HK1069216B

HK1069216B - Developing device and image forming apparatus

Info

Publication number: HK1069216B
Application number: HK05102512.0A
Authority: HK
Inventors: Sato Shougo; Horinoe Mitsuru
Original assignee: Brother Kogyo Kabushiki Kaisha
Priority date: 2003-03-28
Filing date: 2005-03-23
Publication date: 2009-10-23

Description

Developing device and image forming apparatus

Technical Field

The present invention relates to an image forming apparatus like a color laser printer and a developing device installed in the image forming apparatus.

Background

A tandem color laser printer is known as an electrophotographic color laser printer. The tandem color laser printer includes a plurality of process units, the number of which is the same as the number of toner colors of yellow, magenta, cyan, and black. Each process unit has a developer tank, a supply roller, a developing roller, and a photosensitive drum.

In the tandem color laser printer, toner of each color stored in a developer tank is supplied to a developing roller of each process unit by a supply roller. The electrostatic latent image carried on the photosensitive drum is developed by a developing roller, while forming a toner image of each color. A color image is thus formed at substantially the same speed as a black and white laser printer.

Like this tandem color laser printer, japanese patent laid-open No.9-274423 discloses a tandem color laser printer in which each processing unit is horizontally arranged in parallel with each other.

However, in the tandem color laser printer in the previous patent, the developer tank is disposed above the supply roller, and the weight of the toner stored in the developer tank is directly applied to the supply roller from above. As a result, even when the supply roller rotates, the toner scraped off the developing roller by the supply roller cannot circulate, but stays in the vicinity of the supply roller. If toner is supplied from the supply roller to the developing roller, blurring of an image is caused by such a failure of scraping off the toner.

Disclosure of Invention

The invention provides a developing device with better imaging effect and an imaging instrument provided with the developing device.

According to an aspect of the present invention, a developing device detachably attached to a main casing of an image forming apparatus includes a developer tank containing a developer; a developer carrier that carries a developer; a supply device disposed opposite to the developer carrier and for supplying the developer stored in the developer tank to the developer carrier, and a first wall disposed between the developer tank and the supply device and covering an upper portion of the supply device when the developing device is mounted in the main casing of the image forming apparatus. When the developing device is mounted in the main casing of the image forming apparatus, the developer carrier and the supplying device are disposed below the developer tank. According to this structure, when the first wall covering the upper portion of the supplying device is disposed between the developer tank and the supplying device therebelow, the weight of the developer stored in the developer tank can be borne by the first wall, thereby preventing the weight of the developer from directly acting on the supplying device. As a result, the developer scraped off from the developer carrier can flow without interference with the movement of the supplying device, and image blurring caused by failure of developer circulation is reduced, thereby obtaining a good image forming effect. Wherein the first wall is disposed in such a manner that the supply device is stored in a projection plane in a vertical direction of the first wall when the developing device is accommodated in the main casing of the image forming apparatus. Such a structure can more reliably prevent the weight of the developer from directly acting on the supply device.

According to still another aspect of the present invention, the first wall is configured such that when the developing device is disposed in the main casing of the image forming apparatus, the developer is moved between the first wall and the supplying device with movement of the supplying device, resulting in a flowable developer. This structure can ensure sufficient circulation of the developer and prevent blurring of the picture.

According to yet another aspect of the invention, the first wall is disposed adjacent the supply device. This configuration has an advantage in that, when the developing device is mounted in the image forming apparatus, the weight of the developer can be more stably prevented from directly acting on the supplying device.

According to an aspect of the present invention, the developing device may further include: a layer thickness regulating member that regulates a thickness of the developer on the developer carrier at a downstream side from a facing position of the developer carrier and the supplying device with respect to a moving direction of the developer carrier; a second wall having a first end above the layer thickness regulating member near a facing position of the developer and the layer thickness regulating member when the developing device is mounted in the main casing of the image forming apparatus. This configuration has an advantage that the second wall helps the developer to flow over the layer thickness regulating member with the movement of the developer carrier when the developing device is mounted in the image forming apparatus. Thus, the second wall can prevent the developer from accumulating above the layer thickness regulating member. As a result, sufficient circulation of the developer is ensured and image blurring is prevented.

According to one aspect of the invention, the first end of the second wall is inclined downwardly and the second end of the second wall is inclined upwardly. In this way, the flow of the developer generated above the layer thickness regulating member as the developer carrier moves can be guided to the developing chamber through the second wall.

According to an aspect of the present invention, the developer carrier is a developing roller, the supplying device is a supplying roller, the developing roller and the supplying roller are configured such that, when the developing device is disposed in the main casing of the image forming apparatus, an angle formed by a first line horizontally passing through a rotation center of the developing roller and a second line connecting the rotation center of the developing roller and the rotation center of the supplying roller is greater than or equal to 45 °. This structure may be sufficient to ensure that the developer flows out of the developer tank, circulates under the first wall and the area in contact with the supply device, and thereby stably supplies the developer circulated from the supply device to the developer carrier.

According to an aspect of the present invention, the developer is a toner containing spherical particles. Thus, the toner has good fluidity and can stably circulate.

According to one aspect of the invention, the bulk density of the loading of the developer upon initial use is greater than or equal to 0.646 g/ml. At the time of initial use, the developer can be sufficiently transferred from the developer tank to the supply device. Thus, it is possible to prevent a decrease in imaging density in early use, thereby ensuring a good imaging effect.

According to an aspect of the present invention, the developing device may further include an agitator disposed in the developer tank to agitate the developer, the agitator moving in the same direction as the flow of the developer generated in the vicinity of the developer carrier by the movement of the developer carrier, at a position closest to the developer carrier. This structure is characterized in that, when the developing device is mounted in the image forming apparatus, the flow of the developer along with the movement of the developer carrier can be merged into the flow of the developer agitated in the same direction as the agitating device. Thus, the flow of the developer can be more stabilized, thereby stably circulating the developer.

According to an aspect of the present invention, the developer carrier and the supplying device are in face-to-face contact and move in opposite directions at the contact position. Such a configuration enables the developer supplied to the developer carrier by the supply device to be efficiently filled. This can provide a good developing effect. Further, the undeveloped developer remaining on the developer carrier can be removed by the supply device without waste.

