JP2008009178A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a development device of a hybrid development system where the generation of development ghost and carrier scattering is prevented without complicating the development device, while a securely charged toner is fed to a development roller, and stable image quality can be obtained over a long period. <P>SOLUTION: Regarding the image forming apparatus having a development device of a hybrid development system where, upon continuous printing, a toner 5 can be recovered from a toner carrier 2 to a developer carrier 1 in non-development between images or papers, the particle diameter of carriers 4 composing the developer is 30 to 60 μm, and, upon the recovery of the toner 5, the voltage applied to the toner carriers 2 is changed in such a manner that a potential difference of 0 to 100 V is made to the surface potential of an electrostatic latent image carrier 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 particularly uses a two-component developer that charges a nonmagnetic toner using a magnetic carrier, The present invention relates to an image forming apparatus in which only a charged toner is held on a developing roller to fly to an electrostatic latent image and the latent image is developed.

Conventionally, as a developing method using a dry toner in an electrophotographic image forming apparatus, 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.
The two-component development method is suitable for extending the life because a stable charge amount can be obtained over a long period of time. However, the two-component development method is disadvantageous in terms of image quality because of the influence of the magnetic brush described above.

In recent years, in order to take advantage of the advantages of each of these development systems, a hybrid development system that uses a two-component development system for the charged area and a single-component development system for the development of high image quality in consideration of longer life. Is attracting attention. In particular, in a full-color image forming apparatus in which high image quality and long life are important, the characteristics of this development method are sufficiently exhibited.
In the hybrid development system, a two-component developer containing toner and carrier is carried on the surface of a magnetic roller to form a magnetic brush, and only the toner is transferred from the magnetic brush to the surface of the developing roller to form a toner layer. In this method, toner is ejected from the toner layer onto the surface of the photoreceptor on which the electrostatic latent image is formed, and the electrostatic latent image is developed as a toner image.

  However, in this developing system, it is necessary to supply toner from the magnetic brush to the developing roller at the same time while removing the residual toner on the developing roller with the magnetic brush of the magnetic roller. At this time, when the residual toner is not sufficiently peeled off or the toner supply to the developing roller is insufficient, the afterimage after the toner has jumped from the developing roller to the photosensitive member appears on the second round, so-called development. Ghost is likely to occur.

Therefore, various methods have been proposed as countermeasures against the development ghost. For example, in a two-component developer to be used, a method for eliminating toner development ghost by increasing the density of the magnetic brush and increasing the effect of peeling off the toner on the developing roller by making the carrier low magnetization is disclosed. (See Patent Document 1). In addition, a method for promoting toner replacement on the developing roller by applying an AC voltage having an opposite phase to the AC component of the developing roller to the magnetic roller is disclosed (see Patent Document 2). Further, it has been proposed to apply an AC bias in which a DC bias is superimposed on the developing roller at the end of development to collect the toner on the developing roller to the magnetic roller. This is a system using a conductive developing roller, and the carrier does not transfer to the developing roller during collection. (See Patent Document 3).
JP 2003-295613 A JP-A-2005-242281 JP 2003-280357 A

However, for example, in the method disclosed in Patent Document 3, it is difficult to suppress a leak between the developing roller and the magnetic roller at the time of image formation when using the conductive developing roller, and there is only a method for suppressing the bias setting. However, if the bias setting is suppressed, the effect of suppressing the development ghost is reduced. As a result, these are contradictory characteristics and adjustment is difficult.
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus equipped with a hybrid developing type developing device, to prevent development ghosts and carrier pulling without complicating the developing device, and to reliably supply charged toner to the developing roller. An object of the present invention is to provide an image forming apparatus capable of obtaining stable image quality for a long period of time.

As a result of intensive studies to solve the above problems, the present inventors change the applied voltage of the toner carrier so that a predetermined potential difference is obtained with respect to the surface potential of the electrostatic latent image carrier during toner recovery. Alternatively, by changing the surface potential of the electrostatic latent image carrier so that it has a predetermined potential difference with respect to the voltage applied to the toner carrier, development ghosts and carrier pulling are prevented, and charging is ensured. The present inventors have found that stable image quality can be obtained for a long time by supplying the toner to the developing roller, and the present invention has been completed.
That is, the image forming apparatus of the present invention has the following configuration.

