Patent Description:
Conventionally, in a developing device disposed in an image forming apparatus such as a copying machine or a printer, a technology that a filter is disposed in an opening portion formed in the upper part of a developing case for the purpose of preventing toner scattering due to an increase of an internal pressure in the developing device is known (e.g., <CIT>). Specifically, in the developing device in <CIT>, even if the internal pressure inside the developing device is about to rise, the air inside the developing device is discharged to the outside of the developing device through the opening portion in which the filter is disposed, so that the increase of the internal pressure is restricted. Then, when the air inside the developing device is discharged to the outside of the developing device, even if the toner floating in the developing device is about to be discharged to the outside of the developing device together with the air, the toner is collected by the filter. Accordingly, the scattering of toner to the outside of the device is restricted. <CIT> discloses a developing device having a filter in an exterior wall and a corresponding image forming device. <CIT> discloses a filter medium.

In such a conventional technology, there is a possibility that air (discharge object) in the device leaks from lateral sides of the filter together with toner (collection object). In such a case, the function of the filter is not fully exerted, and the toner (collection object) is scattered outside the device. The present disclosure is made to solve the above-described problem and provide a filter holder, a developing device, a process cartridge, and an image forming apparatus that reduce the defect that a discharge object in the device is discharged to the outside of the device together with a collection object.

The present invention provides a developing device according to claim <NUM>.

According to the present disclosure, there is provided a developing device, a process cartridge, and an image forming apparatus that reduce the defect that a discharge object in the device is discharged to the outside of the device together with a collection object.

With reference to the drawings, embodiments of the present disclosure are described below. Note that identical reference numerals are assigned to identical components or equivalents and a description of those components is simplified or omitted.

An overall configuration and operation of an image forming apparatus <NUM> according to an embodiment of the present disclosure are described below with reference to <FIG>. The image forming apparatus <NUM> according to the present embodiment is a tandem multicolor image forming apparatus in which process cartridges 20Y, <NUM>, 20C, and 20BK are arranged in parallel to each other, facing an intermediate transfer belt <NUM>. A developing device <NUM> (see <FIG>) as a filter holding device (a device with a filter) is disposed to face a photoconductor drum <NUM> in each of the process cartridges 20Y, <NUM>, 20C, and 20BK as illustrated in <FIG>.

In <FIG>, the image forming apparatus <NUM>, which is a main body of a color copier in the present embodiment, includes a document conveyor <NUM>, a scanner <NUM> as a document reading device, and a writing device <NUM> as an exposure device. The document conveyor <NUM> conveys a document to the scanner <NUM>. The scanner <NUM> reads image data of the document. The writing device <NUM> emits a laser beam based on input image data. In addition, the image forming apparatus <NUM> includes the process cartridges 20Y, <NUM>, 20C, and 20BK to form yellow, magenta, cyan and black toner images on respective surfaces of the photoconductor drums <NUM> (see <FIG>), respectively, and an intermediate transfer belt <NUM> on which the yellow, magenta, cyan and black toner images are transferred and superimposed. The image forming apparatus <NUM> further includes a sheet feeder <NUM> to accommodate sheets P such as paper sheets, a secondary transfer roller <NUM> to transfer the toner image formed on the intermediate transfer belt <NUM> onto the sheet P, and a fixing device <NUM> to fix an unfixed toner image on the sheet P. The image forming apparatus <NUM> still further includes toner containers <NUM> to supply toners of respective colors to the developing devices <NUM> of the plurality of process cartridges 20Y, <NUM>, 20C, and 20BK and a waste-toner container <NUM> to collect toner collected by cleaning devices <NUM> (see <FIG>) or untransferred toner collected by an intermediate transfer belt cleaner <NUM>.

Each of the process cartridges 20Y, <NUM>, 20C, and 20BK includes the photoconductor drum <NUM> as an image bearer, a charging device <NUM>, and the cleaning device <NUM>, which are united as a single unit as illustrated in <FIG>. Each of the process cartridges 20Y, <NUM>, 20C, and 20BK, which is expendable, is replaced with a new one when depleted in a main body of the image forming apparatus <NUM>. The developing device <NUM> is disposed facing the photoconductor drum <NUM> in each of the process cartridges 20Y, <NUM>, 20C, and 20BK. Each of the developing devices <NUM>, which is expendable, is replaced with a new one when depleted in a main body of the image forming apparatus <NUM>. An operator can independently perform the installation and the removal operation of the developing device <NUM> with respect to the main body of the image forming apparatus <NUM> and the installation and the removal operation of the process cartridges 20Y, <NUM>, 20C, and 20BK with respect to the main body of the image forming apparatus <NUM>, as different operations. In the process cartridges 20Y, <NUM>, 20C, and 20BK, toner images (yellow, magenta, cyan, and black) are formed on the respective photoconductor drums <NUM> as the image bearers.

A description is provided below of operations of the image forming apparatus <NUM> to form a normal color toner image. A conveyance roller of the document conveyor <NUM> conveys a document from a document table onto an exposure glass of the scanner <NUM>. The scanner <NUM> optically scans image data for the document on the exposure glass. The yellow, magenta, cyan, and black image data are transmitted to the writing device <NUM>. The writing device <NUM> irradiates the photoconductor drums <NUM> (see <FIG>) of the corresponding process cartridges 20Y, <NUM>, 20C, and 20BK with laser beams (as exposure light) L based on the yellow, magenta, cyan, and black image data, respectively.

Each of the four photoconductor drums <NUM> rotates clockwise in <FIG> (in a direction indicated by an arrow in <FIG>). The surface of the photoconductor drum <NUM> is uniformly charged at a position where the photoconductor drum <NUM> faces the charging device <NUM> that is a charging roller (a charging process). Thus, the surface of the photoconductor drum <NUM> is charged to a certain potential. When the charged surface of the photoconductor drum <NUM> reaches a position to receive the laser beam L emitted from the writing device <NUM>, an electrostatic latent image based on the image data is formed on the surface of the photoconductor drum <NUM> (an exposure process).

The laser beam L corresponding to the yellow image data is irradiated to the surface of photoconductor drum <NUM> in the process cartridge 20Y, which is the first from the left in <FIG> among the four process cartridges 20Y, <NUM>, 20C, and 20BK. A polygon mirror that rotates at high velocity deflects the laser beam L for yellow so that the laser beam L scans the surface of the photoconductor drum <NUM> along the rotation axis direction of the photoconductor drum <NUM> (i.e., the main scanning direction). Thus, an electrostatic latent image corresponding to the yellow component is formed on the photoconductor drum <NUM> charged by the charging device <NUM>. Similarly, the laser beam L corresponding to the cyan image data is irradiated to the surface of the photoconductor drum <NUM> in the second process cartridge 20C from the left in <FIG>, thus forming an electrostatic latent image for cyan on the surface of the photoconductor drum <NUM>. The laser beam L corresponding to the magenta image data is irradiated to the surface of the photoconductor drum <NUM> in the third process cartridge <NUM> from the left in <FIG>, thus forming an electrostatic latent image for magenta on the surface of the photoconductor drum <NUM>. The laser beam L corresponding to the black image data is irradiated to the surface of the photoconductor drum <NUM> in the fourth process cartridge 20BK from the left in <FIG>, thus forming an electrostatic latent image for black on the photoconductor drum <NUM>.

