JP2002091167A - Developing device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent developed image without any stripe by preventing a toner flocculated body from unevenly abrading an elastic blade at the abutting nip part of the blade even when a developing sleeve is coated with toner excellent in fixing ability and having small particle size by the blade. SOLUTION: A magnet 11 in the developing sleeve 6 of a developing device has repulsive magnetic poles S2 and S3 inside a developing container 12 on the upstream side of the elastic blade 10 made of silicone rubber, and has a bristle cutting spot (h) where magnetic force is zero between the poles S2 and S3. The toner capable of passing through the spot (h) is only toner held on the sleeve 6 by van der Waals force or the like other than magnetic force, and the toner flocculated body T does not pass through the spot (h) because the van der Waals force is weak, and is separated from the sleeve and restored into the container 12. Since the growth of the toner flocculated body due to the repeated passing and the compression of the toner at a nip part H between the blade 10 and the sleeve 6 or the sticking thereof to the sleeve is prevented, the blade is not unevenly abraded and the stripe is not caused on the developed image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, and a process cartridge.

[0002]

2. Description of the Related Art A developing device used in an image forming apparatus such as a laser beam printer or a copying machine uses a powdery developer, and the developer is stored in a developing container of the developing device, and developed. The developer is conveyed to the developer carrier by the developer carrier, held on the developer carrier, and regulated to a predetermined layer thickness by a developer layer thickness regulating member and given a predetermined charge, and the image is transferred in this state. The sheet is transported to a development area facing the carrier, and is used for developing the electrostatic latent image formed on the image carrier.

As one of the developing methods, a latent image on an image carrier is developed with toner (one-component developer) on the developer carrier while the developer carrier is kept out of contact with the image carrier. Jumping development is known.

By the way, in a recent printer device, L
Printers such as EDs and LBPs have become mainstream in the market, and devices having higher resolution, for example, devices having resolutions of 600, 800, and 1200 dpi, have become mainstreams in technical development. Along with this, a higher resolution and higher definition developing method is required.

[0005] An elastic blade (elastic blade) as a developer layer thickness regulating member is brought into contact with a developing sleeve (developer carrying member) so that sufficient charge can be imparted to the toner to improve the image quality. Then, an elastic blade method or the like that regulates the amount of toner coating while giving a triboelectric charge to the toner on the developing sleeve has been put to practical use. In order to charge the toner more uniformly, a toner layer forming method for reducing the amount of toner coating on the developing sleeve has been developed. Further, as a toner, a toner having a smaller particle diameter of 4 to 6.5 μm has been developed in order to improve resolution and sharpness and faithfully reproduce a latent image.

Further, from the viewpoints of energy saving and shortening of the first print time, a contact heating type fixing system having good thermal efficiency and safety has been put into practical use as a fixing device for fixing a toner image transferred onto a transfer material. Therefore, the fixing temperature of the image forming apparatus tends to decrease. The toner used at this time is capable of fixing at a low temperature by improving the binder thermal properties and the wax thermal properties to improve the fixing performance and controlling the melt viscoelasticity of the toner.

Hitherto, Japanese Patent Application Laid-Open No. Hei 10-228168 has proposed a developing method which satisfies the conditions of elastic blade coating for toner having good fixability and small particle diameter.

[0008]

However, in the above-mentioned method, when an elastic blade that is more easily worn, for example, an elastic blade of silicone rubber having a low hardness is used, the elastic blade is unevenly worn, and the shaving powder is generated. There is a problem in that the toner adheres to the surface of the developing sleeve, causing uneven streaks in the developed image.

Conventionally, uneven wear of the elastic blade is caused by a coarse toner powder having a large particle diameter in the pulverized toner (particle diameter: 20 to 50 μm).
It is known that the toner particles are generated by abrasion.However, even when toner particles are fine particles and particles of opposite polarity are externally used, the toner particles are attracted by the opposite polarity particles as electric nuclei. As a result, similar uneven wear occurs.

Originally, the elastic blade exerts an effect of preventing toner from sticking to the developing sleeve and clogging of the toner into the contact nip by uniformly abrading the surface.
When the toner aggregate is held on the developing sleeve, not only does the toner coating amount on the developing sleeve be disturbed, but also the elastic blade is moved in the longitudinal direction (the direction along the longitudinal direction of the developing sleeve) every time the developing sleeve is rotated. Wear unevenly.
The shaving powder of the elastic blade due to the uneven wear adheres to the surface of the developing sleeve to form a film (filming), and non-uniformly increases the electric resistance value of the surface of the developing sleeve. As a result, the density of the charged electric charges is non-uniformly reduced, and as a result, stripe-like light density unevenness or density unevenness, that is, streaking occurs in the developed image.

Therefore, an object of the present invention is to provide a toner having good fixability and a small particle size coated on a developing sleeve with an elastic blade. An object of the present invention is to provide a developing device capable of obtaining a good developed image without streaks by preventing uneven wear of an elastic blade, and a process cartridge equipped with the developing device.

[0012]

The above object is achieved by a developing device and a process cartridge according to the present invention.
In summary, the present invention provides a magnetic field generator having a rotatable developer carrier mounted in a developer container containing a one-component magnetic developer, and a plurality of magnetic poles non-rotatably disposed within the developer carrier. Means, and a developer layer thickness regulating member that abuts on the developer carrier and regulates a developer layer thickness on the developer carrier, wherein the developer has a weight average particle diameter of 6%. 0.5 μm or less, particles of the opposite polarity to the developer are externally added to the developer, and the developer layer thickness regulating member has an abrasion loss at a contact portion with the developer carrier. The device has a wear performance of 3 μm or more in the life of the device, and the magnetic field generating means is located at a position in the developing container upstream of the contact portion with respect to the rotation direction of the developer carrier and in the rotation direction. Characterized by having two repulsive magnetic poles of the same polarity adjacent to each other along It is a developing device.

The present invention also provides a rotatable developer carrier installed in a developer container containing a one-component magnetic developer, and a magnetic field generator having a plurality of non-rotatably disposed magnetic poles in the developer carrier. Means, and a developer layer thickness regulating member that abuts on the developer carrier and regulates a developer layer thickness on the developer carrier, wherein the developer has a weight average particle diameter. 6.5 μm or less, particles of a polarity opposite to that of the developer are externally added to the developer, and the developer layer thickness regulating member has an abrasion loss at a contact portion with the developer carrier. Has a wear performance of 3 μm or more in the life of the developing device,
The magnetic field generating means may include two repulsive magnetic poles of the same polarity adjacent to each other in the rotational direction with the contact portion interposed therebetween at a position near the contact portion with respect to the rotation direction of the developer carrier. This is a developing device characterized by the following.

