JP4944575B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine, a laser printer, a facsimile machine, and the like provided with an image heating apparatus that heat-processes an image on a recording material.

  Conventionally, in a printer using an electrophotographic process, a toner image (unfixed image) based on an image signal from a personal computer or the like is electrostatically carried on a recording material, and this is heated and pressed by a fixing device. The toner image is fixed on the recording material. As an image heating device used for the fixing device of the electrophotographic process, for example, there is a fixing device shown in FIG.

  FIG. 11A is a schematic cross-sectional view of a conventional fixing device, and FIG. 11B is a view of the conventional fixing device as viewed from the upstream side (J direction) in the recording material conveyance direction. A heater unit 100 includes a heater 101 that generates heat when energized, a heat-resistant cylindrical fixing film 102, a film guide 103 that holds the heater 101 and guides the rotation of the fixing film 102, a stay 104, and a flange 105.

  A pressure roller 106 includes a cored bar 114 and an elastic rubber part 115 provided on the outer periphery thereof. The heater unit 100 and the pressure roller 106 are pressed against each other with a predetermined pressure by a pressure unit (not shown) to form a fixing nip portion N.

  A discharge roller pair 107 includes a discharge roller 108 and a discharge roller 109. Reference numerals 110 and 113 denote fixing device casings in which the above-described members are housed, and 112 denotes an inlet guide provided at an upstream portion of the casing 110 in the recording material conveyance direction.

  The pressure roller 106 is rotated by a driving force transmitted from a main motor in the printer main body via a pressure roller gear 116 shown in FIG. 11B, and the fixing film 102 is rotated following the rotation. .

  On the other hand, the heater 101 is supplied with electric power through a temperature control circuit (not shown), and the supplied electric power is adjusted so as to reach a predetermined temperature (fixing temperature).

  In this way, with the pressure roller 106 and the fixing film 102 rotated and the heater 101 heated to a predetermined temperature, the recording material P onto which the unfixed image has been transferred is transferred to the heater unit 100 and the pressure roller 106. To the fixing nip N between the two. The recording material P introduced into the fixing nip N is conveyed while being in close contact with the fixing film 102. As a result, heat from the heater 101 through the fixing film 102 and pressure contact pressure between the heater unit 100 and the pressure roller 106 are applied to the recording material P, and the toner image is fixed on the recording material by heat and pressure.

  Then, the recording material P that has passed through the fixing nip N is conveyed to the output side by a discharge roller pair 107 including a discharge roller 108 and a discharge roller 109.

  However, the conventional fixing device described above has the following problems.

  In the fixing device described above, the pressure roller 106 is driven to rotate, and the fixing film 102 is driven to rotate. For this reason, resistance force R1 (sliding resistance with the film guide 103), R2 (sliding resistance with the heater 101), R3 (sliding resistance with the guide surface of the flange 105) of the portion where the fixing film 102 slides A sliding resistance F2 consisting of Therefore, in order to transport the recording material P, the relationship between the transport force F1 applied to the recording material P from the pressure roller 106 and the sliding resistance F2 is set to satisfy F1> F2.

  However, the recording material is conveyed in a state where the temperature of the pressure roller 106 is still low, for example, until about the first ten sheets when continuously printing in a low temperature state (normal temperature). For this reason, when the recording material P contains a large amount of moisture, the moisture contained in the recording material P evaporates in the fixing nip portion N due to heating by the heater 101, and dew condensation occurs on the surface of the pressure roller 106. As a result, the friction coefficient of the pressure roller 106 decreases. As a result, the relationship between the sliding resistance F2 and the conveyance force F1 becomes F1 <F2, and a situation occurs in which the recording material slips (hereinafter referred to as condensation slip), and the conveyance speed at the fixing nip N is It becomes slower than the conveying speed in the image forming unit. For this reason, the recording material sags between the fixing device and the image forming unit, and an unfixed image on the recording material rubs against a member in the vicinity of the conveyance path. (Hereinafter referred to as jam).

