JP2008076469A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus using an intermediate transfer body, in which image quality is not degraded by preventing scattering of image toner during secondary transfer even when cardboard and an OHP sheet are used. <P>SOLUTION: A pressing means that presses a toner image on the intermediate transfer body is disposed on the downstream of a primary transfer area that is most downstream in the direction of movement of the intermediate transfer body, and upstream of a secondary transfer means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having an intermediate transfer member.

Conventionally, in an electrophotographic copying machine, printer, facsimile, or the like, a toner image on an image carrier (hereinafter also simply referred to as a photoreceptor) is transferred to a recording medium (hereinafter also referred to as a recording material or simply paper). As a method, a method of directly transferring a toner image formed on a photosensitive member to a recording material is known. On the other hand, an image forming method using an intermediate transfer member is known. This method includes another transfer step in the step of transferring a toner image from a photosensitive member to a recording material. After the primary transfer, the primary transfer image of the intermediate transfer member is secondarily transferred to the recording material to obtain a final image. In the so-called full-color image forming apparatus, the intermediate transfer system reproduces a color-separated document image using subtractive color mixing with toners such as yellow (Y), magenta (M), cyan (C), and black (K). In many cases, it is adopted as a method of superimposing and transferring toner images of respective colors.

However, a full-color image forming apparatus using an intermediate transfer member uses so-called thick paper having a basis weight of 130 g / m ² or more, printing paper whose recording material surface is coated with a special resin agent, or an OHP sheet. As a result, the sheet conveyed along the guide plate from the sheet feeding unit hits the intermediate transfer member by the restoring force of the sheet at the moment when the trailing edge of the sheet leaves the guide plate, and the impact of the image on the intermediate transfer member is As a result, the toner is scattered, and as a result, a toner scattered image is transferred and the image quality is deteriorated. Further, the image during the secondary transfer causes a transfer shift due to the impact, and the image quality is also deteriorated. In particular, among the respective color toners sequentially arranged at the time of secondary transfer, toner scattering of the image of the last toner (black toner in this embodiment) is likely to occur.

For the problem of preventing image toner scattering when transferring the above thick paper, conventionally, a mylar film is attached to the front end of the guide plate, the guide plate is brought close to the intermediate transfer body, and the rear end of the paper is the intermediate transfer The impact at the time of collision with the body is alleviated and toner scattering of the image is prevented. Alternatively, apparent scattering is suppressed by controlling the transfer current to some extent (for example, a diagram described in Patent Document 1).
JP 2001-142321 A

  However, the Mylar film system shown in Patent Document 1 cannot cope with various paper types and lacks durability. Although the method of adjusting the transfer current value improves to such an extent that the scattering and misalignment are reduced to some extent, if the current value is set such that it does not occur at all, the density of that portion will change in the whole solid or halftone image. Or image defects occur. In other words, these measures have limitations.

  An object of the present invention is to prevent an image toner from being scattered during secondary transfer and prevent image quality from being deteriorated even in the case of using thick paper and an OHP sheet in an image forming apparatus using an intermediate transfer member. A forming apparatus is provided.

The above object can be achieved by the following configuration. That is, 1. A primary transfer unit that develops electrostatic latent images formed on a plurality of image carriers using a plurality of toners of different colors, and sequentially transfers the toner images for each color onto an intermediate transfer member;
Secondary transfer means for collectively transferring the toner image on the intermediate transfer member to a recording medium;
In an image forming apparatus having
A pressing unit that presses the toner image on the intermediate transfer member at a position downstream of the primary transfer region at the most downstream position in the moving direction of the intermediate transfer member and upstream of the position of the secondary transfer unit. An image forming apparatus comprising:
2. The pressing means includes a first roller having a metal surface that contacts the toner adhesion surface side with the intermediate transfer member interposed therebetween, and a second roller having a core member covered with an elastic member on the back surface side. 2. The image forming apparatus as described in 1 above.
3. 3. The image forming apparatus according to 1 or 2, wherein the pressing unit presses the intermediate transfer member with a force equivalent to at least primary transfer.
4). 4. The image forming apparatus according to claim 2, wherein the first roller is electrically grounded and has an electric field applying unit that applies an electric field to the second roller.
5. 5. The image forming apparatus according to 4, wherein the electric field applying unit applies an electric field corresponding to at least primary transfer to the second roller.
6). The electric field applying unit is provided at a position downstream of the most downstream primary transfer region in the moving direction of the intermediate transfer member and upstream of the position of the secondary transfer unit. Or the image forming apparatus according to 5.

