JP2013024895A - Fixing device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of effectively suppressing occurrence of troubles in a fixing image quality even when a printing speed is increased, and an image formation device having the same.SOLUTION: An fixing device includes: a heating member; a belt member that is stretched by a first roller and a second roller and heated by the heating member; pressure means including a pressure member that forms a press-contact nip part via the belt member at a position facing the stretched positions of the first roller and second roller; and a pressing member that presses the belt member. The pressing member is provided between the stretched position of the first roller and the stretched position of the second roller. An image formation device includes the fixing device and image formation means that forms a developer image on a recording medium.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a printer, a copying machine, a facsimile machine, or a multifunction machine, and more particularly to a fixing device for fixing a developer image formed on a recording medium.

  In an image forming apparatus using a conventional electrophotographic system, the surface of a photosensitive drum is uniformly and uniformly charged by a charging unit such as a charging roller, and then an exposure unit such as an LED (Light Emitting Diode) or a laser beam. Thus, the surface of the photosensitive drum is exposed to form an electrostatic latent image corresponding to the image information. The electrostatic latent image formed on the surface of the photosensitive drum is supplied with a charged developer from a developing unit including a developing roller and a developer image is formed.

  The developer image developed on the surface of the photosensitive drum is transferred to a sheet as a recording medium fed from the sheet feeding device, and then fixed by applying heat and pressure in the fixing device.

  In the image forming apparatus having such a configuration, a nip portion formed by pressing a pressure roller disposed opposite to the fixing roller against the fixing roller via an endless fixing belt heated by a heater. Some include a belt heating type fixing device that applies heat and pressure by nipping and conveying the paper after the developer image has been transferred (see, for example, Patent Document 1).

JP 2009-151115 A

  However, in the conventional belt heating type fixing device, since the nip portion is formed only by the fixing roller and the pressure roller, for example, there is a disadvantage that the quality of the fixed image is lowered when the printing speed is increased.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fixing device capable of effectively suppressing the occurrence of defects in fixed image quality even when the printing speed is increased. And an image forming apparatus provided with the fixing device.

  In order to solve the above problems, a fixing device according to the present invention includes a heating member, a belt member stretched by a first roller and a second roller, and heated by the heating member; the first roller; A pressure member having a pressure member that forms a pressure nip portion through the belt member at a position facing the tensioning position with the second roller; and a pressure member that presses the belt member. Is provided between the stretched positions of the first roller and the second roller.

  The image forming apparatus according to the present invention is stretched by an image forming unit that forms a developer image on a recording medium, a heating member, a first roller, and a second roller, and is heated by the heating member. A pressure member having a belt member, and a pressure member that forms a pressure nip portion via the belt member at a position facing a tensioning position of the first roller and the second roller; and the first roller; A fixing unit that is provided between the second roller and the tensioning position and that presses the belt member, and fixes the developer image formed by the image forming unit. Features.

  According to the present invention, it is possible to provide a fixing device and an image forming apparatus including the fixing device that can effectively suppress the occurrence of a defect in fixed image quality even when the printing speed is increased.

FIG. 2 is a schematic cross-sectional view for explaining a schematic configuration of the printer. It is a block diagram for demonstrating the control system of a printer. FIG. 3 is a side view showing a main part structure of the fixing device. FIG. 4 is a diagram illustrating a configuration of a first fixing roller. It is a figure explaining the structure of the 2nd fixing roller. It is a figure explaining the structure of a pressure roller. It is a figure explaining the structure of a pad. FIG. 3 is a diagram illustrating a configuration of a fixing belt. It is a figure explaining the structure of a heater. FIG. 6 is a view showing a pressure distribution in a nip portion N. It is a figure explaining an evaluation level. It is a figure explaining an evaluation level. It is a figure explaining an evaluation level. It is a figure explaining an evaluation result. FIG. 6 is a view showing a pressure distribution in a nip portion N. FIG. 6 is a view showing a pressure distribution in a nip portion N. FIG. 6 is a view showing a pressure distribution in a nip portion N. FIG. 6 is a view showing a pressure distribution in a nip portion N. FIG. 3 is a side view showing a main part structure of the fixing device. It is a figure explaining the structure of a pad. It is a figure explaining an evaluation result. It is a figure explaining an evaluation result. It is a figure explaining an evaluation result.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it is possible suitably.

[First Embodiment]
FIG. 1 is a schematic cross-sectional view for explaining a schematic configuration of a printer 1 as an image forming apparatus provided with a fixing device according to the present invention. The printer 1 is a color printer capable of printing a color image by an electrophotographic method on a sheet as a recording medium.

  The printer 1 has a paper conveyance path 4 formed in a substantially S-shape starting from a paper cassette 2 that stores paper P before printing and having a stacker 3 formed by using the outer casing of the printer 1 as an end point. Along with the sheet feeding rollers 5a and 5b, a separation piece 6, a conveyance roller 7, a registration roller 8, a conveyance belt 9, a fixing device 14, and discharge rollers 16a and 16b are provided.

  On the upper surface of the transport belt 9, as an image forming unit, toner T as a developer of black (k), cyan (c), magenta (m), and yellow (y) is sequentially formed from the upstream side of the sheet transport path 4. The four independent image forming units 11k, 11c, 11m, and 11y that house the printer 1 are detachably mounted from the printer 1 main body. An exposure head 12 that irradiates light on the surface of the photosensitive drum 18 with light based on image information is disposed immediately above the photosensitive drum 18 provided in each of the image forming units 11k, 11c, 11m, and 11y described later. A transfer roller 13 for transferring the developer image formed on the photosensitive drum 18 onto the paper P is disposed at a position facing the photosensitive drum 18 via the upper surface portion of the conveying belt 9.

  The paper cassette 2 stores the paper P in a stacked state, and is detachably attached to the lower part of the printer 1. The paper feed mechanism including the paper feed rollers 5a and 5b and the separating piece 6 provided on the upper part of the paper cassette 2 takes out the paper P stored in the paper cassette 2 one by one from the uppermost part, and the paper transport path. Pull out to 4.

  The transport roller 7 sandwiches and transports the paper P fed out by the paper feed mechanism. The registration roller 8 corrects the skew of the sheet P conveyed by the conveyance roller 7 and conveys the sheet P to the conveyance belt 9.

