JP2007121942A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device, process cartridge and image forming apparatus capable of suppressing the problems of streak images and the like, caused by fuzzing of the filter and obtaining a satisfactory image output, while pressure removal (toner scatter prevention performance) in an exhaust part having a filter is retained, in a under development system. <P>SOLUTION: An opening 50a serving as the exhaust part is disposed on the upper face side of a developing device 5. The filter 61 for preventing toner leakage is set on the upper side of the opening 50a. The filter 61 is disposed opposite the image carrier face of an intermediate transfer belt 8 as an unfixed image carrier. A porous member 62 for restraining the filter 61 from fuzzing is installed between the intermediate transfer belt 8 and the filter 61. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a plotter, a developing device used in the image forming apparatus, and a process cartridge that integrally includes the developing device and is detachable from an image forming apparatus main body.

In a developing device using a two-component developer composed of a toner and a carrier, the developer and toner are adjusted and controlled on the developing roller (developer carrier) by mixing and stirring the toner and carrier in the device. It is transported to.
The amount of the developer carried on the developing roller is regulated by a doctor blade (developer regulating member) installed above the developing roller, and then is opposed to the photosensitive drum (image carrier) (development). Area).
At that position, the toner in the developer carried on the developing roller adheres to the electrostatic latent image formed on the photosensitive drum, and a desired toner image is formed.

Most of the toner in the developing device is attracted to the carrier by electrostatic force generated by frictional charging with the carrier. The toner adsorbed on the carrier adheres to the electrostatic latent image (image portion) on the photosensitive drum under the influence of the electric field formed between the developing roller and the photosensitive drum in the development region.
That is, the force received from the electric field in the development area exceeds the electrostatic force with the carrier, and the toner leaves the carrier and flies to the photosensitive drum side.

The toner that is powder is not uniform in physical properties, and some toners do not have sufficient charging ability. In addition, there are toners that become insufficiently charged due to insufficient frictional charging with the carrier, such as toner that stays in a part of the apparatus.
Furthermore, since the charging ability of the carrier in the developer in the developing device decreases with long-term use, the toner is insufficiently charged in such a case.
Since such a toner with insufficient charge is not easily restrained by an electric force, it floats in the apparatus by riding on an air current generated in the apparatus. The suspended toner further rides on the air current and scatters out of the developing device and contaminates the inside of the image forming apparatus.

In order to prevent such toner scattering from the developing device, a seal member is generally attached to a gap between the components constituting the developing device.
Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for releasing pressure by providing an opening (exhaust part) in a housing that covers the lower side of the developing roller for the purpose of preventing toner scattering by suppressing an increase in internal pressure in the developing device. Has been.
A filter that prevents toner from leaking out of the apparatus is installed in the opening. As the filter, the most inexpensive and efficient nonwoven fabric type filter is usually used.

JP 2000-122418 A

In recent years, image forming apparatuses having a layout in which a transfer belt is disposed immediately above a developing device are becoming mainstream due to demands for downsizing, stabilization of the apparatus, shortening of first printing, and the like. Hereinafter, such a layout is referred to as a “lower development method”.
In the lower development method, it is possible to contribute to the downsizing of the configuration around the photoconductor and the downsizing of the image forming apparatus by placing the developing device as close to the transfer belt as possible and disposing the exhaust unit above the developing device. It has been found that the punching characteristics are also good. The reason will be described in detail in the embodiment of the present invention.
However, with such a lower development method, it is inevitable that the filter of the exhaust portion faces the image surface (image carrying surface) of the transfer belt and is in an in close proximity state, and the degree of fluffing of the filter is poor, It has been found that there is a problem that streaks are generated on the image when the fluff comes into contact with the unfixed image on the transfer belt and rubs.

  The present invention can suppress problems such as streak images due to fluffing of the filter while maintaining the pressure release (toner scattering prevention performance) in the exhaust section having the filter in the lower development system, and can obtain a good image output. An object is to provide a developing device, a process cartridge, and an image forming apparatus.

