JP4865244B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device used in a printer, a copying machine, a facsimile, or the like that employs an electrophotographic system or an electrostatic recording system.

  Conventionally, various image forming apparatuses are known, and among them, an electrophotographic image forming apparatus in which an image is exposed to a photosensitive member with a laser beam and developed to obtain an image is widely used. Such an image forming apparatus has advantages such as high image quality and high speed, and is widely used as an output device such as a copying machine, a color laser beam printer, and the like.

  In these color image forming apparatuses such as copying machines and color laser beam printers, high productivity (number of prints per unit time) on various paper (recording materials) such as cardboard has been demanded. Yes.

  By the way, in the image forming apparatus to which the electrophotographic method is applied, it is necessary to increase the fixing speed of the fixing device in order to increase high productivity, particularly productivity on a sheet having a large basis weight. However, since paper with a large basis weight loses a lot of heat, the amount of heat required for fixing is significantly larger than when fixing on thin paper, and the fixing speed is reduced when fixing on paper with a large basis weight. At present, the fixing process is performed.

  Therefore, as a technique capable of improving the fixing speed of a color image, the fixing device configurations of Patent Document 1 and Patent Document 2 have already been proposed.

  That is, the image heating and fixing apparatus according to Patent Document 1 includes a fixing member pair that is rotatably arranged while being pressed against each other, and a recording material on which an unfixed image is formed at a nip portion formed by the fixing member pair. In an image heating and fixing apparatus that sandwiches and conveys and heat-fixes an unfixed image on the recording material, one or more external heating members can be brought into contact / retracted with respect to the fixing member pair.

In addition, an external heating device and a fixing device using the same according to Patent Document 2 are provided with an external heating unit that includes a plurality of external heating rolls that press-contact the surface of the member to be heated and heat the surface of the member to be heated from the outside. In the apparatus, there are provided contacting / separating means for pressing and separating a plurality of external heating rolls on the surface of the member to be heated, and adjusting means for uniformly pressing the plurality of external heating rolls on the surface of the member to be heated. It is a thing.
Japanese Patent Laid-Open No. 10-149044 JP 2004-37555 A

  However, the above prior art has the following problems. That is, in the case of the fixing device according to Patent Document 1, Patent Document 2, and the like, even if the recording material (hereinafter referred to as transfer paper) is thick paper, in order to realize high productivity substantially equal to that of thin paper, It is conceivable to increase the amount of heat applied to the surface of the heated member from the external heating roll by increasing the amount of heat of the roll. However, if the heat amount of the external heating roll is simply increased, when the transfer paper is fixed by the fixing device, the transfer paper becomes large on the surface of the member to be heated before the transfer paper enters the fixing portion. If the amount of heat is applied, the surface temperature of the member to be heated becomes too high, and the toner on the transfer paper is melted too much, so that the toner gloss (gloss) becomes too high. Therefore, even if it is attempted to control by the temperature control temperature of the external heating or the temperature control temperature of the member to be heated, the above problem cannot be solved because the heat response of the external heating roller or the member to be heated is poor.

  Also, if the transfer paper tries to give heat to the surface of the heated member from the external heating roll after it enters the fixing section, the temperature of the heated member will drop too much due to the transfer paper transferring the heat of the heated member. As a result, the toner on the transfer paper cannot be melted, the toner gloss (gloss) becomes low, and a toner gloss level difference (gloss unevenness) is formed. For this reason, the surface of the fixing roll, which is a member to be heated, cannot be effectively heated by the external heating roll, and high productivity cannot be realized, or the gloss fluctuation (gloss unevenness) of the color image can occur. As a result, a high-quality color image cannot be obtained.

  Further, in order to solve the above-mentioned problems, the heat amount may be applied from the external heating roll to the surface of the heated member at the moment when the transfer paper enters the fixing unit. Considering the timing of arrival at the heated member (adhesion timing deviation) and the timing of entering the fixing portion of the transfer paper, the amount of heat from the timing when the transfer paper enters the fixing portion and the surface of the heated member from the external heating roll It is impossible to match the timing of giving For example, when transferring a transfer paper at a speed of 300 mm / sec in order to obtain a high production of a copying machine and to obtain a productivity of 70 CPM, a difference in timing of arrival of an external heating roller may be caused by a motor. If responsiveness is taken to be 100 msec and the timing deviation entering the fixing portion of the transfer paper is taken to be 200 msec in consideration of the conveyance speed error, a timing deviation of about 300 msec will occur, and a distance of 90 mm will occur. .

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is from an external heating member such as an external heating roll to a fixing member (heated member) such as a heating fixing roll. The amount of heat applied to the surface of () can be adjusted instantaneously, and even when the recording material is cardboard, the productivity can be greatly improved, and there is no gloss fluctuation (uneven gloss) in the color image. It is an object of the present invention to provide a fixing device capable of obtaining a color image.

  The present invention is a fixing device having the following configuration.

(1) First and second fixing rotators that thermally fix the toner image on the recording material at the nip portion, and first and second heating that abut the first fixing rotator and heat the outer surface. And a rotatable support unit that integrally supports the first heating member and the second heating member, and at the start of a fixing operation, the first fixing rotating body with respect to the first fixing rotating body. After the first heating member is brought into contact, the second heating member is brought into contact so that both the first heating member and the second heating member are brought into contact with the first fixing rotator. In this case, the first heating member is configured so that the recording material enters the nip before the first fixing rotating body rises to a predetermined temperature by the first heating member, and the first fixing rotating body is formed by the recording material. said support uni so they abut the second heating member before the prescribed temperature drop A fixing device, characterized in that it comprises a control unit for controlling the preparative operations, the.

