JP5255772B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and in particular, using a two-component developer that charges a nonmagnetic toner using a magnetic carrier, The present invention relates to an image forming apparatus in which a magnetic brush is formed, a toner thin layer is formed on a developing roller by the magnetic brush, toner in the toner thin layer is ejected to an electrostatic latent image, and the latent image is developed.

Conventionally, in an electrophotographic image forming apparatus, as a developing method using a dry toner, a one-component developing method and a two-component developing method are known.
Since the one-component developing method does not include a carrier, the electrostatic latent image on the photosensitive member is not disturbed by the magnetic brush formed from the carrier and the toner, and is suitable for high image quality. However, in the one-component development method, it is difficult to stably maintain the charge amount of the toner. In the case of a color toner, since transparency is required, it must be a non-magnetic toner. For this reason, full-color image forming apparatuses often employ a two-component development system that uses a carrier as a medium for charging and transporting toner.

  As an image forming method using the two-component developing method, a toner thin layer is formed on a toner carrier with a magnetic brush formed on a developer carrier carrying a two-component developer, and the toner on the toner carrier There is known an image forming method by so-called touch-down development (also referred to as hybrid development) in which an electrostatic latent image on an electrostatic latent image carrier is developed and visualized by a thin layer. However, this development method combines a two-component development method and a one-component development method, and there is a difference between the proper charge amount of toner when developing an electrostatic latent image and the proper charge amount of toner when forming a thin toner layer. In some cases, the toner amount of the toner thin layer is small and an image density defect occurs, or a problem such as a development ghost due to a defective peeling of the toner thin layer that did not contribute to the development may occur. .

  One of the causes of the above problems is the influence of scattered toner. The toner scatters mainly in the developing device, such as when the toner is agitated in the housing and in the vicinity of the magnetic roller. The scattered toner generated in the developing device is scattered inside the electrophotographic apparatus including the electrostatic latent image carrier, the optical system device, the charging device, the transfer device, and the like. Cause image defects and malfunctions.

In order to solve such a problem, in Patent Document 1, a developer that is rotatably provided in a state of being opposed to and separated from the electrostatic latent image carrier is attached to the surface. It has been proposed to prevent toner scattering by using a scattering prevention member that prevents scattering to the outside, and a scraping means that scrapes off the developer adhered on the scattering prevention member. Patent Document 2 proposes a two-component developing method in which a collecting roller is provided in a housing opening of a developing device to collect scattered toner, and the toner is peeled off from the collecting roller and returned to the developing device. .
JP-A-8-137256 JP 2005-242194 A

However, in Patent Document 1, the scraped developer is stressed by contact with the blade, and deterioration is promoted. In particular, the touch-down development method is susceptible to selective development. Accordingly, the external additive is detached or buried due to the stress caused by scraping with the blade, and the toner having changed charging characteristics is returned to the two-component developer container, thereby promoting toner scattering and selective development. Furthermore, it becomes difficult to form an image stably over a long period of time such as an image density defect. In the touch-down development method, since the toner concentration of the two-component developer is high and the developer fluidity is poor, the developer is collected one after another when the magnetic brush is collected in the two-component developer container. Therefore, the air is pushed and compressed, and at the same time, the air loses its place and the toner is discharged to the outside together with the air, so that the toner is more easily scattered. Further, in Patent Document 2, when the toner is peeled off from the collecting roller that collects the scattered toner and returned to the developing device, it is necessary to provide a separate route for returning the toner. Since the toner is peeled off, the deterioration of the toner is promoted. Furthermore, in the touch-down development method, it is more difficult to collect the scattered toner with a high-speed machine in which the drum linear speed is 180 mm / sec or more. Incidentally, as a guideline, the drum linear speed of 180 mm / sec is about 40 sheets / min at the A4 side, about 50 sheets / min at 250 mm / sec, and about 60 sheets / min at 340 mm / sec.
An object of the present invention is to suppress toner scattering in an image forming apparatus including a touch-down developing type developing device and reduce the stress of collected toner, thereby suppressing toner deterioration and stable over a long period of time. An object of the present invention is to provide an image forming apparatus capable of maintaining development characteristics and obtaining a stable image.

As a result of intensive studies to solve the above problems, the present inventor has found that an image forming apparatus having the following configuration can suppress toner deterioration and obtain stable image quality for a long period of time. Thus, the present invention has been completed.
That is, the image forming apparatus of the present invention has the following configuration.

