JP2012088514A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses image failure that occurs when a transfer member is left in contact with an image carrier without an additional complex configuration or cost increase.SOLUTION: An image forming apparatus 100 includes an image carrier 1 that carries a toner image, and a transfer member 5 that is pressure-welded to the image carrier and forms a transfer nip between the image carrier and itself. The image forming apparatus 100 carries out an operation to stop the image carrier in a state where the toner image formed on the image carrier 1 is at least at the transfer nip N.

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile, and more particularly to an image forming apparatus having a transfer member pressed against an image carrier such as a photosensitive drum and an intermediate transfer belt.

  In an image forming apparatus (image recording apparatus) using an image forming process such as an electrophotographic system or an electrostatic recording system, a toner image is formed on an image carrier such as a photosensitive drum or an intermediate transfer belt. Further, the toner image on the image carrier is made to reach a transfer nip formed by the image carrier and a transfer member, and a recording material such as paper is supplied to the transfer nip in synchronization with the transfer nip. A transfer bias is applied to. By this action, the toner image is transferred from the image carrier to the recording material.

  In the image forming apparatus as described above, the transfer member is left in a state of being pressed against the image carrier. For this reason, the surface material of the deteriorated transfer member may be transferred to the surface of the image carrier, or the characteristics of the image carrier surface may be changed by oil or low molecular components that exude from EPDM, CR, urethane, etc. constituting the transfer member. It is known that When left for a long period of time, exuded oil, low molecular components, etc. adhere to the pressure contact portion with the transfer member on the surface of the image carrier, and the transferability at this pressure contact portion deteriorates. May end up. As a result, when a toner image is formed across the pressure contact portion and other portions on the surface of the image carrier, image defects such as white spots may occur.

  For this reason, measures are taken such as using a material that does not bleed out oil as a material constituting the transfer member. However, since the material is limited, it may cause problems such as an increase in cost. Further, Patent Document 1 discloses a method for preventing a change in characteristics of the image carrier and deterioration of the transfer member by separating the image carrier and the transfer member except when necessary.

Japanese Patent No. 2981000

  However, the use of the separating means as described above can cause problems such as a complicated mechanism due to an increase in the number of parts and an increase in the size of the apparatus due to the space. 2. Description of the Related Art In recent years, image forming apparatuses have been reduced in size and cost, and it has become necessary to simplify the apparatus configuration and save space.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing image defects caused by leaving a transfer member in contact with an image carrier without causing complication of the apparatus and cost increase. Is to provide.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus comprising: an image carrier that carries a toner image; and a transfer member that is pressed against the image carrier and forms a transfer nip with the image carrier. An image forming apparatus that performs an operation of stopping the image carrier in a state where a toner image formed on the image carrier is present at least in the transfer nip.

  According to the present invention, it is possible to suppress image defects caused by leaving the transfer member in contact with the image carrier without causing complication of the apparatus and an increase in cost.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a flowchart figure which shows the flow of an example of operation | movement of the image forming apparatus according to this invention. It is a flowchart figure which shows the flow of the other example of operation | movement of the image forming apparatus according to this invention. FIG. 6 is a schematic cross-sectional configuration diagram of an image forming apparatus according to another embodiment of the present invention. It is a flowchart figure which shows the flow of the other example of operation | movement of the image forming apparatus according to this invention.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the following examples are not intended to limit the scope of the present invention only to them.

Example 1
1. First, the overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 shows a schematic cross section of an image forming apparatus 100 in the present embodiment.

  The image forming unit (image forming unit) P1 of the image forming apparatus 100 is provided with a drum-type electrophotographic photosensitive member (photosensitive member) as an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 by a drive motor (not shown) as drive means. Around the photosensitive drum 1, the following units are arranged in order along the rotation direction. First, the charging roller 2 is a charging member as a charging unit. Next, an exposure apparatus (laser scanner) 3 as an exposure unit. Next, there is a developing device 4 as a developing unit. Next, a transfer roller 5 which is a transfer member as a transfer unit. Next, there is a cleaning device 6 as a cleaning means.

  The surface of the rotationally driven photosensitive drum 1 is charged by the charging roller 2, and then an electrostatic latent image is formed by the exposure device 3. The exposure device 3 oscillates a laser beam L based on the image information, and exposes the surface of the photosensitive drum 1 with the laser beam L. As a result, the charge on the surface of the photosensitive drum 1 after charging is removed from the exposed portion to form an electrostatic latent image. Thereafter, the electrostatic latent image is developed by the developing device 4 with toner as a developer. In this embodiment, the developing device 4 is charged to the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) on the portion of the photosensitive drum 1 where the charge has been removed by exposure after the charging process. The electrostatic latent image is developed by a reversal development method in which toner is attached. The transfer roller 5 is pressed against the surface of the photosensitive drum 1 to form a transfer portion (transfer nip) N that is a contact area between the photosensitive drum 1 and the transfer roller 5. The transfer roller 5 is driven to rotate in the direction of the arrow R2 as the photosensitive drum 1 is rotationally driven in the direction of the arrow R1. The toner image formed on the surface of the photosensitive drum 1 is electrostatically transferred to the recording material S at or near the transfer nip N. At this time, a transfer voltage (transfer bias) having a polarity opposite to the normal charging polarity (negative polarity in the present embodiment) of the toner is applied to the transfer roller 5 by a transfer power source 51 as a transfer voltage applying unit. In this embodiment, the transfer power supply 51 has a positive voltage output unit and a negative voltage output unit for cleaning the transfer roller 5 described later, and the transfer roller 5 has both positive and negative polarities. A voltage can be applied.

