JP2024017053A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can prevent the generation of toner dust.SOLUTION: A driving roller 14 for driving an intermediate transfer belt 110 is arranged between a primary transfer nip for the K color and a secondary transfer nip in a surface movement direction of the intermediate transfer belt 110, and a fourth driven roller 13d rotated following the intermediate transfer belt 110 is arranged between the primary transfer nip for the K color and the driving roller 14 in the surface movement direction of the intermediate transfer belt 110. The diameter of the fourth driven roller 13d is equal to or more than the diameter of the driving roller 14.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus.

Conventionally, an intermediate transfer belt contacts an image carrier to form a primary transfer nip where the toner image on the image carrier is primarily transferred, and an intermediate transfer belt contacts the intermediate transfer belt to transfer the toner image on the intermediate transfer belt to a recording medium. A drive roller that drives the intermediate transfer belt is arranged between the primary transfer nip and the secondary transfer nip, and a drive roller that drives the intermediate transfer belt is provided between the primary transfer nip and the secondary transfer nip. Until now, there has been known an image forming apparatus in which a driven roller that rotates as a result of an intermediate transfer belt is disposed.

Patent Document 1 discloses that in the above-mentioned image forming apparatus, an intermediate transfer belt sequentially contacts a plurality of image carriers to form a primary transfer nip, and among the plurality of primary transfer nips, the intermediate transfer belt contacts the plurality of image carriers in sequence, and the intermediate transfer belt contacts the plurality of image bearing members sequentially to form a primary transfer nip. It is described that the diameter of the driven roller disposed between the downstream primary transfer nip and the drive roller is smaller than the diameter of the drive roller.

However, there is a risk that so-called toner dust, in which toner scatters, may occur in the area where the intermediate transfer belt wraps around the driven roller.

In order to solve the above-mentioned problems, the present invention provides an intermediate transfer belt that contacts an image carrier to form a primary transfer nip in which a toner image on the image carrier is primarily transferred; and a secondary transfer member forming a secondary transfer nip for secondarily transferring the toner image on the intermediate transfer belt to a recording medium, the secondary transfer member forming a secondary transfer nip for secondarily transferring the toner image on the intermediate transfer belt to a recording medium, and A drive roller that drives the intermediate transfer belt is disposed between the primary transfer nip and the drive roller, and the intermediate transfer belt is driven in the direction of surface movement of the intermediate transfer belt between the primary transfer nip and the drive roller. The image forming apparatus is provided with a rotating driven roller, characterized in that the diameter of the driven roller is greater than or equal to the diameter of the drive roller.

According to the present invention, it is possible to suppress the occurrence of toner dust.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a schematic diagram of main parts of an intermediate transfer unit. FIG. 7 is a diagram showing the state of the intermediate transfer unit in monochrome mode. FIG. 3 is a diagram showing the state of the intermediate transfer unit in full color mode. FIG. 7 is a diagram showing the state of the intermediate transfer unit in full color special color mode. FIG. 7 is a diagram showing the state of the intermediate transfer unit in special color mode. This is a model of the force involved in the toner on the intermediate transfer belt after primary transfer. FIG. 7 is a diagram showing the relationship between the diameter of the fourth driven roller and the centrifugal force applied to the toner on the intermediate transfer belt. FIG. 7 is a diagram illustrating the state of the toner on the intermediate transfer belt when it passes through the area where it wraps around the fourth driven roller. FIG. 3 is a schematic diagram of the main parts of an intermediate transfer unit in which the diameter of the entrance roller is larger than the diameter of the drive roller.

An embodiment of an image forming apparatus to which the present invention is applied will be described below.
FIG. 1 is a schematic configuration diagram of an image forming apparatus 100 according to this embodiment.
This image forming apparatus includes an image forming section 400 as an image forming means, a feeding section 500 on which the image forming section 400 is placed, a scanner 350 fixed on the image forming section 400, and the like. The scanner 350 also includes an automatic document feeder 600 (hereinafter referred to as ADF) fixed above the scanner 350, an operation display section 700 consisting of a touch panel and various keys, and the like.

The image forming unit 400 includes five image forming units 18S, 18Y, and 18Y for forming toner images of special colors (S), yellow (Y), magenta (M), cyan (C), and black (K). The image forming unit 20 includes 18M, 18C, and 18K. The subscripts S, Y, M, C, and K added after the numbers in each code indicate members for special colors, yellow, cyan, magenta, and black (the same applies hereinafter). The special color is a general term for colors different from any of Y, M, C, and K, and includes, for example, white, transparent, and the like.

In the image forming section 400, in addition to the image forming units 18S, 18Y, 18M, 18C, and 18K, there are an optical writing unit 21, an intermediate transfer unit 17, a secondary transfer unit 22, a pair of registration rollers 49, and a belt fixing system. A fixing device 25 and the like are provided.

The optical writing unit 21 includes a light source, a polygon mirror, an f-theta lens, a reflection mirror, etc., and emits laser light onto the surfaces of the photoreceptors 1S, 1Y, 1M, 1C, and 1K, which are image carriers, based on image data. irradiate.

The image forming units 18S, 18Y, 18M, 18C, and 18K have drum-shaped photoreceptors 1S, 1Y, 1M, 1C, and 1K, as well as a charger, a developing device, a drum cleaning device, a static eliminator, and the like. .