  Therefore, techniques for solving these problems have been proposed. For example, Patent Document 1 discloses a configuration in which water vapor generated in the fixing device is discharged from the opening to the outside of the fixing device by providing an opening at the top of the fixing device. Patent Document 2 discloses a technique for preventing condensation in the fixing device by providing a fan for preventing condensation in the lower portion of the fixing device and operating it according to the driving of the pressure roller.

JP-A-9-297480 Japanese Patent Laid-Open No. 5-134513

  The steam generated in the fixing nip N as described above is likely to scatter particularly on the downstream side in the conveyance direction of the recording material and on the non-recording surface side (pressure roller 106 side). This is because steam generated in the fixing nip portion N easily circulates downstream of the fixing nip N from the conveyance direction of the recording material P and the rotation direction of the pressure roller 106. Further, since the toner image is a film on the recording surface side on which the toner image is placed, it is difficult for the vapor to fly, and the vapor easily circulates to the pressure roller 106 side which is the non-recording surface side. Further, the normal pressure roller 106 is surrounded by a guide member (not shown), a housing (sheet metal frame) and the like so as to maintain heat insulation performance, and the air flow to the outside of the fixing device is substantially blocked. For this reason, the steam circulated in the rotation direction of the pressure roller 106 loses its escape, and eventually adheres to the surface of the pressure roller 106 as water droplets, resulting in condensation slip and jamming. There is also a possibility.

  Therefore, as the process speed increases, the circulation of the steam is faster as the process speed increases, so that the occurrence of dew condensation slips appears remarkably.

  In addition, when the pressure roller 106 is opened to prevent condensation of the pressure roller 106 or when air is blown using a cooling fan, the heat insulation characteristic that the pressure roller should originally have is impaired. That is, although condensation of the pressure roller can be prevented, the pressure roller is cooled. As a result, the fixing of the toner image at the fixing nip portion N becomes unsatisfactory and causes an image defect.

  As described above, in the conventional configuration, it is difficult to achieve both slip jam accompanying condensation on the pressure roller surface and maintaining the heat insulation performance of the pressure roller.

  Accordingly, an object of the present invention is to efficiently discharge the vapor generated during the passage of the recording material to the outside of the fixing device while maintaining the heat insulating performance of the pressure roller, thereby suppressing condensation slip and preventing the occurrence of image defects. It is to be.

In order to achieve the above object, a typical configuration of the present invention includes an image forming unit that forms a toner image on a recording material, a heating rotator, and a pressure roller that contacts the heating rotator and forms a nip portion. A guide member having a guide surface that guides the surface of the recording material facing the pressure roller on the downstream side of the nip portion, and having an opening on the guide surface, and carries a toner image The recording material is heated while being conveyed at the nip portion, and a fixing unit that fixes the toner image on the recording material, and air is blown so that air near the pressure roller is discharged from the opening portion to the outside of the fixing unit. In the image forming apparatus having the blowing unit, air from the blowing unit flows along the outer circumferential surface of the pressure roller in a direction opposite to the rotation direction of the pressure roller, and then the outer circumferential surface of the pressure roller. And the guide member Via the gap formed between the end portion of the recording material conveyance direction upstream side of the id surface, characterized in that it is discharged from the opening.

  According to the present invention, even when the recording material passes through the low temperature pressure nip portion, the steam is discharged from the opening provided on the downstream side of the pressure nip portion and on the non-recording surface side of the recording material. That is, the vapor generated during the passage of the recording material is efficiently discharged outside the image heating apparatus while maintaining the heat insulating performance of the pressure member. As a result, slip jamming due to condensation and the occurrence of image defects can be prevented, and smooth conveyance of the recording material can be realized.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

[First Reference Example ]
An image forming apparatus comprising an image heating apparatus. FIG. 2 is a schematic configuration diagram of the image forming apparatus.

  The image forming apparatus includes a photosensitive drum 1 as an image carrier, and the photosensitive drum 1 is rotationally driven in a direction of an arrow at a predetermined process speed by a main body driving motor (not shown) as a driving unit. Here, the process speed of the image forming apparatus is 200 mm / sec.

