JP2005338559A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the efficiency of removal of residual toner after transfer even when spherical toner is used, in an image forming apparatus comprising a plurality of image carriers, developing devices for forming toner images on the respective image carriers, a transfer belt disposed opposite to the plurality of image carriers, transfer devices for transferring toner images formed on the respective image carriers onto the transfer belt, and cleaning blades for removing residual toners sticking on the image carriers after transfer of the toner images, wherein the toner images transferred onto the transfer belt are transferred onto a recording medium to obtain a recorded image. <P>SOLUTION: Amorphous toner is housed in one developing device 9BK and this toner is conveyed to the respective cleaning blades 14BK, 14Y, 14M, 14C through the transfer belt 3 to form weirs consisting of the amorphous toner near the front edges of the cleaning blades. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, a toner image is formed on each of a plurality of image carriers by a developing device, each toner image is transferred to a transfer belt, and the toner image transferred to the transfer belt is transferred to a recording medium. The present invention relates to an image forming apparatus that obtains a recorded image by transferring a toner image formed on an image carrier onto a recording medium carried on a transfer belt.

  An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile, or a complex machine of these is well known. In this type of image forming apparatus, it is also well known in the art to remove the transfer residual toner adhering to the image carrier after transferring the toner image with a cleaning blade. Such an image forming apparatus is also referred to as a tandem type image forming apparatus because it has a plurality of image carriers arranged side by side.

  In the tandem type image forming apparatus described above, when spherical toner is used, a dense and uniform high quality toner image can be formed on the image carrier. However, if spherical toner is used, the transfer residual toner that adheres to the image carrier after the toner image transfer is likely to pass through the cleaning blade, so that the transfer residual toner cannot be efficiently removed by the cleaning blade, resulting in poor cleaning. Occurs.

  Therefore, the irregular particle supply device supplies irregular particles to the surface of the transfer belt, and the irregular particles are supplied to a cleaning blade pressed against each image carrier to increase the transfer residual toner removal efficiency by each cleaning blade. An image forming apparatus has been proposed (see Patent Document 1). According to this image forming apparatus, even if spherical toner is used in each developing device, it is possible to improve the removal efficiency of the transfer residual toner by the cleaning blade and prevent the occurrence of poor cleaning on the image carrier. However, according to this type of image forming apparatus, since it is necessary to provide an amorphous particle supply device, the cost of the image forming apparatus increases.

JP 2001-166659 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a tandem type image forming apparatus capable of suppressing an increase in cost and preventing occurrence of poor cleaning on an image carrier while taking advantage of using spherical toner.

  In order to achieve the above object, the present invention provides a plurality of image carriers, a developing device for forming a toner image on each image carrier, a transfer belt disposed opposite to the plurality of image carriers, and each image carrier. A toner image transferred to the transfer belt, and a transfer device that transfers the toner image formed on the transfer belt to the transfer belt; and a cleaning blade that removes transfer residual toner adhering to the image carrier after the toner image is transferred. In an image forming apparatus that transfers a toner image to a recording medium to obtain a recorded image, the developing device that first starts to form a toner image on the image carrier is the first starting developing device, and the toner image is formed by the first starting developing device. When the carrier is the most upstream side image carrier, the first starting developing device contains a mixture of amorphous toner and spherical toner or irregular toner, and the other developing devices contain spherical toner. The Then, at the time of non-image formation, the first starting developing device forms a toner image composed of a mixture of amorphous toner and spherical toner or an irregular toner on the uppermost stream side image carrier, and the toner of the toner image is removed. The image is transferred to the transfer belt, and the toner on the transfer belt is reverse-transferred to another image carrier positioned on the downstream side in the transfer belt moving direction from the most upstream image carrier, and the surface of each image carrier; An image forming apparatus is proposed in which a weir made of a mixture of amorphous toner and spherical toner or an irregular toner is formed in a space defined by the tip of the cleaning blade (claim 1). .

  In order to achieve the same object, the present invention provides a plurality of image carriers, a developing device for forming a toner image on each image carrier, a transfer belt disposed opposite to the plurality of image carriers, and each image. A transfer device for transferring a toner image formed on the carrier to a recording medium carried by the transfer belt and conveyed; and a cleaning blade for removing transfer residual toner adhering to the image carrier after the toner image is transferred. In the image forming apparatus, the developing device that first starts to form a toner image on the image carrier is referred to as a first starting developing device, and the image carrier on which the toner image is formed by the first starting developing device is the most upstream image carrier. In this case, the first starting developing device contains a mixed toner of amorphous toner and spherical toner or an amorphous toner, and the other developing devices contain spherical toner. Open A developing device forms a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner on the most upstream image carrier, and transfers the toner image toner onto the transfer belt. The upper toner is reversely transferred to another image carrier positioned downstream in the transfer belt moving direction from the most upstream image carrier, and is partitioned by the surface of each image carrier and the tip of the cleaning blade. An image forming apparatus is proposed in which a weir made of a mixture of amorphous toner and spherical toner or an irregular toner is formed in the space.

  Furthermore, in the image forming apparatus according to claim 1 or 2, the same charging polarity as that of the toner is applied to the transfer apparatus that reversely transfers the toner transferred to the transfer belt to another image carrier during non-image formation. It is advantageous to apply a voltage having a polarity or to apply a voltage that is opposite to the charging polarity of the toner and that is higher than the transfer voltage applied during image formation.

  The image forming apparatus according to claim 3, wherein a plurality of image carriers other than the most upstream image carrier are provided, and the toner transferred to the transfer belt is transferred to the other image carrier during non-image formation. It is advantageous that the voltage applied to each transfer device when reversely transferring to each of the bodies is sequentially set higher toward the downstream side in the transfer belt moving direction (claim 4).