  In order to achieve the above object, according to the first aspect of the present invention, an image carrier and a developing device for visualizing an electrostatic latent image formed on the image carrier are provided. And an unfixed image carrier to which a visible image on the image carrier is transferred with the image surface facing and close to the filter. In the image forming apparatus having a moving configuration, a porous member that covers a surface of the filter facing the unfixed image carrier is disposed between the filter and the unfixed image carrier.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the porous member is provided in the developing device.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the porous member is supported by the main body of the image forming apparatus, the developing device is detachable from the main body of the image forming apparatus, and the developing The porous member covers the opposing surface of the filter in accordance with the mounting operation of the apparatus with respect to the image forming apparatus main body.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the porous member is made of an insulating material.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the porous member is made of nylon.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the size of the opening of the porous member is 20 × 20 μm or more and 1 × 1 mm or less. Features.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, an interval between the filter and the unfixed image carrier is 5 mm or less.

The invention described in claim 8 is characterized in that the developing device has a configuration used in the image forming apparatus described in claim 2.
According to a ninth aspect of the present invention, in the developing device according to the eighth aspect, the porous member is made of an insulating material.
According to a tenth aspect of the present invention, in the developing device according to the ninth aspect, the porous member is made of nylon.
According to an eleventh aspect of the present invention, in the developing device according to any one of the ninth to tenth aspects, the size of the opening of the porous member is 20 × 20 μm or more and 1 × 1 mm or less. And

According to a twelfth aspect of the present invention, the process cartridge includes a developing device and an image carrier used in the image forming apparatus according to the second aspect, and is detachable from the main body of the image forming apparatus. .
According to a thirteenth aspect of the present invention, in the process cartridge according to the twelfth aspect, the porous member is made of an insulating material.
According to a fourteenth aspect of the present invention, in the process cartridge according to the thirteenth aspect, the porous member is made of nylon.
According to a fifteenth aspect of the present invention, in the process cartridge according to any one of the twelfth to fourteenth aspects, the size of the opening of the porous member is 20 × 20 μm or more and 1 × 1 mm or less. And

  According to the present invention, it is possible to prevent problems on the image due to the fluff of the filter while maintaining the layout around the image carrier in an advantageous state without impairing the pressure release function of the developing device.

A first embodiment of the present invention will be described below with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus according to the present embodiment will be described with reference to FIGS. FIG. 1 is a block diagram showing a color copying machine as an image forming apparatus, and FIG. 2 is an enlarged view showing an image forming unit thereof.
As shown in FIG. 1, the image forming units 6Y and 6M corresponding to the respective colors (yellow, magenta, cyan, black) so as to face the lower surface of the intermediate transfer belt 8 as an unfixed image carrier of the intermediate transfer unit 10. , 6C, 6Bk are juxtaposed. Since the four image forming units 6Y, 6M, 6C, and 6Bk installed in the apparatus main body 100 have substantially the same structure except for the color of the toner used in the image forming process, the image forming unit in FIG. In the drawing, the alphabets (Y, M, C, Bk) of reference numerals in the section 6, the photosensitive drum 1, and the primary transfer bias roller 9 as the primary transfer unit are omitted.

As shown in FIG. 2, the image forming unit 6 includes a photosensitive drum 1 as an image carrier, a charging unit 4 disposed around the photosensitive drum 1, a developing device 5 as a developing unit, and a cleaning unit 2. (Only the developing device 5 is shown in FIG. 1). An image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1, and a desired toner image is formed on the photosensitive drum 1.
The photosensitive drum 1, the charging unit 4, the developing device 5, and the cleaning unit 2 constituting the image forming unit 6 are each configured to be detachably installed on the image forming apparatus main body 100. Each is replaced with a new one when it reaches the end of its life.
In the present embodiment, the photosensitive drum 1, the charging unit 4, the developing device 5, and the cleaning unit 2 constituting the image forming unit 6 are each a single unit, but these are integrated into the apparatus main body 100. It can also be a process cartridge that is detachably installed. In this case, workability when performing maintenance of the image forming unit 6 is improved.

The photosensitive drum 1 is rotated in a clockwise direction in FIG. 2 by a driving unit (not shown), and the surface of the photosensitive drum 1 is uniformly charged by the charging roller 4a at the position of the charging unit 4 (charging). Process).
Thereafter, the surface of the photosensitive drum 1 reaches an irradiation position of a laser beam L emitted from an exposure unit (not shown), and an electrostatic latent image is formed by exposure scanning at this position.
Thereafter, the surface of the photosensitive drum 1 reaches a position facing the developing device 5, and the electrostatic latent image is developed at this position to form a desired toner image (developing process).
Thereafter, the surface of the photosensitive drum 1 reaches a position facing the intermediate transfer belt 8 and the primary transfer bias roller 9, and the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 8 at this position. (Primary transfer process).
At this time, a small amount of untransferred toner remains on the photosensitive drum 1.

