JP2007279624A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for achieving improvement in image quality, the reduction of cost of a monochrome print and improvement in the durability of a full color image forming unit as an image forming apparatus for forming a print of a full color image and a monochrome image. <P>SOLUTION: In the image forming apparatus, five image forming units having a photoreceptor drum and a developing means are mounted, latent images are formed on the photoreceptor drums of four image forming units out of them by a writing means, and are developed to toner images by the developing means of the four image forming units with different color toners, and the toner images are superposed to form the full color image. Another image forming unit forms the monochrome image by the developing means with toner of the same color as one of colors of the four image forming units. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a FAX, and more particularly to an image forming apparatus having a color image forming unit.

  In an electrophotographic image forming image forming apparatus having four image forming units, a full color image is formed by superimposing single color images formed by image forming units each having different toner on an intermediate transfer member. ing. In this case, the four image forming units are configured to be connected in series, and each single color toner image is sequentially transferred to the intermediate transfer member and superimposed to form a full color image.

  However, even in a full-color image forming apparatus, for example, a single-color image of only black is frequently formed. With the above configuration, an output time is required for printing one single-color image, and the load on the entire apparatus including the intermediate transfer member is large. Become.

Therefore, the black image forming unit and the other three-color image forming units are separately provided, and when the black printing is performed, the other three-color image forming units are allowed to wait for the black image forming unit which is the first mode. The output time is shortened by transferring directly onto the transfer material using only the image forming unit, and when forming a full-color image in the second mode, the image on the transfer material superimposed with the other three colors via the intermediate transfer member is used. A method of directly transferring a black image is proposed (for example, see Patent Document 1).
JP 2002-182447 A

  However, in the method as described above, since the arrangement positions of the image forming units for black and three colors are separated, image quality defects such as image misalignment are likely to occur. In addition, the consumption frequency of the monochromatic (black) toner is high, the number of times of replacement of the toner bottle and the like is increased, and this is inconvenient from the viewpoint of maintenance of the apparatus.

  The present invention is equipped with five sets of image forming units, and four sets of image forming units for full-color image formation and a single-color image forming unit are arranged separately to avoid image quality defects such as image misalignment. The toner used in one of the four sets of image forming units and the toner of the other one-color image forming unit that is frequently used have the same quality and the same color, and the toner storage means is shared. Accordingly, an object of the present invention is to provide an image forming apparatus capable of improving image quality, reducing the cost of monochromatic printing, and improving the durability of a full-color image forming unit.

  The above object can be achieved by the following configuration.

  An image forming unit having five sets of photosensitive drums and developing means is mounted, and a latent image is formed on the photosensitive drums of four sets of image forming units by writing means. The latent image can be visualized as a toner image by the developing means of the four sets of image forming units, and the toner images can be superimposed to form a full color image. An image forming apparatus, wherein a single color image can be formed by developing means in which toner of the same color as one color in the four sets of image forming units is present.

  Image misalignment can be avoided, the cost of monochromatic printing is reduced, and the durability of a full-color image forming unit is improved.

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

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

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

  In FIG. 1, 10 is a photosensitive drum, 11 is a scorotron charger as charging means, 12 is a writing device as digital exposure writing means, 13 is a developing device as developing means, and 14 is the surface of the photosensitive body 10. 15 is a blade for cleaning the photosensitive drum 10, and the toner scraped off by the blade 15 is conveyed from the cleaning device 14 by the conveying screw 100 to a waste box (not shown). Discarded. However, toner of the same color as that used for monochromatic image formation described later is used for recycling. Reference numeral 16 denotes a developing sleeve, 18 denotes a toner storage unit, and 20 denotes an intermediate transfer belt as an intermediate transfer member.

  The four sets of image forming units 1 include a photosensitive drum 10, a scorotron charger 11, a developing device 13, a cleaning device 14, and the like, and the mechanical configuration of the image forming unit 1 for each color is the same. In FIG. 1, reference symbols are assigned to the configuration of only the Y (yellow) series, and the reference symbols are omitted for the other three sets of M (magenta), C (cyan), and K (black) components.

