JP2006106559A - Development apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining sufficiently thick image density, even when forming an image at a high printing ratio and a high speed, capable of preventing image quality from being reduced and capable of preventing the generation of problems, such as toner scattering and developer deterioration, and to provide a development apparatus that is used for the image forming apparatus. <P>SOLUTION: The development apparatus comprises a first developer carrier for carrying developer to the surface of an image forming body, a second developer carrier arranged on the moving direction downstream side of the surface of the image forming body from the first developer carrier, a developer supply chamber for supplying the developer to the first and second developer carriers, a first developer collection chamber for collecting the developer from the first developer carrier, and a second developer collection chamber for collecting the developer from the second developer carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device and an image forming apparatus.

  In recent years, high-speed and high-quality image quality has been required in electrophotographic image forming apparatuses.

  As the image forming speed increases, it is necessary to increase the rotation speed of the developing roller in order to obtain a sufficient image density in the developing unit. However, when the developing roller is rotated at a high speed, the developer on the developing roller scatters and so-called toner scattering stains occur that contaminates the inside of the apparatus. Further, there are many problems such as insufficient development performance and image density defects.

  As a means for solving this problem, a developing device has been proposed which uses two small-diameter developing rollers and attempts to suppress toner scattering by making the rotational speed of the developing roller equal to the moving speed of the photosensitive drum surface ( For example, see Patent Document 1 and Patent Document 2.)

  Patent Document 1 discloses a system in which a developer conveying magnet roller is provided between two developing rollers and a paddle that supplies developer, and the developer supplied from the paddle is supplied to the upper portion of the developing roller. Yes.

Patent Document 2 discloses a developing device that supplies a developer to each of two developing rollers.
JP 60-49372 A JP 2000-98749 A

  However, in the developing device of Patent Document 1, the developer carried on the first developing roller is transferred to the second developing roller as it is, and the toner contained in the developer used on the first developing roller. The toner density is already low, and when it is transferred to the second developing roller, the toner density is not sufficient to develop the electrostatic latent image. For this reason, there is a problem in that sufficient development ability cannot be exhibited when an image with a high printing rate is formed at high speed.

  In the developing device of Patent Document 2, since the developer in which the toner is used on the developing roller returns to the developer agitating unit, the toner density of the developer provided to the developing roller is increased unless sufficient developer agitation is performed. In electrophotographic copiers that are not stable, high-speed, and high-print-ratio images, the image density differs between the leading and trailing edges of the paper, although it is a solid image, or the longitudinal direction of the developing roller In-page image density differences such as different image densities may occur.

  In view of the above problems, the object of the present invention is to obtain a sufficient image density even when an image having a high printing rate is formed at high speed, there is no deterioration in image quality, and there are problems such as toner scattering and developer deterioration. It is an object of the present invention to provide a developing device that does not occur and an image forming apparatus to which the developing device is applied.

  The above object is achieved by the following configuration.

(Claim 1)
In a developing device of an image forming apparatus that forms a visible image by developing an electrostatic latent image formed on the surface of an image forming body with a developer containing toner,
A first developer carrying member for conveying the developer to the surface of the image forming body;
A second developer carrier disposed downstream of the first developer carrier in the moving direction of the surface of the image forming body and transporting the developer to the surface of the image forming body;
A developer supply chamber for supplying a developer to the first developer carrier and the second developer carrier;
A first developer recovery chamber for recovering the developer from the first developer carrier;
And a second developer recovery chamber for recovering the developer from the second developer carrying member.

(Claim 2)
Toner replenishing means for replenishing toner, developer collected in the first developer collecting chamber, developer collected in the second developer collecting chamber, and toner replenished by the toner replenishing means. A developer stirring chamber for stirring;
The developing device according to claim 1, wherein the developer stirred in the developer stirring chamber is conveyed to the developer supply chamber.

(Claim 3)
3. The developing device according to claim 1, wherein a moving speed of the surface of the second developer carrying member moves at substantially the same moving speed as the surface of the image forming body.

(Claim 4)
In a developing device of an image forming apparatus that forms a visible image by developing an electrostatic latent image formed on the surface of an image forming body with a developer containing toner,
A first developer carrying member for conveying the developer to the surface of the image forming body;
A second developer carrier disposed downstream of the first developer carrier in the moving direction of the surface of the image forming body and transporting the developer to the surface of the image forming body;
A first developer supply chamber for supplying a developer to the first developer carrier;
A second developer supply chamber for supplying a developer to the second developer carrier;
A developing device comprising: a developer collecting chamber for collecting developer from the first developer carrying member and the second developer carrying member.

(Claim 5)
Toner replenishing means for replenishing toner;
A developer agitating chamber for agitating the developer collected in the developer collecting chamber and the toner replenished by the toner replenishing means;
The developing device according to claim 4, wherein the developer stirred in the developer stirring chamber is transported to the first developer supply chamber and the second developer supply chamber.

