JP2008310074A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses deterioration of image quality. <P>SOLUTION: A developing device is equipped with: a developing roll to which predetermined developing potential is applied; a first storing part which is adjacent to the developing roll and supplies developer stored inside to the developing roll; a second storing part which is adjacent to the first storing part and is provided with moving ports through which the developer moves between the first storing part and the second storing part at both ends; a collecting body which is adjacent to the developing roll on a more downstream side than a developing area of the developing roll and on a more upstream side than a position where the developer is supplied to the developing roll from the first storing part, and collects electrified toner in the developer held by the developing roll by application of collecting potential having the same polarity as a relative polarity of latent image potential to developing potential and making a larger potential difference between the developing potential and the collecting potential than a potential difference between the developing potential and the latent image potential; and a feeding part which feeds the electrified toner collected by the collecting body to the second storing part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to image formation in which an image is formed on a recording medium by transferring and fixing the toner image obtained by developing the electrostatic latent image with toner in a developer containing toner and carrier onto the recording medium. Relates to the device.

  Conventionally, an electrostatic latent image is formed on an image carrier, and the electrostatic latent image is developed with toner in a developer containing at least toner and a magnetic carrier to obtain a toner image. An image forming apparatus is known that forms an image composed of a fixed toner image on a recording medium by transferring and fixing the toner image on the recording medium.

  Such an image forming apparatus is provided with a developer accommodating chamber for accommodating a developer, and the developer in the developer accommodating chamber is stirred to charge the toner in the developer by friction with the carrier. Some of them are electrostatically attached to the surface. In addition, such an image forming apparatus is provided with a rotatable developing roll adjacent to the image holding member for holding the magnetic carrier to which the charged toner is attached by a magnetic force, and the charged toner is rotated by the rotation of the developing roll. Thus, the electrostatic latent image is transferred to the development area facing the image carrier and attached to the electrostatic latent image formed on the surface of the image carrier to develop the electrostatic latent image.

  By the way, in the above-described image forming apparatus, for example, when the toner concentration in the developer in the developer accommodating chamber is detected and the toner concentration falls below a predetermined value, the toner is supplied to the developer accommodating chamber. There is something that is.

  However, low-charged toner that has just been newly supplied to the developer storage chamber and still has insufficient friction with the carrier adheres to portions other than the electrostatic latent image formed on the image carrier, so-called fogging. It is known to cause a decline. Further, it is known that the image quality is also deteriorated by a highly charged toner that becomes too charged and remains on the developing roll and adversely affects the image quality.

Therefore, a proposal has been made that toner fine particles that interfere with friction between the toner and the carrier by separating from the toner and accumulating on the carrier surface are removed from the carrier surface and discarded outside the developer storage chamber (Patent Document 1). reference).
JP 2006-201753 A

  However, the above proposal is not sufficient as a countermeasure for increasing the charging of the low-charged toner with a small number of frictions with the carrier, and becomes too charged and remains on the developing roll, which adversely affects the image quality. There is a problem that image quality degradation caused by the applied toner cannot be dealt with.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus in which deterioration in image quality is suppressed.

In order to achieve the above object, an image forming apparatus of the present invention comprises:
An image carrier that holds an image on which an image is formed;
A latent image forming unit for forming an electrostatic latent image having a predetermined latent image potential on the surface of the image carrier;
A developer containing a developer containing the toner, which forms a toner image by attaching toner to the electrostatic latent image formed on the surface of the image carrier;
The developer is
A developing roll to which a predetermined developing potential is applied, which is adjacent to the image carrier and conveys the developer to a developing region facing the image carrier by holding and rotating the developer on the surface. When,
Adjacent to the developing roll and extending along the rotation axis of the developing roll, containing the developer inside and supplying the developer to the developing roll, stirring the contained developer on the rotating shaft A first accommodating portion that conveys in a first direction along;
The developer is accommodated in the interior provided with a moving port for the developer to move to and from the first accommodating portion at both ends, which is adjacent to the first accommodating portion and extends side by side with the first accommodating portion. A second storage unit that is supplied with toner and conveys the developer and the toner in a second direction opposite to the first direction while stirring and mixing the developer;
The developing roll is adjacent to the developing roll on the downstream side of the developing area and on the upstream side of the position where the developer is supplied from the first container to the developing roll, and the latent potential with respect to the developing potential is set. A recovery potential is applied between the developing potential and the developing electrode that has the same polarity as the relative polarity of the image potential and that is greater than the potential difference between the developing potential and the latent image potential. A collecting body for collecting the toner in the developer,
And a feeding portion that feeds the toner collected by the collecting body into the second storage portion.

