JP2024079934A - Image forming device - Google Patents

Abstract

[Problem] To provide an image forming apparatus including an intermediate transfer belt cleaning device that can improve the cleaning performance of an intermediate transfer belt and enable long-term use. [Solution] In an image forming apparatus having a pre-cleaning member that comes into sliding contact with the outer peripheral surface of the intermediate transfer belt, a frictional charging member that frictionally charges paper powder remaining on the outer peripheral surface of the intermediate transfer belt downstream of the pre-cleaning member in the rotation direction of the intermediate transfer belt, and a rotatable cleaning member that collects toner, a high voltage of the same polarity as the toner is applied to the pre-cleaning member, the frictional charging member is charged to the same polarity as the toner by rubbing against the intermediate transfer belt, a high voltage of the opposite polarity to the toner is applied to the first electrostatic cleaning member, and the triboelectric series of the material of the frictional charging member is configured to be between the toner and the paper powder adhering to the intermediate transfer belt. [Selected Figure] Figure 1

Description

The present invention relates to an image forming apparatus having a cleaning brush that electrostatically cleans residual toner on an intermediate transfer belt, and a pre-cleaning brush that is provided upstream of the cleaning brush and pre-charges the toner.

Conventionally, as an image forming apparatus using an electrophotographic method or the like, there is an image forming apparatus of an intermediate transfer method in which toner images formed on a plurality of image carriers are primarily transferred onto an intermediate transfer body so as to be superimposed on each other, and then secondarily transferred onto a recording material such as paper. An intermediate transfer belt, which is an endless belt-like member, is often used as the intermediate transfer body. The primary transfer is often performed by applying a primary transfer bias to a primary transfer member arranged so as to be in contact with the inner peripheral surface of the intermediate transfer belt corresponding to each of the plurality of image carriers, and supplying a current to a primary transfer section where the image carriers and the intermediate transfer belt are in contact. The secondary transfer is often performed by applying a secondary transfer bias to a secondary transfer member arranged so as to be in contact with the outer peripheral surface of the intermediate transfer belt, and supplying a current to a secondary transfer section where the intermediate transfer belt and the secondary transfer member are in contact. In addition, a primary transfer roller and a secondary transfer roller, which are roller-like members, are often used as the primary transfer member and the secondary transfer member.

As in Patent Document 1, toner remaining on the intermediate transfer belt after secondary transfer (secondary transfer residual toner) is collected from the intermediate transfer belt by a rotating brush that serves as an intermediate transfer belt cleaning device. A bias of the opposite polarity to the toner is applied to this rotating brush, and the residual toner on the intermediate transfer belt is electrically attracted and collected. In this type of cleaning device, a pre-cleaning brush may be provided upstream of the rotating brush in the rotation direction of the intermediate transfer belt. The pre-cleaning brush aligns the polarity of the toner passing through the pre-cleaning brush to a predetermined polarity so that the toner can be easily electrically attracted by the rotating roller. To achieve this electrical action, a bias of the same polarity as the toner is applied to the pre-cleaning brush in advance.

JP 2018-205360 A

However, as described in Patent Document 1, not only toner but also foreign matter such as paper dust accumulates on the pre-cleaning brush. At this time, because a bias is applied to the pre-cleaning brush, the foreign matter such as paper dust is likely to be charged to the same polarity as the toner. The charged accumulated matter forms clumps and is released downstream, where it is collected by the cleaning device, which may cause cleaning failure.

The above problem is solved by the image forming apparatus according to the present invention described below. That is, the apparatus includes an image forming unit that forms a toner image, an intermediate transfer belt to which the toner image is transferred, a pre-cleaning brush to which a bias of the same polarity as the normal charging polarity of the toner is applied and which pre-charges the transfer residual toner remaining on the intermediate transfer belt, a recovery brush that is provided downstream of the pre-cleaning brush in the rotation direction of the intermediate transfer belt and to which a bias of the opposite polarity to the normal charging polarity of the toner is applied, and a triboelectric charging brush that is provided downstream of the pre-cleaning brush and upstream of the recovery brush in the rotation direction of the intermediate transfer belt and frictionally charges the intermediate transfer belt, and is characterized in that the triboelectric series of the material of the triboelectric charging brush is located between the toner and the paper powder that adheres to the intermediate transfer belt.

According to the present invention, in a cleaning device that pre-charges and cleans residual toner on an intermediate transfer belt, cleaning defects caused by paper dust collected by the cleaning device after pre-charging are suppressed with a simple configuration.