According to an aspect of the present invention, a developing device detachably attached to a main casing of an image forming apparatus includes: a developer tank containing a developer; a developer carrier that carries a developer; a supply device disposed opposite to the developer carrier and supplying the developer stored in the developer tank to the developer carrier; and a first wall that prevents the weight of the developer contained in the developer tank from directly acting on the supply device. When the developing device is mounted in the main casing of the image forming apparatus, the developer carrier and the supplying device are disposed below the developer tank. According to this structure, when the first wall is disposed between the developer tank and the supply device therebelow, the weight of the developer stored in the developer tank can be borne by the first wall. As a result, the developer scraped off from the developer carrier can flow without interference with the movement of the supplying device, and image blurring caused by failure of developer circulation is reduced, thereby obtaining a good image forming effect.

According to an aspect of the present invention, the developing device further includes: a layer thickness regulating member that regulates a thickness of the developer carried on the developer carrier on a downstream side with respect to a moving direction of the developer carrier from a facing position of the developer carrier and the supplying device; and a second wall that prevents the developer from accumulating above the layer thickness regulating member when the developing device is mounted in the main casing of the image forming apparatus. According to this structure, the second device can cause the developer to flow over the layer thickness regulating member with the movement of the developer carrier when the developing device is mounted in the main casing of the image forming apparatus. This ensures the circulation of the developer, and prevents blurring of the image.

According to an aspect of the present invention, an image forming apparatus may include a host computer and a developing unit detachably connected to the host computer. The developing unit may include: a developer tank containing a developer; a developer carrier that carries a developer; a supply device disposed opposite to the developer carrier and supplying the developer stored in the developer tank to the developer carrier, and a first wall disposed between the developer tank and the supply device and covering an upper portion of the supply device when the developing device is mounted in the main casing of the image forming apparatus. When the developing device is mounted in the main casing of the image forming apparatus, the developer carrier and the supplying device are disposed below the developer tank. According to this configuration, since the image forming apparatus is provided with the developing device which prevents the developer from failing to circulate, the image blur can be reduced, thereby obtaining a good image forming effect.

According to an aspect of the present invention, an image forming apparatus includes a plurality of developer tanks of the same number as a plurality of developer colors, a developer carrier, a supply device, and a first wall. According to this structure, since a developer image can be formed for each color, a color image can be formed quickly. Further, since the first wall or the first means is provided for each color, the circulating current of the developer for each color can be secured, preventing the color image from being blurred.

According to one aspect of the present invention, the imaging apparatus includes a plurality of second walls of the same number as the plurality of developer colors. This structure can ensure the circulating current of the developer of each color, and prevent the blurring of the color image more stably.

According to another aspect of the present invention, a developer unit for use with an electrophotographic printer apparatus includes a housing having a front wall, a rear wall, a top wall, and a pair of side walls. The housing is divided into a toner chamber and a developing chamber. A first wall extends from the front wall into the housing to establish a toner chamber in which an agitator is installed and a developing chamber. The supply roller is mounted in the developing chamber adjacent to the first wall and the front wall, and the developing roller is mounted in the developing chamber in contact with the supply roller on a side away from the first wall. The regulating blade extends from the rear wall and contacts the developing roller. Further, a second wall surface of the free end contacting the regulating blade on a side opposite to a side where the regulating blade contacts the developing roller extends from the rear wall. The second wall is joined to the rear wall closer to the toner chamber than a free end of the second wall is received by the regulating blade. With this structure, it is possible to more reliably prevent the weight of the developer from directly acting on the supply roller, ensure the circulation of the developer and prevent fogging.

Drawings

Embodiments of the invention are described in detail with reference to the following drawings:

FIG. 1 is a side cross-sectional view of a color laser printer core component as an imaging apparatus according to an embodiment of the present invention;

FIG. 2 is an enlarged side sectional view of a core component of the processing unit of FIG. 1;

FIG. 3 is an enlarged side sectional view of the core component of FIG. 2;

fig. 4 is a side sectional view of a core member showing the photosensitive drum and the developing unit attached to and detached from the main casing of the color laser printer shown in fig. 1.

Detailed Description

Fig. 1 is a side sectional view of a core part of a color laser printer as an image forming apparatus according to an embodiment of the present invention.

In fig. 1, a color laser printer 1 is a tandem type laser color printer in which a plurality of process units 16 are arranged in series with each other in a horizontal direction. The color laser printer 1 includes, in a main casing 2: a sheet feeding unit 4 that supplies the sheet 3; an image forming section 5 that forms an image on the sheet 3 fed therein; and a sheet ejecting device 6 for ejecting the image-formed sheet 3.

The main casing 2 has a rectangular box shape in side sectional view. The main housing 2 is configured to be openable from the upper side and has a top cover 7 on the upper side. The top cover 7 is rotatably supported relative to the hinge 8 at the rear side of the main casing 2 (the left side of fig. 1 is considered as the rear side and the right side is considered as the front side in the following description), and is provided so as to be openable and closable relative to the main casing 2 as indicated by the broken lines in the drawings.

The top cover 7 includes: a sheet discharge slot 9 that discharges the sheet 3; a sheet discharge tray 10 recessed toward the sheet discharge slot 9; and a kick-out roller 11 provided at the rear end of the sheet discharge tray 10 in the sheet discharge slot 9. When the top cover 7 is opened or closed, the sheet release slot 9, the sheet release tray 10, and the eject roller 11 move integrally with the top cover 7.

The sheet feeding unit 4 includes a sheet supply tray 12, a sheet supply roller 13, and a conveying roller 14 at the bottom in the main casing 2. The sheet supply tray 12 is detachably attached to the main casing 12 in a horizontal direction from the front side. The sheet supply roller 13 is provided at one end (front side) in an upper portion of the sheet supply tray 12. The conveying roller 14 is disposed on the downstream side of the sheet feeding direction of the sheet supply roller 13.

In the sheet supply tray 12, sheets are stacked in a stack, and the uppermost sheet in the stack is sent one by one toward the conveying roller 14 under rotation of the sheet supply roller 13, and is conveyed from the conveying roller 14 to a conveying position between the conveying belt 67 and the photosensitive drum 56.

A guide member 15 is provided in the vertical direction between the sheet supply roller 13 and the conveying roller 14. The sheet 3 supplied by the sheet supply roller 13 is guided to the conveying roller 14 by the guide member 15, and conveyed by the conveying roller 14 toward the conveying position at the conveying belt 67 and the respective photosensitive drums 56 at the rear position.

The image forming section 5 includes a process unit 16, a conveying section 17, and a fixing section 18. Each of the plurality of color toners is provided with a process unit 16. That is, the process units 16 are a yellow process unit 16Y, a magenta process unit 16M, a cyan process unit 16C, and a black process unit 16K. The processing units 16 are sequentially disposed at prescribed intervals so as to overlap each other in the horizontal direction.

