JP2013113859A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device configured to stably obtain appropriate contact pressure, not too large but not too small, between a cleaning roller and an intermediate transfer belt, while using components with realistic dimensional accuracy for the cleaning roller and the like.SOLUTION: The image forming device includes an intermediate transfer belt 3 and a belt cleaning part 4 therefor. The belt cleaning part 4 includes: a cleaning roller 42, which is formed of a foamed material 46, in contact with a toner image carrying surface of the intermediate transfer belt 3 to perform counter rotation as the intermediate transfer belt 3 moves; a backup member 44 in contact with a non-toner-image carrying surface of the intermediate transfer belt 3; and an elastic member 49 for pressing at least one of the cleaning roller 42 and the backup member 44 to the other. The pressing force of the elastic member 49 attains an excellent contact condition between the cleaning roller 42 and the intermediate transfer belt 3, regardless of swinging accuracy of the cleaning roller 42 and the like.

Description

  The present invention relates to an image forming apparatus having an intermediate transfer belt. More specifically, the present invention relates to an image forming apparatus having a belt cleaning unit for cleaning an intermediate transfer belt.

  2. Description of the Related Art Conventionally, some image forming apparatuses using toner have an intermediate transfer belt, such as the one described in Patent Document 1. An image forming apparatus having an intermediate transfer belt usually has a plurality of photoconductors. Toner images of different colors are created by the plurality of photoconductors, transferred onto the intermediate transfer belt, and superimposed. The toner image, which is superimposed on the intermediate transfer belt and becomes full color, is re-transferred to the paper as the medium.

  A certain amount of toner remains on the intermediate transfer belt even after the toner image is retransferred to the medium. This untransferred toner causes problems such as causing image smearing at the next image formation. Therefore, belt cleaning for cleaning the intermediate transfer belt is provided. That is, at a position downstream from the retransfer position, the toner image carrying surface of the intermediate transfer belt is wiped with the cleaning member to remove the transfer residual toner. A cleaning roller using a foam member may be used as the cleaning member.

  Here, in general, the cleaning roller is arranged to bite into the intermediate transfer belt to some extent (for example, about 0.4 mm). A backup member is provided on the opposite side of the cleaning roller across the intermediate transfer belt. This is for suppressing the fluttering of the intermediate transfer belt during running and to closely contact the cleaning roller. Needless to say, if the adhesion is insufficient, cleaning cannot be performed sufficiently.

Japanese Patent No. 3548140

  However, the conventional techniques described above have the following problems. Due to the tolerance of each part, the adhesion between the cleaning roller and the intermediate transfer belt cannot be stably obtained. This is because the deflection accuracy (eccentricity) of the foaming member of the cleaning roller is about ± 0.2 mm. For this reason, even if the amount of biting into the intermediate transfer belt of the cleaning roller is set to 0.4 mm as described above, the amount of biting during actual rotation fluctuates in the range of 0.2 to 0.6 mm. . That is, the maximum bite amount reaches 0.6 mm. In this case, although it is temporary, the toner is excessively pressed, and the wax component in the toner oozes out and adheres to the surface of the intermediate transfer belt. This lowers the transfer efficiency and deteriorates the image quality. For example, it causes image pattern memory.

  On the other hand, if the maximum amount of biting is suppressed to 0.4 mm, the minimum value is 0.0 mm. This results in uneven cleaning due to poor contact. In this way, it is not possible to stably obtain a biting amount that is neither too much nor too little. Of course, this is a problem that can be resolved by increasing the dimensional accuracy of the cleaning roller. However, this is not realistic in an image forming apparatus that is mass-produced on a commercial scale. In particular, the foamed member used for the cleaning roller is more difficult to increase the processing accuracy than metal materials. Note that the above problem exists regardless of whether the toner is of a one-component type or a two-component type.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. In other words, the problem is that the pressure contact force of the cleaning roller to the intermediate transfer belt can be obtained stably without being too large or too small while using parts with realistic dimensional accuracy such as the cleaning roller. An object of the present invention is to provide an image forming apparatus.

