JP2013061517A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which increases cleaning capability of an intermediate transfer body, and is thereby capable of coping with operation conditions where a residual toner amount is large as well as a fast processing speed operation mode.SOLUTION: An image forming apparatus which transfers a toner image formed on a photoreceptor drum 21 to an intermediate transfer belt 101, and further transfers the toner image to paper comprises equal to or more than three conductive cleaning members 41-44 in the downstream of a transfer-to-paper position 115 on the intermediate transfer belt 101. The cleaning members 41-44 are provided in contact with the intermediate transfer belt 101. Further, high voltage power source parts 61-64 are provided, and biases are applied thereby on the cleaning members 41-44 so as to allow each of them to have an opposite polarity next to each other. With regard to the cleaning members having the same bias polarity (41 and 43, or 42 and 44), the bias output is made larger for the cleaning members (41, 42) in the upper stream-side.

Description

  The present invention relates to an image forming apparatus having an intermediate transfer body that receives a primary transfer of a toner image from a photoreceptor and further secondary-transfers the toner image to a medium. More specifically, the present invention relates to an image forming apparatus provided with a cleaning member for cleaning an intermediate transfer member at a position downstream of a secondary transfer position in the intermediate transfer member.

  Conventionally, an image forming apparatus having an intermediate transfer member is generally provided with a cleaning member for cleaning the intermediate transfer member. This is because a certain amount of toner remains on the intermediate transfer body after the secondary transfer. For example, the image forming apparatus disclosed in Patent Document 1 includes a plurality of fur brushes as cleaning members. Then, a positive bias is applied to the first fur brush at the first position as viewed from the secondary transfer position, and a negative bias is applied to the second fur brush on the downstream side thereof. As a result, the negatively charged toner that remains in the original charged polarity among the residual toner is collected by the first fur brush, and the positively charged toner whose polarity is reversed is collected by the second fur brush. In the image forming apparatus disclosed in Patent Document 2, a fur brush and a foam roller are used in combination as cleaning members.

JP 2002-229344 A JP 2010-145519 A

  However, the conventional technique described above has the following problems. First, the technique of Patent Document 1 has a problem of slipping through residual toner. As a cause, it is considered that when the cleaning member is a fur brush, the degree of adhesion to the intermediate transfer member is lower than that of the roller. In particular, when using special paper (such as embossed paper) with a low transfer rate as a medium, or when forming an image stabilization pattern that does not perform secondary transfer in the first place, a considerable amount of toner is placed at the cleaning member. To reach. For this reason, a lot of toner passes through. As the slipping-out toner circulates, toner filming occurs on the intermediate transfer member. As a result, the surface properties (smoothness and conductivity) of the intermediate transfer member are changed, and the image quality is deteriorated.

  By using a foaming roller as a cleaning member as in Patent Document 2, the problem of toner slipping can be considerably reduced. In recent years, however, the amount of toner that reaches the cleaning member tends to increase as the process speed of the image forming apparatus increases. In order to cope with this, it is necessary to increase the energy applied to the bias between the cleaning member and the intermediate transfer member. However, it is also a problem that the bias application to the cleaning member is simply strengthened (high voltage or high current) with the conventional mechanical configuration. This is because if the bias is too strong, filming due to toner melting occurs at the cleaning member. Thus, in recent image forming apparatuses, it has been required to further enhance the cleaning ability of the intermediate transfer member.

  The present invention has been made to solve the above-described problems of the prior art. That is, the problem is that an image forming apparatus that enhances the cleaning capability of the cleaning member of the intermediate transfer member so that it can cope with an operation state with a large amount of residual toner and an operation mode with a high process speed. It is to provide.

  An image forming apparatus of the present invention, which has been made for the purpose of solving this problem, has a photoconductor and a toner image forming section for forming a toner image on the photoconductor, and receives the transfer of the toner image from the photoconductor and the toner An intermediate transfer member for further transferring the image to the medium, provided in contact with a position downstream of the transfer position of the toner image to the medium on the intermediate transfer member, and cleaning the intermediate transfer member. The conductive cleaning member described above and a bias applying unit that applies a bias to each cleaning member, and the bias applying unit is a bias having a polarity opposite to that of each of the cleaning members disposed adjacent to each other. For a cleaning member to which a bias of the same polarity is applied, the higher the bias output is applied to the cleaning member disposed upstream. To.

