JP2005156692A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of carrier adhesion and scumming even if a small-diameter developing roller is used in an image forming apparatus which has a developing means for developing a latent image on an image carrier by a developer composed of a toner and the carrier and a transfer means for transferring the toner image formed by the developing means to a transfer material, has a nonmagnetic sleeve rotating together with the fixed magnet in the developing means, and has a developing roller arranged to face the developer carrier. <P>SOLUTION: The image forming apparatus is so constituted that the external diameter of the developing roller 51 is ≤18 mm; the developing main pole angle θ of the fixed magnet is inclined 5 to 10° to the upstream side in the rotating direction of the developing roller from a straight line connecting the center of the developing roller and the point nearest to the image carrier in the developing roller; the average grain size of the carrier constituting the developer is 35 to 40 μm; and the electric resistance value measured by a magnetic brush shape of the carrier is 5×10<SP>6</SP>to 5×10<SP>7</SP>Ω. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a facsimile, a printer, an electrophotographic recording apparatus, which is an image forming apparatus equipped with a developing device employing an electrostatic developing system, and a process cartridge that is detachable from the image forming apparatus main body. .

  In an image forming apparatus such as a copying machine or a printer, a two-component developing device is arranged as a developing means so as to face the image carrier, and the developing device includes a fixed magnet and a rotating nonmagnetic sleeve, In general, a developing roller formed of a sleeve is disposed opposite to the image carrier.

  Such an image forming apparatus includes a charging unit that uniformly charges the image carrier, a latent image forming unit that forms a latent image on the image carrier, and a latent image on the image carrier from toner and a carrier. The developing means for developing with the developer, and a transfer means for transferring the toner image formed by the developing means to a transfer material, the developing means comprising a fixed magnet and a rotating nonmagnetic sleeve, and A developing roller is disposed opposite to the image carrier (see, for example, Patent Documents 1 and 2).

  In recent years, while image forming apparatuses have become colored, downsizing of the apparatus main body is desired. For example, in a color image forming apparatus that superimposes four color toners to increase the number of colors, the number of developing rollers used in the developing apparatus is generally four, and the diameter of the developing roller is being reduced for miniaturization. is there. In recent years, developing rollers having a diameter of 18 mm or less are also on the market.

  The developing roller having a diameter of 18 mm or less has an advantage that the rear end blur of the formed image is small in addition to the merit of reducing the diameter. That is, it is considered that the reduction of the diameter reduces the width at which the developer contacts the image carrier, reduces the effect of rubbing the toner image with the developer spike immediately after forming the toner image, and reduces the trailing edge blur of the image.

  On the other hand, when a small-diameter developing roller having a diameter of 18 mm or less is used, there arises a problem that a margin for carrier adhesion to the edge portion or background portion of the latent image and toner adhesion to the background portion is lowered.

In Patent Document 1, the linear speed of the photosensitive drum is 200 mm / s, the linear speed of the developing sleeve is 300 mm / s, the diameter of the photosensitive drum is 50 mm, the diameter of the developing sleeve is 18 mm, the diameter of the magnet roller is 16 mm, and the magnetics constituting the developer. A development method in which the particle size of the particles is 20 μm to 50 μm and the dynamic resistance of the magnetic particles is 10 ⁴ Ω to 10 ⁸ Ω in DR has been disclosed, such as good image quality, prevention of carrier adhesion, stabilization of development characteristics, etc. There is a disclosure that an effect such as cost reduction is obtained in terms of reliability.

  Patent Document 2 discloses that the main pole angle is set to 15 ° to 25 ° at a developing roller diameter of 25 mm or less, so that carrier adhesion and generation of background stains can be prevented, and developing means including two upper and lower developing rollers. As an example, there is disclosed that the main pole angle of the upper developing roller mainly composed of developing ability is set to 10 °, and the main pole angle of the lower developing roller mainly composed of carrier adhesion and background stain prevention is set to 20 °. is there.

JP 2002-365914 A JP-A-11-95558

  An object of the present invention is to provide an image forming apparatus including a developing unit that can suppress the occurrence of carrier adhesion and background contamination even when a small-diameter developing roller is used. Another object of the present invention is to provide a process cartridge equipped with the developing means in order to improve user maintenance.

