JP2005316397A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing image failure resulting from a temperature increase of a belt when images are consecutively formed on a plurality of recording materials. <P>SOLUTION: The image forming apparatus includes: an image forming means for forming an image on a recording material; a heating member heating the image formed on the recording material in a nip portion; an endless belt conveying the recording material toward the nip portion formed between itself and the heating member; and a contacting and separating device for bringing the heating member and the belt into the contact with each other and for separating the heating member and the belt from each other. When images are continuously formed on a plurality of recording materials, a separating operation can be executed by the contacting and separating device during a time period after the immediately preceding recording material passes through the nip portion and before the subsequent recording material arrives at the nip portion. Between sheets of paper during the job of consecutive image formation, the pressure belt 10 is separated from a fixing roller 1 by a detaching mechanism 64. This prevents an unnecessary increase in the temperature of the pressure belt 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material, for example, an image forming apparatus such as a copying machine, a printer, and a FAX.

  Conventionally, in an electrophotographic image forming apparatus, a toner image as a developer image is formed on a recording material such as paper by an image forming method called a Carlson process, and then the toner image is fixed as a permanent image. It was. Various fixing methods for this purpose have been proposed, but in terms of fixing properties, a heat-pressure fixing method in which a toner image is fixed by heating and pressurization is generally used, and in particular, a pair of heating sources are included. 2. Description of the Related Art A roller type fixing device (roller fixing) that fixes a toner image by directly contacting the rotating body is often used.

  In other words, a roller pair of a fixing roller (heat roller) whose temperature is adjusted to a predetermined fixing temperature and a pressure roller that is in pressure contact with the roller is basically configured. A recording material on which an unfixed toner image is formed is introduced into the fixing nip portion, which is a pressure contact portion, and is nipped and conveyed to fix the unfixed toner image on the recording material with heat from the fixing roller and the fixing nip portion pressure. Is.

  Here, the amount of heat given to the recording material on which the unfixed toner image is placed depends on the temperature of the fixing roller and the pressure roller, the time for the recording material to pass through the fixing nip, that is, the fixing nip width and the recording material traveling speed. Depends on. The fixing nip width refers to the length of the fixing nip portion in the recording material traveling direction.

  As a fixing device to be mounted on an electrophotographic apparatus or the like having a higher process speed, a fixing device having a wider fixing nip width is required because of the above heat quantity. In order to widen the fixing nip width in the above roller fixing, it is necessary to increase the diameter of the roller. When the diameter of the roller is increased, the heat capacity of the roller increases and the heat-up time (warm-up time) of the roller becomes longer. There are problems such as.

  Therefore, Patent Document 1 proposes a belt-type fixing device as a fixing device configuration that can ensure a wide fixing nip width without increasing the diameter of the roller.

  In such a belt type fixing device, a heat-resistant and flexible endless belt stretched between a plurality of belt stretching members is brought into pressure contact with a fixing roller which is a rotating body for heating. A nip is formed, and a recording material carrying an unfixed toner image is sandwiched and conveyed in the fixing nip, thereby fixing the unfixed toner image to the recording material with the heat of the fixing roller and the fixing nip pressure. It is something to be made. In this belt-type fixing device, the fixing nip width can be easily set large by adjusting the width of the endless belt against the fixing roller of the endless belt. Further, since the fixing nip width can be secured without depending on the diameter of the fixing roller, the fixing roller can have a small diameter and a small heat capacity, and the start-up time can be shortened.

  By the way, the recording material used in the image forming apparatus includes a resin-coated paper (hereinafter referred to as coated paper) having a high glossiness on the surface or both surfaces of the recording material, which is coated on the front surface or both surfaces of the recording material with acrylic resin or polyolefin resin. ) Exists.

  However, when the toner passes on the coated paper and passes through the fixing device, an image defect called a blister in which the recording material is partially deformed in a fire may occur. This is because the moisture inside the coated paper evaporates due to the heating by the fixing device, and the volume expands, but the vaporized water vapor is not uniformly diffused to the outside of the coated paper by the coated layer on the coated paper surface. It is generated by breaking the coat layer because it is intensively discharged to the outside from a thin part or a missing part.

  Further, in such a fixing device, it can be said that the fixing nip width is wide so that the time during which the fixing roller and the belt are in contact with each other becomes longer and the belt temperature is likely to rise. Furthermore, since the heat capacity of the belt is smaller than that of a conventional pressure roller, the temperature of the belt rises in a short period. That is, there is a problem that the above-mentioned image defect is likely to occur.

In order to improve this problem, Patent Document 2 proposes separating the belt and the fixing roller during standby as a method for reducing the amount of heat applied from the back surface of the recording material.
JP 61-132972 A Japanese Patent Application Laid-Open No. 11-194647

  However, the image forming apparatus described in Patent Document 2 has the following problems.

  In a continuous image forming job in which toner images are continuously formed on a plurality of recording materials, the fixing roller and the belt are in contact with each other even during a period in which the recording material does not exist in the fixing nip (so-called paper interval). When the heat is transmitted to the belt, the temperature of the belt rises, and the above-described image defect may occur. In particular, in a continuous image forming job in which a toner image is continuously formed on a plurality of resin-coated papers, a configuration in which the fixing speed is made slower than the normal speed or the above-described gap between the papers is made longer in consideration of fixability. The above problem was remarkable.

  An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of image defects due to the temperature rise of a belt when images are continuously formed on a plurality of recording materials.

  Further objects of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes an image forming unit that forms an image on a recording material, and a heating member that heats the image formed on the recording material at a nip portion. An image forming apparatus comprising: an endless belt that conveys a recording material toward the nip formed between the heating member; and a separating unit that separates the heating member from the belt. When the image is continuously formed, the separating unit can perform the separating operation during a period from when the previous recording material passes through the nip portion to when the next recording material reaches the nip portion. It is characterized by that.

  In order to achieve the above object, another typical configuration of the image forming apparatus according to the present invention includes an image forming unit that forms an image on a recording material, and heating that heats an image on the recording material at a nip portion. A heating means comprising: a member; and an endless belt that conveys the recording material toward the nip portion formed between the heating member; and a separating means that separates the heating member and the belt. An image forming apparatus comprising: an image forming apparatus having a separating operation performed by the separating unit in response to an interruption of an image forming job when an abnormal situation occurs during the image forming job.

  According to the configuration of the image forming apparatus according to the present invention, the image quality deteriorates from the middle of the continuous image forming job due to the temperature rise of the belt when images are continuously formed on a plurality of recording materials. Can be prevented.

