JP2010164842A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device including: an external heating belt 3 for heating a fixing roller 1 while abutting on the surface of the fixing roller 1; and a cleaning member (scraper 7, cleaning pad 12) that abuts on the external heating belt 3, wherein an offset is prevented from being caused by attaching onto the fixing roller 1 a coating material or the like that is scraped and removed from the external heating belt 3 with the cleaning member and degrading mold releasability of the fixing roller 1. <P>SOLUTION: The fixing device is configured by forming the release layer 1c of the fixing roller 1 with a material having higher in mold releasability than the release layer 2c of a pressure roller 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus and an image forming apparatus including the same.

  As a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a heat roller fixing type fixing device is frequently used. The fixing device of the heat roller fixing system generally includes a pair of rollers (fixing roller and pressure roller) that are in pressure contact with each other, and a heating unit that includes a halogen heater or the like disposed inside or both of the roller pair. After the roller pair is heated to a predetermined temperature (fixing temperature), the recording paper on which the unfixed toner image is formed is fed to the pressure contact portion (fixing nip portion) of the roller pair, and is passed through the pressure contact portion. The toner image is fixed by pressure.

  By the way, in a fixing device provided in a color image forming apparatus, it is common to use an elastic roller provided with an elastic layer made of silicon rubber or the like on the surface of the fixing roller. By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed corresponding to the unevenness of the unfixed toner image, and comes into contact with the unfixed toner image so as to cover the unfixed toner image. A color unfixed toner image can be appropriately fixed. Further, due to the effect of releasing the distortion of the elastic layer at the fixing nip portion, it is possible to improve the releasability from the fixing roller for the color toner that is more likely to be offset than monochrome. Furthermore, since the elastic layer of the fixing roller is deformed into a concave shape, the nip shape of the fixing nip portion is convex upward (the so-called reverse nip shape), so that the paper can be peeled from the fixing roller. The sheet can be peeled off without using a peeling means such as a peeling claw (self-stripping), and image defects caused by the peeling means can be eliminated.

  However, in the fixing device provided in such a color image forming apparatus, if the process speed (moving speed of the recording paper at the fixing nip portion; fixing speed) is increased, sufficient heat cannot be applied to the unfixed toner image. In some cases, it cannot be properly fixed. Therefore, when the process speed is increased, it is necessary to widen the nip width of the fixing nip portion in order to apply sufficient heat to the unfixed toner image and appropriately perform the fixing process. Further, as means for widening the nip width, (1) a method of increasing the elastic layer of the fixing roller or (2) a method of increasing the diameter of the fixing roller can be considered.

  However, since the thermal conductivity of the elastic layer is very low, in the configuration of the fixing roller having the elastic layer and internally provided with heating means, the surface temperature is increased when the process speed is increased. There is a problem that it does not follow the temperature change. For this reason, if the elastic layer is made thicker as described in (1) above, the problem of temperature followability on the surface of the fixing roller becomes more prominent. In the method (1), since the thermal conductivity of the elastic layer is low, there is a problem that the warm-up time for heating becomes long and power consumption increases.

  Further, when the diameter of the fixing roller is increased as in (2) above, since the size of the fixing roller is increased, the heat capacity is increased and the warm-up time for heating is increased, and the power consumption is increased. There is a problem of doing.

  Therefore, as a technique for solving such a problem, a technique (external heating fixing method) has been proposed in which an external heating means is brought into contact with the surface of the fixing roller and the fixing roller is heated from the outside.

  For example, Patent Document 1 includes a fixing member, an endless belt (external heating belt) suspended by a plurality of suspension rollers, and a heating unit that heats the endless belt, and the endless belt is pressed against the fixing member. A fixing device of an external belt heating fixing system that heats the fixing member by causing the fixing member to be heated is disclosed.

  In the fixing device employing this external heating method, the fixing roller is heated from the outside by using a belt having a small heat capacity, so that the fixing roller can be heated quickly and the warm-up time can be shortened. Therefore, while suppressing problems such as a decrease in the temperature followability of the fixing roller and an increase in the warm-up time, a wide nip is provided by providing a thick, low-hardness elastic layer on the fixing roller or increasing the diameter of the fixing roller. A width can be secured.

JP 2007-212896 (published on August 23, 2007)

  However, in the technique of Patent Document 1, the cleaning web is attached to the surface of the fixing roller by bringing the cleaning web into contact with the fixing roller at a position upstream of the contact position of the external heating belt in the fixing roller in the rotation direction of the fixing roller. The toner, paper dust, and the like are removed, and the external heating belt is prevented from being soiled by toner, paper dust, and the like. For this reason, the cleaning web and the surface of the fixing roller rub against each other, so that there is a problem that the fixing roller is damaged and an image defect occurs.

  Accordingly, a cleaning member made of a scraper or a pad is brought into contact with the external heating belt without providing a cleaning web that rubs against the fixing roller, thereby preventing the external heating belt and the fixing roller from being contaminated by toner, paper dust, or the like. (This configuration is a configuration developed by the inventor of the present application and is not a prior art).

