JP2007171277A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-speed and high-quality black image, a black developing device with a small maintenance amount and a long maintenance interval, avoiding an increase in size of an image forming apparatus capable of full color output.
In an image forming apparatus in which a peripheral speed of a first stage developer carrying member is smaller than a peripheral speed of a second stage developer carrying member, the outer diameter of the first developer carrying member is set to the second diameter. By making it smaller than the outer diameter of the developer carrying member, it is possible to avoid an increase in the size of the image forming apparatus capable of full-color output, high-speed and high-quality black images, black development with low developer consumption and long maintenance intervals Providing equipment.
[Selection] Figure 2

Description

  The present invention includes a developing device that forms a toner image by attaching a developer to an electrostatic latent image formed on a latent image bearing member such as a photoconductor, and forms an image by an electrophotographic method or an electrostatic recording method. The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

  In an image forming apparatus (FIG. 9), generally, a latent image carrying member 0 ′ is charged by a charging device 2 ′, and an input image is exposed by an exposure optical system to form an electrostatic latent image on the peripheral surface of the photoreceptor 0 ′. The electrostatic latent image formed on the peripheral surface of the photoreceptor 0 ′ is developed by the developing device 1 ′ to form a toner image.

  Then, the toner image is transferred onto the transfer material M ′ by the transfer means 3 ′, and the toner image is fixed on the transfer paper by the fixing device 8 ′ and discharged. Further, the surface of the photoconductor 0 ′ after the transfer is cleaned by the cleaning device 7 ′, and further, pre-charge exposure 10 ′ is performed to remove the residual charges and prepare for the next image formation.

  In the conventional developing device 1 ′ used in the image forming apparatus described above, a single developer carrying member (hereinafter referred to as a developing sleeve) is usually used to carry and transport the developer and supply the toner to the photoreceptor 0 ′. ) 12 'is arranged in contact with the photoreceptor 0' or with a certain gap.

  By the way, in recent years, an image forming apparatus has been required to further increase the speed. However, in a conventional developing apparatus having a single developing sleeve, it is not easy to cope with the increasing speed.

  In general, development is performed by rotating the developing sleeve at a speed of about 1.5 times the peripheral speed of the photoconductor 0 ′. The speed may have to be about twice the peripheral speed of the photoconductor 0 ′ (conventional example 4).

  This is because unless the peripheral speed of the developing sleeve is increased, the supply of the developer is insufficient and the image density is insufficient.

However, when the peripheral speed of the developing sleeve is increased, there is a risk that problems such as fusion and deterioration of the developer may occur due to the temperature rise in the vicinity of the developing sleeve.

Accordingly, in order to solve the above-described problems, a developing device that includes a plurality of developing sleeves and performs development with each developing sleeve has been proposed (FIG. 12 Conventional Example 2).
In such a developing device, it is possible to cope with a higher speed without increasing the peripheral speed of each developing sleeve, and at the same time, there is an advantage that the toner consumption can be reduced. There has been a problem that the image forming apparatus becomes large and difficult to use particularly in a small office in Japan.

  Therefore, in recent years, a developing device in which a plurality of developing sleeves are close to each other and integrated is proposed.

  Among such developing devices, a developing device having a configuration in which two developing sleeves are close to each other is rapidly developed as a configuration capable of achieving both high speed and downsizing (FIG. 10 Conventional Example 1). .

  An example of a developing device in which two developing sleeves are close to each other and integrated is disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-305352.

  As shown in FIG. 10, the developing device having such a configuration has a first developing sleeve 12a ′ and a second developing sleeve 12b in an opening portion of a developing container 11 ′ containing a developer d ′ facing the photosensitive drum 0 ′. 'Is placed in close proximity. The photosensitive drum 0 ′ rotates in the arrow b direction (clockwise), and the first developing sleeve 12a ′ and the second developing sleeve 12b ′ rotate in the arrow b direction (counterclockwise).

  That is, at the position where the first developing sleeve 12a ′ and the second developing sleeve 12b ′ are close to the photosensitive drum 0 ′, the rotational direction of the photosensitive drum 0, the first developing sleeve 12a ′, and the second developing sleeve 12b ′. The first developing sleeve 12a ′ and the second developing sleeve 12b are in a portion SS where the first developing sleeve 12a ′ and the second developing sleeve 12b ′ are close to each other (hereinafter referred to as an SS portion). The rotation direction of 'is the reverse direction.

  Then, the developer d ′ in the developing container 11 ′ is transported to the vicinity of the second developing sleeve 12a ′ by the stirring / conveying member, and further, as the second developing sleeve 12a ′ rotates in the direction of arrow b (counterclockwise). Thus, the first developing sleeve 12a ′ and the second developing sleeve 12b ′ are sent to the vicinity of the SS portion that is closely opposed.

  Here, the layer thickness is regulated when the developer d ′ passes through the SS portion, and the developer layer d2 ′ is formed on the surface of the second developing sleeve 12b ′. A part of the developer layer d2 ′ is used for development at the closest point to the photosensitive drum 0 ′, but the developer not used for development is collected in the developing container 11 ′.