Schematic cross-sectional view of an image forming apparatus FIG. 1 is a schematic cross-sectional view of a belt cleaning device according to a conventional example; FIG. 2 is a schematic cross-sectional view of the belt cleaning device according to the embodiment; FIG. 1 is a diagram showing the surface potential of a triboelectric charging brush caused by friction with an intermediate transfer belt in this embodiment. FIG. 1 is a diagram showing an intermediate transfer belt cleaning device according to the present embodiment.

The present invention will be described in detail below.

In this embodiment, a tandem-type full-color multifunction device will be described as an example of an image forming device 100.

However, the present invention is not limited to tandem-type full-color image forming devices, and may also be applied to other types of full-color image forming devices.

<Image forming apparatus>
As shown in FIG. 1, the image forming apparatus 100 includes an apparatus main body 96 which is an image forming unit, a sheet discharge unit 97, a control unit 15, an image reading unit 98, and an operation unit 99 which serves as a UI (user interface).

The image forming apparatus 100 can form a four-color full-color image on a recording medium in response to an image signal from an image reading unit 98, a host device such as a personal computer, or an external device such as a digital camera or smartphone. The sheet P is a recording medium on which a toner image is formed. Specific examples include a wide variety of recording media, such as plain paper, thick paper, synthetic resin sheets that are substitutes for plain paper, transparent resin sheets for overhead projectors, envelopes, postcards, coated paper, embossed paper, and waterproof paper (resin sheets, resin-coated paper).

The image forming apparatus 100 of this embodiment is capable of producing full-color images, and each of the four colors, the yellow image forming section Y, the magenta image forming section M, the cyan image forming section C, and the black image forming section K, is provided with a separate image forming member with a similar configuration. For this reason, in FIG. 1, the configurations of the four colors are shown with the same reference numeral followed by a color identifier, but in the specification, they may be described only by the reference numeral without a color identifier. Note that this image forming apparatus 100 is also capable of producing, for example, a black single-color (monochrome) image, a single-color image of one of the four colors, a single-color image using some of the four colors, or a multicolor image.

Each of the image forming units Y, M, C, and K has a photosensitive drum 1 that rotates while carrying a toner image, a charging roller 2, a developing device 4, and a photosensitive body cleaning device 6. Each part of the image forming units Y, M, C, and K is unitized for each color as a cartridge, and is configured to be detachable from the device main body 96. When the life of each part has expired, the cartridges are replaced with new ones, and a new toner image of the four colors can be formed on the intermediate transfer belt 7.

The photosensitive drum 1 is rotatable and carries an electrostatic latent image used in image formation. In this embodiment, the photosensitive drum 1 is a positively charged organic photoconductor (OPC) with an outer diameter of 30 mm, and is rotated by a drive motor (not shown) in the direction of the arrow at a predetermined process speed (circumferential speed). The photosensitive drum 1 has an aluminum cylinder as a base, and has three layers on its surface that are coated and stacked in order: an undercoat layer, a photocharge generation layer, and a charge transport layer.

The charging roller 2 is a conductive rubber roller that comes into contact with the surface of the photosensitive drum 1 and rotates in response, uniformly charging the surface of the photosensitive drum 1. Depending on the voltage applied to the charging roller 2, it can be classified into an AC charging method using AC voltage + DC voltage, and a DC charging method using only DC voltage, but in this embodiment, the AC charging method, which produces less charging unevenness, was adopted.

The exposure device 3 emits laser light 3Y, 3M, 3C, 3K for each color, and forms an electrostatic latent image on the photosensitive drums 1Y, 1M, 1C, 1K for each color. The exposure device 3 emits laser light 3Y, 3M, 3C, 3K for each color onto the photosensitive drums 1Y, 1M, 1C, 1K for each color, which are uniformly charged, in accordance with the image information of the separated colors output from the control unit 15.

The developing device 4 contains a developer (toner) of, for example, a positively charged polarity supplied from a refill toner bottle 14, and develops the electrostatic latent image formed on the photosensitive drum 1 by the laser light from the exposure device 3. In this embodiment, a two-component development method using non-magnetic toner and magnetic carrier is adopted, and toner is supplied to the development area facing the photosensitive drum 1. A development bias (DC voltage + AC voltage) is applied to the developing sleeve (not shown) of the developing device 4 that carries the toner, and the electrostatic latent image formed on the photosensitive drum 1 is developed with toner and made visible.

The toner image developed on the photosensitive drum 1 by the primary transfer roller 5 is primarily transferred onto the intermediate transfer belt 7 at the primary transfer section. After the primary transfer, the photosensitive drum 1 is cleaned by a photosensitive cleaning device 6, for example, by a photosensitive cleaning blade (not shown) that is brought into contact with the photosensitive drum 1 with a predetermined pressure, to remove any residual toner that has not been transferred to the intermediate transfer belt 7. The surface of the photosensitive drum 1 is then neutralized by a pre-exposure device (not shown), and the photosensitive drum 1 is prepared for the next image-making process.