  However, as a result of studying a configuration in which the cleaning member made of a scraper or a pad is brought into contact with the external heating belt without providing a cleaning web that rubs against the fixing roller, the inventor of the present application has studied the cleaning of the scraper or the pad on the external heating belt If the fixing member is brought into contact, the coating member (coating layer) of the external heating belt is scraped by the cleaning member, and the scraped coating material adheres to the fixing roller, which causes a decrease in the releasability of the fixing roller. I found out that

  In particular, when the fixing process is performed on a large-sized sheet immediately after the fixing process is continuously performed on a small-sized sheet, the releasability of the fixing roller in an area where the fixing roller does not contact the small-sized sheet. It was found that the offset due to the decrease in the frequency tends to occur. The reason is considered as follows.

  That is, when a fixing process is performed on a large size paper, the coating material adhering to the fixing roller adheres to the paper, so that the surface of the fixing roller is always cleaned by the paper and the releasability of the fixing roller is maintained. . However, when the small size paper is continuously fixed, the coating material is accumulated in the non-sheet passing portion (the non-contact portion with the small size paper on the surface of the fixing roller). It is lower than the part releasability. Further, when the fixing process is continuously performed on a small-size sheet, the temperature of the non-sheet passing portion is higher than that of the sheet passing portion, so that a high temperature offset is likely to occur. Further, since negatively charged paper (about −500 V) is passed through the paper passing portion, the negative potential becomes higher than that in the non-paper passing portion, so that electrostatic repulsive force with the negatively charged toner is generated. However, since the sheet is not passed in the non-sheet passing portion, the negative potential is lower than that in the sheet passing portion, and the offset is likely to occur. Therefore, if the fixing process is performed on the large-sized sheet immediately after the fixing process is continuously performed on the small-sized sheet, a high-temperature offset is generated in the region corresponding to the non-sheet passing portion for the small-sized sheet in the fixing roller. It tends to happen.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an external heating member that abuts on the surface of the fixing member and heats the fixing member, and an abutment on the surface of the external heating member. In an external heating type fixing device having a cleaning member for cleaning the surface of the external heating member, a substance scraped off from the external heating member by the cleaning member adheres to the fixing member and the releasability of the fixing member The purpose of this is to suppress the occurrence of offset due to a decrease in the image quality.

  In order to solve the above-described problems, the fixing device of the present invention is configured to heat the fixing member in contact with the rotating fixing member, the pressure member pressed against the fixing member, and the surface of the fixing member. An external heating member rotatably supported; and a cleaning member that contacts the surface of the external heating member and removes dirt adhered to the surface of the external heating member. A fixing device that transports a recording material between them and thermally fixes the toner image on the recording material onto the recording material by heat transmitted from the fixing member, the surface of the fixing member being the pressure member It is characterized by higher releasability than the surface.

  Here, the releasability is a property that hardly causes adhesion or seizure to the surface, and is also referred to as non-adhesiveness.

  According to the above configuration, the surface of the fixing member has higher release properties than the surface of the pressure member. For this reason, the adhering matter adhering to the surface of the fixing member moves from the fixing member to the pressure member. As a result, it is possible to prevent the deposits from accumulating on the surface of the fixing member and to suppress a decrease in the releasability of the fixing member, thereby suppressing the occurrence of offset.

  The external heating member may be an endless belt suspended on a plurality of suspension rollers.

  Further, the surface of the fixing member is formed of a non-conductive fluororesin, and the surface of the pressure member is formed of a conductive fluororesin obtained by adding a conductive material to the fluororesin. There may be.

  According to the above configuration, when the conductive material is added, the surface of the pressure member is less releasable than the surface of the fixing member. Therefore, it is possible to prevent the deposits from accumulating on the surface of the fixing member, and to suppress a decrease in the releasability of the fixing member, thereby suppressing the occurrence of offset.

  The contact surface of the external heating member with the fixing member and the cleaning member may be formed of a resin material.

  Generally, when the contact surface of the external heating member with the cleaning member is formed of a resin material, the external heating member is easily scraped by the contact with the cleaning member, and the scraped substance adheres to the fixing member. Although an offset is likely to occur, the above configuration can suppress the occurrence of an offset even in such a case.

  The cleaning member may be a scraper that removes dirt adhered to the surface of the external heating member by bringing the edge portion of the plate-like member into contact with the surface of the external heating member. The scraper may be made of metal.

  According to said structure, the stain | pollution | contamination on an external heating member can be efficiently cleaned by using the scraper excellent in the cleaning performance. As a result, it is possible to suppress the contamination on the external heating member from adhering to the fixing member and from adhering to the recording material and degrading the image quality. In general, the scraper is easy to scrape off a part of the external heating member. However, according to the above configuration, even if a part of the external heating member scraped to the fixing member adheres, this deposit is more releasable. Move to a low pressure roller. For this reason, it is possible to suppress a decrease in the releasability of the fixing member due to the adhering matter, and to suppress the occurrence of offset.

  In addition, the cleaning member may be a cleaning pad that is in surface contact with the surface of the external heating member and removes dirt adhered to the surface of the external heating member. The cleaning pad may be a felt member made of a fluororesin fiber.

  According to said structure, the stain | pollution | contamination on an external heating member can be efficiently cleaned by using a cleaning pad. As a result, it is possible to suppress the contamination on the external heating member from adhering to the fixing member and from adhering to the recording material and degrading the image quality. Further, the amount of the material scraped off from the external heating member by the cleaning member can be reduced, and the occurrence of offset due to the adhesion of the material to the surface of the fixing member can be suppressed.

  Further, the cleaning member may include the scraper and the cleaning pad.