(2) First and second fixing rotators that heat-fix the toner image on the recording material at the nip portion, and first and second heating that abut the first fixing rotator and heat the outer surface. And a rotatable support unit that integrally supports the first heating member and the second heating member, and at the start of a fixing operation, the first fixing rotating body with respect to the first fixing rotating body. After the first heating member is brought into contact, the second heating member is brought into contact so that both the first heating member and the second heating member are brought into contact with the first fixing rotator. In this case, the first heating member is brought into contact with the first fixing rotating body before the recording material enters the nip portion, and the second heating is performed after the recording material reaches the nip portion. control unit for controlling the operation of the support unit so as to abut the member in the first fixing rotator A fixing device characterized in that it comprises a.

(3) In the rotational direction of the first fixing rotator, the first heating member is disposed upstream of the second heating member. (1) or (2) Fixing device.

  That is, in a fixing device having a plurality of external heating members, the contact pressure of each external heating member to the fixing rotator is shifted, or the contact pressure of each external heating member to the fixing rotator is variable. This makes it possible to adjust the amount of heat applied from the external heating member to the surface of the fixing rotator, making it possible to increase the heat capacity of the external heating member and greatly increasing the productivity even when the recording material is cardboard. In addition, it is possible to provide a fixing device that can obtain a high-quality color image with no gloss variation of the color image.

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus. The image forming apparatus of this example is a tandem type color laser printer using a transfer type electrophotographic process.

  The image forming apparatus includes four image forming portions Pa, Pb, Pc, and Pd that are first, second, third, and fourth, and toner images of different colors are used for latent images, development, and transfer, respectively. Formed through a process.

  Each of the image forming portions Pa, Pb, Pc, and Pd includes a dedicated image carrier, in this example, the electrophotographic photosensitive drums 3a, 3b, 3c, and 3d, on the photosensitive drums 3a, 3b, 3c, and 3d. A toner image of each color is formed. An intermediate transfer member (intermediate transfer belt) 130 is installed adjacent to each of the photosensitive drums 3a, 3b, 3c, and 3d, and the toner images of the respective colors formed on the photosensitive drums 3a, 3b, 3c, and 3d are transferred to the intermediate transfer member. Primary transfer onto 130 and transfer onto the recording material P at the secondary transfer portion. Further, the recording material P onto which the toner image has been transferred is fixed by the fixing device 9 by heating and pressurizing, and is discharged as a recording image formed product onto a paper discharge tray 6 outside the apparatus.

  Drum chargers 2a, 2b, 2c, and 2d, developing devices 1a, 1b, 1c, and 1d, primary transfer chargers 24a, 24b, 24c, and 24d, and a cleaner are disposed on the outer periphery of the photosensitive drums 3a, 3b, 3c, and 3d, respectively. 4a, 4b, 4c, and 4d are provided, and laser scanners 5a, 5b, 5c, and 5d are further provided above the apparatus.

  The photosensitive drums 3a, 3b, 3c, and 3d are rotationally driven in the counterclockwise direction indicated by the arrow, and the peripheral surfaces thereof are uniformly primary charged to a predetermined polarity and potential by the drum chargers 2a, 2b, 2c, and 2d. The uniformly charged surfaces of the photosensitive drums 3a, 3b, 3c, and 3d are subjected to scanning exposure with laser light that is modulated in accordance with image signals output from the laser scanners 5a, 5b, 5c, and 5d, A latent image corresponding to the image signal is formed on each photosensitive drum 3a, 3b, 3c, 3d. That is, each of the laser scanners 5a, 5b, 5c, and 5d is provided with a light source device, a polygon mirror, and the like, scans the laser light emitted from the light source device by rotating the polygon mirror, and the light flux of the scanning light Is deflected by a reflecting mirror, condensed on the buses of the photosensitive drums 3a, 3b, 3c, and 3d by an fθ lens and exposed to La, Lb, Lc, and Ld, and thus on the photosensitive drums 3a, 3b, 3c, and 3d. A latent image corresponding to the image signal is formed.

  The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners, respectively, as developers. The developing devices 1a, 1b, 1c, and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and visualize them as cyan toner images, magenta toner images, yellow toner images, and black toner images.

  The intermediate transfer member 130 is suspended around three parallel rollers 13, 14, and 15 and is driven to rotate in the clockwise direction indicated by the arrows at the same peripheral speed as the photosensitive drums 3a, 3b, 3c, and 3d. .

  The yellow toner image of the first color formed and supported on the photosensitive drum 3 a of the first image forming portion Pa passes through the nip portion between the photosensitive drum 3 a and the intermediate transfer member 130 and is transferred to the intermediate transfer member 130. Primary transfer is performed on the outer peripheral surface of the intermediate transfer body 130 by the electric field and pressure formed by the applied primary transfer bias.

  Hereinafter, similarly, the second color magenta toner image and the third color cyan formed and supported on the photosensitive drums 3b, 3c, and 3d of the second, third, and fourth image forming portions Pb, Pc, and Pd. The toner image and the black toner image of the fourth color are sequentially superimposed and transferred onto the intermediate transfer member 130, and a composite color toner image corresponding to the target color image is formed on the intermediate transfer member 130.

