Hagiwara, Kazunari (Numazu, JP)
Ogawa, Kenya (Susono, JP)
Moriya, Shuji (Sunto-gun, JP)
Kichijima, Naoto (Mishima, JP)
Shimizu, Yasushi (Sunto-gun, JP)
Okuda, Koichi (Katsushika-ku, JP)

Plaque It!

11/275729

10/21/2008

01/26/2006

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Canon Kabushiki Kaisha (Tokyo, JP)

399/277

399/270, 399/274

G03G15/09

399/277, 399/150, 399/53, 399/267, 399/270, 399/55, 399/149, 399/274

4281329	Liquid recording medium	July, 1981	Yano et al.	346/1.1
4292387	Magnetic developing method under A.C. electrical bias and apparatus therefor	September, 1981	Kanbe et al.	430/102
4395476	Developing method for developer transfer under A.C. electrical bias and apparatus therefor	July, 1983	Kanbe et al.	430/102
4473627	Developing method for developer transfer under electrical bias and apparatus therefor	September, 1984	Kanbe et al.	430/102
4766458	Developing apparatus for use in image-forming system and developing process employing said developing apparatus	August, 1988	Oka et al.	399/274
4913088	Apparatus for developer transfer under electrical bias	April, 1990	Kanbe et al.	118/651
5032485	Developing method for one-component developer	July, 1991	Kanbe et al.	430/120
5044310	Developing apparatus for non-magnetic developer	September, 1991	Kanbe et al.	118/653
5096798	Developing method for one-component developer	March, 1992	Kanbe et al.	430/120
5194359	Developing method for one component developer	March, 1993	Kanbe et al.	430/120
5283762	Semiconductor device containing voltage converting circuit and operating method thereof	February, 1994	Fujishima
5570166	Developing apparatus that applies voltage to developer layer thickness regulating member	October, 1996	Ohzeki et al.
5682585	Developing apparatus generating electric field between developer carrying member and developer layer regulating member	October, 1997	Yamaguchi et al.	399/274
5708921	Developing device in an image forming apparatus for removing particulate material from the developer	January, 1998	Yagi et al.	399/98
6229980	Developing apparatus featuring first and second developer chambers and guide member for directing stripped-off developer	May, 2001	Ogawa et al.
6272306	Developing apparatus and image forming apparatus having first and second voltages applied to a developing satisfying predetermined relationships	August, 2001	Saito et al.
6463245	Developing apparatus with a DC electric field formed between a developer carrying member and a developer regulating member and image forming apparatus using the same	October, 2002	Suwa et al.
6630275	Magnetic toner and process cartridge	October, 2003	Hiratsuka et al.
7031629	Image forming apparatus which recovers toner by developing device	April, 2006	Kawamura et al.
7233758	Developing apparatus featuring a developer carrying member with an elastic surface layer	June, 2007	Osada et al.	399/267
20050152718	Developing apparatus	July, 2005	Osada et al.
20050196201	Image forming apparatus	September, 2005	Hagiwara et al.
20050214031	Developing apparatus	September, 2005	Hagiwara et al.
20060233572	Developing apparatus	October, 2006	Ogawa et al.

JP5443027	April, 1979
JP5518656	February, 1980
JP0415949	January, 1992
JP0449159	February, 1992
JP6289703	October, 1994
JP8137257	May, 1996
JP10301396	November, 1998			DEVELOPING DEVICE AND PROCESSING CARTRIDGE
JP10307455	November, 1998			IMAGE FORMING DEVICE
JP200192201	April, 2001
JP2001183872	July, 2001			DRY TONER, METHOD FOR PRODUCING SAME AND IMAGE FORMING METHOD USING SAME
JP2001235899	August, 2001			MAGNETIC TONER, IMAGE FORMING METHOD USING THE SAME, IMAGE FORMING DEVICE AND PROCESS CARTRIDGE
JP3225759	August, 2001			DEVELOPING DEVICE
JP2002341590	November, 2002			MAGNETIC TONER AND PROCESS CARTRIDGE

Royer, William J.

Fitzpatrick. Cella, Harper & Scinto

What is claimed is:

1. A developing apparatus comprising: a rotatable developer carrying member carrying a developer thereon to develop an electrostatic image formed on an image bearing member with the developer; non-rotatable magnetic field generating means provided inside said developer carrying member for magnetically attracting the developer toward said developer carrying member; and a developer amount regulating member contacting with said developer carrying member to regulate an amount of the developer carried on said developer carrying member, wherein said developer carrying member is provided with an elastic layer on a surface thereof, and is urged against said image bearing member, wherein the developer is a mono-component magnetic toner having a mean degree of circularity of 0.965 or greater, and wherein a voltage is applied between said developer carrying member and said developer amount regulating member through the developer, and wherein the following expressions and are satisfied:
|Br|/|B|≧0.5
Nsb/(Bs×R)≦0.5, and where B (G) is a magnetic flux density formed on the surface of said developer carrying member by said magnetic field generating means at a contact position between said developer amount regulating member and said developer carrying member, Nsb (mm) is a contact width between said developer amount regulating member and said developer carrying member, Br (G) is a perpendicular component of the magnetic flux density (G) in a direction perpendicular to the surface of said developer carrying member, Bs (rad) is a half-value width of the perpendicular component of the magnetic flux density formed on the surface of said developer carrying member by a nearest magnetic pole of magnetic poles of said magnetic field generating means at the contact position, and R (mm) is a radius of said developer carrying member.

2. A developing apparatus according to claim 1, wherein the mean degree of circularity of said mono-component magnetic toner is 0.970 or greater.

3. A developing apparatus according to claim 1, wherein the following expression is satisfied:
|Br|/|B|≧0.7.

4. A developing apparatus according to claim 1, wherein the following expression is satisfied:
Nsb/(Bs×R)≦0.35.

5. A developing apparatus according to claim 1, wherein the voltage is a DC voltage, and a potential of said developer amount regulating member is more adjacent to a charging polarity of the developer than a potential of said developer carrying member.

6. A developing apparatus according to claim 1, wherein the voltage is a superimposed voltage of a DC voltage and an AC voltage, and a DC component of a potential of said developer amount regulating member is more adjacent to a charging polarity of the developer than a DC component of a potential of said developer carrying member.

7. A developing apparatus according to claim 1, wherein a DC voltage without an AC voltage is applied to said developer carrying member during development.

8. A developing apparatus according to claim 1, wherein a superimposed voltage of a DC voltage and an AC voltage is applied to said developer carrying member during development, and a relation between a maximum value |V|max (V) of an absolute value of the superimposed voltage and an absolute value |Vd| (V) of a dark section potential of said image bearing member satisfies:
|V|max≦|Vd|.

9. A developing apparatus according to claim 1, wherein said developing apparatus is provided in a cartridge detachably mountable to a main body of an image forming apparatus.

10. A developing apparatus according to claim 1, wherein said developing apparatus and said image bearing member are provided in a cartridge detachably mountable to a main body of an image forming apparatus.

11. A developing apparatus according to any one of claims 1 to 10, wherein said developing apparatus collects an untransferred developer residual on said image bearing member.

12. A developing apparatus according to claim 11, wherein said developing apparatus performs a developing operation and at the same time, performs a collecting operation of collecting the untransferred developer residual on said image bearing member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a developing apparatus for developing an image on an image bearing member with a developer, and more particularly to a developing apparatus of a mono-component developing type in which a developer carrying member contacts with an image bearing member to thereby effect development with a mono-component developer.

This developing apparatus is preferably used as developing means for an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric member in a process cartridge or an image forming apparatus such as a copying machine or a printer.

2. Related Background Art

For example, in an electrophotographic image forming apparatus, as a conventional mono-component developing method of developing an electrostatic latent image formed on an electrophotographic photosensitive member as a member to be developed (image bearing member with a mono-component developer), use is widely made of (1) a nonmagnetic contact developing method and (2) a magnetic non-contact developing method, as will hereinafter be described.

(1) Nonmagnetic Contact Developing Method

There has been proposed a method of carrying a nonmagnetic developer on a developing roller (developer carrying member) having a dielectric material layer and bringing the developing roller into contact with the surface of a photosensitive member to thereby effect development (Japanese Patent Application Laid-open No. 2001-92201).

A developer in a developing apparatus (hereinafter referred to as the developing device) is supplied to a developing roller by a mechanical agitating mechanism or gravity. An elastic roller for contacting with the developing roller is provided, and the carrying and supply of the developer are effected by the elastic roller. This elastic roller also performs the function of once removing any developer not transferred to the photosensitive member, but residual on the developing roller, with a view to uniformize the developer on the developing roller. A DC bias is applied between a base material of the photosensitive member and the developing roller.

(2) Magnetic Non-contact Developing Method

This method uses a magnetic mono-component developer, carries the developer on a developing sleeve (developer carrying member) including a magnet (magnetic field generating means) therein, opposes the developing sleeve to the photosensitive member with a predetermined minute gap provided from the surface of the developing sleeve, and develops an image on the photosensitive member with the developer flying in the gap (Japanese Patent Application Laid-open No. S54-43027 and Japanese Patent Application Laid-open No. S55-18656).

The developer in the developing device is carried to the developing sleeve by a mechanical agitating mechanism or gravity and also, the developer receives a constant magnetic force by the magnet and is supplied to the developing sleeve. Then, a constant developer layer is formed on the developing sleeve by regulating means for regulating a developer amount, and is used for development. A force exerted on the developer by the magnet is positively used not only for the carrying of the developer, but also in a developing portion. In the developing portion, the developer is prevented from shifting a non-image portion to thereby cause the occurrence of a faulty image such as fog. This is because during development, the developer receives a magnetic force toward the magnet included in the developing sleeve. For the flying of the developer, use is made of a bias comprising an AC bias superimposed upon a DC bias. The DC bias voltage is adjusted to a value between an image portion potential and non-image portion potential of the photosensitive member. Further, an AC voltage is superimposed, and the developer effects reciprocal movement relative to the image portion and the non-image portion, whereby the image portion is developed with the developer.

