JP2009186828A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is capable of suppressing the occurrence of toner scattering and a void and the wear of an image carrying belt. <P>SOLUTION: A belt guide member 8 projects the intermediate transfer belt portion 1A toward a side of a recording medium sheet S being transferred to the transfer roller 3, by pressing the rear surface 1b of an intermediate transfer belt portion 1A on the upstream side in the transfer direction (direction of A) of the intermediate transfer belt 1, through the endless-shaped belt 7, from a press-contact potion (nip portion) 5 where a transfer roller 3 comes into press-contact with an opposing roller 16 through an intermediate transfer belt 1 and an endless-shaped belt 7, and the belt guide member is fixedly arranged. The endless-shaped belt 7 is stretched on the opposing roller 16 and the belt guide member 8 and the rear surface 1b of the intermediate transfer belt 1 comes into press-contact with the belt guide member 8 through the endless-shaped belt 7, to be pressed by the belt guide member 8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms a toner image on the surface of an endless image bearing belt and transfers the toner image onto a transfer material by a transfer unit.

An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile machine, or a multifunction machine having at least two functions thereof has been conventionally known. The image carrying belt is composed of, for example, a photosensitive belt on which a toner image is formed by a developing device, an intermediate transfer belt on which a toner image is transferred from the photosensitive body, and the like.
FIG. 5 is a schematic diagram showing a configuration of a transfer unit of a conventional image forming apparatus in which an image carrying belt is configured as an intermediate transfer belt. The intermediate transfer belt 1 shown here is stretched around a plurality of rollers, a roller not shown in FIG. 5 and one roller (hereinafter referred to as a counter roller) 2 shown in FIG. Then, toner images of different colors are sequentially superimposed on the surface of the photoconductor (not shown) and transferred. A transfer roller 3, which is an example of a transfer unit, is opposed to the opposing roller 2 that rotates in the direction of arrow E shown in FIG. When transferring the toner image on the surface of the intermediate transfer belt 1 onto a transfer material P made of a recording medium such as transfer paper, the transfer roller 3 is connected to the opposing roller 2 via the intermediate transfer belt 1 as shown in FIG. Pressure contact. At this time, the transfer roller 3 rotates in the direction of arrow F, and the transfer material P moves in the direction of arrow B between the transfer roller 3 and the intermediate transfer belt 1. Thus, the transfer roller 3 is in pressure contact with the counter roller 2 via the intermediate transfer belt 1 and the transfer material P. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the surface of the intermediate transfer belt 1 is applied to the transfer roller 3, thereby causing the transfer roller 3 to contact the surface of the intermediate transfer belt 1 in the direction of arrow B. The toner image on the intermediate transfer belt 1 is transferred onto the surface of the moving transfer material P. The transfer material P that has passed through the pressure contact portion (nip portion) 5 between the opposing roller 2 and the transfer roller 3 passes through a fixing device (not shown). At this time, the toner image transferred to the surface is fixed on the transfer material P. Is done.

  As described above, the transfer material P is fed between the opposed roller 2 and the transfer roller 3 and conveyed from the entrance side I. At this time, the intermediate transfer belt 1 is in the region on the entrance side I. And a transfer material P form a wedge-shaped gap G. At this time, since the transfer voltage described above is applied to the transfer roller 3, the portion of the transfer material P1 located in the vicinity of the pressure contact portion 5 between the opposing roller 2 and the transfer roller 3 is also opposite in polarity to the charging polarity of the toner. Is charged. Therefore, the toner on the intermediate transfer belt 1 electrostatically scatters and adheres to the surface of the transfer material P as indicated by an arrow C. Such a phenomenon is also referred to as “toner scattering”. When such toner scattering occurs, the surface of the transfer material that has passed through the press contact portion 5 scatters around the transferred toner image as described above. The toner adheres in a blurred state, which deteriorates the image quality of the toner image.

