JP2006154070A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of maintaining normal image quality and realizing high image quality and resource economization without requiring a driving device extra by preventing the deterioration in the image quality caused by "fogging" and "black dot defect" inexpensively while saving space by crushing the flocculated body of toner being developer to be recycled. <P>SOLUTION: In the image forming apparatus, a developing device is constituted so that developer stirring screws and a supply screw for supplying the developer to a developing roller are arranged under a partition which partitions a part of the developing device to the upside and the downside, and a developer returning means and a circularly recovering screw for recovering the developer remaining after supplied to a photoreceptor from the developing roller are arranged above the partition, then the circularly recovering screw and one of the stirring screws are disposed proximately through the partition. At least one window for making the developer drop from the upside to the downside so as to circularly stir and convey is opened at a part of the partition, and a mesh is provided on the window so that the developer passing through the mesh is stirred and supplied by the developing roller. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a developer agitating and conveying means in a developing device.

  In recent years, with the advancement of advanced information technology, the need for high-quality image forming apparatuses based on digital technology is increasing. Further, the amount of hard copies printed on paper tends to increase more and more, and there is an increasing social demand for an image printing apparatus capable of printing with energy saving and resource saving. The following technologies have been developed and introduced to meet these requirements. Further challenges are born.

  (1) A developer with a further small particle diameter is employed for high image quality and printed.

  (2) To save energy and resources, the developer once used for image formation is recycled and used repeatedly for image formation.

  The problem here is that as the particle size is reduced, the bulk density of the developer is increased, the gap between the developers is narrowed, the flowability of the developer is lowered, and the developers are easily aggregated. In addition, when the developer once cleaned is reused in the development process again, the external additive on the toner surface is buried or detached, so that the developers come closer to each other and the fluidity is lowered to easily generate toner aggregates. Become.

  Toner agglomerates are not easily loosened in the developing unit, and when used in the developing process as they are, they cannot be sufficiently held by electrostatic force due to “image fogging” caused by insufficient frictional charging with the carrier and carrier spikes on the developing roller. As a result, the toner is scattered and image quality defects such as “black spot defects” and “white defect” occur.

  As a conventional technique, Patent Document 1 proposes a method for suppressing image deterioration caused by recycled toner by controlling a supply amount ratio of new toner and recycled toner to a developing device within a certain range. However, this method requires an operating means for separately controlling the supply amount of the recycled toner collected from the cleaning device and a space for temporarily storing the collected recycled toner, which is problematic in terms of cost and space saving. is there.

  In addition, when recycling the developer, there is a method in which foreign matter to be mixed in and developer aggregates are sent to two magnetic rollers with a non-magnetic filter sandwiched between them, so that the filter is not clogged, and the toner is separated and broken. This is proposed in Patent Document 2. This method can reliably pulverize the developer aggregates or remove foreign substances, but has the disadvantage that a magnetic roller is additionally required, which leads to an increase in cost and enlargement of the developing device, and also increases the space. It is not preferable.

Furthermore, in a developer using a binder resin carrier in which a magnetic agent is dispersed, Patent Document 3 proposes a method for recovering a carrier having a reduced particle size by providing a mesh / guide plate / developer recovery unit in the developing device. Has been. This method has a function of collecting a binder resin carrier that has been broken and reduced in particle size, and could not be applied to a developer using a long-life and highly reliable magnetic core carrier.
Japanese Patent Laid-Open No. 6-110329 JP-A-7-191589 JP-A-9-197831

  The present invention breaks up aggregates of toner, which is a developer that is recycled, and causes “fogging” and “black spot defects” (a large toner lump adheres to a white background or the periphery of a large toner soul in an image area cannot be transferred and becomes white. An image forming apparatus that prevents image quality deterioration due to a ring-like shape) at low cost and space-saving, maintains normal image quality without requiring a separate drive device, and realizes high image quality and resource saving. The challenge is to provide

  This object is achieved by any one of the following technical means (1) to (3).

(1) In an image forming apparatus having a developing unit that visualizes an electrostatic latent image formed on a photoreceptor as an electrostatic latent image carrier with a developer.
In the developing unit, a stirring screw that conveys the developer while stirring and a supply screw that supplies the developer to a developing roller as a developer carrying member are provided below the partition wall that partitions the upper and lower parts of the developing unit. And a developer return means for recovering excess developer supplied from the developing roller to the photosensitive member and a circulation recovery screw for circulating the developer from the developer return means are disposed above the partition wall. One of the circulation recovery screw and the stirring screw is disposed close to each other across the partition wall, and one of the partition walls in the vicinity where the circulation recovery screw and one of the stirring screws face each other at the shortest distance. Open at least one window to drop the developer from the top to the bottom, and provide a mesh in the window, and stir and supply the developer that has passed through the mesh to the developing roller. Image forming apparatus characterized by.

