JP2007101861A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which prevents a heater holder from melting in a a semi pressure fixing. <P>SOLUTION: The fixing device of an image forming apparatus includes a fixing member 11 which has a heat source 19 internally and fixes an image on a recording material; a pressure member 12 which presses the recording material to the fixing member 11 to convey the recording material; an energizing means for pressing the fixing member 11 to the pressure member 12 with a prescribed pressure; a pressure means, which acts upon the energizing means and is capable of having two or more kinds of pressure modes of at least a pressure mode of pressing the fixing member 11 to the pressure member 12 and a pressure mode of applying a lower pressing force. When a fixing operation is performed in the pressure mode of applying the lower pressing force, the fixing temperature control temperature during the intervals of paper passage is set higher than that during paper passage, and a pre-rotation time is made longer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a laser beam printer (referred to as LBP), a printer, a facsimile, a microfilm reader printer, and a recording machine.

  More specifically, using a toner made of heat-meltable resin or the like by timely image forming process means such as electrophotography, electrostatic recording, magnetic recording, etc. An unfixed toner image corresponding to the image information is formed and supported. In the fixing device, the unfixed toner image is heat-fixed as a permanently fixed image on the surface of the transfer material carrying the image.

  In particular, a fixing device of an image forming apparatus having a pressure unit that can have two or more types of pressure modes, that is, a pressure mode in which the fixing member is pressed against the pressure member and a pressure mode in which the pressure is lower. The invention relates to fixing temperature control control when performing a fixing operation using a pressurizing mode with a lower pressing force on special paper such as an envelope. There are various transfer materials such as paper, printing paper, transfer material sheet, electrofax sheet, electrostatic recording sheet, OHT sheet, glossy paper, and gloss film.

  In recent years, image forming apparatuses such as copiers, printers, and facsimiles using electrophotographic technology have been speeded up, colorized, reduced in price, reduced in power consumption, and shortened wait time (quick start performance: operated on demand). Progressing. As a fixing device used in such an image forming apparatus, a film heating type fixing device using a fixing film in which an elastic layer is provided on a fixing film has been put into practical use.

  For colorization, it is necessary to provide an elastic layer on the fixing film. By providing an elastic layer made of silicone rubber or the like on the fixing film, the elastic layer is deformed along the toner layer when the toner image passes through the fixing nip portion. As a result, the toner that is unevenly placed on the image is enveloped by the elastic layer and is uniformly heated, thereby achieving uniform fixing (see, for example, Patent Documents 1 and 2).

  The image fixed uniformly in this way has no gloss unevenness, and has a feature that the light transmittance of the image is excellent particularly when an OHT (transparent sheet for overhead projector) is fixed.

  However, the thermal conductivity of silicone rubber and the like used for the elastic layer of the fixing film is not so high. In order to raise the temperature of the fixing film surface to a desired temperature in a short time, the conventional film overheating method is used. It is necessary to rapidly turn on relatively large electric power as compared with the heat fixing device.

  In addition, since many members are inserted between the fixing film surface and the heater temperature detecting means, the temperature detected by the heater temperature detecting means may be significantly different from the temperature of the fixing film surface. Therefore, it is difficult to control the temperature of the fixing film surface by the heater temperature detection means. In particular, it is difficult to detect by the temperature detection means on the back of the heater that the recording material has passed through the fixing device and took the heat on the surface of the fixing film to reduce the temperature of the surface of the fixing film. It is.

  On the other hand, if the temperature detection means is moved from the heater part to the surface or inner surface of the fixing film and the temperature of the fixing film itself is detected to control the heater driving, Although temperature control can be performed accurately, the temperature of the heater itself cannot be detected.

  For this reason, for example, in a film fixing apparatus in which an elastic layer is provided on a fixing film, the following proposal has been made.

  There are two temperature detection means: a first temperature detection means for detecting the inner surface temperature of the fixing film and a second temperature detection means for detecting the temperature of the back surface of the heater. The second temperature detecting means is used to detect abnormality and the like.

  On the other hand, the fixing device is provided with a pressurizing mechanism for pressurizing the roller with a constant pressure to form a pressure nip between the fixing roller and the pressure roller.

  If the pressure applied by the pressure mechanism is low, the fixed image may not be glossy or the fixing property may be insufficient in the first place.

  However, when the pressure is high, the envelope may be wrinkled when the envelope is passed, or the label paper may be peeled off when the label is passed. This is because the applied pressure is high, and a large stress is applied to the transfer material, so that a plurality of sheets of paper overlap each other like an envelope, and a label sheet has a gap between peel seals. It is caused.

  Therefore, in order to prevent such a problem, it is necessary to set the fixing pressure to be low.

