JP2018136393A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which can efficiently collect fine particles originated from a release agent contained in toner.SOLUTION: A fixing device comprises: a first rotating body 105 which comes into contact with and heats an unfixed toner image S formed on a sheet P by using toner containing a release agent; a second rotating body 102 which is disposed below the first rotating body and forms a nip part 101b between itself and the first rotating body for holding and conveying the sheet; a housing 107 which accommodates the first rotating body and the second rotating body; a cover member 114 which is disposed above the housing and covers the upper surface side 107U of the housing; a filter 51 which is disposed between the cover member and the housing and collects particles D of a predetermined particle diameter originated from the release agent; a suction part 61 for sucking air F3A between the cover member and the upper surface side of the hosing via the filter; and a duct 52 disposed between the filter, the suction part and the cover member.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fixing device that fixes a toner image on a sheet (recording material). The fixing device can be mounted on an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine having a plurality of these functions.

  An electrophotographic image forming apparatus forms an image using toner containing a release agent (wax), and heats and presses a sheet carrying the toner image with a fixing device to fix the image.

  The image forming apparatus described in Patent Document 1 forms a nip between a fixing roller and a pressure roller, and fixes a toner image by passing a sheet through the nip. And the structure for collect | recovering the odorous gas produced when the toner containing a mold release agent is heated is provided. More specifically, a duct for exhausting air in the vicinity of the fixing device to the outside of the image forming apparatus main body, a filter carrying an adsorbent such as activated carbon, and a fan for sucking air in the duct are provided. By adsorbing the gas to the filter, it is possible to suppress the gas from being diffused outside the image forming apparatus main body.

JP 2005-338539 A

  The image forming apparatus disclosed in Patent Document 1 uses a filter carrying an adsorbent such as activated carbon to remove gas. When the toner containing the release agent is heated, not only gas but also fine particles are generated. Fine particles are difficult to efficiently collect using the same filter because the method of adsorption to the filter is different from that of gas.

  An object of the present invention is to provide a fixing device configuration capable of efficiently collecting fine particles caused by a release agent contained in a toner.

  In order to achieve the above object, a typical configuration of the fixing device according to the present invention includes a first rotating body for heating in contact with a toner image formed on a sheet using a toner containing a release agent, A second rotating body that is positioned below the first rotating body and forms a nip portion with the first rotating body to sandwich and convey the sheet, and accommodates the first rotating body and the second rotating body And a cover member that is located above the housing and covers the upper surface side of the housing; a predetermined particle diameter that is located between the cover member and the housing and is caused by the release agent A filter for collecting particles, an air intake section for sucking air between the cover member and the upper surface side of the housing through the filter, and between the filter, the air intake section, and the cover member And a duct disposed on the wall.

  According to the present invention, fine particles resulting from a release agent contained in a toner can be efficiently collected.

1 is a schematic cross-sectional view of a fixing device in an embodiment. 3 is a perspective view of the periphery of a cover member in Embodiment 1. FIG. FIG. 3 is an exploded perspective view around the cover member in the first embodiment. 6 is a perspective view of a cover member in Embodiment 2. FIG. FIG. 6 is an exploded perspective view around a cover member in Embodiment 2. FIG. 6 is a diagram illustrating a sheet passing position in the periphery of the fixing device. 1 is a diagram illustrating a configuration of an image forming apparatus. FIG. 4 is a diagram illustrating a state in which a fixing belt unit is disassembled. (A) is an enlarged view of the vicinity of the nip portion in FIG. 1, (b) is a diagram showing a layer configuration of a belt, and (c) is a diagram showing a layer configuration of a pressure roller. 2 is a partial schematic front view of a fixing device. FIG. It is a block diagram of a control system. (A) is a figure for demonstrating the coalescence phenomenon of the dust D, (b) is a schematic diagram explaining the adhesion phenomenon of the dust D. FIG. FIG. 6 is a diagram illustrating a state of a wax adhesion region on a fixing belt that expands as the fixing process proceeds. It is a figure which shows the relationship between the adhesion area | region of a wax, and the generation | occurrence | production area | region of the dust D. FIG. FIG. 4 is a diagram illustrating the flow of airflow around the fixing belt. It is a figure explaining the flow of the airflow of a cover member lower part by a thermal airflow analysis. It is a figure which shows the relationship between the distance d between a cover member and a housing, and the flow rate ratio c of the same F3A with respect to the airflow F3. It is a figure which shows the relationship between the pressure loss P of a filter, and the filtration rate (alpha) of the dust D. FIG. It is a figure explaining the flow of the airflow of the cover member lower part in Example 2 by a thermal airflow analysis.

  Hereinafter, the present invention will be described in detail with reference to examples. Unless otherwise specified, the various configurations described in the embodiments may be replaced with other known configurations within the scope of the idea of the present invention.

Example 1
(1) Image Forming Apparatus With reference to FIG. 7, an example of the image forming apparatus 1 equipped with the fixing device 103 according to the present invention will be described. The image forming apparatus 1 is a four-color full-color printer (hereinafter referred to as a printer) using an electrophotographic process. The printer 1 controls the various components in the apparatus based on an image signal input from an external information terminal such as a personal computer or an input device 71 such as an image reader to the control circuit unit 70 and controls toner on the sheet P. An image (hereinafter referred to as a toner image) is formed. The sheet P is a recording material (paper) on which an image is formed. Examples of the sheet P include plain paper, cardboard, OHP sheet, coated paper, label paper, and the like.

  The control circuit unit 70 is an electric circuit including a calculation unit such as a CPU and a storage unit such as a ROM, and performs various controls when the CPU reads a program stored in the ROM or the like. The control circuit unit 70 is electrically connected to various components such as the input device 71 and the operation panel 72, and can exchange signal information.