  (2) The image forming apparatus according to (1), wherein the stirring screw that receives the developer from the circulation collection screw through the mesh is a stirring screw that is closest to the developing roller.

(3) In the image forming apparatus described in (1) or (2),
The developer is a two-component developer comprising magnetic carrier particles and non-magnetic toner particles, and the mesh opening is 1.5 to 5 times, preferably 2 to 3.5 times larger than the carrier average volume particle size. An image forming apparatus characterized by that.

  According to the first aspect of the present invention, the developer aggregate passed through the mesh is adapted by the mesh fitted in the window provided in the developer circulation path in the partition wall of the developing device of the image forming apparatus. Since it is below the predetermined size, it is further supplied to the developing roller as a normal toner and carrier developer by a stirring screw, so that high-quality development can be stably performed. In addition, the agglomerates left behind by the mesh are unresolved to an appropriate size or less by the circulation collection screw, so that the agglomerate can be passed through the mesh without any waste. Since it is supplied to the developing roller as a developer for the carrier, it is possible to stably perform high-quality development without fogging, black spots, or white spots.

  According to the second aspect of the present invention, the developer supplied to the developing roller can be regenerated to a normal developer more quickly, and the image forming operation can be dealt with without delay, and the developing device is also downsized. Space is saved and manufacturing costs are reduced.

  According to the invention of claim 3, the developer is a two-component developer comprising magnetic carrier particles and non-magnetic toner particles, and the mesh opening is 1.5 to 5 times the average volume particle diameter of the carrier particles, preferably Is a size of 2 to 3.5 times, so that the process of unraveling aggregates into a normal size developer is shortened, and development of stable and high-quality image formation is efficiently performed. It becomes like this. I do.

  Embodiments of the image forming apparatus of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

  FIG. 1 is an overall configuration diagram of an embodiment of an image forming apparatus of the present invention, specifically, a digital image forming apparatus. An image reading unit A, an image processing unit B, an image forming unit C, and a sheet (sheet as recording paper) The sheet conveying section D is a sheet conveying means for conveying P).

  An automatic document feeder that automatically conveys the document is provided above the image reading unit A. The document placed on the document table 11 is separated and conveyed by the document conveyance roller 12 to the reading position 13a. The image is read. The document after the document reading is completed is discharged onto the document discharge tray 14 by the document transport roller 12.

  On the other hand, the image of the original when placed on the platen glass 13 is read at a speed v of the first mirror unit 15 including the illumination lamp and the first mirror constituting the scanning optical system, and the V-shaped first image is located. Reading is performed by the movement of the second mirror unit 16 including the two mirrors and the third mirror in the same direction at the speed v / 2.

  The read image is formed on the light receiving surface of the image sensor CCD, which is a line sensor, through the projection lens 17. The line-shaped optical image formed on the image sensor CCD is sequentially photoelectrically converted into an electric signal (luminance signal) and then A / D converted, and the image processing unit B performs processing such as density conversion and filter processing. Then, the image data is temporarily stored in the memory.

  In the image forming unit C, as an image forming unit, a drum-shaped photoconductor 21 as an image carrier, a charging unit 22 for charging the photoconductor 21 on the outer periphery thereof, and a potential for detecting the surface potential of the charged photoconductor. A detection unit 220, a developing unit 23 as a development unit, a transfer electrode 24 and a separation electrode 25 as transfer separation units, a cleaning device 26 for the photosensitive member 21, and a PCL (precharge lamp) 27 as an optical charge removal unit are in order of operation. Has been placed. Further, a reflection density detecting means 222 for measuring the reflection density of the patch image developed on the photosensitive member 21 is provided on the downstream side of the developing device 23 as the developing means. The photoconductor 21 is formed by coating a photoconductive compound on a drum base. For example, an organic photoconductor (OPC) is preferably used and is driven to rotate in the clockwise direction shown in the drawing.

  After the rotating photosensitive member 21 is uniformly charged by the charging unit 22, image exposure based on an image signal called from the memory of the image processing unit B is performed by an exposure optical system 30 as an image exposure unit. An exposure optical system 30 serving as an image exposure means serving as a writing means uses a laser diode (not shown) as a light source, passes through a rotating polygon mirror 31, an f.theta. Therefore, image exposure is performed on the photoconductor 21 at the position Ao, and a latent image is formed by rotation (sub-scanning) of the photoconductor 21. In one example of the present embodiment, the character portion is exposed to form a latent image.