  The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, has a toner image forming unit, and forms an image by transferring the toner image formed by the toner image forming unit onto a medium. The intermediate transfer belt having a structure having an elastic layer that receives the transfer of the toner image from the toner image forming unit and retransfers the toner image to the medium, and the intermediate transfer belt downstream of the retransfer position to the medium. A belt cleaning unit provided at a position upstream from the transfer position from the toner image forming unit. The belt cleaning unit is in contact with the toner image carrying surface of the intermediate transfer belt to move the intermediate transfer belt. A cleaning roller made of foam material that rotates counter to the surface, a backup member that contacts the non-toner image carrying surface of the intermediate transfer belt, a cleaning roller, and a back Tsu and resilient member for pressing at least one to the other is provided with up member.

  In this image forming apparatus, the cleaning roller is made of a foam material, and the cleaning roller and the backup member are pressed against each other. For this reason, the cleaning roller is slightly bitten by the backup member and the intermediate transfer belt. For this reason, during operation, the contact state between the cleaning roller and the intermediate transfer belt is well maintained regardless of the deflection accuracy of the cleaning roller. That is, the cleaning performance is high.

Further, in this image forming apparatus, it is desirable that the magnitude of the pressing force by the elastic member does not exceed 12.5 N (Newton) / m (meter) per dimension in the width direction of the cleaning roller or the backup member. This is because such a pressing force is sufficient in terms of ensuring the cleaning performance. Further, if the pressing force is larger than this, an adverse effect due to adhesion of the wax component to the intermediate transfer belt due to the pressure applied to the toner occurs.

  In this image forming apparatus, the amount of deviation of the position of the backup member from the position directly behind the cleaning roller across the intermediate transfer belt is 1/3 of the smaller one of the radius of the cleaning roller and the radius of the backup member. It is desirable that the pressing force by the elastic member is 7.5 N / m or more per dimension in the width direction of the cleaning roller or the backup member. When the arrangement is such that there is almost no deviation, the cleaning performance is good with such a pressing force.

  Alternatively, the amount of deviation is not less than 1/3 of the smaller one of the radius of the cleaning roller and the radius of the backup member, and exceeds the sum of the radius of the cleaning roller, the radius of the backup member, and the thickness of the intermediate transfer belt. The pressing force may be 2.5 N / m or more per dimension in the width direction. The winding of the intermediate transfer belt around the cleaning roller due to the amount of deviation acts in a direction in which the cleaning roller and the intermediate transfer belt are brought into better contact with each other.

In this image forming apparatus, the position of the cleaning roller is fixed with respect to the apparatus main body, and the elastic member may press the backup member toward the cleaning roller. Or conversely, the position of the backup member may be fixed with respect to the apparatus main body, and the elastic member may be configured to press the cleaning roller toward the backup member. In the latter case, it has a cleaner housing that houses the cleaning roller, the position of the backup member is fixed with respect to the apparatus body, the position of the cleaning roller is fixed with respect to the cleaner housing, and the elastic member is The cleaner housing may be pressed so that the backup member is pressed toward the cleaning roller.

  Further, in the present invention, there are two or more sets of cleaning rollers and backup members, each of the cleaning rollers is provided with a recovery member, and a bias unit that applies a bias between the recovery member and the backup member in each set It is desirable that the direction of the bias applied by the bias unit is different depending on the group. As a result, both the transfer residual toner that is normally charged and the transfer residual toner that is reversely charged are cleaned by the cleaning unit.

  According to the present invention, the pressure contact force of the cleaning roller to the intermediate transfer belt can be stably obtained without being too large or too small while using parts having realistic dimensional accuracy as each component such as the cleaning roller. An image forming apparatus is provided.

1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus according to an embodiment. FIG. 2 is a cross-sectional view of an intermediate transfer belt in the image forming apparatus of FIG. 1. FIG. 2 is a cross-sectional view illustrating a main part of a belt cleaner in the image forming apparatus of FIG. 1. It is a top view which shows the backup roller and its press spring in the belt cleaner of FIG. It is sectional drawing which shows the principal part of the belt cleaner which concerns on the 1st modification of this form. It is sectional drawing which shows the principal part of the belt cleaner which concerns on the 2nd modification of this form. It is a graph which shows the test result of the relationship between the pressing force of a backup roller, and memory generation life. It is a graph which shows the test result of the relationship between the pressing force and deviation | shift amount of a backup roller, and cleaning performance.