The present invention has the following configuration in order to achieve the above object.
(1). A charging unit for uniformly charging the image carrier, a latent image forming unit for forming a latent image on the image carrier, and development for developing the latent image on the image carrier with a developer composed of toner and carrier. And a transfer means for transferring the toner image formed by the developing means to a transfer material. The developing means includes a fixed magnet and a rotating nonmagnetic sleeve, and is disposed opposite to the image carrier. In the image forming apparatus having the developing roller, the outer diameter of the developing roller is 18 mm or less, and the developing main pole angle of the fixed magnet is closest to the center of the developing roller and the developing roller is closest to the image carrier. Is inclined at an angle of 5 ° to 10 ° upstream of the developing roller in the rotation direction, and the average particle size of the carrier constituting the developer is 35 μm to 40 μm, and the carrier has a magnetic brush shape. Measured electricity Resistance was to be a ^{5 × 10 6 Ω~5 × 10 7} Ω ( claim 1).
(2). In the image forming apparatus according to (1), the carrier has a resin film layer on a surface thereof.
(3). In the image forming apparatus according to any one of (1) to (3), the linear velocity of the developing roller is 1.5 to 2.0 times the linear velocity of the image carrier. ).
(4). In a process cartridge in which an image carrier and a developing unit are indispensable components, and at least one unit selected from a charging unit and a cleaning unit is integrally supported, and is detachable from an image forming apparatus main body. The developing roller constituting the developing means has an outer diameter of 18 mm or less, and the development main pole angle of the fixed magnet is from a straight line connecting the center of the developing roller and the point where the developing roller is closest to the image carrier. The developer is inclined 5 ° to 10 ° upstream in the rotation direction of the developing roller, the average particle size of the carrier constituting the developer held by the developing roller is 35 μm to 40 μm, and the carrier has a magnetic brush shape. The measured electric resistance value was set to 5 × 10 ⁶ Ω to 5 × 10 ⁷ Ω.
(5). (4) In the process cartridge according to (4), the carrier has a resin film layer on the surface of the core particle.
(6). In the process cartridge according to (4) or (5), the linear velocity of the developing roller is 1.5 to 2.0 times the linear velocity of the image carrier (claim 6).
(7). The image bearing member charged by the charging unit is scanned with scanning light including image information to create an electrostatic latent image, the electrostatic latent image is visualized as a toner image by the developing unit, and the toner image is transferred. In the image forming apparatus for transferring to a medium, the process cartridge described in (4) to (6) can be attached to and detached from the main body of the image forming apparatus.

In the first and fourth aspects of the present invention, even when a small-diameter developing roller is used, it is possible to suppress the occurrence of carrier adhesion and background contamination.
The inventions according to claims 2 and 5 can further stabilize the effect according to claim 1.
According to the third and sixth aspects of the invention, the solid development ability can be maintained.
According to the seventh aspect of the present invention, it is possible to suppress the occurrence of carrier adhesion and scumming in an image forming apparatus with better user maintenance.

[1] Image Forming Apparatus Hereinafter, an example of the present invention will be described with reference to the drawings. A configuration and a process of obtaining a color image will be described with reference to FIG. 1 showing a configuration of a color image forming apparatus suitable for the implementation of the present invention.

[1.1] Device Configuration In FIG. 1, a transfer belt device 10 having an intermediate transfer belt 11 is located at a substantially intermediate position in a box-shaped device main body 100. The intermediate transfer belt 11 is stretched in the left-right direction, and is gently inclined to the lower right. Four image stations ST1, ST2, ST3, and ST4 are arranged along the lower extending surface of the intermediate transfer belt 11.

  Each of these four image stations ST 1, ST 2, ST 3, ST 4 creates various toner images for forming yellow (Y), cyan (C), magenta (M), and black (Bk) toner colors. It is composed of members and has the same structure except for the color of the toner used.

  In FIG. 2, these four image stations ST1, ST2, ST3, ST4 are generalized and denoted by the symbol ST. In FIG. 2, an image station ST includes an image carrier 20 (hereinafter referred to as a photosensitive drum), a charging device 30 as a charging unit disposed around the image carrier ST, a developing device 50 as a developing unit, and a cleaning unit. The cleaning device 40 is provided. Other configurations will be described later. The photosensitive drum 20 is disposed in proximity to the intermediate transfer belt 11.

  Since each image station ST1, ST2, ST3, ST4 has the same basic configuration except for the color of the toner to be handled, in FIG. Later, the yellow image station is indicated by Y, the cyan image station is indicated by C, the magenta image station is indicated by M, and the black image station is indicated by Bk.

