JP2016186636A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device that, when transferring a toner image on an intermediate transfer body onto a recording medium, can suppress the occurrence of scattering of the toner image due to an air held and compressed between the intermediate transfer body and the recording medium.SOLUTION: A transfer device comprises: a transfer member 34 that transfers a toner image held on an intermediate transfer body 26 making a circulation movement while holding the toner image onto a recording medium; an opposing member 32 that is arranged to be in pressure-contact with the transfer member 34 with the intermediate transfer body 26 therebetween; and a preload member 60 that is arranged to be in pressure-contact with the transfer member 34 with the intermediate transfer body 26 therebetween on the upstream side along a direction of movement of the intermediate transfer body 26 with respect to a contact part where the opposing member 32 is in pressure-contact with the transfer member 34 and at a position immediately after the toner image held on the intermediate transfer body 26 starts contact with the recording medium. A pressure applied by the preload member is weaker than the pressure at which the opposing member is in contact with the transfer member.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a transfer device and an image forming apparatus.

  Conventionally, the image forming apparatus includes, for example, an intermediate transfer body on which a plurality of toner images having different colors are transferred, and the plurality of toner images transferred onto the intermediate transfer body are transferred to a transfer roll. In some cases, a color image or the like is formed by performing secondary transfer collectively onto a recording medium.

  In such an image forming apparatus, techniques for improving transferability when a toner image is secondarily transferred from an intermediate transfer member onto a recording medium include, for example, Japanese Patent Application Laid-Open Nos. 11-24444 and 8-254907. Have already been proposed.

  An image forming apparatus according to Japanese Patent Application Laid-Open No. 11-24444 includes an image carrier, a paper carrier or an intermediate transfer member that contacts the image carrier, and a toner image on the image carrier as a paper or intermediate transfer member. In the image forming apparatus, comprising: an electrostatic transfer means to be transferred to the electrostatic transfer means; and a restriction means for restricting discharge from the electrostatic transfer means; and upstream of the electrostatic transfer means and adjacent to the discharge restriction means. A pressing member that contacts the conveyance body or the intermediate transfer body with a certain width is provided, and the pressing member is configured to push up the paper conveyance body or the intermediate transfer body by a certain width in the direction of the image carrier. Is.

  Further, an image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 8-254907 develops a latent image carrier on which a latent image is formed, and develops the latent image with a developer in which toner is dispersed in a liquid carrier. Developing means for forming a toner image; transfer means for transferring the toner image on the latent image carrier to a recording material at a predetermined transfer portion; and the recording material provided near the transfer portion for transferring the latent image to the latent image. According to the pressing means for pressing the carrier, the control means for controlling the pressing force by which the pressing means presses the recording material, and the type of the recording material used for the control means. Input means.

Japanese Patent Laid-Open No. 11-24444 Japanese Patent Laid-Open No. 08-254907

  Incidentally, the problem to be solved by the present invention is that when transferring the toner image on the intermediate transfer member onto the recording medium, the toner image is scattered by the compressed air sandwiched between the intermediate transfer member and the recording medium. It is an object of the present invention to provide a transfer device and an image forming apparatus that can suppress the occurrence of the above.

That is, the invention described in claim 1 is a transfer member that transfers a toner image held on an intermediate transfer member that circulates while holding a toner image onto a recording medium;
An opposing member arranged to contact the transfer member with pressure through the intermediate transfer member;
The toner image held on the intermediate transfer body starts to contact the recording medium on the upstream side in the moving direction of the intermediate transfer body from the contact portion where the opposing member contacts the transfer member with pressure. A preload member disposed so as to contact the transfer member with pressure through the intermediate transfer member at a position immediately after
With
A bias voltage having the same polarity as the charging polarity of the toner forming the toner image is applied to the opposing member, and a bias voltage having a polarity opposite to the charging polarity of the toner forming the toner image is applied to the preloading member. The transfer device is characterized by that.

  In the invention described in claim 2, the transfer member and the preload member are both roll-shaped members, and the outer diameter of the preload member is set smaller than the outer diameter of the transfer member. The transfer device according to claim 1, wherein:

  The invention described in claim 3 is the transfer apparatus according to claim 1 or 2, wherein the pressure applied to the preload member is controlled in accordance with the thickness of the recording medium.

  The transfer device according to any one of claims 1 to 3, wherein the pressure applied to the preload member is controlled in accordance with a charge amount of the toner. .

  According to a fifth aspect of the present invention, in the transfer device according to any one of the first to fourth aspects, the pressure applied to the preload member is controlled according to environmental conditions.

Furthermore, the invention described in claim 6 includes a plurality of image carriers that hold toner images of different colors,
A plurality of primary transfer means for transferring each of the toner images held on the plurality of image holders onto the intermediate transfer member in a multiplexed manner;
Secondary transfer means for performing secondary transfer of the toner images, which have been primary-transferred multiple times onto the intermediate transfer body, onto a recording medium in a batch,
An image forming apparatus using the transfer device according to claim 1 as the secondary transfer unit.