  In order to achieve both gloss and fixability on plain paper, as well as wrinkles on the envelope and peeling of the label paper, the fixing device's pressure can be made variable, and when plain paper is passed, the fixing roller and pressure roller can be used with high pressure. A configuration in which the pressure is set low when the envelope or label paper is passed is conceivable.

  As described above, examples of configurations that can change the pressing force of the fixing device include those described in Patent Document 3 and Patent Document 4.

  Further, it has been proposed to keep the fixing property constant regardless of the setting of the pressure by changing the fixing temperature when the pressure of the fixing device is changed. Examples of such a configuration are disclosed in Patent Document 5 and Patent Document 6, for example.

  An example in which the structure for fixing such an envelope or the like at a setting with a low pressure is applied to a fixing device having an elastic layer on a conventional fixing film as described below will be described below.

  As a fixing film, about 250 μm of a silicone rubber elastic layer is provided on a base layer having a thickness of about 30 μm and φ24 using a metal such as stainless steel. As a surface layer, a coating of a PFA tube having a thickness of about 30 μm using a copolymer of tetrafluoroethylene and perfluoroalkyl perfluorovinyl ether (hereinafter referred to as PFA) is used.

  As the pressure roller, a conductive silicone rubber layer having a thickness of about 2 mm is provided on a cored bar, and a conductive PFA tube having a thickness of about 50 μm is covered as a surface layer. It has an outer diameter of about φ25 and a roller hardness of about 64 (measured when using an Asker C-type hardness meter manufactured by Kobunshi Keiki Co., Ltd. with a total weight of about 1 kgf). A pressure roller for LTR size is used.

  A so-called ceramic heater is used as the heating element, and a heater of about 12.5Ω is used as a 115V rated heater as the resistance value of the heating element. The heater is held by a heater holder using a material such as an engineering plastic such as a liquid crystal polymer (LCP) having a load deflection temperature as a heat resistant temperature of about 300 ° C.

  The normal pressure is about 20 kgf and a nip width of about 8 mm (center) is obtained.

  When the envelope is fed, the nip width is reduced by reducing the pressure to about 10 kgf. In this case, the center nip is about 6.5 mm, and the end is about 4.5 to 5.5 mm. As an example of envelope, with a process speed of about 100 mm / s and a throughput of about 3 sheets per minute, a COM-10 size (4.125 inches x 9.5 inches) of USA, Mailwell, and a paper basis weight of 80 g / m ^ 2 A case where the # 582 envelope is passed on the basis of the center pass will be described.

  An example of each temperature control temperature setting in this conventional example is shown in the table of FIG.

The temperature control target temperature T0 between the papers is 163 ° C., the temperature control target temperature T1 before the fixing film one lap before the front end of the paper enters the fixing nip is 168 ° C., and the temperature at the front end of the paper is one lap after the fixing nip enters. The control target temperature T2 is 170 ° C., and the temperature control target temperature T3 from the first round of the fixing film to the rear end of the sheet is 170 ° C. This is shown in FIG.
Japanese Patent Laid-Open No. 10-10893 Japanese Patent Laid-Open No. 11-15303 Japanese Patent Laid-Open No. 6-11993 Japanese Patent Laid-Open No. 10-282828 JP-A-2-132481 JP 2004-279702 A

  However, in such a fixing device, the following problems newly occur when an envelope or the like is passed through in a state where the half-pressed nip is narrow.

  FIG. 7 shows a graph of the temperature of each part of the fixing device when the envelope is passed through in a half-pressurized state. 7 shows the temperature control target temperature (thick solid line) and the detected temperature (thin solid line) of the main thermistor, which is the temperature detection means of the fixing film, and 2) shows the heater end (so-called non-passage). This shows the heater back temperature in the paper area.

  In this case, the heater back temperature rises to about 320 ° C. when the first sheet is passed, and the heater back temperature rises to a temperature of 300 ° C. or more until about 3 sheets are passed.

  For this reason, since the heater back temperature rises above the heat resistance temperature of the material of the heater holder holding the heater, there is a problem that the heater holder melts or deforms.

  In addition, if the heater holder melts, the nip shape of the generating portion changes, so that paper wrinkles and image gloss unevenness occur, and the rotation behavior of the fixing film changes. There was a problem of lowering. When the fixing temperature is lowered so as not to cause melting of the heater holder, there is a problem that the fixing property is lowered. For this reason, it has been difficult to achieve both prevention of melting and fixing of the heater holder.

  Further, in order to satisfy the fixing property, if the pre-rotation time of the fixing device is lengthened and the fixing device is warmed and then the paper is fixed, the printing time becomes long.

(Object of invention)
A first object of the present invention is to provide a fixing device that satisfies the melting and fixing properties of a heater holder in a fixing mode in which an envelope or the like is passed during decompression.

