JP6035779B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile.

  In recent years, copying machines and printers have become full-color, faster, and higher in image quality, making it possible to form high-definition images at the offset printing level. In particular, in the field of on-demand publications, it is relatively easy to handle a small number of copies, so there is a tendency to produce publications that have been produced by printing methods with full-color copiers and full-color printers. It has become prominent. As a result, the speed of being able to create prints without the hassle of creating plates has increased business opportunities, and recently, competition with offset printing has begun in some commercial light printing fields.

  In an image forming apparatus using such an electrostatic process, an intermediate transfer belt is widely used, and a wide variety of papers (not limited to paper, meaning that an image including OHP is formed). In view of the need for a high-quality image on a recording medium or a recording medium or recording paper), it is preferable to use a secondary transfer belt. In other words, by adsorbing the sheet to the secondary transfer belt, it is possible to pass through the secondary transfer unit stably without causing wrinkles or deformation even on a low-rigidity sheet such as a thin sheet and without causing a jam. be able to.

  On the other hand, in such an image forming apparatus, it is necessary to clean the toner adhering to the secondary transfer belt, and if the cleaning is not performed, dirt or the like is generated on the back surface of the sheet. Although cleaning is becoming more difficult due to full color and high speed, it is very important to prevent backside stains and the like from being generated on a printed matter as a product in commercial printing.

Conventionally, as a method for removing dirt on the secondary transfer belt, a method for mechanically cleaning the secondary transfer belt and a method for electrically cleaning the secondary transfer belt are used.
The mechanical cleaning method of the secondary transfer belt is such that a cleaning member such as a cleaning blade, a roller, or a brush is pressed against the secondary transfer belt with a predetermined pressure, and the dirty toner on the secondary transfer belt is collected with this contact pressure. It is.

  However, in the conventional image forming apparatus, since the cleaning member is always in contact with the secondary transfer belt, wear of the surface of the secondary transfer belt and wear of the cleaning member are caused by friction between the two, and their life is reduced. As a result, the life of the image forming apparatus is reduced, and there is a problem that the running cost increases even if parts are replaced.

  On the other hand, the electrical cleaning method for the secondary transfer belt is a method for collecting the dirty toner by applying a bias to the dirty toner adhering to the secondary transfer belt. However, if toner is only collected electrostatically in this way, the transfer of the dirty toner from the secondary transfer belt is not complete and insufficient.

  In view of this, a method using a mechanical cleaning method and an electrical cleaning method in combination is known (Patent Documents 1 and 2).

  In Patent Document 1, a bias roller arranged on the back side of an endless transfer belt that transfers a toner image formed on a photosensitive drum onto a transfer sheet, and the transfer belt is in contact with the transfer roller and remains attached to the transfer belt. A cleaning blade is used as a cleaning means to remove the toner that is used, and the bias roller is also used as a cleaning means. When the transfer paper does not pass through the transfer portion, a bias voltage is applied to the bias roller to adhere to the transfer belt. An image forming apparatus is disclosed in which the toner being transferred is transferred to a photosensitive drum and the backside of transfer paper is prevented from being stained.

  However, this technology does not support the recent full color and high speed continuous printing, and the cleaning performance is not sufficient. For example, in double-sided continuous printing with mixed paper sizes, dirt accumulated on the secondary transfer belt corresponding to the non-image portion during double-sided printing stains the second surface, which is the printing surface.

  Patent Document 2 has an endless transfer belt suspended on two or more rollers and in contact with the image carrier to form a transfer nip, and a bias is applied to the transfer belt to Transfer means for electrostatically transferring the toner image to the transfer material, first cleaning means for enabling the blade to be released from pressure contact on the transfer belt, and peeling off the toner adhering to the transfer belt when the blade is pressed, and attached to the transfer belt A second cleaning unit that removes the toner that has been removed by an electrostatic roller or toner that has adhered to the transfer belt using a fur brush, and the second cleaning unit always operates, and the first cleaning unit also operates only in a predetermined sequence. An apparatus is disclosed.

  However, in this technique, since the electrostatic roller as the second cleaning unit is separately provided, the apparatus is increased in size and cost.

  Therefore, the present invention can efficiently clean the toner stain on the surface of the secondary transfer member without causing the back side of the paper to be contaminated without increasing the size of the apparatus and without impairing the durability of the member. It is an object to provide a forming apparatus.