The above-mentioned problems occur in the same manner when the image carrying belt is composed of a photosensitive belt or a dielectric belt, and the transfer material P is composed of an intermediate transfer body or a recording medium. The volume resistivity is often made of a medium resistor having a volume resistivity of about 10 ⁸ Ωcm to 10 ¹³ Ωcm, for example. When such an intermediate transfer belt 1 is used, the above-described toner scattering becomes remarkable. As a cause thereof, the force that the toner is electrostatically adhered to the surface of the intermediate transfer belt 1 made of the intermediate resistor is weaker than the electrostatic adhesion force between the insulator and the toner, and the toner is transferred to the intermediate transfer belt 1. It is mentioned that it adheres to the surface of the surface in a relatively mobile state. In particular, when a plurality of color toner images are formed on the surface of the intermediate transfer belt 1, the amount of toner per unit area on the intermediate transfer belt 1 increases, so that the toner on the uppermost layer is particularly easy to move. It has become. When the surface of the intermediate transfer belt 1 to which the toner adheres in such a state that it is easy to move and the charged transfer material P face each other with a minute gap G, the toner on the intermediate transfer belt 1 is electrostatically applied onto the transfer material. The above-described toner scattering is likely to occur.

  Therefore, as shown in FIG. 6, an intermediate between the opposing roller 2 rotating in the direction of arrow E facing the transfer roller 3 rotating in the direction of arrow F and another guide roller 4 supporting the intermediate transfer belt 1. The guide roller 4 is disposed so that the transfer belt portion 1A is substantially parallel to the moving direction B of the transfer material P moving to the press contact portion 5, and is located upstream of the press contact portion 5 in the moving direction of the image carrier belt. It can be considered that the transfer material P is configured to start to come into contact with the surface of the intermediate transfer belt 1 at a location far away. In this way, when the portion 6 of the transfer material P that reaches the vicinity of the press contact portion 5 is charged under the influence of the voltage applied to the transfer roller 3, the transfer material portion P1 has already been transferred to the intermediate transfer belt 1. Therefore, the toner on the surface of the intermediate transfer belt 1 does not fly to the transfer material portion P1, or the amount of toner to fly becomes extremely small. In this way, the occurrence of toner scattering can be suppressed.

By the way, if the diameters of the counter roller 2 and the guide roller 4 that support the intermediate transfer belt 1 are reduced in order to make the counter roller 2 and the guide roller 4 close to each other, they pass through the counter roller 2 and the guide roller 4. The intermediate transfer belt 1 is curled, thereby causing uneven transfer when the toner image is transferred from the intermediate transfer belt 1 to the transfer material P, and the image quality of the transferred toner image is deteriorated. If the diameter of the facing roller 2 facing the transfer roller 3 is too small, the distance (nip width) of the press contact portion 5 in the transfer material conveyance direction is reduced, and there is a possibility that transfer efficiency is lowered. Therefore, the diameters of the facing roller 2 and the guide roller 4 cannot be made too small.
For the above-described reasons, when the diameters of the opposing roller 2 and the guide roller 4 are increased, the distance D of the close contact portion that comes into close contact with the surface of the intermediate transfer belt 1 before the transfer material P reaches the press contact portion 5 increases. Therefore, the transfer material P starts to contact the intermediate transfer belt 1 at a position far away from the upstream side in the moving direction of the transfer material P. At this time, the portion 6 on the upstream side in the transfer material moving direction in the portion of the transfer material P that is in contact with the intermediate transfer belt 1 is far away from the transfer roller 3. Even if it is not charged or charged due to the influence of the applied voltage, its potential is very low. Therefore, the transfer material portion 6 does not adhere to the surface of the intermediate transfer belt 1 in a state where it is strongly adsorbed electrostatically.