According to the present invention, at least the contact portion of the regulating member is made of silicone rubber. The silicone rubber is lined with an elastic support plate.

Further, according to the present invention, in a process cartridge having at least an image carrier and a developing device for developing an electrostatic latent image on the image carrier, the process cartridge is detachably attached to an image forming apparatus main body. The device is a process cartridge that is any of the developing devices described above.

[0016]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic structural view showing an image forming apparatus provided with a developing device of the present invention. This apparatus is an image forming apparatus using an electrophotographic process, and is a laser beam printer of a process cartridge detachable type.

The image forming apparatus includes a rotating drum type electrophotographic photosensitive member, that is, a photosensitive drum 1. The photosensitive drum 1 has a photosensitive layer of an organic photoconductor (OPC) on an outer peripheral surface of a cylindrical aluminum substrate. (Organic photoreceptor) and is used with an aluminum substrate grounded.

The photosensitive drum 1 is rotationally driven in the clockwise direction of the arrow at a predetermined peripheral speed (process speed) of, for example, 50 mm / sec, and its surface is uniformly charged by a charging roller 2 as a contact charging member. In the present embodiment, the charging roller 2 rotates following the rotation of the photosensitive drum 1 and applies an oscillating voltage (AC voltage + DC voltage) to the charging roller 2 from a high-voltage power supply (not shown) to thereby change the surface of the photosensitive drum 1. Is a predetermined negative polarity / potential, for example, Vd = −600 V
(Vd: dark portion potential).

The charged photosensitive drum 1 is output from a laser scanner 5 and is deflected in the direction of the photosensitive drum 1 by a folding mirror 5a and modulated according to a time-series digital image signal of target image information. Scanning exposure is performed by the light L, whereby an electrostatic latent image corresponding to target image information is formed on the surface of the photosensitive drum 1, for example, Vl = −15.
It is formed at 0 V (Vl: bright portion potential).

The electrostatic latent image formed on the photosensitive drum 1 is
The image is reversely developed using a developer by the developing device 3 and is visualized as a toner image. During development, a predetermined developing bias is applied to the developing sleeve 6 of the developing device from a high-voltage power supply (developing power supply) (not shown).

On the other hand, a transfer guide 7
The transfer material P is supplied to the transfer section where the photosensitive drum 1 and the transfer roller 8 are in contact with each other at the same time as the formation of a toner image on the photosensitive drum 1, and is transferred from a high-voltage power supply (transfer power supply) (not shown) to a predetermined transfer. By applying a bias to the transfer roller 8, the toner image on the photosensitive drum 1 is transferred to the transfer material P.

The transfer material P, which has passed the transfer portion and received the toner image, is separated from the photosensitive drum 1 and
Then, the toner image is subjected to a fixing process of the toner image, and is output as an image formed product (print). After the transfer, the photosensitive drum 1 is subjected to the next image formation after the residual toner on the surface is removed by the cleaning device 9.

In this embodiment, the photosensitive drum 1, the charging roller 2, the developing device 3 and the cleaning device 9 are constituted in a process cartridge 16 integrally including these components.
It is removably installed in the main body of the image forming apparatus.

The process cartridge 16 has a slit window 17 on the upper surface thereof into which laser light enters, and an opening / closing shutter (not shown) in an opening below the photosensitive drum 1 below. When the process cartridge is removed from the main body of the device,
The opening is closed to protect the photosensitive drum 1, and when it is mounted, it is opened to expose the lower part of the photosensitive drum 1.

The lower portion of the process cartridge 16 mounted on the printer main body is supported by the positioning support members 14 on the printer main body side, and is thereby held at a predetermined position in the printer main body. When the process cartridge 16 is mounted on the printer body,
Mechanically and electrically coupled with the printer body,
The photosensitive drum 1 and the developing sleeve 6 of the developing device 3 can be driven by the driving mechanism of the printer main body, and the charging roller 2 and the developing sleeve 6 can be driven from the power supply of the printer main body.
And the like can be applied.

In the present invention, the process cartridge only needs to include the developing device 3 on the photosensitive drum 1 and at least one other processing means such as the charging roller 2 and the cleaning device 9.

According to the present embodiment, the developing device 3 has the developing container 12 containing the magnetic toner of the one-component magnetic developer, and the developing agent is provided in the opening of the developing container 12 facing the photosensitive drum 1. The developing sleeve 6 is provided as a carrier,
The developing sleeve 6 is driven to rotate in the direction of arrow b. In this embodiment, the developing sleeve 6 is formed of an aluminum pipe having a thickness of 1 mm and a diameter of 6 mm, and a conductive resin layer is formed on the surface of the developing sleeve 6. The conductive resin layer is
It is made of a material in which phenol resin is mixed with carbon particles and graphite having solid lubricity. By forming this conductive resin layer, the surface of the developing sleeve 6 is roughened. The surface roughness of the developing sleeve 6 is JI
The average surface roughness Ra of the S standard is about 0.4 to 3.5 μm, and in this embodiment, the average surface roughness Ra is 1.0 μm.

In the developing sleeve 6, a roller-shaped magnet (magnet roller) 11 having a plurality of magnetic poles is arranged as a magnetic field generating means.
Is held in the developing sleeve 6 so as not to rotate irrespective of the rotation of the developing sleeve 6.

In this embodiment, as shown in FIG. 2, the magnet 11 has a magnetic pole arrangement of five magnetic poles S1, N1, S2, S3, and N2. The magnetic pole S <b> 1 is located at a position facing the photosensitive drum 1, and its magnetic force is 85% on the surface of the developing sleeve 6.
mT (millitesla). The magnetic pole N1 is located on the downstream side near the elastic blade 10 in the rotation direction of the developing sleeve 6, and has a magnetic force of 70 mT on the surface of the developing sleeve. The magnetic poles S2 and S3 are repulsion magnetic poles that form a repulsive magnetic field and are arranged adjacently with the same polarity along the rotation direction of the developing sleeve, and the magnetic poles S2 and S3 are arranged in the direction of the developing container 12 on the upstream side of the elastic blade 10. It is in the position facing. The magnetic pole S2 has a magnetic force of 65 mT, and the magnetic pole S3 is located upstream of the magnetic pole S2 and has a magnetic force of 65 mT. The magnetic pole N2 is located below the magnet 11 between the magnetic pole S3 and the magnetic pole S1, and has a magnetic force of 70 mT. FIG. 3 shows the magnetic force distribution of the magnet 11.