(3) Cleaner-less (Toner Recycle) System

From the viewpoints of the simplification of the apparatus construction and the elimination of waste, there has been proposed an electrophotographic process of disusing an exclusive drum cleaner which is surface cleaning means after the transferring step from the photosensitive member in an image forming apparatus of a transfer type, and recycling the developer in the apparatus. There has been proposed, for example, an image forming apparatus which uses the aforedescribed nonmagnetic contact developing method to collect any developer untransferred during development simultaneously with the development (Japanese Patent No. 2598131).

There has also been proposed an image forming apparatus which uses the aforedescribed magnetic non-contact developing method to collect any developer untransferred during development simultaneously with the development (Japanese Patent Application Laid-open No. H10-307455).

In the nonmagnetic contact developing method of item (1) above, a reduction in fog performance has been a problem. The characteristic of the developer (hereinafter referred to as toner) is reduced while the mechanical stripping-off by the elastic roller is repeated, and fog is sometimes aggravated by a reduction in the frictional charging characteristic or the like of the toner. The fog refers to a faulty image appearing like a ground stain by the toner being slightly used for development in a blank portion (unexposed portion) which is originally not printed. For the prevention of the reduction in the characteristic of the toner, it is also possible to weaken the frictionally contacting force of the elastic roller, but the compatibility thereof with the fault of a ghost image is difficult. Here, the ghost image is a phenomenon that the hysteresis of a toner amount used for development in the last revolution of the developing roller appears as uneven density in a uniform halftone image with the phase difference of the outer periphery of the developing roller in the next and subsequent revolutions. Also, the presence of a ghost image means that there is some toner not stripped off, but residual on the developing roller.

That is, the toner continuously receives the frictional contact by the elastic roller and therefore, this is not preferable also from the viewpoint of the reduction in the characteristic of the toner. The adjustment of the frictionally contacting force has a problem not only being contrary from the viewpoints of the fog and the ghost image, but also contrary in the single matter of fog.

Also, there has arisen the problem that when the characteristic of the toner is reduced, the toner is liable to be affected by the circulation thereof in the developing device. Specifically, in the mechanical circulation or the circulation using gravity, there is formed particularly an area in which the toner hardly changes places around the developing roller and is not circulated. On the other hand, the toner being circulated suffers from a constant reduction in the characteristic thereof. If such two kinds of toners are mixed together when the toner in a container has decreased, compaction or the like has been caused and this has led to the problem of fog or the like. Further, there is the problem of a faulty image attributable to the elastic roller itself. As the elastic roller, from the viewpoint of the performance of stripping off and supplying the toner, use is made of a roller in the form of a sponge, and the developer is compressed and forms compact clusters in the cells of this sponge, and when these come off from the sponge and appear to the surface thereof, an image defect occurs particularly in the halftone. Also, in a combination with the cleaner-less method, paper dust goes into the elastic roller to thereby cause the image defect of the cycle of the elastic roller.

On the other hand, in the magnetic non-contact developing method of item (2) above, there is the image fault by a magnetic brush. There is the problem that the uniformity of a thin line differs between length and width. When the magnetic brush develops while moving in parallelism to the direction of movement of the photosensitive member (photosensitive drum), the uniformity of the thin line is good and becomes liable to break in a direction orthogonal thereto. Also, an image edge fault is caused. The edge of a high density portion, and particularly the process downstream side thereof is developed darkly, and a halftone portion adjacent to the high density portion is developed lightly. The factor for this is expected to reside in developing while reciprocally moving the developer in non-contact by an AC electric field. In the developing portion, the toner is moved toward the surface, and the toner stagnates particularly downstream of the edge portion and conversely, the toner is drawn near from the outside of the edge to thereby cause the image fault as described above. Further, the image forming apparatus adopting the cleaner-less system is low in the capability of collecting the toner on the photosensitive drum, because of non-contact, and suffers from the problem that the untransferred toner becomes a ghost image and appears in solid white and the halftone. Also, white dots occur in solid black. These white dots are liable to occur when under a high-temperature and high-humidity environment paper dust goes mixed between the developing roller and the photosensitive drum. This is expected to be because bias leak has occurred between the developing roller and the photosensitive drum with a result that the potential of a latent image on the photosensitive drum has risen (to the negative).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a developing apparatus which suppresses an image fault.

It is another object of the present invention to provide a developing apparatus which prevents fog.

It is another object of the present invention to provide a developing apparatus which prevents the occurrence of a ghost image.

It is another object of the present invention to provide a developing apparatus which prevents uneven density.

It is another object of the present invention to provide a developing apparatus which improves the uniformity of a thin line.

It is another object of the present invention to provide a developing apparatus which prevents the edge of an image from becoming dark or light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of Example 1 of an image forming apparatus using Embodiment 1 of the present invention.

FIG. 2 is a schematic view of Example 2 of the image forming apparatus using Embodiment 1 of the present invention.

FIG. 3A shows the magnetic flux density of a magnet roll used in Embodiment 1 in a direction perpendicular to the surface of a developing sleeve.

FIG. 3B shows |Br|/|B| of the magnet roll used in Embodiment 1.

FIG. 4 shows the relation among Nsb, R and Bs.

FIG. 5 is a schematic view of Example 1 of an image forming apparatus using Comparative Example 4.

FIG. 6 is a schematic view of Example 1 of an image forming apparatus using Comparative Example 6.

FIG. 7 is a schematic view of Example 1 of an image forming apparatus using Comparative Example 8.

FIG. 8 is a schematic view of Example 1 of an image forming apparatus using Comparative Example 9.

FIG. 9 is a schematic view of Example 1 of an image forming apparatus using Comparative Example 10.

FIG. 10 is a schematic view of Example 1 of an image forming apparatus using Comparative Example 11.

FIG. 11 is a schematic view of Example 1 of an image forming apparatus using Comparative Example 12.

FIGS. 12A and 12B show the mechanism of occurrence of an edge fault.

FIG. 13 shows the mechanism of cleaning simultaneous with developing.

FIGS. 14A, 14 B and 14 C show the mechanism of occurrence of a solid black image fault.

FIGS. 15A and 15B are typical views when Nsb is small and when Nsb is great.

FIG. 16 is a graph of the result of the evaluation of solid black density difference.

FIG. 17 is a graph of the result of the evaluation of hair line uniformity.

FIG. 18 is a graph of the result of the evaluation of fog.

FIG. 19 is a graph of the result of overall evaluation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Example 1 of Image Forming Apparatus

FIG. 1 schematically shows the construction of a first example of an image recording apparatus (image forming apparatus) using a developing apparatus according to the present invention. This image recording apparatus is a laser printer utilizing a transfer type electrophotographic process.

(1) General Schematic Construction of the Image Recording Apparatus

The process numeral 1 designates an image bearing member as a member to be developed. In the present example, it is a rotatable drum-shaped negative polarity OPC photosensitive member (negative photosensitive member, hereinafter referred to as the photosensitive drum) having a diameter of 24 mm. This photosensitive drum 1 is rotatively driven at a constant speed of peripheral speed 85 mm/sec. (=process speed PS, printing speed) in the clockwise direction indicated by the arrow.

The reference numeral 2 denotes a charging roller as charging means for the photosensitive drum 1 . This charging roller 2 is an electrically conductive elastic roller, and the reference character 2 a designates a mandrel, and the reference character 2 b denotes an electrically conductive elastic layer. This charging roller 2 is brought into pressure contact with the photosensitive drum 1 with a predetermined pressure force to thereby form a charging portion “n” between itself and the photosensitive drum 1 . In the present example, this charging roller 2 is driven to rotate by the rotation of the photosensitive drum 1 .

S 1 designates a charging voltage source for applying a charging bias to the charging roller 2 . In the present example, a DC voltage equal to or greater than a discharge starting voltage is applied from this charging voltage source S 1 between the photosensitive drum 1 and the charging roller 2 . Specifically, a DC voltage of −1300 V is applied as a charging bias to thereby uniformly contact-charge the surface of the photosensitive drum 1 to a charging potential (dark section potential) of −700 V.

The reference numeral 4 denotes a laser beam scanner (exposing apparatus) including a laser diode, a polygon mirror, and the like. This laser beam scanner 4 outputs a laser beam intensity-modulated correspondingly to the time-series electrical digital pixel signal of desired image information, and subjects the uniformly charged surface of the rotatable photosensitive drum 1 to scanning exposure L by the laser beam. Laser power is adjusted so that the potential of the surface of the photosensitive drum 1 may be −150 V when the uniformly charged surface of the photosensitive drum 1 is generally exposed to the laser beam. By this scanning exposure L, an electrostatic latent image corresponding to the desired image information is formed on the surface of the rotatable photosensitive drum 1 .

60 A designates a developing apparatus (developing device) according to Embodiment 1 which will be described later. A toner “t” as a developer bears predetermined frictional charge, and visualizes the electrostatic latent image on the photosensitive drum 1 in a developing area “a” by a developing bias applied between a developing sleeve 60 b as a developer carrying member (toner carrying member) an the photosensitive drum 1 by a developing bias applying voltage source S 2 . The developing apparatus 60 A will be described in detail in each embodiment and each comparative example which will be described later.

The reference numeral 6 denotes a transfer roller of medium resistance as contact-transferring means, which is brought into pressure contact with the photosensitive drum 1 with a predetermined pressure force to thereby form a transfer nip portion “b”. A transfer material P as a recording material is fed to this transfer nip portion “b” at predetermined timing from a sheet feeding portion (not shown) and a predetermined transfer bias voltage is applied from a transfer bias applying voltage source S 3 to the transfer roller 6 , whereby a toner image on the photosensitive drum 1 is sequentially transferred to the surface of the transfer material P fed to the transfer nip potion “b”.