Then, the surface of the photoconductor drum <NUM> having the electrostatic latent image reaches a position opposite the developing device <NUM>. The developing device <NUM> supplies toner of each color onto the surface of the photoconductor drum <NUM> and develops the electrostatic latent image on the photoconductor drum <NUM> into a toner image (a development process). Subsequently, the surface of the photoconductor drum <NUM> after the development process reaches a position facing the intermediate transfer belt <NUM>. The primary transfer rollers <NUM> are disposed at the positions where the photoconductor drums <NUM> face the intermediate transfer belt <NUM> and in contact with an inner circumferential surface of the intermediate transfer belt <NUM>, respectively. At the positions of the primary transfer rollers <NUM>, the toner images on the photoconductor drums <NUM> are sequentially transferred to and superimposed on the intermediate transfer belt <NUM>, forming a multicolor toner image thereon (a primary transfer process).

After the primary transfer process, the surface of the photoconductor drum <NUM> reaches a position opposite the cleaning device <NUM>. The cleaning device <NUM> collects untransferred toner remaining on the photoconductor drum <NUM> (a cleaning process). The untransferred toner collected in the cleaning device <NUM> passes through a waste-toner conveyance path and is collected as waste toner in the waste-toner container <NUM>. Subsequently, a residual potential of the surface of the photoconductor drum <NUM> is removed at a position opposite the discharger, and a series of image forming processes performed on the photoconductor drum <NUM> is completed.

Meanwhile, the surface of the intermediate transfer belt <NUM>, onto which the single-color toner images on the photoconductor drums <NUM> are superimposed, moves in the direction indicated by arrow in <FIG> and reaches a position opposite the secondary transfer roller <NUM>. The secondary transfer roller <NUM> secondarily transfers the multicolor toner image on the intermediate transfer belt <NUM> onto the sheet P (a secondary transfer process). After the secondary transfer process, the surface of the intermediate transfer belt <NUM> reaches a position opposite the intermediate transfer belt cleaner <NUM>. The intermediate transfer belt cleaner <NUM> collects the untransferred toner on the intermediate transfer belt <NUM> to complete a series of transfer processes on the intermediate transfer belt <NUM>. The untransferred toner collected in the intermediate transfer belt cleaner <NUM> passes through the waste-toner conveyance path and is collected as waste toner in the waste-toner container <NUM>.

The sheet P is conveyed from the sheet feeder <NUM> to the position of the secondary transfer roller <NUM> via a registration roller pair <NUM>. Specifically, a feed roller <NUM> feeds the sheet P from top of multiple sheets P accommodated in the sheet feeder <NUM>. The sheet P is conveyed to a registration roller pair <NUM> through a sheet conveyance path. The sheet P that has reached the registration roller pair <NUM> is conveyed toward the position of the secondary transfer roller <NUM>, timed to coincide with the arrival of the multicolor toner image on the intermediate transfer belt <NUM>.

Subsequently, the sheet P, onto which the multicolor image is transferred, is conveyed to the fixing device <NUM>. The fixing device <NUM> includes a fixing roller and a pressure roller pressing against each other. In a nip between the fixing roller and the pressure roller, the multicolor toner image is fixed on the sheet P. After the fixing process, an output roller pair <NUM> ejects the sheet P as an output image to the main body of the image forming apparatus <NUM>. The ejected sheet P is stacked on an output tray <NUM> to complete a series of image forming processes.

Next, with reference to <FIG> and <FIG>, image forming units of the image forming apparatus are described in detail below. The four image forming units disposed in the main body of the image forming apparatus <NUM> (see <FIG>) have a similar configuration except the color of the toner used in the image forming processes. Therefore, parts of the image forming unit such as the process cartridge and the developing device are illustrated without suffixes Y, M, C, and BK, which denote the color of the toner, in the drawings.

As illustrated in <FIG>, the process cartridge <NUM> mainly includes the photoconductor drum <NUM> as the image bearer, the charging device <NUM>, and the cleaning device <NUM>, which are stored in a case of the process cartridge <NUM> as a single unit. The photoconductor drum <NUM> is an organic photoconductor designed to be charged with a negative polarity and includes a photosensitive layer formed on a drum-shaped conductive support. The charging device <NUM> is the charging roller including a conductive core and an elastic layer of moderate resistivity overlaid on the conductive core. A power supply applies a predetermined voltage to the charging device <NUM> that is the charging roller. The charging device <NUM> uniformly charges the surface of the photoconductor drum <NUM> opposite the charging device <NUM>. The cleaning device <NUM> includes a cleaning blade 23a and a cleaning roller 23b that contact the photoconductor drum <NUM>. For example, the cleaning blade 23a is made of rubber, such as urethane rubber, and contacts the surface of the photoconductor drum <NUM> at a predetermined angle with a predetermined pressure. The cleaning roller 23b is a brush roller in which brush bristles are provided around a core.

As illustrated in <FIG> and <FIG>, the developing device <NUM> mainly includes a developing roller 26a (serving as a developer bearer), a first conveying screw 26b1 (serving as a first conveyor) facing the developing roller 26a, a partition 26e, a second conveying screw 26b2 (serving as a second conveyor) facing the first conveying screw 26b1 via the partition 26e, and a doctor blade 26c (serving as a developer regulator) facing the developing roller 26a to regulate the amount of developer borne on the developing roller 26a. The developing device <NUM> in the present embodiment also functions as a filter holding device that holds the filter 26t (toner filter), which is described in detail later.

The developing device <NUM> stores a two-component developer including carrier and toner. The developing roller 26a is opposed to the photoconductor drum <NUM> with a small gap, thereby forming a developing range. As illustrated in <FIG>, the developing roller 26a includes stationary magnets 26a1 inside and a sleeve 26a2 that rotates around the magnets 26a01. The magnets 26a1 generate multiple poles (magnetic poles) around the outer circumferential surface of the developing roller 26a.

