JPH07325475A - Developing device - Google Patents

Abstract

PURPOSE:To provide a developing device capable of preventing the delay of the rising of an initial density, and irregularities in an image in the latter half of a large number of prints. CONSTITUTION:In this developing device using small grain size magnetic toner having 6-9mum volume averaged grain size and a negative polarity as a developer, making the circumferential speed ratio of a developing sleeve 1 carrying the toner to a photoreceptor drum be 1-2 and regulating the toner carried on the sleeve 1 by a blade elastically abutted on the sleeve, the conductive resin coating film 7 of a thin layer composed of two upper and lower coating films 8 and 9 including conductive grains are formed on the surface of the sleeve 1 and the ratio (P/B ratio) of the conductive grain to resin on the upper layer coating film 8 is set higher than that in the lower layer coating film 9. Since the ratio of the conductive grain of the upper layer coating film 8 is high, the toner can be excellently electrified even in an initial state to prevent the delay of the rising of the density and since the ratio of the resin of the lower layer coating film 9 is high, the sticking of the resin coating film 7 to the surface of the sleeve 1 is made high to prevent the shaving of the coating film 7 by the blade.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device in an image forming apparatus using an electrophotographic system used in a copying machine, a laser beam printer or the like.

[0002]

2. Description of the Related Art In recent years, with the widespread use of image forming apparatuses such as electrophotographic copying machines and laser beam printers, the applications thereof have been widespread and demands on the image forming apparatus have become strict. Therefore, there is an increasing demand for an image forming apparatus that can stably supply an image having excellent fine line reproducibility and gradation by using a toner having a small particle size.

On the other hand, small-sized toner particles are often excessively charged by friction with a member (developing sleeve or elastic blade) in the developing device, and when the toner is overcharged, development is performed. However, there is a problem in that the density of an image is reduced and a sleeve ghost occurs.

Therefore, there has been proposed a developing device which does not have the above-mentioned problems even when a toner having a small particle diameter is used and is excellent in fine line reproducibility and gradation (JP-A-2-306274). Such a developing device, as shown in FIG.
A developing sleeve 102 as a developer bearing member, which is disposed so as to face the developing roller 102, a magnet roller 103 having a plurality of magnetic poles which is non-rotatably disposed in the developing sleeve 102, and a developing roller 102 that abuts on the developing sleeve 102 to remove the toner. An elastic blade 104 that regulates the layer thickness, a developing container 101 having a magnetic toner 105 having a small particle size, and the like are configured. The small particle size magnetic toner 105 is a magnetic toner having a particle size of 5 μm or less in an amount of 17 to 60% by number and a volume average particle size of 6 to 9 μm.

In this developing device, the outer peripheral surface of the developing sleeve 102 is coated with a conductive resin coating containing carbon black and / or graphite as conductive fine particles, so that in a normal environment, a toner having a small particle diameter is coated. Even if continuous printing is performed using, the density of the image and the sleeve ghost are prevented from occurring.

However, when the speed of the image forming apparatus is increased, the time required for the developing sleeve 102 to pass through the developable area (indicated by A in the figure) facing the photosensitive drum 111 is shortened, and the developing time is short. Therefore, the density of a solid black image may decrease.

Therefore, the peripheral speed of the developing sleeve 102 is set to v
_1, the peripheral speed of the photosensitive drum 111 as v _2, the ratio v ₁ / v ₂ of the sleeve peripheral speed v ₁ relative to the drum peripheral speed v ₂ 1 to 2
By doing so, the absolute amount of the developer passing through the developable area A is increased, whereby the developability is improved and the density is improved.

