JP2012247577A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which prevents toner adhesion to the tip of a transfer guide member from an image carrier belt and prevents contamination of the tip or edge surface of transfer paper.SOLUTION: An image forming device includes: an image carrier belt 51 which carries a toner image; a contact member 56 having a surface in contact with the image carrier belt to form a transfer nip; a feeding means 71 which feeds recording paper P toward the transfer nip; and a guide member 65 which guides the recording paper P fed by the feeding means toward the nip. The guide member 65 comprises a cantilevered flat flexible member. Between the guide member and the image carrier belt, a toner shielding member 67 is disposed which is always in non-contact with the recording paper.

Description

  The present invention relates to an electrophotographic image forming apparatus using an electrostatic transfer process in a copying machine or a printer.

In an image forming apparatus such as a copying machine, a facsimile machine, or a printer, a toner image is formed on a photoreceptor used as a latent image carrier, and the toner image is electrostatically applied to a recording medium such as paper, an OHP sheet, or tracing paper. The toner image is transferred, and the transferred toner image is fixed to obtain a copy output.
The image obtained as a copy output includes not only a single color but also a plurality of color images including a full color. As one of the configurations for forming a multi-color image, a monochrome-like speed can be obtained even when obtaining a full color. Tandem types having advantages are known.

In this configuration, the image forming units for each color including the photoconductor and a part of the image forming apparatus for the photosensitive member are juxtaposed, and image transfer is sequentially performed on the belt moving between the image forming units, or is conveyed by the belt. A color image is obtained by sequentially transferring and superimposing images on a recording medium such as a sheet to be printed.
In a tandem type image forming apparatus, an image on each photoconductor is sequentially transferred to an intermediate transfer belt used as an intermediate transfer body by a primary transfer device, and then the image on the intermediate transfer belt is transferred to a sheet by a secondary transfer device. Direct transfer system that directly transfers the images on each photoconductor to the recording medium such as transfer paper that is transported by a transfer belt by the transfer device in sequence. There are things.

In the tandem type image forming apparatus, a backup roller is disposed inside the intermediate transfer belt or the conveyance belt as a transfer bias applying member at the time of image transfer, and the backup roller is transferred while being in contact with the back surface of the belt. A bias is applied.
On the other hand, when the process of sequentially transferring the images of the respective colors to the intermediate transfer belt is the primary transfer process, the superimposed color toner images are collectively transferred to the transfer paper in the secondary transfer process. Yes.

A recording medium (to be referred to as transfer paper hereinafter) conveyed toward a secondary transfer position where a secondary transfer process is performed includes a secondary transfer roller and a backup roller that pressurize the intermediate transfer belt toward the backup roller. The transfer roller is nipped and conveyed by the position of the transfer nip, the position of the registration roller for setting the registration timing of the transfer paper fed toward the nip, and the conveyance roller located in the conveyance path of the transfer paper fed out from the paper feeding device. The
In general, the direction of the transfer paper reaching the transfer nip is regulated by a guide member (entrance guide member) or the like in order to define the direction of entering the transfer nip.

The guide member may cause problems such as transfer blur depending on the accuracy, structure, arrangement, etc., and therefore it is required to design the transfer guide member accurately and appropriately in order to maintain image quality. ing.
Functions required for such a guide member provided at the transfer position can be roughly divided into two.
The first function is a function of regulating the position where the transfer paper (image forming medium) comes into contact with the image carrier.
That is, the transfer paper supplied to the transfer position must be brought into contact with the image carrier before the transfer electric field from the transfer member is applied, and the transfer electric field is applied to the transfer paper before the transfer paper contacts the image carrier. Then, the powder image on the intermediate transfer belt is transferred to the transfer paper through the gap, and becomes a so-called dust image.

In order to prevent this, the transfer paper is usually entered and brought into contact with the intermediate transfer belt at a stage before the position where the transfer electric field is applied. However, if the portion in contact with the intermediate transfer belt before the transfer nip is long, the image is rubbed due to a slight difference in linear velocity between the transfer paper and the intermediate transfer belt. Therefore, the contact position between the paper and the intermediate transfer belt is restricted. Function is required.
The second function is a function to weaken a shock that occurs when the trailing edge of the transfer paper leaves the transfer guide member.

  As described in the first function, the guide member must be disposed at a position where the paper is prevented from coming into contact with the belt before the transfer nip. The guide plate supports the transfer paper. Finally, when the rear end of the paper leaves the transfer entrance guide plate, it contacts the transfer belt. This contact force becomes large especially in the case of a transfer paper having a high rigidity such as a thick paper (basis weight of 90 kg paper or more), and this causes a problem that an image is blurred due to an impact at this time.

  That is, when the transfer paper regulated by the guide member moves away from the guide member, it moves toward the intermediate transfer belt and comes into contact therewith. This contact force becomes larger as the paper becomes thicker and has a higher rigidity, and the toner on the intermediate transfer belt is disturbed. Therefore, the contact force is weakened. In order to weaken the contact force, the leading end position of the guide member is arranged at a position close to the intermediate transfer belt. This is because if the distance between the guide member and the intermediate transfer belt is too large, the impact at the time of contact displacement of the transfer belt when the rear end of the transfer paper is separated from the guide member also increases, so the tip position must be kept close. Don't be.

By the way, the above-mentioned guide member has the following problems.
Since the transfer paper always moves while being in contact with the guide member, the guide member is charged by friction between the transfer paper and the guide member, whereby the transfer paper is charged with a polarity opposite to that of the toner and the charge is held. The charging phenomenon of the guide member due to frictional charging is likely to occur mainly in the coated paper, and is more likely to occur depending on the material of the coating agent. When the electric charge held by the guide member increases, it acts to attract toner on the transfer belt, and the toner adheres to the guide member that is in the vicinity of the transfer belt and is contaminated.
In view of this problem with respect to the tip and edge surface contamination, Patent Document 1 below discloses a technique in which a transfer guide member is formed of a conductive member and a repulsive bias having the same polarity as the toner is applied to the guide member. ing.