  In the image forming apparatus of the present invention, the toner that remains on the developing roll increases because the toner is too charged, and a recovery potential capable of recovering the highly charged toner that causes a decrease in image quality such as a decrease in density is applied to the recovery body. The highly charged toner recovered by the recovery body is sent to the second storage unit to which new toner is supplied. Therefore, according to the image forming apparatus of the present invention, by removing from the developing roll the highly charged toner that remains on the developing roll and causes the density reduction, the deterioration of the image quality due to the density reduction is suppressed, and due to insufficient stirring. By actively combining low-charged toner, which has low chance of friction with the carrier and causes low fogging, and high-charged toner removed from the developing roll, it is low from the side of highly charged toner. Charges can be transferred to the charged toner side, and deterioration in image quality due to fogging can be suppressed.

  Here, the developer held on the surface by the developing roll is opened downstream from the position where the collection body is adjacent, and the image forming apparatus of the present invention is a developer with the developing roll opened. It is preferable that a guide member that guides at least a part of the first guide to the second housing portion is provided.

  Thus, the charging of the low-charge toner can be further promoted by feeding the charged toner into the second storage portion by the guide portion.

  According to the image forming apparatus of the present invention, it is possible to suppress deterioration in image quality.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention.

  An image forming apparatus 1 according to the present embodiment shown in FIG. 1 is a monochrome image dedicated machine, and rotates in the direction of arrow A to hold a developed image made of toner, and on the surface of the image holder 100. The charger 110 for applying a predetermined charge and the surface of the image carrier 100 to which a predetermined charge has been applied by the charger 110 are irradiated with exposure light to form an electrostatic latent image on the surface of the image carrier 100. An exposure device 120 to be formed, a developing device 10 that develops the electrostatic latent image with toner, and a developed image formed on the surface of the image holding member 100 by developing the electrostatic latent image by the developing device 10, A transfer roll 140 that transfers onto the recording paper conveyed in the direction of arrow B, and a fixing device that fixes the developed image on the recording paper 100 by heating and pressing the developed image transferred onto the recording paper 100. It is composed of 150

  FIG. 1 shows a paper cassette 160 that stores recording paper, a pickup roll 171 that pulls out the recording paper from the paper cassette 160, and a transport roll 172 that transports the recording paper drawn from the paper cassette 160 by the pickup roll 171. Also shown is a paper transport section 170 comprising

  FIG. 2 is a cross-sectional view of the developing device.

  The developing device 10 shown in FIG. 2 exposes a developing roll 11 having a developing sleeve 111 that moves upward (in the direction of arrow c) and a part of the developing roll 11 in the developing area 100a facing the image carrier 100. In this state, the developing roll 11 is rotatably held, and a housing 12 that contains a developer containing toner and a magnetic carrier, a recovery unit 13 that will be described in detail later, and a developing roll disposed inside the housing 12. And a power supply unit 14 for charging 11 to a predetermined negative potential.

  The power supply unit 14 includes a DC power supply 141 and an AC power supply 142.

  The developing roll 11 has a cylindrical developing sleeve 111 that rotates in the direction of arrow c, and a plurality of magnetic poles arranged in the circumferential direction of the developing sleeve 111 that is fixed inside the developing sleeve 111 independently of the developing sleeve 111. It is comprised with the magnet roll 112 made.

