JP4804064B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a function of forming an image on a recording medium such as a sheet, such as a copying machine, a printer, or a facsimile machine.

  In a conventional fixing device (heating device), a heat roller method or a film heating method is widely used.

  In particular, the film heating method is effective as an energy-saving heating device that can suppress power consumption as much as possible without supplying power during standby.

  This has a heating unit fixedly supported, a heat-resistant film that slides on the heating unit, and a fixing (pressure) roller that presses against the heating unit across the film to form a fixing nip, The heating unit is heated and adjusted to a predetermined temperature, and a recording material on which an unfixed image is formed and supported is introduced between the film of the fixing nip and the pressure member, and the fixing nip portion is nipped and conveyed together with the film. Thus, the unfixed image is fixed on the recording material as a permanently fixed image by the heat from the heating unit via the film and the pressing force of the pressure member.

  In such a film heating type image heating apparatus, a low heat capacity linear heating element such as a so-called ceramic heater can be used as a heating unit, and a thin heat-resistant film as a heat transfer member can be used having a low heat capacity. It is possible to quickly raise the temperature of the fixing nip to a predetermined temperature.

  For this reason, the power consumption can be suppressed as much as possible without supplying power to the device during standby, so power saving and wait time (quick start) can be reduced compared to other image heating devices such as the heat roller method. realizable.

  On the other hand, in the heat roller method, an induction coil is installed inside the fixing roller, a high-frequency current is passed through the induction coil to generate an induced magnetic flux, and an induced current is generated in the conductive layer on the outer periphery of the roller by the induced magnetic flux. The fixing roller is heated by Joule heat.

At this time, in order to prevent the insulation coating from being damaged by self-heating of the coil, a configuration in which cooling fans are installed at both ends of the induction coil is disclosed (for example, see Patent Document 1).
JP 2000-131979 A

  However, in the conventional film heating method, only the fixing roller feeds the recording material, and the heat-resistant film is only driven by the recording material or the fixing roller. Therefore, when the water vapor generated from the recording material during heating is condensed on the outer peripheral surface of the fixing roller, a slip occurs between the recording material and the fixing roller, and there is a possibility that the image defect or the worst will be jammed.

Here, the cooling method disclosed in Patent Document 1 is a cooling method for cooling the induction coil inside the hollow cylindrical fixing roller uniformly over the longitudinal length in the heat roller method, The vertical arrangement must be approximately coaxial with the center of the fixing roller. For this reason, it is difficult to say that it is effective for efficiently discharging the water vapor generated in the heating apparatus to the outside of the apparatus.

  The present invention has been made in view of the above-described circumstances, and by efficiently discharging water vapor generated from the recording material in the fixing device to the outside of the apparatus, condensation on the outer peripheral surface of the fixing roller is prevented, and consequently The purpose is to prevent image defects and jamming.

In order to achieve the above object, the present invention provides:
Image forming means for forming a toner image on the recording material;
A cylindrical fixing film; a heater that is in contact with the inner surface of the fixing film and controlled in temperature ; and a pressure roller that forms a fixing nip portion together with the heater via the fixing film and rotates the fixing film; Fixing means for heating and fixing the toner image on the recording material to the recording material while nipping and conveying the recording material at the fixing nip portion,
A frame for housing the image forming unit and the fixing unit;
A first fan that is installed on the frame body outside one end in the longitudinal direction of the fixing unit, and discharges air from the frame body to the outside of the apparatus;
An image forming apparatus having a second fan that is installed on the frame body outside the other end in the longitudinal direction of the fixing unit and sucks air from outside the apparatus into the frame body ;
The second fan is in a direction normal to the installation surface of the apparatus, closer to the installation surface than the fixing unit, and at a position that does not overlap the fixing unit. Installed in parallel directions,
The first fan is in a direction normal to the installation surface, farther from the installation surface than the fixing unit, and at a position where it does not overlap the fixing unit, and the direction of air flow is parallel to the installation surface. Installed to be
The air sucked into the frame body by the second fan rises to the fixing means by natural convection , passes through the surface of the pressure roller substantially parallel to the rotation axis of the pressure roller, and then the natural convection. Is raised to the position of the first fan, and is discharged out of the apparatus by the first fan.

  According to the present invention, it is possible to prevent condensation on the outer peripheral surface of the fixing roller by efficiently discharging water vapor generated from the recording material in the fixing device to the outside, and in turn, to prevent image defects and jamming. It becomes.

  In an embodiment of the present invention, in an image forming apparatus in which one or a plurality of cooling fans are provided at both ends of a fixing roller in a fixing device, one is a suction fan and the other is a discharge fan. The fan was installed below the rotation center of the fixing (pressure) roller, and the discharge fan was installed above the rotation center of the fixing (pressure) roller.