The transfer roller 6 used in the present example is one of a roller resistance value 5×10 ⁸ Ω having a medium resistance foamed layer 6 b formed on a mandrel 6 a , and a voltage of +2.0 kV was applied to the mandrel 6 a to thereby effect transfer. The transfer material P introduced into the transfer nip portion “b” is nipped by and conveyed through this transfer nip portion “b”, and the toner image formed and borne on the surface of the rotatable photosensitive drum 1 is sequentially transferred to the surface of the transfer material P by an electrostatic force and a pressure force.

The reference numeral 7 designates a fixing apparatus of a heat fixing type or the like. The transfer material P fed to the transfer nip portion “b” and having received the transfer of the toner image from the photosensitive drum 1 is separated from the surface of the photosensitive drum 1 and is introduced into the fixing apparatus 7 , whereby it is subjected to the fixing of the toner image, and is discharged out of the apparatus as an image-formed matter (a print or a copy).

The reference numeral 8 denotes a drum cleaner (a photosensitive drum cleaning apparatus) which scrapes off any untransferred toner residual on the photosensitive drum 1 by a cleaning blade 8 a and collects it into a waste toner container 8 b.

Then, the photosensitive drum 1 is charged again by the charging roller 2 and is repetitively used for image formation.

The reference character 9 A designates a process cartridge into which the photosensitive drum 1 , the charging roller 2 , the developing apparatus 60 A and the drum cleaner 8 are integrally formed, and which is made detachably mountable with respect to the image forming apparatus.

It is to be understood here that a process cartridge refers to at least one of charging means, developing means and cleaning means and an electrophotographic photosensitive member integrally made into a cartridge detachably mountable to a main body of an image forming apparatus.

Example 2 of Image Forming Apparatus

FIG. 2 schematically shows the construction of a second form of the image recording apparatus using the developing apparatus of the present invention. The image recording apparatus of this embodiment is a laser printer utilizing a transfer type electrophotographic process and a toner recycle process (cleaner-less system). The similarities of this example to the aforedescribed Example 1 of the image forming apparatus need not be described again, and the different points thereof will hereinafter be described.

The most different point of this embodiment is that the drum cleaner 8 is disused and the untransferred toner is recycled. The untransferred toner is circulated so as not to adversely affect other processes such as charging, and the like, and the toner is collected into the developing apparatus 60 A. Specifically, the construction has been changed in the following points relative to Example 1 of the image forming apparatus.

About charging, a charging roller 2 similar to that in Example 1 of the image forming apparatus is used, but in the present embodiment, the driving of the charging roller 2 is effected. The number of revolutions of the charging roller 2 is adjusted so that the surface speed of the charging roller 2 and the surface speed (process speed) of the photosensitive drum 1 may become the same. By the charging roller 2 being driven, the charging roller 2 reliably contacts with the photosensitive drum 1 and an abutting member 10 to thereby charge the toner to minus (a regular polarity). Also, the charging roller 2 is provided with the abutting member 10 for the purpose of preventing the charging roller 2 from being stained with the toner. Even when the charging roller 2 is stained with the toner of an opposite polarity (plus polarity) to the charging polarity thereof, the charges of the toner are charged from plus to minus, and the toner is quickly discharged from the charging roller 2 to the photosensitive drum 1 . The toner discharged to the photosensitive drum 1 becomes capable of being subjected to a collecting operation simultaneously with a developing operation being performed by the developing apparatus 60 A. The abutting member 10 used is a film of polyimide of 100 μm, and is made to abut against the charging roller 2 with a line pressure of 10 (N/m) or less. Polyimide is used because it has a frictional charging characteristic giving negative charges to the toner.

The reference character 9 B designates a process cartridge into which the photosensitive drum 1 , the charging roller 2 , the abutting member 10 and the developing apparatus 60 A are integrally formed, and which is made detachably mountable with respect to the image forming apparatus.

EMBODIMENTS AND COMPARATIVE EXAMPLES

Embodiment 1

<Including Contact Development, Elastic Sleeve, Polar Position Regulation, Degree of Circularity 0.976 and Blade Bias>

Description will hereinafter be made of the developing apparatus 60 A (FIGS. 1 and 2) according to the present embodiment. The reference character 60 b denotes the developing sleeve as a developer carrying member (developer carrying and conveying member) including therein a magnet roll 60 a as stationary (non-rotatable) magnetic field generating means. The developing sleeve 60 b is constituted by an aluminum cylinder 60 b 1 and a nonmagnetic electrically conductive elastic layer 60 b 2 formed thereon, and is brought into contact with the photosensitive drum 1 with a constant pressure force. The pressure between the photosensitive drum 1 and the developing sleeve 60 b is adjusted so as to be 200 N/m in terms of drawing pressure. The drawing pressure is a value corresponding to line pressure obtained by converting the force with which an SUS plate having a thickness of 30 μm sandwiched between two SUS plates also having a thickness of 30 μm is drawn out per length 1 m of the SUS plate.

The developing sleeve 60 b was manufactured by kneading a material forming the nonmagnetic electrically conductive elastic layer 60 b 2 , extrusion-molding it, adhesively securing it as the layer 60 b 2 onto the aluminum cylinder 60 b 1 , and thereafter grinding the layer 60 b 2 to a thickness of 500 μm. The microhardness of the developing sleeve 60 b was 72 degrees, and the surface roughness thereof was 3.8 μm in terms of Rz, and 0.6 μm in terms of Ra.

In the present embodiment, the measurement of surface hardness to be measured by a microhardness meter was carried out by the use of a microhardness meter (Asker MD-1F360A: produced by High Molecule Co., Ltd.). As a surface roughness measuring machine, use was made of Surfcorder SE 3400 produced by Kosaka Research Institute (Ltd.) and a contact detection unit PU-DJ2S, and the measuring conditions were a measurement length 2.5 mm, a vertical magnification 2,000 times, a horizontal magnification 100 times cutoff 0.8 mm and filter setting 2CR, and leveling setting was effected by front data.

The magnet roll 60 a is a fixed magnet as magnetic field generating means for generating a magnetic force at each place on the surface of the developing sleeve 60 b . As shown in FIG. 3A, the magnetic flux density on the surface of the developing sleeve 60 b in a direction perpendicular to the surface of the developing sleeve 60 b has peak density in each of a developing portion pole Sa, a conveying portion pole Na, a supplying pole Sb and a trapping pole Nb. That is, the magnet roll 60 a has four magnetic poles, i.e., the developing pole Sa, the conveying pole Na, the supplying pole Sb and the trapping pole Nb. The measurement of the magnetic flux density in the present invention was carried out by the use of Series 9900, Probe A-99-153 of a gauss meter produced by Bell Inc. This gauss meter has a bar-shaped axial probe connected to a gauss meter main body. The developing sleeve 60 b is horizontally fixed, and the magnet roll 60 a therein is rotatably mounted. A probe in a horizontal posture is disposed at right angles with some interval provided with respect to the developing sleeve 6 b , and is fixed so that the center of the developing sleeve 60 b and the center of the probe may be located on substantially the same horizontal plane, and the magnetic flux density is measured in that state. The magnet roll 60 a is a cylindrical member substantially concentric with the developing sleeve 6 b , and the interval between the developing sleeve 60 b and the magnet roll 60 a may be considered to be equal everywhere. Accordingly, what has been measured at all positions with respect to the circumferential direction of the developing sleeve 60 b can be replaced by measuring the magnetic flux density at the surface position of the developing sleeve 60 b and in the direction of a normal at the surface position while rotating the magnet roll 60 a.

The vertical peak intensity of each position was found from the obtained magnetic flux density in the circumferential direction, and was defined as Br.

Next, a vertically disposed probe was rotated by 90 degrees in a tangential direction with respect to the circumferential direction, and the magnet roll 60 a was rotated to thereby measure the magnetic flux density at the surface position of the developing sleeve 60 b and in the tangential direction at the surface position, and this magnetic flux density was defined as Bθ.

From the values of Br and Bθ at each angle, the magnitude
|B|=|Br ² +Bθ ² |½
of the magnetic flux density B was calculated.

Next, the ratio |Br|/|B| of the magnitude |Br| of the vertical component of the developing sleeve surface to the magnitude |B| of the magnetic flux density was found.

The result and Br and Bθ are shown in FIG. 3B. The angle of the axis of abscissas is such that the origin is taken at the trapping pole Sb pole, and the positive direction is selected to a downstream direction (Sb→Na→Sa→Nb→Sb) relative to the rotation direction of the developing sleeve 60 b . The right axis of ordinates shows the intensity of the magnetic flux density, and has the N pole as positive and the S pole as negative, and the left axis of ordinates shown |Br|/|B|.

Toner t 1 : a mono-component magnetic toner t 1 which is a developer is a magnetic mono-component toner (spherical toner) having a mean degree of circularity of 0.976 made by a suspension polymerization method. As a method of making such a magnetic polymerization toner, use was made of a method proposed in Japanese Patent Application Laid-open No. 2001-235899, and the like.

The mean degree of circularity in the present invention is used as a simple method of quantitatively expressing the shape of a particle, and in the present invention, measurement was carried out by the use of a flow particle image analyzer “FPIA-2100” produced by Sysmex, and the degree of circularity (Ci) of each particle measured about a group of particles having a diameter corresponding to a circle of 3 μm or greater was found by the following expression (5), and a value obtained by dividing the sum total of the degrees of circularity of all particles measured as shown by the following expression (6) by the number of all particles (m) is defined as the mean degree of circularity ( C ).