  In this image forming apparatus, the toner image formed on the photosensitive member is transferred to the intermediate transfer member, and further transferred from the intermediate transfer member to the medium. Here, a certain amount of toner remains on the intermediate transfer member even after the toner image is transferred to the medium. This toner remaining on the transfer source after transfer is referred to as transfer residual toner. The transfer residual toner is cleaned by a cleaning member. A bias is applied to the cleaning member by a bias application unit, whereby the transfer residual toner is collected from the intermediate transfer member to the cleaning member. There are a plurality of cleaning members, and the polarity of the applied bias is alternately reversed. For this reason, both of the untransferred toner that remains in the original charged polarity and the toner that has the charged polarity reversed are collected.

  Here, further, when the cleaning members to which the bias of the same polarity is applied are viewed, those applied to the upstream side have a stronger bias. For this reason, at the stage of the upstream cleaning member where there is a large amount of transfer residual toner, the transfer residual toner is efficiently collected by a stronger bias. On the other hand, at the stage of the downstream cleaning member where the residual toner is low, the residual toner is collected by a weak bias without fear of damaging the intermediate transfer member.

  In the image forming apparatus of the present invention, it is further preferable that a recovery member that contacts a position other than the contact position with each intermediate transfer member and collects toner from the cleaning member is individually provided for each cleaning member. . In this case, the bias applying unit applies a bias to each cleaning member via each recovery member. In this way, toner accumulation on the cleaning member is unlikely to occur.

In the image forming apparatus of the present invention, it is further preferable that the cleaning member is a foam roller formed of a conductive foam member. Furthermore, it is better that the opening ratio of the wall surface of the cell of the foam member is in the range of 3% to 50%. Further, the volume resistance of the foamed member is preferably in the range of 10 ³ to 10 ⁷ Ω · cm.

  The cleaning member in the image forming apparatus of the present invention may be a brush roller in which a conductive brush raw yarn is implanted instead of the foaming roller.

  According to the present invention, there is provided an image forming apparatus in which the cleaning capability of the cleaning member of the intermediate transfer member is enhanced, and it can cope with an operation state with a large residual toner amount and an operation mode with a high process speed.

1 is an overall configuration diagram of an image forming apparatus according to an embodiment. 1 is a configuration diagram of a main part of the image forming apparatus as the present invention. It is sectional drawing of the cleaning roller which concerns on embodiment. It is a block diagram (modification) of the principal part as this invention in an image forming apparatus.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to the image forming apparatus shown in FIG. 1 includes an intermediate transfer belt 101, four toner image forming units 1Y, 1M, 1C, and 1K arranged along the intermediate transfer belt 101, and toner from the intermediate transfer belt 101 to a printing sheet. A secondary transfer roller 115 that performs secondary transfer of the image and a cleaning unit 118 that cleans the surface of the intermediate transfer belt 101 after the secondary transfer are included. In addition to these, the image forming apparatus 100 further includes a paper feed unit 112, a paper transport unit 113, a fixing device 130, a paper discharge tray 117, and the like.

  Each of the toner image forming units 1Y, 1M, 1C, and 1K includes a photosensitive drum 21, a charger 20, an exposure unit 30, and a developing unit 10. The developing device 10 in this embodiment uses negatively charged toner. Further, a primary transfer roller 111 is disposed so as to face each photoconductor drum 21 with the intermediate transfer belt 101 interposed therebetween. Further, a toner container 200 for replenishment and a waste toner box 201 are disposed above the intermediate transfer belt 101. As a result, the image forming apparatus 100 forms a toner image on the photosensitive drum 21, transfers the toner image onto the intermediate transfer belt 101, and further transfers the toner image onto the printing paper.

  FIG. 2 shows the periphery of the intermediate transfer belt 101 which is a main part of the present invention in the image forming apparatus 100. As shown in FIG. 2, the intermediate transfer belt 101 is stretched around rollers 102 and 103. Among these, the roller 103 facing the secondary transfer roller 115 is a driving roller. As a result, the intermediate transfer belt 101 in FIG. 2 has its upper part moving from right to left and its lower part moving from left to right. The primary transfer roller 111 is located inside the intermediate transfer belt 101. In FIG. 2, the charger 20 and the exposure unit 30 are omitted. The developing device 10 is shown in a simplified manner.