The first conveying screw 26b1 and the second conveying screw 26b2 as conveyors convey the developer stored in the developing device <NUM> in the longitudinal direction of the developing device <NUM>, thereby establishing a circulation path indicated by the dashed arrow in <FIG>. That is, the first conveying screw 26b1 establishes a first conveyance path B1, and the second conveying screw 26b2 establishes a second conveyance path B2. The circulation path of the developer includes the first conveyance path B1 and the second conveyance path B2. The partition 26e is an inner wall and separates the first conveyance path B1 from the second conveyance path B2, and the first conveyance path B1 and the second conveyance path B2 communicate with each other via first communication openings 26f and second communication openings <NUM> disposed at both ends of the first conveyance path B1 and the second conveyance path B2 in the longitudinal direction. Specifically, with reference to <FIG>, in a conveyance direction of the developer, an upstream end of the first conveyance path B1 communicates with a downstream end of the second conveyance path B2 via the first communication opening 26f. Additionally, in the conveyance direction of the developer, a downstream end of the first conveyance path B1 communicates with an upstream end of the second conveyance path B2 via the second communication opening <NUM>. That is, the partition 26e is disposed along the circulation path except both longitudinal ends of the circulation path. The first conveying screw 26b1 in the first conveyance path B1 is disposed opposite the developing roller 26a. The second conveying screw 26b2 in the second conveyance path B2 is disposed opposite the first conveying screw 26b1 in the first conveyance path B1 via the partition 26e. The first conveying screw 26b1 supplies developer to the developing roller 26a and collects the developer separated from the developing roller 26a after the development process, while conveying the developer in the longitudinal direction of the developing device <NUM>. The second conveying screw 26b2 stirs and mixes the developer conveyed from the first conveyance path B1 after the development process with a fresh toner supplied from a toner supply inlet 26d, while conveying the developer and the fresh toner in the longitudinal direction of the developing device <NUM>. In the present embodiment, the first conveying screw 26b1 and the second conveying screw 26b2 are horizontally arranged in parallel. Each of the first conveying screw 26b1 and the second conveying screw 26b2 includes a shaft and a screw blade wound around the shaft.

In the present embodiment, the developing device <NUM> includes two developing cases (an upper developing case <NUM> and a lower developing case 26j) that can be divided into upper and lower parts as a housing, and is covered by the two developing cases. The developing roller 26a, the first conveying screw 26b1, and the second conveying screw 26b2 are rotatably held in the lower developing case 26j. The doctor blade 26c is also held in the lower developing case 26j. Further, in the upper developing case <NUM>, the filter 26t is disposed in an opening portion 26k1 as described later. The upper developing case <NUM> is detachably attached to the lower developing case 26j in which the developing roller 26a, the first conveying screw 26b1, the second conveying screw 26b2, and the doctor blade 26c are disposed by fastening screws or the like.

The image forming processes, described above, are described focusing on the development process in further detail below with reference to <FIG> and <FIG>. The developing roller 26a rotates in the direction indicated by an arrow in <FIG>. As illustrated in <FIG> and <FIG>, the first conveying screw 26b1 and the second conveying screw 26b2 are disposed facing each other with the partition 26e interposed therebetween and rotate in directions indicated by arrows in <FIG> and <FIG>. Toner is supplied from the toner container <NUM> to the toner supply inlet 26d (serving as an inlet opening) via a toner supply path. As the first conveying screw 26b1 and the second conveying screw 26b2 rotate in the respective directions in <FIG>, the developer stored in the developing device <NUM> circulates together with the supplied toner in the longitudinal direction of the developing device <NUM> (the direction indicated by the dashed arrow in <FIG>) while being stirred and mixed with the supplied toner. The toner is charged by friction with carrier in the developer and electrostatically attracted to carrier. Then, the toner is scooped up on the developing roller 26a together with carrier by a developer scooping pole generated on the developing roller 26a. The developer borne on the developing roller 26a is conveyed in the counterclockwise direction indicated by the arrow in <FIG> to a position opposite the doctor blade 26c. The doctor blade 26c adjusts the amount of the developer on the developing roller 26a to a proper amount at the position. Subsequently, the rotation of the sleeve 26a2 conveys the developer to the developing area in which the developing roller <NUM> faces the photoconductor drum <NUM>. The toner in the developer is attracted to the electrostatic latent image formed on the photoconductor drum <NUM> due to the effect of an electric field generated in the developing area. Thereafter, as the sleeve 26a2 rotates, the developer remaining on the developing roller 26a reaches above the first conveyance path B1 and is separated from the developing roller 26a. The electric field in the developing area is formed by a specified voltage (in other words, a development bias) applied to the developing roller 26a by a development power supply and a surface potential (in other words, a latent image potential) formed on the photoconductor drum <NUM> in the charging process and the exposure process.

The toner in the toner container <NUM> is supplied from the toner supply inlet 26d to the developing device <NUM> via a toner replenishing path as the toner in the developing device <NUM> is consumed. The toner consumption in the developing device <NUM> is detected by a toner concentration sensor that magnetically detects a toner concentration in the developer (i.e., a ratio of toner to the developer) in the developing device <NUM>. The toner supply inlet 26d is disposed above an end of the second conveying screw 26b2 (the second conveyance path B2) in the longitudinal direction (the left and right direction in <FIG>).

The configuration and operation of the developing device <NUM> as the filter holding device according to the present embodiment are described in further detail below. As illustrated in, e.g., <FIG> and <FIG>, the developing device <NUM> in the present embodiment functions as the filter holding device in which the filter 26t is disposed in the opening portion 26k1 that communicates inside of the filter holding device with outside of the filter holding device. Specifically, the opening portion 26k1 (ventilation path) penetrating inside and outside is formed on the ceiling of the upper developing case <NUM> (housing) of the developing device <NUM>. The filter 26t is disposed so as to close the opening portion 26k1. The filter 26t collects toner as powder and ventilates the developing device <NUM>. In other words, the opening portion 26k1 (ventilation path) for sending air from inside to outside of the developing device <NUM> is formed in the upper developing case <NUM>. The filter 26t is disposed in the opening portion 26k1 as a mounting portion. The filter 26t is made of a screen having a mesh size that is smaller than the particle diameter of the toner T or the carrier C and thus allows only air to pass through. In the present embodiment, the opening portion 26k1 is opened in a substantially rectangular shape. The filter 26t, which is in a single state, is formed in a substantially rectangular shape.

A gap H (casing gap) between the developing roller 26a and the upper developing case <NUM> on a downstream side of the development area is set to be within the range of <NUM> to <NUM>. Note that, if the casing gap H is smaller than <NUM>, the developer carried on the developing roller 26a after the development process is not smoothly conveyed through the casing gap H between the developing roller 26a and the upper developing case <NUM>. Accordingly, the developer is likely to leak to the outside of the developing device <NUM>. On the other hand, when the casing gap H is larger than <NUM>, the developer carried on the developing roller 26a is not likely to be in sliding contact with the inner surface of the upper developing case <NUM>, and a suction airflow toward the inside of the developing device <NUM> due to a pump action is hardly generated. As a result, toner scattering from the developing device <NUM>, which is scattering of toner to the periphery of the development area, is likely to occur. Therefore, with the casing gap H kept within an appropriate range, leakage of the developer and toner scattering can be reduced. Further, the internal pressure of the developing device <NUM> is likely to increase due to the suction airflow through the casing gap H described above, and if the internal pressure increases, toner scattering may occur from gaps of the developing device <NUM>. On the other hand, in the present embodiment, since the opening portion 26k1 covered by the filter 26t is provided to collect the toner T, only air is ventilated while preventing the toner T from scattering to the outside. As a result, the increase of the internal pressure of the developing device <NUM> is restrained. That is, this configuration prevents toner scattering caused by the increase of the internal pressure of the developing device <NUM>.