In order to solve this problem, an image forming apparatus of the present invention includes a latent image carrier that carries an electrostatic latent image, a charging device that charges the surface of the latent image carrier, and a latent image on the latent image carrier. A developing device that develops an image to form a toner image; an intermediate transfer member wound around a plurality of rollers including a secondary transfer counter roller at a position facing the latent image carrier; A primary transfer device that transfers the toner image to the intermediate transfer member, a cleaning device that removes toner remaining on the intermediate transfer member, and the secondary transfer counter roller abutting against the intermediate transfer member A secondary transfer body that transfers a toner image on the intermediate transfer body to a recording medium at a secondary transfer position and conveys the recording medium to a fixing device, and is capable of contacting and separating from the secondary transfer body Toner disposed and attached to the secondary transfer member First cleaning means for scraping and applying a bias having a polarity opposite to that of the toner to the secondary transfer counter roller when the recording medium has not passed the secondary transfer position, thereby allowing the secondary transfer member to be applied onto the secondary transfer body. A second cleaning unit that transfers residual toner to the intermediate transfer member, and when the first cleaning unit is not used, the first cleaning unit is separated from the secondary transfer member, and printing is performed. During the process control for adjusting the image density and the positional deviation at the timing of the non-image portion during printing or between recording media during continuous paper feeding or during printing, the first cleaning unit is used as the secondary transfer body. brought into contact, the second cleaning means to clean without operating, contact time to the secondary transfer member of the first cleaning unit, the second transfer member Is the time to rotate at least one revolution, when the process control to adjust the image density and displacement at the timing other than during printing, are brought into contact with the first cleaning means to said second transfer member, and said second cleaning operating the means have rows cleaning, the contact time and the bias application time of by the second cleaning means to the secondary transfer member of the first cleaning means, said secondary transfer member is rotated at least one revolution It is characterized by time.

  According to the present invention, in the cleaning of a secondary transfer body having a paper type compatibility such as thin paper separation property and paper transportability, the cleaning of the scraping method which is easily deteriorated but has high cleaning performance and electrostatic toner In order to return the toner to the intermediate transfer member, the transfer is not complete, but bias cleaning which is difficult to deteriorate is used or combined depending on the situation. Therefore, it is possible to perform the reliable cleaning without reducing the back surface of the paper, the edge surface, and the like while reducing the wear of the first cleaning means.

1 is a schematic configuration diagram of an image forming apparatus according to the present invention. It is a schematic block diagram of a cleaning apparatus. It is a figure which shows the proper use (combination) of the cleaning by the 1st and 2nd cleaning means. It is a figure which shows an example of control of a secondary transfer bias and the 2nd cleaning bias. It is a figure which shows an example of control of a secondary transfer bias and the 2nd cleaning bias. It is a schematic block diagram of another cleaning apparatus. It is a schematic block diagram of another cleaning apparatus.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.
The image forming apparatus 1 has a tandem configuration in which a plurality of photoreceptors as latent image carriers capable of forming an image of a color corresponding to color separation are juxtaposed, and intermediately forms a toner image formed on each photoreceptor. This is a full-color printer capable of forming a multicolor image by superimposing and transferring the image onto a transfer belt and then transferring the superimposed image onto a sheet at a time. The image forming apparatus of the present invention is not limited to a full-color printer, but includes a full-color copying machine, a facsimile machine, a printing machine, and the like.

  In FIG. 1, in the full-color printer 1, an image forming unit 1A is positioned at the center in the vertical direction, a document feeding unit 1B is provided below the image forming unit 1A, and an original document table 1C1 is provided above the image forming unit 1A. Each of the scanning units 1C is arranged.

  In the image forming unit 1A, a transfer unit composed of an intermediate transfer belt 2 having a horizontally extending surface is disposed. Above the intermediate transfer belt 2, an image of a color complementary to the color separation color is provided. The structure for forming is provided.

  In the image forming unit 1A, photosensitive members 3B, 3Y, 3C, and 3M that can carry images of toners of complementary colors (black, yellow, cyan, and magenta) are provided along the extended surface of the intermediate transfer belt 2. It is juxtaposed. In the following description, in the case of contents common to all the photoconductors, the photoconductor is denoted by reference numeral 3. Each of the photoconductors 3B, 3Y, 3C, and 3M includes a drum that can rotate in the same direction (counterclockwise in FIG. 1). A charging device 4, a writing device 5, a developing device 6, and a primary transfer device 7 and a cleaning device 8, which are one of transfer bias applying means, are arranged in the vicinity of the charging device 4, a writing device 5, a developing device 6, and the like. In FIG. 1, for the sake of convenience, the reference numerals of the respective devices are denoted by B for the photosensitive member 3 </ b> B.

  The charging device 4 charges the surface of the photosensitive member 3, the developing device 6 develops the latent image on the photosensitive member to form a toner image, and the primary transfer device 7 transfers the toner image on the photosensitive member to the intermediate transfer belt 2. The secondary transfer belt 9 </ b> C as a secondary transfer member transfers the toner image on the intermediate transfer belt 2 to the sheet at the secondary transfer position and conveys the sheet to the fixing device 11.

  The intermediate transfer belt 2 as an intermediate transfer member is wound around a primary transfer portion to which a visible image from an image forming unit including each photosensitive member is sequentially transferred, and a plurality of rollers 2A to 2D. It is possible to move in the same direction at the opposite position. A roller 2C different from the rollers 2A and 2B constituting the stretched surface is used as a secondary transfer counter roller to which a bias having the same polarity as the toner is applied to the secondary transfer device 9 with the intermediate transfer belt 2 interposed therebetween. The roller 2D is used as a tension roller. The secondary transfer counter roller 2C is connected to a power source capable of reversing the potential polarity applied with a bias as will be described later.