  The cleaning unit 118 is disposed in the upper portion of the intermediate transfer belt 101 in FIG. Of course, this location is a location located downstream in the moving direction of the intermediate transfer belt 101 from the location where the secondary transfer is performed on the intermediate transfer belt 101, that is, the location facing the secondary transfer roller 115. In the cleaning unit 118, four cleaning rollers 41 to 44 are arranged in contact with the outer surface of the intermediate transfer belt 101. The four cleaning rollers 41 to 44 are arranged along the moving direction of the intermediate transfer belt 101.

  The cleaning rollers 41 to 44 in FIG. 2 are all foaming rollers formed of a foamable resin member. The foamable resin member used for the cleaning rollers 41 to 44 is given conductivity by a known means such as blending of metal powder. The configuration of the cleaning unit 118 will be described in more detail using the cleaning roller 41 as an example.

  The cleaning roller 41 is further provided with a collection roller 51. The collection roller 51 is made of metal and is connected to the high voltage power supply unit 61. The recovery roller 51 is provided with a scraper 71. The rotation direction of the collection roller 51 may be either with rotation or counter rotation with respect to the rotation of the cleaning roller 41. On the other hand, a counter roller 81 is disposed on the opposite side of the cleaning roller 41 with the intermediate transfer belt 101 interposed therebetween. The opposing roller 81 is grounded. As a result, the residual toner on the intermediate transfer belt 101 is collected by the cleaning roller 41 to which an electrical bias is applied. The residual toner collected on the cleaning roller 41 is further collected on the collection roller 51 and scraped off by the scraper 71 on the collection roller 51. The scraped residual toner is accommodated in the waste toner box 201 as waste toner.

  Similarly, the recovery rollers 52 to 54, the high-voltage power supply units 62 to 64, the opposing rollers 82 to 84, and the scrapers 72 to 74 are provided for the cleaning rollers 42 to 44, respectively. Each has the same configuration as that of the cleaning roller 41. Note that the functions of the high-voltage power supply units 61 to 64 may be integrated into one power supply device. Further, the number of opposed rollers is not necessarily the same as the number of cleaning rollers. A configuration in which one cleaning roller is also used by two cleaning rollers may be used.

  Here, the cleaning rollers 41 to 44 will be described in detail. Since the cleaning rollers 41 to 44 are the same, the cleaning roller 41 will be described as a representative. As shown in FIG. 3, the cleaning roller 41 is a foaming roller composed of a core metal 41S and a polyurethane foam layer 41F covering the periphery thereof.

  The polyurethane foam constituting the polyurethane foam layer 41F is a foamed member having a large number of cells (bubbles). This polyurethane foam has an open cell structure in which cells do not exist separately but are connected to each other through openings. For each cell, it is desirable that the opening ratio, which is a value obtained by dividing the opening area by the area of the entire wall surface of the cell and multiplying by 100, is in the range of 3% to 50%. The opening ratio within this range in polyurethane foam is naturally higher than the typical value (about 1%) for the closed cell structure. However, since the opening ratio of a general open-cell structure polyurethane foam is about 60%, it is lower than that.

  By using a polyurethane foam having such an opening ratio, the following effects can be obtained. First, the effect of having a higher opening ratio than that of the closed cell structure is that the polyurethane foam layer 41F is highly flexible and easily deformed. For this reason, compared with the closed cell structure, the adhesiveness to the intermediate transfer belt 101 is high and the ability to scrape the residual toner is high. Further, the aggressiveness to the intermediate transfer belt 101 is low. That is, there is little possibility that the cleaning rollers 41 to 44 damage (damage or wear) the surface of the intermediate transfer belt 101.

  On the other hand, the effect of having a lower opening ratio than that of a general open-cell structure is that the toner collected in the polyurethane foam layer 41F is less easily transferred from cell to cell. Therefore, the collected toner hardly penetrates to a deep portion in the polyurethane foam layer 41F. As a result, the polyurethane foam is less likely to be clogged, and the cleaning roller 41 can maintain flexibility over a long period of time.