  Around the photosensitive drum 1, a charging roller 2 as a charging device, an exposure device 3, a developing device 4, a transfer roller 5 as a transfer device, and a cleaning blade 6 as a cleaning device are arranged in order along the rotation direction. ing. These devices and the photosensitive drum constitute image forming means for forming an image on a recording material.

  In addition, a feeding cassette 7 that stores a recording material (paper, printing paper, paper sheet, OHT sheet, glossy paper, glossy film, etc.) P is disposed at the lower part of the apparatus main body. A feeding roller 15, a conveyance roller 8, a top sensor 9, a photosensitive drum 1 and a transfer roller 5, a conveyance guide 10, a fixing device 11, a discharge roller 13, and a discharge tray 14 are sequentially provided along the conveyance path of the recording material P. Has been placed.

  Next, the operation of the image forming apparatus having the above-described configuration will be described.

  The photosensitive drum 1 that is rotationally driven in the direction of the arrow by a main body drive motor (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 2. The exposure device 3 is a laser scanner that outputs a laser beam corresponding to a signal of target image information input from a host device such as a computer or image reading device (not shown), and a folding mirror (not shown) is output by the laser beam. The surface of the photosensitive drum 1 is scanned and exposed. Then, the charge on the exposed portion of the photosensitive drum 1 is removed and an electrostatic latent image is formed. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller, and a developing bias is applied to the developing roller to attach toner to the electrostatic latent image on the photosensitive drum 1 and develop (develop) it as a toner image. The toner image on the photosensitive drum 1 is transferred to the recording material P by the transfer roller 5.

  On the other hand, the recording material P is fed one by one from the feeding cassette 7 by the feeding roller 15, and is conveyed toward the transfer nip portion between the photosensitive drum 1 and the transfer roller 5 by the conveying roller 8. At this time, the leading edge of the recording material P is detected by the top sensor 9 and is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.

  The recording material P carrying the unfixed toner image on the surface by the transfer is transported along the transport guide 10 to the fixing inlet guide 16 and guided to the fixing device 11 as an image heating device. The unfixed toner image is heated and pressurized here and fixed on the recording material P. The recording material P on which the toner image is fixed is conveyed along the discharge separation guide 20 to the separation guide roller 12 and is discharged from the discharge roller 13 onto the discharge tray 14 on the upper surface of the apparatus main body.

  On the other hand, after the toner image is transferred, the toner remaining on the surface without being transferred to the recording material P is removed by the cleaning blade of the cleaning device 6, and the next image formation is performed.

  By repeating the above operation, image formation can be performed one after another.

  Next, details of the fixing device 11 will be described.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of the fixing device 11 according to the first reference example . The fixing device in this reference example is a film heating type fixing device using a ceramic heater as a heating element.

  In FIG. 3, reference numeral 31 denotes a horizontally long heater stay that is a heat-resistant resin as a heating body support member, and serves as a guide member on the inner surface of a heat-resistant endless film 32 (hereinafter referred to as a film). The film 32 is fitted on the heater stay 31 including the heater 33 which is a heating body. The inner peripheral length of the film 32 and the outer peripheral length of the heater stay 31 including the heater 33 are slightly larger than the film 32 (for example, about 3 mm). Accordingly, the film 32 is loosely fitted to the stay 31 including the heater 33 with a sufficient circumferential length. The heater 33 is coated with an electric resistance material (heating element) such as Ag / Pd (silver palladium) to a thickness of 10 μm and a width of about 1 to 5 mm by screen printing or the like along substantially the center of the substrate made of alumina or the like. In addition, glass, fluororesin, or the like is coated thereon as a protective layer. The heater stay 31, the film 32, and the heater 33 constitute a heat generating means 30.