Thereafter, the surface of the photoreceptor 1 reaches a position facing the cleaning unit 2, and untransferred toner remaining on the photoreceptor drum 1 is collected by the cleaning blade 2a at this position (cleaning step). After cleaning, the electric potential of the surface of the photosensitive drum 1 is initialized by the neutralizing roller 11.
Thus, a series of image forming processes performed on the photosensitive drum 1 is completed.

  As shown in FIG. 1, the above-described image forming process is performed in each of the four image forming units 6Y, 6M, 6C, and 6Bk. That is, a laser beam L based on image information from an exposure unit (optical writing device) (not shown) disposed below the image forming unit is applied to the photosensitive drums of the image forming units 6Y, 6M, 6C, and 6Bk. Irradiated towards. Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 8 in an overlapping manner. Thus, a color image is formed on the intermediate transfer belt 8.

The four primary transfer bias rollers 9Y, 9M, 9C, and 9Bk respectively sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1Bk to form a primary transfer nip. The primary transfer bias rollers 9Y, 9M, 9C, and 9Bk are applied with a transfer bias having a polarity opposite to the polarity of the toner.
The intermediate transfer belt 8 runs in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 9Y, 9M, 9C, and 9Bk. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1Bk are primarily transferred while being superimposed on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 onto which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 19 as a secondary transfer unit. The color toner image formed on the intermediate transfer belt 8 is transferred onto a transfer sheet P as a recording medium conveyed to the secondary transfer nip position.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.
A plurality of transfer sheets P are stored in a paper feeding unit 26 disposed in the lower part of the apparatus main body 100, and are separated and fed one by one by a paper feeding roller 27. The fed transfer paper P is temporarily stopped by the registration roller pair 28, and after the oblique deviation is corrected, it is conveyed toward the secondary transfer nip by the registration roller pair 28 at a predetermined timing. Then, a desired color image is transferred onto the transfer paper P at the secondary transfer nip.

The transfer paper P onto which the color image has been transferred at the position of the secondary transfer nip is conveyed to the fixing unit 20, where the color image transferred to the surface is fixed by heat and pressure generated by the fixing roller and the pressure roller. The
After the fixing, the transfer paper P is discharged as an output image to the paper discharge unit 30 formed on the upper surface of the apparatus main body by the paper discharge roller pair 29 and stacked. Thus, a series of image forming processes in the image forming apparatus is completed.
As described above, if the image forming section 6 is arranged in parallel on the lower side of the intermediate transfer belt 8 and the secondary transfer is performed in the vicinity of the most downstream image forming section 6 (lower development system), the intermediate transfer belt is used. Compared with the system in which the image forming unit 6 is arranged on the upper side of 8, it is possible to reduce the moving distance in the state where the unfixed image of the intermediate transfer belt 8 is carried after the completion of the primary transfer. Shortening can be realized.
In FIG. 1, reference numeral 31 denotes a toner replenishing unit, and 32 denotes a reading unit.

Next, the configuration and operation of the developing device 5 in the image forming unit 6 will be described in more detail.
As shown in FIG. 2, the developing device 5 includes a developing roller 51 as a developer carrying member facing the photosensitive drum 1, a doctor blade 52 as a developer regulating member installed below the developing roller 51, a developer Two conveying screws 55 and 56 as developer agitating members disposed in the accommodating portions 53 and 54, a toner concentration sensor 57 (see FIG. 5) for detecting the toner concentration in the developer G, and above the developing roller 51 A case 50 that covers the outer surface of the apparatus, an opening 50a as an exhaust portion provided in the case 50 so as to communicate with the outside of the apparatus, a filter 61 provided in the opening 50a, a porous member 62 that covers the upper surface of the filter 61, and an exhaust of the developing roller 51 It is comprised by the wall part 58 etc. which were integrally provided in case 50 so that the side of a part side might be covered.
In the developer accommodating portions 53 and 54, a two-component developer G composed of a carrier and a toner is accommodated.