  Regarding the relationship between the cell diameter and the cleaning performance of polyurethane foam, the following can be said in general. That is, if the cell diameter is smaller than the size of the foreign material to be collected, the foreign material cannot be taken in. For this reason, the cleaning performance is low. On the other hand, if the cell diameter is too large, the area and contact frequency of the contact surface that actually contacts the location to be cleaned will be small. Therefore, this also has low cleaning performance. In other words, the cell diameter may not be too small or too large. In this embodiment, the location to be cleaned is the intermediate transfer belt 101. For this reason, the object to be cleaned is residual toner or an aggregate thereof, and a cell diameter in the range of 50 to 1000 μm is preferable.

Further, the polyurethane foam constituting the polyurethane foam layer 41F is provided with conductivity as described above. This is because a bias is applied by the high voltage power source 61 to form a predetermined electric field with the intermediate transfer belt 101. The preferred conductivity of the polyurethane foam layer 41F is in the range of 10 ³ to 10 ⁷ Ω · cm in terms of volume resistance. If the resistance of the polyurethane foam layer 41F is too low, the polyurethane foam layer 41F or the intermediate transfer belt 101 may be damaged. This is because an excessive electric field is applied at a portion where the gap between the polyurethane foam layer 41F and the intermediate transfer belt 101 is small to cause a leak. On the other hand, when the resistance of the polyurethane foam layer 41F is too high, the voltage of the high-voltage power source 61 needs to be set high. For this reason, there is a problem of an increase in size and cost of the high-voltage power supply unit 61.

  A preferable range of the pressing force of the cleaning roller 41 to the intermediate transfer belt 101 is within a range in which the amount of biting of the intermediate transfer belt 101 into the cleaning roller 41 is 5% to 20% with respect to the thickness of the polyurethane foam layer 41F. It is. If there is not enough pressure contact, the cleaning ability will be insufficient. If the pressure contact force is excessive, the rotational load of the cleaning roller 41 and the intermediate transfer belt 101 becomes excessive.

  The cleaning roller 41 rotates counter to the movement of the intermediate transfer belt 101. A preferable rotation speed of the cleaning roller 41 is within a predetermined range with respect to the traveling speed of the intermediate transfer belt 101. That is, the peripheral speed of the cleaning roller 41 is preferably in the range of 0.5 to 2 times (in absolute value) the traveling speed of the intermediate transfer belt 101. If it is less than 0.5 times, that is, if the rotation of the cleaning roller 41 is too slow, the cleaning ability is insufficient. Conversely, if the cleaning roller 41 rotates too fast, the rotational load on the cleaning roller 41 and the intermediate transfer belt 101 becomes excessive. Here, the peripheral speed of the cleaning roller 41 refers to the speed at which one point on the surface moves as the cleaning roller 41 rotates. The running speed of the intermediate transfer belt 101 is the speed at which one point on the outer peripheral surface of the intermediate transfer belt 101 moves within the straight section of the intermediate transfer belt 101 during image formation.

  In addition, you may use a brush roller instead of the above-mentioned foaming roller as some rollers or all the rollers of the cleaning rollers 41-44. The brush roller is provided with a brush layer in place of the polyurethane foam layer 41F in the foaming roller described above. That is, a base fabric in which many brush yarns are implanted is wound around the core bar 41S so that the brush yarns face outward. As the base fabric, a fabric woven with conductive yarn or a fabric woven with conductive yarn is used. It is desirable to use a conductive adhesive for bonding the core metal 41S and the base fabric.

As the brush raw yarn, it is possible to use yarns made by blending various materials such as nylon, polyester, acrylic, and rayon with a conductive material. Examples of the conductive material include conductive carbon black and various ion conductive materials. A preferable conductivity of the brush raw yarn is 10 ⁵ to 10 ¹³ Ω · cm in terms of volume resistance. If the conductivity of the brush raw yarn is too high or too low, there is an adverse effect similar to the case where the conductivity of the polyurethane foam layer 41F in the case of the foam roller is too high or too low.

The preferable thickness of the brush yarn is in the range of 0.1 to 1 tex. The preferable range of the density of the brush yarn to the base fabric is 50,000 to 300,000 / inch ² . If the brush yarn is too thin or the flocking density is too low, the ability to scrape foreign matter on the intermediate transfer belt 101 is insufficient. On the other hand, if the brush yarn is too thick or the flocking density is too high, the aggressiveness to the intermediate transfer belt 101 is strong and the surface of the intermediate transfer belt 101 may be damaged. Another problem when the flocking density is too high is that the foreign matter once taken in is poorly discharged. For this reason, the cleaning performance cannot be maintained for a long time.

