JP2013174748A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that fixes an unfixed toner image on a recording sheet carrying the unfixed toner image under application of heat and pressure by pressing an endless belt against a fixing roller with a pressing member arranged on the inner surface side of the endless belt to form a nip between the belt and the fixing roller and causing the fixing roller to be driven to be rotated, and by passing the recording sheet through the nip, and is capable of easily separating the recording sheet from the belt even when the recording sheet passed through the nip for fixing the unfixed toner image is wound around the belt at a nip exit; and an image forming apparatus employing the fixing device.SOLUTION: A fixing device 4A is provided including a recording sheet peeling member 44 capable of contacting from the outer surface side of a belt 42 a loosened part 422 of the belt 42 that is generated on the downstream side of a fixing nip N in a conveyance direction of a recording sheet S for fixing a toner image. Also provided is an image forming apparatus 10 including the fixing device.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these, which can form a toner image on a recording sheet such as recording paper, and in particular, fixing a toner image on a recording sheet The present invention relates to a fixing device.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these that can form a toner image on a recording sheet, an electrostatic latent image is formed on an image carrier in an electrostatic latent image forming process. (For example, an electrostatic latent image is formed on an image carrier such as a photosensitive member in an exposure process), and the electrostatic latent image is developed in a development process to form a visible toner image. The visible toner image is transferred to a recording sheet or temporarily transferred to an intermediate transfer member such as an intermediate transfer belt and then secondarily transferred from the intermediate transfer member to the recording sheet, and transferred to the recording sheet in this way in the fixing process. The toner image can be fixed on the recording sheet.

  A fixing device is used to fix the unfixed toner image formed on the recording sheet onto the recording sheet in the fixing process. Various types of fixing devices are known. One of them is, for example, the type described in Japanese Patent Application Laid-Open No. 2010-14904 (Patent Document 1).

  This type of fixing device is disposed on the inner surface side of a fixing roller having a heat source, an endless belt, and the belt, and presses the belt against the fixing roller to form a nip between the fixing roller and the fixing roller. The toner image is fixed to the recording sheet under heat and pressure by passing a recording sheet carrying an unfixed toner image through the nip.

  As a member for forming the fixing nip, the fixing device adopting an endless belt that has a smaller heat capacity than the roller member and can set the fixing nip width to be low by fixing the fixing nip. This was proposed from the viewpoint of energy saving by reducing the size, reducing the cost, and shortening the warm-up time to the fixing temperature.

  Further, in this type of fixing device employing a belt, a device for separating the recording sheet discharged from the fixing nip downstream in the recording sheet conveying direction for fixing the unfixed toner image from the fixing roller is devised. .

  In Patent Document 1, a pressing member that presses a belt against a fixing roller to form a fixing nip includes a sheet separation pressing portion as its downstream end portion (end portion on the nip outlet side). It is described that the belt is bitten into the fixing roller, whereby the fixing roller surface layer and the belt are partially deformed with a small radius of curvature, thereby separating the recording sheet from the fixing roller.

  Further, in order to improve the separation property of the recording sheet from the belt, the pressing force of such a sheet separation pressing portion is further increased or the shape is further devised, so that the separation pressing portion and the belt fixing roller can be improved. A belt-type auxiliary member that changes the curvature of the belt portion on the downstream side of the fixing nip outlet so as to improve the sheet separability, as described in Patent Document It has also been proposed to abut.

JP 2010-14904 A

  However, in order to improve the separation property of the recording sheet from the belt, if the amount of biting into the sheet separation pressing portion and the fixing roller of the belt is increased, the resistance load of the sheet separation pressing portion is increased, so that the belt wear is accelerated. Torque increases due to the accumulation of wear powder, and chatter noise is generated.

  In any case, the recording sheet cannot be separated from the belt at the fixing nip exit depending on the toner used, the fixing temperature condition, and the like. When a driven roller type auxiliary member is provided on the downstream side of the outlet, the recording sheet wound around the belt reaches the auxiliary member, and it is difficult for the auxiliary member to separate the recording sheet from the belt. Or a situation where the recording sheet remains wound around the belt may occur.

  Accordingly, the present invention provides a fixing roller having a heat source, an endless belt, and an inner surface of the belt, and presses the belt against the fixing roller to form a nip with the fixing roller. A fixing device that includes a pressing member that is driven to rotate by a fixing roller, and fixes the toner image to the recording sheet under heat and pressure by passing a recording sheet carrying an unfixed toner image through the nip. The recording sheet is separated from the belt even when the recording sheet passed through the nip for fixing the toner image is not sufficiently separated from the belt at the exit of the nip and is wound around the belt. It is an object of the present invention to provide a fixing device that can be used.