However, the technique disclosed in Patent Document 1 requires a power source and control means for applying a bias to the conductive member, which complicates the apparatus and leads to an increase in size and cost of the apparatus. There is a problem that.
In Patent Document 2, voltage application means for applying a voltage having a polarity opposite to that of the toner image is provided on the back surface of the intermediate transfer belt before the nip, and by applying a voltage having a polarity opposite to that of the toner, the toner image is intermediated before the transfer nip. Since an electric field attracted to the transfer belt is generated, a technique is disclosed in which toner scattering to the transfer entrance guide plate is eliminated.
However, the technique disclosed in Patent Document 2 similarly requires a power source and control means for applying a bias, which complicates the apparatus and causes an increase in size and cost of the apparatus.

In Patent Document 3, a conductive non-contact toner collecting member is provided on a guide member so that a potential difference between the toner collecting member and the intermediate transfer belt is increased so that toner is concentrated on the toner collecting member. A technique for preventing the transfer paper from being soiled by preventing the toner from adhering to the tip of the guide member is disclosed.
The toner on the belt is concentrated on the collecting member to prevent the toner from adhering to the guide member. However, the toner immediately accumulates on the collecting member, and the accumulated toner comes into contact with the intermediate transfer belt to display an image. In order to disturb, there was a problem that the guide member had to be frequently replaced.

  An object of the present invention is to solve the above-described problems, and is low in cost, prevents toner adhesion from the image carrier belt to the transfer guide member tip, and transfers the leading edge of the transfer paper. An object of the present invention is to provide an image forming apparatus capable of preventing the edge surface from being stained.

  In order to achieve the above object, the invention of claim 1 is characterized in that an endless image carrying belt carrying a toner image on its own surface that moves endlessly, and its own surface that moves endlessly abuts the image carrying belt. And an abutting member that forms a transfer nip, an image feeding device that feeds a recording medium toward the transfer nip, and a guide member that guides the recording material fed from the feeding device toward the nip. In the forming apparatus, the guide member is composed of a flat plate-like elastically deformable flexible member that is cantilevered by a support member, and the recording member is not always in contact between the guide member and the image carrying belt. The toner shielding member is arranged.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the guide member is cantilevered on the surface of the support member opposite to the side facing the image carrier, and the toner shielding member is imaged. It arrange | positions on the surface of the side facing a support body, It is characterized by the above-mentioned.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the protruding lengths of the guide member and the toner shielding member from the support member are the same. .

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first to third aspects, the toner shielding member is a metal member.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the first to third aspects, the toner shielding member is a flexible member that can be elastically deformed.

  According to the present invention, the guide member that guides the transfer paper to the nip is formed of a flat plate-like flexible member, and the toner shielding member is disposed between the guide member and the image carrying belt, thereby causing a toner smear. Since it is possible to prevent the toner on the carrying belt from adhering to the leading end of the guide member, it is possible to prevent the leading edge and the edge of the transfer paper from being stained.

1 is a side view showing an overall configuration of a copying machine as an image forming apparatus according to the present invention. FIG. 2 is an overall side view of an image forming unit of the copier of FIG. 1. FIG. 2 is a partially enlarged side explanatory view of an image forming unit of the copier of FIG. 1. FIG. 2 is a partially enlarged side explanatory view at a transfer position of an image forming unit of the copier of FIG. FIG. 2 is a schematic explanatory view in a bottom view of a transfer position of an image forming unit of the copier of FIG. 1. FIG. 10 is a partially enlarged side view illustrating a transfer position of an image forming unit according to another embodiment of the present invention. It is a schematic side view which shows the whole structure of the color digital copying machine of other embodiment of this invention.

Hereinafter, an image forming apparatus to which the present invention is applied will be described.
In this image forming apparatus, the cantilever guide member is bent so that the swing end thereof is close to the image carrier belt, and the rear end portion of the recording member is transferred to the image carrier belt. It was realized that the momentum of the end portion contacting the image bearing belt was reduced.
FIG. 1 is a schematic configuration diagram illustrating a copying machine M as an electrophotographic image forming apparatus according to the first embodiment. The copying machine M includes a printer unit 1 that forms an image on a recording sheet P as a recording medium, a paper feeding device 200 that supplies the recording sheet P to the printer unit 1, a scanner 300 that reads a document image, and a document on the scanner 300. An automatic document feeder (hereinafter referred to as ADF) 400 that automatically feeds paper is provided.

The scanner 300 is placed on the contact glass 301 as the first traveling body 303 equipped with a document illumination light source or mirror and the second traveling body 304 equipped with a plurality of reflecting mirrors reciprocate. Scanning of a document (not shown) is performed. The scanning light sent out from the second traveling body 304 is condensed on the imaging surface of the reading sensor 306 installed behind the imaging lens 305 and then read as an image signal by the reading sensor 306.
On the side surface of the housing 1 of the printer unit 1, a manual feed tray 2 for manually placing the recording paper P to be fed into the housing 1, and a paper discharge for stacking the recording paper P after image formation discharged from the housing. A tray 3 is provided.