  The preferable range of the amount of biting into the intermediate transfer belt 101 of the brush roller is 10% to 40% with respect to the pile length of the brush raw yarn (the length of the portion protruding from the base fabric of the brush raw yarn). If the amount of bite is insufficient, the cleaning ability will be insufficient. If the amount of biting is excessive, the rotational load of the brush roller or the intermediate transfer belt 101 becomes excessive. The rotational speed is the same as that of the above-mentioned foaming roller even in the case of the brush roller.

Next, the bias applied to the collection rollers 51 to 54 by the high voltage power supply unit 61 will be described. A bias is applied to the collection rollers 51 to 54 by the high voltage power supply unit 61 so as to satisfy the following two conditions.
(Condition 1) The polarity of the bias is reversed between adjacent ones. That is, the most upstream collection roller 51 and the third collection roller 53 have the same polarity, and the second collection roller 52 and the most downstream collection roller 54 have opposite polarities. The polarity here is based on the ground potential of the opposing roller 81.
(Condition 2) Comparing the collection rollers with the same polarity, the bias is higher at the upstream side. Here, a high bias output means that in the case of voltage control, the absolute value of the bias voltage when the ground potential of the opposing roller 81 is used as a reference is large. Of course, in the case of current control, the absolute value of the bias current is large.

  The reason for this setting is as follows. First, the reason for Condition 1 is to efficiently collect the remaining toner with the polarity that was not collected by the previous cleaning roller by the second and subsequent cleaning rollers 42 to 44. Here, the transfer residual toner having a polarity that has not been collected by the previous cleaning roller includes a toner whose polarity is reversed when passing through the previous cleaning roller.

  The reason for condition 2 is the following two points. First, the reason why the upstream collection roller is set to a high bias is to efficiently collect the transfer residual toner at a stage where there is a large amount of transfer residual toner on the intermediate transfer belt 101. In addition, at the stage where there is a large amount of residual toner, damage to the surface of the intermediate transfer belt 101 is not a problem even when a high bias is applied. On the other hand, the reason why the downstream collecting roller is set to a low bias is that it is not necessary to apply a high bias at a stage where the amount of residual toner is low. At this stage, the surface of the intermediate transfer belt 101 is more likely to be damaged by the application of a high bias.

  Note that positive bias application by the high-voltage power supply 61 is not performed on the cleaning rollers 41 to 44. Still, the cleaning rollers 41 to 44 are at a voltage level between the voltage of the corresponding collection rollers 51 to 54 and the ground potential of the counter roller 81. As a result, a bias is indirectly applied to the cleaning rollers 41 to 44. This is because the cleaning rollers 41 to 44 and the collection rollers 51 to 54 are all conductive. As a result, the transfer residual toner from the intermediate transfer belt 101 to the cleaning rollers 41 to 44 and the transfer residual toner from the cleaning rollers 41 to 44 to the recovery rollers 51 to 54 are both favorably performed.

  However, the bias may be directly applied to the cleaning rollers 41 to 44 by the high voltage power supply unit 61. Even in that case, of course, the bias applied to the cleaning rollers 41 to 44 is such that the voltage level of the cleaning rollers 41 to 44 is an intermediate level between the voltage level of the corresponding recovery rollers 51 to 54 and the ground potential. To do. Alternatively, a configuration in which the collecting rollers 51 to 54 are eliminated and the scrapers 71 to 74 are directly applied to the cleaning rollers 41 to 44 can be considered.

  In this embodiment, as described above, the high-voltage power source 61 is connected to the collection rollers 51 to 54, and the opposing rollers 81 to 84 are grounded. However, conversely, the high-voltage power supply 61 can be connected to the opposing rollers 81 to 84 and the collection rollers 51 to 54 can be grounded. In this case, however, the polarity of the bias is reversed. The bias control method may be current control or voltage control. However, the current control is more reliable in collecting the toner.

  Examples of the present invention and comparative examples will be described below. In the examples and comparative examples described below, bizhub Pro C5501 manufactured by Konica Minolta was used as a testing machine, and the belt cleaning portion was modified and used for the test. The content of the modification is to replace the cleaning roller of the testing machine with the aforementioned foaming roller or brush roller. Here, two types of remodeling machines were prepared, the configuration shown in FIG. 2 having four cleaning rollers and the configuration having three cleaning rollers as shown in FIG. In addition, the amount of biting of the cleaning roller, applied bias, and other conditions were adjusted according to the test purpose.

