WO2017115877A1

WO2017115877A1 - Image-forming device

Info

Publication number: WO2017115877A1
Application number: PCT/JP2016/089234
Authority: WO
Inventors: 浩二野島
Original assignee: キヤノン株式会社
Priority date: 2015-12-28
Filing date: 2016-12-27
Publication date: 2017-07-06

Abstract

Provided is an image-forming device with which it is possible to appropriately remove fine particles caused by a release agent contained in a toner. The formula holds, where d is the distance between the intake port of a duct and a heating belt (mm), Fs is the surface area of a nonwoven cloth filter (cm²), and Fv is the speed at which air passes through the nonwoven filter (cm/s).

Description

Image forming apparatus

The present invention relates to an image forming apparatus that forms a toner image on a recording material. This image forming apparatus is used as a copying machine, a printer, a facsimile, and a multifunction machine having a plurality of these functions.

An electrophotographic image forming apparatus forms an image on a recording material using toner containing a release agent. The image forming apparatus includes a fixing device that heats and presses a recording material carrying a toner image to fix the image on the recording material.

The image forming apparatus described in Japanese Patent Laid-Open No. 2013-190651 has a configuration for collecting ultrafine particles generated by heating a toner containing a release agent.
However, with this configuration, there is room for improvement in properly removing the generated fine particles.

An object of the present invention is to provide an image forming apparatus capable of appropriately removing fine particles caused by a release agent contained in a toner.
[Means for solving problems]

The present invention includes an image forming unit that forms an image on a recording material using a toner containing a release agent;
A heating rotator and a pressure rotator that form a nip portion for fixing an image formed on the recording material by the image forming unit;
A duct for discharging air taken in from the vicinity of the inlet of the nip portion through the intake port;
A filter that is provided in a ventilation path of the duct and collects fine particles caused by a release agent;
A fan for drawing air into the duct,
When the distance between the intake port and the heating rotator is d (mm), the area of the filter is Fs (cm ² ), and the air passing velocity in the filter is Fv (cm / s), the following is satisfied: It is characterized by.

[The invention's effect]

According to the present invention, the fine particles caused by the release agent contained in the toner can be appropriately removed.

1A is a view showing how dust is collected in the vicinity of the fixing device, and FIG. 1B is a view showing how the trailing edge of the sheet is splashed.

2A is a perspective view of the periphery of the fixing device, and FIG. 2B is a diagram illustrating a sheet passing position in the vicinity of the fixing device.

3A is an exploded perspective view of the duct unit, and FIG. 3B is a diagram illustrating a state in which the duct unit operates.

FIG. 4 is a diagram showing the configuration of the image forming apparatus.

5A is a diagram illustrating a cross section of the fixing unit, and FIG. 5B is a diagram illustrating a state in which the belt unit is disassembled.

6A is a diagram showing a sheet near the nip portion of the fixing unit, FIG. 6B is a diagram showing a layer configuration of the belt, and FIG. 6C is a diagram showing a layer configuration of the pressure roller.

FIG. 7 is a view showing a pressure mechanism of the belt unit.

8A is a diagram for explaining the coalescence phenomenon of dust D, and FIG. 8B is a schematic diagram for explaining the adhesion phenomenon of dust D.

9A is a graph showing the relationship between the elapsed time of image formation processing and the amount of dust D generation in Verification Example 1, and FIG. 9B is the relationship between the elapsed time of image formation processing and the amount of dust D generation in Verification Example 2. It is a graph which shows.

10A is a diagram illustrating a state of a wax adhesion region on the fixing belt that expands as the fixing process proceeds, and FIG. 10B is a diagram illustrating a relationship between a wax adhesion region and a dust D generation region. is there.

FIG. 11 is a diagram for explaining the flow of airflow around the fixing belt.

FIG. 12 is a diagram showing the relationship between the control circuit and each component.

FIG. 13 is a flowchart for explaining fan control.

14A is a sequence diagram of the thermistor TH, FIG. 14B is a sequence diagram of the first fan, FIG. 14C is a sequence diagram of the second fan, and FIG. 14D is a sequence diagram of the third fan.

In FIG. 15, (a) is a first graph for explaining the effect of air flow control, (b) is a second graph for explaining the effect of air flow control, and (c) is a third graph for explaining the effect of air flow control. Graph (d) is a fourth graph for explaining the effect of air volume control.

16, (a) is a sequence diagram of the thermistor, (b) is a sequence diagram of the first fan, (c) is a sequence diagram of the second fan, and (d) is a sequence diagram of the third fan.

In FIG. 17, (a) is a graph showing the suction air volume Q (L / min) required when the target value of the dust reduction rate α is 50%, and (b) is the target value of the dust reduction rate α of 60%. It is a graph which shows the suction | attraction air volume Q (L / min) required in the case of setting.

FIG. 18 is a graph showing the relationship between the distance d (mm) between the belt surface and the filter and the suction air volume Q (L / min).

FIG. 19 is a graph showing the relationship between the distance d (mm) between the belt surface and the filter and the filter area Fs (cm ² ).

FIG. 20 is a diagram showing an example in which the filter is arranged inside the duct.

FIG. 21 is a diagram showing the relationship between the arrangement of the filter unit and the radiant heat.

FIG. 22 is a diagram showing the relationship between the arrangement of the filter unit and the radiant heat.

FIG. 23 is a diagram showing the relationship between the arrangement of the filter unit and the radiant heat.

24A is a diagram illustrating the relationship between the filter passing wind speed, the filter dust filtration rate, and the filter ventilation resistance, and FIG. 24B is a diagram illustrating the relationship between the filter passing wind speed and the filter area.

Hereinafter, the present invention will be described in detail using 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.

(1) Overall configuration of image forming apparatus

Before describing the features of the present embodiment, the overall configuration of the image forming apparatus will be described. FIG. 4 is a diagram illustrating the configuration of the image forming apparatus. FIG. 12 is a block diagram showing the relationship between the control circuit and each component. The printer 1 forms an image in an image forming unit using an electrophotographic process, transfers the image to a sheet in a transfer unit, and fixes the image on the sheet P by heating the sheet on which the image has been transferred in a fixing unit. It is a device to let you. The printer 1 used in the description of this embodiment is a four-color full-color multifunction printer (color image forming apparatus) using an electrophotographic process. The printer 1 may be a monochrome multifunction printer or a single function printer. Hereinafter, it demonstrates in detail using figures.

The printer 1 includes a control circuit A that controls each component in the apparatus. The control circuit A is an electric circuit including a calculation unit such as a CPU and a storage unit such as a ROM. The control circuit A functions as a control unit that performs various controls when the CPU reads a program stored in a ROM or the like. The control circuit A is electrically connected to various components such as an external information terminal (not shown) such as a personal computer, an input device B such as the image reader 2, and an operation panel (not shown), and exchanges signal information. Is possible. The control circuit A controls the various components in the apparatus based on the image signal input from the input apparatus B to form an image on the sheet P.

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.

As shown in FIG. 4, the printer 1 includes first to fourth

image forming stations

5Y, 5M, 5C, and 5K (hereinafter referred to as stations) as image forming units 5 that form toner images. The

stations

5Y, 5M, 5C, and 5K are provided side by side from the left side to the right side as shown in FIG.

The

stations

5Y, 5M, 5C, and 5K have substantially the same configuration except that the color of the toner used is different. Therefore, when the detailed configuration of the

stations

5Y, 5M, 5C, and 5K is described, the station 5K is described as an example. The station 5K includes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a drum) 6 as an image carrier on which an image is formed. Further, the station 5K includes a cleaning member 41 as a process unit that acts on the drum 6, a developing unit 9, and a charging roller (not shown).

The first station 5Y accommodates yellow (Y) developer (hereinafter referred to as toner) in the toner accommodating chamber of the developing unit 9. The second station 5M stores magenta (M) toner in the toner storage chamber of the developing unit 9. The third station 5C stores cyan (C) toner in the toner storage chamber of the developing unit 9. The fourth station 5 </ b> K stores black (K) toner in the toner storage chamber of the developing unit 9.

A laser scanner unit 8 as an image information exposure unit for the drum 6 is disposed below the image forming unit 5. An intermediate transfer belt unit 10 (hereinafter referred to as a transfer unit) is provided above the image forming unit 5.

The transfer unit 10 includes an intermediate transfer belt (hereinafter referred to as a belt) 10c and a driving roller 10a that drives the intermediate transfer belt 10c. The first to fourth primary transfer rollers 11 are arranged in parallel inside the belt 10c. Each primary transfer roller 11 is disposed to face the drum 6 of each station.

The upper surface of each drum 6 of the image forming unit is in contact with the lower surface of the belt 10 c at the position of each primary transfer roller 11. This contact portion is called a primary transfer portion.

The driving roller 10a is a roller that rotationally drives the belt 10c, and a secondary transfer roller 12 is disposed outside the portion of the belt 10c that is backed up by the driving roller 10a. The belt 10c is in contact with a secondary transfer roller 12 as a transfer unit, and this contact portion is referred to as a secondary transfer portion 12a. A transfer belt cleaning device 10d is disposed outside the portion of the belt 10c backed up by the tension roller 10b. Under the laser scanner unit 8, a cassette 3 for storing sheets P is disposed. The sheet P stored in the cassette P absorbs moisture according to the state of the outside air. A sheet having a higher moisture absorption generates more water vapor when heated.