An elastic blade 10 is in contact with a substantially top portion of the developing sleeve 6 as a developer layer thickness regulating member. The elastic blade 10 regulates the layer thickness of the toner on the developing sleeve 6 and frictionally charges the toner to give an appropriate triboelectric charge (triboelectric charge). The elastic blade 10 is in contact with the surface of the developing sleeve 6 in a counter direction with respect to the rotation direction in order to obtain a stable toner coat on the developing sleeve 6.

According to the present invention, in the elastic blade 10, at least a portion of the elastic member 6b which comes into contact with the developing sleeve 6 is formed of a material having a predetermined wear performance. The elastic blade 10 will be described later.

In FIG. 2, the magnetic toner t in the developing container 12 is transferred to the developing sleeve 6 by the stirring and conveying member 15 in FIG.
And the magnet 11 in the developing sleeve 6
Circulating around the developing sleeve 11 under the influence of the magnetic force of the developing sleeve 6 and the rotation of the developing sleeve 6. The toner t is carried on the developing sleeve 6 by the magnetic force of the magnetic pole S3 of the magnet 11, and is conveyed by the rotation of the developing sleeve 6. Specifically, in the vicinity of the developing sleeve 6, the toner t is attracted to the surface of the developing sleeve 6 by the magnetic force of the magnetic pole S3, and the developing sleeve 6 rotates while being attracted by the magnetic force. Moving. Next, at the contact position between the elastic blade 10 and the developing sleeve 6, a part of the toner is separated from the developing sleeve 6 by the elastic blade 10.

The toner on the developing sleeve 6 is regulated to a predetermined layer thickness while passing through the contact nip H between the elastic blade 10 and the developing sleeve 6, and is given a predetermined triboelectric charge. While being held by the magnetic force of the magnetic pole N1 of the magnet 11, it is transported to the developing area facing the photosensitive drum 1, where the developing sleeve 6 is moved by the magnetic force of the magnetic pole S1.
Ears up from the surface. Then, due to a developing bias (AC voltage + DC voltage) applied from a developing power supply (not shown) between the developing sleeve 11 and the photosensitive drum 1, the toner rising on the developing sleeve 6 flies toward the photosensitive drum 1, The latent image adheres to the electrostatic latent image on the photosensitive drum 1 and reversely develops the latent image.

The toner remaining after the development is returned to the developing container 12 as the developing sleeve 6 rotates,
While being held by the magnetic pole N2, the magnetic pole S2 is guided to the back inside the developing container 12, and is separated from the developing sleeve 6 by the repulsive magnetic field between the magnetic poles S3 and S2 constituting the repelling magnetic pole, and is collected in the developing container 12. The collected toner is mixed with the toner in the container 12.

According to the present embodiment, the elastic blade 10 is made of silicone rubber, and the elastic member 1 is attached to the supporting metal plate 10a.
0b is a structure in which a plate-like silicone rubber is supported. The elastic blade 10 was produced by integral molding by injection molding of silicone rubber. By integrally molding, the accuracy of the position and the thickness of the silicone rubber 10b with respect to the supporting metal plate 10a can be improved.

Specifically, a 1.5 mm-thick gin-coated sheet metal coated with a primer for silicone rubber is placed as a supporting sheet metal 10a in a pre-heated mold, and LTV silicone rubber is LIM injection-molded in the mold. The silicone rubber was vulcanized by injection at a temperature of 150 ° C. for 5 minutes. After cooling, the obtained molded product was taken out and
Heat treatment was performed at 2 ° C. for 2 hours to obtain an elastic blade obtained by integrally molding silicone rubber on a gin-coated sheet metal.

The contact pressure (linear pressure) of the elastic blade 10 against the developing sleeve 6 can be measured as a drawing pressure as shown in FIG. In the present invention, the contact pressure of the elastic blade means this pull-out pressure.

As shown in FIG. 4, a SUS thin plate is prepared as the pulling plate 100, and a SUS thin plate whose length is folded in half is prepared as the sandwiching plate 101, and the drawing plate 100 is placed between the folded sandwiching plates 101. Insert and hold the sandwiching plate 10
1 is inserted into the contact nip between the developing sleeve 6 and the elastic blade 10. Then, pulling the spring scale attached to the extraction plate 100, the extraction plate is extracted at a constant speed,
The load (g) indicated by the spring meter at that time is read. If the value of the spring measurement is divided by 1.5 and the unit is converted into the load per cm, the pulling pressure of the elastic blade 10, that is, the contact pressure (linear pressure) (g / cm) is measured.

The developing device 3 uses a negatively chargeable magnetic toner as the magnetic toner (one-component magnetic developer).
In order to improve the fixability of this toner, the viscosity is increased by controlling the melt viscosity of the toner, and the particle size is reduced.

The average particle size of the toner can be measured by various methods. In the present invention, the average particle size is measured using Coulter Multitizer II (manufactured by Coulter Scientific Japan). Electrolyte is about 1% using primary sodium chloride
To prepare an aqueous solution of NaCl. As a commercially available product, for example, ISOTON®-II (manufactured by Coulter Scientific Japan) can be used.

The measuring method is as follows.
0.1 to 5 ml of a surfactant, preferably an alkylbenzenesulfonate, is added as a dispersant to the resulting solution, and 2 to 20 mg of a toner of a measurement sample is further added. Perform a dispersion treatment for 1-3 minutes,
The volume and the number of the toner were measured by the above-mentioned Coulter Multitizer using an aperture of 100 μm, and the volume distribution and the number distribution were calculated. If the weight-based average particle diameter D4 (unit: μm; the median value of each channel is a representative value for each channel) determined from the volume distribution, this is the weight average particle diameter of the sample.

In the present invention, the weight average particle diameter D4 is 6.5 μm.
m is treated as fine particle toner. To the fine particle toner, a positive external additive having a reverse polarity is added as a measure for preventing image deletion.

In this embodiment, a fine particle toner having a weight average particle diameter of 6 μm was used, and strontium titanate was externally added as a positive external additive to a negative toner of the fine particle toner. Examples of the positive external additive include melanin resin particles in addition to strontium titanate.