There are five types of foaming rollers used in the examples and comparative examples. These are referred to as foam A, foam B, foam C, foam D, and foam E. Table 1 shows the contents of the polyurethane foam layer 41F. All numerical values of raw materials in Table 1 indicate parts by weight. Further, among the raw materials in Table 1, the following were used as materials other than water.
Polyol: Polyether polyol ("Accor ED-37B" (number average molecular weight 3000) manufactured by Mitsui Takeda Chemical)
Isocyanate: Methylene difernine diisocyanate (MDI) ("Millionate MTL-S" manufactured by Nippon Polyurethane)
Amine-based catalyst: Kao Riser No. 23NP
Foam stabilizer: linear dimethylpolysiloxane (“Niaxs silicone” L5614, manufactured by GE Silicones)

The amount of biting of the foaming roller when these foaming rollers were used in this example and the comparative example was as follows.
・ The amount of biting of the foam roller to the intermediate transfer belt 101 → 0.6 mm
-Biting amount of collection rollers 51 to 54 with respect to foaming roller → 0.6 mm

  On the other hand, there are two types of brush rollers used in this example and the comparative example. These are referred to as brush A and brush B. Details of these are shown in Table 2.

The amount of biting of the foaming roller when using these brush rollers in this example and the comparative example was as follows.
・ Brush roller biting amount with respect to the intermediate transfer belt 101 → 1.3 mm
-Biting amount of collection rollers 51-54 with respect to brush roller-> 1.3mm

  In either case of the foaming roller and the brush roller, the rotation of the cleaning rollers 41 to 44 and the collection rollers 51 to 54 was performed as follows in this example and the comparative example. First, regarding the rotational speed of the cleaning rollers 41 to 44, the peripheral speed of the cleaning rollers 41 to 44 and the running speed of the intermediate transfer belt 101 are set to 1: 1. Of course, the rotation direction of the cleaning rollers 41 to 44 is counter rotation with respect to the moving direction of the intermediate transfer belt 101.

  The rotation of the collection rollers 51 to 54 was performed as follows. About the rotation direction, it was set as with rotation with respect to rotation of the cleaning rollers 41-44. The rotation speed was set such that the circumferential speed ratio was 1: 1 between the collection rollers 51 to 54 and the cleaning rollers 41 to 44. That is, complete rotation with respect to the rotation of the cleaning rollers 41-44.

  In addition, said setting is an example regarding the amount of biting and rotation of the cleaning rollers 41-44 and the collection | recovery rollers 51-54, It is not limited to this. The same effect can be obtained even if it is changed within the range described in [0020], [0028], [0029], [0033].

  Subsequently, individual detailed configurations of the present example and the comparative example are shown in Table 3. The column “41, 51” in Table 3 shows the type of the cleaning roller 41 and the applied bias of the collection roller 51. The applied bias is current control, and Table 3 shows numerical values in the unit [μA]. Needless to say, the absolute value of the voltage increases as the absolute value increases. Similarly, the column “42, 52” indicates the type of the cleaning roller 42 and the bias applied to the collection roller 52. The same applies to the columns “43, 53” and “44, 54”.

  Of the examples and comparative examples in Table 3, Examples 1 to 6, 10 to 15, 19 to 21, and Comparative Examples 1, 2, and 4 to 8 have the four configurations shown in FIG. On the other hand, Examples 7-9 and 16-18 and the comparative example 3 are the things of the 3 structure shown in FIG. Examples 1 to 9 and Comparative Examples 1 to 5 are examples in which brush rollers are used as the cleaning rollers 41 to 44. On the other hand, Examples 10 to 21 and Comparative Examples 6 to 8 are examples in which a foaming roller is used as the cleaning rollers 41 to 44. Of these, Example 6 is an example in which “Brush B” is used for two of the four brush rollers on the upstream side and “Brush A” is used for the two on the downstream side. Similarly, in Example 15, “foam B” and “foam C” are mixed. In this way, different types of cleaning rollers may be mixedly mounted. Furthermore, although there is no specific example in Table 3, a brush roller and a foaming roller may be mixed and mounted.