  The image forming apparatus according to any one of claims 1 to 4, wherein when the image forming apparatus is warmed up, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is displayed on the most upstream side. It is advantageous that the toner image is formed on an image carrier and the toner of the toner image is reversely transferred to another image carrier via the transfer belt.

  Further, in the image forming apparatus according to any one of claims 1 to 4, in the non-image forming area corresponding to the space between the recording media of the most upstream image carrier, a mixed toner of amorphous toner and spherical toner or A toner image composed of an irregular shaped toner is formed, the toner of the toner image is transferred to a non-image forming area corresponding to the recording medium of the transfer belt, and the toner on the transfer belt is transferred to another image carrier. It is advantageous that the recording medium is reversely transferred to a non-image forming area corresponding to the recording medium.

  Furthermore, in the image forming apparatus according to any one of claims 1 to 4, a toner image composed of a mixture of amorphous toner and spherical toner or an irregular toner is displayed each time a predetermined number of image forming operations are performed. It is advantageous that the toner image is formed on the most upstream side image carrier, and the toner of the toner image is reversely transferred to another image carrier via the transfer belt.

  Further, in the image forming apparatus according to any one of claims 1 to 4, when one job or a series of a plurality of times of image forming operations is defined as one job, after the end of the one job, an indeterminate toner and a spherical toner. A toner image formed of the mixed toner or the irregular shaped toner is formed on the most upstream image carrier, and the toner of the toner image is reversely transferred to the other image carrier through the transfer belt. (Claim 8).

  Furthermore, in the image forming apparatus according to any one of claims 1 to 8, it is advantageous that the circularity of the spherical toner is 0.96 or more (claim 9).

  In the image forming apparatus according to any one of claims 1 to 9, it is advantageous that the image carrier is an amorphous silicon photoconductor (claim 10).

  Furthermore, in the image forming apparatus according to any one of claims 1 to 9, the image carrier is an organic photoreceptor having a surface layer reinforced with a filler, or an organic photosensitive material using a cross-linked charge transport material. It is advantageous that the organic photoreceptor has the properties of a body or both.

  According to the present invention, since the developing device other than the initial starting developing device contains spherical toner, the image quality of the toner image formed by the developing device can be improved. In addition, since a weir made of a mixture of amorphous toner and spherical toner or an irregular toner is formed in the vicinity of the edge of the cleaning blade pressed against each image carrier, each image carrier is subjected to an image forming operation. The adhered transfer residual toner is blocked by the respective weirs, and the passing through the cleaning blade is effectively suppressed. Thereby, the cleaning performance with respect to each image carrier can be enhanced. Furthermore, since it is not necessary to provide a dedicated device for forming the weir, an increase in the cost of the image forming apparatus can be suppressed.

  FIG. 1 is a schematic view showing an example of an image forming apparatus. The image forming apparatus shown here includes a plurality of image carriers 2BK, 2Y, 2M, and 2C made of a drum-shaped photoconductor, and support rollers 4 and 5. , 6 and the transfer belt 3 is arranged to face the plurality of image carriers 2BK to 2C. Each image carrier 2BK to 2C is rotationally driven in the counterclockwise direction in FIG. 1 while being in contact with the transfer belt 3, and the transfer belt 3 is rotationally driven in the arrow A direction. In the example shown in FIG. 1, four image carriers 2BK to 2C are provided, and toner images of different colors formed on these image carriers are transferred onto the transfer belt 3 in an overlapping manner.

  The configuration in which a toner image is formed on each image carrier 2BK, 2Y, 2M, 2C and the toner image is transferred to the transfer belt 3 is substantially the same except that the color of the toner image is different. Only a configuration in which a toner image is formed on one of the image carriers 2BK and the toner image is transferred to the transfer belt 3 will be described. When the image carrier 2BK is driven to rotate counterclockwise in FIG. 1, the image carrier 2BK is charged to a predetermined polarity by a charging device including a charging roller 7BK to which a charging voltage is applied. The charged image carrier 2BK is irradiated with light-modulated laser light LBK emitted from an optical writing device (not shown), whereby an electrostatic latent image is formed on the image carrier 2BK. This electrostatic latent image is visualized as a black toner image by the developing device 9BK. In the illustrated example, it is assumed that the image carrier 2BK is charged to a negative polarity by a charging device.

  The developing device 9BK includes a developing case 10BK containing the developer DBK and a developing roller 11BK, and the developer DBK is carried and conveyed on the developing roller 11BK that is rotated by applying a predetermined voltage. The electrostatic latent image formed on the image carrier 2BK is visualized as a toner image by the agent. As the developer DBK, a two-component developer having a toner and a carrier or a one-component developer not having a carrier can be used. In the illustrated example, a two-component developer is used. The toner in the developer is triboelectrically charged to a negative polarity, and the toner is electrostatically transferred to an electrostatic latent image, and the latent image is visualized.

  On the other hand, a primary transfer device composed of a transfer brush 12BK is disposed on the opposite side of the image carrier 2BK across the transfer belt 3, and a transfer voltage is applied to the transfer brush 12BK to form the image carrier 2BK. The transferred toner image is transferred onto the transfer belt 3 that rotates in the direction of arrow A. The transfer brush 12BK is applied with a transfer voltage having a polarity opposite to the charging polarity of the toner, that is, a positive polarity, whereby the toner image on the image carrier 2BK is electrostatically transferred to the transfer belt 3. The transfer residual toner adhering to the image carrier 2BK after the toner image transfer is removed by the cleaning device 13BK. The cleaning device 13BK shown here has a cleaning blade 14BK, a cleaning case 15BK, and a toner conveying member 16BK, and the leading edge portion of the cleaning blade 14BK comes into pressure contact with the surface of the image carrier 2BK, and the image The transfer residual toner adhering to the carrier 2BK is scraped off and removed. The scraped toner is transported out of the cleaning case 15BK by the toner transport member 16BK. The surface of the image carrier 2BK cleaned by the cleaning device 13BK is irradiated with the static elimination light from the static elimination lamp 17BK, thereby initializing the surface potential of the image carrier 2BK.