(Claim 6)
The developer conveyed by the second developer carrier is not in contact with the surface of the image forming body,
6. The developing device according to claim 4, further comprising a toner flying unit that causes the toner contained in the developer conveyed by the second developer carrying member to fly to the surface of the image forming body.

(Claim 7)
A toner concentration detecting means for detecting a concentration of toner contained in the developer in the developer agitating chamber; a developing condition of the first developer carrying member based on the toner concentration detected by the toner concentration detecting means; 6. The developing device according to claim 2, further comprising a control unit that controls a developing condition of the developer carrying member.

(Claim 8)
A toner concentration detecting means for detecting the concentration of toner contained in the developer in the developer agitating chamber; a developing condition of the first developer carrier based on the toner concentration detected by the toner concentration detecting means; and the toner 6. The developing device according to claim 2, further comprising a control unit that controls the supply unit.

(Claim 9)
An image forming body, a charging means for charging the image forming body, an exposure means for forming an electrostatic latent image on the surface of the image forming body, and development for developing a visible image by developing the electrostatic latent image with a developer. In an image forming apparatus having an apparatus and a transfer unit that transfers the visible image to a transfer medium,
The image forming apparatus according to claim 1, wherein the developing device is the developing device according to claim 1.

  According to the first and fourth aspects of the present invention, since the developer supply chamber and the developer recovery chamber are separated from each other through the partition wall, the developer mixed with the recovered developer having a low toner concentration can be obtained. The toner can be prevented from being supplied to the developing carrier, and a sufficient toner density can be obtained even when an image having a high printing rate is formed at a high speed, and a good image without unevenness in the image density can be provided. Furthermore, problems such as toner scattering and developer deterioration do not occur.

  According to the second and fifth aspects of the present invention, since the developer agitating chamber for agitating the developer collected in the developer collecting chamber and the toner replenished by the toner replenishing means is provided, the first developer It becomes possible to provide a developer having an appropriate toner concentration for both the carrier and the second developer carrier.

  According to the third aspect of the present invention, the movement speed of the surface of the second developer carrier is approximately the same as that of the surface of the image forming body, so that the toner formed by the first developer carrier. Even when the image comes into contact with the developer conveyed by the second developer carrying member, it is hardly scratched, so that a good image can be obtained.

  According to the sixth aspect of the present invention, the developer conveyed by the second developer carrying member is not in contact with the surface of the image forming body and causes the toner to fly to the surface of the image forming body. Since the toner image formed on the developer carrier is not rubbed by the developer conveyed on the second developer carrier, a good image can be obtained.

  According to the seventh aspect of the present invention, the toner concentration detecting means is provided in the developer agitating chamber, and the control means is configured to carry the first and second developer carriers based on the toner concentration detected by the toner concentration detecting means. Since the body development conditions such as bias application voltage and rotation speed can be controlled, the burden of control processing is reduced and only one toner concentration detection means is required, simplifying the device, contributing to cost reduction, downsizing, and prevention of interference radio waves To do.

  According to the eighth aspect of the present invention, since the toner replenishing means is controlled based on the toner concentration detected by the toner density detecting means installed in the developer stirring chamber, the first developer carrier and the second developer carrying body are controlled. It is possible to provide a developer having an appropriate toner concentration for both of the developer carriers.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a sectional view schematically showing an image forming apparatus according to the present invention.

  An image forming apparatus 100 according to an embodiment of the present invention has an automatic document feeder 1 at the top of the apparatus main body, and includes an image reading unit 2, an image forming unit 3, an image forming body 4, a paper feeding unit 5, and a fixing device. T.

  The automatic document feeder 1 is a device that feeds documents one by one, conveys them to an image reading position, and discharges the document after image reading to a predetermined location.

  The automatic document feeder 1 includes a document placing table 101 on which a document is placed, a document separating unit 103 that separates a placed document, a document transporting unit 105 that transports the separated document, and a discharged document. In a document discharge means 107, a document discharge table 109 on which the discharged document is placed, and a pair of rollers used to reverse the front and back surfaces of the document in a duplex copy mode for reading images on both sides of the document. The document reversing means 111 is provided.

  In terms of the processing process, a plurality of documents (not shown) placed on the document placing table 101 are separated one by one by the document separating means 103 and directed to the image reading position via the document conveying section 105. Are transported.

  The document reading position is provided at a lower portion of the document conveying unit 105, where an image of the document is read through the slit 201 constituting the image reading device 2, and the read document is a document discharge unit 107. Is discharged onto the document discharge tray 109.

  The above process is repeated for the number of documents placed on the document placing table 101.

  The image reading unit 2 receives light from the first mirror unit 205 and the first mirror 215, which are formed by integrating a slit 201, a lamp 213 for irradiating a document, and a first mirror 215 that reflects reflected light from the document. A second mirror unit 207 in which the second mirror 217 and the third mirror 219 to be reflected are integrated in a substantially V shape, and an imaging lens 209 that forms an image of the reflected light from the third mirror 219 on the image sensor. And a linear imaging element (hereinafter referred to as CCD) 211 that photoelectrically converts a light image formed by the imaging lens 209 to obtain image information.