The image forming units 18S, 18Y, 18M, 18C, and 18K for S, Y, M, C, and K have substantially the same configuration as each other, except that they use different toner colors. The image forming unit 18S for S (special color) among each color will be described below.

The surface of the photoreceptor 1S is uniformly charged by a charger serving as a charging means. A laser beam modulated and deflected by the optical writing unit 21 is irradiated onto the surface of the photoreceptor 1S that has been subjected to the charging process. Then, the potential of the irradiation section (exposed section) is attenuated. Due to this attenuation, an electrostatic latent image for S is formed on the surface of the photoreceptor 1S. The formed electrostatic latent image for S is developed by a developing device serving as a developing means to become an S toner image.

The S toner image formed on the S photoreceptor 1S is primarily transferred to the intermediate transfer belt 110. After the primary transfer, the surface of the photoreceptor 1S is cleaned of residual toner by a drum cleaning device.

In the image forming unit 18S for S, the photoreceptor 1S cleaned by the drum cleaning device is neutralized by a static eliminator. Then, it is uniformly charged by a charger and returns to its initial state. The series of processes described above is the same for the other image forming units (18Y, 18M, 18C, 18K).

The intermediate transfer unit 17 includes an intermediate transfer belt 110, a belt cleaning device 90, and the like. The endless intermediate transfer belt 110 is stretched under tension by a plurality of tension rollers such as a drive roller 14 and a secondary transfer opposing roller 16 disposed inside the loop. The rotation of the drive roller 14 driven by the belt drive motor causes endless movement in the clockwise direction in the figure.

The primary transfer rollers 62S, 62Y, 62M, 62C, and 62K for S, Y, M, C, and K are arranged so as to be in contact with the inner peripheral surface of the intermediate transfer belt 110, and are used to transfer the primary transfer output from the power source. Bias is applied. Further, the intermediate transfer belt 110 is pressed from its inner peripheral surface toward the photoreceptors 1S, 1Y, 1M, 1C, and 1K. This pressing causes the front surface of the intermediate transfer belt 110 to come into contact with the photoreceptors 1S, 1Y, 1M, 1C, and 1K for S, Y, M, C, and K. A primary transfer nip is formed for this purpose.

In the primary transfer nip for S, Y, M, C, and K, due to the influence of the primary transfer bias, the photoreceptors 1S, 1Y, 1M, 1C, and 1K and the primary transfer rollers 62S, 62Y, 62M, 62C, and 62K A primary transfer electric field is formed during this period.

The S toner image formed on the S photoreceptor 1S is primarily transferred onto the intermediate transfer belt 110 under the influence of the primary transfer electric field and nip pressure in the S primary transfer nip. On this S toner image, Y toner images, M toner images, C toner images, and K toner images formed on photoreceptors 1Y, 1M, 1C, and 1K for Y, M, C, and K are sequentially superimposed. Primary transfer is performed together. By this overlapping primary transfer, a multicolor toner image is formed on the intermediate transfer belt 110.

The multicolor toner images superimposed and transferred onto the intermediate transfer belt 110 are secondarily transferred onto a sheet material P, which is a recording medium, at a secondary transfer nip, which will be described later. Transfer residual toner remaining on the surface of the intermediate transfer belt 110 after passing through the secondary transfer nip is cleaned by a belt cleaning device 90 that sandwiches the belt between it and the drive roller 14 on the left side in the figure.

A secondary transfer unit 22 disposed below the intermediate transfer unit 17 in the figure brings a secondary transfer roller 23, which is a secondary transfer member, into contact with a portion of the intermediate transfer belt 110 that is wrapped around the secondary transfer opposing roller 16. A secondary transfer nip is formed. A secondary transfer bias having the same polarity as the toner is applied to the secondary transfer opposing roller 16, while the secondary transfer roller 23 is grounded. As a result, a secondary transfer electric field is formed in the secondary transfer nip that electrostatically moves the multicolor toner image on the intermediate transfer belt 110 from the belt side toward the secondary transfer roller 23 side. The sheet material P, which is fed into the secondary transfer nip by the registration roller pair 49 in synchronization with the multicolor toner image on the intermediate transfer belt 110, contains multicolor toner that has been affected by the secondary transfer electric field and nip pressure. The image is secondarily transferred.

The feeding section 500 on which the image forming section 400 is mounted is provided with a feeding cassette 501 and a sheet bank 502 that accommodate a plurality of sheet materials P stacked in a sheet bundle. In the feeding cassette 501 and the sheet bank 502, a feeding roller 503 is pressed against the topmost sheet material P of the sheet bundle. Then, by rotating the feeding roller 503, the uppermost sheet material P is sent out toward the feeding path 504.

A feeding path 504 that receives the sheet material P sent out from the feeding cassette 501 or the sheet bank 502 includes a plurality of pairs of conveying rollers 505. The feeding path 504 of the feeding section 500 communicates with the feeding path 41 of the image forming section 400 . A pair of registration rollers 49 is provided near the end of the feeding path 41 of the image forming section 400 . The sheet material P transferred from the feeding path 504 of the feeding section 500 to the feeding path 41 of the copying machine has its leading end sandwiched between the rollers of the registration roller pair 49.

