JP2014186133A - Heat fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: in a fixing device having a pair of rotating bodies forming a nip part and one rotating body drives to rotate the other rotating body, when air is blown to the entire area of one of the rotating bodies that is not brought into contact with an unfixed toner image with an air blowing member for suppressing dew condensation of the rotating body, a temperature of the rotating body is decreased, which results in a reduction in energy efficiency.SOLUTION: In blowing air to one of rotating bodies that is not brought into contact with an unfixed toner image with an air blowing member, the amount of air blown toward a paper-feeding area of one of the rotating bodies that is not brought into contact with the unfixed toner image is made smaller than the amount of air blown toward a non-paper feeding area of one of the rotating bodies that is not brought into contact with the unfixed image.

Description

  The present invention relates to a heat fixing device used in an image forming apparatus employing an electrophotographic recording method or an electrostatic recording method, such as a copying machine or a printer.

  A heat fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or printer has a pair of rotating bodies that form a nip portion, and the other rotating body is driven to rotate as one rotating body is driven to rotate. The thing of the structure to be used is mainly used. This heat fixing device heats a recording material carrying an unfixed toner image at the nip portion and heats it to fix the unfixed toner image on the recording material. When the heating and fixing device is warmed up, the rotating body that contacts the unfixed toner image is heated to a temperature at which the unfixed toner image can be fixed on the recording material by heating with a heater or by self-heating. To do. On the other hand, the rotating body that does not come into contact with the unfixed toner image may be configured not to be heated by the heater, and may not be sufficiently heated during the warm-up period. As described above, when the recording material that has absorbed moisture is heated at the nip portion while the rotating body that does not come into contact with the unfixed toner image is not heated, water vapor is generated from the recording material, and the surface of the rotating body is condensed by the water vapor. There are things to do. If the rotating body on the side that does not come into contact with the unfixed toner image is condensed, the frictional force at the nip portion is reduced, and the driving force from the rotating body on the driving side is not easily transmitted to the rotating body on the driven side. Condensation slip may occur in which the recording medium is not conveyed due to the rotation of the body.

  Therefore, in order to suppress dew condensation on the rotating body on the side not in contact with the unfixed toner image, a configuration is disclosed in which air is blown to the rotating body on the side not in contact with the unfixed toner image using a blower fan (Patent Document 1). ). The fixing device of Patent Document 1 has a duct that is long in the axial direction of the pressure roller, and blows wind from an opening at an end portion in the longitudinal direction of the duct, and the wind faces the pressure roller of the duct. It is the structure which blows out toward the pressure roller from the some hole provided in the part (FIG. 10 (a) (b)). In Patent Document 1, air is uniformly blown onto the surface of the pressure roller in the axial direction of the pressure roller. By blowing air uniformly on the surface of the pressure roller in this way, water vapor can be diffused and condensation of the pressure roller can be suppressed, so that condensation slip can be suppressed.

JP 2007-206275 A

  However, in the fixing device of Patent Document 1, the temperature of the surface of the pressure roller is lowered in the entire area in the axial direction of the pressure roller by the air blown to the pressure roller by the blower fan. Therefore, in order to maintain the fixing property, there is a problem that a large amount of electric power is supplied to the heater and the energy efficiency is deteriorated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a heat fixing device that can simultaneously maintain fixing performance and suppress condensation slip while minimizing a decrease in energy efficiency.

  According to another aspect of the present invention, there is provided a fixing device in which a nip portion is formed between a first rotating body driven by a driving source and the first rotating body, and the first rotating body is driven by the first rotating body. 2 and a blowing member for blowing air to a rotating body that does not come into contact with an unfixed toner image among the first rotating body and the second rotating body, and at the nip portion, In a fixing device that performs a fixing process in which a recording material carrying an unfixed toner image is heated while being transported to fix the unfixed toner image on the recording material, the air blowing member is at least when the warm-up of the fixing device is started. Of the first rotating body and the second rotating body, the rotating body that is not in contact with the unfixed toner image is driven when the temperature of the rotating body that is not in contact with the unfixed toner image is lower than a threshold temperature. Towards the paper passing area of the rotating body Air volume is being smaller than the air volume towards the non-paper passing area of the rotating member on the side not in contact with the unfixed toner image.

  According to another aspect of the present invention, there is provided a fixing device that is driven by a first rotating body that is driven by a driving source and a first rotating body that contacts the first rotating body to form a nip portion. A second rotating body, and a blower member for blowing air to a rotating body that does not contact an unfixed toner image of the first rotating body and the second rotating body, and the nip portion In the fixing device for performing the fixing process for fixing the unfixed toner image on the recording material by heating while conveying the recording material carrying the unfixed toner image, the blower member starts at least warming up of the fixing device When the temperature of the rotating body that is not in contact with the unfixed toner image of the first rotating body and the second rotating body is lower than a threshold temperature, it is driven and does not contact the unfixed toner image. Recording material on the rotating body Characterized in that it is blown only on the end portion in the direction perpendicular to the direction.

  According to another aspect of the present invention, there is provided a fixing device in which a nip portion is formed between a first rotating body driven by a driving source and the first rotating body and is driven by the first rotating body. A second rotating body to be blown, and a blower member for blowing air to a rotating body that does not come into contact with an unfixed toner image among the first rotating body and the second rotating body, and the nip In the fixing device for performing a fixing process for fixing the unfixed toner image on the recording material by heating while conveying the recording material carrying the unfixed toner image in the section, the blowing member at least warms up the fixing device. When the temperature of the rotating body that is not in contact with the unfixed toner image among the first rotating body and the second rotating body when starting is lower than a threshold temperature, the first rotating body and the second rotating body are driven and are orthogonal to the recording material conveyance direction In the unfixed toner The air flow toward the central portion of the rotating body does not contact the side to and smaller than the air volume towards the end of the rotating member on the side not in contact with the unfixed toner image.

  It is possible to maintain both fixing properties and suppress condensation slip while minimizing a decrease in energy efficiency.

