JP2004226798A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of background fogging in an image forming apparatus provided with a toner recycling means. <P>SOLUTION: A magnetic permeability sensor detecting the toner concentration and a reflecting sensor detecting the density of an image carrier surface are provided inside a developing device. The image carrier surface density in a non image area is observed by the reflecting sensor. When the detected reflected density value is equal to or below a reference value, decision is made by a control means that back ground fogging occurs and toner replenishing control by the magnetic permeability sensor is varied in the direction lowering the toner concentration. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that performs development using a two-component developer by an electrophotographic method, and more particularly, to an image forming apparatus that employs a toner recycling method that collects and reuses transfer residual toner.
[0002]
[Prior art]
In an example of an image forming process for forming an image by an electrophotographic method, an electrostatic latent image is formed on an image carrier such as a photoconductor, and the formed electrostatic latent image is developed by a developing unit to form an image on the image carrier. A toner image is formed, the formed toner image is transferred to a transfer sheet by a transfer unit, and the transferred toner image is fixed to the transfer sheet by a fixing unit to form an image on the transfer sheet. Further, in another example, a toner image on an image forming body such as a photoreceptor is transferred to an intermediate transfer body as an image carrier, and is transferred from the intermediate transfer body to a transfer paper by a transfer unit and fixed. An image is formed on the substrate.
[0003]
In the developing step in the image forming step, development using a two-component developer containing a non-magnetic toner and a magnetic carrier is often used, and a developing bias voltage of a DC bias is applied at the time of development.
[0004]
In the development using the two-component developer, since only the toner is consumed by the development, it is necessary to supply an appropriate amount of new toner corresponding to the consumed amount, and the toner is supplied.
[0005]
Further, the toner image formed on the image carrier is transferred onto a transfer paper or an intermediate transfer body by a transfer unit. At this time, untransferred toner remaining on the image carrier without being transferred is cleaned by a cleaning unit. A recycling method is adopted in which the toner cleaned by the cleaning means and collected in the cleaning device is transported to the developing device and reused. When the recycling method is adopted, a waste toner box for collecting the collected toner is not required, so that the waste can be reduced and the method can be made environmentally friendly.
[0006]
The toner (recycled toner) collected by the cleaning unit in the cleaning device is a toner that has been scraped and conveyed by a cleaning blade or the like. ), The fluidity is low, it is difficult to mix with the carrier, and the chargeability is inferior. When it is developed again, it causes problems such as background fogging, which is also called background fouling, and character thickening in which the character portion is developed thicker. easy. This phenomenon has almost no problem while the ratio of the recycled toner in the developer (toner concentration) in the developer is low, but becomes a problem when the ratio is high. The charge amount (Q / M) of the recycled toner tends to be smaller than that of the new toner, and FIG. 8 shows the relationship between the charge amounts of the new toner and the recycled toner.
[0007]
In addition, when a small particle size toner or a toner manufactured by a polymerization method having a sharp particle size distribution is used, the above-mentioned recycled toner is used because of high image quality such as resolution, gradation, and character reproducibility. The problem when using is remarkably recognized.
[0008]
In an image forming apparatus employing a toner recycling system using a two-component developer, toner replenishment is performed by determining the toner density in the developing device with a magnetic permeability sensor (hereinafter also referred to as an L sensor) as a method of replenishing toner in the developing device. And a method in which the density of a patch image formed on an image carrier is detected by a light reflection type sensor (hereinafter, also referred to as a P sensor), and toner is supplied by judging the density.
[0009]
The L sensor is less affected by environmental changes, developer deterioration, and the like than the P sensor, and can stably detect the toner concentration. However, even if control is performed to supply new toner based on the detection of the toner density in the developing device by the L sensor, background fogging will occur if the charged state of the toner is insufficient.
[0010]
Conventionally, when the state in which image formation is not performed exceeds a predetermined time, the amount of toner adhering to the non-image portion on the image carrier is detected, and the developer is stirred in the developing device based on the detection result. Japanese Patent Application Laid-Open No. H11-163,097 discloses that the amount of toner charge is adjusted or toner density is adjusted to reduce background fog.
[0011]
Further, a toner consumption amount at a predetermined position on an image carrier is detected, and when the toner adhesion amount exceeds a predetermined amount, forcible consumption control is performed so as to forcibly consume the toner (for example, see Japanese Patent Application Laid-Open No. H11-163873). 2).
[0012]
In an image forming apparatus employing the toner recycling method, the amount of toner consumed is calculated from image data to be printed, and the ratio of the recycled toner in the developing device to the toner is estimated based on the calculated amount. Also, transfer conditions are controlled in accordance with the ratio of recycled toner (see, for example, Patent Document 3).
[0013]
[Patent Document 1]
JP-A-2000-75574
[0014]
[Patent Document 2]
JP 2000-75575 A
[0015]
[Patent Document 3]
JP 2000-267366 A
[0016]
[Problems to be solved by the invention]
Since the recycled toner is inferior to the new toner in chargeability, the image forming apparatus employing the toner recycling method tends to cause background stain on the image carrier and transfer paper.
[0017]
{Circle around (1)} A first object of the present invention is to provide an image forming apparatus provided with a recycle unit for automatically transporting toner collected in a cleaning device to a developing device so as to prevent the occurrence of background contamination. An object of the present invention is to provide a forming apparatus.
[0018]
{Circle over (2)} A second object of the present invention is to provide an image forming apparatus provided with recycling means for temporarily collecting the toner collected in the cleaning device in a recycled toner storage tank and conveying the collected toner from the recycled toner storage tank to the developing device. An object of the present invention is to provide an image forming apparatus improved so as not to generate background stain.
[0019]
[Means for Solving the Problems]
The first object is achieved by the structure described in claims 1 to 9, and the second object is achieved by the structure described in claims 10 to 16.
[0020]
According to the first aspect of the present invention, there is provided a method for developing a latent image on an image carrier by using a developer carrier carrying a developer comprising a non-magnetic toner and a magnetic carrier. Developing device, a transfer device for transferring a visible image on the image carrier to transfer paper, a cleaning device disposed downstream of the transfer device for cleaning non-magnetic toner on the image carrier, and a cleaning device for cleaning the cleaned toner. In an image forming apparatus having a recycling unit that conveys to the developing device and a control unit,
The developing device has a magnetic permeability sensor that detects the toner concentration inside,
A reflective sensor for detecting the density of the image carrier surface,
The reflection type sensor monitors the image carrier surface density in the non-image area, and when the detected reflection density value is equal to or less than the reference value, the control unit determines that background fogging has occurred, and supplies toner by the magnetic permeability sensor. An image forming apparatus, wherein control is changed. ".
