JP2005250045A - Transfer transport device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer transport device which is of a type using a transfer transport belt and is easily miniaturized without causing lowering in transfer performance. <P>SOLUTION: In the transfer transport device, a belt constituted of double-layer structure having a high resistance layer 3a on its outer peripheral surface side and a conductive under layer 3b on its inner peripheral surface side is used as the transfer transport belt 3, and a bias applying member 5A for applying transfer bias is installed as an electric field generation means 5 so as to abut on a part downstream, in a belt rotating direction B, of a transfer part TN abutting on an image carrier 2 out of the outer peripheral surface of the belt 3. A conductive roll capable of rotating while abutting on the belt 3 is used as the bias applying member 5A, and a cleaning member 6 cleaning the surface of the conductive roll (5A) while abutting on the surface thereof is installed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a transfer conveyance applicable to an image forming apparatus such as a printer, a copying machine, a facsimile machine, etc., which combines an operation of transferring a toner image onto a recording sheet as a step of image formation, or a composite machine combining those functions. More particularly, the present invention relates to a transfer conveyance device of a type using a transfer conveyance belt that conveys a recording sheet so as to pass through the transfer position.

  In an image forming apparatus such as a printer or a copying machine that employs an electrophotographic system, an electrostatic recording system, or the like, generally, a toner image (as a developer) formed on an image carrier such as a photoconductor that rotates based on image information. The image is formed by transferring a toner image) directly to a recording sheet or via an image carrier of an intermediate transfer member and fixing. Further, in such an image forming apparatus, as an apparatus for transferring the toner image to the recording sheet, an endless shape that conveys the recording sheet while holding the recording sheet so as to pass through the transfer position of the toner image on the image carrier. A device using a transfer conveyance device of a type using a transfer conveyance belt is known (Patent Document 1).

  As shown in FIG. 6, the transfer conveying apparatus forms an end portion TN in contact with a rotating image carrier 200 and conveys a recording sheet (transfer material) P to the transfer portion TN. The belt 210 is used, and the toner image T on the image carrier 200 is moved to the recording sheet P on the opposite side (inner peripheral surface) to the surface (outer peripheral surface) that contacts the recording sheet P of the transfer conveyance belt 210. A conductive roll 230 is provided as an electric field generating means for generating an electric field. Then, the recording sheet P is transported to the transfer portion TN by the transfer transport belt 210, and a transfer bias is applied from the conductive roll 230 to generate a transfer electric field, whereby the toner image T on the image carrier 200 is formed. The recording sheet P is electrostatically transferred to the recording sheet P. In the figure, reference numerals 221 and 222 denote support rolls that rotatably support the transfer conveyance belt 210, and reference numeral 250 denotes a cleaning blade that contacts the outer peripheral surface of the transfer conveyance belt 210 and cleans the belt surface.

The transfer in the transport device, the contact with a volume resistivity on the side is 10 ¹⁴ [Omega] cm or more insulating layers on an image bearing member as a transfer conveyor belt, the opposite side to the volume resistance of 10 ¹⁴ [Omega] cm as shown in Patent Document 1 above A belt formed with the following high resistance layer is used. This makes it possible to control the surface potential of the belt so as to have a desired potential gradient. Therefore, it is less dependent on the environment, and is stable and faithful transfer with high transfer rate without causing toner skipping or void. Is possible.

JP-A-2-110586 (FIGS. 1 and 4 etc.)

  However, in the case of the conventional transfer conveyance device, in order to reduce the size of the entire device, the circumferential length of the transfer conveyance belt stretched rotatably by a plurality of support rolls, the conveyance conveyance distance of the recording sheet, and the like Although it is necessary to shorten the length, it is difficult to secure a space for installing the conductive roll 230 or the like as the electric field generating means installed on the inner peripheral surface side of the transfer conveyance belt. It is a factor to prevent.

  In addition, in a transfer conveyance device of a type using a transfer conveyance belt, the transfer conveyance belt is prevented from meandering and running away (belt walk) due to factors such as manufacturing tolerances and attachment tolerances of its support rolls. Further, it is possible to adopt a measure for suppressing the occurrence of the belt walk by using a material having an elastic base layer made of a rubber material as the base material of the belt and absorbing factors such as each tolerance. However, if the transfer conveyance belt having the base layer made of such a rubber material is used by adding conductivity by mixing conductive materials such as carbon due to the necessity of adjusting the resistance value, the resistance In-plane unevenness (the resistance of each part of the belt surface varies). As a result, there is a problem in that unevenness of image density, which is affected by the resistance unevenness, occurs when a transfer is performed by applying a bias while a conductive roll is brought into contact with the underlying layer. In particular, when a halftone image is transferred, uneven density due to uneven resistance tends to occur.