  The transfer residual toner remaining on the intermediate transfer belt 2 after the secondary transfer is removed by the cleaning device 10. The cleaning device 10 includes a cleaning blade and a rotatable roller-shaped application brush that applies a solid lubricant. The cleaning blade comes into contact with the intermediate transfer belt 2 and scrapes off transfer residual toner from the surface thereof. The application brush scrapes off and applies the solid lubricant pressed by the pressure spring to the intermediate transfer belt 2 while rotating. As described above, the cleaning device 10 has both a function as a cleaning device for cleaning the transfer residual toner on the intermediate transfer belt 2 and a function as a lubricant application device for applying the lubricant to the surface of the intermediate transfer belt 2. . Although the cleaning device 10 of this embodiment is configured by a blade system, an electrostatic cleaning system may be used. In the case of the electrostatic cleaning method, a bias is applied to the cleaning roller or the cleaning brush, and the residual toner adhering to the intermediate transfer belt is electrostatically adsorbed for cleaning.

  The secondary transfer device 9 includes a secondary transfer belt 9C that is wound around the driving roller 9A and the driven roller 9B and is movable in the same direction as the intermediate transfer belt 2 at the secondary transfer position where the secondary transfer device 9 is located. The secondary transfer belt 9C is driven by a driving roller 9A. Although depending on the bias characteristic of the primary transfer device 7 described above, the driving roller 9A may be provided with a charging characteristic so that the sheet is electrostatically adsorbed. In the secondary transfer device 9, the multi-color image superimposed on the intermediate transfer belt 2 in the process of transporting the paper by the secondary transfer belt 9C is transferred by batch transfer or the single color image carried is transferred to the paper. be able to.

  A sheet is fed from the sheet feeding unit 1B to the secondary transfer position. The paper feed unit 1B includes a plurality of paper feed cassettes 1B1, a plurality of transport rollers 1B2 arranged in a transport path for paper fed from the paper feed cassette 1B1, and a registration roller 1B3 positioned in front of the secondary transfer position. ing. In the present embodiment, in addition to the paper conveyance path fed out from the paper feed tray 1B1, the type of paper not stored in the paper feed cassette 1B1 is fed to the paper feed unit 1B toward the secondary transfer position. A possible configuration is provided. This configuration includes a manual feed tray 1A1 and a feeding roller 1A2 provided so that a part of the wall surface of the image forming unit 1A can be turned upside down. In the middle of the sheet conveyance path from the sheet feeding cassette 1B1 to the registration roller 1B3, the sheet conveyance path fed out from the manual feed tray 1A1 joins, and the sheet fed from any conveyance path is registered by the registration roller 1B3. Is set.

  The writing device 5 (indicated by reference numeral 5B for convenience in FIG. 1) is image information obtained by scanning a document on the document table 1C1 in the document scanning unit 1C or image information output from a computer (not shown). Thus, the writing light is controlled to form an electrostatic latent image corresponding to the image information on the photoreceptors 3B, 3Y, 3C, and 3M.

  The document scanning unit 1C is provided with a scanner 1C2 that exposes and scans the document on the document table 1C1, and an automatic document feeder 1C3 is disposed on the upper surface of the document table 1C1. The automatic document feeder 1C3 has a configuration capable of reversing the document fed on the document table 1C1, and can perform scanning on both sides of the document.

  The electrostatic latent image formed on the photoconductor 3 formed by the writing device 5 is subjected to a visible image processing by a developing device 6 (indicated by reference numeral 6B in FIG. 1 for convenience), and is subjected to intermediate transfer by a primary transfer device 7. Primary transfer is performed on the belt 2. When the toner images of the respective colors are superimposed and transferred onto the intermediate transfer belt 2, the toner images are transferred to the secondary transfer position by the secondary transfer device 9, that is, the contact position (2 between the intermediate transfer belt 2 and the secondary transfer roller 9A). At the next transfer nip, secondary transfer is performed on the sheet at once.

  The secondary-transferred paper is conveyed to the fixing device 11 by the secondary transfer device 9 where the unfixed image carried on the surface is fixed. Although not shown in detail, the fixing device 11 includes a belt fixing structure including a fixing belt heated by a heating roller and a pressure roller that faces and contacts the fixing belt. By providing a contact area between the fixing belt and the pressure roller, that is, a nip area, a heating area for the sheet can be expanded as compared with a fixing structure of another roller type. The transport direction of the paper that has passed through the fixing device 11 is switched by a transport path switching claw 12 disposed behind the fixing device 11, and the paper discharge tray 13 is reversed and is directed again toward the registration roller 1 </ b> B <b> 3. Are sent.

  A primary transfer device 7 (indicated by reference numeral 7B in FIG. 1 for convenience) in the image forming apparatus 1 is a roller for applying a positive transfer bias, and is intermediate between a bearing (not shown) and an elastic body such as a compression spring. The photosensitive member 3 is pressed with a predetermined pressure via the transfer belt 2.

  The primary transfer device 7 </ b> B is interlocked with the intermediate transfer belt 2 at a position offset about 1 to 2 mm from the position opposite to the center position of the photoconductor 3 on the downstream side in the moving direction of the intermediate transfer belt 2. It is designed to rotate. This is to prevent pre-transfer that starts transfer by a transfer bias before the normal transfer position and generates an abnormal image such as an image flow.