  The image forming unit 2 that forms a toner image on the sheet P includes four electrophotographic image forming stations (hereinafter referred to as “yellow” (Y), magenta (M), cyan (C), and black (K) toner images). SY, SM, SC, and SK. These stations are provided side by side from the left side to the right side in the figure, and have substantially the same electrophotographic process configuration except that the color of the toner (developer) used is different as described above.

  Each station includes a rotating drum type electrophotographic photosensitive drum (hereinafter referred to as drum) 3 as an image carrier, a charger 4, a laser scanner 5, a developing unit 6, a primary transfer charger 7, and a drum cleaner 8. Have In addition, in order to avoid the complexity of the figure, the entry of symbols for these devices in the stations SM, SC, and SK other than the station SY is omitted. In addition, since the electrophotographic process and the image forming operation at each station are known, the description thereof is omitted.

  A toner image of each color is preliminarily superimposed on the intermediate transfer belt 9 rotating from the drum 3 of each station and is primarily transferred. As a result, a full-color unfixed toner image in which four colors of Y color + M color + C color + K color are superimposed is formed on the belt 9. On the other hand, one sheet P is fed from the cassette 10, passes through the conveyance path 11, and is introduced into a secondary transfer nip portion that is a pressure contact portion between the belt 9 and the secondary transfer roller 12 at a predetermined control timing. As a result, the four-color superimposed toner images on the belt 9 are secondarily transferred to the sheet P in sequence. The sheet P is introduced into the fixing device 103 and undergoes toner image fixing processing.

  The sheet P exiting the fixing device 103 is discharged to the discharge tray 15 through the guide member 13 and the discharge roller pair 14. Transfer residual toner remaining on the belt 9 after the secondary transfer of the toner image to the sheet P is removed from the belt surface by the belt cleaning device 16.

(2) Fixing Device FIG. 1 is an enlarged view of a fixing device 103 portion in the printer 1 of FIG. 7, and this fixing device 103 is a belt heating type lateral path device using electromagnetic induction heating. The fixing device includes a fixing unit 101 having a fixing belt (first rotating body) 105, a pressure roller (second rotating body) 102 which is positioned below the unit 101 and forms a nip portion 101b with the fixing belt 105, An induction heating device 300 for heating the fixing belt 105 is included.

  The fixing device 103 includes a housing 107 that houses the fixing unit 101, the pressure roller 102, and the induction heating device 300, and a cover member 114 that is located above the housing 107 and covers the upper surface side of the housing 107. .

  Here, the longitudinal direction (width direction) of the fixing device 103 or a member constituting the fixing device 103 is a direction parallel to a direction orthogonal to the sheet conveyance direction X in the sheet conveyance path surface. The short direction is a direction parallel to the sheet conveying direction X. Further, the front surface (front surface) of the fixing device 103 is a surface when the device is viewed from the sheet entrance side. The back surface (rear surface) is the opposite surface (sheet exit side). Left and right are left (one end side) and right (other end side) when the apparatus is viewed from the front. Up and down are upper and lower in the direction of gravity (vertical direction).

  The fixing device 103 is a horizontally long device that is long in the left-right direction. When the sheet P in the vicinity of the fixing device is taken out by jamming or the like, the upper surface side of the casing 107 is located above the fixing device 103 so that the operator does not touch the fixing device 103 at a high temperature of, for example, 70 ° C. or higher after the operation. A cover member 114 is installed as a mechanical enclosure so as to cover the cover.

(2-1) Fixing Unit FIG. 8 is an exploded perspective view of the fixing unit 101. A pressure roller 102 is also drawn. The fixing unit 101 is an assembly including a pressure applying member 104, a pressure stay 104a, a fixing belt (hereinafter referred to as a belt) 105, flange members 106L and 106R positioned on one end side and the other end side.

  The belt 105 is a thin, low-heat-capacity cylindrical (endless belt-shaped) member that is flexible as a whole. FIG. 9B is a schematic diagram of the layer structure of the belt 105. The belt 105 is a composite layer member in which an endless (cylindrical) base layer 105a, a primer layer 105b, an elastic layer 105c, and a release layer 105d are stacked in order from the inside to the outside.

  The base layer 105a is made of nickel having an inner diameter of 30 mm and a thickness of 40 μm manufactured by electroforming. The elastic layer 105c is a heat-resistant silicon rubber and is bonded to the base layer 105a through the primer layer 105b. The elastic layer 105c serves to bring the release layer 105d into close contact with the toner image by being deformed when the toner image is pressed.

  The thickness of the elastic layer 105c is preferably set within a range of 100 to 1000 μm. In this embodiment, the thickness of the elastic layer 105c is set to 300 μm in consideration of reducing the heat capacity of the belt 105 to shorten the warm-up time and obtaining a suitable fixed image when fixing a color image. Silicone rubber has a hardness of JIS-A 20 degrees and a thermal conductivity of 0.8 W / mK.

  Further, on the outer periphery of the elastic layer 105c, a fluororesin layer (for example, PFA or PTFE) is provided as a release layer 105d with a thickness of 30 μm. The release layer 105d uses a fluororesin having excellent release properties and heat resistance in order to prevent adhesion of toner and paper powder.

  Inside the belt 105, a pressure applying member 104 and a pressure stay 104a are disposed as an internal assembly. The pressure applying member 104 is a horizontally long member having a substantially semicircular arc shape in cross section, and is formed of a heat resistant resin such as a liquid crystal polymer. The pressure stay 104 a is a horizontally long rigid member having a U-shaped cross section, is formed of a metal such as iron, and is disposed inside the pressure applying member 104.

