JP2017102164A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device that prevents slide marks from being left on a constitutional member even when shipped in a low-pressure state.SOLUTION: An image heating device comprises: a first rotor 41 and a second rotor 50 that form a nip part N for heating a toner image on a recording sheet; a pressure mechanism 80 that presses at least one of the first rotor and second rotor toward the other; and a changing mechanism that can change the pressure applied by the pressure mechanism at the nip part between a first pressure and a second pressure lower than the first pressure. In an unused state, the pressure at the nip part is the second pressure, and a sheet-like member Pa is sandwiched between the rotors.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image heating apparatus for heating a toner image on recording paper. This image heating apparatus can be mounted on an image forming apparatus such as a copying machine such as an electrophotographic system, a printer, a fax machine, or a multi-function machine thereof.

  Conventionally, in an image forming apparatus, a latent image formed on an image carrier based on image data is developed with toner supplied from a developing device, and a toner image as a visible image is formed on the image carrier. The The toner image on the image carrier is transferred onto the recording paper by a transfer device, and is fixed on the recording paper by a fixing device as an image heating device.

  In the fixing device described in Patent Document 1, a pressure roller that is rotatably provided by driving from a drive motor, and a flexible endless belt that is a fixing member provided to face the pressure roller. A fixing belt as a member is brought into pressure contact. Thereby, a fixing nip portion is formed.

  However, when the fixing device is shipped in a pressure contact state, it may be left in such a pressure contact state for a long time during distribution, and as a result, a part of the pressure roller becomes a flat shape, so-called C set phenomenon (compression) Plastic strain: compression set) occurs.

  In this state, when the user uses the image forming apparatus to perform a printing operation and rotates the fixing belt and the pressure roller, noise is generated due to the pressure roller deformed flat, which may cause malfunction and damage to the drive system. Become.

  Also, if the fixing device is shipped with the fixing belt and the pressure roller separated from each other, there is a concern that when the vibration or impact is applied, the fixing belt and the pressure roller are inadvertently contacted and a dent is formed. The

  In order to solve the above-described problem, in a fixing device having a configuration that can be switched to a low pressure state as disclosed in Patent Document 2, a method of packing and shipping in a low pressure state is conceivable.

JP 2005-114959 A JP 2013-164610 A

  However, there are the following problems when packing and shipping in a low-pressure state. Due to the low pressure, when the fixing belt and the pressure roller rotate unintentionally, a speed difference tends to occur between the fixing belt and the pressure roller. Therefore, rubbing marks are likely to be formed on the fixing belt, causing image defects.

  Therefore, an object of the present invention is to provide an image heating apparatus in which a component member is less likely to have rubbing marks even when shipped in a low pressure state.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a first rotating body and a second rotating body that form a nip portion for heating a toner image on a recording paper, and A pressure mechanism that pressurizes at least one of the first rotating body and the second rotating body toward the other; and a pressure at the nip portion by the pressure mechanism is lower than the first pressure. A change mechanism that can be changed to the second pressure, and when not in use, the pressure at the nip portion is the second pressure, and the sheet-like member is sandwiched. It is characterized by being.

  According to the present invention, even if the image heating apparatus is shipped in a low-pressure state, it is difficult for the constituent members to have rubbing marks during distribution.

The perspective view of the form at the time of transport of the fixing device of an Example Configuration model diagram of an example of an image forming apparatus Perspective view of fixing device (A) and (b) are a front view and a longitudinal front view of the fixing device. Enlarged right side view taken along line (5)-(5) in (a) of FIG. (A) and (b) are a left side view of the fixing device and a left side view of a partly cutout. (A) and (b) are a right side view of the fixing device and a right side view of a partly cutout. Schematic diagram of fixing belt layer structure Illustration of the shape of the eccentric cam (pressure release member) Explanatory drawing of belt unit position in pressurization configuration, pressure reduction configuration, and pressure release configuration Explanatory drawing of the force that acts when the paper is transported Explanatory diagram of the force acting on the fixing belt when the paper is not being conveyed Explanatory drawing of the force that acts when the trailing edge of the paper sandwiched in the nip part of the fixing device is fixed

Example 1
(1) Image Forming Apparatus FIG. 2 is a structural model diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as a fixing device, and is a color image forming apparatus (printer) using an electrophotographic system. Y, C, M, and K are four electrophotographic image forming units that form yellow (Y), cyan (C), magenta (M), and black (K) color toner images, respectively, arranged in order from the bottom to the top. Has been. Each image forming unit includes a photosensitive drum 1, a charging device 2, a developing device 3, a cleaning device 4, and the like. An optical system 5 performs laser scanning exposure on the drum 1 of each image forming unit. Since the electrophotographic process for forming a toner image on the drum 1 is well known, its description is omitted.

  The Y, C, M and K toner images respectively formed on the drum 1 in each image forming unit are sequentially superimposed on the endless belt 6 as an intermediate transfer member in a predetermined alignment state by the primary transfer roller 10. And is transcribed. As a result, an unfixed unfixed toner image of four colors of Y color + C color + M color + K color is formed on the belt 6. The belt 6 is stretched between the rollers 7, 8, and 9 and is driven to rotate in the direction of the arrow. The toner remaining on the drum 1 is removed by the cleaning device 4. Note that when only a single color image is formed (single color mode), only that color image is formed.