The intermediate transfer belt 7 is wound around a driving roller 8 and a driven roller 9, contains primary transfer rollers 5Y, 5M, 5C, and 5K, and is equipped with an intermediate transfer belt cleaning device 20. The intermediate transfer belt 7 can be detached and replaced as an intermediate transfer belt unit from the device main body 96, and can be replaced with a new one when the part reaches the end of its life or when it breaks down. The driven roller 9 is a tension roller that controls the tension of the intermediate transfer belt 7 to a constant level. A force is applied to the driven roller 9 by a spring (not shown) that pushes the intermediate transfer belt 7 toward the front side, and this force applies a tension of about 20 to 50 [N] in the conveying direction of the intermediate transfer belt 7. In this embodiment, the intermediate transfer belt 7 is supported by two shafts, but it may be supported by three shafts, for example, and one of the shafts may be used to control the deviation of the intermediate transfer belt 7.

Primary transfer rollers 5Y, 5M, 5C, and 5K are disposed facing photosensitive drums 1Y, 1M, 1C, and 1K, respectively. Primary transfer roller 5 is disposed facing photosensitive drum 1 with intermediate transfer belt 7 sandwiched therebetween, and a primary transfer voltage of the opposite polarity to the toner is applied to the primary transfer rollers 5Y, 5M, 5C, and 5K, thereby primarily transferring the toner image formed on the photosensitive drum 1 onto the intermediate transfer belt 7. The primary transfer voltage applied to primary transfer rollers 5Y, 5M, 5C, and 5K can be individually controlled by control unit 15. In this embodiment, primary transfer roller 5 has an outer diameter of, for example, 15 to 20 mm, an elastic layer of ion conductive foam rubber (NBR rubber) and a core metal. For example, a roller with a resistance value of 1 x 10E+5 to 1 x 10E+7 Ω (measurement conditions: 23°C 50% RH environment, against Φ30 mm aluminum drum, nip width of approximately 7 mm, 2 kV applied) is used.

In this embodiment, the intermediate transfer belt 7 is an endless belt having a three-layer elastic structure consisting of a base layer, an elastic layer, and a surface layer from the back side.

The resin material constituting the base layer is a resin such as polyimide or polycarbonate, or various rubbers containing an appropriate amount of carbon black as an antistatic agent, and the thickness of the base layer is 50 to 150 μm. The elastic material constituting the elastic layer is a material containing various rubbers such as urethane rubber or silicone rubber containing an appropriate amount of ion conductive material, and the thickness of the elastic layer is 100 to 500 μm. The surface layer is a material in which a filler such as fluorine resin is added to polyurethane or acrylic, and is a coating material that reduces the adhesion of toner to the surface of the intermediate transfer belt 7 and makes it easier to transfer the toner to the sheet P at the secondary transfer section, and the thickness of the surface layer is 0.5 to 30 μm. In this embodiment, the base layer is a polyimide resin with conductive material dispersed therein: 70 μm. The intermediate transfer belt 7 used had a total thickness of 371 μm, with an elastic layer of conductive CR rubber (chloroprene rubber): 300 μm, and a surface layer of resin with 60% by weight of PTFE added to polyurethane: 1 μm. The intermediate transfer belt 7 in this embodiment has a volume resistivity of 1×10E+7 to 1×10E+9 Ω·cm (measurement conditions: 23°C 50% RH environment, resistivity meter, 100 V applied), and a surface hardness of 65° (measurement conditions: 23°C 50% RH environment measurement, Wallace hardness meter).

The secondary transfer roller 10 is arranged in pressure contact with the drive roller 8 via the intermediate transfer belt 7. A DC voltage of the opposite polarity to the charge polarity of the toner is applied to the secondary transfer roller 10 as a secondary transfer voltage. The secondary transfer roller 10 then performs secondary transfer of the four-color superimposed toner image that has been primarily transferred onto the intermediate transfer belt 7, all at once onto the sheet P that has been supplied to the nip portion (secondary transfer portion) between the drive roller 8 and the secondary transfer roller 10. The drive roller 8 is connected to a ground potential. In this embodiment, for example, a secondary transfer voltage of +2 to +5 kV is applied to the secondary transfer roller 10, causing a current of, for example, about 50 μA to flow, and the toner image on the intermediate transfer belt 7 is secondarily transferred onto the sheet P.

The primary and secondary transfer voltages or transfer currents are arbitrary values determined according to the material of the photosensitive drum, the charge amount of the toner, the image formation speed, i.e., the rotation speed of the photosensitive drum 1 and the intermediate transfer belt 7, and, in the case of secondary transfer, the material of the sheet P.