(1) The toner is charged by holding and mixing the two-component developer on the developer carrier, and only the toner is uniformly formed on the toner carrier to form a thin layer with the electrostatic latent image carrier. An image forming apparatus having a developing device that superimposes a direct current or alternating current voltage on a space and causes toner to fly to a latent image, and when carrying out continuous printing, the toner is carried on the toner during non-development between images or between papers In the developing device having a configuration capable of being collected from the toner to the developer carrier, the carrier particle diameter constituting the developer is 30 to 60 μm, and the electrostatic latent image carrier is collected when the toner is collected An image forming apparatus characterized in that the applied voltage of the toner carrier is changed so as to have a potential difference of 0 to 100 V with respect to the surface potential of the toner.
(2) The toner is charged by holding and mixing the two-component developer on the developer carrier, and only the toner is uniformly formed on the toner carrier to form a thin layer. An image forming apparatus having a developing device that superimposes a direct current or alternating current voltage on a space and causes toner to fly to a latent image, and when carrying out continuous printing, the toner is carried on the toner during non-development between images or between papers In the developing device having a configuration capable of being recovered from the toner to the developer carrier, the carrier particle size constituting the developer is 30 to 60 μm, and is applied to the toner carrier when the toner is recovered. An image forming apparatus having a configuration in which the surface potential of the electrostatic latent image carrier is changed so as to have a potential difference of 0 to 100 V with respect to the voltage being applied.

  According to the present invention, when the toner is collected, the applied voltage of the toner carrier is changed or applied to the toner carrier so as to have a predetermined potential difference with respect to the surface potential of the electrostatic latent image carrier. By changing the surface potential of the electrostatic latent image carrier so as to have a predetermined potential difference with respect to the voltage, the occurrence of development ghost and carrier pulling can be prevented, and reliably charged toner is supplied to the development roller. Long-term stable image quality can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Image forming apparatus>
As shown in FIG. 1, the image forming apparatus of the present invention includes an electrostatic latent image carrier 3 (hereinafter referred to as a photoreceptor 3), a charging unit 8 that charges the surface of the photoreceptor 3, and the photoreceptor 3. An exposure means 16 for exposing the surface of the toner to form an electrostatic latent image; a developing means 18 for developing the electrostatic latent image as a toner image by attaching toner 5 to the electrostatic latent image; And an image forming apparatus including a transfer unit 22 that transfers to a transfer target (not shown) that moves on the endless belt 20 and a cleaning unit 24 that cleans the surface of the photoreceptor 3.

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. Etc.
Examples of the charging unit 8 include a scorotron system, a charging roller, and a charging brush.
The exposure means 16 includes an LED or a semiconductor laser as the exposure light 10. As the transfer unit 22 and the cleaning unit 24, known ones may be used.

The developing means 18 includes a sleeve-like developer carrier 1 (hereinafter referred to as a magnetic roller 1) that has a plurality of fixed magnets disposed therein and is rotatable around the fixed magnets, and a magnetic roller 1. Toner carrier 2 (hereinafter referred to as developing roller 2) on which toner thin layer 9 is formed by magnetic brush 6 to be formed, power supply 11a for applying a direct current (DC) bias to magnetic roller 1, and to developing roller 2 Formed on the magnetic roller 1, a power source 12 a for applying a direct current (DC) bias, a power source 11 b for applying an alternating current (AC) bias to the magnetic roller 1, a power source 12 b for applying an alternating current (AC) bias to the developing roller 2 The regulating blade 7 for keeping the height of the magnetic brush 6 fixed, the toner container 38 in which the toner 5 is stored, and the toner 5 supplied from the toner container 38 are transferred to the carrier 4 The two components supplied from the stirring mixer 40 at a communicating portion (not shown) formed at the end of the partition plate 42 in the longitudinal direction are arranged with a stirring mixer 40 that stirs and charges together with the partition plate 42. A paddle mixer 44 that supplies developer to the magnetic roller 1 while stirring, and a frame 46 in which the magnetic roller 1, the developing roller 2, the stirring mixer 40, and the paddle mixer 44 are housed are provided.
In the present invention, at the time of toner collection, a surface potential is applied to the photosensitive member 3 by a power source 11a for applying a DC bias to the magnetic roller 1, a power source 12a for applying a DC bias to the developing roller 2, and a charger 8. Is used to set the potential configuration for avoiding the transfer of the carrier 4 to the photoreceptor 3. The surface potential applied to the photoreceptor is adjusted by providing a known grid (not shown) in the corona discharger 8 and adjusting the grid potential to adjust the charged potential on the surface of the photoreceptor. Can do.

