JP2006267549A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of density unevenness of an image even when drive torque of a transfer means changes. <P>SOLUTION: An image forming apparatus has an image carrier, an image forming means for forming an image on the image carrier and the transfer means for transferring the image formed on the image carrier to a transfer material, the image forming apparatus is characterized in that the transfer means has a transfer member which holds the transfer material between it and the image carrier, the transfer member has a transfer member driving gear which is attached to the transfer member and rotates integrally with the transfer member, the transfer member has an abutting member, the image forming apparatus has a transfer member driving means for driving the transfer member via the transfer member driving gear, the transfer member driving means has a transfer member drive force transmission path for transmitting power to the transfer member driving gear and a one-way clutch is installed in the transfer member drive force transmission path. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a printer, a copying machine, or a facsimile.

  In an image forming apparatus such as a copying machine, a printer, or a fax machine, an electrophotographic system using toner is often used. Due to the diversification of printer demand in recent years, there has been a growing demand for marginless (no margin) printing. In particular, the work was to print on a large recording material and then cut the margin to create a print with no margins. Therefore, the need for marginless printing is increasing.

  For example, an image forming apparatus described in Patent Document 1 is proposed as an electrophotographic image forming apparatus capable of printing without margins.

JP 2004-005559 A

  FIG. 6 shows a configuration diagram of the conventional image forming apparatus.

  However, the conventional image forming apparatus 100 is provided with the transfer belt cleaning unit 109 in order to prevent the back side of the paper from being stained due to the toner adhering to the transfer belt 107 caused by the marginless printing. As a result, there is a defect that density unevenness of the image occurs at the time of marginless printing.

  A mechanism that causes density unevenness of an image during marginless printing will be described below.

  When printing without margins, an image larger than the transfer material P is formed on the photosensitive drums 103a, 103b, 103c, and 103d, and an image without margins is formed on the transfer material P. Of the images on the photosensitive drums 103 a, 103 b, 103 c, and 103 d, the portion that protrudes from the transfer material P is attached to the transfer belt 107 and then removed by the transfer belt cleaning unit 109.

  That is, the toner adhering to the transfer belt 107 does not reach the transfer belt cleaning unit 109 during normal printing, whereas the toner adhering to the transfer belt 107 arrives during printing without margins. Due to the variation in the amount of toner reaching the transfer belt cleaning unit 109, the driving torque of the transfer belt 107 varies greatly. Normally, when printing continues, the transfer belt cleaning unit 109 has almost no toner, so that the driving torque of the transfer belt 107 is high due to the frictional force between the transfer belt cleaning unit 109 and the transfer belt 107.

  On the other hand, the drive torque of the transfer belt 107 changes suddenly and becomes small at the moment when the adhered toner reaches the transfer belt cleaning unit 109 during marginless printing. This change in the driving torque of the transfer belt 107 changes the moving speed of the transfer belt 107 and the transfer material P, and is manifested as uneven density in the image formed on the transfer material P.

  Accordingly, a first object of the present invention is to prevent the occurrence of uneven density in an image even if a drive torque change of the transfer means occurs.

  A second object of the present invention is to prevent the occurrence of uneven density in an image even when a change in driving torque of the transfer means occurs due to a contact member that can contact and separate from the transfer member.

  Furthermore, a third object of the present invention is to prevent the occurrence of density unevenness in the image even if the driving torque of the transfer means is different by mounting a plurality of transfer means having different configurations.

  A fourth object of the present invention is to attach a transfer means having a contact member to the transfer member and a transfer means having no contact member to the transfer member, respectively, so that even if the drive torque of the transfer means differs, This is to prevent the occurrence of density unevenness.