  The developing device 13 has a developing sleeve 16 formed of a cylindrical non-magnetic stainless steel or aluminum material that rotates in a direction opposite to the rotation direction of the photosensitive drum 10 while maintaining a predetermined interval with respect to the peripheral surface of the photosensitive drum 10. Have. Of the four sets, three sets (in the embodiment, Y, M, C) of the developing devices 13 are supplied with toner from the toner storage means 18 by a toner transport means (not shown) when necessary.

  The arrangement of the image forming unit 1 for each color is in the order of Y, M, C, K with respect to the traveling direction of the intermediate transfer belt 20. At the time of transfer, the primary transfer roller 25 presses the intermediate transfer belt 20 to the photoreceptor 10. In the pressure bonding region, the photosensitive drum 10 rotates in the same direction as the traveling direction of the intermediate transfer belt 20 and at the same linear speed.

  Reference numeral 1A denotes an image forming unit that operates during monochromatic image formation, and details of the image forming unit 1A will be described later.

  Reference numeral 19 denotes a transport belt unit. Reference numeral 190 denotes a conveying belt having a plurality of holes, which is stretched around a driving roller 191 and a driven roller 192. Reference numeral 193 denotes a suction box having a plurality of holes in the surface in contact with the transport belt 190, connected to a duct and a suction fan (not shown), and a function of sucking the transfer material P onto the traveling transport belt 190. Fulfill. The conveyor belt unit 19 includes a conveyor belt 190, a driving roller 191, a driven roller 192, a suction box 193, and the like. Further, a transfer roller 194 to which a potential having a polarity opposite to that of the toner is applied is disposed at a position facing the photosensitive drum 10 </ b> A via the conveyance belt 190. At the time of full color image formation, the conveyance belt 190 travels at the position indicated by the dotted line, and at the time of monochrome image formation, the transfer roller 194 lifts the belt against tension by a mechanism (not shown) to convey the conveyance belt 190 and the transfer material P. The toner image on the photosensitive drum 10A can be transferred onto the transfer material P.

  The intermediate transfer belt 20 is stretched around a driving roller 21, an earth roller 22, a tension roller 23, a static elimination roller 27, and a driven roller 24. The intermediate transfer belt 20 is intermediated between the intermediate transfer belt 20, the primary transfer roller 25, and a cleaning device 28. The transfer belt unit 2 is configured. The earth roller (backup roller) 22 is a conductive aluminum roller with an aluminum background, and is grounded.

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

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

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

  The primary transfer roller 25 is applied with a DC voltage having a polarity opposite to that of the toner, and presses the intermediate transfer belt 20 against the photosensitive drum 10 from the inside of the belt by a pressure-bonding and pressure-release mechanism (not shown). At the nip S, the toner image formed on the intermediate transfer belt 20 is retransferred (secondary transfer) to the transfer material P.

  Reference numeral 26 denotes a secondary transfer roller as a secondary transfer unit, which presses the ground roller 22 through the transfer material P by a not-shown pressure-bonding and pressure-release mechanism to transfer the toner image on the intermediate transfer belt 20 to the transfer material P. It has a function to transcribe. The secondary transfer roller 26 is made of a conductive solid rubber whose surface is covered with a coating layer, and a reverse polarity bias voltage is applied to the toner during transfer (or a voltage having the same polarity as the toner is applied to the ground roller 22). And the secondary transfer roller 26 may be grounded).

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

  A fixing device 4 includes a heating roller 41 and a pressure roller 42.

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

  70 is a paper feed roller, 71 is a timing roller, 72 is a paper cassette, and 73 is a transport roller. A paper discharge roller 81 discharges the fixed transfer material to a paper discharge tray 82.

