JP2011145455A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure insulation between each of the side surfaces or edge portions in a short-length direction of a conductive substrate of a heating member and a conductive base layer of a flexible member, even when an insulating layer is provided only at the longitudinal center part of the conductive substrate of the heating member which comes in contact with the conductive base layer of the flexible member. <P>SOLUTION: The image heating device includes: the heating member including a long narrow substrate having properties to generate heat when energized, and reduce its resistance value in accordance with a temperature rise, an electrode part provided inside each longitudinal end portion of the substrate, for supplying power to the substrate, and the insulating layer provided at the longitudinal center part of the substrate; a supporting member configured to support the heating member; and the flexible member which moves while being in contact with the insulating layer and includes the conductive base layer which comes in contact with the insulating layer, wherein an image carried on a recording material is heated by heat of the heating member through the flexible member. Both end surfaces in the short-length direction perpendicular to the longitudinal direction of the substrate, on the surface, coming in contact with the flexible member, of the insulating layer are covered with the supporting member. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  As a fixing device (fixing device) mounted on an electrophotographic printer or copying machine, a heater having a heating resistor on a ceramic substrate, a heat-resistant film that moves while contacting the heater, and a heat-resistant film Some have a pressure roller that forms a nip with a heater. Patent Document 1 describes this type of fixing device. The recording material carrying the unfixed toner image is heated while being nipped and conveyed by the nip portion of the fixing device, whereby the toner image on the recording material is heated and fixed to 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, a printer equipped with this fixing device can shorten the time (FPOT: First Print Out Time) from when a print command is input until the first image is output. This type of fixing device also has an advantage that power consumption during standby waiting for a print command is small.

  On the other hand, with the increase in the speed of image forming apparatuses, fixing apparatuses using metals such as stainless steel and nickel as a base layer of a film member such as a heat resistant film have been proposed (Patent Documents 2 and 3). In order to adapt to the speeding up of the image forming apparatus, a metal having a higher thermal conductivity is used as the base layer of the film member in place of the conventional heat-resistant resin, and the heat conductivity of the film member is increased to increase the heater. The heat is transferred to the recording material more efficiently.

  By the way, when a small-size recording material is continuously printed at the same print interval as a large-size recording material in a printer equipped with a fixing device using a film member, an area where the recording material of the heater does not pass (non-sheet passing portion) is excessive. It is known that the temperature rises. 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 using a flexible member has a control for widening the print interval when continuously printing on a small size recording material, compared with the case of continuously printing on a large size recording material. The excessive temperature rise in the paper passing section is suppressed. However, the control to increase the print interval is to reduce the number of output sheets per unit time, and it is desired to suppress the number of output sheets per unit time of a small size recording material to be equal to or greater than that in the case of a large size recording material.

  In view of this, as a heater used in the above-described fixing device, a heater that uses a characteristic (NTC = Negative Temperature Coefficient) that decreases in resistance value due to an increase in temperature has been proposed. Patent Document 4 uses a semicircular rod member mainly composed of silicon carbide (SiC) as an energization heating element, and utilizes the negative resistance temperature characteristic (NTC characteristic) of silicon carbide to increase the temperature of the non-sheet passing portion. It is to suppress. Patent Document 5 discloses a method in which an energization heating element mainly composed of silicon carbide (SiC) is used, and power supply electrodes of a metal molded body are attached to both ends in the longitudinal direction of this member. This is to use the negative resistance temperature characteristic (NTC characteristic) of silicon carbide in the temperature range from room temperature to about 800 ° C. to suppress the temperature rise of the non-sheet passing portion.

JP-A-63-313182 JP 2003-045615 A JP 2003-156554 A JP 06-019347 A JP 2006-134746 A

  In the above-described film heating type fixing device, a conductive material is used as a material for the heating resistor provided on the insulating substrate of the heater. For this reason, in general, a protective layer such as resin or glass is provided on the surface of the heater that comes into contact with the conductive film member, and is insulated from the film member (slider that moves while the film member on the heater surface is in contact). The moving surface is configured to ensure insulation and slidability. On the other hand, when using silicon carbide having NTC characteristics as a heater material, in order to easily obtain a nip width and a desired resistance value, instead of providing a conductive thin film heating resistor on an insulating substrate, It is preferable to use silicon carbide itself as an elongated substrate. However, in this case, since the substrate (SiC) itself has conductivity, care must be taken to ensure insulation. In particular, when a conductive metal film or the like is used as the film member, not only the sliding surface with the substrate film but also the side surface in the short direction perpendicular to the longitudinal direction of the substrate or the side surface of the substrate is slid. A configuration is also required in consideration of ensuring insulation with the edge portion where the moving surface intersects. As a configuration for ensuring insulation from the film, a configuration in which a protective layer is provided so as to cover the entire side of the substrate including the side surface and edge portion of the substrate by coating or the like is considered. It is difficult to obtain a layer. Also, from the viewpoint of cost, coating on the side surface or edge portion of the substrate is not preferable.