The secondary transfer roller 10 has an outer diameter of, for example, 20 to 25 mm, and has an elastic layer of ion-conductive foamed rubber (NBR rubber) and a core metal. The secondary transfer roller 10 uses a roller with a resistance value of 1x10E+5 to 1x10E+7 [Ω] (measurement conditions: 23°C, 50% RH environment, against a Φ30 mm aluminum drum, nip width of approximately 7 mm, 2 kV applied), which is roughly the same as that of the primary transfer roller 5.

The intermediate transfer belt 7 also has an intermediate transfer belt cleaning device 20. The intermediate transfer belt cleaning device 20 removes toner remaining on the intermediate transfer belt 7 after the secondary transfer process. The details of the intermediate transfer belt cleaning device 20 will be described later.

A sheet P is taken out of the cassette 12 by the paper feed roller 11 and transported to the secondary transfer section of the secondary transfer roller 10 at a predetermined timing, following the arrow. The sheet P carrying the secondarily transferred toner image is transported to the fixing section 13.

The fixing device 13, which serves as a fixing means, is equipped with a pressure roller 13b that is in pressure contact with the fixing roller 13a. As the sheet P is sandwiched and transported between the heated fixing roller 13a and the pressure roller 13b, the toner image that has been secondarily transferred to the sheet P is heated and pressurized to be fixed to the sheet P.

The sheet P with the toner image fixed thereon is transported to the sheet discharge section 97, and image formation on the sheet P is completed.

<Intermediate transfer belt cleaning device>
After the primary transfer in each image forming unit, the primary transfer residual toner remaining on the photosensitive drum 1 is cleaned by a photosensitive drum cleaning device 6. After the secondary transfer, the secondary transfer residual toner remaining on the intermediate transfer belt 7 is cleaned by an intermediate transfer belt cleaning device 20.

After the primary transfer, most of what remains on or adheres to the photosensitive drum 1 is primary transfer residual toner. Meanwhile, since the intermediate transfer belt 7 comes into contact with the sheet P during the secondary transfer, what remains on or adheres to the intermediate transfer belt 7 after the secondary transfer includes not only secondary transfer residual toner, but also paper dust and fillers derived from the paper of the sheet P. Also, if the developing device 4 in the image forming section employs a two-component developer, the carrier contained in the two-component developer may adhere.

The intermediate transfer belt 7 can have a single-layer structure with only a base layer, or a two-layer structure with a base layer and a surface layer. In this embodiment, however, as described above, it is an endless belt with an elastic layer having a three-layer structure with a base layer, an elastic layer, and a surface layer from the back side.

The intermediate transfer belt 7 has an elastic layer, which allows the elastic layer to conform to the unevenness of the paper during the secondary transfer, even when the paper is embossed or other textured paper, so it has the advantage of being able to obtain a good image without secondary transfer unevenness.

In the case of the intermediate transfer belt with the single-layer structure that does not have an elastic layer, there is a problem that secondary transfer unevenness occurs and minute image density unevenness occurs even when using plain paper with a slightly rough surface.

In addition, in the intermediate transfer belt of the two-layer structure that does not have an elastic layer, the surface layer is coated with a fluororesin or the like that has good toner releasability. Therefore, even with plain paper with a slightly rough surface, it is possible to obtain a good image without secondary transfer unevenness and without minute image density unevenness. However, since there is no elastic layer, the surface of the intermediate transfer belt cannot follow the uneven parts of paper with large unevenness such as embossed paper. For this reason, gaps are generated between the intermediate transfer belt 7 and the paper at the edges of the concave and convex parts, which reduces the transferability of the toner to the paper, causing the density to become low in those areas and resulting in uneven density.

On the other hand, as mentioned above, an intermediate transfer belt cleaning device for an intermediate transfer belt that has an elastic layer has the disadvantage that a cleaning blade cannot be used.

Then, we will explain the intermediate transfer belt cleaning device 20 that cleans the intermediate transfer belt 7 having the elastic layer in this embodiment.

[Conventional Example]
First, a conventional intermediate transfer belt cleaning device 20 shown in Fig. 2 will be described. As shown in Fig. 1, the intermediate transfer belt cleaning device 20 may be provided between the secondary transfer roller 10 and the primary transfer roller 5Y of the most upstream image forming unit Y in the surface movement direction of the intermediate transfer belt 7. The intermediate transfer belt cleaning device 20 has a rotating brush 22 as a recovery brush that recovers secondary transfer residual toner on the intermediate transfer belt 7, and a recovery roller 23 that recovers toner and the like attached to the rotating brush 22. The intermediate transfer belt cleaning device 20 also includes a cleaning blade 24 that mechanically scrapes off toner and the like on the recovery roller 23. Furthermore, the intermediate transfer belt cleaning device 20 has a pre-cleaning brush 21 located upstream of the rotating brush 22 in the surface movement direction of the intermediate transfer belt 7. The pre-cleaning brush 21 is fixedly arranged in contact with the intermediate transfer belt 7 with light pressure, and contacts the toner and the like on the intermediate transfer belt 7 to inject electric charge.

