JP2006113365A - Image fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image fixing device which can prevent the fixing components from breaking or being smeared by the offset toner and can secure high productivity. <P>SOLUTION: The fixing device which transfers the recording material carrying an image, by using a nip formed with 1st and 2nd fixing components, has a heater in contact with the above 1st fixing component to heat it, a 1st temperature sensor disposed in contact with this heater, and a 2nd temperature sensor disposed in contact with the 1st fixing component. The 1st and the 2nd temperature sensors are disposed at different positions in the length direction of the nip. It is possible to use the recording materials of two or more types of sizes in the length direction of the nip. Further, the 2nd temperature sensor is disposed within the length range of the recording material large in the length direction of the nip at the position outside the length range of the recording material small in the length direction of the nip. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device that heats a recording material carrying an image at a nip formed by first and second fixing members, and an image forming apparatus equipped with the fixing device.

  More specifically, a recording material (paper, printing paper, transfer material sheet, OHT sheet) using a toner made of heat-meltable resin or the like by timely image forming process means such as electrophotography, electrostatic recording, and magnetic recording. A non-fixed toner image corresponding to the target image information formed and supported by the direct method or the transfer method (transfer method) on the surface of glossy paper, glossy film, etc.) on the surface of the recording material carrying the image The present invention relates to a fixing device using a heat fixing process as a permanently fixed image, and an image forming apparatus such as a laser beam printer and a facsimile equipped with the fixing device.

  In particular, the present invention relates to an on-demand fixing device that is suitable for use in a color image forming apparatus and has a low cost and a short rise time (so-called warm-up time).

  In recent years, colorization has progressed in image forming apparatuses such as printers and copiers. As a fixing device used in such a color image forming apparatus, heat roller fixing having an elastic layer on a fixing member is well known. An example of a fixing device using such a fixing roller having an elastic layer is shown in FIG.

  In this fixing device, an unfixed toner image is rotated at a contact nip portion (fixing nip) N of two heating rollers, which is composed of a fixing roller 101 and a pressure roller 102 that are rotationally driven in the direction of an arrow and adjusted to a predetermined fixing temperature. The recording material P on which t is placed is configured to pass therethrough.

  The unfixed toner image t is heated and pressed by the fixing roller 101 and the pressure roller 102 when passing through the nip portion N, and is fixed on the recording material P as a completed image (permanently fixed image).

  Each of the rollers 101 and 102 includes a halogen heater H in the center, and the radiant energy generated from the heater H is absorbed by the aluminum cores 101a and 102a inside each roller and heated. The thermistors 103 and 104 are arranged in elastic contact with the surfaces of the rollers 101 and 102, and the rollers 101 and 102 are connected to the halogen heater H based on the temperatures detected by the thermistors 103 and 104. Power supply is controlled and temperature adjustment is performed.

  Elastic layers 101b and 102b made of silicone rubber having a thickness of 2 mm are provided around the aluminum cores 101a and 102a of the rollers 101 and 102, and toner and paper are provided on the surfaces of the outer rollers. PFA (tetrafluoroethylene / perfluoroalkyl ether copolymer / tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin), FEP (tetrafluoroethylene / hexafluoropropylene copolymer) to prevent sticking of powder, etc. Coating layers 101c and 102c of a resin having good releasability and heat resistance, such as (/ 4 fluorinated ethylene / hexafluoropropylene copolymer resin).

  The reason why the elastic layer 101b is provided on the side of the fixing roller 101, which is a fixing member in contact with the unfixed toner t, in the fixing nip portion N is to fix the toner image surface as uniformly as possible.

  By providing the elastic layer 101b on the fixing roller 101 side, when the toner image t passes through the fixing nip portion N, the elastic layer 101b is deformed along the toner layer, so that the toner that is unevenly placed on the image. Is encased in the elastic layer 101b and uniformly heated, thereby achieving uniform fixing.

  An image that is uniformly fixed in this way has no gloss unevenness, and has a feature that the light transmittance of the image is excellent particularly when an OHT (transparent sheet for overhead projector) is fixed.

  However, in a heat roller type fixing device having such an elastic layer, the heat capacity of the heat roller itself increases, and the time required to raise the temperature of the fixing roller 101 to a temperature suitable for toner image fixing. There was a problem that (warm-up time) was long. Also, the cost of the fixing member is expensive.

  On the other hand, as a low-cost fixing device having a short warm-up time, a film fixing type fixing device used in a monochrome printer or the like is well known. An example of such a film fixing device is shown in FIG.

  In this fixing device, a thin fixing film 111 is sandwiched between a heater 112 fixedly supported on a support member 115 and an elastic pressure roller 114 to form a fixing nip portion N, and the fixing film 111 is placed on the surface of the heater 112. The recording material P carrying the toner image t is nipped and conveyed between the fixing film 111 and the pressure roller 114 in the fixing nip portion, and the heat from the heater 112 via the fixing film 111 is slid. Thus, the toner image on the recording material is heated.

