JP2009145466A - Heating body and image heating device having the heating body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating body capable of preventing a heating element from being ruptured incompletely even if a substrate is ruptured due to runaway in electric conduction and abnormal temperature rise. <P>SOLUTION: The heating body 3 includes the substrate 3a, the heating element 3b energized to generate heat and provided in the longitudinal direction of the substrate on the substrate, and a protective layer 3c covering an opposite-side surface of the heating element to the substrate. The heating element is a carbon-based heating element formed by carbonizing organic substance. The protective layer is composed by blending scale-shaped filler inside heat resistant resin and layering the filler in the thickness direction of the protective layer inside the heat resistant resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heating body used in an image heating apparatus suitable for use as a heating and fixing apparatus mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, and an image heating apparatus having the heating body. In particular, a substrate and a heating element that generates heat upon energization, the heating element provided on the substrate along the longitudinal direction of the substrate, and a protective layer that covers a surface of the heating element opposite to the substrate, And an image heating apparatus having the heating body.

  2. Description of the Related Art A film heating type fixing device is known as an image heating device (fixing device) mounted on an electrophotographic printer or copying machine. This film heating type fixing device includes a heater having an energized heating element on a ceramic substrate, a flexible member that moves while contacting the heater, and the heater and the nip portion via the flexible member. And a pressure roller that forms Patent Documents 1 and 2 describe a film heating type fixing device. The recording material carrying the unfixed toner image is heated while being nipped and conveyed at the nip portion of the fixing device, whereby the unfixed 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, 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.

  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 the above-described fixing device has a control to widen 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 temperature rise is suppressed.

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

  Therefore, it is also considered to use a heater (NTC: Negative Temperature Coefficient) whose resistance value decreases as the temperature increases as the heater used in the above-described fixing device (Patent Document 3). If the heater has an NTC characteristic, the resistance value of the non-sheet passing area is lowered even if the non-sheet passing area is excessively heated, so that the excessive temperature increase (over temperature increase) of the non-sheet passing area can be suppressed. .

Patent Document 4 discloses a fixing device having a structure in which a carbon-based heating element having such NTC characteristics is attached to a substrate and the strength of the heater using the carbon-based heating element is increased.
JP-A-63-313182 JP-A-4-44075 JP 2004-234998 A JP 2006-134746 A

  Usually, the heater used for the fixing device of the film heating system is equipped with a double or triple safety device, but it is necessary to take safety measures in the event of an energized runaway or abnormal temperature rise as a risk assessment. is there. As an example of the safety measure, when the heater has runaway energization or abnormal temperature rise, the heater substrate itself will eventually break due to thermal stress, and the energization heating element will be cut off so that the energization is cut off. It is desirable to construct a heater.

  By the way, in the above heater, when a carbon-based heating element is used as the material of the energization heating element, a heat-resistant resin is applied to the surface of the energization heating element in order to protect the surface (surface) on the flexible member side of the energization heating element. It is conceivable to provide a protective layer made of a material.

  However, if a heat-resistant resin is used as the material of the protective layer, even if the heater substrate is cracked due to thermal stress, the protective layer does not break cleanly and the heat generated when the resin breaks the substrate. The body also tends to break incompletely with this. In that case, energization of the energization heating element may not stop immediately.

  Accordingly, an object of the present invention is to provide a heating element capable of reducing the occurrence of incomplete breakage in a heating element even when the substrate breaks due to energization runaway or abnormal temperature rise, and an image having this heating element. It is to provide a heating device.

  A configuration for achieving the above object is a substrate and a heating element that generates heat upon energization, the heating element provided on the substrate along the longitudinal direction of the substrate, and the heating element opposite to the substrate. A heating layer having a protective layer covering the side surface, wherein the heating element is a carbon-based heating element formed by carbonizing an organic substance, and the protective layer includes a scaly filler inside the heat-resistant resin. And the filler is laminated in the thickness direction of the protective layer inside the heat resistant resin.

  According to the present invention, it is possible to reduce the occurrence of incomplete breakage in the heating element even when breakage occurs in the substrate due to energization runaway or abnormal temperature rise.

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

[Example 1]
(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus in which an image heating apparatus having a heating body according to the present invention can be mounted as a heat fixing apparatus. This image forming apparatus is a laser beam printer using a transfer type electrophotographic process.

  The printer shown in this embodiment includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 101 as an image carrier. The photosensitive drum 101 is 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 102 denotes a charging roller as charging means. The charging roller 102 uniformly charges the outer peripheral surface (surface) of the photosensitive drum 101 to a predetermined polarity and potential. In the printer of this example, the surface of the photosensitive drum 101 is uniformly charged to a predetermined negative potential.

  Reference numeral 103 denotes a laser exposure apparatus as exposure means. The laser exposure apparatus 103 outputs a laser beam L modulated in accordance with image information input from an external device (host device) such as an image scanner or a computer (not shown). The laser beam L scans and exposes the uniformly charged surface on the surface of the photosensitive drum 101. This scanning exposure attenuates or eliminates the charge of the exposed bright portion on the surface of the photosensitive drum 101, and an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 101.