The primary transfer device 7 is configured in such a manner that a rubber material having a medium resistance electric characteristic is wound around a metal core. In this embodiment, the primary transfer device 7 is composed of a medium-resistance foamed rubber, and its volume resistivity is in the range of 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁷ to 10 ⁹ Ω · cm. . The material is not limited to foamed rubber, and medium resistance solid rubber can be used as well. Further, the secondary transfer counter roller 2C is configured in such a manner that a rubber material having a medium resistance electric characteristic is wound around a metal core. In this embodiment, the secondary transfer counter roller 2C is made of medium resistance solid rubber, and its volume resistivity is in the range of 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁷ to 10 ⁹ Ω · cm. . The secondary transfer roller 9A is made of a foam rubber having a medium resistance, and its volume resistivity is in the range of 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁷ to 10 ⁹ Ω · cm.

In the primary transfer process, a constant current power source with a polarity of (+) is used to apply a primary transfer bias to a roller used as the primary transfer device 7, and the current setting value is in the range of approximately 20 to 40 μA. It is. On the other hand, in applying a secondary transfer bias to a roller 2C (hereinafter also referred to as a repulsive roller) used as a secondary transfer counter roller, a constant current power supply with a polarity of (−) is used, and the current setting value is approximately 20 It is in the range of ˜50 μA. In this way, when the roller 2C is used as a repulsive roller, the drive roller 9A is electrically set to ground.
A secondary transfer electric field is applied to the driving roller 9A connected to the ground in a direction in which the toner on the intermediate transfer belt 2 is pushed out to the paper side.

  Specifically, the intermediate transfer belt 2 of this embodiment is composed of PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF (polyvinylidene fluoride), PPS (polyphenylene sulfide). ) And other materials such as urethane, NBR, CR, etc. on the base layer 50-100 μm composed of a medium resistance resin whose resistance is adjusted by carbon dispersion or ionic conductive agent blending. An elastic layer made of a material whose resistance is adjusted by 100 to 500 μm is provided, and the surface layer is coated with a thin layer of fluorine rubber or resin (or a hybrid material thereof) having a thickness of about 1 to 10 μm. The three-layer belt is configured.

The volume resistivity is in the range of 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁸ to 10 ¹⁰ Ω · cm. Further, the surface resistivity is in the range of 10 ⁶ to 10 ¹² Ω / □, preferably 10 ⁸ to 10 ¹² Ω / □. Further, the Young's modulus (longitudinal elastic modulus) of the base layer is desirably 3000 Mpa or more, and sufficient mechanical strength is required to withstand elongation, bending, wrinkling, and undulation by driving. By using such an elastic intermediate transfer belt having at least one elastic layer and a thin layer on the image forming surface, a thick paper, a paper having a low density of paper fibers, or a so-called embossed paper having an unevenness of 20 to 30 μm on the surface. Even in the case of such papers, the solid filling improvement effect that the toner transfer property to the recesses is improved because the elastic layer follows the recesses is known.

  Examples of other intermediate transfer belts 2 include PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF (polyvinylidene fluoride), and PPS (single-layer belts). A medium resistance resin single layer whose resistance is adjusted by carbon dispersion or ionic conductive agent blending in a material such as polyphenylene sulfide may be used. Also, carbon dispersion or ionic conductive agent blended in materials such as PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF (polyvinylidene fluoride), PPS (polyphenylene sulfide) A belt having a surface layer slightly higher in resistance than the volume resistivity of the belt layer itself may be provided only on the surface side of the intermediate transfer belt 2 having a single-layer structure of medium resistance resin, the resistance of which is adjusted. The surface layer thickness is preferably about 1 to 10 μm. This is a type of belt that performs resistance control by dispersing carbon in a resin, and is a secondary transfer process to paper in which resistance has increased once the paper has passed through fixing and the amount of moisture in the paper has decreased. It is known that the phenomenon of “white spots” occurring is improved. The “white spot” is a phenomenon in which a transfer current concentrates due to variation in the carbon dispersion state, and the toner in that portion is repelled and whitened. By providing the high resistance layer on the surface, local concentration of the transfer current is alleviated, so that the abnormal image “white spot” is improved.

Next, a cleaning device that is a feature of the present invention will be described.
The characteristic part of the present invention is a cleaning device for the secondary transfer belt 9C in the secondary transfer device 9, and is a configuration for efficiently removing the dirt toner adhering to the surface of the secondary transfer belt 9C. Since the transfer toner applied from the back surface of the intermediate transfer belt is also applied to portions other than the sheet, the so-called “fogging toner” adhering to the intermediate transfer belt is attached to the secondary transfer belt. It is transcribed above. Further, when the toner does not come to the secondary transfer nip at the time of transfer due to the jam of the paper, or when the toner is stained, a test toner image for density correction is applied to the secondary transfer belt 9C at the non-image portion between the paper. For example, when transferring.