Specifically, the fine particle toner in this embodiment is obtained by adding a magnetic substance to 100 parts by weight of a binder resin.
After uniformly mixing 0 parts by weight and 1 part by weight of a negatively chargeable charge control agent, the mixture is melt-kneaded and pulverized to obtain a toner classified powder having a weight average particle diameter of 6 μm, and further to 100 parts by weight of the classified powder. On the other hand, 1.5 parts by weight of hydrophobic silica fine powder and 0.6 parts by weight of strontium titanate as a positive external additive were dry-mixed to produce.

Image deletion is apt to occur on the non-printing surface where the toner on the photosensitive drum is not applied. In the reversal development using the negative toner, positive particles having a polarity opposite to that of the negative toner easily fly to a white background portion (dark portion potential portion) on the image, and the positive particles that fly to the white background portion intervene, so that the particles are transferred onto paper as a transfer material. To reduce the chance that the talc directly contacts the photosensitive drum,
A low-resistance substance due to talc can be efficiently polished and removed from the surface of the photosensitive drum, and the occurrence of image deletion in the non-printed portion can be prevented.

In the present invention, the toner preferably has a melt index MI of 3 to 30 as an index of fixability. In this embodiment, MI is set to 20.

The MI was measured using a device described in JIS K7120 by a manual cutting method using a measurement sample temperature of 125.
C., a load of 5 kg, and a sample filling amount of 5 to 10 g. The measurement time is converted to a value of 10 minutes.

Conventionally, the aggregated toner is fixed at the nip portion of the elastic blade and adheres to the elastic blade with respect to the toner whose viscosity has been increased for improving the fixing property and which has been made finer for improving the image quality. A streak image due to the aggregated toner was sometimes generated.

Silicone rubber is suitable as a material that does not easily cause toner to adhere to the blade. This is because the silicone rubber is worn and scraped by contact with the developing sleeve, so that the toner hardly adheres to the silicone rubber. Further, silicone rubber has low hardness, and even when the contact pressure of the elastic blade is large, the contact nip is increased and the pressure per area is reduced, so that it is difficult for the toner to adhere to the silicone rubber from this surface.

Therefore, in the present invention, as described above, the elastic blade 10 is made of silicone rubber. However, if the silicone rubber is of a type that is more easily scraped, uneven shaving occurs due to uneven wear of the elastic blade as described in the conventional example, and the density unevenness (streaks) of a somewhat thick band-like streak occurs on the image. did.

Therefore, as shown in Table 1, the rubber hardness was 8
Elastic blades of silicone rubber (rubber 1 to rubber 8) were prepared in different stages, and a test was conducted to examine the effect of different amounts of wear on blade sticking and uneven streaks. The hardness of the silicone rubber was varied by changing the amount of silica as a filler with respect to the rubber and the number of crosslinking points of the rubber.

In the test, the life (nominal life in the specification) 1
An image having a printing ratio of 4% was developed using a developing device for 0000 sheets, and images were continuously formed on 10,000 sheets, and the presence or absence of streaks at that time was evaluated. Further, with respect to the elastic blade after the test, a portion at which a streak occurred at a contact nip portion was cleaned, and a wear depth of the portion was measured by a surface roughness meter. The contact pressure (drawing pressure) was 30 g / cm. Table 1 shows the results.

The wear depth was defined as shown in FIG.
In FIG. 5, H is a nip portion formed at the contact portion between the elastic blade 10 (silicone rubber elastic member 10b) and the developing sleeve 6, and the surface portion of the nip portion H of the silicone rubber elastic member 10b is scraped. Has occurred. In the silicone rubber elastic member 10b, an imaginary line L connecting the uncut surface portions on both sides of the nip portion H (both sides along the circumferential direction of the developing sleeve) is drawn. Is defined as the wear depth. In the example of FIG. 5, the width of the nip portion H is 1.5 m.
m, and the wear depth is 15 μm.

[0055]

[Table 1]

In Table 1, the fixing of the blade was examined by examining a phenomenon in which the toner adheres to the elastic blade and the adhered toner disturbs the toner coat before and after passing through the nip. The meanings of the symbols in the blade fixing column are as follows. ：: No blade sticking occurred. Δ: Blade sticking was observed, but the effect was hardly recognized on the image. X: White streaks are clearly formed on the image due to sticking of the blade.

In addition, for the uneven streaks, the phenomenon that the nip width becomes non-uniform due to the scraping of the elastic blade and the toner coat becomes uneven was examined. The meanings of the symbols in the stripes column are as follows. ：: No streaks occurred. Δ: Scratching unevenness was observed, but on the image there was little effect of uneven streaks. ×: Streaks clearly appear on the image.

From Table 1, (1) The wear depth is correlated with the hardness of the silicone rubber of the elastic blade, and when the hardness is 55 ° (JISA) or less, the rubber is easily shaved.
The wear depth increases. (2) If the abrasion depth is 3 μm or more, it is difficult for the toner to adhere to the elastic blade (however, the abrasion depth needs to be 3 μm or less from the life of the developing device). (3) When the silicone rubber hardness is low, uneven streaks due to scraping are likely to occur.

That is, if the hardness of the silicone rubber is high,
It has been found that when the toner easily sticks to the blade and the hardness is too low, uneven streaks due to uneven scraping of the rubber are likely to occur.

As described above, the toner is fixed to the elastic blade 10 by fixing the elastic member 10b to a material having a wear performance such that the wear amount becomes 3 μm or more in the life of the developing device, preferably silicone rubber. I knew I could do it. However, there was no effect on the aggregation of the toner.

In the present invention, since the toner used has improved fixability, the toner is easily softened by a temperature rise due to friction or the like, and the toner surface is also easily depressed by an external force of an elastic blade or the like. Then, the silica adhered to the surface of the toner and covering the surface becomes easy to be embedded in the resin of the toner, and the embedding starts to reduce the number of silica on the toner surface. Silica is externally added to maintain the fluidity of the toner, and originally exists on the toner surface and acts like a spacer roller. When the number of silica particles on the toner surface decreases, the chances of the toner directly contacting each other without going through the hard silica increase, the van der Waals force between the toner resins increases, and the toner is easily aggregated. .

In the present invention, the toner is made into fine particles (weight average particle size of 6.5 μm or less) for the purpose of improving the image quality. According to the measurement, the contact pressure was required to be 10 g / cm or more. For this reason, the toner aggregation due to the embedding of silica tends to be deteriorated.

In the present invention, as described above, the reversal development system is employed, and positive particles are externally added to the negative toner in order to prevent image deletion. However, when the positive particles are added, aggregation of the toner is likely to occur.