  The present invention can also form a toner image on an image carrier, transfer the toner image to a recording sheet, and fix the image with a fixing device. The fixing device includes a fixing roller having a heat source, an endless shape, and the like. And a pressing member that is disposed on the inner surface side of the belt and that is driven and rotated by the fixing roller while pressing the belt against the fixing roller to form a nip with the fixing roller. An image forming apparatus adopting a fixing device that fixes a toner image to the recording sheet by heating and pressing by passing a recording sheet carrying a toner image through the nip. Even when the recording sheet passed through the nip for fixing a toner image is not sufficiently separated from the belt at the exit of the nip and is wound around the belt, Sheet can be separated from the belt, and to provide an image forming apparatus capable of forming an image by correspondingly inhibiting the reduction in image productivity.

  The present invention provides the following fixing device and image forming apparatus.

(1) Fixing device A fixing roller having a heat source, an endless belt, and an inner surface side of the belt, and pressing the belt against the fixing roller to form a nip between the fixing roller and the fixing roller. A fixing device that includes a pressing member that is driven and rotated by a fixing roller, and fixes the toner image to the recording sheet under heat and pressure by passing a recording sheet carrying an unfixed toner image through the nip. A fixing device in which a recording sheet peeling member that can be contacted from the outer surface side of the belt is disposed at a slack portion of the belt that occurs on the downstream side of the nip in the conveyance direction of the recording sheet for fixing.

(2) Image Forming Apparatus An image forming apparatus capable of forming a toner image on an image carrier, transferring the toner image onto a recording sheet, and fixing the image with a fixing device. The fixing device is a fixing device according to the present invention. An image forming apparatus as a device.

  According to the fixing device of the present invention, the endless belt that is pressed toward the fixing roller by the pressing member to form a nip for fixing a toner image between the fixing roller and the endless belt for fixing the toner image. For this reason, the upstream belt portion adjacent to the nip in the conveyance direction of the recording sheet is drawn into the nip, while the downstream belt portion adjacent to the nip generates slack.

  The recording sheet peeling member is disposed so as to be able to come into contact with the belt slack portion from the belt outer surface side, and the recording sheet peeling member comes into contact with the belt slack portion so that the peeling member is relatively pressed against the belt slack portion. The belt slack part is deformed so as to bite.

  In this way, due to the deformation of the belt slack portion due to the deformation of the belt slack portion and the recording sheet peeling member, the recording sheet is not sufficiently separated from the belt at the exit of the nip and becomes a belt. Even when wound, the recording sheet can be separated (peeled) from the belt.

  As described in Patent Document 1, in the case where the sheet separating and pressing portion is included in a pressing member that presses a belt against a fixing roller to form a fixing nip, torque increase due to belt wear and accumulation of belt wear powder Even if the recording sheet is not sufficiently separated from the belt at the fixing nip exit, as a result, it is avoided to increase the pressing force of the sheet separation pressing portion in order to suppress chatter noise. In the fixing device according to the present invention, the recording sheet can be separated (peeled) from the belt by the recording sheet peeling member capable of contacting the belt slack portion.

  In the image forming apparatus according to the present invention, since the fixing device according to the present invention is adopted as the fixing device, the separation of the recording sheet from the belt in the fixing device is good, and the separation jam in the fixing device is suppressed, Accordingly, image formation can be performed while suppressing a decrease in image productivity.

  According to the inventor's research, there is a correlation between the amount of biting and the pressure contact force with respect to the belt slack portion of the recording sheet peeling member, and if one of the biting amount and the pressure contact force increases, the other increases, If the number decreases, the other tends to decrease.

  The amount of biting and / or the pressing force affects the separation of the recording sheet from the belt. In a state where the belt can be rotated without hindrance despite the contact of the recording sheet peeling member, the greater the amount of biting and / or the pressure contact force, the higher the separability. However, when the amount of biting and / or the pressure contact force increases, the life of the belt tends to be shortened.

  Therefore, the fixing device according to the present invention includes a belt slack changing device that changes a slackness of the belt slack portion in order to adjust a biting amount and / or a pressure contact force of the recording sheet peeling member with respect to the belt slack portion. Also good.

  In the fixing device according to the present invention, the recording sheet peeling member may remain in contact with the belt slack portion at least during the fixing device operation, regardless of the presence or absence of the belt slack variable device.

However, in order to protect the belt and the like, the contact state and the non-contact state may be switched according to the slackness of the belt slack portion.
For example, the recording sheet peeling member is in contact with the belt slack portion when the slackness of the belt slack portion by the belt slack changing device is equal to or greater than a predetermined slackness, and is less than the predetermined slackness (slackness). In a case where it may be said that there is no such a thing), it may be arranged at a position where it does not contact the slack portion of the belt.

  Further, the belt slack changing device is a predetermined time after the leading edge of the recording sheet enters the nip, and the leading edge of the recording sheet can reach the recording sheet peeling member at the shortest. Only during the time required for the recording sheet to pass through the nip, the amount of biting and / or the pressure contact force of the recording sheet peeling member into the belt slack portion is greater than when the recording sheet does not pass through the nip. The degree of looseness of the belt portion may be changed.

