JP2013222110A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a reduction in the rate of reverse transfer of residual toner from an intermediate transfer body to a photoreceptor, in an image forming apparatus that removes a toner that is not secondary-transferred to a sheet and remains on an intermediate transfer belt from the surface of the intermediate transfer belt by reverse transfer of the residual toner from the intermediate transfer belt to a photoreceptor.SOLUTION: When a presence range of residual toner on an intermediate transfer belt 33 and a primary transfer planned range of a toner image to be transferred from a photoreceptor 20 to the intermediate transfer belt 33 overlap with each other, a time period of forming an electrostatic latent image on the photoreceptor 20 is delayed so that reverse transfer of the residual toner from the intermediate transfer belt 33 to the photoreceptor 20 by a primary transfer roller 24 and primary transfer of the toner image from the photoreceptor 20 to the intermediate transfer belt 33 do not occur at the same time.

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that primarily transfers and superimposes toner images of different colors onto an intermediate transfer body, and then secondary-transfers them collectively onto a transfer material. It is.

  As a so-called full-color image forming apparatus, toner images of different colors are formed on a photoconductor as an image carrier, and these toner images are primarily transferred to an intermediate transfer body to be sequentially superposed to form a full-color toner image. There is known an apparatus for secondary transfer to a member to be transferred such as.

  In such a full-color image forming apparatus, an electric field cleaning method is being used from the viewpoint of durability and the like as a method for removing residual toner remaining on the intermediate transfer member from the intermediate transfer member without performing secondary transfer.

  As one of the electric field cleaning methods, a voltage having the same polarity as that of the electrode applied to the primary transfer unit is applied to the cleaning member to reversely charge the residual toner, and the residual toner is removed from the intermediate transfer member during the primary transfer. There has been proposed a method (hereinafter, referred to as “reverse charging method”) in which the toner is reversely transferred to the photoreceptor and collected by a cleaning member for the photoreceptor (see, for example, Patent Documents 1 to 3).

Japanese Patent Laid-Open No. 9-44007 Japanese Unexamined Patent Publication No. 9-50198 JP 2005-250412 A

  As a result of various studies by the present inventors on the proposed reverse charging method, as shown in FIG. 9A, when the remaining toner is reversely transferred in the primary transfer region, the toner is transferred onto the photoreceptor 20. When no image is formed, the residual toner is smoothly reversely transferred from the intermediate transfer member 33 to the photoconductor 20, while a toner image is formed on the photoconductor 20 as shown in FIG. 9B. In this case, the rate at which the residual toner is reversely transferred to the photoconductor 20 becomes extremely low, and the residual toner that could not be collected on the photoconductor side entered the next toner image. When the ratio of the residual toner (black) that entered the toner image (blackened area ratio (%)) was measured, as shown in FIG. 10, the black when no toner image was formed on the photoreceptor 20. The blackened area ratio was 0.2%, whereas the blackened area ratio when the toner image (solid image) was formed on the photoconductor was a significantly high value of 1.0%.

  The present invention has been made in view of such a conventional problem, and an object of the present invention is to not reduce the rate of reverse transfer of residual toner from an intermediate transfer member to a photosensitive member in an image forming apparatus using a reverse charging method. There is.

  An image forming apparatus according to the present invention that achieves the above object includes a rotatable image carrier, a rotatable intermediate transfer member, and an electrostatic latent image formed on the image carrier developed with different color toners. A plurality of developing means, a primary transfer means for primary transfer of the toner image formed on the image carrier to the intermediate transfer body by applying a voltage having a polarity opposite to the charging polarity of the toner; A secondary transfer unit that secondary-transfers the toner image that has been primarily transferred onto the intermediate transfer member to a member to be transferred by applying a voltage having a polarity opposite to the charged polarity of the toner; A charging unit provided on the downstream side in the rotation direction of the transfer body and charging the residual toner remaining on the intermediate transfer body without secondary transfer to the same polarity as the voltage applied to the primary transfer unit; Control for controlling formation of electrostatic latent image on image carrier The residual toner remaining on the intermediate transfer body is charged to the same polarity as the voltage applied to the primary transfer means by the charging means, and the image is transferred from the intermediate transfer body by the primary transfer means. In an image forming apparatus that reversely transfers residual toner to a carrier and removes it from the intermediate transfer member, a residual toner existing range on the intermediate transfer member and a toner image transferred from the image carrier to the intermediate transfer member When the scheduled primary transfer area overlaps, the control means performs reverse transfer of residual toner from the intermediate transfer body to the image carrier by the primary transfer means, and from the image carrier to the intermediate transfer body. The timing of forming the electrostatic latent image on the image carrier is delayed so that the primary transfer of the toner image to the toner does not occur at the same time.