  The unfixed toner image t on the recording material P receives heat and pressure when passing through the fixing nip portion N, and is fixed on the recording material P as a completed fixed image (permanently fixed image).

  The fixing film 111 is, for example, an endless film made of a heat-resistant resin having a thickness of about 50 μm, and a release layer (such as a fluororesin coating layer) having a thickness of about 10 μm is formed on the surface. A resistance heating element is formed on a substrate. The temperature detector 113 is brought into contact with the heater 112, the temperature of the heater 112 is detected, and the temperature of the heater 112 is controlled to be a desired temperature by a control unit (not shown).

  Further, in order to reduce the heat capacity of the fixing film 111, the fixing film 111 is not provided with an elastic layer.

  In the fixing device having such a configuration, since the heat capacity of the fixing film 111 is very small, after the power is supplied to the heater 112, the temperature of the fixing nip portion N is raised to a temperature capable of fixing the toner image in a short time. It is possible.

  However, when a film fixing apparatus using the fixing film 111 not provided with such an elastic layer is used as a fixing apparatus of a color image forming apparatus, unevenness due to the surface of the recording material P, the presence or absence of the toner layer, and the toner itself. The surface of the fixing film 111 cannot follow the unevenness and the like, and there is a difference in heat applied from the fixing film between the convex portion and the concave portion. The convex portion that is in good contact with the fixing film conducts heat well from the fixing film, and the concave portion is less likely to conduct heat from the fixing film than the convex portion.

  In a color image, since a plurality of color toner layers are mixed and used, the unevenness of the toner layer is larger than that of a black and white image, and if the fixing film as a fixing member does not have an elastic layer, uneven glossiness of the fixed image may occur. When the recording material is OHT, the image quality deteriorates due to an increase in image quality, and the transparency is poor when a fixed image is projected, resulting in a decrease in image quality.

  Accordingly, a fixing device that constitutes a low-cost color on-demand fixing device by using a fixing belt (fixing film) having an elastic layer as disclosed in Patent Document 1 for a film fixing device has been proposed. Yes.

  By the way, with the recent widespread use of printers and copiers, recording materials of various paper types and paper sizes have come to be used. In particular, an increasing number of users use narrow recording materials such as envelopes and postcards. When such a small size recording material is passed through the heat fixing device, there is no medium that absorbs heat from the heater in the non-sheet passing area where the recording material does not pass. However, the temperature rises more abnormally than the sheet passing area of the recording material (hereinafter referred to as non-sheet passing portion temperature rise). The heat generated by such an abnormal temperature rise in the non-sheet-passing area may wrap around the end of the small size recording material via the fixing film or the pressure roller. In the vicinity of the fixing film and the pressure roller, the temperature of the fixing film and the pressure roller may increase, and the fixing film and the pressure roller may be stained due to toner offset on the recording material.

  In the film fixing device, in order to prevent toner offset on the small size recording material or thermal damage of the member due to such abnormal temperature rise, the temperature is set at a position corresponding to the non-sheet passing area of the small size recording material on the back surface of the heater. A second temperature detecting means is provided separately from the adjustment control, and when a predetermined temperature is detected, the sheet passing interval of the recording material is extended stepwise or the sheet passing is stopped.

Japanese Patent Laid-Open No. 11-15303 (Patent No. 3051085)

  However, as described above, when the second temperature detecting means is arranged at a position corresponding to the non-sheet passing area of the small size recording material on the back side of the heater and a predetermined temperature is detected, the sheet passing interval of the recording material is gradually increased. When extended control was performed, there were the following drawbacks.

  That is, if the fixing film has an elastic layer having a large thermal resistance, the fixing film elastic layer actually reaches the heat-resistant temperature, or the heater back surface reaches a predetermined temperature before reaching the temperature at which toner offset occurs on the fixing film surface. End up. This tendency becomes conspicuous when the fixing device starts heating from a cold state and enters a fixing operation. In this case, the sheet passing interval becomes longer step by step, and eventually the number of printed sheets per unit time (throughput) decreases.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent heat damage of a fixing member and contamination due to offset toner in an image fixing device, and at the same time to ensure high productivity.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a fixing device in which a recording material carrying an image is nipped and conveyed by a nip formed by first and second fixing members and heated. A first temperature detecting unit that is in contact with the fixing member and has a heating member that applies heat to the fixing member, is disposed in contact with the heating member, and is disposed in contact with the first fixing member. It has 2 temperature detection means.

  According to a second aspect of the invention, in the first aspect of the invention, the first temperature detecting means and the second temperature detecting means are arranged at different positions in the nip longitudinal direction.