  The transport belt 9 is an endless belt member that electrostatically attracts the paper P and transports it in the direction of the arrow in FIG.

  The image forming units 11k, 11c, 11m, and 11y differ only in the toner T that is accommodated, and the other configurations are all the same. Therefore, in the following description, the image forming unit 11y is taken as an example, and k, c, m, and y suffixes indicating the colors of the toner T are omitted.

  The image forming unit 11 forms a developer image by attaching the toner T to the electrostatic latent image formed on the surface of the photosensitive drum 18 by the light emitted from the exposure head 12. Such an image forming unit 11 y includes a photosensitive drum 18, a charging roller 19, a developing roller 20, a supply roller 21, a toner cartridge 22, and a cleaning blade 23.

  The photosensitive drum 18 includes a conductive support and a photoconductive layer. For example, a charge generation layer as a photoconductive layer and a charge transport layer are sequentially stacked on a metal shaft such as aluminum as a conductive support. Is an organic photoconductor configured. The photosensitive drum 18 forms an electrostatic latent image based on the light emitted from the exposure head 12 while rotating in a predetermined direction.

  The charging roller 19 is composed of, for example, a metal shaft such as stainless steel and a semiconductive epichlorohydrin rubber. The charging roller 19 is in contact with the photosensitive drum 18 with a predetermined pressure, and uniformly charges the surface of the photosensitive drum 18 based on a predetermined voltage applied from the high voltage power supply unit 52.

  For example, urethane rubber in which carbon black is dispersed is disposed on the outer periphery of a metal shaft such as stainless steel, and the surface of the developing roller 20 is subjected to an isocyanate treatment. The developing roller 20 is disposed so as to be in pressure contact with the surface of the photosensitive drum 18, supplies toner T to the electrostatic latent image formed on the surface of the photosensitive drum 18, and develops the developer image.

  In the supply roller 21, for example, a semiconductive foamed silicone sponge layer is disposed on the outer periphery of a metal shaft such as stainless steel. The supply roller 21 is in contact with the developing roller 20 with a predetermined pressure, and supplies the toner T supplied from the toner cartridge 22 to the developing roller 20.

  The toner cartridge 22 is a box-shaped container that stores the toner T, and supplies the stored toner T to the supply roller 21 through a supply port provided at the bottom of the container.

  The cleaning blade 23 is, for example, a urethane rubber member, and one end of the cleaning blade 23 is disposed at a position in contact with a predetermined position on the surface of the photosensitive drum 18. The cleaning blade 23 cleans the surface of the photosensitive drum 18 by scraping off the toner T remaining on the surface of the photosensitive drum 18.

  Note that the image forming units 11 are integrally configured, and are detachably attached to the printer 1. For this reason, the upper cover 15 of the printer 1 is configured to be openable and closable.

  The exposure head 12 is, for example, an LED head having a light emitting element such as an LED element and a lens array, and becomes a position where light emitted from the LED element forms an image on the surface of the photosensitive drum 18 based on image information. Are arranged as follows.

  The transfer roller 13 is disposed at a position facing the photosensitive drum 18 via the upper surface portion of the conveyance belt 9, and a developer formed on the photosensitive drum 18 based on a predetermined bias voltage applied from the high voltage power supply unit 52. The image is transferred to the paper P.

  The fixing device 14 is a belt heating type device, and includes a fixing belt unit 31 and a pressure roller 30 as a pressure member as a pressure unit. The fixing device 14 is disposed on the downstream side of the sheet conveying path 4 with respect to the image forming unit 11. When the sheet P on which the developer image is transferred passes through the nip portion maintained at a predetermined temperature, the fixing device 14 is heated. The developer image is fixed by applying pressure and melting the toner T. The fixing device 14 may be integrally attached to the printer 1 or may be detachably attached to the printer 1. The fixing device 14 will be described in detail later.

  The discharge rollers 16 a and 16 b sandwich and convey the paper P that has passed through the fixing unit 14, and discharge the paper P to the stacker 3 formed using the upper cover 15.

  Next, the control system of the printer 1 will be described. FIG. 2 is a block diagram for explaining a control system of the printer 1 according to the present embodiment.

  The control unit 50 is connected to a host device such as a personal computer via a communication line such as a LAN (Local Area Network) cable. In addition, the control unit 50 includes an arithmetic device such as a microprocessor, and has a function of controlling each unit in the printer 1 to execute print processing and the like, a function of controlling communication with a host device, and the like.

  The storage unit 51 includes, for example, a storage device such as a ROM (Read Only Memory), a RAM (Random Access Memory), and an HDD (Hard Disk Drive), and the control program executed by the control unit 50 and various data used for them. The processing result by the control unit 50 is stored.

  The high voltage power source 52 applies a predetermined voltage to the charging roller 19, the developing roller 20, the supply roller 21, the transfer roller 13, and the like based on an instruction from the control unit 50. Note that the charging roller 19, the developing roller 20, the supply roller 21, the transfer roller 13, and the like are electrically connected to the high-voltage power source 52 when the image forming unit 11 is mounted on the printer 1.

  The fixing control unit 53 controls the power feeding circuit 54 based on an instruction from the control unit 50 to supply heating power to a heater 34 of the fixing device 14 described later, and supply power to the fixing motor 38. The first fixing roller 321 is rotated in the paper transport direction. Further, a belt temperature sensor 36 and a pressure roller temperature sensor 37 are connected to the fixing control unit 53, and the surface temperature value of the fixing belt 33 detected by the belt temperature sensor 36 and the pressure roller temperature detection sensor 37. The surface temperature value of the pressure roller detected by is input respectively. Based on the surface temperature value of the fixing belt 33 that has been input, the fixing control unit 53 switches ON / OFF the power to be supplied to the heater 34 via the power supply circuit 54 and sets the surface temperature value of the fixing belt 33 to a predetermined value. The fixing temperature value is maintained.

  Next, the fixing device 14 will be described with reference to FIG. FIG. 3 is a side view showing the main structure of the fixing device 14.

  The fixing device 14 is a belt heating type device, and includes a fixing belt unit 31 and a pressure roller 30 as a pressure member as a pressure unit. As shown in FIG. 3, the fixing belt unit 31 includes a first fixing roller 321 as a first roller, a second fixing roller 322 as a second roller, and a heating member as a heating member inside a fixing belt 33 as a belt member. A heater 34 and a heater holder 35 that holds the heater 34 and also serves as a guide for the fixing belt 33 are disposed. The fixing belt 33 is stretched by these members.