<Overall configuration of image forming apparatus>
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to this embodiment. This image forming apparatus includes a laser beam scanning exposure type printer unit A, an image reader unit B, a document feeder C, and a finisher D using a transfer type electrophotographic process. In this example, devices for forming an image (unfixed image) on a recording material are collectively referred to as an image forming unit, and details of various devices constituting the image forming unit will be described below.

  The document feeding device C feeds the set documents O one by one from the first page in order on the platen glass 21 of the image reader unit B through a curved path, and moves the platen glass 21 over the platen glass 21. The paper is conveyed from left to right and discharged to the paper discharge tray 22.

  At this time, the reader scanner unit 23 of the image reader unit B is held at a predetermined fixed position on the lower side of the platen glass 21, and the image of the downward surface of the document passing over the platen glass 21 is sequentially flowed. Read photoelectrically by reading method.

  That is, the reader scanner unit 23 illuminates the downward surface of the document passing over the platen glass 21 with the light of the lamp 24 through the platen glass 21, and reflects the reflected light from the document surface of the illumination light to the mirrors 25 and 26. , 27, led to the image sensor 29 through the lens 28 to form an image, and the original image is photoelectrically read.

  The photoelectric reading of the document image by the image sensor 29 is performed by conveying the document onto the platen glass 21 by the document feeding device C and temporarily stopping the document. The reader scanner unit 24 and the mirrors 26 and 27 are moved along the lower surface of the platen glass 21. It can also be performed by an optical system moving system that moves from left to right.

  The electrical signal of the document image read by the image sensor 29 is subjected to image processing and sent to an exposure control unit (laser scanner) 30. The exposure control unit 30 outputs a laser beam L that is modulated in accordance with an electrical signal of the document image that has undergone image processing.

Reference numeral 31 denotes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined speed.
In the rotating state, the photosensitive drum 1 is subjected to a uniform charging process with a predetermined polarity and potential by a charger 32, and then subjected to scanning exposure with the laser light L output from the exposure control unit 30 on the charging process surface.

  Thereby, an electrostatic latent image corresponding to the scanning exposure pattern is formed on the surface of the photosensitive drum 31. The electrostatic latent image is developed as a toner image by the developing device 33.

  The toner image formed on the photosensitive drum 31 is transferred from the first or second paper feed cassette 36 or 37, the manual paper feed unit 38, or the double-sided conveyance path 39 to the transfer unit 34. Is transferred to a sheet S as a recording material fed from the sheet.

  The sheet S on which the toner image has been transferred in the transfer unit 34 is separated from the surface of the photosensitive drum 31 and is introduced into the fixing device 40 where the toner image is fixed.

  After the sheet is separated, the surface of the photosensitive drum 1 is cleaned by the cleaning device 35 after removal of residual deposits such as transfer residual toner and paper dust, and is repeatedly used for image formation.

  In the single-sided image forming mode, the sheet that has passed through the fixing device 40 serving as an image heating device is once guided to a path 42 by a flapper 41, and after the trailing edge of the sheet has passed through the flapper 41, the sheet is switched back to return the flapper. 41 guides to the discharge roller 43. As a result, the sheet is discharged from the printer unit A to the finisher D side by the discharge roller 43 with the image-formed surface facing downward (face down).

  In the mode in which a hard sheet such as an OHP sheet is supplied from the manual sheet feeding unit 38 to perform image formation, the sheet that has exited the fixing device 40 passes through the upper side of the flapper 41 without being guided to the path 42. The image forming surface is discharged from the discharge roller 43 in an upward state (face up).

  In the double-sided printing mode in which images are formed on both sides of the sheet, the sheet that has been subjected to the fixing process on the first side by the fixing device 40 is guided to the discharge roller 43 through the upper side of the flapper 41, and the sheet Immediately after the trailing edge passes through the flapper 41, the sheet is switched back, and is guided from the path 42 to the duplex conveyance path 39 by the flapper 41.

  Then, the toner image is transferred to the second side by feeding the sheet from the double-sided conveyance path 39 to the transfer unit 34 in a reverse state, and is again introduced into the fixing device 40 to perform the fixing process of the toner image on the second side. Let it be done.

  Thereafter, as in the case of the single-sided image forming mode described above, the sheet on which double-sided image formation has been performed is discharged from the printer unit A to the finisher D side by the discharge roller 43 in the discharge path.

  The finisher D performs processing such as shift processing, binding processing, and punching. Further, an inserter E is provided on the finisher D, and a cover sheet, a slip sheet, and the like are fed to the finisher D. Further, the alignment plate 44 moves to an angle perpendicular to the conveyance direction when the recording material is shifted and output, such as shift sorting, and discharges the sheet to the back or front of the tray 45.

<Operation panel>
Next, an operation panel as an operation unit for setting various modes by the operator will be described. FIG. 2 is a diagram illustrating a configuration of the operation panel 60 provided in the image forming apparatus. Reference numeral 400 denotes a copy start key for instructing the start of copying.

  Reference numeral 401 denotes a reset key for returning to the standard mode. Reference numeral 402 denotes a guidance key that is pressed when the guidance function is used. Reference numeral 403 denotes a numeric keypad for inputting a numerical value such as a set number of sheets. Reference numeral 404 denotes a clear key for clearing a numerical value. Reference numeral 405 denotes a stop key for stopping copying during continuous copying. Reference numeral 406 denotes a liquid crystal display unit and a touch panel for displaying various mode settings such as a staple mode, a bookbinding mode, and a double-sided print setting, and a printer status. Reference numeral 407 denotes an interrupt key for interrupting and taking an emergency copy during continuous copying or during use as a fax or printer. Reference numeral 408 denotes a personal identification key for managing the number of copies by individual or department. Reference numeral 409 denotes a soft switch for turning on / off the power of the image forming apparatus main body. Reference numeral 410 denotes a function key used when changing the function of the image forming apparatus. Reference numeral 411 denotes a user mode key for entering a user mode in which the user sets items in advance, such as ON / OFF of auto cassette change or a change in setting time until entering an energy saving mode.

Reference numerals 450 to 452 denote recording material type setting keys (means for setting the type of recording material used for image formation), an overhead projector transparency film (hereinafter referred to as an OHP sheet) as a light transmitting resin, This is a key for setting resin-coated paper, which is cardboard, paper having a resin layer on the front or back surface. In this embodiment, the cardboard is a recording material having a basis weight of 110 g / m ² or more. Reference numeral 453 denotes a key for performing duplex printing.