  According to a third aspect of the present invention, in the second aspect of the present invention, it is possible to use recording materials of two or more sizes different in at least the nip longitudinal direction, and the second temperature detecting means has a nip longitudinal size. It is characterized in that it is arranged in a position corresponding to the outside of the longitudinal area of the recording material having a small size in the nip longitudinal direction within the longitudinal area of the large recording material.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the first temperature detecting means detects the temperature of the heating member, and based on the result, temperature control of the heating member is performed. Is made.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the second temperature detecting unit detects the temperature of the first fixing member, and based on the result, determines the conveyance interval or conveyance speed of the recording material. It is characterized by changing.

  According to a sixth aspect of the invention, in the fourth aspect of the invention, the second temperature detecting means detects the temperature of the first fixing member and stops the recording material based on the result. To do.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, a fixing belt comprising a belt-like member provided with an elastic layer is used as the fixing member on the side contacting the image surface of the recording material. It is characterized by.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, characterized in that the second temperature detecting means is arranged in contact with the inner surface of the fixing member.

  According to a ninth aspect of the invention, the fixing device according to any one of the first to eighth aspects is mounted on an image forming apparatus.

  According to a tenth aspect of the present invention, in the ninth aspect, the image forming apparatus is a color image forming apparatus that forms a color image by superimposing a plurality of color toner images.

  According to the present invention, in the image fixing apparatus, it is possible to prevent heat damage of the fixing member and contamination due to the offset toner, and at the same time ensure high productivity.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
(1) Example of Image Forming Apparatus FIG. 1 shows a schematic configuration diagram of a color image forming apparatus according to the present invention.

  The color image forming apparatus of this example is an apparatus that obtains a full color image by superimposing four color toner images of yellow, cyan, magenta, and black using an electrophotographic method, and the process speed is 90 mm / sec, The number of printed sheets per minute is 16 US letter size paper. The time (FPOT) until the first print (First Page Out) is about 15 seconds.

  Y, C, M, and K are four process cartridges that respectively form yellow, cyan, magenta, and black color toner images, which are arranged in order from the bottom to the top. Each process cartridge Y, C, M, and K includes a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging unit, a developing unit 3 for developing an electrostatic latent image, and a cleaning unit for the photosensitive drum. A so-called all-in-one cartridge in which 4 etc. are collected in one container is used. Yellow toner is used for the developing means 3 of the yellow process cartridge Y, cyan toner is used for the developing means 3 of the cyan process cartridge C, magenta toner is used for the developing means 3 of the magenta process cartridge M, and black process cartridge K is used. The developing means 3 is filled with black toner.

  An optical system 5 that forms an electrostatic latent image by exposing the photosensitive drum 1 is provided corresponding to the four color process cartridges Y, C, M, and K. As the optical system 5, a laser scanning exposure optical system is used.

  In each of the process cartridges Y, C, M, and K, the optical system 5 performs scanning exposure based on the image data on the photosensitive drum 1 that is uniformly charged by the charging unit 2. An electrostatic latent image corresponding to the scanning exposure image is formed on one surface. By setting the developing bias applied to the developing roller of the developing means 3 from a bias power source (not shown) to an appropriate value between the charged potential and the latent image (exposed rear) potential, the toner charged to a negative polarity Is selectively attached to the electrostatic latent image on the photosensitive drum 1 and developed.

  That is, a yellow toner image is formed on the photosensitive drum 1 of the yellow process cartridge Y, a cyan toner image is formed on the photosensitive drum 1 of the cyan process cartridge C, and a magenta toner is applied on the photosensitive drum 1 of the magenta process cartridge M. A black toner image is formed on the photosensitive drum 1 of the black process cartridge K.

  The monochromatic toner images developed and formed on the photosensitive drums 1 of the process cartridges Y, C, M, and K are transferred onto the intermediate transfer member 6 that rotates at a substantially constant speed in synchronization with the rotation of the photosensitive drums 1. In this way, a full color toner image is synthesized and formed on the intermediate transfer body 6 by being superimposed and sequentially transferred in a predetermined alignment state.

  In the present embodiment, an endless intermediate transfer belt is used as the intermediate transfer member 6, and is suspended and stretched around three rollers: a driving roller 7, a secondary transfer roller facing roller 14, and a tension roller 8. And is driven by a driving roller 7.

  A primary transfer roller 9 is used as a primary transfer unit of the toner image from the photosensitive drum 1 of each process cartridge Y, C, M, and K to the intermediate transfer belt 6. By applying a primary transfer bias having a polarity opposite to that of toner from a bias power source (not shown) to the primary transfer roller 9, the intermediate transfer belt 6 is placed on the photosensitive drum 1 of each process cartridge Y, C, M, K. A toner image is primarily transferred to the toner image.

  After the primary transfer from the photosensitive drum 1 to the intermediate transfer belt 6 in each of the process cartridges Y, C, M, and K, the toner remaining as a transfer residue on the photosensitive drum 1 is removed by the cleaning unit 4. In this embodiment, blade cleaning using a urethane blade is used as the cleaning means 4.