  Toner that remains on the surface of the photosensitive drum 1 without being transferred to the recording material S during transfer (residual toner) is removed by the cleaning device 6 and collected in a waste toner container. The photosensitive drum 1 whose surface has been cleaned in this way is used for the next image formation starting from charging.

  A recording material S such as paper used for image formation is stored in a paper feed cassette 7 and is supplied to a transfer nip N by a paper feed roller 8 and a transport roller 9. As described above, a transfer bias is applied to the transfer roller 5 at the timing when the recording material S passes through the transfer nip N. The toner image on the photosensitive drum 1 is transferred to the recording material S by this transfer bias. Thereafter, the recording material S is conveyed to the fixing device 10 where the toner image is fixed thereon by being heated and pressed. The recording material S after the toner image is fixed is discharged to the outside of the image forming apparatus 100 by the paper discharge roller 11.

  In addition, a control device 12 is provided in the image forming apparatus 100 as a control unit that comprehensively controls the operation of the image forming apparatus 100. The control device 12 includes a CPU, and receives an image formation start signal from an external information device 13 such as a personal computer, and controls operations of a driving unit, a voltage applying unit, and the like. Further, the control device 12 has a function of feeding back control based on temperature and humidity by an environment sensor (temperature / humidity sensor) 14 serving as an environment detection unit provided in the image forming apparatus 100 and a function of counting the cumulative number of printed sheets. Have.

  In this embodiment, the process speed of the image forming apparatus 100 (corresponding to the peripheral speed of the photosensitive drum 1) is 100 mm / sec, and the photosensitive drum 1 having an outer diameter of 24 mm is used.

  In this embodiment, a roller made of solid rubber is used as the transfer roller 5, and the resistance of this roller is adjusted with a conductive agent. For example, EPDM or NBR is used as the solid rubber. This is because, since the elastic layer is a solid rubber having a high restoring force, the holding force of the recording material at the transfer nip N is high with respect to the sponge type transfer roller. Accordingly, there is an advantage that the recording material S can be transported more stably without being affected by the back tension of the paper feed, the transport resistance generated when the postcard or the cardboard is rubbed into the transport path. However, many of the low molecular components of the base polymer present in the rubber forming the elastic layer of the transfer roller 5 and oil added during production, such as paraffinic oil, are likely to react with the surface of the photosensitive drum 1. When the transfer roller 5 and the photosensitive drum 1 are left in pressure contact with each other for a long time, they exude from the transfer roller 5 and adhere to the surface of the photosensitive drum 1 to modify the surface of the photosensitive drum 1. May end up. In particular, the solid transfer roller 5 has higher hardness than the transfer roller using sponge rubber as an elastic layer, and the transfer nip N is narrowed, so that the pressure contact force with respect to the photosensitive drum 1 per unit area is increased. There is a tendency. For this reason, low molecular components of the material rubber and oil existing in the transfer roller 5 are likely to ooze out on the surface of the transfer roller 5. Therefore, when the transfer roller 5 is left in contact with the photosensitive drum 1 at a fixed position for a long time, the material that exudes to the photosensitive drum 1 adheres and disturbs the image. The surface may be modified and all subsequent images may be disturbed.

In this embodiment, the transfer roller 5 is a roller made of conductive solid rubber, the length in the longitudinal direction (rotation axis direction) is 216 mm, the outer diameter is 15 mm, the hardness is 60 ° (Asuka C), and the resistance is A 10 ⁸ Ω roller was used. In this embodiment, the transfer roller 5 is pressed against the photosensitive drum 1 with a pressure of 9.8 N (1 kgf). In this embodiment, the width of the transfer nip N formed by the photosensitive drum 1 and the transfer roller 5 in the conveyance direction of the recording material S is 1.8 mm.

2. Suppression of image defects after standing One of the purposes of this embodiment is to prevent image defects such as white spots caused by the components contained in the transfer member oozing out and adhering to the image bearing member. It is to suppress without causing an increase.

  In this embodiment, the photosensitive drum 1 is stopped in a state where a toner image exists at least in the transfer nip N that is a pressure contact portion between the photosensitive drum 1 and the transfer roller 5. The toner image (hereinafter, also referred to as “shielding toner image”) blocks (shields) the components that have exuded from the transfer roller 5, and prevents this from adhering to the surface of the photosensitive drum 1. As a result, image defects such as white spots caused by the components that have exuded from the transfer roller 5 adhering to the photosensitive drum 1 are suppressed. Details will be described below.

  FIG. 2 shows an operation for suppressing image defects such as white spots caused by the components exuded from the transfer roller 5 in this embodiment adhering to the surface of the photosensitive drum 1 (hereinafter referred to as “shielding toner image supply operation”). Also shows the flow.

  When the image formation is completed (S101) and the control device 12 does not receive the next image formation start signal within a predetermined time, the post-rotation operation is started (S102). The post-rotation operation is an operation from the end of image formation to the stop of the drive motor. In this embodiment, the shielding toner image supply operation is performed during the post-rotation operation.