  The recording sheet that passes through the nip for fixing an unfixed toner image includes (1) a recording sheet that does not carry a toner image on the opposite side of the recording sheet that carries the unfixed toner image, 2) There is a recording sheet carrying a toner image already fixed on the opposite side of the recording sheet carrying the unfixed toner image. As the latter recording sheet, for example, in the double-sided image forming mode, an image is formed on the first side and an unfixed toner image is fixed on the second side, or the opposite side of the recording sheet carrying the unfixed toner image. There is a recording sheet carrying a toner image formed in the past on the surface.

  Generally speaking, in the fixing device according to the present invention, the recording sheet coming out of the nip generally has a toner image on the surface of the recording sheet that contacts the belt, and the toner image is heated to form a belt. Since it becomes easy to stick, it is difficult to separate from the belt, and it is easy to wind around the belt.

  In view of this, the belt slack changing device has a recording sheet that passes through the nip for fixing an unfixed toner image. (1) A toner image is formed on a surface opposite to a recording sheet carrying an unfixed toner image. In the case of a recording sheet that is not carried, (2) the belt slack portion according to each case of a recording sheet that has a toner image already fixed on the surface opposite to the surface of the recording sheet carrying the unfixed toner image The degree of slackening of the recording sheet is changed, and the amount of biting and / or pressing force with respect to the belt slack portion of the recording sheet peeling member is changed in the recording of (2) than in the case of the recording sheet of (1). You may carry out so that it may become larger in the case of a sheet. In this case, the recording sheet of (1) includes a case where the amount of biting and / or the pressure contact force with respect to the belt slack portion of the recording sheet peeling member is substantially set to “0”.

  As the belt slack changing device, for example, a guide member that applies tension to the belt while contacting the belt inner surface and guiding the belt rotation, and the guide member is reciprocated in a direction in which the belt tension is changed. The thing containing the guide member drive device for this can be illustrated.

  The fixing device according to the present invention is disposed inside the belt, and the inner surface of the belt faces the outside of the belt at the downstream side of the nip and the upstream side of the recording sheet peeling member in the conveyance direction of the recording sheet. A biting amount adjusting member for adjusting the biting amount of the recording sheet peeling member into the belt slack portion by pressing may be further included.

  In any case, examples of the recording sheet peeling member include those in which at least the tip portion can contact the belt so that the recording sheet wound around the belt can be separated from the belt. Moreover, as such a front-end | tip part, the cross-sectional shape can point out the shape of a mountain (in other words, wedge shape), and a plate-shaped thing. When the tip portion is plate-shaped, the entire recording sheet peeling member may be a plate-shaped member.

  Further, the number of the recording sheet peeling members, the size of each recording sheet peeling member in the width direction crossing the recording sheet conveyance direction, the position in the direction crossing the recording sheet conveyance direction, and the like can be used to remove the recording sheet wound around the belt from the belt. There is no particular limitation as long as it can be separated.

  According to the present invention, a fixing roller having a heat source, an endless belt, and an inner surface of the belt are arranged, and the belt is pressed against the fixing roller to form a nip with the fixing roller. A fixing device that includes a pressing member that is driven to rotate by a fixing roller, and fixes the toner image to the recording sheet under heat and pressure by passing a recording sheet carrying an unfixed toner image through the nip. The recording sheet is separated from the belt even when the recording sheet passed through the nip for fixing the toner image is not sufficiently separated from the belt at the exit of the nip and is wound around the belt. A fixing device that can be provided can be provided.

  Further, according to the present invention, a toner image can be formed on an image carrier, the toner image can be transferred to a recording sheet and fixed by a fixing device, and the fixing device includes a fixing roller having a heat source, an endless device, and the like. And a pressing member which is disposed on the inner surface side of the belt and presses the belt against the fixing roller to rotate the fixing roller while forming a nip with the fixing roller. An image forming apparatus employing a fixing device for fixing the toner image to the recording sheet by applying heat and pressure by passing a recording sheet carrying a toner image on the nip. Even when the recording sheet passed through the nip for fixing a toner image is not sufficiently separated from the belt at the exit of the nip and is wound around the belt The recording sheet can be separated from the belt, it is possible to provide an image forming apparatus capable of forming an image by correspondingly inhibiting the reduction in image productivity.

1 is a diagram illustrating an outline of a configuration of an example of an image forming apparatus according to the present invention. FIG. 1A is an example of the fixing device according to the present invention, and is a cross-sectional view of the main part of the fixing device employed in the image forming apparatus of FIG. 1, and FIG. It is a perspective view. It is a figure which shows one example of a belt slack variable apparatus. It is a figure which shows a mode that a belt slack is set largely with a belt slack variable apparatus. It is a figure which shows a mode that a belt slack is set small with a belt slack variable apparatus. It is a figure which shows the other example of the fixing device which concerns on this invention.

Hereinafter, an example of an image forming apparatus employing an example of a fixing device according to the present invention will be described with reference to the drawings.
FIG. 1 shows an example of an image forming apparatus according to the present invention.
An image forming apparatus 10 shown in FIG. 1 is a printer that forms a monochrome image by an electrophotographic method and prints it on a recording sheet such as a recording sheet.

