JP2011164260A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent paper from being stuck to a heat roller of a fixing device. <P>SOLUTION: The fixing device includes a heat rotator 21 and a pressure rotator 22 where a paper sheet is passed through a fixing nip 23 formed by pressing the pressure rotator 22 to the heat rotator 21 to fix an image. A gas discharge outlet for spraying separating gas toward the tip side of the paper sheet delivered from the fixing nip 23 and a gas supply part are provided close to the heat rotator 21, and the gas discharge outlet is installed so that a spraying position to the heat rotator 21 is shorter than the length of an image deletion amount L on the peripheral surface in the rotating direction of the heat rotator 21 with reference to the paper delivery side end of the fixing nip part 23, whereby the paper sheet can be surely prevented from sticking to the heat rotator, uneven glossiness at the leading end and the occurrence of blister caused by a separation failure in fixing can be suppressed, furthermore, the occurrence of jam can be prevented, and a flaw and a contamination caused by mechanical separation can be prevented. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a fixing device that fixes an image formed on a sheet by heating and pressing, and an image forming apparatus including the fixing device.

When forming an image based on image data, the toner image formed on the photoconductor is transferred directly or indirectly to a sheet via a transfer belt, and then the toner image is heated and pressed by a fixing device. To fix.
The fixing device includes a pressure roller and a heating roller, and a fixing nip portion is formed by pressing the pressure roller against the heating roller. By passing the sheet through the fixing nip portion, the image positioned on the heating roller side is heated and fixed.
By the way, in the above fixing device, when the fixing nip portion is discharged, the paper is stuck to the heating roller side by the heated and melted toner, and the paper is curled or the fixed image is unevenly glossy or blistered. There is a problem of doing.
For this reason, means for peeling the paper stuck to the heating roller has been proposed. For example, in the prior art of Patent Document 1, a peeling claw is described that is peeled off by being applied to a sheet attached to a heating roller. However, since the peeling claw has a problem that image damage occurs when it comes into contact with an image, a method of peeling by peeling air instead of a mechanical peeling method has been proposed (for example, Patent Document 1, 2).
In this method, air is blown out through a nozzle, an air flow path is formed in the direction of the contact position between the heating roller and the pressure roller, and the paper stuck to the heating roller is peeled off.

Japanese Utility Model Publication No. 62-164364 JP 2006-113342 A

  However, the above-described peeling method using air is intended to peel off the paper stuck to the heating roller, so that air can be sent to the leading edge of the stuck paper at a position away from the fixing nip. The air blowing position is set. However, once the sheet is discharged from the fixing device while sticking to the heating roller, excessive heating is performed on the sticking portion. For this reason, even if paper separation is performed smoothly by blowing air, it is unavoidable that abrupt curling at the leading edge of the paper and gloss unevenness at the leading edge of the fixed image are unavoidable, leading to a reduction in the quality of the output. Especially in the field where high quality image output is required, the deterioration of the quality becomes a big problem.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fixing device and an image forming apparatus that can prevent occurrence of uneven glossiness of images and paper curl during fixing.

That is, the fixing device of the present invention has a heating rotator and a pressure rotator, and the fixing nip formed by pressing the pressure rotator against the heating rotator is unfixed or unfixed. A fixing device that fixes an image through a sheet on which a complete image is formed,
A gas discharge port that blows a peeling gas toward the leading end side of the paper discharged from the fixing nip portion in the vicinity of the heating rotator; and a gas supply unit that supplies the peeling gas to the gas discharge port; With
The gas discharge port has a spraying position with respect to the heating rotator at a leading end side in the sheet discharge direction of the sheet on a circumferential surface in a rotation direction of the heating rotator with reference to a discharge side end of the fixing nip portion. It is installed so that it may become below the length of an image whiteout amount.
An image forming apparatus according to the present invention includes the fixing device according to the present invention and an image forming unit that performs image formation.

  According to the present invention, when the paper portion on which the image is formed is discharged from the discharge side end portion of the fixing nip portion, or before that, the peeling gas is reliably blown to the front end portion of the paper. The paper is prevented from sticking to the rotating body, and the paper is prevented from suddenly curling and uneven gloss.