  FIG. 2 is a partially enlarged configuration diagram illustrating a part of the internal configuration of the printer unit 1 in an enlarged manner. The printer unit 1 is a transfer unit in which an endless intermediate transfer belt 51 as an image carrying belt is stretched by a plurality of stretching rollers (the belt is stretched between a plurality of rollers). The transfer unit 50 is disposed in a state supported by the housing 1. The intermediate transfer belt 51 is driven by a driving roller 52, a secondary transfer backup roller 53, a driven roller 54, and four primary transfer rollers 55Y, 55Y, 55K, which are driven to rotate clockwise in FIG. While being stretched, the drive roller 52 is rotated endlessly in the clockwise direction in the figure. The subscripts Y, C, M, and K attached to the ends of the symbols of the primary transfer rollers 55Y, C, M, and K indicate members for yellow, cyan, magenta, and black. . Hereinafter, the subscripts Y, C, M, and K attached to the ends of the symbols are the same.

  The intermediate transfer belt 51 is greatly curved at the portions where the intermediate transfer belt 51 is wound around the driving roller 52, the secondary transfer backup roller 53, and the driven roller 54, so that the intermediate transfer belt 51 is stretched in an inverted triangular posture with the bottom side directed vertically upward. ing. The tension surface of the upper part of the belt corresponding to the base of this inverted triangle (the surface of the belt stretched between a pair of rollers in a stretched state) extends in the horizontal direction, and is located above the upper tension surface of the belt. The four process units 10Y, 10C, 10M, and 10K are arranged in a horizontal direction along the extending direction of the upper stretched surface.

  In FIG. 1 described above, an optical writing unit 68 is disposed above the four process units 10Y, 10C, 10M, and 10K. The optical writing unit 68 emits four writing lights L by driving four semiconductor lasers (not shown) by a laser control unit (not shown) based on the image information of the original read by the scanner 300. Then, the drum-shaped photoconductors 11Y, 11C, 11M, and 11K serving as latent image carriers of the process units 10Y, 10C, 10M, and 10K are scanned in the dark by the writing light L, respectively. , K, electrostatic latent images for Y, C, M, and K are written.

In this embodiment, the optical writing unit 68 performs optical scanning by deflecting laser light emitted from a semiconductor laser by a polygon mirror (not shown) and reflecting the laser light by a reflection mirror (not shown) or passing through an optical lens. Is used. Instead of such a configuration, an LED array that performs optical scanning may be used.
FIG. 3 is a partially enlarged configuration diagram showing only the Y and C process units 10Y and 10C together with the intermediate transfer belt 51. The Y process unit 10Y includes a charging member 12Y, a charge eliminating device 13Y, a drum cleaning device 14Y, a developing device 20Y as developing means, a potential sensor 49Y, and the like around a drum-shaped photoconductor 11Y. The printer unit 1 is integrally attached to and detached from the printer unit 1 while being held by a casing as a common holding body.

As shown in FIG. 3, the charging member 12Y is a roller-like member that is rotatably supported by a bearing (not shown) while being in contact with the photoreceptor 11Y. The surface of the photoconductor 11Y is uniformly charged to the same polarity as, for example, the charge polarity of Y toner by rotating in contact with the photoconductor 11Y while a charging bias is applied by a bias supply means (not shown). Instead of the charging member 12Y having such a configuration, a scorotron charger or the like that performs a uniform charging process on the photoreceptor 11Y in a non-contact manner may be employed.
A developing device 20Y in which a Y developer containing a magnetic carrier (not shown) and non-magnetic Y toner is contained in a casing 21Y (contained and held inside) is a developer conveying device 22Y and a developing unit 23Y. have. In the developing unit 23Y, a developing sleeve 24Y as a developer carrying member that is endlessly moved by being rotated by a driving unit (not shown) exposes a part of its peripheral surface to the outside through an opening provided in the casing 21Y. ing. As a result, a developing region is formed in which the photoconductor 11Y and the developing sleeve 24Y face each other with a predetermined gap.

  Inside the developing sleeve 24Y made of a non-magnetic hollow pipe-like member, a magnet roller (not shown) having a plurality of magnetic poles arranged in the circumferential direction is fixed to the casing 21Y side so as not to rotate with the developing sleeve 24Y. . The developing sleeve 24Y is driven to rotate while adsorbing the Y developer in the developer conveying device 22Y, which will be described later, to the surface by the magnetic force generated by the magnet roller, thereby pumping the Y developer from the developer conveying device 22Y. Then, the Y developer conveyed toward the developing area as the developing sleeve 24Y rotates, the doctor blade 25Y having the tip opposed to the surface of the developing sleeve 24Y with a predetermined gap, and the sleeve A doctor gap formed between the surface and the surface is entered. At this time, the layer thickness on the sleeve is regulated to substantially the same thickness as the doctor gap. When the developing sleeve 24Y is rotated and conveyed to the vicinity of the developing area facing the photoconductor 11Y, it receives a magnetic force of a developing magnetic pole (not shown) of the magnet roller and rises on the sleeve to become a magnetic brush. .

  For example, a developing bias having the same polarity as the charging polarity of the toner is applied to the developing sleeve 24Y by a bias supply unit (not shown). As a result, in the development region, non-development in which Y toner is electrostatically moved from the non-image portion side to the sleeve side between the surface of the development sleeve 24Y and the non-image portion (uniformly charged portion = background portion) of the photoreceptor 11Y. Potential (field of electric field state that discharges toner with electrostatic force of the same polarity) acts. Further, a developing potential (electrostatic force having a polarity opposite to that of the toner) in which Y toner is electrostatically moved from the sleeve side toward the electrostatic latent image between the surface of the developing sleeve 24Y and the electrostatic latent image on the photoreceptor 11Y. The field of the electric field state to be attracted acts. The Y toner in the Y developer is transferred to the electrostatic latent image by the action of the developing potential, so that the electrostatic latent image on the photoreceptor 11Y is developed into the Y toner image.