  The printer 10 includes an image forming unit 1 that forms a toner image by an electrophotographic method, a sheet supply unit 2 that supplies a recording sheet S to the image forming unit 1, and a toner image that is formed by the image forming unit 1 from the sheet supply unit 2. The transfer unit 3 for transferring to the supplied recording sheet S, the fixing device 4A for fixing the toner image transferred to the recording sheet S to the sheet S, and the sheet discharge for discharging the recording sheet S holding the fixing toner image to the discharge tray 50. The apparatus 5 and the reverse circulation conveyance path 6 for double-sided image formation are included.

  The printer 10 also includes a control unit C that controls its operation. The operation of each unit of the printer 10 is performed under the instruction of the control unit C. An operation panel Pa operated by a user is also connected to the control unit C. The operation panel Pa is a numeric keypad for setting the number of prints, a key for specifying the recording sheet size to be used, a key for specifying whether to form an image on one side or both sides of the recording sheet, and whether to form an image on plain paper. A key for designating a recording sheet type, a key for instructing the start of printing, etc. in relation to whether to form an image on a recording sheet that is not so, or to form an image on the other side of the recording sheet already formed on one side Have.

The image forming unit 1 includes a drum-type photoconductor 11 that is rotationally driven as an electrostatic latent image carrier. Around the photoconductor 11, a charger 12, a developing device 14, a cleaner 15 and the like are arranged in this order. An image exposure device 13 that performs image exposure on the photosensitive member 11 from between the charger 12 and the developing device 14 is also provided.
The image exposure device 13 is supplied with image information from a scanner, a computer, etc. (not shown), and performs image exposure on the photoconductor 11 with a laser beam.

  The transfer unit 3 includes a transfer roller 31 that can apply a transfer bias from a transfer power supply (not shown). The transfer roller 31 faces the photoconductor 11 on the downstream side of the developing device 14 and the upstream side of the cleaner 15 in the rotation direction (counterclockwise direction) of the photoconductor 11.

  The transfer roller 31 is pressed by a pressing means (not shown) to form a nip portion between the transfer roller 31 and the recording sheet driven by the rotation of the photosensitive member 11 or fed into the nip portion as will be described later. It can be rotated by being driven or driven.

The sheet supply unit 2 includes a cassette 200 on which the recording sheets S are stacked and stored, and a sheet supply device 20 that pulls out and supplies the sheets one by one from the cassette 200.
The fixing device 4A will be described in detail later.

 The sheet discharge device 5 includes a discharge roller pair 51 that discharges the recording sheet S sent from the fixing device 4 </ b> A to the discharge tray 50. A sheet conveyance direction switching member 52 that closes the conveyance path so as to be lifted is disposed on the sheet conveyance path from the fixing device 4 </ b> A to the discharge roller pair 51.

  Immediately before the recording sheet S discharged to the tray 50 by the discharge roller pair 51 is completely discharged to the tray 50 and in a state where the sheet conveyance direction switching member 52 is closed, the recording roller S 51 is reversed to perform the recording. The sheet can be fed into the reverse circulation conveyance path 6 and supplied to a timing roller pair R described later. R in the circulation conveyance path 6 is a sheet guide roller.

According to the printer 10, when the print start key is pressed on the operation panel Pa connected to the control unit C, the supply of the recording sheet S from the recording sheet supply unit 2 is started.
When the recording sheet S supplied from the recording sheet supply unit 2 is detected by a sensor (not shown), the image forming unit 1 starts image formation, and the recording sheet S is temporarily stopped by the timing roller pair R.

  When image formation is started in the image forming unit 1, the photoconductor 11 is rotationally driven counterclockwise in the figure, the surface of the photoconductor is charged to a predetermined potential by the charger 12, and an image exposure device is placed in the charged area 13 is subjected to image exposure according to the image to be formed. As a result, an electrostatic latent image is formed on the photoconductor 11, and in this example, the latent image is reversely developed with negatively charged toner in the developing unit 14 to become a visible toner image.

  The recording sheet S waiting on the timing roller pair R is sent to the transfer unit 3 by the roller pair R so that the transfer of the toner image on the photoconductor 11 to the image forming area, and is transferred from a transfer power supply (not shown). The toner image on the photoconductor 11 is transferred by the transfer roller 31 to which a bias is applied. The recording sheet S to which the toner image has been transferred is continuously fed to the fixing device 4A, where the toner image is fixed under heat and pressure, and the sheet conveying direction switching member 52 is pushed up against its own weight and / or elasticity. While going to the discharge roller pair 51, the discharge roller pair 51 discharges to the discharge tray 50.

  In the double-sided image forming mode, the recording sheet S that is image-formed on one side and is to be discharged to the discharge tray 50 in this way is reversely rotated by a reverse rotation of the discharge roller pair 51 immediately before the discharge to the tray 50 is completed. 6 for image formation on the second side.