  Reference numeral 34 denotes a pressure roller as a pressure member that is rotationally driven while being in pressure contact with the heat generating means 30. The pressure roller 34 is a rotating body that drives the film 32 by forming a fixing nip portion N (pressure nip portion) by sandwiching the film 32 with the heater 33. The pressure roller 34 is composed of an aluminum pressure roller core (shaft) 35 and a pressure roller elastic body portion 36 made of silicone rubber and is attached to the shaft. It is driven to rotate in the direction of the arrow by being driven by a motor which is a driving means (not shown). When the pressure roller 34 is driven to rotate, the film 32 is also driven to rotate.

  When the film 32 is not driven, the remaining part of the film 32 except for the part sandwiched between the fixing nip N between the heater 33 and the pressure roller 34 is substantially tension free.

  When the pressure roller 34 is rotationally driven, the film back surface is rotationally driven in the fixing nip portion N in the direction of the arrow while the film back surface slides on the surface of the heater 33 at substantially the same rotational speed as the pressure roller 34. .

  In a state where the film drive and the heater 33 are energized, the recording material P carrying an unfixed image is introduced between the film 32 and the pressure roller 34 in the fixing nip portion N with the recording surface facing upward. The Then, the recording material P passes through the fixing nip N together with the film 32, and the heat energy of the heater 33 in contact with the back surface of the film in the fixing nip portion N is applied to the recording material P through the film 32 and the toner. The image T is thermally fixed and discharged outside the fixing device.

  Reference numeral 16 denotes a fixing inlet guide, which plays a role of guiding the recording material P conveyed by the conveying guide 10 to the fixing nip portion N of the fixing device 11.

  A discharge separation guide 20 as a guide member plays a role of smoothly guiding the recording material P that has passed through the fixing nip N to the separation guide roller 12 so as not to be wound around the film 32 or the pressure roller 34. Yes.

  The discharge separation guide 20 will be described in more detail. FIG. 1 is a front view and a perspective view of the discharge separation guide 20. The discharge separation guide 20 is provided on the downstream side of the fixing nip portion N and on the non-recording surface side of the recording material. The discharge separation guide 20 has a plurality of separation guide ribs 21 that come into contact with the recording material P, and the separation guide ribs 21 serve to smoothly convey the recording material P with a small friction. In this example, the width of the surface of the separation guide rib 21 in contact with the recording material P is about 1 mm, and is approximately equidistant from the center in the longitudinal direction of the discharge separation guide 20 (the width direction of the recording material orthogonal to the transport direction). Ten are provided.

  Further, the discharge separation guide 20 has an opening 22 connected to the outside of the fixing device 11. The opening 22 is provided between the guide ribs 21. By providing the opening 22 in the discharge separation guide 20 in this way, it is possible to discharge water vapor generated in the fixing nip portion N to the outside of the fixing device 11 while maintaining the heat insulating performance of the pressure roller 34.

  As shown in FIG. 1, the size of the opening 22 is 3 mm or more in the length (height) t1 in the conveyance direction of the recording material, and 2 mm or more in the width direction t2 of the recording material orthogonal to the conveyance direction. It is preferable that The size of the opening 22 is preferably a size that allows the water vapor generated at the fixing nip N to be discharged outside the fixing device 11 within a range in which the heat insulating performance of the pressure roller 34 is maintained. . In this example, the size of the opening 22 is about 7 mm in the transport direction, and the width direction is slightly different, but is 4 to 20 mm.

  As shown in FIG. 3B, the end of the discharge separation guide 20 on the pressure roller 34 side is extended in the conveyance direction of the fixing nip N so that the recording material P does not wrap around the pressure roller 34. It is at the non-recording surface side (lower side in the figure) with respect to the line. In this example, the end portion of the discharge separation guide 20 on the pressure roller 34 side is at a position on the non-recording surface side by a length t3 (about 1.5 mm) with respect to an extension line in the conveyance direction of the fixing nip portion N. . Further, the end portion on the fixing nip portion N side of the discharge separation guide 20 is disposed in the vicinity of the pressure roller 34. Specifically, the end of the discharge separation guide 20 on the fixing nip portion N side is arranged so that the interval t4 with the pressure roller 34 is 2 mm or less. In this example, in order to maintain the heat insulation performance of the pressure roller 34, the distance between the end of the discharge separation guide 20 on the fixing nip N side and the pressure roller 34 is set to 1 mm. This is a value set in consideration of contact with the discharge separation guide 20 when the pressure roller 34 is thermally expanded. Similarly, the position of the end portion on the fixing nip portion N side of the fixing inlet guide 16 is also arranged so that the distance from the pressure roller 34 is 1 mm.