  According to the first aspect of the present invention, when the toner image on the intermediate transfer member is transferred onto the recording medium, the toner image is scattered by the compressed air sandwiched between the intermediate transfer member and the recording medium. Can be suppressed.

  According to the first aspect of the present invention, toner scattering due to discharge of the toner image on the intermediate transfer member can be suppressed.

  According to the second aspect of the present invention, the gap between the intermediate transfer member and the transfer roll can be reduced.

  According to the third aspect of the present invention, it is possible to suppress the occurrence of image quality defects due to excessive cohesive force acting on the toner image on the intermediate transfer member.

  Furthermore, according to the fourth aspect of the present invention, it is possible to suppress the occurrence of image quality defects due to excessive cohesive force acting on the toner image on the intermediate transfer member.

  According to the fifth aspect of the present invention, it is possible to suppress the occurrence of image quality defects due to excessive cohesive force acting on the toner image on the intermediate transfer member.

  According to the sixth aspect of the present invention, when the toner images of the respective colors on the intermediate transfer member are transferred onto the recording medium, the compressed air is sandwiched between the intermediate transfer member and the recording medium. The occurrence of toner image scattering can be suppressed.

1 is a configuration diagram illustrating a main part of an image forming apparatus to which a transfer device according to a first embodiment of the present invention is applied. 1 is an overall configuration diagram showing an image forming apparatus to which a transfer apparatus according to Embodiment 1 of the present invention is applied. It is a block diagram of the conventional secondary transfer part. FIG. 6 is an explanatory diagram illustrating a mechanism that causes toner image scattering. FIG. 6 is an explanatory diagram illustrating a mechanism that causes toner image scattering. FIG. 6 is an explanatory diagram illustrating a mechanism that causes toner image scattering. FIG. 6 is a schematic diagram illustrating scattering of a toner image. It is a block diagram of a secondary transfer part. FIG. 6 is an explanatory diagram illustrating a mechanism for suppressing scattering of a toner image. FIG. 6 is an explanatory diagram illustrating a mechanism for suppressing scattering of a toner image. It is a block diagram which shows the modification of the transfer apparatus which concerns on Embodiment 1 of this invention. FIG. 6 is an explanatory diagram illustrating a mechanism for suppressing scattering of a toner image. FIG. 6 is a schematic diagram illustrating an evaluation example of toner image scattering. 6 is a chart showing evaluation results of occurrence of toner image scattering. It is a whole block diagram which shows the image forming apparatus to which the transfer apparatus which concerns on Embodiment 2 of this invention is applied. It is a block diagram which shows the principal part of the image forming apparatus to which the transfer apparatus which concerns on Embodiment 2 of this invention is applied. It is a block diagram which shows the principal part of the image forming apparatus to which the transfer apparatus which concerns on Embodiment 4 of this invention is applied.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 is a schematic configuration diagram showing a tandem type digital color printer as an image forming apparatus to which the transfer apparatus according to the first embodiment of the present invention is applied. The tandem type digital color printer includes an image reading device, and functions as a full-color copying machine or a facsimile. Of course, the image forming apparatus may not include an image reading apparatus and may form an image based on image data output from a personal computer (not shown).

  In FIG. 2, reference numeral 1 denotes a main body of the image forming apparatus. The image forming apparatus main body 1 has an image reading device 3 that reads an image of a document 2 on the upper side of one side (left side in the illustrated example). I have. In addition, in the image forming apparatus main body 1, image data output from the image reading device 3, a personal computer (not shown) or the like, or image data sent via a telephone line, a LAN, etc. An image processing device 4 that performs predetermined image processing is arranged, and an image is formed inside the image forming apparatus main body 1 based on image data that has been subjected to predetermined image processing by the image processing device 4. Is output.

  The image reading device 3 opens and closes the document pressing cover 6 to place the document 2 on the platen glass 7. The image reading device 3 is placed on the platen glass 7 to illuminate the document 2 with the light source 8. The reflected light image is scanned and exposed on an image reading element 13 composed of a CCD or the like through a reduction scanning optical system composed of a full-rate mirror 9, half-rate mirrors 10 and 11, and an imaging lens 12. An image of the original 2 is configured to be read at a predetermined dot density.

  The image of the document 2 read by the image reading device 3 is, for example, the image processing device 4 as document reflectance data of three colors of red (R), green (G), and blue (B) (for example, 8 bits each). In this image processing apparatus 4, shading correction, position shift correction, lightness / color space conversion, gamma correction, frame deletion, color / moving editing, etc. are predetermined for the reflectance data of the document 2. Image processing is performed.

  The image data that has been subjected to the predetermined image processing by the image processing device 4 as described above is similarly processed by the image processing device 4 in yellow (Y), magenta (M), cyan (C), and black (K). It is converted into image data of four colors, and image exposure units (image forming units) 14Y, 14M, 14C, and 14K for each color of yellow (Y), magenta (M), cyan (C), and black (K) are exposed. The image exposure apparatuses 15Y, 15M, 15C, and 15K perform image exposure with the laser beam LB in accordance with the corresponding color image data.

  Meanwhile, as described above, the image forming apparatus main body 1 includes four image forming units 14Y, 14M, 14C, and 14K of yellow (Y), magenta (M), cyan (C), and black (K). Are arranged in parallel at regular intervals in the horizontal direction.