  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 1 shown in FIG. The image forming apparatus 1 of FIG. 1 includes four image forming units 2Y, 2M, 2C, and 2K and an intermediate transfer belt 3. This is a so-called tandem type image forming apparatus. The image forming apparatus 1 shown in FIG. 1 includes image forming units 2Y, 2M, 2C, and 2K, an intermediate transfer belt 3, a belt cleaner 4, a secondary transfer device 5, a fixing device 6, and a paper feed cassette 7. . This will be described in order below.

As shown in FIG. 2, the intermediate transfer belt 3 in the image forming apparatus 1 has a two-layer structure including a base material layer 35 and an elastic layer 36. The base material layer 35 is made of a resin material such as polyimide and has a thickness of about 80 μm. The elastic layer 36 is made of an elastic rubber material such as NBR rubber and has a thickness of about 200 μm. Both the base material layer 35 and the elastic layer 36 have a conductivity of about 10 ² to 10 ⁶ Ωcm. In the image forming apparatus 1, the intermediate transfer belt 3 is disposed so that the base material layer 35 is on the inner side and the elastic layer 36 is on the outer side, that is, on the toner image carrying surface side.

  Returning to FIG. 1, the intermediate transfer belt 3 is stretched around the stretching rollers 31 to 34, and circulates in the direction indicated by the arrow X in the drawing. The four image forming units 2Y, 2M, 2C, and 2K are structurally the same, and will be described below by using the image forming unit 2Y as a representative. The image forming unit 2Y is provided with a photosensitive drum 21, a charger 22, an exposure unit 23, and a developing unit 24. As a result, a toner image is formed on the surface of the photosensitive drum 21. The developing device 24 may be either one using a one-component developer or one using a two-component developer.

  The photosensitive drum 21 is in contact with the outer surface of the intermediate transfer belt 3. Further, a primary transfer roller 25 is provided on the back side of the intermediate transfer belt 3 when viewed from the photosensitive drum 21. The toner image on the photosensitive drum 21 is transferred onto the intermediate transfer belt 3 by the primary transfer bias between the primary transfer roller 25 and the photosensitive drum 21.

  The secondary transfer device 5 includes a secondary transfer belt 51 stretched by a plurality of rollers. One of the rollers for stretching the secondary transfer belt 51 is a secondary transfer roller 52. In the secondary transfer device 5, the toner image on the intermediate transfer belt 3 is transferred onto the paper P by the secondary transfer bias between the secondary transfer roller 52 and the stretching roller 31 of the intermediate transfer belt 3. It has become. For this reason, the paper P is supplied from the paper feed cassette 7 and enters the nip between the intermediate transfer belt 3 and the secondary transfer belt 51. Further, the toner image is fixed by the fixing device 6 on the paper P to which the toner image has been transferred.

  The belt cleaner 4 is a device that removes toner on the intermediate transfer belt 3. What is removed by the belt cleaner 4 is untransferred toner remaining on the intermediate transfer belt 3 even after transfer by the secondary transfer device 5. When the next image formation is carried out with the transfer residual toner left unattended, the image becomes dirty, and the intermediate transfer belt 3 is cleaned to prevent this. Therefore, the belt cleaner 4 is provided in the intermediate transfer belt 3 at a position downstream of the secondary transfer device 5 and upstream of any of the image forming units 2Y, 2M, 2C, 2K.

  The belt cleaner 4 has a housing 41 and two sets of a cleaning roller 42 and a collection roller 43 arranged therein on the outer surface side of the intermediate transfer belt 3. A backup roller 44 is provided on the back side of the intermediate transfer belt 3 as viewed from the cleaning roller 42.