On the other hand, in the intermediate transfer unit 17, the multicolor toner image formed on the intermediate transfer belt 110 enters the secondary transfer nip as the belt moves endlessly. The registration roller pair 49 sends out the sheet material P sandwiched between the rollers at a timing that allows the sheet material P to be brought into close contact with the multicolor toner image at the secondary transfer nip. As a result, the multicolor toner image on the intermediate transfer belt 110 comes into close contact with the sheet material P in the secondary transfer nip. Then, the image is secondarily transferred onto the surface of the sheet material P, resulting in a full-color image on the white sheet material P. The sheet material P on which the full-color image has been formed in this manner exits the secondary transfer nip as the secondary transfer roller 23 is rotated, and then passes through a sheet conveyance unit equipped with a conveyance belt to the fixing device 25. sent to.

The fixing device 25 includes a belt unit that moves the fixing belt 26 endlessly while being stretched between two rollers, and a pressure roller 27 that is pressed against one of the rollers of the belt unit. The fixing belt 26 and the pressure roller 27 come into contact with each other to form a fixing nip, and the sheet material received from the sheet conveying unit is sandwiched in the fixing nip. Of the two rollers in the belt unit, the roller pressed by the pressure roller 27 has an internal heat source, and presses the fixing belt 26 by the heat generated by this roller. The pressurized fixing belt 26 heats the sheet material sandwiched in the fixing nip. A full color image is fixed on the sheet material P under the influence of this heating and nip pressure.

The sheet material P subjected to the fixing process in the fixing device 25 is either discharged from the image forming section 400 or returned to the secondary transfer nip in order to form a toner image on the other side as well.

When a copy of an original is to be made, for example, a stack of sheet originals is set on the original table 601 of the ADF 600. However, if the original is a one-sided bound original that is closed like a book, it is set on the contact glass 351 of the scanner 350. Prior to this setting, the ADF 600 is opened to the main body of the image forming section 400, and the contact glass 351 of the scanner 350 is exposed. After this, the single-stitched original is held down by the closed ADF 600.

After the original is set in this manner, when the copy start switch on the operation display section 700 is pressed, the original reading operation by the scanner 350 is started. However, when a sheet original is set in the ADF 600, the ADF 600 automatically transports the sheet original onto the contact glass 351 prior to this original reading operation.

In the document reading operation, both the first traveling body 352 and the second traveling body 353 of the scanner 350 start running, and light is emitted from the light source provided on the first traveling body 352. Then, the reflected light from the document surface is reflected by a mirror provided in the second traveling body 353, passes through an imaging lens 354, and then enters a reading sensor 355. The reading sensor 355 constructs image information based on the incident light.

In parallel with such document reading operation, each device in each image forming unit (18S, 18Y, 18M, 18C, 18K), intermediate transfer unit 17, secondary transfer unit 22, and fixing device 25 are driven. Start. Then, the optical writing unit 21 is driven and controlled based on the image information constructed by the reading sensor 355, and electrostatic latent images are formed on the photoreceptors 1S, 1Y, 1M, 1C, and 1K. After the electrostatic latent images for S, Y, M, C, and K are developed into S toner images, Y toner images, M toner images, C toner images, and K toner images, they are superimposed on the intermediate transfer belt 110. They are combined and primary transferred to form a multicolor toner image.

Almost simultaneously with the start of the document reading operation, a feeding operation is started within the feeding section 500. In this feeding operation, one of the feeding rollers 503 is selectively rotated, and the sheet material P is sent out from the sheet bank 502 or the feeding cassette 501. The sent-out sheet material P is separated one by one by a separation roller 506 and enters a feeding path 504, and is then transported by a pair of transport rollers 505 toward a feeding path 41 of an image forming section 400.

A control unit 200 including a CPU and the like that controls each device within the image forming unit 400 is disposed within the housing of the image forming unit 400. The operator sends a command to the control unit 200 through a key input operation on the operation display unit 700 to select the single-sided print mode, which is a mode in which an image is formed on only one side of the sheet material P, or the mode in which images are formed on both sides of the sheet material P. You can specify the duplex print mode, etc.

In recent years, in addition to plain paper, which has conventionally been widely used as sheet material P, special paper having an uneven design on its surface and special sheet material P used for thermal transfer such as iron printing are increasingly being used. When such special paper is used, transfer defects are more likely to occur when the toner image on the intermediate transfer belt 110, in which color toners are superimposed, is secondarily transferred to the paper than in the case of conventional plain paper.

Therefore, in this embodiment, the intermediate transfer belt 110 is configured to have a base layer made of resin and an elastic layer made of an elastic member such as elastic rubber or elastomer. By providing the intermediate transfer belt 110 with an elastic layer having low hardness, it can be deformed against a toner layer or a sheet material with poor smoothness in the secondary transfer nip. Thereby, the surface of the intermediate transfer belt 110 can be deformed to follow local irregularities. Therefore, good adhesion can be obtained without excessively increasing the secondary transfer pressure to the toner layer, there is no hollow transfer of characters, and there is no transfer unevenness even on sheet material P with poor smoothness. Transfer images with excellent uniformity can be obtained.

The base layer of the intermediate transfer belt 110 is provided to prevent the intermediate transfer belt 110 from elongating, and it is preferable to use a resin with little elongation.