In the present embodiment, when the filter 26t is in a single state (state in <FIG>) in which the filter 26t is not disposed in the opening portion 26k1, the filter 26t has a lower weight density per unit volume at a first side (the lower side in <FIG>) than at a second side (the upper side in <FIG>). That is, when the filter 26t is in a single state in which an external force does not act on the filter 26t, the weight density per unit volume is not uniform in the filter 26t. A portion having a low weight density and a portion having a high weight density are formed in a ventilation direction (communication direction). In other words, the filter 26t has a gradient of weight density per unit volume.

More specifically, in the present embodiment, the filter 26t has a two-layer structure. When the filter 26t is in a single state in which the filter 26t is not disposed in the opening portion 26k1, a low-density portion 26t2 having a low weight density per unit volume is formed at the first side (the lower side in <FIG>) of the filter 26t and a high-density portion 26t1 having a high weight density per unit volume is formed at the second side (the upper side in <FIG>) of the filter 26t. That is, in the filter 26t, the low-density portion 26t2 at the first side (upstream side in the ventilation direction) has coarse meshes and is relatively fluffy, while the high-density portion 26t1 at the second side (downstream side in the ventilation direction) has meshes in a denser state. Accordingly, when the filter 26t according to the present embodiment is in the single state, the toner collecting ability of the high-density portion 26t1 is higher than the toner collecting ability of the low-density portion 26t2.

In the developing device <NUM> of the present embodiment, the opening portion 26k1 has a rim 26k10 (wall) extending in a communication direction (ventilation direction, which is the vertical direction in <FIG> and <FIG>) from the inside of the developing device <NUM> to the outside of the developing device <NUM>. The filter 26t has the opening portion 26k1 such that the first side (having the low weight density) is located facing the inside of the developing device <NUM> (the lower side in <FIG>) and the second side (having the high weight density) is located facing the outside of the developing device <NUM> (the upper side in <FIG>). At least a part of the filter 26t disposed in the opening portion 26k1 contacts the rim 26k10 and is compressed in directions intersecting the communication direction (i.e., directions of black arrows in <FIG>). Specifically, the filter 26t is disposed in the opening portion 26k1 in a state where the filter 26t is compressed at the second side (the downstream side in the ventilation direction) by the rim 26k10 in the directions indicated by the black arrows (intersection directions) in <FIG>. More specifically, as illustrated in <FIG>, the filter 26t is disposed in the opening portion 26k1 in a state where the high-density portion 26t1 is compressed by the rim 26k10 in the directions indicated by the black arrows (intersection directions) in <FIG>. That is, in <FIG>, the state in which the filter 26t (high-density portion 26t1) is compressed and disposed (fitted) in the opening portion 26k1 is illustrated two-dimensionally. However, in fact, the filter 26t (high-density portion 26t1) is compressed from all quarters by contact with the substantially rectangular rim 26k10.

More specifically, as illustrated in <FIG>, a length N of the filter 26t in an intersection direction intersecting the communication direction is set to be larger than any one of opening widths M1 and M2 (lengths in the intersection direction) of the opening portion 26k1 in the single state (N > M2 > M1). As illustrated in <FIG>, the filter 26t is disposed in close contact with the opening portion 26k1 in a state of being compressed according to the shape of the opening portion 26k1. Specifically, the high-density portion 26t1 of the filter 26t disposed in the opening portion 26k1 is compressed at a high compression rate.

In the developing device <NUM> of the present embodiment, since the filter 26t is disposed in close contact with the opening portion 26k1, the defect that air (discharge object) leaks from lateral sides of the filter 26t (between the filter 26t and the opening portion 26k1) together with toner (collection object) is reduced. Accordingly, the function of the filter 26t described above is fully performed, and the defect that the toner (collection object) is scattered to the outside of the developing device <NUM> is reduced. In particular, since the filter 26t has a portion having a high weight-density per unit volume and easily enhances adhesion, at least the adhesion of the opening portion 26k1 in the portion is ensured. Thus, the above-described effect can be obtained. The filter 26t is formed such that the weight density increases from the upstream side to the downstream side in the ventilation direction (communication direction). Such a configuration facilitates formation of an air flow from the inside to the outside of the developing device <NUM>. Accordingly, the increase of the internal pressure in the developing device <NUM> can be efficiently restrained. The overall toner collection performance of the filter 26t can be enhanced, and the filter 26t is less likely to be clogged. In the state where the filter 26t is disposed in the opening portion 26k1 (in actual use state), a portion having a high weight density per unit volume (high-density portion 26t1) is compressed to further increase the weight density. The magnitude correlation of the weight density between the high-density portion 26t1 and the low-density portion 26t2 described above is maintained.

In the developing device <NUM> of the present embodiment, the rim 26k10 in the opening portion 26k1 is formed such that the opening area of the opening portion 26k1 continuously increases from the outside to the inside of the developing device <NUM> (from the upper side to the lower side in <FIG>). That is, with respect to a discharge direction (ventilation direction) in which air is discharged to the outside of the developing device <NUM>, the rim 26k10 is inclined (an inclined surface is formed in the rim 26k10) so as to move away from the central portion of the opening from the downstream side to the upstream side in the discharge direction. Such a configuration of the rim 26k10 allows the high-density portion 26t1 that easily enhances the adhesion with the rim 26k10 to be compressed at a higher compression rate. Thus, the adhesion of the filter 26t to the opening portion 26k1 can be enhanced. With the above-described configuration, the filter 26t can be easily assembled and removed from one side with respect to the upper developing case <NUM> in the state of being removed from the developing device <NUM>. Further, the upper end of the inclination of the rim 26k10 functions as a restricting portion for preventing the filter 26t from coming off to the outside of the developing device <NUM>.

In the developing device <NUM> of the present embodiment, stoppers 26r are detachably attached to contact the first side of the filter 26t (a portion having the low weight density, i.e., the low-density portion 26t2) facing the inside of the developing device <NUM> so that the filter 26t does not fall out from the opening portion 26k1 (rim 26k10) into the developing device <NUM>.

Specifically, when the filter 26t is attached, as illustrated in <FIG>, the filter 26t is moved from below the upper developing case <NUM> (opening portion 26k1) in the direction of the white arrow in <FIG>. As illustrated in <FIG>, the filter 26t is fitted into the opening portion 26k1. In order to prevent a defect that the filter 26t comes off downward, the stoppers 26r are fixed (screw-fastened) to the upper developing case <NUM> by screws <NUM> so as to hold the filter 26t from below. Then, the upper developing case <NUM> in which the filter 26t (and the stoppers 26r) is attached is installed in the developing device <NUM> (lower developing case 26j). In the present embodiment, a plate-shaped member having an opening inside is used as the stopper 26r. The stopper 26r is not limited to this as long as the function of the filter 26t is not impaired. As the stopper 26r, for example, a mesh-shaped member having a coarse mesh may also be used. Further, in the present embodiment, the substantially rectangular-parallelepiped filter 26t is used. The shape of the filter 26t is not limited to this. For example, the filter 26t may be formed in a quadrangular-pyramid shape so as to match with the shape of the rim 26k10 having the inclined surface.