As shown in FIG. 4, the printer 1 is provided with a sheet conveyance path (vertical path) Q for conveying the sheet P picked up from the cassette 3 upward. In this sheet conveyance path Q, a roller pair of a feeding roller 4a and a retard roller 4b, a registration roller pair 4c, a secondary transfer roller 12, a fixing device 103, and a discharge roller pair 14 are arranged in order from the lower side to the upper side. ing. A discharge tray 16 is disposed below the image reader 2.
(1-1) Image forming sequence of image forming apparatus

When the printer 1 performs an image forming operation, the control circuit A performs the following control. The control circuit A rotates the drums 6 of the first to

fourth stations

5Y, 5M, 5C, and 5K in a clockwise direction in the drawing at a predetermined speed in accordance with the image formation timing. The control circuit A controls the driving of the driving roller 10a so that the belt 10c rotates in a direction corresponding to the rotational speed of the drum 6 and in a forward rotation direction with respect to the rotational direction of the drum 6. Further, the control circuit A operates the laser scanner unit 8 and a charging roller (not shown).

By performing the above-described control, the printer 1 forms a full-color image as follows.

First, a charging roller (not shown) uniformly charges the surface of the drum 6 to a predetermined polarity and potential. Next, the laser scanner unit 8 scans and exposes the surface of the drum 6 using a laser beam modulated in accordance with image information signals of Y, M, C, and K colors. Thus, an electrostatic latent image corresponding to the corresponding color is formed on the surface of each drum 6. The formed electrostatic latent image is developed as a toner image by the developing unit 9. The toner images of each color of YMCK formed as described above are synthesized by being primarily transferred onto the belt 10c in order in the primary transfer portion. Thus, a full-color unfixed toner image is formed on the belt 10c by combining four color toner images of Y color + M color + C color + K color. The unfixed toner image is conveyed to the transfer unit 12a by the rotation of the belt 10c. The surface of the drum 6 after the toner image is primarily transferred to the belt 10 c is cleaned by the cleaning member 41.

On the other hand, the sheet P in the cassette 3 is fed by one sheet by the feeding roller 4a and the retard roller 4b and conveyed to the registration roller pair 4c. The sheet P is conveyed to the secondary transfer portion in synchronization with the toner image on the registration roller pair 4c belt 10c. The secondary transfer roller 12 is applied with a secondary transfer bias having a polarity opposite to the normal charging polarity of the toner. For this reason, when the sheet P is nipped and conveyed by the secondary transfer portion, the four-color toner images on the belt 10c are secondarily transferred onto the sheet P all at once.

When the sheet P conveyed from the secondary transfer unit is separated from the belt 10c and conveyed to the fixing device 103, the toner image is thermally fixed on the sheet P. The sheet P conveyed from the fixing device 103 is discharged to the discharge tray 16 through the guide member 15 and the discharge roller pair 14. The residual toner remaining on the surface of the belt 10c after the toner image on the sheet P is secondarily transferred is removed from the belt surface by the transfer belt cleaning device 10d.
(2) Fixing device

Next, the fixing device 103 and dust D generated in the vicinity of the fixing device 103 will be described.
(2-1) Fixing device 103

FIG. 5A is a view showing a cross section of the fixing unit. FIG. 5B is a diagram illustrating a state where the belt unit is disassembled. The fixing device 103 according to the present exemplary embodiment is a low heat capacity fixing device that fixes a toner image onto a sheet P using a small-diameter fixing belt 105 (hereinafter referred to as a belt) heated by a heater 101a. The fixing device 103 includes a fixing belt unit 101 (referred to as a fixing unit) including a belt 105 as a rotating body, a pressure roller 102 as a rotating body, a planar heater 101a as a heating unit, and a housing 100. And. As shown in FIG. 5A, the housing 100 is provided with a sheet inlet 400 and a sheet outlet 500, and the sheet P can pass through the nip portion 101 b between the fixing unit 101 and the pressure roller 102. it can. In this embodiment, since the sheet inlet 400 is disposed below the sheet outlet 500 in the gravitational direction, the sheet P is conveyed upward from below in the gravitational direction. This configuration is referred to as a vertical path configuration.

At the sheet entrance 400, a plurality of rollers 100a made of a thin plate-shaped rotating disk are provided side by side in the direction of the rotation axis of the belt 105. The roller 100a suppresses the toner from adhering to the housing 100 by guiding the sheet P that is out of the conveyance path.

A guide member 15 (guide member) that guides the conveyance of the sheet through the nip portion 101b is provided on the downstream side of the sheet outlet 500 in the conveyance direction of the sheet P. In the following description, the downstream side in the transport direction of the sheet P is referred to as the downstream side, and the upstream side in the transport direction of the sheet P is referred to as the upstream side.
(2-2) Configuration of the fixing unit 101

The fixing unit 101 is a fixing unit that abuts against a pressure roller 102 described later, forms a nip portion 101b with the pressure roller 102, and fixes the toner image on the sheet P at the nip portion 101b. As shown in FIGS. 5A and 5B, the fixing unit 101 is an assembly composed of a plurality of members.

The fixing unit 101 includes a planar heater 101a, a heater holder 104 that holds the heater 101a, and a pressure stay 104a that supports the heater holder 104. Further, the fixing unit 101 includes an endless belt 105 and

flanges

106L and 106R that hold one end side and the other end side of the belt 105 in the width direction.

The heater 101 a is a heating member that contacts the inner surface of the belt 105 and heats the belt 105. In this embodiment, a ceramic heater that generates heat when energized is used as the heater 101a. The ceramic heater includes a thin and thin ceramic substrate and a resistance layer provided on the surface of the substrate. The ceramic heater is a low-heat capacity heater that quickly generates heat by energizing the resistance layer.

The heater holder 104 is a holding member that holds the heater 101a. The holder 104 of the present embodiment has a semicircular cross section and regulates the shape of the belt 105 in the circumferential direction. It is desirable to use a heat resistant resin as the material of the holder 104.

The pressure stay 104a is a member that uniformly presses the heater 101a and the holder 104 against the belt 105 in the longitudinal direction. It is desirable that the pressure stay 104a be made of a material that is not easily bent even when a high pressure is applied. In this embodiment, SUS304, which is stainless steel, is used as the material of the pressure stay 104a. A thermistor TH as a temperature sensor is provided on the pressure stay 104a. The thermistor TH outputs a signal corresponding to the temperature of the belt 105 to the control circuit A.

The belt 105 is a rotating body that contacts the sheet P and applies heat to the sheet P. The belt 105 is a cylindrical (endless) belt, and has flexibility as a whole. The belt 105 is provided so as to cover the heater 101a, the heater holder 104, and the pressure stay 104a from the outside.

The

flanges

106L and 106R are a pair of members that rotatably hold the end portion of the belt 105 in the longitudinal direction. As shown in FIG. 2, each of the

flanges

106L and 106R includes a flange portion 106a, a backup portion 106b, and a pressed portion 106c. 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 diameter of the belt 105. The backup unit 106 b is a part that holds the inner surface of the fixing belt and maintains the cylindrical shape of the belt 105. The pressed portion 106c is provided on the outer surface side of the flange portion 106a and receives a pressing force by pressure springs 108L and 108R (see FIG. 7) described later.
(2-2-1) Configuration of fixing belt

FIG. 6A is a view showing the sheet conveyed to the vicinity of the nip portion of the fixing unit. FIG. 6B is a diagram showing the layer structure of the belt. FIG. 6C is a diagram showing a layer configuration of the pressure roller 102.

The belt 105 of this embodiment is composed of a plurality of layers. More specifically, the belt 105 includes an endless (cylindrical) base layer 105a, a primer layer 105b, an elastic layer 105c, and a release layer 105d in order from the inside to the outside.

The base layer 105 a is a layer for ensuring the strength of the belt 105. The base layer 105a is a base layer made of metal such as SUS (stainless steel), and has a thickness of about 30 μm so as to withstand thermal stress and mechanical stress.

The primer layer 105b is a layer for bonding the base layer 105a and the elastic layer 105c. The primer layer is formed by applying a primer with a thickness of about 5 μm on the base layer 105a.

The elastic layer 105c is deformed when the toner image is pressed into contact with the nip portion 101b, and serves to bring the release layer 105d into close contact with the toner image. As the elastic layer 105c, heat-resistant rubber can be used.

The release layer 105 d is a layer having a function of preventing toner and paper powder from adhering to the belt 105. As the release layer 105d, a fluororesin such as a PFA resin excellent in releasability and heat resistance can be used. The thickness of the release layer 105d in this embodiment is 20 μm in consideration of heat transfer properties.
(2-3) Configuration of pressure roller and pressure method

(C) of FIG. 6 is a figure which shows the layer structure of the pressure roller 102. FIG. The pressure roller 102 is a nip forming member that contacts the outer peripheral surface of the belt 105 and forms a nip 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. 7, one end of the cored bar 102a is rotatably supported by the side plate 107L via a bearing 113. The other end side of the cored bar 102a is rotatably supported by the side plate 107R via a bearing 113. 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.

The other end of the metal core 102a is connected to a gear G. When the gear G is driven by a drive motor (not shown), the pressure roller 102 is rotationally driven.

The fixing unit 101 is supported by the side plate 107L and the side plate 107R so as to be slidable in the direction of approaching and separating from the pressure roller 102. Specifically, the

flanges

106L and 106R are provided so as to fit into the guide grooves of the side plate 107L and the side plate 107R. The pressed portions 106c of the

flanges

106L and 106R are pressed with a predetermined pressing force T in the direction toward the pressure roller 102 by the pressure springs 108L and 108R supported by the

spring support portions

109R and 109L.

The flanges 106 </ b> L and 106 </ b> R, the pressure stay 104 a, and the heater holder 104 are biased in the direction of the pressure roller 102 by the pressing force T. Here, in the fixing unit 101, the side having the heater 101 a faces the pressure roller 102. Therefore, the heater 101a presses the belt 105 toward the pressure roller 102. With such a configuration, the belt 105 and the pressure roller 102 are deformed, and a nip portion 101b (see FIG. 6) is formed between the belt 105 and the pressure roller 102.