When the positive toner is not added to the negative toner, the toner is negatively charged and electrically repelled during the process of being carried on the developing sleeve and conveyed, so that the toner does not aggregate. . However, in the present invention, as shown in FIG. 6, since the positive particles m are externally added to the negative toner (having high resistance insulation) t, the negatively charged toner t is positively charged. The toner t is attracted to the periphery of the conductive particles m, and the toner t is aggregated by electrostatic Coulomb force, and the aggregate T of the toner starts to grow.

In particular, a fine particle toner having an average particle diameter of 6.5 μm or less tends to aggregate because of its small particle diameter. That is, when the positive particles are externally added to the fine particle toner, the balance due to the electric repulsion between the fine particle toners is easily broken, and thus the aggregation tends to start.

Therefore, in the present invention, in order to prevent the generation of toner aggregates on the developing sleeve 6 and to prevent the toner aggregates from remaining on the developing sleeve 6 even if they occur, the inside of the developing sleeve 6 is The magnet 11 has a repulsive magnetic pole as described above.

The present inventors have observed the movement of toner near the nip of the elastic blade due to the difference between a magnet having a repulsive magnetic pole and a magnet having no repulsive magnetic pole.

FIG. 7 shows a magnetic pole arrangement of a magnet having no repulsive magnetic pole as a comparative example. The magnetic pole arrangement of the magnet 42 is a four-pole arrangement in which S poles and N poles are alternately arranged, such as magnetic poles S1, N1, N2, and S2.
Reference numeral 1 denotes a position opposite to the photosensitive drum 1, the magnetic force of which is 85 mT on the surface of the developing sleeve 6, and the magnetic pole N 1 has a magnetic force of 75 mT on the downstream side close to the elastic blade 10 with respect to the rotation direction of the developing sleeve 6, and the magnetic pole S2 has a magnetic force of 70 mT at a position facing the developing container 12 on the upstream side of the elastic blade 10, and the magnetic pole S3 has a magnetic force of 70 mT below the magnet 42 between the magnetic poles S2 and S1. FIG. 8 shows the magnetic force distribution of the magnet 42.

In the case of the magnet 42 having no repulsive magnetic pole, the S pole and the N pole are alternately arranged, and there is no point on the developing sleeve 6 where the magnetic force disappears. For this reason, the circulation of the toner near the developing sleeve is poor, and the aggregate T of the toner is easily generated on the developing sleeve 6. Further, when the toner aggregate T is generated on the developing sleeve 6, the toner aggregate T is always held on the developing sleeve 6 by a magnetic force, and cannot escape from the developing sleeve 6. For this reason, the toner aggregate repeatedly passes through the nip portion H of the elastic blade 10 with the developing sleeve 6, and each time the toner aggregate is compressed, the aggregate grows and also absorbs the frictional heat due to the rubbing with the elastic blade. Then, it is finally fixed on the developing sleeve 6.

Each time the fixed toner aggregate T passes through the elastic blade 10, the silicone rubber 10b of the elastic blade 10 gradually wears unevenly to generate worn silicone rubber powder u. Worn silicone rubber powder u
Is retained on the surface of the toner aggregate T for a certain period of time, but eventually separates and is transferred to the surface of the developing sleeve 6,
It adheres to the surface of the developing sleeve 6 in a non-uniform manner in the longitudinal direction, and the portion to which the rubber powder u adheres becomes high in resistance, and the effect appears as streak-like density unevenness in an image.

On the other hand, in this embodiment, the magnet 11
Because of the repulsion magnetic poles S2 and S3, even if particles of opposite polarity are externally added to the fine particle toner, the fine particle toner sufficiently circulates in the vicinity of the developing sleeve and does not aggregate with the opposite polarity particles as nuclei. Even if aggregates are generated, they do not stay on the developing sleeve, and the unevenness of the elastic blade can be reduced.

The magnetic toner, which is a magnetic substance, receives a magnetic force according to the potential gradient of the magnetic field (gradient), but between the repulsive magnetic poles S2 and S3, as shown in FIG. Point h where it becomes 0
Is formed. At this point, the developing sleeve 6
No toner is retained on top. Hereinafter, the point at which the magnetic force is 0 is referred to as the ear break point.

FIG. 9 is a diagram for explaining the operation at the ear break point. Take out the developing sleeve 6 together with the magnet 11 from the developing container 12, rotate the developing sleeve,
The state of holding the toner on the developing sleeve was observed. In order to observe the effect on the toner aggregate at the break of the ear, the toner aggregate was intentionally added onto the developing sleeve 6.

The layer of the magnetic toner t on the developing sleeve 6
The valley was formed at the break point h between the repulsive magnetic poles S3 and S2, and the toner layer was divided into two at the valley. There was some toner at the bottom of the valley, but this was toner held on the developing sleeve by van der Waals force or mirroring force other than magnetic force. Here, when the developing sleeve 6 is rotated in the direction of arrow b, the toner layer portion g on the upstream side between the valleys is obtained.
Swollen to some extent, jumped over the valley as shown by arrow j, and flew to the toner layer portion k on the downstream side of the valley. However, in fact, since the ear break point h is in the developing container 12, the flying of the toner as indicated by the arrow j is prevented by the toner in the developing container 12.

That is, the toner held by the magnetic force on the developing sleeve 6 is removed from the developing sleeve 6 at the cutting point h.
He cannot stay on top and cannot pass through the ear break point h. Only toner retained on the developing sleeve 6 by a van der Waals force or a mirroring force other than the magnetic force can remain on the developing sleeve 6 at the ear break point h.

The toner aggregate T has a size larger than that of the individual toner particles, has weak adhesion to the developing sleeve 6, and therefore has a weak van der Waals force. , The amount of triboelectric charge is low and the mirror power is weak. Therefore, the rotation of the developing sleeve 6 causes the toner aggregate T
Cannot pass through the ear break point h, and separates from the developing sleeve 6 as shown by an arrow r as shown in FIG.
It was observed to be returned inside.

If the toner aggregate T cannot pass through the ear break point h, it does not pass through the nip portion H with the elastic blade 10, and therefore no compression is applied when passing through the nip portion H. The mechanical aggregation by the elastic blade 10 is not added, and the toner aggregate T
Did not grow.

When the toner aggregate T exists near the developing sleeve 6 between the ear break point h and the nip portion H and is captured by the magnetic force of the magnet 11, the aggregate T is removed from the nip portion H. , But is released from the developing sleeve 6 to the ear break point h.