Each rotating member in the intermediate transfer belt cleaning device 20 is rotationally driven in response to instructions from the control unit 15. The rotating brush 22 is rotationally driven in a counter direction (arrow direction in Figure 2 = counterclockwise) so that the brush fibers move against the moving direction of the surface of the intermediate transfer belt 7 so that the toner and the like on the intermediate transfer belt 7 can be sufficiently scraped off and collected. The collection roller 23 is rotationally driven in the same direction as the rotating brush 22 (arrow direction in Figure 3 = clockwise). The rotating brush 22, collection roller 23 and pre-cleaning brush 21 are all conductive.

During image formation, the control unit 15 applies an intermediate transfer belt cleaning electric field to the intermediate transfer belt cleaning device 20 to clean and collect secondary transfer residual toner, etc. on the intermediate transfer belt 7. The polarity (±) and output value (voltage value) of the DC voltage power supplies 25 and 26 are controlled by the control unit 15. When the intermediate transfer belt cleaning electric field is formed during image formation, the power supply 25 applies a direct current voltage (DC voltage) set to the same polarity (+) as the normal charging polarity (+) of the toner to the pre-cleaning brush 21. In this way, the toner (+) and paper powder, etc. on the intermediate transfer belt 7 are aligned to a negative polarity (+) by charge injection from the pre-cleaning brush 21. The pre-charged toner, etc. repels the polarity (+) of the pre-cleaning brush 21 and moves onto the intermediate transfer belt 7 without accumulating on the pre-cleaning brush 21, and is transported to the rotating brush 22 by the rotation of the intermediate transfer belt 7. A direct current (DC) voltage set to the opposite polarity (-) of the normal charge polarity (+) of the toner is applied to the rotating brush 22 by grounding or a power source 26. In this way, under the intermediate transfer belt cleaning electric field, the toner is mechanically and electrostatically scraped off the intermediate transfer belt 7 and collected by the rotating brush 22. The transfer belt 7 is then cleaned, and the toner, etc. collected by the rotating brush 22 is further collected by the collection roller 23 which rotates in contact with the rotating brush 22. The toner, etc. on the collection roller 23 is scraped off by the cleaning blade 24 and falls, and is carried out to a waste toner container (not shown) by a conveying screw (not shown).

In the intermediate transfer belt cleaning device 20 shown in the conventional example, the paper powder and other foreign matter accumulated on the pre-cleaning brush 21 is easily charged to a positive polarity (+) by the DC voltage power supply 25. Therefore, when the deposit is released from the pre-cleaning brush 21, it moves onto the intermediate transfer belt 7 and is transported to the rotating brush 22 by the rotation of the intermediate transfer belt 7. Since the rotating brush 22 is applied with a direct current voltage (DC voltage) set to the opposite polarity (-) of the charge polarity (+) of the deposit by the power supply 26, the deposit is mechanically and electrostatically scraped off from the intermediate transfer belt 7 and collected by the rotating brush 22. Then, the transfer belt 7 is cleaned, and the deposit of paper powder and the like collected by the rotating brush 22 is further collected by the collection roller 23 which rotates in contact with the rotating brush 22. The deposit of paper powder and the like on the collection roller 23 reaches the cleaning blade 24, and depending on the size and shape of the deposit, it may not be scraped off by the cleaning blade 24 and may be sandwiched between the collection roller 23 and the cleaning blade 24. When deposits get caught between the collection roller 23 and the cleaning blade 24, the toner cannot be scraped off from that area, so the toner slips through the cleaning blade 24, resulting in poor image quality.

Therefore, in this embodiment, a friction charging brush with high electrical resistance is added downstream of the conventional pre-cleaning brush (pre-cleaning brush 21 in FIG. 2) to charge the accumulated paper powder and other particles with the polarity (-) opposite to the normal charging polarity (+) of the toner. This prevents the particles from being collected by the intermediate transfer belt cleaning device 20. (FIG. 3) This will be explained in detail below.

As shown in FIG. 1, the intermediate transfer belt cleaning device 20 may be provided between the secondary transfer roller 10 and the primary transfer roller 5Y of the most upstream image forming unit Y in the surface movement direction of the intermediate transfer belt 7. In this embodiment, it is provided opposite the driven roller 9 around which the intermediate transfer belt 7 is wound.