In the present embodiment, as the filter 26t, a filter having a two-layer structure including the high-density portion 26t1 and the low-density portion 26t2 is used. On the other hand, as illustrated in <FIG>, a filter 26t having a single-layer structure can be used. In the single-layer structure, the weight density per unit volume of the filter 26t gradually increases in the direction of the arrow in <FIG> from the first side (facing the inside of the developing device <NUM>) to the second side (facing the outside of the developing device <NUM>) in a single state in which the filter 26t is not disposed in the opening portion 26k1. Such a filter 26t is formed such that the weight density per unit volume gradually increases along the ventilation direction (exhaust direction). Specifically, the filter 26t illustrated in <FIG> has a coarse and relatively fluffy state at the first side, and is denser toward the second side. Further, as illustrated in <FIG>, a filter 26t having a multiple-layer structure (three layers or more) can be used. In the multiple-layer structure, the weight density per unit volume of the filter 26t gradually increases from the first side (facing the inside of the developing device <NUM>) to the second side (facing the outside of the developing device <NUM>) in a single state in which the filter 26t is not disposed in the opening portion 26k1. In such a filter 26t, a plurality of layers are formed such that the weight density per unit volume gradually increases along the ventilation direction (exhaust direction). Specifically, the filter 26t illustrated in <FIG> has a coarse and relatively fluffy state at the first side, and is denser and is laminated toward the second side.

As illustrated in <FIG>, in a developing device <NUM> in a first variation, rims 26k11 and 26k12 of an opening portion 26k1 have the opening area of the opening portion 26k1 gradually increasing from the outside of the developing device <NUM> toward the inside of the developing device <NUM>. Specifically, the opening portion 26k1 having a two-stage structure includes a first rim 26k11 having a small opening area formed on the outside of the developing device <NUM> (upper side in <FIG>) and a second rim 26k12 having a large opening area on the inside of the developing device <NUM> (lower side in <FIG>). In the first variation, a high-density portion 26t1 of a filter 26t is fitted to the first rim 26k11. A low-density portion 26t2 contacts the second rim 26k12 and is compressed in the direction of the black arrow in <FIG>. Even such a configuration can reduce a defect that air in the developing device <NUM> is discharged to the outside of the developing device <NUM> together with toner without passing through the filter 26t. As in the first variation, even when the rims 26k11 and 26k12 are formed so that the opening area stepwisely decreases, similar to the case where the opening area of the rim 26k10 is continuously decreased as illustrated in <FIG>, an attaching and detaching operability of the upper developing case <NUM> to the opening portion 26k1 is improved. The step of the rims 26k11 and 26k12 prevents the filter 26t from coming off the device.

As illustrated in <FIG>, a developing device <NUM> (see <FIG>) in a second variation includes a restricting portion 26k15 that restricts the filter 26t from coming out of the developing device <NUM> from the opening portion 26k1 (rim 26k10). Specifically, the restricting portion 26k15 that protrudes in the direction of narrowing the opening is formed above the opening portion 26k1 (rim 26k10) in the upper developing case <NUM>. The restricting portion 26k15 is formed such that the second side of the filter 26t (a portion having a high weight density, i.e., a high-density portion 26t1) can be contacted. Disposing the restricting portion 26k15 in this way can prevent a defect that the filter 26t disposed in the opening portion 26k1 comes out of the developing device <NUM>. Further, the position of the filter 26t in the opening portion 26k1 in the vertical direction can be easily determined.

As illustrated in <FIG>, in a developing device <NUM> (see <FIG>) in a third variation, a rim 26k10 of an opening portion 26k1 includes a protruding portion 26k20 is formed so as to compress a filter 26t at the second side (a portion having a high weight density, i.e., a high-density portion 26t1) in the directions of black arrows in <FIG> (the directions intersecting the communication direction). Specifically, the rim 26k10 (opening portion 26k1) in an upper developing case <NUM> does not have an inclined surface unlike the upper developing case <NUM> in <FIG>. The rim 26k10 has the protruding portion 26k20 (convex portion) that protrudes in the direction of narrowing the opening at a position above the central portion in the communication direction. In particular, the protruding portion 26k20 is formed over the entire circumference of the substantially rectangular rim 26k10. Even with such a configuration, the high-density portion 26t1 of the filter 26t disposed in the opening portion 26k1 is compressed by the protruding portion 26k20. Thus, a defect that air in the developing device <NUM> is discharged to the outside of the developing device <NUM> together with toner without passing through the filter 26t can be reduced.

As illustrated in <FIG>, in a developing device <NUM> in a fourth variation, the communication direction of an opening portion 26k1 is not the vertical direction as illustrated in <FIG> but the substantially horizontal direction (in the direction of the white arrows in <FIG>). Specifically, the upper developing case <NUM> is formed with a portion extending in a substantially vertical direction at a position facing a developing roller 26a. The upper developing case <NUM> includes the opening portion 26k1 formed in the portion.

The opening portion 26k1 includes a rim 26k10 extending in a substantially horizontal direction. A filter 26t is disposed (fitted) on the rim 26k10. The filter 26t includes a low-density portion 26t2 and a high-density portion 26t1. The low-density portion 26t2 at the first side of the filter 26t is located facing the inside of the developing device <NUM> (right side in <FIG>). The high-density portion 26t1 at the second side of the filter 26t is located facing the outside of the developing device <NUM> (left side in <FIG>). Further, also in the fourth variation, the rim 26k10 has an inclination, and the high-density portion 26t1 is compressed by the rim 26k10 in the directions intersecting the communication direction. Even such a configuration can reduce a defect that air in the developing device <NUM> is discharged to the outside of the developing device <NUM> together with toner without passing through the filter 26t.