  The pad 401 as the pressing member is on the upstream side in the rotation direction (paper conveyance direction) of the first fixing roller 321 and on the downstream side in the rotation direction (paper conveyance direction) of the second fixing roller 322, that is, in the first direction. It is provided between the tensioning positions of the fixing roller 321 and the second fixing roller 322.

  Here, the pressure roller 30 as a pressure member, which is a pressure means, and the first fixing roller 321, the pad 401, and the second fixing roller 322 of the fixing belt unit 31 face each other via the fixing belt 33. The pressure roller 30 is urged in a direction in which the first roller 321 is pressed by a predetermined pressing force of the pressure roller spring 44 against the bearing 301. Note that it is not essential for the pressure member to rotate, and a fixed guide whose surface is covered with a material having a low friction coefficient may be used. In this embodiment, the pressure member rotates following the fixing belt 33. A rotating body is used.

  The pad 401 is urged in a direction in which the pressure roller 30 is pressed via the fixing belt 33 by a pad spring 41 formed of a compression coil spring or the like. Further, the second fixing roller 322 is also urged in the direction of pressing the pressure roller 30 with a predetermined pressing force of the second fixing roller spring 43 against the bearing 326.

  The heater holder 35 is biased in the direction of pressing the fixing belt 33 by a predetermined pressing force of the heater spring 42. Note that the opposite ends of the urging direction of the pad spring 41, the second fixing roller spring 43, and the heater spring 42 are fixed to a frame (not shown).

  As described above, a nip portion N having a predetermined width in the sheet conveyance direction is formed between the fixing belt unit 31 and the pressure roller 30.

  Further, between the heater 34 of the fixing device 14 and the nip portion N, in the vicinity of the upstream side of the nip portion N in the rotation direction of the fixing belt 33, the inner periphery of the fixing belt 33 is in sliding contact with the inner peripheral surface of the fixing belt 33. A belt temperature detecting means (hereinafter referred to as a belt temperature sensor) 36 comprising a thermistor for detecting the surface temperature is disposed. Further, a pressure roller temperature detecting means (hereinafter referred to as a pressure roller temperature sensor) 37 comprising a thermistor that slidably contacts the outer peripheral surface of the pressure roller 30 and detects the surface temperature of the pressure roller 30 is disposed.

  Here, the configuration of the first fixing roller 321, the second fixing roller 322, the pressure roller 30, the pad 401, the fixing belt 33, and the heater 34 will be described in detail.

  As shown in FIG. 4a, the first fixing roller 321 includes a metal core 321a made of a metal pipe such as iron or aluminum alloy, or a shaft, and a heat-resistant elastic layer 321b made of silicone rubber or fluororesin. As shown in FIG. 3, the first fixing roller 321 is rotatably supported by a bearing 325, and the sheet P is fed by a driving force transmitted from the fixing motor 38 via a fixing roller gear provided on the core metal 321a. It is driven to rotate in the conveying direction.

  As shown in FIG. 4b, the second fixing roller 322 includes a cored bar 322a made of a metal pipe such as iron or aluminum alloy or a shaft, and a heat-resistant elastic layer 322b made of silicone rubber or fluororesin. As shown in FIG. 3, the second fixing roller 30 is rotatably supported by a bearing 326, and the rotation of the fixing belt 33 that is driven and rotated by the frictional force in the nip portion N accompanying the rotation of the first fixing roller 321. Along with this, it rotates.

  As shown in FIG. 5, the pressure roller 30 includes a cored bar 30a made of a metal pipe such as iron or aluminum alloy or a shaft, a heat-resistant elastic layer 30b such as silicone rubber or fluororesin, a fluororesin or the like. It is comprised from the mold release layer 30C which consists of. As shown in FIG. 3, the pressure roller 30 is rotatably supported by a bearing 301, and with the rotation of the fixing belt 33 that is driven to rotate by the frictional force in the nip portion N accompanying the rotation of the first fixing roller 321. To rotate.

  As shown in FIG. 6, the pad 401 includes a support base material 401a made of a metal such as iron or an aluminum alloy, a heat resistant elastic material 401b bonded and fixed to the support base material 401a, and a surface of the heat resistant elastic material 401b. And a sliding layer 401c. Here, the heat-resistant elastic layer 401b is a pressing surface corresponding to the shape of the nip portion N formed by the pressure roller 30, that is, the arc surface 401d in the same manner as the curvature of the pressure roller 30 via the fixing belt 33. Is formed. The sliding layer 401c is provided to reduce the frictional resistance with the inner peripheral surface of the fixing belt 33. A plurality of pad springs 41 for urging the pad 401 in the direction of pressing the pressure roller 30 via the fixing belt 33 are arranged in the longitudinal direction of the pad 401, and the longitudinal pressure on the pressure roller 30 is uniform. Is set to By the way, the width of the nip portion N can be appropriately changed by changing the length of the arcuate surface 401d of the pad 401 in the short direction.

  As shown in FIG. 7, the fixing belt 33 includes a cylindrical belt base material 33a formed of a material made of nickel, polyimide, stainless steel, etc., and a silicone rubber and a fluororesin formed on the outer peripheral surface of the belt base material 33a. And a release layer 33c made of a fluororesin or the like formed on the outer peripheral surface of the heat resistant elastic layer 33b. The fixing belt 33 is driven to rotate by the first fixing roller 321 and heated by the heater 34 by the frictional force in the nip portion N accompanying the rotation of the first fixing roller 321.

  As shown in FIG. 8, in the heater 34, an electric insulating layer 34b made of glass or the like is provided on a substrate 34a made of stainless steel or ceramics, and a resistance heating element 34d having an electrode 34c is formed on the insulating layer 34b. This is a planar heater protected by a layer 34e. As the resistance heating element 34d, a material such as a nickel-chromium alloy or a silver-palladium alloy can be used. Further, the protective layer 34e is glass-coated with pressure-resistant glass. The heater 34 having such a configuration is fixedly supported with a heat-resistant adhesive or the like along the longitudinal direction of the central portion of the upper surface of the heater holder 35.