  As shown in FIG. 2, these four image forming units 14Y, 14M, 14C, and 14K are configured in the same manner except for the color of the image to be formed, and are roughly classified in advance along the direction of arrow A. A photosensitive drum 16 as an image carrier that is rotationally driven at a speed (for example, process speed = 440 mm / sec), a scorotron 17 for primary charging that uniformly charges the surface of the photosensitive drum 16, and the photosensitive drum An image exposure device 15 as image writing means for forming an electrostatic latent image by performing image exposure on the surface of the body drum 16 based on image data corresponding to each color, and an electrostatic formed on the photosensitive drum 16 A developing device 18 as developing means for developing the latent image with toner, and a cleaning device 19 for removing toner and the like remaining on the surface of the photosensitive drum 16; It is al configuration.

  As shown in FIG. 2, the image processing device 4 exposes the image forming units 14Y, 14M, 14C, and 14K for the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Corresponding color image data is sequentially output to the devices 15Y, 15M, 15C, and 15K, and laser beams LB emitted according to the image data from these image exposure devices 15Y, 15M, 15C, and 15K correspond. The surfaces of the photosensitive drums 16Y, 16M, 16C, and 16K are scanned and exposed to form electrostatic latent images. The electrostatic latent images formed on the surfaces of the photosensitive drums 16Y, 16M, 16C, and 16K are respectively yellow (Y), magenta (M), and cyan (C) by the developing devices 18Y, 18M, 18C, and 18K. The toner image is reversely developed as a toner image composed of toner of black (K) color (charged to negative polarity).

  Each color of yellow (Y), magenta (M), cyan (C), and black (K) sequentially formed on the photosensitive drums 16Y, 16M, 16C, and 16K of the image forming units 14Y, 14M, 14C, and 14K. As shown in FIG. 2, the toner image is transferred onto the intermediate transfer belt 26 as an endless belt-like intermediate transfer member disposed below each of the image forming units 14Y, 14M, 14C, and 14K at the primary transfer position N1. Multiple transfer is performed by primary transfer rolls 27Y, 27M, 27C, and 27K as primary transfer means. Multiple transfer is performed by the primary transfer rolls 27Y, 27M, 27C, and 27K. The primary transfer rolls 27Y, 27M, 27C, and 27K have a positive polarity voltage that is opposite to the negative polarity that is the charging polarity of the toner, and the metal rotation that constitutes the primary transfer rolls 27Y, 27M, 27C, and 27K. It is applied in a state of constant current control so that the value of the current flowing through the shaft is constant. The intermediate transfer belt 26 is wound around the drive roll 28, the tension applying roll 29, the meandering control roll 30, the driven roll 31, the back support roll 32, and the driven roll 33 with a constant tension. The drive roll 28 is circulated and driven at a predetermined moving speed (for example, approximately 440 mm / sec, which is substantially the same as the process speed, which is the rotational speed of the photosensitive drum) along the direction of arrow B by the drive roll 28. . As the intermediate transfer belt 26, for example, a flexible synthetic resin film such as polyimide or polyamideimide is formed in a belt shape, and both ends of the synthetic resin film formed in the belt shape are connected by means such as welding. Thus, an endless belt shape or an endless belt shape from the beginning is used.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 26 in a multiple manner are the same as the toner by the back support roll 32 as a facing member. A polarity (negative polarity) transfer voltage is applied, and a secondary transfer roll 34 as a grounded secondary transfer member pressed against the back support roll 32 is used as a recording medium by electrostatic force at the secondary transfer position N2. The recording paper 35 that has been secondarily transferred onto the recording paper 35 and onto which the toner image corresponding to the color of the image to be formed has been transferred is transported to the fixing device 38 by the two transport belts 36 and 37. At this time, the back support roll 32 has a negative voltage having the same polarity as the negative polarity that is the charging polarity of the toner, and a voltage value applied to the metal rotating shaft constituting the back support roll 32. It is applied in a state of constant voltage control so as to be constant. The recording paper 35 onto which the toner images of the respective colors have been transferred undergoes a fixing process with heat and pressure by the fixing device 38 and is discharged onto a discharge tray 39 provided outside the image forming apparatus main body 1.

  As shown in FIG. 2, the recording paper 35 is of a desired size and material from the paper feed tray 40 disposed at the bottom of the image forming apparatus main body 1. The paper is fed one by one by a pair of rolls, and is temporarily transported to a registration roll 46 through a paper transport path 45 in which a plurality of transport rolls 42, 43, and 44 are disposed. The recording paper 35 supplied from the paper feed tray 40 is sent to the secondary transfer position N2 of the intermediate transfer belt 26 by a registration roll 46 that is rotationally driven at a predetermined timing. Although only one paper feed tray 40 is shown, a plurality of paper feed trays having recording papers 35 having different sizes or the same size may be provided.

  Prior to that, in the four image forming units 14Y, 14M, 14C, and 14K of yellow, magenta, cyan, and black, as described above, the yellow, magenta, cyan, and black toner images are respectively stored in advance. They are formed sequentially at a predetermined timing.

