JP2007025474A - Heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a more reliable heating device capable of preventing temperature rise at a paper non-passing part without lowering the specification of the device with inexpensive and simple constitution, and to provide an image forming apparatus. <P>SOLUTION: The heating device heats a member to be heated by a heating body comprising: a base plate; a resistance heating element formed on the base plate and having negative resistance temperature characteristic; and an electrode feeding power to the resistance heating element. In the heating device, the resistance heating element is divided into three or more parts in a longitudinal direction, and the power is fed to the respective blocks of the divided resistance heating element so that a current may flow in a direction where the member to be heated is conveyed, and the respective blocks of the divided resistance heating element are electrically connected in series. The shape of the resistance heating element seen from a heating surface is a rectangle or a parallelogram and a trapezoid. It is good to take constitution where the resistance of the resistance heating element is made high near a gap between the respective blocks to compensate the lowering of calorific power at the gap part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heating device such as a copying machine or a laser beam printer, and an image forming apparatus including the heating device.

  2. Description of the Related Art Conventionally, for example, a recording material heating apparatus for image heating and fixing includes a heat roller as a heating body maintained at a predetermined temperature, and a pressure roller as a pressure body in pressure contact with the heat roller. A heat roller system is often used in which a recording material as a material to be heated is introduced into a nip portion to be formed and heated while being nipped and conveyed.

  In addition to these, various systems and configurations such as a flash heating system, an oven heating system, and a hot plate heating system are known and in practical use.

  Recently, in place of such a system, a heat source (hereinafter, referred to as a heating body), a heating member support (stay), and a heat resistant film as a flexible member that is conveyed while being pressed against the heating body. (Hereinafter referred to as a film) and a pressure roller as a pressure member that causes the recording material as the material to be heated to adhere to the heating body via the film, and heat of the heating body to the recording material via the film An image heating and fixing type heating device (film heating type heating device) has been devised (for example, a film heating type heating device) in which a non-fixed image formed and supported on the recording material surface is heated and fixed on the recording material surface by applying (for example, a film heating method heating device) And Patent Documents 1 and 2).

  In this film heating type heating apparatus, a so-called ceramic heater is generally used as a heating element. The ceramic heater basically forms a resistance heating element on a ceramic substrate and heats the resistance heating element by power feeding. The temperature of the heating element is detected by a temperature measuring element such as a thermistor that is in contact with or bonded to the heating element, and the temperature is controlled to be a predetermined temperature based on the detected temperature.

In such a film heating type heating apparatus or image heating and fixing apparatus, a heater having a low heat capacity can be used. For this reason, it is possible to save power and shorten the wait time (quick start) as compared with conventional devices such as a heat roller method and a belt heating method.
JP-A-4-44075-44083 JP-A-4-204980-204984

  In the above-mentioned film heating type heating device, when a recording material (hereinafter referred to as small size paper) having a width that is somewhat smaller than the maximum size recording material (hereinafter referred to as large size paper) is passed. In many cases, the temperature control is performed based on the output of the temperature measuring element provided in the sheet passing portion, and the non-sheet passing portion does not take heat away from the recording material. It rises compared. This is a phenomenon called non-sheet passing portion temperature rise. In addition, especially when small recording paper and thick recording materials (thick paper, envelopes, etc.) are multi-fed and passed, a large amount of heat is taken away by the recording material at the paper passing portion. A large amount of electric power is supplied to the non-sheet-passing portion and the temperature rises significantly. Therefore, when the number of double feeds is large, there is a risk that the heating body, the pressure roller and the like are deteriorated or broken. Further, when the temperature rise at the non-sheet passing portion is large, there is a possibility that a high temperature offset may occur at the end when the large size paper is passed immediately after the small size paper is passed.

  In order to prevent the temperature rise of the non-sheet passing portion, when small-size paper is continuously fed, the throughput is reduced to protect the heating body, pressure roller, etc. of the non-sheet passing portion, or in the longitudinal direction. There has been devised and implemented a method of providing another member (for example, contacting the heat-dissipating roller to the pressure roller) for making the temperature distribution uniform. However, reducing the throughput reduces the specifications of the image forming apparatus, and providing a separate member increases the cost.

  In addition, as a means for fundamentally solving the temperature rise of the non-sheet passing portion, a resistor having a negative resistance temperature characteristic (characteristic that the resistance decreases as the temperature rises) as disclosed in JP-A-6-19347 There has also been devised a heating element in which a heating element is formed in a line strip shape on a substrate and power is supplied in the longitudinal direction. However, in general, a resistance heating element having a negative resistance temperature characteristic has a high volume resistance, and it is often difficult to obtain a resistance in a range that can be used with a commercial power source with a normal resistance heating element pattern.

  The object of the invention according to the present application is to prevent the temperature rise of the non-sheet passing portion without lowering the specifications of the apparatus with a low cost and simple configuration in a heating element using a resistance heating element having a negative resistance temperature characteristic. It is another object of the present invention to provide a heating device and an image forming apparatus with higher reliability.

  In order to achieve the above object, a first invention according to the present application provides a material to be heated by a heating element including at least a substrate, a resistance heating element having negative resistance temperature characteristics, and an electrode that supplies power to the resistance heating element. In a heating device for heating, the resistance heating element is divided into three or more parts in the longitudinal direction, and the divided resistance heating element is fed so that a current flows in the direction of conveying the heated material, and the divided resistance heating element is divided. The bodies are electrically connected in series.

  A second invention according to the present application is characterized in that, in the above-described heating device, the resistance heating element includes graphite.

  A third invention according to the present application is characterized in that, in the above heating apparatus, the heating body is configured to form a resistance heating element on a ceramic substrate.