(1) A two-component developer carrying member that has a magnetic member disposed therein and magnetically holds a developer composed of a carrier and toner, and a toner thin layer on the surface of the two-component developer carrying member by transferring toner from the two-component developer carrying member An electrostatic latent image formed on the surface of the electrostatic latent image carrier by applying a developing bias to the toner carrier and / or the two-component developer carrier. An image forming apparatus for developing an image, wherein a toner collecting roller for collecting scattered toner floating in the vicinity of the toner carrier and the two-component developer carrier is opposed to the two-component developer carrier. place the toner carrying member and a non-contact, magnetic members and different polarity magnetic member of the toner recovery roller inside the two-component developer carrier, only the positions near opposite the magnetic member of the two-component developer carrier Arrangement and, together with adhering to the toner recovery roller surface by intermolecular forces and electrostatic attraction scattered toner floating,
The magnetic member of the toner collecting roller has a magnetic force peak on the upstream side in the rotation direction of the sleeve of the toner collecting roller with respect to the straight line connecting the rotating shaft of the toner collecting roller and the center of the rotating shaft of the two-component developer carrier. The magnetic member of the two-component developer carrying member is arranged so that the peak of magnetic force is located upstream of the straight line in the rotational direction of the sleeve of the two-component developer carrying member. Image forming apparatus.
(2) The toner collecting roller is disposed on the downstream side in the rotation direction of the two-component developer carrier from the closest position of the two-component developer carrier and the toner carrier, and the two-component developer carrier and The image forming apparatus according to (1), wherein the image forming apparatus is disposed between the housing walls.
(3) The image according to (1) or (2), wherein the toner collecting roller and the sleeve of the two-component developer carrier are rotationally driven in the same direction in the circumferential direction at positions facing each other. Forming equipment .
(4 ) The surface magnetic flux density of the magnetic member provided on the toner collecting roller is at least greater than the surface magnetic flux density of the magnetic member provided on the two-component developer carrier, and the toner collecting roller and the two-component The image forming apparatus according to any one of (1) to ( 3 ), wherein the image forming apparatus is small at the closest position of the developer carrying member.
( 5 ) The image forming apparatus according to any one of (1) to ( 4 ), wherein the toner collecting roller is provided with a bias unit that applies a bias voltage for collecting the scattered toner.
( 6 ) The image forming apparatus according to any one of (1) to ( 5 ), wherein a peripheral speed of the electrostatic latent image carrier is 180 mm / sec or more.

  According to the present invention, since the toner collecting roller that collects the scattered toner floating in the vicinity of the toner carrier and the two-component developer carrier is disposed opposite to the two-component developer carrier, intermolecular force and static The scattered toner can be attached to the surface of the toner collecting roller by an electric attractive force or the like, and a magnetic member having a polarity different from that of the magnetic member of the two-component developer carrying member is carried inside the toner collecting roller. The magnetic brush formed between the toner collecting roller and the two-component developer carrier prevents the scattered toner from flowing out of the housing and adheres to the surface of the toner collecting roller. The scattered toner can be efficiently returned to the two-component developer carrier by the magnetic brush. As a result, toner scattering can be suppressed, toner deterioration can be suppressed, and stable image quality can be obtained for a long time.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touch-down development system according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a toner collection roller and a developer carrier for explaining the arrangement of magnetic members according to an embodiment of the present invention. FIG. 3 is a schematic configuration diagram showing a part of the developing means of FIG.

(Image forming device)
The image forming apparatus of the present invention forms a toner thin layer 9 on the developing roller 2 by using the two-component developer carried on the magnetic roller 1 by using the two-component developer comprising the magnetic carrier 4 and the toner 5, and photosensitive. This is an image forming apparatus based on a so-called touch-down development system that develops an electrostatic latent image formed on a body 3 (electrostatic latent image carrier). As shown in FIG. 1, the image forming apparatus includes the photoreceptor 3, and around the photoreceptor 3, a charging unit 8, an exposing unit 16, a developing unit 18, a primary transfer unit 22, and a secondary transfer unit 25. The fixing unit 26, the cleaning unit 24, and the like are disposed.

  Image formation by the image forming apparatus is performed as follows. That is, the surface of the photosensitive member 3 is uniformly charged by the charging unit 8, and the charged surface is exposed by the exposure unit 16 to form an electrostatic latent image. The obtained electrostatic latent image is developed as a toner image by attaching the toner 5 from the developing means 18. This toner image is transferred from the photoreceptor 3 onto the intermediate transfer belt 20 by a primary transfer roller 22 as a primary transfer unit. After the toner images of a plurality of colors are transferred on the intermediate transfer belt 20 in an overlapping manner, a secondary transfer roller 25 as a secondary transfer unit transfers the toner image to a transfer target conveyed from the paper feed cassette 27 to the secondary transfer position. Transfer the toner image. The transferred body is conveyed to a fixing roller 26 as a fixing unit, and after the toner image is fixed on the transferred body, it is discharged to, for example, a discharge tray (not shown). Undeveloped toner remaining on the surface of the photoreceptor 3 after the transfer is removed by the cleaning means 24.