  Further, in a transfer conveyance device of a type using a transfer conveyance belt, generally, the fog toner on the image carrier adheres to the surface (outer peripheral surface) of the transfer conveyance belt, and the recording is conveyed by the transfer conveyance belt. Since the back surface of the sheet may be soiled, it is necessary to install an elastic cleaning blade 250 that is in contact with the transfer conveyance belt 210 as illustrated in FIG. However, when this cleaning blade 250 is installed, there is a problem in that edge wear or chipping occurs on the blade tip side due to sliding friction between the blade tip portion and the surface of the transfer conveyance belt, resulting in a reduction in cleaning ability. . Also, the surface layer on the belt side is worn and damaged due to the sliding contact of the blade, and the toner adheres to the belt surface and stains the back surface of the recording sheet, or the resistance value of the transfer conveyance belt changes. As a result, there are problems such as uneven concentration and pinhole leakage due to dielectric breakdown. In addition, since the belt has an elastic base layer and the blade is an elastic body, the hardness of the elastic base layer and the elastic body changes depending on the environmental temperature, and the cleaning performance also changes due to this influence. There is a bug.

  The present invention has been made in view of such circumstances, and as a transfer conveyance device of a type using a transfer conveyance belt, a transfer that can easily reduce the size of the apparatus without deteriorating transfer performance. A conveying device is provided. The present invention also provides a transfer / conveying apparatus that can be downsized and can be cleaned well over a long period of time without damaging or damaging the surface of the transfer / conveying belt.

  As illustrated in FIG. 1, the transfer conveying apparatus of the present invention capable of solving the above problems forms a transfer portion TN by contacting a rotating image carrier 2 that carries and rotates a toner image T, and the toner image T An endless transfer / conveying belt 3 that holds the recording sheet P to which the image is transferred and conveys the recording sheet P through the transfer portion TN, and a plurality of support rolls 4A that rotatably support the transfer / conveying belt 3 by stretching it. , 4B and a transfer conveying device 1 including an electric field generating means 5 for generating an electric field in a direction in which the toner image T on the image carrier 2 moves to the recording sheet P side. A belt having a multilayer structure having a high resistance layer 3a on the belt outer peripheral surface side and a conductive base layer 3b on the belt inner peripheral surface side is used, and a transfer bias is used as the electric field generating means 5. Applied The bias applying member 5A is disposed so as to abut on a portion of the outer peripheral surface of the transfer conveyance belt 3 that is downstream of the transfer portion TN in the belt rotation direction B. is there. A one-dot chain line with an arrow in the figure indicates a basic conveyance path of the recording sheet P.

  Here, the image carrier 2 may be any material as long as it can carry the toner image T and rotate it to the transfer position TN. As such an image carrier 2, for example, a photosensitive member or the like on which the toner image T is formed itself, or the toner image T is formed of another component (photosensitive member or the like). For example, an intermediate transfer member that temporarily receives and conveys a toner image formed by the above components is used. Further, the image carrier 2 may be a drum shape in addition to the belt shape. The means for forming the toner image T carried on the image carrier 2 is not particularly limited, and a known image forming means using, for example, an electrophotographic method or an electrostatic recording method can be applied. The recording sheet P may be any sheet as long as it can transfer the toner image using the transfer / conveyance device 1, and the material, thickness, form, size, and the like are not particularly limited.

  The transfer / conveying belt 3 can hold at least the entire width of the recording sheet P in the feeding direction, and has a multilayer structure including at least the high resistance layer 3a and the underlayer 3b in the above-described vertical relationship. In particular, the transfer conveyance belt 3 conveys the recording sheet P while being held in an electrostatically attracted state on the outer peripheral surface of the belt by the transfer bias applied from the bias applying member 5A.

The high resistance layer 3a constituting the transfer / conveyance belt 3 preferably has a volume resistivity of, for example, 10 ¹⁰ Ωcm or more, and more preferably in the range of 10 ¹⁰ to 10 ¹² Ωcm. The volume resistivity can be adjusted by adjusting the blending amount of a conductive material such as carbon black in the material for forming the high resistance layer 3a described later. The thickness of the high resistance layer 3a is preferably in the range of, for example, about 4 to 20 μm from the viewpoint of preventing wear during use and making the layer suitable for coating and forming. Such a high resistance layer 3a is formed by a coating means using a material such as urethane. The high resistance layer 3a may be formed as a surface layer that is in direct contact with the image carrier 2 after being formed as a layer having good releasability with respect to the toner, but if necessary, another layer may be formed thereon. It may be formed (however, it is preferable that the other layer satisfies both the resistance value and the thickness satisfying the corresponding conditions of the high resistance layer).