  A fourth invention according to the present application is characterized in that, in the above-described heating device, the shape of each portion of the divided resistance heating element viewed from the heating surface is a parallelogram or a trapezoid.

  According to a fifth aspect of the present application, in the above-described heating device, a part of the resistance heating element in the longitudinal direction has a volume resistance of the resistance heating element different from that of the other part, or the resistance heating element has a different thickness. It is characterized by being different.

  According to a sixth aspect of the present application, at least a heating body, a flexible member that contacts and slides one surface with the heating body, and the other surface contacts the heated material, and the heated material via the flexible member. In a heating apparatus that includes a pressure member that is in close contact with a heating body, and that heats the material to be heated by sandwiching and transporting the flexible member and the material to be heated in a nip formed by the heating body and the pressure body The heating device has the above-described configuration of the heating device.

  According to a seventh aspect of the present application, there is provided an image forming apparatus including an image forming unit that forms an image on a recording material and an image heating unit that heats the image on the recording material. A device is provided.

  By using the heating device and the image forming apparatus having the above-described configuration, it is possible to prevent the temperature rise of the non-sheet passing portion without lowering the specifications of the device with a low cost and simple configuration, and a more reliable heating device. In addition, an image forming apparatus can be provided.

Example 1
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

(1) Image Forming Apparatus Example FIG. 5 is a schematic configuration diagram of an image forming apparatus example according to the present embodiment. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process. In the image forming apparatus of this embodiment, the maximum sheet passing width is A4 size (paper width: 210 mm).

  Reference numeral 101 denotes an electrophotographic photosensitive drum as an image carrier, which is rotationally driven in a counterclockwise direction indicated by an arrow with a predetermined peripheral speed (process speed).

  Reference numeral 102 denotes charging means such as a contact charging roller, and the surface of the photosensitive drum 101 is uniformly charged (primarily charged) to a predetermined polarity and potential by the charging means.

  Reference numeral 103 denotes a laser beam scanner as an image exposure means, which is a laser beam that is on / off modulated in response to time-series electric digital pixel signals of target image information input from an external device such as an image scanner / computer (not shown). Then, scanning exposure (irradiation) is performed on the charged surface of the photosensitive drum 101. By this scanning exposure, the charge in the exposed bright portion of the surface of the photosensitive drum 101 is removed, and an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 101.

  A developing device 104 supplies developer (toner) to the surface of the photosensitive drum 101 from the developing sleeve, and the electrostatic latent image on the surface of the photosensitive drum 101 is sequentially developed as a toner image which is a transferable image. 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 109 denotes a paper feed cassette on which the recording material P is loaded and stored. Based on the paper feed start signal, the paper feed roller 108 is driven and the recording material P in the paper feed cassette 109 is separated and fed one by one, and passes through a sheet path 112 including a transport roller 110, a registration roller 111, and the like. The photosensitive drum 101 is introduced at a predetermined timing into a transfer portion that is a contact nip portion between the photosensitive drum 101 and a transfer roller 106 as a contact / rotary transfer member. That is, when the leading edge of the toner image on the photosensitive drum 101 reaches the transfer site, the conveyance of the recording material P is controlled by the registration roller 111 so that the timing of the leading edge of the recording material P also reaches the transfer site. Is done.

  The recording material P introduced into the transfer portion is nipped and conveyed between the transfer portions, and a transfer voltage (transfer bias) controlled in a predetermined manner is applied to the transfer roller 106 from a transfer bias application power source (not shown). The transfer roller 106 serving as the transfer member and transfer voltage control will be described later. A transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 106, whereby the toner image on the surface of the photosensitive drum 101 is electrostatically transferred onto the surface of the recording material P at the transfer portion.

  The recording material P that has received the transfer of the toner image at the transfer portion is separated from the surface of the photosensitive drum 101 and is conveyed and introduced to the heating device 107 through the sheet path 113, where the toner image is subjected to heating and pressure fixing processing.

  On the other hand, the surface of the photosensitive drum 101 after separation of the recording material (after transfer of the toner image to the recording material P) is cleaned by the cleaning device 105 after removal of transfer residual toner, paper dust, and the like, and is repeatedly used for image formation. Is done.

  The recording material P that has passed through the heating device 107 passes through the sheet path 114 and is discharged from the discharge outlet onto the discharge tray 115.

The transfer roller 106 as a contact type / rotary type transfer member is generally adjusted to a resistance of about 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω with carbon, ion conductive filler, etc. on a core metal such as SUS or Fe. An elastic sponge roller having a semiconductive sponge elastic layer is used. In this embodiment, an ion conductive transfer roller is used in which NBR rubber and a surfactant are reacted concentrically and integrally around the outer periphery of the metal core, and a conductive elastic layer is formed in a roller shape. Resistance values in the range of 1 × 10 ^{8 to} 5 × 10 ⁸ Ω were used.

  It is known that the resistance of the transfer roller is likely to fluctuate according to the temperature and humidity of the ambient environment, and the fluctuation of the resistance of the transfer roller causes a transfer defect or paper trace. Therefore, in order to prevent the occurrence of transfer defects and paper marks due to resistance fluctuations of the transfer roller, the resistance value of the transfer roller is measured, and the transfer voltage applied to the transfer roller is appropriately set according to the resistance value measurement result. “Applied transfer voltage control” is used.

  An example of such applied transfer voltage control is ATVC control (Active Transfer Voltage Control) disclosed in Japanese Patent Laid-Open No. 2-123385. The ATVC control is a means for optimizing the transfer bias applied to the transfer roller at the time of transfer, and prevents the occurrence of transfer failure and paper trace. The transfer bias applies a desired constant current bias from the transfer roller to the photosensitive drum during the pre-rotation stroke of the image forming apparatus, detects the resistance of the transfer roller from the bias value at that time, and transfers the print stroke during the transfer stroke. A transfer bias corresponding to the resistance value is applied to the transfer roller. Also in this embodiment, the above ATVC control is used.