  The heater holder 35 that holds the heater 34 is made of a highly heat-resistant resin such as polyether ether ketone (PEEK) or liquid crystal polymer (LCP), or a metal such as an aluminum alloy. The heater holder 35 is spaced apart from the first fixing roller 321 and the second fixing roller 322 on the opposite side of the inner peripheral surface of the fixing belt 33 from the pressure roller 30 and is opposed to the first fixing roller 321. The heater holder 35 is biased in the direction of pressing the fixing belt 33 by a predetermined pressing force of the heater spring 42, and the fixing belt 33 together with the first fixing roller 321, the second fixing roller 322, and the pad 401. Is supported in a rotatable manner.

  Next, the printing operation of the printer 1 having such a configuration will be described.

  First, when the control unit 50 of the printer 1 receives a print command including image information from the host device, the control unit 50 starts printing based on the received image information. The control unit 50 controls the paper feed mechanism including the paper feed rollers 5 a and 5 b and the separating piece 6 to take out the paper P stored in the paper cassette 2 one by one from the uppermost part and feed it to the paper transport path 4. Make it.

  The paper P fed to the paper transport path 4 by the paper feed mechanism is nipped and transported by the transport roller 7. Then, the paper P is transported to the transport belt 9 while the skew is corrected by the registration rollers 8.

  In parallel with this, the control unit 50 controls the high-voltage power supply 52 to apply a predetermined voltage to the charging roller 19, the developing roller 20, the supply roller 21, the transfer roller 13, and the like.

  The charging roller 19 provided in contact with the surface of the photosensitive drum 18 uniformly charges the surface of the photosensitive drum 18 based on a predetermined voltage applied from the high voltage power source 52. Next, the control unit 50 controls the exposure head 12 to irradiate the surface of the photosensitive drum 18 with light corresponding to the image information, thereby forming an electrostatic latent image based on the image information.

  Next, the developing roller 20 attaches the toner T supplied from the supply roller 21 to the electrostatic latent image formed on the surface of the photosensitive drum 18 and performs reverse development to form a developer image.

  Then, the paper P is transported to the image forming unit 11 by the transport belt 9. The developer images formed on the surfaces of the photosensitive drums 18 of the image forming units 11k, 11c, 11m, and 11y are matched with the timing of passing between the photosensitive drums 18 of the paper P and the transfer roller 13. The images are sequentially transferred onto the paper P by a predetermined bias voltage applied to the transfer roller 13.

  Heat and pressure are applied to the paper P on which the developer image has been transferred when passing through the nip portion of the fixing device 14 maintained at a predetermined temperature, and the developer T is fixed by melting the toner T. The

  The paper P on which the developer image is fixed is nipped and conveyed by the discharge rollers 16a and 16b, and is discharged and accumulated in the stacker 3 formed by using the upper cover 15, and the series of printing operations is completed.

  Next, the fixing operation of the fixing device 14 during the above series of printing operations will be described.

  When the control unit 50 of the printer 1 receives a print command including image information from the host device, the control unit 50 controls the fixing control unit 53 to drive the fixing motor 38. As the fixing motor 38 is driven, the first fixing roller 321 is rotationally driven in the direction in which the paper P is conveyed by the driving force transmitted from the driving motor 38 via the fixing roller gear provided on the core metal 321a.

  As the first fixing roller 321 is driven to rotate, the fixing belt 33 and the pressure roller 30 start to be driven to rotate by the frictional force at the nip portion N.

  At this time, the control unit 50 controls the fixing control unit 53 to generate heat by supplying electric power to the heater 34 via the power supply circuit 54, and heats it from the inner peripheral side of the fixing belt 33. The surface temperature value of the fixing belt 33 heated by the heater 34 is detected by the belt temperature sensor 36 and output to the fixing control unit 53. Based on the surface temperature value of the fixing belt 33 that has been input, the fixing control unit 53 switches ON / OFF the power to be supplied to the heater 34 via the power supply circuit 54 and sets the surface temperature value of the fixing belt 33 to a predetermined value. The fixing temperature value is maintained.

  In this way, when the sheet P on which the developer image has been transferred is conveyed in a state where the surface temperature value of the fixing belt 33 is maintained at a predetermined temperature value, the sheet P passes through the fixing belt 33. The second fixing roller 322, the pad 401, and the first fixing roller 321 and the pressure roller 30 are nipped by a nip portion N. Heat and pressure are applied to the developer image on the paper P via the fixing belt 33, and the toner T melts to fix the developer image.

  Note that, from the viewpoint of preventing excessive temperature rise of the fixing belt 33, it is preferable that the rotation start timing of the first fixing roller 321 is started without leaving a time from when the heater 34 is turned on. Therefore, in this embodiment, the first fixing roller 321 is set to rotate simultaneously with the heater 34 being turned on. In the present embodiment, the target fixing temperature value of the fixing belt 33 is set to 160 ° C., and when fixing is performed after the heater 34 is turned on, the target fixing temperature value becomes a predetermined temperature range having the target fixing temperature value as a median value. Thus, the fixing temperature of the fixing belt 33 is controlled.

[Example 1]
In Example 1, a pipe made of iron (STKM) having a diameter of 21 mm, a thickness of 0.8 mm, and a length of 230 mm was used as the core metal 321 a of the first fixing roller 321. Then, as the heat-resistant elastic layer 321b, the pipe was covered with a foamed silicone rubber (sponge) layer having a thickness of 2 mm and an expansion ratio of 2, and a roller having an outer diameter of 25 mm was obtained. The roller product hardness is ASKER-C70. Further, the outer shape of the first fixing roller 321 is a crown shape in which the outer diameter is 0.2 mm larger than the both ends of the central portion so that the pressure distribution in the longitudinal direction with the pressure roller 30 is uniform.

  As the core metal 322a of the second fixing roller 321, a pipe made of iron (STKM) having a diameter of 18 mm, a thickness of 0.8 mm, and a length of 230 mm was used. Then, as the heat-resistant elastic layer 322b, the pipe was covered with a foamed silicone rubber (sponge) layer having a thickness of 1 mm and an expansion ratio of 2, and a roller having an outer diameter of 20 mm was obtained. The roller product hardness is ASKER-C80. Further, the outer shape of the second fixing roller 322 has a crown shape in which the outer diameter of the center portion is 0.1 mm larger than both ends so that the pressure distribution in the longitudinal direction with the pressure roller 30 is uniform.