  If the printing process is further continued in a state where the dirty toner transferred on the secondary transfer belt is left unattended, the dirty toner adheres to the back surface of the paper, and the print quality of the paper is lowered.

FIG. 2 is a schematic configuration diagram of the cleaning device.
The cleaning device applies toner having a polarity opposite to that of the toner to the cleaning blade 15 as the first cleaning means disposed on the downstream side in the moving direction of the secondary transfer device 9 and the secondary transfer counter roller 2C. And a second cleaning means for transferring to the intermediate transfer belt 2. The second cleaning unit is a constant current power source (not shown) that can apply a potential having a polarity opposite to that of the toner, and is connected to the secondary transfer counter roller 2C.

  The cleaning blade 15 is composed of a rubber blade, and the tip of the cleaning blade 15 is brought into contact with the secondary transfer belt 9C, so that dirt toner adhering to the surface of the secondary transfer belt 9C can be scraped off. Yes. Further, the blade 15 can be brought into contact with and separated from the secondary transfer belt, and cleaning is performed only in contact with a predetermined condition. The dirt toner thus scraped off is taken into the collection tank 17 in which the blade 15 is accommodated.

  In the first cleaning by the cleaning device, the contact time of the cleaning blade 15 with the secondary transfer belt 9C is set to be longer than the time required for the secondary transfer belt 9C to make one revolution. Since there is a possibility that dirt toner adheres to the entire circumference of the secondary transfer belt 9C, in order to remove all the dirt toner by the blade 15, the secondary transfer belt 9C makes at least one round. This is because the first cleaning needs to be executed.

  Further, in the second cleaning by the second cleaning means, the dirty toner adhering to the secondary transfer belt 9 </ b> C having the negative polarity (−) which is the charged polarity charged in the developing device 6 is applied to the intermediate transfer belt 2. In order to make the transition, electric field control is performed in which a positive (+) bias electric field having the opposite polarity is applied to the secondary transfer counter roller 2C.

  Then, the dirty toner adhering to the secondary transfer belt 9C is transferred to the intermediate transfer belt 2 at the secondary transfer position by the electrostatic force of the secondary transfer counter roller 2C to which a bias electric field having a polarity opposite to that of the dirty toner is applied. Then, it is collected by the cleaning device 10.

  However, if there is a large amount of dirty toner remaining on the secondary transfer belt 9C, the transfer of the dirty toner from the secondary transfer belt to the intermediate transfer belt 2 is not performed completely. It is insufficient. However, for example, in the case of mono-color printing, single-sided printing, and large-size paper, dirt toner does not adhere to the back surface of the paper, and the second cleaning alone is not problematic.

  In this second cleaning, the application time of the bias electric field is set to be longer than the time required for the secondary transfer belt 9C to make one revolution. Since there is a possibility that dirt toner adheres to the entire circumference of the secondary transfer belt 9C, in order to remove all dirt toner at the secondary transfer position, the secondary transfer belt 9C is at least completely 1 This is because it is necessary to execute the second cleaning during the rotation.

  Similar to the intermediate transfer belt 2, the secondary transfer belt 9C is a single layer or multiple layer belt such as PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF ( It is made of a material having little resistance unevenness with a medium resistance tree in which resistance is adjusted by carbon dispersion or ionic conductive agent blending in a material such as polyvinylidene fluoride) or PPS (polyphenylene sulfide). On the secondary transfer belt, an optical sensor 14 is provided as a detecting means for detecting a test pattern for process control described later.

Here, the operating conditions for cleaning the secondary transfer belt will be described.
Cleaning by the cleaning blade 15 as the first cleaning means has a high cleaning performance but has a problem in durability due to wear deterioration. The bias cleaning by the second cleaning means electrostatically returns the toner from the secondary transfer belt 9C to the intermediate transfer belt 2, but the transfer is not complete, and cleaning during printing is difficult. Therefore, by appropriately using these cleanings, it is possible to reduce the wear of the blades and to have excellent durability and highly reliable cleaning without causing dirt on the back surface, dirt on the edge surface, and the like.

FIG. 3 shows the proper use (combination) of cleaning by the first and second cleaning means according to a predetermined condition.
As a method of properly using these, when there is a large amount of toner remaining on the secondary transfer belt or when the backside stains are conspicuous (during process control, jam recovery, duplex printing, and non-image area is large), 1 cleaning (can be used together with bias cleaning) is performed, and in other normal times, the second cleaning by bias is performed when the sheet does not pass the secondary transfer position.

  Further, the blade cleaning by the first cleaning means is not performed except when necessary in order to prevent the blade from being worn away from the secondary transfer belt. When necessary, the second cleaning means cannot be used and the cleaning performance is insufficient.

  Specifically, blade cleaning by the first cleaning means is performed during full-color duplex printing. This is because multiple colors increase fog toner compared to mono color, and because the printing surface side (second surface) is stained due to double-sided printing, dirt that is not noticeable on the back surface is noticeable on one side. By becoming easy.

  In addition, blade cleaning by the first cleaning unit is performed during the passage of a small-sized sheet (for example, A4 vertical width or less). This is because the non-sheet passing area increases for small size paper, so the dirt toner normally taken by the paper passing portion accumulates on the secondary transfer belt. This is because the accumulated dirt toner easily adheres to the paper when the paper is passed.