The Y developer that has passed through the developing area as the developing sleeve 24Y rotates is separated from the developing sleeve 24Y due to the influence of the repulsive magnetic field formed between the repelling magnetic poles provided in the magnet roller (not shown). The developer returns to the developer conveying device 22Y.
The developer conveying device 22Y includes two first screw members 26Y, a second screw member 32Y, a partition wall 21w interposed between the two screw members, a toner concentration detection sensor 45Y including a magnetic permeability sensor, and the like. The partition wall 21w divides the first transport chamber, which is a developer transport section, in which the first screw member 26Y is accommodated, and the second transport chamber, which is a developer transport section, in which the second screw member 32Y is accommodated. Openings (not shown) are respectively formed in the partition walls wg in the regions facing both ends in the axial direction of both screw members, and both transfer chambers are communicated with each other through the openings.

The first screw member 26Y and the second screw member 32Y as the agitating / conveying members are respectively provided with a rod-like rotary shaft member whose both ends are rotatably supported by a bearing (not shown), and a spiral projection on the peripheral surface thereof. And a spiral blade. Then, as it is driven to rotate by a driving means (not shown), the Y developer is conveyed in the rotation axis direction by the spiral blade.
In the first transport chamber in which the first screw member 26Y is accommodated, the Y developer is transported from the near side to the far side in the direction orthogonal to the drawing surface as the first screw member 26Y is driven to rotate. . And if it conveys to the edge part vicinity of the back | inner side of casing 21Y, it will approach into a 2nd conveyance chamber via the opening which is not provided in the partition wall 21w.

  The above-described developing unit 23Y is formed above the second transfer chamber in which the second screw member 32Y is accommodated, and the second transfer chamber and the developing unit 23Y communicate with each other in the entire area of the opposing part. ing. As a result, the second screw member 32Y and the developing sleeve 24Y disposed obliquely above the second screw member 32Y face each other while maintaining a parallel relationship. In the second transport chamber, the Y developer is transported from the back side to the near side in the direction orthogonal to the drawing sheet as the second screw member 32Y is driven to rotate. In this transport process, the Y developer around the rotation direction of the second screw member 32Y is appropriately pumped up to the developing sleeve 24Y, and the developed Y developer is appropriately collected from the developing sleeve 24Y. Then, the Y developer transported to the vicinity of the front end of the second transport chamber in the drawing returns to the first transport chamber through an opening (not shown).

A toner concentration detection sensor 45Y, which is a magnetic permeability sensor, is fixed to the lower wall of the first transfer chamber, and the detection result is obtained by detecting the toner concentration of the Y developer conveyed by the first screw member 26Y from below. The voltage according to is output. A control unit (not shown) replenishes an appropriate amount of Y toner into the first transfer chamber by driving a Y toner supply device (not shown) as necessary based on the output voltage value from the toner concentration detection sensor 45Y. As a result, the toner concentration of the Y developer, which has been lowered with the development, is recovered.
The Y toner image formed on the photoreceptor 11Y is primarily transferred onto the intermediate transfer belt 51 at a Y primary transfer nip described later. The transfer residual toner that has not been primarily transferred onto the intermediate transfer belt 51 adheres to the surface of the photoreceptor 11Y after passing through the primary transfer process.

  The drum cleaning device 14Y cantilever-supports the cleaning blade 15Y made of, for example, polyurethane rubber (supports only one end in the longitudinal direction of the plate), and the free end of the cleaning blade 14Y contacts the surface of the photoreceptor 11Y. Touching. Further, a brush tip end side of a brush roller 16Y having a rotating shaft member that is driven to rotate by a driving means (not shown) and an infinite number of conductive brushes erected on the peripheral surface thereof is brought into contact with the photoreceptor 11Y. Yes. Then, the transfer residual toner described above is scraped off from the surface of the photoreceptor 11Y by the cleaning blade 15Y and the brush roller 16Y.

  A cleaning bias is applied to the brush roller 16Y via a metal electric field roller 17Y that is in contact with the brush roller 16Y, and the tip of the scraper 18Y is pressed against the electric field roller 17Y. The transfer residual toner scraped off from the photoconductor 11Y by the cleaning blade 15Y and the brush roller 16Y passes through the brush roller 16Y and the electric field roller 17Y, and then is scraped off from the electric field roller 17Y by the scraper 18Y and is placed on the recovery screw 19Y. Fall. Then, after the recovery screw 19Y is driven to rotate, the recovery screw 19Y is discharged out of the casing, and then returned to the developer transport device 22Y via a toner recycling transport means (not shown).

The surface of the photoreceptor 11Y, from which the transfer residual toner has been cleaned by the drum cleaning device 14Y, is neutralized by the neutralizing device 13Y including a neutralizing lamp, and is then uniformly charged again by the charging member 12Y.
Further, the potential of the non-image portion of the photoreceptor 11Y that has passed the optical writing position by the writing light L is detected by the potential sensor 49Y, and the detection result is sent to a control unit (not shown).

Although the Y process unit 10Y has been described in detail, the process units (10C, M, K) of other colors have the same configuration as that of Y except that the color of the toner to be used is different. .
In FIG. 2 shown above, the photoconductors 11Y, C, M, and K of the process units 10Y, 10C, 10M, and 10K are in contact with the upper stretched surface of the intermediate transfer belt 51 that is endlessly moved in the clockwise direction. Rotating to form primary transfer nips for Y, C, M, and K. On the back side of these primary transfer nips for Y, C, M, and K, the above-described primary transfer rollers 55Y, 55C, 55M, and 55K are in contact with the back surface of the intermediate transfer belt 51.