  On the other hand, of the developer d ′ transported to the vicinity of the SS portion where the first developing sleeve 12a ′ and the second developing sleeve 12b ′ are close to each other, the developer not carried on the surface of the second developing sleeve 12b ′ d ′ is conveyed to the vicinity of the thin layer forming member 14 ′ as the first developing sleeve 12a ′ rotates. Here, the layer thickness is regulated when the developer d ′ passes through the gap between the thin layer forming member 14 ′ and the first developing sleeve 12a ′, and the developer layer d1 ′ is formed on the surface of the first developing sleeve 12a ′. It is formed. A part of the developer layer d1 ′ is used for development at the closest contact point with the photosensitive drum 0, but the developer that has not been used for development is the first development sleeve 12a ′ and the second development sleeve 12b ′. It is sent to the SS section that is closely opposed, where a part is collected in the developing container 11 ′, and the rest is transferred to the second developing sleeve 12b ′ and becomes a part of the developer layer d2 ′.

  In this developing device, the developer (developer) is supplied from the developer supply container (not shown) to the developer container 11 ′ based on the developer remaining amount information detected by the developer remaining amount detection sensor (not shown). Will be replenished.

  By the way, in the developing device having the above-described configuration, the developer layer d1 ′ carried on the surface of the first developing sleeve 12a ′ at the SS portion where the first developing sleeve 12a ′ and the second developing sleeve 12b ′ are closely opposed to each other. Since the developer layer d2 ′ carried on the surface of the second developing sleeve 12b ′ collides in the counter direction, the developer is rubbed in this portion (near the SS portion).

  In particular, when the image forming apparatus is further increased in speed, the peripheral speed of the first and second developing sleeves 12a ′ and 12b ′ is also increased, so that more severe rubbing of the developer occurs in the vicinity of the SS portion. As a result, the surface temperature of the first and second developing sleeves 12a ′ and 12b ′ increases, and there is a risk that problems such as the fusion of the developer to the surfaces of the first and second developing sleeves 12a ′ and 12b ′ may occur. was there.

  Therefore, in order to alleviate the severe rubbing of the developer near the SS portion between the first sleeve 12a ′ and the second sleeve 12b ′, the peripheral speed of the first sleeve 12a ′ or the second sleeve 12b ′ is set to the other sleeve. It has been proposed to reduce the rubbing of the developer near the SS portion by making it slower than the peripheral speed.

  On the other hand, the trend of downsizing and full-color image forming devices in recent years is unrecognized, and as a result, developers need to reduce the size of developing devices, but it is difficult to reduce the size of a two-sleeve developing device in principle. It is.

  An increasing number of image forming apparatuses use an a-Si photoreceptor as a latent image carrying member for the purpose of reducing running costs. The a-Si photosensitive member has an advantage that the image forming apparatus does not need to be replaced until the end of its life because the a-Si photosensitive member is superior to the organic photosensitive member, and is rapidly spreading mainly in high-speed machines and high-end machines. Therefore, it is almost essential that the surface potential is constantly monitored by a potential detection sensor and necessary control is performed.

The potential detection sensor functions in a non-contact manner with the latent image carrying member, but the upper limit of the gap distance for measuring an accurate potential is about 10 mm, and it is necessary to secure a space around the latent image carrying member (see FIG. 11).
JP 2000-305352 A

  The problem to be solved by the invention is to avoid the enlargement of an image forming apparatus capable of full color output, and to provide a high-speed and high-quality black image, and a black developing apparatus with a small maintenance amount and a long maintenance interval. is there.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a rotating latent image carrying member, a developer containing portion that contains a developer, and the developer supplied from the inside of the developer containing portion and thinned. A developing device for transferring the developer to the latent image carrying member by the action of an electric field by bringing the developer carrying member close to or in contact with the latent image carrying member. The second developer carrying member rotates in the same direction at a position close to or in contact with the image carrying member with respect to the moving direction of the image carrying member arranged close to each other with a predetermined gap therebetween. One developer carrying member and a second developer carrying member, wherein the first developer carrying member is located upstream with respect to the rotation direction of the image carrying member and the second developer carrying member. The member is the rotation direction of the image bearing member In the image forming apparatus that is located downstream of the first developer carrying member and whose peripheral speed is lower than the peripheral speed of the second developer carrying member, The diameter is smaller than the outer diameter of the second developer carrying member.

  Further, the mass per unit area of the developer carried on the surface of the first developer carrying member is larger than the mass per unit area of the developer carried on the surface of the second developer carrying member. It was decided.

  Further, the peripheral speed of the first developer carrying member is lower than the peripheral speed of the latent image carrying member.

  Also, the bias applied to the first developer carrying member for generating the electric field and the bias applied to the second developer carrying member for generating the electric field are common. It was.

  The first developer carrying member has a roller shape with an outer diameter of less than 21 mm.

  The developer is made of only magnetic toner.

  Further, the charge imparting ability of the first developer carrying member to the magnetic toner is greater than the charge imparting ability of the second developer carrying member to the magnetic toner.

  The latent image carrying member includes a photosensitive layer containing amorphous silicon atoms.

  Further, the latent image carrying member has a drum shape with an outer diameter of less than 109 mm.

  In addition, a full color image can be formed.