  Also, blade cleaning by the first cleaning means is performed in the inter-sheet process control and non-image portion process control. In this case, when a process control test pattern for image quality adjustment or the like is created, the test pattern is cleaned.

  The process control for image quality adjustment creates and detects a test pattern in order to perform image density control and positional deviation control. The image density control performs toner density, LD writing condition change control, and the like according to the toner adhesion amount developed from the reference pattern, and the misregistration control performs image writing timing control of each color based on the misregistration pattern. As for the detection location, image density control is usually performed by detecting the pattern sensor on the photoconductor or on the intermediate transfer belt immediately downstream after development. It is difficult to provide and often detects on the intermediate transfer belt. The misregistration control in the tandem image forming apparatus controls the misregistration between the photoreceptors and the misregistration due to the writing timing of each color. Therefore, detection on the intermediate transfer belt is essential. Do.

  However, in this embodiment, an elastic intermediate transfer belt having at least one elastic layer and a thin layer on the image forming surface is used, and it is difficult to detect a test pattern on the intermediate transfer belt. I do.

  The reason is as follows. In the detection of the toner pattern on the intermediate transfer belt, first, the LED output light amount is adjusted (Vsg adjustment) so that the sensor output of the surface of the intermediate transfer belt without toner, the so-called background portion, becomes 4.0 V, for example. The toner density is detected from the sensor output. Therefore, the glossiness of the intermediate transfer belt is important for Vsg adjustment. If the glossiness is high, Vsg adjustment can be performed with a low light emission amount of the sensor, and a high S / N ratio with respect to toner can be obtained. However, the elastic intermediate transfer belt has lower gloss than a single layer resin belt such as polyimide, and the reflected light from the intermediate transfer belt is reduced, so that the amount of light emitted from the LED increases and the amount of reflected light from the toner increases. This is because the N ratio becomes low, resulting in poor control in some cases.

  The glossiness of the elastic intermediate transfer belt is lowered because both the elastic layer and the surface layer are flexible and low in strength, so that the elastic blade is easily scratched, and the toner particles are easily caught between the blade edge and the elastic intermediate transfer belt. Therefore, the cleaning property is inferior and filming occurs, and irregular reflection and absorption increase due to scratches and filming. As described above, since it is difficult to perform process control with the test pattern on the elastic intermediate transfer belt, stable process control can be performed by detecting the test pattern transferred onto the secondary transfer belt.

  As described above, a test pattern is formed on the secondary transfer belt during process control (generally, when the power is turned on, before or after printing is started, or after printing a predetermined number of sheets). Therefore, the toner is removed by blade cleaning by the first cleaning means.

  In addition, process control is generally performed outside of printing, but even during printing for further image quality stabilization, between sheets (time or interval between the end of the last image formation and the next next image formation start) ) Or a non-image part, and a density control method for controlling a toner density control reference value (Vref) of a magnetic permeability sensor in some cases is also performed.

  In this case, it is necessary to clean the test pattern toner adhering to the secondary transfer belt during printing (when the paper passes the secondary transfer position), and cleaning by the second cleaning means is difficult. It is.

  Further, when the paper does not come to the secondary transfer nip at the time of transfer due to the jam of the paper, the amount of toner already transferred onto the secondary transfer belt is larger than the fog toner. Blade cleaning is performed by the first cleaning means.

  Under the above conditions, the cleaning blade 15 is brought into contact with the secondary transfer belt, thereby cleaning the secondary transfer belt. Except for the above conditions, the blade 15 is kept away from the secondary transfer belt 9C, so that the wear of the blade is suppressed and the durability is improved as compared with the case where the blade 15 is always in contact.

  Further, as shown in FIG. 3, in order to improve the cleaning performance and shorten the cleaning time, the second cleaning means is used during post-jam recovery operation, which is the operation of the first cleaning means other than during printing, and during normal process control. You may use together the bias cleaning by.

  On the other hand, as shown in FIG. 3, when the cleaning by the first cleaning unit is not performed, the cleaning of the secondary transfer belt is performed by the second cleaning unit. Specifically, it is when the apparatus is turned on when the power is turned on, or when returning from standby, sleep, low power mode, or the like. In these cases, the cleaning by the second cleaning means is performed while the start-up return sequence (such as fixing warm-up and image-forming engine warm-up) is performed.

  In this second cleaning, the application time of the bias electric field is set to be longer than the time required for the secondary transfer belt 9C to make one revolution, and is about 5 seconds in this embodiment. Since there is a possibility that dirty toner adheres to the entire circumference of the secondary transfer belt, in order to remove all the dirty toner, cleaning is performed while the secondary transfer belt makes at least one complete rotation. Thus, the belt can be reliably cleaned. Further, since the second cleaning is completed during the start-up return sequence, the waiting time of the user is not increased.