  In exactly the same manner as described above, a yellow toner image, a magenta toner image, and a cyan toner image are respectively formed on the image carriers 2Y, 2M, and 2C shown in FIG. 1, and these toner images are transferred to a black toner image. Then, the toner images are sequentially transferred onto the transfer belt 3 and a combined toner image is formed on the transfer belt 3. The transfer residual toner on the image carriers 2Y, 2M, and 2C after the toner image transfer is removed by the cleaning devices 13Y, 13M, and 13C, which is the same as in the case of the image carrier 2BK.

  On the other hand, a secondary transfer device composed of a transfer roller 18 is disposed at a position facing the support roller 6 with the transfer belt 3 interposed therebetween, and the transfer roller 18 and a transfer belt portion wound around the support roller 6 are arranged. A recording medium P made of transfer paper or a resin film fed from a paper feeding device (not shown) is fed into the transfer section between them, and at this time, the transfer roller 18 has a polarity opposite to that of the toner (in the example shown in FIG. (Polarity) transfer voltage is applied, whereby the toner image on the transfer belt 3 is transferred onto the recording medium P. Subsequently, the recording medium P passes through a fixing device (not shown), and at this time, the toner image on the recording medium P is fixed to the recording medium by the action of heat and pressure. The recording medium that has passed through the fixing device is discharged out of the apparatus.

  Untransferred toner remaining on the transfer belt 3 without being transferred to the recording medium P is removed from the transfer belt 3 by the belt cleaning device 19. The cleaning device 19 also has a cleaning blade 20 in pressure contact with the transfer belt 3, and the transfer residual toner on the transfer belt 3 is scraped and removed by the cleaning blade 20.

  Each image forming element provided around each image carrier 2Y, 2M, 2C corresponding to each image forming element provided around the image carrier 2BK includes each image around the image carrier 2BK. Instead of the BK of the code attached to the image element, each code with Y, M, and C is added. The developing cases 10Y, 10M, and 10C of the developing devices 9Y, 9M, and 9C contain a two-component developer containing yellow toner, magenta toner, and cyan toner. , DY, DM, and DC are respectively attached.

  As described above, the image forming apparatus of this example includes a plurality of image carriers 2BK to 2C, developing devices 9BK to 9C that form toner images on the image carriers 2BK to 2C, and a plurality of image carriers 2BK. To the transfer belt 3 disposed opposite to 2C, a transfer device for transferring the toner image formed on each of the image carriers 2BK to 2C to the transfer belt 3, and the image carrier 2BK to 2C after the toner image transfer. Cleaning blades 14BK to 14C for removing transfer residual toner are provided, and the toner image transferred to the transfer belt 3 is transferred to the recording medium P to obtain a recorded image.

  On the other hand, in the image forming apparatus shown in FIG. 2, the toner images of the respective colors formed on the image carriers 2BK to 2C are not transferred to the transfer belt 3, but sent out from a paper feeding device (not shown). The recording medium P is carried on a transfer belt 3 that is rotationally driven in the direction of arrow A and conveyed. At this time, the black toner image, the yellow toner image, the magenta toner image, and the cyan toner image formed on each of the image carriers 2BK to 2C are transferred by the operations of the transfer devices including the transfer brushes 12BK, 12Y, 12M, and 12C. The recording material P is transferred onto the recording medium P that is carried and conveyed by the belt 3. The recording medium P leaves the transfer belt 3 and then passes through a fixing device (not shown). At this time, the toner image on the recording medium P is fixed to the recording medium P. The recording medium that has passed through the fixing device is discharged out of the apparatus. Further, the toner adhering to the transfer belt 3 is scraped and removed by the cleaning blade 20 of the belt cleaning device 19. The image forming apparatus shown in FIG. 2 is not provided with a secondary transfer device including the transfer roller 18 shown in FIG. The other basic configuration of the image forming apparatus shown in FIG. 2 is the same as that of the image forming apparatus shown in FIG. 1, and each element in FIG. 2 corresponding to FIG. A duplicate description is omitted.

  As described above, the image forming apparatus illustrated in FIG. 2 includes a plurality of image carriers 2BK to 2C, developing devices 9BK to 9C that form toner images on the image carriers 2BK to 2C, and a plurality of image carriers. A transfer belt 3 disposed opposite to 2BK to 2C, a transfer device for transferring a toner image formed on each image carrier 2BK to 2C to a recording medium P carried on the transfer belt 3, and a toner image transfer Cleaning blades 14BK to 14C for removing transfer residual toner adhering to the subsequent image carriers 2BK to 2C are provided.

  Here, in the image forming apparatus shown in FIGS. 1 and 2, when a toner image is formed on each image carrier with spherical toner, the quality of the toner image is improved as compared with the case where the toner image is formed with irregular toner. Can be increased. However, the transfer residual toner adhering to each image carrier cannot be efficiently removed by the cleaning blade only by using the spherical toner. In order to cope with this problem, the image forming apparatus shown in FIGS. 1 and 2 is configured as follows.