  According to the above configuration, it is possible to suppress the deterioration of the image quality caused by the dirt on the external heating member adhering to the fixing member and adhering to the recording material. Furthermore, since the material scraped off from the external heating member by the scraper can be removed by the cleaning pad, offset caused by the adhesion of the material to the surface of the fixing member can be more appropriately suppressed.

  The image forming apparatus of the present invention includes any one of the fixing devices described above. Therefore, it is possible to suppress the occurrence of offset in the portion where the substance adheres due to the fact that the material scraped off from the external heating member due to contact with the cleaning member adheres to the fixing member and the releasability of the fixing member decreases.

  As described above, in the fixing device of the present invention, the surface of the fixing member has higher release properties than the surface of the pressure member.

  Therefore, the adhering matter adhering to the surface of the fixing member moves from the fixing member to the pressure member. As a result, it is possible to prevent the deposits from accumulating on the surface of the fixing member and to suppress a decrease in the releasability of the fixing member, thereby suppressing the occurrence of offset.

FIG. 2 is an explanatory diagram illustrating a configuration of a fixing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of an image forming apparatus including the fixing device of FIG. 1. FIG. 2 is a front view and a side view of a scraper provided in the fixing device of FIG. 1. It is sectional drawing of the external heating unit with which the fixing device of FIG. 1 is equipped. FIG. 2 is an enlarged view of a main part of a contact portion between an external heating belt and a scraper in an external heating unit provided in the fixing device of FIG. 1.

  An embodiment of the present invention will be described. In this embodiment, the present invention is a color tandem type image forming apparatus that forms a multicolor or single color image on a recording material such as a recording sheet or a recording film in accordance with image data transmitted from the outside. The case where it applies to is demonstrated. However, the application target of the present invention is not limited to this, and an external heating member that contacts the surface of the fixing member and heats the fixing member, and an external heating member that contacts the surface of the external heating member and covers the surface of the external heating member. Any image forming apparatus having an external heating type fixing device provided with a cleaning member for cleaning can be applied.

<Configuration of image forming apparatus>
FIG. 2 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus 100 according to the present embodiment.

  As shown in this figure, an image forming apparatus 100 includes an exposure unit (optical system unit) E, four sets of visible image forming units pa to pd, an intermediate transfer belt unit 110, a secondary transfer unit 114, a fixing device 30, an internal A paper feed unit 116 and a manual paper feed unit 117 are provided. The operation of each member provided in the image forming apparatus 100 is controlled by a main control unit including a CPU (not shown).

  Image data handled in the image forming apparatus 100 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). For this reason, as shown in FIG. 2, four sets of visible image forming units pa to pd corresponding to the respective colors are provided, and four color toners formed by these four sets of visible image forming units pa to pd. Images are superimposed on the intermediate transfer belt 111.

  In the visible image forming unit pa, a charging unit 103a, a developing unit 102a, and a cleaning unit 104a are arranged in this order along the rotation direction of the photoconductor 101a around a photoconductor 101a that is rotatably provided as a toner image carrier. It is the structure arranged by.

  The charging unit 103a is for uniformly charging the surface of the photoreceptor 101a to a predetermined potential. In the present embodiment, the charging unit 103a employs a charging roller method (contact charging method) in order to uniformly charge the surface of the photoreceptor 101a without generating ozone as much as possible. However, the configuration of the charging unit 103a is not limited to this. For example, a non-contact charger such as a corona discharge method may be used, or a contact charger such as a brush charger may be used.

  The developing unit 102a performs a developing process for developing the electrostatic latent image formed on the photoconductor 101a with toner. As the toner, for example, a non-magnetic one-component developer (non-magnetic toner), a non-magnetic two-component developer (non-magnetic toner and carrier), a magnetic developer (magnetic toner) and the like can be used.

  The cleaning unit 104a is for removing and collecting the toner remaining on the surface of the photoreceptor 101a after the toner image is transferred to the intermediate transfer belt 111.

  The visible image forming units pb to pd have substantially the same configuration as the visible image forming unit pa except that the color of the toner used for the development processing is different. That is, black (B), yellow (Y), magenta (M), and cyan (C) toners are stored in the developing units of the visible image forming units pa, pb, pc, and pd, respectively.

  The exposure unit E exposes the photoconductors 101a to 101d charged by the charging units 103a to 103d according to image data, thereby forming electrostatic latent images according to the image data on the surfaces of the photoconductors 101a to 101d. To do. As the exposure unit E, a laser scanning unit (LSU) including a laser irradiation unit 140 and a reflection mirror 141 is used. As the exposure unit E, for example, an EL or LED writing head in which light emitting elements are arranged in an array may be used.

  The intermediate transfer belt unit 110 includes an intermediate transfer belt 111, an intermediate transfer belt driving roller (tension roller) 111a, an intermediate transfer belt driven roller (tension roller) 111b, an intermediate transfer belt cleaning unit 112, and intermediate transfer rollers 113a to 113d. ing.