  In FIG. 1, the lower stretched surface of the transfer belt 11 is configured to travel rightward, and along the lower stretched surface, the leftmost image station ST1 is an image station that forms a yellow image. The body drum 20Y includes a charging device 30Y, a developing device 50Y, a cleaning device 40Y, and the like disposed around the body drum 20Y.

  An image station ST2 for forming a cyan image is positioned to the right of the image station ST1 for forming a yellow image. The cyan image station ST2 includes a photosensitive drum 20C and a charging device 30C, a developing device 50C, a cleaning device 40C, and the like disposed around the photosensitive drum 20C.

  An image station for forming a magenta image is located to the right of the image station ST2 for forming a cyan image. The image station for magenta image includes a photosensitive drum 20M and a charging device 30M, a developing device 50M, a cleaning device 40M, and the like disposed around the photosensitive drum 20M.

  An image station ST4 for forming a black image is positioned to the right of the image station ST3 for forming a magenta image. The image station ST4 for black image includes a photosensitive drum 20Bk and a charging device 30Bk, a developing device 50Bk, a cleaning device 40Bk, and the like disposed around the photosensitive drum 20Bk.

  The primary transfer rollers 12Y, 12C, 12M, and 12Bk are rotated around the belt at positions inside the intermediate transfer belt 11 and facing the photosensitive drums 40Y, 40C, 40M, and 40Bk in each image station. Are arranged.

  The writing device 8 is positioned so as to face each of the image stations ST1 to ST4 in common. As is well known, the writing device 8 obtains scanning light by controlling the laser beam emitted from the laser light source with each color image information signal of Y, C, M, and Bk, and deflects it with a deflector. Then, the light is emitted toward each of the photosensitive drums 20Y, 20M, 20C, and 20Bk.

  A toner bottle containing toner to be supplied to each of the developing devices 50Y, 50C, 50M, and 50Bk is disposed on the upper left side of the intermediate transfer belt 11. From the left in the figure, a toner bottle 60Y filled with yellow toner, a toner bottle 60C filled with cyan toner, a toner bottle 60M filled with magenta toner, 60Bk filled with black toner, etc. The developing devices 50Y, 50C, 50M, and 50Bk for each color are replenished by a predetermined replenishment amount.

  A paper feeding device 70 is disposed below the writing device 8. A paper feed cassette 1 containing transfer paper 2 is mounted on the paper feed device 70. The paper feeding device 70 is also provided with a paper feeding roller 3, and separates and sends out a large number of transfer sheets stored in the paper feeding cassette 1 from the top. The transfer paper that has come out of the paper feed roller 3 travels along a transport path provided upward. A pair of registration rollers 4 is disposed immediately before the secondary transfer roller 5 on the conveyance path.

  The secondary transfer roller 5 is opposed to the roller supporting the right end of the intermediate transfer belt 11 to form a secondary transfer portion, and the conveying path extends further through the secondary transfer portion, It is guided to the paper discharge unit 9 through the fixing device 6 and further through the discharge roller 7. Further, an intermediate transfer belt cleaning device 13 is disposed so as to face the roller supporting the right end of the intermediate transfer belt 11.

[1.2] Image Forming Process The photosensitive drums 20Y, 20C, 20M, and 20Bk that are uniformly charged in advance by the charging devices 30Y, 30C, 30M, and 30Bk are exposed and scanned by the scanning light from the optical writing device 8. . As a result, electrostatic latent images are formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk.

  The electrostatic latent images are developed by the developing devices 50Y, 50C, 50M, and 50Bk for the respective colors, and yellow, cyan, magenta, and black toner images are formed on the surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk.

  Next, the intermediate transfer drum 11 rotates and a voltage is applied to the primary transfer rollers 12Y, 12C, 12M, and 12Bk, and the toner images on the photosensitive drums 20Y, 20C, 20M, and 20Bk are transferred onto the intermediate transfer belt 11. Sequentially overprinted. Here, the image forming operation of each color on each photosensitive drum is performed from the upstream side to the downstream side so that the toner image on each photosensitive drum is transferred to the same position on the intermediate transfer belt 11. It is executed with the timing shifted.