  Examples of the photoreceptor 3 include inorganic photoreceptors such as selenium and amorphous silicon, and organic photoreceptors in which a single-layer or multilayer photosensitive layer containing a charge generating agent, a charge transport agent, a binder resin, and the like is formed on a conductive substrate. (OPC) and the like. Examples of the charging unit 8 include a scorotron system, a charging roller, and a charging brush. As for the exposure means 16, LED or a semiconductor laser is mentioned as exposure light. Moreover, as the cleaning means 24, for example, a doctor blade type or the like can be used, and known ones can be used.

  As shown in FIGS. 2 and 3, the developing means 18 has a sleeve-like shape in which a plurality of magnetic members M1 and M11 are fixed to an inner roller shaft R1, and the outer peripheral portions of the magnetic members M1 and M11 are rotated. The magnetic member M2 (two-component developer carrier) and a magnetic member M2 having a different polarity from the magnetic roller 1 are fixed to the inner roller shaft R2, and the outer periphery of the magnetic member M2 is rotated. A magnetic field is formed by the magnetic force of the different magnetic poles of the sleeve-like developing roller 2 (toner carrier) and the magnetic roller 1 and the developing roller 2, and the magnetic brush 6 formed on the magnetic roller 1 by this magnetic field The control blade 7 is configured to maintain a constant thickness and a toner recovery roller 14 (hereinafter also referred to as a recovery roller) for recovering scattered toner. Further, an alternating current (AC) bias power supply 11a and a direct current (DC: Vdc1) bias power supply 11b applied to the magnetic roller 1, and an alternating current (AC) bias power supply 12a and a direct current (DC: Vdc2) bias power supply 12b applied to the developing roller 2 are used. And. Further, a power source 13 that applies a direct current (DC: Vdc3) bias to the toner recovery roller 14 may be provided. Control means (not shown) for controlling these bias power supplies 11a, 11b, 12a, 12b and 13 is provided.

  The image forming apparatus of the present invention also includes a toner container (not shown) in which the toner 5 is stored and the toner 5 supplied from the toner container to the two-component developer storage unit 45 that stores the two-component developer. The two-component developer supplied to the stirring screw 44 from the stirring screw 40 through both ends of the partition plate 42 is communicated at both ends of the partition plate 42 and stirred with the carrier 4 to be charged. Supplied to the magnetic roller 1, the stirring screw 44 circulates the two-component developer from the other end side to the stirring screw 40 side, and the magnetic roller 1, the developing roller 2, the stirring screw 40, and the stirring screw 44. And a housing 46 in which is stored.

  As shown in FIG. 4, the image forming apparatus of the present invention forms a tandem (indirect transfer tandem system) color image in which four photoconductors 3A, 3B, 3C, and 3D are arranged on the intermediate transfer belt 20. It can use suitably for an apparatus. In this case, using the developing means 18 described above, the developing devices 18A, 18B, 18C, and 18D containing magenta, cyan, yellow, and black toners are electrostatically charged on the photoreceptors 3A, 3B, 3C, and 3D, respectively. The latent image is visualized and a toner image is formed. The toner images visualized on the photoreceptors 3A, 3B, 3C, 3D are sequentially transferred onto the surface of the intermediate transfer belt 20 from the upstream photoreceptor 3A. The full-color image transferred onto the intermediate transfer belt 20 is transferred by the secondary transfer roller 25 to the transfer target conveyed from the paper feed cassette 27 and then fixed by the fixing roller 26. Is discharged.