  A fifth object of the present invention is to prevent the occurrence of density unevenness in the image even when the driving torque of the transfer means is different by mounting a plurality of transfer means having different friction coefficients on the surface of the transfer member. is there.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier, image forming means for forming an image on the image carrier, and an image formed on the image carrier to a transfer material. In an image forming apparatus having a transfer unit,
The transfer unit includes a transfer member that holds the transfer material between the transfer member and the image carrier, and the transfer member has a transfer member driving gear attached to the transfer member and rotating integrally with the transfer member. The transfer member includes a contact member, and the image forming apparatus includes a transfer member driving unit that drives the transfer member via the transfer member driving gear, and the transfer member driving unit includes the transfer member. It has a transfer member driving force transmission path for transmitting power to the drive gear, and a one-way clutch is installed in the transfer member driving force transmission path.

  According to a second aspect of the present invention, in the first aspect of the present invention, the contact member is configured to be able to contact and separate from the transfer member.

The invention according to claim 3 includes an image carrier, an image forming unit that forms an image on the image carrier, and a transfer unit that transfers an image formed on the image carrier to a transfer material. The transfer unit includes a transfer member that holds the transfer material between the transfer member and the image carrier, and the transfer member has a transfer member driving gear attached to the transfer member and rotating integrally with the transfer member. The transfer unit has a unit configuration that is detachable from the image forming apparatus, and the image forming apparatus includes a transfer member driving unit that drives the transfer member via the transfer member driving gear. In the image forming apparatus, the driving unit has a transfer member driving force transmission path for transmitting power to the transfer member driving gear, and a one-way clutch is installed in the transfer member driving force transmission path.
The transfer means includes a plurality of types of units having different configurations, and each transfer means unit can be mounted.

  The invention according to claim 4 is the invention according to claim 3, characterized in that the difference in unit configuration of the transfer means is the presence or absence of a contact member with respect to the transfer member.

  The invention described in claim 5 is the invention described in claim 3 or 4, characterized in that the difference in the configuration of the transfer means is a difference in friction coefficient on the surface of the transfer member.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the function of performing image formation in the first image forming mode for forming an image over the entire area of the transfer material, and the transfer material And a function of performing image formation in a second image forming mode for forming an image in a normal area excluding a predetermined area.

  According to the first aspect of the present invention, it is possible to prevent the occurrence of uneven density in the image even if the drive torque of the transfer means changes.

  According to the second aspect of the present invention, even when the contact member against the transfer member comes in contact with or separates from the transfer member, the occurrence of uneven density in the image is prevented even when the drive torque of the transfer means changes. Is possible.

  According to the third aspect of the present invention, it is possible to prevent the occurrence of uneven density in the image even if the driving torque of the transfer means is different by mounting a plurality of transfer means having different configurations.

  According to the fourth aspect of the present invention, even if the driving torque of the transfer means varies depending on the presence or absence of the contact member with respect to the transfer member, it is possible to prevent the occurrence of density unevenness in the image.

  According to the fifth aspect of the present invention, even if the driving torque of the transfer means is different due to the difference in the friction coefficient on the surface of the transfer member, it is possible to prevent the occurrence of density unevenness in the image.

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

<Embodiment 1>
The configuration of the image forming apparatus of this embodiment will be described with reference to the schematic cross-sectional view of the full-color electrophotographic image forming apparatus shown in FIG. Here, as the first image carrier, a plurality of photosensitive drums 11a corresponding to respective color toners of the first color: yellow, the second color: magenta, the third color: cyan, and the fourth color: black. 11b, 11c, and 11d, and an intermediate transfer belt 1 that is in contact with each of the photosensitive drums 11a, 11b, 11c, and 11d at a primary transfer portion as a second image carrier.

  Each photosensitive drum is a first color (yellow) photosensitive drum 11a positioned at the most upstream position along the moving direction of the intermediate transfer belt 1, and a second color positioned closest to the downstream side of the photosensitive drum 11a. (Magenta) photosensitive drum 11b, third color (cyan) photosensitive drum 11c located closest to the downstream side of the photosensitive drum 11b, and fourth color positioned closest to the downstream side of the photosensitive drum 11c. (Black) photosensitive drums 11d are arranged in this order.

  The photosensitive drums 11a, 11b, 11c, and 11d in the present embodiment have an outer diameter of 30.0 mm and have a layer in which a photosensitive material is applied on an aluminum cylinder.