However, for this reason, the transfer material portion 6 cannot follow the surface unevenness or sagging due to slight curl generated in the intermediate transfer belt 1 and cannot be adhered to the intermediate transfer belt 1, and the transfer material portion 6 is slightly in contact with the intermediate transfer belt 1. May move. As a result, a part of the toner image existing between the surface of the intermediate transfer belt 1 and the transfer material portion 6 is disturbed, and due to this disorder, the density of the toner image transferred onto the transfer material P that has passed through the press contact portion 5 is disturbed. However, there is a possibility that an image dropout that is locally thin occurs and the image quality deteriorates. This image omission is generally referred to as “white omission” because white transfer material P is generally used. In particular, when the speed is deviated within a tolerance range between the intermediate transfer belt 1 and the transfer material P, an image misalignment is likely to occur at the contact portion, and it is difficult to increase the D dimension.
In order to solve these problems, as described in Patent Document 1, the present inventors use a belt guide member having a curved surface that protrudes and contacts the intermediate transfer belt portion 1A toward the transfer material P side as a counter roller. 3 is arranged and fixed on the upstream side to form an intermediate transfer belt portion P1 to suppress the occurrence of toner scattering, and the length of the transfer material portion 6 is made as small as possible to suppress the occurrence of white spots. Proposed to do.
JP 2002-82543 A

However, in the case of Patent Document 1, since the back surface of the endless intermediate transfer belt 1 is transferred while being constantly rubbed against the belt guide member to which the endless intermediate transfer belt 1 is fixed, abrasion powder due to wear on the back surface of the intermediate transfer belt 1 is generated. There is a problem that the transfer failure due to the generated abrasion powder adhering to the surface of the intermediate transfer belt 1 and the surface of the intermediate transfer belt to which the toner image is transferred due to the abrasion powder are scratched to cause image defects. It turned out to be.
The present invention has been made in view of the above circumstances, and provides an image forming apparatus capable of suppressing the occurrence of toner scattering and the occurrence of white spots and the wear of an image bearing belt. Objective.

  In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an endless image carrier belt that is stretched and driven by a plurality of rollers to form a toner image on the surface, and the image carrier belt through the image carrier belt. A transfer unit disposed opposite to one of the plurality of rollers and applying a transfer voltage having a polarity opposite to a toner charging polarity of a toner image formed on the surface of the image bearing belt, The toner image on the surface of the image carrier belt is transferred by applying the transfer voltage from the transfer unit onto a transfer material that moves between the transfer unit and the one roller while being in contact with the surface of the image carrier belt. In the image forming apparatus, the back surface of the image carrier belt portion on the upstream side in the transfer direction of the image carrier belt with respect to a region where the one roller and the transfer device are opposed to each other is pressed to place the image carrier belt portion on the transfer device. A belt guide member that protrudes toward the transfer material being transferred is fixedly arranged, an endless belt is stretched between the belt guide member and the one roller, and the endless belt is connected to the belt guide member. The one end roller is brought into contact with the back surface of the image carrying belt, and the endless belt is moved along with the transfer of the image carrying belt.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the endless belt has a volume resistance value of 10 ⁷ Ωcm to ^{10 10} Ωcm.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the endless belt has a flocked body formed on a surface in contact with the image carrying belt.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects of the present invention, the belt guide member includes a side of a transfer material that is transferring the image carrying belt portion to the transfer unit. It has a curved surface that curves in the direction of projecting to the side, and the curvature radius of the curved surface is set to 10 mm or more.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the curved surface of the belt guide member has a pressing surface for pressing the entire width of the image bearing belt.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image carrying belt is in close contact with the transfer material between the belt guide member and the transfer unit. And the length of the contact portion along the moving direction of the image carrying belt is set within 2 mm to 30 mm.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the transfer means is a transfer roller, and is formed on the surface of the image bearing belt on the transfer roller. The toner image on the surface of the image bearing belt is transferred onto the moving transfer material by applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the image carrying belt is an endless intermediate to which a toner image formed on the surface of the photoreceptor is primarily transferred. A transfer belt, wherein the transfer material is a recording medium.