(2) Heating device 107
Next, the heating device 107 in the present embodiment will be described. FIG. 4 is a schematic configuration diagram of a film heating type heating apparatus according to the present embodiment. This apparatus is a tensionless type apparatus disclosed in Japanese Patent Laid-Open Nos. 4-44075 to 44083 and 4-204980 to 204984.

  This tensionless type film heating type heating device uses an endless belt-shaped or cylindrical heat-resistant film, and at least part of the circumference of the film is always tension-free (in a state where no tension is applied), The film is a device that is rotationally driven by the rotational driving force of the pressure member.

  Reference numeral 1 denotes a stay, which is a heat resistant and rigid member as a heating body holding member and a film guide member. Reference numeral 3 denotes a ceramic heater as a heating body, which is disposed and held on the lower surface of the stay 1 along the length of the stay. Reference numeral 2 denotes an endless (cylindrical) heat-resistant film that is externally fitted to a stay 1 that is a film guide member including a heating element 3. The inner peripheral length of the endless heat-resistant film 2 and the outer peripheral length of the stay 1 including the heating element 3 are about 3 mm larger than that of the film 2, so that the film 2 is fitted with a margin in the peripheral length. ing.

  The stay 1 can be composed of a high heat resistant resin such as polyimide, polyamideimide, PEEK, PPS, liquid crystal polymer, or a composite material of these resins and ceramics, metal, glass, or the like. In this example, a liquid crystal polymer was used.

  Film 2 has a film thickness of 100 μm or less, preferably 50 μm or less and 20 μm or more, heat resistant single layer film such as PTFE, PFA, FEP, polyimide, polyamide, etc. in order to reduce heat capacity and improve quick start performance A composite layer film in which PTFE, PFA, FEP or the like is coated on the outer peripheral surface of a film such as imide, PEEK, PES, or PPS can be used. In this embodiment, a polyimide film having a film thickness of about 50 μm coated with PTFE on the outer peripheral surface was used. The outer diameter of the film 2 was 18 mm.

  Reference numeral 4 denotes a pressure roller as a film outer surface contact driving means for forming a pressure nip portion (fixing nip portion) N with the film 2 sandwiched between the heating member 3 and rotating the film 2. The pressure roller 4 is composed of a cored bar 4a, an elastic layer 4b, and an outermost release layer 4c. The film 2 is sandwiched by a bearing means / biasing means (not shown) with a predetermined pressing force. It is disposed in pressure contact with the surface. In this embodiment, the core metal 4a is an aluminum core, the elastic layer 4b is silicone rubber, and the release layer 4c is a PFA tube having a thickness of about 30 μm. The outer diameter of the pressure roller 4 was 20 mm, and the thickness of the elastic layer 4b was 3 mm.

  The pressure roller 4 is rotationally driven by the drive system M in a clockwise direction indicated by an arrow at a predetermined peripheral speed. By the rotational driving of the pressure roller 4, a rotational force acts on the film 2 by the frictional force between the pressure roller and the film outer surface at the pressure nip portion N, and the film 2 has a heating body at the fixing nip portion N on the inner surface side. 3, while being in close contact with the surface of 3, the outer periphery of the stay 1 is driven counterclockwise in the counterclockwise direction indicated by the arrow at a rotational speed substantially equal to the rotational speed of the pressure roller 4.

(3) Heating body 3
Next, the heating body 3 in the present embodiment will be described. FIG. 2 is a diagram illustrating a front view of the heating body 3 and a circuit for performing energization control in this embodiment. Moreover, FIG. 3 is sectional drawing of the heating body 3 in a present Example.

  The heating element 3 is an elongated heat-resistant / insulating / good heat-conductive substrate 7 whose longitudinal direction is a direction perpendicular to the conveying direction a of the recording material P as a material to be heated, the surface of the substrate (film sliding surface) ) The resistance heating element 6 formed on the side, the heat-resistant overcoat layer 8 that protects the surface of the heating element on which the resistance heating element is formed, and the power supply electrodes 9 and 10 at the longitudinal end of the resistance heating element 6. This is a heating element with a low heat capacity.

  The resistance heating element 6 of this example is obtained by forming a paste prepared by kneading graphite, glass powder (inorganic binder), and organic binder on the substrate 7 by screen printing. The shape and characteristics of the resistance heating element 6 will be described later.

  Reference numeral 7 denotes a heating body substrate having heat resistance and insulation, and for example, a ceramic material such as alumina or aluminum nitride is used. In this embodiment, an alumina substrate having a width of 6 mm, a length of 270 mm, and a thickness of 1 mm is used.

  8 is an overcoat layer of the resistance heating element 6, and its main purpose is to ensure electrical insulation between the resistance heating element 6 and the surface of the heating element 3 and the slidability of the film 2. In this example, a heat-resistant glass layer having a thickness of about 50 μm was used as the overcoat layer 8.

  The power supply electrodes 9 and 10 and the conductive pattern 14 were silver screen printing patterns. Since the power supply electrodes 9 and 10 and the conductive pattern 14 are provided for the purpose of supplying power to the resistance heating element 6, the resistance is sufficiently lower than that of the resistance heating element 6.

  FIG. 2 also shows the back surface (non-film sliding surface) of the heating element 3. Reference numeral 5 denotes a temperature measuring element provided for detecting the temperature of the heating body. In this embodiment, an external contact type thermistor separated from the heating body 3 is used as the temperature measuring element. The external contact type thermistor 5 is provided with a heat insulating layer on a support, for example, and an element of the chip thermistor is fixed on the support, and the element is directed downward (on the back side of the heating body) with a predetermined pressurizing force. It is configured so as to abut. In this example, a highly heat-resistant liquid crystal polymer was used as the support, and ceramic paper was laminated as the heat insulating layer. The external contact type thermistor 5 is provided in the minimum sheet passing area and communicates with the CPU 11.