  In this way, a color-superimposed full-color toner image is formed on the intermediate transfer belt 11 by overlapping transfer of each color, and moves to the right as the intermediate transfer belt 11 moves. On the other hand, the transfer paper 2 is fed from the paper feed cassette 1 by the paper feed roller 3 at the timing so as to meet at the secondary transfer roller portion, and when the leading edge of the transfer paper 2 reaches the registration roller pair 4, it is not shown. The transfer sheet 2 is conveyed by a registration roller pair 4 to a secondary transfer portion formed by a nip portion between the secondary transfer roller 5 and the intermediate transfer belt 11 while being detected by a sensor and timed by this detection signal. The full color toner image formed on the intermediate transfer belt 11 is secondarily transferred to the transfer paper 2 at the secondary transfer portion. The transfer paper 2 onto which the full-color toner image has been transferred is conveyed to the fixing device 6 and thermally fixed, and is sent out and stacked on a paper discharge tray 9 by a discharge roller 7.

  The residual toner on the photoconductive drums 20Y, 20C, 20M, and 20Bk is cleaned by the respective cleaning devices 40Y, 40C, 40M, and 40Bk, and then the charging device 30Y, in which the bias of the AC component is superimposed and applied to the direct current. 30C, 30M, and 30Bk are charged simultaneously with static elimination to prepare for the next image formation. The residual toner on the intermediate transfer belt 11 is cleaned by the intermediate transfer belt cleaning device 13 to prepare for the next image forming process.

[1.3] Image Station FIG. 2 shows an enlarged view of one of the image stations. This image station represents the four image stations ST1 to ST4 shown in FIG. 1 as an image station ST, and its constituent members are attached to identify the colors of the four image stations ST1 to ST4. The reference numerals Y, C, M, and Bk are omitted. In addition, members that are not described in FIG. 1 to avoid complexity are also described here.

  In FIG. 2, the developing device 50 regulates the developing case 55 having an opening, the developing roller 51 disposed so as to face the surface of the photosensitive drum 20, and the developer on the developing roller 51 to a constant layer thickness. The first conveying screw 53 and the second conveying screw 54 are arranged at positions facing the doctor blade 52 and the developing roller 51, and the like.

  The cleaning device 40 includes a cleaning case 43 having an opening, a cleaning blade 41 for cleaning residual toner on the photosensitive drum 20, and a waste toner screw 42 for transporting the cleaned waste toner to a waste toner bottle (not shown). Etc.

  The transfer belt device 10 includes an intermediate transfer belt 11, a primary transfer roller 12 for transferring a toner image on the photosensitive drum 20 to the intermediate transfer belt 11, an intermediate transfer belt case 14 for holding these components, and the like. ing. A charging roller 30 as a charging device is in contact with the photosensitive drum 20, and a cleaning roller 31 for cleaning the charging roller 30 is in contact with the charging roller 30.

  Scanning light from the writing device 8 is applied to a region on the circumferential surface of the photosensitive drum 20 between a position where the charging roller 30 is in contact and a portion where the developing roller 51 is in close proximity. It is like that.

[1.4] Developing Device In FIG. 3 where the developing device 50 and the photosensitive drum 20 as the developing means shown in FIG. 2 are taken out, the developing roller 51 includes a nonmagnetic sleeve that rotates in the direction of the arrow. A plurality of stationary magnets are provided inside the sleeve.

  Among these magnets, the pole disposed opposite to the photosensitive drum 20 is the main pole M1, and the symbol θ indicates the main pole angle. The main pole angle θ here is a main pole on the upstream side in the rotation direction of the developing roller 51 indicated by an arrow from a straight line L connecting the center of the developing roller 51 and the point where the developing roller 51 is closest to the photosensitive drum. It is the angle which shifted the center of. Therefore, in this example, since the image carrier is a drum, the straight line L coincides with a straight line connecting the center of the developing roller 51 and the center of the photosensitive drum 20, and the center of the main pole M1 is shifted with respect to the straight line L. This angle becomes the main pole angle θ.