The underlying layer 3b constituting the transfer / conveying belt 3 serves as a base material for the transfer / conveying belt, and for example, one having a volume specific resistance of less than 10 ¹⁰ Ωcm is preferable, more preferably 10 ⁶ to. It is in the range of 10 ⁸ Ωcm. The base layer 3b can be made of, for example, a so-called electronic conductive type conductive rubber in which a conductive material such as carbon is appropriately blended with a rubber material. This electron conduction type conductive rubber has a drawback that in-plane unevenness of resistance value is likely to occur as compared with a so-called ion conductive conductive rubber appropriately blended with an ionic conductive material such as a quaternary ammonium salt. On the other hand, there is an advantage that there is little resistance change due to a difference in humidity environment, the resistance can be adjusted in a wide range, the adjustment is easy, and the conductive ions are not easily bleed. Moreover, it is preferable that the thickness of the foundation | substrate layer 3b is the range of about 500-1000 micrometers, for example.

  Such an underlayer 3b can be produced by, for example, generally adopting an extrusion molding method or a press molding method. However, when the extrusion molding method is compared with the press molding method, the press molding method has a weak joint strength on the die mating surface, and the resulting belt substrate may break during stretching. Is preferred.

  A plurality of support rolls 4A and 4B are used, but two are preferable from the viewpoint of reducing the size of the transfer / conveyance apparatus 1. Moreover, it is preferable that the support roll 4 has a small diameter as much as possible from the viewpoint of downsizing the apparatus. At least one of the plurality of support rolls 4 is configured as a drive roll for rotating the transfer conveyance belt 3. Further, at least one of the support rolls 4 is installed at a position shifted from the transfer position TN of the image carrier 2 to the upstream side in the feeding direction of the recording sheet P (for example, the position where the support roll 4A is located), and the transfer position It is preferable that the recording sheet P be transported while being held by the transfer transport belt 3 on the near side of TN. The support roll 4 does not normally need to be installed at a position facing the image carrier 2, but is arranged at a position where it passes through the transfer position TN and is separated from the transfer conveyance belt 3 and discharged as necessary. Such a support roll (for example, the support roll 4B) may be installed at a position near the downstream side in the belt rotation direction with respect to the position facing the image carrier 2.

  The bias applying member 5A in the electric field generating means 5 may be any member that can contact the outer peripheral surface of the transfer / conveying belt 3 and apply the transfer bias, and the form is preferably a roll form. The position where the bias applying member 5A is installed is “a part located downstream of the transfer part TN in the belt rotation direction B” when the part in the circumferential direction of the transfer conveyance belt 3 is divided into two equal parts starting from the transfer position TN. This is a region located on the downstream side in the belt rotation direction B from the transfer position TN. Further, the bias applying member 5A installed in such a portion is a peripheral length L1 of the belt from the contact position Q with the transfer conveyance belt 3 to the transfer portion TN along the upstream side in the belt rotation direction B. Is set to have a relationship (L1 ≦ L2) that is equal to or shorter than the circumferential length L2 of the belt from the contact position Q to the transfer portion TN along the downstream side in the belt rotation direction B. It is also the case.

  The portion of the transfer / conveyance belt 3 that corresponds to the above-mentioned two equal portions or the portion where the contact position Q that satisfies the relationship of L1 ≦ L2 is present holds the recording sheet P in the belt 3. An area excluding the passing area (recording sheet non-passing area) is preferable. In the case where the bias applying member 5A is installed in a portion that becomes the sheet non-passing region, the bias applying member 5A does not exist at all in the conveyance path of the recording sheet P (the path indicated by the one-dot chain line in the drawing). It is preferable to install in a state. The application member 5A when installed in such a state may be at a position where at least contact with the recording sheet P or electrostatic interference with the recording sheet does not occur. Further, the application member 5 </ b> A installed in this state is preferably installed in a state separated from the conveyance path of the recording sheet P by a certain distance H.

  In the case where the bias applying member 5A is installed at a portion of the transfer conveyance belt 3 that becomes a sheet non-passing region, it is preferable to install an electrically insulating cover member in a space between the application member 5A and the recording sheet conveyance path. . In addition, the cover member may be provided with an end portion on the side facing the transfer / conveying belt 3 in a proximity state in which a gap about the thickness of the recording sheet is formed with respect to the outer peripheral surface of the belt.

  The transfer bias applied from the bias applying member 5A is not limited as long as it can generate an electric field in the direction in which the toner image T on the image carrier 2 moves to the recording sheet P side. A DC voltage having a polarity opposite to the charging polarity of the toner constituting the toner may be used. Reference numeral 5B in FIG. 1 is a power supply for bias application. Further, the transfer bias may be set to a voltage value that does not cause unnecessary discharge at the transfer position TN (a minute gap between the image carrier 2 and the transfer conveyance belt 3 before and after the transfer position TN).