Figure 3 shows the main parts of the intermediate transfer belt cleaning device 20.

The intermediate transfer belt cleaning device 20 includes a rotating brush 22 that collects secondary transfer residual toner on the intermediate transfer belt 7, and a collection roller 23 that collects toner and other particles adhering to the rotating brush 22. The intermediate transfer belt cleaning device 20 also includes a cleaning blade 24 that mechanically scrapes off toner and other particles on the collection roller 23.

The intermediate transfer belt cleaning device 20 further includes a pre-cleaning brush 21 and a friction charging brush 31 located upstream of the rotating brush 22 in the direction of movement of the surface of the intermediate transfer belt 7.

The pre-cleaning brush 21 may be any material capable of injecting an electric charge by contacting the toner, etc. on the intermediate transfer belt 7, and may be a conductive resin sheet or metal sheet. In this embodiment, a pre-cleaning brush 21 made of conductive fibers held by a conductive holding member is used, so that the pre-cleaning brush 21 can contact the toner, etc. on the intermediate transfer belt 7 as uniformly as possible or under low pressure. The pre-cleaning brush 21 is fixedly disposed in contact with the intermediate transfer belt 7 with light pressure. The pre-cleaning brush 21 is also connected to a high-voltage power source that mainly applies positive voltage.

The triboelectric charging brush 31 charges the brush by friction with the intermediate transfer belt 7 without using a high-voltage power supply, and the polarity of the charge is determined by the material. Figure 4 shows the surface potential when the triboelectric charging brush 31 is rubbed against the intermediate transfer belt 7, and it can be seen that when nylon is used as the brush, it is positively charged, and when the brush is coated with fluororesin, it is negatively charged. In this embodiment, the triboelectric charging brush 31 is made of nylon so that the brush is positively charged by friction. In addition, since the brush is charged by friction, the electrical resistance is preferably 1 x 10E + 11 to 1 x 10E + 15 [Ω/cm] in terms of raw yarn resistance. In this embodiment, the surface potential is configured to be +200V or more when the triboelectric charging brush 31 is rubbed against the intermediate transfer belt 7.

The triboelectric charging brush 31 material in this embodiment is configured to be located between the toner and paper dust in its charge series. Therefore, the triboelectric charging brush 31 allows the toner with normal charge polarity (+) that has passed through the pre-cleaning brush 21 to pass through, and collects a small amount of toner and paper dust with the opposite charge polarity (-). It also has the effect of charging positively charged (+) paper dust to a negative charge. This is thought to be because, when comparing nylon and paper dust in the charge series of materials, paper dust is on the negative side.

Each rotating member in the intermediate transfer belt cleaning device 20 is driven to rotate in response to instructions from the control unit 15. The rotating brush 22 is driven to rotate in a counter direction (arrow direction in Figure 3 = counterclockwise) so that the brush fibers move against the moving direction of the surface of the intermediate transfer belt 7 so that the toner and the like on the intermediate transfer belt 7 can be sufficiently scraped off and collected. The collection roller 23 is driven to rotate in the same direction as the rotating brush 22 (arrow direction in Figure 3 = clockwise).

In this embodiment, the rotating brush 22, the recovery roller 23, and the pre-cleaning brush 21 are all conductive. The rotating brush 22 is, for example, configured by weaving conductive brush fibers (raw yarn) into a conductive base cloth, or a conductive base cloth with a conductive agent coated on the back side. The rotating brush 22 is configured by wrapping the base cloth with the conductive brush fibers woven into it around a core metal and bonding the two together (for example, by using a conductive adhesive) so that they can be electrically connected. The core metal may be formed from a rod, pipe, or the like made of a conductive metal.

Examples of materials for conductive brush fibers include polyamide (nylon, etc.) with dispersed conductive carbon, polyester, acrylic, rayon, etc.

As for the thickness and resistance of the brush fibers, the thickness is 1 to 10 [decitex] in terms of the original yarn diameter, and the resistance is about 1 x 10E + 3 to 1 x 10E + 15 [Ω/cm] in terms of the original yarn resistance. The brush fiber density in the base fabric is 50 to 300 [kF/inch2] (F is the number of fibers [pieces]).

In this embodiment, a rotating brush 22 using such brush fibers is used. Regarding the relationship between the surface movement speed of the intermediate transfer belt 7 and the rotating brush peripheral speed, the peripheral speed ratio θ (rotating brush peripheral speed/belt surface movement speed) is set to about 1 to 5. The peripheral speed of the rotating brush 22 is set to be equal to or faster than the surface movement speed of the intermediate transfer belt 7, thereby improving the efficiency of collecting toner and the like by the rotating brush 21. In addition, the amount of penetration of the rotating brushes 22 and 25 into the intermediate transfer belt 7 is set to be about 0.3 to 2.0 mm.

