Patent Application
20110103862
1. Field of the Invention
Exemplary aspects of the present invention relate to an image forming apparatus and a guide therefor, and more particularly to an image forming apparatus and a guide for guiding a recording medium bearing a toner image from a transferor to a fixing unit.
2. Description of the Related Art
A related art image forming apparatus, such as a copying machine, a facsimile machine, a printer, or a multifunction printer having copying, printing, scanning, and facsimile functions, forms an electrostatic latent image on a photoconductor according to image data. The electrostatic latent image is developed with a developer (e.g., a toner) to form a toner image on the photoconductor. The toner image is transferred onto a recording medium (e.g., a sheet of paper) and sent to a fixing unit. In the fixing unit, a fixing roller and a pressing roller apply heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium.
The toner image formed on the photoconductor may be transferred onto the recording medium directly from the photoconductor or indirectly via an intermediate transfer medium (hereinafter referred to as the intermediate transfer belt). When the toner image is indirectly transferred via the intermediate transfer belt, the toner image formed on the photoconductor is transferred onto the intermediate transfer belt, and further transferred from the intermediate transfer belt onto the recording medium. The photoconductor or the intermediate transfer belt opposes a transfer bias roller to form a transfer nip at which the toner image is transferred from the photoconductor or the intermediate transfer belt onto one side (i.e., front side) of the recording medium. Specifically, the transfer bias roller applies a transfer bias having a polarity opposite to the polarity of a toner forming the toner image to the other side (i.e., backside) of the recording medium. Thus, the recording medium has an electric charge having the polarity opposite to the polarity of the toner and thereby attracts the toner, resulting in electrostatic transfer of the toner image.
When the amount of electric charge on the backside of the recording medium is too large, the recording medium is electrostatically attracted to the photoconductor or the intermediate transfer belt after the recording medium passes the transfer nip. In this case, a problem occurs such that the recording medium cannot separate from the photoconductor or the intermediate transfer belt, resulting in jamming of the recording medium. In addition, a problem which occurs is that the electric charge is abruptly transferred from the backside of the recording medium to a protruding member and/or a metallic member disposed on a downstream side from the transfer nip and on an upstream side from the fixing unit in a conveyance direction of the recording medium. This problem results in formation of a defective toner image, including small circle marks on the recording medium.
Further, when the backside of the recording medium has too large an amount of electric charge, the front side of the recording medium has a substantial amount of electric charge having a polarity opposite to the polarity of the electric charge of the backside of the recording medium. When the electric charge of the front side of the recording medium moves along the surface thereof, the toner image on the front side of the recording medium may be deformed. Specifically, a defective toner image (such as zigzag images) may be formed along a trail of the moving electric charge.
To address the above-described problems, an example of a related art image forming apparatus is proposed which further includes a discharger for discharging the backside of the recording medium immediately after the recording medium passes the transfer nip.
In addition, a related art image forming apparatus is provided which uses a spherical toner manufactured by a polymerization method so as to form a high resolution toner image. Toner particles of the spherical toner make point-contact with each other. Therefore, the toner particles attract each other with a decreased attracting force and have an increased flowability. The toner particles also make point-contact with the photoconductor or the intermediate transfer belt. Therefore, the photoconductor or the intermediate transfer belt attracts the toner particles with a decreased attracting force, thereby increasing transfer efficiency.
In the fixing unit, the fixing roller opposes the pressing roller to form a fixing nip at which the fixing roller and the pressing roller apply heat and pressure to the recording medium bearing the toner image so as to fix the toner image on the recording medium. When the fixing roller scrubs the pressing roller or the recording medium at the fixing nip, the fixing roller may be charged with the polarity opposite to the polarity of the toner by friction between the fixing roller and the pressing roller or the recording medium. When a recording medium bearing a toner image formed with a spherical toner is conveyed toward the fixing nip in a low temperature and low humidity environment, the toner on the recording medium may scatter in the moving direction of the recording medium immediately before the toner image reaches the fixing nip.
The related art image forming apparatus further includes a guide for guiding the recording medium bearing the toner image from the transfer nip toward the fixing unit. While the guide guides the recording medium, the recording medium scrubs the guide. Friction between the recording medium and the guide may charge the guide with the polarity opposite to the polarity of the toner and may charge the backside of the recording medium with the same polarity as that of the toner. The electric charge having the same polarity as that of the toner of the charged backside of the recording medium counteracts the electric charge having the polarity opposite to the polarity of the toner, i.e., the electric charge applied by the transfer bias roller. Thus, the backside of the recording medium has a decreased amount of electric charge having the polarity opposite to the polarity of the toner. This occurs easily in a low temperature and low humidity environment. The discharger also removes the electric charge from the backside of the recording medium. Thus, the recording medium electrostatically attracts the toner with a decreased attracting force. As a result, the above-mentioned toner scatter problem is caused.
This specification describes below an image forming apparatus according to an exemplary embodiment of the invention. In one aspect of the present invention, the image forming apparatus includes an image carrier, a transferor, a fixing unit, and a guide. The image carrier carries a toner image. The transferor opposes the image carrier to form a transfer nip and transfers the toner image on the image carrier onto a recording medium at the transfer nip. The fixing unit fixes the toner image on the recording medium. The guide guides the recording medium bearing the toner image from the transferor toward the fixing unit and includes a surface portion directly contacting the recording medium. The surface portion includes a material for charging the recording medium to have a polarity opposite to the polarity of a toner forming the toner image.