  On the other hand, recording paper (recording material: hereinafter referred to as paper) P in the cassette 11 is fed one by one by driving the feeding roller 12. Then, it is introduced into a secondary transfer nip portion, which is a pressure contact portion between the belt 6 and the secondary transfer roller 14 by a registration roller 13 at a predetermined control timing, and is nipped and conveyed. As a result, the toner image on the belt 6 is transferred (electrostatic transfer) to the paper P.

  The paper P exiting the nip portion is separated from the belt 6 and introduced into a fixing device 16 as an image heating device to undergo a toner image fixing process, and passes through a paper discharge path 17 as a full-color or mono-color image formed product. It is sent out to the paper discharge tray 18. The transfer residual toner on the belt 6 is removed by the cleaning device 15. In the image forming apparatus according to the present exemplary embodiment, the mechanism unit up to the fixing device 16 is an image forming device that forms a toner image on the paper P. “a” indicates the sheet conveyance direction (recording material conveyance direction).

(2) Fixing Device FIG. 3 is a perspective view of the fixing device 16, and FIGS. 4A and 4B are a front view and a longitudinal front view of the device 16. FIG. 5 is an enlarged right side view taken along line (5)-(5) in FIG. 6 (a) and 6 (b) are a left side view of the device 16 and a left side view with a part cut away. 7A and 7B are a right side view of the device 16 and a right side view with a part cut away.

  In the following description, the longitudinal direction of the fixing device 16 or a member constituting the fixing device 16 is a direction parallel to a direction orthogonal to the paper transport direction a in the paper transport path surface. The short direction is a direction parallel to the paper transport direction. Regarding the fixing device 16, the front surface is a surface of the device viewed from the paper entrance side, the back surface is the opposite surface (paper exit side), and the left and right are the left or right when the device is viewed from the front. The upstream side and the downstream side are the upstream side and the downstream side in the paper transport direction a.

  The fixing device 16 of the present embodiment is a belt heating type image heating device using induction heating, and roughly includes the following members and mechanisms.

a: Heating assembly (belt unit) 40 including a flexible endless belt (hereinafter referred to as a fixing belt or a belt) 41 as a first rotating body (fixing member) that contacts the toner image carrying surface of the paper P
b: a pressure roller 50 having elasticity as a second rotating body (pressure member) facing the belt 41
c: Coil unit (induction heating device, magnetic flux generating means) 60 as a heater for heating the belt 41
d: a pressure mechanism 80 that forms a nip portion N that presses the belt 41 and the pressure roller 50 to heat (image heating processing; fixing) an image on a sheet (on a recording material).
e: Change mechanism for changing the pressure of the nip portion N by the pressurizing mechanism 80 The above-described members and mechanisms are disposed (included) between the left and right side plates 30L and 30R of the device chassis (housing) 30 of the fixing device 16. ing.

(2-1) Heating assembly 40
The heating assembly 40 has a belt 41 that is cylindrical and flexible. The belt 41 has a magnetic member (metal layer, conductive member) that generates heat by electromagnetic induction when passing through a region where a magnetic field (magnetic field, magnetic flux) generated from the coil unit 60 exists. In addition, a metal stay 42 inserted into the belt 41 is provided. A pressure pad (nip pad) 43 as a pressure applying member is attached to the lower surface of the stay 42 along the longitudinal direction.

  The pad 43 is a member that forms a nip portion (fixing portion, fixing nip portion) N by applying a predetermined pressing force between the belt 41 and the pressure roller 50, and is made of a heat resistant resin. Since the stay 42 needs rigidity to apply pressure to the nip portion N, it is made of iron in this embodiment. Further, on the upper surface side (coil unit 60 side) of the stay 42, a magnetic core (inner magnetic core) 44 for concentrating the induction magnetic field on the belt 41 in order to efficiently heat the belt 41 is provided on the stay 42. It is arranged over the length.

  The left and right ends of the stay 42 protrude outward from the left and right ends of the belt 41, respectively. Symmetrical flange members (fixing flanges) 45L and 45R are fitted to both ends thereof. The flange members 45L and 45R are regulating members that regulate the movement of the belt 41 in the longitudinal direction (width direction: left-right direction) and the shape in the circumferential direction. The belt 41 is loosely fitted on the assembly of the stay 42, the pad 43, and the core 44 described above. Movement of the belt 41 in the longitudinal direction is restricted by the inward surfaces of the flange members 45L and 45R.

  As will be described later, in the belt 41, the base layer 41a (FIG. 8) is made of a metal that generates electromagnetic induction heat. Therefore, it is sufficient to provide flange members 45 </ b> L and 45 </ b> R having flange portions that simply receive the end portion of the belt 41 as means for regulating the shift of the belt 41 in the rotating state in the longitudinal direction. Accordingly, there is an advantage that the configuration of the fixing device 16 can be simplified.

  A temperature sensor TH such as a thermistor as a temperature detecting means (temperature detecting element) for detecting the temperature of the belt 41 is disposed through a support member 46 having elasticity in the longitudinal center portion of the pad 43. The sensor TH is in elastic contact with the inner surface of the belt 41 by a member 46. As a result, even if a position variation such as the sensor contact surface of the rotating belt 41 undulates, the sensor TH follows this and maintains a good contact state with the inner surface of the belt 41.