  Here, as the generation source of the scattered toner, when the two-component developer on the magnetic roller 1 is mainly collected in the two-component developer container 45, the magnetic brush 6 is compressed, so that the magnetic brush 6 Since the air in between is repelled without entering the two-component developer accommodating portion 45, the toner 5 is also ejected from the two-component developer collecting portion 45 together with the air. In the touchdown development method, the magnetic roller 1 supplies toner 5 on the developing roller 2 near the position closest to the developing roller 2 to form a thin toner layer 9 and contributes to the development of the electrostatic latent image. The undeveloped toner on the developing roller 2 that has not been removed is peeled off and collected. This undeveloped toner has low adhesion to the carrier 4 (compared to the adhesion between the toner 5 and the carrier 4 in the two-component developer when the toner thin layer 9 is formed), and in the touch-down development method, the two-component developer Since the toner density in the inside is kept higher than that in the normal two-component developing method, the fluidity of the two-component developer is low, and the air between the magnetic brushes 6 is difficult to enter the two-component developer containing portion 45. Therefore, toner scattering is likely to occur. Then, various image defects, operation failures, and the like are caused, and in particular, they adhere to the surface of the photoreceptor 3 and the developing roller 2 and become one of the factors that hinder good image formation.

(Toner recovery roller)
The toner collecting roller 14 according to the present invention is for collecting the scattered toner and returning it to the magnetic roller 1. As shown in FIG. 1, the photosensitive member 3, the developing roller 2, the magnetic roller 1, In the arrangement configuration of the agitating screws 40 and 44, the gap between the magnetic roller 1 and the wall of the housing 46 is closed on the downstream side in the rotation direction of the magnetic roller 1 from the closest position of the magnetic roller 1 and the developing roller 2. Thus, the magnetic roller 1 is disposed to face the magnetic roller 1.
With this configuration, the toner moves in the direction of arrow A in FIG. 1 through the scattered toner floating in the vicinity of the developing roller 2 and the magnetic roller 1 and the gap on the lower side of the magnetic roller 1 to move inside the image forming apparatus. The scattered toner scattered on the toner can be adhered to the surface of the toner collection roller 14 by intermolecular force or electrostatic attraction.

  As shown in FIG. 2, the toner collecting roller 14 includes a sleeve in which a magnetic member M3 is disposed and rotates on the outer periphery of the magnetic member M3. The magnetic member M3 is provided on a roller shaft R3 in the collecting roller 14, and is fixed and supported at a predetermined angle in the circumferential direction so as not to rotate. The position of the magnetic member M3 of the collecting roller 14 is preferably arranged on the upstream side in the rotation direction of the collecting roller 14 with respect to the line C connecting the center of the magnetic roller 1 and the center of the collecting roller 14. As shown in FIG. 2, the angle α is 1 to 6 °, preferably about 5 ° upstream. On the other hand, the drawing pole M1 of the magnetic roller 1 is preferably arranged on the upstream side in the rotation direction of the magnetic roller 1 with respect to the line C connecting the centers, and as shown in FIG. °, preferably about 5 ° upstream. If the angle α is less than 1 °, the carrier 4 may be attracted to the collection roller 14, which is not preferable. On the other hand, if the angle α exceeds 6 °, the force to return the toner on the collecting roller 14 to the magnetic roller 1 side is too weak, and the toner may not be collected, which is not preferable. At this time, the magnetic member M3 of the collection roller 14 and the lead-in pole M1 of the magnetic roller 1 are arranged to face each other so that the polarities of the respective distal ends in the radial direction are different from each other. For example, in the example shown in FIG. 2, the magnetic member M3 of the collection roller 14 has an N pole, and the drawing pole M1 of the magnetic roller 1 has an S pole.

  The circumferential rotation direction of the collection roller 14 is the same as the rotation direction of the magnetic roller 1 at the opposite position. The circumferential speed of the collection roller 14 is smaller than the circumferential speed of the magnetic roller 1 and is 0.01 to 0.1 times, preferably 0.03 to 0.06 times the circumferential speed of the magnetic roller 1. .

  The material of the rotating sleeve of the collecting roller 14 can be a metal such as aluminum or stainless steel. It is preferable that the surface is coated with anodized aluminum having a large specific surface area from the viewpoint of adhesion of scattered toner, and / or fluorine resin from the viewpoint of electrostatic adhesion (toner charging characteristics). Is positively charged). The magnetic member M3 is not particularly limited as long as it is a material that generates a magnetic force, but is preferably a magnet, for example, a rubber magnet that can be easily processed. Moreover, the magnetic body which forms a magnetic field by arrange | positioning a magnet in the vicinity may be sufficient.