  A second object of the present invention is to provide a fixing device in which the printing time does not become longer than necessary.

In order to solve the above problems, the first invention of the present invention,
A fixing member having an internal heat source for fixing an image on the recording material, a pressure member for pressing and conveying the recording material against the fixing member, and the fixing member to the pressure member at a predetermined pressure There are two or more types of pressure modes: an urging means for pressing, a pressing mode that acts on the urging means and presses at least the fixing member against the pressing member, and a pressing mode with a lower pressing force. In a fixing device of an image forming apparatus having a pressure unit that can be held,
During the fixing operation in the pressurizing mode with low pressing force, there is a problem by setting the fixing temperature control temperature at the interval between sheets higher than the fixing temperature control temperature at the time of passing paper and extending the pre-rotation time To solve.

In the second invention of the present invention,
A fixing member having an internal heat source for fixing an image on the recording material, a pressure member for pressing and conveying the recording material against the fixing member, and the fixing member to the pressure member at a predetermined pressure There are two or more types of pressure modes: an urging means for pressing, a pressing mode that acts on the urging means and presses at least the fixing member against the pressing member, and a pressing mode with a lower pressing force. In a fixing device of an image forming apparatus having a pressure unit that can be held,
During the fixing operation in the pressurizing mode with low pressing force, the fixing temperature control temperature at the time of paper interval is set higher than the fixing temperature control temperature at the time of paper passing and the pre-rotation time is extended.
A first temperature detecting means for detecting at least the temperature of the fixing member; and a second temperature detecting means for detecting the temperature of the heat source, and the pre-rotation extension time according to the output of the second temperature detecting means. The problem is solved by the feature of switching.

  By using the fixing device according to the present invention, it was possible to satisfy the fixing property while preventing the heater holder from being melted or deformed when printing an envelope or the like during decompression. Further, since the pre-rotation extension time is switched depending on the state of the fixing device, it is possible to prevent the print time from being increased every time.

  Hereinafter, embodiments of the present invention will be described based on examples.

(1) Example of Image Forming Apparatus FIG. 2 is a structural model diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as a fixing device. The image forming apparatus shown in this embodiment is a laser printer using an electrophotographic image forming process.

  The image forming apparatus includes an image forming unit 1a that forms a yellow image, an image forming unit 1b that forms a magenta image, an image forming unit 1c that forms a cyan image, and an image that forms a black image. The image forming unit 1d includes four image forming units (image forming units). These four image forming units 1a, 1b, 1c, and 1d are arranged in a line at a constant interval.

  In each of the image forming units 1a, 1b, 1c, and 1d, drum-type electrophotographic photosensitive members (hereinafter referred to as photosensitive drums) 2a, 2b, 2c, and 2d are installed as image carriers. Around each of the photosensitive drums 2a, 2b, 2c, and 2d, chargers 3a, 3b, 3c, and 3d, developing devices 4a, 4b, 4c, and 4d, and drum cleaning devices 5a, 5b, 5c, and 5d are installed, respectively. ing. Further, exposure devices 6a, 6b, 6c, and 6d are installed above the charger 3 and the developing device 4, respectively. Each developing device 4a, 4b, 4c, 4d contains yellow toner, magenta toner, cyan toner, and black toner, respectively.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is a negatively charged OPC photosensitive member having a photoconductive layer on an aluminum drum base, and a predetermined process speed is clockwise by a driving device (not shown). Is driven to rotate. The chargers 3a, 3b, 3c and 3d as charging means uniformly apply the surface of each photosensitive drum 2a, 2b, 2c and 2d to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown). Charge.

  The developing devices 4a, 4b, 4c, and 4d develop toner images by attaching toners of respective colors to the electrostatic latent images formed on the photosensitive drums 2a, 2b, 2c, and 2d, respectively (visualization). To do. As a developing method using the developing devices 4a, 4b, 4c, and 4d, for example, a two-component contact developing method can be used. This is a developing method in which toner particles mixed with a magnetic carrier are used as a developer, conveyed by magnetic force, and developed in contact with the photosensitive drums 2a, 2b, 2c, and 2d.

  The transfer rollers 7a, 7b, 7c, and 7d as transfer means are constituted by elastic members, and each photosensitive member is passed through an endless belt-like transfer material conveying belt (hereinafter referred to as a transfer belt) 8 at each transfer nip portion. The drums 2a, 2b, 2c and 2d are in contact with each other. Here, the transfer roller 7 is used as the transfer unit, but a transfer blade that is applied with a high pressure when the toner image is transferred onto the transfer material and is in contact with the transfer belt 8 may be used.