[2] Example The configuration and development conditions of an image forming apparatus will be specifically described.
As a developer, a ferrite core material, a saturation magnetization of 72 Am ^ 2 / kg at an applied magnetic field of 5 kOe, a DC resistance value of 5 × 10 6 Ω carrier, a toner having an average particle diameter of 5 μm, a toner concentration accounting for 7% by weight, a doctor The gap between the blade 52 and the developing sleeve (outer diameter portion of the developing roller 51) is 0.50 mm, and the gap (developing gap) between the developing roller (outer diameter portion of the developing roller 51) and the photosensitive drum 20 is 0.35 mm. The diameter of the photosensitive drum 20 is 30 mm, the linear velocity of the outer diameter portion of the photosensitive drum 20 is 155 mm / sec, and the development main pole magnetic force is 105 mT. Here, the direct current resistance value is a value obtained by measuring a resistance value when a voltage of 20 V is applied to the developing sleeve in an image forming apparatus that is actually used and using a grounded aluminum element tube instead of the photosensitive member. It is a result.

  As a developing device similar to this developing device, the developing sleeve diameter is 14 mm, 16 mm, 18 mm, 20 mm, the main pole angle θ is 0 °, 5 °, 10 °, 15 °, the average carrier particle size is 30 μm, 35 μm, 40 μm, The image density, the toner stain on the background, the carrier adhesion, etc. when shaking with 55 μm were examined. The results are shown in Tables 1-3.

  Accordingly, as the developing roller diameter (developing sleeve diameter) becomes smaller, carrier adhesion and background toner contamination tend to worsen. In the image forming process, the carrier adhesion damages a transfer device and a fixing device, which are later processes than the development, and is thus treated as a failure of the image forming apparatus main body. Further, the background toner stains contaminate the output image and is treated as an abnormal image depending on the degree.

  On the other hand, if the diameter of the developing roller is larger than 18 mm, the margin for the image density is slightly reduced, and the larger the machine body, the larger the machine body. The influence on is great and undesirable.

  Also, the smaller the carrier particle size, the worse the carrier adhesion. On the other hand, since the force for scraping off the developed toner at the time of developing the toner on the latent image is weakened, the use of a carrier having a small particle diameter has an advantage that a smooth and uniform solid image can be formed.

  Further, by reducing (decreasing) the main pole angle θ, it is easy to obtain image density, but carrier adhesion and background toner contamination are worsened. On the contrary, by increasing (increasing) the main pole angle θ, the image density is lowered, but carrier adhesion and background toner contamination are improved.

  Consider the effect of increasing the main pole angle θ. The mug brush on the developing roller 51 is composed of a head portion A and a head portion B. Among these, the raised portions A are connected in a chain shape while the carrier holds the toner, and a so-called sparse state is created in which spaces are formed between the respective chains.

  Therefore, the carrier is easy to move in the heading portion A, and the developing ability is high. On the other hand, in the panicle portion B, a carrier holding toner is densely present. Unlike the toner, the carrier itself does not form an image, so the developing ability is low, but since the electric field tends to be uniform, the magnetic force between the carriers is also strong.

  That is, by increasing (increasing) the main pole angle θ, the toner is developed by creating a sparse state at the entrance of the development nip, and a dense state is created near the center of the development nip to prevent carrier adhesion. It is done.

  With regard to only a decrease in image density when the main pole angle θ is increased (increased), it is conceivable to increase the developing capacity by increasing the toner density or by increasing the linear velocity of the developing roller 51. Toner contamination and toner scattering due to increase, toner scattering due to the influence of centrifugal force due to increased development roller linear velocity, carrier adhesion margin decrease, solid density unevenness due to development toner rubbing, etc. are likely to occur. Therefore, it is not a preferable method.

Further, in order to further improve the carrier adhesion margin, the outer diameter of the developing roller (developing sleeve) is 14 mm, 16 mm and 18 mm, the main pole angle θ is 5 ° and 10 °, and the average carrier particle size is 35 μm and 40 μm, respectively. Table 4 shows the results when the carrier DC resistance is shaken as 1 × 10 ⁶ Ω, 5 × 10 ⁶ Ω, 1 × 10 ⁷ Ω, 5 × 10 ⁷ Ω, and 1 × 10 ⁸ Ω in the above combinations. .

According to Table 4, if the carrier resistance is less than 5 × 10 ⁶ Ω, the margin for carrier adhesion decreases. In addition, it was hoped that by setting it to 1 × 10 ⁷ Ω or more, it is possible to maintain other image quality while further improving the margin for carrier adhesion. On the other hand, if the carrier DC resistance is increased to about 1 × 10 ⁸ Ω, a solid portion tip (advancing direction tip) white-out at the boundary between the solid portion and the white portion, which is called a halo image due to the edge effect of the electric field. Problems start to occur.