In the conductive resin coating on the surface of the developing sleeve 102, the compounding ratio of the conductive fine particles (P) to the resin (B), that is, the P / B ratio, is 2 in order to stabilize the concentration and reduce the sleeve ghost. It has been found that a range of / 1-1 / 3 is desirable. The P / B ratio of the coating is P / B <
In the case of 2/1, the adhesion of the coating to the surface of the developing sleeve 102 is deteriorated, the coating is separated from the developing sleeve 102 at the time of printing, and defective coating of the toner on the developing sleeve occurs. On the other hand, when P / B> 1/3, the developing sleeve 102
The charge leak site effect due to the conductive fine particles in the coating on the above toner is not sufficient, and a toner coating failure called blotch occurs on the developing sleeve 102.

[0009]

However, the conventional developing device shown in FIG. 6 still has the following problems when it is used for developing a high-speed and highly durable printer.

(1) Delay in rising of initial density This is because the distribution of the triboelectric charge amount of the toner on the developing sleeve 102 differs between the initial stage up to about 500 prints and thereafter.

That is, at the initial stage of printing, sufficient triboelectric charge cannot be applied to the toner on the developing sleeve 102 only by the triboelectric charging of the elastic blade 104, and the triboelectric charge distribution of the toner on the developing sleeve is shown in FIG. It becomes broad as shown in. On the other hand, print about 500
After one sheet, the toner on the developing sleeve receives a sufficient charge due to the frictional charging of the toner with the blade and the developing sleeve and the frictional charging between the toners, so that the triboelectric charge distribution becomes sharp as shown in FIG. Become. For this reason, the developing property of the toner is different between the initial printing up to about 500 sheets and the subsequent printing, and the ratio of the toner having a low electric charge that does not contribute to the development is large in the initial printing, so that the image density is lowered.

Such a delay phenomenon of rising of the initial density, which makes the solid density thin, has been observed in recent years in an image forming apparatus such as an electrophotographic printer for the purpose of high image quality and high quality by using a digital image signal. , Has become a big problem.

(2) Occurrence of image unevenness in the latter half of printing of a large number of sheets This is because when the number of printed sheets advances, the elastic blade 10
4 is a phenomenon that occurs when the conductive resin film on the surface of the developing sleeve 102 is scraped off by rubbing the surface of the developing sleeve 102 by 4.

The contact pressure of the elastic blade with the surface of the developing sleeve is set to a linear pressure of about 10 to 50 g / cm in order to stably impart triboelectric charging to the toner. However, when a large amount of printing is performed, the resin film on the surface of the developing sleeve is scraped off by the above contact pressure, and the surface roughness Ra of the surface layer of the film is reduced. For this reason, in the latter half of printing a large number of sheets, the amount of toner applied on the developing sleeve decreases, the toner supplied for development becomes insufficient, and density unevenness occurs in a halftone image or a solid black image.

The phenomenon of image unevenness in the latter half of the printing of a large number of sheets is caused by the contact pressure of the elastic blade to the developing sleeve in the longitudinal direction because the developing sleeve has a long length in the longitudinal direction. If unevenness is likely to occur,
Especially noticeable.

It is an object of the present invention to provide a developing device capable of preventing a delay in rising of the initial density and preventing image unevenness in the latter half of printing of many sheets.

[0017]

The above object can be achieved by the developing device according to the present invention. In summary, in the present invention, the developer is composed of a negative polarity magnetic toner having a volume average particle size of 6 to 9 μm, and the peripheral speed ratio of the developer carrying member carrying and carrying the magnetic toner to the image carrying member is 1 to 2. In a developing device in which an elastic regulating member is in contact with the developer carrying member, the upper and lower two layers of conductive resin containing conductive particles in the resin are provided on the surface of the developer carrying member. Form a coating, the ratio of the conductive particles to the resin in the upper layer of the coating,
The developing device is characterized in that the height is higher than that in the lower layer of the film.

According to the present invention, the weight ratio of the conductive particles to the resin in the upper layer of the coating is 2/1 to 1 /.
The ratio of the conductive particles to the resin in the lower layer of the coating film is selected from 1/1 to 1/3 by weight. Preferably, the conductive resin film contains, as conductive particles, at least one selected from carbon black and graphite. The conductive resin coating,
The electrically conductive particles may further contain positively charged particles.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view showing an embodiment of a developing device of the present invention, FIG. 2 is a perspective view showing a developing sleeve arranged in the developing device of FIG. 1, and FIG. It is a figure.