  As shown in FIG. 2, the magnetic member M3 is arranged on the collecting roller 14 and the positional relationship with the magnetic pole M1 of the magnetic roller 1 is set as described above, so that the pulling pole M1 (S pole) of the magnetic roller 1 is set. Since there is a recovery roller 14 magnetic pole M3 (N pole) opposite to the magnetic pole, the magnetic roller 1 and the recovery roller 14 are located upstream of the position where the recovery roller 14 and the magnetic roller 1 are closest to each other. A magnetic field is formed between them, and a layer of the magnetic brush 6 is formed. The magnetic brush 6 is formed between the collection roller 14 and the magnetic roller 1 so as to be inclined to the downstream side in the rotation direction of the magnetic roller 1 as compared with the case where α = β = 0. After the toner is peeled off by the magnetic brush 6 with a mechanical force, the toner is easily conveyed downstream in the rotation direction of the magnetic roller 1. As a result, the collected toner is efficiently collected on the magnetic roller 1 side without stagnation. Furthermore, since the magnetic brush 6 layer is formed between the collecting roller 14 and the magnetic roller 1, the effect of blocking the place of the scattered toner scattered from the two-component developer collecting unit 43 of the magnetic roller 1 to the developing roller 2 side is also achieved. This scattered toner can also be collected and returned to the magnetic roller 1 side at the same time.

  In addition, since the recovery roller 14 and the magnetic roller 1 are rotated in the same direction in the circumferential direction at the opposed positions, the stress applied to the recovered toner is reduced, and deterioration of the recovered toner can be prevented.

  The magnetic pole (surface magnetic flux density) on the surface of the recovery roller 14 in the radial direction of the magnetic member M3 disposed on the recovery roller 14 is 30 to 70 mT, preferably 40 to 60 mT. At this time, the main pole M11 of the magnetic roller 1 is 70 to 100 mT, preferably 80 to 100 mT. The magnetic force (surface magnetic flux density) on the surface of the magnetic roller 1 in the radial direction of the drawing pole M1 is larger than the magnetic member M3 of the recovery roller 14 and smaller than the main pole M11 of the magnetic roller 1, 90 mT, preferably 70 to 90 mT.

  By making the magnetic force of the magnetic member M3 of the collecting roller 14 smaller than the magnetic force of the pulling pole M1 of the magnetic roller 1, a large number of carriers 4 are drawn to the magnetic roller 1 side. Is efficiently collected by the magnetic roller 1 and the carrier 4 on the magnetic roller 1 is not taken to the collecting roller 14 side.

  The collection roller 14 may further include a bias unit 13 for applying a direct current bias voltage (DC: Vdc3) in order to return the scattered toner 5 collected by the collection roller 14 to the magnetic roller 1. By applying the DC bias voltage (DC: Vdc3), the potential difference between the collection roller 14 and the magnetic roller 1 is reduced. Thereby, the collected toner 5 on the collecting roller 14 is easily moved to the magnetic roller 1, and the collected toner is easily peeled off by the magnetic brush 6 and is efficiently collected by the magnetic roller 1.

(Development method)
FIG. 3 schematically shows an example of the developing means according to the present invention. The developing method will be described below.
A magnetic brush 6 comprising a carrier 4 (magnetic particles) that is magnetically constrained by a fixed magnet contained in the magnetic roller 1 and a toner 5 that is charged and held on the surface of the carrier 4 is attached to the surface of the magnetic roller 1. It is rotated and conveyed to the developing roller 2. The surface of the magnetic roller 1 can be conveyed more smoothly by using a blasted or grooved surface.

  As shown in FIG. 3, a developing bias voltage 12 in which an alternating voltage (AC) 12a is superimposed on a direct current voltage (DC: Vdc2) 12b is applied to the developing roller 2, and a direct current voltage (DC: Vdc1) is applied to the magnetic roller 1. ) 11b is applied with a developing bias voltage 11 in which an alternating voltage (AC) 11a is superimposed. The magnetic brush 6 is formed on the magnetic roller 1. The magnetic brush 6 on the magnetic roller 1 is layer-regulated by a regulating blade 7 and conveyed by the potential difference between the magnetic roller 1 and the developing roller 2. Only the charged toner 5 of the magnetic brush 6 moves to the developing roller 2 to form a toner layer 9. Then, the electrostatic latent image on the photoreceptor 3 is developed by the toner layer 9 on the developing roller 2. The DC voltage Vdc is an area center voltage, and changes when the DUTY ratio is changed. In the present invention, the DUTY ratio is a duration T1 applied to the positive polarity side and a duration T2 applied to the negative polarity side in one cycle of the rectangular wave AC voltage, and the DUTY ratio (%) = [T1 / ( T1 + T2)] × 100. At this time, a voltage where the areas of the waveform rising to the positive polarity side and the waveform rising to the negative polarity side are equal to each other is called an area center voltage. A DC voltage may be superimposed as necessary. When a DC voltage is superimposed, Vdc = DC voltage + area center voltage. Vdc when no AC is applied is simply a DC voltage.