  The heating assembly 40 is disposed by engaging the flange members 45L and 45R with the longitudinal guide slit portions 31 disposed on the side plates 30L and 30R, respectively. Therefore, the heating assembly 40 has a degree of freedom to move vertically along the slit portion 31 between the side plates 30L and 30R.

  FIG. 8 is a model diagram showing the layer structure of the belt 41. In this embodiment, the belt 41 has a nickel base layer (magnetic member, metal layer) 41a having an inner diameter of 30 mm and manufactured by electroforming. The thickness of the base layer 41a is 40 μm. A heat-resistant silicone rubber layer is provided as an elastic layer 41b on the outer periphery of the base layer 41a. The thickness of the layer 41b is preferably set within a range of 100 to 1000 μm.

  In this embodiment, the thickness of the layer 41b is set to 300 μm in consideration of reducing the heat capacity of the belt 41 to shorten the warm-up time and obtaining a suitable fixed image when fixing a color image. Silicone rubber has a hardness of 20 degrees JIS-A and a thermal conductivity of 0.8 W / mK. Further, on the outer periphery of the layer 41b, a fluororesin layer (for example, PFA or PTFE) is provided as a surface release layer 41c with a thickness of 30 μm.

  In order to reduce the sliding friction between the inner surface of the belt and the sensor TH, a resin layer (sliding layer) 41d such as fluororesin or polyimide may be provided on the inner surface side of the base layer 41a with a thickness of 10 to 50 μm. In this example, a polyimide layer having a thickness of 20 μm was provided as the layer 41d.

  The belt 41 has a low heat capacity and flexibility (elasticity) as a whole, and maintains a cylindrical shape in a free state. In addition to nickel, a metal such as an iron alloy, copper, or silver can be selected for the metal layer 41a. Moreover, the structure of laminating | stacking these metals on a resin base layer may be sufficient. The thickness of the metal layer 41a may be adjusted according to the frequency of a high-frequency current flowing in an excitation coil 62 (to be described later) of the unit 60 and the permeability / conductivity of the metal layer 41a, and may be set between about 5 and 200 μm.

(2-2) Pressure roller 50
The pressure roller 50 is rotatably disposed between the side plates 30 </ b> L and 30 </ b> R via a bearing 51 with the axial direction being substantially parallel to the longitudinal direction of the assembly 40 on the lower side of the heating assembly 40.

  In this embodiment, the roller 50 has a core rubber 50a made of iron alloy having a diameter of 20 mm at the center in the longitudinal direction and a diameter of 19 mm at both ends provided with a silicone rubber layer as an elastic layer 50b, and an outer diameter of 30 mm. An elastic roller having a crown shape. On the surface, a fluororesin layer (for example, PFA or PTFE) is provided as a release layer 50c with a thickness of 30 μm. The hardness of the roller 50 at the center in the longitudinal direction is ASK-C70 ° C.

  The metal core 50a is tapered (crown shape) because the pressure of the nip N formed by the pressure contact between the belt 41 and the roller 50 is the longitudinal direction of the nip even if the pad 43 is bent when pressed. It is for making it uniform over. In the present embodiment, the short width of the nip portion N is about 9 mm at both ends in the longitudinal direction and about 8.5 mm at the center when the nip pressure is 600N. This has the advantage that paper wrinkles are less likely to occur because the transport speed at both ends of the paper P is faster than the central portion.

  A gear 52 is fixedly disposed at the right end of the cored bar 50a. The driving force of the motor 53 controlled by the control unit 309 is transmitted to the gear 52 via a transmitting means (not shown), and the roller 50 is driven as a predetermined rotating member in the counterclockwise direction indicated by an arrow in FIG. Driven at speed.

(2-3) Coil unit 60
The coil unit 60 is a heater (induction heating means) for induction heating of the belt 41 and is disposed on the upper surface side of the heating assembly 40, that is, on the side opposite to the roller 50 side of the heating assembly 40 by approximately 180 °. The coil unit 60 is an assembly in which an exciting coil (coil that generates magnetic flux) 62, a magnetic core 63, and the like are assembled in a housing 61 that is long along the longitudinal direction of the belt 41.

  The housing 61 is a horizontally-long box-shaped molded product made of heat-resistant resin (an electrically insulating resin mold member) having a longitudinal direction in the left-right direction. The bottom plate 61 a side of the housing 61 is a surface facing the belt 41. The bottom plate 61a is curved inward of the housing 61 so as to be along a substantially semicircular range of the outer peripheral surface of the belt 41 in the cross section.

  The coil unit 60 has both ends of the housing 61 received by the left and right flange members 45L and 45R of the heating assembly 40 via brackets 66. Accordingly, the bottom plate 61a of the housing 61 faces the upper surface of the belt 41 with a predetermined gap (gap) α. In the coil unit 60, the left and right side plates of the housing 61 are tied to the flange members 45L and 45R on the respective sides by wire springs (not shown). That is, the coil unit 60 is integrated with the heating assembly 40.

  Accordingly, when the flange members 45L and 45R of the heating assembly 40 are pressurized and sink as described later, the coil unit 60 also sinks together while maintaining the gap α. Further, when the flange members 45L and 45R are lifted by being depressurized or released, the coil unit 60 is also lifted together while maintaining the gap α.