This specification further describes a guide for guiding a recording medium bearing a toner image from a transferor toward a fixing unit according to an exemplary embodiment of the invention. In one aspect of the present invention, the guide includes a discharger and a surface portion. The discharger discharges the recording medium immediately after the transferor transfers the toner image onto the recording medium. The surface portion directly contacts the recording medium and includes a material for charging the recording medium to have a polarity opposite to the polarity of a toner forming the toner image.
A more complete appreciation of the invention and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing exemplary embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in particular to
As illustrated in
The image forming apparatus 100 may be a copying machine, a facsimile machine, a printer, a multifunction printer having copying, printing, scanning, and facsimile functions, or the like. According to this non-limiting exemplary embodiment of the present invention, the image forming apparatus 100 functions as a color printer for printing a color image on a recording medium using an electrophotographic method.
The image forming unit 9 forms toner images in yellow, magenta, cyan, and black colors. Each of the photoconductors 1Y, 1M, 1C, and 1K has a drum-like shape and rotates in a rotating direction A at a circumferential speed of about 150 mm/sec. The photoconductors 1Y, 1M, 1C, and 1K are disposed in the image forming apparatus 100 in such a manner that rotating shafts of the photoconductors 1Y, 1M, 1C, and 1K horizontally extend from the front to the back of the image forming apparatus 100. The rotating shafts of the photoconductors 1Y, 1M, 1C, and 1K are provided so as to be parallel to each other on the same horizontal plane.
The chargers 4Y, 4M, 4C, and 4K, the development units 6Y, 6M, 6C, and 6K, and the cleaners 2Y, 2M, 2C, and 2K are respectively disposed around the photoconductors 1Y, 1M, 1C, and 1K. The chargers 4Y, 4M, 4C, and 4K uniformly charge surfaces of the photoconductors 1Y, 1M, 1C, and 1K respectively. According to this non-limiting exemplary embodiment, each of the chargers 4Y, 4M, 4C, and 4K includes a charging roller (not shown) which contacts the surface of each of the photoconductors 1Y, 1M, 1C, and 1K and rotates while being driven by each of the rotating photoconductors 1Y, 1M, 1C, and 1K so as to charge the surface of each of the photoconductors 1Y, 1M, 1C, and 1K. However, the chargers 4Y, 4M, 4C, and 4K may be configured to respectively charge the surfaces of the photoconductors 1Y, 1M, 1C, and 1K without contacting the surfaces of the photoconductors 1Y, 1M, 1C, and 1K. A high-voltage power source (not shown) applies alternating and direct current biases to each of the chargers 4Y, 4M, 4C, and 4K. Thus, the chargers 4Y, 4M, 4C, and 4K uniformly charge the surfaces of the photoconductors 1Y, 1M, 1C, and 1K respectively so that each of the photoconductors 1Y, 1M, 1C, and 1K has a surface potential of about −500 V.
The exposure unit 3 is disposed under the image forming unit 9 and emits light 5Y, 5M, 5C, and 5K upward to irradiate the charged surfaces of the photoconductors 1Y, 1M, 1C, and 1K according to image data, resulting in formation of an electrostatic latent image on the surface of each of the photoconductors 1Y, 1M, 1C, and 1K. The image data includes yellow, magenta, cyan, and black image data. Namely, the exposure unit 3 irradiates with the light 5Y, 5M, 5C, and 5K the surfaces of the photoconductors 1Y, 1M, 1C, and 1K according to the yellow, magenta, cyan, and black image data to form electrostatic latent images corresponding to the yellow, magenta, cyan, and black image data, respectively. The exposure unit 3 may include a laser beam scanner using a laser diode.
The development units 6Y, 6M, 6C, and 6K respectively develop the electrostatic latent images formed on the surfaces of the photoconductors 1Y, 1M, 1C, and 1K with yellow, magenta, cyan, and black toners to form yellow, magenta, cyan, and black toner images. According to this non-limiting exemplary embodiment, each of the development units 6Y, 6M, 6C, and 6K develops the electrostatic latent image with a two-component non-magnetic developer including a toner. Specifically, each of the development units 6Y, 6M, 6C, and 6K includes a developing roller (not shown), which contacts each of the photoconductors 1Y, 1M, 1C, and 1K, for carrying the developer. A high-voltage power source (not shown) applies a predetermined developing bias to the developing roller so as to move the toner in the developer carried by the developing roller onto the electrostatic latent image formed on each of the photoconductors 1Y, 1M, 1C, and 1K. The toner adheres to the electrostatic latent image. Thus, a toner image corresponding to the electrostatic latent image forms on the surface of each of the photoconductors 1Y, 1M, 1C, and 1K.
The intermediate transfer belt 10 is disposed above the image forming unit 9. The yellow, magenta, cyan, and black toner images respectively formed on the surfaces of the photoconductors 1Y, 1M, 1C, and 1K are transferred onto the intermediate transfer belt 10 while superimposed to form a color toner image. The intermediate transfer belt 10 has an endless belt-like shape and is looped over the first transfer bias rollers 11Y, 11M, 11C, and 11K, and the rollers 12, 13, 14, and 15. A driving force is transmitted from a driver (not shown) to the roller 12 to drive and rotate the roller 12. The rotating roller 12 rotates the intermediate transfer belt 10 in a rotating direction B. Namely, the roller 12 supports and drives the intermediate transfer belt 10. However, any one of the other rollers may support and drive the intermediate transfer belt 10.