[0021]
According to the first aspect of the present invention, even in an image forming apparatus provided with a recycling unit for automatically transporting the toner collected in the cleaning device to the developing device, background stains on the image carrier and the transfer paper can be obtained. Improvements that do not occur will be made.
[0022]
According to a second aspect of the present invention, there is provided a method of using a toner containing 65% by number or more of toner particles having a volume average particle diameter of 2 to 8 μm and a shape coefficient in a range of 1.2 to 1.6. 2. The image forming apparatus according to claim 1, wherein:
[0023]
According to the second aspect of the present invention, high quality images of high resolution are continuously obtained while a large number of prints are performed, and an improvement is made such that background contamination does not occur on the image carrier or transfer paper. The Rukoto.
[0024]
According to a third aspect of the present invention, there is provided the image according to the first or second aspect, wherein a reflection density of a surface of the image carrier in an area which is not affected by a high-pressure load is set as the image forming condition. Forming apparatus. "
[0025]
According to the third aspect of the present invention, a portion where the toner is not electrostatically attached due to being unaffected by the charged state of the toner on the image carrier is set as a reference value for detecting background contamination. Thus, the background dirt is detected with high accuracy, and an improvement is made so that the background dirt does not occur.
[0026]
The invention according to claim 4 is the image forming apparatus according to any one of claims 1 to 3, wherein the monitored non-image area is a non-image area at an image forming interval. .
[0027]
According to the fourth aspect of the present invention, the most suitable location for detecting the background stain is set as the detection location, so that the background stain can be detected with high accuracy and the background stain does not occur. In addition, since the printing operation is constantly monitored without stopping, the stability of the apparatus can be improved without lowering the productivity.
[0028]
The invention according to claim 5 is the image forming apparatus according to any one of claims 1 to 4, wherein, when it is determined that background fogging has occurred, the control unit prohibits toner supply. .
[0029]
According to the fifth aspect of the present invention, when the control means determines that the background fogging has occurred, the toner concentration is reduced by prohibiting the toner replenishment, the toner chargeability is improved, and the background contamination is prevented. Significant improvements will be made.
[0030]
The image forming apparatus according to any one of claims 1 to 4, wherein, when it is determined that the background fog has occurred, the control unit changes a reference value for performing toner supply determination. Device. "
[0031]
According to the sixth aspect of the invention, when the control means determines that the background fogging has occurred, the reference value for performing the toner replenishment determination is changed to be low, so that the toner density is reduced and the chargeability of the toner is improved. The improvement is made so that the background stain does not occur.
[0032]
The image forming apparatus according to any one of claims 1 to 4, wherein the control unit changes the toner supply amount when it is determined that background fogging has occurred. is there.
[0033]
According to the present invention, when the control means determines that the background fogging has occurred, by changing the toner replenishment amount to be smaller than the normal replenishment amount, the toner density is reduced and the chargeability of the toner is improved. Thus, an improvement is made so that the background stain does not occur.
[0034]
The invention according to claim 8, wherein the image forming apparatus according to any one of claims 1 to 4, wherein, when it is determined that background fogging has occurred, the control unit limits the toner supply amount. is there.
[0035]
According to the present invention, when the control means determines that the background fogging has occurred, the upper limit of the replenishing amount for performing the toner replenishment is limited, so that the toner density is reduced and the chargeability of the toner is improved. Thus, an improvement is made so that the background stain does not occur.
[0036]
According to a ninth aspect of the present invention, there is provided an image forming apparatus, wherein an image is formed by changing toner supply control, and a state where a reflection density value detected by the reflection type sensor exceeds the reference value is a predetermined time or a predetermined printing time. The image forming apparatus according to any one of claims 5 to 8, wherein after a lapse of the number, the control unit determines that the background fog has been improved and returns to a normal toner supply condition. .
[0037]
According to the ninth aspect of the present invention, even after the background dirt is improved, the state is maintained for several prints, and then the normal toner replenishment condition which was initially performed is restored. Then, an improvement is made in which the state in which the background stain is not generated is maintained.
[0038]
According to a tenth aspect of the present invention, there is provided a method for developing a latent image on an image carrier by using a developer carrier carrying a developer comprising a non-magnetic toner and a magnetic carrier. Developing device, a transfer device for transferring a visible image on the image carrier to transfer paper, a cleaning device disposed downstream of the transfer device for cleaning non-magnetic toner on the image carrier, and a cleaning device for cleaning the cleaned toner. In an image forming apparatus having a recycling unit that conveys to the developing device and a control unit,
A toner replenishing unit capable of changing a replenishment ratio between the new toner and the recycled toner to be replenished to the developing device,
A magnetic permeability sensor for detecting a toner concentration inside the developing device,
A reflective sensor for detecting the density of the image carrier surface,
The surface density of the image carrier in the non-image area is monitored by the reflection type sensor, and when the detected reflection density value is equal to or less than the reference value, the control unit determines that the background fog has occurred, An image forming apparatus wherein a supply ratio is changed. ".
[0039]
According to the tenth aspect of the present invention, in the image forming apparatus provided with a recycling unit for temporarily collecting the toner collected in the cleaning device in the recycled toner storage tank and conveying the toner from the recycled toner storage tank to the developing device, An improvement will be made so that background contamination does not occur on the carrier or the transfer paper.
[0040]
According to an eleventh aspect of the present invention, there is provided a method of using a toner containing 65% by number or more of toner particles having a volume average particle diameter of 2 to 8 μm and a shape coefficient in a range of 1.2 to 1.6. 11. The image forming apparatus according to claim 10, wherein:
[0041]
According to the eleventh aspect of the present invention, high-quality high-quality images are continuously obtained while a large number of prints are performed, and an improvement is made such that background contamination does not occur on the image carrier or transfer paper. The Rukoto.