  The coil 62 is formed by using, for example, a litz wire as an electric wire, which is horizontally long and shaped like a ship bottom and is opposed to a part of the peripheral surface and side surface of the belt 41. And it is applied to the inner surface of the bottom plate 61a that is curved to the inside of the housing and is housed inside the housing. A high frequency current is applied to the coil 62 from a power supply device (excitation circuit) 64 controlled by the control unit 309.

  The core 63 is an outer magnetic core (outer magnetic core) that covers the coil 62 so that the magnetic field generated by the coil 62 does not substantially leak outside the metal layer (conductive layer) of the belt 41. The core 63 is disposed along the longitudinal direction of the belt 41, and is divided into a plurality of lines in a direction orthogonal to the paper conveyance direction a, and is arranged around the winding center portion of the coil 62 and the periphery thereof. It is comprised so that it may surround.

  The core 63 which is divided into a plurality is provided in the non-sheet passing portion in order to suppress the temperature rise in the non-sheet passing portion when a sheet having a width narrower than that of the maximum width size usable in the apparatus is passed. The corresponding portion of the split core is moved in a direction to widen the gap with the coil 6 by a moving mechanism (not shown). As a result, the magnetic flux density passing through the belt 41 in the portion corresponding to the non-sheet passing portion is lowered, and the amount of heat generated in the belt portion is reduced. Since the movement control of the split core is out of the gist of the present invention, a detailed description is omitted.

(2-4) Pressurizing mechanism 80 and changing mechanism In this embodiment, the pressurizing mechanism 80 presses the pad 43 of the heating assembly 40 to the roller 50 through the belt 41 with a predetermined pressing force (pressure). The pressure means for forming a predetermined nip portion N between the belt 41 and the roller 50. In this embodiment, the pressure of the pressure mechanism 80 (pressure at the nip portion) can be changed by a changing mechanism.

  Hereinafter, a specific mechanism configuration will be described. A pair of left and right pressure levers 81L and 81R as pressure members that are symmetrical in the left-right direction are disposed on the outer upper portions of the side plates 30L and 30R, respectively.

  The lever 81L is positioned above the pressurized portion 45a of the flange member 45L, and the rear end portion pivots so as to be pivotable in the vertical direction around the support shaft 81a with respect to the side plate 30L behind the flange member 45L. It is worn. That is, the lever 81L can be operated in a direction in which the pressed portion 45a of the flange member 45L is pressed against the supporting shaft 81a or in a direction away from the pressed portion 45a.

  The front end portion of the lever 81L is located in front of the flange member 45L. The lever 81L is always urged to rotate downward about the shaft 81a by the spring force of the spring 82a of a spring-loaded screw 82L as an urging member disposed between the side plate 30L.

  The lever 81R is positioned above the pressurized portion 45a of the flange member 45R, and the rear end is pivotally attached to the side plate 30R behind the flange member 45R so as to be pivotable in the vertical direction about the shaft 81a. Has been. That is, the lever 81R can operate in a direction in which the pressed portion 45a of the flange member 45R is pressed against the supporting shaft 81a, or in a direction away from the pressed portion 45a.

  The front end portion of the lever 81R is located in front of the flange member 45R. The lever 81R is always urged to rotate downward about the shaft 81a by the spring force of the spring 82a of the spring-equipped screw 82R disposed between the lever 81R and the side plate 30R.

  When the levers 81L and 81R are in a free state, the lower surfaces of the levers 81L and 81R have a spring force defined by a spring 82a of a screw with a spring against the upper surfaces of the pressurized portions 45a of the flange members 45L and 45R, respectively. It's pushing enough. In this embodiment, this pressure is set to 550 N, for example. Thereby, in the heating assembly 40, the stay 42 and the pad 43 are pushed down together with the flange members 45L and 45R, and the pad 43 is pressed against the roller 50 against the elasticity of the elastic layer 50b with the belt 41 interposed therebetween.

  By this pressure contact, a nip portion N having a predetermined width is formed between the belt 41 and the roller 50 in the paper conveyance direction a. The pad 43 assists in forming the pressure profile of the nip N. The configuration at this time is hereinafter referred to as a pressurizing configuration.

  A cam shaft 84 is rotatably disposed between the side plates 30L and 30R via bearings 83 and 83. On the left and right ends of the shaft 84, eccentric cams (pressure release members) 85L and 85R that are symmetrical and have the same shape on the outer sides of the side plates 30L and 30R are fixed and arranged in the same phase. The cam 85L is located below the front end portion of the pressure lever 81L. The cam 85R is located below the front end portion of the lever 81R.

  A gear (pressure releasing gear) 86 is fixedly disposed at the left end of the shaft 84. A driving force of a motor (for example, a stepping motor) 87 controlled by the control unit 309 is transmitted to the gear 86 via a transmission means (not shown), and the rotation of the shaft 84, that is, the cams 85L and 85R is controlled. . That is, the control unit 309 rotates the motor 87 according to a predetermined signal to rotate the gear 86 by a predetermined amount in a predetermined direction. The shaft 84 rotates in accordance with the rotation of the gear 86, and the cams 85L and 85R rotate accordingly.

  By controlling the rotation of the cams 85L and 85R, the levers 81L and 81R are lifted and rotated against the spring force of the spring 82a of the spring-loaded screw 82L, whereby the pressure of the pad 43 on the roller 50 is changed.