The intermediate transfer belt 10 includes one or more layers preferably including a material such as PVDFs (polyvinylidene fluoride), ETFEs (ethylene-tetrafluoroethylene copolymers), PIs (polyimide), and PCs (polycarbonate), in which a conductive material including carbon black and the like is dispersed to control the volume resistivity of the intermediate transfer belt 10 in a range of from about 108 Ω·cm to about 1012 Ω·cm and the surface resistivity in a range of from about 108Ω/□ to about 1015Ω/□. When the volume resistivity and the surface resistivity of the intermediate transfer belt 10 respectively exceed the above-described ranges, a higher transfer bias needs to be applied to the intermediate transfer belt 10, resulting in an increased power cost. Further, when a higher transfer bias is applied to the intermediate transfer belt 10, the electric potential of the intermediate transfer belt 10 increases to an extent which can not be reduced by self-discharge. Therefore, a discharging mechanism for discharging the intermediate transfer belt 10 is needed, resulting in increased manufacturing costs. When the volume resistivity and the surface resistivity of the intermediate transfer belt 10 do not respectively reach the above-described ranges, the electric potential of the intermediate transfer belt 10 can be decreased quickly by self-discharge. However, a transfer current, which flows when the toner image is transferred, may easily flow along a surface of the intermediate transfer belt 10, resulting in occurrence of toner scattering. Therefore, it is preferable for the intermediate transfer belt 10 to have the volume resistivity and the surface resistivity in the above-described ranges. The volume resistivity and the surface resistivity of the intermediate transfer belt 10 were measured by the following method:
The intermediate transfer belt 10 may further include a releasing layer on the surface of the intermediate transfer belt 10, if necessary. The releasing layer may include fluoroplastic such as ETFEs, PTFEs (polytetrafluoroethylene), PVDFs, PFAs (perfluoroalkoxy resins), FEPs (tetrafluoroethylene-propylene fluoride copolymers), and PVFs (polyvinyl fluoride). However, the fluoroplastic is not limited thereto. The intermediate transfer belt 10 can be produced by a cast molding method, a centrifugal molding method, or the like. The surface of the intermediate transfer belt 10 may be polished, if necessary.
A high voltage power source (not shown) applies a first transfer bias to the first transfer bias rollers 11Y, 11M, 11C, and 11K over which the intermediate transfer belt 10 is looped. The first transfer bias rollers 11Y, 11M, 11C, and 11K contact an inner circumferential surface of the intermediate transfer belt 10 and respectively oppose the photoconductors 1Y, 1M, 1C, and 1K with the intermediate transfer belt 10 therebetween to each form a first transfer nip. The first transfer nips are respectively formed between the photoconductors 1Y, 1M, 1C, and 1K and an outer circumferential surface of the intermediate transfer belt 10. Each of the first transfer bias rollers 11Y, 11M, 11C, and 11K includes an elastic layer to form the first transfer nip. The first transfer bias rollers 11Y, 11M, 11C, and 11K perform a first transfer at the first transfer nips. Namely, the first transfer bias rollers 11Y, 11M, 11C, and 11K respectively transfer the yellow, magenta, cyan, and black toner images respectively formed on the surfaces of the photoconductors 1Y, 1M, 1C, and 1K onto the outer circumferential surface of the intermediate transfer belt 10 superimposing the toner images thereon.
The cleaners 2Y, 2M, 2C, and 2K respectively remove residual toners remaining on the surfaces of the photoconductors 1Y, 1M, 1C, and 1K after the yellow, magenta, cyan, and black toner images respectively formed on the surfaces of the photoconductors 1Y, 1M, 1C, and 1K are transferred onto the outer circumferential surface of the intermediate transfer belt 10. The cleaning blades 2Yb, 2Mb, 2Cb, and 2Kb contact the surfaces of the respective photoconductors 1Y, 1M, 1C, and 1K to scrape the residual toner remaining on the surfaces of the photoconductors 1Y, 1M, 1C, and 1K.
The paper tray 31 is loaded with a recording medium (e.g., sheets P). The pick-up roller 26 feeds a sheet P from the paper tray 31 toward the feeding roller pair 27. The feeding roller pair 27 further feeds the sheet P toward the registration roller pair 28.
The second transfer bias roller 21 contacts the outer circumferential surface of the intermediate transfer belt 10 and opposes the roller 12 via the intermediate transfer belt 10 to form a second transfer nip. The second transfer nip is formed between the second transfer bias roller 21 and the outer circumferential surface of the intermediate transfer belt 10. The registration roller pair 28 feeds the sheet P to the second transfer nip such that the color toner image formed on the outer circumferential surface of the intermediate transfer belt 10 is transferred to the proper position of the sheet P at the second transfer nip. The second transfer bias roller 21 performs second transfer at the second transfer nip. Namely, the second transfer bias roller 21 transfers the color toner image formed on the outer circumferential surface of the intermediate transfer belt 10 onto the sheet P at the second transfer nip.