[0042]
According to a twelfth aspect of the present invention, there is provided the image according to the tenth or eleventh aspect, wherein a reflection density of an image carrier surface in an area not affected by a high-pressure load is used as the image forming condition as the reference value. Forming apparatus. "
[0043]
According to the twelfth aspect of the present invention, a portion where no toner adheres on the image carrier is set as the reference value for detecting background contamination, so that background contamination can be detected with high accuracy. An improvement will be made so as not to cause stains.
[0044]
The invention according to claim 13 is the image forming apparatus according to any one of claims 10 to 12, wherein the monitored non-image area is a non-image area at an image forming interval. .
[0045]
According to the thirteenth aspect of the present invention, the most suitable portion for detecting the background stain is set as the detection portion, so that the background stain can be detected with high accuracy and the background stain does not occur. Will be performed.
[0046]
According to a fourteenth aspect of the present invention, the control unit performs control to increase the ratio of replenishment of new toner with respect to normal when it is determined that background fogging has occurred. The image forming apparatus described in the above section. "
[0047]
According to the fourteenth aspect of the present invention, when the control means determines that the background fogging has occurred, the ratio of the recycled toner in the developing device is reduced by increasing the ratio of replenishing the new toner, thereby reducing the background contamination. Improvements that do not occur will be made.
[0048]
The invention according to claim 15 is characterized in that, when it is determined that background fogging has occurred, the control means performs control to control or prohibit the supply of the recycled toner to the normal. The image forming apparatus described in the above section. "
[0049]
According to the present invention, when the control means determines that the background fogging has occurred, by reducing the ratio of the recycled toner in the developing device, an improvement is made such that the background stain does not occur. .
[0050]
According to a sixteenth aspect of the present invention, there is provided the image forming apparatus, wherein the image forming is performed by changing the toner replenishment control, and the state where the reflection density value detected by the reflection type sensor is equal to or more than the reference value is a predetermined time or a predetermined time. 16. The image forming apparatus according to claim 14, wherein after the number of prints has elapsed, the control unit determines that the background fog has improved and returns to a normal toner supply condition.
[0051]
According to the sixteenth aspect of the present invention, even after the background dirt has been improved, the state is maintained for several prints, and then the normal toner replenishment condition performed at the beginning is restored. Then, an improvement is made in which the state in which the background stain is not generated is maintained.
[0052]
BEST MODE FOR CARRYING OUT THE INVENTION
Since the image forming apparatuses described in the first and second embodiments of the present invention differ only in the configuration of the toner recycling means, the image forming apparatuses except for the toner supply using FIGS. 1 and 2 are used. The configuration and operation of will be described.
[0053]
(1) The image forming apparatus shown in the cross-sectional configuration diagrams of FIGS. 1 and 2 illustrates an image forming section of a copying machine using an electrophotographic process for forming a monochrome image to which the present invention is applied. However, the present invention is not limited to the configurations and numerical values shown in FIGS.
[0054]
Reference numeral 1 denotes a drum-shaped photoreceptor as an image carrier, in which a phthalocyanine pigment dispersed in polycarbonate as a negatively charged organic semiconductor layer is applied to a grounded metal cylindrical substrate, and the charge is applied. The photosensitive layer including the transport layer has a thickness of 30 μm, and is driven and rotated at a peripheral speed (Vp) of 280 mm / s in a direction indicated by an arrow with a drum diameter of 80 mm.
[0055]
Reference numeral 2 denotes a scorotron charging means for uniformly charging the periphery of the rotating photoreceptor 1 to a predetermined polarity / potential. The distance between the wire and the grid is 7.5 mm, the distance between the grid and the photoreceptor is 1 mm, and the distance between the wire and the back plate. A bias electrode is applied with a grid application voltage of -730 V and a charging current value of -800 [mu] A, and the charging potential of the photoconductor 1 is set to -750 V.
[0056]
Reference numeral 3 denotes an image exposure unit using a laser scanning method, which uses a semiconductor laser (LD) having a laser wavelength of 780 nm and has an output power of 300 μW. The image exposure means 3 emits a laser beam to scan and expose the uniformly charged surface of the photoreceptor 1 to form an electrostatic latent image.
[0057]
The developing device 4 has a magnet roll 41A of a fixed magnet for development inside, and the developer carrier 41 rotating in the direction of the arrow is charged by mutual friction and toner is attached around the carrier. The developer adheres by magnetic force, the layer thickness of the developer is regulated by the layer thickness regulating member 45, and the developer is conveyed to a development area facing the photoreceptor 1 to perform development.
[0058]
The developing container 4 includes a pair of agitating and conveying screws 43A and 43B and a rotary paddle 44, and a developer carrier while mixing and agitating newly supplied toner NT and recycled toner RT with the developer in the container. It is transported to 41. The stirring and conveying screws 43A and 43B are both rod-shaped screw members, one of which conveys the developer while stirring it from the front to the rear of the paper and the other from the rear to the front of the paper. The toners NT and RT fall onto the circulating developer by the stirring and conveying screws 43A and 43B, are mixed and stirred, and are discharged toward the rotary paddle 44. The developer mixed and agitated with the discharged toners NT and RT is further agitated by a water wheel-shaped rotary paddle 44 and supplied to the developer carrier 41. The developer carrier 41 has a configuration in which an aluminum sleeve having a stainless sprayed surface is covered around a magnet roll, and the developer carrier 41 rotates at a roller diameter of φ40 mm and a linear velocity (vs) of 560 mm / s. The linear velocity ratio (vs / vp) with the photoconductor 1 is set to 2. The developer carrier 41 is developed with a DC component developing bias. The DC component is applied with a developing bias of −600 V to perform reversal development.
[0059]
As a two-component developer containing a non-magnetic toner and a magnetic carrier, a polymerized toner having a volume average particle diameter of 2 to 8 μm is preferable. The use of the polymerized toner makes it possible to provide an image forming apparatus having a high resolution and a stable density with very little occurrence of fogging.
[0060]
The polymerized toner is manufactured by the following manufacturing method.
The formation of the binder resin for the toner and the shape of the toner are obtained by polymerization of the raw material monomer or prepolymer of the binder resin and subsequent chemical treatment. More specifically, it is obtained through a polymerization reaction such as suspension polymerization or emulsion polymerization and, if necessary, a step of fusing particles with each other, and in a polymerized toner, a raw material monomer or a prepolymer is uniformly dispersed in an aqueous system. Since the toner is polymerized later, a spherical toner having a uniform particle size distribution and shape of the toner can be obtained.