As illustrated in <FIG>, a rim 26k10 of a developing device <NUM> (see <FIG>) in a fifth variation is formed in a tapered shape such that the opening area of an opening portion 26k1 continuously decreases from the inside of the developing device <NUM> to the outside of the developing device <NUM>. Further, in the fifth variation, a filter 26t is not a two-layer structure of the high-density portion 26t1 and the low-density portion 26t2 but a one-layer structure in which the weight density per unit volume is formed substantially uniformly. In the case of the rim 26k10 (opening portion 26k1) configured in this way, even if the filter 26t is not only in the two-layer structure but also in the one-layer structure, the filter 26t is formed such that the weight density per unit volume on the outside of the developing device <NUM> is larger than the weight density per unit volume on the inside of the developing device <NUM> in a state in which the filter 26t disposed in the opening portion 26k1. That is, in the filter 26t disposed in the opening portion 26k1, the degree of compression on the outside of the developing device <NUM> is larger than degree of compression on the inside of the developing device <NUM>. Accordingly, the defect that air (discharge object) in the developing device <NUM> leaks together with toner (collection object) from the lateral sides of the filter 26t (between the filter 26t and the opening portion 26k1) is reduced. In the present embodiment, since the filter 26t is disposed in close contact with the opening portion 26k1, the defect that air (discharge object) leaks from the lateral sides of the filter 26t (between the filter 26t and the opening portion 26k1) together toner (collection object) is further reduced. As a result, the function of the filter 26t is fully performed, and the defect that toner (collection object) is scattered to the outside of the developing device <NUM> is reduced. The filter 26t is disposed such that the weight density increases from the upstream side to the downstream side in the ventilation direction (communication direction), thus facilitates formation of the air flow from the inside to the outside of the developing device <NUM>. Accordingly, the increase of the internal pressure in the developing device <NUM> can be efficiently restrained. The overall toner collection property of the filter 26t can be enhanced, and the filter 26t is less likely to be clogged. Note that, in the fifth variation, the rim 26k10 can also be formed in a stepped manner so that the opening area of the opening portion 26k1 gradually decreases from the inside of the developing device <NUM> to the outside of the developing device <NUM>.

In the embodiments from here, an opening portion is larger on the outside than on the inside of the developing case. With such a configuration, the following effects can be attained. A filter 26t can be easily replaced without opening the developing case (an upper developing case <NUM> and a lower developing case 26j) during a maintenance of the filter replacement (even if the upper developing case <NUM> is not detachably attached on the lower developing case 26j). Even if the developing cases (the upper developing case <NUM> and the lower developing case 26j) are fixed to each other with an adhesive or the like and the upper developing case <NUM> is not be attached to or detached from a developing case 26j, the filter 26t can be easily replaced. When compressing a rectangular filter, a part with low weight density (small repulsive force) is compressed more, and a part with high weight density (large repulsive force) can be less compressed. A defect such as bending or variation of the casing gap H due to the repulsive force during compression can be reduced. Since the area of the portion having a high weight density and being likely to be clogged can be increased, the product life of the filter 26t can be extended.

In a developing device <NUM> according to the present embodiment, an opening portion 26k1 has a rim 26k10 (wall) extending in the communication direction (ventilation direction, which is the vertical direction in <FIG> and <FIG>) from the inside of the developing device <NUM> to the outside of the developing device <NUM>. A filter 26t disposed in the opening portion 26k1 such that the first side (having a low weight density) is located facing the inside of the developing device <NUM> (lower side in <FIG>), and the second side (having a high weight density) is located facing the outside of the developing device <NUM> (upper side in <FIG>). The filter 26t disposed in the opening portion 26k1 contacts the rim 26k10 and is compressed at the first side (having the low weight density) in directions intersecting the communication direction (directions of black arrows in <FIG>). Specifically, as illustrated in <FIG>, the filter 26t is disposed in the opening portion 26k1 in a state where a low-density portion 26t2 is compressed by the rim 26k10 in the directions indicated by the black arrows (intersection directions) in <FIG>. That is, in <FIG>, a state in which the filter 26t (low-density portion 26t2) is compressed and disposed (fitted) in the opening portion 26k1 is illustrated two-dimensionally. However, in fact, the filter 26t (low-density portion 26t2) is compressed from all quarters by contact with the substantially rectangular rim 26k10.

More specifically, as illustrated in <FIG>, a length N of the filter 26t in an intersection direction intersecting the communication direction is set to be larger than each of opening widths M1 and M2 (lengths in the intersection direction) of the opening portion 26k1 in a single state (N > M1 > M2). As illustrated in <FIG>, the filter 26t is disposed in close contact with the opening portion 26k1 in a state of being compressed according to the shape of the opening portion 26k1. Specifically, although the high-density portion 26t1 of the filter 26t disposed in the opening portion 26k1 is also be compressed to some extent, the low-density portion 26t2 of the filter 26t is compressed at a high compression rate. Even in a state where the filter 26t is disposed in the opening portion 26k1 in such manner, the weight density per unit volume of the high-density portion 26t1 is higher than the weight density per unit volume of the low-density portion 26t2.

As described above, in the developing device <NUM> of the present embodiment, the weight density per unit volume of the filter 26t on the outside of the developing device <NUM> is larger than the weight density per unit volume on the inside of the developing device <NUM>. A defect that air (discharge object) in the developing device <NUM> leaks together with toner (collection object) from the lateral sides of the filter 26t (between the filter 26t and the opening portion 26k1) is reduced. In the present embodiment, since the filter 26t is disposed in close contact with the opening portion 26k1, the defect that air (discharge object) leaks from the lateral sides of the filter 26t (between the filter 26t and the opening portion 26k1) together with toner (collection object) is further reduced. Accordingly, the function of the filter 26t described above is fully performed, and a defect that toner (collection object) is scattered to the outside of the developing device <NUM> is reduced. In particular, since the filter 26t has a portion having a low weight-density per unit volume and is easily compressed, at least the adhesion of the opening portion 26k1 in the portion is ensured. Thus, the above-described effect can be more easily obtained. The filter 26t is formed such that the weight density increases from the upstream side to the downstream side in the ventilation direction (communication direction), thus facilitating formation of the air flow from the inside to the outside of the developing device <NUM>. Accordingly, the increase of the internal pressure in the developing device <NUM> can be efficiently restrained. The overall toner collection performance of the filter 26t can be enhanced, and the filter 26t is less likely to be clogged. In the state where the filter 26t is disposed in the opening portion 26k1 (actual use condition), the portion having a low weight density per unit volume (low-density portion 26t2) is compressed to increase the weight density. However, the portion having the low weight density per unit volume (low-density portion 26t2) is not be increased as much as the portion having a high weight density per unit volume (high-density portion 26t1).

In the present embodiment, the rim 26k10 in the opening portion 26k1 is formed such that the opening area in the opening portion 26k1 decreases continuously from the outside to the inside of the developing device <NUM> (from the upper side to the lower side in <FIG>). That is, the rim 26k10 is inclined (an inclined surface is formed in the rim 26k10) so as to move away from the central portion of the opening from the upstream side to the downstream side in the discharge direction (ventilation direction) in which air is discharged to the outside of the developing device <NUM>. Such a configuration of the rim 26k10allows the low-density portion 26t2, which is easily compressed, to be compressed at a higher compression rate. Thus, the adhesion of the filter 26t to the opening portion 26k1 can be enhanced. The filter 26t can be easily assembled from the outside of the developing device <NUM>, and the filter 26t can be easily removed from the developing device <NUM>. Further, the lower end of the inclination of the rim 26k10 functions as a restricting portion for preventing the filter 26t from dropping into the developing device <NUM>.

In the present embodiment, the filter 26t is formed so as to be attached to and detached from the outside of the developing device <NUM> (outside the device). In the developing device <NUM> of the present embodiment, stoppers 26r are detachably attached to the outside of the developing device <NUM>. The stoppers 26r contact of the filter 26t at the first side (a portion having a high weight density, i.e., a high-density portion 26t1) facing the outside of the developing device <NUM> so that the filter 26t does not fall out from the opening portion 26k1 (rim 26k10) to the outside of the developing device <NUM>.