  The intermediate transfer belt 1 includes a resin film such as a urethane resin, a fluorine resin, a nylon resin, a polyimide resin, a resin film or urethane rubber in which carbon or conductive powder is dispersed in these resins, and resistance is adjusted. An elastomer sheet having a multi-layer structure in which a resin layer is formed as a release layer on the toner carrier surface side of a base layer sheet such as NBR can also be used.

The intermediate transfer belt 1 used in the present embodiment is formed on the belt 1 in a transfer process or the like by dispersing carbon in polyimide and adjusting the surface resistivity ρs = 1 × 10 ¹² Ω to a medium resistance. The added charge can be attenuated without providing a special static elimination mechanism. The intermediate transfer belt 1 is a single-layer endless belt having a circumferential length of 1000 mm and a thickness of 100 μm.

  The surface resistivity measurement is based on JIS-K6911. After obtaining good contact between the electrode and the belt surface by using conductive rubber as an electrode, an ultra-high resistance resistance meter (R8340 manufactured by Advantest) is used. Measured. The measurement conditions were applied voltage = 100 V and voltage application time = 30 s.

  As shown in FIG. 1, the intermediate transfer belt 1 is suspended by three rollers including a drive roller 1a, a support roller 1b, and a separation roller 1c included in the intermediate transfer belt 1. The drive roller 1a, the support roller 1b, and the separation roller 1c are electrically grounded.

The driving roller 1a and the separation roller 1c are rollers having an outer diameter of 29.8 mm composed of an aluminum cored bar having a diameter of 24.0 mm and a hydrin rubber layer having a layer thickness of 2.9 mm, and the resistance is adjusted by adjusting the resistance of the hydrin rubber. The resistance value is 1 × 10 ⁶ Ω.

  The support roller 1b is an aluminum roller having a diameter of 29.8 mm.

  The roller resistance value was measured using an ultra-high resistance resistance meter (R8340 manufactured by Advantest) while the roller to be measured was brought into contact with an aluminum cylinder having a diameter of 30 mm and rotated following the aluminum cylinder. The measurement conditions were applied voltage = 100 V, voltage application time = 30 s, contact force = 9.8 N, and rotational peripheral speed = 117 mm / s.

  The intermediate transfer belt 1 is rotated at a predetermined process speed V1 (117.0 mm / s in this embodiment) by a driving device (not shown) in the direction of the arrow. The photosensitive drums 11a, 11b, 11c, and 11d are 99.0% of the moving speed of the intermediate transfer belt 1 in the same direction as the moving direction of the intermediate transfer belt 1 (115.8 mm / s in this embodiment). And is rotated by a driving device (not shown). The primary transfer efficiency is improved by adding a speed difference ΔVa to the moving speed of each of the photosensitive drums 11a, 11b, 11c, 11d and the intermediate transfer belt 1.

  However, as the speed difference ΔVa between the moving speeds of the photosensitive drums 11a, 11b, 11c, and 11d and the intermediate transfer belt 1 is larger, the photosensitive drums 11a, 11b, 11c, and 11d are caused by the friction with the intermediate transfer belt 1. The occurrence of wear and scratches is promoted. Therefore, in this embodiment, the speed difference ΔVa is set to 1.0% of the process speed (1.17 mm / s in this embodiment) in order to achieve both the primary transfer efficiency and the degree of wear and scratches on the photosensitive drum.

  The photosensitive drums 11a, 11b, 11c, and 11d are uniformly charged by the contact charging rollers 12a, 12b, 12c, and 12d, and lasers from the scanners 13a, 13b, 13c, and 13d modulated by the exposure information signal. An electrostatic latent image is created with light.

  The image information signal sent from the host computer is processed by an image information processing means (not shown) so that the image finally formed on the transfer material can obtain a desired size and chromaticity based on the image information signal. As a result, an exposure information signal is obtained.

