JP2006259305A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which provides satisfactory cleaning performance even when an amount of charged toner in developer changes. <P>SOLUTION: The image forming apparatus develops an electrostatic latent image formed on an image carrier into a toner image by a developing means, transfers the toner image to an intermediate transfer body and then to a transfer material, thereafter removes residual toner on the intermediate transfer body by a cleaning means to which a bias voltage has been applied. The image forming apparatus includes: a control means for controlling a development bias voltage applied between the image carrier and the developing means; and a development current detection means for detecting the value of a current flowing in the developing means. In accordance with the detected value of the development current, the cleaning bias voltage is controlled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a FAX, and more particularly to an image forming apparatus using an intermediate transfer belt.

  Conventionally, as an electrophotographic image forming apparatus using an intermediate transfer belt as an intermediate transfer member, a toner image formed on a photosensitive member as an image carrier is primarily transferred to the intermediate transfer belt, and the image is transferred onto the intermediate transfer belt. The toner image is secondarily transferred onto a transfer material such as paper (recording paper). That is, after a toner image formed on a photoconductor as an image carrier and charged to a predetermined polarity is transferred to an intermediate transfer belt using electrostatic force, the toner image on the intermediate transfer belt is subjected to electrostatic force. Transfer to transfer material using.

  An image forming apparatus using such an intermediate transfer belt uses the electrostatic force to sequentially superimpose toner images formed on the respective photoreceptors on the intermediate transfer belt, and further uses the superimposed toner image as a transfer material. Since it is possible to perform batch transfer, it is widely used as a color image forming apparatus.

  Here, a small amount of toner remains on the intermediate transfer belt after the secondary transfer, and if this is left as it is, image smearing due to the residual toner occurs when the next image is formed.

  Therefore, in order to remove the residual toner on the intermediate transfer belt after the transfer, a plate-like cleaning blade made of synthetic rubber such as polyurethane (hereinafter also simply referred to as a blade) is used, and this edge portion is provided on the surface of the intermediate transfer belt. A blade method is used in which the toner is dammed and removed by damming.

  In recent years, polymerized toner and small-diameter toner have begun to be used for image improvement, and so-called bias cleaning method in which toner is electrostatically collected by a brush roller to which a bias voltage is applied can be considered as an alternative to blades. ing.

  In the bias cleaning device, normally, a brush roller or the like is applied with a voltage so as to have a potential opposite to that of the toner and brought into contact with the intermediate transfer belt to electrostatically remove the toner. The applied voltage needs to be set to a condition where there is a sufficient electric field to move the toner from the belt and the toner does not reattach to the belt due to discharge between the brush and the belt.

  However, since the charge amount of toner varies depending on the environment and usage history, it is difficult to satisfy satisfactory cleaning performance with a certain cleaning bias voltage setting in all toner states.

  In particular, a large amount of toner to be cleaned becomes a severe condition for completely moving the toner by an electric field. For example, when cleaning untransferred toner by forming a toner patch for image density control, cleaning becomes difficult because a larger amount of toner moves to the cleaning unit than when cleaning residual toner.

  As described above, when electrolytically moving a large amount of untransferred toner having various toner charge amounts, which is the most severe condition, it is a problem to always set good cleaning conditions.

Conventional. As a well-known example of countermeasures against contamination on the back surface of a transfer material, in order to set cleaning conditions for a contact transfer member such as a transfer roller, the toner charge amount is detected, and it is determined whether or not the toner charge amount is lower than a predetermined charge amount. A method of changing the cleaning process time of the member or controlling the stirring time after transfer by the amount of charge has been proposed (for example, see Patent Document 1).
JP 2000-3104 A

  An object of the present invention is to provide an image forming apparatus capable of obtaining good cleaning performance even when the toner charge amount in the developer changes.

The electrostatic latent image formed on the image bearing member is visualized as a toner image by the developing means, and the toner image is transferred to the intermediate transfer member and further transferred to the transfer material, and then remains on the intermediate transfer member. In an image forming apparatus that removes toner by a cleaning unit to which a bias voltage is applied, a control unit that applies a developing bias voltage between the image carrier and the developing unit and controls the developing bias voltage; An image forming apparatus comprising: a developing current detecting unit configured to detect a current value of the developing unit, and controlling the cleaning bias voltage in accordance with the detected developing current value.