  Here, a plurality of image carriers and a plurality of primary transfer units are provided corresponding to the plurality of developing units, and the image carrier and the primary transfer unit positioned at the most upstream in the rotation direction of the intermediate transfer member, Thus, residual toner remaining on the intermediate transfer member may be removed from the intermediate transfer member.

  It is preferable that the residual toner existing range on the intermediate transfer member is the existing toner image primary transfer range closest to the intermediate transfer member.

  Further, it is preferable to divide the existence range of the toner image into a grid and determine whether or not there is residual toner for each division.

  Further, the residual toner ratio on the intermediate transfer member is calculated based on at least one of the environmental conditions, the type of member to be transferred, and the color of the toner image primarily transferred to the intermediate transfer member. When the toner ratio is a predetermined value or more, it may be determined that there is residual toner on the intermediate transfer member.

  In the image forming apparatus of the present invention, when the remaining toner existing range on the intermediate transfer member and the scheduled primary transfer range of the toner image transferred from the photosensitive member to the intermediate transfer member overlap, The timing of forming the electrostatic latent image is delayed so that the reverse transfer of the residual toner from the intermediate transfer member to the image carrier and the primary transfer of the toner image from the image carrier to the intermediate transfer member do not occur simultaneously. Therefore, the rate at which the residual toner is reversely transferred from the intermediate transfer member to the photosensitive member is not reduced. As a result, a high-quality image free from noise can be obtained even under special conditions where the amount of residual toner increases.

1 is a schematic diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic view of an intermediate transfer belt 33 and its surroundings in the image forming apparatus of FIG. 1. It is a principal part schematic diagram which shows other embodiment of the image forming apparatus which concerns on this invention. It is a principal part schematic diagram which shows other embodiment of the image forming apparatus which concerns on this invention. It is a principal part schematic diagram which shows other embodiment of the image forming apparatus which concerns on this invention. FIG. 4 is a diagram illustrating a region where residual toner is likely to be generated depending on temperature and humidity. FIG. 6 is a diagram exemplifying the size of a division when dividing the existence range of a toner image into a lattice shape. It is a flowchart of the control implemented in the Example and the comparative example. FIG. 6 is a state diagram when the residual toner is reversely transferred from the intermediate transfer member to the photosensitive member. 6 is a graph showing that the black area ratio varies depending on whether or not a toner image is present on the photoreceptor when the remaining toner is reversely transferred.

  The image forming apparatus according to the present invention will be described below with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is a so-called tandem color printer D. Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. Further, the image forming method is not limited to the tandem method, and other methods, for example, four developing devices are arranged around the rotation shaft, and these are sequentially opposed to the electrostatic latent image carrier to be full color. A so-called four-cycle method for creating an image may be used.

  The image forming apparatus D includes an endless intermediate transfer belt (intermediate transfer member) 33 having conductivity. The intermediate transfer belt 33 is hung on a pair of rollers 31 and 32 disposed on both the left and right sides in the drawing. The roller 32 is connected to a motor (not shown), and the roller 32 rotates counterclockwise by driving the motor, whereby the intermediate transfer belt 33 and the roller 31 in contact therewith are driven to rotate. A secondary transfer roller (secondary transfer unit) 34 is always pressed against the outside of the belt portion supported by the roller 32 by a biasing unit (not shown). A voltage applying device 35 is connected to the secondary transfer roller 34. The toner image formed on the intermediate transfer belt 33 at the nip portion (secondary transfer region) between the secondary transfer roller 34 and the intermediate transfer belt 33 is transferred to the conveyed paper (transfer target member) P. .

  Below the intermediate transfer belt 33 suspended between the rollers 31 and 32, yellow (Y), magenta (M), cyan (C), black ( K) four image forming units 2Y, 2M, 2C, and 2K (hereinafter may be collectively referred to as “image forming unit 2”) are detachably disposed on the apparatus main body. In these image forming units 2, a toner image of a corresponding color is created using each color developer.