  The heating body 3 is fixedly disposed by exposing the surface side on which the overcoat layer 8 is formed and holding it on the lower surface side of the stay 1. By adopting the above configuration, the entire heating element can be reduced in heat capacity as compared with the heat roller system, and a quick start becomes possible.

  The heating element 3 rises in temperature when the resistance heating element 6 generates heat over the entire length by feeding power to the feeding electrodes 9 and 10 at the longitudinal end of the resistance heating element 6. The temperature rise is detected by the temperature sensing element 5, the output of the temperature sensing element 5 is A / D converted and taken into the CPU 11, and the electric power supplied to the resistance heating element by the triac 12 is controlled by phase, wave number control, etc. based on the information. Thus, the temperature of the heating element 3 is controlled. In other words, the heating body 3 is kept at a constant temperature during fixing by controlling energization so that the heating body 3 is heated when the temperature detected by the temperature detecting element 5 is lower than a predetermined set temperature, and is lowered when the temperature is higher than the set temperature. Kept. In this embodiment, the output is changed in 21 steps from 5 to 100% from 0 to 100% by phase control. The output 100% indicates the output when the heater 3 is fully energized.

  Pressure contact formed by the heating body 3 and the pressure roller 4 with the film 2 sandwiched in a state where the temperature of the heating body 3 rises to a predetermined level and the rotational peripheral speed of the film 2 is stabilized by the rotation of the pressure roller 4 A recording material P to be image-fixed as a heated material is introduced into the nip portion N from the transfer portion. Then, when the recording material P is nipped and conveyed together with the film 2 through the pressure nip N, the heat of the heating body 3 is applied to the recording material P through the film 2 and an unfixed visible image (toner on the recording material P). Image) T is heat-fixed on the surface P of the recording material. The recording material P that has passed through the pressure nip N is separated from the surface of the film 2 and conveyed.

  Below, the manufacturing method of the heating body 3 of a present Example is described. First, the power supply electrodes 9 and 10 and the conductive pattern 14 are simultaneously screen-printed on an alumina substrate, dried, and then fired at a firing temperature of about 800 ° C. Next, the above graphite paste is screen-printed, dried and fired. Since the surface oxidation of graphite begins at about 700 ° C, the firing temperature was set to about 600 ° C. Thereafter, the overcoat layer 8 is formed by screen printing, dried and fired. In consideration of the heat resistance of graphite, a glass that can be fired at 400 to 500 ° C. was selected as the material of the overcoat layer 8.

  Next, the shape and characteristics of the resistance heating element 6 of this embodiment will be described in detail. FIG. 1 is a front view of a heating body 3 in the present embodiment. In FIG. 1, the overcoat layer 8 is omitted for simplicity.

  In this embodiment, the resistance heating element 6 is divided into four. The distance a in the longitudinal direction of the divided resistance heating element 6 is 55 mm, the distance d in the width direction is 2.6 mm, and all four have the same shape. Therefore, the total length of the resistance heating element 6 is 220 mm. The thickness of the resistance heating element 6 was about 10 μm. The distance b between the divided resistance heating elements 6 was set to 0.5 mm. The width c of the conductive pattern 14 and the distance c between the conductive patterns were also set to 0.5 mm. The distance e from the substrate edge to the conductive pattern 14 was 0.7 mm. The distances b, c, and e are the minimum values that can be manufactured.

  When power is supplied to the power supply electrodes 9 and 10, the current I flows through the resistance heating element 6 and the conductive pattern 14 in the direction of the arrow shown in FIG. That is, in the divided resistance heating element 6, power is supplied in the conveyance direction of the recording material P (hereinafter referred to as conveyance direction power supply), and the current I flows in the width direction of the substrate 7. And each resistance heating element of conveyance direction electric power feeding is electrically connected in series. In the present embodiment, the power supply electrodes 9 and 10 are provided on the same side of the substrate end (on the right side in FIG. 1), but may be disposed on both ends of the substrate 7.

  Conventional resistance heating elements are generally made of a paste mainly composed of metal such as silver palladium (Ag / Pd), and have positive resistance temperature characteristics (PTC characteristics that increase resistance as temperature rises). Show. On the other hand, the graphite used as a resistance heating element in this example has a negative resistance temperature characteristic (NTC characteristic that the resistance decreases as the temperature rises) below that temperature, and a PTC characteristic above that temperature. The inflection point temperature is about 700 ° C.

  Since the maximum temperature reached by the heating element 3 is about 200 to 300 ° C., the resistance heating element 6 of this embodiment exhibits NTC characteristics when the heating device 107 is actually used. The resistance change rate of the resistance heating element 6 of this example was about -1000 ppm / ° C. (the resistance change rate from 25 ° C. to 200 ° C. is equal to or less than the resistance change rate). Incidentally, the resistance change rate of the silver palladium paste used in the conventional heating body is about 0 to 1000 ppm / ° C.

  In this embodiment, the resistance heating element 6 has a sheet resistance at room temperature of about 100Ω / sq (thickness 10 μm), and the resistance heating element 6 has a total resistance (resistance between the feeding electrodes 9 and 10) of 19Ω at room temperature. did.