$\begin{array}{cc}\mathrm{Degree}\mathrm{of}\mathrm{circularity}\left(\mathrm{Ci}\right)=\frac{\begin{array}{c}\mathrm{circumferential}\mathrm{length}\mathrm{of}a\\ \mathrm{circle}\mathrm{having}\mathrm{the}\mathrm{same}\mathrm{projection}\\ \mathrm{area}\mathrm{as}\mathrm{the}\mathrm{number}\mathrm{of}\mathrm{particles}\end{array}}{\begin{array}{c}\mathrm{circumferential}\mathrm{length}\mathrm{of}\\ \mathrm{the}\mathrm{projection}\mathrm{image}\mathrm{of}\mathrm{particle}\end{array}}& \mathrm{Expression}\left(5\right)\\ \mathrm{Mean}\mathrm{degree}\mathrm{of}\mathrm{circularity}\left(\stackrel{\_}{C}\right)=\sum _{i=1}^m\mathrm{Ci}/m& \mathrm{Expression}\left(6\right)\end{array}$

Magnetic material particles were prescribed by the same weight as binding resin to thereby make magnetic particles capable of being conveyed by a sufficient magnetic force. Here, the amount of magnetic material was 100 parts by weight relative to 100 parts by weight of binding resin, but if the amount of magnetic material relative to 100 parts by weight of binding resin is 70-120 parts by weight, the effect of the present invention can be sufficiently obtained. Also, the mean particle diameter (D 4 ) of the toner was 6 μm.

The mean particle diameter of the toner in the present embodiment refers to a weight mean particle diameter (D 4 ), and can be measured by one of various methods such as Coulter Counter TA-II type and Coulter Multisizer (produced by Coulter Co., Inc.).

Specifically, it can be measured as follows. Coulter Multisizer (produced by Coulter Co., Inc.) is used to connect an interface (produced by Nikkaki) outputting the distribution of particle number and the distribution of volume and PC9801 personal computer (produced by NEC) together, and as regards an electrolyte, 1% NaCl water solution is adjusted by the use of first class sodium chloride. For example, ISOTON R-II (produced by Coulter Scientific Japan) can be used. The measuring procedure is as follows. The aforementioned electrolytic water solution is added by 100-150 ml, and further a measurement sample is added by 2-20 mg. The electrolyte having the sample suspended therein is subjected to dispersion processing for about 1 to 3 minutes by an ultrasonic disperser, and by the aforementioned Coulter Multisizer, the volume and number of toner particles of 2 μm or larger are measured by the use of an aperture to thereby calculate the distribution of volume. Then, the weight mean particle diameter (D 4 ) of the volume standard found from the distribution of volume according to the present invention is found.

The toner t 1 is subjected to layer thickness regulation (developer amount regulation) by a regulating blade 60 c as a developer amount regulating member and the imparting of charges, in the process of being conveyed on the developing sleeve 60 b while receiving the magnetic force by the magnet roll 60 a . The reference character 60 d designates an agitating member for effecting the circulation of the toner in a developer container 60 e and sequentially conveying the toner into the magnetic force reach range around the developing sleeve 60 b.

The present developing apparatus 60 A, in order to obtain a desired toner charging amount and a desired coat amount, uses phosphor bronze having a thickness of 100 μm and microhardness of 100 degrees as the regulating blade 60 c , and the abutting position (regulating position) of the regulating blade against the developing sleeve was set to θ=7 degrees (|Br|/|B|=0.96) in FIGS. 3A and 3B, drawing pressure of 55 (N/m) and a blade free length of 2.0 mm. The blade free length means the length of the free end when the contact portion between the regulating blade 60 c and the developing sleeve 60 b is defined as a fulcrum. Also, it will be called polar position regulation to set the abutting position of the regulating blade 60 c against the developing sleeve 60 b to a magnetic pole area (|Br|/|B|≧0.9) in which a perpendicular magnetic field is dominant, as in the present embodiment.

Further, the nip width Nsb over which the regulating blade 60 c abuts against the developing sleeve 60 b under the present conditions was 1.5 mm.

In the present invention, the measurement of the nip width between the regulating blade 60 c and the developing sleeve 60 b was carried out by the following method. First, in the developing sleeve in the developing apparatus capable of developing, a state in which the developing sleeve is coated with the toner is kept, and only the developing sleeve is removed. Next, the amount of toner corresponding to a half rotation relative to the rotation direction of the developing sleeve coated with the toner is removed (but the toner on the longitudinal end portions is kept). Thereafter, the fixed magnet roller in its detached state is mounted on the developing apparatus which is not filled with the toner. At this time, it is mounted so that the surface from which the toner has been removed may contact with the regulating blade. In this state, the developing sleeve is rotated by one revolution in the rotation direction thereof, and is removed. Then, the toner adhering to the surface of the regulating blade is stripped off by a tape, and is stuck on paper together with the tape. In this case, the toner does not adhere to the contact width between the developing sleeve and the regulating blade, but the toner adheres to the outside thereof. That is, two lines of toner are obtained, and by measuring the interval between the two lines, it is possible to obtain the nip width.

Further, the half-value width Bs about Br of the magnetic pole nearest to the contact position between the regulating blade 60 c and the developing sleeve 60 b is 52 degrees (≈0.91 rad), the radius R of the developing sleeve 60 b which is the developer carrying member is 6.5 mm, and Nsb/(Bs×R)=0.25. This specific disposition relation is shown in FIG. 4.

The toner t 1 coating the developing sleeve 60 b is conveyed to a developing region (developing area portion) which is the opposed portion of the photosensitive drum 1 to the developing sleeve 60 b . Also, a developing bias voltage (DC voltage of −450 V) is applied from the developing bias applying voltage source S 2 to the developing sleeve 60 b.

Further, a DC voltage of −550 V is applied from an applying voltage source S 4 to the regulating blade 60 c with a potential difference of 100 V given between the regulating blade 60 c and the developing sleeve 60 b through the toner.

That is, the potential (−550 V) of the regulating blade side is more adjacent to the polarity side (minus side) of the toner which is the developer than the potential (−450 V) of the developing sleeve 60 b which is the developer carrying member.

In the following, the bias applied to the regulating blade 60 c is called a blade bias. The developing sleeve 60 b is driven at a peripheral speed 1.2 times as high relative to the photosensitive drum 1 . Thereby, the electrostatic latent image on the photosensitive drum 1 is reversal-developed with the toner t 1 . Here, the peripheral speed of the developing sleeve 60 b relative to the photosensitive drum 1 has been mentioned as 1.2 times, but if the peripheral speed of the developing sleeve 60 b relative to the photosensitive drum 1 is 1.0 to 2.0 times, the effect of the present invention can be sufficiently obtained.

Embodiment 2

<Mean Degree of Circularity 0.968>

A developing apparatus according to this embodiment basically conforms to the developing apparatus 60 A described in Embodiment 1, but used a toner t 2 as the developer, as shown below.

Toner t 2 : The mono-component magnetic toner t 2 which is the developer was made via the steps of mixing, kneading and crushing a binding resin, magnetic material particles and a charge controlling agent, and improving the surface quality thereof and classifying them, and adding a fluidizing agent or the like as an extraneous agent (a crushing method, see for example, Japanese Patent Application Laid-open No. 2002-341590). The magnetic material particles were prescribed by the same weight as the binding resin to thereby make magnetic particles which are conveyable by a sufficient magnetic force. Also, the mean particle diameter (D 4 ) of the toner was 6 μm, and the mean degree of circularity found by the above-described method was 0.968.

Comparative Example 1

<Mean Degree of Circularity 0.955>

A developing apparatus according to this comparative example basically conforms to the developing apparatus 60 A described in Embodiment 1, but used a toner t 3 as the developer, as shown below.

Toner t 3 : The mono-component magnetic toner t 3 which is the developer was made via the steps of mixing, kneading, crushing and classifying a binding resin, magnetic material particles and a charge controlling agent, and adding a fluidizing agent or the like as an extraneous agent (crushing method). The magnetic material particles were prescribed by the same weight as the binding resin to thereby make magnetic particles which are conveyable by a sufficient magnetic force. Also, the mean particle diameter (D 4 ) of the toner was 6 μm, and the mean degree of circularity found by the above-described method was 0.955.

Comparative Example 2

<Nsb/(Bs×R)>0.5, Nip Width Great>

A developing apparatus according to this comparative example basically conforms to the developing apparatus 60 A described in Embodiment 1, but differs in the following points from the developing apparatus 60 A.

As the regulating blade 60 c which is the regulating member, use was made of urethane having a thickness of 1.5 mm and having a nonmagnetic electrically conductive layer having a thickness of 50 μm on the surface thereof contacting with the toner. The regulating blade was manufactured by kneading a material providing the nonmagnetic electrically conductive layer, and uniformly applying it onto the surface of the urethane. The microhardness of the elastic layer on the surface of the developing sleeve is 51 degrees, the microhardness of the regulating blade is 58 degrees, Nsb is 3.2 mm, Nsb/(Bs×R)=0.54>0.5, and the drawing pressure is 45 N/m.

Comparative Example 3

<Contact Elastic Sleeve Inter-pole Position Regulation Blade Bias>

A developing apparatus according to this comparative example basically conforms to the developing apparatus 60 A described in Embodiment 1, but differs in the abutting condition of the regulating blade 60 c against the developing sleeve 60 b from the developing apparatus 60 A.

In the present example, the abutting position of the regulating blade 60 c was set to θ=40 degrees (|Br|/|B|=0.03) in FIGS. 3A and 3B, the drawing pressure was set to 55 (N/m), the blade free length was set to 1.5 mm.

Also, it will hereinafter be called inter-pole position regulation (inter-pole regulation to set the abutting position of the regulating blade 60 c against the developing sleeve 60 b to a magnetic pole area (|Br|/|B|≦0.1) in which a perpendicular magnetic field is dominant as in the present example.

Comparative Example 4

<Contact Elastic Sleeve Pole Position Regulation Sleeve Conduction>

Description will now be made of a developing apparatus according to this comparative example. FIG. 5 shows a schematic view of Example 1 of an image forming apparatus using the present comparative example. The developing apparatus 60 B according to the present comparative example basically conforms to the developing apparatus 60 A described in Embodiment 1, but differs in the following point from the developing apparatus 60 A.

In the present example, the regulating blade 60 c is made to conduct with the developing sleeve 60 b , and the two were at the same potential.