  The above process is performed in the process cartridges Y, C, M, and K for each color of yellow, cyan, magenta, and black in synchronization with the rotation of the intermediate transfer belt 6, and the primary transfer toner for each color on the intermediate transfer belt 6. The images are formed one after another. At the time of image formation of only a single color (monochrome mode), the above process is performed only for the target color.

  On the other hand, the transfer material P set in the transfer material cassette 10 serving as a transfer material supply unit is fed by the feed roller 11 and suspended by the registration roller 12 around the secondary transfer roller facing roller 14 at a predetermined control timing. The intermediate transfer belt 6 is conveyed to a nip portion between the intermediate transfer belt 6 and the secondary transfer roller 13 as a secondary transfer unit.

  The primary transfer toner image formed on the intermediate transfer belt 6 is collectively transferred onto the transfer material P by a bias having a polarity opposite to that of a toner applied from a bias application unit (not shown) to a secondary transfer roller 13 as a secondary transfer unit. Transcribed.

  The secondary transfer residual toner remaining on the intermediate transfer belt 6 after the secondary transfer is removed by the intermediate transfer belt cleaning unit 15. In the present embodiment, as with the cleaning means 4 for the photosensitive drum 1, the intermediate transfer member is cleaned with a urethane blade.

The toner image secondarily transferred onto the transfer material P passes through the fixing device F as a fixing unit, and is fused and fixed onto the transfer material P, and is sent out to the discharge tray 32 through the discharge path 31. It becomes an output image of the image forming apparatus.
(2) Fixing device F
FIG. 2 is a schematic configuration model diagram of the fixing device F. The fixing device F of this example is a heating device of a fixing belt heating method and a pressing rotary member driving method (tensionless type).

1) Overall Configuration of Apparatus F Reference numeral 20 denotes a fixing belt as a first fixing member, which is a cylindrical (endless belt-like) member formed by providing an elastic layer on the belt-like member. The fixing belt 20 will be described in detail later in section 3).

  Reference numeral 22 denotes a pressure roller as a second fixing member. Reference numeral 17 denotes a heat-resistant / rigid heater holder having a substantially semicircular arc shape in cross section, and 16 is a fixing heater as a heat source, which is disposed on the lower surface of the heater holder 17 along the length of the holder. The fixing belt 20 is loosely fitted on the heater holder 17. In the present embodiment, the fixing heater 16 is a ceramic heater which will be described in detail later in section 2).

  The heater holder 17 is made of a highly heat-resistant engineering plastic resin, holds the fixing heater 16, and plays a role of guiding the fixing belt 20. Examples of the resin used as the material include PPS (polyphenylene sulfide), PES (polyether sulfide), polyimide, polyimide amide, liquid crystal polymer, fluororesin, and the like. Torelina (trade name AR04: with glass fiber) was used. The maximum usable temperature of AR04 is about 260 ° C.

  The pressure roller 22 is formed by forming a silicone rubber layer having a thickness of about 3 mm on a stainless steel core by injection molding and coating a PFA resin tube having a thickness of about 40 μm thereon. The pressure roller 22 is disposed such that both end portions of the core metal are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 24. On the upper side of the pressure roller 22, the heating assembly composed of the heater 16, the heater holder 17, the fixing belt 20 and the like is arranged in parallel to the pressure roller 22 with the heater 16 facing downward, and both end portions of the heater holder 17. Is biased in the axial direction of the pressure roller 22 by a force of 98 N (10 kgf) on one side and a total pressure of 196 N (20 kgf) by a pressure mechanism (not shown), so that the downward surface of the fixing heater 16 is passed through the fixing belt 20. A fixing nip portion N having a predetermined width necessary for heat fixing is formed by pressing the elastic layer of the pressure roller 22 against the elasticity of the elastic layer with a predetermined pressing force. The pressurizing mechanism has a pressure releasing mechanism, and has a configuration in which the pressurizing is released and the transfer material P can be easily removed at the time of jam processing or the like.

  Reference numerals 23 and 26 denote an entrance guide and a fixing paper discharge roller assembled to the apparatus frame 24. The entrance guide 23 serves to guide the transfer material so that the transfer material P that has passed through the secondary transfer nip is accurately guided to the fixing nip portion N. The entrance guide 23 of the present embodiment is made of polyphenylene sulfide (PPS) resin.

  The pressure roller 22 is rotationally driven by the driving means M in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed. A rotational force acts on the cylindrical fixing belt 20 due to the pressure frictional force in the fixing nip portion N between the outer surface of the pressure roller 22 and the fixing belt 20 by the rotation driving of the pressure roller 22, and the fixing belt 20 The inner surface of the heater holder 17 is slid in close contact with the downward surface of the fixing heater 16, and the outer periphery of the heater holder 17 is rotated in the clockwise direction indicated by the arrow. Grease is applied to the inner surface of the fixing belt 20 to ensure slidability between the heater holder 17 and the inner surface of the fixing belt 20.

