JPH11202621A - Developing device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality image formed from, in particular, magnetic one-component toner. SOLUTION: The device is equipped with a development housing, a developing sleeve, a magnet roller, a regulating member, a magnetic body, and a power source. The magnetic body 52 is fixed further upstream than a developing area 53 in the direction of the rotation of the developing sleeve 50, and near the outer surface of the photoreceptor drum 6. The magnetic body 52 has the form of a plate extending at least over the width of the photoreceptor drum 6, and is provided along the axis of the photoreceptor drum 6 and with one of its long sides situated in the vicinity of the developing area 53. The magnet roller 51 may be provided so that it is freely rotatable or fixed. The fixed magnet roller 51 has a magnetic pole 55 situated further upstream than the developing area 53 in the direction of the rotation of the developing sleeve 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a developing device for an image forming apparatus, and more particularly to a developing device for an image forming apparatus using a developer containing a magnetic toner. In the present invention, the developing region refers to a region formed by the developer layer on the developing sleeve and the photosensitive drum approaching each other. Fogging refers to a phenomenon in which toner adheres to a region where an image is not formed.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine,
For example, an electrostatic latent image based on image data is formed on the photosensitive drum by a laser scan unit. A developing device is provided adjacent to the photosensitive drum, and the developing device causes toner to adhere to the electrostatic latent image on the surface of the photosensitive drum to form a visible image. A developing device using a magnetic toner as a toner includes a developing housing that stores a developer containing the magnetic toner, a developing sleeve that is arranged in contact with or close to the photosensitive drum, and transports the developer while rotating on the developing sleeve. And a magnet roller to be used.

In such a developing device, various devices have been devised in order to obtain a high-quality image, especially when a magnetic one-component toner is used. For example, in a device in which a photosensitive drum is arranged above a developing device, and a collecting roller to which an AC voltage is applied is provided close to a lower side of the photosensitive drum, and the toner is sent upward, the inside of the photosensitive drum and the collecting roller , A configuration in which magnets substantially facing each other are provided.

[0004]

The above structure does not use a developing sleeve for supplying the toner to the photosensitive drum, and the magnetic toner formed upstream of the portion where the photosensitive drum and the collecting roller are opposed to each other. The photosensitive drum is brought into contact with the accumulation of toner, and the toner adheres to the electrostatic latent image area. The toner adhering to an area where the electrostatic latent image is not formed on the photosensitive drum (hereinafter referred to as a non-image area) is collected by a magnetic force acting between the photosensitive drum and the collecting roller and a voltage applied to the collecting roller. I do.

However, in the above-described configuration in which the collecting roller is used in place of the developing sleeve, a large amount of uncharged toner is present in the magnetic one-component toner having no carrier, and considerable fogging actually occurs. Further, in order to prevent the toner from leaking from the developing device to the outside, the developing position is limited to the lower side of the photosensitive drum, and it is difficult for the toner to accumulate below the developing device and use up the toner to the end.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing device for an image forming apparatus, which can form a high-quality image using a one-component toner.

[0007]

According to the present invention, there is provided a developing device for an image forming apparatus for developing an electrostatic latent image formed on a photosensitive drum, comprising: a developing housing; Provided is a developing device of an image forming apparatus including a developing sleeve, a magnet roller, a regulating member, a magnetic material, and a recovery voltage applying unit.

The developing housing contains therein a developer containing a magnetic toner. The developing sleeve has a cylindrical shape, is adjacent to the photosensitive drum, and is rotatably provided in the developing housing, and forms a toner image on the electrostatic latent image on the photosensitive drum. The magnet roller is provided coaxially with the developing sleeve and in the developing sleeve. The regulating member is provided near the developing sleeve, and regulates the height of the developer on the developing sleeve. The magnetic body is fixed at a position upstream of the developing region in the rotation direction of the developing sleeve and close to the outer surface of the photosensitive drum, relative to a developing region formed at a portion where the developing sleeve and the photosensitive drum are close to each other. The collecting voltage applying means applies a DC voltage and / or an AC voltage between the photosensitive drum and the developing sleeve in order to collect the magnetic toner from the area of the photosensitive drum where the electrostatic latent image is not formed to the developing sleeve. Apply.