  The fixing device includes a heating rotator and a pressure rotator, and representative examples of the rotator include rollers and belts. However, the present invention is not limited to a specific one. The heating rotator and the pressure rotator come into contact with each other, and the fixing nip is formed by pressing the heating rotator with the pressure rotator. The fixing nip portion has a predetermined length in the sheet passing direction, and the image is fixed when the sheet passes through this portion. In the present invention, the length of the fixing nip portion is not particularly limited, and the discharge side end of the fixing nip portion where the contact between the heating rotator and the pressure rotator is released and the sheet is discharged is provided. It becomes the standard for gas outlet installation.

The stripping gas used in the present invention is usually air. The air can be easily used by taking in the surrounding air with a gas supply unit constituted by a fan or the like.
The gas discharge port preferably has a nozzle shape having a guide inner surface in consideration of the blowing direction in the vertical direction of the opening. Further, the gas discharge port desirably has a width larger than the maximum width of the sheets to be fixed in the width direction, and further, a width equal to or smaller than the width direction of the heating rotator. It is desirable to set the direction length.
By extending the gas discharge port in the width direction with a width larger than the maximum width of the paper, it is possible to prevent the temperature gradient and temperature distribution of the heating rotator in the width direction, and the surface of the heating rotator to have a uniform temperature. Thus, the quality of the fixed image can be maintained satisfactorily. When a temperature distribution or the like occurs in the width direction in the heating rotator, gloss unevenness or the like occurs.
Moreover, since it is useless even if the width of the gas discharge port exceeds the length in the width direction of the heating rotator, it is desirable to make the width equal to or less than the length in the width direction of the heating rotator.
Note that when the gas is blown out from the gas discharge port extending in the width direction, it is desirable to supply the gas from the gas supply unit so that the wind speed distribution is substantially uniform in the width direction. For this reason, you may make it arrange | position and use a some gas supply part along the width direction so that it may respond | correspond to the width direction of a gas exhaust port.

  The gas discharge port has a spraying position equal to or less than the length of the image blank on the front end side of the sheet on the circumferential surface in the rotation direction of the heating rotator with reference to the discharge side end of the fixing nip. Installed. In order to prevent the image forming unit from being contaminated by the toner, the image blank area sets an area where no image is formed on the periphery of the paper, and the image blank area controls the image formation. Set by the image formation control unit. Some image blanking amounts can be changed. For this reason, it is desirable to determine the installation of the gas discharge port based on the minimum image whiteout amount within a settable range. Thereby, even when the image whiteout amount is changed, the sticking of the paper in the fixing device can be surely prevented.

  In addition, the spray position by a gas exhaust port can be determined based on the opening direction of a gas exhaust port. A position where the opening direction and the peripheral surface of the heating roller intersect can be regarded as a gas spray position. The opening direction of the gas discharge port can be determined by the center line direction of the extending direction of the inner surface of the upper and lower guides of the opening.

  Moreover, the spray position by a gas exhaust port can be determined based on the direction which shows the highest intensity | strength in the vertical wind speed distribution of the gas for peeling blown from a gas exhaust port. That is, the position where the direction and the peripheral surface of the heating roller intersect can be regarded as the gas blowing position.

  The gas blowing direction can usually be determined by the opening direction of the gas discharge port described above, and the opening direction and the direction showing the highest intensity in the wind speed distribution are usually the same. However, when it is difficult to determine the opening direction due to the shape of the opening or the like, the spraying direction, that is, the spraying position with respect to the circumferential surface of the heating roller, can be determined based on the direction showing the highest intensity in the wind speed distribution.

Note that the gas spraying is desirably started with the start of a job for image formation, and the gas spraying operation is preferably started a predetermined time before the sheet is passed through the fixing device.
When the gas is sprayed, the temperature of the heating rotator to which the peeling gas is sprayed decreases. On the other hand, the heating rotator is provided with heating means, and the heating means is controlled so as to reach a predetermined temperature by detecting the temperature on the surface of the heating rotator. When gas is blown and the surface temperature of the heating rotator is lowered, the heating rotator is heated by the heating means and adjusted to a predetermined temperature, so that a certain amount of time is required. Therefore, assuming this time, it is desirable to start the gas spraying operation at an earlier time than the sheet passing through the fixing device.