The developing roller 51 includes a magnet fixed inside, a sleeve rotating around the magnet, and the like. As shown in FIG. 3, the magnet of the developing roller 51 has five magnetic poles, P1 to P5.
By rotating the sleeve around the magnet on which the five magnetic poles are formed, the developer G moves on the developing roller 51 (on the sleeve) with the rotation. Radial line segments attached to the developing roller 51 indicate positions where the respective magnetic forces of the P1 to P5 poles peak.

Specifically, in the region from the P4 pole to the P5 pole of the developing roller 51, both magnetic poles act on a carrier as a magnetic material, and the developer G accommodated in the developer accommodating portion 53 is carried on the developing roller 51. Is done. Part of the developer G carried on the developing roller 51 is scraped off at the position of the doctor blade 52 and returned to the developer containing portion 53.
On the other hand, the developer G carried on the developing roller 51 through the gap with the doctor blade 52 rises at the position of the P1 pole, and the toner in the developer G is a latent image on the photosensitive drum 1. Adhere to. In the region passing through the P1 pole and reaching the P2 pole, as will be described later, gas (air) flows from the developing roller 51 carrying the developer G after the developing process and the case 50 (gap 60). .
Further, in the region from the P3 pole to the P4 pole, the repulsive magnetic field formed by both magnetic poles having the same polarity acts on the carrier, and the developer G after the development process carried on the developing roller 51 is developed. Detached from the roller 51. The detached developer G is returned again to the developer container 53 and circulates in the developer containers 53 and 54. Such a flow of the developer G is repeated.

The magnetic flux density between the P3 pole and the P4 pole is formed to be 10 mT or less. In this way, a repulsive magnetic field having the same polarity is formed so that the magnetic flux density between the poles is reduced, so that the developer passing through the P3 pole is blown off from the developing roller 51. It falls into the housing part 53.
Thereby, the gas above the developer accommodated in the developer accommodating portion 53 receives a strong dynamic pressure, and is urged by this dynamic pressure, so that the gas is efficiently discharged from the opening 50a. Here, since the opening 50a is disposed above the developer accommodating portion 53 and is disposed at a position deviated from the position where the developer falls, the developer that jumps up due to the falling of the developer is prevented. Problems that reach the opening 50a can be suppressed.

The developing roller 51 is installed so that a part of the developing roller 51 is exposed to the opening of the developing device 5 provided at a position facing the photosensitive drum 1. A case 50 made of a resin material or the like is installed above the developing roller 51 so as to cover the developing roller 51.
A doctor blade 52 is installed below the developing roller 51 (below the horizontal axis of coordinates with the rotation center of the developing roller 51 as the origin). By installing the doctor blade 52 below the developing roller 51 in this way, as will be described later, a gas flow path from between the developing roller 51 and the case 50 to the opening 50a is formed in the developer accommodating portion 53. , 54 can be secured without being blocked by the developer G in the inside.

The case 50 installed above the developing roller 51 is provided with a wall 58 and an opening 50a. The wall portion 58 is installed so as to cover the vicinity of the region from the P3 pole to the P4 pole through the P2 pole of the developing roller 51.
The opening 50a is provided at a position via the wall 58 with respect to the developing roller 51 and at a position above the developer containing portion 53 that is not buried in the developer G so as to communicate with the outside of the apparatus. Accordingly, a gas flow path (flow path indicated by a broken line arrow in FIGS. 2 and 3) from between the developing roller 51 and the case 50 to the opening 50a can be secured.

A filter 61 is installed in the opening 50a so as to cover the opening 50a.
The filter 61 employs a non-woven fabric that is most effective in all aspects of cost, pressure loss, and toner collection efficiency. The filter 61 collects the toner entering from the inside of the apparatus and moves the air to the outside of the apparatus. Let it pass.
Thereby, when the gas inside the apparatus (inside the developing section) is discharged from the opening 50a, it is possible to prevent toner scattering outside the apparatus (outside the developing section).
As shown in FIG. 2, the two developer containing portions 53 and 54 are separated from each other by a partition plate 51 except for both end portions in the longitudinal direction (the direction perpendicular to the paper surface in FIG. 2).
Conveying screws 55 and 56 installed in the developer accommodating portions 53 and 54 convey the developer G in opposite directions. As a result, the developer G accommodated in the developer accommodating portions 53 and 54 circulates between the developer accommodating portions 53 and 54 in the longitudinal direction.
As shown in FIGS. 4 and 5, a toner replenishing port 44 is connected above one developer accommodating portion 54. A toner conveying device (not shown) that conveys toner from the toner replenishing unit 31 is connected to the toner replenishing port 44, and fresh toner is appropriately replenished in the developer containing unit 54.