Comparative Example 5

<Contact Elastic Sleeve Inter-pole Position Regulation Sleeve Conduction>

A developing apparatus according to this comparative example basically conforms to the developing apparatus 60 B described in Comparative Example 4, but differs in the abutting condition of the regulating blade 60 c against the developing sleeve 60 b from the developing apparatus 60 B.

In the present example, the abutting position of the regulating blade 60 c was set to θ=40 degrees (|Br|/|B|=0.03) in FIGS. 3A and 3B, the drawing pressure was set to 55 (N/m), and the blade free length was set to 1.5 mm.

Comparative Example 6

<Magnetic Non-contact Developing Method Inter-pole Position Regulation>

Description will now be made of a developing apparatus 60 C according to this comparative example. FIG. 6 shows a schematic view of Example 1 of an image forming apparatus using the present comparative example. A toner t 3 which will be described later was used as the developer.

The reference character 60 f designates a developing sleeve as a developer carrying and conveying member including therein the magnet roll 60 a used in Embodiment 1. The developing sleeve 60 f is constructed by adjusting the roughness of the surface of an aluminum cylinder by sandblast, and is installed with a gap α of 300 μm relative to the photosensitive drum 1 . The microhardness of the developing sleeve 60 f was 100 degrees, the surface roughness Rz thereof was 11.5 μm, and Ra was 1.5 μm. The toner t 3 filling the developing apparatus 60 C is subjected to layer thickness regulation by a regulating blade 60 g of urethane having a thickness of 1.5 mm and the imparting of charges, in the process of being conveyed on the developing sleeve 60 f while receiving the magnetic force by the magnet roll 60 a . The reference character 60 d denotes an agitating member for effecting the circulation of the toner in a developer container 60 e and sequentially conveying the toner into a magnetic force reach range around the developing sleeve 60 f.

In the present developing apparatus 60 C, in order to obtain a desired toner charging amount and a desired coat amount, the abutting position of the regulating blade 60 g against the developing sleeve 60 f was set to θ=40 degrees (|Br|/|B|=0.03) in FIGS. 3A and 3B, the drawing pressure was set to 30 N/m, and the blade free length was set to 1.2 mm. Nsb/(R×Bs) at this time was 0.52.

The toner t 1 coating the developing sleeve 60 f is conveyed to a developing region (developing area portion) “a” which is the opposed portion between the photosensitive drum 1 and the developing sleeve 60 f by the rotation of the developing sleeve 60 f . Also, a developing bias voltage (DC voltage of −450 V, AC voltage (rectangular wave, 1.8 kvpp, 1.6 kHz)) is applied from a developing bias applying voltage source S 5 to the developing sleeve 60 f . The developing sleeve 60 f is driven at a peripheral sped 1.2 times as high relative to the photosensitive drum 1 . Thus, the electrostatic latent image on the photosensitive drum 1 is reversal-developed with the toner t 3 . The toner t 3 was used as the developer, as shown below.

Toner t 3 : This conforms to Comparative Example 1.

Comparative Example 7

<Magnetic Non-contact Developing Method Pole Position Regulation>

A developing apparatus according to this comparative example basically conforms to the developing apparatus 60 C described in Comparative Example 6, but differs in the abutting condition of the regulating blade 60 g against the developing sleeve 60 f from the developing apparatus 60 C.

In the present example, the abutting position of the regulating blade 60 g was θ=7 degrees (|Br|/|B|=0.96) in FIGS. 3A and 3B.

Comparative Example 8

<Magnetic Non-contact Developing Method Pole Position Regulation Blade Bias is Present>

Description will now be made of a developing apparatus 60 D according to this comparative example. FIG. 7 shows a schematic view of Example 1 of an image forming apparatus using the present comparative example. The developing apparatus 60 D according to the present comparative example basically conforms to the developing apparatus 60 C described in Comparative Example 6, but differs in the following points from the developing apparatus 60 C.

In the abutting condition of the regulating blade 60 g against the developing sleeve 60 f , the present comparative example set the abutting position of the regulating blade 60 g to θ=7 degrees (|Br|/|B|=0.96) in FIGS. 3A and 3B.

Further, as the regulating blade 60 g , use was made of an electrically conductive layer having a thickness of 50 μm and applied to the surface of urethane having a thickness of 1.5 mm. The method of making this blade conforms to that in Comparative Example 2. Furthermore, a bias (DC voltage of −550 V, AC voltage (rectangular wave of the same phase as the developing bias, 1.8 kvpp, 1.6 kHz)) is applied to the electrically conductive layer on the surface of the regulating blade by an applying voltage source S 6 . The toner t 3 was used as the developer, as shown below. Toner t 3 : This conforms to Comparative Example 1.

Comparative Example 9

<Rotating Type Multi-pole Magnet Roll>

Description will now be made of a developing apparatus 60 E according to this comparative example. FIG. 8 shows a schematic view of Example 1 of an image forming apparatus using Comparative Example 9.

The reference character 60 r designates a developing sleeve as a developer carrying and conveying member including a magnet roll 60 q therein. The developing sleeve 60 r is constituted by an aluminum cylinder 60 r 1 and a nonmagnetic electrically conductive elastic layer 60 r 2 formed thereon, and is brought into contact with the photosensitive drum 1 with a constant pressure force. The drawing pressure was 200 N/m.

The developing sleeve 60 r was manufactured by kneading a material providing the nonmagnetic electrically conductive elastic layer 60 r 2 , extrusion-molding it, adhesively securing it as the layer 60 r 2 onto the aluminum sleeve 60 r 1 , and thereafter grinding this layer 60 r 2 to a thickness of 500 μm. The microhardness was 94 degrees, and the surface roughness Ra was 1.2 μm.

As the magnet roll 60 q , use is made of a multi-pole magnet roll having eight poles magnetized at regular intervals. Magnetic flux density of 300 G is generated at the absolute value of peak density. Also, the magnet roll 60 q is rotatively driven in a direction opposite to the rotation direction of the developing sleeve 60 r at a number of revolutions equal to that of the developing sleeve 60 r.

The toner t 3 is subjected to layer thickness regulation by the regulating blade 60 c and the imparting of charges, in the process of being conveyed on the developing sleeve 60 r while receiving the magnetic force by the magnet roll 60 q . The reference character 60 d denotes an agitating member for effecting the circulation of the toner in a developer container 60 e and sequentially conveying the toner into a magnetic force reach range around the developing sleeve 60 r.

In the present developing apparatus 60 E, in order to obtain a desired toner charging amount and a desired coat amount, the regulating blade 60 c was set to drawing pressure of 30 N/m, and a blade free length of 1.2 mm.

The toner t 3 coating the developing sleeve 60 r is conveyed to a developing region (developing area portion) “a” which is the opposed portion between the photosensitive drum 1 and the developing sleeve 60 r by the rotation of the sleeve 60 r . Also, a developing bias voltage (DC voltage of −340 V) is applied from the developing bias applying voltage source S 2 to the developing sleeve 60 r . The developing sleeve 60 r is driven at a peripheral speed 1.2 times as high relative to the photosensitive drum 1 . Thereby, the electrostatic latent image on the photosensitive drum 1 is reversal-developed with the toner t 3 .

Toner t 3 : This conforms to Comparative Example 1.

Also, as a construction resembling the present example, there is a developing apparatus disclosed in Japanese Patent Application Publication No. H4-15949.

Comparative Example 10

<Nonmagnetic Contact Developing Method>

Description will now be made of a developing apparatus 60 F according to this comparative example. FIG. 9 shows a schematic view of Example 1 of an image forming apparatus using Comparative Example 10.

The reference character 60 h designates a developing roller constituted by a mandrel 60 h 1 and an electrically conductive elastic layer 60 h 2 formed thereon. Also, the reference character 60 k denotes an elastic roller constituted by a mandrel 60 k 1 and an elastic layer 60 k 2 formed thereon. The developing roller 60 h is brought into contact with the photosensitive drum 1 with a constant pressure force, and the drawing pressure thereof was 20 N/m. Also, the elastic roller 60 k is fixed with a constant axis interval relative to the developing roller 60 h , and the drawing pressure thereof was 40 N/m. Also, the developing roller 60 h is driven at a peripheral speed 1.4 times as high relative to the photosensitive drum 1 , and the elastic roller 60 k is rotatively driven at the same number of revolutions as the developing roller 60 h so that the surface thereof may move in the opposite direction. The rubber hardness of the developing roller 60 h was 50 degrees in terms of ASKER C (load of 500 g), and 42 degrees in terms of microhardness.

A toner t 4 which will be described later is supplied to the elastic roller 60 k by an agitating member 60 d . Further, the elastic roller 60 k supplies the toner t 4 to the developing roller 60 h by the rotation thereof, and the toner t 4 is conveyed to a regulating portion. Then, the toner supplied onto the developing roller 60 h is regulated to predetermined frictional charging and a predetermined coat length by a regulating blade 60 i , and is conveyed to a developing portion a. The toner conveyed on the developing roller 60 h is used for the development of the photosensitive drum 1 in the developing portion a. Also, any toner not used for development but residual on the developing roller 60 h is once stripped off by the elastic roller 60 k and is again circulated in a developer container 60 e , and again coats the developing roller 60 h.

A DC voltage of −340 V as a developing bias was applied to the mandrel 60 h 1 of the developing roller 60 h . Also, the elastic roller 60 k and a regulating blade 60 i were made electrically common to the developing bias, and the same developing bias potential was applied thereto.

Toner t 4 : The mono-component nonmagnetic toner t which is the developer was made by mixing a binding resin and a charge controlling agent together, and via the steps of kneading, crushing and classifying, and adding a fluidizing agent or the like as an extraneous agent (crushing method). Also, the mean particle diameter (D 4 ) of the toner was 6 μm, and the mean degree of circularity thereof was 0.953.

Comparative Example 11

<Nonmagnetic Contact Developing Method Blade Bias Applied>

Description will now be made of a developing apparatus 60 G according to this comparative example. FIG. 10 shows a schematic view of Example 1 of an image forming apparatus using Comparative Example 11. The developing apparatus 60 G according to the present comparative example basically conforms to the developing apparatus 60 F described in Comparative Example 10, but differs in the following point from the developing apparatus 60 F.