  The photosensitive drums 16Y, 16M, 16C, and 16K are prepared for the next image forming process by removing residual toner and the like by the cleaning devices 19Y, 19M, 19C, and 19K after the toner image transfer process is completed. . Further, residual toner, paper dust, and the like are removed from the intermediate transfer belt 26 by a belt cleaner 47 disposed so as to face the driven roll 33.

  Incidentally, as described above, the image forming apparatus configured as described above improves the productivity determined by the number of recording sheets 35 on which an image is formed per unit time. It is set as high as sec. For this reason, it has been clarified by the inventors' research that image defects that do not occur or are unlikely to become a problem in conventional low-speed machines and medium-speed machines occur. However, the image forming apparatus to which the present invention is applied is not limited to a high speed machine, and may be applied to a medium speed machine or a low speed machine.

  That is, in the image forming apparatus, as shown in FIG. 2, not only the photosensitive drums 16Y, 16M, 16C, and 16K, but also yellow (Y) and magenta from above the photosensitive drums 16Y, 16M, 16C, and 16K. The intermediate transfer belt 26 on which the toner images of the respective colors (M), cyan (C), and black (K) are primarily transferred is also circulated at a high speed of 440 mm / sec, which is the process speed described above. Therefore, in this image forming apparatus, as shown in FIGS. 3 and 4, when the toner images 51 of the respective colors primarily transferred onto the intermediate transfer belt 26 are secondarily transferred onto the recording paper 35 collectively, Ambient air 53 is sandwiched and compressed between the surface of the transfer belt 26 and the recording paper 35 and intersects with the moving direction of the unfixed toner image 51, particularly the intermediate transfer belt 26, which is secondarily transferred onto the recording paper 35. It has been clarified by the present inventors that the toner image is scattered in the straight line image 51 along the direction in which the toner flows.

  More specifically, as shown in FIG. 3, the toner image 51 secondarily transferred onto the intermediate transfer belt 26 is moved between the secondary transfer roll 34 and the back support roll 32 as the intermediate transfer belt 26 moves. The recording sheet 35 moves to the pressure contact portion 52 at the secondary transfer position N2 in synchronization with the toner image 51 on the intermediate transfer belt 26 while moving to the pressure contact portion (contact portion) 52 at the secondary transfer position N2 in contact with pressure. And move.

  In this embodiment, as shown in FIG. 3, the secondary transfer roll is interposed via the intermediate transfer belt 26 in consideration of the peelability of the recording paper 35 after passing through the pressure contact portion 52 at the secondary transfer position N2. At the secondary transfer position N2 where the back support roll 32 and the back support roll 32 are in pressure contact, the back support roll 32 is shifted to the downstream side along the moving direction of the intermediate transfer belt 26, and further to the secondary transfer roll 34 side. It is arranged at the displaced position. Therefore, as shown in FIG. 3, the intermediate transfer belt 26 first contacts the surface of the secondary transfer roll 34 at the secondary transfer position N2, and then has a certain length on the surface of the secondary transfer roll 34. The secondary transfer roll 34 and the back support roll 32 are configured to enter a pressure contact portion 52 where the secondary transfer roll 34 and the back support roll 32 are in pressure contact with each other in a state of being wound around.

  Therefore, in the state as it is, as shown in FIG. 3, the intermediate transfer belt 26 and the surface of the secondary transfer roll 34 on the upstream side along the moving direction of the intermediate transfer belt 26 at the secondary transfer position N2 are supported on the back surface. Contact is made in a state where the pressing force of the roll 32 is not directly received, and the pressure P1 between the intermediate transfer belt 26 and the secondary transfer roll 34 is small as shown in FIG.

  In this state, the air 53 sandwiched between the intermediate transfer belt 26 and the recording paper 35 is pressed against the secondary transfer roll 34 and the back support roll 32 as shown in FIG. When moving into 52, it loses its escape and is gradually compressed and pushed backward along the moving direction of the intermediate transfer belt 26. At this time, the toner image 51 transferred rearward along the moving direction of the intermediate transfer belt 26, particularly the toner image 51 along the direction intersecting the moving direction of the intermediate transfer belt 26 (direction perpendicular to the drawing) As shown in the drawing, the air 53 compressed in the press contact portion 52 is scattered toward the rear along the moving direction of the intermediate transfer belt 26, and the toner image 51 is scattered.

  As shown in FIG. 7, such scattering of the toner image 51 is particularly a high-density image with a high image density near Cin = 100%, along the direction intersecting the moving direction of the intermediate transfer belt 26. It has been found that the toner image 51 that forms a black (K) linear image, which is often formed in a straight line, is prominently generated. However, the color of the toner image 51 is not limited to the black (K) color, and naturally occurs in other colors of yellow (Y), magenta (M), and cyan (C).

  Therefore, in order to suppress the occurrence of scattering of the toner image 51 described above, the present inventors support a back support roll that supports the back side of the intermediate transfer belt 26 at the secondary transfer position N2, as shown in FIG. By moving the position 32 to the upstream side along the moving direction of the intermediate transfer belt 26, as shown in FIG. 9, the inlet side of the press contact portion 52 where the secondary transfer roll 32 and the back support roll 34 are in pressure contact with each other. The structure which raises the pressure P2 of was examined.