<Fixing device>
FIG. 3 is a schematic configuration model diagram of the fixing device 40 and a block diagram of a control system. The fixing device 40 is a belt-type heat and pressure fixing device.

  Reference numeral 1 denotes a fixing roller as a heating member (rotating body) including a heating source. In this fixing roller 1, a hollow cored bar 3 is covered with an elastic layer 4 such as silicon rubber, and the surface layer is further covered with a fluorine coating layer 5 as a release layer. Inside the fixing roller 1, a halogen lamp 6 as a heating source is disposed.

  The fixing roller 1 is disposed such that both ends thereof are rotatably supported between a rear side plate and a front side plate (not shown) of the fixing device via bearing members. Reference numeral 7 denotes a thermistor as a temperature detecting means for detecting the surface temperature of the fixing roller 1, and is disposed in contact with the surface of the fixing roller corresponding to the center of the sheet passing area.

  A belt unit 8 is disposed below the fixing roller 1. The belt unit 8 is disposed so as to be rotatably supported in parallel with each other between a unit frame 8a and a side plate 8b (a side plate on the front side not shown) on the back side and the front side of the unit frame 8a. The three rollers 13, 14, 15 as belt stretching members, the endless pressure belt 10 wound around the three rollers 13, 14, 15 and the inner side of the pressure belt 10 are arranged. It is an assembly such as the pressure pad member 11 provided.

  Then, the side plate 8b on the back side and the near side of the unit frame 8a is pivotally supported on the back side and the near side plate of the fixing device, respectively, so that the belt unit 8 is interposed between the back side and the near side plate of the fixing device. The shaft 8c is supported so as to freely swing up and down with respect to the fixing roller 1 around the pivot 8c.

  The pressure belt 10 is formed by molding a heat-resistant resin material such as polyimide into an endless belt shape.

  Of the above three rollers, the roller 13 is a recording material entrance side roller, and has a built-in heating source for heating the belt. The roller 14 is a tension roller that applies tension to the pressure belt 10, and the roller 15 is a recording material separation roller.

  The pressure pad member 11 is made of aluminum in a block shape, and is provided on the recording material inlet side by a push-up spring 18 provided between a back side of the unit frame 8a and a spring receiving seat 17 provided on the side plate 8b on the front side. The inner surface of the pressure belt portion between the roller 13 and the separation roller 15 is brought into a pressing contact state.

  Reference numeral 64 denotes an up-and-down swing mechanism as a separation unit of the belt unit 8 and can be constituted by, for example, an electromagnetic solenoid-plunger mechanism, a cam mechanism, a lever mechanism, or the like.

  The vertical swing mechanism 64 swings the belt unit 8 up and down with respect to the fixing roller 1 around the pivot 8c under the control of the control circuit section (control means) 61.

That is, by the vertical swing mechanism 64,
(1) As shown in FIG. 3, the belt unit 8 is rotated in the pulling direction with respect to the fixing roller 1 to bring the separation roller 15 into pressure contact with the fixing roller 1 with the pressure belt 10 interposed therebetween, and the separation. A first position where the outer surface of the pressure belt portion between the roller 15 and the recording material inlet side roller 13 is in contact with the lower surface of the fixing roller 1 (attachment operation);
(2) As shown in FIG. 4, the belt unit 8 is rotated downward from the fixing roller 1 so that the separation roller 15 and the pressure belt 10 are separated from the lower surface of the fixing roller 1 (de-operation). ),
It is configured to be freely switchable.

  The pressure belt 10 is brought into contact with and separated from the fixing roller 1 by the belt unit 8 that can freely swing up and down with respect to the fixing roller 1 around the pivot 8c and the vertical swing mechanism 64 of the belt unit 8. The contact / separation mechanism is configured.

  As shown in FIG. 3, in a state where the belt unit 8 is switched to the first position, the separation roller 15 is pressed against the fixing roller 1 with the pressure belt 10 interposed therebetween, and the recording material inlet side roller 13 and the separation roller 15 are pressed. The outer surface of the pressure belt portion between the contact surface and the lower surface of the fixing roller 1 is in contact with the lower surface of the fixing roller 1 by the belt pressure pad member 11 by the compression reaction force of the spring 18. As a result, a wide fixing nip portion N is formed between the fixing roller 1 and the pressure belt 10.

  The fixing process of the unfixed toner image t on the sheet S is performed in the state where the belt unit 8 is switched to the first position and the fixing nip portion N is formed between the fixing roller 1 and the pressure belt 10 as described above. Made.

  That is, the fixing roller 1 is rotationally driven at a predetermined speed in the clockwise direction of the arrow by the driving device 62 controlled by the control circuit unit 61. The pressure belt 10 is driven to rotate in the counterclockwise direction of the arrow as the fixing roller 1 is driven to rotate.

  Electric power is supplied from the power supply unit 63 to the halogen lamp 6 which is a heating source of the fixing roller 1, and the fixing roller 1 is heated by radiant heat from the halogen lamp 6.

  At that time, the surface temperature of the fixing roller 1 is detected by the thermistor 7, and the detected temperature is input as an electric signal to the temperature adjustment circuit unit 61 a of the control circuit unit 61.

  The temperature adjustment circuit unit 61a controls the power supply from the power source unit 63 to the halogen lamp 6 so that the electric signal corresponding to the temperature of the fixing roller input from the thermistor 7 is maintained at the electric signal corresponding to the predetermined temperature. The temperature of the surface of the fixing roller 1 is adjusted.

  In addition, the pressure belt 10 receives heat from a heating source built in the roller 13, and the temperature of the pressure belt 10 reaches a predetermined temperature before the start of the fixing operation. The electric power supplied to the heating source in the roller 13 is controlled so that the temperature is set to be lower than the temperature. Even after the start of the fixing operation, the power supplied to the heating source in the roller 13 is controlled so that the temperature of the pressure belt 10 maintains a predetermined temperature.

  When the fixing roller 1 is driven to rotate, the pressure belt 10 is also driven to rotate, and the fixing roller 1 is heated by the halogen lamp 6 and adjusted to a predetermined fixing temperature. A sheet S carrying an unfixed toner image is introduced from the side roller 13 side to the fixing nip portion N, and is nipped and conveyed through the fixing nip portion N. During this nipping and conveying process, the unfixed toner image surface of the sheet S is brought into close contact with the surface of the fixing roller 1, and the toner image is heated by the heat of the fixing roller 1, and is fixed to the surface of the sheet S by heat and pressure. The sheet S is separated from the surface of the fixing roller 1 by the biting (entrance) of the separation roller into the elastic layer 4 of the fixing roller 1 at the sheet exit portion of the fixing nip N, and is discharged and conveyed.