  As described above, according to the present invention, it is possible to avoid an increase in the size of an image forming apparatus capable of full-color output, and to suppress a temperature rise in the vicinity of the developing device and prevent toner fusion, thereby achieving high-speed and high-quality images. Is provided, and an image forming apparatus having a developing device with low toner consumption and low maintenance frequency is provided.

Example 1
FIG. 1 is a schematic cross-sectional view of the image forming apparatus according to the present embodiment.

  This image forming apparatus is a full-color digital copying machine of 40 sheets per minute at a process speed of 200 mm / s during full-color output.

  The copying machine has a width of 800 mm and a height of 790 mm.

  Y, M, C, and K stations are provided, and full-color images of yellow, magenta, cyan, and black can be formed. In the following description, for example, “primary charger 2” refers to the primary chargers 2Y, 2M, 2C, and 2K in the stations of Y, M, C, and K.

  Image formation in the default full color mode is performed as follows.

  First, the photosensitive drum 0, which is a latent image carrier, rotates, and the surface of the photosensitive drum 0 is uniformly charged by the primary charger 2, and then according to an information signal by a light emitting element (not shown) such as a laser. As a result of the exposure, an electrostatic latent image is formed on the surface of the photosensitive drum 0.

  As the latent image carrying members 0Y, 0M, and 0C, organic photoreceptors having an outer diameter of 30 mm are used. The organic photoreceptor has lower durability than the a-Si photoreceptor (lifetime of 100,000 sheets), but can be reduced in diameter, and is suitable for a full-color machine for office use.

  As the latent image carrying member 0K, an a-Si photosensitive member having an outer diameter of 84 mm is used. The a-Si photosensitive member has higher durability (a life of 500,000 sheets) than the organic photosensitive member, and is suitable for a high-speed machine for office use with a high ratio of black output.

  Next, the a-Si photosensitive member 0K will be described with reference to the schematic configuration diagram of FIG.

  FIG. 8 shows a side surface of a cylindrical photoconductor that is partly cut out. This photoreceptor 0K has a substrate 0aK for the photoreceptor and a photosensitive layer 0bK made of a-Si: H, X provided on the substrate 0aK. On the photosensitive layer 0bK, an intermediate layer or a second surface layer 0cK made of a-Si: H, X or a-SiC: H, X is provided as necessary. Further, a surface layer 0dK made of a-SiC: H, X or aC: H, X is provided on the outermost peripheral surface.

  In general, a photoconductor 0K for an image forming apparatus using a-Si: H heats a conductive substrate 0aK, and vacuum deposition, sputtering, ion plating, thermal CVD on the substrate 0aK. (A method, a photo CVD method, a plasma CVD method (hereinafter referred to as “PCVD method”), etc. are used to manufacture a photoconductive layer made of a-Si. A method is preferred in which the gas is decomposed by direct current, high frequency or microwave glow discharge, and the decomposed source gas is deposited on the substrate 0aK to form an a-Si deposited film.

  The surface layer 0dK of the photoconductor 0K shown in FIG. 8 has a center line average roughness Ra of 0.01 μm to 0.9 μm by the manufacturing method as described above.

  The center line average roughness Ra was measured in accordance with JIS, using a surface roughness measuring instrument SE-3300 (manufactured by Kosaka Laboratory) under the condition of a reference length of 0.25 mm.

  The image forming apparatus includes a primary charger 2, a developing device 1, a transfer roller 51, a transfer belt 52, a cleaning device 7 and the like around a photosensitive drum 0.

  In the Y, M, and C stations, this electrostatic latent image is subjected to reversal development with a thin layer of developer carried on the developing sleeve 12a as a developer carrying member of the known developing device 1, and visible as a toner image. Image.

  In this embodiment, the developing operation is performed by a two-component developing method using a two-component developer d having excellent uniformity required for a full-color image.

  Two-component development is composed of magnetic carrier particles and non-magnetic toner.

  At the K station, the electrostatic latent image is normally developed with a thin layer of developer carried on the two developing sleeves 12aK and 13bK as the developer carrying member of the developing device 1K, and is visible as a toner image. (The details of the developing device 1K in this embodiment will be described later).

  In this embodiment, magnetic toner is used which is easy to handle and requires no maintenance work up to the developing sleeve life of 2 million sheets.

  The magnetic toner used in this example is negatively chargeable and has a weight average particle diameter of about 5.8 μm.

  The weight average particle diameter is measured using Multisizer (trademark) (manufactured by Coulter) and the electrolyte using ISOTON R-II (ISOTON is a registered trademark) (manufactured by Coulter Scientific Japan).

  As a measurement method, 0.1 to 5 ml of a surfactant as a dispersant is added to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of particles are measured with the measuring device to calculate the weight average particle diameter.

When the weight average particle size is larger than 6.0 μm, the particle size of 2 to 60 μm is measured using a 100 μm aperture. When the weight average particle size is 3.0 to 6.0 μm, the particle size of 1 to 30 μm is measured using a 50 μm aperture. When the weight average particle size is less than 3.0 μm, particles of 0.6 to 18 μm are measured using a 30 μm aperture.
A potential sensor 90K is disposed immediately upstream of the developing device 1K.