<Development method>
FIG. 2 schematically shows an example of the developing device 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, a surface thereof, and a toner 5 that is charged and held around the surface of the magnetic roller 1. Moved to the developing roller 2. The surface of the magnetic roller 1 can be conveyed more smoothly by using a blasted or grooved surface.
Only the charged toner 5 of the conveyed magnetic brush 6 is transferred to the developing roller 2 by the potential difference provided between the magnetic roller 1 and the developing roller 2 to form a toner thin layer 9 on the surface of the developing roller 2. When forming a thin layer, if an alternating current is applied to the magnetic roller 1 and the developing roller 2, the toner thin layer 9 is more efficiently formed.

The toner 5 is preferably positively charged, and the charge amount is preferably about 10 to 20 μC / g. If the charging 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 formation of the thin layer will be weak.
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 particle size of 30-60 micrometers. If it is smaller than this range, the fluidity of the developer is deteriorated, and uniform dispersion becomes difficult at the time of stirring and mixing with the toner 5, and if it is larger than this, the formation of a thin layer is weakened. 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 4 jumps remarkably, and when it is higher than 90 emu / g, the magnetic brush 6 becomes sparse and a uniform thin layer cannot be formed.
The gap between the magnetic roller 1 and the developing roller 2 is preferably 0.2 to 0.6 mm. 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.

As the bias condition, it is preferable to apply +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.
AC conditions, V _PP (peak AC bias) to the magnetic roller 1 = 300~500V, frequency = 2~4kHz, DUTY ratio of 20~40%, V _PP = 1.0~2.0kV the developing roller 2 , Frequency = 2 to 4 kHz and DUTY ratio = 20 to 40% are preferable. When V _PP is increased, a thin layer is formed more instantaneously, but on the other hand, the leak resistance is weakened and noise is generated. 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. By making the DUTY ratio lower than 40%, an effect of collecting the toner 5 on the magnetic brush 6 with a high potential difference in a short time while forming a thin layer is produced, and the prevention of sticking of the toner 5 to the developing roller 2 is suppressed. effective.
Next, the toner thin layer 9 is formed on the developing roller 2 and then developed on the photoreceptor 3. When the surface of the photoreceptor 3 is charged to +350 to 500 V by the charger 8, an electrostatic latent image is formed using the exposure unit 16. When the OPC photoconductor was used, +70 to 120 V was obtained in the entire exposure, and the post-exposure potential of 10 to 50 V was obtained with the amorphous silicon photoconductor. For the exposure, either a semiconductor laser or an LED can be used.

  The above is the proper setting and bias conditions at the time of image formation. However, if this is continued for a long period of time, there is a problem that the toner 5 is gradually fixed to the developing roller 2. In order to prevent these, there is a method of using a method in which the toner thin layer 9 is temporarily recovered by the magnetic brush 6 between images during continuous printing. There is also a method in which a blade, a roller, or the like is brought into contact with the developing roller 2. Regarding the latter, mechanical stress is applied to the toner 5 when the toner thin layer 9 is peeled off, and pressure is applied to the developing roller 2 as well. Therefore, it can be said that it is not suitable for a system that requires durability. The former can switch the bias between images and collect the toner 5 from the developing roller 2 to the magnetic roller 1, thereby making it possible to vary the collection intensity depending on the collection timing and the potential difference. In addition, since direct stress is not applied to the toner 5 or the like, it can be said that the method is suitable for a long-life system.

As the collecting bias, 0 V is applied to the magnetic roller 1 and +100 V is applied to the developing roller 2, and the toner 5 on the developing roller 2 can be collected through the magnetic brush 6 with a potential difference of 100V. When the potential difference is increased, the collecting power increases, but conversely, the negatively charged carrier 4 is transferred to the developing roller 2 side. When the potential difference is reduced, the recovery of the toner 5 is weakened and the toner 5 is likely to adhere to the developing roller 2. This is more remarkable as the particle size of the carrier 4 becomes smaller.
As an AC condition, it is preferable that the V _PP and the DUTY ratio are the same as those at the time of image formation. By increasing the frequency during collection than during image formation, there is an effect of weakening the transfer of the carrier 4 to the developing roller 2. The value is preferably 5 to 10 kHz, and is preferably set according to the particle size of the carrier 4.
However, it is difficult to completely suppress the transition of the carrier 4 only with the frequency, and the thinning of the thin layer formation is avoided by using a coarse carrier 4 particle diameter. If the particle size of the carrier 4 is reduced, it is effective to instantaneously form a thin layer, and development ghost can be suppressed.