Schematic diagram of transverse cross section of heat fixing apparatus according to embodiment 1. Schematic diagram of a longitudinal section of the heat fixing apparatus according to the first embodiment. Schematic diagram of cross section of fixing film according to Example 1 Schematic diagram of the heater according to Example 1 (A) Schematic diagram of the pressure roller and duct according to the first embodiment, (b) Schematic diagram of the inside of the duct according to the first embodiment. Flowchart of image formation according to Embodiment 1 Schematic diagram of pressure roller and duct according to Example 2 Schematic diagram of pressure roller and duct according to comparative example Sectional drawing of the image forming apparatus which concerns on Example 1 and 2 (A) Conventional fixing device and duct, (b) Conventional duct

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

[Example 1]
(1) Image Forming Apparatus FIG. 9 is a configuration diagram of an image forming apparatus equipped with a heat fixing apparatus according to this embodiment. This image forming apparatus is an electrophotographic laser printer, and forms an image on a recording material according to image information input from an external device (not shown) such as a host computer.

  In the image forming apparatus shown in the present embodiment, when a print command is input from an external device, a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 61 as an image carrier is moved at a predetermined speed (process speed) in the arrow direction. ). In the photosensitive drum 61, the outer peripheral surface (surface) of the photosensitive drum 61 is uniformly charged to a predetermined polarity and potential by a charger 62. Image information is written on the charged surface of the photosensitive drum 61 by a laser scanner 63 as an exposure means. The laser scanner 63 outputs a laser beam L modulated in accordance with a time-series electric digital pixel signal of image information input from an external device to the printer. The laser scanner 63 scans and exposes the charged surface of the photosensitive drum 61 with the laser beam L. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 61. The electrostatic latent image is developed as a toner image (developed image) by the developing device 64 using toner (developer). A toner image on the surface of the photosensitive drum 61 (hereinafter referred to as a toner image) is obtained by rotating the photosensitive drum 61 and the outer peripheral surface (front surface) of the transfer roller 67 disposed so as to face the surface of the photosensitive drum 61. Is sent to the transfer nip portion. The above is the configuration of the image forming unit.

  On the other hand, the recording materials P stacked on the sheet stacking table 68a of the feeding cassette 68 are picked up one by one by a feeding roller 69 driven at a predetermined control timing, and are conveyed by a conveying roller 70 and a conveying roller 70a. Sent to the registration department. In the registration unit, the leading edge of the recording material P is temporarily received by the nip portion between the registration roller 71 and the roller 71a to correct the skew of the recording material P. Thereafter, the recording material P is fed to the transfer nip portion at a predetermined timing in the registration portion. The predetermined timing here is a timing at which the front end portion of the recording material P reaches the transfer nip portion when the front end portion of the toner image on the surface of the photosensitive drum 61 reaches the transfer nip portion.

  The recording material P fed to the transfer nip is nipped and conveyed by the photosensitive drum 61 and the transfer roller 67. Then, the toner image on the surface of the photosensitive drum 61 is transferred to the recording material P by the transfer bias applied to the transfer roller 67 during the conveyance process of the recording material P, and the recording material P is separated from the surface of the photosensitive drum 61 and heated and fixed by the fixing device 72. It is conveyed to. The heat fixing device 72 heats and fixes the unfixed toner image to the recording material P by applying heat and pressure to the recording material P carrying the unfixed toner image at a nip portion N, which will be described later. Drain from part N. The recording material P discharged from the nip portion N of the heat fixing device 72 is conveyed to the discharge roller 74 by the intermediate discharge roller 73. Then, the discharge roller 74 discharges the recording material P onto the discharge tray 75. After the recording material P is separated, the transfer residual toner is removed by the cleaner 65 on the surface of the photosensitive drum 61, and the image is repeatedly used for image formation.

  In the image forming apparatus of this embodiment, a photosensitive drum 61, a charger 62, a developing device 64, and a cleaner 65 are integrated into a process cartridge 66. The cartridge 66 is detachably attached to the image forming apparatus main body 76 constituting the housing of the printer.

  The image forming apparatus main body 76 is provided with a cooling fan 77. The cooling fan 77 is rotated appropriately to take outside air into the image forming apparatus main body 76 to cool the temperature rising portions such as the image forming unit and the electrical board. An environment detection member 78 is provided in the vicinity of the cooling fan 77. When the outside air is taken in by the cooling fan 77, the temperature and humidity of the environment in which the image forming apparatus is installed are detected. The detection result is fed back to the temperature control sequence of the heat fixing device 72.

  The sheet loading table 68a of the feeding cassette 68 is provided with a movable regulation guide (not shown) for loading various types of recording materials having different sizes. The regulation guide is displaced according to the size of the recording material P, and the recording material P is stacked on the sheet stacking table 68a, so that various recording materials of different sizes are fed one by one from the feeding cassette 68 by the feeding roller 69. Can be picked up.

  The image forming apparatus according to the present exemplary embodiment is an image forming apparatus compatible with A4 size paper, and has a printing speed of 52 sheets / minute (A4 landscape).

(2) Heat-fixing device In the following description, regarding the heat-fixing device 72 and the members constituting the heat-fixing device 72, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The longitudinal direction is also a direction orthogonal to the rotation direction of the heating rotator described later. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The width is a dimension in the short direction. Regarding the recording material, the width direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material.

  FIG. 1 is a cross-sectional view of the heat fixing device 72. FIG. 2 is a view showing a longitudinal section of the heat fixing device 72. FIG. 3 is a diagram showing a cross section of the fixing film 10. FIG. 4 is a configuration diagram of an example of the heater 31. The heating and fixing device 72 of this embodiment will be described with reference to FIGS.

  The heat fixing device 72 shown in this embodiment includes a fixing film 10, a heater 31 that contacts the inner surface of the film, and a pressure roller 20 that forms a nip portion together with the heater 31 via the fixing film 10. The heat fixing device 72 further includes a heater holder 41, a pressure stay 42, a pressure unit 43, and a fixing flange 45. The heater 31, the fixing film 10, the heater holder 41, the pressure stay 42, and the pressure roller 20 are all elongated members in the longitudinal direction. The heat fixing device 72 is a heat fixing device of a type in which the pressure roller 20 is driven to rotate and the fixing film 10 is driven and rotated by frictional force acting between the pressure roller 20 and the fixing film 10.