  The image forming unit 2 has a rotatable cylindrical photoconductor 20 as an electrostatic latent image carrier. Around the photoconductor 20, a photoconductor charging device 21, a development device (development device) 23, a primary transfer roller (primary transfer device) 24, and the rotation direction (clockwise direction) in that order, and A photoreceptor cleaning device 6 is arranged. The photoconductor cleaning device 6 includes a cleaning blade, and one end of the photoconductor cleaning device 6 is brought into contact with the outer peripheral surface of the photoconductor 20 to remove and collect toner remaining on the surface of the photoconductor 20. The primary transfer roller 24 is in pressure contact with the photoreceptor 20 with the intermediate transfer belt 33 interposed therebetween to form a nip portion (primary transfer region). An exposure device 22 is disposed below the image forming unit 2.

  In the embodiment shown in this figure, roller-type ones are used as the primary transfer means and secondary transfer means, but the type of transfer means is not particularly limited, and of course, belt-type ones may be used. I do not care.

  Above the intermediate transfer belt 33, hoppers 4Y, 4M, 4C, and 4K (hereinafter sometimes collectively referred to as “hopper 4”) containing toner to be supplied to the developing devices 23 of the respective colors are arranged. A paper feed cassette 50 is detachably disposed as a paper feed device below the exposure device 22. The sheets P stacked and accommodated in the sheet cassette 50 are sent out one by one to the conveyance path in order from the uppermost sheet by the rotation of the sheet feed roller 51 disposed in the vicinity of the sheet cassette 50. The paper P sent out from the paper feed cassette 50 is conveyed to the registration roller pair 52 and is sent out to the secondary transfer area at a predetermined timing.

  The image forming apparatus D can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners.

  An image forming operation example in the color mode will be briefly described. First, in each image forming unit 2, the outer peripheral surface of the photoconductor 20 that is rotationally driven at a predetermined peripheral speed is charged by the photoconductor charging device 21. Next, light corresponding to image information is projected from the exposure device 22 on the surface of the charged photoconductor 20 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by the charged toner supplied from the developing device 23. When the toner images of the respective colors formed on the surface of the photoconductor 20 reach the primary transfer region by the rotation of the photoconductor 20, a voltage having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roller 24, The toner image is primarily transferred from the photoreceptor 20 onto the intermediate transfer belt 33. The toner images are primarily transferred from the photoconductor 20 onto the intermediate transfer belt 33 in the order of yellow, magenta, cyan, and black, and overlapped to form a color toner image.

  On the other hand, residual toner remaining on the photoconductor 20 without being transferred to the intermediate transfer belt 33 is scraped off by the photoconductor cleaning device 6 and removed from the outer peripheral surface of the photoconductor 20.

  The superimposed four color toner images are conveyed to the secondary transfer region by the intermediate transfer belt 33. On the other hand, the paper P is conveyed from the registration roller pair 52 to the secondary transfer region in accordance with the timing. Then, a voltage having a polarity opposite to the charging polarity of the toner is applied from the voltage application device 35 to the secondary transfer roller 34, and the four color toner images are transferred from the intermediate transfer belt 33 to the paper P in the secondary transfer region (2 Next transfer). The paper P on which the four color toner images are transferred is conveyed to the fixing device 1. In the fixing device 1, the paper P passes through the nip portion between the fixing roller 11 and the pressure roller 12. During this time, the paper P is heated and pressurized, and the toner image on the paper P is melted and fixed on the paper P. The paper P on which the toner image is fixed is discharged to a paper discharge tray 54 by a discharge roller pair 53.

  On the other hand, the residual toner remaining on the intermediate transfer belt 33 without being transferred onto the paper P is provided downstream of the nip portion between the secondary transfer roller 34 and the intermediate transfer belt 33 in the rotation direction of the intermediate transfer belt 33. The charging device 9 a is charged with the same polarity as the voltage applied to the primary transfer roller 24. Then, it is reversely transferred from the intermediate transfer belt 33 to the photoconductor 20 in the primary transfer region of the image forming unit 2Y and collected by the photoconductor cleaning device 6. The control of the image forming operation including the control of the exposure device 22 and the control of the transfer operation are performed by the control device (control means) 10.