  The intermediate transfer belt 111 is an endless belt made of a film having a thickness of about 100 μm to 150 μm, and is stretched around the intermediate transfer rollers 113a to 113d, the intermediate transfer belt driving roller 111a, and the intermediate transfer belt driven roller 111b. 2 is rotated in the direction of arrow B shown in FIG. The toner images of the respective colors formed on the photoconductors 101a to 101d are transferred so as to sequentially overlap the intermediate transfer belt 111, and a color toner image (multicolor toner image) is formed on the intermediate transfer belt 111. It is like that. The intermediate transfer rollers 113a to 113d are arranged on the photosensitive members 101a to 101d via the intermediate transfer belt 111 at positions between the opposing portions of the photosensitive members 101a to 101d and the units 102a to 102d and the cleaning units 104a to 104d. The toners on the photoreceptors 101a to 101d are arranged so as to oppose the intermediate transfer rollers 113a to 113d, and a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner is applied to the intermediate transfer rollers 113a to 113d. An image is transferred onto the intermediate transfer belt 111. In addition, the toner image formed on the intermediate transfer belt 111 is conveyed to a facing portion between the intermediate transfer belt driving roller 111a and the secondary transfer unit 114, and is transferred onto a recording sheet conveyed to the facing portion. It has become. The intermediate transfer belt cleaning unit 112 abuts on the intermediate transfer belt 111 and removes and collects toner remaining on the intermediate transfer belt 111 after the toner image is transferred onto the recording paper.

  The fixing device 30 includes a fixing roller (fixing member) 1 and a pressure roller (pressure member) 2 that is pressed against the fixing roller 1 with a predetermined load by a pressing auxiliary unit (not shown). Then, the recording sheet on which the toner image is transferred by the secondary transfer unit 114 is fed to a pressure contact portion (fixing nip portion) between the fixing roller 1 and the pressure roller 2 and is passed through the pressure contact portion to thereby generate heat and pressure. Then, the toner image is fixed. The surface of the recording paper on which the unfixed toner image is formed contacts the fixing roller 1, and the surface of the recording paper opposite to the surface on which the unfixed toner image is formed contacts the pressure roller 2. Details of the fixing device 30 will be described later.

  The internal paper feeding unit 116 is for accumulating recording paper (recording material) used for image formation. The manual paper feed unit 117 is foldably provided on the side wall of the image forming apparatus 100, and is for manually feeding recording paper. The paper discharge tray 118 is a tray for placing recording paper on which images have been formed.

  The image forming apparatus 100 also receives recording paper fed from the internal paper feeding unit 116 by the pickup roller 116 a and recording paper fed from the manual paper feeding unit 117 by the pickup roller 117 a to the secondary transfer unit 114 and the like. A paper transport path for sending the paper to the paper discharge tray 118 via the fixing device 30 is provided. A large number of roller members for conveying the recording paper are arranged in the paper conveyance path.

  Note that the image forming apparatus of the present embodiment is a so-called A4 machine that supports A4 and letter size paper, and is also compatible with smaller A5 and invoice size paper.

<Fixing device>
FIG. 1 is a schematic cross-sectional view showing the configuration of the fixing device 30. As shown in this figure, the fixing device 30 includes a fixing roller (fixing member) 1, a pressure roller (pressure member) 2, an external heating unit 13, a power supply circuit 15, a control unit 16, and a rotation driving unit 18. ing. The power supply circuit 15 supplies power to heater lamps 5a to 5d described later.

  The fixing roller 1 is a roller that is heated to a predetermined fixing temperature and is rotationally driven in the direction of the arrow shown in FIG. 1 by the rotation driving unit 18, and is made of a metal hollow cylindrical core metal 1a and core metal 1a. It is comprised by the 3 layer structure of the release layer (surface layer) 1c which covers the outer peripheral surface of the elastic layer 1b and the elastic layer 1b. The rotation driving unit 18 is for rotating the fixing roller 1 and is configured by a motor, a gear, or the like (not shown). In this embodiment, the moving speed of the surface of the fixing roller 1, that is, the fixing speed (process speed) is set to 225 mm / sec, so that an image can be formed at a copying speed (printing speed) of 40 sheets / minute. It has become.

  In the present embodiment, the outer peripheral surface of a cylindrical cored bar 1a made of aluminum having a thickness of 2 mm is covered with an elastic layer 1b made of silicon rubber having a heat resistance of 2.5 mm, and the elastic layer 1b is further thickened. A fixing roller 1 having an outer diameter of 40 mm covered with a 40 μm thick non-conductive PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) tube was used. In addition, the material of the metal core 1a is not limited to aluminum, For example, you may consist of iron, stainless steel, etc. The material of the elastic layer 1b is not limited to silicon rubber, and for example, fluorine rubber or the like may be used. The release layer 1c may be made of any material as long as it is excellent in heat resistance and durability and has excellent release properties with respect to the toner. In addition to PFA, a fluorine-based material such as PTFE (polytetrafluoroethylene). May be used. However, in the present embodiment, the release layer 1 c of the fixing roller 1 is made of a material having a higher release property than the release layer 2 c of the pressure roller 2.