  According to the image forming apparatus of the present invention, the intermediate transfer member is disposed at a position downstream of the primary transfer region at the most downstream position in the moving direction of the intermediate transfer member and upstream of the position of the secondary transfer unit. By providing a pressing means for pressing the upper toner image, even when using thick paper or an OHP sheet, there is no occurrence of toner scattering on the image on the intermediate transfer member, and image formation that does not deteriorate the image quality A device can be provided.

An embodiment of the present invention will be described. In addition, although this invention is demonstrated based on embodiment of illustration, this invention is not restricted to this embodiment. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.
<Overview of image forming apparatus>
FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus (hereinafter referred to as a copying machine) when viewed from the front.

  The copying machine of the present embodiment is provided with an automatic document feeder 1 at the top of the copying machine main body, and an image reading unit 2, an image forming unit 3, a paper feeding unit 5, a paper discharge / switching unit 7 in the copying machine main body. And a paper storage unit 9.

  The automatic document feeder 1 is a device that feeds documents one by one, conveys them to an image reading position, and discharges the document after image reading to a predetermined location.

  The automatic document feeder 1 includes a document placing table 101 on which a document is placed, a document separating unit 103 for separating the placed document, a document transporting unit 105 for transporting the separated document, and discharging the transported document. A document discharge unit 107 for placing the discharged document, a document discharge table 109 on which the discharged document is placed, and a document reversing unit 111 used for reversing the front and back of the document when reading images on both sides of the document. .

  In view of the processing process, a plurality of documents (not shown) placed on the document placing table 101 are separated one by one by the document separating means 103, and the image reading position is passed through the document conveying section 105. It is conveyed toward.

  The document reading position is provided at a lower portion of the document conveying unit 105, where an image of the document is read through a slit 201 constituting the image reading device 2, and the read document is a document discharge unit. The sheet is discharged onto the document discharge table 109 by 107.

  Such a process is repeated for the number of documents placed on the document placing table 101.

  The configuration of the image reading apparatus 2 will be described in detail. A first mirror unit in which the slit 201, a lamp 213 that is a light source for irradiating light on a document, and a first mirror 215 that reflects reflected light from the document are integrated. 205, a second mirror unit 207 in which a second mirror 217 that reflects light from the first mirror 215 and a third mirror 219 are integrated, and reflected light from the second mirror unit 207, which will be described later. An imaging lens 209 that forms an image above, and a linear imaging element (hereinafter referred to as CCD) 211 that obtains image information by photoelectrically converting a light image formed by the imaging lens 209 are provided.

  The image information is temporarily stored in a memory (not shown) after appropriate image processing.

  In the aspect in which the document fed by the automatic document feeder 1 is read by the image reading device 2, the first mirror unit 205 and the second mirror unit 207 are fixed at positions as shown in the figure.

  By the way, in the aspect of reading the images on both sides of the document, the front and back are reversed by the document reversing means 111 including a pair of rollers in a state where the rear end of the document on which the image on one side is read is sandwiched. In the same manner as described above, the document is transported to the transport unit 105, read at the document reading position, and then discharged onto the document discharge table 109.

  The automatic document feeder 1 is configured to be retractable, and the automatic document feeder 1 is raised to open the platen glass 203 so that the document is directly placed on the platen glass 203. It is configured to be able to.

  In the present exemplary embodiment, the document conveying unit 105 is configured to read the document image while conveying the document. However, the document conveyed via the document conveying unit 105 is stopped on the platen glass. After that, the exposure optical system may be moved so that the image is read in the same manner as when the original is directly placed on the platen glass.

  Here, in the aspect of reading the image of the document placed on the platen glass 203, the first mirror unit 205 and the second mirror unit 207 are moved along the platen glass while maintaining the optical path length. Do.

  The image signals of the respective colors read by the image reading device 2 are sequentially taken out from the memory and input to the exposure optical systems 313 as electric signals.

  In the present embodiment, the image forming unit 3 forms yellow (Y), magenta (M), cyan (C), and black (K) image forming means (hereinafter referred to as an image) that forms a toner image corresponding to a color separation image. The image forming unit includes a photosensitive drum 301 that is an image forming body, a scorotron charger 303, an exposure optical system 313 that is an image writing unit, a developing device 311, and the like. .

  The image forming unit 300 is arranged in the vertical direction (upper surface) along one surface (the stretched surface A) of an intermediate transfer member 401 (also referred to as an intermediate transfer belt 401) that is long in the vertical direction in the upper portion of the paper storage unit 9. , In order of yellow, magenta, cyan, and black), and the four sets have the same mechanical configuration. Therefore, in FIG. It is omitted for convenience.