FIG. 2 is a schematic diagram of the main parts of the intermediate transfer unit 17.
The intermediate transfer belt 110 is stretched by a drive roller 14, a support roller 15, a secondary transfer opposing roller 16, a tension roller 12, and the like. The tension roller 12 is in contact with the outer peripheral surface of the intermediate transfer belt 110 to apply tension to the intermediate transfer belt 110. Five primary transfer rollers 62S, 62Y, 62M, 62C, and 62K, the cleaning opposing roller 11, and the entrance roller 4 are in contact with the inner peripheral surface of the intermediate transfer belt. The entrance roller 4 is disposed near the secondary transfer counter roller 16 on the upstream side in the surface movement direction of the intermediate transfer belt 110 . The entrance roller 4 allows the intermediate transfer belt 110 to contact the secondary transfer roller 23 at a pre-nip region upstream in the surface movement direction of the intermediate transfer belt 110 from the area where the intermediate transfer belt 110 wraps around the secondary transfer counter roller 16 . is formed.

The drive roller 14 is disposed between the K color primary transfer nip and the secondary transfer nip in the surface movement direction of the intermediate transfer belt 110. As a result, the region of the intermediate transfer belt 110 where the plurality of primary transfer nips are formed between the support roller 15 and the drive roller 14 is brought into a tensile state and can be maintained in a taut state. Thereby, it is possible to suppress changes in the contact state of the intermediate transfer belt 110 with the photoreceptor, and it is possible to satisfactorily suppress the occurrence of color misregistration.

Furthermore, first to fourth driven rollers 13a, 13b, 13c, and 13d are in contact with the inner peripheral surface of the intermediate transfer belt 110. The first driven roller 13a is arranged between the support roller 15 and the special color primary transfer roller 62S. The second driven roller 13b is arranged between the primary transfer roller 62S for special color and the primary transfer roller 62Y for Y color. The third driven roller 13c is arranged between the primary transfer roller 62C for C color and the primary transfer roller 62K for K color. The fourth driven roller 13d is arranged between the primary transfer roller 62K for K color and the drive roller 14.

The diameter of the fourth driven roller 13d is greater than or equal to the diameter of the drive roller 14, and is larger than the other driven rollers 13a, 13b, and 13c. The diameter of the drive roller 14 is approximately Φ30 to Φ50 mm depending on the photoconductor arrangement pitch, layout, lifespan, etc. Further, the support roller 15 and the drive roller 14 are arranged below the position of the primary transfer nip of each color so that the intermediate transfer belt 110 is well separated from the photoreceptor of each color by the separation operation by each separation mechanism described later. ing.

The vertical position of the primary transfer nip for each color, which is formed when the photoreceptors 1S, 1Y, 1M, 1C, and 1K are in contact with the front surface of the intermediate transfer belt 110, is the same, and the first driven roller 13a The intermediate transfer belt 110 is horizontal from the fourth driven roller 13d to the fourth driven roller 13d.

Further, the intermediate transfer unit 17 includes four separating mechanisms 201, 202, 203, and 204 for separating the intermediate transfer belt 110 from the photoreceptor. The first separation mechanism 201 rotatably holds the first driven roller 13a and the primary transfer roller 62S for special color, and lowers the first driven roller 13a and the primary transfer roller 62S for special color to transfer the intermediate transfer belt 110 to the special color. the photoreceptor 1S for use.

The second separation mechanism 202 rotatably holds the second driven roller 13b, and lowers the second driven roller 13b in a monochrome mode, which will be described later.
The third separation mechanism 203 rotatably holds primary transfer rollers 62Y, 62M, and 62C for Y, M, and C colors, and lowers these primary transfer rollers 62Y, 62M, and 62C to transfer the intermediate transfer belt 110 to the photoreceptor. Separate from 1Y, 1M, and 1C.

The fourth separating mechanism 204 rotatably holds the third driven roller 13c, the primary transfer roller 62K for K, and the fourth driven roller 13d, and lowers these rollers 13c, 62K, and 13d to transfer the intermediate transfer belt 110 to the photoreceptor. Separate from 1K.

Each spacing mechanism 201 , 202 , 203 , 204 is connected to the control section 200 . The control unit 200 controls the separation mechanisms 201, 202, 203, and 204 according to the image forming mode to separate the intermediate transfer belt 110 from a predetermined photoreceptor.
In this embodiment, the image forming modes include a monochrome mode, a full color mode, a special color full color mode, and a special color mode.

FIG. 3 is a diagram showing the state of the intermediate transfer unit 17 in monochrome mode.
The monochrome mode is a mode in which only a K color toner image is formed, and a monochrome image is formed on the sheet material. As shown in FIG. 3, in the monochrome mode, the first and second driven rollers 13a, 13b and the primary transfer rollers 62S, 62Y, 62C, 62M are lowered from the reference positions shown in FIG. 2. Specifically, the control unit 200 controls the first to third separation mechanisms 201, 202, 203 to move the first and second driven rollers 13a, 13b and the primary transfer rollers 62S, 62Y, 62C, 62M. It is lowered from the reference position shown in FIG.

Since the support roller 15 is arranged below the position of the primary transfer nip, by lowering the primary transfer rollers 62S, 62Y, 62C, 62M and the first and second driven rollers 13a, 13b, the intermediate transfer belt 110 is separated from the photoreceptors 1S, 1Y, 1M, and 1C. As a result, in the monochrome mode, only the K color photoreceptor 1K comes into contact with the front surface of the intermediate transfer belt 110. Further, at this time, the third driven roller 13c and the fourth driven roller 13d are located at the reference position, and the space between the third driven roller 13c and the fourth driven roller 13d of the intermediate transfer belt 110 is horizontal. maintained in condition. This can prevent the contact state between the photoreceptor 1K and the intermediate transfer belt 110 from changing during the monochrome mode, and the K color toner image on the photoreceptor can be primary transferred onto the intermediate transfer belt 110 in a good manner. .