(2-1) Fixing Film As shown in FIG. 3, the fixing film 10 includes a base layer 11 formed in an endless sleeve shape from a material having heat resistance and flexibility, and an outer peripheral surface of the base layer 11. And a release layer 12 that is provided. Further, an elastic layer 13 such as silicone rubber may be provided between the outer peripheral surface of the base layer 11 and the inner peripheral surface side of the release layer 12 in order to improve fixability and image quality.

  The base layer 11 is formed of a heat-resistant resin such as polyimide, polyamideimide, polyetheretherketone or the like and formed into a thin flexible endless belt. The material of the base layer 11 is not limited to a heat resistant resin, and a thin metal such as stainless steel (SUS) or nickel (Ni) having higher thermal conductivity may be used.

  On the outer peripheral surface of the base layer 11, a fluororesin such as PFA, PTFE, FEP or the like is coated as a release layer 12 alone or blended, or a tube is covered. PFA is a perfluoroalkoxy resin, PTFE is a polytetrafluoroethylene resin, and FEP is a tetrafluoroethylene-hexafluoropropylene resin. The thickness of the release layer 12 needs to be 5 μm or more from the viewpoint of durability. On the other hand, if the release layer 12 is too thick, the thermal conductivity is lowered and the fixability is adversely affected. As described above, in order to achieve both durability and fixability, the thickness of the release layer 12 is set to 5 μm or more and 50 μm or less.

When the elastic layer 13 is provided between the outer peripheral surface of the base layer 11 and the inner peripheral surface of the release layer 12, heat can be uniformly applied by wrapping the unfixed toner image T carried by the recording material P. For this reason, it is possible to follow the unevenness formed by the recording material P and the toner image T, suppress the roughness in the halftone image, and obtain uniform and sufficient fixing properties. Further, the elastic layer 13 can wrap the toner image T carried by the recording material P as the thickness of the elastic layer 13 is increased, and can be uniformly heated and fixed on the surface of the recording material P. That is, as the thickness of the elastic layer 13 is increased, the effect of wrapping the unfixed toner image T can be improved. However, if the thickness of the elastic layer 13 is too thick, the heat capacity becomes too large, and the rise of the fixing film 10 is delayed, and the on-demand characteristic peculiar to the film heating method is lowered. Therefore, the thickness of the elastic layer 13 is 50 μm or more and 500 μm or less. Further, the thermal conductivity of the elastic layer 13 is preferably as high as possible, and is preferably 0.5 W / m · K or more. ZnO, Al ₂ O ₃ , SiC, metallic silicon, etc. so as to achieve such thermal conductivity The heat conductive filler is mixed in silicone rubber and adjusted.

  In the fixing film 10, the outer diameter of the fixing film 10 is preferably smaller because the heat capacity can be suppressed. However, if the outer diameter is made too small, the width of the nip portion N becomes narrow, so it cannot be made extremely small.

  Therefore, in the fixing film 10 of this embodiment, SUS is used as the material of the base layer 11 in consideration of conditions such as the speed (process speed) of the image forming apparatus, and the thickness (thickness) of the base layer 11 is 30 μm. The inner diameter of this is 24 mm. The elastic layer 13 is made of silicone rubber having a thermal conductivity of 1.3 W / m · K and has a thickness of 250 μm. As the release layer 12, a PFA coating is used, and the thickness of the release layer 12 is 14 μm.

(2-2) Heater holder The heater holder 41 is shaped like a bowl with a semicircular cross section made of a heat-resistant resin such as liquid crystal polymer, phenol resin, polyphenylene sulfide (PPS), polyether ether ketone (PEEK). Is formed. The lower the thermal conductivity of the heater holder 41, the higher the thermal efficiency when heating the inner surface of the fixing film 10 by the heater 31. Therefore, a hollow filler such as a glass balloon or a silica balloon may be included in the heat resistant resin forming the heater holder 41. A concave groove is provided in the lower surface of the heater holder 41 (the surface on the pressure roller 20 side) along the longitudinal direction of the heater holder 41. And the board | substrate 31 of the heater 31 is hold | maintained by the ditch | groove so that the below-mentioned protective sliding layer 34 of the heater 31 may be exposed from this ditch | groove. The fixing film 10 is loosely fitted on the outer periphery of the heater holder 41. The heater holder 41 to which the fixing film 10 is externally fitted has both ends in the longitudinal direction of the heater holder 41 held by an apparatus frame (not shown).

(2-3) Pressure roller The pressure roller 20 is provided on the core metal 21, the elastic layer 22 provided on the outer peripheral surface of the core metal 21, and the outer peripheral surface of the elastic layer 22. And a release layer 23.

  The cored bar 21 is formed in a round shaft shape from a material such as aluminum or iron. The material of the cored bar 21 is not limited to aluminum or iron, and a ceramic porous body having high strength, low heat capacity, and high heat insulation effect may be used.

  The elastic layer 22 is made of silicone rubber (solid rubber layer) or a sponge layer formed by foaming silicone rubber to provide a heat insulating effect. The elastic layer 22 is not limited to the silicone rubber or the sponge layer, and is a bubble having a porous formed by adding a hollow filler, or a water-absorbing polymer and water in the silicone rubber layer in order to have a more heat insulating effect. A rubber layer or the like may be used. On the elastic layer 22 described above, a fluorine resin release layer 23 such as purple alloalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP) is formed. To do. The release layer 23 may be a tube coated or a surface coated with a paint.

  The pressure roller 20 is disposed below the fixing film 10 so as to face the heater 31. In the pressure roller 20, both end portions in the longitudinal direction of the cored bar 21 are rotatably held by the apparatus frame.

  In the heat fixing device 72 mounted on a relatively high-speed image forming apparatus, it is necessary to form an appropriate nip width at the nip portion N and to secure a certain heat capacity. Therefore, the pressure roller 20 in which the elastic layer 22 is formed using solid rubber having a thickness (thickness) of 3.5 mm was used. The release layer 23 is covered with a PFA tube having a thickness of 50 μm in consideration of durability. Further, the outer diameter of the pressure roller 20 is set to 30 mm.