  The object of the present invention is to provide a lateral side or edge portion in the short direction of the substrate even when an insulating layer is provided only in the longitudinal central portion of the conductive substrate of the heating member that contacts the conductive base layer of the flexible member. An object of the present invention is to provide an image heating apparatus capable of ensuring insulation from a base layer of a flexible member.

  In order to achieve the above object, a typical configuration of the image heating apparatus according to the present invention includes an elongated substrate having a characteristic that heat is generated by energization and a resistance value decreases as the temperature rises, and inside the longitudinal ends of the substrate. A heating member having an electrode portion for supplying power to the substrate and an insulating layer provided at a central portion in a longitudinal direction of the substrate; a support member for supporting the heating member; and the insulating layer A flexible member that moves in contact with the insulating layer and has a conductive base layer in contact with the insulating layer, and an image carried by a recording material is transmitted through the flexible member through the flexible member. In the image heating apparatus for heating with the heat of the substrate, both end surfaces in the short direction perpendicular to the longitudinal direction of the substrate on the surface of the insulating layer in contact with the flexible member are covered with the support member. .

  According to the present invention, even when an insulating layer is provided only in the longitudinal center of the conductive substrate of the heating member that contacts the conductive base layer of the flexible member, It is possible to provide an image heating apparatus that can ensure insulation from the base layer of the flexible member.

1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus. FIG. 2B is a schematic cross-sectional view of the fixing device, and FIG. (A) is the figure showing the back surface of a heater, (b) is the figure showing the surface of the heater. (C) is an enlarged sectional view taken along arrow CC in FIG. (A) is explanatory drawing showing the heat_generation | fever area | region of a heater, (b) is a model figure for demonstrating the emitted-heat amount of the paper passing part and non-sheet passing part in the heat_generation | fever area | region of a heater. (A) is a cross-sectional schematic diagram of the film guide and the heater supported by this film guide, (b) is another example of the film guide and a schematic cross-sectional view of the heater supported by this film guide. (A) is explanatory drawing of the deformation | transformation shape in the fixing nip part of a fixing film in case the overlap part is formed in the film guide. (B) is an explanatory view of a deformed shape in the fixing nip portion of the fixing film when the overlap portion is not formed on the film guide. (A) is a schematic cross-sectional view of the film guide of the comparative fixing device (1) and the heater supported by this film guide, and (b) is the film guide of the comparative fixing device (2) and supported by this film guide. It is a cross-sectional schematic diagram of the heater made. (A) is a cross-sectional schematic diagram of a film guide, a member attached to the film guide for supporting the heater on the film guide, and a heater supported on the film guide by this member, and (b) is a longitudinal center of the member. It is the external appearance perspective view which abbreviate | omitted the part.

[Example 1]
(1) Example of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as a fixing device. This image forming apparatus is an electrophotographic laser beam printer. This printer is a printer compatible with A4 portrait and LTR portrait paper, and the print speed is 50 sheets / minute. The recording material conveyance reference of this printer is defined as the approximate center of the recording material conveyance path (sheet path) in the direction (longitudinal direction) orthogonal to the recording material conveyance direction and the approximate center between the ends of the recording material in this direction. This is the central transport standard for transporting in a consistent manner.

  In the printer shown in the first embodiment, the control unit (control unit) 50 executes a predetermined image formation control sequence in accordance with a print command output from an external device (not shown) such as a host computer, and this image formation control. A predetermined image forming operation is performed according to the sequence. The control unit 50 includes a CPU and a memory such as a ROM and a RAM, and stores an image formation control sequence and various programs necessary for image formation.

  The printer according to the first exemplary embodiment includes an image forming unit that forms an image on a recording material, and a fixing unit (hereinafter, a fixing device) that heat-fixes an image carried by the recording material on the recording material. . When the image forming sequence is executed, in the image forming unit, first, a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier is set to a predetermined peripheral speed (process speed) in the direction of the arrow. Is rotated. The photosensitive drum 1 has a cylindrical drum base formed of aluminum, nickel, or the like, and a photosensitive material layer such as OPC, amorphous Se, or amorphous Si is formed on the outer peripheral surface of the drum base. . The outer peripheral surface (surface) of the photosensitive drum 1 on which the photosensitive material layer is formed is uniformly charged to a predetermined polarity and potential by a charging roller 2 as a charging unit. A laser beam scanner 3 as an exposure unit scans and exposes a charged surface on the surface of the photosensitive drum 1 with a laser beam L that is modulated (ON / OFF controlled) in accordance with image information. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1. This latent image is developed and visualized using the toner t by the developing device 4 as a developing means.