  Immediately downstream of the developing device 1K, a scattered developer collecting device 95K for collecting scattered developer floating in the vicinity of the photosensitive member is formed on the photosensitive member 0K immediately downstream of the scattered developer collecting device 95K. A post charger 96K is provided for increasing the charge amount of the toner image.

  In the Y, M, and C stations, neither the potential sensor 90, the scattered toner collecting device 95 nor the post charger 96 is provided.

  In the Y, M, and C stations, the toner image formed on the photosensitive drum 0 is charged by the post charger 4 and the toner image formed on the photosensitive drum 0K is charged by the post charger 4 in the K station. When reaching the transfer nip NT of the drum 0, the transfer roller 51 and the transfer belt 52, the transfer roller 51 to which a transfer bias having a polarity opposite to that of the developer d is applied is caused by the electrostatic force generated on the photosensitive drum 0 and the transfer roller 51. The image is transferred to the transfer material M on the transfer belt 52.

  Then, the transfer material M is separated from the photosensitive drum 0 by the separation charger 53 to which a separation bias is applied, and is conveyed to the fixing device 8, and in the fixing nip portion between the fixing roller 8 a and the pressure roller 8 b of the fixing device 8. Then, the toner image is fixed on the transfer material M by heating and pressing, and then output to the outside.

  Further, the transfer residual toner remaining on the photosensitive drum 0 after the transfer is removed by the cleaning device 7 and collected.

  When the black output mode is selected, the Y, M, and C stations do not operate and only the K station operates.

  In this case, the process speed is 300 mm / s, and high-speed output of 60 sheets per minute is possible.

  Next, details of the developing device 1K in the present embodiment will be described.

  As shown in FIG. 2, the developing device 1K includes two developing sleeves, a first sleeve 12aK and a second sleeve 12bK, as developer carrying members.

  The first sleeve 12aK and the second sleeve 12bK are close to each other (the gap distance is 200 μm) along the longitudinal direction of the photosensitive drum 0K, close to the opening facing the photosensitive drum 0K of the developing container 11K that stores the magnetic toner t. It is the cylindrical rotary body arranged in parallel.

  Here, the upstream developing sleeve is the first sleeve 12aK and the downstream developing sleeve is the second sleeve 12bK with respect to the rotation direction (clockwise) of the photosensitive drum 0K.

  At the opening of the developing container 11K located above the first sleeve 12a, a thin layer forming member 16K (width 10 mm, thickness 1.6 mm) made of SPCC is provided close to the surface of the first sleeve 12aK (gap distance 240 μum). A developer is formed on the surface of the first sleeve 12aK to form a thin layer by regulating the layer thickness.

  The mass m per unit area of the thin layer developer is 0.9 g / cm ^ 2.

  m is measured by sucking and collecting the thin layer developer with a vacuum cleaner, measuring the mass of the collected developer (M (mg)), and determining the area of the developer suction area on the surface of the developing sleeve. Measure (S (cm 2)), and calculate by dividing M by S.

  The first sleeve 12aK and the second sleeve 12bK are rotatably supported by their respective rotation shafts (not shown) on both side walls (not shown) of the developing container 11K via bearings (not shown).

  In the developing container 11K, two blade-like stirring members 17K and 18K for stirring and transporting the toner t stored therein are provided. The toner t is supplied to the second sleeve 12bK by the rotation of the stirring members 17K and 18K. Transport to near side.

  The toner t transported to the vicinity of the second sleeve 12bK is the SS portion (gap distance) between the first sleeve 12aK and the second sleeve 12bK that are disposed in close proximity with the rotation of the second sleeve 12bK in the direction of arrow b. 400 [mu] m) and the first sleeve 12aK.

  A toner replenishing container (not shown) is provided above the developing container 11K, and the toner t is developed from the toner replenishing container based on the toner remaining amount information detected by the toner remaining amount detecting sensor (not shown). The container 11K is replenished.

  The first sleeve 12aK and the second sleeve 12bK rotate in the same direction.

  Specifically, when the developer carried on each surface of the first sleeve 12aK and the second sleeve 12bK flies (conveys) to the photosensitive drum 0 side, the toner comes from above the first and second sleeves 12aK and 12bK. It rotates in the direction of the arrow a so as to be driven in the direction of rotation in which it flies, that is, the direction of rotation of the photosensitive drum 0K (arrow b).

  The peripheral speeds of the first sleeve 12aK and the second sleeve 12bK are 160 mm / s and 360 mm / s, respectively.

  Incidentally, if the magnitude relationship between the first sleeve 12aK and the second sleeve 12bK is reversed, that is, (the peripheral speed of the first sleeve 12aK)> (the peripheral speed of the second sleeve 12bK), the developer thin layer is disturbed. This leads to image defects and, in turn, failure of the developing device (conventional example 3).

  The reason is that the amount of toner collected in the vicinity of the SS portion is larger than the amount of developer transferred from the first sleeve 12 to the second sleeve 12aK. Therefore, the toner collected in the vicinity of the SS portion exceeds a certain limit. This is because it is transferred to the second sleeve 12bK at once.

  In the first sleeve 12aK, a film in which phenol resin, crystalline graphite, and carbon are mixed at a ratio of 100: 36: 4 is formed on an aluminum alloy tube having an outer diameter of 20 mm.