  The bearings 83 and 83, the shaft 84, the cams 85 </ b> L and 85 </ b> R, the gear 86, and the motor 87 are changing mechanisms that change the pressure of the nip portion N by the pressurizing mechanism 80. Details of the pressure change of the pressurizing mechanism 80 will be described later.

(2-5) Fixing Operation In the standby state of the image forming apparatus, the fixing device 16 has the motor 53 turned off and the rotation of the roller 50 is stopped. The pressurizing mechanism 80 is in a pressure release state, and the pressurization of the nip portion N is released. The power supply to the coil 62 of the coil unit 60 is turned off.

  The control unit 309 puts the pressure mechanism 80 into a pressure state at a predetermined control timing based on the input of the print job start signal (image formation job start signal). As a result, the nip portion N is in a pressurized state. Also, the motor 53 is turned on. As a result, the roller 50 is rotationally driven at a predetermined speed in the counterclockwise direction indicated by the arrow in FIG.

  By the rotation of the roller 50, a rotational force acts on the belt 41 by the frictional force between the surface of the roller 50 and the surface of the belt 41 in the nip portion N. While the inner surface of the belt 41 slides in close contact with the lower surface of the pad 43, the outer periphery of the stay 42, the pad 43, and the core 44 is driven to rotate in the clockwise direction indicated by the arrow in FIG. . A lubricant is applied to the pad 43 to reduce a sliding load with the belt 41. The movement in the thrust direction accompanying the rotation of the belt 41 is restricted by the flange portions of the left and right flange members 45L and 45R.

  The belt 41 is driven and rotated as described above by rotating the roller 50 by the motor 53 controlled by the control unit 309 at least during execution of image formation. This rotation is performed at substantially the same peripheral speed as the conveyance speed of the sheet P carrying the unfixed toner image t conveyed from the secondary transfer nip portion side. In this embodiment, the belt 41 rotates at a surface rotation speed of 300 mm / sec, and a full color image can be fixed at 80 sheets of A4 size and 58 sheets of A4R size per minute.

  The control unit 309 supplies an alternating current (high-frequency current) of 20 kHz to 50 kHz, for example, from the power supply device 64 to the coil 62. The coil 62 generates an alternating magnetic flux (magnetic field) by supplying an alternating current. The alternating magnetic flux is guided to the metal layer 41 a of the belt 41 on the upper surface side of the belt 41 rotating by the core 63. Then, an eddy current is generated in the metal layer 41a, the metal layer 1a is self-heated (electromagnetic induction heat) by Joule heat due to the eddy current, and the belt 41 is heated.

  That is, when the rotating belt 41 passes through the region where the magnetic field generated from the unit 60 is present, the metal layer 41a generates heat by electromagnetic induction and is heated all around. The temperature of the belt 41 is detected by the temperature sensor TH. The sensor TH detects the temperature of the portion of the belt 41 that becomes the paper passing area, and the detected temperature information is fed back to the control unit 309. The control unit (temperature control function unit of the control unit) 309 maintains the detected temperature (information about the detected temperature) input from the sensor TH at a predetermined target temperature (fixing temperature: information corresponding to the predetermined temperature). Thus, the power supplied from the power supply device 64 to the coil 62 is controlled.

  That is, when the detected temperature of the belt 41 rises to a predetermined temperature, the energization to the coil 62 is interrupted. In this embodiment, the temperature is adjusted by changing the frequency of the high-frequency current based on the detection value of the sensor TH and controlling the power input to the coil 62 so that the target temperature of the belt 41 is constant at 180 ° C. Is going.

  In the state where the roller 50 is driven and the belt 41 rises to a predetermined fixing temperature and is adjusted in temperature as described above, the sheet P carrying the unfixed toner image t in the nip portion N passes the toner image carrying surface side toward the belt. It is guided and guided by the guide member 33 toward the 41 side. The sheet P is in close contact with the outer peripheral surface of the belt 41 at the nip portion N, and is nipped and conveyed along the nip portion N together with the belt 41.

  As a result, mainly the heat of the belt 41 is applied, and the unfixed toner image t is fixed to the surface of the paper P by heat and pressure under the pressure of the nip portion N. The sheet P that has passed through the nip portion N is conveyed from the outer peripheral surface of the belt 41 to the outside of the fixing device due to self-separation (curvature separation) due to deformation of the exit portion of the nip portion N. In this embodiment, the paper P is introduced into the fixing device 16 by so-called central reference conveyance centered on the paper width. In FIG. 4A, O is the center reference line (virtual line).

(2-6) Pressure Change Here, in order to fix the toner image t on the paper P having severe fixability such as thick paper and glossy paper, it is desirable to set the pressing force of the nip portion N of the fixing device 16 high. Further, when dealing with a sheet having a long sheet length (width: the sheet short side) in a direction orthogonal to the sheet conveyance direction a such as overlarge, the distortion in the longitudinal direction of the belt 41 and the pressure roller 50 is large. Become. Therefore, in order to obtain an appropriate nip portion N necessary for fixing, it is desirable to set the pressing force higher.