  Reference numeral 19 denotes a fan as belt cooling means. The fan 19 will be described later.

<Fixing control>
Hereinafter, fixing control in a continuous image forming job for continuously forming images on a plurality of recording materials will be described with reference to FIGS. Note that the sheet interval during the continuous image forming job is controlled so as to maintain a predetermined value. In other words, an image forming job in which a predetermined interval between sheets is maintained is called a continuous image forming job. The following fixing control is performed by the control circuit unit 61 which is a control means.

  The flowchart of FIG. 5 executes the operation of separating the pressure belt 10 from the fixing roller 1 according to the presence / absence of the desorption mechanism 64 during the continuous image forming job according to the recording material type set by the recording material type setting means. It is a flowchart for deciding whether or not to do.

  In step S100, any of the OHP sheet (light transmissive resin sheet) selection key 450, the thick paper selection key 451, and the coated paper (resin coated paper) key 452, which is a recording material type setting key on the operation panel 60, or By combining the keys, the job mode corresponding to the type of recording material used is set. The combination of keys refers to, for example, thick paper coated paper or thin paper coated paper, and is a state in which both the thick paper key and the coated paper key are selected.

The cardboard in the present example is a recording paper having a basis weight of 110 g / m ² or more, and the coated paper is a recording in which the surface layer or the front and back surfaces are coated with a resin such as an acrylic resin or a polyolefin resin. It is paper, and the OHP sheet is a resin having optical transparency, and specifically refers to a film made of a polymer resin material.

  Here, the mode setting in step S100 is a step of setting a job mode corresponding to the type of recording material used. Specifically, the job mode when “OHP sheet” is selected, the job mode when “thick paper” is selected, the job mode when “coated paper” is selected, and “plain paper” There are various job modes corresponding to the type of recording material used, such as a job mode when “is selected” and a job mode when “thin paper” is selected.

When the mode is determined, the recording material conveyance speed and the fixing roller temperature set for each mode are changed. In this example, assuming that the recording material conveyance speed is 1 for plain paper (basis weight is less than 110 g / m ² ), the OHP sheet, cardboard, and resin-coated paper have a speed of 1/3 in consideration of fixing properties. The interval between the OHP sheet, the thick paper, and the resin coated paper is naturally longer than that of the plain paper.

  In S101, an image forming job is started by pressing the copy start key 400 on the operation unit. When the image forming apparatus is used as a printer by connecting a personal computer or the like to the image forming apparatus via a LAN cable, an image forming job is started by a print command from the personal computer or the like. .

  First, it is determined whether the type of the recording material selected in S102 is an OHP sheet. If no OHP sheet is set, the process proceeds to S103. In S103, it is determined whether or not thick paper is set. If not set, the process proceeds to S104. In S104, it is determined whether or not coated paper is set.

  If it is not set, the process proceeds to S106, it is determined that the type of the recording material is plain paper or thin paper, and it is determined not to perform the operation of detaching the pressure belt 10 between the sheets in the continuous image forming job. During the continuous image forming job, the fixing roller and the pressure belt remain in pressure contact.

  If it is determined that at least one is set between S102 and S104, the process proceeds to S105, and it is determined to perform the detaching operation of the pressure belt 10 between the sheets in the continuous image forming job.

  In the case of plain paper or thin paper, the reason for “no desorption operation” in step S106 is that, in the case of plain paper or thin paper, even if the pressure belt 10 is heated, an image defect due to blistering (burning) may occur. This is because the durability is basically low (depending on conditions such as the amount of toner applied and the moisture content of the paper), and also to prevent a decrease in the durable life of the desorption mechanism 64 due to frequent desorption operations. .

  In this example, the purpose is to determine whether or not to perform the detaching operation of the pressure belt 10 according to the set recording material, and the paper type for performing the detaching operation is not limited to the above-described example, but as required. You can change it. That is, whether or not the pressure belt 10 is to be detached is determined depending on whether or not the selected recording material has a property of causing image defects such as blistering (burning) as the pressure belt is heated. Decide whether or not.

  Next, when the presence / absence of the desorption operation is determined, the process proceeds to S200 (FIG. 6).

  Next, FIG. 6 shows the control circuit 61, which is a control means, during the continuous image forming job, from when the previous recording material passes through the fixing nip until the next recording material reaches the fixing nip, that is, FIG. 6 is a flowchart when performing pressure belt attachment / detachment control between sheets (interval of recording materials). Details will be described below.

  S200 is the start of printing. Printing refers to a series of processes from formation of a latent image on a photoreceptor, development of the latent image, and transfer of the developed image onto a recording material.

  In S201, it is determined whether the recording material S has reached the predetermined position 150 (registration roller position in FIG. 1). This determination is based on a sheet presence / absence detection signal P1 (FIGS. 3 and 4) received by the control circuit unit 61 from a sheet sensor (not shown) disposed at the registration roller position and detecting that the recording material has reached. Alternatively, it is performed by a paper feed sequence.

  If there is no recording material, the process proceeds to S202, where it is determined whether the pressure belt 10 is in contact with the fixing roller 1.

  If the pressure belt is in contact, the pressure belt 10 is removed in S203, the drive of the pressure belt cooling fan 19 is started in S204, and the process returns to S201.

  If the pressure belt is separated from the fixing roller, the process proceeds to S205. If the pressure belt cooling fan is not in the driving state, the pressure belt cooling fan 19 is driven in S204 and the process returns to S201.

  If the pressure belt cooling fan 17 is being driven, the process directly returns to S201.

  When the recording material reaches the predetermined position 150 in S201, the process proceeds to S206.

  That is, when the recording sheet S is not present at the registration roller position 150 at the start of printing, the pressure belt 10 is separated from the fixing roller 1 by the detachment operation until the presence of the recording sheet is detected (FIG. 4). The cooling fan 19 is driven to prevent the temperature increase of the pressure belt 10.

  In S206, the process is divided depending on the presence / absence of the desorption operation determined in S100 to S106.

  First, the case where it is determined that the pressure belt 10 is attached and detached will be described.

  If there is a detaching operation, it is first determined in S207 whether the pressure belt 10 is in contact with the fixing roller 1.