  According to the present invention, the back surface of the image carrier belt portion on the upstream side in the moving direction of the image carrier belt with respect to the region where the one roller and the transfer device are opposed is pressed to place the image carrier belt portion on the transfer device. A belt guide member that protrudes toward the transfer material being transferred is fixedly disposed, an endless belt is stretched between the belt guide member and the one roller, and the endless belt is connected to the belt guide member. And one roller are brought into contact with the back surface of the image carrier belt and the endless belt is transferred along with the transfer of the image carrier belt, thereby suppressing the occurrence of toner scattering and white spots. It is possible to provide an image forming apparatus capable of suppressing the wear of the support belt.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a copying machine which is an image forming apparatus according to an embodiment of the present invention. In the figure, reference numeral 100 is a copying machine main body, 200 is a paper feed table on which it is placed, 300 is a scanner mounted on the copying machine main body 100, and 400 is an automatic document feeder (ADF) further mounted thereon.
The copying machine main body 100 is provided with an endless intermediate transfer belt 1 in the center. As shown in FIG. 1, the intermediate transfer belt 1 is stretched around a driving roller 14, a support roller 15, and a counter roller 16 in the illustrated example, and is rotated and transferred clockwise (in the direction of arrow A) in the drawing by driving rotation of the driving roller 14. It is possible. The counter roller 16 is provided with a toner scattering and white spot prevention mechanism 30 which will be described later. In the illustrated example, an intermediate transfer body cleaning device 17 is provided on the left side of the support roller 15 to remove residual toner remaining on the intermediate transfer belt 1 after the toner image is transferred to the recording medium sheet S. Further, on the intermediate transfer belt 1 stretched between the driving roller 14 and the support roller 15, an image forming unit 18B that forms toner images of four colors of black, cyan, magenta, and yellow along the conveying direction. The tandem image forming apparatus 20 is configured by arranging 18C, 18M, and 18Y side by side. An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.

  The image forming units 18B, 18C, 18M, and 18Y are provided with drum-shaped photoreceptors 40B, 40C, 40M, and 40Y, respectively, and around these photoreceptors 40B, 40C, 40M, and 40Y. A charging device 37 for uniformly charging the surface, developing devices 38B, 38C, 38M, and 38Y and a cleaning device 39 are provided. Then, electrostatic latent images based on image information corresponding to the respective colors are formed on the surfaces of the photoreceptors 40B, 40C, 40M, and 40Y thus charged by light rays from the exposure device 21, and these electrostatic images are formed. With respect to the latent image, the respective color toners are supplied from the developing devices 38B, 38C, 38M, and 38Y containing the respective color toners, and black and cyan are respectively applied to the respective photoreceptors 40B, 40C, 40M, and 40Y. , Magenta and yellow toner images are formed. The toner image thus formed is transferred onto the intermediate transfer belt 1 by applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image by the transfer roller 62. The toner on the photoreceptors 40B, 40C, 40M, and 40Y remaining after the toner image is transferred onto the intermediate transfer belt 1 in this manner is removed by the cleaning device 39, and a series of image forming steps is completed.

On the other hand, a secondary transfer device 22 is provided on the opposite side of the intermediate transfer belt 1 from the tandem image forming device 20. In the illustrated example, the secondary transfer device 22 is configured such that a secondary transfer belt 24 that is an endless belt is stretched around a driving roller 23 and a transfer roller 3. Then, the transfer roller 3 is pressed against the opposing roller 16 via the intermediate transfer belt 1, an endless belt 7 and a secondary transfer belt 24, which will be described later, and placed on the surface 1a (see FIG. 2) of the intermediate transfer belt 1. The toner image is transferred to a recording medium sheet S made of paper, plastic, or the like as a transfer material by applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image from the transfer roller 3.
A fixing device 25 for fixing the unfixed toner image transferred by the secondary transfer device 22 on the recording medium sheet S is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt. In the illustrated example, a recording medium sheet S is recorded under both the secondary transfer device 22 and the fixing device 25 so as to record a toner image on both surfaces of the recording medium sheet S in parallel with the tandem image forming apparatus 20 described above. Is provided with a sheet reversing device.