The second transfer bias roller 21 is connected to the second transfer power source 50. The second transfer power source 50 applies a second transfer bias to the second transfer bias roller 21. The second transfer power source 50 is connected to the controller 51 for controlling the second transfer bias. The second transfer bias roller 21 includes a core and an elastic layer coated on the core. The core includes a metal (e.g., stainless steel SUS and/or the like). The elastic layer includes polyurethane and a conductive material, and has a resistivity in a range of from about 106Ω to about 1010Ω. When the resistivity of the second transfer bias roller 21 exceeds the above-described range, a transfer current may not easily flow and a higher voltage needs to be applied to the second transfer bias roller 21 to well perform image transferring, resulting in an increased power cost. Further, when a higher voltage is applied to the second transfer bias roller 21, discharge may occur in spaces just before or after the second transfer nip in a sheet conveyance direction, resulting in formation of white spots on a halftone image. When the resistivity of the second transfer bias roller 21 does not reach the above-described range, image transferring cannot be performed well, particularly when the image includes both an image formed by superimposing a plurality of different color toner images and a single color toner image. The reason therefore is as follows. When the resistivity of the second transfer bias roller 21 is low, and a low voltage is applied as the second transfer bias to effectively transfer the portion of the image formed by the single color toner image, a proper transfer current sufficient for properly transferring the portion of the image formed by superimposing the plurality of the different color toner images cannot be flown. In contrast, application of a high voltage as the second transfer bias may provide a transfer current sufficient for transferring the portion of the image formed by superimposing the plurality of the different color toner images, but may not provide a proper transfer current for the portion of the image formed by the single color toner image due to excessive transfer current flow, resulting in decreased transfer efficiency. The resistivity of the second transfer bias roller 21 is calculated based on a current flown when a voltage of about 1,000 V is applied between the core and a conductive metal plate, wherein a load of about 4.9 N (i.e., the both ends of the core receive a total load of about 9.8 N) is applied to each of the ends of the core of the second transfer bias roller 21.
A driving gear (not shown) drives and rotates the second transfer bias roller 21 at a circumferential speed similar to the circumferential speed of the intermediate transfer belt 10. The second transfer bias roller 21 rotates in a rotating direction such that the second transfer bias roller 21 is driven by the rotating intermediate transfer belt 10.
The second transfer bias roller 21 and the intermediate transfer belt 10 feed the sheet P, which bears the color toner image transferred from the outer circumferential surface of the intermediate transfer belt 10 at the second transfer nip, toward the guide 41. The guide 41 includes discharging teeth (described below) at a head of the guide 41. The discharging teeth discharge the charges of the sheet P. The guide 41 separates the sheet P from the intermediate transfer belt 10 and guides the sheet P toward the fixing unit 30.
In the fixing unit 30, the sheet P is fed toward a fixing nip formed between the fixing roller 30a and the pressing roller 30b. At the fixing nip, the fixing roller 30a and the pressing roller 30b apply heat and pressure to the sheet P bearing the color toner image to fix the color toner image on the sheet P. Each of the fixing roller 30a and the pressing roller 30b has a surface resistivity not lower than about 107Ω/□ and a volume resistivity not lower than about 107 Ω·cm. The fixing roller 30a and the pressing roller 30b feed the sheet P bearing the fixed color toner image toward the output roller pair 32. The output roller pair 32 feeds the sheet P to outside of the image forming apparatus 100.
The belt cleaner 19 opposes the roller 13 via the intermediate transfer belt 10. The belt cleaner 19 removes a residual toner remaining on the outer circumferential surface of the intermediate transfer belt 10 even after the color toner image formed on the outer circumferential surface of the intermediate transfer belt 10 is transferred onto the sheet P. The cleaning blade 19b contacts the outer circumferential surface of the intermediate transfer belt 10 to scrape the residual toner off the outer circumferential surface of the intermediate transfer belt 10.
According to this non-limiting exemplary embodiment, a user may specify a monochrome mode, a two-color mode, a three-color mode, or a full-color mode on a control panel (not shown) of the image forming apparatus 100. The monochrome mode forms an image by using any one of yellow, magenta, cyan, and black toner images. The two-color mode forms an image by superimposing any two of yellow, magenta, cyan, and black toner images. The three-color mode forms an image by superimposing any three of yellow, magenta, cyan, and black toner images. The full-color mode forms an image by superimposing yellow, magenta, cyan, and black toner images.
According to this non-limiting exemplary embodiment, the image forming apparatus 100 uses a polymerized toner produced by a polymerization method. The polymerized toner may preferably have a shape factor SF-1 in a range of from about 100 to about 180 and a shape factor SF-2 in a range of from about 100 to about 180.
C=(D2/E)×(100×4π) Equation 1
F=(G2/H)×(100×4π) Equation 2
The shape factors SF-1 and SF-2 of a toner are determined by photographing the toner particles with a scanning electron microscope S-800 available from Hitachi, Ltd. and analyzing the photographed images with an image analyzer LUZEX III available from NIRECO Corporation.