One set of the cleaning roller 42, the collection roller 43, and the backup roller 44 in the belt cleaner 4 is shown in an enlarged manner in FIG. In FIG. 3, the housing 41 is not drawn. As shown in FIG. 3, the cleaning roller 42 is in contact with the outer surface side of the intermediate transfer belt 3 and rotates counter to the moving direction X (arrow Z1). The rotation speed of the cleaning roller 42 is a rotation speed at which the outer peripheral surface speed is equal to the moving speed of the intermediate transfer belt 3. The cleaning roller 42 is a foaming roller having a cored bar 45 and a polyurethane foam layer 46 covering the outer periphery thereof. The core metal 45 has a diameter of about 10 mm, and the polyurethane foam layer 46 has an outer diameter of about 18 mm. The material of the polyurethane foam layer 46 is, for example, as described in [0045] to [0061] of Japanese Patent Application Laid-Open No. 2009-300741, and imparts conductivity of about 10 ² to 10 ⁶ Ωcm. It's okay.

The collection roller 43 is disposed so as to be in contact with the cleaning roller 42 and not in contact with the intermediate transfer belt 3. The collection roller 43 is a metal roller and is driven to rotate by the rotation of the cleaning roller 42 (arrow Z2). The diameter of the collection roller 43 is about 15 mm. The collection roller 43 may be counter-rotated with respect to the rotation of the cleaning roller 42. The recovery roller 43 is provided with a scraper 47 and a cleaning power supply 48. The scraper 47 is fixedly provided, and the tip is in contact with the collection roller 43. The cleaning power supply 48 applies a bias to be described later to the collection roller 43. The axial positions of the cleaning roller 42 and the collection roller 43 are both fixed with respect to the body of the image forming apparatus 1.

  The backup roller 44 is a roller that rotates following the movement of the intermediate transfer belt 3 (arrow Z3). The backup roller 44 is a metal roller like the collection roller 43. The diameter of the backup roller 44 is about 11 mm. However, unlike the power supply connected to the collection roller 43, the backup roller 44 is directly grounded. Or conversely, the recovery roller 43 may be grounded and the cleaning power supply 48 may be connected to the backup roller 44. In short, it is sufficient that a voltage is applied between the collection roller 43 and the backup roller 44. The backup roller 44 may be a foaming roller made of the same material as the cleaning roller 42, instead of a metal roller.

  Further, the backup roller 44 is provided with a pressing spring 49. As shown in FIG. 4, the pressing spring 49 presses the shaft portions 50 at both ends in the width direction of the backup roller 44. The other end of the pressing spring 49 is fixed to an appropriate part 53 of the body of the image forming apparatus 1. The pressing spring 49 is assembled in a compressed state from the free length. As a result, the backup roller 44 is pressed toward the cleaning roller 42 with a pressing force based on the elasticity of the pressing spring 49. During operation, the length of the pressing spring 49 slightly varies due to low deflection accuracy of the cleaning roller 42 and the like. However, the magnitude of the pressing force of the pressing spring 49 hardly changes due to the fluctuation of the length, and can be regarded as constant.

  The magnitude of the pressing force may be in the range of 5 to 12.5 N (Newton) / m (meter) as the linear pressure per dimension in the width direction of the backup roller 44. Thus, the amount of biting of the intermediate transfer belt 3 and the backup roller 44 with respect to the cleaning roller 42 is set within a range of about 0.1 to 0.3 mm. For example, assuming that the size in the width direction of the backup roller 44 is 300 mm, the total pressing force of the two pressing springs 49 may be 3N. This pressing force is in a relatively light category. That is, the backup roller 44 is only lightly pressed against the cleaning roller 42.

  In the belt cleaner 4 configured as described above, during operation, the transfer residual toner 54 on the outer surface of the intermediate transfer belt 3 is first scraped off by the cleaning roller 42. Here, the scraped toner 54 is mainly charged to the opposite polarity to the bias applied by the cleaning power supply 48 among the transfer residual toner 54. The residual transfer toner 54 scraped off is placed on the surface of the cleaning roller 42 and moves with the rotation of the cleaning roller 42. Further, the surface of the cleaning roller 42 moves to the surface of the collection roller 43. Then, it is mechanically peeled off from the surface of the collection roller 43 by the scraper 47. This is the basic principle of cleaning the intermediate transfer belt 3 by the belt cleaner 4.