  Reference numeral 11 denotes a secondary transfer roller. The intermediate transfer body 130 is sandwiched and pressed against the roller 14 out of the three rollers 13, 14, and 15, which are stretched around the intermediate transfer body 130. A secondary transfer nip portion is formed with the body 130.

  On the other hand, the recording material P is separated and fed from the paper feed cassette 10 and waits for a predetermined time by a registration roller 12 as a recording material conveying means so that the image is aligned with the image on the intermediate transfer member. The conveyance is started at a predetermined timing. Then, the recording material passes through the pre-transfer guide and is fed to the secondary transfer nip portion, which is a contact nip between the intermediate transfer body 130 and the secondary transfer roller 11, at a predetermined timing, and is applied from the bias power source. The composite color toner image superimposed and transferred onto the intermediate transfer member 130 is secondarily transferred onto the recording material P all at once by the next transfer bias.

  The recording material P that has received the composite color toner image transferred at the secondary transfer nip is separated from the intermediate transfer body 130 and sequentially introduced into the fixing device 9, and the toner image is fixed by applying heat and pressure to the recording material. Is done.

  After the primary transfer, the photosensitive drums 3a, 3b, 3c, and 3d are cleaned and removed of the transfer residual toner by the respective cleaners 4a, 4b, 4c, and 4d, and are continuously prepared to form the next latent image.

  The toner and other foreign matters remaining on the transfer belt 130 are wiped off by contacting a cleaning web (nonwoven fabric) 19 with the surface of the transfer belt 130.

  When the double-sided copy mode is selected, the recording material P on which the first side image has been formed that has left the fixing device 9 is introduced by the flapper 16 to the sheet path 17 side on the recirculation conveyance mechanism side, and further switched back. Then, the sheet passes through the sheet path 18, is drawn out and conveyed from the sheet path 18, and is guided to the re-conveyed sheet path 19, and passes through the registration roller 12 and the pre-transfer guide from the sheet path 19. The toner is reintroduced at a predetermined timing into the secondary transfer nip portion, which is a contact nip with the roller 11, in an inverted state. Thereby, the secondary transfer of the toner image on the intermediate transfer body 130 is performed on the second surface side of the recording material P. The transfer material P that has received the secondary transfer of the toner image to the second surface at the secondary transfer nip portion is separated from the intermediate transfer body 130 and re-introduced into the fixing device 9, and undergoes a toner image fixing process and double-sided copy. Is discharged to a discharge tray 6 outside the apparatus.

  As described above, since a multicolor toner forms two to four layers in a color image, in an electrophotographic image forming apparatus capable of forming a color image, what is a black and white apparatus for toner? It has different characteristics.

  That is, since this toner is required to have good meltability and color mixing properties when heat is applied, a sharp melt toner having a low softening point and a low melt viscosity is used. By using this sharp melt toner, a color copy having a wide color reproduction range of a copy can be obtained.

  Such sharp melt toners are prepared by melt-kneading and pulverizing toner-forming materials such as binder resins such as polyester resins or styrene-acrylic ester resins, colorants (dyes, sublimation dyes), and charge control agents. It is manufactured by classification.

(2) Image heating and fixing device 9
Next, the configuration of the image heating and fixing device 9 will be described in detail with reference to FIG. The image heating and fixing device 9 includes a fixing roller 40 serving as a first fixing member ( first fixing rotating body) having a halogen heater 40a serving as a heat generating unit, and a halogen heater 41a serving as a heat generating unit. , And a pressure roller 41 serving as a second fixing member (pressure rotator : second fixing rotator ) is rotated while being pressed against each other at a total pressure of about 784 N (about 80 kg) by a pressure mechanism (not shown). It is configured as a pair of fixing members that can be arranged. N is a fixing nip portion formed by pressure contact between the fixing roller 40 and the pressure roller 41. The fixing roller 40 and the pressure roller 41 are rotationally driven in the direction of the arrow by a drive system (not shown).

  Thermistors 42a and 42b, which are temperature detecting means, are in contact with the fixing roller 40 and the pressure roller 41, and the temperatures of the fixing roller 40 and the pressure roller 41 are detected by the thermistors 42a and 42b. On the basis of this, the control device 43 controls the halogen heaters 40a and 41a so that both the fixing roller 40 and the pressure roller 41 are maintained at a constant temperature of about 165 ° C., thereby being transferred onto the recording material P. The unfixed image t formed with a developer such as sharp melt toner passes through the fixing nip N between the fixing roller 40 and the pressure roller 41 and is heated and pressed so as to be fixed on the recording material P. It has become.

  The sharp-melt color toner formed on the recording material P has a high affinity and has a property of being easily offset to the fixing roller 40. Therefore, it is necessary to exhibit high releasability for a long time. It becomes. Therefore, an oil application device 44 serving as a release agent application means and a cleaning device 45 for removing oil and dirt from the fixing roller 40 are provided near the outer periphery of the fixing roller 40, and the pressure roller 41 is provided near the outer periphery of the pressure roller 41. By providing the cleaning blade 46 for removing the oil 41 and dirt 41, the mold release property is further improved.

  The oil application device 44 regulates the oil application amount by the oil application amount adjusting blade 50 through the oil pumping roller 48 and the oil application roller 49 through the dimethyl silicone oil 47a (KF96, 300cs made by Shin-Etsu Chemical) in the oil pan 47. Then, it is applied onto the outer peripheral surface of the fixing roller 40.

  The oil application roller 49 is capable of contacting and separating from the fixing roller 40 and applies oil over the fixing roller development surface length corresponding to a position 5 mm from the front end of the recording material P to a position 5 mm from the rear end. It has become.