  A primary transfer bias having a polarity opposite to the charging polarity of the toner is applied to each of the primary transfer rollers 55Y, 55C, 55M, 55K by a bias supply unit (not shown). Due to this primary transfer bias, a primary transfer electric field is formed in the primary transfer nips for Y, C, M, and K to electrostatically move the toner from the photoreceptor side to the belt side. The Y, C, M, and K toner images formed on the photoreceptors 11Y, 11C, 11M, and 11K are primary for Y, C, M, and K as the photoreceptors 11Y, 11C, 11M, and 11K rotate. When entering the transfer nip, primary transfer is performed by sequentially superimposing on the intermediate transfer belt 51 by the action of the primary transfer electric field and nip pressure. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface (loop outer peripheral surface) of the intermediate transfer belt 51. Instead of the primary transfer rollers 55Y, 55C, 55M, 55K, a conductive brush to which a primary transfer bias is applied, a non-contact type corona charger, or the like may be employed.

On the right side of the K process unit 10K in the figure, an optical sensor unit 69 (see FIG. 2) is disposed so as to face the front surface of the intermediate transfer belt 51 with a predetermined gap. Yes. The optical sensor unit 69 detects a mark (not shown) provided at a predetermined pitch in the belt circumferential direction at one end of the intermediate transfer belt 51 in the belt width direction. The moving speed of the intermediate transfer belt 51 can be measured based on the detection time interval of each mark.
As shown in FIG. 2, a secondary transfer roller 56 as an abutting member is disposed below the intermediate transfer belt 51, and is driven to rotate counterclockwise in the drawing by a driving means (not shown). A secondary transfer nip is formed by abutting the surface of the endlessly moving surface against the front surface of the intermediate transfer belt 51. Then, on the back side of the secondary transfer nip, the secondary transfer backup roller 53 wraps around the intermediate transfer belt 51 (the belt placed on the roller is rotated).

  A secondary transfer bias having the same polarity as the toner charging polarity is applied to the secondary transfer backup roller 53 by a secondary transfer power source (not shown). On the other hand, the secondary transfer roller 56 that is a contact member that is in contact with the front surface of the belt and forms a secondary transfer nip is grounded. As a result, a secondary transfer electric field is formed between the secondary transfer backup roller 53 and the secondary transfer roller 56. The four-color toner image formed on the front surface of the intermediate transfer belt 51 is transferred to the secondary transfer nip with the endless movement of the intermediate transfer belt 51 (the annular body is rotated over a plurality of supports). enter in.

  In FIG. 1 described above, the paper feeding device 200 is fed with a paper feeding cassette 201 for storing the recording paper P, and a paper feeding roller 202 for feeding the recording paper P stored in these paper feeding cassettes 201 out of the cassette. A plurality of separation roller pairs 203 for separating the recording paper P one by one, a plurality of conveyance roller pairs 205 for conveying the separated recording paper P along the delivery path 204, and the like are provided. The sheet feeding device 200 is disposed directly below the printer unit 1 as shown in the figure. The feeding path 204 of the paper feeding device 200 is connected to the paper feeding path 70 of the printer unit 1. As a result, the recording paper P delivered from the paper feed cassette 201 of the paper feed device 200 is sent into the paper feed path 70 of the printer unit 1 via the feed path 204.

Near the end of the paper feed path 70, a registration roller pair 71 is disposed as a feeding means for feeding the recording paper P toward the secondary transfer nip. The recording paper P sandwiched between the rollers is intermediately transferred. The toner is fed into the secondary transfer nip at a timing that can be synchronized with the four-color toner image on the belt 51.
In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 51 are collectively transferred to the recording paper P due to the influence of the secondary transfer electric field and the nip pressure, and combined with the white color of the recording paper P, Become. The recording paper P on which the full-color image is formed in this way is separated from the intermediate transfer belt 51 when discharged from the secondary transfer nip.
The configuration of the transfer position where the secondary transfer nip formed by the secondary transfer backup roller 53 and the secondary transfer roller 56 around the intermediate transfer belt 51 exists will be described later.

On the left side of the secondary transfer nip in the figure, a conveyor belt unit 75 is provided that moves the endless paper conveyor belt 76 endlessly in the counterclockwise direction in the figure while being stretched by a plurality of stretching rollers. . The recording paper P separated from the intermediate transfer belt 51 is transferred to the upper stretched surface of the paper conveying belt 76 and conveyed toward the fixing device 80.
The recording paper P sent into the fixing device 80 is sandwiched in a fixing nip formed by a heating roller 81 containing a heat source such as a halogen lamp (not shown) and a pressure roller 82 pressed toward the heating roller 81. The full color image is sent to the outside of the fixing device 80 while being fixed on the surface by being heated while being pressurized.
As shown in FIG. 2, a small amount of secondary transfer residual toner that has not been transferred to the recording paper P adheres to the surface of the intermediate transfer belt 51 after passing through the secondary transfer nip. The secondary transfer residual toner is removed from the belt by a belt cleaning device 57 that is in contact with the surface of the intermediate transfer belt 51.

A switchback device 85 is disposed below the fixing device 80. When the recording paper P discharged from the fixing device 80 reaches the conveyance path switching position by the swingable switching claw 86, the paper discharge roller pair 87 or the switchback device according to the swing stop position of the switching claw 86. Sent to 85. When the paper is sent toward the paper discharge roller pair 87, the paper is discharged out of the apparatus and then stacked on the paper discharge tray 3.
On the other hand, when it is sent toward the switchback device 85, it is turned upside down by the switchback conveyance by the switchback device 85 and then conveyed toward the registration roller pair 71 again. Then, it enters the secondary transfer nip again, and a full-color image is formed on the other side.
Note that the recording paper P manually fed onto the manual feed tray 2 provided on the side surface of the housing 1 of the printer unit 1 passes through the manual feed roller 72 and the manual separation roller pair 73 and then toward the registration roller pair 71. Sent.