  The exposure optical system 313 is disposed on the downstream side in the rotation direction of the photosensitive drum 301 with respect to the scorotron charger 303. The exposure optical system 313 is an exposure unit composed of a laser optical system, and its configuration is well known.

  In image formation, for example, yellow (Y) image formation is performed as follows. The photosensitive drum 301 rotates counterclockwise by starting the photosensitive drum driving motor, and a potential is applied to the photosensitive drum 301 by the charging action of the scorotron charger 303.

  Thereafter, exposure corresponding to the first color signal, that is, the image signal of (Y) is performed by the exposure optical system 313, and an electrostatic latent image corresponding to the image of (Y) of the document is formed on the photosensitive drum 301. Is done.

  The electrostatic latent image is reversely developed by a developing device 311 to be visualized.

  The toner image (Y) produced by reversal development is transferred onto the intermediate transfer belt 401 by a transfer roller 305 provided facing the photosensitive drum 301 with the intermediate transfer belt 401 interposed therebetween (1). Called the next transfer means).

  The image formation with the other color signals is performed by the same process as described above, and the toner image formed by the magenta (M), cyan (C), and black (K) image forming units is the image with the (Y) toner image. The images are sequentially transferred so as to overlap with the areas, and a superimposed color toner image is formed on the intermediate transfer belt 401.

  In parallel with the image formation, the paper P is sent out by the paper feeding roller 903 (913, 923) from the feeding unit 901 (911, 921) of the paper storage unit 9, and is conveyed to the registration roller 501.

  The registration roller 501 is driven so as to overlap with the color toner image area on the intermediate transfer belt 401, and the color toner image is transferred onto the paper P by the action of the secondary transfer unit 415 in the transfer area.

  The paper P on which the toner image is transferred is separated from the peripheral surface of the intermediate transfer belt 401 and then conveyed to the fixing unit 601. The toner image is melted by the heat and pressure of the fixing roller 603 and the pressure roller 605 having a heater therein, and is fixed on the paper P. The paper P after the fixing process is conveyed by the fixing paper discharge roller 607 and the paper discharge roller 703 and discharged onto the paper discharge tray 705.

  Further, the intermediate transfer belt 401 after the sheet is separated is neutralized by a static eliminator 407 provided opposite to a conductive roller that is grounded with the intermediate transfer belt 401 interposed therebetween, and then the cleaning blade 413. Is rubbed and cleaned.

  The toner remaining on the peripheral surface of the photoconductive drum 301 after the transfer is removed by the drum cleaning unit 309, and the history of the photoconductive drum 301 in the previous image formation is recorded by a uniform exposure device (not shown) before charging. After being eliminated, preparation for the next image formation is made.

  By the way, the paper storage unit 9 includes paper supply units 900, 910 including storage containers 905, 915, and 925 for storing a plurality of sheets P in a stacked state, and delivery units 901, 911, and 921, respectively. 920 is arranged in the vertical direction, and parallel to the paper transport direction and arranged with the lower paper feed unit shifted in the downstream direction with respect to the upper paper feed unit, and at the same time arranged close to the vertical direction It is.

  The delivery parts 901, 911, and 921 are located on one side (side wall) side of the storage containers 905, 915, and 925 and have a structure that can be pulled out integrally.

  The feeding sections 901, 911, and 921 are paper feeding rollers 903 and 903 located in a region protruding from the upper side of the container when the paper feeding units 900, 910, and 920 are pushed into predetermined positions in the apparatus and loaded. 913 and 923, and separation rollers 906, 916, and 926 for preventing feeding of two sheets.

  The alternate long and short dash lines shown in the storage containers 905, 915, and 925 indicate the position of the uppermost paper when a predetermined amount of paper P is stored.

  The paper feeding unit 5 transports a number of transports for transporting the paper P from each of the storage containers 905, 915, and 925 constituting a part of the paper feeding units 900, 910, and 920 to the registration roller 501. Means R1, R2, R3, R4, R5, and R6 are provided, and each of the conveying means is composed of a pair of rollers.

  The paper discharge / switching unit 7 is an area having means for discharging or refeeding the paper after the image formation.