  As the metal core 30a of the pressure roller 30, a pipe made of iron (STKM) having a diameter of 33.6 mm, a thickness of 0.5 mm, and a length of 230 mm was used. Then, the pipe is covered with a foamed silicone rubber (sponge) layer having a foaming ratio of 2 having a thickness of 1.2 mm as the heat-resistant elastic layer 30b, and further, a 30 μm-thick perfluorovinyl ether copolymer is formed as the release layer 30c. The heat-resistant elastic layer 30b was covered with a polymer (PFA) resin tube to obtain a roller having an outer diameter of 36 mm. The roller product hardness is ASKER-C75.

  An aluminum alloy (A6063) was used as the support base material 401a of the pad 401. Then, a foamed silicone rubber (sponge) layer having an expansion ratio of 2 was used as the heat resistant elastic material 401b, and a 30 μm-thick silicone resin was coated on the heat resistant elastic material 401b as the sliding layer 401. In this embodiment, the arc length of the arc surface 401d is set to 5 mm. The silicone rubber hardness was JIS A40. The outer shape of the arcuate surface 401d is a crown shape with a central portion protruding 0.1 mm from both ends so that the pressure distribution in the longitudinal direction with the pressure roller 30 is uniform. By the way, in the present Example, although the sliding layer 401 was comprised as a coating layer, you may comprise so that the heat resistant elastic material 401b may be coat | covered with a sheet-like fluororesin. In the present embodiment, the heat-resistant elastic layer 401 b has the same pressing surface corresponding to the shape of the nip portion N formed by the pressure roller 30, that is, the curvature of the pressure roller 30 via the fixing belt 33. The arc surface 401d is formed as described above. However, the arc surface 401d may be omitted and a planar shape may be used.

  In this embodiment, the gap between the pad 401 and the first fixing roller 321 and the second fixing roller 322 at the nip portion N is set to 1 mm.

  As the belt base material 33a of the fixing belt 33, a cylindrical member made of polyimide (PI) resin having a thickness of 70 μm was used. The cylindrical member is covered with a foamed silicone rubber (sponge) layer having a foaming ratio of 2 having a thickness of 100 μm as the heat-resistant elastic material 33b, and further heat-resistant with a PFA resin tube having a thickness of 15 μm as the release layer 33c. The elastic elastic layer 33b was coated and formed as an endless belt. Further, the fixing belt 33 has an inner diameter that increases the temperature rise time if the belt circumference is long, and conversely, if the belt circumference is short, the space is insufficient, and the outer diameter of the fixing roller necessary for securing the width of the nip portion N is large. The arrangement with the pad base material size becomes impossible. Therefore, in this embodiment, the inner diameter of the fixing belt 33 is set to 45 mm.

  By the way, the pressure roller 30 is urged by a pressure roller spring 44 against the bearing 301 in the direction of pressing the first roller 321 with a total pressing force of 15 kgf on one side and 30 kgf on both sides. Further, the pad 401 is urged in the direction of pressing the pressure roller 30 with a total pressing force of 4 kgf, and the second fixing roller 322 is pressed with a total pressing force of 2 kgf on one side and 4 kgf on both sides. With the above configuration, the width of the nip formed by the pressure roller 30 and the first fixing roller 321 is 5 mm, the width of the nip formed by the pressure roller 30 and the pad 401 is 4 mm, and the pressure roller 30 and the second fixing roller 322. The width of the nip portion formed by each can be set to 3 mm, and the width of the nip portion N in this embodiment was set to about 12 to 14 mm.

  FIG. 9 shows the pressure distribution in the nip portion N set in this way. As described above, the contact area between the portion between the first fixing roller 321 and the second fixing roller 322 and the pressure roller 30 via the fixing belt 33 is the nip portion N.

  Here, in the nip area A, the second fixing roller 322 is pressed against the pressure roller 30, in the nip area C, the pad 401 is pressed against the pressure roller 30, and in the nip area E, the pressure roller 30 is pressed against the first fixing roller 321. And the resulting pressure distribution. Between the nip areas A and C and between the nip areas C and E, the fixing belt 33 is pressed against the pressure roller 30 to form nip areas B and D in a low pressure area. In the nip regions B and D, the fixing belt 33 is pressed against the pressure roller 30 by the belt tension.

In this embodiment, the peak in the longitudinal direction average pressure in the nip region E (hereinafter referred to as nip region E pressure) is ² to 2.5 kgf / cm ² , and the longitudinal direction average pressure in the nip region C (hereinafter referred to as The peak of the nip region C pressure) is 0.8 to 1 kgf / cm ² and the peak of the nip region A longitudinal pressure (hereinafter referred to as nip region A pressure) is 0.8 kgf / cm ^2. Is set to That is, the nip region A pressure and the nip region C pressure are set to be lower than the nip region E pressure.

  In order to examine the arrangement of the members constituting the nip portion N with respect to the configuration of Example 1 described above, a comparative example was created and an evaluation test was performed to confirm the influence on the developer image.

[Comparative Example 1]
As Comparative Example 1, a configuration in which the pad 401 was not disposed between the first fixing roller 321 and the second fixing roller 322 was used.

[Comparative Example 2]
As Comparative Example 2, a configuration in which the length of the arc surface 401d of the pad 401 was extended from 5 mm to 10 mm, except for the second fixing roller 322, was used.

[Comparative Example 3]
As Comparative Example 3, a configuration in which an intermediate fixing roller having the same configuration as the second fixing roller 322 is disposed between the first fixing roller 321 and the second fixing roller 322 instead of the pad 401 is used. In addition, the pressing force of each member was adjusted so that the length of the nip portion N in Comparative Examples 1 to 3 was the same as the length of the nip portion N in Example 1.

[Comparative Example 4]
As Comparative Example 4, a configuration in which the length of the arcuate surface 401d of the pad 401 was shortened from 5 mm to 3 mm except for the second fixing roller 322 was used.

In the evaluation test, the fixing device 14 having the configuration of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 is attached to the printer 1, and at the end of warm-up after the power is turned on, the A4 size is obtained. The printing was performed by continuously printing ten sheets of paper P (Oki Data Excellent Paper; basis weight 64 g / m ² ).