  The image information is temporarily stored in a memory (not shown) after appropriate image processing.

  When the document fed by the automatic document feeder 1 is read by the image reading unit 2, the first mirror unit 205 and the second mirror unit 207 are fixed at positions as shown.

  The image signals read by the image reading unit 2 are sequentially taken out from the memory, and are inputted as electric signals to the respective exposure optical systems as exposure means.

  The image forming unit 3 includes, for example, an image forming body 4 in which a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor is provided on a drum-shaped metal substrate, and a charger that is a charging means having a scorotron type. 320, a cleaning device 350 including an exposure optical system 330 that is an exposure unit, a developing device 8 that visualizes an electrostatic latent image, a transfer unit 340, and a blade (cleaning unit) that cleans the surface of the photosensitive drum 4 after transfer. Is the main component.

  The developing device 8 incorporates a two-component developer including a magnetic carrier (hereinafter simply referred to as a carrier) and a non-magnetic toner (hereinafter simply referred to as a toner), and is fixed in position and has a plurality of magnetic poles in the circumferential direction. It has a built-in magnet array and a non-magnetic rotatable cylindrical developer carrier, etc. The detailed configuration will be described later.

  The exposure optical system 330 is an exposure unit composed of a laser optical system, and the transfer unit 340 faces a part of the peripheral surface of the image forming body 4.

  Image formation by the image forming unit 3 and the image forming body 4 is performed as follows.

  With the start of the image forming process, the surface of the image forming body 4 that rotates clockwise is charged to a predetermined polarity by the charger 320.

  Next, exposure by an image signal by the exposure optical system 330 is performed, and an electrostatic latent image is formed on the image forming body 4.

  The electrostatic latent image is reversely developed by contact or non-contact development processing with a developer in the developing device 8 and converted into a toner image which is a visible image, and then transferred to a transfer medium P (simply called copy paper) by the action of the transfer means 340. ) Is transferred to the top.

  On the other hand, the surface of the image forming body 4 after completion of the transfer process is cleaned by the cleaning means 350, and preparations for new image formation are made.

  The copy paper P to which the toner image has been transferred is separated from the image forming body 4 while being subjected to the action of a separation claw (not shown) and conveyed toward the fixing device T, for example.

  The fixing device T includes a fixing roller T1 including a fixing heater, and a pressure roller T2 that rotates while being in pressure contact with the fixing roller. The toner forming the image is melted by heating and pressing with both rollers. The image is fixed on the copy paper P.

  After completion of the fixing process by the fixing device T, the copy paper P is conveyed by a paper discharge roller 603 provided downstream thereof, and is discharged onto a paper discharge tray provided outside the apparatus main body.

  Note that the toner in the developer is consumed by the development process. This is because a toner concentration detection sensor is provided at an appropriate place in the developing device 8 and the toner in the developing device is based on information from the sensor. Can be provided by known techniques.

  A first embodiment of the developing device according to the present invention will be described with reference to FIGS. FIG. 2 is a schematic sectional view showing the first embodiment of the developing apparatus according to the present invention.

  2, a is the rotation direction of the image forming body 4, b is the rotation direction of the first developer carrier 810, c is the rotation direction of the second developer carrier 820, and D1 is the developer carrier. A developer flow through 810, and D <b> 2, a developer flow through the second developer carrier 820.

  The developing device 8 includes an opening 800 provided at a position facing the image forming body 4, a first developer carrier 810 that faces the image forming body surface 41 at the opening 800 and conveys the developer, A second developer carrying member that is opposed to the image forming member surface 41 at the opening 800 and that is disposed downstream of the first developer carrying member 810 in the moving direction of the image forming member surface 41 and conveys the developer. The first developer carrier 810 and the second developer carrier 820 (hereinafter collectively referred to as a developing sleeve) are cylindrical members made of a nonmagnetic metal material such as aluminum or stainless steel. There is a built-in magnet in a fixed position. As is well known, the magnet has five magnetic poles S1, S2, N1, N2, and N3. Of these magnetic poles, N2 and N3 of the same polarity adjacent to each other form a repulsive magnetic field, and the developer after the development processing on the development sleeve can be peeled off as the development sleeve rotates, so that the first development is performed. The toner drops into the agent recovery chamber 840 and the second developer recovery chamber 850 due to the action of gravity.

  Developers dropped into the first developer recovery chamber 840 and the second developer recovery chamber 850 are respectively transported to the developer agitating chamber 860 by the screws 841 and 851 and newly supplied from toner supply means (not shown). The added toner is added and stirred to maintain the toner concentration appropriately. The developer having an appropriate toner concentration is sent to a developer supply chamber 870 having a developer supply / conveying member 871 and supplied to the first developer carrier 810 and the second developer carrier 820.