As described above, when the pressure roller 102 rotates while the fixing unit 101 and the pressure roller 102 are in close contact with each other, a rotational torque acts on the belt 105 by the frictional force between the belt 105 and the pressure roller 102 in the nip portion 101b. . The belt 105 rotates following the pressure roller 102 (R105). At this time, the rotation speed of the belt 105 substantially corresponds to the rotation speed of the pressure roller 102. In other words, in this embodiment, the pressure roller 102 has a function as a drive roller that rotationally drives the belt 105.

At this time, since the inner circumferential surface of the belt 105 and the heater 101a slide, it is desirable to apply grease to the inner surface of the belt 105 to reduce sliding resistance.
(2-4) Fixing process

Using the configuration described above, the fixing device 103 performs a fixing process during the image forming process. When performing the fixing process, the control circuit A controls a driving motor (not shown) to rotate the pressure roller 102 in the rotation direction R102 (FIG. 1A) at a predetermined speed, and the belt 105 is driven to rotate. Let

Further, the control circuit A starts energizing the heater 101a via a power supply circuit (not shown). The heater 101 a that has generated heat due to this energization applies heat to the sliding belt 105. Thus, the belt 105 to which heat is applied gradually becomes high temperature. The control circuit A controls the power supplied to the heater 101a based on a signal output from the thermistor TH so that the temperature of the belt 105 becomes the target temperature TP. The target temperature TP ((a) in FIG. 14) of this example is about 170 ° C.

When the belt 105 is heated to the target temperature TP, the control circuit A controls each component to convey the sheet P carrying the toner image S to the fixing device 103. The sheet P conveyed to the fixing device 103 is nipped and conveyed by the nip portion 101b.

In the process where the sheet P is nipped and conveyed in the nip portion 101 b, the heat of the heater 101 a is applied via the belt 105. The unfixed toner image S is melted by the heat of the heater 101a and fixed on 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 guided to the discharge roller pair 14 by the guide member 15 and discharged onto the discharge tray 16 by 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 ultrafine 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 S

As described above, the fixing device 103 fixes the toner image on the sheet 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 during the fixing process. This is called an offset phenomenon. Since the offset phenomenon causes image defects, it is desirable to solve this.

Therefore, in this embodiment, 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 a wax molecular structure is called a 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 dissolves 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.

Note that 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 most of the generated fine particles have a particle size of several nm to several tens of nm.

This dust D is a wax component having adhesiveness and easily adheres to various parts of the internal configuration of the printer 1. For example, when the dust D is carried to the periphery of the guide member 15 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 15 and the discharge roller pair 14 and the volume is fixed. There is a risk that. If the guide member 15 or the discharge roller pair 14 is soiled with wax, the wax adheres to the sheet P and causes image defects.
(3-2) Particles (dust) generated from wax during fixing processing

According to the study by the inventors of the present application, it has been found that most of the dust D described above exists in the vicinity of the sheet entrance (FIG. 1) of the sheet 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

The properties of dust caused by wax include the property of increasing the particle size at high temperatures and the property of increasing the particle size of dust D to surrounding solids. FIG. 8A is a diagram for explaining the dust coalescence phenomenon. FIG. 8B is a schematic diagram for explaining the dust adhesion phenomenon.

As shown in FIG. 8A, when a high boiling point substance 20 having a boiling point of 150 to 200 ° C. is placed on the heating source 20a and heated to around 200 ° C., a volatile substance 21a is generated from the high boiling point substance 20. When the volatile material 21a comes into contact with normal temperature air, it immediately becomes below the boiling point temperature, condenses in the air, and changes into fine particles 21b having a particle diameter of about several nanometers to several tens of nanometers. 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.

Also, the gas present in the air is likely 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 are moving in the air by Brownian motion, it is known that they collide with each other and grow into fine particles 21c having a larger particle diameter. 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 presumed to be because the fine particles 21c have a larger inertial force and collide with the wall 23 vigorously. Therefore, as the atmosphere in the vicinity of the belt 105 is kept at a high temperature to promote the increase in the particle size of the dust D, the dust D is more likely to adhere to the configuration in the fixing device (mostly the belt 105). For this reason, the dust D is more difficult to diffuse out of the fixing device as 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) Location where dust D is generated

Next, the location where dust D is generated will be described with reference to FIGS. FIG. 10A is a diagram illustrating a state of the wax adhesion region on the fixing belt that expands as the fixing process proceeds. FIG. 10B is a diagram showing the relationship between the wax adhesion region and the dust D generation region. FIG. 11 is a diagram illustrating the flow of airflow around the fixing belt.

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 of the nip portion 101b than on the downstream side 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 contact with the heater 101a. 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 (release layer 105d) rises after passing through the nip portion 101b in the process of rotating in the R105 direction (FIG. 10), and reaches the maximum near the inlet side of the nip portion 101b. Reach temperature.

On the other hand, the wax that exudes from the toner S on the sheet P intervenes 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. 10A, when a part of the front 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 (135b) of the belt 105. Among these, in the region 135c, since the belt 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 lot of dust D exists in the vicinity of the region 135c, that is, in the vicinity of the inlet of the nip portion 101b (upstream side).

Further, the dust D near the entrance of the nip portion 101b is diffused in the direction of arrow W by the air flow shown in FIG. This will be described in detail as follows. As shown in FIG. 11, 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 nip portion 101b, an airflow F3 is generated along a direction away from the nip portion 101b (W direction).
(3-2-3) Verification

Next, a test was conducted to verify the relationship between the amount of dust D generated and the temperature. FIG. 9A is a graph for explaining the relationship between the elapsed time of the image forming process in Test 1 and the amount of dust D generated.

FIG. 9B is a graph for explaining the relationship between the elapsed time of the image forming process in Test 2 and the amount of dust D generated.

In the test, air in the vicinity of the sheet inlet 400 is sampled during the image forming process by the printer 1, and the number density of particles is measured using a nanoparticle size distribution measuring instrument.

Here, in Test 1, nothing is done during the image forming process, and the air at the sheet entrance 400 (near the nip) is warmed. In Test 2, outside air is blown near the sheet inlet 400 during the image forming process so that the air at the sheet inlet 400 (near the nip portion) is cooled.

As shown in FIG. 9A, the amount of dust D generated in Test 1 increases immediately after the start of the image forming process and gradually decreases after reaching a peak after about 100 seconds. In FIG. 9A, the reason that the amount of dust D generated has decreased with the passage of time is that the temperature around the belt 105 increases as the image forming process proceeds.

As shown in FIG. 9B, it can be seen that the amount of dust D generated in Test 2 increases more rapidly than Test 1 immediately after the start of the image forming process, and reaches a peak after about 20 seconds. At this time, the amount of dust D generated from the start of the image forming process until 200 seconds has elapsed is 2 to 5 times that of Test 1 in Test 2.

On the other hand, when the image forming process starts and exceeds 300 seconds, there is no significant difference in the amount of dust D generated in Test 1 and Test 2. This is presumed to be because peripheral units (not shown) heated by the heat of the fixing device 103 warm the outside air toward the sheet inlet 400 in advance.

As described above, the dust D is likely to be generated in the vicinity of the sheet entrance 400. Therefore, it is desirable for the image forming apparatus to remove the dust D in the vicinity of the sheet entrance 400.

Further, when the air at the sheet entrance 400 is cooled, dust D is likely to be generated. Therefore, it is desirable that the printer 1 suppresses the generation of dust D without cooling the air at the sheet entrance 400. Further, as described above, the dust D is remarkably generated in a certain period immediately after the start of the image forming process. Therefore, it is desired that the printer 1 efficiently collects (filters) the dust D immediately after the start of the image forming process.
(4) Dust D recovery method

Based on the properties of dust D described above, a method for collecting dust D will be described. First, the configuration and operation of the filter unit 50 that filters the dust D will be described, and then the airflow configuration that suppresses the outflow of the dust D from the vicinity of the filter unit 50 will be described. Finally, the air flow operation sequence will be described.

Fig.1 (a) is a figure explaining the arrangement position of a filter unit. FIG. 1B is a view for explaining the state of the trailing edge of the sheet and the shape of the filter unit. FIG. 2A is a perspective view of the configuration around the fixing device. FIG. 2B is a diagram illustrating a sheet passing position around the fixing device. FIG. 3A is an exploded perspective view of the filter unit. FIG. 3B is a diagram illustrating how the filter unit operates. FIG. 12 is a block diagram showing the relationship between the control circuit and each component. FIG. 13 is a flowchart for controlling each fan. FIG. 14A is a sequence diagram of the thermistor in the first embodiment. FIG. 14B is a sequence diagram of the first fan in the first embodiment. FIG. 14C is a sequence diagram of the second fan in the first embodiment. FIG. 14D is a sequence diagram of the third fan in the first embodiment. FIG. 15A is a first graph illustrating the effect of air volume control. FIG. 15B is a second graph illustrating the effect of air volume control. FIG. 15C is a third graph illustrating the effect of air volume control. FIG. 15D is a fourth graph illustrating the effect of air volume control. FIG. 17A shows the relationship between the suction air volume Q (L / min) of the filter unit and the dust ratio α (%) reduced by the operation of the filter unit, and the suction air volume required when α = 50% or more. It is a graph which shows Q. FIG. 17B shows the suction air volume Q required when α = 60% or more. FIG. 18 is a graph showing the relationship between the distance d (mm) between the belt 105 and the filter unit air inlet and the suction air volume Q necessary to achieve a predetermined α. FIG. 19 is a graph showing the relationship between the distance d (mm) and the required area Fs (cm ² ) of the filter 51.
(4-1) Configuration of filter unit

The filter unit 50 is located between the fixing unit 101 and the transfer unit 10 in the sheet P conveyance direction, as shown in FIG. Alternatively, it is located between the nip portion 101b of the fixing device 103 and the transfer portion 12a of the transfer unit in the conveyance direction of the sheet P.