  Next, the applied bias will be described. In Table 3, the bias applied to the collection rollers 51 and 53 has the same polarity in all of Examples 1 to 21 and Comparative Examples 1 to 8. The bias applied to the collection rollers 52 and 54 (excluding the collection roller 54 in the case of the three configuration) is opposite to that of the collection rollers 51 and 53. In this way, the applied biases have opposite polarities between adjacent ones. In only the four examples of Examples 5, 6, 14, and 15, the bias applied to the odd-numbered collection rollers 51 and 53 is negative, that is, the same polarity as the toner charging polarity. In all other examples, the bias applied to the odd-numbered collection rollers 51 and 53 is positive, that is, the same polarity as the charging polarity of the toner.

  In any of Examples 1 to 21, when the bias applied to the collection rollers 51 and 53 is compared in absolute value, the upstream collection roller 51 has a larger value. Further, the same applies to the bias applied to the collection rollers 52 and 54 (except for the three-roller configuration).

  However, this is not the case with Comparative Examples 1 to 8. When the absolute values of the bias applied to the collection rollers 51 and 53 are compared in Comparative Examples 1 to 4 and 6 to 8, the values are the same. Among them, especially in Comparative Examples 4, 6, and 7, the absolute value of any applied bias is a small value. In Comparative Example 5, the collection roller 53 on the downstream side has a rather large value. The same can be said for the bias applied to the collection rollers 52 and 54 (except for the comparative example 3 having three structures).

  Test results for Examples 1 to 21 and Comparative Examples 1 to 8 are shown in Table 4. In this test, two items of cleaning property and filming resistance were evaluated. Specifically, each evaluation was performed as follows.

Evaluation of cleaning performance In the configurations of the examples and comparative examples, the amount of toner on the intermediate transfer belt 101 after passing through the cleaning unit 118 was evaluated. The smaller this, the better the cleaning property. Specifically, an adhesive tape was attached to the surface of the intermediate transfer belt 101 after passing through the cleaning unit 118 and peeled off, and the tape was attached to CF paper manufactured by Konica Minolta. And the color difference (DELTA) E between the location which stuck the tape and the ground paper was measured. The color difference ΔE was measured using a spectral colorimeter “CM-2002” manufactured by Konica Minolta. In this evaluation, the amount of toner on the intermediate transfer belt 101 before entering the cleaning unit 118 was set to 10 g / m ² . The evaluation criteria were as follows.
Evaluation ◎: ΔE <0.5
Evaluation ○: 0.5 ≦ ΔE ≦ 2.0
Evaluation x: 2.0 <ΔE

-Evaluation of filming resistance Durability printing was performed to continuously create a single-layer solid band chart, and then an entire half image was created, and the filming state was evaluated using the entire half image. In the band chart in durable printing, the density of the band portion was 100%. The durable amount of durable printing was 100,000 sheets of A3 size. The evaluation criteria for the full half image were as follows.
Evaluation ◎: Evaluation that there is no significant difference in density between the band and non-band ○: Evaluation that the difference in density is slightly recognized between the band and non-band x: Clearly between the band and non-band And density difference is recognized

・ Comprehensive evaluation Comprehensive evaluation based on the above two items was performed according to the following criteria.
Overall evaluation ◎: Both items are evaluated ◎
Overall evaluation ○: One item is evaluated ◎ and the other item is evaluated ○
Overall evaluation ×: Other than the above

  According to Table 4, in each of Examples 1 to 21, the overall evaluation is ◎ or ○. In particular, in Examples 10 to 21 using a foam roller as the cleaning rollers 41 to 44, up to 10 out of 12 types are comprehensive evaluations ◎.

  On the other hand, all of Comparative Examples 1-8 were comprehensive evaluation x. The reason why Comparative Examples 1 to 8 are comprehensive evaluation x is understood as follows. That is, in the comparative examples 1 to 8, as described above, it is not established that the absolute value of the applied bias is larger between the collecting rollers having the same polarity on the upstream side.

  Particularly in Comparative Examples 1 to 3, 5, and 8, a relatively large bias is applied to the collection rollers 53 and 54 on the downstream side. For this reason, after the residual toner is collected to some extent by the upstream cleaning rollers 41 and 42 and decreases, a strong bias is applied. Therefore, in Comparative Examples 1 to 8, it is considered that the downstream cleaning rollers 43 and 44 are rather in a state where the surface of the intermediate transfer belt 101 is damaged. As a result, the surface state of the intermediate transfer belt 101 is deteriorated, and it is considered that the evaluation result is not good. In Comparative Examples 4, 6, and 7, the bias of all the rollers is low, so it is considered that the cleaning property is poor in the first place.