  The housing 12 is adjacent to the developing roll 11 and is adjacent to the first containing chamber 12a extending along the rotation axis of the developing roll 11 with the wall 121 between the first containing chamber 12a. A second storage chamber 12b extending along the rotation axis of the first storage chamber 12b, and a toner supply chamber 12c adjacent to the second storage chamber 12b across the wall 122 and storing toner to be supplied to the second storage chamber 12b. Yes. In the first storage chamber 12 a, the stored developer is conveyed from the back side to the front side in FIG. 2 along the rotation axis while being stirred by the first auger 121 a extending along the rotation axis of the developing roll 11. In the second storage chamber 12b, the stored developer is conveyed by the second auger 121b extending along the rotation axis of the developing roll 11 from the front side to the back side in FIG. 2 along the rotation axis. is doing. Further, the developer can be circulated at both ends of the first storage chamber 12a and the second storage chamber 12b. The toner supply chamber 12c is provided with a third auger 121c. A wall 122 that partitions the second storage chamber 12b and the toner supply chamber 12c is located near the third auger 121c in the toner supply chamber 12c. An opening (not shown) for feeding the stored toner into the second storage chamber 12b is provided. When the third auger 121c rotates, the toner is fed into the second storage chamber 12b through the opening.

  In this housing 12, the developer containing toner and magnetic carrier is conveyed between the first storage chamber 12a and the second storage chamber 12b with stirring, so that the toner is frictionally charged negatively. It is electrically attached to the magnetic carrier. The magnetic carrier to which the toner is attached is attracted to the magnet roll 112 at the holding position 120a, and the magnetic carrier to which the toner is attached is held on the surface of the rotating developing sleeve 111. As a result, the toner is carried to the development area 100a.

  In the image forming apparatus 1, the developing roll 11 of the developing device 10 is charged to −500 V, and the electrostatic latent image portion of the image carrier 100 is charged to −167 V, which is higher than the potential of the developing roll 11. ing. For this reason, the negatively charged toner overcomes the electrostatic attraction between the carrier and the electrostatic latent image portion of the image carrier 100 from the electrostatic latent image portion of the image carrier 100 toward the developing roll 11 in a static state. Fly to the electric latent image side. The toner that has passed through the developing region 100a while being held by the developing roll 11 is released together with the carrier at a release position 120b upstream of the holding position 120a.

  Here, the collection unit 13 having the collection roll 131 adjacent to the development roll 11 on the downstream side of the development region 100a and the upstream side of the release position 120b will be described.

  The collection unit 13 is a downstream side of the development area 100a and an upstream side of the release position 120b, and a collection roll 131 that collects the toner held by the development roll 11, and a toner collected by the collection roll 131 is peeled off. The scraper 133 includes a guide cover 132 that guides the toner peeled off by the scraper 133 to the second storage chamber 12b.

  In the collection unit 13, the collection roll 131 is grounded and has a higher potential (0 V) than the potential (−167 V) of the electrostatic latent image portion of the image carrier 100. Therefore, the electric field between the developing roll 11 and the collecting roll 131 is strong even if the direction of the electric field between the developing roll 11 and the electrostatic latent image portion of the image carrier 100 is the same. For this reason, the collection roll 131 can collect highly charged toner among the toners that are held by the development roll 11 but did not fly to the electrostatic latent image portion when passing through the development region 100a. The highly charged toner collected by the collection roll 131 is peeled off from the collection roll 131 by the scraper 133 and sent to the second storage chamber 12b by the guide cover 132.