  The fixing roller 40 is provided with an HTV (high temperature vulcanization type) silicone rubber layer 40c as an elastic layer on the outer periphery of an aluminum cored bar 40b, and an RTV (heat resistant elastic layer) on the outer periphery of the HTV silicone rubber layer 40c. Room temperature vulcanization type) A silicone rubber layer 40d is provided, and it has a thickness of 3 mm and a diameter of 60 mm.

  On the other hand, the pressure roller 41 is provided with a 1 mm thick HTV silicone rubber layer 41c as an elastic layer on the outer periphery of an aluminum cored bar 41b, and further with a fluororesin layer 41d on the outer periphery of the HTV silicone rubber layer 41c. The diameter is 60 mm.

  By combining the fixing roller 40 and the pressure roller 41 configured as described above, the releasability with respect to the sharp melt toner is further enhanced.

  In recent years, with the widespread use of color copiers, color is also as fast as black-and-white copiers and convenience, that is, automatic double-sided copying, the use of paper from postcards to large sizes, thin paper to thick paper, It has become necessary to meet various needs such as the use of OHP films and pack print films.

  Therefore, in order to fix the double-sided image, RTV or LTV (low temperature vulcanization type) silicone rubber having a high toner releasing effect is used not only on the fixing roller 40 but also on the surface of the pressure roller 41, and at the same time, color fixing. In order to satisfy the high speed, the diameter of the roller is increased (for example, 80 mm) to increase the fixing nip portion N, and in order to use thick paper, the fixing temperature is increased to improve the fixing property. I am trying.

  In addition, the surface layer silicone rubber originally used for maintaining the releasability and the lower layer silicone rubber for forming the fixing nip N that wraps the sharp melt toner are both used as silicone oil and an Therefore, the silicone rubber enters a large amount in the silicone rubber according to the durability, and the bottom silicone rubber contains a large amount of silicone oil. This may occur. Therefore, in a copying machine that is required to make a large number of copies at high speed, both the fixing roller 40 and the pressure roller 41 are provided between the lower silicone rubber and the surface silicone rubber in order to prevent this peeling. It is preferable to laminate a fluoro rubber as an oil resistant layer that does not absorb and pass silicone oil.

(2-1) External Heating Member Next, the configuration of the external heating member, which is a feature of the present invention, will be described. As shown in FIG. 2, on the outer peripheral surface of the fixing roller 40, first and second external heating rollers 53, 54 (first heating member 53, second heating member 54) serving as external heating members are provided. Are arranged juxtaposed on the upstream side and the downstream side in the rotation direction of the fixing roller 40 and are configured to be able to contact / retreat with respect to the fixing roller 40. The contact / retraction mechanism will be described later.

  In the external heating rollers 53 and 54, the heat response from the fixing roller heater 40a is not in time because the heat conductivity of the rubber layer on the surface of the fixing roller is low with respect to the amount of heat taken by the recording material during fixing. Therefore, it is provided for the purpose of keeping the fixing roller surface temperature constant. In order to increase the speed of the apparatus, two external heating rollers are provided to increase the amount of heat applied from the external heating rollers 53 and 54 to the surface of the fixing roller.

  The external heating rollers 53 and 54 include halogen heaters 53a and 54a therein, and the outer periphery thereof has, for example, a metal such as aluminum, iron, and stainless steel having high thermal conductivity, or has high releasability. The metal surface is coated with rubber, resin or the like. The external heating rollers 53 and 54 are held at both ends by a heat insulating bush having high heat resistance.

  The thermistors 42a, 42b, 42c, and 42d as temperature detecting means are disposed in contact with the fixing roller 40, the pressure roller 41, and the first and second external heating rollers 53 and 54, respectively. The surface temperature of each roller 40, 41, 53, 54 is detected by 42a, 42b, 42c, 42d. During the fixing operation, the controller 43 controls the power supplied to the halogen heaters 40a, 41a, 53a, and 54a based on the temperature information, and the temperature of the rollers 40, 41, 53, and 54 is adjusted. Yes.

  As an example of the temperature control, the first external heating roller 53 is set to be higher in temperature than the fixing roller 40 and the pressure roller 41 as a fixing member pair. For example, the external heating rollers 53 and 54 are 230 ° C., The fixing roller 40 and the pressure roller 41 are set to 165 ° C.

  That is, the control device 43 includes a first control unit that controls the temperatures of the fixing roller 40 and the pressure roller 41 that are fixing members, a first external heating roller 53 that is a plurality of external heating members, and a second external heating member. Second control means for controlling the temperature of the heating roller 54, and the target temperature of the first external heating roller 53 and the second external heating roller 54 by the second control means is determined by the first control means. The temperature is higher than the target temperature of the fixing roller 40 and the pressure roller 41.

  It should be noted that when the temperature of the external heating rollers 53 and 54 is kept higher than the temperature of the fixing roller 40 as a fixing member, the response (heat sensitivity) to the drop of the surface temperature of the fixing roller 40 due to the recording material. Accuracy) Since the heat is supplied from the external heating rollers 53 and 54 to the fixing roller 40, the temperature of the external heating rollers 53 and 54 is set to 75 ° C. higher than that of the fixing roller 40 and the pressure roller 41. ing.

(2-2) Pressure Configuration of External Heating Member Next, a pressure mechanism as a pressure unit for the fixing roller 40 of the external heating members 53 and 54 will be described.