  Thus, by narrowing the space | interval of the pressure roller 34 and the guide members 20 and 16 of the circumference | surroundings, the pressure roller 34 is brought closer to a sealing state and heat insulation is exhibited.

  Next, the flow of water vapor generated in the fixing nip N during conveyance will be described.

  FIG. 4 shows the flow of water vapor when the discharge separation guide 20 has no opening 22. From the moment when the leading edge of the recording material P reaches the discharge separation guide 20 during conveyance until the trailing edge of the recording material P is discharged from the fixing nip N, the discharge separation guide 20, the pressure roller 34, and the recording material A space S closed by P is generated. Although not shown in the drawing, on both the left and right sides in the longitudinal direction (the width direction of the recording material), a housing (for fixing both end shafts of the fixing inlet guide 16, the discharge separation guide 20, and the pressure roller core metal 35 ( Sheet metal frame). For this reason, normally, the steam hardly escapes from the left and right ends in the longitudinal direction.

  When the recording material is fed at a low temperature using the configuration shown in FIG. 4, the amount of water vapor generated on the downstream side of the fixing nip N and on the non-recording surface side exceeds the saturated water vapor amount of the space S described above. As a result, a dew condensation phenomenon occurs in which the water vapor becomes water droplets and adheres to the discharge separation guide 20 or the pressure roller 34. In particular, in a high humidity environment where the humidity is 80%, the amount of moisture contained in the conveyed recording material P is large (10% or more), so the amount of dew condensation becomes more prominent. As a result of water droplets adhering to the pressure roller 34 due to the dew condensation phenomenon, the friction coefficient of the pressure roller 34 rapidly decreases. As a result, the conveying force F1 applied to the recording material P from the pressure roller 34 is weakened, and the relationship between the sliding resistance F2 on the film 32 side and the conveying force F1 becomes F1 <F2. As a result, the subsequent recording material causes condensation slip at the fixing nip portion N, and jamming occurs. In the measurement by the present inventor, jamming occurs at a rate of about 5% in a high humidity environment with a humidity of 80%.

  Even when jamming due to condensation slip does not occur, an image defect such as an image blurring occurs due to the water droplets adhering to the guide rib 21 of the discharge separation guide 20 being transferred to the subsequent recording material.

  On the other hand, as shown in FIG. 5, by providing an opening 22 in the discharge separation guide 20, the discharge separation guide 20 and the pressure roller 34 are provided during the sheet passing on the downstream side of the fixing nip N and the non-recording surface side. And a space closed by the recording material P is not generated. Thereby, the steam generated in the fixing nip portion N is positively discharged from the opening 22, and water droplet adhesion to the discharge separation guide 20 and the pressure roller 34 can be significantly reduced. Therefore, as shown in FIG. 4, it is possible to suppress the subsequent recording material P from slip jamming due to condensation of the pressure roller 34 and the occurrence of image defects due to water droplets adhering to the discharge separation guide 20. In addition, when measurement was performed in the same environment (humidity 80%) using this configuration, the occurrence of jam due to condensation slip is 0%.

  Further, this configuration is to open the portion other than the guide rib 21 of the discharge separation guide 20. That is, the discharge separation guide 20 of this configuration is provided with the opening 22 between the guide ribs 21. For this reason, the portion below the tip of the guide rib 21, that is, the portion below the fixing nip portion N of the pressure roller 34 has the same configuration as the conventional one, and therefore the heat insulation performance of the pressure roller 34 can be maintained. .