  The contact position Q with the transfer conveyance belt 3 on which the bias applying member 5A is installed may be set based on the voltage value of the transfer bias. That is, the distance (L1) from the transfer position TN to the contact position Q is the voltage value when the current value of the transfer bias necessary for transferring the toner image T from the image carrier 2 to the recording sheet P is as described above. The selection can be made by determining whether or not the voltage value Vp (for example, 6 kV) at which the unnecessary discharge does not occur at the transfer position TN can be made.

  In the transfer / conveying apparatus 1 as described above, when a conductive roll capable of rotating in contact with the transfer / conveying belt 3 is used as the bias applying member 5A, the surface of the conductive roll (5A) is contacted. It is good to install the cleaning member 6 which contacts and cleans the roll surface.

  In this case, it is necessary to apply a predetermined bias to the conductive roll 5A. A transfer bias is applied during the transfer operation, but a bias having a condition different from the transfer bias may be applied at a time when the transfer operation is not performed. The bias under the different conditions can be determined based on the charging polarity of the toner or the like adhering to the transfer conveyance belt 3. As the cleaning member 6, for example, a cleaning blade can be used, but a member other than the blade (for example, a brush roll) may be used.

  According to the transfer / conveying apparatus of the present invention, the bias applying member 5A in the electric field generating means 5 is installed so as to contact the outer peripheral surface of the transfer / conveying belt 3, so that the transfer / conveying belt can be used when the apparatus is downsized. 3, it is not necessary to secure an installation space for installing the electric field generating means, and it is possible to arbitrarily shorten the circumferential length of the transfer conveyance belt, the conveyance conveyance distance of the recording sheet, and the like. The apparatus can be easily downsized.

  At this time, the transfer bias applied by the bias applying member 5A is transferred from the contact position Q (corresponding to the application start point) between the applying member 5A and the transfer conveying belt 3 through the belt 3 as the transfer current. A current path that flows to reach is formed. This current path includes a path corresponding to the belt length L1 starting from the contact position Q and a path corresponding to the belt length K2. In the present invention, since the bias applying member 5A is installed in a portion of the outer peripheral surface of the transfer conveyance belt 3 as described above, which is downstream of the transfer portion TN in the belt rotation direction B, it is longer than the belt length K1. The transfer current flowing on the path side corresponding to the belt length K2 having a long distance to the transfer portion TN drops, and the transfer electric field formed on the upstream side in the belt rotation direction of the transfer portion TN is lowered. Therefore, there is no problem such as toner scattering (blurring), and the transfer performance is not deteriorated.

  Furthermore, according to the transfer / conveying apparatus of the present invention, the cleaning member 6 that contacts the bias applying member 5A made of a conductive roll is provided, so that the toner or the like adhering to the transfer / conveying belt 3 is biased to the bias applying member 5A. After the electrostatic transfer adheres to the surface, the cleaning member 6 scrapes the surface, so that the surface of the transfer / conveying belt can be cleaned well without being worn or damaged. In particular, since there is no possibility that the surface of the belt is worn or damaged, the back surface of the recording sheet is not soiled due to toner adhesion to the belt surface, and the transfer performance is maintained for a long time without fluctuation.

  FIG. 2 is a schematic explanatory view showing a main part of the image forming apparatus to which the transfer conveying apparatus according to the first embodiment of the present invention is applied.

  The image forming apparatus 100 includes a photosensitive drum 120 on which a toner image T is formed, a belt-type transfer conveyance device 10 that transfers the toner image T on the photosensitive drum 120 to a recording sheet P, and a transfer to the recording sheet P. And a fixing device 130 for fixing the toner image T. A one-dot chain line with an arrow in the figure indicates a basic conveyance path of the recording sheet P.

  The photosensitive drum 120 is formed by forming a photosensitive layer made of an organic photosensitive material (OPC) on the outer peripheral surface of the drum support, and is supported so as to rotate at a constant speed in the direction of arrow A. A desired toner image is formed on the photosensitive drum 120 by an image forming apparatus using an electrophotographic method (not shown) installed around the drum 120.

  That is, the photosensitive drum 120 is charged in the direction of the arrow A by the charging device, and then the photosensitive layer 120 is exposed on the photosensitive layer in accordance with the image information by the exposure device. It is formed. Next, the electrostatic latent image is developed in the developing device to become a toner image T. As a developing method at this time, a reversal developing method in which a negatively charged toner is attached to the exposed portion of the photosensitive drum 120 is applied. The toner image T is carried on the photosensitive drum 120 and conveyed to the transfer position. Note that the outer peripheral surface of the photosensitive drum 120 after the transfer is cleaned by a cleaning device (not shown).