  Now, when making a copy using this color copying machine, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. When a start switch (not shown) is pressed, when a document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. Immediately drives the scanner 300 and travels through the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The light enters the reading sensor 36 and reads the contents of the original.

  When a start switch (not shown) is pressed, the drive roller 14 is driven to rotate by a drive motor (not shown), the support roller 15 is driven to rotate, and the intermediate transfer belt 1 is transported in the direction A for rotation. At the same time, with the image forming units 18B, 18C, 18M, and 18Y, as described above, the respective drum-shaped photoconductors 40B, 40C, 40M, and 40Y are rotated in the directions of the arrows, and the respective photoconductors 40B, 40C, 40M, and 40Y A monochrome toner image of black, cyan, magenta, and yellow is formed on each of them. Then, along with the transfer of the intermediate transfer belt 1, these single color toner images are transferred onto the surface of the intermediate transfer belt 1 by sequentially transferring a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the surface of the intermediate transfer belt 1. A synthetic color toner image is formed on the intermediate transfer belt 1.

On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the recording medium sheet S is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43. The paper is separated one by one by the separation roller 45 and put into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped. Alternatively, the sheet feeding roller 50 is rotated to feed out the recording medium sheets S on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped.
Then, the registration roller 49 is rotated in synchronization with the composite color toner image on the intermediate transfer belt 1, and the recording medium sheet S is fed between the intermediate transfer belt 1 and the secondary transfer device 22, and the secondary transfer device 22. And a color toner image is recorded on the recording medium sheet S. The recording medium sheet S after the transfer of the toner image is conveyed by the secondary transfer device 22 and sent to the fixing device 25, heated by the fixing belt 26 by the fixing device 25, and simultaneously pressed by the pressure roller 27 to be transferred toner. After fixing the image, the image is switched by the switching claw 55, discharged by the discharge roller 56, and stacked on the discharge tray 57. Alternatively, the recording medium sheet S is switched to the sheet reversing device 28 by switching with the switching claw 55, reversed there and led again to the position of the secondary transfer device 22, and after recording the toner image on the back surface, the discharge roller 56. Is discharged onto the discharge tray 57.
On the other hand, the intermediate transfer belt 1 after image transfer is removed by the intermediate transfer body cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 1 after the toner image is transferred to the recording medium sheet S. Prepare for image formation again.

  Here, in the secondary transfer device 22 according to the present embodiment, the toner scattering and white spot prevention mechanism 30 is employed in order to suppress the occurrence of the toner scattering and white spot described above. The toner scattering and white spot prevention mechanism 30 will be described with reference to FIGS. FIG. 2 is a diagram showing a schematic configuration of a toner scattering and white spot prevention mechanism according to an embodiment of the present invention, and FIG. 3 is a diagram showing a close contact between an intermediate transfer belt and a recording medium sheet S in the toner scattering and white spot prevention mechanism described later. FIG. 4 is a graph showing the relationship between the part distance D, the number of scattered toners, and the image loss occurrence rate, and FIG. 4 shows a schematic configuration of an endless belt used in a toner scattering and white spot prevention mechanism described later according to an embodiment of the present invention. It is sectional drawing shown.

  In the toner scattering and white spot prevention mechanism 30 according to the present embodiment, as clearly shown in FIG. 2, the counter roller 16 that stretches the intermediate transfer belt 1 and the transfer roller 3 that is an example of a transfer unit are intermediate-transferred. Opposing to each other via the belt 1. The intermediate transfer belt 1 in the transport direction (A direction) is more upstream than the pressure contact portion (nip portion) 5 that is in pressure contact with the opposing roller 16 via the transfer roller 3, the intermediate transfer belt 1, and an endless belt 7 described later. A belt guide member 8 that presses the back surface 1b of the intermediate transfer belt portion 1A through the endless belt 7 and projects the intermediate transfer belt portion 1A to the transfer roller 3 toward the recording medium sheet S is fixedly disposed. Yes. Accordingly, the intermediate transfer belt 1 is guided by the belt guide member 8 and is in close contact with the recording medium sheet S conveyed from the B direction by the intermediate transfer belt portion 1A to form the close contact portion 9. Thus, the toner scattering due to the influence of the transfer voltage from the transfer roller 3 can be suppressed.