When toner particles have a sphere-like shape, the toner particles contact each other at a small area. Namely, the toner particles nearly make point-contact with each other and therefore the attracting force between the toner particles becomes weaker. As a result, the fluidity of the toner particles becomes greater. The toner particles also contact the surface of each of the photoconductor 1Y, 1M, 1C, and 1K and the intermediate transfer belt 10 at a small area. Namely, the toner particles nearly make point-contact with the surface of each of the photoconductors 1Y, 1M, 1C, and 1K and the intermediate transfer belt 10 and the attracting force between the toner particles and each of the photoconductors 1Y, 1M, 1C, and 1K and the intermediate transfer belt 10 becomes weaker. As a result, the toner particles can be transferred onto and from the intermediate transfer belt 10 at an increased transfer rate. When any one of the shape factors SF-1 and SF-2 exceeds 180, the toner particle may be transferred onto and from the intermediate transfer belt 10 at a decreased transfer rate. Further, the toner particles adhered to the intermediate transfer belt 10 cannot be easily removed therefrom.
The toner for use in the image forming apparatus 100 of the present invention preferably has a volume average particle size in a range of from about 4 μm to about 10 μm. When the toner has a particle size smaller than the above-described range, it can easily cause a background development problem. In particular, the toner particles can stain the sheet P. In addition, the toner particles have a decreased flowability and easily agglomerate, thereby forming hollow images. In contrast, when the toner has a particle size greater than the above-described range, the toner particles scatter and resolution of an image deteriorates, (i.e., a high-resolution image cannot be formed). According to this non-limiting exemplary embodiment, the image forming apparatus 100 uses toner particles having a volume average particle size of about 6.5 μm.
As illustrated in
The base 41a includes a low-cost insulating material such as ABS (acrylonitrile-butadiene-styrene) resins. The ribs 42 include a plurality of insulating ribs integrally molded with the base 41a. The discharging plate 40 includes a plurality of discharging teeth 40a having a protruding shape. The guide sheet 43 is disposed on the base 41a. The discharging plate 40 is connected to a power source (not shown) for applying a discharging bias having the same polarity (i.e., a polarity opposite to a polarity of the second transfer bias) as the polarity of the toner used. According to this non-limiting exemplary embodiment, the discharging bias has a negative polarity. The power source applies the discharging bias to the discharging plate 40 so that a tip of each of the discharging teeth 40a causes corona discharge to discharge the backside of the sheet P which has passed the second transfer nip and which bears a toner image transferred from the intermediate transfer belt 10 on its front side.
As illustrated in
The guide sheet 43 is disposed on the base 41a and contacts the sheet P. The guide sheet 43 is attached to the base 41a with a double-faced adhesive tape. The guide sheet 43 includes a material for charging the sheet P to have the same polarity as the polarity of the second transfer bias, that is, a polarity opposite to the polarity of the toner on the sheet P, by friction between the guide sheet 43 and the sheet P.
As illustrated in
The sheet P discharged by the discharging teeth 40a separates from the intermediate transfer belt 10 and contacts the guide sheet 43. The sheet P scrubs the guide sheet 43 while the sheet P is conveyed from the second transfer nip toward the fixing unit 30 (depicted in
The following describes test results showing a relationship between a surface resistivity of the guide sheet 43 and an amount of toner scattered from a sheet P, when the guide sheet 43 includes a polycarbonate. A plurality of guide sheets having different surface resistivities were prepared by changing the amount of carbon black in the polycarbonate. The plurality of guide sheets were left overnight in different environments. An image forming operation was performed in a test image forming apparatus not using the guide sheet 43 and in test image forming apparatuses using different guide sheets. Whether or not the toner scattered from the sheet P onto the fixing roller 30a was visually checked. Table 1 illustrates the test results.
In the above table, character N represents that the toner did not scatter from the sheet P onto the fixing roller 30a. Character S represents that the toner slightly scattered from the sheet P onto the fixing roller 30a. Character Y represents that the toner scattered from the sheet P onto the fixing roller 30a. “Without guide sheet 43” means that tests were performed in the test image forming apparatus which does not include the guide sheet 43 but includes the base 41a including an ABS resin and having a surface resistivity of 1014Ω/□.
As illustrated in Table 1, in the test image forming apparatus not including the guide sheet 43, the toner scattered from the sheet P onto the fixing roller 30a under a low temperature and low humidity condition of 10° C. and 15% RH. The toner scattered because friction between the sheet P and the base 41a including the ABS resin charged the sheet P to have the same polarity as the polarity of the toner on the sheet P when the sheet P scrubbed the base 41a. As a result, friction between the sheet P and the base 41a decreased the amount of electric charge on the sheet P having the polarity opposite to the polarity of the toner on the sheet P when the sheet P bearing a toner image transferred from the intermediate transfer belt 10 was conveyed toward the fixing unit 30 while scrubbing the base 41a. Thus, the sheet P had a decreased force for electrostatically attracting the toner. In the low temperature and low humidity environment, friction between the sheet P and the base 41a increased the amount of electric charge on the sheet P having the same polarity as the polarity of the toner on the sheet P. The sheet P could not electrostatically attract the toner. Therefore, the toner scattered from the sheet P onto the fixing roller 30a while the sheet P was conveyed in the fixing unit 30 and then the scattered toner was adhered to the sheet P again.