−550 V was applied to phosphor bronze which is a regulating blade 60 i by an applying voltage source S 4 .

Comparative Example 12

<Non-contact Conveying Roller>

Description will now be made of a developing apparatus 60 H according to this comparative example. FIG. 11 shows a schematic view of Example 1 of an image forming apparatus using Comparative Example 12.

The reference character 60 h designates a developing roller constituted by a mandrel 60 h 1 and an electrically conductive elastic layer 60 h 2 formed thereon. Also, the reference character 60 j denotes a charge eliminating sheet constituted by an electrically conductive sheet 60 j 2 backed with an elastic material 60 j 1 . The developing roller 60 h is brought into contact with the photosensitive drum 1 with a constant pressure force, and the drawing pressure thereof was 20 N/m. Also, the charge eliminating sheet 60 j is fixed to the developing roller 60 h with a constant inroad amount, and the drawing pressure thereof was 55 N/m. Also, the developing roller 60 h was driven at a peripheral speed 1.4 times as high relative to the photosensitive drum 1 . Also, a conveying roller 60 n disposed in non-contact with the developing roller 60 h was provided and was rotatively driven so that the peripheral speed thereof might be the same as that of the developing roller 60 h . The rubber hardness of the developing roller 60 h was 50 degrees in terms of ASKER C (load of 500 g), and 42 degrees in terms of microhardness.

The toner t 4 is supplied to the conveying roller 60 n by an agitating member 60 d . Further, the conveying roller 60 n disposed in non-contact with the developing roller 60 h supplies the toner t 4 to the developing roller 60 h by the rotation thereof. Then, the toner supplied onto the developing roller 60 h is subjected to frictional charging by a regulating blade 60 i , and is regulated to a constant coat length and is conveyed to the developing portion a. The toner conveyed on the developing roller 60 h is used for the development of the photosensitive drum 1 in the developing portion a. Also, any toner not used for development but residual on the developing roller 60 h is once charge-eliminated by the charge eliminating sheet 60 j , is again circulated in the developer container 60 e , and again coats the developing roller 60 h.

A DC voltage of −340 V as a developing bias was applied to the mandrel 60 h 1 of the developing roller 60 h . Also, the conveying roller 60 n and the regulating blade 60 i were made electrically common to the developing bias, and the same developing bias potential was applied thereto.

Toner t 4 : This conforms to Comparative Example 10.

Also, as a construction resembling the present example, there is a developing apparatus disclosed in Japanese Patent No. 3225759.

About the Superiority of the Present Embodiment to the Conventional Art

Method of Evaluating Each Embodiment and Comparative Examples

Image evaluation for examining the differences between the present invention and the comparative examples will hereinafter be described.

(1) Various Image Evaluations in Example 1 of the Image Forming Apparatus

Description will first be made of various image evaluations by Example 1 of an image forming apparatus having a drum cleaner.

a) Fog Evaluation

Fog refers to an image fault that the toner is slightly used for development and appears like a ground stain in a blank portion (unexposed portion) which is originally not printed.

As regards a fog amount, the optical reflectance by a green filter was measured by an optical reflectance measuring machine (TC-6DS produced by Tokyo Denshoku Co.), and was subtracted from the reflectance of recording paper alone to thereby find a reflectance amount corresponding to the fog, and this reflectance amount was evaluated as a fog amount. The fog amount was measured over ten points or more on the recording paper to thereby find the mean value thereof.

x: The fog amount exceeds 2%.

Δ: The fog amount is 1-2%.

∘: The fog amount is 0.5-1%.

∘∘: The fog amount is less than 0.5%.

The evaluation environment was at 32.5° C. and 80% Rh. The fog evaluation was effected at the initial time of 50 sheets, and after the printing of 5,000 sheets. A printing test was carried out with a record image of a lateral line of an image percentage of 2% intermittently passed. “Intermittently” means that after printing, the next printing is effected via a standby state. Also, when other image fault which will hereinafter be described occurred, consideration was paid so that measurement might be effected avoiding that portion and the fog could be purely evaluated.

b-1) Evaluation of the Fog Characteristic when the Remaining Toner Amount is Decreased

A printing test is repeated, whereby the toner stored in the developing apparatus is decreased, and the evaluation image of the lateral line gradually becomes thin and in some cases, breaks. The fog characteristic when the remaining toner amount was thus decreased was discretely evaluated. When in the printing test, the fault of the lateral line image as previously mentioned has occurred, a fog evaluation is effected and thereafter, the developing apparatus is detached from the printer, and the operation of feeding the toner therein to the developing sleeve or the developing roller as by shaking by the hands is performed, and the developing apparatus is again mounted on the printer, and a fog evaluation is effected. By these image evaluations, a fog evaluation similar to the aforedescribed one is effected, and the worst (greatest) result is used as the fog evaluation of the present evaluation.

b-2) The Factor of Fog when the Remaining Toner Amount has Been Decreased

The supply of the nonmagnetic toner to the developing roller is effected by a sponge-like supplying roller being brought into contact with the developing roller so as to be counter-rotated. Accordingly, by this frictional contact between the developing roller and the supplying roller, the deterioration of the toner occurs remarkably and a reduction in a charge imparting property occurs. Thereby, if the number of printed sheets (particularly low coverage rate) increases, the fog amount increases.

Further, in such a toner supplying mechanism, there is formed an area in which the toner hardly changes places around the developing roller and is not circulated, and a toner suffering little from deterioration exists. On the other hand, the toner being circulated suffers from constant deterioration. If during the exhaustion of the toner, the cartridge is detached and the hand is waved, such a toner suffering little from deterioration and the toner having suffered from constant deterioration are mixed together in the developer container. That is, the toners differing greatly in the polarity of charge imparting from each other are mixed together and therefore, the fog amount increases remarkably.

The reason for such an increase in the fog amount is that when in such mixing of the toners, charge imparting is effected to the toners, the toner not deteriorated becomes higher in the charge imparting property and the deteriorated toner can hardly be subjected to charge imparting or has imparted thereto charges of a polarity opposite to the regular polarity. The fog amount is remarkably increased by the toner which cannot be subjected to charge imparting or has imparted thereto the charges of the opposite polarity.

The reason why the toner of the opposite polarity occurs as the fog amount is that the force received in an electric field is in a direction entirely opposite to the toner of the regular polarity, and the toner positively shifts to an ordinary non-print area on the surface of the drum.

In contrast, in the case of the magnetic toner, the toner is conveyed by a magnetic force and therefore, the deterioration of the toner does not remarkably occur and even if the waving of the hand for the process cartridge is effected immediately before the exhaustion of the toner, the toners differing greatly in the polarity are not mixed together and therefore, it is possible to prevent an increase in the fog amount immediately before the exhaustion of the toner.

c-1) Ghost

The supply stripping-off property of the developer was evaluated by a developing ghost. With the peripheral speed and process speed of the developing roller or the developing sleeve taken into account, a ghost image appearing at the cycle of the developing roller or the developing sleeve was evaluated. Specifically, the ghost was judged as an image fault by the ghost in a case where the density difference appearing in a halftone image wherein a solid black patch image of 5 mm square and 25 mm square was printed at the leading edge of paper at the first cycle of the developing roller or the developing sleeve can be visually recognized. In the printer according to each example, image recording was effected by the use of a 600 dpi laser scanner. In the present evaluation, the halftone image means a striped pattern in which one line in a main scanning direction is recorded and thereafter, four lines are non-recorded, and expresses the density of a halftone as a whole.

Here, the image evaluation thereof was carried out on the following standard.

• • x: A ghost is recognized in both patches.
  • Δ: A ghost is recognized in one of the patches.
  • ∘: A ghost is not recognized in any of the patches.

The evaluation environment was at 32.5° C. and 80% Rh. The ghost evaluation was carried out at the initial time of 100 sheets. A printing test was carried out with record images of a lateral line of an image percentage of 2% continuously passed.

c-2) The Factor of the Occurrence of the Ghost

In a developing apparatus comprising a photosensitive drum and a developing sleeve urged against each other and having no stripping-off and supplying roller, a fresh toner is supplied to that portion of the developing sleeve on which the toner has been consumed in the last revolution, and is conveyed to a regulating portion, but during the printing of solid black, a toner of about 90% or more of a coat amount is consumed. The consumed part is supplied onto the elastic sleeve in a state in which the percentage of the newly supplied toner is high relative to a toner not consumed but left, and is conveyed to the regulating portion. On the other hand, in a portion wherein the toner has not been consumed in the last revolution, the toner on the elastic sleeve is intactly returned to the supplying portion and therefore, is supplied onto the elastic sleeve in a state in which the percentage of the newly supplied toner is low relative to the toner not consumed but left, and is conveyed to the regulating portion. That is, the toner conveyed to the regulating portion causes a difference between the percentages of the new and old toners due to the hysteresis of toner consumption in the last revolution. When the changing of places between the upper layer and lower layer of the toner layer, i.e., the stripping-off and supply cannot be sufficiently effected, a ghost image fault reflecting the hysteresis of the toner consumption in the last revolution occurs in a uniform halftone image.

d-1) Uniformity of Hair Line

The image evaluation was carried out by the continuity of vertical and horizontal 1-dot lines. In the printer according to each example, image recording was effected by the use of a 600 dpi laser scanner. The image recording was effected about a 1-dot line parallel to the direction of progress of the process, and a 1-dot line parallel to the main scanning direction of a laser scanning system. Hair lines each having a length of 2 cm are outputted in the apparatus according to each example, and 100 points are extracted at random about each line, and 200 μm square about the line is observed at respective points through an optical microscope, and a half value width of the density of the line is used as a line width, and the standard deflection of the line width is calculated with respect to each direction. Then, the line standard deflection in a process direction is defined as σv, and the laser scanning direction standard deflection is defined as σh, and the ratio between the two is calculated to thereby obtain a line standard deflection ratio σv/σh. By the use of this value, evaluation was carried out on the following standard.

xx: The line standard deflection ratio σv/σh is less than 0.7 or exceeds 1.43, and the break of a 1-dot line can be visually discriminated.

x: The line standard deflection ratio σv/σh is less than 0.7 or exceeds 1.43.