  On the other hand, the reason why the evaluation results were good in Examples 1 to 21 is that, among the collection rollers of the same polarity, the absolute value of the applied bias is larger on the upstream side. For this reason, as described above, most of the residual toner is first recovered at the stage of the upstream cleaning rollers 41 and 42 where the residual toner is high. At the stage of the cleaning rollers 43 and 44 on the downstream side where the residual toner is reduced, the remaining residual toner can be reliably collected without damaging the intermediate transfer belt 101 by the weakly applied bias. . As a result, good evaluation results are obtained. Therefore, those of Examples 1 to 21 can cope with an operation state with a large amount of residual toner and an operation mode with a high process speed.

  In addition, among Examples 1-21, the direction of Examples 10-21 using a foaming roller as the cleaning rollers 41-44 tends to be better as a whole than Examples 1-9 using a brush roller. This is probably because the foam roller has a larger contact area with the intermediate transfer belt 101 than the brush roller.

  As described above, the fifth, sixth, fourteenth, and fifteenth embodiments differ from the other embodiments in that the bias applied to the first collection roller 51 has the same polarity as the charging polarity of the toner. However, even in these examples, evaluation results equivalent to those in other examples are obtained.

  As described above in detail, in this embodiment, the cleaning unit 118 is provided on the downstream side of the secondary transfer position on the intermediate transfer belt 101 to clean the intermediate transfer belt 101. The cleaning unit 118 is provided with three or more cleaning rollers 41 to 44 (43), and a bias is applied to each cleaning roller. Here, with respect to the bias application to each cleaning roller, two conditions are satisfied, that is, the polarity is alternated and that the outputs of the same polarity are lower at the downstream side. This ensures that the transfer residual toner on the intermediate transfer belt 101 is collected without fear of the surface of the intermediate transfer belt 101 being damaged. Thus, the cleaning capability of the cleaning unit 118 is enhanced as compared with the conventional one, and an image forming apparatus that can cope with an operation state with a large amount of residual toner and an operation mode with a high process speed is realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the image forming apparatus 100 may be a copier or a printer, or may have a function of transmitting / receiving with an external line. Moreover, it is not restricted to a color machine. The toner to be used is not limited to the negatively charged type, and may be a positively charged type or may be either a one-component type or a two-component type.

101 Intermediate transfer belt
115 Secondary transfer roller
1Y to 1K toner image forming unit
21 Photosensitive drum
41-44 Cleaning roller 41F Polyurethane foam layer (foamed member)
51-54 Recovery Rollers 61-64 High Voltage Power Supply Unit (Bias Application Unit)

Claims (6)

An image forming apparatus comprising: a toner image forming unit that has a photoconductor and forms a toner image on the photoconductor; and an intermediate transfer body that receives the transfer of the toner image from the photoconductor and further transfers the toner image to a medium. In
Three or more conductive cleaning members that are provided in contact with a position downstream of a transfer position of the toner image on the intermediate transfer member to the medium and clean the intermediate transfer member;
A bias applying section for applying a bias to each cleaning member,
The bias applying unit includes:
Applying a reverse polarity bias to the cleaning members adjacent to each other,
An image forming apparatus characterized in that, with respect to a cleaning member to which a bias of the same polarity is applied, an output of a bias to be applied is increased as the upstream side is disposed. The image forming apparatus according to claim 1,
A collection member that contacts a position other than the contact position with the intermediate transfer member in each cleaning member and collects toner from the cleaning member is provided individually for each cleaning member;
The image forming apparatus, wherein the bias applying unit applies a bias to each of the cleaning members via each of the recovery members. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein the cleaning member is a foaming roller formed of a conductive foaming member. The image forming apparatus according to claim 3,
An image forming apparatus, wherein an opening ratio of a wall surface of a cell of the foam member is in a range of 3% to 50%. The image forming apparatus according to claim 3 or 4, wherein:
The volume resistance of the foamed member is in the range of 10 ³ to 10 ⁷ Ω · cm. The image forming apparatus according to claim 1, wherein:
The image forming apparatus according to claim 1, wherein the cleaning member is a brush roller formed by implanting conductive brush raw yarn.

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