  A thermistor (temperature detection unit) 6b that detects the temperature of the outer peripheral surface is disposed on the outer peripheral surface of the fixing roller 1, and a heater lamp that performs thermal radiation by supplying electric power to the inside of the fixing roller 1. 5c is installed. The heater lamp 5c is a heat source for the fixing roller 1, and the temperature controller 14 provided in the controller 16 controls the power supplied from the power supply circuit 15 to the heater lamp 5c, thereby causing the heater lamp 5c to emit light and radiate infrared rays. Let As a result, the inner peripheral surface of the fixing roller 1 is heated by absorbing infrared rays emitted from the heater lamp 5c, and the entire fixing roller 1 is heated. The thermistor 6b is provided so as to detect the temperature of the central portion in the rotation axis direction (width direction) of the fixing roller 1. Further, in the present embodiment, regardless of the size of the recording paper, the substantially central portion in the direction perpendicular to the recording paper conveyance direction comes into contact with the central portion in the rotation axis direction of the fixing roller 1. Therefore, the thermistor 6b always detects the temperature of the position on the surface of the fixing roller 1 that is a sheet passing area regardless of the sheet size. In the present embodiment, the fixing temperature means the temperature detected by the thermistor 6b when performing the fixing process.

  The pressure roller 2 is pressed against the fixing roller 1 with a predetermined load (360 N in the present embodiment) by a pressure assisting means such as a spring (not shown) and is fixed between the fixing roller 1 and the fixing nip portion 8 (in the present embodiment). A fixing nip width (width in the conveyance direction of the recording paper 9 at the fixing nip portion 8) is 8 mm), and is a roller that is driven to rotate by the fixing roller 1 and, like the fixing roller 1, is a metal hollow cylindrical core. It is configured by a three-layer structure of a gold 2a, an elastic layer 2b that covers the outer peripheral surface of the core metal 2a, and a release layer (surface layer) 2c that covers the elastic layer 2b.

  In the present embodiment, as the pressure roller 2, as with the fixing roller 1, an elastic layer 2b made of silicon rubber having a thickness of 2.5 mm is formed on a core metal 2a made of aluminum having a thickness of 2 mm, and further the elastic layer 2b. What formed the release layer 2c which consists of an electroconductive PFA tube of thickness 40 micrometers on it was used. Specifically, a conductive PFA tube obtained by adding carbon (conductive material) to non-conductive PFA was used as the release layer 2c. Due to the addition of carbon, the releasability of the release layer 2 c is lower than that of the release layer 1 c provided in the fixing roller 1.

  Thus, in this embodiment, the pressure roller 2 is the same shape and material as the fixing roller 1 except for the material of the release layer 2c. However, the configuration of the pressure roller 2 is not limited to this, and any structure may be used as long as the release layer 2c is made of a material having a lower release property than the release layer 1c of the fixing roller 1. For example, a cored bar 2a made of iron or stainless steel may be used, or an elastic layer 2b made of fluororubber or the like may be used. Further, as the release layer 2c, for example, a material obtained by adding a conductive material such as carbon or graphite to a fluorine-based material such as PTFE may be used.

  Further, the hardness of the pressure roller 2 may be higher than the hardness of the fixing roller 1. In this case, the fixing nip portion formed between the pressure roller 2 and the fixing roller 1 can be formed in a reverse nip shape (the shape of the pressure roller 2 is almost unchanged and the fixing roller 1 is slightly recessed). The self-peeling property with respect to the fixing roller 1 when the recording paper is discharged from the fixing nip portion can be improved.

  A thermistor 6 c for detecting the temperature of the outer peripheral surface is disposed on the outer peripheral surface of the pressure roller 2, and a heater lamp 5 d is disposed inside the pressure roller 2. The thermistor 6 c is disposed at the center portion in the rotation axis direction (width direction) of the pressure roller 2, similarly to the thermistor 6 b of the fixing roller 1. The heater lamp 5d is a heat source for the pressure roller 2, and the temperature controller 14 controls the power supplied from the power supply circuit 15 to the heater lamp 5d. The peripheral surface is heated.

  The external heating unit 13 is for heating the outer peripheral surface of the fixing roller 1, and includes heating rollers 4a and 4b, an external heating belt (endless belt) 3, heater lamps (heating units) 5a and 5b, a thermistor 6a, and a scraper. (Cleaning member) 7, cleaning pad (cleaning member) 12, and external heating unit holder (housing) 11 for housing these members.

  The heating rollers 4a and 4b are hollow cylindrical core members made of aluminum having a diameter of 16 mm and a thickness of 2 mm. The material of the heating rollers 4a and 4b is not limited to aluminum, and for example, a metal core material such as iron or stainless steel may be used. Further, the size of the heating rollers 4a and 4b is not limited to the above size, and may be changed as appropriate.

  The external heating belt 3 is an endless belt member suspended on the heating rollers 4a and 4b. Details of the structure will be described later.

  The external heating belt 3 is illustrated at a position downstream of the fixing nip portion in the rotation direction of the fixing roller 1 on the surface (outside surface) of the fixing roller 1 and upstream of the thermistor 6b in the rotation direction of the fixing roller 1. It is provided so as to come into pressure contact with the fixing roller 1 with a predetermined load (40N in the present embodiment) by a pressure assisting means such as a spring. As a result, a heating nip portion (portion where the fixing roller 1 and the external heating belt 3 abut each other) 10 is formed between the fixing roller 1 and the fixing roller 1. The external heating belt 3 is driven and rotated by the fixing roller 1 when the fixing roller 1 is rotated, and the heating rollers 4 a and 4 b are driven and rotated by the external heating belt 3. The heating nip width of the heating nip portion 10 (the width of the heating nip portion 10 in the fixing roller rotation direction) can be appropriately heated by the external heating belt 3 and the external heating belt 3 is fixed by the fixing roller. What is necessary is just to set suitably so that it can be driven to 1 appropriately. In this embodiment, the heating nip width is 20 mm.