  The toner concentration detection unit 861 installed in the developer stirring chamber 860 includes, for example, a magnetic permeability sensor, and detects the toner concentration by measuring the magnetic permeability of the developer in the developer stirring chamber 860. The control means C1 is composed of a CPU (Central Processing Unit), a work memory, etc. (not shown), and controls a developer bias power source and a drive motor (not shown) of the developer carrier 810 and the developer carrier 820 by reading a program. The developing conditions such as the developing bias voltage applied to the image forming body 4 and the surface moving speed are controlled.

  The surface movement direction of the first developer carrier 810 is opposite to the surface movement direction of the image forming body 4, and the surface movement direction of the second developer carrier 820 is the surface movement direction of the image forming body 4. The forward direction. Further, the surface movement speeds of the first developer carrier 810 and the second developer carrier 820 are substantially the same as the surface movement speed of the image forming body 4.

  In the present embodiment, in order to more completely remove the developer from the developing sleeve, the elastic members function as the first developer collecting member and the second developer collecting member, respectively, which are in contact with the developer carriers 810 and 820. A flat plate 801 and an elastic flat plate 802 are provided. Further, a layer thickness regulating member 830 for regulating the thickness of the developer layer that is magnetically attracted and carried on the first and second developer carrying bodies 810 and 820 is provided with the image forming body 4 and the first developer carrying body 810 and 820, respectively. It is provided between the contact position with the first and second developer carriers 810 and 820 and the developer supply member 871.

  In the developer circulation in the developing device 8, the developer discharged from the first developer carrier 810 is collected in the first developer collecting chamber 840 and sent to the developer stirring chamber 860. On the other hand, the developer discharged from the second developer carrier 820 is collected in the second developer collection chamber 850 and sent to the developer stirring chamber 860. The developer merged from the first and second developer recovery chambers 840 and 850 is sent to the developer supply chamber 870 while a new toner is added and stirred, and again the first developer carrier and the second developer. Supplied to the carrier.

  Details of the developer circulation in the developing device 8 according to the first embodiment will be described with reference to FIG. FIG. 3A is a perspective view showing a schematic configuration of the developing device 8, and FIG. 3B is a cross-sectional view when viewed from the direction of arrow A in FIG.

  A screw 841 is provided as means for conveying the developer from the first developer recovery chamber 840 to the developer stirring chamber 860. The screw 841 is inscribed in the first developer recovery chamber 840 housing, and is formed of a spiral rib formed on the outer peripheral surface of a shaft (hereinafter also referred to as a rotation shaft) J1 with a predetermined pitch P1 in the axial direction. Further, a screw 851 is provided in the same configuration as the screw 841 as a means for transporting from the second developer recovery chamber 850 to the developer stirring chamber 860.

  A developer stirring member 843 is incorporated in the developer stirring chamber 860 so as to be substantially inscribed in the housing of the developer stirring chamber 860. The developer agitating member 843 is formed of a spiral rib formed with a pitch P2 in the axial direction over the outer periphery of the axis J2.

  To the developer stirring chamber 860 is connected toner supply means 7 for supplying toner, and the developer concentration in the developer stirring chamber 860 is detected by the toner concentration detection sensor 861 shown in FIG. Based on the detected value, unused toner (hereinafter referred to as new toner) is supplied from the toner replenishing means 7 through the toner supply port 813. The new toner and the developer are stirred by a spiral screw 843 provided with a stirring member, and the toner concentration is controlled appropriately.

  Further, in order to convey the developer in the developer agitating chamber 860 to the developer supply chamber 870, as shown in FIG. 3B, a developer agitating and conveying member comprising a reversible spiral screw in the developer conveying tube 845. 847 is inserted, and the conveying member tube 845 is inserted into the developer discharge port 846 and the developer supply port 848 of the developer supply chamber 870. Further, the developer stirring / conveying member 847 is rotated by power (not shown) via the gear 893. With such a structure, the developer conveyed from the developer stirring chamber 860 can be sequentially supplied to the developer supply chamber 870. In FIG. 3B, t represents the toner flow, and D and D5 represent the developer flow.

  The developer supply chamber 870 has both a function of supplying the developer to the first and second developer carriers 810 and 820 and a function of conveying the developer from the developer stirring chamber 860 to the entire developer supply chamber 870. A supply member 871 is included. The developer supply member 871 is substantially equidistant from the developer carriers 810 and 820 and is disposed at a position where the developer can be supplied to the developer carriers 810 and 820. The developer supply member 871 is a cylindrical member made of a non-magnetic metal material such as aluminum or stainless steel. A spiral magnet is built in the developer supply member 871 so that only the magnet portion can be rotated by power (not shown). is there. With such a structure, the developer conveyed from the developer stirring chamber 860 can be sequentially supplied to the first developer carrier 810 and the second developer carrier 820.

  The developer movement amount in the developer stirring chamber 860 is such that the first developer carrier 810 and the second developer carrier 820 are the first developer collection chamber 840 and the second developer collection chamber 850, respectively. More than the total amount of developer movement.