  On the other hand, the recording materials P stacked and stored in the feeding cassette 9 are fed out one by one by the rotation of the feeding roller 8. The recording material P is conveyed to a registration roller 11 through a sheet path having a guide 10. The registration roller 11 feeds the recording material P to the transfer nip TN between the surface of the photosensitive drum 1 and the outer peripheral surface (surface) of the transfer roller 5 at a predetermined timing. The recording material P is nipped and conveyed by the surface of the photosensitive drum 1 and the surface of the transfer roller 5 at the transfer nip portion TN. Then, the toner image on the surface of the photosensitive drum 1 is transferred onto the surface of the recording material P by the transfer bias applied to the transfer roller 5 during this conveyance process. As a result, the recording material P carries an unfixed toner image. The recording material P carrying the toner image is sequentially separated from the surface of the photosensitive drum 1 and discharged from the transfer nip portion TN. Through the conveyance guide 12, a flexible film 23 and a pressure roller (described later) of the fixing device (fixing device) 6 are used. 24 is introduced into a fixing nip portion (nip portion) N. The recording material P is heated and fixed on the recording material P by receiving heat and pressure while being nipped and conveyed by the flexible film 23 and the pressure roller 24 at the fixing nip portion N. The recording material P exiting the fixing device 6 is conveyed by the conveying roller 13 to the discharge roller 15 through the sheet path having the guide 14. The paper is discharged to a discharge tray 16 by the discharge roller 15. The surface of the photosensitive drum 1 after the transfer of the toner image is removed from the transfer residual toner remaining on the surface of the photosensitive drum 1 by a cleaning device 7 as a cleaning unit, and is used for the next image formation.

  The feeding cassette 9 has a movable regulation guide (not shown) for loading and storing various recording materials P of different sizes inside the feeding cassette 9. The user displaces the regulation guide according to the size of the recording material P, and loads and stores the recording material P in the feeding cassette 5. Accordingly, various types of recording materials P having different sizes can be sent out from the feeding cassette 9 on the basis of the central conveyance reference.

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

  2A is a schematic cross-sectional view of the fixing device, and FIG. 2B is a schematic vertical cross-sectional view of the fixing device. This fixing device is a film heating type fixing device. The fixing device 6 shown in the first embodiment includes a film guide (support member) 21, a heater (heating member) 22, a heat resistant film (flexible member) 23, a pressure roller (backup member) 24, and the like. Have. The film guide 21, the heater 22, the heat resistant film (hereinafter referred to as a fixing film) 23, and the pressure roller 24 are all members that are long in the longitudinal direction. The length of each member is longer than the longitudinal width of the maximum size recording material P used in the image forming apparatus. The configuration of each member will be described below.

3A is a view showing the back surface of the heater, and FIG. 3B is a view showing the surface of the heater. (C) is an enlarged sectional view taken along arrow CC in FIG. The heater 22 has an elongated plate-like heater substrate (hereinafter referred to as a substrate) 22a having a rectangular cross section having a characteristic (NTC characteristic) that generates heat when energized and the resistance value decreases as the temperature increases. The substrate 22a is a low heat capacity heat generation substrate mainly composed of a ceramic resistance heating element whose resistance is adjusted so that the substrate 22a itself generates heat when energized. Among the non-metallic heating elements such as silicon carbide (SiC), lanthanum chromite (LaCrO ₃ ), and carbon (C), the material of the substrate 22a has a temperature coefficient of resistance in the range of room temperature (25 ° C.) to 300 ° C. Those exhibiting negative characteristics are preferred. Of these, silicon carbide (SiC) is preferred because it is less affected by oxidation and the like, or industrially available. The material of the substrate 22a of the first embodiment is a silicon carbide heating element. In general, the resistivity of silicon carbide rapidly decreases in the temperature range of 800 ° C. or less as the temperature rises due to energization heat generation (NTC characteristics). The reason for this is said to be that since silicon carbide is a semiconductor, the number of conduction electrons that can be excited from the impurity level to the conductor increases as the temperature rises. The constituent material of the substrate 22a made of a silicon carbide heating element is not limited to the above. For example, as the silicon carbide heating element, a molded product obtained by processing a material having a trade name shown in the following a) and b) into a necessary shape may be used as the substrate 22a.