  After starting the post-rotation operation, a shielding toner image to be supplied to the transfer nip N is formed on the photosensitive drum 1 by the charging roller 2, the exposure device 3, and the developing device 4 (S103). This shielding toner image is a pattern formed at least in the area of the transfer nip N formed at the pressure contact portion between the photosensitive drum 1 and the transfer roller 5 in the conveyance direction of the recording material S. The length of the shielding toner image in the longitudinal direction (rotation axis direction) of the photosensitive drum 1 and the transfer roller 5 needs to be at least equal to or longer than the image formable area on the photosensitive drum 1 in the same direction. Specifically, it is longer than the length of the transfer roller 5 in the same direction. Then, at the timing when the shielding toner image reaches the transfer nip N, the rotation of the photosensitive drum 1 is stopped (S104). Thereafter, until the next image formation start signal is received, the image forming standby state is entered with the shielding toner image interposed between the photosensitive drum 1 and the transfer roller 5 (S105).

  Next, when the control device 12 receives an image formation start signal (S106), the pre-rotation operation is started (S107). The pre-rotation operation is an operation from the reception of the image formation start signal to the start of image formation. In this embodiment, the transfer roller 5 is cleaned during the pre-rotation operation. In the pre-rotation operation, the drive motor starts driving simultaneously with receiving the image formation start signal, and the shielding toner image held in the transfer nip N is removed from the transfer nip N. In order to clean the transfer roller 5, a voltage having the same polarity as the normal charging polarity of the toner is applied to the transfer roller 5 by the transfer power source 51. Thereby, the toner adhering to the transfer roller 5 is transferred onto the photosensitive drum 1 and then removed from the surface of the photosensitive drum 1 by the cleaning device 6 (S108). Then, following the pre-rotation operation, image formation is started (S109).

  Next, the result of confirming the effect of the shielding toner image supply operation in this embodiment will be described.

  The exudation of contained components from the transfer roller 5 caused by leaving the photosensitive drum 1 and the transfer roller 5 in pressure contact is promoted in a high-temperature and high-humidity environment, and worsens as the leaving time increases. Therefore, here, the effect was confirmed under the condition that the image forming apparatus 100 was left for one week in an environment of a temperature of 40 ° C. and a humidity of 95%. Further, the shielding toner image interposed in the transfer nip N in the shielding toner image supply operation is 3.0 ± 0.5 mm in the circumferential direction of the photosensitive drum 1 (conveying direction of the recording material S), and the longitudinal direction of the photosensitive drum 1. In 225 mm area. When left unattended, the shielding toner image is arranged in the circumferential direction of the photosensitive drum 1 so that the transfer nip N is within the shielding toner image region.

  Table 1 shows whether or not image defects occur when the printing rate of the shielding toner image formed on the photosensitive drum 1 in the shielding toner image supply operation is changed according to the laser light lighting time per pixel. Yes. Specifically, when a solid black pattern (an image having the highest density level on the entire surface) is printed in the image forming apparatus 100 after being left, “OK” is indicated when no image defect occurs. In addition, when an image defect occurs, a solid black pattern is printed after that, indicating the number of sheets on which the image defect is no longer seen.

First, without performing the shielding toner image supply operation in this embodiment (printing rate 0%), after image formation is performed and the image forming apparatus 100 is left in the above-described environment, the recording material S is Xx4200 (basis weight). (75 g / m ² , LTR size) was printed with a solid black pattern. As a result, horizontal strip-like white spots having a period of about 75 mm occurred in the conveyance direction of the recording material S. This period is the period of the photosensitive drum 1. That is, the toner image cannot be developed on the photosensitive drum 1 as a result of charging and developing defects caused by the exuding material from the transfer roller 5 adhering to the pressure contact portion of the surface of the photosensitive drum 1 with the transfer roller 5. , It can be seen that the white area is missing. Actually, when the surface of the photosensitive drum 1 before printing after being left standing was observed, deposits were confirmed at the pressure contact portion with the transfer roller 5. This image defect was improved by printing a solid black pattern, and when 10 solid black patterns were printed, no white spots were seen. This is presumably because the material adhering to the surface of the photosensitive drum 1 and exuding from the transfer roller 5 was peeled off from the surface of the photosensitive drum 1 little by little by paper or toner.

  On the other hand, when the shielding toner image supply operation in the present embodiment is performed, when the solid black pattern is printed on the recording material S after the image forming apparatus 100 is left in the above-described environment, the print rate is a pattern of 30% or more. If so, no image defect occurred. However, when the printing rate was 20%, horizontal strip-like white spots having a period of about 75 mm occurred. Further, when the printing rate is 30% or more, even if the surface of the photosensitive drum 1 after printing after standing is observed, deposits other than the toner of the shielding toner image intentionally supplied to the transfer nip N can be seen. There wasn't. However, although it was a little at a printing rate of 20%, deposits were confirmed at the pressure contact portion with the transfer roller 5 on the surface of the photosensitive drum 1. That is, it can be seen that when the printing rate is 20%, the contained component that exudes from the transfer roller 5 may not be blocked by the shielding toner image and may adhere to the surface of the photosensitive drum 1. The white spots were not seen when one solid black pattern was printed. From this, it can be seen that even when the printing rate is 20%, it is better than the case where the shielding toner image supply operation is not performed. However, in order to more effectively suppress image defects, it is preferable to use a pattern having a printing rate of 30% or more as the shielding toner image.

  As described above, in this embodiment, the shielding toner image supply operation is executed, and the shielding toner image is left in the pressure contact portion between the photosensitive drum 1 and the transfer roller 5 at the time of non-image formation. Preferably, at the time of non-image formation, a shielding toner image having a printing rate of 30% or more is interposed between the photosensitive drum 1 and the transfer roller 5 and left as it is. Thereby, it is possible to suppress the adhesion of the component that exudes from the transfer roller 5 to the surface of the photosensitive drum 1, and to effectively suppress the occurrence of image defects.