When the guide sheet 43 including the polycarbonate was used, the toner did not scatter from the sheet P onto the fixing roller 30a even in the low temperature and low humidity environment. The reason the toner did not scatter from the sheet P onto the fixing roller 30a is that the polycarbonate charged the sheet P to have the polarity opposite to the polarity of the toner on the sheet P by friction between the sheet P and the guide sheet 43 when the sheet P scrubbed the guide sheet 43. As a result, when the sheet P bearing a toner image transferred from the intermediate transfer belt 10 was conveyed toward the fixing unit 30 while scrubbing the guide sheet 43, friction between the sheet P and the guide sheet 43 increased the amount of electric charge on the sheet P having the polarity opposite to the polarity of the toner on the sheet P. Thus, the sheet P had an increased force for electrostatically attracting the toner. Therefore, even in the low temperature and low humidity environment, when the sheet P was conveyed in the fixing unit 30, the toner did not scatter from the sheet P onto the fixing roller 30a.
When the guide sheet 43 had the surface resistivity of 107Ω/□ or 108Ω/□, the toner scattered from the sheet P onto the fixing roller 30a in a high temperature and high humidity environment of 27° C. and 80% RH. Since the guide sheet 43 has a low surface resistivity and electric currents flow easily in the high temperature and high humidity environment, the electric charge with the polarity opposite to the polarity of the toner on the sheet P was transferred from the sheet P to the guide sheet 43 while the sheet P contacted the guide sheet 43. Thus, as the sheet P was conveyed toward the fixing unit 30, the amount of the electric charge having the polarity opposite to the polarity of the toner on the sheet P decreased. As a result, the sheet P had a decreased force for electrostatically attracting the toner and thereby the toner scattered from the sheet P onto the fixing roller 30a.
When the guide sheet 43 had the surface resistivity of 109Ω/□ or higher, the toner did not scatter from the sheet P onto the fixing roller 30a in any environment. The reason therefor is considered to be that the electric charge was not transferred from the sheet P to the guide sheet 43 even in the high temperature and high humidity environment. As a result, the sheet P maintained a force for electrically attracting the toner and the toner did not scatter from the sheet P onto the fixing roller 30a.
The guide sheet 43 can include a PET (polyethylene terephthalate). Tests were performed with test image forming apparatuses including the guide sheet 43 made of a PET in such a manner as described above for the case using the guide sheet 43 made of a PC (polycarbonate). The test results showed that, similar to the above-mentioned case, the toner did not scatter from the sheet P onto the fixing roller 30a in any environment when the guide sheet 43 had the surface resistivity of 109Ω/□ or higher.
The guide sheet 43 can include a PVDF (polyvinylidene fluoride). Tests were performed with test image forming apparatuses including the guide sheet 43 made of a PVDF in such a manner as described above for the case using the guide sheet 43 made of a PC. The test results showed that, similar to the above-mentioned case, the toner did not scatter from the sheet P onto the fixing roller 30a in any environment when the guide sheet 43 had the surface resistivity of 109Ω/□ or higher.
The image forming apparatus 100q may be a copying machine, a facsimile machine, a printer, a multifunction printer having copying, printing, scanning, and facsimile functions, or the like. According to this non-limiting exemplary embodiment of the present invention, the image forming apparatus 100q functions as a color printer for printing a color image on a recording medium using the electrophotographic method.
The image forming unit 9q forms toner images in yellow, magenta, cyan, and black colors. The photoconductive belt 1q has a belt-like shape and is looped over the driving roller 18 and the driven rollers 16 and 17. A driver (not shown) drives and rotates the driving roller 18. The rotating driving roller 18 rotates the photoconductive belt 1q in a rotating direction I. The rotating photoconductive belt 1q rotates the driven rollers 16 and 17.
The charger 4q, the exposure unit 3q, the development units 6qY, 6qM, 6qC, and 6qK, the intermediate transfer belt unit 5q, and the cleaner 2q are disposed around the photoconductive belt 1q. The charger 4q uniformly charges a surface of the photoconductive belt 1q. The exposure unit 3q emits light L onto the charged surface of the photoconductive belt 1q according to image data so as to form electrostatic latent images on the surface of the photoconductive belt 1q. The development units 6qY, 6qM, 6qC, and 6qK respectively develop the electrostatic latent images formed on the surface of the photoconductive belt 1q with yellow, magenta, cyan, and black toners to form yellow, magenta, cyan, and black toner images.
The intermediate transfer belt unit 5q carries the yellow, magenta, cyan, and black toner images transferred from the photoconductive belt 1q. The intermediate transfer belt 10q has an endless belt-like shape and is looped over the first transfer bias roller 11q, the driving roller 15q, and the driven rollers 12q, 13q, and 14q. A driver (not shown) drives and rotates the driving roller 15q and the rotating driving roller 15q rotates the intermediate transfer belt 10q in a rotating direction J. The rotating intermediate transfer belt 10q rotates the driven rollers 12q, 13q, and 14q. The first transfer bias roller 11q opposes the driven roller 16 via the intermediate transfer belt 10q and the photoconductive belt 1q so that the intermediate transfer belt 10q and the photoconductive belt 1q contact each other. A first transfer nip is formed between the intermediate transfer belt 10q and the photoconductive belt 1q. The first transfer bias roller 11q performs first transfer at the first transfer nip. Namely, the first transfer bias roller 11q transfers the yellow, magenta, cyan, and black toner images formed on the surface of the photoconductive belt 1q onto an outer circumferential surface of the intermediate transfer belt 10q to superimpose the toner images thereon. Thus, a color toner image is formed on the outer circumferential surface of the intermediate transfer belt 10q. The mark sensor 23 is provided on the outer circumferential surface of the intermediate transfer belt 10q. The sensor 24 detects the mark sensor 23 so that an image forming process for forming each of the yellow, magenta, cyan, and black toner images starts at a proper time based on the detection result. Thus, the yellow, magenta, cyan, and black toner images can be properly superimposed on the outer circumferential surface of the intermediate transfer belt 10q. The cleaner 2q removes a residual toner remaining on the surface of the photoconductive belt 1q even after the toner images formed on the surface of the photoconductive belt 1q are transferred onto the outer circumferential surface of the intermediate transfer belt 10q.