[0061]
The particle size of the toner used in the present invention is 2 to 8 μm in volume average particle size. More preferably, it is 3 to 7 μm. As a result, an image having a high resolution can be stably obtained, and scattering of toner and defective cleaning can be prevented by taking appropriate measures. If the volume average particle size is less than 2 μm, the toner is scattered and the like, and is not practical.
[0062]
The volume average particle diameter of the toner particle diameter (the same applies to resin particles) can be measured using a Coulter Counter TA-II, Coulter Multisizer, SLAD1100 (Shimadzu Corporation laser diffraction particle size analyzer), or the like. When the Coulter Counter TA-II and the Coulter Multisizer are used, the values measured using an aperture having an aperture diameter of 100 μm and a particle size distribution in the range of 2.0 to 40 μm are shown.
[0063]
The particle size of the toner used in the present invention is, when the toner particles are formed by a polymerization method, in the toner manufacturing method described in detail above, the concentration of the coagulant or the amount of the organic solvent added, or the fusing time, Can be controlled by the composition of the polymer itself.
[0064]
In the toner used in the present invention, the proportion of toner particles having a shape factor of the toner in the range of 1.2 to 1.6 needs to be 65% by number or more, and more preferably 1.3 to 1.6. It is preferable that the ratio of the toner particles in the range is 65 number% or more.
[0065]
The shape factor of the toner is represented by the following equation, and indicates the degree of roundness of the toner particles.
[0066]
Shape factor = ((maximum diameter / 2) ² × π) / projected area
Here, the maximum diameter refers to the width of a particle having a maximum interval between the parallel lines when a projected image of a toner particle on a plane is sandwiched between two parallel lines. The projection area refers to the area of the projected image of the toner particles on the plane.
[0067]
In the present invention, the shape factor can be determined by taking a photograph in which the toner particles are magnified 2,000 times by a scanning electron microscope, and then using SCANNING IMAGE ANALYZER (manufactured by JEOL Ltd.) based on the photograph. It was measured by performing the analysis of. At this time, the shape factor of the present invention was measured using the above formula using 100 toner particles.
[0068]
When the ratio of the toner particles having the shape coefficient in the range of 1.2 to 1.6 is 65% by number or more, the packing density of the toner particles in the toner layer transferred to the transfer material is increased, and the fixing property is improved. And offset is less likely to occur. Further, the toner particles are less likely to be crushed, so that the contamination of the charging member is reduced, and the charging property of the toner is stabilized.
[0069]
The method for controlling the shape factor is not particularly limited. For example, a method of spraying toner particles in a hot air flow, a method of repeatedly applying mechanical energy by an impact force in a gas phase, a method of adding a toner in a solvent that does not dissolve a toner and applying a swirling flow, etc. There is a method in which toner particles having a shape factor of 1.2 to 1.6 are prepared and added to a normal toner so as to fall within the range of the present invention. Further, there is a method in which the overall shape is controlled at the stage of preparing a so-called polymerization toner, and the toner particles whose shape factor is adjusted to 1.2 to 1.6 are similarly added to a normal toner for adjustment.
[0070]
Among the above methods, polymerization toners are preferred in that they are simple as a production method and that they have excellent surface uniformity as compared with pulverized toners.
[0071]
In order to uniformly control the shape coefficient of the toner and the variation coefficient of the shape coefficient without extremely varying lots, resin particles (polymer particles) constituting the toner used in the present invention are prepared (polymerized), and the resin particles are prepared. In the step of fusing and controlling the shape, the proper process end time may be determined while monitoring the characteristics of the toner particles (resin particles) being formed.
[0072]
Monitoring means that a measuring device is incorporated in-line and process conditions are controlled based on the measurement result. That is, for example, in the case of a polymerization toner formed by incorporating measurement of shape and the like in-line and associating or fusing resin particles in an aqueous medium, the shape and particle size are sequentially sampled in a process such as fusing. Is measured, and the reaction is stopped when the desired shape is obtained.
[0073]
Although the monitoring method is not particularly limited, a flow-type particle image analyzer FPIA-2000 (manufactured by Toa Medical Electronics Co., Ltd.) can be used. This apparatus is suitable because the shape can be monitored by performing image processing in real time while passing the sample liquid through. That is, a pump or the like is used from the reaction field to constantly monitor and measure the shape and the like, and stop the reaction when the desired shape and the like are obtained.
[0074]
As the carrier, a ferrite core carrier composed of magnetic particles having a volume average particle diameter of 30 to 65 μm and a magnetization of 20 to 70 emu / g is preferable. Carriers having a particle size smaller than 30 μm tend to cause carrier adhesion. Further, in the case of a carrier having a particle size larger than 65 μm, a case where an image having a uniform density may not be formed may occur.
[0075]
Reference numeral 5 denotes a pre-transfer exposure light source that irradiates to improve the transferability of the toner image, and is an LED having a light wavelength of 700 nm and irradiates with a light output of 10 lux.
[0076]
Reference numeral 6 denotes a transfer pole of the corotron, which is configured to have a distance of 8 mm between the wire and the photoconductor 1 and a distance of 12 mm between the wire and the back plate, and to transfer the toner image on the photoconductor 1 onto the transfer paper under constant current control of a transfer current of 200 μA. Is performed.
[0077]
Reference numeral 7 denotes a separation pole of the corotron, which has a distance of 8 mm between the wire and the photoreceptor 1 and a distance of 12 mm between the wire and the back plate. The separation current of the AC component is 100 μA and the DC component is −200 μA. The separation of
[0078]
The transfer paper P fed from the paper feed unit is fed by the registration roller 21 in synchronization with the toner image formed on the photoconductor 1, and receives the transfer of the toner image by the transfer pole 6 in the transfer nip. . The transfer paper P that has passed through the transfer nip is separated from the surface of the photoconductor 1 by the separation pole 7, and is conveyed to the fixing device 23 by the conveyance belt 22.
[0079]
The fixing device 23 includes a heating roller 23a having a heater disposed therein and a pressure roller 23b. The transfer paper P holding the toner image is heated and pressed between the heating roller 23a and the pressure roller 23b. The transfer paper P on which the toner image is fixed is discharged by a discharge roller 24 onto a discharge tray outside the apparatus.