FIG. 4 is a diagram showing the state of the intermediate transfer unit 17 in full color mode.
The full color mode is a mode in which Y, M, C, and K toner images are superimposed on an intermediate transfer belt to form a full color image on a sheet material.
As shown in FIG. 4, in the full color mode, the control unit 200 controls the first separation mechanism 201 to lower the first driven roller 13a and the special color primary transfer roller 62S. As a result, only the special color photoreceptor 1S is separated from the intermediate transfer belt 110. In addition, in FIG. 4, the third driven roller 13c is positioned at the same height as the primary transfer nip, and the third driven roller 13c is in contact with the intermediate transfer belt 110, but the third driven roller 13c is in the lowered position. The intermediate transfer belt 110 may be located at a distance from the intermediate transfer belt 110.

In this embodiment, the second driven roller 13b is arranged between the primary transfer roller 62S for special color and the primary transfer roller 62Y for Y, and in the full color mode, the second driven roller 13b is positioned at the reference position. let As a result, when the intermediate transfer belt 110 is separated from the special color photoreceptor 1S, the portion of the intermediate transfer belt 110 from the second driven roller 13b to the fourth driven roller 13d is maintained in a horizontal state. As a result, it is possible to prevent the contact state between the photoreceptors 1Y, 1M, 1C, 1K and the intermediate transfer belt 110 from changing during the full color mode, and toner images on each of the photoreceptors 1Y, 1M, 1C, 1K can be properly transferred. The image can be primarily transferred onto the intermediate transfer belt 110.

FIG. 5 is a diagram showing the state of the intermediate transfer unit 17 in the full color special color mode.
The full-color special color mode is a mode in which a special color S toner image and Y, M, C, and K toner images are superimposed on an intermediate transfer belt to form a special color image and a full color image on a sheet material.
As shown in FIG. 5, in the full color special color mode, all the driven rollers 13a to 13d and all the primary transfer rollers 62S to 62K are located at the reference position, and the intermediate transfer belt 110 is moved between all the photoreceptors 1S, 1Y, Bring it into contact with 1M, 1C, and 1K. At this time, the space between the first driven roller 13a and the fourth driven roller 13d of the intermediate transfer belt 110 is maintained in a horizontal state. Therefore, it is possible to prevent the contact state between the photoreceptors 1S, 1Y, 1M, 1C, 1K and the intermediate transfer belt 110 from changing during the full-color special color mode, and the contact state of each photoreceptor 1S, 1Y, 1M, 1C, 1K can be prevented from changing. can be primarily transferred to the intermediate transfer belt 110.
Note that in the full color special color mode, the second driven roller 13b and the third driven roller 13c may be positioned at the lowered position and separated from the intermediate transfer belt 110.

FIG. 6 is a diagram showing the state of the intermediate transfer unit 17 in the special color mode.
The special color mode is a mode in which only a special color toner image is formed, and a special color image is formed on a sheet material.
As shown in FIG. 6, in the special color mode, the control unit 200 controls the third separation mechanism 203 and the fourth separation mechanism 204, and controls the third and fourth driven rollers 13c, 13d, the primary transfer roller 62Y, Lower 62M, 62C, and 62K from their standard positions. The drive roller 14 is arranged below the position of the primary transfer nip. Therefore, by lowering the primary transfer rollers 62Y, 62M, 62C, 62K and the third and fourth driven rollers 13c, 13d, the intermediate transfer belt 110 is separated from the photoreceptors 1Y, 1M, 1C, 1K, and the special color is exposed. Only the body 1S can be brought into contact with the intermediate transfer belt 110.

Further, the first driven roller 13a and the second driven roller 13b are located at a reference position, and the space between the first driven roller 13a and the second driven roller 13b of the intermediate transfer belt 110 is in a horizontal state. maintained. Thereby, it is possible to prevent the contact state between the photoreceptor 1S and the intermediate transfer belt 110 from changing during the special color mode, and it is possible to primary transfer the special color toner image on the photoreceptor to the intermediate transfer belt 110 in a good manner.

In this manner, in this embodiment, by providing the first to fourth driven rollers 13a to 13d, it is possible to prevent the contact state between the intermediate transfer belt 110 and the photoreceptor from changing depending on the image forming mode. As a result, the toner image on the photoreceptor can be primarily transferred onto the intermediate transfer belt 110 in any image forming mode.

In this embodiment, the drive roller 14 is arranged below the position of the primary transfer nip. As a result, when the third and fourth driven rollers 13c, 13d and the primary transfer rollers 62Y, 62M, 62C, 62K are lowered from their reference positions in the special color mode, the intermediate transfer belt 110 moves the photoreceptors 1Y, 1M, Separate from 1C and 1K. In this way, since the drive roller 14 is arranged below the position of the primary transfer nip, when the fourth driven roller 13d is located at the reference position, the intermediate transfer belt 110 is moved to the fourth driven roller 13d. Wrap around. Therefore, in image forming modes other than the special color mode, the toner image on the intermediate transfer belt passes through the area of the intermediate transfer belt 110 wrapped around the fourth driven roller 13d.