  The latent image on the photoreceptor 21 is subjected to reversal development by a developing device 23 as a developing unit, and a visible toner image is formed on the surface of the photoreceptor 21. In the transfer material transport section D, the transport is carried with the paper feed units 41 (A), 41 (B), 41 (C) as sheet storage means in which sheets P as recording papers of different sizes are stored below the image forming unit. A roller 43 is provided, and a manual paper feeding unit 42 that performs manual paper feeding is provided on the side, and the sheet P selected from any of these is fed along the conveyance path 40 by the guide roller 43. Then, the sheet P is temporarily stopped by the registration roller pair 44 that corrects the inclination and bias of the fed sheet P, and then the sheet P is re-fed, and the conveyance path 40, the pre-transfer roller 43a, and the sheet feeding path 46. And the toner image on the photosensitive member 21 is transferred onto the sheet P by the transfer pole 24 and the separation pole 25 at the transfer position Bo, and is conveyed to the conveyance belt of the conveyance belt device 45. The sheet P while being placed conveyed to 54 were separated from the photoreceptor 21 surface, it is conveyed to the fixing device 50 as a fixing means by the conveyor belt device 45.

  As will be described in detail later, the fixing device 50 includes a heating roller 51 as a rotating member heating member and a pressing roller 54 as a pressing member having a heating source, and the sheet P is added to the heating roller 51. By passing between the pressure roller 54, the toner is fixed by heating and pressing. The sheet P on which the toner image has been fixed is discharged onto the paper discharge tray 81.

  The above describes the state in which image formation is performed on one side of the sheet P. In the case of double-sided copying, the sheet discharge switching member 170 is switched, the sheet guide portion 177 is opened, and a sheet called transfer material or recording paper P is conveyed in the direction of the dashed arrow.

  Further, the sheet P is conveyed downward by the conveyance mechanism 178 and is switched back by the sheet reversing unit 179, and the rear end portion of the sheet P so far becomes the leading end portion and conveyed into the duplex copying paper supply unit 130. The

  The sheet P is moved in the sheet feeding direction by a conveyance guide 131 provided in the duplex copying sheet feeding unit 130, and the sheet P is again fed by the sheet feeding roller 132, and the sheet P is guided to the conveyance path 40.

  Again, as described above, the sheet P is conveyed in the direction of the photosensitive member 21, the toner image is transferred to the back surface of the sheet P, fixed by the fixing device 50, and then discharged onto the discharge tray 81.

  Next, the developing unit 23 mounted in the image forming apparatus of the present invention will be described with reference to FIG. 3 which is a side view of FIG.

  In the figure, the developing device 23 includes a developing device main body 230 and a lid member 231 that form an opening S with respect to the photosensitive member 21, and a side wall 230 </ b> A provided therebetween.

  In the side wall 230A, a developing roller 232 as a developer carrying member constituted by a cylindrical non-magnetic sleeve, and a plurality of magnetic fields built in the developing roller 232 (synonymous with inclusion) and forming a rotational sliding surface thereof. A plurality of generating means (synonymous with magnetic poles, hereinafter sometimes referred to as magnetic poles for the sake of explanation) 233A formed on the cylinder and fixed in position, and a plurality of the developer are conveyed while stirring. A stirring screw 234, a supply screw 235 for supplying the developer after stirring toward the developing roller 232, a developer returning means 236 provided in the vicinity of a part of the peripheral surface above the developing roller 232, and the developer A circulation recovery screw 237 for recovering and circulating the developer removed from the return means 236 is attached.

  In the configuration described above, the stirring screw 234 and the supply screw 235 of the stirring supply system are on the lower side, and the developer return means 236 and the circulation collection screw 237 are on the upper side. It is divided into upper and lower portions with a partition wall 238 separating them.

  The developer returning means 236 includes, as main components, a position-fixed magnet in which a plurality of magnetic poles are appropriately arranged in the circumferential direction, and a rotatable cylindrical sleeve incorporating the magnet. .

  The small circular rows on the peripheral surfaces of the developing roller 232 and the developer returning means 236 as the developer carrying member shown in FIG. 2 are the developers shown to facilitate the flow.

  At a position above one end of the circulation recovery screw 237, the lid member 231 at the top of the developing unit 23 is supplied with a supply port 241 for the recovered toner that is cleaned and conveyed by the image forming unit and newly supplied. A new toner supply port 242 is provided.

  Further, one of the circulation recovery screw 237 and the stirring screw 234 is a position facing the shortest distance, and is a position below the other end of the circulation recovery screw 237, and is one above the stirring screw 234. A window 239 is provided in the partition wall 238, which corresponds to the position (2), for dropping the developer from the top to the bottom.