  The paper discharge / switching unit 7 includes a fixing discharge roller 607 that discharges the paper on which the toner image is fixed from the fixing unit 601, a switching unit 701 that switches the conveyance path, and a paper discharge roller 703 for discharging the paper to the outside of the apparatus. A paper discharge tray 705 provided on the side surface of the apparatus main body on which the discharged paper is stacked, a reversing unit 801 for reversing the front and back of the reversely conveyed paper, and re-feeding the reversed paper toward the image forming unit 3 And a reversing conveyance unit 803.

  The switching unit 701 can switch the conveyance path between when the sheet is discharged as it is, when the sheet is reversed after being turned upside down, and when the sheet is fed again to form an image on the back side of the sheet. It has become.

  When the image-formed paper is discharged as it is, that is, with the image-formed surface facing upward, the switching unit 701 is positioned in the posture shown by the one-dot chain line in FIG. 1, and the fixing discharge roller 607 and the discharge roller 703 The paper is discharged to a paper discharge tray 705 outside the apparatus.

  Further, when paper is discharged with the front and back sides of the image-formed paper turned over, that is, when the image-formed surface is discharged downward, the switching unit 701 is positioned in the posture shown by the solid line in FIG. The paper conveyed by the roller 607 is once conveyed in the direction of the reversing unit 801.

  Subsequently, after the sheet passes through the switching unit 701, the sheet is switched back and discharged to a discharge tray 705 outside the apparatus by a discharge roller 703.

  Further, when an image is formed on the back side of the sheet, the switching unit 701 is positioned at a position indicated by a solid line in FIG. 1, and the sheet conveyed by the fixing discharge roller 607 is conveyed in the direction of the reversing unit 801. The switch back is performed to reverse the front and back, and then conveyed to the reverse conveyance unit 803.

The sheet P transported to the reverse transport unit 803 is transported to a registration roller 501 by a transport roller 503, which will be described later, through a transport path similar to that for paper feed from the paper feed units 900, 910, and 920. It is conveyed to the next transfer means 415.
<Pressing means>
Next, the pressing means 30 of the present invention will be described with reference to FIGS. FIG. 2 is a view showing a state where the trailing edge of the paper P passing between the guide plates 511 and 512 collides with the intermediate transfer belt 401 due to the restoring force of the paper when it is separated from the guide plate 512. The toner image on the intermediate transfer belt 401 is scattered by the vibration generated when the collision occurs, and toner scattering occurs. In particular, during the secondary transfer, an image in which this transfer is shifted appears remarkably. In the present embodiment, it is recognized that the toner that causes toner scattering is black toner.

  That is, since the black toner that is finally transferred and overlaid is not in close contact with the intermediate transfer belt 401, the toner is scattered even by slight vibration of the intermediate transfer belt 401. In this phenomenon, the distance t1 from the rear end of the paper P to the area where the toner scatters is equal to the distance t2 between the secondary transfer unit 415 and the guide plate 512 from the visual determination of the defective image quality sample. It is clear from this.

  Therefore, in order to prevent the toner scattering described above, in the image forming apparatus of the present invention, the intermediate transfer belt 401 is sandwiched between the primary transfer unit and the secondary transfer unit that are finally transferred to the intermediate transfer belt 401. Thus, the pressing means 30 constituted by a pair of rollers comprising a first roller 321 (metal roller 321) on the toner adhering surface side and a second roller 322 (elastic roller 322) whose core member is covered with an elastic member on the back surface side. Provided.

  The elastic roller 322 is a toner image on the intermediate transfer belt 401 with a primary transfer pressing force required when the primary transfer unit transfers toner to the metal roller 321 and at least a considerable force (6N in this embodiment). Is pressed.

  The metal roller 321 is made of a conductive metal material such as an aluminum material or a brass material, and the elastic roller 322 is formed by covering the surface of a cored bar 322a made of a conductive metal material with an elastic member 322b made of CR rubber or the like. ing. In the present embodiment, the hardness of the elastic roller is 67 ± 3 ° (JIS A scale). Further, the metal roller 321 is provided with a cleaning blade 323 for cleaning the toner adhering to the surface. The metal roller 321 and the elastic roller 322 are grounded so as to have the same potential.

  In another example of the pressing means, as shown in FIG. 3, the electric field applying means for applying the primary transfer voltage necessary for the primary transfer means is the primary transfer region at the most downstream position in the moving direction of the intermediate transfer body. It is provided at a position downstream of the secondary transfer means and upstream of the position of the secondary transfer means. The elastic roller 322 is applied with a voltage corresponding to the primary transfer voltage from the electric field applying means, and presses at least the pressure corresponding to the primary transfer to the metal roller 321 electrically grounded via the intermediate transfer belt 401. The toner image can be securely adhered onto the intermediate transfer belt 401. In this embodiment, the pressing force is 6 N, the applied voltage is about 2 kV, and the current is 50 microamperes under constant current control.