As shown in FIG. 4, the opening 50 a is set not in the entire longitudinal direction of the developing device 5 but in a range W that is close to the upstream side (near side). A long hole 50b extending in the longitudinal direction of the case 50 on the upper surface substantially corresponds to the opening 50a, and the filter 61 projects from the long hole 50b. The protruding filter 61 is pressed by a synthetic resin presser plate 12 that can be locked in the long hole 50b. The holding plate 12 has a larger dimension around the edge than the long hole 50b, and is engaged by the elasticity of the filter 61 with the edge portion inside the long hole 50b.
As shown in FIG. 6, a porous member 62 described later is attached from the upper side of the holding plate 12 having a plurality of openings to cover the upper surface of the filter 61 (not shown in FIG. 4). The upper surface of the filter 61 may be directly covered with the porous member 62 without using the holding plate 12. The porous member 62 has an adhesive surface such as a double-sided tape around the edge, and is affixed on the case 50.

As shown in FIG. 2, a preset space 59 for storing the developer before the initial use is provided in the middle of conveyance of the conveyance screw 56, and a sheet is pasted on the opening below the preset space 59 at the initial stage. Although it is partitioned, by pulling out this sheet during use, the preset space 59 and the developer accommodating portion 54 can be communicated and used. The preset space 59 is used as a decompression space when in use. That is, when the developer is transported, a dynamic pressure is generated along with the flow of the developer, and the surrounding gas is pushed out to the transport screw 55 side together with the developer at the developer delivery portion, and the end of the developing roller 51 is increased due to a local pressure increase. However, since the preset space 59 is used to reduce the pressure, the pressure is suppressed.
Since the opening 50a is provided in the upper part from the vicinity where the pressure increase occurs, the vicinity of the developer delivery, to the specific range on the downstream side of the conveying screw 55 (the range W shown in FIG. 4), the above pressure increase is achieved. More stable exhaust airflow can be formed while releasing toner, and toner scattering can be further reduced.

The developing device 5 configured as described above operates as follows.
The sleeve of the developing roller 51 rotates in the direction of the arrow in FIG. As described above, the developer G carried on the developing roller 51 by the magnetic field formed by the magnet moves on the developing roller 51 as the sleeve rotates.
The developer G in the developing device 5 is adjusted so that the toner ratio (toner concentration) in the developer G is within a predetermined range. Specifically, the toner is replenished from the toner conveying device into the developer accommodating portion 54 via the toner replenishing port 44 according to the toner consumption in the developing device 5.

The toner replenished in the developer accommodating portion 54 is mixed and stirred together with the developer G by the second conveying screw 56 and the first conveying screw 55, and the two developer accommodating portions 53 and 54 are shown in FIG. Circulate in the direction of the arrow.
The toner in the developer G is attracted to the carrier by frictional charging with the carrier, and is carried on the developing roller 51 together with the carrier by the magnetic force formed on the developing roller 51.
The developer G carried on the developing roller 51 is conveyed in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52. Then, after the developer G on the developing roller 51 is regulated to an appropriate amount at this position, the developer G is conveyed to a position facing the photosensitive drum 1 (development region).
The toner is attracted to the latent image formed on the photosensitive drum 1 by the electric field formed in the development area. Thereafter, the developer G remaining on the developing roller 51 sequentially passes through the surface facing the case 50 and the surface facing the wall 58 as the sleeve rotates. Further, the developer G on the developing roller 51 reaches above the developer containing portion 53 and is detached from the developing roller 51 at this position.

In the series of operations of the developing device 5 described above, a gas flow path indicated by a broken-line arrow in FIG.
That is, the gas flowing from between the developing roller 51 and the case 50 passes through the surface facing the case 50 and the surface facing the wall 58 as the developing roller 51 rotates, and the tip of the wall 58. To. And the gas which flowed in in the apparatus goes around the front-end | tip part of the wall part 58, and is discharged | emitted out of the apparatus from the opening part 50a in which the filter 61 was installed. Here, since the front end portion of the wall portion 58 is installed at a position where it is not buried in the developer G, the gas flowing into the apparatus is not blocked by the developer G in the developer accommodating portion 53, and the opening portion A flow path up to 50a is secured.