For comparison with the present embodiment, a conventional heating element will be described. FIG. 6 is a front view of a conventional heating element. 15 is a resistance heating element of a conventional example, and a paste prepared by kneading silver palladium, glass powder (inorganic binder), and organic binder is 2.6 mm wide and long by screen printing on an alumina substrate 7. It was obtained by forming a wire strip having a thickness of 220 mm and a thickness of about 10 μm (the heating element width, total length, and thickness are the same as in this example). As the resistance heating element 15 of the conventional example, one having a sheet resistance at room temperature of about 0.2Ω / sq (thickness 10 μm) was used. The total resistance was 19Ω at room temperature, as in this example. The resistance change rate of the resistance heating element 15 of the conventional example was about 500 ppm / ° C. As a material of the resistance heating element 15, an electric resistance material such as RuO ₂ or Ta ₂ N may be used in addition to silver palladium.

  The structure of the heating element other than the material and shape of the resistance heating element 15 and the shape of the conductive pattern 14 was the same as in this example. The same overcoat layer as in this example was used, but is omitted in FIG.

  The resistance heating element 15 of the conventional example is fed in the longitudinal direction, and the current i flows in the longitudinal direction shown in FIG. In the conventional heating body, a type in which power is supplied in the longitudinal direction as in the conventional example is common.

  When small-size paper is passed through a heating device having a conventional heating element, the above-described temperature increase in the non-sheet passing portion occurs. Considering the case where the heating body of the conventional example is mounted on the heating apparatus described in the present embodiment, the non-sheet passing portion temperature rise will be described below using a model diagram.

FIG. 7 is a model diagram of a resistance heating element 15 of a conventional example. Here, the resistance heating element 15 is considered to be divided into four parts of length a (= 55 mm), the resistance of the two parts at the center is r1, and the resistance of the two parts at the end is r2. And r1 = r2) if the end temperature is the same. 2 (r1 + r2) is the total resistance, which is 19Ω at room temperature. Assuming that the current flowing through the resistance heating element 15 is i, the calorific value q1 of one block at the center is i ² · r1, and the calorific value q2 of one block at the end is i ² · r2.

  For simplicity, consider the case where small-size paper with a width of 2a (= 110mm) is passed. When the center resistance is r1, the part with resistance r1 is the paper passing part, and when the edge resistance is r2, the part is non-paper passing. Become a part. Since the temperature control of the heating body is performed by the temperature detecting element 5 provided in the paper passing portion, the non-paper passing portion in which the heat is not taken away by the small size paper compared to the paper passing portion where the heat is taken away by the small size paper. The temperature rises. Since the resistance heating element 15 of the conventional example has PTC characteristics, 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 larger than the heat generation amount in the central portion.

Similarly, the heating element 3 of this embodiment will be considered using a model diagram. FIG. 8 is a model diagram of the resistance heating element 6 of this embodiment. The resistance of the resistance heating element 6 divided into four is R1 at the center and R2 at the end (R1 = R2 if the temperature at the center and the end is the same). 2 (R1 + R2) is the total resistance, which is 19Ω at room temperature. That is, if all the temperatures are equal, r1 = r2 = R1 = R2. Assuming that the current flowing through the resistance heating element 6 is I, the calorific value Q1 of one block at the center is I ² · R1, and the calorific value Q2 of one block at the end is I ² · R2.

  As in the case of the heating element in the conventional example, when a small-size paper having a width of 2a (= 110 mm) is passed, the resistance at the center is R1 and the resistance at the end is the resistance. The R2 part is a non-paper passing part. In the heating body of this embodiment, as in the case of the heating body of the conventional example, when small-size paper is passed, the temperature of the non-paper passing portion becomes higher than that of the paper passing portion. Since the resistance heating element 6 of this embodiment has NTC characteristics, 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 in this embodiment, the heat generation amount in the non-sheet passing portion is smaller than the heat generation amount in the central portion.

  The fixing properties of the heating elements of the conventional example and the present example are almost equal because the heating element width is the same 2.6 mm. Therefore, the heat generation amount (= fixability) of the sheet passing portion when the same small size sheet is passed is substantially equal, that is, q1 = Q1. Therefore, the calorific value of the non-sheet passing portion when the same small size sheet is passed becomes q2> Q2, and it can be seen that the temperature rise in the non-sheet passing portion is smaller in this embodiment than in the conventional example.

  Graphite paste has a lower sheet resistance among materials exhibiting NTC characteristics, but has a higher sheet resistance than metal pastes such as silver palladium. Therefore, if a resistance heating element pattern that feeds in the longitudinal direction is formed with graphite paste as in the conventional heating element, the total resistance becomes very large and cannot be used as a heating element (for example, the sheet resistance of this embodiment). If the pattern of the conventional example of FIG. 6 is formed with a thickness of about 10 μm using graphite paste, the total resistance will be about 8500Ω. This is also true for materials exhibiting NTC characteristics other than graphite.

  In order to reduce the total resistance by feeding in the longitudinal direction, it may be possible to increase the thickness of the resistance heating element. However, the sheet resistance graphite paste of this embodiment is used to form the pattern shown in FIG. In addition, it is necessary to make the thickness about 4 mm, and screen printing becomes difficult, and even if it can be printed, the strength of graphite is not so strong, so it is always in a state where it is pressurized with a pressure roller There are many cases where durability is difficult.

  Further, in order to reduce the total resistance with a thin layer in the configuration of feeding in the longitudinal direction, it is conceivable to mix another material having low resistance with the graphite paste. In order to make the total resistance sufficiently small, metal is considered as a low resistance material. However, since the metal has PTC characteristics, the NTC characteristics of graphite are canceled out, and the effect of preventing the temperature rise of the non-sheet passing part Is also reduced.

  After all, when trying to form a heating element that feeds in the longitudinal direction using a resistance heating element of NTC characteristics such as graphite, there is a problem as a heating element, or the effect of preventing the temperature rise of the non-sheet passing portion is not obtained. Or Therefore, a device such as making the substrate in a complicated shape and reducing the total resistance is essential, and the temperature rise of the non-sheet passing portion cannot be prevented with a simple configuration.