  The transfer residual toner remaining on the photoconductor 11 after the toner image transfer is removed and cleaned by a cleaner 15.

  Next, the fixing device 4A will be described. As shown in FIG. 2A, the fixing device 4A includes a fixing roller 41 incorporating a heat source 411 composed of a halogen lamp heater, an endless belt 42, and a pressing member 43 disposed on the inner surface side of the belt 42. Is included. The fixing roller 41 is rotationally driven in the CCW direction in the figure at a predetermined timing by an instruction from the control unit C by a drive motor 412.

  In the fixing roller 41, an elastic layer 41b is provided around a cored bar 41a, and a surface layer 41c is formed on the elastic layer 41b. The elastic layer 41b is made of silicon rubber having high heat resistance in this example, and the surface layer 41c is made of a fluorine-based resin (for example, PFA (perfluoroalkoxy), PTFE (polytetrafluoroethylene) having good releasability in this example. ) Etc.).

  The belt 42 has a cylindrical shape that can be elastically deformed, and is formed of a heat-resistant resin (for example, any one of PI (polyimide), PA (polyamide), PIA (polyimide amide), and the like) in this example.

  The pressing member 43 presses the belt 42 against the fixing roller 41 to form a fixing nip N with the fixing roller 41 and is driven to rotate by the fixing roller 41.

  The pressing member 43 is not limited thereto, but here, an elastic pressing member 431 that presses the belt 42 against the fixing roller 41 to form a fixing nip N, and a downstream end portion in the sheet conveying direction α for fixing the toner image. A sheet separation pressing portion 432 that provides the (nip exit side end portion), a case 434 that supports these, and a spring member 433 that is supported by the case 434 and presses the elastic pressing member 431 in the belt pressing direction. Yes.

The elastic pressing member 431 is made of silicon rubber in this example.
The sheet separation pressing portion 432 has a separation claw-like shape in which a tip portion facing the belt 42 is formed in a flat shape, and is a member having high rigidity. The belt 42 pressed against the fixing roller 41 by the pressing member 43 is elastically deformed along the surface of the fixing roller that is harder than that.

  The sheet separating and pressing unit 432 separates the recording sheet S from the fixing roller 41 mainly at the nip N exit.

  According to the fixing device 4A, the fixing roller 41 is rotated by the motor 412, and the belt 42 is driven to rotate. The recording sheet S carrying the unfixed toner image is held in the nip N by the toner image t. The toner image can be fixed on the surface of the recording sheet under heat and pressure by passing it so as to be directed to 41.

  At this time, since the belt portion 421 adjacent to the upstream side of the nip N in the sheet conveyance direction α is pulled into the nip N, the portion 422 adjacent to the downstream side of the nip N is more loose than the upstream side. The sheet peeling member 44 in a fixed position is relatively pressed against the belt slack portion 422, and the belt slack portion 422 partially changes its curvature.

  As shown in FIG. 2B, the sheet peeling member 44 has a flat claw-like shape having a width dimension w in a direction parallel to the rotation center line of the fixing roller 41 and a tip 441 having a triangular cross section. 2 is a member arranged in a fixed position and a fixed posture (a posture in which the tip end portion 441 is inclined obliquely toward the nip N from below as shown in FIG. 2A), and the rotation center line of the fixing roller 41 of the belt 42 It is in contact with the central portion of the belt 42 in the parallel direction.

  According to the fixing device 4A, even when the recording sheet S is insufficiently separated from the belt 42 at the exit of the fixing nip N and is wound around the belt 42, the partial curvature change of the belt slack portion 422 and the leading end portion are The recording sheet S is reliably and easily peeled from and separated from the belt 42 by the sheet peeling member 44 that is pressed into the belt slack portion 422 and bitten and buried.

  Further, since the separation of the recording sheet S from the belt 42 in the fixing device 4A is good as described above, the separation jam and the like in the fixing device 4A are suppressed, so that an image can be smoothly formed while suppressing a decrease in image productivity. it can.

  In the fixing device 4A shown in FIG. 2, the sheet peeling member 44 has a tip portion 441 that is pointed in a cross-sectional mountain shape (in other words, a wedge shape). For example, a fluorine-based lubricating film (PTFE film, PFA film, etc.) Or may be covered with a silicon film. Further, the sheet peeling member may be made of a resin or a metal plate, or may be coated with a fluorine-based lubricating film (PTFE film, PFA film, etc.) or a silicon film.

  Further, the number of recording sheet peeling members, the size of each recording sheet peeling member in the width direction across the recording sheet conveyance direction, the position in the direction across the recording sheet conveyance direction, and the like are used to remove the recording sheet S wound around the belt 42 from the belt. There is no particular limitation as long as it can be separated.

  The heating means of the fixing roller 41 is not limited to the heat source 411 composed of the lamp heater. For example, the fixing roller 41 includes an electromagnetic induction heating layer, and the electromagnetic induction heating layer is used to generate magnetic flux. A device that generates heat by electromagnetic induction may be used.