Conventionally, the fourth driven roller 13d had the same diameter as the other driven rollers 13a to 13c, and was smaller than the diameter of the drive roller 14. In this conventional configuration, so-called toner dust, in which the toner on the intermediate transfer belt is scattered, may occur in the area where the intermediate transfer belt 110 is wrapped around the fourth driven roller 13d. Toner dust in the area wrapped around the fourth driven roller 13d was particularly noticeable in images with a large amount of toner adhesion due to edge effects, such as characters and lines made of toner of two or more colors. The problem was also noticeable even when the intermediate transfer belt 110 was an elastic intermediate transfer belt having an elastic layer.

On the other hand, the intermediate transfer belt 110 also wraps around the drive roller 14, and in the area where it wraps around the drive roller 14, the occurrence of toner dust was suppressed to a non-problematic level.

As a result of intensive research by the present inventors, it has been found that toner dust in the area where the toner is wrapped around the fourth driven roller 13d occurs due to the following mechanism.

Figure 7 is a model of the forces that are involved in the toner on the intermediate transfer belt after primary transfer, and arrows A to E in the figure indicate the forces that are involved in the toner and the directions of the forces that are applied to the toner. .
Arrow A in the figure indicates electrostatic repulsion between negatively charged toner particles. This electrostatic repulsive force between toners increases as the amount of toner adhesion increases, and for characters and line images of two or more colors, the amount of toner adhesion increases due to the edge effect, so the electrostatic repulsion force between toners increases. becomes larger.

Arrow B in the figure indicates electrostatic attraction force to the intermediate transfer belt 110. This electrostatic attraction force is generated when the intermediate transfer belt 110 is electrostatically separated by the primary transfer electric field at the primary transfer nip, and the front surface of the intermediate transfer belt is positively charged. Since the positive potential on the front surface of the intermediate transfer belt 110 gradually decreases after the primary transfer, the electrostatic attraction force gradually decreases after the primary transfer.

Arrow C in the figure indicates the adhesion force between the toners due to intermolecular force between the toners. Further, arrow D in the figure indicates an electrostatic repulsive force generated by negative discharge charges on the intermediate transfer belt due to discharge at the exit of the primary transfer nip. Since the discharge charge gradually decreases after the primary transfer, the electrostatic repulsive force due to the discharge charge gradually decreases. Arrow E in the figure represents the frictional force between the toners.

As shown by arrows A and D in the figure, the electrostatic repulsive force between the toners and the electrostatic repulsive force due to discharged charges are forces that tend to scatter the toner on the intermediate transfer belt. On the other hand, the electrostatic attraction force to the intermediate transfer belt shown by arrow B in the figure, the adhesion force between toners shown by arrow C in the figure, and the frictional force between toners shown by arrow E in the figure keep the toner on the intermediate transfer belt. It is power. In the area of the intermediate transfer belt 110 that is not wrapped around the roller, (repulsive force between toners + repulsive force due to discharged charge) < (electrostatic attraction force to the intermediate transfer belt + adhesion force between toners + frictional force between toners) meets the relationship. As a result, the toner on the intermediate transfer belt does not scatter, and toner dust does not occur.

However, in the area where the intermediate transfer belt 110 wraps around the fourth driven roller 13d, the following force that tends to scatter the toner is generated. As a result, the force that holds the toner on the intermediate transfer belt is exceeded, and toner dust occurs. Specifically, when the toner image on the intermediate transfer belt 110 passes through the area where it wraps around the fourth driven roller 13d, centrifugal force acts on the toner. This centrifugal force acts as a force that tends to scatter the toner on the intermediate transfer belt. Therefore, in the area where the intermediate transfer belt 110 wraps around the fourth driven roller 13d, the force that tries to scatter the toner on the intermediate transfer belt is (toner repulsion force + repulsion force due to discharged charge + centrifugal force). Become.

The centrifugal force F is expressed as F, where V is the moving speed of the front surface of the intermediate transfer belt 110 in the area where it wraps around the fourth driven roller 13d, m is the mass of the toner, and r is the radius of the fourth driven roller 13d. =(mV ² )/r. As can be seen from this equation, the smaller the radius r of the fourth driven roller 13d, the greater the centrifugal force applied to the toner. Therefore, if the radius of the fourth driven roller 13d is small, (repulsive force between toners + repulsive force due to discharged charges + centrifugal force) > (electrostatic attraction force to the intermediate transfer belt + adhesion force between toners + friction between toners) force), which may cause toner dust.

FIG. 8 is a diagram showing the relationship between the diameter of the fourth driven roller 13d and the centrifugal force applied to the toner on the intermediate transfer belt.
As shown in FIG. 8, it can be seen that when the diameter of the fourth driven roller 13d is 20 mm as a reference, the larger the diameter of the fourth driven roller 13d, the lower the centrifugal force applied to the toner. From this, the larger the diameter of the fourth driven roller 13d, the more the centrifugal force applied to the toner while passing through the area where it wraps around the fourth driven roller 13d can be reduced, and the toner dust can be suppressed.

Furthermore, in the area where the intermediate transfer belt 110 wraps around the fourth driven roller 13d, the intermediate transfer belt 110 is bent following the curvature of the fourth driven roller 13d, and the front surface of the intermediate transfer belt 110 is extended. As a result, as shown in FIG. 9, a gap S is created between the toner particles adjacent to each other in the surface movement direction of the intermediate transfer belt 110 in the area where the toner particles are wrapped around the fourth driven roller 13d. Therefore, the toner in the upper layer enters the gap S between the toner in the lower layer. When the intermediate transfer belt 110 passes through the area where it wraps around the fourth driven roller 13d, the front surface of the intermediate transfer belt 110 returns to its extension and comes into contact again with the toner adjacent to the surface of the intermediate transfer belt 110 in the moving direction ( gap closes). At this time, a force is generated that pushes the upper layer toner that has entered between the lower layer toners in a direction away from the intermediate transfer belt 110. This pushing force also acts as a force that tends to scatter the toner on the intermediate transfer belt.