  In such a configuration, although the effect of suppressing the occurrence of scattering of the toner image 51 to some extent is recognized, as shown in FIG. 8, the intermediate transfer belt 26 and the recording paper 35 at the entrance of the press contact portion 52 , The gap discharge occurs between the intermediate transfer belt 26 and the recording paper 35, and new scattering due to the gap discharge is generated in the toner image 51 that is secondarily transferred from the intermediate transfer belt 26 to the recording paper 35. It was found to occur.

  Therefore, the inventors analyzed the force acting on the toner image 51 constituting the toner image 51 at the secondary transfer position N2 where the intermediate transfer belt 26 is in pressure contact with the recording paper 35 as shown in FIG. The inventors have invented a transfer device that can prevent the toner image 51 from scattering while preventing new scattering due to discharge.

  As the force acting on the toner image, as shown in FIG. 10, the fluid force F acting by the air 53 compressed between the intermediate transfer belt 26 and the recording paper 35 and the reaction force facing the fluid force are as follows: The load f1 that suppresses the scattering of the toner image 51 by pressing and aggregating the toner image 51, which is an external pressure at the entrance of the press contact portion 52, and the toner image 51 is transferred from the intermediate transfer belt 26 to the recording paper 35 side. The electrostatic force f2 to be adsorbed and the toner image 51 can be divided into non-electrostatic force f3 such as van der Waals force that adheres to the intermediate transfer belt 26 and the recording paper 35, and the load f1, electrostatic force f2, and non-electrostatic force f3. Is larger than the fluid force F, that is, the toner image 51 is scattered by being configured to satisfy the relationship of f1 + f2 + f3> F. It can be suppressed.

  In the transfer apparatus 100 according to the first embodiment, as shown in FIG. 1, the position of the back support roll 32 is pressed in the same manner as described in FIG. It is set at a position displaced toward the outlet side of the section 52 and the secondary transfer roll 34 side, and is in a roll shape so as to come into contact with the secondary transfer roll 34 via the intermediate transfer belt 26 with a pressure higher than a predetermined pressure. The preloading roll 60 as the preloading member is arranged.

  As the secondary transfer roll 34, for example, an elastic body layer 342 made of a conductive elastic body such as a rubber material to which a conductive agent is added is provided on the outer periphery of a cored bar 341 made of a metal such as stainless steel. The one coated with is used. As the secondary transfer roll 34, a release layer or the like may be provided on the surface of the elastic layer 342. Similarly, as the back support roll 32, an elastic body layer 322 made of a conductive elastic body such as a rubber material to which a conductive agent is added is similarly determined on the outer periphery of a cored bar 321 made of a metal such as stainless steel. The one coated to a thickness is used.

  The back support roll 32 is rotatably arranged with its position fixed. On the other hand, the secondary transfer roll 34 is arranged so as to be movable in a direction in which the secondary transfer roll 34 is brought into contact with or separated from the back support roll 32 by a moving means (not shown) such as a drive motor or an eccentric cam. The force is configured to be adjustable.

  On the other hand, as shown in FIG. 1, the preload roll 60 is formed into a cylindrical or cylindrical roll-shaped member with a metal such as stainless steel, aluminum, or iron, and the secondary transfer roll 34 or the back support roll 32. The diameter (outer diameter) is set to about 1/2. In this embodiment, a cylindrical roll-shaped member made of stainless steel is used as the preload roll 60. The preload roll 60 is rotatably arranged with its position fixed. Note that the preload member 60 is not limited to a metal roll member, but may be a synthetic resin roll member or a roll member as long as a pressure higher than a predetermined pressure can be applied. A member having a shape other than the member may be used.

  The preload roll 60 is located upstream of the press contact position where the secondary transfer roll 34 and the back support roll 32 are in press contact along the moving direction of the intermediate transfer belt 26, and is a predetermined distance from the back support roll 32. At a distant position, it is disposed at a position where it is pressed against the surface of the secondary transfer roll 34 via the intermediate transfer belt 26. In addition, since the bias voltage may be applied to the preload roll 60 as described later, the interval is determined in consideration of the insulating property of the air layer between the back support roll 32 and the like.

  The position of the preload roll 60 determines the distance from the intermediate transfer belt 26 when the recording paper 35 enters the secondary transfer position N2, and the preload roll 60 is described above. As described above, the diameter is set to about ½ that is smaller than the diameter of the secondary transfer roll 34 and the back support roll 32, and the recording paper 35 is placed between the preload roll 60 and the secondary transfer roll 34. When entering, unlike the case shown in FIG. 8, the distance between the intermediate transfer belt 26 and the recording paper 35 at the entrance of the press contact portion 52 does not increase, and the intermediate transfer belt 26 and the recording paper 35 are not separated. Gap discharge is unlikely to occur, and the toner image 51 that is secondarily transferred from the intermediate transfer belt 26 to the recording paper 35 is configured not to cause new scattering due to the gap discharge.