  According to the inventor's research, there is a correlation between the biting amount and the pressure contact force with respect to the belt slack portion 422 of the recording sheet peeling member 44, and when one of the biting amount and the pressure contact force increases, the other increases, If the number decreases, the other tends to decrease.

  The amount of biting and / or the pressing force affects the separation of the recording sheet from the belt. In a state in which the belt can be rotated without hindrance despite the contact of the recording sheet peeling member 44, the separability tends to be improved as the amount of biting and / or the pressure contact force increases.

  FIG. 3 shows a fixing device 4B provided with a belt slack changing device 7 for changing the slackness of the belt slack portion 422 in order to adjust the amount of biting and / or the pressure contact force of the recording sheet peeling member 44 with respect to the belt slack portion 422. . The fixing device 4B has the same configuration as the fixing device 4A except that the belt slack variable device 7 is provided. The same parts and portions as those of the fixing device 4A are denoted by the same reference numerals as those of the device 4A.

  The belt slack variable device 7 shown in FIG. 3 includes a guide member 71 and a guide member driving device 72.

  The guide member 71 is a member that applies tension to the belt 42 while contacting the portion 420 of the inner surface of the belt 42 opposite to the portion pressed by the pressing member 43 with a convex curved surface 710 to guide belt rotation. .

  As shown in FIG. 3, the guide member 71 extends in the width direction across the recording sheet conveyance direction of the belt 42, and both end portions 711 and 711 protrude from the belt 42. Each end portion 711 is movable by a guide member (not shown). As a result, the entire guide member 71 can reciprocate in the direction approaching and separating from the pressing member 43.

  When the guide member 71 is moved closer to the pressing member 43 as shown in FIG. 4, the belt tension is weakened, the degree of slackness of the belt slack portion 422 on the downstream side of the nip N is increased, and the belt slack portion 422 of the recording sheet peeling member 44 is increased. The pressure contact force and the amount of bite increases.

  When the guide member 71 is moved away from the pressing member 43 as shown in FIG. 5, the belt tension increases, the degree of slackness of the belt slack portion 422 on the downstream side of the nip N becomes small, and the pressure contact of the recording sheet peeling member 44 to the belt slack portion 422 is reduced. The force and the amount of biting are reduced, and finally the peeling member 44 moves away from the belt.

  The guide member driving device 72 is a device for reciprocating the guide member 71 in a direction in which the tension of the belt 42 is changed. The guide member driving device 72 includes a spring 721 that presses each guide member end 711 in a direction away from the pressing member 43, and a cam 722 that pushes each guide member end 711 back against the spring 721 toward the pressing member 43. Contains.

  The cam 722 is attached to a cam shaft 723, and the cam shaft 723 is rotatably supported by a pair of bearing members 724. The cam shaft 723 can be rotated forward and backward by a motor 725, and the operation of the motor 725 is controlled by the controller 70. The controller 70 controls the operation of the motor 725 based on the instruction from the control unit C, rotates the cam shaft 723, and thus the cam 722, thereby moving the guide member 71 to adjust the belt tension and loosen the belt. The size of the portion 422 can be adjusted such that a predetermined peeling member pressing force and / or a peeling member biting amount is set.

  The means for moving the guide member 71 need not be limited to those using the cam device as described above. For example, the guide member 71 may be moved directly by a motor or solenoid, or moved by using an appropriate link mechanism.

  The belt 42 is made of PI (polyimide) as a base material and has a thickness selected from the range of 80 μm to 130 μm. The sheet peeling member 44 has a width in a direction parallel to the rotation center line of the fixing roller 41. A fixed position and a fixed posture in which the dimension w is 5 mm and the tip portion 441 is a flat claw shape having a triangular cross section (a posture in which the tip portion 441 is inclined obliquely from below to the nip N as shown in FIG. 2). The sheet peeling member with respect to the belt slack portion 422 is brought into contact with the central portion of the belt 42 in the direction parallel to the rotation center line of the fixing roller 41 and the belt slack changing device 7 variously changes the belt slack. When the relative pressing force of 44 and the amount of biting were examined, the results shown in the following table were obtained.

Pressure contact force 0.5N 1.0N 1.5N
Biting amount 0.5mm 1.0mm 1.5mm

  Thus, there is a correlation between the biting amount and the pressing force of the recording sheet peeling member 44 with respect to the belt slack portion 422, and if one of the biting amount and the pressing force increases, the other increases and the other decreases. It was confirmed that the other also tended to decrease.

If the separation member 44 is too close to the nip N, the belt 42 is easily deformed. If it is too far from the nip N, the rotational operation of the belt 42 is affected. As a result of repeated research, it was confirmed that the position where the separation performance was most stable was the position rotated approximately 40 degrees along the belt 42 from the exit of the nip N.

  In a state in which the belt can be rotated without hindrance despite the contact of the recording sheet peeling member 44, the separability tends to be improved as the amount of biting and / or the pressure contact force increases. However, when the biting amount and / or the pressure contact force increase, the belt is easily damaged.