  The pressure roller 22 is rotationally driven, and accordingly, the cylindrical fixing belt 20 is driven and rotated, and the fixing heater 16 is energized. The fixing heater 16 is heated to rise to a predetermined temperature. In the adjusted state, the transfer material P carrying an unfixed toner image is guided and introduced along the entrance guide 23 between the fixing belt 20 and the pressure roller 22 of the fixing nip N, and the fixing nip N Then, the toner image carrying surface side of the transfer material P is in close contact with the outer surface of the fixing belt 20, and the fixing nip portion N is nipped and conveyed together with the fixing belt 20. In this nipping and conveying process, heat of the fixing heater 16 is applied to the transfer material P via the fixing belt 20, and an unfixed toner image on the transfer material P is heated and pressurized on the transfer material P to be melted and fixed. . The recording material P that has passed through the fixing nip N is separated from the fixing belt 20 by the curvature, and is discharged by the fixing discharge roller 26.

2) Fixing heater 16
In the present embodiment, the fixing heater 16 serving as a heat source is formed by applying a conductive paste containing a silver / palladium alloy on an alumina substrate into a film having a uniform thickness by screen printing. The ceramic heater which formed the glass coat by pressure-resistant glass on it was used.

  FIG. 3 is a structural model diagram of an example of such a ceramic heater, in which (a) is a partially cutaway surface model diagram, (b) is a back surface model diagram, and (c) is an enlarged cross-sectional model diagram.

This fixing heater 16 is
1. A horizontally long alumina substrate a having a direction perpendicular to the paper passing direction as a longitudinal direction;
2. 10 μm thick conductive paste containing silver palladium (Ag / Pd) alloy that heats when current flows, coated on the surface side of the above-mentioned alumina substrate a in the form of a line or strip by screen printing along the length. Resistance heating element layer b having a width of about 1 to 5 mm,
3. As the power supply pattern for the resistance heating element layer b, the first and second electrode parts cd and extended electric circuit parts ef, which are similarly patterned by screen printing of silver paste on the surface side of the alumina substrate a,
4). A thin-walled material having a thickness of about 10 μm that can withstand the rubbing with the fixing belt 20 formed on the resistance heating element layer b and the extension electric circuit portions e and f to ensure protection and insulation. Glass coat g,
5. Sub thermistor 19 provided on the back side of the alumina substrate a
Etc.

  The fixing heater 16 is supported by being fixed to the heater holder 17 with its surface side exposed downward.

  A power feeding connector 27 is attached to the first and second electrode portions c and d of the fixing heater 16. Power is supplied from the heater drive circuit 28 to the first and second electrode portions c and d via the power supply connector 27, whereby the resistance heating element layer b generates heat and the fixing heater 16 is quickly heated. . The heater drive circuit unit 28 is controlled by a control circuit unit (CPU) 21.

  In normal use, the rotation of the fixing belt 20 starts with the rotation of the pressure roller 22, and the temperature of the inner surface of the fixing belt 20 increases as the temperature of the fixing heater 16 increases. Energization of the fixing heater 16 is controlled by PID control, and the input power is controlled so that the back surface temperature of the fixing heater 16, that is, the detected temperature of the main thermistor 19 becomes 230 ° C.

3) Fixing belt 20
The fixing belt 20 is formed by coating polyimide resin with a 50 μm thick cylindrical endless film, a silicone rubber layer as an elastic layer by a ring coating method, and coating a 30 μm thick PFA resin tube. .

For the silicone rubber layer, it is desirable from the viewpoint of temperature rise to use a material having as high a thermal conductivity as possible and to reduce the heat capacity of the fixing belt 20. In the present embodiment, a material having a thermal conductivity of about 4.19 × 10 ⁻³ J / sec · cm · K and a silicone rubber having a high thermal conductivity are used.

  On the other hand, it is desirable to make the rubber layer of the fixing belt 20 as thick as possible from the viewpoint of image quality such as OHT permeability and “s” (small gloss unevenness) on the image. According to the study by the present inventors, it has been found that a rubber thickness of 200 μm or more is necessary to obtain a satisfactory level of image quality. The silicone rubber layer in the present embodiment has a thickness of 250 μm.