  This is for preventing a ghost image and enhancing the durability of the surface of the first sleeve 12aK.

  The charge imparting ability q of the first sleeve is 9 μC / g.

  Here, the charge imparting ability q was determined as follows.

  In an environment of 23 ° C and 50% RH, 樋 91 (length 300mm, width 40mm, depth 30mm) made of the same material as the first sleeve 12aK is tilted at 60 ° with the Cr plating film facing up. Fix it.

  After grounding 樋 91, the grounding is released and, instead, a commercially available charge meter 92 that has been reset to zero is connected.

  Thereafter, 10 g of the developer stored in the glass beaker 93 is slid gradually over about 10 seconds while shaking the beaker 93 in small increments (FIG. 3).

  Thereafter, the charge amount (μC) of the coulometer was divided by 10 g.

  The first sleeve 12aK is provided with a fixed magnet 14K fixedly disposed therein. The fixed magnet 14K has five poles.

  On the other hand, in the second sleeve 12aK, a film in which phenol resin, crystalline graphite, and carbon are mixed at a ratio of 100: 40: 5 is formed on an aluminum alloy tube having an outer diameter of 24.5 mm. This is for preventing the ghost image and enhancing the durability of the surface of the second sleeve 12bK.

  The charging ability q of the second sleeve is 7 μC / g.

  The charge imparting ability q is measured according to the above-described method (the same applies hereinafter).

  The second sleeve 12bK includes a fixed magnet 15K that is fixedly disposed therein.

  The fixed magnet 15K has four poles clockwise.

  Here, (the diameter of the first sleeve 12aK)> (the diameter of the second sleeve 12bK) is not impossible, but as described above, (the peripheral speed of the first sleeve 12aK)> (the second sleeve 12bK) (Peripheral speed) cannot be set, (peripheral speed of the first sleeve 12aK) ≤ (peripheral speed of the second sleeve 12bK), but it is natural to increase the diameter as the peripheral speed increases. Therefore, (the diameter of the first sleeve 12aK) <(the diameter of the second sleeve 12bK).

If the sleeve diameter is reduced even though the peripheral speed is high, the wear of the sleeve surface and toner scattering increase. (Conventional example 5)
During the developing operation, a DC electric bias of +300 V, a peak-to-peak voltage of 1000 V, and a rectangular wave with a frequency of 3.5 kHz are superimposed and applied to the first sleeve 12aK as an AC bias to generate a developing electric field. The toner layer t1 is made to fly to the electrostatic latent image on the photosensitive drum 0 to form a toner image. At this time, the development contrast is 200V and the fog removal contrast is 100V.

  On the other hand, similarly to the second sleeve 12bK, a DC wave of +300 V, a peak-to-peak voltage of 1000 V and a frequency of 3.5 kHz are superimposed and applied as an AC bias to generate a developing electric field, and on the second sleeve 12bK. The toner layer t2 whose layer thickness is regulated is made to fly to the electrostatic latent image on the photosensitive drum 0K, and is visualized as a toner image.

  At this time, the development contrast is 200V and the fog removal contrast is 100V.

  The development bias high voltage power supply 3K connected to the two sleeves is common, and the cost of this power supply is 1 (relative value).

  Compared to 1.8 of the development bias high voltage power source of Example 4 (each of the development bias high voltage power sources connected to the two sleeves is independent), the cost is low.

  The first sleeve 12aK and the second sleeve 12bK rotate at a circumferential speed of 0.53 times and 1.2 times the circumferential speed of the photosensitive drum 0K, respectively.

  FIG. 13 shows the performance of the image forming apparatus of this embodiment.

  Here, “good image quality” means “the image density is sufficient and there is no image defect such as sleeve ghost, white background fog, vertical stripe” (hereinafter the same).

  Sleeve ghost is an image defect in which a solid image trace appears on the image when a solid image with a high image density is developed and the halftone image is developed when the development sleeve is rotated after the development sleeve is rotated. Say.

  Toner scattering is “many” if the developer on the back side of the image forming apparatus just opens the front door, but “slightly” if the developer flicks from the outside with your finger. However, if the back of the front door was dirty, it was evaluated as “low”. If the front door was magnified with a magnifying glass at a magnification of 5, the developer was evaluated as “very small” (the same applies hereinafter).

  The amount of toner consumed is determined by the amount of toner contained in the developing device that contains the developer when automatic copying of toner from the outside of the developing device is disabled and a text document with an image ratio of 6% is continuously copied on an A4 size transfer material. This is a value obtained by dividing the decrease in mass ΔMdu (mg) by 50.

  It can be understood from FIG. 13 that the image forming apparatus of this embodiment is excellent.

(Example 2)
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  In this embodiment, since m on the first sleeve 12aK is smaller than m on the second sleeve 12bK, the ability of supplying the developer from the first sleeve 12aK to the photosensitive drum 0K is reduced.

  However, even if the developer supply capability to the photosensitive drum 0K is reduced due to the rotation of the first sleeve 12aK, the developer supply capability to the photosensitive drum 0K due to the rotation of the second sleeve 12bK is not reduced. Therefore, it is possible to compensate to some extent by the developing operation by the second sleeve 12bK located on the downstream side of the first sleeve 12aK, so that the image density does not extremely decrease (see FIG. 13).