The filter unit 50 collects the dust D on the filter 51 by drawing the air containing the dust D into the filter 51, which is a non-woven filter provided at the intake port 52a, as shown in FIG. As shown in FIGS. 2 and 3, the filter unit 50 includes a filter 51, a first fan 61 that is an air intake unit for sucking air, and air in the vicinity of the seat inlet 400 so that the air passes through the filter 51. And a duct 52 for guiding.

The first fan 61 is an intake portion for sucking air in the vicinity of the seat inlet 400 to the outside of the apparatus. The first fan 61 is provided in an area outside the sheet P passing area in the longitudinal direction of the fixing unit 101. The first fan is provided in a region outside the nip 101 b in the longitudinal direction of the fixing unit 101. The first fan 61 includes an intake port 61a and an exhaust port 61b, and generates an air flow from the intake port 61a toward the exhaust port 61b. The intake port 61a is connected to the exhaust port 52e of the duct 52 and is an opening for sucking air in the duct 52. The exhaust port 61b is provided toward the outside of the printer 1 and is an opening for discharging the air sucked from the intake port 61a toward the outside of the apparatus.

In this embodiment, a blower fan is used as the first fan 61. The blower fan is characterized by high static pressure, and even if there is a ventilation resistor like the filter 51, a constant air volume (intake volume) can be secured.

The duct 52 is a guide unit for guiding the air in the vicinity of the sheet inlet 400 toward the outside of the apparatus. The duct 52 includes an intake port 52a in the vicinity of the seat inlet 400 and an exhaust port 52e apart from the vicinity of the seat inlet 400.

The intake port 52a is an opening located between the nip portion 101b and the secondary transfer roller 12, and is provided to face the nip portion side. With such a configuration, the intake port 52a can receive the dust D carried by the airflow F3 as shown in FIG.

The exhaust port 52e is provided on the side surface opposite to the air intake port 52a among the plurality of side surfaces of the duct 52 outside the air intake port 52a in the longitudinal direction. As described above, the exhaust port 52e is connected to the intake port 61a.

Further, the filter 51 can be attached to the duct 52 so as to cover the intake port 52a. Specifically, the duct 52 includes an edge 52c of the intake port 52a and a rib 52b including a curved portion 52d. When the filter 51 is fixed to the duct 52 so as to be supported by the edge portion 52c and the rib 52b, the air inlet 52a is covered with the filter 51. The filter 51 of this embodiment is adhered to the edge portion 52c and the rib 52b without a gap by a heat-resistant adhesive. Therefore, the air passing through the intake port 52a always passes through the filter 51. Further, the filter 51 of this embodiment is bonded along the curved portion 52d of the edge portion 52c. In other words, the duct 52 holds the filter 51 in a curved state. At this time, the filter 51 is curved in a direction in which the central portion in the short direction is separated from the nip portion 101b. In other words, the central portion of the filter 51 in the short direction protrudes toward the inside of the duct 52.
The arrangement position of the filter 51 is not limited to the intake port 52a. For example, as shown in FIG. 20, the filter 51 may be provided at a position deeper than the intake port 58 of the duct 57 by a predetermined length H (for example, 3 mm). If it is provided in a deep position, it is possible to reduce the risk of an operator inadvertently touching and damaging the filter 51 when performing work such as disassembly maintenance. However, from the viewpoint of reducing the size of the filter unit, it is better to provide the filter 51 at the intake port as shown in FIG. The position of the filter 51 should be determined depending on whether protection of the filter 51 or downsizing of the filter unit is prioritized.

At this time, the ventilation path inside the duct 57 is at least one of the length range A that is the ventilation path length in the direction perpendicular to the plane of FIG. 20 (in the direction of the rotation axis of the belt 105) in the region from the intake port 58 to the filter 51. Part overlaps the range B of the image forming area in the same direction. This relationship is the same when the filter 51 is attached to the intake port 52a as shown in FIG. 2B, Wf described later corresponds to the length range A, and Wp-max described later corresponds to the length range B. Since dust 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 in which dust can be reliably sucked overlaps with the length range B. Need to be.

In this embodiment, the length range A is set to 350 mm, but the length range A is 200 mm which is a standard maximum image width of a frequently used A4 size sheet (the longitudinal direction of the A4 size sheet is made to coincide with the conveyance direction). If it is over). By doing so, it is possible to effectively reduce dust under actual use conditions.

On the other hand, if the length range A is further increased, not only can the sheet of a larger size be accommodated, but even if the dust diffuses outside the image forming area due to the surrounding airflow or the like, the dust is reliably collected by the filter 51. be able to. However, if the length range A is too long, the filter 51 sucks clean air outside the dust generation region, thereby reducing the dust suction efficiency of the filter unit. From the above considerations, 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 printer, plus the length of the area where dust may diffuse outside. It turns out that it should just be set to the value.

For example, assuming that the maximum image width is 287 mm obtained by excluding a blank area (non-image area) of about 5 mm from the lateral width of 297 mm of the A3 size sheet, it is assumed that dust is diffused to a position about 100 mm away from the outside. To do. In that case, it is appropriate that the upper limit of the length range A is 500 mm with a slight margin added to 487 mm which is a value obtained by adding 200 mm (= 100 mm × 2) to 287 mm.

In summary, it can be understood that the length range A may be appropriately selected from the range of 200 mm to 500 mm in consideration of the size of the sheet to be used and the degree of dust diffusion due to airflow. However, assuming the use of recording materials of various sizes, the length range A is preferably set to be equal to or larger than the width of the minimum width recording material that can be used in the image forming apparatus.
As described above, the filter 51 has a shape extending in the longitudinal direction of the belt 105. By adopting such a shape, the air passing velocity at the air inlet 52a of the duct is uniform in the longitudinal direction. Can be. In other words, by arranging the filter 51, which is a ventilation resistor, at the intake port 52a, 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. 3B 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 F4 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 unit 50 can efficiently collect the dust D generated from the belt 105 (with a minimum air volume).

When the amount of intake air by the filter unit 50 is small, the amount of air flowing into the vicinity of the belt 105 is also small. Therefore, the temperature drop of the air near the belt 105 can be reduced. As a result, generation of dust D can be suppressed. Further, since the temperature drop of the belt 105 can be suppressed, it is advantageous for energy saving.
(4-1-1) Filter properties

The filter 51 is a filter member for filtering (collecting and removing) the dust D from the air passing through the intake port 52a. 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. The electrostatic nonwoven fabric used for the filter 51 of this example has a fiber density, thickness, and charging strength so that the ventilation resistance is about 90 Pa and the filtration rate of dust is about 80% when the passing wind speed is 15 cm / s. Is set. The charging strength has a technical upper limit, and the performance of the electrostatic nonwoven fabric is adjusted by changing the fiber density and thickness. For example, the dust filtration rate can be further increased by increasing the fiber density and thickness. However, in that case, the ventilation resistance becomes high, and it becomes impossible to secure a sufficient air volume with the pressure generated by a standard blower fan used in an office machine or the like. On the other hand, if the fiber density and thickness are reduced, the airflow resistance is lowered, and a fan that is less expensive and has a low generated pressure can be used. However, the dust filtration rate also decreases, which makes it impractical. Further, if the airflow resistance is excessively lowered, unevenness in the longitudinal direction is likely to occur in the wind speed of the air passing through the filter 51. Specifically, the air passing speed increases at locations close to the first fan, and becomes slower at locations far away, making it impossible to collect dust. The ventilation resistance is preferably at least 50 Pa. Considering the factors described above, that is, the level of electrostatic nonwoven fabric charging technology, the use of a standard blower fan, and the uniform air velocity of the air passing through the filter 51, the specification range of the electrostatic nonwoven fabric to be used is naturally It will be decided. The specifications centered on the above numerical values, that is, those having a ventilation resistance (Pa) in the range of 50 to 130 and a dust filtration rate of 60% to 90% at a passing wind speed of 15 cm / s are suitable for use. I can say that.

When trying to filter the toner in the exhaust air, the electrostatic nonwoven fabric is used with a ventilation resistance of 10 Pa or less at a passing wind speed of 10 cm / s. Therefore, it can be said that the filter 51 of this embodiment uses an electrostatic nonwoven fabric having a relatively large ventilation resistance.

Next, the passing wind speed Fv of air passing through the filter 51 will be described. The faster the passing wind speed, the greater the amount of air wind per unit time passing through the filter 51, and the dust can be reliably collected. However, if the passing wind speed is too high, the temperature of the air in the vicinity of the sheet inlet 400 is lowered, and as a result, the amount of dust D generated is increased. Further, the increase in the passing wind speed brings about an increase in ventilation resistance of the filter 51 and a decrease in dust filtration rate.
For this reason, the passing air speed is desirably suppressed to 30 cm / s or less at the maximum, and is desirably at least 5 cm / s or more from the viewpoint of securing the air flow rate. That is, the passing wind speed Fv (cm / s) is preferably 5 or more and 30 or less. In this example, it is a substantially intermediate value between 30 cm / s and 5 cm / s, and the passing air speed setting value is set to a wind speed of 15 cm / s, which is the most balanced from the viewpoint of securing the air volume and filter performance and suppressing the generation amount of dust D.
The air velocity of the air passing through the filter 51 and the airflow resistance of the filter 51 described above were measured with 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.
(4-1-2) Filter length

As shown in FIGS. 2A and 2B, the filter 51 has a long and narrow shape with the direction perpendicular to the sheet conveying direction (the rotational axis direction of the belt 105 serving as a rotating body) as a longitudinal direction. An area indicated by hatching on the sheet P in FIG. 2B is an area Wp-max (corresponding to the above-described length range B) in which an image can be formed when the sheet P having a predetermined width size is used. . In practice, an image is formed on the back side of the sheet P visible in FIG. As illustrated in FIG. 2B, the region Wp-max is a region that is equal to or smaller than the width size of the sheet P. In this area, a toner image is formed on the sheet P. In this area, wax adheres to the belt 105, and dust D is generated in this area.
Therefore, as described above, in the ventilation path of the duct 52, at least a part of the length range A in the rotation axis direction of the belt 105 overlaps with the length range B of the image forming region in the same direction, that is, Wp-max. There must be. Therefore, the length Wf of the filter 51 shown in FIG. 2 (b) must have a length equivalent to the length range A, and is set to a length exceeding Wp-max.