  In the image forming apparatus shown in FIGS. 1 and 2, since the toner images of the respective colors formed on the image carriers 2BK to 2C are transferred onto the transfer belt 3 or the recording medium P, each image carrier 2BK is transferred. Among the plurality of developing devices 9BK to 9C opposed to 2C, the developing device 2BK opposed to the image carrier 2BK located on the most upstream side in the transfer belt moving direction is the first black toner image on the image carrier 2BK. Begin to form. Next, the developing device 9Y starts to form a yellow toner image on the image carrier 2Y, then the developing device 9M starts to form a magenta toner image on the image carrier 2M, and finally the developing device 9C Start forming a cyan toner image on 2C. Therefore, the developing device that first starts to form a toner image on the image carrier is referred to as the first starting developing device as necessary, and the image carrier on which the toner image is formed by the first starting developing device is referred to as necessary. Therefore, it will be referred to as the most upstream image carrier. In the illustrated example, the developing device 9BK that forms a black toner image on the image carrier 2BK is the first starting developing device, and the image carrier 2BK on which the black toner image is formed by the developing device 9BK is the most upstream image carrier. It is. In the developing case 10BK of the first starting developing device 9BK, a mixed toner of amorphous toner and spherical toner or amorphous toner is accommodated, and the developing cases 10Y, 10M, 10C of the other developing devices 9Y, 9M, 9C are accommodated. Contains a spherical toner. In the illustrated example, since a two-component developer is used, is the first start developing device 9Y accommodated with a two-component developer obtained by adding a carrier to a mixed toner of an irregular shaped toner and a spherical toner? A two-component developer in which an irregular toner and a carrier are mixed is contained. The other developing devices 9Y, 9M, and 9C each contain a two-component developer obtained by mixing spherical toner and a carrier.

  The following operation is executed during non-image formation under the above-described conditions (in the illustrated example, during warm-up of the image forming apparatus).

  Even when a print button (not shown) of the image forming apparatus is pressed, the image forming operation is not performed at the time of warming up until the fixing apparatus rises to a temperature suitable for fixing the toner image. During the warm-up, the image carriers 2BK to 2C, the charging rollers 7BK to 7C, the developing rollers 11BK to 11C, the transfer belt 3, and the transfer roller 18 (only in the case of FIG. 1) are the same as those at the time of image formation. It is driven to rotate in the direction of. At the same time, the charge eliminating lamps 17BK to 17C are turned on, and the same predetermined voltages as those at the time of image formation are respectively applied to the charging rollers 7BK to 7C and the developing rollers 11BK to 11C, and the transfer brushes 12BK to 12C will be described later. Polarity voltages are applied respectively. As a result, each of the image carriers 2BK to 2C is charged with a negative polarity as in the image formation, and its surface potential is, for example, -900V. In this state, only the uppermost stream side image carrier 2BK located on the most upstream side with respect to the moving direction of the transfer belt 3 is irradiated with the laser beam LBK emitted from an optical writing device (not shown), and the image carrier 2BK A belt-like electrostatic latent image extending over the entire length in the axial direction is formed. The width of the electrostatic latent image in the circumferential direction of the image carrier is, for example, about 30 mm. The electrostatic latent image is first visualized as a toner image by the start developing device 9BK. A belt-like toner image made of a mixed toner of irregular toner and spherical toner or an irregular toner is formed on the image carrier 2BK. The charging polarity of the toner of this toner image is the same as that at the time of image formation (negative polarity in the example in the figure). The other image carriers 2Y, 2M, and 2C other than the most upstream image carrier 2BK are not irradiated with laser light. Therefore, the surface potentials of these image carriers 2Y to 2C are set to, for example, an initial value of about −900V. The toner image is not formed on these image carriers.

  On the other hand, a voltage (for example, about +1.0 kV) having the same polarity as that at the time of image formation is applied to the transfer brush 12BK, whereby the belt-like toner image on the image carrier 2BK is electrostatically transferred onto the transfer belt 3. Is done. However, a part of the toner image on the image carrier 2BK is not transferred but passes through the transfer region. The toner transferred to the transfer belt 3 moves to a transfer region substantially opposite to the transfer brush 12Y when the transfer belt 3 rotates in the direction of arrow A. At this time, a voltage having a polarity opposite to that at the time of image formation, in other words, a negative polarity having the same polarity as the charging polarity of the toner is applied to the transfer brush 12Y. It moves electrostatically onto the body 2Y. Further, when the toner remaining on the transfer belt 3 reaches the transfer region almost opposite to the transfer brush 12M, a voltage having a polarity opposite to that at the time of image formation, that is, a negative polarity is applied to the transfer brush 12M. As a result, a part of the toner on the transfer belt is electrostatically transferred onto the image carrier 2M. Similarly, a voltage having the same negative polarity as the charging polarity of the toner is also applied to the transfer brush 12C, so that the toner carried to the transfer region almost opposite to the transfer brush 12C is transferred onto the image carrier 2C. Move electrostatically.

  As described above, the toner on the transfer belt 3 is reversely transferred onto the image carriers 2Y, 2M, and 2C other than the most upstream image carrier 2BK. As 2M and 2C rotate, they reach the leading edge portions of the cleaning blades 14Y, 14M, and 14C that are in pressure contact with the image carriers and are held in the vicinity thereof. That is, as shown in FIG. 3, the transfer belt 3 is reversed from the transfer belt 3 into a space defined by the surface of each image carrier 2Y, 2M, 2C and the tip of the cleaning blades 14Y, 14M, 14C pressed against the surface. The mixed toner of the irregularly shaped toner and the spherical toner or the irregularly shaped toner collected is accumulated, and the weir E is formed by the toner. Further, as shown in FIG. 3, the toner that is not transferred to the transfer belt 3 and remains on the most upstream image carrier 2BK reaches the leading edge of the cleaning blade 14BK, and the surface of the image carrier 2Y. In a space defined by the tip of the cleaning blade 14BK that is in pressure contact with the surface, a weir E made of a mixture of amorphous toner and spherical toner or irregular toner is formed. Since the toner constituting the weir E is at least partially made of an irregular toner, the toner does not pass through the cleaning blade as it is, and the toner accumulates in the vicinity of the leading edge of the cleaning blade. E is constituted.

  As described above, at the time of non-image formation, the first starting developing device 9BK forms a toner image composed of a mixture of amorphous toner and spherical toner or an irregular toner on the uppermost stream side image carrier 2BK, and the toner image Is transferred to the transfer belt 3, and the toner on the transfer belt 3 is reversely transferred to the other image carriers 2Y, 2M, and 2C located on the downstream side in the transfer belt moving direction from the most upstream image carrier 2BK. In the space defined by the surface of each of the image carriers 2BK to 2C and the tip of each of the cleaning blades 14BK to 14C, a weir E made of a mixture of amorphous toner and spherical toner or irregular toner is formed. To do.