  On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 2000-58232, a configuration has also been devised in which a resistance heating element having PTC characteristics is fed in the conveyance direction to prevent the temperature rise of the non-sheet passing portion. However, a resistance heating element having a PTC characteristic is generally a metal having a low resistance such as a metal, and if it is configured to feed in the conveyance direction, the total resistance becomes too low to be realized as a heating element.

  In other words, from the standpoint of preventing the temperature rise at the non-sheet-passing section, the longitudinal heating is effective for the NTC resistance heating element, but the total resistance becomes too large, and the PTC resistance heating element is effective for feeding in the conveyance direction but the total resistance. There is a problem that becomes too small. The present invention solves this problem. It is a resistance heating element with high sheet resistance and NTC characteristics, and power feeding in the conveyance direction is used to reduce the total resistance. Are connected in series. In order to prevent the temperature rise of the non-sheet passing portion in the conveyance direction power supply configuration, as described above, the configuration without division (the configuration disclosed in Japanese Patent Laid-Open No. 2000-58232) or the configuration divided in two and connected in series Although the PTC characteristic is effective, the NTC characteristic becomes effective as described in the present embodiment in the configuration in which the PTC characteristic is connected in series with three or more divisions. Therefore, even if it is not divided into four as in this embodiment, the number of divisions is changed in three or more divisions so as to obtain a desired total resistance in accordance with the sheet resistance, heating element width, and thickness of the resistance heating element. Also good.

  In this embodiment, for the sake of simplicity, an example of small-size paper in which the gap between the edge of the paper and the resistance heating element 6 (the portion of length b) coincides is taken as an example to prevent the temperature rise of the non-sheet passing portion. Although the effect has been described, the temperature rise of the non-sheet passing portion can be reduced even in a small size paper having a paper width whose gap does not coincide with the paper edge. In that case, the PTC characteristics are advantageous when considered within one block through which the paper edge passes, but the NTC characteristics are still advantageous when considered over the entire length of the resistance heating element.

  Below, the heating body of a present Example and the comparison of the heating body of a prior art example are shown. In this example and the conventional example, the configuration of the heating device / image forming apparatus other than the heating body is the same, and 100 postcard-sized recording materials are continuously fed from the state where the heating device is sufficiently adapted to room temperature (25 ° C.). At that time, the maximum temperature of the non-sheet passing portion (measured on the back surface of the heating body with a thermocouple) was compared. The fixing temperature was 200 ° C. The input voltage was 100 V, and the process speed of the image forming apparatus was 120 mm / sec. The results are shown in Table 1.

表１に示すように、従来例に比べて大幅に（約50℃）非通紙部温度を下げることができた。

As shown in Table 1, the temperature of the non-sheet passing portion could be lowered significantly (about 50 ° C.) compared to the conventional example.

Next, a cardboard-sized cardboard having a basis weight of 157 g / m ² was forcibly fed and passed, and how many sheets were fed would cause deterioration or breakage of the heating device. The conditions were the same as when the fixing temperature, input voltage, and process speed non-sheet passing temperature rise were measured. The test results are shown in Table 2.

表２に示すように、従来例の加熱体は、非通紙部昇温により基板に発生する熱応力によって、4または5重送で破損に至り、ステー・フィルム・加圧ローラ表層の非通紙部に劣化が認められた。一方、本実施例の加熱体は、2回とも10重送まで重送枚数を増やしていったが破損せず、ステー・フィルム・加圧ローラにも劣化は認められなかった。この結果からも本実施例の加熱体を用いることによって、非通紙部昇温が大幅に低減できていることが分かる。

As shown in Table 2, the heating element of the conventional example is damaged by four or five double feeds due to the thermal stress generated in the substrate due to the temperature rise of the non-sheet passing portion, and the stay, film, and pressure roller surface layer are not passed. Deterioration was observed in the paper. On the other hand, the heating body of this example increased the number of double feeds up to 10 double feeds in both cases, but was not damaged, and no deterioration was observed in the stay, film, or pressure roller. From this result, it can be seen that by using the heating element of this example, the temperature rise of the non-sheet passing portion can be significantly reduced.

(Example 2)
In the present embodiment, a description will be given of a modified shape of the gap portion of the divided resistance heating element described in the first embodiment. The only difference from the first embodiment is the pattern shape of the resistance heating element, and the other configurations of the heating element, heating device, and image forming apparatus are the same as those of the first embodiment. FIG. 9 shows a front view of the heating body of the present embodiment.

  The resistance heating element 6 of this example is obtained by forming a paste prepared by kneading graphite, glass powder (inorganic binder), and organic binder on the substrate 7 by screen printing, as in Example 1. It is a thing. The same resistance heating element 6 as in Example 1 was used. The substrate 7, the power supply electrodes 9, 10, the conductive pattern 14, and the overcoat layer 8 are the same as those in the first embodiment. In FIG. 9, the overcoat layer 8 is omitted for simplicity.

  As in the first embodiment, the resistance heating element pattern of the present embodiment feeds the four divided blocks in the transport direction and connects them in series. The distances a to e are also set to the same values as in the first embodiment. The total resistance of the resistance heating element 6 at normal temperature (resistance between the power feeding electrodes 9 and 10) was also 19Ω as in the first embodiment.

  In Example 1, each block of the resistance heating element 6 is rectangular, and the shape of the gap portion at the distance b is also rectangular. Therefore, when the recording material P passes through the heating device, there is a portion that passes through a region where the resistance heating element 6 does not exist at all, and there is a possibility that the fixing property is deteriorated as compared with other portions. If the overall structure has a sufficient fixability, this deterioration will not normally be a problem, but if paper with a large basis weight or paper with poor surface properties is passed in a low-temperature environment, Problems may become apparent.