  Reference numeral 104 denotes a developing device as developing means. The electrostatic latent image formed on the surface of the photosensitive drum 101 is visualized as a toner image (developed image) by the developing device 104. In the case of a laser beam printer, generally, a reversal development method is used in which toner is attached to an exposed bright portion of an electrostatic latent image for development. Reference numeral 104a denotes a developing sleeve, 104b denotes a developing blade, 104c denotes a developing bias application power source, and t denotes one-component magnetic toner.

  Reference numeral 107 denotes a feeding cassette in which recording materials (transfer materials) P are stacked and stored. The feeding roller 108 is driven based on the feeding start signal, and the recording materials P in the feeding cassette 107 are separated and fed one by one. The fed recording material P passes through the sheet path 109 → registration roller 110 → top sensor 111, and a contact nip portion between the surface of the photosensitive drum 101 and the outer peripheral surface (front surface) of the transfer roller 112 as a transfer unit. Are introduced at a predetermined control timing into the transfer portion Tn. In other words, when the leading end portion of the toner image on the surface of the photosensitive drum 101 reaches the transfer portion Tn, the conveyance timing of the recording material P is controlled by the registration roller 110 so that the leading end portion of the recording material P also reaches the transfer portion Tn. The Further, the image writing timing to the photosensitive drum 101 is controlled based on the recording material leading edge detection signal from the top sensor 111.

  The recording material P introduced into the transfer portion Tn is nipped and conveyed between the surface of the photosensitive drum 101 and the surface of the transfer roller 112. During this time, the transfer roller 112 has a predetermined potential having a polarity opposite to the charged polarity of the toner from the transfer bias applying power source 112a. The transfer bias is applied. As a result, the toner image on the surface of the photosensitive drum 101 is electrostatically transferred sequentially onto the surface of the recording material P at the transfer portion Tn.

  The recording material P that has received the transfer of the toner image at the transfer portion Tn is separated from the surface of the photosensitive drum 101, conveyed through the sheet path 113 to the fixing device 114, which is an image heating device, and subjected to a heat fixing process of the toner image. .

  On the other hand, the surface of the photosensitive drum 101 after the separation of the recording material (after the transfer of the toner image to the recording material) is cleaned by the cleaning blade 105a of the cleaning device 105 after removing the transfer residual toner and paper dust and the like. To be used for image formation.

  The recording material P that has passed through the fixing device 114 passes through the sheet path 115 and is discharged from the discharge port 116 onto the discharge tray 117 on the upper surface of the printer.

  The feeding cassette 107 has a movable regulation guide (not shown) for loading and storing various recording materials P of different sizes in the feeding cassette 107. The regulation guide is displaced according to the size of the recording material P, and the recording material P is stacked and stored in the feeding cassette 107, whereby the recording materials P of different sizes are separated and fed one by one from the feeding cassette 107. be able to.

  In the printer of this embodiment, the four process devices of the photosensitive drum 101, the charging roller 102, the developing device 104, and the cleaning device 105 are collectively configured as a process cartridge 106 that can be attached to and detached from the printer main body. It is.

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

  FIG. 2 is a cross-sectional side view of an example of the fixing device 114. FIG. 3 is a longitudinal side view of the fixing device 114. FIG. 4 is a view of the fixing device 114 as viewed from the recording material introduction side. FIG. 5A is a front view of the stay 1, and FIG. 5B is a bottom view (bottom view) of the stay 1. FIG. 6A is an explanatory view showing the front side of the heater 3, and FIG. 6B is an explanatory view showing the back side of the heater 3. 6C is an enlarged side view of the transverse side of the heater 3 in FIG. 6A, and FIG. 6D is an energizing heating element 3b and an AC feeding electrode 31 (32) at the longitudinal end of the heater 3 in FIG. It is a vertical side surface enlarged view showing the lamination | stacking relationship of a protective layer 3b.

  This fixing device 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. This type of film heating type image heating apparatus uses an endless belt-shaped or cylindrical heat-resistant film as a flexible member. At least a part of the circumference of the heat-resistant film is always tension-free (a state in which no tension is applied), and the heat-resistant film is rotationally driven by the rotational driving force of the pressure member.

  Reference numeral 1 denotes a stay as a heating body supporting member / film guide member. The stay 1 is a rigid member made of a heat-resistant resin having a substantially semicircular saddle-like cross section that is long in the longitudinal direction. In this example, a high heat-resistant liquid crystal polymer was used as the material of the stay 1. On the lower surface of the stay 1, a groove 1 a (FIG. 5) is provided along the longitudinal direction at the center in the short direction of the stay 1. Further, in the vicinity of the central portion in the longitudinal direction of the stay 1, a hole 1b for accommodating a thermistor 5 provided in a substrate 3a of the heater 3 described later is provided in communication with the groove 1a.