  As described above, in the belt cleaner 4, two combinations of the cleaning roller 42, the recovery roller 43, and the backup roller 44 are provided. Each recovery roller 43 is provided with a cleaning power supply 48 separately. Therefore, the bias applied by the cleaning power source 48 is reversed between the upstream side and the downstream side. As a result, both the positively charged and negatively charged transfer residual toner 54 can be removed from the intermediate transfer belt 3.

  In particular, the bias polarity of the upstream cleaning power supply 48 may be opposite to the original charging polarity of the toner, and the downstream bias polarity may be the same as the original charging polarity of the toner. For example, if the original charging polarity of the toner is negative, a positive bias is applied on the upstream side and a negative bias is applied on the downstream side. Thus, the regular charged toner occupying most of the transfer residual toner 54 is first removed by the upstream cleaning roller 42. Next, the reversely charged toner remaining on the intermediate transfer belt 3 is removed by the cleaning roller 42 on the downstream side. In this way, the transfer residual toner 54 is efficiently removed.

  In the belt cleaner 4 of this embodiment, as described above, the backup roller 44 is pressed against the cleaning roller 42 with a constant pressing force by the elastic force of the pressing spring 49. Therefore, even during operation, the amount of biting between the cleaning roller 42 and the backup roller 44 is kept constant regardless of the deflection accuracy of the cleaning roller 42 and the backup roller 44. For this reason, even if the amount of biting of the intermediate transfer belt 3 and the backup roller 44 with respect to the cleaning roller 42 is set to be small as described above, poor contact occurs between the cleaning roller 42 and the intermediate transfer belt 3 during operation. There is no. For this reason, cleaning unevenness does not occur and cleaning is performed satisfactorily. Further, it is not necessary to set the amount of biting of the cleaning roller 42 excessively large.

  Next, a modification of this embodiment will be described. In FIG. 5, the principal part of the belt cleaner 4 which concerns on a 1st modification is shown. In FIG. 5, unlike FIG. 3, the housing 41 is also drawn. The housing 41 in the modified example of FIG. 5 is provided to be rotatable around a fulcrum 55. The position of the fulcrum 55 is fixed with respect to the body of the image forming apparatus 1. A pressing spring 56 is provided on the housing 41 in FIG. One end of the pressing spring 56 is fixed to the body of the image forming apparatus 1 and the other end presses the housing 41. The pressing direction is a direction in which the housing 41 is brought closer to the intermediate transfer belt 3 and the backup roller 44.

  In the modification of FIG. 5, unlike the example of FIG. 3, there is no pressing spring 49 that presses the backup roller 44. The axial position of the backup roller 44 in the modification of FIG. 5 is fixed with respect to the body of the image forming apparatus 1. On the other hand, the axial positions of the cleaning roller 42 and the collection roller 43 in the modification of FIG. 5 are not fixed to the body of the image forming apparatus 1 but to the housing 41. Therefore, the elasticity of the pressing spring 56 acts as a force that presses the cleaning roller 42 against the backup roller 44 in the right direction in the drawing.

  That is, in the example of FIG. 3, the backup roller 44 is pressed against the cleaning roller 42 by the pressing spring 49, whereas in the modified example of FIG. 5, the cleaning roller 42 is reversely pressed against the backup roller 44 by the pressing spring 56. Is pressing. Even with such a configuration, the same effect as in the example of FIG. 3 can be obtained. In FIG. 5, only one set of the cleaning roller 42 and the like is depicted in the housing 41, but in reality, as described in the explanation of the example of FIG. There are pairs.

  In FIG. 5, in the housing 41, the pressing spring 56 is positioned upstream of the fulcrum 55 in the moving direction X of the intermediate transfer belt 3. However, this is not essential and may be reversed. Further, the movement of the housing 41 itself is not necessarily a rotational movement around the fulcrum. It may be configured to move linearly. Furthermore, it is not essential that the pressing spring 56 is configured to press the cleaning roller 42 or the like via the housing 41. A configuration in which the shaft of the cleaning roller 42 or the like is directly pressed without using the housing 41 may be employed. Further, in the example of FIG. 5, the cleaning power supply 48 may be connected to the backup roller 44 and the collection roller 43 may be grounded.