  A mesh 239A is provided at a portion where the developer is dropped from the top to the bottom in the window 239, and the developer that has passed through the mesh is supplied to a developing roller 232 as a developer carrier through a stirring screw 234 and a supply screw 235. To do.

  It is desirable that the window 239 for dropping the developer from top to bottom corresponds to the stirring screw 234 located closest to the developing roller 232 as the developer carrying member. And mesh 239A is provided there.

  Here, an appropriate amount of recycled toner from the cleaning device 26 and new toner to be replenished is calculated based on detection information of a toner density sensor (not shown) provided in the developing unit 23, and each of the supply ports Appropriate amounts are supplied from 241 and 242 and mixed together with the developer that has been circulated so far, and added to the cycle of circulation, recovery, and stirring.

  In the above description based on FIG. 2, the single circulation recovery screw 237 has been described. However, a plurality of circulation recovery screws 237 may be provided in the lateral direction corresponding to the stirring screw 234. However, the former arrangement seems to be sufficient in terms of cost and space.

  The mesh 239A has an opening of 1.5 to 5 times, preferably 2 to 3.5 times the average volume particle size of the carrier particles.

  Using the image forming apparatus of the present invention equipped with such a developing device, a performance confirmation experiment was performed under the following conditions.

  As the developer, a polymerized toner having a material of styrene-acryl and a particle diameter of 6.5 μm was used as the toner. Further, as a carrier, a ferrite carrier made of a silicone resin coated material and having a particle size of 60 μm was used.

  The particle diameter of the carrier is a volume average particle diameter, which is determined by a laser diffraction particle size distribution measuring apparatus equipped with a wet disperser (HELOS KF series manufactured by Sympatec Corporation). Is on a volume basis.

  As the image forming apparatus, the above-described mono-black digital copier and printer were used, and an apparatus having a resolution of 600 dpi and a laser beam diameter of 60 μm in the main scanning direction and 78 μm in the sub-scanning direction was used.

  The experimental environment was set to room temperature and normal humidity with a temperature of 20 ° C. and a humidity of 50% RH.

The paper type to be passed is plain paper, using commercially available Konica copy J paper (A3 size),
Use a document with a print rate of 6% during running.
As for the data for periodic check during running, we collected solid black, full halftone and blank paper.

  As the evaluation method, the following operations (1) and (2) were performed, and a confirmation test of the state of occurrence of developer aggregation was performed.

    (1) Continuous 300,000 copies were made with continuous copying (A3 size original, 6% printing rate).

    (2) Image samples for periodic confirmation were taken 6 times every 50,000 copies. Samples are taken in A3 size, one each for three types (full solid black, full halftone, blank paper).

Evaluation is "fogging" and "black spot defect" due to toner aggregates in the image area and white background area,
A “white spot defect” formed by the toner aggregate in the image area serving as a nucleus and the periphery being unable to be transferred was visually confirmed.

  The criteria for “fogging” is that the image with the worst image fogging of the blank paper portion is visually extracted, and the fog density of the portion with the worst “fogging” of one sheet is measured with an image reflection densitometer. A density of less than 0.006 is judged as “◯”, and a density of 0.006 or more is judged as “X”.

  The criteria for determining “black spot defects” and “white spot defects” are the size and number of black spots on white paper and halftone image samples, and the size and number of white spots on halftone and solid black image samples. Evaluation is performed by observing with a magnifier.

  The black spots and white spots are determined based on the following sizes and numbers, respectively.

    When the equivalent circle diameter <0.3 mm, the number is not limited and “OK” is set.

    0.3 mm ≦ equivalent circle diameter ≦ 0.5 mm → N ≦ 3 or less is OK.

    If there are four or more, NG “x” is assumed.

    When 0.5 mm <equivalent circle diameter, NG “×” is given if one occurs.

  A comparison was made between an example in which the mesh 239A was installed in the window 239 at the opening of the partition wall 238 partitioning the upper and lower sides in the developing unit 23, and the circulating developer was returned to the developing unit 23, and a conventional example in which such a mesh was not provided.

  In the conventional example, there is no means for breaking the toner aggregate, and the circulating developer is reused as it is. In the present invention, a window 239 (upper portion) that is an opening portion of a partition wall 238 that partitions a part of the interior of the developing device 23. The mesh 239A having the following openings (μm, carrier diameter ratio) is respectively installed on one end of the circulating recovery screw 237 on the conveyance direction side at a size of 20 mm × 20 mm. The recycle toner returned through the recycle pipe from the cleaning device 26 is supplied to the supply port 241 at the top of the circulation recovery screw 237, and a new toner replenishment port 242 is provided next to the recycle toner supply port 241, and the new toner is also provided. It is configured to supply.