  FIG. 2 shows a schematic diagram of the intermediate transfer belt 33 and its surroundings. The charging device 9 a rotates counterclockwise and contacts with the intermediate transfer belt 33. The charging brush 91 contacts the intermediate transfer belt 33. The collection roller 92 rotates counterclockwise and contacts the charging brush 91. 93, and a counter roller 94 provided at a position facing the charging brush 91 and the intermediate transfer belt 33. A positive polarity voltage is applied to the charging brush 91 via the recovery roller 92, and the opposing roller 94 is grounded. The opposing roller 94 may be, for example, a plate shape in addition to the roller shape.

The charging brush 91 includes a cored bar and brush fibers provided on the outer periphery of the cored bar. For example, conductive brush fibers are woven into a conductive base fabric that is entirely conductive or a conductive base fabric coated with a conductive agent on the back surface, and the base fabric is wound around a core metal and bonded with a conductive adhesive or the like. The thing which was done is mentioned. As the brush fiber, nylon, polyester, acrylic, rayon and the like can be used, and the resistance can be adjusted by adding a conductive material such as carbon black into the fiber. The resistance of the brush fiber is preferably in the range of 10 ⁵ Ω · cm to 10 ¹³ . The fiber thickness is preferably in the range of 1 denier to 10 denier, and the flocking density is preferably in the range of 50 kf / inch ^{2 to} 300 kf / inch ² . When the fiber thickness is less than 1 denier or when the flocking density is less than 50 kf / inch ² , there is a possibility that a sufficient scraping force cannot be obtained. On the contrary, when the fiber thickness is larger than 10 denier or when the flocking density is higher than 300 kf / inch ² , the load on the intermediate transfer belt 33 is increased, and the intermediate transfer belt 33 may be damaged. In addition, when the flocking density is increased, the scraping power is increased, but the discharging performance of the residual toner that is scraped is deteriorated, and the performance cannot be maintained for a long time.

  The peripheral speed of the charging brush 91 may be appropriately determined according to the peripheral speed of the intermediate transfer belt 33. Specifically, the peripheral speed of the charging brush 91 is preferably in the range of 0.3 to 2 times the peripheral speed of the intermediate transfer belt 33. If the circumferential speed of the charging brush 91 is slower than 0.3 times the circumferential speed of the intermediate transfer belt 33, the scraping force of the residual toner on the intermediate transfer belt 33 may not be sufficiently secured. On the other hand, if it is faster than twice the peripheral speed of the intermediate transfer belt 33, an excessive load is applied to the charging brush 91 and the intermediate transfer belt 33.

  The amount of biting of the charging brush 91 into the intermediate transfer belt 33 is not particularly limited, but generally it is preferably in the range of 10% to 40% of the thickness of the pile length of the brush. If the amount of biting of the charging brush 91 is less than 10% of the thickness of the pile length of the brush, the scraping power of the residual toner on the intermediate transfer belt 33 may not be sufficiently secured. On the other hand, if the amount of biting of the charging brush 91 is less than 40% of the thickness of the pile length of the brush, an excessive load is applied to the charging brush 91 and the intermediate transfer belt 33.

  As the collection roller 92, for example, a metal roller or a metal roller whose surface is covered with a resin is preferably used. As the cleaning blade 93, for example, a metal blade or a rubber blade is preferably used. As the facing roller 94, for example, a metal roller or a foaming roller is preferably used.

  Most of the residual toner remaining on the intermediate transfer belt 33 without being transferred onto the paper P has the same polarity as the voltage applied to the secondary transfer roller 34 (in this case, positive polarity). Exists. The negative polarity residual toner adheres to the charging brush 91. Residual toner adhering to the charging brush 91 moves to the collecting roller 92 at the contact portion between the charging brush 91 and the collecting roller 92 and is collected by the cleaning blade 93 that presses against the collecting roller 92. On the other hand, the positive polarity residual toner is charged by the charging brush 91 and conveyed to the primary transfer area of the image forming unit 2Y by the rotation of the intermediate transfer belt 33.

  In the primary transfer region of the image forming unit 2Y, a positive polarity voltage is applied to the primary transfer roller 24, whereby the residual toner is reversely transferred from the intermediate transfer belt 33 to the photoconductor 20. The reversely transferred residual toner is conveyed to the photoconductor cleaning device 6 and collected by the rotation of the photoconductor 20.