Δ: The line standard deflection ratio σv/σh is 0.7 or greater, less than 0.8 or 1.25 or greater and 1.43 or less.

∘: The line stand deflection ratio σv/σh is 0.8 or greater and less than 1.25.

Evaluation was carried out at the initial time of 50 sheets and at the time of 5,000 sheets. A printing test was carried out with the record image of a lateral line of an image percentage of 2% intermittently passed.

d-2) Factor of the Lowering of Hair Line Uniformity

In magnetic non-contact development, there is the problem that the hair line uniformity differs between length and width. When a magnetic brush develops while moving in parallel to the movement direction of the photosensitive drum the hair line uniformity is good, and becomes liable to break in a direction orthogonal thereto.

e-1) Image Edge Fault

An image edge fault is the image fault that in an image having great density, the boundary of the density difference between the two becomes thin.

Image evaluation was carried out with a solid black image of 25 mm square printed in a halftone image. In the present evaluation, the halftone image means a dotted pattern in which one dot relative to the main scanning direction is recorded, whereafter four dots are non-recorded, and one dot is recorded relative to a direction perpendicular to the main scanning direction, whereafter four dots are non-recorded, and expresses halftone density as a whole. In the halftone and solid black edge portion of the obtained image, on the halftone side of the edge portion, the number of toner particles in one dot of the compacted toner was measured by the use of an optical microscope and further, about a halftone image portion at a position sufficiently separate from the edge portion, the number of toner particles in one dot was likewise measured. In the measurement of the number of toner particles in one dot, fifteen dots were extracted at random in each area to thereby find the mean value of the number of toner particles, which was defined as the number of toner particles in one dot.

x: The number of toner particles measured at the edge is less than 60% of the number of toner particles at the position sufficiently separate from the edge portion.

∘: The number of toner particles measured at the edge is 60% or more of the number of toner particles at the position sufficiently separate from the edge portion.

Evaluation was carried out at the initial time of 100 sheets. A printing test was carried out with record images of a lateral line of an image percentage of 2% continuously passed.

e-2) Factor of the Occurrence of an Image Edge Fault

The factor of an image edge fault will now be considered with reference to FIGS. 12A and 12B. When the Vpp value of an AC voltage is made great, the going and coming of the toner occurs in an area developed by the flight of the toner. If at this time, a print area having a great density difference exists, the toner reciprocally moves near a boundary line, whereupon the toner is drawn near to a print area having greater density, and an area in the boundary portion which is lower in density is considered to become lower.

f) Evaluation of Solid Black Density Difference

In Example 1 of the image forming apparatus, a solid black image having black printed on the whole surface thereof is outputted, and the optical reflection density thereof is measured by a densitometer RD-1255 produced by Macbeth Co., Inc. The solid black density in the solid black image corresponding to the first circumferential length of the developer carrying member immediately after the start of printing and the solid black density corresponding to the second and subsequent circumferential lengths of the developer carrying member are measured about 10 points, respectively, and the means thereof are calculated, and from the difference therebetween, evaluation is carried out by the following standard.

x: is 0.2 or greater.

Δ: is 0.1 or greater and less than 0.2.

∘: is less than 0.1.

Density evaluation was carried out after the apparatus was left unused for 24 hours after the initial time of 100 sheets. A printing test was carried out with record images of a lateral line of an image percentage of 5% continuously passed. Also, an evaluation environment was at 32.5° C. and 80% Rh.

g-1) Halftone Image Defect 1

Image evaluation was carried out from the number of defects of an image with a halftone image outputted. In the printer according to each example, image recording was effected by the use of a 600 dpi laser scanner. In the present evaluation, the halftone image means a striped pattern in which one line in the main scanning direction is recorded, whereafter two lines are non-recorded, and expresses the density of the halftone as a whole.

Particularly in the present invention, importance is attached to the uniformity of a halftone image, and the defect of a white spot or a black spot of 0.3 mm or greater was evaluated.

x: White spots or black spots having a diameter of 0.3 mm or greater exceeding five spots exist in a halftone image.

Δ: One to five white spots or black spots having a diameter of 0.3 mm or greater exist in a halftone image.

∘: Any white spot or black spot having a diameter of 0.3 mm or greater does not exist in a halftone image.

Evaluation was carried out after the printing test of 5,000 sheets. A printing test was carried out with record images of a lateral line of an image percentage of 2% continuously passed.

g-2) Factor of Occurrence of Halftone Image Defect 1

In order to disturb the coat layer by the occurrence of a compact cluster of toner or the mixing of a foreign substance, the defect of the degree of size of the compact cluster or the foreign substance is caused in the halftone image.

h-1) Evaluation of a Ripple Image Fault

In Example 1 of the image forming apparatus, the evaluation of a ripple image fault was carried out. As regards the evaluating method, a solid white image, a solid black image and a halftone image are printed, and the evaluation is visually carried out by the following standard.

x: A ripple-shaped character stain can be confirmed on the solid white image.

Δ: Ripple-shaped unevenness can be visually confirmed in the solid black image or the halftone image.

∘: Ripple-shaped unevenness cannot be visually confirmed in the solid white image, the solid black image and the halftone image.

The evaluation of the ripple image fault was carried out after the apparatus was left unused for 24 hours after the initial printing of 100 sheets. A printing test was carried out with record images of a lateral line of an image percentage of 5% continuously passed. Also, the evaluation environment was at 15.0° C. and 10% Rh.

h-2) Factor of a Ripple Image Fault

Description will hereinafter be made of the factor of occurrence of a ripple image fault. The ripple image fault occurs in the toner layer applied as a coat onto the developer carrying member by the regulating blade when the toner layer is disturbed. Specifically, it occurs by the following process. First, the toner having had charges excessively imparted thereto electrically firmly adheres to the surface of the developer carrying member. It becomes difficult for the firmly adhering toner to change places with a newly supplied toner when it is not used for development in the developing portion but is returned into the developer container. Thereupon, the newly supplied toner comes to lightly ride onto the firmly adhering toner. When such a state occurs, it becomes difficult for the newly supplied toner to obtain the sufficient imparting of charges. That is, in the toner coat layer, a layer differing in the charge amount is formed, and disturbance occurs to the toner coat layer. The newly supplied toner is applied as a coat while the imparting of charges is not sufficiently effected and therefore, a ripple-shaped image fault occurs on a uniform image like a solid black image or a halftone image. Further, when such a charge imparting property as under a low-temperature and low-humidity environment becomes high, a ripple-shaped character stain also occurs in a solid white image.

(2) Various Image Evaluations in Example 2 of the Image Forming Apparatus

Description will now be made of various image evaluations by Example 2 of an image forming apparatus which is a cleaner-less system

A-1) Cleaner-less Toner Collecting Property

The image recording apparatus is stopped during the printing of an evaluation pattern in which a solid black image of about 30-50 mm was printed on the leading edge of a record image, whereafter a solid white image was disposed. The timing at which the image recording apparatus is stopped is a point of time at which the central position of the solid black image on the leading edge has just reached the developing area. Then, the toners having adhered to the surface of the photosensitive drum before and after the development are measured as reflectances, and the ratio thereof is found, whereby it becomes possible to effect the evaluation of the toner collecting efficiency. Actually, the toner on the drum is once transferred to a transparent tape, and the tape to which the toner adheres is stuck on the recording paper or the like, and from on the tape, the net reflectance of the toner is measured as in the measurement of fog.

x: The collection rate is less than 30%.

Δ: The collection rate is 30% or greater and less than 50%.

∘: The collection rate is 50% or greater.

Evaluation was carried out at the initial time of 100 sheets. A printing test was carried out with record images of a lateral line of an image percentage of 2% continuously passed.

A-2) Factor of a Reduction in the Cleaner-Less Toner Collecting Property

The greatest difference of Example 2 of the image forming apparatus is that the drum cleaner is disused, and any untransferred toner is collected into the developing apparatus and is recycled. In the present example, the developing roller which is the developer carrying member is urged against the photosensitive drum which is a member to be developed with predetermined pressure, and a developing bias is applied thereto, and the electrostatic latent image formed on the surface of the photosensitive drum is developed (visualized) with the toner which is a developer and at the same time, the untransferred toner on the non-exposed portion (white ground portion) is collected. That is, it is possible that an electric field by which the toner is used for development from the developing roller to the light portion (exposed portion) of the photosensitive drum and an electric field by which the toner is collected from the dark portion (non-exposed portion) of the photosensitive drum to the developing roller are formed at a time.

As shown in FIG. 13, by the utilization of the potential difference between the developing bias and the potential (V 1 in case of solid black) of the printed portion, the toner is shifted from the developing roller to the photosensitive drum to thereby effect reversal development, and by the utilization of the potential difference between the developing bias and the potential (Vd) of the non-printed portion, the returned toner on the photosensitive drum is shifted onto the developing roller and is collected.

Further, by the developing roller being urged and brought into contact, the distance between the photosensitive drum and the developing roller becomes small and the intensity of the electric field is increased to thereby improve the collecting property simultaneous with developing.

In addition, by the developing roller being urged and brought into contact, the development and collection of the electric field by an increase in the developing nip are reliably effected and also, the making of the returned toner negative by the developing roller is promoted and the physical loosening of the returned toner is effected to thereby improve the collecting property.

On the other hand, if the photosensitive drum and the developing roller are opposed to each other in non-contact with each other, the distance therebetween becomes great and therefore, a magnetic collecting force and an electrical collecting force become weak. Therefore, the collection rate is lowered.