  Since the toner charge amount can be estimated from the development current value, good cleaning performance can be maintained even when the toner charge amount is different.

  First, the image forming apparatus of the present invention will be described with reference to FIG.

  In the description of the embodiment of the present invention, the technical scope is not limited by the terms used in this specification.

  FIG. 1 is a schematic diagram illustrating an example of the overall configuration of the image forming apparatus.

  In FIG. 1, 10 is a photoconductor as an image forming body, 11 is a scorotron charger as charging means, 12 is a writing device as digital image exposure means, 13 is a developing device as developing means, and 14 is a photoconductor. The cleaning device is a cleaning means for cleaning the surface of 10, 15 is a blade for cleaning the photoconductor 10, 16 is a developing sleeve, and 20 is an intermediate transfer belt which is an intermediate transfer member (hereinafter also simply referred to as a belt). Indicates.

  The image forming unit 1 includes a photoconductor 10, a scorotron charger 11, a developing unit 13, a cleaning device 14, and the like. Since the mechanical configuration of the image forming unit 1 for each color is the same, Y ( Reference numerals are given to the configuration of only the yellow (yellow) series, and reference symbols are omitted for the constituent elements of M (magenta), C (cyan), and K (black).

  The arrangement of the image forming means 1 for each color is in the order of Y, M, C, K with respect to the running direction of the intermediate transfer belt 20, and each photoconductor 10 contacts the stretched surface of the intermediate transfer belt 20. The contact point rotates in the same direction as the traveling direction of the intermediate transfer belt 20 and at the same linear speed.

  The intermediate transfer belt 20 is stretched around a driving roller 21, an earth roller 22, a tension roller 23, a static elimination roller 27, a driven roller 24, and an auxiliary roller 29. These rollers and the intermediate transfer belt 20, a transfer roller 25 as a transfer means, The belt unit 3 is constituted by the cleaning device 28 or the like which is a cleaning means.

  The photosensitive member 10 is formed by forming a photosensitive layer such as a conductive layer, an a-Si layer, or an organic photosensitive member (OPC) on the outer periphery of a cylindrical metal base formed of, for example, an aluminum material, and the conductive layer is grounded. It rotates in the counterclockwise direction indicated by the arrow in the figure.

  An electrical signal corresponding to the image data from the reading device 80 is converted into an optical signal by an image forming laser, and is projected onto the photoconductor 10 by the writing device 12 to form an electrostatic latent image.

  The developing device 13 is a developing sleeve formed of a cylindrical nonmagnetic stainless steel or aluminum material that keeps a predetermined interval with respect to the peripheral surface of the photoconductor 10 and rotates in the same direction as the rotation direction of the photoconductor 10. A developing bias voltage is applied between the developing sleeve 16 and the photosensitive member 10 by a developing bias power source 161 to visualize the electrostatic latent image into a toner image.

The intermediate transfer belt 20 is driven by rotation of the driving roller 21 by a driving motor (not shown). The material of the intermediate transfer belt 20 is an endless belt having a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm, such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, and the like. Two layers in which a conductive material is dispersed in an engineering plastic, and a fluorine coating having a thickness of 5 to 50 μm is preferably applied to the outside of a semiconductive film substrate having a thickness of 0.04 to 0.10 mm, preferably as a toner filming prevention layer. It is a seamless belt of the configuration. In addition to this, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber, urethane rubber, or the like can also be used.

  The transfer roller 25 has a function of transferring a toner image formed on the photoreceptor 10 onto the intermediate transfer belt 20 by applying a DC voltage having a polarity opposite to that of the toner. For the transfer function, a corona discharger can be used in addition to the transfer roller.