The gas spraying may be performed by adjusting the presence / absence of spraying and the amount of spraying according to the type of paper to be fixed. These controls are performed by the gas supply control unit. For example, in the case of thick paper, the curling of the paper is difficult to occur, and the sticking of the paper to the heating rotator is also difficult to occur. Therefore, the gas may not be sprayed. In this case, the sheet information is grasped by a control unit that controls image formation, and the presence or absence of gas supply can be controlled based on the sheet information. It is also possible to perform control to change the amount of gas sprayed according to the type of paper. In these cases, it is possible to store in a storage unit such as a flash memory whether or not the supply of the peeling gas and the amount of spraying are changed depending on the type of the paper, and the gas supply can be controlled based on the paper information. .
When the image forming apparatus and the gas supply control are performed by the control unit in the image forming apparatus, the image forming control unit and the gas supply control unit are included in the control unit. The gas supply control unit may be included in the fixing control unit that controls the fixing device.
Moreover, you may enable it for an operator to select whether the gas for peeling is sprayed by an operation part.

  The fixing device may be incorporated as a mechanism in the image forming apparatus, or separate from the image forming apparatus and incorporates paper conveyed from the image forming apparatus for fixing. May be. The fixing device may be provided outside the image forming apparatus and the image forming apparatus. The fixing device usually includes a pair of heating rotators and pressure rotators, but may include a plurality of pairs. In that case, the gas discharge port may be installed for all pairs of heating rotators and pressurizing rotators, and some pairs of heating rotators and pressurizing rotators may be provided. On the other hand, the gas outlet may be installed.

  As described above, according to the fixing device or the image forming apparatus of the present invention, the peeling gas is blown onto the heating rotator after the spraying position is properly determined, so that the sticking of the paper to the heating rotator is surely prevented. This can suppress uneven glossiness and blistering due to poor fixing separation, further prevent JAM, and prevent scratches and dirt due to mechanical separation. Furthermore, the paper passing performance is improved and the speed can be increased.

1 is a diagram schematically illustrating a fixing device of the present invention and an image forming apparatus including the fixing device. Similarly, it is a block diagram of an electric circuit. Similarly, it is an enlarged schematic view of the fixing device. Similarly, it is a figure which shows the heating rotary body further expanded. Similarly, it is a figure which shows the amount of image blanks of a paper. Similarly, it is a figure which shows the gas discharge nozzle and gas supply part which have a gas discharge port. Similarly, it is a figure explaining the gas blowing direction. Similarly, it is a flowchart which shows the procedure of gas spraying control. Similarly, it is a figure which shows the example of a change of a gas discharge nozzle. FIG. 4 is a diagram illustrating an outline of another embodiment of the fixing device of the present invention and an image forming apparatus.

Hereinafter, an embodiment of the present invention will be described.
FIG. 1 shows an image forming apparatus including a fixing device of the present invention.
As shown in FIG. 1, the image forming apparatus 1 includes a printer unit 10, a fixing device 20, and the like.
The printer unit 10 performs electrophotographic image forming processing based on input print data, and includes a sheet feeding tray, a sheet feeding / conveying unit 11, an image forming unit 13, a fixing device 20 and the like (not shown). Configured.

  The sheet feeding / conveying unit 11 conveys a sheet conveyed from a sheet feeding tray or a manual feed tray (not shown) to the image forming unit 13 through a plurality of intermediate rollers, registration rollers 12 and the like. Further, the paper feeding / conveying section 11 carries out image fixing with the fixing device 20 on the sheet having undergone the single-sided image formation processing by switching the conveyance path, and then conveys the sheet to the double-sided conveyance path 14, and the intermediate roller and the registration roller 12 again. Then, it can be conveyed to the image forming unit 13 to form an image on both sides of the paper.