(2-4) Heater FIG. 4 is a configuration diagram of the heater 31. The heater 31 is a plate-like heating element that heats the fixing film 10 while being in contact with the inner surface of the fixing film 10. The heater 31 has a substrate 31 that is elongated in the longitudinal direction. The substrate 31 is an insulating ceramic substrate such as alumina or aluminum nitride, or a heat-resistant resin substrate such as polyimide, PPS, or liquid crystal polymer. A heating resistor 32 such as Ag / Pd (silver palladium), RuO2, or Ta2N is linearly formed on the surface of the substrate 31 (surface on the pressure roller 20 side) along the longitudinal direction of the substrate 31 by screen printing or the like. Alternatively, it is formed by applying a thin strip. The heating resistor 32 has a thickness of about 10 μm and a width of about 1 to 5 mm. In addition, on the surface of the substrate 31, power supply electrodes 33 for supplying power to the heating resistor 32 are provided inside both longitudinal ends of the substrate 31. Further, a protective sliding layer 34 that protects the heating resistor 32 may be provided on the surface of the substrate 31 as long as the thermal efficiency of the heating resistor 32 is not impaired. However, it is preferable that the thickness of the protective sliding layer 34 is sufficiently thin and the surface property of the heating resistor 32 is improved. As the protective sliding layer 34, a heat resistant resin such as polyimide or polyamideimide, a glass coat, or the like is often used.

  In the heater 31, when aluminum nitride or the like having good thermal conductivity is used as the substrate 31, the heating resistor 32 is formed on the back surface (the surface opposite to the pressure roller 20) of the substrate 31. Also good.

(2-5) Pressurization stay The pressure stay 42 is formed in a U-shape with a cross-section facing downward by a material such as a metal having rigidity. The pressure stay 42 is disposed inside the fixing film 10 at the center in the short direction of the upper surface of the heater holder 41 (the surface opposite to the pressure roller 20). Then, both end portions in the longitudinal direction of the pressure stay 42 are urged toward the axis of the pressure roller 20 by the pressure means 43 such as a spring through the fixing flange 45 held by the apparatus frame. As a result, the surface of the substrate 31 of the heater 31 is pressed against the surface of the pressure roller 20 via the fixing film 10, and the elastic layer 22 of the pressure roller 20 is elastically deformed along the substrate 31. As a result, a nip portion N having a predetermined width necessary for heating and fixing the toner image T is formed between the surface of the pressure roller 20 and the surface of the fixing film 10.

(2-6) Fixing Processing Operation A fixing processing operation using the heat fixing device 72 of this embodiment will be described. First, the control unit 44 drives the motor M as a drive source in accordance with the print command to rotate the drive gear G provided at the end in the longitudinal direction of the core metal 21 of the pressure roller 20. As a result, the pressure roller 20 rotates in the arrow direction at a predetermined peripheral speed (process speed). At that time, a rotational force opposite to the rotational direction of the pressure roller 20 acts on the fixing film 10 by the frictional force between the surface of the pressure roller 20 and the surface of the fixing film 10 in the nip portion N. As a result, the fixing film 10 is driven to rotate in the direction of the arrow in the outer periphery of the heater holder 41 at substantially the same peripheral speed as the pressure roller 20 while the inner surface of the fixing film 10 is in contact with the protective sliding layer 34 of the heater 31.

  Further, the control unit 44 energizes the heating resistor 32 from the power source 37 through the power supply electrode 33 of the heater 31 in accordance with the print command. The heating resistor 32 generates heat due to the energization, and the heater 31 is rapidly heated to heat the fixing film 10. The temperature of the heater 31 is detected by a thermistor 35 as a first temperature detection member provided on the back surface of the substrate 31, and the thermistor 35 outputs a temperature detection signal of the heater 31 to the control unit 44. The thermistor 35 is arranged in a region where recording materials P of various sizes that can be used in the printer always pass in the recording material conveyance region of the nip portion N in the longitudinal direction of the heater 31. Further, the control unit 44 takes in the temperature detection signal from the thermistor 35 and controls the amount of power supplied to the heating resistor 32 so that the heater 31 maintains the target temperature based on the temperature detection signal. That is, the control unit 44 appropriately controls the duty ratio and wave number of the voltage applied to the heating resistor 32 so that the heater 31 maintains a predetermined temperature control temperature based on the temperature detection signal from the main thermistor 35. ing.

  Further, a thermo protector 36 such as a thermo switch or a thermal fuse is disposed on the back surface of the substrate 31 of the heater 31. An input terminal (not shown) of the thermo protector 36 is connected in series with the power source 37, and an output terminal (not shown) is connected in series with the heating resistor 32 of the heater 31. Thereby, when the heater 31 becomes a runaway state due to a failure of the thermistor 35 or the like, the thermoprotector 36 detects an abnormal temperature rise of the heater 31 and shuts off the energization to the heating resistor 32.

  The recording material P carrying the unfixed toner image T is introduced into the nip portion N and conveyed while the rotation of the pressure roller 20 and the fixing film 10 is stable and the detected temperature of the heater 31 is maintained at the target temperature. The The recording material P is nipped and conveyed at the nip portion N by the surface of the fixing film 10 and the surface of the pressure roller 20. In the conveyance process at the nip portion N, the toner image T is heated and fixed on the surface of the recording material P by supplying heat from the fixing film 10 and applying pressure to the recording material P.

(2-7) Condensation slip Here, the condensation slip will be described. When the recording material P is left for a long time in a high humidity environment, the recording material P contains a large amount of moisture. Moisture contained in the recording material is instantly evaporated by the heat of the nip portion N 2 and becomes water vapor. The water vapor is more likely to be generated from the non-image forming surface side than the image forming surface side of the recording material P, that is, the pressure roller 20 side of the both surfaces of the recording material P from the surface of the fixing film 10 side. It tends to occur from the surface. This is because the toner T on the recording material prevents the release of water vapor on the image forming surface side of the recording material P. The water vapor released to the pressure roller 20 side spreads from the downstream side in the rotation direction of the pressure roller 20 in the nip portion N to the upstream side by convection generated by the rotation of the pressure roller 20. When the pressure roller 20 is not warmed, water vapor in the vicinity of the pressure roller 20 is condensed on the surface of the pressure roller 20, and slippage occurs between the pressure roller 20 and the fixing film 10. It becomes easy. If slip occurs between the pressure roller 20 and the fixing film 10, the fixing film 10 may not be driven to rotate at the same rotational speed as the pressure roller 20. As a result, the conveyance speed of the recording material at the nip portion N is significantly lower than the conveyance speed at the transfer portion, and the recording material is pushed into the transfer portion due to slack, or the recording material is rubbed in the conveyance path. As a result, the toner image is scattered and an image defect occurs. A phenomenon in which the rotation speed of the fixing film 10 decreases due to the condensation of the pressure roller 20 in this manner and causes an image defect is referred to as a condensation slip.