If the pressure belt 10 is not in contact with the fixing roller 1, the process proceeds to S208, where the pressure belt 10 is applied to fix the unfixed toner image on the recording material, and the process proceeds to S209.
If the pressure belt 10 is in contact with the fixing roller 1 in advance, the process proceeds to S209.

  In S209, it is determined whether the pressure belt cooling fan 17 is being driven. If it is being driven, the driving of the pressure belt cooling fan 17 is stopped in S210, and the process proceeds to S211. If not, the process proceeds to S211.

  In S211, the recording material passes through the fixing nip, that is, waits for the fixing process to end.

  If the fixing process has been completed, it is determined in S212 whether all printing processes have been completed. If it is determined that the printing process has been completed, the process proceeds to S219. If not, the process proceeds to S213.

  In S213, the recording material interval Lm with the succeeding paper is determined. If Lm is equal to or larger than the predetermined recording material interval Lr, the process returns to S201.

  If the recording material interval Lm with the succeeding sheet is less than the predetermined recording material interval Lr in S213, the process returns to S207. In this case, the pressure belt 10 is not detached between the sheets, and the pressure belt remains in pressure contact with the fixing roller.

  Such a series of flows is repeated until the continuous image forming job is completed. When it is determined in S212 that the printing process is completed, the pressure belt is separated from the fixing roller (S219), and the cooling fan is turned on. Driving is started (S220), and a series of jobs is completed (S221).

  Next, the case where it is determined in S206 that the pressure belt 10 is not attached or detached will be described.

  If it is determined that there is no desorption operation, it is determined in S214 whether the pressure belt 10 is in contact.

  If it is determined that the contact state, the process proceeds to S216.

  If it is determined that the contact state is not established, the fixing process is performed, so that the pressure belt 10 is attached in S215, and the process proceeds to S216.

  In S216, it is determined whether or not the pressure belt cooling fan 17 is being driven. If it is being driven, the driving is stopped in S217, and if it is not being driven, the process proceeds to S218.

  In step S218, the process waits for all printing processes to be completed. During this time, the pressure belt is not detached regardless of the recording material interval.

  When all the printing processes are completed, the pressure belt 10 is detached at S219, the pressure belt cooling fan 17 is driven at S220, and the job is terminated at S221.

  Even if it is determined in S206 that the pressure belt 10 is attached / detached, or if it is determined that the pressure belt 10 is not attached / detached, during the standby period until the next job, the fixing roller 1 and the pressure belt 10 are disconnected. By performing de-operation and further cooling the pressure belt 10 with the pressure belt cooling fan 17 (S219, S220), it is possible to prevent the heat of the fixing roller 1 from being applied to the pressure belt 10 unnecessarily and pressurize at the same time. The belt 10 can be cooled, and the temperature of the pressure belt 10 can be prevented from being raised unnecessarily. When the next job start signal is input in the standby mode, the standby mode is returned to the normal mode, and the above-described image forming job is started.

  As described above, when the recording material to be used is an OHP sheet, cardboard, coated paper, or the like in which image defects such as blisters are likely to occur due to the temperature rise of the pressure belt 10, continuous images are used. By adopting a configuration in which the fixing roller 1 and the pressure belt 10 are desorbed even during a forming job, heat from the fixing roller 1 is prevented from being applied to the pressure belt 10 unnecessarily, such as a blister. The occurrence of image defects can be prevented.

  Accordingly, it is possible to prevent the image quality from being deteriorated in the middle of the continuous image forming job. In other words, it is possible to continue forming high quality images during a continuous image forming job.

  Next, with reference to the flowchart of FIG. 7, a description will be given of detachment control when an image forming job is interrupted due to an abnormal situation in which the image forming apparatus cannot continue image formation during the image forming job. This detachment control is also performed by the control circuit unit 61 which is a control means.

  When printing is started in S300, the process is divided according to the presence or absence of the detachment operation determined in S100 to S106 in S301.

  If there is no detachment control, the process waits for the completion of all print processing in S313, and the job is terminated in S314.

  At this time, the detachment control of the pressure belt 10 is not performed regardless of the job state.

  If the attachment / detachment control is present in S301, it waits in S303 whether the job is to be canceled.

  The interruption of the job in this example is performed due to, for example, no paper in the paper feed cassette as the recording material container, toner shortage in the developing device (no toner), jamming of the recording material in the recording material conveyance path, and the like. . Note that the abnormal state of the image forming apparatus is not limited to the above-described example, and can be appropriately set as necessary as long as image formation cannot be continued.

  3 and 4, P2 is a paper out signal, a toner shortage signal, a jam detection signal, etc., which are input to the control circuit unit 61. When this signal P2 is input, the control circuit unit 61 interrupts the job.

  If it is determined that the job is to be interrupted, the contact state of the pressure belt is checked in S304. If it is being separated, the process proceeds to S306. If it is being contacted, the process proceeds to S306. Perform demotion.

  Next, the driving state of the pressure belt cooling fan 17 is checked in S306, and if it is driven, the process proceeds to S308, and if not, the pressure belt cooling fan 17 is driven in S307.

  In step S308, the job waits for the job to be resumed. If the job is resumed, the contact state of the pressure belt 10 is checked again in step S309 and the drive state of the pressure belt cooling fan is checked in step S311. If there is, the landing operation is performed. If the pressure belt cooling fan 17 is being driven, the driving is stopped and the process returns to S302.

  As described above, even if an abnormal situation occurs in any place other than the fixing device in the image forming apparatus, that is, regardless of where the abnormal situation occurs in the image forming apparatus, the image forming job is By performing the separating operation of the pressure belt 10 during a period from the time when the image forming job is resumed to the time when the image forming job is resumed, the pressure belt 10 is prevented from being unnecessarily heated, and is formed after the image forming job is resumed. It is possible to prevent the quality of the image to be deteriorated by the blister or the like.

  FIG. 8 shows an image forming apparatus capable of forming a full-color image, and the present invention can be applied in the same manner as in the first embodiment. Also in this example, devices for forming an image (unfixed image) on a recording material are collectively referred to as an image forming unit, and details of various devices constituting the image forming unit will be described below.

  In FIG. 8, reference numeral 1000 denotes an image forming apparatus main body, and 1101 denotes a platen glass as a document placement table. Reference numeral 1102 denotes a scanner, which includes a document illumination lamp 1103, a scanning mirror 1104, and the like. The scanner 1102 performs reciprocal scanning in a predetermined direction by a motor (not shown). During this reciprocating scanning, the reflected light from the original passes through the lens 1107 via the scanning mirrors 1104 to 1106, and an image of the original is formed on the CCD sensor in the image sensor unit 1108.