  As shown in FIG. 3, the first and second external heating rollers 53 and 54 are rotatably supported by the external heating support frame 30 at both ends thereof via heat insulating bushes and bearings (not shown). It is. The external heating support frame 30 is rotatably supported on the external heating and pressurizing arm 32 by supporting shafts at both ends on the front side and the back side. The external heating support frame 30 is urged by a spring 33 so as to rotate in the direction of arrow a about the support shaft 31, and the external heating rollers 53 and 54 are separated from the fixing roller 40. In the state (a), the abutting portion 30a provided on the external heating frame 30 abuts on the external heating and pressurizing arm 32. The external heating and pressing arm 32 is rotatable about a support shaft 34 with respect to a fixing unit frame (not shown). An external heating and pressing spring 35 is provided on the free end side of the external heating and pressing arm 32, and is urged to rotate in the direction of arrow b about the support shaft 34.

  In the state (c) in which the first and second external heating rollers 53 and 54 are in contact with the fixing roller 40, the external heating roller 53 is driven by the external heating pressure spring 35 and the spring 33. , 54 are configured to be pressurized by the fixing roller 40. The external heating rollers 53 and 54 are brought into pressure contact with the fixing roller 40 with a total pressure of about 392 N (about 40 kg), and are rotated by the rotation of the fixing roller 40. The contact nips (contact lengths) N53 and N54 between the external heating rollers 53 and 54 and the fixing roller 40 are about 5 mm, respectively. When the two rollers 53 and 54 are combined, a nip of 10 mm is obtained. Can be taken.

(2-3) External Heating Member Attachment / Removal Configuration Next, an attachment / detachment mechanism as attachment / detachment means for the first and second external heating members 53, 54 will be described with reference to FIG. As described above, the external heating and pressurizing arm 32 is rotatable about the support shaft 34, and the tip of the pressure releasing arm 36 is at the free end of the external heating arm 32. It is in contact. The pressure release arm 36 is rotatable about a rotation shaft 36a.

As shown in (c), when the first and second external heating rollers 53 and 54 are pressed against the fixing roller 40, the pressure release arm 36 is separated from the external heating and pressing arm 32. When the first and second external heating rollers 53, 54 are separated from the fixing roller 40, the pressure release arm 36 is rotated as shown in FIG. 32 is pushed upward. The pressure release arm 36 is rotated by rotating means M controlled by the control device 43 (FIG. 2). The rotating means M is configured using a known technique such as a spring clutch, a motor, or the like.

  Here, the operation until the external heating rollers 53 and 54 are changed from the separated state to the pressurized state will be described with reference to FIGS.

  9A shows a state where the first and second external heating rollers 53 and 54 are separated from the fixing roller 40, that is, a standby state (when waiting for image formation). From this state, an image formation start signal is output to the image forming apparatus (when the image forming apparatus is used as a copying machine, a signal is generated by pressing a start button from an operation unit such as a liquid crystal. When a printer connected to a network with the external device is used, a signal is generated by a print command from the external device), and image forming preparation operations of various image forming devices in the image forming apparatus are started. The fixing preparation operation of the fixing device is also started.

  Then, a fixing preparation operation is started. When the temperatures of the fixing roller, the pressure roller, and the two external heating rollers reach a temperature sufficient to start fixing, the fixing operation is started. In this example, the fixing operation is started on the basis of the image exposure start timing for the photosensitive member of the fourth image forming unit. Specifically, control is performed so that the operation of the attachment / detachment mechanism is started after a predetermined time has elapsed from the exposure start timing of the fourth image forming unit to the photosensitive member.

  Further, the conveyance timing of the recording material to the secondary transfer portion of the intermediate transfer member, that is, the registration roller conveyance start timing is also performed based on this image exposure start timing.

  That is, the pressure release arm 36 is rotated in the direction of the arrow c, and the external heating and pressing arm 32 is rotated in the direction of the arrow b, so that the external heating support frame 30, that is, the first and second externals are rotated. The heating rollers 53 and 54 start moving in the direction of the fixing roller 40.

  Then, as shown in (b), the first external heating roller 53 first contacts the fixing roller 40, and the heat of the first external heating roller 53 moves to the fixing roller 40. It becomes like this. In this state, the first external heating roller 53 is pressed against the fixing roller 40 by the spring 33.

  When the pressure release arm 36 further rotates in the direction of the arrow c, the external heating support frame 30 rotates in the direction of the arrow d around the rotation shaft 31, and as shown in FIG. The heating roller 54 is also in pressure contact with the fixing roller 40, the heat of the second external heating roller 54 is also moved to the fixing roller 40, and the pressing operation is completed. To do. In this state (c), the first and second external heating rollers 53, 54 are pressed against the fixing roller 40 by the external heating pressurizing spring 35 and the spring 33.

  That is, when the pressure release arm 36 is rotated in the direction of the arrow c, the first external heating roller 53 is first brought into contact with the fixing roller 40, and then a predetermined time is passed. The two external heating rollers 54 are also in contact with the fixing roller 40.

At the start of the fixing operation, the control circuit unit 34 rotates the pressure release arm 36 in the direction of the arrow c by the rotating means M to execute the operations (a) → (b) → (c), thereby fixing. First, the first external heating roller 53 and then the second external heating roller 54 are sequentially brought into contact with the roller 40.

  At the end of the fixing operation, the control circuit unit 34 rotates the pressure release arm 36 in the direction opposite to the direction of the arrow c by the rotating means M, so that (a) → (b) → (c). The reverse operation is performed to return to the initial state (a), that is, the state where both the first and second external heating rollers 53 and 54 are separated from the fixing roller 40. This state is maintained until the start of the fixing operation.