  In this embodiment, for the purpose of reducing the deterioration of the fixability of the gap portion, as shown in FIG. 9, each block of the resistance heating element 6 has a trapezoidal shape with 2 blocks at both ends, and the central 2 blocks have a parallelogram shape. The shape of the gap portion at the distance b is a parallelogram. By making the gap part a parallelogram and making the distance b as small as possible (b = 0.5 mm), when the recording material P passes through the heating device, it passes through a region where no resistance heating element 6 exists. There is no longer to do. Of course, in this embodiment, the fixability of the gap portion is inferior to that of the other portions, but the difference is smaller than that of the first embodiment.

  In the resistance heating element pattern of the present embodiment, it was calculated how much the amount of heat generated in the gap portion was with respect to the amount of heat generated in the other portions. FIG. 10 is an enlarged view of a gap portion of the resistance heating element pattern of this embodiment. The shape of the gap portion of the resistance heating element is determined by the heating element width d, the gap distance b, and the angle θ in FIG. It is considered that the current flows in parallel with the conveyance direction a of the recording material P in a region where there is no gap. Here, in the region of the triangular ABD, it is assumed that the current flows obliquely (for example, the current flows from the point C through the line segment CA to the point A). If the resistance of line segment BA is R0, the resistance of line segment CA is R (x)

となる（線分BC間の距離をxとおいている）。よって、線分BAを電流が流れることによって発生する発熱量をQ0とおくと、線分CAで発生する発熱量Q(x)は

(Distance between line segments BC is set to x). Therefore, if the calorific value generated by the current flowing through the line segment BA is Q0, the calorific value Q (x) generated in the line segment CA is

となる（導電パターン１４の体積抵抗は抵抗発熱体６の体積抵抗に比べて十分小さいので、導電パターン１４における電圧降下は無視し、BA間にかかる電圧とCA間にかかる電圧は同じであるとしている）。

(The volume resistance of the conductive pattern 14 is sufficiently smaller than the volume resistance of the resistance heating element 6. Therefore, the voltage drop in the conductive pattern 14 is ignored, and the voltage applied between BA and CA is the same. )

  The total amount of heat generated in the triangular ABD region is considered to be a value obtained by integrating Q (x) from x = 0 to x = d / tan θ (distance between line segments BD). Therefore, if the total heat generated in the triangular ABD region is P (θ),

となる。この積分はx＝dtanαとおくことで求めることができ、

It becomes. This integral can be obtained by setting x = dtanα,

となる。

It becomes.

  The amount of heat generated in the part with a gap is 2P (θ) because there are two triangular ABDs, and the ratio of the amount of heat generated in the part with and without the gap is the distance d / tanθ · gap in the integral interval of P (θ) Considering the distance b of

となり、発熱体幅d・隙間の距離b・角度θで決まる変数となる。

Thus, the variable is determined by the heating element width d, the gap distance b, and the angle θ.

  FIG. 11 shows the relationship between the angle θ and the heat generation ratio. The heat generation ratio on the vertical axis in FIG. 11 indicates the heat generation amount (%) in a portion with a gap when the heat generation amount in a portion without a gap is 100%. The four curves in FIG. 11 indicate the heat generation ratios when the gap distance b is fixed at 0.5 mm and the heating element width d is changed to 2.6 mm and 2/3/4 mm in this embodiment, respectively (1 ). As can be seen from FIG. 11, the curve of the heat generation ratio has a maximum value at a certain angle θ. Table 3 summarizes the maximum value of the heat generation ratio and the angle θ at that time in each heating element width.

表３に示す通り、発熱体幅dが大きくなるほど、発熱比の最大値とそのときの角度θは大きくなる傾向にある。また、今回の計算では隙間の距離bは固定したが、式（１）を見ても分かるように、隙間の距離bが小さいほど発熱比が大きくなるので、製造上可能な範囲でbを小さくした方が良いのはそこからも明らかである。

As shown in Table 3, the maximum value of the heat generation ratio and the angle θ at that time tend to increase as the heating element width d increases. In this calculation, the gap distance b is fixed, but as can be seen from equation (1), the heat generation ratio increases as the gap distance b decreases. It is clear from there that it is better to do this.

  In this embodiment, since the heating element width d is 2.6 mm, the angle θ is set to 55 °, which has the largest heat generation ratio in calculation and good fixability in the gap portion. In addition, as a result of examining the relationship between the angle θ and the fixability of the gap portion using the heating device of the present embodiment, the angle θ is 55 °, and the fixability of the gap portion is the best, and there is no gap portion. The result that the difference was smaller than Example 1 was obtained.

  Since the heating element width varies depending on the heating device (determined by the relationship between the substrate width and the nip width, etc.), the angle θ at which the heating ratio is maximized is selected according to the heating element width d and the gap distance b of the device. It is desirable.

  Further, it goes without saying that the heating body of the present embodiment also has the effect of reducing the temperature rise of the non-sheet passing portion by the same mechanism as that of the heating body of the first embodiment. Further, the present embodiment also has an advantage that the deterioration of the fixing property in the gap portion essential for dividing the resistance heating element can be made smaller than that of the first embodiment.

(Example 3)
In the present embodiment, a configuration for further reducing the deterioration of the fixability in the gap portion of the resistance heating element described in the second embodiment will be described. The only difference from the first and second embodiments is the pattern shape of the resistance heating element, and the other configurations of the heating element, heating device, and image forming apparatus are the same as those of the first and second embodiments. The front view of the heating body of a present Example is shown in FIG.