  Further, the pressure at which the preload roll 60 is pressed against the secondary transfer roll via the intermediate transfer belt is f1 + f2 + f3> F so as to suppress the scattering of the toner image 51 as shown in FIG. It is set to satisfy the relationship. The pressure applied by the preload roll 60 directly determines the load f1, and in consideration of experiments and other forces acting on the transfer device 100, such as f2 and f3, as shown in FIG. It is set to a value higher than a predetermined pressure capable of suppressing image scattering. For example, the pressure by the preload roll 60 is set to a predetermined value of about 1/3 to 1/2 of the press contact force between the secondary transfer roll 34 and the back support roll 32.

  However, when the pressure of the preload roll 60 is too low, the effect of suppressing the scattering of the toner image is insufficient, which is not desirable. In view of the effect of suppressing the scattering of the toner image, it is desirable to set the pressure at which the preload roll 60 is pressed against the secondary transfer roll 34 via the intermediate transfer belt 26 to a high pressure. If it is too high, it may cause image defects such as a hollow character, so it is not desirable to set the pressure too high.

  Further, in this embodiment, as a modification thereof, as shown in FIG. 11, a voltage having a polarity (positive polarity) opposite to that of the toner image 51 on the intermediate transfer belt 26 is applied to the preload roll 60 by the second power source. You may comprise as follows.

  In this case, it is desirable that the toner image 51 can be reliably prevented from scattering due to gap discharge in the gap between the preload roll 60 and the intermediate transfer belt 26.

  In the above configuration, according to the image forming apparatus in which the toner charge amount detection device is applied to this embodiment, when transferring the toner image on the intermediate transfer body onto the recording medium as follows, the intermediate transfer body The toner image can be prevented from being scattered by the compressed air sandwiched between the recording medium and the recording medium.

  That is, in the image forming apparatus according to this embodiment, as shown in FIG. 2, image forming units 14Y, 14M, and 14C for each color of yellow (Y), magenta (M), cyan (C), and black (K) are used. , 14K, toner images of corresponding colors are formed on the respective photosensitive drums 16Y, 16M, 16C, 16K according to the color of the image to be formed, and these photosensitive drums 16Y, 16M, 16C, 16K are formed. The formed yellow (Y), magenta (M), cyan (C), and black (K) toner images are subjected to predetermined currents on the primary transfer rolls 27Y, 27M, 27C, and 27K at the primary transfer position N1. A positive transfer current whose current is controlled to a constant value is energized, and multiple primary transfers are performed on the intermediate transfer belt 26. Thereafter, the yellow (Y), magenta (M), cyan (C), and black (K) toner images that have been primary-transferred multiple times onto the intermediate transfer belt 26 are secondary-transferred at the secondary transfer position N2. A negative secondary transfer voltage controlled at a constant voltage to a predetermined voltage value is applied to the back support roll 32 facing the roll 34, and the secondary transfer voltage is collectively transferred onto the recording paper 35. The unfixed toner image is fixed by heat and pressure by the fixing device 38 and is discharged onto the discharge tray 39.

  At this time, in the image forming apparatus, as described above, in order to improve productivity determined by the number of recording sheets 35 on which an image is formed per unit time, as described above, for example, the process speed is 440 mm. / Sec and high speed. Therefore, in the image forming apparatus, as shown in FIGS. 3 and 4, when the toner images 51 of the respective colors primarily transferred onto the intermediate transfer belt 26 are secondarily transferred onto the recording paper 35 collectively, Ambient air 53 is sandwiched and compressed between the surface of the transfer belt 26 and the recording paper 35 and intersects with the moving direction of the unfixed toner image 51, particularly the intermediate transfer belt 26, which is secondarily transferred onto the recording paper 35. There is a risk that the toner image will scatter in the straight line image 51 or the like along the direction in which the toner image moves.

  By the way, in this embodiment, as shown in FIG. 1, at the secondary transfer position N <b> 2 where the secondary transfer roll 34 and the back support roll 32 are pressed through the intermediate transfer belt 26, the back support roll 32 is intermediate transfer. A preload roll 60 that is in pressure contact with the secondary transfer roll 34 via the intermediate transfer belt 26 is provided upstream of the pressure contact portion 52a that is in pressure contact with the belt 26, and the preload roll 60 exceeds a predetermined value. The secondary transfer roll 34 is configured to come into pressure contact with a set pressure.

  Therefore, in this embodiment, as shown in FIG. 12, when the toner image 51 transferred onto the intermediate transfer belt 26 comes into contact with the recording paper 35, the preload roll 60 that presses against the secondary transfer roll 34 is Since the diameter is set to be smaller than that of the back support roll 32, the volume of the air 53 sandwiched between the surface of the intermediate transfer belt 26 and the recording paper 35 is smaller than that in the conventional case shown in FIG. . Therefore, the fluid force F itself caused by the surrounding air 53 being sandwiched between the surface of the intermediate transfer belt 26 and the recording paper 35 and being compressed can be reduced as shown in FIG. .