  The drum cleaning devices 5a, 5b, 5c, and 5d remove and collect the transfer residual toner remaining on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively.

  In the exposure apparatuses 6a, 6b, 6c, and 6d, a laser beam modulated in response to a time-series electric digital pixel signal of image information is output from a laser output unit (not shown), and a polygon mirror (not shown) that rotates at high speed. The surfaces of the photosensitive drums 2a, 2b, 2c, and 2d are exposed through, for example. As a result, electrostatic latent images of respective colors corresponding to the image information are formed on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d charged by the chargers 3a, 3b, 3c, and 3d.

  The transfer belt 8 is stretched between the drive roller 9 and the tension roller 10 and is rotated (moved) in the direction of the arrow (counterclockwise) by the drive of the drive roller 9. The transfer belt 8 is made of a dielectric resin such as a polycarbonate, a polyethylene terephthalate resin film, a polyvinylidene fluoride resin film, or the like.

  A fixing device 13 having a fixing film 11 including a heat source and a pressure roller 12 is installed on the downstream side of the transfer belt 8 in the transfer material conveyance direction.

  Next, an image forming operation by the above-described image forming apparatus will be described.

  When the image formation start signal is issued, the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1a, 1b, 1c, and 1d that are rotationally driven at a predetermined process speed are respectively charged by the chargers 3a, 3b, and 3c. , 3d is uniformly negatively charged. The exposure devices 6a, 6b, 6c, and 6d convert the image signal of the output image into an optical signal by a laser output unit (not shown), respectively, and the laser beam that is the converted optical signal is charged to each photosensitive element. Each of the drums 2a, 2b, 2c, and 2d is scanned and exposed to form an electrostatic latent image.

  First, yellow toner is adhered to the electrostatic latent image formed on the photosensitive drum 2a by the developing device 4a to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied. Visualize as an image.

  The transfer material (paper) fed from the paper feed cassette 14 through the transfer material conveyance guide 15 is synchronized with the timing at which the leading edge of the toner image on the photosensitive drum 2a is moved to the transfer portion between the photosensitive drum 2a and the transfer roller 7a. ) P is conveyed to the transfer portion Ta by the registration roller 16. Then, a yellow toner image is transferred onto the transfer material P by the transfer roller 7a to which a transfer bias (polarity opposite to the toner (positive polarity)) is applied to the transfer material P conveyed to the transfer unit.

  The transfer material P onto which the yellow toner image has been transferred is moved to the image forming unit 1b by the transfer material conveyance belt 8. In the transfer unit constituted by the image forming unit 1b and the transfer roller 7b, the magenta toner image formed on the photosensitive drum 2b in the same manner as described above is superimposed on the yellow toner image on the transfer material P. Transcribed.

  In the same manner, cyan and black toner images formed on the photosensitive drums 2c and 2d of the image forming units 1c and 1d on the yellow and magenta toner images superimposed and transferred onto the transfer material P are similarly transferred to the transfer units. In this manner, a full-color toner image is formed on the transfer material P by superimposing them.

  The transfer material P on which the full-color toner image is formed is conveyed to the fixing device 13, and the full-color toner image is heated and pressed at the fixing nip between the fixing film 11 and the pressure roller 12 to be thermally fixed on the surface of the transfer material P. After that, the paper is discharged onto the paper discharge tray 18 by the paper discharge roller 17, and a series of image forming operations is completed.

  When the above image is transferred from the photosensitive drum to the transfer material, the transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d is removed by the drum cleaning devices 5a, 5b, 5c, and 5d, respectively. And recovered.

  When outputting a monochrome image, the above-described image forming process is performed only in the image forming unit 1d that forms a black image.

  Next, the fixing device in this embodiment will be described with reference to FIG.

  FIG. 3 schematically shows the fixing device 13 in FIG.

  The fixing device in this embodiment includes a heater 19, a heater holder 20, a main thermistor 21, a sub thermistor 22, a fixing film 11, a pressure roller 12, and an entrance guide 23.

  The heater holder 20 is formed of a liquid crystal polymer resin having high heat resistance, plays a role of holding the heater 19 and guiding the fixing film 11.

  In this embodiment, model number E4205L B manufactured by Sumitomo Chemical Co., Ltd. was used as the liquid crystal polymer used for the material of the heater holder 20. The maximum usable temperature (load deflection temperature) of this liquid crystal polymer is about 305 ° C.

  The main thermistor 21 is disposed to detect the temperature of the inner surface of the fixing film 11 and perform temperature control.

  In the main thermistor 21, the thermistor element is always attached to the inner surface of the fixing film 11 even when the thermistor element is attached to the tip of the stainless steel arm and the movement of the inner surface of the fixing film 11 becomes unstable due to the swing of the arm. Keep in contact.