  The intensity of the laser light and the irradiation spot diameter are appropriately set according to the resolution of the image forming apparatus and the desired image density, and the electrostatic latent images on the photosensitive drums 11a, 11b, 11c, and 11d are irradiated with the laser light. The remaining portion is held at the bright portion potential VL (about -150V), and the other portions are held at the dark portion potential VD (about -650V) charged by the respective contact charging rollers 12a, 12b, 12c, and 12d as primary chargers. By forming.

  The electrostatic latent image reaches the facing portion of each developing unit 14a, 14b, 14c, 14d by the rotation of each photosensitive drum 11a, 11b, 11c, 11d, and has the same polarity as the surface of the photosensitive drum (in this example, A developer (toner) charged to a negative polarity is supplied and visualized to form a developer image (toner image).

  The developing device 14 in the present embodiment is a developing device that employs a two-component developing system. The developing bias in this embodiment is a bias in which an AC voltage is superimposed on a DC voltage of DC component = −400 V, AC component = 1.5 kVpp, frequency = 3 kHz, waveform = rectangular wave.

  The toner images formed on the photosensitive drums 11a, 11b, 11c, and 11d are in the primary transfer nips that are the proximity or contact portions between the intermediate transfer belt 1 and the photosensitive drums 11a, 11b, 11c, and 11d. The primary transfer bias applied to the primary transfer rollers 15a, 15b, 15c, and 15d in contact with the back surface of the intermediate transfer belt 1 from the primary transfer bias sources 16a, 16b, 16c, and 16d (in this embodiment, a constant voltage control of + 400V). ) To be transferred onto the intermediate transfer belt 1. When the intermediate transfer belt 1 passes through the primary transfer nip with the photosensitive drum 11d, the formation of the four-color image on the intermediate transfer belt 1 is completed, and the primary transfer process is completed.

  On the other hand, the surface of each of the photosensitive drums 11a, 11b, 11c, and 11d after the primary transfer of the toner image is subjected to removal of primary transfer residual toner and the like by a drum cleaning device 17a, 17b, 17c, and 17d formed of a urethane rubber blade. It is cleaned and prepared for the next image forming step.

  The transfer material cassette 5 is provided with a temperature / humidity sensor 51 for detecting the temperature / humidity in the image forming apparatus.

  Next, one transfer material P is taken out from the transfer material cassette 5, and a secondary transfer nip portion that is a portion between the separation roller 1c and the secondary transfer roller 2 as a transfer member with the intermediate transfer belt 1 interposed therebetween. Is inserted.

  At this time, the secondary transfer roller 2 has a polarity opposite to that of the toner, and an optimum bias determined according to the temperature and humidity in the image forming apparatus detected by the temperature and humidity sensor (in this embodiment, 15 ° C./10% RH). +20 μA, 23 ° C./50% RH, +30 μA, 30 ° C./80% RH, +35 μA constant current control) is applied by the secondary transfer bias source 21, and the toner image is transferred to the intermediate transfer belt 1. To the transfer material P.

The secondary transfer roller 2 in the present embodiment is a roller having an outer diameter of 22.1 mm configured by an aluminum core bar having a diameter of 14.0 mm, a silicon rubber layer having a thickness of 4 mm, and a fluororesin layer having a surface thickness of 100 μm. The roller resistance value is adjusted to 1 × 10 8 by adjusting the resistance of silicon rubber and fluororesin.
Ω. By providing the fluororesin layer on the surface layer, it is possible to easily remove the toner adhering to the secondary transfer roller 2 when performing marginless printing with a secondary transfer roller cleaner described later. The hardness of the secondary transfer roller 2 is 45 ° (ASKER-C).

  The secondary transfer roller driving in the present embodiment will be described with reference to a schematic explanatory diagram of the secondary transfer roller driving device 23 shown in FIG. The secondary transfer roller 2 is rotated in the direction of the arrow R2 by the secondary transfer roller driving device 23.