  3 is a heater as a heating body. The heater 3 is fixedly supported by being fitted into a groove 1 a (FIG. 5) provided along the longitudinal direction of the stay 1 at the center in the lateral direction on the lower surface of the stay 1. As shown in FIG. 6A, the heater 3 has an alumina substrate 3a elongated in the longitudinal direction. The substrate 3a is a rectangular parallelepiped having a thickness of 0.65 mm, a width of 8 mm, and a length of 270 mm. On the surface of the substrate 3a (the surface on the nip portion N side), a carbon-based heating element 3b as an energizing heating element is disposed along the longitudinal direction of the substrate 3a at the center in the short direction of the substrate 3a. AC power feeding electrodes 31 and 32 are applied by screen printing with silver Pd (palladium) paste on both ends of the carbon-based heating element 3b in the longitudinal direction so as to cover the ends of the carbon-based heating element 3b. (FIG. 6 (d)). The length of the coating region between the electrodes 31 and 32 of the carbon-based heating element 3b is 220 mm. A protective layer 3c made of a heat-resistant resin containing a flake-like filler is applied on the carbon-based heating element 3b by screen printing so as to have a thickness of 25 μm. That is, the protective layer 3c is obtained by blending a flake-like filler in the heat resistant resin. The protective layer 3c is applied so as to cover the entire surface of the carbon-based heating element 3b opposite to the substrate 3a, leaving only the ends of the electrodes 31 and 32 in the longitudinal direction of the substrate 3a. The length of the coating area of the protective layer 3c is 245 mm.

  The carbon-based heating element 3b is a heating element using carbon as a conductive material, and a raw material containing at least an organic substance (hereinafter referred to as “precursor”) is placed in a non-oxidizing atmosphere of carbon (an atmosphere in which carbon is hardly oxidized). Medium) and heat treated to carbonize organic matter. The reason for using the heater 3 having such a carbon-based heating element 3b is to use the characteristic that the resistance value decreases as the temperature rises, that is, the NTC (Negative Temperature Coefficient) characteristic of the heater 3. By utilizing the NTC characteristic, it is possible to suppress an excessive temperature rise in a region (non-sheet passing region) where the recording material P of the heater 3 does not pass. The reason will be described in the item (4) described later.

  Reference numeral 2 denotes a cylindrical heat-resistant film having excellent heat resistance as a flexible member, and is externally fitted to the outer periphery of the stay 1 that supports the heater 3. The inner peripheral length of the film 2 and the outer peripheral length of the stay 1 including the heater 3 are made larger by about 3 mm for the film 2, for example. Accordingly, the film 2 is loosely fitted on the outer periphery of the stay 1 with a margin in circumference.

  The film 2 has a total thickness of about 100 μm or less in order to reduce the heat capacity and improve the quick start property. Further, as the material of the film 2, 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 2 having a film layer thickness of 60 μm obtained by coating PTFE with a thickness of 10 μm on a polyimide film with a thickness of 50 μm was used as the film 2. The inner peripheral surface (inner surface) of the film 2 is coated with grease in order to improve the slidability with the heater 3.

  A heating assembly 4 is constituted by the stay 1, the heater 3, the film 2, and the like.

  Reference numeral 6 denotes an elastic pressure roller as a backup member. The pressure roller 6 of this example is made of a silicone foam having a length of 240 mm and a thickness of 3 mm as a heat-resistant elastic layer 6 b on a core shaft 6 a of a round shaft made of iron, stainless steel, aluminum or the like having an outer diameter of 13 mm. It is coated. The pressure roller 6 is opposed to the heater 3 held by the stay 1 with the film 2 interposed therebetween. A predetermined pressure is applied between the stay 1 and the pressure roller 6 by a pressure mechanism (not shown). With this pressure, the elastic layer 6 b of the pressure roller 6 is elastically deformed in the longitudinal direction along the heater 3 with the film 2 interposed therebetween. Thus, the pressure roller 6 forms a nip portion (fixing nip portion) N having a predetermined width necessary for heating and fixing an unfixed toner image carried by the heater 3 and the recording material P with the film 2 interposed therebetween.

(3) Heat Fixing Operation of Fixing Device FIG. 7 is a block diagram of an example of a power supply control system of the heater 3.

  The drive roller G (FIG. 4) provided at the longitudinal end of the metal core 6a of the pressure roller 6 is rotationally driven by a drive source M such as a motor so that the pressure roller 6 has a predetermined peripheral speed (process) in the direction of the arrow. Speed). Due to the rotation of the pressure roller 6, a rotational force acts on the film 2 by the frictional force between the outer peripheral surface (surface) of the pressure roller 6 and the outer peripheral surface (surface) of the film 2 in the nip portion N. Then, the film 2 is driven around the stay 1 in the direction of the arrow at the same peripheral speed as the rotational peripheral speed of the pressure roller 6 while the inner surface of the film 2 slides on the surface of the protective layer 3c of the heater 3 at the nip portion N. Rotate. At this time, the stay 1 guides the inner surface of the driven rotating film 2 by the arc-shaped outer peripheral surface of the stay 1.

  On the other hand, as shown in FIG. 7, the electrodes 31 and 32 of the heater 3 are supplied with power from the commercial power supply (AC power supply) 13 through the triac 12 via the power supply connectors 7 and 8. As a result, the carbon-based heating element 3b between the electrodes 31 and 32 generates heat, and the temperature of the substrate 3a of the heater 3 rises rapidly and steeply. The temperature of the heater 3 is detected by a thermistor 5 as temperature detecting means provided on the back surface (surface opposite to the nip portion N) of the substrate 3a, and the output of the thermistor 5 is sent to the A / D converter 10. Via the power supply control unit (MPU) 11 as a control means. The controller 11 maintains the heater 3 at a predetermined temperature by controlling the electric power supplied to the heater 3 by controlling the phase of the triac 12 or controlling the wave number based on the detected temperature information obtained from the thermistor 5. That is, when the temperature detected by the thermistor 5 is lower than a predetermined fixing temperature (target temperature), the heater 3 is raised, and when the temperature detected by the thermistor 5 is higher than the predetermined fixing temperature, the heater 3 is lowered. In addition, the power supplied to the heater 3 is controlled. Thereby, the temperature of the heater 3 at the time of fixing is maintained at a predetermined fixing temperature (target temperature). In this embodiment, the output is changed in 21 steps from 5 to 100% from 0 to 100% by phase control. The output of 100% is when the electric power from the commercial power source is fully energized to the heating element.