The image forming unit 13 includes a charging device, an exposure device, a developing device, a transfer roller, and a cleaning device disposed around the photosensitive drum.
Specifically, an electrostatic latent image is formed by irradiating the photosensitive drum charged by the charging device with light according to the image data from the exposure device. The developing device develops the electrostatic latent image by attaching charged toner to the surface of the photosensitive drum on which the electrostatic latent image is formed. The toner image is transferred onto the paper from the photosensitive drum to which the toner is attached by the developing device. After the toner image is transferred to the photosensitive drum, residual charges, residual toner, and the like on the surface are removed by a cleaning device (not shown).

  The sheet on which the toner image has been transferred is conveyed to the fixing device 20 by the sheet feeding / conveying unit 11 and fixed. The fixing device 20 includes a heating rotator 21 that is a heating rotator having a heat source, and a pressure rotator 22 that presses against the heating rotator 21 to form a fixing nip portion 23. Heat fix the image. Examples of the heating rotator 21 include a heating roller and a heating belt, and examples of the pressure rotator include a pressure roller and a pressure belt. The paper on which the toner image is fixed is carried out from the carry-out port.

FIG. 2 is a block diagram showing an electrical circuit of the image forming apparatus 1.
The control unit 2 controls the entire image forming apparatus, and mainly includes a CPU and a program for operating the CPU.
The storage unit 3 is set and stored with operation parameters of the image forming apparatus, paper information, and supply gas supply operation parameters based on the paper information, and the control unit 2 stores the operations stored in the storage unit 3. The parameters and the like are read and the operation of the image forming apparatus 1 is controlled.
The operation unit 4 is controlled by the control unit 2 and performs various operation inputs by the operator. The operation unit 4 can be configured by a touch panel that also serves as a display unit.
Further, the image forming unit 13 and the fixing device unit 20 are connected to the control unit 2 in a controllable manner, and a gas supply unit 33 described later is also connected in a controllable manner.
Therefore, the control unit 2 functions as an image formation control unit and a gas supply control unit of the present invention.

In the fixing device 20, as shown in FIG. 3, a fixing nip portion 23 is formed with a predetermined length when the pressure rotator 22 presses the heating rotator 21. A gas discharge nozzle 30 that blows air as a peeling gas toward the heating rotator 21 is disposed at the sheet discharge destination of the fixing nip portion 23.
The arrangement position of the gas discharge nozzle 30 is determined by the position at which the air blown from the gas discharge port 31 at the tip of the gas discharge nozzle 30 is blown onto the peripheral surface of the heating rotator 21.

  FIG. 4B shows a conventional fixing device, and the air blowing position is at a position that is considerably away from the discharge side end of the fixing nip portion 53 on the peripheral surface of the heating rotator 51. An air discharge nozzle (not shown) is installed according to the air blowing position.

  On the other hand, in the embodiment of the present invention, as shown in FIG. 4A, the gas discharge port (not shown) is based on the discharge side end of the fixing nip portion 23 on the peripheral surface of the heating rotator 21. Thus, the spraying position is arranged at a position that is the same as or shorter than the image whiteout amount L. FIG. 4A shows a case where the spray position is the same distance as the image whiteout amount L from the discharge side end of the fixing nip 23, that is, the farthest.

As shown in FIG. 5, the image whiteout amount indicates the length of each area set in a quadrilateral frame shape on the paper P on which image formation is performed, and the image forming unit 13 performs image formation. It is a part that is not broken. The image blanking amount is stored in advance in the storage unit 3 as an initial setting, and the control unit 2 reads out this data and disables image formation in the area indicated by this length when forming an image. In addition, when the control unit 2 can set the length of the image whiteout amount, the set length is stored in the storage unit 3. In addition, a settable range can be determined in advance and stored in the storage unit 3, and the length of the image whiteout amount can be set within this range.
Note that when the image whiteout amount is different between the front end, the rear end, and the left and right ends in the transport direction, the image whiteout amount at the front end in the transport direction is used in the present invention.