Also, if the photosensitive drum and the developing roller are urged against and in contact with each other, the attraction and van der Waals force working by objects contacting with each other become forces of the substantially same order between the photosensitive drum and the toner, between the toner and the developing roller, and between the toner and the toner and therefore, they do not become the factor of a reduction in the collecting property. However, when the photosensitive drum and the developing roller are in non-contact with each other, the aforementioned forces work only between the photosensitive drum and the toner and strip off the toner from the photosensitive drum and therefore, this becomes a hindrance and the collecting property is remarkably reduced.

B-1) Halftone Image Defect 2 (Example 2 of the Image Forming Apparatus)

Like the example 1 of the image forming apparatus, the evaluation of halftone image defect will be carried out with respect to the example 2 of the image forming apparatus.

B-2) Factor of Occurrence of the Halftone Image Defect 2

Like the halftone image defect 1, a halftone image defect 2 is caused by the toner compact cluster and the foreign substance. However, in the cleaner-less system which is Example 2 of the image forming apparatus, the collection of the returned toner is done and therefore, the halftone image defect 2 is liable to occur. Particularly, when as in the nonmagnetic contact development, the supplying roller is in contact with the developing roller and is being counter-rotated, physical stress becomes high in the contact portion. When such a construction is used, the compact cluster is liable to occur due to the returned toner and deteriorated toner, and the halftone image defect 2 is remarkably liable to occur.

C-1) Halftone Image Defect Due to Paper Dust

In Example 2 of the image forming apparatus, paper dust (paper fiber) may adhere from the recording paper to the photosensitive drum, and be introduced into the developing apparatus via charging. When the paper dust is introduced into the developing apparatus, the paper dust may become tangled with the developing roller, and the like, to thereby cause an image fault extending in the process progression direction of the developing roller cycle. This was evaluated discretely from the halftone image defect of item B).

A minor axis length of 0.3 mm or greater and a major axis length of 2 mm or greater were regarded as an image fault, and evaluation was carried out with the number of defects in the surface on the following standard.

x: Defects exceeding five points exist in the halftone image.

Δ: One to five defects exist in the halftone image.

∘: No defect exists in the halftone image.

C-2) Factor of Occurrence of the Halftone Image Defect Due to Paper Dust

When paper dust included in the returned toner gets mixed with the interior of the developing apparatus, the paper dust adheres to the sponge-like supplying roller for supplying the toner to the developing roller, to thereby cause a reduction in the stripping-off and supplying property. When the paper dust is accumulated on the supplying roller, the toner layer on the developing roller is disturbed to thereby cause a defect extending in the process direction.

D-1) Evaluation of a Solid Black Image Defect

Image evaluation was carried out with a solid black image outputted and from the number of defects of the image. Particularly in the present example, defects of 0.3 mm or greater were evaluated.

x: White spots having a diameter of 0.3 mm or greater and exceeding fifty spots exist in the solid black image.

Δ: Ten to fifty white spots having a diameter of 0.3 mm or greater exist in the solid black image.

∘: Less than ten white spots having a diameter of 0.3 mm or greater exist in the solid black image.

The evaluation environment was at 32.5° C. and 80% Rh. A printing test was carried out with record image of a lateral line of an image percentage of 5% continuously passed. Evaluation was carried out with three sheets of solid black images outputted after the lapse of 24 hours after the printing of 100 sheets. Image evaluation was typified by the page of these three sheets which included most defects.

D-2) Factor of Occurrence of the Solid Black Image Defect

As shown in FIGS. 14A and 14B, when during the application of an AC voltage, a solid white image is being developed, the difference between the surface potential (dark potential Vd) of the photosensitive drum 1 and the maximum value (Vmax) of the developing bias voltage value becomes maximum electric field intensity to thereby bring about a state in which leak L 3 is liable to occur.

When the leak L 3 occurs, the electrostatic latent image on the photosensitive drum 1 in the pertinent portion is disturbed with a result that part of the potential (dark potential Vd) of a solid white portion on the photosensitive drum 1 approximates to or exceeds light potential (V 1 ) due to the leak and therefore, it is considered that the toner “t” to the photosensitive drum 1 by reversal development shifts with a result that the toner adheres to the pertinent portion of the photosensitive drum 1 and a black-spotted image occurs.

When the leak occurs, there is formed on the photosensitive drum a portion charged with a value of Vmax, irrespective of the intensity of the electric field. If Vmax is great, the contrast (|Vmax−Vdc|) of the developing bias to the DC value Vdc is great and therefore the shift amount of the toner is increased and is very conspicuous on the image.

Further, when the paper dust included in the returned toner comes to the developing area together with the toner (FIG. 14A), leak occurs along the paper dust. When as shown in FIG. 14A, the paper dust F has come to the developing area, the gap with respect to the drum becomes G 4 smaller than G 3 . At this time, the intensity of the localized electric field applied to the paper dust is increased (right in FIG. 14B) and leak becomes liable to occur. Also, under a high-temperature and high-humidity environment, the paper dust adsorbs much moisture and lowers in resistance. If at this time, as shown in FIG. 14C, an external electric field E is applied, the inclination of charges occurs and the charge amount increases at the tip end of the paper dust and the leak becomes further liable to occur. From this, it is considered that in the cleaner-less system, as compared with a system with a drum cleaner, the leak becomes, more liable to occur.

[Measurement of the Toner Magnetic Compaction Amount]

Magnetic compaction means that the toner ranges in the shape of a string of beads and compacts. Although the clear and accurate mechanism of occurrence thereof is not apparent, roughly the following is considered to be the mechanism. First, the toner exists in a strong external magnetic field. Next, constant pressure is applied to the toner in a certain particular direction for a particular time or longer. Thereupon, the toner of a small magnetic polarity produces a magnetic polarity, and ranges in the shape of a string of beads and compacts.

As a method of measuring the magnetic compaction amount in the present example, evaluation was carried out by the use of the photograph of toner shapes classified by particle size obtained by a flow particle image analyzer FPIA2100 produced by Sysmex Co. Inc. As the measuring method by FPIA2100, 0.1-5 ml of interfacial active agent as a dispersant is added to 50-150 ml of measurement solvent, and 2-20 mg of measurement sample picked from on the developing sleeve is further added thereto to thereby provide a suspended solution. The solution having the sample suspended therein is subjected to a dispersing process for about one minute by an ultrasonic dispersing machine and is uniformly dispersed, whereafter about 5 ml thereof is supplied to the aforementioned FPIA2100 and measurement is effected. As the standard of evaluation, the rate of toner compaction ranging in the shape of a straight chain is found in toner particles classified into particle size classes 4 and 5 (particle number mean diameter of 10-40 μm) in FPIA2100. Judgment was done from the mean value obtained as the result of this measurement having been effected three times.

Large: The presence percentage of magnetic compaction is 20% or greater.

Medium: The presence percentage of magnetic compaction is 10% or greater and less than 20%.

Small: The presence percentage of magnetic compaction is less than 10%.

The evaluation of the magnetic compaction was carried out after the printing of 5,000 sheets in a printing test. The printing test was carried out with record images of a lateral line of an image percentage of 5% intermittently passed.

(3) Result of the Evaluation

Table 1 below shows the result of various image evaluations in Example 1 of image forming apparatuses (with a drum cleaner) according to Embodiments 1 and 2 and Comparative Examples 1 to 12.

Also, Table 2 shows the result of various image evaluations in Example 2 of image forming apparatuses (cleaner-less system) according to Embodiments 1 and 2 and Comparative Examples 1 to 12.

	TABLE 1
	Example 1 of image forming apparatus
					a)fog (high-
					temperature
	Mean			Magnetic	high-humidity	b)fog
Embodiments and	degree of			compaction	environment	(toner
Comparative Examples	circularity	|Br|/|B|	Nsb/(Bs × R)	amount	100 th → 5000 th sheet	exhausted)	c)ghost
Embodiment 1	0.976	0.96	0.25	Medium	◯→◯	◯	◯
Contact,
Elastic sleeve
Pole position regulation
with blade bias
Embodiment 2	0.967	0.96	0.25	Medium	◯→Δ	◯	◯
Contact,
Elastic sleeve
Pole position regulation
with blade bias
Comparative	0.955	0.96	0.25	Medium	◯→X	◯	◯
Example 1
Contact,
Elastic sleeve
Mean degree of
circularity low
Pole position regulation
with blade bias
Comparative Example 2	0.980	0.96	0.54	Great	◯→X	◯	Δ
Contact,
Elastic sleeve
Nsb great
Pole position regulation
with blade bias
Comparative	0.980	0.03	0.25	Small	◯→◯	◯	X
Example 3
Contact,
Elastic sleeve
Inter-pole position
regulation
with blade bias
Comparative	0.980	0.96	0.25	Great	Δ→X	Δ	◯
Example 4
Contact,
Elastic sleeve
Pole position regulation
without blade bias
Comparative	0.980	0.03	0.25	Small	◯→X	◯	◯
Example 5
Contact,
Elastic sleeve
Inter-pole position
regulation
without blade bias
Comparative	0.955	0.03	0.52	Small	◯→◯	◯	◯
Example 6
Magnetic non-contact
development
Inter-pole position
regulation
without blade bias
Comparative	0.955	0.96	0.52	Medium	◯→◯	◯	◯
Example 7
Magnetic non-contact
development
Pole position regulation
without blade bias
Comparative	0.955	0.96	0.52	Medium	◯→◯	◯	◯
Example 8
Magnetic non-contact
development
Pole position regulation
With blade bias
Comparative Example 9	0.955	—	—	Medium	◯→Δ	Δ	Δ
Multi-pole magnet
Comparative Example 10	0.955	—	—	—	◯◯→Δ	X	◯
Non-magnetic toner
Comparative	0.955	—	—	—	◯◯→◯	X	◯
Example 11
Non-magnetic toner
with blade bias
Comparative Example 12	0.955	—	—	—	◯→Δ	Δ	◯
Non-contact conveying
roller
	Example 1 of image forming apparatus
						h)ripple wave-