  The transfer conveyance device 10 includes a transfer conveyance belt 30 between a first support roll 41 and a second support roll 42 installed in parallel at a predetermined interval from the first support roll 41 to the fixing device 130 side. And a part of the outer peripheral surface area (sheet holding / conveying area: sheet passing area) E on the upper side of the tensioned transfer / conveying belt 30 is a transfer position of the photosensitive drum 120 (the lowermost part in the illustrated example). ). In this case, a portion where the transfer conveyance belt 30 is in contact with the photosensitive drum 120 is a transfer portion TN. In addition, the transfer conveyance belt 30 is configured to rotate at the same peripheral speed as that of the photosensitive drum 120 in the arrow B direction while being supported by the first support roll 41 and the second support roll 42.

  Further, the transfer conveyance device 10 is provided with a bias roll 51 that rotates in contact with the outer peripheral surface portion of the transfer conveyance belt 30 supported by the second support roll 42 as the electric field generating means 50. The bias roll 51 is electrically connected to a DC bias power supply device 55 as electric field generating means 50 for supplying a transfer bias to the roll. In addition, the cleaning blade 60 is installed in contact with the peripheral surface of the bias roll 30.

  As shown in FIG. 3, the transfer / conveying belt 30 has a two-layer structure of a base layer 31 positioned on the inner peripheral surface side and a surface layer 32 formed on the outer peripheral surface side.

Among these, the base layer 31 is a cylindrical member formed by extruding a conductive rubber material in which a conductive material is dispersed in a rubber material and a volume specific resistance value is adjusted. Specifically, a conductive rubber material in which conductive carbon black is dispersed in chloroprene rubber is extruded in a cylindrical shape from a cylindrical nozzle of an extrusion molding machine, and the extruded product is vulcanized in a state where it is once attached to a mandrel. The surface is polished to adjust the wall thickness. In the first embodiment, a cylindrical base layer 31 having a thickness of 700 μm and an inner diameter of 40 mm was produced. The volume resistivity of the underlayer 31 was about 10 ⁸ Ωcm, and the Mooney clay (ML1 + 4, 100 ° C.) was “42”. On the other hand, the surface layer 32 was formed by applying a urethane / PTFE dispersion paint (manufactured by Nippon Addison) on the outer peripheral surface of the base layer 31 to a thickness of about 7 μm by a spray coating method. The surface layer 32 had a volume resistance of about 10 ¹⁰ cm and a high resistance.

  Incidentally, when the distribution state of each resistance of the transfer / conveying belt 30 produced in the first embodiment is measured by a resistance measuring device, the volume resistance indicating the resistance in the thickness direction is caused by the extrusion molding of the underlayer 31. On the other hand, it is confirmed that the surface resistance on the side of the surface layer 32 has no resistance unevenness such as volume resistance (the resistance value distribution range is narrow). I was able to. In particular, when the resistance distribution state in a minute range was examined, the resistance unevenness existing along the material flow (extrusion direction) at the time of the extrusion molding in the underlayer of the belt (formation material thereof) It was confirmed that the film was made uniform by formation.

  A metal roll having a roll diameter of about 12 mm is used as the first support roll 41, and a metal roll having a roll diameter of about 12 mm is used as the second support roll 42. In the first embodiment, the first support roll 41 is configured as a driven roll, the second support roll 42 is configured as a drive roll, and both the support rolls 41 and 42 are placed in an electrically floating state. The transfer conveyance belt 30 was stretched between the first support roll 41 and the second support roll 42 so that the distance between the roll axes was about 46 mm (elongation rate = about 3%). Further, the transfer conveyance belt 30 stretched in this way has a central portion of the upper outer peripheral surface (sheet passage region) E supported by the two support rolls 41 and 42 as the transfer position of the photosensitive drum 120. It is installed so as to contact the lowermost surface. The outer diameter of the photosensitive drum 120 with which the transfer conveyance belt 30 abuts is about 84 mm.

  As the bias roll 51, a conductive roll made of stainless metal and having an outer diameter of 12 mm is used. The bias roll 51 has a roll uppermost portion 50 a that is more than the axis of the support roll 42 in the outer peripheral surface area of the transfer conveyance belt 30 that is supported around the second support roll 42 that is also used as a drive roll. It is installed at the site located on the lower side. This installation position also corresponds to a portion of the outer peripheral surface of the transfer conveyance belt 30 that becomes a sheet non-passing region on the downstream side in the belt rotation direction B from the transfer portion TN. In this embodiment, the position Q of the bias roll 51 in contact with the belt 30 is set so that the belt circumferential length L1 from the transfer portion TN to the contact position Q is about 23 mm as shown in FIG. In this case, the entire circumference of the transfer conveyance belt 30 in the stretched state is 129.7 mm). The bias roll 51 is pressed against the outer peripheral surface of the transfer conveyance belt 30 with a predetermined pressure, and the contact position Q with the belt 30 is transmitted by transmitting the rotational force of the second support roll 42 with a gear or the like. Are driven to rotate in the same direction.