  The recording material P carrying the unfixed toner image T is introduced into the nip portion N while the temperature of the heater 3 rises to the fixing temperature and the rotational peripheral speed of the film 2 is steady. Then, the recording material P is nipped and conveyed by the surface of the film 2 and the surface of the pressure roller 6 at the nip portion N. In the conveyance process, the pressure of the nip portion N is applied to the recording material P and the heat of the heater 3 is applied through the film 2, whereby the unfixed toner image T on the recording material P is transferred to the recording material P. It is heat-fixed on the surface. Then, the recording material P on which the unfixed toner image T is heat-fixed is separated (curvature separation) from the surface of the film 2 and discharged from the nip portion N.

  Here, the conveyance reference of the recording material in the printer of this embodiment will be described with reference to FIGS.

  The printer of this embodiment uses the center of the recording material P in the paper width as the conveyance reference. Therefore, in the fixing device 114, the center in the longitudinal direction of the heater 3 is a conveyance reference for the recording material P of various sizes. O is a recording material conveyance reference line (virtual line) (FIG. 7). 3 and 7, A is a region (maximum sheet passing region) through which the recording material passes through the heater 3 when a recording material having a fixed maximum paper width usable in the printer is introduced into the nip portion N. This sheet passing area A substantially corresponds to the length of the carbon-based heating element 3 b of the heater 3. B is an area (sheet passing area) through which the recording material passes through the heater 3 when a recording material having a fixed minimum sheet width usable in the printer is introduced into the nip portion N. C is a region (non-sheet passing region) where the recording material does not pass through the heater 3 when a recording material (small size paper) having a paper width smaller than that of the maximum paper width is introduced into the nip portion N. The area width of the non-sheet passing area C varies depending on the size of the small size paper.

  The thermistor 5 for detecting the temperature of the heater 3 is located on the back surface of the substrate 3a of the heater 3 at a position corresponding to the minimum sheet passing area B through which the recording material always passes even if a recording material having a large or small paper width is introduced into the nip portion N. It is provided in contact with.

(4) Heat generation characteristics of NTC heating element Next, the reason why the excessive temperature rise in the non-sheet passing area can be reduced by using the NTC characteristic heater 3 will be described with reference to FIG. FIG. 8 is an electrical model diagram of the heater 3.

The current flowing through the carbon-based heating element 3b of the heater 3 is I, the resistance value at the center (sheet passing area) in the longitudinal direction of the heater 3 is R1, and the resistance value at the end (one side of the non-sheet passing area) is R2. In this case, the heat value W1 at the center is I ² · R1, and the heat value W2 at the end is I ² · R2. For easy understanding, the position where R1 = 2 × R2 in a state where the recording material is not passed (introduced) into the nip portion N, that is, the length of the non-sheet passing region (the sum of the lengths of both ends). ) Is considered to be separated from the non-sheet-passing area at a position where it is equal to the length of the sheet-passing area. Here, in a state where no recording material is passed through the nip portion N, the resistance value per unit length of the carbon-based heating element 3 b is uniform throughout the heater 3.

  Considering a case where a small-size paper is passed through a PTC (Positive Temperature Coefficient) heating element, the heating element contacts the paper through a film, so the heat of the central portion is deprived by the width of the small-size paper. Since the thermistor detects the temperature of the central portion and the energization control is performed so that the temperature of the central portion does not decrease, the end portion where the heat is not taken away by the paper becomes higher than the central portion. In this case, since the resistance value per unit length of the end portion is higher than the resistance value per unit length of the central portion due to the PTC characteristic, the heat generation amount W2 at one end is larger than the heat generation amount W1 at the central portion. Become bigger. That is, the calorific value per unit length of the end portion is larger than that in the central portion. Further, when the heat generation amount increases, the temperature rises, so that the resistance further increases and the heat generation amount further increases.

  On the other hand, the resistance value per unit length at the end is lower than the resistance per unit length at the center because the resistance value is lower at higher temperatures when small-size paper is passed through the NTC heating element. Also lower. Therefore, the heat value W2 at the end on one side is smaller than the heat value W1 at the center. That is, the calorific value per unit length of the end portion is smaller than that in the central portion. For this reason, the heat_generation | fever of both ends can be suppressed rather than the time of a PTC heat generating body.

  For the above reasons, if the resistance heating element has an NTC characteristic, the temperature of the end portion when passing small-size paper can be kept low.