By the way, the fixing device 103 according to the present exemplary embodiment conveys the sheet P with reference to the center in the width direction of the belt 105. Therefore, in the region Wp-max of the sheet size that is frequently used, dust D is likely to be generated regardless of the sheet width size. In order to efficiently collect the dust D, the length Wf of the filter 51 needs to exceed the region Wp-max of the sheet size that is frequently used. As a result, Wf preferably exceeds the standard maximum image width of 200 mm (when the longitudinal direction of the A4 size sheet coincides with the transport direction) of the frequently used A4 size sheet.
(4-1-3) Filter area and position

The area and position of the filter 51 are important parameters that determine the amount of dust reduction by the filter 51. When it is desired to reduce the amount of dust, the filter 51 may be brought close to the belt 105 where dust is generated to suck the dust more effectively, and the area Fs (cm ² ) of the filter 51 may be increased. As shown in FIG. 24A, as the air passing wind speed Fv of the filter decreases, the filter ventilation resistance decreases and the dust filtration rate increases. This is because if the passing wind speed Fv is reduced, the moving speed of the dust contained in the air is also lowered, so that the dust is easily caught by the fibers of the electrostatic nonwoven fabric constituting the filter. As shown in FIG. 24B, the passing wind speed Fv is inversely proportional to the filter area Fs (cm ² ). That is, as the filter area Fs increases, the passing wind speed Fv decreases and the filter ventilation resistance also decreases. If the filter ventilation resistance decreases, the air volume Q (L / min) of air sucked into the filter when the same fan is used increases, and more dust can be drawn into the filter 51. Furthermore, the dust filtration rate of the filter 51 increases as the passing wind speed Fv decreases. That is, dust generated from the printer 1 can be reduced as the filter area Fs is increased. In the following, the relationship between the area and position of the filter and the amount of dust reduction by the filter will be explained in more detail, and a formula for determining the area and position of the filter will be derived.

FIG. 17A and FIG. 17B show the relationship between the suction air volume Q of the filter unit 50 and the dust reduction rate α obtained by experiments. The dust reduction rate α is expressed by the following equation using a dust amount Do generated from the printer 1 when the filter 51 is not used and a dust amount De reduced by using the filter 51.
α (%) = De ÷ Do × 100

From FIG. 17A and FIG. 17B, it can be seen that if the suction air volume Q increases, the dust reduction rate α also increases. This is because more dust D generated from the belt 105 is drawn into the filter 51 as the suction air volume Q increases.
Depending on the length of the filter (belt 105 rotation axis direction length) Wf (mm) and the distance d (mm) between the belt 105 and the filter 51, three lines (Line.A, Line.B, Line.C). As shown in FIG. 20, the distance d means the distance between the surface of the belt 105 and the center 57c of the air inlet 58 of the duct 57 (the midpoint between the air inlet ends 57a and 57b). In the example of FIG. 1, the center 57c in FIG. 20 corresponds to the center 50d in FIG. 1, and the

end portions

57a and 57b correspond to 50b and 50c, respectively.
Line. Of FIG. A and Line. Comparing B, Wf is 350 mm and d is 20 mm and 35 mm, respectively. Line.d = 20. A is Line. This is because the dust generated from the belt 105 can be sucked more effectively as the filter 51 becomes closer to the belt 105.
Line. C is a line when the length Wf of the filter 51 is 40 mm, which is shorter than the length of the image forming area. Line. Under the condition C, only the central part of the dust generation area (area where the image passes and the toner wax adheres) on the belt 105 is sucked into the filter 51. C is Line. A and Line. B is far below B.
In FIG. 17A, the suction air flow rate Q required when α ≧ 50% is 16.3 L / min or more when d = 20 mm (Line A), and d = 35 mm (Line B). Time means 35 L / min or more. FIG. 17 (b) shows that the required suction air volume Q when α ≧ 60% is 35 L / min or more when d = 20 mm (Line. A), and 78. When d = 35 mm (Line. B). It means 4 L / min or more. α ≧ 50% is a numerical value serving as an index when considering a dust reduction target by a filter.
This is because many electrophotographic printers can effectively prevent problems such as image defects due to dust contamination inside the apparatus if the dust is reduced by about 50%. However, some printers may not be able to obtain a sufficient effect unless α ≧ 60%. Therefore, in this example, the required suction air volume Q when α ≧ 60% is estimated in FIG. 17B. Yes. The filter 51 used in the experiment has a ventilation resistance of about 90 Pa when the passing wind speed is 15 cm / s, and a dust filtration rate of about 80%.
Next, FIG. 18 will be described. FIG. 18 shows the relationship between the suction air volume Q (L / min) and the distance d (mm) necessary for achieving the target dust reduction rate α in the data of FIGS. 17 (a) and 17 (b). Based on the plot. When α = 50% is targeted, Q = 16.5 when d = 20 and Q = 35 when d = 35. A line connecting them is represented by Q = 1.25 × d−8.67. Similarly, when α = 60% is targeted, Q = 2.89 × d−22.9. When α is desired to be 50% or more, or 60% or more, Q can be increased, and the following relationship is established.
α ≧ 50%: 1.25 × d (mm) −8.67 ≦ Q (L / min)
α ≧ 60%: 2.89 × d (mm) −22.9 ≦ Q (L / min)
If the suction air volume Q is too large, the heat of the surface of the belt 105 is excessively taken away. If the heat is taken away excessively, the control circuit A increases the power consumption of the entire printer 1 because the control circuit A supplies power to the heater 101a. From the viewpoint of power consumption suppression, the suction air volume Q is preferably 200 L / min or less. When this condition is added to the above equation, the following equation can be obtained.
α ≧ 50%: 1.25 × d (mm) −8.67 ≦ Q (L / min) ≦ 200
α ≧ 60%: 2.89 × d (mm) −22.9 ≦ Q (L / min) ≦ 200
Next, the filter area Fs (cm ² ) is determined. The filter area Fs (cm ² ) is determined by the filter passing wind speed Fv (cm / s).
Q (L / min) = Fs (cm ² ) × Fv (cm / s) ÷ 1000 × 60.
Fs (cm ² ) = Q (L / min) ÷ Fv (cm / s) × 1000 ÷ 60.

By rewriting the above-described formula describing the Q range into a formula using Fs by the above formula, the following formula for determining the position and area of the filter can be obtained.
α ≧ 50%:

α ≧ 60%:

Here, if the passing wind speed Fv is 15 cm / s, Fs is expressed by the following equation.
α ≧ 50%:

α ≧ 60%:

FIG. 19 is a graph showing the range of the above formula. In order to set the dust filtration rate α to 50% or more, Fs and d may be set so as to fall within the range 1 in the figure. If the dust filtration rate α is desired to be 60% or more, Fs and d may be set so as to fall within the range 2 in the figure.
Apart from the range of d determined by the above formula, the value of d has a limit that requires attention. If the filter 51 and the belt 105 are too close to each other, the filter 51 may be thermally deteriorated by radiation from the belt 105, and the filtration performance may be reduced. Therefore, it is desirable that the filter 51 is disposed at an appropriate distance with respect to the nip portion 101b. Specifically, the distance d (shortest distance) between the filter 51 and the belt 105 is preferably 5 or more and 100 or less.
(4-1-4) Curved surface shape of the filter

As described above, when the filter 51 is disposed in the vicinity of the belt 105, the distance between the filter 51 and the conveyed sheet P is also reduced. Therefore, when the conveyance of the sheet P is disturbed, there is a possibility that the intake surface 51a of the filter 51 and the sheet P come into contact with each other. When the filter 51 and the sheet P come into contact with each other, the toner image on the sheet P may be disturbed. Further, the filter 51 may be damaged by the sheet P, and the dust D recovery efficiency may be reduced.

Therefore, in this embodiment, a device for suppressing the contact between the sheet P and the filter 51 is performed.

As the above-mentioned disturbance of the conveyance of the sheet P, there is a phenomenon called trailing edge splashing of the sheet P. The trailing edge splash is a phenomenon in which the trailing edge Pend is greatly displaced in the direction V in the drawing when the trailing edge Pend of the sheet P nipped and conveyed by the nip portion 101b and the transfer portion 12a passes through the transfer portion 12a.

The trailing edge splash is likely to occur when the original shape of the sheet P is deformed (curled). Further, even when the sheet P is thin paper with low rigidity, the sheet P is deformed along the shape of the nip portion 101b, so that trailing edge splash is likely to occur.

In this embodiment, the filter 51 is arranged as shown in FIG. 1A in order to deal with this rear end splash. In other words, the end on the downstream side in the sheet conveying direction of the end portion in the short direction of the filter 51 is the nip portion 101b than the end on the upstream side in the sheet conveying direction of the end portion in the short direction of the filter 51. And the transfer section 12a are separated from the transport path when they are connected by a straight line. With such a configuration, even if the trailing end Pend of the sheet P that has passed through the transfer portion 12a is gradually displaced in the V direction as the conveyance progresses, the filter 51 and the sheet P are difficult to contact. In this embodiment, the filter 51 is curved in a direction away from the conveyance path of the sheet P. With such a configuration, the distance between the belt 105 and the filter 51 is kept at a short distance while dealing with the trailing edge splash.