  Next, a second modification will be described. The second modification shown in FIG. 6 is obtained by slightly shifting the position of the backup roller 44 based on the example of FIG. That is, in the example of FIG. 3, the backup roller 44 is positioned directly behind the cleaning roller 42 with the intermediate transfer belt 3 interposed therebetween. On the other hand, in the modified example of FIG. 6, the backup roller 44 is arranged at a position shifted to the downstream side in the movement direction X of the intermediate transfer belt 3 from the position in FIG. Accordingly, the intermediate transfer belt 3 is slightly wound around the cleaning roller 42 at the position where the backup roller 44 and the cleaning roller 42 face each other. As a result, even if the pressing force by the pressing spring 49 is light as described above, the contact followability of the intermediate transfer belt 3 to the cleaning roller 42 is high, and the cleaning of the intermediate transfer belt 3 by the cleaning roller 42 is surely performed. .

  Note that the amount of deviation F of the position of the backup roller 44 is very small. If the size of the cleaning roller 42 and the like is as described above, a sufficient effect can be obtained if there is a deviation amount F of about 2 mm. The maximum allowable deviation amount F is a total value of the three of the radius of the backup roller 44 and the cleaning roller 42 and the thickness of the intermediate transfer belt 3. A more preferable range of the deviation amount F is within a range from one third to one time with respect to the smaller one of the radius of the cleaning roller 42 and the radius of the backup roller 44. Furthermore, the direction of the deviation may be either the upstream side or the downstream side. FIG. 6 shows an example shifted to the downstream side. Note that the first modification shown in FIG. 5 and the second modification shown in FIG. 6 may be combined.

  Subsequently, tests conducted by the present inventor in order to confirm the effects of the present invention and the results thereof will be described. In this experiment, bizhabPro6500P manufactured by Konica Minolta was used as a tester. However, the cleaning blade of the intermediate transfer belt was removed, and a belt cleaner 4 of this embodiment was mounted instead for the test. The belt cleaner 4 mounted on the testing machine is of the type shown in FIG. 3 in which the backup roller 44 is pressed by a pressing spring 49, and the number of sets is two.

The dimensions and the like of the cleaning roller 42 subjected to the test are as follows.
Diameter of cored bar 45: 10 mm
Polyurethane foam layer 46 outer diameter: 18 mm
Number of cells of polyurethane foam layer 46: 50 cells / 25.4 mm
Hardness of polyurethane foam layer 46: Load at the time of 30% intrusion is 0.196 N / cm
Density of polyurethane foam layer 46: 0.1 g / cm ³
Volume resistivity of the polyurethane foam layer 46: 10 ⁴ Ωcm

As the backup roller 44, a metal roller having a diameter of 11 mm was used. The backup roller 44 is configured to rotate following the intermediate transfer belt. The intermediate transfer belt 3 is obtained by laminating an elastic layer of NBR rubber having a thickness of 200 μm on a polyimide substrate having a thickness of 80 μm. The following two types of tests were performed using the above tester.
1. 1. Test of relationship between pressing force of backup roller and memory generation life Testing the relationship between the pressing force and deviation of the backup roller and the cleaning performance

  First, the test “1.” will be described. In this test, an endurance test was performed in which printing of 5 cm × 5 cm patch images of blue color (magenta toner + cyan toner) was continuously performed. Then, for each 50,000 sheets, one monochrome 1-dot halftone image (density 600 dpi) was printed. It was visually checked whether the afterimage of the pattern of the patch image appeared in the halftone image. The number of printed patch images until the afterimage was visually recognized was defined as the memory generation life.

  In this test, the number of cleaning rollers 42 and the like in the belt cleaner 4 is two. The “deviation” described in FIG. 6 was not provided. The pressing force of the pressing spring 49 was set in five stages within a range of 5 to 25 N / m in terms of linear pressure per width direction. The bias applied to the collection roller 43 was set so that the upstream side was positive, the downstream side was negative, and the bias current value was 40 μA.