  Next, the material and manufacturing method of the carbon-based heating element 3b will be described. In the carbon-based heating element of the present embodiment, the organic substance to be carbonized has a carbonization yield of 5% or more by heat treatment in a non-oxidizing atmosphere of carbon, for example, in a vacuum or an inert gas such as nitrogen gas or argon. Use organic materials shown. As this organic substance, for example, natural high molecular weight having condensed polycyclic aromatics such as chlorinated vinyl chloride resin, polyvinyl chloride, polyacrylonitrile, polyvinyl alcohol, polyvinyl chloride-polyvinyl acetate copolymer in the basic structure of the molecule. Examples include molecular substances. Used. In addition, this organic substance has a condensed polycyclic aromatic group such as a thermoplastic resin such as polyamide, a phenol resin, a furan resin, an epoxy resin, an unsaturated polyester resin, a thermosetting resin such as polyimide in the basic structure of the molecule. Examples include natural polymeric substances. Examples of the organic substance include natural polymer substances having condensed polycyclic aromatics such as lignin, cellulose, gum tragacanth, gum arabic, and sugars in the basic structure of the molecule. In addition, examples of the organic substance include synthetic polymer substances having a condensed polycyclic aromatic compound such as a formalin condensate of naphthalenesulfonic acid and a copna resin in the basic structure of the molecule.

The non-oxidizing atmosphere of carbon (in an atmosphere in which carbon hardly oxidizes) refers to a vacuum (1 × 10 ⁻² Pa or less), a nitrogen gas, or an inert gas. By performing heat treatment in such an atmosphere, oxidation during the heat treatment can be reliably prevented, and a carbon-based heating element can be stably produced.

  The carbonization yield here means the weight of carbonized material (composite such as graphite and amorphous carbon) obtained by heat treatment in a non-oxidizing atmosphere of carbon, the weight of organic material in the raw material before heat treatment, It is the ratio. Thus, for example, a carbonization yield of 5% means that when the weight of the organic material before heat treatment is 100 g, the weight of the carbonized material after heat treatment is 5 g. Incidentally, when an organic material is heat-treated in an oxidizing atmosphere, the oxidation generally starts from a heat treatment temperature of about 500 ° C., depending on the type of organic material used. Since oxidation occurs, carbon decomposes or burns, and a stable carbonized material that can be used as a heater cannot be obtained. In addition, the kind and amount of the organic substance to be used are appropriately selected depending on the resistance temperature characteristic, resistance value, and shape of the carbon-based heating element, and can be used as one kind or a mixture of several kinds of organic substances.

  Further, carbon powder may be mixed in advance with organic matter. The carbon powder here includes carbon black, graphite, coke, and the like, and can be used as one kind or a mixture of several kinds depending on the resistance value and shape of the carbon-based heating element. In this case, electrons flow in the carbon powder mixed beforehand and in the organic substance carbonized by heat treatment. The technique of mixing carbon powder in the raw material in advance is effective when it is desired to reduce the volume resistance of the carbon-based heating element.

  In order to produce a carbon-based heating element having an arbitrary resistance value, it is desirable to heat-treat a raw material in which an insulating material or a semiconductive material is mixed with an organic material. As the insulating material and semiconductive material, metal carbide, metal boride, metal silicide, metal nitride, metal oxide, semimetal nitride, semimetal oxide, and semimetal carbide are preferable. One type or several types may be selected depending on the resistance value and shape.

  Ingredients mixed with insulating materials and semiconducting materials have not only carbon but also insulating materials and semiconducting materials that inhibit the conduction of electrons that flow through carbon. The system heating element can be easily manufactured. By using these methods, the resistance value of the carbon-based heating element and the degree of freedom of shapes that can be taken are expanded.

  That is, an organic substance to be carbonized by heat treatment is mixed with at least one or several insulating or semiconductive substances. If a carbon-based heating element is produced by heat-treating it in a non-oxidizing atmosphere of carbon after molding, the setting range of resistance temperature characteristics, resistance value, and shape of the carbon-based heating element is expanded. Therefore, the carbon-based heating element 3b suitable for the heater 3 of the fixing device 114 using the film 2 can be easily provided. If necessary, not only the insulating material and the semiconductive material, but also carbon powder may be mixed with the raw material.

  Further, boron nitride, alumina, silicon carbide, boron carbide or the like is recommended as the insulating material or semiconductive material. By using such a substance, the resistance value of the carbon-based heating element can be easily controlled.

  Moreover, it is preferable that the heat processing temperature at the time of heat processing of the said carbon-type heat generating body (the highest temperature reached at the time of heat processing) is 850 degreeC or more and 1750 degrees C or less. By performing heat treatment at the above temperature, the rate of change in resistance of the carbon-based heating element can be made near zero or negative. Further, the resistance value of the carbon-based heating element can be adjusted to a practical resistance value, and a fixing device can be provided in which the temperature rise of the non-sheet passing portion is suppressed and the power is not excessive or insufficient.

  Graphitization can be adjusted to some extent by the type of organic matter to be heat-treated and the carbon powder mixed in the raw materials and the amount of mesh, but it depends greatly on the heat-treating conditions of the organic matter to be graphitized. The degree of increases.

  As described above, the carbon-based heating element has a feature that the resistance temperature characteristic can be greatly changed easily only by changing the conditions of the heat treatment and adjusting the graphitization.