The toner image formed on the photosensitive drum 1 through the above process is transferred onto the intermediate transfer belt 8 at the contact portion (nip) with the intermediate transfer belt 8 and is subjected to secondary transfer located on the downstream side of the rotation. It flows toward roller 9.
Here, for example, it is assumed that a yellow toner image is transferred onto the intermediate transfer belt 8 and passes through a cyan developing device 5 located downstream.
Since the distance between the upper surface of the developing device 5 and the surface of the intermediate transfer belt 8 is only about 2 to 3 mm, if even one fluff of about 3 to 5 mm comes out from the filter 61 as a pressure release filter, this is the intermediate transfer belt. When the image holding surface 8 is touched, streaks are generated in the yellow toner image.

The above example is a description of a problem that occurs due to a combination of a yellow image and a cyan unit, but there are other examples where such a problem occurs.
That is, in the combination in which the image developed and transferred on the upstream side with respect to the traveling direction of the intermediate transfer belt 8 passes through the filter portion of the developing device installed on the downstream side, the same problem as described above occurs. .

The filter 61 in this embodiment uses the thing by a nonwoven fabric as mentioned above. Such a filter is usually formed by intertwining fibers such as polyolefin and polyester, and the fiber diameter is several μm to several tens μm.
At the time of processing, the fiber is gathered to a weight of about 50 to 60 g / m ² and compressed while applying heat, so that a part of the fiber is melted and entangled, and an apparently lump filter is completed.
In this process, innumerable minute needles protrude from one side of the plate that sandwiches the fibers, and the fibers are pierced into the gathered fibers during pressing, so that the fibers are entangled more complicatedly. The unity becomes stronger. However, at the time of peeling after pressing, not a few fibers entangled with the needle are pulled out to the outside of the filter, which is one of the causes of fluffing easily.
As described above, the filter itself is an aggregate of fibers, and the process of removing and inserting the needles in the process is performed. Therefore, it is almost impossible to eliminate the fluff from the filter itself. The fluff thus generated is a cause of the above-mentioned problems.

Therefore, in order to prevent the above problems, in this embodiment, the surface of the filter 61 that faces the image holding surface of the intermediate transfer belt 8 is covered with the porous member 62 as described above.
For the porous member 62, a nylon mesh having a thickness of about 0.3 mm is used. As shown in FIG. 7, the mesh 62 can be provided with a large number of uniform and minute holes 62b between the fibers when the fine fibers 62a intersect with each other with a uniform spacing.
Here, the size of each hole 62b is 161 × 161 μm. By covering the mesh 62 over the filter 61, as shown in FIG. 8A, even if the fluff 61a stands from the filter 61, each of the fibers is usually curved. In addition, since it cannot pass through the minute hole 62b of the mesh 62, the fluff 61a can be prevented from standing outside the mesh 62 as shown in FIG.

The mesh 62 has an insulating property due to its material. The insulator is used because the distance between the upper surface of the developing device 5 and the intermediate transfer belt 8 is very close, so as to prevent leakage from the intermediate transfer belt 8 that passes with electric charges to the mesh 62. It is.
Insulating members include those made of polyethylene or polyester in addition to nylon, but nylon is the cheapest and most versatile.
Moreover, when selecting the mesh 62, the opening size between fibers has a very important meaning. This is because if the opening size is too large, the fluff 61a of the filter 61 passes through the hole 62b of the mesh 62, so that the mesh effect cannot be obtained.
On the other hand, if it is too small, it will be a ventilation resistance against the air flow of depressurization, so that the effect of depressurization will be suppressed.