The developer containing the magnetic toner is alternately subjected to magnetic forces of opposite polarity by a magnet roller, is conveyed while being rotated on a rotating developing sleeve, and repeats contact with the developing sleeve and contact between the developing agents. Charge. The regulating member regulates the height of the developer at a constant level and further frictionally charges the toner. The developer transported to the upstream of the developing area receives an electric force from the photosensitive drum and a magnetic force from a magnetic field formed between the magnet roller and the magnetic body.

[0010] The magnetic material produces a magnetization having a polarity opposite to that of the magnetic pole of the magnet roller located on the upstream side in the rotation direction of the developing sleeve from the developing region at an end on the magnet roller side by magnetic induction. Due to the magnetic charge induced at the end of the magnetic body and the magnetic pole of the magnet roller, a mutually attracting magnetic field is formed on the upstream side of the developing area. Due to this magnetic field, the toner once moves to the photosensitive drum side, rotates on the photosensitive drum surface above the developing area, and development is performed so that an edge effect acts on the electrostatic latent image.

Next, when the toner moves to the developing area, the photosensitive drum acts as a counter electrode with respect to the developing sleeve, and the development of the solid image portion is actively promoted.
As a result, it is possible to perform development in which the reproducibility of fine lines such as a character portion by the development with the edge effect and the reproducibility of a solid image portion by the counter electrode effect are both excellent.

As described above, in addition to the electrostatic force from the photosensitive drum, the rotational force due to rotation, the force due to the rotation of the developing sleeve, and the force due to the magnetic field, the toner conveyed to the upstream of the developing area is complicated. In operation, the movement of the magnetic toner onto the electrostatic latent image on the photosensitive drum is promoted. The toner adhering to the non-image area of the photoconductor drum is recovered to the developing sleeve by an appropriate voltage applied between the photoconductor drum and the developing sleeve by the recovery voltage applying means and the magnetic force from the magnet roller. If a rotatable stirring paddle is provided at the preceding stage of the developing sleeve, it is easy to sufficiently supply the toner to the developing sleeve.

According to a second aspect of the present invention, in the developing device of the image forming apparatus, the magnetic material is provided in a plate shape along the axis of the photosensitive drum and provided at least over the width of the photosensitive drum. The side is fixed to be close to the development area. Since the magnetic charge due to the magnetic induction appears concentrated at the end of the long side close to the developing region, a strong magnetic charge can be induced.

According to a third aspect of the present invention, in the developing device of the image forming apparatus, a magnet roller is rotatably provided. The rotatable magnet roller alternately displays magnetic poles of opposite polarity on the upstream side of the developing region in the rotation direction of the developing sleeve. With the rotation of the magnetic pole of this magnet roller,
Magnetic charges of opposite polarity are alternately induced at the end of the magnetic material on the magnet roller side. Similarly to the above, a magnetic field attracting each other is formed between the rotating magnet roller and the end of the magnetic material on the magnet roller side, and the magnetic field promotes the movement of the magnetic toner to the photosensitive drum.

According to a fourth aspect of the present invention, in the developing device of the image forming apparatus, a magnet roller is fixed.
The fixed magnet roller has a magnetic pole located upstream of the developing region in the rotation direction of the developing sleeve.
For example, when the magnetic pole of the magnet roller located on the upstream side in the rotation direction of the developing sleeve is the S pole, the N pole is induced at the magnet roller side end of the magnetic material. The force of the magnetic field formed by the S pole of the magnet roller and the N pole induced by the magnetic material acts on the toner conveyed to the upstream side of the developing area, and the movement of the magnetic toner to the photosensitive drum is performed as described above. Promoted.