(Example 3)
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  In this embodiment, the first sleeve 12aK is made of the same material as the second sleeve 12bK of the first embodiment, and the second sleeve 12bK is made of the same material as the first sleeve 12bK of the first embodiment.

  Despite the low charge imparting capability of the first sleeve 12aK, the amount of developer carried is large, so the outside developer is insufficiently charged, and the toner scattering and fogging are somewhat high, but there is a problem in practical use. (See Fig. 13).

Example 4
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  In this embodiment, the bias applied to the first sleeve 12aK is a DC bias of + 300V and a rectangular wave with a peak-to-peak voltage of 1000V and a frequency of 1.8kHz superimposed as an AC bias, and is applied to the second sleeve 12bK. The bias to be applied is a superposition of a DC bias of +300 V and a rectangular wave having a peak-to-peak voltage of 1000 V and a frequency of 3.5 kHz as an AC bias.

  Since the development bias high-voltage power supplies connected to the two sleeves are independent (3aK, 3bK) (FIG. 5), the cost of the power supply is as high as 1.8 (relative ratio) (FIG. 13).

  Although not shown in FIG. 13, by suppressing the frequency of the AC bias applied to the first sleeve 12a to be low, it is possible to suppress the occurrence of an image defect called “blotch”.

  Note that “blotch” is an abnormality in the formation of a thin layer of toner on the sleeve, and exhibits an irregularly shaped appearance on the image.

  In general, the “blotch” is more likely to occur as the humidity of the atmosphere is lower and the mass of toner on the sleeve is larger.

  Although the cost of the power supply is expensive, the toner state on the two sleeves can be controlled independently according to the ambient temperature, humidity, image type (whether there are many solids or characters), etc. This is an effective method for high-end machines that place more importance on image quality.

(Example 5)
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  In this embodiment, a two-component type composed of a non-magnetic toner and a magnetic carrier is used as the developer.

  The developing device 1K (FIG. 6) includes a developing container 11K, the inside of which is divided into a developing chamber Z1 and a developing chamber Z2 by a partition wall 11Kw, and there is a toner storage chamber Z3 above the developing chamber Z2, in which replenishment is provided. The toner t is accommodated.

  An amount of toner commensurate with the toner consumed in the development falls and is replenished into the developing chamber Z2 from the replenishing port at the bottom of the toner storage chamber Z3.

  On the other hand, the developer d in which the toner t and the carrier are mixed is accommodated in the developing chamber Z1 and the developing chamber Z2.

  The carrier used in the present invention may be made of a ferrite material or a resin material containing a binder resin, a magnetic metal oxide, and a nonmagnetic metal oxide.

  A conveying screw 17K is accommodated in the developing chamber Z1, and the developer is conveyed along the longitudinal direction of the developing sleeve 12aK by rotational driving.

  The developer conveying direction by the screw 18K is opposite to that by the screw 17K.

  The partition 11Kw is provided with openings on the front side and the back side, and the developer conveyed by the screw 17K is delivered to the screw 18K from one of the openings, and the developer conveyed by the screw 18K is It is delivered to the screw 17K from the other one of the openings.

  Therefore, in the developing chamber Z2, the replenished toner t and developer d are thoroughly mixed and stirred by the screw 18K, conveyed to the developing chamber Z1, used for development, and the developer after being used for development is developed in the developing chamber Z2. The amount of toner t consumed by the development is replenished, and the developer d in a fresh state is always circulated so that it is used for the development.

  In the present embodiment, the opening adjacent to the photosensitive drum 0K of the developing container 11K is made of aluminum or nonmagnetic stainless steel, and has a first developing sleeve 12aK having a suitable unevenness on the surface thereof and a second pairing with the first developing sleeve 12aK. A developing sleeve 12bK is provided.

  The first developing sleeve 12aK is arranged at a distance of 400 μm from the photosensitive drum 0K, rotates at a peripheral speed of 300 mm / s in the direction of arrow a, and is formed by a blade-like thin layer forming member 16K at the lower end of the opening of the developing container 11K. After being regulated to an appropriate developer layer thickness, developer d is carried and conveyed to the first developing unit.

  In this embodiment, the thin layer forming member 16K is a nonmagnetic metal plate blade attached with a magnetic plate.

  A magnet 14K is fixedly disposed in the developing sleeve 12aK. The magnet 14K has a developing magnetic pole S1 that faces the photoreceptor 0K. A magnetic pole of developer d is formed by the developing magnetic field formed in the first developing portion Z4, and the magnetic pole is formed on the surface of the developing magnetic pole S1 in contact with the photosensitive member 0K rotating in the direction of arrow b. The electrostatic latent image is developed.

  At that time, the toner adhering to the magnetic brush and the toner adhering to the surface of the developing sleeve 12aK are also transferred to the image area of the electrostatic latent image.