  While it is desirable to deal with these sheets, it is desirable to set the pressing force low particularly for envelopes. Since the envelope has a configuration in which two or more sheets of paper are folded and glued, the speed difference at the nip portion N of the belt 41 and the pressure roller 50 is picked up by the front and back sheets of the envelope, and the downstream side in the envelope conveyance direction Because of this, the distortion due to the speed difference increases and the envelope is likely to wrinkle. In particular, when the pressure is high, the nip portion N is bent in the sheet conveyance direction due to the influence of the curvature separation at the nip portion N, so that the tendency of envelope wrinkles is more prominent. One avoidance method for avoiding envelope wrinkles is to reduce the nip pressure as much as possible.

  In order to cope with these problems, the cams 85L and 85R have two peak shapes as shown in FIG. 9 (FIG. 9). The position of the belt 41 when the cams 85L and 85R rotate will be described with reference to FIG.

  FIG. 10A shows a pressurized state. In this state, the flat portions of the cams 85L and 85R are in the upward rotation angle posture, and the cams 85L and 85R are not in contact with the levers 81L and 81R. Therefore, the spring force of the spring 82a of the spring-loaded screws 82L and 82R sufficiently acts on the levers 81L and 81R, and the pressure of the nip portion N is in a predetermined first pressure (normal pressure) (pressurization) Constitution).

  In this embodiment, in the case of normal pressure (first pressurization mode), the force (total pressure at the nip) applied to the heating assembly (belt unit) 40 is 550N. Examples of the normal pressure include 100N to 900N. Preferably it is 300N-600N.

  When the cams 85L and 85R are rotated in the clockwise direction in the pressurized state of FIG. 10A, the levers 81L and 81R are resisted against the spring force of the spring 82a of the spring-loaded screw 82R. Push it up to the position 1) ((a) → (b)). Then, the pressure on the flange members 45L and 45R is halved, and the position of the belt 411 is raised by ΔY1 ((a) → (b)). Thereby, the pressure of the nip portion N becomes a predetermined second pressure (light pressure) lower (weaker) than the first pressure in the pressurized state (pressure reduction configuration).

  In the case of the light pressure of the present embodiment (second pressurizing mode), the force (total pressure at the nip) applied to the heating assembly (belt unit) 40 is set to 32 ± 3N. Examples of light pressure include 10N to 90N. Preferably it is 30N-60N.

  When the cams 85L and 85R further rotate and push the levers 81L and 81R up to the position of the second highest peak (peak 2), the belt 41 further rises by ΔY2. Then, the pressure of the spring force of the spring 82a of the screw 82R with the spring against the flange members 45L and 45R is invalidated, and the belt 41 and the roller 50 are in a pressure release state (pressure release configuration) ((b) → (c)).

  When the pressure levers 81L and 81R are pushed up to the position of the second peak (peak 2) where the cams 85L and 85R are the highest, the belt 41 further rises by ΔY2, disabling the pressure applied to the flanges 45L and 45R. The force between 41 and the pressure roller 50 is only its own weight. That is, the pressure in the nip portion N is substantially released.

  Thus, the pressurizing mechanism 80 is changed to a pressurizing configuration, a pressure reducing configuration, and a pressure releasing configuration by controlling the rotation of the cams 85L and 85R. Note that the belt 41 rises above ΔY1 and ΔY2 due to the elastic deformation return of the elastic layer 50b of the pressure roller 50 as the pressure in the nip portion N decreases.

  The control unit 309 controls the fixing device 16 to the pressure release configuration shown in FIG. 10C when the image forming apparatus is on standby or non-image forming. When the paper to be passed through the fixing device 16 is other than the envelope, the pressurization configuration shown in FIG. Further, in the case of an envelope, control is performed so as to reduce the pressure as shown in FIG.

  Here, the fixing device 16 in this embodiment has a configuration in which the belt 41 and the pressure roller 50 are not sufficiently separated from each other in the pressure releasing configuration in FIG. This is because the fixing device 16 in this embodiment does not include a heater in contact with the inner surface of the belt 41, but if such a heater is provided, the belt 41 and the pressure roller 50 are sufficiently separated. , Heat of the heater loses escape. Along with this, there is a concern that the temperature rises excessively and heater cracking or the like occurs.

  Therefore, in a fixing device including a heater in contact with the inner surface of the belt 41, the belt 41 and the pressure roller 50 are often not sufficiently separated. In the fixing device 16 of this embodiment, an induction heating method is employed. For this reason, there is no adverse effect even if the heater 41 is not provided and the belt 41 and the pressure roller 50 are sufficiently separated. Even in the case of a fixing device including a heater, the belt 41 and the pressure roller 50 are not sufficiently separated so that the configuration of this embodiment can be used.

  The configuration of the fixing device 16 is summarized as follows. An image heating device 16 that nipping and conveying a sheet (recording material) P carrying a toner image t at a nip portion N and heating it. A belt (first rotating body) 41 that contacts the toner image carrying surface of the paper P and a pressure roller (second rotating body) 50 that faces the belt 41 are provided. In addition, a pressure mechanism 80 that forms a nip portion N by pressing the belt 41 and the pressure roller 50 is provided.

  Further, the pressure state of the nip portion N by the pressurizing mechanism 80 includes at least two states including a first pressure state (pressurization configuration) and a second pressure state lower than the first pressure (pressure reduction configuration). A change mechanism for changing to more than one state.