  The pressure applying member 104 and the pressure stay 104a are members longer than the width (length) of the belt 105, and one end side (left side) and the other end side (right side) protrude outward from the left and right end portions of the belt 105, respectively. ing. In FIG. 8, 104c is an outward projecting portion of the pressure applying member 104, and 104d is an outward projecting portion of the pressure stay 104a. Then, flange members 106L and 106R on one end side and the other end side are fitted to the outward projecting portions 104d on one end side and the other end side of the pressure stay 104a, respectively. The belt 105 is loosely fitted to the assembly of the pressure applying member 104 and the pressure stay 104a between the flange members 106L and 106R.

  Each of the flange members 106L and 106R is a left-right symmetrical molded product made of heat-resistant resin. Both ends of the belt 105 are restricted by the flange members 106L and 106R, and the movement in the width direction is suppressed. The flange members 106L and 106R guide the rotation of the belt 105 together with the pressure applying member 104 while holding the inside of the belt end.

  As shown in FIG. 8, the flange members 106 </ b> L and 106 </ b> R each have a flange portion (seat portion) 106 a, a shelf portion 106 b, and a pressed portion 106 c. The flange portion 106 a is a portion that receives the end face of the belt 105 and restricts the movement of the belt 105 in the thrust direction, and has an outer shape larger than the outer shape of the belt 105.

  The shelf portion 106 b is provided in an arc shape on the flange portion 106 a and holds the inner surface of the end portion of the belt 105 to hold the cylindrical shape of the belt 105. The pressed portion 106c is provided on the outer surface side of the flange portion 106a, receives a pressing force by the pressing springs 108L and 108R shown in FIG. 10, and pressurizes the belt 105 through the pressing stay 104a and the pressure applying member 104. It plays the role of pressing against the roller 102.

(2-2) Pressure Roller FIG. 9C is a diagram showing a layer structure of the pressure roller 102. The pressure roller 102 is a nip forming member that abuts on the outer peripheral surface of the belt 105 and forms a nip portion 101 b with the belt 105. The pressure roller 102 of this embodiment is a roller member composed of a plurality of layers. More specifically, the pressure roller 102 includes a metal (aluminum or iron) cored bar 102a, an elastic layer 102b formed of silicon rubber or the like, and a release layer 102c that covers the elastic layer 102b. The release layer 102c is a tube made of a fluorine-based resin such as PFA and is bonded onto the elastic layer 102b.

  As shown in FIG. 10, the pressure roller 102 is rotatably supported at one end side and the other end side of the cored bar 102a on the side plates 107L and 107R on the one end side and the other end side of the housing 107 via bearings 113, respectively. It is supported. At this time, a portion of the pressure roller 102 having the elastic layer 102b and the release layer 102c is located between the side plate 107L and the side plate 107R.

  A gear G is disposed concentrically and integrally on the other end side of the cored bar 102a. The driving force of the drive motor M (FIG. 11) controlled by the control circuit unit 70 is transmitted to the gear G through a drive transmission mechanism (not shown). As a result, the pressure roller 102 is driven to rotate at a predetermined peripheral speed in the counterclockwise direction indicated by arrow R102 in FIG.

(2-3) Pressure Mechanism FIG. 10 is a partial schematic front view of the fixing device 103, and the induction heating device 300 and the cover member 114 are omitted. Referring to FIGS. 1 and 10, the fixing unit 101 is arranged substantially parallel to the pressure roller 102 on the upper side of the pressure roller 102 with the pressure applying member 104 facing downward, and the side plates 107L and 107R of the casing 107 are arranged. It is arranged in between. The flange members 106L and 107R on one end side and the other end side of the fixing unit 101 are engaged with each other so as to be fitted to the vertical guide grooves (not shown) of the side plate 107L and the side plate 107R.

  In this engaged state, the flange portion 106a of the flange member 106L is located inside the side plate 107L, and the pressed portion 106c is located outside the side plate 107L. The flange portion 106a of the flange member 106R is located inside the side plate 107R, and the pressed portion 106c is located outside the side plate 107R.

  Thus, the flange members 106L and 106R are held so as to be slidable in the vertical direction with respect to the side plates 107L and 107R, respectively. That is, the fixing unit 101 as a whole has a degree of freedom of movement between the side plates 107L and 107R in a direction closer to the pressure roller 102 and a direction away from the pressure roller 102.

  The pressed portions 106c of the flange members 106L and 106R are pressed by pressure mechanisms having pressure springs 108L and 108R, respectively, and receive a predetermined pressure. The pressure springs 108L and 108R are respectively contracted between the pressed portion 106c and the spring receiving seats 109L and 109R. Since the flange members 106L and 106R are respectively fitted to the outward projecting portions 104d on one end side and the other end side of the pressure stay 104a, the pressure stay 104a is also moved downward via the flange members 106L and 106R, respectively. A predetermined equivalent pressure is applied.

  As a result, the pressure applying member 104 and the pressure roller 102 are pressed against each other with a predetermined pressure while sandwiching the belt 105 against the elasticity of the elastic layer 102b of the pressure roller 102. In the fixing device 103 of this example, the lower surface of the pressure applying member 104 functions as a sliding member that contacts the inner surface of the belt 105. Therefore, a nip portion (lateral path) 101 b having a predetermined width in the sheet conveyance direction X is formed between the belt 105 and the pressure roller 102. FIG. 9A is an enlarged schematic view of the nip portion 101b portion in FIG.

(2-3) Induction Heating Device In this embodiment, the induction heating device 300 is disposed on the outer surface of the belt 105 on the upper side of the fixing unit 101 between the one side of the casing 107 and the side plates 107L and 107R on the other end. It is a heating mechanism that is arranged to face each other and electromagnetically heats the belt 105 from outside without contact.