  The main thermistor 21 is connected to a CPU (not shown), and the CPU determines the temperature control control content of the heater 19 based on the output of the main thermistor 21 and controls the energization of the heater 19.

  The sub-thermistor 22 is disposed on the back surface of the heater 19 and plays a role of performing limiter control when the heater 19 is excessively heated for some reason. In this embodiment, the sub-thermistor 22 is arranged at the end in the longitudinal direction of the heater 19 and detects the temperature rise at the end of the fixing device 13 when small-size paper is passed through. If it is determined that the fixing device 13 is overheated, the temperature of the fixing device 13 is prevented from being excessively increased by controlling the fixing temperature to be lowered.

  The fixing film 11 is formed by forming a silicone rubber layer on a SUS film formed by forming a stainless steel (hereinafter referred to as SUS) element tube into a seamless belt shape having a thickness of 30 μm by plastic working. As a layer, a PFA resin tube having a thickness of 30 μm is coated. For the silicone rubber layer, it is desirable from the viewpoint of temperature rise to use a material having as high a thermal conductivity as possible and to reduce the heat capacity of the fixing film 11. In this embodiment, the material having a thermal conductivity of about 1.0 × 10 −3 cal / sec · cm · K and a silicone rubber having a high thermal conductivity were used.

  On the other hand, it is desirable to make the silicone rubber layer of the fixing film 11 as thick as possible from the viewpoint of image quality, such as OHT permeability and “s” (small gloss unevenness) on the image. According to the study by the present inventors, it has been found that a rubber thickness of 200 μm or more is necessary to obtain a satisfactory level of image quality.

  The silicone rubber layer in this example was 250 μm thick. In addition, the inner diameter of the fixing film 11 in this example was 24 mm.

  The heat capacity of the fixing film 11 thus formed was measured and found to be 2.8 × 10 −2 cal / cm 2 K (heat capacity per 1 cm 2 of fixing film). Generally, when the heat capacity of the fixing film 11 is 1.0 cal / cm 2 K or more, the temperature rise becomes dull and the on-demand property is impaired. On the other hand, if it is attempted to reduce the thickness to 1.0 × 10 −2 cal / cm 2 K or less, the rubber layer of the fixing film 11 must be extremely thin, and the image quality such as the OHT permeability and the level of “su” is maintained. Therefore, the thickness of the rubber layer necessary for this cannot be ensured. For this reason, it can be seen that the heat capacity of the fixing film 11 satisfying both on-demand characteristics and image quality is included in the range of 1.0 × 10 −2 cal / cm 2 K to 1.0 cal · cm 2 K.

  Further, by providing a fluororesin layer on the surface of the fixing film 11, the surface releasability is improved, and the offset phenomenon that occurs when the toner once adheres to the surface of the fixing film 11 and moves to the transfer material P again is prevented. can do.

  Further, by using a PFA tube as the release layer 20c on the surface of the fixing film 11, a uniform release layer can be more easily formed.

  The pressure roller 12 is formed by forming a conductive silicone rubber layer having a thickness of about 2 mm on a cored bar and coating a conductive PFA resin tube having a thickness of about 50 μm thereon.

  The entrance guide 23 serves to guide the transfer material so that the transfer material P that has passed through the secondary transfer nip is accurately guided to the fixing nip portion. The entrance guide 23 of the present embodiment is formed of polyphenylene sulfide (PPS) resin.

  The pressure roller 12 and the entrance guide 23 are each assembled to the frame 24.

  Below that, a fixing film unit 25 containing a fixing heater 19, a main thermistor 21, and a sub-thermistor 22 mounted on the heater holder 20 is placed. The fixing film unit 25 is pressed with a force of 20 kgf (10 kgf on one side) by a pressing mechanism (not shown) through a T stay 26 arranged along the heater holder 20.

  In the fixing device of this embodiment, the fixing film 11 is driven to rotate as the pressure roller 12 rotates. At that time, the inner surface of the fixing film 11 and the heater holder 20 are configured to slide. Grease is applied to the inner surface of the fixing film 11 to ensure slidability between the heater holder 20 and the inner surface of the fixing film 11.

  In normal use, the rotation of the fixing film 11 starts with the rotation of the fixing device, and the temperature of the inner surface of the fixing film 11 increases as the temperature of the heater 19 increases.

  Next, the fixing pressure mechanism in this embodiment will be described with reference to FIGS. 1-1, 1-2, 1-3, and 4. FIG.

  FIGS. 1-1 to 1-3 schematically show the pressure release mechanism of the fixing device 13 in this embodiment.