Further, as shown in FIG. 3, the second cleaning unit performs the second cleaning before the start of printing (before paper passing) and after the end of printing (after paper passing).
Specifically, FIG. 4 shows an example of control of the secondary transfer bias and the second cleaning bias. First, a secondary transfer (printing) is performed by applying a negative (−) secondary transfer bias. Here, the positive (+) second cleaning bias is applied at the timing when the copy button of the image forming apparatus is pressed and the sheet feeding is started as shown in FIG. It may be only during the so-called pre-rotation until reaching (II). In addition to during the pre-rotation, cleaning may be performed during the so-called post-rotation from when the trailing edge of the paper exits the secondary transfer nip until the fixing operation is stopped and the operation of the apparatus is stopped (I). In addition, cleaning may be performed only during post-rotation (III).

The bias application time may be one round of the belt at each of the pre-rotation time and the post-rotation time. In this embodiment, the bias application time is 5 seconds.
Further, as shown in FIG. 5, the belt may be used for one rotation of the belt by combining the pre-rotation and the post-rotation in order to shorten the first print time.

  As mentioned above, although some embodiment was shown, this invention is not limited to these. That is, the combination of cleaning operations based on the predetermined conditions is not limited.

  As shown in FIG. 6, in order to improve the cleaning performance of the blade 15 as the first cleaning means, a cleaning brush (fur brush) as a cleaning auxiliary member is upstream of the blade 15 in the rotational direction of the secondary transfer belt 9C. May be added to Residual toner and the like on the secondary transfer belt are first removed with a fur brush, and the cleaning performance is improved by scraping off the residual toner from the surface of the secondary transfer belt with a cleaning blade. Further, even if the pressure contact force (sliding force) of the blade 15 is weakened to some extent, a sufficient cleaning effect can be obtained, so that blade wear can be further reduced.

  Specifically, the transfer residual toner is removed, the fur brush 21 that applies the lubricant to the secondary transfer belt 9C, the flicker 24 that removes the transfer residual toner attached to the fur brush 21 by flicking, and the solid state lubricity imparting agent. A lubricant molded body 22, a pressing spring 23 that presses the lubricant molded body 22 against the fur brush 21 with a predetermined pressure, a cleaning blade 15 that removes transfer residual toner on the surface of the secondary transfer belt and uniformly stretches the lubricant. It has.

  In this embodiment, the fur brush 21 has both a function of removing dirt toner and a function of applying a lubricant. However, the fur brush 21 may be configured not to apply a lubricant. The contact method of the cleaning blade 15 may be either a counter method or a trailing method, but the counter method is particularly preferable. This is because the counter system can efficiently remove the dirty toner even if the contact pressure against the secondary transfer belt 9C is small, and the secondary transfer belt is less worn.

The material for forming the cleaning blade 15 is not particularly limited as long as it is urethane rubber. In particular, in consideration of the molding process of the cleaning blade 15, a liquid thermosetting material is used. As the production method, a prepolymer method, a one-shot method, and a pseudo one-shot method which is an intermediate between them are used. As the liquid forming material, for example, a material mainly composed of a urethane rubber prepolymer and a curing agent is used.
The prepolymer for urethane rubber is obtained by partially polymerizing polyisocyanate and polyol.

  Examples of the lubricant of the lubricant molding 22 include lead oleate, zinc oleate, copper oleate, zinc stearate, cobalt stearate, iron stearate, copper stearate, zinc palmitate, copper palmitate, linolene. Fatty acid metal salts such as zinc acid, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polytrifluorochloroethylene, dichlorodifluoroethylene, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-oxafluoropropylene Fluorine-based resins such as copolymers are listed. In particular, a metal stearate having a large effect of reducing the friction of the secondary transfer belt, and further zinc stearate are preferable. As the molded lubricant 22, a product obtained by melting and solidifying a fatty acid metal salt such as zinc stearate and processing it into a rod shape can be used.

  The fur brush 21 has a shape extending in the axial direction of the secondary transfer belt 9C, and rotates in the same direction as the rotation direction of the secondary transfer belt at a contact portion with the secondary transfer belt. The pressing spring 23 is urged against the fur brush 21 so that substantially all of the lubricant molding 22 is used up. Since the molded lubricant 22 is a consumable item, its thickness decreases with time. However, the lubricant can be scraped off by being always brought into contact with the fur brush 21 by the pressure applied by the pressing spring 23, and then secondary. Supply and apply to the transfer belt 9C. At this time, the amount of lubricant applied to the photoreceptor 3 can be adjusted by adjusting the weight of the molded lubricant 22 or the pressure spring 23.

  The fur brush 21 is made of an insulating polyester fiber and is sewn on an insulating base fabric. Furthermore, an insulating adhesive is attached to the sewn polyester fiber so that the sewn polyester fiber is not unraveled. By making the fur brush 21 insulative, the influence on the potential of the secondary transfer belt 9C can be suppressed, and transfer residual toners having different polarities can be efficiently removed.

  In this embodiment, an insulating fur brush is used. However, a conductive brush may be used, and cleaning may be performed by applying a bias having a polarity opposite to that of the toner. The fur brush is completed by winding the base fabric with the brushes around the core. Further, a fur brush that fell down in the order of rotation of the fur brush was used.