  Here, if the non-sheet passing area of the pressure roller 20 is condensed, the slip between the pressure roller 20 and the fixing film 10 is more likely to occur than the sheet passing area is condensed, and the condensation slip is likely to occur. This is because the non-sheet passing region of the pressure roller 20 is a portion where the pressure roller 20 directly contacts the fixing film 10 when the paper is passing through the nip portion N, and the fixing film 10 rotates. This is because the degree of contribution for providing the driving force is larger than that in the sheet passing area. Further, dew slip is a phenomenon that is more likely to occur with wider paper. When passing a narrow paper, the area where water vapor is generated is narrow, and the non-paper passing area for the pressure roller 20 to rotate the fixing film 10 is wide. Therefore, the non-sheet passing area of the pressure roller 20 is unlikely to condense, and the rotation speed of the fixing film 10 is unlikely to decrease. On the other hand, when a wide paper is passed, the amount of water vapor is large because the region where water vapor is generated is wide, and the non-paper passing region for the pressure roller 20 to rotate the fixing film 10 is narrow. Therefore, the pressure roller 20 has a property that condensation slip is likely to occur because condensation occurs not only in the sheet passing area but also in the non-sheet passing area in the axial direction and the speed of the fixing film 10 is likely to decrease. Further, condensation slip is likely to occur when there is a large difference in easiness of warming between the rotating body in contact with the unfixed toner image and the rotation on the side not in contact with the unfixed toner image. That is, as in the present embodiment, the fixing film 10 is thin and has a small heat capacity and is directly heated by the heater 31 and is easily heated, and the pressure roller 20 has a rubber layer and the like so that the heat capacity is large and is not easily heated. is there. This is because the warm-up of the heat-fixing device is often considered complete when the temperature of the rotating body on the side in contact with the unfixed toner image reaches a fixable temperature, and the rotation on the side where the unfixed toner does not contact at that time This is because the body temperature is not controlled.

  When the maximum width of the paper is passed through the nip portion N, as a method of ensuring the frictional force in the non-sheet passing region of the pressure roller 20, the nip portion is added to the maximum width of the paper passing region. A method of extending the pressure roller 20 in the axial direction is conceivable. By extending, the non-sheet passing area of the pressure roller 20 increases, so that the non-sheet passing area that is not easily affected by water vapor generated from the sheet passing area and does not condense can be increased, so that condensation slip can be suppressed. However, when the fixing film 10 and the pressure roller 20 are extended, there is a problem that the heat fixing device 72 is enlarged.

(2-8) Characteristic Configuration of This Embodiment A characteristic configuration of the heat fixing device 72 of this embodiment will be described with reference to FIGS. In this embodiment, a fan 79 as a blower member is provided on the side surface of the image forming apparatus 1 and is rotated in the suction direction so that outside air outside the apparatus is taken into the apparatus. The heat fixing device 72 includes a duct 50 for guiding the wind of the fan 79 to the pressure roller 20. The duct 50 has a long shape along the axial direction of the pressure roller 20, and is provided on the side opposite to the fixing film 10 with respect to the pressure roller 20. The duct 50 is an opening provided at an end in a direction orthogonal to the recording material conveyance direction, and an opening 53 for taking in the wind of the fan 79 into the inside, and pressurizing the wind taken from the opening 53. A plurality of holes 52 for discharging toward the roller 20. Accordingly, the wind from the fan 79 is taken into the duct interior 55 from the opening 53 of the duct 50 and then flows along the axial direction of the pressure roller 20. Since the end 54 on the opposite side of the opening 53 of the duct 50 is closed, the wind flows from the plurality of holes 52 provided in the region 51 facing the pressure roller 20 of the duct 50. Blow out toward the surface.

  The place where the hole 52 is provided will be described. The water vapor generated at the nip portion N wraps around in the rotational direction of the pressure roller 20 from the downstream side of the nip portion N in the rotational direction of the film 10. Therefore, if the hole 52 is provided in the vicinity of the perpendicular line vl extending from the axial center of the pressure roller 20 to the region 51 of the duct 50 or on the downstream side in the recording material conveyance direction from the perpendicular line vl, water vapor can be effectively diffused.

In the duct 50 of the present embodiment, as the distribution of the airflow in the axial direction of the pressure roller 20 blown by the fan 79, the airflow to the paper passing area of the maximum width of paper that can be passed is the airflow to the non-paper passing area. It is comprised so that it may become smaller. This specific configuration is shown in FIG. The number of holes 52 per unit length of the duct in the direction of the generatrix of the pressure roller provided in the area of the duct 50 facing the sheet passing area of the pressure roller 20 is the area of the duct 50 facing the non-sheet passing area. The number of holes 52 per unit length of the duct in the bus bar direction of the pressure roller provided in the pressure roller is smaller. Further, as shown in FIG. 5B, by providing a partition 56 in the duct interior 55, the above-described air volume distribution is obtained regardless of the distance from the fan 79 to each hole 52. For this reason, by reducing the air volume to the paper passing area of the pressure roller 20 in the maximum width paper (recording material) where condensation slip is likely to occur, the surface temperature of the pressure roller 20 is not greatly reduced, and the non-paper passing area is reached. Therefore, it is possible to secure a necessary and sufficient air volume and suppress dew condensation slip. As a result, since it is not necessary to supply extra power to the heater 31, energy efficiency is good. Further, even if the air volume in the non-sheet passing area of the pressure roller 20 is increased, the effect on the fixability is smaller than that in the sheet passing area, so that the energy efficiency is not greatly reduced.
Next, control of the fan 79 will be described. As a condition where condensation slip is likely to occur, the temperature of the pressure roller 20 is relatively low in a high humidity environment. Therefore, it is determined whether or not the fan 79 is to be driven based on the installation environment of the image forming apparatus and the degree of warming of the pressure roller 20. In this embodiment, the environment sensor 78 is detected as an environment detection member for detecting the environment in which the image forming apparatus 1 is installed, and the thermistor 35 disposed on the back side of the heater 31 is detected as a member for detecting the warming condition of the pressure roller 20. Use temperature and number of prints. The reason why the temperature detected by the thermistor 35 is used is that the heater 31 forms the nip portion N with the pressure roller 20 via the fixing film 10. This is because the temperature of 20 can be estimated.