  Moreover, in this embodiment, as shown in FIG. 12, immediately after the toner image 51 transferred onto the intermediate transfer belt 26 comes into contact with the recording paper 35, it is pressed by the preloading roll 60 that presses against the secondary transfer roll 34. In order to receive the pressure f1, as shown in FIG. 10, the surrounding air 53 is sandwiched between the surface of the intermediate transfer belt 26 and the recording paper 35 and compressed, and the downstream side along the moving direction of the intermediate transfer belt 26 is compressed. Even when the fluid force F is released, the pressure contact force f1 by the preloading roll 60 acts on the position immediately after the toner image 51 transferred onto the intermediate transfer belt 26 contacts the recording paper 35. .

  As a result, the reaction force obtained by adding the other forces f2 and f3 to the pressure contact force f1 by the preload roll 60 exceeds the fluid force F, and the unfixed toner image 51 that is secondarily transferred onto the recording paper 35, particularly the intermediate transfer belt. It is possible to prevent or suppress the scattering of the toner image in the straight line image 51 along the direction intersecting the moving direction of 26.

Experimental Example In order to confirm the effect of the transfer device 100 according to the present embodiment, the inventors made a prototype of an image forming apparatus using the transfer device 100 as shown in FIGS. 1 and 2 and shown in FIG. Thus, a linear image 51 having a thickness of 8 dots and CK 200% is formed on the intermediate transfer belt 26 along the axial direction of the photosensitive drum 16, that is, in the direction intersecting the moving direction of the intermediate transfer belt 26. Whether the toner image scatters depending on whether the pre-loading roll 60 is provided or not when the interval along the moving direction is changed to 1.5 mm, 2.5 mm, 3.5 mm, and 4.5 mm. An experiment was conducted to visually evaluate whether or not the sensory evaluation was divided into five stages from G0: not generated to large G5.

  13 and 14 show the results of the above experimental example.

  As can be seen from FIGS. 13 and 14, when the preload roll 60 is not provided, the toner image scattering is G2 and G4 when the interval between the linear images 51 is 2.5 mm and 3.5 mm. In contrast, when the preload roll 60 was provided, the toner image was not scattered in all cases where the interval between the linear images 51 was 1.5 mm to 4.5 mm.

Embodiment 2
FIG. 15 shows a second embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment. In the second embodiment, the thickness of the recording medium is shown in FIG. Accordingly, the pressure applied to the preload member is controlled.

  That is, in the second embodiment, as shown in FIG. 15, the thickness of the recording medium accommodated in the paper feed tray 40 is detected in the paper feed tray 40 disposed at the bottom of the image forming apparatus main body 1. Detecting means 70 is arranged. For example, the detection unit 70 is configured to identify the type, size, and thickness of the recording medium 35 accommodated in the paper feed tray 40, and an identification protrusion 71 provided on the paper feed tray 40, and the image forming apparatus. It comprises an identification sensor 72 for identifying the protrusion of the paper feed tray 40 provided on the main body 1 side.

  As shown in FIG. 16, the detecting means for detecting the thickness of the recording medium 35 is a user who inputs the type and size including the thickness of the recording medium 35 when the user performs copying or printing. The interface 73 is used, and the thickness of the recording medium is detected when the user inputs a type and size including the thickness of the recording medium to be copied or printed by the user interface 73.

  Then, as shown in FIG. 16, the CPU 200 as the control unit of the image forming apparatus moves the secondary transfer roll 34 on the back surface based on the thickness information of the recording medium 35 detected by the identification sensor 72 or the user interface 73. The press contact force that presses the support roll 32 and the preload roll 60 is controlled by the press contact means 74.

  When the CPU 200 determines that the thickness of the recording medium 35 is thinner than a predetermined threshold, that is, is thin paper, as shown in FIG. 16, the secondary transfer roll 34 is moved to the back support roll 32 and the preload roll 60. The pressure contact force f1 for pressure contact is set higher than a predetermined value, and the occurrence of toner image scattering is reliably suppressed. If the CPU 200 determines that the thickness of the recording medium 35 is thicker than a predetermined threshold, that is, cardboard, as shown in FIG. 17, the secondary transfer roll 34 has the back support roll 32 and the preload roll. The pressing force that presses against the toner 60 is set lower than a predetermined value to prevent the toner image from being scattered and to prevent excessive pressure from being applied, and the excessive cohesive force of the toner image 51 acts. This prevents or suppresses the occurrence of image quality defects.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

Embodiment 3
FIG. 2 also shows a third embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment. In the third embodiment, the toner charge amount is shown in FIG. Accordingly, the pressure applied to the preload member is controlled.

  That is, in the third embodiment, as shown in FIG. 2, the image processing device 4 counts the number of pixels of the image data of each color, and the number of pixels per page is less than the predetermined number of pixels. As in the case where the image is continuously formed on the recording sheet 35 over a predetermined number of sheets, information such as the number of pixels per page and the number of recording sheets 35 continuously formed is included. Based on this, it is determined whether the toner in the developing devices 18Y, 18M, 18C, and 18K is in a high charge state, a low charge state, or a normal state. Is configured to control.