The fifth invention of the present application uses a magnetic one-component toner as a developer. Since the transfer of the toner from the developing sleeve to the photosensitive drum is promoted by magnetic force, a high-quality image can be obtained even if a one-component toner that is less easily charged than a two-component developer is used.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Overall Configuration> An image forming apparatus to which an embodiment of the present invention is applied will be described with reference to FIG.
In FIG. 1, a document table 2 is provided on an upper surface of an image forming apparatus main body 1.
Are fixed, and a document holder 3 is provided on the document table 2 so as to be openable and closable. Paper feed cassettes 13, 14, 15 and a paper feed deck 16 are provided below the image forming apparatus main body 1.

Inside the main body 1 of the image forming apparatus, an exposure section 4 for reading a document is provided at an upper portion thereof. The exposure unit 4 includes a light source, a mirror, a lens unit, and the like. Further, an image forming section 5 for forming a toner image of a read document is provided at a central portion of the image forming apparatus main body 1. The image forming section 5 has a photosensitive drum 6 on the surface of which an electrostatic latent image is formed. Around the photosensitive drum 6, a charging device 7, a developing device 8, a transfer device 9, and a cleaning device 10 are arranged.

A vertical transport path 26 for guiding the paper upward is provided between the paper supply cassettes 13, 14, 15 and the paper supply deck 16 and the image forming section 5 constituted by the photosensitive drum 6 and the like. Have been. Further, on the downstream side of the image forming unit 5, there are disposed a sheet discharge conveyance path 30, a fixing unit 31 for fusing and fixing the toner image on the sheet, and discharge rollers 32 and 33 for discharging the sheet passing through the fixing unit 31. ing. <Developing Apparatus> FIG. 2 is a view showing an embodiment of the developing apparatus 8 in which a magnet is brought close to the developing area from outside the photosensitive drum,
FIG. 3 is an explanatory view when the magnet roller rotates, and FIG.
FIG. 4 is an explanatory diagram when a magnet roller is fixed.

As shown in FIG. 2, the developing device 8 has a developing housing 40, in which a developing sleeve 50, a magnet roller 51, a blade 60, and a stirring paddle 70 are provided. A toner cartridge 80 containing magnetic toner as a one-component developer is mounted on the upper part of the developing housing 40, and supplies the magnetic toner into the developing housing 40.

The developing sleeve 50 has a cylindrical shape and is disposed in the developing housing 40 adjacent to the photosensitive drum 6.
The developing housing 40 is rotatably provided between both side walls (not shown) and rotates in the same direction as the magnetic toner conveying direction.
A power supply 54 is connected to the developing sleeve 50 in series, and applies an AC voltage and a DC voltage to the developing sleeve 50.

Inside the cylindrical developing sleeve 50, a built-in magnet roller 51 is provided rotatably coaxially with the developing sleeve 50, and rotates in a direction opposite to the magnetic toner conveying direction. The magnet roller 51 alternately displays the N pole and the S pole in the circumferential direction, and transports the toner while promoting the rotation of the toner. Outside the developing sleeve 50, a blade 60 is provided close to the surface of the developing sleeve 50 and at least over the width of the developing sleeve 50. The blade 60 promotes triboelectric charging of the toner while controlling the height of the toner on the developing sleeve 50 to a certain range.

The stirring paddle 70 is provided in the developing housing 40 in parallel with the developing sleeve 50, and is rotatably mounted between both side walls (not shown) of the developing housing 40. By providing the stirring paddle 70, it can be expected that the toner is sufficiently supplied to the developing sleeve 50 and the triboelectric charging of the toner is promoted. The magnetic body 52 is provided with the developing sleeve 5.
0 and the photosensitive drum 6 are located on the upstream side in the rotation direction of the developing sleeve 6 with respect to the developing area 53 where the photosensitive drum 6
Is provided in close proximity to the outer surface. The magnetic body 52 is
It is formed in a plate shape along the axis of the photosensitive drum 6 and at least over the width of the photosensitive drum 6. Magnetic body 5
One of the long sides 52a is fixed close to the developing area 53, and the magnetic charge generated by the magnetic induction of the magnet roller 51 appears on the long side 52a side. <Operation of Magnetic Toner> The operation of the magnetic toner in the developing device will be described.