Further, an endless belt 7 is stretched between the opposing roller 16 and the belt guide member 8, and the back surface 1 b of the intermediate transfer belt 1 is in pressure contact with the belt guide member 8 via the endless belt 7. It is pressed by the guide member 8. The endless belt 7 is rotated and transferred in the arrow J direction by the pressure contact between the opposing roller 16 rotating in the arrow E direction and the transfer roller 3 rotating in the arrow F direction as the intermediate transfer belt 1 is transferred. It has become. Accordingly, the back surface 1b of the intermediate transfer belt 1 comes into contact with the endless belt 7 transported at substantially the same speed, so that the back surface 1b of the intermediate transfer belt 1 can avoid sliding contact with the belt guide member 8. Thus, the generation of abrasion powder from the back surface of the intermediate transfer belt 1 by the belt guide member 8 can be suppressed. As a result, the occurrence of white spots due to wear powder, that is, the occurrence of missing images is suppressed.
The belt guide member 8 is composed of a plate-like member that is pressed across the entire width of the intermediate transfer belt 1 via the endless belt 7 and is made of a highly rigid material such as hard resin or metal. Yes. The guide member 8 is fixedly supported by a transfer unit frame (not shown), a frame of the image forming apparatus main body, or the like. Here, the back surface 1b of the intermediate transfer belt 1 is a surface opposite to the front surface 1a onto which the toner image is transferred.

As shown in FIG. 4, the endless belt 7 has a flocked body 7 b planted on the surface of the base material 7 a, and the flocked body 7 b comes into contact with the back surface 1 b of the intermediate transfer belt 1. Accordingly, the contact between the endless belt 7 and the back surface 1b of the intermediate transfer belt 1 is in a smooth state, and even if a deviation occurs between the transfer speed of the endless belt 7 and the transfer speed of the intermediate transfer belt 1. The endless belt 7 can prevent the back surface 1b of the intermediate transfer belt 1 from being worn. In this example, the resistance value of the endless belt 7 is set to a medium resistance (10 ⁷ Ωcm to ^{10 10} Ωcm). Since the endless belt 7 is a medium resistance belt member, it is possible to prevent the occurrence of an abnormal image due to the accumulation of electric charge on the endless belt 7. Further, since the resistance is not too low, it is possible to prevent a transfer failure due to the current escaping from the transfer roller 3 to the endless belt 7.

  By providing the endless belt 7 and the belt guide member 8 on the inlet side I of the press contact portion 5 as described above, the intermediate transfer belt portion 1A between the endless belt 7 and the press contact portion 5 is placed on the recording medium sheet S. The recording medium can be in a substantially parallel state with respect to the moving direction, and on the upstream side of the moving direction of the intermediate transfer belt 1 with respect to the pressing portion 5 where the opposing roller 16 and the transfer roller 3 are pressed when the toner image is transferred. The sheet S can begin to contact the surface of the intermediate transfer belt 1. In order to obtain such a contact timing between the recording medium sheet S and the intermediate transfer belt 1, the belt guide member 8 that is fixedly arranged is intermediate transfer on the upstream side in the moving direction of the intermediate transfer belt 1 with respect to the press contact portion 5. The back surface of the belt portion 1A is pressed so that the intermediate transfer belt portion protrudes toward the recording medium sheet S being transferred to the transfer roller 3. Further, in the present embodiment, the endless belt 7 is stretched around the opposing roller 16 and the belt guide member 8, whereby the aforementioned D dimension can be kept short. Since the endless belt 7 is stretched by at least the opposing roller 16 and the belt guide member 8, the endless belt 7 can be brought closer to the press contact portion 5, and the endless belt 7 is stretched to the opposing roller 16. Since the transfer is performed in a laid state, it is not necessary to provide resistance to the opposing roller 16 and the cost is reduced.