  Further, among the toners transferred from the most upstream image carrier 2BK onto the transfer belt 3, the toner that has passed through these image carriers without being reversely transferred to any of the image carriers 2Y, 2M, 2C 1 and 2, the cleaning blade 20 of the belt cleaning device 19 is reached. As a result, in the same manner as shown in FIG. 3, in the space defined by the surface of the transfer belt 3 and the tip of the cleaning blade 20 that is in pressure contact with the surface, a mixed toner of an amorphous toner and a spherical toner or A weir (not shown) made of irregular shaped toner is formed. In the case of the image forming apparatus shown in FIG. 1, the toner that has passed through each of the image carriers 2 </ b> Y to 2 </ b> C passes through the transfer roller 18. At this time, the transfer roller 18 prevents the toner from adhering to the transfer roller 18. Is preferably separated from the transfer belt 3, or a voltage having the same polarity as the charging polarity of the toner on the transfer belt 3, that is, a negative polarity is applied to the transfer roller 18.

  When the warm-up is completed and image formation is started, a toner image composed of a mixture of amorphous toner and spherical toner or an irregular toner is formed on the most upstream side image carrier 2BK by the first starting developing device 9BK. On the other image carriers 2Y to 2C, toner images made of spherical toner are formed by the other developing devices 19Y, 19M, and 19C, and these toner images are sequentially transferred onto the transfer belt 3. Is done. Further, toner that has not been transferred to the transfer belt 3 and has passed through each transfer region, that is, transfer residual toner, is formed in the vicinity of the leading edge of the cleaning blades 14BK to 14C as the image carriers 2BK to 2C rotate. The dam E is reached and is blocked by the dam E. In FIG. 3, the transfer residual toner blocked in this way is indicated by a reference symbol T. Since the transfer residual toner T is blocked by the weir E in this way, the transfer residual toner on the image carriers 2Y, 2M, and 2C is a spherical toner, but the toner passes through the cleaning blades 14Y, 14M, and 14C. In other words, it is efficiently removed from the surface of each of the image carriers 2Y to 2C and falls downward. Since at least a part of the transfer residual toner on the most upstream side image carrier 2BK is an irregular toner, it is efficiently removed from the image carrier 2BK by the cleaning blade 14BK due to its property. As described above, in the image forming apparatus shown in FIGS. 1 and 2, the transfer residual toner on each image carrier can be efficiently removed, and high cleaning performance can be maintained. In addition, since toner images are formed by spherical toner on the image carriers 2Y, 2M, 2C other than the most upstream image carrier 2BK, the image quality of the final color image transferred and fixed on the recording medium P Can be increased.

  Further, the toner adhering to the transfer belt 3 at the time of image formation is blocked by the above-mentioned weir formed in the vicinity of the tip edge portion of the cleaning blade 20 and removed from the transfer belt 3, so that the toner adheres on the transfer belt 3. The spherical toner thus removed can be removed efficiently, and the cleaning performance for the transfer belt 3 can be improved.

  In the case of the image forming apparatus shown in FIG. 1, a cleaning blade 21 that presses against the transfer roller 18 may be provided in order to remove the toner adhering to the transfer roller 18. When such a cleaning blade 21 is provided, a voltage having a polarity opposite to that of the toner (plus polarity in this example) is applied to the transfer roller 18 at the time of non-image formation such as warm-up, and transferred onto the transfer belt 3. The mixed toner of irregular shaped toner and spherical toner or the irregular shaped toner may be transferred onto the surface of the transfer roller 18, and a weir may be formed in the vicinity of the tip edge portion of the cleaning blade 21 by the toner. By this weir, the spherical toner transferred to the transfer roller 18 at the time of image formation can be efficiently removed.

  During non-image formation, a voltage having the same polarity as the toner charging polarity, that is, a negative polarity is applied to the transfer roller 18, and the spherical toner attached to the transfer roller 18 is transferred to the transfer belt 3 electrostatically. While cleaning the roller 18, the spherical toner transferred to the transfer belt 3 may be removed by a cleaning blade 20 having a weir formed in the vicinity of the leading edge portion.

  By the way, first, a developing device other than the starting developing device 19BK, for example, the developing device 19Y stores mixed toner or amorphous toner of amorphous toner and spherical toner, and other developing devices store spherical toner. At the time of up, it is possible to form a belt-like toner image on the image carrier 2Y by the developing device 19Y, and reversely transfer the toner of the toner image to the other image carriers 2BK, 2M, 2C via the transfer belt 3 It is. In this case, a part of the toner transferred from the image carrier 2Y onto the transfer belt 3 is reversely transferred to the image carrier 2M, and a part of the remaining toner is reversely transferred to the image carrier 2C. The remaining toner is reversely transferred to the image carrier 2BK. To make this possible, when the toner on the transfer belt 3 passes through the cleaning blade 20, the cleaning blade 20 is separated from the transfer belt 3. It is necessary to keep it. Therefore, in order to form a weir near the tip edge portion of the cleaning blade 20, the transfer belt 3 is rotated one more time, and the toner that has passed through each image carrier again is brought into pressure contact with the surface of the transfer belt 3. The toner needs to be transported again to the cleaning blade 20 and dammed up by the leading edge portion, and a great deal of time is required to form the weir near the leading edge portion. On the other hand, in the image forming apparatus shown in FIGS. 1 and 2, the first start developing device 19BK which starts to form a toner image on the image carrier first is mixed with an amorphous toner and a spherical toner or an irregular toner. The toner is reversely transferred to the other image carriers 2Y, 2M, and 2C via the transfer belt 3 and a weir is formed near the tip edge portion of the cleaning blade 20, so that the transfer belt 3 rotates once. All the weirs can be formed.