  In this embodiment, the transfer roller 5 is described as being formed of conductive solid rubber, but the present invention is not limited to this. For example, the same effect can be obtained even when the sponge type transfer roller 5 is used. Also, with regard to the pattern of the shielding toner image, the printing rate is changed according to the laser light lighting time per pixel in this embodiment, but the method of changing the printing rate is not limited to this. That is, in order to change the printing rate (image ratio), it is only necessary to change the area of the toner portion in the printing area, and it is preferable that a shielding toner image in which the area of the toner portion in the printing area is 30% or more can be formed. . For example, a vertical line, a horizontal line, or a dither pattern may be used as the pattern of the shielding toner image.

  As described above, according to the present embodiment, the operation of stopping the photosensitive drum 1 is executed in a state where the shielding toner image exists in the transfer nip N that is the pressure contact portion between the photosensitive drum 1 and the transfer roller 5. As a result, it is possible to reduce the components (oil and low-molecular components) contained in the transfer roller 5 from adhering to the photosensitive drum 1, and image defects such as white spots due to transfer defects resulting from this are complicated and the cost is increased. It can suppress without inviting.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, elements having the same or corresponding functions and configurations as those of the image forming apparatus of Embodiment 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the conditions for performing the shielding toner image supply operation described in the first embodiment are limited, and image defects such as white spots are effectively suppressed while the toner consumption is reduced.

  That is, in Example 1, during the post-rotation operation after the completion of image formation, a shielding toner image is formed on the photosensitive drum 1, the shielding toner image reaches the transfer nip N, and the photosensitive drum 1 is stopped. As a result, image defects such as white spots were suppressed. For this reason, image defects can be suppressed, but toner is consumed for each image formation. As a result, there is a concern that the life of the toner cartridge may be shortened or the waste toner container may be filled up at an early stage.

  However, the problem that the contained components ooze out from the transfer roller 5 and cause image defects does not occur in the same manner under all conditions, and there are conditions that are likely to occur. Therefore, in this embodiment, the shielding toner image supply operation is performed only when such a condition that is likely to occur occurs. Details will be described below.

  First, exudation of contained components from the transfer roller 5 is promoted in a high temperature and high humidity environment. That is, in a relatively low temperature and low humidity environment, the components contained in the transfer roller 5 are less likely to bleed out, and the above-described problems are less likely to occur.

  Further, as the transfer roller 5 is used, components of the recording material S, such as calcium carbonate contained in paper, adhere to the surface and are covered. As the amount increases, the contained component that exudes from the transfer roller 5 is blocked by the component of the recording material S, and the amount adhering to the surface of the photosensitive drum 1 decreases. Therefore, if the frequency of use of the transfer roller 5, that is, the cumulative number of prints of the image forming apparatus 100 (the cumulative number of prints performed using the transfer roller 5) is greater than a certain value, the above-described problem is unlikely to occur.

  In view of these, in this embodiment, the shielding toner image supply operation is performed only when the temperature and humidity of the atmospheric environment are higher than the predetermined values and the cumulative number of printed sheets is less than the predetermined number. In addition, about atmosphere environment, conditions can be satisfy | filled when both temperature and humidity are higher than predetermined value, or one of temperature or humidity is higher than predetermined value.

  FIG. 3 shows the flow of the shielding toner image supply operation in this embodiment.

  When the image formation is completed (S201), the post-rotation operation is started (S202). In the post-rotation operation, the control device 12 first determines whether or not to perform the shielding toner image supply operation from the temperature and humidity of the atmosphere detected by the environmental sensor 14 in the image forming apparatus 100 (S203). When the temperature and humidity of the atmosphere are below the predetermined values, the rotation of the photosensitive drum 1 is stopped (S204), and the image forming standby state is entered (S208). On the other hand, if the ambient temperature and humidity exceed predetermined values, it is next determined from the cumulative number of prints whether or not the shielding toner image supply operation is to be performed (S205). When the cumulative number of prints is equal to or greater than the predetermined number, the rotation of the photosensitive drum 1 is stopped (S204), and the image formation standby state is entered (S208). On the other hand, when the cumulative number of printed sheets is less than the predetermined number, a shielding toner image to be supplied to the transfer nip N is formed on the photosensitive drum 1 by the charging roller 2, the exposure device 3, and the developing device 4 (S206). ). This shielding toner image is a pattern formed at least in the area of the transfer nip N2 formed at the pressure contact portion between the photosensitive drum 1 and the transfer roller 5 in the conveyance direction of the recording material S. In the present exemplary embodiment, for the same reason as described in the first exemplary embodiment, the shielding toner image is a pattern having a printing rate of 30% or more in the area having the above-described width. Then, at the timing when the shielding toner image reaches the transfer nip N, the rotation of the photosensitive drum 1 is stopped (S207). Thereafter, until the next image formation start signal is received, the image forming standby state is entered with the shielding toner image interposed between the photosensitive drum 1 and the transfer roller 5 (S208).

  Next, when the control device 12 receives the image formation start signal (S209), the pre-rotation operation is started (S210). In the pre-rotation operation, as in the first embodiment, after the transfer roller 5 is cleaned (S211), image formation is started (S212).