As shown in FIG. 1, the present developing device includes a developing container 6 containing a negative magnetic toner 5 as a one-component developer.
And in the opening facing the photosensitive drum 2 of the container 6,
The developing sleeve 1 facing the photosensitive drum 1 is rotatably installed. A blade 4 is provided above the developing sleeve 1 so as to contact the developing sleeve 1.

According to the present invention, the above magnetic toner 5 is
The toner is a small particle size toner having a volume average particle size of 6 to 9 μm. Further, assuming that the peripheral speed of the developing sleeve 1 is v ₁ and the peripheral speed of the photosensitive drum 2 is v ₂ , the ratio of the sleeve peripheral speed to the drum peripheral speed v ₁ / v ₂ is 1 <v ₁ / v ₂ <2. The sleeve peripheral speed is set higher than the drum peripheral speed.

Magnetic toner 5 contained in developing container 6
Is carried on the developing sleeve 1 by the magnetic force of the magnet roller 3 contained in the developing sleeve 1, regulated by the pressing by the elastic blade 4, and the developing sleeve 1 rotates while being applied in a thin layer on the developing sleeve 1. By doing so, the toner is conveyed to the developing section facing the photosensitive drum 2.
The toner 5 conveyed to the developing portion is used for developing the latent image on the photosensitive drum 2, and the latent image is visualized as a toner image by the development.

Further in accordance with the present invention, as shown in FIG.
On the surface of the developing sleeve 1, a thin conductive resin film 7 containing carbon black and / or graphite as conductive particles in a binder resin is formed. As shown in FIG. 3, the conductive resin film 7 is composed of two layers, an upper film 8 and a lower film 9. The P / B ratio of the conductive fine particles (P) to the resin (B) is set to the upper coating 8
Is set higher than the lower layer coating 9.

In order to form a conductive resin coating on the surface of the developing sleeve 1, it is sufficient to prepare a coating paint mixed with conductive particles and apply it by a spray method. By adjusting the atomizing pressure, it is possible to form a thin conductive resin film on the surface of the developing sleeve 1 with a predetermined thickness. At this time, the lower and upper coatings 9 and 8 having different P / B ratios can be formed by changing the mixing amount of the conductive particles of the coating material. The coating material is applied to the surface of the developing sleeve 1 and then thermoset to form the lower layer coating 9 and the upper layer coating 8.

In this embodiment, since the developing sleeve 1 having such a two-layered conductive resin film 7 formed on the surface thereof is used, the delay of the rise of the initial density is eliminated and the film is scraped when printing a large number of sheets. It is possible to prevent image unevenness due to This will be described by experiments conducted by the present inventors.

Experiment 1 The magnetic toner 5 as a one-component developer has a particle size distribution of (i) particle size of 5 μm or less: 17 to 60% (ii) particle size of 6.35 to 10.08 μm: 5 to 50 particles % (Iii) Particle size 12.70 μm or more: 2% by volume or less (iv) Volume average particle size: 6 to 9 μm (v) A toner particle group having a particle size of 5 μm or less is represented by the following formula N / V = −0.05n + N N: Magnetic toner satisfying the following conditions: number% of toner particles of 5 μm or less V: volume% of toner particles of 5 μm or less N: positive number of 4.6 to 6.7 n: positive number of 17 to 60 For example, the following magnetic toner was used.

Styrene / butyl acrylate / divinylbenzene copolymer 100 parts by weight (copolymerization ratio 80 / 19.5 / 0.5, weight average molecular weight 320,000) Iron trioxide (average particle size 0.2 μm) 80 Parts by weight Cr complex of azo dye 1 part by weight Low molecular weight propylene-ethylene copolymer 4 parts by weight

The raw materials are mixed, kneaded, coarsely pulverized, in the above-mentioned formulation,
It was put into the steps of fine pulverization and classification to obtain a toner classified product having the following particle size distribution.