  What is important here is that no toner image is formed in the primary transfer region of the photoconductor 20 when the residual toner is reversely transferred from the intermediate transfer belt 33 to the photoconductor 20. In other words, if the remaining toner existing range on the intermediate transfer belt 33 and the scheduled primary transfer range on the intermediate transfer belt 33 of the toner image transferred from the photosensitive member 20 to the intermediate transfer belt 33 overlap, The timing of forming the electrostatic latent image on the body 20 is delayed, and the reverse transfer of the residual toner from the intermediate transfer belt 33 to the photoconductor 20 and the primary transfer of the toner image from the photoconductor 20 to the intermediate transfer belt 33 are performed simultaneously. It is to prevent it from happening. As a result, the remaining toner is smoothly reversely transferred from the intermediate transfer belt 33 to the photoreceptor 20.

  The primary transfer scheduled range on the intermediate transfer belt 33 of the toner image transferred from the photoreceptor 20 to the intermediate transfer belt 33 can be specified from the digital image data transmitted to the printer D.

  On the other hand, the remaining toner existing range on the intermediate transfer belt 33 may be set to the existing image range of the toner image that has been most recently primarily transferred onto the intermediate transfer belt 33. It should be noted that the existence range of the toner image that is most recently primarily transferred onto the intermediate transfer belt 33 can be specified from the digital image data transmitted to the printer D. More preferably, the existence range of the specified toner image is divided into a lattice shape, and it is determined whether there is residual toner for each division (see FIG. 7).

  Whether there is residual toner on the intermediate transfer belt 33 can be determined based on environmental conditions, the type of a member to be transferred, and the like. An example of determining whether there is residual toner on the intermediate transfer belt 33 will be described below.

  First, as shown in FIG. 6, environmental conditions are divided into three regions “A”, “B”, and “C” according to temperature and humidity. Further, the paper types are classified into paper type A, paper type A, paper type C, and paper type D in order from the one having the poor transferability. Then, the residual toner ratio on the intermediate transfer belt 33 is calculated from the environmental conditions and the type of paper to be used. Specifically, a coefficient to be applied to the printing rate of the toner image on the intermediate transfer belt 33 is determined from the environmental conditions and the type of paper, and the result obtained by multiplying the printing rate by the coefficient is set as the remaining toner rate. When the toner image existence range is divided into a grid, the printing rate for each division can be specified from the digital image data transmitted to the printer D. When the calculated remaining toner rate is equal to or greater than a predetermined value (for example, 0.8 or more), it is determined that there is remaining toner in the category. In general, the higher the environmental conditions are, the higher the residual toner rate on the intermediate transfer belt 33 is. Further, the residual toner ratio is higher when the toner image is a black image than when the toner image is a color image. Tables 1 and 2 show examples of coefficients that are multiplied by the printing rate. Table 1 shows the case where the toner image is black, and Table 2 shows the case where the toner image has other colors.

For example, when the environmental condition is “A” and the paper type is “A”, the coefficients are both 0.1 from Table 1 and Table 2, so the coefficient (0.1) is set as the toner image printing rate. The applied residual toner ratio does not exceed the determination criterion (0.8) for the presence or absence of residual toner, and it is determined that there is no residual toner on the intermediate transfer belt 33. On the other hand, when the environmental condition is “C” and the paper type is “A”, the coefficient of the black toner image is 1.0 and the coefficient of the toner image other than black is 0.2 from Tables 1 and 2. In a section where the black toner image print rate is 0.6, the magenta toner image print rate is 0.8, and the cyan toner image print rate is 0.6,
Residual toner ratio = (0.6 × 1.0 + 0.8 × 0.2 + 0.6 × 0.2)
= 0.88
Thus, the determination criterion (0.8) for the presence or absence of residual toner is exceeded, and it is determined that there is residual toner in this category.

  FIG. 3 is a schematic view of a main part showing another embodiment of the image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 3 is different from the image forming apparatus shown in FIG. 2 in that a cleaning device 7 is provided on the upstream side of the charging device 9a. The cleaning device 7 has the same configuration as that of the charging device 9 a, rotates counterclockwise and contacts with the intermediate transfer belt 33, and cleaning roller 71 rotates counterclockwise and contacts the cleaning brush 71. 72, a cleaning blade 73 in pressure contact with the recovery roller 72, and a counter roller 74 provided at a position facing the cleaning brush 71 with the intermediate transfer belt 33 interposed therebetween. A negative polarity voltage is applied to the cleaning brush 71 via the collection roller 72, and the opposing roller 74 is grounded.