  Here, the control of the fan 79 during image formation will be described using the flowchart of FIG. First, when the print signal is received (Step 1), the environmental sensor 78 detects a high humidity environment (Step 2), and the temperature detected by the thermistor 35 at the start of printing (when the heating and fixing device 72 starts warming up) is 120 ° C. It is determined whether it is less than (Step 3). When the above-described two conditions are satisfied, after the start of image formation (Step 4), driving of the fan 79 is started at the timing when the first sheet of printed paper reaches the nip portion N (Step 5). Thereafter, when the image formation is completed within 30 sheets from the start of printing, the fan 79 is stopped simultaneously with the completion of the image formation (Step 12), and the process ends (Step 13). When printing continues for 30 sheets or more, the fan 79 is operated until the 30th sheet, and the driving is stopped when the 30th sheet passes through the nip portion N (Step 8). For the 31st and subsequent sheets, the fan 79 remains stopped until image formation is completed.

  The environmental sensor 78 in step 2 detects the high temperature environment when the humidity detected by the environmental sensor 78 is higher than a predetermined value.

  Here, when the temperature detected by the thermistor 35 at the start of printing is 120 ° C. or higher, it has been confirmed that the pressure roller 20 does not reach a temperature under any conditions during the period until the printing is completed. This is because the temperature of the pressure roller 20 during continuous printing tends to be low in the initial printing and higher as the number of continuous prints increases. Further, in the heat fixing device 72 of this embodiment, the number of sheets reaching the temperature at which the pressure roller 20 does not condense during continuous printing is 30 regardless of the temperature of the pressure roller 20 at the initial stage of printing. It was. Therefore, even if the fan 79 is driven at the beginning of printing, the driving of the fan 79 is stopped after the 31st sheet of continuous printing. In this embodiment, when the temperature behind the heater 31 detected by the thermistor 35 is lower than 120 ° C., it is estimated that the pressure roller 20 is a temperature at which condensation occurs lower than a threshold temperature at which condensation does not occur. On the contrary, when the temperature of the back of the heater 31 detected by the thermistor 35 is 120 ° C. or higher, the pressure roller 20 is estimated to be above the threshold temperature at which no condensation occurs and at which no condensation occurs. .

  As described above, in this embodiment, the temperature detected by the thermistor 35 at the start of printing and the number of prints are used together to estimate whether or not the temperature of the pressure roller 20 is in a temperature range where condensation occurs, and the drive of the fan 79 is controlled. .

  Further, as another means for determining the degree of warming of the pressure roller 20, the pressure roller surface temperature may be directly detected by a temperature detection member such as a thermopile. In this case, it is possible to drive the fan 79 only when the pressure roller surface temperature is lower than a predetermined threshold temperature during paper feeding. Further, a fixing prediction count that predicts the temperature of the pressure roller 20 by adding or subtracting a unique count value at the time of passing paper, at the time of paper gap, at the time of stopping, etc. may be used. As long as the temperature of the pressure roller 20 can be estimated as described above, the method is not limited to the above method.

<Performance evaluation>
As a performance evaluation of this example, the presence / absence of image defects due to condensation slip and fixability are confirmed in a high-temperature and high-humidity environment (32.5 ° C./80%) and compared with the following two conventional examples. The evaluation paper was A4 size paper (60 g / mm 2) left for a long time in the above environment, the print pattern was a solid black image, and 50 sheets were printed continuously from the state where the heating and fixing device was at the same temperature as the room temperature. . The image forming apparatus used is an A4 size paper compatible machine with a printing speed of 52 sheets / minute and FPOT 7.0 seconds. Further, in the present embodiment and the comparative example, the same heater control is considered.

In this embodiment, the total air volume from the dew condensation prevention fan is 0.007 [m ³ / min], and the total air volume is divided into three in the sheet passing area (210 mm) and the non-sheet passing areas at both ends (each 20 mm). A hole was placed in

Comparative Example 1 is different only in the arrangement of the duct holes, and the other configurations and the fan control are the same. The duct of Comparative Example 1 shown in FIG. 8 uses a duct in which holes are arranged so that the air volume to the pressure roller is substantially uniform throughout the entire axial direction of the pressure roller. The duct of Comparative Example 1 is provided with holes so that the total airflow from the fan is 0.007 [m ³ / min] blown substantially uniformly over the entire axial direction of the pressure roller.

  Further, in Comparative Example 2, the duct of Comparative Example 1 was used to reverse the direction of the fan, and the air in the vicinity of the pressure roller was exhausted outside the machine through the duct.

  Table 1 shows the evaluation results of Example 1, Comparative Example 1, and Comparative Example 2 described above. As evaluation items, image defects due to condensation slip and image defects due to deterioration of fixability were evaluated. ○ indicates that no image defect occurred, and x indicates that an image defect occurred.

  In Comparative Example 1, no image defect occurred due to condensation slip. This is because the air is blown almost uniformly on the entire area of the pressure roller in the axial direction by the duct, thereby preventing the water vapor from condensing on the entire surface of the pressure roller. However, since the entire area of the pressure roller in the axial direction is cooled by uniformly blowing air, a part of the solid black image is whitened out in the initial 15 sheets of the relatively low pressure roller temperature or the back side of the succeeding paper is removed. An image defect occurred due to deterioration of the fixing property which was soiled. Since then, the pressure roller has warmed up, so the fixing property has been improved. In order to improve this fixing failure, it is necessary to raise the target temperature of the heater, resulting in poor energy efficiency.