  At this time, the printing was performed with a monochromatic toner duty of 100% and a printing speed of three levels of A4 vertical feed of 40 ppm, 30 ppm, and 20 ppm. Then, fixed image quality such as disturbance, shift, unevenness (hereinafter referred to as image disturbance) of the fixing developer image on the paper P was set as an evaluation item. In the evaluation of image quality, the presence / absence of a non-uniform portion (image disturbance) caused by a deviation from the toner position on the paper P at the time of fixing was determined visually. The image disturbance is that the toner T moves and the background is visible on the paper P, and uneven gloss is visible. In this evaluation, the image disturbance is classified into three levels shown in FIGS. 10a, 10b, and 10c. That is, as shown in FIG. 10a, there is no image disturbance (indicated by a circle), the fixed image has a partial disturbance in the page (indicated by a triangle), and the fixed image disturbance is entirely in the page. And three levels (shown by x).

  FIG. 11 shows the evaluation results of the configurations of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 under the above evaluation conditions. As shown in FIG. 11, only in the configuration (Example 1) in which the pad 401 is disposed between the first fixing roller 321 and the second fixing roller 322, it is confirmed that image disturbance does not occur at a printing speed of 40 ppm. It was.

  On the other hand, FIG. 12 a shows the pressure distribution in the nip portion N according to the configuration of Comparative Example 1. In FIGS. 12a to 12d, the regions corresponding to the nip region C, the nip region E, and the nip region A in the first embodiment are represented by subscripts a to d, respectively. When the pressing force of the pad 401 in the nip region C as shown in FIG. 9 disappears, the regions corresponding to the nip regions B and D in the first embodiment are widened, and as a result, a low pressure region shown as the nip region F is generated. . In the nip region F, it becomes impossible to suppress the movement of air, water vapor and the like generated from the toner layer when passing through the nip portion N of the paper P, and minute slip is likely to occur between the surface of the paper P and the fixing belt 33. Therefore, image disturbance is likely to occur. For example, when a sheet having low air permeability such as a coated sheet is used, the disturbance of the fixed image becomes larger.

  In the first exemplary embodiment, since the pad 401 is disposed between the first fixing roller 321 and the second fixing roller 322, the pressing force between the first fixing roller 321 and the second fixing roller 322 is reduced. Since the widths of the nip areas B and D, which are the low pressure areas, are small, it is possible to prevent the disorder of the fixed image.

  Furthermore, in the first embodiment, the heat-resistant elastic material 401 b of the pad 401 is a pressing surface corresponding to the shape of the nip portion N formed by the pressure roller 30, that is, the fixing roller 33. Since the arc surface 401d is formed in the same way as the curvature, the nip portion start point between the first fixing roller 321 and the pressure roller 30 and the nip portion end point between the second fixing roller 322 and the pressure roller 30 are formed. Since the arcuate tip can enter the vicinity of each point, the width of the nip regions B and D, which are the low pressure regions, can be reduced.

  The pressure distribution in the nip portion N according to the configuration of Comparative Example 2 is shown in FIG. In Comparative Example 2, in order to compensate for the nip area A by the second fixing roller 322, the length of the arc surface 401d is doubled, so that the arc surface has a uniform shape in the paper conveyance direction and the longitudinal direction. It became difficult to manufacture. That is, in the configuration of the comparative example 2, the pressure by the pad 401 is locally non-uniform (nip regions Cb to Db), resulting in a disorder of the fixed image.

  The pressure distribution in the nip portion N according to the configuration of Comparative Example 3 is shown in FIG. In Comparative Example 3, since the pad 401 is changed to the intermediate fixing roller, the pressing force corresponding to the regions B and D of Example 1 is eliminated on both sides in the nip region Cc. That is, a low pressure region is generated in the nip region Bc generated between the first fixing roller 321 and the nip region Dc generated between the second fixing roller 322. In Comparative Example 3, the width of the nip regions Bc and Dc having almost no pressure is shorter than that of the nip region F in Comparative Example 1, so that the disturbance of the fixed image is slightly reduced in the low speed region. For the same reason as in Comparative Example 1, disorder of the fixed image occurs.

  The pressure distribution in the nip portion N according to the configuration of Comparative Example 4 is shown in FIG. In Comparative Example 4, since the length of the arc surface 401d is short, the pressure in the longitudinal direction of the pad 401 can be made relatively uniform as in Comparative Example 2. However, since the length of the nip portion N is shorter than that of the comparative example 2, the printing speed is low.

  In the configuration in which the two pads 401 are arranged except for the second fixing roller 322, the total length of the arc surface 401d is equivalent to that of the comparative example 2, and the friction generated between the pad 401 and the pressure roller 30 is the same. The power doubles. In such a state, the pad 401 is caught on the inner peripheral surface of the fixing belt 33 at the time of sliding, and stick slip or the like is generated, so that the sheet conveyance becomes uneven. As a result, the fixed image was disturbed.

  By the way, in the present embodiment, the outer diameter d1 of the first fixing roller is configured to be larger than the outer diameter d2 of the second fixing roller. In another test, the outer diameter of the first fixing roller <the outer diameter of the second fixing roller (nip area E pressure <nip area A pressure) was evaluated. . In addition, with this configuration, a paper conveyance problem that the paper P enters between the separation guide 38 and the fixing belt 33 occurs.

  The image quality of the fixed image is deteriorated because sufficient fixing is not performed only by the second fixing roller. When the outer diameter of the first fixing roller is smaller than the outer diameter of the second fixing roller, the sheet P is more twisted in the nip portion. This shows that the molten toner T cannot be completely fixed on the paper P when it is conveyed downstream.

That is, the relationship between the outer diameter d1 of the first fixing roller and the outer diameter d2 of the second fixing roller is expressed as follows: the outer diameter d1 of the first fixing roller> the outer diameter d2 of the second fixing roller.
As a result, the toner T melted on the upstream side of the nip portion N can be suppressed with a stronger pressure on the downstream side of the nip portion N, and the disorder of the fixed image can be prevented and the fixability can be secured. Further, by making the outer diameter of the second fixing roller small, the heater 34 can be brought close to the entrance of the nip portion N, and the heat transfer to the fixing belt is minimized, and the toner T is efficiently heated. Can be transmitted.