As shown in FIG. 5, the carrier pulling mechanism is such that the plus toner is collected by the magnetic roller 1 due to the potential difference Δ100V between the developing roller 2 and the magnetic roller 1 at the time of collection, and the negatively charged carrier 4 is transferred to the developing roller 2. This is a phenomenon in which the carrier 4 on the developing roller 2 is transferred to the non-exposed portion of the photosensitive member 3 due to the potential difference Δ330V with respect to the photosensitive member 3.
In particular, it occurs remarkably when the surfaces of the magnetic roller 1 and the developing roller 2 are subjected to insulation processing such as alumite treatment in order to increase the AC voltage during image formation. The toner thin layer 9 at the time of collection is almost eliminated via the magnetic brush 6, and the potential of the surface of the developing roller 2 becomes the applied potential + 100V.

As a technique for suppressing carrier pulling, as shown in FIG. 3, the toner 5 is collected by providing a potential difference for collecting the toner 5 between the magnetic roller 1 and the developing roller 2 during the collection. At this time, even if the carrier 4 may be transferred to the developing roller 2 as described above, the transfer of the carrier 4 to the photosensitive member 3 is reduced by reducing the potential difference between the photosensitive member 3 and the developing roller 2 as much as possible. It is possible to avoid it.
That is, since the potential of the developing roller 2 after being collected becomes equal to the voltage applied to the developing roller 2, this voltage is set equal to the potential of the photosensitive member 3 or set to a voltage that does not cause fogging or the like. It ’s fine. As the set value, it is preferable that the potential difference with respect to the photoreceptor 3 is 0 to 100 V as shown in FIG.

<Other embodiments>
At the time of collection, as described above, the magnetic roller 1 and the developing roller 2 collect the toner 5 by providing a potential difference for collecting the toner 5. At this time, even if the carrier 4 may be transferred to the developing roller 2, the potential difference between the photosensitive member 3 and the developing roll 2 can be reduced as much as possible in the same manner as in the above-described embodiment. It is possible to avoid transfer to the photoreceptor 3.
That is, as shown in FIG. 4, since the potential of the developing roller 2 after being collected becomes equal to the voltage applied to the developing roller 2, this voltage is kept constant, and the potential of the photoreceptor 3 is set to the developing roller. It may be set equal to the potential of 2 or set to a voltage that does not cause fogging. As the set value, it is preferable that the potential difference with the developing roller 2 is 0 to 100 V as shown in FIG.

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

As an image evaluation machine, FSC-5030 (Kyocera Mita, printer) was used. The evaluation machine was evaluated under the following setting conditions.
Image evaluation machine: FSC-5030 (Kyocera Mita, printer)
Process linear velocity = 150 mm / sec
Printing speed = 24ppm
AC condition between images: V _PP = (magnetic roller) 400V, (developing roller) 1500V
Frequency = 6kHz
DUTY ratio = 40%
Photoconductor surface potential: + 430V
Magnetic roller potential: + 400V (at the time of image formation)
Developing roller potential: +100 V (at the time of image formation)
Toner average particle size: D50 = 9 μm
Carrier average particle size: D50 = 30 and 60 μm
(Measurement of carrier)
The carrier 4 transferred to the photoreceptor 3 was peeled off after sticking an adhesive tape on the photoreceptor 3, and the number of carriers 4 in a certain area (3 cm × 10 cm) was measured by using a magnifying glass.
(Recovery bias)
As the timing of applying the bias, as shown in FIG. 6, the voltage applied to the magnetic roller 1 and the developing roller 2 during collection was set to Hi, and the potential of the photosensitive member 3 was the same as that during image formation.
Then, the applied voltages at the time of recovery of the magnetic roller 1 and the developing roller 2 were changed to the voltages shown in Table 1, respectively. 1-12.
The results are shown in Table 1.