The smaller the diameter of the fourth driven roller 13d, the greater the bending of the intermediate transfer belt 110 in the area where it wraps around the fourth driven roller 13d, and the greater the extension of the front surface. Therefore, the toner in the upper layer deeply enters the gap S between the toners in the lower layer. Therefore, when the toner passes through the wrapping area and the front surface of the intermediate transfer belt 110 returns to its original elongation, the force that pushes the upper layer toner away from the intermediate transfer belt 110 becomes stronger. As a result, the force that tries to scatter the toner in the upper layer on the intermediate transfer belt from the intermediate transfer belt 110 exceeds the force that tries to keep it on the intermediate transfer belt 110, and toner dust may occur.

In particular, since the intermediate transfer belt 110 having an elastic layer is thick, the front surface of the intermediate transfer belt stretches a large amount in the area where it wraps around the fourth driven roller 13d. As a result, the toner in the upper layer deeply enters the gap between the toner in the lower layer, and when the surface elongation returns, the force pushing out the toner in the upper layer becomes stronger, making it easier to cause toner dust.

As described above, when the diameter of the fourth driven roller 13d is small, the centrifugal force when passing through the area where it wraps around the fourth driven roller 13d and the pushing force of the toner due to the above-mentioned expansion and contraction of the intermediate transfer belt become strong, resulting in toner dusting. is likely to occur.

On the other hand, in the area where the toner wraps around the drive roller 14 having a diameter of about 30 to 50 mm, the centrifugal force applied to the toner is weak, and the elongation of the front surface of the intermediate transfer belt in the area where it wraps is also suppressed, so the extrusion force is also weak. . Therefore, toner dust could be suppressed to a level that did not pose a problem. Therefore, in this embodiment, as described above, the diameter of the fourth driven roller 13d is set to be equal to or larger than the diameter of the drive roller.

In this way, by making the diameter of the fourth driven roller 13d greater than or equal to the diameter of the drive roller 14, the centrifugal force applied to the toner can be reduced compared to a case where the diameter of the fourth driven roller 13d is less than the diameter of the drive roller 14. It can be weakened. Further, it is possible to suppress the expansion of the front surface of the intermediate transfer belt 110 in the winding region, and it is also possible to weaken the above-mentioned extrusion force when the expansion returns. Thereby, it is possible to suppress the occurrence of toner dust in the area where the intermediate transfer belt 110 wraps around the fourth driven roller 13d.

Further, as shown in FIG. 10, the diameter of the entrance roller 4 disposed between the drive roller 14 and the secondary transfer opposing roller 16 is preferably greater than or equal to the diameter of the drive roller 14. Thereby, compared to the case where the diameter of the entrance roller 4 is less than the diameter of the drive roller 14, it is possible to suppress the occurrence of toner dust in the area where the intermediate transfer belt 110 wraps around the entrance roller 4.

What has been described above is just an example, and each of the following aspects has its own unique effects.
(Aspect 1)
An intermediate transfer belt 110 that contacts an image carrier such as a photoconductor to form a primary transfer nip in which the toner image on the image carrier is primarily transferred; and a secondary transfer member such as a secondary transfer roller that forms a secondary transfer nip for secondary transfer of the image onto a recording medium such as a sheet material P, from the primary transfer nip to the secondary transfer nip in the moving direction of the intermediate transfer belt. A driving roller 14 that drives the intermediate transfer belt 110 is arranged between the primary transfer nip and the driving roller 14 in the moving direction of the intermediate transfer belt, and a fourth driven roller 13d that rotates as a result of the intermediate transfer belt 110. In an image forming apparatus in which a driven roller is arranged, the diameter of the driven roller is set to be larger than the diameter of the drive roller 14.
Centrifugal force acts on the toner on the intermediate transfer belt when it passes through the area where the intermediate transfer belt wraps around the driven roller. The centrifugal force applied to the toner increases as the diameter of the driven roller decreases. Further, when passing through the wrapping area, the front surface of the intermediate transfer belt expands, creating a gap between adjacent toners in the direction of movement of the surface of the intermediate transfer belt, and the stacked toners enter this gap. When the front surface of the intermediate transfer belt returns to its original extension after passing through the wrapping area and the gap between the toner particles closes, a force acts to push out the toner that has entered the gap. The smaller the diameter of the driven roller, the greater the extension of the front surface of the intermediate transfer belt in the winding region, the larger the gap between the toner particles, and the deeper the accumulated toner penetrates into this gap. As a result, the smaller the diameter of the driven roller, the greater the force for pushing out this toner. These centrifugal forces and extrusion forces serve as forces that cause the toner to scatter from the intermediate transfer belt.
In Patent Document 1, in which the diameter of the driven roller is smaller than the diameter of the driving roller, the force that scatters the toner from the intermediate transfer belt, such as the centrifugal force acting in the wrapped region and the above-mentioned pushing force, keeps the toner on the intermediate belt. There is a high possibility that toner dust may occur due to excessive force.
On the other hand, in aspect 1, the diameter of the driven rollers such as the fourth driven roller 13d is set to be equal to or larger than the diameter of the drive roller 14. At times, the centrifugal force and the above-mentioned extrusion force applied to the toner on the intermediate transfer belt can be weakened. As a result, compared to Patent Document 1, it is possible to suppress the occurrence of toner dust in the area where the toner is wrapped around the driven roller.