A): Made by Bridgestone Corporation, trade name: Pure Beta-R
Volume resistivity: About 1 × 10 ⁻¹ Ω · cm (25 ° C. environment) by the four-probe method
Resistance temperature coefficient: about −3000 ppm / ° C. in the range of room temperature (25 ° C.) to 225 ° C.
B): manufactured by Bridgestone Corporation, trade name: Pure Beta-R improved product volume resistivity: about 1 × 10 ⁻² Ω · cm (25 ° C. environment) by four-probe method
Resistance temperature coefficient: about −3000 ppm / ° C. in the range of room temperature (25 ° C.) to 225 ° C.
Here, the temperature coefficient of resistance in the substrate 22a of the first embodiment will be described. For the resistance temperature coefficient (TCR), the resistance value R1 in the 25 ° C. environment and the resistance value R 2 in the furnace 225 ° C. environment are measured for the resistance value between the long side ends of the substrate 22a, and the resistance change rate per unit temperature change Is a value calculated by the following equation.
(R2-R1) / R1 / (225 ° C.-25 ° C.) × 10 ⁶ [ppm / ° C.]
The NTC characteristic generally refers to a characteristic in which the temperature resistance coefficient is negative, but is negative in a temperature range of 25 ° C. to 300 ° C., more preferably a temperature resistance coefficient in a high temperature range of 150 ° C. to 250 ° C. is −2500 [ It is preferable to use a silicon carbide heating element of [ppm / ° C.] or more as the substrate material. The volume resistivity of the substrate 22a used in the fixing device 6 is preferably suppressed to 3 × 10 ⁻¹ Ω · cm or less. When the volume resistivity is 3 × 10 ⁻¹ Ω · cm or more, the substrate 22a needs to be very wide or thick. Or, if the dimensions are standard, there is a problem that the substrate 22a does not generate heat. On the other hand, the lower limit of the volume resistivity depends on the size of the substrate 22a, but it should be noted that the volume resistivity is too low to generate heat. It is confirmed that the above-mentioned volume resistivity 1 × 10 ⁻² Ω · cm product of the Bridgestone Pure Beta-R improved product generates heat at the substrate size described later, and there is no problem.

In the heater 22, a surface protective layer 22 h is provided on a surface 22 a 1 of the substrate 22 a in a region Ar (hereinafter referred to as a contact region) Ar that contacts a conductive base layer 23 a described later of the fixing film 23. Here, the surface of the substrate 22a is a surface on which the fixing film 23 slides (fixing film sliding surface). The main purpose of providing the surface protective layer 22h is to ensure electrical insulation between the substrate 22a and the base layer 23a of the fixing film 23 and to ensure the slidability of the base layer 23a of the fixing film 23 with respect to the substrate 22a. . The surface protective layer 22h is obtained, for example, by coating a glass paste mainly composed of silicon oxide (SiO ₂ ) on the contact region Ar of the surface 22a1 of the substrate 22a and baking it at a predetermined temperature. On the back surface 22a2 of the substrate 22a, an electrode portion 22d for supplying power to the substrate 22a to the longitudinal end portion 22aR and the longitudinal end portion 22aL adjacent to the region Ar ′ corresponding to the contact region Ar of the front surface 22a1 of the substrate 22a. , 22e are formed. Here, the back surface of the substrate 22a refers to a surface on which the fixing film 23 does not slide (fixing film non-sliding surface). As a material for the electrode portions 22d and 22e, a conductive paste mainly composed of silver (Ag), platinum (Pt), gold (Au), or the like is used. The material of the electrode portions 22d and 22e is not limited to this, and a conductive paste mainly composed of silver / platinum (Ag / Pt) alloy, silver / palladium (Ag / Pd) alloy, or the like may be used. In FIGS. 3A and 3B, reference numerals 25 and 25 denote power feeding connectors coupled to the electrode portions 22d and 22e.

The heat generation area of the heater 22 will be described. 4A is an explanatory diagram showing the heat generation area of the heater, and FIG. 4B is a model diagram for explaining the heat generation amount of the sheet passing portion and the non-sheet passing portion in the heat generation area of the heater. As shown in FIG. 4A, when power is supplied from the power control circuit (power supply control unit) 31 to the electrode portions 22d and 22e of the heater 22 through the power supply connectors 25 and 25, the electrode portion 22d of the substrate 22a. , 22e. As a result, the temperature between the electrode portions 22d and 22e of the substrate 22a quickly rises. That is, a region between the electrode portions 22d and 22e in the substrate 22a becomes a heat generation region (hereinafter referred to as a heat generation portion) H. The temperature of the heat generating portion H is detected by a temperature measuring element (temperature detection member) 22i (see FIG. 3A) such as a thermistor provided at the center in the longitudinal direction of the heat generating portion H on the back surface of the substrate 22a. Based on the output signal (temperature detection signal) of the temperature detecting element 22i, the heater 22 is temperature-controlled so as to maintain a predetermined fixing temperature (target temperature). Here, the effect of the NTC characteristic of the heater 22 on the temperature increase of the non-sheet passing portion will be described with reference to FIG. Here, the heating part H is divided into four parts of length a (= 55 mm), and the effect of increasing the temperature of the non-sheet passing part of the heater 22 is considered. The resistances at the two longitudinal center portions of the heat generating part H are r1 and the resistances at the two longitudinal end portions are r2, respectively (r1 = r2 if the temperatures at the longitudinal central portion and the longitudinal end portions are the same). . 2 (r1 + r2) is the total resistance of the heat generating portion H. Assuming that the current flowing through the heat generating portion H is i, the heat generation amount q1 at one of the two longitudinal central portions of the heat generating portion H is i ² × r1, and the heat generation at one of the two longitudinal end portions. q2 is i ² × r2. For the sake of simplicity, considering the case where a small size paper having a longitudinal width 2a (= 110 mm) is passed (introduced) through the fixing nip N, the portion of the heat generating portion H where the resistance in the longitudinal direction is r1 is small. This is an area (paper passing portion) through which the paper recording material passes. A portion where the resistance at the longitudinal end of the heat generating portion H is r2 is a region (non-sheet passing portion) through which the recording material of small size paper does not pass. Since the temperature control of the heater 22 is performed by the temperature detecting element 22i provided in the sheet passing portion, the non-sheet passing portion that does not lose heat to the small size paper compared to the sheet passing portion that takes heat to the small size paper. The temperature rises. Since the substrate 22a made of a silicon carbide heating element has NTC characteristics in the actual use temperature range (250 ° C. or less), r1> r2 when small-size paper is passed. Since the current i is the same in the sheet passing portion and the non-sheet passing portion, q1> q2, and the heat generation amount in the non-sheet passing portion is smaller than the heat generation amount in the central portion in the longitudinal direction, thereby suppressing the temperature rise in the non-sheet passing portion. It becomes possible.