(2-4) Comparative Experiment 1) The first and second external heating members 53 and 54 are in contact with the fixing roller 40 at the same time, so that the recording material P is being heated while the fixing nip temperature is rising. When an external heating member contact control means is provided in which the leading end of the toner enters the fixing nip portion N.

  2) When there is no external heating roller.

  3) When the first external heating roller 53 and the second external heating roller 54 sequentially contact and press the fixing roller 40 after a predetermined time. That is, the external heating roller 53 is brought into contact with the fixing roller 40 immediately before the recording material reaches the nip portion.

  Experiments were performed to compare temperature changes on the surface of the fixing roller 40 in each of the three cases 1), 2), and 3). The result is shown in FIG.

  In FIG. 5, the horizontal axis represents time (seconds), and the vertical axis represents the fixing nip temperature (surface temperature of the fixing roller 40 at the fixing nip N) (° C.).

  Here, the first and second external heating rollers 53 and 54 are hollow aluminum rods having an outer diameter of 30 mm and a thickness of 3 mm. The fixing roller 40 and the external heating rollers 53 and 54 are formed. The nip portions N53 and N54 are each configured to have a width of 4 mm in the rotation direction.

Further, the halogen heater 40a of the fixing roller 40 is 1200 W, the halogen heaters 53a of the external heating rollers 53 and 54 are 500 W, and 54a is 500 W. The paper conveyance speed of the recording material P is 300 mm / sec, and the recording material is 250 g / sec. Experiments were performed using m ² . The heater wattage of the external heating roller is set to a wattage that maintains the surface temperature of the fixing roller even when a 250 g / m ² recording material is continuously fed at 300 mm / sec. .

  In FIG. 5, the point at which the recording material P enters the fixing nip N is A, and the point at which the first and second external heating rollers 53 and 54 start to contact the fixing roller 40 simultaneously. B ′, the point at which the external heating rollers 53 and 54 of the fixing roller 40 start to contact at the same time reaches the fixing nip portion N at the first point B, the first (first) external heating roller The point at which 53 starts to contact the fixing roller 40 is C ′, and the point at which the first external heating roller 53 of the fixing roller 40 starts to contact first reaches the fixing nip portion N. C, point D ′ where the second (second) external heating roller 54 starts to contact the fixing roller 40, and the second external heating roller 54 of the fixing roller 40 starts to contact. The point at which the completed point first reaches the fixing nip N is indicated by D.

  FIG. 5A shows a case where the external heating members 53 and 54 in 2) are not provided. In this case, when the recording material enters the fixing nip N (A), the recording material P is deprived of heat, so that the surface temperature of the fixing roller 40 decreases, and when the thermal response of the fixing heater starts, the fixing roller The surface temperature of 40 rises and returns. The temperature drop of the fixing roller is about 20 ° C., and not only the gloss is lowered, but also a low temperature offset occurs, resulting in fixing failure.

  Here, FIG. 4 is a diagram showing the change (roughness of the image surface) of the gloss (glossiness) of the recording material with respect to the temperature of the fixing nip portion N of the image heating and fixing device 9.

  In the above experiment, even when fixing failure does not occur, the gloss is reduced from 30% to 15%, and since the gloss fluctuation is large, the fixed recording material cannot have high image quality. Therefore, in order to form a high-quality image, it is preferable that the gloss fluctuation is 20% or less in the range.

  In FIG. 5B, the first and second external heating rollers 53 and 54 of 1) above simultaneously contact the fixing roller 40, and heating is started by the two external heating rollers 53 and 54 ( This is a case where the leading end in the conveyance direction of the recording material P reaches the fixing nip portion N after the contacted region has first passed through the fixing nip portion N. In this case, the first and second external heating rollers 53 and 54 are temperature-controlled at 230 ° C., and before the recording material P reaches the fixing nip N, the first and second external heating rollers are controlled. -Since both rollers 53 and 54 start supplying heat to the fixing roller 40, the fixing roller starts from the point B at which the external heating rollers 53 and 54 contact the fixing nip portion N first. The temperature of the roller 40 starts to rise, and the temperature of the fixing roller 40 continues to rise to the point (A) where the recording material P reaches the fixing nip N.

  In such a configuration, the temperature of the fixing roller 40 is increased by a little less than 15 ° C., a gloss change of about 15% occurs, and the gloss on the leading side in the conveyance direction of the recording material P becomes high. That is, in such a configuration, the difference in gloss between the front end side and the rear end side in the conveyance direction of the first recording material is large, resulting in uneven gloss, resulting in a low-quality image.

  FIG. 5C shows a case in which the first and second external heating members 53 and 54 are configured to sequentially contact the fixing roller 40 after a predetermined time according to the present invention, as in the above 3). It is. That is, the recording is performed while the temperature of the fixing nip portion N of the fixing roller 40 is rising (between “C to D”) due to the first and second external heating members 53 and 54 sequentially contacting each other. In this case, the conveyance timing of the recording material is controlled so that the leading end of the material reaches the fixing nip portion N.

  In such a configuration, the first (first) external heating roller 53 starts supplying heat to the fixing roller 40 before the recording material reaches the fixing nip portion N. The temperature of the fixing roller 40 starts to rise from the point C at which the 40 first external heating roller 53 starts to contact the fixing nip portion N, and the temperature of the fixing roller 40 is increased. Continues to rise to the point (A) at which the recording material P reaches the fixing nip N.