(Aspect 2)
In embodiment 1, the intermediate transfer belt 110 includes a plurality of layers including at least an elastic layer.
According to this, as described in the embodiment, the surface of the intermediate transfer belt 110 can be deformed to follow local irregularities. As a result, good adhesion can be obtained without excessively increasing the secondary transfer pressure to the toner layer, and there is no hollow transfer of characters, and it can be used on recording media such as sheet material P with poor smoothness. Even if the transfer image is transferred evenly and with excellent uniformity, it is possible to obtain a transferred image with excellent uniformity.
In addition, in the intermediate transfer belt 110 that includes a plurality of layers including the elastic layer, toner dust is likely to occur in the area where it wraps around the driven roller. Toner dust can be effectively suppressed.

(Aspect 3)
In aspect 1 or 2, the diameter of a driven roller such as the entrance roller 4 that is rotated by the intermediate transfer belt 110 disposed between the drive roller 14 and the secondary transfer nip is driven in the surface movement direction of the intermediate transfer belt 110. The diameter was greater than that of the roller 14.
According to this, as explained using FIG. 10, the occurrence of toner dust can also be suppressed in the area where the toner wraps around the driven roller, such as the entrance roller 4, which is arranged between the drive roller 14 and the secondary transfer nip. I can do it.

(Aspect 4)
In any of Aspects 1 to 3, the diameters of the driven rollers such as the fourth driven roller 13d and the drive roller 14 are set to 30 mm or more.
According to this, as described in the embodiment, it is possible to suppress the occurrence of toner dust in the area where the toner is wrapped around each roller.

(Aspect 5)
In any one of aspects 1 to 4, the intermediate transfer belt 110 includes a plurality of image carriers such as photoreceptors, and the intermediate transfer belt 110 sequentially contacts the plurality of image carriers to form a plurality of primary transfer nips. Among them, the diameter of a driven roller such as a fourth driven roller disposed between the most downstream primary transfer nip and the drive roller 14 in the primary transfer process order is greater than or equal to the diameter of the drive roller.
According to this, the toner image primarily transferred from the image carrier such as a photoconductor to the intermediate transfer belt is transferred to the fourth driven roller disposed between the primary transfer nip at the downstream end and the drive roller 14 in the order of the primary transfer process. It passes through a region where it wraps around a driven roller such as the roller 13d. Therefore, by making the diameter of a driven roller such as the fourth driven roller disposed between the most downstream primary transfer nip and the drive roller 14 in the primary transfer process order larger than the diameter of the drive roller, the occurrence of toner dust can be suppressed. can.

(Aspect 6)
A fifth aspect includes a plurality of image carriers that carry toner images of mutually different process colors of Y, M, C, and K, and an image carrier that carries colored or colorless spot color toner images.
According to this, a full color image and a colored or colorless special color image can be formed.

1: Photoreceptor 4: Entrance roller 11: Cleaning opposing roller 12: Tension roller 13a: First driven roller 13b: Second driven roller 13c: Third driven roller 13d: Fourth driven roller 14: Drive roller 15: Support roller 16 : Secondary transfer opposing roller 17 : Intermediate transfer unit 22 : Secondary transfer unit 23 : Secondary transfer roller 62 : Primary transfer roller 100 : Image forming device 110 : Intermediate transfer belt 200 : Control section 201 : First separation mechanism 202 : Second separation mechanism 203: Third separation mechanism 204: Fourth separation mechanism

JP 2018-205553 Publication

Claims (6)

an intermediate transfer belt that contacts an image carrier to form a primary transfer nip through which the toner image on the image carrier is primarily transferred;
a secondary transfer member that contacts the intermediate transfer belt to form a secondary transfer nip that secondarily transfers the toner image on the intermediate transfer belt to a recording medium;
A drive roller that drives the intermediate transfer belt is disposed between the primary transfer nip and the secondary transfer nip in the surface movement direction of the intermediate transfer belt,
In an image forming apparatus, a driven roller that rotates in accordance with the intermediate transfer belt is disposed between the primary transfer nip and the drive roller in the surface movement direction of the intermediate transfer belt,
An image forming apparatus characterized in that the diameter of the driven roller is greater than or equal to the diameter of the drive roller. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that the intermediate transfer belt includes a plurality of layers including at least an elastic layer. The image forming apparatus according to claim 1,
The diameter of a driven roller disposed between the drive roller and the secondary transfer nip and rotated by the intermediate transfer belt in the direction of surface movement of the intermediate transfer belt is greater than or equal to the diameter of the drive roller. image forming device. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that the diameter of the driven roller and the driving roller is 30 mm or more. The image forming apparatus according to claim 1,
comprising a plurality of the image carriers,
The intermediate transfer belt sequentially contacts the plurality of image carriers to form a plurality of the primary transfer nips,
An image forming apparatus characterized in that, among the plurality of primary transfer nips, a diameter of a driven roller disposed between the most downstream primary transfer nip and the drive roller in the order of the primary transfer process is greater than or equal to the diameter of the drive roller. . The image forming apparatus according to claim 5,
An image forming apparatus comprising a plurality of image carriers that carry toner images of mutually different process colors and an image carrier that carries colored or colorless spot color toner images.

Images