[0080]
On the other hand, the surface of the photoconductor 1 after the transfer of the toner image onto the transfer paper P is cleaned by the cleaning device 8 to remove the transfer residual toner. In this embodiment, a urethane rubber blade is used as a cleaning means, and the cleaning blade is of a counter type and slides on the peripheral surface of the photosensitive member 1 to perform cleaning. The peripheral surface of the photoreceptor 1 whose surface has been cleaned by passing through the cleaning device 8 is irradiated by pre-charging exposure (PCL) means 9 using a light source having a light wavelength of 700 nm and a light output of 10 lux. To the image forming cycle.
[0081]
The toner collected by the cleaning device 8 falls to the bottom of the cleaning device, and the collected toner collected at the bottom is recycled by a toner recycling unit that conveys toner by rotating a conveying screw provided in a toner conveying path 81 described later. Is performed.
[0082]
(2) In the image forming apparatus of the present invention, a reflection type sensor (P sensor) 100 for detecting the reflection density on the surface of the photoconductor 1 is provided. FIG. 3 is a circuit diagram of the reflection sensor 100. The reflection sensor 100 detects the reflection density of the photoconductor 1 as an electric signal, and is a photocoupler including a light emitting element 101 and a light receiving element 102.
[0083]
An LED or the like is used as the light emitting element 101, and the amount of emitted light is adjusted by adjusting the variable resistor 104. Further, a transistor 105 is provided in the circuit so that the light emitting element 101 is turned on in synchronization with a point in time when the reflection density is to be measured. A phototransistor or a photodiode is used as the light receiving element 102. The phototransistor is provided with voltage dividing resistors 106a and 106b for converting an emitter current into a voltage, and the detection sensitivity is adjusted by changing the voltage dividing resistor 106b. Is to be done.
[0084]
In the present invention, the reflection sensor 100 is used to detect the occurrence of background fogging, and the photoconductor 1 is detected by the reflection sensor 100 in a state where a high-voltage charging bias is not statically or dynamically applied by the charging unit 2. Is set as a reference value. The setting of the reference value is performed, for example, by adjusting and fixing the variable voltage dividing resistor 106 so that 5 V is output as the reference value.
[0085]
The detection of the background fogging is performed by detecting the reflection density of the non-image area between the image area and the image area on the photoreceptor 1 by the reflection sensor 100, calculating the difference between the reflection density detection value and the reference value, When the difference value is equal to or more than a certain value (for example, 0.2 V), it is determined that the background fog has occurred. The detection of the reflection density of the non-image area is obtained as an average value of the detection values of a plurality of times. Alternatively, 4.8 V obtained by subtracting 0.2 V from 5 V is set as the determination reference value, and when the determination reference value is smaller than 4.8 V, it is determined that the background fogging has occurred.
[0086]
Further, in the present invention, a magnetic permeability sensor (L sensor) 200 for detecting the magnetic permeability of the developer and detecting the toner density is provided at a position facing the stirring and conveying screw 43B in the developing device 4, The concentration is being detected. The magnetic permeability sensor 200 detects the mixture ratio of the magnetic carrier and the non-magnetic toner as an apparent magnetic permeability, and outputs an analog or digital electric signal. In the developing device 4, new toner and recycled toner are supplied to the toner consumed by the development, so that the toner concentration of, for example, 4.5% by mass (detection voltage 2.5 V) is maintained in the developing device 4. Control has been made.
[0087]
(Embodiment 1)
In the image forming apparatus of the present embodiment shown in FIG. 1, toner supply into the developing device 4 is usually performed as follows.
[0088]
A new toner hopper 42 for storing new toner (NT) is provided above the developing device 4, and a supply valve 42A for supplying the new toner to the developing device 4 is provided below the new toner hopper 42.
[0089]
The control unit monitors the toner density in the developing device 4 with the L sensor 200. When the control unit detects that the toner density value has dropped below the predetermined density value, the control unit opens the supply valve 42A for a predetermined time, or A predetermined amount of new toner is dropped and supplied onto the stirring and conveying screw 43A by means such as rotation.
[0090]
The collected toner collected by the cleaning device 8 is transported by rotation of a transport screw provided in a toner transport path 81 having a pipe shape, and is recycled toner (RT) onto a stirring transport screw 43A in the developing device 4. Supplied as falling. Since the transport screw in the toner transport path 81 uses the same drive source as that of the photoconductor 1, the supply of the recycled toner is performed in conjunction with the rotation of the photoconductor 1.
[0091]
In the image forming apparatus of the present invention, the reflection density on the surface of the photoreceptor 1 is monitored by the P sensor, and when the occurrence of background fog is recognized, the toner supply control performed based on the toner density detection of the L sensor is changed. FIG. 4 is a control block diagram, and FIG. 5 is a flowchart. The present invention will be described with reference to FIGS.
[0092]
When the power is turned on or at the time of warming-up, conditions are set so that the background fogging can be accurately detected by the P sensor 100. That is, in the circuit diagram of the P sensor 100 shown in FIG. 3, the variable resistor 104 and the voltage dividing resistor 106b are automatically adjusted, and the reflection density value on the surface of the photoreceptor 1 in the state where no charging bias is applied by the charging unit 2 is used as a reference. The reference value is set so that the value becomes, for example, 5V. (F1)
The control unit C1A calls the background fog detection program C2A recorded as a memory, and determines whether or not background fog has occurred. That is, at the time of image formation, the reflection density of the non-image area on the photoreceptor 1 is detected by the P sensor 100, and the detected value is compared with a determination reference value (for example, 4.8 V) for determining whether or not the background fog has occurred. I do. (F2)
When the reflection density detection value of the non-image area by the P sensor is larger than the determination reference value, the controller C1A determines that background fogging has not occurred, and normal toner supply is performed. (F3)
In normal toner replenishment, the controller C1A calls a toner replenishment program (normal time) C3A recorded in the memory, and replenishment of new toner is performed according to this program. That is, the control unit C1A detects the toner density in the developing device 4 by the L sensor 200 every print or every few prints, and determines whether the detection value by the L sensor 200 is larger than a reference value (for example, 2.5 V). Is determined. (F31)
When it is determined that the toner concentration detection value by the L sensor 200 is not larger than the reference value (determined that the toner ratio is maintained within a predetermined range), no new toner is supplied. When it is determined that the value detected by the L sensor 200 is larger than the reference value (determined that the toner ratio has decreased), the supply valve 42A is driven to supply a predetermined amount of new toner from the new toner hopper 42. . (F32)
When the reflection density detection value of the non-image area detected by the P sensor 100 in the flow F2 is smaller than the determination reference value, the control unit C1A determines that the background fog has occurred, and the toner replenishment program recorded in the memory when the background fog occurs. Call C4A to change the toner supply condition from normal and supply new toner. (F4)
Any of the following changes (1) to (4) is adopted for the change of the toner supply condition different from the normal condition.