The second transfer bias roller 21q opposes the driven roller 12q via the intermediate transfer belt 10q to form a second transfer nip. A driving gear (not shown) drives the second transfer bias roller 21q to rotate the second transfer bias roller 21q at a circumferential speed substantially the same as the intermediate transfer belt 10q. The base 41b of the guide 41q holds a part of the second transfer bias roller 21q. The contact-separate mechanism 22 causes the second transfer bias roller 21q to contact to and separate from the intermediate transfer belt 10q via the base 41b.
The pick-up roller 26 and the feeding roller pair 27 feed a sheet P from the paper tray 31 toward the registration roller pair 28. The registration roller pair 28 feeds the sheet P to the second transfer nip at a time when a foremost head of the color toner image formed by the superimposed yellow, magenta, cyan, and black toner images on the outer circumferential surface of the intermediate transfer belt 10q enters the second transfer nip. The contact-separate mechanism 22 presses the second transfer bias roller 21q onto the sheet P so that the second transfer bias roller 21q contacts the sheet P at a time when the second transfer bias roller 21q transfers the color toner image from the intermediate transfer belt 10q onto the sheet P. The second transfer bias roller 21q separates from the intermediate transfer belt 10q when the second transfer bias roller 21q does not perform the transfer operation. Specifically, a predetermined bias voltage is applied to the second transfer bias roller 21q. The contact-separate mechanism 22 presses the second transfer bias roller 21q onto the sheet P so that the second transfer bias roller 21q contacts the backside of the sheet P (the backside does not face the intermediate transfer belt 10q). The second transfer bias roller 21q applies a second transfer bias to the sheet P to transfer the color toner image from the intermediate transfer belt 10q onto the sheet P. The second transfer bias roller 21q is connected to the second transfer power source 50q. The second transfer power source 50q applies the second transfer bias to the second transfer bias roller 21q. The second transfer power source 50q is connected to the controller 51q for controlling the second transfer bias.
The belt cleaner 19q opposes the driven roller 13q via the intermediate transfer belt 10q and removes a residual toner remaining on the outer circumferential surface of the intermediate transfer belt 10q after the color toner image formed on the outer circumferential surface of the intermediate transfer belt 10q is transferred onto the sheet P. The guide 41q guides the sheet P bearing the color toner image toward the fixing unit 30.
In the fixing unit 30, the sheet P is fed toward the fixing nip formed between the fixing roller 30a and the pressing roller 30b, which oppose each other. At the fixing nip, the fixing roller 30a and the pressing roller 30b apply heat and pressure to the sheet P bearing the color toner image to fix the color toner image on the sheet P. The fixing roller 30a and the pressing roller 30b feed the sheet P bearing the fixed color toner image thereon toward the output roller pair 32. The output roller pair 32 feeds the sheet P to outside of the image forming apparatus 100q.
The guide 41q is disposed near and downstream from the second transfer nip in the sheet conveyance direction. The guide 41q includes the same structure as the guide 41 (depicted in
The image forming apparatus 100r may be a copying machine, a facsimile machine, a printer, a multifunction printer having copying, printing, scanning, and facsimile functions, or the like. According to this non-limiting exemplary embodiment of the present invention, the image forming apparatus 100r functions as a printer for printing a monochrome image on a recording medium using the electrophotographic method.
The image forming unit 9r forms a toner image. The photoconductor 1r has a drum-like shape and rotates in a rotating direction K. The charger 4r, the exposure unit 3r, the development unit 6r, the transfer bias roller 21r, and the cleaner 2r are disposed around the photoconductor 1r. The charger 4r uniformly charges a surface of the photoconductor 1r. The exposure unit 3r emits light L onto the charged surface of the photoconductor 1r according to image data so as to form an electrostatic latent image on the surface of the photoconductor 1r. The development unit 6r develops the electrostatic latent image formed on the surface of the photoconductor 1r with a toner to form a toner image. The transfer bias roller 21r opposes and contacts the photoconductor 1r to form a transfer nip between the transfer bias roller 21r and the photoconductor 1r contacting each other.