  A secondary transfer roller drive gear 24 is fixed to one end of the secondary transfer roller 2. An output gear 27 connected to the output shaft of the motor 25, which is a drive source, via a one-way clutch 26 meshes with the secondary transfer roller drive gear 24 to rotate the secondary transfer roller 2 in the direction of arrow R2. The speed V2 of the secondary transfer roller 2 is set to 116.6 mm / s, which is 0.3% slower than V1. The one-way clutch 26 is locked in the direction of the arrow R3 and free in the opposite direction. Therefore, when the secondary transfer roller 2 is in contact with the intermediate transfer belt 1, the secondary transfer roller 2 is driven by the intermediate transfer belt 1 without being driven by the motor 25.

  The transfer material P on which the unfixed toner image that has passed through the secondary transfer nip portion reaches the fixing device 3 and is heated and pressurized to obtain a permanent fixed image. The transfer material P discharged from the fixing device 3 is conveyed to a paper discharge tray 6 outside the device.

  After the transfer of the toner image onto the transfer material P, the surface of the intermediate transfer belt 1 is cleaned of secondary transfer residual toner by an intermediate transfer body cleaner 4 having a cleaning blade made of urethane rubber.

  In the present invention, in order to perform marginless printing on the transfer material P, a mask area E for determining a print area in the recording material P by a conventional image forming apparatus is roughly shown by the size of the recording material P as shown in FIG. By increasing the size by 1 mm, it is possible to form an image of the added area on the photosensitive drum. Accordingly, the toner T in the additional area outside the recording material P during the transfer adheres to the secondary transfer roller 2. Since this adhered toner can cause back contamination of the transfer material P, it is removed by the secondary transfer roller cleaner 22 in contact with the secondary transfer roller 2.

  In this embodiment, a urethane rubber blade is used as the secondary transfer roller cleaner 22. However, as the secondary transfer roller cleaner 22, known cleaning means such as a fur brush that is rotationally driven can be used in addition to the urethane rubber blade.

  According to the configuration of the present embodiment, since the marginless printing is performed, a large amount of toner due to the added region is present in the contact portion between the secondary transfer roller cleaner 22 and the secondary transfer roller 2, so that the secondary transfer roller When the driving torque of 2 is sufficiently small, the secondary transfer roller 2 can rotate with respect to the intermediate transfer belt 1. In this state, since the transfer material P is conveyed at the same speed as the intermediate transfer belt 1, a good image without image rubbing can be obtained.

  On the other hand, the normal printing operation that is not marginless printing continued, and the drive torque of the secondary transfer roller 2 increased because only a small amount of toner was present at the contact portion between the secondary transfer roller cleaner 22 and the secondary transfer roller 2. In this case, the secondary transfer roller 2 is rotated by being driven by the secondary transfer roller driving device 23. Therefore, the transfer material P is substantially the same speed as the intermediate transfer belt 1 even when the driving torque of the secondary transfer roller 2 is large (the speed between the speed V1 of the intermediate transfer belt 1 and the speed V2 of the secondary transfer roller 2). ). As a result, it is not possible to obtain a good image level without image rubbing that is obtained when the transfer material P is conveyed with the intermediate transfer belt 1 at a constant speed, but the transfer material P is substantially constant with the intermediate transfer belt 1. Since the sheet is stably conveyed without fluctuation in the conveyance speed, it is possible to prevent occurrence of uneven image density due to fluctuation in the conveyance speed of the transfer material P.

  Therefore, in the present embodiment, by providing a one-way clutch in the transfer roller driving device 23, even if the driving torque of the secondary transfer roller 2 fluctuates greatly, image density unevenness due to the transfer speed variation of the transfer material P is reduced. An image forming apparatus that suppresses occurrence can be provided.

<Embodiment 2>
Next, a second embodiment of the present invention will be described. Constituent elements similar to those in the first embodiment are given the same reference numerals and explanations thereof are omitted.