(I) 5 μm or less: 35.4 number% (ii) 6.35 to 10.08 μm: 36.9 number% (iii) 16 μm or more: 0.5 vol% or less (iv) Volume average particle diameter: 6.5 μm (v) N / V = 3.5 To 100 parts by weight of this classified product, 1.2 parts by weight of silica treated with dimethyl silicone oil was added and mixed to prepare a negatively chargeable insulating magnetic toner.

Further, a phenol resin is used as a binder, and carbon black (CONDUCTEX 900 manufactured by Colombia) and graphite (C manufactured by Nippon Graphite Co., Ltd.) are used.
SPE) was mixed to obtain an upper layer coating solution A and a lower layer coating solution B having a P / B ratio of 1/1.

These coating film forming liquids A and B were diluted with methyl cellocelbu and methanol to form a coating, and the obtained coating films were coated on a sleeve substrate by a spray method. The two coating films were formed at 150 ° C. and 30 ° C. It is heat-cured for a minute to form two layers of conductive resin coating on the upper and lower sides. Created 1. For comparison, the developing sleeve No. 1 in which the conductive resin film is a single layer is used. 2 and 3 were prepared.

An air spray was used for the method of spraying the coating film, but the gun used was No. 601 manufactured by Binks,
Paint pressure ^{0.1Kg / cm 2 ~5K / cm 2} , the air pressure pattern adjustment 5Kg / cm ^2, by adjusting the air pressure for atomizing the ^{0.5Kg / cm 2 ~4Kg / cm 2} , development Sleeve No. The conductive resin coatings 1 to 3 were formed.

These developing sleeve Nos. The coating conditions of 1 to 3 are summarized in Table 1.

[0034]

[Table 1]

The above developing sleeve is used in the developing device shown in FIG. 1 (sleeve peripheral speed / drum peripheral speed = v ₂ / v ₁ = 1.5) to form an image under the environment of 23 ° C. and 60% RT. I did. The results are shown in Table 2.

[0036]

[Table 2]

As shown in Table 2, the developing sleeve N
o. According to No. 1, it was possible to prevent the delay of the rise of the initial density, and it was possible to prevent the image unevenness due to the abrasion of the conductive resin film when printing a large number of sheets. On the other hand, the developing sleeve No. In No. 2, image unevenness occurs, and the developing sleeve No. In No. 3, the delay in rising of the initial concentration was remarkable. The above results will be considered below.

First, in order to eliminate the delay in the rise of the initial density, in order to be able to impart sufficient triboelectric charge to the negatively charging toner even in the initial stage, the charging polarity of the conductive resin film on the developing sleeve surface The resin coating may be configured so that the toner has a negative value that is closer to positive than that of the toner. This is possible by increasing the P / B ratio of the resin coating, and in the present invention, the P / B ratio of the upper resin coating is increased.

The abrasion of the conductive resin film can be prevented by increasing the resin amount of the resin film to increase the adhesion of the film to the surface of the developing sleeve. In the present invention, the P / B ratio of the lower resin film is reduced.

From the above, the developing sleeve N according to the present invention
o. In No. 1, it was possible to eliminate the image unevenness due to the delay in the rise of the initial density and the abrasion of the resin film. On the other hand, the developing sleeve No. In No. 2, the image unevenness due to the scraping of the resin coating is caused by the developing sleeve No. In No. 3, the delay in the rise of the initial concentration became remarkable.

Further, the developing sleeve No. The upper resin coating of No. 1 has a large P / B ratio and a small amount of resin (B), so the adhesive force on the developing sleeve is weak, and after printing about 5,000 sheets, it is rubbed by the elastic blade contacting via the toner. The resin coating is evenly scraped. As a result, the lower layer resin coating having a large amount of resin appears, so that a good image can be obtained even after 5000 sheets and the image quality can be guaranteed even when printing a large number of sheets exceeding 5000 sheets.