Further, when the filter 51 has such a curved surface shape, the surface area of the filter 51 can be increased in a limited space. When the surface area of the filter 51 is increased, the dust D and the filter 51 are easily brought into contact with each other, so that the dust D recovery efficiency is improved.
(4-2) Airflow configuration

Next, the air flow in the printer will be described. In order to efficiently collect the dust D, it is desirable to appropriately control the air flow in the printer, particularly the air flow around the fixing device 103. Hereinafter, a configuration related to the air flow around the fixing device 103 will be described in detail.
(4-2-1) First fan

As described above, when the air volume of the first fan 61 is large, a large amount of air can be sucked, while the temperature of the air in the vicinity of the sheet inlet 400 is easily lowered. That is, if the air volume of the first fan 61 is large, a large amount of dust can be collected, while a large amount of dust D is easily generated. Therefore, in order to reduce the dust D efficiently by the filter unit 50, it is desirable to keep the air volume of the first fan 61 appropriately. Hereinafter, the collection of the dust D by the suction of the first fan 61 is referred to as a dust collection action, and the increase in the amount of dust generated by the suction of the first fan 61 is referred to as a dust increase action.

Here, a test was conducted to verify the relationship between the air volume of the first fan 61 and the amount of dust D generated. In the test, the amount of dust D discharged from the printer during the image forming process is measured. Specifically, the printer 1 installed in the chamber is caused to execute an image forming process, and the exhaust of the printer is acquired. Then, the exhausted air is sampled with a nanoparticle size distribution measuring instrument, and the amount of dust D discharged is measured. This test is performed a plurality of times with different air volumes of the first fan 61 during the image forming process. Here, a plurality of tests are referred to as Test A, Test B, Test C, and Test D.

In test A, the amount of dust D discharged out of the fixing device is measured with the first fan 61 operating at full speed during the image forming process. In test B, the amount of dust D discharged outside the fixing device is measured with the first fan 61 stopped during the image forming process. In test C, the amount of dust D discharged out of the fixing device is measured while the first fan is operating at the minimum speed at which the first fan can operate normally (speed that is 7% of the total air flow rate) during the image forming process. To do. In test D, the amount of dust D discharged out of the fixing device is measured while the first fan is operated at a speed that is 20% of the total air flow rate during the image forming process.

FIG. 15B shows the relationship between the elapsed time after the start of printing in Test A and Test B and the amount of dust D generated. FIG. 15B shows the relationship between the elapsed time after the start of printing in test B and test C and the amount of dust D generated. FIG. 15C shows the relationship between the elapsed time after the start of printing in test C and test D and the amount of dust D generated. FIG. 15D shows the relationship between the elapsed time after the start of printing and the amount of dust D generated in Test B and Example (E).

(A) shows the relationship between the elapsed time from the start of the image forming process in test A and the amount of dust D discharged. (B) shows the relationship between the elapsed time from the start of the image forming process in test B and the amount of dust D discharged. (C) shows the relationship between the elapsed time from the start of the image forming process in test C and the amount of dust D discharged. (D) shows the relationship between the elapsed time from the start of the image forming process in test D and the amount of dust D discharged.

According to FIG. 15A, until about 70 seconds after the start of printing, (A) exceeds the dust discharge amount of (B), and thereafter (A) falls below the dust discharge amount of (B). . This means that the dust increasing action exceeds the dust collecting action until about 70 seconds after the start of printing. As described above, the dust increasing action decreases as the air volume of the first fan 61 decreases. Therefore, if the air volume of the first fan 61 is lowered from the state of the test A, the dust collecting action at the initial stage of printing should eventually exceed the dust increasing action.

As a result of studies by the present inventors, when the air flow rate of the first fan 61 is reduced to 10% of the total air flow rate (the air passing air velocity in the filter 51 is 5 cm / s), the dust collecting action at the initial stage of printing increases the dust. We were able to surpass the action.

According to FIG. 15B, (B) exceeds the dust discharge amount of (C) in the entire period after the start of printing. This means that in (B), the dust recovery action always exceeds the dust increase action.

According to FIG. 15C, (D) exceeds the dust discharge amount of (C) until 90 seconds after the start of printing, and the dust discharge amount becomes substantially equal for a while after that. Then, after about 150 seconds from the start of printing, (D) is below the dust discharge amount of (C).

From this, the first fan 61 is operated with an air volume of 7% until 90 seconds (predetermined time) after starting printing, and the first fan 61 is operated with an air volume of 20% from 150 seconds after starting printing. It can be seen that the amount of dust D discharged can be further reduced. That is, it is desirable to operate the first fan 61 with a small air volume at the initial stage after the start of printing and to increase the air volume of the first fan 61 over time. Based on the above-described result, the air volume control of the first fan 61 is performed in this embodiment. As shown in FIG. 14B, in the present embodiment, the first fan 61 is operated at an air volume of 7% until 90 seconds after the start of printing. This air volume is equal to or higher than the air volume when the fan 61 is rotated at the minimum speed (more than the intake air volume) and is 10% or less of the air volume when the fan 61 is rotated at the maximum speed. From 90 seconds to 390 seconds after the start of printing, the first fan 61 is operated with an air flow of 20%. The first fan 61 is operated at 100% after 390 seconds from the start of printing. (E) shows the relationship between the elapsed time from the start of the image forming process and the amount of dust D discharged in this embodiment.

According to FIG.15 (d), the discharge amount of the dust D is a half or less compared with the test B in a present Example. That is, in this embodiment, the amount of dust D discharged can be halved in the period from the start of image formation to 600 seconds.
(4-2-2) Second fan and third fan

When the sheet P containing moisture is heated by the fixing device 103, water vapor is generated from the sheet P. Due to the water vapor, the space C is in a high humidity state. The space C is a space area downstream of the fixing device 103 and upstream of the discharge roller 14 in the sheet conveyance direction. When the humidity in the space C is high, dew condensation is likely to occur, so that water droplets are likely to adhere on the guide member 15. If a water droplet on the guide member 15 adheres to the conveyed sheet P, an image defect occurs.

Therefore, when the humidity of the space C is increased by the water vapor generated from the sheet P, it is desirable to reduce this humidity.

The second fan 62 is a fan for preventing the condensation on the guide member 15.

The second fan 62 reduces the humidity of the space C by drawing air into the machine from the outside of the printer 1 and blowing the air to the guide member 15. Specifically, when air is blown from the second fan 62, the water vapor in the vicinity of the guide member 15 diffuses around the space C, so that a local increase in humidity in the vicinity of the guide member 15 is suppressed. Even when only the second fan 62 is used, it is possible to suppress the period of the degree of condensation on the guide member 15. However, since the discharge destination of the water vapor is only the gap generated around the discharge roller pair 14, the humidity in the space C gradually increases. Therefore, in this embodiment, the water vapor expelled from the space C by the blowing from the second fan 62 is discharged to the outside by the third fan 63.

The third fan 63 generates an air flow 63a around the fixing device 103 as shown in FIG. The third fan 63 serves to discharge water vapor and hot air in the space C to the outside by the air flow 63a. On the other hand, the third fan 63 sucks out the dust D in the vicinity of the nip portion 101b of the belt 105 and may discharge it outside the apparatus without passing through the filter.

In order to reduce dust D discharged from the image forming apparatus by the third fan 63, a separate filter may be provided downstream of the third fan 63. However, if a filter is attached to the third fan 63, exhaust is hindered by the ventilation resistance of the filter, so that it becomes difficult to sufficiently exhaust the heat and water vapor in the space C to the outside of the machine.

Therefore, in this embodiment, the air flow in the printer 1 is adjusted so that the dust D can be prevented from being drawn toward the third fan 63. Specifically, the air flow in the printer 1 is adjusted such that the air pressure in the downstream side in the sheet conveying direction from the fixing device 103 is higher than the air pressure in the upstream side in the sheet conveying direction from the fixing device 103. It is adjusting.
Even if the air flow adjustment described above is performed, not a little dust D is drawn into the third fan 63, so that the third fan is generated at the beginning of the image forming process where the amount of dust D generated is large (see FIG. 9B). The operation of 63 is suppressed and the discharge of dust D is suppressed. Then, when the image forming process proceeds and the generation of dust D is reduced, the third fan 63 is operated, and the water vapor and hot air in the space C are discharged outside the apparatus.

The period during which the operation of the third fan 63 is suppressed is a period that does not cause a thermal problem in the printer 1. Since the components in the image forming apparatus are not yet sufficiently heated at the beginning of the image forming process, there is no problem even if the heat is not exhausted within a few minutes. Further, as described above, dew condensation can be prevented only by the second fan 62 for a period of about several minutes.
(4-3) Control flow

As described above, the dust D is likely to be generated in the vicinity of the sheet entrance 400. However, some dust D may be generated in the vicinity of the sheet outlet 500. In addition, a part of the dust D existing in the vicinity of the fixing device 103 may be conveyed to the space C on the downstream side of the fixing device 103 in the sheet conveying direction as the sheet P is conveyed. Alternatively, a part of the dust D generated in the vicinity of the sheet inlet 400 may be carried to the space C by thermal convection.

Such a part of the dust D is difficult to be collected by the filter unit 50 and is attached to a member on the downstream side in the sheet conveying direction from the fixing device 103 or discharged outside the apparatus. Examples of the downstream member in the sheet conveying direction include the guide member 15 and the discharge roller pair 14. When dust D adheres to these members, image defects are caused. Therefore, when collecting the dust D using the filter unit 50, it is desirable to contain the dust D in the vicinity of the filter unit 50 in order to increase the collection efficiency. In other words, it is desirable to adjust the air flow in the image forming apparatus so that the dust D does not go to the downstream side in the sheet conveying direction from the fixing device 103.

Therefore, in this embodiment, in addition to the control of the first fan 61 described above, the second fan 62 and the third fan 63 are controlled during the continuous image forming process. Each fan is desirably controlled appropriately in accordance with the temperature state around the fixing device 103. In this embodiment, the temperature state around the fixing device 103 is estimated based on how much time has elapsed from the start of printing, and the first period, the second period, and the third period of the image forming process are estimated. The fan control is different for each.