When the heat capacity of the fixing belt 20 thus formed was measured, it was 1.17 × 10 ⁻¹ J / cm ² · K (heat capacity per 1 cm ^{2 of the} fixing belt). Generally, when the heat capacity of the fixing belt 20 is 4.19 J / cm ² · K or more, the temperature rise becomes dull and the on-demand property is impaired. On the other hand, if it is set to 4.19 × 10 ⁻² J / cm ² K or less, the rubber layer of the fixing belt 20 has to be extremely thin, and the image quality such as the OHT permeability and the level of “su” is increased. The thickness of the rubber layer necessary to maintain the thickness cannot be secured. Therefore, the on-demand property, the heat capacity of the fixing belt 20 that satisfies both of the image quality is found to be included within the scope of the following ^{4.19 × 10 -2 J / cm 2} K or more 4.19J / cm ² K Further, by providing a fluororesin layer on the surface of the fixing belt 20, the surface releasability is improved, and an offset phenomenon occurs when the toner once adheres to the surface of the fixing belt 20 and moves to the transfer material P again. Can be prevented.

Further, when the fluororesin layer on the surface of the fixing belt 20 is a PFA tube, a uniform fluororesin layer can be formed more easily.
(3) Throughput control at the time of small-size sheet passing 19 and 18 are two thermistors of main and sub as first and second temperature detecting means. The main thermistor 19 as the first temperature detecting means is disposed at a location closer to the fixing heater 16 that is a heat source than the sub-thermistor 18, and is in contact with the back surface of the fixing heater 16 in the present embodiment. Detect the temperature of The sub-thermistor 18 as the second temperature detecting means is disposed in a non-contact manner with respect to the fixing heater 16 as a heat source. In the present embodiment, the sub-thermistor 18 is elastically brought into contact with the inner surface of the fixing belt 20 above the heater holder 17. Yes, the temperature of the inner surface of the fixing belt 20 is detected.

  In the sub-thermistor 18, a thermistor element is attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17, and the movement of the inner surface of the fixing belt 20 becomes unstable due to the elastic swing of the arm 25. Even in this state, the thermistor element is always kept in contact with the inner surface of the fixing belt 20.

  FIG. 4 is a perspective view for explaining the longitudinal arrangement state of the sub-thermistor 18 and the main thermistor 19 in the present embodiment.

  In the present embodiment, as the transfer material P, A4-size regular paper (longitudinal width 210 mm) and A5-size regular paper (longitudinal width 145 mm) can be passed on the basis of the center. In FIG. 9, the main thermistor 19 is arranged near the longitudinal center of the fixing heater 16, but the sub-thermistor 18 is positioned 90 mm from the longitudinal center of the fixing belt 20, that is, outside the A5 size paper and A4 size paper. It placed in the position which becomes inside. The sub-thermistor 18 and the main thermistor 19 are connected to a control circuit unit (CPU) 21, and the control circuit unit 21 determines the temperature control content of the fixing heater 16 based on the output of the main thermistor 19, and the heater drive circuit unit The energization to the fixing heater 16 is controlled by 28 (FIG. 4).

  In the present embodiment, for example, when the temperature of the sub-thermistor 18 during the paper feeding is monitored and the temperature reaches a certain level or more in order to prevent a temperature rise at the edge when A5 size paper is continuously fed. In addition, the ability to lower the throughput by increasing the sheet passing interval, further increasing the sheet passing interval when the temperature exceeds a certain level, and gradually reducing the throughput to ease the edge temperature rise. Have.

  FIG. 5 is a flowchart for explaining the operation of the edge temperature increase mitigation function during the output of the small size recording material of the image forming apparatus according to the present embodiment.

  After receiving the code data in step S901, the drive motor and the fixing heater 16 are turned on in step S903, and in step S904, the output of the recording material is started at a sheet interval t0 [msec].

  Next, in step S905, the temperature Ts of the sub-thermistor 18 is detected, and it is determined whether Ts is equal to or higher than the reference temperature T1. Until Ts becomes equal to or higher than T1, the processes from step S904 to step S906 are repeated, and when printing is completed, the process returns to the standby state.

  In step S905, if Ts is equal to or greater than T1, the process proceeds to step S907, a predetermined time t1 is added between the sheets, and the output is continued.

  Then, similarly to step S905, the temperature Ts of the sub-thermistor 18 is detected in S908, and it is determined whether Ts is equal to or higher than the reference temperature T1.

  Until the temperature of Ts becomes equal to or higher than T1, the processes from step S907 to step S909 are repeated, and when printing is completed, the process returns to the standby state.

  In step S908, when Ts is equal to or greater than T1, the process goes to step S910, the predetermined time t2 is added between the sheets, and the output is continued. The processes from S910 to S911 are repeated until the output is completed.

  In the present embodiment, the extension between the papers is performed in two stages, but this may be set to more than that. In addition, although the reference temperature Ts is set to T1 in all cases, it is not necessary to set the reference temperature Ts at the same temperature because the reference temperature Ts can be lowered due to the warming condition of the pressure roller.