  As shown in Table 1, when the potential difference between the magnetic roller 1 and the developing roller 2 exceeded 100 V (Sample Nos. 7 to 12), the carrier 4 was transferred to the photoreceptor 3. In contrast, when the potential difference between the magnetic roller 1 and the developing roller 2 within the scope of the present invention was 100 V or less (sample Nos. 1 to 6), the carrier 4 was not transferred to the photoreceptor 3. This is because the magnetic brush 6 begins to collect the toner 5 and at the same time the carrier 4 starts to transfer to the developing roller 2, but the potential on the developing roller 2 at that position is the voltage applied to Hi, and the photosensitive member 3 at that time. This is because the carrier 4 returns to the magnetic brush 6 without being transferred to the photosensitive member 3 if the potential difference is 100 V or less.

Evaluation was performed in the same manner as in Example 1 except that the bias timing was set as shown in FIG. In other words, as shown in FIG. 7, the bias voltage is set to the low voltage applied to the magnetic roller 1 at the time of recovery, the applied voltage to the developing roller 2 is set to be constant at the time of image formation, and the surface potential of the photosensitive member 3 is set to low. did. Then, the applied voltages at the time of recovery of the magnetic roller 1 and the developing roller 2 were changed to the voltages shown in Table 2, respectively. 13-24.
The results are shown in Table 2.

  As shown in Table 2, when the potential difference between the photosensitive member 3 and the developing roller 2 exceeded 100 V (Sample Nos. 19 to 24), the carrier 4 was transferred to the photosensitive member 3. On the other hand, when the potential difference between the photosensitive member 3 and the developing roller 2 within the scope of the present invention was 100 V or less (sample Nos. 13 to 18), the carrier 4 was not transferred to the photosensitive member 3. This is because the magnetic brush 6 starts collecting the toner 5 and at the same time, the carrier 4 starts to transfer to the developing roller 2, but the potential on the developing roller 2 at that position is constant, and the potential difference from the photoreceptor 3 at that time is 100V. This is because the carrier 4 returns to the magnetic brush 6 without being transferred to the photoreceptor 3 if it is below.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of a hybrid development system according to the present invention. 1 is a schematic configuration diagram illustrating an example of a development device of a hybrid development system according to the present invention. It is a schematic block diagram which shows an example of the electric potential structure at the time of collection | recovery concerning this invention. It is a schematic block diagram which shows an example of the electric potential structure at the time of collection | recovery in other embodiment concerning this invention. It is a schematic block diagram which shows the electric potential structure at the time of collection for demonstrating carrier pull. It is a figure which shows the timing chart of the applied voltage at the time of collection | recovery concerning this invention. It is a figure which shows the timing chart of the applied voltage at the time of collection | recovery in other embodiment concerning this invention.

Explanation of symbols

1 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 Charger 9 Toner Layer 10 Exposure Light 11a AC Power Supply 11b DC Power Supply 12a AC Power Supply 12b DC Power Supply

Claims (2)

The toner is charged by holding and mixing the two-component developer on the developer carrier, and a uniform thin layer is formed on the toner carrier alone, and direct current is formed in the space with the electrostatic latent image carrier. An image forming apparatus having a developing device that superimposes an AC voltage and causes toner to fly to a latent image,
In a developing device having a configuration capable of recovering the toner from the toner carrier to the developer carrier during non-development between images or between papers when continuously printing,
The carrier particle size constituting the developer is 30 to 60 μm,
An image forming apparatus characterized in that, when the toner is collected, an applied voltage of the toner carrier is changed so as to have a potential difference of 0 to 100 V with respect to a surface potential of the electrostatic latent image carrier. . The toner is charged by holding and mixing the two-component developer on the developer carrier, and a uniform thin layer is formed on the toner carrier alone, and direct current is formed in the space with the electrostatic latent image carrier. An image forming apparatus having a developing device that superimposes an AC voltage and causes toner to fly to a latent image,
In a developing device having a configuration capable of recovering the toner from the toner carrier to the developer carrier during non-development between images or between papers when continuously printing,
The carrier particle size constituting the developer is 30 to 60 μm,
An image forming apparatus, wherein the surface potential of the electrostatic latent image carrier is changed so as to have a potential difference of 0 to 100 V with respect to a voltage applied to the toner carrier.

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