  Reference numeral 1170 denotes an automatic document feeder (AutoDocumentFeeder, hereinafter referred to as ADF), which automatically feeds a document to a position where the scanner 1102 can read the document. Reference numeral 1171 denotes an ADF document placing table on which a maximum of 100 documents can be placed. Reference numeral 1172 denotes a document feed roller for feeding an ADF document. Reference numeral 117 denotes a document duplex reversing roller for reading both sides of a document fed from the document feed roller 1172. A document transport belt transports the document transported from the document feed roller 1172 or the document double-side reversing roller 1173 onto the platen glass 1101. When the document is stopped at the reading position or the back side of the document is read. The document is controlled so as to be returned to the document double-side reversing roller 1173 or to be discharged to the document discharge port 1175. The document stacking port 1175 has a maximum stack number of 100 sheets or more, like the document table 1171.

  An exposure control unit 1109 includes a laser, a polygon scanner, and the like. The exposure control unit 1109 is an image carrier that faces the image forming region 1110 with a laser beam 1119 converted into an electric signal by the image sensor unit 1108 and modulated based on an image signal subjected to predetermined image processing described later. The photosensitive drum 1111 is irradiated.

  Around the photosensitive drum 1111, there is a pre-exposure lamp 1121 for erasing the potential on the photosensitive drum 1111, and primary charging for corona discharge by applying a high voltage to a wire for applying a potential to the photosensitive drum 1111. A developing device 1113 to 1116 filled with toner for developing an image formed by an electrostatic latent image by a laser beam 1119 on the photosensitive drum 1111 is accommodated. A developing rotary 1117 that moves so as to contact the drum 1111, a primary transfer roller 1122 that transfers an image to an intermediate transfer body 1118 that temporarily holds an image developed on the photosensitive drum 1111, and a cleaning device 1120 are arranged.

  The photosensitive drum 1111 is rotated by a motor (not shown), and after being charged to a desired potential by the primary charger 1112, the laser light 1119 from the exposure control unit 1109 is irradiated. Thereby, an electrostatic latent image is formed on the photosensitive drum 1111. The developing unit 1113 of the first color is moved to this electrostatic latent image so as to contact the photosensitive drum 1111 by the developing rotary 1117, and the toner in the developing unit 1113 is electrostatically attached to develop on the photosensitive drum 1111. The toner image thus formed can be formed.

  When a full-color image is formed with toner from the four-color developing device accommodated in the developing rotary 1117, the first color toner image developed on the photosensitive drum 1111 is transferred by the primary transfer roller 1122. The toner image is temporarily transferred to an intermediate transfer member 1118 as a transfer medium, and the developing device 1114 for the second color comes into contact with the photosensitive drum 1111 by the developing rotary 1117. At this time, the leading edge of the developed image of the first color primarily transferred onto the intermediate transfer body 1118 and the leading edge of the developed image of the second color developed on the photosensitive drum 1111 are completely at the position of the primary transfer roller 1122. At the same timing, an electrostatic latent image is formed again by the laser light 1119 emitted from the exposure control unit 1109. Then, the developed image of the second color is superimposed on the developed image of the first color that has been primarily transferred onto the intermediate transfer body 1118.

  By repeating this superposition with the third and fourth colors, a four-color full-color developed image is transferred onto the intermediate transfer body 1118.

  On the other hand, recording paper fed from the first paper feed cassette 1133, the second paper feed cassette 1134, the third paper feed cassette 1135, or the fourth paper feed cassette 1136 by the pickup rollers 1125, 1126, 1127, and 1128. Are conveyed toward the registration roller 1143 by paper feed rollers 1129, 1130, 1131, and 1132. The recording paper conveyed to the vicinity of the stopped registration roller 1143 is subjected to a transfer bias of the unfixed toner image formed on the intermediate transfer body 1118 to the secondary transfer roller 1123 so that the leading edge of the image and the leading edge of the paper are aligned. The registration roller 1143 is driven so as to match, and the image is transferred onto the paper. Thereafter, the sheet is fed to the conveyor belt 1144.

  On the other hand, in the intermediate transfer body 1118, residual toner that has not been transferred to the sheet by the secondary transfer roller 1123 remains, and cleaning is started by the intermediate transfer body cleaner 1124. The intermediate transfer body cleaner 1124 is detachably attached to the intermediate transfer body 1118 immediately before the end of the residual toner of the secondary transferred image reaches the intermediate transfer body cleaner 1124, and the first color of the next unfixed toner image. When the image is transferred to the intermediate transfer member 1118 by the primary transfer roller 1122 and the leading end of the image comes immediately before the intermediate transfer member cleaner 1124 again, the image is controlled to be separated.

  The image transferred to the intermediate transfer member 1118 by the primary transfer roller 1122 also has residual toner on the photosensitive drum 1111, which is cleaned by the photosensitive drum cleaner device 1120. Thereafter, residual charges on the photosensitive drum 1111 are erased by the pre-exposure lamp 1121.

  The toner is conveyed to the fixing device 40 by the conveyance belt 1144. The toner image transferred to the recording paper is pressed and heated by the fixing device 40 to be fixed. Thereafter, the recording paper is discharged outside the image forming apparatus main body 1000 by the inner discharge roller 1147 and the outer discharge roller 1148.

  Further, in FIG. 8, reference numeral 1146 denotes a paper discharge flapper, which switches the recording paper path to one of the transport path 1138 and the discharge path 1139. During double-sided recording (double-sided copying) in which images are formed on both sides of the recording paper, the path of the recording paper fed from the internal paper discharge roller 1147 is switched to the reverse path 1139 side by raising the paper discharge flapper 1146 upward. It is done. The recording paper enters the double-side reverse conveyance path (switchback conveyance path) 1140 from the reverse path 1139. The traveling direction is reversed after entering the double-side reverse conveyance path 1140. As a result, the recording paper is guided to the refeeding path 1141 while being turned upside down. Reference numeral 1142 denotes a refeed roller that refeeds the recording sheet to the image forming area 1110.