  In the image forming apparatus shown in FIGS. 1 and 2, the first start developing device 19BK is configured to form a black toner image on the most upstream image carrier 2BK. A toner image other than black may be formed on the most upstream image carrier. However, since this first starting developing device forms a toner image on the most upstream image carrier with the irregular toner or the mixed toner of the irregular toner and the spherical toner, the image quality of the toner image is only the spherical toner. It is inferior to the image quality of the formed toner image. Therefore, it is preferable that the first starting developing device is configured to form an inconspicuous color toner image, for example, a black toner image or a yellow toner image as in the illustrated example, on the most upstream image carrier. In particular, it is preferable that the initial development device is configured to form a black toner image that hardly affects the image quality. In addition, when the initial developing device contains a mixed toner of spherical toner and irregular toner, transparent toner can be used as the irregular toner. In this way, since the transparent amorphous toner does not participate in image formation, the result is the same as that of forming a toner image on the most upstream image carrier with only spherical toner, and the image quality can be improved.

  In addition, magnetic toner containing a magnetic material is used as the irregular toner used in the initial developing device, and the irregular toner constituting the weir E is held by magnetic force using the magnetized cleaning blades 14BK to 14C. Further, it is possible to prevent the irregular toner from falling. Alternatively, as shown in FIG. 4, a blade holder 22 located in the vicinity of the cleaning blades 14BK to 14C is magnetized, or a magnet 23 is arranged inside the image carriers 2BK to 2C as shown in FIG. Further, as shown in FIG. 6, a sleeve 25 containing a magnet roller 24 is disposed in the vicinity of the tip of each of the cleaning blades 14BK to 14C, so that the magnetic amorphous toner constituting the weir E is held by magnetic force. The irregular toner may be prevented from falling. When the configuration in which the weir is held by the magnetic force in this way, a non-magnetic toner is used as the spherical toner used in each of the developing devices 2BK to 2C, and the spherical toner is applied to the cleaning blades 14BK to 14C by the magnetic force. Do not hold near the tip edge.

  In the image forming apparatus shown in FIGS. 1 and 2, the toner transferred from the most upstream image carrier 2BK to the transfer belt 3 during non-image formation is transferred to the other image carriers 2Y, 2M, and 2C. A voltage having the same polarity as the charging polarity of the toner is applied to each of the transfer devices including the transfer brushes 12Y, 12M, and 12C to be reversely transferred. Even when a voltage higher than the voltage is applied to each transfer device, the toner on the transfer belt 3 can be reversely transferred to the image carriers 2Y, 2M, and 2C.

FIG. 7 is a diagram for explaining this. In this figure, the horizontal axis represents the voltage applied to the transfer device, and the vertical axis represents the transfer rate of the toner image from the image carrier to the transfer belt 3 or the recording medium P, and the reverse of the toner from the transfer belt 3 to the image carrier. The rate is shown. The curve indicated by the symbol X in FIG. 7 shows the relationship between the voltage applied to the transfer device during image formation and the transfer rate when the toner image is transferred from the image carrier to the transfer belt 3 or the recording medium P. At the time of image formation, a positive polarity transfer voltage in a range indicated by X1 in which the transfer rate is the highest is usually applied to a transfer device composed of, for example, a transfer brush. Curve Y shows the relationship between the voltage and the reverse transfer rate when a negative polarity voltage is applied to the transfer device to reversely transfer the toner on the transfer belt 3 to the image carrier. Further, a curve Z indicates a voltage and a reverse transfer rate when a voltage having a positive polarity opposite to the charging polarity of the toner is applied to the transfer device and the toner on the transfer belt 3 is reversely transferred to the image carrier. Showing the relationship. As can be seen from curve Z, even when a voltage is applied between the toner and the opposite polarity to the transfer device, when the voltage value becomes the discharge starting voltages V ₁ or more, it is possible to reverse transfer toner little by little. The reverse transfer of toner at this time is due to peeling discharge on the downstream side in the moving direction of the image carrier and the transfer belt. A charging polarity opposite the polarity of the toner, by applying a high V ₂ or more than the voltage applied to the transfer device during image formation on the transfer device, a high reverse transfer rate is obtained on the transfer belt 3 The negative polarity toner can be efficiently reversely transferred to the image carrier.

  In the image forming apparatus shown in FIGS. 1 and 2, a plurality of image carriers 2Y, 2M, and 2C other than the most upstream image carrier 2BK are provided. When the toner transferred to 3 is reversely transferred to the other image carriers 2Y, 2M, and 2C, when the same voltage is applied to the transfer brushes 12Y, 12M, and 12C, the image carrier 2Y is transferred from the transfer belt 3. The amount of toner transferred from the transfer belt 3 to the image carrier 2M is smaller than the amount of toner transferred to, and the amount of toner transferred from the transfer belt 3 to the image carrier 2C is reduced. Therefore, when the toner transferred to the transfer belt 3 is reversely transferred to each of the image carriers 2Y, 2M, and 2C other than the most upstream image carrier 2BK during non-image formation, It is preferable that the voltage to be applied is sequentially set higher as it goes downstream in the transfer belt moving direction. For example, a voltage of −1.5 kV is applied to the transfer brush 12Y shown in FIGS. 1 and 2, and the toner on the transfer belt 3 is reversely transferred to the image carrier 2Y. A voltage of −1.7 kV is applied to reversely transfer the toner on the transfer belt 3 to the image carrier 2M. Further, a voltage of −1.9 kV is applied to the transfer brush 12C and a toner on the transfer belt 3 is applied. Is transferred back to the image carrier 2C.