The first period is a period from when the image forming process is started until a first predetermined time (for example, 90 seconds) is reached. In other words, the first period is a period from when the first sheet P in the continuous image forming process passes through the nip portion 101b until a predetermined time is reached.

The second period is a period from when the first predetermined time elapses until the second work time (for example, 360 seconds) is reached. The third period is a period after the second predetermined time has elapsed. In this embodiment, the elapsed time from the start of the printer is measured by the timer unit provided in the control circuit A.

Note that the method for acquiring the elapsed time from the start of printing is not limited to the timer unit. For example, the control circuit A may acquire the elapsed time from the start of printing based on a counter unit that counts the number of processed sheets P. Therefore, the period from when the image forming process is started to when the first predetermined number of sheets (for example, 75 sheets) P is subjected to the image forming process may be defined as the first period. In other words, the period from when the first sheet P of the continuous image forming process passes through the nip portion 101b to when the first predetermined number of sheets (for example, 75 sheets) passes through the nip portion 101b is the first period. It may be determined as A period from when the image forming process is performed on the first predetermined number of sheets P to when the second predetermined number of sheets (for example, 300 sheets) is subjected to the image forming process may be defined as the second period. A period after the image forming process is performed on the second predetermined number of sheets P may be set as the third period.

If there is a temperature sensor that can detect the ambient temperature of the fixing device 103, the ambient temperature of the fixing device 103 does not have to be estimated. Therefore, the control circuit A is. It is not necessary to acquire the elapsed time from the start of printing. When there is such a temperature sensor, when the detected temperature becomes the first predetermined temperature, S107 is executed, and when the detected temperature becomes a second predetermined temperature higher than the first predetermined temperature It is sufficient to execute S109.

The second fan 62 functions as a blower for blowing air to the space C above the fixing device 103, and the third fan 63 sucks air from the space C above the fixing device 103 and the image forming apparatus. It functions as an air blowing part (exhaust part) that discharges to the outside.

Hereinafter, the details of the operation sequence of each fan will be described with reference to FIG. 13 and FIG. FIG. 16A is a sequence diagram of the thermistor TH in the second embodiment. FIG. 16B is a sequence diagram of the first fan in the second embodiment. FIG. 16C is a sequence diagram of the second fan in the second embodiment. FIG. 16D is a sequence diagram of the third fan in the second embodiment.

When the printer 1 is powered on (turned on), the control circuit A executes a control program (S101).

When the control circuit A receives the print command signal, it proceeds to step S103 (S102). When the control circuit A acquires the output signal of the thermistor TH and the detected temperature is not higher than a predetermined temperature (for example, 100 ° C.) (YES), the control circuit A proceeds to step S104 and starts from the predetermined temperature (for example, 100 ° C.). If it is higher (NO), the process proceeds to S112 (S103).

Note that S103 is a step of determining whether or not the inside of the printer 1 is cooled, in particular, whether or not the ambient temperature of the fixing device 103 is cooled. That is, the control circuit A functions as an acquisition unit that acquires information on the ambient temperature of the fixing device 103 from the thermistor TH.

Note that the control circuit A may obtain information on the ambient temperature of the fixing device 103 from other than the thermistor TH. For example, when there is a temperature sensor that can detect the ambient temperature of the fixing device 103, the control circuit A may acquire information from this temperature sensor.

When the step proceeds to S112, the control circuit A sets the second fan 62 and the third fan 63 to 100 (%) which is the full-speed air volume at the start of printing. Then, the control circuit A stops the operations of the second fan 62 and the third fan 63 after the end of printing (S112).

If the detected temperature of the thermistor TH is higher than 100 ° C. at the start of printing, the ambient temperature of the fixing device 103 is considered to be sufficiently high. Therefore, since the amount of dust D generated is small, the first fan 61 is not operated in this embodiment. However, the first fan 61 may be operated in order to collect minutely generated dust D. At this time, it is preferable that the air volume of the first fan 61 is 100 (%) of the full-speed air volume because the collection efficiency of the dust D is high.
When the temperature detected by the thermistor TH is lower than 100 ° C. at the start of printing, it is considered that the ambient temperature around the fixing device 103 is low. When the ambient temperature around the fixing device 103 is low, condensation is likely to occur in the guide member 15 when printing is started, and dust D is likely to occur. Therefore, it is required to solve each of these problems.

When the step proceeds to S104 and printing is started, the control circuit A sets the air volume of the first fan 61 to 7 (%) and the air volume of the second fan to 100 (%) (S104, S105).

When the step proceeds to S105 and a first time (for example, 90 seconds) has elapsed from the start of printing (YES), the control circuit A proceeds to S107 (S106). If not (NO), the control circuit A maintains the air volume of each fan.

When the step proceeds to S107, the control circuit A sets the air volume of the first fan 61 to 20 (%) and the third fan 63 to 100 (%). At this time, if the air volume of the third fan 63 exceeds the sum of the air volume of the first fan 61 and the air volume of the second fan 62, the dust D becomes the third fan 63.
Will be drawn into. Therefore, in this embodiment, the air volume of the second fan is maintained at “100”,
The air volume of the third fan 63 is set to be lower than the sum of the air volume of the first fan 61 and the air volume of the second fan 62. In other words, when the air blow by the first fan 61 and the air blow by the third fan 63 are performed in parallel, the second fan blows with an air volume larger than the air volume of the difference between the air volume of the third fan and the air volume of the first fan. I do.

When a second time (for example, 90 seconds) elapses from the start of printing (YES), the control circuit A advances the step to S109 (S108). If not (NO), the control circuit A maintains the air volume of each fan.

When a third time (for example, 390 seconds) has elapsed from the start of printing (YES), the control circuit A advances the process to S109 (S108). If not (NO), the control circuit A maintains the air volume of each fan.

When the step proceeds to S109, the control circuit A sets the air volume of the first fan 61 to 100 (%) and proceeds to S110 (S109).

When printing is completed (S110), the control circuit A stops the first fan, the second fan, and the third fan (S111).

Note that when about 10 minutes have elapsed since the start of the image forming process, the amount of dust D generated is significantly reduced. Therefore, when printing is performed for a long time after S109, the blowing of the first fan 61 may be stopped (OFF) without waiting for the end of printing.

In this embodiment, the second fan 62 having a large air volume is always operated at full speed during the image forming process. Therefore, the space C is always in a positive pressure state. Therefore, the dust D from the sheet entrance 400 does not easily flow into the space C. In the present embodiment, the third fan is operated during the execution of the image forming process. However, since the air volume of the third fan 63 is equal to or less than the sum of the air volume of the second fan 62 and the first fan 61, the space C can be maintained at a positive pressure.

In this embodiment, the air volume of the third fan at the start of printing is set to 0 (OFF). However, as shown in FIG. 16, the air volume of the third fan may be set to 50 (%). Good. Even in this case, since the air volume of the third fan 63 is equal to or less than the sum of the air volume of the second fan 62 and the first fan 61, the space C can be set to a positive pressure. In addition, by doing this, it is possible to reliably prevent condensation around the guide member 15 and at the same time to further suppress the temperature rise of the peripheral device of the fixing device 103.

The air volume of the first fan 61 is smaller than that of the second fan 62 and smaller than that of the third fan 63. In this embodiment, the air volume when the first fan 61 is operated at 100% is 5 l / s, and the air volume when operated at 7% is 0.5 l / s. The air volume when the second fan 62 is operated at 100% is 10 l / s. The air volume when the third fan is operated at 100% is 10 l / s. Thus, even if the first fan 61 is operated at full speed, the air volume of the first fan 61 is smaller than the air volumes of the second fan 62 and the third fan 63. Therefore, the atmospheric pressure state of the space C is controlled predominantly by the second fan 62 and the third fan 63. In other words, the control circuit A can control the dust D from flowing into the space C by controlling the second fan 62 and the third fan 63.

According to the present embodiment, inhalation is performed uniformly along the longitudinal direction of the nip portion 101b in the vicinity of the nip portion 101b, and the dust D can be efficiently collected. According to this embodiment, it is possible to suppress the intake air from becoming locally strong in the vicinity of the nip portion 101b, and to suppress a local temperature drop of the fixing belt 105. According to the present embodiment, in the vicinity of the nip portion 101b, the air at the end portion in the longitudinal direction of the nip portion 101b can be reliably sucked, and the dust D at the end portion in the longitudinal direction of the nip portion 101b can be reliably collected.

According to the present embodiment, the air in the vicinity of the belt 105 is sucked so as not to be overcooled, and the generation of dust D can be suppressed. According to the present embodiment, the dust D can be efficiently collected according to the temperature in the vicinity of the belt 105.

According to this embodiment, it is possible to control the air flow in the image forming apparatus and suppress the dust D from flowing out to the downstream side of the fixing device 103.

According to this embodiment, the dust D is sealed in the vicinity of the sheet inlet 400 of the fixing device 103, and the filter unit 50 can efficiently collect the dust D.

Next, Example 2 will be described. FIG. 21 is a diagram illustrating the relationship between the arrangement of the filter units and the radiant heat E in the second embodiment. FIG. 22 is a diagram showing the relationship between the arrangement of the filter units and the radiant heat E in the first modification. FIG. 23 is a diagram showing the relationship between the arrangement of the filter units and the radiant heat E in Modification 2.

In Example 1, in order to improve the recovery efficiency of dust D, the air inlet 52a and the filter 51 of the duct 52 are directed toward the nip portion 101b (belt 105). On the other hand, in the second embodiment, the intake port 52a of the duct 52 is directed toward the transfer unit 12a, thereby suppressing the filter 51 from being heated excessively. The printer 1 of the second embodiment is the same as that of the first embodiment except that the arrangement of the filter unit 50 is different. Therefore, the same code | symbol is attached | subjected about the same structure and detailed description is abbreviate | omitted.