  As described above, since most of the residual toner remaining on the intermediate transfer belt 33 without being transferred to the paper P has the same polarity (plus polarity) as the voltage applied to the secondary transfer roller 34, the cleaning device 7 is provided. As a result, much of the remaining toner can be collected here. In addition, since the residual toner that is negatively charged is collected by the charging device 9a, the residual toner that passes through the cleaning device 7 and the charging device 9a and is conveyed to the primary transfer region of the image forming unit 2Y. Is much less.

  FIG. 4 is a schematic view of a main part showing another embodiment of the image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 4 is different from the image forming apparatus shown in FIG. 2 in that a solid roller type charging device is used. The charging device 9b includes a charging roller 95 that can be rotated clockwise, a cleaning blade 93 that is in pressure contact with the charging roller 95, and a counter roller 94 that is provided at a position facing the charging roller 95 with the intermediate transfer belt 33 interposed therebetween. Have. A positive polarity voltage is applied to the charging roller 95, and the opposing roller 94 is grounded. The charging roller 95 is a solid roller made of a metal material or the like, and is rotated by the rotation of the intermediate transfer belt 33.

  Of the residual toner remaining on the intermediate transfer belt 33 without being transferred onto the paper P, the negative polarity residual toner adheres to the charging roller 95 to which a positive voltage is applied and is collected by the cleaning blade 93. The positive polarity residual toner is adjusted in charge amount by the charging roller 95 and is conveyed to the primary transfer region by the rotation of the intermediate transfer belt 33.

As the charging roller 95, for example, a cylindrical metal core having a resin layer formed on the surface thereof is preferably used. The resistivity of the resin layer is preferably in the range of 10 ⁵ Ω · cm to 10 ¹⁴ Ω · cm, and the thickness of the resin layer is preferably in the range of 20 μm to 5 mm.

  FIG. 5 is a schematic diagram showing the main part of still another embodiment of the image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 5 is different from the image forming apparatus shown in FIG. 2 in that an elastic roller type charging device is used. The charging device 9c rotates counterclockwise, the elastic roller 96 that contacts the intermediate transfer belt 33, the recovery roller 92 that rotates counterclockwise and contacts the elastic roller 96, and the cleaning blade that presses against the recovery roller 92. 93, and an opposing roller 94 provided at a position facing the elastic roller 96 and the intermediate transfer belt 33 therebetween. A positive polarity voltage is applied to the elastic roller 96 via the collection roller 92, and the opposing roller 94 is grounded.

  Of the residual toner remaining on the intermediate transfer belt 33 without being transferred onto the paper P, the negative polarity residual toner adheres to the elastic roller 96 to which a positive voltage is applied and then moves to the recovery roller 92 and is moved by the cleaning blade 93. To be recovered. The positive polarity residual toner is adjusted in charge amount by the elastic roller 96 and conveyed to the primary transfer region by the rotation of the intermediate transfer belt 33.

  As the elastic roller 96, for example, one in which a polyurethane foam layer is formed on the outer periphery of a core metal is preferably used. The polyurethane foam layer has a large number of cells (bubbles), and one cell is connected to an adjacent cell through an opening. When the ratio of the opening area S1 to the area S of the entire cell wall surface is defined as the opening ratio, the cell opening ratio of the polyurethane foam layer is preferably in the range of 3% to 50%. By setting the cell opening ratio of the polyurethane foam layer in such a range, the polyurethane foam layer is easily deformed and is closely adhered to the intermediate transfer belt 33 to improve the scraping property of the residual toner. At the same time, the recovered residual toner is not clogged with the polyurethane foam layer, and the performance can be maintained for a long time. The cell diameter of the polyurethane foam layer is not particularly limited, but is usually preferably in the range of 50 μm to 1000 μm.

In order to form a predetermined electric field between the intermediate transfer belt 33 and the elastic roller 96, the polyurethane foam layer is made conductive. The volume resistance of the polyurethane foam layer is not particularly limited, but is usually preferably in the range of 10 ³ Ω · cm to 10 ⁷ Ω · cm. If the volume resistance of the polyurethane foam layer is lower than 10 ³ Ω · cm, the electric field becomes strong at the portion where the contact gap between the intermediate transfer belt 33 and the polyurethane foam layer becomes small, and leakage occurs. The transfer belt 33 may be damaged. On the other hand, if the volume resistance of the polyurethane foam layer is higher than 10 ⁷ Ω · cm, the power supply voltage must be increased, which increases the size and weight of the power supply device.