Next, a comparison with the conventional example is performed in the case where an A5 size paper is passed (starting from a cold state) using an image forming apparatus equipped with the fixing device of the present embodiment and having a process speed of 90 mm / sec. went.
Comparative Example 1) Main thermistor: inner surface of fixing belt central part 190 ° C temperature control
Sub thermistor: Heater end back surface Reference temperature Ts: 235 ° C
Comparative Example 2) Main thermistor: Heater center inner surface 230 ° C temperature control
Sub thermistor: Heater end back surface Reference temperature Ts: 235 ° C
Example) Main thermistor: Heater center inner surface 230 ° C. Temperature control Sub thermistor: Fixing belt end inner surface reference temperature Ts: 220 ° C.
Here, the temperature control temperature of the main thermistor is a temperature at which the belt surface temperature reaches 180 ° C. at which the image can be fixed 15 seconds after the fixing device is started up by the fixing device 700 W, and the reference temperature of the sub-thermistor Ts is a temperature at which the fixing belt surface portion corresponding to the sub-thermistor becomes 210 ° C. at which hot offset occurs when the fixing device is sufficiently heated by passing paper or the like (referred to as hot). Further, with respect to each comparative example, control for lowering throughput, start-up control, and temperature control are performed in the same manner as in this embodiment except for the arrangement of each thermistor.

  FIG. 6 shows changes in throughput, with the vertical axis plotting throughput in terms of 1 minute and the horizontal axis plotting the number of sheets passed. According to this, in Comparative Examples 1) and 2) in which the sub-thermistor is arranged on the back surface of the heater end, the maximum throughput of 16 ppm is about the initial 4 sheets, and then the throughput is reduced to 8 sheets. Is 4 ppm. In contrast, the present embodiment outputs about 14 sheets at the maximum throughput, and does not fall to 4 ppm until the 25th sheet.

  This is because, as shown in FIG. 7, the belt surface temperature is different when the non-sheet passing portion heater back temperature reaches 235 ° C. at the time of hot start and cold start at the time of small size sheet passing. At this time, the difference between the heater back temperature and the belt surface temperature is 25 ° C. when hot, but also 55 ° C. during cold start. On the other hand, the difference between the belt back temperature and the belt surface temperature is 0 ° C. at cold start and only 10 ° C. at hot start, and the difference between cold start and hot start is smaller when detecting on the back of the belt. . For this reason, the belt surface temperature of the non-sheet passing portion can be accurately predicted even during the cold, and the timing of throughput reduction can be delayed.

  Next, the overshoot near the fixing heater at the time of start-up will be described.

  FIG. 8 shows respective rising curves of the temperature of the contact surface with the heater at the center of the heater holder 17, the belt surface temperature, and the fixing belt inner surface temperature until the belt temperature reaches 180 ° C. from the cold state.

Condition: 700W input at start-up ON / OFF control of ON below temperature control temperature and OFF above temperature control temperature For this example and comparative example 2) in which the main thermistor is arranged on the back of the heater, the temperature overshoot is Although there are few overshoots and undershoots in Comparative Example 1). For this reason, in Comparative Example 1), the heater holder needs to be formed of a liquid crystal polymer resin having high heat resistance. In this embodiment, since there is little overshoot around the heater holder, it is possible to select PPS (polyphenylene sulfide) or the like having a relatively low heat resistance temperature, and the material selectivity is high.

  As described above, by using this embodiment, the productivity at the output of the small size recording material is increased, and the thermal damage of the member can be prevented.

<Embodiment 2>
The present embodiment is characterized in that a metal-based metal fixing belt is used as the fixing belt 20.

  FIG. 8 is a view showing the fixing belt 20 used in this embodiment. As the base layer 20a, a SUS belt is used in which a SUS base tube is formed into a seamless belt shape having a thickness of 50 μm by drawing. Similar to the first and second examples, a rubber layer 20b and a release layer 20c were formed on the SUS belt 20a to obtain the fixing belt 20 of the present embodiment.

By having a base layer made of metal,
1) Since heat transfer in the longitudinal direction is easily performed, the temperature rise of the non-sheet passing portion on the surface of the fixing belt 20 can be suppressed to a low level.

  2) Since heat is easily transferred even in the circumferential direction, the fixing property is excellent. For this reason, temperature control temperature can be set low and a non-sheet passing part temperature rise can be suppressed.

  For the above reasons, it is possible to prevent a decrease in throughput.

  In the present embodiment, stainless steel is used as the material of the base material 20a of the fixing belt 20, but other metals may be used. Specifically, copper, iron, nickel, etc. can be considered. In particular, when a fixing belt base material 20a formed of copper or nickel in a sleeve shape by electroforming is used, it is possible to reduce the film thickness to 40 μm or less, and furthermore, the thermal efficiency is high, so that the fixing belt 20 having excellent rise characteristics can be obtained. Is possible.

<Embodiment 3>
The present embodiment is characterized in that a ceramic heater using aluminum nitride as a base material a instead of alumina is used as the fixing heater 16.

  In the present embodiment, the configuration is exactly the same as that of the first embodiment except that aluminum nitride is used as the substrate a of the fixing heater 16.