  With the above configuration, as in the case of the image forming apparatus shown in FIG. 6 described above, when the transfer material portion P1 that has reached the vicinity of the press contact portion 5 is charged based on the voltage applied to the transfer roller 3, that portion. Since P1 is in close contact with the surface of the intermediate transfer belt 1, even if the toner on the surface 1a of the intermediate transfer belt 1 is electrostatically transferred to the surface of the transfer material portion 8, it does not fly and transfer. . Alternatively, the amount of flying toner is extremely small. Thereby, the occurrence of toner scattering can be effectively suppressed and the image quality of the toner image transferred onto the recording medium sheet S can be improved. In addition, in the example shown in FIG. 6, since the above-described action is obtained by the guide roller 4, there is a transfer material portion 6 that does not adhere to the intermediate transfer belt 1 electrostatically and strongly as described above. However, in the example shown in FIGS. 1 and 2, the recording medium sheet S is brought into contact with the surface of the intermediate transfer belt 1 at an early stage by using a belt guide member 8 other than the guide roller 4 instead of the guide roller 4. Since it is configured, it is possible to eliminate the transfer material portion 6 that is not electrostatically strongly adhered to the intermediate transfer belt 1. Unlike the guide roller 7, the endless belt 7 and the belt guide member 8 can be substantially freely set in shape, size, or installation position thereof, so that the transfer is not electrostatically strongly adhered to the intermediate transfer belt 1. The distance D of the contact portion 9 where the recording medium sheet S adheres to the surface of the intermediate transfer belt 1 before reaching the press contact portion 5 can be set so that the material portion 6 does not exist. This suppresses the occurrence of toner image disturbance that has occurred in the case of the configuration shown in FIG. 6, and effectively eliminates the problem of image omission (so-called white omission) in the toner image transferred onto the recording medium sheet S. Can be suppressed.

  If the distance D is too long, image loss is likely to occur in the transferred toner image as in the image forming apparatus shown in FIG. 6, and conversely if the distance D is too short, the toner scatters. Is likely to occur. In FIG. 3, the vertical axis represents the number of scattered toner generated per 10 mm of the transferred full-color line toner image, and the vertical axis represents the occurrence rate of image omission in the transferred toner image. The axis is a graph showing the distance D of the contact portion. The solid line X represents the number of scattered toners corresponding to the distance D, and the chain line Y represents the image loss occurrence rate corresponding to the distance D. . As can be seen from this graph, the distance D along the intermediate transfer belt moving direction of the contact portion where the transfer material 4 is in close contact with the surface of the intermediate transfer belt 1 before reaching the press contact portion 5 is 2 mm or more and 30 mm or less, preferably 5 mm or more. It can be understood that when the thickness is 20 mm or less, both toner scattering and image omission are reduced, and the image quality of the toner image is improved.

As can be seen from FIG. 2, the belt guide member 8 has a circular arc shape in which a curved surface 8a is formed in a direction protruding toward the front surface side of the intermediate transfer belt 1, but the curvature radius of the curved surface 8a. R is set to 10 mm or more, preferably 15 mm or more. By setting the radius of curvature R to be large in this way, it is possible to prevent or suppress curling of the intermediate transfer belt 1 running while being guided by the endless belt 7, which is caused by curling of the intermediate transfer belt 1. The occurrence of uneven toner image transfer can be suppressed.
In addition, if the curved surface 8a of the belt guide member 8 that is in contact with the back surface of the endless belt 7 is subjected to a flocking treatment, a frictional force acting on the endless belt 7 and the belt guide member 8 is generated by the flocking. Thus, wear with time of the endless belt 7 and the belt guide member 8 can be effectively suppressed.
In this embodiment, the transfer roller 3 is used as a transfer unit, but a transfer charger such as a scorotron, an endless transfer belt, a transfer brush, or the like may be used. However, the transfer device may be a charger or a belt body.