  When copying a document by the copying machine according to the first embodiment, first, the document is set on the document table 401 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 301 of the scanner 300, and the automatic document feeder 400 is closed and pressed. Thereafter, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is sent into the contact glass 301. Then, the scanner 300 is driven and reading scanning by the first traveling body 303 and the second traveling body 304 is started. At substantially the same time, driving of the transfer unit 50 and each color process unit 10Y, C, M, K starts. Furthermore, the feeding of the recording paper P from the paper feeding device 200 is also started. When recording paper P not set in the paper feed cassette 201 is used, the recording paper P set on the manual feed tray 2 is sent out.

FIG. 4 is an enlarged configuration diagram showing a secondary transfer nip formed by the secondary transfer backup roller 53 and the secondary transfer roller 56 wound around the intermediate transfer belt 51 and the surrounding configuration.
In the drawing, a secondary transfer backup roller 53 to which a secondary transfer bias having the same polarity as the toner (negative polarity in the illustrated example) is applied by a secondary transfer power source 59 and a grounded secondary transfer roller 56 are illustrated. A secondary transfer current flows through the intermediate transfer belt 51 between them. The secondary transfer current mainly flows in a path connecting the shafts of both rollers, that is, a position indicated by a white arrow in the drawing. Therefore, the secondary transfer of the toner image from the intermediate transfer belt 51 to the recording paper P is performed at a position connecting the axes (hereinafter referred to as an inter-axis position). If a gap is formed between the front surface of the intermediate transfer belt 51 and the secondary transfer roller 56 slightly upstream of the inter-axis position in the belt movement direction, discharge occurs between the gaps. . As a result, the toner in the toner image that is in the belt area before entering the secondary transfer nip is scattered, causing transfer dust.

Therefore, in this copying machine M, the belt is moved at a position p1 upstream of the inter-axis position in the belt moving direction so that a gap is formed at a position p1 that is relatively distant from the inter-axis position indicated by the white arrow. The secondary transfer roller 56 is forcibly wound. This forcible wrapping is performed by a push-down roller 58 disposed on the upstream side in the belt movement direction from the secondary transfer backup roller 53 inside the loop of the intermediate transfer belt 51. The push-down roller 58 pushes the belt toward the secondary transfer roller 56 from the inside of the belt loop, thereby forcibly winding the belt around the secondary transfer roller 56. By such winding, the generation of transfer dust is effectively suppressed by moving the gap to a position where the secondary transfer current does not reach.
The pressing roller 58 forms a cylindrical metal core 58a made of metal and a resin portion 58b covered on the outer peripheral surface thereof. The contact surface with the intermediate transfer belt 51 is formed of an electrically insulating resin portion 58b, so that the secondary transfer current applied to the secondary transfer backup roller 53 passes through the back surface of the intermediate transfer belt to the pressing roller 58. By flowing in, the transfer current flowing into the secondary transfer roller 56 is prevented from decreasing.

The secondary transfer backup roller 53 has a cylindrical metal core 53a made of metal, and a conductive elastic layer 53b coated on the outer peripheral surface thereof. When using a small size paper such as A5 size, the contact area between the belt and the small size paper in the belt width direction is relatively small in the secondary transfer nip. In spite of the small size paper entering the nip, the direct contact area between the belt and the secondary transfer roller 56 is formed with a relatively large area. In such a case, if the secondary transfer current flows intensively in the direct contact area so as to avoid the small size paper having a large electric resistance, the effective transfer electric field required in the small size paper area is reduced. It becomes impossible to obtain and causes a transfer defect. Therefore, in this copying machine, as the elastic material of the elastic layer 53b of the secondary transfer backup roller 53, a material in which the addition amount of the ion conductive agent is appropriately adjusted is used, and the volume specific resistivity of the secondary transfer backup roller 53 is used. 10 ⁷ [Ω · cm] or more. As a result, the backup roller 53 exerts an electric resistance larger than the paper resistance, thereby avoiding the concentration of the secondary transfer current in the direct contact area.

The secondary transfer roller 56 includes a cylindrical metal core 56a made of metal, a conductive elastic layer 56b coated on the outer peripheral surface thereof, and a surface layer 56c formed of a conductive resin coated on the outer peripheral surface thereof. And have. As a metal core, what consists of metal materials, such as stainless steel and aluminum, can be illustrated.
Examples of the elastic layer 56b of the secondary transfer roller 56 include a rubber material made of a conductive rubber material obtained by adding a conductive material or an ionic conductive agent. In order to make the secondary transfer roller 56 capable of being in close contact with the intermediate transfer belt 51 by flexible deformation of the elastic layer 56b, the elastic layer 56b having a JIS-A hardness of 70 [°] or less is adopted. Is desirable. However, since the cleaning blade 60 described later is brought into contact with the secondary transfer roller 56, if the elastic layer 56b is too soft, cleaning becomes difficult due to its excessively flexible deformation. Therefore, it is desirable that the JIS-A hardness of the elastic layer 56b be 40 [°] or more. In this copying machine, an elastic layer 56b made of epichlorohydrin rubber having a JIS-A hardness adjusted to 50 [°] is employed.

Examples of the surface layer 56c of the secondary transfer roller 56 include those made of ethylene propylene diene rubber (EPDM) or Si rubber in which carbon powder for adjusting electric resistance is dispersed. Further, it may be made of nitrile rubber (NBR) or urethane rubber having an ion conductive function. Since the surface layer 56c plays a role of suppressing toner adhesion to the surface of the secondary transfer roller 56, the toner releasability is naturally superior to the elastic layer 56b.
In the present copying machine, the recording paper P fed from the registration roller pair 71 is moved to a position upstream of the secondary transfer nip formed by the secondary transfer roller 56 and the intermediate transfer belt 51 in the belt moving direction. A guide member (guide plate) 65 (see FIGS. 4 and 5) made of a flat plate-like flexible member that guides toward the entrance of this is disposed. The guide member (guide plate) 65 will be described later.