  As described above, in the developing device 10, since the toner is too charged, the highly charged toner that remains on the developing roller 131 and causes deterioration in image quality is collected by the collecting roller 131, and the uncharged toner is supplied. It is sent into the storage chamber 12b by the guide cover 132. As a result, in the image forming apparatus 1 of the present embodiment, the high-charge toner that remains on the developing roll 131 and causes low density is removed from the developing roll 131, thereby suppressing image quality deterioration due to low density and uncharged. By aggressively bringing the toner and the highly charged toner together to promote the charging of the uncharged toner, it is possible to suppress deterioration in image quality due to fog caused by the lowly charged toner.

  Further, in the developing device 10, a guide plate 123 for feeding a part of the released developer into the second storage chamber 12b in the vicinity of the release position 120b where the developer held on the surface of the developing roll 11 is released. The developer sent into the second storage chamber 12b by the guide plate 123 also contributes to the charging of the uncharged toner sent into the second storage chamber 12b. In the embodiment described above, an example has been described in which both the toner collected by the collection roll 131 and the developer released at the release position 120b are guided to the second storage chamber 12b. If the toner collected in 131 is sent to the second storage chamber 12b, the developer released at the release position 120b may not be sent to the second storage chamber 12b. In the embodiment described above, the potential of the electrostatic latent image portion of the image carrier 100 is set to a potential (−167 V) higher than the potential of the developing roll 11 (−500 V), and the recovery roll 131 is set to the ground. Although the example in which the potential of the collecting roll 131 is set to 0 V by entanglement has been described, the potential of the collecting roll 131 is the same as the relative polarity of the potential of the electrostatic latent image portion with respect to the potential of the developing roll 11, Further, the potential is not limited to 0 V as long as the potential difference between the potential of the developing roll 11 and the potential of the electrostatic latent image portion is larger than the potential difference of the developing roll 11.

  Hereinafter, an experiment performed by modifying the above-described image forming apparatus 1 so that the removal roll 131 and the potential setting can be freely changed and the guide plate 123 can be freely removed will be described.

  First, in Example 1, the potential difference between the collection roll and the developing roll is 1.5 times the potential difference between the collection roll and the electrostatic latent image on the image carrier, and the guide plate is removed. 'Toner scattering' and 'Toner fogging' were determined, and the image quality was evaluated based on these determinations.

  In Example 2, the potential difference between the collecting roll and the developing roll is set to 1.2 times the potential difference between the collecting roll and the electrostatic latent image, and “toner scattering” when the guide plate is removed and 'Toner fogging' was judged and the image quality was evaluated based on these judgments.

  In Example 3, the potential difference between the collecting roll and the developing roll is 1.5 times the potential difference between the collecting roll and the electrostatic latent image, and the “toner scattering” and the “toner” when the guide plate is attached are used. The “fogging” was determined, and the image quality was evaluated based on these determinations.

  On the other hand, in Comparative Example 1, “toner scattering” and “toner fog” when both the collecting roll and the guide plate were removed were determined, and the image quality was evaluated based on these determinations.

  In Comparative Example 2, “toner scattering” and “toner fogging” were determined when the collecting roll was removed and only the guide plate was attached, and the image quality was evaluated based on these determinations.

  In Comparative Example 3, the potential difference between the collection roll and the developing roll is the same as the potential difference between the collection roll and the electrostatic latent image, and 'toner scattering' and 'toner fogging when the guide plate is removed. 'Was judged, and the image quality was evaluated based on these judgments.

  The determination of “toner scattering” and “toner fogging” is “'” if the reduction rate of the toner scattering amount is 80% or more, “◯ +” if it is 75% or more and less than 80%, and 70% or more and less than 75%. If it is less than 70%, it is “△”. If there is almost no effect, it is “X”. For “evaluation”, if there is no problem in image quality, it is “excellent”, and if there is almost no problem in image quality. “Good”, “Yes” if the image quality is acceptable, and “No” if there is a problem with the image quality. Table 1 shown below shows the contents and results of the experiments for Examples 1 to 3 and Comparative Examples 1 to 3.