  1-1 shows a pressure state of the fixing film unit 25, FIG. 1-2 shows a pressure release state of the fixing film unit 25, and FIG. 1-3 shows a half pressure state of the fixing film unit 25. ing.

  The fixing film unit 25 disposed to face the pressure roller 12 is connected at a connecting portion of the connecting member 27. The pressure spring 28 presses the fixing film unit 25 against the pressure roller 12 with a predetermined pressure via the connecting member 27. The predetermined pressure is optimized by the fixing property and the conveyance property of the recording material, and is usually determined within a range of 10 to 50 kgf, and there is a nip between the fixing film unit 25 and the pressure roller 12. N1 is secured. The pressure release cam 29 is disposed substantially opposite to the pressure spring 28 with the connecting member 27 interposed therebetween. The pressure release cam 29 is configured to be rotatable by a drive source (not shown) in the direction of the arrow about the rotation axis.

  As shown in FIG. 4, the pressure release cam 29 includes four cam surfaces 29 a to 29 d.

  FIG. 1-1 is a diagram illustrating a normal pressure state of the fixing device. In this figure, the pressure release cam 29 has a cam surface 29 c facing the connecting member 27, and the cam surface 29 c has a gap with respect to the connecting member 27. Therefore, the force for pressing the fixing film unit 25 against the pressure roller 12 is completely determined only by the pressure spring 28.

  Next, the pressure release state of the fixing roller shown in FIG. 1B is when the paper jam generated during image output is processed, when the low power mode is entered when the printer is not used for a certain period of time, and when the image is output. In order to prevent an unnecessary high pressure from being applied to the pressure roller 12 and the fixing film unit 25 when the power of the forming apparatus main body is turned off, the pressure release cam 29 is rotated. As a specific means, by rotating the pressure release cam 29 approximately 90 ° clockwise, the cam surface 29d of the pressure release cam 29 pushes the connecting member 27 against the urging force of the pressure spring 28. . Further, by maintaining the posture of the pressure release cam 29 by the flat surface of the cam surface 29d, a gap G is generated between the fixing film unit 25 and the pressure roller 12. The gap G only needs to have a distance that facilitates the operation of removing the media that has caused the paper jam from the fixing device 13, and even if the gap G is 0, the media that has caused the paper jam can be removed. It does not matter as long as the extraction pressure can be lowered to a sufficient extent to be removed.

  After the paper jam processing, the image forming apparatus main body is brought into an image output ready state. Therefore, when reproducing the pressurization state as shown in FIG. 1-1 from the pressurization release state, the pressurization release cam 29 in FIG. Is in a state of facing the connecting member 27.

  Furthermore, as shown in FIG. 1-3, the fixing pressure mechanism in the present embodiment has a half pressure state between the pressure state and the pressure release state. In order to realize the half-pressurized state, the pressure release cam 29 is rotated approximately 270 ° clockwise, and the cam surface 29b pushes down the connecting member 27 against the urging force of the pressure spring 28. The posture of the pressure release cam 29 is held by the flat surface of the cam surface 29b. However, the cam surface 29b is set to have a smaller push-down amount of the connecting member 27 than the cam surface 29d. Therefore, as shown in FIG. 1C, the pressure roller 12 and the fixing film unit 25 maintain the contact state, but the pressure is lower than that in the pressure state, and the width is narrower than that in the pressure state. It has a nip N2.

  In the present embodiment, the connecting member 27 moves downward by about 1.5 mm by abutting the connecting member 27 with the pressure release cam surface 29d in the contact state. As a result, the nip N1 that was about 8 mm at the time of normal pressurization became a nip N2 of about 4.5 mm (end).

  The description of parts that are not particularly different from the conventional example is omitted.

  FIG. 5 shows a temperature rise curve of the fixing device when constant power is applied in the normal pressure mode and the half-separation mode. The main thermistor and sub-thermistor temperatures when a constant power is applied from the room temperature state are monitored and plotted in a graph. As shown in FIG. 5, in the half-separation mode, the temperature increase of the main thermistor is moderate in the half-separation mode, whereas the temperature increase rate of the sub-thermistor is very steep. This is because the heat supply from the heater to the fixing film is smaller in the half-separated mode than in the normal pressure mode, so that the electric power supplied to the heater is not used to increase the temperature of the fixing film, and the heater temperature is relative. This is because it is easy to rise.

  FIG. 12 and FIG. 8 show an example of the fixing control in the case where the fixing operation is performed with the envelope and the like under a setting with a low pressure in this embodiment.

  In the conventional example, the fixing temperature control temperature is increased in order from T0 to T1 to T2, and the fixing temperature control temperature at the time of paper passing is set to the highest setting. The temperature control temperatures T0, T1, etc. during the sheet interval are higher than the fixing temperature control temperatures T2, T3, and the pre-rotation time is extended by about 30 seconds. The result of measuring the temperature of each part in this case is shown in FIG.