  The result of the test was as shown in the graph of FIG. In the graph of FIG. 7, the horizontal axis represents the pressing force of the backup roller 44, and the vertical axis represents the memory generation life. 7 that the memory generation life is shorter as the pressing force of the backup roller 44 is higher. This is presumably because, as described in [0006], when the pressing force of the backup roller 44 is strong, the phenomenon that the wax component in the toner adheres to the intermediate transfer belt 3 easily occurs. On the other hand, when the pressing force is light, the memory generation life is good. Here, if there is a memory generation life of 1000K sheets (1 million sheets) or more, the memory is passed and the upper limit of the pressing force is 12.5 N / m.

  Next, the test “2.” will be described. In this test, a blue solid image was formed, the secondary transfer bias was turned off, and the cleaning ability of the belt cleaner 4 was checked. The measurement conditions for this test are four steps in the range of 5 to 20 N / m for the pressing force of the backup roller 44 in the linear pressure per width direction. There were three stages, 2 mm on the side and 4 mm on the downstream side. In other words, the test was conducted under 12 measurement conditions. Both 2 mm and 4 mm are within the range from one third to one time with respect to 5.5 mm which is the smaller radius of the cleaning roller 42 and the backup roller 44. .

  In carrying out this test, the number of cleaning rollers 42 and the like in the belt cleaner 4 was set to one. The bias applied to the collection roller 43 was set so that the polarity was positive and the current value was 40 μA. The toner used is negatively charged. With this setting, the cleaning residual toner on the intermediate transfer belt 3 at the position after passing the belt cleaner 4 was peeled off with a booker tape and attached to a white mount for evaluation. The remaining toner is collected with a booker tape within the area of the entire solid image, and at the front end, center, and rear end in the belt traveling direction, the back end, center, and front end in the belt width direction, respectively. I went to 9 places for convenience. These 9 booker tapes and a new booker tape were pasted on a single mount, and the color was measured.

  For the measurement, a spectrocolorimeter CM-512mk3 manufactured by Konica Minolta Sensing Co., Ltd. was used. With this spectrocolorimeter, the color difference ΔE from the reference of nine booker tapes other than the reference was measured using a new booker tape as a reference. If all nine color differences ΔE were 0.7 or less, the measurement condition was determined to be acceptable, and if ΔE exceeded 0.7 even at one position, the measurement condition was determined to be unacceptable. Note that ΔE of 0.7 is a minute color difference that can be discriminated by visual inspection.

  The measurement results were as shown in FIG. That is, of the 12 types of measurement conditions, only one condition when the pressing force was the lowest and the deviation amount was 0 was rejected, and the other 11 conditions were all acceptable.

  When the distribution of the residual cleaning toner on the intermediate transfer belt 3 was observed in more detail under the rejected conditions, it was found that a cleaning failure occurred at a pitch that coincided with the circumferential length of the cleaning roller 42. From this, it is considered that this cleaning failure is caused by the wobbling of the cleaning roller 42 (see [0006]). That is, since the pressing force of the backup roller 44 against the cleaning roller 42 is weak, it is understood that the contact between the cleaning roller 42 and the intermediate transfer belt 3 becomes defective due to the vibration of the cleaning roller 42. However, it can be seen that even if the pressing force is weak as described above, there is no problem if the shift amount of the backup roller 44 is 2 mm or more. The direction of the deviation of the backup roller 44 is set to the downstream side in this test, but the same result is obtained on the upstream side.

  In addition, although the total six conditions of the pressing forces 15 N / m and 20 N / m in FIG. 8 are determined to be acceptable in FIG. 8, the result of FIG. It is a condition. From the above, taking the above together, the preferable range of the pressing force is 7.5 to 12.5 N / m, more preferably 10 to 12.5 N / m, when there is no deviation in the arrangement of the backup roller 44. Become. When the backup roller 44 is arranged with a deviation amount of 2 mm or more, it is 2.5 to 12.5 N / m, more preferably 5 to 12.5 N / m.