  In this example, the number of guide ribs 21 is 20 in the longitudinal direction, but this can be changed as appropriate according to the main body speed and performance. However, in order to smoothly convey the recording material, it is preferable that there are a plurality (two or more) of them at least from the center in the longitudinal direction. Further, the positions of the guide ribs 21 in the discharge separation guide 20 do not necessarily need to be equidistant from the left and right because of the sensor unit and other functions in the image forming apparatus main body.

  In this example, the size of the opening 22 is 7 mm in height and 4 to 20 mm in width. However, the size of the opening 22 is appropriately changed according to the speed and performance of the main body or the size of the image forming apparatus main body and the fixing device. It shall be possible. However, in order to positively discharge the vapor to the outside of the fixing device, it is naturally preferable that the size of the opening is large (in a range in which the heat insulating performance of the pressure roller is maintained).

  Further, in this example, the interval t4 between the pressure roller 34 tip of the discharge separation guide 20 and the pressure roller 34 is 1 mm, but this can be appropriately changed according to the characteristics (expansion) of the pressure roller. Shall. However, in order to maintain the heat insulation performance of the pressure roller, the distance t4 from the pressure roller 34 needs to be 2 mm or less.

  Further, in this example, on both the left and right sides in the longitudinal direction, there are housings (sheet metal frames) for fixing the both ends of the fixing inlet guide 16, the discharge separation guide 20, and the pressure roller core metal 35. The configuration is such that almost no steam escapes from the left-right direction. However, the present invention is not limited to this. That is, even when there is a steam escape (discharge) port in the longitudinal and lateral directions, the effect of the configuration in which the opening 22 is provided in the guide 20 has been confirmed. That is, while maintaining the heat insulating performance of the pressure roller, the steam generated during the passage of the recording material can be efficiently discharged to the outside of the fixing device, and slip jamming due to condensation and image defects can be prevented. In other words, in view of the rotation direction of the pressure roller, it means that it is more effective to provide the steam discharge port in the transport direction than in the width direction of the recording material.

  As described above, in the discharge separation guide 20 that guides the recording material P that has passed through the fixing nip N, the opening 22 is provided in a portion other than the rib that contacts the recording material. Thereby, even when moisture-absorbing paper is passed in a low temperature state, the steam generated in the fixing nip portion N can be positively discharged to the outside without deteriorating the heat insulation performance of the pressure roller 34. . This also makes it possible to suppress slip jamming due to condensation and prevent image defects, thereby realizing smooth paper conveyance.

[Second Reference Example ]
In the second reference example , in addition to the configuration of the first reference example described above, the opening is opened and closed according to the sheet passing state. Thereby, the heat insulation of the whole fixing apparatus can be kept more. Specifically, when the recording material does not pass through the fixing nip part, such as warm-up time before passing paper or between papers during continuous paper passing, the heat insulation in the fixing device is improved by closing the opening. It is.

A specific operation will be described with reference to FIGS. 6 and 7, the basic functions of the respective members are the same as those in the first reference example . Reference numeral 23 denotes a discharge sensor as a detecting means, which checks the presence or absence of a recording material by turning on / off a photo interrupter (not shown) in the vicinity of the fixing nip portion N according to the operation of a flag. The discharge sensor 23 serves to detect that the recording material P has passed through the fixing nip portion N and has reached the position of the discharge sensor 23. In addition, in the subsequent discharge processing part, it plays a role in taking the timing for sending the recording material P to the double-sided path, or it is determined by the detection time that the recording material P is jammed immediately after fixing. It plays the role of This discharge sensor is also provided in the first reference example although not shown.

