nip portion,
The heater is an elongated substrate formed along the longitudinal direction of the backup member, and has a substrate that generates heat as a whole when energized. The substrate increases with an increase in the heat generation temperature of the substrate. The image is characterized in that it is formed to the outside of both ends in the longitudinal direction of the backup member by a material having a characteristic of decreasing resistance, and the power supply member is in contact with the substrate outside the both ends in the longitudinal direction of the backup member. Heating device.   3. The image heating apparatus according to claim 1, wherein the substrate of the heater has a negative resistance temperature coefficient of 1000 ppm / K or more in a temperature range equal to or lower than a maximum substrate temperature.