  Next, environmental conditions under which image defects occur due to the exudation of contained components from the transfer roller 5 described above and conditions for the cumulative number of printed sheets will be further described. Here, a roller made of conductive solid rubber is used as the transfer roller 5 and has a length in the longitudinal direction (rotation axis direction) of 216 mm, an outer diameter of 15 mm, and a hardness of 60 ° (Asuka C). The experimental results are shown. The transfer roller 5 is pressed against the photosensitive drum 1 with a pressure of 9.8 N (1 kgf). Further, the width of the transfer nip N formed by the photosensitive drum 1 and the transfer roller 5 in the conveyance direction of the recording material S is 1.8 mm.

First, environmental conditions that cause image defects will be described. Table 2 shows the presence or absence of image defects when a solid black pattern is printed after an image is formed without carrying out the shielding toner image supply operation and left for 1 week in each environment. Specifically, “OK” is indicated when no image defect occurs. In addition, when an image defect occurs, a solid black pattern is printed after that, indicating the number of sheets on which the image defect is no longer seen. As the recording material S, Xx4200 (basis weight 75 g / m ² , LTR size) was used.

  In the 40 ° C., 95% environment, 30 ° C., and 80% environment, white spots occurred. By printing 10 solid black patterns, white spots were not seen. In the environment of 20 ° C. and 50%, white spots were still generated, but they were slight and no white spots were observed after printing of two solid black patterns. In the 15 ° C., 25% environment, 10 ° C., 10% environment, no white spots occurred. Therefore, when setting the conditions for performing the shielding toner image supply operation, it is appropriate to provide a threshold value to be implemented when the temperature and humidity of the atmosphere are higher than 15 ° C. and 25%. It is.

Next, conditions for the cumulative number of prints that cause image defects will be described. Table 3 shows the occurrence of image defects when a solid black pattern is printed after image formation is performed for each number of sheets without performing the shielding toner image supply operation, and the image is left for one week in an environment of temperature 40 ° C. and humidity 95%. Indicates the presence or absence. Specifically, “OK” is indicated when no image defect occurs. In addition, when an image defect occurs, a solid black pattern is printed after that, indicating the number of sheets on which the image defect is no longer seen. The image formation up to the accumulated number of sheets was continuously performed by using Xx4200 (basis weight 75 g / m ² , LTR size) as the recording material S. Further, the image formation after being left was performed using Xx4200 (basis weight 75 g / m ² , LTR size) as the recording material S.

  The new transfer roller 5 that was not used at all and the transfer roller 5 that was used for printing 10 sheets had white spots, and no white spots were seen by the printing of 10 solid black patterns. As the number of printed sheets increased, the level of image defect became slight, and no image defect occurred in the transfer roller 5 used for 1000 prints. For this reason, when setting the conditions for performing the shielding toner image supply operation, it is appropriate to set a threshold value to be executed when the cumulative number of printed sheets is less than 1000.

  Next, the result of confirming the effect of the shielding toner image supply operation in this embodiment will be described.

  In this embodiment, the shielding toner image supply operation is set to be performed when the ambient temperature is higher than 15 ° C. or the humidity is higher than 25% and the cumulative number of printed sheets is less than 1,000. The shielding toner image was formed at a printing rate of 100% in an area of 3.0 mm in the circumferential direction of the photosensitive drum 1 (conveying direction of the recording material S) and 225 mm in the longitudinal direction of the photosensitive drum 1.

  Toner images other than the shielding toner image used for image formation during the experiment were formed at a printing rate of 5%. Further, when printing was performed at a printing rate of 5%, an image was formed using a toner amount sufficient to print 1500 sheets until the toner was used up.

  The image formation during the experiment was performed by one-sheet intermittent operation in which the image was left for a fixed time every time one image was formed. The difference in the number of printable sheets was confirmed between the case according to this example and the case according to Example 1 in two types of environments of 30 ° C., 80% environment and 10 ° C., 10% environment.

  No image defect occurred in Examples 1 and 2. The number of printable sheets until the toner runs out was 1256 sheets in the 30 ° C. and 80% environment and 1250 sheets in the 10 ° C. and 10% environment in the case of Example 1. On the other hand, according to this example, the number was 1360 sheets at 30 ° C. and 80% environment, and 1493 sheets at 10 ° C. and 10% environment.

  As described above, according to the present embodiment, when the transfer roller 5 and the photosensitive drum 1 are left in pressure contact with each other, the image defect caused by the exudation of the contained component from the transfer roller 5 can be prevented. The same effect can be exhibited. Furthermore, according to the present embodiment, the toner consumption can be suppressed and the life of the waste toner container can be extended.

  In this embodiment, an environment sensor (temperature / humidity sensor) is used as the environment detection means, but the environment detection means is not limited to this. For example, the temperature and humidity of the environment may be detected (estimated) using the environmental variation characteristic of the electrical resistance value of the transfer roller. For example, by passing a constant current through the transfer roller and detecting the output voltage of the transfer power supply at that time, the electrical resistance value of the transfer roller can be measured, and the temperature and humidity of the environment can be detected (estimated). Alternatively, by applying a constant voltage to the transfer roller 5 and detecting the output current of the transfer power supply at that time, the electrical resistance value of the transfer roller can be measured, and the temperature and humidity of the environment can be detected (estimated). In general, the electrical resistance value of the transfer roller 5 is low in a high temperature and high humidity environment, and the electrical resistance value of the transfer roller is high in a low temperature and low humidity environment. In this case, the transfer power supply is provided with voltage detection means or current detection means. For example, a threshold value of the electrical resistance value (or voltage value or current value) of the transfer roller is used instead of the threshold value of the environmental temperature and humidity in this embodiment. Further, in this embodiment, the shielding toner image supply operation is performed only when both of the two conditions of the temperature and humidity of the atmosphere and the cumulative number of images are satisfied. However, the shielding toner image supply operation is performed only under independent conditions. You may judge whether it is possible.