  In the conventional example, when the temperature is controlled at T0 and T1 during the pre-rotation and the heater back temperature is increased, if the temperature control temperature is increased at T2, the sheet enters the fixing nip and the heat of the fixing film is taken away. In order to cope with this, more electric power is applied to the heater. For this reason, the heater back temperature further rises, exceeds the heat resistance temperature of the heater holder, melts, and deformation occurs.

  In contrast, in this embodiment, the temperature control temperature of T0 and T1 during the pre-rotation is increased, and the pre-rotation time is extended until the sheet enters the fixing nip, and the fixing device is warmed and stored. The heat is used to satisfy the fixing property even when the fixing temperature control temperature during the sheet passing is low. For this reason, when the sheet passes through the fixing nip, the heater power input can be made smaller than in the conventional example. In addition, by extending the pre-rotation time, the target temperature is reached while the pre-rotation time is extended, and the power input to the heater is reduced, so that the paper enters the fixing nip while the heater back temperature has decreased. Since power is supplied to the heater, it is possible to prevent an increase in the heater back temperature due to energization of the heater from a state where the heater back temperature is low.

  In this embodiment, the maximum temperature of the heater back temperature was about 270 ° C., which was higher than the heat resistance temperature of the heater holder (about 305 ° C.), and a sufficient temperature margin for melting and deformation could be secured.

  For example, there is a conventional example as disclosed in Japanese Patent Application Laid-Open No. 11-194656, in which an excessive temperature rise in a non-sheet passing portion is prevented by setting the inter-paper temperature lower than the print temperature. However, when the sheet is passed in a half-pressurized state as in the present invention, the amount of heat taken by the pressure roller in the non-sheet passing portion is reduced as described above, and the temperature rise rate becomes steep. For this reason, if the paper temperature is set lower than the printing temperature as disclosed in Japanese Patent Application Laid-Open No. 11-194656, the control temperature rises at the time of printing after the paper gap, so that the power input to the heater is increased and the heater back side is increased. The temperature rises rapidly, and melting of the heater holder occurs. In Japanese Patent Laid-Open No. 11-194656, a thermistor for performing a fixing temperature control operation detects the temperature of a single heater. On the other hand, in the case of a fixing device in which the thermistor for controlling the fixing temperature detects the temperature of the inner surface of the fixing film and does not directly detect the temperature of the heater as in the conventional example and the embodiment, the temperature control is performed. Since the responsiveness is poor and the heater holder melts more severely, it is different from the example of the fixing device disclosed in JP-A-11-194656.

  In this embodiment, the fixing method is the film fixing method, but other fixing methods, for example, a heat roller method or an electromagnetic induction heating method fixing device may be used.

  In the pressure release device according to the present embodiment, the three states of the normal pressure state, the half pressure state, and the separated state are provided, but a fixing device having more pressure states may be used. . In this embodiment, the separation state is a state in which the fixing film unit and the pressure roller are completely separated from each other, but is set for the convenience of jam processing. Even if it is in contact, there is no problem.

  The image forming apparatus can be applied not only to a color image forming apparatus but also to a monochrome image forming apparatus.

  Furthermore, as a fixing film in this example, a type in which an elastic layer is provided on a metal base layer was used, but only a base layer, a fixing film with a very thin coating on the base layer, and not a metal to compete, polyimide, etc. There is no problem even if a fixing film of a type using the above resin is used.

  This embodiment is characterized in that the pre-rotation time is switched according to the warming state of the fixing device during printing in order to prevent the print time from being extended every time due to the extension of the pre-rotation time in the first embodiment.

  A description of the same parts as those in the first embodiment will be omitted.

  In the first embodiment, even if the fixing device is cold or warm, the pre-rotation time is always extended by 30 seconds, so that the printing time becomes longer every time.

  When the fixing device is warm, the pre-rotation time is not necessarily the same as the time when the fixing device is cold. For this reason, in the second embodiment, the warming state of the fixing device is determined based on the detected temperature of the sub-thermistor.

  In the second embodiment, when the sub-thermistor detection temperature is less than 80 ° C., the same pre-rotation extension time as that in the first embodiment is set to 30 sec. When the sub-thermistor detection temperature is 80 ° C. or higher, the fixing unit is warmed, and the extension of the pre-rotation time is shortened to 5 seconds.

  FIG. 10 shows a flow in the second embodiment. Further, FIG. 11 shows the temperature of each part and the heater back temperature during envelope printing with a pre-rotation extension time of 5 sec in a state where the fixing device of Example 2 is warm.