  In Comparative Example 2, only the air in the vicinity of the pressure roller is sucked out, and no wind is applied to the entire area of the pressure roller in the axial direction. It was. However, image defects due to condensation slip occurred on 8 out of 50 printed sheets. This indicates that, compared with Comparative Example 1, it is more effective to blow air to the pressure roller than to exhaust the air in the vicinity of the pressure roller to the outside through the duct. When the paper continued to pass to some extent, the pressure roller warmed and no condensation slip occurred.

  In Example 1, no image defect occurred. This is because the airflow to the paper passing area that affects the fixability is weak, the influence on the fixability is suppressed, and the airflow to the non-paper passing area, which is important for rotating the fixing film, is increased to suppress condensation. Because it is.

  As described above, in this example, it was possible to achieve both maintenance of fixing performance and suppression of condensation slip without reducing energy efficiency.

  In this embodiment, the heat fixing device 72 includes a cylindrical fixing film, a heater that contacts the inner surface of the fixing film, and a pressure roller that forms a nip portion together with the heater via the fixing film. showed that. However, the heat fixing device 72 includes a first rotating body driven by a driving source, and a second rotating body that is driven by the first rotating body by forming a nip portion between the first rotating body and the first rotating body. If it has, it will not be limited to this. For example, a cylindrical fixing film, a heater that is contained in the fixing film and that heats the inner surface of the fixing film with radiant heat, a nip portion forming member that contacts the inner surface of the fixing film, and the nip portion through the fixing film together with the nip portion forming member And a pressure roller that forms the surface. Further, the apparatus may include a cylindrical belt that self-heats, a nip portion forming member that contacts the inner surface of the cylindrical belt, and a pressure roller that forms the nip portion together with the nip portion forming member via the belt. . The apparatus further includes a fixing roller, a heater for heating the fixing roller, a cylindrical belt, and a nip portion forming member that contacts the inner surface of the cylindrical belt and forms a nip portion with the fixing roller via the belt. But it ’s okay.

  In this embodiment, the sheet passing area and the non-sheet passing area with different air volumes are the sheet passing area and the non-sheet passing area of the maximum width paper (recording material) that can be conveyed by the nip N of the heat fixing device 72. There is, but is not limited to this. The air volume may be different between the sheet passing area and the non-sheet passing area of the recording material having a size other than the maximum width that needs to suppress the condensation slip.

  In the present exemplary embodiment, the recording material is conveyed so that the center in the width direction is aligned with the center in the direction perpendicular to the recording material conveyance direction of the nip portion of the heat fixing apparatus. Any one end in the width direction of the recording material may be conveyed in accordance with the end of the nip portion of the heat fixing apparatus in the direction orthogonal to the recording material conveyance direction.

  In this embodiment, the fan 79 is provided in the image forming apparatus 1, but may be provided in the heat fixing device 72.

  In this embodiment, a difference is provided in the air volume between the paper passing area and the non-paper passing area of the pressure roller 20 depending on the number of holes 52 of the duct 50. However, a difference in the air volume may be provided depending on the size of the hole. .

  Further, although the opening 53 of the duct 50 is provided at the axial end of the pressure roller 20 of the duct 50, it may be provided at the center of the duct 50.

  In this embodiment, the fan 79 is driven so as to blow air toward the pressure roller 20. However, in contrast to this embodiment, the fan 79 sucks air near the pressure roller outside the apparatus. It is also conceivable to drive. However, it is difficult for the configuration for sucking out air in the vicinity of the pressure roller 20 to exhibit the same effect of countermeasures against condensation as the configuration for blowing air to the pressure roller 20. The reason for this will be explained. When air is blown onto the pressure roller 20 as in the present embodiment, it is possible to blow from the duct 50 to a predetermined area of the surface of the pressure roller 20, so that it is effective to use water vapor in a portion where condensation is to be suppressed. Can be scattered. However, when the air in the vicinity of the pressure roller 20 is sucked out of the machine, the air is sucked in all directions from the duct hole 52, so the air in the vicinity of a predetermined region on the surface of the pressure roller 20 is sucked out. This is because it is difficult to obtain a wide range of water vapor as a result.

[Example 2]
The image forming apparatus is required to further improve the throughput and shorten the FPOT, and it is considered that the image forming apparatus is increasingly disadvantageous for the condensation slip.

  For example, if the interval between the preceding paper and the succeeding paper during continuous printing is shortened to improve the throughput, heat is hardly supplied from the rotating body that contacts the unfixed toner image to the rotating body that does not contact the unfixed toner image. Therefore, it is difficult for the pressure roller to warm up, which is disadvantageous for condensation slip. Also, if the heat capacity of the rotating body that comes into contact with the unfixed toner image is further reduced to shorten the FPOT so that it quickly warms up, the warming up occurs before the rotating body that does not contact the unfixed toner image warms up. Will be disadvantageous to condensation slip.

  Therefore, in the present embodiment, a configuration that can suppress the condensation slip while further suppressing the temperature drop of the pressure roller 20 as compared with the first embodiment will be described. Since the configuration other than the duct 50 is the same as that of the first embodiment, a description thereof will be omitted.

  FIG. 7 shows the relationship between the position where the hole 52 of the duct 50 of this embodiment is provided and the maximum width paper that can be passed. The hole 52 of the duct 50 is not provided in the central portion of the maximum width paper passing area, but is provided only in the non-sheet passing area and the end of the paper passing area. By concentrating the holes 52 in the non-sheet passing region of the pressure roller 20, condensation in the non-sheet passing region of the pressure roller 20 can be suppressed without substantially reducing the temperature of the pressure roller 20. Further, by blowing air also on the end of the sheet passing area of the pressure roller 20, it is possible to prevent the water vapor in the sheet passing area from flowing into the non-sheet passing area, thereby more reliably condensing the non-sheet passing area. Can be suppressed.

  At the end of the sheet passing area of the pressure roller 20, the heat of the non-sheet passing portion rises, so that the surface temperature of the pressure roller 20 is not easily lowered even when wind is blown. Therefore, by using the duct 50 of the present embodiment, it is possible to suppress the condensation slip while minimizing the decrease in energy efficiency.

  In this embodiment, the hole 52 is provided at the end of the sheet passing area, but the hole 52 may be provided only in the non-sheet passing area.