  The film guide 21 is formed in a saddle shape having a substantially semicircular cross section. The film guide 21 is a molded product of a heat resistant resin such as PPS (polyphenylene sulfite) or LCP (liquid crystal polymer). The film guide 21 is supported by an apparatus frame (not shown) of the fixing device 6 at one end in the longitudinal direction and the other end in the longitudinal direction of the film guide 21. A groove 21 a is formed along the longitudinal direction at the center in the short direction of the lower surface of the film guide 21. In the groove 21a of the film guide 21, a heater 22 is supported in a state in which a surface 22hs contacting the fixing film 23 of the surface protective layer 22h is exposed. FIG. 5A shows a schematic cross-sectional view of a film guide and a heater supported by the film guide. On the lower surface of the film guide 21, two overhangs projecting from the lower ends of the left and right inner surfaces 21aR and 21aL of the groove 21a toward the center line 22c of the substrate 22a of the heater 22 in the short direction of the film guide 21. Wrap portions 22bR and 22bL are formed. Then, both end surfaces 22hsR, 22hsL in the short direction of the substrate 22a on the surface 22hs of the surface protective layer 22h of the heater 22 are covered with corresponding overlap portions 22bR, 22bL. The film guide 21 is not limited to this, and may be configured as shown in FIG. FIG. 5B shows another example of the film guide and a schematic cross-sectional view of the heater supported by the film guide. The film guide 21 shown in FIG. 5B is composed of two parts 215 and 216 that are symmetrical with respect to the center line 21 c in the short direction of the film guide 21. The two parts 215 and 216 are assembled to form the groove 21a and the overlap portions 22bR and 22bL.

  The fixing film 23 is a cylindrical member loosely fitted on the film guide 21 that supports the heater 22. This fixing film 23 is coated with a release layer 23b on the surface of a cylindrical base film (base layer) 23a whose total thickness is set to 100 μm or less in order to reduce the heat capacity and improve the quick start performance of the apparatus. The composite layer film (see FIG. 2). The total thickness of the base film 23a is preferably 60 μm or less and 20 μm or more. As the material of the base film 23a, resin materials such as PI (polyimide), PAI (polyamideimide), PEEK (polyetheretherketone), and PES (polyethersulfone), and metal materials such as SUS and Ni are used. As the material of the release layer 23b, a fluororesin such as PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether), FEP (tetrafluoroethylene-hexafluoropropylene), or the like is used.

  The pressure roller 24 includes a cored bar 24a made of a material such as iron or aluminum, an elastic layer 24b made of silicone rubber or the like provided on the outer peripheral surface of the cored bar 24a, and the elastic layer 24b. And a release layer 24c made of a fluororesin or the like provided on the outer peripheral surface of the substrate. The pressure roller 24 is disposed below the fixing film 23 in parallel with the fixing film 23, and one end in the longitudinal direction and the other end in the longitudinal direction of the cored bar 24a are rotatably supported by the apparatus frame via bearings. ing. The bearing is urged by a pressure spring (not shown) in a direction orthogonal to the direction of the generatrix of the pressure roller 24 to press the outer peripheral surface (surface) of the pressure roller 24 against the outer peripheral surface (surface) of the fixing film 23. In contact with As a result, the pressure roller 24 is pressed against the surface protective layer 22h of the heater 22 with the fixing film 23 interposed therebetween, and the inner peripheral surface (inner surface) of the fixing film 23 contacts the surface 22hs of the surface protective layer 22h in a pressurized state. As a result, the elastic layer 24 b of the pressure roller 24 is elastically deformed, and a fixing nip portion N having a predetermined width is formed between the surface of the pressure roller 24 and the surface of the fixing film 23.