  Reference numeral 26 denotes a nip S formed by a transfer roller which can be brought into contact with and released from the ground roller 22 via a belt, and retransfers the toner image formed on the intermediate transfer belt 20 onto the transfer paper P. However, when the toner patch for measuring the toner density is formed on the intermediate transfer belt, the transfer roller 26 is released from the belt. That is, the toner patch is conveyed to the cleaning device 28 while remaining on the intermediate transfer belt 20 in an untransferred state.

  An AC voltage in which a DC voltage having the same polarity or opposite polarity as that of the toner is superimposed is applied to the charge removal roller 27, and the charge of the toner remaining on the intermediate transfer belt 20 is weakened after the toner image is transferred to the transfer material P.

  The cleaning device 28 is a means for cleaning the intermediate transfer belt 20 according to the present invention, and details will be described later.

  A fixing device 40 includes a heating roller 41 and a pressure roller 42.

  The heating roller 41 has a cylindrical shape made of thin aluminum and has a halogen heater 47 and the like for heating from the inside to a predetermined temperature. The temperature is a contact (not shown) installed on the heating roller 41. The temperature is detected by the temperature sensor, and the temperature is controlled by the control unit B.

  Next, the image forming process will be described with reference to FIG.

  Simultaneously with the start of image recording, the photoconductor drive motor (not shown) starts to rotate the photoconductor 10 of the color signal Y in the counterclockwise direction indicated by the arrow, and at the same time, a potential is applied to the photoconductor 10 by the charging action of the scorotron charger 11. Is started.

  After the photoconductor 10 is applied with a potential, writing of an image corresponding to the Y image data is started by the writing device 12, and an electrostatic latent image corresponding to the Y image of the original image is formed on the surface of the photoconductor 10. It is formed.

  The electrostatic latent image is reversely developed in a non-contact state by a Y developing unit 13, and a Y toner image is formed on the photoconductor 10 as the photoconductor 10 rotates.

  The Y toner image formed on the photoconductor 10 is transferred onto the intermediate transfer belt 20 by the action of the Y transfer roller 25.

  After that, the photoreceptor 10 is cleaned of residual toner by a cleaning blade 15 and enters the next image forming cycle (hereinafter, the same applies to the M, C, and K cleaning processes, and the description is omitted).

  Next, the writing device 12 performs image writing corresponding to an M (magenta) color signal, that is, M image data, and an electrostatic latent image corresponding to the M image of the original image is formed on the surface of the photosensitive member 10. The The electrostatic latent image is converted into an M toner image on the photosensitive member 10 by the M developing unit 13, and is synchronized with the Y toner image on the intermediate transfer belt 20 by the M transfer roller 25. Is superimposed on the toner image.

  By a similar process, the Y and M superimposed toner images are synchronized, and the C (cyan) toner image is superimposed on the Y and M superimposed toner images by the C transfer roller 25. . Next, the Y, M, and C superimposed toner images that have already been formed are synchronized, and the K toner image is transferred onto the Y, M, and C superimposed toner images by the K transfer roller 25. And a superimposed toner image of Y, M, C, and K is formed.

  The intermediate transfer belt 20 carrying the superimposed toner image is fed clockwise as indicated by the arrow, and the transfer material P is fed from the paper cassette 72 by the paper feed roller 70, passes through the transport roller 73, and then the timing roller 71. Then, the timing roller 71 is driven to synchronize with the superimposed toner image on the intermediate transfer belt 20, and a transfer roller 26 (intermediate) to which a DC voltage having a polarity opposite to that of the toner is applied. The toner image is fed to the transfer area S (in contact with the transfer belt 20), and the superimposed toner image on the intermediate transfer belt 20 is transferred to the transfer material P.

  Thereafter, the intermediate transfer belt 20 travels, the charge of the residual toner is weakened by the charge eliminating roller 27, the residual toner on the belt is cleaned by the cleaning device 28, and the next image forming cycle starts.

  The toner scraped off is collected in the cleaning device 28, conveyed in the axial direction (from the paper surface to the paper back surface in the drawing) by the rotation of the conveying screw 287, and collected in a storage box via a waste pipe (not shown). .