The magnetic toner is supplied from the stirring paddle 70 to the developing sleeve 50. The magnetic toner supplied to the developing sleeve 50 receives the magnetic force of the magnet roller 51 on the rotating developing sleeve 50 to receive the magnetic toner.
The toner is conveyed while rotating in a direction opposite to the rotation direction of the toner, and is repeatedly charged with the contact with the developing sleeve 50 and the contact between the magnetic toners. Further, the magnetic toner causes friction between the blade 60 and the magnetic toner by the blade 60 to promote frictional charging.

As shown in FIG. 3, the magnet roller 5 is located upstream of the developing area 53 in the rotation direction of the developing sleeve 50.
1 when the S pole 55 is located,
A magnetic charge of the N pole is induced at the end 52a close to 3.
Conversely, as shown in FIG. 4, the N of the magnet roller 51 is located on the upstream side in the rotation direction of the developing sleeve 50 from the developing area 53.
When the pole 56 is located, the end 52a of the magnetic body 52 is
A pole magnetic charge is induced. In any case, the magnetic poles 55 and 56 of the magnet roller 51 and the magnetic charge induced at the end 52a of the magnetic body form a magnetic field attracting each other on the upstream side of the developing region 53. By the rotation of the magnet roller 51,
The state shown in FIG. 3 and the state shown in FIG. 4 are formed alternately.

The magnetic toner conveyed to the upper part of the developing area 53 by the mutually attracting magnetic field once moves to the photosensitive drum 6 side, and the developing sleeve 50 and the photosensitive drum With the rotation of the photosensitive drum 6, the surface of the photosensitive drum 6 is rotated, and development is performed such that an edge effect acts on the electrostatic latent image. Then
When the toner moves to the development area 53, the development sleeve 50 and the photoconductor drum 6 come close to each other, so that the photoconductor drum 6 acts as a counter electrode with respect to the development sleeve 50, and the development of the solid image portion is stopped. Will be actively promoted. As a result, it is possible to perform development in which the reproducibility of fine lines such as a character portion by the development with the edge effect and the reproducibility of a solid image portion by the counter electrode effect are both excellent.

As described above, the toner receives not only the electrostatic force from the photosensitive drum, the force of rotation of the toner itself, the rotational force of the developing sleeve 50, but also the magnetic force along the magnetic field lines of the formed magnetic field. Force acts on the toner in a complex manner,
The movement of the toner to the latent image area of the photosensitive drum 6 is promoted. The uncharged toner or non-fully charged toner attached to the non-image area receives power from the electric field generated between the photosensitive drum 6 and the developing sleeve 50 and the magnetic field formed by the magnet roller 51 by the power supply 54. Developing sleeve 5
0 and fogging is prevented. The power supply 54 is adjusted so as to form an electric field between the photosensitive drum 6 and the developing sleeve 50 so that the toner attached to the non-image area can be collected without collecting the toner attached to the latent image area.

<Other Embodiments> (a) In the above embodiment, the one-component magnetic toner is used as the developer.
Component developers can also be used. (B) Although the magnet roller 51 is rotatably provided in FIGS. 3 and 4, the magnet roller 51 may be fixed and only the developing sleeve 50 may be rotatably attached. In this case, as in the case shown in FIGS.
It is provided on the upstream side in the rotation direction of the developing sleeve 50 and near the developing area 53. The magnetic material 52 presents a magnetic charge having a polarity opposite to that of the magnetic pole of the magnet roller at the development region side end 52a, and forms a magnetic field attracting each other between the magnetic material 52 and the magnet roller. May be either N pole or S pole.