Each process unit 16 is the same in shape, structure, and operation, and includes a scanner unit 19, a developing unit 20 as a developing device, and a photosensitive drum unit 21.

The scanning units 19 are spaced from the conveyor belt 67 at prescribed intervals in the vertical direction, and each scanning unit 19 is fixed to the main casing 2.

As shown in fig. 2, the scanning unit 19 includes a laser emitting section (not shown), a polygon mirror 23, two lenses 24, 25, and three reflecting mirrors 26, 27, 28 in a scanning box 22.

The scanner housing 22 is substantially rectangular in side sectional view, and is mounted to the main housing 2 in its longitudinal vertical orientation. A window 29 through which the laser beam is emitted is formed on a wall surface of the scanner box 22 toward the photosensitive drum unit 21.

In the scanning unit 19, the laser beam emitted from the laser emitting portion based on the print data passes through the polygon mirror 23, the lens 24, the mirror 26, the mirror 27, the lens 25, the mirror 28 in order, and is emitted from the window 29. The laser beam emitted from the window 29 directly reaches the photosensitive drum 56 by high-speed scanning.

Each scanning unit 19 is disposed at substantially the same position in the vertical direction. That is, the scanning units 19 are disposed so as to overlap each other in the horizontal direction (fig. 1).

Each developing unit 20 is detachably mounted on the main casing 2, and includes, in the developing tank 30: a toner chamber 31 as a developer container; a supply roller 32 as a supply device; a developing roller 33 as a developer carrier; and a layer thickness regulating blade 34 as a layer thickness regulating member.

The developing tank 30 is substantially rectangular in a side sectional view, and the lower side thereof is openable. A support member 35 for supporting the developing tank 30 is provided on the ceiling wall 42. The support member 35 is configured such that it protrudes upward in a substantially triangular form from the top wall 42 of the developing tank 30 in a side sectional view. The front face of the support member 35 is shaped in a saw-tooth fashion to enable it to be securely held by hand.

The rear wall 43 of the developer tank 30 is configured to be substantially parallel to the plane of the front wall of the scanner tank 22.

The front wall 44 of the developer tank 30 is configured in cross section such that the corner of the top end thereof is curved in an arc line to connect with the top wall 42. The middle portion of the front wall 44 with respect to the up-down direction is configured to be substantially parallel to the rear wall 43. The lower end portion of the front wall 42 is an agitator covering wall 36 as a first wall surface, which is a portion facing the agitator provided in the toner chamber 31, and is configured to be a curved line along the rotational path of the agitator 48 in a side view.

A cover wall 37 covering the supply roller 32 and the developing roller 33 is formed below the agitator cover wall 36 in the front wall 44 of the developing tank 30.

In a side sectional view, the cover wall 37 is bent continuously from the rear end portion of the agitator facing wall 36 to extend toward the rear curve. The cover wall 37 is integrally constituted by a supply roller upper wall portion 38, a supply roller inclined wall portion 39, a supply roller front side cover wall 40, and a developing roller front side cover wall portion 41. The supply roller upper wall portion 38 functioning as a first wall extends forward in the horizontal direction. The supply roller inclined wall portion 39 functioning as a first wall extends forward and rearward from the front end of the supply roller upper wall portion 38. In the side sectional view, the supply roller front side cover wall 40 extends in a curve from the front end of the supply roller inclined wall portion 39 continuously along the outer surface of the supply roller 32 (a curve in which both the top end and the bottom end are set back and the middle portion is set forward). The developing roller front-side cover wall portion 41 is continuously bent from the rear end portion of the supply roller front-side cover wall portion 30 extending curvilinearly rearward, and extends forward and rearward.

The supply roller upper wall portion 38 and the supply roller inclined wall portion 39 are interposed between the toner chamber 31 and the supply roller 32, covering the supply roller 32 from above. Specifically, the supply roller upper wall portion 38 and the supply roller inclined wall portion 39 are close to the supply roller 32, so that the roller portion of the supply roller 32 can be completely placed in the projection plane of the supply roller upper wall portion 38 and the supply roller inclined wall portion 39 in the vertical direction, and particularly, the rear end portion of the supply roller upper wall portion 38 is positioned further rearward than the rear side of the supply roller 32.

A blade support wall 45, which is bent from a lower end portion of the rear wall 43 of the developing tank 30 and extends upward toward the front, is attached to the rear wall 43. The free end of the blade support wall 45 faces the rear side of the developing roller 33.

A guide wall 46 as a second wall extends slightly downward toward the front near the lower end portion of the rear wall 43 of the developing tank 30, and covers the blade support wall 45 from above. More specifically, the rear end of the guide wall 46 extends from the rear wall 43 so that the front end portion is located above the developing roller 33 and near the position where the developing roller 33 and the layer thickness regulating blade 34 face each other. Therefore, the front end portion of the guide wall 46 close to the developing roller 33 and the rear end portion far from the developing roller 33 are inclined downward and upward, respectively, with respect to the horizontal direction while covering the blade support wall 45 and the layer thickness regulating blade 34 from above.

The guide wall 46 is a plane and extends over the entire width of the developing tank 30 (perpendicular to the front-to-rear direction in plan view).

The developing tank 30 is made of a material such as polyethylene resin. The rear wall 43 and the guide wall 46 are formed together. The upper wall 42, the front wall 44 (including the agitator facing wall 36 and the cover wall 37), the blade support wall 45 and the two side walls 51 are formed integrally. Two side walls 51 extend from both side faces of the front wall 44 to the rear wall 43 oppositely with respect to the width thereof. The rear end portion of the top wall 42 and the rear end portions of the two side walls 51 are welded to the upper end portion and the two side portions of the rear wall 43, respectively. The rear end portion of the blade support wall 45 is welded to the lower end portion of the rear wall 43. Thus forming the developing tank 30.

In the developing tank 30, an upper layer inner space from the top wall 42 to a lower end portion of the agitator facing wall 36 (that is, a rear end portion of the agitator facing wall 36 which is bent continuous to the supply roller upper wall portion 38) is constituted as the toner chamber 31. The lower internal space, that is, the bottom space from the supply roller upper wall portion 38 to the lower end portion of the developing roller front-side cover wall portion 41 in the vertical direction, constitutes a developing chamber 47 including the supply roller 32, the developing roller 33 and the layer thickness regulating blade 34 therein.

The toner chamber 31 contains a nonmagnetic single-component polymer toner as a developer, and needs to be charged positively. In the toner chamber 31, each process unit 16 includes one color toner. The yellow process unit 16Y includes yellow toner, the magenta process unit 16M includes magenta toner, the cyan process unit 16C includes cyan toner, and the black process unit 16K includes black toner.