When passing through the nip portion H, the toner agglomerate T scrapes a small amount of the silicone rubber of the elastic blade 10 and adheres the shaved powder u to the surface. The shaved powder u is carried to the spike break point h while adhering to the surface of the aggregate T, and is released from the developing sleeve 6 while adhering to the aggregate T at the spike break point h. Thus, the shavings u are unlikely to stay on the developing sleeve 6, and the developing sleeve 6 is not contaminated by the shavings 6.

In this embodiment, in order to verify the effect of whether the magnet has a repulsive magnetic pole or not, among the factors causing aggregation of the toner, the elastic blade 10
The abutment pressure, the MI value, which is an index of the fixing property of the toner, and the toner particle diameter are fixed at the following values. went.

Elastic blade: silicone rubber, wear index 0.18 mg, hardness 30 ° (JISA), contact pressure 30 g
/ Cm (pull-out pressure) Fine particle toner: MI value 15, average particle size 6.0 μm Smooth stirrer forms continuous images of 10,000 sheets at a printing ratio of 4% in an environment of a temperature of 23 ° C. and a humidity of 60%. The unevenness of the formed image was evaluated. The image flow is made by absorbing paper using talc as a filler sufficiently in an environment of a temperature of 23 ° C. and a humidity of 80%, and using the moisture-absorbed paper in the same environment, printing an image having a printing ratio of 4% on 10,000 sheets continuously. An image was formed, and the image deletion was evaluated for the image after the continuous image formation. Table 2 shows the results.

[0082]

[Table 2]

In Table 2, the meanings of the symbols in the stripes column are as follows. ：: No streaks occurred. Δ: Scratching unevenness was observed, but on the image there was little effect of uneven streaks. ×: Streaks clearly appear on the image. The meanings of the symbols in the image flow column are as follows.
：: No image deletion occurred. X: The image is disturbed as if it were dragged by the elastic blade and flowed.

In Table 2, in Example 1, as shown in FIG. 2, a five-pole magnet having repulsive magnetic poles S2 and S3 is used, and positive particles are externally added to the fine particle toner. Positive particles are a source of toner aggregation, and the negatively charged fine particle toner with the positive particles as a nucleus gathers to promote aggregation. Since the aggregated toner conveyed by magnetic force is not passed, the chance of being compressed by the elastic blade is reduced, the aggregated toner does not grow, uneven wear of the elastic blade due to the toner aggregate is prevented, and the amount is extremely small. Was also released from the developing sleeve together with the agglomerated toner. Therefore, there was no contamination in which the shavings due to uneven wear adhered unevenly to the surface of the developing sleeve, and no uneven streaks were generated. In addition, the positive particles efficiently adhered to the non-printed portion, and suppressed the occurrence of image flow.

In Comparative Example 1, as shown in FIG.
A magnet in which four poles and N poles are alternately arranged is used, and positive particles are externally added to the fine particle toner. Aggregation of the toner was promoted by the positive particles, and further, the magnet captured the aggregate of the toner on the developing sleeve. However, in the reversal development, since the positive toner flies to the non-printing portion and prevents the image from flowing, the image does not flow.

In Comparative Example 2, as in Comparative Example 1, the S pole, N
A magnet having four poles arranged alternately was used, but no positive particles were externally added to the fine particle toner. Since there were no positive particles, toner aggregation was small, but the magnets captured the toner aggregates on the developing sleeve, so that some uneven streaks occurred. Image deletion occurred due to the absence of positive particles.

In Comparative Example 3, as in Example 1, a five-pole magnet having repulsive magnetic poles S2 and S3 was used, but no positive particles were externally added to the fine particle toner. Since there were no positive particles, there was little aggregation of the toner, and no streaks occurred because the aggregated toner was not captured by the developing sleeve due to the effect of the repulsive magnetic field. Image deletion occurred because there were no positive particles.

As described above, in this embodiment, a magnet having a repelling magnetic pole is provided in the developing sleeve, and the repelling magnetic pole is arranged on the side in the developing container. Even if the opposite polarity particles are externally added to the magnetic toner of small particles and the fine particle toner is coated on the developing sleeve by the elastic blade, the toner aggregates and the shavings of the elastic blade are released from the developing sleeve, and It is possible to prevent the toner aggregate from growing at the contact nip portion, and to eliminate uneven wear of the rubber of the elastic member of the elastic blade due to the toner aggregate fixed to the developing sleeve. Therefore, it is possible to obtain a good developed image having no stripes due to uneven wear of the elastic blade.

Embodiment 2 FIG. 10 is an explanatory view showing the arrangement of the magnetic poles of the magnet in the developing sleeve and the movement of the toner around the developing sleeve in another embodiment of the present invention.

This embodiment is different from the first embodiment in that a plate-like silicone rubber 21b is lined with a thin elastic support plate, for example, a SUS plate 21c as a developer layer thickness regulating member, and the SUS plate 21c is attached to the support plate 21a. The feature is that the supported elastic blade 21 is used. Other configurations of this embodiment are the same as those of the first embodiment. In FIG. 10, the same reference numerals as those shown in FIG. 2 indicate the same members.

The elastic blade 21 was manufactured by integral molding as in the first embodiment. A SUS plate 21c having a thickness of 60 μm coated with a silicone rubber primer is placed in a pre-heated mold, and LTV silicone rubber is injected into the mold with a LIM injection molding machine and kept at 150 ° C. for 5 minutes. The silicone rubber was vulcanized, and the obtained molded product was taken out and subjected to a heat treatment at 200 ° C. for 4 hours.
1c is molded integrally with silicone rubber 21c, then SU
The S plate 21c was attached to the supporting metal plate 21a to obtain a target elastic blade.

The above-mentioned elastic blade 21 can be used for the SUS plate 2 even if low elasticity silicone rubber is used for the elastic member.
There is an advantage that a high contact pressure can be obtained by the elastic force of 1c, and the charge amount can be favorably applied to the toner. The contact pressure of the elastic blade 21 with the developing sleeve 6 was 40 g / cm, which was higher than that of the elastic blade 10 of Example 1 being 30 g / cm.

When the contact pressure of the elastic blade is increased by the elastic support plate as described above, aggregates of the fine particle toner are easily generated. However, as in the first embodiment, the magnet roller in the developing sleeve 6 is formed. 11 repulsive magnetic poles S3, S2
Between the toner particles, there is no magnetic force, and therefore, even with the fine particle toner externally added with the positive particles, the growth of the toner aggregate can be suppressed, and the elasticity due to the toner aggregate fixed to the developing sleeve 6 can be suppressed. There is no uneven wear of the blade 21 and a good developed image without streaks caused by uneven wear of the elastic blade can be obtained.