Since this copying machine creates a toner density adjustment pattern between papers in order to enable high-speed printing stably, the toner adheres to the secondary transfer roller 56. Therefore, as shown in FIG. 4, a cleaning blade 60 that mechanically scrapes the toner adhering to the secondary transfer roller 56 is brought into contact with the secondary transfer roller 56. In addition, the toner release property of the secondary transfer roller 56 is further improved by applying the lubricant by the lubricant applying means 62.
The lubricant application means 62 is a lubricant powder obtained by scraping from the solid lubricant 63 by being driven to rotate in contact with both the solid lubricant 63 such as a zinc stearate lump and the secondary transfer roller 56. Are applied to the secondary transfer roller 56, and a coil spring 64 that biases the solid lubricant 63 toward the application brush roller 621 is provided. Further, a paper dust removing brush 61 is disposed upstream of the cleaning blade 60 in order to remove the paper dust.

  As shown in the drawing, since various members are brought into contact with the secondary transfer roller 56, it is not possible to perform a driven rotation accompanying the surface movement of the intermediate transfer belt 51. In order to pass the recording paper P through the secondary transfer nip at high speed, it is advantageous to drive the secondary transfer roller 56 to rotate. For this reason, the secondary transfer roller 56 is rotationally driven by a drive system (not shown). In this configuration, as described above, the conveyance of the recording paper P in the vicinity of the entrance of the secondary transfer nip is caused by the rotational driving force of the secondary transfer roller 56 that is pressed against the leading end side of the recording paper P in the secondary transfer nip. To be ruled. In the vicinity of the entrance of the secondary transfer nip, the recording paper P moves at substantially the same speed as the linear speed of the secondary transfer roller.

  By the way, the secondary transfer roller 56 inevitably generates an outer diameter error of ± 0.5 [%] due to the limit of processing accuracy at the time of manufacture. For this reason, even if the design is made such that the moving speed of the intermediate transfer belt 51 and the linear speed of the secondary transfer roller 56 are the same, a slight difference in linear speed will inevitably occur. Furthermore, since the rotation center is slightly decentered with respect to the outer periphery of the secondary transfer roller 56, the linear velocity of the secondary transfer roller 56 slightly changes even around one rotation. As a result, in the contact area between the belt 51 and the recording paper P in the secondary transfer nip, the speed difference between the moving speed of the recording paper P and the moving speed of the belt cannot be eliminated. Due to this speed difference, image distortion due to the rubbing of the toner image occurs.

In this copying machine, the feeding speed of the recording paper P by the registration roller pair 71 is slightly faster than the transport speed of the recording paper P by the secondary transfer roller 56. This is because the recording paper P in which the leading end side is sandwiched in the secondary transfer nip and the trailing end side is sandwiched in the registration nip of the registration roller pair 71 is excessively tensioned between the secondary transfer nip and the registration nip. It is because it is extended by.
With such a speed setting, as the recording paper P is conveyed, the recording paper P is gradually bent between the secondary transfer nip and the registration nip. It occurs between the support point (tip position) s of the recording paper P by the guide plate 65 and the exit of the registration nip. Since the recording paper P hardly bends between the support point s and the secondary transfer nip entrance, the recording paper P moves at the linear speed of the secondary transfer roller 56 in the vicinity of the entrance of the secondary transfer nip. .

On the other hand, when the leading end position (support point s) of the guide member 65 is disposed at a position away from the secondary transfer nip, the recording paper P is placed between the entrance of the secondary transfer nip and the guide member 65. The bending occurs, and the intermediate transfer belt and the recording paper P come into contact before the entrance to the nip. In the area before the entrance of the secondary transfer nip, the recording paper P moves while being in contact with the intermediate transfer belt 51 with a slight linear velocity difference, so that the toner image rubs and disturbs the image. The guide member 65 needs to be disposed at the tip so as not to cause such a problem.
As described above, the distance between the entrance of the secondary transfer nip and the support point s at the time of contact between the recording paper P and the intermediate transfer belt 51 is regulated to an appropriate value. Move in constant contact. Therefore, the friction between the recording paper P and the guide member 65 causes the guide member 65 to be charged with a polarity opposite to that of the toner, the electric charge is held, acts to attract the toner on the transfer belt 51, and stains due to the toner are removed. There is a problem that occurs.

Further, as shown in FIG. 4, one end of the guide member (guide plate) 65 is cantilevered by a cover member (support member) 66 supported by a frame (not shown) of the transfer unit 50, and the recording paper P is loaded. It consists of a flexible member that guides toward the guidance target point. Here, the cover member 66 fixes the base end of the guide member 65 to the surface opposite to the side facing the intermediate transfer belt 51 and supports the front end (support point) s of the guide member 65 as a free end.
For this reason, when a thick thick paper is passed, the guide member 65 is deformed by the stiffness of the paper (refer to the displacement of the symbol q in FIG. 4), so that the toner stains due to the proximity to the intermediate transfer belt. There is.

Therefore, in this copying machine, the surface facing the intermediate transfer belt (image carrier) 51 as shown in FIG. 4 with respect to the cover member (support member) 66 supported by the frame (not shown) of the transfer unit 50. A toner shielding member 67 made of a metal plate is attached to the belt 51 at a predetermined distance. That is, the cover member 66 cantilever-supports the toner shielding member 67 on the surface facing the intermediate transfer belt 51 and the guide member (guide plate) on the surface opposite to the surface facing the intermediate transfer belt 51. 65 is cantilevered.
The base end of the toner shielding member 67 is cantilevered by a cover member (supporting member) 66, and is arranged in parallel with the guide member 65. The protruding length L1 from the cover member 66 is the same length, and the distal ends of the toner shielding members 67 are stationary. In the state, they are opposed to each other through the gap t1. As shown in FIG. 5, the toner shielding member 67 and the cover member 66 are both flat, and the paper width direction (transport orthogonal direction) perpendicular to the recording paper transport direction is formed with substantially the same width.