  The control unit B1 performs image forming process control, fixing temperature control, transfer material conveyance control, toner density control, and the like.

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

  In the case of full-color image formation (second mode), the photosensitive member 10 of the color signal Y is rotated in the counterclockwise direction indicated by the arrow simultaneously with the start of the photosensitive member drive motor (not shown) simultaneously with the start of image recording, and at the same time the scorotron charging. Application of a potential to the photoconductor 10 is started by the charging action of the device 11.

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

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

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

  After that, the photosensitive drum 10 is cleaned of residual toner by the blade 15 of the cleaning 14 and enters the next image forming cycle (the same applies to the M, C, and K cleaning processes, and the description thereof will be omitted). . The toner removed after cleaning the photosensitive drum 10 of one color among Y, M, C, and K is transported to a storage unit (not shown) by the transport screw 100 and reused for recycling.

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

  By a similar process, the Y and M superimposed toner images are synchronized, and the C (cyan) toner image is superimposed on the Y and M superimposed toner images by the C primary transfer roller 25. Is done. Next, the Y, M, and C superimposed toner images already formed are synchronized, and the K toner image is transferred to the K primary transfer roller 25 by the Y, M, and C superimposed toners. Overlaid on the image, a superimposed toner image of Y, M, C and K is formed.

  The intermediate transfer belt 20 carrying the superimposed toner image is fed clockwise as indicated by the arrow, and the transfer material P is fed from the paper cassette 72 by the paper feed roller 70, passes through the transport roller 73, and then the timing roller 71. Is then transported to the transport belt unit 19 by being driven by the timing roller 71, adsorbed to the surface of the transport belt 190, and synchronized with the superimposed toner image on the intermediate transfer belt 20. The toner images are fed to the nip portion S of the secondary transfer roller 26 (which is in a pressure-bonded state to the intermediate transfer belt 20) to which a reverse polarity DC voltage is applied, and the superimposed toner images on the intermediate transfer belt 20 are collectively transferred. Secondary transfer is performed on the material P. However, the conveyance belt 190 is in a state of being separated from the photosensitive drum 1A (in FIG. 1, the conveyance belt 190 and the transfer roller 194 are in a state indicated by dotted lines).

  Thereafter, the intermediate transfer belt 20 travels, the charge of the residual toner is weakened by the neutralizing roller 27, the residual toner on the belt is cleaned by the blade 29 of the cleaning device 28 by the cleaning device 28, and the next image forming cycle starts.

  The toner scraped off is stored in the cleaning device 28, and is transported in the axial direction (from the front surface of the paper to the rear surface of the paper in FIG. 1) by rotation of a transport screw (not shown), and is stored in a storage box via a waste pipe (not shown). Can be stored.

  The transfer material P onto which the superimposed toner image has been transferred is sent to the fixing device 4, and is nipped, pressed and fixed at the nip portion T between the heating roller 41 and the pressure roller 42. The transfer material P on which the toner image is fixed is conveyed to a paper discharge tray 82 by a paper discharge roller 81.

  Next, the characteristics of the monochrome image forming unit and toner storage means according to the present invention will be described.

  The image forming unit 1A is another set of image forming units used only for monochromatic image formation, and includes a photosensitive drum 10A, a scorotron charger 11A, a writing device 12A, a developing device 13A, a cleaning device 14A, and the like. It is configured.

  The photosensitive drum 10A, the developing unit 13A, and the toner storage unit 18A are made larger than those of the photosensitive drum 10, the developing unit 13, and the toner storage unit 18 in terms of drum diameter, developing sleeve diameter, toner storage capacity, and the like. It has been.

  Therefore, since the usage area of the photosensitive drum 10A and the developer capacity in the developing device 13A are increased, the durability time of the photosensitive drum and the developer can be extended.

  15A is a blade for cleaning the photosensitive drum 10A. The toner scraped off by the blade 15A is conveyed from the cleaning device 14A by the conveying screw 101 and used for the cycle.