  In the present embodiment, the nip region E pressure is larger than the nip region C pressure, and is equal to the nip region C pressure and the nip region A pressure. In another test, when the nip area E pressure was set to a peak value at which the paper P can be separated and evaluated as nip area E pressure <nip area C pressure <nip area A pressure, jitter occurred in the fixed image. It was confirmed.

  When the pressing force of the pad becomes excessively large, the frictional force between the fixing belt and the pad becomes larger than the frictional force between the fixing belt and the pressure roller, and the running performance of the fixing belt is remarkably deteriorated. At this time, it is considered that the occurrence of a slip stick phenomenon on the fixing belt prevents the fixing belt from traveling at a constant speed, leading to a reduction in image quality of the fixed image. Further, when the difference between the nip area C pressure and the nip area A pressure is remarkably increased, the pressure in the nip area C is insufficient, and the fixed image is disturbed.

Based on the above results, the relationship between the nip area E pressure, the nip area C pressure, and the nip area A pressure is expressed as nip area E pressure> nip area C pressure ≧ nip area A pressure. It is possible to prevent deterioration in image quality of the fixed image.

  As described above, according to the first embodiment, the nip is disposed between the first fixing roller and the second fixing roller with respect to the sheet conveying direction of the fixing device, so that the nip is compared with the conventional device. Even when the length of the portion N can be increased and the printing speed is increased, it is possible to effectively suppress the occurrence of defects in the fixed image quality.

[Second Embodiment]
In the fixing device 14 of the second embodiment, the pressure roller 30 is configured as a pressure belt unit 45 with respect to the first embodiment. In the description of the present embodiment, the same portions as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  As shown in FIG. 13, the pressure belt unit 45 includes a first pressure roller 323 serving as a third roller serving as a pressure unit inside the fixing belt 33 serving as a belt member, and rotation of the first pressure roller 323. Direction upstream (paper transport direction) and downstream of the rotation direction (paper transport direction) of the second pressure roller 324 as the fourth roller, that is, the first pressure roller 323 and the second pressure roller 324. The pad 402 is provided between the tension position.

  Here, the first fixing roller 321, the pad 401, and the second fixing roller 322 of the fixing belt unit 31, which is a pressure unit, and the first pressure roller 323, the pad 402, and the second pressure roller of the pressure belt unit 45. Each of the first pressure roller 323 and the first pressure roller 323 is arranged at a position opposite to and parallel to each other with the two fixing belts 33 interposed therebetween. The roller 321 is urged in the direction of pressing.

  Further, the pad 402 is biased in a direction in which the opposing pads 401 are pressed via the two fixing belts 33 with a predetermined pressing force of the pad spring 41 formed of a compression coil spring or the like.

  Further, the second pressure roller 324 is also urged in the direction of pressing the second fixing roller 322 by a predetermined pressing force of the second pressure roller spring 442 against the bearing 328.

  As described above, a nip portion N2 having a predetermined width in the sheet conveyance direction is formed between the fixing belt unit 31 and the pressure belt unit 45.

  Similarly to the fixing belt unit 31, a belt temperature detecting unit 36 is disposed on the upstream side of the nip portion N <b> 2 in the pressure belt unit 45 in the sheet conveyance direction.

  As shown in FIG. 14, the pad 402 includes a support base material 402a made of a metal such as iron or an aluminum alloy, a heat resistant elastic material 402b bonded and fixed to the support base material 402a, and a surface of the heat resistant elastic material 402b. And a sliding layer 402c. Here, the heat-resistant elastic layer 402b is formed to have a pressing surface corresponding to the shape of the nip portion N formed by the pressure roller 30, that is, a flat surface 402d similar to the curvature of the two fixing belts 33. The The sliding layer 402c is provided to reduce the frictional resistance with the inner peripheral surface of the fixing belt 33. A plurality of pad springs 41 that urge the pad 402 in the direction in which the pad 401 is pressed via the fixing belt 33 are arranged in the longitudinal direction of the pad 402, and are set so that the longitudinal pressure on the pad 401 is uniform. ing. By the way, the width of the nip portion N can be changed as appropriate by changing the length of the flat surface 402d of the pad 402 in the short direction.

  The two fixing belts 33 have the same inner diameter of 45 mm, and have the same configuration as the fixing belt 33 described in the first embodiment.

  Further, the first pressure roller 323 and the second pressure roller 324 have the same configuration as the first fixing roller 321 and the second fixing roller 322, respectively.

  By the way, the first pressure roller 323 is urged by a pressure roller spring 441 with respect to the bearing 327 so as to press the first roller 321 with a total pressing force of 20 kgf on one side and 40 kgf on both sides. Further, the pad 402 is biased in the direction of pressing the pad 401 and the second fixing roller 322 by a total pressing force of 5 kgf, and the second pressure roller 324 is pressed by a total pressing force of 3 kgf on one side and 6 kgf on both sides. Yes. With the above configuration, the width of the nip formed by the first pressure roller 323 and the first fixing roller 321 is 5 mm, the width of the nip formed by the pad 402 and the pad 401 is 5 mm, and the second pressure roller 324 and the second fixing. The width of the nip portion formed by the roller 322 can be set to 4 mm, and the width of the nip portion N in this embodiment was set to about 14 to 16 mm. An example having such a configuration is referred to as Example 2.

  FIG. 15 shows the pressure distribution of the nip portion N2 according to Example 2 set in this way. As described above, there is a contact region between the first fixing roller 321 and the second fixing roller 322 and the contact area via the two fixing belts 33 between the first pressure roller 323 and the second pressure roller 324. This is the nip portion N.

  Here, in the nip region A2, the second pressure roller 324 presses the second fixing roller 322, the nip region C2 presses the pad 402 to the pad 401, and the nip region E2 presses the pressure roller 323 to the first fixing roller 321. And the resulting pressure distribution. Between the nip areas A2 and C2 and between the nip areas C2 and E2, the nip areas B2 and D2 of the low pressure area are formed by pressing the fixing belt 33 against the opposing fixing belt 33, respectively. In the nip regions B2 and D2, the fixing belt 33 is pressed against each other by the belt tension.

In Example 2, the peak in the longitudinal direction average pressure in the nip region E2 (hereinafter referred to as the nip region E2 pressure) is 2.5 to 3.0 kgf / cm ² , and the longitudinal average pressure in the nip region C2 ( Hereinafter, the peak of the nip region C2 pressure) is 0.8 to 1 kgf / cm ² and the peak of the longitudinal average pressure in the nip region A2 (hereinafter referred to as nip region A2 pressure) is 0.8 kgf / cm ² . It is set to be. That is, the nip region A2 pressure and the nip region C2 pressure are set to be lower than the nip region E2 pressure.