  In general, heated air becomes a rising air current and has a property of flowing upward. It is considered that water vapor generated from the recording material in the fixing device also rises along the rising airflow.

  Therefore, as in this embodiment, if the suction fan is disposed below the fixing roller and the discharge fan is disposed above the fixing roller, an air flow path (air passage) that flows upward in the vicinity of the fixing roller is formed. Therefore, it is possible to efficiently discharge water vapor outside the apparatus without hindering the flow of the updraft.

  Furthermore, by arranging the suction fan upstream of the fixing roller rotation center and the discharge fan downstream of the fixing roller rotation center with respect to the recording material conveyance direction, the heated air and water vapor are removed from the fixing roller. It is also possible to prevent backflow to the upstream image forming unit.

  In this way, the influence of heat in the image forming unit can be eliminated, and at the same time, water vapor can be efficiently discharged out of the apparatus.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 using an electrophotographic process, and shows a case of a laser printer as an example of the image forming apparatus.

  The main body of the image forming apparatus 1 irradiates laser light based on image information from an optical system 2 onto an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 3 provided in a drum shape as an image carrier, and the photosensitive drum 3. An electrostatic latent image is formed on the surface, and the latent image is developed with toner to form a toner image 4.

  The feeding device includes a feeding tray on which the recording material P is stacked, and a feeding roller 5 as a feeding unit that picks up the recording material P one by one from the loaded recording material P and feeds it into the main body of the image forming apparatus 1. ing.

  The recording material P fed from the feeding roller 5 is conveyed to the transfer device 7 with the orientation of the recording material adjusted by a pair of registration rollers 6 arranged downstream of the feeding roller 5.

  Here, the recording material P can also be manually fed by the manual feeding roller 5a.

  The recording material P conveyed by the registration roller pair 6 enters the nip portion with the transfer roller 8 urged by a predetermined pressing force at a position facing the photosensitive drum 3 in the transfer device 7. At this time, the toner image 4 formed on the photosensitive drum 3 is transferred to the recording material P by applying a voltage to the transfer roller 8.

  The recording material P to which the toner image 4 has been transferred is conveyed to a fixing device 9 as a downstream fixing unit. The fixing device 9 is composed of a pressure roller (fixing roller) 10 as a pressure rotating member and a fixing film 12 having a heating element 11 built in, and is transferred by applying heat and pressure to the passing recording material P. The toner image 4 is fixed on the recording material P.

  The recording material P conveyed from the fixing device 9 is discharged from the main body of the image forming apparatus 1 to the outside by the discharge roller 13 and the discharge roller 14.

  On the other hand, the process cartridge 15 is a cartridge in which the photosensitive drum 3 and at least one process means are integrally formed as described above, and the cartridge 15 is detachable from the image forming apparatus 1.

  Here, as the process means, for example, a charging means for applying a predetermined voltage to the photosensitive drum 3 to charge it, a developing means for developing the latent image formed on the photosensitive drum 3 by attaching toner, and a photosensitive drum 3 is a cleaning means for cleaning the toner remaining on the surface. The image forming means (image forming portion) according to the present invention is configured by means applied to transfer a toner image obtained by developing the electrostatic latent image formed on the photosensitive drum 3 to a sheet. Is done.

  Further, a first cooling fan as discharge air blowing means is located at a distance L1 above the rotation center (predetermined (reference) position) of the pressure roller 10 and downstream in the conveyance direction D of the recording material P. 16, a second cooling fan 17 serving as a suction air blowing means is disposed at a distance L2 below the recording roller P in the conveyance direction D upstream of the rotation center of the pressure roller 10. The 1st cooling fan 16 and the 2nd cooling fan 17 comprise the ventilation means which concerns on this invention. In addition, although the 1st cooling fan 16 and the 2nd cooling fan 17 are respectively comprised by one fan in the figure, you may be comprised by several fans.

Next, the fixing device 9 will be described. FIG. 2 is a schematic configuration diagram showing a film heating type fixing device 9.

  The heat insulating holder 18 is a member that holds the heating unit 19 and prevents heat radiation to other than the fixing nip N. The heat insulating holder 18 is made of a material that is heat resistant and electrically insulating and can withstand a high load, preferably a liquid crystal polymer or a phenol resin. , PPS, PEEK, etc.

  The heat insulating holder 18 of the present embodiment has a shape in which a substantially semicircular arc-shaped cross section is extended to the maximum sheet passing width. It is inserted and fixed and held.

  A cylindrical endless film (fixing film 12) is externally fitted as a heat resistant film on the outer periphery of the heat insulating holder 18, and the heat insulating holder 18 supports the fixing film 12 from the inner surface. At least a part of the circumference of the fixing film 12 is always tension-free (a state in which no tension is applied), and the fixing film 12 is configured to rotate by the rotational driving force of the pressure roller 10.