  The mesh opening level is 75 μm (1.25 times the carrier diameter), 90 μm (1.5 times the same), 120 μm (2 times the same), 180 μm (3 times the same) 210 μm (3.5 times the same), The thickness was 300 μm (5 times the same) and 420 μm (7 times the same).

  As a conventional example (comparative example), no mesh was used.

  The experimental results of Example 1 are shown in Table 1.

  In the conventional case (no mesh), “fogging” after 50,000 copies have passed and “black spot defect” and “white spot defect” both exceed the reference value after 100,000 copies and an image quality defect occurs and becomes NG.

  That is, fogging due to developer aggregates occurred, and image defects due to large developer aggregates or foreign matter contamination occurred.

  When the mesh size is 75 μm (1.25 times the carrier diameter), “mesh clogging” occurs after 200,000 copies over the 250,000-copy durability guarantee period, and “developer spillage” occurs due to poor developer conveyance. Become.

  In the case of an opening of 90 μm (1.5 times), there was no “mesh clogging” until the 250,000-copy durability guarantee period, and image quality defects could be prevented during the target durability guarantee period.

Furthermore, when the image was continued for the endurance guarantee period to confirm the endurance margin, “mesh clogging” occurred at 300,000 copies.

  This was because the mesh opening was slightly small, and the image was continuously drawn for more than the endurance guarantee period, so that a large developer aggregate grew and “clogging” occurred.

  When the mesh size is 120 μm (2 times), 180 μm (3 times), and 210 μm (3.5 times), there is no “mesh clogging” until the 250,000-copy durability guarantee period, and image quality defects are prevented during the target durability guarantee period. did it.

Furthermore, when the endurance guarantee period was confirmed for confirmation of the endurance margin, even after 300,000 copies, “mesh clogging” was not observed, and good results were obtained with no image defects.

  When the mesh opening was 300 μm (5 times), mesh clogging did not occur until the 250,000-copy durability guarantee period, and image quality defects could be prevented during the target durability guarantee period.

  Furthermore, when the image was continued for more than the endurance guarantee period to confirm the endurance margin, fogging occurred at 300,000 copies. It is thought that fogging occurred because the mesh size was slightly large and the developer aggregate could not be sufficiently broken.

  When the mesh size is 420 μm (seven times), image quality defects such as “fogging” after 200,000 copies have passed and “black spot defects” and “white spot defects” after 250,000 copies have occurred and become NG.

  It is considered that the mesh opening is larger than the carrier particle size, so that the developer aggregate is broken or the function of removing foreign matters is low.

1 is an overall configuration diagram of an embodiment of an image forming apparatus of the present invention. It is a side view of an embodiment of a developing device used in the present invention. It is AA sectional drawing of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Photoconductor 23 Developing device 26 Cleaning means 230 Developing device main body 232 Developing roller 233 Cylindrical magnet body 234 Stir screw 235 Supply screw 236 Developer return means 237 Circulation collection screw 238 Partition 239 Window 239A Mesh 241 242 Supply port

Claims (3)

In an image forming apparatus having a developing unit that visualizes an electrostatic latent image formed on a photoreceptor as an electrostatic latent image carrier with a developer,
In the developing unit, a stirring screw that conveys the developer while stirring and a supply screw that supplies the developer to a developing roller as a developer carrying member are provided below the partition wall that partitions the upper and lower parts of the developing unit. And a developer return means for recovering excess developer supplied from the developing roller to the photosensitive member and a circulation recovery screw for circulating the developer from the developer return means are disposed above the partition wall. One of the circulation recovery screw and the stirring screw is disposed close to each other across the partition wall, and one of the partition walls in the vicinity where the circulation recovery screw and one of the stirring screws face each other at the shortest distance. Open at least one window to drop the developer from the top to the bottom, and provide a mesh in the window, and stir and supply the developer that has passed through the mesh to the developing roller. Image forming apparatus characterized by. The image forming apparatus according to claim 1, wherein the stirring screw that receives the developer from the circulation collection screw through the mesh is a stirring screw that is closest to the developing roller. The image forming apparatus according to claim 1, wherein
The developer is a two-component developer comprising magnetic carrier particles and non-magnetic toner particles, and the mesh opening is 1.5 to 5 times, preferably 2 to 3.5 times larger than the carrier average volume particle size. An image forming apparatus characterized by that.

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