  As described above, the toner cleaned by the cleaning device 14 of the image forming unit 1 using the same color toner is also used for recycling.

  The toner bottle BT of the toner storage means 18A is made larger than the toner bottle bt (for Y, M, and C), and the same color and the same color toner are developed with a developing device 13 for forming a full color image and a developing device 13A for forming a single color image. These are made large in size so as to have a storage capacity sufficient for replenishing both of them, and are replenished to the developing devices 13 and 13A via a toner conveying means (not shown) as necessary. Along with this, the fixing device and transfer conditions as post-processing are made common. Therefore, just by installing a large toner bottle BT, it can be shared for full-color image formation and single-color image formation, which is advantageous for maintenance, and the arrangement of the toner storage means can be made compact and the apparatus can be downsized. It becomes possible.

  That is, the durability of the unit is increased by making the photosensitive drum 10A, the developing device 13A, and the toner storage unit 18A of the single-color image forming unit 1A larger than those of the image forming unit 1 (drum diameter, developing sleeve, toner storage unit). As a result, the maintenance of the toner storage means (toner bottle) is improved, and the cost / printing can be reduced by recycling the single color toner.

  In the image forming process in the case of monochromatic image formation (first mode), the operation of the image forming unit 1 and the intermediate transfer belt unit 2 is put on standby, and only the image forming unit 1A performs an image forming job. That is, similarly to the image forming unit 1, a potential is applied to the photosensitive drum 1 by the scorotron charger 11, and the latent image formed by the writing device 12A is visualized as a toner image by the developing device 13, The toner image is synchronized with the timing roller 71 and sent to the nip R between the conveying belt 190 and the photosensitive drum 10A in contact with each other, and the toner image is transferred to the transfer member P. Further, the toner is sucked and transported to the transport belt 193, sent to the fixing device 4, and is nipped, pressed and fixed by the nip portion T between the heating roller 41 and the pressure roller 42. The transfer material P on which the toner image is fixed is conveyed to a paper discharge tray 82 by a paper discharge roller 81. However, the secondary transfer roller 26 is separated from the intermediate transfer belt 20 when passing through the secondary transfer roller 26.

  In this embodiment, K (black) toner, which is frequently used, is used for forming a monochromatic image. However, if the frequency of use is high, any of Y (yellow), M (magenta), and C (cyan) is used. One of them can be used for monochromatic image formation and used as described above.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A Image forming unit 10, 10A Photosensitive drum 11, 11A Charger 13, 13A Developer 14, 14A Cleaning device 15, 15A Blade 18, 18A Toner storage means 19 Transport belt unit 190 Transport belt 193 Suction box 194 Transfer roller 20 Intermediate transfer belt 26 Secondary transfer roller BT, bt Toner bottle 4 Fixing device 41 Heating roller 42 Pressure roller

Claims (6)

  An image forming unit having five sets of photosensitive drums and developing means is mounted, and a latent image is formed on the photosensitive drums of four sets of image forming units by writing means. The latent image can be visualized as a toner image by the developing means of the four sets of image forming units, and the toner images can be superimposed to form a full color image. An image forming apparatus, wherein a single color image can be formed by developing means in which toner of the same color as one color in the four sets of image forming units is present. The image forming apparatus according to claim 1, wherein the another set of image forming units and one set of the four sets of image forming units share a toner storage unit. 3. The image according to claim 1, wherein a toner storage capacity of the toner storage unit for the another set of image forming units is larger than each of the three toner storage capacities of the four sets. Forming equipment. 4. The apparatus according to claim 1, wherein the photosensitive drum and the developing unit of the another set of image forming units are larger than the four sets of the photosensitive drum and the developing unit. 5. Image forming apparatus. 5. The image forming apparatus according to claim 1, wherein the another set of image forming units is engaged with a black monochrome image forming and toner storage unit. 6. The image forming apparatus according to claim 1, wherein the same color toner is recycled.

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