  In the present embodiment, the secondary transfer roller cleaner 22 is configured so as to be able to contact and separate from the secondary transfer roller 2 by a contact / separation mechanism (not shown). Separate for normal printing without printing. By providing the contact / separation mechanism for the secondary transfer roller cleaner 22, it is possible to prevent the wear of the secondary transfer roller cleaner 22 and the wear and scratches on the surface of the secondary transfer roller 2 due to rubbing in the case of normal printing. As a result, it is possible to prevent the occurrence of back contamination due to the cleaning failure of the toner adhering to the secondary transfer roller 2 and to extend the lifetime of the secondary transfer roller 2 and the secondary transfer roller cleaner 22.

  According to the configuration of the present embodiment, the secondary transfer roller cleaner 22 is separated from the secondary transfer roller 2 in the case of normal printing that is not marginless printing, or the secondary transfer roller cleaner in the case of marginless printing. Even when 22 is in contact with the secondary transfer roller 2, there is a lot of toner adhering to the secondary transfer roller 2 due to the added area, and the contact between the secondary transfer roller cleaner 22 and the secondary transfer roller 2 is present. When the driving torque of the secondary transfer roller 2 is sufficiently small due to the presence of a large amount of toner, the secondary transfer roller 2 can be rotated with respect to the intermediate transfer belt 1. In this state, since the transfer material P is conveyed at the same speed as the intermediate transfer belt 1, a good image without image rubbing can be obtained.

  On the other hand, even in the case of marginless printing, even if the secondary transfer roller cleaner 22 is in contact with the secondary transfer roller 2, there is little toner in the added area, and the contact between the secondary transfer roller cleaner 22 and the secondary transfer roller 2 is small. When the driving torque of the secondary transfer roller 2 increases due to the presence of a small amount of toner in the portion, the secondary transfer roller 2 rotates by being driven by the secondary transfer roller driving device 23.

  Therefore, even when the driving torque of the secondary transfer roller 2 is large, the transfer material P is substantially at the same speed as the intermediate transfer belt 1 (the speed is between the speed V1 of the intermediate transfer belt 1 and the speed V2 of the secondary transfer roller 2). ). As a result, it is not possible to obtain a good image level without image rubbing that is obtained when the transfer material P is conveyed with the intermediate transfer belt 1 at a constant speed, but the transfer material P is substantially constant with the intermediate transfer belt 1. Since the sheet is stably conveyed without fluctuation in the conveyance speed, it is possible to prevent occurrence of uneven image density due to fluctuation in the conveyance speed of the transfer material P.

  Therefore, in the second embodiment, it is possible to provide an image forming apparatus that suppresses the occurrence of uneven image density due to the transfer speed fluctuation of the transfer material P by providing a one-way clutch in the secondary transfer roller driving device 23.

<Embodiment 3>
Next, a third embodiment of the present invention will be described. Constituent elements similar to those in the first embodiment are given the same reference numerals and explanations thereof are omitted.

  In the present embodiment, the secondary transfer unit 200 illustrated in FIG. 4 is detachable from the apparatus main body, and the secondary transfer unit 200 includes the secondary transfer roller cleaner 22 and the secondary transfer roller 2. Further, the secondary transfer unit 200 also includes a toner collection container 201 that collects toner adhering to the secondary transfer roller 2 removed by the secondary transfer roller cleaner 22.

  In addition, when printing without margins is not performed on the apparatus main body of the present embodiment, a secondary transfer unit 300 for normal printing can be mounted instead of the secondary transfer unit 200 described above. FIG. 5 shows a secondary transfer unit 300 for normal printing. The secondary transfer unit 300 for normal printing does not need to remove toner adhering to the secondary transfer roller 2 due to marginless printing, and unlike the secondary transfer unit 200, has a secondary transfer roller cleaning unit. Therefore, it can be provided at a lower cost than the secondary transfer unit 200 to users who do not perform marginless printing.

  According to the configuration of the present embodiment, even when the secondary transfer unit 300 for normal printing is attached, or even when the secondary transfer unit 200 is attached, a large amount of adhesion due to the added area on the secondary transfer roller 2. If there is toner and a large amount of toner is present at the contact portion between the secondary transfer roller cleaner 22 and the secondary transfer roller 2, the drive torque of the secondary transfer roller 2 is sufficiently small. It can be rotated following the transfer belt 1. In this state, since the transfer material P is conveyed at the same speed as the intermediate transfer belt 1, a good image without image rubbing can be obtained.