FIG. 6 is a diagram illustrating details of an example of the gas discharge nozzle 30.
The gas discharge nozzle 30 has a plurality of gas discharge passages 32 arranged in parallel along the width direction, and merges on the gas discharge side to form a single long gas discharge port 31.
The gas discharge port 31 extends in the width direction with a length exceeding the sheet width of the sheet having the maximum width among the sheets passed through the heating rotator 21, and the width direction of the heating rotator 21. The width direction length is set to be equal to or less than the length.
The gas discharge path 32 has guide inner surfaces 32a and 32b which are inclined so that the distance between the gas discharge path 31 becomes smaller toward the gas discharge port 31, and a gas supply section is provided on the base side of the gas discharge path 32, respectively. Fans corresponding to 33 are provided, respectively, so that air is supplied from the outside toward the gas discharge path 32. By installing a plurality of gas supply units in parallel, it is possible to equalize the blowing wind force in the width direction.

In the gas discharge nozzle 30, the center line direction of the guide inner surfaces 32 a and 32 b is the blowing direction, and the position where the center line direction intersects the heating rotator 21 is the blowing position.
Further, as shown in FIG. 4A, the blowing direction at the blowing position is preferably within a range from the horizontal direction to the tangential direction with respect to the blowing position. The spray direction is more preferably the horizontal direction. This is because the gas flow extends from the spraying position along the peripheral surface of the heating rotator to the upstream side in the sheet conveyance direction. In addition, the tangential direction has an advantage that it does not interfere with the sheet passing.
It is desirable that the blowing position is as close as possible to the discharge side end of the fixing nip (for example, an interval of about several mm).

In the above, the blowing position is determined by the discharge nozzle opening method, and this embodiment is shown in FIG.
In the discharge nozzle 40 of FIG. 7A, a second gas discharge path 43 is provided substantially downward in the horizontal direction on the lower end side of the gas discharge path 42 extending downward, and upper and lower guides of the gas discharge path 43. The center line direction in the guide direction of the inner surfaces 43a and 43b is the opening direction, and is the direction in which gas is blown.
In the discharge nozzle 50 of FIG. 7B, the gas blowing direction is the direction showing the highest intensity in the wind velocity distribution of the gas in the vertical direction, not the opening direction of the gas discharge port. The position where the spray direction and the peripheral surface of the heating rotator intersect is the spray position.

Next, a control procedure for gas blowing in the fixing device will be described with reference to the flowchart of FIG. In this control procedure, the gas spraying operation is performed when the paper is thin, and the gas spraying operation is not performed when the paper is not thin.
First, as the job is executed, a gas spray control procedure is started.
The control unit 2 determines whether the sheet is thin based on the sheet information of the job (step s1). If the paper is not thin (NO in step s1), the paper is hardly stuck to the heating rotator, and the procedure ends. On the other hand, when the paper is thin (step s1, YES), the air separation fan as the gas supply unit is operated (step s2). The fan operation may be started immediately on the basis of the determination result, and a predetermined time is ensured until the first sheet reaches the fixing device, and a time is set after the job starts. The fan may be activated.

As the paper passes through the fixing device, it is determined whether or not the passed paper is the last page of the job (step s3). If the paper of the last page does not pass through the fixing device (step s3, NO), the operation of the air separation fan is continued. On the other hand, when the paper of the last page passes through the fixing device (step s3, YES), the operation of the air separation fan is stopped (step s4).
According to the above procedure, when gas separation is necessary, the operation of supplying gas is performed, and separation of paper is effectively prevented.
In the above, the presence or absence of gas spraying is determined depending on whether or not the paper is thin paper. However, the separation gas may be sprayed regardless of the paper information, and the operator setting via the operation unit may be performed. Thus, the presence or absence of gas spraying may be determined according to the type of job or paper.