  The electrostatic latent image on the photoreceptor 3 can be formed using the exposure means 16 on the surface of the photoreceptor 3 charged to +250 to 800 V by the charging means 8. When an OPC photoconductor is used, +70 to 220 V is obtained in all exposures, and an amorphous silicon photoconductor provides a post-exposure potential of 10 to 50 V. For the exposure, either a semiconductor laser or an LED can be used.

  After the development is performed as described above, the developing roller 2 having the residual toner layer comes closest to the magnetic roller 1 having the developer layer at the facing position, and the mechanical force by the magnetic brush 6 at the facing position. As a result, the toner layer 9 on the developing roller 2 is scraped off. At the same time, the toner 5 is supplied from the developer layer on the magnetic roller 1 to the developing roller 2 side according to a potential difference (that is, an electric field) formed between the magnetic roller 1 and the developing roller 2.

  At the time of development, it is preferable to apply a bias condition of +300 to 500 V to the magnetic roller 1 and +100 V to the developing roller 2. The potential difference for forming the thin layer is appropriately 200 to 400 V, and may be adjusted according to the balance with the charge amount of the toner 5. By using feedback control or the like, the layer thickness of the toner thin layer 9 can be made constant to some extent.

  When the bias power supply 13 that applies a bias voltage to the toner collecting roller 14 is used, the collecting roller applied voltage (Vdc3) is, for example, positively charged toner 5 in order to move it to the magnetic roller 1 and collect it. It is preferable to apply a higher potential on the collecting roller 14 than on the collecting roller 14. However, in this case, the toner 5 may be attracted to the developing roller 2 having a potential lower than that of the magnetic roller 1, so that the potential of the collecting roller 14 is between the potential of the developing roller 2 and the magnetic roller 1. It should be, preferably +200 to 300V.

The AC conditions are as follows: V _PP (peak AC bias) = 0.1-2.0 kV, frequency = 2-4 kHz, DUTY ratio = 60-80% in the same period and opposite phase as the developing roller 2 in the magnetic roller 1 For the roller 2, V _PP = 1.0 to 2.0 kV, frequency = 2 to 4 kHz, and DUTY ratio = 20 to 40% are preferable. When V _PP is increased, the thin layer is formed more instantly, but on the other hand, the leak resistance is weakened, which causes noise. With respect to these points, it is preferable to increase the insulation by anodizing the surface of the magnetic roller 1 or the developing roller 2 because the margin is widened. The frequency may be adjusted by the charge amount of the toner 5.

The volume average particle diameter of the toner 5 is preferably 4.0 to 7.5 μm. If the thickness is less than 4.0 μm, the influence of non-electrostatic adhesion increases, and developability and recoverability deteriorate. If the thickness is greater than 7.5 μm, it is difficult to obtain a high-quality image such as smooth image quality. The charge amount of the toner 5 is preferably about 6 to 30 μC / g. If the charge amount is lower than this, the toner 5 will fly from the magnetic brush 6 and stain the periphery, and if it is higher than this, the thin layer formation will be weakened.
The toner volume average particle diameter can be measured using Multisizer III (manufactured by Beckman Coulter, Inc.) with an aperture diameter of 100 μm (measurement range: 2.0 to 60 μm).
The toner charge amount can be measured with a QM meter (manufactured by TREK, MODEL 210HS).

As the carrier 4, a known carrier can be used. Preferably, a carrier whose surface is coated with a resin using a ferrite core is preferably used. Moreover, it is preferable to use a carrier particle diameter (weight average particle diameter) of 25-50 micrometers. If it is less than 25 μm, the holding force due to the magnetic force is weakened, so that carrier jumping or the like that causes the carrier 4 to move to the developing roller 2 and the collection roller 14 occurs, and if it exceeds 50 μm, the magnetic brush 6 is not dense enough. Further, the toner thin layer 9 is not smoothly formed and the specific surface area is small, so that the recoverability of the toner 5 is also lowered. Further, the saturation magnetization of the carrier 4 is preferably 35 to 90 emu / g. When the saturation magnetization is lower than 35 emu / g, the carrier jump is remarkably deteriorated. When the saturation magnetization is higher than 90 emu / g, the magnetic brush 6 becomes sparse and a uniform thin layer cannot be formed.
The saturation magnetization of the carrier 4 can be measured with a magnetic field of 79.6 kA / m (1 kOe) using “VSM-P7” manufactured by TOEI.