  The heater lamp 5a is provided in the heating roller 4a and is a heat source for heating the heating roller 4a from the inner surface side, and the heater lamp 5b is provided in the heating roller 4b and heats the heating roller 4b from the inner surface side. As a heat source, the temperature controller 14 controls the power supplied from the power supply circuit 15 to the heater lamps 5a and 5b, whereby infrared rays are radiated from the heater lamps 5a and 5b, whereby the inner peripheral surfaces of the heating rollers 4a and 4b. Is heated. Then, the external heating belt 3 is heated to a predetermined temperature via the heating rollers 4a and 4b, and the fixing roller 1 is brought into contact with the outer peripheral surface of the fixing roller 1 while being heated to the predetermined temperature. The outer peripheral surface is heated from the outside. The external heating belt 3 is heated to 220 ° C. when the fixing temperature is 190 ° C., for example.

  The thermistor 6 a is for detecting the surface temperature of the external heating belt 3. The thermistor 6a is provided so as to detect the temperature of the central portion of the external heating belt 3 in the rotation axis direction (width direction).

  The scraper 7 is for removing dirt such as toner and paper powder transferred from the fixing roller 1 to the external heating belt 3 to clean the outer peripheral surface of the external heating belt 3, and the cleaning pad 12 passes through the scraper 7. Further, the toner and paper dust on the external heating belt 3 are collected.

  That is, as shown in FIG. 1, the fixing roller 1 contacts the surface of the recording paper 9 on which the unfixed toner image is formed in order to fix the unfixed toner. Therefore, dirt such as toner and paper dust on the recording paper 9 adheres to the fixing roller 1. Then, dirt such as toner and paper dust attached to the fixing roller 1 adheres to the external heating belt 3 at the contact portion between the fixing roller 1 and the external heating belt 3. The scraper 7 scrapes and removes dirt such as toner and paper powder adhering to the external heating belt 3 in this way.

  Further, when a part of the dirt such as toner or paper dust adhered to the external heating belt 3 passes through the scraper 7, the outer circumferential surface of the external heating belt 3 is rotated in the rotational direction of the external heating belt 3 by toner or paper powder. In some cases, streaks along the line adhere to the fixing roller 1 and damage the outer peripheral surface of the fixing roller 1. When such streak stains adhere to the outer peripheral surface of the external heating belt 3, a streak scratch (image defect) occurs in the image of the recording paper 9 after fixing. This streak-like image defect is particularly noticeable when printed on cardboard. The cleaning pad 12 is for preventing the occurrence of this streak-like image defect by collecting dirt such as toner and paper dust that has partially passed through the scraper 7.

  The control unit 16 includes a temperature control unit 14 and a rotation control unit 17. The temperature control unit 14 adjusts the temperature of the external heating belt 3, the fixing roller 1, and the pressure roller 2 to a predetermined temperature according to the temperature detection results of the thermistors 6a to 6c, the size of the recording paper, or the like, or The power supplied from the power supply circuit 15 to the heater lamps 5a to 5d is controlled so as to maintain a predetermined temperature. The rotation control unit 17 controls the operation of the rotation driving unit 18 that rotates the fixing roller 1. The control unit 16 may be provided in the main control unit of the image forming apparatus 100, and is provided separately from the main control unit of the image forming apparatus 100 and operates in cooperation with the main control unit. It may be.

  In this way, in the fixing device 30, the recording paper 9 on which an unfixed toner image is formed between the fixing roller 1 and the pressure roller 2 that are heated to respective predetermined temperatures and pressed against each other with a predetermined load. The unfixed toner image is fixed on the recording paper 9 by feeding and passing.

  In the present embodiment, the fixing roller 1 and the pressure roller 2 are provided with heater lamps as heating means. However, the present invention is not limited to this. For example, the heater lamp is provided only on one of the fixing roller 1 and the pressure roller. The heater lamp may not be provided in either the fixing roller 1 or the pressure roller.

  In the present embodiment, the configuration in which the external heating belt 3 is suspended by the two heating rollers 4a and 4b has been described. However, the configuration is not limited thereto, and the external heating belt 3 may be suspended by three or more rollers.

  In this embodiment, the pressure roller 2 is used as a pressure member that presses the fixing roller 1. However, the configuration of the pressure member is not limited to this, and for example, a belt-shaped pressure member is used. Also good.

<Detailed explanation of scraper>
FIG. 3 is a front view and a side view of the scraper 7. The scraper 7 includes a holding part 7b made of stainless steel having a thickness of 0.3 mm, a cleaning part (scraper part) 7a in which the tip of the holding part 7b is bent at an acute angle (angle η; in this embodiment, η = 30 °). It has a V-shape consisting of As shown in FIG. 3, slits (opening portions) 7 c (bending portions are provided at predetermined intervals along the width direction of the external heating belt 3 at positions including the bent portions in the holding portion 7 b and the cleaning portion 7 a. A cut in a direction intersecting the straight line formed). In this embodiment, the slits 7c having a width of 1 mm cut in a direction substantially perpendicular to the straight line formed by the bent portion are provided at intervals of 10 mm.