  The flag of the discharge sensor 23 can be rotated in the rotation direction of FIG. 6, and when the recording material P passes through and defeats the flag of the discharge sensor 23 as shown in FIG. It has a configuration. A shielding plate 24 is an opening / closing member that opens and closes the opening 22 in accordance with detection information of the discharge sensor 23. The shielding plate 24 of this example rotates in the same direction in the figure in conjunction with the rotation operation of the discharge sensor 23. That is, in the non-sheet passing state, the discharge sensor 23 and the shielding plate 24 are at the positions shown in FIG. At this time, the shielding plate 24 is in a state of closing the opening 22 of the discharge separation guide 20. When the sheet passing is started, the recording material P that has passed through the fixing nip N rotates the flag of the discharge sensor 23 in the rotation direction of the drawing, and the shielding plate 24 also rotates in the same direction following this. As a result, the opening 22 is opened.

  In this example, although the structure which opens and closes the shielding board 24 which opens and closes the opening part 22 with the mechanical mechanism according to the flag operation | movement of the discharge sensor 23 was illustrated, it is not limited to this. For example, if the opening / closing control is performed in accordance with the sheet passing timing of the recording material P, such as opening / closing the shielding plate 24 using a solenoid that operates according to ON / OFF of the photo interrupter of the discharge sensor 23, other configurations may be used. good.

As described above, by controlling the opening / closing of the opening 22 according to the sheet passing state, the opening 22 of the discharge separation guide 20 is opened only when the recording material P passes through the fixing nip N. Thereby, in addition to the effect of the reference example described above, the steam generated in the fixing nip portion N can be efficiently discharged. Further, for example, the shield plate 24 blocks the opening 22 of the discharge separation guide 20 in a warm-up state before passing paper or between continuous papers, so that the heat in the fixing device does not escape to the outside. ing. Thereby, not only the heat insulation performance of the pressure roller is further improved, but it is not necessary to apply extra heat in the heating section (heater), so that energy saving can be ensured.

First Embodiment
In the first embodiment, an air path configuration is adopted in which the vapor inside the fixing device is discharged from the opening 22 to the outside of the fixing device and further to the outside of the image forming apparatus main body. As a result, it is possible to perform optimum vapor discharge in accordance with the high speed and durability of the image forming apparatus main body.

  Specifically, as shown in FIG. 9, a cooling fan 25 for cooling the inside of the main body is provided below the fixing device 11. Further, the wind sent from the cooling fan 25 passes through the opening 22 along the discharge separation guide 20 from the bottom hole 28 of the fixing device 11, and generates steam to the outside of the fixing device and further from the louver 26 to the outside of the main body. An air passage (arrow in the figure) 29 to be discharged is configured.

Naturally, the stronger the wind power of the cooling fan 25 is, the more effective it is on the condensation slip. However, if the wind power is too strong, there is a possibility that the heat insulation performance that the pressure roller 34 should have is impaired. In this example, the cooling fan having a wind force of 0.35 to 0.44 m ³ / min at the rated voltage is used so that the wind speed entering from the bottom hole 28 of the fixing device 11 is 0.4 to 0.6 m / sec. In addition, the wind power of the cooling fan 25 is controlled. Thereby, the heat insulation performance of the pressure roller 34 and the condensation slip are both achieved.

  By using such a configuration, the steam generated in the fixing nip portion N is immediately discharged to the outside of the main body, so that the speed of the main body can be increased. Further, since the vapor inside the fixing device is always discharged to the outside of the main body, it is possible to always provide stable images and transportability regardless of continuous paper feeding and durability.

Further, in FIG. 10, as in the second reference example , the airflow path configuration is not made until the recording material P that has passed through the fixing nip portion N defeats the flag of the discharge sensor 23 and simultaneously the shielding plate 24 opens the opening portion 22. It is shown that holds. Here, a new shielding plate 27 is also provided in the bottom hole 28 of the fixing device 11. In this example, the shielding plates 24 and 27 are opened and closed using a solenoid that operates in response to ON / OFF of a photo interrupter (not shown) of the discharge sensor 23.

  By using such a configuration, it is possible to obtain an effect against condensation slip while maintaining the heat insulating performance inside the pressure roller 34 and the fixing device, and provide stable image and transportability.