More specifically, the toner of each color is a polymer toner with substantially spherical particles obtained by copolymerization. The binder resin in the polymer toner is a main component, and is obtained by copolymerizing a styrene-based monomer such as styrene and an acrylic-based monomer such as acrylic acid, alkyl (C1-C4) acrylate and alkyl (C1-C4) methacrylate by a known polymerization method such as suspension polymerization. A colorant, a charge control agent, and a wax are added to the polymer toner to form toner base particles. An external additive is also added to improve the fluidity of the polymerized toner.

As the coloring agent, yellow, magenta, cyan and black coloring agents were prepared. As the charge control agent, a charge control agent obtained by copolymerization of an ionic monomer having an ionic functional group (e.g., ammonium salt) with a monomer copolymerizable with the ionic monomer (e.g., styrene-based monomer and propylene-based monomer) is used. The external additive is an inorganic powder such as metal oxide powder, carbonized powder and metal salt powder. The metal oxide powder includes silicon, aluminum oxide, titanium oxide, strontium titanate, cerium oxide and magnesium oxide.

The polymer toner is prepared by copolymerization, and has spherical particle shape and uniform particle size, so that the polymer toner has good fluidity.

In this example, the toner has a bulk density of 0.646g/ml or more at the initial use (including a non-use state). Such toner can be sufficiently supplied from the toner chamber 31 to the supply roller 32 even at the time of initial use. Thus, it is possible to prevent a decrease in imaging density in early use, thereby ensuring a good imaging effect.

The loading bulk density was obtained by injecting more than 100ml of the toner into a cylindrical tube, beating the cylindrical tube 180 times, separating the upper portion of the cylindrical tube to scrape 100ml of the toner, and measuring the weight thereof with a powder testing instrument PT-R manufactured by Hosokawa Micron.

An agitator 48 as an agitating device that agitates the toner is disposed at a lower portion of the toner chamber 31. The agitator 48 includes a rotary shaft 49 rotatably supported on both side walls 51, and an agitating member 50 composed of a thin film extending radially from the rotary shaft 49.

In the agitator 48, powder is input from a motor (not shown) to the rotary shaft 49, and the rotary shaft 49 starts to rotate, so that the agitator 50 rotates in the arrow direction (clockwise). When the stirring member 50 is in contact with the stirrer facing wall 36 of the front wall 44 of the developing tank 30, the free end of the stirring member 50 is bent toward the downstream side in the rotational direction of the stirring member 50 and slides over the stirrer facing wall 36. By the agitation of the agitator 50, the toner in the toner chamber 31 flows from the rear end portion of the agitator facing wall 36 to the developing chamber 47 (refer to the first flow F1).

The supply roller 32 is disposed along a supply roller front-side cover wall portion 40 formed curvilinearly below the supply roller upper wall portion 38 at the front upper side of the developing chamber 47.

More specifically, the supply roller 32 is located such that it is spaced from the supply roller upper wall portion 38 by a distance of 0-10 mm. The distance between the supply roller 32 and the supply roller front side cover wall portion 40 is set to 0-2 mm.

The supply roller 32 is obtained by wrapping a metal roller shaft 32a with a drum made of conductive sponge. The outer diameter of the supply roller 32 is smaller than the outer diameter of the developing roller 33 (the outer diameter of the supply roller 32 is ≡ 13 in this embodiment). A roller shaft 32a of the supply roller 32 is rotatably supported on both side walls 51 of the developing tank 30, and powder is transported from a motor (not shown) to the roller shaft during development.

When the powder is conveyed from a motor (not shown) to the supply roller 32, the supply roller 32 rotates in the arrow direction (counterclockwise), rotating in the opposite rotational direction to the developing roller 33 at the nip portion where the supply roller 32 contacts the developing roller 33. The peripheral speed of the supply roller 32 is 0.5 to 2 times (0.73 times in this embodiment) the peripheral speed of the developing roller 33.

The developing roller 33 faces the supply roller 32, and presses the supply roller 32 below the supply roller 32 at the front lower side of the developing chamber 47. The developing roller 33 faces the developing roller front-side cover wall portion 41 on the front side and the blade support wall 45 on the rear side. The lower side surface of the developing roller 33 is exposed to the outside of the developing tank 30.

More specifically, as shown in fig. 3, an angle formed by a first line L1 passing horizontally through the rotational center of the developing roller 33 roller shaft 33a and a second line L2 connecting the rotational center of the driving roller 33 roller shaft 33a and the rotational center of the supply roller 32 roller shaft 32a is equal to 45 ° or more than 45 ° and less than 90 ° (70 ° in this embodiment).

As shown in fig. 2, the developing roller 33 is obtained by wrapping a metal roller shaft 33a with a roller portion made of an elastic member such as a conductive rubber material. More specifically, the cylinder portion of the developing roller 33 is provided with an elastic cylinder portion of a double-layer structure and a coating layer covering the surface of the cylinder portion. The elastic roller portion is made of a conductive rubber including carbon-containing particles such as urethane rubber, silicone rubber and ethylene propylene diene terpolymer (EPDM) rubber. The coating material is composed of urethane rubber, urethane resin, polyimide resin or other materials as main components. The outer diameter of the developing roller 33 is smaller than the outer diameter of the photosensitive drum 56 (in this embodiment, the outer diameter of the developing roller 33 is ≡ 20 mm). A roller shaft 33a of the developing roller 33 is rotatably supported on both side walls 51 of the developing tank 30, and powder is transported from a motor (not shown) to the roller shaft 33a during development. When the powder is conveyed from the motor to the developing roller 33, the developing roller 33 rotates in the arrow direction (counterclockwise), rotating in the same rotational direction as the photosensitive drum 56 at the nip portion where the developing roller 33 contacts the photosensitive drum 56. The peripheral speed of the developing roller 33 is 0.5 to 2 times (1.6 times in this embodiment) the peripheral speed of the photosensitive drum 56. During development, a developing bias is applied to the roller shaft 33a of the developing roller 33 from a powder supply (not shown).

A diaphragm member 52 is provided at the developing roller front side cover wall portion 41 to press against the front side surface of the developing roller 33. The film member 52 can prevent toner from leaking out from the gap between the front side surface of the developing roller 33 and the developing roller front-side cover wall portion 41.