  The gap between the magnetic roller 1 and the developing roller 2 is 200 to 600 μm, preferably 300 to 400 μm. The gap is the most effective factor for instantly forming a thin layer. If the width is wide, the efficiency is lowered, and problems such as development ghosts occur. On the other hand, if it is narrow, the magnetic brush 6 that passes through the blade gap cannot pass through the gap and the toner thin layer 9 is disturbed.

  The gap between the magnetic roller 1 and the toner collection roller 14 is such that the magnetic brush 6 comes into contact with the collection roller 14 and should be smaller than the gap between the magnetic roller 1 and the developing roller 2 and is 150 to 500 μm. The thickness is preferably 200 to 300 μm.

By setting the distance between the magnetic roller 1 and the collection roller 14 to be equal to or less than the distance between the magnetic roller 1 and the developing roller 2, scattering toner generated from the periphery of the magnetic roller 1 is prevented from scattering to the developing roller 2 side. It becomes possible to do. Note that if the gap between the magnetic roller 1 and the collection roller 14 is narrowed, a leak occurs. Therefore, in order to suppress this leak, it is necessary to increase the insulation and provide resistance to the surface of the collection roller 14 by anodizing. It becomes. In that case, the electrical resistivity of the surface of the collection roller 14 is preferably 10 ⁷ to 10 ¹² Ω · m.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited only to a following example.

[Example 1]
The image forming apparatus of the present invention shown in FIG. 1 was produced according to the following specifications. The photosensitive member 3 uses a photosensitive drum 30 mm in diameter made of amorphous silicon, the developing roller 2 uses a sleeve 20 mm in diameter made of anodized aluminum, the magnetic roller 1 uses a sleeve 25 mm in diameter made of aluminum, and a recovery roller No. 14 used a 16 mm diameter sleeve made of aluminum. The drum linear velocity of the photosensitive member 3 was 300 mm / sec.

The position of the magnetic pole M3 of the recovery roller 14 is set to α = 5 °, and the position of the drawing pole M1 of the magnetic roller 1 is set to β = 5 °. Further, a rubber magnet was used as the magnetic member M3 of the collecting roller 14, and the magnetic force on the surface of the collecting roller 14 in the radial direction was 55 mT. Further, the magnetic forces on the surface of the magnetic roller 1 in the radial direction of the main pole M11 and the drawing pole M1 of the magnetic roller 1 were 90 mT and 80 mT, respectively.
In addition, the magnetic force measurement measured the magnetic force on the surface of the collection | recovery roller 14 using Teslameter GX-100 (Nippon Electromagnetic Side Co., Ltd. product).

  The peripheral speed of the developing roller 2 is 450 mm / sec (developing roller peripheral speed / photosensitive drum peripheral speed = 1.5), and the peripheral speed of the magnetic roller 1 is 675 mm / sec (magnetic roller peripheral speed / developing roller peripheral speed = 1.5), and the circumferential speed of the collecting roller 14 was 30 mm / sec.

Using the image forming apparatus prepared above, image formation was performed under the following conditions for image formation.
Photoconductor surface potential: + 310V
Q / m of toner (positive charge) in developer: 20 μC / g
Toner particle size (volume average particle size): 6.7 μm
Carrier particle size (weight average particle size): 45 μm
Distance between magnetic roller and developing roller: 350 μm
Distance between magnetic roller and collection roller: 250 μm
Developing roller applied voltage: Vdc2 = 100 V, V _PP = 1.6 kV, frequency f = 2.7 kHz, Duty ratio = 27%
Magnetic roller applied voltage: Vdc1 = 300V, V _PP = 300V in the same cycle as the developing roller = 300V, f = 2.7 kHz, Duty ratio = 73%
Collection roller applied voltage: Vdc3 = 200 V (only DC voltage applied)

[Examples 2 to 12, Comparative Examples 1 and 2]
About the collection roller 14, as shown in Table 1, except for the presence / absence of installation, the mounting angle α and the magnetic force of the magnetic member M3, Examples 2 to 12 and Comparative Examples 1 and 2 were the same as Example 1. An image forming apparatus was produced.

(Evaluation)
Toner scattering was evaluated using the image forming apparatus produced above. The evaluation was made by modifying the member 47 (made of the same ABS resin as the housing) shown in FIG. 1 so that it can be detached from the developing device 18 and adhering to the inner wall portion of the member 47 when 1000 sheets of a document with a printing rate of 6% are output. The amount of toner per unit area was compared. The carrier pulling of the collection roller 14 was also evaluated.
The toner adhering to the member 47 was sucked and its weight was measured using a QRE meter (MODEL 210PS) manufactured by TREK.
The obtained results are shown in Table 1.
Evaluation criteria for toner scattering are as follows.
○: 0.06 mg / cm less than ² △: ^0.06~0.09mg / cm ² less ×: 0.09 mg / cm ² For more carrier pull the magnet whether the carrier 4 on the recovery roller 14 is present Was visually confirmed. The evaluation criteria are as shown below.
○: Adhesion is not confirmed even when the magnet is brought closer.
Δ: Slight adhesion is observed when the magnet is approached.
▲: Slight adhesion is confirmed without magnet.