As a result of further study, P / of the conductive resin film was
It was found that the B ratio (weight ratio) is desirably in the upper layer: 2/1 to 1/1 and in the lower layer: 1/1 to 1/3.

As described above, in this embodiment, the magnetic toner having a small particle diameter having a volume average particle diameter of 6 to 9 μm is used, and the peripheral speed ratio of the developing sleeve carrying the toner to the peripheral speed of the photosensitive drum is 1 to 1. 2 and under the condition that the toner regulating member carried on the developing sleeve is an elastic blade,
A conductive resin coating layer containing conductive particles is formed on the surface of the developing sleeve in upper and lower layers, and the P / B of the coating on the upper layer is formed.
Since the ratio is higher than that of the lower layer, it is possible to improve the delay in rising of the initial density and prevent image unevenness when printing a large number of sheets.

Another embodiment of the present invention will be described. In the present embodiment, it will be shown that the triboelectric charge is more stably applied to the toner at the initial stage and at the time of printing many sheets. FIG. 4 is a sectional view showing the developing sleeve in this embodiment.

In this embodiment, the developing sleeve 10 is
A phenol resin is used as a binder, and a conductive resin coating 13 composed of upper and lower resin coatings 11 and 12 containing conductive particles is formed on the binder.
Contains positively charged particles in addition to carbon and / or graphite as conductive particles.

In this embodiment, since the developing sleeve 10 having the two-layer conductive resin film 13 having the positively charged positive particles added thereto is formed on the surface thereof, the initial density is maintained even in a high temperature and high humidity environment. It is possible to obtain an image in which there is no delay in the start-up and the density does not decrease when printing a large number of sheets. This will be described by experiments conducted by the present inventors.

Experiment 2 As the magnetic toner 5 of the one-component developer, the small-diameter magnetic toner having the volume average particle diameter of 6 to 9 μm used in Experiment 1 was used. Further, in addition to carbon black and graphite, the binder phenol resin was mixed with methylmethacrylate particles as positively chargeable particles to obtain a film forming liquid, which was made into a paint and used for forming a conductive resin film. Otherwise, in the same manner as in Experiment 1, a developing sleeve having two upper and lower conductive positive resin coatings was prepared. This is the developing sleeve N
o. Set to 4.

For comparison, the developing sleeve No. 3 was prepared except that the methyl methacrylate particles were not contained and the amount of carbon black was increased by that amount. In the same manner as in No. 4, the developing sleeve No. 5 was created. Table 3 shows the conductive particle contents of the upper and lower layers of these conductive resin coatings.

Further, the developing sleeve No. Images were formed using the developing devices Nos. 4 and 5 in the developing device shown in FIG. The results are shown in Table 4.

[0050]

[Table 3]

[0051]

[Table 4]

As shown in Table 4, the developing sleeve No. 1 containing positively chargeable particles in addition to carbon black and graphite. In No. 4, the initial rise of the density and the density when printing a large number of sheets were stabilized. The reason will be described below.

Positively chargeable particles are dispersed in the upper and lower coats 11 and 12 of the resin coat 13 formed on the surface of the developing sleeve 10, and the negatively chargeable insulating toner 5 on the developing sleeve 10 is dispersed. Is strongly attracted to the surface of the developing sleeve 10 due to the electrostatic force with the positively charged particles in addition to its own mirroring force. Therefore, the toner 5 is transferred to the developing sleeve 10.
When the roller rotates, the toner is favorably taken into the nip B formed by the developing sleeve 10 and the elastic blade 4, and the frictional charge with the elastic blade 4 gives a strong triboelectric charge. Therefore, the toner 5 on the developing sleeve 10 has a stable charge amount from the beginning of printing, and the charge amount distribution is sharp, so that the density is increased.

Table 5 and FIG. 5 show the results of measurement of the charge amount and charge amount distribution of the toner on the developing sleeve at the initial stage of printing in Experiment 2.