  As described above in detail, in the belt cleaner 4 in the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 3 is sandwiched while the cleaning roller 42 and the backup roller 44 are slightly pressed against each other. For this reason, regardless of the deflection accuracy of the cleaning roller 42, the contact state between the cleaning roller 42 and the intermediate transfer belt 3 is stable, and good cleaning properties are exhibited. Moreover, since the pressing force itself is sufficient, it is good from the viewpoint of memory generation life. Further, a better result can be obtained by arranging the backup roller 44 so as to be shifted upstream or downstream with respect to the cleaning roller 42.

  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, although four image forming units 2Y, 2M, 2C, and 2K are arranged vertically in FIG. 1, this is not essential. It may be arranged side by side. Further, in the configuration shown in FIG. 3 where the backup roller 44 is pressed by the pressing spring 49, the backup roller 44 may be rotated instead of linearly moved as in the case of the movement of the housing 41 in the configuration of FIG. Good.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2Y etc. Image forming part 3 Intermediate transfer belt 4 Belt cleaner 5 Secondary transfer apparatus 41 Housing 42 Cleaning roller 43 Recovery roller 44 Backup roller 48 Cleaning power supply 49 Press spring 56 Press spring F Deviation amount

Claims (8)

In an image forming apparatus having a toner image forming unit and forming an image by transferring a toner image formed by the toner image forming unit onto a medium,
An intermediate transfer belt having a structure having an elastic layer, which receives the transfer of the toner image from the toner image forming unit and retransfers the toner image to a medium;
A belt cleaning unit provided at a position downstream of the retransfer position to the medium and upstream of the transfer position from the toner image forming unit in the intermediate transfer belt;
In the belt cleaning section,
A cleaning roller made of a foam material that contacts a toner image carrying surface of the intermediate transfer belt and rotates counter to the movement of the intermediate transfer belt;
A backup member in contact with the non-toner image carrying surface of the intermediate transfer belt;
An image forming apparatus, comprising: an elastic member that presses at least one of the cleaning roller and the backup member toward the other. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the pressing force of the elastic member does not exceed 12.5 N (Newton) / m (meter) per dimension in the width direction of the cleaning roller or the backup member. The image forming apparatus according to claim 2,
The amount of deviation of the position of the backup member from the position directly behind the cleaning roller across the intermediate transfer belt does not reach 1/3 of the smaller one of the radius of the cleaning roller and the radius of the backup member. Is in range,
The image forming apparatus according to claim 1, wherein the pressing force of the elastic member is 7.5 N / m or more per dimension in the width direction of the cleaning roller or the backup member. The image forming apparatus according to claim 2,
The amount of deviation of the position of the backup member from the position directly behind the cleaning roller across the intermediate transfer belt is 1/3 or more of the smaller one of the radius of the cleaning roller and the radius of the backup member. And the radius of the cleaning roller, the radius of the backup member and the thickness of the intermediate transfer belt do not exceed the sum, and the magnitude of the pressing force by the elastic member is the cleaning roller or the backup member An image forming apparatus having a width per dimension of 2.5 N / m or more. The image forming apparatus according to any one of claims 1 to 4, wherein:
The position of the cleaning roller is fixed with respect to the apparatus body,
The image forming apparatus according to claim 1, wherein the elastic member presses the backup member toward the cleaning roller. The image forming apparatus according to any one of claims 1 to 4, wherein:
The position of the backup member is fixed with respect to the apparatus body;
The image forming apparatus according to claim 1, wherein the elastic member presses the cleaning roller toward the backup member. The image forming apparatus according to claim 6,
A cleaner housing that houses the cleaning roller;
The position of the backup member is fixed with respect to the apparatus body;
The position of the cleaning roller is fixed with respect to the cleaner housing, and the elastic member presses the cleaner housing so that the backup member is pressed toward the cleaning roller. An image forming apparatus. In the image forming apparatus according to any one of claims 1 to 7,
Having two or more sets of the cleaning roller and the backup member;
Each of the cleaning rollers is provided with a collecting member,
A bias portion for applying a bias is provided between the recovery member and the backup member in each set,
An image forming apparatus, wherein a direction of a bias applied by the bias unit is different depending on a group.

Images