There are various types of gas discharge nozzles.
In FIG. 9A, a fan 64 that is a gas supply unit is installed downward, a gas flow path 63 is provided below the fan 64, and a substantially horizontal gas flow path 62 is provided at the lower end of the gas flow path 63. The gas supply nozzle 60 is shown, and a gas discharge port 61 is provided at the tip of the gas flow path 62. In this configuration, the gas flow is sent downward along the gas flow path 63, the direction of the gas flow is changed at the intersection of the gas flow path 63 and the gas flow path 62, and the gas flow direction becomes substantially horizontal, and then from the gas discharge port 61. A peeling gas is blown out.

  In FIG. 9B, a fan 75 as a gas supply unit is installed in a horizontal direction, a slightly downward gas flow path 74 is provided in front of the fan 75, and a further downward gas flow path is provided at the tip of the gas flow path 74. The gas supply nozzle 70 to which 73 is connected is shown. A substantially horizontally oriented gas flow path 72 is provided at the lower end of the gas flow path 73, and a gas discharge port 71 is provided at the tip of the gas flow path 72. In this configuration, the gas blown horizontally from the fan 75 flows slightly downward along the gas flow path 74 and is further sent downward along the gas flow path 73. The direction of the gas flow is changed at the intersection of the gas and becomes substantially horizontal, and the peeling gas is blown out from the gas discharge port 71.

  As described above, various modifications can be considered for the shape of the flow path from the gas supply unit to the gas discharge port, and the present invention is not particularly limited.

  In the above description, the fixing device is described as being housed in the image forming apparatus, but in the following, a fixing device provided separately from the image forming apparatus will be described. Note that the image forming apparatus is also provided with a fixing device, and the fixing device outside the image forming apparatus is used as a second fixing device for the purpose of improving gloss and the like. Hereinafter, a description will be given with reference to FIG.

  The image forming apparatus 1 includes a printer unit 10, a fixing device 20, and the like, as in the above embodiment. The printer unit 10 includes a paper feed tray, a paper feed transport unit 11, and an image forming unit 13 (not shown). And a fixing device 20. Note that details are the same as those in the above embodiment, and a description thereof will be omitted.

A fixing device 100 is connected to the paper discharge side of the image forming apparatus 1. An image is formed in the image forming apparatus 1, and the sheet on which the first fixing is performed is carried out to the fixing device 100. The
One end of the sheet feeding / conveying unit 101 is located on the carry-in side of the fixing device 100. The paper feeding / conveying unit 101 branches into a paper feeding / conveying unit 102 and a bypass path 103 immediately after being carried in, so that the conveyance can be switched. A fixing unit 110 is interposed in the paper feeding / conveying unit 102, and the paper feeding / conveying unit 102 and the bypass path 103 join on the downstream side of the fixing unit 110.

The fixing unit 110 includes a heating rotator 111 having a heat source and a pressure rotator 112 that presses against the heating rotator 111 to form a nip portion 113, and heat-fixes the toner image transferred onto the sheet. A gas discharge nozzle 120 is disposed on the paper discharge side of the heating rotator 111. A gas supply unit (not shown) is connected to the gas discharge nozzle 120, and the tip of the gas discharge nozzle 120 serves as a gas discharge port 121.
The gas discharge port 121 is sprayed on the peripheral surface of the heating rotator 111 at a position that is the same as or shorter than the image whiteout amount L with reference to the discharge side end of the fixing nip portion 113 as in the embodiment. It is arranged so that there is a position. Further, the gas discharge port 121 extends in the width direction with a length exceeding the paper width of the paper having the maximum width among the papers passed through the heating rotator 111. The width direction length is set to be equal to or less than the width direction length.
The blowing position of the gas discharge port 121 is regarded as a position where the opening direction, that is, the guide direction center line direction of the upper and lower guide inner surfaces intersects the peripheral surface of the heating rotator 111.
Further, when it is difficult to determine the opening direction, the position where the direction showing the highest intensity in the wind velocity distribution in the longitudinal direction of the gas and the peripheral surface of the heating rotator 111 is regarded as the spray position.
The fixing device 100 includes a fixing control unit 130 that controls the entire fixing device 100, and the fixing control unit 130 is connected to the fixing unit 110 and a gas supply unit (not shown) in a controllable manner. Further, the image forming apparatus 1 includes a control unit 2 that controls the entire image forming apparatus 1 as in the above-described embodiment, and the fixing control unit 130 is further connected to the control unit 2 in a controllable manner. Therefore, the fixing control unit 130 can control the presence or absence of gas supply in the gas supply unit based on the paper information notified from the control unit 2.