Example 3
Next, another embodiment of the present invention will be described. In the first and second embodiments, the present invention has been described as an example where the present invention is applied to a monochrome image forming apparatus. In this embodiment, a case where the present invention is applied to a secondary transfer portion of an intermediate transfer type color image forming apparatus will be described.

1. FIG. 4 shows a schematic cross section of an image forming apparatus 101 according to the present embodiment. The image forming apparatus 101 includes first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd as an image forming unit (image forming unit) P2. These image forming portions Pa, Pb, Pc, and Pd form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) in this order.

  Each of the image forming units Pa, Pb, Pc, and Pd has the same configuration as that of the image forming unit P1 in the image forming apparatus 100 of the first embodiment. Elements having the same or corresponding functions and configurations as those of the image forming apparatus 100 of the first embodiment are denoted by the same reference numerals. However, an element having the same function and configuration provided in each of the first to fourth image forming units is an element provided for any of the first to fourth image forming units. Subscripts a, b, c, and d are added.

  Each of the image forming portions Pa, Pb, Pc, and Pd is provided with a drum-type electrophotographic photosensitive member (photosensitive member) as a first image carrier, that is, photosensitive drums 1a, 1b, 1c, and 1d. Yes. The photosensitive drums 1a, 1b, 1c, and 1d are rotationally driven in the direction of arrow R1 by a drive motor (not shown) as a drive unit. The following units are arranged around the photosensitive drums 1a, 1b, 1c, and 1d in order along the rotation direction. First, charging rollers 2a, 2b, 2c and 2d which are charging members as charging means. Next, exposure apparatuses (laser scanners) 3a, 3b, 3c, and 3d as exposure means. Next, developing devices 4a, 4b, 4c and 4d as developing means. Next, primary transfer rollers 5a, 5b, 5c, and 5d, which are primary transfer members as primary transfer means. Next, cleaning devices 6a, 6b, 6c, and 6d as photoconductor cleaning means.

  An intermediate transfer belt 21 that is an endless belt-like intermediate transfer member serving as a second image carrier is provided so as to face the photosensitive drums 1a, 1b, 1c, and 1d of the image forming portions Pa, Pb, Pc, and Pd. Has been placed. The intermediate transfer belt 21 is configured endlessly with a dielectric resin, for example, polyimide, polycarbonate, polybutylene terephthalate, or the like. The intermediate transfer belt 21 is stretched around three rollers, that is, a driving roller 22, a driven roller 23, and a secondary transfer counter roller 24, and the arrow R4 is accompanied by the rotation of the driving roller 22 in the arrow R3 direction. Rotate (turn around) in the direction. On the inner peripheral surface side of the intermediate transfer belt 21, the primary transfer rollers 5a, 5b, 5c, and 5d are arranged so as to face the photosensitive drums 1a, 1b, 1c, and 1d. The primary transfer rollers 5a, 5b, 5c, and 5d are pressed toward the photosensitive drums 1a, 1b, 1c, and 1d via the intermediate transfer belt 21, respectively. Thus, primary transfer portions (primary transfer nips) N1a, N1b, N1c, and N1d, which are contact areas between the photosensitive drums 1a, 1b, 1c, and 1d and the intermediate transfer belt 21, are formed. Further, a secondary transfer roller 25 that is a secondary transfer member as a secondary transfer unit is pressed against a position corresponding to the secondary transfer counter roller 24 on the outer peripheral surface (front surface) side of the intermediate transfer belt 21. Between the secondary transfer roller 25 and the intermediate transfer belt 21, a secondary transfer portion (secondary transfer nip) N2 that is a contact area between the two is formed.

  In each of the image forming portions Pa, Pb, Pc, and Pd, yellow, magenta, cyan, and black toner images are formed on the photosensitive drums 1a, 1b, 1c, and 1d, respectively. Since such a toner image forming method is the same as that of the image forming unit P1 of the image forming apparatus 100 of the first embodiment, detailed description thereof is omitted.

  For example, when forming a full-color image, the toner images formed on the photosensitive drums 1a, 1b, 1c, and 1d of the image forming portions Pa, Pb, Pc, and Pd are respectively transferred to the primary transfer nips N1a, N1b, N1c, and N1d. Primary transfer is performed by sequentially superimposing on the intermediate transfer belt 21. At this time, each primary transfer roller 5a, 5b, 5c, 5d is supplied with a primary charging power supply 51a, 51b, 51c, 51d as a primary transfer voltage application means by a normal charging polarity of the toner (negative polarity in this embodiment). A primary transfer voltage (primary transfer bias) having a reverse polarity is applied.

  Then, the four-color toner images primarily transferred to the intermediate transfer belt 21 are electrostatically secondarily transferred to the recording material S at or near the secondary transfer nip N2 by the secondary transfer roller 25. At this time, the secondary transfer roller 25 is supplied with a secondary transfer voltage (with a negative polarity in the present embodiment) by a secondary transfer power source 52 as a secondary transfer voltage application unit. Secondary transfer bias) is applied. In this embodiment, the secondary transfer power source 52 has a positive voltage output unit and a negative voltage output unit for cleaning the secondary transfer roller 25 described later, and the secondary transfer roller. A voltage having both positive and negative polarities can be applied to 25.