  On the other hand, the secondary transfer unit 200 is mounted so that the toner in the added area is small and only a small amount of toner is present at the contact portion between the secondary transfer roller cleaner 22 and the secondary transfer roller 2. When the driving torque increases, the secondary transfer roller 2 rotates by being driven by the secondary transfer roller driving device 23.

  Therefore, even when the driving torque of the secondary transfer roller 2 is large, the transfer material P is substantially at the same speed as the intermediate transfer belt 1 (the speed is between the speed V1 of the intermediate transfer belt 1 and the speed V2 of the secondary transfer roller 2). ). As a result, it is not possible to obtain a good image level without image rubbing that is obtained when the transfer material P is conveyed with the intermediate transfer belt 1 at a constant speed, but the transfer material P is substantially constant with the intermediate transfer belt 1. Since the sheet is stably conveyed without fluctuation in the conveyance speed, it is possible to prevent occurrence of uneven image density due to fluctuation in the conveyance speed of the transfer material P.

  Therefore, in the third embodiment, it is possible to provide an image forming apparatus that suppresses the occurrence of uneven image density due to the transfer speed variation of the transfer material P by providing the secondary transfer roller driving device 23 with a one-way clutch.

<Embodiment 4>
Next, a fourth embodiment of the present invention will be described. Constituent elements similar to those of the third embodiment are given the same reference numerals and explanation thereof is omitted.

In the present embodiment, since the secondary transfer roller 302 for normal printing does not need to remove the toner adhering to the marginless printing, unlike the secondary transfer roller 2, a separation layer such as a fluororesin layer is provided on the surface layer. There is no need to provide a mold layer. For this reason, the secondary transfer roller 302 for normal printing in the present embodiment is a roller having an outer diameter of 22.1 mm composed of an aluminum metal core having a diameter of 14 mm and a silicon rubber layer having a layer thickness of 4.1 mm. The roller resistance is set to 1 × 10 ⁸ Ω by adjusting the resistance of the rubber.

  The surface friction coefficients of the secondary transfer roller 2 and the normal printing secondary transfer roller 302 are greatly different from 0.18 and 0.87, respectively, due to the difference in the material of the outermost layer. Thereby, the driving force differs from the intermediate transfer belt 2 and the transfer material P obtained by the secondary transfer roller due to the difference in the secondary transfer unit.

  For measuring the surface friction coefficient of the transfer roller, an average measured value of 10 points of the sample by HEIDON tribogear muse TYPE: 94i manufactured by Shinto Kagaku Co., Ltd. was used. The sample had a sheet shape corresponding to each secondary transfer roller configuration. That is, the sample of the secondary transfer roller 2 is a 100 mm × 100 mm sheet in which a 4.0 mm thick silicon rubber layer and a surface 100 μm thick fluororesin layer are formed on a 7 mm thick aluminum plate, normal printing A sample of the secondary transfer roller 302 for use is a 100 mm × 100 mm sheet in which a silicon rubber layer having a thickness of 4.1 mm is formed on an aluminum plate having a thickness of 7 mm.

  According to the configuration of the present embodiment, the surface of the secondary transfer roller 302 is made of silicon rubber when the secondary transfer unit 300 for normal printing is attached as compared to the case where the secondary transfer unit 200 is attached. The secondary transfer roller 302 can obtain a large driving force from the intermediate transfer belt 2 and the transfer material P.

  Even when the secondary transfer unit 200 is mounted, there is a lot of toner adhering to the secondary transfer roller 2 due to the added area, and the contact portion between the secondary transfer roller cleaner 22 and the secondary transfer roller 2 is present. When the driving torque of the secondary transfer roller 2 is sufficiently small due to the presence of a large amount of toner, the secondary transfer roller 2 can be rotated with respect to the intermediate transfer belt 1. In this state, since the transfer material P is conveyed at the same speed as the intermediate transfer belt 1, a good image without image rubbing can be obtained.