The pre-cleaning brush 21 may be made of the same brush fibers as those used to form the rotating brush 22. However, the resistance may be lower than that of the rotating brush 22 in order to facilitate smooth charge injection. The brush fibers are woven into the base fabric at a fiber density of about 50 to 300 [kF/inch2] to form the pre-charging brush 21. The amount of penetration of the pre-charging brush 21 into the intermediate transfer belt 7 may be set to about 0.1 mm to 2 mm.

During image formation, the control unit 15 applies an intermediate transfer belt cleaning electric field to the intermediate transfer belt cleaning device 20 to clean and collect secondary transfer residual toner and the like on the intermediate transfer belt 7. The polarity (±) and output value (voltage value) of the DC voltage power supplies 25 and 26 are controlled by the control unit 15.

For example, as shown in FIG. 3, when the intermediate transfer belt cleaning electric field is formed during image formation, the pre-cleaning brush 21 is applied with a direct current voltage (DC voltage) set to the same polarity (+) as the normal charging polarity (+) of the toner by the power source 25. In this way, the toner (+) and paper powder on the intermediate transfer belt 7 are aligned to a positive polarity (+) by charge injection from the pre-cleaning brush 21. The pre-charged toner, etc. repels the polarity (+) of the pre-cleaning brush 21 and moves onto the intermediate transfer belt 7 without accumulating on the pre-cleaning brush 21, and is transported to the friction charging brush 31 by the rotation of the intermediate transfer belt 7.

The toner with the normal charging polarity (+) that is transported to the friction charging brush 31 passes through as is and is transported to the rotating brush 22. In addition, the paper dust that is positively charged (+) is charged to negative polarity (-) by the friction charging brush 31 and is transported to the rotating brush 22 by the rotation of the intermediate transfer belt 7. Furthermore, a small amount of the toner and paper dust that is negatively charged (-) is captured by the friction charging brush 31.

As shown in FIG. 3, a direct current voltage (DC voltage) that is set to the polarity (-) opposite to the normal charging polarity (+) of the toner is applied to the rotating brush 22 by the power source 26. In this way, under the intermediate transfer belt cleaning electric field, the toner with the normal charging polarity (+) is mechanically and electrostatically scraped off from the intermediate transfer belt 7 and collected by the rotating brush 22.

In addition, a small number of paper particles that are negatively charged (-) by the friction charging brush 31 pass through the rotating brush 22 without being collected.

The electric field formed by the power sources 25 and 26 can be either a constant voltage or a constant current, and depends on the rotation speed of the transfer belt 7. In the case of a constant voltage, it is advisable to set it to, for example, ±1 kV or less, and in the case of a current, it is advisable to set it to, for example, ±30 μA or less.

Then, the transfer belt 7 is cleaned, and the toner collected by the rotating brush 22 is further collected by the collection roller 23, which rotates in contact with the rotating brush 22. The toner on the collection roller 23 is scraped off by the cleaning blade 24, falls, and is carried out by a conveying screw (not shown) to a waste toner container (not shown).

This embodiment is the same as embodiment 1 except for the configuration described below.

As shown in FIG. 1, the intermediate transfer belt cleaning device 20 may be provided between the secondary transfer roller 10 and the primary transfer roller 5Y of the most upstream image forming unit Y in the surface movement direction of the intermediate transfer belt 7. In this embodiment, it is provided opposite the driven roller 9 around which the intermediate transfer belt 7 is wound.

Figure 5 shows the main parts of the intermediate transfer belt cleaning device 20.

The intermediate transfer belt cleaning device 20 includes a rotating brush 22 that collects secondary transfer residual toner on the intermediate transfer belt 7, and a collection roller 23 that collects toner and other particles adhering to the rotating brush 22. The intermediate transfer belt cleaning device 20 also includes a cleaning blade 24 that mechanically scrapes off toner and other particles on the collection roller 23.

The intermediate transfer belt cleaning device 20 further includes a pre-cleaning brush 21 and a triboelectric charging brush 31 located upstream of the rotating brush 22 in the direction of movement of the surface of the intermediate transfer belt 7. Furthermore, downstream of the rotating brush 22, a paper dust removal brush 41 and a high-voltage power supply 42 connected to it are included. A direct current voltage (DC voltage) set to the same polarity (+) as the normal charging polarity (+) of the toner is applied to this power supply 42, and the small amount of paper dust charged to a negative polarity (-) by the triboelectric charging brush 31 that passed through without being collected by the rotating brush 22 in Example 1 is captured.