  Further, the toner constituting the weir E formed in the vicinity of the tip edge portion of each cleaning blade gradually falls over time, or a part of the toner slips through the cleaning blade. The amount decreases. If this is left unattended, the cleaning performance with respect to each image carrier decreases. Accordingly, it is necessary to supply toner stored in the first start developing device 2BK to the other image carriers 2Y to 2BK via the transfer belt 3 at a predetermined timing, and to supply the irregular toner to the weir E. There is. The same applies to the cleaning blades 20 and 21.

  Therefore, as described above, when the image forming apparatus is warmed up, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed on the most upstream image carrier 2BK, and the toner of the toner image Are transferred to the other image carriers 2Y, 2M, and 2C via the transfer belt 3. This operation is performed every warm-up. Or you may comprise so that this operation | movement may be performed between what is called paper. That is, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed in a non-image forming area corresponding to the space between the recording media of the most upstream image carrier 2BK, and the toner of the toner image is used. Then, the toner image is transferred to a non-image forming area corresponding to the space between the recording media of the transfer belt 3, and the toner on the transfer belt 3 is transferred to the non-image forming area corresponding to the space between the recording media of the other image carriers 2Y, 2M, 2C. Reverse transcription is performed. Alternatively, each time a predetermined number of image forming operations are performed, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed on the most upstream image carrier 2BK, and the toner of the toner image is formed. The image may be reversely transferred to other image carriers 2Y, 2M, and 2C via the transfer belt 3. Further, when one or a series of image forming operations is one job, after the end of the job, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is carried on the most upstream side. The toner of the toner image can be reversely transferred to another image carrier via the transfer belt 3.

  Further, when the spherical toner used in the image forming apparatus described above has a circularity of 0.96 or more, a particularly high quality image can be formed. Further, if each image carrier is an amorphous silicon photoconductor, the film scraping of the photoconductor can be reduced, and its life can be extended. Similarly, each image carrier is an organic photoreceptor having a surface layer reinforced with a filler, an organic photoreceptor using a cross-linked charge transport material, or an organic photoreceptor having both characteristics. It is possible to prevent the photoconductor from being scraped and to extend its life. Specifically, the outermost layer of the photoreceptor is a polymer or copolymer of a compound selected from vinyl fluoride, vinylidene fluoride, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. As the conductive support, a metal such as aluminum or stainless steel, a cylindrical cylinder such as paper or plastic, or a film is used. An undercoat layer (adhesive layer) having a barrier function and an undercoat function can be provided on these supports. The undercoat layer is used to improve the adhesion of the photosensitive layer, improve coating properties, protect the support, cover defects on the support, improve charge injection from the support, and protect the electrical coating of the photosensitive layer. It is formed. Known materials for the undercoat layer include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cellulose, ethylene-acrylic acid copolymer, casein, polyamide, copolymer nylon, glue, gelatin, and the like. These are dissolved in a solvent suitable for each and coated on a support. The film thickness is about 0.2 to 2 μm. Specific examples of the photosensitive layer include a photosensitive layer having a laminated structure of a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material, a single layer containing a charge generation material and a charge transport material And a photosensitive layer made of Examples of charge generating materials include pyrylium, thiopyrylium dyes, phthalocyanine pigments, anthanthrone pigments, dibenzpyrenequinone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, azo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanine, and quinocyanine. Can be used. Examples of charge transport materials include pyrene, N-ethylcarbazole, N-isopropylcarbazole, N-methyl-N-phenylhydrazino-3-methylidene-9-ethylcarbazole, N, N-diphenylhydrazino-3-methylidene-9 -Ethylcarbazole, N, N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine, N, N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone Triarylmethane compounds such as p-diethylaminobenzaldehyde-2-methylphenyl) -phenylmethane, 1,1-bis (4-N, N-diethylamino-2-methylphenyl) heptane, 1,1,2 , 2-Tetrakis (4-N, N-dimethyl) Polyaryl alkanes such as amino-2-methylphenyl) ethane, and triaryl amines, or the like can be used.

  Each configuration described above can also be applied to various types of image forming apparatuses other than the image forming apparatuses shown in FIGS. For example, the present invention can also be applied to the image forming apparatus shown in FIG. 8. In this image forming apparatus, the image forming apparatus has first and second image carriers 2A and 2B. A black toner image is formed on the image carrier 2 A, and the toner image is transferred to the transfer belt 3. The transfer residual toner adhering to the first image carrier 2A after the toner image transfer is scraped and removed by the cleaning blade 14A. On the other hand, a magenta toner image is formed on the second image carrier 2B by the developing device 9M, and this magenta toner image is transferred onto the transfer belt 3 so as to be superimposed on the black toner image. The transfer residual toner adhering to the image carrier 2B is removed by the cleaning blade 14B. In exactly the same manner, a yellow toner image is formed on the first image carrier 2A by the developing device 9Y, and the toner image is transferred onto the transfer belt 3 so as to be superimposed on the previously transferred toner image, and further developed. A cyan toner image is formed on the second image carrier 2B by the device 9C, and the cyan toner image is transferred onto the transfer belt 3 so as to overlap the previously transferred toner image. Also in this case, the first and second image carriers 2A and 2B after the toner image transfer are cleaned by the cleaning blades 14A and 14B, respectively. The composite toner image thus formed on the transfer belt 3 is transferred to the recording medium P, and the transferred toner image is fixed by a fixing device (not shown). The cleaning blade 20 that cleans the transfer belt 3 is separated from the transfer belt 3 when the toner image passes through it, and is pressed against the transfer belt 3 only when the transfer residual toner on the transfer belt 3 is removed.

  Also in the case of the above-described image forming apparatus, for example, the developing device 9BK is determined as the first starting developing device, in which mixed toner of irregular toner and spherical toner or irregular toner is accommodated, and the other developing devices 9Y, 9M, 9C contains spherical toner. In this state, during non-image formation, the developing device 9BK forms a belt-like toner image on the first image carrier 2A, transfers the toner to the transfer belt 3, and the remaining toner to the cleaning blade 14A. The dam is formed in the vicinity of the leading edge portion of the cleaning blade 14A. On the other hand, the toner transferred to the transfer belt 3 is reversely transferred to the second image carrier 2B, the toner is conveyed to the cleaning blade 14B, and a weir is formed in the vicinity of the leading edge portion of the cleaning blade 14B. Further, a weir is formed in the vicinity of the leading edge portion of the cleaning blade 20 by the toner remaining on the transfer belt 3.