(3) Heat Fixing Operation of Fixing Device The control unit 50 rotationally drives the fixing motor M (see FIG. 2A) in response to a print command. The rotation of the output shaft of the fixing motor M is transmitted to a driving gear G (see FIG. 2B) provided on the cored bar 24a of the pressure roller 24 through a predetermined gear train. As a result, the pressure roller 24 rotates in the direction of the arrow at a predetermined peripheral speed (process speed). The rotation of the pressure roller 24 is transmitted to the fixing film 23 by the frictional force between the surface of the pressure roller 24 and the surface of the fixing film 23 at the fixing nip portion N. As a result, the fixing film 23 rotates (moves) following the rotation of the pressure roller 24 while the inner peripheral surface (inner surface) of the fixing film 23 contacts the surface 22 hs of the surface protective layer 22 h of the heater 22. The control unit 50 starts up the power control circuit 31 in response to the print command. As a result, the power control circuit 31 supplies power to the electrode portions 22 d and 22 e of the heater 22 via the power supply connectors 25 and 25. Electricity is passed between the electrode portions 22d and 22e of the substrate 22a through the electrode portions 22d and 22e, and the heat generating portion H generates heat to heat the fixing film 23. The temperature of the substrate 22a is detected by the temperature measuring element 22i. The control unit 50 takes in an output signal from the temperature sensing element 22i, and controls the power control circuit 31 so as to maintain the heater 22 at a predetermined fixing temperature (target temperature) based on the output signal. In a state where the fixing motor M is rotationally driven and the heater 22 is supplied with power, the recording material P carrying the unfixed toner image T is introduced into the fixing nip portion N with the toner image carrying surface facing upward. The recording material P is sandwiched between the surface of the fixing film 23 and the surface of the pressure roller 24 at the fixing nip portion N, and is transported to the state (nip transport). In this conveyance process, the toner image T on the recording material P is heated and melted by the heater 22 through the fixing film 23 and is heated and fixed on the recording material by being pressurized at the fixing nip N. Then, the recording material P on which the toner image T is heated and fixed is discharged from the fixing nip portion N and conveyed toward the conveying roller 13.

(4) Effects of Overlap Portion of Film Guide In fixing device 6 of the first embodiment, overlap portions 22bR and 22bL of film guide 21 have both end faces 22hsR and 22hsL on surface 22hs of surface protective layer 22h of heater 22 respectively. Covering. Therefore, the overlap portions 22bR and 22bL of the film guide 21 keep the base layer 23a of the fixing film 23 and the both end faces 22hsR and 22hsL of the surface 22hs of the surface protective layer 22 of the heater 22 in a non-contact state, that is, in a non-contact state. be able to. Therefore, even when the surface protective layer 22h is provided only in the longitudinal center portion of the substrate 22a of the heater 22 that is in contact with the base layer 23a of the fixing film 23, the lateral side or edge portion of the substrate 23a and the base layer 23a of the fixing film 23 are provided. Can be secured. Further, since the film guide 21 has the overlap portions 22bR and 22bL, the deformed shape of the fixing film 23 in the fixing nip portion N can be stabilized. Therefore, even when a rigid thin metal film is used as the base layer 23a of the fixing film 23, the behavior during the rotation operation of the fixing film 23 is stabilized through durability. That is, in contrast to the deformation of the fixing film 23 at the flat fixing nip N, the overlap portions 22bR and 22bL in the short direction of the film guide 21 serve as guides for inducing the deformation at the fixing nip N of the fixing film 23. do. As a result, the fixing film 23 can be stabilized to enter the fixing nip portion N, and the behavior of the fixing film 23 during the rotating operation is also stabilized. The deformation shape of the fixing film 23 at the fixing nip portion N will be described with reference to FIG. FIG. 6A is an explanatory diagram of a deformed shape in the fixing nip portion of the fixing film when an overlap portion is formed on the film guide. (B) is an explanatory view of a deformed shape in the fixing nip portion of the fixing film when the overlap portion is not formed on the film guide. When a rigid thin metal film is used as the base layer 23a of the fixing film 23, as shown in FIGS. 6A and 6B, the fixing film 23 is in the vicinity of the fixing nip portion N in the short direction of the film guide 21. It transforms into a wave shape. When the overlap portions 22bR and 22bL are formed on the film guide 21, as shown in FIG. 6A, the thickness and width of the overlap portions 22bR and 22bL along the corrugated shape of the fixing film 23. To optimize. Thus, the overlap portions 22bR and 22bL serve as guides for inducing deformation of the fixing film 23 at the fixing nip portion N. That is, the overlap portions 22bR and 22bL serve as guides for inducing deformation at the fixing nip portion N in the short direction of the film guide 21 with respect to the deformation of the fixing film 23 at the flat fixing nip portion N. As a result, the position of the fixing film 23 relative to the heater 22 in the short direction of the film guide 21 is restricted, and the behavior of the fixing film 23 during the rotating operation is stabilized. When the overlap portions 22bR and 22bL are not formed on the film guide 21, the position of the fixing film 23 relative to the heater 22 cannot be regulated by the corrugated shape of the fixing film 23 as shown in FIG. For this reason, the fixing film 23 tends to fluctuate in the direction of the arrow in the figure, and the behavior of the fixing film 23 during the rotation operation becomes unstable.