  The induction heating device 300 is a device for induction heating the metal base layer 105 a of the belt 105. Referring to FIG. 1, an exciting coil (hereinafter referred to as a coil) 110 provided inside induction heating device 300 is wound with a litz wire in a horizontally long / bottom shape and faces a part of the circumferential surface of belt 105. Are arranged to be. Since the magnetic field generated by the coil 110 passes through the outer magnetic core 111 covering the coil 110 and the base layer 105a of the belt 105, it does not leak to the outside.

  The outer magnetic core 111 that covers the coil 110 and the coil 110 is housed in a case (inner case) 112 made of an electrically insulating resin. The bottom plate portion of the case 112 is shaped to follow the outer peripheral surface of the upper surface portion of the belt 105 and faces the outer peripheral surface of the upper surface portion of the belt 105 with a predetermined gap (gap) therebetween. In the present embodiment, the upper surface plate 107U of the housing 107 is also used as a cover plate (outer case) of the case 112 of the induction heating apparatus 300.

  In the rotating state of the belt 105, a high frequency current of 20 to 50 kHz is applied to the coil 110 from a power supply device (excitation circuit) 73 (FIG. 11) controlled by the control circuit unit 70. The magnetic field generated from the coil 110 causes the base layer 105a of the belt 105 to generate heat.

(2-4) Fixing Operation The operation of the fixing sequence (fixing process) of the fixing device 103 is as follows. The control circuit unit 70 activates the drive motor M at a predetermined control timing to drive the pressure roller 102 to rotate at a predetermined speed in the direction of arrow R102 in FIG. When the pressure roller 102 is driven to rotate, a rotational torque acts on the belt 105 at the nip portion 102b by a frictional force with the pressure roller 102.

  As a result, the belt 105 slides with its inner surface in close contact with the pressure applying member 104, and the outer circumference of the pressure applying member 104 and the pressure stay 104 a moves at a speed substantially corresponding to the speed of the pressure roller 102. Rotate following direction. That is, in this embodiment, the pressure roller 102 functions as a drive roller that rotationally drives the belt 105. Since the inner peripheral surface of the belt 105 and the pressure applying member 104 slide, it is preferable to apply grease to the inner surface of the belt 105 to reduce sliding resistance.

  In addition, the control circuit unit 70 starts energization of the coil 110 from the power supply device 73. By this energization, the coil 110 generates a magnetic field in a partial region of the belt 105 and heats it. This area is a heating area of the belt 105. The temperature rise of the belt 105 due to heating is detected by a thermistor TH (FIGS. 8 and 11) as temperature detecting means provided in the pressure stay 104a. Based on the temperature of the back surface of the belt 105 detected by the thermistor TH, the control circuit unit 70 controls the power supplied to the coil 110 so that the temperature is adjusted to the target set temperature. The target set temperature in this embodiment is about 170 ° C.

  In the above fixing device state, the sheet P carrying the unfixed toner image S is conveyed from the secondary transfer unit side of the image forming unit 2 (FIG. 7) to the fixing device 103 side. Then, the sheet P is introduced into the inlet 101c of the nip portion 101c, and is nipped and conveyed by the nip portion 101b.

  The sheet P is heated by the heated belt 105 in the process of nipping and conveying the nip portion 101b. The unfixed toner image S is melted by the heat of the belt 105 and is fixed to the sheet P by the pressure applied to the nip portion 101b. The sheet P that has passed through the nip portion 101 b is discharged onto the discharge tray 15 by the guide member 13 and the discharge roller pair 14. In the present embodiment, the above-described process is called a fixing process.

(3) Generation of Dust D Next, generation of fine particles (hereinafter referred to as dust D) caused by a release agent (hereinafter referred to as wax) contained in the toner S and properties of the dust D will be described.

(3-1) Wax Contained in Toner As described above, the fixing device 103 fixes the toner image on the sheet P by bringing the high-temperature belt 105 into contact with the sheet P. When the fixing process is performed using such a configuration, a part of the toner S may be transferred (attached) to the belt 105 during the fixing process. This is called an offset phenomenon. Since the offset phenomenon causes image defects, it is desirable to solve this.

  In this embodiment, therefore, wax (release agent) is included in the toner S used for forming the toner image. The toner S is configured so that the internal wax dissolves and exudes when heated. Therefore, when a fixing process is performed on the image formed with the toner S, the surface of the belt 105 is covered with the dissolved wax. The belt 105 whose surface is covered with wax makes it difficult for the toner S to adhere due to the releasing action of the wax.

  In this embodiment, in addition to pure wax, a compound containing the molecular structure of wax is called wax. For example, a compound in which a resin molecule of a toner reacts with a wax molecular structure such as a hydrocarbon chain is also referred to as a wax. Moreover, as a mold release agent, you may use the substance which has mold release effects, such as silicone oil, besides wax.

  As the wax, when the belt 105 is maintained at the target temperature Tp, a wax that melts instantaneously at the nip portion 101b and exudes from the toner S can be used. In this example, paraffin wax having a melting point Tm of 75 ° C. was used while the target temperature Tp was 170 ° C.

  When the wax melts, some of the wax is vaporized (volatilized). This is considered to be because the size of molecular components contained in the wax varies. That is, the wax contains a low molecular component having a short chain and a low boiling point, and a high molecular component having a long chain and a high boiling point, and it is considered that the low molecular component having a low boiling point is vaporized first.

  When the vaporized (gasified) wax component is cooled in the air, fine particles (dust D) of about several nm to several hundred nm are generated. However, it is assumed that many of the generated fine particles have a particle size of several nm to several tens of nm. This can be confirmed by measuring dust.