Although a nonwoven fabric or the like is used as the filter 51 used for collecting the dust D, this nonwoven fabric may be thermally deteriorated in a high temperature environment. When the thermal deterioration of the filter 51 is promoted, the life of the filter 51 is reduced, and therefore it is required to replace the filter with high frequency. However, if the filter 51 is replaced at a high frequency, not only labor for replacement occurs, but also the running cost increases. Therefore, it is desirable that the filter 51 is not heated too much.

One of the causes of the temperature rise of the filter 51 is the heat of air near the sheet inlet 400. However, the filter 51 is intended to collect the dust D from the air in the vicinity of the sheet inlet 400, and has sufficient heat resistance against the air temperature in the vicinity of the sheet inlet 400. Therefore, the lifetime reduction of the filter 51 is not rapidly accelerated only by the heat of the air in the vicinity of the sheet inlet 400.

Another cause of the temperature rise of the filter 51 is radiant heat E from the fixing unit 101. The radiant heat E is heat that is directly transmitted in the form of electromagnetic waves from a high-temperature solid surface to a low-temperature fixed surface. Since the filter 51 is located in the vicinity of the fixing unit 101 which is a heat source, the influence of the radiant heat E from the fixing unit 101 is large.

That is, the intake surface 51a of the filter 51 becomes a high temperature state by the radiant heat E irradiated from the fixing unit 101 in addition to the temperature rise due to the heat of the air near the sheet inlet 400.

Therefore, in this embodiment, the life of the filter 51 is improved by reducing the radiant heat E from the fixing unit 101 to the filter 51.

In the fixing unit 101, the member that radiates the radiant heat E most strongly is the belt 105 having the highest temperature. Radiant heat E radiated from the belt 105 diffuses radially from every point on the surface layer of the fixing belt 105. Therefore, in order to reduce the temperature rise of the filter 51, the filter 51 may be arranged at a position where the radiant heat E from the belt 105 is not irradiated onto the intake surface 51a.

Therefore, in this embodiment, the air inlet 52a of the duct 52 is arranged facing the transfer portion 12a side (transfer roller 12 side). Since the filter 51 is provided so as to cover the intake port 52a, the surface of the filter 51 faces the transfer portion 12a side (transfer roller 12 side) in the configuration described above. The space between the belt 105 and the filter 51 is blocked by the duct 52.

The positional relationship among the belt 105, the filter 51, and the duct 52 will be described in detail with reference to FIG. A contact point between the suction surface 51a and the upper wall of the duct is referred to as M1, and a contact point between the suction surface 51a and the lower wall of the duct is referred to as N1. A contact point with the surface layer of the belt 105 when the line M1-N1 connecting M1 and N1 is extended to the surface layer of the fixing belt 105 is referred to as L1. In order to make it difficult for the radiant heat E to go to the filter 51, the position of the contact L1 is preferably within the range of the region 135d. The region 135d is a fourth region when the fixing belt 105 is divided into four regions in the circumferential direction and counted from the nip portion 101b along the rotation direction.

In this embodiment, the line L1-N1 is a tangent to the belt 105 at the contact L1. In such a configuration, the radiant heat E from the belt 105 does not travel toward the intake surface 51a. Therefore, the temperature rise of the filter 51 can be suppressed.

It should be noted that the angle of the air inlet 52a may be made steep so that the extended line of the line M1-N1 does not intersect the belt 105. Even in such a configuration, the radiant heat E from the belt 105 does not go to the filter 51. For example, as in the first modification shown in FIG. 22, the angle of the intake port 52a may be further steep to block the radiant heat E 'from the pressure roller 102.

A contact point with the surface layer of the pressure roller 102 when the line M1-N1 is extended to the surface layer of the pressure roller 102 is referred to as L2. In order to make it difficult for the radiant heat E to go to the intake surface 51a, the position of the contact L1 is preferably within the range of the region 135d. The region 135e is a third region when the pressure roller 102 is divided into four regions in the circumferential direction and counted from the nip portion 101b along the rotational direction. In the first modification, the line L2-N1 is a tangent line of the pressure roller 102 at the contact point L2. In such a configuration, the radiant heat E of the belt 105 and the radiant heat E ′ from the pressure roller 102 do not travel toward the intake surface 51a. Therefore, the temperature rise of the filter 51 can be suppressed.

Note that the filter 51 is not necessarily inclined with respect to the sheet conveying direction. For example. As in Modification 2 shown in FIG. 23, the filter 51 may be arranged in parallel with the conveyance direction of the sheet P. In this case, it is desirable to provide a shielding portion 55 in the duct 52 so that the radiant heat E does not face the filter 51.

The end of the filter 51 and the upper wall of the duct on the conveyance surface side is referred to as M3, and the contact point between the filter 51 and the lower wall of the duct is referred to as N3. A contact point with the surface layer of the belt 105 when the line M3-N3 connecting M3 and N3 is extended to the surface layer of the fixing belt 105 is referred to as L3. In order to make it difficult for the radiant heat E to go to the filter 51, the position of the contact L3 is preferably within the range of the region 135d. In this embodiment, the line L3-N3 is a tangent line of the belt 105 at the contact point L3. In such a configuration, the radiant heat E from the belt 105 does not travel toward the intake surface 51a. Therefore, the temperature rise of the filter 51 can be suppressed.

According to this embodiment, the temperature rise of the filter 51 can be suppressed. According to the present embodiment, it is possible to suppress a decrease in the lifetime of the filter 51. According to the present embodiment, the replacement frequency of the filter can be reduced. However, the configuration of the first embodiment is preferable in that the dust D can be reliably collected.
(Other examples)

As mentioned above, although this invention was demonstrated using the Example, this invention is not restricted to the structure as described in an Example. Numerical values such as dimensions exemplified in the embodiments are examples, and may be appropriately set within a range where the effects of the present invention can be obtained. Moreover, you may replace the one part structure as described in an Example with the other structure which has the same function in the range with which the effect of this invention is acquired.

The intake surface 51a of the filter 51 does not have to be a curved surface. The intake surface 51a has a flat shape and dust D can be collected. As the filter 51, another filter such as a honeycomb filter may be used instead of the nonwoven fabric filter. When an electrostatic filter which is a nonwoven fabric filter subjected to electrostatic processing is used as the filter 51, the dust D may be collected by the filter 51 after being charged by the charging device. The arrangement configuration of the filter 51 is not limited to that described in the embodiment. For example, two or more filters 51 may be installed at both longitudinal ends of the belt 105. The filter 51 may be installed on the pressure roller side with respect to the sheet conveyance path.

The fixing device 103 is not limited to a configuration that conveys a sheet in a vertical path. For example, the fixing device 103 may be configured to convey a sheet in a horizontal path or obliquely.

The heating rotator for heating the toner image on the sheet is not limited to the belt 105. The heating rotator may be a roller or a belt unit in which a belt is stretched between a plurality of rollers. . However, the configuration of Example 1 in which the surface of the heating rotator becomes hot and dust D is likely to be generated can achieve a greater effect.

The nip forming member that forms the nip portion with the heating rotator is not limited to the pressure roller 102. For example, a belt unit in which a belt is stretched between a plurality of rollers may be used.

The heating source for heating the heating rotator is not limited to a ceramic heater such as the heater 101a. For example, the heating source may be a halogen heater. Further, the heating rotator may be directly heated by electromagnetic induction. Even in such a configuration, dust D is likely to be generated in the vicinity of the sheet entrance 400, and therefore the configuration of the first embodiment can be applied.

The image forming apparatus described using the printer 1 as an example is not limited to an image forming apparatus that forms a full-color image, but may be an image forming apparatus that forms a monochrome image. In addition, the image forming apparatus can be implemented in various applications such as a copying machine, a FAX, and a multifunction machine having a plurality of these functions in addition to necessary equipment, equipment, and housing structure.

According to the present invention, there is provided an image forming apparatus capable of appropriately removing fine particles caused by a release agent contained in a toner.

12a contact portion 15 guide member 50 filter unit 51 filter 52 duct 52a air inlet 61 first fan 62 second fan 63 third fan 101 fixing belt unit 101a heater 101b nip portion 102 pressure roller 103 fixing device 105 fixing belt 400 sheet inlet 500 sheet exit TH thermistor A control circuit Wp-max maximum image width P sheet S toner α dust reduction rate d distance between belt and filter Fs filter area

Claims

An image forming unit that forms an image on a recording material using a toner containing a release agent;
A heating rotator and a pressure rotator that form a nip portion for fixing an image formed on the recording material by the image forming unit;
A duct for discharging air taken in from the vicinity of the inlet of the nip portion through the intake port;
A filter that is provided in a ventilation path of the duct and collects fine particles caused by a release agent;
A fan for drawing air into the duct,
An image satisfying the following when the distance between the air inlet and the heating rotator is d (mm), the area of the filter is Fs (cm 2 ), and the air passing velocity of the filter is Fv (cm / s) Forming equipment.
The image forming apparatus according to claim 1, wherein:
The image forming apparatus according to claim 1, wherein the d (mm) is 5 or more and 100 or less.
The image forming apparatus according to any one of claims 1 to 3, wherein the Fv (cm / s) is 5 or more and 30 or less.
The image forming apparatus according to claim 1, wherein a ventilation resistance (Pa) of the filter is 50 or more and 130 or less.
6. The image forming apparatus according to claim 1, wherein the filter is provided in the intake port.
The image forming apparatus according to claim 6, wherein the filter has a curved shape in which a central portion in a short direction projects toward an inner side of the duct.
The image forming apparatus according to any one of claims 1 to 7, wherein a width of the filter is equal to or larger than a width of a recording material having a minimum width usable in the image forming apparatus.
The image forming apparatus according to any one of claims 1 to 8, wherein the filter is an electrostatic nonwoven fabric.
10. The air intake port according to claim 1, wherein the air intake port is located within a range from a position where an image is formed on the recording material by the image forming unit to the nip portion in the recording material conveyance direction. The image forming apparatus described.