In the present embodiment, in the same manner as in the first embodiment, an image with a printing ratio of 4% is continuously formed on 10,000 sheets in an environment of a temperature of 23 ° C. and a humidity of 60%. Was evaluated. As a result, as in Example 1, a good image without streaks could be obtained. The image quality was further improved.

Embodiment 3 FIG. 11 is an explanatory view showing the arrangement of magnetic poles of a magnet in a developing sleeve and the movement of toner around the developing sleeve in still another embodiment of the developing device of the present invention. 11, the same reference numerals as those shown in FIG. 2 indicate the same members.

In this embodiment, the magnet 11 is
It has five pole arrangements of 1, N1, N2, S2, N3,
The magnetic pole S1 is located at a position facing the photosensitive drum 1, and its magnetic force is 85 mT on the surface of the developing sleeve 6. Magnetic pole N1
And N2 are repulsive magnetic poles that form a repulsive magnetic field adjacently arranged with the same polarity, and the magnetic pole N1 is located on the downstream side close to the elastic blade 10 with respect to the rotation direction of the developing sleeve 6; The surface has a magnetic force of 70 mT,
The magnetic pole N2 is located on the upstream side close to the elastic blade 10 and has a magnetic force of 65 mT. The magnetic pole S is the elastic blade 1
The magnetic force is 70 mT, and the magnetic pole S3 is located below the magnet 11 and has a magnetic force of 70 mT. FIG. 12 shows the magnetic force distribution of the magnet 11.

The magnet 11 having such a magnetic pole arrangement is
As shown in FIG. 13, there is a head break point h between the repulsive magnetic poles N1 and N2. In the same manner as described in Example 1,
Observing the state of holding the toner on the developing sleeve, similarly, the layer of the magnetic toner t on the developing sleeve 6 shows that the toner layer is divided into two right and left at the break point h, and the bottom of the valley of the toner layer is formed. There is a small amount of toner held on the developing sleeve by van der Waals force or mirroring force other than magnetic force. Then, when the developing sleeve 6 was rotated in the direction of the arrow b, the upstream portion of the valley between the toner layer portions g expanded to some extent, jumped over the valley as shown by the arrow j, and flew to the downstream toner layer portion k of the valley. In practice, however, the elastic blade 10 is in contact with the developing sleeve 6 at the ear break point h, as shown in FIG. It is.

That is, as in the case of the first embodiment, the toner retained on the developing sleeve 6 by magnetic force does not stay on the developing sleeve 6 at the break point h but can pass through the break point h. Instead, only toner retained on the developing sleeve 6 by van der Waals force or mirroring force other than magnetic force can remain on the developing sleeve 6 at the ear break point h.

The toner aggregate T is larger in size than the individual toner particles, and has a weaker van der Waals force due to weak adhesion to the developing sleeve 6, and the toner particles electrically collected with the positive particles as nuclei. Since it is an aggregate, the amount of triboelectric charge is low and the mirroring power is also weak.
As a result, the toner aggregate T on the developing sleeve 6 cannot pass through the spike break point h, and separates from the developing sleeve 6 as shown by an arrow r and returns into the developing container 12 as shown in FIG. Was observed.

If the toner aggregate T cannot pass through the ear break point h, the toner aggregate T does not pass through the nip H with the elastic blade 10, and therefore, no compression is applied when the nip H passes. The mechanical aggregation by the elastic blade 10 is not added, and the toner aggregate T
Did not grow.

In this embodiment, in order to verify the effect of whether the magnet has a repulsive magnetic pole or not, in the same manner as in the first embodiment, the elastic blade 10 The abutment pressure, the MI value, which is an index of the fixing property of the toner, and the toner particle diameter are fixed at the following values. went.

Elastic blade: silicone rubber, wear index 0.18 mg, hardness 30 ° (JISA), contact pressure 30 g
/ Cm (pull-out pressure) Fine particle toner: MI value 15, average particle size 6.0 μm Smooth stirrer forms continuous images of 10,000 sheets at a printing ratio of 4% in an environment of temperature 23 ° C. and humidity 60%, The unevenness of the formed image was evaluated. The image flow is made by absorbing paper using talc as a filler sufficiently in an environment of a temperature of 23 ° C. and a humidity of 80%, and using the moisture-absorbed paper in the same environment, printing an image having a printing ratio of 4% on 10,000 sheets continuously. An image was formed, and the image deletion was evaluated for the image after the continuous image formation. Table 3 shows the results.

[0103]

[Table 3]

In Table 3, the meanings of the reference numerals in the stripes column and the image flow column are the same as those in Table 2. That is,
Regarding uneven streaks, ：: no uneven streaks occurred. Δ: Scratching unevenness was observed, but on the image there was little effect of uneven streaks. ×: Streaks clearly appear on the image. Regarding image deletion, ○: no image deletion occurred.
X: The image is disturbed as if it were dragged by the elastic blade and flowed.

In Table 3, in Example 3, as shown in FIG. 11, a five-pole magnet having repulsive magnetic poles N1 and N2 was used, and positive particles were externally added to the fine particle toner. Positive particles are a source of toner aggregation, and the negatively charged fine particle toner with the positive particles as a nucleus gathers to promote aggregation. Since the aggregated toner conveyed by the magnetic force is not passed, the aggregated toner was not compressed by the elastic blade and did not grow. Therefore, there was no uneven wear of the elastic blade due to the toner aggregates, no contamination that shaved powder due to uneven wear adhered to the surface of the developing sleeve unevenly, and no uneven streaks caused by this. In addition, the positive particles efficiently adhered to the non-printed portion, and suppressed the occurrence of image flow.

In Comparative Example 1, what is shown in Table 2 of Example 1 is listed in Table 3 again.
As shown in FIG. 7, a magnet in which four S poles and N poles are alternately arranged is used, and positive particles are externally added to the fine particle toner. Aggregation of the toner was promoted by the positive particles, and further, the magnet captured the aggregate of the toner on the developing sleeve. However, in the reversal development, the positive toner flies to the non-printing area,
No image deletion occurred because image deletion was prevented.

In Comparative Example 2, what is shown in Table 2 of Example 1 is listed in Table 3 again.
As in Comparative Example 1, a magnet in which four S poles and N poles were alternately used was used, but no positive particles were externally added to the fine particle toner. Since there were no positive particles, toner aggregation was small, but the magnets captured the toner aggregates on the developing sleeve, so that some uneven streaks occurred. Image deletion occurred due to the absence of positive particles.