  Reference numeral 1148 denotes an outer discharge roller that is disposed in the vicinity of the paper discharge flapper 1146 and discharges the recording paper whose path is switched to the discharge path 1138 by the paper discharge flapper 1146 to the outside of the image forming apparatus main body 1000. When the recording paper is reversed and discharged from the image forming apparatus main body 1000, the discharge paper flapper 1146 is raised upward so that the path of the recording paper fed from the inner paper discharge roller 1147 is switched to the reverse path 1139 side. The recording sheet enters the reverse path 1139. Then, the reversing roller 1149 feeds the reversing path 1139 to the position where the trailing edge of the recording paper has passed the reversing flapper 1150. Thereafter, the reverse roller 1149 is reversely rotated, and the reverse path of the recording paper is switched to the non-reverse discharge path 1151 by the reverse flapper 1150. As a result, the recording paper is turned over and sent to the discharge roller 1148 side via the non-reverse discharge path 1151.

  Next, the image forming mode will be described. In the case of forming a full-color image, in the image forming apparatus that forms an image using one photoconductor as in the present embodiment, as described above, the intermediate transfer member 1118 is rotated four times to form each color. It is necessary to superimpose images.

  At this time, the number of images that can be formed on the intermediate transfer member 1118 is determined by the peripheral length of the intermediate transfer member.

  The intermediate transfer member 1118 of this example is configured with 168φ, and an image with an image sub-scanning length (circumferential direction of the intermediate transfer member) of up to 472 mm can be formed in consideration of the switching time of the developing device by the development rotary. Further, if the image is up to 236 mm, which is half of the sub-scan length of 472 mm, an image for two pages can be formed on the intermediate transfer body 1118.

  Here, an image forming mode when an image having a sub-scanning length of 236 mm or less is continuously formed a plurality of times is referred to as “two sheets pasting”, and an image having a sub-scanning length longer than 236 mm and not more than 472 mm is continuously formed a plurality of times. The image forming mode at this time is referred to as “single sheet”.

  FIG. 9 is a flowchart for performing desorption control during full-color image formation. Details will be described below. Note that black monochromatic image formation in this embodiment is the same as that in the first embodiment.

  S500 is the start of printing. As described in the first embodiment, printing refers to a series of processes from latent image, development, and transfer.

  First, in S501, the process proceeds to S600 (FIG. 10), and an image forming mode is set. The flow from S600 will be described later.

  In S502, it is determined whether or not the recording material (paper) has reached the position of the registration roller 1143. If there is no recording material, the process proceeds to S503, where it is determined whether the pressure belt 10 is in contact with the fixing roller 1.

  If the pressure belt is in contact with the fixing roller, the pressure belt is removed in S504, the drive of the pressure belt cooling fan 17 is started in S505, and the process returns to S502.

  If the pressure belt is separated from the fixing roller, the process proceeds to S506. If the pressure belt cooling fan is not in the driving state, the pressure belt cooling fan is driven in S505, and the process returns to S502. If the pressure belt cooling fan 17 is being driven, the process directly returns to S502.

  When the recording material reaches the position of the registration roller 1143, the process proceeds to S507. In S507, the process is divided according to the presence / absence of the desorption operation determined in S100 to S106 in FIG.

  That is, the second embodiment also has the same operation panel as the first embodiment. Whether or not to perform the belt attaching / detaching operation is also determined by the processing of S100 to S106 in FIG.

  A case where it is determined that the pressure belt 10 is attached / detached will be described.

  If there is a detaching operation, it is first determined in S508 whether the pressure belt 10 is in contact with the fixing roller 1 or not. If it is not in contact, the process proceeds to S509, the pressure belt 10 is put on, and the process proceeds to S510.

  If the pressure belt has previously contacted the fixing roller, the process proceeds to S510. In S510, it is determined whether the pressure belt cooling fan 17 is being driven. If it is being driven, the driving of the pressure belt cooling fan 17 is stopped in S511, and the process proceeds to S512. If not, the process proceeds to S512.

  In step S512, the process waits for the fixing process to end. If the fixing process has been completed, it is determined in S513 whether all the printing processes have been completed. If it is determined that the printing process has been completed, the process proceeds to S521. If not, the process proceeds to S514.

  In S514, the image forming mode set in S600 is determined.

  If it is determined that “two sheets are pasted”, the process proceeds to S515.

  When the image forming mode is “two sheets pasted”, it is determined whether the second recording material when the two sheets are past has passed through the fixing nip. If it is not passed, the process returns to S508.

  In the case of “2 sheets pasted”, the sheet passes through the fixing device 40 in succession immediately after two sheets. Therefore, the sheet between the first sheet and the second sheet at the time of “2 sheets pasted” is used. Thus, the pressure belt 10 is not detached, and the second sheet when the “two sheets are pasted” passes the fixing nip and then the first sheet when the second “two sheets are pasted” (three sheets of the image forming job). The pressure belt 10 is removed during the period until the recording material of the first eye reaches the fixing nip. That is, every time the two recording materials at the time of “two sheets pasting” pass through the fixing nip, the pressure belt 10 is detached between the sheets. Then, the process returns to S502 with the pressure belt being separated.

  In this way, the separation operation of the pressure belt is not sequentially performed between all the sheets, but the separation operation is performed between the sheets of the succeeding recording material every time a predetermined number of recording materials pass through the fixing nip. It is.

  On the other hand, if it is determined in S514 that the image forming mode is not “2 sheets pasted”, that is, “1 sheet pasted”, the process returns to S502. At this time, as in the first embodiment, the belt separating operation is sequentially performed during a period from when the recording material passes through the fixing nip until the subsequent recording material reaches the fixing nip. That is, the pressure belt separation operation is sequentially performed between all sheets in a continuous image forming job.

  Next, the case where it is determined in S507 that the pressure belt 10 is not attached or detached will be described. If it is determined that there is no desorption operation, it is determined in S516 whether the pressure belt 10 is in a contact state. If it is determined that the pressure belt 10 is in a contact state, the process proceeds to S518.

  If it is determined that the contact state is not established, the pressure belt 10 is attached in S517, and the process proceeds to S518. In S518, it is determined whether or not the pressure belt cooling fan 17 is being driven. If the pressure belt cooling fan 17 is being driven, the driving is stopped in S519, and if it is not being driven, the process proceeds to S520.

  In step S520, the process waits for all printing processes to be completed. During this time, the pressure belt is not detached regardless of the recording material interval. When all the printing processes are completed, the pressure belt 10 is detached in S521, the pressure belt cooling fan 17 is driven in S522, and the job is terminated in S523.