  In this embodiment, since the first developer recovery chamber 840, the second developer recovery chamber 850, and the developer supply chamber 870 are separated by a housing (also referred to as a partition wall), recovery with a low toner concentration is performed. The developer mixed with the developer can be prevented from being supplied to the developer carrying member, and even when an image with a high printing rate is formed at a high speed, a sufficient image density can be obtained and a good image without density unevenness can be provided.

  In addition, the toner density detecting means 861 enters the developer agitating chamber 860 in which the developer conveyed from the first developer collecting chamber 840 and the second developer collecting chamber 850 and the toner replenished from the toner replenishing means 7 are mixed. Thus, the control unit C1 can control the development conditions based on one toner density, and stable image formation can be achieved with a simple configuration.

  A second embodiment of the developing device according to the present invention will be described with reference to FIGS. FIG. 4 is a sectional view conceptually showing a second embodiment of the developing apparatus according to the present invention.

  In FIG. 4, e is the rotation direction of the first developer carrier 811, f is the rotation direction of the second developer carrier 821, D3 is the developer flow through the developer carrier 811, and D4 is the first flow. The flow of the developer passing through the two developer carriers 821 is shown. Note that the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The developing device 8b according to the second embodiment includes a first developer carrier 811 provided in an opening 803 provided at a position facing the image forming body 4, and a first developer carrier 811. And a second developer carrier 821 disposed in the opening 804 on the downstream side in the moving direction of the image forming body surface 41 (hereinafter collectively referred to as a developing sleeve), and as the developing sleeve rotates. The developed developer on the developing sleeve is peeled off and falls into the developer collecting chamber 852 due to the action of gravity.

  The developer sent to the developer recovery chamber 852 is further conveyed to the developer stirring chamber 860 by the screw 845, and the developer having an appropriate toner concentration is the first developer supply chamber 875 having the developer supply member 877. And the second developer supply chamber 876 to be supplied to the first developer carrier 811 and the second developer carrier 821. The control means C1 controls the development conditions of the first developer carrier 811 and the second developer carrier 821 based on the toner density detected by the toner density detector 861.

  Further, the surface movement direction of the first developer carrier 811 is the forward direction with respect to the surface movement direction of the image forming body 4, and the surface movement direction of the second developer carrier 821 is the surface movement direction of the image forming body 4. Is the opposite direction. Further, the surface movement speeds of the first developer carrier 811 and the second developer carrier 821 are substantially the same as the surface movement speed of the image forming body 4.

  Further, the image forming body 4 and the second developer carrier 821 are installed at a predetermined interval, that is, in a non-contact state, and the developer conveyed by the second developer carrier 821 Toner flying means H for flying the contained toner onto the image forming body surface 41 is provided.

  The toner flying means H applies a superimposed bias voltage in which an AC bias voltage is superimposed on a DC bias voltage, which is used in a known “jumping development system”, to fly the toner to the surface of the image forming body. For example, it is constituted by a power source that generates a bias voltage, and the flying condition of the toner including the DC bias voltage and the AC bias voltage is controlled by the control means C1. By doing so, the toner image developed by the first developer carrier 811 is further developed by flying the toner in a non-contact state with the second developer carrier 821, so that the second development is performed. Sufficient image density can be obtained without the toner image being disturbed by rubbing with the agent carrier 821.

  Layer thickness regulating members 831 and 832 for regulating the thickness of the developer layer that is magnetically attracted and carried on the developer carrying bodies 811 and 821 are the image forming body 4 and the first and second developers. It is provided in the middle of the contact position with the carriers 811 and 821 and the first developer supply chamber 875 and the second developer supply chamber 876.

  In the developer circulation in the developing device 8b, the developer discharged from the first developer carrier 811 and the developer discharged from the second developer carrier 821 merge into the developer recovery chamber 852. The merged developer is fed with new toner and stirred and sent to the first developer supply chamber 875 and the second developer supply chamber 876. The first developer carrier and the second developer supply chamber 876 are again sent from the respective developer supply chambers. 2 is supplied to the developer carrier.

  Details of the developer circulation in the developing device 8b according to the second embodiment will be described with reference to FIG. FIG. 5A is a perspective view showing a schematic configuration of the developing device 8b, and FIG. 5B is a cross-sectional view seen from the direction indicated by the arrow B in FIG.

  The developer recovery chamber 852 has a screw 845 as a means for transporting the developer. The screw 845 is a spiral member that is inscribed in the housing of the developer recovery chamber 852, and the developer conveyed by the screw 845 falls to the developer stirring chamber 860 by gravity.

  In the developer agitating chamber 860, as in the developing device 8 according to the first embodiment, the new toner and developer supplied from the toner replenishing means 7 are agitated by the developer agitating member 843 so that the toner concentration is appropriately adjusted. In a controlled state, they are conveyed to the first developer supply chamber 875 and the second developer supply chamber 876, respectively.

  In the developer agitation chamber 860, a developer agitation transport member 845 that transports the developer to the first developer supply chamber 875 and the second developer supply chamber 876 is fitted into the developer discharge port 846.