(2-7) Transmission of conveyance force at nip portion Transmission of force at the nip portion N will be described. As described above, the sheet P on which the toner image has been electrostatically transferred passes through the nip portion N of the fixing device 16 to fix the toner image on the sheet P. However, when the sheet P passes through the nip portion N. This conveying force is received from the pressure roller 50 on the driving side. That is, the paper P is conveyed by receiving a frictional force from the pressure roller 50 as the pressure roller 50 rotates.

  FIG. 11 is a diagram for explaining the force acting on the paper P sandwiched between the belt 41 and the pressure roller 50 when the paper P is conveyed. The pressure at the nip N is F, the friction coefficient between the paper P and the belt 41 is μ1, and the friction coefficient between the paper P and the pressure roller 50 is μ2. Here, in this embodiment, F = 550N, and the surface layers of the belt 41 and the pressure roller 50 are each covered with PFA, so μ1 = μ2 = 0.25 to 0.4 (coefficient of friction between PFA and paper). It is said.

  When the paper P is conveyed to the nip portion N and the paper P is nipped by the nip portion N, the belt 41 receives the conveying force μ1 · F from the pressure roller 50 via the paper P. Accordingly, when viewed from the sheet P side, when the sheet P passes through the nip portion N, the sheet P receives the conveying force μ2 · F from the pressure roller 50, and the sheet conveying direction a from the belt 41 side. The reverse force (reverse transport force) μ1 · F acts.

  On the other hand, in a state where the sheet P is not conveyed to the nip portion N, the driven belt 41 is also rotated by receiving a frictional force from the pressure roller 50 as the pressure roller 50 rotates. FIG. 12 is a diagram illustrating the force acting on the belt 41 when the paper P is not being conveyed. The friction coefficient between the belt 41 and the pressure roller 50 is μ12, and the friction coefficient between the belt 41 and the pad 43 is μ ′. In this embodiment, μ12 = 0.1 to 0.15 (friction coefficient between PFA and PFA). Further, since the sliding load between the belt 41 and the pad 43 is reduced by the lubricant, μ ′ is made minute.

At this time, since the belt 41 is pressed by the pad 43 at the nip portion N, a force in the direction opposite to the rotation direction acts from the pad 43 as a sliding resistance μ ′ · F. Here, when the pressure F is 550N, the belt 41 and the pressure roller 50 are in contact with each other in the entire longitudinal area, and pressure is applied to the entire longitudinal area of the belt 41, so μ ′ is very small.
μ12 · F> μ '· F
Thus, the belt 41 can rotate with the pressure roller 50 at substantially the same speed.

  Here, in the case of applying pressure with the above-described pressure reduction configuration of FIG. 10B (32 ± 3 N in the present embodiment), the pressure roller 50 has a crown shape, and the belt is partially in the longitudinal direction. There is a part which does not contact 41. However, since the belt 41 and the pressure roller 50 are thermally expanded by applying heat and are in contact with each other in the entire longitudinal direction, the belt 41 can rotate with the pressure roller 50 at substantially the same speed.

(2-8) Problems during Transportation When the fixing device 16 is shipped in the pressurization configuration shown in FIG. 10A, there is a case where it is left in this pressurization configuration state for a long time during physical distribution. A so-called C-set phenomenon occurs in which a part of the roller 50 becomes flat. In this state, when the user performs a printing operation using the image forming apparatus and rotates the belt 41 and the pressure roller 502, noise is generated due to the pressure roller 50 in the C-set state, resulting in malfunction or damage to the drive system. Cause.

  On the other hand, when the fixing device 16 is shipped in the pressure release configuration shown in FIG. 10C, the belt 41 and the pressure roller 50 are not sufficiently separated in this embodiment. The self-weight acts between 50. However, since the fixing is not sufficient only by its own weight, there is a concern that the belt 41 and the pressure roller 50 may be moved unintentionally due to the influence of dropping or vibration during transportation.

  Therefore, at the time of transportation from shipment to installation (distribution), it is possible to increase the stability of the parts while eliminating the C set phenomenon by adopting the pressure decreasing configuration of FIG. 10B. However, due to vibration during transportation, the pressure roller 50 rotates in a state where there is a portion that does not contact the belt 41 at a part of the length, and a speed difference occurs between the belt 41 and the pressure roller 50, and the belt 41. There is concern that rubbing marks will be attached to the surface.

(2-9) Response to problems during transportation Accordingly, as a response to problems during transportation, the fixing device 16 is a single unit or an image forming apparatus on which the fixing device 16 is mounted is distributed ( When transported, that is, in an unused state), the pressure state of the nip portion N is changed to the second pressure state (pressure reduction configuration). Further, a sheet-like member (contact prevention member) Pa is sandwiched in the nip portion N.

  In FIG. 1, the fixing device 16 is in a state of being distributed, and the pressure state of the nip portion N is the second pressure state (pressure reduction configuration). (Recording material) P is sandwiched.

  An effect of sandwiching the sheet-like member (contact prevention member) Pa (P) in the nip portion N during transportation in the pressure reduction configuration will be described. FIG. 13 is a diagram for explaining the force acting when the paper Pa (P) is sandwiched in the nip portion N of the fixing device 16 and the rear end of the paper Pa (P) is fixed.