In Comparative Example 3, as in Example 3, a five-pole magnet having repulsive magnetic poles N1 and N2 was used, but no positive particles were externally added to the fine particle toner. Since there were no positive particles, there was little aggregation of the toner, and no streaks occurred because the aggregated toner was not captured by the developing sleeve due to the effect of the repulsive magnetic field. Image deletion occurred because there were no positive particles.

As described above, in this embodiment, a magnet having a repulsive magnetic pole is provided in the developing sleeve, and the repulsive magnetic pole is arranged before and after the contact portion of the elastic blade, so that the fixing property is good. Even if the opposite polarity particles are externally added to the magnetic toner having a small particle size and the fine particle toner is coated on the developing sleeve with an elastic blade, the toner aggregate is released from the developing sleeve and the contact nip portion is formed. Thus, it is possible to prevent the toner aggregate from growing, and to eliminate uneven wear of the rubber of the elastic member of the elastic blade due to the toner aggregate fixed to the developing sleeve. Therefore, it is possible to obtain a good developed image having no stripes due to uneven wear of the elastic blade.

Embodiment 4 In this embodiment, the elastic blade in which the plate-like silicone rubber 21b used in Embodiment 2 is lined with a thin SUS plate 21c as the developer layer thickness regulating member in Embodiment 3 is used. 21 was used. Others were the same as Example 3.

In this embodiment, in the same manner as in Embodiment 3, an image having a printing ratio of 4% was continuously formed on 10,000 sheets in an environment of a temperature of 23 ° C. and a humidity of 60%. Was evaluated. As a result, as in Example 3, a good image without streaks could be obtained. The image quality was further improved.

[0112]

As described above, according to the present invention,
Since a magnet having a repelling magnetic pole is provided in the developing sleeve and the repelling magnetic pole is arranged on the side of the developing container or at the location of the elastic blade, the fixability is good and the particle size is 6.5 μm.
m or less, external polarity particles are externally added to the magnetic toner of fine particles of
Even when the fine particle toner is coated on the developing sleeve by the elastic blade, the toner aggregate is released from the developing sleeve, and the toner aggregate can be prevented from growing at the contact nip portion, and the toner aggregate is fixed to the developing sleeve. The uneven wear of the elastic member of the elastic blade due to the toner aggregate can be eliminated. Therefore, it is possible to obtain a good developed image having no stripes due to uneven wear of the elastic blade.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus provided with a developing device of the present invention.

FIG. 2 is a sectional view showing the arrangement of magnetic poles of a magnet in a developing sleeve and movement of toner around the developing sleeve in the developing device of FIG.

FIG. 3 is a diagram illustrating a magnetic force distribution of the magnet of FIG. 2;

FIG. 4 is an explanatory diagram showing a method for measuring a contact pressure of an elastic blade contacting the developing sleeve of FIG. 2;

FIG. 5 is an explanatory diagram showing a wear depth of an elastic blade abutting on the developing blade of FIG. 2;

FIG. 6 is a schematic view showing an aggregate of toner which is accelerated when positive particles are externally added to a negative fine particle toner used in the present invention.

FIG. 7 is a cross-sectional view illustrating a magnetic pole arrangement of a magnet in a developing sleeve and a movement of toner around the developing sleeve in a comparative example.

FIG. 8 is a diagram showing a magnetic force distribution of the magnet of FIG. 7;

FIG. 9 is an explanatory diagram showing a behavior of toner at a break point of the magnet in FIG. 2;

FIG. 10 is an explanatory diagram showing a magnetic pole arrangement of a magnet in a developing sleeve and a movement of toner around the developing sleeve in another embodiment of the present invention.

FIG. 11 is an explanatory view showing the arrangement of magnetic poles of a magnet in a developing sleeve and the movement of toner around the developing sleeve in still another embodiment of the present invention.

12 is a diagram showing a magnetic force distribution of the magnet 11 of FIG.

FIG. 13 is an explanatory diagram showing the behavior of the toner at the break point of the magnet in FIG. 11;

FIG. 14 is an explanatory view showing the arrangement of magnetic poles of a magnet in a developing sleeve and the movement of toner around the developing sleeve in still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 3 developing device 6 developing sleeve 10, 21 elastic blade 10b, 21b silicone rubber 21c SUS support plate 11 magnet 12 developing container H contact nip t toner T toner aggregate

Claims (5)

[Claims] A rotatable developer carrier installed in a developer container containing a one-component magnetic developer; a magnetic field generating means having a plurality of magnetic poles arranged non-rotatably in the developer carrier; In a developing device having a developer layer thickness regulating member that abuts on the developer carrier and regulates a developer layer thickness on the developer carrier, the developer has a weight average particle diameter of 6.5 μm or less. Wherein the developer has externally added particles of a polarity opposite to that of the developer, and the developer layer thickness regulating member has an abrasion loss at a contact portion with the developer carrier, and a wear amount of the developing device is reduced. Has a wear performance of 3 μm or more, and the magnetic field generating means is adjacent to the position in the developing container on the upstream side of the contact portion with respect to the rotation direction of the developer carrier, along the rotation direction. Developing device having two repulsive magnetic poles of the same polarity combined . 2. A rotatable developer carrier installed in a developing container containing a one-component magnetic developer, a magnetic field generating means having a plurality of magnetic poles non-rotatably disposed in the developer carrier, In a developing device having a developer layer thickness regulating member that abuts on the developer carrier and regulates a developer layer thickness on the developer carrier, the developer has a weight average particle diameter of 6.5 μm. In the following, particles of a polarity opposite to that of the developer are externally added to the developer, and the developer layer thickness regulating member has an abrasion amount of a contact portion with the developer carrier, the amount of wear of the developing device. The magnetic field generating means has a wear performance of 3 μm or more in a life, and is adjacent to the position near the contact portion in the rotation direction of the developer carrier along the rotation direction with the contact portion interposed therebetween. A developing device having two repulsive magnetic poles of the same polarity. 3. The developing device according to claim 1, wherein at least said contact portion of said regulating member is made of silicone rubber. 4. The developing device according to claim 3, wherein said silicone rubber is lined with an elastic support plate. 5. A process cartridge comprising at least an image carrier and a developing device for developing an electrostatic latent image on the image carrier, wherein the developing device is detachably mountable to an image forming apparatus main body. Item 5. A process cartridge which is the developing device according to any one of Items 1 to 4.