  During normal image formation, when a yellow toner image is first formed by the developing device 9Y on the first image carrier 2A and then a black toner image is formed by the developing device 9BK, the first starting developing device is used. Becomes the developing device 9Y, and the weir is formed by the mixed toner or the irregular toner of the irregular toner and the spherical toner accommodated therein.

1 is a schematic diagram illustrating an example of an image forming apparatus. It is the schematic which shows the image forming apparatus of another form. It is a figure which shows the weir formed in the front-end | tip edge part vicinity of a cleaning blade. It is a figure which shows the example holding a weir by magnetic force. It is a figure which shows the example holding a weir by magnetic force. It is a figure which shows the example holding a weir by magnetic force. It is a figure which shows the voltage applied to a transfer apparatus, and the transfer rate and reverse transfer rate of a toner. FIG. 10 is a schematic diagram illustrating still another example of the image forming apparatus.

Explanation of symbols

2BK, 2Y, 2M, 2C, 2A, 2B Image carrier 3 Transfer belt 9BK, 9Y, 9M, 9C Developing device 14A, 14B, 14BK, 14Y, 14M, 14C Cleaning blade P Recording medium

Claims (11)

A plurality of image carriers, a developing device for forming a toner image on each image carrier, a transfer belt disposed opposite to the plurality of image carriers, and a toner image formed on each image carrier on the transfer belt A transfer device for transferring, and a cleaning blade for removing residual toner adhering to the image carrier after transferring the toner image, and transferring the toner image transferred to the transfer belt to a recording medium to obtain a recorded image; In the image forming apparatus,
When the developing device that first starts forming a toner image on the image carrier is the first starting developing device, and the image carrier on which the toner image is formed by the first starting developing device is the most upstream image carrier, the first start is performed. The developing device contains a mixture of amorphous toner and spherical toner or irregular toner, and the other developing device contains spherical toner. A toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed on the most upstream image carrier, and the toner of the toner image is transferred to the transfer belt. In the space defined by the surface of each image carrier and the tip of the cleaning blade, the image is reversely transferred to another image carrier located downstream of the most upstream image carrier in the transfer belt moving direction. An image forming apparatus characterized by forming a mixed toner or weir consisting irregular toner of irregular toner and spherical toner. A plurality of image carriers, a developing device for forming a toner image on each image carrier, a transfer belt disposed opposite to the plurality of image carriers, and a toner image formed on each image carrier on the transfer belt In an image forming apparatus comprising: a transfer device that transfers to a recording medium that is carried and conveyed; and a cleaning blade that removes transfer residual toner adhering to the image carrier after the toner image is transferred.
When the developing device that first starts forming a toner image on the image carrier is the first starting developing device, and the image carrier on which the toner image is formed by the first starting developing device is the most upstream image carrier, the first start is performed. The developing device contains a mixture of amorphous toner and spherical toner or irregular toner, and the other developing device contains spherical toner. A toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed on the most upstream image carrier, and the toner of the toner image is transferred to the transfer belt. In the space defined by the surface of each image carrier and the tip of the cleaning blade, the image is reversely transferred to another image carrier located downstream of the most upstream image carrier in the transfer belt moving direction. An image forming apparatus characterized by forming a mixed toner or weir consisting irregular toner of irregular toner and spherical toner. During non-image formation, a voltage having the same polarity as the toner charging polarity is applied to the transfer device that reversely transfers the toner transferred to the transfer belt to another image carrier, or the polarity opposite to the toner charging polarity. The image forming apparatus according to claim 1, wherein a voltage higher than a transfer voltage applied during image formation is applied. A plurality of image carriers other than the most upstream side image carrier are provided, and when transferring the toner transferred to the transfer belt to each of the other image carriers in the non-image formation, The image forming apparatus according to claim 3, wherein the voltage to be applied is sequentially set higher as going to the downstream side in the transfer belt moving direction. When the image forming apparatus is warmed up, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed on the most upstream image carrier, and the toner of the toner image is passed through the transfer belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is reverse-transferred to another image carrier. In a non-image forming area corresponding to a space between the recording media of the most upstream image carrier, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed, and the toner of the toner image is 5. The toner image on the transfer belt is transferred to a non-image forming area corresponding to the space between the recording media of the transfer belt, and the toner on the transfer belt is reversely transferred to a non-image forming area corresponding to the space between the recording media of the other image carriers. The image forming apparatus according to any one of the above. Each time a predetermined number of image forming operations are performed, a toner image composed of a mixture of amorphous toner and spherical toner or an amorphous toner is formed on the most upstream side image carrier, and the toner of the toner image is transferred to the transfer side. The image forming apparatus according to claim 1, wherein reverse transfer is performed to another image carrier via a belt. When one or a plurality of times of a series of image forming operations is one job, after the end of the one job, a toner image composed of a toner mixture of amorphous toner and spherical toner or an amorphous toner is transferred to the most upstream image carrier. The image forming apparatus according to claim 1, wherein the toner of the toner image is reversely transferred to another image carrier via the transfer belt. The image forming apparatus according to claim 1, wherein the spherical toner has a circularity of 0.96 or more. The image forming apparatus according to claim 1, wherein the image carrier is an amorphous silicon photoconductor. 10. The image bearing member is an organic photoreceptor having a surface layer reinforced with a filler, an organic photoreceptor using a cross-linked charge transport material, or an organic photoreceptor having both characteristics. The image forming apparatus according to any one of the above.

Images