The layer thickness regulating blade 34 is disposed across the entire width of the developing tank 30 toward the downstream side of the developing roller 33 in the rotational direction of the developing roller 33, where the developing roller 33 faces the supply roller 32. The layer thickness regulating blade 34 includes a blade body 53 made of a metal plate spring member and a pressing member 54 provided at the free end of the blade body 53, made of an insulating silicone rubber, and having a substantially semicircular cross section.

The blade main body 53 is attached at a proximal end to the top surface of the blade support wall 45, and a free end of the blade main body 53 extends forward from the blade support wall 45 and faces the upper side surface of the developing roller 33.

Sponge material (not shown) is placed on the top surface (toward the guide wall 46) at the free end of the blade body 53, and the free end of the guide wall 46 is in contact with the sponge material from above. This structure can prevent the toner scraped off by the developing roller 33 from flowing between the guide wall 46 and the layer thickness regulating blade 34 and accumulating on the upper side of the layer thickness regulating blade 34.

The pressing member 54 is provided on the bottom surface at the free end of the blade body 53, and is pressed by the upper side surface of the developing roller 33 due to the elasticity of the blade body 53.

In the above-described configuration, the upper side of the developing roller 33 is in contact with the supply roller 32 on the front side and in contact with the pressing member 54 of the layer thickness regulating blade 34 on the rear side at a distance from the nip formed with the supply roller 32. Therefore, the contact of the upper side of the developing roller 33 with the toner is at the gap between the nip with the supply roller 32 and the contact portion with the pressing member 54. The gap distance is set to 2 to 10mm (7 mm in this embodiment), which is the length of the developing roller 33 in the circumference.

In the above configuration, the leading end of the guide wall 46 is joined to the top surface of the free end of the vane main body 53, and the trailing end is connected to the rear wall 43, so that the rear of the guide wall is at an angle of 0 degree or more with respect to the horizontal(20 degrees in this embodiment) is angled upward, covering the vane body 53 and the vane support wall 45.

In the above-described configuration, the supply roller upper wall portion 38, the supply roller 32, and the developing roller 33 overlap each other in the vertical direction. More specifically, in the vertical direction, the supply roller 33 is completely covered by the supply roller upper wall portion 38, and the rear side surface of the developing roller 33 is exposed outside the supply roller upper wall portion 38.

When the toner stored in the toner chamber 31 flows from the rear end of the agitator facing wall 36 toward the developing chamber 47 by the agitation of the agitating member 50, the toner is supplied to the developing roller 33 by the rotation of the supply roller 32 while being charged with positive charge between the supply roller 32 and the developing roller 33. At this time, when the supply roller 32 and the developing roller 33 rotate in opposite directions at the nip, the toner supplied from the supply roller 32 to the developing roller 33 is effectively charged, achieving a good developing effect. Further, the toner that has not been developed to the photosensitive drum 56 and remains on the developing roller 33 can be carried away by the supply roller 32 without waste.

When the toner supplied to the developing roller 33 by the frictional charging enters between the pressing member 54 of the layer thickness regulating blade 34 and the developing roller 33 with the rotation of the developing roller 33, the toner is uniformly regulated to a prescribed thickness and is carried on the developing roller 33.

In the developing chamber 47, during development, the toner flows from the toner chamber 31 to the developing chamber 47 with the stirring of the stirring member 50 through the rear end portion of the stirrer confronting wall 36, thereby forming a first flow F1. With the rotation of the supply roller 32, the toner flows from the supply roller 32 to the developing roller 33, thereby forming the second flow F2. The toner scraped off from the upper side surface of the developing roller 33 by the layer thickness regulating blade 34 is returned to the toner chamber 31 along the guide wall 46 by the rotation of the developing roller 33, thereby forming a third flow F3.

In the toner chamber 31, the toner of the third flow F3 flows into the toner chamber 31 by the agitator 48 in the same rotation as the flow direction of the third flow F3, is agitated in the toner chamber 31, and then flows as the first flow F1 from the rear end portion of the agitator facing wall 36 toward the developing chamber 47.

In this way, during development, the toner can be sufficiently circulated in each developing unit 20.

Each of the developing units 20 is substantially at the same position in the vertical direction, that is, overlaps each other in the horizontal direction (see fig. 1). More specifically, each developing unit 20 and each scanning unit 19 are alternately overlapped with each other in the horizontal direction above the sheet supply tray 12 (fig. 1).

Each of the photosensitive drum units 21 is detachably fixed to the main casing 2, and includes a photosensitive drum 56 and a scorotron charger (scorotron charger)57 housed in a drum casing 55. The photosensitive drum 56 faces the developing roller 33.

The drum cover 55 is formed with the drum storage member 58 and the backup plate portion 59. The drum storage part 58 is substantially a rectangular frame with a through opening, and the supporting plate portion 59 extends upward from the drum storage part 58 to accommodate the cover wall 37 of the developing tank 30.

The photosensitive drum 56 is constituted by a metal cylindrical tube made of aluminum, and is coated with a photosensitive layer of an organic photosensitive composition containing polycarbonate as a main component. The outer diameter of the photosensitive drum 56 is larger than the outer diameter of the developing roller 33 (the outer diameter of the photosensitive drum 56 is ≡ 30mm in this embodiment). The photosensitive drum 56 is rotatably supported on both side walls of the drum storage member 56 via a rotary shaft 60. During powder transfer, powder is transferred from a motor (not shown) to the rotating shaft 60. When the powder is conveyed from the motor, the photosensitive drum 56 rotates in the arrow direction (clockwise), rotating in the same rotational direction as the conveying belt 67 at the nip portion where the photosensitive drum 56 contacts the conveying belt 67.

The scorotron charger 57 is fixed to the rear wall of the drum storage 58 at a distance from the rear side of the photosensitive drum 56. The scorotron charger 57 is of the positive charge type, and generates a corona discharge by a charging wire like a tungsten wire. The scorotron charger 57 uniformly charges the surface of the photosensitive drum 56 with positive charges by applying a voltage from a power supply (not shown).

When the photosensitive drum 56 rotates, the scorotron charger 57 uniformly charges the surface of the photosensitive drum 56 with a positive charge. Then, as the photosensitive drum 56 rotates, the laser beam emitted from the scanner unit 19 scans the surface of the photosensitive drum 56 at high speed, thereby forming an electrostatic latent image with reference to image data. When the photosensitive drum 56 faces the developing roller 33, the positively charged toner carried on the developing roller 33 moves to a portion of the electrostatic latent image formed on the surface of the photosensitive drum 56, the potential of which becomes low due to exposure to the laser beam. As a result, the latent image becomes visible, resulting in a positive image. Thus, a toner image of each color is formed on the surface of the photosensitive drum 56.