  In this example, the wind power of the cooling fan 25 is controlled so that the wind speed entering from the bottom hole 28 of the fixing device 11 is 0.4 to 0.6 m / sec. This is appropriately determined depending on the printing speed and performance of the main body. It can be changed. However, in order to achieve both the heat insulating performance of the pressure roller 34 and the condensation slip, it is preferable to control the wind speed entering from the bottom hole 28 of the fixing device 11 in the range of 0.3 m / sec to 0.8 m / sec.

  As described above, by adopting an air path configuration in which the steam inside the fixing device is discharged from the opening 22 to the outside of the fixing device and further to the outside of the main body using the cooling fan 25, further prevention of condensation slip is achieved. It is possible to provide stable images and transportability. In addition, since the steam generated in the fixing nip N is immediately discharged outside the main body, it is possible to cope with higher speed of the main body. Further, since the vapor inside the fixing device is always discharged outside the main body, the effect on the durability of the main body can be exhibited. Furthermore, the heat insulating performance of the pressure roller and the fixing device can be further maintained by opening the shielding plate only when the recording material passes using the discharge sensor.

  In the above-described embodiment, the image heating fixing device of the image forming apparatus is exemplified as the image heating apparatus. However, the present invention is not limited to this, and other images such as an image surface heating polishing apparatus and a hypothetical landing apparatus are used. It can also be effectively used as a heating device.

  In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and other image forming apparatuses such as a copying machine and a facsimile apparatus, or their functions are used. Other image forming apparatuses such as a multi-function machine in combination with the above may be used. The same effect can be obtained by applying the present invention to an image heating apparatus used in these image forming apparatuses.

Front view and perspective view showing discharge separation guide of image forming apparatus in first and second reference examples and first embodiment Schematic showing the image forming apparatus Cross-sectional view of the fixing device of the image forming apparatus in the first reference example Schematic showing the circulation of steam in a fixing device without an opening Schematic showing the steam circulation of the fixing device in the first reference example Schematic showing the operation of the discharge separation guide and shielding plate of the image forming apparatus in the second reference example Schematic showing the operation of the discharge separation guide and shielding plate of the image forming apparatus in the second reference example Schematic showing the circulation of steam generated at the fixing nip Schematic showing the circulation of steam of the fixing device in the first embodiment Schematic showing the circulation of steam when the shielding plate in the first embodiment is used (A) is a schematic sectional view showing a conventional fixing device, and (b) is a schematic longitudinal view showing a conventional fixing device.

Explanation of symbols

N: Fixing nip (pressure nip)
P: Recording material 11: Fixing device (image heating device)
16 ... Fixing inlet guide 20 ... Discharge separation guide (guide member)
21 ... Separation guide rib 22 ... Opening 23 ... Discharge sensor (detection means)
24: Shield plate (opening / closing member)
25 ... Cooling fan 26 ... Louver 27 ... Shield plate 28 ... Bottom hole 29 ... Air passage 30 ... Heating means 31 ... Heater stay 32 ... Film 33 ... Heater 34 ... Pressure roller (pressure member)

Claims (2)

Image forming means for forming a toner image on a recording material;
A heating rotator, a pressure roller that contacts the heating rotator to form a nip portion, and a guide surface that guides a surface of the recording material facing the pressure roller on the downstream side of the nip portion. A fixing member for fixing the toner image to the recording material by heating the recording material carrying the toner image while conveying the recording material at the nip portion, and a guide member provided with an opening on the guide surface;
A blower that blows air so that air near the pressure roller is discharged from the opening to the outside of the fixing unit;
The air by the blowing means flows along the outer peripheral surface of the pressure roller in the direction opposite to the rotation direction of the pressure roller, and then the recording material on the outer peripheral surface of the pressure roller and the guide surface of the guide member An image forming apparatus, wherein the image forming apparatus is discharged from the opening through a gap formed with an end on the upstream side in the transport direction. The image forming apparatus according to claim 1, wherein air discharged from the opening to the outside of the fixing unit is discharged to the outside of the apparatus.