  On the other hand, the secondary transfer unit 200 is mounted so that the toner in the added area is small and only a small amount of toner is present at the contact portion between the secondary transfer roller cleaner 22 and the secondary transfer roller 2. When the driving torque increases, the secondary transfer roller 2 rotates by being driven by the secondary transfer roller driving device 23.

  Therefore, even when the driving torque of the secondary transfer roller 2 is large, the transfer material P is substantially at the same speed as the intermediate transfer belt 1 (the speed is between the speed V1 of the intermediate transfer belt 1 and the speed V2 of the secondary transfer roller 2). ). As a result, it is not possible to obtain a good image level without image rubbing that is obtained when the transfer material P is conveyed with the intermediate transfer belt 1 at a constant speed, but the transfer material P is substantially constant with the intermediate transfer belt 1. Since the sheet is stably conveyed without fluctuation in the conveyance speed, it is possible to prevent occurrence of uneven image density due to fluctuation in the conveyance speed of the transfer material P.

  Therefore, in the present embodiment, it is possible to provide an image forming apparatus that suppresses the occurrence of uneven image density due to the transfer speed fluctuation of the transfer material P by providing a one-way clutch in the secondary transfer roller driving device 23.

It is a figure explaining the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the secondary transfer roller drive device concerning Embodiment 1 of the present invention. It is a figure explaining the mask area | region of the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the secondary transfer unit which concerns on Embodiment 3 of this invention. It is a figure explaining the secondary transfer unit for normal printing which concerns on Embodiment 3 of this invention. It is a figure explaining the image forming apparatus which concerns on the prior art example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt 2 Secondary transfer roller 5 Transfer material cassette 6 Paper discharge tray P Transfer material

Claims (6)

In an image forming apparatus comprising: an image carrier; an image forming unit that forms an image on the image carrier; and a transfer unit that transfers an image formed on the image carrier to a transfer material.
The transfer unit includes a transfer member that holds the transfer material between the transfer member and the image carrier, and the transfer member has a transfer member driving gear attached to the transfer member and rotating integrally with the transfer member. The transfer member includes a contact member, and the image forming apparatus includes a transfer member driving unit that drives the transfer member via the transfer member driving gear, and the transfer member driving unit includes the transfer member. An image forming apparatus comprising a transfer member driving force transmission path for transmitting power to a driving gear, and a one-way clutch installed in the transfer member driving force transmission path.   The image forming apparatus according to claim 1, wherein the contact member is configured to be able to contact and separate from the transfer member. An image carrier, an image forming unit that forms an image on the image carrier, and a transfer unit that transfers an image formed on the image carrier to a transfer material. The transfer unit includes the image carrier. A transfer member that holds the transfer material therebetween, and the transfer member includes a transfer member driving gear that is attached to the transfer member and rotates integrally with the transfer member, and the transfer unit forms an image. The image forming apparatus includes a transfer member driving unit that drives the transfer member via the transfer member driving gear, and the transfer member driving unit includes the transfer member driving gear. In the image forming apparatus having a transfer member driving force transmission path for transmitting power to the transfer member, and a one-way clutch installed in the transfer member driving force transmission path,
2. The image forming apparatus according to claim 1, wherein the transfer unit includes a plurality of types of units having different configurations, and each transfer unit can be mounted.   4. The image forming apparatus according to claim 3, wherein the difference in unit configuration of the transfer means is the presence or absence of a contact member with respect to the transfer member.   5. The image forming apparatus according to claim 3, wherein the difference in the transfer unit configuration is a difference in friction coefficient on the surface of the transfer member.   A function of forming an image in the first image forming mode for forming an image over the entire area of the transfer material, and an image formation in the second image forming mode for forming an image in a normal area excluding a predetermined area of the transfer material. The image forming apparatus according to claim 1, further comprising a function for performing the operation.

Images