  Therefore, for example, in the case of the fixing device 4B, the contact between the sheet peeling member 44 and the belt slack portion 422 may be performed using the belt slack variable device 7 as follows.

  For example, the recording sheet peeling member 44 contacts the belt slack portion 422 when the slackness of the belt slack portion 422 by the belt slack changing device 7 is equal to or greater than a predetermined slackness, and the slackness (slackness) is smaller than the predetermined slackness. In this case, the belt may be disposed at a position where it does not contact the belt slack portion 422. Here, as the “predetermined degree of slack of the belt slack portion 422”, the amount of biting and / or the pressure contact force of the peeling member 44 recognized as necessary for the separation of the recording sheet by a preliminary experiment or the like can be set. The degree of belt slack can be exemplified. The degree of belt slack may be set in a plurality of stages more than two stages according to the recording sheet type and the like.

  Further, in order to protect the belt, the belt slack changing device 7 has a predetermined time after the leading edge of the recording sheet S enters the nip N, and the leading edge of the recording sheet S is at least the recording sheet peeling member 44. The amount of biting and / or pressure contact with the belt slack portion 422 of the recording sheet peeling member 44 can be reached only when the recording sheet S passes through the nip N at the longest. It may be controlled to change the degree of slackness of the belt portion so that the force becomes large (so that the recording sheet is surely peeled off).

  Further, the belt slack changing device 7 changes depending on the toner image fixing condition (recording sheet type, toner type, etc.) to the recording sheet so that the recording sheet can be peeled off from the belt 42 at the nip N outlet side more reliably. The degree of slackness of the belt slack portion 422 is changed so as to appropriately set the amount of biting into the belt slack portion 422 and / or the pressure contact force of the recording sheet peeling member 44 according to the toner image fixing conditions that may come. It may be controlled.

  For example, for a recording sheet that passes through the nip N in order to fix an unfixed toner image, (1) a recording sheet that does not carry a toner image on the opposite side of the recording sheet carrying the unfixed toner image (2) There is a recording sheet carrying a toner image that has already been fixed on the surface opposite to the surface of the recording sheet carrying an unfixed toner image. As the latter recording sheet, for example, in the double-sided image forming mode, an image is formed on the first side and an unfixed toner image is fixed on the second side, or the opposite side of the recording sheet carrying the unfixed toner image. There is a recording sheet carrying a toner image formed in the past on the surface.

  Generally speaking, the recording sheet coming out of the nip N has a toner image on the surface of the recording sheet in contact with the belt 42, and the toner image is heated so that it easily sticks to the belt. It is difficult to separate and easy to wind around the belt.

Therefore, the belt slack changing device 7 has the following effect: the recording sheet that passes through the nip N to fix the unfixed toner image is (1) the toner image is formed on the surface opposite to the recording sheet carrying the unfixed toner image. In the case of a recording sheet that is not carried, (2) a belt slack portion 422 corresponding to each case of a recording sheet that has a toner image already fixed on the surface opposite to the surface of the recording sheet carrying an unfixed toner image. The degree of slackening of the recording sheet is changed, and the amount of biting and / or the pressure contact force of the recording sheet peeling member 44 with respect to the belt slackening portion 422 is changed as compared with the case of the recording sheet of (1). You may carry out so that it may become larger in the case of a sheet. In this case, with respect to the recording sheet of (1), the amount of biting and / or the pressure contact force with respect to the belt slack portion 422 of the recording sheet peeling member 44 may be set to substantially “0”.
The recording sheet (2) carries an unfixed toner image in the case of a recording sheet in which an image is formed on the first side and an unfixed toner image is to be fixed on the second side in the double-sided image formation mode. The amount of biting and / or the pressure contact force with respect to the belt slack portion 422 of the recording sheet peeling member 44 is larger than in the case of the recording sheet carrying the toner image formed in the past on the surface opposite to the recording sheet surface. The degree of slack may be set.

  FIG. 6 shows another example 4C of the fixing device according to the present invention. The fixing device 4C is the same as the fixing device 4A except that the biting amount adjusting member 8 is provided inside the belt 42. The same parts and portions as those of the fixing device 4A are denoted by the same reference numerals as those of the device 4A.

  The biting amount adjusting member 8 is a roller member having a circular cross section in this example, and presses the inner surface of the belt 42 toward the outer side of the belt on the downstream side of the nip N and the upstream side of the recording sheet peeling member 44 in the recording sheet conveyance direction. Thus, the amount of biting into the belt slack portion 422 of the peeling member 44 is adjusted. The member 8 is long in the belt width direction and both ends thereof are supported by bearings (not shown) and can be driven to rotate by the belt 42.

  By providing the member 8 in this manner, the belt 42 is deformed, and a step is generated in which the peeling member 44 bites into the belt 42. Thereby, the amount of biting for sheet peeling of peeling member 44 can be obtained more certainly.