  The resistance heating element 16 of this example is formed on the substrate 7 by screen printing a paste prepared by kneading graphite, glass powder (inorganic binder), and organic binder as in Examples 1 and 2. It was obtained. The substrate 7, the feeding electrodes 9, 10, the conductive pattern 14, and the overcoat layer 8 are the same as those in the first and second embodiments. In FIG. 12, the overcoat layer 8 is omitted for simplicity.

  In the resistance heating element 16 of this embodiment, the sheet resistance of the resistance heating element is changed between the vertical line portion (rectangular region) and the shaded portion (triangular region) in FIG. Except for changing the sheet resistance of the resistance heating element, the pattern is exactly the same as in Example 2, and the distances a to e are also set to the same values as in Examples 1 and 2. The total resistance of the resistance heating element 16 at normal temperature (resistance between the power feeding electrodes 9 and 10) was also 19Ω as in Examples 1 and 2.

  In Example 2, since the angle θ is 55 °, the amount of heat generated in the gap portion is 82.0% of the portion without the gap according to Table 3. In this embodiment, in order to completely eliminate this decrease in the heat generation amount, the sheet resistance of the shaded portion is set to 1.22 times (= 1 / 0.82) of the sheet resistance of the vertical line portion, and the heat generation ratio calculated by the equation (1) is 100%. (In this embodiment, the angle θ is 55 °). Specifically, the sheet resistance of the vertical line portion is about 100 Ω / sq (thickness 10 μm) as in the first and second embodiments, and the sheet resistance of the hatched portion is about 122 Ω / sq (thickness 10 μm). Actually, as a result of comparing the fixability of the portion having a gap and the portion having no gap using the heating device of this example, the same fixability was shown.

  When the angle θ is changed in the resistance heating element configuration of this embodiment, how many times the sheet resistance of the shaded portion is set to the sheet resistance of the vertical portion (= resistance ratio f), the heat generation ratio becomes 100% Can be obtained based on equation (1). The relationship between the angle θ and the resistance ratio f is shown in FIG. The curve in FIG. 13 is opposite to the curve in FIG. 11, and when the angle θ is 55 °, the resistance ratio f takes a minimum value of 1.22.

  Also in the heating body of the present embodiment, the same mechanism as that of the heating bodies of Embodiments 1 and 2 has the same effect of reducing the temperature rise of the non-sheet passing portion as in Embodiments 1 and 2. Furthermore, in this embodiment, it is possible to completely eliminate the deterioration of the fixing property in the gap portion which is essential for dividing the resistance heating element, and to ensure a uniform fixing property in the longitudinal direction even under a condition where the fixing property is poor. In this respect, it is superior to the first and second embodiments.

  In this embodiment, the sheet resistance of the resistance heating element in the vicinity of the gap is increased to compensate for the decrease in the heat generation amount in the gap, but the resistance is increased by making the resistance heating element in the vicinity of the gap thinner. May be. In the configuration of the present embodiment, the amount of heat generation can be made equal by setting the thickness of the hatched portion to 82.0% of the vertical line portion.

Front view of the heating element in Example 1 Front view of heating body and explanatory diagram of power supply control system in Embodiment 1 Sectional drawing of the heating body in Example 1 The schematic block diagram which shows the principal part of the heating apparatus in this invention 1 is a schematic configuration diagram showing a main part of an image forming apparatus according to the present invention. Front view of heating element in conventional example Model of resistance heating element in the conventional example Model diagram of resistance heating element in Example 1 The front view of the heating body in Example 2 The enlarged view of the resistance heating element in Example 2 Diagram showing the relationship between angle θ and heat generation ratio Front view of the heating body in Example 3 Diagram showing the relationship between angle θ and resistance ratio f

Explanation of symbols

1 stay 2 film 3 heating element (heater)
4 Pressure roller 5 Temperature sensor (external contact type thermistor)
6 Resistance heating elements of Examples 1 and 2 7 Heating substrate 8 Overcoat layer 9 · 10 Power supply electrode 11 CPU
12 Triac 13 AC Power Supply 14 Conductive Pattern 15 Resistance Heating Element of Conventional Example 16 Resistance Heating Element of Example 3
N Nip part
P Recording material
T toner
a Recording material conveyance direction

Claims (7)

  In a heating apparatus that heats a material to be heated by a heating element including at least a substrate, a resistance heating element having negative resistance temperature characteristics, and an electrode that supplies power to the resistance heating element, the resistance heating element includes three or more resistance heating elements in the longitudinal direction. Heating is divided into parts, and the divided resistance heating elements are fed so that current flows in the direction of conveying the heated material, and the divided resistance heating elements are electrically connected in series apparatus.   2. The heating device according to claim 1, wherein the resistance heating element includes graphite.   3. The heating apparatus according to claim 1, wherein the heating body is configured to form a resistance heating element on a ceramic substrate.   4. The heating device according to claim 1, wherein the shape of each portion of the divided resistance heating element viewed from the heating surface is a parallelogram or a trapezoid.   5. The heating device according to claim 1, wherein, in a part of the resistance heating element in a longitudinal direction, the volume resistance of the resistance heating element is different from that of the other part, or the thickness of the resistance heating element is different from that of the other part. Heating device characterized.   At least a heating body, a flexible member that contacts and slides one surface with the heating body and the other surface contacts the heated material, and a pressurizing body that causes the heated material to closely contact the heated body via the flexible member. And a heating device that heats the heated material by sandwiching and conveying the flexible member and the heated material at a nip formed by the heated body and the pressure body. A heating apparatus having the structure described in any one of the above.   7. An image forming apparatus comprising: an image forming unit that forms an image on a recording material; and an image heating unit that heats an image on the recording material. An image forming apparatus comprising a heating device.

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