  However, as compared with the case of FIG. 5B in which the first and second external heating members 53 and 54 are simultaneously pressed / contacted with the fixing roller 40, the recording material P is fixed to the fixing nip. When the temperature reaches the portion N, the temperature increase rate of the fixing roller 40 is reduced, the temperature increase of the fixing roller 40 is suppressed to 4 ° C., and the gloss on the leading and trailing ends of the recording material P in the conveyance direction is reduced. Can be prevented from greatly differing, and a high-quality image can be obtained.

  This is because when the leading edge of the recording material reaches the fixing nip portion N, the first (first) external heating roller 53 has a small amount of heat applied to the fixing roller 40, so that the recording material P is deprived of heat. When the surface temperature of the fixing roller 40 drops and the point where the second (second) external heating roller 54 comes into contact with the fixing nip N first passes through the point D, the first and second Since the amount of heat applied from the external heating rollers 53 and 54 to the fixing roller 40 is increased, the temperature of the fixing roller 40 is restored to a desired temperature adjustment temperature (165 ° C. in this example). . That is, while maintaining high image productivity when forming images on a plurality of recording materials, the temperature drop of the fixing roller 40 is about 3 ° C. compared to the fixing roller temperature of 165 ° C., and the surface temperature of the fixing roller is increased. It has been found that the descent of can be suppressed considerably.

  As described above, by using the external heating member contact control means of this embodiment (in the case of FIG. 5C), the temperature change of the fixing roller 40 can be suppressed to about 7 ° C. in the range. Thus, it was found that the gross change was suppressed to about 8%, and high productivity was possible with high image quality.

  In this example, since the image forming speed (fixing speed) is very high, the two rollers 53 and 54 are used as external heating members to compensate for the temperature drop of the fixing roller 40 due to the recording material and toner. Thus, a plurality of recording materials are continuously passed through the nip portion so as to cope with a continuous image forming job for fixing.

  Furthermore, as described above, since the external heating members 53 and 54 are for compensating for the temperature drop of the fixing roller 40, the temperature adjustment temperature is set to a temperature higher than the temperature adjustment temperature of the fixing roller 40. If the time until the recording material passes through the fixing nip portion after abutting such an external heating member on the fixing roller is too long, the surface temperature of the fixing roller 40 increases excessively, which causes a fixing failure. End up.

  Therefore, within a predetermined time after the first external heating roller 53 comes into contact with the fixing roller 40, that is, the external surface temperature (in the nip portion) of the fixing roller 40 is adjusted to a temperature adjustment temperature (165 ° C.) by the external heating roller 53. It is preferable to perform control so that the leading edge of the recording material starts to enter the fixing nip N within a predetermined temperature, specifically within a time period until the temperature rises by 10 ° C.

  Since this rising temperature of 10 ° C. is a time for dealing with the above-mentioned gloss unevenness, the present invention is not limited to such a numerical value, and it is a matter of course that an appropriate numerical value may be set for each apparatus. .

Then, within a predetermined time after the leading edge of the recording material enters the fixing nip portion N, that is, within a time during which the outer surface temperature of the fixing roller 40 is lowered by a predetermined temperature, specifically 10 ° C., from the temperature adjustment temperature. In addition, it is preferable to start the second external heating roller 54 in contact with the fixing roller 40.
That is, the recording material enters the nip portion before the fixing roller 40 rises by a predetermined temperature by the first external heating roller 53, and the second before the fixing roller 40 drops by the recording material by a predetermined temperature. The external heating roller 54 is brought into contact.

  Similarly, the lowering (falling) temperature of 10 ° C. is a time for coping with the above-mentioned gloss unevenness, and the present invention is not limited to such a numerical value. Of course it is good.

  In this example, the first and second external heating rollers 53 and 54 that are external heating members perform contact / retraction operations with respect to the fixing roller 40 that is a fixing member pair, and the timing at which the recording material P is conveyed ( In order to correspond to the timing at which the fixing roller 40 and the pressure roller 41 enter the fixing nip portion), the image writing timing (photosensitive member) of the fourth image forming portion (image forming station) Pd at the most downstream side. The exposure start timing of the first and second external heating rollers 53 and 54 was controlled with respect to the fixing roller 40 as a trigger (exposure start timing).

  In addition, when the fixing process to the last recording material of the continuous image forming job on a plurality of recording materials is completed, the first and second external heating rollers 53 and 54 are controlled to be immediately retracted from the fixing roller 40. The

  Although the example in which the external heating rollers 53 and 54 are used as the external heating member has been described above, in addition to the roller, a belt-shaped member that rotates following the fixing roller 40 made of resin, rubber, metal, or the like is used. It is also possible to configure.

  Further, the case where the external heating rollers 53 and 54 as the external heating members are configured to be able to contact / retreat with respect to the fixing roller 40 as the fixing member pair has been described. However, as another configuration, the external heating rollers 53 and 54 are configured. May be configured to be able to contact / retreat with respect to the pressure roller 41 as a pair of fixing members.

  In addition, the pair of fixing members is constituted by two roller systems including the fixing roller 40 and the pressure roller 41, but a belt-like member may be used in addition to the rollers.

Example 2 will be described with reference to FIG. This embodiment, during the fixing operation is started, a fixing device in which the contact pressure against the fixing roller 40 of the first and second external heating rollers 53 and 54 to sequentially Tsugidai hear.