  The first developer supply chamber 875 and the second developer supply chamber 876 have a function of supplying the developer to the first developer carrier 811 and the second developer carrier 821, respectively, and the developer stirring chamber. A developer supply member 877 having a function of conveying the entire area from 860 to the first and second developer supply chambers 875 and 876. The developer supply member 877 is disposed at a position where the developer can be supplied to the first and second developer carriers 811 and 821. The developer supply member 877 has the same structure as the developer supply member 871 in FIG.

In this embodiment, since the first developer supply chamber 875 and the second developer supply chamber 876 are separated by the housing, the developer mixed with the collected developer having a low toner concentration is loaded with the developer. It can be prevented from being supplied to the body, and a sufficient image density can be obtained even when an image having a high printing rate is formed at high speed.
Further, in the present embodiment, the developer recovery chamber 852 communicates with the developer agitation chamber 860, and the developer recovery chamber 852 is arranged so that the developer in the developer recovery chamber 852 falls into the developer agitation chamber 860. Since it is positioned directly above the developer stirring chamber 860, it is not necessary to provide a special conveying member, and the configuration can be simplified.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<Example 1>
The developing device 8 shown in FIGS. 2 and 3 is mounted on the image forming apparatus 100 shown in FIG. 1 to form an image.

  In the developing device 8, the first developer carrier 810 and the second developer carrier 820 are both 18 mm diameter aluminum tubes, and the first developer carrier 810 and the second developer carrier. The speed ratio of the image forming body 820 to the image forming body 4 (developer carrying member moving speed / image forming body moving speed: hereinafter, development θ) was 1.0.

The main configuration of the image forming apparatus 100 is as follows, and the same configuration is used in the following examples and comparative examples.
Image forming apparatus: A4 width 80 monochrome / monochrome digital image forming body moving speed (process speed) V: 400 mm / second image forming body drum diameter: 80 mm
Charging voltage V ₀ by the charging device: −700 V (variable: standard value on the left)
Exposure means: Semiconductor laser (wavelength 780 nm)
Image forming body surface potential Vi during solid exposure by exposure apparatus: −50 V
Developer carrier potential Vdc: -500 V (variable: left is standard value)
Development bias voltage AC component Vac: rectangular wave of 1 kVp-p (frequency 5 kHz)
Developer carrier-photoreceptor distance Ds: about 0.30 mm
Developer transport amount D on developer carrier: about 25 mg / cm ²
Developer carrier magnetization length L: 310 mm
Toner: Polymerized toner having a volume average particle diameter of 4.5 μm described in JP-A No. 2004-38113
Carrier: Magnetic carrier having a volume average particle diameter of 25 μm and a magnetization strength of 60 emu / g described in JP-A No. 2004-38113 <Example 2>
Instead of the developing device 8 of Example 1, the developing device 8b shown in FIGS. 4 and 5 was mounted on the image forming apparatus 100 to form an image.

  In the developing device 8b, the first developer carrier 811 and the second developer carrier 821 both use aluminum tubes having a diameter of 18 mm, and the development θ is 1.0.

<Comparative Example 1>
In place of the developing device 8 of the first embodiment, the single developing roller type developer non-circulating configuration shown in FIG. 6 (developer supply / recovery chamber 802 is not divided between the developer supply side and the recovery side) The apparatus 8c was mounted on the image forming apparatus 100 to form an image. The developer carrier 801a was an aluminum tube having a diameter of 18 mm, and development θ = 2.0.
<Comparative example 2>
In the developing device 8c of Comparative Example 1, an image was formed with development θ = 1.2.
<Comparative Example 3>
Instead of the developing device 8 of the first embodiment, a developing device having a single developing roller type developer 1 circulation configuration (a configuration in which the developer supply chamber 802a and the developer recovery chamber 802b are separated by a partition wall) shown in FIG. 8d was attached to the image forming apparatus 100 to form an image. The developer carrying member 801a was an aluminum tube having a diameter of 18 mm, and the development θ was 2.0.
<Comparative example 4>
In the developing device 8c of Comparative Example 1, the developer carrier 801a was replaced with an aluminum tube having a diameter of 30 mm, and an image was formed with development θ = 2.0.
<Comparative Example 5>
In the developing device 8d of Comparative Example 3, the developer carrying member 801a was replaced with an aluminum tube having a diameter of 30 mm, and an image was formed with development θ = 2.0.

<Comparative Example 6>
Instead of the developing device 8 of the first embodiment, the two developer roller type developer delivery type shown in FIG. 8 (a configuration in which the developer is delivered from the first developing roller 801b to the second developing roller 801c), and A developing device 8e having a developer non-circulation configuration (a configuration in which the developer supply / recovery chamber 802 is not divided between the developer supply side and the recovery side) is mounted on the image forming apparatus 100 to form an image. Both the first developing roller 801b and the second developing roller 801c were aluminum tubes having a diameter of 18 mm, and development θ = 1.0.