  The pressure contact force of the elastic roller 96 to the intermediate transfer belt 33 is not particularly limited, but generally, if the pressure contact force is small, there is a possibility that the remaining toner on the intermediate transfer belt 33 cannot be cleaned, and the pressure contact force is large. An excessive load is applied to the polyurethane foam layer, which may reduce durability.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these examples at all.

Examples 1-6
As the image forming apparatus, the cleaning part of the intermediate transfer belt of “bizhub Pro C6000L” manufactured by Konica Minolta Co., Ltd. is modified to the structure shown in FIGS. The remaining toner was cleaned and the image forming efficiency was evaluated. The evaluation results are summarized in Table 3.

(Control pattern)
FIG. 8 shows a control flowchart. From the environmental conditions and the paper type to be used, a coefficient to be applied to the printing rate is determined using, for example, Table 1 and Table 2 (step S101). Then, the remaining toner rate is calculated for each section (step S102). Next, it is determined whether or not there is a category in which the calculated remaining toner rate is 0.8 or more (step S103). If there is no section with a remaining toner ratio of 0.8 or more, it is determined that there is no remaining toner on the intermediate transfer belt, and the control is terminated. On the other hand, if there is a category having a residual toner ratio of 0.8 or more, it is determined that there is residual toner in the category, and whether the category in which residual toner exists and the primary transfer scheduled range of the next toner image overlap. Is then determined (step S104). If the remaining toner area does not overlap with the primary transfer scheduled range of the next toner image, the control ends. On the other hand, when the remaining toner area and the next primary toner image scheduled transfer range overlap, the remaining toner area and the next toner image primary transfer scheduled area do not overlap. The formation time of the electrostatic latent image on the photoconductor is delayed (step S105).

(Configuration of charging device used in the apparatus shown in FIG. 2)
(Charging brush)
Conductive nylon fiber density: 240 KF / inch ²
Raw yarn resistance: 10 ¹⁰ Ω · cm
Outer diameter: 16mm
Biting into the intermediate transfer belt: 1.2mm
Peripheral speed ratio to the intermediate transfer belt: 1.0
(Recovery roller)
SUS metal roller outer diameter: 16mm
Biting amount for the charging brush: 1.2m
Peripheral speed ratio with respect to charging brush: 1.0
(Applied voltage)
+40 μA was applied to the collecting roller at a constant current.

(Configuration of the charging device used in the apparatus shown in FIG. 3)
(Charging brush, cleaning brush)
Conductive nylon fiber density: 240 KF / inch ²
Raw yarn resistance: 10 ¹⁰ Ω · cm
Outer diameter: 16mm
Biting into the intermediate transfer belt: 1.2mm
Peripheral speed ratio to the intermediate transfer belt: 1.0
(Recovery roller)
SUS metal roller outer diameter: 16mm
Biting amount for the charging brush: 1.2m
Peripheral speed ratio with respect to charging brush: 1.0
(Applied voltage)
+40 μA and −40 μA were applied to each collecting roller at a constant current.

(Configuration of the charging device used in the apparatus shown in FIG. 4)
Charging roller: Metal roller surface with resin coating Resistance: 10 ⁵ Ω
Outer diameter: 16mm (metal roller 14mm, resin thickness 1mm)
Pushing amount against the intermediate transfer belt: 0.4 mm
Rotation: Followed rotation

(Size of division)
As shown in FIG. 7, the size of the division when dividing the existence range of the toner image into a lattice shape is determined as two types, and the presence or absence of residual toner in each division is determined.
Classification "Large": 2cm x 2cm
Classification "small": 0.5cm x 0.5cm

(Cleanability evaluation)
The cleaning property was evaluated according to the following criteria.
“◎”: In all environments and paper types, no residual toner entered the toner image.
“◯”: In some environments and paper types, residual toner entered the toner image, but there was no problem in quality.
“X”: In some environments and paper types, the residual toner entered the toner image, and there was a problem in quality.
“XX”: In some environments and paper types, the residual toner entered the toner image, and there was a problem in quality.

(Evaluation of image formation efficiency)
Image formation efficiency was evaluated according to the following criteria.
“◎”: Image formation efficiency was not lowered at all.
“◯”: In some environments and paper types, the image formation efficiency decreased, but the effect was small.