Specifically, when the filter 26t is attached, as illustrated in <FIG>, the filter 26t is moved from above the developing device <NUM> (opening portion 26k1) in the direction of the white arrow in <FIG>. As illustrated in <FIG>, the filter 26t is fitted into the opening portion 26k1. In order to prevent a defect that the filter 26t comes off upward, the stoppers 26r are fixed (screw-fastened) to the developing case (the upper developing case <NUM> and the lower developing case 26j) by screws <NUM> so as to press the filter 26t from above. In the present embodiment, a plate-shaped member having an opening inside is used as the stopper 26r. The stopper 26r is not limited to this as long as the function of the filter 26t is not impaired. As the stopper 26r, for example, a mesh-shaped member having a coarse mesh may also be used. Further, in the present embodiment, the substantially rectangular-parallelepiped filter 26t is used. The shape of the filter 26t is not limited to this. For example, the filter 26t may be formed in a quadrangular-pyramid shape so as to match with the shape of the rim 26k10 having an inclined surface.

In the present embodiment, as the filter 26t, a filter having a two-layer structure including the high-density portion 26t1 and the low-density portion 26t2 is used. On the other hand, as illustrated in <FIG>, a filter having a structure so that the weight density per unit volume of the filter 26t gradually increase in the direction of the arrow in <FIG> from the first side (facing the inside of the developing device <NUM>) to the second side (facing the outside of the developing device <NUM>) in a single state in which the filter 26t is not disposed in the opening portion 26k1 can be used. That is, such a filter 26t is formed such that the weight density per unit volume gradually increases along the ventilation direction (exhaust direction). Specifically, the filter 26t illustrated in <FIG> has a coarse and relatively fluffy state at the first side and is denser toward the second side. Such a filter 26t can be manufactured, for example, by laminating a plurality of layers having different weight densities per unit volume, as illustrated in <FIG>.

As illustrated in <FIG>, in a developing device <NUM> in a sixth variation, rims 26k11 and 26k12 of an opening portion 26k1 have the opening area of the opening portion 26k1 stepwisely decreasing from the outside of the developing device <NUM> toward the inside of the developing device <NUM>. Specifically, the opening portion 26k1 having a two-stage structure includes a first rim 26k11 having a large opening area formed at the second side facing the outside of the developing device <NUM> (upper side in <FIG>) and a second rim 26k12 having a small opening area formed at the first side facing the inside of the developing device <NUM> (lower side in <FIG>). In the sixth variation, a high-density portion 26t1 of a filter 26t is fitted to the first rim 26k11. A low-density portion 26t2 contacts the second rim 26k12 and is compressed in the directions of black arrows in <FIG>. Even such a configuration can reduce a defect that air in the developing device <NUM> is discharged to the outside of the developing device <NUM> together with toner without passing through the filter 26t. As in the first variation, even when the rims 26k11 and 26k12 are formed such that the opening area is stepwisely decreased, similar to the case where the opening area of the rim 26k10 is continuously decreased as illustrated in <FIG>, the attaching and detaching operability of the filter 26t with respect to the opening portion 26k1 is enhanced. The step of the rims 26k11 and 26k12 restrains the filter 26t from dropping in the developing device <NUM>.

As illustrated in <FIG>, A developing device <NUM> in a seventh variation includes a restricting portion 26k15 that restricts a filter 26t from dropping in the developing device <NUM> from an opening portion 26k1 (rim 26k10). Specifically, the restricting portion 26k15 that protrudes in the direction of narrowing the opening is formed below the opening portion 26k1 (rim 26k10) in the developing case (the upper developing case <NUM> and the lower developing case 26j). The restricting portion 26k15 is formed such that the first side of the filter 26t (a portion having a low weight density, i.e., a low-density portion 26t2) can be contacted. Such a configuration of the restricting portion 26k15 can prevent a defect that the filter 26t disposed in the opening portion 26k1 drops inside the developing device <NUM>. Further, the position of the filter 26t in the opening portion 26k1 in the vertical direction is easily be determined.

As illustrated in <FIG>, in a developing device <NUM> of an eighth variation, stoppers 26r (filter cover) are detachably attached to the outside of the developing device <NUM>. The stoppers 26r contact the first side (a portion having a high weight density, i.e., a high-density portion 26t1) of a filter 26t so that the filter 26t does not come off from an opening portion 26k1 (rim 26k10) to the outside of the developing device <NUM>. The stopper 26r in the eighth variation has a plurality of projections 26r1 (ribs) capable of contacting the filter 26t (high-density portion 26t1) from the outside of the developing device <NUM>. Specifically, the projections 26r1 are formed so as to protrude downward from a plate-shaped portion that is not an annular plate-shaped member and not provided with a through-hole. At least four projections 26r1 are provided at intervals in the longitudinal direction and the lateral direction so as to press the substantially rectangular parallelepiped filter 26t in a well-balanced manner. The stopper 26r is formed such that the portions other than the plurality of projections 26r1 face the filter 26t with a gap. The air that has passed through the filter 26t from the inside of the developing device <NUM> is discharged to the outside of the developing device <NUM> through the gap between the stopper 26r and the filter 26t. Pressing the central portion of the filter 26t with the stopper 26r provided with the plurality of projections 26r1 in this way can reduce a defect that the central portion of the filter 26t is lifted by the air discharged from the developing device <NUM>. The stopper 26r is preferably attached to and detached from the developing device <NUM> by a snap-on clip or the like so that only a part of the outer rims (for example, four corners) of the plate-shaped portion of the stopper 26r does not interfere with the exhaust from the above-described gap.