  FIG. 4 is a cross-sectional view of the external heating unit 13. As shown in this figure, the holding portion 7 b of the scraper 7 is fixed to the inner side surface of the external heating unit holder 11 so that the tip of the cleaning portion 7 a in the scraper 7 contacts the external heating belt 3. The tip of the cleaning unit 7a is in a free state position of the external heating belt 3 suspended with tension applied between the two heating rollers 4a and 4b (the inner surface of the external heating belt 3 is heated). At a position not in contact with the rollers 4 a and 4 b), it is in contact with the outer surface of the external heating belt 3. Further, the front end (edge portion) of the cleaning unit 7 a is in a counter direction with respect to the rotation direction of the external heating belt 3, that is, from the contact portion of the external heating belt 3 with the scraper 7. The surface of the scraper 7 including the contact portion with the external heating belt 3 with respect to the outer surface of the upstream portion in the rotational direction, and the side facing the outer surface of the upstream portion in the rotational direction from the contact portion in the external heating belt 3 The contact is made so that the contact angle θ (θ = 150 ° in the present embodiment), which is the inclination angle of the surface, is greater than 90 °.

  FIG. 5 is an enlarged view of a main part of a contact portion between the external heating belt 3 and the scraper 7 in the external heating unit 13. As shown in this figure, the shape and installation position of the scraper 7 are such that the tip of the cleaning section 7a in the scraper 7 is connected to the external heating belt 3 and the ideal trajectory of the external heating belt 3 (that is, the scraper 7 and the external heating belt 3). A predetermined pressing amount d (d = 0 in this embodiment) with respect to the contact portion of the two external heating rollers 4a and 4b positioned on the upstream side and the downstream side in the rotation direction of the external heating belt 3 .6 mm).

  In this embodiment, as shown in FIG. 4, the scraper 7 for cleaning the surface of the external heating belt 3 is externally heated at a position where the inner surface of the external heating belt 3 is not in contact with the heating rollers 4a and 4b. The belt 3 is in contact with the outer surface of the belt 3.

  As a result, the sliding load generated between the cleaning member and the external heating belt can be reduced compared to the conventional configuration in which the cleaning member is brought into contact with the external heating belt at the position where the external heating belt is suspended by the suspension roller. can do. Therefore, it is possible to prevent the external heating belt from being damaged due to the rubbing between the cleaning member and the external heating belt, or the external heating belt from slipping due to an increase in the load in the direction of preventing the rotation of the external heating belt.

<Detailed explanation of cleaning pad>
As shown in FIG. 4, the cleaning pad 12 has a configuration in which a felting member for cleaning (cleaning member) 12a is attached to a felt holding member 12b. In the present embodiment, a felt made of PTFE (polytetrafluoroethylene) fluororesin fiber is used as the felt member 12a. The felt holding member 12 b is a plate-like member made of stainless steel having a thickness of 0.2 mm, and is fixed to the external heating unit holder 11 so as to press the felt member 12 a against the outer surface of the external heating belt 3.

<Detailed explanation of external heating belt>
In the present embodiment, the external heating belt 3 is an endless belt made of a polyimide belt base material having a diameter of 31.5 mm and a thickness of 90 μm when it is made circular. A coating layer made of a non-conductive PTFE coat (coating material) having a thickness of 20 μm is provided on the outer surface of the external heating belt 3 in order to improve releasability. However, the configuration of the external heating belt 3 is not limited to this. For example, a conductive coating material containing carbon or the like may be used. Further, instead of a belt base material made of polyimide, a hollow cylindrical (endless) belt base material made of another heat resistant resin or a metal material such as stainless steel or nickel may be used.

  Further, in order to reduce the offset force of the external heating belt 3 (the force acting to move the external heating belt 3 in the rotation axis direction (width direction) when the external heating belt 3 rotates), You may give the coating which consists of PTFE etc. to a side surface.

<Experimental result>
Next, a description will be given of the results of experiments conducted to examine the relationship between the material of the release layer 1c of the fixing roller 1 and the release layer 2c of the pressure roller 2 and the offset.

  In this experiment, small-size paper of invoice size (215.9 mm × 139.7 mm) is vertically fed for a plurality of cases in which the material of the release layer 2 c of the pressure roller 2 is different in the image forming apparatus 100 described above. 100 sheets are continuously fed at a width of 139.7 mm (perpendicular to the transport direction) to form an image. Immediately thereafter, letter-size (279.4 × 215.9 mm) regular size paper is fed longitudinally (transport) Whether or not an offset occurs in the area corresponding to the non-sheet passing portion of the invoice paper in the letter size paper is formed by continuously feeding five sheets with a width of 215.9 mm in the direction perpendicular to the direction. Confirmed by The conditions of each case were the same except that the material of the release layer 2c of the pressure roller 2 was changed.

  Table 1 shows the materials of the release layer 1c of the fixing roller 1 and the release layer 2c of the pressure roller 2, and the evaluation results of the offset. In Table 1, the case where no occurrence of offset was observed in the visual inspection was marked with ◯, and the case where the occurrence of offset was remarkable was marked with x.

  In Comparative Example 1, the same non-conductive PFA tube is used as the release layer 1c of the fixing roller 1 and the release layer 2c of the pressure roller 2. That is, in Comparative Example 1, the releasability on the surface of the fixing roller 1 and the releasability on the surface of the pressure roller 2 are the same.