Each of the photosensitive drum units 21 is substantially at the same position in the vertical direction, that is, overlaps with each other in the horizontal direction (see fig. 1). The respective photosensitive drums 56 face the respective developing rollers 33 of the respective developing units 20 and overlap each other in the vertical direction.

The developing unit 20 and the photosensitive drum unit 21 are detachably attached to the main casing 2 in the vertical direction, see fig. 4. On the upper rear side, guide shafts 61 are attached to both side walls 51 of each developing tank 30, protruding outward with respect to the width of the process unit 16.

The developing unit guide grooves 62 are formed on the side wall of the main casing 2 in association with designated positions of each developing unit 20. The developing unit guide grooves 62 extend perpendicularly to the side wall of the main casing 2. When the top cover 7 is opened, the upper end of the developing unit guide groove 62 is opened upward from the upper end of the main casing 2. A buffer spring 63 is disposed at a lower end of each developing unit guide groove 62 to elastically contact the guide rod 61 when the developing unit 20 is in place.

Drum unit guide grooves 64 are formed on the side walls of both sides of the main casing 2 in association with the designated positions of each of the drum units 21. The photosensitive drum unit guide groove 64 extends perpendicularly to the side wall of the main casing 2 and is parallel to the developing unit guide groove 62. When the top cover 7 is opened, the upper end of the photosensitive drum unit guide groove 64 is opened upward from the upper end of the main casing 2. A torsion spring 71 is disposed at the lower end of each photosensitive drum unit guide groove 64, pressing on the rotary shaft 60 of the photosensitive drum 56.

By engaging the rotary shaft 60 of the photosensitive drum 56 and the guide rod 61 of the developing tank 30 in the photosensitive drum guide groove 64 and the developing unit guide groove 62, respectively, and moving them downward, the developing unit 20 and the photosensitive drum unit 21 can be placed in the positions shown by the solid lines. The developing unit 20 and the photosensitive drum unit 21 can be detached from the specified positions as indicated by broken lines.

When the developing unit 20 and the photosensitive drum unit 21 are at the specified positions, the rotary shaft 60 of the photosensitive drum 56 is positioned due to the pressure of the torsion spring 71.

On the upper front side, one contact lever 72 is attached on both sides of each developing tank 30, protruding outward with respect to the width of the process unit 16. When the developing tank 30 is at the specified position, the contact lever 72 is pressed by the pressing lever 73 on the main casing 2, thereby positioning the developing roller 33 with respect to the photosensitive drum 56.

The plunger 73 moves to a retracted position shown by a broken line and a pressing position shown by a solid line in accordance with driving of a motor (not shown). When the photosensitive drum 56 rotates, the pressing lever 73 moves to the pressing position, and when the photosensitive drum 56 stops rotating, the pressing lever 73 moves to the retracted position. Therefore, the setting of the developing roller 33 can be reliably brought into contact with the photosensitive drum 56. The pressing lever 73 can be operated by the opening/closing time of the top cover 7 without depending on the motor.

In the color laser printer 1, the developing unit 20 is detachably attached to the photosensitive drum unit 21, the developing unit 20 and the photosensitive drum unit 21 may be separated together from the main casing 2, and the developing unit 20 may be separated from the photosensitive drum unit 21 and remain attached to the main casing 2.

The conveying member 17 opposes each developing unit 20 via each photosensitive drum 56 in each main casing 2, as shown in fig. 1. The conveying member 17 includes a driving roller 65, a driven roller 66, a conveying belt 67, and a transfer roller 68. The transfer roller 68 and the photosensitive drum 56 are opposed to each other.

The drive roller 65 is disposed forward and leads the photosensitive drum 56 in the yellow process unit 16Y. The driven roller 66 is disposed rearward and behind the photosensitive drum 56 in the black process unit 16K.

The conveyor belt 67 is an endless belt made of conductive resin such as polycarbonate and polyimide, in which conductive particles such as carbon particles are dispersed. The conveyor belt 67 extends between the drive roller 65 and the driven roller 66. The conveyor belt 67 is in contact with all the photosensitive drums 56 of the respective process units 16 on the outer contact surface thereof.

When the driving roller 65 is driven, the driven roller 66 rotates, and the conveying belt 67 revolves counterclockwise between the driving roller 65 and the driven roller 66 in the same direction as the photosensitive drum 56 of each process unit 16 on the contact surface.

The transfer roller 68 is disposed inside the conveyor belt 67, and opposes each photosensitive drum 56 of each process unit 16 via the conveyor belt 67. The transfer roller 68 is made by wrapping a metal roller shaft with a roller made of an elastic member such as a conductive rubber material. The transfer roller 68 rotates in the counterclockwise direction, rotating in the same direction as the conveyor belt 67 at the contact surface between the transfer roller 68 and the conveyor belt 67. During conveyance, the transfer roller 68 may be subjected to conveyance deviation.

The sheet 3 supplied from the sheet feeding unit 4 is conveyed by the conveying rollers 14, passing between the conveying belt 67 moved by the driving roller 65 and the driven roller 66 and the photosensitive drum 56 of each process unit 16. As the sheet 3 passes therebetween, the toner image of each color formed on the photosensitive drum 56 of each process unit 16 is transferred onto the sheet 3, so that a color image appears on the sheet 3.

For example, when the yellow toner image formed on the photosensitive drum 56 of the yellow process unit 16Y is transferred onto the sheet 3, the magenta toner image formed on the photosensitive drum 56 of the magenta process unit 16M is transferred onto the sheet 3 to which the yellow toner image has been transferred. In this order, the cyan toner image formed by the cyan process unit 16C and the black toner image formed by the black process unit 16K are sequentially transferred and superimposed, so that a color image is formed on the sheet 3.

When the color laser printer 1 is a tandem printer, since the photosensitive drums 56 of the respective colors are included, the image forming speed of the toner images of the respective colors is substantially the same as that of the black-and-white image, and thus a faster color image is obtained.

The fixing member 18 is disposed on the rear side, at a position behind the process unit 16 and the conveying member 17, on the downstream side in the sheet conveying direction. Fixing unit 18 includes heat roller 70 and pressure roller 69. The heat roller 70 is made of a metal tube having a release layer on the surface thereof and contains a halogen lamp in its axial direction. The surface of the heat roller 70 is heated to a fixing temperature by a halogen lamp. Pressing roller 69 is used to press heat roller 70.

The color image transferred onto the sheet 3 is heat-fixed while passing between the heat roller 70 and the pressure roller 69 on the fixing section 18.