Therefore, an appropriate range exists for the opening size of the mesh. According to experiments by the present inventors, it was confirmed by repeated mounting of parts that there is no problem up to 1 × 1 mm as the maximum value that can hold down the fluff 61 a of the filter 61.
On the other hand, as for the minimum value, when the internal pressure of the developing device 5 is measured and the change in the internal pressure due to the presence or absence of the mesh is compared, as shown in FIG. 9, the change amount of the internal pressure is 1 Pa or less at 20 × 20 μm or more. Not confirmed.
Considering the balance between the effect and the cost within the above effective range, a 161 × 161 μm mesh is adopted in the present embodiment.
When installing the porous member 62, as shown in FIG. 10, you may make it cover the filter 61 by moving from the side substantially horizontally. In this way, even if the fluff 61a that extends straight is surely fallen down, the accuracy of preventing the fluff 61a from protruding after the porous member 62 is installed can be improved, and the mesh opening size has a margin. Can be made.

In this embodiment, the distance between the filter 61 and the unfixed image surface, that is, the surface of the intermediate transfer belt 8 (image holding surface) is 5 mm or less.
Here, the distance is about 3 mm. However, if the distance is longer than 5 mm, fuzz of 5 mm or more is necessary to cause the above-described problem. However, since the fluff extending to 5 mm or more easily falls down, even if it comes into contact with the intermediate transfer belt 8, a force that disturbs the image is not generated. Therefore, the present invention is effective under conditions of 5 mm or less.

Considering the layout shown in FIG. 2, if the developing device 5 is lowered, the distance between the intermediate transfer belt 8 and the filter 61 can be increased, and it is easy to secure an interval of 5 mm or more.
However, if the layout of the image forming unit 6 is narrowed down from the viewpoints of miniaturization, high performance, etc., the form as shown in FIG. 2 is most desirable, and only from the viewpoint of eliminating problems due to the presence of the filter 61, the developing device 5. As a result, the advantage of suppressing the fluff problem in the state where the filter 61 and the intermediate transfer belt 8 are close to each other is larger than that in the case of lowering the value. The reason will be described below.

As shown in FIG. 11A, in the arrangement configuration in which the filter 61 and the intermediate transfer belt 8 are close to each other (configuration shown in FIG. 2), other members (the charging unit and the charging unit and the photosensitive drum 1 are excluded). Whereas the degree of freedom of arrangement of the cleaning unit or the like is F1, when the developing device 5 is lowered, the degree of freedom of arrangement F2 becomes narrow as shown in FIG.
This degree becomes more prominent as the size of the photosensitive drum 1 increases.
If the degree of freedom F of arrangement is large, the arrangement space of the image forming elements (charging unit, cleaning unit, etc.) around the photosensitive drum 1 can be afforded, and this can be used to enhance the function of the image forming element. Become. That is, it becomes easy to install additional equipment or the like for enhancing the function of each element.
In addition, as shown in FIG. 11B, when the developing device 5 is lowered, the space between the upper surface of the developing device 5 and the intermediate transfer belt 8 (the space of height H) becomes a dead space. Inhibits downsizing.

It is also conceivable to lower the positions of only the opening 50a and the filter 61 without lowering the developing device 5. However, in this case, a good pressure release (exhaust) characteristic cannot be obtained. The reason will be described below.
As shown in FIG. 12A, as described above, the wall portion 58 is necessary so that the developer does not immediately go to the filter 61, that is, in order to protect the filter 61.
However, when the wall portion 58 is provided, the front end portion thereof is close to the magnetic pole that separates the developer from the developing roller 51, so that the developer tends to accumulate on the back side of the front end portion of the wall portion 58 due to the magnetic force. In the case of a two-component developer, it tends to accumulate due to the influence of magnetic density.
Even if the developer accumulates, if the filter 61 is separated upward, the air flow path and the width of the opening 50a are sufficiently secured, and the function of the filter 61 is maintained normally.
As shown in FIG. 12B, when the filter 61 is lowered, the width of the opening 50a becomes narrow due to the influence of the developer accumulation, and the depressurization characteristic is deteriorated at an early stage. That is, the life of the developing unit or process cartridge is shortened.

  In consideration of the above, it is desirable that the developing device 5 be as close to the intermediate transfer belt 8 as possible, and the filter 61 be as close to the upper surface side of the developing device 5 as possible. From this point of view, the fluff countermeasures by the porous member 62 can improve the image forming elements around the photosensitive drum 1 with a simple configuration, and can contribute to extending the life of the developing unit and the process cartridge. Significance is enormous.