  The pressurizing configuration / detaching configuration of the external heating member in the present embodiment is the same as the configuration of the first embodiment in FIG.

  FIG. 6A shows a state in which the first and second external heating rollers 53 and 54 are separated from the fixing roller 40, and from this state, the pressure release arm 36 has an arrow. By rotating in the direction c, the external heating and pressurizing arm 32 rotates in the direction of the arrow b, and the external heating support frame 30, that is, the first and second external heating rollers 53 and 54 are displayed. Starts moving in the direction of the fixing roller 40.

  In the present embodiment, the first and second external heating rollers 53 and 54 abut against the fixing roller 40 almost simultaneously, but the first external heating roller 53 abuts. The contact is made in a state where the pressure is larger than the contact pressure of the second external heating roller 54. Further, as the pressure release arm 36 is rotated in the direction of the arrow c, the contact pressure of the first external heating roller 53 and the second external heating are caused by the pressing force of the spring 35 as shown in FIG. The contact pressure of the roller 54 increases sequentially, and the contact pressure becomes maximum when the pressure release arm 36 is separated from the external heating and pressurizing arm 32 as shown in FIG. The contact pressure of the first external heating roller 53 and the contact pressure of the second external heating roller 54 are substantially the same.

At the start of the fixing operation, the control circuit section 34 rotates the pressure release arm 36 in the direction of the arrow c by the rotating means M to execute the operations (a) → (b) → (c). The contact pressures of the first and second external heating rollers 53 and 54 with respect to the fixing roller 40 are sequentially increased and brought into contact with the fixing roller 40.
That is, the recording material enters the nip portion before the fixing roller 40 rises by a predetermined temperature by the first external heating roller 53, and before the fixing roller 40 falls by a predetermined temperature by the recording material. The contact pressure of the second external heating roller 54 is increased.

  At the end of the fixing operation, the control circuit unit 34 rotates the pressure release arm 36 in the direction opposite to the direction of the arrow c by the rotating means M, so that (a) → (b) → (c). The reverse operation is performed to return to the initial state (a), that is, the state where both the first and second external heating rollers 53 and 54 are separated from the fixing roller 40. This state is maintained until the start of the fixing operation.

  In the second embodiment, the pressure of the external heating roller is controlled by maintaining the pressure release arm as in the state of (b), thereby controlling the nip length of the external heating roller. Thus, the same effect as in the first embodiment is obtained.

That is, if the total nip length of the external heating rollers 53, 54 in (b) is W1 + W2, and the total nip length of the external heating rollers 53, 54 in (c) is W3 + W4, (W1 + W2) <(W3 + W4) It has become a relationship. Further, the nip length of W1 + W2 is more different in fixing condition, in the same manner as in Example 1 W1 + W2 = (W3 + W4 ) / 2 is preferable.

  With the above configuration, it is possible to greatly improve the productivity of cardboard as in the case of Example 1, and it is possible to obtain a high-quality color image free from color image gloss fluctuation (gloss unevenness). A fixing device can be provided.

  Here, the fixing device of the present invention includes an image heating device that presupposes an unfixed image and an image heating device that reheats the recording medium carrying the image to improve the surface properties such as gloss.

1 is a schematic configuration diagram of an example of an image forming apparatus. 1 is a schematic configuration diagram of a fixing device. FIG. 3 is an explanatory diagram of a pressure configuration / detachment configuration of an external heating member in the fixing device according to the first exemplary embodiment. FIG. 6 is a diagram illustrating a relationship between a fixing roller temperature and gloss. FIG. 6 is a graph showing a change in fixing roller temperature. FIG. 10 is an explanatory diagram of a pressure configuration / detachment configuration of an external heating member in the fixing device of Embodiment 2.

Explanation of symbols

  40 ..Fixing roller, 41 ..Pressure roller, 53, 54 ..External heating roller, 30 ..External heating frame, 31 ..External heating and pressure arm, 35. .External heating and pressure spring, 36..Pressure release arm

Claims (3)

First and second fixing rotators that thermally fix the toner image on the recording material at the nip portion; first and second heating members that contact the first fixing rotator and heat the outer surface; In a fixing device having
A rotatable support unit that integrally supports the first heating member and the second heating member;
At the start of the fixing operation, the first heating member is brought into contact with the first fixing rotator, and then the second heating member is brought into contact with the first heating member and the second heating member. When both of the heating members are brought into contact with the first fixing rotator, the recording material enters the nip portion before the first fixing rotator rises by a predetermined temperature by the first heating member. And a controller that controls the operation of the support unit so that the second heating member is brought into contact with the recording material before the first fixing rotator is lowered by a predetermined temperature.
A fixing device. First and second fixing rotators that thermally fix the toner image on the recording material at the nip portion; first and second heating members that contact the first fixing rotator and heat the outer surface; In a fixing device having
A rotatable support unit that integrally supports the first heating member and the second heating member;
At the start of the fixing operation, the first heating member is brought into contact with the first fixing rotator, and then the second heating member is brought into contact with the first heating member and the second heating member. When both of the heating members are brought into contact with the first fixing rotator, the first heating member is brought into contact with the first fixing rotator before the recording material enters the nip portion. A control unit for controlling the operation of the support unit so that the second heating member is brought into contact with the first fixing rotating body after the recording material reaches the nip portion;
A fixing device. In the rotation direction of the first fixing rotator, wherein the first heating member fixing apparatus according to claim 1 or claim 2, characterized in that disposed upstream of the second heating member .