As shown in Table 1, when an image forming apparatus in which a collecting roller 14 that collects scattered toner is arranged to face the magnetic roller 1 and a magnetic member M3 is arranged inside the collecting roller 14, the amount of toner scattered is 0.01 to 0.06 mg / cm ² , and toner scattering was suppressed (Examples 1 to 12). Carrier pulling was also good.
On the other hand, when the magnetic member M3 was not used, the toner scattering amount was 0.1 mg / cm ² , and much toner scattering occurred (Comparative Example 1). Further, when the collection roller 14 was not installed, the amount of toner was 0.5 mg / cm ² , and more toner scattering occurred (Comparative Example 2).

1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touchdown development system according to an embodiment of the present invention. FIG. 4 is an explanatory diagram of a toner collection roller and a two-component developer carrier for explaining the arrangement of magnetic members according to an embodiment of the present invention. It is a schematic block diagram which shows a part of developing means of FIG. FIG. 2 is a schematic configuration diagram illustrating an example of a tandem color image forming apparatus using the developing unit illustrated in FIG. 1.

Explanation of symbols

1 Two-component developer carrier (magnetic roller)
2 Toner carrier (developing roller)
3 Electrostatic latent image carrier (photoreceptor)
4 Carrier 5 Toner 6 Magnetic Brush 7 Regulating Blade 8 Charging Means 9 Toner Thin Layer 11a AC Power Supply 11b DC Power Supply 12a AC Power Supply 12b DC Power Supply 13 DC Power Supply 14 Toner Collection Roller 16 Exposure Means 22 Primary Transfer Means 24 Cleaning Means 25 Secondary Transfer Means 26 Fixing means

Claims (6)

A two-component developer carrying member that magnetically holds a developer composed of a carrier and toner by arranging a magnetic member inside, and a toner thin layer on the surface of the two-component developer carrying member by transferring toner from the two-component developer carrying member A toner carrier is provided at least in the housing, and a developing bias is applied to the toner carrier and / or the two-component developer carrier to develop the electrostatic latent image formed on the surface of the electrostatic latent image carrier. An image forming apparatus for performing
A toner collecting roller that collects the scattered toner floating in the vicinity of the toner carrier and the two-component developer carrier is disposed opposite to the two-component developer carrier and in non-contact with the toner carrier; A magnetic member having a polarity different from that of the magnetic member of the two-component developer carrying member is disposed in the collecting roller only in the vicinity of the position facing the magnetic member of the two-component developer carrying member, and the floating scattered toner is intermolecular force. And adhere to the surface of the toner recovery roller by electrostatic attraction ,
The magnetic member of the toner collecting roller has a magnetic force peak on the upstream side in the rotation direction of the sleeve of the toner collecting roller with respect to the straight line connecting the rotating shaft of the toner collecting roller and the center of the rotating shaft of the two-component developer carrier. The magnetic member of the two-component developer carrying member is arranged so that the peak of magnetic force is located upstream of the straight line in the rotational direction of the sleeve of the two-component developer carrying member. Image forming apparatus.   The toner collecting roller is downstream in the rotational direction of the two-component developer carrier from the closest position of the two-component developer carrier and the toner carrier, and the two-component developer carrier and the housing wall The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed between the two.   3. The image forming apparatus according to claim 1, wherein the toner collecting roller and the sleeve of the two-component developer carrying member are rotationally driven in the same direction in the circumferential direction at positions facing each other. The surface magnetic flux density of the magnetic member provided on the toner collecting roller is at least greater than the surface magnetic flux density of the magnetic member provided on the two-component developer carrier, and the toner collecting roller and the two-component developer are carried. the image forming apparatus according to any one of claims 1 to 3, wherein the small at the closest position of the body. It said toner collecting roller, the image forming apparatus according to any one of claims 1 to 4, characterized in that a biasing means for applying a bias voltage for collecting the scattered toner. The image forming apparatus according to any one of claims 1 to 5, the peripheral speed of the electrostatic latent image bearing member, characterized in that at 180 mm / sec or more.

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