  In this embodiment, the fixed magnet 14K has N1, N2, N3, and S2 poles in addition to the developing magnetic pole S1, and of these, the moving direction a of the first developing sleeve 12aK is downstream of the developing magnetic pole S1. The N3 pole located at the portion facing the second developing sleeve 12bK and the N2 pole located downstream and on the inner side of the developing container 11K are adjacent to each other with the same polarity, and the developer d Is prevented from entering from the opposing portion of the developing sleeve 12aK and the second developing sleeve 12bK, and only the well-stirred developer d in the developing chamber Z1 pumped up by the N2 pole which is the second magnetic pole is thin. A barrier is formed against the developer d in the vicinity of the portion facing the second developing sleeve 12bK so as to be conveyed to the position of the layer forming member 16K.

  Avoiding between the N2 and N3 poles of the opposing magnetic pole, the developer d is pumped up from the developing chamber Z1 by the N2 pole inside the developing container 11K, and the magnetic pole S2 facing the thin layer forming member 16K is rotated according to the rotation of the developing sleeve 12aK. Then, after being restricted by the developer amount, the developer goes out of the developing container 11K, passes through N1, and reaches S1, which is the developing magnetic pole. The N3 pole is downstream of the facing portion between the developing sleeve 12aK and the photosensitive member 0K, which is the position of the developing magnetic pole S1.

  In the present embodiment, the second developer is carried in a region substantially opposed to both the first developing sleeve 12aK and the photoreceptor 0K so as to be parallel to the first developing sleeve 12aK at the opening of the developing container 11K. The second developing sleeve 12bK, which is a body, is disposed so as to be rotatable at a peripheral speed of 360 mm / s in the direction of arrow a which is the same as the rotational direction a of the first developing sleeve 12aK.

  Similar to the first developing sleeve 12aK, the second developing sleeve 12bK is arranged with a distance of 400 μm from the photosensitive drum 0K and is made of a non-magnetic material. The second magnet 15 is installed in a non-rotating state.

  Here, the second magnet 15K has three poles of magnetic poles S3, S4 and N4. Among these, the N4 pole faces the photoconductor 0K at the second developing portion Z5, and the second developing portion Z5 has a second time with respect to the surface of the photoconductor 0K after passing through the first developing portion Z4. Develop.

  The developer after development in the development section Z5 is the second development and the S3 pole located in the opposite portion to the first development sleeve 12aK on the opposite side of the development magnetic pole N4 as the development sleeve 12bK rotates. The S4 pole adjacent to the upstream in the same direction as the sleeve 12bK and located on the inner side of the developing container 11K is the same pole, and a repulsive magnetic field is formed between the S3 pole and the S4 pole and passes through the developing portion Z5. The developed developer that has returned to the inside of the developing container 11K is separated from the second sleeve 12bK and dropped into the developing chamber Z1, and a barrier is formed against the developer d.

  The S3 pole faces the N3 pole of the fixed magnet 14K included in the first developing sleeve 12aK in the vicinity of the position where both sleeves are closest. The S4 pole, which has the same polarity as the S3 pole and is adjacent to the upstream side thereof, is located in the vicinity of the opening inside the developing container 11K here.

  Because the repulsive magnetic field is formed between the N3 pole and N2 pole of the first developing sleeve 12aK and between the S3 pole and S4 pole of the second developing sleeve 12bK, the layer thickness of the regulating blade 16K is restricted by the S2 pole. The developer d is transported on the first developing sleeve 12aK, and the developer passing through the developing portion Z4 reaches the N3 pole, and moves to the second developing sleeve 12bK side according to the magnetic force line extending from the N3 pole to the S3 pole direction. .

  Then, according to the rotation of the second developing sleeve 12bK, the developing container 11K is separated from the developing sleeve 12bK by the repulsive magnetic field of the S3 and S4 poles, and is conveyed to the conveying screw 17K in the developing chamber Z1.

  As in this embodiment, by providing the second developing sleeve 12bK under the first developing sleeve 12aK, the developer flows at the position of the first developing sleeve 12aK in the fixed magnet 14K and inside the developing container 11K. After N2 → S1 → N1 → S1 → N3 facing the regulating blade 16K, the developer on the first developing sleeve 12aK is blocked by the repulsive magnetic fields N2 and N3, S3 and S4 of both sleeves, and N3 and It moves to the second developing sleeve 12bK by the magnetic field formed between the opposing S3.

  The second developing sleeve 12bK is transported in the order of S3 → N4 → S4, blocked by the repulsive magnetic field at the S4 pole, the developer d is peeled off again into the developing chamber Z1, and the developer is newly fed by the N2 pole of the fixed magnet 14K. Pumped to the first developing sleeve 12bK.

  The developing bias applied to both sleeves 12aK and 12bK is a composite rectangular wave (FIG. 4) including a resting portion.

(Example 6)
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  In this embodiment, a negatively chargeable organic photoreceptor having a diameter of 84 mm is used as the latent image carrying member 0K.

  In both the first sleeve 12aK and the second sleeve 12bK, a -500V DC bias, a peak-to-peak voltage of 1300V, and a frequency of 3.5 kHz are applied as an AC bias, and the developer layer d1 on the first sleeve 12a is applied. A toner image is formed by flying the electrostatic latent image on the photosensitive drum 0. At this time, the development contrast is 300V and the fog removal contrast is 200V.

  Maintenance life is high because the lifetime of the organic photoconductor is as short as 300,000 sheets, but there is less potential unevenness than the a-Si photoconductor, and there is no discoloration in terms of image quality (Fig. 13).