Thus, the toner shielding member 67 made of a metal plate is cantilevered on the surface of the cover member 66 facing the intermediate transfer belt 51, so that the toner on the intermediate transfer belt 51 is directly guided to the guide member. It is possible to adopt a configuration in which it is not opposed to 65 and covered so as not to adhere to the guide member 65.
Further, the reason why the protruding length L1 of the guide member 65 and the toner shielding member 67 from the cover member 66 is set to the same length is as follows.
For example, when the guide member length> the toner shielding member length), toner contamination occurs at the tip of the guide member 65 not covered with the toner shielding member 67, and (guide member length <toner shielding). In the case of (member length), the recording paper P and the toner shielding member 67 come into contact with each other, and dirt on the toner shielding member 67 adheres. For this reason, the protruding length L1 of the guide member 65 and the toner shielding member 67 is set to be the same length to prevent the recording paper P from being contaminated with toner and the edge surface.

In the copying machine of FIG. 1, the guide member 65 that guides the recording paper P to the nip is formed of a flat plate-like flexible member, and the toner shielding member 67 is disposed between the guide member 65 and the image carrying belt 51. As a result, even if the toner on the belt 51 adheres to the toner shielding member 67, the guide member 65 that is in contact with the recording paper P can be prevented from being contaminated with toner, so that the front end and the edge surface can be prevented from being stained.
In the first embodiment described above, the toner shielding member 67 is supported by being overlapped on the surface of the cover member 66 facing the intermediate transfer belt 51, and the toner shielding member 67 is cantilevered along the same surface. However, only this component may be replaced as shown in FIG. 6 as the second embodiment. In the second embodiment, the toner shielding member 67a is arranged so as to be attached to and supported by the cover member 66a with a predetermined amount from the surface facing the intermediate transfer belt 51 and inclined with respect to the surface.

  Here, a second cover member 68 is provided in the vicinity of the cover member 66 a that supports the guide member 65 a, and both cover members 68 are supported by a frame (not shown) of the transfer unit 50. Here, the toner cover member 67a is cantilevered by the second cover member 68, and is supported in a state close to the inclination of the intermediate transfer belt 51 while being inclined with respect to the guide member 65a. Also in this case, the guide member 65a and the toner shielding member 67a are set to have the same protruding length L2, and the distal ends of the guide member 65a and the toner shielding member 67a are arranged to face each other via the gap t2 in a steady state. In this case, in addition to the same effects as those of the first embodiment, the degree of freedom in arrangement of the toner shielding member 67a is increased, and the toner contamination of the guide member 65a in contact with the recording paper P can be prevented more accurately. Dirt and edge stains can be prevented.

Although a plurality of embodiments of the present invention have been described above, the present invention is not limited to the specific configurations of the above-described embodiments, and various configurations can be made within the scope described in the claims.
For example, the color digital copying machine M1 as the second embodiment may be configured. In this case, as shown in FIG. 7, the image forming units 10Y, 10C, and 10M constituting the transfer unit 50b (the same reference numerals as those attached to the same functional members in the first embodiment) are transferred. It is arranged in the vertical direction on the left side of the belt 51b, stretched in a loop shape so as to protrude the lower part of the intermediate transfer belt 51b, and the secondary transfer backup roller 53b (located inside the image carrier belt) at a position protruding to the lower part. And a second transfer roller 56b (located opposite to the outer surface of the image carrier belt). As in the first embodiment, the toner shielding member 67b is disposed between the guide member 65b and the image carrying belt 51b below the second intermediate transfer portion, so that the toner on the belt 51 is transferred to the toner shielding member. Even if it adheres to 67b, since the toner contamination of the guide member 65b in contact with the recording paper P can be prevented, the same effect as in the first embodiment that the front end contamination and the edge surface contamination can be prevented can be obtained.

  In the above description, an example of a copying machine that uses an intermediate transfer belt as the image carrying belt has been described. However, the copying machine may be applied to other printers that use the image carrying belt, a facsimile, or a multifunction machine including them. The present invention may be applied to other image forming apparatuses.

51 Image bearing belt (intermediate transfer belt)
56 Secondary transfer roller (contact member)
65, 65a Guide member (guide plate)
67 Toner shielding member 71 Registration roller pair (feeding means)
L1 Length M, Ma Copier (image forming device)
P Recording paper (recording medium)

JP 11-338276 A JP 2004-61908 A JP 2008-003449 A

Claims (5)

  An endless image bearing belt that carries a toner image on its surface that moves endlessly, a contact member that forms a transfer nip by bringing its surface that moves endlessly into contact with the image bearing belt, and a recording medium In an image forming apparatus comprising: a feeding unit that feeds toward a transfer nip; and a guide member that guides a recording body fed from the feeding unit toward the nip, the guide member is cantilevered by a support member. An image forming apparatus comprising: a flat plate-like elastically deformable flexible member, and a toner shielding member that is always in non-contact with the recording medium between the guide member and the image carrying belt. apparatus.   2. The guide member according to claim 1, wherein the guide member is cantilevered on a surface opposite to the side facing the image carrier of the support member, and the toner shielding member is arranged on a surface facing the image carrier. The image forming apparatus described.   3. The image forming apparatus according to claim 2, wherein the guide member and the toner shielding member have the same protruding length from the support member.   The image forming apparatus according to claim 1, wherein the toner shielding member is a metal member.   The image forming apparatus according to claim 1, wherein the toner shielding member is a flexible member that is elastically deformable.

Images