[0055]

[Table 5]

As shown in Table 5 and FIG. 5, when the electrically conductive resin film (upper layer film, lower layer film) contains positively chargeable particles, the triboelectric charge amount of the toner is higher and the charge amount thereof is higher. It can be seen that the distribution is also sharp.

In the present invention, resin particles can be used as the positively chargeable particles. The positively chargeable resin particles can be produced by a spray drying method, a suspension polymerization method, an emulsion polymerization method, a seed polymerization method, or the like. Positively chargeable resin particles have a shape-retaining property of particles. }, From the point of GPC
The weight average molecular weight measured by a chromatography method is preferably 10,000 to 200,000.

Positively chargeable resin particles include methyl methacrylate, dimethylaminoethyl methacrylate, N-
Resin particles obtained by polymerizing a vinyl monomer such as methyl-N-phenylaminoethyl methacrylate, diethylaminoethyl methacrylamide, dimethylaminoethyl methacrylamide, 4-vinylpyridine, 2-vinylpyridine or a mixture of these monomers are used.

In order to give the resin particles positive chargeability,
A method of polymerizing a monomer using a nitrogen-containing polymerization initiator may be used, or a method of polymerizing a monomer composition containing a nitrogen-containing vinyl monomer may be used.

The resin particles can achieve the purpose if they are positively charged, but may be subjected to a surface treatment for facilitating the removal of negative charges from the particles, if necessary. As the method of surface treatment, a method of adhering a metal such as iron, nickel, cobalt, copper, zinc, gold or silver to the surface of the resin particles by a vapor deposition method or a plating method, or the above-mentioned metal, magnetic material or conductive oxide By fixing metal oxides such as zinc on the surface of resin particles by ion adsorption or external addition, or by coating or externally adding triboelectrically chargeable organic compounds such as pigments, dyes, and polymer resins. There is a method of supporting the resin particles on the surface.

The positively chargeable resin particles thus obtained have an average particle size of 0.1 to 1.0 μm, preferably 0.2 to 1.0 μm. When the average particle size of the positively chargeable resin particles is less than 0.1 μm, the conductive resin film 13 on the surface of the developing sleeve 10 containing the positively chargeable resin particles is less than 0.1 μm.
Has a small effect of imparting a triboelectric charge to the toner. On the other hand, when it exceeds 1.0 μm, the resin particles have a poor binding property with the phenol resin as a binder and a poor mixing property with carbon black and graphite particles. The resin coating 13 is
It becomes difficult to make these resin particles, carbon black, etc. uniformly dispersed.

The positively chargeable resin particles have a triboelectric charge amount of preferably 50 to 600 μC / g, more preferably 100.
˜600 μC / g is used. When resin particles whose triboelectric charge amount is less than 50 μC / g are used, it is difficult for the resin coating 13 to adsorb the toner 5, and the triboelectric charge amount to the toner 5 at the nip portion B with the elastic blade 4 is reduced. Since the impartation is not sufficient, it cannot be expected to improve the image density.

The amount of the positively chargeable resin particles contained in the resin coating 13 is 3 to 10% by weight, preferably 5 to 10% by weight.
Is good. When the content of resin particles is less than 3% by weight,
The developing sleeve 10 is provided with a coating 13 in which resin particles are uniformly dispersed.
Since it cannot be formed on the surface, the improvement of the image density is small, and when it exceeds 10% by weight, the reverse charging property of the toner 5 becomes strong.

As the surface condition of the developing sleeve 10 having the conductive resin coating 13 formed thereon, the center line average roughness Ra is 0.
3 to 5.0 μm, 10-point average roughness Rz is 1.0 to 30.
The range of 0 μm is a necessary condition for applying the toner 5 on the developing sleeve 10 in a uniform thin layer.