(Comprehensive evaluation)
Comprehensive evaluation was performed according to the following criteria.
“◯”: There was no problem in quality in both the evaluation of the cleaning property and the image forming efficiency.
“X”: There was a problem in quality in evaluation of at least one of cleaning property and image formation efficiency.

Comparative Examples 1-3
Examples 1 to 3 were performed except that the control for delaying the formation time of the electrostatic latent image on the photosensitive member was not performed so that the remaining toner existing range and the primary transfer scheduled range of the next toner image do not overlap. In the same manner as described above, image formation was performed, and the cleaning property and image formation efficiency of the remaining toner were evaluated. The evaluation results are summarized in Table 3.

  As is clear from Table 3, the image forming apparatuses of Examples 1 to 6 had good cleaning properties and image forming efficiency, and excellent overall evaluation. On the other hand, the image quality devices of Comparative Examples 1 to 3 also had a poor overall evaluation because of poor cleaning properties.

  In the image forming apparatus of the present invention, when the remaining toner existing range on the intermediate transfer member and the scheduled primary transfer range of the toner image transferred from the photosensitive member to the intermediate transfer member overlap, The timing of forming the electrostatic latent image is delayed so that the reverse transfer of the residual toner from the intermediate transfer member to the image carrier and the primary transfer of the toner image from the image carrier to the intermediate transfer member do not occur simultaneously. Therefore, the rate at which the residual toner is reversely transferred from the intermediate transfer member to the photosensitive member is not reduced. As a result, a high-quality image free from noise can be obtained and useful even under special conditions where the amount of residual toner increases.

9a, 9b, 9c Charging device (charging means)
P paper (transferred member)
10 control means 20 photoconductor (image carrier)
23 Developing device (developing means)
24 Primary transfer roller (primary transfer means)
33 Intermediate transfer belt (intermediate transfer member)
34 Secondary transfer roller (secondary transfer means)

Claims (5)

A rotatable image carrier;
A rotatable intermediate transfer member,
A plurality of developing means for developing the electrostatic latent image formed on the image carrier with toners of different colors;
Primary transfer means for primary transfer of the toner image formed on the image bearing member to the intermediate transfer member by applying a voltage having a polarity opposite to the charging polarity of the toner;
Secondary transfer means for secondarily transferring the toner image primarily transferred onto the intermediate transfer member to a transfer member by applying a voltage having a polarity opposite to the charged polarity of the toner;
The residual toner, which is provided on the downstream side in the rotation direction of the intermediate transfer body with respect to the secondary transfer means and remains on the intermediate transfer body without being subjected to the secondary transfer, has the same polarity as the voltage applied to the primary transfer means. A charging means for charging the image bearing member and a control means for controlling formation of an electrostatic latent image on the image carrier,
The residual toner remaining on the intermediate transfer member is charged to the same polarity as the voltage applied to the primary transfer unit by the charging unit, and the residual toner is transferred from the intermediate transfer member to the image carrier by the primary transfer unit. In the image forming apparatus for reversely transferring and removing from the intermediate transfer member,
When the residual toner existing range on the intermediate transfer member and the scheduled primary transfer range of the toner image transferred from the image carrier to the intermediate transfer member overlap, the control means is based on the primary transfer means. Then, the reverse transfer of the residual toner from the intermediate transfer member to the image carrier and the primary transfer of the toner image from the image carrier to the intermediate transfer member do not occur at the same time on the image carrier. An image forming apparatus characterized by delaying the timing of forming an electrostatic latent image. A plurality of image carriers and a plurality of primary transfer units are provided corresponding to the plurality of developing units,
The image forming apparatus according to claim 1, wherein residual toner remaining on the intermediate transfer member is removed from the intermediate transfer member by an image carrier and a primary transfer unit positioned at the most upstream in the rotation direction of the intermediate transfer member.   The image forming apparatus according to claim 1, wherein the presence range of the residual toner on the intermediate transfer member is set as the presence range of the toner image primarily transferred to the intermediate transfer member most recently.   The image forming apparatus according to claim 3, wherein the existence range of the toner image is divided into a lattice shape, and it is determined whether or not there is residual toner for each division.   The residual toner rate on the intermediate transfer member is calculated based on at least one of environmental conditions, the type of a member to be transferred, and the color of the toner image primarily transferred to the intermediate transfer member. The image forming apparatus according to claim 3, wherein it is determined that residual toner is present on the intermediate transfer member when the value is equal to or greater than a predetermined value.