  The transfer material P onto which the superimposed toner image has been transferred is further sent to the fixing device 40, and is sandwiched and pressed between the heating roller 41 and the pressure roller 42 to be fixed. The transfer material P on which the toner image is fixed is conveyed to a paper discharge tray 82 by a paper discharge roller 81.

  Next, the cleaning process for the intermediate transfer belt according to the present invention will be described with reference to FIG.

  In an electrophotographic image forming apparatus, when toner density is detected, a toner patch is formed on an image carrier, the density of the toner patch is measured, and the toner supply is determined by comparison with a reference density.

As described above, since the charge amount of the intermediate transfer belt cleaning device varies depending on the environment and usage history, it is difficult to maintain good cleaning performance with a certain cleaning bias voltage setting in all toner states. There's a problem.

  That is, the toner patch is not transferred to a transfer material or the like, and will be cleaned when measurement is completed. However, it is always good when toners of various charge amounts are not transferred and reach a cleaning portion in large quantities. Difficult to maintain clean performance.

  The present invention has been proposed to solve this problem. Even if the toner charge amount changes by measuring the developing current, estimating the toner charge amount from the measured current, and controlling the cleaning bias voltage. It is characterized by good cleaning performance.

  FIG. 2 is a diagram for explaining the setting of the cleaning bias voltage in accordance with the relationship between the development current and the toner charge amount.

  In FIG. 2, the cleaning device 28 includes brush rollers 281 and 282 (hereinafter also simply referred to as brushes) that are conductive brushes, conductive toner collection rollers 283 and 284, toner scrapers 285 and 286, a conveying screw 287, and the like. It consists of

  Most of the toner patches on the front intermediate transfer belt 20 are negative toners and positive toners are also mixed. However, the positive toner is applied by the upstream brush 281 to which a negative voltage is applied by the bias power source V1. Is removed, adheres to the toner collection roller 283, and is scraped off by the scraper 285. On the other hand, the negative polarity toner remains on the belt 20 and is conveyed to the brush roller 282 to which a positive voltage is applied by the bias power source V2 on the downstream side, adheres to the toner recovery roller 284, and is written off by the scraper 286.

  However, a large amount of toner such as a toner patch (see FIG. 3) that is untransferred toner has a different toner charge amount depending on the environment, usage history, and the like. Not kept. Therefore, by measuring the development current as a means for detecting the toner charge amount, estimating the measured toner charge amount, and setting the cleaning bias voltage according to the result, even if the toner charge amount differs, Since the cleaning bias voltage can be set, it is possible to always ensure good cleaning performance.

  FIG. 3 shows a toner patch for measuring the toner adhesion amount (toner density) formed on the photoreceptor.

  That is, as shown in FIGS. 1 and 2, the toner charge amount is calculated by measuring the current flowing through the developing sleeve (flowing through the developer). By setting an appropriate cleaning bias voltage according to the calculated toner charge amount, it is possible to always obtain a good cleaning performance even when the toner charge amount is different.

  Hereinafter, the result of conducting a confirmation experiment on the performance of the embodiment of the present invention will be described.

・ Confirmation experiment 1
First, three types of developer (toner charge amount: 40 μC / g, 50 μC / g, 60 μC / g) with known toner charge amounts are used, and the brush cleaning bias voltage V2 is set as shown in FIGS. The toner patch cleaning (CL) performance was changed.

Experimental conditions Intermediate transfer belt: PI (polyimide resin), volume resistance 10 ⁹ Ω, conductive brush: conductive nylon, surface resistance 10 ¹¹ Ω, wire diameter 6d,
Original yarn resistance value 10 ¹⁰ Ω, linear speed 220mm / sec (belt running and reverse rotation)
Apply a constant negative bias voltage to the upstream brush
Apply a variable (control) positive bias voltage to the downstream brush, ground the brush counter roller (follower roller 24) with aluminum, and bite the stainless flicker rod 1 mm into the brush and attach it to the toner recovery roller.
Write down with a toner scraper.

Experimental environment: Low temperature and low humidity (10 ° C, 20%)
·result
As shown in Table 1, it was found that the proper cleaning bias voltage range was different from the maximum toner adhesion amount of 0.5 mg / cm ² with a toner charge amount (−40 to −60 μC / g). It was found that the cleaning bias voltage setting needs to be changed according to the state of the charge amount.