[0093]
(1) Prohibit toner supply
(2) Change toner supply reference value
③ Change toner supply amount
(4) Restriction of toner supply amount
{Circle around (1)} The detection value of the toner density by the L sensor 200 is compared with a reference value. (F41) However, in this case, replenishment of new toner is not performed even when the detected value is larger than the reference value. (F42) Since the supply of new toner is not performed, the toner density in the developing device 4 decreases, and the image density tends to gradually decrease. Sufficiently, the toner, especially the recycled toner, which causes background fogging, has a good charge state and is developed. The occurrence of the background fogging is eliminated while repeatedly following the flows F41 and F42 a plurality of times. (Not displayed in the flow)
{Circle around (2)} The detection value of the toner density by the L sensor 200 is compared with the newly changed reference value. That is, the toner supply reference value by the L sensor 200 is changed from a normal reference value, for example, 2.5 V (corresponding to a toner concentration of 4.5% by mass) to 2.8V (corresponding to a toner concentration of 3.5% by mass). Then, it is determined whether or not the toner density detection value detected by the L sensor 200 is larger than a newly changed reference value, for example, 2.8V. (F41) When NO is determined, the supply of new toner is not performed. When the determination is YES, the toner is supplied. (F42)
By performing such toner replenishment control, the toner concentration in the developing device 4 is reduced from, for example, 4.5% by mass to 3.5% by mass, and is managed. The frictional charging is sufficiently performed, and the toner, particularly the recycled toner which causes the background fog, is in a favorable charged state and the development is performed. The occurrence of the background fogging is eliminated while repeatedly following the flows F41 and F42 a plurality of times.
[0094]
{Circle around (3)} It is determined whether or not the toner density detection value by the L sensor 200 is larger than a reference value, for example, 2.5 V (corresponding to a toner density of 4.5% by mass). (F41)
When the determination is NO, the supply of the new toner is not performed. When YES is determined, new toner is supplied. However, the replenishment amount of the new toner is changed in a direction to decrease the replenishment amount of the toner as compared with the normal amount, for example, to 2/3 of the normal replenishment amount. (F42)
By performing such toner replenishment control, the toner density in the developing device 4 is managed in a state lower than usual, but the frictional charging is sufficiently performed between the toner and the carrier, and In particular, the recycled toner, which causes background fog, is developed in a favorable charged state. The occurrence of the background fogging is eliminated while repeatedly following the flows F41 and F42 a plurality of times.
[0095]
{Circle around (4)} It is determined whether or not the toner density detection value by the L sensor 200 is larger than a reference value, for example, 2.5 V (corresponding to a toner density of 4.5% by mass). (F41)
When the determination is NO, the supply of the new toner is not performed. When YES is determined, new toner is supplied. However, the upper limit of the replenishment amount of the new toner is controlled with respect to the normal replenishment amount, and control is performed so that the replenishment amount of the toner is not more than a predetermined amount. (F42)
By performing such toner replenishment control, the toner density in the developing device 4 is managed in a state lower than usual, but the frictional charging is sufficiently performed between the toner and the carrier, and In particular, the recycled toner, which causes background fog, is developed in a favorable charged state. The occurrence of the background fogging is eliminated while repeatedly following the flows F41 and F42 a plurality of times.
[0096]
When the background fog detected by any one of the processes (1) to (4) described above is eliminated, the determination of NO is made in the flow F2 executed as needed, and the normal toner in the flow F3 is executed. Return to the supply state. However, when returning to normal toner replenishment, the developer is likely to fall into an unstable state, so after a specified number of prints or a specified time has elapsed after the background fog has not been observed, The operation returns to toner supply.
[0097]
(Embodiment 2)
In the image forming apparatus of the present embodiment shown in FIG. 2, toner supply into the developing device 4 is usually performed as follows.
[0098]
A new toner hopper 42 for storing new toner (NT) is provided above the developing device 4, and a supply valve 42A for supplying new toner is provided below the new toner hopper 42.
[0099]
Further, the collected toner collected by the cleaning device 8 is conveyed by a conveying screw that rotates with the rotation of the photosensitive drum provided in a pipe-shaped toner conveying path 81 and is stored in a collected toner hopper 82. A supply valve 82A that supplies the collected toner to the developing device 4 is provided below the collected toner hopper 82.
[0100]
The control unit monitors the toner density in the developing device 4 with the L sensor 200, and when it detects that the toner density value has dropped below a predetermined density value, the control unit opens the supply valves 42A and 82A for a predetermined time, respectively. Alternatively, the new toner (NT) and the recycled toner (RT) having a predetermined amount and a predetermined ratio are dropped and supplied onto the stirring and conveying screw 43A by means such as rotating a predetermined number of times.
[0101]
In the image forming apparatus of the present invention, the reflection density on the surface of the photoreceptor 1 is monitored by the P sensor, and when the occurrence of background fog is recognized, the toner supply control performed based on the toner density detection of the L sensor is changed. FIG. 6 is a control block diagram, and FIG. 7 is a flowchart. The present invention will be described with reference to FIGS.