(5) Evaluation The characteristics of the fixing device 6 of the first embodiment will be described in more detail. The effects of the fixing device 6 of Example 1 were confirmed using fixing devices configured as in Comparative Examples 1 and 2 below. In this evaluation, for the fixing devices of Comparative Example 1 and Comparative Example 2, members / portions common to the fixing device 6 of Example 1 are denoted by the same reference numerals. In the following description, the fixing device of Example 1 is referred to as Example fixing device (1), the fixing device of Comparative Example 1 is referred to as Comparative Example Fixing Device (1), and the fixing device of Comparative Example 2 is referred to as Comparative Example Fixing. It is described as device (2).

In the exemplary fixing device (1), the above-described Pure Beta-R improved product manufactured by Bridgestone is used as the substrate 22a of the heater 22. The substrate 22a is formed into an elongated plate shape having a width of 5 mm, a length of 270 mm, and a thickness of 0.5 mm. On the back surface 22a2 of the substrate 22a, electrode portions 22d and 22e were formed with a thickness of 10 μm using silver (Ag). At this time, the length of the heat generating portion H formed between the electrode portions 22d and 22e was 220 mm. A surface insulating layer 22h was formed to a thickness of 50 μm on the surface 22a1 of the substrate 22a. The overlap portions 22bR and 22bL of the film guide 21 have a thickness of 1 mm and a width that overlaps at least 1.5 mm from the short-side end and the short-side end of the substrate 22a of the heater 22, respectively. Shaped. FIG. 7A is a schematic cross-sectional view of the film guide of the comparative fixing device (1) and the heater supported by the film guide. The comparative fixing device (1) has the same configuration as that of the exemplary fixing device (1) except that a film guide 31 having no overlap portion is used. FIG. 7B is a schematic cross-sectional view of the film guide of the comparative fixing device (2) and the heater supported by the film guide. The comparative fixing device (2) has the same configuration as that of the exemplary fixing device (1) except that a heater 722 having the following configuration is used instead of the heater 22. The heater 722 forms a conductive heating resistor 722b by applying Ag / Pd paste in a strip shape on the surface of a substrate 722a made of aluminum oxide (Al ₂ O ₃ ), and fluorine so as to cover the conductive heating resistor 722b. The resin protective layer 722c is formed. Further, the image forming apparatus on which the embodiment fixing device (1), the comparative example fixing device (1), and the comparative example fixing device (2) are respectively mounted has the same configuration. In these three image forming apparatuses, the B5 size small-size paper from the state in which the example fixing device (1), the comparative example fixing device (1), and the comparative example fixing device (2) are each sufficiently adapted to room temperature (25 ° C.). (Basis weight 128 g / mm ² ) was continuously fed (introduced) into the fixing nip part by 200 sheets. At this time, the temperatures of the non-sheet passing portions of the heaters of the example fixing device (1), the comparative example fixing device (1), and the comparative example fixing device (2) were measured. The temperature of the non-sheet passing portion was measured by a number of temperature measuring elements disposed along the longitudinal direction on the back surface of the substrate. The input voltage was 120V and the fixing temperature was 200 ° C. In addition, with respect to the example fixing device (1) and the comparative example fixing device (1), a durability test was conducted by a 100,000 sheet passing test.
The results are shown in Table 1.

In the case of the comparative fixing device (1) using the heater having the NTC characteristic, since the temperature rise in the non-sheet passing portion is suppressed, the temperature is 210 ° C. even after passing 200 sheets, and there is no problem. On the other hand, in the comparative fixing device (2), the temperature of the non-sheet passing portion is increased along with the number of sheets passed by continuous passing of small size paper, and after 200 sheets are passed, the pressure roller rubber (the elasticity of the pressure roller 24) Some deformation was observed on the pressure roller surface beyond the heat resistance temperature (230 ° C.) of the layer 24b). As a result of the endurance life test, both the example fixing device (1) and the comparative example fixing device (1) were good with no problems at the time of passing 50,000 sheets (1). On the other hand, at the time of passing 100,000 sheets (2), in the comparative fixing device (1), the surface protective layer of the heater has the surface protective layer at the edge in the short direction of the substrate due to the sliding of the fixing film. Worn out. For this reason, insulation between the base layer of the fixing film and the substrate of the heater is not maintained, power supply to the substrate becomes unstable, and problems such as defective heat generation occur. On the other hand, in the example fixing device (1), the heater stably generated heat even after passing 100,000 sheets, and there was no problem in the pressure resistance test (1 kV application) performed after passing 100,000 sheets.

[Example 2]
Another example of the fixing device will be described. In the second embodiment, the same reference numerals are given to the same members and portions as those of the fixing device of the first embodiment, and the description thereof is omitted. 8A is a schematic cross-sectional view of a film guide, a member attached to the film guide for supporting the heater on the film guide, and a heater supported on the film guide by this member, and FIG. It is the external appearance perspective view which abbreviate | omitted the longitudinal direction center part.