The pick-up roller 26 and the feeding roller pair 27 feed a sheet P from the paper tray 31 toward the registration roller pair 28. The registration roller pair 28 feeds the sheet P to the transfer nip at a time when the toner image formed on the surface of the photoconductor 1r is properly transferred onto the sheet P. The transfer bias roller 21r transfers the toner image formed on the surface of the photoconductor 1r onto the sheet P. The transfer bias roller 21r is connected to the transfer power source 50r. The transfer power source 50r applies a transfer bias to the transfer bias roller 21r. The transfer power source 50r is connected to the controller 51r for controlling the transfer bias. The cleaner 2r removes a residual toner remaining on the surface of the photoconductor 1r even after the toner image formed on the surface of the photoconductor 1r is transferred onto the sheet P. The guide 41r guides the sheet P bearing the toner image toward the fixing unit 30.
In the fixing unit 30, the sheet P is fed toward a fixing nip formed between the fixing roller 30a and the pressing roller 30b, which oppose each other. At the fixing nip, the fixing roller 30a and the pressing roller 30b apply heat and pressure to the sheet P bearing the toner image to fix the toner image on the sheet P.
The guide 41r is disposed near and downstream from the transfer nip in the sheet conveyance direction. The guide 41r includes the same structure as the guide 41 (depicted in
As seen in
As seen in
According to the above-described embodiments, when a sheet P bearing a toner image scrubs the guide 41, 41q, or 41r while being conveyed from the second transfer nip or the transfer nip to the fixing unit 30, friction between the sheet P and the guide 41, 41q, or 41r charges the sheet P to have the polarity opposite to the polarity of the toner. Thus, the sheet P can electrostatically carry the toner image effectively. Therefore, the toner is prevented from electrostatically moving from the sheet P to the fixing roller 30a easily. Namely, scatter of the toner from the sheet P onto the fixing roller 30a can be suppressed.
The guide 41, 41q, or 41r at least includes a surface portion which directly contacts the sheet P and includes a PET, a PC, or a PVDF. Thus, even in a low temperature and low humidity environment, scatter of the toner from the sheet P onto the fixing roller 30a can be suppressed.
The surface portion directly contacting the sheet P includes the guide sheet 43 (depicted in
The surface portion directly contacting the sheet P has a surface resistivity of about 109Ω/□ or higher. Even in a high temperature and high humidity environment, the electric charge having the polarity opposite to the polarity of the toner on the sheet P is not transferred from the sheet P to the guide 41, 41q, or 41r. Thus, when the sheet P is conveyed toward the fixing unit 30, the amount of the electric charge having the polarity opposite to the polarity of the toner on the sheet P does not decrease. As a result, the force of the sheet P for electrostatically attracting the toner does not decrease. Even in the high temperature and high humidity environment, the toner is not electrostatically transferred from the sheet P to the fixing roller 30a easily when the sheet P is conveyed in the fixing unit 30. Thus, scatter of the toner from the sheet P onto the fixing roller 30a can be suppressed.
The guide 41, 41q, or 41r includes the discharging teeth 40a (depicted in
In the image forming apparatus 100 or 100q, plural color toner images are transferred onto a sheet P via the intermediate transfer belt 10 or 10q in an indirect transfer method. Namely, plural color toner images formed on the photoconductors 11Y, 11M, 11C, and 11K or the photoconductive belt 1q are transferred onto the intermediate transfer belt 10 or 10q such that the toner images are superimposed thereon. The superimposed toner images are further transferred onto the sheet P. A larger variety of sheet materials can be used in the indirect transfer method compared to a direct transfer method in which plural color toner images formed on photoconductors are directly transferred onto a sheet such that the toner images are superimposed thereon. In the direct transfer method, a conveying belt opposing the photoconductors electrostatically attracts the sheet. The conveying belt conveys the sheet so that the toner images formed on the photoconductors are transferred onto the sheet at transfer nips formed between the photoconductors and the conveying belt. The conveying belt may not stably attract thick paper which is not easily charged. The thick paper may slip on the conveying belt and may not be conveyed to the transfer nips at predetermined times when the toner images formed on the photoconductors are properly transferred onto the thick paper such that the toner images are superimposed thereon. For example, the thick paper may be conveyed to the transfer nips at delayed times. As a result, the toner images are misaligned when the toner images are transferred on the thick paper. To form a high quality image on a sheet, the thick paper cannot be used in an image forming apparatus using the direct transfer method. In the image forming apparatus 100 (depicted in
The intermediate transfer belt 10 (depicted in
The intermediate transfer belt 10 or 10q may also be formed of a plurality of layers having a plurality of functions. For example, when the intermediate transfer belt 10 or 10q includes an outermost layer including a material having high releasing property and resistivity, the intermediate transfer belt 10 or 10q can provide an improved transfer property and thereby the toner scattering problem is not caused.
The image forming apparatuses 100, 100q, and 100r (depicted in
According to the above-described embodiments, when a sheet P bearing a toner image scrubs the guide 41, 41q, or 41r (depicted in
The present invention has been described above with reference to specific exemplary embodiments. Note that the present invention is not limited to the details of the embodiments described above, but various modifications and enhancements are possible without departing from the spirit and scope of the invention. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-317788 | Oct 2005 | JP | national |
The present application is a continuation of application Ser. No. 11/588,340, filed on Oct. 27, 2006, which is based upon and claims priority to Japanese patent application No. 2005-317788 filed on Oct. 31, 2005 in the Japan Patent Office, the entire contents of each of which are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11588340 | Oct 2006 | US |
| Child | 12986732 | US |