[0102]
When the power is turned on or at the time of warming-up, conditions are set so that the background fogging can be accurately detected by the P sensor 100. That is, in the circuit diagram of the P sensor 100 shown in FIG. 3, the variable resistor 104 and the voltage dividing resistor 106b are automatically adjusted, and the reflection density value in the state where the charging bias by the charging unit 2 of the photosensitive member 1 is not applied is set to the reference value. The reference value is set to be, for example, 5V. (E1)
The control unit C1B calls the background fog detection program C2B recorded as a memory and determines whether or not the background fog has occurred. That is, at the time of image formation, the reflection density of the non-image area on the photoreceptor 1 is detected by the P sensor 100, and the detected value is compared with a determination reference value (for example, 4.8V) for determining whether or not background fogging has occurred. I do. (E2)
When the reflection density detection value of the non-image area by the P sensor is larger than the determination reference value, the control unit C1B determines that background fogging has not occurred, and normal toner supply is performed. (E3)
In normal toner replenishment, the control unit C1B calls a toner / recycled toner replenishment program (normal time) C3B recorded in the memory, and a predetermined amount of new toner and recycled toner is supplied in accordance with this program at a predetermined ratio. That is, the control unit C1B detects the toner density in the developing device 4 by the L sensor 200 every print or every few prints, and determines whether the detection value by the L sensor 200 is larger than a reference value, for example, 2.5V. Make a determination. (E31)
When it is determined that the toner concentration detection value by the L sensor 200 is not larger than the reference value (determined that the combined toner ratio of the new toner and the recycled toner is maintained within a predetermined range), the toner is not supplied. . When it is determined that the value detected by the L sensor 200 is larger than the reference value (determined that the toner ratio has decreased), the supply valves 42A and 82A are driven to drive the new toner hopper 42 and the recycled toner hopper 82 by a predetermined amount. Is supplied with new toner and recycled toner. (E32)
When the reflection density detection value of the non-image area detected by the P sensor 100 in the flow E2 is smaller than the determination reference value, the control unit C1B determines that the background fog has occurred, and the toner replenishment program recorded in the memory when the background fog occurs. C4B is called, and the toner supply condition is changed from normal to supply new toner and recycled toner. (E4)
Any of the following changes (1) and (2) is adopted for the change of the toner supply condition different from the normal condition.
[0103]
(1) Increase new toner supply ratio
(2) Suppress or prohibit supply of recycled toner
(1) It is determined whether or not the toner density detection value detected by the L sensor 200 is larger than a reference value, for example, 2.5 V (corresponding to a toner density of 4.5% by mass). (E41)
When the determination is NO, toner supply is not performed. When the determination is YES, the same amount of toner is replenished as usual. However, as for the ratio of the toner to be replenished, for example, when the ratio between the new toner and the recycled toner is normally 7: 3, a change to increase the new toner replenishment ratio, such as changing the ratio to 9: 1, may be used. Then, toner supply from the supply valves 42A and 82A is performed. (E42)
By performing such toner supply control, the ratio of the recycled toner in the toner in the developing device 4 to the toner is reduced. Since the insufficiently charged recycled toner causes background fogging, recognized background fogging is prevented.
[0104]
(2) It is determined whether or not the toner density detection value detected by the L sensor 200 is larger than a reference value, for example, 2.5 V (corresponding to a toner density of 4.5% by mass). (E41)
When the determination is NO, toner supply is not performed. When YES is determined, toner supply is performed with toner supply conditions changed. As for the new toner, a predetermined amount of new toner is supplied, which is the same as usual. The replenishment of the recycled toner is controlled so as to be reduced as compared with the normal replenishment amount, or the replenishment is controlled to be prohibited. (E42)
By performing such toner supply control, the ratio of the recycled toner in the toner in the developing device 4 to the toner is reduced. Since the insufficiently charged recycled toner causes background fogging, recognized background fogging is prevented.
[0105]
When the background detected by any one of the processes (1) and (2) described above has been resolved, a NO determination is made in the flow E2 that is performed as needed, and normal toner replenishment in the flow E3 is performed. Returns to the state. However, when returning to normal toner replenishment, the developer is likely to fall into an unstable state. Therefore, after the specified number of prints or the specified time has elapsed after the background fog is not observed, The operation returns to toner supply.
[0106]
【The invention's effect】
According to the first aspect of the present invention, even in an image forming apparatus provided with a recycle unit for automatically transporting the toner collected in the cleaning device to the developing device, background contamination occurs on the image carrier and the transfer paper. Improvements will be made.
[0107]
According to the second aspect of the present invention, high-quality images of high quality are continuously obtained while a large number of prints are made, and an improvement is made such that background contamination does not occur on the image carrier or transfer paper. It will be.
[0108]
According to the third aspect of the present invention, since a portion on the image carrier on which no toner adheres is set as a reference value for detecting background contamination, the background contamination can be detected with high accuracy, and the background contamination can be detected. This is an improvement that does not occur.
[0109]
According to the fourth aspect of the present invention, since a portion most suitable for detecting background dirt is set as a detection portion, the background dirt can be detected with high accuracy, and an improvement such that background dirt does not occur can be achieved. Will be done.
[0110]
According to the fifth aspect of the invention, when the control means determines that the background fogging has occurred, the toner concentration is reduced by prohibiting the toner replenishment, the toner chargeability is improved, and the background contamination is prevented. Improvements will be made.
[0111]
According to the sixth aspect of the present invention, when the control means determines that the background fogging has occurred, the reference value for performing the toner replenishment determination is changed to a low value, thereby lowering the toner density and improving the chargeability of the toner. An improvement will be made so as not to cause stains.
[0112]
According to the seventh aspect of the present invention, when the control unit determines that the background fogging has occurred, the control unit changes the toner replenishment amount to be smaller than the normal replenishment amount, thereby lowering the toner density and improving the chargeability of the toner. The improvement is made so that the background stain does not occur.
[0113]
According to the invention described in claim 8, when the control means determines that the background fogging has occurred, the upper limit of the replenishing amount for performing the toner replenishment is limited, so that the toner density is reduced and the chargeability of the toner is improved. The improvement is made so that the background stain does not occur.
[0114]
According to the ninth aspect of the present invention, even after the background dirt is improved, the state is maintained for several prints, and then the normal toner replenishment conditions that were initially performed are restored, so that the developer is in a stable state. After that, an improvement is made in which the state in which the background stain is not generated is maintained.
[0115]
According to the tenth aspect of the present invention, in the image forming apparatus provided with a recycling unit for temporarily collecting the toner collected in the cleaning device in the recycled toner storage tank and conveying the toner from the recycled toner storage tank to the developing device, An improvement will be made so that background stains do not occur on the body or transfer paper.