1 is a cross-sectional view illustrating a schematic configuration of a copying machine that is an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a schematic configuration of a toner scattering and white spot prevention mechanism according to an embodiment of the present invention. FIG. 6 is a graph showing a relationship between a contact distance D between the intermediate transfer belt and the recording medium sheet S in the toner scattering and white spot prevention mechanism, the number of scattered toners, and an image missing rate. 1 is a cross-sectional view illustrating a schematic configuration of an endless belt used in a toner scattering and white spot prevention mechanism according to an embodiment of the present invention. FIG. 10 is a schematic diagram illustrating a configuration of a transfer unit of a conventional image forming apparatus. FIG. 10 is a schematic diagram illustrating a configuration of a transfer unit of an image forming apparatus according to another conventional embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt, 1A Intermediate transfer belt part, 2 Opposite roller, 3 Transfer roller, 4 Guide roller, 5 Pressure contact part, 6 Transfer material part, 7 Endless belt, 7b Hair transplant body, 8 Belt guide member, 8a Curved surface, DESCRIPTION OF SYMBOLS 9 Contact part, 14 Drive roller, 15 Support roller, 16 Opposed roller, 18B, 18C, 18M, 18Y Image forming means, 21 Exposure device, 22 Secondary transfer device, 25 Fixing device, 37 Charging device, 38B, 38C, 38M , 38Y Developing device, 39 Cleaning device, 40B, 40C, 40M, 40Y

Claims (8)

An endless image carrier belt that is stretched and driven by a plurality of rollers and forms a toner image on the surface thereof, and is disposed opposite to one of the plurality of rollers via the image carrier belt And a transfer means for applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the surface of the image carrying belt, while being in contact with the surface of the image carrying belt and the 1 In an image forming apparatus for transferring a toner image on the surface of an image bearing belt by applying the transfer voltage from the transfer unit onto a transfer material that moves between two rollers.
A transfer material that is moving the image carrier belt portion to the transfer device by pressing the back surface of the image carrier belt portion on the upstream side in the transfer direction of the image carrier belt relative to a region where the one roller and the transfer device are opposed to each other The belt guide member that protrudes toward the side is fixedly arranged,
An endless belt is stretched between the belt guide member and the one roller, and the endless belt is brought into contact with the back surface of the image carrying belt by the belt guide member and the one roller. An image forming apparatus, wherein the endless belt is transferred along with the transfer of the image carrying belt. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the endless belt has a volume resistance value of 10 ⁷ Ωcm to ^{10 10} Ωcm. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the endless belt has a flocked body formed on a surface in contact with the image carrying belt. The image forming apparatus according to any one of claims 1 to 3,
The belt guide member has a curved surface that curves in a direction in which the image carrying belt portion protrudes toward the transfer material being transferred to the transfer means, and the curvature radius of the curved surface is set to 10 mm or more. An image forming apparatus. The image forming apparatus according to claim 4.
The image forming apparatus according to claim 1, wherein the curved surface of the belt guide member has a pressing surface for pressing the entire width of the image carrying belt. The image forming apparatus according to claim 1,
The image carrying belt has a close contact portion that is in close contact with the transfer material between the belt guide member and the transfer unit, and a length along the moving direction of the image carrying belt of the close contact portion is within 2 mm to 30 mm. An image forming apparatus that is set. The image forming apparatus according to claim 1,
The transfer means is a transfer roller, and an image on the moving transfer material is applied to the transfer roller by applying a transfer voltage having a polarity opposite to the toner charge polarity of the toner image formed on the surface of the image bearing belt. An image forming apparatus for transferring a toner image on a surface of a carrier belt. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the image carrying belt is an endless intermediate transfer belt onto which a toner image formed on the surface of a photoreceptor is primarily transferred, and the transfer material is a recording medium.

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