<Comparative Example 7>
In place of the developing device 8 of the first embodiment, the two developer roller type developer delivery type shown in FIG. 9 and the developer 1 circulation configuration (the developer supply chamber 802a and the developer recovery chamber 802b are separated from each other by a partition wall). The developing device 8f having a configuration separated in (1) was mounted on the image forming apparatus 100 to form an image. Both the first developing roller 801b and the second developing roller 801c were aluminum tubes having a diameter of 18 mm, and development θ = 1.0.

<Comparative Example 8>
Instead of the developing device 8 of the first embodiment, the two independent developing roller type developer developer type shown in FIG. 10 (a configuration in which the developer is supplied to each of the first developing roller 801b and the second developing roller 801c), In addition, an image was formed by mounting the developing device 8g having a developer non-circulating configuration on the image forming apparatus 100. Both the first developing roller 801b and the second developing roller 801c were aluminum tubes having a diameter of 18 mm, and development θ = 1.0.

  6 to 10, an arrow G indicates the direction in which the developer is conveyed. Line F indicates the flow of the developer.

<Evaluation method and evaluation criteria>
The images obtained in Examples 1 and 2 and Comparative Examples 1 to 8 were ranked as follows. The obtained results are shown in Table 1.

(Image density)
The image density at the four corners of the A3 size whole surface solid image was measured.
When the 4-point average density was 1.35 or more, it was judged as ◯, and when the 4-point average density was less than 1.35, it was judged as x.
In addition, when the difference between the front side and the back of the rear end of the image traveling direction was less than 0.05, it was judged as ◯, and when it was 0.05 or more, it was judged as x.
Furthermore, when the density difference between the front end and the rear end on the near side of the image was less than 0.05, it was judged as ◯, and when it was 0.05 or more, it was judged as x.

(Sweeping / Missing)
Visual evaluation (use limit sample samples) of whether solid or halftone patch images have thinned portions (= chips) or darkened portions (= sweep) at the leading and trailing edges of the paper in the paper conveyance direction did.
If there was no chipping or sweeping, it was judged as “good”, and if any one was present, it was judged as “poor”.

(Toner spent)
A real image test (A4 size continuous 10,000 prints with an average printing rate of 6%) was performed, the developer was collected, and the toner spent on the carrier surface was measured.
Toner spent is ○ when the carrier transmittance is 85% or more when 5 g of the carrier obtained by separating the toner from the developer is dissolved in 100 ml of methyl ethyl ketone solvent (MEK), and 80% or more and less than 85%. Was Δ, and when it was less than 80%, it was judged as x.

(Toner scattering)
After the actual shooting test was completed, the toner scattering state around the developing roller was visually evaluated, and it was judged as ◯ when there was no scattering, Δ when it was smudged with a finger, and x when it was clearly visible.

  As is apparent from Table 1, when one developing roller is used, a developing roller of 18 mm in diameter secures development θ = 2.0 in order to obtain a sufficient image density in a high-speed process at a process speed of 400 mm / second. Therefore, it is necessary to set the rotation speed of the developing roller higher than that of the developing roller having a large diameter of 30 mm (Comparative Example 1). However, in this case, developer durability performance and toner scattering performance deteriorate. If the rotation speed of the developing roller is set to be the same as that of a developing roller having a large diameter of 30 mm (Comparative Example 2), the development θ becomes low and a sufficient image density cannot be obtained.

  Further, when a single developing roller is used and a large-diameter 30 mm developing roller is used, there is an advantage that a sufficient image density can be obtained without setting the developing roller speed high (comparison). Example 4) Since the width of contact of the developer on the developing roller with the surface of the photosensitive member (expressed as contact width) is wide, image defects such as chipping and sweeping are likely to occur at the leading and trailing edges of the patch image. It is disadvantageous in terms.

  When a single developing roller is used, in addition to the above problems, in the case of a developing roller having a diameter of 18 mm or a developing roller of 30 mm in diameter, in the case of a developer non-circulating configuration, a difference in the density of the front and rear ends and a difference in the front and back densities Will occur. By adopting the developer 1 circulation configuration, the problems of the front-rear end density difference and the front-rear density difference are solved (Comparative Example 3 and Comparative Example 5). Such a problem is not solved.

  In the case of using the two developing rollers and the developer delivery type (Comparative Example 6 and Comparative Example 7), the developer carried and transported by the first developing roller remains as it is in the second developing roller. Since it is transferred to the developing roller and used for development, when developing a portion with a high image printing ratio, the developer after being used for development with the first developing roller already has a low toner concentration. When developing with the second developing roller, sufficient developing ability cannot be exhibited. In this case as well, in the case of the developer non-circulation configuration (Comparative Example 6), there are a front-rear edge density difference and a front-rear density difference.

  In addition, when two developing rollers are used and the developer independent supply type, since both of the two developing rollers have sufficient developing ability, a sufficient level of image density can be obtained. However, in the case of the developer non-circulating configuration (Comparative Example 8), there are a front-rear end density difference and a front-rear density difference.