  In order to examine the arrangement of the members constituting the nip N with respect to the configuration of Example 2 described above, a comparative example was created and an evaluation test was performed to confirm the influence on the developer image.

[Comparative Example 5]
As Comparative Example 5, a configuration in which the pad 402 was not disposed between the second pressure roller 323 and the second pressure roller 324 was used.

  The evaluation test was performed in the same manner as in the first embodiment, and printing was performed at three printing speeds of A4 vertical feed of 50 ppm, 45 ppm, and 40 ppm.

  FIG. 16 shows the evaluation results of the configurations of Example 2 and Comparative Example 5 under the above evaluation conditions. As shown in FIG. 16, only in the configuration (Example 2) in which the pad 402 is disposed between the first pressure roller 323 and the second pressure roller 324, image disturbance does not occur at a printing speed of 50 ppm. confirmed.

  On the other hand, FIG. 17 shows the pressure distribution in the nip portion N according to the configuration of the comparative example 5. In the configuration of Comparative Example 5, since the pad 402 does not exist, the pressure by the pad 401 is locally non-uniform (nip regions C2 ′ to D2 ′), resulting in a disorder of the fixed image.

  In the second embodiment, the pad 402 is disposed between the first pressure roller 323 and the second pressure roller 324 so that the pressing force between the first pressure roller 323 and the second pressure roller 324 is obtained. Can be prevented, and since the width of the nip areas B2 and D2 which are low pressure areas is small, it is possible to prevent the fixed image from being disturbed.

  In the configuration of this embodiment, the first fixing roller 321, the pad 401, and the second fixing roller 322 in the fixing belt 33 are axially fixed, so even if the pressing force of the opposing pressure belt unit 45 increases. Stable running of the fixing belt 33 is possible.

  As described above, according to the second embodiment, it is possible to increase the pressing force as a configuration in which each member position in the fixing belt unit is fixed and pressure is applied by a member in the pressure belt unit. That is, according to the present embodiment, high-speed printing with an increased nip width and pressure is possible.

  In the description of this embodiment, a color printer has been described as an example of an image forming apparatus. However, the present invention is not limited to this, and the present invention is not limited to this. Applicable.

In the description of each embodiment, the printing paper is described as plain paper. However, the present invention is not limited to this, but an OHP sheet, a card, a postcard, a thick paper having a basis weight of 250 g / m ² or more, an envelope, and a heat capacity. Coated paper having a large size can be used.

  Furthermore, in the description of each embodiment, the heater has been described as a planar heater. However, even if the sliding contact surface with the fixing belt has the same degree of curvature as the fixing belt, the heater has a cylindrical heater shape. It may also be a halogen heater. Furthermore, induction heating can be performed by configuring the fixing belt with an electromagnetically inducible material, and the type and shape of the heater are not limited. In the description of each embodiment, the heater is described as being disposed inside the fixing belt. However, the heater may be provided outside the fixing belt.

DESCRIPTION OF SYMBOLS 1 Printer 2 Paper cassette 3 Stacker 4 Paper conveyance path 5a, 5b Feed roller 6 Separation piece 7 Conveyance roller 8 Registration roller 9 Conveyance belts 11k, 11c, 11m, 11y Image forming unit 12 Exposure head 13 Transfer roller 14 Fixing device 16a, 16b discharge roller 18 photosensitive drum 19 charging roller 20 developing roller 21 supply roller 22 toner cartridge 23 cleaning blade 30 pressure roller 31 fixing belt unit 321 first fixing roller 322 second fixing roller 323 first pressure roller 324 second addition Pressure roller 33 Fixing belt 34 Heater 35 Heater holder 401, 402 Pat

Claims (11)

A heating member;
A belt member stretched by a first roller and a second roller and heated by the heating member;
A pressure means having a pressure member that forms a pressure nip portion via the belt member at a position opposite to a tension position between the first roller and the second roller;
A pressing member that presses the belt member;
The fixing device according to claim 1, wherein the pressing member is provided between stretched positions of the first roller and the second roller. The pressure member is
The fixing device according to claim 1, wherein the fixing device is a rotating body. When the outer diameter of the first roller is d1, and the outer diameter of the second roller is d2,
The fixing device according to claim 1, wherein the relationship d1> d2 is satisfied. The longitudinal average pressure generated between the first roller and the pressure member is E1, and the longitudinal average pressure generated between the second roller and the pressure member is A1, and the pressing member and the pressure member are When the longitudinal average pressure generated between the pressure member and C1 is C1,
The fixing device according to claim 1, wherein a relationship of E1> C1 ≧ A1 is satisfied. The pressurizing means is
A pressure belt member stretched by a third roller and a fourth roller;
The fixing device according to claim 1, further comprising: another pressing member that is provided between the third roller and the fourth roller and that presses the pressure belt member. When the outer diameter of the third roller is d3 and the outer diameter of the fourth roller is d4,
The fixing device according to claim 5, wherein a relationship of d3> d4 is satisfied. The longitudinal average pressure generated between the first roller and the third roller is E2, and the longitudinal average pressure generated between the second roller and the fourth roller is A2, and the pressing member and the other When the longitudinal average pressure generated between the pressing member and C2 is C2,
The fixing device according to claim 5, wherein a relationship of E2> C2 ≧ A2 is satisfied. The pressing member is
The fixing device according to claim 1, further comprising a pressing surface corresponding to a shape of the press-contact nip portion formed by the pressing unit. The heating member is
The fixing device according to claim 1, wherein the fixing device is a planar heater. The heating member is
The fixing device according to claim 1, wherein the fixing device is a halogen heater. Image forming means for forming a developer image on a recording medium;
The belt member stretched by the heating member, the first roller and the second roller and heated by the heating member, and the belt member at a position facing the stretched position of the first roller and the second roller A pressurizing unit having a pressurizing member that forms a press-contact nip portion via a pressing member, and a pressing member that is provided between the stretched positions of the first roller and the second roller and presses the belt member. And an image forming apparatus comprising: a fixing unit that fixes the developer image formed by the image forming unit.