  Since the flicker 24 is not U-shaped but a plate-like member, residues such as transfer residual toner attached to the fur brush 21 can be stably removed over a long period of time. Due to the shape of the fur brush 21 and the effect of falling down, the torque can be kept low even if the flicker 24 is present.

  In addition, since the shaving amount of the lubricant molded body 22 can be reduced, the use period of the lubricant molded body 22 is extended and the life is improved.

  As shown in FIG. 7, instead of the fur brush described above, a cleaning roller 26 may be added as a cleaning auxiliary member upstream of the blade 15 in the rotational direction of the secondary transfer belt 9C. As the secondary transfer belt rotates, the cleaning roller 26 rotates while being in sliding contact with the secondary transfer belt to remove the toner remaining on the intermediate transfer belt. Next, the cleaning performance is improved by scraping the toner on the secondary transfer belt, which could not be removed by the cleaning roller, with a cleaning blade. Further, sufficient cleaning performance can be obtained even if the contact pressure of the blade is reduced. As a result, blade wear is reduced, and durability is further improved.

  The cleaning roller 26 is provided with a scraper 28 that scrapes off transfer residual toner attached to the cleaning roller. As the cleaning roller 26, an elastic roller such as a sponge roller or a rubber roller can be used, but in general, a sponge roller is preferably used.

  Further, the cleaning roller 26 is normally provided so as to be driven and rotated with respect to the secondary transfer roller 9A. However, the rotation direction of the secondary transfer roller 9A is not driven and rotated by using an appropriate driving mechanism or the like. It is also possible to provide it so as to rotate in the same direction. Alternatively, a conductive cleaning roller may be used, and cleaning may be performed by applying a bias having a polarity opposite to that of the toner.

2 Intermediate transfer belt (intermediate transfer member)
2C Secondary transfer counter roller 3 Photoconductor (latent image carrier)
4 Charging device 6 Developing device 7 Primary transfer device 9C Secondary transfer belt (secondary transfer body)
10 Cleaning device 14 Optical sensor (detection means)
15 Cleaning blade (first cleaning means)

JP 2000-29367 A JP 2002-91181 A

Claims (8)

A latent image carrier for carrying an electrostatic latent image; a charging device for charging the surface of the latent image carrier; a developing device for developing a latent image on the latent image carrier to form a toner image; An intermediate transfer member that is wound around a plurality of rollers including a secondary transfer counter roller at a position facing the latent image carrier, and a primary transfer device that transfers a toner image on the latent image carrier to the intermediate transfer member And a cleaning device that removes toner remaining on the intermediate transfer member, and a toner image on the intermediate transfer member is recorded at a secondary transfer position in contact with the intermediate transfer member against the secondary transfer counter roller. A secondary transfer body that transfers the recording medium to the fixing device and transfers the recording medium to a fixing device,
A first cleaning means disposed so as to be able to contact with and separate from the secondary transfer body and scraping off toner adhering to the secondary transfer body; and when the recording medium does not pass through the secondary transfer position. A second cleaning means for transferring the toner remaining on the secondary transfer body to the intermediate transfer body by applying a bias having a polarity opposite to that of the toner to the secondary transfer counter roller;
When the first cleaning unit is not used, the first cleaning unit is separated from the secondary transfer member,
During the process control for adjusting the image density and the positional deviation at the timing of the non-image portion during printing and during continuous printing or during printing, the first cleaning means is used as the secondary transfer body. The cleaning is performed without operating the second cleaning unit , and the contact time of the first cleaning unit with the secondary transfer member is a time during which the secondary transfer member rotates at least once. Yes,
When the process control to adjust the image density and displacement at the timing other than during printing, the first cleaning means is brought into contact with the secondary transfer member, and a row physician cleaning by operating the second cleaning means The contact time of the first cleaning unit to the secondary transfer member and the bias application time of the second cleaning unit are times for the secondary transfer member to rotate at least once. Forming equipment.   The image forming apparatus according to claim 1, wherein the first cleaning unit contacts the secondary transfer body when the recording medium is returned after jamming or when duplex printing is performed.   3. The image forming apparatus according to claim 1, wherein the second cleaning unit operates when the apparatus is started up or when the apparatus is returned from standby, sleep, or low power mode.   The image forming apparatus according to claim 1, wherein the second cleaning unit operates before printing is started and / or after printing is finished. The upstream side in the rotation direction of the secondary transfer member than the first cleaning means, the image forming apparatus according to any one of claims 1 to 4, characterized in that it has a brush as a cleaning auxiliary member. The upstream side in the rotation direction of the secondary transfer member than the first cleaning means, the image forming apparatus according to any one of claims 1 to 4, characterized in that it has a roller as a cleaning auxiliary member. The intermediate transfer member, the image forming apparatus according to any one of claims 1 to 6, characterized in that an elastic intermediate transfer belt having a thin layer to at least one elastic layer and the image forming surface. A detection means for detecting a test pattern used provided to adjust the image density and displacement, according to claim 1-7, characterized in that for detecting the test pattern on said secondary transfer member by said detecting means The image forming apparatus according to claim 1.

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