(C) In the above embodiment, the AC voltage and the DC voltage for collecting the toner in the non-image area are applied to the developing sleeve 50, but the method of applying the voltage is not particularly limited. It is sufficient that an electric field capable of collecting the toner in the non-image area without collecting the toner in the latent image area can be generated between the photosensitive drum 6 and the developing sleeve 50. For example, an AC voltage or a DC voltage may be applied to the photosensitive drum 6, or may be applied to both the photosensitive drum 6 and the developing sleeve 50. Apply AC voltage to developing sleeve 50
Alternatively, a DC voltage may be separately applied to the photosensitive drum 6, or vice versa.

[0030]

According to the developing device of the present invention, a magnetic field for positively moving the toner is formed in a developing region where the photosensitive drum and the developing sleeve are close to each other, and a suitable magnetic field is provided between the photosensitive drum and the developing sleeve. By providing a large voltage difference, a sufficient amount of toner can be supplied to the developing sleeve, unnecessary toner can be collected, and a high-quality image can be provided.

[Brief description of the drawings]

FIG. 1 is an image forming apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a diagram showing an embodiment of a developing device 8 in which a magnetic material is attached near a developing area outside a photosensitive drum.

FIG. 3 is an explanatory diagram when a magnet roller rotates.

FIG. 4 is an explanatory diagram when a magnet roller rotates.

[Explanation of symbols]

 6; photoreceptor drum 40; developing housing 50; developing sleeve 51; magnet roller 52; magnetic body 52a;

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiichi Yamashita 1-2-28 Tamazo, Chuo-ku, Osaka-shi Inside Mita Industries Co., Ltd. (72) Inventor Yuichiro Hisagawa 1-2-28 Tamazo, Chuo-ku, Osaka Mita (72) Inventor Tsutomu Nagata 1-2-28 Tamazo, Chuo-ku, Osaka-shi Mita Industries Co., Ltd. (72) Inventor Masanori Kawasumi 1-2-28 Tamazo, Chuo-ku, Osaka-shi Mita (72) Inventor Masahiro Tsutsumi 1-2-28 Tamazo, Chuo-ku, Osaka-shi Inside Mita Kogyo Co., Ltd.

Claims (5)

[Claims] 1. A developing device for an image forming apparatus for developing an electrostatic latent image formed on a photosensitive drum, comprising: a developing housing in which a developer containing a magnetic toner is housed; A cylindrical developing sleeve which is provided adjacently and rotatably in the developing housing and forms a toner image on an electrostatic latent image on the photosensitive drum; and A magnet roller provided in the sleeve; a regulating member provided in close proximity to the developing sleeve to regulate the height of a developer layer on the developing sleeve; and a portion in which the developing sleeve and the photosensitive drum are in proximity to each other. A magnetic material fixed on the upstream side in the rotation direction of the developing sleeve from the developing region formed near the outer surface of the photosensitive drum, and an electrostatic latent image on the photosensitive drum Recovering voltage applying means for applying a DC voltage and / or an AC voltage between the photosensitive drum and the developing sleeve in order to collect the magnetic toner from the unformed area to the developing sleeve. The developing device of the forming device. 2. The magnetic body is plate-shaped along the axis of the photosensitive drum and is provided at least over the width of the photosensitive drum, and is fixed with one long side close to the developing area. The developing device of the image forming apparatus according to claim 1. 3. The developing device for an image forming apparatus according to claim 1, wherein said magnet roller is rotatably provided. 4. The magnet roller is fixed,
The developing device of the image forming apparatus according to claim 1, wherein the fixed magnet roller has a magnetic pole positioned upstream of the developing region in a rotation direction of the developing sleeve. 5. The developing device according to claim 1, wherein the developer is a magnetic one-component toner.