  In the carbon-based heating element 3b provided on the surface of the substrate 3a of the heater 3, other desired functions such as a heat-resistant lubricant layer are provided on the film sliding surface sliding with the inner surface of the film 2 as necessary. Layers can also be added.

(5) Specific example of heater 3 The structure of the example heater 1 and the example heater 2 will be described below as a specific heater example. In addition, as a comparative example of the example heater 1 and the example heater 2, configurations of the comparative example heater 1 and the comparative example heater 2 will be described.

  The external form of each heater of the example heater 1, the example heater 2, the comparative example heater 1 and the comparative example heater 2 is the same as that of the heater 3 shown in FIG. 6, but the component and thickness of the protective layer of each heater are different. ing. Table 1 shows the configuration of each heater.

In each heater, a common carbon-based heating element 3b was used. That is, chlorinated vinyl chloride resin, graphite powder, and boron nitride are dispersed and kneaded as a precursor of the carbon-based heating element 3b, formed into a rod shape with an extrusion molding machine, and then vacuumed (0.01 Pa or less) at 1500 ° C. By performing the heat treatment, a substrate having a predetermined specific resistance is obtained in a room temperature environment. The temperature of the room temperature environment is 20 ° C., and the specific resistance is 30.1 × 10 ⁻³ Ω · cm. Then, this base material was processed into a shape of length 250 mm × width 5 mm × thickness 0.2 mm, and a total resistance value of 75.2Ω was used as the carbon-based heating element 3b. About the protective layer 3c, while changing the component of the protective layer 3c in each heater, the method of making the protective layer 3c adhere to the carbon heating element 3b was changed.

(5-1) Example heater 1
In the example heater 1, the carbon-based heating element 3b is bonded to an alumina ceramic substrate (hereinafter referred to as an alumina substrate) 3a with an epoxy adhesive (not shown) over the entire longitudinal direction. is there. The protective layer 3c covering the carbon-based heating element 3b is composed of a layer in which a filler of ticker boron as a scaly filler is dispersed by 35% by weight in a polyimide resin as a heat-resistant resin. That is, boron nitride is used as a material for the flake-like filler. The protective layer 3c is provided on the surface of the carbon heating element 3b opposite to the alumina substrate 3a so as to have a thickness of 25 μm.

  A manufacturing procedure of the example heater 1 will be described.

  First, the electrodes 31 and 32 were formed with silver Pd (palladium) so as to cover both ends of the carbon-based heating element 3b on the alumina substrate 3a (FIG. 6D). The silver Pd paste was applied by screen printing and then baked to form electrodes 31 and 32 so as to have a thickness of 15 μm.

Next, a polyimide varnish mixed with boron nitride is applied by screen printing so as to cover the entire area of the carbon-based heating element 3b on the opposite side of the alumina substrate 3a and the ends of the electrodes 31 and 32. A layer (hereinafter referred to as a polyimide protective layer) 3c was formed. Boron nitride having a flake-like shape and an average particle diameter of 6 μm was used. The scaly filler may be semiconductive or insulating. Therefore, as a material for the flake-like filler, a flake-like filler such as plate-like alumina, glass flake, molybdenum disulfide (MoS ₂ ), tungsten disulfide (WS ₂ ), mica and the like is used in addition to boron nitride. You can also. However, from the viewpoint of fixing properties, the higher the thermal conductivity of the scaly filler material, the better. Therefore, it is desirable to use a ceramic or glass-based filler as the scaly filler material. The term “flakes” as used herein is a general term for plate-like ones, and is not a whisker shape, a needle shape, a spherical shape, or a combination of these.

  (A) of FIG. 9 is the figure which represented typically the orientation state of the flaky boron nitride filler inside the polyimide resin of the polyimide protective layer 3c. The flake-like particles of ticker boron dispersed in the polyimide varnish follow the surface of the carbon-based heating element 3b opposite to the alumina substrate 3a (the surface of the carbon-based heating element 3b) when screen-printed. Since it receives force, it is distributed so as to be laminated on the surface of the carbon-based heating element 3b. That is, the scaly boron nitride filler that is a scaly filler is laminated in the thickness direction of the polyimide protective layer 3 c inside the polyimide resin that is a heat-resistant resin.

  FIG. 9B is a diagram schematically showing a state of deformation of the polyimide protective layer 3c when irregularity occurs during energization of the heater 3 and the heater 3 becomes abnormally hot. At such an abnormally high temperature, the surface of the polyimide protective layer 3c is deformed due to the thermal expansion of the alumina substrate 3a or the thermal expansion of the resin itself, and stress is generated inside the polyimide protective layer 3c. The internal stress concentrates on the polyimide resin sandwiched in a narrow area between the scaly fillers because the scaly boron nitride filler is harder than the polyimide resin. As a result, the polyimide protective layer 3c is easily broken starting from the polyimide resin between the flake fillers. Conversely, when there is no flake-like filler in the polyimide resin, the internal stress due to deformation is dispersed in a relatively wide range and the strength of the polyimide resin is exerted, so compared with the case where the flake-like filler is mixed. It is quite difficult to tear.

(5-2) Example heater 2
The configuration of the example heater 2 is the same as that of the example heater 1 except for the configuration of the protective layer. Therefore, the same components are denoted by the same reference numerals and the description thereof is omitted.