  As the bias power supply device 55, a DC power source controlled by constant current is used. The transfer bias supplied from the power supply device 55 to the bias roll 51 has a voltage value of 4 kV having a positive polarity when it is appropriate that the transfer current flowing into the photosensitive drum 120 at the transfer portion TN is 40 μA. Set. Further, the transfer bias was set to continue to be applied at least during the image forming operation.

  As the cleaning blade 60, a plate-like elastic blade made of urethane rubber and having a thickness of about 2 mm is used. The blade 60 was installed so that its tip end was pressed with a predetermined pressure over the axial direction of the lowermost surface portion of the bias roll 51. A storage box 65 for temporarily storing toner scraped off by the blade 60 is disposed below the blade 60.

  Further, in this transfer / conveyance apparatus 10, as shown in FIG. 2, an electrically insulating cover 70 made of ABS is installed in a space between the bias roll 51 and the bias roll 51 (a chain line with an arrow in the figure). doing. The insulative cover 70 has a surface portion that covers the upper side of the bias roll 51, and in particular, the end portion 70 a facing the transfer conveyance belt 30 is spaced from the outer circumferential surface of the belt ( It is installed in a close proximity so that about 100 μm) is formed.

  In such a transfer / conveyance apparatus 10, the toner image is transferred as follows.

  First, as described above, when the transfer timing of the toner image T formed on the photosensitive drum 120 is reached, the recording sheet P is moved from the storage unit (not shown) to the introduction side of the sheet holding and conveying area E of the transfer and conveying belt 30 in accordance with the timing. It is transported and supplied. The recording sheet P is electrostatically adsorbed on the outer peripheral surface on the upper side supported by the first support roll 41 of the transfer conveyance belt 30 that rotates in the direction of arrow B while a transfer bias is applied from the bias roll 51. After the start, it is conveyed toward the transfer portion TN as the belt rotates.

  At the transfer portion TN, a negatively charged toner image on the photosensitive drum 120 between the photosensitive drum 120 and the photosensitive drum 120 is transferred to the recording sheet P side by the transfer bias applied from the outer peripheral surface of the transfer conveyance belt 30 by the bias roll 51. A transfer electric field is formed in the direction of movement. As a result, the toner image T on the photosensitive drum 120 is electrostatically transferred to the recording sheet P side by the transfer electric field with respect to the recording sheet P passing between the photosensitive drum 120 and the transfer conveyance belt 30 at the transfer portion TN. Is done.

  The recording sheet P onto which the toner image T has been transferred in this way is conveyed in the rotational direction B while being sucked and held by the transfer conveyance belt 30 even after passing through the transfer portion TN, and the peripheral surface of the second support roll 42 When the transfer conveyance belt 30 moves so as to bend along the curvature (the end portion of the sheet holding and conveyance area E), it is separated from the belt surface and discharged and conveyed toward the fixing device 130 as a subsequent process. . The recording sheet P after the transfer is sent to the fixing device 130 and passes through and is subjected to a fixing process in which heat and pressure are applied, so that a desired image composed of a fixing toner image is formed on the recording sheet P. .

  The transfer / conveying apparatus 10 has the bias roll 51 installed on the outer peripheral surface side of the transfer / conveying belt 30, and as shown in FIG. 4, from the transfer portion TN to the end of the second support roll 42 (in the drawing). The dimension L3 from the rightmost end of the sheet to about 31 mm and the dimension L4 from the transfer site TN to the end of the bias roll 51 can be set to about 23 mm.

  This is smaller than the conventional transfer conveyance device (FIG. 6) in which the conductive roll of the electric field generating means is installed on the inner peripheral surface side of the transfer conveyance belt described above. That is, in the conventional transfer device, the transfer conveyance belt (210) has an inner diameter of 84 mm, and is stretched and supported by the two support rolls (221, 222) at the same expansion rate as in the first embodiment. In the case where the recording sheet introduction side from the transfer portion (TN) is installed under the same conditions as those of the apparatus 10 of the first embodiment, the end of the support roll (222) on the downstream side in the belt rotation direction from the transfer portion TN. Compared to the dimension L10 (FIG. 6) up to about 110 mm, the size can be reduced by about 80 mm (= L10−L3).