  When the fixing unit is warm, the input power to the heater during the pre-rotation may be small and the pre-rotation time is short, so that the paper enters the fixing nip before the heater back temperature rises high and enters the heater. Therefore, an increase in the heater back temperature can be suppressed to about 260 ° C.

  In the present embodiment, since the pre-rotation extension time is switched depending on the state of the fixing device, it is possible to prevent the pre-rotation extension time from being long every time printing is performed and the printing time from becoming long.

  In this embodiment, the temperature detection of the fixing device is performed at the detection temperature of the sub-thermistor. However, the temperature sensor in the main body or other means may be used without being limited thereto.

  Also, other settings may be used for the temperature for determining the warming state of the fixing device (in this embodiment, the detection temperature of the sub-thermistor is 80 ° C.) and the pre-rotation extension time (30 sec and 5 sec). It is possible to obtain the same effect by setting.

It is a figure explaining operation | movement of the pressurization mechanism in 1st Example of this invention, and is a figure showing a normal pressurization state. It is a figure explaining operation | movement of the pressurization mechanism in 1st Example of this invention, and is a figure showing a separation state. It is a figure explaining operation | movement of the pressurization mechanism in 1st Example of this invention, and is a figure showing the state of half separated mode. 1 is a cross-sectional view of an image forming apparatus to which the present invention is applied. 1 is a cross-sectional view of a fixing device to which the present invention is applied. It is a figure which shows the shape of the pressure release cam in this invention. 6 is a graph for explaining a temperature rise when a constant power is supplied to the fixing device according to the present invention. Explanatory drawing of temperature control temperature control sequence during envelope mode paper feeding in the conventional example Graph of each part temperature and heater back temperature when envelope mode paper is passed in the conventional example Explanatory drawing of temperature control sequence at the time of envelope mode sheet feeding in Example 1 The graph of each part temperature and heater back temperature at the time of envelope mode paper passing in Example 1 Explanatory drawing of temperature control flow at the time of envelope mode paper feeding in Example 2 Graph of each part temperature and heater back temperature when envelope mode paper is passed in Example 2 FIG. 6 is a diagram for explaining an example of each temperature control temperature setting in a conventional example and an example of fixing control in a case where an envelope or the like in Example 1 is subjected to a fixing operation at a setting with a low pressure.

Explanation of symbols

1a to 1d Image forming units 2a to 2d Photosensitive drums 3a to 3d Chargers 4a to 4d Developing devices 5a to 5d Drum cleaning devices 6a to 6d Exposure devices 7a to 7d Transfer rollers 8 Transfer material conveying belt (transfer belt)
9 Driving roller 10 Tension roller 11 Fixing film 12 Pressure roller 13 Fixing device 14 Paper feed cassette 15 Transfer material conveyance guide 16 Registration roller 17 Paper discharge roller 18 Paper discharge tray 19 Heater 20 Heater holder 21 Main thermistor 22 Sub thermistor 23 Entrance guide 24 Frame 25 Fixing film unit 26 T stay 27 Connecting member 28 Pressure spring 29 Pressure release cam

Claims (7)

A fixing member having an internal heat source for fixing an image on the recording material, a pressure member for pressing and conveying the recording material against the fixing member, and the fixing member to the pressure member at a predetermined pressure There are two or more types of pressure modes: an urging means for pressing, a pressing mode that acts on the urging means and presses at least the fixing member against the pressing member, and a pressing mode with a lower pressing force. In a fixing device of an image forming apparatus having a pressure unit that can be held,
During the fixing operation in the pressure mode with a low pressing force, the fixing temperature control temperature during the sheet interval is set higher than the fixing temperature control temperature during the paper passing, and the pre-rotation time is extended. apparatus.   At least a first temperature detecting means for detecting the temperature of the fixing member, and a second temperature detecting means for detecting the temperature of the heat source, and the pre-rotation extension time is set according to the output of the second temperature detecting means. The fixing device according to claim 1, wherein the fixing device is switched.   3. The fixing device according to claim 1, wherein the heat source is a ceramic heater in which a resistance heating element is provided on a ceramic.   4. The fixing device according to claim 1, wherein the member that holds the heat source is made of resin.   5. The fixing device according to claim 1, wherein a fixing film having at least a sleeve-like flexible substrate is used as the fixing member.   6. The fixing device according to claim 1, wherein a fixing film in which an elastic layer is provided on at least a sleeve-like flexible substrate is used as the fixing member.   At least a first temperature detecting means for detecting the temperature of the fixing member and a second temperature detecting means for detecting the temperature of the heat source, wherein the first temperature detecting means or the second temperature detecting means are respectively 7. The fixing device according to claim 1, wherein the fixing device is disposed in contact with a fixing member or a heat source.

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