  In this way, when the toner in the developing devices 18Y, 18M, 18C, and 18K is in a low-charged state, a pressing force with which the secondary transfer roll 34 presses against the back support roll 32 and the preload roll 60 is determined in advance. When the toner in the developing devices 18Y, 18M, 18C, and 18K is in a highly charged state, the secondary transfer roll 34 is set to be higher than the set value to suppress the occurrence of toner image scattering. The pressure contact force that presses against the back support roll 32 and the preload roll 60 is set to be lower than a predetermined value to prevent the toner image from being scattered and to prevent excessive pressure from being applied. The occurrence of image quality defects due to the action of the cohesive force of the image 51 is avoided or suppressed.

  Of course, the toner charge amount may be directly detected by other toner charge amount detection means.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

Embodiment 4
FIG. 17 shows a third embodiment of the present invention. The same parts as those of the first embodiment will be described with the same reference numerals. The pressure applied to the preload member is controlled.

  That is, in the fourth embodiment, as shown in FIG. 17, at least one of temperature and humidity is detected inside the image forming apparatus main body 1, and in this embodiment, the environmental sensor 80 detects both environmental conditions of temperature and humidity. The pressure applied to the preload roll 60 is controlled in accordance with the detection result of the environmental sensor 80.

  That is, in the fourth embodiment, as shown in FIG. 17, since the detection result of the environment sensor 80 is likely to cause scattering of the toner image in a high temperature and high humidity environment, the secondary transfer roll 34 and the back support roll 32 and The pressure contact force that presses against the preload roll 60 is set to be higher than a predetermined value to suppress the occurrence of toner image scattering, and the detection result of the environment sensor 80 indicates that the toner image is scattered under a low temperature and low humidity environment. Therefore, the pressing force with which the secondary transfer roll 34 presses against the back support roll 32 and the preload roll 60 is set lower than a predetermined value to suppress the occurrence of toner image scattering. Further, excessive pressure application is prevented, and occurrence of image quality defects due to excessive cohesion of the toner image 51 is avoided or suppressed.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

  26: intermediate transfer belt, 32: back support roll, 34: secondary transfer roll, 52a: pressure contact portion, 60: preload roll.

According to a fifth aspect of the present invention, in the transfer device according to any one of the first to fourth aspects, the pressure applied to the preload member is controlled according to environmental conditions.
The transfer device according to any one of claims 1 to 5, wherein the transfer member controls a pressing force with which the transfer member presses against the opposing member and the preload member by a pressing unit. It is.

The invention described in claim 7 includes a plurality of image holding bodies that hold toner images of different colors,
A plurality of primary transfer means for transferring each of the toner images held on the plurality of image holders onto the intermediate transfer member in a multiplexed manner;
Secondary transfer means for performing secondary transfer of the toner images, which have been primary-transferred multiple times onto the intermediate transfer body, onto a recording medium in a batch,
An image forming apparatus using the transfer device according to claim 1 as the secondary transfer unit.

According to the fifth aspect of the present invention, it is possible to suppress the occurrence of image quality defects due to excessive cohesive force acting on the toner image on the intermediate transfer member.
According to the sixth aspect of the present invention, it is possible to control the pressures of both the opposing member and the preload member by a single pressure contact means.

Furthermore, according to the seventh aspect of the invention, when the toner images of the respective colors on the intermediate transfer member are transferred onto the recording medium, the compressed air is sandwiched between the intermediate transfer member and the recording medium. The occurrence of toner image scattering can be suppressed.

Claims (6)

A transfer member for transferring the toner image held on the intermediate transfer member that circulates and moves while holding the toner image onto the recording medium;
An opposing member arranged to contact the transfer member with pressure through the intermediate transfer member;
The toner image held on the intermediate transfer body starts to contact the recording medium on the upstream side in the moving direction of the intermediate transfer body from the contact portion where the opposing member contacts the transfer member with pressure. A preload member disposed so as to contact the transfer member with pressure through the intermediate transfer member at a position immediately after
With
A bias voltage having the same polarity as the charging polarity of the toner forming the toner image is applied to the opposing member, and a bias voltage having a polarity opposite to the charging polarity of the toner forming the toner image is applied to the preloading member. A transfer device characterized by that.   2. The transfer according to claim 1, wherein each of the transfer member and the preload member is a roll-shaped member, and an outer diameter of the preload member is set smaller than an outer diameter of the transfer member. apparatus.   The transfer apparatus according to claim 1, wherein a pressure applied to the preload member is controlled in accordance with a thickness of the recording medium.   4. The transfer device according to claim 1, wherein a pressure applied to the preload member is controlled in accordance with a charge amount of the toner.   The transfer apparatus according to claim 1, wherein a pressure applied to the preload member is controlled in accordance with an environmental condition. A plurality of image carriers that hold toner images of different colors;
A plurality of primary transfer means for transferring each of the toner images held on the plurality of image holders onto the intermediate transfer member in a multiplexed manner;
Secondary transfer means for performing secondary transfer of the toner images, which have been primary-transferred multiple times onto the intermediate transfer body, onto a recording medium in a batch,
An image forming apparatus using the transfer device according to claim 1 as the secondary transfer unit.

Images