  The protective layer 3c of the example heater 2 has a configuration in which boron nitride flake filler is dispersed by 35% by weight in a fluororesin (PFA) as a heat resistant resin.

  When this protective layer (hereinafter referred to as a fluorine protective layer) 3c is applied, a dispersion (water-based) in which a fluororesin and a boron nitride filler are dispersed is prepared. Then, the dispersion is sprayed on the alumina substrate 3a on which the carbon-based heating element 3b and the electrodes 31, 32 are provided. The same region as the heater 1 of the embodiment, that is, the surface of the carbon-based heating element 3b and the ends of the electrodes 31, 32 are used. It was applied so as to cover the part. The applied dispersion was dried and then baked at about 380 ° C. so as to have a thickness of 10 μm. Incidentally, the particle diameter of boron nitride was the same as that of the heater 1 of the embodiment, and an average particle diameter of 6 μm was used.

  The boron nitride filler distribution state in the fluorine protective layer 3c of the example heater 2 is also in a state of being laminated inside the fluororesin, as in FIG. 9A, which is the boron nitride filler distribution state of the example heater 1. Yes. This is because when the spout from the spray containing the flaky boron nitride filler lands on the surface of the carbon-based heating element 3b, the flaky filler receives a force to follow the surface of the carbon-based heating element 3b. is there.

(5-3) Comparative heater 1
The configuration of the comparative heater 1 is the same as that of the embodiment heater 1 except for the protective layer 3c. Therefore, the same components are denoted by the same reference numerals and the description thereof is omitted.

  The protective layer 3c of the comparative example heater 1 is different from the protective layer 3c of the example heater 1 only in that boron nitride is not mixed in the polyimide resin. The protective layer 3c was formed in exactly the same manner.

(5-4) Comparative heater 2
The configuration of the comparative example heater 2 is the same except for the configuration of the example heater 2 and the configuration of the protective layer 3c. Therefore, the same components are denoted by the same reference numerals and the description thereof is omitted.

  The protective layer 3c of the comparative example heater 2 is different from the protective layer 3c of the example heater 2 only in that boron nitride is not mixed in the fluororesin (PFA). The protective layer 3c of the example heater 2 was formed exactly the same.

  Below, the result of having performed the risk assessment test about Example heater 1, Example heater 2, Comparative example heater 1, and Comparative example heater 2 is shown. Here, as the risk assessment test, an abnormal temperature increase test assuming a local abnormal temperature increase due to multiple feeding of narrow cardboard (small size cardboard) as the recording material P, and energization of the heater at the time of stop were performed. Two energizing runaway tests were performed. By the way, neither risk assessment test actually occurs unless there is an abnormality that is more than a double failure.

  First, the following method was used as a method for an abnormal temperature rise test. That is, several bundles of six envelopes (COM10) are prepared, and these are continuously passed through a fixing device that is temperature-controlled at a process speed of 120 mm / sec at regular intervals of 12 PPM. It was tested whether the heater was broken. Usually, an image forming apparatus such as a copying machine or a printer is designed to have a structure in which double feeding is not performed by a paper feed opening mechanism. In addition, the image forming apparatus includes a mechanism for stopping the driving by detecting the double feeding by monitoring the change in the transfer current at the transfer unit even if the double feeding is performed.

  In the energization runaway test, only the heater was energized without driving the pressure roller from the coldest condition in the morning, causing the heater to rise rapidly, and the heater was forcibly and thermally destroyed. . As a condition for energization, the energization was performed in a full energization mode with an input voltage of 240 V without control by a thermistor. This energization condition is also detected by double detection such as simultaneous failure of the safety circuit which detects the energization runaway due to the MPU failure of the image forming apparatus and the abnormal voltage (output at abnormally high temperature) of the thermistor and turns off the relay forcibly. It won't happen unless it breaks down.

  As shown in the risk assessment test results in Table 2 above, the comparative heater 1 and the comparative heater 2 were incomplete fractures in which the protective layer 3c did not fracture in any of the tests.

  On the other hand, the example heater 1 exhibited an effect both in the abnormal temperature rise test and the energization runaway test, and completely broken including the protective layer 3c.

  FIG. 10B is a diagram schematically showing a state in which the complete breakage including the protective layer 3c has occurred in the heater 1 of the embodiment. FIG. 10A is a diagram schematically showing an incomplete break in which the protective layer 3c is not broken in the comparative heater 1 and the comparative heater 2. FIG.

  When the protective layer 3c is incompletely broken, as shown in FIG. 10A, the protective layer 3c is connected even if the carbon-based heating element 3b is broken. Therefore, the carbon-based heating element 3b is still not sufficiently separated, and in the worst case, the energization may not be cut off, which is not preferable in terms of risk assessment. On the other hand, when the protective layer 3c is completely broken, the carbon-based heating element 3b is sufficiently separated after breaking as shown in FIG.

  In the example heater 2, the protective layer 3c was not completely broken in the energization runaway test, but the effect was shown in the abnormal temperature rise test, and the example heater 2 was completely broken. Example heater 2 used PFA as the heat-resistant resin for protective layer 3c, but in the mode in which the temperature was raised from the cold in the morning as in the energization runaway test, PFA was only softened, and the PFA resin still remains. This is because the ductility is maintained and it is difficult to tear. On the other hand, the effect of the abnormal temperature rise test is due to the fact that the temperature rises after warming up before passing the paper, so that the heat spreads and the temperature rises, so that the PFA is broken.