[0116]
According to the eleventh aspect, while a large number of prints are performed, a high-resolution, high-quality image is continuously obtained, and an improvement is made such that background contamination does not occur on the image carrier or the transfer paper. It will be.
[0117]
According to the twelfth aspect of the present invention, a portion where no toner adheres on the image carrier is set as a reference value for detecting background contamination, so that background contamination can be detected with high accuracy, and background contamination can be detected. This is an improvement that does not occur.
[0118]
According to the thirteenth aspect, since a portion most suitable for detecting the background dirt is set as the detection portion, the background dirt can be detected with high accuracy and the improvement that the background dirt does not occur can be achieved. Will be done.
[0119]
According to the fourteenth aspect of the present invention, when the control means determines that the background fogging has occurred, the ratio of the recycled toner in the developing device is reduced by increasing the ratio of replenishment of the new toner, thereby causing the background contamination. Improvements will be made.
[0120]
According to the invention described in claim 15, when the control means determines that background fogging has occurred, by reducing the ratio of the recycled toner in the developing device, an improvement is made such that background fouling does not occur.
[0121]
According to the sixteenth aspect of the present invention, even after the background dirt is improved, the state is maintained for several prints, and then the normal toner replenishment condition that was initially performed is restored, so that the developer is in a stable state. After that, an improvement is made in which the state in which the background stain is not generated is maintained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus according to a first embodiment.
FIG. 2 is a cross-sectional configuration diagram of an image forming apparatus according to a second embodiment.
FIG. 3 is a circuit diagram of a reflective sensor.
FIG. 4 is a control block diagram according to the first embodiment.
FIG. 5 is a flowchart of the first embodiment.
FIG. 6 is a control block diagram according to a second embodiment.
FIG. 7 is a flowchart of the second embodiment.
FIG. 8 is a graph showing charge amounts of a new toner and a recycled toner.
[Explanation of symbols]
1 Photoconductor
2 Charging means
3. Image exposure means
4 Developing device
8 Cleaning device
42 New Toner Hopper
42A supply valve
82 Collected toner hopper
82A supply valve
100 reflection type sensor, P sensor
200 permeability sensor, L sensor

Claims (16)

An image carrier that carries the latent image, a developing device that visualizes the latent image on the image carrier with a developer carrier that carries a developer including a non-magnetic toner and a magnetic carrier; A transfer device for transferring the visible image of the non-magnetic toner on the transfer paper, a cleaning device disposed downstream of the transfer device for cleaning the non-magnetic toner on the image carrier, and a recycling unit for conveying the cleaned toner to the developing device; In the image forming apparatus having a control unit,
The developing device has a magnetic permeability sensor that detects the toner concentration inside,
A reflective sensor for detecting the density of the image carrier surface,
The reflection type sensor monitors the image carrier surface density in the non-image area, and when the detected reflection density value is equal to or less than the reference value, the control unit determines that background fogging has occurred, and supplies toner by the magnetic permeability sensor. An image forming apparatus, wherein control is changed. 2. The polymerized toner according to claim 1, wherein the volume average particle diameter of the toner is 2 to 8 [mu] m, and a polymer toner containing 65% by number or more of toner particles having a shape factor in a range of 1.2 to 1.6 is used. The image forming apparatus according to any one of the preceding claims. The image forming apparatus according to claim 1, wherein the reference value is a reflection density of a surface of the image carrier in an area that is not affected by a high-voltage load as an image forming condition. The image forming apparatus according to claim 1, wherein the non-image area to be monitored is a non-image area at an image forming interval. 5. The image forming apparatus according to claim 1, wherein the control unit prohibits toner supply when it is determined that background fogging has occurred. 5. The image forming apparatus according to claim 1, wherein when it is determined that background fogging has occurred, the control unit changes a reference value for determining toner replenishment. 6. The image forming apparatus according to claim 1, wherein the control unit changes the toner supply amount when it is determined that the background fog has occurred. 5. The image forming apparatus according to claim 1, wherein the control unit limits the toner supply amount when it is determined that the background fogging has occurred. After the toner supply control is changed to form an image, and the state where the reflection density value detected by the reflection type sensor exceeds the reference value has passed a predetermined time or a predetermined number of prints, the control means 9. The image forming apparatus according to claim 5, wherein it is determined that the background fog has been improved and the normal toner supply condition is restored. An image carrier that carries the latent image, a developing device that visualizes the latent image on the image carrier with a developer carrier that carries a developer including a non-magnetic toner and a magnetic carrier; A transfer device for transferring the visible image of the non-magnetic toner on the transfer paper, a cleaning device disposed downstream of the transfer device for cleaning the non-magnetic toner on the image carrier, and a recycling unit for conveying the cleaned toner to the developing device; In the image forming apparatus having a control unit,
A toner replenishing unit capable of changing a replenishment ratio between the new toner and the recycled toner to be replenished to the developing device,
A magnetic permeability sensor for detecting a toner concentration inside the developing device,
A reflective sensor for detecting the density of the image carrier surface,
The surface density of the image carrier in the non-image area is monitored by the reflection type sensor, and when the detected reflection density value is equal to or less than the reference value, the control unit determines that the background fog has occurred, An image forming apparatus wherein a supply ratio is changed. 11. The polymerized toner according to claim 10, wherein the toner has a volume average particle diameter of 2 to 8 [mu] m and contains 65% by number or more of toner particles having a shape factor in a range of 1.2 to 1.6. The image forming apparatus according to any one of the preceding claims. The image forming apparatus according to claim 10, wherein the reference value is a reflection density of a surface of the image carrier that is not affected by a high-voltage load as an image forming condition. The image forming apparatus according to claim 10, wherein the non-image area to be monitored is a non-image area at an image forming interval. 14. The image forming apparatus according to claim 10, wherein when it is determined that background fogging has occurred, the control unit performs control to increase a ratio of new toner replenishment with respect to a normal case. 14. The image forming apparatus according to claim 10, wherein when it is determined that the background fogging has occurred, the control unit performs control to reduce or prohibit the supply of the recycled toner from the normal amount. After the toner supply control is changed to form an image, and the state where the reflection density value detected by the reflection type sensor is equal to or more than the reference value has passed a predetermined time or a predetermined number of prints, the control is performed. 16. The image forming apparatus according to claim 14, wherein the means determines that the background fog has been improved and returns to a normal toner supply condition.

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