As illustrated in <FIG>, a filter 26t disposed in a developing device <NUM> in a ninth variation is also formed in a substantially rectangular parallelepiped shape in a single state. Specifically, in the state of a single state, the filter 26t has a rectangular shape, and has a thickness Z1 (thickness in the communication direction), a length D in the longitudinal direction (longitudinal direction orthogonal to the communication direction), and a length N in the lateral direction (orthogonal in the communication direction). In the ninth variation, in a state where the filter 26t is disposed in an opening portion 26k1 (developing device <NUM>), the thickness in the longitudinal direction orthogonal to the communication direction is smaller at both ends in the longitudinal direction than the thickness in the central portion in the longitudinal direction. That is, as illustrated in <FIG>, when the filter 26t disposed in the opening portion 26k1 is viewed in the longitudinal direction (the direction corresponding to the vertical direction of paper surface in <FIG>), in the filter 26t, the thickness Z2 at both ends in the longitudinal direction is smaller than the thickness Z1 at the central portion in the longitudinal direction (Z1 > Z2). Specifically, in the developing device <NUM> in the ninth variation, the opening portion 26k1 has a two-stage structure. A first rim 26k11 having a large opening width D' (which is equal to or slightly smaller than the directional length D of the filter 26t) is formed at the second side facing the outside of the developing device <NUM> (upper side of <FIG>) when viewed in the longitudinal direction. A second rim 26k12 having a small opening width is formed at the first side facing the inside of the developing device <NUM> (the lower side in <FIG>). The depth Z2 (length in the communication direction) of the first rim 26k11 is set smaller than the thickness Z1 of the filter 26t (Z2 < Z1). The filter 26t disposed in the two-stage opening portion 26k1 is in a state where both ends in the longitudinal direction are pressed in the vertical and horizontal directions by the stepped portions. Even when the dimensional tolerance of the length D in the longitudinal direction of the filter 26t is large, both ends in the longitudinal direction are surely pressed by the above-described step of the opening portion 26k1 and come into close contact with the opening portion 26k1. Accordingly, a defect that air in the developing device <NUM> is discharged to the outside of the device together with toner from between the opening portion 26k1 and the filter 26t can be reduced. That is, in the ninth variation, when the filter 26t disposed in the opening portion 26k1 is viewed in the lateral direction (the direction corresponding to the left-right direction in <FIG>), as illustrated in <FIG>, the filter 26t is disposed in the opening portion 26k1 (the rim formed in a tapered shape) with the lower part compressed to the dimension M2 (< M1 ≤ N) in the lateral direction. In this way, only both ends in the longitudinal direction of the filter 26t are pressed in the vertical direction (thickness direction), and both ends in the lateral direction are not pressed in the vertical direction (thickness direction). This is because if the filter 26t in the lateral direction is pressed in the vertical direction, the degree of compression of the low-density portion 26t2 may be too large and the filter function may be reduced.

As described above, the developing device <NUM> in the present embodiment is a filter holding device in which the filter 26t is disposed in the opening portion 26k1 that communicates the inside and the outside of the developing device <NUM>. The opening portion 26k1 has a rim 26k10 extending in a communication direction from the inside of the developing device <NUM> to the outside of the developing device <NUM>. The filter 26t is formed such that the weight density per unit volume at the first side of the filter 26t is lower than the weight density per unit volume at the second side of the filter 26t in a single state in which the filter 26t is not disposed in the opening portion 26k1. The filter 26t is disposed in the opening portion 26k1 such that the first side is located facing the inside of the developing device <NUM> and the second side is located facing the outside of the developing device <NUM>. At least a part of the filter 26t is compressed in the direction that intersects with the communication direction by contact with the rim 26k10. Specifically, in a state where the filter 26t is disposed in the opening portion 26k1, the filter 26t has a larger weight density per unit volume at the second side facing the outside of the developing device <NUM> than at the first side facing the inside of the developing device <NUM>. Accordingly, a defect that air (discharge object) in the developing device <NUM> is discharged to the outside of the developing device <NUM> together with toner (collection object) can be reduced.

In the present embodiment, the process cartridge <NUM> does not include the developing device <NUM>, and the developing device <NUM> is a unit that can be independently attached to and detached from the main body of the image forming apparatus <NUM>. Alternatively, the developing device <NUM> may be one of the constituent members of the process cartridge <NUM>, and the process cartridge <NUM> may be configured to be integrally attached to and detached from the main body of the image forming apparatus <NUM>. In such a configuration, similar effects to those of the above-described embodiments and variations can also be attained. It is to be noted that the term "process cartridge" used in the present disclosure means a removable unit including an image bearer and at least one of a charging device to charge the image bearer, a developing device to develop a latent image on the image bearer, and a cleaning device to clean the image bearer that are united together, and is designed to be detachably attached as a united part in the body of the image forming apparatus.

In the present embodiments, the present disclosure is applied to the developing device <NUM> in which two conveying screws 26b1 and 26b2 (serving as the conveyors) are horizontally arranged in parallel and the doctor blade 26c is disposed below the developing roller 26a. The configuration of the developing device to which the present disclosure is applied is not limited to the above-described configurations. The present disclosure may be applied to other developing devices such as a developing device in which three or more conveyors are arranged in parallel in the horizontal direction, a developing device in which multiple conveyors are arranged in parallel in the vertical direction, and a developing device in which the doctor blade is disposed above the developing roller. In the present embodiments, the present disclosure is applied to the developing device <NUM> that contains the two-component developer including toner and carrier. Alternatively, the present disclosure may also be applied to a developing device that contains the one-component developer (i.e., toner, which may include additives). Such cases also provide substantially the same effects as the effects described above.

In the present embodiments, the present disclosure is applied to the developing device <NUM> as the filter holding device, but the filter holding device to which the present disclosure is applied is not limited to this. The present disclosure can be applied to any type of device containing powder such as toner inside, for example, the toner containers <NUM>, the waste-toner containers <NUM>, the cleaning devices <NUM>, the intermediate transfer belt cleaner <NUM>, the toner replenishment devices, and the toner conveyors. Further, in the present embodiments, the present disclosure is applied to the developing device <NUM> as a filter holding device configured to discharge an air as a discharge object to the outside of the developing device <NUM>. The filter holding device (combination of the discharge object and the collection object) to which the present disclosure is applied is not limited to this. For example, the present disclosure can be applied to the main body of the image forming apparatus <NUM> as a filter holding device configured to collect ozone as a collection object and discharge air as a discharge object (air not containing ozone) to the outside of the image forming apparatus <NUM>. Further, in the present embodiment, the high-density portion 26t1 of the filter 26t is configured to be largely compressed in the direction intersecting the communication direction by the inclined surface of the rim 26k10. The entire side surface (non-ventilated surface) of the filter 26t can also be configured to be compressed by the rim 26k10 in the direction intersecting the communication direction. A portion other than the high-density portion 26t1 may be configured to be compressed by the rim 26k10 in a direction intersecting the communication direction. If the adhesion (sealability) between the side face of the filter 26t and the rim 26k10 can be ensured, such a configuration may be adopted. Such cases also provide substantially the same effects as the effects described above.

The present embodiments are illustrative and do not limit the present disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present disclosure. It is therefore to be understood that within the scope of the present disclosure, the present disclosure may be practiced otherwise than as specifically described herein. Further, the number, position, shape, and the like, of components are not limited to those of the present embodiment, and may be the number, position, shape, and the like, that are suitable for implementing the present disclosure.

Claim 1:
A developing device (<NUM>) comprising:
an opening portion (26k1) configured to communicate an inside of the developing device with an outside of the developing device, the opening portion having a rim (26k10) that extends in a communication direction from the inside of the developing device toward the outside of the developing device; and
a filter (26t) disposed in the opening portion, the filter including:
a first side facing the inside of the developing device; and
a second side facing the outside of the developing device,
characterized in that
the filter has a larger weight density per unit volume at the second side than at the first side in a state in which the filter is disposed in the opening portion, and
wherein in the state in which the filter is disposed in the opening portion such that the first side of the filter faces the inside of the developing device and the second side of the filter faces the outside of the developing device, the filter is compressed at the first side in intersection directions intersecting the communication direction by contact with the rim.