  In Example 1, a non-conductive PFA tube is used for the release layer 1 c of the fixing roller 1, and a conductive PFA tube is used for the release layer 2 c of the pressure roller 2. As the conductive PFA tube, the same non-conductive PFA as that of the release layer 1c of the fixing roller 1 was added with carbon. By adding carbon, the conductive PFA tube (release layer 2c of the pressure roller 2) is less releasable than the non-conductive PFA tube (release layer 1c of the fixing roller 1). Yes.

  As shown in Table 1, in Comparative Example 1 in which the releasability on the surface of the fixing roller 1 and the releasability on the surface of the pressure roller 2 are the same, toner offset was significant. On the other hand, in Example 1 where the releasability on the surface of the fixing roller 1 is higher than the releasability on the surface of the pressure roller 2, the occurrence of offset could be suppressed.

  The reason is considered as follows. That is, when the cleaning material (scraper 7, cleaning pad 12) is rubbed against the external heating belt 3 and the coating material or the like of the external heating belt 3 is scraped, the cleaning member and the external heating of the scraped coating material or the like are removed. What passes through the belt 3 adheres to the fixing roller 1 from the external heating belt 3. If these coating materials adhere to the surface of the fixing roller 1 and accumulate, the releasability of the fixing roller 1 deteriorates. For this reason, in Comparative Example 1, as a result of the coating material and the like adhering and accumulating on the fixing roller 1, the releasability of the fixing roller 1 is lowered and offset occurs.

  On the other hand, in the first embodiment, the surface of the fixing roller 1 has higher releasability than the surface of the pressure roller 2, so even if a coating material or the like adheres to the fixing roller 1 from the external heating belt 3. These deposits move from the fixing roller 1 to the pressure roller 2. As a result, the amount of the coating material and the like accumulated on the surface of the fixing roller 1 can be reduced, so that a decrease in the releasability of the fixing roller 1 can be suppressed and the offset can be improved.

  The coating material or the like attached to the pressure roller 2 is attached to the back surface (the surface on which the unfixed toner image is not formed) of the recording paper when the recording paper is passed for fixing processing. As a result, the surface of the pressure roller 2 is cleaned without degrading the image quality of the image formed on the recording paper.

  In the present embodiment, the configuration including the scraper 7 and the cleaning pad 12 as the cleaning member has been described. However, the present invention is not limited to this. For example, a configuration including only one of the scraper 7 and the cleaning pad 12 may be provided, or another cleaning member such as a cleaning web may be provided instead of the scraper 7 or the cleaning pad 12.

  In the present embodiment, the configuration in which the external heating unit 13 includes the external heating belt 3 as an external heating member that contacts the fixing member and heats the fixing member has been described. It is good also as a structure provided with the roller member.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can be applied to a fixing device used in an electrophotographic image forming apparatus.

1 Fixing roller (fixing member)
1a Core metal 1b Elastic layer 1c Release layer (surface layer)
2 Pressure roller (pressure member)
2a Core 2b Elastic layer 2c Release layer (surface layer)
3 External heating belt (external heating member, endless belt)
4a-4b Heating roller (suspension roller)
5a-5d Heater lamp (heating unit)
6a-6c thermistor 7 scraper (cleaning member)
7a Cleaning unit 7b Holding unit 7c Slit 9 Recording paper (recording material)
11 External heating unit holder 12 Cleaning pad (cleaning member)
12a Felt member (cleaning member)
12b Felt holding member 13 External heating unit 14 Temperature control unit (control unit)
15 Power supply circuit 16 Control unit 17 Rotation control unit (control unit)
18 Rotation Drive Unit 30 Fixing Device 100 Image Forming Device

Claims (10)

A rotating fixing member; a pressure member that presses against the fixing member; a rotatably supported external heating member that contacts the surface of the fixing member and heats the fixing member; and A cleaning member that contacts the surface and removes dirt adhered to the surface of the external heating member, transports the recording material between the fixing member and the pressure member, A fixing device for thermally fixing the recording material by heat transmitted from the fixing member;
The fixing device according to claim 1, wherein the surface of the fixing member has higher releasability than the surface of the pressure member.   The fixing device according to claim 1, wherein the external heating member is an endless belt suspended by a plurality of suspension rollers.   The surface of the fixing member is formed of a non-conductive fluororesin, and the surface of the pressure member is formed of a conductive fluororesin obtained by adding a conductive material to the fluororesin. The fixing device according to claim 1 or 2.   4. The fixing device according to claim 1, wherein a contact surface of the external heating member with the fixing member and the cleaning member is formed of a resin material. 5.   The cleaning member is a scraper that removes dirt adhering to the surface of the external heating member by bringing the edge portion of the plate-like member into contact with the surface of the external heating member. The fixing device according to claim 1.   The fixing device according to claim 5, wherein the scraper is made of metal.   5. The cleaning pad according to claim 1, wherein the cleaning member is a cleaning pad that comes into surface contact with the surface of the external heating member to remove dirt attached to the surface of the external heating member. Fixing device.   The fixing device according to claim 7, wherein the cleaning pad is a felt member made of a fluororesin fiber.   As the cleaning member, a scraper for contacting the surface of the external heating member by bringing the edge portion of the plate-like member into contact with the surface of the external heating member, and a surface contact with the surface of the external heating member The fixing device according to claim 1, further comprising a cleaning pad that removes dirt attached to the surface of the external heating member.   An image forming apparatus comprising the fixing device according to claim 1.

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