  Next, as Example 1, the elastic roller 322 presses the toner image on the intermediate transfer belt 401 against the metal roller 321 with a force equivalent to primary transfer, as shown in FIG.

  As Example 2, an applied current was further applied to the elastic roller in Example 1 as shown in FIG. 3 to evaluate the image toner scattering level and the transfer deviation.

Furthermore, as a comparative example, image quality evaluation was performed in a state where only the applied current was applied to the elastic roller and the toner image on the intermediate transfer belt 401 was not pressed.
Common condition image forming apparatus: Full color image forming apparatus shown in FIG. 1 Paper used: 256 g / m ² paper A4 size Line speed: 220 mm / second Image pattern: 0.2 mm pitch half dot pattern Secondary transfer roller: φ30, hardness 67 ± 3 ° (JIS-A scale)
Resistance value: 4 × 10 ⁷ Ω
Elastic roller: φ30, hardness 67 ± 3 ° (JIS-A scale)
Resistance value: 4 × 10 ⁷ Ω
Pressing force: 6N
Elastic roller applied current of Example 2: 50 microampere metal roller by constant current control: Examples 1 and 2 were both grounded by an aluminum roller.
Evaluation: Image toner scattering of 20 mm from the trailing edge of the paper was visually determined.
<result>
In either Example 1 or Example 2, image toner scattering and transfer deviation did not occur. However, in the comparative example, image toner scattering and transfer deviation occurred slightly.

  As shown in the above embodiments, the intermediate transfer belt 401 is placed at a position downstream of the primary transfer region at the most downstream position in the moving direction of the intermediate transfer body and upstream of the position of the secondary transfer means. The pressing means comprising a pair of rollers comprising a metal roller 321 on the toner adhering surface side and an elastic roller 322 whose core member is covered with an elastic member is provided on the back surface, and the elastic roller 322 is against the metal roller 321. The toner image on the intermediate transfer belt 401 is pressed with a force equivalent to the primary transfer (6N), and further, a voltage corresponding to the primary transfer voltage (microampere) is applied to the elastic roller 322, whereby the toner image is transferred to the intermediate transfer belt. An image shape that can be closely adhered to 401 and prevents occurrence of image toner scattering during secondary transfer even when thick paper or an OHP sheet is used, and image quality does not deteriorate. It was able to provide a device.

1 is a schematic diagram illustrating a configuration when an image forming apparatus is viewed from the front. FIG. 6 is a diagram illustrating a position where a rear end of a sheet collides with an intermediate transfer belt 401. It is a figure of the press means which shows the electrical grounding of a 1st roller and a 2nd roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Automatic document feeder 2 Image reading device 3 Image forming part 5 Paper feeding part 7 Paper discharge / switching part 9 Paper storage part 30 Pressing means 90 Separating part 300 Image forming means 321 First roller (metal roller)
322 Second roller (elastic roller)
401 Intermediate transfer member (intermediate transfer belt)
801 Reversing unit 901 Sending unit P Recording medium (recording material, paper)

Claims (6)

A primary transfer unit that develops electrostatic latent images formed on a plurality of image carriers using a plurality of toners of different colors, and sequentially transfers the toner images for each color onto an intermediate transfer member;
Secondary transfer means for collectively transferring the toner image on the intermediate transfer member to a recording medium;
In an image forming apparatus having
A pressing unit that presses the toner image on the intermediate transfer member at a position downstream of the primary transfer region at the most downstream position in the moving direction of the intermediate transfer member and upstream of the position of the secondary transfer unit. An image forming apparatus comprising: The pressing means includes a first roller having a metal surface that contacts the toner adhesion surface side with the intermediate transfer member interposed therebetween, and a second roller having a core member covered with an elastic member on the back side. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the pressing unit presses the intermediate transfer member with a force equivalent to at least primary transfer. The image forming apparatus according to claim 2, wherein the first roller is electrically grounded, and further includes an electric field applying unit that applies an electric field to the second roller. The image forming apparatus according to claim 4, wherein the electric field applying unit applies an electric field corresponding to at least primary transfer to the second roller. The electric field applying means is provided at a position downstream of the primary transfer region at the most downstream position in the moving direction of the intermediate transfer member and at a position upstream of the position of the secondary transfer means. Item 6. The image forming apparatus according to Item 4 or 5.

Images