  In this embodiment, the fixing device 100 is described as having a gas discharge port. However, the fixing device 20 provided in the image forming apparatus 1 shown in FIG. 10 may similarly have a gas discharge port. Further, the fixing device may not have a gas discharge port, and only the fixing device 100 may have a gas discharge port.

  Although the present invention has been described based on the above-described embodiment, the present invention is not limited to the description of the above-described embodiment, and naturally, appropriate modifications can be made within the scope of the present invention. is there.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Control part 3 Memory | storage part 13 Image forming part 20 Fixing apparatus 30 Gas exhaust nozzle 31 Gas exhaust port 33 Gas supply part 100 Fixing apparatus 120 Gas exhaust nozzle 121 Gas exhaust port 130 Fixing control part

Claims (17)

Passing through a sheet having a heating rotator and a pressure rotator and having an unfixed or incompletely fixed image formed in a fixing nip formed by pressing the pressure rotator against the heating rotator. A fixing device for fixing an image,
A gas discharge port that blows a peeling gas toward the leading end side of the paper discharged from the fixing nip portion in the vicinity of the heating rotator; and a gas supply unit that supplies the peeling gas to the gas discharge port; With
The gas discharge port has a spraying position with respect to the heating rotator at a leading end side in the sheet discharge direction of the sheet on a circumferential surface in a rotation direction of the heating rotator with reference to a discharge side end of the fixing nip portion. A fixing device, wherein the fixing device is installed so as to be equal to or less than a length of an image blank area.   The fixing device according to claim 1, wherein the spray position is a peripheral surface position of the heating rotator in an opening direction of the gas discharge port.   The fixing device according to claim 2, wherein the opening direction is a center line direction of the upper and lower inner surfaces of the gas discharge port.   The said spraying position is a peripheral surface position of the said heating rotary body in the direction which shows the highest intensity | strength in the wind speed distribution of the gas which blows off from the said gas exhaust port. The fixing device described.   The fixing device according to claim 1, wherein a blowing direction of the gas discharge port is within a range from a horizontal direction with respect to the blowing position to a tangential direction of the heating rotating body.   The fixing device according to claim 1, wherein the gas discharge port has upper and lower guide inner surfaces extending in a substantially blowing direction.   The fixing device according to claim 1, wherein the image whiteout amount is set by an image formation control unit that controls the image formation.   The fixing device according to claim 7, wherein the gas discharge port is installed so as to be equal to or less than a minimum length within a range of the image blanking amount that can be set.   The gas supply control unit that controls the operation of the gas supply unit, wherein the gas supply control unit controls gas supply based on sheet information obtained by the image formation control unit. The fixing device according to 7 or 8.   The fixing device according to claim 9, wherein the control of the gas supply is adjustment of the presence / absence of gas supply and / or a blowing amount.   The fixing device according to claim 1, wherein the gas discharge port extends in the width direction with a length exceeding a paper width of the paper having the maximum width.   The fixing device according to claim 11, wherein the gas discharge port extends in a width direction not more than a length in a width direction of the heating rotator.   The fixing device according to claim 1, wherein the heating rotator includes a heating roller, and the pressure rotator includes a pressure roller.   14. A plurality of heating rotators and pressurizing rotators to be paired, wherein the gas discharge port is provided for at least a pair of heating rotators and pressurizing rotators. The fixing device according to any one of the above.   The fixing device according to claim 1, wherein the fixing device is disposed in an image forming apparatus that forms an image on a sheet.   The fixing device according to claim 1, wherein the fixing device is disposed outside an image forming apparatus that forms an image on a sheet and is connected to the image forming apparatus.   An image forming apparatus comprising: the fixing device according to claim 1; and an image forming unit that forms an image on a sheet.

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