As described above, in this embodiment, the magnetic toner having a small particle diameter having a volume average particle diameter of 6 to 9 μm is used, and the peripheral speed ratio of the developing sleeve carrying the toner to the peripheral speed of the photosensitive drum is 1 to 1. 2 and under the condition that the toner regulating member carried on the developing sleeve is an elastic blade,
Since a conductive resin coating film containing conductive particles containing positively charged particles was formed on the upper and lower two layers on the surface of the developing sleeve, and the P / B ratio of the upper coating film was made higher than that of the lower coating film.
Even in a high temperature and high humidity environment, the upper coating prevents the initial rise of the density from rising, and after the upper coating has been scraped off, the lower coating may impart triboelectric charge to the toner and scrape the coating. Image unevenness can be prevented. Therefore, a stable image can be printed under a high temperature and high humidity environment regardless of the number of prints.

Needless to say, in a low temperature and low humidity environment, the conductive resin film on the developing sleeve acts as a charge leak site for the toner, and can prevent density decrease and sleeve ghost due to toner charge-up.

[0067]

As described above, according to the present invention, a magnetic toner having a small particle diameter having a volume average particle diameter of 6 to 9 μm is used as a one-component developer, and an image bearing member of a developer bearing member carrying the toner is used. In a developing device having a peripheral speed ratio with respect to the peripheral speed of 1 to 2, and a toner regulating member carried on a developer carrying member is an elastic regulating member, a resin is provided with conductive particles on a surface of the developer carrying body. Since the conductive resin coating layers containing the above are formed in upper and lower layers and the ratio of the conductive particles to the resin in the upper coating (P / B ratio) is made higher than that in the lower coating, It is possible to improve the rising delay and prevent image unevenness due to abrasion of the resin coating when printing a large number of sheets. Therefore, by providing the image forming apparatus with the developing device of the present invention, it is possible to always obtain a good image regardless of the use environment.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a developing device of the present invention.

FIG. 2 is a perspective view showing a developing sleeve arranged in the developing device of FIG.

FIG. 3 is a sectional view of the developing sleeve.

FIG. 4 is a sectional view showing a developing sleeve according to another embodiment of the present invention.

5 is a diagram showing the distribution of the triboelectric charge amount of toner on the developing sleeve in Experiment 2 using the developing sleeve of FIG. 4 together with the case of the developing sleeve of the comparative example.

FIG. 6 is a configuration diagram showing a conventional developing device.

7 is a diagram showing the distribution of the triboelectric charge amount of toner on the developing sleeve installed in the developing device of FIG. 6 at the initial stage of printing.

FIG. 8 is a diagram showing the distribution of the amount of triboelectric charge of toner on the developing sleeve after printing about 500 sheets.

[Explanation of symbols]

 1, 10 Development sleeve 2 Photosensitive drum 3 Magnet roller 4 Elastic blade 5 Magnetic toner 7, 13 Conductive resin coating 8, 11 Upper layer coating 9, 12 Lower layer coating

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Hiroaki Sakai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Minoru Matsukuma 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Takayasu Yukino 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masaharu Okubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 72) Inventor Yasunari Ohara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A developer is composed of a negative polarity magnetic toner having a volume average particle size of 6 to 9 μm, and a peripheral speed ratio of a developer carrying body carrying and carrying the magnetic toner to an image carrying body is 1 to 2. In a developing device in which an elastic regulating member is in contact with the developer carrying member and is in contact with the developer carrying member, two upper and lower thin conductive resin films containing conductive particles in resin are formed on the surface of the developer carrying member. A developing device, wherein the ratio of the conductive particles to the resin formed in the upper layer of the coating is higher than that in the lower layer of the coating. 2. The weight ratio of the conductive particles to the resin in the upper layer of the coating is selected from 2/1 to 1/1, and the weight ratio of the conductive particles to the resin in the lower layer of the coating is 2. The ratio is selected from 1/1 to 1/3.
Developing device. 3. The developing device according to claim 1, wherein the conductive resin film contains, as conductive particles, at least one selected from carbon black and graphite. 4. The developing device according to claim 3, wherein the conductive resin film further contains positively chargeable particles as conductive particles.