The dust measurement was performed using a high-speed response type particle sizer (FMPS) manufactured by TSI. This FMPS can measure the particle size distribution, the number concentration (pieces / cm ³ ), and the weight concentration (μg / m ³ ). In the present invention, fine particles having a particle size of 5.6 nm or more and 560 nm or less that can be measured by FMPS are used as particles (dust) D having a predetermined particle size caused by the release agent.

  This dust D is a wax component having adhesiveness and easily adheres to various parts of the internal configuration of the printer 1 (FIG. 7). For example, when the dust D is carried to the periphery of the guide member 13 and the discharge roller pair 14 due to the rising air flow caused by the heat of the fixing device 103, the wax adheres to the guide member 13 and the discharge roller pair 14 and the volume is fixed. There is a risk that. If the guide member 13 and the discharge roller pair 14 are soiled with wax, the wax adheres to the sheet P and causes image defects. Further, there is a risk of clogging by adhering to the gas filter 600 installed in an exhaust (exhaust heat) mechanism that exhausts the atmosphere around the fixing device 103.

(3-2) Particles (dust) generated from wax during fixing processing
According to the study by the present inventors, it has been found that most of the dust D described above exists in the vicinity of the sheet inlet portion 101 c of the nip portion 101 b of the fixing device 103. Further, it was found that the dust D has a large particle size and easily adheres to neighboring members when the temperature is high. Details will be described below.

(3-2-1) Properties of Dust Properties of dust caused by wax include properties that increase the particle size at high temperatures and properties that dust D that has increased in size adheres to surrounding solids. (A) of FIG. 12 is a figure for demonstrating the coalescence phenomenon of dust, (b) is a schematic diagram explaining the adhesion phenomenon of dust.

  As shown to (a) of FIG. 12, when the high boiling point substance 20 whose boiling point is 150-200 degreeC is set | placed on the heating source 20a and it heats around 200 degreeC, the volatile matter 21a will generate | occur | produce from the high boiling point substance 20. FIG. When the volatile material 21a comes into contact with room temperature air, the volatile material 21a immediately becomes a boiling point temperature or less, condenses in the air, and changes to fine particles 21b having a particle diameter of about several nm to several tens of nm. This phenomenon is the same as the phenomenon in which when water vapor falls below the dew point temperature, it becomes minute water droplets and generates mist.

  At this time, the aggregation / particulation of gas in the air is more likely to be inhibited as the air temperature is higher. This is because the higher the air temperature, the higher the gas vapor pressure, and the easier it is for gas molecules to maintain a gaseous state. Therefore, the number of fine particles 21b generated decreases as the air temperature increases.

  Further, the gas present in the air tends to gather around the already generated fine particles 21b and aggregate. This is because the energy required for the gas molecules to agglomerate around the microparticles 21b is lower than the energy required for the gas molecules to aggregate and newly generate the microparticles 21b. is there.

  Further, since the fine particles 21b move in the air by Brownian motion, it is known that they collide with each other and coalesce to grow into particles 21c having a larger particle size. This growth is promoted as the fine particles 21b move more actively, in other words, as the air temperature is in a higher temperature state (Brownian motion becomes stronger). As a result, the fine particles generated from the belt 105 increase in particle size and decrease in number as the space temperature near the belt 105 increases.

  The increase in the size of the fine particles gradually slows down and stops when the fine particles become a certain size or more. This is presumably because Brownian motion becomes inactive when the size of the particles increases due to coalescence, and the collision frequency between particles decreases.

  Next, the adhesion of fine particles will be described with reference to FIG. When the air α including the fine particles 21b and the fine particles 21c larger than the fine particles 21b travels toward the wall 23 along the air flow 22, the fine particles 21c larger than the fine particles 21b are more likely to adhere to the wall 23. This is presumably because the fine particles 21c have a larger inertial force and collide with the wall 23 more vigorously.

  Accordingly, as the atmosphere in the vicinity of the belt 105 is maintained at a high temperature to increase the particle size of the dust D, the dust D is more likely to adhere to the configuration in the fixing device 103 (mostly the belt 105). For this reason, the dust D is more difficult to diffuse out of the fixing device 103 as the increase in the particle size of the dust D is promoted.

  As described above, the dust D has two properties, that is, coalescence is promoted at a high temperature and the particle size is increased, and that the particle size is easily adhered to a peripheral object. Note that the ease of coalescence of the dust D depends on the component, temperature, and concentration of the dust D. For example, the higher the concentration of the dust D, the higher the collision probability between the dusts D, and the lower the viscosity of the dust D, the easier it is for the dusts D to merge.

(3-2-2) Dust D Generation Location Next, the dust D generation location will be described with reference to FIGS. FIG. 13 is a diagram showing a state of the wax adhesion area on the belt 105 that expands as the fixing process proceeds. FIG. 14 is a diagram illustrating a relationship between a wax adhesion region and a dust D generation region. FIG. 15 is a diagram for explaining the flow of airflow around the belt 105.

  As a result of verification by the inventors, it has been found that the amount of dust D generated from the fixing device 103 is larger on the upstream side in the sheet conveyance direction of the nip portion 101b than on the downstream side in the sheet conveyance direction of the nip portion 101b. The mechanism will be described below.

  Since the surface (release layer 105d) of the belt 105 immediately after passing through the nip portion 101b is deprived of heat by the sheet P, its temperature is lowered to about 100 ° C. On the other hand, the temperature of the inner surface / back surface (base layer 105a) of the belt 105 is kept high by induction heat generation. Therefore, after the belt 105 passes through the nip portion 101b, the heat of the base layer 105a maintained at a high temperature is transmitted to the release layer 105d via the primer layer 105b and the elastic layer 105c.

  Therefore, the temperature of the surface of the belt 105 (the release layer 105d) rises after passing through the nip portion 101b in the process of the belt 105 rotating in the R105 direction, and is the highest near the sheet entrance side of the nip portion 101b. A high temperature is reached.