  The fixing device 6 according to the second exemplary embodiment uses the member 25 attached to the film guide in order to support the heater 22 on the film guide 21, and both end surfaces 22 hsR in the short direction on the surface 22 hs of the surface protective layer 22 h of the heater. It is configured to cover 22 hsL. The member 25 is an elongated member that can be fitted into the groove 21 a of the film guide 21. The member 25 has a pair of side walls 25aR and 25aL in the short direction of the member 25. The pair of side walls 25aR and 25aL are connected at both ends of the member 25 in the longitudinal direction. Overlap portions 25R and 25L are formed at the lower ends of the pair of side walls 25aR and 25aL so as to protrude from the inner surface side of the lower ends to the center line 22c in the short direction of the substrate 22a of the heater 22. An opening 25w for exposing the surface 22hs of the surface protective layer 22h of the heater 22 is formed between the overlap portions.

  When the film guide 21 is used to support the heater 22 using the member 25, both end surfaces 22hsR and 22hsL of the surface 22hs of the surface protective layer 22h of the heater 22 are placed on the back surfaces of the overlap portions 25R and 25L of the member 25. The heater 22 is held by the member 25. Then, the side walls 25aR and 25aL of the member 25 are fitted into the groove 21a of the film guide 21 from the lower surface side of the film guide 21, thereby supporting the member 25 in the groove 21a. Thereby, the member 25 is attached to the groove 21 a of the film guide 21 in a state where the heater 22 is supported. In this state, the overlap portions 25R and 25L of the member 25 cover both end faces 22hsR and 22hsL of the surface 22hs of the surface protective layer 22h of the heater 22. Therefore, the fixing device 6 of the second embodiment can obtain the same effects as the fixing device 6 of the first embodiment.

[Other examples]
The fixing devices according to the first and second embodiments are not limited to use as a fixing device (image heating device) that heat-fixes an unfixed toner image on a recording material. For example, it can also be used as an image heating device that presupposes an unfixed toner image on a recording material, or an image heating device that increases the gloss of the surface of a toner image that is heat-fixed on a recording material.

22 Heater, 22a Heater substrate, 22d, 22e Electrode, 23 Heat resistant film, 24 Pressure roller, P Recording material, N Fixing nip, T Toner image, 22bR, 22bL Overlapping Part, 22h ... surface protective layer, 22hs ... surface, 25 ... member, 25R, 25L ... overlap part

Claims (7)

An elongated substrate having a characteristic of generating heat when energized and having a resistance value decreasing with an increase in temperature, and an electrode portion provided inside both longitudinal ends of the substrate, the electrode portion for supplying power to the substrate, and the longitudinal direction of the substrate A heating member having an insulating layer provided in a central portion in the direction, a supporting member for supporting the heating member, and a flexible member that moves while being in contact with the insulating layer and is in contact with the insulating layer. An image heating apparatus that heats an image carried by a recording material with the heat of the heating member via the flexible member, and a flexible member having a base layer.
An image heating apparatus, wherein both end surfaces of the insulating layer on the surface in contact with the flexible member are covered with the support member at both end surfaces in a short direction perpendicular to the longitudinal direction of the substrate.   The support member has an overlap portion that protrudes toward a center line in a short direction perpendicular to the longitudinal direction of the substrate, and the support member has a surface that contacts the flexible member of the insulating layer at the overlap portion. The image heating apparatus according to claim 1, wherein both end faces in a short direction perpendicular to the longitudinal direction of the substrate are covered. An elongated substrate having a characteristic of generating heat when energized and having a resistance value decreasing with an increase in temperature, and an electrode portion provided inside both longitudinal ends of the substrate, the electrode portion for supplying power to the substrate, and the longitudinal direction of the substrate A heating member having an insulating layer provided in a central portion in the direction, a supporting member for supporting the heating member, and a flexible member that moves while being in contact with the insulating layer and is in contact with the insulating layer. An image heating apparatus that heats an image carried by a recording material with the heat of the heating member via the flexible member, and a flexible member having a base layer.
A member attached to the support member for supporting the heating member on the support member, and in a short direction perpendicular to the longitudinal direction of the substrate on the surface of the insulating layer in contact with the flexible member. An image heating apparatus, wherein both end faces are covered with the member.   The member exposes an overlap portion that projects toward a center line in a short direction perpendicular to the longitudinal direction of the substrate, and a surface that contacts the flexible member of the insulating layer between the overlap portions. A short direction perpendicular to the longitudinal direction of the substrate on the surface of the insulating layer that contacts the flexible member at the overlap portion when attached to the support member. The image heating apparatus according to claim 3, wherein both end faces of the image heating apparatus are covered.   The image heating apparatus according to claim 1, wherein the material of the substrate is a ceramic resistance heating element.   The image heating apparatus according to claim 1, wherein a material of the substrate is a silicon carbide heating element.   The image heating apparatus according to claim 1 or 3, wherein the temperature coefficient of resistance of the substrate is negative in a range of 25 ° C to 250 ° C.