  The toner (residual toner) that is not transferred to the recording material S and remains on the intermediate transfer belt 21 during the secondary transfer is disposed on the downstream side of the secondary transfer nip N2 in the rotation direction of the intermediate transfer belt 21. Is uniformly charged. Thereafter, the toner is transferred to the photosensitive drums 1a, 1b, 1c, and 1d by applying a primary transfer bias in the primary transfer nip N1 of the image forming portions Pa, Pb, Pc, and Pd. The toner is removed from the photosensitive drums 1a, 1b, 1c, and 1d by the cleaning devices 6a, 6b, 6c, and 6d.

2. In the present embodiment, the intermediate transfer belt 21 is stopped in a state where a toner image exists at least in the secondary transfer nip N2 that is a pressure contact portion between the intermediate transfer belt 21 and the secondary transfer roller 25. The toner (shielding toner image) blocks (shields) oil and low-molecular components that ooze out from the secondary transfer roller 25, and prevents this from adhering to the surface of the intermediate transfer belt 21. As a result, image defects such as white spots caused by adhesion of the component exuded from the secondary transfer roller 25 to the intermediate transfer belt 21 are suppressed. Details will be described below.

  FIG. 5 illustrates an operation (blocking toner image supply operation) that suppresses image defects such as white spots caused by adhering components that have exuded from the secondary transfer roller 25 to the surface of the intermediate transfer belt 21 in this embodiment. ).

  When the image formation is completed (S301), the post-rotation operation is started (S302). The post-rotation operation is an operation from the end of image formation to the stop of the drive motor. In this embodiment, the shielding toner image supply operation is performed during the post-rotation operation.

  After the post-rotation operation is started, a shielding toner image is formed on the photosensitive drum 1d of the fourth image forming unit Pd for black by the charging roller 2d, the exposure device 3d, and the developing device 4d (S303). This shielding toner image is a pattern formed in a width larger than the area of the secondary transfer nip N2 formed at least at the pressure contact portion between the intermediate transfer belt 21 and the secondary transfer roller 25 in the conveyance direction of the recording material S. is there. In the present exemplary embodiment, for the same reason as described in the first exemplary embodiment, the shielding toner image is a pattern having a printing rate of 30% or more in the area having the above-described width. Note that the length of the shielding toner image in the longitudinal direction (rotation axis direction) of the secondary transfer roller 25 needs to be at least equal to or longer than the image formable area on the intermediate transfer belt 21 in the same direction. Is longer than the length of the secondary transfer roller 25 in the same direction. The shielding toner image formed on the photosensitive drum 1d is electrostatically transferred to the intermediate transfer belt 21 by the primary transfer roller 5d (S304). Then, at the timing when the shielding toner image transferred onto the intermediate transfer belt 21 reaches the secondary transfer nip N2, the rotation of the driving roller 22 that drives the intermediate transfer belt 21 is stopped (S305). After that, until the next image formation start signal is received, the image forming standby state is entered with the shielding toner image interposed between the intermediate transfer belt 21 and the secondary transfer roller 25 (S306).

  Next, when the control device 12 receives the image formation start signal (S307), the pre-rotation operation is started (S308). The pre-rotation operation is an operation from the reception of the image formation start signal to the start of image formation. In this embodiment, the secondary transfer roller 25 is cleaned during the pre-rotation operation. In the pre-rotation operation, the drive motor starts driving simultaneously with receiving the image formation start signal, and the shielding toner image held in the secondary transfer nip N2 is removed from the secondary transfer nip N2. Then, the intermediate transfer belt 21 and the secondary transfer roller 25 are simultaneously cleaned (S309). The cleaning operation is executed by applying a voltage having the same polarity as the normal charging polarity of the toner to the secondary transfer roller 25 from the secondary transfer power source 52. As a result, the toner adhering to the secondary transfer roller 25 is transferred to the intermediate transfer belt 21 and is then uniformly charged by the cleaning charging device 26. The toner is transferred to the photosensitive drums 1a, 1b, 1c, and 1d of the image forming portions Pa, Pb, Pc, and Pd and collected by the cleaning devices 6a, 6b, 6c, and 6d. Then, following the pre-rotation operation, image formation is started (S310).

  In this embodiment, the process speed of the image forming apparatus 101 (corresponding to the peripheral speed of the photosensitive drum 1 and the intermediate transfer belt 21) is 100 mm / sec, and the intermediate transfer belt 21 having a peripheral length of 600 mm is used.

  Further, in this embodiment, as the secondary transfer roller 25, the same roller as that used as the transfer roller 5 in Embodiment 1 and made of conductive solid rubber is used. However, for example, in the case of an image forming apparatus that forms a full-color image with four color toners, a large amount of toner is transferred during secondary transfer. Thus, the secondary transfer roller 25 is pressed against the intermediate transfer belt 21 with a pressure of 68.6 N (7 kgf), which is higher than that of the transfer roller 5 of the first embodiment. The outer diameter of the secondary transfer roller 25 is 24 mm, and the width of the secondary transfer nip N2 formed by the intermediate transfer belt 21 and the secondary transfer roller 25 in the conveying direction of the recording material S is 2.4 mm. It is.

  Next, the result of confirming the effect of the shielding toner image supply operation in this embodiment will be described.