  A characteristic of the fixing film 12 is that the film thickness is 100 μm or less, preferably about 10 to 50 μm in order to increase heat transfer and reduce heat capacity, and the material is a single material of PTFE, PFA, FEP having heat resistance. A composite layer film having a film thickness of about 60 μm in which a layer, or an outer peripheral surface of polyimide, polyamideimide, PEEK, PES, PPS or the like is coated with PTFE, PFA, FEP or the like can be used.

  The pressure roller 10 as a pressure member is composed of a cored bar and a heat-resistant rubber such as silicon rubber or fluorine rubber or an elastic layer formed by foaming silicon rubber on the outside, and further, PFA on the outer peripheral surface thereof. , PRFE, FEP, etc. may be coated.

  The pressure roller 10 is held by a bearing member (not shown), the fixing film 12 is sandwiched against the downward surface of the heat insulating holder 18, and is necessary for heat fixing from both ends in the longitudinal direction by a pressing means (not shown). Pressure is sufficiently applied to form the fixing nip portion N.

The heating unit 19 is a ceramic insulating substrate 20 such as Al ₂ O ₃ or AlN, and an electric resistance material such as Ag / Pd (silver palladium) is applied on the surface of the insulating substrate 20 by screen printing or baking. The plurality of heating elements (heating resistors) 11 and a protective layer 21 such as glass or fluororesin that protects the heating elements 11. The heating part 19 can be heated quickly by energizing the heating element 11 to generate heat over the entire length in the longitudinal direction. Further, a plurality of temperature detection thermistors (not shown) are provided on the non-sheet passing surface side of the heating unit 19 to detect the voltage and perform temperature control.

  The pressure roller 10 is rotationally driven in a counterclockwise direction CCW in the figure by a driving means (not shown). The outer peripheral surface of the fixing film 12 is brought into contact with the outer peripheral surface of the pressure roller 10 at the fixing nip portion N, and the inner peripheral surface thereof is in close contact with the surface of the heating unit 19 while sliding. It is driven and rotated at a peripheral speed almost corresponding to the speed.

  At this time, in order to reduce sliding resistance between the fixing film 12, the heating unit 19, and the heat insulating holder 18, a small amount of a lubricating member such as heat resistant grease is interposed on the surfaces of the heating unit 19 and the heat insulating holder 18. Thereby, the fixing film 12 can be rotated smoothly.

  The pressure roller 10 is rotationally driven, and accordingly the fixing film 12 is driven and rotated, the heating unit 19 is energized, and the fixing nip N is heated to a predetermined temperature by feedback control using a temperature detection thermistor. The recording material P carrying the unfixed toner image 4 is fed from the direction of the arrow D and introduced into the fixing nip portion N, and the unfixed image carrying surface is in close contact with the outer periphery of the fixing film 12 and fixed. The fixing nip portion N is nipped and conveyed together with the film 12.

  In this process, heat from the heating unit 19 is applied to the recording material P through the fixing film 12, and the unfixed toner image 4 is permanently fixed to the recording material P by heat and pressure.

  When the recording material P passes through the fixing nip portion N, the recording material P is separated from the outer peripheral surface of the fixing film 12 and is discharged out of the main body of the image forming apparatus 1 by the discharge roller 13 and the discharge roller 14.

  FIG. 3 is a schematic diagram of the image forming apparatus 1 viewed from the A direction shown in FIG. In FIG. 3, reference numeral 1a denotes a frame of the image forming apparatus.

  Here, the first cooling fan (for discharging) 16 is installed at a distance L3 upward from the rotation center of the pressure roller 10, and the second cooling fan (for suction) 17 is installed on the pressure roller 10. It is installed at a position of distance L4 downward from the center of rotation.

  At this time, as indicated by arrows in the drawing, the air flow in the image forming apparatus 1 is gradually increased in the vicinity of the pressure roller 10 by the cooling air flowing in from the second cooling fan (for suction) 17. The first cooling fan (for discharging) 16 is formed to be discharged out of the apparatus.

  That is, since the air path is formed to the first cooling fan (for discharging) 16 without hindering the rising airflow of the air heated by the heating unit 19 or the water vapor, the water vapor can be efficiently discharged. .

  Further, in this embodiment, the first cooling fan (for discharging) 16 and the conveyance of the recording material P are located at a distance L1 on the downstream side in the conveyance direction D of the recording material P with respect to the rotation center of the pressure roller 10. Since the second cooling fan (for suction) 17 is disposed at the position of the distance L2 upstream in the direction D, the air or water vapor heated by the heating unit 19 goes outside the apparatus without flowing back to the image forming unit. Can be discharged.

  That is, since the temperature rise and water vapor in the image forming unit can be prevented, a good image can be obtained.