  Aluminum nitride having a thermal conductivity of 95 W / m · K was used. Since the thermal conductivity of alumina is 4.75 times that of 20 W / m · K, even when the main thermistor 19 is placed on the back surface of the fixing heater 16, Since it becomes possible to have better temperature followability, there is little occurrence of uneven gloss. In addition, since the heat transfer coefficient in the longitudinal direction is good, it has an advantage that the throughput is hardly reduced as compared with the conventional heater.

  <Others.

  1) The first and second fixing members for forming the fixing nip are not limited to the forms of the fixing belt and the pressure roller in the embodiment. An apparatus having a heat source in both the first fixing member and the second fixing member may be provided.

  2) Of course, the form of the ceramic heater as the heat source is not limited to that of the embodiment. Further, the heat source is not limited to the ceramic heater, and may be constituted by an electromagnetic induction heating member such as an iron plate and a magnetic field generating means, for example.

  3) The heat source is not necessarily located at the fixing nip N. For example, the heat source can be disposed on the upstream side of the fixing nip portion N in the fixing belt moving direction.

  4) Although the fixing device of the embodiment is a pressure rotating body drive system, a driving roller may be provided on the inner peripheral surface of the endless fixing belt and driven while applying tension to the fixing belt. The fixing belt may be a roll-ended end-like web and may be driven to travel.

  5) In the present invention, the fixing device includes not only a fixing device that heat-fixes an unfixed image as a permanent image on a recording material, but also a heating device that presupposes an unfixed image on the recording material, and a recording material that carries the image. A heating device or the like that modifies the image surface properties such as gloss by re-heating is also included.

  6) The image forming method of the image forming apparatus is not limited to the electrophotographic method, and may be an electrostatic recording method, a magnetic recording method, or the like, or may be a transfer method or a direct method.

1 is a schematic configuration diagram of a color image forming apparatus using Embodiment 1 of the present invention. 1 is a schematic configuration diagram of a fixing device F using Embodiment 1 of the present invention. FIG. 3 is an explanatory diagram of a configuration of a fixing heater. It is a perspective model diagram which shows the positional relationship of a fixing heater, a main thermistor, and a sub thermistor. 3 is a flowchart showing an algorithm for throughput control when a small-size sheet is passed in Embodiment 1 of the present invention. 6 is a graph showing the relationship between the number of small-size sheets passing and throughput in the first embodiment of the present invention and a comparative example. 6 is a table showing belt temperatures in a non-sheet passing portion heater back temperature 235 ° C. dictionary when A5R is passed through the fixing device according to Embodiment 1 of the present invention. It is a graph which shows transition of the heater back vicinity temperature at the time of starting of Embodiment 1 and a comparative example of the present invention. It is a cross-sectional model diagram of a fixing belt in Embodiment 2 of the present invention. It is a schematic sectional view of a fixing device using a conventional fixing roller. It is a schematic sectional drawing of the conventional film fixing apparatus.

Explanation of symbols

16 Fixing heater 17 Heater holder 18 Sub thermistor 19 Main thermistor 20 Fixing belt 22 Pressure roller

Claims (10)

In a fixing device that heats a recording material that carries an image in a nip formed by a first fixing member and a second fixing member.
A first temperature detecting unit disposed in contact with the first fixing member; and a first temperature detecting unit disposed in contact with the first heating member, in contact with the first fixing member; A fixing device comprising: a second temperature detecting unit disposed.   The fixing device according to claim 1, wherein the first temperature detection unit and the second temperature detection unit are arranged at different positions in the nip longitudinal direction.   Two or more types of recording materials having different sizes in the longitudinal direction of the nip can be used, and the second temperature detecting means is within the longitudinal area of the recording material having a large size in the longitudinal direction of the nip and has a small size in the longitudinal direction of the nip. The fixing device according to claim 2, wherein the fixing device is disposed at a position corresponding to the outside of the longitudinal region of the recording material.   The fixing device according to claim 1, wherein the first temperature detecting unit detects the temperature of the heating member, and the temperature of the heating member is controlled based on the result.   The fixing device according to claim 4, wherein the second temperature detection unit detects the temperature of the first fixing member and changes the conveyance interval or conveyance speed of the recording material based on the result.   5. The fixing device according to claim 4, wherein the second temperature detecting unit detects the temperature of the first fixing member and stops the recording material based on the result.   7. The fixing device according to claim 1, wherein a fixing belt in which an elastic layer is provided on a belt-like member is used as a fixing member on the side in contact with the image surface of the recording material.   The fixing device according to claim 1, wherein the second temperature detection unit is disposed in contact with an inner surface of the fixing member.   An image forming apparatus comprising the fixing device according to claim 1.   The image forming apparatus according to claim 9, wherein the image forming apparatus forms a color image by superimposing a plurality of color toner images.

Images