  From Comparative Example 1 to Comparative Example 3, the evaluations of “toner scattering” and “toner fog” are both “x” in Comparative Example 1 and Comparative Example 3, and therefore a recovery roll is provided. However, when the potential difference between the collecting roll and the developing roll is the same as the potential difference between the collecting roll and the electrostatic latent image on the image carrier, it was confirmed that no effect was obtained. “Evaluation” is both “not possible”. In Comparative Example 2, the evaluations of “toner scattering” and “toner fogging” are both “Δ”, so that the effect is small even if only the guide plate is provided, and the evaluation of Comparative Example 2 is “impossible”. It has become.

  Further, from Examples 1 and 2, both “toner scattering” and “toner fogging” in Example 1 are judged as “◯ +”, whereas “toner scattering” in Example 2 is evaluated. Since the determination of “◯” and “toner fog” is “△”, the potential difference between the collecting roll and the developing roll is larger than the potential difference between the collecting roll and the electrostatic latent image. It can be confirmed that the effect also increases along with that, and the evaluation of Example 1 is generally “good” and the evaluation of Example 2 is “good”.

  From Example 1 and Example 3, the determination of “toner scattering” and “toner fog” in Example 1 is “◯ +”, whereas “toner scattering” and “toner fog” in Example 3 are both. Since both of the determinations are “◎”, it can be confirmed that the effect is further improved by attaching the guide plate. Evaluation of Example 3 is “Excellent” compared to “Good” of Example 1. 'And more highly rated.

  From the above results, it was confirmed that by collecting the highly charged toner and actively feeding it into the second storage chamber, the toner charge amount can be increased and the image quality can be suppressed from being lowered. Furthermore, it was confirmed that the toner charge amount is also increased by positively feeding the developer released at the release position into the second storage chamber, thereby further suppressing the deterioration of the image quality.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention. It is sectional drawing of a developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Charger 100 Image holding body 100a Developing area 11 Developing roll 12 Housing 12a 1st accommodating chamber 12b 2nd accommodating chamber 12c Toner supply chamber 120a Holding position 120b Release position 121, 122 Wall 123 Guide plate 13 Collecting part 131 Collection roll 132 Guide cover 133 Scraper 14 Power supply

Claims (2)

An image carrier that forms an image on the surface and holds the image;
A latent image forming unit for forming an electrostatic latent image having a predetermined latent image potential on the surface of the image carrier;
A developing unit containing a developer containing the toner, which forms a toner image by attaching toner to the electrostatic latent image formed on the surface of the image carrier;
The developer is
A developing roll to which a predetermined developing potential is applied, which is adjacent to the image holding member and conveys the developer to a developing region facing the image holding member by rotating while holding the developer on the surface. When,
Adjacent to the developing roll and extending along the rotating shaft of the developing roll, containing the developer inside and supplying the developer to the developing roll, stirring the contained developer on the rotating shaft A first accommodating portion that conveys in a first direction along;
The developer is accommodated in the interior, which is provided adjacent to the first accommodating portion and extends in parallel with the first accommodating portion, at both ends provided with moving ports for moving the developer between the first accommodating portion and the first accommodating portion. A second storage unit that is supplied with toner and conveys the developer and the toner in a second direction opposite to the first direction while stirring and mixing the developer;
The developing roll is adjacent to the developing roll on the downstream side of the developing area and on the upstream side of the position where the developer is supplied from the first container to the developing roll, and the latent potential with respect to the developing potential is set. A recovery potential is generated between the development potential and the same polarity as the relative polarity of the image potential, which is larger than the potential difference between the development potential and the latent image potential. A collecting body for collecting the toner in the developer,
An image forming apparatus comprising: a feeding portion that feeds toner collected by the collecting body into the second storage portion. The developing roll opens the developer held on the surface downstream of the position where the recovery body is adjacent,
The image forming apparatus according to claim 1, further comprising a guide member that guides at least a part of the developer opened by the developing roll to the second storage unit.

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