            In Table 1, “◯” indicates that no cleaning failure occurred on the belt, “Δ” indicates slight cleaning failure visually, and “x” clearly indicates the occurrence of cleaning failure.

・ Confirmation experiment 2
Next, the developing current was measured as a means for detecting the toner charge amount. Further, the developing conditions are controlled so that the output of the reflection type density sensor S1 is constant (the toner adhesion amount is constant). A toner patch was formed again under these conditions, and the current flowing through the developing sleeve 16 during development was measured with an ammeter 162.

・ Development conditions
Toner: Cyan (C) toner, particle size 6.5 μm (specific gravity 1.1)
Toner patch: 50 mm wide x 10 mm long (see FIG. 3)
Linear velocity: 220mm / sec
Toner adhesion amount: 6 g / m ²
At this time, if the development current value flowing through the ammeter 161 is calculated from the formula I = dQ / dt, a toner patch of 50 mm × 10 mm passes in 1/22 sec, so I = (toner adhesion amount per unit) × Linear velocity × (toner patch area) × q (charge amount) = {(6 × 10 ⁻⁴ ) g / cm ² × 5 cm × 22 cm / sec} q (μC / g) = 6 × 5 × 22 × 10 ⁻⁴ Since q (μC / g), the results shown in Table 2
It will be fruit.

FIG. 4 is a diagram showing a linear expression y = 0.066x−2 × 10 ^{−14 in} which the measured values in Table 2 are plotted.

  Table 3 shows the results of image confirmation after setting a cleaning bias voltage capable of performing good cleaning with respect to the developing current based on the relationship between the expressions in Tables 1 and 2 and FIG.

  As described above, the toner charge amount can be detected from the measured development current value, and the cleaning bias voltage can be controlled in accordance with the result, so that a good cleaning performance can be obtained even if the toner charge amount changes. It has become possible.

  The combination of the toner charge amount and the optimum cleaning bias voltage is stored in the table of the control unit B. If the toner charge amount is obtained, the best cleaning bias voltage corresponding to the toner charge amount is selected.

  The above toner patch formation and cleaning bias voltage control and setting are performed only at the time of image adjustment. For example, the toner patch is performed at the start of operation of the first device in the morning or at a predetermined number of prints such as every several hundred copies. It is preferable.

1 is a schematic diagram illustrating an example of an overall configuration of an image forming apparatus. FIG. 6 is a diagram for describing setting of a cleaning bias according to a relationship between a developing current and a toner charge amount. A toner patch for measuring the toner adhesion amount (toner density) formed on a photoreceptor is shown. It is a figure which shows the linear type y = 0.066x-2 * 10 < ^-14 > which plotted the measured value of Table 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming means 10 Photoconductor 13 Developing device 16 Developing sleeve 161 Developing bias power supply 20 Intermediate transfer belt 21 Drive roller 24 Driven roller 28 Cleaning device 281, 282 Conductive brush 283, 284 Toner recovery roller 283 Toner recovery roller 285, 286 Scraper S1 Reflective density sensor S1

Claims (4)

The electrostatic latent image formed on the image bearing member is visualized as a toner image by the developing means, and the toner image is transferred to the intermediate transfer member and further transferred to the transfer material, and then remains on the intermediate transfer member. In an image forming apparatus that removes toner by a cleaning unit to which a bias voltage is applied, a control unit that applies a developing bias voltage between the image carrier and the developing unit and controls the developing bias voltage; An image forming apparatus comprising: a developing current detecting unit configured to detect a current value of the developing unit, and controlling the cleaning bias voltage in accordance with the detected developing current value. The image forming apparatus according to claim 1, wherein the developing unit includes a developing sleeve that conveys a developer. The image forming apparatus according to claim 1, wherein the cleaning unit includes a brush roller that rotates in contact with the intermediate transfer member. The image forming apparatus according to claim 1, wherein the cleaning bias voltage is controlled only for untransferred toner on the intermediate transfer member.

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