The sheet ejecting section 6 includes a sheet discharge slot 9, a sheet discharge tray 10, and an ejecting roller 11. The sheet 3 on which the image has been heat-fixed is ejected from the main casing 2 by the eject roller 11 from the sheet discharge slot 9 and is stacked on the sheet discharge tray 10.

In each developing unit 20 of the color laser printer 1, a supply roller upper wall portion 38 is provided at the front wall 44 of the developing tank 30, and the supply roller upper wall portion 38 covers the upper portion of the supply roller 32 so as to be separated from the toner chamber 31. Thus, the weight of the toner stored in the toner chamber 31 is received by the supply roller upper wall portion 38, thereby preventing the weight of the toner from directly acting on the supply roller 32.

Thus, the toner between the supply roller upper wall portion 38 and the upper portion of the supply roller 32 flows along the rotation of the supply roller 32, so that the second flow F2 in which the toner flows from the supply roller 32 toward the developing roller 33 is generated. This prevents the flow of toner generated by the rotation of the supply roller 32 from being stopped. The toner scraped off from the developing roller 33 by the supply roller 32 flows along the second flow F2, joins the toner of the third flow F3, enters the toner chamber 31, and is mixed with other toner to form a circulating flow.

Specifically, the supply roller upper wall portion 38 has a supply roller inclined wall portion 39 integrally formed to store the entire roller portion of the supply roller 32 in a vertically protruding plane close to the supply roller 32. Thus, the weight of the toner stored in the toner chamber 31 can be more reliably prevented from directly acting on the supply roller 32.

In addition, in each developing unit 20, a guide wall 46 is provided near the opposing position between the layer thickness regulating blade 34 and the developing roller 33. The toner scraped off from the developing roller 33 by the layer thickness regulating blade 34 flows along the guide wall 46, thereby generating a third flow F3 of toner returning to the toner chamber 31. Thus, the toner scraped off from the developing roller 33 by the layer thickness regulating blade 34 is not accumulated on the blade support wall 45, and the circulation of the toner can be ensured, thereby preventing the fogging of the image.

In other words, if the guide wall 46 is not provided, the toner scraped off from the developing roller 33 by the layer thickness regulating blade 34 partially returns to the toner chamber 31 but partially flows to the layer thickness regulating blade 34 and the upper portion of the blade support wall 45, resulting in failure of the toner to circulate and accumulate on the blade support wall 45.

However, the guide wall 46 is provided as described above so as to cover the blade support wall 45 and the layer thickness regulating blade 34 from above, and the guide wall 46 is inclined with respect to the horizontal line, descending near the front end of the developing roller 33, and ascending away from the rear end of the developing roller 33. Thus, the toner scraped off from the developing roller 33 by the layer thickness regulating blade 34 flows along the rotation of the developing roller 33 without accumulating on the blade supporting wall 45, and is guided into the toner chamber 31 by the guide wall 46, so that the third flow F3 of the toner returning to the toner chamber 31 is generated. As a result, not only accumulation of toner on the blade support wall 45 is prevented, but also circulation of toner is ensured, and fogging is prevented.

As shown in fig. 3, in each developing unit 20, the developing roller 33 is disposed so that the θ 1 angle is greater than or equal to 45 degrees, where the θ 1 angle is constituted by a first line L1 passing horizontally through the rotational center of the developing roller 33 and a second line L2 connecting the rotational center of the supply roller 32 and the rotational center of the developing roller 33. Thus, as shown in fig. 2, an appropriate area of the back side surface of the supply roller 32 is obtained to be in contact with the toner flowing from the toner chamber 31 in the first flow F1. As a result, the toner circulates from the supply roller 32 to the developing roller 33, which can be stably supplied. Thus, stable circulation of the toner can be ensured, and fogging is prevented.

In each developing unit 20, the rotation direction of the agitator 48 provided in the toner chamber 31 is the same as the direction of the toner flow near the developing roller 33 generated by the rotation of the developing roller 33, i.e., the third flow F3 in which the toner returns to the toner chamber 31. Thus, the toner flowing in accordance with the third flow F3 can be combined in the same direction as the toner flow stirred by the stirrer. The toner flowing in accordance with the third flow enters and is agitated in the toner chamber 31, and then flows as a first flow F1 from the rear end portion of the agitator facing wall 36 toward the developing chamber 47. In this way, a more stable toner flow is established, so that the toner can be circulated more stably.

In the printer 1, a polymer toner that is actually spherical particles is used, and thus the fluidity of the toner is improved. So that the toner can be circulated more stably.

Particularly in the laser printer 1, since the toner loading bulk density used earlier (including an unused state) is greater than or equal to 0.646g/ml, it can be efficiently supplied from the toner chamber 31 to the supply roller 32. This can prevent the decrease in the imaging density in the previous use state, and thus can achieve better imaging.

The above description is based on the direct transfer type tandem laser printer 1 in which transfer is performed from the photosensitive drum 56 directly onto the sheet 3, however, the present invention is not limited to this type of printer. The present invention is also applicable to an indirect transfer type tandem laser printer in which each color toner image is transferred from each photosensitive member onto an intermediate conversion member as a conversion member at once and then transferred onto a sheet by one operation.

In the above description, the first wall of the present invention is constituted by the agitator facing wall 36, the supply roller upper side wall portion 38, and the supply roller inclined wall portion 39. However, the first wall may be constituted only by the agitator facing wall 36 of the front wall 44 by extending the supply roller front side covering wall portion 40 upward so as to be continuous with the upper portion of the agitator facing wall 36, and the supply roller upper side wall portion 38, the supply roller inclined wall portion 39 are no longer required. However, in order to generate the second flow F2 of the toner flowing along the rotation of the supply roller 32 in the developing chamber 47, it is also preferable to form the supply roller upper side wall portion 38, the supply roller inclined wall portion 39.

Examples of the present invention

Toner, two different additives of different particle sizes were added to the toner base particles in the ratios shown in table 1.

The loading bulk density of each toner (equivalent to that used in the initial stage) was determined before use by the following method. With the color laser printer in the foregoing embodiment, each toner was evaluated based on the comparison between the picture printed with the new developing unit 20 (immediately after the first printing) and the picture obtained after a given time. Fig. 1 shows the evaluation results.

Method for measuring bulk density of filling: the cylindrical test tube was filled with more than 100ml of the toner using a powder tester PT-R manufactured by Hosokawa Micron, then the cylindrical test tube was knocked 180 times, the upper portion of the test tube was separated to scrape off 100ml of the toner, and then the weight thereof was measured, thereby obtaining the loading bulk density of each toner.