  FIG. 4 is a schematic configuration diagram showing the configuration of the image forming apparatus in Embodiment 2 of the present invention. The configurations of the image forming unit and the fixing device are the same as those in the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted.

  The first cooling fan (for discharge) 16 is installed at a distance L3 ′ above the rotation center of the pressure roller 10, and the second cooling fan (for suction) 17 is the rotation center of the pressure roller 10. It is installed in the position of distance L4 'below.

  At this time, the air flow in the image forming apparatus 1 is such that the cooling air flowing in from the second cooling fan (for suction) 17 gradually rises in the vicinity of the pressure roller 10 and the first cooling fan (for discharge). 16 is formed to be discharged out of the apparatus.

  That is, since the air path is formed to the first cooling fan (for discharging) 16 without hindering the rising airflow of the air heated by the heating unit 19 or the water vapor, the water vapor can be efficiently discharged. .

  FIG. 5 is a top view of the image forming apparatus 1 viewed from the B direction shown in FIG.

  The first cooling fan (for discharging) 16 is located at a distance L1 ′ downstream of the recording material P in the conveyance direction D with respect to the rotation center of the pressure roller 10, and the distance L2 is upstream of the recording material P in the conveyance direction D. Second cooling fans (for suction) 17 are arranged at positions'.

  Here, the suction direction of the second cooling fan (for suction) 17 is set in a direction substantially parallel to the conveyance direction D of the recording material P, and before introducing the cooling air to the fixing device 9, the distance L2 is set. It is also possible to cool the heat source installed between.

  At this time, the cooling air in the image forming apparatus 1 can be discharged outside the apparatus without the air or water vapor heated by the heating unit 19 flowing back to the image forming unit, as indicated by arrows in the figure.

  That is, since the temperature rise and water vapor in the image forming unit can be prevented, a good image can be obtained.

1 is a schematic configuration diagram of an image forming apparatus using an electrophotographic process in Embodiment 1. FIG. FIG. 3 is a schematic configuration diagram illustrating an example of a film heating type fixing device. FIG. 2 is a schematic view of the image forming apparatus viewed from the direction A in FIG. 1. FIG. 5 is a schematic configuration diagram of an image forming apparatus using an electrophotographic process in Embodiment 2. FIG. 5 is a top view of the image forming apparatus viewed from a direction B in FIG. 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Optical system 3 Electrophotographic photoreceptor 4 Toner image 5 Feed roller 5a Manual feed roller 6 Registration roller pair 7 Transfer device 8 Transfer roller 9 Fixing device 10 Pressure roller 11 Heating element 12 Fixing film 13 Discharge roller 14 Discharge roller 15 Process cartridge 16 First cooling fan (for discharge)
17 Second cooling fan (for suction)
18 Heat insulating holder 19 Heating unit 20 Insulating substrate 21 Protective layer D Transport direction of recording material P L1, L1 ′ Transport direction distance from pressure roller 10 center to first cooling fan (for discharge) 16 L2, L2 ′ Pressurization Distance in conveyance direction from roller 10 center to second cooling fan (for suction) 17 L3, L3 ′ Vertical distance from pressure roller 10 center to first cooling fan (for discharge) 16 L4, L4 ′ Vertical distance from roller 10 center to second cooling fan (for suction) 17 N fixing nip P recording material

Claims (2)

Image forming means for forming a toner image on the recording material;
A cylindrical fixing film; a heater that is in contact with the inner surface of the fixing film and controlled in temperature ; and a pressure roller that forms a fixing nip portion together with the heater via the fixing film and rotates the fixing film; Fixing means for heating and fixing the toner image on the recording material to the recording material while nipping and conveying the recording material at the fixing nip portion,
A frame for housing the image forming unit and the fixing unit;
A first fan that is installed on the frame body outside one end in the longitudinal direction of the fixing unit, and discharges air from the frame body to the outside of the apparatus;
An image forming apparatus having a second fan that is installed on the frame body outside the other end in the longitudinal direction of the fixing unit and sucks air from outside the apparatus into the frame body ;
The second fan is in a direction normal to the installation surface of the apparatus, closer to the installation surface than the fixing unit, and at a position that does not overlap the fixing unit. Installed in parallel directions,
The first fan is in a direction normal to the installation surface, farther from the installation surface than the fixing unit, and at a position where it does not overlap the fixing unit, and the direction of air flow is parallel to the installation surface. Installed to be
The air sucked into the frame body by the second fan rises to the fixing means by natural convection , passes through the surface of the pressure roller substantially parallel to the rotation axis of the pressure roller, and then the natural convection. Is raised to the position of the first fan, and is discharged out of the apparatus by the first fan. The second fan is disposed upstream of the rotation axis of the pressure roller in the recording material conveyance direction,
The image forming apparatus according to claim 1, wherein the first fan is disposed downstream of a rotation shaft of the pressure roller.

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