  Conversely, the reason why the heater 1 of the example is effective in both the abnormal temperature rise test and the energization runaway test is that the heat-resistant resin of the protective layer 3c is a thermosetting resin polyimide resin. In the first place, polyimide resin is not as ductile at a low temperature as fluororesin such as PFA, and it becomes brittle because it becomes hard even at high temperature, so that it easily breaks.

  As described above, the protective layer 3c of the heater 3 has a flake-like filler blended inside the heat resistant resin, and the filler is laminated in the thickness direction of the protective layer 3c inside the heat resistant resin. . Therefore, as seen in the example heater 1 and the example heater 2, the protective layer 3c on the surface of the carbon-based heating element 3b can be easily torn when the substrate 3a is broken due to a runaway current of the heater 3 or abnormal temperature rise. The carbon-based heating element 3b can be broken more stably. That is, it is possible to reduce the occurrence of incomplete breakage in the carbon-based heating element 3b when the substrate 3a is broken.

  Further, the protective layer 3c can be easily avoided by using ceramics or glass as a material for the flake-like filler.

  Moreover, the protective layer 3c exhibits the effect excellent in abrasion property by using a thermosetting resin as a material of a heat resistant resin.

  Further, the fixing device 114 having the heater 3 of the present embodiment can surely break the heater due to energization runaway or abnormal temperature rise.

[Others]
1) A through-hole may be provided in the substrate 3a of the heater 3 as necessary in order to easily break the substrate 3a.

  2) Other desired functional layers such as a heat-resistant lubricant layer can be added to the surface of the protective layer 3c of the heater 3 on which the inner surface of the film 2 slides, if necessary.

  3) In the fixing device 114, the driving method of the film 2 which is a flexible member is not limited to the pressure roller driving method of the embodiment. A driving roller may be provided on the inner peripheral surface of the endless flexible member and driven while applying tension to the flexible member, or the flexible member is formed into a roll-ended web shape. It is also possible to adopt a device configuration that travels and moves while feeding it out.

  4) In the fixing device 114, the backup member is not limited to the roller body, but may be a rotating belt body.

  5) The temperature detection means provided in the heater 3 is not limited to the thermistor. Various types of contact type or non-contact type can be used.

  6) The image heating apparatus according to the present invention is not limited to the fixing device of the image forming apparatus. In addition, the image heating apparatus that presupposes an image and the surface property such as gloss are improved by reheating the recording medium carrying the image. It can also be used as an image heating device.

  7) In the above embodiment, the base material obtained by firing the precursor is processed into the shape of the heating element to obtain the carbon-based heating element 3b, which is adhered and disposed on the alumina substrate. As another example of disposing the carbon-based heating element 3b on the alumina substrate, the carbon-based heating element is disposed on the alumina substrate by directly applying the precursor onto the alumina substrate by screen printing or coextrusion and then baking. It can also be made.

1 is a schematic configuration diagram of an example of an image forming apparatus. It is a cross-sectional side model diagram of an example of a fixing device. It is a vertical side view model diagram of the fixing device. FIG. 3 is a diagram of the fixing device as viewed from the recording material introduction side. It is explanatory drawing of a stay. It is explanatory drawing of a heater. It is a block diagram of an example of the electric power feeding control system of a heater. It is an electrical model figure of a heater. (A) is the figure which represented typically the orientation state of the flaky boron nitride filler inside the polyimide resin of a polyimide protective layer. (B) is the figure which showed typically the mode of a deformation | transformation of the polyimide protective layer when a heater became abnormally high temperature. (A) is the figure which represented typically the incomplete fracture | rupture which the protective layer in the comparative example heater 1 and the comparative example heater 2 has not fractured. (B) is the figure which represented typically the state by which complete fracture | rupture including the protective layer in Example heater 1 occurred.

Explanation of symbols

2 ... Heat-resistant film 3 ... Heater 3a ... Substrate 3b ... Carbon-based heating element 3c ... Protective layer 6 ... Pressure roller 114 ... Fixing device N ... Nip part P ... Recording material, T ... Unfixed toner image

Claims (5)

A heating element that generates heat when energized, the heating element provided on the substrate along a longitudinal direction of the substrate, and a protective layer that covers a surface of the heating element opposite to the substrate. In the heating element,
The heating element is a carbon-based heating element formed by carbonizing an organic substance, and the protective layer contains a flake-like filler in the heat-resistant resin, and the filler is added in the heat-resistant resin. A heating body characterized by being laminated in the thickness direction of the protective layer.   The heating body according to claim 1, wherein the filler material is ceramics.   The heating body according to claim 1, wherein the filler material is glass.   The heating body according to claim 1, wherein the material of the heat resistant resin is a thermosetting resin. A heating member; a flexible member that moves in contact with the heating member; and a backup member that forms a nip portion with the heating member via the flexible member, and carries an image at the nip portion. In an image heating apparatus that heats a recording material to be sandwiched and conveyed,
An image heating apparatus comprising the heating body according to claim 1 as the heating body.