DESCRIPTION OF SYMBOLS 10 Fixing film 20 Pressure roller 31 Heater 50 Duct 52 Hole 55 Duct inside 79 Fan

Claims (20)

A first rotator driven by a drive source and a second rotator driven by the first rotator by forming a nip portion between the first rotator and the first rotation And a blowing member for blowing air to a rotating body that does not contact the unfixed toner image of the second rotating body, and transports the recording material carrying the unfixed toner image at the nip portion. In a fixing device for performing a fixing process for fixing the unfixed toner image on a recording material by heating while
At least the temperature of the rotating member that does not contact the unfixed toner image among the first rotating member and the second rotating member when the warming-up of the fixing device is started is lower than a threshold temperature. In this case, the air volume toward the sheet passing area of the rotating body that is driven and does not contact the unfixed toner image is the air volume toward the non-sheet passing area of the rotating body that does not contact the unfixed toner image. Smaller than the fixing device.   An image forming apparatus including the fixing device includes an environment detection member that detects humidity of an environment in which the image forming apparatus is installed, and the air blowing member is driven when the humidity detected by the environment detection member is higher than a predetermined value. The fixing device according to claim 1, wherein:   3. The fixing according to claim 1, wherein the sheet passing area and the non-sheet passing area are a sheet passing area and a non-sheet passing area of a recording material having a maximum width that can be conveyed by the fixing device. apparatus. A duct having an opening for taking in the wind of the air blowing member and a hole for discharging the wind taken in from the opening toward the rotating body that does not contact the unfixed toner image; ,
The number of the holes per unit length of the duct in the generatrix direction of the rotating body provided in the duct area facing the sheet passing area is the area provided in the area facing the non-sheet passing area. The fixing device according to claim 1, wherein the number of the holes per unit length of the duct in the direction of the generatrix of the rotating body is smaller. A duct having an opening for taking in the wind of the air blowing member and a hole for discharging the wind taken in from the opening toward the rotating body that does not contact the unfixed toner image; ,
The size of the hole provided in the area of the duct facing the paper passing area is smaller than the size of the hole provided in the area facing the non-paper passing area. The fixing device according to claim 1.   The fixing device according to claim 4, wherein the hole is provided on the downstream side of the nip portion in the recording material conveyance direction.   The hole provided in the duct area facing the non-sheet passing area is provided in a wider range in the recording material conveyance direction than the hole provided in the duct area facing the sheet passing area. The fixing device according to any one of claims 4 to 6, wherein the fixing device is one of the following.   8. The rotating body on the side not in contact with the first rotating body and the unfixed toner image is a pressure roller, and the second rotating body is a cylindrical film. The fixing device according to claim 1.   The fixing device according to claim 8, further comprising a heater in contact with an inner surface of the film, wherein the heater forms the nip portion together with the pressure roller via the film. A first rotating body driven by a driving source; a second rotating body that contacts the first rotating body to form a nip portion and is driven by the first rotating body; and the first rotation. And a blowing member for blowing air to a rotating body that does not contact the unfixed toner image of the second rotating body, and transports the recording material carrying the unfixed toner image at the nip portion. In a fixing device for performing a fixing process for fixing the unfixed toner image on a recording material by heating while
At least the temperature of the rotating member that does not contact the unfixed toner image among the first rotating member and the second rotating member when the warming-up of the fixing device is started is lower than a threshold temperature. In this case, the fixing device is driven and blown only to an end portion in a direction orthogonal to the recording material conveyance direction of the rotating body that does not contact the unfixed toner image.   An image forming apparatus including the fixing device includes an environment detection member that detects humidity of an environment in which the image forming apparatus is installed, and the air blowing member is driven when the humidity detected by the environment detection member is higher than a predetermined value. The fixing device according to claim 10, wherein the fixing device is used.   A region of an end portion of the rotating body that is not in contact with the unfixed toner image in a direction perpendicular to the recording material conveyance direction and blown by the blowing member includes a non-sheet passing region. The fixing device according to claim 10 or 11.   The fixing device according to claim 12, wherein the non-sheet passing region is a non-sheet passing region of a recording material having a maximum width that can be conveyed by the fixing device. A duct having an opening for taking in the wind of the air blowing member and a hole for discharging the wind taken in from the opening toward the rotating body that does not contact the unfixed toner image; ,
11. The hole is provided only in a region facing an end portion in a direction orthogonal to a recording material conveyance direction of a rotating body on a side not contacting the unfixed toner image of the duct. 14. The fixing device according to any one of items 13.   The fixing device according to claim 14, wherein the hole is provided downstream of the nip portion in the recording material conveyance direction.   Holes provided in a region facing the end of the duct that is not in contact with the unfixed toner image in the direction orthogonal to the recording material conveyance direction are provided in a wide range in the recording material conveyance direction. The fixing device according to claim 14, wherein the fixing device is a fixing device.   17. The rotating body on the side not in contact with the first rotating body and the unfixed toner image is a pressure roller, and the second rotating body is a cylindrical film. The fixing device according to claim 1.   The fixing device according to claim 17, further comprising a heater that contacts an inner surface of the film, wherein the heater forms the nip portion together with the pressure roller via the film. A first rotator driven by a drive source and a second rotator driven by the first rotator by forming a nip portion between the first rotator and the first rotation And a blowing member for blowing air to a rotating body that does not contact the unfixed toner image of the second rotating body, and transports the recording material carrying the unfixed toner image at the nip portion. In a fixing device for performing a fixing process for fixing the unfixed toner image on a recording material by heating while
At least the temperature of the rotating member that does not contact the unfixed toner image among the first rotating member and the second rotating member when the warming-up of the fixing device is started is lower than a threshold temperature. In this case, the air volume toward the central portion of the rotating body that is driven and does not contact the unfixed toner image in the direction orthogonal to the recording material conveyance direction is the end of the rotating body that does not contact the unfixed toner image. The fixing device is characterized in that the air volume is smaller than the air flow toward the part.   An image forming apparatus including the fixing device includes an environment detection member that detects humidity of an environment in which the image forming apparatus is installed, and the air blowing member is driven when the humidity detected by the environment detection member is higher than a predetermined value. The fixing device according to claim 19, wherein the fixing device is used.

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