(Example 7)
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  The image forming apparatus according to the present embodiment is a full-color digital copying machine having a process speed of 500 mm / s at the time of black output at 105 sheets per minute and a process speed of 300 mm / s at the time of full color output at 75 sheets per minute.

  In order to cope with the higher speed, an a-Si photosensitive member with a diameter of 120 mm is used as the latent image carrier member 0K, an organic photosensitive member with a diameter of 60 mm is used as the latent image carrier members 0Y, 0M, and 0C, and the peripheral speed of the first sleeve 12aK 270mm / s, and the peripheral speed of the second sleeve 12bK is 600mm / s.

  The size of the image forming apparatus is 900 mm in width and 840 mm in height as the latent image carrying member, the fixing device, and the like increase in size.

  Although the image forming apparatus has been slightly increased in size, productivity commensurate with it is ensured. There is no discoloration in terms of image quality (Figure 13).

(Example 8)
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  The image forming apparatus according to the present embodiment is exclusively for black output and cannot perform full color output.

  Since the number of stations is small, the dimensions of the image forming apparatus are small, with a width of 560 mm and a height of 790 mm (FIG. 13).

Example 9
The image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and redundant description is omitted.

  In the image forming apparatus according to the present embodiment, the peripheral speed of the first sleeve 12aK is 310 mm / s.

  While the developing device is new, the image density is high, but after that it has decreased slightly, but does not fall below the allowable lower limit (FIG. 7).

  Toner scattering is slightly higher, but there is no practical problem (Figure 13).

  For reference, a list of configurations of the image forming apparatus described in detail so far is shown (FIG. 14).

1 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 1 of the present invention. 1 is a schematic cross-sectional view showing a developing device of an image forming apparatus according to Embodiment 1 of the present invention. The figure which shows the measuring method of charge provision ability. FIG. 10 is a diagram illustrating a developing bias waveform of an image forming apparatus according to Embodiment 5 of the present invention. FIG. 9 is a schematic cross-sectional view illustrating a developing device of an image forming apparatus according to Embodiment 4 of the present invention. FIG. 10 is a schematic cross-sectional view illustrating a developing device of an image forming apparatus according to Embodiment 5 of the present invention. FIG. 10 is a diagram illustrating image density transition of an image forming apparatus according to Embodiment 9 of the present invention. Sectional drawing of an a-Si photoreceptor. 1 is a schematic configuration diagram showing a general image forming apparatus. FIG. 6 is a schematic configuration diagram illustrating an example of a two-sleeve developing device according to a conventional technique. The figure which shows the positional relationship of a photoreceptor and a photoreceptor surface potential sensor. FIG. 6 is a schematic configuration diagram illustrating an example of a two-sleeve developing device according to a conventional technique. 6 is a table showing a list of performances of the image forming apparatus according to the present exemplary embodiment. 6 is a table showing a list of configurations of the image forming apparatus according to the present exemplary embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 0 Latent image carrying member 1 Developing apparatus 11 Developer accommodating part 12a First developer carrying member 12b Second developer carrying member 16b Dedicated member for forming a thin developer layer on the surface of the second developer carrying member 3 Development bias power supply d Developer t Toner

Claims (11)

A rotating latent image carrying member;
A developer containing portion for containing the developer, and two developer carrying members for carrying the thinned developer supplied from within the developer containing portion on the surface, the developer carrying member as a latent image carrying member A developing device for transferring the developer to the latent image carrying member by the action of an electric field in proximity or contact;
A first developer that rotates in the same direction at a position close to or in contact with the image carrying member with respect to a moving direction of the image carrying members arranged opposite to each other with a gap provided as the second developer carrying member. A developer carrying member and a second developer carrying member, wherein the first developer carrying member is located upstream with respect to the rotation direction of the image carrying member, and the second developer carrying member is In the image forming apparatus, which is located downstream with respect to the rotation direction of the image carrying member, the circumferential speed of the first developer carrying member is smaller than the circumferential speed of the second developer carrying member.
An image forming apparatus, wherein an outer diameter of the first developer carrying member is smaller than an outer diameter of the second developer carrying member. The mass per unit area of the developer carried on the surface of the first developer carrying member is larger than the mass per unit area of the developer carried on the surface of the second developer carrying member. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein a peripheral speed of the first developer carrying member is smaller than a peripheral speed of the latent image carrying member. The bias applied to the first developer carrying member for generating the electric field and the power source of the bias applied to the second developer carrying member for generating the electric field are common. The image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein the first developer carrying member has a roller shape with an outer diameter of less than 21 mm. 6. The image forming apparatus according to claim 1, wherein the developer comprises only magnetic toner. 7. The image according to claim 6, wherein the charge imparting capability of the first developer carrying member to the magnetic toner is greater than the charge imparting capability of the second developer carrying member to the magnetic toner. Forming equipment. 8. The image forming apparatus according to claim 1, wherein the latent image carrying member includes a photosensitive layer containing amorphous silicon atoms. 9. The image forming apparatus according to claim 1, wherein the latent image carrying member has a drum shape with an outer diameter of less than 109 mm. 10. The image forming apparatus according to claim 1, wherein a full color image can be formed. The developing device according to claim 1.

Images