  When the pressure roller 50 is unintentionally rotated due to the influence of vibration or the like during transportation, a conveying force μ2 · F acts between the pressure roller 50 and the paper Pa (P). However, since the rear end of the paper Pa (P) is fixed to the upper surface of the apparatus chassis (housing) 30 and the unit 60 of the fixing device 16 by the fixing member T as shown in FIG. The reaction force μ2 · F acts on the fixed portion. In this example, an adhesive tape (tape material) is used as the fixing member T in order to facilitate peeling during installation. The leading edge of the paper Pa (P) is also fixed by the fixing member T. In this case, the paper P is not conveyed. Therefore, no force in the conveying direction is applied to the belt 41, and the belt 41 does not rotate. Therefore, even if the pressure roller 50 is rotated by vibration during transportation, the belt 41 is not rubbed.

  Therefore, when the fixing device 16 is transported by the above configuration, the paper Pa (P) is sandwiched between the nip portions N by the pressure reducing configuration as shown in FIG. It is possible to easily prevent 41 from being rubbed. This protection configuration can also be implemented when transporting an image forming apparatus equipped with a fixing device 16 in an unused state.

  When the fixing device or the image forming apparatus is installed, the sheet P and the fixing member T as the sheet-like member Pa sandwiched between the nip portions N are removed by the installer. The sheet-like member (contact prevention member) Pa is not limited to the paper (recording paper) P. A plastic sheet or cloth may be used. Further, although the fixing member T uses a tape material in this embodiment, an adhesive, a hook-and-loop fastener, or the like may be employed.

<< Other Examples >>
(1) The numerical values such as dimensions exemplified in the embodiments are examples, and are not limited to these numerical values. The numerical value can be appropriately selected within a range where the present invention can be applied. Moreover, you may change suitably the structure as described in an Example in the range which can apply this invention.

  That is, the pressure state of the nip portion N is set to the second pressure state (pressure reduction configuration) during transportation from shipment to installation of the fixing device, and the sheet-like member Pa is interposed in the nip portion N. To this extent, another embodiment in which a part or all of the configuration of the embodiment is replaced with the alternative configuration can be implemented.

  (2) In the embodiment, the image heating apparatus has been described by taking a fixing apparatus that heats and fixes an unfixed toner image formed on a sheet (on a recording sheet) as an example, but is not limited thereto. The present invention can also be applied to an apparatus (gloss enhancement apparatus) that increases the gloss (glossiness) of an image by reheating a toner image fixed or assumed on the paper P.

  It can also be implemented in a decurling device that improves paper quality, a paper drying device that heats and dries paper before an image is formed, and the like. The present invention can also be implemented in a paper transport device including a paper transport member that transports paper while heating. In this case, although detailed description is omitted, in the above-described embodiment, the fixing device 16 may be read as a recording material conveying member having a built-in heater.

  (3) The pressurizing mechanism is a mechanism configuration that pressurizes at least one of the first rotating body and the second rotating body 41 that form the nip portion N for heating the toner image on the recording paper toward the other. It can be.

  (4) The first rotating body and the second rotating body may both be a roller structure, or both may be an endless belt, or one may be a roller body and the other. The device configuration may be an endless belt.

  (5) Any device configuration may be used as long as at least one of the first rotating body and the second rotating body is externally heated or internally heated by a heater, and the heater is not limited to the induction heating in the embodiment. It may be a contact type heater or heat ray irradiation heating. In the case of a contact-type heater, the heater can be configured so as to be opposed to the pressure roller 50 and in contact with the inner surface of the belt 41, for example.

  (6) The image forming apparatus is not limited to the image forming apparatus that forms a full-color image as in the embodiment, and may be an image forming apparatus that forms a monochrome image. In addition, the image forming apparatus can be implemented in various applications such as a copying machine, a FAX, and a multifunction machine having a plurality of these functions in addition to necessary equipment, equipment, and housing structure.

16 .... Image heating device (fixing device), 41 ... First rotating body (fixing belt), 50 ... Second rotating body (pressure roller), N ... Nip part, 80 ... Pressing mechanism , P ... Recording material, t ... Toner image, Pa ... Sheet-like member (contact prevention member), T (fixing member)

Claims (8)

A first rotating body and a second rotating body that form a nip portion for heating the toner image on the recording paper;
A pressurizing mechanism that pressurizes at least one of the first rotating body and the second rotating body toward the other;
A change mechanism capable of changing the pressure at the nip portion by the pressure mechanism to a first pressure and a second pressure lower than the first pressure,
An image heating apparatus, wherein the pressure at the nip portion is the second pressure in an unused state, and the sheet-like member is sandwiched.   2. The image heating apparatus according to claim 1, further comprising a housing that encloses the first rotating body and the second rotating body, wherein the sheet-like member is fixed to the housing by a fixing member. .   The image heating apparatus according to claim 2, wherein the fixing member is a tape material.   The image heating apparatus according to claim 1, wherein the sheet-like member is removed during installation.   The image heating apparatus according to claim 1, wherein the sheet-like member is recording paper.   The image heating apparatus according to claim 1, wherein the changing mechanism can substantially release pressure at the nip portion.   The image heating apparatus according to claim 1, wherein the first rotating body is an endless belt, and the endless belt is rotationally driven by the second rotating body.   The image heating apparatus according to claim 7, further comprising a heater disposed to face the second rotating body and in contact with an inner surface of the first rotating body.