In table 1, o indicates that the stable image density is obtained from the fifteenth sheet or later; Δ indicates that the stable image density is obtained from the thirtieth sheet or before, and x indicates that the stable image density is obtained from the thirtieth sheet to the sixteenth sheet.

TABLE 1

Toner number	1	2	3	4	5	6	7
Toner number	1	2	3	4	5	6	7	Small particle size additive (heavy)％)1	0.5	1	0	0	0.5	1	1
Large particle size additive (% by weight)2	0	0	0.5	1	1	0.5	1	Small particle size additive (heavy)％)1	0.5	1	0	0	0.5	1	1
Large particle size additive (% by weight)2	0	0	0.5	1	1	0.5	1	Packing bulk density (g/ml)	0.646	0.658	0.635	0.639	0.652	0.656	0.649
Printing pictures with new developer units	○	○	×	×	○	○	○	Packing bulk density (g/ml)	0.646	0.658	0.635	0.639	0.652	0.656	0.649
Printing pictures with new developer units	○	○	×	×	○	○	○	Pictures printed after a time interval	○	△	○	○	○	○	○

^*1: the small particle size additive has an average particle diameter of about 20mm

^*2: the average particle diameter of the large particle size additive was about 40mm

As is apparent from table 1, the toner having a packed bulk density of 0.646g/ml or more is suitable for preventing the deterioration of the image quality of the initial printing. It is also apparent from table 1 that a toner having a packed bulk density of less than 0.656g/ml is suitable for preventing degradation of printed image quality after a specific interval.

Claims

1. A developing device detachably mountable to a main casing of an image forming apparatus, comprising:

a developer container containing a developer;

a developer carrier that carries a developer;

a supply device disposed facing the developer carrier, the supply device supplying the developer stored in the developer container to the developer carrier, the developer carrier and the supply device both being disposed below the developer container when the developing device is mounted in the main casing of the image forming apparatus;

a first wall disposed between the developer container and the supplying device and covering an upper portion of the supplying device when the developing device is mounted in the main casing of the image forming apparatus,

the first wall is provided to completely cover the supplying device in a vertical direction when the developing device is mounted in the main casing of the image forming apparatus.

2. The developing device according to claim 1, wherein the first wall is provided so that the developer between the first wall and the supplying device moves with movement of the supplying device when the developing device is mounted in the main casing of the image forming apparatus.

3. The developing device according to claim 1 or 2, wherein the first wall is provided adjacent to the supplying device.

4. The developing device according to claim 1 or 2, further comprising:

a layer thickness regulating member that regulates a thickness of the developer on the developer carrier on a downstream side of a facing position of the developer carrier and the supplying device with respect to a moving direction of the developer carrier;

a second wall has a first end located above the layer thickness regulating member when the developing device is mounted in the main casing of the image forming apparatus.

5. The developing device according to claim 4, wherein the first end of the second wall is inclined downward and the second end of the second wall is inclined upward.

6. The developing device according to claim 1 or 2, wherein the developer carrier is a developing roller, the supplying device is a supplying roller, and the developing roller and the supplying roller are disposed so that an angle formed by a first line passing horizontally through a rotational center of the developing roller and a second line connecting the rotational center of the developing roller and the rotational center of the supplying roller is 45 degrees or more when the developing device is mounted in the main casing of the image forming apparatus.

7. The developing device according to claim 1 or 2, wherein the developer is a toner having substantially spherical particles.

8. The developing device according to claim 1 or 2, wherein the developer has a bulk density of 0.646g/ml or more at the time of initial use.

9. The developing device according to claim 1 or 2, further comprising an agitating member provided in the developer container to agitate the developer, wherein the agitating member is moved at a position close to the developer carrier, and a moving direction is the same as a flowing direction of the developer generated near the carrier by the movement of the developer carrier.

10. The developing device according to claim 1 or 2, wherein the developer carrier and the supplying device are urged to contact each other at a relative position, and are moved in opposite directions at the contact position.

11. A developing device detachably mountable to a main casing of an image forming apparatus, comprising:

a developer container containing a developer;

a developer carrier on which a developer is loaded;

a supply device disposed facing the developer carrier, the supply device supplying the developer stored in the developer container to the developer carrier, the developer carrier and the supply device being disposed below the developer container when the developing device is mounted in the main casing of the image forming apparatus;

for preventing the weight of the developer contained in the developer container from directly acting on the first wall of the supplying means,

12. The developing device according to claim 11, further comprising:

and a second wall for preventing the developer from accumulating on the layer thickness regulating member when the developing device is mounted in the main casing of the image forming apparatus.

13. An image forming apparatus, characterized by comprising:

a main frame and a developing unit detachably mounted on the main frame;

the developing unit includes:

a developer container containing a developer;

a developer carrier that carries a developer;

14. The image forming apparatus as claimed in claim 13, further comprising a plurality of developer containers, developer carriers, supply means, first walls, as many as the number of the plurality of developer colors.

15. The image forming apparatus according to claim 14, further comprising a plurality of second walls equal in number to the plurality of developer colors, each second wall being opposed to a respective first wall and having a free end extending toward said developer carrier, and said second walls covering the layer thickness regulating member from above when the developing device is mounted in the main casing of the image forming apparatus.

16. A developer unit for use with an electrophotographic printing apparatus, said developer unit comprising:

a housing having a front wall, a rear wall, a top wall, and a pair of side walls, the housing being divided into a toner chamber and a developing chamber;

a first wall extending from the front wall into the housing to establish a toner chamber and a developing chamber;

an agitator installed in the toner chamber;

a supply roller installed in the developing chamber adjacent to the first wall and the front wall;

a developing roller in contact with the supply roller at a side away from the first wall in the developing chamber;

a regulating blade extending from the rear wall and contacting the developing roller; and

a second wall extending from the rear wall with a free end contacting the regulating blade on a side opposite to a side where the regulating blade contacts the developing roller, wherein the second wall is joined to the rear wall closer to the toner chamber than the free end of the second wall contacts the regulating blade;

the first wall is provided to completely cover the supply roller in a vertical direction when the developing unit is mounted.

17. The developer unit of claim 16, wherein the first wall and the front wall form a recessed portion that completely contains the supply roller.

18. The developer unit of claim 17, wherein, of the angles formed by the plane passing through the axis of the supply roller and the axis of the developer roller and the horizontal plane passing through the axis of the developer roller when the developer unit is installed in the printing apparatus, the angle adjacent to the first wall and the front wall is an acute angle.