  As described above, the fixing roller 1 and the pressure belt 10 are detached and attached during one image forming job, and the pressure belt cooling fan 17 applies pressure when the pressure belt 10 is in the detached state. By cooling the belt 10, the heat of the fixing roller 1 can be prevented from being applied to the pressure belt 10 unnecessarily, and at the same time, the pressure belt 10 can be cooled, and the temperature of the pressure belt 10 can be prevented from being unnecessarily increased. I can do it.

  Next, the image forming mode determination means in this embodiment will be described with reference to FIG. When the process proceeds from S501 to S600, the sub-scanning length of the image to be subjected to the image forming process is determined in S601. As described above, the intermediate transfer member in this example has a circumferential length that enables the two-sheet pasting mode when the sub-scanning length of the recording material is 236 mm or less.

  Therefore, it is determined whether the sub-scanning length is 236 mm or less. If it is determined that the distance is 236 mm or less, the process proceeds to S602.

  In step S602, the number of sheets to be subjected to image formation processing is determined. If it is determined that the number of image forming processes on the recording material in this image forming job is two or more, the image forming mode is set to the two-sheet pasting mode in S603, and the process returns to S502.

  If it is determined in S601 that the sub-scanning length is greater than 236 mm, or if it is determined in S602 that the number of image forming processes of the main image forming job is one, each image forming mode is set to S604 in S604. The paste mode is set, and the process returns to S502.

  As described above, not only an image forming apparatus that forms a full-color image with toners of four colors of yellow, magenta, cyan, and black, but also forms a full-color image by using a dark color toner and a light color toner having the same hue and different densities. The same can be applied to the image forming apparatus. For example, in the case of an apparatus that forms a full-color image using six types of toners of yellow, dark magenta, light magenta, dark cyan, light cyan, and black, the intermediate transfer member must be rotated at least six times. Therefore, the effect of applying the present invention is high.

[Modification]
1) In the first and second embodiments, manual setting is performed in the setting unit in which the operator sets the type of the recording material by the operator (when there is no setting instruction from the operator, (It is supposed to perform image formation by recognizing that it is thin paper), but it is automatically set by providing paper type automatic detection means that automatically detects the paper type of the recording material that has been passed. A device configuration can also be adopted.

  2) The structure for heating the fixing roller 1 is not limited to the internal heating method in which the heating means as in the above-described embodiment is arranged and heated inside the fixing roller, and the heating means is arranged outside the fixing roller and heated. An external heating method, an internal heating method, and an external heating method may be used in combination. Further, the fixing roller itself can be configured to generate heat by an electromagnetic induction heating method.

  3) The detaching mechanism for contacting and separating the pressure belt 10 from the fixing roller 1 is not limited to the configuration of the above embodiment, and can be arbitrarily configured.

  4) The belt cooling means is not limited to the configuration of the fan 19, and may be a cooling device using, for example, a heat radiating fin or a heat pipe that removes heat by contacting the belt.

  5) The fixing device of this example includes an image heating device that presupposes an unfixed toner image on the recording material, and image heating that reheats the image presupposed on the recording material to change the glossiness of the image. Devices can also be included.

  6) The configuration of the image forming means for forming an image on the recording material is not limited to the above-described electrophotographic system, and various image forming principles and processes such as electrostatic recording and magnetic recording may be used.

  According to each embodiment described above, it is possible to prevent image quality from being deteriorated in the middle of a continuous image forming job.

Schematic explanatory diagram of the image forming apparatus of the embodiment External view of the operation panel Schematic model diagram of fixing device (pressure belt in contact) and control system block diagram Schematic configuration model diagram of the fixing device (pressure belt in the separated state) and control system block diagram Print mode decision flowchart Pressure belt attachment / detachment control flowchart according to the recording material interval Pressure belt attachment / detachment control flowchart according to job status Sectional drawing of the image forming apparatus main body which is 2nd Example of this invention Pressure belt attachment / detachment control flowchart according to image forming mode Flow chart of image forming mode determination means

Explanation of symbols

  1. . . Fixing roller, 6. . . 6. Halogen lamp, . . Thermistor, 10. . 10. pressure belt, . Pressure pad member, 19. . . Pressure belt cooling fan, 61. . . Control circuit section, 450. . . OHP sheet setting key, 451. . . Thick paper setting key 452. . . Coated paper setting key, 453. . . Duplex printing setting key

Claims (12)

An image forming unit that forms an image on a recording material, a heating member that heats an image formed on the recording material at a nip portion, and a recording material that is conveyed toward the nip portion formed between the heating members In an image forming apparatus having an endless belt, and a separating unit that separates the heating member and the belt,
When image formation is continuously performed on a plurality of recording materials, a separation operation is performed by the separation unit during a period from when the previous recording material passes through the nip portion to when the next recording material reaches the nip portion. An image forming apparatus capable of being executed.   The image forming apparatus according to claim 1, wherein whether or not the separation operation is performed in the period is switched according to a type of recording material.   The image forming apparatus according to claim 2, further comprising a changing unit that changes the length of the period according to the type of the recording material.   The heating member and the belt are separated when the length of the period is equal to or longer than a predetermined time, and the heating member and the belt are kept in contact when the length of the period is less than the predetermined time. The image forming apparatus according to claim 3. When the basis weight of the recording material is 110 g / m ² or more, the heating member and the belt are separated from each other, and when the basis weight of the recording material is less than 110 g / m ^{2, the} heating member and the belt are kept in contact with each other. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 4, wherein the heating member and the belt are separated when the recording material is a light-transmitting resin or when the recording material is resin-coated paper.   The image forming apparatus according to claim 1, further comprising a cooling unit that cools the belt when the heating member and the belt are separated from each other.   The image forming apparatus according to claim 1, wherein the heating member is in contact with an image on a recording material at the nip portion. Image forming means for forming an image on a recording material;
A heating unit comprising: a heating member that heats an image on a recording material at a nip portion; and an endless belt that conveys the recording material toward the nip portion formed between the heating members;
In the image forming apparatus including the heating member and a separating unit that separates the belt,
Have
An image forming apparatus characterized in that when an abnormal situation occurs during an image forming job, a separating operation is executed by the separating means in accordance with the interruption of the image forming job.   The image forming apparatus according to claim 9, wherein when an abnormal situation occurs in an image forming job other than the heating unit, the separating unit executes a separating operation in response to the interruption of the image forming job.   The image forming apparatus according to claim 9, further comprising a cooling unit that cools the belt when the heating member and the belt are separated from each other.   The image forming apparatus according to claim 9, wherein the heating member is in contact with an image on a recording material at the nip portion.