  Further, in this transfer / conveying device 10, the bias roller 51 is positioned on the outer peripheral surface of the transfer / conveying belt 30 away from the transfer portion TN by the belt length L1 (= 23 mm) downstream in the belt rotation direction B (contact position Q). As shown in FIG. 5, the transfer bias applied from the bias roll 51 is conductive from the surface layer 32 which is a high resistance layer of the transfer conveyance belt 30 at the contact position Q as a transfer current. After being transmitted to the base layer 31, the base layer 32 is transmitted along a route S1 in which the base layer 32 flows in the direction opposite to the belt rotation direction B on the side close to the transfer portion TN and reaches the transfer portion TN. At this time, the transfer current passes through the surface layer 32 having a higher resistance than that of the base layer 31 at the contact position Q and the transfer portion TN twice. However, since the surface layer 32 has less uneven resistance, the base layer The resistance unevenness existing in 31 is masked by the resistance of the surface layer 32.

  As a result, even if there is uneven resistance in the surface of the underlying layer 31 produced by the extrusion molding method of the transfer conveyance belt 30, the toner image transferred to the recording sheet P at the transfer portion TN as described above. In the image, density unevenness due to the resistance unevenness hardly occurs. Actually, when a halftone image (an image having a Cin of 60%) was formed, it was confirmed that a halftone image having a substantially uniform image density was obtained.

  In addition, in this transfer / conveying apparatus 10, the transfer / conveying belt 30 is installed in such a form that its sheet holding / conveying area E is also located on the front side of the transfer part TN, and the recording sheet P is sucked and held on the transfer / conveying belt 30. In this state, the transfer is introduced to the transfer site TN, and the installation position (contact position Q) of the bias roll 51 is a limit voltage value at which the transfer bias voltage value causes discharge at the transfer site TN (in this embodiment, 6 kV). ), The discharge blur (toner scattering phenomenon) hardly occurs at the position immediately before reaching the transfer portion TN. In fact, when line images were formed, no occurrence of discharge blur was observed.

  Further, in this transfer / conveying apparatus 10, unnecessary toner or the like adhering to the transfer / conveying belt 30 during the transfer is electrostatically collected by the bias roll 51, and then scraped off by the cleaning flade 60 in contact with the peripheral surface of the roll. Finally, it falls into the storage box 65 and is collected. As described above, the bias roll 51 also functions as a cleaning device for the transfer / conveyance belt 30. As a result, it is not necessary to separately install a belt cleaning device, and the contact with the transfer / conveyance belt 30 is rotated. Therefore, there is no problem that the belt surface is rubbed and worn or damaged. In addition, when the toner or the like adhering to the transfer / conveying belt 30 cannot be electrostatically attracted due to the polarity of the transfer bias, the transfer / conveying device 10 has a polarity opposite to that of the transfer bias at a time other than the transfer step. The bias may be applied to the bias roll 51 to separately perform a belt cleaning operation.

  Further, in this transfer / conveyance apparatus 10, since the insulating cover 70 is provided so as to cover the bias roll 51, it is possible to prevent erroneous contact with the bias roll 51. Further, since the end portion 70a of the cover 70 on the side facing the transfer belt 30 is disposed with a slight gap from the outer peripheral surface of the belt, for example, a recording sheet (such as thin paper) having a low waist is transferred after transfer. Even if it proceeds while adhering to the belt surface without being peeled off from the transfer / conveying belt 30, it is peeled off by being caught at the front end portion 70 a of the cover.

  Further, since the transfer / conveyance device 10 is downsized as described above, the transfer holding device 10 and the end portion of the sheet holding / conveying area E of the transfer / conveyance belt 30 (the portion that starts to be supported by the second support roll 42) are correspondingly reduced. The sheet conveyance distance W (FIG. 2) with the fixing device 130 (the sheet holding portion thereof) can be set longer than in the conventional device. Thus, when the sheet conveying speed of the fixing device 130 is slower than the speed of the transfer conveying belt 30, the recording sheet P having a long conveying direction length such as A3 plate is held on both the transfer conveying belt 30 and the fixing device 130. Even if the sheet is curled, the amount of curving is reduced by the curl as the sheet conveying distance W is increased. Therefore, the recording sheet P contacts the parts existing on the conveying path and the unfixed toner There is no risk of the image being disturbed.

  For comparison, instead of installing the bias roll 51 in the transfer conveyance apparatus 10 according to the first embodiment, a transfer bias is supplied from the bias power supply device 55 to the second support roll 42 as shown in FIG. A transfer conveyance device (Comparative Example 1) having the same configuration except that the above was prepared, and image formation similar to that in Embodiment 1 was performed.