A second embodiment will be described with reference to FIG. The same parts as those of the above-described embodiment are denoted by the same reference numerals, and the description of the configuration and functions already described will be omitted unless necessary, and only the main parts will be described.
In the first embodiment, the porous member 62 is provided in the developing device 5 so as to cover the filter 61. However, the present embodiment is characterized in that the image forming apparatus side includes the porous member 62.

As shown in FIG. 13A, a porous member 62 is provided inside the image forming apparatus main body 100 at a position corresponding to the filter 61 when the process cartridge (image forming unit) 6 is mounted. . One end of the porous member 62 is fixed to the support member 15 having an opening fixed to the image forming apparatus main body 100, and as shown in FIG. Cover the top surface. The porous member 62 may be attached to the lower surface of the support member 15.
The fuzz holding function of the porous member 62 here is the same as the lateral movement method shown in FIG.
In the configuration in which the porous member 62 is provided on the image forming apparatus side, it is not necessary to newly provide the porous member 62 for each developing unit or each process cartridge.

  In each of the embodiments described above, measures against the filter of the exhaust unit in the developing device are exemplified, but the same applies to a configuration in which an exhaust unit / filter configuration exists other than the developing device and the unfixed image carrier moves in proximity thereto. Can be implemented.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. It is an expanded sectional view of an image creation part. It is a figure which shows the structure of the developing roller vicinity. It is a disassembled perspective view of a developing device. It is a perspective view which shows the back | inner side part of a developing device. It is a perspective view which shows the holding structure of a filter. It is a principal part enlarged view which shows the fiber structure of a porous member. It is a figure which shows the pressing function of the fluff of the filter by a porous member. It is an experimental graph which shows the relationship between a mesh size and the internal pressure change of a developing device. It is a figure which shows the modification of the setting of the porous member with respect to a filter. It is a figure for demonstrating the advantage of the layout which a developing device and an unfixed image carrier adjoin. It is a figure for demonstrating that it is advantageous to install a filter as much as possible above a developing device. It is a figure which shows the filter covering operation | movement by the porous member in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum as image carrier 5 Developing device 5a Opening part as exhaust part 6 Process cartridge as image forming part 6 Filter 62 Porous member

Claims (15)

An image carrier and a developing device that visualizes an electrostatic latent image formed on the image carrier, and the developing device includes an exhaust part for pressure release and a filter provided in the exhaust part. ,
In the image forming apparatus having a configuration in which the unfixed image carrier to which the visible image on the image carrier is transferred moves in a state where the image surface is opposed to and close to the filter,
An image forming apparatus, wherein a porous member that covers a surface of the filter facing the unfixed image carrier is disposed between the filter and the unfixed image carrier. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the porous member is provided in the developing device. The image forming apparatus according to claim 1.
The porous member is supported by the image forming apparatus main body, the developing device is detachable from the image forming apparatus main body, and the porous member is attached to the image forming apparatus main body as the porous member is attached to the image forming apparatus main body. An image forming apparatus that covers an opposing surface. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the porous member is made of an insulating material. The image forming apparatus according to claim 4.
The image forming apparatus, wherein the porous member is made of nylon. The image forming apparatus according to any one of claims 1 to 5,
The size of the opening of the porous member is 20 × 20 μm or more and 1 × 1 mm or less. The image forming apparatus according to any one of claims 1 to 6,
An image forming apparatus, wherein a distance between the filter and the unfixed image carrier is 5 mm or less.   A developing device used in the image forming apparatus according to claim 2. The developing device according to claim 8, wherein
The developing device, wherein the porous member is made of an insulating material. The developing device according to claim 9, wherein
The developing device, wherein the porous member is made of nylon. The developing device according to any one of claims 9 to 10,
The developing device according to claim 1, wherein the opening of the porous member has a size of 20 × 20 μm or more and 1 × 1 mm or less.   A process cartridge which is integrally provided with a developing device and an image carrier used in the image forming apparatus according to claim 2 and which is detachable from a main body of the image forming apparatus. The process cartridge according to claim 12,
The process cartridge according to claim 1, wherein the porous member is made of an insulating material. The process cartridge according to claim 13, wherein
A process cartridge, wherein the porous member is made of nylon. The process cartridge according to any one of claims 12 to 14,
The process cartridge according to claim 1, wherein the size of the opening of the porous member is 20 × 20 μm or more and 1 × 1 mm or less.

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