  As the biting amount adjusting member, a slidable plate material, a block material, or the like may be used in addition to the above. Further, the biting amount adjusting member does not have to have the width of the belt 42 (belt width in a direction crossing the sheet conveying direction), and has at least the same width as that of the peeling member so as to correspond to the peeling member. It only has to be.

  Although not shown, a device similar to the driving device 72 that reciprocates the guide member 71 in the belt slack changing device 7 in the fixing device 4B can be adopted as means for adjusting the position movement of the biting amount adjusting member 8. . The means for moving the biting amount adjusting member 8 is not necessarily limited to that using a cam device. For example, the member 8 may be moved directly by a motor or a solenoid, or with an appropriate link mechanism as an intermediate.

  The image forming apparatus (printer) described above is a monochrome image forming apparatus. However, the fixing device according to the present invention can be applied to a color image forming apparatus of a tandem type, a four-cycle type, etc. The present invention can also be applied to a copier, a facsimile machine, and a multi-function machine that combines two or more of a copier, a facsimile machine, a printer, and the like.

  In the present invention, an endless belt is pressed against a fixing roller by a pressing member arranged on the inner surface side thereof, and is driven to rotate by the fixing roller while forming a nip with the fixing roller, thereby recording an unfixed toner image. In a fixing device for fixing a toner image on a recording sheet by heating and pressing the sheet through the nip, the recording sheet passed through the nip for fixing an unfixed toner image is wound around the belt at the nip outlet. Even in this case, the present invention can be used to provide a fixing device that can easily separate the recording sheet from the belt and an image forming apparatus that employs the fixing device.

10 Printer (example of image forming device)
DESCRIPTION OF SYMBOLS 1 Image formation part 2 Sheet supply part 3 Transfer part 4A, 4B, 4C Fixing device 41 Fixing roller 411 Heat source 42 Belt 422 Belt slack part 43 Press member 44 Recording sheet peeling member N Nip 5 Sheet discharge device 6 Reverse circulation conveyance path C Control Part S Recording sheet 7 Belt slack changing device 71 Guide member 72 Guide member driving device 70 Controller 8 Biting amount adjusting member

Claims (8)

  A fixing roller having a heat source, an endless belt, and an inner surface of the belt. The belt is pressed against the fixing roller to form a nip between the fixing roller and follow the fixing roller. A fixing device for fixing the toner image to the recording sheet under heat and pressure by passing a recording sheet carrying an unfixed toner image through the nip. A fixing device, wherein a recording sheet peeling member that can be contacted from the outer surface side of the belt is disposed in a slack portion of the belt that occurs on the downstream side of the nip in the conveyance direction of the recording sheet.   The fixing device according to claim 1, further comprising a belt slack changing device that changes a slackness of the belt slack portion in order to adjust a biting amount and / or a pressing force of the recording sheet peeling member with respect to the belt slack portion.   The recording sheet peeling member is in contact with the belt slack portion when the slackness of the belt slack portion by the belt slack changing device is greater than or equal to a predetermined slackness, and when the slackness is smaller than the predetermined slackness, the belt slackness is detected. The fixing device according to claim 2, wherein the fixing device is disposed at a position not in contact with the portion.   The belt slack changing device has a predetermined time after the leading end of the recording sheet enters the nip, and the leading end of the recording sheet can reach the recording sheet peeling member at the shortest, and the recording sheet at the longest. The belt so that the amount of biting and / or the pressure contact force of the recording sheet peeling member into the slack portion of the recording sheet is larger than the time when the recording sheet does not pass through the nip only during the time required for the recording sheet to pass through the nip. The fixing device according to claim 2, wherein the degree of looseness of the portion is changed.   The belt slack variable device has a recording sheet that passes through the nip for fixing an unfixed toner image. (1) The toner image is carried on the surface opposite to the recording sheet surface carrying the unfixed toner image. (2) The slack of the belt slack portion corresponding to each of the recording sheets having a toner image already fixed on the surface opposite to the surface of the recording sheet carrying the unfixed toner image. The amount of biting and / or the pressure contact force with respect to the belt slack portion of the recording sheet peeling member is changed in the recording sheet of (2) than in the case of the recording sheet of (1). The fixing device according to claim 2, 3 or 4, wherein the fixing is performed so that the case becomes larger.   The belt slack changing device includes a guide member that applies tension to the belt while contacting the belt inner surface and guiding the belt rotation, and a guide for reciprocating the guide member in a direction in which the belt tension is changed. The fixing device according to claim 2, further comprising a member driving device.   The recording sheet peeling member is arranged on the inner side of the belt and presses the inner surface of the belt toward the outer side of the belt at the downstream side of the nip and the upstream side of the recording sheet peeling member in the recording sheet conveyance direction. The fixing device according to claim 1, further comprising a biting amount adjusting member for adjusting a biting amount of the belt into the slack portion of the belt.   An image forming apparatus capable of forming a toner image on an image carrier, transferring the toner image to a recording sheet, and fixing the image on a recording sheet. The fixing apparatus according to any one of claims 1 to 7. An image forming apparatus which is the fixing device described above.