  On the other hand, the wax that exudes from the toner S on the sheet P is present at the interface between the belt 105 and the toner image when the fixing process is performed. Thereafter, a part of the wax adheres to the belt 105. As shown in FIG. 13, at the stage where a part of the leading end side of the sheet P passes through the nip portion 101b, the wax transferred from the toner S to the belt 105 exists in the region 135a. In this region, since the temperature of the belt 105 is low and the wax is difficult to volatilize, dust D is hardly generated.

  As the sheet P advances through the nip portion 101b, the wax is in a state of being present on substantially the entire circumference (region 135b) of the belt 105. Among these, in the region 135c, since the belt 105 is at a high temperature, the wax tends to volatilize. Then, dust D is generated when the volatilized wax from the region 135c condenses. Therefore, a large amount of dust D exists in the vicinity of the region 135c, that is, in the vicinity of the sheet entrance (upstream side) of the nip portion 101b.

  Further, the dust D in the vicinity of the sheet entrance of the nip portion 101b is diffused in the arrow W direction by the air flow shown in FIG. This will be described in detail as follows. As shown in FIG. 15, when the belt 105 rotates in the R105 direction, an air flow F1 along the R105 direction is generated near the surface of the belt 105. Further, when the sheet P is transported along the X direction, an air flow F2 along the transport direction X of the sheet P is generated. When the airflow F1 and the airflow F2 collide in the vicinity of the sheet entrance of the nip portion 101b, an airflow F3 is generated along a direction away from the nip portion 101b (W direction).

  FIG. 16 shows the result of thermal air flow analysis around the fixing device 103. FIG. 16 shows the destination of the airflow F3. The airflow F3 is separated from the vicinity of the sheet entrance of the nip portion 101b, and then flows between the cover member 114 and the upper surface plate 112U (the upper surface side of the housing 112) of the housing 112, and the airflow that flows outside the fixing device 103. Divided into F3B.

  The flow ratio of the air flows F3A and F3B to the air flow F3 is determined by the minimum value of the distance d [mm] between the cover member 114 and the upper surface plate 112U of the housing 112. FIG. 17 shows the distance d and the flow ratio c of the airflow F3A to the airflow F3 (the ratio of the airflow F3 from the nip portion 101b toward the excessive portion of the cover member 114) obtained from the thermal airflow analysis result.

  When the flow rate ratio c is 1, it means that the air flow F3 goes to the 100% air flow F3A. As the distance d increases, the flow rate ratio c increases. That is, the greater the distance d, the easier the flow from the airflow F3 flows in the direction of the airflow F3A. For example, when the distance d is 3 mm, the flow rate ratio c is 0.5, and when the distance d is 5.8 mm, the flow rate ratio c is 0.9. The curve shown in FIG.

(4) Dust D Recovery Configuration Based on the properties of dust D described above, the dust D recovery configuration will be described. In the present embodiment, the dust D collecting configuration includes a filter 51 that is located between the cover member 114 and the housing 112 and that collects particles having a predetermined particle diameter caused by the release agent. In addition, an air intake portion 61 that sucks air between the cover member 114 and the upper surface side of the housing 112 through the filter 51 is provided. Further, a duct 52 is provided between the filter 51, the intake section 61, and the cover member 114.

  That is, the lateral path fixing device generates an upward airflow due to the hot airflow from the fixing device. Therefore, the dust D also moves upward along the hot air flow. A cover member 114 for the enclosure exists above the fixing device, and an air current stays below the cover member. Then, it becomes a dust reduction measure by collect | recovering the air containing the dust D which convects to a cover member lower part via the elongate nonwoven fabric filter 51. FIG.

(4-1) Configuration of Filter FIG. 2 is a diagram illustrating the positional relationship between the filter 51 and the cover member 114 in FIG. FIG. 3 is an exploded perspective view of the periphery of the cover member 114.

  The dust D moves between the housing 112 and the cover member 114 by the airflow F3A. In order to collect the dust D that has reached the bottom of the cover member 114, a filter 51 is provided at the bottom of the cover member 114. The filter 51 is a long surface filter, and the air under the cover member 114 can be filtered by being sucked by a fan 61 as an air intake. Sealing between the filter 51 and the fan 61 by the duct 52 and the cover member 114 prevents air from being exhausted without being filtered from the gap.

  FIG. 6 is a perspective view of a main part in the width direction of the filter. At least a part of the length range A which is the length in the longitudinal direction of the filter 51 (in the same direction as the rotation axis direction of the belt 105) overlaps with the length range B which is the length of the image forming region in the same direction. Since the dust D is generated from the wax transferred from the toner image formed on the sheet P to the belt 105, at least a part of the length range A that is a range where dust can be reliably sucked overlaps the length range B. Need to be.

  In this embodiment, the length range A is 350 mm. However, if the length range A exceeds 200 mm (when the longitudinal direction of the A4 size sheet coincides with the conveying direction), which is a standard maximum image width of an A4 size sheet that is frequently used, actual use conditions It is possible to effectively reduce dust.

  On the other hand, if the length range A is further increased, not only can a sheet of a larger width be accommodated, but even if dust is diffused outside the image forming area due to surrounding airflow or the like, the dust is reliably collected by the filter 51. can do. However, if the length range A is too long, the filter 51 sucks clean air outside the dust generation area, and reduces the dust suction efficiency of the filter 51.

  Based on the above consideration, the upper limit of the length range A is the maximum image width of the maximum size sheet that can be used in a general electrophotographic image forming apparatus, and the length of the area where dust may diffuse outside. It can be understood that the value obtained by adding

  For example, let us consider a case where the maximum image width is 287 mm, which is obtained by excluding a blank area (non-image area) of about 5 mm from the lateral width 297 mm of an A3 size sheet. In this case, assuming that dust diffuses to a position about 100 mm away from the outside, the upper limit of the length range A has a slight margin of 487 mm, which is a value obtained by adding 200 mm (= 100 mm × 2) to 287 mm. It is appropriate to make it 500 mm.