Since the high-voltage power supply 42 has the same polarity as the high-voltage power supply 25, it may be connected to the high-voltage power supply 25 instead of the high-voltage power supply 42.

The material, resistance, fiber density, etc. of the paper dust removal brush 41 are preferably the same as those of the pre-cleaning brush 21 in Example 1.

In this embodiment, any paper dust that is not collected by the rotating brush 22 is then captured, making it less likely that poor image quality due to poor cleaning will occur.

[Effects of this embodiment]
Tables 1 and 2 show the results of experiments evaluating the cleaning performance when the yarn resistance of the friction charging brush 31 was changed in the conventional example, the examples 1 and 2, respectively.

In this experiment, an image forming apparatus was used to print low-density blue halftone solid images on A4-sized plain paper (Canon Red Label Presentation (80 gsm)), and 500,000 to 2,000,000 sheets were output. After printing 500,000 sheets, 700,000 sheets, 900,000 sheets, 1,500,000 sheets, and 2,000,000 sheets in each configuration, the solid images were evaluated, and the presence or absence of toner that was not collected due to poor cleaning was visually evaluated according to the following criteria.
A: No visible image defects B: A slightly visible streak-like image defect C: A clearly visible streak-like image defect When the yarn resistance is 1 x 10E+10 [Ω cm] or less, the surface potential of the friction-charging brush 31 is low, and as in the conventional example, image defects due to poor cleaning occur after printing 1,000,000 sheets.

When the cleaning blade 24 was observed under an optical microscope after the image defect occurred, clumps of paper powder were confirmed at the location where the streak-like image defect occurred.

When the yarn resistance is 1 x 10E+12 [Ω·cm] or more, no image defects occur even after printing 2,000,000 sheets. This is thought to be because the paper powder is negatively charged (-) on the friction charging brush 31 and does not reach the collection roller 23 or cleaning blade 24.

From the above results, the intermediate transfer belt cleaning device 20 shown in this embodiment can improve the cleaning performance of the intermediate transfer belt and enable long-term use simply by adding an inexpensive friction charging brush 31.

Description of the Reference Signs 1Y, 1M, 1C, 1K Photosensitive drum 2Y, 2M, 2C, 2K Charging roller 3 Exposure device 3Y, 3M, 3C, 3K Exposure light 4Y, 4M, 4C, 4K Development device 5Y, 5M, 5C, 5K Primary transfer roller 6Y, 6M, 6C, 6K Photosensitive drum cleaning device 7 Intermediate transfer belt 8 Drive roller 9 Driven roller 10 Secondary transfer roller 11 Paper feed roller 12 Cassette 13 Fixing device 14Y, 14M, 14C, 14K Replenishment toner bottle 15 Control unit 20 Intermediate transfer belt cleaning device 21 Pre-cleaning brush 22 Rotating brush 23 Collection roller 24 Cleaning blade 25, 26, 42 DC voltage power supply 31 Friction charging brush 41 Paper dust removing brush 15 Control unit 96 Apparatus body 97 Sheet discharge unit 98 Image reading unit 99 Operation unit 100 Image forming apparatus P Sheet (recording medium)

Claims (5)

an image forming unit that forms a toner image;
an intermediate transfer belt onto which the toner image is transferred;
a pre-cleaning brush to which a bias having the same polarity as the normal charging polarity of the toner is applied, and which pre-charges the transfer residual toner remaining on the intermediate transfer belt;
a recovery brush provided downstream of the pre-cleaning brush in the rotation direction of the intermediate transfer belt, the recovery brush being applied with a bias of a polarity opposite to the normal charging polarity of the toner;
a frictional charging brush that is provided downstream of the pre-cleaning brush and upstream of the recovery brush in a rotation direction of the intermediate transfer belt and that is frictionally charged with the intermediate transfer belt;
an image forming apparatus comprising: a brush having a brush and a toner cartridge; a brush having a brush and a toner cartridge; The image forming apparatus according to claim 1 further comprises a paper dust removal brush, which is provided downstream of the collection brush in the rotation direction of the intermediate transfer belt and upstream of a primary transfer section that primarily transfers a toner image onto the intermediate transfer belt, and to which a positive bias is applied. The image forming apparatus according to claim 1, characterized in that the yarn resistance of the friction charging brush 31 is 1 x 10E + 12 [Ω cm] or more. The image forming apparatus according to claim 1, characterized in that the surface potential of the friction charging brush becomes +200 V or more when the friction charging brush rubs against the intermediate transfer belt. The image forming apparatus according to claim 1, characterized in that the material of the friction charging brush 31 is nylon.

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