As a method of forming a uniform solid image, eliminating toner stains on the background, and suppressing the carrier adhesion that is highly damaging to the machine body, the developing roller diameter is reduced to a small diameter of 18 mm or less, and the carrier particle size is reduced. Has been found to be 40 μm or less (35 μm to 40 μm), a main pole angle of 5 ° to 10 °, and a carrier direct current resistance of 5 × 10 ⁶ Ω to 5 × 10 ⁷ Ω. Item 1).

  Here, the carrier had a resin film layer (resin coat) on the surface of each body particle. As described above, by providing the resin coat layer on the carrier, the toner particle charge amount can be stably applied over a long period of time by friction between the carrier and the toner and / or peeling charging. Can be made more stable (claim 2).

  As a material for controlling the electric resistance of the carrier core material and / or the coat layer, a conventionally known material may be used. Examples thereof include metals such as iron, gold and copper, iron oxides such as ferrite and magnetite, and carbon black. And the like.

  Among these, in particular, by using a mixture of furnace black and acetylene black, which is one of carbon blacks, the conductivity can be effectively adjusted with the addition of a small amount of resistance adjusting fine powder, which is preferably used.

  These resistance adjusting fine powders preferably have a particle size of about 0.01 to 10 μm, and are preferably added in an amount of 2 to 30 parts by weight with respect to 100 parts of the core material or coat layer resin. A coupling agent such as a silane coupling agent or a titanium coupling agent is added to the magnetic material dispersion type core material particles as an auxiliary agent for the purpose of improving the adhesion or dispersibility of the resistance control material. May be.

  As means for adjusting the direct current resistance of the carrier, a resin film layer is coated on the carrier core material, and an appropriate amount of an additive material such as alumina, aminosilane, or carbon is added to the coat. The kind and amount of the additive material may be within the scope of the present invention, and are not limited to the above materials.

  In order to maintain a uniform solid development capability, it is desirable that the rotation linear velocity ratio of the developing sleeve to the photosensitive member be 1.5 to 2.0. If the linear velocity ratio is increased beyond this range, the centrifugal force increases, and the carrier and toner tend to scatter due to the centrifugal force, and the solid density tends to decrease due to the rubbing marks of the developing toner. There is. Moreover, if it is less than this range, the solid density does not appear (Claim 3).

  As a method for evaluating carrier adhesion, a method of counting the number of carrier adhesions on the photosensitive drum of the photosensitive drum using an actual machine is used. After the background potential image (non-exposed white image) created by the photoreceptor background potential and the development potential is developed, the main power supply is turned off.

Here, in the area after development and before transfer, the number of carriers attached on the photoconductor is counted, and the number in the actual machine background potential control range is converted to an area of 75 cm ² arbitrarily installed. Perform this work while shaking the ground potential, the worst value of the number of carrier adhesion conversion in the ground potential control range,
In case of 40 or less ... ○
In case of 41 to 70 ...
In case of 71 or more… ×
It was determined.

As an evaluation method of background toner stains,
The degree of toner adhesion on the photoreceptor at the time of carrier adhesion determination,
Good, if there is no toner adhesion ...
Slightly bad ・ In the case of very slight toner adhesion… △
If it is bad or there is toner adhesion ... ×
It was performed by rank evaluation.

As a method for evaluating the image density, in order to determine the developing ability, the main power is turned off after the solid patch image is developed on the photoconductor with an actual machine. Here, in the region after development and before transfer, the amount of toner adhered per unit area on the photoreceptor is measured,
In the case of 0.5mg / cm ² or more ... ○
In the case of 0.4 to 0.5 mg / cm ² ... △
In case of less than 0.4 mg / cm ² ... ×
It was determined.

According to the fourth aspect of the present invention, the photosensitive drum 20 and the developing device 50 are indispensable, and at least one means selected from the charging device 30 and the cleaning device 40 is integrally supported in this configuration, and the image forming apparatus main body The developing roller 51 has an outer diameter of 18 mm or less, and the development main pole angle θ of the fixed magnet is the center of the developing roller 51 and the developing roller 51 is photosensitive. It is inclined 5 ° to 10 ° upstream of the straight line connecting the point closest to the body drum 20 in the rotation direction of the developing roller 51, and the average particle size of the carrier constituting the developer is 35 μm to 40 μm, And the electrical resistance value measured with the magnetic brush shape of the carrier is 5 × 10 ^{6 to} 5 × 10 ⁷ Ω.