  In summary, it can be understood that the length range A may be appropriately selected from a range of 200 mm to 500 mm in consideration of the width size of the sheet to be used and the degree of dust diffusion due to airflow. However, when mainly using a small size sheet such as a postcard size smaller than the A4 size sheet, the length range A should be set to a value shorter than 200 mm.

  As described above, the filter 51 has a shape extending in the longitudinal direction of the belt 105. By adopting such a shape, the passing air velocity of the air passing through the filter 51 is made uniform in the longitudinal direction. can do. In other words, by disposing the filter 51 that is a ventilation resistor, the entire back region of the filter 51 can be maintained at a constant negative pressure. That is, the negative pressures at the points 53a, 53b, and 53c shown in FIG. 3 are substantially the same value. This is because the ventilation resistance of the filter 51 is much larger than the ventilation resistance in the duct 52.

  If the negative pressures at the points 53a, 53b, and 53c are at the same level, the wind speed of the air sucked into the filter 51 is made uniform over the entire surface of the filter 51. As a result of the uniform wind speed, the filter 51 can efficiently collect the dust D generated from the belt 105 (with a minimum air volume).

(4-1-1) Properties of the filter The filter 51 is a filtering member for filtering (collecting and removing) the dust D from the passing air. When collecting the dust D caused by the wax, the filter 51 is preferably an electrostatic nonwoven fabric filter. The electrostatic nonwoven fabric filter is a non-woven fabric formed of fibers that retain static electricity, and can filter dust D with high efficiency.

  The electrostatic nonwoven fabric filter has higher filtration performance as the fiber density is higher, but on the other hand, pressure loss tends to increase. This relationship is the same when the thickness of the electrostatic nonwoven fabric is increased. Moreover, if the charging strength (static strength) of the fiber is increased, the filtration performance can be improved while keeping the pressure loss constant. It is desirable that the thickness and fiber density of the electrostatic nonwoven fabric and the charging strength of the fibers are appropriately set according to the filtration performance required for the filter.

  However, there is a technical upper limit on the charging strength, and when adjusting the performance of the electrostatic nonwoven fabric, it is performed by changing the fiber density and thickness. For example, the dust filtration rate can be further increased by increasing the fiber density and thickness.

  In FIG. 18, the performance of the electrostatic nonwoven fabric filter in a present Example is shown. FIG. 18 shows the relationship between the pressure loss P [Pa] of the electrostatic nonwoven fabric filter and the filtration rate α of dust D in this example. When the filtration rate α is 1, it means that dust can be filtered 100%. As the pressure loss P increases, the filtration rate α increases. For example, when the pressure loss P is 43 Pa, the filtration rate α is 0.5, and when the pressure loss P is 143 Pa, the filtration rate α is 0.9. The curve shown in FIG.

  When attempting to filter the toner in the exhaust air, the electrostatic nonwoven fabric is used at a pressure loss of 10 Pa or less when the toner filtration rate is 0.9 or more. Therefore, it can be said that the filter 51 of this embodiment uses an electrostatic nonwoven fabric having a relatively large pressure loss.

  The pressure loss of the filter 51 described above was measured by a multi-nozzle fan air flow measuring device F-401 (Tsukubarika Seiki). The dust filtration rate of the filter 51 was determined by measuring the dust concentration upstream and downstream of the filter 51 using Fast Mobility Particle Sizer (FMPS) manufactured by TSI. The difference between the upstream and downstream concentration is divided by the upstream concentration, and the numerical value expressed as a percentage is the dust filtration rate.

  The advantages of using a substantially flat nonwoven fabric filter are summarized as follows. The airflow passing through the nonwoven fabric filter is made uniform by the ventilation resistance of the nonwoven fabric filter. By making the air flow uniform, the suction efficiency of the dust D can be increased and the amount of air flow can be reduced (if there is too much air flow, the vicinity of the belt is cooled, so the amount of dust generated increases). Since a part of the duct 52 serves as a filter support portion, a filter installation space can be reduced.

  The width of the nonwoven fabric filter is set to a length that covers the image forming area of the sheet P as described above. The nonwoven fabric filter can reliably suck / filter dust generated from the wax transferred from the toner image to the belt.

(5) Filter configuration As described above, in the present embodiment, the configuration required depending on the rate at which the air F3 containing dust D reaches the lower portion of the cover member 114 and the rate at which the installed filter 51 filters the dust D. Is decided. Then, the distance d and the pressure loss P are in the following ranges from Equations 1 and 2.

1.77 (1-log (1-c)) <d [mm] Formula 3
−62.12log (1-α) <P [Pa] Equation 4
That is, the pressure loss P [Pa] of the filter 51 and the filtration rate α of the dust D, the ratio c of the air flow F3 from the nip portion 101b toward the lower portion of the cover member 114, and the space between the cover member 114 and the housing upper surface side 107U. The relationship of the minimum distance d [mm] satisfies Expressions 3 and 4.

  In addition, in many electrophotographic printers, if the dust D is reduced by about 50%, problems such as image defects caused by dust contamination inside the apparatus can be effectively prevented. The goal is to be able to do it. Therefore, assuming that the flow rate ratio c and the filtration rate α are at least 0.5, the following range is obtained.

≦ d [mm] Formula 5
43 ≦ P [Pa] Equation 6
In addition, if the distance d is too large, the size of the apparatus is increased. Therefore, the distance d is generally set to about 10 mm or less, and the pressure loss P is generally used in an electrophotographic printer. Since the maximum static pressure of 760 Pa is 760 Pa, it is rarely used beyond that.