  The experimental method is the same as in Example 1. In other words, the effect was confirmed under the condition that the image forming apparatus 101 was left for one week in an environment of a temperature of 40 ° C. and a humidity of 95%. Further, the shielding toner image interposed in the secondary transfer nip N2 in the shielding toner image supply operation is 3.0 ± 0.5 mm in the circumferential direction of the intermediate transfer belt 21 (the conveyance direction of the recording material S), and the secondary transfer. The roller 25 was formed in a region of 225 mm in the longitudinal direction. When left unattended, the shielding toner image is disposed in the circumferential direction of the intermediate transfer belt 21 so that the secondary transfer nip N2 is within the region of the shielding toner image.

  Table 5 shows whether or not an image defect occurs when the printing rate of the shielding toner image formed on the intermediate transfer belt 21 in the shielding toner image supply operation is changed by the laser light lighting time per pixel. ing. Specifically, when a solid black pattern is printed in the image forming apparatus 101 after being left, “OK” is indicated when no image defect occurs. In addition, when an image defect occurs, a solid black pattern is printed after that, indicating the number of sheets on which the image defect is no longer seen.

  In this embodiment, the peripheral length of the intermediate transfer belt 21 is 600 mm. For this reason, even if printing is performed on the LTR size Xx4200 (paper length 276 mm) as the recording material S, there is a possibility that the pressure contact portion between the intermediate transfer belt 21 and the secondary transfer roller 25 at the time of leaving does not come to the first printed sheet. is there. Therefore, it was adjusted and printed so that the press contact portion would surely come on the first sheet.

First, without performing the shielding toner image supply operation in this embodiment (printing rate: 0%), after image formation is performed and the image forming apparatus 101 is left in the above-described environment, the recording material S is Xx4200 (basis weight). (75 g / m ² , LTR size) was printed with a solid black pattern. As a result, horizontal band-like white spots occurred. When 13 solid black patterns were printed, white spots were not seen.

  On the other hand, when the shielding toner image supply operation in the present embodiment is performed, when the solid black pattern is printed on the recording material S after the image forming apparatus 100 is left in the above-described environment, the print rate is a pattern of 30% or more. If so, no image defect occurred.

  As described above, in this embodiment, in the intermediate transfer type image forming apparatus, the shielding toner image supply operation is executed, and the shielding toner is applied to the pressure contact portion between the intermediate transfer belt 21 and the secondary transfer roller 25 during non-image formation. Leave with an image. Preferably, at the time of non-image formation, a shielding toner image having a printing rate of 30% or more is interposed between the intermediate transfer belt 21 and the secondary transfer roller 25 and left as it is. As a result, it is possible to suppress the adhesion of the component that oozes out from the secondary transfer roller 25 to the surface of the intermediate transfer belt 21, and to effectively suppress the occurrence of image defects.

  In this embodiment, the shielding toner image supplied to the secondary transfer nip N2 is formed by the black (K) image forming portion Pd. However, the present invention is not limited to this. The shielding toner image may be formed by other image forming units such as yellow (Y), magenta (M), and cyan (C) image forming units Pa, Pb, and Pc.

  Further, in the intermediate transfer type image forming apparatus as in this embodiment, as described in the second embodiment, the conditions for performing the shielding toner image supply operation may be limited.

  Further, in this embodiment, an operation of stopping the image by interposing a shielding toner image in the secondary transfer nip N2 formed by the intermediate transfer belt 21 as an image carrier and the secondary transfer roller 25 as a transfer member will be described. did. Alternatively, the toner image can be stopped by interposing a shielding toner image in a primary transfer nip N1 formed by a photosensitive drum as an image carrier and an intermediate transfer belt as a transfer member. In this case, it is possible to suppress image defects such as white spots that occur when the resin-containing components constituting the intermediate transfer belt ooze out and adhere to the photosensitive drum.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Transfer roller 14 Environment detection means 21 Intermediate transfer belt 25 Secondary transfer roller

Claims (8)

In an image forming apparatus comprising: an image carrier that carries a toner image; and a transfer member that is pressed against the image carrier and forms a transfer nip with the image carrier.
An image forming apparatus that performs an operation of stopping the image carrier while at least a toner image formed on the image carrier is present in the transfer nip.   2. The image forming apparatus according to claim 1, wherein the toner image formed on the image carrier in the operation is a toner image having a pattern with a printing rate of 30% or more.   3. The image forming apparatus according to claim 1, further comprising means for detecting temperature and humidity of the atmosphere, wherein the operation is executed when the temperature and / or humidity of the atmosphere is higher than a predetermined value.   3. The image according to claim 1, further comprising a unit that counts an accumulated number of prints performed using the transfer member, wherein the operation is executed when the accumulated print number is less than a predetermined number. Forming equipment.   Means for detecting the temperature and humidity of the atmosphere, and means for counting the total number of prints performed using the transfer member, and the operation is performed when the temperature and / or humidity of the atmosphere is higher than a predetermined value, and The image forming apparatus according to claim 1, wherein the image forming apparatus is executed when the cumulative number of printed sheets is less than a predetermined number.   The image forming apparatus according to claim 1, wherein the image carrier is a photoconductor, and the transfer member is a transfer roller that transfers a toner image from the photoconductor to a recording material. apparatus.   The image bearing member is an intermediate transfer member, and the transfer member is a transfer roller that transfers a toner image from the intermediate transfer member to a recording material. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the image carrier is a photosensitive member, and the transfer member is an intermediate transfer member to which a toner image is transferred from the photosensitive member. .

Images