  As a result, in the apparatus of Comparative Example 1, there was no blurring of the line image, but periodic density unevenness corresponding to the resistance unevenness in the underlying layer 31 of the transfer conveyance belt 30 occurred in the entire halftone image. Was confirmed. Further, as shown in FIG. 7, as a cleaning device for the transfer conveyance belt 30, a conductive roll 61 is installed on the outer peripheral surface portion of the transfer conveyance belt 30 supported by the second support roll 42, and the conductive roll The cleaning blade 60 </ b> A was placed in contact with 61 as in the case of the first embodiment. Then, when a predetermined bias (the same polarity as the transfer bias) was applied to the conductive roll 61 from the bias power supply device 55 and the cleaning condition was examined, it was applied to the first support roll 42 by the bias applied to the conductive roll 61. It was confirmed that problems such as density reduction occurred due to changes in the transfer bias. Incidentally, when a cleaning blade is installed on the transfer conveyance belt 30 in order to avoid such a problem, the problem in the conventional apparatus as described above similarly occurs.

  For comparison, the outer peripheral surface portion of the transfer conveyance belt 30 supported by the first support roll 41 as shown in FIG. 8 instead of the installation position of the bias roll 51 in the transfer conveyance apparatus 10 according to the first embodiment. A transfer conveyance device (Comparative Example 2) having the same configuration except that the bias roll 51A is installed at a portion that contacts the belt (portion upstream of the transfer portion TN in the belt rotation direction) is the same as in the case of the first embodiment. Similar image formation was performed.

  As a result, in the apparatus of Comparative Example 2, there was no density unevenness with respect to the entire halftone image, but it was confirmed that blurring was significantly generated with respect to the line image.

  In the first exemplary embodiment, the case where the photosensitive drum 120 is used as the image carrier that forms the transfer portion by contacting the transfer conveyance belt 30 of the transfer conveyance device 10 is illustrated. Alternatively, a drum-shaped intermediate transfer member may be used.

It is explanatory drawing which shows the outline | summary of the transfer conveyance apparatus of this invention. FIG. 2 is a schematic explanatory diagram illustrating a main part of an image forming apparatus to which the transfer conveyance device according to the first embodiment is applied. It is a cross-sectional explanatory view showing the layer structure of the transfer conveyance belt. It is explanatory drawing which shows the installation position of a bias roll, the dimension of a transfer conveyance apparatus, etc. It is explanatory drawing which shows the concept of the route through which a transfer bias flows, and the resistance of each route. It is explanatory drawing which shows the conventional belt-type transfer conveyance apparatus. FIG. 6 is an explanatory diagram illustrating an overview of a transfer conveyance device of Comparative Example 1; FIG. 10 is an explanatory diagram showing an overview of a transfer conveyance device of Comparative Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,10 ... Transfer conveyance apparatus, 2 ... Image carrier, 3,30 ... Transfer conveyance belt, 3a ... High resistance layer, 3b, 31 ... Underlayer, 4A, 4B ... Support roll, 5,50 ... Electric field generation means, 5A ... bias application member, 6 ... cleaning member, 32 ... surface layer (high resistance layer), 41A ... first support roll, 41B ... second support roll, 51 ... bias roll (bias application member), 60 ... cleaning blade ( (Cleaning member), 120 ... photosensitive drum (image carrier), P ... recording sheet, T ... toner image, B ... belt rotation direction, TN ... transfer site, L1 ... transfer along the belt rotation direction upstream from the contact position. Belt length to reach the site.

Claims (3)

An endless transfer / conveying belt which forms a transfer portion by contacting a rotating image carrier and carries a toner image, holds a recording sheet to which the toner image is transferred, and conveys the transfer portion through the transfer portion; ,
A plurality of support rolls that rotatably support the transfer conveyance belt;
A transfer conveying device comprising an electric field generating means for generating an electric field in a direction in which the toner image on the image carrier moves toward the recording sheet;
As the transfer conveyance belt, a belt having a multi-layer structure having a high resistance layer on the belt outer peripheral surface side and a conductive underlayer on the belt inner peripheral surface side is used.
In addition, as the electric field generating means, a bias applying member for applying a transfer bias is installed so as to abut on a portion of the outer peripheral surface of the transfer conveyance belt that is downstream of the transfer portion in the belt rotation direction. A transfer conveying apparatus characterized by that.   The bias applying member has a circumferential length of the belt from the contact position with the transfer conveyance belt to the transfer site along the upstream side in the belt rotation direction along the downstream side in the belt rotation direction from the contact position. The transfer / conveying apparatus according to claim 1, wherein the transfer / conveying apparatus is installed so as to have a relationship equivalent to or shorter than a circumferential length of the belt leading to the transfer portion. As the bias application member, use a conductive roll that can rotate in contact with the transfer conveyance belt,
And the transfer conveyance apparatus of Claim 1 or 2 which installed the cleaning member which contact | abuts the surface of this electroconductive roll, and cleans the roll surface.

Images