  As described above, by appropriately setting the distance d and the pressure loss P, the dust D can be collected effectively and efficiently. Further, the distance d and the pressure loss P in this embodiment are set as d = 4 mm and P = 100 Pa, respectively.

Example 2
Next, Example 2 will be described. FIG. 4 is a diagram illustrating the arrangement relationship of the filters 51 in the second embodiment. FIG. 5 is an exploded perspective view of the periphery of the cover member.

  The cover member 114 has an opening 54, and the filter 51, the duct 52, and the fan 61 are disposed in the opening 54. Further, a gap 55 through which air can pass is vacant between the duct 52 and the cover member 114. The duct 52 is provided with a connecting portion 52a, and the duct 52 and the cover member 114 are supported and fixed by a screw, an adhesive, or the like through the connecting portion 52a. Further, the connection member 52a includes only a part of the duct 52, and the gap 55 is not lost between the duct 52 and the cover member 114.

  That is, by providing an opening in the cover member 114, airflow concentrates in the direction of the opening, and by installing a filter in the opening, dust can be collected efficiently. FIG. 19 shows the result of thermal air flow analysis around the fixing device 103. (A) shows the fixing device 103 in which the cover member 114 has a gap 55 in the second embodiment, and (b) shows the fixing device 103 in which the cover member 114 has no gap 55. Comparing (a) and (b), it can be seen that if there is a gap 55, the air flow is concentrated in the gap 55.

  Further, the flow velocity between the cover member 114 and the housing 112 is about 20% faster when the gap 55 is present. This means that if the distances d are equal, the flow rate flowing between the cover member 114 and the housing 112 increases. By increasing the flow rate, the flow rate ratio c increases, and the recovery efficiency of the dust D is further improved. Further, since it is not necessary to increase the distance d, the fixing device 103 can be prevented from being enlarged.

《Other matters》
1) The first rotating body in the fixing device is not limited to the belt body of the embodiment. It may be a roller body. The second rotating body is not limited to the roller body of the embodiment. It may be a belt body.

  2) The heating mechanism for heating the first rotating body is not limited to the electromagnetic induction heating device 300. Other heating mechanisms using a halogen lamp, a ceramic heater, or the like may be used. Moreover, it is not restricted to the heating mechanism which heats a 1st rotary body externally. A heating mechanism for internal heating may be used.

  3) In addition to a device that fixes an unfixed toner image as a fixed image, the fixing device is an image quality that improves glossiness by re-heating and pressurizing a toner image that has been presupposed to a sheet or a toner image that has been heat-fixed once. A reformer (referred to as this fixing device) is also included.

  4) The fixing device according to the present invention is not limited to a built-in fixing device fixed inside the image forming apparatus, but is a unit that is unitized and can be attached to, detached from, or connected to the apparatus main body of the image forming apparatus. It may be. In addition, the image forming apparatus may be an apparatus that can be used alone, independent of the image forming apparatus.

  5) In the image forming apparatus, the image forming unit (image forming mechanism unit) that forms the toner image on the sheet P is not limited to the transfer type electrophotographic image forming unit of the embodiment. For example, an electrophotographic image forming unit may be used in which a photosensitive paper is used as a sheet and a toner image is directly formed thereon. Further, it may be a transfer type electrostatic recording image forming unit or a magnetic recording image forming unit using an electrostatic recording dielectric or a magnetic recording magnetic material as an image carrier. Alternatively, an electrostatic recording image forming unit or a magnetic recording image forming unit may be used in which electrostatic recording paper or magnetic recording paper is used as a sheet and a toner image is directly formed thereon. A mono-color image forming unit may be used.

  103..Fixing device, 105..First rotating body (fixing belt), 102..Second rotating body (pressure roller), 101b..Nip part, 107..Case, 114..Cover member , 51 .. Filter, 52 .. Duct, 61 .. Air intake part (fan), P. Sheet, S. Toner image

Claims (9)

A first rotating body for heating in contact with a toner image formed on a sheet using a toner containing a release agent;
A second rotating body that is located below the first rotating body and forms a nip portion with the first rotating body to sandwich and convey the sheet;
A housing for housing the first rotating body and the second rotating body;
A cover member located above the housing and covering the upper surface side of the housing;
A filter that is located between the cover member and the housing and that collects particles having a predetermined particle diameter caused by the release agent;
An air intake section for sucking air between the cover member and the upper surface side of the housing through the filter;
A fixing device comprising: the filter, a duct disposed between the intake portion and the cover member. The pressure loss P [Pa] in the filter, the filtration rate α of the particles in the filter, the ratio c of the air flow from the nip portion toward the lower part of the cover member, the upper surface side of the cover member and the housing, The relationship of the minimum distance d [mm] between the following formulas 1.77 (1-log (1-c)) <d [mm]
−62.12 log (1-α) <P [Pa]
The fixing device according to claim 1, wherein:   The fixing device according to claim 2, wherein the distance d is 3 ≦ d [mm], and the pressure loss P is 43 ≦ P [Pa].   4. The fixing device according to claim 1, wherein a length of the filter along a length of the first rotating body is 200 mm or more and 500 mm or less. 5.   The fixing device according to claim 1, wherein a part of the cover member is a part of the duct.   The fixing device according to claim 1, wherein a gap is provided between the cover member and the duct.   The fixing device according to claim 1, wherein the release agent is a wax, and the predetermined particle size is 5.6 nm or more and 560 nm or less.   The fixing device according to claim 1, further comprising a heating mechanism that externally heats or internally heats the first rotating body.   The fixing device according to claim 8, wherein the heating mechanism is a coil that electromagnetically heats the first rotating body.