  According to a fifth aspect of the present invention, in the above process cartridge, the carrier has a resin film layer on the surface of the core particle, and the sixth aspect of the present invention sets the linear velocity of the developing roller 51 to the linear velocity of the photosensitive drum 20. The speed is 1.5 to 2.0 times.

  Each of the photosensitive drums 20 is in the form of a process cartridge in which the developing device 50 according to claims 1, 2, and 3 is integrally supported. In the configuration of the combination of the integrated photosensitive drum 20 and the developing device 50, a process cartridge in which a charger as a charging unit and a cleaning device 40 as a cleaning unit are integrally configured may be used. The cartridge has better user maintenance.

  A seventh aspect of the invention is an image forming apparatus in which the process cartridges of the fourth, fifth and sixth aspects are detachable from the main body of the image forming apparatus. FIG. 4 shows a state in which the process cartridges 160Y, 160C, 160M, and 160Bk for Y, C, M, and Bk colors are about to be extracted from the apparatus main body. In these process cartridges 160Y, 160C, 160M, and 160Bk, the developing device 50, the charging device 30, and the cleaning device 40 are integrally configured on the photosensitive drum 20. As a result, the user can replace the image carrier, the developing device, or the charging unit and the cleaning unit together in a cartridge form.

1 is a front view illustrating a configuration of an image forming apparatus suitable for implementing the present invention. It is the front view which took out and showed the composition of arbitrary image stations and its peripheral part. FIG. 6 is a diagram illustrating a magnetic force distribution around a developing roller. It is the perspective view explaining the process cartridge which can be attached or detached with respect to a main body.

Explanation of symbols

51 Developing roller

Claims (7)

A charging unit for uniformly charging the image carrier, a latent image forming unit for forming a latent image on the image carrier, and development for developing the latent image on the image carrier with a developer composed of toner and carrier. And a transfer means for transferring the toner image formed by the developing means to a transfer material. The developing means includes a fixed magnet and a rotating nonmagnetic sleeve, and is disposed opposite to the image carrier. In an image forming apparatus having a developed developing roller,
The developing roller has an outer diameter of 18 mm or less, and the developing main pole angle of the fixed magnet is a rotation direction of the developing roller from a straight line connecting the center of the developing roller and the point where the developing roller is closest to the image carrier. The carrier is inclined at an angle of 5 ° to 10 ° on the upstream side, the carrier constituting the developer has an average particle size of 35 μm to 40 μm, and the electrical resistance value measured by the magnetic brush shape of the carrier is 5 × 10 ^6. An image forming apparatus characterized by having an impedance of Ω to 5 × 10 ⁷ Ω. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the carrier has a resin film layer on a surface thereof. The image forming apparatus according to any one of claims 1 to 3,
3. The image forming apparatus according to claim 1, wherein a linear velocity of the developing roller is 1.5 to 2.0 times a linear velocity of the image carrier. In the process cartridge in which the image carrier and the developing unit are indispensable components, and at least one unit selected from a charging unit and a cleaning unit is integrally supported on the image carrier and is detachable from the main body of the image forming apparatus. The developing roller constituting the developing means has an outer diameter of 18 mm or less, and the developing main pole angle of the fixed magnet is developed from a straight line connecting the center of the developing roller and the point where the developing roller is closest to the image carrier. The carrier is inclined 5 ° to 10 ° upstream of the rotation direction of the roller, the average particle size of the carrier constituting the developer held by the developing roller is 35 μm to 40 μm, and measured with the magnetic brush shape of the carrier A process cartridge characterized by having an electrical resistance value of 5 × 10 ⁶ Ω to 5 × 10 ⁷ Ω. The process cartridge according to claim 4, wherein
A process cartridge, wherein the carrier has a resin film layer on a surface of a core particle. The process cartridge according to claim 4 or 5,
A process cartridge wherein the linear velocity of the developing roller is 1.5 to 2.0 times the linear velocity of the image carrier. The image bearing member charged by the charging unit is scanned with scanning light including image information to create an electrostatic latent image, the electrostatic latent image is visualized as a toner image by the developing unit, and the toner image is transferred. In an image forming apparatus that transfers to a medium,
7. An image forming apparatus, wherein the process cartridge according to claim 4 is removable from a main body of the image forming apparatus.

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