  On the other hand, in the case of the developer 1 circulation configuration (Example 1 and Example 2), there is no difference between the front and rear end density differences and the front and rear density differences at a sufficient level of image density, and the image quality is also good. Furthermore, the developer durability performance and the toner scattering performance were at a level with no problem, and all the performance required in the high-speed process could be satisfied.

1 is a cross-sectional view schematically showing an image forming apparatus according to the present invention. 1 is a schematic sectional view showing a first embodiment of a developing device according to the present invention. FIG. 3A is a perspective view showing a schematic configuration of the developing device according to the first embodiment, and FIG. 3B is a cross-sectional view seen from the direction of arrow A in FIG. is there. It is a schematic sectional drawing which shows 2nd Embodiment of the developing device which concerns on this invention. FIG. 5A is a perspective view illustrating a schematic configuration of the developing device according to the second embodiment, and FIG. 5B is a cross-sectional view as viewed from the direction indicated by the arrow B in FIG. is there. 6 is a cross-sectional view showing a schematic configuration of a developing device according to Comparative Examples 1, 2, and 4. FIG. 6 is a cross-sectional view illustrating a schematic configuration of a developing device according to Comparative Examples 3 and 5. FIG. 10 is a cross-sectional view illustrating a schematic configuration of a developing device according to Comparative Example 6. FIG. 10 is a cross-sectional view illustrating a schematic configuration of a developing device according to Comparative Example 7. FIG. 10 is a cross-sectional view illustrating a schematic configuration of a developing device according to Comparative Example 8. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Automatic document feeder 2 Image reading part 3 Image forming part 4 Image forming body 5 Paper feeding part 8 Developing device 810, 811 First developer carrier 820, 811 Second developer carrier 840 First developer Recovery chamber 850 Second developer recovery chamber 852 Developer recovery chamber 860 Developer agitation chamber 861 Toner concentration detection means 870 Developer supply chamber 875 First developer supply chamber 876 Second developer supply chamber C1 control means

Claims (9)

In a developing device of an image forming apparatus that forms a visible image by developing an electrostatic latent image formed on the surface of an image forming body with a developer containing toner,
A first developer carrying member for conveying the developer to the surface of the image forming body;
A second developer carrier disposed downstream of the first developer carrier in the moving direction of the surface of the image forming body and transporting the developer to the surface of the image forming body;
A developer supply chamber for supplying a developer to the first developer carrier and the second developer carrier;
A first developer recovery chamber for recovering the developer from the first developer carrier;
And a second developer recovery chamber for recovering the developer from the second developer carrying member. Toner replenishing means for replenishing toner, developer collected in the first developer collecting chamber, developer collected in the second developer collecting chamber, and toner replenished by the toner replenishing means. A developer stirring chamber for stirring;
The developing device according to claim 1, wherein the developer stirred in the developer stirring chamber is conveyed to the developer supply chamber. 3. The developing device according to claim 1, wherein a moving speed of the surface of the second developer carrying member moves at substantially the same moving speed as the surface of the image forming body. In a developing device of an image forming apparatus that forms a visible image by developing an electrostatic latent image formed on the surface of an image forming body with a developer containing toner,
A first developer carrying member for conveying the developer to the surface of the image forming body;
A second developer carrier disposed downstream of the first developer carrier in the moving direction of the surface of the image forming body and transporting the developer to the surface of the image forming body;
A first developer supply chamber for supplying a developer to the first developer carrier;
A second developer supply chamber for supplying a developer to the second developer carrier;
A developing device comprising: a developer collecting chamber for collecting developer from the first developer carrying member and the second developer carrying member. Toner replenishing means for replenishing toner;
A developer agitating chamber for agitating the developer collected in the developer collecting chamber and the toner replenished by the toner replenishing means;
The developing device according to claim 4, wherein the developer stirred in the developer stirring chamber is transported to the first developer supply chamber and the second developer supply chamber. The developer conveyed by the second developer carrier is not in contact with the surface of the image forming body,
6. The developing device according to claim 4, further comprising a toner flying unit that causes the toner contained in the developer conveyed by the second developer carrying member to fly to the surface of the image forming body. A toner concentration detecting means for detecting a concentration of toner contained in the developer in the developer agitating chamber; a developing condition of the first developer carrying member based on the toner concentration detected by the toner concentration detecting means; 6. The developing device according to claim 2, further comprising a control unit that controls a developing condition of the developer carrying member. A toner concentration detecting means for detecting the concentration of toner contained in the developer in the developer agitating chamber; a developing condition of the first developer carrier based on the toner concentration detected by the toner concentration detecting means; and the toner 6. The developing device according to claim 2, further comprising a control unit that controls the supply unit. An image forming body, a charging means for charging the image forming body, an exposure means for forming an electrostatic latent image on the surface of the image forming body, and development for developing a visible image by developing the electrostatic latent image with a developer. In an image forming apparatus having an apparatus and a transfer unit that transfers the visible image to a transfer medium,
The image forming apparatus according to claim 1, wherein the developing device is the developing device according to claim 1.

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